mailto:adisuryadi@eng.uir.ac.id 1. introduction 2. geology and geomorphology regional 3. methodology 3.1 data collection for water infiltration 3.2 data collection for subsurface sediment profiling 4 result 4.1 infiltration rate 4.2 subsurface profiling of quaternary deposits 5. discussion 6. conclusion 7. acknowledgement references uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 8. no 2-2. june 2023 stspecial issue from “the 1 international conference on upstream energy technology and digitalization (icupertain) 2022” issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually p-issn 2503-2161 e-issn 2541-5794 scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) guest editor prof. rudy sayoga gautama benggolo (indonesia) harya dwi nugraha, phd (dic) (indonesia) dr.eng. paramita jaya ratri (indonesia) dara ayuda maharsi, m.si. (indonesia) dr.eng. tirta rona mayangsari (indonesia) mailto:jgeet@journal.uir.ac.id http://journal.uir.ac.id/index.php/ preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 08 no 02-02 2023 as a special issue from “ the 1st international conference on upstream energy technology and digitalization (icupertain) 2022”. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content machine learning application of two-dimensional fracture properties estimation ....................................................................................................................................... 1 machine learning prediction of tortuosity in digital rock ...................................................... 6 investigation of geological structure using magnetotelluric and gravity data optimization on non volcanic geothermal, bora, centre of sulawesi .............................. 13 possibilities study of a non-condensable gas exhaust system through the condensate injection pipe at pltp wayang windu ............................................................... 18 seismic vulnerability analysis using the horizontal to vertical spectral ratio (hvsr) method on the west palu bay coastline .................................................................... 23 analysis of petrophysical parameter on shaly sand reservoir by comparing conventional method and shaly sand method in vulcan subbasin, northwest australia .......................................................................................................................................... 35 field development with scenario reactivation of non-active zones through reservoir simulation: a case study of the kappa offshore field, west natuna............. 43 stress analysis of existing underground gas pipeline due to new road crossing with odol transportation .......................................................................................................... 58 ambient noise data processing to obtain group velocity for subsurface structure identification: preliminary research in hululais geothermal field, sumatra, indonesia ....................................................................................................................... 67 1d geomechanical model for wellbore stability in z field, y well sanga sanga working area, kutai basin .............................................................................................. 72 cover jgeet vol 8 no 2 2 june 2023.pdf (p.1) editorial member.pdf (p.2) preface vol 8 no 2-2.pdf (p.3-4) jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 08 no 02 2023. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content exploration of the magnetic rocks potential of mount penanggungan: a study of myth, history, and its implications for educators and mountaineers ................. 84 morphological analysis of anak krakatau volcano after 22 december 2018 eruption using differential interferometry synthetic aperture radar (dinsar) ............... 90 sensitivity analysis of geomechanics influence on the success of hydraulic fracturing in shale gas reservoir .............................................................................................. 99 biostratigraphic interpretation of lutut beds, kerek formation, based on foraminifera fossils ...................................................................................................................... 105 basaltic lava characteristic in goa pandan area, sukadana, east lampung: inferences from stratigraphy and petrography analysis ....................................................... 112 exploring the mechanism of vetiver system for slope reinforcement on diverse soil types – a review .................................................................................................... 123 model for optimizing land use to support sustainable environmental economic strengthening in the upper kampar river basin ................................................. 131 hydrocarbon spectra slope (hyss): a spectra index for quantifying and characterizing hydrocarbon oil on different substrates using spectra data .................. 138 cover jgeet vol 8 no 2 june 2023.pdf (p.1) editorial member.pdf (p.2) preface vol 8 no 2.pdf (p.3-4) uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 8. no 1. march 2023 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 08 no 01 2023. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content study of current patterns in tanjung pasir banten for supporting the ncicd seawall development plan ........................................................................................................ 1 petrogenetic study of ultramafic rocks from waturapa and surrounding areas, south konawe regency, southeast sulawesi province, indonesia ......................... 10 lineament density and implications for the distribution of ground fissures after 2021 mw 7.3 flores sea earthquake on kalaotoa island, indonesia ......................... 17 geological and morphometric characteristics of quaternary pyroclastic aquifers in salak and pangrango stratovolcano .................................................................... 27 electrical resistance tomographic by using current injection and magnetic field induction ............................................................................................................................... 39 design and implementation of a composite array resistivity data logger for high-resolution 2d inversion modeling .................................................................................. 44 analysis the effect of column height variation on the perfomance of increased building structure ....................................................................................................... 56 analysis of land subsidence in peatlands in the awareness area of pekanbaru, riau, indonesia......................................................................................................... 62 experimental study of improving the physical properties of peat soil using sand and bio-grouting techniques with the assistance of bacillus subtilis bacteria ........................................................................................................................................... 69 economic evaluation of water production management with rpm (relative permability modifier) treatment based on gross split contract in “re” well in “dn" field ........................................................................................................................................ 77 cover jgeet vol 8 no 1 march 2023.pdf (p.1) editorial member.pdf (p.2) preface vol 8 no 1.pdf (p.3-4) jgeet_cover_print_15 journal of geoscience, engineering, environment and technology issn. 2503-2161 e-issn. 2541-5794 volume 1. no 1. december 2016. p 1-100 fault analysis to determine deformation history of kubang pasu formation at south of unimap stadium hill, ulu pauh, perlis, malaysia adi suryadi page 1 rock physics modeling and seismic interpretation to estimate shally cemented zone in carbonate reservoir rock handoyo*, m rizki sudarsana, and restu almiati page 45 the paleogene tectonostratigraphy of northern part masalima trench basin luhut pardamean siringoringo , dardji noeradi page 7 * organic geochemical characteristic of crude oils from orange graben, south sumatra basin m. syaifudin page 25 control structure of garba formation through petrography analysis in tanjung beringin, south oku regency, south sumatra ridho widyantama putra, frillia nasution, nurlita putri, rahmat alfath page 35 stratigraphy seismic and sedimentation development of middle baong formation, aru area, north sumatera basin nanda natasia*, ildrem syafri, m. kurniawan alfadli, kurnia arfiansyah page 51 list of content journal of j eetgeoscience engineering environment and technology publisher uir press preliminary analysis of slope stability in kuok and surrounding area tiggi choanji, dewandra bagus ep page 41 limnic condition in rheotrophic peat type as the origin of petai coal central sumatera basin, indonesia budi prayitno page 63 geotourism potential of sandbar and oxbowlake at buluh cina village kampar-riau, indonesia yuniarti yuskar page 59 issn 2503-2161 e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: web: http://jurnal.uir.ac.id/index.php/jgeet jgeet@journal.uir.ac.id; executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eetgeoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief fault analysis to determine deformation history of kubang pasu formation at south of unimap stadium hill, ulu pauh, perlis, malaysia.........1 rock physics modeling and seismic interpretation to estimate shally cemented zone in carbonate reservoir rock.................................................... 45 the paleogene tectonostratigraphy of northern part masalima trench basin..........................................................................................................7 organic geochemical characteristic of crude oils from orange graben, south sumatra basin............................................................................................25 control structure of garba formation through petrography analysis in tanjung beringin, south oku regency, south sumatra ....................................35 stratigraphy seismic and sedimentation development of middle baong formation, aru area, north sumatera basin..............................51 list of content preliminary analysis of slope stability in kuok and surrounding area............41 limnic condition in rheotrophic peat type as the origin of petai coal central sumatera basin, indonesia.....................................................................63 geotourism potential of sandbar and oxbowlake at buluh cina village kampar-riau, indonesia..................................................59 uir press issne-issn jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: website: http://jurnal.uir.ac.id/index.php/jgeet jgeet@journal.uir.ac.id page 1 page 2 page 3 page 4 page 5 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 dianardi, kholqi et al./ jgeet vol 03 no 04/2018 187 research article characteristics of groundwater on the eastern slope of mount ciremai, kuningan regency, west java, indonesia kholqi dianardi 1, *, jumhari 2 , m. sapari dwi hadian 1 , t. y. m. iskandarsyah 3 1 faculty of geological engineering, padjadjaran university, jl. bandung sumedang km. 21, jatinangor, west java, indonesia 2 energy and mineral resources center, kuningan, west java, indonesia 3 water center, faculty of geological engineering, padjadjaran university, west java, indonesia * corresponding author : kholqi64.geounpad10@gmail.com tel.: +62-821-1514-9890 received: may 24, 2018; accepted: september 16, 2018. doi: 10.24273/jgeet.2018.3.4.1606 abstract water is a very important component for the survival of living things. groundwater is water that has better quality compared to other water types, so groundwater is widely used to meet the needs of clean water. the research area is located on the eastern slope of mount ciremai which is a volcanic area that has great groundwater potential, it is seen from the many springs with large groundwater discharge. the study aims to determine the physical and chemical characteristics of groundwater on the eastern slopes of mount ciremai which also the district of kuningan. the research method is done by collecting geological data and hydrogeological data. to find characteristics of groundwater chemistry, groundwater sampling was taken at 10 locations, and then tested the laboratory to determine the chemical content of groundwater. based on the results of the research, the physical characteristics of water were shown with ec values ranging from 76,8 to 228 µs/cm, tds from 50 to 151 mg/l, ph value from 6.4 to 7.65, water temperature 19.3 to 25.9 o c. while one of the observation location is hc. 11 is a hot spring that has a water temperature of 36.1 o c, ec 832 µs/cm, tds 428 mg/l and ph 6.8. chemical analysis results from pipe diagram show the developing facies are ca: hco3, ca. mg: hco3, na.k:cl.. keywords: groundwater, volcano, geology, hydrogeology, physical properties, facies 1. introduction water in the volcano region generally has a very good quality and has interesting characteristics to be studied. volcano area is a high altitude, is a catchment area as well as absorption of rain water is good. the research area is located on the eastern slope of mount ciremai which is a volcanic area that has great groundwater potential, it is seen from the many springs with large groundwater discharge. the type of spring that appears generally is the fracture type and depression type (irawan et al., 2006). mount ciremai has a height of 3072 meters from sea level, located 10 kilometers to the south of the cirebon regency, with radius from peak to foot mountain as far as 10 kilometers. surrounded by three areas: kuningan regency from the east, majalengka regency from the west, and cirebon regency from the north. mount springs, such as minerals, fertile soils, and functions as nature conservation area and water catchment zone area. 2. slope of research area volcanoes are generally cone-shaped by division starting from central facies, proximal facies, medial facies, and distal facies (bronto, 2006). research area is located at the proximal facies and the medial facies with elevation at 425 1312.5 masl. the slope is divided become two types, namely: i. decline area (2° 4°) ii. rather steep and steepest (4° 16°) 3. field location and geology to determine the characteristics of groundwater, geological and hydrogeological data collection methods are used (hadian et al., 2017). geological data obtained by means of geological mapping of lithology data. hydrogeological data is done by means of hydrogeological mapping in form of measurement of physical properties of groundwater and groundwater sampling which will then be analyzed cation and anion content in the laboratory. the types of cations and anions analyzed are na, k, ca, mg, hco3, cl and so4 (kumaresan & riyazuddin p., 2006). to determination of groundwater chemical analysis by using piper diagram to find out groundwater facies that developed in the research area. http://journal.uir.ac.id/index.php/jgeet 188 dianardi, kholqi et al./ jgeet vol 03 no 04/2018 fig 1. geological map of research area (no scale) fig 2. hydrogeological map of research area. 4. result and discussion 4.1 geological mapping of research area based on regional geological map analysis and geological mapping, stratigraphic research area form the old to the young is divided into three stratigraphic units, among others: volcanic breccia 1 (qbv 1), volcanic breccia 2 (qbv 2), and andesitic lava (qla) (djuri, 1973). the division of stratigraphy can be seen in the geological map of research area (fig 1). based on research conducted by previous researchers using geoelectric surveys, the measurement areas enter the depths of the qbv 1 which has several lithologies: breccia, lava, tuff sand, and lapilli from the eruption from the eruption of mount ciremai (alfadli et al., 2017). dianardi, kholqi et al./ jgeet vol 03 no 04/2018 189 4.1.1 volcanic breccia 1 this unit has a visibility in the research area of varying thickness, from 0.5 meter to 4 meter. volcanic breccia with matrix more than 50%, bad disaggregated and open pack. it has a gray andesitic igneous rock component that contains plagioclase minerals with little quartz. matrix is tuff vitric with brownish brown color and composed of mineral glass. 4.1.2 volcanic breccia 2 volcanic breccia with less than 50% matrix, bad disaggregated and closed pack. this volcanic breccia is relatively hard. it has a gray andesitic igneous rock component that contains plagioclase minerals with little quartz. matrix is tuff vitric with brownish brown color and composed of mineral glass. 4.1.3 andesitic lava (qla) this unit has a visibility in the research area of varying thickness, from 0.5 meter to 3 meter. andesite lava has a fresh gray color and a grayish brownies color. has porphyritic granularity with good packing and the degree of hypo-crystalline crystallization because composed of crystals and groundmass. with a very hard hardness, with a structure that looks massive in the field. 4.2 hydrogeology of research area based on hydrogeology map, research area can be divide into 2 hydrogeology units (fig 2) that is moderately productive aquifers and extensive productive aquifers (soetrisno, 1983). 4.3 groundwater physical characteristics the results of measuring the physical properties of ground water directly in the field of the spring show heterogeneous characteristics (fig 3). range of ec values is 76.8 to 228 µs/cm, tds values from 50 to 151 mg/l, ph value from 6.4 to 7.65, water temperature 19.3 to 25.9 o c. one location of observation that is hc. 11 is hot springs having water temperature 36.1 o c, ec 832 µs/cm, tds value 428 mg/l and ph 6.8. fig 3. section for reconstruction of groundwater physics data and groundwater chemistry 190 dianardi, kholqi et al./ jgeet vol 03 no 04/2018 4.4 groundwater chemistry characteristics from the results of chemical analysis of groundwater in the laboratory obtained the major elements contained in groundwater (tab 1), then converted into units of meq/l (tab 3). the element analyzed is na, k, ca, mg, hco3, so4 and cl. table 1. data of groundwater ion concentration from laboratory analysis no kode sampel na k ca mg cl hco3 so4 (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) 1 hc.1 8.89 4.64 27.68 9.34 9.99 108.32 7.06 2 hc.5 4.23 3.02 19.29 2.41 8.26 56.60 2.95 3 hc.9 6.13 1.43 27.83 7.17 2.98 110.7 3.25 4 hc.11 469.21 74.2 124.1 31.74 913.2 171.5 2.36 5 hc.16 4.29 2.59 18.41 2.09 5.95 53.88 3.47 6 hc.19 3.93 1.94 16.69 3.26 4.85 54.42 3.47 7 hc.22 5.05 2.63 18.40 4.26 6.43 65.70 4.57 8 hc.23 10.38 4.05 29.72 11.31 14.50 107.70 17.78 9 hc.24 5.15 2.66 18.43 4.73 7.03 66.30 4.27 10 hc.25 5.58 3.01 19.39 4.85 8.97 59.55 8.37 to convert ion concentration in ppm unit into unit of meq/l used by dividing ion concentration in ppm with equivalents number of each elements (table 2). table 2. number of equivalents on the major elements ion number of equivalents cation na + 22,9898 k + 39,102 ca 2+ 20,04 mg 2+ 12,156 anion so4 2 48,031 cl 35,453 hco3 2 61,017 the data of cation-anion concentration in meq/l unit then validated by ion equilibrium equation, valid data if error balance (cbe) does not exceed 10%. percent error is calculated by equation: cbe % = number of cations−number of anions number of cations +number of anions (1) table 3. the data of ionized water ion concentration converted into meq/l and calculation of cbe no sample code na k ca mg cl hco3 so4 charge balance error (cbe) (meq/l) 1 hc.1 0.39 0.12 1.38 0.93 0.28 1.78 0.15 9.28% 2 hc.5 0.18 0.08 0.96 0.20 0.23 0.93 0.06 7.57% 3 hc.9 0.27 0.04 1.39 0.59 0.08 1.81 0.07 7.44% 4 hc.11 20.41 1.90 6.19 2.61 25.76 2.81 0.05 4.17% 5 hc.16 0.19 0.07 0.92 0.17 0.17 0.88 0.07 8.95% 6 hc.19 0.17 0.05 0.83 0.27 0.14 0.89 0.07 9.11% 7 hc.22 0.22 0.07 0.92 0.35 0.18 1.08 0.10 6.85% 8 hc.23 0.45 0.10 1.48 0.93 0.41 1.76 0.37 7.69% 9 hc.24 0.23 0.07 0.92 0.39 0.20 1.10 0.10 7.04% 10 hc.25 0.24 0.08 0.97 0.40 0.25 0.98 0.17 9.16% based on the results of the analysis of the piper diagram (fig 4) the study area is divided into three groundwater facies, as follows: 1) facies ca:hco3, this shows in this group the circulation of groundwater has not been too far and ca content in the exchange of groundwater ions with rocks. the dominant ca content in this facies is caused by the water interaction with volcanic breccia rocks. 2) facies ca.mg:hco3, this facies found in one location that is hc.1. groundwater in this facies has a relatively long circulation compared to facies ca:hco3. emergence of facies ca.mg:hco3 in this facies is at the location of hc.1, possibly caused by the interaction of rocks against groundwater that has been long enough because it has experienced mixing, it can be seen from the percentage of ca and mg ion enrichment is balanced. 3) facies na.k:cl, this facies found in one location that is hc.11. the hc.11 spring is the only hot springs in the study area. springs in this sangkanhurip area have temperature 31.6 °c. temperature is thought to be derived from geothermal activity beneath the surface that flows through the fracture that is indicated as a result of geological structure. dominant na and k content are caused by the interaction of water with the mineral constituent of rocks, while the high content of cl may be due to the interaction with sedimentary rocks. this can be proved by the location of the springs that are located close to the ciherang formation and halang formation in the west of the research area which is a sedimentary rocks. the high cl content indicates that the groundwater flow system is derived from a deep and predominantly regional aquifer far from the springs (domenico, 1972). dianardi, kholqi et al./ jgeet vol 03 no 04/2018 191 fig 4. piper diagram show chemical facies of research area 5. conclusion groundwater characteristics in the research area were obtained based on geological data and hydrogeological data analysis. based on the physical characteristics of groundwater show in the research area into the fresh water category. while based on chemical analysis, groundwater characteristics in the research area is divided into three groundwater facies that is ca: hco3, ca. mg: hco3 dan na.k:cl. 6. acknowledgement the author thanks to yudi listiawan, st., mt, ridfansayah, st., and all those who helped, so this article can be completed. references alfadli, m., & natasia, n., 2017. geoelectricity data analysis for identification the aquifer configuration in bandorasawetan, cilimus, kuningan, west java province. journal of geoscience, engineering, environment, and technology, 2, 278-284. bronto. 2006. fasies gunungapi dan aplikasinya. jurnal geologi indonesia, 1. djuri. 1973. peta geologi regional lembar ardjawinangun, jawa. direktorat geologi bandung. domenico, p.a. and schwartz, w.f., 1990. physical and chemical hydrogeology. john wiley and sons, inc., canada, 824p. irawan, d.e., puradimaja, d.j., notosiswoyo, s., sumintadireja, p., 2006. hydrogeology of stratovolcano of ciremai, west java, indonesia. iaeg congress. hadian, m., waliana, t., sulaksana, n., putra, d., & yuskar, y., 2017. hydrochemistry and characteristics of groundwater: case study water contamination at citarum river upstream. journal of geoscience, engineering, environment, and technology, 2, 268-271. kumaresan m., riyazuddin p., 2006. major ion chemical of environmental samples around suburban of chennal city. current sci., 91(12), 1668 1677. piper, a. m. 1944. a graphic procedure in the geochemical interpretation of water analysis. trans, am. geophysics. union, washington, d.c. soetrisno, s. 1983. peta hidrogeologi lembar v bandung skala 1:250.000. direktorat geologi tata lingkungan. bandung. © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. slope of research area 3. field location and geology 4. result and discussion 4.1 geological mapping of research area 4.1.1 volcanic breccia 1 4.1.2 volcanic breccia 2 4.1.3 andesitic lava (qla) 4.2 hydrogeology of research area 4.3 groundwater physical characteristics 4.4 groundwater chemistry characteristics 5. conclusion 6. acknowledgement references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” pertiwi, t.b. et al./ jgeet vol 08 no 02-2 2023 13 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 research article investigation of geological structure using magnetotelluric and gravity data optimization on non volcanic geothermal, bora, centre of sulawesi tiaraningtias bagus pertiwi1, yunus daud2,3,*, fikri fahmi3 1master program in geothermal exploration, department of physics, universitas indonesia, depok 16424, indonesia 2geothermal research centre of the university of indonesia, depok 16424, indonesia 3pt newquest geotechnology, pesona khayangan estate dc no.12, depok 16411, indonesia * corresponding author : ydaud@sci.ui.ac.id tel.:+62-21-787-5602; fax: +62-21-787-5603 received: may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13876 abstract the existence of geological structures is one of the important parameters in determining the permeability zone in a geotherma l system. this research was conducted in a non-volcanic geothermal field, bora, located in the province of central sulawesi, aiming to identify the subsurface features, especially geological structures related to permeability zones by optimizing geophysical data. magnetote lluric (mt) 3d inversion modelling is some of the latest methods to identify geological structural patterns in geothermal systems. the results of the mt model and analysis its parameters can find variations in the distribution of subsurface resistivity, orientation of the direction of the prospect area, and indications of geological structure zones. the type and geometry of the geological structure associated with the high permeability zone can be complemented by determining the contrast of gravity values and analysis of the maximum first horizontal derivative (fhd) and zero of the second vertical derivative (svd). based on the analysis of geophysical data, it is possible to identify the permeability zone associated with the main structure, namely the palu-koro fault, delineate the geothermal reservoir at a depth of 15002000 meters and determine the location of well drilling. to visualize the geothermal system comprehensively, a conceptual model is developed by integrating the geophysical model with geological and geochemical data that are correlated with each other, therefore it can assist in determining the location of production well development. keywords: non-volcanic geothermal system, geological structure, 3d inversion magnetotelluric, permeability 1. introduction the bora geothermal field is classified as a type of nonvolcanic system. it is located on one of the fault zones systems namely palu-koro fault. this region's geology is composed of pre-tertiary metamorphic rocks, tertiary plutonic intrusive rocks, and quaternary sediment. current tectonic activity is probably causing the formation of a depressed zone, which sets off a rock intrusion process that transfers heat effectively. geothermal manifestations in bora village seem to be driven by hydrothermal activity in the palu-koro fault zone. this fault is trending northwest to south-southeast which is in the central sulawesi arm (psdg, 2010). the permeable zone inside the geothermal reservoir can be controlled by geological features like faults. it is a difficult task to map the presence of subsurface fracture zones since some features, such as faults or fractures, are typically not connected to the surface. therefore, this research has focused on how to optimize geophysical technologies to determine the geological structure. the magnetotelluric (mt) method is very efficient in assisting geothermal exploration stages, with greater penetration than other methods. the relationship between resistivity and clay mineral content allows the use of the mt resistivity cross-section to determine the conductive layer as a clay cap in the geothermal system. although the reservoir cannot be definitively identified using this method, the bottom of the clay cap (boc) can be distinguished (ussher et al., 2000). analyzing parameters is one method of improving geothermal system comprehension. by using the outcomes of the 3dimensional inversion derived from the mt model, it was possible to analyze the splitting pattern from the mt curve, the orientation elongation of polar diagrams, as well as the delineation of subsurface structures. in addition, the identification of geological structures from mt data can be assisted by gravity analysis. this method utilizes the measurement of the gravitational field at the earth's surface. gravity data are analyzed using the first horizontal derivative (fhd) and second vertical derivative (svd) techniques (daud et al., 2019). this study was conducted to identify feature anomalies in order to find fault types and geological structures. the permeability zone should be more clearly identified by combining the results of the studies mentioned. 2. material and methods 2.1 geological setting sulawesi island is geologically at the intersection of the eurasia, indo-australian, and pacific tectonic plates. as a result, both volcanic and non-volcanic hosted geothermal zones are formed due to these tectonic events (idral and mansoer, 2015). the focus area of this study is bora village in sigi district, central sulawesi, which is located in an http://journal.uir.ac.id/index.php/jgeet mailto:ydaud@sci.ui.ac.id 14 pertiwi, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 active tectonic environment, namely the palu-koro fault and has a complex geological environment with a depression zone. hot springs with temperatures around 90.1 °c, hot ground (100.6 °c), and altered rocks are all evidence of the hydrothermal activity found in this area (psdg, 2010). these factors, therefore, make bora village a potential site for geothermal fields. according to research (wibowo et al., 2011), the stratigraphic composition of the rocks from oldest to youngest consists of schist units (trs), granite genes (trg), filit (kf), salubi granite (tgs), oloboju granite (tgo), sediments (qs), and alluvium (qal). there are four fault structures developing in the research area as shown in fig. 1, namely the palu-koro fault trending north-south, the sidera fault trending west-east, the oloboju fault trending west-east, and the bora fault trending northwestsoutheast. there are several manifestations in bora, that five hot springs namely bora, sidera, mantikole 1 & 2 and lompio as well as hot soil and altered rocks. the structure of the palu-koro fault is considered to control the emergence of the mantikole and lompio hot springs. the sidera fault controls the appearance of the sidera hot springs and the bora fault controls the bora hot springs. fig. 1. geological map of bora geothermal field (wibowo et al., 2011) 2.2 magnetotelluric method the magnetotelluric (mt) method is a geophysical method that utilizes the principle of natural electromagnetic (em) induction to estimate the resistivity value of subsurface rocks. transverse electric (te) and transverse magnetic (tm) modes describe how electromagnetic waves move through the medium (simpson and bahr, 2005). in the mt approach, both modes play a significant role. the te mode, also known as the polarized electric field, describes an electric current flowing in parallel and the induction of a magnetic field perpendicular to the strike. meanwhile, the tm mode has characteristics that are inversely proportional to the te mode. the existence of a structure which is a heterogeneous and anisotropic zone for the em waves can be shown by resistivity contrast in fig. 2. the response of the structure to this scenario is splitting on the curve and impedance polarization of mt data. 2.2.1 geological setting vertical structures have a resistivity contrast that can separate components on the mt curve. curve splitting is the term used to describe the characteristic difference that separates the te and tm curves upon vertical contact. due to this, tm mode exhibits lateral sensitive changing characteristics in contrast to te mode. the sensitivity of the subsurface conductivity is impacted by the vertical magnetic field in te mode (daud et al., 2015; rosid and ghufron, 2021). the pattern of the separation curve will depend on how much resistivity contrast there is, and the extent of the separation will depend on how far the structure is from the mt station. it is expected that subsurface permeability zones connected to structural indications can be determined using curve splitting analysis (daud et al., 2015). 2.2.2 polar diagram field observations indicate that impedance is controlled by the direction of the em wave propagation axis as well as the spatial variation of subsurface resistivity. the dependence of impedance on the orientation of the measurement axis can be visualized on a polar diagram as shown in fig. 2. a polar diagram uses the amplitude of the impedance tensor component on each axis. the axis configuration of a polar diagram is a good indicator of changing the dimensions of the earth's electrical structure. meanwhile, the elongation of the polar diagram could provide information on the strike direction, in which the polar diagram gives the response relatively parallel or perpendicular to the strike (daud et al., 2015; vozoff, 1991). fig. 2. curve splitting (above) and impedance polar diagram (below) at mt station 1, 2, 3 and 4 (vozoff, 1991). 2.3 gravity method the geological agency provided the gravity and magnetotelluric data utilized in 2010 (indonesian center for geological resources). the gravity method can provide information about subsurface density distribution. a complete bouguer anomaly (cba) has been produced using the gravity observation data that have been processed and corrected using the equation (1). cba= gobs-gf+fa-bc+tc (1) gravity data processing will separate regional anomalies and residual anomalies from the cba map. the residual anomaly describes the result of shallow penetration, which is obtained by using the trend surface analysis method and the first order polynomial equation (daud et al., 2018). gravity data are frequently used to locate the density contrast using the first horizontal derivative (fhd) and second vertical derivative (svd). geological feature anomalies are investigated to identify fault types and structural or lithological contrasts. if there is contrast on the contours of the fhd map, this indicates an anomaly as a pertiwi, t.b. et al./ jgeet vol 08 no 02-2 2023 15 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 horizontal contact with different densities which is a fault structure. furthermore, svd is very helpful for observing vertical contacts which can confirm the presence of structures in areas indicated by fault structures (fig. 3). fig. 3. distribution of mt data (left) and gravity data (right); line profile that will be used for structure analysis 3. results and discussion the surface geological structure in the bora geothermal area has a dominant orientation towards nw-se and nesw. the structures most likely have an impact on how the local geothermal system develops. the analysis of curve splitting, polar diagrams, and 3d inversion of mt data obtained using ssmt2000 and mt3d inv-x by newquest geotechnology, as well as the study of density contrast from fhd and svd with geosoft. these results are used to identify the surface geological structure generated from observation data. the western palu-koro fault zone is numbered 01, while the central part is numbered 02, and the bora fault is numbered 03. 3.1 curve splitting analysis fig. 4 displays the result of line a's curve splitting and 3d inversion. from the modeling result, it is possible to determine the continuation of 4 faults in the subsurface. the western palu-koro fault zone is identified from the mtbr-08 curve splitting pattern. the confluence of the central palu koro fault zone and the bora fault is likely to be the basis for splitting the mtbr-13 and mtbr-14 curves. fig. 4. curve splitting and 3d inversion result of line a the presence of faults is also supported by the curve splitting on mt station (mtbr-20, mtbr-24, mtbr-25, mtbr-26) as shown in fig. 5. at the bora fault zone, there is a newly identified fault in a resistive dome feature which provides supporting conditions of resistivity contrast at shallow depths. this possibility can be correlated with the existence of structures and the presence of surface manifestations around the fault zone. fig. 5. curve splitting and 3d inversion result of line b in fig. 6 for line c, the existence of identified faults continues, supported by the splitting of the mtbr-11 and mtbr-25 curves. the existence of the confluence of two faults between the bora fault and the central zone of the palu-koro fault is also supported by the emergence of hot springs on the surface. from this curve splitting analysis, it is known that the permeable zone is estimated to be in the southeastern region with continuous identified faults in the three lines. fig. 6. curve splitting and 3d inversion result of line c 16 pertiwi, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 3.2 polar diagram analysis polar diagrams support the analysis of 3d inversion and curve splitting results. these faults are confirmed by the elongation of the polar diagram, which is typically parallel to the fault. in contrast, the polar diagram of the mt stations that are situated between the two faults reveals an elongation that is perpendicular to the fault strike (daud et al., 2015). the elongation of the polar diagrams in the bora geothermal area often follow the ne-sw and nw-se directions. fig. 7 shows a clear depiction of the fault structure. the elongation of the polar diagram serves as supporting information for the identified faults, such as the western and central zones of the palu-koro fault, and the bora fault. in the zone between two faults, the polar diagram shows the elongation perpendicular to the structure. this indicates that there is a higher resistivity between the two faults compared to the other areas. it also confirms that the existence of the domes found in the mt model in line a and line b can be associated with the graben and horst forms of the fault. fig. 7. structural analysis of the polar diagram at a frequency of 100, 10, 1 and 0.1 hz 3.3 the gravity anomaly the contours of bouguer anomaly closely match the patterns of geological fault distribution, and this indicates that the depression zone's width is decreasing from north to south. in fig. 8, the bouguer anomaly and residual gravity anomaly are depicted. the cba value is between -16 and 32 mgal. there is a pattern of high to low gravity anomalies moving from west to east and vice versa. most of the residual gravity anomaly results have a contour pattern similar to cba mapxxzc. in general, the gravity result in the bora geothermal field has a low gravity anomaly. several phenomena are seen in the high gravity anomaly which appears more clearly in the western region. this anomaly partially shows its similarity with the bouguer anomaly which implies local structural conditions. in the southern zone of the field, there is a low anomaly between -14 and 2 mgal. this could indicate the location of shallow layers like reservoir rock or a fault zone that have the same pattern as the mt analysis. fig. 8. complete bouguer anomaly map (left) and residual anomaly map (right) of bora geothermal field. 3.4 the gravity derivative analysis let’s see qualitatively at fig. 9 shows the higher fhd anomaly in the western area, which has values varying between 0.009 and 0.004 mgal/m represented in blue to magenta. the high contrast in gravity values between one site and another may reveal the fault structure that actually occurred. the reverse fault shown on the geological map can be confirmed as the fault structure found and shown in the picture. the hot springs are close to fault lines which have a pattern similar to the mt model results. they are hence considered to be the discharge zone in this field. fig. 9. first horizontal derivative and second vertical derivative analysis svd analysis is applied to find out the types of faults indicated in fhd analysis. the fault in fig. 9 is shown with zero svd anomaly, while the maximum and minimum anomalies have solid contours on both sides. the location of the fault on both maps will be exactly the same if the fhd and svd contour maps align. to determine the types of faults that are detected by svd value, if g" max is greater than g" min, the type of defect is a typical fault. meanwhile, the value of g" max is smaller than g" min, the type of defect is a reverse fault. based on the analysis of existing faults, lane a and lane b show the type of reverse fault, while lane c shows the type of normal fault. the presence of structures indicates possible permeability. the fault correlation results between mt and gravity have the same pattern. therefore, the probability of showing good permeability of the fault produced in this analysis is estimated to be a shallow fault. the potential bora geothermal prospect area is estimated pertiwi, t.b. et al./ jgeet vol 08 no 02-2 2023 17 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 to be in the middle of the research area, at the confluence of the central zone of the palu koro fault and the bora fault. 4. conclusion the formation of a geothermal system in the bora field is thought to be closely related to tectonic activity which controls the emergence of geothermal manifestations. the prospect area is concentrated in the center of the research area, showing the bora fault and the central zone of the palu koro fault which have surface hot springs. meanwhile, the reverse fault in western zone of palu-koro fault could act as a border or barrier in the bora geothermal system. the results of the curve splitting and polar diagrams of the mt data, which shows the fault connected with the palukoro fault is a good permeable zone. these are consistent with the geological structure analysis derived from the fhd and svd analysis. acknowledgements the author would like to thank the geological agency under the ministry of energy and mineral resources of the republic of indonesia for providing geophysical data and giving permission to publish this paper. thanks also to the management of pt. newquest geotechnology to support this research by providing software. references daud, y., aswo, w., mulki, d., fahmi, f., pratama, s.a., hadi, j., 2015. identification of subsurface geological structure in a geothermal system using mt imaging technology. proceeding of world geothermal conference (melbourne, 19-25 april 2015), 1-4. daud, y., rosid, m.s., pati, g.p., maulana, m.r., khoiroh, m., 2018. reconstructing structural signature over the blawan-ijen geothermal area using gravity technology. aip conference proceedings 2023, 020280 (2018) doi: 10.1063/1.5064277. daud, y., sulistya, a., fahmi, f., nuqramadha, w.a., fitrianita., sesesega, r.s., et al., 2019. iop conference series: earth and environmental science 254(1), 012008. doi: 10.1088/1755-1315/254/1/012008 idral, m., mansoer, w.r., 2015. integrated geophysical studies of palu-koro depression zone, indonesia: implications for geothermal resources in bora central sulawesi 1. proceedings world geothermal congress 2015. corpus id: 202739716 psdg., 2010. final report of the integrated geological and geochemical survey of the bora geothermal area, sigi regency, central sulawesi province. bandung, pusat sumberdaya geologi. rosid, m s., ghufron, e., 2021. curve splitting analysis of synthetic mt data to identify permeable zone at geothermal field “x”. journal of physics: conference series 1816, 012082. doi:10.1088/17426596/1816/1/012082 simpson, f., bahr, k., 2005. practical magnetotelluric. cambridge, cambridge university press. ussher, g., harvey, c., johnstone, r., anderson, e., 2000. understanding the resistivities observed in geothermal system. proceedings of the world geothermal congress. kyushu tohoku, japan. vozoff, k. (1991). the magnetotelluric method. in m. n. nabighian (ed.), electromagnetic methods in applied geophysics 22, 1943-1961). doi: 10.1190/1.9781560802686.ch8. wibowo, a.e.a., hermawan, d., widodo, s., 2011. integrated geology and geochemical investigations in the bora geothermal regency, central sulawesi province geothermal research group (book 1: energy sector). proceedings of the activity results of the center for geological resources. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 chaerul, m. et al./ jgeet vol 02 no 01/2017 9 limestone facies and diagenesis on tondo formation at kaisabu village bau-bau city southeast sulawesi province muhammad chaerul 1, *, la ode ngkoimani 1 , sofyan sadri 1 1 universitas halu oleo, kendari, sulawesi tenggara . * corresponding author : * chaerul_geouho@yahoo.co.id abstract this study aims to determine the limestone facies and diagenesis on tondo formation. the method used was petrographic method bypolarizing microscope. based on the physical characteristics and biota contained, the carbonate rocks on tondo formation (tmtl) can be grouped into two facies, namely: wackestone and packestone. the diagenesis process that occurred in tondo formation research area is microbial micritization, cementation and neomorphism which indicate that the tondo formation has existed on diagenetic environment of marine phreatic, meteoric phreatic and meteoric vadose. keywords: tondo formation, diagenesis, limestone facies. 1. introduction the research area is a tondo formation (tmtl) located in one of the areas of bau-bau city. earlier, the researcher describes tondo formation (tmtl) as a formation of early miocene middle miocene period. the existence of limestone lithology in the research area is a unique and attractive geological phenomenon to serve as the research object in the final work. the development of highly sensitive limestone that affects the geological condition change will provide excellent information about the geological history. in the research area is included in tondo formation (tmtl), a formation composed of lithology of reef limestone and calcarenite. mixing between sediment which is a destruction of shallow marine sediments that is rich in benthic foraminifera with deep sea sediments is typical of this formation.the objective of the study is to determine the diagenetic process of limestone facieson tondo formation (tmtl) and the type of limestone faciesbased on the thin section analysis of the research area. 1.1 regional geology buton area is composed by rock unit which can be grouped into mesozoic and cenozoic rocks. the group of mesozoic rocks of triassic to upper cretaceous period and the group of cenozoic of miocene and pleistocene period. rock group that included in mesozoic consists of winto formation (trw), ogena formation (jo), rumu formation (jr) and tobelo formation (ktt) which are precipitated from the triassic to the late cretaceous period. the sedimentary rock group included in cenozoic then covers most of buton area which consists of tondo formation (tmtc), sampolakosa formation (tmps) and wapulaka formation (qpw) precipitated on the early miocene to pleistocene.buton stratigraphy according to davidson (1991) is classified into four tectonostratigraphy events, namely the pre-rift sedimentation consists of doole formation, winto formation, ogena formation; rift-drift sedimentation consists of rumu formation, tobelo formation; syn and post orogenic sedimentation consists of tondo formation and sampolakosa formation; younger deformation sedimentation (wapulaka formation) (davidson, 1991). tectonic events that occur repeatedly cause the older rocks experience several times of structure deformation, so that the older rocks are commonly encountered with the relatively sharp layer slope, while the younger rocks have relatively sharp layer slope than the old rocks. according to sikumbang, n., et al., (1995) the tectonic event has occurred several times starting from pre-eocene, where the tectonic pattern is difficult to determine due to the whole rock has undergone several folding and faulting. the main tectonic movement that forms the structure pattern until now is expected to occur in the eocene-oligocene period forming the trending imbrication structure of northeast-southwest. the next tectonic activity occurs between the pliocene-pleistocene resulting received: jan 15, 2017. revised : 18 jan 2017, accepted: feb 20 , 2017, published: 1 march 2017 doi: 10.24273/jgeet.2017.2.1.14 mailto:*chaerul_geouho@yahoo.co.id 10 chaerul, m. et al./ jgeet vol 02 no 01/2017 in the fold of pre-pliocene rocks. the last tectonic activity that occurred since pleistocene and has continued until now resulted in the uplifting of buton and muna island slowly, in time with the formation of reef limestoneon wapulaka formation that shows the steps. 1.2 diagenesis diagenesis is the process that occurs after the sedimentation process in a rock including chemical and physical process, but this change is not caused by changes in temperature and pressure (metamorphism) (scholle and (ulmer scholle, 2003 in flugel, 2004).diagenesis process is affected by several factors such as pressure, temperature, mineral stability, equilibrium conditions, rate of water influx, time and structure control. three main processes in diagenesis are dissolution, cementation and replacement. each process is characterized by different appearance depends on who interprets the condition of carbonate rocks formation. here is the process that occur in diagenesis: a. microbial micritization this process occurs in marine environment, which is formed by the presence of grains drilling activity by endolithic algae, fungi and bacteria around skeletal later the formed hole filled with fine-grained sediments or micrite envelope cement, i.e. micrite surrounding shell. e, so it will produce a shell that is completely micrited. this is an important process which generally occurs in the environment of stagnant marine phreatic zone and active merine phreatic zone (longman, 1980). b. dissolution the process of dissolution is known by their unstable minerals that dissolve and form other stable minerals at the new environment, due to the differences of diagenetic environment. it can occur in vadose zone and freshwater phreatic (longman, 1980). c. cementation cementation process is the main diagenetic process in carbonate sediment when the pore water phase has been saturated on the cement phase and there are no kinetic factors that may impede the cement precipitation. this process requires the large circulation of fresh water or sea water. diagenetic environment is indicated by the different mineralogy and cement fabric depending on the composition of pore water, speed of carbonate supply and precipitation. d. neomorphism neomorphism is the process of replacement and recrystallization when the change in mineralogy occurred. for example, the coarsening of crystal size on carbonate mud or micrite (aggrading neomorphism) and replacement of aragonite shells and cement by calcite (calcitization) (tucker and wright, 1990). this process may occur at the beginning of phreatic freshwater sedimentation and deep burial; e. dolomitization dolomitization is the process of replacement of mineral calcite into dolomite caused by the increase of mg content in carbonate rocks. factors that accelerate the dolomite precipitation is the magnitude of mg/ca ratio in minerals, the magnitude of co2 content, high temperature and ph, low sulphate content, low salinity content as well as the effect of organic material. dolomitization process may change into replacement by the precipitation process or in the form of cementation, which may occur in the environment of mixing zoneand deep burial(morrow. 1982). f. compaction according to tucker and wrigth (1990), the compaction process is divided in 2 types, namely: 1) mechanical compaction occurs when the loading becomes larger which cause cracks in the grains, grains are in contact to each other, porosity reduced. 2) chemical compaction occurs when the grains are in contact, experience dissolution, which produce suture contacts and concavo-convex contacts. studying the diagenesis products which present in a particular environment is the key to predict the tendency to porosity in carbonate rocks. according to longman (1980) in tucker and wright, (1990) the diagenetic environment is divided into five namely:marine phreactic zone, mixing zone, meteoric phreactic zone, meteoric vadose zone, and burial zone. 2. research methods the research area was located in the east of the bau-bau city, precisely in the area of kasiabu village, sorawolio sub district, bau-bau city, southeast sulawesi province. this type of research was a kind of field observation study, with the lithological data collection to determine the limestone facies and diagenesis on tondo formation. the research method used was petrographic analysis methodbyusing polarizing microscope 3. results and discussion 3.1 limestone diagenesis of the research area based on the results of the petrographic incision observation from the limestone sample, the diagenesis products contained in limestone on tondo formation (tmtl) are found, namely: a. microbial micritization this diagenesis product shows the type of microbial micritizationformed on petrographic incision.microbial micritizationis a diagenesis product formed at an early stage which is in the marine phreatic environment (longman, 1980). this product exists in almost all petrographic incision of carbonate rocks where the fossils grains with membranes made of micrite. the membrane chaerul, m. et al./ jgeet vol 02 no 01/2017 11 serves to protect the fossil shells so that it is more resistant to the dissolution. (figure 1) fig. 1. micritisasi microbial on foraminifera fossil in limestone (petrographic analysis cross nicol with magnifications 10x ) b. cementation this diagenesis product shows the type of cement that formed on petrographic incision. the type of cement at blocky petrographic incision analysis with calcite composition can be formed on a diagenetic environment of meteoric phreatic. (figure 2) fig. 2. blocky cement in limestone (petrographic analysis cross nicol with magnifications 10x ). c. microbial micritization petrographic observation at station 3 is a microbial micritization. micrite is a matrix that is usually dark in color. on the limestone, it is present as very fine grain. micrite has a grain size of less than 4 micrometers. in the electron microscopy study, it shows that micrite is not homogeneous and shows a rough to fine size with the boundaries between crystals planar, curved, jagged or irregular shape. micrite may suffer from alteration and may be replaced by a rough mozaicmicrospar (tucker, 1991). (figure 3) d. microbial micritization this diagenesis product shows the type of microbial micritizationformed on petrographic incision. this process occurs in marine environment, which is formed by the presence of grain drilling activity by endolithic algae, fungi and bacteria around skeletal. fig. 3. micritisasi microbial on foraminifera fossil in limestone (petrographic analysis cross nicol with magnifications 10x ) then the hole formed is filled with finegrained sediments or micrite envelope cement which is the micrite surrounding the shell. such produce a shell that is completely micrited. according to longman 1980, in tucker and wright 1990, it is an important process that generally occurs in an environment of stagnant marine phreatic zone and active marinephreatic zone. (figure 4) e. neomorphism from the results of the petrographic incision observation what is produced by this process is aggrading neomorphism which is micrite recrystallization into crystals the large-sized crystal is called microspar. the crystals formed have a more turbid microspar appearance because these crystals come from micrit recrystallization of carbonate mud. tucker and wright (1990) state that neomorphism occurred in diagenetic environment of meteoric phreatic and meteoric vadose. neomorphism is the process of replacement and recrystallization when the change in mineralogy occurred. for example, the coarsening of crystal size on carbonate mud or micrite (aggrading neomorphism) and replacement of aragonite shells and cement by calcite (calcitization) (tucker, 1990). (figure 5). based on the observations on diagenesis product both from field observations at the outcrop and the petrographic incision analysis it can be interpreted that the diagenetic environment traversed by limestone on tondo formation (tmtl), including the environment of marine phreatic, meteoric phreatic and meteoric vadose.micrite membranes due to boring organism (microbial micritization) on foraminefera and alga of one identifier of marine phreatic diagenetic environment. the presence of the type of cement of blocky of calcite composition shows the diagenetic environment of meteoric phreatic. neomorphismmicrite becomes microspar which 12 chaerul, m. et al./ jgeet vol 02 no 01/2017 shows the diagenetic environment of meteoric vadose (figure 6). fig. 4. micritisasi microbial on foraminifera fossil in limestone (petrographic analysis cross nicol with magnifications 10x ). fig. 5. changes in the size of the matrix becomes larger microspar (petrographic analysis cross nicol with magnifications 10x ). 3.2 limestone facies of the research area based on field observations and petrographic incision in the research area, it is concluded that there are two types of limestone facies, namely: a. packestone facies this facies found in reef limestoneunit in the research area which are scattered in the south to the east of kaisabu area. in this facies zone, the outcrop is characterized by limestone that does not have bedding. the rock characteristics in this zone in the outcrop scale has a moderate sorting with open container, generally the fragments are floating and matrix, generally the color of carbonate mud is light to massive.based on the observation in the field and the results of petrographic analysis on the rock samples, in the outline it is seen as dominated by packestonefacies. packestonefacies contained in this zone has the characteristics that contains fossil fraction in the large enough size namely the abundance of dominant red algae and there are also many shells of foraminifera.based on petrographic analysis on packestonefaciesit has the characteristics of abundance carbonate mud and dominated by grain. b. wackestone facies this facies found in calcarenite unit exists in the research area are scattered in the east to the west part of kaisabu area. in this facies, the rock outcrop is in grayish fresh color and generally massive and there are pores in it. the components are in the form of carbonate minerals such as calcite and dolomite. based on the field observation and the results of petrographic analysis of the rock samples, in the outline it is seen as dominated by wackestonefacies. the facies in this zone has the characteristics that contains an abundance of coral, dominant red algae and there are algae fraction along with other fossil fraction that cannot be identified.based on the results of petrographic analysis of wackestonefacies sample, it has the characteristics of very fine grain size and has associations with larger clastic fragments but not dominant. fig. 6. scheme diageneis environmental changes that occurred in the study area (tucker and wright, 1990) (petrographic analysis cross nicol with magnifications 10x ) 4. conclusions based on the analysis which has been conducted, the author concludes that: 1. the diagenetic process that occur in the research area of tondo formation is microbial micritization, cementation and neomorphism which indicate that the tondo formation has existed on diagenetic environment of marine phreatic, meteoric phreatic and meteoric vadose. 2. limestone research area is composed by two facies associations, namely algae facies foramineferapackestone and algae facies foraminefera wackestone. acknowledgement authors thank profusely to all parties who has support this research. chaerul, m. et al./ jgeet vol 02 no 01/2017 13 references boggs, s., jr., 1992, petrology of sedimentary rocks; macmillan pub. co., new york, 707 p. davidson, 1991, regional stratigraphy column of buton islands. dunham, r.j., 1962, classification of carbonate rocks according to depositional texture, in ham, e.e., ed.classification of carbonate rocks, aapg memoir i, p. 108-121. flugel, e., 2004. microfacies of carbonat rock. springer, inc, new york. longman, m. w.,1980. carbonate diagenetic textures from nearsurface diagenetic environment,bulletin aapg, 64, 461 -485. morrow, d. w., 1982. diagenesis 2 : dolomite, part 2. the geological association of canada. tucker, m.e., wright, v.p., 1990. carbonate sedimentology. blackwell publishing ltd., pp. 422 467. doi:10.1002/9781444314175.refs 1. introduction 1.1 regional geology 1.2 diagenesis 2. research methods 3. results and discussion 4. conclusions acknowledgement e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 anurogo w, et al./ jgeet vol 03 no 01/2018 15 modified soil-adjusted vegetation index in multispectral remote sensing data for estimating tree canopy cover density at rubber plantation wenang anurogo 1, *, muhammad zainuddin lubis 1 , mir'atul khusna mufida 2 , 1 geomatics engineering , politeknik negeri batam, batam riau island province, indonesia, 29461. 2 informatics engineering, politeknik negeri batam, batam riau island province, indonesia, 29461 . * corresponding author : wenang@polibatam.ac.id tel.:+6285743322991; office:+62778-469856 ext: 2510; fax: +62778-463620 received: dec 08, 2017. revised : jan 27, 2018, accepted: feb 07, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.1003 abstract forest inventories such as tree canopy density information require a long time and high costs, especially on extensive forest coverage. remote sensing technology that directly captures the surface vegetation character with extensive recording coverage can be used as an alternative to carrying out such inventory activities. this research aims to determine the level of vegetation canopy cover density on rubber plants that became the location of the research and know the accuracy of the resulting data. the method used in this research is a combination of remote sensing image interpretation, geographic information system, and field measurement. information retrieval from remote sensing data is done by using aster data imagery. this stage includes three parts, namely: pre-field stage, field stage, and post-field stage. the pre-field stage includes the collection of data to be used (including literature studies related to the theme of the study), image processing (geometric and radiometric correction), cropping, masking, land cover classification, vegetation index transformation, and sample determination. the final result of data processing showed that the density of the vegetation canopy in the research area ranged between 7.31 12.952 cm / m2 in each grade of vegetation density. these values indicate the range of low-class vegetation canopy cover density to high-class vegetation canopy cover density in the research area. in this research error rate or root mean square error obtained from the calculation of canopy cover density is equal to 1.89. keywords: canopy cover density, remote sensing, aster imagery, transformation vegetation index 1. introduction forest is one of the commodities that greatly affect the economic development of a country. however, forests are heavily influenced by socioeconomic pressures, along with increasing human demand for processed products from forests (anurogo & murti, 2013). this product can be a major forest product such as wood or forest products in the form of processed materials commonly used for industrial purposes. part of the use of this forest is to use land from forest areas to be converted into areas considered beneficial to human civilization in the vicinity of forest areas (diniyati & achmad, 2016). as a consequence of the increasing demand for forest products, there is a change of forest area into plantations and other lands. one of the many plantations in indonesia is rubber plantation. in some parts of indonesia, rubber crops are an important crop, in addition, can be used to obtain rubber commodities, rubber plants can also be used to meet the needs of forest supply areas. forest cover or forest canopy cover is the top of the vegetation that provides protection to the environment beneath it. the presence of canopy density information is important to assess as the canopy in forest cover can detect forest status indicators or interventions in forest resource management such as indications of degradation forest product quality, although forest cover classes are unchanged (noormasari & murti, 2014). forest inventories such as tree canopy density information require a long time and high costs, especially on extensive forest coverage. remote sensing technology that directly captures the surface vegetation character with extensive recording coverage can be used as an alternative to carrying out such inventory activities (anurogo et al., 2015; raharjo & sadono, 2008). remote sensing is a science or technology to obtain information or a natural phenomenon through an analysis of the data obtained from the recording object, area or phenomenon being studied (danoedoro, 2012; lubis et al., 2017). remote sensing technology in its development has a very fast development. this is indicated in the recording system or remote sensing data collection is done by using sensing devices installed on aircraft or satellites that have undergone rapid development so as to produce mailto:wenang@polibatam.ac.id 16 anurogo w, et al./ jgeet vol 03 no 01/2018 better quality and quantity of spatial data. the application of remote sensing satellites has been able to provide data/information on land natural resources and marine resources regularly and periodically (sari & lubis, 2017; karlinasari et al., 2012). the availability of remote sensing data in digital form enables computer-based analysis in a quantitative and consistent ways. furthermore, remote sensing data can be used as independent input for field verification. with remote sensing technology, field data retrieval can be reduced so that it will save time and cost when compared with direct measurement in the field (anurogo et al., 2017). remote sensing data analysis is an activity to re-recognize the appearance of objects that have been captured by the satellite-carrying sensors. the appearance of the image in the presentation of data details is influenced by the level of spatial resolution (sukarna, 2015; nadi and murad, 2017; taki et al., 2017). msavi is a transformation of vegetation index developed from ndvi transformation to minimize the effect of soil reflection on ndvi. there are two basic notions of the use of the vegetation index and its development. the first assumption is the vegetation index is a multi-channel algebra combination that can produce certain information about vegetation. the second assumption is that the open ground on the image will produce an imaginary line which is then called the land line. the line is assumed as a representative line without vegetation (anurogo et al., 2015). the transformation of the vegetation index has been developed to produce results that are sensitive to the spectral response of vegetation objects. 2. research method this research is about estimating the density of canopy cover by using remote sensing data technology. the method used in this research is a combination of remote sensing image interpretation, geographic information system, and field measurement. information retrieval from remote sensing data is done by using aster data imagery. the aster image data has a spatial resolution of 15 m on visible near infra-red channel. the channels used in this research is channel of visible and near infrared (vnir). the aster data image spatial resolution is shown in table 1. table 1. the aster data image spatial resolution type number of channels spectrum ground resolution vnir 3 bands 0.52 0.86 um 15 m swir 6 bands 1.60 2.43 um 30m tir 5 bands 8.125 11.65 um 90m source: (anurogo & murti, 2013) the location of the research lies in universal transverse mercator coordinate x: 444800,391 y: 9194335,339. the location of the research is shown in fig 1. fig 1. location of the research area anurogo w, et al./ jgeet vol 03 no 01/2018 17 stages of this research is a step that must be done to answer the purpose of research conducted. this stage includes three parts, namely: pre-field stage, field stage, and post-field stage. the pre-field stage includes the collection of data to be used (including literature studies related to the theme of the study), image processing (geometric and radiometric correction), cropping, masking, land cover classification, vegetation index transformation, and sample determination. the field stage aims to obtain information from a predetermined sample. post-field stage is intended to process the data that has been collected, statistical analysis, test the accuracy of the results. the transformation of vegetation index used in this research is msavi. msavi is a transformation of a vegetation index developed from ndvi transformations to minimize the effect of soil reflections on ndvi. msavi = {2(nir) + 1 8{(nir) red}/2 (1) the transformation reduces the reflection of the soil which is the background of the vegetation where the transformation is considered suitable for the rubber plant characteristic model, where the rubber plant has a canopy which is said to be less dense so that the waves emitted from the sensor are likely to continue to the ground so that the reflection received from the sensor is partially soil reflection so as to reduce or minimize the appearance of reflections from the soil, used msavi transformation. to minimize this effect, the l factor is given to the vegetation index formulation. the values for this l factor differ for each density level, for high vegetation cover, l value is 0,0 and for low vegetation cover the value of l is 1.0. while for medium size vegetation, then the value of l is 0.5. the existence of this soil object will contribute as a background to the reflection of vegetation, thus affecting the value of reflected in the digital data remote sensing (anurogo et al., 2015). the l value of the factor used is 0.5 because the rate of that constant can balance the reflection of the vegetation object and the reflection of the soil that become the background of the image data recording. the next stage is the data taking of canopy width values in the field with the transformation of the vegetation index. at this stage, measurements of trunk diameter, canopy width, and height of branch free rods were measured. in addition, field work serves as a test of accuracy, ie matching the results of interpretation of the image with the condition of the field. the accuracy test method used is with an error matrix or confusion matrix. this method uses an independent set of data that is logically more acceptable to the truth. this accuracy test includes two main things: to test the accuracy of the classification result of land cover and to find the data of vegetation density. the plot of the sample field is shown in fig 2. fig 2. plot shape in the measurement of vegetation density the data is then later correlated with the value of each pixel image transformation to obtain a map of plant canopy density. correlation and regression analysis is used to find the relationship between vegetation index transformation used with rubber plant density data obtained from the field so that if through the statistical approach found strong correlation result between the two variables, there is a correlation between the transformation of vegetation index which is used with rubber plant canopy density. 3. results and discussion the first image tapping process is a land cover analysis using a multispectral classification. multispectral classification is intended to facilitate the exploration of objects contained in images that have a similarity of spectral value. the multispectral classification used to obtain this land cover information is a supervised multispectral classification with the maximum likelihood method. the maximum likelihood method describes the pixels in the image based on the probability of a pixel to fit into a particular class. the land cover class that is sought is the class of land cover which is aimed to distinguish between vegetation object and non-vegetation object. the object of this vegetation is very prominent in aster composite image 321 with the dominant color of vegetation is a red color, so the result of multispectral classification can be compared with the color composite result, by comparing the pattern of color distribution in each view. the class input of this maximum likelihood classification is the training area used to collect the samples used as the basis for class classification. this training area is taken from the region of interest (roi) by taking samples of each object in one scene image area of study. the selection of roi based on the vegetation appearance of the image channel composite and based on the reflected reflectance value recorded on the image data. the boundary of the research area is the boundary of the rubber plantation. the boundary of the research was obtained by using multispectral classification data as the basis and the visual interpretation used to 18 anurogo w, et al./ jgeet vol 03 no 01/2018 help further reinforce the boundary of the study location taken. the multispectral classification is used to isolate vegetation and non-vegetation objects. red color indicates the vegetation area based on the value of reflect spectral while green color is non vegetation area. the multispectral classification result is shown in fig 3. fig 3. multispectral classification result after the multispectral classification, then processing the transformation of msavi index on vegetation classification class which will serve as one of the sampling field basis in order to obtain information of vegetation canopy density. the research mapping unit was obtained from the land cover that had been created combined with the visual interpretation result data, resulting in the boundary of the research area in the form of border of rubber plantation located in tembir, salatiga. the boundary of the mapping unit is then used as the basis for field sampling to retrieve information that cannot be extracted directly using remote sensing image data. sampling is done by purposive sampling that each class is taken a sample by purpose. this field survey aims to test the level of similarity between the data we have worked on before the field and to retrieve the necessary data that cannot be known directly from remote sensing image and can only be obtained through direct measurement or retrieve existing data from the agency or service related. the assumption is that the more possible the rubber plant is at maximum productive age, then the greater the width of the existing canopy cover. of all the areas studied, 42 samples were measured and used to represent the entire rubber plantation area. the msavi transformation is shown in fig 4. fig 4. the msavi transformation index anurogo w, et al./ jgeet vol 03 no 01/2018 19 the result of transformation processing of msavi index shows that the range of values for the vegetation class is at 0.2699 0.467. these values indicate the range in low-class vegetation canopy cover density to high-class vegetation canopy cover density in the research area. the transformed value range data is then correlated with data of canopy cover width obtained from the field survey. to 42 field samples then divided into two parts. the first part is a collection of samples used to create a model of regression correlation analysis between the two variables. another sample part is to test the sample accuracy by using root mean square error (rms e) to determine the error rate of the model. the model sample is shown in table 2. table 2. model sample between canopy and msavi index no canopy cover width (cm) msavi index 1 8.226 0.363 2 7.48 0.305 3 8.96 0.319 4 9.98 0.353 5 6.09 0.271 6 9.168 0.325 7 9.33 0.353 8 10.218 0.323 9 8.3 0.343 10 8.12 0.301 11 9.78 0.325 12 8.15 0.28 13 6.82 0.258 14 8.58 0.302 15 7 0.231 16 5.56 0.252 17 8 0.28 18 7.04 0.263 19 8.04 0.29 20 8.18 0.305 the correlation model constructed is the relationship between the width of the canopy cover (density of the canopy) and the value of the transformation vegetation index used. the values of the transformation vegetation index are seen from the image of the transformation index on each sample unit, based on the vegetation index values found in each sample coordinate were taken. the result of the correlation between the index value of msavi vegetation index with the width of the canopy shows that the two variables are related to each other. this is indicated by the magnitude of r 2 value on the results of the correlation of both variables is 0.709. the value is large and acceptable when viewed from the number of samples used to construct this model. the number of samples used to build this model is 20 samples, whereas in the diagram of the appendix table it is mentioned that with 20 samples, the minimum value of r 2 that can be used is 0.32, so with the r 2 value of 0.709, the value is quite good and the two variables are interconnected. the 2-dimensional diagram of regression is shown in fig 5. fig 5. the 2-dimensional diagram of regression between msavi and canopy the accuracy test is performed to find out how much error rate is generated from the field data that has been taken to create the model. this accuracy test is performed on variables directly related to variables from remote sensing data to ascertain whether information derived from remote sensing data can be used. the variable that is done by the accuracy test is the canopy cover with the transformation value of the vegetation index used. the result of y1 accuracy test (canopy diameter) with msavi vegetation index value gives standard error value (se) equal to 1.89. the value of se is arguably very small for the error rate of the data used. this value indicates that at each value generated in the study, it only experienced a shift of 1.89 in the transformation model created. so, when viewed from the value, then the data canopy diameter generated ranges greater or less than the value of se produced. from the value of the standard error that is not too large, prove that the data extraction using remote sensing image can be used as a tool in the calculation and delivery of spatial information about the density of canopy cover. the accuracy sample shown in table 3. the final result of data processing showed that the density of the vegetation canopy in the research area ranged between 7.31 12.952 cm / m 2 in each grade of vegetation density. these values indicate the range in low-class vegetation canopy cover density to high-class vegetation canopy cover density in the research area. canopy cover density distribution of data displayed in fig 6. y = 36,139x 4,2365 r² = 0,7098 0 2 4 6 8 10 12 0 0,2 0,4 0,6 20 anurogo w, et al./ jgeet vol 03 no 01/2018 table 3. the accuracy sample model no canopy cover width (cm) msavi index y1' msavi y1-y1' msavi 1 6.18 0.2996 6.588548 0.166911468 2 7.6 0.302 6.67526 0.855144068 3 8.42 0.342 8.12046 0.089724212 4 8.4 0.356 8.62628 0.051202638 5 7.825 0.367 9.02371 1.436905664 6 9.875 0.384 9.63792 0.056206926 7 6.725 0.338 7.97594 1.564850884 8 9.9 0.36 8.7708 1.27509264 9 6.945 0.316 7.18108 0.055733766 10 7.5 0.342 8.12046 0.384970612 11 7.7 0.351 8.44563 0.555964097 12 8.325 0.359 8.73467 0.167829509 13 6.875 0.334 7.83142 0.914739216 14 7.2 0.306 6.81978 0.144567248 15 7.15 0.329 7.65077 0.250770593 16 9.45 0.292 6.31396 9.834746882 17 7 0.342 8.12046 1.255430612 18 10.575 0.368 9.05984 2.295709826 19 8.425 0.347 8.30111 0.015348732 20 8.425 0.367 9.02371 0.358453664 21 6.725 0.311 7.00043 0.075861685 22 9 0.379 9.45727 0.209095853 75.67967615 rms e 1.898366167 fig 6. the distribution of canopy cover density anurogo w, et al./ jgeet vol 03 no 01/2018 21 4. conclusions the measurement of canopy density levels in vegetation can be calculated using aids from remote sensing image data. the use of such technology aids using a variety of approaches to get more accurate results. the final result of data processing using msavi transformation in measuring the density of the canopy showed that the density of the vegetation canopy in the research area ranged between 7.31 12.952 cm / m2 in each grade of vegetation density. these values indicate the range in low-class vegetation canopy cover density to high-class vegetation canopy cover density in the research area. in this research error rate or root mean square error obtained from the calculation of canopy cover density is equal to 1.89. references anurogo, w., lubis, m.z., khoirunnisa, h., pamungkas, d.s., hanafi, a., rizki, f., surya, g., situmorang, a.d.l., timbang, d., sihombing, p.n. and lukitasari, c.a., 2017. a simple aerial photogrammetric mapping system overview and image acquisition using unmanned aerial vehicles (uavs). journal of applied geospatial information, 1(01), pp.11-18. anurogo, w., murti, s.h. and khakhim, n., 2015. analisis perubahan hutan mangrove dalam penentuan kawasan rehabilitasi dan perubahan stok karbon menggunakan data penginderaan jauh (di teluk banten, serang provinsi banten) (doctoral dissertation, universitas gadjah mada). anurogo, w. and murti, s.h., aplikasi penginderaan jauh untuk estimasi produksi tanaman karet (hevea brasiliensis) di kota salatiga, jawa tengah. danoedoro, p., 2012. pengantar penginderaan jauh digital. yogyakarta: andi. diniyati, d. and achmad, b., 2015. kontribusi pendapatan hasil hutan bukan kayu pada usaha hutan rakyat pola agroforestri di kabupaten tasikmalaya. jurnal ilmu kehutanan, 9(1), pp.23-31. karlinasari, l., sabed, m., wistara, n.j., purwanto, a. and wijayanto, h., 2012. karakteristik spektra absorbansi nir (near infra red) spektroskopi kayu acacia mangium willd pada 3 umur berbeda. jurnal ilmu kehutanan, 6(1), pp.45-52. lubis, m.z., anggraini, k., kausarian, h. and pujiyati, s., 2017. marine seismic and side-scan sonar investigations for seabed identification with sonar system. journal of geoscience, engineering, environment, and technology, 2(2), pp.166-170. nadi, p.a. and murad, a., 2017. reviewing the use of geographic information system (gis) to measure sustainable urban transport performance. journal of geoscience, engineering, environment, and technology, 2(2), pp.171-177. noormasari, m. and murti, s.h., 2014. pemanfaatan citra alos avnr-2 untuk estimasi produksi tanaman jati dengan menggunakan metode transformasi spektral indeks vegetasi (daerah kajian: sebagian kabupaten gunung kidul) (doctoral dissertation, universitas gadjah mada). raharjo, j.t. and sadono, r., 2008. model tajuk jati (tectona grandis lf) dari berbagai famili pada uji keturunan umur 9 tahun. jurnal ilmu kehutanan, 2(2), pp.89-95. sari, d.p. and lubis, m.z., 2017. pemanfaatan citra landsat 8 untuk memetakan persebaran lamun di wilayah pesisir pulau batam. jurnal enggano, 2(1). sukarna, r.m., perubahan struktur dan komposisi hutan rawa gambut menggunakan citra penginderaan jauh dan pendekatan ekologis di kawasan bekas pengembangan lahan gambut provinsi kalimantan tengah. jurnal ilmu kehutanan, 7(2), pp.129-146. taki, h.m., maatouk, m.m.h., qurnfulah, e.m. and aljoufie, m.o., 2017. planning tod with land use and transport integration: a review. journal of geoscience, engineering, environment, and technology, 2(1), pp.84-94. 1. introduction 2. research method 3. results and discussion 4. conclusions references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 03 2018 134 moreno, wilmer.e g. / jgeet vol 03 no 03/2018 research article analysis of colombian seismicity as a way to explain and understand the bucaramanga nest wilmer emilio garcía moreno 1, * 1 geophysical engineering, earth science department, simon bolivar university, caracas, venezuela. * corresponding author : wilgm93@gmail.com tel.: +55 51 9 8563 4471 received: june 13, 2018; accepted: august 11, 2018. doi: 10.24273/jgeet.2018.3.3.1709 abstract colombia is region with high seismicity due to the convergence of panama block, nazca and caribbean plates with the south american plate, however there is a complex area named the bucaramanga nest which was the motive of this research means of its complexity, being that there have been different studies which have not been able to explain the reason of this phenomenon, for that motive this work has as objective finding this answer by the use of 3679 earthquake information in colombia, with a mw higher than 3.5. having information from all the earthquakes, they were localized on its epicenters to notice how they were distributed, after that, five lines were chosen to make, along them, the benioff zone, obtaining the geometry of the slabs for nazca and caribbean plates, knowing the angle of subduction of them and how it changed, also, thirty earthquakes near the five lines were selected to see the focal mechanisms along the slabs and knowing the fault system in the bucaramanga nest. beside all it was said before, it was modeled an approximation of the subduction zones by a contour map along the studied region. at the end, it was able to reach an answer about the reason of why the bucaramanga nest happened, defining its vertical and lateral extension too. keywords: bucaramanga nest, slab, nazca plate, caribbean plate and south american plate 1. introduction south america is a region with complex seismicity, having every kind of plate boundaries, and colombia is not the exception, being a good example of this, due to it exhibits three limits of tectonic plates, which are south american plate, caribbean plate and nazca plate, although taboada, et al. (2000) mentioned a fourth plate, being added the panama block as the last one and, for that reason, all this interaction has become colombia in a seismic active area where it can be found some nests as the cauca and bucaramanga nest, being the last one the most important and the reason of different studies and this research too. a nest could be defined as a high seismological activity confined in a volume and it can be noticed in certein subduction zones (zarifi, et al., 2007), however, the remarkable things is because of the activity in the bucaramanga nest is clustered in a spaced much smaller than other nest around the world (pennington, et al., 1979) within a 30km-cube centered at 6.8ºn and 73ºw inside an average depth of 160km (frohlich, et al., 1995), and with a relative paucity activity compared wiht the surronding areas (schneider, et al., 1987). the reasons of this intense activity is still unknown and it could be owing to lack of local data and tectonic complexitivity (zarifi, et al., 2007), nevertheless, there are some researchings where different models are proposed, such as the bucaramanga nest befalls by partial melting (shih, et al., 1991), otherwise, it is said that nazca and caribbean plates have no volcanism correlation (chen, et al., 2001). on the other hand, there are different ideas for example, the caribbean plate is the only plate that intervents and there is no relation with nazca plate wich has effect in the cauca nest (malavé & suárez, 1995), also the subducting slab, which is supposed to be the caribbean plate, tears off (cortés & angelier, 2005). antoher model proposed says that the bucaramanga nest is induced because of an overlaping of nazca plate over caribbean plate in north (van der hilst & mann, 1994) or at the boundary between them (corredor, 2003) and, also, with the interaction between these plates, the nazca slab could tear off due to a transition to caribbean plate (vargas & mann, 2013) (fig. 1). in spite of the different existing models and the uncertainty about plate boundaries mentioned before, the principal objetive of this research is to find why and how the bucaramanga nest happens, studying a set of seismological data in colombia, provided by usgs, doing analysis of the information by profiles, mapping, tectonical setting and focal mechanism. http://journal.uir.ac.id/index.php/jgeet mailto:wilgm93@gmail.com moreno, wilmer.e g. / jgeet vol 03 no 03/2018 135 fig. 1. regional tectonic system. br: baudo range; wc: western cordillera; cc: central cordillera; ec: eastern cordillera; rf: romeral fault; uf: uramita fault; bof: bocono fault. modified from: cortés & angelier (2005) 2. regional tectonic setting the south american northwestern area is an interesting zone due to its tectonic activity (moncayo, et al., 2018) for that reason, colombia is, still, an discussed issue without reaching an agreement (ojeda & havskov, 2001), however, the last proposed model suggests the convergence of four plates (nazca, caribbean and south american plate and the panama arc) (taboada, et al., 2000). fig. 2. colombian tectonic features. modified from ojeda & havskov (2001) on the other hand, this region gives a good case of stress field, being that, it is evolved in it because of an oblique convergence of the panama arc collisions at subduction zone (egbue, et al., 2013) and the gps studies gives a context to understand the widespread of this arc and its collision with south america (vargas & mann, 2013). fig. 3. configuration and plate boundaries. modified from cortés & angelier (2005) besides the panama block, there are the other three existing plates; one of them is the nazca plate, which has a displacement of around 5-7 cm/yr (freymueller, et al., 1993) subducting the south american plate on the southwest region. in addition, another caribbean plate vel: 20 mm/yr nazca plate vel: 54 mm/yr south american plate south american plate nazca plate caribbean plate panama block bucaramanga s ou th american plate c ari bbean plate naz ca pl ate bucaramanga 136 moreno, wilmer.e g. / jgeet vol 03 no 03/2018 subductingplate is the caribbean plate with an average movement of 2 cm/yr from nw to ne (trenkamp et al., 2002); nonetheless, the boundary caribbean-south american plate is still not well-defined (ojeda & havskov, 2001). the south american plate has a block named north andes block, which received all the strain from the other plates and block. also, this block has a strike-slip fault (santa marta-bucaramanga fault) and a frontal fault system which are surrounding the bucaramanga nest (fig. 2) and all the interaction between plates can be seen on fig. 3. 3. methodology to reach all the results it was followed the next steps and, at the end, they were integrated to obtain the principal objective. 3.1. data upload it was downloaded information (table 1) from different 3679 earthquakes from the usgs site (fig. 4) which will be analyzed. table 1. data parameters data name minimum value maximum value date november 1921 june 2018 latitude (º) 1 13 longitude (º) -78.5 -70.5 magnitude (mw) 3.5 depth (km) 200 fig. 4. location of the worked area. the red square is where the earthquakes are located 3.2 benioff zone and focal mechanism analysis after downloading the data from usgs, five lines (fig. 5) were chosen to make the benioff zones graphing depth vs distance along the five lines and noticing in origin pro how the slab configuration is. in addition, it was selected 30 earthquakes that had associated focal mechanisms. this information was conjugated with the benioff zone to know how the fault systems are, giving information about the bucaramanga nest configuration. finally, in this point, it was calculated an approximately angle of dipping for every benioff zones. 3.3 mapping the subduction zone having all the data, the earthquakes were localized with their coordinates in a xy area, where it was made a contour map using the depth information and, in this way, getting an approximation of subduction geometry. fig. 5. location of the lines 4. results following every step mentioned on methodology, the results obtained were: 4.1. data upload all the seismic data was uploaded as it is shown on fig. 6. in this image, it can be notice two earthquake clustered datas, one on sw that is the cauca nest and other on the ne, near venezuela, and it is the bucaramanga nest fig. 6. fig. 6. all the seismic data located. the meaning of the colored circles are the depths; orange: 0-33km; yellow: 33-70km; green: 70-150km; blue: 150km or deeper besides the observed clusters, it is possible to moreno, wilmer.e g. / jgeet vol 03 no 03/2018 137 appreciate a tendency on the earthquake depths from the plate limits (west, northwest and north) to the both nests and the depth around the bucaramanga nest is consistent, approximately 160km deep. 4.2 benioff zone and focal mechanism analysis all the 30 earthquakes were located near the lines shown on fig. 5 to observe how the kind of existing faults. also, five focal mechanisms were located on the bucaramanga nest as it is noticed on fig. 7. fig. 7. location of focal mechanisms using these focal mechanisms, they were located to their corresponded lines on the benioff zones, as they can be seen on the next figures (from fig. 8 to fig. 12). fig. 8. benioff zone (line 1) fig. 9. benioff zone (line 2) fig. 10. benioff zone (line 3) fig. 11. benioff zone (line 4) 138 moreno, wilmer.e g. / jgeet vol 03 no 03/2018 fig. 12. benioff zone (line 5) noticing the benioff zones, it is clearly shown the bucaramanga nest due to a cluster at an approximately depth of 160 km (lines 1, 3, 4 & 5), where are localized five focal mechanisms (fig. 14), which correspond to oblique faults, specifically, reverse faults with a strikeslip component, with a fault plane around 15-40º. besides, at the same time, this fault system is saying that the bucaramanga nest is a stressed region with it is receiving an external force. from the slabs gotten on benioff zones, it was calculated the different angle of subduction (table 2) which they are symbolized by a blue triangle. it is remarkable saying that the lines 1 and 4, two angles of subduction were calculated means of it changed before arriving to the bucaramanga nest. table 2. subduction angles in the lines line 1 line 2 line 3 line 4 line 5 angle (º) 13.5 36 25 14.5 14 42 27 from the table of angles and knowing the configuration of tectonic plates (nazca plate: lines 1, 2 & 3; caribbean plate: lines 4 & 5) it is noticed that the nazca plate is reducing its angle of subduction from south to north. on the other hand, the caribbean plate it is consisted with its angle. 4.3 mapping the subduction zone with the depth of every earthquake, it was possible to make a contour map to observe an approximation of how the subduction is in colombia and how it can be seen on the bucaramanga nest. fig. 13. earthquake depth contour map it is clearly well-defined the tendency of subduction and the depth around the bucaramanga nest. another thing is that deepest areas are where the cordilleras are located. fig. 14. focal mechanisms on bucaramanga nest moreno, wilmer.e g. / jgeet vol 03 no 03/2018 139 fig. 15. slab geometry 5. discussions after noticing all the gotten results it was able to design the plate subduction structures (fig. 15) that lets to know why the bucaramanga nest happens. observing the subduction geometry for the tectonic plates, the supposed theory is that there is a collision between the caribbean plate and the nazca plate, nonetheless, this collision occurs obliquely due to they have an angle of contact, being that, as is it shown on fig. 15, there is a place on the west which no plate is subducting. besides, means of the angle of subductions of every plate, mentioned on table 2, and the oblique contact, these plates only have this kind of contact and after that, they continue their subduction. on the other hand, from the benioff zones it was possible to get the contact surface (fig. 16). 6. conclusions bucaramanga is a complex area, difficult to define, nevertheless in this work it was able to find a possible answer which could explain how the bucaramanga nest happens, due to a collision between the two slabs, being that, the nazca plate changes is subduction angle at north, letting it reach the caribbean plate path. on the other hand, the tectonic configuration in colombia should be more studied, first to define better the plate limits and also to reach an answer more agreed upon the bucaramanga nest. 7. acknowledgement thanks to the usgs platform which has available seismic data to download without any kind of payment, being, in this way really, important to do this paper. fig. 16. colition contact surface references chen, p.-f., bina, c. & okal, e., 2001. variations in slab dip along the subducting nazca plate, as related to stress patterns and moment release of intermediate‐depth seismicity and to surface volcanism. geochemistry, geophysics, geosystems, 03 december. https://doi.org/10.1029/2001gc000153 corredor, f., 2003. seismic strain rates and distributed continental deformation in the northern andes and three-dimensional seismotectonics of northwestern south america. september, 372(3-4), 147-166. https://doi.org/10.1016/s00401951(03)00276-2 cortés, m. & angelier, j., 2005. current states of stress in the northern andes as indicated by focal mechanisms of earthquakes. tectonophysics, july, volume 403, 29-58. https://doi.org/10.1016/j.tecto.2005.03.020 egbue, o., kellogg, j., aguirre, h. & torres, c., 2013. evolution of the stress and strain fields in the eastern cordillera, colombia. journal of structural geology, january, 58, 8-21. https://doi.org/10.1016/j.jsg.2013.10.004 freymueller, j., kellogg, j. & vega, v., 1993. plate motions in the north andean region. journal of geophysical research, 10 december, 98(b12), 21,853-21,863. https://doi.org/10.1029/93jb00520 frohlich, c., 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(http://creativecommons.org/licenses/by-sa/4.0/). https://arxiv.org/abs/1804.07235v1 https://doi.org/10.1023/a:1012053206408 https://doi.org/10.1029/gl006i002p00065 https://doi.org/10.1029/jb092ib13p13913 https://doi.org/10.1130/0091-7613(1991)019%3c0807:saaasp%3e2.3.co;2 https://doi.org/10.1130/0091-7613(1991)019%3c0807:saaasp%3e2.3.co;2 https://doi.org/https:/doi.org/10.1016/s0895-9811(02)00018-4 https://doi.org/https:/doi.org/10.1016/s0895-9811(02)00018-4 https://doi.org/10.1130/0091-7613(1994)022%3c0451:tiotio%3e2.3.co;2 https://doi.org/10.1130/0091-7613(1994)022%3c0451:tiotio%3e2.3.co;2 https://doi.org/10.1785/0120120328 https://doi.org/10.1016/j.tecto.2007.06.004 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. regional tectonic setting 3. methodology 3.1. data upload 3.2 benioff zone and focal mechanism analysis 3.3 mapping the subduction zone 4. results 4.1. data upload 4.2 benioff zone and focal mechanism analysis 4.3 mapping the subduction zone 5. discussions 6. conclusions 7. acknowledgement references jgeet_cover_print_vol 2 no 3 2017.cdr p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 .(0761) 72126 , fax. 0761-674834phone e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. mursyidah, 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waters its relation to indian ocean dipole (iod) .......................................................................... 255 5. mapping of vegetation and mangrove distribution level in batam island using spot-5 satellite imagery .................................................................. 264 6. hydro chemistry and characteristics of groundwater: case study water contamination at citarum river upstream ................................................ 268 7. slope stability analysis based on type, physical and mechanical properties rock in teluk pandan district, east kutai regency, east kalimantan province ..................................................................................................... 272 8. geoelectricity data analysis for identification the aquifer configuration in bandorasawetan, cilimus, kuningan, west java province .......................... 278 author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should 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doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press p-issn jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet e-issn page 1 page 2 page 3 page 4 page 5 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 180 austin, o.e et al./ jgeet vol 03 no 04/2018 research article cross plot analysis of rock properties from well log data for gas detection in soku field, coastal swamp depobelt, niger delta basin okoli emeka austin 1 , agbasi okechukwu ebuka* 2 , onyekuru samuel 1 , sunday edet etuk 3 1 department of geology, federal university technology, owerri, nigeria. 2 department of physics, michael okpara university of agriculture, umudike, nigeria 3 department of physics, university of uyo, uyo, nigeria * corresponding author : ebukasean09@yahoo.com tel.: +237069547850 received: august 31, 2018; accepted: october 04, 2018. doi: 10.24273/jgeet.2018.3.4.1318 abstract the cross plotting of rock properties for fluid and lithology discrimination was carried out in a niger delta oil field using well data x-26 from a given oil field in the coastal swamp depobelt. the data used for the analysis consisted of suites of logs, including gamma ray, resistivity, sonic and density logs only. the reservoir of interest horizon 1, was identified using the available suite of logs on the interval where we have low gamma ray, high resistivity, and low acoustic impedance specifically at depths 10,424 ft (3177.24 m) to 10 724 ft (3268 m). we first obtained other rock attributes from the available logs before cross plotting. the inverse of the interval transit times of the sonic logs were used to generate the compressional velocities and the s-wave data was generated from castagna´s relation. employing rock physics algorithm on hampson russell software (hrs), rock attributes including vp/vs ratio, lambda-rho and mu-rho were also extracted from the well data. cross-plotting was carried out and lambda rho (λρ ρ) cross-plots proved to be more robust for lithology identification than vp versus vs crossplots, while λρ versus poisson impedance was more robust than vp/vs versus acoustic impedance for fluid discrimination, as well as identification of gas sands. the crossplots were consistent with rock physics templates (rpts). this implies the possibility of further using the technique on data points of inverted sections of various avo attributes within the field in areas not penetrated by wells within the area covered by the seismic. keywords: compressional velocities, coastal swamp depobelt, impedance, lambdarho, murho 1. introduction cross plots are visual representations of the relationship between two or more attributes, and they are used to visually identify or detect anomalies which could be interpreted as the presence of hydrocarbon or other fluids and lithologies. cross plot analysis are carried out to determine the attributes that better discriminate the reservoir (omudu et al., 2007). cross plotting appropriate pairs of attributes so that common lithologies and fluid types generally cluster together allows for straightforward interpretation. the off-trend aggregations can then be more elaborately evaluated as potential hydrocarbon indicators (chopra et al., 2003). rock physics describes a reservoir by physical properties such as porosity, rigidity, compressibility; properties that would affect how seismic waves physically travel through the rocks. it, thus, seeks to establish relations between these material properties and the observed seismic response thereby developing a predictive theory so that these properties may be detected seismically (dewar, 2001). velocities and elastic parameters are basically what link these physical rock properties to seismic expression, and to establish this relationship, we need; i) knowledge about the elastic properties of the pore fluid and rock frame. ii) models for the rock-fluid interactions. these are initially obtained from well-log data (dewar 2001). the first step in rock physics analysis is to obtain these elastic properties from well logs within select geologic units and cross-plot them. the knowledge of the crossplot cluster pattern at known well location would be used to investigate other locations without well penetration covered by the seismic. in interpretational practice, modeling and well templating help to define the type of trends an interpreter should be looking for (burianyk and pickford, 2000). http://journal.uir.ac.id/index.php/jgeet austin, o.e et al./ jgeet vol 03 no 04/2018 181 rock physics is usually integrated with avo analysis for a better understanding of lithology and fluid differentiation. rock physics creates a link between geophysical observable to geological parameters and nowadays becomes an important part of reservoir characterization (golyan, 2012). various rock physics models have their benefits and limitations. fluid and lithology discrimination are carried out for reservoir by applying different rock physics templates (rpts). by plotting acoustic impedance (ai) versus vp/vs ratio (where vp and vs are velocities of primary waves and velocity of secondary waves respectively), data points concentrate within a narrow zone indicating high ai and vp/vs ratio suggest that application of rock physics template in the study area needs significant modification compared to generalized rpts. as typically used in the oil and gas industry, the term rock physics is usually applied to the measurement, modeling, and interpretation of elastic wave propagation in sedimentary rocks (golyan, 2012). this article shows the application of cross plotting of rock properties for fluid and lithology discrimination based on trends established from the rock physics templates in a field in the coastal swamp depobelt. an important question to be answered would be, which attributes would be most helpful in discriminating gas sand? 2. field location and geology the tertiary niger delta is geologically divided into three formations representing prograding depositional facies distinguished mostly on the basis of sand-shale ratio (inyang, et al 2015; short, et al 1967; kulke, 1995). these three formations are the benin formation or continental alluvial sands, the paralic agbada formation and the prodelta marine akata formation (akpabio, et al 2014: agbasi, et al 2017). the akata formation is the basal part or unit of the tertiary niger delta complex (agbasi, et al 2013; mode, and anyiam, 2007). it is of marine origin and composed of thick shale sequences which on the basis of geochemistry are believed to be the source rock of the niger delta petroleum system (ubong, et al 2017). in the deepwater region of the niger delta such as the bonga field, turbidite sandstone with minor amount of clay and silt compose the major reservoir units. the akata formation is believed to have formed during low stands when terrestrial organic matter and clays were transported to deep-sea waters characterized by low energy conditions and oxygen deficiency (inyang, et al 2015; inyang, et al 2017; starcher, 1995). the formations in the niger delta, nigeria consist of sands and shale with the former ranging from fluvial (channel) to fluvial-marine (barrier bar), while the later are generally fluvial-marine or lagoon. these formations are mostly unconsolidated and it is often not feasible to take core samples or make drill stem tests (agbasi, et al 2017). x-field is located some few kilometers southwest of port harcourt within the niger delta basin as shown in fig. 1. the niger delta lies between latitudes 3° n and 6° n and longitudes 5° e and 8° e. the structure in xfield is a complex collapsed crest, rollover anticline, elongated in an east-west direction. the zone of interest is typically a sand/shale/sand sequence. the well is located at the northwestern region of the field and used for the cross plot analysis. fig 1. location map showing x-field in the niger delta 182 austin, o.e et al./ jgeet vol 03 no 04/2018 3. data and methodology the data used in this work is a well log data (fig. 2) coastal swamp depobelt within the niger delta basin. the data consist of a suite of well logs from x-26. this data was analyzed using hampson russell software (hrs). the suite of wireline log data comprises density log, caliper log, gamma ray log, resistivity log, and sonic log. the inverse of the interval transit times of the sonic logs were used to generate the compressional velocities for the well. we generated s-wave data from castagna´s relation since shear log data are not available. lambdarho and mu-rho were extracted from the well data using rock physics algorithm, rock attributes, including vp/vs ratios as shown in fig. 3. this available suite of logs can be grouped into two categories, namely, properties that affect seismic wave propagation (e.g., compressionaland shearvelocity log and density log) and properties of interest for reservoir description but which indirectly affect seismic-wave propagation (e.g., ratio). petrophysical analysis through conventional cross plot was used in this work as the key to relating the two groups. fig. 2 flow chart diagram of the method of study. fig. 3. suite of logs for x-26 showing computed vp/vs ratio and p-impedance, λρ, µρ, s-impedance, swave, water saturation logs. austin, o.e et al./ jgeet vol 03 no 04/2018 183 fig. 4. horizon-1 was delineated from the gamma ray, resistivity, and sonic logs and tied to seismic. the first stage of this workflow which involve identifying the zone of interest. in this step, the zone of interest representing the producing interval is mapped out using the resistivity log, gamma ray log, p-wave velocity log and density log curves in the well. we can observe the unavailability of neutron log and sp log that has restrained further discrimination of the wells regarding their fluid contacts and fluid type. the logs then passed through a series of log editing operations. the log editing operations applied in this work include mainly median filtering and checkshot correction using the log math function of the hampson russell elog tool. the true vertical depth (tvd) of investigation ranges from 10,424 ft (3177.24 m) just at horizon 1 top to 10 724 ft (3268 m) at the hydrocarbon-watercontact (hwc), as shown in fig. 4. 4. result dan discussion from the results of the study observed in the site of watuadegpillow lava, there were many damages which made during the development of the geoheritage site so that become not maintained, thus reducing the value of education and attractiveness, especially in the geological context. evidence of damage to the geoheritage site of watuadegpillow lava is the construction of irrigation by the local government which is the function of irrigation development, namely for surface water channels and the availability of water for agriculture. however, the development of irrigation in the beds of pumice and tuffs of semilir formation around it is very influential on the geological history and geological processes that occur and take place in the area, especially as stratigraphic correlation data that are connecting the surrounding rocks. we can better discriminate our fluids in a cross plot of p-impedance against vp/vs ratio, as seen in fig. 6. the vp/vs ratio is a fluid indicator because compressional waves are sensitive to fluid changes, whereas shear waves are not except in the particular case of very viscous oil. acoustic impedance and vp/vs ratio contrast shows the position of gas-sand, brinesand and shale (bello and igwenagu, 2015). within relatively high vp/vs ratio, we can identify our gas sands in green oval at very low impedances. as impedance increases we move from gas sands to oil sands in yellow oval and finally brine sands consistent with increasing bulk density values possibly caused by changes in fluid type as seen in fig. 6. shales were identified in grey oval with varying ranges of vp/vs ratio and relatively higher impedances. combining vp and vs impedances which depend on nsity, and not isolating the density term, we arrive at attributes that characterize the incompressibility (lambdarho) and the rigidity (murho) of the rocks and the fluids in their pore spaces. considering from the basic principle that sandstones are more incompressible than shales, and that water filled sandstones would be more incompressible than gas-filled sandstones, also that shales have less rigidity than sandstones and changes in the fluid would not affect rigidity, crossplot of these properties would be more revealing on discriminating lithologies and fluids. cluster pattern for different lithologies is separated more easily in the crossplot of the lambdarho against the murho as compared to the crossplot between the vp and vs impedances, as observed in fig. 6 and 7. 184 austin, o.e et al./ jgeet vol 03 no 04/2018 fig 5. cross plot of p-impedance against s-impedance. fig. 6. cross plot of vp/vs ratio against p-impedance fig 7. cross plot of murho (µρ) against lambdarho austin, o.e et al./ jgeet vol 03 no 04/2018 185 fig. 8. cross plot of lambdarho (λρ) against poisson ratio from fig. 7, a crossplot of lambdarho versus murho, low values of lambda-rho, corresponding to low values of mu-rho indicate the presence of hydrocarbons within sand reservoirs. the plot indicates that λρ is more robust than ρ in the discrimination of fluids in this field and that ρ values are unexpectedly relatively low for the reservoir sand. a better tool for fluid discrimination would be the crossplot between the lambdarho and poisson ratio. this is because relatively low values of lambdarho corresponding to low values of poisson ratio would help identify our gas sands as we can see in the green oval, in fig. 8. finally, a quick look at lithology interpretation tool will be the crossplot of murho against density constraining with resistivity. considering fig. 9 below, the shales identified in the dark grey oval and the hydrocarbon sands in the green oval. fig. 9. cross plot of murho against density 5. conclusion achieving successful exploration and production of hydrocarbons, it is important to characterize the hydrocarbon reservoir accurately concerning its fluid properties and lithology. hence, good knowledge of petrophysical parameters must be known to understand the lithology and fluid content. acoustic impedance, lambda-rho, mu-rho, and poisson impedance attributes were found to be most robust in lithology and fluid discrimination within the reservoir in the crossplot. from the discussion above, data points taken for horizon 1 in x-field were consistent with rock physics models for lithology and fluid discrimination. the data implies the possibility of further using the crossplot technique on data points of inverted section of various avo attributes in areas not penetrated by wells within the area covered by the seismic. references a. o. ebuka, a. o. akankpo and u. e. essien., 2017. estimation of reservoir potentials of two wells in niger delta region, nigeria. journal of geosciences and geomatics, 2017, 5, 87-95. doi: 10.12691/jgg-5-2-5. akankpo, a.o.,umoren e.b., agbasi o.e., 2015. porosity estimation using wire-line log to depth in niger delta, nigeria. iosr journal of applied geology and geophysics (iosr-jagg) 3, 31-38. www.iosrjournals.org. askeladddiscovery, norwegian barents sea. retrieved from http://urn.nb.no/urn:nbn:no-32607. burianyk, m. and pickford, s., 2000. amplitude-vs-offset and seismic rock property analysis: a primer: the canadian society of exploration geophysicist recorder, 11, 114. bello, r., igwenagu, c. l., onifade, y. s., cross plotting of rock properties for fluid and lithology discrimination using well data in a niger delta oil field. j. appl. sci. environ. manage. 19, 539-546. castagna, j.p., batzle, m.l., and eastwood, r.l., 1985, relationship between compressional-wave and shearwave velocities in clastic silicate rocks, geophysics, 50: 571-581. chopra, s., vladmir a., yong x., 2003, 3d avo crossplotting an effective visualization technique. the leading edge dewar, j., 2001, rock physics for the rest of us an informal discussion: the canadian society of exploration geophysicist recorder, 5, 43 49. golyan. m., f., 2012. compaction, rock property evolution and rock physics diagnostics of askeladd discovery, norwegian barents sea (dissertation). i. akpabio, j .c. ibuot, o. e. agbasi and o.t. ojo., 2014. petrophysical characterization of eight wells from wireline logs, niger delta nigeria. asian journal of applied science, 02, 105 -109. inyang, namdie j., akpabio. o. and agbasi 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rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. field location and geology 3. data and methodology 4. result dan discussion 5. conclusion e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 myaing et al./ jgeet vol 03 no 01/2018 8 fluid inclusion study of the tumpangpitu high sulfidation epithermal gold deposit in banyuwangi district, east java, indonesia yu yu myaing 1,2 , arifudin idrus 1, *, anastasia dewi titisari 1 1 geological engineering department, faculty of engineering, universitas gadjah mada, yogyakarta, indonesia. 2 department of geology, mandalay university, mandalay, myanmar. *corresponding author: arifidrus@ugm.ac.id tel.: +62-274-513668+81-22-813-8438; received: dec 31, 2017. revised : feb 23, 2018, accepted: feb 25, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.1039 abstract the tumpangpitu high sulfidation (hs) epithermal gold deposit is located in the south coast of east java, banyuwangi district, east java province, indonesia. this area lies within the central portion of the cenozoic sunda‐banda magmatic arc which trends southeast from northern sumatra to west java then eastward through east java, bali, lombok, sumbawa and terminating at banda sea. the geology of the tumpangpitu is predominantly occupied by late oligocene to middle miocene low-k calc-alkaline to alkaline andesitic volcanic rocks and interbedded with volcaniclastic rock sequences, which are associated with low-k intermediate intrusions. the mineralization style at the tumpangpitu area is composed of a high‐ sulfidation (hs) epithermal gold-copper system which is typically associated with concealed gold-rich porphyry copper system. the hs epithermal mineralization is hosted by volcanic and volcaniclastic rocks in this research area. the mineralization domains are divided into zone a, zone b and zone c which are situated along nw-se-trending silica ledges zones. the hs epithermal mineralization is texturally occurs as vuggy replacements mineralization as well as stockworks, disseminated forms, fractures and veins. fluid inclusion study was conducted for 6 quartz vein samples which petrographically entrapped fluid inclusions. homogenization temperature (th) and melting temperature (tm) can microthermometrically be determined by fluid inclusion analysis. the average homogenization temperature (th) of the fluid inclusions gives 180 to 342 are from -0. -1. . tm corresponds to the salinities ranging from 0.1 to 4.5 wt% nacl equivalent. the paleodepth of ore formation can be estimated from the salinity of fluid. since the deposit was not formed at boiling condition, the minimum paleodepth of ore (quartz) samples taken from both shallow level (53.35 m) and deep level (135.15 m) is determined at 650m and 1,220 m, respectively. the microthermometric data point out that the tumpangpitu deposit formed at moderate temperature and low salinity by magmatic fluid mixing and dilution by meteoric water during the hydrothermal fluid evolution. on the basis of the fluid inclusion microthermometric data and its other key characteristics, the tumpangpitu gold mineralization shares some similarities compared to other typical hsepithermal gold deposits worlwide although it also shares few differences. keywords: fluid inclusion study, high sulfidation epithermal gold deposit, tumpangpitu, east java, indonesia 1. introduction the tumpangpitu deposit is located in sumberagung village, banyuwangi regency, on the south-eastern coast of the java island, east java province, indonesia. it lies about 205 kilometers southeast of surabaya (the capital of east java), 60 kilometers southwest of the regional center of banyuwangi and 120 km due west of denpasar in bali. this research area is within-existing infrastructure, with the presence of an active world-class operating mine at batu hijau on sumbawa and copper-gold smelter at gresik east java. it is defined as high-sulfidation (hs) epithermal cu-au-ag mineralization with a concealed porphyry cu-au mineralization underneath (maryono et al., 2014). microthermometric results from the fluid inclusion study can be used to estimate the formation temperature of the deposit and the salinity of the hydrothermal fluid. the aim of this fluid inclusion study is to understand the physicochemical characteristics of the hydrothermal fluids which responsible for the formation of the tumpangpitu hs epithermal gold deposit. 2. research methods fluid inclusion study is very important method to know the conditions of the hydrothermal fluids and their origin. we conducted the fluid inclusion study at the mineral resource lab, department of earth resource engineering, kyushu university, japan. for the fluid inclusion study, the four selected quartz vein samples were taken from the drill core samples crossing the tumpangpitu mailto:arifidrus@ugm.ac.id myaing et al./ jgeet vol 03 no 01/2018 9 deposit at the depth of 57.55 meter and the two samples are taken from the depth of 135.15 meter respectively of the drill hole no 12-003. firstly, we made the double polished thin-section of the thickness between 50 inclusion petrography. over 130 fluid inclusions were measured to get the microthermometric data by using linkam thmsg600 stage. we noted the shapes, the sizes, the phases of fluid inclusion, homogenization temperature, melting temperature of the fluids based on the standard citation of roedder, 1984 and bodnar et al.,1985. we can determine the salinity of fluid inclusion from the last ice melting temperature (tm) by using the equation of bodnar el al.,1983 and bodnar and vityk, 1994: sal. = 0.00 + 1.78 (tm) 0.0442 (tm) 2 + 0.000557 (tm) 3 where: sal. = salinity (wt%nacl equivalent), tm = ice melting temperature ( ). 3. geological setting 3.1 regional geology this area lies within the central portion of the ceonozoic sunda‐banda magmatic arc which trends southeast from northern sumatra to west java then eastward through east java, bali, lombok, sumbawa and terminated at banda sea. the eastern sunda arc is located along the tectonically active zone that marks the convergence of three major plates: eurasian, indo-australian, and pacific plates (fig. 1). the western segment of the arc (west to east java) developed on thick continental crust on the southern margin of sundaland, whereas the eastern segment (east java to sumbawa) was constructed on a thinner island arc crust bounded by australian continent crust further east (sumba and timor) (maryono et al., 2014). the eastern sunda arc is located along the tectonically active zone that marks the convergence of three major plates: eurasian, indoaustralian, and pacific plates (fig. 1). the western segment of the arc (west to east java) developed on thick continental crust on the southern margin of sundaland, whereas the eastern segment (east java to sumbawa) was constructed on a thinner island arc crust bounded by australian continent crust further east (sumba and timor) (maryono et al., 2014). the geology of eastern sunda arc is mainly composed of island arc-type volcano sedimentary successions of oligocene to quaternary age and igneous rocks of paleocene-eocene age (hellman, 2011). in east java the upper miocene volcanic units are represented by wuni formation which is widespread at blitar and lumajang area (fig.2). late oligocene to middle miocene magmatic rocks are widespread and continuously distribution along the whole belt. the volcaniclastic rocks of late miocene to pliocene age are more abundant than the older volcanic rocks in the southern margin of the belt and low-k calcalkaline to weakly alkaline andesitic volcanic and interbedded volcaniclastic rocks, associated low-k intermediate intrusions and minor shallow water marine sedimentary rocks extend from java to bali, lombok and sumbawa (macpherson and hall, 1999). in the sunda plate, the metallic occurrences are abundant and these are associated with subduction-related volcanic centers. there are six categories of cu-au deposits within the arcs: porphyry copper-gold, high sulphidation epithermal, low sulphidation epithermal, goldsilver-barite-base metal, skarn, and sedimenthosted mineralization (carlile and mitchell, 1994). fig. 1. map of se asia highlighting major tectonic plates and plate boundaries (mapcherson and hall, 1999) 10 myaing et al./ jgeet vol 03 no 01/2018 fig. 2. regional geological map of the southeast corner of java and the red rectangle is prospect area (achdan and bachri, 1993) 3.2 deposit geology the tumpangpitu area is predominantly occupied by late oligocene to middle miocene low-k calc-alkaline to alkaline andesitic volcanic and interbedded volcaniclastic rock sequence, associated with low-k intermediate intrusions and minor shallow water marine sedimentary rocks (harrison, 2012). in the shallow of the tumpangpitu is dominated by epithermal environment and in the deeper portion is characterized by porphyry system. fig 3 is geological map of tumpangpitu area. in this research, we emphasized only in epithermal environment. the typical rock types of this area are diorite, volcanic breccia, diatreme breccia, hydrothermal breccia and andesitic lava and breccia. 4. ore mineralization the mineralization at tumpangpitu is composed of an au‐rich porphyry cu‐au‐mo system associated with high‐sulfidation epithermal cu‐au‐ag system (hellman, 2011). the hs epithermal mineralization is hosted by volcanic and volcaniclastic rocks in the research which especially covering 3 domains of mineralization consisting of zone a, zone b and zone c. the three domains are extended along nw-se trending silica ledges zones (fig. 4). the mineralization generally occurs hosted by lapilli tuffs and vuggy replacements mineralization as well as stockworks, disseminated forms, arrays of sulfide fractures and veins, containing pyrite +/‐ enargite +/‐ tetrahedrite‐tennantite +/‐ chalcocite +/‐ bornite that occur widely within the more silica‐ rich portions of the silica ledges (fig 5, 6, 7,8). mineralization generally occurs as vug filling or massive replacement within silica ledge zone. the dissemination mineralization found in the advanced argillic altered rock. in open space or fractures, veinlets and some micrro-veinlets mineralization can be found in the research area. in open space or fractures, veinlets and some micrroveinlets mineralization can be found in the research area (fig. 5). gold mineralization is mainly associated with pyrite and enargite mineral and it can be found in massive/ vuggy silica zone, advanced argillic alteration zone and some are in silicic core. fig. 3. geological map with drill point of the tumpangpitu deposit, banyuwangi regency, east java and cross section of the area along a-b (source from bsi company). myaing et al./ jgeet vol 03 no 01/2018 11 fig. 4. 3d view for tumpangpitu domains: zone a mineralized zones dip moderately to the southwest. zone bmineralized zones strike north‐south and dip steeply to the east. zone cmineralized zones dip moderately to the northeast. zone emineralized zones dip moderately to north-south (source from bsi company). fig. 5. ore textures: (a) vuggy quartz (b) massive sulfide (pyrite) vein texture and (c) small sulfide veinlet intercalated with clay. fig. 6. photomicrograph showing intergrowth of pyrite, enargite, luzonite, sphalerite, chalcopyrite, covellite in vugs. (py=pyrite, eng=enargite, luz=luzonite, tnt=tennantite, ccp=chalcopyrite, sp=sphalerite and cv=covellite fig. 7. photomircograph show (a) euhedral pyrite with cracks along the fracture and (b) euhedral-anhedral pyrite grains within networks of alunite laths (py=pyrite, alu=alunite, eng=enargite and sp=sphalerite) fig. 8. photomircographs of (a) pyrite vein with groundmass and (b) quartz and alunite vein with pyrite vein (py=pyrite, alu=alunite, qz= quartz). 5. fluid inclusion study 5.1 petrography abundant primary and secondary fluid inclusions are found in quartz vein samples taken from the deposit. the homogenization temperature and melting temperature were measured only on the primary inclusions. the sizes of fluid inclusion in the quartz phenocrysts . the morphologies of the fluid inclusions are generally spheroidal, elongate, and prismatic forms. some of representative forms of fluid inclusions described details in fig. 11.the two-phase (liquid+vapor) fluid inclusion are common. there are two type of fluid inclusions consisting of vaporrich and liquid-rich inclusions. the vapor dominated inclusions are not common and it contain 5 to 15 percent of total fluid inclusions. fig. 10. photographs of some quartz samples associated with enargite and pyrite mineralization which has inclusions entrapped in quartz. 12 myaing et al./ jgeet vol 03 no 01/2018 fig. 11.photomicrographs of fluid inclusions petrography: (a) the slightly flatted negative crystal form, (b and c) the slightly rounded negative crystal form with secondary filling in microfracture, (d) the fluid inclusion in cubic form ,(e) the oblated tubular form and (f) necking in a long tubular inclusion form. 5.2 microthermometry fluid inclusion microthermometric data were collected from the conducting of the temperature of homogenization and melting temperature. we conducted the fluid inclusion analysis from the two different depths (at 57.55 meter and at 135.15 meter). based on the fluid inclusion data, the homogenization temperature at 57.55 meter is (180 ◦c -340 ◦c) and at the depth of 135.15 meter is (230 ◦c -360 ◦c) (fig. 12). the distribution of homogenization temperatures of fluid inclusions (histograms) are shown in fig 11. according the homogenization temperature of histogram, the formation temperature of shallow depth is 270 ◦c and the deeper is 310 ◦c. the measurement of melting temperature of fluid inclusion data is range from -0.1 ◦c to -1.4 ◦c. 5.3 salinity of hydrothermal fluid of fluid inclusion is calculated from the melting temperature. the salinity value is range from 0.1 to 4.5 wt % nacl equiv and the average salinity is (0.5 2 wt.% nacl eq.) (fig. 13). based on the average homogenization temperature ranges (270 ºc and 310 ºc) and the averaging salinity is of 1 wt.% nacl eq. belong to the epithermal system (wilkinson, 2001). the salinity variations are controlled by fluid mixing. it shows a trend of isothermal mixing (fig 14). based on the plotting of these data, the tumpangpitu area falls in the epithermal deposit. the results for the depths of formation of quartz veins from recent depth of 57.55 m (the red line) and 135.15 m (the blue line) respectively are shown in fig 15. fig.12. frequency distribution of homogenization temperatures (th) of fluid inclusions study at the depth of (a) 57.55 m and (b) 135.15 m. fig.13. frequency distribution of salinity (nacl wt.% eq..) of hydrothermal fluid (a) shallow sample taken at 57.55 m and (b) the deeper sample at 135.15 m. 6. discussion based on the study of the fluid inclusions, the tumpangpitu was not observed for boiling evidence. it is possibly related with the isothermal fluids mixing and possibly related to surface fluid dilution processes (fig 14). the formation temperature can be estimated from the fluid myaing et al./ jgeet vol 03 no 01/2018 13 inclusion microthermometric data and the formation depth can be estimated from the boiling point curve of hass, 1971 (shepherd et al., 1985). the formation temperature is plot on the temperature axis and the salinity value is plot on the curves of salinity (fig. 15). according to the plotting data (fig. 16), the tumpangpitu area belongs the epithermal environment (cf. wilkinson, 2001). fig. 14. salinity (wt.% nacl eq..) versus homogenization temperatures (th, ºc) for fluid inclusions of the tumpangpitu deposit. fig.15.the formation depth of quartz vein samples from the shallow samples (57.55 m blue line) and deep samples (135.15 m; red line). fig 16. salinity vs th illustrating typical ranges for inclusions from different types of deposits (wilkinson, 2001). the fluid inclusions from the tumpangpitu area fall in the epithermal field. 7. conclusion in the tumpangpitu research area, the mineralization is hosted by volcanic and volcaniclastic rocks and it occurred as vuggy replacements mineralization as well as stockworks, disseminated forms, fractures and veins. by assuming the temperature of homogenization is identical to the formation temperature, the tumpangpitu hs epithermal gold deposit was formed at temperature between 270◦c and 310◦c. the average melting temperature is -0.3 ◦c and -0.7◦c corresponding to the salinity of hydrothermal fluid of 0.5 to 2 wt% nacl equivalent. the paleo-depth of both shallow and deep samples taken are about 650m and 1220m, respectively (fig 15). the microthermometric data suggest that the tumpangpitu deposit formed at moderate temperature and low salinity by magmatic fluid mixing and dilution by meteoric water during the hydrothermal fluid evolution. although the tumpangpitu hs epithermal gold deposit exhibits few differences in characteristics, but in general it hares some similarities compared to other typical hs-epithermal gold deposits worlwide. 8. acknowledgements we would like to be grateful to the aun/seednet (asean university network southeast asia engineering education development network) program and jica (japanese international cooperation agency) for financial support. we are thankful to pt bumi suksesindo (pt. bsi) company for their permission and support during fieldwork. references achdan, a., & bachri, a., 1993. peta geologi lembar blambangan, jawa timur: geological map of the blambangan quadrangle, east java. bandung: pusat penelitian dan pengembangan geologi. bodnar, r.j., 1993. revised equation and table for determining the freezing point depression of 14 myaing et al./ jgeet vol 03 no 01/2018 h2o nacl solutions, geochimica et cosmochimica acta 57, 683 684. bodnar, r.j., reynolds, t.j., and kuehn, c.a., 1985. fluid inclusion systematics in epithermal systems, reviews in economic geology 2, 73 79. bodnar, r. j. and vityk m.o., 1994. interpretation of microthermometric data for h2o-nacl fluid inclusions. carlile, j.c. and mitchell, a.h.g., 1994. magmatic arcs and associated gold copper mineralization in indonesia, journal geochemical exploration, 50, 91 142. hass, j.l., 1971. the effect of salinity on the maximum thermal gradient of a hydrothermal system at hydrostatic pressure, economic geology 66, 940 946. harrison. r., 2012. indonesia basin summaries, north east java sea basin and north east java basin, p. 69-94, 2006. hellman, p. l., 2011. intrepid mines limited, tujuh bukit project, report on mineral resources, located in east java, indonesia, technical report for intrepid mines limited. macpherson, c.g. & hall, r., 1999. tectonic controls of geochemical evolution in arc magmatism of se asia. proceedings pacrim, 99, 359-367. maryono, setidjaji, l.d., arif .j., harrison, r., soeriaatmadja, e., 2014, gold, silver, and copper metallogeny of the eastern sunda magmatic arc indonesia, majalah geologi indonesia, vol.29 no.2 august 2014: 85-99. roedder, e., 1984. fluid inclusions, mineralogical society of america, review in mineralogy 12, 646. shepherd, t.j., 1985. a practical guide to fluid inclusion studies, balckie, p. 237. wilkinson, j.j., 2001. fluid inclusions in hydrothermal ore deposits, lithos 55, 229 272. 1. introduction 2. research methods 3. geological setting 3.1 regional geology 3.2 deposit geology 4. ore mineralization 5. fluid inclusion study 5.1 petrography 5.2 microthermometry 5.3 salinity of hydrothermal fluid 6. discussion 7. conclusion 8. acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 4 2022 182 idrus, a. et al./ jgeet vol 7 no 4/2022 research article characteristics and potential of placer gold deposit in lakan bilem block, west kutai district, east kalimantan, indonesia arifudin idrus 1*, ni’matul azizah raharjanti2, sufriadin3 1 department of geological engineering, universitas gadjah mada, yogyakarta, indonesia. 2 undergraduate progam of geological engineering, universitas muhammadiyah kalimantan timur, indonesia. 3 department of engineering, universitas hasanuddin, indonesia * corresponding author : arifidrus@ugm.ac.id tel.:+62-274-513668; fax: +62-274-513668 received: oct 23, 2022; accepted: dec 7, 2022. doi: 10.25299/jgeet.2022.7.4.10772 abstract kalimantan is recognized as one of indonesian islands with huge prospect of minerals particularly gold both primary and secondary deposit styles. however, the publication of the gold resources is still restricted to be described in regional/district scale maps or exploration company internal reports, hence, a detailed study on deposit scale remains limited. this study is aimed to document the characteristics and the estimation of potential or resources of the secondary (placer) gold deposit in lakan bilem block, west kutai district, east kalimantan province, indonesia. the study was done by field observation followed by microscopic analysis and simple resources estimation of the gold. gold in the study area occur in the semi-consolidated paleo alluvial deposit as trace mineral. the gold morphologies show platy to angular form with coarse surface which indicates the process of gold deposition is predominantly controlled by hydrodynamic transportation at a relatively moderate regime. estimation of the indicated resources of gold results a total of 4.96 tonnes of gold potentially occurred in the study area. exploration drilling with 100 spacing grid is suggested to delineate lateral and vertical distribution of the gold deposit. the drilling also will upgrade confidence level of the resources from indicated to measured resources. keywords: placer gold deposit, gold characteristics, resources estimation, lakan bilem block, kalimantan 1. introduction kalimantan or borneo island is located in the continental margin of eurasia plate which is known to be host of petroleum and coal resources. kalimantan is also recognized as the island with huge mineral resources and prospects, especially gold. gold prospect in kalimantan island is hosted by tertiary volcanic belt which elongated from western kalimantan to the east – northeast identified as central borneo gold belt. gold deposits occur either as primary or secondary types. moreover, base metal and other metal deposits also occur along the belt (figure 1). the study area is located in lakan bilem block, nyuatan sub-district, west kutai district, east kalimantan province which is identified as secondary or placer gold prospect. this area has been explored by many companies including a national private mining company, i.e. pt. nugraha insan kencana mining (pt. nikm) (nikm, 2013). the prospect is situated in the eastern part of central borneo gold belt (harahap et al., 2013; setijadji et al., 2010; van leeuwen, 2018) (figure 1). the study area is also located near the two major productive gold mining namely gunung muro and kelian which identified as primary gold epithermal deposits (van leeuwen, 2015). another mineral deposit potentials identified near the study area are beruang kanan and busang (anjarwati et al., 2019; hackman, 2015; slater et al., 2020). in kalimantan, secondary/ placer gold deposits are found in many places such as ampalit, cempaga in kasongan district (seeley and senden, 1994), mempawah in west kalimantan (seeley and senden, 1994; van leeuwen, 2018), and the study area. the geological information about this study area is only available in form of regional data and company exploration report. the report is based on ground survey data. hence, there are no publications on the characteristics and potential of the placer gold prospect in the study area. this study, therefore, is aimed to document the characteristics and the estimation of potential or resources of the placer gold in study area as the fundamentals for more detailed and advanced gold exploration in the region. 2. regional geology gold mineralization at the lakan bilem block, nyuatan sub-district, west kutai district is hosted by tertiary sedimentary rock that deposited in kutai basin. according to the topography characteristics, the kutai basin is divided into two sub-basins namely upper kutai basin and lower kutai basin, and the location of the study area is included in upper kutai basin (chambers et al., 2004; supriatna et al., 1995; winarno et al., 2019) (figure 2). the kutai basin covers almost all the area in east kalimantan with the sediment supply from the central part of the kalimantan island. this indicates that the central part of kalimantan was intensively uplifted and eroded during the tertiary period (supriatna et al., 1995). regionally, the sedimentary rocks identified in the study area and its vicinity include pamaluan formation, warukin formation, and the north part of the area is occupied by haloq formation. pamaluan formation consists of sandstone intercalated with claystone, shale, marl, siltstone, tuff, coal, iron oxide and lenses of limestone. the rock formation is formed at upper oligocene to lower miocene and deposited in a neritic environment. the warukin formation consists of quartz sandstone intercalated with siltstone and carbonaceous clay. the age of the formation is interpreted from middle miocene to upper miocene (supriatna et al., 1995). http://journal.uir.ac.id/index.php/jgeet idrus, a. et al./ jgeet vol 7 no 4/2022 183 fig. 1. location map of research area in lakan bilem, nyuatan district, which is identified as placer gold prospect situated within the central borneo gold belt (modified from (setijadji et al., 2010)). fig. 2. regional geology of lakan bilem and the surrounding area as the part of upper kutai basin (modified from (chambers et al., 2004)). 3. research methods this study was started by field observation followed by laboratory analysis and potential estimation. the field observation was done by geological mapping in the study area and sampling was done by digging the alluvium deposit in some small rivers. moreover, sampling was also done by making 5 test pits where each pit has 3 m depth. the observation and sampling location is indicated in map (figure 3). alluvial material taken from sampling points was panned to identify the mineral content in the concentrate especially gold. the estimation of placer gold resources/ potential was based on the level of general exploration to achieve the indicated resources according to standard nasional indonesia or sni-4726 (jorc, 2012; standar nasional indonesia (sni) 4726:2011, 2011). the mass of gold was estimated based on gold grain size from the binocular microscopic analysis at universitas gadjah mada. various mineralogy and characteristics of gold grains were also observed by using a binocular microscope. alluvium gold grade is normally stated as g/m3, therefore, the weight of each sample needs to be converted to this unit. the samples were taken by a bucket which has volume 5 liters. from the samples point, there were two categories of samples. sample labeled as a (example pca1; pc-a2), the number of deposits that panned was 4 buckets which equal to 20 liters. on the other hand, the samples categorized as b code (example pc-b1, pc-b2, etc.). the amount of panned material was 2 buckets which equal to 10 liters. the grade estimation of the placer gold deposit (in g/m3) is stated equation 1. grade (g/m3) = weight of the gold grain x (1000/the amount of panned material in liters) (1) next step is estimation of the resources or potential of the placer gold deposit by using the formula in equation 2. potential or resources (t) = grade (gr/m3) x volume of the deposit (m3). (2) 184 idrus, a. et al./ jgeet vol 7 no 4/2022 fig. 3. observation/sampling location map. samples were taken from the alluvial deposit. index map is sourced from www.google.com (2022). 4. result and discussion 4.1 geology of the study area the study area consists of gentle slope topography that varies from low to middle undulating hill. the main river of the prospect area flows relatively in direction north-south, the namuk river flows from northwest to southeast and joins with lakan river in the center of the area. lithology units observed in study area are dominantly comprised of quartz sandstone and carbonaceous claystone. the quartz sandstone is characterized by grey colored, poorly sorted, with grain size from fine sandstone to gravel. the carbonaceous claystone has characteristics of greycolored, fine grained with the composition of clay and carbonaceous material (figure 4). the strike and dip of the rocks unit are interpreted to have a direction of strike northwest-southeast and dipping to the southwest. based on the observation of its characteristics, the quartz sandstone in the study area is interpreted to a part of warukin formation which formed in middle miocene to upper miocene (carlile and mitchell, 1994; supriatna et al., 1995; wahyudiono, 2017). the andesite intrusion was observed cutting the quartz sandstone (figure 4). the andesite has characteristics of dark grey colored, porphyro-aphanitic, with mineral contents of pyroxene and plagioclase phenocrysts and aphanitic groundmass (pellant, 2021). the magnetite was found in the panned concentrate as an accessory mineral of the andesite. soerja-atmaja et al., (1999) stated that the volcanic rocks series from central kalimantan belt is the product of calc-alkaline magmatism in the early tertiary (carlile and mitchell, 1994; soeria-atmadja et al., 1999). the k/ar dating was performed for andesite samples collected from area between kelian and mt. muro showing the age of 22.9 ± 0.5 ma. the http://www.google.com/ idrus, a. et al./ jgeet vol 7 no 4/2022 185 geochronological result of the volcanic rock represents a phase of late oligocene-early miocene calc-alkaline magmatism (soeria-atmadja et al., 1999; van leeuwen, 2015). fig. 4. the outcrop of the quartz sandstone with carbonaceous claystone (a) and andesite (b) in the study area. the alluvial deposit was the youngest lithological unit observed in the study area. the alluvial deposit is distributed following the drainage pattern that composed by fragments and matrix. the fragments of the alluvial deposit are dominated by quartz, whereas the fragments of igneous and metamorphic rocks were less abundant. 4.2 placer gold characteristics the gold deposit in general classified as 2 types namely primary gold and secondary gold deposit. the primary gold deposit mainly associated with magmatic processes which the examples of the deposit such as epithermal, porphyry, and volcanic massive sulphide (vms) deposit. on the hand, secondary gold deposit which one of them identified as placer deposit is formed by mechanical concentration of the resistant and high specific gravity mineral from the weathered source rock. gold has high specific gravity (15.5 – 19.4) accumulated from the primary gold deposit by the flowing of water such as fluvial or marine processes (arndt et al., 2017, 2015; moon et al., 2006). the gold in the research area was found in alluvial deposit which formed from the fluvial process. alluvial deposit in the concession area is divided into semiconsolidated alluvial and unconsolidated types. the first type is a paleo alluvial deposit, which is interpreted as gold bearing sediment with the thickness of around 0.5 m (figure 5). the second alluvial deposit is a modern sediment which doesn’t contain gold. fig. 5. (a) the outcrop of the semi consolidated paleo alluvial deposit as the gold bearing sediment which predominantly consist of quartz fragment, matrix supported with composition quartz and clay minerals, (b) the mined material which is ready to be panned. laboratory analysis of the placer gold grain from study area was conducted using binocular microscope for the concentrate of panning samples (figure 6). the result shows that the minerals in the concentrate predominantly consist of ilmenite at 30 65% volume of the sample. the characteristics of the ilmenite are black, metallic luster, rounded shaped with the grain size of around 0.1 to 2 mm. the second abundant mineral is magnetite of 10 -25% volume, which is typified by black colored, metallic luster, rounded shape, short prismatic, granular and ferromagnetic. the other mineral identified is zircon which displays long prismatic shaped, transparent and dominantly pink in color or colorless, and grain size varying between 0.1and 1.5 mm. quartz also identified as colorless mineral and has abundance proportional to ilmenite. the gold in the samples consist as trace mineral. gold grain identified using microscope shows characteristics of yellowish gold colored, dominant platy and tabular shapes, as well as coarse and angular surface textures. the grain size of gold is typically ranging from 0.1 to 1.2 mm (figure 6). based on the gold morphologies including platy, angular and coarse surface, it may indicate that the process of gold deposition is predominantly controlled by hydrodynamic transportation at a relatively moderate regime (alam et al., 2019; girard et al., 2021; mclachlan et al., 2018; wierchowiec, 2002). the study area is a part of central kalimantan gold belt which hosts cenozoic au-ag epithermal low – intermediate mineralization (van leeuwen, 2018) the placer gold prospect in the study area is located in the west of kelian gold deposit which is confirmed as the intermediate epithermal deposit (idrus and prihatmoko, 2021; john et al., 2018; van leeuwen, 2015). it may suggest that the primary gold deposit in the study area is of a low – intermediate epithermal gold type. 186 idrus, a. et al./ jgeet vol 7 no 4/2022 fig. 6. the minerals consist in panned samples identified using binocular microscope. ilmenite (ilm), magnetite (mag), zircon (zrn), and quartz (qz) observed as dominant minerals. the gold (au) consists as trace mineral showing yellowish gold colour also platy and tabular shaped. table 1. the estimated indicated resources value from placer gold deposit in the study area. sample code mass of the gold (mg) material volume (m3) gold content (g/m3) indicated resources (t) blok i (l = 97.5 ha or 975,000 m2; average thickness= 2.2 m) pc-ta3 18.2 0,02 0.99 pc-a5 9.5 0.02 0.47 block volume = 975,000 x 2.2 = 2,145,000 m3 pc-a6 1.6 0.02 0.08 pc-a10 9.9 0.02 0.50 pc-a11 25.0 0.02 1.25 pc-a12 34.1 0.02 1.71 pc-tb9 29.2 0.01 1.92 average content 0.98 2.1 blok ii (l = 55.8 ha ore 558,000 m2; average thickness = 2.1 m) pc-ta1 17.5 0.02 0.87 block volume = 558,000 x 2.1 = 1,171,000 m3 pc-ta2 3.1 0.02 0.16 pc-a3 10.5 0.02 0.53 pc-a4 44.4 0.02 2.22 pc-a7 24.3 0.02 1.22 pc-a8 44,8 0.02 2.24 average content 1.21 1.42 blok iii (l = 50,4 ha or 504.000 m2 ; average thickness = 2.0 m) pc-b1 9.1 0.01 0.91 block volume = 504,000 x 2.0 = 1,008,000 m3 pc-b2 3.9 0.01 0.39 pc-b3 4.2 0.01 0.42 pc-tb4 40.0 0.01 4.00 average content 1.43 1.44 the total of indicated resources 4.96 note: the average thickness for each block is based on field observation and drilling data from the previous exploration activity. 4.3 placer gold potential the potential or resources of the placer gold deposit in the study area is estimated based on general exploration level, therefore, the resource is categorized into an indicated resource (jorc, 2012; standar nasional indonesia (sni) 4726:2011, 2011). the potential/ indicated resources of three blocks of exploration target within the study area were estimated. the grade of the alluvial gold is normally stated in g/m3 so the idrus, a. et al./ jgeet vol 7 no 4/2022 187 concentrate from the panning activities which are noted as liter, converted into g/m3 unit. in this study, the samples taken and coded as a has volume 20 l for each sampling point, while from the zone b the volume of samples taken was l0 l for each sampling point. potential/ indicated resources of placer gold in three blocks within the study area were estimated (table 1). block 1 contains 2.1 t gold, block 2 hosts 1.42 gold, and block 3 has 1.44 t gold, and the total is 4.96 t gold. the recommendation of the next exploration is providing more drilling location. the drilling plan with gridding method with the space of each point of 100 meters. the suggestion of the priority block of drilling location based on the accessibility to the location even though the gold population mostly found in priority block ii. the expected result of the grid drilling is lateral and vertical distribution of the mineral deposit (hadar, 2018; moon et al., 2006). the drilling data also will upgrade the confidence level of the resources from indicated resource to the measured resources (standar nasional indonesia (sni) 4726:2011, 2011). 5. concluding remarks the gold deposit from the lakan bilem block, nyuatan sub-district, west kutai district, east kalimantan is a placer gold deposit that deposited from paleo semi consolidated paleo alluvial deposit. the microscopic observation shows the characteristic of the gold which is predominantly platy shaped, some of them tabular, coarse surface texture, with angular tip indicating the source of the gold relative moderate. the study area is located in the central kalimantan gold belt, which is confirmed as a low-intermediate epithermal deposit, so the source of the placer deposit in the lakan bilem block is interpreted from the epithermal deposit. acknowledgements the research was supported by pt. nugraha insan kencana mining (pt. nikm). the author would like to thank you to the company for their permission to do the fieldwork, and take the samples for the analysis. references alam, m., li, s., santosh, m., yuan, m., 2019. morphology and chemistry of placer gold in the bagrote and dainter streams, northern pakistan: implications for provenance and exploration. geol. j. 54, 1672–1687. https://doi.org/10.1002/gj.3262 anjarwati, r., idrus, a., setijadji, l.d., 2019. petrography and ore mineral study at beruang kanan site, gunung mas regency, central of kalimantan province. j. phys. conf. ser. 1242, 012052. https://doi.org/10.1088/1742-6596/1242/1/012052 arndt, n.t., fontboté, l., hedenquist, j.w., kesler, s.e., thompson, j.f.h., wood, d.g., 2017. future global mineral resources. geochem. perspect. 1–171. https://doi.org/10.7185/geochempersp.6.1 arndt, n.t., kesler, s.e., ganino, c., 2015. metals and society, 2nd ed. ed. springer international publishing. https://doi.org/10.1007/978-3-319-17232-3 carlile, j.c., mitchell, a.h.g., 1994. magmatic arcs and associated gold and copper mineralization in indonesia. j. geochem. explor. 50, 91–142. https://doi.org/10.1016/0375-6742(94)90022-1 chambers, j.l.c., craig, j., carter, i., moss, s.j., cloke, i.r., paterson, d.w., 2004. thin-skinned and thickskinned inversion-related thrusting—a structural model for the kutai basin, kalimantan, indonesia, in: mcclay, k.r. 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 56 olabaniye, k., et al./ jgeet vol 8 no 1/2023 research article analysis the effect of column height variation on the perfomance of increased building structure kuboye olabaniye 1,*, ngolo oyedele 1, charles scott 1 1 department of civil engineering, university of ibadan, nigeria. * corresponding author : olabaniye@gmail.com tel.:+234-804-714-8054 received: oct 1, 2022; accepted: march 20, 2023. doi: 10.25299/jgeet.2023.8.1.13462 abstract indonesia is a country with a high earthquake risk. thus, indonesia often experiences earthquakes and the consequences of these earthquake waves cause damage to buildings ranging from light damage to heavy damage. dealing with the case, it is necessary to plan and implement earthquake-resistant building structures, especially in high-rise buildings. another factor that needs to be considered is the function of the room which affects the column height when the column height is different and it causes uneven stiffness from the ground floor to the top. the aim of this study was to find out the effect of variations in column height on the performance of multi-storey building structures in terms of shear forces, floor drift and buckling load (pc). the method used in this study was the response spectrum method. the spectrum response is the maximum response of a single degree of freedom (sdof) structural system, both acceleration, velocity and displacement due to the structure being loaded by a certain external force. before carrying out the analysis using the response spectrum method, a structural model was undertaken by varying the column height on the 1st floor into 3 variations. dealing with the results of the analysis on the building structure model with varying column height on the 1st floor, it indicated that the higher the column the maximum base shear force value increases. the higher the 1st floor column, the maximum floor deviation value increases. the higher the column the value of the column slenderness ratio increases and the euler buckling load decreases. keywords: column, earthquake, shear force, floor drift, buckling 1. introduction indonesia is a country with a high risk of earthquakes, because indonesia is at the confluence of three world tectonic plates, namely the indian-australian plate, the pacific plate, and the eurasian plate. in addition, indonesia is also part of the pacific ring of fire, which is the path of active earthquakes in the world (dept. pu, 2014). earthquake forces in the vertical and horizontal directions will burden the points on the mass of the structure. the impact of the earthquake caused damage to different buildings, ranging from light damage to heavy damage. to prevent damage to buildings that cause material losses and casualties, it is necessary to plan and implement earthquake-resistant building structures, especially in highrise buildings. in the planning of building structures based on the stiffness of a building. the stiffness of the structure can be measured by the magnitude of the deviation between floors, the smaller the deviation between floors, the stiffer the building will be (hartoyo, 2010). in planning the structure of the building, it is also necessary to pay attention to the function of the room, due to the main cause of the function of the building itself is the building and it must be strong and safe without reducing the function of the room. the function of the room can cause different story heights or column heights. especially at the lower levels of buildings, such as parking lots, lobbies and others which have different column heights, causing an uneven distribution of stiffness throughout the building vertically (siajaya, 2018). based on the above background, this research was carried out structural analysis with various variations of the first floor column height in the building structure model to determine the effect of column height on structural performance in terms of the amount of shear and displacement that occurs in the building structure and buckling load/critical load (pc) in column. 2. literature review previous studies apriani. 2017 “analysis of the effect of column span variations on building structure performance”, the purpose of this study was to analyze the effect of column span variations on structural performance, in order to obtain the most optimal column spans. in order to obtain the optimal span, this paper will examine the correlation between the span on the stiffness of the building structure and the strength of the structure. the research method is a simulation using the help of the finite element method program on a 3-storey reinforced building (12 meters) with a horizontal span of 20 meters. the results of the study show that from the structural stiffness factor, the most optimal scheme in terms of stiffness can be obtained, namely the shortest span scheme (scheme 1) with spans of 4m-4m-4m4m-4m. in terms of structural strength, the shortest span scheme (scheme 1) has the highest optimization/dimensional reduction percentage compared to the other two schemes. in terms of structural strength, scheme 1 has the smallest moment among the other schemes. limbongan 2016. “analysis of flat column reinforced concrete structures in multi-storey buildings”. planning or design is a very decisive factor to ensure the strength and safety of a building structure, buildings with large loads also require large supporting structures, so that they are able to withstand the existing loads. columns with large enough dimensions will have an impact on the size of the room which is getting smaller. this can cause the function of the room to be disrupted. meanwhile, if the column is too small, the size http://journal.uir.ac.id/index.php/jgeet mailto:olabaniye@gmail.com olabaniye, k., et al./ jgeet vol 8 no 1/2023 57 of the room becomes larger, but it is not necessarily strong enough to withstand the existing load. from the results of the model analysis with variations in thickness, namely 15cm, 20cm, and 25cm, as well as variations in the height of each floor, namely 3m, 3.2m, and 3.5m, it shows that a wall thickness of 15cm has an optimal floor height which is small compared to a wall thickness of 25cm which has a floor height which is larger, but from some considerations 20cm thick is considered an economical option ridwan, 2014. “evaluation on the behavior of fivestory building structures using short columns due to earthquake loads”. evaluating the behavior of a five-storey reinforced concrete building structure with short columns using a two-dimensional portal model to determine the deformation values that occur along the height of the building. this modeling is carried out with four types of short column positions which will be analyzed with the sap 2000 program which is designed according to sni 03-2874-2002 and sni 03-1726-2012 regulations. 3. theoritical basis 3.1 analysis procedure in accordance with sni-1726-2012, the analytical procedures that may be used must be based on the seismic design category and structural characteristics. as for the irregular configuration of the building structure, it can be divided into horizontal and vertical irregularities. horizontal structural irregularities (clause 7.3.2.1) consist of torsional irregularities, excessive torsion, interior angles, diaphragm discontinuities, transverse displacements to the plane and nonparallel systems. vertical structural irregularities (clause 7.3.2.2) consist of soft story stiffness irregularities, excessive soft story stiffness, weight (mass), vertical geometry, plane direction discontinuities in vertical lateral force resisting element irregularities, discontinuities in story lateral strength irregularities and discontinuities in irregularities excessive level lateral strength. according to the source sni_1726-2012, in general, structural analysis of earthquake loads is divided into two types, namely static analysis and dynamic analysis. each type of analysis has its own advantages and disadvantages which can be seen in table 1. table 1. priority factor of earthquake category priority factor of earthquake i or ii 1,00 iii 1,25 iv 1,50 spectrum response method spectrum response is an approach concept used for building planning purposes. the definition of spectral response is the maximum response of a single degree of freedom (sdof) structural system, both acceleration, velocity and displacement due to the structure being loaded by a certain external force. according to sni 1726-2012, the design spectral response must first be made based on existing data. intersection between ramps dealing with sni 1726-2012 article 7.8.6, the deviation between floors is only one performance, namely at the ultimate limit performance. the determination of the design story drift (∆) shall be calculated as the difference in deflection at the center of mass of the upper and lower floors under consideration. the deflection of the center of mass at level x (δx) (mm) must be determined according to the following equation: 𝛿𝑥= 𝐶𝑑𝛿𝑥𝑒 𝐼𝑒 where: 𝐶𝑑 : deflection magnification factor 𝛿𝑥𝑒 : deflection at the location required in this article determined by elastic analysis 𝐼𝑒 : priority factor 4. research method this research is a literature study, where literature study is a method used to collect data or sources related to the topic raised in a study. such as journals and books related to earthquake planning using the response spectrum method. the reference books used include, among others, procedures for planning earthquake resistance for building and nonbuilding structures sni 1726:2012, minimum load regulations for the design of buildings and other structures sni 1727:2013, requirements for structural concrete for buildings sni 2847:2013. the analysis used was dynamic analysis with response spectrum method. after the data was collected, the data will then be analyzed. calculating loading. loading calculations were undertaken in accordance with the supporting data. calculate the loads acting on the structure in the form of dead loads, live loads. the dead load was calculated based on the existing modeling where the self-load in the program was included in the dead load case, while the additional dead load that cannot be modeled in the program was in the super dead load case. the calculation of self-weight in the program for dead was 1, while super dead was 0, where the load for dead has been calculated automatically by the program, while for super dead loads the load needs to be entered manually according to existing data. calculating the design spectrum response. calculating the design spectrum response to obtain a response spectrum curve that refers to the site coefficients and the maximum earthquake acceleration spectral response parameters that are considered the target risk. analyzing a structural model with a spectrum response to obtain a spectrum response curve according to the earthquake area analyzed with the help of the program. the data needed in the spectrum response analysis are the function of the building, the location of the building to the earthquake area, the type of soil and the type of structure. 58 olabaniye, k., et al./ jgeet vol 8 no 1/2023 research stage fig 1. research flow 5. finding 5.1 level of sliding style dealing with the results of the structural analysis carried out using the response spectrum method, the story shear due to the maximum loading combination was obtained. based on table 2, it can be seen that the maximum shear force on the 1st floor due to the combined load in the x direction is increasing. the shear force that occurs is in model 1 (3m) of 3,080.24 kn, model 2 (4m) of 3,094.62 kn, and model 3 (5m) of 3,099.65 kn. table 2. shear force in the x direction floor model 1 model 2 model 3 fx (kn) vx (kn) fx (kn) vx (kn) fx (kn) vx (kn) floor 5 947,07 947,07 911,54 911,54 861,81 861,81 floor 4 837,06 1.784,13 826,34 1.737,88 834,93 1.696,74 floor 3 600,08 2.384,21 574,43 2.312,31 560,42 2.257,16 floor 2 473,24 2.857,45 468,78 2.781,09 465,78 2.722,94 floor 1 222,79 3.080,24 313,53 3.094,62 376,71 3.099,65 start determining the data of building structure structure modeling loading calculation: 1. additional dead load 2. live load 3. earthquake load by using the method data analysis: 1. determining the structure sliding style 2. determining the deviation between floors 3. calculating the column blend result and discussion conclusion and suggestion done olabaniye, k., et al./ jgeet vol 8 no 1/2023 59 dealing with table 3, it can be seen that the maximum shear force on the 1st floor due to the combined load in the y direction is increasing. the shear force that occurs in model 1 (3m) is 3,080.45 kn, model 2 (4m) is 3,099.15 kn, and model 3 (5m) is 3,107.13 kn. it can be seen that the maximum shear force on the 1st floor due to the combined load on the x direction increases. the shear force that occurs is in model 1 (3m) of 3,080.24 kn, model 2 (4m) of 3,094.62 kn, and model 3 (5m) of 3,099.65 kn. table 3. shear force in the x direction floor model 1 model 2 model 3 fy (kn) vy (kn) fy (kn) vy (kn) fy (kn) vy (kn) floor 5 918,16 918,16 882,53 882,53 832,34 832,34 floor 4 858,02 1.776,18 845,41 1.727,94 849,71 1.682,05 floor 3 618,40 2.394,58 595,09 2.323,03 582,78 2.264,83 floor 2 472,29 2.866,87 472,35 2.795,38 473,43 2.738,26 floor 1 213,58 3.080,45 303,77 3.099,15 368,87 3.107,13 5.2 dealing with the results of the analysis of building structures using the response spectrum method, the maximum deviation of the structure due to the maximum loading combination is obtained according to sni 1726-2012. based on the data in table 4 and figure 2, it can be seen that the maximum deviation in the x direction on the 5th floor due to the increasing influence of variations in the height of the first floor columns. the biggest maximum deviation in the x direction occurs in the model 3 structure (5m high) of 85.828 mm. based on the data in table 4 and figure 2. it can be seen that the maximum deviation in the y direction on the 5th floor due to the increasing influence of variations in the first floor column height. the biggest maximum deviation in the y direction occurs in the model 3 structure (5m high) of 77.681 mm. table 5. maximum deviation floor deviation (mm) model 1 model 2 model 3 direction x direction y direction x direction y direction x direction y floor 5 71,483 64,464 77,463 69,962 85,828 77,681 floor 4 62,195 56,467 68,526 62,272 77,193 70,266 floor 3 47,140 43,037 53,932 49,267 62,949 57,607 floor 2 27,280 25,079 34,248 31,504 43,325 39,954 floor 1 7,337 6,799 12,891 12,007 20,596 19,293 fig 2. maximum deviation in the x direction fig 3. maximum deviation in the y direction 60 olabaniye, k., et al./ jgeet vol 8 no 1/2023 5.3 deviation between the floor according to sni 1726-2012, the deviation between floors (δ) is the difference between the maximum deviation between the floor and the floor below it. the drift between floors should not exceed the allowable drift (δa = 0.015 x hsx), hsx is the floor height. based on table 5 and figure 4 it can be seen that the deviation between floors in the x direction on the 1st floor is increasing. the largest deviation between floors occurs in the model 3 structure (5m high) of 75.518 mm, does not meet the allowable deviation limit table 6. deviation between the floor in the x direction floor model 1 model 2 model 3 (δ) (δα) ket (δ) (δα) ket (δ) (δα) ket (mm) (mm) (mm) (mm) (mm) (mm) floor 5 34,055 60 m 32,768 60 m 31,664 60 m floor 4 55,201 60 m 53,512 60 m 52,228 60 m floor 3 72,821 60 tm 72,173 60 tm 71,954 60 tm floor 2 73,125 60 tm 78,309 60 tm 83,340 60 tm floor 1 26,902 45 m 47,268 60 m 75,518 75 tm fig 4. deviation between the floor in the x direction in accordance with table 6 and figure 5 above, it can be seen that the deviation between floors in the y direction on the 1st floor is increasing. the largest drift between floors have occurred in the model 3 structure (height 5m) of 70.74 mm, it still meets the permissible drift limit table 7. deviation between the floor in the y direction floor model 1 model 2 model 3 (δ) (δα) desc (δ) (δα) desc (δ) (δα) desc (mm) (mm) (mm) (mm) (mm) (mm) floor 5 29,322 60 m 28,197 60 m 27,188 60 m floor 4 49,242 60 m 47,682 60 m 46,415 60 m floor 3 65,847 60 tm 65,132 60 tm 64,728 60 tm floor 2 67,025 60 tm 71,489 60 tm 75,759 60 tm floor 1 24,931 45 m 44,026 60 m 70,740 75 m fig 5. deviation between the floor in the y direction 5.4 column bay inspection results the results of checking the slenderness ratio and column buckling load can be seen in table 7. si m pa ng an (m m ) si m pa ng an (m m ) olabaniye, k., et al./ jgeet vol 8 no 1/2023 61 based on the table above, it can be seen that the columns in model 1, model 2, and model 3 are slender columns because the column slenderness ratio klu/r > 22. or the critical load is getting smaller. the value of the slenderness ratio (𝝀) is in model 1 (height 3m) is 35.911, model 2 (height 4m) is 45.640, and model 3 (height 5m) is 55.345. table 8. test result of column buckling model column height k 𝒌𝒍𝒖 𝝀 = < 𝟐𝟐 𝒓 buckling load (pc) (m) (kn) model 1 3 2,38 35,911 15239,327 model 2 4 2,21 45,640 9435,479 model 3 5 2,11 55,345 6417,182 6. conclusion 1. dealing with the results of the analysis, it indicated that the higher the floor column 1, the shear force value that occured increases. the maximum shear force occured in model 3 of 3,107.13 kn in the y direction. 2. the result of the analysis showed that the higher the 1st floor column, the deviation between floors was increasing. the biggest deviation between floors occurred in model 3 (height 5m) in the x direction of 75.518 mm, not meeting the permissible deviation limit. 3. the results of the buckling examination on the first floor column, it indicated that the columns in model 1 (height 3m), model 2 (height 4m), and model 3 (height 5m) include slender columns and experience buckling. the higher the value of the column, the slenderness ratio of the column increases. the biggest slenderness ratio occurs in model 3 of 55.345 and buckling load (pc) of 6417.182 kn references apriani, widya., anggraini, muthia,. trisep haris, virgo., 2017, analisis pengaruh variasi bentang kolom terhadap kinerja struktur gedung, pekanbaru. budiono, bambang., dan supriatna, lucky., 2011.studi komparasi desain bangunan tahan gempa dengan menggunakan sni 03-1726-2002 dan rsni 03-1726201x. bandung: penerbit itb. departemen pekerjaan umum, 1987. pedoman perencanaan pembebanan untuk rumah dan gedung. pppurg. jakarta. departemen pekerjaan umum, 2012. tata cara perencanaan ketahanan gempa untuk struktur bangunan gedung. jakarta. departemen pekerjaan umum, 2013. persyaratan beton struktural untuk bangunan. jakarta. departemen pekerjaan umum, 2013. beban minimum untuk perencanaan bangunan gedung dan struktur lain sni 03 – 1727 – 2013. jakarta. hartoyo, 2010. syarat – syarat struktur bangunan gedung beton bertulang floor banyak, (http://hartoyohartoyo.blogspot.com/2010/01/syaratsyarat-strukturbangunan-gedung.html?m=1) limbongan, steven, 2016. analisis struktur beton bertulang kolom pipih pada gedung bertingkat. jurnal sipil statik. 4(8):499-508. rendra, rezky, 2015, analisis kinerja struktur akibat beban gempa dengan metode respon spektrum dan time history. tugas akhir, program studi teknik sipil fakultas teknik universitas riau. schueller, wolfgang, 1989, struktur bangunan bertingkat tinggi, pt. bresco, bandung. siajaya, kiemberly, 2018, respons struktur gedung bertingkat dengan variasi kekakuan kolom akibat gempa berdasarkan sni 03-17266-2012, jurnal sipil statik, 6(6):411-422 sukoco, mabruri, 2017, analisa beban gempa dasar rencana (base shear) dan detailing penulangan struktur dengan membandingkan sni 03– 1726–2002 dan sni 03 –1726–2012 pada gedung rektorat universitas islam riau. tugas akhir. program studi teknik sipil fakultas teknik universitas islam riau. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://hartoyo-hartoyo.blogspot.com/2010/01/syarathttp://hartoyo-hartoyo.blogspot.com/2010/01/syarathttp://hartoyo-hartoyo.blogspot.com/2010/01/syarathttp://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 39 al-dubai, et al/ jgeet vol 02 no 01/2017 composition and characteristic of the surficial sediments in the southern corniche of jeddah, red sea coast talha. a. al-dubai 1, *, satria antoni 1, *, aaid. g. al-zubieri 1, *, jawad majeed 1, * 1 king abdulaziz university /marine geology department / jeddah, kingdom of saudi arabia . abstract this work discusses the composition and characteristic of the surficial sediments in the southern corniche of jeddah, saudi red sea coast, in an attempt to infer the surficial distribution pattern of minerals and provenance of sediments. twenty-six superficial sediments samples were collected from backreef and forereef areas and were analyzed for grain size, caco3 content, and mineralogy. the textural of grain size range from gravel to mud fraction. the mud-dominated substrates (<63 µm) occur generally in the back-reef area near the shoreline (sheltered area) and in the lagoon. gravel rich-sediments are mostly found in forereef regions. the highest content of aragonite and mg-calcite occur in the forereef area, probably because to suitability the forereef region for chemical and biochemical precipitation of these minerals. high mg-calcite and dolomite are low in both the regions. the pyrite occurs in lagoon; this indicates the reductive conditions in this part. however, on the contrary the percentage of carbonate minerals were low in the backreef-flat area, which could be attributed to the supply of non-carbonate terrigenous materials. the terrigenous material contains quartz, k-feldspar, plagioclase and amphibole minerals and are dominant in backreef-flat area with averages of 12.7%, 7.13%, 2.93% and 0.65%, respectively. their abundance could be attributed to the supply of terrigenous materials by aeolian deposits and intermittent wadis. keywords: carbonate minerals, red sea, saudi arabia, southern corniche and coral reef. 1. introduction the southern corniche of jeddah (scj) is located south of jeddah city on the western side of the saudi arabian red sea coast (fig. 1). it is situated in arid and hot a climate with scarce rainfall and no perennial river runoff. the shallow water environment of the scj are areas of extensive carbonate production and accumulation as indicated by the occurrence of many reefal and calcareous deposits. the shallow water carbonate deposits comprise mainly of biogenic sand enriched in calcareous algae, coral debris, skeletons remain of molluscs, and foraminiferal tests (bahafzallah and el-askary, 1981; durgaprasada rao and behairy, 1984, 1986; basaham, 2009; al-dubai, 2011; bantan and abu-zied, 2014). chemical and biochemical carbonate deposits also take place in the coastal hypersaline shallow areas (winter et al., 1983; ellis and milliman, 1985; basaham, 2009). wright and burchette (1996) reported that carbonate deposits are very frequent and consist of biogenic carbonate (detrital bioclastics and non-detrital calcareous organisms), peloids, coated grains (e.g., ooids), aggregates, lithified clastics and matrix (mud-grade carbonate). other constituents of the bottom sediments of the scj consist of terrigenous sediment. they are limited and conveyed by aeolian processes from an adjacent area that are covered by old alluvium and fan deposits derived from the nearby metamorphosed sediments and basic volcanics of the jeddah group (el-sabrouti, 1983). durgaprasada rao and behairy (1982) mentioned that aeolian transport is a major supplier with a maximum of 0.06 g m-2 day-1 of the modern non-biogenic nearshore sediments of the saudi red sea coast. moreover, terrigenous sediments are supplied by an intermittent wadis (ephemeral rivers) in the southern part of the scj, especially during the rainy seasons (morcos, 1970). however, influx from the wadis has little importance since most of the sediments transported by wadis occasional not reach directly to the shoreline and may remain trapped in the neighboring coastal plains. terrigenous particles are also introduced by tidal movements (phleger, 1969) or by wave erosion of old reefal limestone terraces that occupying the coastal plain (durgaprasada and behairy, 1982). mineralogy and sedimentation processes of the coastal sediments of jeddah coast were studied by many authors (behairy, 1980; bahafzallah and elaskary, 1981; durgaprasada rao and behairy, 1982; el-sabrouti, 1983; behairy and el-sayed 1984; * corresponding author : talhadubai@yahoo.com, satria.scientist@yahoo.com, aaid222@yahoo.com, majeed.jawad@hotmail.com tel.:+966568602781 received: feb 1, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017 doi:10.24273/jgeet.2017.2.1.19 mailto:talhadubai@yahoo.com mailto:satria.scientist@yahoo.com mailto:aaid222@yahoo.com https://mg.mail.yahoo.com/neo/launch?.rand=71c37e65qgr73 40 al-dubai, et al/ jgeet vol 02 no 01/2017 durgaprasada rao et al., 1987; basaham, 1998, 2004; el-sayed et al., 2002; bantan and rasul, 2003; bantan, 2006; rifaat et al., 2007). none of these studies have focused on conducting a comparison between the characteristics and composition of modern sediments of the forereef and backreef regions of the scj from a mineralogical point of view. therefore, the present study is intended to investigate of characteristics and distribution of minerals pattern in the bottom sediments of the forereef and backreef regions of the scj. 2. materials and methods 2.1. study area and site characteristics the the southern corniche of jeddah (scj) is located ~10 km south of jeddah city on the eastern side of the saudi arabian red sea coast (fig. 1). it extends to a length of 20 km south of the jeddah city. the present study deals only with the marine coastal (backreef) area of the scj that occurs between jazirt ghurab and al-sarum guard station, which is located between latitudes 21 o 10` to 21 o 20` n and longitudes 39 o 10` to 39 o 06` e (fig. 1). it occupies a total area of approximately 43 km2 with length of 19.5 km and extends into the sea of ~1.5 km wide. it is divided by the breaker zone (coral reef crest) into back-reef region (a narrow coastal strip) including tidal flats and ghurab lagoon. the width of back-reef area varies considerably but with an average of 500 m. the bottom topography (bathymetry) of the study area is variable due to the dominance of coral reef communities (fig. 1). water depth of the back-reef area varies from 0.0 (shoreline) to 2 m, whereas water depth of the forereef area reaches 60 m. after the reef crest (breaker zone), the sea bottom descends rapidly reaching maximum depths (60m) in the study area (fig. 1). the central part of scj, especially at al-budhai area is covered by mangrove trees (fig. 1). the eastern side is bordered by old reefal limestone terraces (0.5-1m in height), covering a vast area from the shore to about 10 km inland (basaham, 2004). these terraces were probably formed during the latest pleistocene high sea level stand (skipwith, 1973). this old reefal limestone overlies a bed of conglomerate with argillaceous cement, which is in turn underlain by basalts of the trap series (elsabrouti, 1983). 2.2. samples and techniques of study this work is based on data from 26 superficial sediments samples. they were collected from the backreef and forereef of the scj, using a stainless steel van veen grab sampler (hydro bios kiel) on board of fishing boat and by hand in the shallower areas. the coordinates of the sediment samples (fig. 1) were assigned by geographic position system (gps). fig. 1. map of the study area the mineralogy was determined in the bulk powdered sub-samples that less than 0.063 mm by x-ray diffraction (xrd) using a shimadzu 6000 xray generator. the sub-samples were placed on glass holders and scanned from 2 to 60o 2θ at a speed of 2o/minute using a cu-k α _ radiation tube, ni filter and a voltage of 30 kv and 20 ma. the relative percentages of the various minerals in powdered sub-samples were determined by measuring the heights of the main reflections according of milliman (1974) and tucker (1988). graphic grain size parameters were determined according to folk`s classification (folk, 1980) after mechanical sieving of backreef and forereef sediments. calcium carbonate (caco3) concentrations were determined by treating a known weight of each sub-sample with an appropriate volume of cold dilute hydrochloric acid (1m hcl) using a calcimeter (wika) with an accuracy of ± 0.25%. 2.3 sediment grain size the raw weights for each grain-size class were converted to weight percent for each sub -sample and classification to four sizes mud (silt and clay), coarse sand, fine sand and gravel. the median, standard error, standard deviation and mean of the grain size for each sub-sample were calculated using spss v.11.5/2002 for (windows-based software). contour maps were plotted for the al-dubai, et al/ jgeet vol 02 no 01/2017 41 sediments and minerals using remote sensing (imagine 8.7), arcgis 9 and surfer v.8 (golden software). triangle diagram of distribution of gravel, sand and mud were plotted using golden software grapher 5 software. 3. results sediment characteristics and substrate types the coarse sand fraction (150 µm to 2 mm) predominates in the northern part of the studied area, representing about 53% of the total sediment fraction (fig. 2). the fine sand fraction (63-150 µm) predominates in the lagoon and the southern part of the studied areas, representing about 25% of the total sediment fraction (fig. 2). the mud-dominated substrates (<63 µm) occur generally in the back-reef area near the shoreline (sheltered area) and in the lagoon, representing about 5% of the total sediment fraction (fig.2). however, gravel rich-sediments are mostly found in forereef regions such as that of albudhai area with an average of 17% (fig. 2). fig. 2. relative abundance distribution of mud, sand and gravel sediments in the studied area of the scj. in general, the sand and gravel sediments dominate studied part of the scj. microscopic studies indicate that the sand sediment (>63 µm) is composed mainly of bioclastic materials, such as foraminiferal tests, ostracod carapaces, pelecypod and gastropod shells, sponges, tubes of polychaetes, corals debris and coralline algae. lithic particles of sand are relatively few. the bottom sediments of the lagoon and those occurring near the sewage outlet are characterized by having grey to blackish colors. according to folk`s classification method (folk, 1980), seven textural classes are identified (fig. 3). most of the samples are generally vary between sand to gravelly sand, while few samples were muddy sand. overall, the backreef zone of the scj is generally flat and covered by thin layer of soft sediments overlying hard substrates. 3.1 calcium carbonate the bottom sediments of the scj consist mainly of calcium carbonate (caco3). their contents vary from 59 to 99%, with a mean value of 84.5%. the high content of caco3 occurs in forereef area, the low content (59%) of caco3 occurs in the lagoon (fig. 4). the calcium carbonate in the bottom sediments of the al-budhai area ranges from 73 to 94%. the highest value of caco3 in the bottom surface sediments of the scj is usually linked with the coarse-grained sediments (fig. 4). fig. 3. gravel, sand and mud (clay plus silt) triangle diagram for the southern corniche sediments of jeddah. 3.2 mineral composition the mineralogy of the studied sediment samples from the forereef and backreef-flat region of the scj is characterized by the existence of carbonates minerals (e.g., aragonite, mg-calcite, calcite and dolomite), plagioclase, amphibole, k-feldspar, quartz, pyrite and halite (table 1). overall, carbonate minerals represent more than 70% of the bottom surface sediments. samples from the forereef area show higher aragonite and higher mg-calcite content than the samples from the backreef-flat. the average percentage of aragonite ranges from 37.47 to 79.85%, and the highest percentage of aragonite occur in the forereef part and decreases towards the shoreline of the studied area. mg-calcite content varies from 9.69% to 32.96 with an average of 18.31%. dolomite occurs in considerable amounts; especially in the surface sediment samples which collected from backreef-flat. however, dolomite and calcite occur in minor content, especially in the samples collected from backreef-flat and shoreline, 42 al-dubai, et al/ jgeet vol 02 no 01/2017 with averages of 0.87 and 1.08%, respectively (table 1). the non-carbonate mineralogy of the bulk surface bottom sediments is dominated by terrigenous quartz k-feldspar, plagioclase and amphibole minerals. they occur in considerable amount, especially in the surface sediment samples which collected from backreef-flat and shoreline (table 1). it is apparent that quartz and k-feldspar are more in abundance in the backreef-flat part and shoreline, especially in al-budhai area (fig. 5) with average amounts of 12.71% and 7.13% respectively; while plagioclase and amphibole minerals are abundant along the northern part of the studied area. halite occurs in considerable amounts in most of the studied samples, it constitutes about 4.42% of the whole sediments of the scj. in some samples, pyrite is present in lesser amounts, especially in the northern part in ghurab lagoon. it forms 0.34% of the bulk mineralogy of the samples. therefore, it can be noted that the scj sediments are composed mainly of aragonite, mg-calcite, quartz and kfeldspar. tabel 1 mineralogy and their relative concentration (in %) of the sediment samples from scj carbonate minerals detrital minerals evaporate mineral pyrite % s no. aragonite % calcite % mgcalcite % dolomite % quartz % kfeldspar % plagioclase % amphibole % halite % 1 45.31 3.49 9.92 18.50 5.36 9.92 2.95 3 53.44 13.99 16.28 8.91 2.80 4.58 8 61.15 17.29 2.51 7.27 9.77 2.01 12 50.76 2.72 10.27 21.45 8.16 3.02 3.63 14 44.62 15.75 25.72 9.45 1.84 2.62 21 60.53 20.57 2.15 3.83 7.18 5.74 25 43.35 21.01 20.74 10.64 4.26 31 56.46 26.84 2.03 4.30 5.82 4.56 33 46.15 22.56 19.49 8.72 3.08 35 79.85 13.93 6.22 36 38.02 25.75 29.94 6.29 39 59.37 31.12 5.19 4.32 40 63.59 26.12 2.37 7.92 46 54.47 32.96 1.68 5.31 5.59 47 54.99 32.74 2.05 5.12 5.12 50 51.53 4.34 16.58 16.58 6.38 4.59 51a 64.41 2.76 14.29 6.27 8.02 4.26 52 48.92 13.01 1.93 19.52 6.02 5.30 5.30 53 39.23 10.17 1.69 20.34 9.44 2.91 7.26 8.96 54 46.15 2.56 9.69 1.99 17.38 7.41 5.13 3.13 6.55 56 65.23 20.98 6.61 2.30 4.89 58 37.47 3.47 12.90 22.33 8.68 6.20 3.47 5.46 60 39.62 3.83 12.30 2.46 16.12 6.56 4.37 14.75 61 47.78 1.97 14.04 1.72 22.41 6.90 3.45 1.72 62 43.51 14.50 18.07 4.83 11.45 2.29 5.34 63 44.44 2.85 16.81 10.26 6.27 9.40 3.13 6.84 average 51.55 1.08 18.31 0.87 12.71 7.13 2.93 0.65 4.42 0.34 al-dubai, et al/ jgeet vol 02 no 01/2017 43 figure 4. bathymetry, distribution of calcium carbonate (caco3). figure 5. distribution of mineralogy in the studied bottom sediments of the scj. 4. discussion and conclusions the studied area of the scj can be divided into two major zones, namely: (1) the backreef-flat zone, which is considered as sheltered-low energy zone and (2) the forereef zone, which is considered as an open sea. the superficial sediments of the backreef-flat of scj are muddy sand and consist mainly of carbonate and terrigenous minerals. carbonate minerals are represented by mg-calcite, calcite, aragonite, and dolomite, while terrigenous mineral is represented by quartz, k-feldspar, plagioclase and amphibole. moreover, the presence of halite and pyrite minerals in sediments of the backreef -flat zone is also noticed. the mineralogy of the backreef-flat zone shows significant variations in their distribution and compositions, in the northern part of the studied area especially in lagoon, it contains some pyrite minerals that could be attributed to the occurrence of reducing conditions in this lagoon due to dominance of organic matters. terrigenous materials in backreef-flat are dominated by quartz and k-feldspar and low abundance of plagioclase and amphibole; these minerals could be attributed to the nature of the source rocks, such as igneous and volcanic basalts rocks, which formed the bordering mountains of the red sea, and apparently transported to backreef-flat area by intermittent wadi stream and wind. many studies indicated that these minerals are intimately associated with terrigenous deposition and introduced to sea-marginal flat environments in the red sea by winds (sneh and friedman, 1985 and phleger, 1969). wadi fatima is dry intermittent stream and flows during the rainy season in the main wadi and the southern part of the scj. the abundance and supplies of the terrigenous materials in the backreef-flat area could be responsible for the low abundance of aragonite and mg-calcite. this low average carbonate minerals in backreef-flat are probably due to dilution by terrigenous input which transported by wind and seasonal freshwater discharge to the coastal area (khalaf and ala, 1980). however, this dilution by the terrigenous material gradually decreases towards the forereef region. moreover, inorganic precipitation of carbonate deposits (carbonate minerals) in seawater is inhibited by the presence of dissolved organic and inorganic chemicals (suess 1973; rushdi et al. 1992). the relative abundance of the halite was close to the shoreline; especially in shallow water sheltered area could be attributed to high rates of evaporation, and very low precipitation and runoff. the concentration of pyrite mineral in backreefflat area, especially in ghurab lagoon could be attributed to the early diagentic processes that occur as response to the reducing environmental conditions. basaham (1998) reported that pyrite in the surface sediments of al-arbaeen lagoon was a product of early diagenetic reactions in highly reducing environment. the recent superficial sediments in forereef area of the scj are gravely sand and consist mainly of carbonate materials, while the terrigenous matters (e.g., quartz, k-feldspar, plagioclase and amphibole) are rare in this region. the high value of aragonite and high magnesium calcite in forereef zone sediments could be attributed to high degree of saturation of seawater with respect to calcium carbonate (rushdi et al., 1992). it is noted that aragonite and mg-calcite formed the majority among other carbonate minerals in forereef region, where it has been shown that aragonite is kinetically favored to precipitate in a solution with magnesium-to-calcium concentration ratio more 44 al-dubai, et al/ jgeet vol 02 no 01/2017 than 4 such as in seawater (kitano 1964; rushdi 1993; rushdi et al. 1992). based on the previous discussion, it is suggested that the mineralogical compositions of surface sediments of the scj are derived from the following sources: fluvial deposits which discharged in the southern part of the scj by wadi fatima, chemical and biochemical precipitation from the sea water, and eroded the reefal terraces on the shoreline and the reef crest (breaker zone). the low value of aragonite and mg-calcite in backreef-flat sediments could be attributed to supply of the terrigenous materials. on other hand, the abundance of aragonite and mg-calcite in forereef area, probably due to the high levels of seawater saturation with respect calcium carbonate and the decline of the terrigenous inputs. references al-dubai, t.a. 2011. environmental assessment of the southern corniche of jeddah using of remote sensing, gis and fieldstudy. m.sc. thesis. king abduaziz university. saudi arabia. bahafzallah, a.a. and el-askary, m.a. 1981. sedimentological and micropaleontelogical investigations of the beach sand around jeddah, saudi arabia, bull. fac. earth sci., kau, 4:25-42. bantan, r.a. 2006. morphological features and sedimentological aspects of wadi al-kura, north of jeddah, western coast of saudi arabia. j. kau: fac. mar. sci., 17: 153-165. bantan, r.a. and abu-zied, r.h. 2014. sediment characteristics and molluscan fossils of the farasan islands shorelines, southern red sea, saudi arabia, arab j geosci., 7:773 787. bantan, r.a. and rasul, n.m. 2003 impact of developments on the configuration of sharm obhur and its bottom sediments. j. environ. sci., 261: 319-337. basaham, a.s. 1998. the composition and diagenetic features of the inland quaternary coralline limestone, south sharm obhur, red sea coastal plain of saudi arabia. j. kau: mar. sci., 9: 75-87. basaham, a.s. 2004. digenetic processes and the paleo-climate of the quaternary raised coral reef terraces, red sea coast of saudi arabia, journal of environmental sciences, 28: 163189. basaham, a.s. 2009. geochemical of jizan shelf sediments, southern red sea coast of saudi arabia, arab j geosci., 2: 301-310. behairy, a.k.a. 1980. clay and carbonate mineralogy of the reef sediments north of jeddah, west coast of saudi arabia. bull. fac. sci. kau, 4: 265-279. behairy, a.k.a. and el-sayed, m.a. 1984. carbonate cements in a modern red sea reef, north of jeddah, saudi arabia, mar. geo., 58: 443-450. durgaprasada rao, n.v., al-imam, o.a.o. and behairy, a.k.a. 1987. earil mixed-water dolomitization in the pleistocene reef limestones, west coast of saudi arabi. sedimentary geology, 53: 231-245. durgaprasada rao, n.v.n, and behairy, a.k.a. 1982. erosion and sedimentation: vital factors in the jeddah coastal management. journal of the faculty of marine science, 2: 17-25. durgaprasada rao, n.v.n, and behairy, a.k.a. 1984. mineralogical variations in the unconsolidated sediments of el qaser reef, north of jeddah, west coast of saudi arabia, cont. shelf res., 3: 489-498. durgaprasada rao, n.v.n, and behairy, a.k.a. 1986. nature and composition of shore-zone sediments between jeddah and yanbu, eastern red sea. marine geology, 70: 287305. ellis, j.p. and milliman, j.d. 1985. calcium carbonate suspended in arabian gulf and red sea water: biogenic and detrital, not 808. el-sabrouti, m.a. 1983. texture and mineralogy of the surface sediments of sharm obhur, west red sea coastal of saudi arabia. marine geology, 53: 103-116. el-sayed, m.a., basaham, a.s. and gheith, a.m. 2002. distribution and geochemical of trace elements in central red sea coastal sediments, inter. j. environ. studies, 591: 131. folk, r.l. 1980. petrology of sedimentary rocks hemphill publishing company, austin, texas. khalaf, f.i. and ala, m. 1980. mineralogy of the recent intertidal muddy sediments of kuwait arabian gulf. marine geology, 35: 331-342. kitano, y. 1964. on factors influencing the polymorphic crystallization on calcium carbonates found in marine biological system. in recent researches in the field of hydrosphere, atmosphere and nuclear chemistry. y. miyake, and t. koyama eds. tokyo. milliman, j.d. 1974. marine carbonate. springerverlag., berline, new york, p. 375. morcos, s.a. 1970. physical and chemical oceanography of the red sea. oceanogr. mar. biol. annu. rev., 18: 73-202. phleger, f.b. 1969. a modern evaporate deposit in mexico. american association of petroloeum geologists bulletin, 53: 824-829. rifaat, a.e., basaham, a.s., el-mamoney, m. and elsayed, m.a. 2007. mineralogical and chemical composition of dry atmospheric deposition on jeddah city, eastern coast of the red sea. jkau: mar. sci., 19: 167-188. rushdi, a.i. 1993. kinetics of calcite overgrowth as a function of magnesium concentrations and supersaturation in artificial seawater. journal of the faculty of marine science, 4: 39 54. al-dubai, et al/ jgeet vol 02 no 01/2017 45 rushdi, a.i., pytkowicz, r.m., suess, e. and chen, c.t. 1992. the effects of magnesium-tocalcium ratio, in artificial seawater at different ionic products, upon the induction time, and the mineralogy of calcium carbonate: a laboratory study. geol rundsch, 81: 571 578. senh, a. and friedman, g.m. 1985. hypersaline seamarginal flats of the gulf of elat and suez. in hypersaline ecosystems. ecological studies. 53: friedman, g.m. & krumbein, w.e., eds. springer-verlag, berlin, heidelberg, new york, pp. 103-135. skipwith, p. 1973. the red sea and coastal plain of the kingdom of saudi arabia. tech. rep. tr. 1973-1. dgmr, saudi arabia, 149 p. suess, e. 1973. interaction of organic compounds with calcium carbonate. geochim cosmochim acta., 34:157 168. tucker, m. 1988. techniques in sedimentology. blackwell scientific publications. oxford, london, 386 p. winter, a. almogi-labin a., erez, y., haliez, e., luz, b. and reiss, z. 1983. salinity tolerance of marine organisms deduced from red sea quaternary record. mar. geol., 53: 1417-1422. wright, v.p. and burchette, t.p. 1996. shallowwater carbonate environments. in: reading, h.g. ed sedimentary environments: processes, facies and stratigraphy. 3nd., blackwell science. ltd. oxford, london, 326 pp. chapter 9. 1. introduction 2. materials and methods 2.1. study area and site characteristics 2.2. samples and techniques of study 2.3 sediment grain size 3. results 3.1 calcium carbonate 3.2 mineral composition 4. discussion and conclusions references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 2 2023 hermonita, d., et al./ jgeet vol 8 no 2/2023 99 research article sensitivity analysis of geomechanics influence on the success of hydraulic fracturing in shale gas reservoir desti hernomita1, tomi erfando1,* 1 universitas islam riau, petroleum engineering department, jl. kaharuddin nasution 113 pekanbaru, indonesia * corresponding author : tomierfando@eng.uir.ac.id tel.: +6285265322405 received: feb 28, 2023; accepted: jun 6, 2023. doi: 10.25299/jgeet.2023.8.2.12351 abstract shale gas has a permeability of <0.1 md and a porosity of around 2% 8% to produce gas that rises to the surface through hydraulic fracturing and horizontal drilling. geomechanics is one of the important factors that influence the success of a hydraulic fracturing job. technology in fractures makes geomechanics a clear factor in predicting the success or failure of rocks in deformation and knowing the properties that will be faced by fracture fluids which will later be used to see the effectiveness of fracture fluids in resisting fractures. high operational costs need to be studied further to determine the parameters that affect hydraulic fracturing work, especially from the geomechanical aspect to minimize production failures and work safety. the research conducted this time focuses on the sensitivity of geomechanical parameters by using cmg (gem) reservoir simulations for reservoir models and conducting response surface methodology (rsm) in selection and ease when applied in the field prior to the hydraulic fracturing process. in this sensitivity study carried out on 5 parameters namely stress, poisson's ratio, young's modulus, biot coefficient, and pore pressure. the geomechanical parameter that has the most influence on hydraulic fracturing work based on the sensitivity results carried out through 500 data sets using the analysis of variance obtained r2 = 0.99 with the results based on the importance value of the pore pressure variable of 3.8. then young's modulus is 0.28, stress is 0.12, poisson's ratio is 0.08, and biot coefficient is 0.04. keywords: hydraulic fracturing, shale gas, cmg, response surface methodology (rsm), geomechanics. 1. introduction currently, the development of artificial intelligence is very actively developing and entering into all aspects of life including the oil and gas industry. the application of artificial intelligence is very helpful and facilitates human life. this is because machine learning and artificial intelligence are more efficient and economical and fast when performing manual correlation and integration. shale gas has a very complex rock structure, so it is important to study rock mechanics and the factors that influence the direction of fracture in shale gas (tao et al., 2021). fracture directions can be determined based on design, fracturing fluids, and geomechanics (bastos fernandes et al., 2020). this parameter determines the success of the hydraulic fracturing work. in addition, geomechanics is used to evaluate the interaction between rock stress and pressure, mechanical properties, and geometry. geomechanics plays an important role in determining the design and optimizing the stimulation of hydraulic fracture in shale gas reservoirs (nagel, 2019). technology in fracking makes geomechanics a clear factor in predicting the success or failure of rocks in deformation and knowing the properties that will be faced by fracturing fluids which will later be used to see the effectiveness of rocks against fracturing fluids in holding fractures. development challenges and decision-making in the unconventional field are due to uncertainty in the sub-surface and economic factors so it is necessary to study geomechanical aspects to minimize production failures (tamimi et al., 2020). a combination of reservoir simulation models and respon surface methodology an be used to analyze the sensitivity of parameters so that it becomes an alternative to optimize response (liu et al., 2018). this study focuses on predicting the parameters that affect rock geomechanics during hydraulic fracturing work which has previously been calculated using the computer modeling group (cmg-gem) software and conducting a sensitivity test with the response surface methodology. 2. methodology 2. 1 research methodology in order to meet the needs of the dataset that will be used to conduct sensitivity studies using the response surface methodology (rsm). in this study, to begin, run a reservoir simulation with reservoir simulation software (cmg) to model the basic case and cmost to assist with modeling iterations. table 1. reservoir and fracture properties properties unit value the model dimensions grid 66 x 20 x 3 the model dimenssions ft 9900 x 4000 x 45 reservoir pressure psi 2950 reservoir temperature f 150 matrix porosity fraction 0.06 matrix permeability md 0.00015 rock density lb/ft3 120 fracture half length ft 300 rock comparability psi-1 3x10-6 fracture spacing ft 100 fracture conductivity md.ft 1 bottom hole pressure psi 500 source: (jamshidnezhad, 2015; roussel & sharma, 2011). in order to meet the needs of the dataset that will be used to conduct sensitivity studies using the response surface http://journal.uir.ac.id/index.php/jgeet mailto:tomierfando@eng.uir.ac.id 100 hermonita, d., et al./ jgeet vol 8 no 2/2023 methodology (rsm). in this study, the authors first carried out reservoir simulations using reservoir simulation software (cmg) to model the base case (fig.1) and cmost which functioned to help carry out modeling iterations. this study uses secondary data on barnett's field obtained from (jamshidnezhad, 2015; roussel & sharma, 2011) as the base case. the data are as follows (table 1 and table 2). fig 1. reservoir model table 2. value parameter properties value stress 6000 (t. h. kim et al., 2016) poisson ratio 0.25 (t. h. kim et al., 2016) modulus young 7.3 x106 (roussel & sharma, 2011) biot coefficient 0.7 (jamshidnezhad, 2015) pore pressure 5463 (jamshidnezhad, 2015) response surface methodology is a set of statistical techniques that improve and optimize processes (myers, r.h.; montgomery, 2009). according to (liu et al., 2018), a combination of reservoir simulation models and rsm can be used to analyze the sensitivity of parameters. in this study, a sensitivity analysis of geomechanical parameters was carried out using a response surface methodology with upper and lower values limited to 30% of the actual value based on the research conducted (nguyen-le & shin, 2019). the data are as follows in table 3. table 3. value parameter geomechanics properties lower upper unit total stress 4200 7800 psi poisson ratio 0.175 0.325 v modulus young 5.11x106 9.49x106 psi biot coefficient 0.49 0.91  pore pressure 3824 7101 psi after running the input data according to the range that has been determined using the cmg cmost, there will be a total of 500 simulation data scenarios that will be reused for analysis by rsm. 2. 2 hydraulic fracturing the hydraulic fracturing method is by injecting fracturing fluid to expand the fracture and then inserting a buffer so that the fracture does not close again on condition that the proppant has permeability. the fracture direction is determined based on rock mechanics, overburden pressure, and formation depth. if the stress is the smallest and has a vertical direction, the fracture will form horizontally and vice versa. 2. 3 geomechanic in designing well maintenance, rock mechanics has an important role as a controller of fracture geometry. geomechanics is a scientific discipline that integrates rock mechanics, geophysics, geology, and petrophysics to analyze quantitatively how a rock responds to a disturbance caused by the influence of drilling activity, fluid flow, formation pressure, in-situ stress, and formation temperature (anis, 2008). in the case of a geomechanical model with compaction, it can affect flow because the permeability of the formation changes. reserves without a geomechanical model will be different from the presence of a geomechanical model, this is influenced by the nature of the rock. geomechanics is very useful for analyzing overpressured reservoirs with the main effects given such as the effect on permeability which is pressure dependent (yilmaz and nur correlation) and the effect of formation comparability depending on pressure (dobrynin correlation) (temizel et al., 2020). rock mechanics consists of stress and strain, poisson ratio, shear modulus, bulk modulus, young's modulus, and overburden pressure. according to (liu et al., 2018), most reservoir simulation studies do not address the effects of geomechanics on fracturing. in addition, differences in rock types affect the value of rock mechanics such as influencing the value of pore pressure, young modulus, passion ratio, fracture pressure, maximum vertical stress, minimum stress, and strength. a) stress and pore pressure according to (hu et al., 2016) shear and strain affect the strength of the rock when a fracturing fluid is injected. if the differential stress is greater then the shear in the rock will collapse. so it is necessary to pay attention to minimize the differential stress due to the greater bottom hole pressure. then, pore pressure becomes an important part of hydraulic fracturing to control the final stimulation of the fracture geometry (arias ortiz et al., 2021). b) biot coefficient one of the parameters to determine and minimize geomechanical effects during the process fracturing job is the biot’s coefficient. if, less than 0.1, the better in minimizing the failure of geomechanical effects on the fluid (joridis, 2014). according to (belyadi et al., 2016) when a rock has high porosity, the rock compatibility value is close to 1. if the porosity is low, the value is close to 0. so, the equation is as follows: α = 1(cmatrix/cbulk) (1) if the value of a rock does not have a porosity value and a geomechanical value can be calculated using the following equation: α=0.64+0.854 × 𝜽 (2) c) modulus young and poisson ratio a high modulus young may reduce the fracture gap due to limited deformation and vice versa, leading the fracturing fluid to reach the tip fracture quickly and provide high conductivity. furthermore, according to research conducted shows an effect young's modulus and the poisson ratio control the length of the fracture, which grows longer and wider before shrinking. (ye and colleagues, 2020) the knowledge that it raises the ratio of stress horizontal minimum becomes an important aspect of measuring the fragility of a rock. as the stress horizontal minimum increases, the fragility index decreases. 2. 4 recovery factor hermonita, d., et al./ jgeet vol 8 no 2/2023 101 the recovery factor or recovery factor is a ratio between the amount of hydrocarbons that have been taken with the total amount of hydrocarbons before being taken (initial). in the gas reservoir, the recovery factor can be formulated as follows: rf = retriveable vgas/ initial gas =1p2z1/ p1z2 (3) 2. 5 computer modeling group cmg, or computer modelling group, is a reservoir simulation company based in calgary, canada. this simulation is used for reservoirs with one or more phases and can be employed in two or three dimensions. on cmg, the simulator types include imex, star, and gem. the distinction between the three is in the sort of fluid to be imitated. cmg-gem is often used to model pressure changes in fluids and gases. the benefit of adopting cmg is that it is typically less expensive than competitors. furthermore, simple usage (computer modeling group ltd, 2018). 2.6 modde 5 modde 5 is a single application window that generates and evaluates statistical experimental designs. the purpose is to conduct an investigation factor that has a significant impact on the outcomes, the optimal factor of a system, and anticipate results. 2.6 respon surface methodology algorithm ml and ai are gaining ground in the oil industry as they generate precise information using the integration of logs and core data. one of these methods is very important in predicting the geomechanical properties of shale which is considered as the most heterogeneous rock with wettability which is unfavorable for hydrocarbons to flow (syed et al., 2021). the advantage of rsm is that it can interpret results with few factors. however, the drawback is that it is difficult to interpret more than 3 factors. rsm is particularly successful in reducing costs and increasing efficiency in shale gas reservoirs with unknown reservoirs. in rsm the technique used to understand system response is to develop a regression model (interaction regression). linear squared) and sequential factors (f test, fit test, and r-squared value) were then checked and analyzed for variance (anova) (myers, r.h.; montgomery, 2009). the study's (liu et al., 2018) findings were analyzed utilizing the response surface methodology. a mix of simulation models reservoir and rsm can be used to examine the sensitivity of parameters, which can then be used to optimize the response to this problem. wang et al., 2016 investigated the sensitivity using rsm of 7 parameters which included thickness, cohesion, dip angle, spacing, friction angle, ir, and sd through 46 designs obtained the most influential results in maximizing stimulation volume reservoir (srv) in the thickness. this research is one of the reasons for using rsm because rsm is easy to implement with fewer factors with the result of carrying out a combination of data using machine learning and artificial intelligence later it can be known the influential parameters to provide an overview of exploration and development shale gas. 4. result and discussion 4.1 respon surface methodology cmost modeling was carried out using cmg-gem by entering a dataset of 500. parameters tested included stress, poisson ratio, modulus young, biot’s coefficient and pore pressure as input and output are recovery factors, formed from a random sample using upper and lower bounds. data dissemination utilizes continuous real distribution, where the parameter value cannot be estimated (fu et al., 1991). the sensitivity test was carried out to obtain results where the geomechanical parameters have an effect on when a hydraulic fracturing job is carried out. 4.2 analysis of variance (anova) analysis of variance (anova) is a statistical test to detect differences in group means when there is one parametric dependent variable and one or more independent variables. predictive modeling is done to see the accuracy of the data. r2 explains the level of confidence and explain the value of the data from the independent variable or model input. r2 has a value of 0 to 1 which means that the closer to 1 the better and does not have an error large (hair et al., 2014). fig 2. distribution continuous real 102 hermonita, d., et al./ jgeet vol 8 no 2/2023 fig 3. plot anova r2 = 0.99 demonstrates the outcomes. the r2 statistic can be used as a benchmark to determine whether a regression model is robust enough to be used with a value higher than 0.85. to further analyze the impact of parameters on recovery factors, ranking parameters are used (mousavi et al., 2020). fig 4. n-plot of effect for recovery factor effects plotted on a cumulative normal probability scale can only be used to determine important effects with at least a model with 10 effects. this plot is based on parameters that are robust and normally distributed so that effects significantly different from 0 will be outside the normal line. fig 5. variable importance plot hermonita, d., et al./ jgeet vol 8 no 2/2023 103 variable importance plot helps visualize the strong relationship between features and the predicted response while considering all the features present in the model (wei et al., 2015). vip with the highest 5 in this study, pore pressure 3,8. young's modulus is thus 0.28.stress is 0.12, passion ratio is 0.08, and biot coefficient is 0.04 (table 4). thus, the results obtained from this study are the dominant geomechanica parameters contained in the parameters of pore pressure. then the second stage and so on there are parameters stress, young modulus, poisson ratio, and biot coefficient. when pore pressure and stress increase causing excessive deformation which causes blow out happens so it needs monitoring when hydraulic fracturing will be carried out (zhao & huang, 2021) table 4. variable importance parameter vip coeff (cum) recovery factor~ pp 3,80404 0,067349 s*v 0,436132 -0,000264751 s*a 0,304498 -3,8785e-005 e 0,285323 -0,000152669 v*e 0,220132 -0,000153699 s*pp 0,144606 -0,000101427 s*e 0,136605 0,000306946 a*pp 0,12722 0,000271854 e*pp 0,127144 0,00069356 s 0,123577 2,15349e-005 v*a 0,0994813 -0,000503091 e*a 0,0929126 0,000369517 v 0,08863 0,000439638 a 0,0411581 -0,000429696 v*pp 0,0343111 0,000448073 n = 504 cond. no. = 1,3712 df = 488 y-miss = 0 comp. = 2 5. conclusion based on the findings and analysis of the research, it can be said that pore pressure (3.8) had the greatest influence on geomechanical parameters during hydraulic fracturing operations using 500 data sets and the analysis of variance (r2 = 0.99). thus, young's modulus is 0.28, stress is 0.12, passion ratio is 0.08, and biot coefficient is 0.04. acknowledgments the authors would like to acknowledge this research as supported by the universitas islam riau. references anis. 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shale gas reservoirs and its influence on fracability. energies, 13(2). doi:10.3390/en13020388 zhao, x., & huang, b. 2021. distribution relationship of pore pressure and matrix stress during hydraulic fracturing. acs omega, 6(45), 30569–30579. doi:10.1021/acsomega.1c04268 © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn: 2541-5794 p-issn: 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 darmawan, d. et al./ jgeet vol 8 no 1/2023 39 research article electrical resistance tomographic by using current injection and magnetic field induction dudi darmawan1*, deddy kurniadi2, suprijanto2 1 engineering physics, universitas telkom, jl telekomunikasi no 1, jawa barat, indonesia 2instrmentasi dan kontrol, institut teknologi bandung, jl. ganesha 10, jawa barat, indonesia * corresponding author: dudiddw@telkomuniversity.ac.id tel.:+081320500247 received: sep 20, 2022; accepted: mar 17, 2023. doi: 10.25299/jgeet.2023.8.1.10560 abstract a critical issue in electrical tomography is ill-posed problems due to low sensitivity. in the electric current injection method, the placement of the injection electrode on the object boundary can influence it. this condition causes the reconstruction result of parameter change far away from the boundary to be inferior in quality. another excitation method is using magnetic field induction proposed to overcome these problems. each reconstruction image was obtained using two methods with three types of parameter changes, that represented the edge and the cent er of the object position. both reconstruction results are merged and further processed to enhance the quality of the image, bas ed on the average value of the resistivity of each element. the results show that the final image reconstruction has a smaller root mean square error (rmse) than the electric current injection method. keywords: iii-posed; sensitivity; current injection; magnetic field induction; reconstruction image 1. introduction an important issue in electrical impedance tomography is ill-posed problems (gong et al., 2016) (lópez c. et al., 2015) (harikumar, prabu, and raghavan, 2013) (khan and ling, 2019). the things that cause the appearance of ill-posed are mismatch model, non-linear, low sensitivity, and the limited amount of data (information) (alsaker, hamilton, and hauptmann, 2017) (seppänen et al., 2009) (chitturi and farrukh, 2017). these factors have been the subject of attention from some of the research related to current injection tomography. the issue of sensitivity is influenced by several factors, including the large injection currents, the current position of the injection point, the position of the measurement electrodes, and electrode measurement conditions. these factors form a system of data collection on the current injection tomography. therefore, a solution to overcome this problem is to find the appropriate configuration of data collection systems, such as adjacent, cross, opposite, multireference, and adaptive. however, all of those data collection systems use excitation electrodes attached to the object boundaries. this condition causes the changes in the parameters in the middle of the object to be hard to be detected. another method that can be used to overcome the low sensitivity is the use of another excitation method, i.e. the magnetic field. the induction of a magnetic field to the inside of the object is expected to overcome the low sensitivity. this is possible because the stimulation of the magnetic field is done to the entire object (wang et al., 2018) (feldkamp and quirk, 2019) (ma, wei, and soleimani, 2013) (ma and soleimani, 2017). in this way, the same sensitivity to the whole object can be reached so that the spatial resolution of the uniform resistivity distribution is obtained (seppänen et al., 2009) (chitturi and farrukh, 2017). however, this raises another problem which is irregularities of the magnetic field given part. the solution to solve this issue is to find the optimal configuration of the induction system (darmawan et al., 2015) (wang et al., 2018) (alsaker, hamilton, and hauptmann, 2017). the induction system includes the shape and dimensions of the coil inducer, induction number, position, and configuration of the induction. one form of alternative coil used is the rectangular coil that has been used for imaging using the eddy current method (deddy kurniadi, 2014) (darmawan et al., 2015). experiments were performed using a variety of frequency values and give good results. therefore, the selection of a rectangular shape is attractive to apply to the case of tomography. this form is believed to provide the homogeneous distribution of the magnetic field, especially attached to the square-shaped object. therefore, the incorporation of the current injection method for magnetic field induction method is attractive for development. the ability of the current injection method in detecting parameter changes in the edge can be accomplished by the method of magnetic field induction. providing a magnetic field to the center of the object is expected to address the issue of sensitivity in the current injection method. this study was conducted to obtain the reconstructed image of each method. furthermore, both image reconstruction results are combined and evaluated. this image fusion has been widely used in various image processing and merging methods (rane, kakde, and jain, 2017) (zhao, li, and cheng, 1993). 2. methods http://journal.uir.ac.id/index.php/jgeet 40 darmawan, d. et al./ jgeet vol 8 no 1/2023 2.1 forward and inverse model of current injection method in the current injection method, an electrical current is injected through some point in the object's surface. currents will spread and cause electric potential distribution inside the object. the relationship between the electric potential (v), and resistivity (r) was formulated by the laplace equation (darmawan et al., 2016) (ma and soleimani, 2017) (darbas et al., 2021). 𝛻 ∙ 1 𝜌 𝛻𝑉 = 0 in  (1) with boundary conditions of potential and current density on the surface, 𝑉 = 𝑉0 on 𝜕 (2) 1 𝜌 𝜕v 𝜕𝑛 = 𝐽0 on 𝜕 (3) in the current injection tomography, the forward model is the mapping function that states the value of the electric potential distribution as a function of the resistivity distribution, 𝐹(𝜌) → 𝑽|_. the electric potential function is obtained through the solution of the laplace equation. in this study, a solution of forward models is obtained through the concept of current conservation. this concept states that the net amount of current in each element is equal to zero. in other words, the current coming into each element is equal to the current coming out of that element. in the case of two dimensions, the concept of current conservation is obtained through the application of double integrals in equation (1). ∬ (𝛻 ∙ 1 𝜌 𝛻𝑉) 𝑆 ∙ 𝑑𝑆 = 0 (4) by using the divergence theorem, the surface integral along s on the left side of equation (4) turns into an integral along a closed path l surrounding one element. ∮ 1 𝜌 𝛻𝑽 ∙ 𝑑𝑙 = 0 𝑙 (5) the left side of equation (5) states the sum of the current flux penetrated to the entire surface of the boundary surrounding the element. in 2 dimensions, numerical solutions to equation (5) produce equation (6). ∑ 1 𝜌 𝛻𝑽 . 𝑙 = 0 𝑙 (6) with the boundary condition being current flux density (je, i) [15]. 𝐽𝑒(𝑖) = { 𝐽, 𝑓𝑜𝑟 𝑖𝑛𝑗𝑒𝑐𝑡𝑒𝑑 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 0, 𝑓𝑜𝑟 𝑛𝑜𝑡 𝑖𝑛𝑗𝑒𝑐𝑡𝑒𝑑 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 this is a neumann boundary condition. furthermore, equation (6) is applied to all elements and produces some linear equations connecting the potential value of an element with the potential values of neighboring elements. the linear equations of potential values of all elements can be arranged in the matrix-vector form, such as equation (7). 𝐺𝑁×𝑁. 𝑉𝑁×1 = 𝐶�̅�×1 (7) with g = admittance matric �̅� = potential vector 𝐶̅ = current source vector n = number of elements furthermore, obtaining the resistivity distribution from the boundary potential distribution observed is done by using the linearization method. a function that maps the boundary potential distribution back into the resistivity distribution, 𝐹−1[𝑉] → 𝜎| is known as the inverse model. through the linearization method, it was found that changes in resistivity become proportional to the potential boundary changes, according to the equation (8). ∆�̅� = 𝑆 ∆�̅� (8) with s as the sensitivity matrix. the tikhonov regularization (dingley and soleimani, 2021) is used to get a solution so that equation (8) turns into equation (9). ∆�̅� = (𝑆 + 𝛼𝐼)−1∆�̅� (9) and finally, resistivity reconstruction results were obtained through 𝜌𝑎𝑛𝑜𝑚𝑎𝑙𝑖 = 𝜌ℎ𝑜𝑚𝑜𝑔𝑒𝑛 + ∆�̅� (10) reconstruction results are evaluated numerically using the parameters of root mean square (rms) as equation (11), and it’s called error. 𝐸𝑟𝑟𝑜𝑟 = 1 𝑁 √(𝜌𝑟𝑒𝑘𝑜𝑛𝑠𝑡𝑟𝑢𝑘𝑠𝑖 − 𝜌𝑢𝑗𝑖 ) 2 (11) 2.2 forward and inverse model of magnetic field method in the method of magnetic field induction, the magnetic field change is raised in the coil. the induced current will appear in the object. the relationship between the electric potential (v), resistivity (), and magnetic potential (a) is defined by equation (12), which is known as poisson's equation [20] 𝛻 ∙ 1 𝜌 𝛻𝑉 = −𝜔𝐴 𝛻 1 𝜌 (12) the solution of equation (12) is obtained by the same approach as in section 2.1. ∬ (𝛻 ∙ 1 𝜌 𝛻𝑉) 𝑆 𝑑𝑆 = ∬ (−𝝎𝑨 𝜵 1 𝜌 ) 𝑆 𝑑𝑆 (13) the numerical solution of equation (13) is equation (14). ∑ 1 𝜌 𝛻𝑽 . 𝑙 = − 𝜔𝐴 . 𝛻 1 𝜌 ∆𝑆 𝑙 (14) furthermore, the completion of some linear equations of all elements is done using equation (7). 2.3 magnetic field simulation calculation of the magnetic field 𝐴 by the rectangular coil is carried out as follows: induction of a magnetic field at a point by the 𝑑𝑙 ⃗⃗ ⃗⃗ ⃗conductive segment which is electrified by i satisfies the biot-savart equation. darmawan, d. et al./ jgeet vol 8 no 1/2023 41 𝐴 = ∫ 𝜇𝑜𝐼 4𝜋 𝑑𝑙⃗⃗⃗⃗ 𝑥 �̂� 𝑟 2 (15) with 𝐴 = magnetic field 𝜇0 = permeability 𝐼 = current 𝑑𝑙 ⃗⃗⃗⃗⃗⃗ ⃗ = coil segment 𝑟 = distance to the observation point if defined 𝑟 = √𝑥2 + 𝑦2 + 𝑧2 and 𝐾 = 𝜇0 4𝜋 then the magnitude of the magnetic field by the current conductive segment is formulated in equation (16). 𝑑𝐴⃗⃗⃗⃗⃗⃗ = 𝜇𝑜𝐼 4𝜋 𝑑𝑙⃗⃗⃗⃗ × �̂� 𝑟 = 𝐾𝐼 (𝑖 ̂𝑑𝑥 + 𝑗 ̂𝑑𝑦 + 𝑘 ̂𝑑𝑧) 𝑟 × 𝑟 𝑟 (16) the magnitude of the magnetic potential by the conductor along l is obtained by integrating equation (16) so that the magnetic potential is obtained by a straight conductor in equation (17). 𝐴 = 𝐾𝐼 ∫ (𝑖 ̂𝑑𝑥+𝑗 ̂𝑑𝑦+𝑘 ̂𝑑𝑧) 𝑟 × 𝑟 𝑟 𝐿 0 (17) thus the magnetic potential by the four sides of the rectangular coil conductor is obtained by adding up the magnetic field potential by the four rectangular sides. 𝐴 = ∑ 𝐾𝐼 ∫ (𝑖 ̂𝑑𝑥+𝑗 ̂𝑑𝑦+𝑘 ̂𝑑𝑧) 𝑟 × 𝑟 𝑟 𝐿 0 4 1 (18) the following is a numerical calculation of the magnetic field potential by one side of the rectangular coil. suppose the starting point of the line conductor is at coordinates (x1, y1) and the endpoint of the line conductor is at coordinates (x2, y2). divide the length of the conduit into n-line segments. if the distance of the two points to the observation surface is the same, z1 = z2 = z. the length of each delivery segment is ∆𝑥 = 𝑥2 − 𝑥1 𝑛 ∆𝑦 = 𝑦2 − 𝑦1 𝑛 the distance of a certain conductive segment to the magnetic potential calculation point satisfies equation (19) 𝑟 2 = (𝑥𝑝 − 𝑥1) 2 + (𝑦𝑝 − 𝑦1) 2 + (𝑧𝑝 − 𝑧1) 2 (19) the magnetic potential components of any segment satisfy equation (20). ∆𝐴𝑥𝑖 = 𝐾𝐼(𝑧𝑝 − 𝑧) ∆𝑦 𝑟 ∆𝐴𝑦𝑖 = −𝐾𝐼(𝑧𝑝 − 𝑧) ∆𝑥 𝑟 ∆𝐴𝑧𝑖 = 𝐾𝐼[(𝑦𝑝−𝑦)∆𝑥−(𝑥𝑝−𝑥)∆𝑦] 𝑟 (20) the magnetic potential component at an observation point by all conveying segments satisfies equation (21). 𝐴𝑥 = ∑ ∆𝐴𝑥𝑖 𝑛 𝑖=1 , 𝐴𝑦 = ∑ ∆𝐴𝑦𝑖 𝑛 𝑖=1 , 𝐴𝑧 = ∑ ∆𝐴𝑧𝑖 𝑛 𝑖=1 (21) the magnitude of the resultant magnetic potential at a point is obtained by complying with equation (22). 𝐴 = √𝐴𝑥 2 + 𝐴𝑦 2 + 𝐴𝑧 2 (22) 3. results and discussion 3.1 simulation results of forward and inverse model of current injection method the simulation results of the forward model using the method of the adjacent, cross, and opposite injection with 16 times the injection shown in figure 1. the simulation results for the best reconstruction of the current injection method with three different anomalies are shown in table 1. the simulation of the forward model of magnetic field induction is done 16 times. simulation results which show the distribution of magnetic field and electric potential distribution produced, are shown in figure 2. (a) (b) (c) fig. 1. potential distribution as the solution of the forward model of current injection method (a) adjacent (b) cross (c) opposite. 42 darmawan, d. et al./ jgeet vol 8 no 1/2023 3.2 simulation results of forward and inverse model of magnetic field induction method the simulation of the forward model of magnetic field induction is done 16 times. simulation results show the distribution of magnetic field and electric potential distribution produced, shown in figure 2. (a) (b) fig. 2. (a) magnetic field distribution and (b) potential distribution as the forward model solution of magnetic field induction method. table 1. reconstruction results of resistivity distribution by current injection method table 2. reconstruction results of resistivity distribution by magnetic field induction method anomaly reconstruction results of 16 times injection image error 0,0060 0,0080 0,0090 average 0,0077 furthermore, in the same way as the current injection method, determining the resistivity distribution on the magnetic field induction method is performed using equation (6) in equation (10). the best reconstruction results obtained are shown in table 2. 3.3 merging of reconstruction result of current injection and magnetic field induction merging cell value of the reconstruction results between the current injection and magnetic field method is conducted using 4 ways, namely minimum, maximum, maxmin, and average value (kumar et al., 2016) (arai, 2020) (noushad, 2017) (wang, 2020). minimum value this way takes the smallest value of the value of each element of both methods, thus formulated as 𝜌 = 𝑀𝐼𝑁(𝜌(𝑘), 𝜌(𝑑)) maximum value this way takes the greatest value from the value of each element of both methods, thus formulated as 𝜌 = 𝑀𝐴𝑋(𝜌(𝑘), 𝜌(𝑑)) max-min value this way retrieves the value of the smallest value of both methods if both resistivity values are smaller than a specified value and takes the greatest value if both resistivity values are greater than that specified value. 𝜌_ = { 𝑀𝐼𝑁(𝜌(𝑘), 𝜌(𝑑)), 𝜌(𝑘) 𝑎𝑛𝑑 𝜌(𝑑) < 𝛿 𝑀𝐴𝑋(𝜌(𝑘), 𝜌(𝑑)), 𝜌(𝑘) 𝑎𝑛𝑑 𝜌(𝑑) > 𝛿 𝐴𝑉𝐺(𝜌(𝑘), 𝜌(𝑑)) , 𝑓𝑜𝑟 𝑜𝑡ℎ𝑒𝑟𝑠 average value this way takes the value of the average of the value of both methods, thus formulated as 𝜌 = (𝜌(𝑘) + 𝜌(𝑑))/2 with k index for injection d index for induction anomaly reconstruction results in 16 times induction image error 0,0071 0,0102 0,0086 average 0,0086 darmawan, d. et al./ jgeet vol 8 no 1/2023 43 by using these ways, the simulation results of the merging of the two methods are shown in table 3. 4. conclusion the results of the reconstruction of the two methods, which were carried out separately, confirmed the advantages of each method. tomography using the current injection method gives better results in detecting anomalies at the edges. while the magnetic field induction method gives better results in detecting anomalies in the middle of the test object. furthermore, merging the reconstructed image of the two methods increases in image quality. this is indicated by the merged image which is better than the reconstructed image of each method. through the three types of anomalies tested, the average method produces better results. acknowledgments this work is supported by hibah penelitian pasca doktor 2019, ministry of research, technology and higher education of the republic of indonesia references alsaker, m., hamilton, s. j. and hauptmann, a. 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(1993) ‘image enhancement using fuzzy logic’, international conference on fuzzy theory and technology proceedings, abstracts and summaries, pp. 74–75. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” nurcahya, a. et al./ jgeet vol 08 no 02-2 2023 1 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 research article machine learning application of two-dimensional fracture properties estimation ardian nurcahya, aldenia alexandra, satria zidane zainuddin, fatimah az-zahra, m. i. khoirul haq, irwan ary dharmawan* department of geophysics, faculty of mathematics and natural science, universitas padjadjaran, jatinangor, indonesia * corresponding author : iad@geophys.unpad.ac.id received: may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13874 abstract fractures are substantial contributors to solute transport sedimentary systems that form pathways. the pathway formed in a fracture has two physical parameters, there are mean aperture and surface roughness. mean aperture is the thickness of the pathway tha t the fluid will pass through, and surface roughness is the roughness of the fracture pathway. the two physical parameters of the fracture are important to determine since they affect the permeability value in petroleum reservoir analysis. we developed a machine learn ing algorithm based on the convolutional neural network (cnn) to predict those two parameters. furthermore, image processing analysis is performed to generate the datasets. the results show that the cnn algorithm shows good agreement with the reference results. in addition, the algorithms showed efficient performance in terms of computational time. cnn is a type of deep neural designed to perform analysis on multi-channel images that can classify fracture geometry. the best model was determined using a benchmark dataset with a cnn model provided by keras. the results of experiments conducted on fracture geometry images show that the machine learning model created is able to predict the mean aperture and surface roughness values. keywords: fracture, mean aperture, surfaces roughness, machine learning, cnn 1. introduction energy is an essential part of daily life, which one of the main energies used is fossil energy. fossil energy is the main energy source and source of foreign exchange for indonesia, but fossil energy sources have negative impacts on the environment, such as air pollution, greenhouse gas emissions, and global warming. in addition, high demand for fossil energy is another issue. increasing demand for fossil energy such as oil is accompanied by rising prices, which leads to diminishing reserves of fossil energy. oil production has decreased over 10 years from 346 million barrels or 949 thousand barrels per day (bpd) in 2009 to around 283 million barrels or 778 thousand bpd in 2018. this is because the majority of wells are older, while the production of new wells is relatively limited (esdm, 2019). fractures are important objects or structures, especially in oil and gas exploration, because fractures are one of the secondary petroleum reservoirs (koesoemadinata, 1980). this is also supported by herdiansyah who stated that volcaniclastic reservoirs in indonesia are reservoirs with significant production where one of the most important factors is natural fractures that determine the quality and quantity of the reservoir (herdiansyah et al., 2020). at first glance, the fracture shape only looks like a line, but in reality the fracture geometry has many variations because there are parameters that can affect the fracture geometry such as surface roughness and mean aperture. fig. 1. physical parameters mean aperture and surface roughness in fracture (a) mean aperture 15 lu and surface roughness 0.1, (b) mean aperture 15 lu and surface roughness 0.9, (c) mean aperture 40 lu and surface roughness 0.1, and (d) mean aperture 40 lu and surface roughness 0.9 mean aperture is the relative mean heights between the two surfaces used to define the fracture aperture. the unit used in the mean aperture used is the lattice unit (lu). surface roughness is commonly used to indicate the roughness level of the surface in the fracture, which has a range of values from 0 to 1. fig. 1 shows that when the surface roughness value is close to 0, the surface will be more rough, while when the surface roughness value is close to 1, the surface will be smoother. the surface roughness value that is often found in the field is between 0.45 0.85 (wang et al., 2021). the complex and irregular shape of the fracture surface geometry is another major factor that impacts the permeability value in petroleum reservoir analysis, therefore it is necessary to further investigate the fluid flow within the fracture medium. as it is known that the experiments at the laboratory especially http://journal.uir.ac.id/index.php/jgeet mailto:iad@geophys.unpad.ac.id 2 nurcahya, a. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 in oil and gas exploration have high operational costs and require a significant amount of time. in addition, the physical parameter values of the fracture are obtained through numerical simulation of fluid dynamics, but that method also requires a considerable amount of computation time (dharmawan et al., 2016). therefore, in this research, machine learning algorithms is used as one of the alternative to solve cases or problems in the oil and gas field. machine learning has been widely developed as a solution in science and technology fields such as production optimization and hydrocarbon drilling. it is also being applied to simplify and speed up the computational process in estimating fracture physical parameters. artificial neural network (ann) are a popular type of machine learning model used to solve complex problems. they are based on the structure of human nerves that adaptively solve tasks. a typical ann consists of multiple layers with multiple perceptrons in each layer. the basic building block of an ann is the perceptron, which is modeled after neurons in the human brain. in an ann, the input for one layer serves as the output for the next layer. one ann algorithm that is often applied to solve image recognition problems is the cnn. cnn uses a convolution method that applies filters of a certain size to various locations of the input data. from the convolution of the input data and filters, the machine obtains new representative information. the output of the convolution is then used as the input for the neural network layer below. because the feature extraction and training process in the cnn algorithm is done by the computer simultaneously, cnn is a good solution for estimating the physical parameters of fractures with complex patterns. it is also beneficial because it does not require testing, such as fluid dynamics modeling, and can calculate physical parameter values in less time. a cnn is a deep learning algorithm that can take in an input image, assign importance (learnable weights and biases) to various aspects or objects in the image, and differentiate one from the other. it is a promising tool for solving pattern recognition problems (gao and mosalam, 2018). cnns are a specialized type of ann that use a mathematical operation called convolution in place of general matrix multiplication in at least one of their layers. they are designed to process pixel data and are used in image recognition and processing. a cnn consists of an input layer, hidden layers, and an output layer, with the hidden layers including layers that perform convolutions. a cnn can have tens or hundreds of layers, each learning to detect different features of an image. filters are applied to each training image at different resolutions, and the output of each convolved image is used as the input to the next layer. the general layout of the layers of the cnn architecture is shown in fig. 2. fig. 2. cnn scheme to predict an image convolution puts the input images through a set of convolutional filters, each of which activates certain features from the images. the rectified linear unit (relu) allows for faster and more effective training by mapping negative values to zero and maintaining positive values. pooling simplifies the output by performing nonlinear downsampling, reducing the number of parameters that the network needs to learn. after learning features in many layers, the architecture of a cnn shifts to classification. the final layer of the cnn architecture uses a classification layer to provide the final classification output. cnns provide an optimal architecture for uncovering and learning key features in image and time series data, and are key technology in applications such as object detection, audio processing, and synthetic data generation (talo, 2019). in this research, the problem to be solved is image recognition. the pre-trained model architectures used in this research are those available in the keras library which have been tested and have good performance. the three types of pretrained models used in this research are densenet201, densenet169, and xception. 2. material and methods the dataset was generated using the smartfract application, which is based on matlab. this software uses a fractional brownian motion algorithm, which is a random movement of a value with a gaussian process in continuous time starting from zero and centered at a mean of zero based on a covariance function. the generated data was used for training with a total of 45,000 data points, including 36,000 for training and 9,000 for validation. the variations in this data consist of two classes, mean aperture and surface roughness, as shown in table 1. table 1. variation of data used no mean aperture (lu) surfaces roughness number of data 1 5 0.1 to 0.9 4,500 2 10 0.1 to 0.9 4,500 3 15 0.1 to 0.9 4,500 4 20 0.1 to 0.9 4,500 5 25 0.1 to 0.9 4,500 6 30 0.1 to 0.9 4,500 7 35 0.1 to 0.9 4,500 8 40 0.1 to 0.9 4,500 9 45 0.1 to 0.9 4,500 10 50 0.1 to 0.9 4,500 total 45,000 the method in this study employs a cnn to identify object parameters in fracture geometry. this research utilizes transfer learning, a machine learning approach that leverages previously acquired knowledge to solve related problems in different classes. transfer learning can significantly speed up the training process by using a pretrained model, eliminating the need for trial and error. it also has the potential to produce more accurate predictions with higher success rates and faster training times using fewer training data points, as it builds upon prior knowledge. a schematic comparison of transfer learning and traditional machine learning is shown in fig. 3. nurcahya, a. et al./ jgeet vol 08 no 02-2 2023 3 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 3. the comparison between traditional machine learning and transfer learning (a) traditional machine learning, (b) transfer learning. the pre-trained densenet201, densenet169, and xception architectures used in this study are provided by keras. these models use feedforward connections between every layer to mitigate vanishing-gradient problems, enhance feature propagation, encourage feature reuse, and significantly reduce the number of parameters. activation functions in the model should also be carefully considered as they can impact the parameter values of the resulting model. in this study, the rectified linear activation function (relu) was used to predict fracture parameter values. the densenet201 architecture takes advantage of a compact network, allowing for easy training and highly efficient models due to the ability of different layers to reuse features, which increases the diversity of inputs to subsequent layers and improves performance (huang et al., 2017). the densenet201 architecture has been widely used in image recognition tasks, such as determining the type of weather based on available weather datasets, and has shown good performance in estimating object parameter values. this architecture can be used for object classification or value estimation (naufal and kusuma, 2022). mean relative error (mre) is used to determine the value of data deviation relative to the actual data. the relative error value is obtained by subtracting the predicted data 𝑦𝑖 from the actual data 𝑦 and then dividing by the actual data 𝑦. relative error is generally used in determining the error in percentage form so that the error can be more easily read. the equation of the relative error can be written as follows. 𝑀𝑅𝐸 = ∑ 𝑛𝑖=1 𝑦𝑖−𝑦 𝑦 (1) mean squared error (mse) is a value used to estimate a certain quantity in data. rse is commonly used to estimate unobserved quantities in a training model. the mse value can be used to see how far the estimated value is from the predicted value with the estimated value 𝑦𝑖 and the predicted value 𝑦𝑖. mse can be written in the following equation. 𝑀𝑆𝐸 = 1 𝑛 ∑ 𝑛𝑖=1 (𝑦𝑖 − 𝑦�̄�) 2 (2) mean absolute error (mae) is a function used for regression models. mae is the sum of absolute differences between the target and independent variables. it measures the average of the residuals, where 𝑛 represents the number of observations, 𝑦𝑖 is the predicted price at the point of sale 𝑖 and 𝑦𝑎 is the actual value. 𝑀𝐴𝐸 = ∑ 𝑛𝑖=1 |𝑦𝑖 − 𝑦𝑎 | (3) root mean square error (rmse) is another commonly used metric to evaluate the accuracy of predictions obtained by a model. it takes the residuals between actual and predicted values and compares the prediction errors of different models for particular data. the primary advantage of using rmse is that it penalizes large errors and scales the results in the same units as the forecast values. 𝑅𝑀𝑆𝐸 = √ 1 𝑛 ∑ 𝑛𝑖=1 (𝐴𝑖 − 𝐹𝑖 ) 2 (4) 𝑅2 is a widely used statistical measure in regressionbased machine learning. it indicates the percentage of the variance in the dependent variable that the independent variables explain collectively. the closer the value of 𝑅2 to 1, the better the model is fitted. 𝑅2 = 1 − ∑ 𝑛𝑖=1 (𝐴𝐼−𝐹𝑖 ) 2 ∑ 𝑛𝑖=1 𝐴𝑖 2 (5) 3. results and discussion as a result of this research, two models using a cnn were developed to predict mean aperture and surface roughness values. these models were able to predict the values using linear regression. the performance of each model can be seen in fig. 4, which is presented as a histogram. fig. 4. histogram prediction surface roughness and mean aperture, (a) base on surfaces roughness with densenet201 architecture, (b) base on surfaces roughness with dense169 architecture, (c) base on surfaces roughness with xception architecture, (d) base on mean aperture with densenet201 architecture, (e) base on mean aperture with dense169 architecture, (f) base on mean aperture with xception architecture the surface roughness can be predicted using a model. based on fig. 4, the model performs fairly well in estimating the roughness values in the range of 0.1 to 0.7, as indicated by the high number of accurate predictions in that range. however, the model is weaker in predicting roughness values greater than 0.7, as shown by the decrease in data readings in that range in the histogram in fig. 4. the performance of the mean aperture model can also be seen in fig. 4, where the shape of the model's graph shows that the predictions are not too far off. in addition, fig. 4 shows that the highest prediction results for mean aperture data occur in the range of 1 to 10, and then remain fairly stable from 15 to 45. however, the model is weaker in predicting low mean aperture values, as shown in fig. 4. the distribution of the data for each model can also affect the prediction results and errors in the test data process. the actual and predicted data can be plotted to show the distribution of the experimental results, as seen in fig. 5. 4 nurcahya, a. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 5. linear regression predict and actual value base on surfaces roughness and base on mean aperture, (a) base on mean aperture with densenet201 architecture, (b) base on mean aperture with dense169 architecture, (c) base on mean aperture with xception architecture, (d) base on surfaces roughness with densenet201 architecture, (e) base on surfaces roughness with dense169 architecture, (f) base on surfaces roughness with xception architecture. the performance of the model can be evaluated by plotting the distribution of data points and creating a linear regression line. according to fig. 5, some data points have a large deviation from the regression line, indicating poor accuracy of the trained model in certain ranges. for instance, fig. 5 shows poor performance in predicting surface roughness in the range of 0.8 to 0.9, as indicated by the missing data in the range of 0.95 and the large distance between the data and the linear regression line, resulting in a high standard deviation in that range. a high standard deviation can significantly affect the error generated by the model, as a larger distance between data points leads to a larger error. on the other hand, the mean aperture model training results shown in fig. 5 demonstrate better performance, with data points not deviating significantly from the regression line, resulting in better image prediction. however, it should be noted that the mean aperture training model clearly shows poor performance in the range of 1 to 10, as shown by the clustering of data points at one point in this range. as a result, the test performance results for the mean aperture range of 1 to 10 are not recommended due to their poor performance. in contrast, the mean aperture training model shows quite good performance in the range of 10 to 50, as demonstrated by the data distribution shown in fig. 6 and the boxplot in fig. 6. fig. 6. boxplot of dataset densenet201 (a) base on surfaces roughness and (b) base on mean aperture boxplots are used to show quartiles or boundaries at the top and bottom. the boundary at the top is the third quartile (q3), which means that 75% of the predicted data is below the other quartiles. in fig. 6, it can be seen that q3 for the surface roughness model has a value of 0.6, and q3 for the mean aperture training model has a value of 38. the bottom boundary is the first quartile (q1), which represents the minimum value with 75% of the data below it. in fig. 6, it can be seen that the q1 value for the predicted data has a value of 0.2, while the q1 value for the mean aperture training model is in the range of 10. the median value or second quartile (q2) of the data can be seen in fig. 6, which is at a value of 0.4 for the surface roughness model and 23 for the mean aperture model. the boxplot created does not show any outliers, meaning that the predicted data is within the range of the maximum and minimum observation data. in addition, the performance of the model can be evaluated by directly determining the error, as shown in table 2 below. table 2. error value densenet201 no type error surfaces roughness error mean aperture error 1 mre 0.097 1.86 2 mae 0.16 0.087 3 rmse 0.12 2.53 4 mse 0.015 6.42 5 r2 0.95 0.97 table 2 shows the errors between the predicted and actual data from the model created with the densenet201 architecture. the calculation of the mre shows a value of 0.18 for the surface roughness model and 0.14 for the mean aperture model. mre has a relationship with mse, so based on the obtained errors, the mean aperture model performs better than the surface roughness model. however, in the mae and rmse values, the error value for the mean aperture model is higher compared to the error generated by the surface roughness model. this is a common occurrence due to the different range of values in the classes. the range of values in the surface roughness class is from 0.1 to 0.9, while the range of values in the mean aperture class is from 5 to 50, resulting in a larger standard deviation in the class with a higher range of values. in the coefficient of determination (r2) results, it can be seen that both models have good performance, with a value of 0.93 for the surface roughness model and 0.97 for the mean aperture model. 4. conclusion based on the results and discussion, the machine learning model can accurately estimate the surface roughness and mean aperture values. the model, built using a cnn, performs reasonably well, although it does show a drop in performance over a certain range. two models were created, one for surface roughness and the other for mean aperture. the best model in the results of this research is the model created with the densenet201 architecture. the results of the model show good performance at q1 and q2 values, but decreased performance at q3 and above, as shown in fig. 6. this is in contrast to the average aperture training model, which has the highest performance at q2 and q3, while its performance at q1 is low, as shown in fig. 6(b). in addition, the model shows good performance in the calculation of the coefficient of determination (r2) with values of 0.93 for surface roughness and 0.97 for average aperture. therefore, the training model can be used to estimate the surface roughness and mean aperture values in fracture geometry images. further research is needed to improve the performance of the model, particularly in predicting real data from a single fracture, so that the model can be applied in industry. nurcahya, a. et al./ jgeet vol 08 no 02-2 2023 5 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 acknowledgements the authors acknowledge the department of geophysics universitas padjadjaran supercomputing resources "rockexplorer" made available for conducting the research reported in this paper. references dharmawan, i. a., ulhaq, r. z., endyana, c., aufaristama, m., 2016. numerical simulation of non-newtonian fluid flows through fracture network. in iop conference series: earth and environmental science 29(1), 012030. doi: 10.1088/1755-1315/29/1/012030. esdm., 2019. outlook energi indonesia (oei) 2019. ministry of energy and mineral resources republic of indonesia. retrieved from https://www.esdm.go.id/assets/media/content/co ntent-outlook-energi-indonesia-2019-bahasaindonesia.pdf gao, y., mosalam, k. m., 2018. deep transfer learning for image based structural damage recognition. computer-aided civil and infrastructure engineering 33(9), 748–768. herdiansyah, h., negoro, h. a., rusdayanti, n., shara, s., 2020. palm oil plantation and cultivation: prosperity and productivity of smallholders. open agriculture 5(1), 617-630. huang, g., liu, z., der, v., weinberger, k. q., 2017. densely connected convolutional networks. 2261–2269. ieee conference on computer vision and pattern recognition (cvpr). doi: 10.1109/cvpr.2017.243 koesoemadinata, r.p., 1980. geologi minyak dan gas bumi (1st ed). penerbit itb, bandung. naufal, m.f., kusuma, s.f., 2022. weather image classification using convolutional neural network with transfer learning. aip conference proceedings 2470(1), 050004. talo, m., 2019. convolutional neural networks for multiclass histopathology image classification. arxiv:1903.10035. wang, d., de boer, g., neville, a., ghanbarzadeh, a., 2021. a new numerical model for investigating the effect of surface roughness on the stick and slip of contacting surfaces with identical materials. tribology international 159, 106947. doi: 10.1016/j.triboint.2021.106947 © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). https://www.esdm.go.id/assets/media/content/content-outlook-energi-indonesia-2019-bahasa-indonesia.pdf https://www.esdm.go.id/assets/media/content/content-outlook-energi-indonesia-2019-bahasa-indonesia.pdf https://www.esdm.go.id/assets/media/content/content-outlook-energi-indonesia-2019-bahasa-indonesia.pdf http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” amirudin et al./ jgeet vol 08 no 02-2 2023 23 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 seismic vulnerability analysis using the horizontal to vertical spectral ratio (hvsr) method on the west palu bay coastline amirudin1, iktri madrinovella1*, sofian2 1 geophysical engineering, pertamina university, dki jakarta 12220, indonesia 2 palu class i geophysical station, meteorological, climatological and geophysical agency, indonesia * corresponding author: iktri.madrinovella@universitaspertamina.ac.id received: may 20, 2023. revised : may 31, 2023. accepted: june 10, 2023. published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13879 abstract this research was carried out to make a map of the dominant frequency (f0), amplification factor (a0), seismic susceptibility index (kg), vs30 , sediment layer thickness (h) and peak ground acceleration (pga). microtremor measurements were carried out with a three component seismometer of the tdl-303s type as many as 27 measurement points. the data was analyzed by the horizontal to vertical spectral ratio (hvsr) method. the pga calculation was carried out using the kanai equation with a reference to the palu -donggala earthquake on september 28, 2018. the results showed that the distribution of the dominant frequency value (f0) ranged from 0.4149 hz-0.8869 hz, the soil amplification factor (a0) ranged from 2,199–4,884, the seismic vulnerability index (kg) ranged from 8.79 s2/cm41.41 s2/cm, the shear wave velocity to a depth of 30 meters ( vs30) ranged from vs30 197.7 m/s-320.2 m/s , the thickness of the sedimentary layer ranges from 260.3 m-291.1 m and the peak ground acceleration (pga) of kanai ranges from 137.3 gal – 234.2 gal by using mw 7.4 earthquakes with an intensity scale (mmi) vi to vii. the coastal area of west palu bay has an intermediate seismic vulnerability ii to a high seismic vulnerability iv so that it will be vulnerable in the event of an earthquake disaster. are as that have a very high vulnerability index are in the upper western and easternmost regions while those with a lower level tend to have a lower vulnerability index value. keywords: passive seismic, microtremor, hvsr, seismic vulnerability index, peak ground acceleration, palu-donggala 1. introduction the motion of the palu-koro fault activity is the main cause of the earthquake disaster that occurred in palu city. the palu–koro fault is approximately 240 km, which leads from northern palu to southern palu (malili) until it reaches bone bay. the fault is cytostral and very active with a fault movement speed of about 25 to 30 mm per year, causing frequent earthquakes in the palu city area. the palu-koro fault passes through the west palu district, where in west palu district has many important buildings that become the economic center for the people of palu city, such as universities, schools, hotels, malls, banks, health centers, village offices and sub-district offices. the geological map shows that the research area (west palu bay coastline) has the lithology of alluvium and coastal deposit, which means the area has less dense rock. the west palu bay coastline is likely vulnerable if an earthquake occurs near the area. fig 1. geological map review palu sheet, central sulawesi (bmgk kota palu, 2018) 24 amirudin et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 the horizontal to vertical spectral ratio (hvsr) method from nakamura is one of the methods that can be used to utilize microtremor data. it can generate the dominant frequency value and amplification of the soil in an area, to compute the seismic vulnerability index and the thickness of the sedimentary layer. the purpose of this study was to determine the level of seismic vulnerability in the study area by making a map of the distribution of the dominant frequency value, amplification factor, seismic vulnerability index, shear wave velocity and sediment layer thickness. 2. material and methods 2.1 microtremor microtremor is a continuous subsurface vibration that has a low amplitude ranging from 0.2-20 hz, the source of vibration comes from various kinds of surface activities such as wind interactions with trees, ocean waves, vehicles, and human activities that can cause below-surface vibrations (kanai, 1983). these harmonic vibrations are retained in the sedimentary layer on the surface and are constantly reflected by the boundary plane of the layer. 2.2 hvsr method nakamura (2008) the spectral ratio of horizontal components to vertical component called the hvsr method with the assumption that shear waves predominate in microtremor and surface waves (rayleigh and love waves) are ignored. the transfer function between wave vibrations in sediments and bedrock is considered as the ratio of the horizontal and vertical spectra of surface vibrations. this means that the peak period of h/v and the peak value itself correspond to the dominant period and its amplification factor. 2.3 amplification factor (a0) nakamura (2008) states that the value of the soil strengthening factor (amplification) is related to the ratio of the impedance contrast of the surface layer with the layer below. if the contrast ratio of the impedance of the two layers is high, the value of the strengthening factor is also high, and vice versa. 2.4 dominant frequency (f0) the dominant frequency or the natural frequency of the soil or rock is the most dominant or most frequently appearing frequency value. the parameter of the dominant frequency is that it can indicate or be a reference to the type and characteristics of a rock. 2.5 shear wave velocity at the depth of 30 m (vs30) vs30 is the average speed of the surface shear wave is up to a depth of 30 meters. it is one of the local site effect variables that contribute to variations in the level of earthquake shocks on the surface. to estimate the speed of the shear wave (vs) can be done by various methods, including drilling (borehole). the calculation of vs30 is using topography slope, which is published by usgs (united states geological survey) as open-source data based on allen and wald (2007). other reference, herak (2008) introduced a technique for estimating the speed of shear waves (vs) using hvsr microtremor inversions based on body waves by the equation: 𝑉𝑠30 = ℎ30 ∑ ℎ𝑖 𝑉𝑠𝑖 (1) vs30 is the shear wave velocity at the depth of 30 m (m/s), h30 is the depth of 30 m, hi is the depth of the i-th layer (m) and vsi is the shear wave velocity of the i-th layer (m/s). 2.6 sediment thickness (h) the characteristics of sedimentary rocks that are loose, are not compact with relatively low mass density so that the propagation speed of shear waves is slower than that of the bedrock below. the value of f0 is related (inversely proportional) to the thickness of the sediment layer where the greater the dominant frequency value, the thinner a sedimentary layer, on the contrary, when the dominant frequency value is smaller, the thicker the sedimentary layer. the thicker the sediment layer results in an increased risk or impact of soil susceptibility to earthquakes. here is the formula for the relationship of the thickness of the sedimentary layer to the dominant frequency. ℎ = 𝑉𝑠30 4𝑓0 (2) h is the sediment thickness (m), vs30 is the shear wave velocity at the depth of 30 m (m/s), fo is the dominant frequency (hz). 2.7 seismic vulnerability index (kg) seismic vulnerability index is used to identify the vulnerability degree of the subsoil that deformations due to earthquakes occur. high seismic vulnerability index values will generally be found on soils with soft sedimentary rock lithologies. a high seismic vulnerability index value can identify that the area is prone to earthquakes and will experience strong shocks, and vice versa, small seismic vulnerability index values are generally found in soil layers with solid building rock lithologies so that when an earthquake occurs it does not experience much strong shaking. 𝐾𝑔 = 𝐴0 2 𝑓0(𝜋 2𝑉𝑏 ) (3) ao is the amplification factor, fo is the dominant frequency (hz) and vb is the shear wave velocity of the bedrock (m/s). 2.8 peak ground acceleration (pga) peak ground acceleration (pga) is the largest soil vibration acceleration value that has ever occurred somewhere caused by an earthquake wave. earthquake shocks felt on the surface can be described descriptively with an illustration scale based on the level of shock and impact. the formula of pga uses kanai method (1966) modified by douglas (2004). 𝑃𝐺𝐴 = 5 √𝑇0 10 0.61𝑀−(1.66+ 3.6 𝑅 ) log 𝑅+0.67 1.83 𝑅 (4) pga in gal, m is the magnitude of an earthquake near the site, r is the distance between the hypocenter and the site (km). 2.9 data acquisition the acquisition of microtremor data was carried out on the coastline of west palu bay, palu city, central amirudin et al./ jgeet vol 08 no 02-2 2023 25 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 sulawesi accompanied by bmkg class i palu on march 10-14, 2022. the location of each station was determined by using gps (coordinates and elevations) by leveling or adjusting the position, connecting the seismometer, measuring in 60 minutes for each station, saving the data in trace (*trc) format, and reformatting to miniseed (msd) format. fig 2. microtremor data acquisition equipment the instrument used for data acquisition is seismometer ds-4a to measure the ground motion, digital portable seismograph tdl-300s with sampling frequency 100 hz, geological compass to define the sensor direction, gps garmin for the measurement point location, gps antenna to define the time and location, connector cable to connect the instruments, laptop to monitor and check the recorded signal in digital portable seismograph, and logbook to write the coordinates, time of measurements and field conditions. fig 3. microtremor data acquisition location map 2.10 hvsr analysis with geopsy software the microtremor data is obtained from the 3 (three) component short-period digital seismometer, which consists of 2 (two) horizontal components (north-south direction and east-west direction) and 1 (one) vertical component. the data is stored in digital waveform with sampling rate 100 hz, and it must be transformed into frequency domain so the spectral ratio can be analyzed. the process of transforming the data from time domain into frequency domain is called fast fourier transform (fft). 2.11 fast-fourier transform: 𝐹(𝑡) = ∫ 𝑓(𝜔)𝑒𝑖𝜔𝑡𝑑𝑡 ∞ −∞ (5) 26 amirudin et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 4. 3-component microtremor signal the first step of hvsr analysis is to define the parameter of filtering, windowing, smoothing. the filtering used is low pass filter of 20 hz, according to the characteristics of the low frequency microtremor signal. the windowing length is 60 s which means the frequency spectrum is computed for every 60 s of data. however, there are high frequency noise that will disturb the data. it must be removed by determining the data by using the ratio of short-term average (sta) to long-term average (lta) of the data amplitude. the length for sta determination used is 1 s and lta is 30 s. fig 5. windowing every signal in every time window is transformed into frequency spectrum. the frequency spectrum from the horizontal component (north-south and east-west) is being computed using quadratic mean. the ratio of h/v component means the ratio of the frequency spectrum of the vertical component (z) to the quadratic mean of the horizontal components. amirudin et al./ jgeet vol 08 no 02-2 2023 27 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 6. the calculation of h/v spectral ratio (https://www.geopsy.org/documentation/geopsy/hv.html) the maximum number of the h/v of the average spectrum means the value of the amplification factor (ao), and the frequency of the ao is the value of the dominant frequency. the average h/v curve is determined by the length of window (60 s), so the standard deviation value is used to validate the curve reliability and peak clarity using the sesame criteria (2004). https://www.geopsy.org/documentation/geopsy/hv.html 28 amirudin et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 7. hvsr curve fig 8. h/v curve criteria for reliable curve and clear peak (sesame criteria) the h/v curves derived by all the 27 measurement points generally meet the sesame criteria (2004) almost 100% for the reliable curve and 80% for the clear peak. the seismic vulnerability index is computed using the value of the dominant frequency and the amplification factor of the h/v curve. and the each point data of the h/v curve is used to generate the vs30 value using depth inversion method. 2.12 hvsr inversion with dinver software the dinver software is used to calculate the shear wave velocity (vs) using the ellipticity curve method, which is one of the hvsr inversion methods that can be used to identify subsurface structures to obtain a grounf profiles curve that shows the vs value of each depth. the h/v curve model is constructed using model parameters in the form of primary wave velocity (vp), amirudin et al./ jgeet vol 08 no 02-2 2023 29 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 secondary wave velocity/shear wave velocity (vs), and layer depth (h), as well as input condition parameters (poisson ratio) and ρ (rock density). the matching process is carried out repeatedly, each iteration (iteration) is corrected to each of the initiation parameters, until the final model curve has the smallest mismatch of the observed hvsr curve. the result of the smallest misfit is obtained in the form of vp and vs each depth corresponding to the hvsr curve from the observation data 𝜎. the parameters used in the inversion of the hvsr curve can be seen in table 1 where the number of layers used in this study is 6 layers, the model parameters are p-wave velocity (vp), shear wave velocity (vs), poisson’s ratio (𝜎), and density (ρ). the maximum depth used is 300 m. table 1. initial model parameter vs (m/s) vp (m/s) poisson’s ratio density (kg/m3) maximum depth (m) layer 1 layer 2 layer 3 layer 4 100-400 300-460 460-580 480-760 160-1000 480-1150 576-1450 768-1900 0.2-0.5 2000 300 layer 5 660-1000 1056-2500 layer 6 900-1300 1440-3250 the results of the hvsr inversion are the ellipticity curve and the ground profile curve. the ellipticity curve serves to check the similarity between the initial parameter of the model and the observation. the ground profile curve generates the vs value to the depth below the surface. fig 9. the ellipticity curve and the ground profile curve. the dinver software used the algorithm introduced by wathelet (2008) based on sambridge (1999) and wathlet (2005). 30 amirudin et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 10. the flow chart of hvsr analysis and inversion 3. results and discussion the distribution map shows the dominant frequency value in range 0.4149 – 0.8869 hz. based on the classification of the dominant frequency of nakamura, the soil type is classified as the alluvial formation with frequency less than 2.5 hz and the sediment thickness above 30 m. the geology study shows that the area is formed by the delta sedimentation, top soil, sand, mud, and gravel. the eastern part of the fault plane shows the significantly low dominant frequency, which indicates the high potential of damage if an earthquake occurs. amirudin et al./ jgeet vol 08 no 02-2 2023 31 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 11. the dominant frequency map the amplification factor shows the strength of the shaking after the seismic wave propagates in the less dense rock is 2.199-4.884 times stronger than in the bedrock. the amplification factor of the research area shows the medium level, which the western and the center area shows the biggest amplification factor number. the amplification number can be increased if the rock has undergone deformation (weathering, folding, roughing) that changes the physical properties of the rock. fig 12. the amplification factor map the shear velocity at the depth of 30 m is called vs30, and it ranges between 197.7 – 320.2 m/s. the vs30 is generated by hvsr curve inversion, and it shows the lower value in the center part of the research area or the center of palu city. this area has lower vs30 value (<200 m/s) and fo value (0.4 0.5 hz), also has the higher amplification factor value (>4), which needs to be concerned. fig 13. the vs30 map 32 amirudin et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 based on the sediment layer thickness map in range 260.3 – 291.1 m, it shows the center of palu city also has the thicker layer (> 280 m). in the north-western part of the fault plane, it also shows the thicker sediment layer (> 280 m), lower fo value (0.5 – 0.6) and higher amplification factor value (>4). it has crowded infrastructure in this area, such as malls, hotels, markets, hospital and schools. fig 14. the sediment layer thickness map the result of the seismic vulnerability index by using the amplification factor and the dominant frequency data shows the range between 8.791 – 41.41 s2/cm which is classified as high index. the center area of palu city and the north-western part of the fault plane has the highest index (more than 30 s2/cm). table 2. the classification of the seismic vulnerability index (bmkg palu, 2018) kg index < 0.16 0.16 6 6 – 9 9 – 12 12 – 16 16 – 18 low middle i middle ii middle iii middle iv high i 18 – 21 high ii 21 – 24 high iii > 24 high iv based on the seismic vulnerability index result and table 2, the west palu bay coastline has the vulnerability index middle to high. the geological map shows the entire area consists of alluvium and coastal deposit, and the highest index is in the western and the center part of the research area (high iii – high iv). the highest index shows the most vulnerable area of the west palu bay coastline, which can be damaged severely if an earthquake occurs near the area. the western part (west palu) and the center part (central palu) are the location of houses, malls, hotels, markets, hospitals. the review of ground motion after palu-donggala earthquake 2018 reported by bmkg shows the response of citizens that has significantly corrected the earthquake intensity in palu city. it is consistent to the seismic vulnerability index, the area of palu city has greater damage when the earthquake occurs. fig 15. the seismic vulnerability index map amirudin et al./ jgeet vol 08 no 02-2 2023 33 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 16. bmkg shakemap of the palu earthquake, 2018 before (left) and after (right) correction the calculation of peak ground acceleration (pga) is also conducted to view the impact of the dominant frequency. thera are many empirical ways to calculate pga by using parameter magnitude and distance between the source and the site. by using the kanai formula, the pga calculation can consider the geological effect that is represented by the dominant frequency value. the calculation uses the palu-donggala earthquake (mw 7.4, september 28, 2018) as the magnitude and the source location parameter. the pga result ranges between 137.3 – 234.2 gal, which the highest pga located in the south-western part of the fault plane. the pga result is consistent to the dominant frequency, but inconsistent to the other parameter (ao, vs30, kg, h). it can be concluded that this pga formula does not associate with the result effectively, but it has strong relationship with the dominant frequency. fig 17. the pga map (left) and the bmkg shakemap of the palu-donggala earthquake on september 28, 2018 (bmkg palu, 2018) the result of pga using kanai formula and bmkg shakemap shows the similarity in the south-western part of the fault plane, but inconsistent to the other part. 7. conclusion 1. the south-western part of the fault plane and the center part of the palu city are the most potentially vulnerable area with the lower dominant frequency (fo 0.4 – 0.6 hz), lower shear velocity (vs30 < 200 m/s) higher amplification factor (a0 > 4), higher seismic vulnerabity index (kg 30 – 41 s2/cm), thicker sediment layer (h 280 – 290 m). it is pretty crowded in the south-western part area which has malls, hotels, markets, hospital and schools. the center of the palu city also has many houses, university, and markets. it is also consistent to the shakemap of bmkg (the review of palu-donggala earthquake 2018) which shows the greater intensity after the correction (felt by people). 2. the result shows that the area of west palu and central palu are the most vulnerable area, 34 amirudin et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 they have the potential to be severely damaged if a great earthquake occurs. 3. the pga value is affected majorly by the dominant frequency factor, so the result of the pga value does not associate effectively with other parameters (ao, vs30, kg, h). 4. the research area does not cover the map of the liquefaction or affected area of the 2018 earthquake. but the vulnerable area is still counted as the area that can be affected by the motion of the palu-koro fault. 5. these results and methods can be implemented in other study area, as long as the area has similar geological and seismological conditions. however, the validation used in this research is limited, so it can have potential error in analysis. to improve the confidence of this result, other similar method or computation should be conducted. acknowledgment we acknowledge the meteorological, climatological and geophysical agency (bmkg), especially palu class i for providing the data and the opportunity to conduct the field acquisition. references allen, t. i., wald, d. j. 2007, topographic slope as a proxy for global seismic site conditions (vs 30) and amplification around the globe: u.s. geological survey open-file report 2007-1357, 69. https://doi.org/10.1785/0120060267 bmkg kota palu., 2018. laporan akhir analisis indeks kerentanan seismik kota palu. bmkg kelas i palu. kota palu. douglas., 2004, ground motion estimation equation 19642003, south kensington campus press, london. geopsy tutorial: h/v measurement (modified 2008-1021) https://www.geopsy.org/documentation/geopsy/hv.ht ml herak, m., 2008, modelhvsr: a matlab tool to model horizontal-to-vertical spectral ratio of ambient noise. computers and geosciences 34, 1514-1526. https://doi.org/10.1016/j.cageo.2007.07.009 kanai, k., 1983, seismology in engineering, tokyo university, japan. kanai., 1966, improved empirical formula for characteristics of stray earthquake motion. proceedings of the japanese earthquake symposium (1-4). japan: reported in trifunac & brandy (1975). nakamura, y., 2008. on the h/v spectrum, the 14th world conference on earthquake engineering: beijing, china. sambridge, m., 1999, geophysical inversion with a neighbourhood algorithm: i. searching a parameter space. geophysical journal international 138, 479494. https://doi.org/10.1046/j.1365246x.1999.00876.x sesame., 2004, guidelines for the implementation of the h/v spectral ratio technique on ambient vibratio measurement, processing and interpretation, european commission reseacrh general directorate. wathelet, m., 2005, array recordings of ambient vibrations: surface-wave inversion. phd thesis universite de liege belgium. wathelet, m., 2008, an improved neighborhood algorithm: parameter conditions and dynamic scaling. geophysical research letters 35, l09301. https://doi.org/10.1029.2008gl033356.pdf © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1785/0120060267 https://www.geopsy.org/documentation/geopsy/hv.html https://www.geopsy.org/documentation/geopsy/hv.html https://doi.org/10.1046/j.1365-246x.1999.00876.x https://doi.org/10.1046/j.1365-246x.1999.00876.x http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 changming, b., et al./ jgeet vol 8 no 1/2023 77 research article economic evaluation of water production management with rpm (relative permability modifier) treatment based on gross split contract in “re” well in “dn" field boqin changming1,*, liang longwei1 1 department of petroleum engineering, tunghai university, taiwan abstract the "re" well in the "dn" field is an oil well produced in june 2004 with an initial water cut value of 15% as time went on there was a fairly high increase in the water cut value reaching 97% which means that it caused increased water production. and oil production decreased from 387 bopd to 11 bopd. appropriate handling in overcoming excessive water production, one of which is by using a method that can selectively restrain water production without restraining hydrocarbon production with rpm (relative permeability modifier) treatment. rpm (relative permeability modifier) is a type of polymer with a high molecular weight as the main molecule of rpm. rpm can be done without isolating the layer zone so that it can be injected bullhead into all layer zones to reduce water permeability. this final project research has been seen from increasing the rate of oil production and decreasing the water cut. the selected well is the "re" well in the "dn" field which has an increasing water cut value and decreased oil production. then calculate the economy using the gross split method to calculate the feasibility level of the rpm (relative permeability modifier) treatment project. keywords : rpm (relative permeability modifier) treatment, water coning, gross split 1. introduction one of the factors causing a decrease in the rate of oil production from a well is water coning. water coning is a situation around the wellbore where the boundary of oil and water rises to form a cone reaching the lowest perforation point, which will cause water to be produced earlier so that the increase in water production becomes faster. (ahmed, 2001). various applications to avoid or just to slow down the occurrence of water coning include using water production wells to maintain the speed of rising water levels and calculating the length of the perforation hose and the optimum rate of water production, then by producing aquifer water. however, all of them will still arrive at a condition where water breakthrough from the aquifer will reach the wellbore and cause water production on the surface. (subaruto & ariadji, 2006). appropriate handling in overcoming excessive water production is by using a method that can selectively restrain water production without restraining hydrocarbon production with rpm (relative permeability modifier) treatment. rpm is a kind of polymer with high molecular weight as the main molecule of rpm. rpm can be done without isolating the layer zone so that it can be injected bullhead into all layer zones to reduce water permeability. this final project research is seen from increasing the rate of oil production and decreasing the water cut. the selected well is the "re" well in the "dn" field which has an increasing water cut value and decreased oil production. then calculate the economy using the grosssplit method to calculate the feasibility level of the rpm (relative permeability modifier) treatment project. 2. literature review 2.1 reserve determination reserves can be defined as the estimated amounts of crude oil, natural gas, gas condensate, liquid phase recovered from natural gas, and other materials (e.g. sulfur), which are considered of commercial value to be recovered from accumulation in the reservoir using existing technology at some point in the economic conditions and with government regulations in force at the same time. (permadi, 2004). 2.2. rpm (relative permeability modifier) treatment to overcome the problem of increasing high water production, one of the methods of water conformance is the relative permeability modifier treatment. this treatment is carried out by injecting a relative permeability modifier type chemical and several other chemicals together with water into the reservoir formation hole (darlymple & jaripatke, 2009). 2.3. mechanics of rpm (relative permeability modifier) treatment the working principle of this treatment is by injecting a chemical relative permeability modifier and several additives into the reservoir, rpm is the main polymer (single-polymer) used and functions to reduce the water flow rate over the oil flow rate, as can be seen in the figure (darlymple & jaripatke, 2009). 2.4. treatment design the amount of treatment fluid is determined by calculating the required volume of fluid calculated from the wellbore. this radial penetration must occur at the desired treatment height. the equation for this calculation is shown below (pietrak, stanley, weber, & fontenot, 2005). 2.5. gross split the existence of the gross split scheme is one of the goals to eliminate the debate regarding cost recovery. the method used is to eliminate the element of cost recovery in the pattern http://journal.uir.ac.id/index.php/jgeet 78 changming, b., et al./ jgeet vol 8 no 1/2023 of sharing oil and gas profits. this is because cost recovery is often suspected of being the root of the problem, even being accused of being a means to misuse oil and gas operating funds. others see cost recovery as a "sin". the gross split concept, which eliminates cost recovery, means eliminating the responsibility of the government and skk migas to reimburse some of the oil operating costs, which are usually borne professionally according to the cost recovery scheme. with the loss of cost recovery, skk migas' obligation to control and supervise cost recovery is erased. 2.6. the difference between psc and gross split contracts: kurniawan, temmy surya and jemmy jainudin (2017) are in contrast to cost recovery pscs, the split between the government and contractors in the gross psc split is determined at the outset. direct gross revenue is split between the government and contractors with a base split, namely 57%:43% for oil, and 52%:48% for natural gas. the split provided that the operating costs are fully the responsibility of the contractor. so, there is no more cost recovery. the split has not considered additional taxes for the government. 2.7. gross split production sharing contract (permen esdm number 08 of 2017), gross split production sharing contract is a production sharing contract in upstream oil and gas business activities based on the principle of sharing gross production without a mechanism for returning operating costs. psc gross split applies to new working areas and working areas whose contract period has ended but not extended. for oil and gas working areas whose contract has been extended, they can choose whether to continue using the previous contract (psc cost recovery) or using a gross split psc. 2.8 economic of migas oil and gas economy investment is based on the profit earned. the profit indicator is needed as a parameter for decision making. to assess the economics of a project or prospect, it is necessary to look at all aspects of expenditure and income throughout the life of the project, so that the evaluation of a project will be based on income during the project cycle until the expenditure and income are the same or close to the same. (cash flow) to assist in making decisions to continue or reject the project. however, cash flow alone cannot be used as a reference, we need other parameters such as npv and irr as considerations for making decisions (benny lubiantara, 2012). 2.9 investment investment is the initial financing for projects of economic value that are offered. investment in the development of energy resources in indonesia includes exploration costs in finding new sources of reserves and field development. investments can be grouped into capital investment (tangible investment) and non-capital investment (intangible investment). 2.10. gross revenue gross revenue (gr) is the result of multiplying the rate of production (bpd) by the price of oil. the rate of oil production is determined based on the predicted production profile that has previously been calculated. the price of indonesian crude oil depends on the world crude oil market price. . the oil price used is the indonesian crude price (icp). 2.11. escalation factor in calculating net cash flow, it is also advisable to take into account the possibility of inflation in the future. the existence of inflation will affect the increase in investment in the form of capital and operating costs. for example, in the future the cost to build (production facilities) will be affected by rising steel prices and labor costs that will build these facilities. the amount of inflation is stated in the escalation rate. donald g. newnan (1984). 2.12. depreciation depreciation is related to the cost of capital, which means a reduction in the value of capital goods as a result of damage or a decrease in use value over time. the length of time for depreciation depends on the contractual agreement, and the depreciation method used in this study is the declining balance method. in this case, the value of an item will decrease rapidly over time. 2.13. non capital cost non-capital costs consist of costs incurred in the years of conducting field exploration and development, these costs will be recovered immediately in the first year of production without depreciating. 2.14. operating cost operating cost is costs incurred either in connection with production operations (variable costs) or costs that are certain to be incurred by the company in the form of general administration which do not affect the size of production (fixed costs). 2.15. recovered cost recovered is cost that gained by the contractor and it is accordance with benny lubiantara (2012) 2.16. unrecovered cost unrecovered cost is a cost that cannot be recovered by the contractor because the gross revenue is less than the total cost recovery. unrecovered cost can only be calculated in the following year after knowing the total cost recovery that can be obtained by the contractor. 2.17. taxable income taxable income is taxable income. 2.18. tax tax is one source of government revenue. the government takes its share of oil and gas production through a tax imposed on the contractor's income derived from the business. the tax system created by the government is intended to maximize government revenue. the current tax on contractors is 25%. this tax is imposed on taxable income. 2.19. contractor share contractor share (cs) is the total income that can be received by the contractor after splitting it with a base split. 2.20. net cash flow net cash flow (ncf) or is the contractor's net income or the amount of contractor's income that has been taxed. 2.21. government share government share (gs) is the total revenue of the state (government) after dividing by base split. 2.22. government take and contractor take government take (gt) and contractor take (ct) are the percentage of total government and contractor revenue from project profits. changming, b., et al./ jgeet vol 8 no 1/2023 79 2.23. economic indicator economic indicator is a factor to determine the advantages and disadvantages of the contract. economic indicators that are often used are: npv (net present value), irr (internal rate of return), and pot (pay out time). npv and irr are always related to the time value of money (time value of money), while pot is not. time value of money is the time value of money which is a method for knowing the value of money or profits from a cash flow in the future. (newnan donald g, 1984). 2.24. net present value (npv) the net present value (npv) is the difference between the money received and money spent taking into account the current time value of money. npv shows the value of net profit received from a business during the life of the business at a certain discount factor level. a project is said to be feasible if the npv is positive, if the npv value of a project is negative, it can be said that the project is experiencing a loss. the npv value of a project is zero, so the amount of expenditure is equal to the amount of revenue (newnan donald g, 1984). 2.25. internal rate of return (irr) the internal rate of return (irr) is an indicator value that is identical to how much interest the investment can provide compared to the prevailing bank interest rate or the minimum attractive rate of return (marr). at the irr interest rate, npv = 0 will be obtained, in other words, the irr implies an interest rate that can be given by investment, which will give an npv value = 0 (newnan donald g, 1984). 2.26. payouttime (pot) pay out time (pot) or pay back period is a period needed to be able to recoup investment expenses. pot can be known from the accumulated net cash flow (cummulated net cash flow), the pot mechanism can be found by using the interpolation equation. some of the weaknesses of pot are that it ignores the time value of money (time value of money) and cannot show the amount of profit to be obtained or in other words pot is not a measuring tool for "profitability" but only a measuring tool for the speed of return of funds. a project is said to be feasible if the pot is small compared to the age of the project or smaller than the minimum target time the company can return its capital or investment. 3. research method this final project research was conducted at pt. pertamina asset i field jambi by collecting data related to rpm treatment related to well production data, well completion data, and reservoir data. the research method used is field research or this research uses data from oil fields. the data used are secondary data provided by field supervisors, previous research, journals, papers, expert opinions, principles and theories from guaranteed literature, petroleum engineering textbooks, relevant journals and discussions with supervisors which lead to conclusions which are purpose of research. fig 1. research diagram start data collection a. history production data (fluid production speed, oil production speed, water cut) b. reservoir data (rock physical trait and fluid physical trait) c. rpm data of treatment report processing stages a. determining cumulative production and remaining reserve of “re” well “dn” field before conducting relative permeability modifier (rpm) treatment. b. analyzing the excessive problem of water production using k.s. chan diagnostic plot and critical flow speed craft and howkins method. c. evaluating the success of relative permeability modifier (rpm) treatment. d. calculating the economy of relative permeability modifier) job gross split contract. data evaluation and discussion conclusion and suggestion done 80 changming, b., et al./ jgeet vol 8 no 1/2023 4. finding and discussion 4.1. determination of the amount of reserves and remaining reserves of the "re" well calculation of total reserves (ooip) is a stage considered important considering how many reserves and potential remain in the "re" well, so that it will determine the success of fluid production. the following is the "re" well data, among others: in calculating the number of remaining reserves, looking at the cumulative production of the reservoir, the cumulative production (np) for the reservoir well "re" is 133,862 bbl. so that the remaining reserve can be calculated as follows: dealing with the calculation above, it can be seen that the remaining reserves of the "re" well are still very large. 4.2. identification of water coning identification of water coning is by looking at whether the "re" well is proven to have water coning or not, namely by the k.s. chan and then analyzed the coning free flow rate (critical flow rate) with the craft & hawkins method. before carrying out a water coning analysis, first evaluate the water cut performance in the "re" well (figure 2). fig 2. water cut performance "re" well dealing with the evaluation of the water cut performance of the "re" well, at the start of production the water cut value was only 15%, but over time oil production has decreased and the water cut value has increased, and since the end of 2009 the "re" well has been producing with a water cut value which reached a high of 97%, as seen from the stable water cut trendline in these conditions. from the results of this water cut evaluation it was concluded that the main problem in the "re" well was water production, then with the k.s. chan identified whether water coning was the cause of the high water production in the "re" well. identification of water coning with the k.s. diagnostic plot method. chan is a plot between wor and wor derivative (wor') vs time. 4.2.1. chan plot water coning was identified using the k.s. chan on the well "re". plot between wor and wor' vs time and compared with the results of analysis from k.s chan. plot of wor and wor' results from cumulative production on the first to last day of production. can be seen in figure 3. fig 3. wor plot and wor' (derivative) for "re" well and comparison with k.s. chan curve. changming, b., et al./ jgeet vol 8 no 1/2023 81 4.2.2. determination of critical flow rate determination of the critical flow rate uses the craft and hawkins method to determine whether the oil flow rate in production wells has exceeded the maximum flow rate. the following is the "re" well data, among others: oil zone thickness (h) = 50.2 f effective permeability of oil = 60 md well dewatering radius (re) = 250 ft well radius (rw) = 0.29 ft oil formation volume factor (bo) = 1.24 bbl/scf oil viscosity (µo) = 2.64 cp static pressure (ps) = 1525 psi well bottom flow pressure (pwf) = 933.98 psi penetration fraction (f) = 0.196 the calculation of the critical flow rate of the "re" well is as follows:  calculating ratio productivity  calculating critical flow speed 4.3. evaluation of the success of the rpms treatment evaluation of the success of the rpms treatment can be seen from the production tests and production rates achieved. the parameters used in assessing the success of the rpm treatment are by looking at the production rate of the well after the test and the reduction in the water cut contained in the oil. 4.3.1. production evaluation the following results of the production of the "re" well before and after the rpm treatment can be shown in table 4.1 as follows: tabel 1. results of the production of the "re" well before and after the rpm treatment date gross nett water wc bfpd bopd bwpd 1-jan-09 402 20 382 95 1-feb-09 389 18 371 94 1-march-09 531 15 516 78 1-apr-09 541 26 516 95 1-may-09 521 25 496 95 1-jun-09 520 23 497 96 1-jul-09 506 19 487 96 1-aug-09 478 19 459 96 1-sept-09 476 18 459 96 1-oct-09 448 17 431 96 1-nov-09 416 12 403 97 1-dec-09 339 11 328 97 rpm treatment 1-jan-10 379 88 291 77 1-feb-10 390 84 306 78 1-marc-10 380 81 299 79 1-apr-10 379 77 302 80 1-may-10 376 74 302 80 based on table 4.1, before the rpm treatment, the water production was 328 bwpd. therefore, the rpm injection treatment was carried out. after the rpm treatment at the end of december 2009, oil production has increased where previously it was 11 bopd became 88 bopd, and this shows the success of the rpm treatment due to an increase in oil production. data on the results of the "re" well production test before and after the rpm treatment can be seen in figure 4. fig 4. production result before and after treatment 82 changming, b., et al./ jgeet vol 8 no 1/2023 4.3.2. water cut evaluation after conducting a production evaluation, an evaluation of the water cut performance is then carried out to see the changes in the water cut that occur before and after the rpm treatment. the water cut performance of the "re" well can be seen in figure 4.5 below: fig 5. water cut performance before and after rpm treatment 4.4. economic evaluation an economic evaluation of the rpm treatment is carried out to find out whether the commerciality of the work is profitable or not. the economic study was carried out based on the vi generation production sharing contract, as shown in the psc generation vi flow chart in figure 2.6. the rpm treatment work aims to increase the productivity of the wells, so as to make a profit. the economic parameters needed in this calculation include: npv (net present value), ror (rate of return), pot (pay out time) and cash flow. 4.5. gs method economic calculations an economic evaluation of the rpm treatment is carried out to find out whether the commerciality of the work is profitable or not. the economic study is carried out based on the gross split contract. 4.5.1. economic analysis of rpm treatment gs method tabel 2. economic well "re" economy parameter "re" well recoverable reserve 73.674,95 stb gross revenue 4.361.459,75 us$ project age 8 tahun investment 26.688 us$ operating cost 2.145,34 us$ net contractor take 1.179.739,76 us$ npv contractor 923.999,39 us$ ror contractor 1956,5 % pot contractor 0,049 tahun dpir contractor 34,62 table 3. contractor cash flow after rpm treatment year ncf discount rate $(000) 0% 5% 10% 15% 20% 25% 30% 0 (26,688) (26,688) (26,688) (26,688) (26,688) (26,688) (26,688) (26,688) 1 540,254 540,254 514,527 491,140 469,786 450,211 432,203 415,580 2 168,924 168,924 153,219 139,607 127,731 117,309 108,112 99,955 3 155,567 155,567 134,385 116,880 102,288 90,027 79,650 70,809 4 127,483 127,483 104,881 87,073 72,889 61,479 52,217 44,635 5 43,003 43,003 33,694 26,701 21,380 17,282 14,091 11,582 6 65,632 65,632 48,975 37,047 28,374 21,980 17,205 13,597 7 64,148 64,148 45,589 32,918 24,116 17,903 13,453 10,223 8 41,417 41,417 28,032 19,321 13,539 9,632 6,949 5,077 npv 1,179,739.76 1,036,614.77 923,999.39 833,415.05 759,135.05 697,191.62 644,770.91 it can be seen in table 4.2 the results of the economic analysis seen in the economic parameters of the "re" well indicate that the rpm treatment work that has been carried out is profitable because the economic indicator npv value obtained is positive, ror > marr of 15%, pot (return on investment spending) 0.049 years , while the economic indicators of cash flow can be seen in table 4.3. changming, b., et al./ jgeet vol 8 no 1/2023 83 fig 6. graph of pay out time 5. conclusion dealing with the calculations and discussion of the evaluation of the water coning problem and its handling in the "re" well, it can be concluded as follows: 1. the "re" well has a cumulative production of 133,669 bbl with a remaining reserve of 1,574,892 bbl. 2. the results of the k.s. diagnostic plot analysis. chan on the "re" well, the graph shows the slope between the wor and wor derivative and it can be seen from the slope of the wor derivative that the slope is negative (below) which is a characteristic that indicates an indication of water coning then by determining the critical flow rate craft & hawkins the actual flow rate of oil (qo = 387 bopd) is greater than the critical flow rate (qoc = 196.8 bopd) indicating the main problem of the "re" well is water production. 3. evaluation of the success of handling water coning with rpm treatment on the "re" well, where the acquisition of oil production increased from 11 bopd to 88 bopd, and the water cut decreased from 97% to 77%. 4. in accordance with the economic calculations, the "re" well obtained revenue of us$ 4,361,459 with an npv of us$ 923,999, ror of 1956.5%, pot for 0.049 years and dpir of 34.62. references ahmed, t.(2001). reservoirengineering handbook (2ndhous ed.).texas: gulf publishing company. ariyon, m. (2013) analisis ekonomi pemilihan electric submersible pump pada beberapa vendor , 4 9-19. ariyon, m. et al 2020 iop economic feasibility study of onshore exploration oil field development using split contract. ariyon, m. 2018 studi perbandingan keekonomian pengembangan lapangan minyak marginal menggunakan production sharing contract dan gross split.in proceding seminar nasional teknologi dan rekayasa. astutik, w. (may, 2007). a study of downhole water sink (dws) techlogyoptimum dws design in vertical well considering reservoir parameters. paper presented at the 2007 indonesia petroleum association (ipa). chan, k.s. (1995). water control diagnostic plots, spe 30775, spe annual technical conference and exhibition, dallas-usa. dalrymple, d., & jaritpake, o.(2009). relative permeability modifiers in fracture stimulation applications.middle east oil & gas show and conference, bahrain. donald g. newnan 1984, engineering economic analysis giatman, m. (2007).engineering economy.jakarta: raja grafindo persada. houston, j. f et al. (2006). dasar dasar manajemen keungan.jakarta: salemba empat inikori, s.u. (agustus, 2002). numerical study of water coning control with downhole water sink (dws) well completions in vertical and horizontal weels. ireson, w. g (1966).dasardasar ekonomi teknik.rhineka cipta. jokowinomics di sektor migas : saat gross split menantang cost recovery". ekonomi.bisnis.com. 15 juli 2019. kaplan, s. (1983). energy ekonomics for engineering and management decision making. new york: mc.grawhill lubiantara, b, 2012. ekonomi migas tinjauan aspek komersial kontrak migas. gamedia widiasarana indonesia. nandasari, p .&priadythama, li. (2019). analisis keekonomian proyek perusahaan minyak dan gas bumi : studi kasus abc oil. partowidagdo, w. (2002).manajemen dan ekonomi minyak dan gas bumi, program studi pembangunan pasca sarjana itb, bandung, permadi, a.k. (november, 2004). diktat teknik reservoir. edisi pertama. institut teknologi bandung. pietrak m.j., stanley, f.o., weber, b.j., fontenot, j.s. (2005). relative permeability modifier treatments on gulf of mexico frac-packed and gravel-packed oil and gas wells. spe annual technical conference and exhibition, dallas. pudyantoro, a. rinto (21 april 2019). "meneropong akar masalah psc gross split". katadata.co.id rangkuti, f. (2012).studi kelayakan bisnis &investasi.jakarta: gramedia pustaka. rukmana, d., kristanto, d., & aji, v.d.c. (2011).teknik reservoir teori dan aplikasi (4nd ed). yogyakarta: pohon cahaya. sari, n. (2001). ekonomi teknik ,yayasan himoniora, surabaya. subenarto, a.w., ariadji, t. (2006).desain konseptual optimasi produksi untuk sumur horizontal yang diproduksi dari reservoir karbonat dan mempunyai masalah water coning.simposium nasional & kongres ix, jakarta. soeband, koesmawan a. & koasih, s. (2014). manajemen operasi.mitra wacana media. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). c u m u la ti v e d is c o u n te d n c f , u s $ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 4 2022 suhendro, i. et al./ jgeet vol 7 no 4/2022 151 research article rock characteristics of post-caldera volcanoes in dieng volcanic complex (dvc), central java, indonesia indranova suhendro 1*, muhammad nadafa isnain1, rizky wahyudi1 1 department of environmental geography, faculty of geography, universitas gadjah mada, sekip utara jl. kaliurang, bulaksumur, yogyakarta, 55281, indonesia * corresponding author : indranova.suhendro@mail.ugm.ac.id tel.:+62-889-526-3638 received: jul 11, 2022; accepted: dec 8, 2022. doi: 10.25299/jgeet.2022.7.4.10015 abstract the dieng volcanic complex (dvc) has one of the densest post-caldera volcanisms activity presents in indonesia, yet its population density is considerably high. therefore, it is important to identify the rock characteristics produced by the dvc post-caldera volcanoes to understand the risks and future hazards (i.e., eruption style). based on lithology, we have classified dvc post-caldera volcanoes as (1) pyroclastic domain (pd; including pagerkandang, merdada, and pangonan), and (2) lava domain (ld; including prambanan, kendil, pakuwaja, sikunir, sikari m, and seroja). pd is characterized by the domination of pyroclastic materials (mostly ash and lapilli) with oxidized scoria and volcanic lithics (fresh and/or altered) as the main components. the oxidized scoria clasts are moderately vesicular (27–41 % vesicularity; ϕ𝑉 ) and phenocryst poor (<5 % phenocryst crystallinity, ϕ𝑃𝐶 ), with plagioclase, pyroxene, and oxides as the main phenocryst phases. the ld is composed predominantly of lava. the observed lavas are typically dense (mostly <1 % ϕ𝑉 ), phenocryst rich (21–47 % ϕ𝑃𝐶 ), and include plagioclase, pyroxene, biotite, amphibole, and oxides as the main phenocryst phases. such differences in mineralogy and textures (i.e., vesicularity and crystallinity) suggest that pd and ld were likely sourced from different magmatic sources with different eruption styles (explosive and effusive styles, respectively). we have suggested that civilization settlements near pd are facing major threats from explosive magmatic, phreatomagmatic, and phreatic eruptions that could produce significant fallouts, ballistic materials, and highly destructive pyroclastic density currents. lds pose a threat in the form of effusive magmatic eruptions such as lava flows and/or domes. keywords: dieng volcanic complex, post-caldera volcanism, lava, pyroclastic rocks, eruption 1. introduction post-caldera volcanism is known to reflect active magmatic conditions after the collapse of a volcanic edifice (sigurdsson, 2000). such processes might occur through (1) centralized vents (e.g., sakurajima in the aira caldera, barujari in the samalas caldera, and batur in the batur caldera; araya et al., 2019; rachmat et al., 2016; reubi and nicholls, 2004) and/or (2) random-scattered vents in the inner and rim of a caldera (e.g., aniakchak, dieng, and ijen volcanic complexes; browne et al., 2022; harijoko et al., 2016; suhendro, 2016). in the first type, predicting future eruptions may be relatively easy because the magma extrusion takes place from centralized vent(s) (araya et al. 2019; rachmat et al. 2016; rubin’ et al. 1989). however, predicting future eruptions from the second type may be very challenging owing to the uncertainty of the vent(s) location. it is therefore important to identify the pattern and behavior of the second type of post-caldera volcanism (including the eruption style, deposition characteristics, and stratigraphy) to gain a better understanding of its eruption dynamics, which can be utilized as a basis for hazard assessment. to shed light on this issue, we have studied the post-caldera volcanoes of dieng volcanic complex (dvc) in central java, indonesia (fig. 1a, b). we selected this area for our study for two main reasons: (1) dieng is known as a volcanic complex that hosts one of the densest post-caldera volcanisms activity in indonesia (there are approximately nine post-caldera volcanoes occupying the inner caldera (ca. area of ±40 km2)), and (2) the dvc is a home of abundant civilization settlements (approximately 1794 people/km2) (badan pusat statistik kabupaten wonosobo 2020). this has become more serious because there are many settlements situated very close (less than 200 m) to the active craters, such as sileri, sinila, and sikidang. moreover, the phreatic eruption of the sinila crater in 1979 has shown us how dangerous a post-caldera volcano can be, even without any magma extrusions (the eruption released a co2-dominated gas and killed 142 people; le guern et al., 1982). herein, we report the results of fieldwork on nine postcaldera volcanoes in the dvc, namely sikunir, seroja, pakuwaja, sikarim, kendil, prambanan, pangonan, merdada, and pagerkandang (fig. 1b). these fieldwork results were then combined with qualitative morphometric observations to produce a geological map of the study area. subsequently, we have then reported the results of quantitative analyses of the grain size distribution (gsd), componentry, phenocrysts (modal mineralogy and phenocryst content), and vesicles (bulk vesicularity and vesicle number density). however, gsd and componentry analyses can only be performed for pyroclastic materials. in addition, we have reported the chemical composition of the scoria clast groundmass glass. finally, quantitative and chemical analyses were performed to understand the eruption dynamics of the dvc post-caldera volcanoes. we suggest that syn-eruptive processes (degassing and decompression rate) coupled with external factors (i.e., groundwater and lake) play an important role in controlling the eruption style (effusive or explosive), and ultimately, the future hazards that can possibly occur (i.e., lava http://journal.uir.ac.id/index.php/jgeet 152 suhendro, i. et al./ jgeet vol 7 no 4/2022 flows, lava domes, pyroclastic fallouts, pyroclastic density currents (pdcs)). fig. 1. (a) location of dieng volcanic complex (dvc). (b) map showing the distribution of our sampling locations. red circle denotes lava flows and/or domes, while blue circle represents pyroclastic deposits. data source of the topographic map: badan informasi geospasial, 2018. note that pd volcanoes are typically having large crater sizes compared to ld volcanoes. fig. 2. lavas in the proximal zone (vent area) shows foliation (a), flow-banding structure (b), brecciation (c), with abundant phenocryst content (d). distal lavas are typically massive (with minor sheeting joints) and contain less abundant phenocryst content than the proximal lavas (e, f). intercalation of ash and lapilli falls from pagerkandang (g) and merdada (h). by contrast, pangonan shows a relatively simpler stratigraphic section than the later, as there are only two pyroclastic layers (pf 8-1 and pdc 8-1) above the paleosoil (i). bomb sag of large lithic clasts cause the discontinuity of pf 8-1 and pdc 8-1 layers (j). representative images of oxidized scoria clasts (k) suhendro, i. et al./ jgeet vol 7 no 4/2022 153 fig. 3. (a) stratigraphic column of merdada, pagerkandang, and pangonan. (b) deposits of pagerkandang and merdada were resulted from pyroclastic fall, while pangonan comprise of pyroclastic fall and pyroclastic density current (flow). 2. dieng volcanic complex (dvc) the dieng volcanic complex (dvc) is a quaternary volcano in central java, indonesia (fig. 1a) (harijoko et al. 2016). its caldera structure has a circular depression which extend from the northern to the eastern side of the dvc (gunung prau, fig. 1b). although the dvc is thought to have experienced a caldera formation process (sukhyar et al., 1986), such fundamental information on its caldera-forming eruption deposits is still lacking (i.e., a thick sequence of pumice and/or scoria fall and ignimbrite deposits). this may be caused by intense post-caldera volcano activities, as the deposition of younger volcanic products will bury the older deposits. sukhyar et al. (1986) classified dvc rocks into the categories of pre-collapse, second, and youngest episodes. the oldest group (pre-collapse episode) is represented by the rocks from gunung prau with an estimated age of 1.1±0.9 ma (harijoko et al. 2016). this group covers a narrow variation in the bulk-rock chemical compositions (basalt to basaltic andesite, (±49–57 wt. % sio2) with phenocryst variations of plagioclase (pl), clinopyroxene (cpx), orthopyroxene (opx), olivine (ol), and oxides (ox) (harijoko et al. 2015). the second episode was represented by rocks from pagerkandang, bucu, and pangonan-merdada, with the magma compositions ranging from basalt to andesite (±51.6–63.1 wt. % sio2) (harijoko et al. 2016). however, there have been no reports on the mineral assemblages in the second episode. based on k-ar analysis, the age of second episode group is found to be 0.46–0.37 ma (harijoko et al. 2016). the youngest episode represents the youngest and most evolved rocks in dvc (±0.27–0.07 ma and 59.6–64.5 wt. % sio2, respectively), with plagioclase as the most abundant mineral phase, followed by clinopyroxene, orthopyroxene, biotite, amphibole, and various oxides. it is worth noting that there is a tendency of increasing silica content from the pre-caldera to the youngest episodes (harijoko et al. 2016). such evidence coupled with the fact that hydrous minerals (i.e., biotite and amphibole) only exist in the youngest episode suggests that the dvc has experienced an intensive fractional crystallization process. 3. fieldwork in general, post-caldera volcanism in the dvc displays typical distinctive rock types between the south and -southeast (s-se) and west-northwest (w-nw) sectors. in particular, the s-se sector (sikunir, seroja, pakuwaja, sikarim, kendil, and prambanan) is dominated by lava flows and/or domes, whereas the w-nw sector (pangonan, merdada, pagerkandang) is predominantly composed of pyroclastic materials (fig. 1b). hereafter, we consider the s-se and w-nw sector post-caldera volcanoes as the lava domain (ld) and pyroclastic domain (pd), respectively. the ld outcrops are typically thick (up to several tens meters), massive, intensively fractured, and phenocryst-rich (fig. 2a-f). some may display foliations (fig. 2a) and flowbanding structures (fig. 2b), but they are exclusive to the proximal zone (vent area). it is worth noting that proximal lava outcrops tended to have higher phenocryst content than distal lava (fig. 2d and f). the pd outcrops are characterized by the stratification of pyroclastic materials (mostly ash and lapilli; fig. 2g-j). in particular, we have identified (at least) nine, six, and two main tephra layers at locs 6, 7, and 8, respectively (figs. 2 and 3), with oxidized scoria as the only juvenile component (fig. 2k). unlike the ld, juveniles from the pd were apparently aphyric (phenocryst-poor). lithics in pagerkandang and merdada are fresh (dark to grey in color, most of them display porphyritic textures), whereas most of the lithics in the pangonan have been intensively altered to a yellowish-white colour. 4. methods samples from the lava and pyroclastic domains (ld and pd, respectively) were collected from random and accessible locations. for the pyroclastic deposits (which consisted of several layers), sampling was started from the lower layer to avoid contamination from the upper layer (suhendro et al. 2021). the pyroclastic samples were sieved manually (-6ϕ (>32 mm) to 3 ϕ (1/8 mm)). next, we identified and counted all of the grains from -6ϕ to -2ϕ (>32 to 4 mm) sieves to obtain the componentry data. based on qualitative traits, we found that each eruptive unit consisted of homogeneous juvenile materials (i.e., lava and scoria). therefore, each unit is represented by only one thin section. in particular, 14 thin sections (six lava domes, five lava flows, and three scoria clasts) from each unit were observed for petro-graphic analysis to obtain the modal mineralogy and 154 suhendro, i. et al./ jgeet vol 7 no 4/2022 phenocryst content (ϕ𝑃𝐶 ). first, all of the observed phenocrysts (from each thin section studied) were manually traced using corel draw x7. second, each resultant image was processed using image-j (i.e., suhendro et al., 2021, 2022) to obtain the total number and area of the measured phenocrysts. finally, the vesicle-free phenocryst content was obtained from the following equation (suhendro et al., 2021): ϕ𝑃𝐶 = ∑ 𝐴𝑃𝐶 𝑁 𝑛=1 (𝐴𝑆−∑ 𝐴𝑉 𝑁 𝑛=1 ) (1) where ∑ 𝐴𝑃𝐶 𝑁 𝑛=1 is the total phenocryst area, 𝐴𝑆 is sample area in the thin section, and ∑ 𝐴𝑉 𝑁 𝑛=1 is the total vesicle area. table 1. glass chemical compositions of scoria clasts. all major elements are shown in weight percent (wt. %). because scoria clasts are aphanitic, such glass compositions might not differ with the bulkrock chemical compositions, in agreement to harijoko et al. (2016). loc 6 (n=5) loc 7 (n=5) loc 8 (n=5) sio2 56.7 56.9 57.0 al2o3 18.1 18.4 17.8 mgo 4.0 3.9 4.0 cao 5.9 5.5 5.4 tio2 3.1 3.1 3.1 fe2o3 7.9 7.8 7.7 k2o 2.3 2.4 2.6 na2o 1.9 2.0 2.0 total 99.9 99.9 99.7 the glass chemical compositions of the scoria clasts (table 1) were determined by scanning electron microscope (sem) at the lembaga pusat penelitian dan pengembangan teknologi universitas gadjah mada (lppt-ugm), yogyakarta, indonesia, using point analysis with a focused beam current of 3 μm (diameter) and an accelerating voltage of 15 kv. as the ld samples were typically dense and lacked vesicles, our textural analysis of the vesicles included only five scoria clasts from pd (merdada=2, pagerkandang=2, pangonan=1). because the fragmentation process of a phreatomagmatic eruption involves an external agent (i.e., water), a modification of vesicle textures might ha ve occurred. therefore, the observed scoria clasts were selected from a layer which was interpreted to be of magmatic origin (pf6-1 and pf6 for merdada, pf7-3(a) and pf 7-5 for pagerkandang, and pf8-1 for pangonan). vesicles seen at 500x image magnification were manually traced using a corel draw x7. similar to the petrographic analysis, each resultant image was processed using imagej to obtain the total number and area of the measured vesicles. finally, the bulk-vesicularity (ϕ𝑉 ) and vesicle number density (vnd) were obtained using the following equations (suhendro et al. 2021, 2022): ϕ𝑉 = ∑ 𝐴𝑉 𝑁 𝑛=1 (𝐴𝑆−∑ 𝐴𝑃𝐶 𝑁 𝑛=1 ) (2) vnd (𝑁𝑉 ) = ( 𝑁𝑎 𝑑 ) (1−ϕ𝑉 ) (3) where ∑ 𝐴𝑉 𝑁 𝑛=1 is the total vesicle area, 𝐴𝑆 is sample area in the thin section, and ∑ 𝐴𝑃𝐶 𝑁 𝑛=1 is the total phenocryst area, 𝑁𝑎 is the number of vesicles per unit area, and d is the average vesicle diameter. vesicles from 500x image magnification were manually traced using a corel draw x7. 5. results and discussions 5.1 magmatic source based on the petrography, it was found that the pd and ld displayed significant differences in mineralogical content and phenocryst content (fig. 4). in particular, the scoria clasts from the pd are typically phenocryst poor (3–4 % ϕ𝑃𝐶 ) and comprise only plagioclase, pyroxene, and oxides as the main phenocryst phase, while lava samples are characteristically phenocryst rich (21–47 % ϕ𝑃𝐶 ) and includes hydrous minerals (biotite and amphibole) other than plagioclase, pyroxene, and oxides. this distinctive petrographic characteristic suggests that both domains were sourced from different magmatic bodies, where the presence of hydrous minerals represents a lower temperature and more silicic magma composition, and vice versa (mcbirney 2007; ridolfi and renzulli 2012). this idea was confirmed by the fact that the pd and ld have different bulk-rock chemical compositions (andesite for pd, and andesite-dacite for ld; harijoko et al., 2016). fig. 4. diagram showing the fractions of each phenocryst phase in lava domain (ld) and pyroclastic domain (pd). blue: plagioclase, orange: pyroxene, light green: biotite, dark green: amphibole, black: oxides. note the significant differences in phenocryst content and mineralogical variations between ld and pd. 5.2 eruption mechanisms: magmatic or hydromagmatic? based on the median size (mdϕ) and relative skewness, we found that deposits from pd volcanoes can be grouped into two regimes: (1) coarse-dominated (>2 mm mdϕ, positive skewness) and (2) fine-dominated (<2 mm mdϕ, negative skewness) (figs. 3 and 5). interestingly, the coarse-dominated regime tended to be scoria-rich, whereas the fine-dominated regime was typically lithic-rich. a scoria (and also pumice) is believed to represent the juvenile phase (primary product of magma fragmentation); hence, its domination may imply that the eruption was magmatic with no and/or minor contribution from external factor such as water. on the other hand, a lithic represents a non-juvenile phase from preexisting rocks; hence, its domination may suggest that the eruption lacked the contribution from primary magma fragmentation. moreover, it is known that the grain size distribution can be used to depict eruption processes (fragmentation, transport, and deposition) (jutzeler, proussevitch, and allen 2012; walker 1971; wohletz, sheridan, and brown 1989), where finer grain sizes result in a higher fragmentation index and vice versa (wohletz and heiken, 1992). therefore, we suggest that a coarse(positive skewness) and scoria-dominated regime was likely produced from a magmatic eruption (figs. 5 and 6), while a fine (negative skewness) and lithic-dominated regime was likely produced from phreatomagmatic and/or phreatic eruptions (depending on the presence or absence of juvenile clasts) (figs. 5 and 6). the magmatic deposits from pangonan (pf8-1) have comparatively higher lithic contents compared to those of merdada and pagerkandang which might result from an suhendro, i. et al./ jgeet vol 7 no 4/2022 155 external factor, that is, alteration. this process may change all of the original rock-forming minerals into clay and ultimately reduce the rock strength (heap et al., 2021, lowell and guilbert, 1970). consequently, the ascending magmas can easily erode the conduit wall (even though the fragmentation index is low, such as in magmatic eruptions), producing lithicrich magmatic-fall deposits. the fact that the lithics in pangonan predominantly consist of altered types does not rule out this possibility (figs. 3 and 5). when the conduit became larger and surpassed the threshold value of a buoyant plume, the eruption starts to generate pdcs (suhendro et al., 2021, wilson et al., 1980) (fig. 6). as the formation of lava flows and/or domes do not show any association with pyroclastic deposits, it can be inferred that the lava domain (ld) originates from a ‘dry’ (magmatic) eruption. fig. 5. histograms and pie-charts showing the grain size distributions (gsds) and componentry data from merdada, pagerkandang, and pangonan. star symbol represents median grain size. note that coarsedominated layers are scoria-rich and positively skewed, whereas finedominated layers are lithic-rich and negatively skewed. m, pm, and p abbreviations are magmatic, phreatomagmatic, and phreatic eruptions, respectively. fig. 6. cartoon showing the formation process of ld (upper) and pd (lower). in case of ld, the final morphology of lava (flows or domes) seems to depend on the phenocryst abundance. in case of pd, the eruption mechanisms (magmatic, phreatomagmatic, or phreatic) have strong dependence on the contact ratio between magma and water. 5.3 the role of bubbles (observed as vesicles in the pyroclasts) in an ascending magma vesicles are fossil gases in magmas that act as the main driving force for volcanic eruptions (toramaru 2006). therefore, quantifying the number density may provide some clues on the degree of explosivity and magma decompression rate (a higher vnd represents a more energetic and faster magma ascent rate and vice versa; shea, 2017, toramaru, 2006). however, it is important to note that vesicles in an effusive product (e.g., lava) are not representative of vnd measurements as they have experienced intense modification (bubble expansion and coalescence) due to the very slow magma ascent rate. based on the aforementioned idea, we can assume that the pd results from an explosive eruption due to the presence of moderately vesicular (27–41 % ϕ𝑉 ) and high vnds (1.1×105mm-3 4.9×105mm-3) scoria clasts (fig. 7). such vnd values were found to be higher than those of pyroclastic coneproducing eruptions (i.e., ichulbong, south korea and black point, usa) (fig. 7) due to the difference in silica compositions (pangonan, merdada, and pagerkandang are andesitic, whereas ichulbong and black point are basaltic; murtagh et al., 2011, 156 suhendro, i. et al./ jgeet vol 7 no 4/2022 murtagh and white, 2013) and the magma decompression rates (a higher magma decompression rate results in a higher vnd; toramaru, 2006). such an explosive manner becomes the main reason why the crater sizes of the pd volcanoes are typically large (4.3×105-8.9×105 m2) (fig. 1b). on the other hand, the ld must originate in an effusive manner because the main eruptive products are lava domes and/or flows. this is the main reason why the ld has characteristically small crater sizes (0.1×1051.5×105 m2) (fig. 1b). moreover, our petrographic data (fig. 3) also show that lava dome samples typically have higher phenocryst content than the lava flows (avg. ϕ𝑃𝐶 of 40 % and 36 %, respectively). this implies that a more phenocryst-rich magma tends to produce a lava dome because of its higher effective viscosity, whereas less phenocryst magmas imply a lower effective magma viscosity, thus forming lava flow. fig. 7. (a) representative vesicle images of scoria clasts erupted from pyroclastic domain (pd) volcanoes. scale bars correspond to 500, 100, and 50 microns for 30x, 200x, and 500x image magnifications, respectively. (b) comparison between vnd and vesicularity values of pd volcanoes (this study) with ichulbang and black point. 5.4. possible hazards as discussed in the previous sub-sections, the ld and pd form under different eruption manners, that is, effusive and explosive, respectively. this implies that the s-se and n-nw sectors have different volcanic styles. in particular, the ld tends to produce “dry” and weak (qualitatively very low vnd) magmatic eruptions, making lava flows and/or domes the main volcanic hazard that threatens civilization settlements in the sse sector. on the other hand, the formation of the pd includes an intercalation between explosive magmatic, phreatomagmatic, and phreatic eruptions. most of hydromagmatic eruptions occur in the w-nw sector because of the existence of a geothermal system beneath pagerkandang, merdada, and pangonan (harijoko et al. 2016). consequently, such dynamic conditions make the prediction of future eruption styles becomes difficult. we pointed out 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punggur sea of the riau islands muhammad zainuddin lubis 1, *, wenang anurogo 1 , hanah khoirunnisa 1 sudra irawan 1 , oktavianto gustin 1 , arif roziqin 1 1 department of informatics engineering, geomatics engineering batam polytechnic, batam kepulauan riau, 29461 indonesia abstract punggur sea has many habitats, object, and structured of seabed with hight tide and wave. side scan sonar is an underwater acoustic instrument for identification of seabed. this research aims to classify types of seabed and measure seabed identification into the sea water with grain size (db), location, altitude (m) and target using side scan sonar instrument. this research also uses one types of side scan sonar in one places with 3 line of collecting data to get more variant seabed. side scan sonar data of 20 km of side-scan sonar profiling (cm2, c-max ltd, uk) with altitude max 20 m and a working acoustic frequency of 325 khz with the zone is taken in the punggur sea (104°08.7102 e, 1°03.2448 n until 1°03.3977n 104°08.8133 e). the data side scan sonar processed using max view software to display the image of the seabed. results of seabed imagery in the punggur sea on track 1 have objects found on the ship coordinates 03.3101n 1 ° and 104 ° 08.7362 e with the highest gain value is 6 db, altitude 18 m on ping 75. linear regression has y = 0.7016x+12.952 with r 2 = 0.4125 (41%). track 2 has target 1 is the sunken object on the seabed, while objects in the form of sand can be seen clearly. objects found on the sunken object coordinates 1°02.8143 n ° and 104°08.5228 e with highest gain value is 9 db with altitude 17.7 m and data ping 69. linear regression has y = 0.2093+12.577 with r 2 = 0.2093 (20%). track 3 has target 1 is the ship object on the seabed, while objects in the form of sand can be seen clearly. objects found on the sunken object coordinates 1°02.5817 n and 104°08.7337 e with the highest gain value is 8 db with altitude 16.5 m and data ping 3984. linear regression has y = 0.5106x +12.84 with r 2 = 0.5106 (51%). track 1 has many targets identification results compared track 2 and 3. keywords: punggur sea, seabed identification , side scan sonar (sss), gain (db), altitude (m). 1. introduction punggur sea is the part of the riau islands in indonesia. generally punggur sea still rarely done research on the identification of seabed using the acoustic wave technology. acoustic wave technology is a hydroacoustic method are increasingly being used in all kinds of aquatic ecosystems in order to acquire detailed information about stock estimation about fish abundance and seabed identification (lubis and wenang 2016). the acoustic instrument has sound waves through the medium of water that will be backscatter by objects in the water column and seabed. that backscatter on waveform characteristics can be analyzed to get information base object seabed. side scan sonar is acoustic instruments can be transmitted pulse by the beam or sound waves to the left and right side with a specific frequency (medwin and clay 1998). the aim of this hydroacoustic survey was to estimate the total biomass of fish in sikka regency waters using long transects sampling patterns and calculation methods of biomass in hydroacoustic method (lubis and pujiyati, 2016, lubis et al., 2016). research on the seabed using side scan sonar has been done, such as detection and interpretation on the seabed using side scan sonar instruments (sari and manik 2009). side scan data are traditionally displayed as gray images and interpreted with some knowledge of the side-scan system and the sea-floor geology, together with some independent observations (so(somers et al., 1978). the sonar data are preprocessed to correct for the influences of the sonar beam pattern and timevarying gain (tvg) (capus et al., 2004 and diaz et al., 2002) this paper seeks to consider about identification of the target position on the outcome of the identification image of the seabed, the value of gain (db), altitude (m), beam sweep area of side * corresponding author : zainuddinlubis@polibatam.ac.id tel+6281342578087, office : 778-469856 ext : 2510; fax: +62-778-463620 received: jan 15, 2017. revised : 1 feb 2017, accepted: feb 20 , 2017, published: 1 march 2017 doi: 10.24273/jgeet.2017.2.1.11 mailto:zainuddinlubis@polibatam.ac.id 2 lubis, m. z. et al./ jgeet vol 02 no 01/2017 scan sonar, and object identification in punggur sea of the riau islands in indonesia. 2. materials and method the research was conducted in december 2016 in the punggur sea of the riau islands in indonesia. (104°08.7102 e, 1°03.2448 n until 1°03.3977n 104°08.8133 e) (fig 2). tracking of cruise side scan sonar and research location have 3 tracking line (fig 2). acoustic data acquisition was done using instruments cm2 side scan sonar system was used to survey the modiolus bed off the point of ayre. the side-scan-sonar tow fish was set at high frequency (325 khz) and with a total swath width of 200 m (fig 1). the tow fish was towed at a speed of approximately 4 knots at an altitude of 12-18 m above the seabed. the broad-scale surface sediments characterization was performed using a high-resolution c-max cm2 side scan sonar, providing digital side-scan sonar imagery. the system allowed the user to operate it under dual acoustic signal frequencies, at 325 khz. the system gain g includes the effects of timevaried gain and correlation as well as the transducer pressure-voltage gains and amplifier gains. the 12bit value is then compressed into a coded 8-bit value before being stored. our estimate of g is probably accurate to within 6 db; this is one of the largest sources of error in our calculations.this time-varied gain (tvg) is used to compensate for the decreasing intensity of the backscattered signal and keeps the signal output within the dynamic range of the recorder. the tvg is not continuous but is actually produced in a series of 1.5-db steps (mitchell & somers 1989). the time-varied gain function (ignoring the step-like nature of the tvg) is approximated by: tvg = (db 30 log 10 (range) 8.2 x 10 -4 range)90/db (db) (1) where db is a constant and range is in meters. the voltage ratio is tvg (range) = 10 tvg/20 (2) to attenuate sidelobes in the correlator output, the rectangular fm pulse is correlated with an amplitude shaded (hamming in mitchell & somers 1989) reference, rather than with a matched rectangular pulse. the equation of this hamming function in (mitchell & somers 1989) is given by: t/2 < t < t/2 (3) where t is the pulse length (usually 2 s), showed in fig 3. . fig. 1. altitude measuring and main beam of side scan sonar c-max cm2 sonar system and side sonar scheme in acquisitions data. lubis, m. z. et al./ jgeet vol 02 no 01/2017 3 fig 2. tracking of cruise side scan sonar and research location in punggur sea punggur sea of the riau islands in indonesia. fig 3. signal attenuation due to time-vaned gain, correlation with a shaded pulse and eclipsing. 3. result and discussion 3.1 image classification sediment image classification of sediment carried by the qualitative analysis, which is to distinguish the type of sediment is based on the results of the scan sonar imagery. the results of c-max cm2 side scan sonar (sss) is an image with a high frequency of 325 khz. max-view capable of displaying in fig 4, total ping 2336 pings, measure selected record is 362 m, and the distance between pins is 13900 km (fig 4). this happens because of side -max cm2 side scan sonar (sss) has a short duration pulse with simultaneous observations (maclennan and simmonds 2005). target, time, location, ping, gain, and altitude value on track 1, punggur sea showed in table 1. 4 lubis, m. z. et al./ jgeet vol 02 no 01/2017 target 1 target 2 target 3 target 4 target 5 target 6 target 7 fig 2. image classification and position target 17 on sediment track 1, punggur sea table 1. target, time, location, ping, gain, and altitude value on track 1, punggur sea target time latitude longitude ping gain (db) altitude (m) 1 13:43:12 am 1°03.2448 n 104°08.7102 e 417 3 13.8 2 13:43:20 am 1°03.2109 n 104°08.8057 e 458 1 14.5 3 13:44:05 am 1°03.2992 n 104°08.7471 e 678 4 18 4 13:42:56 am 1°03.2207 n 104°08.7180 e 339 5 14.5 5 13:44:57 am 1°03.3977 n 104°08.8133 e 931 2 13.8 6 13:44:11 am 1°03.3101 n 104°08.7362 e 705 6 18.1 7 13:42:53 am 1°03.1832 n 104°08.7875 e 331 3 14.8 lubis, m. z. et al./ jgeet vol 02 no 01/2017 5 fig 3. linear regression of gain (db) with altitude (m) on track 1, punggur sea fig 2 shows the image of seabed sediments that have a target number of 7. target 6 is the object of the sunken ship on the seabed, while objects in the form of sand can be seen clearly. objects found on the ship coordinates 03.3101n 1 ° and 104 ° 08.7362 e with the highest gain value is 6 db with altitude 18 meter. the port (right side) seen the entrenchment of a lighter color. their excavation led to differences in texture, roughness, and slope of the seabed sediments. besides excavation occurred on the seabed allegedly causing sediment coarser grain size larger particles beneath it lifted up. according to urick (1983) grain size, scale sediment surface roughness and slope significant variations can be the important role in the acoustic response. linear regression has y = 0.7016x+12.952 with r 2 = 0.4125, by looking at the equation it is clear that the correlation between the gain and the altitude at the track 1 by 41% with alpha is 5 (fig 3). colliers and brown (2005), said that the phenomenon of backscattering seabed has relationships with the roughness. the more coarse sediment would reflect highest backscatter. image classification and position target 16 on sediment track 2 showed in fig 4. target 1 target 2 target 3 target 4 target 5 target 6 fig 4. image classification and position target 16 on sediment track 2, punggur sea y = 0,7016x + 12,952 r² = 0,4125 0 5 10 15 20 0 1 2 3 4 5 6 7 a lt it u d e ( m ) gain (db) series1 linear (series1) 6 lubis, m. z. et al./ jgeet vol 02 no 01/2017 table 2. target, time, location, ping, gain, and altitude value on track 2, punggur sea target time latitude longitude ping gain (db) altitude (m) 1 14:28:13 am 1°02.8143 n 104°08.5228 e 69 9 17.7 2 14:28:28 am 1°02.7913 n 104°08.5229 e 283 8 13.3 3 14:28:25 am 1°02.7981 n 104°08.5178 e 178 4 14.5 4 14:28:20 am 1°02.8050 n 104°08.5184 e 232 6 15.3 5 14:28:51 am 1°02.7556 n 104°08.5554 e 17 7 14.8 6 14:28:30 am 1°02.7880 n 104°08.5253 e 583 8 16.4 fig 5. linear regression of gain (db) with altitude (m) on track 2, punggur sea fig 4 shows the image of seabed sediments that have a target number of 6. target 1 is the sunken object on the seabed, while objects in the form of sand can be seen clearly. objects found on the sunken object coordinates 1°02.8143 n ° and 104°08.5228 e with highest gain value is 9 db with altitude 17.7 m and data ping 69 . the port (right side) seen the entrenchment of a dark color (shadow zone). according to (kenny et al., 2003) sweep of side scan sonar can produce mosaics, geological and sedimentology features that are easily recognized and interpreted qualitatively so as to provide information about the dynamics of the seabed. based on data from the movement of side scan sonar found on the sensor pitch movements occur up to 15 degrees from a standstill 0 degrees roll movements occur up to 10 degrees from its current position silent 0 degrees. unlike the sediment mud, sand sediment has particularly rough look more like in fig. 4. linear regression has y = 0.2093+12.577 with r 2 = 0.2093, by looking at the equation it is clear that the correlation between the gain and the altitude at the track 2 by 20% with alpha is 5 (fig 5). differences in sediment forming material thought to affect the image side scan sonar that biogenic sand looks more rugged. effect of seabed slope in the punggur sea will also affect the condition of sediment due to gravitational forces. however, based on the image side scan sonar can be seen clear differences in texture and roughness on the sand sediments, biogenic sand and clay. image classification and position target 15 on sediment track 2 showed in fig 6. y = 0,3937x + 12,577 r² = 0,2093 10 11 12 13 14 15 16 17 18 19 3,8 4,8 5,8 6,8 7,8 8,8 9,8 a lt it u d e (m ) gain (db) series1 linear (series1) lubis, m. z. et al./ jgeet vol 02 no 01/2017 7 target 1 target 2 target 3 target 4 target 5 fig 6. image classification and position target 15 on sediment track 3, punggur sea table 3. target, time, location, ping, gain, and altitude value on track 3, punggur sea target time latitude longitude ping gain (db) altitude (m) 1 15:11:10 am 1°02.5817 n 104°08.7337 e 3984 8 16.5 2 15:11:14 am 1°02.5787 n 104°08.7326 e 4029 5 15.2 3 15:10:55 am 1°02.6248 n 104°08.7302 e 3558 6 14.4 4 15:10:39 am 1°02.5853 n 104°08.7589 e 3770 4 14.5 5 15:11:19 am 1°02.5744 n 104°08.7251 e 4107 7 15 fig 7. linear regression of gain (db) with altitude (m) on track 3, punggur sea y = 0,38x + 12,84 r² = 0,5106 14 14,5 15 15,5 16 16,5 17 3,8 4,8 5,8 6,8 7,8 8,8 a lt it u d e ( m ) gain (db) series1 linear (series1) 8 lubis, m. z. et al./ jgeet vol 02 no 01/2017 fig 4 shows the image of seabed sediments that have a target number of 6. target 1 is the ship object on the seabed, while objects in the form of sand can be seen clearly. objects found on the sunken object coordinates 1°02.5817 n and 104°08.7337 e with the highest gain value is 8 db with altitude 16.5 m and data ping 3984. linear regression has y = 0.5106x +12.84 with r 2 = 0.5106, by looking at the equation it is clear that the correlation between the gain and the altitude at the track 3 by 51% with alpha is 5 (fig 7). the blind zone is shadow zone in tracking figure of side scan sonar instrument. the influence factor of width blind zone will be has image seabed identification not be specific. the influence width of the blind zone so small in the area is result sweep of side scan sonar instrument (figure 2, 4, and 6). 4. conclusion research in punggur sea using c-max cm2 side scan sonar system with a frequency of 325 khz, obtained on the seabed is the sediment of sand than clay and find the shipwreck that sunk in track 1 and track 3. highest gain value is on line 2 in the coordinates 1 02.8143 ° n 08.5228 ° and 104 ° e, and is the lowest that is on track 1 at coordinates 03.3101n 1 ° and 104 ° 08.7362 e. relations between value gain and heights that have the highest correlation on track 3 (51%). track 1 has many targets identification results compared track 2 and 3. the influence factor of width blind zone is beam pattern of side scan sonar instrument with altitude from position of towfish. acknowledgements this work was funded was financed by marine instrumentation and application club (miac) member: fikriansyah, dirgan t, adit, fajar, ganda, sandi, bayu, andrew, diaz, perdi, batam polytechnic, indonesia and pt hidronav tehnikatama, indonesia. references capus, c., ruiz, i. t., & petillot, y. 2004. compensation for changing beam pattern and residual tvg effects with sonar altitude variation for sidescan mosaicing and classification. in 7th. eur. conf. underwater acoustics, delft, the netherlands. collier js dan cj brown. 2005. correlation of sidescan backscatter with grain size distribution of surficial seabed sediments. journal of marine geology, geochemistry and geo physhics (214). 431-449. diaz, d., cuevas, k., buchanan, m., gordon, s., & perret, w. s. 2002. side scan sonar in oyster management. in oceans'02 mts/ieee (vol. 1, pp. 141-145). ieee. kenny aj, cato i, desprez m, fader g, schüttenhelm rte dan side j. 2003. an overview of seabed mapping technologies in the context of marine habitat classification. ices journal of marine science (60): 411-418. lubis, m. z., & anurogo, w. 2016. fish stock estimation in sikka regency waters, indonesia using single beam echosounder (cruzpro fish finder pcff-80) with hydroacoustic survey method. aceh journal of animal science, 1(2). lubis, m. z., s. pujiyati. 2016. detection backscatter value of mangrove crab (scylla sp.) using cruzpro fishfinder pcff-80 hydroacoustic instrument. journal of biosensor and bioelectronic, 7(2): 1000205. lubis, m. z., wulandari, p. d., mujahid, m., hargreaves, j., & pant, v. 2016. echo processing and identifying surface and bottom layer with simrad ek/ey 500. journal of biosensors and bioelectronics, 7(3), 1000212. maclennan dn dan simmonds ej. 2005. 2th fisheries acoustic: theory andpractice. oxford (uk): blackwell science. medwin, h., & clay, c. s. 1998. fundamentals of acoustical oceanography academic. new york, 24. medwin, h., & clay, c. s. 1998. fundamentals of acoustical oceanography academic. new york, 24. mitchell, n. c., & somers, m. l. 1989. quantitative backscatter measurements with a long-range sidescan sonar. ieee journal of oceanic engineering, 14(4), 368-374. sari sp dan hm manik. 2009. deteksi dan interpretasi target di dasar laut menggunakan instrumen side scan sonar. seminar nasional teori dan aplikasi teknologi kelautan. 25-30. somers, m. l., carson, r. m., revie, j. a., edge, r. h., barrow, b. j., & andrews, a. g. 1978. gloria ii an improved long range sidescan sonar. in oceanology international (vol. 78, pp. 16-24). urick rj. 1983. principles of underwater sound. 3rd ed. new york (us): mc-graw-hill. 1. introduction 2. materials and method 3. result and discussion 3.1 image classification sediment 4. conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 yuniarti, y. et al./ jgeet vol 03 no 01/2018 63 quaternary sediment characteristic of floodplain area: study case at kampar river, rumbio area and surroundings, riau province yuniarti yuskar 1, *, dewandra bagus eka putra 1 , m. revanda 1 1 department of geological engineering, universitas islam riau, jl. kaharudding nasution no 113 pekanbaru, 28284, indonesia. * corresponding author : yuniarti_yuskar@eng.uir.ac.id tel.:+62-821-6935-4941 received: oct 1, 2016. revised : 15 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 (filled by editor) doi: 10.24273/jgeet.2018.3.1.1226 abstract the study area is located in some floodplains of meandering river environment along the kampar river, rumbio. typical morphology of meandering river that found in this area can be classified as stream channel, floodplain, abandoned channel, and sand bars deposit. meandering river system carries sediment supply by suspended and bed load (mixed load) in conjunction with low energy into a particular characteristic on sediment deposition. this study aims to determine the characteristics of the sediments, changes in vertical and lateral spread of sediment deposition on the floodplain environment. this study conducted by field survey using a hand auger of 1.5m 4m depth and trenching which is a layer that has been exposed of 1-2 meters depth. further analysis had been carried out using granulometri method and core data analysis to determine the characteristics and depositional facies. sediment deposit that formed along the kampar river is the result of the main channel migration of kampar river. the characteristic of quaternary sediment facies is coarse to gravelly sand on the bottom followed by fine to very fine sand with pattern fining upwards and silt to clay and abundant terrestrial organic matter at the uppermost layer. depositional facies are determined based on the characteristics of sediment facies which can be grouped into a stream channel, oblique accretion deposits, sand bars and overbank deposits. keywords: quaternary sediment, floodplain, facies, meander river, kampar 1. introduction the problem of quantitatively characterizing the plan geometry of meandering stream channels has intrigued engineers and earth scientists for more than 80 years ( abrahams, 1986). a meander was formed by the continuous erosion process at the river bank as a result of river bend. meandering river was transported and deposited by suspended and bedload (mixed load) process which characterized as low energy. the bedload is carried by the flow in the channel, with the coarsest material carried in the deepest parts of the channel. finer bedload is also carried in shallower parts of the flow and is deposited along the inner bend of a meander loop where friction reduces the flow velocity (nichols, 2009). types of sediment that formed by meandering pattern are channel deposit, point bar, natural leeve, floodplain, oxbow lake, and crevasse splay (yuskar and choanji, 2017). the study area is located in some floodplains of meandering river environment along the kampar river, rumbio. typical morphology of meandering river that found in this area can be classified as stream channel, floodplain, abandoned channel, and sand bars deposit. floodplains have received considerable attention in recentvyears because of the valuable social and ecological functions of these systems, such as flood control, sediment and nutrient retention, recreational opportunities, timber production, and wildlife habitat (pierce and king, 2008). erosion from the banks of meandering rivers causes a local influx of sediment to the river channel (lauer and parker, 2008). understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology (knox, 2006). floodplains are dynamic feature that co-evolve with channel so at the present time there is no universal theory that available to predict floodplain width in natural rivers (as a function of drainage area, bank-full discharge, or sediment flux, etc) because floodplain morphology dynamically integrates across these and the other factors, over some unconfined time interval in the environment history of the watershed (belmont, 2011). mailto:yuniarti_yuskar@eng.uir.ac.id 64 yuniarti, y. et al./ jgeet vol 03 no 01/2018 floodplain is a strip of land that borders a stream channel and that is normally inundated during seasonal floods. sediment is transported over the flooding as bed load and suspended load during floods. the sediment comes from the main channel, the valley sides and the floodplain itself (posamentier, roger g.; walker, 2006). sediment of point bar deposited medium sand with good sorting and upwards fining couplets during flood events. some flood channels become enlarged during floods, and may become the dominant channel (wood et al., 2008). the relative contribution of a variety of accretion deposits to the formation of meandering river floodplains have been the subject of prolonged discussion in the geomorphological literature. the geometry of river channels and their flow style are controlled by a complex interplay of factors, including discharge, slope, climate and vegetation, amongst others (stanistreet et al., 1993). this study aims to determine the characteristics of the sediments deposit in the floodplain area that is resulted from abandoned channel, oblique and lateral accretion deposits and sediment that was carried during flooding in its surrounding. vertical changing and lateral deployment of sediment deposit on the floodplain area can also be seen by looking at the physic and biology characteristics of these sediments. 2. geological setting one of the meandering river system in the riau province, indonesia is the kampar river. kampar river on the sumatra island in indonesia originates in the mountainous bukit barisan of west sumatra, and empties into the malacca strait on the island's eastern coast. the river is the confluence of two big tributaries, kampar kanan river and kampar kiri river. the tributaries meet in the langgam subdistrict, pelalawan regency, before flowing into the malacca strait as the kampar river. koto panjang, an artificial lake upstream of the river, is used to power a hydroelectric generating plant. the river has a lenght of 413 km and an average depth of 7.7 km and average width of 143 m (yuskar and choanji, 2017). fluvial meander system developed typical oxbow lake morphology with tropical rain forest, sand bar and river with fishery product. it has been used as a local attraction (yuskar, 2016); (choanji et al., 2018). rumbio is a district in kampar regency with elevation ranging between 25 to 50m above sea level. the landscape that developed in research area were channel, floodplain, natural leeve, point bars, abandoned channel, and oxbow lake. this area is gently sloping and the occurrence of heavy rainfall may cause flooding. sediment distribution in research area shows by quaternary age landforms. along the kampar kanan river was deposited young alluvium (qh) during holocene aged that consist of gravels, sands and clays (clarke, m.c.g; kartawa, w.; djunuddin, a.;suganda, e.; bagdja, 1982). fig. 1 location of study areas = study area yuniarti, y. et al./ jgeet vol 03 no 01/2018 65 3. methodology field survey had been conducted to collect the data by using hand auger drilling in eight different points and trenching method in two localities (fig.1). laboratory analysis such as grain size analysis or sieve analysis,core analysis, and facies analysis had been carried out to obtain the result. the depths of drilling core ranging from 1.5 to 4m. trenching was done around the drilling points to observed the sedimentary layers that had been exposed in the surface with 1-3m thickness. grain size determination was done using sieve analysis method, mesh size 2.38mm, 1.19mm, 0.6mm, 0.297mm, 0.149mm and 0.074mm. the sample also being described to identify the sediment characteristic up to depositional facies. 4. result and discussion morphological condition of the study area was flat ramp that lying on the floodplain and abandoned channel environment of kampar river. the difference of physical and biological characteristic are the main parameters in determination of sedimentary facies. sieve analysis result of core and trenching data shows coarse to gravelly sand at the bottom layer followed by fine to very fine sand with pattern fining upwards and silt to clay and abundant terrestrial organic matter at the uppermost layer. there are three observed layers in to-05 with 3.5m thickness. bottom layer (0-50cm) have reddish brown color and coarse sand vey coarse sand in grain. second layer (51-200cm) have blackish brown color, coarse sand very coarse sand in grain and overgrown by plant roots. the uppermost layer (201-350cm) is medium sand fine sand. the sedimentary layers at this locality shown fining upward changing in grain size (fig.2). fig 2. sieve analysis shown the grain size percentage of each layer in to-05. fig 3. sieve analysis shown the grain size percentage of each layer in to-10 . two sedimentary layers had been observed in to-10. bottom layer (30cm thick) has brownish grey weathered color and grey fresh color. grain size distribute from silt to very fine sand and the plant roots was found in this layer. the upper layer (203cm thick) has pebble to boulder floating grain size, brownish grey weathered color, grey fresh color and more plant roots compare to the lower layer. there are three to seven sedimentary layers can be observed in to-08 with thickness 10m (fig. 4). bottom layer (100cm thick) have reddish grey weathered color and grey fresh colour, very fine sand to silt and ripple mark because of water flowing. then, at top of the first layer were deposited clay sediment with reddish grey colour and paralel lamination sedimentary structure. after that, pebble coarse sand and fining up layer became fine sand. then sicnificantly, thick layers of pebble coarse sand were deposited (100cm to 250cm thick). furthermore, the grain size sediment changing become fine to very fine sand with 250cm thick and at the other part of the section, this layer have 550cm thick. the colour of this layer is greyish white at the bottom layer and become reddish grey at the top layer is caused intensively weather. the toppest layer is soil with plant root. 4.1. sediment facies based on the sieve analysis result of core and trenching data (fig.4) and from the core description (fig.5), there are several sediment facies in this study area: 1. pebble coarse sand coarse sand to pebble have blackish brown color and intercalation with thin reddish sand, resulting from the oxidation process. 0 20 40 60 80 100 0,010,1110 v o lu m e ( % ) grain diameter (mm) to-05 layer 1 layer 2 layer 3 0 20 40 60 80 100 0,010,1110 v o lu m e ( % ) grain diameter (mm) to-10 layer 1 layer 2 66 yuniarti, y. et al./ jgeet vol 03 no 01/2018 fig. 4 profile analysis of trenching data (to-08) fig. 5 sieve analysis of drill core (rp-01, rp-03 and rp08). this facies was found in 150-145cm depth at core rp-1, 250-220cm depth at core rp-2, 320194cm depth at core rp-5 and 350-261 depth at core rp-8. 2. pebble coarse sand coarse sand to pebble have blackish brown color and intercalation with thin reddish sand, resulting from the oxidation process. this facies was found in 150-145cm depth at core rp-1, 250-220cm depth at core rp-2, 320-194cm depth at core rp-5 and 350-261 depth at core rp-8. 3. silt to clay intercalation with thin red sand silt to clay sediment, greyish brown color was found in 145-120cm depth at core rp-1. this layer intercalation with thin orange sand that contain fe and had been oxidized. 4. clay sediment this lithofacies was found in 242-162cm depth at core rp-7. sediment deposit is black clay that 0 20 40 60 80 100 0,011 v o lu m e ( % ) grain diameter (mm) rp 08 layer 1 layer 2 layer 3 layer 4 layer 5 layer 6 0 20 40 60 80 100 0,011 v o lu m e ( % ) grain diameter (mm) rp 01 layer 1 layer 2 layer 3 layer 4 layer 5 0 20 40 60 80 100 0,011 v o lu m e ( % ) grain diameter (mm) rp 03 layer 1 layer 2 layer 3 layer 4 layer 5 layer 6 yuniarti, y. et al./ jgeet vol 03 no 01/2018 67 rich in organic material or carbon and wood pieces. 5. very fine sand with minor terrestrial organic matters brown very fine sand in 134-120cm depth at rp-1, in 139-121cm depth at rp-5. intercalation of reddish orange sand and fine roots also found in this layer. the changing of color to grey is the characteristic of very fine sand at core rp-6 in 264-179cm depth. 6. fine sand with terrestrial organic matters and oxidation fine grain sand, brownish color, presence of small plant roots and intercalation of red sand caused by the oxidation process. found in 15195cm depth at core rp-3 and 92-42cm depth at core rp-5 but brownish grey color and without intercalation of reddish sand. 7. silt with terrestrial organic matters silt with reddish orange color and overgrown by fine roots, found in 100-67cm at core rp-3 and 22-0cm at core rp-5, grey color. at core rp8 in 124-52cm depth, blackish brown color, overgrown by fine roots and found the presence of floating pebble (0.2-1cm in size). 8. clay with terrestrial organic matters blackish brown clay with larger part of plant. found in 51-25cm depth at core rp-3. 4.2. depositional fasies based on the sedimentary facies analysis of core and trenching data, the depositional facies can be categorize into channel deposit, oblique accretion deposit and overbank deposit (fig. 6). 1. channel deposit found at the bottom layer, characterized by fining up succession and constantly begin with coarse sand to pebble. several sediment facies had been found such as pebble coarse sand, silt to clay with oxidation sand and clay sediment. 2. oblique accretion deposit the drilling point was located in the river loop where the erosion occurred and deposition of lateral accretion deposit took place. this deposit characterized by fining up succession, fine sand very fine sand in grain size and the sediment facies was very fine sand to fine sand with minor terrestrial organic matters. 3. sand bar deposit this deposit characterized by coarsening up succesion, fine to medium sand in grain size and the sediment facies was fine sand with terrestrial organic matters and oxidation. 4. overbank deposit sediment that carried by the flood and frequently outside of the channel. deposited at the upper layer, silt to clay in grain size and overgrown by plant roots. several sediment facies were found such as fine sand with terrestrial organic matters and oxidiation, silt with terrestrial organic matters, and clay with terrestrial organic matters. fig. 6 depositional facies analysis of core data (rp-01, rp03 and rp-08). 68 yuniarti, y. et al./ jgeet vol 03 no 01/2018 5. conclusion the research area was a floodplain environment that formed as a result of multistory channel caused the author would like to say thanks to lembaga penelitian dan pengabdian kepada masyarakat (lppm) universitas islam riau (uir) for funding and support this research. we also say thanks to all sedimentology and hidrology laboratorium team member (batara, dilla permata sari, peter syahputra, desi wijayanti, miftahul jannah, bayu defitra, tristan aulia, genta rier, muchtar zafir, sandi masdrianto, susilo and m. iqbal) who help us in this research. references belmont, p., 2011. floodplain width adjustments in response to rapid base level fall and knickpoint migration. geomorphology 128, 92 101. doi:10.1016/j.geomorph.2010.12.026 choanji, t., rita, n., yuskar, y., pradana, a., 2018. connectivity relationship of fluid flow on deformation band: analog study at petani formation, riau, indonesia. bull. sci. contrib. geol. 15, 193 198. clarke, m.c.g; kartawa, w.; djunuddin, a.; suganda, e.; bagdja, m. (1982). geological map of the pakanbaru quadrangle, sumatra. pppg. knox, j.c., 2006. floodplain sedimentation in the upper mississippi valley: natural versus human accelerated. geomorphology 79, 286 310. doi:10.1016/j.geomorph.2006.06.031 lauer, j.w., parker, g., 2008. net local removal of floodplain sediment by river meander migration. geomorphology 96, 123 149. doi:10.1016/j.geomorph.2007.08.003 ams, 1986. the problem of quantitatively characterizing the plan geometry of meandering stream channels has intrigued engineers and earth scientists for more than 80 yrs (jefferson, 1902). j. hydrol. 83 337--353 elsevier sci. publ. b.v., amsterdam -print. netherlands [1l 83, 337 353. nichols, g., 2009. sedimentology and stratigraphy, journal of chemical information and modeling. doi:10.1017/cbo9781107415324.004 pierce, a.r., king, s.l., 2008. spatial dynamics of overbank sedimentation in floodplain systems. geomorphology 100, 256 268. doi:10.1016/j.geomorph.2007.12.008 posamentier, roger g.; walker, h. w. (2006). facies models revisited. (h. w. posamentier, roger g.; walker, ed.). sepm society for sedimentary geology. stanistreet, i.g., cairncross, b., mccarthy, t.s., 1993. low sinuosity and meandering bedload rivers of the okavango fan: channel confinement by vegetated levées without fine sediment. sediment. geol. 85, 135 156. doi:10.1016/0037-0738(93)90079-k wood, s.h., ziegler, a.d., bundarnsin, t., 2008. floodplain deposits, channel changes and riverbank stratigraphy of the mekong river area at the 14th-century city of chiang saen, northern thailand. geomorphology 101, 510 523. doi:10.1016/j.geomorph.2007.04.030 yuskar, y., 2016. geo-tourism potential of sand bars and oxbow lake at buluh. j. geosci. eng. environ. technol. 1, 59 62. yuskar, y., choanji, t., 2017. uniqueness deposit of sediment on floodplain resulting from lateral accretion on tropical area  : study case at kampar river , indonesia 2, 14 19. jgeet_cover_print_vol 3 no 2 2018.cdr p-issn. 2503-216x e-issn. 2541-5794volume 3 no 2 june 2018. p 69 133 structural analysis of northwest sabah basin by 2d reconstruction of seismic sections mohd akhmal bin muhamad sidek, umar hamzah page 69 structure and tectonic reconstruction of bayah complex area, banten jemi saputra ahnaf, aton patonah, haryadi permana, ismawan page 77 the adsorption and regeneration of natural pumice as low-cost adsorbent for nitrate removal from water denny helard, shinta indah, chintia maya sari, hestia mariesta page 86 macerals analysis seam m2 muaraenim formation, : implication toward coal facies and coal rank in kendi hill, south sumatra yonathan mangatur rajagukguk, stevanus nalendra jati page 94 geology of tanjung medan ,rokan iv koto , rokan hulu district, riau province budi prayitno, susilo page 123 list of content estimation microporosity value of fontanebleau sandstone using digital rock physics approach reza rizki, handoyo page 103 journal of j eetgeoscience engineering environment and technology journal of geoscience, engineering, environment and technology uir press publisher a study on influence of organic ligands on migration of heavy metals through compacted clayey soil sudheer kumar yantrapalli, hari krishna p, srinivas k page 107 characteristics of coal and cleat attributes in ulak lebar and surroundings area, lahat regency, south sumatra mutia armilia rahmawati, siska linda sari, alan triyoga, idar wati page 116 lithofacies and depositional analysis environment of west section kolok nan tuo village, sawahlunto city, west of sumatera catur cahyaningsih, anjas latif ritonga, shaury aldila, zulhikmah page 128 p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. mursyidah, m.sc. 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(indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing our new issue vol 03 no 02 2018. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. husnul kausarian, ph.d editor-in-chief journal of j eet geoscience engineering environment and technology list of content original research article 1. structural analysis of northwest sabah basin by 2d reconstruction of seismic sections ...................................................................................69 2. structure and tectonic reconstruction of bayah complex area, banten ..77 3. the adsorption and regeneration of natural pumice as low-cost adsorbent for nitrate removal from water ..........................................86 4. macerals analysis seam m2 muaraenim formation, : implication toward coal facies and coal rank in kendi hill, south sumatra ............. 94 5. estimation microporosity value of fontanebleau sandstone using digital rock physics approach ....................................................................... 103 6. a study on influence of organic ligands on migration of heavy metals through compacted clayey soil ............................................................ 107 7. characteristics of coal and cleat attributes in ulak lebar and surroundings area, lahat regency, south sumatra .............................. 116 8. geology of tanjung medan ,rokan iv koto , rokan hulu district, riau province ............................................................................................. 123 9. lithofacies and depositional analysis environment of west section kolok nan tuo village, sawahlunto city, west of sumatera ................. 128 author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press p-issn jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet e-issn page 1 page 2 page 3 page 4 5. section headings e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 rizki, r. & handoyo/ jgeet vol 03 no 02/2018 102 estimation microporosity value of fontanebleau sandstone using digital rock physics approach reza rizki 1, *, handoyo 1 1 geophysical engineering, institut teknologi sumatera, south lampung, indonesia. * corresponding author : rezarizki07@yahoo.com tel.: +6285220243152 received: 27 apr, 2018. revised : 24 may, 2018, accepted: 30 may, 2018, published: 1 june 2018 doi 10.24273/jgeet.2018.3.2.1544 abstract the technology of digital rock physics (drp) allowed to predict the physical properties in core data sample, for example to predict value of porosity of data sample. this research applied the digital rock physics technique to predict the microporosity in sandstone sample: fontainebleau sandstone. the data are digital images from fontainebleau sandstone with high resolution scanned from micro tomography ct-scan processing. the result of image processing shown in 2d and 3d image. from the data, the value of microporosity fontainebleau sandstone are between 6% 7%. this result confirmed by the quartz cemented sample of fontainebleau sandstone. the scale and sub-cube give the different value of microporosity which is indicated the scale influence to value of porosity value. so the simplest and best way is to average the all result from sub-cubes. keywords: digital rock physics, image sample, microporosity 1. introduction the application of digital rock physics (drp) has been widely used in some examples of sandstone sample data analysis. applications are performed to predict the physical parameters of rocks such as porosity, permeability, and elastic properties of rocks (handoyo et al. 2014; arns et al. 2004; wiegman et al., 2012). digital image (3d image) rock can be obtained by scanning using the ct-scan and combined with digital simulation software. in addition, the digital image has been applied to visualize of rocks and predict physical parameters. many research have done in fontainebleau sandstone data sample using digital rock physics approach. for example by saxena et al., 2017 and fourier et al., 2014. this paper discusses the digital simulation to visualize complex pore and predict value of microporosity from fontainebleau sandstone (fb). 2. data and method 2.1 data the study of sandstone sample: fontainebleau sandstone (fb) are well analyzed with laboratory measurements from han, 1986; gomez, 2009; and saxena et al., 2017. the value of porosity varying <10% in cemented sample and >20% in clean sample. fontainebleau sandstone is well-sorted consist of almost quartz and small fragment of feldspar. the resume of fontainebleau sandstone illustrated in table 1 and fig. 1. 2.2 method a rock sample (sandstone) generally consists of two main parts: pores and rock solid matrix (fig. 2). quantity of rock pore is expressed by the value of porosity. porosity ( ) is the ratio between the pore volume (vpore) of the total volume of rock (vtotal) which is mathematically written as the bounds as (mavko et al., 2009): (1) the process of drp (digital rock physics) begins with an image of a large fb sample at a relatively high resolution to cover a large field of view (cube). at this stage, rock fabrics larger than the image resolution are resolved while smaller ones are unresolved (sub-cube). information concerning the unresolved rock fabrics is analyzed from additional images acquired at a finer resolution and smaller area of view. the porosity calculated from grayscale image of fb data sample. in general, the stage of the drp analysis shown in fig. 3. total matriks total pore v v v v  1 mailto:rezarizki07@yahoo.com rizki, r. & handoyo/ jgeet vol 03 no 02/2018 103 table 1. data of porosity and mineral description fontainebleau sandstone (gomez, 2009) data sample porosity mineral description clean fontainebleau > 20 % quartz with minimal rock fragments and feldspar presents cemented fontainebleau < 10 % fig. 1. mineral description from thin slice sem from fontainebleau sandstone (saxena et al., 2017) fig. 2. a visualization is shown by the pore spaces between rock-solid matrix (modified from mavko and nur, 2009) fig. 3. drp data processing stages on sandstone sample. stage begins with digital image processing to the calculation of microporosity 3. result and discussion 3.1 result the result of image processing of fontainebleau sandstone shown in fig. 4, which shown the natural scale of 2d image data with dimension 800 × 800 pixels, (b) the region of interest with dimension 400 × 400 pixels, and (c) the 3d model of fb sample with dimension 800 × 800 × 400 pixels. the result of 2d image already visualized the pore and solid matrix (fig. 4a). the geometry of pore generally well visualized as an angular type. to calculate the value of porosity. the image must separate in pore and grain image purely. this way to make sure the image only consists of pore and solid grain matrix of sample data. the image is shown in fig. 5. the white color is representing of solid matrix and the black color is representing of pore image. also visualized the noise in image result. next step, the result of microporosity value shown in table 2. the main cube with dimension 800 × 800 × 400 pixels breaks down to small cube with dimension 400 × 400 × 400 pixels. this way to simplify of the process calculating in digital simulation. the value of microporosity from fb sample approximately between 6% 7%. table 2. the result of microporosity calculation in 8 cubes of fontainebleau sandstone no of cube porosity fb 1 7.2 % fb 2 7.2 % fb 3 6.2 % fb 4 6.6 % fb 5 6.8 % fb 6 7.4 % fb 7 7.0 % fb 8 6.4 % core data of sandstone reservoir digital rock imaging using ct-scan image segmentation rock imaging at finer resolution and smaler field of view drp analysis: 2d and 3d analysis microporosity value rizki, r. & handoyo/ jgeet vol 03 no 02/2018 104 fig. 4. the result of image processing in 2d and 3d natural image of fb sample fig. 5. the result of image processing in 2d and 3d grayscale image of fb sample 3.2 discussion from the data, the value of microporosity fb sandstone are between 6% 7%. this result confirms by the quartz cemented sample of fb sandstone. the resulting deal with the data from gomez, 2009. the scale and sub-cube give the different value of microporosity which is indicated the scale influence to value of porosity value. so the simplest and best way is to average all result from sub-cubes. 4. conclusions digital rock physics application successfully applied in fontainebleau (fb) sandstone sample. from the digital simulation to prediction elastic properties of fontainebleau sandstone sample, it indicates the value of porosity is generally homogenous in 6% 7%. the result indicates the quartz cemented is influence to decreasing the value of porosity. quartz cement present and identified in sem visualization. the 3d scale of subcube also contributes to making the different of porosity value of data sample. acknowledgments thanks to saxena et al., 2017 to open data in the & voxel size on micro-ct computed effective transport & elastic properties usa. thanks also for the rock physics network eth zurich for the open source data of fontainebleau sandstone images. references andrä, h., combaret, n., dvorkin, j., glatt, e., han, j., kabel, m., keehm, y., krzikalla, f., 376 lee, m., madonna, c., marsh, m., mukerji, t., saenger, e.h., sain, r., saxena, n., ricker, 377 s., wiegmann, a., zhan, x., 2013a. digital rock physics benchmarks part i: imaging and 378 segmentation. comp. geosci. 50, 25 32. rizki, r. & handoyo/ jgeet vol 03 no 02/2018 105 arns, c.h., knackstedt, m.a., pinczewski, w.v., garboczi, e. g., 2002. computation of linear elastic properties from microtomographic images: methodology and agreement between theory and experiment. geophysics, 67, 1396-1405. bourbié, t., coussy, o., and zinszner, b., 1987, acoustics of porous media. houston, tx: gulf publishing co. dvorkin, j., nur, a., and yin, h., 1994, effective properties of cemented granular materials, mechanics of materials, 18, 351-366. dvorkin, j., and nur, a., 1996, elasticity of high porosity sandstones: theory for two north sea datasets, geophysics, 61, 1363-1370. fourier, d.e.l., 2014. analysis of permeability and tortuosity of fontainebleau sandstone and its models using digital rock physics approach. physics of earth and complex system, faculty of mathematics and natural sciences, bandung institute of technology, indonesia. gomez, c., 2009, reservoir characterization combining elastic velocities and electrical resistivity measurements. ph.d. dissertation, stanford university. han, d., 1986, effects of porosity and clay content on acoustic properties of sandstones and unconsolidated sediments: ph.d. dissertation, stanford university. handoyo., fatkhan., fourier, d.e.l., 2014. digital rock physics application: structure parameters characterization, materials identification, fluid modeling, and elastic properties estimation of saturated sandstones, hagi proceeding 2014 solo, bandung institute of technology, indonesia. mavko, g., and nur, a., 2009, the rock physics handbook, second edition tools for seismic analysis of porous media. cambridge university press the edinburgh building, cambridge cb2 8ru, uk saxena, nishank, day-stirrat, ruari j., 2017. effect of image segmentation & voxel size on micro-ct computed effective transport & elastic properties. marine and petroleum geology article. usa. wiegman, et all. 2012. predicting effective elastic properties with elastodict. fraunhofer itw. germany. 1. introduction 2. data and method 2.1 data 2.2 method 3. result and discussion 3.1 result 3.2 discussion 4. conclusions acknowledgments references author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2237 abstract the study area around gankot in pithoragarh district of uttarakhand belongs to the thalkedar limestone unit of mandhali formation, tejam group in inner sedimentary zone of lesser himalaya, which exposes complexly folded and refolded structures. geometric analysis carried out on the profile section of the fold tracing using dip isogon and orthogonal thickness parameters revealed presence of all the fold geometry suggested by ramsay (1967) however the class 3 followed by class 1b are the most dominant classes in the study area when individual layers of the fold were studied. the study of folds as multilayered unit reveals that folds in study area belong to strongly non-analogous fold class of anisodeviatoric folds. in fold, the strain analysis has been done by drawing strain ellipse obtained by inverse thickness method which is useful in estimating -dimensional flattening strain ratio (rs) value ranged between 1 and 3.14 with an average rs value of 1.60. the method of srivastava and gairola (2003) has also been used to obtain shear strain and flattening strain for the multilayered folds of study area. the results reveal that the multilayered folds around gankot area are moderately flattened with mean flattening strain varying between 1.06 and 2.28. a very high degree of variation in shearing ranging about 70o in both clockwise and anticlockwise directions has been noticed. the shear strains (γ) in folds have been found to vary between -2.75 to + 3.27 with an average of +0.33. the shearing and strain patterns are suggestive that the most dominant folding mechanism has been the flexure-shear for the folds of the study area which are overprinted by the fold flattening and other subsequent deformations. keywords: fold geometry, strain, flattening, shearing, lesser himalaya, multilayered fold 1. introduction the folded layer may or may not maintain uniform thickness across the full profile view of the fold. the variation of fold geometry within a rock layer during folding depends on the internal stresses it is forced to bear which are the lines obtained by connecting points of equal inclination on the outer and inner bounding surfaces of the α -the α -the axial plane parallel thickness parameter in the folded layers and developed a scheme of fold classification based on variations in these thickness parameters with respect to dip angle α. based on the pattern of variation ramsay (1967) and ramsay and huber (1987) classified fold layer geometry as class 1a, 1b, 1c, 2 and 3. later zagorčev (1993) extended the fold class to include further more categories as 1a1, 1a2, 1a3, 3a, 3b and 3c classes in 1a and 3 classes respectively. these classification schemes hold good to describe the geometry in a single layer of the fold. in nature however, most of the folds occur as multilayered sequence. in field the folds may or may not exhibit simplicity due to variations in the amount and direction of applied stresses, composition, viscosity, porosity, shape and size of grains in different layers, thus the variety of intermediate fold types are found. to describe the degree of variation in the geometry of constituents layers in multilayered fold a few schemes of classification exclusively for multilayered folds, were developed by srivastava and gairola (1997, 1999, and 2003). the study of geometry of the folds is often useful in interpreting the mechanism of fold development in a region. therefore, in present work the geometry of folds in mandhali formation around gankot village (fig.1) of pithoragarh district of lesser kumaon himalaya have been studied to know about the possible fold development mechanism which might be significant in deducing the overall tectonic history of the area. in this work the analysis of the fold have also been done to obtain the flattening strain too by using method of srivastava and gairola (2003). http://journal.uir.ac.id/index.php/jgeet 20 lata, s. et al./ jgeet sp vol 04 no 02-2/2019 fig. 1. location of study area around gankot in the geological map of a part of kumaon himalaya (after valdiya 1980). 2. geology of the area there has been significant contributions on the geology of kumaon himalaya by workers like rupke (1974), valdiya (1980) , chamyal (1991), azmi and paul (2004), tiwari (2008), rao and sharma (2009, 2011), patel et al. (2011) and chakrabarti (2016). the study area around gankot lies in the kumaon himalaya in pithoragarh district of uttarakhand between latitudes 29° °3 ° ° rocks of the study area belong to the inner sedimentary belt of lesser himalaya and form a part of the mandhali formation (sor + thalkedar formation) of lesser kumaon himalayan region (valdiya, 1980: fig. 1). the study area is located around north and north-western margin of majhaon danda hill (elev. 1826m) dominantly consisted of carbonate rocks. the lithology belongs to calc zone of pithoragarh, as it is consisted dominantly of dolomitic limestone, limestone, slaty limestone and slate indicative of low grade regional metamorphism in the region. according to valdiya (1980) the syncline is present between the bhalpatal dhar (elev. 1941m) to majhaon danda (elev. 1826m) which is well discernible between balkot through bisar to paganna and hureti. the rock types found in the study area during field survey are phyllitic limestone (argillaceous limestone), laminated limestone, grey coloured massive dolomitic limestone, slate and dolerite. the structural analysis has been carried out considering the geological structures as planar fabrics, linear fabrics and fold. the area has experienced at least three stages of ductile deformation under compressional tectonics causing development of three generation of folds and thus exhibiting a complex folded sequence of rocks. the aim of the present work however, is focused on analyzing the geometry of the mesoscopic folds found in the study area and flattening strain and shearing experienced by these folds. fig. 2. mesoscopic structures showing refolding in limestone (a and c) and slate (b) and shearing in limestone (d) of the study area lata, s. et al./ jgeet sp vol 04 no 02-2/2019 21 3. analysis of fold profile geometry the study area around gankot village in pithoragarh district of uttarakhand possesses complex but interesting structures:fig. 1. the field observations are indicative that the entire area has undergone repeated phases of deformation as a result of multi-phased himalayan orogeny resulting into an intricate system of superimposed folds, faults and fracture development at different scales:fig. 2. in the study area although folds are present in all rocks at all scales from microscopic, mesoscopic to macroscopic levels, the mesoscopic folds have been chosen for geometrical analysis for convenience in the study. in order to geometrically analyze the fold in present study the folds have been traced from field photographs, field tracings and cut-and polished sections of the hand specimen samples. cares have been taken so that the tracings as far as possible represent the profile section of the fold. these fold profiles along with their dip isogons have been presented in fig. 3. fig. 3. dip isogons on the tracings of profile sections of folds from the study area. in order to analyze the geometry according to ramsay (1967) the orthogonal thickness tα were measured from the limbs of each fold layer separately on the fold profile. the orth α were obtained by dividing tα with t0 ( α = tα/ t0), where α is the dip angle which is taken at interval of 10 o in present work. fig. 4 α versus α diagram given by ramsay (1967) for the geometric analysis of the folds. the plots are indicative that folds of the study area do not restrict themselves to a particular type of fold geometry rather, a large variation is observed in them. the folds in fact, show that all type of geometries suggested by ramsay and huber (1987) but in differing proportions. therefore, in order to obtain a meaningful interpretation the results have been subjected to further statistical analysis and presented with help of a bar diagram in fig. 5. it can now be concluded with the help of fig. 5 that the folds of the study area mostly exhibit class 3 fold geometry which accounts near 50% of all fold types, followed by 1b (27%) and 1a (15%). the class 1c (7%) and class 2 (1%) fold geometries are less abundant. it was also observed that the most abundant classes (i.e. class3 and class 1b) receive good contributions from isogons from increasing α value. the high abundance of class 3 geometry suggests that major fold mechanism has been the differential compression in the area. however, other mechanism such as flexural folding (1b) and fold flattening (1c) are also important. the passive shear folding mechanism which is generally responsible for class 2 geometry is rare. 22 lata, s. et al./ jgeet sp vol 04 no 02-2/2019 a. b. fig. 4. α versus dip angle α for the fold profile geometry shown in a. l and r represent left and right limbs of the fold respectively, and 1, 2, 3 and 4 for their constitutive layers. 4. geometrical analysis of multilayered fold the folds of the study area generally multilayered therefore they have been studied as multilayered sequence too using the scheme given by srivastava and gairola (1999). the scheme utilizes the variation in the fold geometry of each constituting layers of a multilayered fold at a particular dip isogon (α) by obtaining the α) values. fig. 6 represents the plot given by srivastava and gairola (1999), in which all the curve a, b, c, and d are originated from the origin point and separating the two different geometric class. if not, they are termed analogous, sub-analogous, sub-nonanalogous, nonanalogous, and strongly nonanalogous fold classes. the data obtained from the analyzed multilayered folds of the study area are plotted and given in fig. 6. the multilayered folds of the study area (fig.3) were treated according to srivastava and gairola (1999) and thereafter plotted in the their standard graph(fig. 6). it has been found that the majority of the folds of the study area belong to the strongly non-analogous fold category. fig. 6 reveals that the folds do not exhibit definite fold geometry and the plots are distributed in more than one class. therefore, the fold data were once again analyzed to know their frequency in different classes and the analysis is presented with the help of bar diagram in fig. 7. it reveals that though fold data fall in almost all the classes but majority of the folds belong to the strongly nonanalogous class. this indicates that the folds of the gankot area do not have regular geometry in the multilayered sequence and the degree of variation is very high suggesting strong influence of multiple phased deformations on these folds. the great deviation from any consistent regular fold geometry may be the effects of folding and refolding which are often visible in the rocks of the study area: fig. 2. fig. 5. bar diagram showing frequency of different fold classes (ramsay, 1967) in the study area. lata, s. et al./ jgeet sp vol 04 no 02-2/2019 23 fig. 6. variation in geometry of multilayered folds of the study area plotted in standard σn α) versus dip angle α diagram (after srivastava and gairola, 1999); a, s, r, and l represents fold, antiform, synform, right limb and left limb respectively for folds (fig.3). fig. 7. frequency distribution of mesoscopic multilayered folds classes (fig.3& fig. 6) of study area. 5. flattening and shearing in folds a buckle or flexure fold does not change the orthogonal thickness of the layer, therefore such folds exhibit class 1b geometry. however, if the folds are subsequently compressed the layers fail to maintain this thickness and they change their geometry from class 1b to 1c because of flattening. thus a unit circle of 1b fold obtained by inverse thickness method (lisle 1992) changes to an ellipse; the axial ratio of this ellipse gives the finite flattening strain ratio (srivastava and gairola 2003). the folds after their formation due to progressive deformation or subsequent co-axial deformation may undergo flattening. sometimes the flattening may be associated with shearing also that may also be recognized by the method of srivastava and gairola (2003). thus the method is often useful not only in partitioning out the flattening strain but it is also capable of detecting the sense of rotation by shearing. in fold, the strain analysis has been done by drawing strain ellipse obtained by estimating flattening st has been applied on the folds of the study area and a part of which is given in fig. 8. 24 lata, s. et al./ jgeet sp vol 04 no 02-2/2019 fig. 8. flattening strain estimation for fold layers (of fold no vii, fig.3); rs= finite 2-d flattening strain ratio; β = inverse shear angle (β= -ψ); shear strain γ = tanψ (after srivastava and gairola, 2003). a total of 67 limbs of the folded layers belonging to 10 different multilayered folds comprising of 3 to 5 layers have been analyzed and the results are presented in table 1. the folds are widely distributed over the study area and it was observed that the finite two-dimensional flattening strain ratio (rs) values range between 1 and 3.14 with an average rs value of 1.60. it suggested that at places the fold layers of the study area have remained unflattened (rs = 1) while at other places they are subjected to high degree of flattening. as a multilayered unit the folds of the study area have shown mean finite flattening strain ratio (mean rs) values from 1.06 to 2.28. following srivastava and gairola (2003) a total of 64 limbs of the folded layers belonging to 10 different multilayered folds comprising of 3 to 4 layers have been analyzed for shear strain (γ) and the results are presented in table 2. representative analysis of a multilayered fold is given in fig. 8 as well. table 2 reveals that shear strain is not uniformly distributed in the folded layers and it varies between -2.75 and +3.27. the negative sign is indicative of anticlockwise and the positive sign is for clockwise sense of shearing. these extreme values of shear strain (γ) correspond to the shear angle (ψ) as high as -70 o to +73 o in the individual layers however the mean shear angle (ψ) remains ~18 o in clockwise direction. it was also observed that the different constituting layers of a single multilayered fold have shown positive and negative shear senses which indicate that shear strain have been developed and received differently by the individual layers due differing slippage among the constituting layers. the variation in amount of shear strain and sense may be attributed to differing compositions and other mechanical anisotropies of the constitutive layers of the fold. when analyzed as multilayered fold, the average shear strain (mean γ, table 2) were found to vary between -0.56 to +2.70 within an individual fold but the overall average of the 10 multilayered fold (+0.33) account for the low overall shearing of the folds which accounts for only 18 o of general overall shear angle (ψ). however there might be great fluctuation form this mean shear strain (mean γ) of a multilayered fold and standard deviation may be as high as 1.91. therefore it seems that the shearing in the folded layers is mainly due to the slippage among different lata, s. et al./ jgeet sp vol 04 no 02-2/2019 25 constituting layers of the folds which is indicative that perhaps the dominant folding mechanism seems to be the flexure-shear mechanism (twiss and moores, 2007). table 1 finite 2-d flattening strain ratio (rs) obtained from different multilayered folds from the study area. fold no. flattening strain ratio (rs) mean rs l1 l2 l3 l4 l5 i 1.59 2.77 2 2.77 2.28 iia 1.47 1.11 1.11 1.92 1.4 iis 1.85 1.33 1.26 2 1.61 iii 1.6 1.81 1.75 1.72 iv 1.46 1 1.57 1.68 1.04 1.35 va 1.79 1.47 1.68 1.75 1.67 vs 3.14 1.65 2.07 1.42 2.07 via 1.31 2 1.87 1.47 1.47 1.62 vis 1.85 2.82 1.56 1.35 1.69 1.85 viia1 1.39 1.56 1.71 1.47 1.53 viia2 1.93 1.5 1.5 1.64 viis 1.75 1.53 2.23 1.84 viiia 1.71 1.19 1.39 1.43 viiis1 1.05 1.04 1.72 1.27 viiis2 1.67 1.8 1.48 1.65 ixa 1.4 1.53 1.67 1.53 ixs 1.05 1.05 1.07 1.06 x 1.17 1.17 1.18 1.18 1.18 average 1.60 table 2 shear strain (γ) obtained from different layers of folds from the study area. 6. discussion and conclusion many workers have discussed about the kumaon himalaya pertaining to different aspects of structure and tectonics in this region (bhattacharya, 2008; valdiya and pande, 2009; joshi and tiwari, 2009; agarwal et al. 2010, 2016; agarwal and sharma, 2011; bhargava, 2011; patel et al., 2007, 2011; srivastava et al. 2011; verma and bhattacharya, 2011; jain et al. 2012, 2016; shah et al, 2012; singh et al., 2012; jade et al. 2014; dubey 2014; banerjee et al. 2015; bhattacharya and ahmed 2016)and their works have thrown much light on the tectonic evolution of the rocks of the region which are highly folded and tectonically much complex. the mesoscopic folds have been used by many workers for the analysis of the folding and the strain conditions (dieterich and fold no. shear strain (γ) mean γ sd l1 l2 l3 l4 i 1.43 1.73 -2.75 1 0.35 1.81 ii,a 1.8 0.12 0.12 2.75 1.20 1.13 ii,s 2.9 3.27 1.88 2.75 2.70 0.51 iii 0.14 -0.14 -0.18 -0.06 0.14 iv -2.75 0 0.09 -0.58 -0.81 1.15 v,a 0.81 0.55 0.23 0.58 0.54 0.21 v,s 1.11 1.73 1 -0.58 0.81 0.85 vi,a 1.67 1.19 -0.84 0.36 1.59 1.09 vi,s 2.75 -1.54 -1.73 -1.73 -0.56 1.91 vii,a1 -0.18 0 -0.1 -0.27 -0.14 0.1 vii,a2 -0.9 0.27 -0.42 -0.35 0.48 vii,s -0.34 -0.27 -0.73 -0.45 0.2 viii,a -0.47 -0.36 -0.27 -0.37 0.08 viii,s1 -0.21 0 1.19 0.33 0.62 viii,s2 -0.21 2.47 2.9 1.72 1.38 ix,a -0.31 -0.09 0.18 -0.07 0.2 ix,s -0.84 -0.18 0 -0.34 0.36 x 0.27 0.3 -0.1 -0.1 0.09 0.21 average +0.33 26 lata, s. et al./ jgeet sp vol 04 no 02-2/2019 carter, 1969; roberts and strömgard, 1972; hudleston, 1973; sanderson, 1976; bhattacharya, 1978; hudleston, and holst, 1984; lisle, 1992; bastida, 1993; bastida et al., 2003; srivastava, 1995, 2003; srivastava and gairola, 2003). to unravel the complexities of the fold geometries significant work include those by srivastava and sinha (1987); jain and anand (1988); srivastava et. al.(2011); katiyar and srivastava (2012) which have utilized the fold profiles of mesoscopic folds in himalayan region. the present study area which belongs to the thalkedar limestone unit of mandhali formation, tejam group of lesser himalaya, district pithoragarh possesses complexly folded sequence of limestone and slate. on the basis of presence of microfossils, tiwari and pant (2009) consider the gangolihat limestone of kumaon himalaya as neoproterozoic age. the folding in these neoproterozoic rocks must have been developed in multiple phases during the himalayan orogeny in tertiary. patel et al. (2011) recognized four phases of deformation (d1 to d4) in the higher himalayan crystallines of kumaun himalaya, which are responsible for complex geometries of the folds in the region. analysis of fold geometry and strain in this region however, is very much lacking. in the present study our aim is to quantify the overall deformation status in terms of strain and shearing in the mesoscopic folds without differentiating the folds of different generations. therefore, in the present work we have attempted not only the geometric analysis of the mesoscopic folds but the flattening strain conditions after their formation is also discussed. we have applied the schemes proposed by srivastava and gairola (1999 and 2003) for the folds of study area because this scheme allows the fold to be studied as multilayered sequence too. the study reveals that folds in study area belong to strongly non-analogous fold class of anisodeviatoric fold of srivastava and gairola (2003). most of the folds of the study area however exhibit class 3 fold geometry which is indicative that thickness of the layers in limb portion is much less than those at the hinge zone. this may be due to the additive deformation caused by subsequent folding, refolding, flattening and shearing etc. after the first folds were formed. however the class 3 geometry is next succeeded in abundance by class 1b geometry of ramsay (1967) which reveals that a significant number of the folds in the study area have still maintained their orthogonal thickness perhaps because some of the layers were compositionally competent enough and were not significantly affected by later deformations. the subsequent deformations however, are arrested in folds in the comparatively less competent layers in the form of flattening strain and shearing which have been partitioned out by the method after srivastava and gairola (2003). the finite two-dimensional flattening strain ratio (rs) value ranged between 1 and 3.14 with an average rs value of 1.60 in individual folded layers however, in multilayered folds around gankot area it varied between 1.06 and 2.28 which is suggestive of moderate flattening in the folds in general. the shear strains (γ) in folds have been found to vary between -2.75 to +3.27 with an average of +0.33. a very high degree of variation in shearing ranging about 70 o in both clockwise and anticlockwise directions has been detected in the folds of the study area. the shearing and strain patterns have also been examining by observing their amount and direction in the next above and below layers. the patterns are suggestive that the most dominant folding mechanism has been the flexure-shear for the folds of the study area. flattening strain in these folds must have been overprinted obviously in subsequent deformations after the fold formation which might have modified the original shearing too. the possibility that the original shear patterns also get modified when the folds occur in the vicinity of a shear zone in the study area, cannot be ruled out. acknowledgements the authors are thankful to the facilities provided by the head as well as coordinator cas, geology department, banaras hindu university, varanasi, india. rk is thankful for the rg national fellowship. references agarwal, a., agarwal, k. k., bali, r., chandra, p., joshi, g., 2016. back-thrusting in lesser himalaya: evidence from magnetic fabric studies in parts of almora crystalline zone, kumaon lesser himalaya. j. earth system science 125, 873-884. agarwal, k.k., sharma, v.k., 2011. quaternary tilt-block tectonics in parts of eastern kumaon himalaya, india. zeitschriftfür geomorphologie n.f. 55, 197-208. agarwal, k.k., jahan, n., agarwal, a., 2010. modification of fold geometry in almora crystalline shear zone, lesser himalaya. j. geol. soc. india 75, 411-414. azmi, r.j., paul, s.k., 2004. dolomite of inner kumaun lesser himalaya: implication on age and correlation. current science 86, 1653-1660. banerjee, s., matin, 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srivastava, v., gairola, v.k., 2003. recent classification schemes for multilayered folds: an overview. milestones in petrology (ed. mohan, a.), memoir of the geological society of india 52, 395-408. tiwari, m., 2008. additional neoproterozoic sponge spicules from gangolihat dolomite, kumaun lesser himalaya, india. himalayan geology. 29, 49-55. tiwari, m., pant, i., 2009. microfossils from the neoproterozoic gangolihat formation, kumaun lesser himalaya: their stratigraphic and evolutionary significance. j. asian earth science 35, 137-149. twiss, r.j., moores, e.m., 2007. structural geology, w. h. freeman, new york. valdiya, k. s., 1980. geology of kumaun lesser himalaya. wadia institute of himalayan geology.dehradun. valdiya, k.s., pande, k., 2009. behavior of basement-cover decoupling in compressional deformation regime, northern kumaun (uttarakhand) himalaya. proc. indian nat. sci. acad. 75, 27-40. verma, a.k., bhattacharya, a.r., 2011. reorientation of lineation in central crystalline zone, munsiari-milam area of the kumaon greater himalaya. j. earth system science 120, 449458. zagorčev, i.s., 1993. the geometric classification of folds and distribution of fold types in natural rocks. j. structural geology 15, 243 251. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geology of the area 3. analysis of fold profile geometry 4. geometrical analysis of multilayered fold 5. flattening and shearing in folds 6. discussion and conclusion references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 idrus a./ jgeet vol 03 no 01/2018 30 halogen chemistry of hydrothermal micas: a possible geochemical tool in vectoring to ore for porphyry coppergold deposit arifudin idrus 1, * 1 geological engineering department, faculty of engineering, universitas gadjah mada, yogyakarta, indonesia. *corresponding author: arifidrus@ugm.ac.id tel.: +62-274-513668+81-22-813-8438; received: dec 31, 2017. revised : feb 23, 2018, accepted: feb 25, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.1022 abstract porphyry copper-gold deposit commonly exhibits an extensive alteration zone of hydrothermal micas particularly biotite and sericite. this study is aimed to analyze and utilize the chemistry of halogen fluorine and chlorine of biotite and sericite to be a possible tool in vectoring to ore for copper porphyry deposits. to achieve the objectives, several selected altered rock samples were taken crossing the batu hijau copper-gold mine from inner to outer of the deposit, and hydrothermal micas contained by the rocks were analyzed petrographically and chemically. mineral chemistry was detected by electron microprobe analyzer, whilst biotite is petrographically classified as either magmatic or hydrothermal types. sericite replacing plagioclase occurred as fine-grained mineral and predominantly associated with argillic-related alteration types. biotites in the batu hijau deposit are classified as phlogopite with a relatively low mole fraction magnesium (xmg) (~0.75) een the xmg and halogen contents are -f and mginner part of the deposit which is represented by early biotite (potassic) zone where the main copper-gold hosted, to the outer part of the deposit. however, chlorine in both biotite and sericite from each of the alteration zones shows a relative similar concentration, which suggests that it is not suitable to be used in identification of the alteration zones associated with strong copper-gold mineralization. h2o content of the biotite and sericite also exhibits a systematic increase outward which may also provide a possible geochemical vector to ore for the copper porphyry deposits. this is well correlated with fluorine content of biotite in rocks and bulk concentration of copper from the corresponding rocks. keywords: biotite, sericite, halogen chemistry, vector to ore, porphyry copper-gold deposit 1. introduction a number of researchers have suggested that fluorine and chlorine are intimately involved in the hydrothermal transport of metals (zhu and sverjersky, 1991; shinohara, 1994; gammons and williams-jones, 1997; selby and nesbitt, 2000). the halogen contents, therefore, may have potential as pathfinder elements in geochemical prospecting for many different types of ore mineral deposits. in the rock forming minerals, f and cl generally occupy the hydroxyl sites of hydroxysilicate minerals, including micas such as biotite and sericite (parry et al., 1984; selby and nesbitt, 2000; sarjoughian et al., 2015; zhang et al., 2016). this paper is aimed to investigate the halogen (f and cl) chemistry of biotite and sericite as well as the use of halogens for geochemical vector ore, where the batu hijau copper-gold porphyry deposit as a case study. the batu hijau deposit is located in southwest corner of sumbawa island, indonesia (fig 1). it contains 914 million metric tons of ore at an average grade of 0.53 % cu and 0.40 g/t au (clode et al., 1999). the batu hijau deposit occurs in steeply incised terrain, with the highest point on the deposit at 555 m above sea level. in general, the pre-mineralisation rock units consist of interbedded andesitic lithic breccia, and fine-grained volcaniclastic sandstones and mudstones, porphyritic andesite intrusive and at least two texturally distinct quartz diorite intrusive bodies. these rocks are intruded by multiple phases of tonalite porphyries, which acted as ore mineralization-bearing intrusions (clode et al., 1999; garwin, 2002) (fig 2). the emplacement of tonalite porphyries and mineralisation are spatially and temporally associated with northsouth (n-s) and northeast-southwest (ne-sw) trending structures (priowarsono and maryono, 2002). hydrothermal alteration and mineralization developed in four temporally and spatially overlapping stages consists of the early alteration stage is divided into biotite (potassic), actinolite (inner propylitic) and chlorite-epidote (outer propylitic) zones (idrus, 2005). the transitional alteration stage is typified by a chlorite-sericite (intermediate argillic) zone (idrus, 2005). the late mailto:arifidrus@ugm.ac.id idrus a./ jgeet vol 03 no 01/2018 31 alteration stage is characterized by destruction of feldspar and the formation of pyrophylliteandalusite (advanced argillic) and sericiteparagonite (argillic) zones (idrus, 2005). the very late alteration stage is characterized by illite and sericite replacement of feldspar. alteration zones of the batu hijau porphyry copper-gold deposit can be seen in fig 3. biotite is observed in the biotite, chloritesericite and actinolite alteration zones, while sericite occurs intensively in the biotite and chlorite-sericite zones as well as in the pyrophyllite-andalusite and sericite-paragonite alteration zones. fluorine and chlorine contents were analyzed in both hydrothermal micas (biotite and sericite) from these alteration zones. batu hijau project praya lombok strait selong mataram alas strait sumbawa besar flores sea indian ocean fig 1. the batu hijau porphyry copper-gold mine site in sumbawa island, indonesia, and study area location (black box). t d u 30 30 35 80 35 c r 4 n w f a u l t t o n g o l o k a f a u l t z o n e d 35 5 8°8 0° 8 5° 8 0° 8 5° 8 0° 7 0° 8 5° 7 0° 8 5° 8 0° 35 zigzag fault nagin fault c r -3 n w f a u l t cr-2 n w fau lt 5 8° 8 5° 42 rinjani fault 8 0° 8 0° 7 2° sem er u fa u lt l a w u f a u l t k e l u d f a u l t 8 9° m erb a bu fa u lt 8 5° 8 0° 7 9° 8 5° 8 5° 8 0° b a t o k b r o m o fa u l t 30 a n a k ka ta l a fa u lt 30 75 7 5° 5 0° 7 0° 7 0° 7 0° 6 5° 5 0° 4 5° 4 3° 8 0° 7 8° 3 5° 7 0° 7 0° 7 0° 8 0° 5 0° 4 5° 4 0° 4 5° 4 5° 2 9° 6 5° 7 5° 8 5° 7 5° 7 6° 7 8° 4 5° 6 0° 8 0° 6 5° 8 0° 3 9° 8 0° 8 2° 7 5° 8 0° 8 5° 7 5° 8 0° 4 5° 4 0° 2 5° 7 5° 8 0° 3 5° 7 8° 4 0° 8 0° 7 0° 7 0° 5 0° 7 0° 6 7° 7 5° 8 5° 8 0° 6 5° 6 6° 7 0° 4 4° 8 2° 5 0° 7 5° 8 2° 7 9° 8 0° 7 5° 7 5° 7 9° 7 5° 6 0° 7 0° 7 5° 8 5° 8 5° 8 5° 8 0° 7 5° 7 7° 8 0° 7 2° 8 5° 6 0° 8 0° 8 5° 7 5° 7 4° 8 0° 3 0° 7 5° 8 5° 8 5° 8 0° 5 5° 6 1° 4 5° 7 5° 7 5° 4 3° 7 5° 3 5° 4 0° 6 5° 8 0° 5 0° 7 0° 8 0° 7 5° 3 5° 8 0° 7 5° 7 8° 7 5° 6 5° 8 0°8 0° 8 0° 8 0° 8 0° 7 0° 7 5° 8 0° 7 0° 7 0° 6 0° 6 0° 7 5° 6 5° 5 0° 4 0° 4 0° 3 0° 4 0° 3 5° 6 5° 6 5° 8 0° 8 0° 3 0°6 0° 5 0° 8 7° 8 0° 8 0° 7 0° 3 5° 70 80 80 80 80 80 4 0° 4 0° 7 0° 7 5° 80 7 5° 8 5° 5 0° 8 0° 5 2° 5 0° 5 5° 6 7° 8 0° 7 0° 8 0° 7 0° 8 5° 4 5° 4 0° ? ? ? ? ? d u 6 0° 6 8 ? ? ? ? 5 0° 7 5° 80 70 70 70 50 45 80 75 70 75 70 80 70 80 3581 80 40 85 75 70 7 0° 6 0° 7 8° 7 0° m e r a pi fa u lt 6 5° 8 0° 7 8° 3 0° 4 5° 3 9° 7 5° 6 8° 80 75 the batu hijau deposit 1st qtr-2002 geology c om pilation based on end of marc h topography young tonalite (yt) newm ont nusa tenggara corp., 2002 interm edia te tonalite (it) legend equigranular quartz diorite (qde) porphyritic quartz diorite (qdp) undifferentiated quartz diorite (qdu) porphyritic andesitic intrusive (adp) volc anic lithic brec c ia (vxl) fine grained volc anic lastic s (vfg) n o 100 200 scale 1: 2500 bedding (with dip & dip d irec tion) jointing (with dip & dip direc tion) fault with dip direc tion contac t lithology ultim ate p it lim it ult ima te pit lim it qde qde qdp vfg vfg vxl vxl vfg adp vxl qdu it it yt yt to ng o lo ka-pun a fault 4 8 5 0 0 0 e 4 8 6 2 0 0 e 9008400n 9009000n 9009600n 9010200n 9010200n 9009600n 9009000n 9008400n 4 8 5 0 0 0 e 4 8 5 6 0 0 e 4 8 5 6 0 0 e 4 8 6 2 0 0 e section 9080n sec tion 9080n “t o n g o lo ka -b a tu h ija u ” fa u lt c o rr id o r fig 2. geological map of the batu hijau deposit (newmont nusa tenggara corp., 2002). 32 idrus a./ jgeet vol 03 no 01/2018 early c entral biotite zone (bt) the batu hijau deposit 1st qtr-2002 alteration c om pilation based on end of marc h topography 9008400n bt newm ont nusa tenggara corp., 2002 legend n ult ima te pit lim it 4 8 5 0 0 0 e transitional c hlorite-seric ite zone (chl-ser) early proxim al ac tinolite zone (ac t) early distal c hlorite-epidote zone (chl-ep) max. bt extent and ac t present (appx.) epidote present mafic pa rtly altered to sec ondary biotite (bt) late seric ite-paragonite zone (ser-pg) late pyrophyllite-a ndalusite zone (prl-and) late argillic zone (undiff.) very late illite-seric ite zone (ill-ser) ultim ate pit scala 1:2500 0 100 200 9009000n 9009600n 9010200n 4 8 5 6 0 0 e 4 8 6 2 0 0 e 9010200n 9009600n 9009000n 9008400n 4 8 5 0 0 0 e 4 8 5 6 0 0 e 4 8 6 2 0 0 e bt ac t chl-ser chl-ep prl-and ser-pg argillic (undiff.) ill-ser chl-ser prl-and ac t chl-ep argillic (undiff.) fig 3. hydrothermal alteration map of the batu hijau deposit (newmont nusa tenggara corp., 2002; idrus, 2005). 2. analytical methods a suite of representative altered samples was systematically taken crossing from inner to outer part of the batu hijau porphyry copper-gold mine in sw sumbawa island, indonesia. several selected rock samples were analyzed petrographically and mineral-chemically. petrographic methods include the analyses of thin and polished thin sections under a polarized-light microscope, to identify primary and hydrothermal minerals, their textures and occurrences. mineral chemistry analysis utilizes electron probe micro analyzer (epma) jeol idrus a./ jgeet vol 03 no 01/2018 33 jxa-8900r to determine the chemical composition of the biotite and sericite in each of their related alteration zones from the inner to outer part of the deposit. element determinations (si, al, fetota1, mg, ti, mn, na, k, f and cl) were carried out using a beam size 3 µm, an accelerating potential voltage of 15 kv, a probe current of 2.35 na, and a counting time of 20 second for each element analyzed. natural apatite, jadeite, rutile, tugtupite, fayalite, spinel, orthoclase, and plagioclase standards were used in the analytical procedure for f, na, ti, cl, mn, fe, mg, al, k, ca and si. matrix effects were corrected using the zaf software provided by jeol. the accuracy of the reported values for the analyses is 1-5 % (1σ) depending on the abundance of the elements. a microprobe analysis is defined as the arithmetic mean of 110 spot analyses of the biotite and sericite depending on mineral grain size. the oh values are calculated on the basis of 24 oxygens. a computer software program minpet 2.02 was primarily used to calculate the structural formula of the analysed minerals. all analyses were carried out at the institute for mineralogy and economic geology, rwth aachen university, germany. 3. results and discussion 3.1 biotite petrography biotites are petrographically classified as either magmatic or hydrothermal types (fig 4). the term crystallized directly from silicate melt. magmatic biotite grain is further subdivided into least-altered and altered varieties (selby and nesbitt, 2000). the present in hydrothermal assemblages (e.g. potassic, phyllic and propylitic). the magmatic biotites of batu hijau is only observed as altered magmatic biotite in few intermediate and young tonalite samples. magmatic biotite occurs characteristically as euhedral to subhedral phenocrysts and microphenocrysts and euhedral to subhedral flakes. some magmatic biotite is ragged, splintery or inferred to have precipitated from the hydrothermal fluid. hydrothermal biotite is petrographically distinct from magmatic biotite, occurring as aggregates of fine grained flakes. biotite that has partially or completely replaced igneous hornblende and occurring as biotite veinlet 3.2 sericite petrography hydrothermal sericite is a common alteration product in many hydrothermal deposits. the batu hijau porphyry copper-gold deposit exhibits extensive argillic alteration styles, in which sericite becomes a major constituent surrounding or superimposed on the central biotite alteration. the argillic alteration styles include the transitional chlorite-sericite (intermediate argillic), late pyrophyllite-andalusite (advanced argillic) and late sericite-paragonite (argillic) alteration zones. however, very minor sericite occurs in the central biotite (potassic) alteration zone. the sericite associated with the central biotite alteration zone partially replaces plagioclase phenocrysts in the tonalite porphyries. a complete replacement is locally observed in the young tonalite. the replacements mostly occur in the cores, rather than in the rims of the zoned plagioclase grains. in comparison to the intermediate tonalite, the plagioclase in the young tonalite is more intensely dusted by the sericite. the sericites are present in a small portion ( 1 %), and commonly occur as an aggregate of fine to medium-grained flakes (up to 0.8 mm in length). the transitional chlorite-sericite alteration zone occupies a temporal position between the central biotite and late argillic alteration styles (pyrophyllite-andalusite and sericite-paragonite zone). this alteration zone is characterized by weak-moderate chloritization and sericitization (fig 5a). the plagioclase grains are partially to completely replaced by sericite. the replacement is more conspicuously in the equigranular quartz diorite than in the andesitic volcaniclastic rocks. the hydrothermal sericite is present in variable portion (5-25 %) of the rock volume. the mineral occurs mostly as fine-grained flakes, with length of up to 0.4 mm (commonly < 0.04 mm). fig 4. petrographic images of biotite types in rocks from batu hijau deposit: (a) euhedral-subhedral altered magmatic biotite contained by tonalite porphyries, and (b) fine-grained hydrothermal biotites replacing hornblende in equigranular quartz diorite. 34 idrus a./ jgeet vol 03 no 01/2018 fig 5. grey-petrographic images of sericite: (a) intergrowth of chlorite replacing ferromagnesian minerals and sericite replacing plagioclase) of transitional chlorite-sericite-altered volcaniclastic rocks, (b) euhedral-subhedral andalusite (high relief) after sericite-paragonite replacing plagioclase of late andalusite-pyropyllite (advanced argillic)-altered quartz diorite. mineral abbreviations: ser = sericite, chl = chlorite, pg = paragonite, and = andalusite, kln/ill = kaolinite/illite, ccp = chalcopyrite, and py = pyrite. the sericite in the late pyrophyllite-andalusite alteration zone occurs in a relatively minor to moderate amounts (2-20 %) (fig 5b), and is associated with pyrophyllite, andalusite, kaolinite, diaspore and dickite. the sericite replaces the plagioclase grains completely. they occur as very fine-grained flakes, with a length mostly < 0.04 mm. in comparison to those in the pyrophylliteandalusite alteration zone, the sericites related to the late sericite-paragonite alteration zone are characterized by relatively fine to medium-grained flakes (up to 0.8 mm). the xrd data indicates that the white-mica solid solutions are predominantly composed of sericite and paragonite end-members. the rietveld program quantifies the phases as the major components (30-60 % of the rock) (idrus, 2005). 3.3 biotite and sericite chemistry biotite, a trioctahedral mica with the generalized formula (k, na, ca, ba) (fe +2 , fe +3 , mg, ti, mn, al)3 (al, si)4o10(oh, f, cl)2 is a common constituent in many copper porphyry deposits. the previous studies of biotite chemical composition in copper porphyry deposits have mostly concentrated on the determination of f and cl contents, with the objective of distinguishing between mineralized and barren plutons. biotites in the batu hijau deposit are classified as phlogopite k2mg6[si6al2o20](oh) with a relatively low mole fraction magnesium (xmg) (~0.75) compared to the et al., 1998). representative composition of the batu hijau biotites is given in table 1. some elements show a systematic compositional variation in the central biotite (bt) and partly chloritized (partly -sericite (chlser) to the outer actinolite (act) alteration zones. the relationship between the xmg and halogen -f and mgmunoz, 1984; idrus, 2005). table 1. representative microprobe data of major oxides and halogen chemistry of biotite in various altered rocks taken from the inner (central) to the outer part (peripheral) of the deposit elements alteration zone (inner  outer deposit) bt partly chl'd chl-ser act sio2 41.08 39.85 39.52 38.85 tio2 2.38 1.69 2.15 4.92 al2o3 13.12 14.18 15.20 13.37 feo 10.49 10.66 11.17 13.68 mno 0.05 0.11 0.12 0.35 mgo 19.92 19.59 17.78 15.31 cao bd 0.03 0.03 0.02 na2o 0.16 0.15 0.15 0.17 k2o 8.74 8.92 9.38 9.18 f 0.99 0.98 0.64 0.38 cl 0.19 0.22 0.25 0.31 h2o 3.66 3.48 3.75 3.81 total 100.78 99.86 100.13 100.32 si 5.90 5.79 5.75 5.72 al iv 2.10 2.21 2.25 2.28 al vi 0.12 0.22 0.35 0.04 ti 0.26 0.19 0,24 0.55 fe +2 1.26 1.30 1.36 1.69 b a idrus a./ jgeet vol 03 no 01/2018 35 elements alteration zone (inner  outer deposit) bt partly chl'd chl-ser act mn 0.01 0.01 0.01 0.04 mg 4.27 4.24 3.86 3.36 ca 0.00 0.01 0.00 0.00 na 0.04 0.04 0.04 0.05 k 1.60 1.65 1.74 1.73 f 0.90 1.14 0.59 0.35 cl 0.09 0.11 0.13 0.15 oh 3.51 3.37 3.64 3.75 xfe 0.77 0.77 0.74 0.67 xmg 0.24 0.26 0.31 0.34 xphl 0.72 0.71 0.66 0.59 -ser = chlorite-sericite (phyllic); and act = actinolitic (inner propylitic) alterations. table 2. representative microprobe data of major oxides and halogen chemistry of sericite in various altered rocks taken from the inner (central) to the outer part (peripheral) of the deposit elements alteration zone (inner  outer deposit) bt chl-ser prl-and ser-pg sio2 47.07 47.65 47.00 45.90 46.9 tio2 0.18 0.21 0.14 0.19 0.09 al2o3 33.01 30.13 32.70 37.26 36.25 feo 1.83 2.97 2.03 0.74 1.29 mno bd 0.07 0.02 bd bd mgo 1.97 3.30 1.96 0.19 0.55 cao 0.03 0.05 0.01 bd bd na2o 0.52 0.08 0.37 2.01 1.36 k2o 10.32 9.93 10.43 8.37 9.09 f 0.39 0.37 0.24 0.11 0.l5 cl 0.04 0.04 0.01 0.01 0.02 h2o 4.29 4.26 4.34 4.47 4.48 total 99.64 99.05 99.26 99.25 100.21 si 6.30 6.44 6.32 6.08 6.18 al iv 1.70 1.56 1.68 1.92 1.82 al vi 3.50 3.23 3.49 3.89 3.80 ti 0.02 0.02 0.01 0.02 0.01 fe 0.20 0.34 0.23 0.08 0.14 mn 0.00 0.01 0.00 0.00 0.00 mg 0.39 0.66 0.39 0.04 0.11 ca 0.00 0.01 0.00 0.00 0.00 na 0.14 0.02 0.10 0.52 0.35 k 1.76 1.71 1.79 1.41 1.53 f 0.33 0.31 0.21 0.09 0.12 cl 0.02 0.02 0.01 0.00 0.01 oh 3.83 3.84 3.89 3.95 3.93 xser 0.93 0.99 0.95 0.73 0.81 xpg 0.07 0.01 0.05 0.27 0.19 note: -ser = chlorite-sericite (phyllic) alteration; prl-and = pyrophyllite-andalusite (advanced argillic); and ser-pg = sericite-paragonite (intermediate argillic) alterations. sericite, is a term given to fine grained, white mica including muscovite, phengite, illite, and other solid solution end members. sericite often occurred in mineral aggregates in which chlorite, sericite or albite may be intermixed and therefore not distinguishable with the microprobe optics. batu hijau sericites show an inhomogeneity degree in the chemical composition, it may contain unitthick layers of smectite and chlorite, and/or submicrometerized patches of kaolinite, quartz, and other minerals. representative composition of the batu hijau sericites is shown in table 2. mole fractions of sericite (xser) decrease relative to those in the late alteration zones including pyrophyllite-andalusite (prl-and) and sericiteparagonite (ser-pg) as a decrease of their forming temperatures. in general, sericite chemistry exhibits insignificant variation in the composition (table 2). however, si and f decrease as well as al and mg increase to the late alteration zones. 3.4 f-oh exchange of biotite-sericite pairs the f and oh contents of biotite, sericite, and hydrothermal fluids in natural systems allow an evaluation of exchange equilibrium between the biotite, sericite and hydrothermal fluids in natural systems allow an evaluation of exchange equilibrium between the biotite, sericite and the fluids (parry et al., 1984; selby and nesbitt, 2000; siahcheshm et al., 2011; sarjoughian et al., 2015; zhang et al., 2016). the f content of sericites from early biotite alteration zone has a positive correlation with the xmg as shown in fig 6, whereas those from transitional chl-ser as well as late prl 36 idrus a./ jgeet vol 03 no 01/2018 and and ser-pg alteration zones show a scatter relationship. the positive correlation of the xmg and f suggest that mg controls the f-oh exchange (munoz, 1984; selby and nesbitt, 2000; zhang et al., 2016). fig 6. a positive correlation of xmg and f in sericite from the early biotite (potassic) and transitional-late alteration zones. the experimentally calibrated f-oh exchange relations of munoz et al. (1974) and computational techniques of gunow et al. (1980) have been used to evaluate exchange equilibrium between biotite and sericite at the batu hijau deposit. a generalized reaction for f-oh exchange of biotite or sericite with hydrothermal fluid can be written as: oh(mica) + hf(fluid) = f(mica) + h2o(fluid) (1) if the f and oh mix ideally on the hydroxyl sites, the equilibrium expression is: log k = log (xf/xoh)mica + log (fh2o/fhf)fluid (2) where x denotes mole fraction and f is fugacity. experimental equilibrium constants for exchange reactions have been applied to natural micas of variable composition by parry et al. (1984) and gunow et al. (1980) using the following constants: log kbiotite = 2100/t + 1.523(xphlogopite) + 0.416(xannite) + 0.079(xsiderite) (3) and log ksericite=2100/t+1.523(xmg) + 0.4l6(xfe) 0.l l(xal) (4) combination of exchange reactions and equilibrium constants for these two micas produces a relationship between the mica independent of temperature and fluid composition. which can be used to evaluate exchange equilibria between the hydrothermal mica pairs. ohbiotite + fsericite = fbiotite + ohsericite (5) log k(biotite+sericite)= 1.523 (xphlogopite-xmg+0.416(xannite-xfe) +0.079 (xsericite 0.11 xal) (6) log k = log (xf/xoh) biotite + log (xoh/xf) sericite (7) equilibrium constants calculated from f-oh content of the sericite-biotite pairs (equation 7) produce values ranging between 0.61-1.12 and an average of 0.82 (idrus, 2005). 3.5 variation in halogen fugacity ratios the fugacity ratios of [h2o] and [hf] as well as [h2o] and [hcl] of hydrothermal fluids were calculated using the equations from (munoz, 1992) which are based on the revised coefficients for fcl-oh exchanges between the biotite and the fluid (zhu and sverjersky, 1991, 1992). our results suggest that the ratios increase systematically to the outer alteration zones. by using the same equations (zhu and sverjersky, 1991, 1992), the halogen fugacity ratios of fluids based on the sericite chemistry have also been computed and show an increase towards the outer (late) alteration zones (fig 7). fig 7. fugacity ratios of sericite increasing from inner to outer part of alteration zones. calculation based on forming temperatures at 510, 475, 360 and 250°c for the early, transitional and late alteration zones, respectively (temperature data from idrus, 2005). 3.6 halogen chemistry used for vector to ore the concentration of halogen fluorine and chlorine in rocks might provide an indication of mineralization and thus find utility as an exploration tool. the f and cl used in exploration has limited to lithogeochemical studies. due to availability of epma analysis, nowadays, the f and cl studies are more concentrated on hydrous minerals, including biotite and sericite in the rocks, both barren and mineralized rocks. a strong correlation between the f and cu contents of biotites in mineralized plutons from basin and range province, usa has been described by (parry and jacobs, 1975). the high content of f in biotites at casino cu-au-mo porphyry deposit (canada) and lar cu-mo porphyry deposit (iran), respectively is strongly associated with potassic and phyllic alterations, in which high copper-gold mineralization occurred (selby and nesbitt, 2000; moradi et al., 2016). idrus a./ jgeet vol 03 no 01/2018 37 fig 8. the fluorine content of biotite and sericite regularly increase toward central deposit (potassic). fig 9. water content of both biotite and sericite decreased toward central deposit fig 10. a positive correlation between fluorine (f) content in biotite and bulk concentration of copper (cu) in corresponding altered rocks (idrus, 2005). fig 8 shows a compositional variation of fluorine in biotite and sericite at the batu hijau deposit. the f content decrease systematically from inner part of the deposit which is represented by early biotite (potassic) zone where the main copper-gold is hosted, to the outer part of the deposit. however, chlorine in both sericite and biotite from each of the alteration zones shows a relative similar concentration, which suggests that it is not suitable to be used in identification of the alteration zones associated with strong coppergold mineralization. the latest result has also been observed at other deposits worldwide, for instance, the casino porphyry deposit, canada (selby and nesbitt, 2000), dalli porphyry deposit (ayati et al., 2008), kahang porphyry deposit, iran (afshooni et al., 2013) and dexing porphyry deposit, se-china (bao et al., 2016). in addition, h2o content of the biotite and sericite also exhibits a systematic increase outward which may suggest an increase the role of meteoric water in alteration toward outer part of the deposit (fig 9). the variation of water content may also provide a possible geochemical exploration tool in vectoring to ore for the copper porphyry deposits. the fluorine content of biotite in rocks and bulk concentration of copper from the corresponding rocks indicates a positive correlation (fig 10). copper concentration of the altered-rocks increases with an increase of fluorine content of the biotite in the rocks. the highest fluorine and copper contents occur in the central early biotite (potassic) alteration zone and decrease to the outer alteration zones of the porphyry deposit. the central biotite zone contains relative higher copper (fig 10) compared to average grade of copper in sw pacific porphyry deposits (~0.52%) (titley and beane, 1981; cooke et al., 1998; cooke et al., 2005). 4. conclusions the high concentration of halogen, particularly fluorine in hydrothermal micas (biotite and sericite) is strongly associated with central orebearing biotite (potassic) alteration zones in copper porphyry systems. this may imply the important role of halogen particularly fluorine and chlorine in hydrothermal transportation of copper and gold in form of halogen copper and gold complexes. the fluorine content decreases systematically toward the outer part of the deposit. however, the chlorine content of biotite and sericite shows unsystematic variations crossing those alteration zones, suggesting it is not suitable to be used for vector to ore in exploration. the systematic compositional variation of fluorine and h2o contents in the hydrothermal micas might provide a possible geochemical tool in vector to ore for porphyry copper-gold deposits. 5. acknowledgements this study was fully facilitated by institute of mineralogy and economic geology, rwth aachen university, germany. sincere gratitude goes to prof. dr. franz michael meyer and staff members for their discussion and collaboration. the author is also thankful to newmont nusa tenggara which gave permission and facilitated the field works. thomas derich as well as dr. annemarie wiechowski and roman klinghardt are thankful for sample preparation and assistances for electron microprobe analysis, respectively. valuable longdistance discussion on sericite chemistry with professor william t. parry (university of utah, usa) was very appreciated. this research project was made possible through financial support from daad germany. references afshooni, s.z., mirnejad, h., esmaeily, d., asadiharoni, h., 2013. mineral chemistry of hydrothermal biotite 38 idrus a./ jgeet vol 03 no 01/2018 from the kahang porphyry copper deposit (ne isfahan), central province of iran. ore geol. rev. 54, 214 232. ayati, f., yavus, f., noghreyan, m., haroni, h.a., yavuz, r., 2008. chemical characteristics and composition of hydrothermal biotite from the dalli porphyry copper prospect, arak, central province of iran. mineral. petrol. 94, 107 122. bao, b., webster, j.d., zhang, d-h., goldoff, b.a., zhang, rz., 2016. compositions of biotite, amphibole, apatite and silicate melt inclusions from the tongchang mine, dexing porphyry deposit, se china: implications for the behavior of halogens in mineralized porphyry systems, ore geol. rev. 79, 443-462. clode, c., proffett, j., mitchell, p., munajat, i., 1999. relationships of intrusion, wall-rock alteration and mineralisation in the batu hijau copper-gold porphyry deposit. proceedings pacrim congress 1999, bali-indonesia, 485-498. cooke, d.r., hollings, p., walshe, j.l., 2005, giant porphyry deposits: characteristics, distribution, and tectonic controls, econ. geol. 100, 801-818. garwin, s.l., 2002. the geologic setting of intrusionrelated hydrothermal systems near the batu hijau porphyry copper-gold deposit, sumbawa, indonesia: global exploration 2002, integrated methods for discovery, colorado, usa, society of economic geologists special publication 9, p. 333366. gammons, c.h., and williams-jones, a.e., 1997. chemical mobility of gold in the porphyry-epithermal environment: econ. geol. 92, 45-59. gunow, a.j., ludington, s., munoz, j.l., 1980. flourine in micas from the henderson molybdenite deposit, colorado. econ. geol. 75, 1127-1137. idrus, a., 2005. petrology, geochemistry and composional changes of diagnostic hydrothermal mineral within the batu hijau porphyry coppergold deposit, sumbawa island, indonesia. doctor dissertation, rwth aachen university, 352 p. mitchell, p.a., proffett, j.m., dilles, j.h., 1998. geological review of the batu hijau porphyry copper-gold deposit, sumbawa island, indonesia. unpublished newmont nusa tenggara company final report, 164 p. moradi, r., boomeri, m., bagheri, s., nakashima, k., 2016. mineral chemistry of igneous rocks in the lar cumo prospect, southeastern part of iran: . 25, 418-433. munoz, j.l., 1984. f-oh and cl-oh exchange in micas with applications to hydrothermal ore deposits. in reviews in mineralogy, bailey, s.w., eds., 13, 469-494. munoz, j.l., 1992. calculation of hf and hcl fugacities from biotite compositions: revised equations. geological society of america, abstract programs 24, a221. munoz, j.l., ludington, s.d., 1974. flouride-hydroxil exchange in biotite. am. jour. sci. 274, 396-413. newmont nusa tenggara corp., 2002. first quarter 2002 hydrothermal alteration compilation map of the batu hijau deposit. unpublished internal report. parry, w.t., ballantyne, j.m., jacobs, d.c., 1984. geochemistry of hydrothermal sericite from roosevelt hot springs and the tictic and santa rita porphyry copper systems. econ. geol. 79, 72-86. parry, w.t., jacobs, d.c., 1975. flourine and chlorine in biotite from basin and range plutons. econ. geol. 70, 554-558. priowarsono, e., maryono, a., 2002. structural relationships and their impact on mining at the batu hijau mine, sumbawa, indonesia: prosiding ikatan ahli geologi indonesia (iagi), pertemuan ilmiah tahunan ke xxxi, surabaya, 1-11. sarjoughian, f., kananian, a., ahmadian, j., murata, m., 2015. chemical composition of biotite from the kuh-e dom pluton, central iran: implication for granitoid magmatism and related cu au mineralization, arab j geosci. 8, 1521 1533. selby, d., nesbitt, b.e., 2000. chemical composition of biotite from the casino porphyry cu-au-mo mineralisation, yukon, canada: evaluation of magmatic and hydrothermal fluid chemistry. chem. geol., 171, 77-93. shinohara, h., 1994. exsolution of immiscible vaper and liquid phases from a crystallizing silicate melt: implications for chlorine and metal transport: geochim. et cosmochim. acta, 58, 5215-5221. siahcheshm, k., calagari, a.a., abedini, a., lentz, d.r., 2012. halogen signatures of biotites from the maher-abad porphyry copper deposit, iran: characterization of volatiles in synto postmagmatic hydrothermal uids. int. geol. rev. 54, 1353 1368. titley, s.r., beane, r.e., 1981. porphyry copper deposits; part i, geologic settings, petrology and tectogenesis, in skinner, b.j., eds., econ. geol. 75 th anniversary volume, 214-235. zhang, w., lentz, d.r., thorne, k.g., mcfarlane, c., 2016. geochemical characteristics of biotite from felsic intrusive rocks around the sisson brook w mo cu deposit, west-central new brunswick: an indicator of halogen and oxygen fugacity of magmatic systems, ore geol. rev. 77, 82 96. zhu, c., sverjersky, d.a., 1991. partitioning of f-cl-oh between minerals and hydrothermal fluids. geochim. et cosmochim. acta, 55, 1837-1858. zhu, c., sverjersky, d.a., 1992. partitioning of f-cl-oh between biotite and apatite. geochim.et cosmochim. acta, 56, 3435-3467. http://www.sciencedirect.com/science/journal/01691368 1. introduction 2. analytical methods 3. results and discussion 3.1 biotite petrography 3.2 sericite petrography 3.3 biotite and sericite chemistry 3.4 f-oh exchange of biotite-sericite pairs 3.5 variation in halogen fugacity ratios 3.6 halogen chemistry used for vector to ore 4. conclusions 5. acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 2 2021 alfadli et al./ jgeet vol 6 no 2/2021 74 research article resistivity data modeling for subsurface volcanostratigraphy construction of cibadak sub-watershed, bogor, west java, indonesia. muhammad kurniawan alfadli1, undang mardiana1, nanda natasia1, febriwan mohammad1, deden zaenudin mutaqin1 1faculty of geological engineering, padjadjaran university, sumedang, west java 45363, indonesia. * corresponding author : m.kurniawan@unpad.ac.id tel.:+62-85669298592; fax: +62-22-7796545 received: oct 29, 2018; accepted: may 20, 2021. doi 10.25299/jgeet.2021.6.2.2274 abstract in mt. salak, there are six volcanic facies divided by eruption time seen from geomorphology data analysis and to identified the subsurface layer dc resistivity method is applied. beside resistivity, geostatistical parameters also influence the result model interpretation, so for obtain best model correlation parameters such as tilting, surfacing, variogram, grid method, and logar ithmic distribution is applied. using 18 points of acquisition data subsurface model is produce and then section model made to describe vertical resistivity distribution then correlated with facies lithology model. based on that, produce three facies resistivity type namely: 0 – 100 ohm.m (low resistivity value) interpreted as pyroclastic material composed as tuff and breccia that lies under lava. 100 – 300 ohm.m (medium resistivity value) interpreted as breccia lithology type. harder that pyroclastic material due to by this product is avalanches of lava. and >300 ohm.m (high resistivity value) interpreted as lava lithology that lies at high elevation and the hardest lithology in this area. from the model, pyroclastic layer that is modeled found at low elevation and based on the direction it described as oldest facies layer, but at the bottom of this layer lies high resistivity value that unknown product. it can be mt. pangrango product due to at low e levation predicted as combine area product from product of mt. salak and pangrango. high resistivity value show lava lithology and lava facies located in high elevation and medium resistivity describe breccia lithology as avalanche product of lava (youngest pyroclasti c facies) and found at 500 – 100 meters msl. keywords: resistivity, volcanostratigraphy, modeling, mt. salak, geostatistics parameters, correlation. 1. introduction mount salak is a stratovolcano mountain located in west java which have much potential such as geothermal (hochstein and sudarman, 2008). eruption type is vulcanian due to found intermediate composition such as andesite lithology (parfitt and wilson, 2008). this eruption type made high mass of material product and needed specified model to imaging the facies layer. based on previous research (aprilina et al., 2015; endyana et al., 2016; hochstein and sudarman, 2008; natasia et al., 2018; stimac and sugiaman, 2000). salak mt. have complexity geology start from lithology type until structural geology. based on geological result, there are six volcanic facies divided by eruption time seen from geomorphology data analysis (scheidegger 1925-, 1970). each facies consist of several lithology type, such as pyroclastic product and lava (natasia et al., 2018). to proven subsurface facies needed specified model to illustrated the facies and presence of the geological structure. from previous study, dominant fracture have relatively north-south trend (endyana et al., 2016). to enhancement subsurface result, dc resistivity section will be produced to layering facies and structural geology based on previous study case (kearey et al., 2002; telford et al., 1990). 2. method 2.1 resistivity method resistivity described specially properties of volcanic rock and used to distribution and configuration the product (zou, 2013). one of geophysical method to obtained resistivity data is vertical electrical sounding (ves) (kearey et al., 2002; telford et al., 1990). ves method utilize resistance of the earth multiplied with geometry electrical spread factor (k). fig 1. resistivity parameters 𝑅 = 𝑉 𝐼 = 𝜌 ( 𝐿 𝐴 ) (1) http://journal.uir.ac.id/index.php/jgeet alfadli et al./ jgeet vol 6 no 2/2021 75 the total resistance r may be obtained experimentally through ohm’s law, r = v/i, where v is the potential difference between the ends of the cylinder and i is the total current flowing through the cylinder. edge effects are not considered. the resistivity of the material, an intrinsic property of the material, is then related to experimentally measured extrinsic parameters by 𝜌 = 𝑉 𝐼 ( 𝐴 𝐿 ) = 𝑅𝑎𝑝𝑝𝐾 (2) in eq. 2 , the resistivity is given by the product of the ‘‘apparent resistance’’ rapp (v/i) and a ‘‘geometric factor’’ k = (a/l) that carries information about the geometry of the cylinder. this type of product of an apparent resistance and a geometric factor will appear again when the resistivity of the ground is determined (herman, 2001). while for electrode spread used schlumberger electrode configuration (figure 2), the spaced of current electrode further apart than potential (kearey et al., 2002; telford et al., 1990). figure 2 shows a general linear electrode configuration fora typical resistivity survey. all four electrodes are chosen to be in a straight line in the present work for simplicity. in general, the electrodes are not restricted to being collinear, although solving the electromagnetic field equations that accompany such arrays becomes more difficult. the ac current source is in series with an ammeter, which measures the total current i going into the ground through the electrodes at points a and b. a voltmeter attached to the two electrodes at points m and n measures the potential difference v between these points. by convention, the electrodes at the four surface points a, m, n, b are also named a, m, n, b. the ratio (v/i) obtained is the apparent resistance for the entire subsurface. section below will show how to obtain the appropriate geometric factor that, along with the apparent resistance, will construct the apparent resistivity (𝝆) (herman, 2001). fig 2. schlumberger electrode spread the electric potentials measured at m and n in the general linear array of fig. 2 are superpositions of the potential of eq. 2 due to each of the two source electrodes located at a and b. with the distances between the electrodes given by am, mb, etc., and v = 0 infinitely far from the current source, the potentials at m and n are given by 𝑉𝑀 = 𝜌𝑙 2𝜋 ( 1 𝐴𝑀 − 1 𝑀𝐵 ) (3) and 𝑉𝑁 = 𝜌𝑙 2𝜋 ( 1 𝐴𝑁 − 1 𝑁𝐵 ) (4) the total potential difference between the electrodes m and n is thus 𝑉𝑀𝑁 = 𝑉𝑀 − 𝑉𝑁 = 𝜌𝑙 2𝜋 [( 1 𝐴𝑀 − 1 𝑀𝐵 ) − ( 1 𝐴𝑁 − 1 𝑁𝐵 )] (5) this may be rearranged to yiel 𝜌 = 𝑉𝑀𝑁 𝐼 𝐾 (6) where 𝐾 = 2𝜋 [( 1 𝐴𝑀 − 1 𝑀𝐵 ) − ( 1 𝐴𝑁 − 1 𝑁𝐵 )] (7) is the ‘‘geometric factor’’ that will acquire a particular value for a given electrode spacing (herman, 2001). 2,2 geostatistical method simple linear interpolation is applied to made subsurface modeling from resistivity data. the geostatistical method is used to estimated intermediated point between observation processing data. linear interpolation is reasonable to apply due to spare of original data and estimated value is placed between each pair of observation data (davis, 1990). prediction error are accompanied estimated prediction to satisfy strict statistical assumption. kriging (plain geostatistics) is used to predicted assumption model to define subsurface model based on resistivity model (hengl, 1986). beside kriging parameters, another parameter influences the model are warp algorithm calculation, logarithmic model, polygon barrier, and top and bottom boundary. algorithms such as the horizontal lithoblending strongly bias the interpolation in a horizontal fashion. the "warp" option introduces structure while still allowing the modeling to be horizontally biased. logarithmic modeling: helpful for modeling highly anomalous data. if this parameter activated, control point g values are converted to natural logarithms, the model is interpolated, then the nodes are converted back to the original units. the statistical process more complicated but very useful to help produce objective maps, understand the data distribution and error, and depict area that need to revisited (hengl, 1986). experimental variogram influence the anisotropy and correlation between produce model and the data. best type of variogram will be chosen to obtain best model to observe the subsurface. 3. data 3.1 resistivity data available data are 18 point of ves acquisition. the data has random distribution along cibadak watershed boundary (figure 3). beside the acquisition data, topography data also using for modeling as top surface boundary of the modeling and tilting estimation for modeling input. topography data extracted from dem (digital elevation model) with 38x38 m grid. although it does not have good vertical resolution, this data still could be used for analysis. 3.2 geological background for geology data, it came from previous study surrounding this area which located in cihideung and ciparakali (natasia et al., 2018). regional information be references to validated the previous study for lithological information. from geomorphology information, this area separated in nine geomorphology type that contain two type of lithology, namely pyroclastic and lava (figure 4). the geomorphology analytic process separated with three analysis, namely morphography, morphometry and morphogenetic which shown in figure 4. 76 alfadli et al./ jgeet vol 6 no 2/2021 fig 3. ves point data distribution geomorphology unit color symbol morphography morphometry morphogenetic volcanic facies steep volcanic lava iii slope upper slope, subparallel river steep volcanism, weathered, erosional lava gently steep pyroclastic v slope upper slope, subdendritik river gently steep volcanism, weathered, erosional pyroclastic steep volcanic lava i slope upper slope, subparallel river steep volcanism, weathered, erosional lava steep volcanic lava ii slope upper slope, subparallel river steep volcanism, weathered, erosional lava and pyroclastic gently steep pyroclastic iv slope lower slope, subdendritik river gently steep volcanism, weathered, erosional pyroclastic tilted pyroclastic ii slope lower slope, subdendritik river tilted volcanism, weathered, erosional pyroclastic gently flat pyroclastic i slope lower slope, subdendritik river gentrly flat volcanism, weathered, erosional pyroclastic gently steep lava ii slope upper slope, subparallel river gently steep volcanism, weathered, erosional lava gently steep pryroclastic ii slope lower slope, subparallel river gently steep volcanism, weathered, erosional pyroclastic fig 4. geomorphology analysis in cibadak watershed (natasia et al., 2018) figure 4 shows that steep slope area found approaching the summit of mt salak and domination lithology is lava. while, for pyroclastic lithology dominated found at declivous area and far from the summit. at this area found six facies of lithology separated by lithology and elevation combination data. facies 1: lapilli, facies 2: tuff breccia and tuff lapilli, facies 3: lava, facies 4: tuff breccia, facies 5: lava, facies 6: tuff breccia. figure 5 shows the facies correlation from two river at cibadak watershed. lava be as separator of eruption time, and older lithology layer bellow the lava is pyroclastic lithology. alfadli et al./ jgeet vol 6 no 2/2021 77 fig 5. facies correlation between two river at cibadak watershed (natasia et al., 2018) 4. result 4.1 processing result based on processing step, true resistivity value that modeled from 5 – 2366 ohm.m which can describe several lithology. the dominant curve pattern is higher along with increasing depth but there is a lowing pattern in some parts of depth, this shows that the curve pattern in this area are forms a combined curve pattern of several quantitative interpretation curves (telford et al., 1990). figure 6 shown the processing result with block model that illustrated the true resistivity value. from the true resistivity model will be produce isoresistivity map that describe true resistivity value distribution. map will be guide to interpreted the volcanic facies based on pattern distribution of true resistivity value (figure 7). fig 6. processing result of ves data after guiding by map, range resistivity value for each facies will be divided with several depth. figure 6 shows that at depth from 0 – 10 meters, found transformation shape of the distribution pattern of true resistivity values, so that classified as a limit of interpretation depth. depth of 10 meters develop as boundary between a depth of 0 – 10 meters with depth of 25 – 75 meters. in part at 10 meters it is interpreted as a part of its own volcanic facies separating the two depths with limited 20 meters depth. whereas started from depth 75 – 200 meters is shown the same pattern of distribution of values but different geometry. this is a reference interpretation that a depth of 75 – 200 meters develop as one type of volcanic facies. 78 alfadli et al./ jgeet vol 6 no 2/2021 fig 7. iso-resistivity map 4.2 modeling result for obtain the best model for define the subsurface, several methods of variogram are applied. the references variogram is chose must have good correlation value and low anisotropy value to reduce the bias model in no data area. for this area gaussian with nugget variogram is chosen due to has best correlation value (0.92) and low anisotropy value (0.52), while another method has lower anisotropy value than this method, the correlation value is more attention due to in this parameter describe the relationship of the data and the model. based on the variogram result, the section is produced to illustrated the resistivity distribution in vertical and lateral. to obtain the resistivity range of the volcanic facies, correlation between the section and geological information is needed. outcrop data in cibadak watershed composed by pyroclastic layer and lava. pyroclastic layer is dominated in this section and andesitic lava only as intercalated layer flanked by pyroclastic (figure 8). from the geological stratigraphy, tuff-breccia/pyroclastic materials located in low elevation from 400 – 800 meters msl and interpreted as oldest facies. lava andesitic found at higher elevation and interpreted as the younger materials than pyroclastic which reveal at low elevation. the youngest facies in stuy area are pyroclastic material that is reveal above lava and is an avalanche of lava material at a higher elevation. this facies lithology dominated by breccia and found at 900-1000 meters msl. fig 8. cibadak watershed outcrop volcanostratigraphy. fig 9. cibadak watershed facies based on outcrop data alfadli et al./ jgeet vol 6 no 2/2021 79 arrangement of this stratigraphy are produced from outcrop data in different elevation. and then, to correlated with resistivity model, the geological section also produced (figure 10) and then compared with resistivity to obtain resistivity range and applied to geostatistics model. from figure 9 that illustrated geology facies in cibadak watershed, resistivity range value that can describe subsurface correlated with geological surface condition presented in table 1. section map show at figure 12. table 1. range resistivity from cibadak watershed correlation. no resistivity range (ωm) range classification description 1 0 – 100 low resistivity value interpreted as pyroclastic material composed as tuff and breccia that lies under lava. 2 100 – 300 medium resistivity value interpreted as breccia lithology type. harder that pyroclastic material due to by this product is avalanches of lava 3 >300 high resistivity value interpreted as lava lithology that lies at high elevation and the hardest lithology in this area. the resistivity range for interpretasion is obtain from data correlation between processing modeling and geology outcrop data. in area with resistivity value dominant found at near surface and east area, dominated by pyroclastic lithology. the medium and high resistivity value which dominant found at medium depth (25-200 m) and west research area is correlated with breccia and lava lithology (figure 6). a. b. fig 10. geostatistical cross section model (a) and interpreted model combine with geology for facies construction (b). fig 11. map of section resistivity model the urgency for made the profile is to shown the resistivity modeling distribution and correlated with geological information that already made by previous research. this modeling profile shown at figure 10 above. all calculated model controlled by geostatistical parameters that applied. for obtain fit model with geology, tilting distribution value must be applied caused the data is controlled by elevation and directional. due to oldest facies found in low elevation, so the tilting applied is 3˚ perpendicular with elevation to obtain best model. from this model, pyroclastic layer that is modeled found at low elevation and based on the direction it described as oldest facies layer, but at the bottom of this layer lies high resistivity value that unknown product. it can be mt. pangrango product due to at low elevation predicted as combine area product from product of mt. salak and pangrango (endyana et al., 2016). high resistivity value show lava lithology and lava facies located in high elevation and medium resistivity describe breccia lithology as avalanche product of lava (youngest pyroclastic facies) and found at 500 – 100 meters msl. most of resistivity model from cibadak cross-section show best correlation with geology model with several parameters that applied. 5. conclusion in cibadak watershed there are several variation lithology that can be classified be four facies type. the oldest facies are composed by tuff and breccia lithology and illustrated with low until medium resistivity value which located in low elevation (below 500 meters msl). this facies in geology, separated with two facies type but in resistivity can’t separate due to data resolution which bias to separate the model. then the lava lithology classified as younger (ωm) 80 alfadli et al./ jgeet vol 6 no 2/2021 facies than pyroclastic and describe with high resistivity value, it found at high elevation (above 1000 meters msl). the youngest facies is breccia lithology and classified as pyroclastic layer in geology interpretation. this layer is avalanche from lava lithology. in addition, it was also found that the high resistivity values at the bottom of the oldest pyroclastic layer were identified as products from mt. pangrango because at this height it was mixing area of two volcanic products. in addition, the parameters in the modeling greatly influence the final model for the distribution of resistivity values. so, in this model is created tilt distribution of resistivity value of 3 degrees perpendicular to the surface. acknowledgement this research is unpad internal grant which was carried out for the development of unpad human resources, thanks are fully given to padjadjaran university for providing the opportunity to carry out this research. this ackwoledgement also gived to the entire civitas who have supported this research. references aprilina, n.v., satya, d.y., rejeki, s., golla, g., waite, m., 2015. geologic modeling workflow for volcanic hosted geothermal reservoirs: case study from salak geothermal field. world geotherm. congr. 2015 3, 12. davis, j.c., 1990. statistics and data analysis in geology, 2nd ed. john wiley &amp; sons, inc., new york, ny, usa. endyana, c., hendarmawan, sukiyah, e., dharmawan, i.a., 2016. controlling groudwater system by pattern fracture approach in subsurface volcanic deposit: mt.salakmt.pangranggo, west java, indonesia. iop conf. ser. 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wilson, l., 2008. fundamentals of physical volcanology, bull. volcanol. scheidegger 1925-, a.e., 1970. theoretical geomorphology [by] adrian e. scheidegger. springer-verlag, berlin. stimac, j., sugiaman, f., 2000. the awi 1-2 core research program: part i , geologic overview of the awibengkok geothermal field, indonesia. world geotherm. congr. 2000 2221–2226. telford, w.m., geldart, l.p., sheriff, r.e., 1990. applied geophysics, 2nd ed. cambridge university press, cambridge. https://doi.org/doi: 10.1017/cbo9781139167932 zou, c., 2013. volcanic reservoirs in petroleum exploration, first edit. ed, volcanic reservoirs in petroleum exploration. elsevier. https://doi.org/10.1016/c2011-0-06248-8 © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 192 cahyaningsih, c. et al./ jgeet vol 03 no 04/2018 research article petrography, geology structure and landslide characterization of sumatra fault deformation: study case in km 10-15 highway, koto baru sub district, west of sumatra catur cahyaningsih 1,* , puja fransismik crensonni 1 , yogi aditia 1 , adi suryadi 1 , tiggi choanji 1 , dewandra bagus eka putra 1 1 geological engineering department, faculty of engineering, universitas islam riau, jln. k.h nasution no. 113 perhentian marpoyan, 28284, pekanbaru, indonesia * corresponding author : caturcahyaningsih@eng.uir.ac.id tel.: +6282284013121 received: august 24, 2018; accepted: november 30, 2018. doi: 10.24273/jgeet.2018.3.4.2062 abstract research area is around tanjung balik, koto baru sub base, lima puluh kota district, west sumatra province. located along the highway km 10-15 riau '' bt. the purpose of research to identify petrography, microstructure, types of landslides and the geological condition. the methods using polarization microscope, stereography, landslide identification survey and geological mapping. the result of study shows the petrography analysis of lithology of study area are classified into three types of rocks are feldspathic greywacke, lithic arenite, and slate. microstructures trending system show the foliation structure that is relatively southeast-northwest. types of landslide which dominates in the research area are debris avalanche and translational landslide. geological analysis show some of rock units are classified into two units: sandstone unit and slate unit. sandstone unit spread in the northern part of the study area, while slate unit spread in the southern part of the study area. the characteristics of these rocks showed pematang formation. keywords: landslide, petrography, microstructure, geology 1. introduction location is administratively in the lima puluh kota district of west sumatra province. the geographical position of the research area is located of research area are based on a topographical, the lowest elevation 80 meters above sea level until the highest elevation 345 meters above sea level. the purposes of research to figure out the geological condition, lithology characterization, microstructure patterns and types of landslides to happened in the area of research. definition of landslide is a movement down the slope of the land mass and or rocks making up the slope toward the foot of the slopes, as a result of disruption of the stability of soil or rocks making up the slope. if the land mass dominates the moving masses and it is moving through a field on a slope, in the form of an inclined plane or curved, then the movement is called a landslide (nugraha et al., 2015; taylor et al., 2015; chang and wan, 2015; tacconi stefanelli et al., 2016; margottini et al., 2013; sassa et al., 2014; xu et al., 2015). the factor of the movement on the slope also depends on the condition of rocks and soil making up the slope, geological structure, rainfall, vegetation cover and land use on the slopes, but the outline can be distinguished as natural and human factors (shanmugam, 2015; taylor et al., 2015; kumar et al., 2015; choanji et al., 2018). factor of topography and morphology of the zone located in tanjung balik sub base, lima puluh kota district included into the path of barisan hill (sumatra et al., 2018), which gives effect to the slope of the land is quite high, hydrology rainfall with high intensity and quality of physical-chemical soil, then some of these factors to led speed ground movement occurs (mairizki and cahyaningsih, 2016; cahyaningsih, 2016; yuskar et al., 2017; catur cahyaningsih, arrachim maulana putera, gayuh pramukti, 2018). the geological structure in the form of faulting also resulted in the region's vulnerability to ground motion hazard (samuel et al., 1995; crampin and gao, 2012; fatriadi et al., 2017; dewandra bagus eka putra, yuniarti yuskar, catur cahyaningsih, 2017; shah, 2015; shah, 2013). the sumatra fault zone classified as a highly active fault, which is triggered some geological hazard such as earthquake, tsunami, and landslide. the area in the regional geological map sheet pekanbaru, sumatra, issue 2, scale 1: 250,000, shown in fig 1. the unavailability of small scale maps making it difficult to get more detail information about the http://journal.uir.ac.id/index.php/jgeet cahyaningsih, catur et al./ jgeet vol 03 no 04/2018 193 geology of the area and geological structures, especially in west sumatra. this research is essential to aim at more comprehensively data about lithology, deformation; microstructure has been working in the research area, which causes frequent landslides. the research area consists of four formation namely: kuantan formation (puku), bahorok formation (pub), pematang formation (tlpe) and sihapas formation (tms), the stratigraphic sequence of central sumatera basin shown in table 1. a. kuantan formation (puku) the oldest rocks exposed in the study area is metasediments and slate spread to the southwest of research area, which consists of slate, quartzite and meta-quartz arenite, this formation age paleozoic permian carbon. mesozoic paleozoic rock , consisting of meta-volcanic and hornfel, slate and a bit of old limestone with age permian carbon to jurassic. these formations are spread in the southwestern of research area (a. j. barber, m. j. crow, 2005). b. formation bahorok (pub) bahorok formation composed of metamorphic wacke, slate, metamorphic quartz sandstone, siltstone, metamorphic conglomerate, which suspected carbon to early permian age (a. j. barber, m. j. crow, 2005). c. pematang formation (tlpe) pematang formation (tlpe) is a bed of sedimentary central sumatra basin, the age is middle eocene to oligocene, which is precipitated as unconformity bedrock on the top. this formation consists of red and mottled mudstone, conglomerate, breccia and sandstones conglomerate deposited in fluvial lacustrine environment (a. j. barber, m. j. crow, 2005). d. formation sihapas (tms) sihapas formation (tms) is the early miocene consists of quartz sandstone, shale carbonaceous siltstone, and conglomerates (a. j. barber, m. j. crow, 2005). research area is part of the central sumatra basin, one of the three basins sumatra back-arc basin formed during the period of early tertiary (eocene oligocene), consists of a series of blocks of horst and graben formed in response to the extension behind the arc (a. j. barber, m. j. crow, 2005). the thickness of the sediments in the basin reached 2.5 3 km, consists of sequences sync rift and post-rift pemantang group in eocene oligocene, early miocene age is sihapas group, petani group is middle miocene pliocene and pliopleistocene of minas formation. this basin with the north sumatra basin is separated by asahan arc, while the south sumatra basin separated by tiga puluh high (widayat et al., 2016; natalie et al., 2015; de coster, 1974; cahyaningsih et al., 2018). structures of the research area characterized by a pattern of blocks transcurrent fracture and fault shows in fig 2. fault blocks system have a parallel orientation with the north-south form a series of horst and graben (a. j. barber, m. j. crow, 2005). the pattern of existing structures in central sumatra basin is the result of at least three separate major tectonic phases, namely orogenesis of middle mesozoic, tectonics of late cretaceous-early tertiary, and orogenesis of plio pleistocene (de coster, 1974; a. j. barber, m. j. crow, 2005). fig 1. map show geology regional of research area. central sumatra basin has two sets of faults which has trending pattern north-south and northwestsoutheast. north south fault trend estimated age in paleocene, while northwest-southeast fault trend estimated in late neocene age. both sets of the fault repeatedly reactivated throughout the tertiary by the forces at work (holis and sapiie, 2012; de coster, 1974; hidayat et al., 2016; natalie et al., 2015; joseph e. laing, 1994). table 1. stratigraphic sequence column of central sumatera basin, red box show formation of research area. there are seven types of landslides, namely: translational landslides, rotational landslide, block movement, soil creep, topple, debris flows and complex type (hungr et al., 2014). from six types of landslides, translational and rotational landslide types most 194 cahyaningsih, catur et al./ jgeet vol 03 no 04/2018 common in indonesia, it is because a high degree of rock weathering, so that the soil is formed thick enough (umitsu et al., 2007; santoso et al., 2013; yaman et al., 2013; cahyaningsih et al., 2018; catur cahyaningsih, arrachim maulana putera, gayuh pramukti, 2018). figure 2. framework for regional tectonic central sumatra basin, red box show research location 2. method the object of research are the slopes that failed along riau-west sumatra highway km 10-15. type of lithology, coordinates of landslides location, geology structure, type and geometry landslides become the focus of the research object. lithological sampling is orientation sample. the methods are consists of the polarization microscope, stereo net and landslide identification survey and geological mapping. data processing phase consists of laboratory and analytical work in the studio. the analysis in the laboratory is petrographic analysis. while the analysis is done in the studio include geological mapping, analysis of microstructures (monica price & walsh, 2005; george, 1943). geological mapping method is plotting by gps (the global positioning system) and a description of the type of lithology, texture, grain size, roundness, sorting, fabric, structure(aydin, 2010), and mineral composition. the petrographic analysis aims to determine the volumetric amount of the composition to determine precisely the name, and rock texture, this method using the polarizing microscope (mennell, 1913; hughes, 1982). under a microscope, the percentage of grain composition is done by point counting method. thin section of clastic sedimentary rocks are encountered in the study area were classified using the classification of clastic sedimentary rock (fig 3) which makes the percentage of some components such as grains of quartz, feldspar, rock fragments, matrix (fine material) and cement solution; george, 1943; correns et al., 1969; mairizki and cahyaningsih, 2016; cahyaningsih et al., 2018). metamorphic rocks are classified based on both composition and texture (grain size, mineral composition, presence or absence of foliation) (frost and frost, n.d.), shown in table 2. the stereo net method use rose diagram, the data are based on thin section of rock samples, which taken by oriented. reading microstructure as foliation analyzed to get directions trend (çelik, 2013; aydin, 2010; sharma et al., 2015; nlomngan et al., 2013). methods to determine the type of landslide using varnes classification 1977; hungr et al., 2014), which divides into seven types of landslides are: translational slides, avalanches rotation, block movement, rock fall, soil creep, and complex landslide, are shown in table 3. weathered rock profile description do when analyzing types of landslides. weathering is the process of changing rocks into the soil, physical or mechanical and chemical processes (decomposition) (yaman et al., 2013; onyelowe and okoafor, 2012; vinay and mahalingam, 2015; cahyaningsih, 2016; cahyaningsih et al., 2018; yaman et al., 2013; onyelowe and okoafor, 2012; vinay and mahalingam, 2015) (cahyaningsih, 2016; cahyaningsih et al., 2018). decomposition process can lead to new minerals (anderson et al., 2002) 3. result lithology constituent in the research area was classified into 3: feldspathic greywacke, lithic arenite, and slate. feldspathic greywacke located at station 2 area of research has the characteristics of fresh color is white gray, weathered color is brownish gray, grain size 1 mm, rather compact, rounded, fine texture, close fabric, well sorted and high porosity, shown in fig 4. the thin section shows the optical characteristics color of plane polarized light (ppl) is dirty white, on cross-polarized light (xpl) color is grayish black, grain shape is rounded, well sorted, closed fabric, mineral composition consists of quartz, feldspar, rock fragments and cement, with amount 45%, 35%, 5% and 15% respectively, while other minerals include of accessory mineral less than 1%, this rock classified as feldspathic greywacke, shown in fig 5. fig 4. geological photo shows station 2 a) feldspathic greywacke outcrop b) feldspathic greywacke outcrop from near angle c) hand specimen of feldspathic greywacke. cahyaningsih, catur et al./ jgeet vol 03 no 04/2018 195 fig 5. photomicrograph shows the results of petrographic thin section of feldspathic greywacke at station 2. lithic arenite at station 3 of research area shows the characteristics of fresh-colored grayish white, the weathered-colored is grayish-brown, grain size is medium, compaction is rather compact, rounded, medium texture, the fabric is closed, medium sorted and high porosity, shown in fig 6. fig 6. geological photo shows station 3 a) lithic arenite outcrop b) lithic arenite outcrop from near angle c) hand specimen of lithic arenite. the thin section shows the optical characteristics color of plane polarized light (ppl) is dirty white, on cross-polarized light (xpl) color is brownish black, the mineral composition consists of quartz, feldspar, rock fragments, cements, with amount 40%, 25%, 25%, and 10% respectively. as the main mineral is quartz and feldspar. this rock classified into lithic arenite, shown in fig 7. slate located at station 7 areas of research shows the characteristics the fresh color is reddish brown, the weathered color is dark brown, the grain size is very fine, derived from metamorphic mudstone, the texture is relict tar, the structure is foliation and there are geological structures such as joint. slate outcrop can be seen in fig 8. the thin section of slate shows the optical color characteristics of plane polarized light (ppl) is dark brown, on cross-polarized light (xpl) color is brown, composition of mineral consist of clay, silt and sand, with amount 70%, 15% and 5% respectively. the grain size is 0.2mm. photomicrographs showed a low degree metamorphism indication is foliation called slaty. the name of rock called slate, shown in fig 9. fig 7. photomicrograph shows the results of petrographic thin section of lithic arenite at station 3. fig 8. geological photo shows station 7 a) slate outcrop b) slate outcrop from near angle c) hand specimen of slate. fig 9. photomicrograph shows the results of petrographic of slate at station 7. analysis of slate microstructure with 40 times magnification using a polarization microscope showed 196 cahyaningsih, catur et al./ jgeet vol 03 no 04/2018 the presence of foliation structure with a distance of 0.1 mm, the orientation of azimuth direction with average and back azimuth direction average is showed in fig 10a. relative trend pattern is northwestsoutheast, which have same direction with sumatra fault zone, shown in rose diagram in fig 10b. the analysis of the negative lineation pattern of the study area which is relatively trend north-west-southeast, this further strengthens the evidence that microstructures are formed by this lineation pattern that has a large influence from the sumatra fault. the analysis is shown as lineation map and rose diagram in fig 14. fig 10. (above) photomicrograph show microstructure analysis of slate at station 7, red line is foliation; (below) rose diagram analysis show trend pattern from northwestsoutheast. slate at 8 stations in the research area showed the presence of the orientation directions of foliation with azimuth back azimuth showed in fig 11 rose diagram analysis show pattern of relative trend is northwest-southeast, can be seen in microstructure analysis of foliation trend patterns at stations 8 and 7 relatively the same direction. microstructure presence caused by the fault, estimated in late neocene age. based on analysis of the type of landslides in research area are classified into two, namely, debris avalanche and translational landslide. material debris avalanche with a mixture of clay and silt moving at relatively high speed, with a steep slope topography. the very high degree of weathering profile reached number 6 in the dominant pattern of relative landslide northwest-southeast. spreads almost 80% throughout the research area, debris avalanche type can be seen in fig 12. fig 11. (above) photomicrograph show foliation microstructure analysis of slate at station 8, red line is foliation structure. (below) rose diagram analysis show northwest-southeast trending pattern. fig 12. photo geology show debris avalanche type in research area fig 13. photo geology show translational landslide in research area. cahyaningsih, catur et al./ jgeet vol 03 no 04/2018 197 translational landslide with the material such as silt and clay moving on slopes gently to undulating, with a degree of weathering profile is very high with profile number is 6. pattern of landslides relatively show trend system between northwest-southeast. spreads almost 20% in the research area, the translational landslide can be seen in fig 13. based on the geological analysis of research area consist of two types of rocks unit, namely slate unit and sandstone unit. sandstone unit classified into two: feldspathic greywacke and lithic arenite. this unit spread in the northern part of the research area, while slate unit spread in the southern part of the research area. those lithologies are interpreted in the study area included in pematang formation, which is part of the formation in central sumatra basin. geological map of the study area can be seen in fig 15 and stratigraphic column of research area consist of slate unit as the oldest and followed by sandstone unit as the youngest rock unit, show in table 5. 4. conclusion based on the analysis, pangkalan koto baru, riausumbar highway kilometer 10-15, it can be concluded that: geologic research area is divided into two types, namely slate units and sandstone units. compose the lithology in research area are feldspathic greywacke, lithic arenite, and slate. microstructure experienced is foliation structure, which has trend is southeastnorthwest, which has influenced by sumatra fault. this type of movement are dominated by debris avalanches and translational landslide type. this landslide mapping needs further research, especially on the riauwest sumatra highway fig. 14. map is showing negative lineament pattern and he lineament trend pattern is 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accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2138 abstract the granite and gneisses rocks are well exposed around toneta, tilwara and chirbatiyakhal region in the lesser garhwal himalaya have less studied which consider as paleoproterozoic age. the granites from toneta area are classified as k-rich peraluminous granite with low na2o varies from 0.74 to 2.4 wt.% and high k2o content varies from 5.0 to 6.91 wt.%. the average al2o3 (12.7 wt.%) in the granite is greater than the total alkalies (na2o+k2o = av. 7.62 wt.%), the tio2 content is low ranging from 0.1 to 0.28 wt. %. in the y + nb rb, y nb, ta + yb rb, and yb ta discrimination diagram of pearce et al. (1984) show that the toneta granites mostly plots within the syn-collision granite fields. this is typical collisional granite. keywords: paleoproterozoic granite, garhwal himalaya, syn-collision granite, geodynamic setting, lesser himalaya 1. introduction to granites have provided a constant focus for controversy among geologists on account of their inherent diversity and their association with very wide spectrum of geological phenomenon since the beginning of the himalayan mountain belt has evolved due to the collision of the eurasian and indian plates and extends along an arc having a convexity towards south (patriat and achache, 1984). it measures for about 2400 km in length with a width of about 320 km. the himalaya is broadly classified as i) sub-himalaya, ii) lesser himalaya, iii) higher himalaya, iv) tethys himalaya, and v) trans himalaya (fig. 1a). lesser himalayan sequence is separated from the higher himalayan crystalline by a deep seated tectonic lineament called main central thrust (mct; heim and gansser, 1939). fuchs and sinha (1978), sinha (1989), thakur (1992), gansser (1993) and saklani (1993) suggest that the mct is not a single thrust in the garhwal region, but composed of three tectonic planes i.e. mct-i, -ii and iii developed by the duplex mechanism of thrust tectonics (fig. 1b; saklani et al., 1991). the extensive work of valdiya (1980) from kumaon himalaya show that several paleoproterozoic granites bodies occur in lesser himalayan sequence and it found all along the 2000 km himalayan belt starting from besham in swat valley (nw himalaya) to the bomdila gneiss in the ne himalaya (islam et al., 2005; phukon et al., 2018 and references therein). the granites occurring in the himalaya are classified in to four groups (islam et al., 2005): i) proterozoic granites (2200 1800 ma; 1400 1200 ma; from lesser and higher himalaya), ii) early paleozoic granites (600 500 ma), iii) intrusive phases of ladakh plutonic complex (102 ± 3 ma and 42 30 ma), and iv) tertiary leucogranites (30 12 ma). granitic gneisses and granitic augen gneisses exposed in the lesser himalayan zone have extended as proterozoic ages (2200 1800 ma; table 1). these rocks from lesser and higher himalaya are considering as part of the peninsular india, and the occurrences of granites from lesser himalayan sequence are well exposed in himachal and garhwal kumaon regions (saklani et al., 1991; saklani, 1993; singh et al., 1998). the outer himalaya and indo-gangetic plain formed, after eroded material from higher himalaya during himalayan orogeny, towards south of lesser himalaya. http://journal.uir.ac.id/index.php/jgeet 30 mishra, s. et al./ jgeet sp vol 04 no 02-2/2019 fig. 1. (a) general tectonic map of himalaya after gansser (1964), and (b) general tectonic map of garhwal himalaya after valdiya (1980). table 1. summarized geochronological ages of himalayan proterozoic granites (after islam et al., 2005; singh et al., 2009). locality age references jeori wangtu 1860 ma miller et al., (2000) wangtu, sutlej 2025 to 2075 ma kwatra et al., (1986) wangtu 1895+64 ma rao et al., (1995) wangtu 1866+10 ma (u-pb zr) singh et al., (1994) magladgad 2068+5 ma (u-pb zr) bandal 1840+0.0027 ma frank et al., (1977) nirath-baragaon 1430+150 ma bhanot et al., (1978) bandal 1220+100 ma bhanot et al., (1979) dhakuri 2315+135 ma pandey et al., (1981) chailli, bhilangna valley 2121+60 ma raju et al., (1982) rihee-gangi, bhilangna valley 1841+86 ma singh et al., (1986) ghuttu, bhilangna valley 1763+116 ma singh et al., (1985) chirpatiyakhal, bhilangna valley 1708+131 ma amritpur 1585+192 ma joshimath-guptakashi 1950+200 ma pandey et al., (1981) naitwar, tons valley 1811+133 ma singh et al., (1986) hanumanchatti, yamuna valley 1972+102 ma bhatwari, bhagirathi valley 2047+119 ma munsiari 1830 to 1890 ma bhanot et al., (1977) rameshwar granite 1820+130 ma trivedi et al., (1984) chiplakot crystalline belt (granite gneiss) 1920.7 ± 4.2 ma phukon et al., (2018) namik 1910+88 ma singh et al., (1985) tawaghat 1906+220 ma almora askot 1620+90 ma powell et al., (1979) askot dharamgarh 1795+30 ma pandey et al., (1981) ramgarh granite 1765+60 ma trivedi et al., (1984) gwaldam granite 1300+80 ma pandey et al., (1981) 1700+70 ma trivedi et al., (1984) lingtse granite, ne himalaya 1678 ma (rb sr whole rock) paul et al., (1996) darjeling sikkim, granite gneiss 1792 ma (pb pb age) bomdila gneiss 1874+24 ma (u pb zr) rao, (1998) 1827+95 ma (u pb zr) mishra, s. et al./ jgeet sp vol 04 no 01-2/2019 31 the lesser himalayan zone comprises paleoproterozoic granite, paleozoic sedimentaries (e.g. slates, phyllites, quartzites) with pene-contemporaneous mafic volcanic (1.83 1.88 ga sm-nd t-chur modal ages; miller et al., 2000). there is a period of felsic volcanism and granite emplacement occurred around 1.86 1.84 ga in nw himalaya. nd model ages for these granitic rocks extend to 2.63 ga, indicating recycling of archean continental crust (miller et al., 2000). still more studies are required especially from garhwal himalaya where limited data are available to set up proterozoic magmatism. therefore, palaeoproterozoic granites are selected from toneta area, tilwara section for whole rock geochemical analysis to establish tectonic environment and geodynamic setting. 2. geology of the area it is supposed that the indian crust was imbricated and different parautochthonous of deeper rocks from various tectonics levels by the duplex mechanism and thrusted on metasedimentary rocks of the lesser himalayan sequence. the study area is constituted by granite, quartzite, schist, gneisses and metabasics (fig. 2). the undeformed granite exposed around toneta area is considered as bhatwari (= chail/ ramgarh) group (valdiya 1980; saklani et al., 1991). this rock unit has sheared up to 500 meters having brittle ductile deformation (mainly indian plates basement rocks medium to high metamorphic grade) consider as characteristics of mct-iii zone in the lesser himalayan sequence. the rocks of chail group are tectonically separated by chail thrust (mct-iii) with massive white quartzite of the garhwal group towards south (valdiya, 1980; saklani et al., 1991; singh et al., 1998). fig. 2. geological map of the area around toneta, rudraprayag, lesser garhwal himalaya (after valdiya, 1980). analysed granite samples are given in table 2. the toneta granites extend from 1.5 km west of tilwara to chirbatiyakhal in the east. they are well exposed around toneta village and hence the name (negi et al., 1980). these granitic rocks sometime associated with tourmaline granite, gneiss and quartz sericite schist (fig. 3a). tourmaline granite is medium to coarse grained with feldspar and quartz having subordinate tourmaline and biotite. the sample n-4, n-5 and n-6 are medium to coarse grained containing feldspar (microcline and plagioclase) and quartz, and accessory minerals are biotite and tourmaline. it is typical for mpg (muscovite-bearing peraluminous granitoids) which common for collisional setting (barbarin, 1999). striation in tourmaline grains is seen near toneta, where the grains are 0.5 cm × 0.3 cm 32 mishra, s. et al./ jgeet sp vol 04 no 02-2/2019 (avg.) in dimensions. near jakhal village and about 1 km west of toneta, regular black band of tourmaline are seen in the granites, with a thickness of 0.5 cm to 1 cm and rock exposures occurring around 3 to 7 m bands. there is also sericitization of feldspar. at places the granite has become vary coarse grained, nonfoliated porphyritic and rich in biotite (fig. 3b). n-5 sample is fresh and fine grained rocks occur in very small area about 3km west of toneta village, exist in a road cutting section and have undeformed (fig. 3b). the sample n-5 contains quartz and feldspar and subordinate mica minerals with fine grains. the other granite samples are also fresh which have developed crude foliation and schistosity (fig. 3c). the granitegneiss (sample no. s-1, s-4 and s-5) are exposed around mayali having quartz and flaky minerals. about 1 km south east of mayali, augen gneisses are observed and some boudinage of quartzites are exposed in the granite gneiss. similar structures are also reported by negi et al. (1980) along the helang gad fault and the rocks are highly scattered. the fine to medium grained quartz-talc-schist is reported by negi et al. (1980) from toneta to mayali traverse which extending further towards north and have elongated quartz grains. quartz sericite schist is well developed in sheared zones, particularly along the alaknanda thrust and in the upper lastar gad valley and correlated with mct-iii of saklani et al. (1991) which show thrusted contact with quartzite at southern side. these granites have well developed joint system and also traversed by epidiorites. 3. sampling and analytical techniques based on criteria least alteration, seven representative samples of granite were analysed. the chemical composition of the rocks was determined at the testing and matter analysis centre, institute of geology, karrc, ras, petrozavodsk, russia. the detail methodology and precision is described by svetov et al. (2015), singh and slabunov (2015), which profusely discussed in slabunov and singh (2018). to estimate rock-forming element concentrations, sample powder was first melted with sodium carbonate, and the resultant melt was then leached with diluted hydrochloric acid. sio2 was first precipitated with gelatin from the resultant solution, and its percentage was estimated by the gravimetric method. al, fe, ca and mg concentrations in the solution were then calculated complexometrically and ti and p concentrations photometrically. calculation accuracy was determined from acceptable discrepancy between the results of two parallel estimations which does not exceed 0.7% for si, 0.5% for al, fe, ca and mg and 0.3% for ti and p. the concentrations of minor elements in the samples were estimated by the inductively coupled plasma mass spectrometry (icp-ms) method on an х series-2 icp-ms (thermo scientific, usa). the samples were decomposed by acid dissolution in an open system. weighted portions of samples with a mass of 0.1 g were used for analysis. the samples analyzed were decomposed together with reference samples (blank samples) and one standard sample. the major elements and their calculated cipw weight norms and also trace elements data are given in table 2 and table 3. table 2. major oxides (wt.%) elemental data and cipw weight norms for the analyzed sample of granites, tilwara, lesser garhwal himalaya (sample locations are marked in fig. 2). sample name s-1 s-4 s-5 n-4 n-6 n-5 n-9 lat. (n) 30°22'35'' 30°22'33'' 30°22'14'' 30°22'11'' 30°21'59'' 30°21'57'' 30°21'42'' long. (e) 78°53'47'' 78°53'22'' 78°53'44'' 78°53'53'' 78°54'15'' 78°54'10'' 78°54'45'' sio2 73.05 76.62 74.8 76.68 74.66 71.84 95.06 tio2 0.2 0.1 0.22 0.18 0.25 0.28 0.11 al2o3 13.5 12.24 12.43 11.67 12.67 13.7 1.64 fe2o3 0.16 0.69 0.054 0.46 0.66 0.63 0.33 feo 1.14 0.86 1.43 1.44 1.44 1.94 0.72 mno 0.012 0.014 0.018 0.013 0.024 0.024 0.013 mgo 1.86 0.46 0.62 1.13 0.76 0.82 0.51 cao 1.01 0.29 1.44 0.36 0.29 0.36 0.36 na2o 0.85 2.27 2.38 1.27 0.74 2.4 0.04 k2o 6.63 5.3 5.55 5.0 6.91 6.42 0.31 p2o5 0.22 0.15 0.2 0.16 0.16 0.12 0.31 h2o 0.03 0.17 0.03 0.1 0.07 0.17 0.08 cipw weight norms q 37.67 41.86 35.25 47.26 41.83 30.47 92.49 c 3.62 2.60 0.37 3.90 3.83 2.44 1.24 or 39.18 31.32 32.80 29.55 40.84 37.94 1.83 ab 7.19 19.21 20.14 10.75 6.26 20.31 0.34 an 3.57 0.46 5.84 0.74 0.39 1.00 0 hy 6.29 2.02 3.80 4.81 3.63 4.67 2.16 mt 0.23 1.00 0.08 0.67 0.96 0.92 0.48 il 0.38 0.19 0.42 0.34 0.48 0.53 0.21 ap 0.521 0.36 0.48 0.38 0.38 0.29 0.65 sum 98.65 99.01 99.16 98.38 98.58 98.55 99.39 mishra, s. et al./ jgeet sp vol 04 no 01-2/2019 33 4. geochemistry and tectonic settings the k-rich granites from toneta area are mostly calc-alkaline in nature classified as granite (fig. 4a). the normative feldspar classification diagrams [albite (ab) orthoclase (or) barker, 1979] indicate that the toneta granite falls in granite field (fig. 4b). in granitoids na2o is low and varies from 0.74 to 2.4 wt.% and k2o content varies from 5.0 to 6.91 wt.%. the al2o3 content varies from 11.67 to 13.7 wt.% except sample n-9 (95% silica). the rocks are highly rich in sio2 having range from 71.84 to 76.68 wt.%. alumina content (al2o3: av. 12.7 wt.% in the granitoids is greater than the total alkalies (na2o+k2o: av 7.62 wt. %), the tio2 content in the granitoids are low ranging from 0.1 to 0.28 wt.%. cipw norms calculations, all the samples show normative corundum values ranging from 0.37 to 3.89 which is a typical in all granite samples of the lesser garhwal himalaya with high normative orthoclase and less normative albite-anorthite feldspar minerals (table 2). the granites belong to high-k calc alkaline and shoshonite series (fig. 5a), with mostly peraluminous in nature (fig. 5b). table 3. trace elements (in ppm) analytical data of the granites, tilwara, lesser garhwal himalaya. sample name s-1 s-4 s-5 n-4 n-6 n-5 n-9 cr 20.2 23.01 18.83 40.12 23.09 25.92 43.66 ni 12.03 9.53 10.15 8.34 13.24 15.28 20.91 co 1.78 1.13 1.73 1.65 2.24 4.88 2.19 sc 5.05 6.23 6.22 6.69 6.85 7.78 4.70 v 26.03 49.46 44.97 47.01 25.59 109.80 57.32 cu 5.13 4.83 8.18 7.51 18.74 10.56 5.49 pb 11.84 19.72 39.24 16.47 32.29 22.40 3.37 zn 21.82 24.13 39.95 29.65 87.93 44.35 9.23 bi 1.59 0.93 0.57 1.88 37.93 0.25 0.19 cd 0.09 0.07 0.14 0.14 0.14 0.08 0.06 sn 23.79 27.83 13.06 11.76 14.51 9.51 5.28 w 3.75 5.26 6.36 3.97 4.76 3.90 5.02 mo 0.36 0.46 0.31 0.44 0.46 0.59 0.91 sb 0.27 0.27 0.23 0.41 0.32 0.24 0.27 rb 386.7 434.8 374.8 301.5 438. 333.1 21.2 cs 13.52 17.97 12.44 16.99 15.56 12.52 0.88 ba 161.1 64.18 179.8 155. 275.40 491.6 34.4 sr 15.11 15.30 40.68 16.31 18.31 45.68 10.57 tl 1.94 2.06 1.94 1.38 2.54 1.84 0.14 ga 18.28 17.90 17.23 17.14 18.06 19.43 3.31 li 13.44 8.71 9.02 18.23 13.13 14.07 3.82 ta 1.66 2.28 1.56 1.95 1.61 0.95 0.48 nb 10.77 10.69 11.27 12.60 12.28 11.03 4.93 hf 2.73 2.32 2.70 3.52 4.70 <po 1.91 zr 63.08 50.20 70.74 93.74 117.10 1.89 57.89 y 25.38 27.23 23.70 26.93 41.93 16.21 5.75 th 25.74 23.93 20.55 25.03 25.66 50.98 19.50 u 9.88 12.97 3.52 6.83 9.27 3.28 6.22 la 29.85 14.59 22.10 28.79 31.37 66.33 19.22 ce 61.83 33.25 44.93 59.19 62.66 137.60 37.84 pr 7.21 3.59 5.38 7.07 7.44 15.67 4.28 nd 24.75 12.47 18.61 24.16 26.14 53.84 14.18 sm 4.23 2.90 2.88 3.55 3.67 7.16 2.70 eu 0.37 0.19 0.47 0.42 0.51 0.83 0.39 gd 5.76 3.74 4.51 5.50 6.24 7.17 2.38 tb 1.00 0.79 0.80 0.94 1.15 0.96 0.32 dy 5.20 4.99 4.49 5.13 7.24 4.03 1.44 ho 0.91 0.96 0.85 0.96 1.42 0.66 0.23 er 2.01 2.44 2.06 2.27 3.77 1.34 0.58 tm 0.26 0.34 0.29 0.32 0.53 0.13 0.08 yb 1.37 2.00 1.62 1.61 3.16 0.66 0.49 lu 0.18 0.26 0.21 0.23 0.42 0.07 0.07 be 2.85 2.08 3.71 2.26 2.23 1.95 1.72 chondrite normalized rare earth-element patterns (mcdonough & sun 1995) of the granitoids show pronounced negative eu anomaly (eu/eu* = 0.18 to 0.36, fig. 6a), pronounced enrichment in lree and highly fractionation of heavy rare earth elements (hree; lan/lun = (5.81 to 101.34). these rocks are also rich in lile: cs, rb, th, u, and pb (see primitive mantle normalized, mcdonough & sun 1995, fig. 6b) and display negative nb ti anomalies (fig. 6b). 34 mishra, s. et al./ jgeet sp vol 04 no 02-2/2019 in the yb + ta versus rb and nb versus y discrimination diagram of pearce et al. (1984), the toneta granites mostly plots within the syn-collision granite fields (fig. 7). the r1 r2 [r1 = 4si 4+ -11(na + +k + ) 2(fe 3+ +ti 4+ ), molar; r2 = 6ca 2+ +2mg 2+ +al 3+ , molar] tectonic discrimination diagram show syncollision to post-orogeny field tectonic setting (fig. 8). fig. 4. (a) total alkalis (na2o + k2o) versus silica (sio2) diagram (after middlemost, 1994) for paleoproterozoic granitoids of toneta area of lesser garhwal himalaya, (b) normative feldspar classification diagrams [albite (ab) orthoclase (or) fig. 5. (a) sio2 vs. k2o diagram (peccerillo and taylor, 1976). (b) a/nk versus a/cnk diagram (after shand, 1943). 5. discussion phukon et al. (2018) discussed that the granitoids from the chiplakot crystalline belt, kumaun himalaya are associated with the columbia supercontinent subduction system in the paleoproterozoic. frank et al. (1977) assign a whole rock rb-sr age of 1840 + 70 ma for bandal and sainj granites, documenting an existence of proterozoic granitic magmatism in the himalaya. islam et al. (2005) stated that the proterozoic granites of the lesser himalaya are silica and k2o enriched with high a/cnk value (>1.1) and show presence of normative corundum. islam et al. (2005) also pointed out that the granite, granitic gneisses and associated metasedimentaries rocks in nw himalaya experienced up to upper amphibolites facies metamorphism which might suggest that the proterozoic granitic gneisses were derived as basement slivers from middle crustal level (a probable extension of the northern indian craton). singh et al. (2009) also indicated that the paleoproterozoic (ca. 1860 ma) felsic magmatic rocks are widespread in the lesser himalayan zone to basal part of the higher mishra, s. et al./ jgeet sp vol 04 no 01-2/2019 35 himalayan crystalline (hhc) probably remobilization of older crustal material which exhumed due to collisional tectonics during the himalayan orogeny. the proterozoic tourmaline-bearing granitoids rocks from nw himalaya have typical for collisional mpg (barbarin, 1999) petrography. they are enriched in lree and moderately depleted hree along with a pronounced negative eu anomalies and characterized by negative ba, nb, sr, p and ti anomalies and high rb, th and u content (miller et al., 2000). the sr and nd isotopic characteristics of these rocks show their high initial 87 sr/ 86 sr ratios (0.711-0.721) and initial epsilon nd values are -5.8 to -8.8 which suggest large-scale reworking of archean sialic protolith (miller et al., 2000). singh (2011) suggested that 1800-2000 ma granites from lesser and higher himalaya can be correlated for tectono-thermal (collisional) event which also noticed as huge hydrothermal activity occur ca. 1.9-1.8 ga in bundelkhand craton (slabunov et al., 2017), southern adjacent part of garhwal himalaya. it seems to be similar granitic magmatism occurs in the lesser garhwal himalaya and further studies are needed to establish the remobilization of archean crust could be of bundelkhand or aravalli cratons. fig. 6. (a) the chondrite normalized (after mcdonough and sun, 1995) ree plot for toneta granites. (b) mantle normalized multi element spider diagram of toneta granites (after mcdonough and sun, 1995). 36 mishra, s. et al./ jgeet sp vol 04 no 02-2/2019 fig. 7. discrimination diagram of rb-y +nb, nb-y (pearce et al., 1984) for the toneta granites org: ocean ridge granites; syncolg: syn-collision granites; vag: volcanic arc granites; wpg: within plate granites. fig. 8. r1-r2 multicationic variation diagram [r1 = 4si 4+ 11 (na + +k + ) (fe 3+ +ti 4+ ), molar; r2 = 6ca 2+ + 2mg 2+ +al 3+ , molar], (batchelor and bowden, 1985). mishra, s. et al./ jgeet sp vol 04 no 01-2/2019 37 6. conclusions to the collision tectonics nature of granites exists in garhwal himalaya demonstrate felsic magmatic phase implication occur during paleoproterozoic ages. the lesser garhwal himalaya toneta granites formed syn-collision to post-orogeny tectonic environment, which resemble with ca. 1800-1900 ma existing hydrothermal activity in bundelkhand craton suggest a possible linkage to it. however, the questions are still unanswered and required more studies to understand about the nature of granitic rocks of garhwal himalaya whether these rocks have formed due to the melting and recrystallization of pre existing archean continental crust of bundelkhand or aravalli cratons? acknowledgements we thanks to the director prof. s.s. svetov, institute of geology, karrc, ras, petrozavodsk, russia for providing lab facilities for geochemical analysis. sm is thankful to dst/ inspire fellowship/ [if160096] for financial assistance. references barbarin, b., 1999. a review of the relationships between granitoid types, their origins and their geodynamic environments. lithos 46, 605 626, doi:10.1016/s0024-4937(98)00085-1 barker, f., 1979. trondhjemite: definition, environment and hypotheses of origin. in: barker, f. 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(eds.) paleoproterozoic supercontinents and global evolution. the geological society london, special publicaltion 323, 283300. doi: 10.1144/sp323.14 singh, v.p., bhanot, v.b., singh, r.p., 1985. geochronology of the granitic and gneissic rocks from munsiari, namik and tawaghat areas of the central crystalline zone, kumaun himalaya, u.p. 3rd national symposium on mass spectrometry, hyderabad, september 22 24 singh, v.p., singh, r.p., bhanot, v.b., 1986. rb sr isotopic studies for the granitic and gneissic rocks of almora area of almora crystallines, kumaun himalaya, u.p. 4th national symposium on mass spectrometry, bangalore, eps-1, 1 4. singh, v.k., 2011. structural and metamorphic evolution of the rocks of the garhwal himalaya: possible linkage with bundelkhand craton, india. proceeding of the 2nd international conference precambrian continental growth and tectonism (editors: v.k. singh & ram chandra), 20-35. singh, v.k., slabunov, a., 2015. the central bundelkhand archaean greenstone complex, bundelkhand craton, central india: geology, composition, and geochronology of supracrustal rocks. international geology review 57, 13491364. singh, v.k., singh, s.p., saklani, p.s., dubey, c.s., 1998. mesostructures and deformational history of the central crystallines: an example from garhwal himalaya, india. j. nepal geol. soc., 17, 59-69. sinha, a.k., 1989. geology of the higher central himalaya. john wily & sons, 219. slabunov, a.i., singh, v.k., 2018. meso neoarchaean crustal evolution of the bundelkhand craton, indian shield: new data from greenstone belts. international geology review, doi:10.1080/00206814.2018.1512906. slabunov, a.i., singh, v.k., shchiptsov, v.v., lepekhina e. n., kevlich v.i., 2017. a new palaeoproterozoic (1.9-1.8 ga) event in the crustal evolution of the bundelkhand craton, india: the results of (shrimp) dating of zircons from giant quartz veins. in: slabunov, a.i., svetov, s.a., and baltibaev, sh.k. (eds.), early precambrian vs modern geodynamics. extended abstracts and field trips guide. petrozavodsk: karrc ras, 239-241. svetov, s.a., stepanova, a.v., chazhengina, s.y., svetova, e.n., rybnikova, z.p., mikhailova, a.i., paramonov, a.s., utitsyna , v.l., ekhova, m.v., kolodey, b.s., 2015, precision geochemical (icp-ms, la-icp-ms) analysis of rock and mineral composition: the method and accuracy estimation in the case study of early precambrian mafic complexes. proceedings of the karelian research centre ras. no 7. precambrian geology series 54 73. doi: 10.17076/geo140 thakur, v.c., 1992 geology of western himalaya, pergamon press ltd., london, 355. trivedi, j.r., gopalan, k., valdiya, k.s., 1984. rb sr ages of granitic rocks within the lesser himalayan nappes, kumaun, india. journal of geological society of india 25, 641 653. valdiya, k.s., 1980. geology of the kumaun lesser himalaya. wadia institute of himalayan geology, dehradun, 291. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geology of the area 3. sampling and analytical techniques 4. geochemistry and tectonic settings 5. discussion 6. conclusions acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology special vol 04 no 02-2 2019 singh, m.m. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 3 special volume geochemistry and tectonic setting of the supracrustal rocks from the central part of the bundelkhand craton, india m.m. singh 1 , vinod k. singh 1, * 1 department of geology, bundelkhand university, jhansi, up, india-284128 * corresponding author : vinodksingh@bujhansi.ac.in tel.:+91-9415258237; fax: +91-5102321667 received: sept 25, 2018; accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2175 abstract supracrustal rocks (mafics and ultramafics) occurs along with banded iron formation, and felsic volcanics around babina, dhaura, and mauranipur linear east west trends in central part of the bundelkhand craton represent archean crust. the mafic and ultramafic rocks geochemically classified into komatiite and basaltic komatiite and have high fe tholeiitic in composition which may relate with the primitive mantle. the major and trace element geochemistry of mafic and ultramafic rocks correspond to hydrated mantle with wedge tectonic sources and ocean ridge geological characteristics. keywords: bundelkhand craton, komatiite, island arc, archean crust, subduction tectonic setting. 1. introduction archean cratons of the world have become the nerve centers for study to decode the earlier crustal history of earth. the formation of supracrustal rocks or first landmass is in fact an irreversible process in the geological history of earth, which led the processes of initiation of stabilization, continental growth, micro-continent, and supracontinental growth (pearce and peate, 1995; fitton et al., 2003; naqvi, 2005; condie, 2014, 2015). the archean from the island arc and collisional settings of the archean to the lithospheric extension and global continental rifting in the early paleoproterozoic (bogina et al., 2015). the indian shield comprises two major northern (bundelkhand, aravalli carton) and southern (dharwar, bastar, singhbhum craton) indian crustal blocks separated along the e w trending son narmada lineament known as central indian tectonic zone (naqvi, 2005; ramakrishnan and vaidyanadhan, 2010; slabunov and singh, 2018). mostly the central part of each craton consisting of ttg gneisses and granitoids, commonly associated with sequences of meta-sedimentaries, metavolcanics and unstratified ultramafic and mafic volcanic rocks (naqvi, 2005; mohan et al., 2013; jayananda et al., 2015). the bundelkhand craton begin with the ca. 3.55 ga crustal component growth signatures around the babina and mauranipur areas, as preserve in the form of ttg gneissic rocks (sarkar et al., 1996; mondal et al., 2002; kaur et al., 2014; singh, 2015; saha et al., 2016; singh et al., 2019a). the ca. 3.4 ga ancient basaltic rocks are mostly exposed contemporaneous with ttg in central part of the craton (singh et al., 2018, 2019b). the mafics and ultramafic rocks are widely exposed around baragaon, dhaura, babina villages. singh and slabunov (2015a) suggest two distinct greenstone complex occur in the craton i.e. (i) central bundelkhand (babina; mauranipur belts) greenstone and (ii) southern bundelkhand (girar) schist belts. singh (2005, 2015) has carried out detailed study on geology and structure of babina mauranipur areas and in present paper authors using petrological and geochemical data to determine tectonic settings of these archean basaltic rocks of the central bundelkhand craton. 2. geological setting of bundelkhand craton represents a semicircular outcrop, which is overlain by low grade metamorphic rocks of the bijawar group (paleoproterozoic) to the south, southeast, and vindhyan supergroup (mesoproterozoic to neoproterozoic) to the southeast, south, southwest, and west (basu, 1986; sarkar et al., 1996; singh et al., 2007; ramakrishnan and vaidyanadhan, 2010; fig. 1). the major part of the craton comprises the different phases of archean magmatism, low-grade metamorphism, paleoproterozoic mafic dykes and quartz veins. singh (2005, 2015) mapped the older crustal components from the central part of the bundelkhand craton which are scattered in the e w shear zones http://journal.uir.ac.id/index.php/jgeet 4 singh, m.m. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 of 3 5 km width (fig. 2). metabasics, banded iron formation (bif) and felsic volcanic rocks exposed from 3 km south of the babina town to mauranipur in the east consider as a part of the central bundelkhand greenstone complex (singh and slabunov, 2015a, 2015b; slabunov and singh, 2018; fig. 1). the doleritic dykes are usually dark greyish green in colour and have nnw sse to nw se trend (basu, 1986; sharma and rahman, 2000; pradhan et al., 2012). these mafic dykes are subalkaline to tholeiitic in composition and display continental affinity (pati et al., 2008). a general characteristic of highly jointed quartz veins occur mostly about ne sw to nne ssw trend. the supracrustal rock comprises mafic ultramafic rocks, banded iron formations, felsic volcanics occur along e w linear trends, generally dipping towards north. fragments of low-grade metamorphosed mafic ultramafic rocks are occur nearby boundary between banded iron formation and ttg gneisses, at the south of babina area (near pura village), mauranipur and dhaura villages (figs. 1 and 2). these rocks are intruded by k-rich granitoids (~2500 ma) at babina, dhaura and rash pahari near mauranipur villages. the pegmatite veins are also observed at many places. fig. 1. geological map of the bundelkhand craton (after ramakrishnan and vaidyanadhan, 2010 and slabunov and singh, 2018), inset map shows the different cratons of indian shield. fig. 2. geological map of the babina gora traverse, central bundelkhand greenstone complex (after singh and slabunov, 2015a). singh, m.m. & singh, v.k./ jgeet sp vol 04 no 01-2/2019 5 the small body of mafic and ultramafic rocks, exposed along with bif near village kuraicha in mauranipur greenstone belt (fig. 3a). basic ultrabasic rocks also exist in babina greenstone belt (fig. 3b) which is resembled with mauranipur greenstone belt. exposures of felsic volcanics are observed at north of babina (fig. 3c), paponi, and dhaura areas. intrusions of granite are noticed in the felsic volcanics which indicate their younger age. ttg gneisses are exposed at babina, dhaura, gora and mauranipur areas. field relation between basaltic, banded iron formation and ttg gneisses rocks shows its tectonic colleagues (fig. 3b; singh and slabunov, 2015a). the voluminous pink granites are mostly inhabit of the craton during neoarchean period in multiple phases (mondal et al., 2002; verma et al., 2016; kaur et al., 2016; joshi et al., 2017; mishra et al., 2018; singh et al., 2019c). slabunov and singh (2018) noted that meso neoarchean felsic rocks formed in a subduction geodynamic setting from the central bundelkhand greenstone complex. 3. geochemistry and tectonic setting fresh samples of ultramafics and mafics from central bundelkhand region have been collected and pulverized in agate ball mill for geochemistry. the samples have analysed at the geochemical lab of ngri, hyderabad for major, trace and ree using inductively coupled plazma mass spectrometry (icp-ms) while xrf method was used at wadia institute of himalayan geology, dehradun. the whole rock major and trace element compositions of the analysed samples are given in table 1. the different variation diagrams and discrimination diagrams have been obtained using the free access gcdkit 3.00 computer program. the ultramafic and mafic rocks are classified as subalkaline/tholeiitic picritic, basalt to basaltic andesite with 36.56 55.15 sio2 wt. % (fig. 4a). the rocks display a tholeiitic trend on the afm diagram (irvine and baragar, 1971) (fig. 4b). in the jensen (1976) diagram, most rock points are into komatiite, komatiitic basalt, and high fe tholeiite fields (fig. 4c). these rocks vary considerably in mgo (5.66 28.24 wt. %), tio2 (0.19 2.52 wt. %), ni (31 975 ppm) and cr (67 3121 ppm) concentrations (table 1). al2o3 concentrations range from 6.58 to 14.25 wt. %. the fe2o3 in these rocks ranges from 11.89 to 24.3 wt. % which is to some extent high value for tholeiitic magma. geochemical compositions are plotted on several variation and tectonic diagrams against mgo vs oxides (wt. %; tio2 and p2o5) and trace elements (ppm; rb, sr, y, and zr) to examine crystallization behavior, which show decreasing trend with increasing mgo contents (fig. 5), suggesting that these were more or less incompatible with any fractionating phases. fig.3. (a) the mafic and ultramafic rocks exposed at the base of bif near village kuraicha, kamla sagar dam in mauranipur greenstone belt (size of hammer 15 inch); (b) the underlain basic rocks show tectonic contact with bif exposed in babina greenstone belt; (c) felsic volacnics exposed at 3 km north of babina with granite intrusion (size of coin 2.5 cm diameter). 6 singh, m.m. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 fig. 4. classification diagrams of mafic ultramafic rocks (a) sio2 na2o + k2o (le bas et al. 1986), (b) afm (irvine and baragar, 1971), (c) cation diagram feo*+tio2 al2o3 mgo (jensen, 1976). table 1. major (wt. %) and trace (ppm) element analytical data of mafic and ultramafic rocks from the central bundelkhand greenstone complex. sample o14 o16 p57 s2a s3 s4a d2b d13 37 38 j3a locality kuraicha kuraicha dhaura dhaura dhaura dhaura dhaura dhaura babina babina babina sio2 44.23 36.56 42.4 48.06 49.58 55.15 51.31 50.92 49.72 49.18 47.81 tio2 0.19 1.56 2.52 0.51 2.01 2.22 0.79 1.53 1.03 1.36 0.61 al2o3 9.15 10.37 11.56 6.58 11.53 13.07 9.61 14.25 11.72 10.87 10.86 fe2o3 11.89 24.3 23.5 12.51 17.76 12.28 14.22 14.98 16.11 19.98 13.63 mno 0.22 0.35 0.19 0.27 0.23 0.18 0.17 0.23 0.24 0.28 0.24 mgo 28.24 14.99 11.55 21.29 6.91 5.66 9.62 6.9 7.74 6.26 12.21 cao 6.35 4.7 1.22 11.11 9.55 6.75 13.95 8.77 9.04 9.85 10.94 na2o 0.33 0.02 0.95 0.42 1.6 2.82 0.06 2.6 2.48 1.72 1.44 k2o 0.06 0.03 0.47 0.1 0.27 1.48 1 1.61 0.62 0.44 1 p2o5 0.04 0.21 0.13 0.09 0.24 0.35 0.11 0.17 0.11 0.14 0.07 cu 85 31 47 28 175 39 20 99 zn 120 131 101 83 105 72 130 131 co 59 75 60 51 59 73 80 78 ni 900 118 51 975 75 31 69 93 63 34 255 ga 15.9 16.7 12.1 20.5 17.5 7.4 26.9 8.7 rb 2.7 3.5 13 5.8 18 81 34.9 48.2 42.5 8.1 61.3 ba 129 68 44 492 135 45 102 114 sr 12 299 9 68 140 208 174 163 144 106 82 y 23.7 30.5 16.1 21.7 25.4 9.7 34.6 14 zr 7 808 199 30 166 277 77 110 89 102 35 nb 1 67.3 7 2.7 11 18 4.1 7 4.7 5 2.8 th 1.9 5.8 2.5 2 0.5 1.6 49.2 3.3 sc 51 60 45 58 43 40 36 24 pb 11.7 10 8 9.8 2.8 14.6 27.5 19.1 u 1.4 0.3 1.8 1.1 1.4 0.3 1.9 0.5 cr 67 105 908 370 170 3121 743 2441 nb/th 0.53 11.60 2.8 5.5 36 2.56 0.14 0.85 zr/nb 7 12.01 28.43 11.11 15.09 15.39 18.78 15.72 18.94 20.4 12.5 nb/y 0.04 2.21 0.44 0.51 0.71 0.42 0.20 0.2 zr/y 0.30 26.49 12.36 7.65 10.91 7.94 3.18 2.5 the three fields of mantle domains i.e. enriched mantle (em), depleted mantle (dm), and hydrated mantle (hm) are define using nb/th and zr/nb ratio discrimination plot (condie, 2003, 2005, 2015). the ratios of nb/th singh, m.m. & singh, v.k./ jgeet sp vol 04 no 01-2/2019 7 is less than 8 and with variable zr/nb ratio, show the archean basalts mostly falls under hydrated mantle domain (condie, 2015). the zr/nb ratio is greater than 10 and nb/th less than 10 indicate arc setting (condie, 2015). the samples from the central bundelkhand greenstone belt plotted on diagram which show mostly hydrated mantle field and under arc setting conditions (fig. 6). the sample no o16 which have 11.6 nb/th value likely consider an enriched mantle source (condie, 2015). the sample no s4a have very high nb/th value (36) due to less value of th noticed in specimen may not provide convincing interpretation. fitton et al. (2003) describe the nb/y versus zr/y discrimination diagram which distinguish nmorb and iceland basalts on nb incompatible element. the lower limit of iceland data array as reference line defined a the mafic and ultramafic rocks from the central bundelkhand greenstone complex plotted on fitton et al. (2003) discriminant diagram which falls mostly in the vicinity of nb/zr=0.06 line with oib field and some samples falls in iceland basaltic type (fig. 7). the compositions of mafics and ultramafics rocks are associated to arc type tectonic setting for the magmatism. singh et al. (2019b) suggest that the mafic-ultramafic rocks from central bundelkhand greenstone complex have been interpreted to be derived from oceanic crust in a subduction-related setting with depleted mantle composition. similar rocks are also reported by malviya et al. (2006) from mauranipur area and stated that komatiite basalt is nearly constant along the olivine fractional crystallization trend but enriched lree and lile as modern boninite formed at a plate convergent margin. fig. 5. geochemical variation diagrams between mgo (wt%) and minor oxides (tio2 and p2o5; wt%) and trace elements (rb, sr, y, and zr; in ppm). 8 singh, m.m. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 fig. 6. discrimination diagrams for distinguishing tectonic setting using nb/th and zr/nb ratios (condie, 2015). fig. 7. zr/y versus nb/y discrimination diagram (after fitton et al., 2003); nmorb: normal mid-ocean ridge basalt, oib: oceanisland basalt. 4. discussion and conclusions the supracrustal rocks of babina and mauranipur consist of low k tholeiitic basalt, basaltic komatiite, volcanosediment and bif followed by andesite to rhyodacite volcanics which are similar to those reported from various archean greenstones (paris, 1987; kusky et al., 2001; polat et al., 2003; manikyamba et al., 2005). condie (2015) discussed that nb/th and zr/nb incompatible element ratios are useful to illustrate their tectonic setting where the ratio of nb/th is less than 8 and with variable zr/nb ratio, falls under hydrated mantle domain mainly of archean oceanic basalts. several hypotheses have been discussed as accretions of oceanic terrain form by plume impact explain the unusual high mgo content of komatiite (hertzberg, 1995; xie et al., 1995; arndt et al., 1997) causes the large degree of melting and the pyrope bearing peridotite source material is usually considered for the source of komatiite magma. the accretion of oceanic volcanic arc may explain a geochemical similarity between komatiite and modern arc related volcanic for supracrustal rocks of the central bundelkhand region (malviya et al. 2006). the discussions of occurrences of metabasic and ultrabasic rocks and generation of various type of parent (basaltic/komatiitic) magma reveal related to different tectonic environment even in smaller tectonic provinces too (bose, 1997; barley et al., 2000; massaki et al., 2001; svetov et al., 2001; shimizu et al., 2005; verma et al., 2015). fitton et al. (2003) provides a useful discriminant logarithmic plot of nb/y versus zr/y between icelandic basalt and nmorb (i.e. plume and nonplume basalt). the nb/y versus zr/y plotted mafics and ultra mafics rocks from central part of the bundelkhand craton show mostly oib type plume basalt (fig. 7). the initial komatiite composition of magma altered to komatiitic basalt and tholeiitic compositions, either due to fractionation or singh, m.m. & singh, v.k./ jgeet sp vol 04 no 01-2/2019 9 contamination or metasomatic activities in the area. geochemically the mafic and ultramafic rocks are very similar to the komatiitic and komatiite basalts of greenstone belts. singh and slabunov (2015a) estimated as paleo neoarchean time for the formation of supracrustal metabasic rocks from central bundelkhand greenstone complex. the ultramafic and mafic sequences in babina and mauranipur greenstone belt are related to arc type subduction related magmatism (malviya et al., 2006; singh, 2015, condie, 2015). singh et al. (2018, 2019b) stated that εndt value of +2.0 to +5.6 for the basalts from babina greenstone belt indicate depleted mantle source at ca.3.4 ga. thus, the geochemical characteristics conclude that the protolith of supracrustal rocks of the central bundelkhand greenstone complex be produced in hydrated mantle field with arc tectonic setting in archean time. the komatiitic tholeiitic association of greenstone formed in narrow belt along the babina mauranipur greenstone belt. acknowledgements mms gratefully acknowledges financil support provided by ministry of mines, government of india, new delhi vide letter f. no.14/17/2002-met.iv dated 27th february 2003 to bundelkhand university jhansi, up. vks is thankful to dst, gov. of india, for providing the financial support as grants no. 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from the central bundelkhand greenstone complex, bundelkhand craton, india. journal of asian earth sciences 118, 125 137. xie, q., me cuaig, t.c., kerrich, r., 1995. secular trends in the melting depth of mantle plumes: evidence from hfse/ ree systematics of archean high mg lava and modern oce¬anic basalt. chemical geology 126, 29-42. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geological setting of bundelkhand craton 3. geochemistry and tectonic setting 4. discussion and conclusions acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 erfando, t., et al / jgeet vol 04 no 01/2019 49 research article the key parameter effect analysis of the polymer flooding on oil recovery using reservoir simulation tomi erfando 1 *, novia rita 1 , romal ramadhan 1 1 petroleum engineering department, engineering faculty, universitas islam riau jl. kaharuddin nasution 113 pekanbaru, riau, 28284 indone sia * corresponding author : tomyerfando@eng.uir.ac.id received: september 10, 2018; accepted: january 1, 2019. doi: 10.25299/jgeet.2019.4.1.2107 abstract as time goes by, there will be decreasing of production rates of a field along with decreasing pressure. this led to the necessity for further efforts to increase oil production. therefore, pressure support is required to improve the recovery factor. supportable pressure that can be used can be either water flooding and polymer flooding. this study aims to compare recovery factor to scenarios carried out, such as polymer flooding with different concentrations modeled in the same reservoir model to see the most favorable scenario. the method used in this research is reservoir simulation method with computer modeling group (cmg) stars simulator. the study was carried out by observing at the pressure, injection rate, and polymer concentration on increasing field recovery factor. this study used cartesian grid with the assumption of homogeneous reservoir, there are no faults or other geological condition in the reservoir, and driving mechanism is only solution gas drive. this reservoir, oil type is light oil with i and layer of conglomerate rock. the simulation result performed with various scenarios provides a good result. where the conditions case base case field recovery factor of 6.7%, and after water flooding produced 25.5% of oil, whereas with tertiary recovery method is polymer flooding was carried out with four concentrations of 640 ppm, 1,500 ppm, 3,000 ppm, and 4,000 ppm obtained optimum values at 4,000 ppm polymer concentration with recovery factor 28.9%, sor reduction final value 0,5255, polymer adsorption of 818,700 ppm, reservoir final pressure 1,707 psi, and an increase in water viscosity to 0.94 cp. keywords: polymer flooding, sor reduction, polymer adsorption 1. introduction the rate of oil production will decrease over time, due to reduced reservoir pressure and reduced amount of oil reserves in the field. in early stages of primary recovery, several oil wells used artificial technology lift, but this technology was no longer optimal in producing oil to the surface (el-khatib, 2001). therefore, efforts are needed to increase oil production and recovery factors from the area, the effort to be carried out is water injection or waterflood (erfando et al., 2017; erfando and herawati, 2017; rita, 2016). water flooding is a proven method for improving offtake rate and ultimate recovery from conventional oil reservoirs. although relatively inexpensive and straightforward to operate, the dynamics and eventual performance of waterflooded reservoirs are controlled by complex interactions of several factors. due to this complexity, it has been challenging to develop a robust, consistent and yet simple normalizing parameter for comparing the performances and recoveries of different reservoirs under waterflood (tetegan et al., 2015). the conversion of conventional waterflood to a polymer flood entails significant injectivity reduction, up to 50% or more. the maintenance of complete voidage replacement (vrr = 1) would thus require an increase in the number of injectors or a reduction of total production rate or both. as both interventions reduce the economic returns (san blas and vittoratos, 2014). polymer flooding was initially used in 1960s and since then has been used frequently to increase sweep efficiency by reducing the mobility mismatch of oil and aqueous phase. it helps in near wellbore region to improve the water flooding process. in waterflooding projects, an increase in injected water viscosity is expected. the key measure of success of these projects is the stability of the displacement process during water injection (temizel et al., 2017). polymer flooding has been used to enhance oil production and reduce water cut for a long time. however, there are still many fundamental challenges in characterizing the multiphase-fluid flow, even the single-phase-fluid flow, associated with polymer flooding. various eor techniques are being tested and used for recovering some of the oil left behind after conventional waterflooding. among the eor approaches, polymer flooding may be one of the most widely used, promising, and cost-effective methods. the preinjection of polymers has been proposed as a means for improving reservoir sweep efficiency by reducing permeability contrasts (li et al., 2014). http://journal.uir.ac.id/index.php/jgeet mailto:tomyerfando@eng.uir.ac.id 50 erfando., t., et al. / jgeet vol 04 no 01/2019 hydrocarbon recovery increases when oil as displaced fluid and water as the displacing fluid has a mobility ratio near one. when volumetric sweep efficiency increases, the mobility ratio decreases. if the mobility ratio is higher than one, polymers or gels can help to increase the viscosity of injected fluids for increasing oil recovery. polymer flooding and gel treatment are one of the most common eor techniques that have been used over four decades due to its reasonable recovery rates and suitable application. polymers are added to the injection fluid to increase its viscosity, thereby reducing their mobility ratio, and resulting in increased oil recovery (cenk et al., 2017). recently, there are increasing interest on polymer flooding due to its high enhanced oil recovery (10% 20% ooip in field tests in daqing) and much lower cost compared to surfactant-polymer (sp) flooding and alkali-surfactant-polymer (asp) flooding (guo, 2017). this study was carried out without considering the cost of polymer prices and polymer flooding process, the only focused on which concentration worked best on increasing oil recovery. 2. materials and methods 2.1. reservoir fluid and reservoir rock characteristics table 1. reservoir fluid characteristics (pertamina, 2016) oil properties density 0.835 viscosity 1.13 cp formation volume factor 1.14 rb/stb api gravity 40.3 0 api specific gravity 0.82 oil type light oil bubble point pressure 993 psig table 2. reservoir rock characteristics (pertamina, 2016) parameter value unit rock type conglomerate thickness 20 ft porosity 16.5 % horizontal permeability 100 md vertical permeability 100 md rock compressibility 5. 10−6 psi−1 2.2 methods the method used in this research is reservoir simulation method with computer modeling group (cmg) stars simulator. this research was conducted by taking field data on barito basin, borneo island, indonesia 3. polymer properties this study used gel polymer (pregel) with a molecular weight of 10,206 lb/lb mole, the density of 1,000 [lb/ft] 3 and viscosity of 20 cp. analysis of concentration is polymer needed to optimize oil recovery in the process of polymer flooding. the concentration polymer used in this study was 640 ppm, 1,500 ppm, 3,000 ppm, and 4,000 ppm. the parameter of polymer flooding: injection is carried out 1.2 pv, with the total fluid injected 614,473 barrels of polymer solutions for 2.5 years, with polymer solutions injected per day is 670 barrels for 916 injection. injection pressure is set at 2,000 psi. the selection of polymer flooding concentrations is based on gao, jiang, zhang, et al., 2016 paper, according to them, oil displacement experiment results show that when the polymer solution dosage is 640 ppm, the incremental oil recovery is only 1.98% with polymer concentration increasing from 1000 ppm to 3000 ppm. when the polymer dosage is reach 1280 ppm. pv, the incremental oil recovery is also only 2.2% with polymer concentration increasing from 1000 ppm to 3000 ppm. only increasing both polymer concentration and dosage, can good oil displacement effect be obtained when the polymer dosage reaches up to 1280 ppm. pv and polymer concentration increases to 2000 ppm; the incremental oil recovery can reach above 10%. thus, the incremental oil recovery can be increase greatly by increasing both polymer concentration and dosage after polymer flooding. table 3. polymer flooding parameters of injection no parameter value 1 pv 1.2 pv 2 injection rate 670 bpd 3 injection time 916 days 4 injection pressure 2,000 psi 4. result and discussion 4.1. polymer concentration analysis according to (gao et al., 2016) high concentration polymer flooding can further enlarge sweep volume and improve mobility ratio between the displacing fluid and crude oil, which is effective to exploit the remaining oil after polymer flooding. high concentration polymer flooding after polymer flooding has good mobility control ability and can enlarge swept volume to enhance oil recovery. meanwhile, high concentration polymer has good viscoelasticity, which is able to pull residual oil and reduce all kinds of residual oil volume, thus increases microscopic displacement efficiency. high concentration polymer flooding (hcpf) has been one of the enhanced oil recovery (eor) methods since conventional polymer flooding because its higher viscoelasticity can improve the oil displacement efficiently. hcpf produced liquid is characterized by high viscosity, and strong emulsification tendency and stability. the emulsification effect of the low water cut produced liquid is more obvious as the polymercontaining concentration rising up, leads to the phase inversion point, at which the emulsion transformed from water-in-oil (w/o) to oil-in-water (o/w) or water-in-oil-in-water (w/o/w) (yang et al., 2015). polymer flooding is an advanced stage that is carried out after water flooding as tertiary oil recovery. the polymer is injected to reduce water mobility as a erfando., t., et al. / jgeet vol 04 no 01/2019 51 driving fluid by increasing its viscosity. for this reason, it is necessary to regulate concentration polymer in an effort to reduce water mobility so that it is more optimal in the oil pressing process. fig. 1 shows that for each increase in concentration polymer, the recovery factor for the field also increases. polymer flooding 640 ppm of produces recovery oil of 28.5% of the total ooip. while polymer flooding with a concentration of 1,500 ppm can increase oil production to 28.6%. for injection with a concentration of 3,000 ppm can produce oil of 28.8% from ooip, and a concentration of 4,000 ppm can increase oil recovery by 28.9%. table 4. comparison of polymer concentration on oil recovery polymer concentrations, ppm oil production cumulative, bbl oil recovery factor, % 640 90,306 28.5 1,500 90,723 28.6 3,000 91,219 28.8 4,000 91,332 28.9 rf increase is not too significant for polymer flooding even though the concentration polymer that has been injected has been increased with a large enough value, because injection with concentrations above 640 ppm requires greater pressure to reach the production well, this is related to the injection viscosity polymer which is increasingly thick with increasing concentration, because concentration polymer too high can cause blocking in small permeability. based on the value of rf and the cumulative production obtained in this study, the maximum results were shown on polymer flooding with a concentration of 4,000 ppm which resulted in rf of 28.9% of total reserves with cumulative production of 91,332 barrels of total ooip on the field. this study was carried out without considering the cost of polymer prices and polymer flooding process, the only focused on which concentration worked best on increasing oil recovery. 4.2. sor reduction analysis according to sheng et al., 2015 technical screening criteria for polymer flooding are empirical, mainly based on field-project data and technical knowledge describing polymer flooding. many parameters can affect the polymer-flooding process, but the most critical are reservoir temperature, formation-water salinity, divalent contents, clay contents, oil viscosity, and formation permeability. most polymer-flooding projects were carried out in sandstone reservoirs. fewer applications were carried out in carbonate reservoirs because anionic polymers such as hydrolyzed polyacrylamide (hpam) have high adsorption in carbonates. also, various carbonate reservoirs have a low-permeability matrix, which large polymer molecules may not be able to enter. fig 1. effect of polymer concentration on oil recovery factor 52 erfando., t., et al. / jgeet vol 04 no 01/2019 fig. 2. sor reduction after polymer flooding by various concentrations fig. 2 shows the deployment in the conditions initial and final after three years of production. based on picture 4.8 the sor condition of the initial field is at a value of 0.765. then after producing for three years the final saturation of the field decreases. the difference in oil saturation values in the final condition on the entire field is caused by oil pressure by polymer flooding two and a half years. thus, oil saturation in the reservoir is reduced. reducing the oil saturation value in the final condition shows the amount of oil that has been produced from the field. oil saturation in this reservoir is equal until it is produced, after production the saturation will decrease. the higher the concentration of polymer injection, the more oil production will be. table 5 the initial and final sor differences after polymer flooding scenarios sor initial sor final polymer 640 ppm 0.7650 0.5275 polymer 1500 ppm 0.7650 0.5266 polymer 3000 ppm 0.7650 0.5257 polymer 4000 ppm 0.7650 0.5255 4.3. polymer adsorption analysis adsorption is a process whereby contact between the fluid in the form of gas and liquid, with solid, where the substances in the fluid are absorbed by the surface of the solid, resulting in changes of the composition of the unadsorbed fluid. the adsorption process is usually characterized by mass transfer from liquid to solids. a liquid concentration higher before flowing in solid pores will cause higher adsorption on solid surface. commonly used material as adsorbent are very ingredients porous, and adsorption takes place on pore walls or in certain locations within particles (widyarso et al., 2006). according to rita, 2011 the adsorption of reservoir rocks in polymer injection occurs due to the attraction between polymer molecules and reservoir rock and the magnitude of this force depends on the magnitude of the affinity of the reservoir rocks affinity the polymer. if the adsorption is very strong, the polymer becomes thinner, consequently the ability to increase the sweep efficiency decreases. the polymer concentration is directly proportional to the polymer adsorption of rock gradually, the higher concentration, the greater the adsorption occurring to the polymer solution on a rock surface. conversely, the lower the concentration, the smaller the adsorption that occurs to the polymer solution on a rock surface. polymer adsorption that occurs in all four concentrations carried out by the above polymer adsorption theory. polymers with a concentration of 640 ppm resulted in the lowest polymer adsorption, whereas polymers with 4,000 ppm concentrations resulted in the highest polymer adsorption. erfando., t., et al. / jgeet vol 04 no 01/2019 53 fig. 3. polymer adsorption at various polymer concentrations table 6. polymer adsorption at various concentration scenarios polymer adsorption (ppm) polymer 640 ppm 680,000 polymer 1,500 ppm 790,000 polymer 3,000 ppm 818,500 polymer 4,000 ppm 818,700 fig. 4. pressure final condition after polymer flooding fig. 4 shows the deployment value of pressure on the field in the final condition. observable from the color of its spread, there is a pressure difference in the reservoir. the highest pressure is on the injection wells with values ranging from 1,800 psi, then increasingly fig. 5. pressure on some concentrations of polymer flooding towards the production well the pressure decreases. this pressure drop is what causes the production to drop in the field. therefore, polymer injection is required with the aim of keeping the pressure at a sufficient level in order to produce oil no less than the minimum production limit. there was a difference in reservoir pressure after polymer flooding at different concentrations. at polymer concentration of 640 ppm final pressure reservoir is 1,671 psi, while for polymer concentration 1,500 psi, 3,000 psi, and 4,000 psi are 1,681 psi, 1,696 psi, 1,707 psi. fig. 5 shows the higher the polymer concentration injected, the greater the pressure increases. -100000 0 100000 200000 300000 400000 500000 600000 700000 800000 900000 09/2017 04/2018 10/2018 05/2019 12/2019 06/2020 01/2021 07/2021 a d s o rp ti o n ( p p m ) time 640 ppm 1500 ppm 3000 ppm 4000 ppm 54 erfando., t., et al. / jgeet vol 04 no 01/2019 fig. 6 pressure effects on production rate fig. 6 shows that simultaneous pressure changes follow oil production fluctuations. changes in pressure from january 2018 to july 2018 occurred sharply as production relied only on reservoir pressure without any effort to maintain reservoir pressure. in july 2018, after polymer flooding, it can be seen in fig. 7. that constant pressure changes until september 2020, then increased until 2021. the temporary increase in chart shows the decrease in oil production can be caused by water breakthrough that has reached well production, so oil production decreases because there is water produced at the same time. 4.4 increasing of water viscosity analysis polymer injection is an enhanced water injection to improve oil recovery by increasing its viscosity. polymer injections of different concentrations will cause an increase in different water viscosity. typically, these two parameters are directly proportional to each other. low-concentration polymer injections will lead to a low increase in value when compared to higherconcentration injections. increased viscosity is very important due to: one way to avoid the early breakthrough and high watercut is to deploy a polymer flood rather than a waterflood. polymer flooding is an enhanced oil recovery technique that aims at improving the mobility ratio between the injected and in-situ fluids by viscosifying the injected water. moreover, the increased viscosity also results in improved volumetric sweep efficiency (anand and ismaili, 2016). increasing flooding-solution viscosity with polymers provides a favorable mobility ratio compared with water flooding and hence improves volumetric sweep efficiency. flooding with a polymer solution exhibiting elastic properties has been reported to increase displacement efficiency, resulting in a sustained doubling of the recovery enhancement compared with the use of conventional viscous-polymer flooding (clarke et al., 2016). in this study, polymer flooding was performed at a means that the viscosity of pure water under these conditions is 0.5 cp. so by doing polymer flooding, the water viscosity will increase along with the polymer concentration injected. polymer flooding has been used to improve the development effect and to enhance oil recovery for dozens of years, which is a type of common and matured technology. polymers cannot be used on ideal conditions to sweep oil if the reservoir temperature exceeds 70 °c if it exceeds that temperature it will cause rapid thermal degradation (wu et al., 2015). scenarios above were done by comparing the four concentrations performed under the same conditions. at a concentration of 640 ppm, the viscosity value was 0.55 cp, for a concentration of 1,500 ppm the viscosity increased to 0.59 cp, whereas for a concentration of 3,000 ppm the viscosity increased by 0.82 cp, and for a concentration of 4,000 ppm the viscosity increased to 0.94 cp. fig. 7. increasing water viscosity by various concentrations of polymer flooding. 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 9/17 4/18 10/18 5/19 12/19 6/20 1/21 7/21 w a te r v is c o s it y , (c p ) time 640 ppm 1500 ppm 3000 ppm 4000 ppm erfando., t., et al. / jgeet vol 04 no 01/2019 55 table 7. polymer viscosity at various concentration polymer concentration polymer viscosity 640 ppm 0.55 cp 1,500 ppm 0.59 cp 3,000 ppm 0.82 cp 4,000 ppm 0.94 cp 5. conclusion the most critical factor in the polymer flooding process is the injection concentration, because it will have impacts on sor reduction and increased pressure from the reservoir, on the adsorption of polymers in rock matrix, and an increase in water viscosity which helps in increasing sweep efficiency. based on the results of research and discussion that has been done, then the conclusions obtained from this study is the tertiary recovery method of polymer flooding conducted with four concentrations, the optimum value obtained at 4,000 ppm polymer concentration with recovery factor 28.9%, sor reduction with final value 0,5255, polymer adsorption of 818,700 ppm, final reservoir pressure 1.707 psi, and water viscosity increase to 0.94. references anand, a., ismaili, a., 2016. de-risking polymer flooding of high viscosity oil clastic reservoirs a polymer trial in oman. spe annu. tech. conf. exhib. https://doi.org/10.2118/181582-ms cenk, t., dike, p., henny, a., raul, m., 2017. economic comparison of hydrocarbon recovery under injection of different polymers. spe/iatmi asia pacific oil gas conf. exhib. https://doi.org/10.2118/186414-ms clarke, a., howe, a.m., mitchell, j., staniland, j., hawkes, l.a., 2016. how viscoelastic-polymer flooding enhances displacement efficiency. spe j. 21, 0675 0687. https://doi.org/10.2118/174654-pa el-khatib, n.a.f., 2001. the application of buckley-leverett displacement to waterflooding in non-communicating stratified reservoirs. spe middle east oil show. https://doi.org/10.2118/68076-ms erfando, t., herawati, i., 2017. analysis of petroleum downstream industry potential in riau province. j. geosci. eng. environ. technol. 2, 178 182. https://doi.org/10.24273/jgeet.2017.2.2.304 erfando, t., rita, n., marliaty, t., 2017. optimasi laju injeksi pada sumur kandidat convert to injection (cti) di area x lapangan y. j. earth energy eng. 6. https://doi.org/10.22549/jeee.v6i2.992 gao, s., jiang, z., zhang, k., liu, h., fu, q., yan, w., fu, b., 2016. high concentration polymer flooding field test with well infilling to change fluid flowing direction after polymer flooding. spe eor conf. oil gas west asia. https://doi.org/10.2118/179794-ms guo, h., 2017. how to select polymer molecular weight and concentration to avoid blocking in polymer flooding? spe symp. prod. enhanc. cost optim. https://doi.org/10.2118/189255-ms li, k., sun, w., li, f., qu, y., yang, y., 2014. novel method for characterizing single-phase polymer flooding. spe j. 19, 695 702. https://doi.org/10.2118/152988-pa pertamina, 2016. unpublished report. rita, n., 2016. analisis sensitivitas 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reservoirs. spe niger. annu. int. conf. exhib. https://doi.org/10.2118/178355-ms widyarso, a., swadesi, b., wisnu aji wibowo, s., 2006. studi laboratorium pengaruh injeksi polimer dengan berbagai konsentrasi terhadap peningkatan perolehan minyak pada reservoir karbonat. ikat. ahli tek. perminyakan indones. 15 17. wu, x., xiong, c., xu, h., zhang, j., lu, c., lu, x., li, j., cao, h., zhang, n., cui, g., chen, j., ye, y., jia, x., lv, j., yang, z., 2015. a novel particle-type polymer and ior/eor property evaluation. abu dhabi int. pet. exhib. conf. https://doi.org/10.2118/177421-ms yang, l., zhihua, w., xianglong, z., shanzhe, w., 2015. study on emulsification behavior and optimized separation technology of high concentration polymer flooding produced liquid in daqing oilfield. spe middle east oil gas show conf. https://doi.org/10.2118/172768-ms © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.2118/181582-ms https://doi.org/10.2118/181582-ms https://doi.org/10.2118/181582-ms https://doi.org/10.2118/186414-ms https://doi.org/10.2118/186414-ms https://doi.org/10.2118/186414-ms https://doi.org/10.2118/186414-ms https://doi.org/10.2118/174654-pa https://doi.org/10.2118/174654-pa https://doi.org/10.2118/174654-pa https://doi.org/10.2118/68076-ms https://doi.org/10.2118/68076-ms https://doi.org/10.2118/68076-ms https://doi.org/10.24273/jgeet.2017.2.2.304 https://doi.org/10.24273/jgeet.2017.2.2.304 https://doi.org/10.24273/jgeet.2017.2.2.304 https://doi.org/10.22549/jeee.v6i2.992 https://doi.org/10.22549/jeee.v6i2.992 https://doi.org/10.22549/jeee.v6i2.992 https://doi.org/10.2118/179794-ms https://doi.org/10.2118/179794-ms https://doi.org/10.2118/179794-ms https://doi.org/10.2118/179794-ms https://doi.org/10.2118/189255-ms https://doi.org/10.2118/189255-ms 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http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ the key parameter effect analysis of the polymer flooding on oil recovery using reservoir simulation 1. introduction 2. materials and methods 2.1. reservoir fluid and reservoir rock characteristics 2.2 methods 3. polymer properties 4. result and discussion 4.1. polymer concentration analysis 4.2. sor reduction analysis 4.3. polymer adsorption analysis 4.4 increasing of water viscosity analysis 5. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” nurlatifah & purwakusumah/ jgeet vol 08 no 02-2 2023 18 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 research article possibilities study of a non-condensable gas exhaust system through the condensate injection pipe at pltp wayang windu annisa nurlatifah1, anton purwakusumah1,* 1 wayang windu geothermal power station, tromol pos 1, margamukti pangalengan, bandung, indonesia * corresponding author: anton.purwakusumah@starenergy.co.id may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13878 abstract wayang windu geothermal power plant, located in pangalengan, bandung regency, west java with an installed capacity of 227 mwe has two units to generate electricity and deliver to the jawa, madura, and bali grid. the steam extracted from the reservoir contains noncondensable gas of about 1-1.2% of total steam extracted, with the gas composition is co2 92%, h2s 2%, nh3 0.1%, and residual gasses 4.9%. possibilities study of a non-condensable gas exhaust through the condensate injection pipe was created as the efforts in the environmental conservation aspect for reducing carbon released to the atmosphere and reinjected back into the reservoir. this study was simulated in wayang windu unit 2 by calculating the non-condensable gas flow rate from the gas removal system into the condensate injection pipe near of cooling tower blowdown power station area. the analysis result of this study indicates that the non-condensable gas requires a higher flow rate of condensate to dissolve the entire non-condensable gas, and may cause the slug flow pattern which would endanger the condensate pipeline system also destabilize the non-condensable gas exhaust operation process from the condenser through the gas removal system. to deal with this problem, the possibility of exhausting the non-condensable gas produced by the gas removal system can be alternated by flowing its non-condensable gas into a flash absorber system and converting its non-condensable gas into other eco-friendly products and power plant safe. keywords: non-condensable gas, condensate, gas removal system, geothermal, carbon capture, reservoir, condensate reinjection, pipeline, flash absorber, power plant, eco-friendly. 1. introduction every power plant almost always impacts the environment to a different degree depending on the technology used. gas emissions from power plants come from non-condensable gases carried by steam from the reservoir. the geothermal fluid that comes out of the well usually still contains gas that cannot be condensed in the condenser so if left unchecked it can cause the pressure in the condenser to rise and decrease turbine efficiency. pltp wayang windu is equipped with a gas exhaust system consisting of a two-stage steam jet ejector and a vacuum pump, so it is called a two-stage hybrid gas exhaust system. the gas that is carried along with the steam from the well that is not condensed in the condenser is sucked in by the grs and then discharged into the atmosphere through the cooling tower with the help of a fan drive. 1.1 solubility of ncg in water absorption is the process of dissolving the components of the gas phase into the liquid phase. gas has a small density, if the gas is in contact with a liquid, a number of gas molecules will seep into the liquid with different solubility. the concentration of dissolved gases is highly dependent on the specific temperature and pressure. according to henry's law, the solubility of a gas in a liquid is directly proportional to the pressure of the gas before it enters the solution. dalton’s law of partial pressures states that, for a mixture of non-reacting gases, the total of the partial pressure of each gas is equal to the total pressure exerted by the mixture, at constant temperature and volume. the pressure in the transfer medium is the sum of the gas pressure and the water pressure. this applies according to dalton's law of partial pressure. make sure that placing and numbering of equations is consistent throughout your manuscript. eqn. 1, 2, and 3 are written as follow: 𝑃𝑡𝑜𝑡𝑎𝑙 = 𝑃𝑔𝑎𝑠𝑒𝑠 + 𝑃𝐻2𝑂 (1) 𝑃𝑔𝑎𝑠 = 𝑃𝐶𝑂2 + 𝑃𝐻2𝑆 + 𝑃𝑁𝐻3 (2) 𝑝𝑉 = 𝑛𝑅𝑇 (3) the pressure of the gases on the ncg can be found using henry's law equation (eqn. 4). 𝑃𝑔𝑎𝑠 = 𝐾𝑔𝑎𝑠 𝑥 𝐶𝑔𝑎𝑠 (4) with: 𝑃𝑔𝑎𝑠 𝐾𝑔𝑎𝑠 𝐶𝑔𝑎𝑠 = partial pressure of the gas (pa) = henry’s constant value (l.atm/mole) = mole fraction of the gas this equation also applies to other gases by including the number of moles from the henry constant which has been applied based on the partial henry gas law (eqn. 5). 𝑆𝑔 = 𝐾ℎ 𝑥 𝑃𝑔 (5) with: 𝑆𝑔 𝐾ℎ 𝑃𝑔𝑎𝑠 = solubility of the gas = henry’s constant value (l.atm/mole) = partial pressure of the gas (atm) http://journal.uir.ac.id/index.php/jgeet nurlatifah & purwakusumah/ jgeet vol 08 no 02-2 2023 19 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 1.2 horizontal flow of a two-phase fluid when two phases flow in a pipe, the different phases can contribute in terms of flow pattern which will cause different flow hydrodynamics, as well as the mechanisms of momentum, heat, and mass transfer around the fluid. the two-phase flow pattern has two flow models: homogeneous and separable. in the homogeneous model, the steam and water are assumed to be completely miscible, so that the water and gas mixture acts like a single-phase fluid with properties averaging depending on the properties of the individual phases. with this assumption, the flow pattern is considered a calculation method for single-phase flow in the separated flow model the flow pattern is assumed to flow together in the pipe separately, each phase distributed in an occupying part of the pipe flow (saptadji, 2001). beggs and brill grouped the two-phase flow patterns in the horizontal plane into 3 groups, namely: segregated flow, intermittent flow, and distributed flow. the segregated flow pattern is divided into three, namely stratified flow, wavy flow, and annular flow (beggs and brill, 1973). intermittent flow patterns are divided into slug flow and plug flow, while the distributed flow pattern is divided into flows bubbles and mist flow. segregated flow patterns occur when frm <l1, distributed flow patterns occur when frm>l1 and frm >l2, and intermittent flow pattern occurs when l1<frm<l2. fig. 1. shows the flow patterns on the beggs and brill correlations. fig. 1. beggs and brill flow pattern (beggs and brill, 1973). the value of the froud number and liquid content can be determined by the eqn. 6-11. 𝐶𝐿 = 𝑄𝐶𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒 𝑄𝐶𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒 + 𝑄𝑁𝐶𝐺 (6) with: 𝐶𝐿 𝑄𝐶𝑜𝑛𝑑𝑒𝑛𝑠𝑎𝑡𝑒 𝑄𝑁𝐶𝐺 = liquid hold up = flow of condensate = flow of the non-condensable gas 𝐹𝑟𝑚 = 𝑉𝑚 2 𝑔 𝑥 𝐷 (7) 𝐿1 ∗ = 316cl0.302 (8) 𝐿2 ∗ = 0.000925cl-2.4684 (9) 𝐿3 ∗ = 0.1cl-1.4516 (10) 𝐿4 ∗ = 0.5cl-6.738 (11) with: 𝐹𝑅𝑚 𝑉𝑚 2 𝑔 d l = froud number = flow of condensate = flow of the non-condensable gas = inside diameter of pipe = liquid content 2. material and methods the ncg flow rate at the grs output fluctuates depending on the gas content in the steam flowing from the well. in this study, the data to be analyzed as reference data is the daily average data of the monitoring system in realtime human-machine interface (hmi) from the distributed control system (dcs), while the ncg content data contained in steam is the monthly average data of the results testing by laboratory technicians. ncg content in the steam is seen in table 1. ncg data, condensate data, and injection pipe data pressure are shown in table 2, table 3, and table 4, respectively. gas removal system pltp wayang windu is shown in fig. 2. fig. 2. gas removal system pltp wayang windu. table 1. ncg content in the steam. month output flow ncg content in the steam ph h2o u-1 tgc co2 h2s nh3 [kg/s] [w%] [w%] [w%] [w%] [w%] aug2022 2.56 4.84 99.25 0.750 0.729 0.015 0.071 sept2022 2.21 5.18 99.2 0.800 0.668 0.013 0.072 oct2022 2.49 4.77 99.1 0.900 0.632 0.009 0.064 table 2. ncg data. 20 nurlatifah & purwakusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 mont h atmosfe r pressur e dry bulb tem p wet bulb tem p ncg grs flow ncg grs tem p ncg grs pressur e [bar] [deg c] [deg c] [kg/s ] [deg c] [bar] aug2022 0.832 18.7 8 16.9 7 2.56 46.4 6 0.2 sept2022 0.833 18.8 17.0 2 2.21 44.5 6 0.2 oct2022 0.832 17.8 9 16.6 4 2.49 44.5 6 0.2 table 3. condensate data. month u-1 cond. flow u-2 cond. flow total cond. flow u-1 cond. temp u-2 cond. temp [kg/s] [kg/s] [kg/s] [deg c] [deg c] aug2022 63.45 33.16 96.61 51.82 44.41 sept2022 82.09 1.86 83.95 49.53 44.61 oct2022 77.05 14.76 91.81 50.14 44.88 table 4. injection pipe data pressure. month scrubber header ss1 area j5 low point branchline well cond. inj wellhead [bar] [bar] [bar] [bar] [bar] aug2022 -0.51 -0.08 2.17 0.14 -0.70 sept2022 -0.51 -0.19 2.05 -131.92 -0.69 oct2022 -0.52 -0.18 2.18 0.32 -0.70 3. results and discussion 3.1 injection point selection based on table 4, injection pipe pressure data at various points, it is possible to remove ncg output from grs in the scrubber header area, ss1 area, and the condensate injection wellhead considering that the pressure at these locations is lower than the ncg pressure output from grs. the scrubber header area was chosen as a possible location for gas injection considering that this location is the closest distance from the grs, so that back pressure on the vacuum pump which can disrupt the generation and ncg extraction process from the condenser will not occur. in addition, the cost of piping installation is also reduced. this point is also a branch point for mixing condensate water from unit-1 and unit-2. injection point selection is seen in fig. 3. fig. 3. injection point selection. 3.2 non-condensable gas solubility the solubility of gases in water can be done by henry's law, but the henry constant used is not henry's constant in standard conditions but henry's constant due to the influence of temperature, so the calculation results for henry's constant in august-october for each gas are as follows (table 5). table 6 shows solubility of gases to the condensate. nurlatifah & purwakusumah/ jgeet vol 08 no 02-2 2023 21 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 table 5. henry’s constant. month gas temp (k) c kh (l.atm/mole) kh (mole/l.atm) kh’ (l.atm/mole) kh (mole/l.atm) aug-22 co2 319.46 2400 29.41 0.034 17.12 0.0198 h2s 2100 11.49 0.087 7.16 0.0542 nh3 4100 0.0169 0.61 0.0067 0.2421 sept-22 co2 317.56 2400 29.41 0.034 17.91 0.0207 h2s 2100 11.49 0.087 7.44 0.0564 nh3 4100 0.0169 0.61 0.0072 0.2614 oct-22 co2 317.56 2400 29.41 0.034 17.12 0.0207 h2s 2100 11.49 0.087 7.16 0.0564 nh3 4100 0.0169 0.61 0.0067 0.2614 table 6. solubility of gases to the condensate. gas month s s flow gas flow cond. dissolved gas solubility required condensate mole/lh2o gr/kgh2o kg/s kg/s kg/s % kg/s co2 aug 0.004 0.199 2.49 96.61 0.019 0.772 12517.54 sept 0.004 0.217 1.85 83.95 0.018 0.989 8484.94 okt 0.004 0.208 1.75 91.81 0.019 1.092 8409.41 h2s aug 0.010 0.582 0.05 96.61 0.056 109.880 87.92 sept 0.011 0.630 0.04 83.95 0.053 147.267 57.01 okt 0.011 0.606 0.02 91.81 0.056 223.326 41.11 nh3 aug 0.030 1.657 0.24 96.61 0.160 66.064 146.24 sept 0.035 1.932 0.20 83.95 0.162 81.557 102.93 okt 0.032 1.789 0.18 91.81 0.164 92.786 98.95 based on the calculation of solubility gases to the condensate, for the solubility of co2 gas which has a small solubility, the condensate flow rate required to dissolve the co2 gas released from the gas removal system is not large enough to dissolve all of the co2 gas. for the solubility of h2s and nh3 gases, both gases based on calculations can dissolve into the condensate stream with fairly high solubility. 3.3 fluid flow pattern based on the calculation of the two-phase fluid flow pattern using the beggs and brill calculation method, the flow pattern obtained is as follows (table 7). table 7. superficial velocity of fluid. a vcondensate vco2 vm cl frm 1.4 ft2 2.46 33.68 36.14 0.068 30.520 by entering cl and frm values in the liquid content (l) formula, the flow pattern using the beggs and brill method can be determined. table 8 shows liquid content. table 8. liquid content. 𝑳𝟏 ∗ 𝑳𝟐 ∗ 𝑳𝟑 ∗ 𝑳𝟒 ∗ 140.308 0.705 4.953 36,814,698.19 from the results of the liquid content (l) calculation, the condition is obtained (eqn. 12): 0.01≤cl< 0.4 and l3 <frm≤l1 (12) the type of flow that occurs when co2 from the gas removal system flows through condensate water pipes in this condition is intermittent flow, namely slug flow and plug flow. intermittent flow patterns consisting of slug flow and plug flow can result in unstable flow conditions in the pipeline. if the superficial velocity of the gas is high then the type of flow is slug flow, whereas if the superficial velocity 22 nurlatifah & purwakusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 of the gas is low then the type of flow is plug type flow (rogero, 2009). from the results of the calculation of the data above it is known that the superficial velocity of the gas is very high, so it can be concluded that the type of fluid flow from this type of intermittent flow is the slug flow type. this type of slug flow can cause vibration and be dangerous to the pipe structure (rogero, 2009) so it will interfere with the ncg removal process from the grs and the condensate reinjection process from the condenser and cooling tower. in the absence of an absorber and packing column, the contact time between the gas stream and the condensate in the pipe is fast at the point of injection. with poor diffusion of gas into the condensate or a small amount of gas that can be absorbed, the gas will further endanger the condition of the pipeline with high superficial gas velocities. 4. conclusion based on the results of the solubility analysis and fluid flow pattern, the non-condensable gas requires a higher flow rate of condensate to dissolve the entire gas because of its low gas solubility and large superficial fluid velocity. it also may cause the slug flow pattern which would endanger the condensate pipeline system and destabilize the noncondensable gas exhaust operation process from the condenser through the gas removal system. solubility is also affected by ph, it would be better for further research to look for the effect of ph on gas solubility in condensate. as a way to increase the solubility of the noncondensable gas in condensate, a flash absorber column can be installed, and the solubility of the gas that dissolves into the condensate can become larger. another solution is to utilize the co2 gas contained in non-condensable gas to be produced into dry ice products. dry ice is made by lowering the temperature and applying high pressure so that co2 gas can become a solid and turn into dry ice. by this carbon capture method and utilization of the gas, co2 as one of the greenhouse gasses can be useful and turn into eco-friendly products. acknowledgements this work was supported by star energy geothermal wayang windu ltd. therefore, we are grateful for this funding and support of this research. references aksoy, n, gok, o. s, mutlu.h and kilinc, g. 2015. co2 emission from geothermal power plant in turkey. proceedings world geothermal congress 2015. melbourne, australia, 19-25 april 2015. andritsos, n., harnratty, t. j. 1987. interfacial instabilities for horizontal gas liquid flows in pipelines. j. multiphase flow, 13, 583. beggs, h.d., and brill, j.p., 1973. a study of two-phase flow in inclined pipes. jpt, trans., aime, 255. mamrosh, d. l, mcintush, douglas, fisher. removal of hydrogen sulfide and recovery of carbon dioxide from geothermal non-condensable gas using water. murray, 2001. gases and gas exchange. univ. washington. ozcan, n. y, gokcen, g. 2010. performance analysis of single-flash geothermal power plants: gas removal systems point of view. proceedings world geothermal congress 2010 bali, indonesia, 25-29 april 2010. purwakusuma, a., 2016. study of non condensable gas exhaust system through condensate reinjection pipeline in wayang windu geothermal powerplant, master's program thesis, institut teknologi bandung. rybach, l. 2010. co2 emission mitigation by geothermal development – especially with geothermal heat pumps. proceedings world geothermal congress 2010 bali, indonesia, 25-29 april 2010. rogero, e. c., 2009. experimental investigation of developing plug and slug flows. desertasi doktor ingineer. technische universität münchen: münchen,germany. saptadji, n.m., 2002. teknik panas bumi. bandung: departemen teknik perminyakan itb. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 10 hasria et al./ jgeet vol 8 no 1/2023 research article petrogenetic study of ultramafic rocks from waturapa and surrounding areas, south konawe regency, southeast sulawesi province, indonesia hasria1*, masri1, muhammad arba azzaman1, muhamad jerniawan1 1department of geological engineering, halu oleo university, kendari, indonesia * corresponding author : hasriageologi@gmail.com tel.: +62-852-4185-7853 received: nov 24, 2022; accepted: mar 17, 2023. doi: 10.25299/jgeet.2023.8.1.11035 abstract the petrogenesis study of ultramafic igneous rocks in the south konawe region has been carried out by several previous researchers. however, petrogenesis of ultramafic igneous rocks in the waturapa region (located in south konawe) has never been carried out in detail due to the unexposed ultramafic rock. with the exposure of ultramafic rocks by mining activity, it is important to understand the process and tectonic setting of the formation of the rocks. therefore, this study aims to determine the characteristics and petrogenesis of ultramafic igneous rocks in the waturapa area using petrographic and geochemical analysis using the xrf method. petrographic analysis was carried out to determine the relative abundance percentage of primary minerals in the form of olivine, clinopyroxene, orthopyroxene, and opaque minerals as well as secondary serpentine minerals which were formed later. meanwhile, xrf geochemical analysis is used to determine the major and minor oxide content in rocks. this geochemical data is used to determine ultramafic rock types, and magma series and to interpret the tectonic setting of the research location. the results showed that the ultramafic rocks in the study area consisted of olivine websterite and lherzolite, both of which have been serpentinized which is characterized by the presence of serpentine minerals such as lizardite and chrysotile. these serpentine minerals are present as replacement minerals and fracture-filling minerals. the geochemical characteristics of the analyzed rocks showed a sio2 content of less than 45%, high mgo content, and low k2o, tio2, na2o3, and p2o5 compounds. the igneous rocks in the study area are classified as ultramafic rocks (peridot gabbro). ultramafic rocks in the study area belong to the tholeiitic magma series that formed in oceanic islands or oceanic intraplate margins. keywords: petrogenesis, ultramafic rocks, waturapa, south konawe, serpentine, oceanic island. 1. introduction sulawesi island is part of the confluence of three large plates that form the territory of indonesia, two of which are still actively moving. the western part is the eurasian continental plate, also known as the relatively stationary sunda shelf. the southeastern part is formed by the australian continental plate, which is moving northward, and the eastern part is occupied by the pacific ocean plate, which is moving westward. the collision between these plates causes subduction which results in the lifting of oceanic crust rocks and deep-sea sediments to the surface which is called ophiolite (surono, 2013). ultramafic rocks are present as the main component of the upper mantle beneath the continental or oceanic crust (kadarusman et al., 2004). in simple terms, ultramafic rocks are known as a host for some ore minerals such as chromite, nickel sulfide, magnetite, and nickel laterite (sufriadin et al., 2017). petrogenesis of igneous rocks includes the characteristics of the magma source and the conditions of gradual melting, as well as the extent of changes that occur after the magma is transported (wilson, 1989). petrogenesis studies are considered very important because they can be used to interpret the processes and tectonic settings of rock formation (erzagian et al., 2016). previous researchers have previously conducted research on petrogenesis in the east arm region and the results indicated that the east arm ophiolite of sulawesi was formed in the tectonic environment of the mid oceanic ridge, oceanic plateau, and minor island arc (kadarusman et al., 2004). meanwhile, a petrogenesis study of ultramafic igneous rocks in the southeastern arm of sulawesi was conducted by aznah (2019) with the conclusion that ultramafic rocks in the lalembuu region, konawe selatan, southeast sulawesi were formed in a tectonic setting in the form of oceanic ridge and floor or mid-oceanic ridge basalts. referring to the regional geological map (simandjuntak et al., 1993), ultramafic rocks in the study area, specifically in the waturapa area, south konawe, southeast sulawesi, were unmapped regionally. however, mining activities in this area exposed ultramafic rocks that were previously covered by the sulawesi molasse (langkowala formation and eemoiko formation). with the exposure of ultramafic rocks, it is important to carry out research related to petrogenesis to understand the process and tectonic setting of the formation of these rocks. 2. geological setting sulawesi island is located in the central part of indonesia and is the location where three plates meet, namely the eurasian plate, the pacific-philippine plate and the indian-australian plate (hall and wilson, 2000). this situation makes sulawesi a geologically complex island. rocks that were once at the bottom of the ocean are now found exposed on the surface. this is reflected in the widespread distribution of ultramafic rocks in the eastern http://journal.uir.ac.id/index.php/jgeet hasria et al./ jgeet vol 8 no 1/2023 11 and southeastern arms of sulawesi (atmadja et al., 1974; panggabean and surono, 2011; surono, 2013). in the study area, located in the southern part of the southeastern arm of sulawesi, to be precise in the waturapa area, palangga selatan district, south konawe regency, ultramafic rock is exposed locally and belongs to the east sulawesi ophiolite (eso) belt (fig. 1) which is covered by neogene and quaternary sediments (kadarusman et al., 2004). regionally, the waturapa area is included in the regional geology of the kolaka sheet (simandjuntak et al., 1993). based on this geological map, the waturapa area (study area) is composed of two rock formations, from old to young, namely, the langkowala formation (composed of conglomerates, sandstones, shales, and local calcarenite) and the eemoiko formation (consisting of calcarenite, coral limestone, sandstone, and marl) (fig. 2a). simandjuntak et al. (1993) considered the langkowala formation and eemoiko formation to be miocene and pliocene in age, respectively (fig. 2b). on the other hand, surono (2013) stated that the langkowala formation and eemoiko formation are part of the sulawesi molasa, both of which are miocene in age and have a stratigraphic relationship fingering each other. recent research on sulawesi molasses shows that the langkowala formation and eemoiko formation also have a finger-finger stratigraphic relationship with a relatively longer depositional age range, from miocene to pleistocene (fig. 2c) (nugraha et al., 2022). in fig. 2a, regionally, the study area (red rectangle) does not appear to be composed of ultramafic complexes (ku). however, ultramafic rocks are found locally exposed in this area due to mining activities. fig. 1. simplified geological map of sulawesi (kadarusman et al., 2004) and the location of fig. 2 3. materials and methods the samples used in this study are ultramafic rocks exposed in the study area (fig. 3). as can be seen in fig. 2a, samples were taken from five locations and labelled as hst.008, hst.028, hst.030, hst.033 and hst.042. hand specimen-sized samples from each location were described macroscopically. to determine the texture, structure, and mineral composition microscopically, petrographic analysis was applied. in this analysis, the rock sample is thinly sliced to a thickness of about 0.03 mm and observed under a polarizing microscope. thin section preparation and petrographic analysis were carried out at the petrography and mineral optics laboratory, department of geological engineering, hasanuddin university, makassar. the content of major and minor oxides was analyzed using the x-ray fluorescence (xrf) method. this analysis involved five ultramafic rock samples and was carried out at the central laboratory of hasanuddin university, makassar. the data from the xrf analysis were utilized to interpret the type of magma, magma affinity, and the tectonic environment for magma formation using the geochemical data toolkit (gcdkit) software. 12 hasria et al./ jgeet vol 8 no 1/2023 fig. 2. (a) regional geological map of the southern kolaka sheet (simandjuntak et al., 1993) and the location of the study area; (b) and (c) regional stratigraphy according to (simandjuntak et al., 1993) and (nugraha et al., 2022), respectively. red texts indicate the rock formations that make up the study area 4. results and discussion 4.1 field observation and petrography based on the results of field observation, megascopic description, and petrographic analysis, ultramafic rock samples in the study area fall into two rock types. samples such as hst.008 and hst.042 are classified as olivine websterite, while samples with codes hst.028, hst.030, and hst.033 are plotted as lherzolite (streckeisen, 1976). megascopically, olivine websterite has a white-gray weathered color, blackish green fresh color, shows a texture of crystallinity: holocrystalline, granularity: phaneritic, inter-crystal relationships: equigranular, crystal form: euhedral-anhedral, composed of pyroxene, serpentine, and opaque minerals. the results of the petrographic analysis show a more detailed rock composition with varying abundances. the mineral olivine occurs at 10% abundance and still exhibits a relic texture. the minerals of orthopyroxene (enstatite) and clinopyroxene (augite) are present at 11% abundance each. another primary mineral identified is an angular-shaped opaque mineral with an abundant of 3% and slightly oxidized at the edges. generally, the rocks are strongly deformed and serpentinized, indicated by the abundant lizardite and chrysotile-type serpentine minerals showing a mesh texture together with olivine mineral (fig. 3). serpentine minerals are very dominant and reach an abundance of 65%. hasria et al./ jgeet vol 8 no 1/2023 13 fig. 3. (a) typical olivine websterite outcrop and hand specimen. (b) photomicrograph of olivine websterite on plane-polarized light (ppl) and (c) crossed-polarized light (xpl) of hst.008. notes: cpx = clinopyroxene (augite), cry = chrysotile (serpentine), lz = lizardite (serpentine), ol = olivine, opq = opaque mineral, opx = orthopyroxene (enstatite). lherzolite found at locations of hst.028, hst.030, and hst.033 crop out at the mining site (fig. 4a) and generally show a litlle different characteristics compared to previous ultramafic rock samples. megascopically, lherzolite is gray (weathered sample) and dark green in colour (fresh sample). under the polarized microscope observation, the rock composed of euhedral to anhedral crystals shows a holocrystalline and equigranular-phaneritic texture. compared to olivine websterite, this rock contains more olivine minerals, with an abundance of up to 14%. other minerals that are also present are orthopyroxene (enstatite, 7%), clinopyroxene (augite, 9%), and opaque minerals (2%). this rock also experiences serpentinization alteration, characterized by the abundant lizardite (54%) and chrysotile (14%) serpentine minerals. both minerals are present as fracture-filling and replacement minerals and form mesh texture showing olivine minerals surrounded by serpentine (fig. 4b–fig. 4e). fig. 4. (a) typical outcrop and hand specimen of lherzolite. (b) and (c) are photomicrographs of the hst.028 sample on ppl and xpl, respectively. (d) and (e) are photomicrographs in ppl and xpl for lherzolite (hst.033). notes: cry = chrysotile (serpentine), cry vein = 14 hasria et al./ jgeet vol 8 no 1/2023 chrysotile vein, cpx = clinopyroxene (augite), lz = lizardite (serpentine), lz vein = lizardite vein, ol = olivine, opq = opa que mineral, opx = orthopyroxene (enstatite) , mesh = mesh texture 4.2 whole-rock geochemistry table 1 shows the results of rock geochemical analysis using the xrf method. as we can see, the geochemical characteristics of the rock analyzed show a sio2 content of less than 45%, a high mgo content, and relatively lower k2o, tio2, na2o, and p2o5 compounds. we utilize this geochemical data to determine several parameters of rock petrogenesis, such as rock type, magma series, and magma origin. table 1. major and minor oxides of ultramafic rocks in the study area oxides (in wt.%) sample id hst.008 hst.028 hst.030 hst.033 hst.042 sio2 40,31 43,2 39,8 41,21 39,41 mgo 13,2 14,3 10,13 10,51 9,12 fe2o3 24,97 25,09 24,7 21,91 23,65 feo 15,92 24,41 21,78 17,96 21,32 na2o 0,0367 < 0,01 0,0347 < 0,01 < 0,01 al2o3 2,36 2,12 2,35 0,09 1,07 cao 1,19 1,78 1,18 1,5 1,59 sb2o3 0,0073 0,0123 0,0097 0,0097 0,0132 nio < 0,01 < 0,01 < 0,01 < 0,01 < 0,01 mno 0,473 0,429 0,522 0,453 0,372 p2o5 < 0,01 0,0038 0,0144 0,0243 0,0463 tio2 < 0,01 0,0531 0,0356 0,0241 0,0224 v2o5 < 0,01 < 0,01 < 0,01 < 0,01 < 0,01 k2o < 0,01 0,0011 0,3 0,0096 0,0013 cuo < 0,01 < 0,01 < 0,01 < 0,01 < 0,01 rh2o3 0,0063 0,0106 0,0092 0,0075 0.0108 in2o3 0,0116 0,0182 0,0170 0,0158 0,0184 total 82,5397 86,977 79,0667 75,8174 75,282 the type of ultramafic igneous rock is determined by referring to the classification of igneous rock according to (middlemost, 1994). this classification is divided based on the weight percent content of total alkali (na2o + k2o) and weight percent of silica (sio2). we use the geochemical data of five samples and plot them into the diagram. the results show that all rock samples include in ultrabasic rocks group or ultramafic rocks. the graphic also exhibits that two of the five rock samples analyzed geochemically (hst.028 and hst.033) fall into peridot gabbro (middlemost, 1994) (fig. 5). fig. 5. the classification of plutonic rocks (middlemost, 1994) and the result of the plotted geochemical data of five rock samples. after knowing the types of ultramafic rocks that make up the research area, then the magma series is determined. a magma series is a compositional group that can describe the evolution of magma. initially, magma from the mantle hasria et al./ jgeet vol 8 no 1/2023 15 has an ultramafic composition rich in mg and fe. as a result of magma differentiation (fractional crystallization), the composition of magma will evolve into more acidic magma, characterized by relatively lower mg and fe contents (wilson, 1989 and winter, 2014). determination of the magma series that forms ultramafic rocks can be carried out by utilizing the afm triangle diagram (a = na2o + k2o; f = feo + fe2o3; and m = mgo). genetically, vermeesch and pease (2021) have proposed a new classification of the magma series into tholeiitic or calc-alkaline by replacing the f component (feo + fe2o3) with tio2. however, because the tio2 content in this study sample was very little, the determination of the magma series still used the afm diagram by irvine and baragar (1971). the plot results in the afm diagram show that the five ultramafic igneous samples from the study area with sample codes hst.008, hst.028, hst.030, hst.033, and hst.042 belong to the tholeiitic magma series (fig. 6a). tholeiitic magma series is formed when magma is reduced (osborn, 1959). in reduced magma, the content of iron (fe) and magnesium (mg) will relatively decrease because these two components are crystallized as ferromagnesian minerals such as olivine and pyroxene (fig. 3b and 3c; and fig. 4b – fig. 4e). the tholeiitic magma series may form in several tectonic settings, either in island arcs, mid-oceanic ridges, oceanic islands, or continental rift zone environments (wilson, 1989). to interpret the tectonic environment of the origin of the ultramafic rock-forming magma in the study area, we used the triangular diagram by pearce et al. (1977), in which this diagram compares the main elements of rock in the form of feot (total), mgo and al2o3 (fig. 6b). the plotting results in the diagram show that the ultramafic rocks in the waturapa area formed in an oceanic island environment (pearce et al., 1977) or widely known as oceanic intraplate margin (wilson, 1989; winter, 2014). an illustration of the oceanic island tectonic environment is provided in fig. 7. it is well-known that hawaiian islands are an example of a product of oceanic intraplate volcanism (winter, 2014). fig. 6. (a) determination of magma series using afm diagrams (irvine and baragar, 1971) and (b) interpretation of tectonic settings (pearce et al., 1977). notes: a = na2o + k2o; f = feot = feo + fe2o3; and m = mgo interpretation of the tectonic setting of the magma that formed ultramafic rocks in the eastern and southeastern arms of sulawesi has also been carried out by previous researchers and the results show that these ultramafic rocks originate from mid-oceanic ridges (atmadja et al., 1974; asfar and eric, 2019; hasria et al., 2020) and suprasubduction zone (bergman et al., 1996; parkinson, 1998). nonetheless, kadarusman et al. (2004) interpret that the ultramafic rocks in the eastern and southeastern arms of sulawesi are grouped as east sulawesi ophiolite (eso) belt, originating from mid-oceanic ridges, oceanic plateaus or seamounts, and minor supersubduction zones (ssz) where the oceanic plateau or seamount is the product of the oceanic intraplate volcanism (winter, 2014). fig. 7. illustration of the location of magma formation and their tectonic setting association (after winter, 2014). the yellow block is the result of the tectonic setting interpretation of the study area 5. conclusions the conclusions of this study are as follows:  based on the petrographic analysis, the ultramafic rocks in the study area consist of olivine websterite and lherzolite, characterized by the presence of chrysotile and lizardite minerals which appear as fracture-filling minerals and replacement minerals  the results of geochemical data interpretation indicate that the igneous rocks in the study area are classified as ultramafic/ultramafic rocks (peridot gabbro) exhibiting a tholeiitic magma series and formed in an oceanic island or oceanic intraplate margin. references asfar, s., eric, s., 2019. karakteristik batuan ultrabasa pada 16 hasria et al./ jgeet vol 8 no 1/2023 kompleks ofiolit desa paka indah kabupaten konawe utara provinsi sulawesi tenggara. jurnal rekayasa geofisika indonesia, 1(1), 24–37. http://dx.doi.org/10.56099/jrgi.v1i01.8317 atmadja, r.s., golightly, j.p., wahju, b.n., 1974. mafic and ultramafic rock associations in the east arm of sulawesi (indonesia). proc. bandung inst. technol. 8 (2), 67– 85. aznah, y.s., 2019. analisis geokimia dan petrogenesis batuan beku ultramafik daerah lalembu dan sekitarnya kabupaten konawe selatan provinsi sulawesi tenggara. (undergraduate thesis, universitas halu oleo) bergman, s.c., coffield, d.q., talbot, j.p., garrard, r.a., 1996. tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait, indonesia: evidence for a miocene continent-continent collision. geol. soc. spec. publ. 106, 391–429. https://doi.org/10.1144/gsl.sp.1996.106.01.25 erzagian, e., setijadji, l.d., warmada, i.w., 2016. studi karakteristik dan petrogenesis batuan beku di daerah singkawang dan sekitarnya, provinsi kalimantan barat. seminar nasional kebumian ix, universitas gadjah mada, yogyakarta, 421–432. hall, r., wilson, m.e.j., 2000. neogene sutures in eastern indonesia. j. asian earth sci. 18, 781–808. https://doi.org/10.1016/s1367-9120(00)00040-7 hasria, hasan, e.s., deniyatno, salihin, l.m.i., asdiwan, 2020. characteristic of ultramafic igneous rock ofiolite complex in asera district, north konawe regency, southeast sulawesi province, indonesia. journal on geoscience, engineering, environment, and 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sulawesi tenggara. proceeding, seminar nasional kebumian ke-10, universitas gadjah mada, yogyakarta. 980–989. surono, 2013. geologi lengan tenggara sulawesi, badan geologi kementerian energi dan sumber daya mineral, bandung. vermeesch, p., pease, v., 2021. a genetic classification of the tholeiitic and calc-alkaline magma series. geochemical perspective letters. 19, 1-6. https://doi.org/10.7185/geochemlet.2125 wilson, m., 1989. igneous petrogenesis: a global tectonic approach. springer, london. https://doi.org/10.1180/minmag.1989.053.372.15 winter, j.d., 2014. principles of igneous and metamorphic petrology, 2nd ed, pearson prentice hall. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 106 yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 a study on influence of organic ligands on migration of heavy metals through compacted clayey soil sudheerkumar yantrapalli 1, *, hari krishna p 2 , srinivas k 3 1 geotechnical engineering division , nit warangal, india 2 department of civil engineering, nit warangal, india * corresponding author : sudheerkumar@student.nitw.ac.in tel.:+91 9866938516 received: 27 des, 2017. revised : 16 apr, 2018, accepted: 24 may, 2018, published: 1 june 2018 doi: 10.24273/jgeet.2018.3.2.1036 abstract this paper presents the feasibility study on utilization of locally available clayey soil as compacted clay liner based on its contaminant migration capacity under the presence of organic chemical edta (ethylene diamine tetra acetic acid) which is abundantly released into the environment. lead, nickel, cadmium and chromium ions was selected as contaminants and its migration properties are assessed by conducting column studies with a single and multiple heavy metal solution with the edta. from the experimental investigations, it is revealed that with the presence of edta, the contaminant breakthrough time get reduced due to soluble metal edta complex formation. at ph 2, interaction with multi metal, the mobility was increased and the order of mobility was observed as cr > cd > ni > pb. with the presence of edta in multi metal system at ph 2, the order of the mobility was cr > ni > cd > pb and at ph 7 the mobility of heavy metals were increased the order was cr > ni > pb > cd. this study reveals that locally available clayey soil is capable of retaining heavy metals and it may be used as a compacted clay liner, where organic chemical like (edta) ingression is present. keywords: clayey soil, compacted clay liner, lead, nickel, cadmium, chromium, edta, column studies 1. introduction the rapid growth of industrialization and urbanization, the amount as well as the rate of generation of waste is increasing substantially, thereby insisting us to think about the need of disposal of waste (consisting mainly house hold and industrial rejects) in an effective and scientific way (rajesh et al., 2014). basically, the disposed waste comprised of different types of toxic and non-toxic elements i.e. heavy metals, organic and inorganic matter etc. of them, the more emphasis is given to heavy metals which are mainly responsible for contamination of surface and subsurface environment (marina et al., 2003, kumar and singh., 2005; li et al., 2012). further, it was observed that, most of the causes of ground water pollution initiated from the landfill area where there was no provision of installing engineered liners and leachate collection system (goodall and quigley., 1977). to prevent such surface and subsurface contamination, it is necessary to place a barrier the between waste and surrounding environment (mulligan et al., 2001). to construct a barrier or liner, with commercially available materials such as bentonite or geo-membranes can be used (gleason et al 1997). but, using those material landfill lining system may lead to cracking up under elevated temperature and also under aggressive chemicals in landfill. koerner and daniel (1993) and rowe (2005) observed that, using geo-membrane as a bottom liner seems to be ineffective due to the improper handling and placement. high leakage rate has been observed through geo-membrane and geo synthetic clay liner due to tear created in the membrane caused by the improper handling and placing. so, to counter these problems, if locally available clayey soil meeting the basic requirements of landfill liner such as hydraulic conductivity, and good adsorption capacity, it is possible to construct a secure landfill (mohamedzein et al., 2005). past findings revealed that the studies on the soil leachate compatibility mainly focused on how heavy metals are being adsorbed by the soil and migrated through. but the adsorption of heavy metals by the soil and migration of heavy metals is unlike under the presence of organic chemicals. the very common organic chemical which is disposed of from household detergents and textile industries is edta (ethaline diamine tetra acetic acid). the volume of edta disposed into the environment from these sources is almost 51% (oviedo and rodríguez, 2003). the government of telangana (india) proposed to construct textile industry beside the existing landfill leachate pond. so, disposal of edta along with textile industrial waste water on leachate pond causes desorption of metal ions which is retained by the soil then causes the ground water contamination problems in and around landfill areas (oviedo and rodríguez, 2003; chen et mailto:sudheerkumar@student.nitw.ac.in yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 107 al., 2008). though many researchers have focused on the utilization of edta for extraction of heavy metals from the soils and sediments (reddy et al. 2003; reddy et al. 2010), but excessive utilization of edta may pose severe environmental problems (peters and shem, 1992; peters., 1999). so, utilization of edta needs to be scrutinized because this edta can influence the mobility of heavy metals through the soil. and the presence of organic and inorganic chemicals in waste water or in landfill leachate may seriously affect the adsorption of various metal ions (bowers and huang, 1985). there is a little information available about adsorption behavior of heavy metals with known parameters like type of soil and concentration of organic chemicals present and ph of the leachate. in the present study, efforts were being made to understand the migration of heavy metal ions through the clayey soil with the presence of edta. column studies were performed to calculate the diffusion coefficient from the column data obtained. so, by obtaining these parameters, it may be possible to design safe and secure compacted clay liner systems where the organic chemicals present in the landfill leachate. 2. transport of chemicals through soil transport of chemicals through the soil consists of three main process namely, advective transport, diffusive transport and chemical reactions between the chemicals and the soil. the concentration profile of a chemical in the soil medium in 1d transport equation which can be expressed in equation 1, ∂c ∂t = d r ∂c ∂z2 − vs r ∂c ∂z (1) the solution of the 1-d transport equation was proposed by ogata and banks (1961) and rearranged by shackelford (1994); mohammad and anita (1998) for landfill liner application. the solution was expressed in terms of a relative concentration. this is the ratio of concentration as a function of depth and time to the initial concentration of the solution, as expressed in the equation 2. 𝐶 (𝑧,𝑡)) 𝐶0 = 1 2 {𝑒𝑟𝑓𝑐 ( 𝑍−𝑉𝑠 𝑡 2 √𝐷𝑇 ) + exp ( 𝑉𝑠 𝑍 𝐷 ) 𝑒𝑟𝑓𝑐 ( 𝑍+𝑉𝑠 𝑡 2 √𝐷𝑇 )} (2) r: retardation factor; c: effluent concentration (mg/l); c0: influent concentration (mg/l); z: thickness of the soil; vs: velocity of fluid through soil (m/sec); t: time to achieve breakthrough time (hr); erfc: complementary error function 3. materials and methods locally available black cotton soil (ch soil) is obtained from warangal, telangana, india were used in the study and properties and the chemical composition of the soil is presented in table 1 and 2. table 1. properties of the soil property is 2720 clayey soil gravel (%) part iv 0 sand (%) 30 silt (%) 39 clay (%) 31 liquid limit (%) part v 61 plastic limit (%) 21 plasticity index 40 classification (is) ch mdd (g/cc) part vii 1.7 omc (%) 19.6 free swell index part xxxx 50 cec (meq/100g) part xxiv 75 k (10 -10 m/sec) part xvii 0.505 mdd: maximum dry density; omc: optimum moisture content; cec: cation exchange capacity; k: permeability table 2. chemical composition of the ch soil soil composition % soil compositio n % sio2 43.6 k2o 0.63 al2o3 22.8 mno 0.47 fe2o3 14.7 p2o5 0.28 cao 7.5 na2o 0.225 mgo 7.3 so3 0.14 tio2 1.71 %: percentage 3.1 chemicals all the chemicals used in the present study were analytical grade and the stock solution of 1000 mg/l were prepared from the salts. from the 1000 mg/l stock solution, the initial concentration of 30 mg/l of each heavy metal pb (ii), ni (ii), cd (ii) and cr (vi) prepared. the initial concentration was selected mainly because of the maximum heavy metal concentration present in the leachate. the leachate composition presented in table 3. table 3. chemical composition of leachate parameter concentration (mg/l) nickel (ni) 37 chromium (cr) 22 cadmium (cd) 1.1 lead (pb) 0.7 the ph of the influent solution was maintained as 2 for pb, ni and cd mainly because, these metals were having less percentage removal at ph 2 (liu et al, 2010; soares et al, 2011; li et al, 2012; hamadneth et al, 2015). for cr (vi) the ph was maintained as 7 because of cr (vi) having less percentage removal at ph 7 (gosh et al, 2013). when edta present along with heavy metals (pb, ni, cd and cr (vi)), the ph of the solution was maintained as ph 7 because, the edta present in 108 yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 the solution have low heavy metal adsorption at ph 7 (li et al, 2012) and in case of multi heavy metal interaction, the ph was maintained 2 and 7. the ph of the solution was adjusted by using 0.1m hno3 and 0.1m naoh solution. 3.2 experimental procedure sample preparation and placement in the column column tests were conducted to determine the transport parameters of the ch soil. the soil samples were prepared by adding deionized water to the air-dried soils to achieve water content 2% wetter than the optimum water content in order to obtain the lowest hydraulic conductivity of soil sample (daniel, 1994; benson et al, 1999). substantially, the samples were compacted in accordance with an adaptation of the standard proctor compaction method using a mould of 6.74 cm diameter and 2 cm height. fig. 1. small scale column setup the sample was permeated initially with di water in order to achieve the first exposure effect and hence it reduced the hydraulic conductivity of the samples (shackelford, 1994; quaranta et al, 1996; gleason et al, 1997). the flow was induced by maintaining the constant head throughout the experiment. after 24 hr of permeation with the di water, the di water removed and heavy metal solutions were introduced and then periodically collected the heavy metal effluents and its concentration were analysed by using agilent made icp oes. the schematic representation of the column setup used in the investigation is given in fig. 1. the column was placed on the stand to remain vertically and sufficiently above the floor for outlet. the column tests were observed up to a point when 90% of the breakthrough was achieved. 4. results and discussion the breakthrough curves are plotted between the relative concentration (c/c0) along ordinate and time along abscissa are shown in figures 2 to 12. the data used for finding breakthrough curves include the results obtained from the column experiments conducted on ch in the presence of single and composite metal solution in the presence of edta. the diffusion coefficients for each condition was sown in table 4 and 5.  single heavy metal interaction nickel (ii) solution based on the effluent concentration obtained, breakthrough curve is drawn with respect to time calculated from the starting of experiment to the point of collection expressed in hours for ch soil. the breakthrough curves are shown in fig 2 for ch soil considering only ni solution as an incoming synthetic pollutant. 0 2000 4000 6000 8000 10000 12000 14000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) heavy metal : nickel without edta ph : 2 c 0 (mg/l) : 30 t 50 (hr) : 6000 fig. 2. breakthrough curve of ch soil for nickel (ni) it has been observed from the fig 2 the breakthrough time required for achieving 50% breakthrough of ni for ch soil is 1200 hours. this is because of higher cation exchange capacity of ch soil.  lead (ii) solution based on the effluent concentration obtained, breakthrough curve is plotted with respect to time calculated from the starting of experiment to the point of collection of effluent expressed in hours for ch soil. the breakthrough curve is shown in fig 3 for ch soil considering only pb solution as an incoming synthetic pollutant. 0 2000 4000 6000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) heavy metal : lead without edta ph : 2 c 0 (mg/l) : 30 t 50 (hr) : 3600 fig. 3. breakthrough curve for pb yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 109 similar trend is observed in case of pb as in case of ni i.e., the delayed breakthrough has been found for ch soil. moreover, from fig 3, it is also observed that pb shows more mobility when compared to ni.  cadmium (ii) solution the breakthrough curve for cadmium is given in fig 4, in case of ch soil with mentioning of the time required for achieving 50% breakthrough. 0 2000 4000 6000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) heavy metal : cadmium without edta ph :2 c 0 (mg/l) : 30 t 50 (hr) : 2600 fig. 4. breakthrough curve for cd the fig 4 shows the time required to get 50% break through is 2600 hr. finally the order of migration observed for the three heavy metals such as pb, ni and cd has been given based on the breakthrough time. it has been noticed that, compared to pb and ni, the cd is showing more mobility at ph 2 for ch soil. at ph 2, the order of heavy metal mobility was ni, pb and cd from low mobility to high mobility.  chromium (vi) solution the column studies were conducted for hexavalent chromium (cr (vi)) with ph 7. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c n e tr a ti o n ( c /c 0 ) time (hr) heavy metal: chromium ph : 7 c 0 (mg/l) : 30 t 50 (hr) : 5.5 fig. 5. breakthrough curve for cr (vi) the breakthrough curve obtained from column studies for cr (vi) were presented in fig 5. the result shows higher mobility of cr (vi) was observed when compared to mobility of pb (ii), ni (ii) and cd (ii). this is mainly because, as cr (vi) is present in anionic from, the cr (vi) will repel with negative charged soil surface as a result it will not adsorbed on the soil surface leads to early migration of the cr (vi). by considering all the above results, in the term of breakthrough curves in a single metal system, it can be observed that at ph 2, the decreasing order of mobility for heavy metals expressed as ni < pb < cd. this is because, at ph 2, electronegativity of the metal ion plays an important role in getting adsorbed by soil active sites. higher the electronegativity of metal, the greater chance to get adsorbed by the soil through easier dissociation of h + ion from the functional groups of the soil mineral (paulo et.al, 2001). the sequence of electronegativity for the three metals are ni (1.91) > pb (1.8) > cd (1.69). the column studies are shows similar behaviour supported by the electronegativity concept. at low ph, the adsorption of cd is decreased by the protonation of silica and alumina group i.e. si o and al o respectively (abollino et.al, 2003). on the other hand, the adsorption of cr (vi) decreases with increase in ph. this is due to increase of negative charge in the soil solid phase (sherene 2010) with increase in ph which leads to higher mobility of (vi) and also the mobility was expected to be increased by probable decrease in the plastic limit of the soil after interaction of cr (vi) with the soil. hence, it increases the hydraulic conductivity of the tested soils due to decrease in the thickness of diffused double layer (wang p. et al, 2015).  composite heavy metal system in case of composite metal system, four heavy metals (pb, ni, cd and cr) have been considered for study. the ph of the final solution was set at 2 by adding 0.1m hno3. the composite solution was then transferred to soil column for further study. ph 2 has been chosen to eliminate the metal hydroxide compound formation. the breakthrough curves are plotted and shown in fig 6 based on the results obtained from column tests performed on ch soils. 0 2000 4000 6000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 r e la ti e v e c o n c n e tr a ti o n ( c /c 0 ) time (hr) lead t 50 : 2000 hr nickel t 50 : 600 hr cadmium t 50 : 300 hr chromium t 50 : 150 hr ch soil multi metal at ph 2 fig. 6. breakthrough curve for composite heavy metal system 110 yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 from fig 6, it has been observed that the time required to accomplish half breakthrough for multi metal system is less for multi metal system when compared to single heavy metal system for ch soil. the reduction in breakthrough time can be observed for three bivalent metal ions i.e. ni (ii), cd (ii) and pb (ii) and for cr (vi), the breakthrough time increases when compared to the result obtained in case of single metal system. this is mainly because, the reduction in adsorption for three heavy metals can be stated by considering the competitive effect between the metals with hydrogen ion (h + ). at lower ph, due to the presence of hydrogen ion (h + ) in the soil solution the competition occurs between h + ions and the other three bivalent metals for occupying adsorption sites (raymond and yuwaree 1993). as a result, the mobility of three bivalent ions (pb, ni and cd) were increased, which leads to quick breakthrough in case of multi heavy metal system. but in case of cr (vi) which is present in oxyanionic form, the reverse behaviour can be observed due to the transformation of cr (vi) ion into cr (iii) ion in presence of h + ion. the equilibrium equation for the yielding of trivalent chromium ion at lower ph is given in equation 3 (daneshvar et. al, 2002). cr2o7 2 (aq) + 14h + (aq) + 6e ----- 2cr 3+ (aq) + 7h2o (3) the newly formed cr (iii) ion can be retained by the soil through cation exchange process due to its higher positive charge ultimately resulting in greater adsorption of cr (vi) present in multi metal system at ph 2.  single heavy metal system with edta to find the effect of synthetic organic compound i.e. edta on the mobility of heavy metals passing through the ch soil. the same procedure was then followed as in case of single metal system without the presence of edta. the breakthrough curve obtained based on the available data for each heavy metal separately in the presence of edta are presented in figures 7 to 12.  nickel (ii) solution with edta based on the effluent concentration of ni (ii) obtained, the breakthrough curve was plotted and presented in fig 7 for ch soil. 0 150 300 450 600 750 900 1050 1200 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) heavy metal : nickel ph :2 c 0 (mg/l) : 30 edta : 1.0 mm t 50 (hr) : 3750 fig. 7. breakthrough curve for ni (ii) in presence of edta from fig 7 it is observed that, in the presence of edta, the time for achieving 50% breakthrough is reduced compared to the absence of edta in single metal system. it can be concluded that the chelating ability of edta increase the solubility of ni by forming complex product (kim et.al. 2003).  lead (ii) solution with edta the breakthrough curve for lead (ii) in the presence of edta is represented in this context. the time required for attaining half breakthrough is also approximately mentioned by sorting it out from the breakthrough curve. the breakthrough curve for ch soil are shown in fig 8. 0 2000 4000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c n e tr a ti o n ( c /c 0 ) time (hr) heavy metal : lead with edta ph : 2 c 0 (mg/l) : 30 mg/l edta : 1 mm t 50 (hr) : 2230 fig. 8. breakthrough curve for pb (ii) in presence of edta from fig 8, it is observed that, the mobility of pb (ii) increased in the presence of edta due to the pb edta complex formation. the effect of edta complexation with metal ion can be quite presumed based on the obtained breakthrough data.  cadmium (ii) solution with edta in presence of edta, the mobility of cd (ii) can be shown through the breakthrough curve plotted on the basis of the results obtained from column test. the time required for achieving 50 % breakthrough shown in fig. 9. the breakthrough curve was presented with respect to time expressed in hours. cd (ii) was also not an exception case from the other two bivalent metal ions (pb and ni). but the reduction in time for achieving half breakthrough due to increase in mobility of metal ions through the formation of stable metaledta complex product was more in case of cd (ii) compared to ni (ii) and pb (ii) . in the presence of edta, the increasing order of mobility was observed as: cd (ii) > pb (ii) > ni (ii). the observed behaviour of the three bivalent metals (pb, ni and cd) can be explained by employing of complexation constant which determines the stability of metaledta complex. the stability constants of cd, pb and ni are 16.5, 18 and 18.6 respectively. the higher the value of complexation constant, the greater will be the chance of forming more stable metaledta complex. the increasing order of the stability constant in case of heavy metal ions is as follow: cd (ii) < pb (ii) < ni (ii) and yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 111 from this as stability constant of metal edta complex increased, the mobility of heavy metal is reduced (nastaran and alain, 2009). 0 50 100 150 200 250 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) heavy metal : cadmium ph : 2 c 0 (mg/l) : 30 edta : 1.0 mm t 50 (hr) : 440 fig. 9. breakthrough curve for cd (ii) in presence of edta  chromium (vi) solution with edta the breakthrough curve for hexavalent chromium solution in the presence of edta have been shown in fig. 10. which shows the time required for 50 % breakthrough for ch soil at ph 7. 0 50 100 150 200 250 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) heavy metal : chromium ph : 7 c 0 (mg/l) : 30 edta : 1.0 mm t 50 (hr) : 105 fig. 10. breakthrough curve for cr (vi) in presence of edta from fig 10, it was observed that, the mobility of cr (vi) is reduced in the presence of edta in case of ch soil when compared with without edta condition. this is mainly because, at greater ph the presence of hydroxyl ion (oh ) may compete with edta for complexation with the metal ions which tends to hydrolyse and precipitate as hydroxides (jose et.al. 2014).  composite heavy metal system with edta the column tests were performed on composite heavy metal system (i.e. pb (ii), ni (ii), cd (ii) and cr (vi)) in the presence of edta at two different ph (2 and 7) to know the breakthrough behaviour of heavy metals. all the results obtained from each test are represented in the form of breakthrough curves which are plotted and presented in fig 11 and 12.  composite heavy metal with edta at ph 2 based on the concentration of effluents and the time of collection of effluents emitting from the soil columns, the breakthrough curves were plotted and further represented in the context. 0 2000 4000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 r e la ti e v e c o n c n e tr a ti o n ( c /c 0 ) time (hr) lead, t 50 :1300 hr nickel, t 50 :900 hr cadmium, t 50 :2010 hr chrmoium, t 50 :400 hr ch soil multimetal edta ph 2 fig. 11. breakthrough curve for composite heavy metal in the presence of edta form the fig. 11, it is observed that, there are many variations in the results that can be observed in multi metal system under the influence of edta when compared to single metal system in the presence of edta. this is mainly due to the competitive effect existing between ni (ii) and pb (ii) with other metals and h + ion present in multi metal system and higher complexation constants prevailing in the metaledta complexation reactions for both bivalent metals, the mobility is enhanced in case of ni (ii) and pb (ii) for ch soil. in case of cd (ii), this is mainly due to the low stability constant of cd (ii) edta complex product and shortage of free edta ions available for complexation while having higher affinity of edta towards other bivalent ions. for cr (vi), after transforming into trivalent ion i.e. cr (iii) the chance for forming complex with edta is reduced due to increase in its ionic radius compared to cr (vi) (jose et. al 2014).  composite heavy metal with edta at ph 7 comparative analyses have been done based on the results obtained at two different ph (2 and 7) with supporting expectable reasons which more or less confirm to the explanations provided by the researchers. the break through characteristics of composite heavy metals in the presence of edta at ph 7 was presented in fig. 12, from fig 12, it is observed that, the break through time is reduced significantly in the presence of edta at ph 7 condition when compared with composite heavy metals at ph 2 condition in the presence of edta. this is due to the formation of metal edta complexes that exist in the solution in the form of negative charged molecule (bradl 2004), as a result of the negative charged soil surface is competing with the metal edta complex leads to the early migration of heavy metals through the soil. 112 yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 0 500 1000 1500 2000 2500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 r e la ti e v e c o n c e n tr a ti o n ( c /c 0 ) time (hr) lead t 50 :850 hr nickel t 50 :450 hr cadmium t 50 :1020 hr chromium t 50 :150 hr bc soil multi metal edta ph 7 fig. 12. breakthrough curve for composite heavy metal in the presence of edta  diffusion coefficient (d*) the diffusion co-efficient (d*) are calculated by using equation 2 on the basis of t50 (time required to achieve 50 % breakthrough) obtained from each breakthrough curve for the corresponding case (ramakrishna et.al. 2011). the parameter d* is having greater significance in designing and checking the effectiveness of the landfill liner.  diffusion coefficient (d*) for black cotton soil (ch) the effective diffusion coefficient (d) calculated for single heavy metal solution interaction is presented in the table 4. table 4. diffusion coefficient for single metal solution single heavy metal without edta ph heavy metal d* (m 2 /sec) 7 cr 2.45x10 -08 2 cd 4.16x10 -11 2 pb 3.50x10 -11 2 ni 2.10x10 -11 single heavy metal with edta 7 cr 1.15x10 -09 2 cd 2.74x10 -10 2 pb 5.39x10 -11 2 ni 3.18x10 -11 from this table it is observed that the diffusion coefficient is reduced about 1.54, 1.51 and 6.58 times for pb (ii), ni (ii) and cd (ii) respectively after edta present in the influent solution. this is mainly because, when the influent solution passes through the soil column, because of the alkali nature of the soil, the solubility of the metal edta complex is increasing as a result, the mobility of the heavy metal increasing. in case of the cr (iv), after interacted with edta the diffusion coefficient is reduced by 21 times, this is due to the this cr (iv) reduces to cr (iii) after interacting with edta and this cr (iii) forms the precipitated wit in the soil due to the alkali nature of the soil and these precipitates are blocking the flow paths in the soil that leads the decrease in the mobility of cr (vi) through the soil column. the table 5 shows the diffusion coefficients of ch soil interacted with multi metal solution with and without edta at two different ph conditions (2 and 7). table 5. diffusion coefficient for multi-metal solution multi heavy metal at ph 2 heavy metal d* (m 2 /sec) cr 6.0x 10 -10 ni 2.01x 10 -10 pb 6.10x10 -11 cd 4.02x10 -10 multi heavy metal edta at ph 2 cr 3.02x10 -10 ni 1.34x10 -10 pb 9.25x10 -11 cd 5.98x10 -11 multi heavy metal edta at ph 7 cr 8.6x10 -10 ni 2.68x10 -10 pb 1.42x10 -10 cd 1.180x10 -10 from this table it is observed that, the mobility of pb (ii), ni (ii) and cd (ii) increased about 1.74, 9 and 9.5 time when compared to single metal solution. the mobility of cr (vi) decreased when compared with the single heavy metal solution. this is mainly due to the complex formation with the other heavy metals. from the table 5 it can also observed that, the mobility is decreased when the ch soil interacted with the multi metal solution with edta at ph 2 this is mainly because, at ph 2 most of the metal edta complexes are not that much strong and these metal edta complex will get precipitated at ph 2 that leads to decrease in the mobility of metal trough the soil column. the multi metal solution with edta at ph 7, the mobility got increased about 2.3, 1.3 and 1.43 times respectively for pb (ii), ni (ii) and cd (ii) the mobility got decreased about 3 times because of the competition between metal edta complexes. table 5 also shows the mobilization of heavy metals through the soil column under the influence of edta at ph 2 and 7. the mobility of heavy metals are increased about 1.53, 2, 1.97 and 2.84 times respectively for pb (ii), ni (ii) and cd (ii) compared with ph 2 condition. this is mainly because, the stable metal complex formation lead to early migration of the heavy metal migration through the soil column. these diffusion coefficients can be effectively used to predict the migration of heavy metals along the thickness of the liner (1-d case). hence, it also provides a quite yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 113 precise idea about choosing the appropriate design specifications of the liner that can be installed in the landfill area under the prevailing environmental conditions. although the values determined by using the advectivediffusion equations can reliably be used, somehow it over predicts the value of diffusion coefficient as the seepage velocity term included in the equation was calculated by considering initial hydraulic conductivity. 5. conclusions 1. breakthrough behaviour of heavy metal depends upon several factors such as ph of the soil and heavy metal solution, initial concentration of the metal solution, bed depth of the liner provided in the landfill, presence of organic ligand in the landfill waste, existence of other heavy metals and physical and mineralogical properties of the soil. 2. at lower ph, the adsorption of metal ions mainly takes place through cation exchange process which in-turn depends upon the electronegativity of the metal. while at higher ph, immobilization of heavy metals occurs through hydroxide precipitate formation which also indirectly depends upon the radius of first hydrolyzed product of metal. 3. in multi-metal system, the cause for attaining quick breakthrough can be explained by the competitive effect between the other heavy metal ions and hydrogen ion (h + ) for occupying the adsorption sites of the soil. 4. the chelation effect of edta to form metal edta complex product depends upon various factors such as the type of metal, the size of metal ion, ph of the solution and magnitude of complexation constant which determines the rate of complexation reaction. 5. soil having higher cation exchange capacity (cec) generally increases the breakthrough time by providing more adsorption sites for metal ions. ch soil is having higher cation exchange capacity that makes it capable of retaining more bivalent metal ions (pb, ni and cd) considered for study. but for hexavalent chromium ion, mobility is increasing in case of ch soil due to repulsion between its oxyanionic form and negative charges on the soil surface. single heavy metal solution: 1. for ch soil, the order of selectivity for three heavy metals (pb, ni and cd) is observed as pb > ni > cd at ph 2. for cr (vi), it shows more mobility at ph 7. for bivalent metal ions ph 2 was considered as that ph at which immobilization of metals can possibly occur through cation exchange process rather than hydroxide formation and same case happens for hexavalent chromium (vi) at ph 7. although the effective diffusion coefficients (d*) itself show the greater mobility in case of cr (vi) at ph 7 compared to other three heavy metals. 2. in presence of edta, the breakthrough time get reduced due to soluble metal-edta complex formation. the order of mobility for bivalent ions in this case is observed as ni pb > cd at ph 2. the effect of edta on mobilizing cr (vi) at ph 7 was comparatively more pronounced from the aspect of effective diffusion coefficient (d*) than other heavy metals at ph 2 condition. 3. ch soils show almost same breakthrough behaviour for four heavy metals in presence of edta. multi-heavy metal solution: 1. at ph 2, the transformation of cr (vi) into cr (iii) after reacting with h + cause some sort of adsorption what is not happening at ph 7 in case of single metal solution. the other three bivalent heavy metals are showing more mobility in case of multi-metal system due to competitive effect between the metal ion with other ions and hydrogen ion for occupying active sites of the soils. 2. at ph 2, three heavy metals i.e. cr (vi), ni (ii) and cd (ii) are showing less mobility in presence of edta when compared to multimetal solution without edta except for pb (ii) where the higher mobility has been observed at ph 7. references abollino o., acceto m., malandrino m., sarzanini c and mentasi e., 2003. adsorption of heavy 16 metals on na-montmorillonite. effect of ph and organic substances. water research, 37(7), pp.1619 1627. benson c. h., daniel d. e and boutwell g. p., 1999. field performance of compacted clay liner. journal of geotechnical and geo environmental engineering, 125(5), pp. 390 403. bowers a. r and huang c. p., 1985. adsorption characteristics of metal edta complexes onto hydrous oxides. journal of colloid and interface science, 110(2), pp. 575 590. bradl h. b., 2004. adsorption of heavy metal ions om soils and soil sediments. journal of colloid and interface science. 277, pp. 1 18. chen s. s., hsu h. d., lin y. j and chin p. y., 2008. removal of edta from low ph printed-circuit board wastewater in a fluidized zero valent iron reactor . water science and technology, 58(3):pp.661 667. daneshvar n., salari d., aber s., 2002. chromium adsorption and cr (vi) reduction to trivalent chromium in aqueous solutions by soya cake. journal of hazardous materials, b94; pp. 49 61. daniel d. e., 1994. state of the art: laboratory hydraulic conductivity tests for saturated soils. hydraulic conductivity and waste contaminant transport in soil, astm stp 1142, pp.30 78. gleason, m. h., daniel, d. e and eykholt, g. r., 1997. calcium and sodium bentonite for hydraulic containment applications. journal of geotechnical and geo-environmental engineering, asce 123 (5), 438 445. goodall d. c and quigly r. m., 1997. pollutant migration from two sanitary landfill sites near sarnia, ontario. canadian geotechnical journal, 14, pp. 223 236. gosh s., mukherjee s., al hamdan a. z and reddy k. r., 2013. efficiency of fine grained soil as landfill liner 114 yantrapali, s., khrisna h and k, srinivas/ jgeet vol 03 no 02/2018 material for containment of chrome tannery sludge. geotech geologic engineering, 31, pp.493 500. hamadneth i., zurayk r. a., irmaileh b. a., bozeya a and al dujaili a. h., 2015. adsorption of pb (ii) on raw and organically modified jordanian bentonite. clay minerology, 50, pp.485 496. is 2720-iv., 2006. indian standard methods of test for soils (is : 2720 (part iv) 1985 (reaffirmed 2006)). pp.1 43. is 2720-v., 2006. indian standard methods of test for soils (is : 2720 (part v) 1985 (reaffirmed 2006)). pp.1 20. is 2720-vii., 2011. indian standard methods of test for soils (is : 2720 (part v) 1980 (reaffirmed 2011)). pp.1 16. is 2720-xl., 2002. indian standard methods of test for soils (is : 2720 (part v) 1977 (reaffirmed 2002)). pp.1 10. is 2720-xvii., 2002. indian standard methods of test for soils (is : 2720 (part xvii) 1986 (reaffirmed 2002)). pp.1 18. is 2720-xxiv., 2010. indian standard methods of test for soils (is : 2720 (part xxiv) 1976 (reaffirmed 2010)). pp.1 11. jose e. r., mateus a. g., luiz c. a. o., elaine f. f. c and teodorico c. r., 2014. use of ethylene diamine tetra acetic acid as a scavenger for chromium from wet blue lather waste: thermodynamic and kinetic parameters. journal of chemistry, 2014, pp. 1 8. koerner, r. m. and daniel, d.e., 1993. manufacturing and construction quality control and quality assurance of geosynthetics. proceedings gri-6, mqc/mqa and cqc/cqa of geosynthetics, 1-14. kumar p. r and singh d. n., 2005. a novel technique for monitoring contaminant transport through soils. environmental monitoring and assessment, 109; pp: 147 160. li x., yang l., yanfeng, ye. z and he a., 2012. efficient removal of cd 2+ from aqueous solutions by adsorption on ps-edta resigns: equilibrium, isotherms, and kinetic studies . journal of environmental engineering asce 138(9), pp. 940 948. liu y., li h and zhu x. h., 2010. competitive adsorption of ag + , pb 2+ , ni 2+ , and cd 2+ ions on vermiculite. separation science and technology, 45(2), pp.277 287. marina i., margherita l., angle n and alfredo p., 2003. toxicity identification evaluation of leachates from municipal solid waste landfills: a multispecies approach. chemosphere. 52, pp. 85 -94. mohamed, a.m.o and antia, h.e., 1998. geoenvironmental engineering, 82, elsevier science, netherlands. mohamedzein y. e. a., al rawas a. a., al aghbari mohammad y., ahmed q and abdul h.a. r., 2005. assessment of crushed shales for use as compacted landfill liners. engineering geology, 80(3 4): pp.271 281. mulligan c. n., yong r. n and gibbs b. f., 2001. remediation technologies for metal contaminated soils and ground water: an evaluation. engineering geology, 60, pp. 193 207. nastaran m and alain b., 2009. edta in soil science: a review of its application in soil trace metal studies. terrestrial and aquatic environmental toxicology (global science book). ogata a and banks r. b., 1961. a solution of the differential equation of longitudinal dispersion in porous media. u. s. geological survey professional paper 411 a, u. s. geological survey, washington. d. c. oviedo c and rodríguez j., 2003. edta: the chelating agent under environmental scrutiny. quimica nova, 26(6): pp.901 905. paulo c. g., mauricio p. f. f., aberbal g. s., eduardo s. m and andre r. n., 2001. selectivity sequence and competitive adsorption of heavy metals by brazilian soils. journal of soil science society of america, 65, pp. 1115 1121. peters r. w and shem l., 1992. adsorption/desorption characteristics of lead on various types of soil. environmental progress and sustainable energy, 11(3): pp.234 240. peters r.w., 1999. chelant extraction of heavy metals from contaminated soils. journal of hazardous materials, 66(1 2): pp.151 210. quaranta, j., gabr, m., bowders, j., 1996. first exposure performance of the bentonite component of a gcl in a low-ph, calcium-enriched environment. in: well, l.w. (ed.), testing of geo-synthetic clay liners, astm stp 1308. astm, west conshohocken, pa, pp. 162 177. rajesh r. p., lewlyn l. r. r., asish o. m and sunith h., 2014. impact of urbanization on municipal solid waste management: a system dynamic approach. international journal of renewable energy and environmental engineering, 2(1), pp. 31 37. ramakrishna c. h., naik m., sumalatha j and sivapullaiah v., 2011. diffusion coefficient of ions in migration through soil liners. international journal of the physical sciences vol. 6(30), pp. 7044 -7054. raymond n. y and yuwaree p., 1993. ph influence on selectivity and retention of heavy metals in some clay soils. canadian geotechnical journal, 30(5), pp.821 833. reddy k. r., chaparro c and saichek r. e., 2003. removal of mercury from clayey soils using electro kinetics. part a, toxic/hazardous substances and environmental engineering, journal of environmental science and health, 38(2): pp.307 338. reddy k. r., danda s., yukselen a.y and alhamdan a.z., 2010. sequestration of heavy metals in soils from two polluted industrial sites: implications for remediation. land contamination and reclamation, 18(1): pp.13 23. rowe, r.k., 2005. long-term performance of contaminant barrier systems. géotechnique, 55(9), 631-638. shackelford c. d., 1994. critical concepts for column testing. journal of geotechnical engineering, 120 (10), pp. 1804 1828. shackelford, c.d., 1994. waste soil interactions that alter hydraulic conductivity. in: daniel, d.e., trautwein, s.j. (eds.), hydraulic conductivity and waste containment transport, astm stp 1142. astm, west conshohocken, pa, pp. 111 168. sherene t., 2010. mobility and transport of heavy metals in polluted soils environment. biological forum an international journal, 2(2), pp. 112 121. soares r. m., casagrande j. c and mouta e. r., (2011. nickel adsorption by variable charge soils: effect of ph and ionic strength. brazilian archives of biology and technology, 54(1), pp. 207 220. wang p and keller a., 2008. particle-size dependent sorption and desorption of pesticides within a watersoil-nonionic surfactant system. environmental science and technology, 42(9): pp.3381 3387. wang p, xue q, li j. s and zhang t. t., 2015. effect of ph on leaching behaviour of compacted cement solidification/ stabilization lead contaminated soil. environmental progress and sustainable energy, 35(1), pp. 149 155. 1. introduction 2. transport of chemicals through soil 3. materials and methods 3.1 chemicals 3.2 experimental procedure 4. results and discussion  single heavy metal interaction  lead (ii) solution  cadmium (ii) solution  chromium (vi) solution  composite heavy metal system  single heavy metal system with edta  nickel (ii) solution with edta  lead (ii) solution with edta  cadmium (ii) solution with edta  chromium (vi) solution with edta  composite heavy metal system with edta  composite heavy metal with edta at ph 2  composite heavy metal with edta at ph 7  diffusion coefficient (d*)  diffusion coefficient (d*) for black cotton soil (ch) 5. conclusions references jgeet_cover_print_vol 3 no 1 2018.cdr p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing our new issue vol 03 no 01 2018. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. husnul kausarian, ph.d editor-in-chief journal of j eet geoscience engineering environment and technology list of content original research article 1. experimental study to reinforce the weak subgrade soil for low-volume roads by coir geotextile mats ........................................................................ 1 2. fluid inclusion study of the tumpangpitu high sulfidation epithermal gold deposit in banyuwangi district, east java, indonesia .................................... 8 3. modified soil-adjusted vegetation index in multispectral remote sensing data for estimating tree canopy cover density at rubber plantation .......... 15 4. a study on influence of real municipal solid waste leachate on properties of soils in warangal, india .......................................................................... 25 5. halogen chemistry of hydrothermal micas: a possible geochemical tool in vectoring to ore for porphyry copper-gold deposit ................................... 30 6. the phenomena of flood caused by the seawater tidal and its solution for the rapid-growth city: a case study in dumai city, riau province, indonesia ..................................................................................................... 39 7. spatial statistical analysis for potential transit oriented development (tod) in jakarta metropolitan region ................................................................... 47 8. infiltration rate of quarternary sediment at rumbio jaya, kampar, riau ... 57 9. quaternary sediment characteristic of floodplain area: study case at kampar river, rumbio area and surroundings, riau province .................................. 63 win10 draft author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are 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end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type 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(do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press p-issn jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet e-issn page 1 page 2 page 3 page 4 5. section headings author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 03 2018 174 faizal, m et al./ jgeet vol 03 no 03/2018 research article efforts on geological conservation to watuadeg-basalt pillow lavas at west sumber, berbah district, sleman regency, yogyakarta special region-indonesia mohamad faizal 1 , rydo faisal arisandy 1 , ariel afrandi tatawu 1 , shandi hargian wijaksono 1 , frando ryan alansa 1 , muhammad nur arifin 1 , s. mulyaningsih 1, * 1 teknik geologi, fakultas teknologi mineral institut sains & teknologi akprind yogyakarta * corresponding author : sri_m@akprind.ac.id tel.:+64-563029; fax: +64-563847 received: july 16, 2018; accepted: aug 31, 2018. doi: 10.24273/jgeet.2018.3.3.2035 abstract site of berbah pillow lavas is an important geological heritage that is currently as one of the main tourism destination area located in yogyakarta special region, indonesia. it has a unique appearence of pillow structures with diameters of 0.5-1.0 m and the flow length of 2-5m.the pillow structures are interpreted as product of deep sea volcanism, that happening during late oligocene to early miocene. this site is used to visited by students and earth researchers becouse of its unique geological history, i.e as submarine ancient volcano. this study was approached with geotourism and geoconservation points of view. the research method uses qualitatively field geological observations. data analysis was carried out by assessing the feasibility study of the geological conditions that had been produced in relation to the development of educational tourism. in its condition, this site ever suffered damage by the development impacts in the surrounding area and was once an object of agate mining so that its condition was increasingly not maintained. in order to maintain this site and become a protected geological site, there must be seriousness of various parties in an effort to map the geological conditions of the pillow lava complex, an important role that geologists have to inform and disseminate to all stakeholders and local residents to be able to independently manage the potential of geotourism. in addition, it also needs the local government commitment in protecting the object of pillow lava and struggle for it to become a protected geological reserve. keywords: pillow lava, basalt, geotourism, damage and geoconservation 1. introduction the study area is located in the east of yogyakarta special region, precisely located on the lips of the opak river with coordinates 7⁰ 42 '5 "s and 110⁰ 26' 35" e (fig. 1). the area has a variety of geological processes, supported by natural and geological resources with potential geoheritage objects focussing on panoramic aspects and geology. not only for the natural tourism, cultural tourism and geological tourism, but also for cullinary and shopping tours. watuadeg basalt pillow lava was a main geological site in yogyakarta, for students and volcanologist to studying submarine ancient volcano. now, this area has been manuvered to become a major tourism located 5 km east of the study area and ancient nglanggeran volcano located about 20 km to the southeast. the development of the geoheritage is certainly very good for the people who live around it. however, every development certainly produces changes in land form, which inevitably will eliminate some of the related geological data. this also applies to the watuadeg geoheritage of the basalt pillow lava. the study is focussed on the impact of the occurence of the geoheritage; producing more benefits or disadventages for geological educational interests. 2. geotourism in a fact, the concept of geotorism is not to different with geopark concept. in indonesia, geotourism is development of a region based on a sustainable manner that combines three diversities, namely: geodiversity, biodiversity, and cultural diversity (yuliawati et al., 2016). mulyaningsih et al (2009) argued that watuadeg basalt pillow lavas were volcanic deep sea materials. the pillow lava was originally a high-temperature liquid magma resulting from a volcanic eruption that froze quickly due to being exposed to sea water to form lumps resembling a pillow formation. these pillow lavas can be used as evidence to show the initial process of forming ancient volcanoes on the island of java. determination of an area into an object of geoheritage will have a considerable impact on the http://journal.uir.ac.id/index.php/jgeet faizal, m et al./ jgeet vol 03 no 03/2018 175 community around the area. in addition, the impact caused in the geoheritage sector also has a very large effect in it; in the economic, social and cultural fields. according to newsome & dawling (2006), geotourism should be covered geographical, cultural, social economic which sit under the scope of geographic tourism. in the implementation of the development of tourism, whatever ideas are implanted, it will affect to the social, economic, cultural, livestyle and environment, such as its ecosystem and landuse. this has happened in the development of geotourism in bromo-tengger (hakim et al., 2017), lake toba (ginting et al., 2017), nglanggeran (abidin, 2017) and others (yuskar, 2016). at the watuadeg pillow lava, the local government has made efforts to preserve and maintain this geological site. these efforts include: the existence of homestays in this region so that it can have an impact on the welfare of the surrounding residents, the infrastructureconstruction connectingthe pillowlava and other geoheritage areas,such as breccia cliff at candi ijo (prambanan) and ancient nglanggeran volcano (gunungkidul), irrigation development in the area and other supporting infrastructure facilitiyconstructionson each geoheritage object. 2.1 geological setting locally, the research area is the body of the river and small hills which have a height of less than 100 m, surrounded byin fertile rice fields. these small hills are composed by tertiary volcanic rocks, i.e beds of pumice and tuffs of semilir formation in the east and south and pyroxenic basalt in the west. the surrounding rice fields consist of quaternarry fluviovolcanic deposits which are products of merapi volcano in the north. geologically the study area is covered in the regional geological map of yogyakarta sheet (rahardjo et al., 1995). basaltic pillow lavasare found in the kebobutak formation, including bayat, tegalrejo and gunung sepikul (bronto et al., 2009). however, pillow lava in watuadeg is not clearly included in the kebobutak formation which is because it is not associated with the kebo-butak formation sedimentary rocks and is directly overlain by the semilir formation (bronto et al., 2008; mulyaningsih & sanyoto, 2012). the basaltic lava flow is characterized by rich in pyroxene minerals, having pillow structures with n70oe directional flow structure in the north to n150oe in the south, located on the opak river body. at 200 m to the west there is a small hill which is also composed by basalt pyroxene, the results of the k / ar age analysis find data 56.3 ± 3.8 ma (ngkoimani, 2004). 3. method the study uses qualitative and quantitative primary and secondary data. the primary data collected during field observation, include distributing the questionairre for people around the study area and educational people including students and the other visitors. an other primary data were observations of geomorphological, cultural, social and economical all data has been compilled using overlay system. fig. 2 flow chart diagram of the method of study. data from observations in the field, collection of questionnaires, changes in landforms before and after the watuadeg pillow lava tour are then tabulated, and a graph is prepared explaining the positive and negative impacts. from the results of the statistical data analysis, further improvement measures are planned, which may be done in order to reduce the rate of change in geomorphology, social, economic, cultural and ecosystem. the method can be read in fig. 2. 4. result from the results of the study observed in the siteof watuadegpillow lava, there were many damages which made during the development of the geoheritage site so that become not maintained, thus reducing the value of education and attractiveness especially in the geological context. evidence of damage to the geoheritage site of watuadegpillow lava is the construction of irrigation by the local government which is the function of irrigation development, namely for surface water channels and for the availability of water for agriculture. however, the development of irrigation in the beds of pumice and tuffsof semilir formation arround it is very influential on the geological history and geological processes that occur and take place in the area, especially as stratigraphic correlation data that connecting the surrounding rocks. fig 2. graph of improving the economy of the people towards the existence of watuadeg geoheritage. 176 faizal, m et al./ jgeet vol 03 no 03/2018 the dissemination of the tracking questionnaire for the level of satisfaction of citizens towards the existence of watuadeg geoheritage has been carried out based on its response to improving the economic level of citizens, social and culture. tracking results found that most of the residents felt economically assisted in relation to parking, ticketing, security and culinary arrangements (fig. 2). based on social and cultural tracking, the existence of the geoheritage has changed the behavior of the people from those who initially worked as construction laborers, so now most of the young people switch professions as local guides and event presenters (fig. 3). questionnaires were also given to the academic community, including students, researchers, lecturers and secondary school students. the average respondent feels that the development of geoheritage has changed the educational zone into an exclusive zone, which can only be entered by tourists. students who have been able to freely visit, do research and learn about ancient volcanoes of watuadeg and semilir, can no longer find contact between the rock members of the semilir formation and the basalt pillow lava. in addition, several parts of the pillow body that have a specific flow direction have been cut during the construction.figure 4 is the result of tracking the response of academics in addressing the existence of watuadeg geoheritage. fig 3. graph of providing employment for the people towards the existence of watuadeg geoheritage. stratigraphically, the position of the basalt lava with a pillow structure in the opak river (watuadeg) is located below the semilir formation. radiometric analysis with the k-ar method gave the age of 56.3 ± 3.8 million years ago (late paleocene), while the age of the semilir formation was the early miocene early middle miocene (surono et al., 1992; rahardjo, 2007) or about 16 million years ago. the pillow lava age was older than the pillow lava age in pacitan (42.73 ± 9.78 33.56 ± 9.69; soeria-atmadja et al., 1994), so re-testing was needed. but if it is true, or at least equal to pacitan pillow lava age, a very long period of time (17-40 million years) between pillow watuadeg lava formation and sedimentation of semilir formation has occurred. this very long period of time allowed tectonic deformation and various other geological processes to occur after watuadeg pillow lava volcanism but before the formation of semilir formation. one of them is the possibility of an inconsistency between the two. in addition to age, evidence of non-alignment and a very long grace period can be viewed from the aspects of sedimentology, magmatism and volcanism. fig 4. graph of providing employment for the people towards the existence of watuadeg geoheritage. observations in the field on the existence of watuadeg geoheritage encountered changes in land use.it has occurred along the riverbanks and hills geomorphology located the south, southeast to the east. these changes need to be done in relation to the potential mass movements taking place within the region. this is mainly found on the south side of the river wall, which is composed by quaternary fluviovolcanic deposits and distal lahars. another change occurred on the north side, which is located under the bridge, the area has been covered with cement, so it does not allow visitors to learn the boundaries or contact unconformity between the basalt pillow lava with layers of pumice breccias and tuffsabove it. to explain the absence of the unconformity boundary, it is still uncovered as well as rocks which consist of basalt breccias on the southern side of the opak river. however, the riverbed cannot be observed properly when it flows by river water, especially in the rainy season, where river water always overflows in the basalt body of the pillow lava in it. the non-alignment limit is characterized by the presence of basalt fragments floating in the tuff and pumice matrix (fig. 6). the other damage is the taking ofpillow lavas to be used as agate done by the surrounding community, thus making the geometry of the pillow lava increasingly unattended and changing from its original condition. from the damage and changes that occur, so that it can reduce geological data that should be very important and useful when used for geological research related to submarine ancient volcano.behind the efforts to develop the geoherotage, the government actually has a noble goal of enhancing the standard of living of the surrounding communities, thus becoming a positive added value to the region. faizal, m et al./ jgeet vol 03 no 03/2018 177 fig 5. the geomorphological changes at watuadeg geoheritage fields; clockwise is watuadeg river before the development of geoheritage, after development, the educational area that has not found basal breccia and before development. in addition, the development of tourism-based geoheritage also aims to increase the number of tourist visits, especially special interests, both domestic and foreign. unfortunately, this is not offset by the protection of educational points, which of course not all regions in yogyakarta and java generally have it. in this case, managers, government and academics sit together to discuss points with educational values that must be protected. 5. discussion as mention above, development area to be a main tourism destination, always change the morphology and use of the land. biodiversity loss as a consequence of the forest disturbance in the bromo-tengger-arjunowelirang geotourism and geoheritage has been reported by hakim et al. (2017). this conflict causes biodiversity to decrease in various ways, through (1) intensive withdrawn forest resources and (2) conversion of forest into farmland. to reduce the impact to the forest biodiversity, the management . the government policy to preserve the pillow lava geoheritage site in watuadeg-berbah has not fully done well. government regulation in terms of granting building permits for building geoheritage areas. in relation to conservation efforts, a place that becomes a geoheritage area must be protected and preserved so that it does not change the shape of the landscape because it already has the legal power of the geological agency. this is of course very unfortunate with what is happening now, and the role of the regional government must make efforts and consequences to establish an area as a tourist attraction as well as fight for it to become a protected geological reserve. therefore in this case the government must be assertive and improve coordination on the granting of building permits to prevent further damage to the geoheritage site of watuadeg-berbah pillow lava. the beauty and uniqueness of the watuadeg pillow lava that has been set by the geological agency of the ministry of energy and mineral resources as a geological heritage is indeed extraordinary. the presence of large boulders in a round shape, a little like a pillow, pops up not only at the edge of the river, but sometimes in the middle of opak river ripples. but along with the times, this nature reserve site has become uncontrollable in its development, and precisely reduces the value of uniqueness and its geological history is very unfortunate. to protect this site especially for the development of protected geological reserves, geoconservation is necessary. the important role of geologists is to provide an understanding of the importance of the site. besides that, it must also provide information such as making sign boards and mapping them. from the other side, geologiawan must socialize to all stakeholders, tourism awareness groups (pokdarwis) and local residents to be able to independently manage and utilize the geotourism potential as well as protect it. 178 faizal, m et al./ jgeet vol 03 no 03/2018 efore the development of geoheritage, after development (with joglo-house), the educational area of basal breccia:dry (dry season) and wet (rainy season); now both are not revealed anymore. conclusion the naturereserve site of pillow lava in watuadegberbah has undergone significant changes in geological and economic, social and cultural aspects. on the other hand, the development of watuadeg geoheritage has had a positive impact, in the form of the availability of infrastructure that can participate in increasing the potential value of the region and the standard of living, social, cultural and economic community. weighting between positive and negative values, of course cannot be done only unilaterally. comprehensive study is needed about the management system which can also be protected by geological reserves. the commitment of local governments, communities and academics in conserving the site of pillow lava and fighting them to become conserved; will not be in vain if all components are aware of the limitations of the conservingin it. the important role of the geologists is needed to provide understanding, training and brief teaching on geology and geological processes that might occur, related to the ancient volcanic geological reserve at watuadeg. acknowledgements a big thank you to the institute for research and community services, geological engineering study program, and all parties at the akprind institute of science & technology who have helped both during the research, questionnaires and data processing that cannot be mentioned individually. references abidin, a.r., 2017. analisis pengaruh citra, ekspektasi dan kualitas pariwisata dalam european performance satisfaction index terhadap komitmen masyarakat. bronto, s,, mulyaningsih, s., hartono, g., dan astuti, b., 2008, gunung api purba watuadeg: sumber erupsi dan posisi stratigrafi, jurnal geologi indonesia, 3 (3), 117-128. ginting, n., rahman, n.v. and sembiring, g., 2017, march. tourism development based on geopark in bakkara caldera toba, indonesia. in iop conference series: materials science and engineering 180 (1), 012086. hakim, l. and soemarno, m., 2017. biodiversity conservation, community development and geotourism development in bromo-tengger-semeru-arjuno biosphere reserve. geojournal of tourism and geosites, 20, 220-230. mulyaningsih, s. and sanyoto, s., 2012. geologi gunung api merapi sebagai acuan dalam interpretasi gunung api komposit tersier di daerah gunung gede imogiri daerah istimewa yogyakarta. in prosiding seminar aplikasi sains & teknologi (snast) periode iii. newsome, d. and dowling, r., 2006. the scope and nature of geotourism. geotourism, 3-25. ngkoimani, l.o., 2005, magnetisasi pada batuan andesit di pulau jawa serta implikasinya terhadap paleomagnetisme dan evolusi tektonik, disertasi s3, itb, 110. putra, g.z.m., sutrisno, fandi, m.i., dan hedratno, a., 2016, analisis geosite dan geomorphosite pantai menganti sebagai potensi geowisata indonesia, yogyakarta. faizal, m et al./ jgeet vol 03 no 03/2018 179 rahardjo, w., sukandarrumidi, dan rosidi, h.m.d, 1995. peta geologi lembar yogyakarta, jawa, skala 1 : 100.000. pusat penelitian dan pengembangan geologi, bandung. surono, b. toha dan i. sudarno, 1992, peta geologi lembar surakarta giritontro, jawa, skala 1 : 100.000, puslitbang geologi, bandung. yuliawati, a.k., hadian, m.s.d., rahayu, a. and hurriyati, r., 2016. developing geotourism as part of sustainable development at ciletuh sukabumi, west java, indonesia. journal of environmental management & tourism, 7, 57. yuskar, y., 2016. geo-tourism potential of sand bars and oxbow lake at buluh cina, kampar riau, indonesia. j. geosci. eng. environ. technol. 1, 59 62. © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geotourism 2.1 geological setting 3. method 4. result 5. discussion conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 2 2023 hidayati, a.m., et al./ jgeet vol 8 no 2/2023 123 review article exploring the mechanism of vetiver system for slope reinforcement on diverse soil types – a review anissa maria hidayati1, kadek hindhu kedaton1, silvia gabrina tonyes1,2, elizar4, yenni ciawi1,2,3 * 1 civil engineering department, udayana university, bali 80361, indonesia 2 doctoral program in engineering sciences, udayana university, bali 80234, indonesia 3 environmental engineering department, udayana university, bali 80361, indonesia 4 civil engineering department, riau islamic university, pekan baru 28284, indonesia * corresponding author: yenniciawi@unud.ac.id tel.:+62-8133-796-576; received: apr 19, 2023; accepted: jun 6, 2023. doi: 10.25299/jgeet.2023.8.2.12705 abstract landslide, one of the important geomorphological processes, is essentially a natural phenomenon that is often exacerbated by human-induced activities. a stable sloping terrain will tend to collapse when it is subjected to forces that tend to destabilise it. slope instability is one of the main factors leading to disasters that might be catastrophic to the environment and human life. since the beginning of the year 2000 only, thousands of fatalities annually occurred globally due to landslides. with its predominantly sloping topography, the landslide is also a frequent natural disaster in indonesia. bnpb data stated that between 2013 and 2022, there were 7,297 recorded cases of landslides in the country with more than 100 casualties on one occasion. to mitigate the impact of this disaster, measures such as reinforcing slopes or implementing retaining walls in vulnerable areas are urgently required. in recent decades, bio-engineering techniques gain more attention in slope reinforcement by combining the mechanical and hydrological abilities of vegetation in erosion control and slope stabilisation. vetiver grass is one of the vegetation species used in bioengineering techniques due to its low cost and more sustainable solutions in many infrastructure projects. in this paper, a qualitative literature review is conducted and processed using descriptive-analytical methods to address the mitigation of landslides and their potential domino effects on the economy and people's welfare. keywords: disaster mitigation, landslide, bio-engineering, vetiver 1. background landslides are significant geomorphological processes that can be exacerbated by human activities. these events, characterized by a decline in slope shear strength, contribute to sediment fluxes in mountainous regions and often manifest as shallow slope failures and hillside debris flows triggered by rainfall-induced soil erosion (ma et al., 2020; yuskar et al., 2017). the ecological and man-made consequences of landslides include land degradation, infrastructure hazards, and fatalities (shu et al., 2019). due to its high rain intensities and steep topographical conditions, indonesia is particularly susceptible to landslides (isnaini, 2019; zamroni et al., 2020). according to (ritchie et al., 2022), landslides have claimed thousands of lives worldwide since the year 2000. indonesia, with its predominantly hilly terrain, has experienced 7,297 landslide incidents resulting in over 100 deaths in a single instance from 2013 to 2022, as reported by (bnbp, 2023). urgent measures are necessary to mitigate the impact of this disaster, such as slope reinforcement and the construction of retaining walls in vulnerable areas. slope reinforcement involves increasing the soil's shear strength to withstand destabilizing forces. conventional slope reinforcement methods typically employ hard engineering techniques, such as constructing retaining walls using materials like concrete, stone, or timber (ciptaning et al., 2018). alternatively, other approaches aim to prevent water accumulation and soil saturation through geometric adjustments, adequate drainage, and soil reinforcement methods, such as incorporating geotextiles, geogrids, and soil nails, and employing bio-engineering techniques. the latter approach involves utilizing plants (islam, 2013) or utilizing plant roots (khosiah and ariani, 2017) to address slope landslides. historically, upland farmers have developed specific measures for landslide prevention, including maintenance strategies and early-stage erosion stabilization, such as closing stress cracks in the grass (löbmann et al., 2020). however, in the mid-1980s, the world bank introduced the vetiver system (vs) as a biotechnological approach to agricultural land management in india. currently, it is being developed as a technique to stabilize steep slopes and cliffs (badriyah and wulandari, 2020), as well as for wastewater disposal, and phytoremediation of contaminated soil and water (abaga et al., 2021; ambarwati and bahri, 2018; chen et al., 2021; dorafshan et al., 2023; komarawidjaja and garno, 2016; mahmoudpour et al., 2021), coastal erosion (indriasari and akhwady, 2017; sufyan et al., 2020a), and rehabilitation of former mining lands (kiiskila et al., 2020; napitupulu and purwanti, 2022; putri, 2019). additionally, the vetiver system is employed in the development of sustainable land use strategies from ecological, socio-economic, and environmental protection perspectives (löbmann et al., 2020; truong and loch, 2004). the objective of this study is to investigate the application of the vetiver system in sloping terrains as a cost-effective, sustainable, and easily reproducible method for mitigating landslides and controlling soil erosion. http://journal.uir.ac.id/index.php/jgeet 124 hidayati, a.m., et al./ jgeet vol 8 no 2/2023 2. slope stability a thorough literature search was conducted using the keywords "vetiver," "slope stability," and "soil type”. a total of 66 relevant sources were analyzed, including journals, and websites dating from 2010-2023. the search was conducted through a variety of search engines, such as google, google scholar, ncbi pubmed, science direct, mdpi, iop science, and research gate. 3. soil shear strength in geotechnical engineering, a slope is defined as the surface of the earth that forms a certain angle with the horizontal plane. on a sloping ground surface, the gravitational force component, i.e. the vertical force due to gravitational action, tends to move the soil downward. slope failures occurred when there is a force acting upon the slope surface exceeds the internal soil shear strength (das, 2019) soil shear strength, one of the soil geotechnical characteristics, is inversely determined by its water content: an increase in water content will result in a decrease in soil shear strength. most slope failures occur after/during heavy or prolonged rains. in addition to reducing the shear strength of the soil, water that infiltrates into the soil pores also increases the weight of the soil adding vertical forces on the slope. the combination of the two can result in slope failures. the annual rainfall characteristics influence the frequency of landslides. the softening of slope-forming materials due to the increase of the soil water content due to rain, as well as rising groundwater levels during the rainy season also affects the speed of soil mass movement. rising groundwater level causes a reduction in the average shear strength of the soil. the increase in pore water pressure in the vicinity of the potential landslide area reduces the effective stress, thereby reducing the shear strength (sinarta and basoka, 2019). when it rains and water infiltrates into the ground, the soil around the soil surface gradually becomes saturated. simultaneously with the increase in the water content in the soil, the shear strength of the soil gradually decreases, especially for fine-grained soils. this is because the pore water pressure, which was originally negative, moves to be positive (blanco-canqui et al., 2010). the shear strength of the soil is affected by the surface tension in the pore water at the point of contact between the grains, which when the soil becomes saturated the surface tension disappears. as a result of the influence of surface tension, the sand seems to have cohesion (i.e. an apparent cohesion). in practice, under the influence of apparent cohesion, moist fine sand slopes can be excavated in upright conditions, even at relatively deep excavation depths. this visible cohesion sometimes does not disappear during heavy rains, however, as soon as the slope is submerged in water, the slope immediately collapses. a rise in the water level that causes an increase in pore water pressure can also cause slope failure on river banks, ponds or reservoirs. the speed of ground movement tends to increase with increasing water level. the shear strength of the soil can also be reduced by the presence of open cracks when fine-grained soils become dry or shrink. these shrinkage cracks can develop in shale or clay if the surface is not protected by sand or grass (das, 2019). there are two main factors controlling slope stability, i.e. the forces that tend to destabilise the slope and the inherent component of soil to resist those forces. these two factors are commonly known as factors of safety (fos) or safety factors (sf). the factor of safety is defined as the ratio between the resisting force and the driving force, as given in eqn 1. d sf    (1) where τ is the maximum shear resistance that can be exerted by the soil (or available shear strength), τd is the shear stress that occurs due to the weight of the soil that will slide (or the shear strength mobilized by the soil to maintain balance), and sf is the factor of safety. according to the mohr-coulomb theory, the maximum shear resistance (τ) that can be mobilized by the soil, along its sliding plane, is expressed by eqn. 2:  tan c (2) with c = cohesion, σ = normal stress, and ϕ = friction angle in the soil. the values of c and ϕ are the parameters of the shear strength of the soil along the failure plane. in the same way, the equation for the shear stress that occurs (τd) due to soil loads and other loads on the sliding plane can be written in eqn. 3: ddd c  tan (3) where cd and ϕd are the cohesion and internal friction angles that occur or are required for balance in the sliding plane. from the substitution of eqn. 2 and eqn. 3 into eqn. 1, the equation for the safety factor is obtained, as in eqn. 4. ddc c sf   tan tan    (4) eqn. 4 can also be written in the form of eqn. 5: sfsf c c dd   tan tan  (5) then the factor of safety for each component of the shear strength is written as eqn.6 and 7: d c c c sf  (6) d sf    tan tan  (7) where sfc = safety factor for cohesion components and sfϕ = safety factor for friction components. in general, the boundary balance method assumes sfc = sfϕ, this indicates that the cohesion components c and friction (ϕ) are mobilized in equal proportions simultaneously along the failure plane. the safety factor has to be above 1 and typically has values ranging from 1-1.5. 4. factors instigate slope failure landslides on slopes can arise from various factors, including geological and hydrological conditions, topography, climate, and weather variations that influence slope stability, ultimately leading to landslides the stability of slopes can be compromised by natural elements such as weathering, intense hidayati, a.m., et al./ jgeet vol 8 no 2/2023 125 or prolonged rainfall, seismic activity, and the presence of a vulnerable superficial soil. additionally, human activities like excavation at the base of the slope and construction on its surface can also contribute to slope failure. in the case of clay soil slopes, landslides often occur due to erosion caused by river water flow or excavation activities at the slope's base. the erosion of the riverbed, particularly near the foot of the slope, can result in a steeper and deeper slope, rendering it unstable (das, 2019; fadilah et al., 2019). the occurrence of heavy rainfall frequently triggers significant erosion, especially in areas with easily erodible soil on steep hillsides, aggravated by human-induced vegetation damage. to effectively manage the erosion process, it is crucial to implement sustainable and costeffective solutions such as employing bioengineering techniques that utilize vetiver grass (azis, 2022; hamdhan et al., 2020). 5. bioengineering for slope reinforcement bio-engineering is interdisciplinary bioscience and engineering that is applied in bio-system-based engineering to increase the efficiency of the functions and benefits of biosystems. slope erosion is a natural disaster that often occurs on natural and artificial slopes (sriwati et al., 2018). slope erosion mostly occurs during the rainy season. soil-bioengineering can be an alternative method of slope stabilization (balangcod et al., 2015; sittadewi, 2018). the analysis was carried out by comparing the soil shear strength values (cohesion and internal shear angle) from the results of triaxial soil tests without and with vetiver reinforcement. the use of vetiver as a stabilization method is proven to increase slope stability (sittadewi and tejakusuma, 2019). 6. vetiver and bio-engineering 6.1 characteristics of vetiver root plants vetiver root or vetiver grass in the plant classification belongs to the graimineae family. the latin name for vetiver is vetivera zizanioides stapf (chou et al., 2016) or also called andropogon zizanioides urban or a. muicatus retz (gautam and agrawal, 2021) or asquarrosus linn (sunandar, 2011). vetiver with the application of the vetiver system (vs) is reclassified as chrysopogon zizanioides l roberty (garzón et al., 2020a; sari, 2021). vetiver in indonesia known as root vetiver (vetiveria zizanioides), is a type of large grass that has many features. this magic grass in indonesia has been used as a producer of essential oils (sufyan et al., 2020). it grows upright and reproduces quickly to form large clumps that can survive and thrive in cold weather. in very cold weather the shoots die or become dormant but the underground growth parts persist. vetiver is very effective in dealing with erosion because of its long roots that penetrate the earth with a height of 1.5 m and can grow up to 2-4 meters (wijayakusuma, 2007). the roots of several species that produce essential oils can grow to a depth of 3-5 m (ambarwati and bahri, 2018; teshale and legesse, 2022). 6.1.1 morphological characteristics vetiver root has a strong and massive structure, has no teeth or rhizomes, and reaches 3-4 meters in length. its stems are stiff and upright and can remain standing even in strong currents (sari, 2021; sufyan et al., 2020). vetiver is resistant to pests, disease and fire (brandt, 2006), withstands snow, traffic and heavy grazing pressure resulting from new shoots developing from its crown in the soil and filters sediment effectively when densely planted (löbmann et al., 2020) (fig.1b and 1c). the physical form of vetiver is given in fig.1a. a. b. c. fig. 1.a. vetiver (pineiro, 2021a), b.vetiver planted on hillside (pineiro, 2021b), c.vetiver planted on coast (new, 2021) 6.1.2 physiological characteristics vetiver root can withstand extreme climate changes such as floods, prolonged drought, submersion and extreme weather from -14˚c to +55˚c (winata, 2018), has a soil ph that varies from 3.3 to 12.5 which made it able to survive without soil amendment. vetiver is also efficient in absorbing soluble soil nutrients such as n and p and heavy metals in polluted water (hailu et al., 2020; susilawati and veronika, 2016), as well can tolerate medium to a high level of alkalinity, solidity, acidity, salinity (novita et al., 2022; sari, 2021). in addition, vetiver is tolerant to high herbicides and pesticides (susilawati and veronika, 2016). it can withstand pollution of hazardous toxic substances such as atrazine (zhang et al., 2023), various dyes (aarthy et al., 2022), edta and metals and heavy metals such as mg, al, mn, as, cd, cr, ni, pb, hg, se and zn in the soil (kereeditse et al., 2023; sari, 2021). 6.1 ecological characteristics vetiver is an ecologically versatile plant that can survive for many years under normal conditions without being overly aggressive (sari, 2021). it has been observed to withstand extreme environmental conditions such as droughts lasting several months or floods lasting up to 45 days. vetiver can grow in a variety of environments, including sea-level swamps and mountains up to 2600 meters. unlike other plants, vetiver does not become a weed and does not spread uncontrollably, making it a suitable option for reducing rain flow speed and increasing the absorption of rainwater and plantation productivity. additionally, vetiver can form dense, upright hedges that are easy and inexpensive to create and permanent on the soil surface. while there are reports of vetiver being unable to survive in areas with very strong waves on the coast, leading to all being uprooted (sufyan et al., 2020), the application of vetiver for beach and sand dune stabilisation proved to be very effective in reducing erosion in the coastal area. vu et al. (2013) reported that vetiver grass can reduce up to 60% wave overtopping. in brazil, pereira et al. (2015) reported vetiver plantation in front of a hotel complex keeps the beach safe from erosion, even in extreme weather. the fact that vetiver is unable to survive a daily high tide, but can withstand fortnightly tidal surges (bertel and truong, 2013). the important factors determining the effectivity of vetiver grass in saline and/or coastal environment is the regular maintenance 126 hidayati, a.m., et al./ jgeet vol 8 no 2/2023 and keeping the grass root not to be directly immersed continuously in saline/brackish water. bertel and truong (2013) suggested growing vetiver grass above the high tide, and in case the area to be protected is submerged in the water regularly, planting a more salt-tolerant species, e.g. sea ferns, on the foot of vetiver plants to keep the environment save for the vetiver roots 6.1.1. how vetiver works to slow down or prevent landslide vetiver root has a unique way of working, which is to stop the rate of water run-off and erosion material that is carried along with the body (hamdhan et al., 2020; sari, 2021). in fig.2 it can be seen that vetiver leaves and stems can slow down the flow of sediment carried by run-off at point a so that it accumulates at point b, while water will continue to flow down the lower slope at point c (susilawati and veronika, 2016) (fig.2). the soil is bound by plant roots to a depth of 3 meters so that it looks like a pole and will be effective if planted in rows that form a fence (holanda et al., 2022; susilawati and veronika, 2016). fig. 2. mode of action of vetiver in preventing soil erosion (wijayakusuma, 2007) 6.2.1. application of vetiver system on red soil the application of the vetiver system on compacted embankment soil was also examined for the response of root growth. dense soil structure will inhibit the rate of root penetration, and this condition has implications for root fibres not contributing to the increase in soil shear strength because the root fibres have not crossed the slip surface in surface landslides. in the planting medium in the form of coarsegrained clay silt soil reddish brown or often called red soil, at the planting age of 90 days, the roots of vetiver grass plants can penetrate the compacted red soil layer with a dry unit weight (γd) ranging from 1.28 – 1 .34 gr/cm3 and 16.8 cm thick. at the bottom of the pot, there is a collection of roots due to the roots not being able to penetrate the gutter closure. root length can reach an average of 29.69 cm and root diameter of 0.40 mm. this shows that vetiver can develop well on slopes with a reddish-brown coarse-grained silt loamy soil type or often called red soil. the closeness of the relationship between variables such as dry unit weight of soil, number of roots, root length and root diameter in response to root growth is that the more the average number of roots is possible the greater the average root diameter. the higher the dry unit weight of the soil, the larger the average root diameter will be. in addition, the relationship between root length and diameter shows a similar distribution pattern for relatively the same level of density (andiyarto and purnomo, 2012). 6.2.2. application of vetiver on silty sand soil and sandy silt soil in a research conducted by azis (2022), six small-scale models were created, one without vetiver grass and five with vetiver grass, having a slope angle of 37°. artificial highintensity rainfall was applied to all six models one year after planting, to observe the role of the canopy and vetiver roots in erosion and runoff control. out of the five small-scale models, one was made with silty sand soil while the other four models were planted in sandy silt soil media to see the effect of soil texture. the results of the study showed that for sandy silt, the inclusion of vetiver reduced soil loss (erosion) by 94%–97% and soil loss rates were reduced by 95%. canopy cover showed a positive impact in reducing both of these quantities. increasing the average root diameter from 1.6 to 2.5 mm increased soil loss due to its negative impact on cohesion addition. cohesion addition showed a linear negative correlation with soil loss. the vetiver and jute geotextile composite system was the most effective in reducing erosion among the four vegetation models with sandy silt. under the same vetiver planting layout, the grass-covered silty-sand model resulted in 84% lower erosion and 62.5% lower runoff than the grass-covered model on sandy silt soils. vetiver is more effective in reducing erosion and runoff for soils with a greater percentage of sand, and the soil type dominates the erosion process (azis, 2022; islam et al., 2016). 6.2.3. application of vetiver on high plasticity soil badriyah and wulandari (2020) conducted a study on slope modelling with dimensions of 150 cm x 50 cm x 70 cm and slopes of 700 and 800. the researchers tested the soil properties both physically and mechanically before and after strengthening with vetiver. direct shear strength testing was conducted on samples at depths of 0-30 cm and 30-60 cm before and after planting vetiver. the results showed that the vetiver roots were able to significantly increase the cohesion value at both depths on both slopes. on slope 700, the cohesion value increased by 358.037% at a depth of 0-30 cm and 218.182% at a depth of 30-60 cm. on slope 800, the cohesion value increased by 251.928% at a depth of 0-30 cm and 220.514% at a depth of 30-60 cm. this study suggests that planting vetiver can be an effective method for strengthening slopes and reducing the risk of landslides (badriyah and wulandari, 2020). 6.2.4. application of vetiver on silty clay soil garzón et al. (2020a) analyzed to evaluate the effect of vetiver reinforcement on slope stability using two types of prototypes with a planting time of 16 weeks and an 80° slope, namely the 3-bud prototype and the 6-bud prototype. the soil medium used was silty clay. the study aimed to investigate the impact of chrysopogon zizanioides (vetiver) on the hydrophysical properties of soil and infiltration rate to prevent soil erosion in slopes. the study was carried out in guatemala using selected grounds, and the soil samples analyzed showed a predominant sand fraction and a plasticity index of 7.9%, which suggested non-swelling, slightly acidic soils with negligible salinity. nitrogen adsorption-desorption analysis indicated a specific surface area ranging from 11.7-15.5 m2/g, with pore sizes between 17-160 µm that changed to 20-100 µm, with a predominant pore size of approximately 40 µm after hidayati, a.m., et al./ jgeet vol 8 no 2/2023 127 cultivation. the soil was found to possess cohesion (2.05 t/m2) and an internal friction angle ф = 31.69º. after vetiver planting, a decrease in cohesion and an increase in internal friction angle were observed. additionally, the sowing of vetiver resulted in a decrease in soil infiltration rate due to compaction caused by the plant roots. these results were obtained using the kostiakov-lewis classical model, which was mathematically fitted to the data. the findings of garzón et al. (2020a) and kurniawati p. & wulandari s. (2020) indicate that planting vetiver can effectively stabilize slopes and prevent soil erosion caused by heavy rainfall. results from a 16-week test showed that the qu value increased by 121.74% and the cohesion value increased by 260% in prototype 3 buds, while prototype 6 shoots had a 137.7% increase in the qu value and a 1200% increase in cohesion value. analysis results also showed that the slope safety factor (sf) in prototype 3 increased from 0.516 to 1.519, indicating a safety increase of 194.38%, while in prototype 6, the sf increased from 0.201 to 1.545, indicating a safety increase of 668.6%. therefore, it can be concluded that planting vetiver can enhance slope stability. analysis of soil shear strength with vetiver grass reinforcement was also carried out by comparing the soil shear strength values (cohesion and soil shear angle) from the results of triaxial soil tests without and with vetiver reinforcement. the test results show an increase in the shear strength of the soil. the use of vetiver as a stabilization method is proven to increase slope stability. the cohesion value (c) contributes more to the increase in soil shear strength compared to the internal friction angle (ϕ). the percentage increase in soil shear strength varies depending on the diameter, number and slope of the roots. likewise, plant spacing and root depth greatly affect the increase in slope safety scores (agustina, 2012; fata et al., 2022). on the other hand, garzón et al. (2020a) reported that the planting of vetiver resulted in a decrease in cohesion and an increase in the internal friction angle of sandy soil in guatemala. the authors concluded that this plant protected the slope by reducing the infiltration rate due to soil compaction caused by the roots. moreover, wang et al. (2023) found that the presence of vegetation enhanced the soil's ability to increase matric suction, which was attributed to the increase in soil root surface area index. specifically, the matric suction of vegetation soil was significantly greater than bare soil at the same water content. however, li et al. (2021) found that a capillary barrier system was more effective in stabilizing slopes than vetiver, as it limited antecedent rainwater infiltration. 6.2.5. application of vetiver on coarse grain soil to accurately assess the mechanical characteristics of soil, samples with grass ages ranging from 2 to 8 months as well as bare soil were processed and prepared. experimental outcomes demonstrated that the shear strength of the soil was boosted by the presence of grassroots and matrix suction. as the age of grass or matrix suction increased, the peak shear strength and cohesion of grassed soil tended to rise. in addition, matrix suction was found to have a more significant strengthening effect than grassroots in increasing the overall cohesion of the soil sample. furthermore, grassed soils displayed higher water retention capacity, and soil specimens with older grass ages showed a greater volumetric water content under the same matrix suction conditions. the study outcomes illustrate an increase in the unsaturated mechanical properties of grassed soil (he et al., 2023a; nguyen et al., 2020). from some of the research results above, it can be concluded that vetiver with a bio-engineering system as soil reinforcement on slopes can be concluded, among others: (1) can increase soil cohesion; (2) can increase the friction angle in the soil; (3) can increase the value of qu; (4) can increase the shear strength of the soil; (5) can increase soil stability; (6) peak shear strength and turf soil cohesion tended to increase with increasing grass age and root planting depth. 6.2.6. effectiveness of vetiver in soil stabilization under high annual rainfall several studies have been conducted to evaluate the effectiveness of vetiver in soil stabilization under high annual rainfall conditions (he et al., 2023b; suyana and nugraheni, 2022). a study conducted in thailand found that vetiver hedgerows reduced soil erosion by 82% and sediment yield by 75% (leknoi and likitlersuang, 2020). the study also found that the plant's deep roots improved soil porosity and water infiltration rates, leading to improved soil quality (hailu et al., 2020). another study conducted in nigeria found that vetiver hedgerows reduced soil erosion by 90% and sediment yield by 95%. (ewetola et al., 2021). several studies have shown that vetiver grass is effective for slope stabilization (he et al., 2023b; suyana and nugraheni, 2022). in one study conducted in the philippines, vetiver grass was found to reduce soil erosion on slopes by 80-90% (asio et al., 2015). another study in guatemala showed that the use of vetiver grass reduced soil erosion by 96% and increased soil stability by 98% (garzón et al., 2020b). in addition, vetiver is effective in reducing landslides, and it has been used successfully in landslide-prone areas in india, china, and indonesia (abaga et al., 2021; liu et al., 2022; suyana and nugraheni, 2022). 7. conclusion reducing the risk of landslides, which are significant geological disaster that damages natural and social environments, is important. various types of mass movement on slopes, such as rockfalls, falls, and debris flows, contribute to landslides. therefore, natural methods must be used to reduce disaster risk. the morphological, physiological, and ecological characteristics of vetiver roots make them a suitable candidate for bio-engineering in landslide-prone areas, but this approach requires community involvement. building resilience for disaster risk reduction is a complex process that necessitates a comprehensive, whole-of-society approach, which requires the commitment, good faith, knowledge, experience, and resources of all stakeholders involved in disaster risk reduction. therefore, applying vetiver with bio-engineering as a soil reinforcement on slopes can improve the efficiency of biosystems' functions and benefits. this literature review emphasizes the importance of guidelines for planting vetiver grass as a soil-strengthening method on slopes, enabling the widespread and comprehensive application of this technique. references aarthy, m., banu, k.s.p., karthikeyan, g., suganya, k., haripriya, s., 2022. vetiver floating wetlands for dyeing effluent. ijecc 798–805. 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indonesia: a review. j. geoscience eng. environ. technol. 5, 139–144. https://doi.org/10.25299/jgeet.2020.5.3.4676 zhang, f., sun, s., rong, y., mao, l., yang, s., qian, l., li, r., zheng, y., 2023. enhanced phytoremediation of atrazine-contaminated soil by vetiver (chrysopogon zizanioides l.) and associated bacteria. environ sci pollut res. https://doi.org/10.1007/s11356-023-25395w © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 mohammed, a., et al./ jgeet vol 04 no 01/2019 7 research article assessment of geothermal potentials in some parts of upper benue trough northeast nigeria using aeromagnetic data abdulwahab mohammed 1 , taiwo adewumi 2, *, salako a kazeem 1 , rafiu abdulwaheed 1 , abbass a. adetona 1 , and alhassan usman 1 1 department of physics, faculty of physical science, federal university of technology, minna, niger state, nigeria. 2 department of physics, faculty of science,federal university of lafia, nasarawa state, nigeria. * corresponding author : tydon4real@yahoo.co.uk , adewumi.taiwo@fulafia.edu.ng received: aug 30, 2018; accepted: feb 11, 2019. doi: 10.25299/jgeet.2019.4.1.2090 abstract the assessment of geothermal potentials over part of the upper benue trough corresponding to kaltungo, guyok, lau and dong areas, north eastern nigeria using spectral depth analysis of aeromagnetic data has been carried out. the study area is bounded by latitudes 9 o o o o this research work is necessitated by the need for renewable and alternative sources of energy for use in nigeria. regional/residual separation was carried out on the total magnetic field using polynomial fitting method of order one. the residual map was divided into nine overlapping blocks for the spectral analysis. the centroid depths and depth to top of basement were obtained from the plot of log of power spectrum against wavenumber. these two parameters were used to estimate the curie point depth using 𝑍𝑏 = 2𝑍𝑜 − 𝑍𝑡, where 𝑍𝑏 , 𝑍𝑜 and 𝑍𝑡 are curie depth, centroid depth and depth to top of basement respectively. the results from the spectral analysis suggested that in the parts of the upper benue trough, the basement is deepest at the south western portion towards the lau area and varies between 0.55 and 3.8 km, while the centroid depth varies from 7.26 to 18.00 km. from the same portion of the trough, the curiepoint depths vary between 12.43 and 33.91 km and the corresponding geothermal gradient and heat flow values varying from 17.10 to 46.66 0 c/km with an average of 30.75 0 c/km and 42.75 to 116.65 mw/m 2 with an average of 75.91 mw/m 2 respectively. the maximum heat flow is found around the south western portion of the study area (lau). the entire study area with high heat flow values might probably be good sources for geothermal and thereby recommended for both geothermal exploration and exploitation. keywords: aeromagnetic data, curie point, geothermal gradient, heat flow 1. introduction the study involves the quantitative estimation of curie-point depths (cpd), geothermal gradients and subsurface heat flow anomalies for the assessment of geothermal potentials in some parts of the upper benue trough northeast nigeria using spectral analysis of the recently acquired high resolution aeromagnetic data. the high resolution aeromagnetic data was obtained from the nigerian geological survey agency (ngsa) as part of the airborne magnetic survey data acquired between 2005 and 2009. several studies have shown that regional magnetic data can be used extensively to determine the thermal environments (spector and grant, 1970; nur et al., 1999; bhattacharyya and leu, 1975, 1977; tanaka et al., 1999; ravat et al., 2007; bansal et al., 2011, 2016; nwankwo et al., 2011; eletta and udensi, 2012; kasidi and nur, 2012, 2013; nwankwo and sunday, 2017). for example, dominant magnetic minerals in crust pass from ferromagnetic to paramagnetic state at temperature, commonly called curie-point temperature (cpt). magnetite (fe3o4) is the most common magnetic material in igneous rocks and has an approximate cpt value of 580 o c (nwankwo and sunday, 2017). at temperature above cpt, the thermal agitation causes the spontaneous alignment of the various domains in the mineral to be destroyed (or randomized) to the extent that the ferromagnetic minerals become totally paramagnetic (nwankwo and sunday, 2017). the curie-point is the temperature at which the spontaneous magnetization vanishes and magnetic minerals show paramagnetic susceptibility. the curiepoint depth is known as the depth at which the dominant magnetic minerals in the crust pass from a ferromagnetic state to a paramagnetic state under the effect of increasing temperature (nagata, 1961). for this purpose, the basal depth of a magnetic source from aeromagnetic data is considered to be the curie-point depth. curie point temperature varies from region to region depending on the geology and the mineralogical content of the rocks. the assessment of the variations in the curie-point depth of an area can provide valuable information about the regional temperature distribution at depth and the potential of subsurface geothermal energy (tselentis, 1991). the geothermal http://journal.uir.ac.id/index.php/jgeet mailto:tydon4real@yahoo.co.uk mailto:adewumi.taiwo@fulafia.edu.ng 8 mohammed, a., et al./ jgeet vol 04 no 01/2019 increases with depth. the temperature in sedimentary basins increases downward with depth while heat is transferred upward by a process known as heat flow. assessment of geothermal energy involves studies and research aimed at assessing the nature and energy production capacity of geothermal systems. it is based on the data available at any given time, or stages in the development of a system, such as surface exploration data, the results of the drilling of exploration and production wells, as well as production monitoring data. so far, geothermal issues have not been widely known in nigeria, although investigation of subsurface temperature of rock mass was carried out in hundreds wells due to exploration for oil and gas within sedimentary basins. there were several projects being aimed at exploration of subsurface temperature distribution, carried out with the use of data from oil and gas boreholes as well as shallow water wells. the results of those studies as well as investigation of geothermal surface manifestations give an idea about geothermal conditions of nigeria (kurowska and schoeneich, 2003). the idea of using aeromagnetic data to estimate cpd is not new, and it has been widely applied to various parts of the world. bhattacharyya and leu, (1975) mapped curie point isothermal surface for geothermal reconnaissance of the yellowstone national park in usa. in this area, cpd was estimated 4 8 km. tselentis (1991) calculated cpd in greece from was to understand the nature and extent of the regional geothermal system at a depth beneath the area of greece by constructing the curie isotherms. the results of his investigations revealed that the cpd varies considerably beneath greece, reaching 20 km towards western greece and about 10 km beneath the aegean. in east and southeast asia, cpd was determined based on the spectral analysis of magnetic anomaly data by tanaka et al. (1999). in this study, they used many heat flow data from the boreholes. the estimated cpd for this area using centroid method varied from 9 to 46 km. in addition, they predicted cpd from heat flow data. the cpd estimated from the heat flow data were very similar to the results of the cpd analysis of magnetic data. eletta and udensi (2012) investigated the cpd from magnetic data in the benue trough. their area of investigation lay between 7°n and 9°30´n and between half toward the southern region and lies within the sedimentary formation of the middle benue trough and partly in the basement complex region of northcentral nigeria. their estimated cpds varied between 2 and 8.4 km. also, that the aeromagnetic anomalies suggest that a series of buried ne sw lineaments of incipient rifts controlled the deposition of the individual complexes. onuba et al. (2012) interpreted aeromagnetic data over parts of the upper benue trough and southern chad basin within latitudes of 10°30´n to 11°30´n and longitudes of 12°e to 13°e. they obtained depths to magnetic sources ranging from 0.5 to 2.5 km and concluded that the estimated depths were representative of the sedimentary thicknesses and intrusive bodies within the area. the present study utilizes spectral analysis to estimate the curie-point depth and the heat flow to determine the geothermal history of the region. alagbe and sunmonu (2014) conducted evaluations on aeromagnetic data from the upper benue trough within latitudes of 7°n to 8°n and longitudes of 11°e to 12°e. their estimated depth to the magnetic sources ranged between 0.01 and 3.45 km. they attributed the shallow depths to near-surface intrusive rocks in their study area. with a rapidly growing world-population, and everincreasing environmental concerns, sustainable energy development has become an issue of crucial importance for mankind (tiwari and ghosal, 2005). geothermal resources have the potential of contributing significantly to sustainable energy use in many parts of the world. in nigeria, the quest for a sustainable power supply has been a great challenge to the government (past and present) for the smooth running of the economy and the sustenance of lives and property. this research aims to provide an insight into the geothermal energy potential of the study area as an alternative source of sustainable energy production of power (for electricity generation or direct use for heating residential houses, or both) by identifying and delineating the areas with favourable geothermal conditions and utilizations, through the estimation of the curie-point depth, geothermal gradient and heat flow.. 2. location and geology of the study area the study area (figure 1) which is part of the upper arm of the benue trough lies between latitude 9 o n and 10 o n and longitude 11 0 e and 12 0 e with an estimated area of about 12,100 km 2 . the area is accessible with a good network of roads and rural feeder roads. the benue trough is a major ne-sw trending rift basin of 50 150 km width and over 100 km length. it is geographically sub-divided into lower, middle and upper portion. the upper benue trough (figure 2) is y shaped made up of three arms, namely: the e w trending yola arm, n s trending gongola arm or gongola basin and the ne sw trending main arm (muri lau basin) (shettima et al., 2016). the outcrops of various lithologic units of the upper benue trough are inliers of the prominent bima sandstones (onuba et al., 2008) and deposited as extrusive lithographic units during the albian transgressive phase (ukaegbu and akpabio, 2009). this transgressive episode led to the deposition of the various formations that made up the sedimentary basin which outcrops or occurs as shallow marine deposit of limestone, shale and mudstone. ogungbesan and akaegbobi (2011) however observed that the outcrop units of the formation consist of sandstone, shale and basaltic rocks lying unconformably on the basement rocks. these aptian albian pyroclastics sediments were described as the earliest sedimentation of the entire benue trough. mohammed, a., et al./ jgeet vol 04 no 01/2019 9 fig.1. general geology map of nigeria showing the location of the study area. (modified from obaje, 2009) fig. 2. geological map of the study area (extracted from geological map of nigeria, ngsa) 10 mohammed, a., et al./ jgeet vol 04 no 01/2019 3. materials and method four aeromagnetic maps (sheets 173,174,194 and 195) covering kaltungo, guyok, lau and dong areas of part of the upper benue trough were acquired from the nigerian geological survey agency (ngsa). these maps were obtained as part of the nationwide aeromagnetic survey of 2009 sponsored by the ngsa. the data were acquired along a series of ne sw flight lines with a spacing of 200 m and an average flight elevation of about 80 m while tie lines occur at about 500 m interval. the geomagnetic gradient was removed from the data using the international geomagnetic reference field (igrf), 2005. the data were made available in the form of grids on a scale of 1:100,000. these data were processed and merged together into a common dataset. in this study, the total area to be covered is about 12,100 sq.km extending from latitude 9 o n 10 o n and from longitude 11 o e 12 o e. the procedures involved in this study include the following; production of total magnetic intensity (tmi) map using oasis montaj software, separation of the regional and residual anomalies, division of residual map into nine overlapping blocks, performing spectral analysis on each blocks, evaluating the depth to the magnetic source using spectral analysis, estimating the geothermal gradient and heat flow. theory of methods; calculation of curie-point depth, geothermal gradient and heat flow. the centroid depth is calculated from the low wave number part of the scaled power spectrum as ln [ p(k) 1/2 / k] = a |k| z0 (1) where ln is the natural logarithm, p (k) is the radially averaged power spectrum, k is the wave properties magnetization and its orientation and z0 is the centroid depth of the magnetic sources (tanaker et al., 199). for the high wave number part, the lower spectrum can be related to the top of the magnetic sources by a similar equation: ln [ p(k) 1/2 / k] = b |k| zt (2) where b is a constant: z1 is the depth to the top of the magnetic sources. the depth of the bottom of magnetization zb is : zb = 2zo zt (3) summarily, the depth to the base of the magnetic source (the curie point depth) is calculated in four steps (tanaka et al., 1999): i. calculate the radially averaged power spectrum of the magnetic data in each window ii. estimate the depth to the top of the magnetic source(zt) using the high wave number portion of the magnetic anomaly power spectra iii. estimate the depth to the centroid of the magnetic source (zo) using a lower wave number portion of the magnetic anomaly power spectra iv. calculate the depth to the base of the magnetic source (zb) using zb = 2zo zt. the value of the zb is the curie point depth/dbms. therefore, the geothermal gradient in relation to the heat flow q. (tanaka et al., 1999): q = k 𝛳°𝐶 𝑑 (4) the surface temperature is θ o c and 𝑑𝑇 𝑑𝑍 will remain constant provided there are no heat sources or heat sinks depth. the curie temperature depends on magnetic mineralogy. for example, although the curie temperature of magnetite (fe3o4) is at approximately 580 o c, an increase of titanium (ti) contents of titanomagnetite (fe2-xtixo3) will cause a reduction of the curie temperature. a curie temperature of 580 o c and thermal conductivity of 2.5 w m -1 o c -1 which is the average thermal conductivity for igneous rocks will be used in the study as standard (nwankwo et al., 2011; tanaka et al., 1999), we then calculate the value for k the geothermal gradient in the study area using the empirical relation between curie point, curie temperature and geothermal gradient. heat flow estimates on the crust may therefore be made using the depth and thickness information. the curie point temperature at which rocks lose their ferromagnetic properties provides a link between thermal models and models based on the analysis of magnetic sources. the magnetic susceptibility and strength of the material that make up the crust are controlled by the temperature. at temperature higher than the curie point, magnetic ordering is loose and both induced and remanent magnetization disappear, while for temperatures greater than 580 o c those materials will begin to experience ductile deformation. the basic relation for conductive heat transport is assumption that the direction of the temperature variation is vertical and the temperature gradient 𝑑𝑇 𝑑𝑍 is q = -k 𝑑𝑇 𝑑𝑍 (5) where q is heat flow and k is thermal conductivity. the curie temperature 𝛳 o c can also be defined as: 𝛳 o c = ( 𝑑𝑇 𝑑𝑍 )d (6) where d is the curie point depth (as obtained from the spectral magnetic anomaly). 4. results and discussion the total magnetic intensity map (tmi) of the study area (fig. 3) shows that the magnetic intensity of the study area is divided into regions of high and low magnetic signatures respectively. the high magnetic signature is depicted by the pink colouration on the map and the low magnetic signature is by the blue colouration on the map. the high magnetic signature mohammed, a., et al./ jgeet vol 04 no 01/2019 11 region is well pronounced in the north eastern and south western part of the tmi map of the study area, showing that the high magnetic signature trends northeast southwest in the study area the variation in magnetic signatures could be as a result of degree of strike, variation in depth, difference in magnetic susceptibility and lithology. the low magnetic signature is also pronounced in the south eastern part of the study area. also, low magnetic signature could be found in south-western and north western part of the study area, although the low magnetic signature is less pronounced in these parts of the study area. the residual magnetic intensity map (fig. 4) of the study area shows that the magnetic intensity values ranges from -52.8 nt to 50.3 nt respectively. the high magnetic anomaly signatures are majorly observed in the north-eastern, south-eastern north western part of the study area. although, scattered traces are also observed in the south west and the central parts of the study area. the low magnetic anomaly signatures can be observed in the south-east and trending towards the south-west and northwards, while scattered traces are observed elsewhere in the northern, eastern, southern and western parts of the study area. the high magnetic anomalies might be as a result of basement intrusion into the sediments while low magnetic anomalies are associated with the sedimentary region. fig. 3. total magnetic intensity (tmi) map of the study area (igrf of 33000 nt must be added to get the exact value at any point). 12 mohammed, a., et al./ jgeet vol 04 no 01/2019 fig. 4. residual map of the study area (magnetic unit in nt) the residual map (fig.4) of the study area was divided into nine spectral blocks (spct a i) of overlapping sections. the divisions of the residual map into spectral sections were done manually and the spectral energies were plotted within it. the spectral data obtained were later exported to microsoft excel worksheets one after the other. the spectral blocks energy files were used as input files into a spectral program plot (spp) developed with matlab. the whole nine spectral energies were plotted using a matlab with the developed program. graphs of logarithms of the spectral energies against frequencies estimated for various blocks were obtained and the results tabulated (table 1). the graphs (fig. 5) of the logarithm of the spectral energy against frequency for block a, where the first graph of the figure shows the slope of the lower-wave-number part of the wave-number-scaled spectra, which leads to the estimation of centroid depth (zo), while the second graph shows the slope of the high-wave-number portion of the spectra, which leads to the estimation of the depth to the top of magnetic sources (zt). equation 3 was then applied to estimate the curie point depths (zb). using equation 6, a curie-point temperature of 580 o c and the derived curie-point depth, the geothermal gradients in the study area were calculated. also, equation 4, the geothermal gradients and thermal conductivity of 2.5 wm -1 o c -1 (nwankwo et al., 2009) was subsequently used to estimate the corresponding heat flow anomalies in the study area. the estimated results (table 1) shows that the estimated cpd varies from 12.43 to 33.91 km with an average of 18.83 km. the curie point depth contour map usually varies greatly with different geological settings (tanaka et al., 1999). tanaka et al.,1999, after a compilation of cpd results from several researchers across the globe, inferred that volcanic, tectonic and associated geodynamic environments have cpd shallower than 10 km, while cpds ranging between 15 and 25 km are as a result of island arcs and ridges, and deeper than 25 km in plateaus and trenches. mohammed, a., et al./ jgeet vol 04 no 01/2019 13 fig. 5. zo and zt plots of energy against frequency for block a table 1. estimated curie point depth and succeeding geothermal parameters from spectral analysis in the study area blocks longitude ( 0 e) latitude ( 0 n) centroid depth z0 (km) depth to the top zt (km) curie depth zb (km) geothermal gradient ( 0 c/km) heat flow (mw/m 2 ) a 11.25 9.75 8.70 1.31 16.09 36.05 90.13 b 11.75 9.75 7.26 0.55 13.97 41.52 103.80 c 11.25 9.25 7.72 3.01 12.43 46.66 116.65 d 11.75 9.25 8.86 0.97 16.75 34.63 86.58 e 11.50 9.75 14.70 1.30 28.10 20.64 51.60 f 11.50 9.25 13.00 3.69 22.31 26.00 65.00 g 11.25 9.50 12.20 3.80 20.60 28.25 70.63 h 11.75 9.50 14.30 2.72 25.88 22.41 58.03 i 11.50 9.50 18.00 2.09 33.91 17.10 42.75 average 11.64 3.46 18.83 30.75 75.91 table 1 similarly shows that the geothermal gradient varies between 17.10 and 46.66 o c /km with an average of 30.75 o c /km. the corresponding heat flow values vary from 42.75 to 116.65 mw/m 2 with an average of 75.91 mw/m 2 . the heat flow in the study area also exhibits a ne-sw trending with the derived amounts increasing from the central portion towards the northeast and southwest. the heat flow contour map (fig. 6) is closely related to the geothermal gradient, meaning that most areas of high heat flow correspond to high geothermal gradient. among the four areas making up the study area, the maximum heat flows are found around guyok and dong areas. all current literatures state that curie-point depths and heat flows greatly depend on geological conditions. in geothermal exploration, heat flow is the primary observable parameter. generally, high heat flow values correspond to volcanic and metamorphic region since the two units have high heat conductivities (nwankwo et al., 2011). additionally, heat flow is significantly affected by tectonically active regions (tanaka et al., 1999). geothermal energy does also occur in areas where basement rocks that have relatively normal heat flow are covered by thick blanket of thermally insulated sediments (ofor and udensi, 2014). it can be inferred that the average high heat in the study area may be a direct consequence of the rift associated with the upper benue trough. it may also be associated with areas where thick blanket of thermally insulated sediments cover basement rocks since there is no evidence of volcanic activities in the study area. in thermally normal continental regions the average heat flow is about 60 mw/m 2 , values between 80 and 100 mw/m 2 are good geothermal source, while values greater than 100 mw/m 2 is an indication of anomalous geothermal conditions (nwankwo and sunday, 2017). in view of this, the average heat flow of 75.91 mw/m 2 estimated in the study area corresponding to kaltungo, guyok, lau and dong areas makes the study area to be of favourable geothermal potentials. 14 mohammed, a., et al./ jgeet vol 04 no 01/2019 fig. 6. heat flow contour map of the study area (contour interval of 5 mw/m 2 ) 5. conclusion the results of the estimated curie-point depth for the study area reveals that, the curie point depth varies inversely with heat flow; this shows that heat flow in the study area decreases with increase in curie depth. the inferred curie point depth obtained ranges from 12.43 to 33.91 km with an average of 18.83 km. the results compared favourably well with what was obtained by nur et al. (1999). it also confirms that, curie depths are indirect indicator of the thermal structure of the area. the calculated geothermal gradient in the study area based on the cpd varies between 22.41 to 46.66 o ckm -1 with an average of 30.75 o ckm -1 . the corresponding heat flow values estimated from the geothermal gradient in the study area varies between 42.75 and 116.65 mwm -2 with an average of 75.91 mwm -2 . the average heat flow value of 75.91 mwm -2 obtained in the study area agrees favourably with the range of values obtained by nwankwo and sunday (2017). the result is so good that it can be utilised for exploration of geothermal energy as an alternative source of power in these parts of the upper benue trough. references alagbe, o.a., sunmonu, l.a., n.d. interpretation of aeromagnetic data from upper benue basin, nigeria using automated techniques. iosr j. appl. geol. geophys. 2, 22 40. bansal, a.r., gabriel, g., and dimri, v.p., 2010. power law distribution of susceptibility 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aquitatine 22, 153 185. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://article.sciencepublishinggroup.com/pdf/10.11648.j.ijees.20180304.11.pdf http://article.sciencepublishinggroup.com/pdf/10.11648.j.ijees.20180304.11.pdf http://dx.doi.org/10.3923/ajes.2011.20.28 http://dx.doi.org/10.3923/ajes.2011.20.28 http://dx.doi.org/10.3923/ajes.2011.20.28 http://dx.doi.org/10.3923/ajes.2011.20.28 https://doi.org/10.5194/gtes-5-1-2017 https://doi.org/10.5194/gtes-5-1-2017 https://doi.org/10.5194/gtes-5-1-2017 https://doi.org/10.5194/gtes-5-1-2017 https://doi.org/10.5194/gtes-5-1-2017 https://doi.org/10.1190/1.1440092 https://doi.org/10.1190/1.1440092 https://doi.org/10.1016/s0040-1951(99)00072-4 https://doi.org/10.1016/s0040-1951(99)00072-4 https://doi.org/10.1016/s0040-1951(99)00072-4 https://doi.org/10.1016/s0040-1951(99)00072-4 https://doi.org/10.1007/bf00878889 https://doi.org/10.1007/bf00878889 https://doi.org/10.1007/bf00878889 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. location and geology of the study area 3. materials and method 4. results and discussion 5. conclusion references e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 84 taki, m.h. et al./ jgeet vol 02 no 01/2017 planning tod with land use and transport integration: a review herika muhamad taki 1, *, mohamed mahmoud h.maatouk 2 , emad mohammad qurnfulah 1 , mohammed omayer aljoufie 1 1 king abdulaziz university, urban and regional planning department, jeddah, saudi arabia 2 king abdulaziz university, urban and regional planning department, jeddah, saudi arabia and minia university, department of architecture, egypt * corresponding author : htaki0001@stu.kau.edu.sa tel.:+622-54-359-1911 received: jan 23, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017. abstract transit oriented development (tod) implementation in urban development is globally adopted by many countries in the world in a rapid manner. however, the city and regional acute problems is still propagating. an in-depth study to examine this problem is required. thus, this paper review various study related to the integration of land use and transport with tod. the subject of the paper will be described as follow: method, criteria and indicators of tod's research, reviewing the strategic plan and the public transport plan in the worldwide, and cross-continent comparison of integration planning. in conclusion, practice and integration of tod through land use and transportation is an alternative solution in acquiring the objective of the master plan and to solve urban issues such as urban congestion, reduce travel time, and car dependency. keywords: planning, transit oriented development (tod), transport, land use, integration 1. introduction transit-oriented development (tod) is a notionoriented city-region development to provide maximum access to passengers (curtis & scheurer, 2010; hasibuan & soemardi, 2014), especially public transport such as trains and bus with the purpose of the creation of comfortable atmosphere with friendly environment and are equipped with various facilities such as parking, parks, offices, and more, this requires a mix of residential and commercial areas of the compact and the mixture to facilitate become a base for the development of public transport transit area-based (cervero & dai 2014). tod, in general, is the part of the public transport system (black et al. 2016). the positive results of tod was obtained by a city include: creating a healthy environment due to the declining number of pollution (dou et al. 2016), the city's economic efficiency due to the increasingly large amounts of transportation costs and speed the travel time (li et al. 2013), the creation of the city transportation system efficiency because of the many passengers who switch from private cars topublic vehicles and reduced congestion (boschmann & brady 2013), and land use had inflicted because of area around the station settings appropriate allocation that is compact and mixed (ratner & goetz 2013). 1.1 urban planning and tod the concept of tod is very closely related to urban planning because it is a derivation from the movement of the garden city movement was popularized by ebenezer howard in the late 19th century (black et al. 2016). howard called on to decentralize the cities too dense. the concept now known as classic town plans are characterized by a pattern of radial road pattern grid which converges on a focal point or in town centers. the master plan includes the urban garden, and put forward the use of the public (arrington & cervero 2008). the road is designed to achieve a balance between pedestrian and vehicular, accommodate trees, sidewalks, and street furnishing while also providing visibility and ride comfort and on-street parking. the buildings directly facing made to roads with features that create the excitement of public spaces. a tod generally have an embodiment in the form of the commercial core with the distance reached by residents, a grid-shaped road network well connected, the width of the road that are not too large with parking on a side street as a buffer for the pedestrian, a back-lot alley, land use mixedresidential use, with different types of density (dorsey & mulder 2013). the area resembles the traditional community form tod with unique characteristics and different where the transit station and its surrounding areas became the focal point (ulloa 2011). mailto:htaki0001@stu.kau.edu.sa taki m.h. et al./ jgeet vol 02 no 01/2017 85 1.2 integration land use and transport using tod concept transit oriented development is a part of urban development with emphasis on a growth point to minimize the occurrence of sprawl (zhang 2008). through the concept of tod, a city developed at some points grow, which is the point of rest mass transportation. consequently, there is the division point of growth based on the route to public transportation stops (xie & levinson 2009). this concept is also a regional design that makes up an accessibility network in regional scale and it becomes an integrated union. the unity was formed through an integrated transport network and land use that creates a territorial integration (wieberneit 2007). the station area was developed by integrated tod and pedestrian-oriented creates an environment with convenient, secure, fun and sufficient for the pedestrian walkable environment) (wey & chiu 2013). the mixture of various function's activities generates a shorter trip and quickly. these functions are the land use includes commercial area center, offices, retail, services, and localities with a population density of medium to high density and public open space (wey 2015). in thetransportation point of view,tod involved the inhabitants in the everyday interaction and reduce auto-oriented activities. inhabitants who have limitations in the use of private vehicles (due to economic reasons, the age of children or the elderly) still had access to many facilities and meet his needs (vos et al. 2014). 1.3 the research problem urban transportation activities have a significant effect on the increase of traffic congestion and air pollution. there are solutions that have been implemented, but still limited to practical approaches. furthermore, the problems of urban transport need to be reviewed through a systemic approach, namely, the establishment of the urban transport system in a macro integrates aspects of land use and transportation. the current paradigm of the cities in the world in addressing the problems is by starting to implement innovative strategies through the application of the integration system concepts. one of them is the concept of transit oriented development (tod). 1.4 the objectives of research the objective of this paper is to encourage application of tod as one of the alternative solutions in addressing the problems of congestion and pollution of the city through the integration between the transport nodes with land use in adjecent of the station. this paper emphasizes the study of linkages characteristics-based tod transit area to encourage movement of ridership using mass transit. 2. the methods this paper provides evidence of integration between transport and land use with tod from literature by formulating a long list indicators of the district-based tod through study literature regarding tod practices in cities in the world. the formulation of the protracted lists is done by a qualitative descriptive analysis technique through the theoretic approach to the concept of tod. the formulation of the protracted lists, which is performed to confirm suitability indicator concepts for the tod was adapted in the local context. the stakeholders are the key to understanding the characteristics of the area and transportation. formulation of criteria-based tod area is obtained using descriptive method and comparative analysis between existing conditions of the area with tod indicator that has been deduced from the study of literature. 3. result and discussion 3.1 planning and assessment of tod research in the last 5 years covermethods, criteria and indicators. efforts to develop a tod research has been discussed in some study and continue to grow in accordance with developments in the public transport sector. this section discuss some of the studies (see table 1). a study by atkinson-palombo & kuby (2011) about tod discusses tod typologies, several stations classified based on the type of overlay zoning, the method used was factor analysis and cluster analysis with the result that is ranking from low to high advance tod each station, although data based on multi-criteria but in separate discussions and after that created relationship between lrt and tod. prasertsubpakij & nitivattananon (2012) measured metro station in bangkok metropolis, thailand by measuring tod access, various values of some variable research made the comparison using the accessibility score, t-test, and t-significant values. data collection was obtained from questionnaire with approximately 600 respondents. binglei & chuan (2013) measured the tod mode analysis with dea (data envelopment analysis) mathematical formula using software. this study obtained the ranking by making evaluation of actual tod with land use and urban rail transit as variables. in his study, fard (2013) found the tod index using smca (spatial multi-criteria analysis) i.e. counting criteria and indicator of spatial data, the results obtained are tod level based on the potential area for construction of the new station. his study is equipped with hot-spot analysis techniques to observe potential differences between areas. ratner & goetz (2013) divided type of tod based on urban structure and land use, the study elaborated data of land use and urban form in the 86 taki, m.h. et al./ jgeet vol 02 no 01/2017 comparison of denver area. the results are the typology and its impact on the development of denver city, the study emphasize on descriptive variables and describing the relationships between variables. tod typologies were introduced by kamruzzaman & baker (2014) i.e. categorizing each tod based on cluster analysis and node place typology. the multinomial logistic regression is applied as statistical analysis to obtain tod cluster. tod level is not very clearly presented in the final value yet elaborated based on the typology of each station, where the variable based on typology research is taken. study of singh (2015) which discussed tod composite study stated tod index findings using weighted method from each of the criteria indicators followed by the assessment of each station based on the gained index, the study orientation is in stenberg, netherlands, using multicriteria analysis using arcgis and ilwiss software to produce tod score map. papa & bertolini (2015) compared the value of tod between 6 metropolitan areas in europe, the study using node-place model with various indicator tod and rail-based accessibility. the study observe existing area of the metropolitan with the result that accessibility is higher in urban areas. table 1. method, criteriaand indicators of tod research taki m.h. et al./ jgeet vol 02 no 01/2017 87 88 taki, m.h. et al./ jgeet vol 02 no 01/2017 vale (2015) studied tod classification to obtain the relationship between land use, transport, and pedestrian accessibility. the node-place model, pedestrian shed ratio with cluster analysis wes implemented in the study. gis application was complemented in the study. based on the analysis of three values, the study concluded a balanced place-node is not necessarily. higgins & kanaroglou (2016) discussed the performance of tod based on inputs and outcomes. they applied latent class model-based clustering with multi-criteria research method. the study also outlined the type of station, based on the concept, and a significant level of the statistical indicators of each variable. 3.2 the strategic plan and the public transport plan worldwide. some of the strategy plan and public transport plan that implement tod in transit areas in the world is a lesson that is applicable taken in real life, in the form of policies and actual implementation of the strategy as well as the contributing factors, in the form of the circulation which also passing the urban area (see table 2). dorsey & mulder (2013) describe a strategic plan and public transport in ogden, utah, usa. the strategic plan aim is to balance three things that are important in the development of the city, namely private aspects, society and government. fig1. proposed ogden streetcar routes. source: (dorsey & mulder 2013). all three components should work in harmony to achieve the goal of moving the city in the future. . the public transportation applied in the routes which being developed is able to commute the people and conjugates with other means of transportation. this is important to evoke the impression of a comfortable environment of the city as well as the awareness of the social interaction. north-pas-de-calais region in french practices development using tod for many years (feudo 2014). application of tod in this region is expected to be made as the model for other cities development in france that offer mixed land use, locations near the point of transit, reduce land consumption, punctuality of transportation, and good quality of life in urban areas. taki m.h. et al./ jgeet vol 02 no 01/2017 89 fig. 2. scales of tod. source (feudo, 2014). policy integration between land use and transport on the view of regional planning implementation emphasize in supporting the activities near transit corridors to encourage the use of urban transport. in brisbane, queensland, australia, the strategy plan objective is to make australia a strong, intelligent, green, and healthy nationby reducing congestion and by cutting one-third of the current carbon emissions (kamruzzaman & baker 2014). fig. 3. spatial distribution of ccd clusters in brisbane. source: (kamruzzaman & baker 2014). table 2. the strategic plan and the public transport plan worldwide 90 taki, m.h. et al./ jgeet vol 02 no 01/2017 the strategic plan and the public transport plan as above facilitate the development of better land use through transportation activities in the existing corridors. therefore, future planning of the corridors can be developed for long term anticipation of a growing urban area. a new paradigm of urban strategy plan of sejong city, south korea, focuss on the construction of the city that reflects the experience of korea. the public transportation system was implemented to provide service which support the development by establishing stations located along the routes of pedestrian, bicycle paths, on-site retail community, and public facilities (kwon, 2015). fig. 4. the construction of the master plan that reflects the experience of korea. source: (kwon 2015). 3.3 cross-continent comparison of the transport and land use integration with tod tod has been applied in many parts of the world, it was originated in usa, further spread to europe, australia and asia. each country has different characteristics in applying tod. this section explained the successfull implementation of tod with combines land use and transport (see table 3). usa is an excellent model of tod application by the case of new york city (loo et al. 2010) and san jose (mathur & ferrell 2013).. integration of transport and land use in tod underscore the serious interest to the mixed land use because it is expected to maintain the traffic flow of passanger. extensive network and high transit ridership of new york residents supported by the provision of heavy rail system. tod is implemented within the transit are in which the interaction between modes of transportation is occured, such as bus and ferries. tod in the san jose is served by a complete transit system using light rail line, commuter rail service and rapid transit district (bart). integration of land use and transport is done by exposing both into a cooperative development on the station. the transit system was built by having the 67 of train that operates on the working days and 62 of train on the weekend. the interval time each train is 15 minutes. the stations located at the intersection of two major highways. fig. 5. the railway network of new york city. source (loo et al. 2010) lisbon, portugal and the region of scania, sweden are the examples of successful application of the tod integration in the city and region scale. the application of tod integration in scania region, sweden is carried out by the regional strategy to move the accessibility based on sustainable social facilities and environment (qviström 2015). the point is the development of the city structure as the engine of growth towards sustainability and efficient, with no appeal of social and environmental. fig. 6. the train station locations in lisbon. source (vale 2015) taki m.h. et al./ jgeet vol 02 no 01/2017 91 table 3. cross-continent comparison of integration planning of transport and land use with tod practice 92 taki, m.h. et al./ jgeet vol 02 no 01/2017 in line with scania, lisbon, portugal also apply tod integration through planning suburban areas and strengthen the outskirts of the city as the main place of transportation interchanges. transport and land use are the key features of urban development in lisbon (vale 2015). therefore, the application of urban planning in surrounding area of the station is important for the station sustainability. perth and sydney experience of integration tod is by applying a relation between form, use, transportation, density, urban development and the effect on the behaviour of human as the dominant factor. tod in perth started since the opening of the mandurah railway station in 2007. integration of tod in transportation planning rejuvinates the quality of urban planning and social life of the community. the planning emphasize on the creation of a mixed use and density of settlements, other plan emphasize to attract pedestrian, i.e. putting the station on the intersection of the main distributor roads and freeways. the station also serve users of private car and service a bus feeder system along the distributor in suburban areas. tod and smart city was implemented in sydney, australia. tod is in adjecent with the smart city movement where the concept of adaptation from beyond and performed by adjusting with the local conditions (black et al. 2016) fig. 7. integration planning of tod in sydney. source (olaru et al. 2011). . integration planning of tod in sydney put on the land use development that located along the bus way or public transport lanes outside of the city. in addition, planning suburban road by implementing the transit way or a bus rapid route. cities in asia have been an orientation to transit, such as seoul, korea and shenzhen, china. in seoul, taki m.h. et al./ jgeet vol 02 no 01/2017 93 tod is integrated through the application of compact land use patterns (sung & oh 2011). the planning of the quality and quantity of the tod services is done through the creation of the features of the urban design and road network in the surroundingarea of the train stop. the city government manage the rapid growth by emphasizing the concentration of areas within a radius of 1 km from the train station. fig. 8. railway system in seoul, south korea. sources (sung & oh 2011). integration of tod in china stressed on the development of the area around the station with prioritizing land quota and applying special zone (li et al. 2013). it connects two adjacent cities to evoke the tourism industry and urban development. fig. 9. public transport plan in china. source: (li et al. 2013). 3.4 finding the concept of tod ensure the existence of urban transport sustainability by integrating transportation networks to the growth of the city. this objective is manifested through the centralization of activities and developments around transit area. the concentration of activities near transit area will encourage the use of tod. therefore, it can gradually reduce car dependence. identification of the integration between transport and land usewith tod in various cities of the world shows the transit area has an affinity towards many commuters. the transit area with a compact and diverse land use, which also completed with pedestrian path access, significantly able to attract larger numbers of commuters and it helps to decrease traffic congestion and environmental pollution. tod is an alternative to encourage the attainment of sustainable urban development where the principles of planning and designing adjusted for the purposes of the development level of the strategic urban environment. 4. conclusion efforts to address problems of congestion and air pollution have been performed by the city governments globally by implementing transport strategy. one of the above mentioned strategy is transport system plan-based mass transit in the city or regional scale. this planning is supported by structuring space and providing a connecting mode of transportation to facilitate passenger accessibility from origin to their destination. however, the provision of mass public transport alone is not enough to cope with the urban problems such as congestion and pollution. a solution is required, in which the solution musta able to integrate land use and transport. one of the best solution is transit oriented development (tod). based on a review of the previos studies incorporated in this paper, practice and integration of tod through land use and transportation showed that tod can be the alternative solution in addressing the problems of developing urban area. the implementation of tod is able to reduce congestion by facilitating the population preference of public transport compare to private modes of transportation and improved environmental quality. however, of course, it takes a strong commitment and consistency of the stakeholders to be involved in the implementation of tod in a persistent manner. references arrington, g.b. & cervero, r., 2008. tcrp report 128: effects of tod on housing, parking, and travel. transportation research board of the national academies, washington, dc, 3. atkinson-palombo, c. & kuby, m., 2011. the geography of advance transit-oriented development in metropolitan phoenix, arizona, 2000 2007. journal of transport geography. binglei, x. & chuan, d., 2013. an evaluation on coordinated relationship between urban rail transit and land-use under tod mode. journal of transportation systems engineering. black, j., tara, k. & pakzad, p., 2016. planning and design elements for transit oriented developments/smart cities: examples of cultural borrowings. procedia engineering. boschmann, e. & brady, s., 2013. travel behaviors, sustainable mobility, and transit-oriented developments: a travel counts analysis of older adults in the denver, colorado metropolitan area. journal of transport geography. 94 taki, m.h. et al./ jgeet vol 02 no 01/2017 cervero, r. & dai, d., 2014. brt tod: leveraging transit oriented development with bus rapid transit investments. transport policy. curtis, c. & scheurer, j., 2010. planning forsustainable accessibility: developing tools to aid discussion and decision-making. progress in planning. dorsey, b. & mulder, a., 2013. planning, place-making and building consensus for transit-oriented development: ogden, utah case study. journal of transport geography. dou, y. et al., 2016. an empirical study on transit-oriented low-carbon urban land use planning: exploratory spatial data analysis esda on shanghai, china. habitat international. feudo, f., 2014. how to build an alternative to sprawl and auto-centric development model through a tod scenario for the north-pas-de-calais region? lessons from an. transportation research procedia. hasibuan, h. & soemardi, t., 2014. the role of transit oriented development in constructing urban environment sustainability, the case of jabodetabek, indonesia. higgins, c. & kanaroglou, p., 2016. a latent class method for classifying and evaluating the performance of station area transit-oriented development in the toronto region. journal of transport geography. kamruzzaman, m. & baker, d., 2014. advance transit oriented development typology: case study in brisbane, australia. journal of transport. kwon, y., 2015. sejong si city: are tod and tnd models li, g. et al., 2013. value capture beyond municipalities: transit-oriented development and inter-city delta. journal of transport geography. loo, b., chen, c. & chan, e., 2010. rail-based transitoriented development: lessons from new york city and hong kong. landscape and urban planning. mathur, s. & ferrell, c., 2013. measuring the impact of suburban transit-oriented developments on singlefamily home values. transportation research part a: policy and practice. olaru, d., smith, b. & taplin, j., 2011. residential location and transit-oriented development in a new rail corridor. transportation research part a: policy. papa, e. & bertolini, l., 2015. accessibility and transitoriented development in european metropolitan areas. journal of transport geography, 47, pp.70 83. prasertsubpakij, d. & nitivattananon, v., 2012. evaluating accessibility to bangkok metro systems using multidimensional criteria across user groups. iatss research. qviström, m., 2015. putting accessibility in place: a relational reading of accessibility in policies for transit-oriented development. geoforum. ratner, k. & goetz, a., 2013. the reshaping of land use and urban form in denver through transit-oriented development. cities. sung, h. & oh, j., 2011. transit-oriented development in a high-density city: identifying its association with transit ridership in seoul, korea. cities. ulloa, c., 2011. transit oriented regeneration: stedenbaan stations as drivers of urban regeneration in the south wing of the randstad. vale, d., 2015. transit-oriented development, integration of land use and transport, and pedestrian accessibility: combining node-place model with pedestrian shed ratio to evaluate. journal of transport geography. vos, j. de, acker, v. van & witlox, f., 2014. the influence of attitudes on transit-oriented development: an explorative analysis. transport policy. wey, w., 2015. smart growth and transit-oriented development planning in site selection for a new metro transit station in taipei, taiwan. habitat international. wey, w. & chiu, y., 2013. assessing the walkability of pedestrian environment under the transit-oriented development. habitat international. wieberneit, n., 2007. service network design for freight transportation: a review. or spectrum, 301, pp.77 112. xie, f. & levinson, d., 2009. modeling the growth of transportation networks: a comprehensive review. networks and spatial economics, 93, pp.291 307. zhang, r., 2008. transit-oriented development strategies and traffic organization. in transportation and development innovative best practices 2008. reston, va: american society of civil engineers, pp. 277 283. 1. introduction 1.1 urban planning and tod 1.2 integration land use and transport using tod concept 1.3 the research problem 1.4 the objectives of research 2. the methods 3. result and discussion 3.1 planning and assessment of tod research in the last 5 years covermethods, criteria and indicators. 3.2 the strategic plan and the public transport plan worldwide. 3.3 cross-continent comparison of the transport and land use integration with tod 3.4 finding 4. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” tsamara & puja/ jgeet vol 08 no 02-2 2023 58 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 research article stress analysis of existing underground gas pipeline due to new road crossing with odol transportation taqiya tsamara1,*, i. g. n. wiratmaja puja2 1 mechanical engineering department, faculty of mechanical and aerospace engineering, bandung institute of technology, ganesha street no. 10, bandung 40132, indonesia 2 mechanical engineering department, faculty of technology industry, universitas pertamina, teuku nyak arief street, jakarta 12220, indonesia * corresponding author : taqiyatn@gmail.com received: may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13882 abstract pipelines are the main choice for transport oil and gas due to its resilience, reliability, safety, and lower cost. most road crossing pipelines are located underground where protections from the loads can be used such as additional pavement. underground road crossing pipelines withstand stresses caused by the internal load, earth load, and live load. these loads are affected by the pipe and fluid specifications, soil and environment data, and also the vehicle data. over dimension and over loading (odol) vehicles are a very common problem found in indonesia. hence, a stress analysis towards the underground road crossing pipeline being crossed by odol veh icles are relevant. a manual calculation of the stress analysis can be done by using api rp 1102: “steel pipelines crossing railroads and highways”. a stress analysis using the finite element method (fem) is conducted using a computer software, namely abaqus, which also sho ws the displacement of the pipeline. the case study is an underground road crossing pipeline with depth of 8 feet and uses rigid pave ment. the use of rigid pavements over the soil decreases the stress experienced by the pipeline. the results of the total effective stress show a value of 4,785 psi which is still within the allowable range. the stress is found to be directly proportional to the displacement v alue obtained using fea. by conducting parametric studies, it is also found that the total effective stress decreases as the burial depth of the pipe is larger. keywords: pipeline, road crossing, underground, stress, api rp 1102, computer software, finite element 1. introduction oil and gas industry is one of the most crucial industries in the energy sector. as of now, fossil fuel is consistently on top of the list of main energies used in the world. according to data published in 2020 by the british petroleum company, the three largest energy consumptions in the world are oil, coal, and natural gas (british petroleum, 2021). data obtained from skk migas shows that the energy productions in indonesia in 2020 for crude oil and natural gas has high values of 708.5 thousand barrels of oil per day (mbopd) and 6,679 million standard cubic feet per day (mmscfd), respectively (skk migas, 2021). electricity, vehicles, household needs, and power plants are among the many things fossil fuel energy are used for (van dyke, 1997). noting the high demand towards the oil and gas industry, transportation or distribution system of the oil and gas produced is important to be accounted for. pipelines are one of the predominant methods to transport oil and gas from one facility to the other. in indonesia, pipelines are still the main choice for transport oil and gas – among them being due to its safety, resilience, reliability, and lesser cost (nugroho, 2006). natural gas pipelines can be found underground and also subsea. fluid properties, environmental conditions, economics, material, protection, environmental impact, and operation are just a few among the many aspects affecting the pipeline system. underground pipeline system may be placed under road crossing. a study by tawekal and idris (2012), discusses the design and analysis of a crossing pipeline. the load given by the vehicle crossing the pipeline would certainly have an effect towards the safety of the underground road crossing pipeline. in indonesia, over dimension and over loading (odol) is a problem that is still highly common, with data from indonesia’s ministry of transportation in 2020 showing 59% out of 1,425,051 vehicles reviewed have tested odol (puslitbang jalan dan perkeretaapian, 2021). the load of odol trucks in indonesia could even reach 200 percent of its original weight. aside from vehicles crossing – the soil, pavement, and design of the pipeline will affect the safety of the pipe. a study has been conducted by mosadegh and nikraz (2015), of the use of finite element analysis on buried pipeline subjected to traffic load with varying surface pressures and burial depths. while another study by xi et al. (2019) has been conducted on the reliability of a buried polyethylene pipe that is also subjected to traffic load. it is highly important to design and construct a pipeline in detail and in accordance to the guidelines set by the codes, standards, and government regulations. a study by fahrudin et al. (2020) regarding the stress an underground road crossing pipeline using pipe material of api 5l x52 while this paper will review the material of api 5l x42. in this paper, the observed section of the gas pipeline is a buried or underground road crossing pipeline which will be crossed by heavy vehicle. the pipe specifications given shows that the pipeline was initially designed for residential crossings. hence, the paper aims to analyse the stress and safety of the underground road crossing pipeline http://journal.uir.ac.id/index.php/jgeet tsamara & puja/ jgeet vol 08 no 02-2 2023 59 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 due using analytical approach using the recommended practice of api rp 1102: “steel pipelines crossing railroads and highways” and using numerical method base on finite element using abaqus software. 2. material and methods 2.1 data in order to achieve this paper’s objective, the following pipe and soil data are used to complete the analytical and numerical analysis of the underground road crossing pipeline using the recommended practice of api rp 1102 and abaqus. table 1 shows the technical data of the pipe, table 2 shows the pipe material, and table 3 shows the soil material which is classified using uscs (howard, 1986). table 1. pipe technical data. parameters value pipe material outside diameter api 5l x42 6.625 inch wall thickness 0.561 inch operating pressure 780 psi smys 42,000 psi design factor 0.72 longitudinal joint factor (american society of mechanical engineers, 2020) operating temperature 1 90°f temperature derating factor (american society of mechanical engineers, 2020) 1 type of longitudinal weld seamless table 2. pipe material properties. parameters value density 0.284 lb/in3 young’s modulus 30,000 ksi poisson’s ratio 0.3 coefficient of thermal expansion 0.0000065 per °f table 3. soil material properties. parameters value soil type ch modulus soil reaction 0.2 ksi resilient modulus 5 ksi density 0.069 lb/in3 young’s modulus 725 psi poisson’s ratio 0.3 cohesive strength 3.6 psi friction angle 20° dilation angle 2° the installation temperature of the underground road crossing pipeline will use the environment temperature at the location which is 86 °f (badan pusat statistik, 2014). the burial depth from the top of the pipeline to the top soil will be varied by 3, 4, 6, 8, and 10 feet deep. while the pavement type evaluated will be rigid pavement and no pavement. the study will review the safety of the underground road crossing pipeline using a vehicle that is over dimension and over load (odol) by 200%. table 4 shows the data of the vehicle’s front and rear axle weight that is multiplied by 200%. table 4. odol vehicle’s axle weight. parameter value front axle 16 ton rear axle 52 ton to help visualize the case study conducted in this paper, an illustration of the case is shown in fig. 1. fig. 1. illustration of the underground road crossing pipeline (not drawn to scale). 2.2 api rp 1102 methodology shown in fig. 2 is the flowchart of the calculation using the api rp 1102 methodology. the pipelines’ barlow internal pressure, total effective stress, fatigue girth weld, and fatigue longitudinal weld will be evaluated and checked against its’ maximum allowable value (american petroleum institute, 2017). it is conducted to obtain whether the underground road crossing pipeline is safe when crossed by odol vehicles. the api rp 1102 equations of the stresses experienced by the pipeline are shown below in accordance to the flowchart in fig. 2. 1. circumferential stress due to internal pressure (barlow check) one of the required checks for the allowable stress is by using barlow formula (code of federal regulations (cfr), 2022). the barlow formula is used to obtain the circumferential stress caused by the internal pressure, which must not exceed the allowable maximum value. the following will show the calculation to check the barlow internal pressure (eqn. 1). 𝑆𝐻𝑖 (𝐵𝑎𝑟𝑙𝑜𝑤) = 𝑝𝐷 2𝑡𝑤 ≤ 𝐹 × 𝐸 × 𝑇 × 𝑆𝑀𝑌𝑆 (1) where: 𝑆𝐻𝑖 (𝐵𝑎𝑟𝑙𝑜𝑤)= barlow formula 𝑝= operating pressure 𝐷= outside diameter 𝑡𝑤= wall thickness 𝐹= design factor 𝐸= longitudinal joint factor 𝑇= temperature derating factor 𝑆𝑀𝑌𝑆= specified minimum yield strength 2. circumferential stress due to internal pressure (eqn. 2) 𝑆𝐻𝑖 = 𝑝(𝐷−𝑡𝑤) 2𝑡𝑤 (2) where: 𝑆𝐻𝑖= circumferential stress caused by internal pressure 60 tsamara & puja/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 2. api rp 1102 methodology. tsamara & puja/ jgeet vol 08 no 02-2 2023 61 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 3. circumferential stress due to earth load (eqn. 3) 𝑆𝐻𝑒 = 𝐾𝐻𝑒 𝐵𝑒 𝐸𝑒 𝛾𝐷 (3) where: 𝑆𝐻𝑒= circumferential stress due to earth load 𝐾𝐻𝑒 = stiffness factor for circumferential stress due to earth load 𝐵𝑒=burial factor for circumferential stress due to earth load 𝐸𝑒= excavation factor for circumferential stress due to earth load 4. impact factor due to live load the impact factor is used to increase the live load acting on the pipe and it is a function of the burial depth, h. the impact factor value is found using the graph shown in fig. 3. fig. 3. recommended impact factor versus depth. 5. applied design surface pressure (eqn. 4) 𝑤 = 𝑃𝑡 𝐴𝑝 (4) where: 𝑤 = applied design surface pressure 𝑃𝑡= design wheel load 𝐴𝑝= wheel contact area 6. cyclic circumferential stress due to live load (eqn. 5) ∆𝑆𝐻ℎ = 𝐾𝐻ℎ 𝐺𝐻ℎ𝑅𝐿𝐹𝑖 𝑤 (5) where: ∆𝑆𝐻ℎ= cyclic circumferential stress due to live load 𝐾𝐻ℎ= stiffness factor for cyclic circumferential stress from highway 𝐺𝐻ℎ= geometry factor for cyclic circumferential stress from highway 𝑅= highway pavement type factor 𝐿=axle configuration factor 𝐹𝑖 = impact factor 7. cyclic longitudinal stress due to live load (eqn. 6) ∆𝑆𝐿ℎ = 𝐾𝐿ℎ 𝐺𝐿ℎ 𝑅𝐿𝐹𝑖 𝑤 (6) where: ∆𝑆𝐿ℎ= cyclic longitudinal stress due to live load 𝐾𝐿ℎ= stiffness factor for cyclic longitudinal stress 𝐺𝐿ℎ= geometry factor for cyclic longitudinal stress 8. maximum circumferential stress (eqn. 7) 𝑆1 = 𝑆𝐻𝑒 + ∆𝑆𝐻 + 𝑆𝐻𝑖 (7) where: 𝑆1= maximum circumferential stress 9. maximum longitudinal stress (eqn. 8) 𝑆2 = ∆𝑆𝐿 − 𝐸𝑠 𝛼𝑇 (𝑇2 − 𝑇1) + 𝑣𝑠 (𝑆𝐻𝑒 + 𝑆𝐻𝑖) (8) where: 𝑆2= maximum longitudinal stress 𝐸𝑠= young’s modulus 𝛼𝑇= coefficient of thermal expansion 𝑇2= maximum or minimum operating temperature 𝑇1= installation temperature 𝑣𝑠 = poisson’s ratio 10. maximum radial stress (eqn. 9) 𝑆3 = −𝑝 (9) where: 𝑆3= maximum radial stress 11. total effective stress the effective stress is used to check the yielding of the pipeline (eqn. 10). it is examined by comparing the value of the smys multiplied by the design factor with the effective stress and ensuring that it is larger than the effective stress. 𝑆𝑒𝑓𝑓 = √ 1 2 [(𝑆1 − 𝑆2) 2 + (𝑆2 − 𝑆3) 2 + (𝑆3 − 𝑆1) 2] (10) where: 𝑆𝑒𝑓𝑓= total effective stress the potential of fatigue occurring in the pipeline in the girth and longitudinal weld can also be estimated by referring the api rp 1102. below are the equations to conduct the fatigue check in accordance to api rp 1102 methodology. 1. girth weld fatigue (eqn. 11) ∆𝑆𝐿𝐻 ≤ 𝑆𝐹𝐺 × 𝐹 (11) where: 𝑆𝐹𝐺= fatigue resistance of girth weld 2. longitudinal weld fatigue (eqn. 12) ∆𝑆𝐻ℎ ≤ 𝑆𝐹𝐿 × 𝐹 (12) where: 𝑆𝐹𝐿= fatigue resistance of longitudinal weld 2.3 finite element analysis methodology the finite element analysis will utilize abaqus software to obtain the stress and displacement of the underground road crossing pipeline section being reviewed. the methodology of the finite element modelling in abaqus will be depicted in fig. 4. the pipe and soil material properties, element load, and boundary conditions will be the main input of the pipe and soil modeling in abaqus. the pipeline is modelled as a 3d deformable shell with the length of 98 ft, while the soil is 62 tsamara & puja/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 modelled as a 3d deformable solid body as a block with the dimension of 98 ft x 32 ft x 32 ft. the thermal effects will also be given to the pipeline, with known thermal coefficient, initial temperature, and final temperature. fig. 4. finite element analysis methodology. an interaction of the pipe and soil will be created by defining the contact between the pipe and soil which is modelled to interact as a surface-to-surface contact between the external surface of the pipeline and the inner surface of the soil. the loading conditions will consist of the gravity, internal pressure, and the vehicle load on top of the soil. the gravity force and internal pressure will be constant throughout the analysis with values of 2.2 lbf and 780 psi, respectively. meanwhile, the vehicle load given will depend on the area of contact between the vehicle and the soil. next, the pipe and soil model are given boundary conditions. boundary conditions of the soil’s sides are given rollers. the reason is because the infinite or semi-infinite soil element is assumed to move only vertically when a critical amount of the soil element is considered in the finite-element analysis (lee, 2010). to confine both horizontal and vertical movement of the bottom surface of the soil element, the part is given fixed boundary conditions. the ends of the pipe are given rollers to ensure that the pipe will still be able to move vertically and because an infinite length of pipe is considered in this analysis. it will make movement of the pipe due to the soil possible. fig. 5 shows the boundary conditions applied to the pipe and soil model. fig. 5. boundary conditions of the model. after completing the steps mentioned before, the mesh will be generated and the analysis will be conducted by the software. a convergence test is then conducted to be able to refine the mesh. if the results are unsatisfying, a modification of the underground road crossing pipe should be performed. same as the api rp 1102, the study will consist of the differing burial depths and pavement types. the burial depths reviewed are 4 and 8 feet with two pavement types which are rigid pavement and without any pavement. 3. results and discussion 3.1 api rp 1102 calculation two pavement types are analysed in this paper with different burial depths, varying from 3, 4, 6, 8, and 10 feet. the pipe specifications passed the check using barlow formula. the next check would be to calculate the total effective stress. the results when rigid pavement is applied with the varying burial depth are tabulated in table 5 and is depicted in fig. 6. the results when no pavement is applied with the varying burial depth are tabulated in table 6 and is depicted in fig. 7. the results show that the circumferential stress due to the internal pressure is not affected by the difference in burial depth and pavement type. while the circumferential stress caused by the earth load shows an increase as the burial depth gets deeper. this shows that the circumferential stress caused by the earth load is directly proportional to the burial depth but shows no difference between the two types of pavements. therefore, it is only affected by the parameters of the soil and burial depth. the cyclic circumferential and longitudinal stress caused by the live load both decreases as the burial depth increases. although, there is no difference seen in the values for the burial depth of 3 and 4 feet. it is also seen that live load or vehicle’s effect on the stress towards the pipe will have less effect when the pipe is buried deeper in the soil. both the cyclic circumferential and longitudinal stress caused by the live load when no pavements are applied shows a significantly higher value of stress in comparison to using a rigid pavement. the decrease of the stresses due to the live load is more significant than the increase of the circumferential stress caused by the earth load, which affects the values of the maximum circumferential stress. the maximum circumferential and maximum longitudinal stresses show a decrease as the pipe is buried deeper, except for the burial depth between 3 to 4 feet which shows a slight increase. it also shows that the use of rigid pavement will have a significantly lower stress value than no pavement. however, the maximum radial stress remains the same for all burial depths and pavement types due to it only being affected by the operating pressure of the pipe. the total effective stress obtained shows a decrease as no no yes yes tsamara & puja/ jgeet vol 08 no 02-2 2023 63 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 the burial depth increases. this shows that the effective stress is inversely proportional to the burial depth. the total effective stress also shows a lower value of stress when a rigid pavement is applied. although, with the increase in burial depth, there is a smaller difference of values of the total effective stress withstood by the pipe between the two pavement types. this shows that the pavement type will have a less significant effect as the burial depth gets deeper. from the api rp 1102 calculations, in all burial depth reviewed, the girth weld and longitudinal weld fatigue assumed to be safe and have passed the check. table 5. total effective stress results for rigid pavement. burial depth (ft) parameters 3 4 6 8 10 circumferential stress from internal pressure (psi) 4215.62 4215.62 4215.62 4215.62 4215.62 earth load circumferential stress (psi) 143.36 162.56 170.24 172.80 174.08 live load cyclic circumferential stress (psi) 861.66 861.66 665.63 495.89 377.72 live load cyclic longitudinal stress (psi) 2921.59 2921.59 2560.67 2258.56 1996.32 maximum circumferential stress (psi) 5220.64 5239.84 5051.48 4884.31 4767.42 maximum longitudinal stress (psi) 3449.28 3455.04 3096.43 2795.09 2533.23 maximum radial stress (psi) -780 -780 -780 -780 -780 total effective stress (psi) 5340.05 5355.35 5140.78 4961.38 4834.4 allowable (psi) 30240 30240 30240 30240 30240 pass/fail pass pass pass pass pass factor of safety 5.6 5.6 5.8 6.1 6.2 fig. 6. rigid pavement api rp 1102 calculation results. -2000 -1000 0 1000 2000 3000 4000 5000 6000 0 1 2 3 4 5 6 7 8 9 10 11 12 s tr e ss ( p si ) burial depth, h (ft) rigid pavement api rp 1102 calculations internal pressure circumferential stress earth load circumferential stress live load cyclic circumferential stress live load cyclic longitudinal stress maximum circumferential stress maximum longitudinal stress maximum radial stress 64 tsamara & puja/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 table 6. total effective stress results for no pavement. burial depth (ft) parameters 3 4 6 8 10 circumferential stress from internal pressure (psi) 4215.62 4215.62 4215.62 4215.62 4215.62 earth load circumferential stress (psi) 143.36 162.56 170.24 172.80 174.08 live load cyclic circumferential stress (psi) 1053.14 1053.14 813.55 606.09 461.66 live load cyclic longitudinal stress (psi) 3570.83 3570.83 3129.71 2760.46 2439.95 maximum circumferential stress (psi) 5412.12 5431.32 5199.4 4994.51 4851.36 maximum longitudinal stress (psi) 4098.53 4104.29 3665.46 3296.99 2976.86 maximum radial stress (psi) -780 -780 -780 -780 -780 total effective stress (psi) 5651.01 5665.59 5379.05 5140.45 4966.88 allowable (psi) 30240 30240 30240 30240 30240 pass/fail pass pass pass pass pass factor of safety 5.35 5.33 5.62 5.88 6.09 fig. 7. no pavement api rp 1102 calculation results. -2000 -1000 0 1000 2000 3000 4000 5000 6000 7000 0 1 2 3 4 5 6 7 8 9 10 11 12 s tr e ss ( p si ) burial depth, h (ft) no pavement api rp 1102 calculations internal pressure circumferential stress earth load circumferential stress live load cyclic circumferential stress live load cyclic longitudinal stress maximum circumferential stress maximum longitudinal stress maximum radial stress total effective stress tsamara & puja/ jgeet vol 08 no 02-2 2023 65 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 3.2 finite element analysis using abaqus the finite element analysis is conducted with two types of pavements, namely rigid and without pavement, with varying burial depths at 4 and 8 feet. the results obtained from this analysis is the von-mises stress and the pipe’s displacement. fig. 8 shows the loading conditions of the model, namely the gravitational force, internal pressure, and the vehicle load. fig. 8. loading conditions of the model. the results of the von-mises stress obtained from abaqus is compared with the results of the total effective stress from the api rp 1102 calculations since the total effective stress has the same formula as the von-mises. the results of the von-mises stress from abaqus shows little error ranging from 3.4% to 4.9% in comparison to api rp 1102 stress results. one of the results obtained from abaqus, which is the underground road crossing pipeline with burial depth of 8 feet and no pavement is shown in fig. 9 for its von-mises stress and fig. 10 for its displacement results which are shown in si units. fig. 9. von-mises stress result for depth of 8 feet without pavement. fig. 10. displacement result for depth of 8 feet without pavement. the von-mises stress from abaqus and the total effective stress obtained from api rp 1102 is depicted in a graph shown in fig. 11. the results of the von-mises stress and displacement from abaqus is tabulated in table 7. as seen in fig. 11, the underground road crossing pipe of 8 feet depth and using the rigid pavement obtained using abaqus has the lowest value of stress. while the highest stress value occurs when the underground road crossing pipe is of 3 feet depth and does not use any pavements when calculated using api rp 1102. all the stress results show the same trend of gradually decreasing as the burial depth rises. fig. 11. pipeline abaqus and api rp 1102 stress results. 4700.00 4800.00 4900.00 5000.00 5100.00 5200.00 5300.00 5400.00 5500.00 5600.00 5700.00 5800.00 0 2 4 6 8 10 12 s tr e ss ( p si ) burial depth, h (ft) pipeline von-mises and total effective stress rigid pavement api rp 1102 no pavement api rp 1102 rigid pavement abaqus no pavement abaqus 66 tsamara & puja/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 the displacement of the underground road crossing pipeline was also obtained using abaqus. since the error between the api rp 1102 calculations and abaqus shows a small amount of difference, it is safe to assume that the displacement obtained using abaqus is valid. table 7. von-mises stress and displacement results from abaqus. burial depth (ft) rigid pavement no pavement vonmises stress (psi) displacement (in) vonmises stress (psi) displacement (in) 4 5,146 1.56 5,388 1.79 8 4,785 0.94 4,963 1.14 table 7 shows that the von-mises stress modelled using a concrete slab or rigid pavement is lower than the results shown without any pavement protection. the trend of the stress withstood by the pipe is the same as the calculation results by using api rp 1102, whereas the von-mises stress decreases as the depth of burial increases. as for the displacement, the stress being given to the pipe is directly proportional to the displacement of the pipe. the displacement occurred is affected by other values being input in the model, such as the density, poisson’s ratio, and the modulus of elasticity of the soil. from the finite element analysis, the largest displacement happens to occur when the pipe is buried 4 feet deep and does not use any pavements. the smallest amount of displacement occurs when the underground road crossing pipeline is protected by a rigid pavement and is buried with a depth of 8 feet. from the results, it can be recommended that the best option for the underground road crossing pipe would to be use rigid pavement and to be buried with a burial depth of 8 feet or 10 feet. according to the stress and fatigue results, the pipe is assumed to be safe. the underground road crossing pipeline is found to still be able to withstand the stresses, even when the worst case was analysed which was having the vehicles being over dimension and over loading (odol). 4. conclusion the stress of the underground road crossing pipeline obtained from the api rp 1102 ranges between 5,355 – 4,834 psi when using rigid pavement and 5,665 – 4,966 psi when not using pavement with varying burial depths. the stress values are all still within the allowable value of 30,240 psi. the results of the von-mises stress obtained from the abaqus software shows values within the range of error of 3.45% – 4.9% in comparison to the results obtained from api rp 1102. the displacement of the underground road crossing pipeline is known to be in the range of 0.94 – 1.79 in obtained from the abaqus analysis. the stress and displacement experienced by the underground road crossing pipeline are affected by the pipe and soil materials, fluid specifications, as well as the live load and gravitational force. the protection given towards the underground road crossing pipeline by using a concrete slab plays a significant role in lowering the stress experienced by the pipe. the analysis towards the varying burial depths shows that the total effective stress decreases as the pipe is buried deeper. the underground road crossing pipeline are still safe and within the range of the maximum allowable stress and fatigue limit. references american petroleum institute, 2017. steel pipelines crossing railroads and highways. american petroleum institute, washington. american society of mechanical engineers, 2020. b31.8 gas transmission and distribution pipeline. american society of mechanical engineers, usa. badan pusat statistik, 2014. statistik daerah kota jambi 2015. badan pusat statistik kota jambi, jambi. british petroleum, 2021. british petroleum statistical review of world energy. british petroleum, uk. code of federal regulations (cfr), 2022. transportation of natural and other gas by pipeline: minimum federal safety standards 49 cfr 192. office of federal register, usa. fahrudin, h.t., yudo, h., amiruddin, w., 2020. analisa tegangan pada saluran pipa transmisi gas bawah tanah pt. citra panji manunggal dengan menggunakan software berbasis elemen hingga. jurnal teknik perkapalan 8, 282–289. howard, a.k., 1986. soil classification handbook: unified soil classification system. geotechnical branch, division of research and laboratory services, engineering and research center, bureau of reclamation, denver. lee, h., 2010. finite element analysis of a buried pipeline (master thesis). university of manchester, uk. mosadegh, a., nikraz, h., 2015. finite element analyses of buried pipeline subjected to live load using abaqus. geoquebec, canada. nugroho, e.s.h., 2006. trasnporting natural gas from east kalimantan to java: why did we choose a pipeline option? presented at the the 2nd asian pipeline conference & exhibition, kuala lumpur. puslitbang jalan dan perkeretaapian, 2021. kajian dampak kebijakan dan strategi implementasi penertiban odol. puslitbang jalan dan perkeretaapian, jakarta. skk migas, 2021. skk migas’ annual report 2020. skk migas, jakarta. tawekal, j.r., idris, k., 2012. desain dan analisis tegangan pipeline crossing. institut teknologi bandung, bandung. van dyke, k., 1997. fundamentals of petroleum. petroleum extension service, oklahoma. xi, z.s., ying, w., wei, j.p., 2019. reliability analysis of buried polyethylene pipeline subject to traffic loads. advances in mechanical engineering (sage publications inc.) 11. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 22 syahputra, r., et al./ jgeet vol 04 no 01/2019 research article correlation between fracture azimuth, surface lineaments and regional tectonics: a case study from belik district, central java, indonesia reza syahputra 1, *, felix m. h. sihombing 1 , octria a. prasojo 1 1 geology study program, universitas indonesia, kampus ui depok, depok, west java, 16424, indonesia. * corresponding author : syahputra.reza@sci.ui.ac.id tel.:+62-87883917464 received: nov 6, 2016; accepted: nov 20, 2016. doi: 10.25299/jgeet.2019.4.1.2294 abstract two major strike-slip faults with northeast-southwest and northwest-southeast orientation have shifted the southern central java, including belik district. consequently, many smaller faults that have the same direction as the major faults and west-east direction folding systems were emerged. the orientation of these geologic structures could be observed from morphological features such as ridge and river. a quantitative approach was carried out to unravel the impacts of those geologic structures on the geomorphology of the study area, which is located between slamet mountain and sindoro mountain, central java province. the method used in this research was the structural geology analysis, including the interpretation of ridge and river lineament, the distribution of fractures, and statistical analysis. the research location is divided into four different segments based on its lineament and morphology. the lineament that has similar characteristics was tested using normality test of kolmogorov-smirnov. the spearman test was used to obtain the correlation between surface lineament and fracture azimuth. all fracture azimuth, ridges and rivers tend to have northwest-southeast and northeast-southwest direction. these results show similar direction with strike-slip regional structural pattern. the statistical calculation and field observation indicate the landform. keywords: fracture azimuth, lineament, spearman, belik 1. introduction the morphology of central java tends to have indentation. it is interpreted as the cause of major right and left lateral faults movement in that area (satyana, 2005, 2006, 2009). it is also considered to be intensively affected by tectonics (widagdo, et al, 2018). on the other hand, the condition of the outcrop is sometimes highly affected by weathering and erosion which make the tectonic features difficult to be observed. the research location is situated between 109 0 109 0 0 7 0 south latitude, which is in the central java province (fig. 1). it is bordered by purbalingga district on the south, paninggaran on the east side, and mount slamet at the west side. djuri et al. (1996) divided the stratigraphy of the study area from the youngest to the oldest into late pliocene lava of mount slamet, early miocene of rambatan formation, and middle to late miocene of halang formation. he stated that the rambatan formation consist of shale and marl alternates with light grey calcareous sandstone, while the halang formation have interlaminated sandstone and shale. the central java province was influenced by wrench fault systems from late cretaceous to paleogene, where it cut each other with left-lateral fault from northeast to southwest in muria-kebumen and right-lateral fault from northwest-southeast in cilacap-pamanukan (satyana, 2005). according to fault kinematic ellipsoid, the muriakebumen and cilacap-pamanukan faults may provoke other strike-slip fault and foldings around the research area (mcclay, k. r., 1991). most folds between these two strike-slip faults have west-east direction. the lineament from mount slamet, sindoro, sumbing and merbabu also showed the same direction with the folding (pacey, et al, 2013). the geologic structures can be observed with several different techniques including the direct observation in the field and laboratorial analysis and interpretation. the landscape morphology can be affected by endogenic process such as plate tectonic deformation or local geological structure. the http://journal.uir.ac.id/index.php/jgeet mailto:syahputra.reza@sci.ui.ac.id syahputra, r., et al./ jgeet vol 04 no 01/2019 23 structural geology evidence in a tropical country like indonesia, is difficult to observe because of the high weathering rate (bnpb, 2010). hence, laboratorial analysis and interpretation become crucial in the identification of the deformation process. fig. 1. map showing the research location. the strike-slip fault cut each other in the opposite slip and trend. modified from satyana (2005). we propose a combination approach, employing field acquisition and statistical analysis to study geologic structures. a combination of these methods may increase the chance of having a better result and eliminate the uncertainty. many successful cases have applied statistics to determine the landscape morphology evolution related with tectonics (zadeh, et al, 2013; vannametee et al., 2014; yudhicara, et al, 2017). this research employs the bivariate analysis to evaluate the relationship between the fracture azimuth and the surface lineament direction. this method was chosen because of its efficiency and effectiveness to decipher the main factors that affect their development. this statistical analysis must be supported by other geological evidence in order to minimize or eliminate the error and misinterpretation. the landscape morphology in central java province tend to emerge by following the folding direction, which shows the west-east direction parallel to the folding direction. this research aims to unravel the influence of tectonics process on the formed landscape morphology and to determine which processes were more dominant compare to other geological processes. 1.1 regional geology tectonic pattern from neogene central java sub basin on the northern part is a part of back-arc basin. it is formed between magmatic arc on the south (southern java) and the sundaland on the north as a result of subduction between eurasia and indoaustralian plate. the research area which is located in besuki majenang high is part of north serayu mountain zone. the mountainous zone extends from west to east with the width ranging from 30 to 50 kilometers (van bemmelen, 1949) situmorang et al. (1976) postulated the faulting mechanism in java based on riedel shear concept. furthermore, he explained it was resulted from the collision between eurasia and indo-australia plate in the middle cretaceous and then formed specific fault and fold pattern. kusumayudha (1994) explained that the meridional fracture system or west to east structural orientation was affected by the compressional force from north to south (n 350 0 e). the wrench faults which were resulted on the left and right of the folding system lead to 45 0 to its compressional force. hence, java is divided into three blocks. the first one is positioned higher than the second and third block. each of blocks is bordered by a couple of strike-slip fault with northwest-southeast direction between the first and the second and northeast-southwest direction between the first and the third one. all the structural from the main compressional force are categorized as a r1 and r2 system in riedel shear model. the north serayu mountain experienced three episodes of tectonics activity: (1) miocene to pliocene, (2) pliocene to pleistocene, and (3) holocene (van bemmelen, 1949; n. ratman and g. robinson,1996). 2. methodology this research attempted to support field observation with statistical analysis. basic geological mapping was first carried out to check the lithology and structural geology evidence. these parameters then used to help the statistic calculation. the research area was divided into several segments based on its morphology before the lineament was drawn. it was conducted by manual interpretation and aimed to have precise lineament trend that fit with its group, so it can represent the direction of actual alignment. the lineament from ridge and river were calculated thoroughly. they were resulted from the topographic map and the satellite imagery. to better signify the intensity the length of lineaments is put into consideration in statistical calculation using weighting method. the result then compared with fracture measurements in the field to find out the correlation. the fracture azimuth and lineament were compared based on its segments. for example, we compare the fracture from segment 1 to ridge and river in the same segment and others. then we considered to calibrate the lineament with the main regional tectonics force in each segment. before each data compared to each other, all lineaments and fractures data were tested whether the data distribution has a normal trend or not using kolmogorov-smirnov test. we use bivariate analysis to test correlation between fracture and lineament. pearson test was used when data distribution is normal, while spearman test was u distribution. r value is expressing magnitude of the correlation, while p value is expressing level of significance. the statistical results were managed using spss software (statistical product for social science) © version 25.0. the result was interpreted by combining the geological condition (such as geomorphology, lithology, and drainage pattern) with the statistical calculation. a good match between those parameters 24 syahputra et al./ jgeet vol xx no xx/20xx lead to a better understanding of the endogenic and exogenic processes in the past. 2.1 data availability the lithology, the morphometry, and the fracture azimuth were acquired through field mapping. the lithology distribution has been confirmed with 33 macroscopic observation sites and 10 petrographic analysis (fig.2). the morphometry was obtained using slope analysis (van zuidam, 1985) (eqn. 1) and reconfirmed by field visit. more than four hundred of fracture azimuth were measured to determine its main direction. (1) where: s : slope (%) n : the number of contours cutting by a line ci : contour interval (meters) d : the distance between the highest and the lowest contour (meters) sp : scale on the map the drainage pattern was obtained through the studio analysis and combined with the calculation of river order from strahler (1952). the first order which crosses into each other result in the second order, and if the first order runs into the second one, it remains the second order. the river order was conducted to analyze the river stages, whether it was young or old enough to be influenced by a geological process. the lineament data were obtained from ridge and river using satellite imagery and topography map, respectively. we used channel 4, 5, and 7 in this satellite imagery to see the lineament trend and the drainage pattern, and successfully gained more than hundreds of lineaments. these data were then used to reconfirm the field data. 3. results 3.1. lithology there are four lithology in the research location that can be simply distinguished by their texture and composition (fig.2). more than 15 % lithology in the research area is covered by andesitic lava flow from slamet mountain. the research area is also dominated by 30 % of feldspathic wacke sandstone from halang formation and 50 % of shale from rambatan formation. some diorite intrusion was covered only 5 % on the western part of the research area. it can be concluded from field observation that the andesitic lava from mount slamet always covers the lowest part of the research area with 0 7 % of slope, filled in the nearby valleys and rivers. it is dark or black in color and has a porphyritic texture and vesicular structure. besides, the feldspathic wacke sandstone usually lies on the higher ground between 200 1,150 meters with 10 20 % of slope which has the interlaminated sandstone and mudstone characteristic. most of the sandstone has a stiff rock strength. it proved by the hammer when was used to take the sample which brought out fire sparks. the shale of rambatan formation is overlapped with the sandstone from halang formation in between 100 850 meters. and the diorite intrusion has located on the 650 1,000 meters elevation with 20 50 % of slope. fig. 2. field photographs (left) and photomicrographs (right) of representative samples from research location. all photomicrographs originated from the outcrop on the left and were taken using x-nicol. (a-basalt lava flow from mt. slamet; (brambatan fm.; (cgranodiorite intrusion. (k-fs=k-feldspar; pl=plagioclase; px=pyroxen; qz=quartz) 3.2. morphology the elevation of the research area varies from 100 m to 1,000 m above sea level. the topography is grouped into five slope classes, namely flat (0 % 1.8 %), slightly sloping (3.6 % 5.4 %), sloping (7.1 % 14 %), slightly steep (16 % 20 %), and steep (16 % 41 %). the sloping topography is covering 55 %, and the the slightly steep slope covering 30 % of northeast and south part of research area in, and the other classes are scattered evenly. most slopes are consisted of rambatan and halang formation, except for flat and steep slope which consisted of andesitic lava and granodiorite intrusion, respectively. the valley is categorized as dull to sharp v-shape and dull u-shape. according to the elevation and slope classification of van zuidam, r., a, (1985), 90 % of research area assigned into a hilly landform and the other 10 % was %100 ).1(     spd cln s syahputra, r., et al./ jgeet vol 04 no 01/2019 25 categorized into mountainous and valley landform on southwest. 3.3. drainage pattern the drainage pattern has been categorized into three different group based on topographic map, river order, and observation in the field. they were then compared with basic and modified drainage pattern (howard, 1967). they are classified into sub-parallel, parallel, and dendritic. the sub-parallel covered around 70 % of the research area. the lithology in sub-parallel is dominated by mudstone from rambatan formation. on the other hand, the parallel pattern is in the long and continuous mountainous landform with steep slope area. the lithology is dominated by sandstone from halang formation, which is more resistant than rambatan formation. the summit of the mountain act as a water divided, and the river run from south to north. and the last one is dendritic pattern that covered the southeast and southwest of research area (fig. 3). fig. 3. interpreted drainage pattern and river order. the river order was categorized into five order. the smaller order represents the earliest stage of river development and becomes mature as the order escalate. most river is dominated by first and second order. the third, fourth, and fifth order have the total of 20, 9, and 1, respectively. the river run along in two directions. the river on the south side is dominated by the river which run from north to south while the rest flow from south to north (fig. 3). 3.4. structural geology the folding is composed of two synclines (mendelem and majakerta) and two anticlines (gombong and karangmanggu). most of the folding relatively extending from west to east except for majakerta syncline which has a northwest-southeast direction. the fault in the research location can only be observed from the map or satellite imagery. the fault interpretation was helped by the regional structural geology. it was interpreted that there are two local right-lateral fault. however, there was no slicken-side evidence in the field except the fractures. (one of the fractures is documented on fig. 2c) fig. 4. ridge lineament interpretation from satellite imagery has been divided into four segments. the fracture azimuth only available at the segment 1 and 3. the fracture azimuth has been collected from 14 different stations in the southwest and northeast side of the study area (fig. 4). but we were not able to measure the fracture azimuth in other area because the weathering rate was intensively occurred. most of the 26 syahputra et al./ jgeet vol xx no xx/20xx fractures are located on the sandstone and no fracture was found on shale and igneous rocks. field observation showed the direction of the fracture azimuth in two different dominant orientation, which are northeast-southwest and northwest-southeast. the fracture from the stereographic projection interpreted that it was dominated by the intermediate principle stress (fig. 5). then we assumed that the fracture found as shear component. however, in few stations we also found the tensional fractures. fig. 5. both principal stress from segment 1 and 3 interpreted as a result of strike-slip fault. the slicken-side has not been found in the field, only small displacement in the outcrop located at k13. the fracture azimuth showed that the data distribution can not be represented in normal. the statistical calculation of the fracture azimuth direction is also represented by the same direction by field observation (table 1). 3.5. the lineament trend the lineament was mapped by utilizing the ridge and the river lineament from the satellite imagery and topographic map. based on normality test of kolmogorov-smirnov, the lineament azimuth is not categorized into normally distributed data set. the ridge lineament was drawn by considering a continuous morphological which formed by specific geological processes. some of the ridge had a distinct shape but some hadnot. the differences acknowledge trough the color and the shadow from satellite imagery. the mode of ridge lineament in each segment showed four different trends. then the research area was divided into four different segments. segment 1 is dominated by n 174 0 e (northeast-southwest) while segment 2 is dominated by two different orientation, n 57 0 e and n 121 0 e (northeast-southwest and northwest-southeast). segment 3 is directed into different trend direction, which is n 150 0 e (northwestsoutheast). and segment 4 was dominated by n 91 0 e trend (west-east) (fig. 6). table 1. descriptive analysis of lineament and fracture azimuth. segmented of research area lineamen t and fracture trend n median mode std. deviati on segment 1 ridge 104 147 174 49,55 river 424 293 302 113,23 fracture 258 205,50 205 79,32 segment 2 ridge 144 104,50 57; 121 27,31 river 439 154 69 63,48 segment 3 ridge 142 74 150 42,19 river 289 135 157 44,94 fracture 169 140 140 92,46 segment 4 ridge 88 90 91 28,78 river 124 131 67; 103; 200 81,74 the river lineament composed of two kinds set of data, longer and shorter. the longer river was located on several main river while the shorter one came with a great deal of number and dominated the river branching (fig. 6). most river lineament is dominated by the same pattern direction with the ridge in each segment and while the rest show opposite direction. fig. 6. river lineament and structural feature syahputra, r., et al./ jgeet vol 04 no 01/2019 27 3.6. correlation between fracture azimuth, ridge and river lineament all data set are not normally distributed, then the spearman test performed. we found that there were plenty of which had different correlation, even if it was in the same segment. in segment 1 we found that there was statistically significant correlation between fracture azimuth and ridge, and the correlation strength was categorized into medium. it also had the same significant correlation between ridge and river lineament, but it was the weak one. in segment 2 there was only ridge and river lineament which compared to each other. they showed a meaningful correlation, but it was very weak. different with segment 1 and 2, the fracture and river lineament in segment 3 has a negative correlation and there was no correlation between fractures and ridge lineament in this segment. segment 4 was almost the same with segment 2, which only has ridge and river lineament to be compared. it showed no statistical correlation were found between these parameters. we also compared fractures from segment 1 and 3 with the ridge and river lineament from outside this segment. but the result showed no significance, except the correlation between fracture in segment 3 with ridge in segment 4 which showed the negative correlation. the correlation was also compared with fractures and corrected lineament. it was corrected to the main tectonic force angle, which was interpreted came from the north side of java. after reducing the lineament with the main tectonic force, we got no significant changes using this method. some of data which had no correlation remain the same. however, the negative correlation between fracture in segment 3 and ridge lineament in segment 4 become not significant. table 2. the correlation between segment. (fr=fracture; rd=ridge; rv=river. the number indicate the segment). *p < 0.05 and r (+) = significant and linear correlation; **p < 0.05 and r (-) = significant and opposite correlation; ***p > 0.05 = not significant correlation intra and between segment p (significant level) r (correlation strength) fr1-rd1 * 0.0 0.436 fr1-rv1 *** 0.882 0.09 rd1-rv1 * 0.03 0.293 fr1-rd2 *** 0.112 -0.133 fr1-rv1 *** 0.233 -0.74 rd2-rv2 * 0.001 0.278 fr3-rd3 *** 0.602 0.044 fr3-rv3 ** 0.0 -0.324 rd3-rv3 *** 0.906 -0.10 fr3-rd4 ** 0.0 -0.409 fr3-rv4 *** 0.13 -0.222 rd4-rv4 *** 0.187 0.142 4. discussion regional tectonic at research location was interpreted between paleocene and recent. martodjojo (1994) grouped tectonic deformation in the research area into the meratus and sumatra trend which formed between late cretaceous and paleocene. the oldest stratigraphy at research location was deposited from middle to late miocene, which indicates that the fractures and lineaments must be younger than those regional strike-slip. we presumed that even there was time gap between regional strike-slip and geologic structures at the research location, the dominant lineament and fracture azimuth showed a similar pattern with right-lateral cilacap-pamanukan fault (northwest-southeast) and left-lateral muria-kebumen fault (northeast-southwest). the main tectonic force tends to come from north, created a synthetic (r1) muria-kebumen and antithetic (r2) cilacap-pamanukan shear fault according to reidel shears model. the principle stress from fractures (segment 1 and 3) showed that the intermediate stress was the dominant force which affected fractures direction. this result also had the same direction with the indian oceanic subduction from the late cretaceous to the present. field observation has succeeded to classify the morphology based on its lithology. we found that most resistant rocks (sandstone from halang formation and granodiorite intrusion) are located on the mountainous landform at altitude more than 500 meters above sea level with sloping and slightly steep slope. however, some of the sandstone still can be found at the hilly landform together with mudstone from rambatan formation. this distribution showed that the weathering rate in the research location is increasing downward. the valley shape become an indicator for weathered rocks. most sandstone and intrusion landform showed a sharp v-shaped valley (vertically eroded). except for intrusion, the sandstone from the halang formation were distributed in a long and continuous mountain. on the other hand, the landform with mudstone and andesitic lava dominated by the ushaped valley (horizontally eroded). the statistical descriptive showed that most of the lineament and the fracture azimuth assembled into the second quadrant. however, several lineament and fractures fall into the first and third quadrant (see mode in table 1). according to this information the lineament has two major direction, which are northwestsoutheast and northeast-southwest. the fracture azimuth also has the same direction with the lineament. the fractures direction in segment 1 is represented by northeast-southwest direction, while the fracture from segment 3 dominated by northwestsoutheast direction. in segment 1 the river and ridge lineament tend to have northwest-southeast direction while the fracture has the northeast-southwest. the opposite direction between these parameters were caused by the less dominant of fracture azimuth direction (northwestsoutheast). it was proved by the coefficient correlation 28 syahputra et al./ jgeet vol xx no xx/20xx that falls into medium category. however, the fracture might not the main influence because the slope is slightly steep, and the drainage pattern is sub-parallel, which means external factor could possibly have a role in this segment. in the segment 2 and 4, neither the ridge nor the river has a correlation with the fracture from segment 1 and 3. most likely the formation of ridge and river were controlled by the denudational process. we interpreted this was due to the absence of fractures. moreover, the slope is categorized into sloping and the drainage pattern is dominated by sub-parallel. the ridge, river, and fractures in segment 3 have the same direction. however, the significant correlation only resulted between fractures and river lineament. the fracture possibly less affected the formation of the river because the coefficient correlation has negative value, thus it might be not fully controlled by fractures or the fracture was not greater than external factors such as weathering. insignificant correlation between fractures and ridge proved the lithology and external factor could possibly control the morphology in segment 3. otherwise, the ridge could be influenced by less dominant fracture orientation, which was northeast-southwest. we were able to interpret this because one of the correlations between fracture and lineament still meaningful. however, if both of lineament do not have meaningful correlation to the fracture then no correlation will be significant statistically. the correlation between calibrated and noncalibrated lineament showed no significance difference. this could possibly happen because the main tectonic force has only small angle value, thus the changes could not be significantly detected. our research limitation includes the absence of morphometric characteristic such as bifurcation ratio, drainage density, etc. it occurs since our research area was not big enough to discuss about the catchment area. other factors that may become the limitation of our study are the absence of fault evidence that may affect the landform changes. 5. conclusion the regional fault in central java compare to the lineament and fracture azimuth have the same direction with the research area, which is northwestsoutheast and northeast-southwest. however, they have different dominant direction in each segment. the lineament in segment 3, especially the river, was probably controlled by the cilacap-pamanukan fault. however, the negative correlation and field data showed that the weathering process also had a role on this lineament. there is orientation difference between the fracture and lineament in segment 1. however, the correlation between ridge and river in this segment is weak and linear. the weak correlation showed that there might be another fault mechanism which affected the ridge and river lineament. since the position of this research area in the middle of two strike-slip regional fault, there is a possibility that the landform was built with different lineament orientation. the direction possibly caused by another regional fault which is muriakebumen fault. based on statistical calculation, the morphology of the research area was not probably fully controlled by the regional fault. evidence in the field also showed the external factors such as erosion as the factor of changes in landform (proved by weathered shale of rambatan formation from fig. 2b). the river order is dominated by lower order, which characterizes the younger rivers. the vertical erosion dominated the weathering processes, indicated by the great number of lower river order. the drainage pattern also showed less significant effect to be affected by the fault. observation from the field showed that only three synclines and two anticlines that were probably affecting the landform change. acknowledgement the greatest contribution gave to dr. radhiyatam mardhiyah and dr. charlie h. wu who gave much better understanding in statistical calculation. we would also like to thank the geological agency for the provided map and satellite imagery. references badan nasional penanggulangan bencana, 2009. peta indeks ancaman bencana gempa bumi di indonesia. djuri, m., samodra, h., amin, t.c., gafoer, s., 1998. geological map of the purwokerto and tegal quadrangles, jawa. geological research and development 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https://doi.org/10.29118/ipa.1210.53.67 https://doi.org/10.29118/ipa.1210.53.67 https://doi.org/10.29118/ipa.1210.53.67 https://doi.org/10.29118/ipa.1210.53.67 https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/63/9/923/4513/dynamic-basis-of-geomorphology?redirectedfrom=fulltext https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/63/9/923/4513/dynamic-basis-of-geomorphology?redirectedfrom=fulltext https://searchworks.stanford.edu/view/1642900 https://searchworks.stanford.edu/view/1642900 https://searchworks.stanford.edu/view/1642900 https://doi.org/10.1016/j.geomorph.2014.05.032 https://doi.org/10.1016/j.geomorph.2014.05.032 https://doi.org/10.1016/j.geomorph.2014.05.032 https://doi.org/10.1016/j.geomorph.2014.05.032 https://doi.org/10.24273/jgeet.2018.3.3.1715 https://doi.org/10.24273/jgeet.2018.3.3.1715 https://doi.org/10.24273/jgeet.2018.3.3.1715 https://doi.org/10.24273/jgeet.2018.3.3.1715 https://doi.org/10.17014/ijog.4.3.193-208 https://doi.org/10.17014/ijog.4.3.193-208 https://doi.org/10.17014/ijog.4.3.193-208 https://doi.org/10.17014/ijog.4.3.193-208 https://doi.org/10.4172/2327-4581.1000109 https://doi.org/10.4172/2327-4581.1000109 https://doi.org/10.4172/2327-4581.1000109 https://doi.org/10.4172/2327-4581.1000109 https://doi.org/10.4172/2327-4581.1000109 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ correlation between fracture azimuth, surface lineaments and regional tectonics: a case study from belik district, central java, indonesia 1. introduction 1.1 regional geology 2. methodology 2.1 data availability 3. results 3.1. lithology 3.2. morphology 3.3. drainage pattern 3.4. structural geology 3.5. the lineament trend 3.6. correlation between fracture azimuth, ridge and river lineament 4. discussion 5. conclusion acknowledgement references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 herald, d. et al./ jgeet vol 03 no 02/2018 86 the adsorption and regeneration of natural pumice as lowcost adsorbent for nitrate removal from water denny helard 1, *, shinta indah 1 , chintia maya sari 1 , hestia mariesta 1 1 department of environmental engineering, faculty of engineering, universitas andalas * corresponding author: dennyhelard@eng.unand.ac.id received: 29 apr 2018. revised: 25 may 2018, accepted: 29 may 2018, published: 1 june 2018 doi: 10.24273/jgeet.2018.3.2.1545 abstract the potential of adsorption and regeneration of indonesian natural pumice to remove nitrate from aqueous solution was studied in multiple adsorption-desorption cycles. batch experiments were performed to examine the effect of various experimental parameters on the removal of nitrate. the optimum condition of nitrate removal by natural pumice were obtained at 3 of ph solution, 0.3 g/l of adsor concentration with 54.79% of removal efficiency and 164.37 mg/g of nitrate uptake. the experimental data obtained were fitted with the freundlich adsorption isotherm within the concentration range studied. although complete desorption were not achieved, the result confirmed that hcl can be used as desorbing and recovery agent, which be desorbed 10-13% of nitrate ion. the used natural pumice also could be regenerated and reused up to three successive adsorption-desorption cycles. overall results revealed that the ability of natural pumice to adsorb nitrate will create more interest to develop a new adsorbent from local mineral for pollutant removal from water. keywords: adsorption, natural pumice, nitrate, regeneration 1. introduction nitrate contamination in ground and surface water has become an increasing and severe environmental problem due to its harmful effect. the most common sources of nitrate in water resources are fertilizers, septic tank effluents, biodegradation of nitro-organic compounds, discharge of raw wastewater, production of explosives, and pharmaceuticals. due to its high water solubility, nitrate is possibly the most widespread groundwater contaminant in the world, imposing a serious threat to drinking water supplies and promoting eutrophication (bhatnagar & sillanpa, 2011; liao, 2003). high concentrations of nitrate in drinking water cause health problems, such as cyanosis among children and cancer due to formation of nitrosamine. therefore, world health organization (who) and the us environmental protection agency (epa) set the maximum acceptable contaminant level for nitrate for drinking water are 50 mg/l and 45 mg/l of nitrate respectively (ward et al., 2005). numerous techniques for the removal of nitrate from water samples have been reported. these include biological de-nitrification (schipper et al., 2001), chemical reduction (hu et al., 2001), reverse osmosis, electrodialysis (pinter et al., 2006), and ion exchange (baes et al., 2002). adsorption is another effective technique for nitrate removal and has been shown to be an economical and effective alternative for removing ions from water because of its interesting features, including low costs, easy design, and operation. different adsorbents have been used for nitrate removal (islam et al., 2010) such as zeolite (sehperi et al., 2014), kaolinite (tribe et al., 2012) and iron-modified pumice (golestanifar et al., 2015). pumice is one of natural pozzolan created by release of gases during cooling and solidification of lava. pumice has low weight, porous structure and a large surface area. the utilization of pumice mainly is for structural applications such as aggregate in light weight concrete, cements, and filters. however, nowadays, pumice also has been used as adsorbent for pollutant removal from water and wastewater (shayesteh et al., 2016, indah et al., 2017). so far the studies of nitrate removal from water were mostly performed by using modification of pumice (golestanifar et al., 2015) and only few studies used the natural pumice (kim et al., 2015). however, in spite of the capability of adsorbents to remove pollutant in the water, the used adsorbent may raise a problem to environment because they have to be discarded after it becomes exhausted. moreover, the use of mineral like natural pumice as adsorbent may reduce the availability of natural resources. hence, the regeneration and reuse of the adsorbents are necessary to make the operation environmental friendly and minimize the requirement of adsorbent. for this, desorption and reuse of the adsorbents in adsorption desorption cycles could help in reducing the residues. however, so far, there is only limited investigations on the mailto:dennyhelard@eng.unand.ac.id herald, d. et al./ jgeet vol 03 no 02/2018 87 adsorption and desorption as well as regeneration of natural pumice to remove pollutant in water or wastewater. at sungai pasak, west sumatra, indonesia, pumice is available in a great abundance, as byproduct of the process of sand mining in that area. in this study, the capability of that local mineral to remove nitrate from aqueous solution under different experimental conditions was examined. batch experiment and isotherm studies were conducted on a laboratory scale to determine the adsorption capacity of natural pumice. the parameters affecting the adsorption process such as ph of solution, dose of adsorbent, contact time, diameter of adsorbent and initial concentration on removal of nitrate were studied. furthermore, to study regeneration ability of the natural pumice, sequential adsorption-desorption cycles were conducted three times using the same adsorbent. the results of this study could provide more information about the capability of the natural pumice, mainly from local natural resources and also to solve the problem of high nitrate concentration that may become a serious common water quality problem in agricultural regions, like in indonesia. 2. methods 2.1 preparation of adsorbent pumice samples were collected from riverside of sungai pasak, west sumatera, indonesia as byproduct of the process of sand mining in that area. pumice samples were washed with distilled water several times and dried out at room temperature, then crushed and sieved in order to produce the desired particle size fractions. a scanning electron microscopy (sem, model s3400n, hitachi, japan) was used to observe the surface morphology of pumice and energy dispersive x-ray (edx) spectroscopy was also employed to obtain information on the oxide content of the natural pumice. 2.2 batch adsorption experiments batch adsorption experiment were performed at room temperature (20-25 o c) by varying ph (4-8), dose of adsorbent (0.3 30 mg/l), contact time (1575 min), diameter of adsorbent (<63-600 µm) and initial concentration of nitrate (15-90 mg/l). in each experiment, 100 ml of nitrate solutions was contacted with pumice and gently agitated at 100 rpm. after a period of time, the mixture was filtered paper no 42 and the concentration of nitrate in the filtrate was determined by a uv vis spectrophotometer (shimadzu uv-2600). the amount of nitrate adsorbed by the natural pumice was obtained as the difference between the initial and final concentration of the solutions. all experiments were repeated three times, and results presented are consequently the averaged values of replicate tests. the removal efficiency and the nitrate uptake (qe, mg/g) on natural pumice was calculated by the following mass-balance equation: 𝑅𝑒𝑚𝑜𝑣𝑎𝑙 (%) = 𝐶0− 𝐶𝑒 𝐶0 × 100% (1) 𝑞𝑒 = 𝐶0 − 𝐶𝑒 𝑚 × 𝑉 (2) where 𝐶0 is the initial concentration of nitrate (mg/l), 𝐶e is the equilibrium concentration of nitrate g(mg/l), 𝑉 is the volume of the solution (l), and m is the mass of the pumice (g). 2.3 batch desorption experiment the desorption experiment was carried our using pumice with total chromium adsorbed on the surface at the end of the adsorption experiment. samples were mixed with 0.1 m hcl (a 1:200 solid to solution ratio), shaken at 100 rpm for 60 min and at room temperature (25oc). subsequently, the mixture was filtered paper no 42 and the concentration of nitrate ions in the filtrate was determined a uv vis spectrophotometer (shimadzu uv-2600). all experiments were repeated three times, and results presented are consequently the averaged values of replicate tests. the desorbed total chromium was calculated as percentage using equation (eq. (3)) 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑜𝑓 𝑑𝑒𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛 = concentration of metal desorbed concentration of metal adsorbed × 100% (3) 3. results and discussion 3.1 pore structure and elemental composition of natural pumice fig. 1 shows the sem image showed the surface morphology of natural pumice from sungai pasak, west sumatra, indonesia. fig. 1. sem micrograph of pumice from sungai pasak, west sumatra, indonesia. 88 herald, d. et al./ jgeet vol 03 no 02/2018 the image indicated that the pumice had a highly porous, smooth surface, cellular and irregular texture with larger cavities, which provides suitable sites for adsorption. as shown in table 1, si, al and fe are the major elements in natural pumice from sungai pasak, as determined by edx. other elements, except k, ca, na and mg were present in relatively smaller amounts (less than 3%). from sungai pasak. in table 1, the elemental compositions of pumice fro lombok, west nusa tenggara is also presented to compare with pumice. there are some differences in the weight percentage of the element in the both pumice. it shows the different locations of pumice have different elemental compositions that may affect the adsorption capabilities of the pumices. the elemental compositions of the pumice also indicate the absence of hazardous or carcinogenic substances, thus the pumice are considered appropriate as adsorbent to treat polluted water. table 1. elemental and oxide composition of natural pumice from sungai pasak, west sumatra and lombok, west nusa tenggara, indonesia element % weight sungai pasak, indonesia lombok, indonesia o 56.38 43.34 na 0.49 4.54 mg 0.06 al 3.89 9.81 si 32.56 34.94 k 2.41 3.21 ca 1.2 1.23 fe 3 2.92 3.2 effect of ph adsorption of nitrate by natural pumice was investigated in the ph range 4-8. fig. 2 shows that the adsorption of nitrate on natural pumice is strongly ph dependent. the removal efficiency and nitrate uptake decreased with increasing ph and the most effective ph value for nitrate removal was 4, the lowest ph of the variation of ph studied. the reason for this might be due to at the lower ph, the amount of h + ions in the solution are more than oh ions. it caused the reduction of the negative charge on the surface due to the excess of protons in the solution and as a result, the number of positively charged sites increase. a positively charged surface site on the adsorbent favors the adsorption of the nitrate anions due to electrostatic attraction. a sharp decline in removal efficiency of nitrate occurred at higher ph that may be due to electrostatic repulsion of anionic nitrate by the negatively charged adsorbents surface. the decrease in sorption capacity at the higher ph (ph > 4) can be due to the competition for the active sites anionic nitrate by the negatively charged surface of natural pumice. in addition, the phpzc (ph point of zero charge) values of pumice are in the range of 67, as reported in the literature (karimaian et al., 2013; sepehr et al., 2013). when ph< phzpc, the surface of the sorbent has got more positive charge which causes the electrostatic attraction between positively charged surface ions and nitrate ions (sepehr et al., 2013). since generally, ph values of soil and groundwater are ranging from 5 to 9, the natural pumice could be used as adsorbent for removal of nitrate effectively (golestanifar et al., 2015). similar finding on ph trend has been reported in adsorption of nitrate studies by other researchers (öztürk and bektas, 2004; golestanifar et al., 2015). thus, above all the following experiments were carried out with ph values of 4. fig. 2. effect of ph on nitrate uptake onto natural pumice (nitrate concentration = 75 mg/l; adsorbent dose = 0.3 g/l; data represent averages of triplicates ± se. 3.3 effect of adsorbent dose fig. 3 shows the removal efficiency and nitrate uptake as a function of adsorbent dosage. the nitrate removal efficiency increases from 47.90 to 77.52% as the adsorbent dose increases from 0.3 to 30 mg/l which is due to the increase in the available active sites and larger surface area of the adsorbents. however, on the contrary, decreasing of nitrate uptake gradually was observed from 119.75 to 1.94 mg/g as the adsorbent dose increases from 0.01 g to 0.1 g. the results revealed that the higher adsorbent dose will result in a lower nitrate uptake indicating the heterogeneous of adsorbent surface sites. according to the surface site heterogeneity model, the surface is composed of sites with a spectrum of binding energies. at a low adsorbent dose, all types of sites are entirely exposed and the adsorption on the surface is saturated faster, showing a higher adsorption capacity whereas at a higher adsorbent dose the availability of higher energy sites decreases with a larger fraction of lower energy sites occupied, resulting in a lower adsorption capacity. in addition, as the adsorbent dose increased, the agglomeration of adsorbent herald, d. et al./ jgeet vol 03 no 02/2018 89 particles may occur that reducing the available external surface area and an increase in diffusional path length both of which contribute to decrease in amount adsorbed per unit mass. similar results are documented in the literatures reported by the other investigators (dash et al., 2015; shayesteh et al., 2016; indah et al., 2017). the highest nitrate uptake at equilibrium of 119.75 mg/g was observed for a natural pumice dose of 0.3 g/l. thus, 0.3 g/l of adsorbent dose was determined to be the optimum dose in this study and above all the following experiments were carried out with this dose. fig. 3. effect of adsorbent dose on nitrate uptake onto natural pumice (nitrate concentration = 75 mg/l; diameter 4; contact time = 60 min). data represent averages of triplicates ± se. 3.4 effect of contact time contact time is an important parameter to determine the equilibrium time of adsorption process. the sorption of nitrate on natural pumice was investigated as a function of contact time (15 75 min) and the effect of the time on the removal efficiency and nitrate uptake is shown in fig. 4. as it is shown, by increasing contact time from 15 to 30 min, the removal efficiency and nitrate uptake increased and reached to the highest values, 57.21% ant 143.03 mg/g, respectively. fig. 4. effect of contact time on nitrate uptake onto natural pumice (nitrate concentration = 75 mg/l; diameter of 4; adsorbent dose = 0.3 g/l). data represent averages of triplicates ± se. nevertheless, at increasing time to 90, 120 and 150 min, the decreasing of removal efficiency and nitrate uptake was observed. the result denoted that the adsorption of nitrate is most rapid in the initial stages and gradually decreases until the equilibrium is reached. it was attributed to the fact that during the initial stage of adsorption, a large number of vacant surface sites of pumice was available for adsorption resulted the increasing removal efficiency and nitrate uptake. after an interval in time, due to repulsive forces between the solute molecules on the adsorbent surface and the bulk phase, the remaining vacant surface sites of pumice were occupied (golestanifar et al., 2015; shayesteh et al., 2016). therefore, the equilibrium time for the removal of nitrate from aqueous solution by natural pumice is found to be 30 min and applied for further experiments. 3.5 effect of diameter of adsorbent fig. 5 shows the effect of particle sizes of natural pumice on the adsorption of nitrate. for this, five variations of diameter representing the variation of particle size of adsorbent were applied. the removal efficiencies decreased from 57.07 to 29.19% and nitrate uptakes decreased from 142.68 to 72.97 mg /g as diameter of adsorbent increase from <63 to 500-600 µm the results indicated that the removal efficiency and nitrate uptake depend on the size of adsorbent; as the diameter of adsorbent decreases, the removal efficiency and nitrate uptake increase. it may due to the wider exchange surface area provided at the adsorbent that have fine particles for the adsorption of the nitrate ions. similar results were also reported in the literature using other adsorbents (lopez-nuñez et al., 2014; zhang et al., 2015). thus, <63 µm was determined as the optimum diameter of adsorption and were applied for the further experiments. fig. 5. effect of diameter of absorbent on nitrate uptake onto natural pumice (nitrate concentration = 75 mg/l; ph = 4; adsorbent dose = 0.3 g/l; contact time = 30 min). data represent averages of triplicates ± se. 3.6 effect of initial concentration the influence of initial nitrate concentration on adsorption was presented in fig. 6. the initial concentration of nitrate solution was varied from 15 to 75 mg/l. results revealed that the removal efficiencies and nitrate uptakes increased from 36.70 to 54.79% and 18.35 to 164.37 mg/g, respectively, as the initial nitrate concentration increased from 15 to 90 mg/l. this behavior is due to higher availability of nitrate ions in the higher 90 herald, d. et al./ jgeet vol 03 no 02/2018 concentration of solution, which provides a stronger driving force to overcome mass transfer resistance of nitrate ions between the aqueous and solid phases. this phenomenon generate higher probability of collision between nitrate ions and active sites of natural pumice that leading to a higher nitrate uptake. the results demonstrate that the adsorption of nitrate onto natural pumice is dependent on initial metal concentration and is consistent with the finding by other investigators (golestanifar et al., 2015). fig. 6. effect of initial concentration on nitrate uptake onto natural pumice (ph = 4; adsorbent dose = 0.3 g/l; contact represent averages of triplicates ± se. 3.7 adsorption isotherm models in order to describe how solutes interact with adsorbents and how the molecules are distributed between the liquid and the solid phases at equilibrium during the adsorption process, an adsorption isotherm is important to study. moreover, the adsorption isotherm also could give information on the maximum capacity of the adsorbent or the amount needed to remove a unit mass of pollutant under the system conditions. a number of isotherm models have been developed to describe equilibrium relationships and identifying the best-fit isotherm is critical for optimizing the adsorption process design. linear forms of the freundlich, langmuir and elovich adsorption isotherm models ((4), (5) and (6), respectively) are as follows: 𝑙𝑜𝑔 𝑞𝑒 = 𝑙𝑜𝑔 𝐾𝐹 + 1 𝑛 𝑙𝑜𝑔 𝐶𝑒 (4) 𝐶𝑒 𝑞𝑒 = 𝐶𝑒 𝑞𝑚𝑎𝑥 + 1 𝐾𝐿×𝑞𝑚𝑎𝑥 (5) 𝑙𝑛 𝑞𝑒 𝐶𝑒 = ln 𝐾𝐸 𝑞𝑚𝑎𝑥 − 𝑞𝑒 𝑞𝑚𝑎𝑥 (6) where 𝐶𝑒 is the equilibrium concentration, 𝑞𝑒 is the amount of adsorbate adsorbed per unit mass of adsorbent, 𝑞𝑚ax is the maximum adsorption capacity, kf is the freundlich isotherm constant related to adsorption capacity (indicating the quantity of nitrate adsorbed onto the adsorbent), 𝑛 is the freundlich isotherm constant related to adsorption intensity (indicating the favorability of the adsorption process), kl is the langmuir constant related to the adsorption rate and 𝐾𝐸 is the elovich equilibrium constant. fig. 7. freundlich (a), langmuir (b) and elovich (c) isotherm plots for the adsorption of nitrate onto natural pumice (nitrate concentration = 15-90 mg/l; adsorbent dose = 0.3 g/l; contact time = 30 min; ph = 3). the freundlich model assumes that reactions take place in several sorption sites and as the amount of solute adsorbed rises, the binding surface energy decreases exponentially which means multilayer sorption. the linear form of the freundlich isotherm model yields a straight line. the slope and intercept of the obtained fit are used to calculate the freundlich constants 1/𝑛 and kf (freundlich, 1906). the langmuir isotherm is based on the assumptions that adsorption takes place at specific homogeneous sites within the adsorbent, there is no significant interaction among adsorbed herald, d. et al./ jgeet vol 03 no 02/2018 91 species, and the adsorbent is saturated after the formation of one layer of adsorbate on the surface of adsorbent. from the slopes and the intercepts, a linear fit to the langmuir equation yields langmuir constant (kl) and the maximum adsorption capacity (𝑞𝑚ax), respectively (langmuir, 1916). the elovich model is based on a kinetic principle assuming that the adsorption sites increase exponentially with adsorption, which implies a multilayer adsorption. the elovich maximum adsorption capacity and elovich constant can be calculated from the slopes and the intercepts of the plot of ln (𝑞𝑒/𝐶𝑒) versus 𝑞𝑒 (elovich and larinov, 1962). the applicability of the isotherm equations to describe the adsorption process was judged based on the maximum value of adsorption and correlation coefficients (𝑅 2 ), which are a measure of goodness of fit. the adsorption isotherm of nitrate adsorption onto natural pumice was determined by varying the initial nitrate concentration in the interval ranging from 15 to 90 mg/l with 3 of ph and 0.3 g/l of adsorbent dose. fig. 7 shows the langmuir, freundlich and elovich isotherm plots and table 2 presents the isotherm model constants for the adsorption. from table 2, it was revealed that compared to langmuir and elovich isotherm models, the freundlich isotherm model offers the highest 𝑅2 value (0.992) indicated the model fitted well with the equilibrium data. the result described that the adsorption of nitrate onto natural pumice is multilayer sorption, which the adsorption occurred on the heterogeneous surface of pumice and the active sites of pumice have different energy, as the freundlich isoth (freundlich, 1906). table 2. isotherm model constants for adsorption of nitrate onto natural pumice isotherm constants r2 freundlich 1/n kf (l/g) 0.992 1.561 0.556 langmuir qmax (mg/g) kl (l/mg) 0.823 -114.943 -0.01 elovich qmax (mg/g) ke (l/mg) 0.874 -200.0 0.996 it is shown in table 2, the value of the langmuir isotherm constants are negative, indicated the inadequacy of this model for explaining the adsorption process (öztürk and bektas, 2004). from the freundlich isotherm model, the adsorption of nitrate onto natural pumice from sungai pasak resulted 0.556 mg/g of kf as adsorption capacity and 1.561 of 1/n. the 1/n value describes the linearity of adsorption and typically the values range from 1 downwards. when 1/𝑛 < 1, it corresponds a normal l-type langmuir adsorption isotherm, while 1/𝑛 > 1 reflects a co-operative adsorption (kumar and jiang, 2015). smaller value of 1/n implies an effective interaction between the adsorbent and adsorbate. however, the value of 1/n from this study was obtained 1.561 and it reflected that co-operative adsorption may occur in the system. co-operative adsorption is the adsorption where adsorbed adsorbate has an effect on the furthermore, 1/n values of > 1 are also indicative of s-type isotherms, according to the giles et al. (1960) classification. the s curve of the adsorption isotherm generally reflects strong competition between the solvent and the adsorbed species for the adsorbent surface sites. the s-type characterized first by a weak adsorption which then gradually increases suggesting a weak surface interaction and competitive adsorbate-adsorbate interactions. in order to generate a stronger interaction between natural pumice as adsorbent and nitrate solution as adsorbate for this study, more attempts could be made, such as modify the surface of the adsorbent physically or chemically using thermal treatment, protonation or metal oxides impregnation (sepehr et al, 2014). 3.8 desorption study to investigate the regeneration and recycling of spent adsorbents, batch desorption experiments were conducted. for this, the adsorptiondesorption experiments in three consecutive cycles by using 0.1 m hcl as desorbing agent were carried out. the efficient removal of loaded nitrate from the natural pumice was necessary to ensure its long term use for repeated adsorption-desorption cycles. the regeneration of the adsorbent is likely to be a key factor in accessing the potential of the adsorbent for commercial application. fig. 8. adsorption and desorption efficiencies as well as nitrate uptake onto pumice at 3 cycles of adsorptiondesorption (ph = 3; adsorbent dose = 0.3 g/l; contact time concentration = 75 mg/l). data represent averages of triplicates ± se. as shown in fig. 8, the desorption efficiencies for nitrate ions by using 0.1 m hcl as desorbing agent were in the range of 10-13%. desorption efficiency slightly increased approximately 3 % at the second desorption cycle (desorption 2). it may due to the accumulation of nitrate ions that could not release until the second adsorption (adsorption 2). 92 herald, d. et al./ jgeet vol 03 no 02/2018 although complete desorption were not achieved, the result confirmed that hcl can be used as desorbing and recovery agent. in desorption process, the residence time is very essential because the higher the residence time, the longer the contact between the desorbing agent and the loaded adsorbent, so that the desorption efficiency may increase . desorption efficiency of cr(vi) ion from natural pumice obtained from tikmeh dash reign, east azerbaijan, iran reached 94.3% after 300 min contact time with 1 m hcl (sepehr et al., 2014). in this study, the desorption time was 30 min. if the contact time is extended, it may be possible to reach 100% desorption. 4. conclusions to solve high nitrate concentration problem in water that may occur at the agricultural regions, natural pumice as local mineral from sungai pasak, west sumatra, indonesia, was investigated to become an alternative low-cost adsorbent for nitrate removal from water. this pumice is available in a great abundance, as by-product of the process of sand mining in that area. from the batch experiments, it was revealed that the adsorption of nitrate onto natural pumice was dependent on ph, adsorbent dose, contact time, diameter of adsorbent and initial nitrate concentration. the optimum condition of nitrate removal by natural pumice were 3 of ph solution, 0.3 g/l of adsorbent dose, 30 particle size, and 90 mg/l of nitrate concentration with 164.37 mg/g of nitrate uptake onto pumice. the experimental data were fitted well to within the concentration range studied as it presents higher 𝑅 2 value than that of the langmuir and elovich isotherms. it reflected that the adsorption of nitrate onto natural pumice is multilayer sorption and the active sites of pumice have different energy. from the desorption experiment, it was confirmed that, although complete desorption were not achieved, the result confirmed that hcl can be used as desorbing and recovery agent, which be desorbed 10-13% of nitrate ion. thus, the used natural pumice also could be regenerated and reused up to three successive adsorption-desorption cycles. from the overall results, it can be remarked that easy availability of natural pumice as local mineral in west sumatra, indonesia and its ability to adsorb and retain nitrate will create more interest to develop new natural adsorption method of pollutant removal from solution. acknowledgement the authors are thankful to faculty of engineering, universitas andalas, indonesia (grand no. 046/un16.09.d/pl/2017) for supporting this work. references baes, b.u., jung, y.h., han, w.w., shin, h.s., 2002. improved brine recycling during nitrate removal using ion exchange. water research 36: 3330-3340. doi: 10.1016/s0043-1354(02)00012-x bhatnagar, a., sillanpa, m., 2011. a review of emerging adsorbents for nitrate removal from water. chemical engineering journal 168: 493 504. doi: 10.1016/j.cej.2011.01.103 dash, s.s., sahu, m.k., sahu, patel, e.r.k., 2015. fluoride removal from aqueous solutions using cerium loaded mesoporous zirconium phosphate. new journal of chemistry 39: 7300-7308. doi: 10.1039/c5nj01030f elovich s.y., larionov, o.g., 1962. theory of adsorption from solutions of non electrolytites on solid adsorbents. russian chemical bulletin 11: 191-197. doi: 10.1007/bf00908016 freundlich, h., 1906. uber die adsorption in losungen. zeitschrift für physikalische chemie 57: 385 470. giles, c.h., macewan, t.h., nakhwa, s.n., smith, d., 1960. a system of classification of solution adorption isotherms and its use in diagnosis of adsorption mechanisms and in measurement of specific surface areas of solids. journal of the chemical society 0: 3973-3993. doi: 10.1039/jr9600003973 golestanifar, h., asadi, a., alinezhad, a., haybati, b., vosoughi, m., 2015. isotherm and kinetic studies on the adsorption of nitrate onto nanoalumina and iron-modified pumice. desalination and water treatment 57:5480-5487. doi:10.1080/19443994.2014.1003975 hu, h.y., goto, n., fujie, k., 2001. effect of ph on the reduction of nitrite in water by metallic iron. water research 35: 2789-2793. doi: 10.1016/s00431354(00)00570-4 indah, 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adsorption onto various materials. journal of hazardous materials 112: 155 162. doi: 10.1016/j.jhazmat.2004.05.001 pinter, a., batista, j., 2006. improvement of an integrated ion-exchange/catalytic process for nitrate removal by introducing a two-stage denitrification step. applied catalysis b: environmental 63: 150-159. doi: 10.1016/j.apcatb.2005.10.006 schipper, l.a., vukovic, m.v., 2001. five years of nitrate removal, denitrification and carbon dynamics in a denitrification wall. water research 35: 3473-3477. doi: 10.1016/s0043-1354(01)00052-5 shayesteh, h., a. rahbar-kelishami, and r. norouzbeigi modified pumice for congo red removal in batch mode: kinetic, equilibrium, and thermodynamic uids 221: 1 11. doi: 10.1016/j.molliq.2016.05.053 sepehr, m.n., sivasankar, v., zarrabi, m., kumar, m.s., 2013. surface modification of pumice enhancing its fluoride adsorption capacity: an insight into kinetic and thermodynamic studies. chemical engineering journal 228: 192 204. doi: 10.1016/j.cej.2013.04.089 sepehr, m.n., amrane, a.b., karimaian, k.a., zarrabi, m., ghaffari, h.r., 2014. potential of waste pumice and surface modified pumice for hexavalent chromium removal: characterization, equilibrium, thermodynamic and kinetic study. journal of the taiwan institute of chemical engineers 45: 635 647. doi: 10.1016/j.jtice.2013.07.005 tribe, l., hinrichs, r., kubicki, j. d., 2012. adsorption of nitrate on kaolinite surfaces: a theoretical study. journal of physic chemistry b, 116 (36), 1266 11273. ward, m.h., dekok, t.m., levallois, p., brender, j., gulis, g., drinking-water nitrate and health recent findings perspective 113: 1607 1614. doi: 10.1289/ehp.8043 oxygen demand and nitrogen using different particle-sizes of anthracite coated with nine kinds of 5: 15146. doi: 10.1038/srep15146 1. introduction 2. methods 2.1 preparation of adsorbent 2.2 batch adsorption experiments 2.3 batch desorption experiment 3. results and discussion 3.1 pore structure and elemental composition of natural pumice 3.2 effect of ph 3.3 effect of adsorbent dose 3.4 effect of contact time 3.5 effect of diameter of adsorbent 3.6 effect of initial concentration 3.7 adsorption isotherm models 3.8 desorption study 4. conclusions acknowledgement references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 198 ernawati.r / jgeet vol 04 no 03/2019 research article mineralogy and geochemistry of gold ore low sulfidation epithermal at lamuntet, brang rea, west sumbawa district, west nusa tenggara province rika ernawati 1* , arifudin idrus 2 , himawan tri bayu murti petrus 3 1 department of mining engineering , universitas pembangunan nasional veteran yogyakarta, , indonesia 2 department of geological engineering, universitas gadjah mada indonesia. 3 department of chemical engineering, universitas gadjah mada, indonesia * corresponding author : rika.ernawati@upnyk.ac.id tel.:+ 62-815-6856-984 received: june 29, 2018; accepted: june 21, 2019. doi: 10.25299/jgeet.2019.4.3.1653 abstract there are two artisanal small scale gold mining (asgm) location in lamuntet, brang rea subdistrict, west nusa tenggara regency, namely nglampar and song location. nglampar and song location are included in the low sulfidation epithermal gold deposit system. the research purposes to analyze mineralogy and geochemistry of gold vein deposits and determine system of low sulfidation gold ore in nglampar, lamuntet village. the methods used to determine the mineralogy of gold vein deposits are petrography, mineragraphy and x-ray diffractometer (xrd) analysis, while geochemical analysis using scanning electron microscope (sem) with energy dispersive x-ray spectroscopy (eds), fire assay (fa) and atomic absorption spectrophotometry (aas). the results showed that the minerals contained were quartz (qz), sericite (ser), chalcedon (chc), chlorite (chl), pyrite (py), sphalerite (sph), galena (gn) , gold (au), chalcopyrite (cp), argentite (ag), arsenopyrite (apy), azurit (az), malakit (mal) and bornite (bn). abundant mineral availability such as sphalerite, galena, chalcopyrite and arsenopyrite are characterized by high levels of zn, pb, cu and as the metal in vein deposits. this can be seen on the chemical content of ore in gold vein deposits ie au 0.1 ppm -27.8 ppm, ag 3 ppm-185 ppm, pb 101 ppm 35,800 ppm, zn 73 ppm-60,200 ppm, cu 26 ppm 1,740 ppm, and as 150 ppm 6,530 ppm. based on the results of sem-eds analysis shows that the type of gold mineral is the electrum because of the content of ag> 20%. based on those characteristics of the mineralogy and geochemistry in this study showed that low sulfidation gold ore in this area is categorized as polymetallic gold-silver system. keywords: geochemical, gold ore, ls-epithermal, lamuntet, mineralogy, west nusa tenggara 1. introduction gold is an important natural resource in indonesia and many of it is done by small scale community called asgm (unep, 2013). there are two asgm in lamuntet namely nglampar and song location. both sites are included in the low sulfidation epithermal gold deposit (anonymous, 2015) . previous research only stated that gold deposits in the area are low sulfidation gold deposits, while low sulfidation gold deposits style are based on variations in ore minerals, gangue minerals and wall rock mineralogy divided into several systems (corbett, 2002). the purpose of this research is to analyze mineralogy and geochemistry of gold vein deposits and determine system of low sulfidation gold ore in nglampar, lamuntet village. the asgm of nglampar is located administratively in lamuntet village, brang rea subdistrict, west sumbawa regency, west nusa tenggara province, . the coordinate of research location at 08037'0 "s 08052'0" s and 116048'02 "e116058 ' 0 "e. (fig. 1). this mineralogical and geochemical study was conducted as subsequent research on the effect of epithermal gold deposits on gold processing using borax as a substitute for mercury. 2. the geology of sumbawa the nusa tenggara archipelago is located in the eastern part of indonesia and the western part of the banda arc. the sumbawa island is at the tectonic active centre of indonesia. east-west direction which is the meeting point of the three main plates of the sunda-banda magmatic arc, namely indo-australia, eurasia, and the pacific plates. (hamilton, 1979). the interaction of the three plates forms a complex tectonic especially in the eastern indonesia plate boundary (hamilton, 1979). the nusa tenggara archipelago formed the subduction of the indoaustralian plate beneath the sunda-banda arc in the tertiary period, where these bearings formed a volcanic arc on the interior of the nusa tenggara (hamilton, 1979). http://journal.uir.ac.id/index.php/jgeet ernawati.r/ jgeet vol 04 no 03/2019 199 fig. 1. map of location research in lamuntet, scale 1:425.000 (bakosurtanal, 2002). the sumbawa island lies in the arch of banda islands, which is a continuation of the solo zone (van bemmelen, 1949). the east-west-oriented arc is a collision between the indo-pacific plate and the continental edge of the australian plate (hamilton, 1979). taliwang gold mineralization is formed in the the epithermal mineralization system spread from the upper super large crustiform-colloform to the lower calidic cesedonic calm at a depth range between 250150 m below the paleosurface (herman , 2007). generally, lamuntet blocks are dominated by chlorite-calcite-magnetite alterations formed on volcanic andesite rocks, whereas rock samples at the nglampar site exhibit pyrite-sphalerite-galena ± chalcopyrite mineralization. quartz veins carrying high oxidized au-ag-cu mineralization are hematitelimonite. the main quartz veins are commonly northeastern with an estimated zone length of 400 m and have a width of 1-2 meters. quartz vein texture consists of comb composed by coarse euhedral, vuggy and sugary / sacharoidal / fine grained crystalline quartz crystalline quartz (nd, 2015). 3. research methods the asgm of lamuntet village is located in the north of brang rea subdistrict, reachable by flight from praya international airport in central lombok regency, and then drive four-wheeled vehicles to the east approximately 1.5 hours to kayangan harbor in east lombok. next take the ferry boat about 2 hours to poto tano in west sumbawa. from poto tano to lamuntet village, approximately 1.5 hours away by four-wheeled vehicles, while to reach asgm site in the ngampar mountains from lamuntet village walk as far as 5.8 km for about 2 hours. analytical methods used for mineralogy are petrography, mineragraphy and xrd analysis, while for analyzing mineral geochemistry using sem-eds analysis, fa and aas. the petrographic analysis was carried out on a thin section that aims to determine the type of mineral as much as 30 samples. mineragraphy analysis was done on polished section to know the type of metal mineral amounted to 30 samples. xrd analysis was done on bulk samples to confirm the type of minerals found from petrographic analysis, as much as 5 samples. sem-eds analysis was done on polished section to know gold mineral type in the sample as much as 5 sample, and fa and aas to know the content of metal element as much as 15 sample. 4. result and discussion 4.1. petrography analysis petrography and mineragraphy analysis using a microscope with the brand euromax. the results of petrographic analysis conducted on 30 samples stated that the types of minerals encountered in thin section were quartz (qz), sericite (ser), chalcedon (chc), chlorite (chl), pyrite (py) and opaque minerals (opq). in megascopic minerals can be seen in fig. 2. the presence of comb-textured quartz veins is composed by a coarse-grained euhedral crystalline, 200 first author et al./ jgeet vol 04 no 03/2019 sugar-like (sugary). ghost-bladed textured quartz consists of a thin sheet of quartz anhedral crystals formed as a replacement for other minerals (usually calcite), and during its precipitation is affected by impurities (allen, 1996) . the alteration of sediment is phyllic and texture encountered ie gradation crystals, gradation-veinlet crystals, comb and vuggy cavities. several thin section analyses are shown in fig. 3. on a plane polarized light (ppl) the gray-thin section of the grey rock and the crossed polarized light (xpl) shows a light grey color; texture of rocks with minerals size <0.1-4 mm, subhedral-anhedral crystals; mineral compositions were prepared by quartz (3560%), sericite (5-25%), chalcedon (5-10%), mineral oxide (5-15%), pyrite (5-20%), and opaque minerals (10-20%). the percentage of mineral availability, the size of each mineral, the type of alteration and texture contained in the deposit can be seen in table 1. the gangue minerals are dominated by quartz which is equal to 35-60%, while pyrite amounts to 520%. the quartz is a gangue mineral that exists in almost all low sulfidation gold deposit systems, only in some having relatively large values. this is because it occurs at the final stage of paragenetic, especially in the high crust level, the entry of meteoric water into the ore environment results in a large addition of quartz (corbett. 2013). the same with carbonates as gangue minerals, it will decrease due to different depositional environments (corbett, 2002). low sulfidation gold ore style divided into the arc-low sulfidation gold ore and the rift-low sulfidation gold ore, based on derivation of magmatic source rock and circulating meteoric geothermal waters (corbett, 2002). epithermal gold deposits are formed at shallow depths in the hydrothermal system associated with magma and generally occur in volcanic arcs (cooke and simmons, 2000). the arc-low sulfidation devided into quartzsulphide gold ± copper, polymetallic gold-silver, carbonate base-metal gold and epithermal quartz gold-silver. those classification are not only based on distance from magmatic source rock (corbett and leach, 1998) but also varying of ore, gangue mineral and wall rock mineralogies (corbett, 2002). the rift-low sulfidation comprises adularia-sericite epithermal gold, which formed circulating meteoric geothermal waters (corbett, 2002). mineragraphy analysis results show that the metallic minerals seen in the polished section are sphalerite (sph), galena (gn), pyrite (py), electrum (el), gold (au), chalcopyrite (cp), argentite (ag), arsenopyrite (apy), azurit (az), malakit (mal) and bornite (bn). the appearance of these minerals is shown in fig. 4. the texture of the ore seen from the polished section is the texture of the exsolution on the inclusion of au, el, the replace texture of py-cp, sphag, py-sph, cp-gn, cp-apy. the size of minerals, the percentage of ore mineral and the texture of the ore can be seen in table 2. vein is dominated by sphalerite, galena, pyrite and acanthite, while chalcopyrite is only about 1%, it indicates that epithermal deposits are included in polymetallic gold. polymetallic gold-silver is transition between quartz-sulphide gold±copper and carbonate base-metal gold but it is different (corbett, 2002). galena and sphalerite abundance is reflected in the geochemical results of ore which can be seen in fig. 9, and mineragraphy gold ore in fig. 4. the highest grades of pb and zn were 35800 ppm and 60200 ppm respectively, pb and zn indicate galena and sphalerite minerals. sphalerite and galena are common in low epithermal gold ore, while pyrite is abundant (white and hedenquist, 1995). fig. 2. the appearance of vein texture. (a). comb texture, (b) ghost-bladed texture. a b ernawati.r/ jgeet vol 04 no 03/2019 201 table 1. characteristics of epithermal deposit in lamuntet mineral percentage of mineral (%) size of mineral (mm) vein texture type of alteration quartz (qz) sericite (ser) chlorite (chl) chalcedon (chc) pyrite (py) opaque mineral (opq) oxide mineral (oxd) 35 -60 5 -25 525 510 520 10 20 5 15 0,2 1,5 <0,1 <0,1 1,5 <0,5 0,5 3 4 gradation crystall, gradation crystallveinlet, comb dan vuggy cavities. phillic fig. 3. the appearance of quartz, sericite, pyrite, chalcedon, chlorit and opaque mineral (ppl is parallel polarized light, xpl is crossed polarized light). xrd analysis using a tool with rigaku multiflex 2 kw brand, with emitting x-ray using cu metal target, emitting voltage ie 32 kv, 20 ma current and 0.64 kw power. xrd analysis results in some samples showed there were minerals dominated by quartz, pyrite, calcite, sericite, pyroxene, hornblende and plagioclase. similarly, it is observed in a thin section that the minerals present in rocks are quartz (qz), sericite (ser), chlorite (chl) and pyrite (py). the results of xrd analysis can be seen in fig. 5. all of the minerals present in site indicated that there was a match between the observed results in thin section and xrd test results that the existing mineralized associations were predominantly dominated by quartz (qz), sericite (ser), calcite (cal), chlorite (chl) and pyrite (py). 1 mm 1 1 1 1 1 ppl ppl ppl xpl xpl xpl py opq opq opq chl chc ser qz ox qz qz ser ser chc chc py py 202 first author et al./ jgeet vol 04 no 03/2019 4.2. xrd analysis quartz (qz), sericite (ser), calcite (cal), chlorite (chl) and pyrite (py) are the dominant gangue mineral in polymetallic gold-silver (corbett, 2002), which can be seen in fig.3. formation of polymetallic vein occurs in the basement rock associated with the formation of carbonate base-metal gold which is a mixture of magmatic sources and bicarbonate water which then comes out as subvolcanic intrusion (corbett, 2002). 4.3. chemical of gold analysis microscopic observations of samples on polishing section indicate that the gold minerals are very small (10grain size of gold (grayson, 2007). it is also stated on the results of sem-eds analysis (figs. 6 and 7). from result of sem-eds then done calculation and got atomic ratio (atomic ratio) in sample that percentage of atom from ag> 20% hence gold mineral type lamuntet area is electrum (table 3). according to harris (1990), if the content of ag more than 40% then the type of gold mineral called aurian silver. the dominant of galena and sphalerite is the basis for the presence of silver ore. low metal grade, even though it can be mined, occur increased in a dilatation structure. the dilatant structure is caused by repeated mineralization (corbeet, 2002). 4.4. geochemical ore analysis geochemical analysis of ore aims to determine the chemical element content of ore in the sample that is using fa and aas. elements that are analyzed are elements of minerals contained from the analysis mineragraphy that au, ag, pb, zn, as, cu and hg. the results of the analysis can be seen in fig. 5 and 9. the geochemical composition of the ore-forming fluid will determine the mineral assemblages (zhu et.al.,2011). fig.5 shows the highest au content found in the l1 and l15 samples of 27.8 ppm and 26.1 ppm respectively. while the highest levels of ag were found in l1, l5 and l15 samples which were 115 ppm, 185 ppm and 121 ppm, respectively. figure 9 shows that vein samples in lamuntet have high grades of pb, zn, cu and as. the highest level of pb was found in l1 which was 35,800 ppm. this pb metal indicates that samples contain abundant galena minerals. this can be seen also in the mineragraphy analysis that many visible galena minerals (gn) in the sample. similarly, the presence of zn metal, especially with the highest content of 60,200 ppm in l1 samples indicates that the sphalerite (sph) mineral concentration in the sample is quite abundant. table 2. characteristic of ore mineral epithermal mineral percentage of mineral (%) size of ore (mm) ore texture sphalerite (sph) galena (gn) pyrite (py) gold (au) chalcopyrite (cp) argentite (ag) bornite (bn) arsenopirite (apy) azurit (az) malakit (mal) 8 15 5 15 9 -25 <1 1 3 6 5 25 3 5 4 5 3 5 3 5 0,05 2 0,1 2,5 0,1 2 <0,1 0,01 0,5 0,1 1 0,5 1,5 0,1 1 0,5 1 0,1 0,5 exsolution texture in inclusion au, el, replace texture py-cp, sph-ag, pysph, cp-gn, cp-apy fig. 4. the appearance of sphalerite (sph), pyrite (py), galena (gn), quartz (qz) and gold (au) in polished section skala:163µm py qz au gn skala:100µm au au gn gn sph qz ernawati.r/ jgeet vol 04 no 03/2019 203 table 3. weight of au and ag into sample. mineral weight wt% atom mass element mole atomic ratio atomic (%) mineral l1 l5(1) l14(1) au ag au ag au ag 56,28 43,72 57 43 34,9 65,1 196,97 107,87 196,97 107,87 196,97 107,87 0,29 0,41 0,29 0,40 0,18 0,60 0,41 0,59 0,42 0,58 0,23 0,77 41 59 42 58 23 77 electrum electrum electrum l15(1) 1 2 3 au ag au ag au ag 53,88 44,48 55,52 46,12 57,39 42,61 196,97 107,87 196,97 107,87 196,97 107,87 0,27 0,43 0,28 0,41 0,29 0,40 0,39 0,61 0,41 0,59 0,42 0,58 39 61 41 59 42 58 electrum electrum electrum l15 (4) 1 2 3 4 au ag au ag au ag au ag 48,85 51,15 48,5 51,5 46,63 53,37 40,95 59,05 196,97 107,87 196,97 107,87 196,97 107,87 196,97 107,87 0,25 0,47 0,50 0,48 0,24 0,49 0,21 0,55 0,34 0,66 0,34 0,66 0,32 0,68 0,28 0,72 34 66 34 66 32 68 28 72 electrum electrum electrum electrum fig. 5. grade of au, ag and hg in lamuntet vein 0 50 100 150 200 l1 l2 l3 l4 l5 l6 l7 l8 l9 l10 l11 l12 l13 l14 l15 l16 au ppm 27.8 2.46 4.98 0.1 8.29 1.14 3.08 4.38 1.01 1.64 0.7 4.58 1.41 16.2 26.1 1.4 ag ppm 115 5 10 3 185 7 15 54 6 5 7 14 20 24 121 11 hg ppm 1.89 0.12 1.3 0.23 0.08 0.35 g ra d e (p p m ) sample au ppm ag ppm hg ppm 204 first author et al./ jgeet vol 04 no 03/2019 fig. 6. xrd result ernawati.r/ jgeet vol 04 no 03/2019 205 fig. 7. spot analysis of gold in l.1 code of polished section (magnification 2.000 x, scale 20 µm). 206 first author et al./ jgeet vol 04 no 03/2019 fig. 9. grade of pb, zn, cu and as in lamuntet vein. table 4. characteristic of ore at nglampar block in lamuntet characteristic of ore nglampar block in lamuntet type of gold electrum size of gold ore 10-60 micron gangue mineral dominated by quartz and pyrite association mineral quartz (qz), sericite (ser), chalcedon (chc), chlorite (chl), pyrite (py) opaque mineral (opq). ore sphalerite (sph), galena (gn), pyrite (py), electrum (el), chalcopyrite (cp), argentite (ag), arsenopyrite (apy), azurit (az), malakite (mal) bornite (bn). element content au : 0,1 ppm -27,8 ppm ag : 3 ppm-185 ppm cu : 26 ppm 1.740 ppm pb : 101 ppm 35.800 ppm zn : 73 ppm-60.200 ppm as : 150ppm 6.530 ppm hg : 0,08ppm-1,89ppm s : 5,10%-25,3% texture gradation crystall, gradation crystall-veinlet, comb and vuggy cavities. abundance of chalcopyrite and arsenopyrite minerals was also seen from high cu and as levels of 1,740 ppm in l15, and 6,530 ppm in l2. according to chryssoulis and cabri (1990), the presence of as elements can identify submicroscopic gold carrying minerals, arsenopyrite and pyrite. it can also be said that the presence of as is the most commonly used element as the pathfinder element of the existence of gold in geochemical exploration (boyle, 1965, webb, 1958). based on the description of mineralogy and geochemical analysis, the characteristics of gold 0 20000 40000 60000 80000 l1 l2 l3 l4 l5 l6 l7 l8 l9 l10 l11 l12 l13 l14 l15 l16 pb ppm 3580 101 1780 558 2430 416 1620 1200 1610 430 3440 3030 8600 1620 1030 1250 zn ppm 6020 170 3230 73 6900 359 3290 1500 2230 1930 2310 5620 4520 3670 3100 660 cu ppm 923 26 246 130 370 49 188 272 268 251 122 202 531 241 1740 68 as ppm 5610 6530 1540 150 4370 900 1560 750 210 630 290 490 990 1280 6340 610 g ra d e (p p m ) sample pb ppm zn ppm cu ppm as ppm ernawati.r/ jgeet vol 04 no 03/2019 207 deposits in nglampar block lamuntet can be summarized as in table 4. 5. conclusion based on those characteristics of the mineralogy and geochemistry in this study showed that low sulfidation gold ore in this area is categorized as polymetallic gold-silver system. acknowledgements the authors would like to thank the ministry of research, technology and higher education of pascasarjana dalam negeri (bppdoctoral programme. and also thankfully appreciate the supports to mr. nurudin didin sumantri from the energy and mineral resources department of west nusa tenggara province and mr. hasbul fifkri from the energy and mineral resources department of west sumbawa district during the field work at lamuntet. references allen , r., 1996, atlas of alteration, a field and petrographic guide to hydrothermal alteration minerals, editors thompson a.j.b. and thompson j.f.h., canadian cataloging in publication data. anonimous, 2015, laporan kajian wilayah pertambangan rakyat kabupaten sumbawa barat, energi dan sumberdaya mineral 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1995, epitermal gold deposits: styles, characteristics and exploration, published in seg newsletters, 1995, no.23, p. 1, 9-13. zhu, y., an, f., tan, j., 2011, geochemistry of hydrothermal gold deposit : a review, geoscience frontiers 2(3), pp. 367-374. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ mineralogy and geochemistry of gold ore low sulfidation -epithermal at lamuntet, brang rea, west sumbawa district, west nusa tenggara province 1. introduction 2. the geology of sumbawa 3. research methods 4. result and discussion 4.1. petrography analysis 4.2. xrd analysis 4.3. chemical of gold analysis 4.4. geochemical ore analysis 5. conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 200 khan, a & khan, m.a./ jgeet vol 03 no 04/2018 research article groundwater quality assessment for drinking purpose in gulistan-e-johar town, karachi, pakistan adnan khan 1, *, muhammad akif khan 1 1 department of geology, university of karachi, pakistan * corresponding author : adkhan@uok.edu.pk received: august 29, 2018; accepted: november 1, 2018. doi: 10.24273/jgeet.2018.3.4.2086 abstract the main objective of present study is to evaluate the groundwater quality of gulistan-e-johar town for drinking. for this purpose, groundwater samples (n=18) through electrically pumped wells were collected from shallow aquifers (mean depth = 36 m). collected samples were subjected to determine the physical characters (tds, ph, temperature), major (na, k, ca, mg, cl, so4, hco3, and no3) and minor ions (fe, mn and f). data reveal very high content of tds (mean: 2862 mg/l) coupled with elevated concentration of na (mean: 974.6 mg/l), cl (mean: 545.3mg/l), so4 (mean: 600mg/l), mn (mean: 0.04 mg/l) and f (mean: 1.7 mg/l). the results indicated that groundwater of gulistan-e-johar is not suitable for drinking purpose and may lead to dangerous health impacts. the wqi value of groundwater is found to be 183 which is also endorsing that groundwater of gulistan-e-johar is unfit for drinking purpose. keywords: groundwater quality, physicochemical parameters, water quality index (wqi), gulistan-e-johar. 1. introduction water is one of the vital constituents for all lives among other blessings. it can be obtained by surface sources including rivers, canals, lakes, streams etc. and underground sources like groundwater abstraction from wells and borehole (mcmurry and fay, 2004). more than half of the population depends on groundwater for survival worldwide (unesco, 1992). water resources are decreasing as the population is increasing day by day. it is widely believed that about 80% of all the diseases are water borne (who, 2011). the attributes of water depend on its chemical composition which is controlled by natural and anthropogenic activities in context of measurable quantities (kumar, 1997). thus, the ability to forecast the hazards and pollution resulting from the groundwater flow has dynamic importance for the precise evaluation (khan et al., 2017). karachi is the largest and densely populated city of pakistan where water is mainly supplied through pipelines. besides, groundwater is the other major source for domestic use. due to rapid population growth and up-country migration the balance between water demand and supply has been disturbed. as a result, people are switching over to exploit groundwater for their needs. the over abstraction of groundwater depletes water table and accelerates the contaminant transport from the land to the aquifer (shah and roy, 2002) which ultimately pollute the aquifers. domestic sewage and industrial effluent contribute to an increase in concentration of different pollutants in groundwater (reghunath et al., 2002). gulistan-e-johar is newly developed residential area with no industrial activity. army cantonment areas and air force base coupled with central ordinance depot surround the area. upper-middle class with satisfactory literacy rate live in this part of karachi city. this town covers an area of about 10.84 sq. km which serves as the largest centre of flat projects in karachi. there is a rapid decline in municipally supplied water since last couple of decades. as a result, switch over to groundwater is frequent to meet the domestic needs. moreover, people are heavily dependent on the bottled water for drinking purpose which is mined from groundwater of study area and processed in the reverse osmosis (r.o) plants. despite of switch over to groundwater for drinking and installation of large number of ro plants no study has been carried so far to screen the quality of groundwater in the study area. therefore, present study is pilot evaluation of groundwater in study area by determining the physicochemical parameters of collected water samples. 2. geology of study area geologically, gulistan e johar town rests on gaj formation of miocene age which in turn is comprised of four members. gulistan-e-johar member is the youngest among all members ofgaj formation (fig. 2). this member is spread over the study area where it shows lihtic character as variegated series of shallow marine clastics followed by fossiliferous limestones. http://journal.uir.ac.id/index.php/jgeet khan, a & khan, m.a./ jgeet vol 03 no 04/2018 201 the bed rocks, on which study area, rests are mainly composed of sandstone, siltstone with interbedded shale and subordinate limestone followed by soft to hard sandstone which is highly conductive due to the dominance of sandy silt (pithawalla and martin-kaye, 1946; shah, 2009). due to the occurrence of variable rock resistance and rheology the topography of study area is highly undulatory. fig. 1. map showing sample locations plotted on the google earth image. fig. 2. geological map of gulistan-e-johar town, karachi. 202 khan, a & khan, m.a./ jgeet vol 03 no 04/2018 3. materials and methods 3.1 sample collection water samples (n=18) were collected through boring wells at a depth range of 10 to 75 metres from various localities of gulistan-e-johar town. water was electrically pumped for 2-3 minutes to get representative samples. location of the boreholes were taken by using global positioning system (gps) and marked on the google image (fig. 1). water samples were taken in polyethene bottles of 1 litre capacity for physico-chemical analysis. bottles were rinsed thoroughly with distilled water and subsequently with the sample water on sampling site. samples were separately collected in bottles of 200 ml capacity to determine nitrate content. about 1 ml of boric acid solution was added in each water sample to stop any further reaction. 3.2 groundwater analysis all the samples were examined for physicochemical parameters in the laboratory of department of geology, university of karachi except fluoride test, which was analyzed in pakistan council of research in water resources (pcrwr). the ph & tds of collected samples were determined by using ph meter (adwa ad 111) and tds meter (adwa ad 330) respectively. sodium and potassium concentrations were determined by using flame photometer (model no. jenway pfp7). sulphate concentration was determined by gravimetric method, while chloride and bicarbonate ions were estimated by argenometric titration method. for the determination of calcium and total hardness, edta titration method (1992) was applied. amount of magnesium was determined by taking the difference of hardness and calcium using standard formula. concentration of nitrate was determined by cadmium reduction method (ha ch-8171) on spectrophotometer while the iron and manganese were determined by using atomic absorption spectroscopy. 3.3 water quality index one of the most operational techniques to collect information of the water quality for the policy makers and the citizens is water quality index (yisa and jimoh, 2010). it was first proposed by horton in 1965 which was later generalized by brown et al. in 1970. water quality index (wqi) is a number that evaluates the quality of water by gathering different parameters, lower values refers to good or excellent quality while higher values refers to the bad or poor quality (bharti, 2011). weighted arithmetic index method of wqi proposed by brown et al (1970) was applied to evaluate the groundwater quality of gulistan-e-johar town. physicochemical parameters including ph, tds, major cations (ca, mg, na and k) and anions (so4, cl, hco3, no3, fe, mn and f) were used to calculate wqi of groundwater in study area. table 1 wqi range, status and possible usage of the water sample wqi status possible usages 0-25 excellent drinking, irrigation and industrial 25-50 good domestic, irrigation and industial 51-75 fair irrigation and industrial 76-100 poor irrigation 101-150 very poor restricted use for irrigation above 150 unfit for drinking proper treatment required before use it is simple method aimed at interpreting the concentration of parameters present, to express them into a single value. it provides an extensive clarification to rate the quality and its suitability for different purposes including; drinking, irrigation, industrial, restricted etc. wqi is calculated using following formula. iwn n (1) where ,qn is the quality rating of nth water quality parameter, wn is the unit weight of nth water quality parameter. the quality rating qn is calculated using the equation : qn =100 x [(vn vi) / (vs vi)] (2) where, vn is the actual amount of nth parameter present, vi is the ideal value of the parameter, vi = 0, except for ph (vi = 7), vs is the standard permissible value for the nth water quality parameter. unit weight (wn) is calculated using the formula wn = k/vn (3) where, k is the constant of proportionality and it is calculated using the equation s (4) 4. results and discussion 4.1 physicochemical characteristics groundwater samples (n=18) were collected from various parts of gulistan-e-johar town through electrically pumped wells installed at various depths (range = 34-250 feet). the results of all physicochemical parameters have been summarized in table 2. due to large variation in the well depths shallow (depth < 100 feet) and deep (depth > 100 feet) aquifers have been addressed separately. 4.2 shallow aquifers one third of total collected samples have been tapped from shallow aquifers ranging in depth between 34-75 feet (table 2). the ph of these samples is found to be slightly acidic (mean: 6.8). low ph of these water samples seems to be controlled by the geology of study area as rocks hosting these water bodies are mainly khan, a & khan, m.a./ jgeet vol 03 no 04/2018 203 comprised of sandstone. the lowering of ph is attributed to organic acids, by dissolution of sulphide minerals or decaying of vegetation (davis and dewiest, 1966). the study area was densely vegetated before urbanization. due to construction activities, removal of such plants (herbs/shrubs) may cause plants decaying and organic acid generation which can dissolve silicates more effectively as compared to inorganic acids (zhang et al., 2009) leading to lower the ph groundwater. moreover, sewage mixing with such shallow aquifers is also plausible to increase acidity. sewage mixing is evident by draining such water into the open channels and pits (fig. 3). total dissolved solids (tds) content in these shallow aquifers is found to be very high (mean: 2818 mg/l) which is far above permissible limit of both who (500 mg/l) and pakistani guidelines (1000 mg/l) for drinking. high salt content in these water samples seems to be associated with acidic ph conditions. organic matter decomposition is accompanied with the release of a large amount of organic acids into the water phase. when the water enters into the aquifer rocks, the contained organic acids could accelerate the complete decomposition of feldspar. besides, it also helps to reduce the ph value of pore water in original aquifer rocks, which becomes an important factor for further dissolution of feldspar (zhang et al., 2009). total hardness of these wells is very high (mean 359.2 mg/l) which is mainly influenced by chloride content (mean: 433.1 mg/l) of such water as compared to hco3 (134.3 mg/l). table 2. physico-chemical parameters of groundwater samples (n=18) collected from gulistan-e-johar town. s.no. physical parameter major cations major anions minor elements depth (ft) ph tds (mg/l) hardness (mg/l) na (mg/l) k (mg/l) ca (mg/l) mg (mg/l) cl (mg/l) so4 (mg/l) hco3 (mg/l) no3 (mg/l) fe (mg/l) mn (mg/l) f (mg/l) gj-1 35 6.86 2140 550 870 57 220 80.19 333.23 639.6 91.145 32 0.03 0.148 1.31 gj-2 34 6.91 3000 350 1540 42 60 70.47 524.66 558.2 171.35 17.4 0.03 0.022 1.38 gj-3 40 6.8 2800 280 580 44 172 26.24 177.25 602.4 123.96 18.3 0.02 0.023 1.23 gj-4 38 6.81 3640 285 76 39 248 8.99 638.1 716.4 109.37 1.88 0.4 0.035 1.57 gj-5 42 6.8 3420 320 98 45 248 17.49 496.3 935 127.6 18.9 0.03 0.03 1.43 gj-6 102 7.02 2210 360 68 40 128 56.38 333.23 795.4 58.333 4.32 0.02 0.023 1.14 gj-7 175 7.19 3750 265 2000 24 232 8.02 726.73 705.2 72.916 0.78 0.04 0.01 1.21 gj-8 170 6.53 3870 270 2370 23 208 15.1 847.26 814 87.499 0.84 0.25 bdl 1.14 gj-9 120 7.13 4550 260 2700 29 200 14.58 957.15 739.6 94.791 0.62 0.25 0.013 1.08 gj-10 75 6.88 1910 370 68 21 128 58.81 428.95 695.4 182.29 9.62 0.28 0.163 2.08 gj-11 120 7.39 1010 260 44 11 160 24.3 159.53 244.2 123.96 1.33 0.02 bdl 2.01 gj-12 180 7.23 1360 420 61 15 40 92.34 276.51 407.8 204.16 2.62 0.03 0.037 2.71 gj-13 130 7.38 3030 730 94 14 112 150.2 726.73 573.5 302.6 35 0.01 0.008 3.01 gj-14 120 7.07 3260 480 2000 20 80 97.2 868.53 438.4 233.33 10.22 0.31 0.006 2.76 gj-15 180 7.36 2390 195 1420 8 52 34.75 567.2 237.8 116.67 1.98 0.05 bdl 1.74 gj-16 170 7.32 1990 290 73 25 164 30.62 194.98 607.3 145.83 3.33 0.05 0.022 1.32 gj-17 160 7.02 4250 325 1840 20 204 29.4 1169.9 513 131.25 2.56 0.04 0.024 1.86 gj-18 250 7.24 2930 345 1640 10 140 49.82 389.95 576.1 109.37 0.74 0.24 0.033 1.56 who limit 6.58.5 <1000 500 200 30 200 150 250 250 ngvs 10 0.3 0.02 1.5 fig. 3. sewage water drained into open channel near old track of karachi circular railway. 204 khan, a & khan, m.a./ jgeet vol 03 no 04/2018 major solutes varied in the order of na > ca > mg > k where na and k contents are sourced from feldspars of sandstone while ca and mg from limestone units of gaj formation. presence of organic acid, decrease of ph value and water salinity favors the dissolution of feldspar. under acidic conditions; albite shows higher dissolution rate than k-feldspar (zhang et al., 2009). this may be the reason of high sodium content (538.7 mg/l) as compared to potassium (41.33 mg/l) in the groundwater of study area. nitrate content is very high in four wells (17.4-32 mg/l) exceeding the who permissible limit of 10 mg/l (table 2). strong correlation of no3 with k (r 2 = 0.57) and mg (r 2 = 0.48) clearly indicate that it is mainly sourced from clay minerals where organic matter is available for degradation by bacteria. the oxidation of ammonia to strong acids by nitrifiers leads to ph decrease (elbanna et al., 2012) which is also evident by the acidic ph in shallow aquifers of gulistan e johar. 4.3 minor and trace solutes concentration of fe and mn varies in the range of 0.02-0.4 and 0.02-0.16 mg/l respectively. although mean value of iron (0.13 mg/l) is within permissible limit (0.3 mg/l) but one sample (gj-4) shows elevated (0.4 mg/l) content. contrary to this, mean concentration of mn (0.07 mg/l) is above who guidelines (0.02 mg/l) where three samples show objectionable content of mn (table 2). naturally fe and mn are sourced by the weathering of minerals possessing fe and mn like iron sulphide, amphibolite, and iron bearing clay minerals specially found in reduced environment; both fe and mn dissolved in the aquifer water, in the regions where groundwater passes through organic rich soil (ahmad, 2012). the anoxic condition is favorable for high level of manganese prevailing in lakes, reservoirs and in groundwater. reported concentration for neutral groundwater is more than 1300 µg/l, while for acidic groundwater is up to 9600 µg/l (astdr, 2012). in aquifers, water infiltrates through the soils rich in organic matter where dissolved oxygen in soil is utilized by the microbes and decomposition of organic matter takes place. the decomposition process reduces ph due to microbial action. in combination with the oxygen deficiency, the fe and mn atoms also gets reduced from fe3+ to fe2+ and mn4+ to mn2+ (ahmad, 2012). under the ph of 5 to 8 the most occurring form is the soluble fe+2 for dissolved iron which is consisting with the low ph of groundwater in shallow aquifers of study areas. the process of oxidation starts which releases carbon dioxide from groundwater to atmosphere, when groundwater pumped up to the surface and gets contact with the air o2 which enters to the solution. as a result, the values of ph increase and the iron and manganese changed from fe2+ to fe3+ and mn2+ to mn4+ into insoluble minerals (ahmad, 2012). for the determination of manganese content in groundwater the geological factors for the soil & subsoils are considered as prime factor. in the soils, the origin of manganese found in four phases which are; adsorbed over iron-oxide, as silicates, carbonates and manganese-oxides, in exchanging mn+2 and soluted condition and within the organic compounds (rott and lamberth, 1993). anthropogenic sources for iron and manganese are landfill leakages, industrial wastes, acid mine drainage, casing of well, piping, parts of pump, and storage tanks correspondingly serving for fe and mn contamination to groundwater (nova scotia environment, 2008). fluoride content varies in the range of 1.23-2.1 mg/l with a mean of 1.5 mg/l where only one sample (gj-10) shows objectionable concentration (2.1 mg/l) against who guideline value of 1.5 mg/l. table 3. statistical description of the groundwater samples (n=18) from gulistan-e-johar town. shallow aquifers (depth < 100 ft) (n = 6) deep aquifers (depth >100 ft) (n = 12) *parameter min. max. mean st. dev. min. max. mean st. dev. depth (ft) 34 75 44 20.5 102 250 156.4 74 ph 6.8 6.9 6.8 0.05 6.5 7.4 7.15 0.45 tds 1910 3440 2818 765 1010 4550 2883 1770 hardness 280 550 359.2 135 195 730 350 267.5 na 68 1540 538.7 736 44 2700 1193 1328 ca 60 248 179.3 94 40 232 143.3 96 mg 8.9 80.19 43.7 35.645 8 150.2 50.23 71.1 k 21 57 41.33 18 8 40 19.92 16 so4 558.2 935 691.2 188.4 237.8 814 554.4 288.1 cl177.3 638.1 433.1 230.4 159.5 1117 601.5 478.75 hco3 91.15 182.3 134.3 45.575 58.3 302.6 140.1 122.15 no3 1.88 32 16.35 15.06 0.62 35 5.36 17.19 fe 0.02 0.4 0.13 0.19 0.1 0.31 0.12 0.105 mn 0.02 0.16 0.07 0.07 0.01 0.04 0.02 0.015 f 1.23 2.1 1.5 0.435 1.08 3.01 1.79 0.965 khan, a & khan, m.a./ jgeet vol 03 no 04/2018 205 4.4 deep aquifers two third of total collected samples (n=18) are regarded as deep aquifers in the study area where water is tapped from depth range of 102-250 feet. the ph of these wells is slightly alkaline (range: 6.5-7.4; mean: 7.15). tds content is almost 6 and 3 times higher than the who (500 mg/l) and pakistani guidelines (1000 mg/l) where it is more variable (range: 10104550 mg/l) as compared to shallow aquifers. sodium and potassium contents varied in the range of 44-2700 and 8-44 mg/l respectively. both the elements show inverse concentration from corresponding shallow aquifers. the highest concentration of na is almost double (2700 mg/l) in deep well as compared to corresponding shallow well (1540 mg/l). contrary to this, mean concentration of k in shallow well is double (41 mg/l) its content in the deep well (19.9 mg/l). it suggests the adsorption of ions to clay surfaces screening of ions from surface to aquifer depth. moreover, ph increase causes formation of clays from decomposed feldspars leading to scavenge the dissolved ions (k, na). similarly, high salinity of water favors the formation of clay minerals (zhang et al., 2009) which is evident by relatively higher salinity in the deep wells as compared to shallow aquifers in the study area. calcium and mg contents fluctuate in a wide range of 40-232 and 8-150.2 mg/l respectively. the concentration of ca (mean: 143.3 mg/l) is almost three times higher than corresponding mg content (50.23 mg/l) in these deep wells. despite large variation, concentration of both the elements is within the permissible limit of who for drinking purpose. nitrate content (range: 0.62-10.22 mg/l) varies within the permissible range (10 mg/l) of who for drinking but one sample (gj-12) shows three-fold higher concentration of no3 (table 3). on the other hand, iron and manganese concentrations span between 0.1-0.31 and 0.01-0.04 mg/l respectively. both these ions are within the corresponding permissible guidelines suggesting that deep aquifers are free from any oxidation reaction which is governed by the presence of organic matter and anaerobic bacteria. 4.3.1 fluoride content fluoride concentration in the deep aquifers of gulistan e johar is relatively higher (1.79 mg/l) as compared to corresponding shallow aquifers. it varies between 1.08-3.01 mg/l where about two third of total collected samples from deep wells show elevated fluoride content (1.56-3.01 mg/l). very strong positive correlation of fluoride with hco3 (r 2 = 0.87) and mg (r 2 = 0.75) is observed (table 4) indicating that beside desorption from clays as a result of hydrolysis in silicate minerals, fluoride is also resulting from the body excretion through urine. for the human health, the consumption of fluoride under the permissible limits of 0.5 1.0 mg/l is beneficial for maintenance of the healthy bones and teeth (wood, 1974). from all over the world, among 25 nations more than 200 million of people are suffering from endemic fluorosis, which is caused by the excess consumption of fluoride in drinking water (ayoob and gupta, 2006; fordyce et al., 2007; gao et al., 2013; ghosh et al., 2013; mesdaghinia et al., 2010; moghaddam and fijani, 2008; oruc, 2008). the importance of defluoridation techniques have been increased because of high concentration of fluoride in drinking water and its effects on human health (adler and organization, 1970; epa, 1975). the measures are being made for defluoridation of drinking water to prevent and control the diseases. consequently, the extent of the fluorosis is reducing in contesting the devastating fluorosis (ama, 1975; chand, 1999). concerning to public health, fluoride is well recognised element and it exists in almost every type of water especially high content in groundwater, rocks, mineral and earth crust etc. the range of the fluoride concentration in drinking water should be from 1.0 to 1.5 ppm recommended by who. multiproportional health hazards fallout by the ingestion of fluoride greater than 6 ppm, common occurrence is deformation of bones in children and adults, skeletal and dental fluorosis (hubner, 1969; ramamohana rao and rajyalakshmi, 1974; susheela et al., 1993). permanent suppression of growth is caused by the continuous intake of non-fatal fluoride dose. usually fluoride ion form complexes with the ions of magnesium and other metal, inhabiting various type of enzymes (ramesam and rajagopalan, 1985; rao, 1992; rao and naidu, 1973). sources of fluoride are fluorite, apatite and fluorapatite in bedrock aquifer system; these minerals occur as detrital grains in sedimentary rocks, as dispersed grains in unconsolidated deposits or as evaporites (basavarajappa and manjunatha, 2015). fluoride in groundwater shows variation due to distinct geological settings. factors on which concentration of fluoride depend are soil temperature, ph, oxidation-reduction process, amount of soluble and insoluble fluoride in host rocks, size and type of geological formation, anion exchange capacity of aquifer materials (i.e., ohfor f-), rainfall, contact of water with rock and its duration (basavarajappa and manjunatha, 2015). 4.5 wqi result water quality of collected samples is unfit for drinking purpose, as the value of wqi is above 150 (table 5). it implies that proper treatment of groundwater is required before its use for drinking purpose. conclusion calculated value of wqi shows that the groundwater falls into the unfit category for drinking. generally, the groundwater of study area is poor for drinking purpose but relatively deeper aquifers (depth > 100 feet) are better than shallow (depth < 100 feet). however, fluoride contamination is prevailing in deep wells. detailed studies are needed to trace the source of high fluoride in the deep aquifers and to find out the reasons of changed chemistry of aquifers at both depth ranges. . 206 khan, a & khan, m.a./ jgeet vol 03 no 04/2018 table 4. correlation matrices among all physico-chemical parameters. ph tds hardness na k ca mg cl so4 hco3 no3 fe mn f ph 1 tds -0.372966 1 hardness 0.125784 -0.129476 1 na -0.136777 0.686071 -0.248508 1 k -0.647161 0.148932 0.064019 -0.145062 1 ca -0.444693 0.481252 -0.226802 0.079815 0.448252 1 mg 0.29297 -0.311664 0.908285 -0.235727 -0.140723 -0.613452 1 cl -0.161626 0.839011 0.043485 0.694131 -0.175605 0.203578 -0.052127 1 so4 -0.647811 0.484761 0.002154 0.020682 0.591416 0.629941 -0.268802 0.15876 1 hco3 0.310676 -0.173781 0.69126 -0.25424 -0.346372 -0.547255 0.79559 0.08096 -0.330399 1 no3 -0.192392 -0.155926 0.658871 -0.182882 0.566978 0.126667 0.47979 -0.180897 0.109573 0.157279 1 fe -0.333524 0.365949 -0.13351 0.288126 -0.112323 0.167518 -0.180166 0.355197 0.220076 -0.021307 -0.295765 1 mn -0.306951 -0.307614 0.288583 -0.291197 0.362225 0.112208 0.185732 -0.26106 0.213725 -0.007118 0.56127 0.1337 1 f 0.430868 -0.296476 0.623499 -0.27454 -0.540174 -0.551706 0.742544 0.090892 -0.518584 0.87871 0.047157 0.023336 -0.010757 1 table 5. correlation matrices among all physico-chemical parameters. parameters ph tds (mg/l) hardness (mg/l) na (mg/l) k (mg/l) ca (mg/l) mg (mg/l) cl (mg/l) so4 (mg/l) hco3 (mg/l) no3 (mg/l) fe (mg/l) mn (mg/l) f (mg/l) observed value (vn) 7.052 2862 353.056 974.6 27.06 155.3 48.05 545.3 600 138.1 11.64 0.117 0.04 1.697 who limit (vs) 8.5 500 500 200 12 75 150 250 250 300 10 0.3 0.02 1.5 ideal value (vi) 7 0 0 0 0 0 0 0 0 0 0 0 0 0 qn 3 572 70 487 225 207 32 218 239 46 116 38 199 113 wn=k/vn 0.0026 0.0000 0.0001 0.0000 0.0007 0.0001 0.0004 0.0000 0.0000 0.0001 0.0016 0.1587 0.4959 0.8841 qn*wn 0.008 0.004 0.00366 0.009 0.153 0.025 0.012 0.007 0.007 0.006 0.184 6.032 98.68 99.9 wqi 3 572 70 487 225 207 32 218 239 46 116 38 199 113 wqi avg. 183.2142857 khan, a & khan, m.a./ jgeet vol 03 no 04/2018 207 acknowledgement authors extend sincere regards to prof. dr. shahid naseem, chairman, department of geology, for providing the analytical facilities. mr. wasi haider is acknowledged for his technical support to analyze the samples. ms. sumera asif khan is also thanked for her help in statistical analysis. references adler, p., organization, w.h., 1970. fluorides and human health. ahmad, m., 2012. iron and manganese removal from groundwater: geochemical modeling of the vyredox method. ama, 1975. efficacy and safety of fluoridation. chicago. astdr, 2012. toxicological profile: manganese. atlanta, ga, united states ,. ayoob, s., gupta, a.k., 2006. fluoride in drinking water: a review on the status and stress effects. crit. rev. environ. sci. technol. 36, 433 487. https://doi.org/10.1080/10643380600678112 basavarajappa, h., manjunatha, m., 2015. groundwater quality analysis in precambrian rocks of chitradurga district, karnataka, india using geo-informatics technique. coast. ocean eng. 4, 1354 1365. chand, d., 1999. fluoride and human health-cause for concern. indian j. environ. prot. elbanna, k., el-shahawy, r., atalla, k., 2012. a new simple method for the enumeration of nitrifying bacteria in different environments. plant soil environ. 58, 49 53. epa, 1975. national interim primary drinking water regulations. fordyce, f.m., vrana, k., zhovinsky, e., povoroznuk, v., toth, g., hope, b.c., iljinsky, u., baker, j., 2007. a health risk assessment for fluoride in central europe. environ. geochem. health 29, 83 102. https://doi.org/10.1007/s10653-006-9076-7 gao, h., jin, y., wei, j., 2013. health risk assessment of fluoride in drinking water from anhui province in china. environ. monit. assess. 185, 3687 3695. https://doi.org/10.1007/s10661-012-2820-9 ghosh, a., mukherjee, k., ghosh, s.k., saha, b., 2013. sources and toxicity of fluoride in the environment. res. chem. intermed. 39, 2881 2915. https://doi.org/10.1007/s11164-012-0841-1 hubner, m., 1969. geochemische interpretation nonfluoride/hydroxide. geo. geol. wise. b. miner. lagerstatten forsch 1415. khan, a., bakhtiari, a.e., anjum, s., 2017. groundwater quality and fate of public health in new karachi town, karachi, pakistan. int. j. phys. educ. heal. sport. allied sci. 1, 73 86. kumar, n., 1997. a view on fresh water environment. ecol. env. cons 3, 3 4. mcmurry, j., fay, r.c., 2004. hydrogen, oxygen and water, in: mcmurry fay chemistry. pearson education, new jersey, . 575 599. -b. of environmental, 2010, undefined, 2010. monitoring of fluoride in groundwater resources of iran. bull. environ. contam. toxicol. 84, 432 437. https://doi.org/doi:10.1007/s00128010-9950-y moghaddam, a., fijani, e., 2008. distribution of fluoride in groundwater of maku area, northwest of iran. environ. geol. 56 116. nova scotia environment, 2008. iron and manganese. oruc, n., 2008. occurrence and problems of high fluoride waters in turkey: an overview. environ. geochem. health 30, 315 323. https://doi.org/10.1007/s10653-008-9160-2 pithawalla, m., martin-kaye, p., 1946. geology and geography of karachi and its neighbourhood [with plates].]. ramamohana rao, n. v., rajyalakshmi, k., 1974. studies of water quality and incidence of fluorosis in andhra pradesh. proc. symp. fluorosis 477 485. ramesam, v., rajagopalan, k., 1985. fluoride ingestion into the natural waters of hard-rock areas, peninsular india. j. geol. soc. india 25, 125 132. rao, n., 1992. factors affecting optimum development of groundwaters in crystalline terrain of the eastern ghats, visakhapatnam area, andhrapradesh, india. j. geol. soc. london. 40, 462 467. rao, r., naidu, m., 1973. geochemistry of high-fluoride natural waters if jaggaiahpalem, fluorosis-endemic village near visakhapatnam district, andhra pradesh. inst. symp. recent res. appl. geochemistry 6. reghunath, r., murthy, t., raghavan, b., 2002. the utility of multivariate statistical techniques in hydrogeochemical studies: an example from karnataka, india. water res. elsevier 2437 2442. rott, u., lamberth, b., 1993. groundwater clean up by in-situ treatment of nitrate, iron and manganese, water-supply oxford-11,. shah, s.m.i., 2009. stratigraphy of pakistan, geological survey of pakistan. gsp mem. 284 301. shah, t., roy, a.d., 2002. intensive use of groundwater in india, iwmi-tata water policy program. anand, india. susheela, a., kumar, a., bhatnagar, m., bahadur, r., 1993. prevalence of endemic fluorosis with gastrointestinal manifestations in people living in some north-indian villages. fluoride 26 26, 97 104. unesco, 1992. groundwater unesco. who, 2011. guidelines for drinking water quality (no. 4th edition). geneva. wood, j., 1974. biological cycles for toxic elements in the environment. sci. jstor 183, 1049 1052. yisa, j., jimoh, t., 2010. analytical studies on water quality index of river landzu. am. j. appl. sci. 7, 453. zhang, y., zeng, j., yu, b., 2009. experimental study on interaction between simulated sandstone and acidic fluid. pet. sci. 6, 8 16. https://doi.org/10.1007/s12182-0090002-3 © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geology of study area 3. materials and methods 3.1 sample collection 3.2 groundwater analysis 3.3 water quality index 4. results and discussion 4.1 physicochemical characteristics 4.2 shallow aquifers 4.3 minor and trace solutes 4.4 deep aquifers 4.3.1 fluoride content 4.5 wqi result conclusion acknowledgement references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 69 structural analysis of northwest sabah basin by 2d reconstruction of seismic sections akhmal sidek 1, , umar hamzah 2 1 petroleum engineering department, institute for oil and gas, fcee, universiti teknologi malaysia 2 geology programme, ppssa, faculty of science and technology, universiti kebangsaan malaysia. * corresponding author : makhmal@petroleum.utm.my received: 2 apr, 2018. revised : 26 apr 2016, accepted: 7 may, 2018, published: 1 june 2018 doi : 10.24273/jgeet.2018.3.2.1413 abstract the tectonic evolution of thrust-fold belt and thrust sheet zone in northwest sabah basin was described based on balanced reconstruction of seismic sections representing mid-miocene to recent deposits. the study area is located at the center of a wide crustal deformational zone bordered by the sunda shelf on the northeast, sulu sea in the southwest and the south china sea in the northwest. balancing cross section can be applied after the deformed geological structure geometry is accurately determined from seismic sections and 7 seismic stratigraphic unit from 15 ma until recent is consecutively restored. there are four steps involved in retro-deformation processes beginning with removing all faults displacements followed by unfolding the folds, isostasy correction and finally the removal of each compacted layer parts or decomposition. wider fold wavelengths with least thrust faults were observed from south to north in the seismic sections ranging from 12 to 4 km with an average of about 7 km, while smaller fold wavelengths and more thrust faults were observed in the north based on the same seismic sections. in general, the reconstructed cross sections revealed compressional tectonic deformation activity as shown by shortening strain trending nw-se. measurement of total shortening shows that thrust fold belt is imbalance by an exceeds of 14.7 km and more active compared to thrust sheet zone which has only 0.9 km. results of the study also indicate facies destruction due to shortening which is decreasing towards pliocene or younger deposits. keywords: 2d reconstruction, nw sabah basin, 2d seismic profiles, retro-deformation 1. introduction nw sabah basin, which is also generally known as sabah-brunei basin, northwest borneo basin or baram-balabac basin proposed by cullen (2010) is bordered in its east-west to major part of the north sarawak basin. these two basins are separated by a steep slope sea bed of west baram lineament which is connected to nw-se trending tinjar strike slip fault (mazlan madon, 1999; tan & lamy, 1990) sabah basin is a trench associated basin or sometimes is called as fore-arc basin (levell 1987). based on previous gravity, depositional history and sequence stratigraphy studies, this basin is expanding as a foreland basin followed by collision of continents below the south china sea and west sabah (hazebroek et al. 1994; noor azim ibrahim 1994; milsom et al. 1997). sabah basin is also formed by thinning of continental crust layer due to dispersion of south china sea (tjia & mohd idrus ismail, 1994). the sabah basin is considered as a compressional dynamic tectonic zone of northwest-southeast trend. there are some variations in previous study on the tectonic activity of sabah basin where abdul manaf & wong (1995), mohd idrus et al. (1995) and hamilton (1979) reported that the study area was in passive condition without any earth movement and seafloor spreading during early eocene. but this hypothesis was rejected due to the discovery of highly compressional deformation in the miocene to recent sedimentary rocks as well as evidence from tensional movements measurement by global positioning system (gps) technique (ingram et al. 2004; simons et al. 2007; king et al. 2010). king et al. (2010) used 2d dynel computer software for structural reconstruction of southern sabah basin only. results of their study show a decrease in crustal shortening towards the north into baram delta. the subject of crustal mobility and the mechanism to enhance the formation of sabah basin is still under discussion until today. it is hoped that the study of structural reconstruction based on seismic data and well in the area of thrust fold belt and thrust sheet by using latest 2dmove computer software would resolve some of the problems. in this study we used the same technique to propose some crustal restoration and reconstruction by using seismically derived cross sections or profiles in the thrust fold and thrust sheet zones. the analysis is hoped to optimize the use of seismic sections in increasing the understanding related to the tectonic mechanism that is controlling the formation of folds and thrust faults 70 sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 in the study area by using 2dmove computer software. 1.1. geological setting sabah basin constitutes of 85% marine or offshore deposits towards the south china sea while the rest covered along the west coast of western sabah and north of western sarawak. the basin is about 350 km length and 140 km width trending along northeast-southwest covering an area of about 47075 km squares with thickness of about 10 km of mostly tertiary siliciclastic sediments (ccop, 1991) bol & hoorn (1980) studied the structural style across nw sabah continent and basically found out that the structural style along northwest to southeast was dominated by compressional deformation with minor early tensional stage. in some of the area, the structural pattern was dominated by tensional activity with some compressional effect. the third structural style was mainly compressional with thrust belt due to gravitational sliding and subduction or both. tan & lamy (1990) and hazebroek et al. (1994) has identified six structural regions namely inboard belt, outboard belt, sabah trough, dangerous ground, thrust sheet zone and active delta (baram delta) thrust-fold based on the structural style differences and depositional history. the study area covers the whole region of geologically complex tectonic structure of nw sabah basin (fig. 1). in terms of depositional history, the siliciclastic sediment of shelf slope was deposited progradationally towards the sea during early miocene after the early phase of deep sea deposition. the depositional processes were interrupted by several episodes of tectonic activities leading to formation of regional unconformities which have been used to divide the sabah basin into several stages. these stages were separated by major unconformities resulted from tectonic movements and uplifted towards the southeast near the basin boundary. the most major regional unconformity in the study area is the deep regional unconformity (dru) which is separating the underlying post-mid miocene deep marine rock sequence from the top mid miocene to quaternary slope-shelf sediments. 2. methodology a total of 10 seismic sections basically representing nine sequence boundaries divide the quaternary sediment overlying the basement. these seismic sections were then traced and divided into 2dmove polygonal shapes for structural interpretation and fold types classification. sequences 1 to 6 represent post-rift mid-miocene episodes while sequences 7 and 8 represent depositional units formed during the rifting processes taken place in lower miocene. these sequences (7 and 8) are also both considered to be the top surface of shale basement or the base of thrust faults (fig. 2) as refer to previous work by akhmal sidek et al. (2015). cross section restoration or sometime known as retro-deformation process is carried out for reconstructing the formation of structural geometry deformation or to bring back the original sedimentary layers before they are being deformed by tectonic process. the reconstruction process includes removing the effect of faulting and folding. there are four sequential algorithms involved in the retro-deformational processes to generate the algorithmic cross sectional model resulting from the deformational phases. the algorithmic sequence begins with removing the faults displacement, unfolding of folds, isostatic correction and lastly is removing the layer which has been compacted by compression during the deformation to its original position (decompaction). fig.1. tectono-stratigraphic provinces of sabah basin and location of seismic lines. (after hutchison, 2004) sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 71 the assumption made during the processes is no input and output movement must originate from the sedimentary layer during the tectonic deformation (midland valley 2012). the correct algorithm is determined by the horizon mechanic of each layer and the boundary situation. nevertheless, the restored model is not necessarily representing the correct pre-deformed geometry or the structural evolution movement. suitable algorithmic model selection in the study is concentrated to tri-sheared technique for fault shift algorithm while the sliding technique is used in the algorithm for unfolding the folds. these techniques are particularly used to resolve both types of tectonic regimes represented by compressional thrust-fold belt and tensional inboard belt observed in northwest sabah basin. the measurement for isostasy correction depends on the loading dimension acted upon the sediment layer plus the rigidness of lithospheric. in this respect the elastic thickness has to be assumed as fixed and constant in time and space even though it has different lithospheric rigidity (watts & talwani, 1974) the elastic thickness value (te) and the average wavelength (ʎ) is about 8 km and 6 km respectively (braitenberg et al. 2004). these parameter values are used in general for subduction analysis in south china sea and the values are constant for the whole process of kinematic model development. parameters used for isostasy modelling in this study are given in table 1. table 1. parameters for 2dmove kinematic modelling in nw sabah basin. layer model unit bulk density, kg/m 3 young modulus, gpa u1 (late pliocene-recent) 2.24 1.12 u2 (early pliocene) 2.28 1.90 u3 (late miocene) 2.30 2.11 u4 (mid-miocene) 2.34 2.35 u5 (mid-miocene) 2.37 2.50 u6 (early miocene) 2.40 2.85 sea water 1.03 mantle 3.33 kinematic model in this study is a kind of inverse modeling since its purpose is to analyze retrodeformational process involving thrust fold and normal fault structures. it is also meant for predicting fault development, kinematic analysis and layer length in designing the pre-deformed structural architecture. kinematic modelling analysis in this study is carried out with the aim of measuring the percentage and rate of layer model total shortening. shortening percentage represents qualitative value of compressional tectonic process experienced by the area. 2dmove is used in kinematic model development for geometrical interpretation in line with the geological concept. all seismic sections in segy format were imported into the software for analysis involving five complete stages. in stage 1, structural geometry or faults positions, footwall and hanging wall blocks were identified from the seismic sections. selection of fault shifting algorithm by tri-shear technique is carried out in the following stage 2 and clearing the fault shift by downward movement along the dip direction is accomplished in stage 3. selection of algorithm for unfolding the fold by flexural slip technique, completing the restoration process for upper section and calculation of shortening length are carried out in stage 4. finally, the restored upper section is cleared from the model for de-compaction process and isostasy correction in stage 5. shortening percentage is calculated after the fault shifting algorithm and fold unfolding for every layer section or balanced restoration is completed. the equations for the shortening percentage length is l = pin1 pin2 where l is the distance in meter between pin1 and pin 2. pin 1 is fixed while pin 2 is moved during the restoration process. the differen = l (final) l (initial) where l (final) is the section length after restoration and l (initial) is the length before restoration. the equation for calculating the total of shortening percentage is σ length of each section. the uncertainty for each shortening magnitude calculation is about 15 % considering the uncertainty in seismic depth-time conversion, error in horizon picking during the interpretation and uncertainty in the restoration processes. 3. result structural fold in the study area are closely related to thrust faulting and classified as gentle to open. it can be observed in many seismic sections within thrust fold belt and only few in sabah trough as well as in thrust plate. maximum and minimum fold wavelengths in the nw sabah basin is 12 km and 4 km respectively. the maximum fold wavelength is observed in the south of study area along seismic line lsd while the minimum fold wavelength is observed in seismic line lsl located in the north of study area. average fold wavelength is about 7 km and the fold type is considered as low angle based on its size calculated between fold wings. the calculated average value is not very far different from what has been reported by morley et al. (2011). they found that the average fold wavelength in nw borneo is about 10 km. 72 sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 fig. 2. example of seismic section (a) polygonal model and sequences (b) determination of inter-limb angle and fold fig.3. schematic cross section traced from seismic line lsa representing south of study area illustrating structural restoration from mid-miocene (6) to recent (1).wavelength (c) fold type classifications (d). sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 73 the restoration processes began with layer unit of recent to mid-miocene in age (15 ma) numbered as 1 representing the youngest age to 6 for the oldest one. fig.s 3 to 5 are examples of kinematic models representing south to north of the study area. fig. 4. schematic kinematic model for seismic line lsf representing the center of study area. fig. 5. schematic kinematic model for seismic line lsl representing north of study area. overall, the restored cross sections show compressional deformation tectonic activities displayed by shortening strain that striking from northwest to southeast. this deformation is interpreted to be related to thrust faulting activities within thrust-fold belt and all normal faults in the shelf slope. 4. discussion thrust faults in the study area were originated from compressional tectonic while all the normal faults were from tensional zone. based on total shortening calculation, structures in deep water northwest sabah basin is dominated by compressional activity. the value of total shortening percentage is calculated along 230 km length from seismic line lsa to lsl as shown in fig. 6. the plotted curves include uncertainty limit with total shortening length of 0.9 km to 14.7 km. the curves also record the age of each reconstructed layer unit during the formation of sequence stratigraphy unit 6 to unit 1. the lowest value of total shortening (0.9 km) is observed in the north along seismic line lsl while the highest value (14.7 km) is calculated in the south along seismic line lsb. length of total shortening is found increasing from 11.6 km in south seismic line (lsa) to 14.7 km in northern seismic line (lsb) and then decreased again to 6.5 km along seismic line lsc. the significant decrease in total shortening in seismic line lsc may probably be due to error during the seismic interpretation process. most likely the complete image of thrust fault structures were failed to be identified due to the quality of available seismic sections. total shortening is increased from 7.7 km along seismic line lsd to 9.4 km along seismic line lse and then started to decrease towards the north from 5.7 km in lsf to 3.6 km along seismic line lsh. a very small total shortening of 3.2 km is observed in seismic line lsi, 1.6 km along lsk and eventually the shortest shortening of 0.9 km is observed in seismic line lsl. the major shortening with a magnitude of about 14.4 km was observed in restoring unit 3 along seismic line lsb (fig. 6). it can be interpreted as due to thick sediment supply from the continental shelf into the slope occurs during 7 to 8.5 ma (million years) in the southern part of the study area. the rate of shortening is relatively decreasing in 15 ma to recent. fig. 7 shows the difference rate of total thrustfold belt by previous researchers and in this study. hesse et al. (2010) reported similar study in structural restoration based on a total of 6 seismic sections in the same thrust-fold belt. four of the seismic sections overlapped with lsa, lsb, lsd and lsf and in conclusion they divided the sections into 5 sedimentary sequences as opposed to 7 sequences that found in this study. 74 sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 fig. 6. curves showing the shortening values against distance of seismic lines with uncertainties bars from mid-miocene (15 ma) until pliocene (4 ma). hesse et al. (2010) also observed crustal total shortening (8-13 km) in the thrust-fold belt from recent to miocene. shortening of about 5 to 7 km for each layer was observed in recent to pliocene unit sequence while a much smaller shortening of 2-4 km was observed in the early to late pliocene sequences. a shortening of approximately 3 km was calculated in layer sequence of early pliocene to miocene in age. in general, the rate of shortening in sedimentary sequence is found decreasing from older towards younger. basically their findings are not so much in difference from the results of this study where the major shortening was reported in the southwest particularly along seismic line lsb. based on seismic line positions, major tectonic compression was towards nw-se which is almost similar to what was reported by king et al.(2010) that obtained the tectonic trend by investigating a total of about 200 wells in baram thrust-fold belt and in some part of sabah basin thrust-fold. 5. conclusion the seismic cross sections used in the structural reconstruction of the study area are considered as effective for estimating the rate of crustal shortening. the tectonic compressional activity which is considered as the main factor to cause the shortening and destroying the sedimentary depositional facies from parallel to chaotic seismic facies as observed in several seismic sections within the thrust-fold belt and thrust sheet. the values of total shortening measured in thrust-fold belt and thrust sheet zones indicate that both areas are not in equilibrium and had different rate of tectonic intensities. exceeding balanced about 0.9 km and 14.7 km lengths were observed in crustal shortening of thrust-fold belt and thrust sheet zone both representing compressional area. this study is only completed if the value of crustal shortening is also measured from seismic lines representing the extensional zones located in shallow bathymetry (<200 m) area of sabah basin. the reconstruction system is balanced when the rate of crustal shortening observed in compressional and extensional zones are equal. higher rate of crustal shortening indicates higher degree of compressional tectonic suffered by that particular crustal area resulting to formation of many thrust fault structures. sidek, a. & hamzah, u./ jgeet vol 03 no 02/2018 75 fig.7. comparison of structural reconstruction results by previous researchers and in this study. comparison based on seismic lines (a) and comparison based on rose diagrams (b). acknowledgements authors would like to thank petronas especially petroleum resource exploration (prex) and petroleum management unit (pmu) for providing the subsurface data in this study area. the kingdom suite 8.8 and 2dmove software was used in interpreting seismic lines and retro-deformation. this study was supported by malaysian government under fundamental research grant scheme (frgs) vot: r. j130000.7846.4f954 and potential academic staff (pas) vot: q. j130000.2746.02k90. 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fax: +91-5102321667 received: sept 18, 2018; accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2125 abstract the gneisses and granitoids emplaced along e w sub vertical crustal shear zones are represented as important tectonic units in the bundelkhand craton. the tonalite trondhjemite granodiorite (ttg) gneisses (3.5 3.2 ga; oldest unit), and streaky to mafic gneisses structurally deformed in d1 deformation. the gneisses, metabasic, felsic, banded iron formation (bif) and metasedimentaries of greenstone complex exposed in central part, have characteristics of three sets of folding (f1 f3) generally evolved in d2 compressive phase, which are not occurring in northern part of craton. the k rich neoarchean granitoids (2.6 2.49 ga) were intruded as granitic complex (d3 magmatic phase) and the e w strike slip raksa garhmau shear zone reported as important tectonic unit, evolved in a syn to post tectonic d3 phase. the dolerite dykes (ca. 2.0 ga) were emplaced along nw se fractures in extension setting during d4 magmatic event and ne sw riedel shears occupied by giant quartz veins (reefs) evolved in neoarchean paleoproterozoic during d5 endogenic activity. the relationship between macro and microstructural fabrics has been documented by mylonitic foliation, stretching lineation, s c planes and rotated fabrics, reflect mesoscopic shear indicators, as noted in three types of mylonitic rocks. i) the rotated porphyroclasts of quartz, feldspars and asymmetric pressure shadows showing strong undulose extinction, deformation lamellae, and dynamic recrystallization are characteristic features of protomylonite where altered orthoclase and kinked plagioclase are noticed, ii) mylonite, a distinct mylonitic foliation represented by parallel orientation of elongated quartz and feldspar with flakes of mica, iii) the ground matrix of recrystallized quartz with few protoliths of quartz and feldspar are observed, important features of ultramylonite. the asymmetric microstructures viz. σa and σb mantled porphyroclasts, other microstructures were progressively deformed by crystal plastic (non coaxial) strain softening process under low to moderate temperature conditions. the sinistral top to sw sense of shear movement was dominant. the microfractures/ microfaults, kinking and pull apart structures observed in k feldspars are indicative of overprinting of brittle deformation on ductile shearing. keywords: shear indicators, microstructures, crustal shear zone, bundelkhand craton, central india 1. introduction implications of macro and microstructures observed in crustal shear zones have become more significant in understanding the tectonic growth of continental crusts in archean cratons. the imprints of scattered features preserved in the cratons were significantly interpreted for the existence of crustal shear zones on major and minor scale. such crustal shear zones play significant roles in exhumation of deeper crustal materials and provide passages for intrusion granitic magma into continental crust (hutton, 1988). shear zones are localized areas of intense deformation with large values of shear strain accumulated in these domains relative to surrounding rocks (ramsay and huber, 1987). small scale structures that developed in response to progressive simple shear in a shear zone and characterized by a protracted history of deformation are immensely useful in delineating the strain history and kinematics of a shear zone (simpson and schmid, 1983; choukroune et al., 1987; carreras et al., 2005; passchier and trouw, 2005). the existence of e w crustal shear zones in the central domains of the bundelkhand craton showing intensive mylonitisation, are considered potential zones to depict the tectonic evolution of neoarchean crust. in the present paper the attempts were made to understand the tectonic significance of shear indicators of mylonites emplaced along raksa garhmau shear zone. the asymmetrical shear indicators viz. rotated porphyroclasts, mylonitic foliation, s c planes, stretching lineation and minor faults examined on mesoscopic and microscopic scales were used to decipher sense of shear movement. http://journal.uir.ac.id/index.php/jgeet 12 bhatt, s.c. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 2. geological setting bundelkhand craton belonging to northern segment of peninsular india spreads in 29,000 km2 area in central india (fig. 1). the eastern and western margins are bordered by vindhyan and bijawar basins and are separated from southern indian block by a central indian tectonic zone(basu, 1986). the contact between aravalli and bundelkhand craton is tectonically delineated by great boundary fault. the northern boundaries separated by deep himalayan basins are tectonically marked by yamuna fault. three important lithological complexes were identified in this cratonic block; i) ttg gneissic complex, constituting ttg and gneisses, associated with migmatites, schists and amphibolite, ii) greenstone complex consists of supracrustal belt of basic, banded iron formation (bif) and less metamorphosed felsic volcanic sedimentary rocks, iii) k rich granitoids constitutes various types of granites, giant quartz veins (reefs), pegmatites and aplite dykes (basu, 1986; bhatt and hussain, 2008, 2012; bhatt and mahmood, 2008, 2012; bhatt and gupta, 2009, 2014; bhatt et al., 2011, 2017; bhatt, 2014; singh and slabunov, 2013, 2015a, 2016; slabunov et al., 2017a; slabunov and singh, 2018a; singh et al., 2019a). the oldest ttg rocks were reported in central part of the budelkhand craton (sarkar et al., 1996; kaur et al., 2014; saha et al., 2016). mauranipur and mahoba gneisses dated 3.27 ga as one set of ttg magmatism and are considered a oldest deformation phase (mondal et al., 2002). the vast intrusive of sanukitoids, granodiorites, diorites, and high k granites rocks were evolved during neoarchean time (2.55 2.52 ga; mondal et al., 2002; kaur et al., 2016; verma et al., 2016; singh et al., 2019b). a nw se trending dolerite dyke swarm was intruded in ca. 2000 1800 ma (rao et al., 2005). patil et al. (2007) reveals that the dolerite dykes have a palaeomagnetic vga position at about 2150 ma. keeping in view the complicated geological setup, the detailed field investigations were carried out and a tectonic set up was reconstructed in raksa garhmau sector. fig. 1. geological map of bundelkhand craton with location of raksa garhmau sector, inset map show the location. 2.1 raksa garhmau sector the geology of this sector was partly discussed by basu (1986); senthiappan (1993); bhatt and gupta (2009, 2014), and bhatt (2014). lithologically the raksa garhmau sector has broadly grouped into (i) granodioritic, and (ii) granitic complex (fig. 2). the granodiorite gneisses are exposed in north and south of dinara and purwa khiriya villages (fig. 2) and are represented by a foliation and mineral lineation. the antiquity of ttg rocks are distinctly marked by their occurrence as smaller xenoliths (5 to 15 cm) within granodiorite gneisses (fig. 3a). the e w to ese wnw trending foliated granitic rocks are occurred in the northern and southern extremities of gora village and in the surroundings of the dinara quartz reef (fig. 2). the foliated granite was mylonitised and emplaced along e w crustal shear zone (300 500m) near villages; gora, bamer, rajapur and shivgarh (fig. 2). the ene wsw to e w striking mylonitic foliation showing northerly dips is represented by parallel alignment of porphyroclasts of quartz, feldspar and mica flakes. the stretching lineation lying sub horizontal (5 10°) to mylonitic foliation is defined by stretched fabrics of quartz and feldspar (fig. 3b, c). the protomylonite (fig. 3b) to highly foliated mylonite (fig. 3c) zones confined to the low to high shear domains were noticed in the southern terrains of bachoni, rajapur, bamer, and shivgarh villages. the fine grained ene wsw to ne sw trending ultramylonites occurring near rajapur (fig. 3d) is bordered by pink and grey granites in north and south respectively (fig. 2). the enclaves of porphyritic grey granite found near simardha, jhansi, bamer, and bachoni villages constitutes large phenocrysts of feldspar (mostly microcline) and quartz (1 8 cm) with lesser amount of biotite. at some places these rocks are intruded by quartz and epidote veins and the porphyries of hornblende. these granites mainly contain fine to medium grained hornblende, bigger phenocrysts of quartz and feldspar and flakes of mica. the gneissic xenoliths (10 cm to 1 m) are also found within these granites near simardha and south of garhmau railway crossing. bhatt, s.c. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 13 few fine dark green e w lensoidal bodies (100 300 meter) of amphibolite consisting of hornblende and feldspathic minerals are exposed in the south of raksa and north of bamer villages. the e w to ese wnw trending dark grey granite exhibiting moderate to steep dips (45 70°) are occurred in the southeast of bamer village (fig. 2). at places the isolated lensoidal bodies of dark grey porphyritic granite (20 60m) are occurred within the pink granite. the massive undeformed, medium coarse grained grey granite are widely exposed in the southern extremities of ductile brittle shear zone near jhansi, shivgarh, rajapur and bachoni villages (fig. 2). at few places the brittle fractures healed by pegmatite, quartz and aplite veins are frequently seen within these granitic bodies. the higher percentage of mafic minerals and less number of potash feldspar were noticed in the coarse grained biotite granite comparatively to porphyritic coarse grained granite. the wide occurrence of medium coarse grained pink granite is seen in the north eastern and northern territories of jhansi town and northern part of bamer, bachoni, bamer and garhmau villages (fig. 2). the faulted contact between pink and grey granite is also noticed near lahargird village. the coarse grained lensoidal enclaves of porphyritic pink granite are isolated in the southwest of simardha village. the sheared contact with pink granite and ene wsw trending ductile shear zone is also recognised near shivgarh and lahargird villages (fig. 2). these granitoids evolved in later phase of magmatic activity and recorded as younger granites. fig. 2. geological map of raksa garhmau sector, bundelkhand craton, central india (after bhatt and gupta 2014). numerous ne sw linear quartz veins (reefs) are exposed near garhmau, jhansi (bundelkhand university campus), shivagarh, and dinara villages. the quartz reefs passing from dinara and purwa khiriya and shivagarh and lahargird villages are offset by several nw se and nne ssw oblique faults respectively (fig. 2). the e w and ene wsw crustal shear zones are also truncated by fractures near raksa and lahargird villages. at places the inclined (nne ssw) and vertical (ne sw) joints are observed as prominent features in these reefs. the conjugate sets of quartz veins and presence of milky to pinkish white quartz and lumps of galena and diaspore are reported as important mineral deposits. 3. deformation pattern and relationship with shearing the older ttg gneissic and greenstone sequences of bundelkhand craton were deformed and produced in three sets of folding (f1 f3) under the influence of compressive tectonic episodes (d1 d2; bhatt et al., 2011; bhatt, 2014). the different types of granitoids were elegantly exhumed along fractures and shears in the d3 phase of tectonic event. the e w crustal shear zones predominantly transecting the gneissic and granitic rocks were evolved in syn to post tectonic d3 phase under brittle ductile environment (singh and slabunov, 2015a, 2015b). the dolerite dykes were emplaced along nw se trending fractures in extensional tectonic setting during d4 magmatic phase. the linear hillocks developed along ne sw shears (riedel shears?) were predominantly occupied by quartz reefs in the last endogenic activity (d5; slabunov et al., 2017b; slabunov and singh, 2018b). bhatt and hussain (2008, 2012), bhatt and mahmood (2008, 2012), and bhatt et al. (2011) pointed out that the nnw to nw plunging (40 50°) f1 folds showing tight and isoclinals shapes and nne plunging (30°) open to reclined f2 folds are commonly noticed in bif, mafic and biotite gneisses, migmatites and quartz-sericite schist rocks. their axial planes trend in n s to nnw sse directions. the f3 folds exhibiting open to tight geometry are plunging 45° to 50° in different directions. the elliptical folds are commonly observed in banded (mafic) gneisses. these folds occur as isoclinal plane pattern, and provide strong evidences for intensive ductile and brittle ductile shearing in the area. due to intense shearing effects the fold axes in tight close folds were rotated and reoriented and at some places extensional crenulation cleavage and shear bands were formed. 14 bhatt, s.c. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 4. shear zones and shear indicators the shear zones can be mapped from hand specimen to plate boundary scales and are considered vulnerable zones for reactivation over very long time span. the high shear strain domains are classified as ductile and brittle ductile shear zones and form important mechanical heterogeneities (butler et al., 1997). the geometry of mylonitic foliation, asymmetrical fabrics and stretching lineation (berthe et al., 1979; matlauer et al., 1981) and implications of shear criteria (simpson and schmid, 1983) strongly support the criteria for the determination of sense of shear movement in most of the crustal scale shear zones. the crystal plasticity and pressure solution have been identified important mechanism to control the deformation of quartzo-feldspathic granitic rocks (berthe et al., 1979). passchier and trouw (2005) discuss that the proto mylonite were initially developed under low to moderate strain conditions whereas the s c mylonite were evolved under moderate to high shear strain conditions. proto mylonites, s c mylonites and ultramylonites are recognized in raksa garhmau shear zone of the bundelkhand craton. fig. 3. (a) an enclave of ttg rock embedded within porphyritic granite gneiss; (b) well foliated mylonitised granite gneiss showing stretching lineation and rotated porphyroclast of quartz and feldspar in protomylonite zone; (c) intensively foliated mylonite zone showing stretched fabrics of quartz and feldspar; (d) sheared granitic rocks showing formation of s c mylonite zone represented by termination of s planes and evolution shear bands (c planes). diameter of coin is 2.4 cm and length of pen is 14 cm. 4.1. raksa garhmau shear zone a north dipping brittle ductile crustal shear zone (100 to 500 meter wide and about 45 to 50 km in length) transecting granodiorite gneiss and granite rocks is traced near purwa khiriya, gora, rajapur, bamer, raksa, lahargird and garhmau villages, located in the intracratonic domains of the bundelkhand craton (fig. 2). its width is consistently decreasing 100 to 50 meter near lahargird and garhmau villages and is possibly died out in the eastern flanks of garhmau village (senthiappan, 1993). the discontinuity of this shear zone is manifested by development of other sets of minor shear zones, which were at some places terminated by another shear bands (c planes) or brittle fractures (fig. 3d). the parallel to subparallel ne sw trending shear zones/ riedel shears (?) were possibly evolved in syntectonic setting along which the quartz vein (reefs) were emplaced. the granites were mylonitised and emplaced along this shear zone during progressive shearing effects. this e w to ene wsw trending steep crustal shear zone is sinistrally dislocated by faults near lahargird and raksa villages and shows dextral displacement near dinara and purwa khiriya villages (fig. 2). the protomylonite zone consisting of large porphyroclasts of quartz and feldspar (<50%) with low percentage of matrix are widely occurred near bamer and bachoni villages (fig. 3b). the mylonitic foliation striking in e w to ene wsw directions is defined by preferred orientation of quartz and feldspar grains (10 mm to 3 cm) with flakes of mica exhibits steep (60° 70°) north dips (fig. 3c). the both dextral and sinistral movement observed in the rotated pophyroclasts. however, a prominent sinistral rotation indicating top to sw shearing movement is exhibited by most of the porphyroclasts of quartz and feldspar. the stretching lineation defined by parallel alignment of quartz feldspar and flakes of mica lies at 10 20° to the mylonitic foliation and at few places it is displaced by minor strike slip fault and conjugate quartz veins. bhatt, s.c. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 15 the sheared genesis having s c fabrics is marked by variation in obliquity between s and c planes. the first stage of evolution (berthe et al., 1979) of the s c planes is demonstrated by high degree angle (40 45°) and is remarkably noticed in the south of rajapur village (fig. 3d). it was observed that the major shear zone represented by existing mylonitic foliation (s planes) was truncated by secondary c bands (c planes). due to intensive effects of rotational stresses in high shear strain domains such s c mylonites were progressively developed in major to small scale shear zones (fig. 3d). passchier and trouw (2005) denoted such types of shear bands as c' type of shear band cleavage, which are lying at 15° 35° to main mylonitic foliation (passchier, 1991; blenkinsop and treloar, 1995). a transition zone between mylonite and fine grained ultramylonite was noticed in the southeast of rajapur village (fig. 3d). the width these ultramylonitic bands vary from few millimetres to several centimetres. the microstructural analysis reveals that the quartz and k feldspar are characterized by strong undulose extinction and dynamic recrystallisation (fig. 4a, b). the alteration effects (microclinisation) and twinning are observed in few phenocrysts of orthoclase and plagioclase respectively. the protomylonite dominantly consist large protoliths of quartz and feldspar (about 0.2 mm to 1.0 mm constitutes ~50%) with few recrystallised quartz grains and matrix (fig. 4a, c, d). the sinistrally rotated pressure shadows wrapped by flakes of mica mainly consists of recrystallised quartz grains in the tails (fig. 4a). a well developed planar fabric (mylonitic foliation) and stretching lineation are present in mylonite zone. the deformation lamellae are also observed within few k feldspar grains. the kinking and twining effects observed in few grains of plagioclase are indicative of low temperature and pressure conditions (300 400° c). the phenocrysts of quartz and feldspar were changed into elongated and ribbon shapes (aspect ratio 5:1 8:1) under intensive shearing and moderate to high shear strain conditions (fig. 4b), selected for kinematic shearing sense. the mantled porphyroclast of k feldspar consisting of fine grained mantle nucleus displays σ type of geometry (passchier and simpson, 1986). the σ type of porphyroclast exhibits the top to left (sinistral) sense of shear movement in mylonitised granite (fig. 4a, c). two types of σa and σb mantled porphyroclasts are found in few thin sections and are distinctly characterised by two planar and curve faces. σa mantled clast mainly isolated in a mylonitic matrix (fig. 4c) whereas the σb mantle clast is generally associated with s c fabrics (fig. 4d). the δ type mantled porphyroclast showing narrow wing and stepping are rarely noticed (fig. 4d). in few mantle σ porphyroclast microcracks and fracturing became prominent which led to produce bookshelf sliding structures (fig. 4c). the micro cracks and extensional fractures examined in few ribbons of quartz grains are indicative of overprinting of brittle deformation on ductile deformation (fig. 4b) and were developed under low grade temperature conditions (below 300° c). under such conditions the brittle fracturing, pressure solution and solution transfer processes became more pronounced and produced fractures, undulose extinction, deformation lamellae and kink bands in quartz and feldspar (fig. 4a, b, c; van daalen et al., 1999; stipp et al., 2002). figure 4: (a) σa mantled rotated porphyroclast of quartz (q) forming pressure shadow and exhibiting sinistral sense of shear movement; (b) ribbon of k feldspar showing displaced microcracks (r) and dynamic recrystallisation quartz (rq) in the marginal contacts; (c) σb mantled porphyroclast of k feldspar displaced by microfaults and exhibiting bookshelf structures; (d) k feldspar showing δ type mantled porphyroclast and deciphering sinistral sense of shear movement. 16 bhatt, s.c. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 5. discussion the bundelkhand craton occupies the major part of northern indian shield but its evolution in terms of crustal growth and tectonism is poorly understood (roday et al., 1993; bhatt, 2014, singh and slabunov, 2015a, 2016; slabunov et al., 2017a; slabunov and singh, 2017, 2018a). the geometrical and kinematic analysis of folds and asymmetrical structures preserved in deformed and sheared rocks of babina and mauranipur area, infer that the archean gneissic complex was characterised by three different sets of folding (f1 f3). the f2 and f3 (open to reclined) folds were displaced orthogonally by sheared planes in the later episode of shearing (bhatt and hussain; 2008, 2012; bhatt and mahmood; 2008, 2012; bhatt et al., 2011). the mesoscopic and microfabric analysis reveal that the crustal shear zones emplaced along central domains of bundelkhand craton were syn tectonically deformed during progressive shearing under low temperature pressure conditions in a brittle ductile environment. under low to moderate shear/ strain conditions, the protomylonite containing bigger porphyroclasts of quartz and feldspar were evolved and shows the higher percentage of (50 90%) of these relic fragments (passchier and trouw, 2005). the asymmetrical geometry of porphyroclasts (quartz and feldspar) and pressure shadows and angular relationship between s c fabrics imply that the mylonites were produced under the influence of non coaxial (simple shear) deformation in a ductile regime under low to medium temperature conditions. due to intensive deformation the elongated and ribbon shaped quartz and feldspar grains were developed under high strain conditions and noticed that the degree and intensity of deformation was consistently increased from margin to central part of the shear zone. the small scale minor faults were also developed in the later stage of deformation in cataclastic regime and under brittle conditions (fig. 3d). the sinistral movement of microfaults displayed by few phenocrysts of quartz and k feldspar were produced in brittle deformation under cataclastic regime (fig. 4b). the development of pressure shadow and elongated to ribbon fabrics was possibly controlled by pressure solution and dynamic recrystallization under moderate to high shear strain conditions. the undulose extinction, deformation lamellae, and dynamic recrystallisation characteristics of strain softening processes in plastic deformation of quartz grains in ductile and low to medium temperature conditions (pryer, 1993; ji, 1998a, 1998b; hippertt and hongen, 1998; passchier and trouw, 2005), evident in the bundelkhand craton. the crystal plastic deformation became dominant under moderate to high temperatures and led to initiate the dynamic recrystallisation and stretching of quartz and feldspar (pryer, 1993; stipp et al., 2002; passchier and trouw, 2005). the mylonitised rocks formed under the influence of low to medium shear strain and temperature conditions in a non coaxial flow at marginal contacts. the rotated porphyroclasts, s c fabrics and other asymmetrical structures dominantly exhibit sinistral toptosw shear movement. the presence of microcracks and minor faults are indicative of overprinting of brittle shearing on ductile shearing. the mineral assemblages and geometrical orientations in newly formed mylonites were changed due to excessive effects of simple shear (non coaxial deformation) and pressure solution. the geometry of c surface and extensional crenulation cleavage provide strong evidences for predominance of extensional tectonics in the development of ductile shear zones at late stages. the ductile shearing took place in the initial phase of deformation and subsequently followed by brittle shearing in late stages of deformation. the presence of σa mantled porphyroclasts in moderate to high strain shear zones infer that these fabrics were evolved under the influence of crystal plastic deformation (passchier and trouw, 2005). the twinning and kinking displayed by few grains of plagioclase imply that the mylonites were deformed in a specific crystal plastic deformation under lower temperature and pressure solution conditions (passchier and trouw, 2005). quartz forming the main constituents of matrix in mylonite has been excessively affected by grain size reduction in ductile regime. the most of phenocrysts of quartz and feldspar were subjected to strain hardening due to instant decrease in strain rate and enhancement of differential stresses. eventually the extensional cracks and brittle fractures were formed in cataclastic regime. the microfracturing, bookshelf structures, kinking examined in k feldspar and plagioclase are indicative low temperature and brittle deformation conditions. the back rotation of foliation between closely spaced shear planed are occurred due to progressive effects of shearing and eventually produced crenulation crinkles. the ubiquitous presence of mylonitic foliation, stretching lineation, asymmetrical rotated porphyroclasts, and s c fabrics imply that the brittle ductile to ductile crustal shear zones in the bundelkhand craton were evolved under the influence of moderate to high shear strain. due to lack of evidences, it would be difficult to differentiate between younger and older movement of these shear zones. the imprints of folding are not found in the rocks of the k rich granitoids while it formed in subduction environment, later it was followed by extensional tectonics during the synmagmatic granitic diapirism (neoarchean). the oldest gneisses of this craton associated to metabasic enclaves were subjected to earlier magmatism and metamorphic melting at ca. 3.3 3.2 ga. this event may be corresponding with the d1 phase of deformation in the present work. the major compressive tectonic phase (d2) responsible to generate three sets of folding (f1 f3) in basics, ttg gneisses, bif with metasedimentary rocks took place between ca. 3.2 to 2.7 ga. saha et al. (2011) pointed out that the babina greenstone rocks was record high presure at 18 20 kbar and ca. 630° c to lower metamorphic p t conditions of 11+3 kbar ca. 630° c at ca. 2.78 ga age. it may reveals that the neoarchean high pressure metamorphism in the craton be associated with d2 phase of tectonic compression. the 2.57 2.54 ga k bhatt, s.c. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 17 rich granitoid resemble with extensive magmatic phase (d3) of bundelkhand craton (singh et al., 2019b; slabunov and singh 2018a). the field setting and other signatures infer that the quartz reefs were exhumed from the intermediate to shallow depth crustal levels along ne sw trending shear zones. some mylonitised granitic rocks were also sinisterly displaced by ne sw oblique faults and may be formed due to emplacement of huge quartz reefs (endogenetic movement) in ductile to brittle environment. 6. conclusions based on above observations, the following conclusions can be drawn: i) the ttg gneisses, mafic and streaky gneisses along with amphibolite and schist were deformed and folded in two regional compressive tectonic phase (d1 d2). the main phase of granitic intrusion probably took place in d3 magmatic phase (2.57 to 2.5 ga) along major fractures and shear planes. ii) the subvertical e w trending raksa garhmau shear zone, is strike slip crustal shears, reveal sinistral top to sw (left lateral) shear movement and were evolved at intermediate to shallow depth within intracratonic domains of bundelkhand craton in late d3 phase. iii) the shear indicators infer that the mylonites were evolved under crystal plastic and strain softening processes in brittle ductile (non coaxial) environment under low to moderate temperature conditions. acknowledgements the department of science and technology (dst) govt. of india is thankfully acknowledged for providing financial support to scb under dcs (ess/16/255/2005) and to vks under dst rfbr (int/rus/rfbr/p-279), dstiltp (int-iltp/b-2.72) and dst (sr/s4/es-399/2008) sponsored projects. references basu, a.k., 1986, geology of parts of the bundelkhand granite massif central india. record geol. sur. of india 117, 61-124. berthe, d., choukroune, p., jegouzo, p., 1979. orthogenesis mylonite and non-coaxial deformation of granites: the example of the south armorican shear zone: j. of structural geology 1, 31-42. bhatt, s.c., 2014. geological and tectonic aspects of bundelkhand craton, central india. angel publication, bhagwati publishers and distributors c-8/77-b, keshav puram, new delhi, 190. bhatt, s.c., gupta, m.k., 2009. tectonic significance of shear indicators in the evolution of dinara-garhmau shear zone, bundelkhand massif, central india, in kumar, s., ed., magmatism tectonism and mineralization, macmillan publishers india ltd., new delhi, india, 122-132. bhatt, s.c., gupta, m.k., 2014. microstructural analysis and strain pattern in mylonites and implications of shear sense indicators in evolution of dinaragarhmau shear 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3053. pryer, l.l., 1993, microstructures in feldspar from a major crustal thrust zone: the grenvile front, ontario, canada: j. of structural geology 15, 21-36. ramsay, j.g., huber, m.i., 1987. the techniques of modern structural geology, v.2: folds and fractures, academic press, london, 309-700. rao, j.m., rao, g.v.s.p., widdowson, m., kelley, s.p., 2005. evolution of prtoerozoic mafic dyke swarms of the bundelkhand granite massif, central india: current science 88, 502-506. roday, p.p., diwan, p., pal, a., 1993. a two stage model for the development of karitoran/shear zones, lalitpur district, uttar pradesh, india: journal of the geological society of india 42, 481-492. saha, l., frei, d., gerdes, a., pati, j.k., sarkar, s., patole, v., bhandari, a., nasipuri, p., 2016. crustal geodynamics from the archaean bundelkhand craton, india: constraints from zircon u pb hf isotope studies. geol. mag. 153, 79 192. saha, l., pant, n.c., pati, j.k., upadhyay, d., berndt, j., bhattacharya, a., satynarayanan, m., 2011. neoarchean high-pressure margarite-phengitic muscovite-chlorite corona mantled corundum in quartz-free high-mg, al phlogopite chlorite schists from the bundelkhand craton, north central india. contributions to mineralogy and petrology 161, 511 530. sarkar, a., paul d.k., potts, p.j., 1996. geochronology and geochemistry of the mid archean, trondhjemitic gneisses from the bundelkhand craton, central india, in saha, a.k., ed., recent researches in geology 16, 76-92. senthiappan, m., 1993. geology of the area along the raksa shear zone jhansi district, u.p.: record geological survey of india 73, 73-76. simpson, c., schmid, s.m., 1983. an evaluation of criteria to deduce sense of movement in sheared rocks: bulletin geological society of america 94, 1281-1288. singh, p.k., verma, s.k., moreno, j.a., singh, v.k., malviya, p.k., oliveira, e.p., mishra, s., arima, m., 2019a. geochemistry and smnd isotope systematics of metabasalts from the babina and mauranipur greenstone belts, bundelkhand craton: implications for tectonic setting and paleoarchean mantle evolution. lithos 330 331, 90 107. singh, p.k., verma, s.k., singh, v.k., moreno, j.a., oliveira, e.p., mehta, p. 2019b. geochemistry and petrogenesis of sanukitoids and high-k anatectic granites from the bundelkhand craton: implications for the late-archean crustal evolution. j. of asian earth sciences, 174c, 263 282, https://doi.org/10.1016/j.jseaes.2018.12.013 singh, v.k., slabunov, a., 2013. the greenstone belts of the bundelkhand craton, central india: new geochronological data and geodynamic setting, in singh, v.k., and chandra, r., eds., international association for gondwana research conference series no. 16, 3rd international conference precambrian continental growth and tectonism, jhansi, india, 170-171. singh, v.k., slabunov, a., 2015a. the central bundelkhand archaean greenstone complex, bundelkhand craton, central india: geology, composition, and geochronology of supracrustal rocks. international geology review 57(11-12), 1349-1364. singh, v.k., slabunov, a., 2015b. geochemical characteristics of banded iron formation and metavolcanics from babina greenstone belt of the bundelkhand craton, central india. j. of economic geol. and georesource manage. 10, 63-74. singh, v.k., slabunov, a., 2016. two types of archaean supracrustal belts in the bundelkhand craton, india: geology, geochemistry, age and implication for craton crustal evolution. journal of the geological society of india 88, 539-548. slabunov, a., singh, v.k., 2017. central bundelkhand greenstone complex of the bundelkhand craton, india: new geochronological data, a geodynamic setting and the position of the craton in the kenorland supercontinent structure. in: slabunov, a.i., svetov, s.a., baltibaev, sh.k. (eds.): early precambrian vs modern geodynamics. extended abstracts and field trips guide. petrozavodsk: karrc ras, 239-241. slabunov, a.i., singh, v.k., 2018a. meso neoarchaean crustal evolution of the bundelkhand craton, indian shield: new data from greenstone belts. international geology review, https://doi.org/10.1080/00206814.2018.1512906 slabunov, a.i., singh, v.k., 2018b. bundelkhand and dharwar cratons (indian shield): comparison of crustal evolution in archean time. archaeology & anthropology: open access, 3 (suppl-2), 42 48. slabunov, a., singh, v.k., joshi, k.b., li, x., 2017a. paleoarchean zircons from quartzite of south bundelkhand supracrustal complex: origin and implications for crustal evolution in bundelkhand craton, central india. current sci. 112, 794-801. slabunov, a.i., singh, v.k., shchiptsov, v.v., lepekhina e. n., kevlich v.i., 2017b. a new paleoproterozoic (1.9-1.8 ga) event in the crustal evolution of the bundelkhand craton, india: the results of (shrimp) dating of zircons from giant quartz veins. in: slabunov, a.i., svetov, s.a., and baltibaev, sh.k. (eds.), early precambrian vs modern geodynamics. extended abstracts and field trips guide. petrozavodsk: karrc ras, 239-241. stipp, m., stünitz, h., heilbronner, r., schmid, s.m., 2002. the eastern tonale deformation of quartz over a temperature range from 250 to 700°c: journal of structural geology 24, 1861-1884. van daalen, m., heilbronner, r., kunze, k., 1999. orientation analysis of localized shear deformation in quartz fibers at the brittle-ductile transition: tectonophysics 303, 83-107. verma, s.k., verma, s.p., oliveira, e.p., singh, v.k., more, j.a., 2016. la-sf-icp-ms zircon u pb geochronology of granitic rocks from the central bundelkhand greenstone complex, bundelkhand craton, india: j. of asian earth sciences 118, 125 137. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geological setting 2.1 raksa–garhmau sector 3. deformation pattern and relationship with shearing 4. shear zones and shear indicators 4.1. raksa–garhmau shear zone 5. discussion 6. conclusions acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology special vol 04 no 02-2 2019 singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 43 special volume new observations of tin mineralization potential vis-à-vis ore petrographic, alteration and geochemistry in the southeastern part of bastar craton, central india abhimanyu singh 1 , vinod k. singh 2 * 1 institute of environment and development studies, bundelkhand university jhansi284 128, india 2 department of geology, bundelkhand university jhansi284 128, india * corresponding author : vinodksingh@bujhansi.ac.in tel.:+91-9415258237; fax: +91-5102321667 received: sept 22, 2018; accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2144 abstract the tin mineralizations occur around the katekalyan area, hosted in the acid magmatic rocks. the evolution differentiating granitic magma shows residual melt enrichment where end products intruded as pegmatites into the rocks. the different kind of pegmatite occur as simple unzoned, recrystallized (granitic pegmatite), and metasomatic greisenised and albitised pegmatites which emplaced within the pre-existing rocks of metabasic intrusive, granite (kg), granite gneiss (kgg). sometimes it also found in metasediments as mineralised and non-mineralised characters along the fractures and foliation planes trending n-s, e-w and more frequently are observed nnw-sse trends. cassiterite is most important tin-ore mineral and associated with pegmatites. some cassiterite samples exhibit colourless to brown shades zoning which indicate multi stage growth. the cassiterite samples contain significant amounts of sn, nb, ta with minor w. the partial melting model shows that the variation 5 to 50% partial melting of bulk continental crust for kg as well as kgg rocks but bulk distribution coefficient for sr (dsr) shows low i.e. <<10. the upper limit of partial melting of bulk crust estimates ~50 % for kg and kgg rocks are consistent with required rheological, critical melt percentage to leave the source region has decreased granite melt which were capable to mineralised tin ore elements. it is interesting to note that the snf4 and sncl4 probably not stable in presence of water under geologically reasonable conditions. keywords: tin-mineralisation, cassiterite, katekalyan, bastar craton, central india 1. introduction ore petrography is studied on polished ore section which is always difficulties mainly due to their hardness, variation in mineral and ore composition. the bastar area is known for a potential zone of metallic and nonmetallic deposits. previous workers have taken special attention to deposits in different part of the craton special references to the kondagaon and bhopalpatnam areas (mishra et al., 1984, 1988), sukmakonta-dantewada area (ramakrishanan, 1990). the detailed geological, structural and petrological works in bastar craton have carried out by babu (1983) and ramesh babu et al. (1984, 1993). singh and singh (2011) stated that tin-bearing granitoids of the acid magmatic rocks namely biotite granite (kbg), tourmaline granite (ktg), hornblende granite (khg) and also granite gneiss (kgg) have special significance to their possible mineralization episode of the katekalyan area, bastar craton. the authors have selected opaque sections studies with suitable sized ore samples, and put to coarsegrinding on steel plate using 200-400 and 600-mesh carborandum powder followed by fine grinding in similar way on glass plate using 800-mesh powder. in the next stage some finer grinding was done by dry method, using 2/0, 3/0, 4/0 and 5/0 emery polishing papers. after this, the specimens were subjected to polishing by chrome oxide powder followed by alumina or synthetic diamond paste for about 3 hours. the precautionary measures were strictly taken in such cases during alumina or diamond polishing was done very slowly but with uniform light pressure. therefore, integrated approach as ore petrographic, alteration and geochemistry used to determination of tin mineralization in south-eastern part of bastar craton, central india. 2. geological setting in peninsular india, the se-part of the bastar craton surrounded by the eastern ghat granulites on the east, bailadilla iron ore group of rocks to the west, high grade metamorphics of sukma group in the south (fig. 1). the volcano-metasediments rocks occur in studied area belong to bengpal group (babu, 1983). narainpur, indravati http://journal.uir.ac.id/index.php/jgeet 44 singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 and sabri group of rocks occurring as isolated basins of sediments unconformable are overlying the igneous complex (fig. 1). the regional geological map with radiometric age data of the tin mineralized belt in parts of bastar craton is given in fig. 1 from published literature. the bengpal metasediments found as enclaves in the basement gneisses and migmatitic rocks whereas the granites occur as discrete unites within the gneisses association with the supracrustal rocks. the gneissicmigmatite complex constiuting more than 65% of the bengpal metamorphites and is similar to the peninsular gneissic complex of south india. the katekalyan area consists of andalusite sericite schist, quartz-sericite schist, banded magnetite quartzite, grunerite-magnetite quartzite, metabasic intrusive and metabasic extrusive rocks (singh et al., 2011). the nnw-sse trends with steep northerly dipping granite show gneissosity characteristics in the area. three phases of deformation related to granitic activity have been noticed (murthy et al., 1982). the first phase f1 is along ene-wsw to e-w followed by f2 along nne-ssw to nw-se and the last f3 along n-s to nne-sse. the granitoids (kg and kgg) have been subjected to subsequent pneumatolytic and hydrothermal alteration viz; microclinisation, albitisation, greisenisation and sericitisation are more prominent. fig. 1. location map of the study area and regional geological map with radiometric dates (billions of years) of the primary tin mineralised belt in the southeastern part of bastar craton, central india. (a): sukma supracrustal suite, (b): bengpal metasediments, (c): metabasic intrusives, (d): stanniferous granite complex, (e): mineralised pegmatites, (f): silicified shear zone. locality: 1. metapal 2. katekalyan 3. kopanar 4. kondaras dongri 5. pinjupara 6.parcheli 7. koapal 8.bothapara 9. marjun 10. tongpal 11. chidpal 12. chuirwada 1 3. bedanpal 14. bodawada 15. govindpal 16. kudripal 17. jongarpal 18. mundwal 19. pushpal 20. kikripal 21. bondey 22. mundaguda. 3. mineralisation potential of the area the tin mineralizations occur around the katekalyan area, hosted in the acid magmatic rocks. the evolution differentiating granitic magma shows residual melt enrichment where end products intruded as pegmatites into the rocks. the cassiterite is mainly associated with columbite, tantalite, lepidolite, beryl and fluorite which may point out that niobium, tantalum, lithium, beryllium, fluorine and rare earths were intimately involved in the transportation of tin from magmatic to pneumatolytic stage. the younger intrusive type of coarse-grained non-foliated porphyritic biotite granite characteristics of third type phase of tin-bearing pegmatites, which occurring in the pre-existing granitic gneiss. the biotite granite at singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 45 lokharas area is soda-rich (fine-grained aplitic nature) concentrated 50 ppm sn whereas the porphyritic leucogranite having 100 ppm of sn near katekalyan village which indicates that stanniferous nature of the granite (murthy et al., 1982). occurrence of discrete cassiterite crystals especially in the unzoned pegmatites can be related to the pegmatitic phase of acid magmatism. the enriched tin-bearing pegmatites occur in meta-basic rocks. however, for the first time pegmatite with discrete crystals of cassiterite have been found emplaced within granite at kondaras dongri and benglur areas. in the greisenised pockets portion of the pegmatites where the tourmaline (boron-metasomatism), fluorite and rare minerals of niobium and tantalum generally associated with cassiterite bearing pegmatites. the post-magmatic metasomatic process form pegmatites due to actions of chemically active aqueous solutions and volatiles, where the tin has been fixed in the lattice of rock forming minerals subsequently remobilized and reconcentrated for tin ore mineralisation. 4. microscopic observations optical characters of the ore minerals in the polished ore sections were studied with the help of a polarising ore microscope (carl zeiss, jena, the then g.d.r.) and consulted standard work of ramdohr (1969). the preliminary observations of the ore samples reveal that cassiterite was the most abundant tin ore mineral in katekalyan area. the other associated ore minerals like columbite, tantalite, tapiolite, microlite and wolframite were also identified in small amount. limonite (mainly goethite) was the common secondary ore mineral, and was recognised as the alteration products. the gangue minerals associated with the ore are quartz, fluorite, zinnwaldite and k-feldspar. the texture and structure of the ore and their petrography distinguish it into two main classes, namely primary and secondary ore minerals with the salient features are given below. 4.1 primary ore minerals 4.1.1 cassiterite (sno 2 , tetragonal): cassiterite is most important ore mineral associated with pegmatites in the studied area which occurs as coarse disseminated grains with euhedral to subhedral shape, bypyramidal form and massive in nature. the mineral is dark gray to black in colour with grayish to brown streak and greasy to admantine lustre. it shows brownish grey to light grey in colour and have pitted (poor polishing) to non-pitted surface in reflected light. the internal reflection colour (fig. 2a) shows distinct anisotropism from light grey to dark grey and a brick red to yellow pale brown due to its numerous inclusions and impurities to its high tantalum and iron content in the lattices. twinning was noted as common feature in many sections but zoning was not distinct, may be because of the strong internal reflection. cassiterite is easily distinguished from columbite-tantalite by its micro-hardness, poorly polished sections, cracks and crevices and low reflectivity (brownish gray). in polished sections of cassiterite, two sets of very feeble cleavage traces have been observed only under cross-nicols (fig. 2a). exsolution texture among cassiterite, columbite-tantalite and tapiolite is a common phenomenon and helpful in the understanding the genesis of mineralisation. the intensity of the colour of cassiterite is lower than that of associated columbite-tantalite. few cassiterite samples exhibit zoning from colourless to brown shades (fig. 2a) indication of multi stage growth. the colourless zone is free from any inclusion whereas the reddish brown and brownish red shade zone contains numerous inclusions possibly of ta-w-bearing phases. the paragenetic relationship suggest that the bright coloured (unzoned/inclusion free part) that is ta-free cassiterites were crystallised first which is followed by the dark crystallization of coloured ta-sn rich zones during the lowering of temperature. the coarse grains of cassiterite are usually fractured which are filled by the quartz and columbite-tantalite minerals (fig. 2b). 4.1.2 columbite-tantalite {(fe, mn) (ta, nb) 2 o 6 , orthorhombic} : columbite-tantalite is usually present in minor quantities, as inclusions in cassiterite but occasionally it occurs as separate mineral. the exsolved grains of columbite-tantalite (fig. 2c) are irregular in shape and vary in size from small globules to large lamellar grains. the larger grains of columbite-tantalite are definitely the product of normal intergrowth. the columbite-tantalite minerals show moderate reflectivity (whitish grey) than that of cassiterite, and weak but distinct pleochroism. columbite/tantalite shows very weak anisotropism and straight extinction. the columbite-tantalite has the solid solution series between columbite (femn)nb 2 o 6 and tantalite(fe,mn)ta 2 o 6 (babu,1993) and similar view interpret for cassiterite in katekalyan area. 4.1.3 tapiolite [(fe, mn) (ta, nb) 2 o 6 − tetragonal] : the tapiolite mineral occur in minor amount, usually associated with cassiterite, showing similar physical properties and makes it difficult to distinguish in the field. tapiolite mostly occurs as very small grains, bluish grey in colour with brownish tint and characteristics of low reflectivity (fig. 2d). the tapiolite, ore petrography is characterized by weak reflection pleochroism (but very distinct in oil). it shows strong anisotropism but generally it is masked by its internal reflection. however, cassiterite distinguished in better polishing, due to its slightly higher reflectivity, lower micro-hardness and moderate anisotropism (fig. 2e). in general, the paragenetic relation of tapiolite mineral associated with other ores indicates that it has intergrowth with cassiterite or as replacement type texture with the original tin mineral, whereas very rare textural relationship with columbite-tantalite mineral. 46 singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 4.1.4 microlite [(cana) 2 (ta 2 o 6 ) (o, oh, f) − isometric]: the microlites occur at peripheral part of the columbite-tantalite and might be of the later phase. the microlite (white internal reflection) noticed in the form of irregular, disconnected and randomly oriented patches (fig. 2f). 4.1.5 wolframite [(fe,mn)wo 4 − monoclinic] : the tungsten mineral found as inclusions in cassiterite, columbite-tantalite and rarely in tapiolite. it has moderate reflectivity and similar to columbite-tantalite. the wolframite mineral, more grayish white distinguished from whitish gray of columbite-tantalite (fig. 2c). moreover, it is having much deeper red internal reflection and sometimes the bladed form with slanting terminations properties distinguished from other opaques. reflection pleochroism is quite low and can be seen along grain boundaries. the textural study points the presence of tiny inclusions, which suggest that it may be related with early paragenetic sequence than cassiterite. 4.2 secondary mineral goethite is noticed as intergrowth in many samples of cassiterite and other minerals like columbite-tantalite and tapiolite. the fine veins and veinlets of goethite (fig. 2e), were noticed randomly with tin ore and show grayish reflection colour in reflected light. it also show dull gray to bright gray with a bluish tint variation. the dull gray colour reflection, suggest the iron hydroxide is not fully crystalline. 4.3 alteration environment the cassiterite mineral is mainly associated with pegmatites in the later phase of granitic rocks in the bastar craton. the cassiterite associated with other metasomatic alteration minerals encountered by the exchange and receives elements from the wall rocks with combined effects of pneumatolytic gases and some aqueous mineralised solutions, which existing the halogen elements, water phosphorus and a few alkali metals. the different metasomatic activities which leads to the formation of rare metal mineralisation in the craton, reveal four distinct zones of formation of cassiterite along with nb and ta mineral compositions, viz, microclinisation (potash-metasomatism), albitisation (soda-metasomatism), greisenisation (pneumatolytic activity) and sericitisation, on the basis of field evidences, petrographic and geochemical studies in the katekalyan granites and pegmatites. source of the alteration solutions is highly debated. the apical zones of tin-bearing granitoids are sites of intense and complex metasomatic activity with the transportation of tin ions leading to the formation of discrete crystals of cassiterite. the albitised pegmatites can be identified by their monomineralic nature, predominant of plagioclase feldspars and sub-ordinate quartz and incipient mica. the feldspar is mostly albite or cleavelandite variety, which were formed by the replacement of microcline indicating the prevalence of albite due to the soda metasomatism. the phenomenon of albite enrichment is accompanied by the presence of disseminated cassiterite rich with minor columbite and tantalite minerals. greisenisation is represented by the decomposition of feldspars and biotite and by the formation of quartz, mica, topaz and ore minerals in the granite and pegmatite. the oh, f, li, sn, w, b introduce and the removal alkalies (especially na, less pronounced k) are the most significant, while si, al remains essentially constant. greisenised pegmatites constituting mainly of quartz and muscovite intercalations with lepidolite, associated with cassiterite, beryl, tourmaline were formed mainly due to the actions of pneumatolytic activity in the marginal areas of the pegmatites. muscovitisation of kfeldspar is more intense than plagioclase feldspar due to volatile rich fluid activities. highly sericitisation of feldspar were observed due to metasomatic hydrothermal fluid activity in the pegmatites. tourmalisation is also intense at the contact of granites and quartz veins. wall rocks are composed of tourmaline, muscovite, chlorite, apatite, fluorite and opaque minerals. the mineralisation is associated with wall rock alteration where the intensity of alteration is directly proportional to the degree of mineralisation in the katekalyan area. 5. geochemistry of cassiterite eight representative samples of cassiterite have been analysed. three samples were taken from placer deposits and five samples were selected from mineralized pegmatite zone of the different localities. the analytical data are given in table 1. the element analyses of cassiterite (table 1) indicated the admixture of tin as major constituent with subordinate quantities of niobium, tantalum, tungsten, iron, manganese and other trace elements. tin (sn) content in the cassiterite ranges from 56.57 to 71.84% indicating that basically 70 to 90% is as sno 2 mineral phase. the niobium metal content ranges from 0.52 to 0.97% whereas tantalum varies from 1.87 to 2.29%. the concentration of tantalum is more than that of niobium content. thus, on the whole tin, niobium and tantalum concentration constitute more or less 80%. the wo 3 varying from 1.83 to 2.58%, feo (t) ranges from 0.01 to 11.58%; mno content varying from 2.09 to 7.22%; mgo ranges from 1.99 to 3.79%; tio 2 varying from 0.07 to 0.45% and cao ranges from 1.16 to 3.98%. trace elements like ni, ga and rb are present as low in content. hence, it is evident that a number of metallic cations are known to enter into the solid solution in cassiterite. it is presumed that the presence of nb, ta and w will have no effect on the cell dimension of the cassiterite. singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 47 fig. 2: shows photomicrographs of ore minerals (a): cassiterite mineral shows two sets of very feeble cleavage traces. in the other portions, microlite shows white internal reflection whereas tapiolite gives reddish internal reflection (reflected light, 1.6  0.32  4; crossed); (b): columbite-tantalite (whitish gray) is present in the highly fractured cassiterite crystal and also observed the veinlets of cassiterite (brownish gray) and quartz (dark gray) (reflected light, 10  7; uncrossed); (c): intergrowth of pitted cassiterite and columbite-tantalite (whitish gray) and the wolframite (grayish white) is present at the contact of cassiterite (reflected light, 10  7; uncrossed); (d): exsolution texture among cassiterite (brownish gray), columbite-tantalite (white) and tapiolite (brown gray) within the mass of cassiterite (light gray) (reflected light, 10  7; uncrossed); (e): cassiterite (dark) is showing intergrowth with tapiolite (bright) present as twin lamellae and at the sides of this intergrowth, columbite-tantalite (yellowish cream) appears to replace it and also show the presence of goethite (reflected light, 10  7; uncrossed); (f): cassiterite (brownish gray) shows the inclusions of columbite-tantalite (whitish gray) and also microlite (white internal reflection) in the form of irregular, disconnected and randomly oriented patches, (reflected light, 10  7; uncrossed). table 1: element analyses of cassiterite from katekalyan area, bastar craton, india. sample no. r89/517 r89/612 r89/790 r89/830 r89/915 r89/1305 r89/1399 r89/1405 average ref./ spot no. cf/1210 cf/1220 cf/1230 cf/1240 cf/1250 cp/5 cp/99 cp/105 sn (%) 56.57 61.98 60.12 71.84 70.76 63.68 69.78 62.34 64.63 nb (%) 0.97 0.52 0.89 0.76 0.96 0.79 0.84 0.75 0.81 ta (%) 2.11 2.29 2.18 1.99 1.87 2.16 2.05 1.89 2.07 wo 3 (%) 2.54 2.48 1.83 2.38 2.46 1.95 2.58 2.19 2.30 feo t (%) 11.58 11.49 10.99 11.38 11.27 na 0.01 0.13 8.12 mno (%) 7.22 5.86 6.78 7.17 6.86 2.16 2.09 2.38 5.06 mgo (%) 2.13 2.34 2.09 1.99 2.19 3.79 3.69 3.56 2.72 tio 2 (%) 0.11 0.09 0.14 0.18 0.07 0.45 0.39 0.41 0.23 cao (%) 1.39 1.28 1.43 1.32 1.16 3.98 3.76 3.57 2.24 ni (ppm) 16.00 14.00 18.00 13.00 17.00 16.00 15.00 17.00 15.75 ga (ppm) 42.00 40.00 43.00 41.00 41.00 94.00 89.00 95.00 60.62 rb (ppm) 53.00 51.00 51.00 54.00 49.00 52.00 51.00 48.00 51.12 niobium (nb) and tantalum (ta) are characteristically oxyphile forming a number of complex minerals. they enter isomorphously into minerals of iron, manganese, titanium, tin, tungsten, uranium, thorium and rare earth 48 singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 elements. niobium (nb) indicates close relationship with titanium, tungsten, thorium and the rare earths of cerium group. however, tantalum (ta) correlates with zirconium, tin, the rare earths of yttrium group, uranium and lithium. mineral occurring in sodic alkali granites and syenites are generally niobium rich, whereas those in lithium pegmatites are tantalum rich (ginzburg, 1972). the high content of mn and ti corroborate the presence of mangano-ilmenite minerals. 6. discussion the geochemical data of granitoids of studied area were plotted on ternary diagram which falls in the bearing of tin field (fig. 3; singh and singh 2011). there is no definite relationship observed among the variation of tin with other major oxides. several lines of field, petrographic analysis and bulk geochemistry of kg, kgg and pegmatites (kp) reveal that stanniferous peraluminous kg and kgg granitic melt originated from the crustal anatexis i.e. partial melting of crustal source. fig. 3: ternary diagram sio2-(feo* + mgo + cao) (al2o3 + na2o + k2o) of the tin bearing granitoids (a) and pegmatites (b) of the katekalyan area, district dantewada, chhattisgarh (stemprok and sulcek, 1969). the microclinisation process show the enrichment of k 2 o at the expense of na 2 o and change in petrochemical composition, where plagioclase is replaced by the microcline in the granitic rocks. albitisation seems more frequent than microclinisation and may be accompanied by lithium enrichment. the partial melting model given in figure 4 and this shows that the variation of kg as well as kgg can be explained by varying degree of partial melting (5 to 50%) of bulk continental crust but distribution coefficient for sr (dsr) must be very low i.e. <<10. the anorthite content of feldspar is very sensitive to determine the distribution coefficient of sr, therefore, a small changing dsr will shift the vertical trend of partial melting of source towards higher or lower sides of sr content. the result of partial melting modeling at least suggests that the differentiation of kg and kgg melt are more governed by partial melting of bulk crust rather than fractional crystallization. the estimates upper limit of partial melting i.e., 50 % of bulk crust noted for kg and kgg are consistent with required rheological, critical melt percentage to leave the source region has decreased granite melt which were capable to mineralised tin ore elements. singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 49 fig. 4: partial melting models (1 and 2) of bulk crust composition (sr = 260 ppm, rb = 32 ppm) of taylor and mc lennan (1985) calculated at dsr = 20 and dsr = 10 respectively as shown by gasparon et al. (1993) and compared with the variation of kg and kgg, approximately by 5-50% melting of average crust silicate. dsr<<10. see text for discussion. winchester and max (1983) have used the trace element parameters viz., rb/sr vs sn (fig. 5a) and tio2 vs sn (fig. 5b) as originally proposed by lehman (1982), which discriminate sn-rich and sn-poor compositional trends from the greenville granite gneiss. the granite (kg) and granite gneiss (kgg) both follow sn-enriched trend (fig. 5). this feature of tin enrichment trend may probably indicate that generation of kg melt by melting of kgg protolith and further enriched in the late stage fractionation of kg, because the later is relatively richer in tin content compared to the former one. fig. 5: rb/sr vs sn (a) and tio2 vs sn (b) variation diagrams (after lehmann, 1982; winchester and max, 1983) contrasting sn-rich and sn-poor trends. note that kg (kbg and khg) and kgg mostly coincides with sn rich trends. the broken line separates the sn-poor and snrich fields. 7. conclusions the tin (sn) content in kbg (av. 76.55 ppm) is found more than the saturation level of 50 ppm, comparison to kgg (av. 16.14 ppm) might be due to the effect of post-magmatic and late metasomatic processes. the partial melting modeling at least suggests that the differentiation of kg and kgg melt is more governed by partial melting of bulk crust rather than fractional crystallization. the association of cassiterite, lithium mica (lepidolite) and fluorite in the pegmatites may be possible that the tin transported in the gaseous stage as snf4 or sncl4. the apical zones of tin-bearing granitoids are sites of intense and more complex metasomatic activity with the transportation of tin ions leading to the formation of discrete crystals of cassiterite. acknowledgements as is thankful to the director of wadia institute of himalayan geology, dehradun (u.k.) for providing lab facility. references babu, t.m., 1983. different phases of tin, niobium and tantalum mineralization in bastar district, m.p. workshop of mineralisation associated with acid magmatism, igcp-26 [mawam] under iugs, unesco, geol. surv. india, spl. publ. no. 13, 77-80. babu, t.m., 1993. comparative studies of tin fertile granitic rocks in space and time. resource geology 43, 355 363. gasparon, m., inuocentri, f., hanneti, p., peccerillo, a., tsegaye, a., 1993. genesis of the pliocene to recent biomodal mafic felsic volcanism in the debrezeyt area, central ethiopia: vocanological and geochemical constraints. jour. african. earth sci. 17, 145-165. ginzburg, a.i., ovchinnikov, l.n., solodov, n.a., 1972. genetic types of tantalum ore deposits and their economic importance. international geology review 14, 665-673. lehmann, b., 1982. metallogeny of tin: magmatic differentiation versus geochemical heritage. econ. geol., v., 77, 50-59. 50 singh, a. & singh, v.k./ jgeet sp vol 04 no 02-2/2019 mishra v.p., dutta n.k., kanchan v.k., vatsa u.s., guha k., 1984. archaean granulite and granite gneiss complexes of kondagaon area, bastar district, m.p. rec. geol. surv. ind., vol. 113, 150-158. mishra, v.p., singh, p., dutta, n.k., 1988. stratigraphy, structure and metamorphic history of bastar craton, rec. geol. surv. ind., vol. 117, pts. 3 to 9, 1-26. murthy, k.s., jaiswar, h.p., jesani, r.s., 1982. geology in relation to tin mineralisation in bastar district, m.p. presented at the workshop on mineralisation associated with acid magmatism, nagpur, geol. surv. india. spl. publ., no. 13, 61-70. ramakrishnan, m., 1990. crustal development in southern bastar, central indian craton, geol. surv. ind. spl. publ., no. 28, 4446. ramdohr, p., 1969. ramesh babu, p.v., dwivedi, k.k., jayaram, k.m.v., 1984. geochemistry of tin-rich granites of paliam & darba, bastar, m.p. proc. fifth ind. geol. congress, bombay, pp. 313-319. ramesh babu, p.v., pandey, b.k., dhana raju, r., 1993. rb-sr ages on the granite and pegmatitic minerals from bastar-koraput pegmatite belt, m.p. and orissa, india. jour. geol. soc. india 42, 33-38. singh, a., singh, v.k., 2011, petrogenetic history and geochemistry of the tin-bearing granitoids of the southern bastar craton, india. in: (eds: singh, v.k. and chandra, r.) 2 nd proc. of precambrian continental growth and tectonism, angel publiation, new delhi, pp. 111-124. singh, a., singh, v.k., singh, r.a., 2011. petrographical studies vis-a-vis tin-bearing granitoids, southern bastar craton, india. in: (eds: singh, v.k. and chandra, r.) 2 nd proc. of precambrian continental growth and tectonism, angel publiation, new delhi, pp. 103-110. stemprok, m., sulcek, z., 1969. geochemical profile through an ore bearing lithium granite. economic geology 64, 392-404. taylor, s.r. and mclennan, s.m. 1985. the continental crust: its composition and evolution. blackwell, oxford, 295 p. winchester, j. a., max, m. d., 1983. a note on the occurrence of stanniferous granite gneiss in county mayo. geol. surv. ire. bull. 3, 113-119. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geological setting 3. mineralisation potential of the area 4. microscopic observations 4.1 primary ore minerals 4.1.1 cassiterite (sno2, tetragonal): 4.1.2 columbite-tantalite {(fe, mn) (ta, nb)2o6, orthorhombic} : 4.1.3 tapiolite [(fe, mn) (ta, nb)2o6 ( tetragonal] : 4.1.4 microlite [(cana)2 (ta2o6) (o, oh, f) ( isometric]: 4.1.5 wolframite [(fe,mn)wo4 ( monoclinic] : 4.2 secondary mineral 4.3 alteration environment 5. geochemistry of cassiterite 6. discussion 7. conclusions acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 suryadi a./ jgeet vol 1 no 1/2016 1 fault analysis to determine deformation history of kubang pasu formation at south of unimap stadium hill, ulu pauh, perlis, malaysia adi suryadi 1, * 1 geological engineering program, faculty of engineering, islamic university of riau pekanbaru, riau * corresponding author : adisuryadi@eng.uir.ac.id tel.:+6282283896947 received: oct 1, 2016. revised : 15 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi: 10.24273/jgeet.2016.11.1 abstract the kubang pasu formation at south of unimap stadium hill has suffered deformation that produced fault with various types and orientations. first deformation (st1) is southeast northwest were resulted normal, reverse, dextral and sinistral fault. at station 32, reverse fault (n94 0 e/48 0 ) from st1 was cut by reverse fault (n48 0 e/40 0 ) result of second deformation (st2). another cross cutting fault found at station 108, third deformation (st3) with stress direction from northeast southwest that produced reverse fault with strike direction n134 0 e and 68 0 of dip angle was cutting the reverse fault (n87 0 e/66 0 ) from second deformation. the youngest deformation (st4) has stress from east west. at station 110, normal fault (n90 0 e/30 0 ) is representing the youngest deformation was cutting the reverse fault (n154 0 e/52 0 ) from third deformation. keywords: deformation, reverse fault, normal fault, dextral fault, sinistral fault, cross cutting. 1. introduction the study area is located at bukit stadium of is bounded by latitude 06 0 28.246' n to 06 0 28.273' n and longitude 100 0 20.923'e to 100 0 (figure 1). the outcrop is hill-cut at south of bukit stadium with extensive approximately 320 m 2 . this area was mapped as kubang pasu formation that consist of clastic sedimentary rock (gobbet, 1973 and jones, 1981). history of deformation can be determined by observation of tectonic structure. study about tectonic structure was carried by zaiton harun et al. (1999), gobbet (1973), and abdul hadi et al. (1999) at kubang pasu formation. relationship between structures can be used to determine the relative age of deformation. cross cutting law is one of many methods to determine the relative age. fig 1. map of the study area 2. general geology and stratigraphy based on geological map of peninsular malaysia show that study area is located at kubang pasu formation. the kubang pasu formation is exposed well at north and center of perlis and extended to north of kedah (basir jasin et al., 2003). kubang pasu and singa formation at north of peninsular malaysia is same age, the typical characteristic of kubang pasu is consist of thick quartz sandstone and interbedded with mudstone (gobbet, 1973). thickness of kubang pasu formation is more than 1500 m that consist of sandstone and mudstone (foo, 1983). at bukit temiang, there are passage beds from clastic rock of kubang pasu formation become limestone of chuping formation. hassan and lee (2002) said, sometimes there are pebble and cobble at mudstone and shale layers. the age of kubang pasu formation is determined by fossil that found. trilobite cyrtosymbole (waribole) was found at red and grey shale at gunung hutan aji together with bellerophontide, pelecypode, bacutalitide, brakiopode and crinoid stem. all those fossil represent at late devonian till early carbon (kobayashi and hamada, 1973). complete sequence of kubang pasu formation exposed at ex-quarry ladang cheong chong kaw, south of kampong panchor and at kampong belukar. bottom part of this formation consist of dark mudstone and dark grey of chert. these layer overlay by interbedded of thin sandstone and thick mudstone. interbedded of sand stone and mudstone with same thickness is the upper part of kubang 2 suryadi a./ jgeet vol 1 no 1/2016 pasu formation (zaiton harun and basir jasin, 1999). at kaki bukit and gunung hutan aji, lower paleozoic unit (setul formation) and upper paleozoic unit (kubang pasu formation) is exposed adjacent. there is no clear evidence that show unconformity between paleozoic unit and devonian unit. lithostratigraphy of study area are divided into the facies association, they are interbedded of sandstone which is the bottommost sequence, followed by fossiliferous thick mudstone and massive sandstone at the uppermost of the sequence. 3. structure of study area north part of peninsular malaysia is associated with bok bak mega fault. bok bak fault at bukit jabi was discussed by zaiton harun and basir jasin (1999), mahang formation overlay the kubang pasu formation that younger than it. the boundary between those formations is a milonite zone result of thrust fault caused by bok bak fault. structure geology of study area is show at figure 2. the bedding in this area has two dominants direction that are east west and northeast southwest. the dip ranging from 10 0 80 0 toward south and southeast. furthermore, the dominant structure in the study area is fault. the fault identified in the field are reverse fault, normal fault, sninstral fault and dextral fault. the fault can be identified by presence of mylonite, fault breccias, slickenside, and displacement figure 3. fig 2. geological structure map of study area fig 3. indication of fault; a. slickenside; b. fault breccia; c. displacement; d. mylonite 3.1 reverse fault 34 strike and dip data of reverse fault was taken from the field. all the data plotted to sterionet to get the major reverse fault and the result shown that there are 4 major reverse faults named as ss1, ss2, ss3 and ss4 (figure 4). all those faults interpreted as pure reverse fault. besides that, also there is reverse sinistral fault with pitch toward n76 0 e named as ssg. result of reverse fault analysis represent at table 1. the result show that there are 4 main stress (compressional stress) which are east-west (ss1 and ss4), southeast-northwest (ss2), north-south (ss3) and northeast-southwest (ssg). a b c d suryadi a./ jgeet vol 1 no 1/2016 3 fig 4. sterionet analysis of reverse fault table 1. stress analysis result of reverse fault fault plane strike and dip pitch direction compressional stress σ1 stress direction ss1 n7 0 e/70 0 n97 0 e n277 0 e east-west ss2 n40 0 e/59 0 n130 0 e n310 0 e southeast-northwest ss3 n86 0 e/42 0 n176 0 e n356 0 e north-south ss4 n162 0 e/80 0 n252 0 e n72 0 e east-west ssg n90 0 e/42 0 n76 0 e n318 0 e n138 0 e northeast-southwest 3.2 normal fault from 47 strike and dip data of normal fault was taken 4 major normal fault labeled as sn1, sn2, sn3 and sn4 (figure 5). aside from all those pure normal fault, there are 2 another normal faults found at field. they are normal dextral fault with pitch toward n240 0 e (sng1) and normal sinistral fault with pitch toward n6 0 e (sng2). the result of normal fault analysis (table 2) show that there are 4 extensional stress which are north-south (sn1), northwest-southeast (sn2), east-west (sn3) and northeast-southwest (sn4, sng1 and sng2). 3.3 dextral fault 5 major dextral fault plane was got from plotting 18 strike and dip data from field observation. 5 major dextral fault interpreted as pure dextral fault that labeled as ska1, ska2, ska3, ska4 and ska5 (figure 6). data and results of analysis of dextral fault show at table 3. there are 3 main stress (compressional stress) that generate all of those faults at study area, they are stress from northeastsouthwest (ska1), north-south (ska2 and ska3) and northwest-southeast (ska4 and ska5). 4 suryadi a./ jgeet vol 1 no 1/2016 fig. 5 sterionet analysis of normal fault table 2. stress analysis result of normal fault fault plane strike and dip pitch direction extensional stress σ3 stress direction sn1 n98 0 e/43 0 n8 0 e n188 0 e north-south sn2 n52 0 e/37 0 n142 0 e n322 0 e northwest-southeast sn3 n349 0 e/73 0 n79 0 e n259 0 e east-west sn4 n313 0 e/72 0 n43 0 e n223 0 e northeast-southwest sng1 n106 0 e/22 0 n240 0 e n42 0 e n222 0 e northeast-southwest sng2 n4 0 e/74 0 n6 0 e n243 0 e n63 0 e northeast-southwest fig 6. stress analysis result of dextral fault suryadi a./ jgeet vol 1 no 1/2016 5 table 3. stress analysis result of dextral fault fault plane strike and dip compressional stress σ1 stress direction ska1 n205 0 e/90 0 n55 0 e n235 0 e northeast-southwest ska2 n350 0 e/70 0 n199 0 e n19 0 e north-south ska3 n322 0 e/65 0 n177 0 e n357 0 e north-south ska4 n90 0 e/48 0 n292 0 e n112 0 e northwest-southeast ska5 n114 0 e/80 0 n325 0 e n145 0 e northwest-southeast 3.4 sinistral fault from 12 strike and dip data of sinistral fault was taken 3 major sinistral fault labeled as ski1, ski2 and ski3 (figure 7). all of them interpreted as pure sinistral fault. based on analysis of sinistral fault (table 4), there are 3 main stresses which are north-south (ski1), northwest-southeast (ski2) and northeast-southwest (ski3). table 4. stress analysis result of sinistral fault fault plane strike and dip compressional stress σ1 stress direction ski1 n27 0 e/90 0 n358 0 e n178 0 e north-south ski2 n177 0 e/88 0 n150 0 e n330 0 e southeastnorthwest ski3 n81 0 e/61 0 n55 0 e n235 0 e northeastsouthwest 4. discussion on the whole, there are 4 main stress that generate fault at study area. all of them are northwest-southeast (st1), north-south (st2), northeast-southwest (st3) and east-west (st4). stress from northwest-southeast (st1) were generated some structures such as ss2, sn4, sng1, sng2, ska4, ska5 and ski2. another structure which are ss3, sn3, ska2, ska3 and ski1 were generated by stress from north-south (st2). for stress from northeast-southwest (st3) were resulted ss4, ssg, sn2, ska1 and ski3 while stress from east-west (st4) were caused form ss1 and sn1 (table 5). to determine relative age of all of main stress, cross cutting law was used. at filed, cross cutting between faults were found. at station 32, st1 that represented by reverse fault with strike n48 0 e and dip 30 0 was cut by reverse fault n94 0 e/48 0 from st2. that mean st1 is older than st2 because it was cut by st2. meanwhile at station 108, reverse fault n134 0 e/68 0 that represent st3 was cutting reverse fault n87 0 e/66 0 that generated by st2. in other hand, st 4 that generated normal fault n90 0 e/30 0 at station 110 was cutting 2 reverse fault n154 0 e/52 0 and n160 0 e/36 0 that result of st3. based on cross cutting between fault that found at field, the relative age of main stress was determined where the oldest stress is from northwest-southeast (st1), following by north-south (st2) and northeast-southwest (st3). whilst stress from east-west is the youngest stress at study area (table 5). table 5. history of deformation at study area based on analysis of fault relative age main stress compressional stress (σ 1) extensional stress (σ 3) structures formed oldest st 1 southeast-northwest northeast-southwest ss2, ska4, ska5, ski2, sn4, sng1 and sng2 st 2 north-south east-west ss3, ska2, ska3, ski1 and sn3. st 3 northeast-southwest southeast-northwest ss4, ssg, ska1, ski3 and sn2 youngest st 4 east-west north-south ss1 and sn1 5. conclusion 4 type of fault which are reverse fault, normal fault, dextral fault and sinistral fault were identified by indication of slickenside, fault breccias, displacement and presence of mylonite. analysis of fault indicate that there are 4 main stresses were controlled the deformation at study area. the relative age of main stress was determined by cross cutting evidence between faults that found during observation at field. the oldest main stress is st1 with the direction from northwest-southeast. the fig 7. stress analysis result of sinistral fault 6 suryadi a./ jgeet vol 1 no 1/2016 second main stress is from north-south (st2) and following by third main stress from northeastsouthwest (st3). meanwhile, the youngest main stress is st4 with direction from east-west. all the main stresses were represented the history of deformation at study area. acknowledgements i wish to thank dr. zaiton harun as my supervisor for his guidance and all constructive comments during this study. i would like to thank mrs. nazirah rahman who help me to collect data at field and give me some ideas for this paper. lastly, thank you very much to all lecturers from geology program, universiti kebangsaan malaysia. references [1] gobbett, d. j. 1973. upper paleozoic. in. gobbett, d. j. & hutchison, c. s. (edt). geology of the malay peninsular: 61-95. new york: john wiley & sons, inc. [2] jones, c.r. 1981. the geology and mineral resources of perlis, north kedah, and langkawi island. geological survey malaysia district memoir 17: 67-84. [3] zaiton haron & basir jasin. 1999. implication of the bok bak fault movements on the structure and lithostratigraphy of the pokok sena area. proceeding mineral and energy resource of southeast asia: 145153. [4] zaiton harun & basir jasin. 1999. sempadan litostratigrafi batuan paleozoik zon baratlaut semenanjung malaysia. dynamic stratigraphy & tectonics of peninsular malaysiaseminar ii, the western belt & paleozoic of peninsular malaysia: 101104 [5] stratification and significance. dynamic stratigraphy and tectonic of peninsular malaysiaseminar ii: the western belt and paleozoic of peninsular malaysia: 87-100. [6] abdul hadi, a. r. 1999. the upper paleozoic singakubang pasu mega-sequence: some thoughts on basin initiation, depositional and tectonic hostory. dynamic stratigraphy and tectonic of peninsular malaysia seminar ii: the western belt and paleozoic of peninsular malaysia: 58-68 [7] basir jasin, zaiton harun & siti norhajar hasan. 2003. black siliceous deposits in peninsular malaysia: their occurance and significance. annual geological conference 2003 46: 149-154 [8] foo, k. y. 1983. the paleozoic rocks of peninsular malaysia-stratigraphy and correlation. proceeding of the workshopon stratigraphy correlation of thailand and malaysia 1: 1-19. [9] hassan, m. h. & lee, c. p. 2002. stratigraphy of the jentik formation, the transitional sequence from the setul limestone to the kubang pasu formation at guar sanai, kampung guar jentik, beseri, perlis a preliminary study. geological society of malaysia annual geological conference 2002: 169-178. [10]kobayashi, t. & hamada, t. 1973. cyrtosymbolids (trilobita) from the langgon red beds in northwest malaya, malaysia. geology & palaeontology of southeast asia 12: 1-28. http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 44 hidayah, b.a. et al./ jgeet vol 8 no 1/2023 research article design and implementation of a composite array resistivity data logger for high-resolution 2d inversion modeling a.bahrul hidayah 1,*, m.irsan sadri 2, safruddim 1, m.rafli 1, a. ildha dwi puspita 3, 1geology engineering department, faculty of engineering, hasanuddin university,south sulawesi, indonesia. 2electrical engineering department, faculty of engineering, hasanuddin university, south sulawesi, indonesia. 3civil engineering deparment, faculty of engineering, hasanuddin university, south sulawesi, indonesia. * corresponding author: bahrul.hidayah@unhas.ac.id tel.:+62812-1344-0863 received: nov 4, 2022; accepted: mar 20, 2023. doi: 10.25299/jgeet.2023.8.1.10875 abstract the use of resistivity meters to model subsurface conditions is widespread. however, commercial instruments are mostly limited to conventional configurations, such as wenner, schlumberger, and dipole-dipole. moreover, we cannot modify the program on the instrument. in this study, we designed and implemented a dc resistivity meter that can potentially be developed in the future and can be used in composite array configurations. this instrument uses a half-bridge smps as a power supply, which is capable of generating a large power, an arduino uno, and several sensor modules as part of a flexible and easy-to-program control unit. we conducted laboratory and field tests, comparing two types of configurations, namely wenner and composite arrays (dipole-dipole and gradient). we then processed the data using resipy software, which enables displaying complex data sets in the form of 2d cross-sections and assessing the quality of post-processing data. we obtained good data with low rms misfit that matched the synthetic media created in laboratory testing and compared well with previous research. keywords: resistivity; array-configuration; inversion; 1. introduction subsurface geological conditions have two interrelated aspects: the potential for natural resources and the risk of geological disasters. information on near subsurface geological conditions is required to utilize the potential of natural resources and mitigate the risk of geological disasters (field et al., 2018). one of the most common methods is to use a geophysical instrument called a resistivity meter, which uses variations in resistivity and conductivity values in electrical resistivity tomography to generate a two-dimensional crosssectional subsurface model (cardarelli & fischanger, 2006). exploring the nearby subsurface with the aid of physical science, technology, and concepts is known as applied geophysics. these physical fields, such as magnetic or electric fields, are invisible to human sight. the goal is to transform these detection fields into interpretable maps and graphs at this point. matter can also be "seen" through medical imaging techniques like magnetic resonance tomography and x-rays. traditional geophysical techniques include exploring dc resistivity. two electrodes are used to inject electricity into the ground, while the remaining two electrodes are used to monitor the electric potential difference. the measurements are frequently made along a line or in a specific location on the surface of the ground, and the potential differences that are subsequently seen are transformed into sounding curves or pseudosections of apparent resistivities that show the resistivity variations of subterranean rocks. (mitchell & oldenburg, 2023). in any case, on the demand side, applied geophysics helps us discover and characterize aquifers. it can map soil parameters, whose subsurface composition and geometry can be determined using some supplementary information on the field of study. it can, to a certain extent, determine the location of faults, the thickness of clay layers, and more, for example, it can mark contaminated areas, find buried metal objects or outline the foundations of former settlements. (florsch & muhlach, 2018). the principle of measurement using the geoelectric method is to inject a current (i) (in ma) into the earth and then measure the resulting potential difference (v) (in mv) between the two electrodes. the apparent resistance value ( ρ_a ) is derived from calculating the current and potential difference for each electrode distance (loke, 2001). resistivity imaging is a non-invasive geophysical method widely used for subsurface exploration. one of the crucial components in resistivity imaging is the data acquisition system, which plays a crucial role in the accuracy and resolution of the imaging results (wróbel et al., 2022). in this study, we designed a hardware system based on a microcontroller and a half-bridge switching topology power supply to implement a composite array for resistivity imaging. the decision to use a microcontroller-based system was made to increase the flexibility and control of the data acquisition process (hercog & gergič, 2014). the halfbridge switching topology power supply was designed to provide high voltage and high current output (hongxia, 2009) for deeper and better-resolved imaging. the implementation of a composite array allows for better resolution and accuracy of the imaging results (balasco et al., 2022) . the design and implementation of this resistivity data logger system offer several advantages over previous http://journal.uir.ac.id/index.php/jgeet hidayah, b.a. et al./ jgeet vol 8 no 1/2023 45 systems. the microcontroller-based system provides real-time monitoring and control of the data acquisition process, allowing for better accuracy and flexibility in imaging. the half-bridge switching topology power supply provides a high voltage and high current output, resulting in better signal-to-noise ratio and deeper imaging. the implementation of a composite array allows for higher resolution imaging, especially in complex geological formations (okpoli, 2013). analyses of these data enable us to find the underground resistivity anomalies or outline the subsurface geological structure. with the development of computer technology and numerical computational techniques, accurate numerical simulations of subsurface electrical field and acquiring a large amount of data in fields become possible , so that the traditional dc resistivity exploration was developed to a computerised geotomography technique, called electrical resistivity tomography, which employs a multielectrode equipment (capa-camacho et al., 2022). on the apparent resistivity data, the inverse modeling technique is applied through the inversion process. software called resiipy is used to perform process inversion. to translate the apparent resistivity value of the material into its actual resistivity value, the inversion method is used for complex datasets (blanchy et al., 2020). 1.1 earth resistivity an indicator of how much a material opposes the flow of electricity is its electrical resistivity. the unit of measurement for resistivity is the ohmmeter (ω m). a material has low resistivity if electricity can easily pass through it. high resistivity refers to a material's difficulty in allowing electricity to flow through it (heaney, 2003). however, to determine the depth of the underground layer, we first measure the earth's resistivity. table 1 shows how this measurement can be used to determine the depth of the underground layer. table 1. soil types and their apparent soil resistivity (nassereddine et al., 2013). type of soil or water typical resistivity (ω/m) usual limit (ω/m) sea water 2 0,1 to 10 clay 40 8 70 ground well and spring water 50 10 150 clay and sand mix 100 4 300 shale, slate, sandstone 120 10 1000 peat, loam, mud 150 5 250 lake and brook water 250 100 400 sand 2000 200 3000 morana gravel 3000 40 – 10000 ridge gravel 15000 3000 30000 solid granite 25000 10000 – 50000 ice 100000 10000 100000 the table shows that the resistivity values vary depending on the type of soil layer. based on its resistivity value, this value is then utilized as a reference for underground mapping. 1.2 electrical resistivity tomography the two-dimensional electrical resistivity tomography (2d ert) technology is particularly capable of resolving subsurface structures in fact, constructing a 2d representation of ground using two current electrodes and measuring the potential drop (v) across the other two electrodes (thapa, 2020). the measured voltage drop is directly proportional to the electrical resistivity, which can be related to the medium's distinguishing features as follows: ρ=k ∆v/i (1) where i represent current (ampere), ∆v represents potential difference (v), k represents the geometric factor (meter) and ω represents resistivity value (ohm.m). using a large number of resistivity measurements from electrodes arranged in any geometric form, the ert method determines the subsurface distribution of electrical resistivity. ert uses four electrodes to minimize the impact of contact resistance at the interface between the soil pore water and the electrode. a known current is driven through two electrodes, and the potential difference on the other two electrodes is monitored (daily et al., 2005). all conceivable linearly independent combinations from an array of electrodes are employed to obtain the high number of separate impedance measurements required for tomographic inversion. various configurations can be used to generate these pairings. a wenner alpha measurement scheme is a prominent approach for field measurement. fig 1. wenner alpha array configuration (aktarakçi, 2017). fig 2. dipole-dipole array configuration (oyeyemi et al., 2022). to obtain apparent resistivity in the field, many electrode sets were developed in the traditional dc resistivity exploration. in principle, ert requires high data density and good earth surface coverage for highresolution subsurface target imagery. data retrieval in this study carried out experiments using 2 array configurations, namely the 'conventional' wenner 46 hidayah, b.a. et al./ jgeet vol 8 no 1/2023 configuration and the composite configuration of a combination of dipole-dipole and gradient configurations 1.3 inversion process optimization inverse methods must be used to convert geoelectrical measurements into geoelectrical attributes. these techniques seek to identify the geoelectrical parameter distribution that is most compatible with measured data. to do this, the mismatch between the set of readings from four electrodes and the anticipated response from a geoelectrical model must be minimized. resipy is a program for geophysical data analysis, modeling, and inversion that makes the issue simple and gives users complete control over complex modeling and inversion parameters through a clear graphical user interface. resipy offers a platform for interdisciplinary projects where trustworthy outcomes are provided through a nonlinear user interface that is simple to use. resipy is perfect for educational uses as it enables modeling and inversion of 2d and 3d resistivity and ip data. while the majority of inversion algorithms and software on the market can perform simple data filtering, resipy offers a comprehensive data-cleaning technique. both the gui and the api have been used to successfully implement resipy in a variety of modeling and field applications (blanchy et al, 2020). 2. instrument design 2.1 hardware design the initial process of this tool is through a safety device in the form of a voltage protection relay, then the input voltage which was previously 12v is increased to approximately 400v using a dc-dc boost converter. the increased input voltage is then measured, if no current is detected, we can take measurements. as many as 24 electrodes will be plugged into the ground, where the electrode configuration will be changed through the switch box. then the ampere meter and volt meter will detect the value of voltage and current. we can monitor the voltage and current values of the electrodes via the lcd, and the data will automatically be recorded to the sd card. fig 3. resistivity meter data-logger design schematic laptops are used to enter data display programs on the lcd screen and record data on the sd card into the microcontroller. where the microcontroller here plays an important role as the brain of the arduino circuits. fig 3. is a rough idea of how this tool will be made 2.2 power supply switch mode dc power sources frequently employ dc/dc converters. the output voltage regulation of the dc/dc converter is accomplished from an energy perspective by continuously changing the energy absorbed from the source and that injected into the load, which is in turn regulated by the relative durations of the absorption and injection intervals. a switching cycle is made up of these two fundamental energy absorption and injection processes (hasaneen & elbaset mohammed, 2008). half-bridge switch-mode power supplies (smps) are commonly used in high voltage and high current applications due to their capability to handle high power levels while being cost-effective. according to a study by h. yang et al. (2017), a halfbridge smps is suitable for high voltage applications due to its ability to step up voltage levels efficiently. the authors demonstrated that a half-bridge smps can be designed to operate at high voltages up to 1 kv with an efficiency of over 90%. in terms of high current applications, a half-bridge smps can also be designed to handle high current levels. a study by r. devi et al. (2020) demonstrated the design and implementation of a half-bridge smps capable of delivering high current up to 10 a. the authors also showed that the use of a half-bridge smps resulted in lower cost and better efficiency compared to a full-bridge smps. overall, a half-bridge smps is capable of handling high voltage and high current applications while being cost-effective. the design and implementation of a halfbridge smps should take into consideration the specific requirements of the application to optimize its performance. in dc resistivity measurements, the use of a high voltage and high current power supply can result in better signal-to-noise ratio (snr) and lower root mean square (rms) misfit. according to a study by r. kumar et al. (2016), high voltage and high current can help to overcome the limitations of low snr and high rms misfit in dc resistivity measurements. the authors found that increasing the current and voltage in the measurement system can improve the quality of the acquired data and reduce the uncertainty in the results (sirota et al., 2022). another study also supported the use of high voltage and high current power supplies in dc resistivity measurements. the authors demonstrated that using a high voltage and high current power supply can improve the accuracy and precision of the measurements, particularly in low-resistivity regions (balasco et al., 2022). as in the schematic diagram in fig 4. two transistors are used in the half-bridge topology of a dc-dc converter to start switching activity, which sends current pulses to a load. this dc-dc converter topology offers pulses that can be smoothed to a nominal dc power value in addition to rectification and smoothing with a capacitor bank. this topology can be isolated, allowing it to produce high voltages when linked in series from multiple boards, with output power being coupled through a transformer or optocoupler. if the gate driver circuit is an integrated circuit, isolation may be applied within it by junction hidayah, b.a. et al./ jgeet vol 8 no 1/2023 47 isolation. transformer coupling may also be used in nonisolated topologies to increase or decrease the output voltage (fathy et al., 2006). fig 4. half-bridge dc-dc boost converter schematic circuit due to their simplicity, flyback and forward topologies are frequently used in isolated dc-dc converters for low power supply units (psu) with less than 1 kw. in contrast to the flyback converter, the forward converter's high-frequency transformer does not store energy, making it more suitable for applications requiring high output current (ezra et al., 2022). 2.3 switch box each new measurement necessitated the movement of all four electrodes. single-channel imaging equipment that can switch the current injection and potential reading locations between a restricted number of electrodes became commercially accessible in the 1990s. today, more advanced instruments use several channels to address enormous numbers of electrodes (binley & slater, 2020). this was the main idea of this manual switch box. the development of multi-electrode instrumentation in the late 1980s stimulated parallel advances in algorithms for 2d imaging of resistivity. by adjusting the relationship between the voltmeter (p1 and p2) and the ammeter (c1 and c2) on the switch box that is connected to the electrode as needed, researchers can perform a variety of electrode array configurations with only one implant of electrodes. fig. 5. (a) switch box design; (b) electrode distribution based on switch box fig 6. the voltage sensor, current sensor, rtc, data storage, voltage reference, and lcd screen are all connected and work simultaneously and that is controlled by the microcontroller. (a) (b) 48 hidayah, b.a. et al./ jgeet vol 8 no 1/2023 2.4 microcontroller an embedded computer control application-specific single-chip computer is known as a microcontroller. these devices are relatively inexpensive and very simple to utilize in digital control applications. the majority of microcontrollers come with the integrated circuitry required for computer control applications. for instance, a microcontroller might include a/d converters to enable the sampling of external signals. additionally, they contain parallel input-output connections that allow the microcontroller to read or produce digital data.(ibrahim, 2006). the primary brain of the programmed components is the microcontroller. the microcontroller in this case is set up to read data from the voltmeter, ammeter, and real-time clock and show it on the lcd screen while concurrently writing the data to the sdcard (rtc). the microcontroller component can be seen in fig 6. 2.5 voltage protection relay the following schematic circuit diagram in fig 7 is intended as protection in the form of overvoltage and undervoltage protection which works in conditions when the input voltage is more than 14.5v or less than 11.6v. when the overvoltage is above 14.5v, the comparator in the circuit will cut off the no connection to the relay from the power source, as well as when the voltage is below 11.6v. fig 7. voltage protection module schematic circuit the comparator will disconnect the no from the relay from the power source. this protection is intended to protect the boost converter when the voltage is excessive and protect the power source (battery) when it is at a voltage of less than 11.6v. the opposing activities that create overvoltage can result in undervoltage. undervoltage conditions will result in the potential for electronic device failure, and a decrease in the reactive power output from capacitor banks. (kotb et al., 2018). 2.6 performance testing setup laboratory tests are carried out after the tools have been successfully assembled and meet the proper requirements including controlled test media for laboratory tests in fig 9. the electrodes used in this experiment are made of stainless steel. because stainless steel electrodes are typical metal electrode that is relatively inert and affordable. (binley et al., 1996). this test was carried out in the hasanuddin university campus environment, and fig 5b and fig 8. and shows how the electrode and the resistivity meter are set up in field tests. where data was obtained twice in this test utilizing different electrode setups we will then compare the measurement data from the wenner alpha configuration with those from the gradient dipole arrangement. fig. 8. field testing setup after all components of the resistivity meter data logger are assembled hidayah, b.a. et al./ jgeet vol 8 no 1/2023 49 fig. 9. synthetic media consisting of layers of soil, sand, and high resistivity object (plastic bottle) 3. result in this study, we compared the results of similar previous studies by comparing the quality of the data produced by looking at the percentage of rms misfit in the 2d inversion results also compared the performance of a tool in measuring resistivity parameters using two electrode configurations. additionally, we put the tool to the test by determining whether its output accurately describes the situation of the controlled test material utilized in laboratory testing. in the test medium, an object with high resistivity was placed in the middle of two layers of dirt and sand. following laboratory testing, the tool was also tested in the field using two distinct electrode configurations. rms misfit is a commonly used parameter for evaluating the accuracy of 2d resistivity models, as mentioned by olayinka & yaramanci, 2000. the rootmean-square misfit is calculated by taking the square root of the average of the squared differences between the observed and modeled resistivity values. a low rms misfit value is generally considered to be acceptable for 2d resistivity models, while a high rms misfit value indicates a poor fit between the observed and modeled resistivity values. uhlemann et al., 2018 conducted a geophysical investigation using electrical resistivity tomography (ert) as a tool to guide ornamental stone extraction. the researchers shows the inverted resistivity model, for which the relative root-mean-squared (rms)misfit between modelled and measured data was rms = 2.1%. for visualizing and interpreting theresistivity models, all cells with sensitivities <5×10−3 were removed from the model. using this approach, the depth of investigation can be approximated to be about 10 m. the study identified factors that affected the rms misfit values, including variations in the electrode configurations, measurement errors, and subsurface heterogeneity. abdullah et al., 2018 assessing the reliability and performance of optimized and conventional resistivity arrays for shallow subsurface investigations. the researchers reported an rms misfit value of 1.36% 6.9% for the study. the study identified several factors that influenced the rms misfit values, including the accuracy of the electrode placement, the presence of noise in the data dahlin & zhou, 2006 conducted research twodimensional resistivity imaging using composite arrays, wenner and dipole-dipole electrode arrays was carried out at two field sites in sweden and one in nicaragua, with the objective of confirming the practical applicability of results obtained with numerical modelling. the results support earlier numerical modelling studies that concluded that the composite array, using multiple current electrode combinations, has resolution as good as or better than the commonly used wenner array. the array behaved well in terms of sensitivity to noise at the test sites, and the results obtained generally agree with dipole-dipole array results, although the latter at two of the sites gave resistivities that differed significantly from the other arrays in the deeper parts of the inverted model drawing on prior research, laboratory experiments were conducted to evaluate the efficacy of the instrument, we proceeded to conduct measurements in the field using the wenner alpha and dipole-dipole composite array electrode configurations. the resistivity meters were used to take measurements with both electrode configurations. these measurements were then further processed with resipy, an opensource software, which produced a temporary resistivity value. the data were iterated further until a fairly low rms value was achieved. the initial design of the test medium for these measurements is shown in fig. 9. 3.1 laboratory test (dipole – dipole gradient configuration) the apparent resistivity value in the experiment is shown in the graphic below (fig. 10) using a composite configuration and the data captured by the device that has been made. some points appear empty because that data has a high transfer resistance rate and may be considered invalid, the data is then removed and left blank so that the software algorithm can interpolate it automatically later. 50 hidayah, b.a. et al./ jgeet vol 8 no 1/2023 fig. 10 laboratory test: composite array configuration apparent resistivity fig. 11 final result: composite two-dimensional resistivity imaging after importing the data and getting a pseudo resistivity value, it will be further processed to get the original resistivity value by examining the geometric factor and doing several iterations to reduce the rms (root-mean-square) error value in the data obtained. two-dimensional resistivity imaging shows a fairly clear picture of layers and shapes of different resistivity values on the test media, where the coarse sand mixed with soil at the bottom of the media shows a resistivity range of 60-236 ohm.m, in the upper layer which is consisting of soil mixed with clay showing resistivity values in the range <12 87 ohm.m while the round resistive object in the center of the test medium has a resistivity value of <237 ohm.m, represented in fig. 10 and fig 11. 3.2. field measurement test: (field test, apparent resistivity) the fig.12 and fig 13. depicts the apparent resistivity value derived from the measurement data, which can be viewed as a dot in the image representing the datum. where the data is recorded by the tool, the distribution of the dots in the image is determined by the configuration of the electrodes. as a result, the number of points in the image denotes that the data obtained by these measurements correspond to the number of dots in the image. fig. 12 (composite array) and fig. 13 (wenner alpha configuration) show that the amount of data recorded from the two configurations differs significantly. in fig. 12 (composite configuration) the apparent resistivity values are in the range of 120000 ohm m to -20000 ohm m and in the image, it can be seen that the data has a fairly high density. in fig.13 (wenner alpha configuration), the apparent resistivity values are in the range of 2500 ohm m to -17500 ohm m and the data density is quite far compared to the data density from the composite configuration. hidayah, b.a. et al./ jgeet vol 8 no 1/2023 51 fig. 12 field test: apparent resistivity using composite array dipole-dipole gradient. fig. 13 field test: apparent resistivity using wenner alpha array configuration. 3.2.1 field test, iteration & root-mean-square (rms) error of inversion results fig. 14 and fig. 15 show the relationship between iterations and the rms misfit value resulting from this measurement. this iteration is one stage of the underground depiction interpretation process, where the inversion process requires iterations to reduce the rms error value from the measurement results. it can be seen that the two configurations below have been carried out with several iterations to reduce the rms error value. in figure 15 (dipole-dipole configuration) the initial rms error value is 21.12% and after six iterations, the final rms error value is 1%, while in figure 16 (wenner alpha configuration), it can be seen in the graph that the initial rms error value is quite high at 42.46%. after ten iterations, the rms error value decreased to the level of 1.32%. fig. 14 field test: iteration & rms value (dipole-dipole gradient) initial rms misfit: 21.12 final rms misfit: 1.00 52 hidayah, b.a. et al./ jgeet vol 8 no 1/2023 fig. 15 field test: iteration & rms value (wenner alpha) 3.2.2 field test, normalized error fig.16 and fig. 17 below illustrate the spread of data errors where the data has gone through the inversion process including iteration. in fig. 16 which uses a gradient dipole configuration, it can be seen that the data error spread is in the range of 1.5% to 1.5%. while in figure 17 which illustrates the spread of data errors using the wenner alpha configuration, it can be seen that the error value is past 2% but does not exceed the specified fault tolerance limit. this is most likely influenced by the amount of data that has a significant difference between the two types of electrode configurations. where interpolation or depiction can be easier or more precise when you have a lot of data. fig. 16 field test: normalized error (dipole-dipole gradient) fig. 17 field test: normalized error (wenner alpha) 3.2.3 field test, final result the two images below are obtained after going through several stages of the process to get the results of the depiction based on the data obtained by the tool. initial rms misfit: 42.46 final rms misfit: 1.32 hidayah, b.a. et al./ jgeet vol 8 no 1/2023 53 it can be seen that the two images below (fig. 18 and fig.19) are almost identical to each other. this can be a consideration that the results given are appropriate because after doing two measurements the results are still almost the same. in fig. 18 with a composite electrode configuration, it can be seen that the resistivity value recorded is more detailed or has a fairly highresolution value, while figure 19 does produce almost the same image but the resistivity value recorded produces a fairly rough image in the mapping. fig. 18 field test: final result (composite array configuration) fig. 19 field test: final result (wenner alpha configuration) 4. conclusions the laboratory test results are satisfactory, the resistivity meter test results show the performance as expected, getting a relatively small rms misfit value when compared to existing research.. the resulting twodimensional profile is quite good in describing the test media that have been made. voltage and current measurements performed with this tool produce good results because the data that obtained is also still within the error tolerance limit of +/ 3%, the theoretical test may be declared to be successful, allowing the instruments to be tested in the field. this was based on (binley et al., 1995), where the values of error should be generally between -3 and +3 percent, with no obvious patterns, if the zero mean uncorrelated error assumptions are true. when we ran the test on the field with the composite configuration, we got a +/1.5% normalized error. following that, we performed a second measurement using the wenner alpha configuration, with an error value of +/2.5%. this could be related to the enormous amount of data that differs between the two configurations, based on the data generated by the wenner alpha configuration, which has a greater error value than the dipole-dipole configuration. whereas the wenner alpha configuration generates approximately 80 datums, the dipole arrangement generates approximately 520 datums. the measurement findings demonstrate that the wenner alpha configuration, which uses significantly less data than the dipole-dipole configuration, can depict the lateral split of the field more clearly. however, the dipole-dipole configuration measurement outcomes offer processed data with a greater resolution or make the shape of the item more obvious. acknowledgments we thank the ministry of higher education of indonesia and hasanuddin university for providing a research grant. we also thank the geological engineering department students at hasanuddin university (gowa) for supporting us during the field survey. this research was funded 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(2022). integrated geophysical imaging and remote sensing for enhancing geological interpretation of landslides with uncertainty estimation—a case study from cisiec, poland. remote sensing, 15(1), 238. https://doi.org/10.3390/rs15010238 © 2023 journal of geoscience, engineering, environment, and technology. all rights reserved. this is an open-access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.3390/min8110491 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 03 2018 164 farazi et al./ jgeet vol 03 no 03/2018 research article a case study based slope stability analysis at chittagong city, bangladesh atikul haque farazi 1. *, abu jafor mia 1 , md. ilias mahmud 1 1 department of geology and mining, university of barisal, bangladesh . * corresponding author : ahfarazi@barisaluniv.ac.bd tel.:+8801867880529 received: june 10, 2018; accepted: aug 20, 2018. doi: 10.24273/jgeet.2018.3.3.1690 abstract heavy rainfall occurs almost every year in bangladesh and induces landslides in the hilly regions of this country. among them the chittagong city has the worst scenario―as there lives a dense population, extending from the plain lands to the hilly area. so, for risk mitigation and management in this landslide prone city, slope safety margin should be determined. from this context, this article presents factor of safety (fs) values in terms of landslide hazard at chittagong city, based on geotechnical parameters and slope geometry. thus a preliminary idea on the allowable stress for slope design could be made from this study. in total, 16 hazard sites of the 2007 and 2008, rainfall induced, landslides were examined as a case study along with subsequent collection of in situ soil samples of the failed slopes for geotechnical laboratory analysis. for fs calculation, the limit equilibrium nd at the hazard sites. the results imply that fs value more than 1.57 should be used for slope safety margin. moreover, from a probabilistic approach, the authors recommend fs > 1.80 as optimum value for the region. furthermore, a relationship between slope height to slope length ratio, or slope angle and fs was established for this region for a quick calibration of fs value by simple on-field measurement of slope parameters. it is expected that this scenario based finding would contribute in mitigation of landslide hazard risk at the study area. additionally, site specific fs values were presented in a 3d contour map. this research could ascertain the location wise slope strength requirement and be considered as a guideline for future calculation for slope safety design against rainfall triggered landslides in this city. keywords: landslide hazard, slope stability, limit equilibrium method, stability chart, simple slope, allowable stress, probabilistic approach 1. introduction landslide or slope instability is a result of stress exceeding the shear strength of the slope material. the excess stress could be added with increasing pore water, excessive overburden pressure due to external load, etc. moreover, poor soil condition, weathering, slope geometry, soil stratification, discontinuities in the rock body, etc. are some other common factors to decrease soil strength for slope instability (islam et al., 2014). slope height and steepness is also pivotal―as described by putra and choanji (2016)―with increasing slope height, surface runoff and water transport energy also increase by the action of higher gravity, and at the same time steep slopes tend be eroded more quickly; both leads to instable slopes. chittagong city, in the southeastern hilly region of bangladesh, is a landslide prone city, where almost every year devastating landslides result in casualties and damage to properties (islam et al., 2017, mia et al., 2017). table 1 represents some of the major historic and recent landslide events. it is the second largest city of the country―also regarded as the business capital. almost one-third area of the chittagong city corporation is occupied by hilly terrains. these hilly portions of the city are also being chosen for settlements due to rapid urban growth. unsafe construction on the hills or foothills is the major cause for the worst scenario of landslide events. it is documented that excessive rainfall triggers the landslide phenomenon in bangladesh, and is more facilitated in many places by hill cutting and deforestation (islam et al, 2014; islam et al., 2017; mia et al., 2017). population is growing in this city as well in the hill sites due to continuously incoming population for livelihood and therefore constructions are made more rapidly on the hills and foothills (islam et al., 2017). therefore, determination of appropriate and site specific real factor of safety (fs), based on geotechnical parameters of the slope materials where there the hazard has already been taken place, is important and would be really useful for inferring the degree of strength required for slope design. http://journal.uir.ac.id/index.php/jgeet mailto:ahfarazi@barisaluniv.ac.bd farazi et al./ jgeet vol 03 no 03/2018 165 table 1. historical landslides (in ascending chronology) in bangladesh (modified after mia et al., 2017). date location deaths total wounded cause of landslide 16 jul 1968 kaptai-chondroghona road section -02 removal of protective vegetation and heavy rainfall 26 jun 1970 ghagra-rangamati road section 01 - removal of protective vegetation and heavy rainfall 30 may 1990 chittagong university 11 25 extremely heavy rainfall 11 jul 1997 and chittagong 30 10 heavy rainfall 15 aug 1999 chittagong 12 09 heavy, incessant rainfall 13 aug 1999 bandarban 07 14 heavy, incessant rainfall 11 aug 1999 chittagong 10 13 heavy, incessant rainfall 24 jun 2000 chittagong university and city area 13 20 torrential rainfall 11 jun 2007 chittagong 135 213 extremely heavy rainfall 18 aug 2008 03 09 heavy rainfall 18 aug 2008 chittagong 11 20 heavy rainfall 31 jul 2009 lama, bandarban 10 -incessant rainfall 15 jun 2010 50 100 a series of rainfall 26 jun 2012 lebubagan, foys lake 90 150 heavy rainfall 2 jun 2017 chittagong 146 20 heavy rainfall factor of safety (fs) is a very popular term that civil engineers use ubiquitously for risk free infrastructure development, and as a classical approach to project the possible relationship between soil strength and expected stress. among various geohazard, landslide is a potential one that is reported to cause serious damage to life and properties. that is why engineering structures in landslide prone areas are needed to be given proper design and strength considering the appropriate fs value along with proper site selection. in this research, fs values were determined following the conventional limit equilibrium method for slope stability analysis. engineering parameters of soils alongside slope characteristics of sites where landslide events have already taken place, in 2007 and 2008, were the basis of this disquisition. some authors, e. g., islam et al. (2014), islam et al. (2015), etc. have previously determined safety factor as per slope stability analysis at various locations of the chittagong city, but this study provides safety factor based on data from the failed slope as a case study. some of these data were previously used by mia et al (2017). notably, devastating rainfall triggered landslide events took place in the city in 2007 and 2008, which caused death of about 149 people (khan et. al., 2012). the limit equilibrium method is a common and widely used procedure for slope stability analysis. simplicity and requirement of less parameters compared to other methods have hold popularity of this method up even though the method has disadvantages like constant fs along the slope plain, and negligence of ground response (baba et al., 2012). another important factor is that in this method of analysis there is no requirement to consider strain and uncertainties regarding engineering parameters of slope soil, and are only restricted to shear strength properties, which has also attracted civil engineers for widely accepting these methods (kakou et al., 2001). however, the differences of fs values from this method with those of others are reportedly less than 6% and even though having some drawbacks, this method is frequently used with pragmatic experience that slopes could be comprehensively delineated by this analytical method (duncan, 1996; blake et al., 2002; baba et al., 2012). in this method, fs value in terms of slope stability is assessed considering the state of equilibrium between the assumed stress and the soil strength along a surface of failure. as a result, in these methods of analysis assumption of sliding surface shape is crucial. the shapes popularly in use are straight line, circular arc, logarithmic spiral, etc., along which both linear applied (koranne et al., 2011). among the various limit (taylor, 1948) and the friction-circle method consider the whole mass to move freely while the others divide the whole mass into vertical slices to assess the equilibrium condition individually for each slice and are known broadly as the methods of slices (koranne et al., 2011). in addition, another categorization of this analysis could be mentioned where one is based on the assumption of infinite slopes whereas the other considers the slopes as a finite surface. however, in this article simple limit equilibrium model of infinite slopes―with materials having both cohesive and frictional strength―was used along with cousins (1978) stability chart for simple slopes to determine the fs values: as the existing data best facilitates. slope stability chart was proposed primarily by taylor (1937), and now it is ubiquitously used for assessment of fs of simple slopes with characteristically uniform soil (sun and zhao, 2013; javankhoshdel and bathurst, 2014). these graphical methods require simple calculations, rendering quick estimation of fs of a slope. hence, these charts could be particularly useful for preliminary design and estimating purposes. all of the limit equilibrium methods compare the forces, moments, or stresses resisting sliding of a mass with those that could render instability to a slope by examining the equilibrium condition of a slope in response to gravitational pull. factor of safety (fs) values could be obtained at the end of the analysis that is the ratio of the shear strength to the shear stress. 166 farazi et al./ jgeet vol 03 no 03/2018 moreover, critical slip surface is assumed to be the location where there has the lowest value of fs. as dynamic slope stability is related to its static stability, static factor of safety for each point, e.g. in-situ field measurements on slope can yield dynamic stability of a slope. as per regional analysis we used a relatively simple limit equilibrium model of infinite slope with material having both frictional and cohesive strength. in general, fs is determined by the following formula: fs = s t (1) where, s = shear strength and t = shear stress. is the ratio between the forces that prevent the slope from failing i.e., shear strength of the slope to that make the slope fail i.e., shear stress (kakou et al., 2001). in common practice, fs > 1 indicates stable conditions whereas fs < 1 unstable. slope stability analysis with inhomogeneous dip and/or soils are now done by software. but, slopes with homogeneous inclinations and isotropic soils are conventionally studied, for slope safety, by charts as a quick tool. taylor (1937) is one of the pioneers who introduced such chart (michalowski, 2001; sun and zhao, 2013). moreover, these charts could rapidly render fs value with easier calibration process and also could be handy for preliminary site characterization, design and planning (sun and zhao, 2013; huang, 2014). the stability number, pertaining to the chart, a dimensionless parameter (λcⱷ) for homogeneous soil slopes, he defined using the chart is also widely used and were later adopted and described by a number of authors, e, g., janbu (1956), cousins (1978), rahman and khan (1995), michalowski (2002), etc., and generally is expressed as: λcⱷ = γh tan ⱷ c (2) where, γ = unit weight, h = slope height, ⱷ = angle of friction, and c = cohesion of soil. for cohesionless (c = 0) soils λcⱷ becomes infinite; this is when the circle runs on the point where there is slope toe in a 2d view and then critical slip surface becomes plane parallel to the slope surface (rahman and khan, 1995; duncan and wright, 1980). cousins (1978), however, used simple slope with homogeneous soil (fig. 1) for his stability chart, known as cousins stability chart (fig. 3). hence, as the next step of this analysis we used cousins (1978) stability chart for simple slope, and finally fs values were calculated using the following equation: fs = nf c γh (3) where, nf = cousins stability number, which would be determined from cousins chart (fig. 2). cousins (1978) assumed the critical plane of failure as a circular arc passing through the toe of the infinite slope. he variably utilized the friction-circle method to construct the chart from which fs values, critical slip circles and toe circles could be yielded for soils having both friction and cohesion. but this chart could be used for slope angles (β) up to 45 o . because of this, fs values of some places (samples ctg03, ctg05, ctg07 and ctg09), where slope angle is more than 45 o , could not be determined using this chart. estimation of the fs values with cousins chart was performed manually. later, an optimum fs value was recommended for the study area based on probabilistic regression. after that, spatial distribution of the fs values were also presented by a 3d map to show site specific and spatial variation of the degree of slope strength requirement within the region. the amount of allowable stress could also be inferred from the fs values. the authors expect that the fs values presented in this article would be useful in landslide hazard risk management and proper land use planning in this region. fig. 1. a typical simple slope with isotropic soil. fig. 2. cousins (1978) stability chart for simple slopes. 2. study area the chittagong city is located between 22 o 14 to 22 o 24 30 north latitudes and between 91 o 46 e to 91 o 53 east longitudes (fig. 3). it is the second largest city of bangladesh after the capital city dhaka. farazi et al./ jgeet vol 03 no 03/2018 167 the city comprises almost of 160.99 sq. km area with a total population of about 2,068,082 (bangladesh population census, 2011). this tropical region experiences monsoon mostly from the month of june to october, with average rainfall recorded more than 2540 mm in this period (islam et al., 2017). 2.1 geology and geomorphology the study area comprises a part of chittagong hill tracts, which is geologically in the western margin of the chittagong-tripura folded belt (ctfb) and more precisely in the plunged zone of the sitakund anticline (islam et al., 2018). this tertiary fold belt in the eastern margin of the bengal basin―the basin itself is situated in the eastern periphery of the indian plate―has come into existence because of intricate interaction among the indian plate, the eurasian plate, and burmese platelet (rahman et al., 2017; farazi et al., 2018). like all other anticlines of ctfb, sitakund anticline also has nnw-sse axial trend. therefore, various rock formations, i.e., dupi tila sandstone formation, tipam sandstone formation, and bokabil formation, are exposed from east to west in the study area. sandstones of the dupi tila formation lie at the top and, therefore, exposed at the surface of the hill tracts of the city. sandstones of this formation are loose and friable, hence, has less shear strength whereas sandstones of tipam formation are mostly hard and compacted unless highly weathered (islam et al., 2015). varied geomorphology and topography is observed in chittagong city because of its position in the hilly region. the northern and the eastern part of the city has hilly terrains. otherwise, the western portion is surrounded by the coastal plain and the bay of bengal while the southeastern, and the northeastern parts pf the city is covered by karnafuli river and the floodplain of the halda river, respectively (mia et al., 2017). three geomorphologic units are largely seen in this region 1) hills and associated valleys in the north, with 12-80 m elevation, 2) fluvio-tidal plains in the west and south, including tidal plains of the bay of bengal, with 5-10 m elevation, and 3) the karnafuli river floodplain having 5-10 m elevation (mia et al., 2017). fig. 3. location map of chittagong city showing the study locations of 2007 and 2008 landslide sites. 168 farazi et al./ jgeet vol 03 no 03/2018 3. materials and methods this article examines factor of safety (fs) values of the slopes of the landslide hazard sites of the chittagong city to recommend the minimum fs value that should be considered in this region. therefore, in-situ samples from 16 hazard sites of 2007 and 2008 landslides were collected along with necessary slope parameters, i.e., slope height and slope angle or inclination, to calibrate fs values against landslide as a case study. fs values were calculated by means of the (1978) chart combining with simple limit equilibrium method of infinite slopes. the collected samples of the slope materials belong to the dupi tila sandstone formation. slope geometry was measured in the field by measuring tape and clinometer. notably, during the investigation we found that the slumping took place principally with the sandstones of the dupi tila formation. so, samples of this formation were collected by augar for laboratory analysis. table 2 represents the slope characteristics and geotechnical parameters of soil samples regarding this study. strength parameters, i.e., friction angle and soil cohesion of the soil samples were obtained by direct shear test under consolidated drained condition at the engineering geology laboratory of geological survey of bangladesh (gsb). astm d3080 standard was followed for this analysis. following the estimation of the fs values, a power based regressive curve for these values against the tangent of the slope angles (tanβ) was drawn (fig. 4). table 2. slope geometry or parameters, and soil characteristics or engineering parameters of soils of 2007 and 2008 landslide locations used in this study. sample id slope parameters soil parameters lithology of landslide materials height (m) angle (⁰) unit weight (n/m 3 ) angle of friction (⁰) soil cohesion (pa) ctg01 10 48 950 33 460 yellowish brown medium to fine grained sandstone occasionally interbedded with shale ctg02 30 64 950 33 562 yellowish brown medium to fine grained sandstone with carbonaceous matter ctg03 38 84 950 32 460 yellowish brown medium to fine grained sandstone with silty shale in places ctg05 14 55 940 32 443 light yellow to brown medium to fine grained sandstone with minor shale beds ctg06 8 24 940 32 448 grey to yellow, fine to medium grained sandstone ctg07 16 47 946 34 360 grey to yellow, fine to medium grained sandstone ctg08 16 41 948 30 450 grey to yellow fine to medium grained sandstone ctg09 18 50 947 29 540 yellowish brown fine to coarse grained sandstone, but lower part is interbedded with shale ctg10 14 43 946 27 580 yellowish brown fine to coarse grained sandstone, but lower part is interbedded with shale ctg11 15 37 946 26 607 grey to yellow fine to medium grained sandstone ctg12 6 36 949 32 320 grey to yellow fine to medium grained sandstone ctg13 7 35 946 26 600 grey to yellow fine to medium grained sandstone ctg14 6 42 941 27 480 grey to yellow fine to medium grained sandstone ctg15 12 40 949 33 530 yellowish brown medium to fine grained sandstone interbedded with shale ctg16 20 45 948 33 500 yellowish brown medium to fine grained sandstone interbedded with shale ctg17 12 43 948 33 662 yellowish brown medium to fine grained sandstone interbedded with shale farazi et al./ jgeet vol 03 no 03/2018 169 in this case, it should be noted that tanβ is the ratio of the slope height to slope length. the reason behind selecting the power based regressive curve is that the highest value of the coefficient r 2 was found for power curve compared to other curves like linear, logarithmic, exponential, etc. again, islam et al. (2017) showed that all the failed slopes in the chittagong city has slope angle (β) > 15 o . therefore, we assumed the fs values below the crossing point of the line representing tan15 o and the best-fit curve as unsafe and the fs values above the point as safe in terms of rainfall induced landslide hazard in the study region. thus the optimum fs value we inferred from this probabilistic approach was > 1.80. additionally, we found from this probabilistic approach that the relationship between tanβ (x) and fs (y) is: tan 𝛽 = 1.227𝐹𝑆−.035 (4) this relationship could be used as a quick tool for on-field primary estimation of the requirement of the degree of strength for slope design in the study area, in terms of the optimum fs value, by simply measuring the slope height, slope length and/or slope angle. after derivation of fs values at various hazard sites, they were plotted on a 3d map (fig. 5) was produced using arcgis software and finally a map showing spatial variation of the fs values by means of contour lines of equipotential fs value. the map represents spatial variability by means of contour lines with equipotentil fs values. the map was produced in arcgis environment, and contouring was performed by interpolation. moreover, 30 m digital elevation model (dem) was used for 3d mapping. in this work contouring was performed by kriging method in arcgis environment. it should be noted that the sand dominating soil samples were not truly homogeneous at each of the locations as presented by table 2. rather, minor shale beds were present within the sand dominating units at some places. but, still we assumed the slope materials as homogeneous for simplification of this study. 4. result and discussion table 3 represents site specific factor of safety (fs) values in terms of landslides―based on the data collected at various landslide hazard sites at the chittagong metropolitan area as per deciphering slope stability condition there. this study was carried out by simple limit equilibrium method for infinite slopes, and cousins (1978) chart, which was the best suit within the limitation of current facilities and data. these data were collected from 2007 and 2008 landslide locations. as the use of the cousins chart is limited up to slope angles of 45 o , fs values of the locations regarding samples ctg03, ctg05, ctg07 and ctg09 could not be determined. we found that the fs values in this area range from 0.94 to 1.57. the highest value was found at sikandarpara (ctg06) and the lowest at kusumbagh (ctg02). here, it should be kept in mind that whatever the fs value is, it is from a failed slope. fig 4. power based regression curve from the plot of tanβ vs fs. the red line indicates tan15 o = 0.27. fs values above the crossing point of the regression curve and the line representing tan15 o has been marked safe (fs > 1.80, above the green line) and the values below the point has been marked unsafe (fs < 1.80) for chittagong city. 170 farazi et al./ jgeet vol 03 no 03/2018 table 3: factor of safety (fs) values in terms of slope stability at various locations of chittagong city. sample id location name latitude longitud e factor of safety (fs) ctg01 baizid bostami 22 0 23ꞌ 17ꞌꞌ 91 0 49ꞌ 04ꞌꞌ 1.26 ctg02 kusumbagh 22 0 21ꞌ 19ꞌꞌ 91 0 49ꞌ 18ꞌꞌ 0.94 ctg03 lalkhanbazar 22 0 20ꞌ 49ꞌꞌ 91 0 48ꞌ 59ꞌꞌ _ ctg05 sikandarpara 22 0 26ꞌ 07ꞌꞌ 91 0 47ꞌ 51ꞌꞌ _ ctg06 sikandarpara 22 0 26ꞌ 06ꞌꞌ 91 0 47ꞌ 51ꞌꞌ 1.57 ctg07 sikandarpara 22 0 26ꞌ 04 ꞌꞌ 91 0 47ꞌ 52ꞌꞌ _ ctg08 lebubagan 22 0 25ꞌ 01ꞌꞌ 91 0 48ꞌ 36ꞌꞌ 1.18 ctg09 lebubagan 22 0 24ꞌ 58ꞌꞌ 91 0 48ꞌ 36ꞌꞌ _ ctg10 lebubagan 22 0 24ꞌ 56ꞌꞌ 91 0 47ꞌ 37ꞌꞌ 1.18 ctg11 lebubagan 22 0 24ꞌ 54ꞌꞌ 91 0 48ꞌ 35ꞌꞌ 1.15 ctg12 lebubagan 22 0 24ꞌ 53ꞌꞌ 91 0 48ꞌ 39ꞌꞌ 1.50 ctg13 lebubagan 22 0 24ꞌ 53ꞌꞌ 91 0 48ꞌ 41ꞌꞌ 1.54 ctg14 kechuarghona 22 0 25ꞌ 20ꞌꞌ 91 0 48ꞌ 27ꞌꞌ 1.46 ctg15 kechuarghona 22 0 25ꞌ 27ꞌꞌ 91 0 48ꞌ 22ꞌꞌ 1.29 ctg16 kechuarghona 22 0 25ꞌ 25ꞌꞌ 91 0 48ꞌ 21ꞌꞌ 1.05 ctg17 kechuarghona 22025ꞌ 48ꞌꞌ 91 0 48ꞌ 15ꞌꞌ 1.44 this research was conducted upon failed slopes of 2007 and 2008 landslides, and the fs values were calculated within particular failure blocks, which means that fs value as high as 1.57 is not enough for slope design for this region, or in other words there is full probability that this value is inadequate for slope safety. so, fs > 1.57 could be recommended for safe slope design in this region. but, being further advanced a probabilistic approach for more accurate evaluation of slope strength requirement was employed in this study. the fs values above the crossing point of the regressive curve from the plot of tanβ vs fs and the line presenting tan15 o was assumed safe (fig. 4). thus fs > 1.80 would render slope safety while fs < 1.80 would provide unsafe condition. moreover, a relationship such as tan 𝛽 = 1.227𝐹𝑆−.035 (eqn. 4) was established between tangent of slope angle (tanβ), or slope height to slope length ratio and fs for this region. using this probabilistic relationship, fs values could be used for slopes with slope angle (β) > 45 o for the hills of the city an overcome. another advantage of the outcome of this probabilistic approach could be that the relationship between tanβ and fs could be used as a quick tool for estimation of fs and slope safety requirement as well. simply, on-field measurement of slope height and slope length, or even only measurement of the slope angle (β) could serve the purpose. because, tanβ is the ratio of slope height to slope length. in addition, spatial variability of fs values were presented by a 3d contour map (fig. 5), so that site specific strength requirement or allowable stress could be discerned. this map could practically substitute the existing geographic information system (gis) and dem based landslide hazard potential maps for the chittagong city. notably, it could be seen from table 2 that all of the failed slopes has slope angles exceeding internal frictional angle, except for the sample ctg06. the exception was made probably by hill cutting, which escalated the landslide phenomena at that particular place. geotechnical engineers use fs conventionally is based on experience. fs is useful because it minimizes the degree of uncertainty and helps assessing the risk associated with slope stability analysis as accurate computation is nearly impossible (duncan, 1999; huang, 2014). furthermore, stress design or the stress limit, he maximum stress that soils of a particular location can absorbs without rendering collapse, or damage, could be inferred from fs values. because we know from harris (1995), farazi and quamruzzaman (2013), etc. that: 𝐴𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝑠𝑡𝑟𝑒𝑠𝑠 (𝜎𝑎 ) = 𝑇𝑜𝑡𝑎𝑙 𝑠𝑡𝑟𝑒𝑠𝑠 (𝜎) 𝐹𝑎𝑐𝑡𝑜𝑟 𝑜𝑓 𝑠𝑎𝑓𝑒𝑡𝑦 (𝐹𝑆) (5) so, the fs values of failed slopes of the chittagong city would be highly useful in proper slope design prior to construction at the hilly portions. engineers and planners would get a guideline from this article about the strength of soil required and the stress limit for infrastructure development and/or about which area is suitable for masonry work. therefore, this article can show a primary way out for landslide hazard risk free civil engineering work, and eventually for capacity building and sustainable development in this region. farazi et al./ jgeet vol 03 no 03/2018 171 5. conclusions slope stability analysis with the notion of factor of safety (fs) was performed at 16 locations of chittagong city. the analysis was carried out by limit equilibrium method for infinite slopes and cousins stability chart. slope geometry data and in situ soil samples for this research were collected from failed slopes of 2007 and 2008 rainfall induced landslide locations. we found fs values ranging from 0.94 to 1.57 within the study area. so, it is clear from this study that 1.57 is not the adequate value in terms of slope safety requirement in this region. further, based on a probabilistic approach, we recommend that fs > 1.80 should be used for slope design with proper strength. on top of that, a relationship between slope height to slope length ratios, or tangent of slope angles (tanβ) and fs values was established for this particular region that is: tan 𝛽 = 1.227𝐹𝑆−.035. this relationship could be handy for a quick assumption of fs value and hence, slope safety requirement by simple on-field measurement of slope height and slope length, or only slope angle. another important factor is that at each of the hazard sites slope angle exceeds the internal friction angle of soils, except one site that we inferred because of hill cutting. spatial variation of the fs values were depicted in a 3d contour map, from which site specific strength requirement or maximum allowable stress for slope design would be predicted as a nascent guideline. stability charts provide the preliminary design purpose of slope by slope stability analysis. the fs values and their relation to slope geometry, and the engendered map from this article would act as a primary guideline for landslide risk mitigation and risk management in this locality as well as a base for future estimation of slope safety requirement. besides, this article could also play a useful role in taking remedial measures, ground improvement, and risk informed landuse planning for this city. fig 5. a 3d contour map showing spatial variation of factor of safety (fs) of slopes within the hilly areas of chittagong city. 172 farazi et al./ jgeet vol 03 no 03/2018 acknowledgements the authors are thankful to geological survey of bangladesh (gsb) for permitting to use their engineering geology laboratory. the authors also express their deep gratitude to fansab mustahid, assistant manager (geophysics), bangladesh petroleum exploration company limited (bapex) for his kind contribution in preparing this manuscript. references bangladesh population census, 2001. bangladesh bureau of statistics. baba, k., bahi, l., ouadif, l., akhsas, a., 2012. slope stability evaluations by limit equilibrium and finite 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(eds), 2002. recommended procedures for implementation of dmg special publication 117. guidelines for analyzing and mitigating landslide hazards in california; southern california earthquake centre, usa. california: california department of conservation. cousins, b.f., 1978. stability charts for simple earth slopes. j. geotechnical engineering division, asce 104(2), 267-279. http://cedb.asce.org/cedbsearch/record.jsp?dockey=0007 912 duncan, j.m., wright, s.g., 1996. the accuracy of equilibrium methods of slope stability analysis, in: s. l. koh (ed.), 'mechanics of landslides and slope stability'. engineering geology 16(1), 5-7. doi : 10.1016/0013-7952(80)90003-4. duncan, j.m., 1996. state of the art: limit equilibrium and finite-element analysis of slopes. j. geotechnical engineering, asce 122(7), 577-596. doi:10.1061/(asce)0733-9410(1996)122:7(577) duncan, j.m., 1999. factors of safety and reliability in geotechnical engineering. spencer j. buchamen lecturetexas a&m university. 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preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. doi: doi : 10.24273/jgeet.2016.11.5 rahman, m.h., khan, y.a., 1995. landslides and stability of coastal cliffs of cox's bazar area, bangladesh. natural hazards 12: 101-118. doi : 10.1007/bf00613071 rahman, m.z., hossain, m.s., kamal, a.s.m.m., siddiqua, s., fansab, m., farazi, a.h., 2017. seismic site characterization for moulvibazar town, bangladesh. bulletin of engineering geology and the environment 121. doi: 10.1007/s10064-017-1031-6 sun, j., zhao, z., 2013. stability charts for homogenous soil slopes. j. geotechnical and geoenvironmental engineering, asce 139(12). doi: 10.1061/(asce)gt.19435606.0000938. http://dx.doi.org/10.4236/ojce.2012.21005 http://cedb.asce.org/cedbsearch/record.jsp?dockey=0007912 http://cedb.asce.org/cedbsearch/record.jsp?dockey=0007912 https://doi.org/10.1016/0013-7952(80)90003-4 https://doi.org/10.1061/(asce)0733-9410(1996)122:7(577) http://www.theijes.com/papers/v2-i3/l023069074.pdf http://www.theijes.com/papers/v2-i3/l023069074.pdf http://dx.doi.org/10.3329/jsr.v10i2.34225 http://www.asce.org/templates/publications-book-detail.aspx?id=6760 http://www.asce.org/templates/publications-book-detail.aspx?id=6760 https://www.ijser.org/onlineresearchpaperviewer.aspx?landslide-problem-in-lalkhan-bazar-area-of-the-chittagong-city-bangladesh.pdf https://www.ijser.org/onlineresearchpaperviewer.aspx?landslide-problem-in-lalkhan-bazar-area-of-the-chittagong-city-bangladesh.pdf https://www.ijser.org/onlineresearchpaperviewer.aspx?landslide-problem-in-lalkhan-bazar-area-of-the-chittagong-city-bangladesh.pdf https://www.ijser.org/paper/disaster-due-to-slope-failure-in-the-pahartoli-area-of-the-chittagong-city.html https://www.ijser.org/paper/disaster-due-to-slope-failure-in-the-pahartoli-area-of-the-chittagong-city.html http://stmjournals.com/tech/index.php?journal=joge&page=article&op=view&path%5b%5d=568 http://stmjournals.com/tech/index.php?journal=joge&page=article&op=view&path%5b%5d=568 https://doi.org/10.4236/ijg.2017.84031 https://doi.org/10.1139/cgj-2013-0385 https://doi.org/10.1007/s12665-011-1483-0 http://www.iosrjournals.org/iosr-jmce/papers/vol14-issue4/version-4/f1404044348.pdf http://www.iosrjournals.org/iosr-jmce/papers/vol14-issue4/version-4/f1404044348.pdf https://doi.org/10.1061/(asce)1090-0241(2002)128:4(351) https://doi.org/10.1061/(asce)1090-0241(2002)128:4(351) https://doi.org/10.24273/jgeet.2016.11.5 https://doi.org/10.1007/bf00613071 https://doi.org/10.1007/s10064-017-1031-6 https://doi.org/10.1061/(asce)gt.1943-5606.0000938 https://doi.org/10.1061/(asce)gt.1943-5606.0000938 farazi et al./ jgeet vol 03 no 03/2018 173 taylor, d.w., 1937. stability of earth slopes. j. boston society of civil engineers 24(3). reprinted in: contributions to soil mechanics. 1925 to 1940; boston society of civil engineers 337 386. taylor, d.w., 1948. fundamentals of soil mechanics. john wiley & sons, usa. © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. study area 2.1 geology and geomorphology 3. materials and methods 4. result and discussion 5. conclusions acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 yantrapalli et al./ jgeet vol 03 no 01/2018 25 a study on influence of real municipal solid waste leachate on properties of soils in warangal, india sudheerkumar yantrapalli 1, *, hari krishna p 2 , srinivas k 2 1 geotechnical engineering, nit warangal, warangal, india 2 department of civil engineering, nit warangal, warangal, india * corresponding author : sudheerkumar@student.nitw.ac.in tel.:+91 9866938516 received: jan 2, 2018. revised : feb 22, 2018, accepted: feb 26, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.1047 abstract warangal city generates three hundred tons of garbage daily which is dropped into the rampur dump yard by warangal municipal corporation (wmc). dumping of wastes will lead to the formation of leachate which in turn will cause environmental issues like soil and ground water contamination. chemical analysis of leachate indicates that calcium, chloride, sodium and magnesium are the major ions, along with organic content. this leads to contamination of soil as well as ground water bodies. in this study, authors have attempted to know the behavior of soil under the influence of leachate. contaminated specimens were prepared and tested for atterberg limits, shear strength, swell potential and hydraulic conductivity of inorganic clays, high plasticity, fat clays (ch) and sand-clay mixtures (sc) which are present in the dumping yard. index properties, hydraulic conductivity and swell potential decreased with increase in leachate concentration. unconfined compressive strength also showed an increase. the decrease in hydraulic conductivity indicated the clogging of pores. in a nutshell, the present work deals with the impact of leachate on the index and engineering properties of ch and red soil. keywords: soil contamination, leachate, atterberg limits, unconfined compressive strength (ucs), swell potential, hydraulic conductivity. 1. introduction rapid industrialization, urbanization and the rise in community living standards have tremendously increased the generation of enormous quantity of municipal solid wastes (pandey, 2011; orhan, 2013). municipal solid waste (msw) is mostly a combination of domestic wastes such as plastic, electrical, battery wastes and industrial wastes which are more aggressive in nature and causes severe contamination to the soil and surrounding water bodies (uppot and stephenson, 1989; khan and pise, 1994; soule and burns, 2001). in order to prevent the adverse effects caused by the unscientific disposal of these wastes, the most common disposal methods employed are incineration, stabilization/ solidification and landfilling. among all these methods, landfilling is considered to be a safe and economical method to contain the waste (reddy et al., 2017). any negligence in waste management will contribute to numerous environmental problems and may even affect living things. also, soil-leachate interactions may alter the properties of soil (ramakrishna et al., 2011; khan et al., 1994). leachate is a hazardous liquid produced in landfills when moisture interacts with municipal solid waste (msw) (sabrina et al., 2013). the major environmental impacts related to landfill leachate are pollution of the surface and sub-surface water (peter et al., 2013). previous studies have shown that the soil properties were changed after interacting with leachate (mesri and olson, 1970; sridharan and venkatappa rao, 1979; sridharan et al., 1981; sivapullaiah and savitha, 1997; sunil et al., 2006). most of the studies were related to the influence of leachate on geotechnical properties such as atterberg limits and strength properties, while the swelling behavior of the leachate contaminated soil was largely untouched. this paper mainly deals with the influence of msw leachate on the swelling behavior of locally available soils (ch and sc: inorganic clays, low to moderate plasticity). 2. materials and methodology 2.1 materials the material used in this study was collected from nit warangal campus and msw leachate was collected from rampur open dump yard. the properties of nitw campus soils are presented in table 1 and the soils were classified as highly compressible clay (ch) and clayey sand (sc). the soils used in this study was collected from national institute of technology (nit) warangal (nitw) campus and msw leachate was collected from https://www.google.hu/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahukewj72m3pksvyahvrp5okhacdahwqfggnmaa&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fnational_institute_of_technology%2c_warangal&usg=aovvaw3zoobkk-uonn4msifmfkyn https://www.google.hu/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahukewj72m3pksvyahvrp5okhacdahwqfggnmaa&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fnational_institute_of_technology%2c_warangal&usg=aovvaw3zoobkk-uonn4msifmfkyn 26 yantrapalli et al./ jgeet vol 03 no 01/2018 rampur open dump yard in warangal. the properties of nitw campus soils are presented in table 1 and the soils were classified as ch and sc soil. the leachate, collected from the dump yard, was stored at 4°c to avoid microbial growth. the leachate composition is presented in table 2. table 1. properties of soil parameters bc soil red earth gravel (%) 4 8 sand (%) 26 51 silt (%) 30 8 clay (%) 40 33 classification ch sc specific gravity 2.6 2.67 liquid limit (%) 62 58 plastic limit (%) 26 24 plasticity index (%) 36 34 mdd (g/cc) 1.55 1.59 omc (%) 24.7 23 fsi (%) 40 30 mdd: maximum dry density, omc: optimum moisture content and fsi: free swell index table 2. chemical composition of landfill leachate parameter concentration (mg/l) method cod 50800 open reflux bod 28000 winkler s ec 13.62 conductivity meter tds 30000 tds meter tss 85450 filtration ta 11820 phenolphthalein th 112350 edta titration chloride 500 io n c h ro m a to g ra p h y sulphate 72 sodium 368 potassium 17 calcium 876 magnesium 318 io n c h ro m a to g ra p h y manganese 67 ammonium 48 mercury 3 zinc 37 iron 67 cobalt 38 lead 0.7 ph 7 ph meter cod: chemical oxygen demand bod: biological oxygen demand ec: electrical conductivity (mi mhor /cm) tds: total dissolved solids tss: total suspended solids ta: total alkalinity th: total hardness 3. results and discussions 3.1 atterberg limits variation of atterberg limits for two soil samples (ch and sc) mixed with various percentages of leachate are shown in figs 2 and 3. the liquid limit for uncontaminated ch soil was observed as 62% (fig 2). 0 5 10 15 20 25 0 10 20 30 40 50 60 70 l iq u id l im it ( % ) percentage of leachate (%) liquid limit plastic limit plasticity index fig. 2 variation of atterberg limits fig. 2 shows that there is a considerable decrease in the liquid limit and plasticity index of the soil after interaction with 5% percentage of leachate. the results indicate that there is no significant differences between the liquid limit and the plasticity index with the increase in the percentage of leachate. the liquid limit for uncontaminated sc soil was found as 58% (fig. 3). 0 5 10 15 20 25 15 20 25 30 35 40 45 50 55 60 l iq u id l im it ( % ) percentage leachate (%) sc soil liquid limit plastic limit plasticity index fig. 3 variations of atterberg limits after mixing the leachate contaminant to the soil at various percentages (0%, 5%, 10% and 20%) by weight of soil, it was observed that the liquid limit showed a decrease with an increase in the concentration of leachate and the variation of these atterberg limits were slightly less when compared to the ch soil sample. this decrease in the atterberg limits are due to the predominant influence of the increased electrolyte concentration and organic chemicals present in the leachate on the diffuse double layer thickness of soil. the reduction in the diffuse double layer thickness of soil caused due to yantrapalli et al./ jgeet vol 03 no 01/2018 27 the increased electrolyte concentration and the reduction in the inter-particle cohesive nature due to the adsorption of the organic chemicals on the clay particles led to the decrease in the atterberg limits (mathew and rao, 1997; eric et al., 2005). 3.2 unconfined compressive strength the variation of unconfined compressive strength (ucs) in fig. 4 shows value for the two soil samples (ch type and sc type) mixed with various proportions of leachate. it was observed that the uncontaminated ch soil has a ucs value of 1.7 kg/cm 2 . after mixing the leachate with the soil at various percentages (0%, 5%, 10% and 20%) by weight of soil with a curing period of 3 days, it was observed that there is a slight increase in ucs with increase in percentage of leachate. for uncontaminated sc soil, the unconfined compressive strength (ucs) was observed as 1.66 kg/cm 2 . at 20% leachate, the increase in strength was 7% compared with uncontaminated ch soil, whereas the increase is only 4% for sc soil. this increase in ucs is due to the electrolyte concentration in the msw leachate which results in particle aggregation to a flocculated structure, thereby leading to an increase in the ucs of the soil (mitchell and soga, 2005). 3.3 hydraulic conductivity the hydraulic conductivity (k) test on the soil samples were conducted by using variable head permeameter (is 2720 part 17 and roque and didier, 2006). the hydraulic conductivity (k) of ch soil and sc soil samples were found as 6.8 × 10 -7 cm/sec and 1.7 × 10 -4 cm/sec, respectively after permeating the soil sample with water and 3.2 × 10 -7 cm/sec and 3.4 × 10 -5 cm/sec, respectively after leachate permeation. the percent reduction of hydraulic conductivity for ch and sc soil samples were observed as 52% and 80% respectively. the reduction of hydraulic conductivity for ch and sc soils after interacting with leachate is 52 and 80 percentage respectively. 0 5 10 15 20 25 1.65 1.70 1.75 1.80 1.85 u c s ( k g /c m 2 ) percentage of leachate (%) ch soil sc soil fig. 4 ucs after interaction with msw leachate the reduction in hydraulic conductivity is mainly due to the presence of suspended particles and biological activity (small bacteria) obstructing the flow of leachate through the voids of the soil. table 3 shows that the reduction in hydraulic conductivity is more in sc soil when compared to ch soil. this is due to the formation of more bacterial activity and suspended particles getting accumulated in the bigger void spaces of sc soil. table 3 variation of hydraulic conductivity for ch and sc soil types with water and leachate. soil type hydraulic conductivity (k = cm/sec) percentage reduction in hydraulic conductivity water leachate ch 6.8 × 10 -7 3.2 × 10 -7 52 sc 1.7 × 10 -4 3.4 × 10 -5 80 3.4 swelling potential two table 4. variation of swelling potential for two soil types with water and leachate. soil type swelling potential (%) decrease in swelling potential water leachate ch 22 13 9 sc 9.7 6 3.7 it was observed that the decrease in swelling potential for ch soil was about 9% more than sc soil which was about 3.7%. from the results of swelling potential, it is observed that the swelling potential depends on clay content and minerals present in the soil. thus, the ch soil is found to be more reactive with leachate than sc soil. from fig 5, it is clear that the percentage swelling for ch soil with water is 22%, whereas swelling potential with leachate is reduced to 13%. the decrease in the percentage swell is due to changes in the diffuse double layer repulsive forces caused by the presence of organic chemicals and also due to the smaller dielectric constant of leachate (foreman and daniel, 1986; murat and mustafa 2009). 0 5 10 15 20 25 30 35 0 5 10 15 20 25 s w el l p o te n ti al ( % ) time (days) ch soil + water ch soil + leachate also, it was observed that as the percentage of leachate concentration in the soil increased, the 28 yantrapalli et al./ jgeet vol 03 no 01/2018 plasticity of the soil was reduced simultaneously. since swelling is a function of plasticity, the swelling potential is reduced. it was observed from fig 6, that the swelling potential for sc soil with water is 9.7%, whereas percent swell with leachate is decreased to 6%. the changes in swelling in the soils might be due to changes in repulsive forces and the reduction in the plasticity of the soil. when compared to the sc soil, the ch soil shows more swelling and after interacting with leachate, the swelling of both sc and ch soils reduced significantly. 0 5 10 15 20 25 0 1 2 3 4 5 6 7 8 9 10 s w e ll p o te n ti a l (% ) time (days) sc soil + water sc soil + leachate fig. 6 variations of swelling potential with water and leachate in sc soil 3.5 scanning electron microscope (sem) the uncontaminated soil samples and samples contaminated with leachate were collected from the oedometer after completion of the swell tests. these collected samples were tested for morphological changes. the results are as shown in fig. 7a and 7b. uncontaminated soil contaminated soil fig. 7a sem of ch soil uncontaminated soil contaminated soil fig. 7b sem of sc soil the sem images of the contaminated and uncontaminated soil samples of ch and sc soils show the changes in the morphology of the soil particle after interacting with the leachate. the morphology of both the soils are associated with the arcuate steps, imbricated blocks, fractured plates, meandering ridges and irregular depressions which indicate the aggregation of the soil particles. this leads to the decrease in the plasticity index and the swell potential and the increase in the unconfined compressive strength (ucs) of the leachate contaminated soil when compared to uncontaminated soil. 4. conclusions from the above experimental study, it is concluded that the liquid limit and plasticity index decrease with an increase in the percentage of leachate. these changes are more for the ch soil sample than sc soil sample. the unconfined compressive strength (ucs) also showed an increase with the presence of leachate for both ch and sc soil samples. the hydraulic conductivity of the soil after permeating with leachate decreased due to the blockage of pores by leachate and the hydraulic conductivity of ch soil is well within the range of usepa specified liner material requirement (i.e. < 1 × 10 -7 cm/sec). the swelling potential with water for ch soil was more than for sc soil. the decrease in swelling potential with leachate for ch soil was more than that for sc soil. from the above study, it is concluded that the landfill leachate was more reactive with ch soil than sc soil and it persisted its hydraulic conductivity after interaction with leachate. references eric m.f., ernest k., yanful,. 2008. interactions between three tropical soils and municipal solid waste landfill leachate. journal of geotechnical and geo-environmental engineering134, 379 395. foreman, d.e., daniel, d.e., 1986. permeation of compacted clay with organic chemicals. journal of geotechnical engineering, asce 112 (7), 669 681. is 2720-10., methods of test for soils, part 10. determination of unconfined compressive strength. is 2720-4., methods of test for soils, part 4. grain size analysis. is 2720-5., methods of test for soils, part 5 determination of liquid and plastic limit. khan, a.k., pise, p.j., 1994. effect of liquid wastes on the physico-chemical properties of lateritic soils. proceedings of indian geotechnical conference, 189 194. khan, s.a., rao, c.u., bandyopadhyay, m., 1994. characteristics of leachates from solid wastes. indian journal of environmental health 36 (4), 248 257. mathew p.k., rao, s.n., 1997. influence of cations on compressibility behaviour of a marine clay. yantrapalli et al./ jgeet vol 03 no 01/2018 29 journal of geotechnical engineering 123 (11), 1071 1073. mesri, g., olson, r.e., 1970. shear strength of montmorillonite. geotechnique 20 (3), 261 270. mitchell, j. k and soga, k., 2005. fundamentals of soil behavior. john wiley & sons, inc., new york, n.y. murat, o., mustafa, y., 2009. effect of organic fluids on the geotechnical behavior of a highly plastic clayey soil. journal of applied clay science, 48, 615 621. orhan, a., 2013. municipal solid waste landfill site selection using geophysical information system: a case study from corlu, turkey . arob journal of geoscience. pandey, p.c., sharma, k.l., and nathawat, m. s., 2011. geospatial strategy for sustainable management of municipal solid waste for growing urban environment. environ monit assess, 184, 2419 2431.d peter, k., morton, a.b., alix, p.r., anders, b., anna, l and thomas, h.c., 2013. present and long-term composition of msw landfill leachate: a review. critical reviews in environmental science and technology, 32(4), 297 336. ramakrishna, g.c., ramakrishna, y., shiva shankar, r., sivapullaiah, p.v., 2011. geotechnical properties of shedi soil affected by alkali contamination. international journal of environmental protection 4, 45-52. reddy, k.r., girish, k., and rajiv, k.g., 2017 system effects on bioreactor landfill performance based on coupled hydro-bio-mechanical modeling. journal of hazardous, toxic, and radioactive waste, 22 (1), 1 15. roque, a.j., and didier, g., 2006. calculating hydraulic conductivity of fine grained soils to leachates using linear expressions. journal of engineering geology, uk85 (1), 147 157. sabrina, l. b., and craig, h. b., 2013. effect of municipal solid waste leachate on hydraulic conductivity and exchange complex of geosynthetic clay liners. journal of geotechnical and geo-environmental engineering, 140 (4), 1 -17. sivapullaiah, p.v., savitha, s., 1997. performance of bentonite clay liner with electrolytic leachates. proc. of indian geotechnical conference, vododara, india, 363 366. soule, n. m., and burns, s. e., 2001. effects of organic cation structure on behavior of organobentonites. journal of geotechnical and geo-environmental engineering, asce 127 (4), 363 370. sridharan, a., nagaraj, t. s., and sivapullaiah, p.v., 1981. heaving of soil due to acid contamination. proc. of international conference on soil mechanics foundation engineering, vol. 2, pp. 383 386. balkema, stockholm. sridharan, a., and venkatappa rao, g., 1979. shear strength behaviour of saturated clays and the role of the effective stress concept. geotechnique 29 (2), 177 193. sunil, b m., sitaram, n s., and srihari., 2006. effect of ph on geotechnical properties of laterite soils. journal of engineering geology, vol. 85, pp 197203. uppot, j. o., and stephenson, r.w., 1989. permeability of clays under organic permeants. journal of geotechnical engineering, asce 115 (1), 115 131. 1. introduction 2. materials and methodology 2.1 materials 3. results and discussions 3.1 atterberg limits 3.2 unconfined compressive strength 3.3 hydraulic conductivity 3.4 swelling potential 3.5 scanning electron microscope (sem) 4. conclusions references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 264 rizki, f. et al./jgeet vol 02 no 04/2017 mapping of vegetation and mangrove distribution level in batam island using spot-5 satellite imagery fajar rizki 1, *, arini dewi lestari situmorang 1 , nirwana wau 2 , muhammad zainuddin lubis 1 , wenang anurogo 1 1 department of informatics engineering, geomatics engineering, politeknik negeri batam, batam kepulauan riau, 29461 indonesia. * corresponding author : fajarsgia@gmail.com tel+6281342578087, office : 778-469856 ext : 2510; fax: +62-778-463620 received: nov 1, 2017. revised : nov 15, 2017, accepted: nov 30, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.1002 abstract mangrove is a plant that plays a significant role in the balance of the ecosystem and coastal environment. batam island which is one of the islands in batam island become one of the areas rich in mangrove plants. as time goes by, mangrove forests are getting worse. this research uses spot-5 imagery data in analyzing mangrove density value in batam island with msavi (modified soil adjusted vegetation index) method. the results of this study have mangrove density in batam island which is divided into four classes, which is very tenuous, tenuous, medium, and very tightly where batam island is dominated by a class of density. theoretically, ndvi values range from -1 to +1 but the mangrove vegetation index values are generally in the range between +0,1 to +0,7. ndvi values greater than this range are associated with a representation of a better level of vegetation health in the islands of batam. keywords: mangrove, vegetation index, msavi, spot-5 satellite imagery 1. introduction mangrove forest is a type of forest overgrown with typical mangroves along the coast or river estuaries and affected by tidal water (hidayah & wiyanto, 2013; ajithkumar et al., 2008). mangrove is a type of plant that lives in brackish water located on the coastline and is influenced by sea tides. the unique mangrove ecosystem is one of the factors why mangrove has a significant role in maintaining environmental and ecosystem balance such as preventing coastal erosion and abrasion, living on the source of food sources of some animals, and contributing to the formation of the island as well as stabilizing the coastal area (anurogo et al., 2015). riau islands are one of the provinces in indonesia which has a large mangrove forest, one of them is batam city, but the condition of mangrove forest in the city of batam increasingly critical is marked by the extensive depth of mangrove forest in batam city which originally 27% until now only remaining 4.7 %. riau islands is one of the provinces in indonesia which has a large mangrove forest, one of them is batam city, but the condition of mangrove forest in the city of batam increasingly critical is marked by the extensive depth of mangrove forest in batam city which originally 27% until now only remaining 4.7 % (lubis & daya, 2017; anurogo et al., 2017. along with the development of technology especially in the field of remote sensing allows us to monitor and examine the condition of mangrove forest in the city of batam by using satellite imagery (farizki & anurogo, 2017). with remote sensing technology, spectral values in satellite imagery can be extracted into mangrove object information in the range of near-visible spectra (suwargana, 2008; sari, & lubis, 2017; lubis et al., 2017; conchedda et al., 2008). in this research is to know the distribution and value of mangrove density in batam city using spot-5 satellite image, using the composite technique of band 3,2,1 in vegetation identification using band 2 as red spectrum and band 3 as near infrared (nir). fig. 1. research location mailto:fajarsgia@gmail.com rizki, fajar. et al./jgeet vol 02 no 04/2017 265 2. material and methodology the location of the study was conducted in the area of batam, riau islands province at coordinates 01º 08 'lu 104º 00' bt. satellite data used is spot5 imagery with the date of acquisition 09 april 2014 which previously been done by geometric and radiometric correction process. map of research location can be seen in fig. 1. 3. data processing method analysis of image data for the determination of mangrove vegetation refers to the results of rgb 321 composite image exploration and supervised classification (green et al., 2000). the value of mangrove vegetation density was determined by using ratio method between infra red channel and red channel (green et al., 2000) with the following formula: (1) information: ndvi = normalized difference vegetation index infrared = channel 3 spot-5 imagery red = channel 2 spot-5 imagery in addition to ndvi, there are several transformations that can be used to determine the density value of a vegetable object, we used msavi (modified soil adjusted vegetation index) method. msavi is a transformation developed from ndvi transformation to minimize the effect of soil reflections on ndvi, with the following formula: msavi = {𝟐 (𝑵𝑰𝑹)+𝟏− √{𝟐(𝑵𝑰𝑹)+𝟏}𝟐−𝟖 {(𝑵𝑰𝑹)−𝑹𝒆𝒅 𝟐 (2) where nir (near infra red) is band 3 and red is band 2 for spot-5 imagery. then the class value of ndvi is reclassified into five classes, ie very rare density, rare, medium, meeting and very tight. calculation of the density class interval based on the formula (huete,1988) are as follows: 𝐾𝐿 = 𝑥𝑡−𝑥𝑟 𝑘 (3) where kl is the interval class, xt is the highest value, xr is the lowest value and k is the desired number of classes. the research flow diagram can be seen in fig. 2. before doing the processing and identification of mangrove on spot-5 imagery first done geometric and radiometric. geometric correction for geometric correction is the process of positioning an image that corresponds to the actual world map coordinates. to improve the pixel image that looks more clear, by performing the mathematical calculation of the required band. there are three stages in the radiometric correction process: a. dn to radiance 𝑳 = 𝐃𝐍 𝐀 (4) where : dn = band a = gain b. radiance to reflectance (5) where: ρ = unitless planetary reflectance lλ aperture d2 = earth-sun distance in astronomical units esunλ = mean solar exoatmospheric irradiances θ = solar zenith angle in degrees fig. 2. the research flow diagram 4. results and discussion the results of rgb 321 composite image analysis and image classification shows that the existence of this ecosystem is only found to spread on the coastal city batam (fig. 3). object detection (mangrove location) sample can be seen in fig. 4. by doing its classification between mangrove and nonmangrove then we can identify mangrove plants 266 rizki, f. et al./jgeet vol 02 no 04/2017 found around coastal areas in some areas of batam island, especially in batu aji subdistrict. the mangrove density value is explained based on the pixel value of the transformation of msavi which has been done and explained into 4 classes namely; very tenuous, tenuous, medium, tight and very tight. with the lowest pixel value 0.134842247 and the highest pixel value 0.364502162 (see table 1). the vegetation index (ndvi) can represent the density (biomass) or greenish level calculated as the ratio between the measured reflections of the red band (r) and the near infra red band (nir) on the spectrum of electromagnetic waves. both bands were chosen because their size results were most influenced by the absorption of leaf chlorophyll. the red light (r) is very slightly reflected while the near infrared light (nir) is reflected strongly. theoretically, ndvi values range from -1 to +1 but the mangrove vegetation index values are generally in the range between +0,1 to +0,7. fig. 3. value of mangrove density on batam island (a) (b) fig. 4. detection example of mangrove on research location (spot-5 visible) (a), composite band 321 spot-5 (b) rizki, fajar. et al./jgeet vol 02 no 04/2017 267 table 1. range value of density class of mangrove 5. conclusion the mangrove condition in batam island is dominated by the density of tenuous with the widest mangrove distribution in the southern area of batam city, that means the preservation of mangrove forests should continue to be done in order to maintain the balance of the environmental ecosystem of batam as one of the coastal areas in indonesia. references ajithkumar, t.t., thangaradjou, t. and kannan, l., 2008. spectral reflectance properties of mangrove species of the muthupettai mangrove environment, tamil nadu. journal of environmental biology, 29(5), pp.785-788. anurogo, w., lubis, m.z., khoirunnisa, h., pamungkas, d.s., hanafi, a., rizki, f., surya, g., situmorang, a.d.l., timbang, d., sihombing, p.n. and lukitasari, c.a., 2017. a simple aerial photogrammetric mapping system overview and image acquisition using unmanned aerial vehicles (uavs). journal of applied geospatial information, 1(01), pp.11-18. anurogo, w., murti, s.h. and khakhim, n., 2015. analisis perubahan hutan mangrove dalam penentuan kawasan rehabilitasi dan perubahan stok karbon menggunakan data penginderaan jauh (di teluk banten, serang provinsi banten) (doctoral dissertation, universitas gadjah mada). conchedda, g., durieux, l. and mayaux, p., 2008. an objectbased method for mapping and change analysis in mangrove ecosystems. isprs journal of photogrammetry and remote sensing, 63(5), pp.578589. farizki, m. and anurogo, w., 2017. pemetaan kualitas permukiman dengan menggunakan penginderaan jauh dan sig di kecamatan batam kota, batam. majalah geografi indonesia, 31(1), pp.39-45. green, e.p., p.j. mumbay, a.j. edwards, and c.d. clark. 2000. remote sensing hand book for tropical coastal management.unesco publishing. hidayah, z. and wiyanto, d.b., 2013. analisa temporal perubahan luas hutan mangrove di kabupaten sidoarjo dengan memanfaatkan data citra satelit. jurnal bumi lestari, 13(2). huete, a.r., 1988. a soil-adjusted vegetation index (savi). remote sensing of environment, 25(3), pp.295-309. lubis, m.z. and daya, a.p., 2017. pemetaan parameter oseanografi fisik menggunakan citra landsat 8 di wilayah perairan nongsa pulau batam. jurnal integrasi, 9(1), pp.9-15. lubis, m.z., sari, d.p., aprilliyanti, t., daulay, a.k., hanafi, a., ananda, f., saputri, d.a., aminah, s., zabid, m.a.p. and ibrahim, m.m.r., 2017. penggunaan citra landsat 8 untuk pemetaan persebaran lamun di pesisir pulau batam. dinamika maritim, 6(1), pp.7-11. purwanto, a.d., asriningrum, w., winarso, g. and parwati, e., 2014. analisis sebaran dan kerapatan mangrove menggunakan citra landsat 8 di segara anakan, cilacap. in proceeding of seminar nasional penginderaan jauh. bogor. sari, d.p. and lubis, m.z., 2017. pemanfaatan citra landsat 8 untuk memetakan persebaran lamun di wilayah pesisir pulau batam. jurnal enggano, 2(1). suwargana, n., santo, j., lapan, j.l. and timur, p.p.r.j., 2008. updating informasi spasial tutupan lahan propinsi kalimantan selatan dengan menggunakan citra landsat-7/etm+. lapan, jalan lapan, 70. class range very tenuous 0.1348422470.177338373 tenuous 0.177338373-0.195421831 medium 0.195421831-0.211696943 density 0.211696943-0.228876228 very density 0.228876228-0.364502162 1. introduction 2. material and methodology 3. data processing method 4. results and discussion 5. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 03 2018 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 141 research article building of turbiditic gas field dynamic model with a simplified 3d simulation software octria adi prasojo 1, *, reza syahputra 1 1 geology study program., fmipa, universitas indonesia, kampus ui depok, depok 16424, indonesia * corresponding author: octria.adi@sci.ui.ac.id tel.: +62 8211 716 4416 received: july 18, 2018; accepted: aug 26, 2018. doi: 10.24273/jgeet.2018.3.3.1857 abstract this study provides a novel approach of building 3d simulation model with extremely shorter time needed using rubis simulation software from kappa engineering. the study focused on x field that is located in a turbiditic setting, mainly consisted of separated channel bodies filled with gas, located in a slope apron or passive continental margin of mahakam delta. methods of the study is quite contradictive with common reservoir simulation where it includes data integration, data quality control, model geometry building, reservoir properties distribution, and is followed by wells definition to build the 3d simulation model. afterward, the reliability of the structural model was checked by the volume calculation for each segment from geox model where all dynamic and static data used in the simulation were checked using history matching data derived from well-testing. in conclusion, simulation was run and x field will be producing for 23 years with 3 years and 10 months plateau rate. where the static and dynamic data are already provided, the simulation conducted here was very beneficial during the exploration phase of a gas field where the whole process of modeling and simulation could be done only for 3 to 6 months. keywords: turbidite, simulation, well-test interpretation, mahakam 1. introduction x field is composed of stacked gas reservoirs located 75 kilometre of borneo island (fig. 1) (internal report, 2011). it is located within deep-water continental slope setting on the tip of a delta front. the field is currently under early development phase and the first gas production has been expected in the next few years (internal report, 2011). this field consist of 2 main segments: x north east (ne) field and x main field where it is separated in the distance of 5 kilometre. this study would be focused in x main field where it has more gas in place during the previous exploration phase study. x main field was indicated as turbiditic reservoir deposited in the slope of passive continental margin (internal report, 2011). this type of depositional environment would have the characteristic of intercalation between sand and shale with the shape of channel-like geometry. in the x main field, it consisted of mainly 10 separated independent segments that would be modeled and simulated during this study. it will compile the seismic data, core, special core analysis (scal), well logs, and well test data to build reliable yet quick 3d simulation model using rubis software. 1.2 aim the aim of this study is to use all the data available during the exploration phase of this field to build simplified 3d reservoir model using rubis software and to see if this model is quick and reliable enough to be compared with simpler model such as material balance model. in order to build the simplified reservoir, it would be started by building structural model using the seismic interpretation available (internal report, 2011). afterward, all well log data will be used to give the value of net to gross (ntg) and average porosity for each reservoir segment (internal report, 2011). while for the permeability value, porosity versus permeability values derived from core plug measurement from one exploratory well will be distributed in all segments. this might be representative enough for the homogeneous lithology deposited under the same turbiditic condition. scal data will provide the extended capillary pressure (pc) curve to better estimate the value of irreducible water saturation (internal reservoir study, 2011). at the end, the ultimate objective of the study was to build a simplified 3d reservoir numerical model using rubis software in a much faster way than using petrel and eclipse. rubis (rubis software (kappa engineering), 2015) is somewhere located in between 1d material balance and the massive 3d simulation models. it replaces neither but does give reliable perspective of reservoir performance of a dry gas field. this study would highly benefit the reservoir engineer and geoscientist during the exploration or early http://journal.uir.ac.id/index.php/jgeet 142 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 development phase by building reliable simulation model in very short amount of time. 2. geological framework 2.1 regional geology x main field is located in kutai basin which was formed as a product of the interaction between three main plates: eurasian plate, indo-australian plate, and pacific plate. located in the top east of kalimantan/borneo, kutai basin covers about 165.000 sq. km, and is one of the deepest of the tertiary basins in indonesia which contains up to 12.000 m of tertiary sediment (alam et al, 1999). the similarity between the eocene strata of the barito, asem-asem and kutai basins has led many workers to suggest the three basins formed a single eocene depocentre (e.g. heryanto, 1993; mason et al., 1993; panggabean, 1991; pieters et al., 1987; van bemmelen, 1949; van de weerd and armin, 1992 kalimantan mega ba e.g. heryanto et al., 1996). the kutai basin became separated in the early oligocene due to down-throw on the northern side of the paternoster fault (witts et al, 2012). x main field was deposited in a continental slope where it was characterized by numerous stacked gas charged channels in the pliocene succession (internal report, 2011). high energy deposition of turbidite complex produced sand-shale intercalation channel shape reservoir with bouma sequence as a common sedimentological feature (bouma, 1962). the channels can be up to several kilometres wide and hundreds of kilometers long, and provide the transport pathways for large quantities of sediment, nutrients and carbon talling et al, 2007). x main field is located in a confined channel geometry, where the x ne field is located in the downstream part of a submarine slope where lateral distribution is more extensive in this particular field (fig.1) (internal report, 2011). fig. 1. depositional environment of x main and x north east field (internal report, 2011). this field was composed of 10 separated segments that was based on its depositional environment. each segment was filled by a single deep-water turbidite channel. it would be modelled as 10 different layers surrounded by shale (zero flow capacity lithology) based on its natural behaviour. these 10 layers were named as segment b2, a2, a, c, d, e, f, g, i1, and i2 from the shallowest to the deepest. reservoir would have channel geometry with around 762 meter wide and 6,7 km long based on the seismic interpretation. with the intercalation of sand-shale lithological features inside the reservoir caused by the deep water turbidity current, it will make a challenging reservoir to be modelled and simulated either by geologist or reservoir engineer. theoretically, turbidity currents tend to make their way through channels and bound themselves by many natural levees (salaheldin et al, 2000).these channels open paths for the turbidity currents and directing sediments to the lower regions of submarine fans. with the gradual decrease of both slope angle and gravitational potential energy, the rate of sediment deposition decreased, forming a concave profile. therefore there is expected loss of momentum to bring particle of sand onto far distances. the fine materials such as silt and clay are essential factors in turbidity currents to transport sand-sized particle (reading and richards, 1994). in the presence of the fine particles, turbidity currents able to keep enough momentum to produce suspension so the sands are able to travel along the channels (mutti and lucchi, 1972). yet in the reservoir geometry modelling process, the channel would have the shape of elongated separated lobes with a concave base for each lobe. 3. method this study would compile seismic data, cores, scal, well log, and well test data in order to build 3d simulation model. based on the seismic, log, core, and well testing data on well kc-2, the reservoir model would be built based on this following workflow: 1. geometry building, which is integration of depth structure maps (either top or bottom of an interval), isochore maps, and reservoir segments extensions into a structural model. fig. 2. x main field location (internal report, 2011) 2. reservoir properties modelling with data obtained either from the field analogues, wells, cores, well tests, or scal as an input. 3. wells placement, integrating trajectory, perforations, completions, and well controls. then rubis would build the grid automatically with the properties and wells in it. 4. fine tuning of the model, including local grid refinement (lgr) around wells. 5. pressure and saturation initialization. schedule, time steps, and output such as simple x main field x north east field x field kc – 2 dir well kc – 3 well kc – 1 well prasojo, octria a. et al./ jgeet vol 03 no 03/2018 143 plots or 3d maps showing pressure or saturation distribution in the model at different time steps. nevertheless, there were several assumptions during the building of this simplified gas reservoir. these assumptions were extracted based on the software capability to model the reservoir and due to the data limitation (table 1). table 1. assumptions used in creating the reservoir model static data  reservoir geometry was defined deterministically by seismic amplitude  non reservoir layers were considered as shale  isochore maps were based on seismic interpretation dynamic data  permeability values are the same for both x and y lateral direction  relative permeability (kr) versus pc was derived from sand facies only  cored interval will be used as the reference to populate the reservoir in other segments  vertical lift performance is using beggs and brill correlation 3.1 availability data well data available in the x main field that is summarized in table 2. kc-1, kc-2 dir, and kc-3 dir were the exploratory wells and the other wells were development wells that will be used for the gas production later on (internal report, 2011). interpreted seismic lines crossing all reservoir segments were also available during this study. table 2. available data in x main field well name well log core & scal well test kc-1 v kc-2 dir v v v kc-3 dir v kc-4 v kc-5 v kc-6 dir v kc-7 dir v kc-8 v 3.2 seismic data seismic interpretation has been done in order to understand the shape of the reservoir geometry, connectivity between the reservoirs, reservoir distribution, and fluid contacts. as mentioned before, the reservoirs are separated by shale-dominated zones in between. based on amplitude anomalies on seismic line from north to south, seismic interpretation produced non-continuous top and bottom boundary of each separated reservoir segment. the seismic section was then used to create depth structure map of the whole field (fig. 3). submarine canyon and channel geometries with their confined boundaries could be clearly seen from the map. fig. 3. seismic section showing depth structure map of the field (a) (b) fig 4. subsurface maps were created by the seismic interpretation (a) depth structure map of a reservoir segment (b) isochore map of a reservoir segment. this seismic interpretation would then be used to build basic structural model of the field. first of all, all the interpreted lines will be a guide on building the depth structural maps for each segment by running a time to depth conversion using check shots data available in the wells. afterward, isochore map was built based on the true vertical depth (tvd) subtraction of the top to bottom structural maps (fig 4a). this thickness map would be used to distribute the thickness of the reservoir in each segment (fig. 4b). 144 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 3.3 core and well log data core data is available in well kc-2 dir in segment f where core description, routine core analysis (rcal) and scal were available. these data would be used as the reference to populate the reservoir dynamic properties in other segments. in general, segment f consisted of mostly intercalation of sand and shale with fining upward sequence as the main characteristic of turbiditic flow product (fig. 5). overall, 3 main lithofacies were recognized. they are described in the following lines from finer to coarser grain size. (a) (b) (c) fig. 5 detail of core description (a) facies 1 consisted mostly of silt (b) facies 2 consisted of equal proportion of fine sand and siltstone intercalation (c) facies 3 consisted of mostly medium to thick-bedded layers of medium to coarse grain sand fig. 6. lithofacies defined from the core description was inline with the electrofacies showed from the well log data in the cored-interval. facies 1 showing the shale interval indicated by high value of gr facies 1 consisted of very thin graded beds of silt, silty clay, silty sand, and coaly flakes. the presence of grading and lack of traction features indicate that these are pure fallout from a sediment-water suspension or may be a deposited pelagic sediment, representing the surrounding reservoir lithology (zero flow capacity) or outside the main channel bodies. brownish siderite (feco3) nodules and bands are often present. regarding the bouma sequence, it may be included as td or te of the sequence. facies 2 consisted of intercalation of gradedlaminated fine sands and graded siltstones with almost equal proportions. sand layers show pure traction features (traction ripples). thicker sand beds are often characterized by the occurrence of laminated intervals that are very rich of coaly flakes. the laminated intervals are describing cycles of current velocity increase and decrease. this was associated to tc of bouma sequence. facies 3: mostly medium and thick-bedded layers of medium to coarse grain sand, containing intervals rich in disorganized coaly flakes and small mudstone clasts. beds display a sharp, locally erosive base and wavy tops. these beds are the products of moderately concentrated sediment gravity flows. these layers represent the sedimentation within the channel bodies and might be considered as ta of bouma sequence. as a consequence, during the modelling, facies 1 would be considered as a non-reservoir facies. facies 2 and 3 would be distributed inside the channel reservoir bodies where these facies have more flow capacity compared to facies 1. while well log characteristics of these 3 lithofacies were noticeable from the value of gamma ray (gr), resistivity (res), sonic, neutron and density log (nphi-rhob) (fig. 6). 3.4 special core analysis scal data was available in well kc-2 dir with 8 samples used for capillary pressure measurement and relative permeability measurement. pc curve was obtained using air-brine in centrifuge at overburden pressure, while kr curve was obtained using brine acting as the reservoir liquid (wetting phase) and nitrogen acting as the non-wetting phase. x-ray was also used in order to monitor the saturation changes during steady state testing. fig. 7. dynamic rock typing was defined by leverett jfunction. three types of dynamic rock type (rt1, rt2, and rt3) were defined based on their wettability and pore types mimicked by the j-function curve. all core plugs from scal were used to obtain dynamic rock typing. dynamic rock typing was defined using the leverett j-function (leverett, 1940). this function had been used for correlating capillary pressure data for rocks with similar pore types and wettability. this technique was appropriate for correlating capillary pressure data from samples having a similar pore size distribution; as a consequence, this was not appropriate where there was heterogeneity of rock types within the reservoir (eqn. 1). plotting the leverett j-function resulted in 3 dynamic rock types that are easily distinguished (fig. 7). (1) where: pc : capillary pressure  : interfacial tension of the fluid (72 dynes/cm was used)  : contact angle (0 degree for perfectly water-wet system gr res sonic nphi-rhob chrom facies 1 facies 2 facies 3 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 145  : porosity k : permeability 3.5 well test analysis well testing had been done in one exploration well, testing particularly segment f. this deviated well was penetrating more or less in the central part of high amplitude channel shape reservoir (fig. 9). thus well test interpretation could be expected to show two parallel boundaries. this segment consists of mostly sandstone with average porosity of 0.28 and wide range of permeability from 85 to 1500 md based on core plugs measurement in ambient stress condition (800 psig). this interval was perforated from 7272-7377 ft md and 7386-7402 ft md (fig. 10). from the well log data, this interval consists of 2 different sandstone intervals separated by one shale layer in between. reservoir properties are very good and lead to 70 feet of net pay. the interval is dry gas bearing. it has 0.6 specific gravity and consists mostly of methane with no h2s. fig. 9. kc-2 dir well location mdt data was also available in this interval (fig. 11.). the mdt data showed that segment f consists only of 1 connected segment, despite the presence of 2 sand packages on the logs. this is coherent with the geological environment of the reservoir where in a turbiditic setting, a reservoir body that already settled before could be cut by the next sedimentation event on top of it. fig. 10. tested interval consisted of 2 separated net pays interval this would form stacked-channel reservoir with shaly thin shale layer in between the sand bodies. therefore it is possible to have vertically connected sand bodies like in this segment with non-continuous shale layer in between. this data then will strongly drive the well test interpretation. fig. 11. mdt data from segment f main build up analysis showed that several models could be used for matching. there are homogeneous single layer model with parallel boundaries, dual permeability model with parallel boundaries, and even 2 layers with parallel boundaries. but the most reliable model that should be used was homogeneous single layer model. the data plot, log-log plot, and semi-log plot were well matched especially in late time (after 1 hour) (fig. 12). fig. 12. log-log plot, history plot, and semi-log plot perfectly matched with homogeneous single layer model with parallel boundaries. 3310 3330 p re s s u re [ p s ia ] 140 150 160 170 180 190 200 210 220 time [hr] 0 5000 10000 15000 g a s r a te [ m s c f/ d ] history plot (pressure [psia], gas rate [mscf/d] vs time [hr]) 1e-4 1e-3 0.01 0.1 1 10 time [hr] 1e+5 1e+6 1e+7 g a s p o te n ti a l [p s i2 /c p ] log-log plot: m(p)-m(p@dt=0) and derivative [psi2/cp] vs dt [hr] -5 -4 -3 -2 -1 superposition time 7.26e+8 7.3e+8 7.34e+8 g a s p o te n ti a l [p s i2 /c p ] semi-log plot: m(p) [psi2/cp] vs superposition time 146 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 fig. 13. interpretation of vertically connected channel reservoir body based on well-test analysis. well test interpretation resulted in early time small wellbore storage (due to downhole shutting), infinite acting radial flow and homogeneous reservoir during middle time and two parallel boundaries during late time. this was coherent with overall geological model and mdt data which indicated single layer reservoir. extrapolated final build-up pressure (p*) was plotted with mdt pressure data, showing a 4 psia difference, which is acceptable (fig. 13). table 3. well test interpretation result c 0.000468756 barrel/psi skin 0.7 hw 89 feet zw 35 feet h 75 feet p* 3341 psia @ 6581.7 ft tvdss k.h. 8000 md.feet k 114 md kz/kr 0.01 1st boundary 500 feet 2nd boundary 2000 feet based on the detail result of well test interpretation, the permeability value had a mismatch between values from well test and from core plugs measurement (table 3). arithmetic average permeability obtained from the core plugs was 395 md. this might be due to cores not being fully representative of the whole sand package and therefore by-passing some lower quality intervals. this might be also due to different (p, t) laboratory conditions compared to reservoir conditions. nevertheless, this difference was still within the acceptable range (same degree of magnitude), thus permeability value from well testing would be applied for the model. as discussed before, the interpretation strongly respected the geological setting of the field where the 70 feet net pay corresponded to a stacked channel body. even though there was 9 feet shale layer in between, this shale layer was probably not continuous enough to be an efficient vertical flow barrier between those two sand bodies. this might be a typical noncontinuous shale layer in turbiditic environment representing fall-off or pelagic sediment. there were 2 boundaries interpreted to be located 500 feet and 2000 feet from the well, which was consistent with the seismic interpretation presented before. these boundaries were interpreted as sealing boundaries, with typical 1/2 slopes in derivative plot. in the turbiditic environment mostly consisting of intercalations between sand and shale, formation heterogeneity was represented by 0.01 vertical anisotropy with overall k*h of 8000 md.ft. this well test interpretation would then be used to support the reservoir properties and behavior of the 3d reservoir model. 4. reservoir simulation as mentioned earlier regarding the workflow of building the reservoir simulation (see fig. 2), reservoir simulation would be started by building the structural model or geometry building, followed by reservoir properties distribution across the field, placing the wells, fine tuning, pressure and saturation initialization, and running the simulation which will create a production forecast. step by step details on building the reservoir model will be discussed in the following sections. 4.1 geometry building during this step, the reservoir lateral extension and the number of geological layers were defined. the x main field consisted of 10 separated segments with specific reservoir properties in each segment. using the data from well log correlation and seismic amplitude, layers and the extension of reservoir segments could be defined. lateral extension of the reservoir segment were defined by the depth structure map based on the seismic interpretation (fig. 14). in rubis software, simplified segment polygons are necessary in order to optimize cpu time without jeopardizing model accuracy in terms of in place volumes. where quality control (qc) of in place volume will better guide the robustness of the reservoir model. regarding the 3d extension of the reservoir, depth structure map from petrel was imported to the model and the depth contour points were determined manually based on the depth structure map available. beside the reservoir geometry or boundaries laterally, depth structure map could be also extracted during the contouring step (fig. 15a). the depth structure map should be traced in rubis software for some major contour points (i.e. every 250 feet). afterward, rubis would interpolate points in between using several geostatistical methods that could be independently chosen. in this case, simple linear interpolation was chosen to create the top segment or boundary of the reservoir layer. as long as the interpolated map in rubis was still in accordance with detail depth structure map from the seismic interpretation, any methods to interpolate the contour points would remain considerable. the next step after the contouring was to define the reservoir base layer. at that time, the isochore maps were available to be extracted as the thickness for each reservoir segment. it was started by using the isochore maps based on seismic interpretation to be traced in every point in order to mimic the thickness heterogeneity inside the segment (fig. 15b). this step is kc-2 dir prasojo, octria a. et al./ jgeet vol 03 no 03/2018 147 quite similar with the previous step, the only difference was only the data used during this step. fig. 14. depth structure map polygons as the basic for geometry building in rubis software (a) (b) fig. 15. detail 3d reservoir geometry building (a) depth structure map derived from seismic interpretation was used as reservoir lateral boundary and contouring of top reservoir layer (b) isochore map was used as reservoir thickness determination 4.2 reservoir properties during this step, properties in each reservoir segment was defined. in rubis software, heterogeneity inside a reservoir segment could not be managed to be heterogeneous. therefore, simplification of reservoir properties for each reservoir segment would be done. one value of permeability, porosity, ntg, saturation, and kr-pc derived from well data penetrated each reservoir segment would be spread inside a reservoir segment. ideally, populating the reservoir properties inside the reservoir segment should follow the sedimentological concepts of deep-water turbidite system with the bunch of data. but due to the limitation of the software capability and well data, permeability property would be mitigated by using phi-k law obtained from core plug measurement in well kc-2 dir. the result of the reservoir properties in each reservoir segment are homogeneous for ntg and porosity, but for the permeability distribution, it follows the phi-k law obtained in well kc-2 dir (fig. 16). (a) (b) (c) fig. 16. distribution of each reservoir property in the model that was derived from well data penetrating each reservoir segment (a) net to gross property was homogenous in each reservoir segment (b) porosity distribution across reservoir segments were derived from well log data that was simplified having a same value for each reservoir segment (c) permeability distribution across reservoir segments followed the phi-k relationship from sandstone interval in kc-2 dir well. 4.3 wells definition during this step, well trajectory, perforations, completion, and well control would be defined. this field consisted of 3 exploration wells and 5 development wells. all the development wells would be completed as producing wells while the exploratory wells would be used for well test history matching. trajectory for each deviated well was defined with the deviation, kick-off point, well length, and total depth from the drilling information. the actual trajectory was using coordinate system, while in the model, well tracjectory and position were simplified using the actual position found in petrel model. unfortunately, rubis software encountered several errors where the deviated wells were created. the 148 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 errors mainly due to the well that was too close to the segment boundary or too close to another well. in order to overcome this problem, several 3 deviated wells were represented as vertical wells. 4.4 grid building after the grid was designed and filled with both static and dynamic properties, rubis would automatically build the grid with minimum number of cells. however if needed, the user has the freedom to define the number of cells and the geometry of the cells manually both vertically or laterally. for the sake of running simulation time, 2 vertical cells were defined for each reservoir segment. total cell worked in this simulation consisted of 23.627 active cells with hexagonal geometry having 100 meter length of each side of polygon. regarding the near wellbore area, the most important parameter was the upscaling factor with a range between 0-100% value. this parameter would control the grid refinement around the well during the simulation. with no upscaling (0%), the cells surrounding the well will be kept with very fine size. while 100% scaling would make the number cells around the wells to be highly reduced allowing for a faster simulation run. this well module option would be particularly useful in case of water coning or very heterogeneous properties. 4.5 model quality control in order to be able to build reliable model, quality control was done before running the simulation. quality control consisted of both dynamic and static parameter. dynamic parameter consisted of history matching in segment f using kc-2 dir well test data while the static parameter would comprise of comparison of segment in place volume between rubis model and geox model. the history matching was done by inputting the rate and pressure data from well test analysis and interpretation in saphir was imported directly to rubis. simulated pressure in the model matched perfectly with the well testing pressure. there was 4 psia difference during final flow and 2 psia difference during the main buildup stage which were acceptable. afterward, in place volume for each segment was compared with p50 in place volume estimated in geox model. some adjusments in geometrical modelling were needed in order to get a good match between in place volume from geox model and rubis model. at the end, average total volume in place difference between geox and rubis model was 3.47%. 4.6 initialization and simulation setting in this step, intial state was defined with reference depth, reference initial pressure, water gas level (wgl), and kr-pc relationship for each reservoir segment. those data were gathered based on scal result in kc-2 dir well and would be populated throughout all reservoir segments. rubis software would calculate the saturation distribution in each cell based on the capillary pressure, relative permeability, and wgl given. during the initialization, rubis will use pc values available to get pc curve as a function of height above free water level in equilibrium using hydrostatic pressure equation. afterward, the relationship between pc and sw will be approached using j-function where it takes into account the reservoir characteristic (porosity, permeability, and wettability). based on this pc-sw relationship, rubis would have a height as a function of water saturation and would be spread across the reservoir segments. maximum gas saturation above fwl would be 0.72 in all segments, this value was based on the irreducible water saturation value derived from scal (0.28) with very thin transition zone. in a gas/water system, large difference between gas and water density quickly leads to high capillary pressure, limiting the extension of the transition zone. table 5. simulation scenario from rubis compared with mbal case base case mbal case mbal trans case 288 mmscf/d 288 mmscf/d mmscf/d produced from 10 segments using 5 development wells produced from 10 segments using 5 development wells produced from 10 segments using 5 development wells constraint: 35 bar minimum wellhead pressure constraint: 35 bar minimum wellhead pressure 35 bar minimum wellhead pressure phi-k law from kc-2 dir well core measurement had been applied to distribute permeability tank volume and relative permeability were based from kc-2 dir scal data tank has been divided into 2 similar volumes, connected by transmissibility factor of 0.5 the simulation would be run from 2017 to december 2032. all the perforations in the development wells would be opened with the surface gas rate target of 57.600 mscf/d and 35 bars minimum surface pressure. when simulation started, 3 scenarios were made in order to compare the result from 2 mbal cases and base case from rubis model (table 5). 5. results and discussion with the same field target rate, those models produced different results. the shortest plateau rate was obtained by the base case model, the mbal case could provide longest plateau rate with the highest recovery factor, while mbal trans case produced in between (fig.17). in the base case, the field will produce 815 bscf of gas with the recovery factor of 66%. the gas peak rate of 288 mmscf/d can be retained up to 3 years and 10 months (table 6). the preliminary study of the gathered data from seismic, well, core, and well testing had been used in order to build simplified 3d simulation model from prasojo, octria a. et al./ jgeet vol 03 no 03/2018 149 kucing field. the result of the study had been presented as follow: fig. 17. x main field gas production forecast table 6. detail simulation result from each case scenario igip (bscf) gas produced (bscf) recovery factor plateau duration base case 1235 815 66% 3 years and 10 months mbal case 1235 971 82% 6 years mbal trans case 1235 927 75% 4 years using rubis as 3d reservoir simulation software has several advantages and disadvantages that one should be aware of. several advantages using rubis could be explained below:  user friendly rubis is very easy to use where everything has a simple figure to make the user understands very clearly. simulation steps are also well-organized thus the one can follow from pvt, field geometry, to running the simulation very easily.  time efficiency this software was not intended to build very detail model nor complex model. as well as simplification of the model and integration between static and dynamic model in one platform could save time efficiently. building this x main field model took more or less 3 months, while running the full field simulation only took 30 minutes. comparing with other software, rubis is the efficient one in term of time consuming.  grdecl input as another benefit, it is possible to load grdecl that may contain net to gross, porosity, or permeability distribution that may have been built by another software. while some disadvantages from this software would be explained below:  well control limitation not like in other 3d simulator software, rubis could not have any field control. that means the field should be control per well. for example in this case, where the field should produce with 288 mmscf/d plateau rate, it could be defined as each well in this field will produce with 57.6 mmscf/d surface gas rates where there are 5 wells available in x main field. this could lead into some difficulties for reservoir engineer to target and control the field production. the other effect of this limitation (particularly in x main field) was the rough decreasing rate of x main field.  software instability since this software was not intended to model a complex field, building x main field where there were several separated segments with more than 50 regions were created could encounter some errors. also some deviated wells could not be assigned perfectly in this model due to the complexity of the field. in order to anticipate these errors and be able to successfully build 3d simulation model in rubis, based on this case, several recommendations could be proposed: 1. rubis is highly recommended to model a simple field where the segments were not separated like in x main field or other turbiditic channels field. 2. rubis may also be useful to model the field that has no deviated well. this due to the design of the well that could not be perfectly represented in rubis. 3. to check the reliability of the model, several quality controls could be done. quality control might consist of history matching, compared volumetric with previously available in-house volume, well tops quality control, and when it is available, rubis model should be compared with the more detail eclipse model. 6. conclusion 1. well log data, core description, and scal result led to the determination of lithofacies, petrofacies, and electrofacies, while further analysis of scal result ‟ pc curve and visual inspection of scal result to help the determination of the dynamic rock typing. 2. from well test interpretation, segment f behaved as a single homogeneous layer with 2 parallel boundaries indicating a channel reservoir body with k=114 md. this result then was used as a reference to populate the reservoir properties in other segments. 3. the quality control had been done by doing history matching based on short historical data from well testing in segment f. it gave only 2 psia differences between the model and historical data. while structural model quality control had been done as well by comparing the well tops and segment volume that gave 3.47% volume discrepancies. 4. the production forecast indicated that the field would produce in plateau rate of 288 mmscf/d for 3 years and 10 months. at the end, as a new approach in building 3d simulation model, rubis could be a powerful tool to build reliable yet simple 3d simulation model with very short time needed to build one (more or less 3 months) compare to build a complex eclipse simulation model where it will take approximately a year. 150 prasojo, octria a. et al./ jgeet vol 03 no 03/2018 acknowledgment the major contribution came from my supervisors matthieu plantevin and vladimir choque flores from ifp school, financially supported by france ministry of foreign affairs master degree scholarship. references alam, h., patersonb. d.w., syarifuddina, n., busonoa, i., corbina, s.g., 1999, reservoir potential of carbonate rocks in the kutai basin region, east kalimantan, indonesia, journal of asian earth sciences 17, 203-214. https://doi.org/10.1016/s0743-9547(98)00047-6 bouma, a. h., 1962. sedimentology of some flysch deposits. a graphic approach to facies interpretation. amsterdam: elsevier. http://lib.ugent.be/catalog/rug01:000978747 galy, v. et al., 2007, efficient organic carbon burial in the bengal fan sustained by the himalayan erosional system. nature 450, 407 410. https://doi.org/10.1038/nature06273 heryanto, n., nawawi, a., mason, a.d.m., ingram, f.t., pederson, d.e., davis, r.c., 1996. exploratory update in the north tanjung block, south kalimantan. in: proceedings indonesian petroleum association 25th annual convention, jakarta, 55 68. http://archives.datapages.com/data/ipa/data/025/025001 /55_ipa025a0055.htm heryanto, r.b., 1993. neogene stratigraphy of kalimantan. geological research and development centre, bandung, indonesia, 82 91. leverett, m.c., 1941. capillary behavior in porous solids. trans. aime 142, 152 169. https://doi.org/10.2118/941152-g mason, a.d.m., haebig, j.c., mcadoo, r.l., 1993. a fresh look at the north barito basin, kalimantan. in: proceedings indonesian petroleum association 22 nd annual convention. ipa93-1.1-219, 1 18. http://archives.datapages.com/data/ipa/data/022/022001 /589_ipa022a0589.htm settentrionale : introduzione all analisi di facies. mem. della soc. geol. ital. 11, 161 199. panggabean, h., 1991. tertiary source rocks, coals and reservoir potential in the asem asem and barito basins, southeastern kalimantan, indonesia. phd thesis, university of wollongong, australia, wollongong. https://ro.uow.edu.au/theses/2113/ pieters, p.e., trail, d.s., supriatna, s., 1987. correlation of early tertiary rocks across kalimantan. in: proceedings indonesian petroleum association 16th annual convention. ipa87-11/11, 1 16. http://archives.datapages.com/data/ipa/data/016/016001 /291_ipa016a0291.htm reading, h.g., richards, m., 1994. turbidity systems in deepwater basin margins classifed by grain size and feeder system. aapg bulletin 78 (5), 792-822. https://www.osti.gov/biblio/7029174 rubis software (kappa engineering), 2015, retrieved from https://www.kappaeng.com/software/rubis/overview salaheldin, t.m., imran, j., chaudhry, m.h., reed, c., 2000. role of fine-grained sediment in turbidity current flow dynamics and resulting deposits. journal of marine geology 171, 21-38. https://doi.org/10.1016/s00253227(00)00114-6 talling, p., wynn, r., masson, d. & frenz, m., 2007, onset of submarine debris flow deposition far from original giant landslide, nature 450, 541 544. http://dx.doi.org/10.1038/nature06313 van bemmelen, r.w., 1949. the geology of indonesia: general geology of indonesia. government printing office, nijhoff, the hague, 732. van de weerd, a., armin, r.a., 1992. origin and evolution of the tertiary hydrocarbon bearing basins in kalimantan (borneo), indonesia. american association of petroleum geologists bulletin 76 (11), 1778 1803. http://archives.datapages.com/data/bulletns/199293/data/pg/0076/0011/0000/1778.htm witts, d., hall, r., nichols, g., morley, r., 2012, a new depositional and provenance model for the tanjung formation, barito basin, se kalimantan, indonesia, journal of asian earth sciences 56, 77-104. https://doi.org/10.1016/j.jseaes.2012.04.022 2011, internal report of x field plan of development: unpublished 2011, internal reservoir study of x field: unpublished © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1016/s0743-9547(98)00047-6 http://lib.ugent.be/catalog/rug01:000978747 https://doi.org/10.1038/nature06273 http://archives.datapages.com/data/ipa/data/025/025001/55_ipa025a0055.htm http://archives.datapages.com/data/ipa/data/025/025001/55_ipa025a0055.htm https://doi.org/10.2118/941152-g http://archives.datapages.com/data/ipa/data/022/022001/589_ipa022a0589.htm http://archives.datapages.com/data/ipa/data/022/022001/589_ipa022a0589.htm https://ro.uow.edu.au/theses/2113/ http://archives.datapages.com/data/ipa/data/016/016001/291_ipa016a0291.htm http://archives.datapages.com/data/ipa/data/016/016001/291_ipa016a0291.htm https://www.osti.gov/biblio/7029174 https://www.kappaeng.com/software/rubis/overview https://doi.org/10.1016/s0025-3227(00)00114-6 https://doi.org/10.1016/s0025-3227(00)00114-6 http://dx.doi.org/10.1038/nature06313 http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0011/0000/1778.htm http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0011/0000/1778.htm https://doi.org/10.1016/j.jseaes.2012.04.022 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 1.2 aim 2. geological framework 2.1 regional geology 3. method 3.1 availability data 3.2 seismic data 3.3 core and well log data 3.4 special core analysis 3.5 well test analysis 4. reservoir simulation 4.1 geometry building 4.2 reservoir properties 4.3 wells definition 4.4 grid building 4.5 model quality control 4.6 initialization and simulation setting 5. results and discussion 6. conclusion acknowledgment references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 62 travis, k., et al./ jgeet vol 8 no 1/2023 research article analysis of land subsidence in peatlands in the awareness area of pekanbaru, riau, indonesia kevin travis 1,*, izzati nazra1, john thor1, william adam1 1 department of environmental, university of the sunshine coast, australia * corresponding author : traviskvn01@gmail.com tel.:+61-491-570-110 received: oct 1, 2022; accepted: march 20, 2023. doi: 10.25299/jgeet.2023.8.1.13461 abstract this study area is administratively located in parit indah district, bukit raya district, pekanbaru city, riau province. geographically, the research area is located at coordinates 0° 28' 30.92" n 101° 28' 9.45" e n 0° 27' 25.63" 101° 29' 47.30" e. the aim of this study was to find out the effect of peat soil types on subsidence. the data collection method in this study was carried out using sieve analysis, water content analysis, specific gravity, subsidence analysis, and soil testing in the laboratory. the effect of peat soil on subsidence has a significant effect between the type of peat and subsidence, the higher the maturity level of the peat, the lower the level of subsidence on peat soil. based on the results of the study, the soil consolidation test with a depth of 75cm-3m had a soil settlement value of 0.467. it is recommended to do this to reduce the impact of subsidence in the land area such as the research area so that it does not have too much impact on the construction which i s carried out by hardening the location using the vertical wick drain method, as well as for building foundations it can be done using chicken claw foundation. keywords: characteristics, peat soil, subsidence, consolidation test 1. introduction the area of indonesian peatlands is estimated to range from 17-21 million hectares (soil research institute, 2011), and riau is one of the provinces in indonesia located on the island of sumatra which has an area of approximately 8.7 million hectares, of which 3.9 million hectares is peat land. fibrous peat soils have poor physical and technical properties, namely high water content and void ratio, low specific gravity and carrying capacity, and large and uneven compression. peatlands that are dry and no longer store water which then causes subsidence or subsidence. there are two types of subsidence, namely endogenic subsidence and exogenic subsidence. endogenic subsidence is caused by natural forces from within the earth such as plate movements, folding and faulting of the earth's surface and earthquakes. exogenic subsidence is caused by human activities such as underground mining, excess groundwater extraction, oil and gas drilling activities and changes in soil composition. the construction of a housing complex which carried out in the research area is the basis for research to be able to calculate the impact of peatland subsidence and solutions to inhibit peatland subsidence. 2. study area administratively the research area is located in a conscious housing area in the awareness area of tangkerang labuai village, marpoyan damai district, pekanbaru city, riau province. "101° 29' 47.30" e. stratigraphically, the study area is composed of rocks which are surface deposits, namely old surface deposits (qp) based on clarke, m.c.g et al., 1982. geological map of pekanbaru sheet, riau. f i g 1. research area i n pekanbaru city ( source : bappeda kota pekanbaru ) 3. methodology 3.1 research object to carry out all the research methodology, we summarize all the research steps as 1. sampling by hand auger method 2. sieve analysis, is an analysis of filtering a soil sample through a set of sieve 3. liquid limit is a certain water content where the behavior changes from plastic to liquid. plastic limit is defined as the water content in a position between plastic and semi-solid. 4. the relationship between the atterberg limit and soil properties is useful for estimating the properties and knowing the type of soil the water content in the soil is the ratio between the weight of the water contained in http://journal.uir.ac.id/index.php/jgeet mailto:traviskvn01@gmail.com travis, k., et al./ jgeet vol 8 no 1/2023 63 the soil and the weight of the soil grains, and is expressed in percent. 5. specific gravity is the ratio between the weight of soil and the weight of water using the same volume. 6. consolidation analysis 3.2 sieve analysis the use of sieve analysis is to find out the physical properties of the soil to be tested. while the purpose of sieve analysis is to find out a soil to be tested, whether it is poorly graded, uniformly graded or well graded, as well as to determine grain size. the results of the sieve analysis are generally depicted on semi-logarithmic paper, which is known as the grain size distribution curve. the parameters of the grain size distribution curve include; 1. the effective size is the diameter in the grain size distribution curve corresponding to the finer 10% (passes the sieve), 2. the uniformity coefficient is a coefficient that shows the uniform properties of the soil. if : cu = d60/d10. the value of cu and cz = 1, then the soil grains are the same size. cu value > 5, the soil grains are increasingly non-uniform. cu value < 3, then the soil grains are more uniform. 3. the coefficient of gradation is a coefficient that shows the distribution of grain size variations if: cz < 5 graded well, if value cz> 5 graded badly. 4. sorting cooeficient so = √d75/d25 if : so < 2.5, then the sorting is good. so 2.5 – 4, then the sorting is moderate. so > 4, then the sorting is bad 3.3 moister content (content of water in soil) the water content in the soil is the amount of water in the pore space between the soil grains which is dried using an oven. this analysis is carried out to determine the amount of water in the soil expressed as a percent – the age of dry soil mass. the following is the formula for calculating the water content in the soil weight of water = w2 – w3 dry soil weight = w3 – w1 moisture content (%) = (w2 – w3 / w3 – w1) x 100% note: w1 is the weight of the container. w2 is wet soil sample + container. w3 is dry soil sample + container. table 1. calculation table of moisture content number of treatment per.01 per.02 per.03 wet ground mass + cup 𝑚2 gr dry ground mass + cup 𝑚3 gr cup mass 𝑚1 gr water mass 𝑚2 − 𝑚3 gr dry ground mass 𝑚3 − 𝑚1 gr f. 𝑚 2 − 𝑚3 x 100% 𝑚 3 − 𝑚 1 water content in the ground % if: the water content in the soil is 20% 100%, then the soil is normal. the water content in the soil is > 100%, then the soil is saturated with water. the water content in the soil is <20%, then the soil is dry. 3.4 consolidation test the consolidation test is used to determine the compression properties of a soil sample, namely the nature of the change in contents and the process of water escaping from the soil due to axial pressure acting on the soil. 4. result and discussion 4.1 hand auger in the drilling that has been carried out in the study area (figure 2), there is 1 log out of 10 drilled holes, this is because all types of peat in all drill holes in the study area are the same physically, namely: figure 2. the sampling process using the hand auger method 4.1.1 bore hole 06 pada lubang bor 06 dengan koordinat n 00°27'12.74'' e 101°28'49.85'' dengan kedalaman 3 meter ditemukan 2 jenis in bore hole 06 with coordinates n 00°27'12.74'' e 101°28'49.85'' with a depth of 3 meters, 2 types of lithology were found, namely clay (soil stockpile) and peat. this lithology is found at different depths as can be seen in figure 3. the following drill hole 06 logs have been made: figure 3. borehole log 06 4.2 sieve analysis in the study area, the soil types in this study area were dominated by fibrous soils or peat soils, so that sieve analysis was used to determine the grain size distribution of the soil. cz = (𝐷30) 𝐷60 𝑥 𝐷10 64 travis, k., et al./ jgeet vol 8 no 1/2023 the following is the result of sieve analysis in the laboratory from the drill hole 6 sample: 4.2.1 bore hole 06 (depth :75 cm – 3m) total unit weight: 79.23 grams table 2. data from bore hole sieve analysis results 06 depth 0.75 – 3 m sieve size individual retained ( gram ) cumulative retained ( gram ) percent retained ( % ) percent passing ( % ) inch mm # 4 4.75 14.75 14.75 18.62 81.38 # 10 2.00 17.23 31.98 40.36 59.64 # 20 0.850 19.42 51.40 64.87 35.13 # 40 0.425 5.94 57.34 72.37 27.63 # 60 0.250 2.94 60.28 76.08 23.92 # 140 0.106 5.85 66.13 83.47 16.53 # 200 0.075 1.15 67.28 84.92 15.08 fig 4. graph of bore hole 06 sieve analysis dealing with the data in figure 4, it can be seen that the smaller the size of the filter hole, the less sample is filtered. for example, with a sieve size of 4.75, 81.38% of the sample was filtered out, which is the largest filter hole size and the number of samples that pass through the filter is also the largest. on a 2.00 mm sieve hole size, the less the sample passes the sieve, which is as much as 59.64%. at the smallest sieve size of 0.075 mm, the least filtered sample is 15.08 mm. figure 4 can be seen that the sieve analysis graph shows that the sample contains fine sand to medium gravel material. after obtaining the above data, it is then plotted onto a sieve analysis diagram to find out the grain distribution of the bore hole 06 sample with a depth of 75cm – 3m, and the following calculations are also obtained: a. sorting coefficient(so) 𝑆𝑜 = √(𝑑75/𝑑25) 𝑆𝑜 = √(6𝑚𝑚/0,5𝑚𝑚) 𝑆𝑜 = 3,4mm dealing with the results of figure 4, it can be concluded that in bore hole 06 with a depth of 75cm – 3 m, the grain size distribution of fine sand is obtained. however, the data cannot be determined for the cu and cz calculation values because the value of 𝐷10 is not known. because the sample has stopped on the 200 sieve with a larger presentation than 10%, but cu and cz can still be known through the curve graph of the sieve analysis results above where the sample curve is in the type of fine sand to medium gravel, with sand in the size of 0.7mm – 2mm and graval from 2mm – 9mm, which means that the sample in the study area is non-uniform and well graded, and from the calculation results obtained so = 3.4, which means moderate sorting. 4.3 water content in soil the water content in the soil in the study area is very influential on the consistency of the soil, and the suitability of the soil for cultivation in the study area. because the amount of peat water in the study area has a big effect on the soil derivatives that will occur. the following are the results of the analysis of soil water content from the bore hole samples: table 3. data from analysis of water content in soil data unit mass cup weight+wet ground gr 48,03 cup size+dry ground gr 18.54 cup weight gr 8,5 water weight gr 29.49 berat dry ground gr 10,04 water content % 293,73 regarding to he soil water content test experiments in this study, the experimental results were obtained as follows: w = m2−m1 m3−m1 𝑥100 w = 48,03 gram −18,54 gram 18.54 gram −8.5 gram 𝑥100 w = 29,49 gram 10,04 gram 𝑥100 w = 293,73 w = moisture content 𝑚1 = weight of cup 𝑚2 = weight of cup + wet soil 𝑚3 = large cup + dry soil based on the data that has been analyzed above, the percentage of water content in peat soil at a depth of 0.75-3 meters is 293.37%, which means that the type of peat soil in this study area is water saturated. the water content in the soil in the study area is influenced by the organic content in the soil. dry soil has a low organic content while water-saturated soil has a high organic content. evidenced by the discovery of many roots and stems of plants. fig 5. an example of an organic content in the soil in the study area 4.4 test of atterberg limit the atterberg limit test is divided into two tests, namely: 4.4.1 liquid limit test the following is an analysis of the results of the liquid limit test in the laboratory, namely: liquid limit test bore hole 01 depth 75cm-3m the following is a table of the results of the liquid limit test for soil samples and a graph of the relationship between the travis, k., et al./ jgeet vol 8 no 1/2023 65 number of knocks and the liquid limit for soil samples at a depth of 75 cm to 3 meters. table 4. results of the liquid limit test for soil samples at a depth of 75 cm – 3 m water limit test (soil type: sand) cup number 1 2 3 4 cup weight gram non plastic cup weight + wet ground gram cup weight + dry ground gram weight of wet ground gram weight of dry ground gram water weight gram water content (ll) % number of hit kali soil samples at a depth of 0.75 – 3 m cannot be tested for liquid limit values because the type of soil at this depth is sandy soil, where sand is semi-solid and dense or because the liquid limit is the boundary between a semi-liquid and semi-plastic state, so the type of soil that is the only liquid limit test that can be tested is clay soil, silt soil, or sandy soil containing a mixture of clay, in other words, soil that has a mixture of plastic materials, so that soil samples at a depth of 0.75 to 3 meters cannot be tested. . 4.4.2 plastic limit the plastic limit is defined as the water content in the soil between the plastic and semi-solid phases. if the water content in the soil decreases, the soil becomes harder and has the ability to withstand deformation. the plastic limit test is intended to determine the amount of water content in the soil sample when the soil changes from the plastic phase to the semi-solid phase or vice versa. plastic limits of soil samples at a depth of 0.75cm – 3m the following is the result of the plasticity limit test for soil samples at a depth of 75cm – 3m which has a sandy soil type. table 5. results of the plastic limit test for soil samples at a depth of 75 cm – 3m plastic limit test (soil type : sand) cup number 1 2 3 4 cup weight gram non plastic cup weight + wet ground gram cup weight + dry ground gram berat wet ground gram berat dry ground gram water weight gram water content (ll) % average plastic limit (pl) % soil samples at a depth of 0.75 – 3 meters cannot be tested for plastic limit values because the type of soil at this depth is sand, where sand is semi-solid and dense or because the plastic limit is the boundary between a plastic and semi-solid state, so the only soil type can be tested the liquid limit is clay soil, silt soil, or sandy soil containing a mixture of clay, in other words the soil at a depth of 0.75 – 3 meters has almost no plasticity. 4.5 spesific gravity tests specificgravity or specific gravity is the ratio between the grain weight of the soil and the grain volume at a certain temperature. the soil referred to here is the grain weight of the soil itself without water or air (without pores). while the volume of soil referred to in this case is the volume of soil without containing pores. following are the results of the specific gravity analysis on drill hole 06 in the study area: table 6. data from the specific grafity analysis data unit mass pignimeter gr 162.0 sand weight gr 102.3 pigno weight + water gr 659.4 cup weight + water + dry ground gr 692.9 weight of dry ground gr 33.5 gr 68.8 spesific gravity gr 1.487 in the table above, the w2 value or sand weight is 102.3gr and the dry weight or w6 is 68.8gr. following are the results of specific calculations from the soil samples in the study area: gs = w2 w6 gs = 102,3 68,8 gs = 1,487 description: w1 = pignimeter w2 = sand weight w3 = piqno weight + water w4 = cup weight + water + dry resistant w5 = weight of dry soil the results of calculating specific gravity analysis data in the study area, a specific gravity of 1,487 grams was obtained, which means that in the study area the type of soil is peat soil/organic soil because the distance ranges from 1.25-1.80. the research area is included in the low specific gravity where it will be easier to decrease. figure 6. one of the spgr test process documentations 4.6 consolidation test consolidation is divided into two, namely direct consolidation and gradual consolidation. in this analysis, gradual consolidation is used. the following are the results of the study area consolidation analysis: 4.6.1 consolidation coefficient (cv) the consolidation coefficient states the speed of the consolidation process of a soil and this analysis is used to determine the velocity of water flow in the vertical direction in the soil. the following results of calculating the cv value can be seen from the table below: table 7. data from consolidated coefficient analysis results pkpa cv 50.00 0.16667 100.00 0.36259 200.00 0.48006 400.00 0.37581 in the table above, we can see that at a minimum pressure of 50.00 kpa, there is a decrease in speed of 0.16667. when the pressure is increased to 100.00 kpa, the decreasing speed also experiences a greater change, namely 0.36359. at a pressure of 200.00 kpa, the greatest decreasing speed is 0.48006. however, at the maximum pressure of 400.00 kpa, the decrease speed is 0.37581 which is smaller than the pressure of 200.00. for more details, see the cv chart below: 66 travis, k., et al./ jgeet vol 8 no 1/2023 fig 7. data graph of consolidated coefficient analysis results from the results of the consolidation coefficient (cv) above, we can see that peat has a relatively high increase in cv. this is because peat soil has high permeability properties, so it is easily penetrated by water. due to the nature of high permeability when pressure is applied, water will flow out of the soil quickly so that the soil subsidence that occurs is also greater and the faster it reaches a stable layer of soil when it has run out of compressed pore water. the land will continue to decrease until it is in a stable position. 4.6.2 compression coefficien (cc) compression coefficien or compression index is used to calculate the amount of settlement that occurs in the study area, as a result of consolidation can be determined from the curve that shows the relationship between pore and pressure. more details can be seen in table 8 of the compression index calculation results in the study area: table 8. compression coefficien analysis result data pkpa voidratio 50.00 4.130 100.00 3.942 200.00 3.797 400.00 3.700 from the table above, the relationship between void ratio and effective pressure shows that the void ratio decreases in proportion to the increase in the applied pressure. this decrease indicates a reduction in the number of existing soil pores, thereby reducing the size of the void ratio. it can be seen in the table above that at a pressure of 50.00 it produces a void ratio of 4.130 kpa, the greater the pressure, the smaller the void ratio. for example, the maximum pressure of 400.00 kpa produces the smallest void ratio, namely 3,700. the additional load only occurred three times because the consolidation test sample had reached its maximum settlement so that it was unable to accept any additional load. this is due to the very high water content of the peat soil consolidation test sample. from the table above we can calculate: cc = e1−e2 log p2−log p1 cc = 4.130−3.700 log 400−log 50 cc = 0.43 0.91 cc = 0,472 description: cc = compression coefficient e1 = largest cc value e2 = smallest cc value w4 = cup weight + water + dry resistant w5 = weight of dry soil for more details, see the picture below; fig 8. graph of compression coefficien analysis results from the graph above, we can see that the greater the pressure, the smaller the pores in the soil. this is caused by the release of pore water contained in the soil due to pressure. based on the analysis that has been carried out starting from sieve analysis, soil water content analysis, soil consolidation tests in the study area have grain distribution ranging from sand to gravel with uniform soil grains. poorly graded (soil having uneven grain sizes from large to small grain sizes) and uniform sorting or sorting of grains (medium sorting). furthermore, having a water content in the soil is dominated by water-saturated soil with a moisture content of > 100%. the water content in the soil in the study area is influenced by the organic content in the soil which is quite high. the following are the general results from the research area in the conscious residential area, awareness walk, beautiful ditch, namely: table 9. data analysis results no analysis result 1. sieve analysis size of sand grain until gravel 2. uniformity good 3. gradation bad 4. sortation medium 5. water content in the soil water saturated soil 6. atterberg limit 7. gs 1,487 8. consolidation 0,476 after carrying out all of the above analysis, the conscious area has decreased, this decline continues depending on the weight of the load and the water content in the soil until the soil is compressed. this primary decline will slowly damage the uilding infrastructure above it, such as bumpy ground or cracks in the house, as shown below: fig 9. one of the documentations in the research area house travis, k., et al./ jgeet vol 8 no 1/2023 67 fig 10. one of the documentation of building damage due to land subsidence on the soil in the research area is not too good for building construction. but there are several ways that can be done to reduce the impact of subsidence on land areas such as research areas so that they don't have too much of an impact on the development being carried out. there are several efforts that can be made before building construction on peat soil for the peat soil road paving process itself. it will go through several stages. the first thing to do is to repair the existing peat area. the repair process can be done by digging or peeling. then the part excavated will be filled with soil or sand in better condition. the excavated peat soil will be compacted by applying a load on the surface, either with soil or sand, for a certain period of time. in order for the soil compaction process to take place more quickly, you can use a vertical sand drain which must be installed at a certain distance. then another way can be by using synthetic materials where the installation is vertical. this method is known as vertical wick drain. in the vertical wick drain method itself can also be done by adding a vacuum pump. the goal is for the soil to solidify faster. later the water and air in each layer of soil will come out. fig 11. example of vertical wick drain modeling however, if the peatland area is not too large like the research area, then the method can be done by using a chicken claw foundation. after the foundation has been installed, the top layer can be loaded with soil or sand for compaction. then later the peat road paving construction can be built on the top surface. besides that, there is also a way that costs quite affordable, namely by using dolken or known as bamboo. in addition, you can use geo-textile which has a light weight but has great traction when receiving loads on it and the price is also not expensive. figure 12. example of chicken claw foundation modeling for the type of pavement on peat soil itself, the most recommended is to use a flexible construction pavement. on peat soils, this type of pavement is more suitable because it is lighter. if you use a rigid pavement then the results are actually not good. stiff pavement on peat soil pavement will cause the pavement to crack. this is because rigid pavements tend to be heavier in nature. before peat soil is processed, it is necessary to carry out a stabilization process. for peatlands, this process takes longer because they have to use conventional methods. the term is also known as pre-loading. the soft and organic nature of peat makes it more difficult to move than normal soil. many say that peat land is unfavorable land to use for the development process. that is what then makes the pavement process more complicated. 5. conclusion dealing with the results of the analysis and calculation of land subsidence in conscious housing, the pekanbaru awareness road which was carried out on drill 6, it can be concluded that: 1. regarding to the results of the sieve analysis, it can be concluded that the grain size distribution in the study area was fine sand to medium gravel in size, which means that the grain in the study area is not uniform and has good grades. 2. based on the results of calculating the water content in the data that has been analyzed, the percentage of water content in peat soil at a depth of 0.75-3 meters was 293.37%, which means that the type of peat soil in this study area is water saturated and not very good for the construction of roads and buildings. 3. based on the calculation of specific gravity analysis data in the study area, it was found that the specific gravity was 1,487 gr, which means that in peat/organic soil areas. and research is included in a low specific gravity where it will be easier to decrease. 4. from the results of land subsidence using the consolidation test, it can be concluded that the coefficient of consolidation (cv) of peat had a relatively high increase in cv. this is because peat soil has high permeability properties. and experienced a decrease of 0.476. the settlement continues continuously depending on the weight of the load and the water content in the soil until the soil is compressed. references bowles, j.e. 1989. “sifat-sifat fisis dan geoteknis tanah”. erlangga. jakarta. bowles, j.e. 1996; 1997. foundation analysis and design, mcgraw-hill kogakusha, ltd., tokyo, japan. 68 travis, k., et al./ jgeet vol 8 no 1/2023 braja m. das., nur endah., indra surya b. muchtar, mekanika tanah, erlangga, jakarta chen, f.h., 1975, foundation on expansive soils, elsevier scientific publishing company, new york clarke, m.c.g., kartawa, w., djunuddin, a., suganda, e. dan bagdja, m., 1982.peta geologi lembar pakanbaru, sumatra.pusat penelitian dan pengembangan geologi. jakarta. das, b. m., 1993, mekanika tanah. (prinsip – prinsip rekayasa geoteknis). jilid i, penerbit erlangga, jakarta. das, b. m., 1995, mekanika tanah. (prinsip – prinsip rekayasa geoteknis). jilid ii, penerbit erlangga, jakarta. de beer, e and marten, a, (1957), method of computation of an upper limit for the influence of heterogeneity of sand layer in the settlement of bridges, proc of 4th issmfe, london, vol. 1, pp.275-82. fauziah, ali. 2016. kajian geoteknik untuk perencanaan pembangunan pemukiman baru pada kawasan handil berkat makmur, kabupaten kapuas, kalimantan tengah. universitas diponegoro, semarang. fhwa nhi-06-088, 2006.soil and foundation, reference manual, volume i, national highway institute, us departement of transportation, federal highway administration. hardiyatmo, h. c., 1992, mekanika tanah 1, pt. gramedia pustaka utama, jakarta. hardiyatmo, h. c., 2002, mekanika tanah 2, pt. gramedia pustaka utama, jakarta. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 4 2022 158 adhari, m.r. et al./ jgeet vol 7 no 4/2022 research article estimation of density log and sonic log using artificial intelligence: an example from the perth basin, australia muhammad ridha adhari1,*, muhammad yusuf kardawi2 1department of geological engineering, universitas syiah kuala, jl. syeikh abdurrauf as sinkili no.7, darussalam, banda aceh, indonesia. 2department of computer engineering, universitas syiah kuala, jl. syeik abdurrauf as sinkili no.7, darussalam, banda aceh, indonesia. *corresponding author: mr.adhari@usk.ac.id tel.:+6285271432373 received: jul 14, 2022; accepted: dec 6, 2022. doi: 10.25299/jgeet.2022.7.4.10050 abstract it is well understood that with a large number of data, an excellent interpretation of the subsurface condition can be produced, and also our understandings of the subsurface conditions can be improved significantly. however, having abundant subsurface geological and petrophysical data sometimes may not be possible, mainly due to budget issues. this situation can generate issues during hydrocarbon exploration and/or development activities. in this paper, the authors tried to apply artificial intelligence (ai) techniques to estimate outcomes values of particular wireline log data, using available petrophysic data. two types of ai were selected and these are artificial neural network (ann), and multiple linear regression (mlr). this research aims to advance our understanding of ai and its application in geology. there are three objectives of this study: (1) to estimate sonic log (dt) and density log (rhob) using different types of ai (ann and mlr); (2) to assess the best ai technique that can be used to estimate certain wireline log data; and (3) to compare the estimated wireline log values with the real, recorded values from the subsurface. findings from this study show that ann consistently provided a better accuracy percentage compared to mlr when estimating density log (rhob). while using different set of data and technique, estimation of sonic log (dt) produced different accuracy level. moreover, crossplot validation of the results show that the results from ann analysis produced higher trendline reliability (r2) and correlation coefficient (r) than the results from mlr analysis. comparison of the estimated rhob and dt log data with the original recorded data shows minor mismatch. this is evident that ai technique can be a reliable solution to estimate particular outcomes of wireline log data, due to limited availability of the original recorded subsurface petrophysic data. it is expected that these findings would provide new insights into the application of ai in geology, and encourage the readers to explore and expand the many possibilities of the application of ai in geology. keywords: wireline log data, hydrocarbon, artificial intelligence (ai), artificial neural network (ann), multiple linear regression (mlr) 1. introduction a successful oil and gas exploration, production, and development activities may rely on the availability of subsurface data (e.g. petrophysics data, seismic data, among others) and an excellent subsurface interpretation, besides the presence of a working petroleum system. having a significant number of subsurface data is important in order to have a better insights and understanding of the source rocks, reservoirs, and cap rocks, to avoid failures in the exploration and/or development activities. petrophysics data, which are a record of subsurface rock’s petrophysical properties are considered as an important data needed to gain insights into the subsurface (cannon, 2016). due to budget limitation, however, many oil and gas companies sometimes decided not to record a complete, full set of petrophysics/wireline log data during the exploration and/or development stage. a limited type and number of wireline log data may affect the interpretation of the subsurface rocks and conditions, and could cost a significant lost to the oil and gas companies. artificial intelligence (ai) may provide a solution to the limited subsurface wireline log data. this technique can estimate values of certain petrophysical properties using available dataset, either from the same well, or from the vicinity wells (lv et al., 2021). the application of ai in geology is still limited, with a few authors have successfully applied this technique for various geological purposes (e.g. tariq et al., 2019; lv et al., 2021; pang et al., 2021; zheng et al., 2021). this relatively new technique can help in providing estimated values for certain type of wireline log data, and hence contribute to a better subsurface interpretation, and a successful hydrocarbon exploration, production, and development activities. ai has been successfully applied to the field of geology for various purposes. ai can help denoise seismic data in a supervised fashion (birnie et al., 2021), to determine reservoir rock properties (cuddy, 2021), to optimise drilling operation, and to improve hydrocarbon recovery (solanki et al., 2022), and for mineral prospectivity mapping (sun et al., 2019). moreover, ai can also be used to estimate elastic properties of rock for geo-engineering purposes (tariq et al., 2019), and to predict tunnel geology, its construction time and costs (mahmoodzadeh et al., 2020). there are many other applications of ai in geology that are not possible to be mentioned in this paper/section. a better understanding of this techni-que may also unlock the application of this method to provide solution to many other geology-related problems. this paper aims to better understand the application of ai in geology. there are three objectives of this study: (1) to estimate sonic log (dt) and density log (rhob) using different types of ai (artificial neural network (ann) and multiple linear regression (mlr); (2) to assess the best ai technique that can be used to estimate certain wireline log data; and (3) to compare the estimated wireline log values with the real, recorded values http://journal.uir.ac.id/index.php/jgeet adhari, m.r. et al./ jgeet vol 7 no 4/2022 159 from the subsurface. it is expected that the results from this study would improve our understanding of the ai techniques, its application in petrophysical analysis, and how this ai technique could help and assist geoscientists in analysing and interpreting subsurface conditions. 2. data and methods the data used in this study are from three wells located onshore of the northern perth basin, western australia. original well’s name have been changed, due to confidentiality issues, and these wells were renamed to well-a, well-b, and well-c. these studied wells are situated close to each other, within the radius of 10 km. wireline logging data from well-a and well-b include neutron porosity log (nphi), gamma ray log (gr), density log (rhob), and sonic log (dt). while data from well-c include neutron porosity log (nphi) and gamma ray log (gr). this study decided to estimate rhob and dt using ai techniques, due to the importance of these logs to support the interpretation of the subsurface, and because wellc does not have these two logs. all the aforementioned wireline logging data used in this study are the data of the late permian beekeeper formation, a proven mixed carbonate-siliciclastic reservoir in the northern perth basin, western australia (crostella, 1995; mory and iasky, 1996; norvick, 2004; thomas, 2014). fig 1. workflow used in this study to estimate rhob and dt from the available dataset. two types of ai techniques were used to achieve the aim and objectives of this study, which are artificial neural network (ann), and multiple linear regression (mlr). ann and mlr techniques were selected due to their excellent ability to estimate certain outcome values by relying on the input data (multiple type of data), with high level accuracy. processing of the data using these techniques were conducted using spssibm software. workflow of how these methods used for this study is shown in fig.1. visualisation of the data and results of this study were carried out with the help of microsoft excel and adobe illustrator. ann is an ai method that tries to mimic how human brain analyses and processes data (gurney, 2004). this method builds several processing units based on interconnected connections and consists of an arbitrary number of cells or nodes or units or neurons that connect the input set to the output (dastres and soori, 2021). ann acquires the knowledge of the model, and discover the structure of the data through training, and then apply it to unknown data for the purpose of classification, prediction, time series analysis, etc (wesolowski and suchacz, 2012). ann is better than traditional computers in processing the data because it can adapt to new environments by learning, can process fuzzy (imprecise) data, can work with noisy or erroneous data, and can perform classification tasks very quickly (buscema, 1998). mlr is a statistical technique that uses several explanatory variables to predict the outcome of a response variable (uyanık and güler, 2013). mlr technique uses correlations between variables (this study: input well log data) to explain variance in outcome variables and predict specific outcome values (abbott, 2017). this mlr technique allows us to investigate how a set of explanatory variables is associated with a dependent variable of interest, but does not allow us to make causal inferences (tranmer and elliot, 2008). 3. geological settings the perth basin is an elongate, north-south trending trough underlying approximately 100,000 square kilometres of the western australian margin between geraldton and augusta (fig.2). slightly more than half the basin lies offshore in water depths of up to 1,000 m (mory and iasky, 1996). the perth basin consists of a series of northerly striking sub-basins, troughs and uplifts, and covers an area of ca. 45,000 km2 onshore and 55,000 km2 offshore (song and cawood, 2000). to the north, the basin is bounded by the northampton block and the eastern margin of the perth basin is defined by the darling fault (thomas, 2014). to the south, the harvey ridge, another shallow basement feature, extends obliquely northwest from the darling fault and separates the dandaragan trough from the bunbury trough, and westward, sediments thicken into the vlaming sub-basin (cadman et al., 1994). it is possible that a northwest extension of the precambrian leeuwin block and a fault system extending southwest from the edward's island block, merge to form the western boundary of the vlaming sub-basin (cadman et al., 1994). strata within the perth basin range mainly from permian to cretaceous in age and locally reach up to 15,000 m in thickness in major depocentres like the dandaragan trough (song and cawood, 2000). basement of the perth basin consists of archaean and proterozoic blocks, overlain by an early paleozoic sequence (tumblagooda sandstone), recognised in the northern part of the basin and probably coincided with local block faulting (song and cawood, 2000; song and cawood, 2010). the perth basin developed through the interplay of phases of extension and transtension, resulting in a complex history of faulting and synsedimentary fault block movement (mory and iasky, 1996; norvick, 2004; thomas, 2014). two main rifting phases in the permian and jurassic to earliest cretaceous have been recognised in both offshore and onshore (mory and iasky, 1996; song and cawood, 2000). the younger event corresponds to final rifting and breakup of gondwana lithosphere between australia and greater india and, entails 160 adhari, m.r. et al./ jgeet vol 7 no 4/2022 dextral strike–slip deformation and basin inversion as well as margin orthogonal extension (norvick, 2004; thomas, 2014; geoscience-australia, 2020). fig 2. the perth basin is situated in the western australia, with more than half the basin lies offshore (modified from sharifzadeh and mathew, 2011). most hydrocarbon accumulations in the perth basin are in structures associated to strike–slip deformation, although rollover anticlines have also proved as successful exploration sites (crostella, 1995). basement structures have been reactivated during basin formation and control the linear, northstriking structural grain of the basin (song and cawood, 2000). the basin is compartmentalised by a series of northweststriking transfer faults which formed during break-up (e.g. abrolhos and cervantes transfer zones), but which were probably localised along pre-existing basement structures (mory and iasky, 1996). 4. results the application of ai techniques to estimate density log (rhob) and sonic log (dt) using input data of neutron porosity log (nphi), and gamma ray log (gr) as the independent variables/covariates yielded excellent results (fig.3, and 4), with average accuracy of >95% (table 1), and crossplot validation showing trendline reliability (r2) and correlation coeffcient (r) values of more than 0.6 (fig.5, and 6). the accuracy percentage of the results of each sample data was calculated using the abs function in microsoft excel, while r was calculated using the correl function. findings of this study consistently show that ann produced better results compared to mlr when estimating rhob (table 1, fig.5, and 6), either using the input data from well-a or well-b. this suggests that ann is more reliable when used to estimated rhob. the accuracy of the estimated rhob values is ranging between 74.9%-100%, with the average accuracy value between 97.98%-98.87% (table 1). in well-a, the average accuracy of rhob using ann is 98.47%, slightly higher than the 97.98% accuracy of mlr (table 1). moreover, the average accuracy of rhob in well-b using ann, which is 98.87%, is also slightly higher compared to 98.85% of mlr (table 1). the accuracy for the estimated dt values is not consistent, as different dataset and ai techniques produced different accuracy level (table 1). accuracy for estimated dt from wella is ranging between 78.18%-99.99%, with average value ranging between 96.03%-96.08% (table 1). these results from well-a show that mlr is a better choice when estimating dt values. however, results from well-b show that ann produced a better results and accuracy compared to mlr when estimating dt values. the accuracy of the estimated dt value from well-b is ranging between 79.29%-99.99%, with the average value ranging between 96.88%-96.98% (table 1). crossplots analysis between the recorded dt and rhob and the estimated dt and rhob, from both well-a, and well-b were conducted to validate the application and results of ai methods (fig.5, and 6). the results show that the r2 (trendline reliability) and r (correlation coefficient) values of the studied data are more than 0.6 (except fig.5.d), and these are considered as good-excellent results (fig.5, and 6). the nearer r2, and r are to 1, the better the trendline fits the data/better correlation between the data. moreover, results from crossplot validation show that ann analysis consistently produced higher r2 and r, compared to mlr, either in well-a (fig.5) or well-b (fig.6). this is suggestive that ann analysis is better than mlr analysis in estimating dt and rhob. these goodexcellent crossplots results validate that the results from ai analysis are reliable and acceptable. training and testing of the data from well-a and well-b showed high level accuracy results, as has been explained in the earlier paragraphs. on the basis of these excellent results, ai techniques were then applied to estimate rhob and dt values for well-c, using the input data from well-a, well-b, and well-c. results of this study show that the estimated rhob and dt of well-c are similar to the recorded and estimated rhob and dt from well-a and well-b (fig.7, 8, and 9). low nphi (<5%), and low gr (20-40 api) correspond to low dt (<55 us/f). moderate nphi (5-10%), and moderate gr (40-60 api) correspond to moderate dt (55-65 us/f). high nphi (>10%), and high gr (>60 api) correspond to high dt (>65 us/f). on the other hand, the trend for rhob log is slighly different compared to the trend for dt log. low nphi (<5%), and low gr (20-40 api) correspond to low rhob (<2.6 g/cm3). moderate (5-10%) to high (>10%) nphi, and moderate (40-60 api) to high (>60 api) gr correspond to moderate (2.6-2.7 g/cm3) rhob. high nphi (>10%), and high gr (>60 api) correspond to high rhob (>2.7 g/cm3). therefore, on the basis of these patterns and trends similarities, the authors consider the estimated dt and rhob values of well-c are reasonable, reliable, and acceptable (fig.7). comparison of the estimated rhob and dt values with the recorded data shows a minor mismatch between logs, and shows similar pattern with the original recorded data (fig.3, and 4). these results are evident that ai techniques (ann and mlr) are suitable, applicable, and acceptable to be carried out to estimate particular subsurface petrophysical data. adhari, m.r. et al./ jgeet vol 7 no 4/2022 161 fig 3. comparison of the results from ai (ann, mlr) analysis and the original recorded data. the estimated values of sonic log (dt) of well-a, and well-b are quite similar with the original recorded data. minor mismatch between the logs can clearly be seen in this figure. y axis = subsurface depth (m), x axis = sonic log (dt, in us/f). 2240 2250 2260 2270 2280 2290 2300 2310 2320 2330 2340 2350 45 55 65 75 well a-dt dt-recorded dt-estimated-ann dt-estimated-mlr 2200 2210 2220 2230 2240 2250 2260 2270 2280 2290 2300 2310 40 50 60 70 80 90 well b-dt dt-recorded dt-estimated-ann dt-estimated-mlr 162 adhari, m.r. et al./ jgeet vol 7 no 4/2022 figure 4. comparison of the results from ai (ann, mlr) analysis and the original recorded data. the estimated values of density log (rhob) of well-a, and well-b are quite similar with the original recorded data. minor mismatch between the logs can clearly be seen in this figure. y axis = subsurface depth (m), x axis = density log (rhob, in g/cm3). table 1. accuracy of the ai results are ranging between 74.9%-100%. with this level of accuracy, the results of this ai analysis are considered acceptable and reliable. accuracy percentage for each sample data was calculated using the abs function in microsoft excel. rhob = density log (g/cm3), dt = sonic log (us/f), ann = artificial neural network, mlr = multiple linear regression. 2240 2250 2260 2270 2280 2290 2300 2310 2320 2330 2340 2350 2,0 2,2 2,4 2,6 2,8 well a-rhob rhob-recorded rhob-estimated-ann rhob-estimated-mlr 2200 2210 2220 2230 2240 2250 2260 2270 2280 2290 2300 2310 2,3 2,4 2,5 2,6 2,7 2,8 well b-rhob rhob-recorded rhob-estimated-ann rhob-estimated-mlr well-a well-b rhob-estimated dt-estimated rhob-estimated dt-estimated accuracy (%) accuracy (%) accuracy (%) accuracy (%) ann mlr ann mlr ann mlr ann mlr min 89.53 74.90 79.48 78.18 88.01 87.98 79.29 79.31 max 99.99 100.00 99.98 99.99 100.00 100.00 99.99 99.99 avg 98.47 97.98 96.03 96.08 98.87 98.85 96.98 96.88 adhari, m.r. et al./ jgeet vol 7 no 4/2022 163 fig 5. results from crossplot analysis of well a. a. crossplot between recorded dt and estimated dt (using ann) produced r2 = 0.65, and r = 0.80. b. crossplot between recorded dt and estimated dt (using mlr) produced r2 = 0.60, and r = 0.77. c. crossplot between recorded rhob and estimated rhob (using ann) produced r2 = 0.72, and r = 0.76. d. crossplot between recorded rhob and estimated rhob (using mlr) produced r2 = 0.21, and r = 0.45. the nearer r2, and r are to 1, the better the trendline fits the data/better correlation between the data. r2 = trendline reliability, and r = correlation coefficient. dt = sonic log (us/f), and rhob = density log (g/cm3). fig 6. results from crossplot analysis of well b. a. crossplot between recorded dt and estimated dt (using ann) produced r2 = 0.80, and r = 0.90. b. crossplot between recorded dt and estimated dt (using mlr) produced r2 = 0.79, and r = 0.89. c. crossplot between recorded rhob and estimated rhob (using ann) produced r2 = 0.13, and r = 0.36. d. crossplot between recorded rhob and estimated rhob (using mlr) produced r2 = 0.13, and r = 0.36. the nearer r2, and r are to 1, the better the trendline fits the data/better correlation between the data. r2 = trendline reliability, and r = correlation coefficient. dt = sonic log (us/f), and rhob = density log (g/cm3). a b c d a b c d 164 adhari, m.r. et al./ jgeet vol 7 no 4/2022 fig 7. nphi and gr are the input data used to estimate rhob and dt of well-c. the data are from subsurface depth of 2165-2230 m. fig 8. original recorded wireline log data of well-a. these data were trained and tested to estimate rhob and dt. the data are from subsurface depth of 2240-2350 m. adhari, m.r. et al./ jgeet vol 7 no 4/2022 165 fig 9. original recorded wireline log data of well-b. these data were trained and tested to estimate rhob and dt. the data are from subsurface depth of 2200-2310 m. 5. discussion this paper contributes to the advancement of ai in geology, in particular field of petrophysical analysis. findings from this study showed the possibility of applying ai to estimate particular wireline log data (rhob and dt) that yielded high level accuracy results. ai is a relatively new technique that can be used to provide a solution to many problems, in many field of sciences, including geology (chen et al., 2020). however, the application of this technique in geology is still in its infancy, and much development is needed (chen et al., 2020). findings of this study, using the data from well-a, well-b, and well-c, consistently show that ann produced better results compared to mlr when estimating rhob. this is interpreted to be caused by the algorithm of ann that relies on the deep learning process, multilayer perceptron, with multiple hidden layers, and this makes ann a more reliable technique compared to mlr. moreover, data used for this study are subsurface rock data with inconsistent trends/patterns and random relationship between each data, and ann is best to estimate a particular outcome with the input of this type of data. ann has an excellent capability (adaptive learning) to identify specific patterns and trends, and in categorising information (dastres and soori, 2021). there is no consistent best techique to estimate dt, as shown by the results of this study. this may be due to the nature of the dt data that are highly sensitive to the type of the subsurface rocks. vertical distribution of the dt data is highly dispersed, and this make the estimation of this type of data more difficult. both ann and mlr may produce dt results with the best/better accuracy level, depending on the type of the input data. these results show that estimating dt needs to be done carefully, and the selection of the ai methods needs to be done with caution. different ai methods may produce results with different accuracy level for dt estimation. comparison of the estimated rhob and dt with the original recorded rhob and dt data show a minor mismatch, and the log trends and patterns are quite similar. this is evident that the selected ai methods used for this study (ann and mlr) are reliable techniques that can produce results with high level accuracy and confident. although the results from these two analyses are quite similar, the procedure for mlr is much simpler than ann. therefore, we encourage the readers to first choose mlr when estimating particular wireline logging data (e.g. rhob and dt), and if the results are considered as less reliable, then we suggest the reader to apply ann analysis. it is also a wise choice if the readers decide to run both ann and mlr analyses simultaneously to compare and see the results from both analyses, as the different algorithm used for each analysis may produce different results. 6. conclusion this study provides some new insights into the application of ai in geology, in particular in the field of petrophysical analysis. problems commonly occur during hydrocarbon exploration and/or development stage, due to the lack of subsurface wireline log data can be tackled by the application of ai techniques to estimate particular well log data. the contribution from this paper is expected to improve our understanding of ai, and encourage the development of ai not only in the field of petrophysics, but also in other branches of geology. ai, which is a relatively new method, can be used to estimate certain wireline log data using input data of available subsurface petrophysical dataset with high level accuracy and confident. this study used ann and mlr (types of ai) to estimate rhob and dt, and it yielded excellent results (average 166 adhari, m.r. et al./ jgeet vol 7 no 4/2022 accuracy >95%). ann is proven to be a better choice when used to estimate rhob. besides, results from this study show that both ann and mlr can produce the best/better results when estimating dt, depending on the type of the input data. selection of the type of ai technique may need to be done carefully when used to estimate dt. acknowledgements this study utilised well log data provided by the department of mines, industry regulation and safety (dmirs) of the government of western australia. the authors would like to thank dmirs for providing the data, and for their permission to publish the studied well log data. references abbott, m.l., 2017. using statistics in the social and health sciences with spss and excel. wiley, canada. birnie, c., ravasi, m., liu, s. and alkhalifah, t., 2021. the potential of self-supervised networks for random noise suppression in seismic data. artificial 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234-240. wesolowski, m. and suchacz, b., 2012. artificial neural networks: theoretical background and pharmaceutical applications: a review. j aoac int, 95(3): 652-68. zheng, w., tian, f., di, q., xin, w., cheng, f. and shan, x., 2021. electrofacies classification of deeply buried carbonate strata using machine learning methods: a case study on ordovician paleokarst reservoirs in tarim basin. marine and petroleum geology, 123. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 4 2022 ariyon, m. et al./ jgeet vol 7 no 4/2022 189 research article economic feasibility analysis of fishing job operation in well ys13 muhammad ariyon 1*, bella santika 1, fitrianti 1 1 department of petroleum engineering, faculty of engineering, islamic university of riau, jalan kaharuddin nst no. 113 marpoyan, pekanbaru, riau, indonesia * corresponding author : aryonmuhammad@eng.uir.ac.id tel.: +62 813 2151 4121 received: oct 1, 2022; accepted: nov 20, 2022. doi: 10.25299/jgeet.2022.7.4.10190 abstract oil consumption in indonesia has increased from year to year. however, the increasing demand for oil and natural gas is inver sely proportional to oil and gas production, which always declines from year to year. one of the factors causing the decline in production is the well damage. well ys13 is a well that is damaged in the form of fish in the well. a fishing job is the most appropriate option to solve the problem of the presence of fish in the well because the fish in the well must be removed to continue well production activities or drilling activities. this study aimed to determine the economic feasibility of fishing job activities to be carried out at the ys13 well. the research begins with the preparation of the required data, then calculate the predicted production of the ys13 well with the decline curve method, estimates the cost of the fishing job, and economic fishing time (eft). and determines the economic feasibility of the fishing job project by calculating profit indicators, namely net present value (npv), internal rate of return (irr), and pay out time (pot). the results of calculations using the decline curve method obtained that the total production for 20 months is 4293.52 bbl. the eft value is 3 days with ps = 10% and the total cost of fishing is $28.657,70. the economic value of the project with discount rate = 12%, marr = 12%, npv = $147.367,20, irr = 114%, and pot = 1.44. from the results of the calculation of the economic feasibility, the project is considered feasible to be carried out. keywords: fishing job, decline curve, economic fishing time (eft), npv, irr. 1. introduction oil and gas are indispensable resources for the community in supporting daily activities. hence, it contributes significantly to the economy and industry of a country and is one of the economic and income supports of the state (erziyanti, 2019). oil consumption in indonesia is increasing year after year. in 2015, oil demand was recorded at 1.5 million barrels of oil a day (bopd), and it grew to 1.6 million bopd in 2016 and 1.7 million bopd in 2017 (taher, 2019). however, the increasing demand for oil and natural gas is inversely proportional to indonesian oil and gas production, which has been in decline for the last few years. the condition of old wells is often the cause of not optimal exploitation activities resulting in a decrease in the amount of production (utama, 2014). in addition to the condition of old wells, another factor that causes a decrease in production is damage to wells that still have potential (wibisono, 2018). one of the damages to the well is the presence of fish in the well which hinders well production activities. fish is material or equipment left in the well: it can be stuck pipe, broken pipe, drill collar, bit, hand tool, cable, etc. (degeare, 2015). this fish or equipment left behind needs to be removed to continue the operation to be carried out. most fish occur during drilling activities, but it is possible for fish to occur in wells that are already operating. fish in operating wells will certainly hamper production activities which can lead to a decrease in the amount of production. therefore, the fish in the well should be removed if deemed economically viable. activities that can be used to remove fish from boreholes are fishing job operations (lyons and plisga, 2005). well ys13 is a directional well that was completed in 2012 and has a potential production of 20 bopd. however, in 2014 the esp (electric submersible pump) circuit broke and was left in the well which caused the production to stop. therefore, it is necessary to carry out well maintenance to produce the well again. well maintenance carried out is a fishing job operation to remove a series of esp left in the well. the fishing job activity is a well maintenance activity that requires a large amount of money due to time and the equipment needed and are inputs to determine if the activity can still be considered profitable (adkins, 1993). to determine the economic feasibility of well ys13, maintenance activities will be calculated from the net present value (npv), internal rate of return (irr), and pay out time (pot) (ariyon, setiawan and reza, 2020) (william, kartoatmodjo and prima, 2017). 2. methods 2.1 fishing job operation fishing is a technique of removing lost or trapped objects from the wellbore. fishing job is part of planning in drilling and workover operations (degeare, 2015). the factors that cause the occurrence of fish include: 1. mechanical failure such as, pump failure, lifting equipment, subsurface equipment 2. deviation factor, dogleg, and crooked hole 3. human error. fishing can be called a risk management strategy. when fishing is successful, the well will be safe and if not, it will suffer a considerable loss (degeare, 2015). cost fishing is the cost incurred during fishing job activities carried out. the cost of fishing will be even greater if there is an increase in rig cost due to excessive depth or in more complex wells. http://journal.uir.ac.id/index.php/jgeet 190 ariyon, m. et al./ jgeet vol 7 no 4/2022 daily fishing cost = equipment cost +rig cost + operator cost (1) the ys13 well is an off-production well that will be reactivated by carrying out fishing operations to retrieve fish left in the well. to calculate the fishing economy of the ys13 well, the economic fishing time (eft) parameter is used. eft= ps ×lpo dfc (2) eft : economic fishing time (days) ps : probability of success (%) lpo : loss potential oil ($) dfc : daily fishing cost ($/day) in this eft concept which condisers not only the cost but also the operation’s probability of success (cunha, 1994). in this case, for a well with a probability ps of a successful fishing job, there will be the following possibilities: a. do not perform the fishing job and lost potential oil production b. do the fishing job successfully in a time t and expend dcf.t c. do the fishing job unsuccessfully during the time t and then abandon the fish and do perforation on other zone the probability of success is used to determine the time that will be used in a fishing operation. the percentage value of ps ranges from 5% to 85%. the percentage is obtained from operations that have been carried out previously, although no fishing operation is exactly the same (kemp, 1986). loss potential oil is the potential oil that will be produced if a fishing job is carried out, the value used is the cumulative income from the well (pertamina, 2015). daily fishing cost is the cost used in fishing operations per day. 2.2 decline curve analysis production from time to time will cause a decrease in pressure which will cause a decline in the production rate per unit of time. this is due to the limited volume of the oil reservoir. the combination of time, production rate, and cumulative production can be used to determine the remaining reserves and production life of a well or oil and gas field (lyons, plisga and lorenz, 2015). decline curve analysis is a method used to estimate oil and gas reserves based on production data after a certain time interval (irwin, 2015). fig. 1. decline curve plot decline curves are generally divided into three types based on the exponent decline (b): 1. exponential (b=0) : curve tends to be straight (constant slope) 2. hyperbolic (0<b<1) : curve tends to be flat 3. harmonic (b=1) : steep curve (steep decline from beginning) 2.2.1 trial error & x2 chisquare-test method the trial error & x2 chisquare-test method is a method that estimates the price of production rate (q) assuming various prices of b and determines the smallest difference between q-actual and q-forecast that has been calculated previously (rukmana and kristanto, 2011). in addition to the trial error & x2 chisquare-test method, there is also a loss ratio method which is also often used in research. the calculation procedure for this method is as follows (rukmana and kristanto, 2011): a. create a tab that contains: time (t), qactual, qforecast and di with various prices b, and x2 b. assume the value of b is from 0 to 1 (b = 0 for exponential, b = 0.1 – 0.9 for hyperbolic, b = 1 for harmonic) c. calculate di with equations: a) b = 0 di = ln ( qi qt ) tt (3) b) b = 0.1 – 0.9 di = ( qi qt⁄ ) b − 1 b. tt (4) c) b = 1 di = ( qi qt ) − 1 tt (5) d. calculate qforecast with equations: a) b = 0 di = qne −di.t (6) b) b = 0.1 – 0.9 di = qi(1 + bdit) −1 b⁄ (7) c) b = 1 di = qi(1 + dit) −1 (8) the value of qi = qactual, the value of di is obtained from step 3 and the value of t = dt e. calculate the x2 equation (difference between actual and forecast) using the chisquare-test equation:         fi fifi x 2 2 )( (9) where : fi = observation data (actual) data points being analyzed fi = expected data (estimate) f. repeat the calculation procedure in steps 3 to 5 to calculate the next steps. g. determine ∑ the smallest value of x2. the smallest value of ∑ x2 shows the most suitable curve to ariyon, m. et al./ jgeet vol 7 no 4/2022 191 represent the data points being analyzed with the price of: a) exponential decline : b= 0 b) hyperbolic decline : b = 0.1 – 0.9 c) harmonic decline : b = 1 2.3 economic feasibility oil and gas activities carried out in the oil and gas industry must be carried out with precise calculations so that the potential for financial loss are minimized. for this reason, it is necessary to carry out an economic analysis of the activities (rahman and damayanti, 2021). this analysis will determine whether the activity is feasible or not. the economic analysis carried out is to calculate the feasibility parameter for oil and gas activities, namely the net present value (npv), internal rate of return (irr), dan pay out time (pot) (novrianti, 2017). 2.3.1 net present value (npv) npv is a method of calculating net value at the present time. the present time in question is the initial time of calculation in year 0 in the calculation of investment cash flow (drs. m. giatman, 2006). npv is used to assess the feasibility of a project. if the npv is positive, then the project is worth doing, because it will provide benefits (shereih, 2017). npv = nfc0 + nfc1 (1+i)1 + nfc2 (1+i)2 + ⋯ + nfcn (1+i)n (10) nfc0 = cash flow year-0 nfcn = cash flow year-n i = discount rate 2.3.2 internal rate of return (irr) irr or internal rate of return is the interest price that causes the value of cash inflow to be equal to cash outflow if this cash flow is discounted for a certain time (fiqri, 2013). irr can be interpreted as the interest rate that causes npv = 0 (shereih, 2017). the value of the irr can be expressed in the following equation: irr = i1+ ( npv1 npv1-npv2 ) ×(i2-i1) (11) npv1 = net present value (+) npv2 = net present value (0) i1 = discount rate (npv (+)) i2 = discount rate (npv (0)) 2.3.3 pay out time (pot) pay out time (pot) is the time required to return capital or investment (sari, 2011). pot is calculated to find out how long it will take for the investment to be returned (drs. m. giatman, 2006). the pot value can be expressed in the following equation: 𝑃𝑂𝑇 = 𝑛1+(𝑛2 − 𝑛1) ( 𝐶𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝑁𝐶𝐹1 (𝐶𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝑁𝐶𝐹1 + 𝐶𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝑁𝐹𝐶2) ) (12) pot = pay out time nfc1 = net cash flow 1 nfc2 = net cash flow 2 n1 = year when cumulative ncf is negative (-) n2 = year when cumulative ncf is positive (+) 3. results 3.1 production forecast determination of the type of decline curve with the trialerror method is carried out by calculating the estimated production rate at various exponential decline values (b), namely from b = 0 to b = 1. the x2 chi-square method is used to determine the decline curve that best fits the q vs t graph in the previous trial-error method. from the production data used in the calculation of this method, it is found that the most suitable type of decline curve is the exponential type with b = 0 and the decline rate value = 0.14086. table 1. trial-error & x2 chi-square tabulation time month q (bopd) exponential hyperbolic b = 0 b = 0.1 b = 0.2 b = 0.3 b = 0.4 di = 0.14086 di = 0.15685 di = 0.17531 di = 0.19665 di = 0.2214 qo x2 qo x2 qo x2 qo x2 qo x2 1 01-21 1138 988.55 0.15 974.06 0.17 957.96 0.19 940.15 0.21 920.54 0.24 2 02-21 985 742.95 0.33 723.05 0.36 701.69 0.40 678.97 0.45 655.03 0.50 3 03-21 1240 812.83 0.53 783.13 0.58 752.24 0.65 720.49 0.72 688.20 0.80 4 04-21 2241 1275.90 0.76 1219.69 0.84 1162.88 0.93 1106.16 1.03 1050.22 1.13 5 05-21 1030 509.31 1.02 484.13 1.13 459.32 1.24 435.17 1.37 411.95 1.50 6 06-21 1033 443.74 1.33 420.31 1.46 397.74 1.60 376.26 1.75 356.03 1.90 7 07-21 1270 473.69 1.68 448.02 1.83 423.78 2.00 401.13 2.17 380.18 2.34 8 08-21 1216 393.91 2.09 372.76 2.26 353.13 2.44 335.09 2.63 318.63 2.82 9 09-21 1149 323.30 2.55 306.69 2.75 291.51 2.94 277.75 3.14 265.33 3.33 10 10-21 1041 254.38 3.09 242.36 3.29 231.53 3.49 221.80 3.69 213.12 3.88 11 11-21 1022 217.02 3.71 208.05 3.91 200.05 4.11 192.94 4.30 186.63 4.48 12 12-21 570 105.17 4.42 101.63 4.61 98.50 4.79 95.74 4.96 93.31 5.11 13 01-22 598 95.84 5.24 93.52 5.40 91.48 5.54 89.69 5.67 88.12 5.79 14 02-22 655 91.10 6.19 89.92 6.28 88.89 6.37 87.98 6.44 87.19 6.51 15 03-22 138 16.63 7.27 16.63 7.27 16.63 7.27 16.63 7.27 16.63 7.27 ∑ 40.35 42.14 43.96 45.78 47.60 192 ariyon, m. et al./ jgeet vol 7 no 4/2022 table 2. trial-error & x2 chi-square tabulation time hyperbolic harmonic b = 0.5 b = 0.6 b = 0.7 b = 0.8 b = 0.9 b = 1 di = 0.25017 di = 0.2836635 di = 0.322754 di = 0.36846 di = 0.422 di = 0.4849 qo x2 qo x2 qo x2 qo x2 qo x2 qo x2 1 899.10 0.27 875.81 0.30 850.74 0.34 824.02 0.38 795.83 0.43 766.47 0.48 2 630.06 0.56 604.31 0.63 578.09 0.70 551.73 0.78 525.57 0.87 499.93 0.97 3 655.79 0.89 623.66 0.99 592.21 1.09 561.81 1.21 532.76 1.33 505.31 1.45 4 995.75 1.25 943.34 1.38 893.50 1.51 846.61 1.65 802.92 1.79 762.54 1.94 5 389.89 1.64 369.14 1.79 349.83 1.94 332.01 2.10 315.68 2.26 300.81 2.42 6 337.18 2.06 319.77 2.23 303.82 2.40 289.31 2.57 276.16 2.74 264.31 2.91 7 360.96 2.52 343.45 2.70 327.60 2.88 313.31 3.05 300.48 3.23 288.98 3.39 8 303.72 3.00 290.28 3.19 278.21 3.37 267.42 3.55 257.78 3.72 249.17 3.88 9 254.20 3.52 244.24 3.70 235.36 3.88 227.45 4.05 220.42 4.21 214.16 4.36 10 205.38 4.07 198.51 4.24 192.41 4.41 186.99 4.56 182.18 4.71 177.91 4.85 11 181.04 4.64 176.10 4.80 171.72 4.95 167.85 5.09 164.41 5.22 161.36 5.33 12 91.16 5.25 89.26 5.39 87.59 5.51 86.11 5.62 84.79 5.72 83.63 5.82 13 86.74 5.90 85.52 5.99 84.45 6.08 83.50 6.16 82.66 6.24 81.91 6.30 14 86.49 6.57 85.88 6.62 85.34 6.67 84.86 6.71 84.44 6.75 84.06 6.79 15 16.63 7.27 16.63 7.27 16.63 7.27 16.63 7.27 16.63 7.27 16.63 7.27 ∑ 49.42 51.23 53.01 54.77 56.50 58.18 the estimated production of the ys13 well is calculated using the exponential decline curve method. estimated production is calculated from april 1, 2022 – november 1, 2023 (20 months), the ys13 well is capable of producing 4293.52 bbl of oil. table 3. forecast production time (t) q (bopd) np (bbl/month) 1-apr-22 20 600.00 1-may-22 17.37 521.16 1-jun-22 15.09 452.69 1-jul-22 13.11 393.21 1-aug-22 11.38 341.54 1-sep-22 9.89 296.67 1-oct-22 8.59 257.69 1-nov-22 7.46 223.83 1-dec-22 6.48 194.42 1-jan-23 5.63 168.87 1-feb-23 4.89 146.68 1-mar-23 4.25 127.41 1-apr-23 3.69 110.67 1-may-23 3.20 96.13 1-jun-23 2.78 83.50 1-jul-23 2.42 72.53 1-aug-23 2.10 63.00 1-sep-23 1.82 54.72 1-oct-23 1.58 47.53 1-nov-23 1.38 41.28 3.2 economic of fishing the economic calculation of fishing jobs in the ys13 well is carried out with several parameters, namely production potential of 20 bopd, an oil price of $74.73 per bbl, estimated time of economic production for 13 months, and production cost (esp rental) of $249.55 per day. in table 3, the well production and income generated are calculated for 20 months. however, in the 14th month, production was deemed uneconomical because the income was smaller than the cost of production. ariyon, m. et al./ jgeet vol 7 no 4/2022 193 table 4. production income time (month) production (bopd) cumulative production (bbl/month) income ($) cumulative income ($) 1 20 600 $ 44,838.00 $ 44,838.00 2 17.37 521.16 $ 38,946.58 $ 83,784.58 3 15.09 452.69 $ 33,829.26 $ 117,613.85 4 13.11 393.21 $ 29,384.32 $ 146,998.17 5 11.38 341.54 $ 25,523.42 $ 172,521.58 6 9.89 296.67 $ 22,169.81 $ 194,691.39 7 8.59 257.69 $ 19,256.84 $ 213,948.23 8 7.46 223.83 $ 16,726.62 $ 230,674.86 9 6.48 194.42 $ 14,528.85 $ 245,203.71 10 5.63 168.87 $ 12,619.86 $ 257,823.57 11 4.89 146.68 $ 10,961.69 $ 268,785.26 12 4.25 127.41 $ 9,521.40 $ 278,306.66 13 3.69 110.67 $ 8,270.35 $ 286,577.01 14 3.20 96.13 $ 7,183.68 $ 293,760.69 15 2.78 83.50 $ 6,239.79 $ 300,000.49 16 2.42 72.53 $ 5,419.93 $ 305,420.41 17 2.10 63.00 $ 4,707.78 $ 310,128.20 18 1.82 54.72 $ 4,089.21 $ 314,217.41 19 1.58 47.53 $ 3,551.92 $ 317,769.33 20 1.38 41.28 $ 3,085.22 $ 320,854.55 table 5. daily fishing job cost daily operation cost $ 4,247.04 supervise $ 62.23 bbm $ 246.84 fishing tools $ 3,500.00 fishing jars $ 2,000.00 total $ 10,056.11 table 6. probability of success and eft well ys13 probability of success (%) economic fishing time (days) 5% 1 10% 3 15% 4 20% 6 25% 7 30% 9 35% 10 40% 11 45% 13 50% 14 55% 16 60% 17 65% 19 70% 20 75% 21 80% 23 85% 24 to calculate the economics of fishing jobs, it is necessary to calculate the economic fishing time (eft). eft is the time limit for carrying out fishing operations that are still considered economical. to calculate it, daily fishing cost data is needed, as also the probability of success. in table 4, it can be seen the costs needed to carry out fishing operations per day. the eft calculation is highly dependent on the probability of success (ps) value. in the fishing operation, the ys13 ps well is determined at 10% and the eft is obtained for 3 days. 10% ps is selected based on estimates of fishing job operators who have carried out fishing operations before. looking at the condition of the well ps by 10% is suitable for use. with a duration of 3 days, the fishing operation requires a total cost of $ 28,657.70. 3.3 economic feasibility in table 6, it can be seen that the economic parameters of the ys13 well used in the economic feasibility analysis of the ys13 well fishing job are assessed from the npv, irr, and pot. irr value must greater than marr (minimum attractive rate of return), the minimum profit an investor expects to make from an investment. produce the ys13 well, requires production costs in the form of esp rental with a total of $ 7486.50 per month. the cash flow of the ys13 well can be seen in table 7. table 7. economic feasibility parameters capex $ 28,657.70 oil price $ 74.73 i (discount rate) /year 12% marr ( 12% esp rent (/day) $ 249.55 3.3.1 net present value (npv) calculation of npv in well ys13 using a discount rate (i) of 12% per year or 1% month, the results obtained are npv = $ 147,367.20 for 12 months. with a positive npv value, the fishing operation on the ys13 well is considered feasible because it is considered economical. 194 ariyon, m. et al./ jgeet vol 7 no 4/2022 table 8. cash flow well ys13 time (month) np (bbl/month) cash in cash out net cash flow cumulative ncf 0 0 $ $ 28,657.70 $ (28,657.70) $ (28,657.70) 1 600.00 $ 44,838.00 $ 7,486.50 $ 37,351.50 $ 8,693.80 2 521.16 $ 38,946.58 $ 7,486.50 $ 31,460.08 $ 40,153.88 3 452.69 $ 33,829.26 $ 7,486.50 $ 26,342.76 $ 66,496.64 4 393.21 $ 29,384.32 $ 7,486.50 $ 21,897.82 $ 88,394.47 5 341.54 $ 25,523.42 $ 7,486.50 $ 18,036.92 $106,431.38 6 296.67 $ 22,169.81 $ 7,486.50 $ 14,683.31 $121,114.69 7 257.69 $ 19,256.84 $ 7,486.50 $ 11,770.34 $132,885.03 8 223.83 $ 16,726.62 $ 7,486.50 $ 9,240.12 $142,125.15 9 194.42 $ 14,528.85 $ 7,486.50 $ 7,042.35 $149,167.51 10 168.87 $ 12,619.86 $ 7,486.50 $ 5,133.36 $154,300.87 11 146.68 $ 10,961.69 $ 7,486.50 $ 3,475.19 $157,776.06 12 127.41 $ 9,521.40 $ 7,486.50 $ 2,034.90 $159,810.96 table 9. net present value (npv) well ys13 time (month) net cash flow pv factor pv 0 $ (28,657.70) 1 $ 37,351.50 0.9901 $ 36,981.68 2 $ 31,460.08 0.9803 $ 30,840.20 3 $ 26,342.76 0.9706 $ 25,568.02 4 $ 21,897.82 0.9610 $ 21,043.38 5 $ 18,036.92 0.9515 $ 17,161.51 6 $ 14,683.31 0.9420 $ 13,832.34 7 $ 11,770.34 0.9327 $ 10,978.41 8 $ 9,240.12 0.9235 $ 8,533.10 9 $ 7,042.35 0.9143 $ 6,439.10 10 $ 5,133.36 0.9053 $ 4,647.16 total pv $ 176,024.90 npv $ 147,367.20 3.3.2 internal rate of return (irr) the internal rate of return (irr) of the ys13 well is calculated using goal seek in microsoft excel so that the npv value = 0. from the calculations carried out, the irr value = 114%, which means the project is considered feasible because the irr is greater than marr (12 %). table 10. internal rate of return (irr) well ys13 time (month) net cash flow pv factor pv 0 $ (28,657.70) 1 $ 37,351.50 0.4669 $ 17,438.75 2 $ 31,460.08 0.2180 $ 6,857.64 3 $ 26,342.76 0.1018 $ 2,680.91 4 $ 21,897.82 0.0475 $ 1,040.47 5 $ 18,036.92 0.0222 $ 400.13 6 $ 14,683.31 0.0104 $ 152.08 7 $ 11,770.34 0.0048 $ 56.92 8 $ 9,240.12 0.0023 $ 20.86 9 $ 7,042.35 0.0011 $ 7.42 10 $ 5,133.36 0.0005 $ 2.53 total pv $ 28,657.70 npv $ (0.00) 3.3.3 pay out time (pot) according to calculations already done, the pot of the ys13 well was acquired at 1.44 months. the project is declared feasible and capital refunds can be accomplished in a relatively short period of time. 4. conclusions based on research already done it can be concluded that: ariyon, m. et al./ jgeet vol 7 no 4/2022 195 1. the production of the ys13 well is capable of producing 4293.52 bbl of oil in the period 1 april 2022 – 1 november 2023 (20 months). 2. the results of the economic analysis of fishing wells ys13 with a probability of success of 10% obtained the eft value is 3 days and requires a total cost of $ 28,657.70. 3. economic feasibility analysis on ys13 well with a capital of $ 47,012.59, oil price $ 74.73/bbl, discount rate 12% per year, and production cost (esp rental) $249.55/day. obtained an npv value of $ 147,367.20, an irr of 114%, and a pot of 1.44 months, which is considered a feasible project to do. references adkins, c. s. 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(2017) ‘studi kelayakan keekonomian pada pengembangan lapangan’, seminar nasional cendekiawan, pp. 273– 278. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” akmal, f. et al./ jgeet vol 08 no 02-2 2023 6 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 research article machine learning prediction of tortuosity in digital rock fadhillah akmal1, m. cisco ramadhan dzulizar1, muhammad faizal rafli1, fatimah azzahra1, m. i. khoirul haq1, irwan ary dharmawan1,* 1 department of geophysics, faculty of mathematics and natural science, universitas padjadjaran, raya bandung sumedang km. 21 street, jatinangor 45363, indonesia * corresponding author : iad@geophys.unpad.ac.id received: may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13875 abstract physical rock property measurement is an important stage in energy exploration, both for hydrocarbons and geothermal sources. the value of physical rock properties can provide information about reservoir quality, and one of these properties is tortuosity. tortuosity is an intrinsic property of porous materials that describes the level of complexity of the porous arrangement when a fluid passes through it. conventionally, tortuosity values are measured through laboratory analysis and numerical simulation, but these measurements can take a long time. an alternative method for measuring tortuosity is using machine learning with a convolutional neural network (cnn). a cnn is a type of deep neural network designed to analyze multi-channel images and has been applied successfully to classification and nonlinear regression problems. by training a cnn on a dataset of digital rock samples that have been simulated using numerical computation to obtain their tortuosity values, it is possible to demonstrate that cnns can accurately predict the tortuosity of digital r ock. the result is that the cnn model can predict tortuosity values with the xception model being the most accurate with the lowest rmse value of 0.90962. keywords: tortuosity, digital rock, machine learning, convolutional neural network 1. introduction porous media are important in the field of energy exploration, where the properties of porous rocks can provide a lot of useful information, especially on hydrocarbon sources or geothermal sources. one of those properties is tortuosity. tortuosity is an intrinsic property of porous media that describes the level of complexity of fluid pathways, which is described as the length of the pathway relative to its effective length, as shown in fig. 1. regarding the condition of the reservoir, it is crucial to identify reservoir rock features such tortuosity. however, since analytical solutions cannot be used, this requires laboratory testing or numerical simulations, making it challenging to complete (ladopoulos, 2014). the determination of tortuosity values may also be carried out using machine learning techniques. fig. 1. depiction of tortuosity in porous media. the red line indicates the pathway that can be travelled by fluid, the blue line indicates the effective length of the pathway. machine learning has been developed and applied widely in science and technology fields such as production optimization and hydrocarbon drilling. it has also begun to be used to simplify and accelerate the computational process in the estimation of physical parameters of porous rocks. artificial neural networks (anns) are one of the popular machine learning models used to tackle complex problems. ann algorithms are modelled on human nerves that adaptively train to complete a task. a typical ann structure consists of several layers, each with a number of perceptrons. perceptrons are the fundamental building blocks of anns and are modelled on the neurons in human brain networks. in an ann, the input for one layer serves as the output for the following layer. one of the ann algorithms that is frequently applied to solve picture recognition issues is the convolutional neural network (cnn). cnn uses a convolution method that applies filters of a specific size to various input data locations, resulting in the creation of new representative information from the convolution of the input data and the filters. this output from the convolution is then used as the input for the next layer of the neural network. because the feature extraction and training processes in the cnn algorithm are carried out simultaneously by the computer, it is a good solution for estimating the physical properties of porous rocks with intricate patterns. cnn method has been proven to be used to predict the fundamental quantity value of porous media (graczyk and matyka, 2020). in recent studies, transfer learning, or the method of using pre-trained cnn models has obtained good results in determining rock parameters, especially on small datasets and out of range problems (tang et al., 2022). http://journal.uir.ac.id/index.php/jgeet akmal, f. et al./ jgeet vol 08 no 02-2 2023 7 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 table 1. digital rock sample and the amount of digital rock data used in the study. there is an experimental error of ± 0.5 % for porosity and ± 10 % for permeability (neumann et al., 2021). no name porosity permeability formation number of data 1 bandera brown sandstone 24.11 % 63 md desmoinesian 2740 2 bentheimer sandstone 22.64 % 22.64 md valaginian 2740 3 berea cores sandstone 18.96% 18.96 md upper devonian 2740 4 buff berea sandstone 24.02 % 275 md upper devonian 2700 5 castlegate sandstone 26.54 % 269 md late cretaceous 2700 6 leopard sandstone 20.22 % 327 md paleozoic 2690 7 parker sandstone 14.77 % 10 md paleozoic 2250 8 kirby sandstone 19.95 % 62 md 2740 the general layout of the layers of the cnn architecture is shown in next section. the cnn was chosen for this research because it allows for the calculation of physical parameter values in a shorter time without the need for laboratory testing by injecting fluid into porous rocks, thereby avoiding damage to the porous rocks. in order to conduct this research, a 3d digital rock sample of sandstone was obtained from the digital rock portal and pre-processed before being input into the cnn architecture (neumann et al., 2020). 2. material and methods this research begins with the creation of datasets from several types of digital rock data. the rock data used is porous rock data from ct-scan images. the digital rocks used in this study are a set of sandstone samples. sandstone lithology considered a classic sedimentary rock primarily comprised of quartz, silica, and sand-sized minerals, which is converted into a three-dimensional array of size 1000 x 1000 x 1000 voxels. table 1 shows digital rock sample and the amount of digital rock data used in the study. this array consists of a value of 0, representing a rock pore, and a value of 1, representing an obstacle. the ct-scan array is then resampled to a smaller array of size 128 x 128 x 128 voxels in order to lighten the computational load and create a larger dataset. the three-dimensional array is then calculated based on the connected path between its boundaries to obtain its tortuosity value. this was done with the help of tort3d software. the way the software works is by reading digital rock data and looking for connected paths in data that has void space. after getting all the valid paths, the tortuosity value of one of the flow directions can be calculated as average of all path length divided by size of the image in the direction of flow (alraoush and madhoun, 2017). the calculation results are then used as dataset labels in the machine learning model architecture. the total number of datasets totals 21300 images, with a range of tortuosity values between 1.08 113.09. the largest distribution of data is in the range of 1.08 to 13.52, totaling 19764 data. the distribution of dataset tortuosity value is shown in fig. 2. instead of using a three-dimensional array as input for machine learning, certain parts of the array are selected to represent the entire array. these selected parts are slices of the plane on the three main axes, each 128 x 128 in size. these three plane slices are then stacked into a threechannel image as a synthetic rgb image. the total dataset consists of 21,300 samples as shown in table 2, with 1,300 set aside as testing data that are not used in training. the remaining 20,000 samples are divided into a trainvalidation dataset, with 85% designated as the training set and 15% as the validation set. the illustration of the creation of synthetic rgb images is shown in fig. 3. fig. 2. distribution of dataset tortuosity value. this research uses a transfer learning strategy by utilizing four types of pre-trained model architectures in order to obtain the best model. transfer learning is a machine learning technique in which a model is trained and developed for one task and then reused for a second, related task. it involves exploiting what has been learned in one setting to improve optimization in another setting (gao and mosalam, 2018). the transfer learning strategy is applied in this study to reduce training time and speed up the process of obtaining models with small errors. a pretrained model is a model that has been trained on a large benchmark dataset and is capable of solving problems similar to the new problem that needs to be solved (iorga and neagoe, 2019). in this research, the problem to be solved is image recognition. the pre-trained model architectures used in this research are those available in the keras library (https://keras.io/api/applications/), which have been tested and have good performance. the four types of pre-trained models used in this research are densenet201, xception, inceptionv3, and mobilenetv2. stages of synthetic. convolutional neural network work in projecting images can be seen in fig. 4. 8 akmal, f. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 3. stages of synthetic rgb image creation. fig. 4. convolutional neural network work in projecting images. dense convolutional networks or densenet is a pretrained model architecture built with a structure where each layer is connected to subsequent layers (huang et al., 2017) as shown in fig. 5. densenet architecture can reduce the occurrence of overfitting by utilizing dense connection techniques especially when the number of datasets used is small (talo, 2019). fig. 5. densenet201 architecture. extreme inception or better known as xception is a model that uses the depthwise separable convolution technique in its architecture as shown in fig. 6. the xception architecture consists of three main parts, namely entry flow, middle flow, and exit flow. xception is noted to have better performance than inceptionv3 even though it has fewer parameters (chollet, 2017). mobilenet is a pre-trained model architecture that utilizes depthwise separable convolution in its architecture which is a combination of depthwise convolution and pointwise convolution. the mobilenet architecture has a total of 28 layers with its architectural illustration shown in fig. 7 (howard et al., 2017). the architecture of the cnn model used can be seen in fig. 8. the model is trained by learning the relationship between the input which is an rgb synthetic image of digital rocks and the labels which is the actual tortuosity value until the error between the predicted value and the actual value is minimized. the predicted value is the result of machine learning trying to get the tortuosity value from the synthetic rgb image. while the actual value is the dataset labels that are the tortuosity values obtained based on software calculations. in order to compare the performance and prediction accuracy of the different algorithms, three metrics are used as a loss function to determine the error value: mean absolute error (mae), root mean square error (rmse), and r2. mae is a function used for regression models (eqn. 1). mae is the sum of absolute differences between the target and independent variables. it measures the average of the residuals, where 𝑛 represents the number of observations, 𝐹𝑖 is the predicted price at the point of sale 𝑖 and 𝐴𝑖 is the actual value. mae is very good to use when there are outliers in the data and has a simple interpretation (ansari and binninger, 2022). 𝑀𝐴𝐸 = ∑ | 𝐴𝑖−𝐹𝑖 𝐴𝑖 |𝑛𝑖=1 (1) akmal, f. et al./ jgeet vol 08 no 02-2 2023 9 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 6. xception architecture. fig. 7. mobilenetv2 architecture. fig. 8. architecture of the cnn models, the input of the model is the synthetic rgb image data created from the digital rock, and the output of the model is the predicted tortuosity value of the rock. 10 akmal, f. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 rmse is another commonly used metric to evaluate the accuracy of predictions obtained by a model (eqn. 2). it takes the residuals between actual and predicted values and compares the prediction errors of different models for particular data. this metric is very useful for measuring how close the prediction is to the actual value, and gives a larger penalty to large errors. it is therefore suitable in cases where the difference between the predicted and actual values is critical, such as in rock modelling (dandekar et al., 2018). 𝑅𝑀𝑆𝐸 = √ 1 𝑛 ∑ (𝐴𝑖 − 𝐹𝑖 ) 2𝑛 𝑖=1 (2) the variable 𝑅2 is a widely used statistical measure in regression-based machine learning (eqn. 3). it indicates the percentage of the variance in the dependent variable that the independent variables explain collectively. the closer the value of 𝑅2 to 1, the better the model is fitted. r-squared provides information on how well the linear model fits the observed data and how much variation in the data can be explained by the model. 𝑅2 = 1 − ∑ (𝐴𝐼−𝐹𝑖 ) 2𝑛 𝑖=1 ∑ 𝐴𝑖 2𝑛 𝑖=1 (3) 3. results and discussion four cnn models were trained using 20,000 digital porous rock data that was converted into synthetic rgb images, then the model was tested using 1,300 images from datasets. different cnn model performance was measured by looking at three metrics to determine the error value, namely mae, rmse, and r2. the performance of each model can be seen in table 2 as follows. table 2. evaluation result of densenet201, inceptionv3, mobilenetv2, and xception in tortuosity value prediction. no model mae rmse r2 1 densenet201 33.539 1.02666 0.98635 2 inceptionv3 34.538 0.98445 0.98724 3 mobilenetv2 32.552 1.02465 0.98737 4 xception 33.901 0.90962 0.98636 based on table 2, it is known that the pre-trained model with the smallest error is produced by the mobilenetv2 architecture with an mae of 32.552, then the xception model with an rmse value of 0.90962, and mobilenetv2 with r2 value of 0.98737. the results show that the xception model is the best model out of the four models. the four models all have r2 values over 0.98 and similar mae values, indicating that they are all quite accurate. the rmse values of the four models are then comparable, with the xception model having the best rmse value at 0.90962. this demonstrates that, when compared to the other four models, the xception model has the least error and makes predictions that are most accurate. the ability of the cnn model to predict values of data can also be seen using a scatter plot with the horizontal axis being the actual tortuosity value and the vertical axis being the predicted tortuosity value. the scatter plot result of the models can be seen in fig. 9. the data plotted in fig. 9 is prediction data that has undergone outlier reduction. this reduction also shows that the cnn model created is able to have good performance under certain conditions and in a certain range. the out-of-range problem case was also found in research on using a cnn model to predict the permeability of synthetic rocks (tang et al., 2022). (a) (b) (c) (d) fig. 9. predicted tortuosity values compared to actual values in small tortuosity value, (a) result from xception model, (b) result from inceptionv3 model, (c) result from densenet201 model, and (d) result from mobilenetv2. akmal, f. et al./ jgeet vol 08 no 02-2 2023 11 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 the black diagonal line represents the real tortuosity value of the data, with the blue dots indicating the distribution of model-predicted values. of the 1,300 test data, predictions with a small range of values were taken into account. as shown in table 2, the xception model had more accurate results compared to the other models. this can be seen from the predictions, which are close to the actual result value. the xception model has a smaller rmse value and has similar mae and r2 value. these models are only able to accurately predict at smaller tortuosity values, with increasing inaccuracy as the tortuosity values increase. this research has shown that the input to the cnn model is not three-dimensional rock data itself, but rather slices of data that are combined to form a synthetic rgb image representing the whole data set. the data also has a non-uniform distribution and is largely comprised of data with small tortuosity values. these factors contribute to the model's low prediction accuracy and its ability to accurately predict only data within a narrow range of small tortuosity values. fig. 10. boxplot showing the distribution of tortuosity values of the dataset. as shown in fig. 10, a box plot is used to visualise the distribution of the data. in the plot, the red line shows the median of the dataset, and where the two whisker lines limit the values where most of the dataset is located. the circle marks above the upper whisker line are outlier data values that have a large tortuosity value. which reveals that the data in the dataset is concentrated at a smaller value of tortuosity. there is also a large number of outlier data points that can potentially impact the quality of the data. this clustering of data distribution is also reflected in the model's predictions, which are most accurate when predicting values within the small value range where the data is most densely distributed. from the results obtained, we can see the limitations of using the cnn method in this study. where the accuracy of the model prediction will depend on the consistency of the data set used. where there is an out-of-range problem, it will interfere with the performance of the model. where outlier data value is vastly different from the training data, the model prediction will be inaccurate. another limitation is the difficulty to predict rocks using larger data sets, such as three-dimensional rock data or higher resolution rock images. due to the application's limited memory and processing time. moreover, only sandstone rocks are used in this study. the results obtained by other types of rocks have not yet been evaluated. 4. conclusion this research developed a machine learning model using a cnn algorithm to estimate the physical parameters of digital rock tortuosity. the cnn model was selected from among several pre-trained model architectures, including mobilenetv2, densenet201, inceptionv3, and xception, based on its performance. the results suggest that all four models are quite accurate, with the xception model being the most accurate with the lowest rmse value of 0.90962 and mae and r2 values that are comparable to other models. however, the model's predictions were found to be most accurate for small tortuosity values, with decreasing accuracy as tortuosity values increased. further research is needed to improve the performance and accuracy of the model, including the inclusion of additional rock types other than sandstone and a more balanced distribution of tortuosity values in the dataset. acknowledgements the authors acknowledge the department of geophysics universitas padjadjaran supercomputing resources "rockexplorer" made available for conducting the research reported in this paper. 12 akmal, f. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 references al-raoush, r.i., madhoun, i.t., 2017. tort3d: a matlab code to compute geometric tortuosity from 3d images of unconsolidated porous media. powder technology 320, 99–107. https://doi.org/10.1016/j.powtec.2017.06.066 ansari, o.b., binninger, f.-m., 2022. a deep learning approach for estimation of price determinants. international journal of information management data insights 2, 100101. https://doi.org/10.1016/j.jjimei.2022.100101 chollet, f., 2017. deep learning with python. manning publications, new york. dandekar, a.y., sondergeld, c.h., rai, c.s., 2018. machine learning for digital rock characterization: opportunities and challenges. 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d., li, h., 2022. predicting permeability from 3d rock images based on cnn with physical information. journal of hydrology 606, 127473. https://doi.org/10.1016/j.jhydrol.2022.127473 © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 2 2023 84 rizki, i.a., et al./ jgeet vol 8 no 2/2023 research article exploration of the magnetic rocks potential of mount penanggungan: a study of myth, history, and its implications for educators and mountaineers iqbal ainur rizki1, eko hariyono1,*, muhammad nurul fahmi1, madlazim1, eka puji astuti2, muhammad eka abdul ghofar3, luthfi aryani4 1physics department, universitas negeri surabaya, surabaya, indonesia 2history education department, universitas negeri surabaya, surabaya, indonesia 3mechanical engineering department, universitas negeri surabaya, surabaya, indonesia 4geological engineering department, universitas gadjah mada, yogyakarta, indonesia * corresponding author : ekohariyono@unesa.ac.id tel.:+62-812-1718-435 received: jan 20, 2023; accepted: jun 6, 2023. doi: 10.25299/jgeet.2023.8.2.11954 abstract this study explores the potential of magnetic stones on mount penanggungan and their relation to history and myths circulating in the community and climbers. this research is important to do in order to minimize the rate of injury caused by fatigue for climbers on this mountain. in addition, aspects of physics and history can be implications for educators to deliver material on the subject. this research uses a qualitative design with the type of case study—data collection methods through observation, interviews, and document studies. the results of this study show that some rocks on mount penanggungan, especially when approaching their peak, have a magnetic field anomaly up to 4 times larger than the magnetic field on the earth’s surface, characterized by its darker color or cave walls. based on the mythical and historical review, the role of magnetic stones underlies the reason ancient people performed hermitage on rocks and in mount penanggungan. this study implies that it can be information for climbers that rocks with a strong magnetic field magnitude can accelerate the relaxation of the body. in addition, educators can integrate this research’s findings, including physical phenomena and historical/mythical aspects on mount penanggungan, into learning. keywords: magnetic rocks, mount penanggungan, educators, mountaineers 1. introduction mount penanggungan is a mountain located in pasuruan regency and mojokerto regency with an altitude of 1,653 meters above sea level (masl) (paripurno et al., 2018). this mountain offers natural beauty, so many tourists want to visit (m n l khakim et al., 2020). this mountain is a stratovolcano type with a uniqueness that is almost perfectly conical in shape (kusumayudha, putra and pratiknyo, 2018). therefore, when it is already at the top of this mountain, the beautiful scenery of the surrounding city will be seen. because of its extraordinary beauty, mount penanggungan is one of the favorite places for mountaineers (atmadi, 2019). although classified as having a low altitude, this mountain has an uphill terrain, especially when it is about to reach its peak with an elevation angle of up to 70° (fahmi, 2021). this has caused many climbers to suffer injuries, such as fatigue and sprains, especially when mountaineers climb at night with low vision. one of the efforts that climbers can use to reduce injuries, especially due to fatigue, is to relax blood vessels (govindaraj et al., 2016). this relaxation can be done through magnetic field therapy because it can facilitate human blood circulation (akar, esfahani and mousavi shaegh, 2019). when blood flow increases, oxygen and other nutrients will automatically be distributed to the body faster. sources of magnetic fields can be encountered through some natural objects, such as rocks containing magnetite (ojo, omotoso and adekanle, 2014). mount penanggungan has many stones with unique characteristics that can only be found when going to the top, as shown in figure 1. the stone has a magnetic field anomaly that can affect the body's condition. this can be an educational aspect regarding physical and biological phenomena in humans. fig 1. one example of a rock located at an altitude of 1535 masl of mount penanggungan since long ago, mount penanggungan has been considered sacred by the surrounding community. this is closely related to http://journal.uir.ac.id/index.php/jgeet rizki, i.a., et al./ jgeet vol 8 no 2/2023 85 the myths and history that developed in the community and climbers of mount penanggungan. according to legend, this mountain is one of the sacred mountains on java island (munandar, 2013). according to ancient javanese beliefs, its sanctity is not located on the top of the mountain. however, the entire area of mount penanggungan, including its slopes, is a sacred area. this is corroborated by the discovery of temple site relics and ancient objects in this mountain area totaling 198 (moch. nurfahrul lukmanul khakim et al., 2020). in addition, many histories record that many great people hermit until they reach their moksa on this mountain. so many myths circulate about natural phenomena that occur on this mountain. until now, there has been no research on exploring magnetic phenomena and their relation to the history and myths on mount penanggungan. therefore, this study explores the potential of magnetic stones on mount penanggungan and its relation to history and myths circulating in the community and mountaineers. this research is important to do in order to minimize the rate of injury caused by fatigue for climbers on this mountain. in addition, aspects of physics and history can be implications for educators to deliver material on the subject. 2. research method this research uses a qualitative design with the type of case study (creswell and creswell, 2018). a case study can be interpreted as the process of in-depth, detailed, and detailed investigation or examination of a particular event. this research will investigate in-depth the potential of magnetic stones on mount penanggungan and its relation to myths and history. this research was carried out on july 9, 2022, on the mount penanggungan hiking track via tamiajeng, trawas, mojokerto. the instrument in this study is a magnetic field detection device installed on a mobile phone application. three different applications are used to get accurate measurements: magnetic field & dc current detector, magnetometer, and physics toolbox magnetometer. the three applications are used to measure the magnitude of the magnetic field found in rocks close to the top of mount penanggungan. in addition, the main instrument in qualitative research is the researcher himself (wambaleka, 2020). data collection techniques in this study are through observation, interviews, and document studies. observations are carried out through the results of magnetic field readings using three different applications so that more accurate data is obtained. interviews are unstructured with the surrounding community so that more in-depth and natural data are obtained. finally, document studies are carried out by reading documents related to the history of mount penanggungan. the collected data was analyzed using the miles and huberman model (suliyanah et al., 2021), which includes data reduction, data presentation, and verification. in addition, to increase the trustworthiness of the data that has been collected, triangulation of data sources is carried out by comparing data through three methods: observation, interviews, and document studies (sugiyono, 2020). 3. results and discussion 3.1 potential of magnetic rocks in mount penanggungan based on the results of observations utilizing three different magnetic field-measuring smartphone applications, data was obtained as in table 1. it can be seen that some rocks have magnetic field anomalies, as in stone number 3, which has a magnitude (116; 106; 115) μt. while stones number 1 and 2 have magnetic field magnitudes (43; 61; 46) μt and (34; 39; 34) μt, respectively. in contrast to stone number 4, the wall of a cave with a magnetic field magnitude (226; 110; 230) μt. the measurement results using three applications show differences in each application. this difference is due to the different spatial orientations of the application, where in app 1 and app 3, it has a portrait measurement orientation, while in app 2 it has a landscape orientation. according to arribas et al. (2015) research, the xyz spatial axis of a mobile phone used to measure the magnetic field can affect the magnitude of the measurement results, as shown in figure 2. fig 2. spatial orientation on smartphones stones number 3 and 4 can be said to be anomalous because they have a magnitude of the magnetic field above the general. according to khan et al. (2017), the magnitude of the magnetic field on the earth’s surface is 25 to 65 μt. thus, rock number 3 has twice the magnitude of the magnetic field, and rock number 4 has a magnitude four times greater than the average magnitude. this is because this rock is included in the igneous rock type because based on previous research shows that this mountain has been dormant for about 1000 years, and the last eruption is estimated to have occurred around 200 m. these rocks are the result of the eruption of mount penanggungan since thousands of years ago. the magma that erupted then cooled to form igneous rock. these rocks have a high magnetic field because they contain iron-bearing minerals (cox, bell and pankhurst, 1979; li et al., 2010). iron is a compound that has the properties of elementary magnets that are easily regulated so that it is easy to produce magnetism. fig 3. comparison of magnetic field magnitudes in two darker (left) and brighter (right) rocks 86 rizki, i.a., et al./ jgeet vol 8 no 2/2023 additionally, when viewed based on the characteristics of the rock, stones number 1 and 2 have a lighter color than stones number 3 and 4. this is because dark-colored rocks are composed of mafic minerals, while brighter rocks are composed of felsic minerals. iron material is easier to associate with mafic minerals and become a constituent element of these minerals (cao et al., 2019; singh and singh, 2019). hence, dark-colored rocks have a greater magnetic field magnitude than brighter ones. it also supported by the measurement results of two stones adjacent to the level of color darkness, as shown in figure 3. however, brighter rocks may be due to exposure to dust which can reduce the intensity of the magnetic field that appears. table 1. results of magnetic field measurements on several rocks on mount penanggungan rock number magnetic field & dc current detector (app 1) magnetometer (app 2) physics toolbox magnetometer (app 3) remarks 1 this rock is located on a track with an altitude of ± 1606 masl 2 this rock is located on a track with an altitude of ± 1573 masl 3 this rock is located on a track with an altitude of ± 1535 masl 4 this rock is the wall of a cave at an altitude of ± 1561 masl 3.2 mythical and historical review mythical and historical review of the magnetic rocks of mount penanggungan is known based on the results of interviews and document studies. some interviewees claim that ancient people performed hermitage on rocks as well as in the caves of mount penanggungan. it is expressed by them as follows. “it could be that people used to ‘niteni’ (=observe) when sitting on the rock feeling something different, such as feeling fitter, being able to think more smoothly. in addition, the rock is also located on the east side of the mountain, making it the ideal place to enjoy the sunrise.” this opinion is also supported by other interviewees, as follows. “some ancient people were devotees of the solar god, which was called surya sewana so that it became a tribute to the rising sun. the position of rock on mount penanggungan is also located on the east side without any barriers. they worship the sun god when the sun rises from the east.” based on this claim, there is some perception that the ancestors or ancient peoples used stones or caves on mount penanggungan as a medium in carrying out asceticism. this is because ancient society was still thick with the ancestors' animism and dynamism beliefs. people tend to believe in the mystical power of an object or spirit of the ancestors. generally, many people do hermitage on stones or caves to pray to their ancestors. people believe in using stone pedestals as hermitages because they give rise to one’s own strength or more focused concentration (kasnadi, 2017). in addition, the ancient people believed that in order to gain powerful power, they had to go to the hermitage for days in caves and stones where their ancestors were. the ancients considered the use of caves as a place of tranquility and focus when praying, while stone pedestals were used as a sense of comfort because they could blend into nature (putri and sukarman, 2022). furthermore, mount penanggungan is one of the clearest evidences of the historical relics of puratrophobic, which became an honorable place and a holy place of worship. according to the view of the javanese people, mount rizki, i.a., et al./ jgeet vol 8 no 2/2023 87 penanggungan is a reflection of the sacred place in india, namely shang nyang mahameru. this is because mahameru is one of the mountains where the gods reside (muhammad and pamungkas, 2016). when the god arrived on java island, he left several lands of mount mahameru until he arrived at mountains like mount penanggungan. the rest of several mahameru mountains, namely the top, are released to form their own mountain, namely mount penanggungan with the name pawitra (sidomulyo, 2013). in sanskrit, pawitra is defined as clear, holy, and clean. thus, mount penanggungan became a sacred site for worshipping the gods or practicing asceticism to the gods.this is also evidenced by the relics of inscriptions and buildings around mount penanggungan. moreover, the sacred inscription (851 saka) tells the story of maharaja reke hino mpu sindok, who ordered the relocation of cunggrang village to sima due to the obligation to maintain the village's sacred buildings, namely shanghyang dharmasrama ing pawitra and shanghyang prasada silunglung (munandar, 1990). in addition, in ancient times, mount penanggungan was also used as a hermitage during the time of king airlangga. as is known, king airlangga cannot be separated from the lives of three religions, namely shiva, buddhism, and asceticism. king airlangga led a hermit life during difficult times. airlangga was depressed when there was a massacre of his army carried out by wura-wari troops, so that he had to divide the kingdom into two, namely jenggala and panjalu. therefore, to calm down and refocus, airlangga did asceticism on mount penanggungan (muhammad and pamungkas, 2016). according to this story, mount penanggungan sent a moral message as a sacred building during the royal period, demonstrating the presence of religious diversity in the area. generally, until now, there were still people who practiced worship or asceticism in the penanggungan area as a form of worship. this is evidenced by the discovery of many relics in the form of pathirtans, hermitage caves, and sacred buildings (temples), as seen in figure 4, that were used as communication with gods. reliefs scattered in sacred buildings (temples) also have the meaning of the distribution of culture and religious life from time to time (muhammad, 2016). thus, mount penanggungan exemplifies the diversity of religions found throughout indonesia, with a cultural pattern emerging from time to time. fig 4. candi lurah, one of the sacred temple in mount penanggungan 3.3 implications for educators educators can incorporate both the phenomenon of magnetism and the historical review of the findings of this study into aspects of learning, such as teaching materials. the relevant lesson with this material is physics and history at the high school level. in addition, the university can also study more deeply the phenomenon of magnetism that occurs in rocks on mount penanggungan. historical reviews of the ancestors reflecting positive moral values can be actualized in learning. learning that is integrated with this local phenomenon is called ethnoscience-based learning. the ethnoscience approach is a strategy to create an environment and design student learning experiences based on the phenomenon of the secular environment (solheri, azhar and yohandri, 2022). the phenomenon is magnetism in the rocks of mount penanggungan as part of the learning process of science or myth and history on this mountain. ethnoscience learning is still rarely taught to students by revealing potential phenomena and cultures in the local area (nurcahyani et al., 2021). therefore, science learning with this ethnoscience approach needs to be applied and developed by combining surrounding phenomena. science learning with an ethnoscience approach aims to allow students to get to know the original science of a society that has developed by carrying out direct investigations such as observation and then being associated with scientific science (dewi, khery and erna, 2019). 3.4 implications for mountaineers the track conditions when approaching the top of mount penanggungan have a slope angle of up to almost 70°. this has left many mountaineers injured due to the difficulty of the track. it is coupled with the track conditions, a mixture of fine sand and rocks, so mountaineers will slip easily. therefore, mountaineers can rest on rocks with a high magnetic field magnitude when they feel exhausted. based on this study's findings, rocks with a high magnetic field are characterized by their darker color or are cave walls. magnetic fields’ biological impacts have frequently been related to nitric oxide (no), which is responsible for changes in vessel width following magnetic field exposure (mckay, prato and thomas, 2007). magnetic fields have recently been found to benefit various human systems. varshney et al. (2010) reveal that low-intensity magnetic fields can increase blood flow in most of the human body. this can certainly accelerate the relaxation of the body when feeling exhausted due to the faster flow of oxygen circulating throughout the body. in addition, exposure to magnetic fields can also increase the speed of nerve regeneration (suszyński et al., 2014). other studies have also noticed that humans are electromagnetic objects because they contain iron ions (fe) in hemoglobin, making blood magnetic (zhang, yarema and xu, 2017; mayda et al., 2020). some other fluids in the body that contain hydrogen (protons) are also magnetic. therefore, exposure to magnetic fields in the rocks of mount penanggungan can affect and facilitate human blood circulation, especially among mountaineers. 4. conclusion some rocks on mount penanggungan, especially when approaching its peak, have magnetic field anomalies up to 4 times larger than the magnetic field on the earth’s surface. this rock is characterized by its darker color or cave walls. this rock is a type of igneous rock that was formed after this mountain erupted thousands of years ago. the ancient people used stones and caves as a medium for asceticism or meditation. this is due to several reasons, such as the beliefs of the ancestors of animism and dynamism, niteni, and worshipping the sun god. this research has implications for educators to integrate the findings of this research which include physical phenomena and historical/mythical aspects on mount penanggungan in learning. the relevant subjects are physics and high school history, hoping to provide a real learning experience for students based on the surrounding environment. in addition, this study also has implications for mountaineers, when feeling tired while climbing mount penanggungan, they can rest on rocks or caves that have been mentioned because they can speed up the body’s relaxation process. this relaxation process is 88 rizki, i.a., et al./ jgeet vol 8 no 2/2023 faster due to the influence of the magnetic field on the physiological and biological body of the human body. the limitations of this study are: 1) the lack of the number of rocks explored by their magnetic field; 2) not specifying the measured rock; and 3) the time in conducting the interview is too short. therefore, the recommendations for future research are: 1) increase the number of stones explored while specifying each stone in order to obtain better data and evidence. this can be done through experimental studies to determine the characteristics of rocks with the strongest magnetic field magnitude. 2) conduct more in-depth interviews so they can dig up much information about myths and histories believed by the people around mount penanggungan. acknowledgments thank you to my fellow mountaineers, iru & amd, and interviewees who have helped carry out this research. in addition, thanks to the mount penanggungan basecamp via tamiajeng for granting climbing permits. references akar, s., esfahani, j.a. and mousavi shaegh, s.a. 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(2017) biological effects of static magnetic fields. singapore: springer singapore. doi:10.1007/978-981-10-3579-1. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 2 2023 kurniasih, a., et al./ jgeet vol 8 no 2/2023 105 research article biostratigraphic interpretation of lutut beds, kerek formation, based on foraminifera fossils anis kurniasih 1,*, ikhwannur adha2, hasnan lutfi dalimunthe1, reddy setyawan1, wahyu budhi khorniawan1, nurakhmi qadaryati1, anita galih ringga jayanti1, fadyaz pugu wijaya1 1 department of geological engineering, diponegoro university, jl. prof. h. soedharto s.h. tembalang semarang indonesia 2 department of geological engineering, universitas pembangunan nasional veteran yogyakarta, jl. padjajaran (lingkar utara), condong catur, sleman, yogyakarta, indonesia * corresponding author : anis.kurniasih@live.undip.ac.id tel.:+62-82-13534-0602 received: mar 16, 2023; accepted: jun 06, 2023. doi: 10.25299/jgeet.2023.8.2.12462 abstract lutut beds are the sandstone beds exposed in the northwest margin of kendeng basin, which contain abundant metamorphic-quartz grains, frequent recycled sedimentary quartz, and reworked bioclasts. lutut beds are not shown on the regional geological map and are often neglected in determining the geological history of kendeng basin. however, they have significant roles because it was deposited on the basin edge, which may carry important keys. this study aims to discover the larger and smaller foraminifera fossils contained in the lutut beds. outcrop samples were collected in kali lutut and its surrounding area, including lutut beds and its overlying layers. larger foraminifera was identified within 3 of 11 thin sections, mostly of order rotaliida, which occur as reworked bioclasts. the smaller foraminifera was barely found in most samples except for the samples from the overlying layers of lutut beds. the study reveals that lutut beds were deposited during early to middle miocene, marked by the occurrence of miogypsina sp. and miogypsinoides sp. and also contains reworked eocene – early oligocene larger foraminifera such as nummulites sp., discocyclina sp., and dictyoconus sp. besides, the overlying layer of lutut beds is identified to be deposited in the middle miocene to pliocene based on the occurence of smaller planktonic foraminifera, sphaeroidinella subdehiscens. the bathymetric interpretation based on smaller benthic foraminifera showed that lutut beds were deposited in the upper-middle bathyal zone. we also believe that the larger benthic foraminifera fossils in lutut beds were transported along the slope from its original life position. accordingly, it is considered as allochthonous fossils. keywords: foraminifera, lutut beds, reworked bioclasts 1. introduction lutut beds are the layer of sandstone exposed on the northwestern edge of the kendeng basin. its type locality, kali lutut, is located on the border of kendal and temanggung regencies, central java. van bemmelen (1949) grouped lutut beds into members of the merawu formation from north serayu, while thaden et al., (1996) concluded that the lutut beds series is part of sedimentary rocks from the kerek formation of the kendeng basin. apart from its lithostratigraphic position, lutut beds is believed to be one of the most important sandstone layers due to its composition. lutut beds is unique because it contains abundant quartz fragment composition in sandstone and conglomerate layers and was deposited in the miocene period, where the source rock of deposition was not known. the lutut beds has very distinctive sandstone units with coarse nonvolcanic clasts dominantly composed of mixture of lithic fragments, polycrystalline quartz, and meta-sediments. locally, limestone fragments and fossils are also presents in the conglomerate section (lunt, 2013). smyth et al. (2008) considered lutut beds part of the kendeng basin, a quartz sandstone with mixed source rock consisting of metamorphic, volcanic, recycled sedimentary rocks and plutonic quartz. this rock unit also contains bioclastic lithic fragments from eocene and oligocene fossils. the potential source rock of the metamorphic-quartz grains in lutut beds is the upper cretaceous metamorphic series as exposed in the karangsambung and jiwo hills. based on the abundance of volcanic material and undulating eocene and oligocene fauna, the lutut beds are interpreted as the product of miocene uplift and erosion of lower cenozoic and older bedrock in the southern arc mountains (smyth et al., 2008). in the previous study, smyth et al. (2005) stated that lutut beds is interpreted to have been deposited at the southern boundary of the kendeng basin, and has experienced deformation and moved north due to reverse faults. furthermore, they concluded that the lutut beds sandstone is the only quartz-rich sandstone in eastern java with clear evidence of disturbance on older cenozoic sedimentary rocks exposed on land. adha and sapiie (2019) classify the geological structure of the kali lutut area into normal faults, thrust faults, and strike-slip faults. furthermore, they assume that these structures are the last deformation that occurred in the kendeng basin, which is thought to have occurred in the pliocene pleistocene. these structures also caused the lutut beds sedimentary series to move from its original position to its present position. the importance of the lutut beds in terms of sedimentation and development of kendeng basin is that it contains abundant re-working various rock fragments which reserves information about its source and tectonic cause. during miocene, the northern sundaland platform had been covered by the miocene limestone of kujung formation except for karimunjawa, while the south had been covered with thick volcanic products http://journal.uir.ac.id/index.php/jgeet 106 kurniasih, a., et al./ jgeet vol 8 no 2/2023 (lunt, 2013). in result, it is not clear whether the potential source rocks were available for erosion during the lutut beds formation. therefore, comprehend knowledge of lutut beds is necessary not only to resolve the depositional setting itself but also to answer related questions about the development of sedimentary basins in northern java. based on the importance of lutut beds mentioned above, we analyzed the fossils, especially foraminifera fossils, to determine the deposition time and paleoenvironment of lutut beds. the results of this study are expected to increase knowledge about the process of lutut beds formation. 2. methods the main objective of this study was to analyze foraminifera fossils, including smaller and larger foraminifera, contained in rock samples that are representative of lutut beds. analysis of larger foraminifera was performed by thin section description under a polarizing microscope of 11 rock samples. the sampling location is shown in fig. 1. identification of larger foraminifera following the catalog compiled by renema et al. (2003) and boudagher-fadel, (2018). age determination of larger foraminifera followed tertiary letter stages by vlerk (1955) and lunt and allan (2004). fig. 1. map of the study area showing sampling locations for petrographic and microfossil analysis. smaller foraminifera analysis was performed by grain sample description on nine rock samples, 4 of which were from lutut beds. the foraminifera analysis stage begins with preparation according to the procedure described by armstrong and brasier (2005), namely by immersing the crushed sample in a hydrogen peroxide (h2o2) solution for ± 24 hours. after 24 hours, the samples were washed thoroughly using running water on a 500 mesh sieve. the clean samples were dried in an oven (50 ℃) until dry. the samples were then flicked to separate foraminifera fossils grain from other sediment grains kurniasih, a., et al./ jgeet vol 8 no 2/2023 107 under an sz61-type olympus zoom stereo microscope. this process was carried out for each sample until all the fossils contained in the sample were finished. the fossils taken are then placed in a particular container, and the fossils are ready to be determined. the determination of foraminifera fossils refers to postuma (1971), morkhoven et al. (1986), and loeblich and tappan (1988). determining the age of planktonic foraminifera refers to postuma (1971), and determining the environment of benthic foraminifera follows holbourn et al. (2013). 3. results and discussion 3.1 lithostratigraphic interpretation based on field investigations, we observe that, in general, the lutut beds consist of carbonaceous sandstone-claystone profiles that vertically exhibit fining upward succession (fig. 2). the bottom of the succession is characterized by a conglomeratic sandstone lithology which has a grain-supported and poorly sorted texture, contains quartz, chert, basalt, larger foraminifera shells, and carbon fragments (fig. 2) which does not show a particular orientation. among all these fragments, the quartz fragment appears to be the most dominant and has a rounded grain shape. this observation is supported by petrographic observations, which show the same result (fig. 4). we also observed distinct sedimentary structures such as convolute (fig. 3), cross-bedding, slump, and load cast. the middle part of the succession is characterized by alternating sandstone lithology with claystone (fig. 3). we noticed the presence of rock fragments in the sandstone layers that were also found in the previous succession but with smaller grain sizes. in this section, the layer of claystone is thickening upward. the lithology changes at the very top of the succession as the sandstone layer becomes thicker. the claystone layers become thin intercalations between the sandstone layers. lithic fragments are still found in the sandstone layer, but the number is less. based on the lithological characteristics mentioned above, we interpret the lutut beds depositional environment to be in a deep marine environment, namely in the middle–distal facies of the submarine fan. 3.2 smaller foraminifera analysis the foraminifera analysis was carried out on nine samples taken at several locations (fig. 1). four represent lutut beds (714-05, 710-06, 78-04, 79-01). among the four samples, one sample, taken from the observation station area 714-05, has fairly abundant planktonic foraminifera fossils, although most of them are fragile and break easily; and the very rare benthic foraminifera (fig. 5). samples from station 710-06 had very rare planktonic foraminifera and no benthic foraminifera. in samples from stations 79-01, only benthic foraminifera was found with low populations and diversity, while in samples 7804, no foraminifera was found. the foraminifera taxa found in samples 714-05 are sphaeroidinella subdehiscens, orbulina universa, globorotalia obesa, globigerinoides immaturus, globigerinoides trilobus, and orbulina bilobata (table 1). fig. 2. the lower layer outcrop from lutut beds, shows fragments of various materials at observation stations 712-02 (left) and convolute sedimentary structures at the same observation station (right). fig. 3. an outcrop photo taken at station 713-04 shows a succession of fining upward claystones intercalated by sandstones. 108 kurniasih, a., et al./ jgeet vol 8 no 2/2023 fig. 4. the petrographic section of rock samples at stations 712-02 shows lithic fragments and larger foraminifera shells. based on the fossil assemblage, the relative age of the sample representing lutut beds is n13 – n18 (following the biozonation by blow, 1969) or middle miocene to pliocene. sample 710-06 has a pliocene age based on the presence of globorotalia plesiotumida, globorotalia tumida, globigerinoides immaturus, orbulina bilobata, globorotalia acostaensis, and orbulina universa (n18-n21; blow, 1969). in the sample, there is also a collection of older foraminifera from the middle miocene age, which are suspected to be reworked fossils, namely globorotalia siakensis, globigerinoides subquadratus, and globigerina praebulloides. based on the analysis of planktonic foraminifera fossils mentioned above, we agreed that the relative age of lutut beds rocks is middle miocene – pliocene. this was obtained from the appearance of the diagnostic fossil sphaeroidinella subdehiscens (n13 – n20 in biozonation by blow, 1969). thus the lutut beds biozonation based on planktonic foraminifera fossils found in the study area is the sphaeroidinella subdeshiscens zone. the bathymetric analysis on the two samples (714-05 and 79-01) based on benthic foraminifera showed that lutut beds were deposited in the upper-middle bathyal (table 2). 3.3 larger foraminifera analysis analysis of larger foraminifera using thin sections was taken from 11 petrographic samples to determine the relative age and depositional environment. of all the samples, we identified the presence of larger foraminifera in three samples, 710-01c, 710-06a, and 711-02a. at least seven genera were found in sample 710-01c, namely miogypsina, miogypsinoides, lepidocyclina, nummulites, dictyoconus, discocyclina, and assilina (fig. 6). according to vlerk (1955) and lunt and allan (2004), miogypsina and miogypsinoides are early miocene diagnostic fossils, while lepidocyclina is generally found in early oligocene to late miocene rocks. in addition, nummulites were also found, known as diagnostic fossils for the eocene – early oligocene, along with other paleogene foraminifera such as dictyoconus, discocyclina, and assilina. therefore, we have found two distinct ages of the large foraminiferal assemblages, eocene–early oligocene and early miocene (table 3), and we agree that the eocene–early oligocene fossil assemblages occurred as reworked fossils. thus, the lutut beds sandstones are interpreted to have been deposited in the early miocene based on large foraminifera. meanwhile, the petrographic analysis showed that these reworked fossils occurred as part of lithic bioclasts. similar results were also seen in the other two samples. petrographic observations indicated the presence of nummulites in sample 710-06a and large fragments of nummulites, which partially recrystallized in sample 711-02a (fig. 4, left). as stated in the previous samples, the numulites in the last two samples also appeared as lithic fragments/bioclasts. based on these results, we assume that the biostratigraphic zonation of lutut beds based on larger foraminifera is miogypsina – miogypsinoides zone. fig. 5. planktonic foraminifera fossils in sample 714-05 (left) and benthic foraminifera in sample 79-01 (right). lithic fragment larger foraminifera lithic fragment quartz o. bilobata s. subdehiscens cibicidoides pachiderma bathysiphon sp. kurniasih, a., et al./ jgeet vol 8 no 2/2023 109 table 1. relative age determination of the sample representing lutut beds indicating middle miocene late miocene and pliocene; the species in the yellow table are identified as reworked fossils. table 2. bathymetric determination based on benthic foraminifera in samples representing lutut beds which shows upper bathyal to middle and upper bathyal zone. sample code benthic foraminifera bathymetric zone littoral inner neritic outer neritic upper bathyal middle bathyal lower bathyal abyssal 714-05 cibicidoides barnetti elphidium crispum bathysiphon sp. 79-01 quinqueloculina sp. cibicidoides barnetti cibicidoides pachiderma cibicidoides praemundulus bathysiphon sp. table 3. relative age determination based on the presence of larger foraminifera in the lutut beds samples. sample 710-01c has two groups of larger foraminifera assemblage which respectively show early miocene and eocene-oligocene (reworked) ages. reworked fossils from the nummulites genus were also found in samples 710-06a and 711-02a. sample code planktonic foraminifera planktonic foraminifera biozonation (blow, 1969) oligocene miocene pliocene pleistocene early middle late n1 n2 n3 n4 n5 n6 n7 n8 n9 n10 n11 n12 n13 n14 n15 n16 n17 n18 n19 n20 n21 n22 n23 714-05 sphaeroidinella subdehiscens orbulina universa globorotalia obesa globigerinoides immaturus globigerinoides trilobus orbulina bilobata 710-06 globorotalia tumida globorotalia siakensis globigerinoides immaturus orbulina bilobata globigerinoides subquadratus globorotalia acostaensis globigerina praebulloides orbulina universa sample code larger foraminifera taxa paleocene eocene oligocene miocene pliocene early early middle late early late early middle late t.a1 t.a2 t.a3 t.b t.c t.d te.1 te.2-3 te.4 te.5 t.f1 t.f2 t.f3 t.h 710-01c lepidocyclina miogypsina miogypsinoides assilina nummulites dictyoconus discocyclina 710-06a nummulites 711-02a lepidocyclina nummulites 110 kurniasih, a., et al./ jgeet vol 8 no 2/2023 fig. 6. appearance of larger foraminifera fossil assemblages in 71001c (left) and 710-06a (right) samples. meanwhile, we tried to analyze the depositional environment based on larger foraminifera, but several limitations prevented this from being carried out. reworked fossils are not used for this purpose, so we only use early miocene fossil assemblages as indicators of depositional environment. most larger foraminifera genera occupy a neritic environment near the reef ecosystem. some genera are part of the reef ecosystem (boudagher-fadel, 2018). hottinger (1983) notes that light penetration and water are the two most important parameters affecting the distribution of larger foraminifera, whereas temperature and salinity are factors that act only locally. thus, we can use larger foraminifera as an indicator of depth. we noted the presence of miogypsinamiogypsinoides in sample 710-01c. we suspect these fossils appear to be allochtonous, meaning they cannot be used as indicators of paleoenvironments. boudagher-fadel (2018) and boudagher-fadel and price (2013) mentioned that miogypsina-miogypsinoides were occurred only in shallow water marine limestones, associated with fossil algae. they believe that miogypsinids such as miogypsina cannot grow on flat surfaces, requiring them to attach to curved substrates such as macroalgae or seagrass. therefore, if miogypsina is to be fossilized as a living (autochtonous) assemblage, the macroalgae must be found in thin rock sections. however, we found no algae fossils in the samples during our observations. thus, we assume that the foraminifera fossil grains were most likely transported from their habitat and preserved as dead assemblages (allochtonous or thanatocoenosis fossils). in addition, we observed in thin sections that miogypsinamiogypsinoides grains were preserved along with lithic grains from undulated sandstones, quartz, and bioclasts. this strengthens the argument that this larger foraminifera was transported and preserved together with other grains available at the bottom of the waters. we believe the larger foraminifera fossils in the lutut beds were transported along the slope. hohenegger and yordanova (2001) concluded that larger foraminifera could be transported due to three factors, one of which was the steepness of the slope. on steep slopes (>30˚), the main possible transport mechanism is by gravity, and on flat slopes, transport is primarily driven by water movement. to support this assumption, we confirm the lithostratigraphic description. sedimentary structures such as convolute, load cast, and slump, referred to as water-escape structures by lowe (1975), are common in rocks deposited on steep slopes. these structures exhibit unconsolidated sediment displacement or movement in environments with steep slopes and fast sedimentation rates. this interpretation is also consistent with the results of depth zone analysis based on smaller benthic foraminifera, which shows lutut beds were deposited in the upper to middle bathyal zones. this depth zone generally has a seabed morphology in the form of steep slopes. 4. conclusion we conclude that lutut beds sandstones were deposited in the middle miocene to pliocene or n13 – n18 according to the planktonic foraminifera biozonation by blow (1969) based on planktonic foraminifera fossils from sample 714-05. meanwhile, based on the analysis of large foraminifera in sample 710-01c, we interpret that the lutut beds sandstone is early miocene age. this discrepancy is due to random sampling in the field without considering the stratigraphic position. therefore, we assume that sample 714-05 is younger than sample 714-05 and both samples did not come from an identical stratigraphic position. we also found that lutut beds contain larger foraminifera from the eocene – early oligocene fossil assemblages, such as nummulites, dictyoconus, discocyclina, and assilina which are present as lithic bioclasts. analysis of the depositional environment based on fossil characteristics and lithostratigraphic data, we conclude that lutut beds was deposited in a steep slope environment in the upper-middle bathyal zone. acknowledgment the author would like to thank imam farchan b.r., nicholas dwika, gilang agatra, and puyo, who have helped while collecting field data, and other parties who cannot be mentioned one by one for their input and suggestions in writing this paper. references adha, i., sapiie, b., 2019. rekonstruksi struktur geologi kali lutut dan sekitarnya, temanggung, jawa tengah. j. geosains dan teknol. 2, 61–68. armstrong, h, brasier, m., 2005. microfossils 2nd edition. blackwell publishing, australia. blow, w.h., 1969. late middle eocene to recent planktonik foraminiferal biostratigraphy. 1st int. conf. planktonik microfossils proc. 199–421. boudagher-fadel, m.k., 2018. biology and evolutionary history of larger benthic foraminifera, in: evolution and geological significance of larger benthic foraminifera foraminifera. ucl press, p. 45. boudagher-fadel, m.k., price, g.d., 2013. the phylogenetic and palaeogeographic evolution of the miogypsinid larger benthic foraminifera. j. geol. soc. london. 170, 185–208. https://doi.org/10.1144/jgs2011-149 hohenegger, j., yordanova, e., 2001. displacement of larger foraminifera at the western slope of motobu peninsula nummulites sp. nummulites sp. miogypsina sp. miogypsinoides sp. kurniasih, a., et al./ jgeet vol 8 no 2/2023 111 (okinawa, japan). palaios 16, 53. https://doi.org/10.2307/3515552 holbourn, a., henderson, a.s., macleod, n., 2013. atlas of deep-sea benthic foraminifera. wiley-blackwell. hottinger, l., 1983. processes determining the distribution of larger foraminifera in space and time. utr. micropaleontol. bull. 30, 239–253. https://doi.org/10.1007/978-1-4020-6374-9_6 loeblich, a.r., tappan, h., 1988. foraminiferal genera and their classification. j. foraminifer. res. 18, 271–274. https://doi.org/10.2113/gsjfr.18.3.271 lowe, d.r., 1975. water escape structures in coarse‐grained sediments. sedimentology 22, 157–204. https://doi.org/10.1111/j.1365-3091.1975.tb00290.x lunt, p., 2013. the sedimentary geology of java. indonesian petroleum association. lunt, p., allan, t., 2004. a history and application of larger foraminifera in indonesian biostratigraphy , calibrated to isotopic dating. grdc museum workshop on micropaleontology. morkhoven, f.p.c.m., berggren, w.a., edward, s.a., 1986. cenozoic cosmopolitan deep-water benthic foraminifera. pau.elf-aquitaine.postuma, j.a., 1971. manual of planktonic foraminifera, micropaleontology. elsevier publishing company, amsterdam. 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geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/) http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 kurlov, d. et al./ jgeet vol 8 no 1/2023 69 research article experimental study of improving the physical properties of peat soil using sand and bio-grouting techniques with the assistance of bacillus subtilis bacteria dejan kurlov 1,*, tej marcovic1 1 department of geotechnical engineering, university of maribor, slovenia. * corresponding author : kurlov.dj@gmail.com tel.:+386-987-209 received: jan, 2023; accepted: march, 2023. doi: 10.25299/jgeet.2023.8.1.13464 abstract peat soil was categorized as soft soil, which means that the soil is in bad condition and problematic when construction was built on it. it was necessary to increase the carrying capacity of peat soils, one of which is chemical stabilization of the soil, by adding additives that can react with the soil and using new environmentally friendly methods. in this study, samples of peat soil were taken from buana makmur village km55, dayun district, siak regency. the stabilizing agent used was sand as much as 5% by weight of dry soil, bacillus subtilis bacteria obtained from the agriculture laboratory of the islamic university of riau, and also cacl₂ and urea. the method for stabilizing the physical properties of peat soil in this study is the bio-grouting method, testing the physical properties of peat soil follows the procedures of astm (american society for testing and materials) and sni 1965 -2008 for testing methods for determining water content for soil and rock in the laboratory. sni 1964-2008 test method for soil specific gravity, sni 8460-2017 geotechnical design requirements, sk sni -04-05-1989-f fine sand used for construction, sni-02-2801-1998 urea standard. to test the physical properties was carried out by providing variations in the mixing of bacterial cementation solutions with levels of 0% (without treatment), 5%, 10%, 15%, 20%, and 25% and then allowed to stand for 14 days using a tightly closed plastic container. the results of testing the physical properties of peat soil found that the peat soil was included in the original soil type with water content = 407.45% and specific gravity (gs) = 1.30gr, while from the physical properties tests carried out the highest water content occurred in the addition of bacterial cementation solution 10% = 177.2% and the lowest specific gravity occurs when the bacterial cementation solution is added 10% = 1.27gr. keywords: bio-grouting, bacillus subtilis, cacl₂, sand, stabilization, physical properties, urea 1. introduction 1.1 background peat soil is soil that comes from the remains or weathering of plants, thus peat soil is categorized as soft soil which usually has a low carrying capacity value. if a construction is to be built on it, soil improvement efforts are needed to increase the ability of the soil. the peat soil to be tested comes from buana makmur village km55, dayun district, siak regency. stabilization is an improvement to the properties and parameters of the original soil thus the soil can be used in construction. one of the efforts to increase the carrying capacity of peat soils is by improving the soil or stabilizing it chemically, by adding a mixture that can react with peat soil, the additional ingredients are sand and bacillus subtilis bacteria using the biogrouting method. biogrouting is a soil stabilization technique involving microorganism-induced calcium carbonate (caco3) precipitation. precipitation of calcium carbonate acts as a binding crystal between cells that stimulates the process of cementation between soil grains. in applying bio-grouting technology, it is necessary to consider the type of soil to be stabilized and the type of microorganism used as a bio-grouting agent. several studies related to bio-grouting have been extensively tested during the last few years. dejong et al, (2006) used bacillus pasteurii to stabilize loose, collapsible sand. nur and sofyan showed that bio-grouting through bacillus subtilis can reduce the permeability of sandy clay. bacillus subtilis is also described to stabilize marine sandy loam soils by strengthening and reducing soil permeability. bacillus is a gram-positive rod-shaped bacterium with an optimum temperature for growth between 25-35°c. although bacillus was considered to be strictly aerobic, it was discovered later that they can live anaerobically under defined conditions. bacillus is naturally found in soil, they colonize root systems and compete with other microorganisms such as fungi. bacillus subtilis is known to be safe for use in food products as a probiotic and part of food ingredients. under harsh conditions, bacillus can form stress-resistant endospores as a defense mechanism. spores are resistant to exposure to heat, radiation, and chemicals, and are resistant to desiccation. for this reason, stabilization of peat soil is very necessary if you are going to carry out construction, soil stabilization is an effort to increase the stability and carrying capacity of the soil. 2. library survey there are several previous studies related to compressive strength, shear strength, organic soils, and the addition of sand to increase soil carrying capacity which can be used as a reference in the discussion of this study. in this study, previous research was presented, namely firman syarif et al (2019), willy (2015), setiawan (2014), angelina lynda (2013), afriani (2008) nugroho (2008) and dejong, j.t. (2006). sharif et al (2020), has conducted research with the title, "application of the biocementation technique by bacillus subtilis and its effect on permeability in organic soils" http://journal.uir.ac.id/index.php/jgeet 70 kurlov, d. et al./ jgeet vol 8 no 1/2023 willy, 2015 carry out direct shear strength tests by mixing clay with sand with a mixture percentage of 10%, 20%, 30%, and 40%. from the test results obtained the value of the relationship between the percentage of the mixture and the shear angle setiawan, 2014 in his research on the effect of organic soils at optimum conditions, the wet side of the optimum and dry side of optimum on compressive strength. from the results of this study, it can be concluded that the compressive strength value at the optimum condition of organic soil is 0.063 kg/cm². lynda (2013), has conducted research with the title "characteristics of soil shear strength using biogrouting stabilization method of bacillus subtilis bacteria". afriani, 2008 researched the effect of adding sand to clay soil. nugroho, 2008 has researched the stabilization of peat swamp soil using a mixture of portland cement and synthetic gypsum (caso42h2o) in terms of the california bearing ratio (cbr) value. dejong, j.t. (2006) has researched biological grouting technology known as bio-grouting technology through the mechanism of calcium carbonate deposition. 3. theoretical basis soil is a material that consists of solid mineral grains that are not chemically bound to each other and from organic materials that have weathered together with liquid and gas substances that fill the empty spaces between the solid particles (das, 1988). weak bonds between soil particles are caused by the influence of carbonates or oxides that are compounded between the particles, or they can also be caused by the presence of organic material. soil). ground transport media in the form of gravity, wind, water, and glaciers. when moving, the size and shape of the particles can change and are divided into several size ranges. soil according to bowles (1989) is a mixture of particles consisting of one or all types. table 1. particle according bowles (1989). particles description boulder bigger than 250 mm until 300 mm and for size range 150 mm – 250 mm, fragment of these stones are called cobbles/ pebbles. sand size 0,074 mm – 5 mm, ranging from rough (3 mm–5 mm) until fine (< 1 mm). silt size from 0,002 mm – 0,074 mm clay size more than 0,002 mm colloid (colloids) size more than 0,01 mm. gravel size more than 5 mm until 150 mm peat soil is soil that contains many organic components, the thickness of which is from several meters to tens of meters underground. organic soils are black and are the main constituent of peatlands. this type of soil is generally prone to large settlements. table 2. soil type based on organic content (road embankment construction plan on peat using a preloading method, 2004) soil type organic level clay <25 organic clay 25-27 peat >75 the physical properties of peat soil have a very high organic content, whereas the soil formation process itself comes from plants. the high water content and large pore value cause the seepage coefficient of peat soil to resemble sand, this is because the large pores cause the water in the pores to easily escape, especially when there is a load on it. the small volume of peat soil indicates that the density of peat soil is not like that of soil in general and when it is associated with a high water content, the weight of the water contained in peat soil is 6 (six) times heavier than the weight of the peat soil grain. table 3. physical characteristics of indonesian peat soil (mochtar, 2002) no physical trait value 1 organic content (oc) 95 99% 2 volume weight (t) 0,9 1,25 t/m³ 3 water level (w) 200% 900% 4 pore number (e) 5 – 15 5 ph 4 – 7 6 ash level (ac) 1 – 15% 7 gravity specification (gs) 1,38 – 1,95 8 seepage (k) 2−02 s/d 1,2−06 table 4. engineering properties of peat soil (mochtar, 2002) no trait value description 1 soil cohesion/shear strength 0 non cohesive 2 compressibility very high sensitive towards 3 bearing capacity 5 – 7 kpa scandinavia 4 inside sliding angle > 50 degrees especially fibrous 5 soil tek coefficient at rest max 0,5 smaller than 6 consolidation very long 4 4. research methods the sampling location for peat soil was taken from the buana makmur village area km 55, dayun district, siak regency, for bacteria from the agricultural laboratory of the islamic university of riau, pekanbaru. in this study, the materials used are: 1. the soil used was peat soil peat soil samples in unstable or disturbed conditions, where the samples were taken at a depth of ± 50𝑐𝑚 from the top soil surface using a hoe and makeshift tools, then the soil sample is taken to the laboratory for testing, before being tested the soil sample is dried first by utilizing the sun's heat, then after drying the soil sample is sieved using a no4 sieve until it passes. 2. sand was a natural aggregate that comes from volcanic eruptions, rivers, soil, and beaches, therefore sand can be classified into three types, namely dug sand, sea sand, and river sand. 3. bacillus subtillis was a gram-positive, rod-shaped, and catalase-positive bacterium. like other bacteria of the bacillus genus, bacillus subtilis can form endospores, to survive extreme environmental conditions of temperature and desiccation. bacillus subtillis is a facultative anaerobe and was considered an obligate aerobe until 1998. 4. urea, alcalled nitrogen (n) fertilizer, has a nitrogen content of 46%. urea is made from the reaction between ammonia and carbon dioxide in a chemical process to become solid urea in the form of prills (1-3 mm in size) or granules. 5. cacl2 (kalsium kloride) kurlov, d. et al./ jgeet vol 8 no 1/2023 71 stage process flowchart fig 1. research flowchart 5. results and discussion the results of the observations were in the form of tests, namely the characteristics and physical properties of peat soil using a mixture of sand and bacillus subtilis bacteria using the bio-grouting method. the effect of bacillus subtilis on the engineering properties of organic soils is still not fully understood. organic soils and sandy loams show different characteristics. in general, organic soils are problematic soils associated with low unit weight, unsatisfactory strength characteristics, and high compressibility. these undesirable organic soil properties can cause serious foundation problems. therefore, organic soils need to be stabilized before civil infrastructure is built on them. preliminary testing is carried out before mixing peat soil with sand and bacillus subtilis bacteria using the bio-grouting method. this test is carried out using peat soil as a test. several tests include testing the original soil water content, a specific weight (gs), and compaction testing. soil water content. the procedure for testing the water content is carried out following the procedure in astm d2216. from the water content test carried out on the soil, the water start preparation of tools and materials preliminary testing of peat soil physical properties 1. standard proctor testing 2. water content testing 3. specific gravity testing sample making making bacterial solutions mixing samples with bacterial solution 0%, 5%, 10%, 15% 20% dan 25% main tests of physical properties of bacterial solution stabilized peat soil 1. rate water 2. specific gravity data analysis results and discussion conclusions and recommendations finished 72 kurlov, d. et al./ jgeet vol 8 no 1/2023 content value was 407.5%. the high water content is because native soil consists of organic fiber (peat) which can absorb a lot of water, according to the center for transportation infrastructure research and development, while peat moisture content ranges from 200% to 900%. procedure for testing the specific gravity (specific gravity) was carried out following astm 854. from the tests that have been carried out on the original soil, the specific weight (gs) value of the soil used is, can be seen in appendix a-2. the specific weight value (gs) is affected by wood fiber and other organics. maximum soil density compaction testing was carried out to obtain a maximum dry unit weight (γd max) value of 0.467 gr/cm3 and an optimum moisture content (omc) of 157% of native soil. maximum soil density compaction testing was carried out to obtain a maximum dry unit weight (γd max) value of 0.467 gr/cm3 and an optimum moisture content (omc) of 157% of native soil fig 2. dry volume weight relationship with water level the high value of the optimum moisture content (omc) is caused by the large pores in the soil because the soil consists of plant (organic) fibers causing the soil to absorb a lot of water to achieve optimum density. the optimum moisture content (omc) obtained from the compaction test on the original soil is used as a comparison to the soil conditions used in the modeling test. according to the dry unit weight obtained, the classification of peat is based on the dry unit weight at the level of weathering or decomposition > 0.2 gr/cm3 (mutalib, et al., 1991) peat soil originating from siak is categorized as saprik peat to the influence of soil minerals 5.1 properties of peat soil based on the tests carried out, the physical properties of the soil can be summarized. the following table shows the physical properties of peat soil obtained from preliminary testing. tabel 4. properties of peat soil. no traits size unit 1 specific weight, gs 0,544 2 water level, w 407,5 % 3 wet volume weight, γ 0,983 kn/m3 4 dry volume weight, γd 0,168 kn/m3 5 maximum dry content weight, (γd maks) 0,467 gr/cm3 6 optimum water level, (omc) 157 % 5.2 testing of bacterial solution stabilized physical properties testing of physical properties uses the methodbiogrouting namely by mixing the bacteria bacillus subtiliswhich is made into a solution (cementation solution) with the addition of sand. the percentage of sand in the specimen sample is as much as 5% by weight of the peat soil sample. the following is the percentage of addition of cementation solution to the sample of the test object: a. sample 1 = 0% b. sample 2 = 5% c. sample 3 = 10% d. sample 4 = 15% e. sample 5 = 20% f. sample 6 = 25% 5.3 stabilized water content of bacterial solution test the water content in the sample of the test object mixed with the addition of cementation solution table 5. value of moisture content (w) against the addition of cementation solution no treatment of bacterial solution (%) water level (%) 1 0% 166,6 2 5% 172,7 3 10% 177,2 4 15% 164,6 5 20% 169,7 6 25% 162,5 kurlov, d. et al./ jgeet vol 8 no 1/2023 73 table results 5 value of water content (w) to the combination of adding bacterial cementation solution 0% 5% 10% 15% 20% and 25% can be seen in the following graphic : fig 3. relationship of water content (w) to the addition of bacterial solution looking at the results of figure 3 on the graph of the relationship between water content (w) and mixing of bacterial solutions, it can be concluded that the addition of 5% and 10% bacterial solutions experienced an increase in water content (w) when the addition of 15% bakery solution decreased by 6% from the water content. (w), on the addition of 20% bacterial solution, the water content (w) increased again by 3.1%, and on the addition of 25% bacterial solution, the water content (w) decreased again by 4.1%. the highest water content (w) occurred in the treatment of adding 10% bacterial solution with a value (w) = 177.2% with an increase of 10.6% from the sample of the test object without treatment or 0%. in the 0% treatment, there was an increase in water content due to the addition of sand this study, which was 5% of the sample weight of the test object in each treatment. 5.4 bacterial solution stabilized specific gravity specific gravity tests on peat soil samples mixed with a bacterial solution can be seen in table 6. table 6. value of specific gravity (gs) of peat soil against the addition of bacterial solution bakteri no treatment of bacteria solution (%) soil specific gravity (gr) 1 0 1,56 2 5 1,62 3 10 1,27 4 15 1,67 5 20 1,77 6 25 1,80 table results6 specific gravity (gs) for the addition of 5%, 10%, 15%, 20% and 25% bacterial solution is explained in the graph below: fig 4. relationship of specific gravity (gs) value to the addition of bacterial solution water level (%) w a te r l e v e l (% ) treatment (%) soil specific gravity (gr) bacteria treatment (%) s p e c if ic g r a v it y v a lu e ( g r ) 74 kurlov, d. et al./ jgeet vol 8 no 1/2023 the results of figure 4 in the graph above the relationship of specific gravity (gs) to the addition of bacterial solution, it can be concluded that the addition of 5% bacterial solution increases the specific gravity (gs) of = 0.06gr from the sample of the test object without treatment. when the 10% bacterial solution was added, the specific gravity decreased by = 0.35gr from the addition of 5% bacterial solution, and the addition of 15%, 20%, and 25% bacterial solution continued to increase in specific gravity (gs) from 10% addition. the highest specific gravity (gs) value occurred in the addition of 25% bacterial solution with a specific gravity value (gs) = 1.80gr with an increase (gs) = 0.25gr from the (gs) value of the test object without treatment. 5.5 comparison of gs values (specific gravity) from stabilization withbiogrouting and other stabilization comparison between stabilizationbio-grouting with tabilization and the materials are usually seen in table 7 below this. table 7. comparison of the gs value of stabilization with bio-grouting with other stabilization: no cement level (nugroho, 2008) lime level (nugroho, 2008) non organic soil (nugroho, 2008) bio-grouting (this research) 1 % value % value % value % value 2 0 1,40 0 1,49 0 1,48 0 1,56 3 2 1,45 2 1,61 10 1,55 5 1,62 4 4 1,51 4 1,85 20 1,59 10 1,27 5 6 1,55 6 1,89 30 1,61 15 1,67 6 8 1,64 8 2,35 40 1,72 20 1,77 7 50 1,90 25 1,80 from the comparison table above, the highest gs values are in peat soils which are stabilized with lime content, while those with the lowest gs values are stabilized with cement content. below is a line diagram image of each peat soil stabilization with the addition of different materials: 1. line diagram of the relationship between the specific gravity of peat soil and the addition of cement content fig 5. relationship of specific gravity to addition of cement content in peat soil (nugroho, 2008) from figure 6, the relationship between specific gravity and the addition of cement content in peat soils can be concluded that the addition of a stabilizing agent in cement content causes an increase in specific gravity. fig 6. relationship of specific gravity to addition of lime content in peat soil (nugroho, 2008) soil specific gravity (gs) cement level treatment (%) s p e c if ic g r a v it y v a lu e ( g r ) soil specific gravity (gs) s p e c if ic g r a v it y v a lu e ( g r ) treatment of lime level (%) kurlov, d. et al./ jgeet vol 8 no 1/2023 75 from figure 7, the relationship of specific gravity to the addition of lime content in peat soils can be concluded that along with the addition of a stabilizing agent, the lime content also causes an increase in specific gravity. fig 7. relationship of specific gravity to addition of non-organic soil in peat soil (nugroho, 2008) from figure 8, the relationship between specific gravity and the addition of non-organic soil to peat soil can be concluded that along with the addition of a stabilizing agent, lime content also causes an increase in specific gravity. fig 8. relationship of specific gravity to bacterial addition bacillus subtilis on peat from figure 9 the relationship of specific gravity to the addition of bacteria bacillus subtilison peat soil it can be concluded that the decrease occurred when the addition of bacteria as much as 10%, then subsequently caused an increase in specific gravity. fig 9. line diagram comparison of gs values from stabilization withbiogrouting with other stabilization, on the z axis is the value of the specific gravity (gr) of each stabilization and x is the treatment of additional stabilization materials (%). the effect of bacillus subtilison the engineering properties of organic soils are still not fully discovered. organic soils and sandy loams show different characteristics. in general, organic soils are problematic soils associated with low unit specific gravity (gs) s p e c if ic g r a v it y v a lu e ( g r ) non organic soil treatment (%) soil specific gravity (gr) bacteria treatment (%) s p e c if ic g r a v it y v a lu e ( g r ) s p e c if ic g r a v it y v a lu e ( g r ) lime level non organic soil cement level 76 kurlov, d. et al./ jgeet vol 8 no 1/2023 weight, unsatisfactory strength characteristics, and high compressibility. these undesirable organic soil properties can cause serious foundation problems. therefore, organic soils need to be stabilized before civil infrastructure is built on them 6. conclusion peat soil which was stabilized by adding sand and bacterial solution for testing the water content did not fully improve and the decrease in water content even experienced a significant increase in the addition of a 10% bacterial solution, an increase of 10.6% from the test object sample without treatment or 0%. peat soil which was stabilized by adding sand and the help of a bacterial solution for specific gravity testing also did not fully improve and the specific gravity value increased. the highest increase in specific gravity occurred in the addition of 25% bacterial solution with a specific gravity value (gs) = 1.80 with an increase of 0.25 from the value (gs) of the sample without treatment or 0%3 the relationship between water content and the specific gravity value of peat soil with the addition of sand and the help of a bacterial solution is compatible with each addition of 10% bacterial solution where the higher the water content, the lower the specific gravity value and the compatibility also occurs with the addition of 25 bacterial solutions. %, there shows that the lower the water content, the higher the specific gravity value. references akiyama, masaru. 2010. microbially mediated sand solidification using calcium phosphate compounds, faculty of engineering, hokkaido university, kata 13, nishi 8, kita-ku, sapporo, hokkaido 060-8628, japan. angelina lynda, 2013. karakteristik kuat geser tanah dengan metode stabilisasi biogrouting bakteri bacillus subtilis afriani, 2008. pengaruh penambahan tanah pasir pada tanah lempung dejong, j.t. (2006). teknologi grouting secara biologi yang di kenal dengan teknologi biogrouting melalui mekanisme pengendapan kalsium karbonat das, braja m. 1988. mekanika tanah jilid 1. jakarta:erlangga. karol, rh. 2003. chemical grouting and soil stabilization. new york. p558. mochtar, ne, yulianto fe dan rendy st. 2014. pengaruh usia stabilisasi tanah gambut beserta yang distabilisasi dengan campuran caco3. jurnal teknik sipil. surabaya. 21(1): 50-64 nugroho, 2012 stabilisasi tamah gambut riau menggunakan campuran tanah non organik dan semen sebagai bahan timbunan jalan setianwan, 2014, dalam penelitiannya tentang pengaruh tanah organik pada kondisi optimum, wet side of optimum dan dry side of optimum terhadap kuat tekan. syarif dkk, (2019), penerapan teknik biocementation oleh bacillus subtilis dan pengaruhnya terhadap permeabilitas tanah organik. sni 1965-2008 cara uji penentuan kadar air untuk tanah dan batuan di laboratorium sni 1964-2008 cara uji berat jenis tanah sni 8460-2017 persyaratan perancangan geoteknik sk sni-5-04-1989-f. pasir yang baik digunakan untuk sebuah konstruksi sni-02-2801-1998. standar urea van de meene. 1984. geological aspects of peat formation in the indonesianmalyasin lowlands, bulletin geological research and development centre, 9, 20-31. willy, 2015. kuat geser langsung dengan mencampurkan tanah lempung dengan pasir dengan persentase campuran dan sudut geser © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 4 2022 176 raharjo, s. et al./ jgeet vol 7 no 4/2022 research article the role of fractal micro-pore to absorption of methane gas, case study: coal of tanjung formation, arang alus area, banjar district, south kalimantan, indonesia sugeng raharjo1*, basuki rahmad1, ketut gunawan2, budi prayitno3 1 geological engineering universitas pembangunan nasional veteran yogyakarta, indonesia 2 mining engineering universitas pembangunan nasional veteran yogyakarta, indonesia 3department of geological engineering, universitas islam riau, riau, indonesia *corresponding author : sugengrhj@upnyk.ac.id tel.: +62 812-2607-1611 received: sep 20, 2022; accepted: dec 7, 2022. doi: 10.25299/jgeet.2022.7.4.10565 abstract the tanjung formation is one of the coal bearing formations in the barito basin, south kalimantan. the coal seams in the tanjung formation in the arang alus area have 4 (four) seams,there are seam a, b, c, and d. the age of these coal seams are eocene oligocene with a thickness between 0.5 2 meters. this study aims to determine the characteristics of micropore fractal and methane gas absorption from coal samples taken by channel sampling on exposed coal in the open pit. the method used is sem analysis, vitrinite reflectance (ro,max), adsorption isotherm, and fractal calculation. the four coal seams based on vitrinite reflectance values (0.52 %0.62 belong to the sub-bituminous rank. based on the methane gas absorption capacity for coal seam c of 450 scf/ton while coal seams a, b and d of 308 scf/ton, 336 scf/ton and 407 scf/ton, the fractal pore dimension value in seam coal c = 1.963 is higher than seam coal a = 1.933, b = 1.940 , and d = 1.943. the small size of the fractal pore dimension value caused by the degree of regularity of the micropore distribution in each coal seam methane differences. keywords: vitrinite reflectance, adsorption, fractal, micropore, methane gas 1. introduction the research area is located in the arang alus area, banjar district, or 60 km from banjarmasin, indonesia, towards the north. this location was revealed by coal seams found in the tanjung formation. tanjung coal has a thickness of 50 cm to 300 cm. coal in the tanjung formation is a coal-bearing formation in south kalimantan, barito basin. the coal seams in this formation has 4 (four) main seams; there are seam a, b, c, and d. the age of the tanjung formation is eocene – oligocene (heryanto, 2009). the rank of coal in this formation is classified as bituminous. megascopically, tanjung formation coal has shiny black (bright banded), conchoidal, and light fractions. coal is a methane gas reservoir rock, storing gas mainly by adsorption on the surface of pores. the structure of coal pores, including the pore shape, pore distribution, pore size, and pores interconnected, determine the porosity and permeability of coal, further affecting the gas absorption capacity and gas volume (zhang & li, 1995); (c. j. liu, wang, sang, gilani, & rudolph, 2015). the success of methane gas exploitation is highly dependent on the heterogeneity of the coal pore structure. therefore, understanding the characteristics of coal adsorption and pore structure is very important to predict the size of the gas volume in the exploration of coal bed methane. pore structure characteristics are influenced by coal type and coal rank, which are two interdependent factors (clarkson & bustin, 1996) based on pore size in coal divides into: micropore (diameter < 2 nm, mesopore (2 nm < diameter > 1000 nm, and macropore (diameter > 1000 nm). the size of the pores has a different absorption effect on the absorption capacity of methane gas. in general, micropores and mesopores are the main space for the absorption of methane gas. fractal geometry, first created by (mandelbrot, 1982) has proven to be a proper analysis of materials with irregular pores and rough surfaces, including coal (friesen & mikula, 1987); (pyun & rhee, 2004). fractal geometry analysis can be used to determine the relationship between pore or surface structure and the absorption capacity of methane gas. the fractal theory is an effective method for characterizing pore structure heterogeneity. however, this research was previously carried out by several experts using various methods, including scanning electron microscope (sem) (pyun & rhee, 2004), transmission electron microscopy (tem) , nuclear magnetic resonance (wang, cheng, lu, jin, & zhao, 2014), and porosimetry of mercury (cuerda-correa, et al., 2006). all of the above methods are used to investigate fractal characterization from porous media. however, only the mercury porosimetry method cannot get accurate information about the micropore. the mercury porosimetry is used to characterize mesopores and macropores. therefore, methane gas adsorption analysis was used to characterize micropores and mesopores. based on the physical description of fractal pore dimension and pore structures, research by (cuerda-correa et al., 2006) and (yang, ning, & liu, 2014) concluded that micropores have a more significant influence on fractal pore dimension than mesopores and macropores. the calculation for gas absorption is using the langmuir equation. several experts have applied these calculations before calculating coal methane gas absorption, which is considered a monolayer (gregg & sing, 1982). although coal methane absorption is not a monolayer, langmuir's model can still be applied. the coal has the type of adsorption isotherm. therefore, it is necessary to conduct a more detailed study in the exploration of coal methane gas. this study aims to determine the relationship of fractal pore dimension to the behavior of coal methane absorption. this http://journal.uir.ac.id/index.php/jgeet raharjo, s. et al./ jgeet vol 7 no 4/2022 177 research was conducted on coal, which has almost the same rank. this study and the results can help to understand the pore system and absorption of methane gas in coal exploration in indonesia. the research location is in the arang alus area, tapin regency, south kalimantan province, indonesia. 2. method primary data in this study were collected from field data from four sampling locations, and it is represented by coal seam a, b, c, and d. the sampling locations can be seen in the following table (table1). coal sample data were taken using the method channel sampling from top to bottom of each coal seam. each coal seam correlated with outcrop at coordinates 292858,693 meters east and 9638682,718 meters north (figure.1). coal samples were dried at 40˚c then crushed, then samples were taken using a reliable 250 grams method, then sieved with 1 mm particle for coal petrographic and 0.012 mm for isotherm analysis. table 1. location sampling coordinate seam coals m e m n a 294610 9638026 b 294612 9638039 c 294613 9638040 d 294620 9638085 the samples resulting from sieving 0.6 1.0 mm, were used to make polishing sections with the meta serv 250 tool, standard observation procedures. vitrinite reflectance was measured using the craic coal pro microscope. the procedure to determine vitrinite reflectance is to standardize the sample first with the vitrinite reflectance measurement standard in the microscope: spinel = 0.427, sapphire = 0.505, n last 46 a = 1.37, after standardizing the vitrinite reflectance and then observing the magnitude of the vitrinite reflectance. fig 1. well log correlation using outcrop and number sampling the isotherm adsorption test requires a weight of 250 grams of the sample, the sample is crushed with a crusher to form a grain-sized powder that passes through the screen 0.121 mm (80 mesh) opening. the initial isotherm adsorption test process uses astm d1412-85. the sample reconditioning must weigh and place the sample in the decicator below given a k2 so4 solution then in a vacuum condition conditioned at 300 c. the adsorption isotherm test is carried out based on the volumetric method to determine sorption capacity as a function of pressure; the gas used is methane gas (ch4) purity 99.9%. the volumetric method refers to australia's commonwealth scientific and industrial research organization (csiro). in this method, the volume of gas absorbed by the sample is measured indirectly by injecting methane gas gradually with pressure varying to 16 mpa (2320 psi) with varying temperatures. this test kit is operated automatically via a computer with the software adsorption isotherm system (csiro) so that the pressure when injection can control. the relationship of volume pressure at a certain temperature (sorption isotherm) can be used to determine the gas storage capacity and estimate the volume of released gas from the sample in line with the decrease in reservoir pressure. in general, the relationship between storage gas capacity and pressure uses the langmuir equation: gs = (vl p) (pl+p) …………………..1 where: gs = storage gas capacity, m3 / ton p = pressure, kpa vl = langmuir volume constant, m3 / ton pl = langmuir pressure constant, kpa at the image processing stage, the sample is analyzed with sem. the sample is scanned with a relatively large current source of 50 µa, the source of the voltage is 60 kv, the lighting time is 8 seconds. the image generated from the scanning process is a digital image and image from the grayscale scale sample. the next process is image processing using matlab software. this process distinguishes between solids and pores of coal by changing a gray image into a binary image, and then thresholding is performed. this binary image serves to distinguish between black pores and the edges of white granular solids. each black pore boundary area values 0 pixels (black), and a stable pore border value is 254 pixels (white). the fractal pore dimension calculation uses the box-counting method (mandelbrot, 1982). the usual dimensions are denoted by d, which states each object's topological dimensions of a fractal. the resulting number of sub-segments from the iteration of a fractal object is denoted by n, while the length of the subsidy denoted is by r. so the relationship between d, n, and r is stated as follows: n = (r). by taking the logarithm of the two segments of the equation, the dimensions can be searched by the equation below: dimbox d = lim r→0 { log nr log ( 1 r ) } …… 2 where log (nr) is the number of boxes that cover the pore, log (r) is the measure of the pore length of the box's side. 3. result and discussion laboratory test results from the analysis of porosity, fractal pore dimension, and vitrinite reflectance (ro, max,%) shows in table 2. the results show that four coal samples' porosity ranged from 2.38% to 2.63%, with an average value of 2.54%. the results of calculating fractal pore dimension using formula 2 of coal pores have values ranging between 1,933 1,964 (table 2). laboratory results from vitrinite reflectance analysis showed that the coal samples have ro, max ranging from 0.52% to 0.62% (bituminous) 178 first author et al./ jgeet vol xx no xx/20xx table 2. results of porosity, permeability, fractal pore dimension, vitrinite reflectance, and adsorption of methane. sampel code porosity, % permeability m darcy fractal pore dimension, d vitrinite reflectan,% adsorption of methane, scf/t a 2.51 0.341 1.933 0.52 294 b 2.63 0.221 1.94 0.53 315 c 2.38 0.356 1.963 0.58 431 d 2.64 0.12 1.943 0.62 425 each coal seam shows a different porosity value from seam a to seam d (table 2). coal seam c has a small porosity value of 2.38%, while coal seam a, b, and d, are 2.51% to 2.64%. table 2 shows that the fractal pore dimension is inversely proportional to porosity, the higher the fractal pore dimension in the coal seam. c = 1,963, the porosity value is small = 2.38%. coal seams a, b, and d have smaller fractal pore dimension than coal seam c, while the porosity value of coal seams a, b, and d are higher than seam coal c. the higher the fractal pore dimension value, then the smaller the pore size. whereas the fractal pore dimension also shows irregular pore distribution and the higher the fractal pore dimension, the more irregular the pore distribution, and vice versa. fig 2. the results of data processing using the box-counting method the pore fractal dimension is an intrinsic property of the pore surface of coal and coal structure related to coal rank and maceral composition (nie et al., 2016). the characteristics of coal pores, including pore shape, pore distribution, and interconnected pores, determine the porosity and permeability of coal and affect gas uptake and transportation (c. j. liu et al., 2015). different pores will have different effects on the absorption ability of methane gas. generally, micropores and mesopores are the main space for methane gas absorption. the pore surface area is inherently related to the pore size distribution, where the increasing pore surface area will cause a decrease in pore size for a given pore volume (chalmers & marc bustin, 2007). the coal-burning process and the maceral composition have different effects on the pore surface and the inter-pore relationship, which will cause coal differences in gas absorption and permeability. during the coal process, the polycondensation of coal molecules will increase the coal rank (fu et al., 2017). as a result of mass compaction during the polycondensation process, the rank of coal was increased, and the mesoporous and micropore pores were homogeneously distributed. the intensive polycondensation process of coal molecules will cause even mass compaction so that micropores and cracks will gradually develop in the coal (fu et al., 2017); thus, coal will have a complex pore structure. the ongoing coal-burning process will lead to the development of mesoporous and micropores abundant and evenly distributed. (x. liu & nie, 2016). this is evidenced by the increase in coal rank in the tanjung formation, which will increase the value of the pore fractal dimension. the correlation of the pore fractal dimension with coal rank has determination coefficient (r2) = 0.2367 (figure 3). fig 3. relationship between coal rank and fractal pore dimension. in general, the correlation between coal rank and fractal pore dimension shows a bad correlation. this correlation is bad because coal has almost the same value, ro,max = 0.53% 0.62%, which indicates a relatively similar value. fractal pore dimension affects coal porosity; when fractal pore dimension increases in general, the porosity will decrease (chen et al., 2015). the deeper the coal seam (tanjung formation coal) with ro, maxs> 0.50% the more it has a slightly smaller porosity (figure 4). fig 4. correlation between porosity and pore fractal dimensions with determination coefficient (r2 = 0.4536) the picture above shows that the greater the porosity value, the lower the fractal pore dimension, meaning that the lower the porosity, the more macropores and mesoporous numbers. the higher the fractal pore dimension, the greater the number of mesoporous and micropores, which will result in smaller porosity. increasing the coal process and imperfect physical compaction will cause the coal pores, there are macropores, mesoporous, and fractures to be spread unevenly. as a result, it will cause the fractal pore dimension value to be smaller than higher rank coal. on the other hand, the coalburning process continues and is combined with continued physical compaction. it will result in the pores in the coal, namely mesopores and micropores, which will be relatively evenly distributed on the coal, resulting in a large fractal pore dimension value. tanjung coal has a permeability between 0.12 0.356 m darcy (table 2). this data shows that the higher the rank of raharjo, s. et al./ jgeet vol 7 no 4/2022 179 coal, the smaller its permeability. the permeability of bituminous coal is relatively smaller because the pores that develop on the coal are mesoporous and micropores. in bituminous coal, the pores are spread evenly and regularly on the coal surface due to the compacting; thus, it has relatively larger fractal pore dimension. the absorption capacity of coal is highly dependent on the adsorption pores on its surface, generally micropores and mesopores (chen et al., 2015). the size of the absorption of methane gas is also due to differences in depth (anggayana, kamarullah, suryana, & widayat, 2017). the deeper the seam of coal will cause, the greater the absorption of methane gas. increasing the rank of coal will cause the pore volume in the micropore and mesoporous pores to decrease so that it will cause the porosity and permeability of the coal to be smaller. the absorption capacity also depends on the pore size distribution and the complexity of the pore surface structure (chen et al., 2015). the smaller the pore size and the more complex the pore surface, the larger the pore surface area, which will result in greater absorption capacity of the methane gas. increasing the rank of coal will increase the average diameter of micropores and mesopores, which will cause an increase in surface area (chen et al., 2015). increasing the rank of coal causes the pores of both micropores and mesopores to experience changes in their distribution; at the rank of bituminous coal, the pores are evenly distributed (figure 5). fig 5. a. photomicrography of sem coal seam b shows regular pores. b. photomicrography of sem coal seam c shows irregular pores the relationship between the fractal pore dimensions and the absorption volume of coal methane gas can be seen in figure 6. figure 6 shows that the correlation between methane gas absorption and fractal pore dimension has a positive correlation with determination coefficient (r2) = 0.805. the larger the fractal pore dimension, the greater the gas absorption because coal has mesopores and micropores, which are spread evenly. coal with small fractal pore dimension has a small absorption of methane gas, this is because the coal has macropores and mesopores that are spread unevenly. an increase in the rank of coal will increase methane gas absorption, which will increase the value of the fractal pore dimension. according to (yao et al., 2009) concluded that high pore structure is associated with pore heterogeneity, affecting gas adsorption. however, from the research results, researchers where the fractal pore dimension have a positive correlation with adosprtion of methane. when fractal pore dimension increase in small pores increase compared to large pores in coal, the effect of small pores on in surface area is much higher than in large pores. as a result of the small pores that develop, the fractal pore dimension value becomes large; this is shown in the coal seam c, which has large fractals. fig 6. relationship between adsorption of methane gas and fractal pore dimension based on previous research by (li et al., 2015) , micropores have a large surface area and can provide a large absorption of methane gas. gas absorption does not depend on pore volume but depends on the pore surface, and ordinary pore surface will have less methane gas absorption than the irregular pore surface. meanwhile fractal pore dimension are related to micropores, where a decrease in pores causes a more regular pore diameter, which results in a decrease in fractal pore dimension. fig 7. the value of adsorption methane gas, ash, reflectance vitrinite, and pyrite content a b 180 first author et al./ jgeet vol xx no xx/20xx in seam c it is known that the largest absorption of methane gas, while the fractal pore dimension value is large, shows that the coal seam shows many micropores and a relatively rough surface. the fractal value is influenced by whether the pore surface is regular or not. if the pore surface is regular, the pore surface will cause a small absorption of methane gas, but if the pore surface is irregular, it will cause a large methane gas absorption. the coal seams a, b, and d have small fractal pore dimension value compared to coal seam c, and this shows that coal seams a, b, and d have a regular porous surface while coal seam c has an irregular porous surface. the pores surface shows that the absorption capacity of coal seams a, b, and d is smaller than seamless coal c, see figure 7. ash and pyrite minerals are impurities in the coal, especially on pore surfaces, which will affect the absorption of methane gas (figure 7). previous researchers (laxminarayana & crosdale, 1999) explained that ash content and the mineral matter would reduce methane gas's absorption capacity. besides that, mineral matter, especially pyrite, will fill micropores, which will reduce the absorption capacity of methane gas. minerals on the pore surface influence the regularity of the micropore surface the presence of pyrite minerals that fill inertinite group macerals, especially fusinite, semifusinite, and sclerotinite (figure 8). fig 8. photomicrography of sem shows pyrite minerals that fill inertinite group maceral if the pyrite mineral meets the maceral group, it will cause irregularity. the microsurface, which causes the fractal pore dimension to be small, will cause the absorption of methane gas to decrease. in comparison, coal rank has an important influence on the fractal pore dimension. however, coals of the same rank will have almost the same fractal pore dimension. according to the research results by (yao et al., 2009) on carbon content, the more coal that contains relatively high carbon, the higher the fractal pore dimension of coal, which have a relatively similar rank of coal. the coal seam c has a higher fractal pore dimension and adsorption of methane gas than the coal seams a, b, and d, which shows that coal seam c has a higher carbon content than coal seams a, b, and d. 4. conclusion the fractal pore dimension calculation using the box counting method can determine whether the pore volume and pore surface are regular or irregular. coal with irregular pores has a large fractal pore dimension, while regular surface pores have small fractal pore dimension. the irregular surface of the pores affects the absorption of methane gas. coal with a regular pore surface will absorb less methane gas than an irregular pore surface. the absorption of methane gas increases with the rank of coal. in coal, which has almost the same rank, the fractal pore dimension difference is minimal. seam c coal has abundant methane gas absorption with large fractal pore dimension, but its porosity is small because this pore volume automatically affects the absorption of methane gas. the value fractal pore dimension of seam c is high, indicating that coal has a surface and pore structure heterogeneity. fractal pore dimension can be used to determine the size of coal porosity. acknowledgements the research was carried out by upn “veteran” yogyakarta, ministry of education and culture of republic of indonesia. the authors thank the institute of research and community service, universitas pembangunan nasional "veteran" yogyakarta and pt tanjung alam raya for which the authors expressed their gratitude. references anggayana, k., kamarullah, d. r., suryana, a., & widayat, a. h. 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(1995). determination of the surface fractal dimension for porous media by mercury porosimetry. industrial and engineering chemistry research, 34(4), 1383–1386. https://doi.org/10.1021/ie00043a044 © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1016/j.fuel.2014.08.035 https://doi.org/10.1016/j.fuel.2016.05.110 https://books.google.co.id/books/about/the_fractal_geometry_of_nature.html?id=3npmsweacaaj&redir_esc=y https://books.google.co.id/books/about/the_fractal_geometry_of_nature.html?id=3npmsweacaaj&redir_esc=y https://books.google.co.id/books/about/the_fractal_geometry_of_nature.html?id=3npmsweacaaj&redir_esc=y https://doi.org/10.1007/s10450-016-9778-9 https://doi.org/10.1007/s10450-016-9778-9 https://doi.org/10.1016/j.electacta.2004.04.012 https://doi.org/10.1021/ef5014055 https://doi.org/10.1016/j.fuel.2013.07.040 https://doi.org/10.1016/j.cageo.2008.09.005 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ jgeet_cover_print_vol 3 no 3 2018.cdr p-issn. 2503-216x e-issn. 2541-5794 volume 3 no 4 december 2018. p 180 236 cross plot analysis of rock properties from well log data for gas detection in soku field, coastal swamp depobelt, niger delta basin okoli emeka austin, agbasi okechukwu ebuka, onyekuru samuel, sunday edet etuk page 180 list of content journal of j eetgeoscience engineering environment and technology journal of geoscience, engineering, environment and technology uir press publisher characteristics of groundwater on the eastern slope of mount ciremai, kuningan regency, west java, indonesia kholqi dianardi, jumhari, m. sapari dwi hadian, t. y. m. iskandarsyah page 187 petrography, geology structure and landslide characterization of sumatra fault deformation: study case in km 10-15 highway, koto baru sub district, west of sumatra catur cahyaningsih1, puja fransismik crensonni, yogi aditia, adi suryadi, tiggi choanji, dewandra bagus eka putra page 192 groundwater quality assessment for drinking purpose in gulistan-e-johar town, karachi, pakistan adnan khan, muhammad akif khan page 200 festivals and deterioration of aquatic environment: a case study of idol immersion in tapi river, india n.c.ujjania, azahar a. multani, chaitali a. mistry, mitali s. patel page 208 interpretation of 2d-subsurface resistivity data in the iron ore prospect area of eastern binangun coastal, regency of cilacap, central jawa sehah, sukmaji anom raharjo, fajar destiani page 214 arsenic survey in dried sediments of maharlu saline lake mohammad mehdi taghizadeh page 221 groundwater exploration using vertical electrical sounding (ves) method at toro jaya, langgam, riau adi suryadi, dewandra bagus eka putra, husnul kausarian, budi prayitno, reza fahlepi page 226 gold-silver mineralization in the neo-tectonism of honje formation and cipacar formation, in cibaliung block, banten province dudi nasrudin usman, nana sulaksana, febri hirnawan, iyan haryanto page 231 p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. sabah a. ismail (iraq) editorial member dr. kurnia hastuti (indonesia) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. eng. takahiro miyazaki (japan) dr. mursyidah, m.sc. (indonesia) dr. sapari dwi hadian mt (indonesia) dr. emi sukiyah st., mt (indonesia) bambang setiadi ph.d (indonesia) dr. vijaya isnaniawardhani (indonesia) dr. anas puri s.t, m.t (indonesia) mirza muhammad waqar, m.sc (pakistan) good fried panggabean, s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) yuta izumi m.eng (japan) kageaki inoue, m.eng (japan) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) yuta izumi, m.eng (japan) yuniarti yuskar s.t, m.t (indonesia) muhammad zainuddin lubis s.ik m.si (indonesia) pakhrur razi, s.si, m.si (indonesia) babag purbantoro, s.t, m.t (indonesia) budi prayitno s.t, m.t (indonesia) joko widodo, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing our new issue vol 03 no 04 2018. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. husnul kausarian, ph.d editor-in-chief journal of j eet geoscience engineering environment and technology list of content cross plot analysis of rock properties from well log data for gas detection in soku field, coastal swamp depobelt, niger delta basin ............................... 180 characteristics of groundwater on the eastern slope of mount ciremai, kuningan regency, west java, indonesia ......................................................... 187 petrography, geology structure and landslide characterization of sumatra fault deformation: study case in km 10-15 highway, koto baru sub district, west of sumatra .......................................................... 192 groundwater quality assessment for drinking purpose in gulistan-e-johar town, karachi, pakistan ..................................................... 200 festivals and deterioration of aquatic environment: a case study of idol immersion in tapi river, india .......................................................................... 208 interpretation of 2d-subsurface resistivity data in the iron ore prospect area of eastern binangun coastal, regency of cilacap, central jawa ........................ 214 arsenic survey in dried sediments of maharlu saline lake ............................... 221 groundwater exploration using vertical electrical sounding (ves) method at toro jaya, langgam, riau ................................................................ 226 gold-silver mineralization in the neo-tectonism of honje formation and cipacar formation, in cibaliung block, banten province ............................ 231 page 1 page 2 page 3 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology special vol 04 no 02-2 2019 singh, v.k. / jgeet sp vol 04 no 02-2/2019 1 special volume geology, geomorphology and tectonics of india: introduction vinod k. singh* department of geology, bundelkhand university, jhansi 284128, india * corresponding author : vinodksingh@bujhansi.ac.in tel.:+91-9415258237; fax: +91-5102321667 received: dec 18, 2018; accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2447 the earth crustal growth since its formation still need in depth research is the conclusion of the three international conferences on precambrian continental growth and tectonism, in 2005, 2009 and 2013, organised at the institute of earth sciences of bundelkhand university, jhansi, india and its proceedings have valuable source for advance research published the great ideas and achievements from scientists (chandra et al. 2007; singh and chandra, 2011 and singh et al., 2015). therefore, this thematic issue planned for consider of crustal growth and tectonic evolution of indian shield which include 7 research articles on geodynamic evolution of earth, geomorphology, structural, petrologic, isotopic, tectonic, and geochemistry investigations related to the indian shield and its economic importance (fig. 1). fig. 1: main tectonic division of indian shield (modified after ramakrishnan and vaidyanadhan, 2010 and slabunov and singh, 2018). the first paper is by m.m. singh and v.k. singh reconstruct the tectonic evolution of supracrustal rocks from babina and mauranipur greenstone belts (i.e. known as central bundelkhand greenstone complex) which mostly occur in hydrated mantle field and under arc setting conditions. the archean maficultramafic rocks mostly falls in the vicinity of oceanic island basalt field, indicate subduction tectonic setting for evolution of bundelkhand craton, india. the contribution from s.c. bhatt and v.k. singh provides information about neoarchean paleoproterozoic crustal shear zones and exercise for tectonic evolution of bundelkhand craton, india. mostly these e w trending http://journal.uir.ac.id/index.php/jgeet 2 singh, v.k./ jgeet sp vol 04 no 02-2/2019 shear zones are traversed in archean granitoids which have not involved on the paleoproterozoic dolerite dykes and quartz veins in the craton. the ne sw to ese wsw trending shear zones are also occur in the region which containing both dextral and sinistral antithetic and synthetic shears, formed during an n s crustal subduction and its growth. s. lata et al., discuss the geometry of folds in mandhali formation rocks occur in inner sedimentary zone of lesser himalaya, which exposes complexly folded and refolded structures. they indicate that the shearing and strain patterns are most dominant folding mechanism, has been the flexure-shear for the folds which are overprinted by the fold flattening and other subsequent deformations, on the basis of geometric analysis using dip isogons and orthogonal thickness parameters. s. mishra et al., present geochemistry and geodynamic setting of paleoproterozoic granitic rocks from the lesser garhwal himalaya, india, which suggests syn-collision origins and typical collisional granite. these granites suggest a possible linkage with 1800 1900 ma magmatism hydrothermal activity in bundelkhand craton, required more data for solving the problem of the melting and recrystallization of archean continental crust of bundelkhand craton. primary sm nd data indicate a neoarchean protolith for these lesser himalayan granites, may be link to bundelkhand craton as source material existing in south. r. kumar et al., focuses on the geology and mineral potential in kulu district of himachal pradesh, india in particular for copper-silver mineralization. the naraul formation of the larji group contains the major strata bound copper mineralization at many places in sainj valley of kulu district exposing the proterozoic northwestern himalayan belt where silver mineralisations also occur around manikaran. these ore mineralization seems to be alike the copper silver deposit of the revett formation of montana and idaho, usa. a. singh and v.k. singh studied potential zone of metallic and non-metallic deposits and tin mineralizations hosted in the acid magmatic rocks in the katekalyan area, bastar craton. the evolution differentiating granitic magma shows residual melt enrichment where end products intruded as pegmatites into the rocks. cassiterite is most important tin-ore mineral which associated with pegmatites and have significant amounts of sn, nb, ta with minor w. the association of cassiterite, lithium mica (lepidolite) and fluorite in the pegmatites may be possible that the tin transported in the gaseous stage as snf4 or sncl4 and precipitate with the addition of water mainly in the condition of aqueous volatile solutions. g.k. dinkar et al., documents the geology and mineral deposits of south and southwestern part of uttar pradesh which is mainly covered with gangatic alluviums. the alluvium cover belongs to holocene age and is mainly dominated by varanasi older sediments consisting fine grained, well compacted and more mature sediments. the peninsular part of uttar pradesh is covered by the rocks of archean to mesozoic age. the hard rocks are mainly igneous and metamorphic rocks and are exposed as isolated hills. the oldest rocks of the peninsular belong to bundelkhand craton, beside this the bijawar group, mahakoshal group and ajabgarh group rocks are equivalent to delhi supergroup. acknowledgements i gratefully acknowledge prof. husnul kausarian, editor in chief of journal of geoscience, engineering, environment, and technology for his help and also to journal that providing the opportunity to publish this thematic issue. i express my sincere thanks to prof. m.m. singh, head of the department of geology, bundelkhand university, jhansi, india for providing the necessary facilities to complete this thematic issue and all contributors in this issue and very well-wishers for their help in many ways. this special issue will be useful for geologists, academics, research scholars and also for those interested in problems of the earth crust evolution history of india. references chandra, r., singh, v.k., sivaji, ch., piper, j.d.a., 2007. precambrian continental growth and tectonism: introduction. gondwana research 12(3): 199-201; doi.org/10.1016/j.gr.2006.10.019 ramakrishnan, m., vaidyanadhan, r., 2010. geology of india. journal of geological society of india, 556. singh, v.k., chandra, r., 2011. precambrian continental growth and tectonism: introduction. in: singh, v.k., chandra, r. (eds.), proceeding of the 2 nd international conference precambrian continental growth and tectonism, angel publication, india, pp. 1-2. singh, v.k., chandra, r., basu, a.r., verma, s.p., biswal, t.k., 2015. precambrian crustal growth and tectonics: introduction. international geology review 57(11-12): v-viii. slabunov, a.i., singh, v.k., 2018. meso neoarchaean crustal evolution of the bundelkhand craton, indian shield: new data from greenstone belts. international geology review, doi.org/10.1080/00206814.2018.1512906 © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 03 2018 widagdo et al./ jgeet vol 03 no 03/2018 155 research article morphotectono-volcanic of menoreh-gajah-ijo volcanic rock in western side of yogyakarta-indonesia asmoro widagdo 1,2, *, subagyo pramumijoyo 1 , agung harijoko 1 1 geological engineering department, gadjah mada university, indonesia. 2 geological engineering department, jenderal sudirman university, indonesia. * corresponding author : asmoro.geologi@gmail.com received: june 14, 2018; accepted: july 23, 2018. doi: 10.24273/jgeet.2018.3.3.1715 abstract menoreh-gajah-ijo have a very distinctive shape, where there are form of circular structure of volcano that is still intact and the other has not been intact. these morphologies are the morphology of the remaining volcanoes formed by tectonics and certain volcanisms. this study was conducted through a series of interpretations of volcanic body distribution, constructing a slope map, constructing a slope direction map, constructing an alignment interpretation on satellite imagery and field mapping work. the formation of menoreh-gajah-ijo morphologies are strongly influenced by tectonics and volcanic processes. the process of tectonism that produces the strike-slip fault structures, the normal faults, and the uplift have formed the lineaments of the valleys and hills with various directions patterns. the menoreh-gajah-ijo volcanisms that have occurred form the structure of volcanic remains. distribution of menoreh-gajah-ijo volcanic rocks form some semicircle structures because of the normal fault structure that has occurred. keywords: tectonic, volcanic, morphology, alignment, fault. 1. introduction menoreh-gajah-ijo volcanics are located in the southern part of java island, central java-indonesia. volcano-tectonically, the menoreh-gajah-ijo mountains are part of the sunda-banda arc, which is a tertiary (ancient volcanic arc) up to the quarternary volcanic arc (recent volcanic arc). this volcanic arc is formed as a result of subduction of oceanic plate in the south of java island. this is the normal subduction of the indian ocean plate northward under the eurasian continental plate. the location of the menoreh-gajahijo areas are shown in figure 1 below. the position of subduction in southern java island progressed closer and further away from the mainland of java, but the location of the arc was relatively constant (soeria-atmadja, et al., 1994). this results in the occurrence of superimposed volcanic activity from time to time in the menoreh-gajah-ijo mountains. budiadi (2009) and sudradjat, et al. (2010), concludes that the unique morphological expression of the menoreh-gajah-ijo mountains is caused by the general trend of tectonics that has occurred in java since eocene. 2. regional geology of menoreh-gajah-ijo the stratigraphy of menoreh-gajah-ijo areas are included in the old volcanic area, composed by sedimentary rock formations of nanggulan and volcanic rocks of kebo butak formation. figure 1. the menoreh-gajah-ijo tertiary volcanics location the nanggulan and kebo butak formations are intruded by shallow intrusive rocks in the form of microdiorite, andesite and dacite which have generally been altered. rahardjo, et al. (1995), rahardjo, et al. (2012) and harjanto (2011) state these volcanics group are covered unconformitically by the shallow sea sediments of the jonggrangan formation and sentolo formation. http://journal.uir.ac.id/index.php/jgeet 156 widagdo et al./ jgeet vol 03 no 03/2018 van bemmelen (1949), explains that nanggulan formation is the oldest rock in western of yogyakarta area. its lithology consists of sandstones with lignite (harley and morley, 1995, rahmad et al., 2008, ansori et al., 2015), sandstone, limonite, marl and limestones, sandstones, tufs rich in foraminifera and molluscs, estimated thickness 350 m. based on the study of planktonic foraminifera, the nanggulan formation has an age range between the middle eocene to the oligocene (van bemmelen, 1949, bolliger and de ruiter, 1975, premonowati, 1994, harley and morley, 1995, smyth et al., 2005, saputra and akmaludin, et al, 2015). this formation is formed in a shallow marine environment to transition (prasetyadi, 2008). the volcanic rock of old andesite formation (van bemmelen, 1949) formed unformitycally above the nanggulan formation. lithologycally, this formation consist of volcanic breccia with andesite fragments, andesite intrusive rocks (suroso et al. 1987, rahardjo, et al. 1995, harjanto, 2011, hartono and pambudi, 2015, rahardjo, et al. 2012), dasit intrusion (rahardjo et al. (1995), harjanto, 2011, rahardjo, et al. (2012), basal intrusion (suroso, et al. 1987), lapilli tuff, tuff, lapili breccia, andesite lava flow, agglomerates, and volcanic sandstones exposed in many locations in the menorehgajah-ijo regions. satyana and purwaningsih (2003) and satyana (2005) state that above the old andesite formation deposited jonggrangan formation, unconformitically at the volcanic heights. generally, this formation at the bottom consists of conglomerates, tuffaceous marl, and sandstone with molluscs and claystone with lignite. sulistyoningrum and rahardjo, et al. (2010) states that at the top, the composition of this formation is bedded limestone and coralline limestone. the thickness of the constituent rocks is 200-500 meters (van bemmelen, 1949) and its age is the early to middle miocene. this formation, at the bottom is inter-fingered with the bottom part of the sentolo formation. this formation formed the mountains and conical hills and spread in the middle of menoreh-gajah-ijo mountains. sentolo formation is also deposited above the old andesite formation, in addition to the jonggrangan formation. the relationship between the sentolo formation and jonggrangan formation is interfingered. it consists of limestones and marl calcareous sandstone. it lower part consists of a conglomerate piled by tuffaceous marl with tuff. these rocks upward gradually transform into a nice layered coffin rich in foraminifera. the thickness of this formation is about 950 m. according riandari and wiyono (2013), the age of this formation is the early miocene to pliocene. 3. research method the method used in this menoreh-gajah-ijo research is through a series of morphological analysis work, tectonic and volcanic body in menoreh-gajah-ijo mountains. morphological analysis includes the interpretation of menoreh-gajah-ijo volcanics body distribution and making the morphological crosssections of each volcanic body. interpretation of menoreh-gajah-ijo volcanics body distributions are done by terrasar-x satellite image. tectonic analysis includes alignment interpretations on satellite imagery, drawing of rosete diagrams, and field geology studies resulting in the distribution of geological structures on the geological map. the results of previous research by some researchers are used in supporting the analysis and synthesis of this study. 4. volcanism in menoreh-gajah-ijo mountains area 4.1 gajah volcanism gajah volcano is a volcano located in the middle of menoreh-gajah-ijo mountains and some researcher state to be the oldest volcano in this area (fig. 2). this volcanic product is centered on the western part and stretches east, north and slightly westward. the western and southern sides of this mountain have been broken and missing covered by younger volcanic materials or sediments. figure 2. the body of gajah and ijo volcano which have oligocene age and menoreh which has late miocene age. central facies of gajah volcanic body which is the place of magma from the earth to the surface located in the west part or in the purworejo region. this part is characterized by lava rock associations and a variety of semi-volcanic intrusions such as volcanic necks and dykes. harjanto (2011) states this central facies region as the body of pencu mountain. he mentioned that the rocks of this region in the form of andesit intrusion, lava and breccia of mount pencu. 4.2 ijo volcanism in the southern part, there is a circular pattern that is still intact from ijo volcano. this intact circular pattern covers gajah volcano in the middle part of the mountain. ijo volcano more shows a circular pattern (circular features) and still intact, while gajah volcano widagdo et al./ jgeet vol 03 no 03/2018 157 no longer shows this structure. this happens because gajah volcano is covered by the presence of rock from ijo mountain. this cross-cutting relationship shows that gajah volcano comes first and then ijo volcano comes to close part of gajah volcano's body. almost the entire body of gajah volcano covering the proximal, medial and distal facies on the south side has been collapsed and covered by the material of ijo volcano. the center of this volcano is the location of hydrothermal activity that affects the surrounding facies, resulting in the formation of altered rocks and even mineralization in surrounding facies such as in kokap and surrounding areas (purnamawati and tapilatu, 2012). setiabudi (2005) proposed in the sangon area which is a proximal facies, found gold mineralization in quartz veins. it effected to the erosional proces and finally to the geomorphological features. 4.3 menoreh volcanism in the northern part of the mountains there is a halfcircular pattern of menoreh volcanoes. this volcano has been cut and only half of it. the rest of this volcano opens to the north. the foot of this volcano is located on the body of gajah volcano in the north. image analysis added jonggrangan formantion, indicating that menoreh volcano is above the jonggrangan formation. thus menoreh volcano is younger than gajah volcano, ijo volcano and jonggrangan formation. menoreh volcano is a volcano located in the northern part of the lineaments of menoreh-gajah-ijo mountains as the youngest volcano. menoreh volcano is separated from gajah volcano and ijo by a long period of time covering the post-ijo erosional period, the settling period of jonggrangan and the postjonggrangan erosion period. this semi-circular structure of the volcano can still be seen clearly (figure 4.). akmaludin et al. (2005) conducted an absolute age analysis by k-ar method of a taken from the volcanic center near borobudur temple (north side of the mountain). hornblende age analysis showed age of 12.4 ± 0.7 million years ago or late miocene. on regional geological appearance, menoreh volcanic rocks are above nanggulan and jonggrangan formation. menoreh volcano is also above the medial and distal faces of the north side of gajah volcano. the central facies of menoreh volcano as a place where magma came out appears in the middle of the semicircle structure. this area characterized by igneous rock associations such as lava, volcanic neck and dyke (idrus, et al., 2013; idrus, et al., 2014; rahardjo, et al., 1995; rahardjo, et al., 2012). this area is the site of the formation of hydrothermal fluid, which affects the surrounding area. therefore, it resulted in the formation of rocks alteration or mineralizations in the surrounding area in proximal facies. the proximal facies of menoreh volcano is outward from the central facies. this area is dominated by lava flows and pyroclastic breccia. this area has undergone a very intensive rock alteration so that the soil layer formed is very thick. this area is a site highly affected by hydrothermal fluid, thereby resulting in the formation of alteration rocks or even mineralization in the surrounding area such as mount gupit in salaman and borobudur subdistrict, magelang regency (idrus, et al., 2013) and in kalisat area-magelang (idrus, et al., 2014). medial facies menoreh volcano develops to the east, south and west of the volcanic body. in this area, as it is further away from the location of the volcanic source, lava flows and agglomerates have been reduced. in this area breccia andesite and tuff are very dominant. laharic breccia has already begun in this area but lava menoreh still reaches this part, showing the very dilute nature of lava. this rock group is very resistant, thus forming the height of suroloyo and its surroundings. 5. volcanic residual morphology proximal facies rocks such as lava and pyroclastic breccia of gajah volcano develop in the east, west and north of the central facies. this area is dominated by lava flows and pyroclastic breccia, which are highly resistant, thus forming a pile or height influenced by the northwest-southeast (nw-se) trending normal faults. intrusion of dyke andesite is found in the southern part of gajah volcano directed northwest-southeast (nw-se) cut off andesite lava rock. its position is adjacent to the hydrothermal gajah volcano, causing the area to undergo hydrothermal alteration. this results in changes of some minerals to clay minerals in rocks. the flow of the river develops following the structure and the argilic alteration zones where clay minerals develop intensively. this leads to these close facies, lower in elevation than in the central gajah volcano and the intermediate facies of gajah volcano area (fig. 3 section 1 and 2). medial facies rock such as laharic breccia of gajah volcano, develops in the east and north side of proximal facies. there is a litle of lava because of more far away from the volcanic source. laharic breccia and tuff are start to dominant. generally, laharic breccia has angular to sub-rounded form. conggomerate with rounded-sub rounded form, sandstone, siltstone and claystone presents at this area. the rocks of this area are not affected by hydrotermal alteration, so they are still resisten. as the position is more high, these area then to be the place of growing corall as the source of jonggrangan formation in the east side of gajah volcano (fig. 3 section 3). in the eastern part of gajah volcano, andesite breccia, conglomerate, sandstone, siltstone, thin limestone are develop at the distal facies. east-west faults form some river and morphology at fig. 3 section 4. morphologically, this area controlled by east-west normal fault and northeast-southwest thrust fault which bring nanggulan formation to exspose. proximal facies of ijo volcanic rocks such as lava and pyroclastic breccia develop around the central facies (fig. 4). a small part of this rock group is very resistant, so some form hills, hills of intrusion and lava surrounding the central facies. most of these lava bodies have undergone alteration and mineralization, thus forming a low relief surrounding the height of the volcanic center (fig. 4 section 1). 158 widagdo et al./ jgeet vol 03 no 03/2018 figure 3. east-west and north-south morphological cross-section of gajah volcano medial facies rocks such as andesite breccias and lava develop around the proximal facies on the slopes of ijo volcano, both on the western, southern, northern and eastern sides. this area is dominated by breccia tuff, andesite breccia and tuff. the process of alteration and mineralization does not develop intensively in all parts of this facies, thus the resistance of the rock to the facies is still maintained. generally these facies form a high altitude morphology (fig. 4 section 2, 3 and 4) surrounding the proximal facies of ijo volcano. the circular or circular pattern of ijo volcano body can be easily recognized through the image and topographical map through the delineation of this medial facies. in the upper girimulyo and kokap areas, this rock becomes the site of the growth of coral reefs forming the jonggrangan limestone formation (fig. 4 section 3). distal facies rocks do not develop intensively on the slopes of ijo volcano either on the south west, north and east. locally these distal facies are found in the eastern part of ijo volcano (fig. 4). this is likely due to a fault that cuts out the distribution of this facies or because it is covered by the sentolo carbonate sediment formation. morphology of the menoreh volcano shows a semicircular shape facing northeast (ne). this morphology is highly controlled by normal faults and hydrothermal alterations in the middle part. the loss of half of this mountain is due to a normal fault of the east-west trending in the north side (cut in fig. 5 section 4). the circular pattern is seen to be more controlled by the erosion of the argillic alteration zone which is rich in the hydrothermal clay of the andesite lava rocks. meanwhile, in the unalterated medial facial breccia, there is no strong erosion (fig. 5 section 2 and 3). figure 4. the cross-sectional view of ijo volcano. widagdo et al./ jgeet vol 03 no 03/2018 159 figure 5. cross-sectional of menoreh mountain morphology. 6. tectonism reviews of menoreh-gajah-ijo mountains tectonism include interpretation and analysis of geological structure alignment, as well as an overview of geological structures on the geological map generated from this study. the alignment according to sabins (1996) is a phenomenon on the surface of the earth that shows the characteristics of a straight appearance or an arch associated with a fault or a weak zone. the flow pattern is a common geomorphological expression of straightness. the different types of rocks also allow a contrasting appearance in remote sensing imagery observations. figure 6. lineaments interpretation and rose diagram of lineaments in menoreh-gajah-ijo mountains area interpretation of the lineaments are done by drawing lines on the image (fig. 6), where in the field can be a pattern flow channel, a row of hills that form straightness, straightness scrap, straightness of the valley and straightness due to similar rock types. the types of straightness can not be directly determined from the line drawing on the image, therefore, to the structure of the structure of the results of image interpretation, conducted field review to ensure the results of interpretation. fieldwork is also needed to find geological structural data and field measurements. the results of the image interpretation and fieldwork will be related to the distribution of rocks on the geological map, resulting in a relationship between geological structures with the distribution of rock formations in the menoreh-gajah-ijo mountains. figure 7. geological structures and stereographic analysis of the structures 160 widagdo et al./ jgeet vol 03 no 03/2018 gajah volcano as the oldest volcanic rock in the menoreh-gajah-ijo mountains shows the highest lineaments of 430 pieces or 41.99% of all the data. the number of lineaments is the largest compared to other rock groups in menoreh-gajah-ijo mountains. as the oldest volcanic rocks, some of the structures formed on the volcano's body are also the recording of the structure to the youngest rocks (menoreh volcano). ijo volcano as the second volcanic rock present in menoreh-gajah-ijo mountains, shows the presence of 345 data or 34.69% of the alignment of all the straightness in the study area. menoreh volcano as the youngest volcanic rocks present in menoreh-gajah-ijo mountains, shows the presence of 249 lineaments or as many as 24.31% of the overall straightness. in the following geological map, we can see the distribution of three units of tertiary rocks namely gajah volcano, ijo volcano and menoreh volcano. these rocks are unconformity above the nanggulan formation exposed on the eastern side of gajah volcano and the central part of ijo volcano. the sentolo formation is found on the eastern side of menorehgajah-ijo mountains. jonggrangan formation is found in the height in the middle of the mountains. in the map of the geological structure (fig. 7) above, it is illustrated the faults in the west part of gajah volcano. this fault is the oldest fault in the menorehgajah-ijo areas because it develops in the oldest rock and causes the collapse of gajah volcano on the south side with the same direction that is northwestsoutheast (nw-se). stereographic analysis of shear fracture and brecciation data resulted in a normal fault. referring to the age of ijo volcano which was born in oligocene age, then the age of this fault is also still oligocene. there is a long fault that cuts menoreh-gajah-ijo mountains from south to north. because of this fault cut menoreh volcano, as the youngest rock, the fault is active last time at post-menoreh (post late miocene). however, if we refers to smyth et. all, 2005, hall et al, 2007, smyth et al, 2008 and husein and nukman 2015 then this fault is an old fault that existed since the late oligocene. based on stereographic analysis of shear fracture data, brecciation and tension fracture in lava of gajah volcanic rock, this type of fault is a sinistral fault or left lateral strike slip fault. this sinistral progo fault extends to mount muria in the north of java island. smyth et al, 2005, hall et al, 2007, smyth et al, 2008 and husein and nukman 2015 refer to it as the progo-muria fault. normal faults in ijo volcano develop in the northern part of ijo volcano. this fault cuts the northern part of ijo volcano, cuts jonggrangan limestone rock formation and also crosses the sinistral progo fault. based on the stereographic analysis of the striation data in the fault plane, the tension-forming direction of this fault is southwest-northeast (sw-ne). this tectonic extension produces some normal faults on the north side of ijo volcano. on the northern side of the menoreh-gajah-ijo mountains, menoreh volcano is cut off by a west-east (e-w) trending structure. this trending fault is intensively formed in this section and less developed in other parts of the menoreh-gajah-ijo mountains. based on stereographic analysis of striation data, this normal fault is formed by a north-south trending extension. on the eastern side of gajah volcano there is an eocene rock outcrop, which is very rare injava island. this phenomenon is controlled by the existence of a thrust fault that lifts it from the depth so it is exposed on the surface. based on stereographic analysis of striation data, it is generated that the movement of thrust fault is caused by the compression force from the southeast direction. this compression force also led to the exposure of sedimentary rocks of the sentolo formation, extensively on the east side of ijo volcano, and not at all on the western side. this is supported by the presence of folds in the naggulan formation and sentolo formation which have the axis of the northeast-southwest (ne-sw) trending fold. the presence of this style is also supported by the dominance dipping layers of the sentolo formation rocks, which are tilted to the southeast. 6. discussion the morphology of the menoreh-gajah-ijo mountains is composed of gajah, ijo and menoreh volcanic bodies. this row of mountains has a relatively north-easterly direction (nne). smyth et al. 2005 describes this tertiary volcano and progo-muria fault line. hall et al. 2007 also describes this straightness as the boundary of archean continental plate in the southern mountains of java. husein and nukman 2015 also describe the progo-muria straightness originally derived from the transform fault that accommodates east java's microcontinent shifts. based on field data analysis such as brecciation, shear fractures and tension fractures and striation along this fault line, it can be concluded that this fault is a horizontal fault or sinistral fault. by delineation of the fault line can be obtained pattern of fault is left stepping left lateral fault. figure 8. emergence volcanic according to nakamura (1977) model and emergence volcanic in the menoreh-gajah-ijo mountains model nakamura (1977), illustrates the emergence of volcanoes in extensional and contractional tectonic regions (fig. 8). in the proposed model, in the tectonic extension zone, the polygenetic volcano develops extending perpendicular to the extension force. in the contractional tectonic zone, the polygenetic volcano develops relatively in the direction of the compression widagdo et al./ jgeet vol 03 no 03/2018 161 force. in this second model, he describes the presence of the geological structure of the fault of sinistral and dexstral, but no alignment of the polygenetic volcano follows both directions of the structure. the menorehgajah-ijo mountains are zones of polygenetic volcanoes formed on two volcanic arcs in java. gajah volcano and ijo volcano are on the late eocene-early miocene arc volcano. while menoreh volcano is on the late miosen-pliocene volcano arc in the north. these three volcanoes form the north-northeast straightness (nne), which is controlled by the left horizontal fault (the sinistral progo fault), which forms a left stepping sinistral fault pattern. the directions of the fault lineament are forming an angle of about 30° from the direction of main compression (fig. 8 section c). progo fault or progo-muria fault is indicated as an old and active fault since before the oligocene. the left stepping pattern of sinistral fault is one of the fault patterns that allow the formation of tension zones due to normal faults that develop. this zone makes it possible to create sedimentary basins or rise of magma to the surface forming a volcano. the presence of oligocene volcano and the late miocene volcano show this fault is very old and continues to be activated. a complex of volcanism according to alvarez et al. (2002) allowed to develop on the base of sedimentary rock basins with particular tectonic controls. the sedimentary basin can evolve, from sedimentation of sedimentary material which is decreased to be buried by volcanism. the result of this change is the formation of sediment and volcanic body which is higher than the surrounding rocks (the menoreh-gajah-ijo mountain is higher than the area in the west and east). in the menoreh-gajah-ijo mountain rocks grow on eocene sediments, late miocene volcanism grows above the jonggrangan formation and oligocene volcanic rocks. alvarez et al. (2002) states, based on kinematics fault, stratigraphy and volume of volcanic rock, the volcanic body allows it to form due to the maximum extension, which allows magma to flow into the low pressure zone. volcanic rock sequences show that volcanism is related to normal faults and magma occupies the room in the strain zone produced by strike-slip fault. in the menoreh-gajah-ijo mountains, left lateral progo-muria fault, patterned left stepping can create tension zones composed of normal faults that allow magmatism and vulcanism to grow in this low pressure zone. concha-dimas et al. (2005) states that volcanism is often associated with faults and tensional fractures that allow magma to flow and fill in existing space. preexisting tectonic geological structures such as faults and joints contribute to the straightness of the volcanic body. fig. 9, illustrates the sketch of the influence of volcano-tectonic properties and models on the formation of volcanic collapse (concha-dimas et al., 2005). in fig. 9 part a, illustrats the appearance of a contour pattern showing the tendency of the dyke and parasitic volcanic vent directions. in the study area, the dike is commonly found in gajah volcano, in the northwest-southeast direction, in the direction of the normal faults that cause the collapse of gajah volcano. intrusion hills such as mount kukusan, mount telu, gunung kuku, gunung agung around the volcanic center of ijo volcano is a parasitic volcanic vent that develops in the menoreh-gajah-ijo mountains. figure 9. effect of volcano-tectonic properties and models on volcanoes according to concha-dimas et al. (2005). in fig. 9 part b, it depicted the presence of dyke and direction of the volcanic slope collapse. in some places the presence of dyke is indicated to control the occurrence of landslides. the presence of dyke on the rocks in the field is cutting the rock body with a certain position. the rock in front of or above the slope of the dyke, where its position is a slope will be easy to landslide. while the rocks under the dyke, will be protected by the dyke body. fig. 9 part c describes the presence of a normal fault in the volcanic bedrock. the collapse of gajah volcano on the southern side is due to the structure according to the drawing model c. figure d, the state of strike-slip faults occurs on menoreh volcano on the northern side of menoreh-gajah-ijo mountain. the collapse of menoreh volcano is also controlled by a normal fault according to the f-figure model where the vertical fault plane is not centered. figure e, volcanic conditions at normal faults in the central part of the volcano and the influence of the oblique fault field. this happened in the western part of gajah volcano, which resulted in the body of gajah volcano no longer symmetry. 6. conclusions 1. n-s compression that produces left stepping left lateral fault, allowing the tertiary volcano in menoreh-gajah-ijo mountains to be in one direction of nne-ssw straightness. 2. compression from the southeast (se) to form thrust fault and normal faults on the east side of gajah volcano, resulting in the emergence of 162 widagdo et al./ jgeet vol 03 no 03/2018 nanggulan formation and morphology of northwest trending hills. 3. morphology of the southern and western sides gajah volcano has been collapsed by normal faults in the oligocene. 4. north side menoreh volcano has been collapsed by normal west-east faults by n-s extension force on pliocene age. references akmaluddin, setijadji, d.l., watanabe, k., and itaya, t., 2005. new interpretation on magmatic belts evolution during the neogene-quarternary 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10.1016/0743-9547(94)90062-0 sudradjat, a., syafri, i., dan budiadi, e., 2010. the geotectonic configuration of kulon progo area, yogyakarta. proceeding pit iagi lombok 2010, the 39 th iagi convention and exhibition, lombok. sulistyoningrum,d. dan rahardjo, w., 2010. identification and paleoecology of coraline fossil (cnidaria: anthozoa) from https://doi.org/10.1016/0034-6667(94)00133-5 https://doi.org/10.1016/0034-6667(94)00133-5 https://doi.org/https:/doi.org/10.1016/0377-0273(77)90012-9 https://doi.org/https:/doi.org/10.1016/0377-0273(77)90012-9 https://doi.org/10.2110/jsr.2008.039 https://doi.org/10.1016/0743-9547(94)90062-0 widagdo et al./ jgeet vol 03 no 03/2018 163 jonggrangan limestone, western slope of kucir hill, west progo area, yogyakarta special province. proceedings pit iagi lombok 2010, the 39th iagi annual convention and exhibition. suroso, rodhi, a., dan sutanto, 1987. usulan penyesuaian tata nama litostratigrafi kulon progo, daerah istimewa yogyakarta. kumpulan makalah pertemuan ilmiah tahunan xv ikatan ahli geologi indonesia, yogyakarta, 1, van bemmelen, r.w., 1949. the geology of indonesia. vol. ia, general geology of indonesia and adjacent archipelago, government printing office, the hague. © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. regional geology of menoreh-gajah-ijo 3. research method 4. volcanism in menoreh-gajah-ijo mountains area 4.1 gajah volcanism 4.2 ijo volcanism 4.3 menoreh volcanism 5. volcanic residual morphology 6. tectonism 6. discussion 6. conclusions http://journal.uir.ac.id/index.php/jgeet e-issn: 2541-5794 p-issn: 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 nugraha, b. et al./ jgeet vol 8 no 1/2023 27 research article geological and morphometric characteristics of quaternary pyroclastic aquifers in salak and pangrango stratovolcano bayu nugraha1,*, mohammad ghozi1, arif fadillah2, azwar satrya muhammad2, teuku yan waliyana muda iskandarsyah1, nathalie dörfliger3, valérie plagnes4, hendarmawan hendarmawan1. 1faculty of geological engineering, universitas padjadjaran, jatinangor, sumedang, 45363, indonesia 2danone aqua group, department of water resources, jakarta, indonesia 3water institute by evian, water resources and sustainability division, danon waters, evian-les-bains, france 4sorbonne universite, cnrs, ephe, umr 7619 metis, f-75005 paris, france * corresponding author : bayu10011@mail.unpad.ac.id tel.: +62-856-225-9060 received: dec 5, 2022; accepted: mar 17, 2023. doi: 10.25299/jgeet.2023.8.1.11171 abstract the study area is located in the lido catchment area (lca), which is situated between two distinct volcanic slopes and not many discovered especially in indonesia. springs on the volcano's slopes are widely used for domestic, irrigation, and industry water use. investigating the characteristics of aquifers and springs is essential to ensure groundwater sustainability by providing a robust geological framework. geological and morphometric analysis at lca is the basis of important information. we applied a comprehensive geological and morphometric analysis to obtain detailed information about the aquifer. this study aime d to determine the characteristics of aquifers in pyroclastic rocks and their relationship to the formation of springs. from the research conducted, the characteristic of water can be distinguished based on the geological conditions of its constituents. hydrogeology setting is distinct into four categories aquifer: highly productive aquifer, locally productive aquifer, moderately productive aquifer, and an extreme ly rare groundwater region. the results of the morphometric analysis show different value variations based on rock formations related to the processes of spring occurrence. there are 6 different lithological characteristics in the study area: polymict breccia, monomict breccia, lapilli, lapilli tuff, coarse tuff, and fine tuff. from the lithology variations obtained, breccia, lapilli, and coarse tuff can play a good role as aquifers. thin section analysis of the rock shows the characteristics of the alteration minerals. geological correlations and groundwater systems in the study area show groups of superficial, mixed, and alteration springs. the system of water flows in aquifers through inter-grains or rock fractures. the types of springs in lca are dominated by depression and fracture types. these results are fundamental information for understanding hydrogeological systems. understanding the qualities of aquifers and spring characteristics properly may aid in the construction of more effective studies in the future. keywords: pyroclastic aquifer, lido catchment area, spring characteristics 1. introduction 1.1 sub introduction utilization of water sourced from volcanic rocks in the tropics is found in southeast asia, central africa, and others (lu et al., 2015; gourcy et al., 2020; purwantara, 2020; gaikwad et al., 2020; wisitthammasri et al., 2020; maria et al., 2021; ligate et al., 2021). depending on the conditions and characteristics of the geology, hydrogeology, hydrology, and other features of the water cycle, the genesis of water occurs over a period of time that varies (alfadli and natasia, 2017). with a relatively large average population, groundwater resources must be effectively and responsibly managed. volcanic rocks have complex variations and characteristics in terms of shape, grain size, mineral content, and distribution (rüpke et al., 2002; schaefer and kattenhorn, 2004; pratama et al., 2018). hydrogeology systems in volcanic settings result from various interactions and processes that are influenced by the characteristics of minerals and rocks (delcamp et al., 2016; baud et al., 2021). however, the study of the geological context of hydrogeological system occurrences is not given specific consideration. in reality, geology is the host of groundwater and its occurrences, such as the dynamics of aquifers, flow processes, and the presence of groundwater in an area. several interesting volcanic aquifer research have resulted from advances in science and technology. numerous studies of groundwater have examined volcanic aquifer characteristics diversely. as a result, springs can have a wide variety of traits. hawaiian, canary island, and andesitic volcanism settings are among the models of aquifer characteristics that have been researched using various method approaches. lowland basal aquifers are characteristic of aquifers in volcanic environments of the hawaiian type (ingebritsen and scholl, 1993). the canary model describes an aquifer with steep domes and low permeability that is continuous. the bromo tengger (west java) andesitic volcanism model features a perched aquifer system among lava flows and a pyroclastic complex that contributes to the discharge spring (toulier et al., 2019). the ciremai volcano, as a stratovolcano type demonstrates the characteristics of the aquifer, which are characterized by being unconfined with a variety of flow patterns (irawan et al., 2009). it is http://journal.uir.ac.id/index.php/jgeet 28 nugraha, b. et al./ jgeet vol 8 no 1/2023 apparent from the previous mentioned points that various geological circumstances can characterize various aquifer features. lca is situated on two distinct quaternary volcanic slopes: the eastern slope of salak volcano and the western slope of pangrango volcano. lca features an interfingering pyroclastic deposit system with lava flows on the center and medial volcanic facies (effendi & hermanto, 1998; muhardi & tjahjono, 2014; mardiana et al., 2019; alfadli et al., 2021). hydrogeology setting is distinct into four categories aquifer: highly productive aquifer, locally productive aquifer, moderately productive aquifer, and an extremely rare groundwater region (ministry of public works et al., 1990). in general, there are two types of aquifers: unconfined aquifers and confined aquifers with varying potentials (rengganis and harnandi, 2011; pangestu and waspodo, 2019). the lca has much groundwater potential, but it's not been described specifically, especially geological control of groundwater. deepening is needed, especially in studies on a more precise scale. properly comprehending the properties of aquifers and spring characteristics might support the development of more effective studies in the future, for instance, on the conservation and sustainability of groundwater. this research aims to determine the kind or types of aquifers and springs in the lca region by morphometric and geological methods, which need to be deepened. before conducting more specialized investigations, a more in-depth examination of geological factors can offer information about the mechanisms behind the emergence of groundwater in springs. this is fundamental because geology provides an essential base for hydrogeology study. this work provided updated information that can be used as a basis for future research into hydrogeochemistry and hydrogeology conceptual models. 2. description of study area lca is part of the upper cisadane sub-watershed (junaidi and tarigan, 2012). the upper cisadane watershed has water sources from the salak volcano and the pangrango volcano (delani and dasanto, 2015). sources of surface water or groundwater in the upstream cisadane area play an important role in providing water needs for irrigation, drinking water, and other needs for the bogor regency and surrounding areas (jihad, 2018). administratively the lca, located in the bogor regency in indonesia. geographically the research area situated at the coordinates 106o 45’ 3.45” – 106o 55’ 42.70” e dan 06o 43’ 14.10” – 06o 46’ 31.76” s. the lca study area has an area of 46,348 km2 and a cross-sectional length of 21.2 kilometers. the altitude of the research area is an elevation of 454 – 2165masl (figure 1). the average monthly precipitation indicates that lca has a wet climate (alim et al., 2018). according to the data provided by meteorology and geophysics agency, indonesia (bmkg), the pasir jaya station is the rain station that fits the study region. observation of rainfall data at pasirjaya station in 2010 has the highest value of 6081mm/year (figure 2). meanwhile, in the research area which is located in a tropical climate, the lowest rainfall value was 1519mm/year in 1999. the average temperature at pasir jaya station was 21.59°c, and the average evapotranspiration value was 88.22mm/year. fig 1. research locations lido catchment area (lca) in the upstream cisadane watershed area. the yellow circle symbol shows the name of the area. fig 2. total monthly rainfall from 1990 2020, sourced from pasir jaya station under the meteorology and geophysics agency, indonesia. 3. material and methodology 3.1 geology and hydrogeology mapping the mapping and collecting geological and hydrogeological data is a crucial step in characterizing the features of the groundwater system (dianardi et al., 2018; lo et al., 2021). collecting of hydrogeological features of the area was completed in the rainy season, and gather 24 springs observation. the objective of this fieldwork is to measure the physio-chemical composition of the water. physio-chemical measurements of water using a multiparameter water test tool hanna instrument hi 9811 nugraha, b. et al./ jgeet vol 8 no 1/2023 29 5 series. the measurement data are in the form of ph values, water temperature, electro conductivity (ec) and total dissolved solid (tds). in addition, the results of the earlier study, such as regional hydrogeology map, are incorporated to provide context for the data presented. mapping of the geological features of the area was completed to gather primary research data, observations were made at 37 outcrops. these rocks exhibited the characteristics of igneous and pyroclastic rocks, both of which are formed due to volcanic activity. the grain size, grain shape, outcrop thickness, and other characteristics are included in the megascopic description. rock hand specimens were analyzed using the petrographic method with thin section analysis of the rock. fig 3. regional hydrogeological map sheet bogor regency (modification, ministry of public works et al., 1990) with dugwells and springs observation data in the study area based on hydogeological mapping (2021). 3.2. soil infiltration test infiltration tests were conducted to measure the surface soil's ability to absorb water which related to vertical hydraulic conductivity. the infiltration test was carried out using a 3-inch pvc pipe plugged into the ground and then filled with water and calculated how much water infiltrated a certain amount in a particular time. the calculation of the infiltration rate value uses the eqn.1 formula. 𝑉𝑤 = (3.14 × ∅ 2 × ℎ0) − (3.14 × ∅ 2 × ℎ1) (eqn. 1) 𝑉𝑤 is the volume of water infiltrated, ∅ 2 is the radiant of the pvc pipe, ℎ0 𝑎𝑛𝑑 ℎ1 consists of the initial water level in the pipe and the end water level. the calculation is based on the formula for determining the volume of a cylinder. 3.3. morphometric analysis lineament density (ld), drainage density (dd), and slope are the results of a morphometric analysis of digital elevation model (dem) data. this data is one of the important instruments in analyzing ld and dd because it is related to the topography or morphology feature. data were collected from the site's source https://tanahair.indonesia.go.id/demnas/#/. the image used is geospatial information agency indonesia's demnas (seamless digital elevation model and national bathymetry). demnas imagery is a combination of ifsar (5m resolution), terrasar-x (5m resolution), and alos palsar (5m resolution) image analysis (11.25m resolution). using the egm2008 vertical datum, a demnas image with a 0.27-arcsecond resolution. demnas data has been widely used to analyze topography, morphometric features, or watershed management with an accuracy of 8m resolution (iswari and anggraini, 2018; bawasir and handayani, 2021). dd or ld values are determined using a formula developed by (horton, 1932) (eqn. 2 and eqn. 3): 𝐷𝐷 = 𝛴𝐿𝐷 𝐴 (eqn. 2) 𝐿𝐷 = 𝛴𝐿𝐿 𝐴 (eqn. 3) σ𝐿𝐷 is the total length of the stream flow in a certain area and a is the total area calculated. for value calculation ld, σ𝐿𝐿 is the total length of the lineament in a certain unit area. table 1. the results of morphometric analysis on different geological units along with the number of occurrences of springs and the type of rock. topography slope geology formation lithology ld (m/km2) dd (m/km2) slope (°) number of spring effendi & hermanto (1998) geological mapping salak qvsb lahar tuffaceous breccia monomict breccia, polymict breccia, & breccia tuff 19,491.952,30 9,56137,97 1.12-28.09 9 pangrango qvt pumiceous tuff breccia tuff 19,49506,50 9,56-22,45 0.88-24.63 3 pangrango qvpo older deposit lahar lapilli, lapilli tuff, & tuff 506,501.952,30 0,96-22,45 2.08-46.56 13 https://tanahair.indonesia.go.id/demnas/#/ 30 nugraha, b. et al./ jgeet vol 8 no 1/2023 4. rock thin section analysis handspecimens collected from outcrops in the field are studied using the thin-section petrography method. the zeiss primotech series microscope was used to identify the composition of primary minerals, secondary minerals, and porosity in thin sections of rock in percent form. this is necessary to determine the precise rock characteristics. the results of the rock thin section analysis can be seen in thin section analysis of rocks is based on theoretical and technical approaches to petrographic analysis (philpotts, 2003). 4. result and discussion 4.1. morphometric and spring characteristics morphometric analysis consisting of lineament density (dd), drainage density (dd), and slope. twentyfour spring observation stations are dispersed across two of the volcano's slopes—eleven spring observation stations on the slopes of salak. meanwhile, thirteen spring observation sites are located on the slopes of pangrango (table 1). generally, the spring distribution follows the analysis of topographic lineaments and stream lineaments interpretation in lca. the spring location was plotted on the ld, dd, and slope maps to assess the relationship between the presence of springs and the study area's morphological features. springs on the slopes of salak are located at intervals of ±0-30°, while on the slopes of pangrango are found at intervals of ±0-50° (fig 4.a). the appearance of springs on a steep slope characterizes the type of depression spring due to gravity (bryan, 1919; erlinawati et al., 2021). this type of spring is caused by the surrounding topography cutting off the groundwater table, exposing the groundwater table, and forming a conduit for overflowing water (bryan, 1919; gilbert, 2016). on the slopes of salak, the spring data plot on the dd map depict five locations at 9,56-22,45m/km2 value intervals and four data at 22,45-137,97m/km2 value intervals. the ld analysis reveals three spring data are located at intervals of 795,66-1.952,30m/km2 on the salak slopes, two spring data at intervals of 506,50-795,66m/km2, while four are at intervals of 19,49-506,50m/km2. on the salak slopes, two data are not included in the dd and ld analysis zones. (fig 4.a and b). on the slopes of pangrango, three springs are located at dd 0,96-9,66mm/km2, and the other five are located at 22,45-137,97m/km2 (fig 4.b). the ld analysis reveals that six spring data are located at 795,66-1.952,30m/km2 intervals, one spring data are located at 506,50-795,66m/km2 intervals, one spring data are located at 19,49-506,50m/km2, and one spring data is not included in the analysis zone (fig 4.c). endogenous and exogenous factors influence the formation of topographic lineament patterns, stream, and slopes. tectonic activity or faults are two examples of endogenous processes. the greater the ld value in a region, the greater the endogenous activity, which affects the rock properties that are better at infiltrating or discharging water, and vice versa (sener et al., 2005; mogaji et al., 2011). the results of the collected field data show the association between the dd value and the infiltration rate value. dd can be associated with the features of the constituent rocks or the amount of surface runoff water value (dingman, 1978; sukristiyanti et al., 2018). a high dd value indicates that the rocks are often lenient and significantly better at storing water (dingman, 1978; pallard et al., 2009). a high dd value suggests a soil infiltration rate of 0.550cm/s on average. however, the average infiltration rate is 0.188cm/s at a low dd value (fig 4.c). this proves that a high dd value is better at infiltrating water. ld and dd values are often directly proportionate in lca. the larger the soil or rock's ld and dd values, the greater its capacity to recharge or discharge water. the association between ld and dd values at each observation point depends on the groundwater spring type. however, uncertainty in this interpretation can occur due to limited data on infiltration rate measurements in the field. more dense data can result in better information. fig 4. [a] slope map with lineament analysis of topography and rivers. the density value means the slope angle in degree units. [b] drainage density map with the distribution of the symbols of the infiltration rate test observation stations, denoted by the green box symbol. [c] lineament density map. the slopes of salak is a relatively plain slope compare to the slopes of pangrango. steep slopes can be controlled by erosion factors or subsidence due to water-resistant bedrock, which causes the soils on the surface to be eroded (liu et al., 2000). based on the previous discussion, it can be concluded that the groundwater depression zone influences the emergence of springs on the slopes of salak and pangrango due to topographic nugraha, b. et al./ jgeet vol 8 no 1/2023 31 collapse, which causes the contour of the groundwater table to be cut. in addition, the springs on the slopes of salak and pangrango are influenced by fracture zones that serve as pathways for the springs to discharge. the results of morphometric analysis and its correlation to the emergence of springs show a difference between the slopes of pangrango and salak. the slope factor causes differences in the ability to recharge, store, and discharge water. in this case, the pangrango slope is relatively better for recharged water than the salak slope. on the slopes of salak, the ld and slope values in the qvsl formation show the highest ld but lowest dd values. meanwhile, the ld and slope values in the qvsb formation show the lowest value but the highest dd value. on the pangrango slope, the qvpo formation has the highest ld, dd, and slope values, in contrast to the qvt formation, which has the lowest ld, dd, and slope values (table 1). therefore, the qvsb formations on the salak slopes and qvpo on the pangrango slopes are rock formations that can recharge or discharge better than other formations. the qvsb and qvpo formations may acts as aquifers. these results are consistent with the morphometric analysis and spring emergence that the qvsb and qvpo formations constitute the majority of rocks on both the salak and pangrango slopes. in addition, these results relate to several previous researchers regarding the conductivity values of volcanic rock, which have similarities with well-sorted sand well-sorted gravel with a value of 10-3-1cm/s and can act as an aquifer properly (fetter, 2014). table 2. thin section analysis results from several rock around lca. geology formation lithology (geological mapping) petrography result lithology sample code fragment (%) matrix (%) altered mineral (%) total porosity (%) feldspar amphibole pyroxene plagioclase volcanic glass plagioclase microlite chlorite iron oxide sericite clay mineral total altered mineral qvsb monomict breccia, polymict breccia, & breccia tuff gpsg31 7 0 0 0 35 0 2 5 3 0 10 50 lithic tuff gpsg28a 0 3 5 25 7 40 3 5 7 0 15 25 andesite gpsg28b 10 0 2 0 30 0 5 20 15 0 40 5 vitric tuff gpsg28c 10 0 0 0 10 0 15 5 5 0 25 5 lithic tuff gpsg44 15 0 0 0 5 0 5 10 5 0 20 25 lithic tuff gpsg30 10 0 0 0 40 0 15 5 20 0 40 5 vitric tuff qvt breccia tuff gpss-6 5 0 0 0 40 0 15 10 5 0 30 10 vitric tuff gpsg26 5 0 0 0 20 0 20 10 5 0 35 15 lithic tuff gpsg-2 5 0 0 0 15 0 10 5 5 0 20 20 lithic tuff gpsg29 5 0 0 0 10 0 10 10 5 0 25 10 lithic tuff gpsg11 3 0 0 0 10 0 7 10 3 0 20 35 lithic tuff qvpo monomict breccia, breccia tuff, coarse tuff gl-06 a 10 3 0 0 45 0 5 5 0 10 20 30 vitric tuff gl-02 5 0 0 0 60 0 2 3 0 0 5 25 vitric tuff gl-05 0 0 0 0 5 0 40 20 10 0 70 0 crystal tuff gl-04 5 2 3 0 40 0 5 8 2 5 20 30 vitric tuff gl-07 3 2 0 0 30 0 3 5 0 0 8 55 lithic tuff mal02 5 0 0 0 60 0 2 3 10 0 15 25 vitric tuff mal06 5 3 0 0 20 0 0 10 7 15 32 20 lithic tuff gpsg27 5 0 0 0 50 0 0 0 0 5 5 10 vitric tuff gpsg35 5 0 0 0 25 0 3 7 0 10 20 40 lithic tuff 4.2 volcanic geology and aquifer characteristics lca is comprised of four distinct geological formations. the salak slope is composed of qvsl formations formed of lava flows and andesitic basalt. lahar and tuffaceous breccias constitute the qvsb formation. the older lava deposits of the qvpo formation dominate the pangrango slope. on the downstream side of the pangrango slope, pumiceous tuff deposits comprise the qvt geological formation. the general stratigraphic correlation of the studied region indicates that the rocks on the salak slopes are younger than those on the pangrango slopes (effendi et al., 1998; agustin and bronto, 2019). on the slopes of salak volcano, the qvsb formation has two lithological characteristics (fig 5 and fig 7). in the north part of the qvsb formation on lca, polymict breccias predominate, while monomict breccias predominate in the southern part. according to the sorting between rock fragments and matrix, the qvsb formation's rock was deposited by a flow mechanism (natasia et al., 2018; mutaqin et al., 2019a, 2019b; alfadli et al., 2021). polymictic breccias (qvsb 1) are thought to have been deposited after monomict breccias (qvsb 2) (fig 8.a). plagioclase and feldspar minerals are easily distinguishable in the megascopic matrix fragments of qvsb 2 and qvsb 1 rocks hand specimens. the results of thin rock sections and petrographic investigation indicate that the porosity value range for polymict breccias in the qvsb formation is between 5 and 50%. in contrast, monomict breccias have a porosity percentage of 5%. (table 2). the identified alteration mineral at qvsb 2 depicts components are chlorite, iron oxide, and sericite, with a total percentage value range of 10% to 40%. (table 2). fig 5. geology observation station map. the red-dash line describes the geology cross section on each geology formation. the red circle describes the petrography analysis location. 32 nugraha, b. et al./ jgeet vol 8 no 1/2023 the greater vitric concentration is the result of comparatively low-temperature eruptive activity (ma et al., 2016; aulia and setiawan, 2019). qvsb 1 contain major minerals such as feldspar, amphibole, pyroxene, and plagioclase. this differs from qvsb 2, which are feldspardominated. volcanic geology research revealed that the qvsb formation consists of two rock groups. there are four springs with water flowing through fractures and rock pores on the qvsb 1 and qvsb 2 sections near gpsg 31, gpsg 30, gpsm 9, and gpsm 8 stations. stratigraphic analysis of qvsb is in the proximal – medial facies from 500-1462 masl (fig 8). fig 6. the results of rock thin section analysis on several samples from the salak slopes and pangrango slopes. gpsg 28 vitric tuff, gpsg 31 lithic tuff, mal 06 lithic tuff, and gl 04 vitric tuff. fig 7. lca geological map along with distribution of outcrop points and distribution of volcanic facies. the red and blue circles represent the rock thin section analysis results for porosity and alteration minerals. fig 8. cross section of outcrops correlation results. [a] qvsb formation. [b] qvt formation. [c] qvpo formation. line section on fig 5 nugraha, b. et al./ jgeet vol 8 no 1/2023 33 the southernmost slope of the lca to the north is composed of the qvt geological formation. outcrop investigations of the qvt formation reveal four distinct lithological characteristics: fine tuff, coarse tuff, lapilli tuff, and lapilli (fig 8. section e-f and section g-h). fine tuff, coarse tuff, lapilli tuff, and lapilli form a reverse grading pattern when examined in order (cas and wright, 1995). texture grading of rocks in the qvt formation permits various pyroclastic material deposition events or depositional events of the same material. however, different volcanic activity occurs during the same period (cas and wright, 1995). the results of field observations show that fine tuff (qvt 1) has a relatively diverse sorting and fragment size, which is the key to the flow deposition system (fisher and schmincke, 1984). likewise, coarse tuff, lapilli tuff, and lapilli (qvt 2). this was also proven by the petrographic analysis of thin sections, which showed the presence of alteration minerals around the rock pores, which were controlled by flow/hydrothermal processes. other analyzes show that chlorite, iron oxide, and sericite are found in rock tip incisions as alteration minerals. the percentage of the total value of alteration minerals in coarse tuff, lapilli tuff, and lapilli ranges from 25-35%, while in fine tuff, it is 20% (table 2). the percentage of rock porosity in the qvt geological formation ranges from 10-35%, with the dominance of rock fragments (lithic tuff) (fig 6). in addition, feldspar was determined to be the predominant mineral in the rock. analysis reveals that the qvt formation consists of two distinct rock groups. at the lido 63 and gps 29 observation stations, there are two springs in the qvt formation in the form of water seepage through the pores of the lapilli rock. qvt is located in the pangrango medial facies between elevations 499 and 650 masl. the qvpo formation comprises monomict breccias, fine tuff, and coarse tuff. monomict breccias and coarse tuff have diverse rock fragment sortations and sizes, one of the characteristics of flow deposit type (mutaqin et al., 2017). fine tuff at gpsg 27 has the same features as fine tuff at the qvt formation. according to its depositional position, the qvpo formation is younger geologically than the qvt formation. qvpo 2 is below qvpo 1 based on its position (fig 8. section g-h and section k-l). this indicates that qvpo 2 is older than qvpo 1. the composition of qvpo 1 is monomict breccias. the constituents of qvpo 2 are coarse tuff and fine tuff. qvpo 1 has a blackish-brown color and is different from monomict breccia on the salak slopes. the fragments of rock are composed of andesitic igneous rocks. the thickness of monomict breccia on qvpo 1 is between 1.5-35m. the results of thin section analysis show that the matrix tuff belongs to the types of lithic tuff, vitric tuff, and crystal tuff (fig 6 and 7) qvpo is generally composed of feldspar, amphibole, and pyroxene minerals. at station gl-05 the total alteration minerals are around 70%, consisting of chlorite, sericite, iron oxide, and clay minerals. the overall susceptibility of alteration minerals at qvpo 1 is between 5-70%, with a susceptible porosity percentage ranging from 0-35% qvpo 2 has a reddish brown fresh color. the rock fragments with various sorting and grain sizes show a flow pattern of pyroclastic deposition (cas and wright, 1995). the thickness of the qvpo 2 formation from field observations is only around ±0.4-1.5m. lithic tuff and vitric tuff are types of pyroclastic material in qvpo 2, resulting from rock-thin section analysis (fig 6). comparable to qvpo 1, qvpo 2 is formed of similar alteration minerals but in a different proportion. the total percentage of alteration minerals in qvpo 2 is 8-20%. the percentage value of vulnerable rock porosity is 10-55%. based on this value, the qvpo formation can recharge and discharge water; this is evidenced by the many springs that appear in the qvpo formation with a larger discharge than qvsb on the salak slopes. from the cross sections of the i-j and k-l line, a total of 7 springs overflowed into the monomict breccia and coarse tuff. qvpo enters the medial pangrango facies from a height of 499-2225masl (fig 8. section i-j and seciton k-l). 4.3 spring occurrence the results of the geological analysis in the qvsb geological formation demonstrate that water can flow with a flow system between rock pores or fractures, which generate aquifers. the springs in the qvsb formation are distributed over the proximal-medial facies based on the volcanic facies. the morphometric analysis reveals that the spring emergence pattern aligns with a lineament or a meeting of two separate lineaments. the relative emergence of springs at 10-35° is shown by slope analysis, with low dd values but high ld values. fractures and depressions characterized the appearance of springs in the qvsb formation, according to field observations from 9 spring locations. according to the geological analysis, breccias have a high potential to serve as aquifers. furthermore, the soil conditions on the salak slopes have a higher average infiltration rate than qvpo and qvt. spring occurrences in the qvsb formation are usually found in topographical collapse, which creates depression springs and is found in quite intense rock fractures (fig 9). according to additional evidence, the average spring discharge value on the salak slopes is 5.12l/s. according to the description, springs in the qvsb formation can properly discharge and infiltrate, causing more water to seep rather than runoff (endyana et al., 2016). this can result in a comparatively high number of springs but a lower surface runoff than the pangrango slopes. the qvt formation is included in the pangrango middle facies. coarse tuff and lapilli in the qvt formation have the potential to become aquifers because water can flow through the rock's inter-porous system (fig 9). in contrast to the qvsb and qvpo formations, there are no springs on the lineaments of the qvt formation. morphometrically, springs are found on slopes between 10-35°, with low dd values or in the zone between low and high dd values. in the ld analysis, most springs have low values, whereas only one has high ones. in general, five springs denote the type of depression or contact. however, several qvt formation springs have a relatively low discharge. a soil cover with a low infiltration rate may result in a limited infiltration process and a high surface runoff rate. comparing the qvt formation to the qvsb and qvpo formations, the qvt formation is the geological formation with the least potential of groundwater. in the qvpo formation, springs appear in breccias and lapilli in the pangrango medial facies. in general, springs appear directly on a lineament or at the intersection of two or more lineaments. in general, springs are located on slopes values >35°. the majority of spring types observed at eight stations were depression types. breccia has the potential to become an aquifer in the qvpo formation. the results of the geological interpretation indicate that monomictic breccias within the qvpo formation can 34 nugraha, b. et al./ jgeet vol 8 no 1/2023 function as effective aquifers. this is indicated by the average discharge rate of 4,083l/s from the observed springs. the occurrence of springs in the qvsb formation is common in the topographical collapse, which causes the groundwater table to be cut off and causes a depressiontype spring to appear. the relatively greater porosity percentage value compared to the qvsb formation makes it easy for water to overflow into springs within the breccia (endyana et al., 2016). in addition, the value of the water infiltration rate in the soil on the pangrango slopes is relatively smaller than on the salak slopes. based on dd, ld, and soil infiltration value, it can be synthesised that the amount of water that seeps, overflows, and flows on the surface will be the same depending on the amount of rainfall in qvsb formation. fig 9. groundwater spring on the field observation. the red box on the sm ldo-07 spring indicates the spring discharge at the rock's fracture and pores. spring discharge in rock pores is indicated by the yellow box on sm ldo-09 (breccia). 4.4 groundwater electrical conductivity (ec) the ec content correlates with the study area's elevation data of springs. the decreasing altitude indicates an increasing ec concentration. the spatial distribution of the ec value is determined by several variables, groundwater movement, water temperature, soil or rock dissolution characteristics, discharge magnitude, groundwater flow velocity, and the distance between the infiltration area and the discharge (dahaan et al., 2016). the plot of the ec value to the elevation on the scatter graph shows 3 different types of springs in the lca (fig 10). superficial springs occur due to the recharge process, and the discharge is relatively short (c. winter et al., 1998). ec value on the superficial spring <100µs/cm. superficial spring recharge processes can occur in local recharge systems. the mixed spring type is a spring that has varies ec values of 100 to 230µs/cm. this group of springs occurs because the flow process of recharge to discharge area is relatively short, with intensive water-rock interaction related to the porosity and permeability factor. in addition, when springs flow through aquifers and interact with rocks, surface water intercepts can occur, which causes this type to be categorized as a mix. the last type of spring is the alteration type. this type of spring has an ec value of >300µs/cm. the results of the geological analysis show that the rocks around this type of spring have a higher percentage of alteration minerals than the others (fig 10). when waterrock interactions occur, this can cause the enrichment of minerals in the water, which causes the ec value to increase. in addition, factors that can affect the high ec content are the relatively long process of groundwater flow in the aquifer or the influence of deeper water flows (dahaan et al., 2016). this relates to the fact that the qvsb formation contains three different kinds of springs, while the qvt formation contains two types of springs (superficial and mix), and the qvpo formation contains three distinct types of springs as well (fig 10). fig 10. scatterplot of ec and elevation values from spring data on salak and pangrango slopes. 4.5 discussion the first step in the investigation was to analyze the geological setting using outcrop data, thin rock sections, and morphometric analysis. developing a geological framework is critical to comprehend the process and occurrence of groundwater or its aquifer features (hadian et al., 2017). even though it cannot determine the condition of the rocks beneath the surface, this study is essential. however, the methods employed yielded satisfactory results regarding the groundwater system in the research area. spring occurrence is closely related to geological control and the physical properties of its elements. as a result, changes in the geological and physical features of the constituents might result in a variety of spring types (falah et al., 2017; ghimire et al., 2019). the study's application of analytical methods and techniques revealed some essential basic information. the pattern of spring occurrence on the salak and pangrango slopes differs. this difference stems from the lithological composition of each slope (effendi et al., 1998; mutaqin et al., 2017, 2019a; alfadli et al., 2021). nugraha, b. et al./ jgeet vol 8 no 1/2023 35 ld, dd, and slope are morphological features related to the characteristics of the material or the constituent rocks. a high ld value indicates a higher fracture zone than a low value (mogaji et al., 2011). high dd values indicate greater surface runoff rates and are formed of rocks that get saturation rapidly (dingman, 1978; moglen et al., 1998; pallard et al., 2009). in addition to causing higher surface runoff flows, high dd values represent the permeability or porosity values of the rock, which are related to the rock saturation level. a high slope value illustrates a higher surface runoff velocity compared to areas with relatively low values (altın and altın, 2011; anitha, 2020). ld, dd, and slope are closely related to the rock's porosity and permeability. in general, porosity and permeability have a positive correlation; an increase in porosity can increase permeability (šperl and trckova, 2008). this physical characteristic is important, because it is related to the process of infiltration or discharge of water into springs. in addition, ec is another important parameter in studying the process and occurrence of springs (dahaan et al., 2016). the salak and pangrango slopes contain aquifer rocks composed of pyroclastic rock. field observations, morphometric analysis, and rock-thin section analysis prove this. the origin and occurrence of springs on the slopes of pangrango and salak have distinct patterns and characteristics. the salak pattern consists of aquifers formed of polymict and monomict breccias with porosities ranging from 5-50%. in general, springs are found with fractures and depressions where the water flows through rock fractures and the spaces between them. the alteration of rock on the slopes of salak causes a higher ec content during the water-rock interaction process (ludwig et al., 2012). generally, springs are found on steep slopes formed by topographical collapse. high ld and dd values followed by a high slope value indicate a relatively small spring ec value (superficial spring type). a high ld value, a low dd value, and a downward slope show a relatively small – moderate ec value (mix spring type). a low ld value and a high dd value at a low slope value indicate a rather large spring ec value due to the interaction of water with altered rock (alteration spring type) (fig 11). fig 11. [a] distribution of springs and cross-sectional lines between springs. [b] cross-section of salak 1 with variations in the values of dd, ld, slope, and soil infiltration in a bar graph. [c] cross section of salak 2 with the same description as picture b. [c] pangrango crosssection with the same description as pictures b and c. the pangrango pattern comprises aquifers consisting of monomict breccias, lapilli, and coarse lapilli. what differentiates the features of the aquifers on the pangrango slopes from those on the salak slopes is the significantly different discharge value. typically, the porosity ranges from 0 to 55%. on the slopes of pangrango, most springs are depressions in which water flows through the spaces between grain fragments. most springs on the pangrango slope are located on the river-wall body with a high slope value due to erosion or topographical collapse. high ld and dd values followed by low slope values indicate relatively small-medium ec values (mix spring type). a high ld value but a low dd and slope value indicate a relatively small spring ec value (superficial spring type). low ld, dd, and slope values indicate large ec values (alteration spring type) (fig 11). both slope and dd demonstrate the inverse function. however, a low slope value suggests an enormous dd. the ec concentration is proportional to the potential water flow velocity, more significant when the slope value is lower. the decreased water transmittance in the aquifer results in more intense water-rock interactions and a high saturation state with an increasing ec concentration. therefore, high ec values are typically associated with high dd values, and vice versa (fig 4.b). high dd values indicate rock layers with relatively low permeability, whereas low dd values indicate rock layers with relatively high permeability. 17 spring, or around 73%, have low-to-moderate dd levels or transition from high to medium or low dd values. thus, the presence of springs in volcanic geological settings on the salak and pangrango slopes is governed by weathering and rock erosion processes, primary genetics, and secondary 36 nugraha, b. et al./ jgeet vol 8 no 1/2023 rock development, which generates varying k values along the slopes. the geological and morphometric investigation that has been conducted indicates that the pangrango slope has greater potential than the salak slope. different chemical conditions might result from each slope's specific physical characteristics—the proximity of the salak and pangrango volcanic facies in the middle influences the potential of water mixing. the findings of this study enhance knowledge of the groundwater system from the perspective of geological control in a region over the aquifer's features and spring. 5. conclusions the implemented method generates positive findings to perform a geological study to comprehend the groundwater system in the research region. the classification of rock types based on the results of mapping and analysis of thin rock sections elucidates the state of the rock and its properties, particularly for identifying the condition of aquifer rock. in addition, the use of remote sensing in the conducted morphometric analysis is associated with the presence of springs in the research area. understanding the geological setting and its relationship to the occurrence of groundwater springs in the study area is one of the most important outcomes of the analysis results. the geological analysis reveals six distinct rock properties in three geological formations. some area show geology regions with an alteration mineral content greater than 30%. in addition, certain regions have a porosity value >30%, as determined by examining thin rock sections. in the qvsb formation, polymict breccias serve as suitable aquifers; in the qvt formation, lapilli and coarse tuff; and in the qvpo formation, monomictic breccias. the mineral concentration of groundwater is correlated with variations in rock properties. based on the results of the geological and morphometric investigation, six possible chemical properties of groundwater can be identified. in the meantime, the findings of the ec value study reveal three types of springs with distinct flow systems (superficial, mix, and alteration types). this spring discharges through a network of inter-porous rocks and fractures. based on the magnitude of the discharge value, breccia has a greater capacity to discharge water than coarse tuff and lapilli. in displaying the distribution of aquifers, it is impossible to describe the subsurface geometry. incorporating geophysical survey data can provide a more comprehensive depiction of subsurface conditions. verifying some of the results with groundwater chemical and isotope data can provide a strong foundation for reconstructing the occurrence of springs and the conceptual hydrogeological system in the studied area. acknowledgements this research is the result of a joint initiative on the part of danone, pt. tirta investama, sorbonne university, and universitas padjadjaran. both danone and pt. tirta investama provided financial assistance and support for this study. the author would like to express their gratitude to the indonesian meteorology and geophysics agency for granting permission to use secondary climate data, as well as to all parties who have contributed to the research. in addition, the authors would like to express their gratitude to the co-authors and reviewers of this scientific article for their contributions and recommendations that led to the substantial edits that were made. references agustin, f., bronto, s., 2019. volkanostratigrafi inderaan jauh kompleks gunungapi gede dan sekitarnya, jawa barat, indonesia. j. geol. dan sumberd. miner. 20, 9. https://doi.org/10.33332/jgsm.2019.v20.1.9-16 alfadli, m.k., mardiana, u., natasia, n., mohammad, f., mutaqin, d.z., 2021. resistivity data modeling for subsurface volcanostratigraphy construction of cibadak sub-watershed, bogor, west java, indonesia. j. geosci. eng. environ. technol. 6, 74–80. https://doi.org/10.25299/jgeet.2021.6.2.2274 alfadli, m.k., natasia, n., 2017. geoelectricity data analysis for identification the aquifer configuration in 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and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 8 no 1 2023 rachman et al./ jgeet vol 8 no 1/2023 1 research article study of current patterns in tanjung pasir banten for supporting the ncicd seawall development plan reno arief rachman1,2*, haryo dwito armono1, dinar catur istiyanto2, khusnul setia wardani2, hanah khoirunnisa2, reni wijayanti3 1 departement of ocean engineering, faculty of marine technology, sepuluh nopember institute of technology, sukolilo, 60116 surabaya, indonesia. 2 research center for hydrodynamics technology, national research and innovation agency, sukolilo, 60112 surabaya, indonesia. 3 research centre for oceanography, national research and innovation agency, pasir putih street, east ancol 14430, jakarta, indonesia * corresponding author : reno001@brin.go.id tel.:+6285-22222-333-2; fax:+6285-22222-333-2 received: oct 27, 2022; accepted: mar 17, 2023. doi: 10.25299/jgeet.2023.8.1.10801 abstract hydrodynamic (hd) numerical modeling around tanjung pasir waters was carried out using mike 21 hd flexible mesh software; this modeling was carried out to obtain current pattern conditions (current speed and direction) during the west and east monsoons; this activity was carried out to support ncicd's sea wall construction plan. in addition, the results that will be obtained in this modeling are the conditions of the speed and direction of the current in various tidal conditions during spring and neap. the data used in this modeling include wind speed and direction from european centre for medium-range weather forecast (ecmwf). based on the research, the validation value of naotide tidal data for field tidal data is 93.8%. the hd mike 21 surface elevation modeling results on field survey data have a validation value of 93.4%. extract points 4 and 5 which are the northernmost, have the highest current velocity values compared to the other points. in addition, when conditions are approaching high tide, both spring and neap conditions, the value of the current velocity has the highest value. keywords: sea wall, numerical modelling, tidal condition, current condition 1. introduction the national capital integrated coastal development program (ncicd) is part of the national strategic program in the 2020-2024 national medium-term development plan (rpjm). the program is included in the main strategic priority project number 27, the coastal security 5 urban pantura java. conceptually, the ncicd program was implemented to anticipate several prominent issues, such as the threat of flooding, land subsidence, little raw water, and the arrangement of transportation and settlement systems. several further studies that need to be carried out immediately include a typical design study and a study on detail engineering design for the construction of dams, as well as other follow-up studies that can support the implementation of the ptpin program. one of the following steps is planning to construct an offshore reservoir (wlp), which is proposed as a holistic and sustainable solution to the problems faced in jakarta bay (wibowo et al., 2022a). in the wlp concept, it is planned to build an embankment with a length of ± 50.6 km at a depth of -20 m stretching from muara cisadane (banten province) to muara gembong (west java province). the dam will create a reliable flood defense system, storage ponds, and raw water treatment, and also develop coastal areas in jakarta bay. the construction is planned to start at the mouth of the cisadane river as a wlp pilot plant. this development requires planning and study before its implementation to determine the impact and influence of the structural construction. one of the studies needed is a current study in the planned area of the reservoir construction. this study was carried out with numerical modeling to determine the current conditions. this coastal area is a very dynamic area with various interconnected ecosystems. changes in the coastline are one form of dynamics of the coastal region that occurs continuously. shoreline changes that occur in coastal areas are in the form of erosion of coastal bodies (abrasion) and the addition of coastal bodies (sedimentation or accretion) (suhana, 2015). these processes occur due to the movement of sediments, currents, and waves that interact with the coastal area directly. in addition to these factors, shoreline changes can occur due to anthropogenic factors, such as human activities in the vicinity (wibowo, 2012). important hydrooceanographic parameters include bathymetry, tides, currents, waves, floating sediments, and bottom sediments. bathymetry is the depth of the sea expressed in depth figures or depth contours measured against a specific vertical datum. the bathymetry condition is temporary because the sea sand extraction location changes continuously. tides are fluctuations in sea level due to the attraction of objects in the sky, especially the sun and moon, to seawater masses on earth (gaol et al., 2017). knowledge of tides (highest and lowest water level elevation) is critical in planning coastal and harbor buildings (triatmodjo, 2012, 1999). tides greatly affect human activities living on the coast and are needed for various aspects such as shipping, port layout, pollutant distribution, fisheries development, etc. (yona et al., 2017). ocean currents are the movement of seawater transportation. ocean currents are mainly affected by wind movement and heat differences in the oceans. ocean currents are more effective as a medium for spreading and diluting pollutants that enter the marine environment (mukhtasor, 2006). in addition, currents are also strongly influenced by tides. tidal currents play an essential role as a carrier of nutrients and plankton; they also play an http://journal.uir.ac.id/index.php/jgeet 2 rachman et al./ jgeet vol 8 no 1/2023 essential role in diluting and flushing waste that reaches the sea (mukhtasor, 2006). floating sediment is all solid substances or particles suspended in water in the form of living (biotic) and inanimate (abiotic) components. floating sediment is the residue of the total solids retained by a sieve of 2 m or more in size (lukisworo, 2011). in the west season in the cisadane river area, the distribution pattern of floating sediment originating from the cisadane river estuary is very visible; on the contrary, for the east season for the 1-year simulation, the dominant concentration is around 0.12 kg/m3 and the highest is 0.26 km/m3 (wibowo et al., 2022b). during pre-reclamation, the current velocity in the southern part of the bay ranged from 0 to 0.94 m/s, while after reclamation, the current velocity decreased to 0 to 0.88 m/s (aprilia and pratomo, 2017). one of the reasons for the decrease in the average current velocity after reclamation is the length of the current flow that must be traversed following the shape of the reclamation islands so that the current experiences a decrease in velocity energy (aprilia, 2017). with the holding of the reclamation project in jakarta bay, the main problem is the decrease in the overall flow velocity in the research area. however, there was an increase in current in several locations around the reclamation island. procurement of reclamation also causes an increase in the bottom sediment of the waters, leading to an increase in the silting process in the research area. the hydrodynamic modeling around the thousand islands has been carried out by khoirunnisa et al. (2021). based on the modeling results, the validation value between the tidal driver model (tmd) data and mike 21 hd is 92 %. thermal dispersion modeling has also been carried out around the muara karang pltu using three-dimensional mike 3 flow model flexible mesh (khoirunnisa et al., 2021b). based on research conducted by saputra (2018), the current velocity in the master plan condition is smaller than the post-reclamation condition; this is due to the deflection of the current in the reclamation island (saputra, 2018). based on the hydrodynamic modeling that has been carried out by prihantono et al. (2018), during the west season, the longshore currents in tanjung pontang dominantly move eastward, while during the east season, some of the longshore currents in tanjung pontang move eastward, and some move towards the east and some part move south to banten bay (prihantono et al., 2018). this study aims to determine the condition of the current pattern around the cisadane river during the existing conditions using mike 21 flexible mesh (fm) software for hydrodynamics (hd) and spectral wave (sw) modules (mike 21 dhi, 2017). as input data in this study, secondary data from several source providers and the results of models and field data were used from 30 october to 14 november 2021 (btipdp, 2021). current modeling and sediment distribution is very important as a step to determine the impact of a natural phenomenon (such as seasonal changes), as well as anthropogenic activities (such as the addition of buildings or land) on the condition of the aquatic environment (nugraha, 2022). until now, studies on currents at the research location planned to build a wlp between the mouth of the cisadane river and the waters of tanjung pasir, tangerang, banten (figure 1) have not been widely carried out. therefore, a preliminary study of currents in tanjung pasir waters was carried out by considering the input discharge value in the cisadane river. need an understanding of the dynamics hydrooceanographic conditions in these waters. the dynamics of these waters can be known by recognize the oceanographic parameters of the waters meaning (kumajas et al., 2007). fig 1. research location around tanjung pasir waters, banten (google earth, 2022). 2. data and methods 2.1 material and data source the data used in the current modeling around the cisadane river are primary data obtained through field surveys conducted on 30 october – 14 november 2021 (btipdp, 2021) and secondary data. the primary data used is bathymetric data around the cisadane river, which results from a field survey (btipdp, 2021). the data is then interpolated using the national bathymetry (batnas) data with a spatial interval of 180 m x 180 m (big, 2021). table 1. material and data source data source and detail bathymetry field survey prth-brin november 2021 and batnas v1.5 spacing grid 180 m x 180 m wind data ecmwf : era 5 (coordinate 5.5 s ; 106.5 e) time interval = 3 hours (2021-2022) (https://cds.climate.copernicus.eu/ cdsapp#!/dataset/reanalysis-era5-singlelevels?tab=eqc) coastline data field survey prth-brin november 2021 tidal field survey prth-brin november 2021 and naotide (https://www.miz.nao.ac.jp/ staffs/nao99/index_en.htm cisadane river discharge term report of bappenas and itb 2021 in addition, the surface elevation of the hydrodynamic model was validated against tidal data from the field survey using the normalization root mean square deviation (nrmsd) equation. the secondary data used in this hd-sw modeling include data on wind speed and direction, height, and wave period for one year in 2021 with a time interval of 3 hours and a resolution of 0.5 o x 0.5 o. in addition, the secondary data used in this modeling is tidal data with a data length of one year extracted through the naotide model (padman and erofeeva, 2005), which has 16 constituents and has been developed by the japan national astronomical observatory (matsumoto et al., 2000; miwa and ikeno, 2008; saputra, 2018; sato et al., 2001). material and data source are presented in table 1. 2.2 method 2.2.1 stage of study the stages of a research activities start from measurment in the field to modeling of current patterns (figure 2). (https:/cds.climate.copernicus.eu/%20cdsapp#!/dataset/reanalysis-era5-single-levels?tab=eqc (https:/cds.climate.copernicus.eu/%20cdsapp#!/dataset/reanalysis-era5-single-levels?tab=eqc (https:/cds.climate.copernicus.eu/%20cdsapp#!/dataset/reanalysis-era5-single-levels?tab=eqc https://www.miz.nao.ac.jp/ rachman et al./ jgeet vol 8 no 1/2023 3 fig 2. flowchart of stage activities 2.2.2 model description the hd – sw modeling uses the dhi mike zero – mike 21 hd module, licensed software realease at 2011 from dhi denmark. models and methods descriptions are presented in table 2 table 2. model and method description models method description hd module from mike 21 3645 flexible mesh time simulation from january 1 to december 31, 2021, with a timestep of 300 seconds the number of mesh generated is 10000 mesh with a domain area of 29875 x 44715 m (figure 3) the essential roughness used in this modeling is 42.3 m1/3 flexible mesh software with a mesh count of 3645 (mike 21 dhi, 2019). the hd validation modeling was carried out for 20 days from october 30, 2021, to november 19, 2021, with a timestep of 15000 and an interval of 120 seconds. in addition, the essential roughness used in this modeling is 42.3 m1/3. the data used in this modeling are wind speed, wind direction from ecmwf (mike 21 dhi, 2017; molteni et al., 1996). other data used in this modeling is data on the average discharge of the cisadane river and naotide tides. the next step is to prepare a setup file for hydrodynamic modeling using mike 21 software module mike 21/3 integrated models, coupled model fm (.mfm) with modeling time simulation from january 1 to december 31, 2021, with a timestep of 300 seconds (mike 21 dhi, 2019). mesh domain modeling for the waters around tanjung pasir. in this modeling, the number of mesh generated is 10000 mesh with a domain area of 29875 x 44715 m (figure 3). fig 3. interpolation results of secondary bathymetry data and field data around tanjung pasir waters. 3. results and discussion 3.1 tidal data validation harmonic analysis of the recorded data is carried out to obtain important water level elevation values such as highest high water level, mean higher high water, mean lower high water, mean higher low water, mean lower low water, and lowest low water level, the results of the analysis are tidal constants tides used in calculating the critical elevations of tides in rivers (wiguna et al., 2020). figure 4 shows a comparison graph between tidal model data and field collection data. based on the results of this comparison, the error value of each tidal model data on the field data is shown in table 3., which is 6.2 %, while the most significant error is obtained in the mike 21 model data is 12.6 %. therefore, the tidal model data from naotide will then be used as input data for hd-sw modeling, both existing and design conditions. table 3. nrmsd value between tidal model data and field survey data no sumber nrsmd (%) 1 topex 7.2 2 tmd 9.2 3 mike21 12.6 4 naotide 6.2 based on figure 4 (matsumoto, 2022), the validation between the naotide tidal model and the 2021 field survey around the mouth of the cisadane river is 93.8 %. in addition, figure 5 shows the validation results between the surface elevation values of the mike 21 model and field survey data. based on the figure, the validation value is 93.4 %, and the error is 6.6 %. 4 rachman et al./ jgeet vol 8 no 1/2023 fig 4. the validation graph between tidal model data (topex, tmd, mike 21, and naotide) contains field survey data in 2021. fig 5. the validation results between the surface elevation values of the mike 21 model and field survey data. 3.2 ocean current data validation currents in the river channel are strongly influenced by the ebb and flow of seawater, where when the tide goes upstream and vice versa when it recedes, the current direction goes downstream (wiguna et al., 2020). validation of ocean currents data from hydrodynamic modeling with mike 21 was also carried out on field ocean currents data. table 4 shows the current field data collection coordinates around tanjung pasir waters. table 4. coordinate points of field flow data collection with adcp bottom mounted longitude (e) latitude (s) adcp 106.631 -5.988 l 106.669 -6.010 ul1 106.668 -6.000 ul2 figure 6 shows the average value of the current velocity at the adcp l point based on the results of the mike 21 model and field data collection. figure 7 compares the direction and velocity of the current mike 21 hd modeling results with the field results at the adcp l point. based on this figure, the difference between the current velocity values from the model results and the field values is 0.03 m/s. in addition, the dominant current direction indicates eastward for both the current velocity of the hydrodynamic model and the results of field data collection. fig 6. the average value of the current velocity at the adcp l point based on the results of the mike 21 model and field data collection. fig 7. comparison between current rose from field data collection and mike 21 model results. figure 8 shows the condition of comparing the speed and direction of the current in a time series between the field data and the data from the mike 21 hydrodynamic modeling. in the figure, a black box shows similar conditions between the field data and the data from the mike 21 model. fig 8. comparison of the speed and direction of the current at the adcp l point between the field data and the data from the mike 21 model 3.3 seasonal conditions of current speed and direction at each point based on the comparison and calculation of the deviation between the modeling results for one year and naotide, validation was carried out by calculating the nrmsd (normalized root mean square deviation) value. the sample data calculation was carried out at the northern point of the wlp (-5.9596 north latitude and 106.59 east longitude), and the nrmsd value was 0.26 %. figure 9 is a surface elevation overlay image from mike 21 hd modeling with naotide in june 2021 (1-month sample). fig 9. overlay results between the surface elevation of the mike 21 model and the tides of naotide 1 month (1 june 2021-30 june 2021) figure 10 below shows the location of the modeling carried out, which is around the waters of tanjung pasir, banten, with a small point of tidal data collection for one month (1 30 november 2021) depicted as the location of the tanjung pasir tpi. the following is the location of the tanjung pasir tpi 684801.00 m e, 9334365.00 m (utm zone 48s). in addition, the figure also illustrates the area of the hydrodynamic modeling along with the points that will be the focus of data extraction. among them are 5 points, namely the adcp point, the estuary point, the north point of the wlp, the west point of the wlp, and the top east point of the wlp, with location details contained in the description of table 5. data lapangan model mike 21 mike model field data field data rachman et al./ jgeet vol 8 no 1/2023 5 fig 10. location of tidal field data collection at tpi tanjung pasir station (above) and location of extract points for analysis of hydrodynamic modeling and spectral wave existing scenarios (bottom) table 5. extract point location in muara cisadane existing scenario point easting northing information 1 684717.96 9335407.97 adcp 2 681500 9336800 estuary 3 673000 9336000 western wlp 2022 4 676000 9341000 northern wlp 2022 5 685000 9340000 north eastern wlp 2022 3.4 analysis of the direction and magnitude of currents in the west and east monsoons one of the outputs of hydrodynamic modeling is current velocity. this study will analyze the current speed seasonally, namely the west and east monsoons at each observation point (nugraha, 2022). based on figures 11 and 12 below, it can be seen the tidal pattern that occurred for one year around the cisadane estuary. the following is a flowing plot from hydrodynamic modeling, sampled during the west and east monsoons at the five observation points. 3.4.1 point 1 adcp at point 1 or at the adcp point location, it can be seen from figure 11 that in the western season (january-february 2021), the dominant surface current moves eastward, while in the east season (june-august 2021), the predominant surface current moves westward. then the velocity distribution in the west season is dominated by currents with a magnitude of 0.10-0.20 m/s of 63.3 %, while in the east monsoon is dominated by currents with a volume of 0.00-0.10 m/s of 58.2 %. fig 11. the velocity of the west monsoon (left) and east monsoon (right) at point 1 (adcp) 3.4.2 point 2 estuary at point 2, or a location near the estuary, it can be seen from figure 12 that the surface currents are equally present in the western season (january-february 2021) and the eastern season (june-august 2021), dominant moving to the northwest. then for the distribution of the velocity in the west monsoon, it is dominated by currents with a magnitude of 0.10-0.20 m/s of 6 rachman et al./ jgeet vol 8 no 1/2023 70.5 %, while in the east monsoon, it is dominated by currents with a volume of 0.00-0.10 m/s of 58.4 %. fig 12. the velocity of the west monsoon (left) and east monsoon (right) at point 2 (estuary) 3.4.3 point 3 western wlp at point 3, or at the western location of the wlp, it can be seen from figure 13 that in the west monsoon (januaryfebruary 2021) and the east monsoon (june-august 2021), the surface currents are equally dominant moving to the northwest. then the velocity distribution in the west season is dominated by currents with a magnitude of 0.10-0.20 m/s of 65.3 %, while in the east monsoon is dominated by currents with a volume of 0.10-0.20 m/s of 61.3 %. fig 13. the velocity of the west monsoon (left) and east monsoon (right) at point 3 (western wlp) 3.4.4 point 4 northern wlp at point 4, or the northern location of the wlp, it can be seen from figure 14 that in the west monsoon (january-february 2021) and the east monsoon (june-august 2021), the surface currents are equally dominant moving to the northwest and slightly to the southeast. . then for the distribution of the velocity in the west season is dominated by currents with a magnitude of 0.10-0.20 m/s of 46.6 % while in the east monsoon is dominated by currents with a volume of 0.10-0.20 m/s of 44.3 %. at the north point of the wlp, both in the west and east monsoons, the currents are more significant than at points 1, 2, and 3. this is because the north point of the wlp is directly adjacent to the high seas, thus affecting the value of a more significant current velocity. fig 14. the velocity of the west monsoon (left) and east monsoon (right) at point 4 (northern wlp) 3.4.5 point 5 north eastern wlp at point 5 or in the upper eastern location of the wlp, it can be seen from figure 15 that in the west monsoon (januaryfebruary 2021), the dominant surface current moves to the northwest, while in the east monsoon (june-august 2021), the predominant character current activities to the southeast. . only at this point 5, the pattern of the dominant current direction is seen according to the influence of the wind direction. when the west monsoon moves from asia to australia, the current also moves to the southeast. while in the east monsoon, the wind shifts from australia to asia, causing the current to move to the southwest. at points 1, 2, and 3, this pattern does not appear to be possible because the location of the point is closer to the mainland and the coastal influence is still dominant; at point 4, the effect of the coastal area has begun to decrease along with its location which is further away from the mainland/estuarine. then the velocity distribution in the west season is dominated by currents with a magnitude of 0.10-0.20 m/s of 35.6 %, while in the east monsoon is dominated by currents with a volume of 0.10-0.20 m/s of 36.1 %. at the north point of this wlp, in the west and east seasons, the currents are more significant than at points 1, 2, 3, and 4. this is because the north point of the wlp is directly adjacent to the high seas, thus affecting the value of the current velocity, which is more significant. fig 15. the velocity of the west monsoon (left) and east monsoon (right) at point 5 (north eastern wlp) 3.5 analysis of existing current velocity and elevation conditions in spring and neap conditions analysis of surface current velocity conditions was carried out on four conditions, namely at high tide, high tide, low tide, and low tide, respectively, during spring and neap. the following is a sample that will be taken for analysis for these conditions shown in table 6. table 6. extract point location in muara cisadane existing scenario condition spring neap towards flood 21-23 jun 2021 5-8 mar 2021 flood 24-26 jun 2021 9-11 mar 2021 towards ebb 28-30 jun 2021 12-14 mar 2021 ebb 2-3 jul 2021 15-17 mar 2021 3.5.1 towards flood based on figure 16 above, it can be seen that in conditions leading to high tide according to the data above, in spring conditions, the current dominant moves east to the southeast, while in neap situations, the current dominant moves west to northwest. in spring conditions, statistical results from stations 1 to 5 show the average current is 0.095 m/s with a maximum speed of 0.35 m/s. while in neap conditions, the statistical results from stations 1 to 5 show the average current is 0.09 m/s with a top speed of 0.35 m/s. rachman et al./ jgeet vol 8 no 1/2023 7 fig 16. surface current velocity when toward flood in spring (left) and neap (right) conditions 3.5.2 flood based on figure 17, the current dominant moves east to southeast at high tide conditions, according to the sample data above, in spring and neap conditions. in spring conditions, statistical results from stations 1 to 5 show the average current is 0.107 m/s with a maximum speed of 0.37 m/s. while in neap conditions, statistical results from stations 1 to 5 show the average current is 0.87 m/s with a maximum speed of 0.26 m/s. fig 17. surface current velocity when flood in spring (left) and neap (right) conditions 3.5.3 towards ebb based on figure 18, it can be seen that at low tide conditions, according to the sample data above, in spring and neap conditions, the dominant current moves northwest to north. in spring conditions, statistical results from stations 1 to 5 show the average current is 0.084 m/s with a maximum speed of 0.33 m/s. while in neap conditions, statistical results from stations 1 to 5 show the average current is 0.071 m/s with a maximum speed of 0.23 m/s. fig 18. surface current velocity when toward ebb in spring (left) and neap (right) conditions 3.5.4 ebb based on figure 19, it can be seen that at low tide conditions, according to the sample data above, in spring and neap conditions, the dominant current moves northwest to north. in spring conditions, statistical results from stations 1 to 5 show the average current is 0.079 m/s with a maximum speed of 0.26 m/s. while in neap conditions, statistical results from stations 1 to 5 show the average current is 0.071 m/s with a maximum speed of 0.26 m/s. 8 rachman et al./ jgeet vol 8 no 1/2023 fig 19. surface current velocity when ebb in spring (left) and neap (right) conditions the results of these statistics can be seen in tables 7 and 8 below: table 7. statistics of average, maximum and minimum flow velocity in spring conditions from stations 1,2,3,4,5 spring average speed (m/s) maximum speed (m/s) toward flood 0.095 0.35 flood 0.107 0.37 toward ebb 0.084 0.33 ebb 0.079 0.26 table 8. statistics of average, maximum and minimum flow velocity in neap conditions from stations 1,2,3,4,5 neap average speed (m/s) maximum speed (m/s) toward flood 0.09 0.35 flood 0.088 0.26 toward ebb 0.071 0.23 ebb 0.071 0.27 on the long island of the panjang islands, east of the waters of tanjung pasir, obtained the following results: in the spring conditions, the difference between the highest and lowest current velocities are pretty large (0.018-0.199 m/s); on the other hand when the tides are common in the neap condition (0.008-0.144 m/s), (khoirunnisa et al., 2021a), these results are almost the same as the results of this study (tables 7 and 8). 4. conclusion the hd mike 21 modeling output is the speed and direction of the current in various tidal conditions during spring and neap. the data used in this modeling include wind speed and direction, wave height, wave period, and wave direction. based on the research that has been done, the validation value of naotide tidal data on tidal field data is 93.8 %. hd mike 21 surface elevation modeling results on field survey data have a validation value of 93.4%. extract points 4 and 5 which are the northernmost, have the highest current velocity values compared to the other points. in addition, when conditions are approaching high tide, both spring and neap conditions, the value of the current velocity has the highest value. acknowledgement thank you to the management and staff of the research centre for hydrodynamics technologybrin, especially to members of the prth-brin topo-hydro survey laboratory and members of the prth-brin coastal dynamics numerical modeling laboratory, as well as to all project implementers. assessment and application of technology in the maritime sector-innovation of port technology and coastal dynamics for fiscal year 2021. also, thanks to the degree by research (dbr)-brin program and the departement of ocean engineering, faculty of marine technology, sepuluh nopember institute of technology (its). references aprilia, e., 2017. 3-dimensional hydrodynamic modeling of pre and post-reclamation sedimentation distribution patterns in jakarta bay. bachelor thesis. department of geomatics engineering, faculty of civil engineering and planning, sepuluh nopember institute of technology. aprilia, e., pratomo, d.g., 2017. 3-dimensional hydrodynamic modeling of preand post-reclamation sedimentation distribution patterns in jakarta bay reklamasi teluk jakarta. jurnal teknik its 6, 2337– 3520. big, 2021. seamless digital elevation model (dem) and batnas (batimetri nasional) of tanjung pasir waters. batnas. btipdp, 2021. bathymetry and tidal survey report of cisadane estuary. agency for the assessment and application of technology. jogjakarta. gaol, a.s.l., diansyah, g., purwiyanto, a.i.s., 2017. analysis of seawater quality in the southern bangka strait. maspari journal 9, 9–16. google earth, 2022. google earth : maps of tanjung pasir waters, banten. google earth. khoirunnisa, h., wibowo, m., gumbira, g., hendriyono, w., karima, s., 2021a. numerical modeling of the effects of reclamation and proposed infrastructures on thermal dispersion of power plant wastewater at pltgu muara karang, jakarta bay, in: iop conference series: earth and environmental science. iop publishing ltd. https://doi.org/10.1088/1755-1315/832/1/012043 khoirunnisa, h., wibowo, m., hendriyono, w., wardani, k.s., 2021b. hydrodynamic and boussinesq wave modeling for the n219 amphibious aircraft seaplane dock rachman et al./ jgeet vol 8 no 1/2023 9 development plan in panjang island. majalah ilmiah pengkajian industri 15, 87–89. kumajas, m., kumaat, j.c., moninhkey, a., 2007. study on hydro-oceanographic and bathymetry conditions of bajo–popareng beach, south minahasa regency. jurnal geografi dan pembangunan wilayah. manado state university iii. lukisworo, b., 2011. how to test total suspended solids (tss) gravimetrically, in: cara uji padatan tersuspensi total (total suspended solid, tss) secara gravimetri. matsumoto, k., 2022. tidal prediction system nao99b. (accessed jan 2022). nao.99b tidal prediction system. matsumoto, k., takanezawa, t., ooe, m., 2000. ocean tide models developed by assimilating topex/poseidon altimeter data into hydrodynamical model:a global model and a regional model around japan. j oceanogr 56, 567–581. mike 21 dhi, 2019. mike 21 flow model hydrodynamic module user guide. dhi. mike 21 dhi, 2017. mike 21 spectral waves fm spectral wave module user guide. dhi. mike 21 dhi, 2017. mike 21 hydrodynamic module. dhi. miwa, h.;, ikeno, h., 2008. a setup method of tide level variations at open boundary in estuaries for numerical tidal flow analysis, in: iche 2008. proceedings of the 8th international conference on hydro-science and engineering. molteni, f., buizza, r., palmer, t.n., petroliagis, t., 1996. the ecmwf ensemble prediction system: methodology and validation. quarterly journal of the royal meteorologial society 122 (529), 73–119. mukhtasor, 2006. coastal and marine pollution. pt pradnya paramita jalan bunga 8-8a. jakarta., jakarta. nugraha, t., 2022. hydrodynamic model and cohesive sediment transport in jakarta bay coastal system. doctoral dissertation. institut pertanian bogor, bogor. padman, l., erofeeva, s., 2005. tide model driver (tmd) manual, in: tide model driver (tmd manual). earth and space research. https://www.miz.nao.ac.jp/staffs/nao99/index_en.html. prihantono, j., fajrianto, i.a., kurniadi, y.n., 2018. hydrodynamic modeling and sediment transport in coastal waters around tanjung pontang, serangbanten regency. jurnal kelautan nasional 1. https://doi.org/10.15578/jkn.v1i2.6614 saputra, r.a., 2018. modeling of post-reclamation sedimentation and master plan in jakarta bay using mike21. doctoral dissertation. faculty of science and technology state islamic university sunan ampel surabaya. sato, t., hanada, h., matsumoto, k., takanezawa, t., ooe, m.,2001. a program for the computation of oceanic tidal loading effects: “gotic” study of earth rotation, preceission, and nutation view project lunar physical libration and navigation view project gotic2: a program for computation of oceanic tidal loading effect, journal of the geodetic society of japan. suhana, m.p., 2015. hydro-oceanographic studies for detection of coastal dynamics processes (abrasion and sedimentation). postgraduate marine science, bogor agricultural university. triatmodjo, b., 2012. perencanaan bangunan pantai, 3rd edition 2014. ed, beta offset. yogyakarta. triatmodjo, b., 1999. teknik pantai, 8th edition 2016. ed. beta offset, yogyakarta. wibowo, m., khoirunnisa, h., wardhani, k.s., wijayanti, r., 2022a. pemodelan pola sedimentasi di muara cisadane untuk mendukung pengembangan terpadu pesisir ibukota negara. jurnal kelautan tropis 25, 179–190. https://doi.org/10.14710/jkt.v25i2.13732 wibowo, m., khoirunnisa, h., wardhani, k.s., wijayanti, r., 2022b. modeling of sedimentation patterns in the cisadane estuary to support the integrated development of the national capital coast. jurnal kelautan tropis 25, 179–190. https://doi.org/10.14710/jkt.v25i2.13732 wibowo, y.a., 2012. dinamika pantai (abrasi & sedimentasi). faculty of engineering and marine sciences. hang tuah university, surabaya. wiguna, e.a., wibowo, m., rachman, r.a., aziz, h., nugroho, s., 2020. hydrooceanographic conditions of the jelitik river estuary, sungailiat, bangka, bangka belitung province. buletin oseanografi marina 9, 9–18. https://doi.org/10.14710/buloma.v9i1.23363 yona, d., sartimbul, a., iranawati, f., sambah, a.b., hidayati, n., harlyan, l.i., sari, s.h.j., fuad, m.a.z., rahman, m.a., 2017. fundamental oseanografi. ub press – universitas brawijaya university, malang. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.15578/jkn.v1i2.6614 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 kausarian, h et al./ jgeet vol 03 no 01/2018 39 the phenomena of flood caused by the seawater tidal and its solution for the rapid-growth city: a case study in dumai city, riau province, indonesia husnul kausarian 1, *, batara 2 , dewandra bagus eka putra 1 1 department of geological engineering, universitas islam riau, jl. kaharuddin nasution no. 113, pekanbaru, indonesia 2 geolog forensic, jl. arifin achmad, pekanbaru, indonesia * corresponding author : husnulkausarian@eng.uir.ac.id tel.:+62-761-674674; fax: +62-761-674834 received: jan 13, 2018. accepted: feb 23, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.1221 abstract a strategic city located on the northern coast of sumatera island known as dumai city. this city is a growth and industrial city that always increase everyday economically. this city faces the flood problem that not only from the excess water from the rain, but also from the phenomena of seawater tidal. the tidal should not reach the mainland for the ideal situation, but the urbanization and development problem made it happen. field observation and satellite data analysis shows the problem that happened in this city, also find out the solution how to make the seawater tidal will not being the flood when it occurs. the flood caused by the inadequate drainage condition is exacerbated by the low awareness of people who still do not maintain cleanliness, a lot of garbage that accumulates in the drainage causing the process of water flow to be inhibited. geologically, the base rock of dumai city consists of sand and peat which logically is a good system to absorb water because sand and peat are materials that have high porosity. topographically, the city of dumai is at an average height of three meters above sea level, so in fact, this city could be spared from the flood caused by the tide when it occurs. the solutions that can be proposed for this city are making the rivers being clean with normalization, well-designed drainage, watergate and making an artificial lake for sinking the tidal seawater. keywords: dumai city, flood, tidal, urbanization, environment 1. introduction dumai city (figure 1) is a strategic city (budidarsono et al., 2013) located on 101 0 101 0 .8".13' east and 1 0 .23 .23 1 0 .24 .23 north on the northern coast of sumatera island, making it economically provide hope and opportunity (habibah et al., 2013) for people to settle and move in the largest city in indonesia based on their area. the city has an area of 2,039.35 km² and has 316,668 inhabitants in 2014. the problem appears when urbanization activities increased in dumai city, with high community activity and development, giving a tremendous impact on environmental issues (alkhatib et al. 2007; amin et al., 2009; badrun, 2017), especially those related to tidal phenomena. the tidal of sea water (lubis et al. a,b , 2017) that caused flooding (harwitasari and van ast, 2011; he et al., 2007) in many parts of dumai city. but now, the flood that only happened around the mouth of the river and around the shore at the past time, extends to most areas of the city. this issue if left continuously will make dumai city will one day drown when the tide of seawater occurs (lubis et al., 2017). this time count depends on the growth rate of development and urbanization improvement in dumai city, especially since dumai has been declared as one of the national strategic industrial cities, it is not impossible that the sinking of dumai city will be faster. fig. 1. riau province in sumatra island (above) and dumai city as the research area and a part of riau province (below). mailto:husnulkausarian@eng.uir.ac.id 40 kausarian, h et al./ jgeet vol 03 no 01/2018 2. problem background as a city on the coast, of course, dumai city has a problem that can not be separated from the influence of the tide of sea water (largier and taljaard, 1991; marfai et al., 2008). this problem is also faced by cities in other parts of the world, such as chiba city in japan, amsterdam in the netherlands, goldcoast in australia and many others. but cities in developed countries never experience flooding when tides occur (marfai and king, 2008). it is also certainly influenced by good residential governance in this city. the high number of development gives new problems to think about how to "run" the water from the flood. currently, indeed the local government of dumai city is actively making drainage, but this drainage is still not able to accommodate excess water discharge during the occurrence of pairs or rain. the inadequate drainage condition is exacerbated by the low awareness of people (figure 2) who still do not maintain cleanliness, a lot of garbage that accumulates in the drainage causing the process of water flow to be inhibited. fig. 2. above and below: the low awareness of environment cleanness by the citizen. 3. material and method for this research, we used some material and method to conduct and find the problem. one of them is field observation for the field measurement regarding the tidal flood. results prove when the tide of seawater happened, the half-city area from the estuary to the central part of the city has been drowned (see figure 2). compared to the past (within a matter of two decades), the dumai city area experiencing flooding from tidal water has increased, meaning that the distribution of flood-affected areas now extends to the center of the city. geologically, the base rock of dumai city consists of sand and peat which logically is a good system to absorb water because sand and peat are materials that have high porosity. topographically, the city of dumai is at an average height of three meters above sea level, so in fact, this city could be spared from the flood caused by the tide when it occurs. the method was used in software (global mapper) is analyze contours using srtm map as a base map, the result of the analysis is a map of elevation or topographic the area. the simulate water level rise/ flooding command allows the user to simulate the water coverage/ flooding if increase the water level by some depth over either a fixed single elevation (like 0 for sea level) or from a selected area feature, like a floodplain area. other data used in addition to field observations are topographic data of srtm (sumatera srtm 57_12) and landsat 7 (kausarian et al., 2016; 2017; 2017). topographic (figure 3) and satellite data processing of dumai city that has been used, then processed and simulated for the ideal condition of dumai city into the potential water rise for this city. fig. 3. above: elevation map of dumai city that shows the topographic pattern, below: 3d morphological map of dumai city kausarian, h et al./ jgeet vol 03 no 01/2018 41 4. result and discussion from the field observation and data analysis, the spatial arrangement based on the geology setting, geography, and topography of the area that influenced by the tide is different. for the dumai city, actually greatly benefited by geography, because in front of this city there is an island named rupat (butar butar and fidiatur, 2016; kausarian et al., 2017) which naturally becomes a protective shield from the swift currents coming from the straits of melaka. geologically, the base rock of dumai city consists of sand and peat which logically is a good system to absorb water because sand and peat are materials that have high porosity. topographically, the city of dumai is at an average height of three meters above sea level (figure 4), so in fact, this city could be spared from the flood caused by the tide when it occurs. and when the sinking simulation has been made, the city will be drowned when the water comes in 5-50 meters high (figure 5). the simulation of the total area that will be drowned by the tide phenomena can be seen in table 1. satellite data shows the river flow in dumai city consists of meanders, this is advantageous can accommodate the amount of water debit in high volume, so if the rivers used properly, for example by doing addition depth and normalization, this could serve as a catchment area of excess water caused by tidal phenomena in dumai. moreover, dumai city is supported by 15 rivers, so that when the tide occurs, this problem can be solved well, because the research data shows the maximum tide that occurs only as high as three meters. another thing that can be taken into consideration is to make a water gate that must be higher than when the maximum tide. when the tide occurs, the water gates lead to the sea can be closed, so that at high tide, the water is not too much into the mainland. another proposal is to do water bank trapping pattern, this concept is made by engineered the flow of water by making canals at some point and collected in one catchment area.this can be developed in another direction, such as making artificial lake as one of the alternative tourist entertainment for residents in dumai. finally, of course, by taking advantage of the participation of companies engaged in activities at the sea edge of dumai city. the local government entitled to ask them to participate to actively fix the beach, for example by raising the area of the beach, making water gates flow of the estuary. table 1. the prediction of the affected area caused by tide flood by the simulation of the water high. no. water level (in meter) flood area (m 2 ) 1. 2. 3. 4. 5. 6. 7. 8. 0 3 5 10 15 25 35 50 0 1,117.4 4,696.3 9,565.5 16,613 19,367 20,268 21,744 42 kausarian, h et al./ jgeet vol 03 no 01/2018 kausarian, h et al./ jgeet vol 03 no 01/2018 43 fig. 4. the cross section for the potetial area of dumai city as the representative of flood possible based on the topography profile. (clockwise: a-southeast, c-east, dnortheast-southwest). 44 kausarian, h et al./ jgeet vol 03 no 01/2018 kausarian, h et al./ jgeet vol 03 no 01/2018 45 fig. 5. the simulation of flooding in dumai city for the ideal condition, from the simulation, the water height that can caused the flood is above 3 meters. 5. conclusion to overcome the flooding problems caused by the tidal seawater in the dumai city, a thorough review needs to do that involves all aspects. dumai city which continues to grow as an industrial city, need special treatment and attention in the future development. especially for issues related to urbanization and the environment. the solution for the flooding phenomenon caused by the tidal water in this city should be increased as early as possible in order to avoid complex problems that will arise later. references alkhatib, m., jennerjahn, t.c. and samiaji, j., 2007. biogeochemistry of the dumai river estuary, sumatra, indonesia, a tropical black‐water river. limnology and oceanography, 52(6), 2410-2417. amin, b., ismail, a., arshad, a., yap, c.k. and kamarudin, m.s., 2009. gastropod assemblages as indicators of sediment metal contamination in mangroves of dumai, sumatra, indonesia. water, air, and soil pollution, 201(1-4), 9-18. badrun, y., 2017. sandbar formation in the mesjid river estuary, rupat strait, riau province, indonesia. the indonesian journal of geography, 49(1), 65. budidarsono, s., susanti, a., and zoomers, a., 2013. oil palm plantations in indonesia: the implications for migration, settlement/resettlement and local economic development. in biofuels-economy, environment and sustainability. intech. butar butar, r. and fidiatur, n., 2016. sedimentological aspects and relative sedimentation rates in the dumai coastal waters, riau province indonesia. habibah, a., hamzah, j., er, a.c., buang, a., selvadurai, s. and mushrifah, i., 2013. city-city tourism collaboration in the straits of malacca development region: key success factors. asian social science, 9(13), 40. harwitasari, d. and van ast, j.a., 2011. climate change adaptation in practice: people's responses to tidal flooding in semarang, indonesia. journal of flood risk management, 4(3), 216-233. he, b., lai, t., fan, h., wang, w. and zheng, h., 2007. comparison of flooding-tolerance in four mangrove species in a diurnal tidal zone in the beibu gulf. estuarine, coastal and shelf science, 74(1-2), 254-262. kausarian, h., sumantyo, j.t.s., kuze, h., karya, d. 46 kausarian, h et al./ jgeet vol 03 no 01/2018 and panggabean, g.f., 2016. silica sand identification using alos palsar full polarimetry on the northern coastline of rupat island, indonesia. international journal on advanced science, engineering and information technology, 6(5), pp.568-573. kausarian, h., sumantyo, j.t.s., kuze, h., karya, d. and wiyono, s., 2016. the origin and distribution of silica mineral on the recent surface sediment area, northern coastline of rupat island, indonesia. arpn journal of engineering and applied sciences, 12(4), 980989. kausarian, h., sri sumantyo, j.t., kuze, h., aminuddin, j. and waqar, m.m., 2017. analysis of polarimetric decomposition, backscattering coefficient, and sample properties for identification and layer thickness estimation of silica sand distribution using l-band synthetic aperture radar. canadian journal of remote sensing, 43(2), 95-108. kausarian, h., 2017. geological mapping and full polarimetric sar analysis of silica sand distribution on the northern coastline of rupat island, indonesia (doctoral dissertation, 千葉大学= chiba university). largier, j.l. and taljaard, s., 1991. the dynamics of tidal intrusion, retention, and removal of seawater in a bar-built estuary. estuarine, coastal and shelf science, 33(4), 325-338. lubis, m.z., anggraini, k., kausarian, h. and pujiyati, s., 2017. marine seismic and side-scan sonar investigations for seabed identification with sonar system. journal of geoscience, engineering, environment, and technology, 2(2), 166-170. lubis, m.z., anurogo, w., kausarian, h., surya, g. and choanji, t., 2017. sea surface temperature and wind velocity in batam waters its relation to indian ocean dipole (iod). journal of geoscience, engineering, environment, and technology, 2(4), pp.255-263. lubis, m.z., kausarian, h. and anurogo, w., 2017. seabed detection using application of image side scan sonar instrument (acoustic signal). journal of geoscience, engineering, environment, and technology, 2(3), 230-234. marfai, m.a., king, l., sartohadi, j., sudrajat, s., budiani, s.r. and yulianto, f., 2008. the impact of tidal flooding on a coastal community in semarang, indonesia. the environmentalist, 28(3), 237-248. marfai, m.a. and king, l., 2008. coastal flood management in semarang, indonesia. environmental geology, 55(7), 1507-1518. sutikno, s. and merian, r.d., 2017. numerical model for pollutant dispersion in the dumai estuary. in matec web of conferences, vol. 101, 04001. edp sciences. thariqa, p. and sitanggang, i.s., 2015. spatial online analytical processing for hotspots distribution based on socio-economic factors in riau province indonesia. procedia environmental sciences, 24, 277-284. 1. introduction 2. problem background 3. material and method 4. result and discussion 5. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 35 research article analysis of petrophysical parameter on shaly sand reservoir by comparing conventional method and shaly sand method in vulcan subbasin, northwest australia ulrike johanna1, epo prasetya kusumah1,* 1geological engineering department, universitas pertamina, jakarta selatan 12220, indonesia * corresponding author : epo.pk@universitaspertamina.ac.id may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13880 abstract vulcan subbasin is an area with a lot of oil and gas exploration where is located in the bonaparte basin, northwest australia. there is some formation identified as sandstone reservoir with clay content which is usually called shaly sand based on the screening between resistivity log and density log. clay content caused lower resistivity log readings so the shaly sand reservoir is considered as non-reservoir. to overcome this, a method besides the conventional method was applied to analyze the petrophysical parameters of shaly sand reservoir, it was shaly sand method. petrophysical analysis is an analysis of rock physical parameters such as shale volume, porosity, and water saturation based on well log data. in this study, petrophysical analysis was carried out in the vulcan subbasin using 35 well log data, including gamma ray log, resistivity log, neutron log, and density log for the conventional method and shaly sand method involved stieber equation and thomas stieber plot. the results obtained from this study are the comparison of petrophysical parameter values a nd pay summary between the conventional method and the shaly sand method, also its relation to the shale distribution type. by applying the shaly sand method, the average shale volume has decreased, the average porosity has increased, the average water saturation h as increased, the average net to gross has increased, the average net thickness has increased, and the average net pay has increased. changes in the average value were caused by laminated-dispersed shale distribution type which is influenced by diagenesis and the depositional environment of the formation. keywords: vulcan subbasin, petrophysical analysis, shaly sand, stieber equation, thomas stieber plot 1. introduction bonaparte basin is one of the most productive offshore hydrocarbon-producing basins in australia. one of the areas that has many exploration wells is vulcan sub-basin (geoscience australia, 2021). vulcan sub-basin is a mesozoic northeast-southwest trending extensional depocenter located in the bonaparte basin, northwest australia, that consist of horst, graben, and terrace (pattillo & nicholls, 1990). it borders ashmore platform to the west and londonderry high to the east (figure 1). exploration is carried out to find hydrocarbon reserves. well log data can be evaluated to increase hydrocarbon productivity by finding other possible productive reservoirs, such as shaly sand reservoir. shaly sand reservoir is a reservoir that not only has sandstone lithology but also contains shale within the sand (mkinga et al., 2020). characteristics of shaly sand can affect the welllog readings so that the reservoir interval of shaly sand is considered non-reservoir. therefore, a petrophysical analysis was carried out on the reservoir. petrophysical analysis was conducted to calculate the values of petrophysical parameters such as shale volume, porosity, and water saturation (harsono, 1997). these parameters can be used to determine the reservoir thickness. in addition, another method of petrophysical calculation is needed for shaly sand conditions, especially for shale volume and porosity parameters. the method applied to the calculation of shale volume is the stieber equation, and the method of porosity calculation is the thomas stieber plot. thomas stieber can also be used to determine the shale distribution type present in the formation. therefore, two petrophysical calculation methods were carried out, the conventional method and the shaly sand method. then the results of the two methods are compared to determine the effect of the presence of shale on petrophysical parameters and pay summary. fig. 1. location area of study (frankowicz & mcclay, 2010). http://journal.uir.ac.id/index.php/jgeet mailto:epo.pk@universitaspertamina.ac.id 36 johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 2. material and methods 2.1 data this research used 35 well log data that consisted of gamma ray log, resistivity log, neutron log, and density log. the data was downloaded from national offshore petroleum information management system (nopims) website which is provided by geoscience australia (2021). 2.2 methodology the steps of analysis are precalculation, zone determination, conventional petrophysical analysis, shaly sand petrophysical analysis, and comparison between petrophysical parameters and pay summary results obtained from the two methods. 2.2.1 screening for shaly sand method low resistivity readings at reservoir intervals (low resistivity pay zone) are caused by several factors, such as clay content in the reservoir and conductive minerals. the way to identify the cause of low resistivity is by using a cross plot between the resistivity log and the density log. conductive mineral is characterized by a low resistivity value and a high density value. meanwhile, the clay content is indicated by a low resistivity value and a intermediate density value. fig. 2. crossplot between rt and rhob for screening shaly sand method. based on the cross plot above in figure 2, data distribution is mostly found in areas classified as low resistivity and intermediate density. therefore, the cause of the low resistivity pay zone in the formation is the clay content in the reservoir, so petrophysical analysis using the shaly sand method can be used. 2.2.2 precalculation precalculation is calculating the temperature at each well by temperature data or temperature gradient from each well and data from the nearest well. 2.2.3 zone determination the zones are determined based on top formation from each well. zones were determined by formation based on the assumption that each formation has the same age and depositional mechanism. in this study, the formation target are puffin formation, montara formation, and plover formation. 2.2.4 conventional petrophysics analysis conventional method analyzes petrophysical parameters without considering the presence of shale within the shaly sand reservoir. the calculated parameters include shale volume, porosity, and water saturation. parameter picking and the equations used in the conventional analysis are as follows. • shale volume parameter picking for shale volume was conducted by determining the shale baseline (grmax) and sand baseline (grmin) on the gamma ray log histogram, which consists of the number of data frequencies so that the determination of the value is more detailed, as seen in figure 3. fig. 3. parameter picking for shale volume. the equation used to calculate shale volume is according to the linear equation: 𝑉𝑠ℎ = 𝐼𝐺𝑅 = 𝐺𝑅𝑙𝑜𝑔 − 𝐺𝑅𝑚𝑖𝑛 𝐺𝑅𝑚𝑎𝑥 − 𝐺𝑅𝑚𝑖𝑛 where: 𝑉𝑠ℎ=𝐼𝐺𝑅= shale volume 𝐺𝑅𝑙𝑜𝑔= gamma ray log reading 𝐺𝑅𝑚𝑖𝑛= minimum gamma ray 𝐺𝑅𝑚𝑎𝑥= maximum gamma ray • porosity parameter picking for porosity was conducted by determining the wet clay point on the neutron-density plot. wet clay point is a point that shows the condition of the clay volume equal to 100%, consisting of neutron wet clay (neu wet clay) and density of wet clay (rho wet clay), as seen in figure 4. g r m in g r m ax johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 37 fig. 4. parameter picking for porosity. the equation used to calculate porosity is according to equation: ∅𝐸 = ∅𝑇 (1 − 𝑉𝑠ℎ) where: ∅𝐸 = effective porosity ∅𝑇 = total porosity 𝑉𝑠ℎ= shale volume • water saturation parameter picking for water saturation was conducted by determining the water zone on the pickett plot, a plot between resistivity and porosity. the value obtained is the water resistivity (rw) as input on water saturation. the parameter picking can be seen in figure 5. fig. 5. parameter picking for water saturation. the equation used to calculate water saturation is according to archie equation: 𝑆𝑤 = √ 𝑎 × 𝑅𝑤 ∅𝑚 × 𝑅𝑡 𝑛 where: 𝑆𝑤 = water saturation 𝑎= tortuosity factor 𝑅𝑤= water resistivity ∅= porosity 𝑚= cementation factor 𝑅𝑡= formation resistivity 𝑛= saturation exponent 2.2.5 shaly sand petrophysics analysis another method is used for shaly sand reservoir to determine the impact of shale occurrence on the calculation of petrophysical parameters. shaly sand method is applied to the petrophysical parameters such as shale volume and porosity. shale volume calculation is based on the stieber equation (stieber, 1970), while the porosity calculation is based on the thomas stieber plot. the equations that shaly sand method use are as follows. • shale volume parameter picking for shale volume by shaly sand method was conducted in the same way as the conventional method, which determined gr min and gr max. the difference is shaly sand method applied stieber equation for shale volume calculation. by applying stieber equation, shale volume value will be different. the graph below compares shale volume between linear and stieber (figure 6). fig. 6. shale volume comparison between linear and stieber equation. stieber equation is used as written below: 𝑉𝑠ℎ 𝑆𝑡𝑖𝑒𝑏𝑒𝑟 = 𝐼𝐺𝑅 3 − 2𝐼𝐺𝑅 wet clay point 38 johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 where: 𝑉𝑠ℎ 𝑆𝑡𝑖𝑒𝑏𝑒𝑟 = shale volume by stieber equation 𝐼𝐺𝑅= gamma ray index or shale volume by linear equation • porosity parameter picking for porosity was conducted by picking phimax and phitcl point in thomas stieber plot. phimax is a point that indicates the porosity of clean sand. phitcl is a point that indicates the porosity of shale. the two points are determined according to the distribution of the plot data as seen in figure 7. fig. 7. parameter picking for porosity in thomas stieber plot. then, the equation is applied as below: ∅𝐸 𝑠𝑠 = ∅𝐸 (1 − 𝑉𝑙𝑎𝑚) where: ∅𝐸 𝑠𝑠= effective porosity by shaly sand method ∅𝐸 = effective porosity by conventional method 𝑉𝑙𝑎𝑚= shale volume of shale lamination 2.2.6 shale distribution thomas steiber plot also defines shale distribution from shale volume and total porosity cross plot as seen on figure 8. thomas stieber plot is based on calculating the laminar shale volume from the total volume, and the remaining shale volume is considered structural shale or dispersed shale. the principle of this method is to remove the laminar shale effect from the porosity of the sand. removing the shale affects the net to gross ratio of shale and sand (ghaleh et al., 2017). this method requires input from maximum porosity or clean sand porosity and total shale porosity to calculate the shale distribution model that consist of laminated shale, structural shale, and dispersed shale. fig. 8. thomas stieber plot shows the shale distribution model (thomas & stieber, 1975 in ali et al., 2016). 2.2.7 cut off determination cut off is needed to obtain net to gross (ntg), net thickness, and net pay. cut off value is determined by a frequency plot between effective porosity and shale volume for shale volume cut off and porosity cut off (figure 9). in contrast, water saturation cut off is determined by effective porosity and water saturation frequency plot (figure 10). fig. 9. shale volume cut off and porosity cut off determination. fig. 10. water saturation cut off determination. phimax phitcl johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 39 3. results and discussion 3.1 shale volume shale volume was obtained by parameter picking of grmax and grmin, then calculated by linear equation. while the shaly sand method used stieber equation to calculate the shale volume the average value of shale volume by conventional and shaly sand method is written in table 1. table 1. average shale volume by conventional and shaly sand method formation average shale volume (%) conventional shaly sand puffin formation 11,5 6,242 montara formation 8,413 5,625 plover formation 10,453 9,042 3.2 porosity porosity was obtained by parameter picking of wet clay point, then calculated by the effective porosity equation. while the shaly sand method used thomas stieber plot to determine the porosity value. the average value of porosity by conventional and shaly sand method is written in table 2. table 2. average porosity by conventional and shaly sand method formation average porosity (%) conventional shaly sand puffin formation 29,374 30,184 montara formation 20 20,15 plover formation 16,332 16,4 3.3 shale distribution shale distribution model was determined by thomas stieber plot, which includes laminated shale, structural shale, scattered shale, or a combination of each other. laminated shale exists as shale layers within the rock matrix. structural shale exists in the form of a fragment considered a part of the matrix. dispersed shale occupies the pore spaces between the matrix by adhering to the surface of the grains. based on the thomas stieber plot, puffin formation, montara formation, and plover formation dominantly have a combination of laminated-dispersed shale because the major scatter plot between shale volume and total porosity of each formation in most of the wells falls in the area between the laminated and dispersed line. in contrast, structural shale is rare, as shown in the example of thomas stieber plot below in figure 11-13. fig. 11. shale distribution in puffin formation. fig. 12. shale distribution in montara formation. fig. 13. shale distribution in plover formation. 40 johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 3.4 water saturation water saturation was obtained by parameter picking of water resistivity, then calculated by the archie equation. in the shaly sand method, water saturation was calculated by same equation as conventional method, archie equation because there is limited data to apply the other equations (dwiyono & winardi, 2014). but, the water saturation value is based on the porosity input that obtained from shaly sand method by thomas stieber plot. the average water saturation value by conventional and shaly sand method is written in table 3. table 3. average water saturation by conventional and shaly sand method formation average water saturation (%) conventional shaly sand puffin formation 57,8 61,439 montara formation 34,987 35,85 plover formation 48,04 50,164 3.5 cut off and summation shale volume cut off, porosity cut off, and water saturation cut off can be seen in the table 4 below. table 4. cut off value formation cut off (%) shale volume (≤) porosity (≥) water saturation (≤) puffin formation 55 22 90 montara formation 72 17 77 plover formation 57 8 80 the results of the pay summation from the application of the cut off value in the conventional method and the shaly sand method can be seen in table 5 and table 6 below. table 5. pay summation of conventional method formation net to gross (%) net thickness (m) net pay (m) puffin formation 29,295 102,318 19,991 montara formation 18,913 65,846 27,056 plover formation 46,274 88,275 14,107 table 6. pay summation of shaly sand method formation net to gross (%) net thickness (m) net pay (m) puffin formation 35,326 118,276 21,072 montara formation 21,9 81,609 31,151 plover formation 56,916 108,498 16,479 3.6 comparison between conventional method and shaly sand method after getting the result, comparing the petrophysical parameters and pay summary between the conventional and shaly sand methods was conducted. applying stieber equation to shale volume calculation decreased the average shale volume in each formation, as seen in figure 14. this decrease in shale volume is due to the common radioactive characteristics of the formation, thus giving a lower shale volume value than the linear equation. applied the thomas stieber plot to calculate porosity also increases the average porosity value (figure 15). the shale distribution model influences the increase slightly in porosity. based on the thomas stieber plot, each formation has laminateddispersed shale model. the dominant laminated combined with dispersed shale model has a minor effect on porosity, so when thomas stieber is applied, the porosity calculation does not increase much. in addition, the water saturation value increases in the shaly sand method (figure 16). the difference in water saturation values in the conventional and shaly sand methods is influenced by the porosity as input on water saturation calculation. the increase in value is caused by the equation used, which is archie equation, so it still causes an overestimation of the water saturation value in shaly sand (poupon & leveaux, 1971). the shaly sand method generally increases the average net to gross, net thickness, and net pay (figure 17-19), so the shaly sand method can be effective for reservoir characterization and thickness calculations more optimistic, although there must be other applications for water saturation parameters. fig. 14. shale volume comparison between conventional and shaly sand method. johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 41 fig. 15. porosity comparison between conventional and shaly sand method. fig. 16. water saturation comparison between conventional and shaly sand method. fig. 17. net to gross comparison between conventional and shaly sand method. fig. 18. net thickness comparison between conventional and shaly sand method. fig. 19. net pay comparison between conventional and shaly sand method. 4. discussion the petrophysical parameter includes shale volume, porosity, water saturation, and pay summary includes net to gross, net thickness, and net pay were calculated using conventional and shaly sand methods. conventional method analyzed petrophysical parameters without considering the presence of shale within the shaly sand reservoir. in the conventional petrophysical method, linear equation was applied in shale volume calculation, it also used effective porosity and archie equation in water saturation. meanwhile, shaly sand method analyzed the petrophysical parameter by considering the shale content in the shaly sand reservoir. stieber equation is used in the shale sand method to calculated shale volume, and the thomas stieber plot is used to determine porosity. but it also used archie equation in water saturation calculation, as same as conventional method, due to the research limitation. so, if the shaly sand method applied, the value of petrophysical parameter would change. the different results between conventional method and shaly sand method were caused by the type of shale distribution found in the shaly sand reservoir. shale distribution type contained in the formation is also influenced by rock diagenesis and depositional environment. in this study, the dominant type of shale distribution in the target formation is laminated shale and dispersed shale. laminated shale is in the form of layers of flakes that fill the spaces between grains. the clay that 42 johanna & kusumah/ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 makes up this shale is an allogenic clay that undergoes transportation, then is deposited between the pore of grains. the lamination condition is caused by constant sediment sources and depositional currents. dispersed shale is the shale that sticks to the grain's surface. the constituent clays are authigenic clays formed after deposition due to chemical precipitation between minerals and formation water. the development of dispersed shale is affected by changes in temperature, pressure, and formation water conditions during loading and compaction. 5. conclusion the application of the shaly sand method to shale volume, porosity, and pay summary, such as net to gross, net thickness, and net pay makes values more optimistic average value for reservoir calculations, where the shale volume is lower, and porosity, net to gross, net thickness, and net pay are greater than the conventional method. however, the calculation of water saturation must be considered, and must apply other methods to lower water saturation and give more optimism for shaly sand reservoirs. acknowledgements we would like to thank geoscience australia for providing the national offshore petroleum information management system (nopims) website as the open data source for this research. references ali, a., hussain, m., rehman, k., toqeer, m., 2016. effect of shale distribution on hydrocarbon sands integrated with anisotropic rock physics for ava modelling: a case study. acta geophysica 64(4), 1139-1163. https://doi.org/10.1515/acgeo-2016-0041 dwiyono, i. f., winardi, s., 2014. kompilasi metode water saturation dalam evaluasi formasi [compilation of water saturation methods in formation evaluation]. in prosiding seminar nasional kebumian ke-7, yogyakarta, pp. 30-31. frankowicz, e., mcclay, k. r., 2010. extensional fault segmentation and linkages, bonaparte basin, outer north west shelf, australia. aapg bulletin, 94(7), 977-1010. https://doi.org/10.1306/01051009120 geoscience australia, 2021. regional geology of the bonaparte basin. retrieved from: https://www.ga.gov.au/scientifictopics/energy/province-sedimentary-basingeology/petroleum/acreagerelease/bonaparte ghaleh, s. p., taghizadeh, m., far, e. r., kordavani, a., & mirzaei, m, 2017. evaluation of laminated shaly sand sequences in ahwaz oil field using (via) thomas stieber method and conventional petrophysical logs. journal of petroleum science and engineering 152, 564-574. https://doi.org/10.1016/j.petrol.2017.01.041 harsono, a., 1997. evaluasi formasi dan aplikasi log. jakarta: schlumberger oilfield services. mkinga, o. j., skogen, e., kleppe, j., 2020. petrophysical interpretation in shaly sand formation of a gas field in tanzania. journal of petroleum exploration and production technology 10(3), 1201-1213. https://doi.org/10.1007/s13202-019-00819-x pattillo, j., nicholls, p. j., 1990. a tectonostratigraphic framework for the vulcan graben, timor sea region. the appea journal 30(1), 27-51. poupon, a., leveaux, j., 1971. evaluation of water saturation in shaly formations. in spwla 12th annual logging symposium. onepetro. stieber, s. j., 1970. pulsed neutron capture log evaluationlouisiana gulf coast. in fall meeting of the society of petroleum engineers of aime. onepetro. thomas, e. c., stieber, u. s., 1975. the distribution of shale in sandstones and its effect upon porosity. in spwla 16th annual logging symposium. onepetro. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). https://doi.org/10.1515/acgeo-2016-0041 https://doi.org/10.1306/01051009120 https://doi.org/10.1016/j.petrol.2017.01.041 https://doi.org/10.1007/s13202-019-00819-x http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 128 afifah.p.d & setiawan.b/ jgeet vol 04 no 02/2019 research article middle miocene black shale of airbenakat formation in berau areas, jambi: are they potential as a source rock putri dwi afifah 1* , budhi setiawan 2 1 geological engineering study program, sriwijaya university, srijaya negara street, bukit besar, palembang * corresponding author : afifahputridwi@gmail.com tel.:+ 628-237-774-5121 received: july 02, 2018; accepted: may 03, 2019. doi: 10.25299/jgeet.2019.4.2.1774 abstract geologically, the research area is located in jambi sub-basin that composed by peneta formation (kjp), airbenakat (tma), and muaraenim (tmpm). the research focuses on the physical characteristics and geochemistry of middle miocene black shale from airbenakat formation. the research aims to determine the potential of middle miocene black shale of airbenakat formation as a source rock. the research methods were field observation which included the description of rock samples and geological mapping, and laboratory analysis including rock geochemical analysis that show pyrolysis measurement and total organic carbon. three samples were taken from black and fine-grained shale. total organic carbon (toc) values of the three samples ranged from 0.38-0.42%, the weight of toc indicates a potentially close enough to produce hydrocarbons. the pyrolysis results showed that the value of s1and s2 data were below 0.5 and 2.5 hc/g rock respectively, so it can be seen that the three rock samples were not sufficient enough to produce hydrocarbons. overall the sample have the s2/s3 ratio ranging from 0.09-0.23 and tmax-hi data has values ranging from 8-19 mg hc/g toc, therefore the s2/s3 ratio was less than 1 and the value of the index hydrogen was below 50 mg hc/g toc, it can be concluded that the samples were type iv kerogen. the maximum temperature (tmax) of pyrolysis showed a value of less than 4350c, ranging from 350-4280c. so, it can be interpreted that the three samples are immature source rocks because the cathagenesis phase to produce hydrocarbons has not been achieved. the conclusions is the three samples of black shale indicate potential as immature source rock and has the close enough ability to produce hydrocarbons. keywords: source rock, shale, airbenakat formation 1. introduction 1.1 sub introduction geographically, the research area is located in berau village, cermin nan gadang district (figure 1). geologically, the location of this research is in the airbenakat formation of jambi sub-basin. jambi sub-basin is part of south sumatra basin which is in the back arc basin (barber, et al., 2005). south sumatra basin has diverse geological characteristics, including geomorphological, stratigraphic, and geological characteristics. so that, the south sumatra basin is an excellent object to be studied. the airbenakat formation in this researh area composed by sand and gray to black shale. the presence of black shale is being the background of this research. geochemical analysis of black shale aims to find out whether this black shale has a potential or not as a source rock in jambi sub-basin. 2. geological framework according to pulunggono, et al. (1992), south sumatra basin with the southern part of sumatra island oriented to nw-se. the area of this basin is around 85.670 km2 and consists of two sub-basins, namely jambi and palembang sub-basin. jambi sub-basin is oriented towards the ne-sw and is bounded by the tigapuluh mountain in the north, southern lampung in the south, sunda shelf in the east, and barisan mountain in the west. palembang sub-basin is nnwsse trending, and between them is separated by normal ne-sw faults. south sumatra basin is a large basin. the uneven relief as well as the reactivation of the bundle fault control the sedimentation and folding of the tertiary layer. tectonic developments in this basin are divided into four phases (pulunggono, et al., 1992) (figure 2). http://journal.uir.ac.id/index.php/jgeet afifah.p.d & setiawan.b./ jgeet vol 04 no 02/2019 129 fig.1 research location map (bnpb of jambi province, 2010). fig.2 tectonic developments of south sumatra basin (pulunggono, et al.., 1992). • phase 1 (jurassic-lower cretaceous) the occurrence movement of the indian ocean plate to the northwest, the mechanism will be compressed and in tandem with tectonic control, which is tilted towards the wnw-ese line of sundaland which induces its volcanic and accompanies the direction of its sliding fault (fault zone) which is currently seen as straightness musi and alignment of the lematang with n 30o w directed center of indian ocean plate to a wnw-ese sundaland side edge line, convergence angle is 30o. as a result there is volcanism which produce granitoid intrusion, along with direction of fault of shear dekstral (lematang fault) cutting n-s fault. lematang fault activity and the n-s fault is silent at an angle of 60°. • phase 2 (upper cretaceous-lower tertiary) the second phase develops an extensional phase. this force is oriented n-s and wnw-ese experiencing the spreading form graben or depression. this causes the lematang fault to be east of the kikim fault originating strike slip fault sw-ne (n 30° e), becoming a normal fault of n 300° e. subsequent developments into limau produce horst and grabben blocks. the block is the basement builder of the south sumatra basin. volcanic intrusions shifting and producing garba hill is the result of subduction pathways that has been spreading. • phase 3 (sedimentation process) the commencement of sediments filling into grabben blocks over the bedrock along the volcanic activity. this is the phase of tectonic miocene which causes uplift at the edges of the basin and followed by the precipitation of the clastic material. when this occurs, the formation of barisan mountain is oriented n 320 ° e. it also makes in the third phase called bukit barisan orogeny. as a result, strike slip fault structures developed during the middle miocene period were accompanied by an increase in the rate of volcanic activity. • phase 4 (plio-pleistosen) compressional phase, the subduction zone changing from sumatra island to the oblique convergence and its direction n 6° e. this makes a "semangko" shear fault block formed. as a result of wrenching product, rejuvenation and tectonic inversion. this barisan mountain stretches from the north-south oblique and nwse oriented. these mountain are limiting the south sumatra basin to the southwest with bengkulu basin. 2.1 stratigraphy according to barber, et al. (2005), the stratigraphy of the basins in sumatra is divided into four phases of tectonostratigraphy: pre-rift phase, horst and graben phases (high and valleys), transgressive phases, and regressive phases (figure 3). 130 afifah.p.d & setiawan.b./ jgeet vol 04 no 02/2019 • pre-rift phase (eocene) the pre-rift phase of the sumatra basin occurred during the eocene period which, after some time in a stable state, was affected by tectonic regime changes indicated by sedimentation on sundaland's periphery. the sediments formed include the eocene nummulitic limestone found at the edge of the bengkulu basin. in the period before the horst and graben periods indicated active volcanism activity was reinforced by the discovery of kikim tuffs consisting of tuffed sandstone, conglomerate, breksia, and clay, late cretaceous and early paleocene and the discovery of old andesites. • horst dan graben phase (late eocene-oligocene) after the pre-rift phase, in the late eoceneoligocene period there is a change of tectonic regime where the lifting occurs causing the formation of horst and graben is then filled by rift sediments called lahat/lemat formation in middle miocene until the final oligocene. the lahat formation consists of breksia, a polymic conglomerate, and sandy gray sandstones. the conglomerate fragments are derived from bedrock consisting of slate, phyllite, metasandstone, marble, basalt, andesite, and quartz veining. the depositional environment of lahat formation is interpreted as fluvial, alluvial fan, and lacustrin in the center of the basin. the lemat formation consists of tuffed shales, rocks, greenbrown flakes, and sandstone with thin intercalation of coal, carbonate, and glauconite. in areas between finegrained materials sometimes there is a granite wash material that interpreted as the result of erosion of the deposited granite not far from the source rock. this phase has yet to separate sedimentation between the back arc basin and fore arc basin. the barisan mountain which separates the sedimentation area of back and fore arc basin marks the occurrence of regional tectonic changes in the final oligocene which resulted in inversion by the folding of sediments deposited in the horst and graben periods. the appointment of barisan mountain accompanied by erosion also causes unconformity during subsequent sedimentation. • transgressive phase (late oligocene-middle miocene) the transgressive phase occurred during the middle oligocene-middle miocene, marked by regional subsidence in almost all basins in sumatra. at this phase especially in the late oligocene there is also the appointment of barisan mountain or the establishment of the sumatran arc system and separate the sedimentation of the back arc basin and sedimentation of the fore arc which the source of the sediment comes from barisan mountain. sediments deposited in the early stages of this transgressive phase are talang akar formations consisting of sandstones, rocks and shales that gradually change into carbonaceous flakes by insertion of coal into the basin with a precipitation environment that varies from fluvial to shallow marine. due to the subsidence of the basin and transgressive phase in the early miocene, the source of clastic rock in the north began to decrease as the sunda plain has undergone denudation and upgrading, and the entire south sumatra basin becomes the suspected carbonate deposition environment of the ramp/platform type. high areas such as the musi high and the northern palembang high, remain relatively high compared to the lowland areas and evidenced by the growing environment of reef which is easily exposed to the surface in connection with the decrease of sea water. the peak of regional subsidence leads to marine transgression in almost all of south sumatra basin, which indicates the presence of marine deposits. the baturaja and gumai formations are formed at this stage. maximum sea thread occurs in the middle miocene, where at present the barisan mountain is almost all drowned. baturaja formation consists of limestone sediment platforms and limestone reefs formed above the high of bedrock. in some places or more layered limestone textures with shale deposited in deeper environments. the gumai formation consists of shale containing patches containing foraminifera, the rocks with fine glauconitic sandstone inserts and tuff lenses. fig. 3. tertiary regional column of south sumatra basin (barber, et al., 2005) afifah.p.d & setiawan.b./ jgeet vol 04 no 02/2019 131 • regressive phase (middle miocene-recent) the subduction process accompanied by the reappointment of the barisan mountains causes the delta and coastal sediments to prograded away from the high areas so that barisan mountain becomes a source of sediment. the sediments formed in this phase are airbenakat, muaraenim, and kasai formation. airbenakat formation (lower palembang formation) deposited during middle miocene and followed by the depositional of coal from muaraenim formation (middle palembang formation) at pliocene. the lithology of airbenakat formation includes shale with glauconite sandstone and limestone constituents deposited on the neritic environment at the bottom to a shallow marine environment at the top. in general the rock formation of this formation is deposited during the regressive phase. the layer coating of this formation is a middle miocene shaped elbow composed of seafloor with glauconite and microforam in several places and layers of sandstone. the muaraenim formation was formed in the late miocene to early pliocene as shallow sea deposits, sublittoral and delta sediments consist of claystone, shale with sandstone intercalation and coal seams (spruyt, 1956). this unit is deposited in marine brackish environments (at the bottom), delta plain, and non-marine environments. the fauna data from this formation does not exist, but it is estimated that this formation is upper miocene-pliocene. the peak of lifting and erosion period of the barisan mountains occurred in the late pliocene and followed by intensive volcanism activities. the kasai formation was deposited at this time, largely a product of erosion from the elevations of barisan and the tigapuluh mountains, and by the lifting of folds that occurred in the basin during the orogenesis. this formation consists of tuffed sandstone, gravel clay, and there is a thin layer of coal with varying thickness and composition. 2.2. geology structure ginger and fielding (2005) divides the tectonic history of the sumatra basin into three megasekuen tectonics. first is the syn-rift megasequence, it is characterized by subduction in the western part of sumatra that produces the north-south trending horizontal graben sequence. second is the post rift megasequence, in this megasekuen initially a thermal decline so that the phase of transgresi still occur, at the end of this megasekuen no thermal decline and increased sediment supply, there was a regression phase until depositional of muaraenim formation. the third is inversion megasequence, this megasekuen is marked by the rise of barisan mountain on the western part of sumatra island, this megasekuen produces a structure that has a direction from the south-east fold. the three megasekuen tectonic changes lead to the formation of different lineaments according to the phases in the geological period. the structural pattern of sumatra island is relatively southeast based on the direction of semangko fault, due to the process of south sumatra basin has three antiklinorium consist of antiklinorium pendopolimau, palembang, and muara enim. the muara enim anticline is characterized by an assymetrical-overtuned wing with a fairly steep wing on the north with the general direction of the northwest to southeast. the development of structures and the evolution of the basin since tertiary is the result of interaction of three main structural directions, northeast-southwest direction or called jambi pattern, and sumatra pattern in southsoutheast direction, and north-south direction called sunda pattern. this is what makes the geological structure in south sumatra basin more complex than other basins on sumatra island. the geologic structure of jambi pattern is very clearly observed in the jambi sub-basin. the formation of northeast-southwest trending structures in this area is associated with the formation of a graben system in the south sumatra basin. the folding structure that develops on the jambi pattern is caused by the reactivation of normal faults in the plio-plistocene compressive period associated with horizontal fault. 3. method methods of this research are field observation and laboratory analysis. field observations consist of geological mapping, lithologic descriptions, and rock sampling. the sample for laboratory analysis comes from 3 rock samples taken laterally (figure 4 and 5). each sample was given a sample number and code of the location, then megascopically description was carried out. in the laboratory of research and development of oil and gas technology (lemigas). geochemical analysis aims to determine total organic carbon (toc) and rock eval pyrolysis, the results of rock eval pyrolysis are a way to know the hydrogen content. rock eval pyrolisis can estimate the hydrogen content from organic content through the value of s2. in addition, by measuring rock eval pyrolysis, we can obtain s1, s3, maximum temperature (tmax) data and potential yield (the sum of s1 and s2), oil production index (division between s1 snd potential yield), hydrogen index ((s2/toc)x100)), and oxygen index ((s3/toc)x100)). 4. sample description the sample for the geochemical analysis in this research is shale of airbenakat formation with megascopic characteristics are fresh, solid, black (as an indication of organic content), massif structure, rounded, and very well sorted. the three samples taken on the limbs of the berau anticline, so that, tectonically, the three samples affected by the geological structure. 5. data and analysis as an analogy study of source rock formation, sediment samples in the jambi sub-basin area have been evaluated by rock eval analysis and toc content. the results of the analysis will be used in determining rock organic content, rock capacity as source rock, type of organic content, level of thermal maturity, and rock potential in producing hydrocarbons (table 1) table 1. total organic carbon (toc) and rock eval pyrolysis from geochemical analysis. 132 afifah.p.d & setiawan.b./ jgeet vol 04 no 02/2019 toc : total organic content py : pyrolysis yield (s1+s2) s1 : quantity of free hydrocarbon pi : production index = s1/(s1+s2) s2 : hydrocarbon quantity from kerogen hi : hydrogen index (s2/toc) x 100 s3 : organic carbondioxide (co2) oi : oxygen index (s3/toc) x 100 tmaks : maximum temperature ( 0 c) for hydrocarbon formation from kerogen fig. 4. geological map of research area, the three samples taken in the location with symbol o on the map. fig. 5. three black shale samples were taken for geochemical analysis (a) sample of observation location 35, (b) 36, and (c) 42. no. code of sample lithology toc (%) s1 s2 s3 py pi tmax( 0 c ) hi oi (mg hc/g sample) 1. sfab 1 black shale 0,38 0,04 0,07 0,30 0,11 0,36 414 19 80 2. sfab 2 black shale 0,39 0,02 0,03 0,31 0,05 0,40 428 8 79 3. sfab 3 black shale 0,42 0,03 0,07 0,36 0,10 0,30 350 17 87 afifah.p.d & setiawan.b./ jgeet vol 04 no 02/2019 133 5. 1. total organic content one of the parameters that must be considered to determine the potential of source rock is the value of total organic carbon (toc). toc is a parameter that measured in percent (%), which is the percentage of organic carbon from the total weight of the rock sample. the toc value generated by the sample has a range of 0.38-0.42%. a rock have potential as a source rock if it has a toc content of more than 1.5% (clayton, 2005). so that, it can be seen that the three samples are categorized as rocks with the capacity as negligible source rock (waples, 1985) or have insufficient potential (poor) to produce hydrocarbons (peters and cassa, 1994) (table 2). table 2. the organic content in the three rock samples analyzed based on the classification of rocks potential in producing source rock (peters and cassa, 1994). sample result of analysis toc (%) classification of hydrocarbon potential 0-0,5 poor sfab 1 0,38 0,5-1,0 fair sfab 2 0,39 1,0-2,0 good sfab 3 0,42 2,0-4,0 very good >4,0 excellent the data of s1 represents the amount of free hydrocarbons present in the rock (clayton, 2005). the samples showed that the s1 is less than 0.5 mg hc/g and s2 showed values less than 2.5 mg hc/g of rock. thus it can be concluded that the organic content in the three rock samples is not sufficient enough to produce hydrocarbons (peters and cassa, 1994). 5. 2. type of organic content types of organic content are important in determining the potential of source rock. the material referred to this study is kerogen. kerogen is an organic carbon deposited on rocks and composed of various organic contents such as algae, pollen, spores, and plant resins. kerogen types will determine hydrocarbons that will be formed such as oil, gas, or oil and gas. the type of organic content from the three samples was determined using an s2/s3 ratio and hydrogen index value (hi) (figure 6). the plot of data shows that the ratio of s2/s3 ranges from 0.1 to 0.23, while the hi value ranges from 8-19 mg hc/g toc. so that it can be seen that organic content from the three samples are type iv kerogen. if the value of the s2/s3 ratio is below 1 and the hydrogen index value is below 50 mg hc/g toc then the type of organic content is type iv kerogen (peters and cassa, 1994). the determination of organic content type can also be determined using the tmax vs hi diagram (peters, 1986). based on the results of the plot diagram, it is found the suitability with the results of the previous diagram that showed the type of organic matter is kerogen type iv (figure 5). based on these results it can be concluded that the three rocks come from type iv kerogen of organic content that cannot produce hydrocarbons (peters and cassa, 1994). fig. 6. diagram of s2/s3 ratio versus hydrogen index (hi) type iv kerogen is interpreted come from organic content that have undergone oxidation process. the kerogen are materials that have been transportated from the environment where the material comes from (waples, 1985; peters and cassa, 1994; mc carthy et al., 2011). this interpretation is in line with the depositional environment of black shale airbenakat formation which is deposited on the marine environment, where sedimentary material is the result of transportation from terrestrial material. fig. 7 diagram of tmax versus hydrogen index (hi) (peters, 1986) 5.3. thermal maturity based on tmax data (table 1), all three samples have tmax values ranging from 350-4280c. the value range is less than 4350c which is the lower limit of the rock maturity value. therefore, it can be concluded that 134 afifah.p.d & setiawan.b./ jgeet vol 04 no 02/2019 all three samples are categorized as immature source rock. 6. discussion based on the analysis and interpretation, it is possible to evaluate the source rock for the entire sample. the sample has low total organic content so that the capacity of source rock is negligible (waples, 1985) and categorized as insufficient potential (poor) to produce hydrocarbon (peters and cassa, 1994). in this regard, it is necessary to verify the sample before analyzing toc and rock eval pyrolysis. the dark color contained in rocks is not only because it has a high content of organic matter but can be given by mineral pyrite which is abundant or can also be because the sample is in wet conditions. type of organic content in the sample is type iv kerogen. this type of kerogen cannot produce hydrocarbons (peters and cassa, 1994) because it comes from organic content that have undergone oxidation and transport processes from the environment where the material comes, this is makes the reduction of organic carbon value in rocks eventually decrease. this case was in line with the interpretation of the depositional environment of black shale airbenakat formation which is deposited in the marine environment, where sedimentary material is the result of transportation from terrestrial material. the entire sample shows a thermal maturity value of less than 4350c, the rock sample has not reached thermal maturity (immature) because the cathagenesis phase to produce hydrocarbons has not been reached. this is affected by the young age and shallow depth of the formation, so there is a low burrial procees that makes small pressure values and low geothermal gradients. 7. conclusion source rock evaluation of three black shale of airbenakat formation through toc and rock eval pyrolysis gives the following conclusions: 1. the source rock evaluation in this research focuses on elements that must be fulfilled to be said as source rock, such as the total of organic content, types of organic content, and thermal maturity. 2. total organic carbon indicates the poor category to produce hydrocarbons. 3. the types of organic content is type iv kerogen, which suitable to the depositional environment of the airbenakat formation. 4. tmax value less than 4350c indicates that the entire sample is in immature condition (the sample has not reached the cathagenesis phase). acknowledgments acknowledgment tribute to laboratory of research and development of oil and gas technology (lemigas) for analysis support. references barber, a. j., crow m. j., and milsom j. s., 2005. sumatra : geology, resources, and tectonic evolution, geological society. oxford. clayton, c., 2005. petroleum generation and migration. nautilus, ltd. ginger, d., and fielding, k., 2005. the petroleum system and future potential of the south sumatra basin. proceeding 30th annual convention and exhibition, indonesian petroleum association., 2005. mccarty, k., rojas, k., niemann, m., palmowsky, d., peters, k., and stankiewicz, a., 2011, oilfiel review summer: 23/2, schlumberger. peters, k. e., 1986, guidelines for evaluating petroleum source rock using programmed pyrolysis, the american association of petroleum geologists bulletin, no. 3, vol. 70, p. 318-329. peters, k.e and cassa, m.r., 1994, applied source rock geochemistry in the petroleum system from source to trap, usa: aapg memoir. pulunggono, a., haryo, a. and kosuma, c.g., 1992. pretertiary and tertiary fault systems as a framework of the south sumatera basin; a study of sar-maps. in proceedings indonesian petroleum association 21th annual convention. spruyt, j.n., 1956. subdvisions and nomenclature of the tertiary sediments of the jambi-palembang area. pertamina internal report. waples, d., 1985. geochemistry in petroleum exploration. boston, s.n. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc bysa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 1.1 sub introduction 2. geological framework 2.1 stratigraphy 2.2. geology structure 3. method 4. sample description 5. data and analysis 5. 1. total organic content 5. 2. type of organic content 5.3. thermal maturity 6. discussion 7. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 170 oo, k. et al./ jgeet vol 04 no 03/2019 research article ore forming fluid of epithermal quartz veins at cisuru prospect, papandayan district, west java, indonesia khayay oo 1,3, *, wayan warmada 1 , anastasia dewi titisari 1 , koichiro watanabe 2 1 department of geological engineering, gadjah mada university, yogyakarta, indonesia 2 department of earth resources engineering, kyushu university, fukuoka 819-0395, japan 3 department of geology, dawei university, dawei, myanmar * corresponding author : khayayoo123@gmail tel.:+ 959 44779801009 received: jul 19, 2019; accepted: august 07, 2019. doi: 10.25299/jgeet.2019.4.3.2279 abstract the cisuru area is located in talegong sub-district, garut regency, west java, indonesia which is belongs to the central part of southern mountain slope. the aim of this research is to understand the nature and characteristic of fluid inclusion from quartz veins (especially drill core samples) in the study area. rock units in the area are characterized by tertiary volcanic rocks and volcaniclastic sequence which is mainly composed of andesite, andesitic breccia, volcanic breccia, lapilli tuff, dacite and related to the intrusion of diorite. the cisuru epithermal mineralization is dominantly hosted by andesite, dacite, breccia and lapilli tuff, and would probably be controlled by both permeable rocks and ns and ne-sw trending strike-slip faults. the mineralization is shown as void filling and replacement within the silica zone, veinlets along with the open space/fractures and dissemination. fluid inclusion from quartz veins was studied to know nature, characteristics and origin of hydrothermal fluids. microthermometric measurements of fluid inclusions were realized by using a linkam thmsg 600 combined freezing and heating stages. homogenization temperature and final ice melting temperature were measured for primary two-phase inclusion from quartz veins. base on the study of the fluid inclusion, the value of homogenization temperature (th) range from 200 ºc to 395 °c and ice melting temperature range from -0.1 to 4.5 where salinity range from 0.2 to 7.2 wt. % nacl equivalent. fluid inclusion petrography and microthermometric measurement data exhibit that fluid mixing, dilution and boiling were main processes during the hydrothermal evolution. the formation temperature of each quartz vein is 260 ºc to 290 ºc and also their formation depth is estimated between 560m to 925m respectively. combination of fluid inclusions petrography, microthermometric measurement, and estimate paleo depth from cisuru area were suggested under the epithermal environment. keywords: quartz veins, homogenization temperature, salinity, paleo-depth, epithermal high sulfidation, cisuru prospect 1. introduction the cisuru area is one of the prospect of cjilulang gold project, parpandayan district, garut regency, west java, indonesia which belongs to central part of southern mountain slope (fig. 1). the cisuru prospect lies west java area. southern mountains [8], is one of the mineralized regions in west java. the research area is categorized as the high sulfidation epithermal prospect in the parpandayan district. this prospect was discovered by the p.t aneka tambang (antam) mining company. the research is mainly composed of volcanic and volcaniclastic rocks in tertiary age such as andesite, lapilli tuff, dacite, breccia, andesitic breccia and diorite. the presence of high sulfidation epithermal deposit at cisuru is hosted in lapilli tuff, andesite lava and breccia. it is characterized by extensive alteration of silicification (vuggy/massive silica) with advanced argillic, argillic and prophylitic alteration. generally, hydrothermal alteration in study area were suffered silicic alteration (vuggy / massive silica), advanced argillic alteration (quartz-kaolinite-dickite pyrophyllite-pyrite), argillic alteration (quartzkaolinite-illite-smectite) and prophylitic alteration (quartz-chlorite-illite-smectite). moreover, mineralized vein are observed in silicic alteration and advanced argillic alteration which occurs as vugs filling, massive vein, veinlet, replacement, dissemination and matrix in the hydrothermal breccia. the recent study focuses on nature and characteristic of fluid inclusion from quartz veins in cisuru area. based on the fluid inclusion studies, two types of fluid inclusions were distinguished in quartz veins. they are two-phase liquid-rich inclusion with vapour rich inclusions and single-phase vapour rich inclusions. the two-phase of inclusion are predominant in sample and thus used for observational homogenization temperature (th) and salinity (nacl wt. % equivalent) analyses. quartz has low salinity (0.2 to 7.2 nacl wt. % equiv) with th ranging from 210º to 385ºc. http://journal.uir.ac.id/index.php/jgeet oo, k. et al./ jgeet vol 04 no 03/2019 171 fig. 1. location map of cisuru area, parpandayan district, garut regency, west java, indonesia. fig. 2. regional geological map from sindangbarang and bandarwara sheet and rectangle showing the research area (alzwar et al., 1992). 2. geology background indonesia is situated between the eurasian plate and indo-australian and pacific plates (hall, 2009). java island is part of the sunda banda magmatic arc, which is the longest magmatic arc in indonesia. west java formed as a part of sunda banda magmatic arc system which has resulted from the subduction of indo-australian plate beneath the eurasia plate during the cenozoic time. most deposits and major prospects are associated with miocene to pliocene magmatic arcs. according to soeria-atmadjia et al., 1998, two distinct magmatic events observed within the magmatic arc. the early magmatism gas provided n coast of java island (southern mountains) in late eocene to early miocene age. the late neogene activities have produced medium to high-k calc-alkaline volcanic products such as basaltic to dacitic rocks, and their intrusive equivalents in late miocene to pliocene. the cisuru prospect is lie in the southern mountains of west java. the research area is mainly composed of tertiary calcalkaline volcanic and volcaniclastic rocks. koleberes formation and undifferentiated old volcanics including tuff, breccia and lava of the tertiary and quaternary age, are widely distributed in study area. regional geology and rock sequence of the research area and surrounding area are shown in fig 2. own mining company, pt. antam, tbk and straits resources limited (srl) since (1966), pt antam tbk in (2011) such stream sediment survey, geological mapping, geophysical survey, trenching and drilling. 172 oo, k. et al./ jgeet vol 04 no 03/2019 verdiansyah et al . 2012, described on the highsulfidation epithermal gold occurrences in the cijulang area. they were studying the type of alteration and mineralization found in volcanic rocks. alteration type occurs as advanced argillic (kaolinite, dickite, pyrophyllite, alunite, sericite pyrite), massive silica -vuggy quartz, and prophylitic (chlorite, smectite, pyrite) with crystalline tuff, phreatomagmatic breccia and dacite host rock. mineralization occurs as dissemination and fracture filling by pyrite, enargite, tennantite, sphalerite, galena, chalcopyrite in advanced argillic and massive silica. high sulfidation epithermal mineralization with gold grade> 0.4 g/t from advanced argillic. hatmanda (2013) carried out the investigation on geology and characteristics of high-sulfidation epithermal gold deposits in cijulang prospect. tun (2015) described the surface geology, mineralogy, geochemistry and origin of cijulang prospect in west java, indonesia. he was studying the surface geology and some drill core of the cjiulang area. 3. geology of the study area cisuru area is mainly composed of eocenemiocene sediments such as andesite, lapilli tuff, dacite, breccia, andesitic breccia and diorite. the main structure in the study area could be recognized by nesw trending strike-slip fault system that lies along the chikahuripan river at the central part of the area (fig. 3). mineralization is mainly hosted by tuff, andesite, and dacite which are associated with silicic and advanced argillic alterations. mineralization occurs as vugs filling, massive vein, veinlet, replacement, dissemination and matrix in the hydrothermal breccia. mineralization probably to be controlled by both permeable rocks and ne-sw trending strike-slip faults. fig. 3. geological map of research area. oo, k. et al./ jgeet vol 04 no 03/2019 173 fig 4. cross-section of drill cores dcjl 04 and dcjl 09. 4. research methods the samples were collected from drill cores which are dcjl-09 49, 56 and 293m and dcjl-04 -241m (fig. 4). quartz vein samples were prepared doublepolished section where the thickness of slice was approximately between 150 -300 µm. and then, these wafers were analyzed by microscopic study to know sizes, shapes, phases and nature of occurrences within fluid inclusions. moreover, fluid inclusion microthermometry was conducted to obtain homogenization temperature and final ice melting point of fluid inclusions using linkam thms600 heating / cooling stage. the salinity of fluid inclusions was calculated as wt. % nacl equivalent using an equation given by bondar et al.,1983. this analysis was done at the department of earth resources engineering, kyushu university, japan. 5. results 5.1. fluid inclusions petrography fluid inclusion was conducted from mineralized quartz veins in research area (fig .5). the shape of fluid inclusions shows circular, rounded, elongated, prismatic, negative crystal faceted. the size of fluid inclusion in this research ranges from 2-25 µm. the common size of fluid inclusions are 10-20 µm. these fluid inclusion have occurred along the growth zones. it was classified primary fluid inclusions as well as secondary fluid inclusions. the primary fluid inclusion were occurred within mega-quartz cement characterized by their alignment along concentric growth zones. and then, secondary fluid inclusions were observed trapped along the fracture. in addition, secondary necking inclusions are found in this sample which is a typical dissolution precipitation process that are led to negative crystal faceted. all measured fluid inclusions are vapour + liquid phase (fig. 6). the vapour bubbles were occupied 10-80 vol. % of the inclusions. there are three types of fluid inclusions are identified based on their phase relation (a) two-phase (l+v) liquid-rich inclusions (fig 6-c, f, and d), (2) twophase (l+v) vapor-rich inclusion (figure 7-e) and (3) two-phase (l+v) vapor and liquid-rich inclusions (fig. 6). liquid and vapour characteristic of fluid inclusions are commonly utilized to determine where or not boiling has observed within the hydrothermal system. two-phase fluid inclusions with constant ration of liquid and vapour are exhibited that consistent condition of temperature and pressure (non-boiling condition) in hydrothermal system. on the other hand, two-phase fluid inclusions are coexisting liquid-rich and vapour rich in the same place which is indicating the boiling or effervescence fluid system (fig. 6, a). 174 oo, k. et al./ jgeet vol 04 no 03/2019 fig 5. photograph of mineralized quartz veins showing the a) quartz vein found in lapilli tuff dcjl-04 241m, b) quartz sulfide veinlet observe in lapilli tuff dcjl-09 49m, c) vuggy quartz occur as vein dcjl-09 56m, d) quartz sulfide veins occur in andesite dcjl-09 283m. fig 6. (a) photomicrograph of fluid inclusions in quartz (a, b) two phase fluid inclusion from dcjl -09 283m, (c, d) liquid rich fluid inclusion from dcjl-09 49m, 56m, (e) vapor rich fluid inclusion from dcjl-04 241m, (f) necking down fluid inclusion from dcjl-09 49m. (l = liquid, v = vapor). oo, k. et al./ jgeet vol 04 no 03/2019 175 5.2 fluid inclusion microthermometry in this research, fluid inclusion microthermometry can be measured to estimate formation temperature, salinity and paleo depth of hydrothermal fluid. the homogenization temperature (th) were measured range from 200 to 334 °c with ice melting temperature range from -01 to -3.1°c at dcjl -09 49m, 250 to 308 °c with ice melting temperature range from -0.2 to -3 °c at dcjl -09 56m, 210 to 385 ºc with ice melting temperature range from -0.2 to -4.5 °c at dcjl -09 283m respectively (fig. 7). additionally, homogenization temperature (th) of dcjl 04 241m range of 230 to 395 ºc (fig. 7-d) with ice melting temperature range from -0.2 to -2.7 °c. the formation of ice melting temperature were shown -0.8 and -1 °c for dcjl-09 49m, -0.5 °c for dcjl09 56m, -2.2 and -2.7 °c for dcjl-09 283m and -1 and 1.2 for dcjl-04 241m (fig. 7-a,b,c, d). as a result, the homogenization temperature of fluid inclusions for cisuru area ranging from 200 to 395 ºc that suggested by high sulfidation epithermal deposit. the salinity of fluid inclusions from homogenization temperature (tm) of each sample were calculated, ranging from 0.2 to 5.1 wt. % nacl equivalent for dcjl-09 49m, 0.4 to 5.0 wt. % nacl equivalent for dcjl-09 56m, 0.4 to 7.2 wt. % nacl equivalent for dcjl-09 283m, 0.4 to 4.5 wt. % nacl equivalent for dcjl-04 241m. a plot salinity versus homogenization temperature and salinity are used in order to recognize the mineral deposits (wilkinson, 2010). especially, salinity and homogenization temperature of fluid inclusions were very important for estimating the formation temperature, trapping pressure, paleo-depth, fluid evolution process and deposit type. fig 7. histogram showing the homogenization temperature of fluid inclusion in quartz veins (a) dcjl-09 49m, (b) dcjl-09 56m, (c) dcjl-09 283m and (d) dcjl-04 241m. based on salinity and homogenization temperature (th) diagram, the trend of increasing temperature and salinity (positive directions) estimates fluid dilution process for dcjl-09 49m and for dcjl-04 241m (fig.8a,d). moreover, the trend of decreasing temperature with increasing salinity (negative directions) indicates boiling process for dcjl-09 56m (fig .8-b). otherwise, fluid mixing also could be happening by adding and mixing with more or less saline solutions some fluid in specific mixing trend in fig.10-c. fig 8. the salinity and th of fluid inclusions in quartz veins (a) dcjl-09 49m, (b) dcjl-09 56m, (c) dcjl-09 283m and (d) dcjl-04 241m. 5.3 discussions based on the fluid inclusion petrography and microthermometric measurement results, which is estimated the cooling, mixing and boiling of fluid inclusions, formation depth, pressure, temperature and type of deposit. according to the fluid inclusion petrography, characteristics of two phase (l+v) fluid inclusions were dominantly classified to determine whether or not boiling has observed within the hydrothermal system. fluid inclusions are trapped in immiscible or boiling fluid system, some of the fluid inclusion will trap in the liquid phase, some will trap in the vapor phase, and some will trap in the mixture of the two phases (bodnar et al. 1985). in the research area, intergrowth of liquid rich and vapor rich fluid inclusions were indicated boiling condition. moreover, vapor rich fluid inclusion were indicating the intense boiling condition (moncada and bondar, 2012). in addition, dominant two phase fluid inclusions, moderate th (200-395 ºc) and low salinity (>7.5 wt. % nacl equ.) are closely similar to high sufidation epithermal system (arribas et al., 1995). depend on the fluid inclusion microthermometry, homogenization temperature and salinity were determined to show fluid characteristics. salinity and homogenization temperature (th) diagram assumed that positive direction estimates fluid dilution process (fig 8-a, d) and negative trend indicates boiling process (fig 8-d). and then, coexistent of two phase liquid rich and vapor rich fluid inclusions are observed in same place (fig. 6-a) were indicating the boiling or effervescence fluid system. moreover, fluid mixing also could be happen by adding and mixing with a more or less saline solutions some fluid in specific mixing trend in fig-c. in place, the mixing process can be caused by meteoric fluid, or falling water table due to uplift and erosion roedder, 1984 and bondar et al., 1985. the homogenization 176 oo, k. et al./ jgeet vol 04 no 03/2019 temperature and salinity fluid inclusion data from the study area belongs the epithermal environment where mixing, boiling and dilution have been taken place in fluid system (fig. 9). otherwise, dominant two phase fluid inclusions, moderate th (200-395 ºc) and low salinity (>7.5 wt. % nacl equ.) are classified as high sufidation epithermal system . salinity and homogenization temperature (th) result from research area can be suggested that it occupied within the epithermal deposit (fig. 10). the fluid densities are important with respect to the mechanism of fluid flow and evaluation of spatial variations in fluid that constrain on the flow process (wilkinson, 2001). density of fluid inclusion in the study area shows range from 0.6 to 0.9 g/cm3 (fig. 10). the formation temperature of fluid inclusion from quartz veins can be used to know formation temperature and their salinity content in fluid. the effect of salinity on the temperature-depth relation of brain adjuata the boiling curve to determine the paleodepth where including fluid inclusions which indicate boiling of the brain (hass, 1971). the formation depth of fluid inclusion can assumed that 270°c for dcjl-09 49m, 280 °c for dcjl-09 56m, 290 °c for dcjl -09 283m and 260 °c for dcjl-04 241m respectively. the estimated formation depth are 560m for dcjl-04 241m, 660m for dcjl-09 49m, 790m for cjl09 56m and 930m for dcjl-09 283m below the paleo water table (fig. 11). fig. 9. salinity versus homogenization temperature th (◦c) for fluid inclusion in four quartz veins from cisuru deposit. (wilkinson, 2001). fig 10. salinity vs homogenization temperatures th (ºc) diagram illustrating typical range for fluid inclusion from different type of deposits and their density range. note that files should not be considered and compositions exist outside the ranges (wilkinson, 2001). oo, k. et al./ jgeet vol 04 no 03/2019 177 fig 11. diagram of temperature and paleo depth with boilingpoint curves for brines of constant composition given in wt. % nacl equv. [12], showing an estimation of average minimum formation depth of quartz veins from cisuru deposits. 6. conclusions fluid inclusion study is very important to know the condition of hydrothermal fluids and their origin. according to fluid inclusion petrography and microthermometric results, quartz veins of research area are suggested by moderate homogenization temperature (th) and low salinity. most of the fluid inclusion trapped in growth zone of quartz veins which shows mega-quartz crystal where two-phase fluid inclusions (l+v). these inclusions are liquid-rich, whereas coexisting of vapor rich inclusions are occurred in the sample indicating that boiling observed in the hydrothermal system of research area. the homogenization temperature and ice melting were measured two-phase of primary fluid inclusion. the homogenization temperature are ranging from 200 to 395 ºc for four quartz veins. the salinity of fluid inclusion range from 0.2 to 7.2 wt. % nacl for all quartz veins. moreover, formation temperature of all quartz veins are 260 to 290 ºc and also their formation depth are estimated between 580 m to 925 m. according to fluid inclusions petrography and microthermometric measurement, it can be suggested that the mineralization the research area is classified into the high sulfidation epithermal deposit. acknowledgement i would like to grateful thank aun/seed-net (jica) japan international cooperation agency for supporting to carry out this research. i am special thanks to pt antam tambang, tbk for their permission to do research in this area. references arribas, a. jr., 1995, characteristics of high-sulfidation epithermal deposits, and their relation to magmatic fluid: mineralogical association of canada short course, 23, 419 454 alzwar, m., akbar, n. and bachri, s. 2004 ge ological map of the garut and pameungpeuk quadrangle, jawa, in: gafoer, s., amin, t.c. and simandjuntak, t.o. (eds.), garut 1208-6 & pameungpeuk 1208-3, second edition. geological research and development centre, bandung. scale 1: 100.000aspden, j.a., stephenson, b., and cameron, n.r., 1982a, tectonic map of northern sumatra (1:500,000) british geological survey. bodnar, r.j. 1993. revised equation and table for determining the freezing point depression of h2o-nacl solution, geochimica et cosmochimica acta 57: 683-684. bodnar, r.j., reynolds, t.j., and kuehn, c.a., 1985. fluid inclusion systematic in epithermal systems: reviews in economic geology, 2, 73 97. hamilton, w.h., 1979. tectonics of the indonesian region. u.s. geological survey professional paper, 1078, 345 haas. j.l. jr., 1971. the effect of salinity on the maximum thermal gradient of a hydrothermal system at hydrostatic pressure. econ geol. 66, 940 946. hatmanda. m, geology and characteristics of highsulfidation epithermal gold deposits in cijulang prospect, papandayan district, garut, west java. thesis (msc) (unpublished), 2013. roedder. e, 1984. mineral., vol. 12, no. reviews in mineralogy. soeria-atmadja, r., suparka. s., abdullah. c., noeradi. d., and sutanto, 1998. magmatism in western indonesia, the trapping of the sumba block and the gateways to the east of sundaland. journal of asia earth science, 16,1, 1-12. tun, m.m. 2015. geology, mineralogy, geochemistry and origin of cijulang high sulfidation epithermal gold prospect, west java. ph.d .thesis. van bemmelen, r.w., 1949, the geology of indonesia, v.f.a. government printing office, the hague, 732 verdiansyah, o., bangun, p., and rahmat, i., 2012. high sulfidation epithermal gold occurrences in cijulang area, garut, west java. proceeding of pit iagi yogyakartar 2012, the 14 th iagi annual convention and exhibition. wilkinson, j.j., 2001. fluid inclusions in hydrothermal ore deposits. elsevier science, lithos 55 (2001), 229-272. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ ore forming fluid of epithermal quartz veins at cisuru prospect, papandayan district, west java, indonesia 1. introduction 2. geology background 3. geology of the study area 4. research methods 5. results 5.1. fluid inclusions petrography 5.2 fluid inclusion microthermometry 5.3 discussions 6. conclusions acknowledgement references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 83 research article alteration, mineralization and geochemistry of metamorphic rocks hosted hydrothermal gold deposit at rumbia mountains, bombana regency, southeast sulawesi, indonesia hasria 1 , arifudin idrus 2 , i wayan warmada 2 1 department of geological engineering, halu oleo university, indonesia 2 department of geological engineering, gadjah mada university, indonesia *corresponding author : hasriageologi@gmail.com received: nov 11, 2018; accepted: may 30, 2019. doi: 10.25299/jgeet.2019.4.2.2346 abstract in indonesia, gold is commonly mined from porphyry, epithermal and skarn type deposits that are commonly found in volcanic/magmatic belts. however, were recently numerous gold prospects discovered in association with metamorphic rocks. this paper is intended to describe an alteration and ore mineralogy hosted by metamorphic rocks at rumbia mountains, bombana regency, southeast sulawesi province, indonesia. the study area is found the placer and primary gold hosted by metamorphic rocks. the placer gold is evidently derived from gold-bearing quartz veins hosted by pompangeo metamorphic complex (pmc). this study is conducted in three stages, three stages including desk study, field work and laboratory analysis. desk study mainly covers literature reviews. field work includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rocks types, altered rocks and gold-bearing veins. laboratory analysis includes the petrologic observation of handspecimen samples, petrographic analysis of the thin section and ore microscopy for polished section, xrd (x-ray diffraction), icp-aes (inductively coupled plasma atomic emission spectroscopy), icp-ms (inductively coupled plasma emission mass spectrometry and fa/aas (fire assay/atomic absorbtion spectophotometry) analysis. the results shows that the alteration characteristics of hydrothermal gold deposits in mendoke and rumbia mountain consist of 3 (three) alterations namely sericitic, argillic dan propylitic. characteristics of mineralization hydrothermal gold deposits in the research area are generally p related to gold-bearing quartz veins/veinlets consist of chalcopyrite, pyrite, chrysocolla, covellite, cinnabar, magnetite, hematite and goetite in rocks categorized into greenschist facies. there are three generations of veins identified including the first is parallel to the foliations, the second crosscut the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage. the quartz veins commonly deformed, segmented, massive, laminated, irregular, brecciated, and occasionally sigmoidal. the veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18,4000 at found in third generation veins which are laminated quartz±calcite in argillic alteration. ppm. the protoliths of metamorphic rocks in rumbia mountain, which comes from sedimentary rocks, spesifically pelitic rocks and graywacke. based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposits type. the orogenic gold deposit is one of the new targets for exploration in indonesia. keywords: alteration, ore mineralogy, hydrothermal gold deposit, metamorphic rocks, rumbia mountains, southeast sulawesi. 1. introduction gold has had an impact on the everyday economic activities of ordinary people since at least egypt in 1400 bc, where it was used as a monetary standard. perhaps the most famous usage of gold was as money under various gold standards. gold is one metal of the most malleable, ductile, dense, conductive, nondestructive,brilliant, and beautiful ofmetals. this unique set of qualities has made it a coveted object for most of human history in almost every civilization ( et al., 2015). based on this, many researchers and mining companies are trying to find gold reserves to explore. commonly, gold is mostly mined in indonesia from hosted by vulkanic rocks including porphyry, epithermal, and skarn type deposits that are commonly found in volcanic belts along island arcs or active continental margin settings. several gold deposits were discovered are batu hijau in sumbawa island island (idrus et al., 2007; imai & ohno, 2005) and grasberg in papua including porphyry type; pongkor in west java java (warmada, 2003), gosowong in halmahera island including epithermal type and erstberg, kucing liar, deep ore zone (doz) in papua including skarn type. in sulawesi island, gold is also predominantly related to volcanic rocks, which are extended along western and northern http://journal.uir.ac.id/index.php/jgeet 84 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 neogene magmatic arcs of the island island (idrus, 2009) (fig. 1). however, were recently in gold exploration activities are not only focused along volcanicmagmatic belts, but also starting to shift along metamorphic and sedimentary terrains because numerous gold prospects discovered in association with metamorphic and sedimentary rocks. several primary gold deposits were discovered with metamorphic rocks for instance, langkowala area and wumbubangka mountaints, bombana in southeast sulawesi (idrus & prihatmoko, 2011; idrus, et al., 2011; idrus et al., 2012), , awak mas in south sulawesi; poboya lsepithermal in central sulawesi (wadji et al., 2011) and gunung botak in buru island, mollucas (idrus et al., 2014). gold-bearing quartz veins are also recognized in derewo metamorphic belt at northern and northwestern part of central range papua. some exploration reports categorized the derewo metamorphic-related quartz veins into mesothermal gold deposit type (idrus et al., 2014). fig. 1. geological setting of sulawesi island and location of the study area in rumbia mountains (squared area), southeast sulawesi (modified from leeuwen and pieters, 1992). fig. 2. geological geological map of rumbia mountains area occupied by paleozoic metamorphic rocks (pompangeo complex; mtpm) (modified from simandjuntak et al., 1993). squared area indicates the location area of this study. hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 85 the gold mineralization genetically occurs in association with sedimentary rocks is paningkaban, banyumas regency, central java (idrus et al., 2015). rumbia mountains area is located in the bombana regency of southeast sulawesi, indonesia (fig. 2). this research aims to explore the alteration and ore mineralogy of metamorphic rocks hosted hydrothermal gold deposit at rumbia mountains by the application of petrographic, ore microscopy and xrd (x-ray diffraction), icp-aes (inductively coupled plasma atomic emission spectroscopy), icp-ms (inductively coupled plasma emission mass spectrometry) and fa/aas (fire assay/atomic absorption spectrometry) analysis. this study is an important stage for the next exploration of gold in the area or other areas that have an identical setting of geology. metamorphic rock-hosted gold deposits could represent the new targets for gold exploration particularly in indonesia. 2. geological setting the stratigraphy in the southeastern arm of sulawesi consists of three constituent rocks are sulawesi molasse composed of clastic sediments and carbonate, ophiolite complex are dominated by mafic and ultramafic rocks and continental terrain composed of metamorphic rocks. contacts between the ophiolite complex and continental terrain, including their basement rocks are faulted. the sulawesi mollase unconformably overlies both the ophiolite complex and continental terrain. the mountains rumbia is a part of continental terrain is subsequently occupied by metamorphic rocks (pompangeo complex, mtpm) consisting of mica schist, quartzite, glaucophane schist and chert. the continental terrain, which was first described by surono, 1994. the metasediments and metamorphic rocks are of permiancarboniferous in age and occupy the mendoke and rumbia mountains. mica schist and metasediments particularly meta-sandstone and marble are commonly characterized by the presence of quartz veins various width up to 2 meters, containing gold in some places (idrus et al., 2011). the langkowala formation is unconformably underlain by paleozoic metasediments and metamorphic rocks (pompangeo complex, mtpm) and conformably overlain by the eemoiko formation (tmpe), which is composed of corraline limestone, calcarenite, marl and sandstone; and boepinang formation (tmpb), which is composed of sandy claystone, sandy marl and sandstone. the eemoiko and boepinang formations were reported having pliocene age (surono, 2013). 3. research methods field investigation was carried out in rumbia mountains area of southeast sulawesi. the samples consist of altered rock, veins and clay samples collected from different hydrothermal alteration zones and ore samples. this study is conducted in four stages including fieldwork, laboratory analyses, data analyses and interpretation. fieldwork includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rock types, altered rocks and gold bearing veins. laboratory work includes slab, vein textural dan structural analyses and mineralogy (petrography, ore microscopy and xrd (x-ray diffraction); rock geochemistry (icp-aes (inductively coupled plasma atomic emission spectroscopy) and icpms (inductively coupled plasma emission mass spectrometry); ore geochemistry or bulk-ore chemistry fa/aas (fire assay/atomic absorbtion spectrometry) analysis. the mineralogical analysis was conducted at department of geological engineering, gadjah mada university; rock geochemistry and bulk-ore chemistry was done at als global geochemistry analytical laboratory in north vancouver, bc, canada, als canada ltd in canada. 4. characteristics of quartz veins the quartz veins in the study area consist of three generations. the first is parallel to the foliations, the second crosscuts the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage (fig. 3). the texture of quartz veins are mostly sheared/ deformed, irregular vein, brecciated, and relatively massive segmented, laminated in accordance with the criteria of yilgarn block orogenic gold deposits in western australia, racetrack west australia and sigma mine in canada (groves, 1993; groves et al., 1998). based on data shows that gold-bearing quartz (qz) veins/veinlets have been discovered in association with paleozoic metamorphic rocks particularly mica schist, actinolite schist, phyllite and metasandstone which are petrologically categorized into facies of greenschist, where this type of metamorphic facies mostly become the host of orogenic gold deposits in entire world, such as yilgran block orogenic gold deposits in western australia, juneau gold belt, talkeetna mts south-central, east-central, seward peninsula in alaska, slave province, canada (groves, 1993; groves et al., 1998; goldfarb et al., 2015); and in wiluna, racetrack, mt charlotte, golden mile, lancefield in western australia and in ross mine, kircland lake, dome, canada, hollinger mcintyre in canada, muruntau in uzbekistan, morro velho in brazil, ashanti in ghana, homestake in usa and bendigo in australia , mother lode in the united states (groves et al., 1998; 2003; gebre-mariam et al., 1995). 5. characteristic of hydrothermal alteration hydrothermal alteration and mineralization underlie within all lythologic units found in the research area. widespread zones of hydrothermal alteration are found on the surface. alteration is typically pervasive and selective pervasive with intensity ranges from weak to strong, so it is very rare to observe good outcrops in the area. in general, the wallrocks are weakly altered. strong alteration zone is only restricted surrounding quartz veins (like halos/selvage). hydrothermal alteration in rumbia mountains is determined by surface geological data, petrography analysis, and supported by xrd analysis. the determination of alteration zone in rumbia mountain is based on corbett and leach, 1997 and thompson and thompson, 1996. 86 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 fig. 3. characteristics of quartz vein : (a). brecciated, sheared/deformed quartz vein (first generation) parallel to the foliation, b) massive, crystalline of quartz vein, (first generation) which is parallel to the foliation, c) brecciated, sheared/ deformed quartz vein (second generation) d). irregular vein, sheared/segmented of quartz vein crosscutting foliation (second generation), (e) a cluster of sheared/deformed laminated quartz vein (third generation), (f) laminate quartz vein (third generation). hydrothermal alteration in rumbia mountains comprises 3 (three) types (fig. 4), namely sericitic, argillic and prophyllitic alteration. sericitic alteration is characterized by the presence of muscovite and or sericite-quartz-opaque; argillic alteration is characterized by the presence of clay minerals/clayquartz-opaq; prophyllitic alteration is characterized by the presence of chlorite-epidote-calcite and others minerals like pyrite and opaque minerals. clay mineralogy of altered rocks was identified in detail by xrd studies. based on xrd analysis, the clay at argillic alteration consists of illite and kaolinite minerals. the three alterations were corresponding to kalgoorlie orogenic gold deposits in australia, val d'or in canada, ashanti in ghana and mother lode in the united states (groves et al., 1998). 5.1 ree geochemistry discrimination rare earth elements can potentially be remobilized during alteration, particularly k-silicate (potassic), sericitic, argillic and propylitic alterations (idrus et al, 2009). ree diagram-chondrite normalized must use the same sample with some variations of alteration to determine the enriched and depleted of ree elements in one type of rock based on the analysis result from icpaes and icp-ms. the patterns show that the ree are depleted with increasing alteration intensity from the least-altered rock (shaded area), through prophyllitic, sericitic and argillic alteration. the value of ree elements in chlorire-schist rock in rumbia mountains has a decreasing trend started from prophyllitic alteration, followed by sericitic, and ended by argillic. characteristics of ree geochemistry rumbia mountains has significantly depleted of ree elements in high/total intensity of argillic alteration samples with pervasive texture. the value of ree is commonly depleted together with increasing in alteration intensity (fig. 5). the depletion of ree is also closely related to the stability of hydrothermal minerals during alteration. the lree in the altered rocks of the chlorite-epidote and transitional chlorite-sericite alteration zones, however, are slightly increased which may indicate that epidote and chlorite accommodate the released ree during the breakdown of the primary phases. the sericite altered rocks are commonly enriched in the hree, due to the ability of sericite and possibly chlorite to absorb the released elements. the argillic altered rocks display the strongest ree depletion, which is explained by the complete breakdown of the primary feldspar and mafic minerals during the alteration. hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 87 fig. 4. hyrdothermal alteration types : (a,b). sericitization, (c,d). argillic, (e,f). propylitic alteration. the scale bar without expression in each of photomicrograph on this paper indicates 1 mm. x-nicol 40x. opq= opaq, ms= muscovite, ser= sericite, qz= quartz, rt= rutil, gln= glaucophane, cly=clay,, chl= chlorite, ep= epidote, 88 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 fig. 5. ree-chondrite normalized patterns discriminating various alteration zones within the rumbia mountains deposit with respect to the chloritic schist rocks with several alteration zones(sun & mcdonough, 1995). 6. characteristics of mineralization based on field relationship, ore microscopy, electron microprobe analyses, there some precious metal identified consist of native gold and ore mineralization including pyrite (fes2), chalcopyrite (cufes2), hematite (fe2o3), cinnabar (hgs), covelite (cus), chrysocolla ((cual)2h2si2o5nh2o), sinnabar (hgs), magnetite (fe3o4) and goethite (feho2) (fig. 6) which related to the yilgarn block orogenic gold deposits in western australia (groves, 1993). the presence of sb and hg in all samples genetically indicates that the orogenic gold deposits in epizonal and mesozonal zones as same as wiluna deposits, racetrack, mt. charlotte, golden mile, lancefield, in western australia and in ross mine, kircland lake, dome, in canada (groves, 1993; groves et al., 1998; gebre-mariam et al., 1995). idrus et al. (2012) also reported the presence of tripuhyite (fesbo4) and rare arsenopyrite (feass2) are present in the quartz veins and silicified metamorphic wallrocks. the presence of geological structure is a controlling factor of mineralization, which is southeast-northwest oriented faults and northeast-southwest oriented faults. gold, stibnite, and arsenopyrite which can not be found in rumbia mountain with ore microscope but have minor possibility to be present due to fa/aas analysis, those are au = < 0.0002-18.4 ppm; as = 0.69-1,840 ppm; sb = 0.635-6,170 ppm. pyrite, hematite, cinnabar and stibnite are present abundantly in the primary mineralization gold deposits, present in the quartz veins and wallrocks; and commonly present at alteration rocks (fig. 7). pyrite occurs as isolated idiomorphic crystals, angular fragmens,, strongly brecciated fragments, anhedral shape, medium reflectance and isotropic. some pyrite grains are partly enclosed by hematite, chalcopyrite and possibly stibnite. fractures and brittle cavities in pyrite are often filled by hematite and chalcopyrite. hematite is typically pinkish orange in color and commonly present in altered rocks, internal purple reflections, subhedral-anhedral crystals, present as sulfide mineral interactions with oxygen causing the oxidation of sulphide minerals, especially pyrite. hematite is looked replacing pyrite. chalcopyrite is associated with pyrite while cinnabar is typically pinkish red in color and commonly occurred in the form of mineralized layers along foliations of the metamorphic rocks. pyrite, hematite, cinnabar and stibnite are genetically closely related to gold mineralization (hasria et al., 2017). hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 89 fig. 7. ore minerals in study area. a. goethite. b. hematite is looked replacing pyrite. c. chrysocolla is replacing chalcopyrite. d. chalcopyrite is looked replacing covelite and hematite is looked replacing pyrite. e. magnetite and hematite. f. the present of abundantly cinnabar in mineralization of hydrothermal gold deposits. g. chrysocolla is replacing chalcopyrite. h. hematite is looked replacing pyrite. goethite. the scale bar without expression in each of photomicrograph on this paper indicates 1 mm. py= pyrite, ccp= chalcopyrite, hem= hematite, cin= cinnabar, gth= goethite, mag = magnetite, ccp= chalcopyrite, ccl = chrysocolla. bulk-ore chemistry the concentration of carrier minerals of gold (au), copper (cu), silver (ag), lead (pb), zinc (zn), arsen (as), stibnium (sb), and mercury (hg) by geochemistry analysis from fa/aas (table 1.). the concentration of gold in vein ranging from < 0.0002 ppm to 18.400 ppm. the highest concentration is found in third generation veins which are laminated quartz±calcite in argillic alteration. to show the correlation between two orecarrier minerals, a linear function logarithmic graph was generated (fig. 7.). those sulfides could be pathfinder minerals for the exploration of the metamorphic-hosted gold deposit. in general, gold is very fine-grain, but occasionally native gold is visible in quartz veins. bulk-ore chemistry analyzed by fa/as (fire assay/atomic absorption spectrometry) indicates a very broad and erratic variation of gold grade ranging from below detection limit <0.0002 ppm to 18.4000 ppm au (table 1). based on linear function logarithmic graph (fig. 8) between gold 90 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 (au) and arsen (as), au to stibnium (sb), and au to mercury (hg) show linear graphics, so that sb, as, and hg can be seen as pathfinders to find the occurence of gold (au) in study area. however, au and other elements do not show any linear graphic. this indicates that the elements can not be seen as path finders in determining gold occurence in the study area. however the relation of arsen (as) to stibnium (sb), sb to mercury (hg), and as to hg, also show the presence of linear graphic. this indicates that as can be seen as path finder to find sb and hg. the same thing happens to sb, it can be used as a path finder to find hg and as. based on linear function logarithmic graph which is characterized by the linear correlation between sb and hg, then it can be concluded that the deposits in study area is orogenic gold deposits and if correlated to the concept of orogenic gold deposits by gebre-mariam, et al (1995) due to the formation zone of orogenic gold deposits, then it is possible that the zone is in epizonal and mesozonal zone. table 1. ore geochemistry of metamorphic-hosted gold quartz veins/reefs from rumbia mountains, bombana (in ppm). samples code elements (ppm) au ag as cu hg pb sb zn dhr 11 0.0007 1.170 0.69 17.15 0.007 29.9 3.86 45.2 dhr 15 0.0007 0.232 2.53 45.1 0.021 8.22 0.975 56.1 dhr 16 <0.0002 1.620 4.22 71.8 <0.004 29.3 7.33 66.8 dhr 20 <0.0002 0.138 3.85 31.7 0.072 13.20 0.675 47.1 dhr 24 0.0004 1.420 5.38 28.1 0.013 48.2 6.85 87.9 dhr 25 0.0008 0.161 5.35 13.75 0.005 8.18 1.285 12.7 dhr 34 0.0048 0.619 27.8 123.5 0.015 24.4 2.46 34.7 dhr 35a 0.0779 0.093 194.5 7.70 0.577 4.22 19.60 4.3 dhr 50 0.0017 0.650 1810 43.0 1.375 83.0 6170 109.5 dhr 55 0.0124 0.014 49.1 61.9 0.287 11.15 1.795 59.5 dhr 62 0.0049 0.405 17.50 7.79 0.065 11.40 28.0 12.3 dhr 66 0.0071 0.191 160 708 0.085 10.10 3.21 138.5 dhr 74b 0.0009 0.491 2.52 4.70 0.010 19.45 5.06 10.8 dhr 76a 0.0009 0.103 3.23 17.70 0.076 19.35 0.733 48.4 dhr 81a 0.0014 0.564 32.4 179.0 0.014 9.10 2.06 61.3 dhr 85a 0.0024 3.10 2.44 1505 0.020 3.99 0.739 59.4 dhr 87 0.0002 0.281 2.88 1150 0.010 8.44 6.30 11.8 dhr 87a 0.0015 0.112 4.11 30.8 0.032 24.4 0.635 27.9 dhr 97a <0.0002 0.041 4.48 51.00 0.011 4.68 1.835 39.9 dhr 101 0.7200 0.300 1840.0 43.00 0.080 6.00 21.000 53.0 dhr 103 0.0800 0.100 69.00 26.00 0.210 2.00 2.000 14.0 dhr 104 18.4000 0.300 192.00 44.00 0.310 27.00 62.000 52.0 dhr 105 0.9800 < 0.100 292.00 23.00 0.150 28.00 17.000 49.0 dhr 107 3.7600 0.100 852.00 25.00 0.340 11.00 37.000 42.0 dhr 108 0.2600 0.100 201.00 44.00 0.440 9.00 148.000 57.0 dhr 109 0.6300 < 0.100 118.00 28.00 0.070 9.00 32.000 53.0 dhr 110 0.1500 0.300 279.00 43.00 0.290 18.00 160.000 77.0 dhr 111 0.2200 0.100 75.00 45.00 0.080 11.00 34.000 20.0 dhr 113 < 0.0100 0.100 18.00 15.00 0.430 < 2.00 7.000 11.0 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 91 fig. 8. linear function logarithmic graph showing the correlation between au to cu, ag, pb, zn, as, sb, and hg; and the correlation between as to sb, sb to hg, as to cu, as to zn, sb to pb, as to hg, as to pb, and hg to pb. 8. conclusion hydrothermal alteration of gold deposits consists of three zones such as sericitic, argillic, propylitic alterations. the quartz veins consist of 3 (three) types of veins such as quartz vein lied parallel to the foliation, quartz veins which crosscuts the first generation of veins/foliations and the laminated quartz vein which is the gold bearing quartz vein. as for how the characteristics of quartz vein which associated with the ore minerals, the quartz vein texture is generally deformed, segmented, laminated, massive, brittle, and sometimes sigmoidal. the gold-bearing-quartz vein is commonly found in metamorphic rocks such as mica schist, chlorite schist, and phyllite which are petrologically categorized into facies of greenschist, where this type of metamorphic facies mostly become the host of orogenic gold deposits in the entire world. the veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18,400 ppm. mineralogically, gold is genetically related to consist of pyrite (fes2), chalcopyrite (cufes2), hematite (fe2o3), cinnabar (hgs), stibnite (sb2s3) and goethite (feho2). it shows that the element of stibium, arsenic and mercury can be used as a pathfinder (reference) to find the existence of gold. gold is mainly identified in the form of 'free gold' among silicate minerals particularly quartz. based on characteristics hydrothermal alteration, quartz vein, host rock and mineralogically, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposit type . the orogenic gold deposit is one of the new targets for exploration in indonesia. acknowledgments completed at the department of geological engineering, faculty of engineering, gadjah mada university yogyakarta, indonesia. this study was made possible through financial support from ristekdikti. the authors are very thankful to the management of the panca logam makmur (plm) 92 hasria, idrus a and warmada i. w./ jgeet vol 04 no 02/2019 company, which has given permission to do. thanks to mr. la ode ngkoimani and suryawan asfar for facility assistance during field fieldwork. special thanks to my students from the department of geological engineering, halu oleo university for their assistance during the fieldwork. we also would like to thank the head and staff of the geological engineering department, faculty of engineering, gadjah mada university who gave me permission to access to the laboratories. references corbett, g.j & leach, t.m., 1997. southwest pacific rim goldcopper system : structure, alteration and mineralization, short course manual, corbett geological services 29 carr street north sydney nsw 2060 australia and terry leach and co coromandel new zealand. gebre-mariam, m., hagemann, s.g., and groves, d.i., 1995. a classification scheme for epigenetic archaen lode-gold deposits. mineralium deposits, 30, 408-410. goldfarb, r.j., and groves, d.i., 2015. orogenic gold : common or evolving fluid and metal sources through time. lithos, 233, 2-26 goldfarb, r.j., baker, t., dube, b., groves, d.j., hart, c.j.r., and gosselin, p., 2005. distributioncharacter and genesis of gold deposits in metamorphic terrains. in: hedenquist, j.w., thompson, j.f.h., goldfarb, r.j., richards, i.p (eds.), economic geology. one hundred th anniversary volume, p. 407-450. groves, d.i., 1993, the crustal continuum model for latearchaean lodegold deposits of the yilgarn block, western australia: mineralium deposita, v. 28, p. 366 374. groves, d. i., goldfarb, r. j., and robert, f., 2003. gold deposit in metamorphic belts: overview or current understanding, outstanding problems, future research, and exploration significance. economic geology, 98, p.1-29. groves, d. i., goldfarb, r. j., gebre-mariam, m., hagemann, s. g., and robert, f., 1998. orogenic gold deposit: a proposed classification in the context or their crustal distribution and relationship to other gold deposit types. ore geology review, 13, p.7-27. hasria., idrus, a., warmada, i.w. 2017. the metamorphic rocks-hosted gold mineralization at rumbia mountains prospect area in the southeastern arm of sulawesi island, indonesia. journal of geoscience, engineering, environment, and technology, 2, 213-227. idrus, a., 2009. potensi sumberdaya mineral bijih pada busur magmatik sulawesi bagian barat dan utara, invited speaker makassar, 3 oktober 2009, 26pp. idrus, a., fadlin., prihatmoko, s., warmada, i.w., nur, i., and meyer, f.m., 2012. the metamorphic rock-hosted gold mineralization at bombana, southeast sulawesi: a new exploration target in indonesia. jurnal sumber daya geologi, (22) 1: 35-48. idrus, a., hakim, f., warmada, i.w., aziz, m., kolb, m and meyer, f.m., 2015. geology and ore mineralization of neogene sedimentary rock hosted ls epithermal gold deposit at paningkaban, banyumas regency, central java, indonesia.journal of southeast asian applied geology,volume 7(2), pp. 73-79. idrus, a., kolb, j., and meyer, f.m., 2007. chemical composition of rock-forming minerals in copper-goldbearing tonalite porphyry intrusions at the batu hijau deposit, sumbawa island, indonesia: implications for crystallization conditions and fluorine-chlorine fugacity, special issue. resource geology, 57 (2), p.102-113. idrus, a., kolb, j., and meyer, f.m., 2009. mineralogy, lithogeochemistry and elemental mass balance of the hydrothermal alteration associated with the gold-rich batu hijau porphyry copper deposit, sumbawa island, indonesia. resource geology, 59, 215-230. idrus, a., nur, i., warmada, i w., and fadlin., 2011. metamorphic rock-hosted orogenic gold deposit type as a source of langkowala placer gold, bombana, southeast sulawesi. jurnal geologi indonesia, (6) 1: 43-49. idrus, a., prihatmoko, s., hartono, gh., idrus., ernowo, franklin, moetamar and setiawan, i., 2014. some key features and possible origin of the metamorphic rockhosted gold mineralization in buru island, indonesia. indonesian journal on geoscience, 1, 9-19. idrus, a. and prihatmoko, s., 2011. the metamorphic-hosted gold mineralization at bombana, southeast sulawesi. a new exploration target in indonesia. proceedings mgei conference mineral resources of sulawesi, manado, 2011 imai, a. and ohno, s., 2005. primary ore mineral assemblage and fluid inclusion study of the batu hijau porphyry cu-au deposit, sumbawa, indonesia. resource geology, 55, p.239248. o'connor, f.a., lucey, b.m., batten, j.a., and baur, d.g., 2015. the financial economics of gold-a survey. international review of financial analysis, 1-20p. simandjuntak, t.o., surono, and sukido., 1993. peta geologi lembar kolaka, sulawesi, skala 1 : 250.000. pusat penelitian dan pengembangan geologi, bandung. surono., 2013. geologi lengan tenggara sulawesi. badan geologi, kementerian energi dan sumber daya mineral. bandung, 169p. thompson, a.j.b, and thompson, j.f.h. 1996. atlas of alteration a field and petrographic guide to hydrothermal alteration minerals. geological association of canada, mineral deposits division, department of earth sciences, 118p. van leeuwen, t.m. and pieters, p.e. 1992. mineral deposits of sulawesi, geological agency, bandung. wadji, m.f., santoso, s.t.j., kusumanto, d., and digdowirogo, s., 2011. metamorphic hosted low sulfidation epithermal gold system at poboya, central sulawesi : a general descriptive review, proceedings of the sulawesi mineral seminar, manado 28-29 november 2011, p. 201-210. warmada, i w., 2003. ore mineralogy and geochemistry of the pongkor epithermal gold-silver deposit, indonesia. dissertation. papierflieger, clausthal-zellerfeld. isbn: 389720-658-7. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geological setting 3. research methods 4. characteristics of quartz veins 5. characteristic of hydrothermal alteration 5.1 ree geochemistry discrimination acknowledgments references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 taghizadeh, m.m. jgeet vol 03 no 04/2018 221 research article arsenic survey in dried sediments of maharlu saline lake mohammad mehdi taghizadeh 1 1 islamic azad university estahban branch, iran * corresponding author : tgmehdi@yahoo.com received: september 20, 2018; accepted: november 31, 2018. doi: 10.24273/jgeet.2018.3.4.2074 abstract being on the steep slope of shiraz city and getting the main drainages, maharlu lake is always home to extensive levels of urban pollution. prolonged droughts and drying of surface sediments of the lake usually happen in warm seasons of the year, and with the continuation of the droughts particles spread out from the surface into the surroundings of the lake. arsenic and its compound are well known for its toxicity and carcinogenicity. industrial and farming waste in upstream of the lake are the main sources of arsenic and may disperse in maharlu lake. in this study, by meshing the lake s surface and by sampling 15 points 3 kilometers away there determined the arsenic amount. then, the toxicity indexes and mueller index together with its risks were studied before zoning of the lake through gis and verification. the results showed that the average concentration of arsenic was 3.5 mg/ kg of surface sediment. the concentration has gone in most parts of the lake below normal as shown by mueller index so that its contamination and lower-than-usual toxicity is deemed anthropogenic. interpolations by gpi, lpi, and idw methods demonstrated the north part of the lake more concentrated, likely due to the north lake farming and being the entrance of river soltanabad. the verification of data has recognized the idw method as the most accurate as regards interpolation. according to the importance of heavy metals in the dust, samples should be taken from winds coming from the lakeside as dust hotspot to control the metals concentration. keywords: arsenic, maharlu lake, gis, zoning, mueller index, toxicity index 1. introduction being on the steep slope of shiraz city and getting the main drainages, maharlu lake is always home to extensive levels of urban pollution. prolonged droughts and drying of surface sediments of the lake usually happen in warm seasons of the year, and with the continuation of the droughts particles spread out from the surface into the surroundings of the lake. environmental hazards, abnormal decomposition of arsenic and its transmission along with the particles in micron sizes make the investigation on arsenic concentration, dispersion, and toxicity a must. arsenic is a metalloid element, primarily existing in its inorganic form in water. the toxic impact of arsenic on human health has been documented in numerous studies; to the extent that the international agency has classified it for research on carcinogens (iarc) and the national toxicity program (ntp) as a known human carcinogen (who, 2012; department of health and human services, 2011). apart from its cancerous consequences, long-term exposure to arsenic has been associated with developmental effects, cardiovascular disease, neurotoxicity and diabetes (who, 2016). inorganic arsenic can easily cross the human and animal placenta and has been reported to increase the risk of adverse pregnancy outcomes such as spontaneous abortion, stillbirth, impaired fetal growth and infant mortality rate (quansah,2015). besides natural pollution from geogenic sources, specific attention has been paid to anthropogenic contribution of as., in certain areas (fendorf et al., 2010; moriarty et al., 2014). the primary anthropogenic sources of as including mining, smelting of non-ferrous metals and burning of fossil fuels, use of arsenic-containing pesticides, and use of arsenic in the preservation of timber (smedley and kinniburgh, 2002) the sediments of the seas and the lakes are frequently the sinks of heavy metals as contaminants, and various studies have proved that these gathering places had much above the allowable limit of contaminants (aksu et al., 2012; kishe & machwa, 2003; evseev & krasovskaya, 2015; fukue et al., 2006). the studies of moore et al., 2009 on heavy metals in maharlu lake has also shown that the pollution of the water in this regard has been beyond the standard limit, and described arsenic pollution as an anthropogenic source. hence, more specific studies on heavy metals as surface sediments toward maharlu lake are needed particularly since the beyond standard concentrations of arsenic in recent years are probable. in this research, keeping the arsenic threats in view, we study dispersion of this toxic metal in the dried sediment surface of the lake. http://journal.uir.ac.id/index.php/jgeet mailto:tgmehdi@yahoo.com 222 taghizadeh, m.m. jgeet vol 03 no 04/2018 2. materials and methods 2.1 maharlu lake spread about 25000 hectares with a 6×10 km2 dimension, maharlu lake is located in 23 km south-east of shiraz to the west of lake bakhtegan, between latitudes the rivers and waterways flown to it. the most important to be mentioned are khosk (dry) river, chenar-e rahdar river, nazarabad river, and soltanabad river (see fig. 1). a few springs of water also enter the lake. maharlu lake is the easternmost part of the shiraz plain with very salty water and is considered as one of the enormous deposits of salt in iran. salt procession from this lake is performed by the salt extraction complex affiliated to shiraz petrochemical company. villages and agricultural lands surround maharlu lake, and on account of inflow of khoshk river which passes through the city of shiraz leading to the lake and is a seasonal river pestered by various kinds of household, commercial, industrial, and agricultural wastewaters, the quality of its water much affects on the lake with regard to heavy metals pollution. fig.1. location of saline maharlu lake 2.2 sampling the samplings were performed in summer 2015. since the aim of the research was an investigation of likelihood of heavy metals dispersion by dust during the dryness of the lake, the samples were taken from the surface of the lake sediments. the number of sampling points was 15 for the selection of which the lake was divided by meshes 3 kilometers away from each other in order for all areas to be sampled. afterward, the geographical coordinates of the selected points in the provided map were determined via google earth software. then, using gps, the points were spotted on the lake. it was tried that the samples be taken of a one square meter surface. the full dryness of the lake was conducive to having access to all points. fig. 2 shows the sampling locations, and table 1 contains the coordinates of the sampled points. 2.3 experiments to determine concentrations of arsenic after the samples were dried in desiccator, they were digested in acid, and then all arsenic in the samples (not only soluble metals) were measured using atomic absorption system. the test method was done according to as journal 893 of institute of water and soil research fig. 2. sampling locations in saline maharlu lake table 1. coordinates of the sampled points. location coordinate x y station 1 29.52089 52.769514 station 2 29.49751 52.720733 station 3 29.29798 52.766449 station 4 29.49654 52.801394 station 5 29.49886 52.846025 station 6 29.46656 52.733275 station 7 29.46736 52.767336 station 8 29.65906 52.798644 station 9 29.43386 52.835439 station 10 29.43531 52.799764 station 11 29.39947 52.833225 station 12 29.39947 52.832653 station 13 29.36453 52.866639 station 14 29.33249 52.899494 2.4. the method of analyzing the results 2.4.1. comparison with geochemical criteria håkanson designated the geochemical criteria such as enrichment factor (ef) and mueller index (lgeo), 1980 as the main computation indices to evaluate contamination of sediments. the mueller index was calculated from the following relation (moore et al., 2009): igeo=log 2[cn/1.5bn] (1) in which cn is the concentration of the tested pollutant, and bn is the background pollution of the same pollutant before pollution, and the references usually use the average global shale as regards (turekian & wedepohl, 1961), and some use the highest concentration of earth crust (taylor & mclennan, 1985). the average concentration of arsenic in global shale is taghizadeh, m.m. jgeet vol 03 no 04/2018 223 equal to 0.3 ppm (kabata-pendias & mukherji, 2007). however, not all of these world standards could be applied in the local areas (dekov et al., 1998; roussiez et al., 2005). in the studies conducted by moore et al. (2009) in maharlu region, the local background values for arsenic was equal to the average global ones. the obtained values were compared with those of the references. table 2 shows the classification and the annotations of mueler land accumulation index. 2.4.2. evaluation of toxicity for ecosystem to evaluate the toxic effects of the heavy metals on the environment, the obtained results were compared with the sediment quality guidelines (sqgs) (mcdonald et al., 2000). the values of sqgs are the determiners of threshold effect level (tel). this level for arsenic is equal to 5.9, for evaluation of the effect in the ecosystem. 2.4.3 drawing of geo statistic and zonings data using arcgis interpolation methods for preparing the gis maps are helpful method for analyzing dispersion pollutant in water, soil and air (dehghani, 2013; dehghani, 2014) 1. method of inverse distance raised to the power of 2 (idw) 2. lpi. methods 3. gpi. methods 2.5. method of verification evaluation to choose a suitable way for interpolation the method of reciprocal evaluation was adopted. in this method, an observed point is removed in each stage and then its value is estimated by the other observed points. this process is repeated for all observed points so that ultimately there would exist estimates the same number of observed points. having the real estimated values, one could obtain the error as well as the deviation of the method. in this research, to find the best interpolation way, the root-mean-square-error measure is used. table 2. classification and the annotations of mueller land accumulation index. mueler land accumulation index designation of sediment quality 0 uncontaminated 0-1 uncontaminated to moderately contaminated 1-2 moderately contaminated 2-3 moderately to strongly contaminated 3-4 strongly contaminated 4-5 strongly to extremely contaminated 5< extremely contaminated table 3. classification and the annotations of mueller land accumulation index. statistical indexes arsenic min (mg/kg) 0.36 max(mg/kg) 6.31 average (mg/kg) 3.52 standard division 1.54 table 4. mueller index and toxicity for arsenic concentration in sampling places no of station tel muler class (table2) muler index arsenic (mg/kg) level of toxicity 1 5.9 zero -4.437405312 0.9 nontoxic 2 5.9 zero -1.607330314 6.4 toxic 3 5.9 zero -5.799975392 0.35 nontoxic 4 5.9 zero -1.963474124 5 nontoxic 5 5.9 zero -1.99262047 4.9 nontoxic 6 5.9 zero -4.519867472 0.85 nontoxic 7 5.9 zero -5.285402219 0.5 nontoxic 8 5.9 zero -2.099535674 4.55 nontoxic 9 5.9 zero -1.906890596 5.2 nontoxic 10 5.9 zero -1.8259706 5.5 nontoxic 11 5.9 zero -2.007417472 4.85 nontoxic 12 5.9 zero -1.736965594 5.85 nontoxic 13 5.9 zero -1.99262047 4.9 nontoxic 14 5.9 zero -3.799975392 1.4 nontoxic 15 5.9 zero -4.147898695 1.1 nontoxic average 5.9 zero -2.46982679 3.52 nontoxic 224 taghizadeh, m.m. jgeet vol 03 no 04/2018 fig.3. geostatistical interpolation in research area. (left) inverse distance weighting, (middle) lpi interpolation, and (right) gpi interpolation. 3. results and discuss 3.1. geochemical indexes and environmental toxicity the calculated of mooler indexes in various sampling stations are listed in table 4. as the fourth column of table 4 is shown, theses indexes in all stations are lower than zero and about table2, all stations are ranked in zero class and it indicates that concentration as is not a contaminant in all stations. on table 4, also compare the as concentration to the tel these results showed that the arsenic concentration is upper than tel only in the station 2 and in the other stations it is lower than tel. the concentration of arsenic in station 2 is toxic for animates. the station 2 is located in the entrance of soltanabad river to the lake. in this part of the lake, the sedimentation of particles happened. moreover, all of the pollutants that have been absorbed in particulate materials, such as, mud and clay settle in this part. as concentrations are shown from high to low by colors. the highest concentration is shown by red and lowest one is shown with green color. interpolation with the idw method as showed that the higher concentration belongs to the south-west of the lake that is located in the entrance of soltanabad river. this part is a landform that forms from the deposition of sediment carried by the soltanabad river as the flow leaves its mouth and enters slower-moving or stagnant water. as idw interpolation shown another part of the lake in the middle, it is red. there are many garden and farms in the north and south of the lake. arsenic compounds are using in some fertilizer and poisonings. the run-off from these forms may be a reason for increasing the arsenic in the middle part of the lake. albeit, as. concentration in this part is not reached to the toxic limit. the interpolation with the lpi method showed that the higher concentration belonged only to the middle part of the lake. in this method of interpolation, the single points of high concentration of pollutant are neglected. the result of interpolation with the gpi method is quite similar with lpi methods. 3.3 data verifications the verifications of various geo-statistic methods using the least average squares approach (table 6). this table is shown that interpolation with the iwd method is more real than other methods. table 6. verifications of various geo-statistic methods using the least average squares approach. parameter idw lpi gpi as 2.104574 2.638558 2.990969 rms root mean square 4.conclusion the average concentration of arsenic is 3.52mg/kg of surface sediment. the investigations on arsenic concentration in surface sediments done by moore et al. in 2009 have shown the average concentration as 0.52 mg/kg. attesting that the arsenic level has been increased during the 5 year interval between the two studies, and it may increase dramatically in following years, so it needed to more notice to arsenic source in farming and industrial waste and wastewater. the results also show that the uncontaminated of arsenic in many stations, based on mueller index is perceived. in only one station, arsenic is above the minimum level for creating toxicity in the sediments. one of the reasons of low concentration of arsenic in the lake sediments may be regarding to high adsorption capacity of clay particles in the run-off path. these particles are settled before receiving to the lake. the interpolations performed by gpi, lpi and idw methods show the north and west parts of the lake heavier in concentration due to being affected by the farming in north of the lake as well as by the entrance of soltanabad river. also, data verification highlights idw as the most accurate interpolation method. according to the significance of heavy metals in the dust, samples should be taken from winds blowing from the lakeside as dust concentration. given of the results on hand and knowing the way the heavy metals enter into the lake, it is suggested that use of chemical fertilizers and toxins taghizadeh, m.m. jgeet vol 03 no 04/2018 225 be controlled particularly on edge and at the basin of the lake, mainly in the agricultural areas due north. acknowledgments the studies in this article were sponsored by the environmental protection agency of fars province in the research project scheme. at this moment, the cooperation of both the agency and the authorities of the protected area of maharlu lake is appreciated. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. https://doi.org/10.24273/jgeet.2016.11.7 putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. 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167-177 https://doi.org/10.1016/j.envpol.2005.02.004 smedley, p.l., kinniburgh, d.g., 2002. a review of the source, behaviour and dis-tribution of arsenic in natural waters. appl. geochem. 17, 517-568. https://doi.org/10.1016/s0883-2927(02)00018-5 taylor, s.r. and mclennan, s.m. 1985 the continental crust; its composition and evolution; an examination of the geochemical record preserved in sedimentary rocks. blackwell, oxford. 312. turekian, k.k. and wedepohl, k.h. 1961 distribution of the elements in some major units of the earth's crust. geological society of america, bulletin 72, 175-192. who, 2012 international agency for research on cancer. arsenic, metals, fibres and dusts. a review of human carcinogens; international agency for research on cancer, world health organisation: geneva, switzerland,. available online: http://www.who.int/mediacentre/factsheets/fs372/en/ (accessed on 15 january 2017). doi:10.1007/978-3-64203608-8. © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc bysa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.24273/jgeet.2016.11.7 https://doi.org/10.24273/jgeet.2016.11.5 https://doi.org/10.1007/978-3-642-03608-8 https://doi.org/10.1016/j.marpolbul.2012.02.018 https://doi.org/10.1016/j.marpolbul.2012.02.018 http://dx.doi.org/10.1155/2013/670590 https://doi.org/10.1016/j.gexplo.2015.05.018 https://doi.org/10.15625/0866-7187/40/1/10971 https://doi.org/10.1016/0043-1354(80)90143-8 https://doi.org/10.1016/0043-1354(80)90143-8 https://doi.org/10.1007/978-3-540-32714-1 https://doi.org/10.1007/s002440010075 https://doi.org/10.1016/j.scitotenv.2013.07.005 https://doi.org/10.1289/ehp.1307894 https://doi.org/10.1016/j.envpol.2005.02.004 https://doi.org/10.1016/s0883-2927(02)00018-5 http://www.who.int/mediacentre/factsheets/fs372/en/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. materials and methods 2.1 maharlu lake 2.2 sampling 2.3 experiments to determine concentrations of arsenic 2.4. the method of analyzing the results 2.4.1. comparison with geochemical criteria 2.4.2. evaluation of toxicity for ecosystem 2.4.3 drawing of geo statistic and zonings data using arcgis 2.5. method of verification evaluation 3. results and discuss 3.1. geochemical indexes and environmental toxicity 3.3 data verifications 4.conclusion acknowledgments references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” tappi & cherdasa/ jgeet vol 08 no 02-2 2023 72 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 research article 1d geomechanical model for wellbore stability in z field, y well sanga sanga working area, kutai basin navrianta tappi1,*, jeres rorym cherdasa1 1universitas pertamina, kebayoran lama, jakarta 12220, indonesia * corresponding author : 101318055@student.universitaspertamina.ac.id received: may 20, 2023. revised : may 31, 2023, accepted: june 20, 2023, published: july 31, 2023 doi: 10.25299/jgeet.2023.8.02-2.13871 abstract this research is about 1d geomechanical model for wellbore stability in z field, y well sanga sanga working area, kutai basin where wells have been drilled. the purpose of this research is to analyze the stability of the well starting from knowing the stre ss regime that occurs, predicting the occurrence of wellbore failure, and determining safe mud weight window for next drilling. the method u se in this research is a numerical modelling method using log data and drilling data that has been obtained and then managed using techlog software. the result of this research show the magnitude of mechanical properties of the rock that have been obtained, then i n general the stress regime that occurs in the z field formation is the normal regime even though the strike slip and reverse regime are inserted at a certain depth, then based on the prediction results of failure in this well is wide breakout, which in general occurs in li thology with sandstone, finaly safe mud weight window can be estimated properly, so that it can be used for further well drilling. keywords: wellbore stability, drilling mud weight, failure, stress, pore pressure, rock strength, rock elastic 1. introduction there are several things that need to be analyzed in the development of oil and gas fields, especially the stability of the wellbore. wellbore stability analysis has an impact on the drilling process to the production of a well because if there is damage to the well during drilling, it will reduce drilling efficiency and increase drilling costs (darvishpour et al., 2019). in order to know the parameters or factors that influence the stability of the wellbore, a geomechanics reservoir research is needed. geomechanics is a science that focuses on the calculation of pressure/stress and its application to problems of fault and fluid flow in formations (zoback, 2007). models or tools that can be used to perform geomechanical analysis are numerical model and mechanical earth models (mem) (zain-ul-abedin and henk, 2020). this research area is located on the onshore field in the sanga sanga working area, kutai kartanegara, east kalimantan. sanga sanga working area is located in the lower kutai basin. the kutai basin is the largest tertiary basin in indonesia which has an area of 160,000 km2 with a thickness of sediment deposits of approximately 15,000 meters (syarifuddin and busono, 1998; bppka, 1997). figure 1 shows the boundaries of this basin. to the north it is bounded by the sangkulirang fault and the mangkalihat high which separate the kutai basin from the tarakan basin, to the east by the mahakam delta which opens to the makassar strait, to the southeast there is the paternoster shelf which is separated by the adang fault, and to the west it is bounded by the kuching high. the tectonic setting of the kutai basin is formed from the interaction between three plates, namely the pacific, australian, and eurasian, where the direction of the structure in this basin is southwest-northeast (sw ne) formed from the samarinda anticlinorium which is in the east southeast area of the kutai basin (supriatna et al., 1995). fig 1. regional tectonic map kalimantan (syarifuddin and busono, 1998) the stratigraphy in the kutai basin consists of several lithologies, namely sandstone, claystone, coal and carbonate. the kutai basin consists of several formations, from bottom to top, it is : pamaluan formation, this formation has a thickness of 1500 m which is mostly in a http://journal.uir.ac.id/index.php/jgeet 73 tappi & cherdasa / jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 deep marine depositional environment. this formation consists of sandstone with interclations of claystone, shale, lime stone, and siltstone. bebuluh formation, this formation has a thickness of 900 m which is intersected with the pamaluan formation and is dominated by limestone formed in the early miocene with interlamination of sandy limestone and clay shale. pulau balang formation, this formation covers the pamaluan formation and the bebuluh formation which were deposited in a deltaic environment to shallow marine. the lithology in this formation consists of sandstone, graywacke, limestone, claystone, dacite tuff, and coal interlamination with a thickness of 3 to 4 meters. balikpapan formation, this formation has a thickness of 1000 to 1500 meters overlies pulau balang formation which is mostly deposited in a deltaic environment. the lithology in this formation consists of quartz sandstone, claystone, shale, and coal with a thickness of 5 to 10 meters. kampung baru formation, this formation has a thickness of 900 meters which was deposited in a delta environment. the lithology of this formation consists of quartz sandstone with interlaminations of clay, shale, silt and coal with a thickness of 3 meters. alluvial, deposition that occurs unconformably over the kampung baru formation which is in a river, swamp, beach and delta environment that has continued to the present day. this deposition consists of gravel, sand, and silt. fig 2. kutai basin stratigraphy (satyana et al., 1999) 2. material and methods 2.1 1 dimension geomechanical model initially the formation of a field is in a balanced condition before the well is drilled. although during drilling, the drilling fluid can replace the rock that has been drilled, the presence of the wellbore can cause a redistribution of stress around the wellbore. if the stress exceeds the strength of the rock, it can make the well unstable, causing problems in the well (kang et al., 2009). there are several problems if the well becomes unstable, namely: hole collapse, stuck pipes, hole enlargement, fracture, lost circulation, and others, so that these problems increase drilling costs and decrease drilling efficiency (albukhari et al., 2018). to prevent these things from happening, it is necessary to evaluate the stability of the wellbore by creating a geomechanical model to reduce the risk in drilling wells and to provide recommendations for safe mud weight in drilling (plumb et al., 2000). 1 dimensional geomechanical model is usually called the 1d mechanical earth model (mem). 1d mem is a numerical representation of in-situ stress conditions and mechanical properties along the well. 1d mem can provide information about the condition of the well so that it can provide solutions to any well problems if unwanted things occur. in addition, this 1d model can help optimize field development such as the optimal location for injection and production wells, determine the optimal trajectory for wellbore stability, design well development, and predict a safe range of drilling mud weight values (plumb et al., 2000). illustration of the geomechanical model can be seen in figure 3. creating 1d geomechanical model, several data are needed, such as core data, drilling reports, and well log data such as calipers, gamma rays, density, sonic, neutron porosity, and resistivity to represent well conditions (zainul-abedin and hank, 2020). the results of the data processing can be in the form of values of pore pressure, insitu stress, elastic properties of rock, rock strength (plumb et al., 2000). tappi & cherdasa / jgeet vol 08 no 02-2 2023 74 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 3. schematic mechanical earth model (plumb et al., 2000) 2.2 pore pressure & fracture pressure pore pressure is an important parameter for determining effective stress in 1d mem (zain-ul-abedin and hank, 2020). pressure can be divided into three types, it is underpressure, normal pressure, and overpressure. normal pressure is a condition where the formation pressure is equal to the hydrostatic pressure. generally, the normal pressure value is 0.433 psi/ft for fresh water. underpressure is a condition where the formation pressure is below hydrostatic pressure. while overpressure is a condition where the formation pressure is above the hydrostatic pressure (swarbrick et al., 1998). to obtain pore pressure values can be done with various correlations, one of which is the eaton method. eaton's method can utilize data obtained from sonic logs and resistivity logs. the following is the equation of the eaton method (eaton, 1975). log sonik 𝑃 = 𝑆 − ((𝑆 − 𝑃𝑛) × ( ∆𝑡𝑛 ∆𝑡 ) 3 ) (1) log resistivitas 𝑃 = 𝑆 − ((𝑆 − 𝑃𝑛) × ( 𝑅𝑖 𝑅𝑛 ) 1.2 ) (2) in determining the overpressure zone using the eaton method, it does not only use log data results, but requires another parameter called the normal compaction trend (nct). nct is a normal line which becomes a benchmark in the event of overpressure. the image illustrating the nct line on the sonic log can be seen in figure 4. fig 4. normal compaction trand on sonic log (eaton, 1975) determining fracture pressure can be obtained using several equations, one of which is the matthews & kelly method. the fracture pressure value can be calibrated using the results obtained from the lot test to ensure that the calculated data is correct. the following is the equation used to calculate fracture pressure (paul et al., 2009). 𝐹𝑅𝑃 = ( 𝜇 1−𝜇 ) (𝑆 − 𝑃) + 𝑃 (3) 2.3 elastic property elastic property is needed for 1d geomechanical modeling, where the parameters consist of young's modulus, shear's modulus, bulk's modulus, and poisson's ratio. elastic property is a measurement of the strength of a solid material to return to its original shape and size after being subjected to a force, then the force is removed, however, if the stress limit is exceeded, it will leave permanent damage to the solid material (zoback, 2007). elastic property is divided into two categories namely static and dynamic. in measuring the dynamic elastic property can be done using certain logging data. while the measurement of static elastic property can be done using core data analysis that comes from tests in the laboratory. although the dynamic data does not yet represent the actual static data, these values can be transferred using empirical correlations that depend on lithology data whose 75 tappi & cherdasa / jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 application can be validated with calibration data, if core data is available (abeden hank.2020). the correlation between dynamic modulus and static modulus is (albukhari et al., 2018): dynamic young's modulus has a greater value than static young's modulus, the ratio between dynamic and static modulus approaches usually becomes one when confining pressure increases, the dynamic poisson ratio is generally has a smaller value than the static poisson ratio. 2.4 rock strength rock strength is a very important parameter if the geometric stresses from laboratory tests are obtained specifically (fjaer et al., 2008). several correlations involving rock strength can be used to identify geomechanical characters when core data is not available. rock strength parameters : unconfined compressive strength (ucs), friction angle, tensile strength, and cohesion (ayoub et al. 2019). ucs is an important parameter in limiting the maximum horizontal stress and obtaining an envelope that is suitable for the formation. the ucs obtained is usually correlated with various petrophysical and geomechanical parameters such as compressional velocity, porosity, shale volume, and young's modulus, where this type of correlation can improve ucs predictions from well log derived data without a laboratory core test (albukhari et al. 2018). the following is the ucs equation based on horsrud 2001: 𝑈𝐶𝑆 = 0.77 + ( 304.8 ∆𝑡𝑐 ) 2.92 (4) correlating friction angle (fang) with petrophysical parameters is quite limited because even weak formations have high friction angle values, therefore the right approach to obtain friction angle values is when you have completed the ucs test (albukhari et al. 2018). using petrophysical data, the friction angle can be calculated using the plumb correlation as follows: 𝐹𝐴𝑁𝐺 = 26.5 − 37.4(1 − 𝜙 − 𝑉𝑐𝑙𝑎𝑦) + 62.1(1 − 𝜙 − 𝑉𝑐𝑙𝑎𝑦)2 (5) in addition to using the equation above to measure the value of the friction angle, you can use the empirical correlation that is in the slb techlog software (figure 5). this method uses gamma ray data to obtain a friction angle value with a linear correlation and uses a cutoff as shown below (albukhari et al. 2018). fig 5. determining friction angle from data gr in order to evaluate the tensile failure of the well wall related to the stress concentration, it is necessary to know the tensile strength criteria. correlation analysis shows that the best tensile strength for reservoir rock is 1/10 of ucs (ayoub et al. 2019). to calculate the value of tensile strength in this research using the griffith equation (1921) as follows. 𝑇𝑆𝑇𝑅 = 𝐾 × 𝑈𝐶s (6) 2.5 in-situ stress horizontal stress and vertical stress are in-situ stresses that can be used to represent the three principal stresses in rock formations, where the horizontal stress represents two values, namely horizontal maximum and horizontal minimum. estimating the horizontal stress is the key to accurately modeling the stress regime (ayoub et al. 2019). determination of horizontal stress in this research uses a poro-elastic approach using the following equation (abeden hank, 2020). shmin = v 1−v sv − v 1−v ∝ pp +∝ pp + e 1−v2 εh + ve 1−v2 εh (7) shmax = v 1−v sv − v 1−v ∝ pp +∝ pp + e 1−v2 εh + ve 1−v2 εh (8) to find the vertical pressure value, it can be obtained by calculating the overburden pressure based on density (abeden hank.2020). overburden pressure can be defined as the vertical pressure generated by the weight of all material, both fluid and granules, which are in the formation layer above it. so from this, the overburden gradient value is generally 1 psi/ft (albukhari et al. 2018). overburden pressure can be calculated using the following equation (abeden hank. 2020). 𝑆𝑣 = 𝑔 ∫ 𝜌𝑏(𝑧) 𝑇𝑉𝐷 0 (9) the vertical pressure in this case is calculated using the extrapolation method available in the techlog software. the following is an equation using the extrapolation method. 𝜌𝑒𝑥𝑡𝑟𝑎𝑝𝑜𝑙𝑎𝑡𝑒𝑑 = 𝜌𝑚𝑢𝑑𝑙𝑖𝑛𝑒 + 𝐴0 × (𝑇𝑉𝐷 − 𝐴𝑖𝑟𝐺𝑎𝑝 − 𝑊𝑎𝑡𝑒𝑟 𝐷𝑒𝑝𝑡ℎ) 𝛼 (10) 2.6 stress regime with the values of vertical stress, minimum horizontal stress, and maximum horizontal stress, the stress regime of the formation can be identified. based on anderson's classification (1951) stress regime is divided into three conditions, namely (zoback, 2007): normal stress regime. in this condition, the vertical stress value is greater than the maximum and minimum horizontal stress values, while the maximum horizontal stress is greater than the minimum horizontal stress (sv > shmax > shmin). in this regime the vertical stress value is very large so that normal faulting can occur. strike-slip stress regime. in this condition, the largest value is the maximum horizontal stress, then the vertical stress in the middle, and the smallest is the minimum horizontal stress (shmax > sv > shmin). in this regime the maximum value of the horizontal stress works very large and if the difference in value between shmax and shmin is very large then faulting can occur. reverse stress regime. in this condition, the maximum horizontal stress is the largest, then followed by the minimum horizontal stress in the middle, and the smallest is the vertical stress (shmax > shmin > sv). in this regime the maximum value of the horizontal stress works very large which is then followed by the minimum horizontal stress so that it can cause reverse faulting or commonly called thrust faulting. tappi & cherdasa / jgeet vol 08 no 02-2 2023 76 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 6. stress regime illustration based on anderson’s classification (zoback, 2007) 2.7 failure criteria failures that occur in the integrity of the wellbore always cause increased costs, more difficult repair operations, and allow for contamination of the surrounding environment (wu et al., 2020). shear and tensile failure are the main causes of mechanical instability in boreholes (darvishpour et al., 2019). shear failure can occur if the shear stress exceeds the shear strength of the rock around the wellbore. differences in failure criteria can provide different recommendations for drilling mud weights. if it is below a predetermined limit (minimum mud weight), the pressure of the drilling fluid will cause shear failure on the wall of the wellbore so that the occurrence of shear failure is the minimum value of the weight of the drilling mud (darvishpour et al., 2019; kang et al., 2009). tensile failure occurs when the stress of the drilling mud exceeds the tensile strength of the formation. tensile failure generally occurs when the effective principal stress exceeds the tensile strength of the rock formation (kang et al., 2009; pasic et al., 2007). determination of tensile failure can be an indication in determining the weight of drilling mud. if it exceeds the specified upper limit (maximum mud weight), the drilling mud will cause tensile failure on the wellbore. therefore, tensile failure is a sign of the upper limit of the safe value of drilling mud weight (darvishpour et al., 2019). 2.8 safe mud weight window the predicted weight of drilling mud can be determined if the pore pressure, elastic property, rock strength, and principle stress orientation are known. prediction of drilling mud weight with appropriate drilling fluid density is carried out to control wellbore stress induction in maintaining wellbore stability and minimizing drilling fluid invasion into the reservoir (darvishpour et al., 2019). figure 7 illustrates the pressure and weight of drilling mud that affect wellbore stability. the wellbore pressure must be higher than the pore pressure that causes collapse and must be lower than the minimum horizontal stress strength, so that from this the well is stable and does not cause failure in accordance with the failure criteria. if the mud weight value is below the minimum mud weight value, a breakout mud weight can occur, causing shear failure, whereas if it exceeds the maximum mud weight value, it can cause a breakdown of the mud weight, which causes tensile failure (pasic et al., 2007). fig. 7. effect of mud weight on the stress in wellbore wall (pasic et al., 2007) 3. methods this research was conducted using qualitative and quantitative methods using log data, numerical data, drilling data and graphic data which were reviewed objectively. in this research, 1d geomechanical modeling was made using software, namely techlog. with the help of this software it will assist in processing and calculating geomechanical parameters such as pore pressure, fracture pressure, elastic properties, rock strength, and in-situ 77 tappi & cherdasa / jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 stress. after the 1d geomechanical modeling is formed, wellbore stability analysis can be carried out so that recommendations for safe drilling mud can be determined for planning or developing drilling in field z. the data collection method in this research was obtained from companies located in the kutai basin area. the data collection used in this research came from well logging data and drilling data. the following is the data that has been obtained, where the mark (v) indicates the well has the data listed and the mark (x) indicates the well does not have the data. table 1 research data availability data sumur z keterangan gamma ray v mandatory density / rhob v sonic dt compressional slowness v sonic dts shear slowness x resistivity x neutron porosity / nphi x caliper logs x trajectory / deviation for offset and plan well x equivalent circulating density / ecd log x validation formation pressure point (mdt) v image logs (fmi, ubi, etc) x lot / xlot v rock mechanics laboratory core test result x mud weight v 4. results and discussion the research location is in the lower kutai basin, sanga sanga working area, field z well y. the formation of the 1d geomechanical model aims to determine the mechanical properties & stress regime, predict the weight of drilling mud that is safe to use, and analyze the stability of the well. in this research using the techlog software to assist in processing logging data to create 1 dimensional geomechanical model. 4.1 zonations determination of lithological zones is a very important factor in analyzing 1d geomechanical models, because each zone has different criteria and this can affect the calculation of 1d geomechanical model parameters. in this research, the division of zones was carried out based on lithological zones, where there are two lithologies, such as sandstone and shale. this zone division was carried out using rhob logs and gr logs which were then re-validated using shale volume data obtained based on gr logs. the rhob log and gr log data are used to create a data crossplot, from which the data is restricted by using sandstone criteria obtained from the literature. from the literature, the criteria for sandstone are based on log gr is greater than 15 api and less than 55 api while from log rhob is greater than 2.2 g/cm3 and less than 2.6 g/cm3. the results of the data are then validated using shale volume data obtained at 0.35. the results of determining the lithology zone can be seen in figure 8 below: tappi & cherdasa / jgeet vol 08 no 02-2 2023 78 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig. 8. lithology zone 4.2. pore pressure pore pressure is very important because it has an effect on determining the stability of the wellbore. calculation of pore pressure can be done using the eaton method. calculation of pore pressure by the eaton method can be carried out using resistivity logs and sonic logs, but with limited data in this research, the logs used are only sonic logs. the eaton method uses a trandline called the normal compaction trand to determine the pressure conditions in the well. based on the calculation results that have been obtained, there is an increase in pressure at a depth of 2850 ft which continues to increase with increasing depth. from these indications at a depth of 2850 ft overpressure has occurred. the results of calculating the pore pressure can be seen in figure 9 below: fig 9. pore pressure using eaton method note : shale sandstone 79 tappi & cherdasa / jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 4.3. in-situ stress in-situ stress is divided into three conditions, namely vertical stress, maximum horizontal stress, and minimum horizontal stress. the results of the in-situ stress calculation can be used to determine the stress regime that occurs in the formation. in this research, the vertical stress was calculated using the density log using the extrapolation method. figure 10 shows the vertical stress value which continues to increase with increasing depth, because the value obtained is the value of the load above it plus the load at that depth, which is called overburden. therefore the vertical stress can also be said to be overburden pressure. to validate this value, based on the literature, the normal vertical stress gradient value is equal to 1 psi/ft. fig 10. vertical stress data the calculation of horizontal stress in this research using a poro-elastic approach where the input parameters are poisson's ratio, young's modulus, vertical stress, and pore pressure. to adjust the horizontal stress value, it is necessary to use the strain/epsilon value, where in this research the values were divided into two, it is the maximum and minimum values. the maximum epsilon value (εh) in this research was 0.0003 and the minimum epsilon (εh) was 0.00015. these values are obtained based on calibration carried out using data leak off test (lot). figure 11 shows the magnitude of the maximum and minimum horizontal stress values where the values obtained for both the maximum and minimum horizontal stress are not much different. with the two horizontal stress values that are not much different, the formation in the well can be said to be isotropic. figure 12 shows the distribution of horizontal stress data where the maximum horizontal stress value is 0.83 psi/ft and the minimum horizontal stress value is 0.81 psi/ft. tappi & cherdasa / jgeet vol 08 no 02-2 2023 80 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 11. horizontal stress data fig 12. gradient histogram horizontal maksimum (a) & minimum (b) 4.4 stress regime the stress regime can be determined using the result value of in-situ stress. figure 13 show the in-situ stress log data, from these logs it can be seen that, in general the stress regime that occurs is the normal regime, where the vertical stress value is greater than the horizontal stress value and the maximum horizontal stress is greater than the minimum horizontal stress (sv>shmax >shmin). however, at certain depth intervals there are different stress regimes such as at depth intervals of 2524 ft – 2561 ft where the maximum horizontal stress value has the largest value followed by the minimum horizontal stress then the vertical stress (shmax>shmin>sv), so that at these depth intervals the stress the regime is called the reverse stress regime or what is called a thrust fault. (a) (b) 81 tappi & cherdasa / jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 13. in-situ stress log data 4.5 1 dimension geomechanical model 1d geomechanical model is needed to analyze the stability of the wellbore which is useful for knowing what happens to the well, in addition to predicting the safe mud weight window and failure in each well. to determine the stability of the wellbore requires several parameters such as pore pressure, elastic properties, rock strength, and insitu stress. each parameter has an effect on the failure factor in the formation. rock strength will determine the value of the shear strength of the rock. if the rock strength is greater, then the rock has a large shear strength value so that it can withstand the impact of shear stress, but if the shear stress strength exceeds the shear strength it can form shear failure, whereas if the tensile stress strength exceeds the tensile strength it can form a tensile failure. the presence of shear and tensile failure will have an impact on the wellbore such as: pipe sticking, fracture, hole collapse, lost circulation, enlargement of the wellbore, and others. in addition, the values obtained from pore pressure, in-situ stress, and elastic properties will affect the value of the safe drilling mud weight window. figure 14 shows 1d geomechanical model. each mechanical property has an influence on the geomechanical results. if young's modulus, friction angle, and ucs increase while the poison ratio decreases, then the range of drilling mud weight in the results of geomechanical model will increase, and vice versa. based on the figure, shear failure occurs at every depth interval with sandstone lithology, while tensile failure does not occur in this well. this is effected by the value of the weight of the drilling mud where at the depth before the overpressure occurs the weight of the drilling mud is 9 ppg to 12 ppg while in the overpressure zone the drilling mud increases from 13 ppg to 16 ppg. overpressure occurred in this wellbore. the overpressure is known based on the increasing pore pressure value, and on the other hand the window/range of the effective stress value gets smaller with increasing depth. the impact of this overpressure causes the kick limit value to increase with increasing depth, thus making the mud weight window smaller. this condition is validated by the history of drilling mud weight where in the history of drilling mud weight continues to increase with increasing depth, it even increases rapidly at a depth of 2600 ft, indicating that overpressure zones are starting to occur at that depth. the reduction in the mud weight window can be seen from a depth of 2850 ft where the overpressure zone has occurred. by reducing the mud weight window, events such as kicks are prone to occur in these wells. after the wellbore stability analysis has been carried out, a safe drilling mud weight values can be determined. tappi & cherdasa / jgeet vol 08 no 02-2 2023 82 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 14. 1d geomechanical model well y 4.6 safe mud weight window the weight of the drilling mud can affect the stability of the wellbore, therefore an accurate prediction is needed to determine the drilling mud weight in order to prevent damage to the well. figure 15 shows the predicted of drilling mud weight window that is safe to use in well y. the determination of the safe drilling mud weight is considered based on the values of fracture pressure, share failure and the column where the kick occurs which can represent the value of pore pressure. the results show that at a depth of 300 ft – 2560 ft the safe weight of drilling mud is 10.2 ppg, at intervals of 2560 – 2876 ft the safe weight of drilling mud is 12.8 ppg, then at depth intervals of 2876 ft – 3150 ft safe drilling mud weight is 14,5 ft, at depth intervals of 3150 ft – 3480 ft safe drilling mud weight is 16.1 ft and at depth intervals 3480 – 3957.77 ft safe drilling mud weight is 17.8 ppg, then based on figure 14, the red line is the maximum drilling mud weight and the blue line represents the minimum drilling mud weight. table 2 safe mud weight window interval kedalaman (ft) berat lumpur pemboran (ppg) mw min mw max mw opt 300 – 2560 8,8 11,5 10,2 2560 – 2876 12 15,2 12,8 2876 – 3150 13,4 15,4 14,5 3150 – 3480 14,8 16,6 16,1 3480 – 3957,77 16,5 18,4 17,8 83 tappi & cherdasa / jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 fig 15. prediction safe mud weight window 5. conclusion determination of well stability in field z well y uses calibration data of drilling mud weight. the data is useful for adjusting predictions of failure in wellbore. the results of the well stability model in this research are that at every depth interval with sandstone, shear failure will generally occur. the factor that causes this to happen is the pressure value exerted by the weight of the drilling mud is lower than the value of shear failure. after the well stability analysis has been carried out, the determination of the safe drilling mud weight can be carried out in this research. in this research the recommended safe drilling mud weight is 10.2 ppg starting from a depth of 300 ft – 2560 ft, then 12.8 ppg at a depth of 2560 ft – 2876 ft, then at a depth of 2876 ft – 3150 ft the recommended mud weight is 14 .5 ppg, then 16.1 ppg at depth intervals of 3150 ft – 3480 ft, and at depth intervals of 3480 ft – 3957.77 ft the recommended drilling mud weight is 17.8 ppg. acknowledgements the author would like to convey his sincere thanks to the oil and gas companies in the working area of sanga sanga who have provided data for this research, and also thank dr. jeres rorym cherdasa for his valuable guidance in writing this paper. references albukhari, t.m., beshish, g.k., abouzbeda, m.m. and madi, a.b.d.a.s.a.l.a.m., 2018, march. geomechanical wellbore stability analysis for the reservoir section in jnc186 oil field. in isrm 1st international conference on advances in rock mechanics-tunirock 2018. onepetro. bppka, p., 1997. petroleum geology of indonesia basins: principles, methods, and applications, vol. x south sumatra basins. darvishpour, a., seifabad, m.c., wood, d.a. and ghorbani, h., 2019. wellbore stability analysis to determine the safe mud weight window for sandstone layers. petroleum exploration and development, 46(5), 1031-1038. eaton, b.a., 1975, september. the equation for geopressure prediction from well logs. in fall meeting of the society of petroleum engineers of aime. onepetro. fjaer, e., holt, r.m., horsrud, p. and raaen, a.m., 2008. petroleum related rock mechanics. elsevier. kang, y., yu, m., miska, s. and takach, n.e., 2009, october. wellbore stability: a critical review and introduction to dem. in spe annual technical conference and exhibition. onepetro. pašić, b., gaurina međimurec, n. and matanović, d., 2007. wellbore instability: causes and consequences. rudarsko-geološko-naftni zbornik, 19(1), 87-98. paul, s., chatterjee, r. and kundan, a., 2009. estimation of pore pressure gradient and fracture gradient from well logs: a theoretical analysis of techniques in use. in international oil & gas review symposium, mumbai, india. plumb, r., edwards, s., pidcock, g., lee, d. and stacey, b., 2000, february. the mechanical earth model concept and its application to high-risk well construction projects. in iadc/spe drilling conference. onepetro. satyana, a.h., nugroho, d. and surantoko, i., 1999. tectonic controls on the hydrocarbon habitats of the barito, tappi & cherdasa / jgeet vol 08 no 02-2 2023 84 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 kutei, and tarakan basins, eastern kalimantan, indonesia: major dissimilarities in adjoining basins. journal of asian earth sciences, 17(1-2), 99122. supriatna, s., sudrajat, a. and abidin, h.z., 1995. geological map of the muara teweh quadrangle kalimantan. geological research and development centre, bandung. swarbrick, r.e., osborne, m.j. and yardley, g.s., 2001. aapg memoir 76, chapter 1: comparision of overpressure magnitude resulting from the main generating mechanisms. syarifuddin, n. and busono, i., 1999. regional stress alignments in the kutai basin, east kalimantan, indonesia: a contribution from a borehole breakout study. journal of asian earth sciences, 17(1-2), 123135. wu, y., patel, h., salehi, s. and mokhtari, m., 2020. experimental and finite element modelling evaluation of cement integrity under diametric compression. journal of petroleum science and engineering, 188, 106844. zain-ul-abedin, m. and henk, a., 2020. building 1d and 3d mechanical earth models for underground gas storage—a case study from the molasse basin, southern germany. energies, 13(21), 5722. zoback, m.d., 2007. reservoir geomechanics. cambridge university press. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 03 2018 arisona et al./ jgeet vol 03 no 03/2018 151 research article assessment of microgravity anomalies of soil structure for geotechnical 2d models a. arisona 1,2, *,mohd nawawi 2 , amin e. khalil 2,3 , abdullahi abdulrahman 4 1 geophysical department, haluoleo university, 93232, kendari, indonesia 2 school of physics, universiti sains malaysia, 11800, penang, malaysia 3 geology dept., faculty of science, helwan university, egypt, mesir. 4 department of physics, abubakar tafawa balewa university, bauchi, nigeria. * corresponding author : arisona1972@hotmail.com tel.: +60 14607608 received: july 16, 2018; accepted: aug 31, 2018. doi: 10.24273/jgeet.2018.3.3.2058 abstract a microgravity investigation on bedrock topography was conducted at maluri park in kuala lumpur, malaysia. the study characterized the subsurface structure to delineate soil structure for the geotechnical application. cross-section modelling of the residual anomaly generated the maluri bouguer anomaly model for test site. the 2d microgravity models produced the contour map, displaying the characterization due to density contrast in rock types while mapping the subsurface geological structure at different depths. moreover, a synthetic model was initiated with the assumption of lateral distance on the left and right sides taken at 50 m and a depth of 60 m. the results of modeling confirmed that the soil and rock type composition on models test site, i.e: topsoil (1.1 g/cm3), soil (1.8 g/cm3), clay (1.63 g/cm3), gravel (2.0 g/cm3), sand (1.7 g/cm3), shale (2.40 g/cm3), sandstone (2.76 g/cm3) and limestone (2.9 g/cm3). the 2d gravity synthetic model show a good match with the observed microgravity data. keywords: microgravity, anomaly, soil, density contrast, modelling. 1. introduction the microgravity method is widely used for a geophysical investigation, especially in the detection of cavities, karsts phenomena, subsoil irregularities, or hidden landfills. micro geotechnical investigation appreciates lateral variations in subsurface structure generated by density contrasts (ebbing et al., 2001). in many cases, deep or small-scale heterogeneities generating low amplitude anomalies have to be detected, and the reliability of further interpretation requires highly accurate measurements, carefully corrected for any quantifiable disturbing effects (debeglia and dupont, 2002). generally, microgravity for a sphere or cylinder is the same as for a point mass, talwani (1960) gave an equation (1) in the form: ∆𝑔 = 𝐺𝑚𝑧 (𝑥2 + 𝑦2)3/2 (1) g is component of gravitational attraction measured by a gravimeter (mgal); x is the horizontal distance from the observation point to a point directly above the centre of the sphere (m); z is the vertical distance from the surface to the centre of the sphere (m). g is universal gravitational constant (i.e.: g = 6.67 x 10 -11 nm 2 / kg 2 ). y is vertical distance from the surface to the centre of the sphere or cylinder (m). in actuality, one term in this expression for each point mass. if there are n point masses, this equation can be written more compactly as (equation 2), ∆𝑔 = ∑ 𝐺𝑚𝑧𝑖 ((𝑥 − 𝑑𝑖)2 + 𝑧𝑖 2 )3/2 𝑁 𝑖=1 (2) the microgravity method can be a relatively easy geophysical technique, in data acquisition, processing, and interpretation. it requires only simple but precise data processing, and for detailed studies, the icult because it is time-consuming (lilie, 1999; kearey et al., 2002). however, the technique has good depth penetration when compared to ground penetrating radar, high frequency electromagnetic and dcresistivity techniques and is not affected by the high conductivity values of near-surface clay-rich soils. additionally, lateral boundaries of subsurface features can be easily obtained in particular through the measurement of the derivatives of the gravitational field (kearey et al., 2002). modeling microgravity data in profile form is useful for the calculation of the depth of various features and can be done by either forward or inverse algorithms. in similarity with other geophysical methods, the interpretation of microgravity data is non-unique http://journal.uir.ac.id/index.php/jgeet mailto:arisona1972@hotmail.com 152 arisona et al./ jgeet vol 03 no 03/2018 because many possible models could result in the same microgravity anomaly. constraints, such as depths to rock obtained from useful information, rock densities, or other geophysical interpretations, are required during the modeling process to remove the ambiguity. this study focused on microgravity models using physical parameters that are robust in characterizing soil structures and soil properties. 2. site description and geology the study site is the area around taman maluri, jalan chereas, kuala lumpur (kl) (fig. 1). the bedrock within the maluri area is a limestone formation. kl limestone is well known for its highly unusual karstic features (tan, 2005). furthermore, due to the inherent karstic features of limestone bedrock, the depth of the limestone bedrock is highly irregular (samsudin, 2003).the overburden soils above kl limestone are mainly silty sand. the thickness of overburden soils varies significantly due to the irregular topography of the limestone bedrock. figure 1. slices of maluri park map that was obtained from google map figure 2. bedroc kl contour map at maluri park based on the results of 2 boreholes (bh) in the area, the bedrock is determined to be between 31 m to 34 m depth. the soil in the maluri area is light greyish-brown in colour and mostly sandy. this trends showed that thickness of overburden soil varied between 3 m and 5 m from the surface. on the other hand, the residual soil underline by limestone bedrock (fig.2) is mainly loose fine-grained materials. they are described and named according to the fine-grained naming method such as silty clay, clayey silt, silty sand, and sandy clay. 3. methodology microgravity data from the survey area were processed using surfer ®13 software which reduced bouguer anomaly values at each park of the microgravity survey. fig.3 shows that the modeling has been well constrained because the parameters required to obtained the bedrock topography were well defined from the bh data. the post-processing procedure checked the microgravity instrument corrections for latitude and longitude, diurnal variations and instrument drift using base park polynomial drift values and relative elevation.this procedure is merged with the respective microgravity park topographic survey data which is used to calculate the bouguer correction for all survey data sets. figure 3. residual microgravity contour map at taman maluri compiled from topography and bouguer anomalies at test site. subsequent processing was the elevation correction to address the variation in data points due to the topography (tajuddin,2004). this evaluation is necessary for the 2d geotechnical modeling (pringle,2012). furthermore, the removal of regional values (low frequency and high amplitude) to express the residual anomalies (high frequency and low amplitude) was performed using the upward arisona et al./ jgeet vol 03 no 03/2018 153 continuation approach. the modeling of the residual software. however, qualitative interpretation using geological maps are used only as additional information. 4. results and discussion 4.1 gravity overview of maluri bedrock the results of this investigation confirmed earlier bh results which indicated the presence of the cavities. however, the uneven distribution and clustering of the data necessitate the use of an interpolation algorithm to create a uniformly spaced grid. all data processing in the contour map were generated with ®13 software. the survey results were represented in contour maps for delineating anomalies varying from negative to positive value. according to kamal et al. (2010), negative values are interpreted as low density subsurface layers and for the possibility of the existence of cavities. table 1 presents the density of rock types that were reviewed in this study. the typically have densities ranging from 1.0 gr/cm 3 to 2.90 g/cm 3 (telford, 2010). the qualitative interpretation explains the anomaly by geological and geophysical information. on this basis, the geological structure and distribution of masses of different densities may be delineated. the difference in density values can be correlated to divergent material types such as soil, rock, and cavities. 4.2 interpretation of 2d geotechnical models for microgravity anomaly at maluri site maluri site consists of lowlands in the north and highlands in the south, and this pattern is confirmed by the microgravity anomalies with the lower regions displaying higher microgravity values. fig 4 show results of the microgravity data of maluri site for the residual anomalies. the profile displays the tendency of response towards positive anomalies, and yet it was not significant to influence the microgravity anomaly around model test site. in additional, fig.4 shows the residual microgravity anomaly at model test site, characterized by negative values, probably due the inhomogeneous geo-materials consisting of a mixture of clay and silt with grain sizes which is from fine to medium. fig. 5 show results of the 2d geotechnical model was adopted from extracts of residual anomaly the results of profiles test site. the curves for the model at the test site confirmed the product of a minute misfit of 4.44 % between calculated curves with observed curves. furthermore, model calculated microgravity confirmed density contrast at model test site as shown in table 2. the results of synthetic models showed that there are eight rock types from the microgravity profiles; topsoil (1.1 g/cm3), soil (1.8 g/cm3), clay (1.63 g/cm3), gravel (2.0 g/cm3), sand (1.7 g/cm3), shale (2.40 g/cm3), sandstone (2.76 g/cm3) and limestone (2.9 g/cm3). moreover, the synthetic model shows that inhomogenities in the variation of the subsurface material and density contrast in the covered layers. fig. 4. results of gravity field measurements at maluri site for profiles test site using extracted techniques from anomaly contour maps. figure 5 geotechnical 2d models site test-1 of the survey area (top) with corrected gravity data and model-calculated gravity (bottom). models show best-fit corrected gravity data with rms error = 4.44 %. 5. conclusion the gravity field data showed the good impression of the 2d geotechnical models. the result obtained from the grav2dc v.2.10 software correlates the modelcalculated gravity and the corrected gravity data in site tests have minimal percentage errors. the results of modeling showed that that there are eight rock types from the gravity profiles; topsoil (1.1 g/cm 3 ), soil (1.8 g/cm 3 ), clay (1.63 g/cm 3 ), gravel (2.0 g/cm 3 ), sand (1.7 g/cm 3 ), shale (2.40 g/cm 3 ), sandstone (2.76 g/cm 3 ) and limestone (2.9 g/cm 3 ). utilization of extracted technique characterized the density contrast due rock type and mapped subsurface geological structure at different depth. -0,015 -0,01 -0,005 0 0,005 0,01 0 5 10 15 20 25 30 35 40 45 50 r e s id u a l a n o m a ly ( m g a l) distance (m) a'a 154 arisona et al./ jgeet vol 03 no 03/2018 models of microgravity distribution in the ground could be useful for the mapping of variations in soil composition. the changes in gravity anomaly observed throughout the sections were due to the heterogeneities in the composition of the subsurface materials and density contrasts in the study area. table 1 rock types density values rock type density range (gr/cm 3 ) average (gr/cm 3 ) overburden (topsoil) 1.10 soil 1.20 to 2.40 1.92 clay 1.63 to 2.60 2.21 gravel 1.70 to 2.40 2.00 sand 1.70 to 2.30 2.00 sandstone 1.61 to 2.76 2.35 shale 1.77 to 3.20 2.40 limestone 1.93 to 2.90 2.55 dolomite 2.28 to 2.90 2.70 table 2. estimated density contrast from model-calculated gravity for the 2d geotechnical model at model test site density (g/cm 3 ) rock type 1.10 1.80 top soil (overburden) soil 1.63 clay 2.00 gravel 1.70 sand 2.40 shale 2.76 sandstone 2.90 limestone * rms error = 4.44 % acknowledgements first of all, we thank to the directorate general of higher education (dghe) of indonesia who has giving us scholarship. the authors thank jamaluddin othman of owner/principal geophysicist for providing the borehole results and gravity data of maluri park area. the field support from technical staff of geophysics programme, school of physics, universiti sains malaysia is highly appreciated. references debeglia, n., dupont, f., 2002. some critical factors for engineering and environmental microgravity investigations. journal of applied geophysics 50, 435 454. https://doi.org/10.1016/s0926-9851(02)00194-5 ebbing, j., braitenberg, c., götze, h.-j., 2001. forward and inverse modelling of gravity revealing insight into crustal structures of the eastern alps. tectonophysics 337, 191 208. doi:10.1016/s0040-1951(01)00119-6 kamal, h., taha, m, and al-sanad, s.,2010. environmental engineering and geotechnics, geoshanghai 2010 international conference. (accessed 02.03.17) kearey, p., brooks, m., hill, i., 2011. an introduction to geophysical exploration. blackwell publishing, malden, ma. lillie, r.j., 1999. whole earth geophysics: an introductory textbook for geologists and geophysicists. prentice hall, upper saddle river, nj. https://nla.gov.au/anbd.biban13624882 pringle, j.k., styles, p., howell, c.p., branston, m.w., furner, r., toon, s.m., 2012. long-term time-lapse microgravity and geotechnical monitoring of relict salt mines, marston, cheshire, u. k. geophysics 77. https://doi.org/10.1190/geo2011-0491.1 samsudin, hj., t., 2003. a microgravity survey over deep limesone bedrock, geological society of malaysia, bulletin 46, pp 201-208 (accessed 12.11.16). http://archives.datapages.com/ data/ geological-societyof-malaysia/bulletins/ 046/ 046001/ pdfs/ 201.htm tan, s., m. ,2005. karstic features of kuala lumpur limestone. bulletin of the institution of enginner malaysia, june 2005, 6 -11. (accessed 08.02.17) tajuddin, a. and lat, c. n., 2004. detecting subsurface voids using the microgravity method-a case study from kuala lipis, pahang, geological society of malaysia, bulletin 48, p. 31 35. (accessed 11.01.16) http://archives.datapages.com/data/geological-societyof-malaysia/bulletins/ 048/ 048001/ pdfs/ 31.htm telford, w.m., geldart, l.p., sheriff, r.e., 2010. applied geophysics. cambridge univ. press, cambridge. talwani, m., ewing, m., 1960. rapid computation of gravitational attraction of three‐dimensional bodies of arbitrary shape. geophysics 25, 203 225. https://doi.org/10.1190/1.1438687 © 2016 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1016/s0926-9851(02)00194-5 https://doi.org/10.1016/s0040-1951(01)00119-6 https://nla.gov.au/anbd.bib-an13624882 https://nla.gov.au/anbd.bib-an13624882 https://doi.org/10.1190/geo2011-0491.1 http://archives.datapages.com/%20data/%20geological-society-of-malaysia/bulletins/%20046/%20046001/%20pdfs/%20201.htm http://archives.datapages.com/%20data/%20geological-society-of-malaysia/bulletins/%20046/%20046001/%20pdfs/%20201.htm http://archives.datapages.com/data/geological-society-of-malaysia/bulletins/%20048/%20048001/%20pdfs/%2031.htm http://archives.datapages.com/data/geological-society-of-malaysia/bulletins/%20048/%20048001/%20pdfs/%2031.htm https://doi.org/10.1190/1.1438687 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. site description and geology 3. methodology 4. results and discussion 4.1 gravity overview of maluri bedrock 4.2 interpretation of 2d geotechnical models for microgravity anomaly at maluri site 5. conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 166 lubis, m.z. et al./ jgeet vol 02 no 02/2017 review : marine seismic and side-scan sonar investigations for seabed identification with sonar system muhammad zainuddin lubis 1, *, kasih anggraini 2 , husnul kausarian 3, , sri pujiyati 4 1 department of informatics engineering, geomatics engineering batam polytechnic, batam kepulauan riau, 29461 indonesia. 2 research center for oceanography lipi, jakarta, indonesia. 3 department of geological engineering, universitas islam riau, jl. kaharudin nasution no. 113, pekanbaru, riau 28284, indonesia. 4 department of marine science and technology, bogor agricultural university jln. agatis, kampus ipb dramaga bogor 16680 indonesia. abstract marine seismic reflection data have been collected for decades and since the mid-to late1980s much of this data is positioned relatively accurately. marine geophysical acquisition of data is a very expensive process with the rates regularly ship through dozens of thousands of euros per day. acquisition of seismic profiles has the position is determined by a dgps system and navigation is performed by hypack and maxview software that also gives all the offsets for the equipment employed in the survey. examples of some projects will be described in terms of the project goals and the geophysical equipment selected for each survey and specific geophysical systems according to with the scope of work. for amplitude side scan sonar image, and in the multi-frequency system, color, becoming a significant properties of the sea floor, the effect of which is a bully needs to be fixed. the main confounding effect is due to absorption of water; geometric spread; shape beam sonar function (combined transmit-receive sonar beam intensity as a function of tilt angle obtained in this sonar reference frame); sonar vehicle roll; form and function of the seabed backscatter (proportion incident on the seabed backscattered signal to sonar as a function of the angle of incidence relative to the sea floor); and the slope of the seabed. the different angles of view are generated by the translation of the sonar, because of the discrete steps involved by the sequential pings, the angular sampling of the bottom. keywords: marine seismic, marine geophysical, side scan sonar (sss), seabed, angels 1. introduction marine exploration with acoustic system has any function for: marine seismic, marine fisheries, determine abundance of fish in marine fisheries (lubis and manik, 2017), fish stock estimation echosounder instrument with hydroacoustic system (lubis and wenang, 2016), echo processing and identifying surface and bottom layer (lubis et al., 2016). marine seismic reflection data have been collected for decades and since the mid-to late 1980s much of this data is positioned relatively accurately. this older data provides a valuable archive, however, it is mainly stored on paper records that do not allow easy integration with other datasets. marine geophysical acquisition of data is a very expensive process with the rates regularly ship through dozens of thousands of euros per day. in addition, the survey often remote sites and can cause huge overhead on the transit time. sub-bottom reflection data has been collected for the decade but much older data is stored with paperrecords and not so easy to integrate with modern bathymetric data at this time (owen et al., 2015). seismic reflection surveys have been used to map the sub-surface since 1921 with marine reflection surveys coming to prominence in the 1950s when they were used to map bathymetry, seabed identification using multibeam and side scan sonar instrument (manik et al., 2014), seabed identification using side scan sonar c maxcm2 in punggur sea with acoustic method (lubis et al., 2017). sonar system used sound to detect or find objects that are specifically located in the sea. multibeam sonar is an acoustic instrument that has the ability to perform three-dimensional mapping of the ocean floor (bartholoma, 2006). the water depth measurement using multibeam instrument are fast and has a high accuracy, where this can not be done by a single beam echosounder. in addition to the instrument's ability to perform basic scanningthe seawater with very high accuracy and coverage are also able to produce information in the form of backscatteringvalues which can be used to determine the distribution ofseafloor sediment type (manik, 2011). modern seismic data (including multichannel seismics, 3d seismics and parametric techniques), * corresponding author : zainuddinlubis@polibatam.ac.id tel+6281342578087, office : 778-469856 ext : 2510; fax: +62-778-463620 received: mar 31, 2017. revised : may 20, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.253 mailto:zainuddinlubis@polibatam.ac.id lubis, m.z. et al./ jgeet vol 02 no 02/2017 167 stored, processed and interpreted digitally, can provide more detail than older data (mohammedyasin et al., 2016). in particular, accurate analysis of reflector polarity (yoo et al., 2013) may not be possible when data is converted from a paper record. however, this does not mean that data acquired in the past is not useful. that acquired since the mid-1980s will often have relatively precise and accurate navigation data allowing integration with other modern datasets with acoustic methods. marine sandy deposits vary in terms of composition, size, thickness, horizontal continuity, and admixture with other materials such as biogenic matter, mud, and gravel or rock. according to (de souza et al., 2015) beach-quality sands have very specific parametric ranges in properties that are acceptable for placement on beaches, it is necessary. 2. acquisition of seismic profiles the position is determined by an dgps system and navigation is performed by hypack and maxview software that also gives all the offsets for the equipment employed in the survey. examples of some projects will be described in terms of the project goals and the geophysical equipment selected for each survey and specific geophysical systems according with the scope of work. in fig 1 is showed a figure of the set of geophysical equipment employed for sand search survey, and fig 2 showed a figure of the result seabed identification using side scan sonar in punggur sea. for amplitude side scan sonar image, and in the multi-frequency system, color, becoming a significant properties of the sea floor, the effect of which is a bully needs to be fixed. the main confounding effect is due to absorption of water; geometric spread; shape beam sonar function (combined transmit-receive sonar beam intensity as a function of tilt angle obtained in this sonar reference frame); sonar vehicle roll; form and function of the seabed backscatter (proportion incident on the seabed backscattered signal to sonar as a function of the angle of incidence relative to the sea floor); and the slope of the seabed. absorption and geometrical spreading effect can be corrected relatively straightforward. the effect of the functions of the sonar beam and seabed functionality angular backscatter which is on the effect of time-varied and more difficult to take into account. it is only relatively recently that sufficient correction has been designed (tamsett et al., 2016). the seabed backscatters incident sonar signal because: there are acoustic impedance contrasts across the seabed interface; and the seabed interface is rough in comparison to the wavelength of the sonar carrier wave. the seabed interface comprises usually a seabed seabed surfaces between contrasting materials. high absorption of ultrasound in sub-seabed materials severely limits the skin depth of the interface. the backscatter response of a seabed to the incident sonar signal, being dependent on seabed interface roughness, is therefore dependent seabed is acoustically colourful (buscombe, 2017). that the seabed is intrinsically acoustically colourful may be recognised in developing a sonar technology and data at multiple sonar frequencies acquired and mapped to optical primary colour frequencies to generate optical colour images of the seabed for human visualization. the principal advantage of colour imagery over greyscale is that at each pixel, a colour datum occupies a position in a three-dimensional (3d) rgb (red, green, blue) data space. if colour data are reduced to greyscale, the data in three dimensions are projected onto and will then occupy positions on a line (e.g., the diagonal across the rgb data space). as econdary advantage of colour sonar images of the seabed is that they can (subject to the eye of the beholder) be very beautiful (engquist et al., 2017). fig 1. figure of set of geophysical equipment for sand search surveys (de souza et al., 2015). 168 lubis, m.z. et al./ jgeet vol 02 no 02/2017 fig 2. image classification and position target 16 on sediment track 2, punggur sea (lubis et al., 2017). 3. acoustic colour of the seabed before considering methods for rendering multi-frequency sonar data as colour images,we look a little more deeply at the concept of the acoustic colour of the seabed. where a sonar system is calibrated, the calibrated backscatter amplitude response of the seabed may be computed from: (1) where: scal is the calibrated or natural amplitude response of the seabed, this being the ratio of the acoustic signal amplitude backscattered from a seabed to the signal incident on the seabed along the same line (0 to 1.0); s is the sonar amplitude response of the seabed (a large integer) corrected for: geometrical spreading incorporating the effect of the area of absorption, and the sonar beam function (data along the trace are normalised to the response at frame of reference); rcal is the ratio of the amplitude response of the sonar receiver in sonar amplitude units (a large integer) to the pressure amplitude at the receiver in micro-pascal; tcal is the amplitude of the sonar pulse in micropascal one meter from the transmitter in the direction of the reference inclination angle. the calibrated amplitude response of the seabed scal, is afunction of sonar carrier wave frequency ν and angle of incidence with respect to the frame of reference of the seabed (the grazing angle) θ. the function scal (ν, θ) is two-dimensional and is the broadband seabed backscatter function encapsulating the acoustic backscatter characteristics of a seabed. the dependence on frequency is what makes the seabed acoustically -colour property inherent in scal (ν, θ) cannot be directly visualised. the generalised function scal(ν, θ) must be reduced to values at three discrete frequencies (or averaged over three frequency bands) and the values scaled to 8-bit values (zero to 255) for display in pixels in digital visual technologies: (2) the values of ndatr (θ), etc., may then be used for computing rgb components of the natural lubis, m.z. et al./ jgeet vol 02 no 02/2017 169 acoustic colour of the seabed for the frequencies vlow, vmed, vhigh as a function of grazing angle θ, i.e., the values may be used to present the seabed backscatter function measured by a colour sonar system as a line of colour. to display a sonogram montage as a chart, the backscatter values along traces (across sonograms) are normalised to the seabed response at the reference inclination angle θref, say 30 (tamset et al., 2016). at angles much less than normal incidence, the natural backscatter amplitudes are small and visually not very distinguishable from shadow. to generate midrange colours more appropriate for practical human visualisation, an amplitude gain might need to be applied. (3) these values may be directly used as parameters for displaying colour for human visualisation or may be used as input to a process for generating other rgb parameters for colour display. optical colour derived from these values should be been generated with respect to: the values of the carrier wave frequencies of the system (or the means of bands); the reference inclination angle; and the amplitude gain applied. the relative rgb values are objectively determined n data. an example of a colour sonogram presented in rgb colour is shown in figure 3. the values for ndatr, ndatg and ndatb are proportional to the sonar amplitudes as a function of frequency. a value of zero represents shadow and appears as black. a value of 255 represents saturation and appears white. a strongly backscattering seabed appears as light shades of colour, e.g., the light shades of blue running up the right side of figure 3 bare strongly backscattering. conversely, aweakly backscattering seabed appears as dark shades of colour; the dark shades of blue running up the left side of figure 3 are a very weakly backscattering seabed. fig 3. mid-frequency and componentsofamulti-frequency sonar swath represented as negative greyscale images. 4. angular bining of the sonar the different angles of view are generated by the translation of the sonar. because of the discrete steps involved by the sequential pings, the angular sampling of the bottom within the ranges described in the previous section is not continuous (haniotis et al., 2015). we are looking here at the optimal binning of the grazing angles {gi} used to sort the backscatter angular responses, to provide a gapless coverage. the trajectory of the platform is assumed to be a straight line, with the forward step being a of clarity, one considers the stop and hop scenario. in addition, the angular sampling is studied in the vertical plane that contains the platform track, the ground profile being horizontal, at depth h below the antenna. a point of the bottom lying at the abscissa x ahead of the sonar nadir (y = 0) during a ping is arctan ≪ h, the change between successive pings in the angle of view of the same 2 g (fig. 4). δg (case δg < g). to provide a gapless angular sampling of the bottom, the longitudinal extent δx of the segments intercepted on the bottom by the sectors δγ corresponding to the bin that contains the grazing the sonar between pings, i.e., there must be δ an upper bound of the bin widths is given by the few meters, and the water level, h, is a few tens of meters. statistics made on the processed surveys ץ given an initial grazing angle γ0 (= 69°), the first part of the partition is thus built recursively by considering constant longitudinal footprints, i.e., :maxץ (4) 170 lubis, m.z. et al./ jgeet vol 02 no 02/2017 fig 5. binning of the grazing angles in the interval [69°, γmax = 5º and δץend = 2º. (top) angular bin width δγ. (bottom) longitudinal extension of the bins. for low grazing angles, the width of the bins dictated by a constant longitudinal interval δ turns out to be very small, which is not justified by the experimental accuracy and increases unnecessarily the number of bins. consequently, the second part of the partition is built with a constant angular bin width when it reaches a chosen threshold, δץend = 2° (fig. 5). the resulting grazing angles at the limit of the bins are displayed in fig. 6. fig 6. grazing angles at the limits between bins. references bartholoma a. 2006. acoustic bottom detection and seabed classification in the german bight, southern north sea. springer : wilhelmshaven, germany. vol (26): 177 184. buscombe, d. 2017. shallow water benthic imaging and substrate characterization using recreational-grade sidescan-sonar. environmental modelling & software, 89, 1-18. de souza, j. a., do carmo barletta, r., franklin, l., & benedet, l. 2015. utilization of multiple geophysical sources and geotechnical sampling to search for offshore sand deposits for beach restoration in brazil. in acoustics in underwater geosciences symposium (rio acoustics), 2015 ieee/oes (pp. 1-4). ieee. engquist, b., frederick, c., huynh, q., & zhou, h. 2017. seafloor identification in sonar imagery via simulations of helmholtz equations and discrete optimization. journal of computational physics, 338, 477-492. haniotis, s., cervenka, p., negreira, c., & marchal, j. 2015. seafloor segmentation using angular backscatter responses obtained at sea with a forward-looking sonar system. applied acoustics, 89, 306-319. lubis, m. z., & anurogo, w. 2016. fish stock estimation in sikka regency waters, indonesia using single beam echosounder (cruzpro fish finder pcff-80) with hydroacoustic survey method. aceh journal of animal science, 1(2). lubis, m. z., & manik, h. m. 2017. acoustic systems (split beam echo sounder) to determine abundance of fish in marine fisheries. journal of geoscience, engineering, environment, and technology, 2(1), 76-83. lubis, m. z., anurogo, w., khoirunnisa, h., irawan, s., gustin, o., & roziqin, a. 2017. using side-scan sonar instrument to characterize and map of seabed identification target in punggur sea of the riau islands, indonesia. journal of geoscience, engineering, environment, and technology, 2(1), 1-8. lubis, m. z., wulandari, p. d., mujahid, m., hargreaves, j., & pant, v. 2016. echo processing and identifying surface and bottom layer with simrad ek/ey 500. journal of biosensors and bioelectronics, 7(3), 1000212. manik, h. m. 2011. underwater acoustic detection and signal processing near the seabed, in sonar systems. edited by nikolai kolev. first edition. intech, croatia. hal. : 255274. manik, h. m., rohman, s., & hartoyo, d. 2014. underwater multiple objects detection and tracking using multibeam and side scan sonar. international journal of applied information system, 2(2), 1-4. mohammedyasin, s. m., lippard, s. j., omosanya, k. o., johansen, s. e., & harishidayat, d. 2016. deepseated faults and hydrocarbon leakage in the snøhvit gas field, hammerfest basin, southwestern barents sea. marine and petroleum geology, 77, 160-178. owen, m. j., maslin, m. a., day, s. j., & long, d. 2015. testing the reliability of paper seismic record to segy conversion on the surface and shallow sub-surface geology of the barra fan (ne atlantic ocean). marine and petroleum geology, 61, 6981. tamsett, d., mcilvenny, j., & watts, a. 2016. colour sonar: multi-frequency sidescan sonar images of the seabed in the inner sound of the pentland firth, scotland. journal of marine science and engineering, 4(1), 26. yoo, d. g., kang, n. k., bo, y. y., kim, g. y., ryu, b. j., lee, k., & riedel, m. 2013. occurrence and seismic characteristics of gas hydrate in the ulleung basin, east sea. marine and petroleum geology, 47, 236-247. 1. introduction 2. acquisition of seismic profiles 3. acoustic colour of the seabed 4. angular bining of the sonar 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(do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press p-issn jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet e-issn page 1 page 2 page 3 page 4 page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 56 handoyo et al./ jgeet vol 5 no 2/2020 research article rock physics formula and rms stacking velocity calculation to assist acoustic impedance inversion that constrain well data handoyo1, mochammad puput erlangga1, fatkhan2, paul young3 1geophysical engineering, institut teknologi sumatera, south lampung, indonesia. 2geophysical engineering, institut teknologi bandung, west java, indonesia 3tgs nopec geophysical company asa, perth, australia * corresponding author : handoyo.geoph@tg.itera.ac.id tel.: +6285295400039 received: apr 29, 2020. ; accepted: jun 4, 2020 doi: 10.25299/jgeet.2020.5.2.3089 abstract this research ilustrate the generation of acoustic impedance inversion in the absence of well log using stacking velocity input in salawati basin, papua, indonesia using data obtained from seismic lines and stacking velocity section. initial acoustic impedance models were first before the inversion process and were created by spreading the value of well log data to the all seismic cdp. the calculated acoustic impedance logs from standard sonic and density logs were used to build the initial model of acoustic impedance. first, the stacking velocities was first interpolated on a grid that has the same size as the seismic data using by means of polynomial algorithm. this was closely followed by the conversion of the stacking velocities to interval velocities using dix’s equation. the matrix densities were estimated by simple rock physics approach i.e. gardner’s equation as a velocity function. the initial model of acoustic impedance was calculated by multiplying the densities section and interval velocities section. the resulting initial model of acoustic impedance was inverted to obtain the best of acoustic impedance section based on reflectivity. keywords: acoustic impedance, rock physics, stacking velocity, wellog 1. introduction to conduct an acoustic-impedance inversion using bandlimited seismic data, the elastic parameters information must be given from the other data than the seismic reflectivity estimate. well logs are commonly used for this purpose (lindseth, 1979); however, stacking velocities can also be used to provide the low-frequency component (oldenburg et al, 1984). in this paper, an attempt was made to carry out seismic inversion using interval velocity model from stacking velocity due to non-availability of well log data. we also used the gardner’s relationship to calculate the density. thus, we get the initial model of acoustic impedance section by multiplying the interval velocity and the density that resulted from gardner relationship. this initial model was inverted to obtain the acoustic impedance volume based on the seismic reflectivity. 2. data and method 2.1 data salawati basin is a foreland basin trending east–west and located in the northern part of indo–australia plate (figure 1). this basin is bounded by deformation zone of sorong fault in the northernand western part. in the southern part, the basin is bounded by misool–onin high, while the eastern boundary is the ayamaru plateau. salawati basin records the stratigraphy and tectonic histories from paleozoic until recent (satyana, 2003). generally, the stratigraphy of salawati basin can be divided into two parts base on age, pre-tertiary and tertiary (figure 2). the oldest stratigraphic sequence in salawati basin is metamorphosed continental bedrock of kemum formation with age of silurian–devonian. mesozoic sediments (tipuma and kembelangan group) were deposited only in the south because of uplifting or non-deposition in the nort (satyana, 2003). there are three exploration wells in the western part of salawati island which that penetrated to cretaceous granitic rocks intruding paleozoic metamorphics (situmeang, 2012). fig1. geologic setting of salawati basin south of sorong fault. sorong fault major control for geologic configuration of the basin (satyana, 2003). 2.2 method stacking velocities are generated during the processing of the seismic data in velocity analysis step. for this paper we used the hussar data set as described in lloyd and margrave [2],[3]. the method of this study follow the steps: (1) extract the stacking (rms) velocity trace from stacking velocity section; (2) make the selected stacking velocity trace as velocity log data; (3) horizon picking and create the stacking (rms) velocity model; (4) convert the stacking (rms) velocity section into interval velocity section; (5) create the density section from interval velocity section using gardner http://journal.uir.ac.id/index.php/jgeet handoyo et al./ jgeet vol 5 no 2/2020 57 relationship; (6) create the acoustic impedance section from interval velocity section and density section; (7) make the acoustic impedance section as the initial model and then do the model based inversion. fig 2. regional stratigraphic setting of salawati basin.the stratigraphy of salawati basin can be divided intotwo major parts based on age pre-tertiary and tertiary (satyana, 2003). to convert the stacking velocities to interval velocities using the standard dix interval velocity calculation (margrave, 2002). the equation is shown below: 1 1 2 1 2      nn nnnn n vv v   (1) after obtaining the interval velocity section from the stacking (rms) velocity section, the densities can be calculated using the empirical rock physics relation between velocity and density relationship e.g. gardner’s equation from mavko et al, 2009: 25.0 310 p v (2) where ρ are the density and vint are the interval velocity. then, the acoustic impedance is calculated by the following equation: p vai  (3) the material of this study consist of 2d line seismic data and stacking velocity from the field area, south salawati basin. 4. result and discussion 4.1 result the result of the extract stacking (rms) velocity trace from stacking velocity section to make the synthetic log is as shown in figure 3. the synthetic well was located in a position that have been preiously choosen. then, the lithostratigraphic horizon of interest were interpreted in some area. the result of these process is shown in figure 4. the horizon indicate the different lithology (physical properties) and the possibility of carbonate existence. fig 3. the result of syntetic log velocity extracted from stacking velocity section after the horizons interpretation, the value of stacking (rms) velocity from well to all seismic cdp trace was spread. the spreading of stacking (rms) velocity value from well was guided by the seismic horizons. the rms velocity section tend to be the low frequency model and the smoothing technique was applied to the section. the result of rms velocity section is shown in figure 5. fig 4. the horizon interpretation results and display of well location. we propose four interest horizons. after obtaining the rms velocity section, the next step was the calculation of the interval velocity using equation 1. the result of interval velocity section is shown in figure 6 (a). then, the acoustic impedance was calculated by equation 2 and 3, and make it as an initial model of the acoustic impedance. the result of initial acoustic impedance model section shown in figure 6 (b). fig 5. the result of rms velocity section. the final step was the acoustic impedance inversion using model based inversion technique. the inversion input was based on using the initial model of acoustic impedance as 58 handoyo et al./ jgeet vol 5 no 2/2020 shown in figure 6 (b). the result of acoustic impedance inversion is shown in figure 7. fig 6. (a) the interval velocity section and (b) the initial model of acoustic impedance. fig 7. inverted acoustic impedance. 4.2 discussion because the inversion was mainly dependent on well data or accurate stacking velocities, picking them with the intent of using them for inversion helped the results greatly. in this study, they were very sparse laterally so picking more locations would help constrain lateral variation. picking more structure samples vertically also helped constrain any anomalies, however making picks too close together created instabilities in the conversion to interval velocities. in this study, we used a very simple way of calculating interval velocities. there are more advanced methods of calculating interval velocities and they should be investigated. oldenburg et al. (1984) discussed using weighted least squares methods to produce a smooth variation. they also discussed using known interval velocities as controls when converting the stacking velocities to interval velocities. 5. conclusions this study conclude that it is possible to get a good acoustic impedance estimation using the stacking velocities and rock physics equation. however, when well log data is absent or the well position coordinate is so far to the seismic line, stacking velocities provide an interesting alternative. we can generate the initial model of acoustic impedance using interval velocity from stacking velocity and the density from velocity. the dix’s equation is able to convert the stacking velocity to the interval velocity and the gardner relationship can convert the density from the interval velocity as well. acknowledgements the authors are very grateful to data courtesy of tgs for the permission publish this article. references lindseth, r. o., 1979, synthetic sonic logs – a process for stratigraphic interpretation: geophysics, vol. 44, no. 1. margrave, g. f., 2002, methods of seismic data processing lecture notes geophysics 577: university of calgary. mavko g., mukerji t. and dvorkin j. 2009. the rock physics handbook: tools for seismic analysis in porous media. cambridge university press. oldenburg, d. w., levy, s. and stinson, k., root-mean-square velocities and recovery of the acoustic impedance. geophysics, vol. 49 no. 10. 1653-1663. situmeang, m., 2012, karakteristik reservoar karbonat menggunakan inversi sparse spike di lapangan ”panda” formasi kais cekungan salawati, papua [unpublished]: yogyakarta, universitas pembangunan nasional “veteran”, 76p. satyana, a. h., 2003, sorong fault and reversal of the salawati basin: indonesian petroleum association newsletter, jakarta, march 2003. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 harbowo et al./ jgeet vol 02 no 02/2017 137 stiva cave: a new discover of prehistoric hominid underwater cave danni gathot harbowo 1. *, stiva alouw 2 , theresia gerungan soetamanggala 2 , and azalia gerungan 2 1 institut teknologi sumatera, south lampung, indonesia 2 octopus dive indonesia, nusa penida, bali, indonesia abstract stiva cave is an underwater cave (15,3 m below recent sea level), which located in nusa penida, bali, indonesia. nusa penida is a karst landscape island in southern bali island. no many underwater caves are known and explored in this area, stiva cave is a first underwater cave which explored and discovered in nusa penida area. in this cave we found a number of fossils that we identified as vertebrate fossil and unique process that very potential for geotourism, especially for fun diving tourism. we mapped entire cave tunnel and measure a safety and risk for scuba diving, then we identified the fossil. at the result, there a several risk that need to be aware and several safety procedures that must be allow for observer. in other way, we found many similar fossils that and it spread in different tunnel that very potential for education in geotourism. we suggest that this cave is a shelter for hominid species when last glacial maximum happens, before 21.000 years ago. keywords: underwater cave, hominid, fossil, last glacial maximum 1. introduction nusa penida located in southern bali, mostly underground river system which has connection to other river system. based on its genesis, karst in nusa penida has three sequences which can derived based on its characteristics in lithology. in several discussions, this ecosystem start at miocene (23,5 millon years ago). until today, sedimentation of carbonate in this system still produce, almost in shoreline in nusa penida (p.h. barber, 2000). stiva cave is an underwater cave in nusa penida, bali, indonesia. it is has been found in 2016 by local diver. this cave located in below recent mean sea levels. stiva cave is one attractive site for tourism in toyapakeuh, nusa penida (n:8.685659, w:115.479822), see fig. 1. but until we start to explore this cave, no one realized that there are several fossil which deposited in this cave because these fossil covered by sediment. so in this research we aim to discover all the cave tunnels, fossil that deposited, and reconstructing how these fossil deposited in this cave. this research hopefully gave advice for guiding diver in moment entered the cave fig 1. location of stiva cave, toyapakeuh,nusa penida, bali, indonesia. 2. method cave mapping. there are three parts mapping sections, this procedure necessary to do because we need to calculated the oxygen tank, because it is our limitation when mapping in underwater cave and it in dark condition (see fig. 2). we measured the width and height in every part cave tunnels for sketching its tunnel morphology. in every section, we collected sediment sample using * corresponding author : danni.gathot@itera.ac.id tel.:+852-946-85303 received: may 3, 2017. revised : may 25 2017, accepted: may 30, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.300 mailto:danni.gathot@itera.ac.id 138 harbowo et al./ jgeet vol 02 no 02/2017 tube coring, completed with thick of the sediment for further analysis. we also collected several fossils for identification and reconstructing the paleoenvironment of this cave. fig. 2. stiva cave condition, we need plan more comprehensive for underwater mapping sediment analysis. this procedure necessary to do. we can identify how this cave submerge at few step based their sediment characteristic. we classify sediment based their size (sand, silt, and clay) by its percentage. 3. result stiva cave enterance at 15,3 m below mean sea level. it is heading to northeast and has height 280 cm and width 510 c has two branches heading to east ( ) and south ( ). the cave tunnel has 179 m, south tunnel is the longest tunnel in this system, 37,5 m and the other is 25,8 m. we can find several chamber in along tunnel (see fig. 3) fig. 3. sketch of the stiva cave tunnel and its position from mean sea level. the thickness of sediment layer from mouth to edge is gradually thinny and smoothy. percentation of clay increase gradually into deep cave, follow by decreasing percentation of sand and silt. we can found several chamber in each tunnel branch. the east tunnel/right-hand branch tunnel/lefte) has 2 chamber too (see fig. 3 and fig. 4). we also found several vertebrate, its looks accumulated in chambers. there are proboscidea mandibular that can be found in front chamber, the sarchum of turtoise in 1 st chamber i right hand branch, then the femur and vertebrate of cervidae in 2 nd chamber. in left-hand branch we also can found more cervidae fossil and probocidea scapula, accumulated in 3 rd and 4 th chamber (see fig. 5). fig. 4. distribution of sand, silt, and clay in each tunnel of stiva cave (top) and their fossil distribution (bottom). 4. discussion stiva cave form from sub-surface hydrology system of karst landscape. the freshwater from the rain penetrated into body of carbonate rock to crack and weak rock then eroded and made it into a cave tunnel. when the carbonate rocks exposed into atmosphere, it will react with the air and the acid from rain. when this cave form it will make tunnel bigger and bigger in time. but it very fragile and has potential to break if the tunnel this cave is big enough to entered by dwarf humanoid, but very difficult to enter by scuba. it needs special technique to access safely. harbowo et al./ jgeet vol 02 no 02/2017 139 fig. 5. there are several fossil that can be found in stiva cave, that is cervidae antler (a), femur (b), humerus (c), vertebrate (d). also we can found turtoise sarchum (e) and probocidae mandibular (f). based on location of fossil in that cave, it has potential that in past time this cave is a prehistoric hominid cave. we predict, in the past time, this cave is a shelter for cavern hominid. there are a group of hominid carrying the hunted pray into their shelter, share, and eat them together. they share it to each other then, left the bone into cave floor. when the cave abounded, the bone deposited in this cave until the cave submerge, and gradually change into fossils. fig. 6. the sea level change graphic began in pleistocene (21.000 years ago) to recent mean sea level. we suggest that this cave is a terrestrial cavern system, specially at the end of pleistocene, around 21.000 years ago, the sea level is -114 m below recent sea level (see fig. 6), it known as last glacial maximum (liu, j. p., & milliman, j. d. 2004; tjia, h. d. 1992; tjia, h. 2014) in this condition, stiva cave still exposed to the atmosphere and can be access by terrestrial fauna include the hominid (fairbanks, 1989; hanebuth, et al, 2000; solihuddin, 2014). cave in karst ecosystem is the best for hominid shelter, it will cool in heat atmosphere condition, and it will warm if in cold condition. karst can maintain the temperature more stable in fluctuative environment temperature. it must be good to be shelter. after the pleistocene ending, the global temperature is rising faster and make the ice in earth polar melting faster (abdussamatov, 2011; geyh, et al, 1979; sathiamurthy and voris, 2006). the implication of that, sea level rising faster and reach into recent sea level. when sea level rising, stiva cave will drown by sea water and left the bone in that cave and fossilized, it can explain why in that cave we can found fossil so many in specific type and accumulated in specific location in cave. the sediment in this cave can explain how sedimentation happen in that time. in front of cave we can found more course sediment correlated in more deep tunnel. the beach sand can enter the cave, but it more hard to enter, if sea more deep. this cave has geological value, especially in paleontology. 5. conclusion stiva cave is one of underwater cave that has rich vertebrate fossil. the fossil preserved well in cave condition, which expels from the sunlight and covered by sediment which has small grain. we suggest that the rich fossil in this cave is a result of prehistoric hominid activity, that carry they hunted and eat them in this cave. this cave must be exposed to the atmosphere at that time, 140 harbowo et al./ jgeet vol 02 no 02/2017 when global mean sea level still far below compared with recent. it could be happened when last glacial maximum happens, 21.000 years ago. then this cave abounded by them, when this cave close enough with shore or frequently flooded at high tides. acknowledgements we would like to say thanks to octopus dive indonesia and institut teknologi sumatera for totally giving us support of this research. reference abdussamatov, h. i. 2011. bicentennial decrease of the total solar irradiance leads to unbalanced thermal budget of the earth and the little ice age. applied physics research 4 no. 1, doi: 10.5539/apr.v4n1p178. p.h. barber s.r. palumbi m.v.erdmann m.k. moosa. 2000. a marine wallace's line? nature 406. doi: 10.1038/35021135p.h. barber s.r. fairbanks, r. g. 1989. a 17,000-year glacioeustatic sea level record: influence of glacial melting rates on the younger dryas event and deep-ocean circulation. nature , 342, 637-642. doi:10.1038/342637a0. geyh, m. a., kudrass, h., & streif, h. 1979. sea level changes during the late pleistocene and holocene in the strait of malacca. nature. 278 , 441-443. doi:10.1038/278441a0. hanebuth, t., stattegger, k., & grootes, p. m. 2000. rapid flooding of the sunda shelf : a lateglacial sea level record. science , 288, 10331035. 10.1126/science.288.5468.1033. hesp, p. a., hung, c. c., hilton, m., ming, c. l., & turner, i. m. 1998. a first tentative holocene sea-level curve for singapore. journal of coastal research , 14 (1), 308-314. doi:10.1029/2005jb003891. liu, j. p., & milliman, j. d. 2004. reconsidering melt-water pulses 1a and 1b: global impacts of rapid sea-level rise. journal of ocean university of china (oceanic and coastal sea research),3(2),183-190.doi:10.1007/s11802004-0033-8. sathiamurthy, e., & voris, h. k. 2006. maps of holocene sea level transgression and submerged lakes on the sunda shelf. the natural history journal of chulalongkorn university , 2, 1-44. doi: 10.1002/oa.2226. solihuddin, t. 2014. a drowning sunda shelf model during last glacial maximum (lgm) and holocene: a review. indonesian journal on geoscience,1(2),99-107. doi: p.10.1038/ 382241a0. tjia, h. d. 1992. holocene sea-level changes in the malay-thai peninsula, a tectonically stable environment. geol. soc. malaysia , 31, 157176. doi: 10.1191/0959683605hl891rp. tjia, h. 2014. stepwise sea-level changes since mid-holocene in peninsular malaysia. sea ngc. voris, h. k. 2000. maps of pleistocene sea level in southeast asia: shoreline, river system and time duration. journal of biogeography 27, 1153-1167. doi: 10.1046/j.1365-2699.2000. 00489.x. 1. introduction 2. method 3. result 4. discussion 5. conclusion acknowledgements e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 64 novriansyah, adi et al./ jgeet vol 02 no 01/2017 an experimental study on effect of palm shell waste additive to cement strenght enhancement adi novriansyah 1 , novrianti 2, *, mursyidah 2 , sepria catur hadiguna 2 1 sejong university, a department of energy and mineral resources engineering, republic of korea 2 petroleum department, universitas islam riau, jln. kaharuddin nst no. 113, pekanbaru, riau abstract enhancing the cement strength through attaching chemical additive has been popular to meet the required condition for a particular well-cementing job. however, due to a low oil-price phenomenon, pouring and additive should be reconsidered because it can raise the cost and make the project become uneconomic. another additive material in nanocomposite form will be introduced through this experimental study. the nanocomposite material consist of silica -shell-waste, which is abundant in indonesia. before making a nanocomposite, the palm-shell should be burned to obtain a charcoal form, ground and sieved to attain a uniform size. the study focuses on the two parameters, compressive strength and shear bond strength, which can reflect the strength of the cement. these values are obtained by performing a biaxial loading test to the cement sample. various samples with different concentration of nanocomposite should be prepared and following the mixing, drying, and hardening process before the loading test is carried out. the result from the test shows a positive indication for compressive strength and shear bond strength values, according to the representative well cementing standards. increasing the nanocomposite concentration on the cement will increase these values. furthermore, an investigation on the temperature effect confirms that the sample with 700 o c burning temperature have highest compressive-strength and shear-bond-strength values. this is a potential opportunity utilizing a waste-based material to produce another product with higher economic value. keywords: nanosilica, nanocomposite, compressive strength, shearbond strength, cementing. 1. introduction the cement strength issue is a common problem in the oil-well cementing operation. the strength can be reflected from its compressive strength (cs) and shear-bond strength (sbs) values, which is appropriate to the proper standard. (rubiandini et al., 2005) in oil and gas industry, these values should refer to the american petroleum institution standard (institut, 2002). cs defines as the ability of cement to withstand the horizontal force such as formation and casing pressure while sbs describes the capacity of the cement in resisting the vertical force such from the casing string weight. (palmer, 1990) enhancing the slurry with chemical additives is a solution to keep our design consistent with the required condition. (rubiandini et al., 2005) enhancement of pozzolanic material and other supportive material into the slurry has successfully increased the cement strength. (siregar, n.d.) according to astm c618-93, material which contains silicon oxide, iron oxide, and aluminium oxide more than 70% can be utilized as an additive material. (al-dahlaki, 2007) other engineered particle such as silica, iron oxide, and aluminium oxide nanoparticle can raise up the cement strength and reducing the filtration loss phenomenon (ershadi et al., 2011) this experimental study uses nanocomposite additive, a combination of nanosilica and palm-oil shell, which is commonly found in indonesia. palm-oil trees flourish in almost over 33 million acres, where 70% of this plantation site lies in sumatera. an abundant source of palm-oil, which is nearly 17.3 ton per year, leads to other waste product such as liquid waste, (palm oil mill effluent, pome), fibres, and shell. (dirjenbun, 2015) one ton of palm-oil will dispose 700 kg pome and 190 kg of fibres and shell. (haryanti a., norsamsi,sholiha p.s.f., 2014). the shell from the palm-oil-fruit contains silica (worathanakul et al., 2009). moreover, another work by (bae, 2016) has yielded an optimum concentration for nanocomposite additive, where * corresponding author : novrianti@eng.uir.ac.id tel.:+81-22-2000489; received: feb 1, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017 doi: 10.24273/jgeet.2017.2.1.33 mailto:novrianti@eng.uir.ac.id novriansyah, adi et al./ jgeet vol 02 no 01/2017 65 cs and sbs reach its maximum values for sample with 3wt% nanocomposite additive. the effect of heating temperature has been observed (hadiguna, 2016). experiment by using palm-shell carbon additive have shown the optimum heating temperature is 700 o c. however, the optimal temperature for a sample with nanocomposite temperature is not studied yet. the objective of this paper is to investigate the effect of the heating temperature to cement strength. 2. material and methods 2.1. material the cs and sbs values can be obtained by performing the tri-axial test. the sample should be prepared carefully to keep the quality of the recorded data. a class g cement powder from pt holcim has been purchased. class g cement is applicable in the well cementing environment (falode et al., 2013). furthermore, nanosilica from aldrich company, where the physical properties are listed in the table 1, is procured. table 1. characteristic of nanosilica (novriansyah et al., 2015) physical properties explanation density 2.17-2.66 gr/cm 3 melting point ± 1700 0 c boiling point 2230 0 c color white particle size 10-20 nanometer bulk density 0.011 gr/ml one of the palm-oil company in indonesia, cv berkat jaya, located in sampit, kalimantan has supported us by providing the shell from the palmoil fruit. the shell was ground and sieved to obtain the uniform size (200 mesh). the shells in powdery form, is then heated by using the oven furnace. to see the effect of heating temperature, six shells sample will be roasted with different temperature, from 500 o c to 900 o c with 100 o c escalation to obtain its charcoal form, known as palm shell carbon (psc). table 2 comprise the chemical compositions of the psc chemical compounds content (%) mgo al2o3 sio2 4.9 2.2 30.1 p2o5 so3 19.6 3.28 k2o cao 17.5 14.6 fe2o3 cuo 5.08 0.388 zno 2.30 source : siregar, 2012 2.2. experiment procedure six cement samples will be prepared based on the table 3. water should be kept in turbulent condition by maintaining a high speed propelled mixer in constant condition (1200 + 500 rpm). it is important because the cement and the palm-oil shell should mixed completely. after the cement powder and the palm-oil are decanted into the mixing container, the mixer speed will be increased to the 4000 + 200 rpm for 15 minutes. cement suspension is then placed into the mold and dried for 24 hours at 140 o f. after sample totally dried, a sample is taken out and then positioned in the hydraulic press apparatus. a certain amount of hydraulic force will burdened to the sample until the crack was generated and the rock rupture. the load was recorded as maximum load and cs and sbs values can be calculated by using this parameter. the procedure will be repeated for other sample with different heating temperature of psc. the structure and the crystal content of the sample will be identified by using xray diffraction (xrd) and scanning electron microscope (sem) apparatus. table 3 cement slurry composition sample name explanation s1 0.019% nano-sio2 + 3% psc 400°c s2 0.019% nano-sio2 + 3% psc 500°c s3 0.019% nano-sio2 + 3% psc 600°c s4 0.019% nano-sio2 + 3% psc 700°c s5 0.019% nano-sio2 + 3% psc 800°c s6 0.019% nano-sio2 + 3% psc 900°c 3. results and discussion the effect of heating temperature on cs and sbs values is depicted in fig 1 and 2 respectively. according to the api standard, the cs and sbs values are acceptable and can be implemented in the field condition. the positive trend has been illustrated in the fig 1, where the cs value increases up to more than 1400 psi for sample with 700 o c heating temperature, compared to the sample with 500 o c heating temperature. however, the greater cs value is not established for the sample with higher heating temperature. similar thing occurred in the sbs plot in fig 2, where the highest sbs value was recorded for the sample with 700 o c heating temperature. fig 1 and 2 clearly expresses that cs and sbs values will improve if the heating temperature of the psc higher. performing the heating process 66 novriansyah, adi et al./ jgeet vol 02 no 01/2017 with higher temperature will trigger the charcoal purification process, yield to the increment of psc-active-carbon-content up to 90%. more carbon active improve the bonding quality of the cement, resulting higher cs and sbs value. however, the active carbon will decrease after the heating temperature exceeds 700 0 c. this due to the presence of hydrogen gas, which can lessen the bonding quality of the cement. fig 3.a and 3.b display the xrd result of the samples with different heating temperature. sample with 700 o c heating temperature in fig 3.a exhibit a higher trend, compared to the other with 300 o c in fig 3.b. furthermore, sample with higher heating temperature has greater crystal content (82.2% compares to 62.5%). sample with greater crystal content tend to strengthen the interparticle bonding, resulting a high strength concrete. fig 1. compressive strenght of sample fig 2. shear bond strenght of sample novriansyah, adi et al./ jgeet vol 02 no 01/2017 67 fig 3a (left). xrd curve from psc 700°c sample , b (right) xrd curve from psc 300°c sample fig 4a. (left) surface structure sample with 700°c psc, b. (right). surface structure sample without psc result from the sem have indicated the psc temperature has effective covered more pore space in the cement sample. it is clearly shown in fig 4.a and 4.b, where the sample without psc (fig 4.b) has wider void space (darker area) when we compare to the sample with psc (fig 4.a). hence, the presence of the psc material, combined with nanosilica can plug more pore, resulting a more compact structure of cement. 4. conclussion an experimental study has been accomplished to investigate the effect psc heating temperature to the cement strength in the oil-well cementing job, which are described from the cs and sbs value of the cement. the object of the experiment is a cement concrete, which is enriched with the nanocomposite additive. the nanocomposite comprises of nanosilica and psc, a waste material from the palm-oil mill. result from the tri-axial loading test conclude that the more heating temperature of the psc, the higher cs and sbs value will be acquired. an optimum heating temperature, which yield the highest cs and sbs value, is obtained for a sample with 700 o c heating temperature psc. moreover, result from the xrd and sem result confirm that psc has a potential opportunity to be a product with a higher economic value. references al-dahlaki, m.h., 2007. effect of fly ash on the engineering properties of swelling soils. j. eng. dev. 11, 1 11. bae, w.s., 2016. utilization of nanosilicapalm shell nanocomposite to enhance cement strength in well cementing 58 61. dirjenbun, 2015. kelapa sawit. tree crop estate stat. indones. 2014-2016 79pp. ershadi, v., ebadi, t., rabani, a., ershadi, l., soltanian, h., 2011. the effect of nanosilica on cement matrix permeability in oil well to 68 novriansyah, adi et al./ jgeet vol 02 no 01/2017 decrease the pollution of receptive environment. int. j. enviromental sci. dev. 2, 128 132. falode, o.a., salam, k.k., arinkoola, a.o., ajagbe, b.m., 2013. prediction of compressive strength of oil field class g cement slurry using factorial design. j. pet. explor. prod. technol. 3, 297 302. doi:10.1007/s13202013-0071-0 hadiguna, s.c., 2016. laboratory study: effect of temperature on palm oil shell carbon to increase strength drilling cement 2016. haryanti a., norsamsi,sholiha p.s.f., p.n.p., 2014. studi pemanfaatan limbah padat kelapa sawit. konversi 3. institut, a.p., 2002. api 10a/iso 10426-1-2001 effective specification for cements and materials for well cementing 49. novriansyah, a., rita, n., husbani, a., 2015. effect of nanosilica injection to oil recovery factor in low porosity and permeability reservoir 9, 11 13. palmer, c., 1990. edited by. critique 42000. doi:10.1016/b978-0-444-53858-1.00028-4 rubiandini, r., siregar, s., suhascaryo, n., efrial, d., 2005. the effect of cao and mgo as expanding additives to improve cement isolation strength under hpht exposure. itb j. eng. sci. 37, 29 47. doi:10.5614/itbj.eng.sci.2005.37.1.3 siregar, e., n.d. studi laboratorium : pemanfaatan limbah abu sekam padi dan arang cangkang kelapa sawit sebagai light weight additive untuk meningkatkan strength semen pemboran program studi teknik perminyakan , fakultas teknik , universitas islam riau. worathanakul, p., payubnop, w., muangpet, a., 2009. characterization for post-treatment effect of bagasse ash for silica extraction 3, 339 341. 1. introduction 2. material and methods 2.1. material 2.2. experiment procedure 3. results and discussion 4. conclussion cover front jgeet.cdr journal of geoscience, engineering, environment and technology volume 4. no 2. june 2019. p 1 90 issn (print) : 2503-216x issn (online): 2541-5794 uir press p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually our journal has accredited as a scientific journal (s2) by the ministry of research, technology, and higher education no 30./e/kpt/2018 period : 2017 2021 scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. sabah a. ismail (iraq) editorial member dr. kurnia hastuti (indonesia) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. eng. takahiro miyazaki (japan) dr. mursyidah, m.sc. (indonesia) dr. sapari dwi hadian mt (indonesia) dr. emi sukiyah st., mt (indonesia) bambang setiadi ph.d (indonesia) dr. vijaya isnaniawardhani (indonesia) dr. anas puri s.t, m.t (indonesia) mirza muhammad waqar, m.sc (pakistan) good fried panggabean, s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) yuta izumi m.eng (japan) kageaki inoue, m.eng (japan) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) yuta izumi, m.eng (japan) yuniarti yuskar s.t, m.t (indonesia) muhammad zainuddin lubis s.ik m.si (indonesia) pakhrur razi, s.si, m.si (indonesia) babag purbantoro, s.t, m.t (indonesia) budi prayitno s.t, m.t (indonesia) joko widodo, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 04 no 02 2019. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content depositional environmental changes of cimanceuri formation based on mollusk fossil assemblages in bayah, banten province .................................. 66 identification and stratiraphic position of mollusk type locality at west progo stage .................................................................................................... 76 alteration alteration, mineralization and geochemistry of metamorphic rocks hosted hydrothermal gold deposit at rumbia mountains, bombana regency, southeast sulawesi, indonesia ......................................................... 83 an earth science topic tidal ellipses analysis based on flow model hydrodynamic data acquisition in mandeh bay, west sumatera .................... 93 petrogenesis of volcanic arc granites from bayah complex, banten, indonesia ........................................................................................................ 104 assessment of the leachate contamination level of groundwater resource at a dumpsite, in minna, north central, nigeria using resistivity method ......... 116 middle miocene black shale of airbenakat formation in berau areas, jambi: are they potential source rock? ....................................................................... 128 review : bathymetry mapping using underwater acoustic technology .......... 135 case studies : adaptation to the climate change impact through community participation on customary land use ............................................................. 139 1: front cover page 2 author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press p-issn jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet e-issn page 1 page 2 page 3 page 4 page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 3 2022 102 boya, l. et al./ jgeet vol 7 no 3/2022 research article petrography and geochemistry for proposal of geodynamic model for the irbiben granite in tagragra d’akka inlier, (western antiatlas, morocco) boya t. k. lionel-dimitri*1, gnanzou allou 1, kouadio f. jean luc h. 1, adingra martial p. k. 1, goulihi d. david1, m’rabet souad² 1 university felix houphouët-boigny, training and research unit in earth sciences and mineral ressources, laboratory of geology, mineral and energy resources, 22 bp 582 abidjan 22, côte d’ivoire . 2 university ibn tofaïl of kenitra, faculty of sciences, laboratory of geosciences and environment, kenitra, morocco * corresponding author : lionelboya2000@yahoo.fr tel.:+225-07-77-17-27-75; received: aug 16, 2022; accepted: sep 23, 2022. doi: 10.25299/jgeet.2022.7.3.10275 abstract this study aims to contribute to improve the knowledge on the setting of the irbiben granites, located south of the gold deposit of this locality (tagragra d'akka buttonhole, anti-atlas, morocco). the petrographic characterization showed leucocratic porphyry rocks, with a mineralogy dominated by quartz and phenocrysts of plagioclase, alkali feldspars of sometimes centimetric size as well as very small sulphides of metallic luster. two generations of quartz have been identified: a qiquartz with undulating extinction phenocrysts testifying to an episode of deformation orchestrated in this inlier, and a qii quartz with more rounded and limpid minerals indicating an intense silicification. plagioclase and alkali feldspars are deeply altered to sericite and epidote. geochemical characterization classifies these rocks as calc-alkaline series granites, rich in potassium, with a peraluminous character indicating their crustal origin. their arc geochemical signature, ba enrichment, and negative nb, ti, and p anomalies are characteristic of a subduction zone. this subduction could be associated with an episode of convergence between an oceanic lithosphere located in the north and the west african craton in the south, as shown by the proposed geodynamic model. keywords: petro-geochemistry, granite, geodynamic model, irbiben, anti-atlas, morocco 1. introduction located north of the west african craton, morocco shows signs of activity from several geological periods (mortaji, 1989, lama et al., 1993, walsh et al., 2002) manifested by abundant magmatism accompanied by topographic bulges. the anti-atlas, a domain located north of the reguibat ridge, has several inliers including the tagragra d'akka inlier, located in its western part. this precambrian inlier with paleoproterozoic basement and adoudounian cover hosts gold mineralization distributed in several deposits including irbiben (zouhair, 1992, benbrahim, 2005, boya, 2014). some granites in the area have been the subject of petrogeochemical studies (mortaji, 1989) and several subsequent works (zouhair, 1992, benbrahim, 2005). however, some results are still debatable, especially the petrogenesis and the source of the magma. it is with the aim of deepening the knowledge on the irbiben granite that this study is registered. it consists of a petrographic characterization, to be compared with geochemical data, and then leads to a proposal for a model of setting of these rocks 2. geological setting boya's work in 2014 revealed different rock origins in the irbiben deposit, split into three groups: a magmatic origin, a sedimentary origin, and a metamorphic origin (fig.1). the magmatic rocks consist of basic dykes, granites and aplites. the dykes are widespread in the deposit, close to the mineralized structures and further in the southern part of the deposit, where they present a contact with a granite. they are generally oriented n40 to n60. fig. 1. location and geological map of the tagragra d'akka inlier; (mortaji 1989, benbrahim, 2005, modified) the sedimentary rocks are grauwackes while the metamorphic rocks, initially sedimentary, are composed of http://journal.uir.ac.id/index.php/jgeet boya, l. et al./ jgeet vol 7 no 3/2022 103 metagreywackes, metasandstone and sandstone schists alternating at metric scale with metapelites. fig. 2. schistosities, fracturations and folding in irbiben gold deposit (boya, 2014) the deformation in this area is materialized by several structural markers such as schistosities, folds and fractures, previously dated and attributed to the eburnian and panafrican orogenic cycles (pothérat et al., 1991; zouhair, 1992). four families of schistosity have been described in the entire inlier (hassenforder, 1987; marignac, 1990; pothérat et al., 1991; zouhair, 1992), two of which have been identified at irbiben, with a third, less likely, designated "f-fracture". the s1 schistosity is penetrative and parallel everywhere to the s0 stratification that it follows, thus forming a s0s1 factory (fig. 2a). this factory will be affected by folds giving a z-shape observable in the area (fig. 2b). its direction, identical to that of the stratification, may change from n40 to n65, depending on the intensity of the folding. the s2 schistosity is of fracture type, with average directions from n05 to n30, with a subvertical dip towards the west. it corresponds to the s2 schistosity recognized in the inlier (zouhair, 1992). it intersects the s0s1 at a prominent angle (fig. 2a) and combined with the s1, it is responsible for the frit flow of the shales in the deposit (boya, 2014). it is affected by some folding (fig. 2b). it is associated with the major deformation episode d2 dating from the early pan-african (zouhair, 1992). f fracturation appears as a network of fractures, with directions between n140 and n170 as shown in figure 2c (boya, 2014). fracture schistosity is well developed in some basic dykes. its direction corresponds to that of the faults recorded in the area, responsible for the dextral movements in the basic dyke. host and quartz veins are regularly folded in the area, in the form of a z (fig. 2b), testifying to a predominantly dextral ductile deformation. the folds observed in the sandstone shales have axial planes with a direction close to n40 to n60 (ne-sw) and vertical axes (fig. 2d) (boya, 2014). numerous quartz veins, of variable size and type, have also been identified. these are four types of quartz: (i) q1 smoky quartz, set in the stratification, (ii) grey q2 quartz (fig. 3c), which intersects the stratification and some diorite dykes, (iii) grey to smoky grey q3 quartz, which fills in late veinlets within q2 quartz or in the metasedimentary host rock, and finally (iv) the later q4 quartz. the emplacement of the q2 quartz follows a shearing event associated with a complex deformation event. it is associated with gold mineralization. q3 quartz also hosts gold mineralization. q4 quartz is different from the others in that it is lighter in colour and cross-cuts the other preexisting structures. it is not related to the gold mineralization in the entire inlier. 3. methodology thirteen (13) granite samples were collected from the study area, 7 of which were selected for the preparation of 7 thin sections and 6 geochemical analyses on total rock. the thin sections were made in the litholamellage unit of the geology, mineral and energy resources laboratory (grme) of the félix houphouet-boigny university. these slides were microscopically characterized using the optika b-150 microscope, equipped with an image capture device linked to a computer. this characterization allowed the classification of these rocks based on their mineralogy and texture. the geochemical analyses (major elements, loss on ignition and trace elements) were carried out by mass spectrometry coupled to an inductive plasma (icp-ms) at the reminex research center of guemassa in marrakech. this instrumental technique based on the separation, identification and quantification of the constituent elements of a sample according to their mass is based on the coupling of a plasma torch generating ions and a mass spectrometer that separates these ions in mass. the analytical data were processed using the gcdkit software for plotting and the results allowed the geochemical characterisation of these rocks through their classification, the mobility of their elements as well as their geodynamic context of setting. table 1. proportions (% wt) of oxides in samples samples si02 tio2 al3o2 fe2o3 feo mno mgo cao na2o k2o p2o5 pf gran 1 75,16 0,17 13,58 0,23 2,07 0,01 0,47 1,27 1,6 4,13 0,04 1,34 gran 3 74,13 0,18 14,09 0,22 1,96 0,01 0,43 1,46 1,67 4,62 0,03 1,3 gran 6 78,83 0,03 13,22 0,07 0,65 0,01 0,13 1,11 2,03 3,71 0,05 0,8 gran 7 74,6 0,19 14,04 0,22 1,97 0,01 0,33 1,31 0,030 4,53 0,04 1,1 gran 12 76,39 0,03 14,15 0,07 0,59 0,01 0,18 1,77 1,49 3,91 0,04 1,4 gran 13 75,23 0,25 13,54 0,14 1,24 0,02 0,44 1,84 2,04 4,15 0,03 1,66 104 boya, l. et al./ jgeet vol 7 no 3/2022 table 2. proportions (ppm) of trace elements in samples 4. results 4.1. petrographic data in order to highlight the different minerals in samples, this section presents a synthesis of observations. it is composed of microscopic description of two representative samples and of a mineralogical synthesis from all samples observations. 4.1.1 sample gran 3 massive leucocratic rock with a porphyroid grainy texture, this sample is composed of medium-sized quartz, plagioclase and centimetric automorphic alkali feldspar phenocrysts, metallic luster sulphides and millimetre-sized chlorites (fig. 3a). alteration of the alkali feldspars and plagioclases gives the rock a pinkish colour. the glittering of the small sulphide crystals disseminated between the quartz and feldspar grains gives it a more or less brilliant luster. under the microscope, its mineralogy is dominated by clear minerals such as quartz, plagioclase and alkali feldspars, which make it colourless in natural light. it also contains alteration minerals (sericite, chlorite and epidote) and automorphic opaque minerals (sulphides and oxides). fig. 3. macroscopic and microscopic views of sample gran 3 quartz is variable in size, xenomorphic with a light grey polarisation hue. they are the most abundant in the rock. some are coarse and less clear. however, others often appear as small clear crystals in the other minerals and sometimes form clusters in the interstices. there are thus two generations of quartz (fig. 3b): coarse qi quartz and qii quartz, generally resulting from recrystallisation, with smaller crystals. plagioclases, in the form of phenocrysts or sometimes medium-sized crystals, are abundant and deeply altered into sericite and epidote, making their macles difficult to observe. sericite, an alteration mineral progressively replacing plagioclase and alkali feldspar, is abundant. colourless in natural light, it has an orangeyellow polarisation (fig. 3d and 3e). it is generally associated with epidotes, which are bright blue to purplish blue polarization (fig. 3b). this assemblage sometimes moulds the quartz crystals and occupies almost all the spaces left between the primary minerals. some chlorites are observed in these rocks. they are subautomorphic, pleochroic with a greenish polarisation showing oxides in their cleavage plane. these come from the alteration of biotites. the rare microcline crystals occur as a coarse beach with numerous inclusions of quartz, plagioclase and orthoses giving it a perthitic appearance (fig. 3e). opaque minerals probably representing oxides or sulphides are automorphic (fig. 3c) and often cluster in places. 4.1.2 sample gran 13 if symbols are defined in a nomenclature section, symbols and units should be listed fig. 4. macroscopic and microscopic views of sample gran 13 altered granitoid, leucocrate and porphyroid grainy texture, its mineralogy is dominated by coarse grains of quartz, plagioclase and orthose of variable sizes from millimeter to centimeter. hydrothermalism is very advanced (fig. 4a). microscopically, the quartz is coarse and xenomorphic. a parcularity is observed in the arrangement of these quartz, it is the "triple point" (fig. 4c). this arrangement testifies to the presence of stresses probably generated during the different orogenic cycles that affected the precambrian rocks of the tagragra d’akka inlier. plagioclases are also abundant and occur as automorphic phenocrysts, often with a dirty appearance. this reflects a very advanced sericitisation, materialised by the formation of sericite and an obliteration of the polysynthetic macles of the altered plagioclases (fig. 4b and 4d). the sericite often forms a brightly coloured samples as pb sb se sn sr w y zn rb zr ba be bi cd co cr cu ge li mo nb ni gran 1 44 87 32 40 39 3 23 3 18 426 0,2 20 5 7 56 189 10 15 8 8 17 gran 3 8 66 32 40 45 43 23 4 12 218,79 76,94 464 0,2 20 4 22 43 80 10 15 8 8 17 gran 6 17 74 32 40 20 26 23 3 11 125 0,2 20 4 14 50 66 10 15 8 8 17 gran 7 21 64 32 40 20 59 23 3 4 119 88,49 563 0,2 20 4 7 56 87 10 15 8 8 17 gran 12 18 64 32 40 37 78 23 3 22 147,63 18,13 252 0,2 20 4 22 49 87 10 15 8 8 17 gran 13 8 53 32 40 35 86 23 4 13 165,77 166,41 817 0,2 20 4 9 55 79 10 15 8 9 17 boya, l. et al./ jgeet vol 7 no 3/2022 105 assemblage with the epidotes. in addition to plagioclases, some sericites progressively replace the weathering alkali feldspars (fig. 4b). some subautomorphic, pleochroic, green to greenish-brown polarising minerals have oxides in their cleavage plane. these are chlorites resulting from the alteration of biotites. the opaque minerals are automorphic and can be assimilated to sulphides and oxides. 4.2 mineralogical synthesis tables 3 and 4 below summarize the main microscopic observations. the irbiben granite is porphyroid, generally with qi quartz, plagioclase and orthose phenocrysts, qii quartz of which constitute the primary minerals. biotite and/or muscovite are sometimes added to these. some perthites have been observed. the alteration minerals are generally composed of sericite, generally associated with epidote, and then chlorite. they are respectively derived from the alteration of plagioclase and alkali feldspars and biotite. table 3 summarizes the petrographic description while table 4 presents the mineralogical proportions per sample. table 3 : summary description of irbiben granite samples samples aspect colour texture origin mineralogy metallography gran 3 massive leucocrate porphyroid grainy plutonic qi and qii quartz, plagioclases, microcline, orthose, sericite, chlorite, epidote automorphic sulphides gran 5 massive leucocrate porphyroid grainy plutonic qi and qii quartz, plagioclases and alkali feldspars, sericite, epidote, muscovite, biotite automorphic sulphides gran 7 massive, low altered leucocrate grenue porphyroïde plutonic qi and qii quartz, plagioclases, microcline, sericite, epidote, orthose phenocrists, perthite automorphic sulphides gran 8 massive, low altered leucocrate grenue porphyroïde plutonic plagioclases, qi and qii quartz, sericite, epidote, biotite, chlorite, orthose phenocrists, perthite automorphic sulphides gran 9 massive leucocrate porphyroid grainy plutonic qi and qii quartz, plagioclases, orthose, sericite, biotite, perthite automorphic sulphides gran 12 massive leucocrate porphyry micrograiny periplutonic qi and qii quartz, orthose, plagioclases, sericite, epidote no sulphide gran 13 massive, altered leucocrate grenue porphyroïde plutonic qi and qii quartz, plagioclase, orthose, séricite, epidote no sulphide table 4 : mineralogical proportions of irbiben granite samples minerals gran 3 gran 5 gran 7 gran 8 gran 9 gran 12 gran 13 qi quartz + + + + + + + + + + + + + + + + + + + + + + qii quartz + + + + + + + + + + + + + + + + + + + + + + + + + + plagioclase + + + + + + + + + + + + + + + + + + + + + + orthose + + + + + + + + + + + + + microcline + + séricite + + + + + + + + + + + + + + + + + + + epidote + + + + + + + + + + + + chlorite + + muscovite + + biotite + + + + perthite + + + sulphide/oxide + + + + + + + 4.2. geochemical data 4.2.1 general features the six granite samples studied show almost identical characteristics: high sio2 content between 74.13 and 78.83 %, high al2o3 contents from 13.22 to 14.15 %, with an average content of 13.77 % and an al2o3/(cao+na2o+k2o) molecular ratio higher than 1.13. the sum of the alkalis na2o+k2o generally varies between 4.56 and 6.29% ; the ratio (na2o+k2o)/cao can reach 4.51. k2o is the more important alkali. the sum of tio2+feot+mno+mgo is between 0.81 and 2.72. this indicates a very low proportion of coloured minerals, such as observed in thin sections. 4.2.2 nomenclature and classification the middlemost (1994) and qapf streickeisen (1974) diagrams reveal that the samples are granites (fig. 5), with relative high silica contents, especially that of sample gran 7, falling in the lower part of high content quartz granitoids. + + + + very high + + + high + + medium + rare 106 boya, l. et al./ jgeet vol 7 no 3/2022 fig. 5. nomenclature of irbiben granite using middlemost diagram (1994) fig.6. nomenclature of irbiben granite using streickeisen diagram (1974) fig. 7. diagram of k2o vs sio2 4.2.3 evolution of the chemical composition during differentiation the oxide k2o shows a very clear negative correlation with sio2 (fig.7), linked to some alkaline mobility during the alteration processes. indeed, lithophilic elements with high atomic radius (l.i.l.e) such as ba, rb and k are very mobile elements during weathering (ngom, 1995). the basr diagram (fig. 8) shows an increase in strontium (sr) accompanied by an increase in barium (ba). this positive correlation would be linked to the fixation of these elements in the structure of plagioclase and biotite (hanson, 1978, n'dri, 2014), minerals concentrated in the melt residue. according to rickwood's k2o=f(sio2) diagram (1989), these rocks are derived from highly potassic calc-alkaline magmatic series (fig.9). fig. 8. diagram of ba vs sr fig. 9. irbiben granite in rickwood diagram (1989) 4.2.4 spider diagrams the trace element compositions of the different granite samples studied are plotted in the thompson (1982) chondrite-normalized diagram (fig.10). positive anomalies in ba and k indicate an enrichment in these elements while negative anomalies in p, sr and ti indicate a depletion in these elements. fig. 10. chondrite-normalized trace elements diagram (thompson, 1982) boya, l. et al./ jgeet vol 7 no 3/2022 107 4.2.5 geotectonic context plottind of the geochemical data into the granite discrimination diagram of pearce et al. (1984) reveals that the irbiben granites are volcanic arc granites (vag) (fig. 11). this indicates a subduction mode of emplacement for these granites. plotting of the data of the studied rocks in the maniar and piccoli alumina saturation diagram (a/cnka/nk) for igneous rocks (1989) reveals that the irbiben granitoids are peraluminous (fig.12), with a ratio al2o3/cao+na2o+k2o higher than 1.1. this peraluminous character would thus prove a crustal origin of the granites. . fig. 11. irbiben samples granite in discrimination diagram of pearce et al. (1984) fig. 12. irbiben samples granite in maniar and piccoli (a/cnka/nk) diagram (1989) 5. discussion 5.1. petrography, geochemistry and nomenclature petrographic results show coarse-grained granites in south of the irbiben god deposit. their mineralogy consists of a large proportion of quartz of variable size, plagioclase and orthoses phenocrysts. these results corroborate those of mortaji (1989) who identified in the northern part of the buttonhole leucogranites, either equigranular or porphyroid. furthermore, the diagrams of streickeisen (1974) and middlemost (1994) confirmed the petrographic description : all the samples appear in the field of granites. the microscopic study revealed two generations of quartz, the first of which is composed of phenocrysts that are sometimes isolated and the second of small quartz (microcrystalline), very clear and grouped in clusters. these different generations of quartz had already been mentioned by hassenforder (1987), marignac (1990), pothérat and ait kassi, (1991) in areas of the western antiatlas of morocco. zouhair (1992) agrees with them with his work revealing that three structural phases are recorded in the akka inlier, with a quartzogenesis marked by four generations of quartz (qi, qii, qiii and qiv), of which two could be described at irbiben. benbrahim and aissa (2005) and boya (2014) have shown the link between gold mineralisation and 2 generations of quartz, qii and qiii, with qii quartz well expressed in the irbiben deposit. the plagioclases in high proportion as phenocrysts are partially altered to sericite. the irbiben granite has thus been subject to hydrothermal alteration, even if moderate. this has also been described in the host rocks of the gold mineralisation in the ore deposit by boya (2014). this hydrothermal activity led to the formation of secondary minerals such as epidote, sericite, chlorite or neoformed quartz. the poverty of ferromagnesian minerals (fe2o3+mgo < 1.5) and the low y contents (≤ 3ppm) mark the highly fractionated character of these rocks, indicating that it is a highly fractionated rock as underlined by kouamelan (1996) on the vavoua granites in ivory coast. 5.2. petrogenesis and geotectonic the granites studied are derived from potassium-rich calc-alkaline magmatism. the potassic character of these rocks proves that they are differentiated, as indicated by tagini (1971) for whom an evolved rock is rich in potassium. furthermore, gamsonre (1975) studying the granitoids of ouahigouya (upper volta), attributes this abundance of potassium to the destruction of ferromagnesian minerals, specifically biotite. for this author, the various granitisation processes lead to a progressive destruction of the biotite which then leads to a progressive release of potassium. this potassium accumulates in the rocks as they evolve or differentiate. this could explain the lack of biotite in these rocks. the results of this work show that the irbiben granites are peraluminous, and therefore of crustal affinity, as shown by debon and lefort (1983). indeed, the positive ba anomaly of these rocks cannot be justified only by magmatic differentiation; it would also prove a crustal origin. according to yobou (1993), high contents of certain elements such as rb, ba and sr rather suggest crustal contamination. from a geotectonic point of view, these rocks mainly show an arc geochemical signature (vag: volcanic arc granite), which implies their formation in a subduction context. however, many studies on arc magmatism (marquer et al., 2000; morris et al., 2000, n'dri, 2014) show that these characters are not automatically linked to contemporary subduction but can be inherited. from this point of view, it is possible to suggest that the irbiben granite was emplaced during the eburnian cycle, but inherited arc features from earlier magmatism. the existence of a volcanic arc is still questionable due to the total absence of volcaniclastic formations in the irbiben area, which would imply a back-arc context. however, felsic metatufs have been dated at 2072 ± 8ma by walsh et al. (2002) in the tagragra of tata inlier, an inlier close to the tagragra d’akka. this lack of volcanism may be explained by a weak low-temperature subduction event, resulting in the partial melting of silicate sediments, leading to the formation of granitic magma. this viscous magma, due to the great thickness of the continental crust, could not rise to the surface. furthermore, the silico-clastic nature of the paleoproterozoic sedimentary series in which these granites were emplaced confirms the presence of a continental domain of pre-eburnean age. 108 boya, l. et al./ jgeet vol 7 no 3/2022 5.3. geodynamic model the sedimentary products resulting from the disintegration of antebirimic micro-cratons produce sediments materialized by a succession of sandstones and pelites. the basement is then affected by the first phase of tectonic-metamorphic deformation d1 (fig.13). the d1 deformation is marked in the basement by the s1 schistosity and the formation of the qi exudation quartz, followed by folds. the s1 schistosity is related to regional greenschist metamorphism. the folds are linked to a compressive episode which is the origin of the relief of the buttonhole but also of the modeling of the pi formations. the d1 deformation preceded magmatism, which saw the formation of the granites from which the enclosing basement formations were dated. an episode of convergence occurred between an oceanic lithosphere to the north and a continental lithosphere to the south, which would be the west african craton. the density of the ocean floor, combined with a large volume of sediment from the continents, caused subduction. more low-temperature silicates were therefore carried to depth during this subduction. the partial melting thus initiated affects the low-temperature minerals in the sediments by producing felsic magmas. according to cocherie (1978), for high a/cnk ratios (1.21 to 1.91 in our case), the molten material would probably be of sedimentary origin. thus, in the thick continental crust, large stocks of granites have accumulated which may correspond to low temperature melts and which, because of their low fluidity, could not reach the surface. the irbiben granites in the akka inlier are suspected to be derived from this felsic magma. figure 13 shows the proposed geodynamic model for the setting of the irbiben granite. fig. 13. geodynamic model proposed for the setting of the irbiben granite. 6. conclusion the petrogenetic study of the irbiben granite has shown that it is porphyroid, with phenocrysts of primary felsic minerals, often with biotite and/or muscovite added. subject to hydrothermal alteration, a secondary mineralogy has been highlighted and consists of sericite, the most pronounced alteration mineral, epidote often associated with sericite and then chlorite. the presence of two generations of quartz, in particular a recrystallisation quartz qii, is associated with the metamorphism affecting the zone. the processing of geochemical data shows that this granite, which comes from a calc-alkaline series rich in potassium, is an evolved rock. its peraluminous character suggests a crustal origin. combined with its volcanic arc signature, this rock is expected to have originated from a subduction zone or to have inherited arc characteristics from magmatism that preceded it. in order to give our readers a sense of continuity, we encourage you to identify acknowledgements the samples were collected from the irbiben deposit, previously exploited by akka gold mining, a subsidiary of the managem mining group, which also funded for the boya, l. et al./ jgeet vol 7 no 3/2022 109 geochemical analyses. we would like to thank the managers of this company. references benbrahim, m. and aissa, m. 2005. the iourirn gold deposit (tagragra d'akka buttonhole, western anti-atlas, morocco): an example of mesothermal mineralisation in paleoproterozoic formations. bulletin de l'institut scientifique, rabat, section sciences de la terre, 2005, 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d'ivoire (ferkéssédougoumarabadiassa). magmatic evolution and geodynamic context. thesis unique in science n°: 2781, université de paris-sud centre d'orsay. 309 p. zouhair, m. 1992. les paléocirculations fluides dans la tagragra d'akka (anti-atlas, maroc). etude combinée des inclusions fluides et de la déformation des quartz aurifères: conséquence pour la métallogénie de l'or, phd thesis, inpl. 384 p.. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 122 susilo & prayitno, b./ jgeet vol 03 no 02/2018 geology of tanjung medan ,rokan iv koto , rokan hulu district, riau province susilo 1 , budi prayitno 1, * 1 department of geological engineering, universitas islam riau, jl. kaharuddin nasution no. 113 pekanbaru, 28284, indonesia. * corresponding author: budiprayitno@eng.uir.ac.id tel.:; 0852-2550-1217 received: 21 may, 2018. revised: 29 may, 2018, accepted: 30 may, 2018, published: 1 june 2016 doi: 10.24273/jgeet.2018.3.2.1597 abstract the administrative of research area has been in tanjung medan, rokan iv koto, rokan hulu, riau province and geographically located at 0 ° 37 '28.488 "0 ° 40' 10.3692" lu and 100 ° 24 '55.6884 "100 ° 27 '37.5804 "bt. research method used approach method and laboratory analysis to get data of geology modeling and re-construction of geological history in research area. based on surface observation, the geology of research area consists of slate (permian-carbon), granite intrusion (permian-trias) with distribution southwest-southeast on the center of map. arenite sandstone unit (easly eocene) unconformity with slate on the bottom. alluvial rokan river crosses all type off rocks from north to south of map. while structure growth in the research area have been joints structure with main stress southwest-northeast, its similar with trend tectonic setting of sumatra island, on the other hand reverse fault indicates the formation of a basin of extension stress in the early eocene. the formation of basins in basement rocks begun at the time of the formation of the north-south trending northern form of the fault block forming horst and graben as well as accommodated the precipitation of pre-tertiary clastic materials. whereas the oligocene trans-tensional compression system accommodating the sedimentation system in the formed of arenite sandstone (sbpa) unconformity above the basement rocks simultaneously on the basin base decrease. the distribution of arenite sandstones based on the geological reconstruction covering all parts of the rock distribution which then undergoes the same weathering process of the formation of bukit barisan volcanic path that controls the development of geological structure up to the present. keywords: rokan hulu, intrusion, granite, arenite sandstone. 1. introduction the central sumatra basin has a back-arc basin type that extends along the edge of sunda exposure in south east asia (heidrick and aulia, 1993). the basin was formed by subduction of the indian ocean plate moving relative to the north subduct to the asian continent plate that produced the bukit barisan mountain path and bordering directly on the edge of the central sumatra basin (clarke et al.,1983). regionally the research area has built on the bedrock of greywacke, quartzite, granite and argillite of paleozoic aged kuantan formation. the clastika formation sihapas was formed by early miocene above on the field of erosional / disconformity to kuantan formation and rokan granite intrusion. this research is interesting to describe the history of geology and at the same time data re-registration that can be used as new data in the local area. the research method for mapping and field survey was conducted using the regional geological map sheet of lubuk sikaping as the geological approach and the base map of the scale of 1: 12.500 cm to produce more detailed information about the geological aspects in the research area. administratively, the research area is located in tanjung medan village, rokan iv koto sub-district, rokan hulu district, riau province. geographically the study area is located at the coordinates of 0 ° 37 '28.488 "0 ° 40' 10.3692" north latitude and 100 ° 24 '55.6884 "100 ° 27' 37.5804" east longitude, covered by bakosurtanal map rokan sheet, bakosurtanal 0716 code -62. fig. 1. map of administration of research area 2. geology and regional stratigraphy the regional stratigraphy of the central sumatra basin is composed of several units of mailto:budiprayitno@eng.uir.ac.id susilo & prayitno, b./ jgeet vol 03 no 02/2018 123 formation and rock groups, respectively from the old to the young, the basement, the pematang group, the sihapas group, the farmers formation and the minas formation. 1. base rock (basement). the tertiary pre-existing basement serves as the cornerstone of the central sumatra basin. eubank and makki (1981) and heidrick and aulia (1993) mentioned that the central sumatra basin rocks consist of mesozoicaged rocks and paleozoic-mesozoic metamorphic carbonate rocks. unconformity over the bedrock precipitated succession of tertiary sedimentary rocks. tertiary stratigraphy in the central sumatran basin from the oldest to the youngest was the pematang group, the sihapas group (menggala formation, bangko, bekasap and duri), telisa formation, farmers formation and terminated by minas formation. 2. group of pematang (pematang group). pematang group is the oldest sedimentary layer of eocene-oligocene deposited in an unconformity over the bedrock. the group pematang sediments have been referred to as the syn rift deposits. this group has been deposited in fluvial and lake environments with sediments derived from the surrounding height. in its lithologic fluvial environment it consists of a conglomerate, coarse sandstone, and multicolored claystone. while the lithologic lake environment consists of claystone and fine sandstone with lake flakes rich in organic material eubank and makki (1981) and heidrick and aulia (1993). 3. sihapas group (sihapas group). the sihapas group has been deposited above the group of pematang, a series of sediments as tectonic activity begins to decrease, occurring during the late oligocene to the middle miocene. the localized compression has characterized by the formation of faults and folds at the inversion stage that occurs regression in global sea level. the geological process occurring at the time was the formation of an almost flat morphology (peneplain) that occurred in the group of pematang and the exposed basement. this period is followed by subsidence any longer and transgression into the basin. the sihapas group consists of menggala formation, bangko formation, bekassap formation, duri formation and telisa formation. 2.1 regional structure the central sumatra basin has two main structural directions; the older ones trend tended to the north (nne ssw) and the northwest trending (nnw sse). block-fracture systems, especially north-north-trending, form a series of horst and graben, which controlled the sedimentation pattern of lower tertiary sediments, especially paleogene rocks (heidrick and aulia, 1993). fig. 2. regional stratigraphy of central sumatera basin (modified from heidrick and aulia, 1993). the northward-oriented structure associated with the pre-tertiary orientation found in peninsular malaysia was a structure that influences the direction of precipitation of paleogenic rocks. the northwest-trending structure, which is younger than the tertiary structure, controls the current structure. both affect tertiary sediment deposition, tertiary structure growth and subsequent fault section. the structures currently existing in the central sumatra and south sumatra basin are the result of three main tectonic phases, namely central mesozoic orogenesis, tectonic cretaceous-early tertiary and pliopleistocene orogenesis. heidrick and aulia (1993) divide the tertiary tectonic order in the central sumatra basin in three tectonic episodes (fig. 3), fig. 3. tectonic evolution of the central sumatera basin (heidrick and aulia, 1993). 124 susilo & prayitno, b./ jgeet vol 03 no 02/2018 1. f1 (50-26) ma. the tectonic phase of f1 takes place at the time of eo-oligocene (50-26) ma. as a result of the collision of the indies plate to southeast asia at about 45 ma formed a transtensional fracture system extending southward from southern china to thailand and to malaysia to sumatra and south kalimantan (heidrick and aulia, 1993; yarmanto and aulia, 1988). this formation led to the formation of a series of half graben in the central sumatra basin. half graben is then a lake where sediment of pematang formation made. at the end of phase f1 there is a shift from a fraction to a basin decline marked by weak structural reversals, denudation and the formation of a plain plate. the result of the erosion is paleosoil deposited on upper red bed formation. 2. f2 (26-13) ma. the tectonic phase of f2 (26-13) ma takes place in the early miocene middle miocene. at the beginning of this episode or the end of the f1 phase there was dextral fault with north-south direction. in this phase the central sumatra basin has been transgression and sediments from the sihapas group are deposited. 3. f3 (13 now).. the tectonic phase of f3 (13present) occurs at the miocene end until now, also called the compression phase. f3 tectonic symptoms along with the expansion of the andaman sea ocean floor, regional appointment, volcanic mountain formation. at this phase formed regional unconformity and precipitated petani and minas formations have been unconformity above the sihapas group. 3. research methods the methods used in the study are divided into two methods. the first method has been using research literature to get a regional description of the formation basins was formed and field survey to determine the geological conditions in the study area (hindartan, 1994; rock et al, 1983) . the second method has laboratory analysis to determine the micro-optical type including type of rock and reconstruction of geological history that has occurred in the research area. the detailed stratigraphic measurements including qualitativequantitative data in the form of lithologic observations, textures, primary-secondary sedimentary structures, biogenic sedimentary structures, mineral rock compositions (pettijohn, 1975; dunham, 1962; streickesen, 1976), the thickness of each layer and the general layers of rock layers (kausarian et al., 2018). measurement structures include taking primary and secondary data in the form of indications that shown structural processes that occur such as joint, fold, and fault (choanji, 2016; prayitno, b, 2016; prayitno b., 2017; yuskar et al, 2017). 4. results and discussions based on the results of research, rock units found in the research area of the old-young in succession can be divided into three units of rock, namely slate, granite, arenite sandstone and alluvial. fig. 4. geological map of research areas fig. 5. slate outcrop from pawan member 1. slate. slate spreads range 25% residing section southwest along the map with southeastnorthwest straightness from the research area. microscopic slate description is dark brownish gray color and fresh gray color, nematoblastic foliation, lepidoblastic, with mineral size: 0.05 mm 0.3 mm, composed of top mineral quartz (45%), muscovite (35%), chlorite (10%), biotite (5%), opak mineral (o'dunn and sill, 1986). slate in the research area is a basement rock with terrestrial environment. slate on the research area has been member of pawan kuantan formation, was made in paleozoic era. eubank & makki (1981), heidrick dan aulia (1993) mentioned basement of central sumatra basin consist of paleozoic mesozoic rocks. the characteristic of slate in research area shown strong deformation with had mylonite zone, at several observation points susilo & prayitno, b./ jgeet vol 03 no 02/2018 125 associated with the tectonic motion for approximately 45 ma last. here is the distribution of batusabak in the research area. 2. granite. the spread of granite in the research area ranges from 45% in the southeast to the northwest. this granite unit consists of granite lithology that has; blackish brownish color, fresh white to brass color, holocrystalline, inequigranular texture. the composition of mineral composition of minerals plagioklas (10%), quartz (45%), k-feldspar (30%), biotite (10%), and opak mineral (5%). the subhegralanhedral (iugs, after steickeisen 1979) classification, in regional compatibility the presence of granite units is a breakthrough rock (intrusion). granite intrusion in the study area has been indicated as the backbone of sumatra island which is now a range of bukit barisan on plio-plistosen. the presence of muscovite minerals in some parts of the study sites showed symptoms of pressure from over pressure at 260 ° c at stress minerals likes kfeldspar. this condition is shown there has pegmatite type of intrusion process form tiation late level. here is a location observation of granite intrusion and muscovite minerals in granite in the study area. (figs. 6 and 7). fig. 6. granite outcrop and limits pegmatite zone fig. 7. muscovite sample from thermal intrusion action on late pegmatite type 3. arenite sandstone units. distribution of arenite sandstone units in the research area ranges 20% which is adjacent northeast and 10% in southwest region research area. this arenite sandstone unit consists of arenite sandstone lithology, siltstone and granite. microscopically arenite sandstones have dull gray-gray color and gray-gray color, grains of 0.05-1.5 mm, roundabout corners, open packs, massive sedimentary structures, medium sorting, good permeability, non-carbonate, compactness rather loud, and erosional contact. the composite mineral composition is quartz (70%), alkali feldspar (10%), lithic (5%), and opaque mineral (5%). so the name of this sandstone is arenite (pettijohn, 1972). this unit is deposited unconformity above the granite intrusion with the fluvial ground environment. here is arenite sandstone units in the research area.( fig. 8) 1. 2. 3. 4. 5. 6. 7. 8. 9. fig. 8. arenite sandstone from sihapas formation 4. alluvial. in the research area the spread of alluvial units approximately 10% located next to the northwest and the southwest along the rokan river, consisting of sand lithology, pebbles, cracks to boulder. distribution alluvial area in the southwest and the northwest of map and shown main river of rokan consist of loose material in the form of sand, gravel, pebble to cobble and mud. here are alluvial deposits around rokan river floodplains. (fig. 9). fig. 9. alluvial deposition of rokan hulu river 4.1 geological structure the development of geological structure in the research area are joints structure and reverse fault. based on surface observation research area has main stress southwest northeast which that influenced in the development of the basin. while reverse fault, north-east trending also followed the development of geological structures in the research area. the following is the result of structural analysis and offset of lithology in the study area. the following is the result of structural 126 susilo & prayitno, b./ jgeet vol 03 no 02/2018 analysis and offset of lithology in the study area. (figs. 10 and 11) fig. 10. development of main stress structure which trending southwest fig. 11. fold related fault structure indication on field. 5. conclusion based on surface observation research area consists of some rocks, such as slate intrusion by granit on plioplistosen, and unconformity with arenit sandstone unit on the top at early eocene and alluvial consist of loose material in the form of sand, gravel, kerakal to bongkah and mud. structure grown in the research area consist of joints structure and reverse fault. acknowledgment the biggest thanks to all colleagues during the data collection and the parties involved in this research and the universitas islam riau who permitted field observation, and hopefully this journal can be useful as it should. references choanji, t., nugraha, i., sofwan, m., & yuskar, y., 2018. landslide hazard map using aster gdem 30m and gis intersect method in tanjung alai, xiii koto kampar sub-district, riau, indonesia. paper presented at the proceedings of the second international conference on the future of asean (icofa) 2017 volume 2, singapore. dunham, r.j. 1962. spectral subdivision of limestone type. w.e ham (ed), classification of carbonate rocks, am.assoc.pet.mem,1,hlm 62 84. eubank and makki, 1981, structural geology of the central sumatra back-arc basin, jakarta : indonesian petroleum association. heidrick, t.l., aulia, k., 1993. a structural and tectonic model of the coastal plain blovk, central sumatera basin, indonesia. indonesian petroleum association, proceeding 22 annual convection, jakarta, vol. 1,p. 285-316. hindartan and handayana, a., 1994. pemetaan geomorfologi sistematis untuk studi geologi, pit iagi ke 23. kausarian, h., choanji, t., karya, d., kadir, e.a., suryadi, a., 2018. geological mapping of silica sand distribution on the muda island and ketam island, estuary of kampar river, indonesia proceedings of the second international conference on the future of asean (icofa) 2017 volume 2, singapore, pp. 973 982. n.m.s. rock, d.t. aldiss, j.a. aspden, m.c.g. clarke, a. djunuddin, w. kartawa, miswar, s.j. thompson, r. whandoyo., 1983. peta geologi pekanbaru, pettijohn, f.j. 1975. sedimentary rock. marker and bow publisher. third edition. prayitno, b., 2016. limnic condition in rheotrhopic peat type as the origin of petai coal , central sumatra basin , indonesia. journal of geoscience, engineering, environment, and technology, 1, 63-69. prayitno, b., & ningrum, n. s., 2017. development of funginite on muaraenim and lower members of telisa formations at central sumatra basin indonesia. journal of geoscience, engineering, environment, and technology 2(2), 149-145. streckeisen, a. 1976. to each plutonic rock its proper name. earth sci. rev.,12. hlm:1-34. van zuidam, r.a., 1985, aerial photo interpretation in terrain analysis and geomorphologic mapping, the hague: smits. yarmanto dan aulia, k., 1988, the seismic expression of wrench tectonic in the central sumatra basin : iagi seventeenth annual convention, jakarta, p.35. yuskar, y., putra, d. b. e., suryadi, a., choanji, t., & cahyaningsih, c., 2017. structural geology analysis in a disaster-prone of slope failure, merangin village, kuok district, kampar regency, riau province. journal of geoscience, susilo & prayitno, b./ jgeet vol 03 no 02/2018 127 engineering, environment, and technology, 2, 249-254. zakaria, z., 2005, sesar cimandiri bagian timur dan implikasinya terhadap longsoran di citatah, padalarang, jawa barat, majalah geologi indonesia, vol. 20, no. 1,april 2005,hal 41-50. 1. introduction 2. geology and regional stratigraphy 2.1 regional structure 3. research methods 4. results and discussions 4.1 geological structure 5. conclusion acknowledgment references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 217 research article volcanism in the pre-semilir formation at giriloyo region; allegedly as source of kebo-butak formation in the western southern mountains sri mulyaningsih 1 , muchlis 1 , nur w. a. a.t. heriyadi 1 , desi kiswiranti 1 1 geological engineering of ftm-ist akprind yogyakarta,jl. kalisahak no. 28 yogyakarta, indonesia * corresponding author : sri_m@akprind.ac.id tel.:+62-274-563-027; fax: +62-274-563-847 received: oct 25, 2018. accepted: july 25, 2018 doi: 10.25299/jgeet.2019.4.3.2262 abstract kebo-butak formation was known to be the oldest volcanic rocks limited in regional terms in the lower baturagung hills, gedangsari area, gunungkidul regency. the main constituents of the kebo-butak formation consist of intersection of volcanic-clastic rocks and calcareous sediments, locally also found basalt lava with pillow structures; which distinguished it from other volcanic rock formations in the southern mountains. this study aims to determine the relationship of volcanic rocks exposed in giriloyo with the kebo-butak formation in the baturagung hills; the chronostratigraphy and the history of volcanic activities that produced the volcanic rocks of giriloyo. this research was approached by volcanic geological mapping using surface mapping suported by gravity anayses. from the bottom to the top of the frontier areas result volcaniclastic rocks consisting of black tuffs with several fragments of volcanic bombs with basalt composition intersecting with thin basaltic lava inserted by calcareous claystone having an age of n5-7 (early miocene); pyroxene-rich basalt volcanic sequence consists of thick layers of tuff with creamy-brown color intersecting with lava and breccia inserted by calcareous sandstone aged n7-8; dikes, lava and agglomerates with basaltic composition and lava and agglomerates with andesitic composition. stratigraphically, the volcanic rocks exposed at giriloyo correlated with the volcanic rocks exposed at karangtalun (wukirsari) were under the semilir formation, bordered with normal fault n210 o e/77 o , the hanging wall composed by light grey tuff of semilir formation. gravity analyses found high anomalies below the semilir formation exposed at karangtalunmunthuk (east of study area) continued to below the giriloyo area. the high anomalies were identified as the igneous/ignimbrite volcanic sequence. descriptively and stratigraphically, the giriloyo volcanic sequence are a part of kebobutak formation. the petrogenesis of the volcanic rocks will be discussed in further research to interpret magmatological properties, the evolving paleo-volcano, and the absolute age of the rocks. keywords: volcanic rock, kebo-butak formation, black tuffs, basaltic lava, agglomerate, and stratigraphy 1. introduction giriloyo is part of sudimoro range, which is administratively located in wukirsari village, imogiri district, bantul regency, yogyakarta special region, at 7 o -7 o o -110 o fig. 1). earthquake, took place on 27 may 2006, has exposed volcanic rocks beneath the nglanggeran and semilir formations on the surface, consisting of layers of black tuffs, breccias and basaltic lavas, agglomerates and basalt dikes in the wide areas of imogiri district (mulyaningsih et al., 2009), one of them was pucungdengkeng area (mulyaningsih & sanyoto, 2012) and giriloyo-wukirsari 2km south of dengkeng (mulyaningsih et al., 2018). descriptively, volcanic rocks that exposed at giriloyo have similarities with the members of the kebo-butak formation exposed at gedangsari (gunungkidul regency), and stratigraphically, those rocks were beneath the semilir formation. landscape of giriloyo as a part of sudimoro range saw circular feature facing to the west. regionally, lithology composed sudimoro range were semilir formation and locally of nglanggeran formation, such as wonolelo and dengkeng (bronto et al., 2009; mulyaningsih & sanyoto, 2012). rahardjo et al. (1995) and surono et al. (1992) determine the southern mountain stratigraphy; from the bottom to the top are kebo-butak formation, semilir formation, nglanggeran formation, sambipitu formation, oyo formation and wonosari formation; the three oldest formations were volcanic origin, while the others were calcareous sedimentary rocks. the kebo-butak formation was volcanic origin deposited in submarine, so that often intersecting with calcareous sedimentary rocks in the frontier facies, while the nearest vents were lava with pillow structures and thick beds of tuff http://journal.uir.ac.id/index.php/jgeet 218 mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 and lapillistone (mulyaningsih, 2016). the distinguished volcanic origin of the semilir formation was composed by very widely distributed volcanic sequences of dacitic-ryolitic tuff and lapillistone by very explossive plinian-mega-plinian volcanic eruptions (mulyaningsih & sanyoto, 2012; mulyaningsih et al., 2011; bronto et al., 2008). according to mulyaningsih, et al. (2018) the ancient volcano of giriloyo was formed in a constructive phase of the sub-marine, at the top of the lower miocene n59 (mulyaningsih, 2009). circular with horseshoe-shape geomorphology, radially sloping to the east, north, and south forming dome, so that geomorphologically it was thought to had been formed by active tectonism of submarine volcanoes, and by extraterrestrial descent, further deformed with varied structural patterns. the volcanic sequence should be part of the kebo-butak formation, not to nglanggeran formation even semilir formation, covering central to the proximal facies, with a period of activity as long as the kebo-butak formation that located at baturagung range. the aims of study were to determine the volcanic origin of giriloyo formation, the relationship of the volcanic sequence with the kebo-butak formation in the baturagung range, and the chronostratigraphy and history of the volcanic activities that built giriloyo volcanic facies. fig. 1. stress map of the study area. mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 219 2. regional geological setting subduction of indian-australian plate beneath the eurasian plate has recorded under south of java island (smith et al., 2005; zahirovic, et al., 2014; zulfakriza et al., 2014). it controlled the tectonic of study area since late eocene resulted tertiary volcanic arc along southern mountain, south java island (suria-atmadja, et al., 1994; koulali et al., 2017). that tectonic setting referred to the long-lived volcanism since late eocene to late miocene (smith at al., 2011). evidence of the earliest magmatism was late eocene located at pacitan resulted basalt with pillow structures (suriaatmadja, et al., 1994); represented to the lowermost part of besole formation aged oligocene-early miocene. in central java at the same time, the magmatic event resulted tholeiitic volcanic rocks, as luk ulo formation. the resultant volcanic products of this event were old andesite formation (oligoceneearly miocene) which is limited to the center of west progo mountain. outcrops of calc-alkaline basalt flow with pillow structures underlie the volcani-clastic of the semilir formation (middle miocene), as called as kebo-butak formation (late oligocene-early miocene). referring to rahardjo et al. (1995), regional stratigraphy of the western southern mountains, respectively, is composed of middle miocene of semilir formation, middle miocene of nglanggeran formation, middle-upper miocene of sambipitu formation, upper miocene of oyo formation and late miocene to early pliocene of wonosari formation. on the top of wonosari formation, there is a pliocene kepek member. furthermore, rahardjo et al. (1995) also describe the development of geological structures that are horizontal faults directed northwestsoutheast which cut thrust faults of southwestnortheast, leaving a wedge extending on the northnorthwest to the west of the southern mountains in imogiri area. according to surono et al. (1992), the rocks in the publication of rahardjo et al. (1995) hitched above the lower-middle miocene of kebobutak formation, at gedangsari-terbah (gunungkidul regency). according to surono et al (1992), surono (2008), kebo-butak formation from the bottom to the top are composed of basalt lava with pillow structures, intersecting of marls, calcareous claystones and calcareous sandstones, glassand crystalsrich sandstones. mulyaningsih (2016) determined the kebo-butak formation as deep-to-neritic volcanic rocks of construction phase volcanic origin, shown by the intersecting volcanic deposits and calcareous marine sediments. semilir formation lies on kebobutak formation in an unconformity manner, consisted of basal layer with basalt fragments which was locally exposed at watuadeg (bronto & mulyaningsih, 2001). above semilir formation was volcanic rocks of nglanggeran formation, consisted of andesitic agglomerate, breccia and lava, nglanggeran formation is formed by volcanism which takes place in a very long time duration in the constructive phase (bronto et al, 2008). 3. method the research was approached by ancient volcanic geological studies referring to the present volcanoes. the concept of the present is the to the past was used to identify the genesis of lithology. principally, an igneous rock was always produced by magmatic activity, implementing to the volcanic origin nor pluton; rhyolitic, dacitic, andesitic and basaltic should be volcanic origin. a volcano can be a composite that formed by less viscous magma building stratotype, less viscous ultrabasic magma built shield volcano, and a very viscous-plastic magma (as dacitic-rhiolytic) capable to blockage the vents under the crater triggering very explosive eruptions (bronto, 2010; mulyaningsih, 2013; and schminche, 2004). the hypothesis is that volcanic rocks which are composed of andesiticbasaltic origin must be resulted by composite volcanoes activities, which were able to build their bodies forming high cones. as a result, magma flowed through the cracks that formed around the crater pipe to form a parasitic volcanic cone. the study was begun with reference to collect the secondary data, followed by field geological mapping. mapping included stratigraphic measure sections, rock samplings (for thin sections), collecting and measuring geological structures, and gravity. the work was continued with laboratory analyses; 11 sites have been sampled on black tuffs, bomb fragments of volcanic breccias, agglomerates, lava, and dykes, resulted 14 samples (fig. 2). all of them were analyzed under a polarized microscope using magnificent of 40x-200x, and 8 others were carried out bulk chemistry using x-ray fluorescence. thin section analyses were done in the laboratory of petrology of ist akprind own. x-ray fluorescence analyses were done in the laboratory of center for nuclear mines technology (ptbgn-batan). all data have been compiled, and synthesized using overlay system. 4. results tracks of geological observations throughout cengkehan-watulumbung, giriloyo-cengkehan and cengkehan river (fig. 2). in general, geomorphology of study area forms hilly landscape extending westeast, separated by cengkehan river as part of a circular feature of sudimoro range, trending southwest-northeast facing to the west-northwest (fig. 3). many deformations are illustrated within the 3d dem (fig. 3). in the central landscape, precisely to the north of sudimoro range (+ 507 m), the circular consists of tight pattern of contours on the opening area, then turns to the northeast to form a basin between muntuk (near becici hill) and sudimoro. the western site of the opening feature is mount makbul (+ 339 m) and in the east is becici hill (+ 306 m; dlingo district). inside the opening circular are tuff and lapillistone of semilir formation, in a sub-dendritic drainage pattern. 220 mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 fig. 2. map of the track and location of observation fig. 3. the morphological appearance is based on dem observation, describing the height in the middle with red feature as hilly topographic with east-west orientation. mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 221 the high landscape of sudimoro range consists of andesitic breccias, lava and dykes that composed of amphibole-rich andesite and pyroxene-rich andesite. stratigraphically, the volcanic rocks composing giriloyo are pyroclastic breccias, tuffs, lava, agglomerates and dykes varying in compositions; i e., basalt, pyroxene-rich andesite (basaltic andesite) and andesite. from the bottom to the top is intersecting tuff with black colour and basalt lava in about 15-20 m thickness; then intersecting black tuff and massive basalt breccia in about 10-12m thickness; calcareous claystone with laminated structures above the sequence having ages of n5-6 (early miocene). above the calcareous claystone is brownish grey to yellowish dark grey (fresh), massive to layered tuff and pyroxene-rich andesitic breccia with the total thickness of 8-12m, unconformably above the breccia is agglomerate with pyroxene-rich andesitic bombs. thin section analyses of lava and fragments of agglomerate show less vesicular structure, porphyritic-poikilitic, with very large phenocryst composed by 15-20% of augite-hedenbergite (pyroxene), 20-25% of smaller labradorite (plagioclase), ~5% of little grains of olivine embedded within smaller crystals and glass. some lava has a layer of autoclastic breccia, some others then continually covered by agglomerate which is increasingly massive, and some others have pillow structures. the thickness of lava varies between 10 cm to 3 m. sheetlike near waterfall to columnar near watulumbung. at karangtalun and bronjong (near cegokan) at 7 o 52'58,3 "s and 110 o 26'39,7" e); its lithology consists of distinguished brown colour of pyroxene-rich sandstone, layered, @ 10-20 cm, having lithic fragments, and less calcareous. those sedimentary rocks are looked interrelated to columnar very different feature into nglanggeran even semilir formation. the deposits are having an age of n5-7. massive volcanic breccia with block, bomb and little bit coral fragments were exposed at pucungpilang and sitimulyo at the coordinates of 110 o 25 '40.5 "bt 7 o 51' 28.4"s. below the volcanic breccia was layers of mudstone and calcareous sandstone having an age of n8-9 (upper early miocene). about 100m east of the outcrops, there was andesitic lava with andesine-labradorite, augite and pale green hornblende, the thickness is ~30-50m. it is vesicular, porphyritic with subhedral-anhedral shapes, 0.0208mm ø embedded in light grey glass. this lava is also exposed at wonolelo (north of sudimoro), that riches in sulphid minerals (pyrite). layers of light grey tuff cover the volcanic breccia and lava at wonolelo and cinomati, munthuk and lower becici. it is correlated to the upper volcanic sequence at giriloyo; i e. andesitic lava, agglomerate and dykes. fig. 4. stratigraphic profiles of the volcanic rocks of giriloyo-cengkehan paleovolcano fields exposed at study area; green lines are interpreted faults (deformations) 222 mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 fig. 5. volcanic rock outcrops along with giriloyo-cengkehan hamlets, composed by lithic and crystal tuff with thin lava layers, breccias, lava and agglomerate, and dykes from the north to the south through dengkeng to cengkehan, in the coordinates of 110 o 25'3,2-11"e and 7 o 53'48-55"s, there are layers of dark-grey fine-tuffs and mudstone, covering black coarse tuff with layers of basaltic lava in about 10m thickness, dark brown crystal and lithic tuff. among the layers of tuff and lava, there are chlorinated green tuff with granules of pyrite and rounds of basaltic bombs as matrix supported. coverring tuff and lava is calcareous mudstone globoquadrina praedehiscens blow and banner, globigerinoides primordius blow & banner, tripartite globigerina koch and globigerina binaiensis koch having ages of n8-9. andesitic breccia, lava and agglomerate lie on the sedimentary rocks. as mention above, cengkehan river is flowing in the middle of sudimoro range, separated south and north parts, forming giriloyo palaeo-crater. covering an area with the altitude of 100-260m above sea level, the lithology consists of intersecting black tuffs and lavas; layers of black tuffs with bombs ø 40cm, black tuffs, agglomerates and lava; layers of brown tuff, lapillistone, andesitic breccia and lava; sheets and columnar lava; dikes and chlorinated volcanic-clastic rocks. section along watulumbung-grenjeng (north of cengkehan) consists of massive agglomerates and breccias, dikes, and massive lava. lapillistone, lithic tuff and matrix-supported breccia in dark green color till very dark grey dominated the lithology at grenjeng. normal faults and dextral slip faults in the volcanic sequence shawn triggering the mass movements. fig. 4 explains measure sections stratigraphy at study area. the outcrops of giriloyo volcanic rocks are explained in fig. 5. thin section analysis on black tuff (sample of c1) determines deeply diagenetic tuff with poorly sorted of angular to very angular lithic and crystal clasts, with tuff sizes and composed by basaltic fragments, glasses, and crystals of pyroxene (augitehedenbergite) and plagioclase (labradorite) cementing with silica. agglomerate fragment (sample of c13) shows very hollow structure (due to the exhalation of gas when it freezes in the air), porphyritic with plagioclase (labradorite-andesine) and pyroxene (augite) phenocrysts in the groundmass of glass. the dike (sample of c10c) shows less vesicular, porphyritic with very large phenocrysts of pyroxene (augite) and plagioclase (labradorite) within the groundmass of fine-sized of aphanite crystals. lava with columnar joints exposed at watulumbung (sample no. c10b) is less vesicular, porphyritic with very large phenocrysts of pyroxene (augite) and plagioclase (labradorite) within the groundmass of glass and fine-sized of aphanite crystals. sample no. c10a is lava with sheeting joints exposed at watulumbung; vesicular structure, porphyritic with plagioclase (labradorite) and pyroxene (augite) phenocrysts in groundmass of glass. most of the volcanic rocks exposed at giriloyo were deeply deformed, forming shear faults, oblique normal faults, and normal faults trending north-south and east-west. those faults are mostly cutting surface soils, so those are still active. fig. 6 explains the thin sections of the varying volcanic rocks exposed at giriloyo. mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 223 observation near mount makbul reccords thick layers to massive lapillistone with pumice fragments and tuff of semilir formation. above them is nglanggeran formation that composed by agglomerate, breccia and lava that were resulted by constructing phase volcanism (mulyaningsih, 2015). 5. discussion the discovery of a group of volcanic rocks with the main composition of lava and andesite breccia under the semilir formation provides evidence of the construction stage of a composite volcano in giriloyoimogiri. the distribution of the old volcanic rocks is indeed very wide from the imogiri district to the east, but no contact with semilir formation in giriloyo; it is directly boarded by agglomerates of nglanggeran formation. tight contacts are found in dengkengpucung (wukirsari; ± 1.5 km to the north of giriloyo) and wonolelo (pleret district). in pucung and wonolelo, at the boundary between the layers of andesite lava and pyroclastic breccia (below) as primary products of composite volcanic cones and semilir formation (upper) nor the opposite, are epiclasticic sediments, both in the form of conglomerates and calcareous sediments of sandstone, siltstone and claystone, and mudstone. so, it was a time interval between not having a long enough volcanism and the stages of composite construction (nglanggeran formation) with the destruction stage of the caldera formation (semilir formation). the assumption is every basaltic volcanic rock are kebo-butak formation, every dacitic volcanic-clastic rocks are semilir formation, and every andesitic volcanic rock is nglanggeran formation. wide distributed volcanic rocks were at gunung gede, dengkeng-pucung, giriloyo-cengkehan, munthuk-karangtalun and wonolelo-sudimoro. this situation answers the hypothesis that the sudimoro range, in which is giriloyo, was an ancient volcano. volcanic activity can take place for a long time, resulting in sulphidic mineral deposits. however, by the submarine situations, it was associated with clastic calcareous sediments. layers of the fine-grains volcaniclastic deposits with dark-coloured rich in volcanic bombs in cengkehan are increasingly coarse into watulumbung and other places around it, aged in the ranges of n5-9 (lower-middle miocene), indicates that volcanic activity was at least sourced in these. fig. 6. parallel nikol of lithic tuffs exposed at cengkehan; from the upper right counterclockwise are c01a, c01b, c02, and c03. it shows lithic fragments with irregular shapes but some featuring circle shape, vuggy and cementing with silicic materials 224 mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 based on the regional geology by the previous studies, reported kebo-butak formation aged late oligocene to early miocene, was exposed at tegalrejogedangsari (gunungkidul; mulyaningsih, 2016) and gunung kebo and butak (bayat, klaten; surono et al., 1992). it consisted of submarine volcaniclastic deposits associated with calcareous sediments. the distinguished volcanic rocks were basalt (as sill, dykes and lava), black colour of rich-glass crystal tuffs, layered yellowish to creamy crystal tuff, and laminated light grey dacitic tuff (mulyaningsih, 2016). that s why, surono (2009) interpreted kebo-butak formation as deep-sea turbiditic sequence affected by volcanic origin. but, petrologically, every lava nor shallow intrusion (such as andesite and basalt dyke and sill) should be volcanic origin (mulyaningsih, 2015), so kebo-butak formation were not turbiditic origin, but volcanic constituents. the problem was, those volcanic rocks were assumed as submarine; kebo-butak formation as deepsea up to neritic, semilir formation could be neritic, transition to subaerial, and nglanggeran formation was neritic-transition. according to mulyaningsih (2016), surono et al. (1995) and surono (2009), kebo-butak formation were composed of intersecting fine-grains volcaniclastic rocks with basalt lava and calcareous sediments, some of them (massive lapillistone) contained coral and blocks of basalt fragments. the upper layers were crystal tuff with pyrite granules in basaltic-andesitic volcanic beds. locally, there is basalt lava with pillow structures. correlated to the volcanic rocks exposed at giriloyo, there are some similarities for the structure, texture and composition. the volcanic rocks of giriloyo consist of intersecting black colour of basaltic tuff riches lithic and crystals and basalt lava and breccia. above them are basaltic to andesitic volcanic-clastic deposits. both basaltic and andesitic sequences were separated by calcareous sediments of n5-9 (relatively). watulumbung volcanic rock consists of lava with columnar joints, dykes, agglomerates and transitional lava and dikes (with sloping column structures). gravity (fig. 7) shows 3 peaks of bouguer anomalies of 1.3-1.9 mgal (red-pink); among them are basins with low anomaly of -2.1 mgal in blue. the high anomalies are interpreted as volcanic/shallow igneous, while low anomaly is sedimentary rocks deposited between the volcanic highs. the gravity also illustrates a red shade overlaps to a circular high. that explains any superimposed volcanism, could be the nglanggeran formation over the other nglanggeran formation, or the kebo-butak formation and the nglanggeran formation. so based on the similarities as mention above, the superimposed volcanism must be kebo-butak formation overlie by nglanggeran formation. in general, the high of east-southeast giriloyo was the main volcano, while giriloyo as a parasitic cone adjacent to the main volcano. microseismic data collected at watulumbung encountered weak fields in the south, that increasingly stronger to the north (fig. 8). the weak fields are having east-west orientation interpreted as fault systems. between them are heights that interpreted consist of lava and dykes. those distinguished subsurface lineaments trending northsouth near waterfall (c13) and east-west through grenjeng and cut off lineaments near waterfall. it can be synthesized that volcanism and tectonism were continually presented in long time duration. fig. 7. the subsurface geological appearance of the giriloyo volcanic rocks compiled with surface geological structures mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 225 fig. 8. general description of subsurface geological survey using microseismic method at watulumbung (stopcite c10 and c13); on the surface composed of igneous intrusions, lava, and agglomerate lithology exposed at giriloyo and the surrounding area consists of volcanic rocks, i e., intersections of blackish crystal tuff, lithic tuff and basalt lavas of creamy-brown colour crystall and lithic tuff, basalticandesitic breccia and lava, andesitic lava nd agglomerates, and basaltic-andesitic dikes. stratigraphically, the rocks are below the semilir formation. there are no fossils found in those volcanic rocks, but about 500m to the west, northwest, east and north in giriloyo, pucung, lower cengkehan, munthuk and karangtalun; there are calcareous sedimentarry rocks above the blackish tuff age of n5-6, n5-7 (early miocene), the calcareous rocks above the semilir formation are n8-9 and n5-n9 (lower middle miocene). if the volcanic rocks of semilir formation are formed by a very explosive eruption that can form a caldera, it only takes a short time. so, volcanic activity that produces volcanic rocks below the semilir formation is certainly not much older than the rocks that make up the semilir formation. when compared with regional geological data, stratigraphically, the giriloyo volcanic rocks were same age as the kebobutak formation. referring to kebo-butak formation exposed at gedangsari and bayat, the volcanic rocks composing the giriloyo area are part of a tertiary volcano cluster developing in the early miocene. the composition of volcanic rocks in giriloyo consists of dike, lava, agglomerate and fragmented tuff with bombs and blocks fragments; indicates as central volcano, or very close to the central facies. the columnar structure of the lava can be interpreted as a large volume of lava mass impounded within a basin (should be crater) and then stagnated and frozen slowly, to form a stocky column. planar columns on a wide rock distribution, containing sulphide mineral, reflects the intrusion taking place over and over again. subsurface data interpret the volcanic rocks extends at the bottom and deeply deformed. based on gravity anomalies recognized at least three volcanic rock formations, (a) beneath the semilir formation, (b) semilir formaton and (c) nglanggeran formation. thin section observation into black tuffs are arranged by lithic and subhedral to euhedral crystals. the lthics are basaltic with labradorite plagioclase, which is well-certified within silicic cement. andesiticbasaltic lava is vesicular, porphyritic, consists of labradorite (40%) and augite phenocrysts (30%) within glassy groundmass. basalt with sloping column is vesicular, porphyritic consists of augite-hedenbergite (up to 4mm in diameter), large labradorite in glassy groundmass; basalt with planar column is massif, in equigranular, hypocrystalline (less glass), consists of small percent of labradorite (~20-30%) and larger augite (up to 6mm in diameter; 60%) and glass. those rocks can be referred to as andesite, but compositionally, is very different to the nglanggeran formation exposed at mount nglanggeran (at baturagung range), that dominated by andesine, amphibole and clinopyroxene (bronto et al., 2009). both stratigraphy and petrology of giriloyo volcanic sequence is older than the nglanggeran formation. it is worth being of kebo-butak formation in the late oligocene to early miocene. 6. conclusion giriloyo was submarine ancient volcano since late oligocene-early miocene to middle miocene, resulting kebo-butak formation and nglanggeran formation. no semilir formation between them. active tectonism under controlled by volcanism carried out since the volcanism until now as well as intensive terrestrial denudation. those were implicated by the repeated volcanism, during the long period. the evolving 226 mulyaningsih, s. et al./ jgeet vol 04 no 03/2019 volcano is needed further research to interpret the magmatological and evolving volcanic activities. acknowledgements our acknowledgements address to the ministry of research and high education (ristekdikti) which was funding the research by the first year of penelitian terapan perguruan tinggi (ptupt scema) on 2018. special thanks tend to the government of bantul regency, the head of wukirsari and the staff, the giriloyo and cengkehan communities, pokdarwis, as well as forcib aryabhata, who have provided the research facilities, accompanied the research and gave a variety of very warm supports. a big appreciation is supervised to lppm ist akprind for the opportunities to reach the ptupt grant. references bothe, a. ch. d., 1929, djiwo hills and southern ranges, excursion guide, ivth pacific sci. cong., bandung, 23 p. bronto, s., mulyaningsih, s., hartono, g., & astuti, b. 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sebagai acuan dalam interpretasi gunung api komposit tersier di daerah gunung gede-imogiri daerah istimewa yogyakarta, prosiding seminar nasional aplikasi sains & teknologi (snast) periode iii issn: 1979-911x yogyakarta, 3 november 2012. mulyaningsih, s., husadani, y.t., umboro, p., sanyoto, s., dan purnamawati, d.i., 2011. aktivitas vulkanisme eksplosif penghasil formasi semilir bagian bawah di daerah jetis imogiri, jurnal teknologi technoscientia ,4, 1, 64-78. mulyaningsih, s., 2016. volcanostratigraphic sequences of kebo-butak formation at bayat geological field complex, central java province and yogyakarta special province, indonesia, indonesian journal on geoscience 3, 2, 77-94. rahardjo, w., 1983. paleoenvironmental reconstruction of the sedimentary sequence of the baturagung escarpment gunung kidul area, central java, proceed. pit xii iagi, yogyakarta, 6-8 dec. 1983, 135-140. rahardjo, w., 2007, prelimanary result of foraminiferal biostratigraphy of southern mountains tertiary rock, yogyakarta special province, abstrak, seminar dan -29 november 2007. rahardjo, w., sukandarrumidi dan h.m. rosidi, 1977, peta geologi lembar yogyakarta, jawa, skala 1 : 100.000, direktorat geologi, bandung. smyth, h., hall, r., hamilton, j. and kinny, p., 2005. east java: cenozoic basins, volcanoes and ancient basement. in proceedings of the indonesian petroleum association, 30th annual convention. indonesian petroleum association. smyth, h.r., crowley, q.g., hall, r., kinny, p.d., hamilton, p.j. and schmidt, d.n., 2011. a toba-scale eruption in the early miocene: the semilir eruption, east java, indonesia. lithos, 126(3-4), pp.198-211. soeria-atmadja, r., r.c. maury, h. bellon, h. pringgoprawiro dan b. priadi, 1994, tertiary magmatic belts in java, journ. se asian earth sci., 9, 13-12. srijono dan s. husein, 2007, tinjauan geomorfologi pegungan selatan diy/ jawa tengah: telaah peran faktor endogenik dan eksogenik dalam proses pembentukan pegunungan, yogyakarta, 27-29 november 2007. zahirovic, s., seton, m. and müller, r.d., 2014. the cretaceous and cenozoic tectonic evolution of southeast asia. solid earth, 5, 227. zulfakriza, z., saygin, e., cummins, p.r., widiyantoro, s., nugraha, a.d., lühr, b.g. and bodin, t., 2014. upper crustal structure of central java, indonesia, from transdimensional seismic ambient noise tomography. geophysical journal international, 197, 630-635. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc bysa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ volcanism in the pre-semilir formation at giriloyo region; allegedly as source of kebo-butak formation in the western southern mountains 1. introduction 2. regional geological setting 3. method 4. results 5. discussion 6. conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 46 jannah, m. et al./ jgeet vol 02 no 01/2017 geological structure analysis to determine the direction of the main stress at western part of kolok mudik, barangin district, sawahlunto, west sumatera miftahul jannah 1 , adi suryadi 1, *, muchtar zafir 1 , randi saputra 1 , ihsanul hakim 1 , riki ariyuswanto 1 , ulfa yusti 1 1 department of geological engineering, universitas islam riau, jl, kaharuddin nasution no 113, pekanbaru, riau 28284 *corresponding author: adisuryadi@eng.uir.ac.id tel. +6282283896947 abstract on the study area there are three types of structure, those are fault, fold and joint. types of fault were found in the study area, reverse fault with the strike/dip is n215 o e/75 o , normal fault has a fault directions n22 o e and n200 o e with pitch 35 o , and dextral fault with pitch 10 o and strike n219 o e. fold and joint structures used to determine the direction of the main stress on the study area. further, an analysis used stereonet for data folds and joints. so that from the data got three directions of main stress, those are northeast southwest (t1), north south (t2) and southeast northwest (t3). on the northeast southwest (t1) stress there are four geological structures, anticline fold at st.3 , syncline folds at st. 13a, st. 13b, st. 13c and st. 33, chevron fold at st. 44 and joint at st. 2. on the north south (t2) stress there are three geological structures, those are syncline fold at st. 35, anticline fold at st. 54 and joints at st. 41, st. 46 and st. 47. on the southeast northwest (t3) stress were also three geological structures, those are chevron fold at st 42a, overturned fold at st. 42b, syncline fold at st. 42c and joints at st. 5 and st. 34. keyword: fault, fold, joint, stress. 1. introduction the study area is located at western part of kolok mudik, kecamatan barangin, kotamadya sawahlunto, sumatera barat. study area is bounded by longitude 100 o 100 o 43 o 0 o the topography of sawahlunto is hilly areas with elevation about 250 650 meters above sea level (pebri aldi, 2015). the topography grown could be interpreted that on the study area be affected by tectonic activity such as fold or fault (koesoemadinata and matasak, 1981). its can be seen from shape of river that nudge, indicated that river formed due to crack or fracture is relatively weak zone and then eroded along fracture (fig 2). hilly area would be described that this area has occured uplift and then formed a fold (koesomadinata and matasak, 1981). the study area is within ombilin basin. overall the strucuture of the basin ombilin showed transtensional duplex or pull apart duplex systems. woodcock and fischer (1986) said in situmorang, et.,al (1991). subduction of geometry from duplex faults would be meet in sub basin became single shear zone. fig 1. map of the sawahlunto city (basmoera, 2008) study area received: jan 1, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017 doi: 10.24273/jgeet.2017.2.1.20 mailto:adisuryadi@eng.uir.ac.id jannah, m. et al./ jgeet vol 02 no 01/2017 47 figure. 2. map of drainage in the study area; (a) meander; (b) subparallel; (c) subtrellis this condition is so different with the geological structure of the northern part of central sumatra basin that was developing at the time of neogen and asymmetrical shape that led northwest-southeast (nw-se) which is a pattern of young structure (kausarian, 2017). 2. general geology and stratigraphy based on peta geologi lembar solok (1995), the study area has two formation and one deposition, that are silungkang formation, brani formation and porphyry deposition. the silungkang formation there are andesit hornblende, andesit argit, meta-andesit with thin interbedded tuff, limestone, shale and clay shale (ph. silitonga and kastowo, 1995). there is also a fusulinida fossil (koesomadinata and matasak, 1981). the brani formation there is conglomerate interbedded with sand. the porphyry deposition consist of porphyry quartz with quartz phenocrysts and feldspar (ph. silitonga and kastowo, 1995). furthermore, wolud be found fractures on the body of rocks and alteration that happened on wall rocks (berger, et.al,2008). after observation on the study area, we found three formation, that are silungkang formation, brani formation and sangkarewang formation. silungkang formation consists of limestone with mudstone type, sandstone and conglomerate. on the brani formation there are conglomerate, sandstone and shale. meanwhile sangkarewang formation consists shale, sandstone, slump and crossbedding. 3. methodology the methodology used in this research were literature review, field survey and stereonet analysis. the first literature review to known structure types on the study area. the study area in the field showed by plotting points to generate the geological mapping (kausarian, 2016). after that field survey was done to get the data that needed to determine the direction of main stress from geological structure. the last analysis used streonet from the data. all of data has plotted on stereonet to get the direction of main stress at the study area (adi suryadi, 2016). 4. geological structure on the study area 4.1 faults geological structures on the study area are faults, folds and joints (fig 3). indication of fault is difficult to found in the field, because the rocks on the study area have been a heavily weathering (rizky prata, 2011; (putra and choanji, 2016). on the study area, there are three types of fault, these are reverse fault, normal fault and dextral fault. reverse fault located in southwest the study area with value fault plane is n215oe/75oon station 2. normal fault located at central of study area, these are in station 10 with direction n200oe and pitch 35o, station 56 and station 57 has same direction is n22oe. dextral fault located in north of study area with pitch 10o. fault would be known if we found indications in the field, like waterfall, displacement of bedding and slickenside etc. 4.2 folds on the study area were found four types of folds, there are anticline fold, syncline fold, chevron fold and overturned fold. the all of data would be plotted in stereonet to known the direction of main stress (fig 5). based on stereonet analysis result, there are three direction of main stress, those are northeast southwest, north south and southeast northwest (table 1). 4.3 joints on the study area, joints data took at southwest north of the study area. based on joints data that has been obtained and analysis used stereonet (figure 6), there are three direction of main stress, northeast southwest, north south and southeast northwest (table2). 48 jannah, m. et al./ jgeet vol 02 no 01/2017 fig 3. geology map on the study area fig. 4. (a) dextral fault; (b) reverse fault; (c) normal fault jannah, m. et al./ jgeet vol 02 no 01/2017 49 fig. 5. stereonet analysis of folds on the study area table. 1. stress analysis result of folds station hinge line hinge surface axis surface plunge axis line directions of major stress st. 3 25 o , n24 o e 18 o , n251 o e 72 o , n178 o e 18 o , n251 o e 72 o , n116 o e steeply inclined fold gently plunging fold northeast southwest st. 13a 18 o , n219 o e 26 o , n315 o e 72 o , n131 o e 26 o , n315 o e 44 o , n87 o e moderately inclined fold gently plunging fold northeast southwest st. 13b 28 o , n196 o e 21 o , n232 o e 66 o , n45 o e 21 o , n232 o e 80 o , n21 o e steeply inclined fold gently plunging fold northeast southwest st. 13c 5 o , n23 o e 35 o , n251 o e 65 o , n137 o e 82 o , n20 o e 35 o , n251 o e moderately inclined fold vertical fold northeast southwest st. 33 3 o , n204 o e 21 o , n256 o e 80 o , n126 o e 21 o , n256 o e 80 o , n114 o e steeply inclined fold gently plunging fold northeast southwest st. 35 9 o , n23 o e 70 o , n279 o e 30 o , n118 o e 70 o , n279 o e 84 o , n188 o e upright fold steeply inclined fold north south st. 42a 51 o , n140 o e 5 o , n225 o e 44 o , n329 o e 5 o , n225 o e 46 o , n186 o e moderately inclined fold horizontal fold northwest southeast st. 42b 25 o , n130 o e 52 o , n241 o e 44 o , n21 o e 52 o , n241 o e 70 o , n330 o e steeply inclined fold moderately plunging fold northwest southeast st. 42c 12 o , n349e 32 o , n249 o e 54 o , n91 o e 32 o , n249 o e 54 o , n80 o e moderately inclined fold moderately plunging fold northwest southeast st. 44 8 o , n307 o e 38 o , n38 o e 72 o , n212 o e 38 o , n38 o e 62 o , n130 o e steeply inclined fold moderately plunging fold northeast southwest st. 54 20 o , n5 o e 24 o , n270 o e 64 o , n156 o e 24 o , 270 o e 68 o , n181 o e steeply inclined fold gently plunging fold north south hinge surface initial line tho1 and tho3 hinge line direction of main stress limb 1 limb 2 50 jannah, m. et al./ jgeet vol 02 no 01/2017 fig. 6. joints analysis used stereonet table.2.stress analysis result of joints station direction of main stress st. 2 northeast southwest st. 5 southeast northwest st. 34 northwest southeast st. 41 north south st. 46 north south st. 47 north south 5. discussion analysis result for folds and joints used stereonet, were met three main stress with direction, northeast southwest (t1), north south (t2) and southeast northwest (t3). northeast southwest (t1) main stress formed some structures, there are syncline folds, anticline folds, chevron fold and joint. north south (t2) main stress generated some structures, there are syncline folds, anticline folds and joints. southeast northwest (t3) main stress resulted three structures, there are chevron fold, overturned fold, syncline fold and joints. table.3.stress analysis on the study areas stress direction of main stress station geological structure t1 northeast southwest st. 3, st. 13a, st. 13b, st. 13c, st. 33, st. 44 and st. 2 anticline fold, syncline folds, chevron fold and joint. t2 north south st. 35, st. 54, st. 41, st. 46 and st. 47 anticline fold, syncline fold and joints t3 southeast northwest st. 42a, st. 42b, st. 42c, st. 5 and st.34 overturned fold, chevron fold, syncline fold and joints jannah, m. et al./ jgeet vol 02 no 01/2017 51 figure. 7. direction of main stress at study area 6. conclusion based on analysis of geological structure were found three main stress that deform the geological condition of study area. the first stress is northeast southwest (t1) this stress generated some structures, these are syncline folds, anticline folds, chevron fold and joint. another stress is from north south (t2) that resulted syncline folds, anticline folds and joints. the last main stress with direction southeast northwest (t3) was form chevron fold, overturned fold, syncline fold and joints. 7. acknowledgements we would like to say thanks for our parents that always prayed us. for our advisor is mr. adi suryadi, b.sc(hons)., m.sc that has been faithful guided us until this paper are adlan rahmat, arsyad and yogi aditya that always have companied us when we are collected data in the field. references aldi, pebri. 2015. sekilas tentang kota sawahlunto.kompasiana. url http://www.kompasiana.com/aldi/sekilastentangkotasawahlunto_54fd6acaa33311022150fd86. basmoera, z,. 2008. peta wilayah kota sawahlunto, provinsi sumatera barat. berger, byron r., ayuso, robert a., wynn, jeffrey c., dan seal, robert r., 2008, preliminary model of porphyry copper deposits, open file report 2008 1321 u.s. geological survey, reston, virginia. kausarian, h, j. t. s. sumantyo, h. kuze, k. detri, g. f. panggabean, 2016. silica sand identification using alos palsar full polarimetry on the northern coastline of rupat island, indonesia. international journal on advance science, engineering and information technology (ijaseit). vol. 6, no. 5, 568-573. kausarian. h., j. t. s. sumantyo, h. kuze, k. detri, s. wiyono, 2017, the origin and distribution of silica mineral on the recent surface of rupat island, indonesia, arpn journal of engineering and applied sciences. vol. 12, no.4, february 2017, issn 1819-6608. koesomadinata, r.p., dan matasak, t., 1981, stratigraphy and sedimentation ombilin basin central sumatra (west sumatra province), proceedings indonesian petroleum association 10 th annual convetion, hal 217 249. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. prata, rizky. 2011. geologi daerah sikalang dan sekitarnya kecamatan barangin kotamadya sawahlunto provinsi sumatera barat. bandung. hal 33 68. silitonga p.h. dan kastowo., 1995, peta geologi lembar solok sumatera, peta geologi bersistem sumatera, pppg, bandung. situmorang, b., yulihanto, b., guntur, a., himawan, r.s., dan jacob t.g., 1991, structural basin development of the ombilin basin, proceedings indonesian petroleum association 10 th annual convetion, hal 217 249. suryadi, adi. 2016. fault analysis to determine deformation history of kubang pasu formation 52 jannah, m. et al./ jgeet vol 02 no 01/2017 at south of unimap stadium hill, ulu pauh, perlis, malaysia. journal geology engineering environmental and technology (jgeet), pekanbaru, riau. vol. 1 woodcock, n. h. dan fischer, m. 1986.strike-slip duplexes. j. struct. geol., vol. 8, p. 725 735, doi: 10.1016/0191-8141(86)90021-0. van bemmelen, r.w., 1949, the geology of indonesia vol. 1 a. government printing office, the hague, martinusnijhoff, vol. 1 a netherlands. 1. introduction 2. general geology and stratigraphy 3. methodology 4. geological structure on the study area 4.1 faults 4.2 folds 4.3 joints 5. discussion 6. conclusion 7. acknowledgements e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 prayitno, b. and ningrum n.s./ jgeet vol 02 no 02/2017 149 development of funginite on muaraenim and lower members of telisa formations at central sumatra basin indonesia budi prayitno 1, *, nining sudini ningrum 2 1 department of geological engineering, universitas islam riau, jln. kaharuddin nasution km .113 pekanbaru, riau 28284 2 ppptekmira-bandung/ jln. jendral sudirman no. 623 bandug 40211. abstract petrography analysis of coal is the study organic and inorganic components of coal bearing formations. this research conducted observation method under microscopic of thin incision to identify organic maseral group. the organic composition of coal from muaraenim formation is known to average for vitrinite maseral group 79.30%, inertinite 10%, liptinite 3.4%, and non-organic 7.3%. while the composition of coal from the bottom members of telisa formation for the average of vitrinite maseral group 66.4%, mineral matter 30.32%, inertinite 3.26%. the liptinite maseral group is not present as a coal component in the study area. the funginite development of the muaraenim formation is quite abundant 2.8% indicating peat swamp ecosystem in wet-dry conditions in ph 3 -5. in contrast, the development of funginite lower members of telisa formation is known to be absent which is replaced by the presence of frambiodal pyrite and indicates peat ecosystem in wet conditions at ph 6 7. keywords: funginite, inertinite, maceral, petrographic, telisa formation. 1. introduction the astronomical part of indonesia is at 0 ° 0'00'' 10 ° 0'00'' 0'00'' lu and 0 ° 10 ° 0'00''ls separated by the equator and 90 °00' 00''bb 140 ° 0'00''bt. indonesian region based on geographical conditions has a tropical climate and is at the eastern hemisphere. indonesia has two seasons only in every year, rainy season and dry season. in general, the intensity of peat accumulation is affected by the tropical climate (dehmer, 1993;. grady et al, 1993; esterle and ferm, 1994; hawke et al. and dehmer, 1999). funginite / sclerotinite as coal component influenced many geological characteristics including swamp forest ecosystems during the decomposition of organic matter takes place.. funginite / sclerotinite is an organic component of coal origin (tertiary) sclorentinite (paleogene). in tertiary coals, a variety of forms are present as sclerotinite; sclerotia (resting spores), teleutospores, mycorrhizomes (symbiotic associations of fungal tissue with higher plant roots) and stromata/fungal fruiting bodies -ruiz et al., 2012). this study will be discussed in more detail with respect to the development funginite /sclorentinite on tertiary coal deposits (member of the lower telisa and muaraenim formation). 2. geological setting the research area has the tectonic framework of sumatra which located at the central sumatra basin. regional geology of research area is based on the geological research and development center, bandung detail at the geological map of rengat sheets (suwarna, budhitrisna, 1994) and geological map of solok sheet of lower members of telisa formation (silitonga, ph & kastowo, 1994). the muara enim formation as a coal carrier formation has characteristic ripple structure composed of clastic sedimentary material in the form of fine clays of lignite coal insertion which precipitated the phase of regresion at the end of the miocene. whereas the lower members of the telisa formation have characteristic of intercalation between the shale and very fine sand of subbituminous coal type a lenses deposited on maximum transgression phase at the beginning to mid miocene (barber and crow, 2005) regional geological maps on research location are shown in fig. 1. * corresponding author : budiprayitno@eng.uir.ac.id tel.:+62 0852 2550 -1217 received: may 5, 2017. revised : may 25, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.342 mailto:budiprayitno@eng.uir.ac.id 150 prayitno, b. and ningrum n.s./ jgeet vol 02 no 02/2017 fig 1. (above) geological maps of rengat (suwarna, budhitrisna, 1994); (below) geological maps of solok (silitonga, ph & kastowo, 1994) prayitno, b. and ningrum n.s./ jgeet vol 02 no 02/2017 151 table 1. the composition of analysis result group of maceral and mineral matter no no sampel vitrinite (% v) liptinite (% v) inertinite (% v) mineral (% v) 1 871/2015 81.0 1.4 6.0 11.6 2 872/2015 78.6 7.0 9.4 5.0 3 873/2015 82.0 3.0 6.6 8.4 4 874/2015 75.6 2.2 18.0 4.2 table 2.the composition ofanalysis result group of maceral and mineral matter no no sampel vitrinite (% v) liptinite (% v) inertinite (% v) mineral (% v) 1 2p/1/16 58.00 2.6 39.40 2 3p/1/16 52.24 2.6 45.16 3 4p/1/16 89.00 4.6 6.40 table 3.the composition of the coal maceral composition of coal maceral (%) maseral group nama maseral 871/2015 872/2015 873/2015 874/2015 vitrinite (huminite) telocolinite 5.4 10.4 4.6 6.4 densinite 4.4 3.0 1.0 2.6 desmocollinite 66.8 62.8 75.0 65.0 corpogelinite 4.4 2.4 1.4 1.6 liptinite (exinite) sporinite 0.8 0.4 cuntinite 0.4 1.6 0.6 resinite 1.0 3.6 0.6 2.2 inertinite fusinite 0.6 4.4 5.2 funginite 4.0 2.6 6.0 7.6 introdetrinite 1.4 2.4 0.6 4.0 minerals matter pyrite 1.0 1.6 1.0 1.6 clay 10.6 3.4 7.4 2.6 table 4. the composition of the coal maceral composition of coal maceral (%) maseral group maseral 1p/1/16 2p/1/16 3p/1/16 4p/1/16 vitrinite (huminite) telocolinite 11.0 11.0 27.0 densinite 16.0 21.0 18.0 1.0 desmocollinite 20.4 26.0 23.4 60.4 corpogelinite 0.6 liptinite (exinite) sporinite cutinite 1.6 1.0 2.6 resinite 1.6 1.6 2.6 2.0 inertinite funginite minerals matter oksida pyrite 32.4 28.4 34.0 6.4 clay 28.0 11.0 11.0 152 prayitno, b. and ningrum n.s./ jgeet vol 02 no 02/2017 3. methods the method for this research, starting with crushed the coal samples into a maximum size of 1 mm and placed in resin blocks. the sample blocks were polished with a specified polisher. microscopic investigation was carried out with a carl zeiss microscope and point counter model f was conducted to determine the micro-organic components of coal (fig. 2). during maceral analysis, 500 points with a minimum distance of huminite particles under oil immersion. fifty points of huminite reflectance were made on each sample. fig 2. carl zeiss microscope and point counter model f with 500 x magnification the sample selection in this research uses "channel sampling" method from selected ideal coal samples as well as representing research area. the sample selection also bases on quality and quantity to meet the standard of test fixation. treat samples from coal bodies, less likely to avoid direct oxidation in a long time to keep capillary moisture as well as coal surface. the sample sampling preparation for microscopic observation was taken from the sample to be analyzed, then crushed until it passed the 1 mm filter and carried out the division so as to obtain 15 gram representative samples for petrographic analysis. the 1 mm sample is mixed with epoxy / transsoptic powder resin, printed in rectangular or rounded mold. after hard the surface is rubbed with a 600, 800 and 1200 emery paper, then polished to obtain a smooth coal surface for petrographic analysis. the maseral analysis is performed under a microscope using the immersion oil on the surface of the sample. this analysis uses 25x, 32x, 50x or even 60x lenses and an automatic 0.4 mm transverse counting machine and 0.5 mm vertical. approximately 500 points were observed excluding visible resins and minerals. maseral can be observed or counted as a group of maseral or as sub-maseral. in performing a duplicate analysis of 3% difference for each accepted maseral. the reflection measurements are performed on the surface of vitrinite particles, in monochromatic green light, wavelength 546 mm. all equipment should be lit at least half an hour before calibration. to measure maximum reflection, the polarizzer is set in position 45o. next turn the 360o microscope and do the reading. to measure this reflection the lens used is high magnification (50 or 60x) and should be placed right in the middle. the readings are repeated from 50 to 100 readings (petrology, 2011). 4. result and discussion in general, the main organic composition of coal is dominated by vitrinite group which is the main ingredient of wood and bark tissue. while inertinite, liptinite and mineral matter groups may be higher or lower than others. the composition of the coal mine the muaraenim formation is known to average for vitrinite maseral group 79.30%, inertinite 10%, liptinite 3.4%, and non-organic 7.3%. while the composition of coal coal members bottom line telisa for the average of vitrinite maseral group 66.4%, mineral matter 30.32%, inertinite 3.26%. the liptinite maseral group is not present as a coal component in the study area. the coal coal composition is given in tables 1 and 2. the development of funginite maseral from the inertinite maseral group, is known to spread quite abundantly and is colonial among fusinite thin wall cells berkwok turmeric white to yellowish. the development of funginite from muaraenim formation coal is given in 3a and 3b. in general, the development of funginite can be caused by surface moisture or capillary of a material between wet and dry or ph 3 5. coal formation muaraenim based on the calculation of maseral composition obtained facies of limnic deposits that turn into limnotelmatic in the atmosphere of the swamp ecosystem is poor will supply water / ombrhotropic mires (prayitno, 2016a) such a condition allows the water supply or surface line to the peat layer to vary according to the supply or rainfall during peat decomposition. the condition of peat swamps that rely solely on water supply from rainfed can ultimately lead to the development of bacterial as an important component responsible for the decomposition process of organic matter to be disrupted, in this case will have an effect on the effectiveness of decomposition of organic matter. moreover, the topographic changes from the limnine to the limnotelmatic conditions influence the groundwater level limit to be lower than the surface layer or peat layer, so that the peat layer is more wet to dry (anggayana et al., 2014). the development of funginite maseral is not only influenced by local factors such as water supply, ph value, depth of peat layer to water surface, also determined by more global tectonic motion such as basal decline and sea level change, in this case succession of sedimentation sediment materials are affected by transgression or regression conditions. in contrast to the muaraenim formation deposited in the regression phase, which causes the ineffectiveness of the decomposition and gelification process of peat materials, the lower prayitno, b. and ningrum n.s./ jgeet vol 02 no 02/2017 153 members of telisa formation are precipitated at the peak phase of transgression. fig. 3 (above) funginite and mineral matter asosiation with desmocolinite coal,reflectant white light, 500x. (below) funginite asosiation with desmocolinite coal, reflectant white light, 500x. coal on lower members telisa formation based on calculation of organic maseral composition obtained facies of limnic deposition in an atmosphere rich in water supply / rheotrophic mire (prayitno, 2016b) table 2. rheotrophic mires is a peat swamp that has a water supply from two sources. first supali water that comes from rain-fed, usually the volume increases with the rainy season. both come from ground water which is a process of infiltration through rock pores or rock fractures. during the dry season, this type of peat swamp is possible still in wet conditions. development of funginite lower members telisa formation based on microscopic observation is known not present as a coal-forming component. peat swamps in the rheotropic mire atmosphere allow the peat layer to be always well below the water surface and in ph 6 8 this causes the development of funginite can not develop properly. however, the mineral matter content of mineral pyrite is quite abundant to form the frambiodal pyrite structure which indicates the average surface water far above the peat surface. abundance of mineral matter coal members bottom line of telisa formation is given in the fig 4.a.b.c. thus the relationship between funginite development and mineral matter abundance may be inversely proportional. the formation of pyrite minerals can be as syngenetic pyrite or epigenetic pyrite. the abundance of mineral matter in the form of syngenetic pyrite and funginite development can be attributed to the basic active basin motion in a certain period so that local and regional tectonic factors can be an important factor for the development of both. fig 4. (above) pyrite and resinite associated with desmocolinite in coal, reflectant white light, 500x. (middle) pyrite framboidal associated with desmocolinite in coal, reflectant white light. 500x. (below) mineral matter in coal, reflectant white light, 500x. 5. conclusions the development of funginite locally can be influenced by chemical, biological and chemical conditions of settling environment. while the global factor is more determined by the basin motion. the development of funginite and mineral matter in a deposition period can indicate certain climatic conditions at the time of deposition. acknowledgments thanks to the department of geological engineering, universitas islam riau as a research funginite funginite 154 prayitno, b. and ningrum n.s./ jgeet vol 02 no 02/2017 funder. and also ppptekmira-bandung, which also supports parties involved in this research. references anggayana, k., rahmad, b., hede, a.n.h., widayat, a.h., 2014. limnic condition in ombrotrophic peat type as the origin of muara wahau coal, kutei basin, indonesia. j. geol. soc. india 83, 555 562. doi:10.1007/s12594-014-0083-5 barber, crow, 2005. sumatra: geology, resources and tectonic evolution (references). tectonics 21, 1040. doi:10.1029/2001 dehmer, 1993;. grady et al, 1993; esterle and ferm, 1994; hawke et al., 1999, dehmer, 1999. petrology and organic geochemistry of peat samples from a raised bog in kalimantan (borneo). organic geochemistry 1999. petrology, o., 2011. iccp training course on dispersed organic matter chapter 2 microlithotypes 1 71. prayitno, b., 2016a. limnic condition in rheotrhopic peat type as the origin of petai coal , central sumatra basin , indonesia. j. geoscience, engineering, environment, and technology 1, 63 69. prayitno, b., 2016b. maseral batubara lesongbatu dan sekitarnya kecamatan rengat barat kabupaten indragiri hilir propinsi riau indonesia. pros. semin. nas. geofis. 2016. silitonga, ph & kastowo, d., 1994. peta geologi lembar solok. -ruiz, i., flores, d., mendon??a filho, j.g., hackley, p.c., 2012. review and update of the applications of organic petrology: part 1, geological applications. int. j. coal geol. 99, 54 112. doi:10.1016/j.coal.2012.02.004 suwarna, budhitrisna, s. and a.m., 1994. peta geologi lembar rengat. 1. introduction 2. geological setting 3. methods 4. result and discussion 5. conclusions acknowledgments references uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 7. no 4. december 2022 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 07 no 04 2022. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content evolution magmatism of nagasari volcano dieng, central java, indonesia .................... 140 rock characteristics of post-caldera volcanoes in dieng volcanic complex (dvc), central java, indonesia ................................................................................................... 151 estimation of density log and sonic log using artificial intelligence: an example from the perth basin, australia ................................................................................................... 158 identification of potential geotourism destination in the river subayang areas of kampar, riau, indonesia ......................................................................................................... 167 the role of fractal micro-pore to absorption of methane gas, case study: coal of tanjung formation, arang alus area, banjar district, south kalimantan, indonesia .................................................................................................................. 176 characteristics and potential of placer gold deposit in lakan bilem block, west kutai district, east kalimantan, indonesia ...................................................................... 182 economic feasibility analysis of fishing job operation in well ys13 ................................ 189 control structure on damage zone and fault plane to geometry of quartz veins and calcite in muaradua ogan komering ulu selatan, south sumatra, indonesia ........................................................................................................................................ 196 cover jgeet vol 7 no 4 december 2022.pdf (p.1) editorial member.pdf (p.2) preface vol 7 no 4.pdf (p.3-4) http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 76 pandita. h & hartono/ jgeet vol 04 no 02/2019 research article identification and stratiraphic position of mollusk type locality at west progo stage hita pandita 1* , hill gendoet hartono 2 1 jurusan teknik geologi, sekolah tinggi teknologi nasional, yogyakarta, * corresponding author : hita@sttnas.ac.id received: feb 12, 2019; accepted: june 19, 2019. doi: 10.25299/jgeet.2019.4.2.2682 abstract the location of the discovery of mollusk fossils on the island of java is spread in various places. one location is in the kulon progo region known as west progo beds. however, due to the lack of studies of mollusk fossils in the kulon progo region, this resulted in a lack of understanding of the location of the discovery. this study was intended to re-record the location of fossil molluscs discovery in the kulon progo region, with the aim of contributing to the stratigraphic arrangement in kulon progo. research methods include literature studies, field investigations and laboratory analysis. the literature study includes libraries of the dutch colonial era regarding the location of the discovery of mollusk fossils. field studies in the form of stratigraphic measurements and sampling. laboratory investigations include petrographic observations and identification of micro and macro fossils. the results of the investigation successfully re-identified the kembang sokkoh and spolong locations which are two types of locations on the west progo beds. based on the lithological characteristics of the two locations included in the jonggrangan formation, with the lower miocene age based on an analysis of the fossil content of the molluscs. keywords: type locality, mollusks, jonggrangan, west progo, kembang sokkoh, spolong 1. introduction during the dutch colonial period, geological investigations on java were always helped by the discovery of fossil mollusks in various places. these discoveries spread almost in all physiographic zones on java. one of the locations of the discovery was in the kulon progo area, which martin (1919) referred to as west progo beds. there are two important locations that represent the age of the early miocene, namely in kembang sokkoh and spolong (van den hoek ostend, et al, 2002). research on the use of mollusk fossils in indonesia is still little done, some of which have already done include pandita and zaim (2009), pandita, et al (2013), kase et al. (2008), and kase, et al. (2015). this condition results in fossils of mollusks not being an important asset in the utilization in the field of geology. one of the important things in utilization is biostratigraphy. mollusk fossils have not been utilized in geological aspects, especially biostratigraphy, because there is still little information about various places containing fossil mollusks (pandita, et al, 2013. based on the old literature review, it is estimated that there are more than 20 locations of fossil mollusk discoveries on java (martin, 1919; van es, 1931). these locations are spread in west java, central java, yogyakarta and east java. in the yogyakarta region these locations are located in kembang sokkah and mount spolong, which represent the west progo level (martin, 1919) the stratigraphic position of each location needs to be reviewed again both in terms of biostratigraphy and lithography. one interesting location to study is the west progo stage. the location needs to be identified again both from the stratigraphy and also the location coordinates, because there is no coordinate point listed when the location was examined (martin, 1919). the lack of clarity about the location has an uncertain stratigraphic position. 2. the objectives this research is intended to re-identify the location of the type of mollusk fossil discovery that represents the west progo stage. in addition, it is also intended to record fossils of mollusks and microfossils that can still be found. while the final goal is to find out the description of the stratigraphic position of the location 3. methods the research method carried out in the form of field investigations and laboratory investigations. field investigations were carried out in the form of measuring stratigraphy, rock and fossil sampling. in laboratory activities it consists of observing thin rock section, identifying macro and micro fossils. after conducting field and laboratory investigations various analyzes were carried out. the analysis carried out in the form of rock type analysis, age analysis and depositional environment. the last stage is a synthesis http://journal.uir.ac.id/index.php/jgeet pandita.h & hartono / jgeet vol 04 no 02/2019 77 of the stratigraphic position of the west progo type location. 4. regional geology 4.1 physiography the physiographically of the study area are located in the kulonprogo mountains sub zone (van bemmellen, 1949) (figure 1). this sub zone is restricted to the western part with the south serayu mountain zone while in the east it is bounded by the yogyakarta plain. in the north it borders the central depression zone of central java, while in the south with the south coast of java (van bemmellen, 1949). the kulonprogo mountains zone itself is a dome that extends north-south. some researchers think the formation of this dome was controlled by tertiary volcanic activity (van bemmellen, 1949). however, a number of other researchers such as sopaheluwakan (1994) and soeria atmadja, et al. (1991) assume that the formation of this dome is related to the existence of twice the tectonic phase in this area. 4.2 stratigraphy the lithostratigraphy of kulonprogo dome has been proposed by several researchers such as van bemmellen (1949), rahardjo, et al. (1995), kadar (1985), pringgoprawiro and riyanto, (1988). based on some of these researchers the stratigraphic sequences from the oldest to the young are as follows (bemmelen, 1949; kadar, 1985 and rahardjo, 1995). the oldest formation found in kulonprogo is the nanggulan formation. this formation is estimated to have formed in the middle eocene based on fossil content of nummulites and discocyclina (van bemmelen, 1949). the depositional environment is estimated to begin in the transition area transformed into a shallow sea. unconformity overly the nanggulan formation deposited by the old andesite formation. the naming of this formation was proposed by bemmelen (1949) for all volcanic rocks in sumatra and java that formed in late paleogene to the early miocene. a number of name revisions to this formation were submitted by many authors relating to naming that did not follow the rules of the indonesian stratigraphic code. purnamaningsih and pringgoprawiro (1981) proposed two names namely the kaligesing formation for units characterized by sediments in the sea, and the hamlet formation for volcanic rocks formed on land. rahardjo, et al. (1995) gave the name of the kebobutak formation because of the lithological characteristics that are similar to the rock units found in the southern mountains of east java. this formation is composed of volcanic rocks in the form of andesite breccia with andesite lava. this formation is thought to be deposited in two different environments, namely the sea and land facies. this rock is thought to have formed in the oligocene early miocene. the thickness of this formation is estimated at 660 m (rahardjo, et al., 1995). overly the old andesite formation is unconformity deposited by the jonggrangan formation. the lower part of the jonggrangan formation is composed by conglomerates which are overlain by tuffaceous marbles and side sandstones with lignite inserts. the upper direction of the jonggrangan formation transforms into layered limestone and coral limestone. this formation is expected to form in the early miocene and at the bottom of the formation with the sentolo formation. the thickness of the jonggrangan formation is estimated at 250 m (rahardjo et al. 1995). figure 1. physiography of central and east java (van bemmelen, 1949), red box research location. pandita.h & hartono / jgeet vol 04 no 02/2019 78 interfingering with the jonggrangan formation is deposited by the sentolo formation. in the giripurwo area, conformity contact found between the sentolo formation at the top and the old andesite formation at the bottom. the lower part of the sentolo formation is a base conglomerate which is boarded by tufaceous marl with a thin layer vitric tuff. this rock upward gradually turns into layered limestone rich in foraminifera. from the results of the planktonic foraminifera analysis several previous studies concluded that this formation was estimated to have formed during the early miocene to the pliocene (n7 n21). the thickness of this formation is estimated at 950 m (rahardjo et al., 1995). unconformable overly the tertiary-aged rocks are quarter volcanic breccias. this volcanic breccia originates from old merapi mountain and young merapi mountain. the distribution of this unit is in the yogyakarta basin which extends between the river progo in the west to the opak river in the east (rahardjo, et al., 1995). 5. data and analysis field investigations were carried out at three locations namely ks01, ks02 and ks05 located on the eastern slope of mount kelir, kulonprogo (figure 2). site selection is based on written information from martin (1919) which describes the location of discovery of mollusk fossils from the west progo level. table 1. kulon progo stratigraphic correlation from several researchers. figure 2. research location based on yogyakarta regional geological map from rahardjo, et al. (1995), green is the jonggrangan formatio n, brown color of the old andesite formation. pandita.h & hartono / jgeet vol 04 no 02/2019 79 5.1 ks01 location the ks01 location is in the kembang soka area with geographic coordinates of 7o46 '5.47' ls and 110o6 '59.7' bt. outcrops of ± 15 m thick show very strict lithological changes where the lower part of the igneous rock is brownish red, while on top of it is brownish sandstone (figure 3). the outcrop conditions at the bottom experience weathering which is controlled by oxidation. in handspecimen observation fresh gray color, porphyritic fanatic rock texture, with massive structure, mineral composition include pyroxene, plagioclase feldspar, k-feldspar, hematite, hornblende, quartz, with a period of basic alteration minerals, which are interpreted as altered basal porphyry. frozen rocks have undergone purple alteration at the bottom. at the top there are brownish white sandstones. the sandstone is resembled by fossils of architectonica molluscs. mollusk fossils cannot be taken because the location has become a tourist spot for the soka kembang waterfall. based on a literature review of the location of the type of mollusk fossil discovery in the kulon progo region (martin, 1919), it is likely that this ks01 location is the location of the sokkah flower. this is in accordance with the description of the location of martin (1919) which illustrates that one location type of the lower miocene level is on the slopes of mount kelir in the village of kembang sokkoh. 5.2 ks02 location the location of ks02 is north of kembang soka, located on the edge of the road that connects jonggrangan village to the sermo reservoir, located at coordinates 07o45'38.8 "ls, 110o07'41.5" bt (figure 4). at this location stratigraphic measurements are carried out, with a thickness reaching almost 50 meters. from the results of measured stratigraphic measurements can be found several lithological variations from young to old layers (figure 5). at the bottom, calcarenite is found with lignite inserts and carbonate sandstones. a number of mollusk fossils can be found in this location such as haustator subulata which becomes an index at the level of west progo (oostingh, 1938). in the middle it changes to calcarenite with the insertion of a crystalline limestone. mollusk fossils are still found with unfavorable and cracked preservation conditions. lignite inserts are also found in this section. figure 3. (a) contact between andesite at the bottom with sandstones at ks01 location, kembang soka tourism site . (b) fossil architectonica found in sandstones. figure 4. initial location of ms at ks02b. a b pandita.h & hartono / jgeet vol 04 no 02/2019 80 5.3 ks05 location the ks05 location is to the east of kiskenda cave and to the west of jonggrangan village, known as sibolong hill. located on the edge of the road that connects jonggrangan village with kiskenda cave, located at coordinates 07o44'47.5 "ls, 110o08'26.4" bt (figure 6). at this location stratigraphic measurements are carried out. thickness reaches almost 25 meters. based on microscopic analysis showed bioclastic limestones, which are composed of large foraminifera fossils, benthic small foraminifera and shell fragments of molluscs. figure 5. measured stratigraphic section of ks02. pandita.h & hartono / jgeet vol 04 no 02/2019 81 figure 6. a) location of ks05 in the mount sibolong area, b) the mollusk fossil found at the site. the rock conditions generally have experienced a strong crystallinity process, so that the shells of mollusks cannot be separated from rocks. currently this location is also a tourist spot in mount sibolong. this is an obstacle for the preparation of sampling mollusk fossils. based on the description of the sepolong location carried out by martin (1919), it is likely that mount sibolong is a spolong type location. martin (1919) explained the location of the spolong located west of jonggrangan village. 6. paleontology data from the three observation locations, paleontological analysis has been carried out both macrofossil and microfossil. some of the fossils identified are mollusks, ostracoda, foraminifera, and coral. the complete results of the fossils identified from the three locations can be seen in table 2. specific sampling locations for ks05 were not possible due to the prohibition of taking rocks at that location. 7. stratigraphic analysis martin (1919) describes two locations representing the levels of west progo beds, namely sokkoh and spolong flowers. kembang sokkoh is described as being on the eastern slope of mount kelir located in the flow of the waterfall. meanwhile the described spatial area is to the west of jonggrangan hamlet. based on the second description of the location of martin (1919) and the findings in the field, the ks01 and ks02 locations are most likely the kembang sokkoh location. whereas the ks05 location which is to the west of jonggrangan village is the location of spolong, this is also from the resemblance of spolong and sibolong names. based on the fossil content found in the field, age analysis can be carried out from both types of locations. based on the content of mollusk fossils of haustator subulata and conus spolongensis it is thought to have early miocene age (martin, 1919). some fossils of benthic foraminifera have a very long life span, such as gyroidina soldanii (oligocene to recent), elphidium sp (miocene to recent) and quinqueloculina sp (miocene to recent). fossils ostracoda that appear also range in longevity such as laxoconcha (oligocene to recent) and dolerocypris sinensis (miocene-pleistocene). based on these fossils, it is estimated that rocks exposed in kembang soka and spolong have early miocene age. 8. discussion referring to the purpose of the study to identify the location of the west progo type, the location of the kembang soka and the spolong hill are two locations that were once studied by martin (1919). the west progo type location is arranged by martin (1919), lithostratigraphy is part of the jonggrangan formation. the name jonggrangan formation itself was first introduced by van bemmellen (1949) and placed its age in the early miocene. table 2. fossils found at the location of the kembang soka no. sample mollusk ostracoda foraminifera ks01 architetonica na na ks02 haustator subulata loxoconcha nonion lncisum cushman conus spolongensis dolerocypris sinensis elphidium sp melanoides sp bythocypris ozawaia tongaensis pyrgo bradyi quinquelaculina sp gyraidina soldanii cibicides sp nodosoria sp a b pandita.h & hartono / jgeet vol 04 no 02/2019 82 the results of this study indicate that the age of the two locations, kembang soka and sibolong showed an estimate in the early miocene. this condition is the same as that proposed by martin (1919) and also van bemmelen (1949). however, the determination of the age of the two outcrop locations still needs to be strengthened by another age analysis. this is because the paleontological data used for analysis still has a long range, namely miocene to resen. two methods that need to be used are radiometric dating and nannoplankton. 9. conclusion overall data from the results of the study succeeded in re-identifying the location of the type of mollusk fossil discovery from the west progo level compiled by martin (1919). both locations are located in kembang soka and spolong hill. there is an addition of paleontological data in the form of ostracoda, although it needs to be examined in more detail. the stratigraphic position can also be determined namely in the early miocene with its lithography as part of the jonggrangan formation. acknowledgement paper is part of the research on competency based research in the form of basic research funded by dipa kopertis wilayah v with a decree number 3 / e / kpt / 2018. thank you to the ministry of research and higher education for funding. not to mention also to the sttnas p3m who had facilitated this research in reporting and drafting proposals. references kadar d, 1986, neogene planktonic foraminiferal biostratigraphy of the south central java area indonesia, geological recearch and development centre, bandung. kase, t., kitao, f., aguilar, y.m., kurihara, y., pandita, h., 2008, recontruction of color markings in vicarya, a miocene potamidid gastropod (mollusca) from se asia and japan, paleontological research, vol. 12, no. 4, pp. 345 353, paleontological society of japan. kase, t., kurihara, y., aguilar, y.m., pandita, h., fernando a.g.s., and hayashi, h., 2015, a new cerithioidean genus megistocerithium (gastropoda; mollusca) from the miocene of southeast asia: a possible relict of 19(4):299-311. the palaeontological society of japan, http://dx.doi.org/10.2517/2015pr013 martin, k., 1919, unsere palaeozoologische kenntnis von java, mit einleintenden bemerkungen uber die geologie der insel, 158 pp., 4 pls. e. j. brill, leiden oostingh, c. h., 1938, mollusken als gidsfossielen voor het neogeen in nederlandsch-indie, handelingen van het achste nederlandsch-indisch natuurwetenschap-pelijk congres gehouden te, soerabaja van 20-23 juli 1938, pp. 508-516. pandita, h., dan zaim, y., 2009, paleoekologi formasi pucangan di daerah kabuh ditinjau dari kandungan fosil moluska, prosiding seminar nasional retii ke 4, sekolah tinggi teknologi nasional yogyakarta. pandita, h., zaim, y., aswan, dan rizal y., 2013, relationship of biometrical aspect of turritellidae with geochronological aspect in west java, international journal of geoscience, vol. 4, no. 4, scientific research publishing. pringgoprawiro,h. dan riyanto, b. (1988), formasi andesit tua suatu revisi, bandung inst.technologi, dept.geol.contr., 1-29. purnamaningsih, s. dan pringgoprawiro, h. (1981), stratigraphy and planktonic foraminifera of the eocene-oligocene nanggulan formation, central java, geol.res.dev.centre pal.ser. bandung,indonesia, no. 1, 9-28. rahardjo, w., sukandarrumidi, dan rosidi, h.m.d., 1995, peta geologi lembar yogyakarta, jawa, pusat penelitian dan pengembangan geologi, bandung. soeria-atmadja, r., maury, r. c., bellon, h., pringgoprawiro, h., polves, m., and priadi, b; tertiary magmatic belts in java, journal of southeast asian earth science, 9, pp. 13-27 (1994). sopaheluwakan j. (1994), critiques and a new perspecrive on basement tectonic studies in indonesia : a review of current results and their significance in geological exploration, prosiding tridasawarsa puslitbang geoteknologi lipi, ii, 163-175. van bemmellen, r.w., 1949, the geology of indonesia. the hague, martinus nijhoff, vol. ia. van den hoek ostende, l. w., leloux, f. p. j., wesselingh, f& winkler prins, c. f., 2002, cenozoic molluscan types from java (indonesia) in the martin collection (division of cenozoic mollusca), national museum of natural history, leiden van es, l.j.c., 1931, the age of phitecanthropus, the hague martinus nijhoff, pp 122. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. the objectives 3. methods 4. regional geology 4.1 physiography 4.2 stratigraphy 5. data and analysis 5.1 ks01 location 5.2 ks02 location 5.3 ks05 location 6. paleontology data 7. stratigraphic analysis 8. discussion 9. conclusion acknowledgement references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 yuskar, y and choanji, t/ jgeet vol 02 no 01/2017 14 uniqueness deposit of sediment on floodplain resulting from lateral accretion on tropical area: study case at kampar river, indonesia yuniarti yuskar 1, *, tiggi choanji 1 1 department of geological engineering, universitas islam riau, jl. kaharuddin nasution no 113 pekanbaru, 28284, indonesia. abstract kampar rivers has a length of 413 km with average depth of 7.7 m and width of 143 m. sixty percent of this rivers are meandering fluvial system which transport and deposit a mixture of suspended and bed-load (mixed load) along low energy. river channel that moving sideways by erosion is undergoing lateral migration and the top of the point bar becomes the edge of the floodplain and the fining-upward succession of the point bar will be capped by overbank deposits of kampar bend migration on the suspended-load channels of kampar watershed. this formation consist of succession of fine to medium sand and silt/mud, with root traces, that form as drapes on the prograding bank. these beds dip mostly channel model is presented showing how -grained within channel deposits in -bar deposits containing alternating sandstone and shale sequences are common in the lowespecially kampar rivers. keywords: kampar rivers, lateral accretion, floodplain, meandering, depositional model. 1. introduction meanders develop by erosion of the bank closest to the thalweg, accompanied by deposition on the opposite side of the channel where the flow is sluggish and the bed-load can no longer be carried and river is considered to be meandering if there is accumulation of sediment on the inside of bends. meandering rivers transport and deposit a mixture of suspended and bed-load (mixed load) a long low energy. the bed-load is carried by flow in the channel, with the coarsest material carried in the deepest parts of the channel. finer bed-load is also carried in shallower parts of the flow and it is deposited along the inner bend of a meander loop where friction reduce the flow velocity (nichols, 2009). type of sediment is formed by meandering pattern are channel deposit, point bar, natural leeve, floodplain, oxbow lake, and crevasse splay. the relative contribution of a variety of accretion deposits to the formation of meandering river floodplains have been the subject of prolonged discussion in the geomorphological literature (page et al., 2003). a channel moving sideways by erosion on the outer bank and deposition on the inner bank is undergoing lateral migration and the deposit on the inner bank is point bars and it will show finingup from coarser material at the base to finer at the top (nichols, 2009). migration of meanders produces a general fining-upward point bar deposits and, in turn silty and muddy floodplain deposits (allen, 1965; boggs, 2005). multiple episodes of meander migration produce vertical stacking of fining-upward succession in meandering-river deposit (boggs, 2005). floodplains are dynamic feature that co-evolve with channel so at present no universal theory is available to predict floodplain width in natural rivers (as a function of drainage area, bank-full discharge, or sediment flux, etc) because floodplain morphology dynamically integrates across these and the other factors, over some unconfined time interval in the environment history of the watershed (belmont, 2011) .in this study we focus on floodplain deposit resulting from lateral accretion surface at river bend of kampar kanan river, riau province. lateral accretion surfaces are most distinct when there has been an episode of low discharge allowing a layer of finer sediment to be deposited on the point bar surface (allen, 1965; bridge, 2003; collinson, j.d.; mountney, n ; thompson, 2006; nichols, 2009). * corresponding author : yuniarti_yuskar@eng.uir.ac.id tel.:+62-821-6935-4941 received: feb 1, 2017. revised : 15 feb 2016, accepted: feb 20, 2017, published: 1 march, 2017 doi: 10.24273/jgeet.2017.2.1.12 mailto:yuniarti_yuskar@eng.uir.ac.id yuskar, y and choanji, t/ jgeet vol 02 no 01/2017 15 2. overview of kampar river one of the meandering river system in the riau province, indonesia is the kampar river. kampar river on the island of sumatra in indonesia originates in the mountainous bukit barisan of west sumatra, and empties into the malacca strait on the island's eastern coast. the river is the confluence of two big tributaries are kampar kanan river and kampar kiri river. the tributaries meet in the langgam subdistrict, pelalawan regency, before flowing into the malacca strait as the kampar river. koto panjang, an artificial lake upstream of the river, is used to power a hydroelectric generating plant. study area is located in one of the kampar kanan river bends at buluh china village, kampar district, riau province, indonesia (fig 1). the river has a lenght of 413 km and an average depth of 7.7 km and average width of 143 m. fluvial meander system develop typical morphology that oxbow lake with tropical rain forest, sand bar and river with fishery product. it has been used as a local attraction. this study is one of the appreciation of buluh cina village community that has been keeping the forest and natural conditions so this area can be used as one of the geo-tourism in the riau province. 2.1. geomorphic and geological setting buluh cina village is plain area with an elevation of 2 6 m above sea level. the landscape of study area is characterized mainly by active channels, abandoned channels , natural leeve, backswamps and floodplain. the study area is the floodplain of kampar kanan river, so this area will flood if higher rainfall. distribution of geomorphic feature throughout the tudy area suggests that the landforms were developed mostly during quaternary. along the kampar kanan river is deposited young alluvium (qh) during holoceneaged. young alluvium (qh) are consist of gravels, sands and clays. fig 1. location of study area. the stratigraphy formation in the buluh cina village are older alluvium (qp) aged pleistocene to holocene. this sediments are consist of gravels, sands, clays, vegetation rafts and peat swamps (clarke, m.c.g; kartawa, w.; djunuddin, a.; suganda, e.; bagdja, 1982). most of sand deposit along kampar kanan river has become mining site location, whether they have permission or illegally. this activity not only will affects the deposition process that happen naturally in the river, but also affects the river biota, tourism and water resources become damaged due to the mining. morphological changes is forming in the kampar kanan river happen because of natural leeve (riverbank) erosion and sand mining, it make sliding riverbank and deepening of the riverbed. 2.2. floods buluh cina area located as floodplain area from kampar kanan river. this water are provided from large catchment area up to 5.321 km2 came from gadang mountain and surroundings, with debit of water about 700 1000 m3/s and relative slope 0,0008. in headwater part, there are hydroelectric power plant at koto panjang that built beside for electricity, and also to control volume of water. if the top side area and the dam of power plant cannot endure it, the condition will become a big flood that will be affected to this area. and this event has happened in january 2016, which the water of the river rising about 3 m from the condition at dry season, and flooding all the area. 3. methodology data that used for this research consist of three data location of trench (tr-01, tr02, and tr-03), two drilling data (bc-01 and bc-02), and satellite image from landsat. the methodology for this study are consist of several steps and measurement, starting from scouting field surveys to check condition and to mark the drilling position, and then continued doing trenching at three position which located 2 m and 400 m away from the river. some of them are already excavated and exposed, and revealed a 1 2 m thick sequence of sediment. drilling also conducted at two location up to 5 m depth using hand auger for coring, located 5 m from river and 400 m away from the river. this drillng data will provide a better visualization of the texture of sediment from bottom to top of the layer. all of sediment that taken from trenching and drilling, will be analyze with sieve analysis by using mesh from 2.38 mm, 1.19 mm, 0.6 mm, 0.297 mm, 0.149 mm, and 0.074 mm to measure the weight each grain size and define the dominate grain size in every layer collected from field. interpretation of satellite image are using landsat image from april 1989 until april 2016. this image provide visual image to seek the geometrical changes of the river, and interpret the migration of the channel, and also correlate it with field survey data. 16 yuskar, y and choanji, t/ jgeet vol 02 no 01/2017 4. lateral accretion and floodplain deposit 4.1 lateral accretion deposit on kampar kanan river at buluh cina village based on the comparison of satellite image data in 1989 and 2016, it shows a migration of the channel that occured in kampar kanan river that located near the buluh cina village (fig 2). the basic dynamics of flow around meanders leads to erosion on the outside parts of bends and deposition on the point bars. helical flow transport sediment, eroded from the cut bank, across the stream along the bottom and deposits it by lateral accretion on the point bar (boggs, 2005). as the channel migrate the top of the point bar become the edge of the floodplain and the fining-upward succession of the point bar will be capped by overbank deposits. fig 1. (a) satellite image that showing geometrical changes the position of the river and image of point bar as result from river migration, and (b). erosion at the nothern side of the river. field observations indicate that lateral accretion consists of a point bar, oblique accretion and overbank deposit. sediment of point bar deposited medium sand with good sorting and upwardsfining couplets during flood events. some flood channels become enlarged during floods, and may become the dominant channel (wood et al., 2008). oblique accretion sediment is defined here as the lateral accumulation of fine-grained floodplain deposit by progradation of a relatively steep convex bank in assosiation with channel migration (page et al., 2003). oblique accretion are developed on the meandering low energy rivers of kampar kanan river. the presence of oblique-accretion deposits in buluh cina floodplain was demonstrated by preliminary investigations at natural bank exposure, coring to a depth 5m, and trenches excavated at kampar kanan rivers. when the point bars occur, oblique accretion deposit occupy that part of the convex bank directly above at the point bar (page et al., 2003). at site oblique-accretion layers consist of sand, muddy fine sand strata dipping conformably with bank surface (fig 3). dip angles vary from near horizontal at the top and the bottom to less than 150 while at the bottom, there are point bar deposit with dip angle more than 150. (fig 3). on trench location (tr-01 and tr-03) shows very fine to fine sand sediments, root plant on the top and bioturbation on the top layer. it indicates as oblique accretion deposit. the decreasing rootplant and bioturbation and sediment with medium sand on the bottom layer and it indicates as point bar deposit (fig 4). on tr-02 (trench) location consist of very fine sediment at the bottom of the layer (125 75 cm) which indicates an oblique accretion deposit, and then silt mud with 75 m thick that interpret as overbank deposit (fig 5). the boundary between silt and fine sand are gradual contact which affected from different grainsize and hardness, and also activity of organism and pedogenesis. overbank sediment deposited on a floodplain was identified in the field using standard criteria (allen, 1965; brown, 1987; guccione, 1993). it was distinguished from channel deposits and colluvium by general lack of gravel, the lateral fining of texture with increasing distance from the channel and general lack of bedding , except proximal to channel (guccione, 1993). yuskar, y and choanji, t/ jgeet vol 02 no 01/2017 17 fig 3. deposit at western side of the river meander which shows sand bar deposit at bottom position with relative steep slope and deposit of oblique accretion at top with gentle slope than sand bar deposit. fig 2. deposit of lateral accretion which characterize with fine sand sediment at two different location ( tr-01 and tr-03). fig 5. succession at trench (tr-02) that shows oblique accretion on bottom of the layer and overbank deposit at the top. 18 yuskar, y and choanji, t/ jgeet vol 02 no 01/2017 based on sieve analysis from tr-01, tr02, and tr-03, considered from two different deposit shows that medium sand dominate at the bottom and very fine to fine sand sediment dominate at the upper part (fig 6). fig 3. sieve analysis that shows percentage of grain size distribution of each layer at four location (tr-01, tr-02, tr-04, and tr-05). 4.2. lateral accretion deposit on kampar kanan river at buluh cina village floodplain is a strip of land that borders a stream channel and that is normally inundated during seasonal floods. sediment is transported over the flooding as bed load and suspended load during floods. the sediment comes from the main channel, the valley sides and the floodplain itself (bridge, 2003; posamentier, roger g.; walker, 2006). based on drillling data using 5 m depth of core hand auger, it shows that floodplain formation originated from lateral accretion as sandbar, oblique accretion and overbank. sandbar deposit located at the bottom and continued with oblique accretion deposit, and covered with overbank deposit at the top. the overbank deposits are not always shown in the floodplain formation, due to erosion process. stratigraphy of this floodplain formation are showing repetitive deposit of sandbar and oblique accretion that there are two event happened in this area as shown on fig 7. fig 7. analysis stratigraphy define from core data (bc-01 and bc-02) . yuskar, y and choanji, t/ jgeet vol 02 no 01/2017 19 5. discussion based on this research, it considered that lateral accretion gives a big contribution to the formation of floodplain. this formation form two type of deposit which are sandbar and oblique accretion that form at low energy in meandering river. floods that happen periodically in this area also bring finer sediment such as silt and mud that characterize overbank deposit but not significally shown in this area. therefore, in floodplain formation, lateral accretion gives bigger contribution than vertical accretion. lateral accretion deposit characterize with fine to medium sand while overbank characterize with finer sediment (silt and clay).] the floodplain model that modified by (page et al., 2003) state that there are three models of stratigraphy produced by oblique accretion for different floodplain seetings: floodplain with point bar, floodplain with no point bar and floodplain with point bar and scrolls. based on the model, this area are include in model of floodplain with point bar (fig 8). fig 4. model of stratigraphy in study area that related with floodplain model with point bar (modified from page, et al 2003). 6. conclusion  floodplain formation in study area are related with model floodplain with point bar which consist of succession of fine sand to medium sand with steep dip beds as sandbar and fine sand with gentle dip bed as oblique accretion deposit, and silt/mud, with root traces as an overbank deposit, all of this deposit form as drapes on the prograding bank. these beds dip mostly channel wards and quickly wedge out as  in this study, showing that lateral accretions grained within channel deposits in acknowledgements we would like to say thanks to uir for all the support and the students on the department of geological engineering, faculty of engineering, universitas islam riau for helping us on this research. references allen, j.r.l., 1965. a review of the origin and characteristics of recent alluvial sediments. sedimentology 5, 89 191. doi:10.1111/j.1365-3091.1965.tb01561.x belmont, p., 2011. floodplain width adjustments in response to rapid base level fall and knickpoint migration. geomorphology 128, 92 102. boggs, s., 2005. principles of sedimentology and stratigraphy (4th edition). prentice hall. bridge, j.s., 2003. rivers and floodplains: forms, processes, and sedimentary record. blackwell publishing, malden, ma. brown, a.g., 1987. holocene floodplain sedimentation and channel response of the lower river severn, united kingdom. zeitschrift für geomorphol. 31, 293 310. clarke, m.c.g; kartawa, w.; djunuddin, a.; suganda, e.; bagdja, m., 1982. geological map of the pakanbaru quadrangle, sumatra. pppg. collinson, j.d.; mountney, n  ; thompson, d., 2006. sedimentary structure. terra publishing, london. guccione, m.j., 1993. grain-size distribution of overbank sediment and its use to locate channel positions, in: alluvial sedimentation. blackwell publishing ltd., pp. 185 194. doi:10.1002/9781444303995.ch14 nichols, g., 2009. sedimentology and stratigraphy 2nd. john wiley & sons ltd, west sussex, united kingdom. page, k.j., nanson, g.c., frazier, p.s., 2003. floodplain formation and sediment stratigraphy resulting from oblique accretion on the murrumbidgee river, australia. j. sediment. res. 73, 5 14. doi:10.1306/070102730005 posamentier, roger g.; walker, h.w. (ed.), 2006. facies models revisited. sepm society for sedimentary geology. wood, s.h., ziegler, a.d., bundarnsin, t., 2008. floodplain deposits, channel changes and riverbank stratigraphy of the mekong river area at the 14th-century city of chiang saen, northern thailand. geomorphology 101, 510 523. 1. introduction 2. overview of kampar river 2.1. geomorphic and geological setting 2.2. floods 3. methodology 4. lateral accretion and floodplain deposit 4.1 lateral accretion deposit on kampar kanan river at buluh cina village 4.2. lateral accretion deposit on kampar kanan river at buluh cina village 5. discussion 6. conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology special vol 04 no 02-2 2019 kumar, r. et al./ jgeet sp vol 04 no 02-2/2019 39 special volume geology and mineral potential of copper-silver mineralization in kulu district of himachal pradesh, india rajinder kumar 1* , surendra kumar 1 , ratikant sikdar 1 1 geological survey of india, chandigarh, india * corresponding author : rajindergsi@gmail.com tel.: +91-9313502359 received: sept 14, 2018; accepted: mar 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2127 abstract naraul formation of the larji group in kulu district of himachal pradesh contains the major strata bound copper mineralization at many places as observed through old working near naraul, danala and kanda in sainj valley of kulu district exposing the proterozoic northwestern himalayan belt. the same structural belt is also known for silver mineralisation around manikaran. at naraul, a regional stratigraphic and mineralogical framework of the naraul formation for mineralogical resource assessment was viewed. the old workings within 4-5 km long and 200-300m wide along the nwse trending structural trend cover the main ore potential zones. the ore mineralisation seems to be alike the copper silver deposit of the revett formation of montana and idaho, usa. the deposit in naraul needs further more drilling investigation and exploration for actual reserve assessment. keywords: kullu, naraul, copper deposit, sainj valley 1. introduction generally, the strata-bound copper-silver deposit contain 23 percent of all the copper silver resource and form the second important global source of these metals after the porphyry copper deposits. the naraul formation of larji group in the nw-se himalayan and the kulu group of rocks at uchich, both trending along nw-se as a belt, are known for copper mineralisation around naraul in sainj valley and silver mineralisation at uchich in parvat valley of kulu district in himachal pradesh. the copper-silver mineralisation in nw-se trending quartzite at naraul contains the most significant resource known only from the past old workings only. it may become one among the significant strata-bound cu-ag deposit. the naraul formation constituting different types of rocks like calc-quartzite, siltite, impure carbonate (limestone) and quartzite out of which the fine to medium grained calc quartzite/siltite do contains mainly the large stratabound base metal mineralization. the present study reveals that naraul-danala-kanda may contain significant copper-silver mineralisation in siltite/quartzite having a resemblance with the revett-type mineralisation of montana, usa. 2. origin of the coper-silver mineralisation the naraul formation of the larji group forms a part of the mesoproterozoic age which consists of quartzite, siltite, and argillite (very fine grained to medium grained), quartz-rich metamorphosed sedimentary deposits. the thick vertical to steep dipping beds of massive white calc-quartzite of the naraul formation showing the malachite and azurite basically form the main significant hoist for copper and other associated minerals namely silver and nickel. metals were deposited where oxidized metals bearing brine upwelled along the faults/ thrust plains as well; and migrated laterally altering the preexisting pyrite-hematite interfaces in the sediments. the ore mineralization occurs as syngenetic dissemination type in the form of specks, grains and strings of chalcopyrite, covellite, siegenite, and pyrite. the mineralization is characterized by mineralised and alternation zones which provide source and guide for minerals. regional changes in the mineral zones, thickness and grain size variation in hoist rocks and the geological structure provide evidence of fluid movements in the sediments and during formation of cu-ag deposits and provide a framework to evaluate the potential for undiscovered deposits. 3. ore-mineralization the ore minerals identified at naraul old workings include chalcopyrite, pyrrhotite, chalcocite and pyrite. potential mineralisation zones occur in two major valleys in the study area i.e. garsha valley and sainj valley. a http://journal.uir.ac.id/index.php/jgeet mailto:rajindergsi@gmail.com 40 kumar, r. et al./ jgeet sp vol 04 no 02-2/2019 number of old workings are present in the garsha valley on either side of the hill range running in the nw-se direction. the mineralisation occur in two parallel discontinuous zones which preserve & mark old working and define the mineralised parts. the old workings present in the area follow strike parallel extensions having dip wise deep extensions for manual extraction and crude mining of ore loads since earlier times. the important old workings include gobha, naraul, lalgi, kalpana, danala and dudhru. most of these are situated on steep escarpment faces and have difficult accessibility. structurally the mineralization is confined to the strata bound hoists and show remobilization and relocalisation along the pervasive structural elements. generally, disseminations, streaks and thin stringers of chalcopyrite, pyrite and specularite are reported from rocks of the naraul formation. the hosts rocks towards east on the hanging wall side consists of conglomeratic quartzite and phyllite, whereas, the hoist rocks on footwall side comprises grey phyllite and quartzite. at places, the mineralization confined to their hosts is of very sparse and sporadic nature. structurally controlled mineralization is usually localized and remobilised mineralisation is associated with the shears and fractures. few quartz veins do invariably carry mineralization. a prominent longitude shear zone along n15°w-s15°e in almost all the old workings indicates a conduit for the base metal mineralization. the old workings are confined to the calc-quartzite hoisted in naraul formation. the copper mineralisation in the gadsha valley extends from gobha in the north through naraul, lalgi, kalpana, and danala to dudhru in the south. the sporadic occurrence of the old workings at the above localities bears testimony to the extensive mining activity in the recent pasts. besides, sporadic specks dissemination and stringers of chalcopyrite and pyrite are present. malachite and azurite stains and encrustations on rock surfaces have specks, sporadic thin stringers and fine disseminations of chalcopyrite, pyrite and rarely covellite. association of massive quartzite, conglomeratic quartzite and calcareous quartzite belonging to naraul formation. a persistent linear shear/fracture along nnw-sse with small oblique shears appear to act as conduit for the mineralizing solutions. old working at gobha in massive quartzite show sparse, fine disseminations of chalcopyrite and pyrite and stains of malachite and azurite and forms the northern most old-working at 2240 msl towards northwest of naraul. the mineralization occurs along n-s trend over a length of about 50m having about six-meter width of the exposed old working. old working at naraul showing the vertical facing escarpment supports 13 old small old workings along a nnw-sse extending linear trend for over a distance of about 350 meter. the ore minerals occur within calcquartzite trending along nnw-sse strike having dips of 45° to 65° towards east. the width of mineralization zone in naraul old workings varies from 5m to 15 m among the forest cover. at places, the inner walls of old workings reveal cobalt (co) and nickel (ni) ore minerals besides copper ores. on surface, the encrustation of malachite, azurite and chalcanthite are very common. the hoist rocks at old workings around naraul show fine disseminations and thin stringers of chalcopyrite and pyrite. the samples from heaps of slag in the proximity of the nearby villages of naraul and mahun indicate the past smelting. the slag samples from mahun indicated 1.11 to 2.25% copper and samples from naraul show 1.76% copper and 0.17% cobalt. the average grade of cu is 1.11% with an average thickens of 3.86m over a strike length of 180m. moreover, minerals like cobalt and nickel with average values of 438 ppm and 243 ppm are also associated with copper (sharma, 1997). these old-workings structurally occur in the vertical escarpment face within the massive and conglomeratic quartzite. the shapes of these old workings are usually lensoidal. very sparse and fine disseminations of chalcopyrite with some pyrite were observed in these old workings. similarly, the 30 m long and ten-meter-wide old working at lalgi, two kilometre southwest of naraul old workings, on the western face of the jamir ridge also show similar features. pockets cobalt bloom and chalcopyrite were noticed observed in mine. the mineralization appears to occurs within the calcareous quartzite over a strike length of about 27 m. along ne shear zone. the base metal mineralization is richer in the portions traversed by the vein quartz within a width of 2.5 m showing chalcopyrite and malachite stains. similarly, the old working at danala and dudhru, indicate copper ore mineralization at 2400 m elevation in 90m x 45m dimension within white siltite showing high density of joints. the south-east extension of danala-dudhru old workings are traceable around naraul, phabiari, kanda and spangani in the sainj area. during regional deformation & metamorphism, the ore minerals have remobilised and are structurally controlled. 4. mineral potential the present study reveals nature of distribution of ore minerals, grain size and primary distribution and alteration of mineralogy and the stratigraphic of the naraul formation. the field observations reveal that the strata bound copper silver deposit in naraul formation, need more drill core sections to understand potential and the flow paths of the brines in the sedimentary hoists rocks where mineral recourse development must be weighed against other land-uses. this study will be a useful guide for actual mineral resource. resource assessment of the cu-ni naraul deposit needs further promising explorations in the surrounding area in nw-se structural extensions which constitutes the strata bound minor silver prospects at uchich near varshaini at manikaran in parvati valley of kulu district in himachal pradesh. the silver mineralisation at uchich is hoisted along tectogenic thrust in carb-phyllite of manikaran formation of rampur group. besides, the base metal kumar, r. et al./ jgeet sp vol 04 no 02-2/2019 41 mineralization at naraul is another such considerable strata bound deposit at naraul in kulu district of himachal pradesh. the copper (cu) content of ores varies from 0.007% to 0.95% while nickel and cobalt occur in traces. the old workings having slags from mahun indicated 1.11 to 2.25% cu (copper) and from naraul it is about 1.76% cu and 0.17% co (cobalt) (sharma, 1968;sharma, 1992). the average grade of cu is 1.11% with an average thickens of 3.86m over a strike length of 180m. moreover, minerals like cobalt and nickel with average values of 438 ppm and 243 ppm are also associated with copper (sharma, 1997). in calcareous and conglomeratic quartzite around gobha and khaniari the base metals show higher values of cu, pb, zn,co, ag,cd, and mn in stream sediments (kumar , 2005). the pyritohedron crystals of pyrite present in the sheared white quartzite indicate group-ii type of metamorphogenic pyrite deposit hoisted in the deltaic plain and lacustrine meta-sediments (murowchicka and barnses,1987). fig.1 open cast old working at lalgi mine in calcareous quartzite, sainj valley, kulu. fig.2: face of an old working showing oxide ore minerals in sheared quartzite at naraul, sainj valley, kulu. fig.3 malachite and azurite stains in calcareous quartzite of naraul formation, kanda, sainj valley, kulu. fig.4.:malachite in grey calcareous quartzite, at naraul, sainj valley, kulu. 5. discussion the ore mineralization hoisted in the proterozoic northwestern himalayan belt in the naraul formation of larji group in kulu district of himachal pradesh is known for major strata bound copper-silver mineralization as notices through old working in naraul area in gadsha and sainj valley of kulu district. the ore mineralisation seems to be alike the copper silver deposit of the revett formation of montana and idaho, usa. the old workings in naraul area are confined within 4-5 km long and 200-300m wide along the nwse trending structural trend covering the main ore potential zones in siltites. the area shows low to medium grade of metamorphogenic characters of ore minerals. the pyritohedron crystals of pyrite found in the sheared white quartzite indicates 42 kumar, r. et al./ jgeet sp vol 04 no 02-2/2019 group-ii type of metamorphogenic pyrite deposit which indicates deltaic plain and lacustrine palaeoenvironments of the metamorphosed host rocks. references kumar, r., 2005. report on geochemical mapping in parts of gadsha-naraul area, in kulu district of himachal pradesh, geological survey of india, chandigarh. murowchick, j.b., barnes, h.l., 1987. effects of temperature and degree of super-saturation of pyrite morphology, american mineralogist, 72, 1241-1250. sharma, r. k.,1968. report on mineral investigation of base metals at naraul, kullu district, himachal pradesh, geological survey of india, chandigarh sharma, r. k.,1992. report on mineral investigation of base metals at naraul, kullu district, himachal pradesh, geological survey of india, chandigarh sharma, r.k.,1997. report on mineral investigation of base metals at naraul, kullu district, himachal pradesh, geological survey of india, chandigarh. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. origin of the coper-silver mineralisation 3. ore-mineralization 4. mineral potential 5. discussion references cover front jgeet.cdr journal of geoscience, engineering, environment and technology special edition volume 4. no 2-2. june 2019. p 1-59 issn (print) : 2503-216x issn (online): 2541-5794 uir press p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually our journal has accredited as a scientific journal (s2) by the ministry of research, technology, and higher education no 30./e/kpt/2018 period : 2017 2021 scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. sabah a. ismail (iraq) editorial member dr. kurnia hastuti (indonesia) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. eng. takahiro 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(indonesia) dr. sapari dwi hadian mt (indonesia) dr. emi sukiyah st., mt (indonesia) bambang setiadi ph.d (indonesia) dr. vijaya isnaniawardhani (indonesia) dr. anas puri s.t, m.t (indonesia) mirza muhammad waqar, m.sc (pakistan) good fried panggabean, s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) yuta izumi m.eng (japan) kageaki inoue, m.eng (japan) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) yuta izumi, m.eng (japan) yuniarti yuskar s.t, m.t (indonesia) muhammad zainuddin lubis s.ik m.si (indonesia) pakhrur razi, s.si, m.si (indonesia) babag purbantoro, s.t, m.t (indonesia) budi prayitno s.t, m.t (indonesia) joko widodo, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing special volume 04 no 02-2 2019. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content geology, geomorphology and tectonics of india: introduction ...................... 1 geochemistry and tectonic setting of the supracrustal rocks from the central part of the bundelkhand craton, india ............................................................ 3 neoarchean crustal shear zones and implications of shear indicators in tectonic evolution of bundelkhand craton, central india ................................. 11 geometric and strain analyses in folds of the area around gankot, district pithoragarh, uttarakhand, india ..................................................................... 19 geochemistry and geodynamic setting of paleoproterozoic granites of lesser garhwal himalaya, india ................................................................................. 28 geology and mineral potential of copper-silver mineralization in kulu district of himachal pradesh, india. ............................................................................ 39 new observations of tin mineralization potential vis-à-vis ore petrographic, alteration and geochemistry in the southeastern part of bastar craton, central india ................................................................................................... 43 geology of south and southwest part of uttar pradesh and its mineral significance .................................................................................................... 51 1: front cover page 2 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 4 2022 martania, d.r. et al./ jgeet vol 7 no 4/2022 167 research article identification of potential geotourism destination in the river subayang areas of kampar, riau, indonesia dwita rega martania 1, mira hafizhah tanjung2, adi suryadi3 1departement of urban and planning, faculty of engineering, universitas islam riau, jl. kaharudin nasution.no 113 pekanbaru, 28284, indonesia 2departement of geological engineering, faculty of engineering, universitas islam riau, jl. kaharudin nasution.no 113 pekanbaru, 28284, indonesia * corresponding author : martaniadwita@gmail.com tel.:+6281275162829 received: aug 29, 2022; accepted: nov 21, 2022. doi: 10.25299/jgeet.2022.7.4.10394 abstract the readiness of an area to be able to develop tourism potential as geotourism is seen from various aspects, including the existing geological heritage, as well as the enthusiasm of the local community which is the main focus in creating good geotourism, while the government acts as the main mover. in kampar regency, riau province, to be precise in the sushadow river area, the rimbang balling area located in the kampar kiri hulu sub-district, there are natural attractions that the subayang river passes through, in addition to the river being so clear, upstream we can find a stone wall waterfall, possibly having a waterfall. this paper, shows the potential of geotourism froum various aspects of geomorphology and community life, such as economic, social, cultural and infrastructure and discusses the role of society and sectors as tourism actors in subayang river using the rap-fish method. geotourism studies can be drawn from various integrations of existing theories, conceptual analyzes and practices of nature-based tourism and closer collaboration with relevant social sciences so that they can play a role in the promotion of tourism among the public and professionals. keywords: geotourism, suistanable, subayang river. 1. introduction tourism destinations are developed from geographic areas which include tourism products, services, communities and institutions that all support the potential for tourism development and attract tourists to come to the place (saeroji et al., 2018; yacob et al., 2019; wisudawati et al. , 2020). tourism can increase public awareness to preserve the environment as an effort to increase economic value through tourist villages (yacob et al., 2019) (irham et al., 2021). as it is a relatively new concept in the tourism industry (heggie, 2009, p. 257), there are two main approaches to the definition of the term, as either geological or geographical tourism (dowling, 2013, p. 62). hose defined geotourism as, “provision of interpretative facilities and services to promote the value and societal benefit of geologic and geomorphologic sites and their materials, and ensure their conservation, for the use of students, tourists and other recreationists”. the latter approach has been characterized by national geographic society. according to the association, the prefix geo in geotourism is related to geography and does not necessarily relate to geology or geomorphology. geotourism is relatively a new concept in a young stage, approximately two decades years old. however, it has become one of the most important tourism activities performed at geological and geomorphological sites. it is seen as a part of sustainable tourism, as its main objectives are to contribute to natural, social and economic environments of geosites and to provide conservation awareness of these places, as well as to create tourist satisfaction (prof and tetik, 2016). geotourism utilizes geological heritage as its attraction by being supported by tourism facilities and infrastructure which aims to fulfill geotourism needs as long as they are in geotourism destinations. geotourism is a concept that was developed in the 1990s, understanding geotourism in research refers to the process and form of geology supported by various tourist facilities for geotourism, geotourism refers to two components, namely geo components related to geological, geomorphological and natural resource features and processes involving tourism activities through tourist visits to geological sites with the main goal for recreation, wonder, appreciation, and learning (wulung et al., 2019). geotourism also promote wider awareness of geoheritage and its values beyond the geoscience community as a means to gain support for geoconservation at a time when sustainable development and ecoor nature-based tourism were attracting increasing attention (gordon, 2018). geotourism is sustainable tourism with a primary focus on geological features, which promotes environmental and cultural understanding, appreciation and conservation, and it is locally beneficial, and is a form of activity special interest tourism whose main focus on the geological features of the earth's surface as well as those contained therein in order to encourage understanding of environment, nature and culture, more further as a form of appreciation, and activities conservation, as well as having a concern for preservation of local wisdom. (hermawan, 2018). geotourism has been added to the mix of sustainable tourism approaches. the common principles across these sustainable tourism frameworks are the respect for the resource base and the environment as well as for the host country and local residents, while providing meaningful and rewarding visitor experiences (christian, 2018) the government should also tend to be an active participant in indigenous tourism, which has a role in meeting the needs of the community. the media are also a major player in the indigenous tourism system. indigenous tourism is influenced by trends in the economic, social, political and physical world. http://journal.uir.ac.id/index.php/jgeet 168 martania, d.r. et al./ jgeet vol 7 no 4/2022 these trends represent external influences that are largely beyond the control of the local or global tourism industry (butler, 2007) (vieira, 2018). the readiness of an area to be able to develop tourism potential as geotourism is seen from various aspects, including the existing geological heritage, as well as the enthusiasm of the local community which is the main focus in creating good geotourism, while the government acts as the main mover. in kampar regency, riau province, on the subayang river, the rimbang balling area in the kampar kiri hulu subdistrict covers 12 villages, from tanjung belit village to gema village. there are natural attractions in 3 villages that the subayang river passes, besides the river is so clear, and the scenery is beautiful, in the upper reaches of the river we can find the batudinding waterfall. in addition, various existing traditions are still carried out every year so that it adds to the value of the beauty of the subayang river. the natural beauty and uniqueness of the subayang river area, may have the potential to make subayang a geotourism in riau province. therefore, this study aims to identify geotourism potential in subayang river and through this paper, a more in-depth analysis is carried out on the potential of the subayang river as geotourism, both in terms of geology, as well as spatially as well as from a social and economic perspective. so that it will be known the potential and feasibility of the subang river as a sustainable geotourism destination and maintain local culture, and can encourage the improvement of the economy of the community around the subayang river. 2. the distribution of tourism in the subayang river area the existence of a tourist area must be based on sustainable function based on its development with emphasize development aspects sustainable, regional development tourism is not a stand-alone system,but is closely related to the system other development plans inter-sectoral and inter-regional. the development of tourism areas must based on conditions and carrying capacity with the intention of creating interaction mutual long term profit among achievements tourism development goals, improvement of community welfare local, and sustainable carrying capacity environment in the future (subhadra & nadra, 2006). one of the priority elements in an economic plan is that an area or country has sufficient clean water to support its people and maintain water quality for the needs of the city, industry and energy. water is also a major component in carrying out life processes, about 3% of electrical energy is used to carry water in the quota required for utilization. even a country cannot be said to be independent if it does not have sufficient water. (bamba bukengu muhaya et al., 2017) from historical perspective, the protection of biotic components of nature had the priority. geological and geomorphological elements of nature were considered to be more resistant and less vulnerable than other elements of the environment (reynard and coratza 2007; farsani et al. 2014). geotourism, which claim educational, preservative and economic justification, must find its place in the already formed system of territorial nature and landscape protection. geotourism emphasizes the biotic component, notes the characteristics of the landscape, even the character of the historic settlement as a subject of protection. this does not mean complete absence of references to abiotic values and specific values of geological heritage. protection of the nature also means care for ecosystems (tourism, 2016). some of the sites are already exploited for geotourism purposes, but some of them (despite its potential) are not. in specific cases, the exploitation for geotourism and recreational purposes is not in accordance with conservation strategies, (kubalíková et al., 2021) there are some conflict between geotourism and geoconservation similar to those identified by williams et al. (2020). 2.1 camping area the camp area is located around the edge of the subayang river, especially on holidays and weekends, the subayang river will be filled with tents that have been provided by the tour manager, in the morning our eyes will be spoiled with dew covering the hills in the villages around the river. subayang which can be seen from the river, and the clear and beautiful water of the subayang river. fig 1. subayang river camping area 2.2 batudinding waterfall geotourism initiatives implemented outside. a study conducted by gladfelter and mason in yosemite national park concluded that while geotourism projects have the potential to influence visitor patterns and congestion problems in popular national parks and can make a positive contribution to stakeholder engagement, they can also increase environmental impact.(ólafsdóttir and tverijonaite, 2018) batu wall waterfall is located in tanjung belit, kampar regency, has a natural beauty that is not owned by other districts. this waterfall is located a little hidden and access to it can only be reached by foot. the scenery of batu wall waterfall is very beautiful surrounded by heterogeneous forest areas. batu wall waterfall can spoil tourists who come here with its cold, clear and fresh water with a depth of about 4 meters. batu wall waterfall can be accessed via the sushadow river by boat which is also provided by the tour manager. fig 2. batu dinding waterfall seen from the subayang river 2.3 cultural festival the tourism potential of an area does not only depend on the number of building sites, or artifacts, but is also supported by cultural heritage (intangible) and cultural identity. the interaction of the two dimensions between urbanization and eternal culture is an inspiration for reflection (jansen-verbeke, martania, d.r. et al./ jgeet vol 7 no 4/2022 169 2008: 128). according to the official definition, a geotourism is not just about geology, but includes the relationship between its geological features and all other aspects of the natural, cultural and intangible heritage of the area. the word 'geotourism' has no official definition, but often refers to a new type of tourism connected with geoparks, which pursues sustainable local economic development. (nishitani et al., 2021). in addition, geotourism is also side by side with stories from the community. every year or every 6 months, cultural festivals are held in the subayang river area, such as performances of regional dances, harvesting fish in lubuk ban with traditional rituals and various other cultural performances. fig 3. batu dinding waterfall 3rd level fig 4. top level batu dinding waterfall fig 5. taking fish with tradition rituals 2.4 subayang river odum (1996) states that rivers are flowing waters (lotic) which are characterized by direct and relatively fast currents, with speeds ranging from 0.1 to 1.0 m/second, and are strongly influenced by time, climate, landscape (topography and slope). bedrock type and rainfall. rivers as reservoirs and distributors of water coming from the upper upstream areas, will be greatly affected by land use and the extent of watersheds, so that the effect will be seen on the quality of river water. river water quality is affected by all activities man. (wulandari et al., 2018). fig 6. art show in cultural festival every year fig 7. semah rantau tradition fig 8. subayang river area fig 9. subayang river area to the batu dinding waterfall 3. methods 3.1. research area this research located at 01°00’40” n 00°27'00”' s and 100°28'30” 101°14'30” e and is traversed by the equator 170 martania, d.r. et al./ jgeet vol 7 no 4/2022 or the equator which lies at latitude 0°. kampar regency consists of 21 sub-districts. fig 10. map of study area one of them is the kampar kiri hulu sub-district. this research is located in kampar kiri hulu district, which has an area of 85,000 hectares and 24 villages (bps kabupaten kampar, 2020) and the author's case study in this study is only around the subayang river which is located in the village of gema and tanjung belit. fig 11. regional geological maps of kampar distric fig 13. kampar district slope map kampar kiri hulu sub-district has an area of 85,000 hectares and 24 villages. the village with the largest area is kota lama village with an area of 8,400 hectares. in 2017, kampar kiri hulu district had the highest number of rainy days in january as many as 20 days. while the highest rainfall occurred in november, namely 363 mm. kampar kiri hulu district is dominated by a fairly low slope between 25% to 45% 2.5 rapid appraisal (rap) method for the potential model of the subayang river geotourism (rap-geotourism in this study, the rap+mds application was developed for aspects of geodeversity, biodeversity and cultural diversity, so it is called rap-geotourism in evaluating the sustainability aspects of the geotourism potential in the martania, d.r. et al./ jgeet vol 7 no 4/2022 171 research area. the stages in this study to analyze rapgeotourism were carried out through several stages, namely (anna et al., 2018). (pratama, rahman aulia, 2020) rapfish analys stages as referring to the guidelines operational rapfisheries analysis stage includes steps: a. evaluate and determine attributes of three dimensions tourism area sustainability mandeh (ecology, economics, and social) (attribute review) b. give an assessment of each attribute that has been compiled from each dimension in the scale ordinal 0 3. c. calculate index value and rate sustainability status d. determining the lever (leverage factor) e. assessment of accuracy (goodness of fit) in order to determine the dimensional accuracy and dimensional assessment f. monte carlo analysis use predict the effect of level random error (random error) on model generated from analysis multi-dimensional scaling the rap-rice ordination technique through the multi dimensional scaling (mds) method is a statistical technique that tries to transform multidimensional into simpler dimensions (fauzi and anna, 2005). 2.6 rapid appraisal (rap) method for the potential model of the subayang river geotourism (rap-geotourism) the analytical method in this study uses : (1) the rap-rice ordinance technique through the multi dimensional scaling (mds) method to assess the index and identify potential geotourism aspects in the subayang area, rimbang baling and its sustainability, as well as identify sensitive attributes that affect the sustainability index in each area. -each dimension through leverage analysis, and (2) prospective analysis to determine the dominant potential that greatly influences the feasibility of subayang as a geotourism in riau province. each dimension is represented by a variable or attribute. 2.7 live observation there are main principles in geotourism (wulung et al., 2019) , namely: 1. geotourism can encourage economic feasibility,increase community and geoconservation (sustainable). 2. geotourism is an attraction for people who want to interact with the earth's environment in developing knowledge, awareness and appreciation (geologically informative). 3. local communities can be involved in geotourism activities through the provision of knowledge (interpreters), services, locally beneficial facilities and products; and 4) security, comfort, informative, experience, and service must match or exceed the visitor's realistic expectations (geotourist satisfaction in). assessment of geoheritage assets, values and benefits within a cultural ecosystem services framework can enable a more holistic approach to geotourism which acknowledges the connections between people, geoheritage and the landscape. as such, adhering to good geoethical practice is an essential element of geotourism both for providers and for participants (ólafsdóttir, 2019). in this study, 5 dimensions will be analyzed consisting of ecology, economy, social institutions, and infrastructure / technology. determination of attributes on each dimension of ecology, economy, socio-culture, technology and as well as institutions refers to indicators from rapfish (kavanagh ; 2001), tesfamichael and pitcher (2006), fauzi and anna (2002) which are modified. these data are included in primary data and are carried out using observation methods and direct measurements in the field, while secondary data are both in the form of quantitative data and qualitative data. obtained from all information relating to several agencies. rap-geotourism analysis was carried out in 2 villages, namely: gema, and tanjung belit,. table 1. dimensions used to identify geotourism potential 3.5 scoring scoring analysis for the rap method for the potential of the subayang geotourism. in this study, the rap geotourism dev application was developed to identify existing standards with conditions of existence in the geotourism area. for each attribute of the overall 5 dimensions the score is estimated, namely a score of 3 for good condition (good), 0 means bad (bad) and between 0-3 for conditions between good and bad. the definitive score is the mode value, which is analyzed to determine the points that reflect the position of sustainability relative to the good and bad points using the mds statistical ordinance technique. (anna et al., 2018). determination of geological resource potential. the index of geological resource potential in the sushadow river geotourism area has a range between 0-100% where 0% is the worst condition "bad" and 100% the best condition is "good''. fauzi and anna (2005), divide the status of the sustainability index value into 4 categories: unsustainable “poor : not continuous” has a range of 0-25, less sustainable “less sustainable” between 25.01-50, fairly sustainable “quite sustainable” the value range is 50.01-75 and "very sustainable" with a value of 76-100. giving value to 5 attributes provides an overview of the condition of the sustainability of geological resources, whether good or bad in the sushadow river area, kampar regency, riau province. 3. result dimensions attribute geology water resources (rainwater, river water, groundwater) natural disaster ecology biodiversity (animals, plants) environmental conservation social cultural diversity community demographics (total population, population density, population classification by gender, population classification by age group) community education type of community work public perception institution legislation regional spatial planning (provincial rtrw, regency rtrw, exsisting condition of land use, mining vusiness area role of government (central government agencies, provincial government agencies, district government agencies) the role of college the role of private sector non-governmental organization economy geological diversity (geotourism, education) resident income infrastructure supporting infrastructure (status, function and condition /technology of roads, and other supporting infrastructure) 172 martania, d.r. et al./ jgeet vol 7 no 4/2022 the current of the subayang river is not too heavy and the depth can still be reached by adults in general. along the river, there are large rocks on the right and left sides of the river until it finally reaches the rock wall area. these rocks occur due to the natural process of sedimentation. from the results of the table above, several parameters of statistical test results such as stress values and coefficients of determination indicate that the rap-geotourism method is quite well used to assess the potential and feasibility of the subayang river area, kampar as a geotourism. 4.1 rap-geotourism ordinance analysis of potential geotourism in the subayang river area in a geological perspective table 2. rap-geotourism ordinance analysis in geological prespevtive index status geological 66,64 quite suistainable stress : 0,14 r2 : 0,95 fig 14. rapfish chart geological sustainable dimensions fig 15. rapfish chart geological sustainable dimensions monte carlo scatter plot judging from the calculations above, from the geological dimensions, namely, groundwater, river water, disasters, to rocks, the subayang river has the potential to become geotourism in riau province. 4.2 rap-geotourism ordinance analysis of potential geotourism in the subayang river area in a ecological perspective table 3. rap-geotourism ordinance analysis in ecological prespevtive index status ecological 74,75 quite suistainable stress : 0,13 r2 : 0,95 fig 16. rapfish chart ecological sustainable dimensions fig 17. rapfish chart ecological sustainable dimensions monte carlo scatter plot -60 -40 -20 0 20 40 60 0 50 100 150 o th e r d is ti n g is h in g f e a tu r e s geological sustainability 2d rapfish ordinations (median with inter-quartile error bars (50% of scatter) -60 -40 -20 0 20 40 60 0 50 100 150 o th e r d is ti n g is h in g f e a tu r e s geological sustainability rapfish ordination monte carlo scatter plot -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s fisheries sustainability rapfish ordination (median with error bars showing 95%confidence of median) -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s fisheries sustainability rapfish ordination monte carlo scatter plot martania, d.r. et al./ jgeet vol 7 no 4/2022 173 in the waters of the subayang river there are 22 types of vegetation, 81 types of plankton and 24 types of benthos with different diversity index values from the 3 stations observed. the highest index of vegetation diversity was in tanjung belit village with a value of 2.511, while the highest index of plankton and benthic diversity was in batu songgan village with values of 3,342 and 2,682, respectively. (wulandari et al., 2018) 4.3 rap-geotourism ordinance analysis of potential geotourism in the subayang river area in a social perspective table 4. rap-geotourism ordinance analysis in social prespevtive index status social 55,39 quite suistainable stress : 0,15 r2 : 0,94 fig 18. rapfish chart sociall sustainable dimensions fig 19. rapfish chart social sustainable dimensions monte carlo scatter plot from the results of the calculations above, from the social dimension of the surrounding community, the subayang river is quite potential even though the value is considered low in the "quite potential" circle. 4.4 rap-geotourism ordinance analysis of potential geotourism in the subayang river area in a institution perspective table 5. rap-geotourism ordinance analysis in institution prespevtive index status institution 46,97 less suistainable stress : 0,15 r2 : 0,94 fig 20. rapfish chart institution sustainable dimensions fig 21. rapfish chart institution sustainable dimensions monte carlo scatter plot -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s social sustainability rapfish ordination (median with error bars showing 95%confidence of median) -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s social sustainability rapfish ordination monte carlo scatter plot -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s institution sustainability rapfish ordination (median with error bars showing 95%confidence of median) -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s intitution sustainability rapfish ordination monte carlo scatter plot 174 martania, d.r. et al./ jgeet vol 7 no 4/2022 seen from the results of the calculations above, the institutional dimensions do not have the potential for geotourism sustainability, because there is still a lack of roles from various sectors 4.5 rap-geotourism ordinance analysis of potential geotourism in the subayang river area in a economy perspective table 6. rap-geotourism ordinance analysis in economy prespevtive index status economy 61,20 quite suistainable stress : 0,14 r2 : 0,95 fig 22. rapfish chart economy sustainable dimensions fig 23. rapfish chart economy sustainable dimensions monte carlo scatter plot sustainability tourism is a complex system that is connected with social systems, environmental access to resources and ecology through tourism activities and actions done. tourism is one of the largest industries that lies in services and production that provide high economic returns. (fennell, 1999) (khattab and haggar, 2015). from the results of the calculation of the economic dimension, the subayang river is quite sustainable and feasible to be used as a geotourism because it is enough to affect the income of local people and is sufficient in terms of serving the needs of tourists. 4.6 rap-geotourism ordinance analysis of potential geotourism in the subayang river area in a infrastucture/technology perspective table 7. rap-geotourism ordinance analysis in infrastructure/technology prespevtive index status infrastucture 50,38 quite suistainable stress : 0,15 r2 : 0,94 fig 24. rapfish chart infrastructure/technology sustainable dimensions fig 25. rapfish chart infrastructure/technology sustainable dimensions monte carlo scatter plot -60 -40 -20 0 20 40 60 0 50 100 150 o th e r d is ti n g is h in g f e a tu r e s economy sustainability rapfish ordination (median with error bars showing 95%confidence of median) -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s economy sustainability rapfish ordination monte carlo scatter plot -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s infrastructure sustainability rapfish ordination (median with error bars showing 95%confidence of median) -60 -40 -20 0 20 40 60 0 20 40 60 80 100 120 o th e r d is ti n g is h in g f e a tu r e s infrastructure sustainability rapfish ordination monte carlo scatter plot martania, d.r. et al./ jgeet vol 7 no 4/2022 175 from the results of the calculations above, from the ifrastructure dimension, the subayang river is quite potential even though the value is considered low in the "quite potential" circle. 5. conclusion the river has very good clarity, even the source of drinking water for the local community also comes from the river. this river has a gentle current and at certain points there is a strong current, and has an island in the middle which forms a forked river. about 80% of the island's surface and surrounding plains are covered with various trees, grasses, and agriculture judged from several dimensions and attributes in the method used, most of the dimensions and attributes used to see the potential of the subayang river are quite feasible and quite sustainable, the ecological and geological dimensions have high values compared to other dimensions, while the lowest dimension is less sustainable and less feasible are the institutional and infrastructure dimensions rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. concluded by różycka and migoń, different types of visitors may have different reasons and motivations, not necessarily focusing on geoheritage value. therefore, they will view the geosite in different ways (štrba et al., 2020). in this regard, due to the limited work and collaboration between current biodiversity conservationists and earth scientists, it is important to integrate and link biotic and geological conservation, for example, by suggesting geoconservation in protected areas already recognized by local authorities and people living and working in the area. in it. if we are to place geodiversity and geological heritage directly in nature conservation programs, the geoconservation community must work to ensure that geodiversity and geological heritage in protected areas become of great importance in local, national and international contexts. references anna, z., padjadjaran, u., padjadjaran, u., rizal, a., padjadjaran, u., geopark, c.p., java, w., 2018. sustainable development of geopark national ciletuh-palabuhanratu in the infrastructure perspectiv. ayu, k.y., agus, r., mohamad, s.d.h., 2020. manajemen pemasaran geowisata. bamba bukengu muhaya, clarisse zoza kunyonga, sonia catherine mulongo, faustin zigabe mushobekwa, arthur mubwebwe bisimwa, 2017. trace metal contamination of sediments in naviundu river basin, luano and ruashi rivers and luwowoshi spring in lubumbashi city, democratic republic of congo. j. 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distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 124 idrus, a. et al./ jgeet vol 02 no 02/2017 metamorphic rock-hosted orogenic gold deposit style at bombana (southeast sulawesi) and buru island (maluku): their key features and significances for gold exploration in eastern indonesia arifudin idrus 1, *, sukmandaru prihatmoko 2 , ernowo harjanto 3 , franz michael meyer 4 , irzal nur 5 , wahyu widodo 3 & lia novelia agung 3 1 department of geological engineering, gadjah mada university, yogyakarta 2 pt. sjr-pama group, jakarta. 3 geological agency of indonesia, bandung 4 department of mineralogy and economic geology, rwth aachen university, germany 5 department of geological engineering, hasanuddin university, makassar. * corresponding author : arifidrus@ugm.ac.id tel.: +62-2754-513668 abstract in indonesia, gold is commonly mined from epithermal-, porphyry-, and skarn-type deposits that are commonly found in volcanic belts along island arcs or active continental margin settings. numerous gold prospects, however, were recently discovered in association with metamorphic rocks. this paper focuses on metamorphic rock-hosted gold mineralization in eastern indonesia, in particular the bombana (se sulawesi) and buru island (maluku) prospects. at bombana, gold-bearing quartz-veins are hosted by the pompangeo metamorphic complex. sheared, segmented veins vary in thickness from 2 cm to 2 m. gold is mainly prese tripuhyite, and in places, minor arsenopyrite. the gold distribution is erratic, however, ranging from below detection limit up to 134 g/t. at least three generations of veins are identified. the first is parallel to the foliation, the second crosscuts the first generation of veins as well as the foliation, and the late-stage laminated deformed quartz-calcite vein represents the third mineralization stage. the early veins are mostly massive to crystalline, occasionally brecciated, and sigmoidal, whereas the second-stage veins are narrower than the first ones and less subjected to brecciation. gold grades in the secondand third-stage veins are on average higher than that in the earlier veins. microthermometric and raman spectrometric studies of fluid inclusions indicate abundant h2o-nacl and minor h2o-nacl-co2 fluids. homogenization temperatures and salinities vary from 114 to 283 ºc and 0.35 to 9.08 wt.% nacl eq., respectively. crush-leach analysis of fluid inclusions suggests that the halogen fluid chemistry is not identical to sea water, magmatic or epithermal related fluids, but tends to be similar to fluids in mesothermal-type gold deposits. in buru island (gunung botak and gogorea prospects), two distinct generations of quartz veins are identified. early quartz veins are segmented, sigmoidal discontinuous and parallel to the foliation of the host rock. this generation of quartz veins is characterized by crystalline relatively clear quartz, and weakly mineralized with and ~1,000 m in length. gold mineralization is intensely overprinted by argillic alteration. the mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by n-s or ne-sw-trending structures. gold-bearing quartz veins are characterized by banded texture particularly following host rock foliation and sulphide banding, brecciated and rare bladed-like texture. alteration types consist of propylitic (chlorite, calcite, sericite), argillic and carbonation represented by graphite banding and carbon flakes. ore mineral comprises pyrite, native gold, pyrrhotite, and arsenopyrite. cinnabar and stibnite are present in association with gold. ore chemistry indicates that 11 out of 15 samples yielded more than 1 g/t au, in which 6 of them graded in excess of 3 g/t au. all high-grade samples are composed of limonite or partly contain limonitic material. this suggests the process of supergene enrichment. interestingly, most of the high-grade samples contain also high concentrations of as (up to 991ppm), sb (up to 885ppm), and hg (up to 75ppm). fluid inclusions in both quartz vein types consist of 4 phases including l-rich, v-rich, l-v-rich and l1-l2-v (co2)-rich phases. the mineralizing hydrothermal fluid typically is co2-rich, of moderate temperature (300-400 ºc), and low salinity (0.36 to 0.54 wt.% nacl eq). based on those key features, gold mineralization in bombana and buru island tends to meet the characteristics of orogenic, mesothermal types of gold deposit. metamorphic rock-hosted gold deposits could represent the new targets for gold exploration particularly in eastern indonesia. keywords: characteristics, orogenic gold, bombana, buru island, indonesia. received: may 2, 2017. revised : may 25, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.291 mailto:arifidrus@ugm.ac.id idrus, a. et al./ jgeet vol 02 no 02/2017 125 1. introduction 1.1 background study during last few decades, in indonesia gold has mostly been extracted from volcanic-hosted hydrothermal deposits, including ls epithermal type e.g. pongkor in west java, gosowong in halmahera island, hs epithermal type e.g. martabe (sumatra), cijulang (jawa) and lanut, doup (sulawesi), skarn type e.g. erstberg, big gossan, kucing liar, deep ore zone (doz) in papua and porphyry type e.g. in grasberg (papua), batu hijau (sumbawa island) and tombulilato (sulawesi). however, currently gold is not only found in volcanic terrain, but also many discoveries of placer (secondary) and primary gold mineralization are genetically occurred in association with metamorphic rocks, for instance, awak mas mesothermal (querubin& walters, 2011), poboya ls-epithermal (wajdi et al., 2011) and rampi (north luwu) (idrus et al., 2016). gold-bearing quartz veins are also recognized in derewo metamorphic belt at northern and northwestern part of central range papua. some exploration reports categorized the derewo metamorphic-related quartz veins into mesothermal gold deposit type. in bombana (se sulawesi) (fig.1), gold deposit is hosted by metamorphic rocks of the pompangeo metamorphic complex (mtpm). in addition, in this area placer gold is also being mined from miopliocene sediments of langkowala formation. this placer gold is interpreted to be sourced from primary gold deposit hosted by the mtpm. similarly, gold deposit is also discovered in buru island (gunung botak and gogorea), maluku (fig.1), which is hosted by wahlua metamorphic complex (pzw). both mtpm and pzw are of upper carboniferous until lower permian age (simanjuntak et al. 1993; tjokrosapoetro et al., 1993). the genetic type of the bombana and buru island gold mineralization are still debatable. this paper is aimed to discuss some key characteristics of the primary deposit including host rock petrology, quartz vein texture and structure, hydrothermal alteration, ore mineral and chemistry and mineralizing hydrothermal fluid properties. it is expected that the result would be important for a better understanding of the genesis of thegold mineralization, and would be useful in designing future exploration strategy for gold deposits in indonesia. 2 research methods this study has been carried out through several approaches including desk study, fieldwork and sampling for laboratory analyses. there is no previous detailed study and publication that was focused specifically on the primary gold mineralisation both in bombana and buru island. therefore, during the desk study only few literatures related to bombana placer gold can be reviewed, e.g. makkawaru & kamrullah (2009) and surono & tang (2009). quartz vein samples were taken, and geochemically analyzed by fire assay combined with aas, gravimetric fire assay (ga), cold vapour aas (cv) conducted in its laboratory, jakarta and aas laboratory of georesources research center, bandung. data of quartz vein assays from prihatmoko et al, (2010) that were taken adjacent to the studied area are also incorporated into discussion. a single icp-ms analysis from buru island sample was done by prof. victor okrugin in kamchatka university, russia. mineral chemistry of stibnite as a diagnostic ore mineral was also analyzed using epma (electron probe micro analyzer) at rwth aachen university. fluid inclusion in various generations of quartz veins was micro thermometrically analyzed by linkam thms600 heating and freezing stage at rwth aachen university, germany and geotechnology research centre, lipi, bandung. raman spectrometry and crush-leach analysis of fluid inclusion was done at georesources research center, bandung and leoben university, austria, respectively. fig. 1 location map of study areas i.e. bombana (se sulawesi) and buru island (moluccas) 126 idrus, a. et al./ jgeet vol 02 no 02/2017 3. result and discussion 3.1 deposit geology bombana gold deposit the area is occupied by mio-pliocene langkowala formation (tmls) consisting of conglomerate and sandstone. the langkowala formation is unconformably underlain by mesozoic metasediments and metamorphic rocks (pompangeo complex, mtpm) (simanjuntak et al., 1993). the metamorphic rocks consist of mica schist, quartzite, glaucophane schist and chert. the metasediments and metamorphic rocks occupy the mendoke and rumbia mountains. mica schist and metasediments particularly meta-sandstone and marble are commonly characterized by the presence of quartz veins/veinlets with various width up to 2 meters, containing gold in some places. interpretative e-w-trending faults, which are relatively parallel to the foliation attitude of the metamorphic rocks apparently acts as mineralization-hosting shear zones that formed first generation of quartz veins/reefs in the area. the ne trending faults are thought to be the main control of the formation of second generation of quartz veins (that cross-cut the foliations). the regional geology of bombana (including langkowala) and local geological map are shown in fig. 2. as explained previously, the quartz veins are predominantly hosted by metamorphic rocks particularly mica schist. mica schist is the predominant rock type in the area. some outcrops at wumbubangka shows a general foliation of n 300oe/60o. some foliation variations e.g. n80ºe/6070º was reported (prihatmoko et al., 2010). petrographic study of the mica schist indicates that the rock is abundantly composed of muscovite, chlorite and quartz with a small amount of actinolite, albite, epidote, sericite and opaque minerals. based on those mineral assemblages, it is considered that the metamorphic rock is categorized into green schist facies (cf.yardley, 1989). it is also important to note that the majority of the metamorphogenic-related gold deposits worldwide are hosted by greenschist facies (gebremariam et al., 1995). fig. 2 geological map of langkowala area occupied by langkowala formation (tml) and unconformably overlain paleozoic metamorphic rocks (pompangeo complex; mtpm) in the south (wumbubangka and rumbia mountain range) (base map from simandjuntak et al., 1993). squared area indicates the location area of this study. fig. 3 geological map of buru island (tjokrosapoetro et al., 1993). gunung botak and gogorea are occupied by pzw (wahlua metamorphic rock complex). gogorea gnbotak idrus, a. et al./ jgeet vol 02 no 02/2017 127 buru island gold deposit similar to those of bombana gold veins, gold mineralization in buru island is also hosted by mica schist of carboniferrous to permian wahlua metamorphic complex (pzw) (fig.3). hence, it is important to note that the rock characteristics and the ages of both pzw and mtpm are exactly the same. petrographic study exhibits that mica schist in buru island is composed of muscovite, chlorite and sericite suggesting of a green schist facies (cf.yardley, 1989). gold mineralization in buru occurred in form of quartz veins/veinlets/reef. two types/generations of quartz veins are recorded namely (1) quartz veins which are segmented, sigmoidal, discontinuous and parallel to the foliation of the metamorphic rocks. the vein distribution and pattern is intimately controlled by foliation orientation in the area. mineralogically, the quartz vein is lack of sulfides, weak mineralized, crystalline, relatively clear and gold may be poor; length. gold mineralization is strongly overprinted with argillic alteration zone. although it is still lack of field data, the mineralization-alteration zone is probably parallel to the mica schist foliation. according to field data and buru geological map (cf. tjokrosapoetro et al., 1993), it is interpreted that gold mineralization may be strongly controlled by n-s or ne-sw-trending geological structures (strike-slip faults?). artisanal and small scale gold mining (asgm) activities are currently concentrated along the structural-controlled mineralization zone. 3.2 gold-bearing quartz veins bombana at least there are three generations of the quartz veins identified. the first generation of quartz vein is parallel to the foliation of mica schist, phyllite and metasediment with general orientation of n 300oe/60o (fig. 4a). it was occasionally observed that this first generation of quartz vein is crosscut by quartz veinlets/ stockwork/stringers. the second quartz vein generation crosscut the first-generation quartz veins and as well as the foliation of hostrocks (fig. 4b); whereas the third vein generation is characterized by deformed laminated quartz+calcite vein, which is interpreted as the latest stage of vein formation in the studied area (fig. 4c). the first generation of quartz veins (that are parallel to foliation) are commonly 2 cm to 2 m in width, whereas the second phase quartz veins have commonly less than 10 cm in width. the thirdgeneration quartz veins hosted by metasediment identified in zones up to 15 meters wide. the first generations of quartz veins are mostly massive to crystalline, occasionally brecciated and sigmoidal, whereas the second quartz veins are narrower than the first and relatively brecciated. in addition, as observed by prihatmoko et al. (2010), druzy/sugary and some pseudomorph bladed carbonate textures have also been recognized associated with quartz veins/reefs cross cutting foliation. in the onggomate hill the veins formed a breccias zone composed of quartz as matrix, massive to crystalline, crackle to mosaic, with mica schist and phyllite fragments. in the roko-roko hill quartz veins (1-30 cm) hosted by mica schist and metasediment are commonly massive to crystalline quartz (druzy textures) with pseudomorph bladed carbonate textures. therefore, at least 2 later stages of veinings (after the first generation veinings) could be identified, including (1) vein breccias and (2) later quartz veinlets, 1-10 mm, which are commonly crystalline and containing native gold (fig. 4c) (prihatmoko et al., 2010). fig. 4 gold-bearing orogenic quartz vein characteristics: (a). brecciated/deformed quartz vein (first generation) which is paralel to the foliation of the mica schist (n 300ºe/60º), (b) highly oxidized / mineralized deformed second quartz vein cross cutting foliation, (c) a cluster of deformed laminated quartz veins hosted by metasediment buru island field and handspecimen observation indicates that gold-bearing quartz veins are characterized by vuggy, banded texture particularly colloform following host rock foliation and sulphide banding (fig. 5a) and brecciated texture. bladed-like texture is also observed, but it is rare (fig. 5b). those textures are more like developed in classic ls epithermal vein deposits. however, a few anomalies from shallow gold systems in the yilgarn block of western australia are notable. comb, cockade, crustiform and colloform textures at the racetrack deposit, australia, deposited from co2-poor fluids in lower greenschist facies rocks are also recognized (gebre-mariam et al., 1993). similar textures at the wiluna gold deposits in sub green schist facies rocks, as well as δ18oquartz measurements as light as 6 7 per ml, provide some of the strongest 128 idrus, a. et al./ jgeet vol 02 no 02/2017 evidence of meteoric water involvement in some of al systems (hagemann et al., 1992, 1994). although it is uncommon, but pseudomorph bladed carbonate texture could be present in orogenic quartz veins/reefs if the hydrothermal fluids forming the ore deposit have the right phase separation condition (personal comm.., richard j. goldfarb, 2011). fig. 5 hand specimen of quartz vein. (a) handspecimen of second quartz vein type with banding (colloform texture quartz vein following foliation), graphite and sulphide banding, (b) handspecimen of highly oxidized/limonitic quartz vein with bladed-like texture indicating a boiling condition (?). 3.3 alteration and ore mineralogy bombana the wallrocks (metamorphic rocks) are strongly weathered, so it is very rare to observe good outcrops in the area. trenching program by the company along the spurs of wumbubangka metamorphic mountain range has opened up the soil cover, and exposed clearly the presence of quartz veins and hydrothermally altered rocks. the hydrothermal alteration types recognized in the field includes silicification, clay-sericite±-silica (argillic), carbonate alteration and carbonization. silicification is represented by silicified metasediment and mica schist, whereas claysericite±silica (argillic) is mostly present surrounding quartz veins or along structural zones. prihatmoko et al. (2010) also reported the presence of narrow clay-sericite alteration halo (tens cm to 1 m) around the quartz veins in the roko-roko hill. carbonate alteration is typified by the presence of calcite veinlets/stringers, while carbonization is represented by rare occurrences of graphite/carbon with common black color in the quartz vein/adjacent to the altered wall rocks. the carbonization is considered to be one of the alteration type characteristics, associated with orogenic/metamorphic-hosted gold deposit. quartz veins/reefs/veinlets contain very small amount of sulphide minerals (up to 5 %). pyrite, chalcopyrite, cinnabar (hgs), stibnite (sb2s3), tripuhyite (fesbo4) and rare arsenopyrite (feass2) are present in the quartz veins and silicified metamorphic wallrocks. cinnabar is typically pinkish red in color and present abundantly in both primary mineralization and in placer gold deposit. on the other hand, in the primary mineralization, cinnabar commonly occurred in the form of mineralized layers along foliations of the metamorphic rocks (fig. 6a). stibnite and tripuhyite seem to be filling fractures parallel to foliations (fig. 6b) and disseminated within the silicified wall rocks. in general, gold is very fine-grain, but occasionally native gold is visible in quartz veins (fig. 6c,d). cinnabar and stibnite are genetically closely related to gold mineralization. those sulfides could be pathfinder minerals for the exploration of the metamorphic-hosted gold deposit. aas ore chemistry indicates a very broad and erratic variation of gold grade ranging from below detection limit (0.005 g/t) to 84 g/t au (based on present study and prihatmoko et al. (2010)), even a single analysis of quartz vein sample (bval01) from the valentino cave (a natural cave) in wumbubangka at the northern part of the rumbia mountain shows a high au grade of 134 g/t. few of the typical pathfinder minerals associated with orogenic/metamorphic-hosted gold deposit are stibnite and tripuhyite. the chemical composition of the minerals analyzed using epma (electron probe micro analyzer) indicates that both antimony-bearing minerals (stibnite and tripuhyite) contain a significant amount of as of up to 1 wt.%. fig. 6 diagnostic sulfides associated with bombana orogenic gold mineralization: (a). layer-like pinkish cinnabar paralel to mica schist foliation, (b). fibrous stibnite mainly parallel to the foliations, (c). visible native gold in multiple quartz veins, and (d). fotomicrograph of free gold in quartz vein. buru island as outlined above, gold mineralization zone is intimately associated with argillic-altered mica schist delineating an obvious high au grade zone of about 100 m width and 1,000 m length. clay mineral types characterizing argillic alteration zone are unknown. petrographic analysis shows host rock is also propyllitically altered typified by the presence of chlorite, calcite and sericite. carbonation alteration style represented by graphite banding and carbon flakes is a typical alteration type occurred in metamorphic-related hydrothermal ore deposits. ore mineralization is idrus, a. et al./ jgeet vol 02 no 02/2017 129 characterized by pyrite, native gold, pyrrhotite and arsenopyrite. as found in bombana, cinnabar and stibnite are also identified in association with gold. in general, sulphide minerals are rare (<3%). this is consistent with mineralogical features of other metamorphic rock-hosted gold mineralizations worldwide (cf. groves et al., 1998, 2003). 3.4 ore mineralizing fluids bombana a total of 6 quartz veins/reefs from three different generations were prepared for fluid inclusion analysis. this study has enabled to understand the characteristics including temperature, salinity and composition of mineralizing hydrothermal fluids that formed the three generations of quartz veins.the data show that tm of fluid inclusions hosted by first generation of quartz veins (that are parallel to the foliation) tend to be lower ranging from -2.3 to -10 ºc (mean -3.2 to -5.9 ºc) corresponding to relatively higher salinity ranging from 5.26 to 9.08 wt.% nacl eq.) in comparison to those of other generations of quartz veins/reefs. the temperature of homogenization (th), interpreted to be the formation temperature of the first generation of quartz vein varies from 185 to 245 ºc, that are relatively higher than those of other two generations of quartz veins/reefs.the second generation of quartz veins, that cross-cut foliation and have generally higher gold content, is formed in moderate temperatures of 132-283 ºc (mean 158-209 ºc) and salinity of 3.55-5.86 wt.% ncl eq. the latest generation stage of veining represented by quartz+calcite laminated veins was originated at the lowest temperature of 114-176 ºc and salinity of 0.35-4.03 wt.% nacl eq. fig. 7 displays the plotting between th and salinity of fluid inclusions from all quartz vein generations. it is clearly indicatived that the first quartz vein reted that the first quartz generation is dominantly originated from hydrothermal magmatic fluid mixing with metamorphic fluids. during the mixing, the temperature change is minor or relatively isothermal, but the salinity decreases significantly. the second and third quartz vein generations are likely formed from mixing of the magmatic and metamorphic fluids, and with cooler less saline meteoric water. this is shown by a systematic decrease of temperature and salinity (fig. 7). the evidences of the contribution of metamorphic fluid, hydrothermal magmatic fluids and meteoric water that formed the quartz veins are represented by h2o-nacl-co2 fluid inclusions (fig. 8a,b). petrographically the carbonic fluid inclusions are occasionally observed and may contain small portion of co2, probably max. 4% co2 (personal comm., richard j. goldfarb, 2011). raman spectrometric analysis confirms the presence of dissolved carbon dioxide (co2) in primary fluid inclusion with a certainty of up to 92.73% ((fig. 8c).). fig. 7. temperature of homogenization (th) vs salinity of fluid inclusions from three different quartz vein generations at bombana metamorphic-hosted gold deposit. the hydrothermal fluid evolution of the three types of quartz veins are also shown and discussed in the text. schematic model of fluid evolution is adapted from shepherd et al. (1985). fig. 8 fluid inclusion study: (a) and (b). co2-rich l-v fluid inclusions hosted by quartz veins, and (c). raman spectrometric analysis of carbonic fluid inclusion containing dissolved co2 with certainty up to 92.73%. buru island a total of 5 quartz veins/reefs from two different types were analysed for fluidinclusion study. four samples contain measurable fluid inclusions, and those of one sample (b05va) are too small to be measured.the data in table 1show that tm of fluid inclusions hosted by first type of quartz veins (that are crystalline, clear, weak mineralized and parallel to the foliation) tend to have tm ranging from -0.1 to -0.3 ºc (average -0.22 ºc) corresponding to salinity ranging from 0.18 to 0.53 wt.% nacl eq.(average 0.36 wt.% nacl eq.), relatively lower than those of second quartz vein type (tm = -0.2 to 0.3 ºc; average -0.27 ºc) which correspond to salinities of 0.36 to 0.54 wt.% nacl eq., averaging 0.48 wt.% nacl eq. the temperature of 130 idrus, a. et al./ jgeet vol 02 no 02/2017 homogenization (th), interpreted to be the formation temperature of the first type of quartz vein varies from 234 to 354 ºc, that are relatively lower than those of second quartz veins type (th = 321 to 400 ºc). petrographic study indicates that fluid inclusions in both quartz vein types consist of 4 phases including l-rich, v-rich, l-v-rich and l1l2-v (co2)-rich phases. in addtion, sample b05vb is characterized by abundant v-rich and l-rich inclusions which may imply a boiling condition with an elevated temperature of 400 ºc. in fact, this sample was taken from gunung botak where the artisanal and smal-scale mining (asgm) situated. crush-leach analysis of fluid inclusions from bombana and buru island gold veins suggests that the halogen fluid chemistry (br/cl vs i/cl plot) is not identical to magmatic or epithermal related fluids, but tends to be similar to fluids in mesothermaltype gold deposits (fig. 9). tabel 1. microtermometric data of fluid inclusions within quartz veins associated with gold mineralization in buru island fig. 9 crush-leach analysis of halogen content (i/cl and br/cl ratios) in fluid inclusion showing mineralizing fluids are not identical to magmatic fluid (a), epithermal (meteoric water-dominated) and porphyry cu (b), but tends to be similar to fluids in mesothermal-type gold deposits. 4. conclusions and significances for exploration 4.1 conclusions briefly concluded that primary gold mineralization in bombana particularly in wumbubangka area, at the northern flank of the rumbia mountain range is predominantly hosted by mica schist which is petrologically categorized into greenschist facies. this type of metamorphic facies mostly hosts the orogenic gold deposits worldwide, e.g. mt. charlotte, lancefield and golden mile (gebre-mariam et al., 1995; goldfarb, 2009). the presence of pathfinder minerals such as cinnabar, stibnite and tripuhyite genetically indicates that the orogenic gold deposit in the bombana is emplaced into transition between epizonal and mesozonal referred to the conceptual model of orogenic gold deposit (cf. groves et al., 1998, 2003) (fig. 10). it implies that the mineralization may be formed at approximately 5 km depth below paleosurface. in addition, the observable characteristics of goldbearing quartz veins/veinlets have met with the criteria of orogenic gold type, i.e. sheared/deformed, segmented, brecciated and occasionally sigmoidal, which are the key indications for brittle condition of the epizonal-mesozonal transition. the quartz veins/reefs are commonly characterized by massive and crystalline textures. however, druzy and pseudomorph bladed carbonate textures are also occasionally recognized. although it is uncommon, but bladed carbonate could be present in orogenic quartz veins/reefs if the hydrothermal fluids forming the deposit have the right phase separation situation (personal comm., richard j. goldfarb, 2011).ore mineralizing fluid is characterized by moderate to low salinity ranging from 5.26 to 9.08 wt.% nacl eq., 3.55-5.86 wt.% ncl eq. and 0.35-4.03 wt.% nacl eq. as well as moderate to low temperature of homogenization (th) varying from 185 to 245 ºc, 132 to 283 ºc, and 114 to 176 ºc for first, second and third generation veins, respectively. -4 -3.5 -3 -2.5 -2 -7 -6 -5 -4 -3 -2 lo g ( b r/ c l) log (i/cl) am_unmin. am_min. qv_ wb qv_kb qv_b sea water brusson lode gold capitan magmatic a 0.00010 0.00100 0.01000 0.10000 0.000000 0.000001 0.00001 0.0001 0.001 0.01 b r/ c l i/cl am_unmin. am_min. qv_ wb qv_kb qv_b sea water epithermal au mesothermal gold porphyry cu b idrus, a. et al./ jgeet vol 02 no 02/2017 131 fig. 10. the bombana and buru island metamorphic-hosted gold deposit plotted on the conceptual orogenic gold deposit model from groves et al. (1998, 2003) emplaced into shallow level at the transition between epizonal and mesozonal (approximately 5 km below paleosurface). co2-rich fluid inclusion is present in small portion, but its presence is well confirmed by raman spectrometric data. crush-leach analysis of fluid inclusion shows that mineralizing fluid characteristics are not identical to both epithermal (meteoric water-dominated) and magmatic fluids, but tends to fit with the properties of mesothermal related fluids. similarly, buru island gold mineralization is hosted by mica schist, which is composed of muscovite, chlorite and sericite, thus this metamorphic rock is grouped into green schist facies. two generations of gold-bearing quartz veins are identified. first quartz veins are typically segmented, sigmoidal, discontinuous and parallel to the foliation of the metamorphic rocks. second about 100 m in width and ~1,000 m in length. the mineralized quartz vein is probably parallel to the mica schist foliation. mineralized zone is generally brecciated and overprinting with argillic alteration zone with n-s or ne-sw orientation. mineralized zone may strongly be controlled by n-s or ne-swtrending strike-slip faults. second quartz vein texture is characterized by brecciated, banding texture such as colloform following foliation, sulphide banding and occasionally bladed-like texture. host rock is altered to propylitic, argillic, silicification and carbonation. carbonation is shown by graphite banding and carbon flakes associated with quartz banding. typically, sulphide minerals are rare (<3%). cinnabar, stibnite, arsenopyrite, pyrite and native gold are identified, those mineral are indicative of mineralization systems of orogenic gold. assay results indicate that 11 of 15 samples yielded more than 1 g/t au, in which 6 of them are in excess of 3 g/t au. it can be noted that all highgrade samples are originally or containing limonitic materials, that suggest the role of supergene enrichment. interestingly, most of the high-grade samples contain also high grade as (up to 991ppm), sb (up to 885ppm), and hg (up to 75ppm). hydrothermal fluid is typified by co2-rich fluid, moderate temperature of 300(0.36 to 0.54 wt.% nacl eq), which suggests that the metamorphic fluid is responsible for the formation of the buru gold deposit. 132 idrus, a. et al./ jgeet vol 02 no 02/2017 4.2 significance for gold exploration although gold mineralization both in bombana and buru island has some discrepancies, but by considering all key features discussed above, the primary metamorphic-hosted gold mineralization epithermal or other hydrothermal deposit types. therefore, the discovery of the metamorphichosted gold deposit in the rumbia metamorphic mountain range, buru island (gunung botak and gogorea prospects) and its vicinity has opened up more targets and challenges for gold exploration in the region, and other terrains in indonesia particularly eastern indonesia that have identical geological setting. it is also important to note that all high-grade samples are originally or containing limonitic/oxidized materials, that suggest the role of supergene enrichment. a further study on other genetic parameters of the deposit such as ratios of detailed mineralogy (sulfides & gangue), base metals, pathfinder elements, specific features, etc is needed for a better understanding of the genesis of the bombana and buru island gold deposits. acknowledgements the authors wish to express a gratitude to the directorate of higher education, department of 694/sp2h/pp/dp2m/x/2009 granted to the first author as a principal researcher. we are also indebted to the energy and mineral resources agency of southeast sulawesi and bombana regency, respectively for their permission. the supports and permission from management of pt. panca logam makmur are much acknowledged. some field data/ report provided by pt. agc indonesia are acknowledged. this study is also made possible through financial support from barry smith and research cooperation program 2013 between the first author with geological resources research center (psdg) bandung. prof. victor okrugin (kamchatka university, russia) provided an icp-ms single analysis. crush-leach analysis of fluid inclusion was done in leoben university, austria. those supports are highly acknowledged. fadlin idrus and satriadin abdullah are thankful for their fieldwork assistances and data processing. references gebre-mariam, m., hagemann, s. g., and groves, d. i., 1995, a classification scheme for epigenetic archaean lode-gold deposits. mineralium deposita 30: 408-410. groves, d. i., goldfarb, r. j., gebre-mariam, m., hagemann, s. g. and robert, f., 1998, orogenic gold deposit: a proposed classification in the context or their crustal distribution and relationship to other gold deposit types. ore geology review 13: 7-27. groves, d. i., goldfarb, r. j., and robert, f., 2003, gold deposit in metamorphic belts: overview or current understanding, outstanding problems, future research, and exploration significance. economic geology 98: 1-29. hagemann, s.g., groves, d.i., ridley, j.r., vearncome, j.r., 1992. the archaean lode-gold deposits at wiluna, western australia. high level brittle-style mineralisation in a strike-slip regime. econ. geol. 87, 1022 1053. hagemann, s.g., gebre-mariam, m., groves, d.l., 1994. surface-water influx in shallow-level archean lode-gold deposits in western australia. geology 22, 1067 1070. idrus, a., mansur, s., ahmad, rahmayuddin & mahdi, a., 2016, occurrences and characteristics of gold mineralization in rampi block prospect, north luwu regency, south sulawesi province, indonesia, jounal of applied geology, volume 8, january-june 2016 edition, accepted. prihatmoko, s., lubis, h., hernawan, s., 2010, evaluation report of bombana gold prospects, southeast sulawesi, unpublished report, pt. agc indonesia, 41p. querubin, c.d., walters, s., 2011, geology and mineralization of awak mas: a sedimentary hosted gold deposit, south sulawesi, indonesia, proceedings of the sulawesi mineral seminar, manado 28-29 november 2011, p. 211-229. simandjuntak, t.o., surono, sukido, 1993, peta geologi lembar kolaka, sulawesi, p3g, bandung. shepherd, t.j., rankin, a.h., alderton, d.h.m., 1985, a practical guide to fluid inclusion, blackie, london, 239p. tjokrosapoetra, s., budhitresna, t., rusmana, e., 1993, peta geologi lembar buru, maluku, pusat penelitian and pengembangan geologi (p3g), bandung. wajdi, m.f., santoso, s.t.j., kusumanto, d., digdowirogo, s., 2011, metamorphic hosted low sulphidation epithermal gold system at poboya, central sulawesi: a general descriptive review, proceedings of the sulawesi mineral seminar, manado 28-29 november 2011, p. 201210. yardley, b. w. d., 1989, an introduction to metamorphic petrology. longman scientific & technical, essex, 247p. 1. introduction 1.1 background study 2 research methods 3. result and discussion 3.1 deposit geology bombana gold deposit buru island gold deposit 3.2 gold-bearing quartz veins bombana buru island 3.3 alteration and ore mineralogy bombana buru island 3.4 ore mineralizing fluids bombana buru island 4. conclusions and significances for exploration 4.1 conclusions 4.2 significance for gold exploration acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 irawan, s., et al./ jgeet vol 04 no 01/2019 1 research article an analysis of the accuracy of time domain 3d image geology model resulted from pstm and depth domain 3d image geology model resulted from psdm in oil and gas exploration sudra irawan 1, *, yeni rokhayati 2 , satriya bayu aji 1 1 geomatics engineering study program, politeknik negeri batam, ahmad yani street batam center, indonesia. 2 multimedia and network engineering study program, politeknik negeri batam, ahmad yani street batam center, indonesia. * corresponding author : sudra@polibatam.ac.id tel.: +62857-4341-9535 received: sept 14, 2018; accepted: february 28, 2019. doi: 10.25299/jgeet.2019.4.1.2121 abstract this study aims to obtain a geological model which is close to the truth and compare accuracy between the time domain 3d image of the pstm results with the depth domain 3d image of psdm results. there are 3 parameters to determine the accuracy of an interval velocity model in the production of a geology model: depth gathering that is already flat, semblance that has concurred with zero residual move-out axes, and depth image which conforms to the marker (well seismic tie). the analytical method employed is horizon based tomography, which is a method to correct the seismic wave travel time error along the analyzed horizon. reducing errors in the travel time of the seismic wave will decrease depth errors. this improvement is expected to provide correct information about subsurface geological conditions. the results showed that the depth domain image generated by the psdm process represents the actual geological model better than time domain image produced by the pstm process, evidenced by the sharpening of the reflector continuity, reduction of pull-up effect, and high resolution. keywords: geology model, time domain 3d image, pstm, psdm, horizon-based tomography 1. introduction 3d seismic data processing is a method that is being widely used in the world of seismic exploration. 3-d seismic data processing consists of 3-d dip-moveout correction, 3-d refraction and residual statics corrections, and 3-d migration (yilmaz, 2001). more complicated acquisition and longer, more expensive processing cause 3d seismic has only been used recently. 3d seismic method can provide a better subsurface picture compared to 2d seismic because it can provide complete information about the subsurface structure of the earth so that the surface image obtained is not just a 2d structure but a description of the entire volume of the acquisition area. kirchhoff migration is the most popular method of 3d dimensional prestack depth migration because of its flexibility and efficiency (hill, 2001). pre stack depth migration (psdm) is a migration technique before stacking, with very complex medium velocity variations such as thrust belt, zone around carbonate (reef), salt dome, etc. the difference in time migration and depth migration is not a time domain or depth domain problem but depends on the velocity model used. time migration has smooth velocity variations, while depth migration has a complex velocity (evita et al., 2014). pre stack time migration (pstm) only accommodates vertical velocity variations. a prestack reverse time‐migration image is not properly scaled with increasing depth. the main reason for the image being unscaled is the geometric spreading of the wavefield arising during the back‐propagation of the measured data and the generation of the forwardmodeled wavefields (shin et al., 2001). in psdm using explicit extrapolators, the attenuation and dispersion of the seismic wave have been neglected so far (mittet, 1995). lateral velocity variations present complex geological models with variations in velocity not only in the vertical direction but also in the lateral direction (irawan and khoirunnisa, 2017). however, psdm requires an accurate interval velocity model. without an accurate velocity model, the final result obtained will not be better than time migration. this velocity model requires several stages starting from the creation of the root mean square (rms) velocity model, the creation of an interval velocity model to the improvement of the interval velocity model using specific methods. strong refraction of waves in the migration velocity model introduces kinematic artifacts-coherent events not corresponding to actual reflectors-into the image volumes produced by prestack depth migration applied to individual data bins (stolk, et al., 2004). http://journal.uir.ac.id/index.php/jgeet mailto:sudra@polibatam.ac.id 2 irawan, s., et al./ jgeet vol 04 no 01/2019 fig. 1.a illustrates cases when the lateral velocity is constant, which produces a travel time curve in the form of hyperbole with its peak just below the geophone datum. in the event of time migration, the hyperbole curve will both be added to the top of hyperbole (fig.1.b). if there are lateral velocity variations, the travel time curve will not form a hyperbole as in fig. 1.b. in fig. 1.c, the lateral velocity is not constant (varies), caused by overburden structures such as reef carbonates or salt domes. the formed hyperbole peak shifts its position to the geophone datum position of the signal recorder on the x-axis (fig. 1.d). this distortion means that time migration is incompatible in areas that have high lateral velocity variations because of the occurrence of ray bending at the boundaries of the layers. this beam deflection causes the spreading time of the wave not to form a hyperbolic, making the amplitude and travel time unsuitable for the use of conventional common mid point (cmp) stacking. this assumption is based on a hyperbolic curve. if conventional cmp stacking is still used, then the stack results will be farther from the ideal zero-offset section (guo, n. and fagin, s., 2002). fig. 1. (a) reflections on the medium with constant lateral velocity, (b) travel time curve from image (a) with the peak just below the geophone (datum b) the recipient, (c) reflection that occurs on the medium with lateral velocity changes, (d) there is an error in the peak position of the travel time that is no longer right under the receiving geophone. information from geological data shows that there is a complex structure in the north west java extension field basin (sbi). this is characterized by the presence of reef carbonate. in complex structures such as this, high lateral velocity variations are expected. the presence of lateral velocity variations causes ray bending when it passes the boundaries of the layer, causing the propagation time of the wave to not form a hyperbole (purnawati and minarto, 2016). high lateral velocity variations in the sbi field of the north west java basin cause migration in the time domain, commonly known as pstm. rms velocity model is not accurate because it is only sensitive to vertical velocity variations. therefore, migration is required in the depth domain (psdm) using the interval velocity model which is sensitive to vertical or horizontal velocity variations. however, psdm requires an accurate interval velocity model. one way to produce accurate interval velocity models is by analyzing the residual depth move-out and employing horizon-based tomography analysis (irawan et al., 2014). tomography is a method used to improve velocity models when psdm is done with an inaccurate velocity model. tomography uses a measure of residual moveout as input and tries to find or even make other models by moving the error that occurred (washbourne and tomoseis, 2001). tomography uses a residual move-out from the pre-stack migration gathers as an input, and turning error depth δz and offset into an extended time error (crp) for the same offset. in determining the tomographic equation, the relationship between time error 𝛿𝜏, time model that has been updated 𝛿𝑡𝑣, and slowness error 𝛿𝑧 is required. the conversion from depth error into time error is done when point a, which has shifted vertically, is forrmulated as δz and result of change in running time (woodward et al., 2008). tomography and psdm technology to compensate the phase, frequency and amplitude loss due to shallow absorption, thus improving structure imaging and potentially accurate avo/dhi analysis underneath shallow gas (zhou et al., 2011). the accuracy level of the interval velocity model can be seen from the error value which is due to inaccuracies in the estimation of the layer velocity and reflector geometry. based on the research conducted by irawan et al. (2014), there are 3 ways to find out the error in the resulting interval velocity model: (1) the depth gathering analysis of psdm result, (2) the semblance residual move-out analysis, and (3) the analysis of depth image psdm with the marker. based on these 3 methods, this research was conducted to obtain a geological model which is close to the truth and compare the accuracy of the time domain 3d image of the pstm with the depth domain 3d image of psdm. 2. materials and method in this research, two main devices (hardware and software) were used. the hardware consists of redhat enterprise linux as 5.0 central processing unit, two 24 inch monitors, sgi altix 450/suse linux enterprise server 9.0, 32 gb, 32 x 2,6 ghz processor server, and gigabit 1 gb/s network adapter. the software used is seismic processing and imaging by paradigm. the details are as follows: (1) geodepth velocity modeling (epos 41) to create a 3d model map with rms velocity as well as to create and improve interval velocity model, (2) geodepth migrations software (epos 41) [3d k. pstm (16 cpus) to run the pstm process and 3d k; psdm (fermat/eikonal) to run the psdm process], (3) geodepth 3d tomograpy software (epos 4.1) to run tomography process. the data consists of two types: seismic data and well data. the seismic data consist of common depth point (cdp) gathers and rms velocity, while the well irawan, s., et al./ jgeet vol 04 no 01/2019 3 data comprise sonic log, density log, resistivity log, gamma ray (gr) log, and neutron log. the log data is used to calculate the estimated hydrocarbon reserves. data processing in this research consists of 3 main activities: (1) creating a 3d rms velocity model map, (2) creating and correcting interval velocity models, (3) creating a 3d pstm and psdm sectional drawing model. fig. 2. research flow chart the input in the pstm process consists of cdp gathering and rms velocity volume obtained from research data. the pstm results are used for horizon picking. determination of the horizon is based on the target to be searched, which is based on geological information and marker information taken from the log in the well. in this research, 9 horizons were used: horizon 1 (upper cisubuh formation), horizon 2 (parigi formation), horizon 3 (lower parigi formation), horizon 4 (pre-parigi formation), horizon 5 (cibulakan formation), horizon 6 (upper mmc formation), horizon 7 (lower mmc formation), horizon 8 (baturaja formation), dan horizon 9 (talang akar formation). afterward, from the picking results for each horizon in the sectional drawing of the pstm, a map of time migration interpretation is made. furthermore, from the 9 horizons, three-dimensional (3d) model maps are created. from the 3d map, time migration model will be generated for each horizon, then intersection of vertical functions with rms velocity from input data is done. this process is called the rms velocity interpretation, which results in a 3d model map of rms velocity interpretation for each horizon. in converting rms velocity maps to interval velocity maps, dix transformation is used. from the results of the conversion of the rms velocity to the interval velocity, the velocity map of the interpretation interval is generated for each horizon. in the conversion process from the time map migrated horizon to the depth map, the image ray migration method is used. furthermore, depth map editing is carried out, which includes filtering, smoothing, and extrapolation. 3d model map of interval velocity and depth for each horizon are the inputs to make the initial interval velocity volume. the geometry weight calculation is then carried out to find the acquisition parameters and offset range values which will be used as an input parameter in the psdm process. the input data needed for psdm processes consists of the 3d velocity interval model and cdp gathers. the type of migration used in this study is 3d kirchoff prestack depth migration. there are two stages in this process: (1) calculation of travel time using the eikonal equation, (2) the migration process in the depth domain with the kirchoff method. there are several parameters that must be included: inline and crossline target, aperture, offset range and type of input data (interval velocity model and cdp gathers) contained in the seismic data manager. residual move-out analysis is carried out after an inaccurate interval velocity model application is carried out on seismic data. if the interval velocity model has been estimated accurately, the depth gathering generated from psdm with the interval velocity model should show have shown flat events. unfortunately, this is not the case. this can be seen from the existence of a move-out, or the difference in travel time between far-offset and near-offset. this shows that there is still an error in the interval velocity model. this error can occur at the layer velocity or reflector geometry. therefore, in the next step, a residual move-out is analyzed. in the next process, the results of residual move-out picking were put onto a grid and were processed into a depth residual move-out map for all layers analyzed. finally, map editing, which includes filtering, smoothing, and extrapolation is performed to remove the remaining noises. 4 irawan, s., et al./ jgeet vol 04 no 01/2019 a depth map of the residual move-out 3d model resulted from the analysis of the residual move-out is used as the input for the tomography process with the horizon-based tomography method. this method calculates the travel time error used to correct (or update) the interval velocity model and depth map. one parameter that must be determined is ray-tracing step, which shows the origin of the location of the ray (ray-tracing starts or is traced from this point). there are 3 analyses carried out: (1) analysis of interval velocity models, which involves comparing interval velocity models before and after residual move-out correction using horizon based tomography method. the analysis is prioritized for target areas where well data (sonic log and well marker) has been taken. in addition, identification of errors in interval velocity models is carried out at each stage, (2) analysis of sectional drawing of the obtained pstm and final psdm, especially the clarity and continuity of the reflector throughout the seismic section in the target area, which will then be compared, (3) analysis of the sectional drawing of psdm of the target before and after tomography by looking at the reflector on each seismic section. 3. result and discussion 3.1 interval velocity model analysis the rms velocity value is shown in fig. 3, which ranges from 1578 m/s to 3401 m/s. furthermore, the sectional drawing of the resulted pstm is analyzed to determine the target and horizon zones that will be used in the next process. fig. 4 shows the result of the pstm process with the acoustic impedance value in the pstm section ranging from 10000 kg / m 2 s to 98104.5 kg / m 2 s. fig. 3. interval velocity model. fig. 4 is a solid model made from the time migrated horizon map (pstm picking result). the application of different color code at each horizon are useful in the process of identifying formations during horizon and semblance picking. fig. 4. the result of the pre-stack time migration (pstm) process with cdp gathers input and rms velocity volume model. fig. 5. solid model created from time migration horizon map from the result of horizon picking in the sectional drawing of the pstm. there are three ways to find out the error in the resulting interval velocity model: (1) depth gathers analysis of psdm result, (2) semblance residual moveout analysis, and (3) analysis of psdm depth image along with the marker. the first method is depth gathers analysis of psdm results. this method is done by looking at events at the depth gathering, whether it has shown a relatively flat event or not. the application of an inaccurate velocity model will result in gather which is not flat or still contain a residual move-out (a difference in travel time between near and far offset). there are two types of residual move-out, positive residual move-out (the event is bent down) and negative residual move-out (the event is bent up). as shown in fig. 6, the positive residual move-out is an indication that the velocity used is too high (fig. 6a), while negative residual move-out is an indication that the velocity used is too low (fig. 6b). the existence of a residual move-out means that events coming from a similar reflection point do not have the same depth. events that come from the same reflection point should have the same depth at the depth gathers. this is based on the psdm concept that maps every event coming from the same reflection irawan, s., et al./ jgeet vol 04 no 01/2019 5 point at the same actual depth or position (if the velocity model used is accurate). improved interval velocity models are carried out until the events are obtained at a relatively flat depth gathers. fig. 6 (a) positive residual move-out (event is bent down), which indicates that the velocity is too high, (b) negative residual move-out (event is bent up), which indicates that the velocity is too low. the second method in identifying the interval velocity model error is semblance residual move-out analysis. semblance residual move-out is calculated from depth gathers. gathers that contain a residual move-out will result in a semblance peak which is not on the zero-residual axis move-out. this means that if the gathering has coincided with the zero residual axis move-out (gathers are flat), then the gathers do not contain a residual move-out. fig. 7 gives an example of semblance residual move-out that is not on the residual axis move-out after the application of the initial interval velocity model at horizon 2. fig. 7. semblance residual move-out which still shows an error in the initial interval velocity model the third way is the analysis of psdm depth image along with the marker. incompatibility between depth image maps and reflectors related to the layer boundary at the depth image can be seen when both are displayed in one section (overlay). the layer boundary on the interval velocity model will experience a deviation from the reflector (layer boundary) it represents in the resulted depth image (without the red arrow in fig. 7). another error can be identified from the well marker which has not been tied to the horizon, which has to do with well seismic tie. 3.2 comparative analysis of the accuracy of geological model of pstm and psdm based on the value of rms velocity, interval velocity before and after tomography, and sonic log velocity, velocity value at a certain depth or horizon can be compared. interval velocity value for each horizon after tomography have values that are almost the same as the velocity value in the sonic log at a depth of each horizon, while the velocity model before tomography proves to be less precise (less accurate). this proves that interval velocity model produced after tomography resembles more to the actual geology model. generally, in the rms velocity model and interval velocity model, the velocity value will increase gradually according to an increase in depth because the wave propagation in a denser medium will be faster than a less dense (less massive) medium as the depth increases. however, the results of the interval velocity modeling after tomography indicates the existence of velocity anomalies under the baturaja formation in the form of reduction in velocity from the baturaja toward the talang akar formation, from a maximum velocity of 2939 m/s to 2674 m/s (blue box in table 1). this decrease in velocity value is caused by the difference in lithology between the baturaja and the talang akar formation. the baturaja formation has a relatively higher density than the talang akar formation, which is relatively lower. the baturaja formation has rock formations which consist of massive limestone which becomes more porous as the depth decrease, while the talang akar formation has a rock formation comprising the mixture of sandstone and limestone. one way to validate the result of the psdm produced is by using the depth image and the well marker. in the inline section of the 2222 inline psdm resulting from the last iteration, it can be seen that the horizon of the interval velocity model is located on the reflector it represents. these horizons are related to layer boundaries. judging from the structure produced, this makes sense geologically (conform to the geological information). in fig. 8, there are 4 wells crossing the inline: well 1, well 2, well 3, and well 4. well 1 is a vertical well with 8 markers. (horizon 1 is the upper cisubuh formation. not all of the wells are equipped with markers.) it can be seen that 7 markers have a tie with the seismic data and there are still 1 marker (horizon 6, mid main carbonates top layer) that has not been tied to the seismic data. this is understandable because the manufacture of markers was carried out on the 6 irawan, s., et al./ jgeet vol 04 no 01/2019 sectional drawing of the pstm which still contains errors in the reflector due to the pull up effect caused by the presence of reef carbonate at the top of the mmc layer, causing a lift in the horizon 6 reflector. fig. 8. the 2222 inline psdm section results from running psdm using the final interval velocity model (fifth iteration) in fig. 9, it can be seen that the graph of well 1, well, 2 and well 4 shows the trend of decreasing curve (reduction in depth error) as the number of iterations increases. in well 1, the biggest depth error before tomography occurs at horizon 7 (mmc bottom formation), at around 96.54 meters, while the remaining error after tomography is only around 2.52 meters. the average depth error after tomography on well 1 ranged from 1 to 3 meters. this means that the tomographic process carried out successfully corrects depth errors. fig. 9. graph of the relationship between the number of tomographic iterations and the depth error of well 1 and after tomography (1 st -5 th iteration) 4. conclusion the interval velocity model generated by horizonbased tomography can improve the parameters of interval velocity model, which includes layer velocity and depth. this is evident from the depth gathering that is already flat, semblance that has concurred with zero residual move-out axis, and depth image which conforms to the marker (well seismic tie). depth domain image generated by the psdm process represents the actual geological model better than time domain image produced by the pstm process, evidenced by the sharpening of the reflector continuity, reduction of pull-up effect, and high resolution. references evita, a., danusaputro, h. and mualimin, m., 2014. pengolahan model kecepatan menggunakan metode ray tracing untuk migrasi domain kedalaman (pre stack depth youngster physics journal, 3, 77-82. guo, n. and fagin, s., 2002. becoming effective speed-model builders and depth imagers, part 1 the basics of prestack depth migration. the leading edge, 21, 12051209. hill, n.r., 2001. prestack gaussian-beam depth migration. geophysics , 66, 1240 -1250. https : //doi.org/10.1190/ 1.1487071 irawan, s. and khoirunnisa, h., 2017. identification of reservoir thickness and estimation of hydrocarbon reservation used the pre-stack depth migration (psdm) in cikung area. journal of applied geospatial information, 1, 5-10. irawan, s., sismanto, sukmatiawan, a., 2014. applying the horizon based tomography method to update interval velocity model, identify the structure of pre-stack depth migration 3d and estimate the hydrocarbon reserve in sbi 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zdraveva, o., whitfield, p. and johns, t., 2008. a decade of tomography. geophysics, 73, ve5-ve11. https://doi.org/10.1190/1.2969907 zhou, j., birdus, s., hung, b., teng, k.h., xie, y., chagalov, d., cheang, a., wellen, d. and garrity, j., 2011. compensating attenuation due to shallow gas through q tomography and q-psdm, a case study in brazil. in seg technical program expanded abstracts 2011, 33323336. society of exploration geophysicists. https://doi.org/10.1190/1.3627889 © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://ejournal3.undip.ac.id/index.php/bfd/article/view/5279 https://ejournal3.undip.ac.id/index.php/bfd/article/view/5279 https://ejournal3.undip.ac.id/index.php/bfd/article/view/5279 https://ejournal3.undip.ac.id/index.php/bfd/article/view/5279 https://ejournal3.undip.ac.id/index.php/bfd/article/view/5279 https://doi.org/10.1190/1.1487071 https://doi.org/10.1190/1.1487071 https://jurnal.polibatam.ac.id/index.php/jagi/article/view/329 https://jurnal.polibatam.ac.id/index.php/jagi/article/view/329 https://jurnal.polibatam.ac.id/index.php/jagi/article/view/329 https://jurnal.polibatam.ac.id/index.php/jagi/article/view/329 https://jurnal.polibatam.ac.id/index.php/jagi/article/view/329 https://jurnalteknologi.utm.my/index.php/jurnalteknologi/article/view/3240/0 https://jurnalteknologi.utm.my/index.php/jurnalteknologi/article/view/3240/0 https://jurnalteknologi.utm.my/index.php/jurnalteknologi/article/view/3240/0 https://jurnalteknologi.utm.my/index.php/jurnalteknologi/article/view/3240/0 https://jurnalteknologi.utm.my/index.php/jurnalteknologi/article/view/3240/0 https://jurnalteknologi.utm.my/index.php/jurnalteknologi/article/view/3240/0 https://doi.org/10.1190/1.1443882 https://doi.org/10.1190/1.1443882 https://doi.org/10.1190/1.1443882 file:///c:/users/win10/downloads/10.12962/j23373520.v5i2.17086 file:///c:/users/win10/downloads/10.12962/j23373520.v5i2.17086 file:///c:/users/win10/downloads/10.12962/j23373520.v5i2.17086 https://doi.org/10.1046/j.1365-2478.2001.00279.x https://doi.org/10.1046/j.1365-2478.2001.00279.x https://doi.org/10.1046/j.1365-2478.2001.00279.x https://doi.org/10.1046/j.1365-2478.2001.00279.x https://doi.org/10.1190/1.1707076 https://doi.org/10.1190/1.1707076 https://doi.org/10.1190/1.9781560801580.fm https://doi.org/10.1190/1.9781560801580.fm https://doi.org/10.1190/1.9781560801580.fm https://patents.google.com/patent/us6269310b1/en https://patents.google.com/patent/us6269310b1/en https://patents.google.com/patent/us6269310b1/en https://doi.org/10.1190/1.2969907 https://doi.org/10.1190/1.2969907 https://doi.org/10.1190/1.2969907 https://doi.org/10.1190/1.3627889 https://doi.org/10.1190/1.3627889 https://doi.org/10.1190/1.3627889 https://doi.org/10.1190/1.3627889 https://doi.org/10.1190/1.3627889 https://doi.org/10.1190/1.3627889 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. materials and method 3. result and discussion 3.1 interval velocity model analysis 3.2 comparative analysis of the accuracy of geological model of pstm and psdm 4. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02-2 2023 special edition special issue from “the 1st international conference on upstream energy technology and digitalization (icupertain) 2022” dwikorianto, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 67 research article ambient noise data processing to obtain group velocity for subsurface structure identification: preliminary research in hululais geothermal field, sumatra, indonesia tavip dwikorianto1, yunus daud2,*, agustya adi martha3, aditya a juanda4 1doctoral program in geothermal, department of physics, faculty of mathematics and natural sciences, universitas indonesia, in donesia. 2doctoral program in geothermal, department of physics, faculty of mathematics and natural sciences, universitas indonesia, indonesia. 3national research and innovation agency, bogor 16911, indonesia 4pt pertamina geothermal energy, jakarta 10110, indonesia. * corresponding author : ydaud@sci.ui.ac.id tel.:+62-211-7867-222; fax: +62-211-7867-222 received: may 20, 2023. revised : may 31, 2023, accepted: june 10, 2023, published: 31 juli 2023 doi: 10.25299/jgeet.2023.8.02-2.13883 abstract hululais area lies in the pull-apart basins of the ketaun segment and musi segment fault as a part of the sumatra fault zone (sfz). the boundary normal faults of pull-apart basins play an important role as major discharge zones for geothermal fluid because the extensional stress is concentrated in the boundary normal faults. in order to identify the geothermal reservoir structure in hululais geo thermal field (hgf), we introduce the local-scale study of the rayleigh wave group velocity structure using ambient noise tomography (ant). the ant studies were collected using 18 seismometers inside 12 km2 area with a spacing of 125 – 500 meters, deployed across the fault structure for 1 month. more than two thousand rayleigh green’s functions are extracted by cross-correlation at available station pairs. using the estimated green function in this preliminary research, the group velocity as a function of the period can measure the dispers ion curve by using multiple filter technique (mft) and fast marching surface tomography (fmst) scheme to obtain group velocity images. the tomography result as group velocity image shows the subsurface rayleigh wave structure variation. the nw-se main structure is reflected by the contrast velocity structure between the central part and the north eastern-south western sides. the central part shows the low periods which are associated with low wave velocity however the margin of the central part shows the high velocity in all periods. the ant studies have been efficient in time and cost, however useful in subsurface structure interpretation in hululais geotherma l field. keywords: pull-apart basin; rayleigh wave, green function, ambient noise tomography, cross-correlation, group velocity 1. introduction the ant is the passive seismic method that uses the signal permanent source from surface waves which is considered to be related to the interaction of ocean swells with the seafloor near coastlines so the advantage is that it does not depend on the earth-quake occurrence and can be recorded at any time and any location (yang y et al., 2008). classical reservoir imaging, particularly for oil and gas exploration, is based on active seismic surveys that rely on artificial impulsive sources (explosions and vibrator trucks). however, such operations have a high cost compared to the overall budget of a deep geothermal project and might affect the social acceptance of the project, especially in urban areas (lehujeur m et al., 2015). the ant studies have been efficient in time and cost because the data will be recorded in somedays even in somehours so it will reduce cost respectively. ambient noise seismic is used for the regional study of tectonic and basin, volcano, and geothermal in many fields of the world. it is applied in indonesia for the study of some basins in central java (zulfakriza et al., 2012); western east java (martha et al., 2015), east java (martha et al., 2016), east java and bali (martha et al., 2017); bandung – west java (wuryani et al., 2019); sulawesi island (panshori et al.,2019). the study of the volcanic area in merapi and surrounding volcanic centers (koulakov et al., 2016); the agung-batur volcano complex, bali (zulfakriza et al., 2020). ambient seismic noise is also applied in geothermal studies, such as in jailolo (vita et al., 2022), and wayang windu (wahida et al., 2018). theoretical and experimental research has shown that the cross-correlation of ambient noise records from two receivers provides an estimate of the empirical green’s function between the receivers/seismometer (snieder, 2004). in the previous study, the average spacing distance between station pairs ranged from 1 to 25 km. in this study we tried to use a tighter spacing compared to previous studies, from 0.5 – 1 km to be 0.125 – 0,5 km, in order to obtain tomography images at shallower depths in the geothermal field. 2. geological setting hululais geothermal field (hgf) is situated in rejang lebong district, bengkulu province, sumatera island, http://journal.uir.ac.id/index.php/jgeet mailto:ydaud@sci.ui.ac.id 68 dwikorianto, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 indonesia. this field is located about 150 km from bengkulu city towards the bukit barisan mountain in the north. hululais is one of thirteen geothermal systems situated in pull-apart basins on sumatra island which is the special tectonic setting where the major strike-slip sumatran fault and volcanic zone coexist. hululais area lies in the southwestern margin of the dextral strike-slip fault couples of the ketaun segment to the north and musi segment to the south as a part of the sumatra fault zone (fig. 1). these segment movements form a basin approximately 15 km in length and 5 km wide. fig. 1. tectonic setting of hululais there are at least three main trending geological structures direction, specifically northwest-southeast (nw-se), north east-south west (ne-sw) and north-south (n-s) patterns (fig. 2). lineament structure are indicated from satellite imagery. the nw-se lineaments orientation are stepping suban agung fault faults, nibung fault and semelako fault, interpreted as musi segment. the n-s lineament orientation are cemeh fault, gregok fault and nusuk fault. the nw-se lineament orientation, i.e., manghijau fault. these faults are a minor fault of musi segment formed by n-s compression stress from subduction australian-pacific plate movement. fig. 2. geological map of hululais the reservoir zone in below of 1500 meter depth has high temperature reaches 300 oc and high permeability in the southern up flow zone. meanwhile in the northern out flow zone has a temperature below 215 oc that encountered by wells whose the permeability is very low. by plotted in fs-hsh diagram, the gas sample that taken from the fumarole and the wells indicate that the reservoir is water/liquid dominated system. 3. data and method seismic waveform data was recorded by seismograph stations which the stations were equipped with the seismographic sensors of lennartz 3d lite, the digitizer of taurus, the time synchronizer of a gps antenna, and the power supply of the accu battery. the seismograph has 3 components, i.e. vertical component (z) and the horizontal component (n-s and e-w) which the z component is used to construct the green function. the tube concrete 40 cm in length was set in the hole of the observation station as a seismograph sitting for reducing the local noise from trees, humans or animals, etc. noise recorded by these stations was used to image the group velocity under the research area. fig. 3. the distribution of seismographic station locations in the research area the main part of the network was composed of 141 stations settled on the grid in about 12 km square coverage area with an average interstation distance of 500 meters and 125 meters in a certain area. the seismic waveform data was recorded by 15 portable and 3 stationary seismographs. the 3 static stations are set in the margin area in the northern (n004), the southern (n143), and the western (n042). the measurement in 15 stations was done in 1 – 4 days and then relocated to the next station. fig. 4. flow chart of the ant methodology the initial stage of the ant method is data acquisition by using a seismometer. then the ambient noise data processing procedure divides into four principal phases as shown in fig. 4 : (1) single station data preparation, (2) cross-correlation and temporal stacking, (3) measurement of dispersion curves, and (4) tomography (starting by resolution test, including error analysis and selection of the acceptable measurements). the first phase of data processing consists of preparing waveform data from each station individually in sac data. after the preparation of the daily time series, the next step dwikorianto, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 69 in the data processing scheme (phase 2) is cross-correlation and stacking. cross-correlation is performed daily in the frequency domain. after the daily cross-correlations are returned to the time domain they are added to one another, or ‘stacked’ into weekly, monthly, yearly, etc. time series. after the daily cross-correlations have been computed and stacked, the resulting waveform is an estimated green function. using the estimated the green function, the group velocity as a period function can be measured using the multiple filter technique (mft). the study obtains dispersion group velocities of the surface waves by applying multiple band-pass filters to the impulse response in the frequency domain using do_mft. program in seismology’s do_mft allows for the numbers of different input parameters. this study sets the units to counts, the type to rayleigh and the filter parameter (α) 12.5 for all interstation distances. suitable filter parameters (α) are needed to produce clear information and help the balance of resolution trade-off between the time and frequency domains. the study performs multiple filter analysis on periods of 0.5–12.5 s because this includes the highest energy band or the highest spectral amplitudes. the dispersion curve gives various color information (bluegreen-red) at each period and group velocity. red color represents the highest energy and has the smallest degree of ambiguity than green and blue. finally, using the fast marching surface tomography (fmst) scheme to obtain group velocity images. fmst implements forward and inverse problems using the fast marching method (fmm) (rawlinson and sambridge 2005) and subspace, respectively. the combination of the fmm for the calculation of the forward problem and subspace methods for inversion provide strong and stable condition at tomographic imaging. fmm (rawlinson and sambridge, 2004) is a grid-based eiconal equation used in the first step inversion to define the problem in the future. meanwhile subspace method works by projecting squares approximation of φ to an n-dimensional subspace of the model space. the disruption given by: (1) where a is the projection matrix of m × n, g is the fréchet derivative matrix, γ is the gradient vector (γ = ∂ φ / ∂ m and γ = w mγ). search direction is given by aj in which the first search direction a1 is appropriate with the steepest ascent. once the model is estimated disturbance, the study can update the current model and then retrace the propagation paths using fast marching method (fmm) scheme. 3.1 cross-correlation the cross-correlation of noise on the surface of the earth began to be developed by shapiro and campillo (2004) demonstrated empirical cross-correlation calculations of seismic noise wavefield recorded on two seismographs. the time derivative of the ambient noise cross-correlation cij (1, 2, t) between two different seismograph stations, station 1 (located at r1 recording component i) and station 2 (located at r2 recording component j) to the time domain green’s function (tdgf) gij(r1; r2, t). (2) the tdgf gij(r1; r2, t) relates a unit concentrated impulse displacement in the direction i at r1 to the displacement response in direction j at receiver r2. the tdgf which comes from random noises that propagate from stations 1 to 2 produces a positive correlation time delay t and the time-reversed tdgf produces a negative correlation time delay −t (cited from martha, et al., 2017). the data processing consists of preparing waveform data from each station individually. the recording data from the seismograph was in minisheet and ascii data and then converted into sac (seismic analysis code) data to get a smaller size of the data. fig. 5. a. cross-correlation processing schemes in this research, for a and b pair stations (martha et al., 2017), b. results of cross-correlation between station n026 and other stations for cross-correlation processing data, the data series reading was made in 23 segments per day which in each segment has a 1-hour time window. the sampling frequency was set to 100 samples per second in a window. the cross-correlation process was done in the first segment between 2 stations and continued to the 23rd segment then stack all of the segments in a day for getting the result of the cross-correlation of the pairing station in a day (fig. 5a). the result of the cross-correlation of the pairing station in the whole day's survey was derived by stacking all crosscorrelation of the first to the end of the day (fig. 5b). we used a bandpass filter with a frequency limit between 1 to 1.8 hz to extract all pairs of stations in the study area. 3.2 dispersion measurement after the daily cross-correlations have been computed and stacked, the resulting waveform is an estimated green function. using the estimated green function, the group velocity as a period function can be measured using the multiple filter technique (mft). fig. 6. a. example of the cross-correlation waveform at pair stations. b. dispersion curve. the dispersion curve (fig. 6b) is derived from a crosscorrelation waveform (fig. 6a) by conversion from period amplitude to period-velocity series where warm colours indicate the highest quality data with larger amplitudes. dots indicate all possible dispersion curves. 70 dwikorianto, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 4. results and discussion 4.1 checkerboard test before performing the inversion with real data, we investigated the capability of the array to solve the velocity structure at different periods through the checkerboard test. the resolution test by using a checkerboard should be done in order to get a good resolution of the tomography image. parameters resolution tests of grid size, smoothing, and dumping was done by trial and error. the grid size is made in 0.3 km to 0.6 km and the dumping and smoothing parameters are made in the range of 1-50. fig. 7. resolution test by using the grid size of 0.3 km fig. 7 shows the resolution test with the grid size of 0.3 km, the dumping of 10, and the smoothing of 10 shows that the velocity model in all periods is not reconciled with the initial model. fig. 8. resolution test by using the grid size of 0.4 km fig. 8 shows the resolution test with a grid size of 0.4 km, the dumping of 10, and the smoothing of 10. the result is good in all periods because they reconcile with the initial model. fig. 9. resolution test by using the grid size of 0.6 km fig. 9 shows the resolution test with a grid size of 0.6 km, the dumping of 10, and the smoothing of 10. the velocity model in the eastern is better than in other areas due to the interstation distance in the eastern is denser (~125 meters) than in other areas (~250 meters). the result is good in periods of 0.1 to 1.9 seconds but not in periods of 2.5 seconds. from the three modeling above, the grid size of 0.4 km and using the dumping of 10, and smoothing of 10 are used for the tomography process in building the group velocity map in some periods. 4.2 group velocity the two-dimensional distributions of group velocities were computed based on the iterative tomographic inversion of the group-velocity data for all available station pairs. after selecting the highest quality dispersion curve measurements, we compute group velocity maps from 0.1 to 4 s period. the two-dimensional distributions of group velocities were computed based on the iterative tomographic inversion of the group-velocity data for all available station pairs. fig. 10. group velocity map by using a grid size of 0.4 km; dumping and smoothing of 10 in certain periods fig. 10 shows the tomography process in period 0.1 to 0.4 s which indicating the distribution of low velocity in almost cover in the whole area, however the velocity increase simultaneously with the period increasing (fig. 10). it is interpreted as soft formation in the upper zone with a period of 0.1 – 0.4 s and harder formation below it with a period of 1.3 – 2.2 s. the soft formation is interpreted as caprock, and the harder formation is the reservoir. the period of 0.7 – 1.0 s is interpreted as a transition zone from caprock to reservoir. in some areas, the low-velocity anomaly in a high period (> 1.3 sec) is interpreted as a permeable zone. 5. conclusion seismic ambient noise tomography by cross-correlation of seismic ambient noise using seismographic data from several portable seismograph deployments describes the condition of the subsurface structure of hululais area. from the dispersion curve measurement, the short inter-station distance will cover the shallow formation and the longer inter-station distance will cover the deeper formation. and from the group velocity identification, the low velocity anomalies in the shallow zone are correlated with caprock and the higher velocity anomalies in the deeper zone are correlated with the reservoir. however, the low anomalies in the deeper zone are interpreted as the permeable zone. acknowledgment grateful and appreciative to pge’s exploration and exploitation division for supporting the data, information, and discussion. also, the authors thank pt pertamina geothermal energy for permission to publish this study in dwikorianto, t.b. et al./ jgeet vol 08 no 02-2 2023 special issue from the 1st international conference on upstream energy technology and digitalization (icupertain) 2022 71 the international conference up stream energy technology and digitalization. references koulakov, i., maksotova, g., jaxibulatov, k., kasatkina, e., shapiro, n.m., luehr, b.g. et al., 2016. structure of magma reservoirs beneath merapi and surrounding volcanic centers of central java modeled from ambient noise tomography. geochem. geophys. geosyst 17, 4195–4211. doi:10.1002/2016gc006442 lehujeur, m., vergne, j., schmittbuhl, j., maggi, a., 2015. characterization of ambient seismic noise near a deep geothermal reservoir and implications for interferometric methods: a case study in northern alsace, france. geothermal energy 3, 3. doi 10.1186/s40517-014-0020-2 martha, a.a., widiyantoro, s., cummins, p.r., saygin, e., masturyono., 2015. upper crustal structure beneath east java from ambient noise tomography: a preliminary result. aip conf proc 1658, 030009. doi: 10.1063/1.4915017 martha, a.a., widiyantoro, s., cummins, p.r., saygin, e., masturyono., 2016. investigation of upper crustal structure beneath eastern java. aip conf proc1730, 020011. doi: 10.1063/1.4947379 martha a.a, cummins p, saygin e, widiyantoro s, masturyono., 2017. imaging of upper crustal structur beneath east java–bali, indonesia with ambient noise tomography, geosci. lett., 2017) 4:14 doi 10.1186/s40562-017-0080-9 panshori, a., martha, a.a., maryanto, s., 2019. imaging the velocity structure of rayleigh wave in sulawesi island using ambient noise tomography, ijasre 5(1), 85095. doi: 10.31695/ijasre.2019.33072 rawlinson, n., sambridge, m., 2005. the fast marching method: an effective tool for tomographic imaging and tracking multiple phases in complex layered media. exploration geophysics 36(4), 341–350. doi: 10.1071/eg05341 saphiro, n.m., campillo, m., 2004. emergence of broadband rayleigh waves from correlations of the ambient seismic noise. geophysical research letters 31, l07614. doi:10.1029/2004gl019491 snieder, r., 2004. extracting the green’s function from the correlation of coda waves: a derivation based on stationary phase. phy. rev. e 69, 046610. 10.1103/physreve.69.046610 vita, a.n., zulfakriza, z., martha, a.a., rohadi, s., heryandoko, n., milkerreit, c., 2022. preliminary result of rayleigh wave tomography beneathjailolo volcanic complex, north moluccas, indonesia using ambient noise. j. phys.: conf. ser 2243, 012024. doi:10.1088/1742-6596/2243/1/012024 wahida, a., wijaya, h., yudistira, t., sule, m.r., 2018. ambient noise tomography for geothermal exploration, a case study of wws geothermal field. international symposium on earth hazard and disaster mitigation (isedm). aip conf. proc. 1987, 020101. doi: 10.1063/1.5047386 wuryani, s.d., yudistira, t., widiyantoro, s., 2019. surface wave tomography using seismic ambient noise data for subsurface imaging beneath bandung basin, west java and its surrounding. iop conf. ser.: earth environ. sci. 318, 012032. doi: 10.1088/17551315/318/1/012032 yang, y., ritzwoller, m.h., 2008. characteristics of ambient seismic noise as a source for surface wave tomography. geochemistry, geophysics, geosystems 9(2), q02008. doi:10.1029/2007gc001814 zulfakriza, z., nugraha, a.d., widiyantoro, s., cummins, p., sahara, d.p., rosalia, s. et al., 2020. tomographic imaging of the agung-batur volcano complex, bali, indonesia. front. earth sci 8, 43. doi: 10.3389/feart.2020.00043 © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 110 winantris et al./ jgeet vol 02 no 02/2017 paleoenvironment of tanjung formation barito basincentral kalimantan based on palynological data winantris 1, *, helman hamdani 1 , ellin harlia 1 1 padjadjaran university abstract the research area is located in the muara teweh, north barito, central kalimantan. the cocking coal deposits are well known as they were produced from this area. upper part of tanjung formation is target coal production. the study objectives are to analyze paleoenvironment and to determine the relative age of coal deposits based on palynological data. preparing palinological analysis used standard procedure by hydrofluoric acid method.palynomorphs data grouped into six types of ecology, and the sequence is as follows ; fresh water and lowland (41,75 %), brackish water swamp (30,10%), peat and freshwater swamp (17,96%), marine element (7,77 %), back mangrove (1,46%) and upland element (0,97). palmae pollen is very dominant, especially from freshwater and peat swamp that grow around coastal area i.e. dicolcopollis, proxapertites cursus, proxapertites operculatus, longapertites and palmaepollenites kutchensis. although marine fossil found, but the frequency less than one percent, that was the evidence of influence sea water to swamp area. the palynomorphs indicate the coal sedimented at upper delta plain. fossil index of relative age consist of proxapertites cursus, proxapertites operculatus, magnastriatites howardi verrucatosporites usmensis, retistephanocolpites , and ixonantes type which refer to late eocene. key world: paleoenvironment, pollen, tanjung formation, central kalimantan. 1. introduction tertiary barito basin spread through central kalimantan until south kalimantan. the northern basin bordered by west kutai basin, and in the west by schwaner high, to the east by meratus high, in the south of the java sea. the basin covering an area of some 75,000 km2, sediment thickness varies from about 2000 to 5000 meters. basin formation started at the late cretaceous after the collision microcontinent between paternoster and sw borneo microcontinent (satyana and idris, 2006). the complete cycle sedimentation of sedimentary rock is found in this basin from eocene to miocene by regression and transgression series. tanjung formation rocks is an oldest sedimentary rock in this basin which was deposited unconformity above pretertiary basement rock. sediment deposition process takes place in an environment fluvio-deltaic, delta front until neritic zone. the tanjung formation occurred since late paleocene until late eocene (satyana and silitonga, 1994). coal was a sedimentary rock that filled the earliest tanjung formation, so that coal is the oldest sedimentary rocks that formed in the barito basin. tanjung formation generates cooking coal that estimated formed in the late eocene (belkin dan tewalt, 2007; friederich, et al, 2009; nas dan hindartan, 2010). construction of tanjung formation started since paleocene until late eocene (satyana and silitonga, 1994). the area spread from central kalimantan until south kalimantan, so very possibly to occupy various environment. research focus on coal tanjung formation of muara teweh, central kalimantan. this objective of study to determine the age and depositional environment condition during the sedimentation of tanjung formation which was exposed in the study area. the tanjung coal formation are outcropping in the northern part of barito basin. the coordinates of coal sample is 1 o 3'39,74'' s and 114 o 38'37,26'' e within 50 km to the southwest of muara teweh district and about 250 km to the northeast from palangkaraya city, situated is established between 1 o 3'39,74'' s and 114 o 38'37,26''e (fig 1). 2. stratigraphy bariro basin stratigraphy barito basin in research area arranged into five formation and an alluvium sediments (fig 2), as follows: tanjung formation is the oldest rock sediment. the lower part of tanjung formation consists of alternating among glauconitic sandstones, shale, siltstone and conglomerate of various materials, some of which are calcareous. conglomerate's components consist of quartz, feldspar, granite, schist, gabbro and basalt. * corresponding author : win.oncos@gmail.com tel.:+81-80-929-1466; fax: +81-72-867-1658 received: 2 may, 2017. revised : 28 may 2017, accepted: 30 may, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.305 mailto:win.oncos@gmail.com winantris et al./ jgeet vol 02 no 02/2017 111 fig. 1. location of coal sample (right) and coal outcrop (left) fig. 2. stratigraphy of research location (modified from supriatna et.al,1981) 112 winantris et al./ jgeet vol 02 no 02/2017 the upper part consists of alternating quartz sandstone, siltstone, limestone, and coal. the relative age of tanjung formation is late eocene, it lays unconformity on the basement mesozoic rocks, a thickness of sediment about 1,300 meters and the depositional environment is the swamp. berai formation composed of gray and white limestone, fine to medium grained, partly recrystallized, contains a large foraminifera and coral, partially layered, it lays conformity on the tanjung formation, relative age about middle oligocene to late oligocene, deposited in shallow marine environment, the thickness reach 1.250 meters, it occupies a steep karst hills. karamuan formation composed of consists of gray mudstone, partly calcareous and fossilized; quartz sandstones; gray siltstone; light-gray tuffaceous siltstone, there is fossil insert in the limestone, carbonaceous siltstone, shally siltstone overlie the tanjung formation conformably, and estimated interfingering with berai formation, deposited in shallow marine to outer self. montalat formation characterized by white quartz sandstones, cross bedding structures, partly calcareous, deposited overlie the formasi tanjung conformably in a marine environment, interfingering with berai formation, oligocene, the sediment about 1.400 meters thick. warukin formation, the character of the sandstone includes beds that are medium grained, well sorted. contain carbonaceous mudstone, carbonaceous siltstone. party conglomeration sandstone, semi-solid, cross and parallel laminations. this formation overlies the berai formation, the depositional environment of the warukin formation is coastal at middle miocene, estimated to be 500 meters in thickness. alluvial deposit consist of gravel, pebbles, sand, mud and plant debris. 3. material and methods sample have been prepared by the standard method using hydrofluoric acid digestion continued by oxidation. the function of each chemical material is; concentrated hydrofluoric acid to remove silica, potassium hydroxide to remove humic acid, hydrogen chloride to remove carbonate, zinc chloride with specific gravity 2.2 to separate palynomorphs from others material. acetolysis is a process to remove cellulose. before making slides, palynomorphs colored by safranin. examination of palynomorphs was using transmission light microscope in different magnification of 100x, 400x, and 1000x. based on the environment of palynomorphs origin then grouped based on their environmental, in this case grouped into six i.e: marine, back mangrove, brackish water swamp, freshwater swamp, freshwater and upland element. marine palynomorphs which observed only dinocyst and linning test foraminifera, both of them were found in the sample. back mangrove element referred to pollen and spore that produced by vegetation which grows behind mangrove environment. freshwater swamps elements are pollens and spores that came from around streams or lake which influenced by rain and seasonal flooding so causes water levels to fluctuate swampy condition. freshwater elements are pollen, spore, and algae which came from the freshwater environment around lowland area. the upland element is pollens and spore which produced by vegetation came from mountain vegetation. type of vegetation environmen have been publish by haseldonxk (1974). 4.result and discussion 4.1.paleoenvirnment acquired 206-grain palynomorphs that comprising 7.84% of the marine environment, which consists of dinoflagellate cyst and linning test foraminifera. brackish water swamp 19.61%, consisting of pollen/spore derived from the fact brackish environment is derived from mangrove and back mangrove. peat and freshwater swamp 30.39%, those are pollen and spore which produced by plants from peat swamps, freshwater swamps, and riparian. freshwater and lowland 41.18%, consist of pollen which produced by lowland and freshwater plants. upland pollen 0.98%, the result of windtransported pollen (fig 3).overall palmae pollen is the highest pollen that consisting of proxapertites cursus, proxapertites operculatus, palmapollenites kuthensis, longapertites and dicolcopollis. the plants grow in the coastal areas, especially in the brackish marshes that position area is behind the mangrove until around the river. this fact supported by acrostichum aureum spores were found at the site as indicator brackish area.the collision of india and asia plate in the middle eocene to propagate plants from india to southeast. asia region. at that time both the northern region of the indian plate and the sunda region experiencing always wet climate, which is reflected in the equatorial climate and common events coal formation in both areas (morley1998, 2003). pollens are considered developing in the sunda region follow the collision and found at the study area are palmapollenites kutchaensis, retistephonocolpites , magnastritatites grandiosus / magnastriatites howardii, ixonanthes type / spiniulotriporites spinous, lakiapollis ovatus.even marine fossils obtained very few, its presence indicates that the sediment deposition occured in the transitional basin. dinoflagellate cyst and inner test foraminifera are marine fossils that transported by tidal current through a channel and a connection between the deposition area and the sea. based on palynomorphs composition which dominated by pollen and spore from swamp environment that refers to the delta environment, particularly delta plain. winantris et al./ jgeet vol 02 no 02/2017 113 fig.3. palynomorphs group in quantity and percentage fig. 4. cicatricosisporites eocenicus (1), palmapollenites kutchensis (2), proxapertites cursus (3) dicolcopollis (4) inner test foraminifers (5), podocarpidites (6) 114 winantris et al./ jgeet vol 02 no 02/2017 table 1. ecological group of palynomorphs no ecological group palynomorphs 1 marine element marine dynocyst foraminifera test linning 2 back mangrove acrostichum aureum 3 brackis water swamp proxapertites operculatus proxapertites cursus dicolcopollis 4 fresh water swamp blumeodendron lakiapollis ovatus lanagiapollis emerginatus longapertites palmapollenites kutchaensis polygalacidites sp sapotaceoidaepollenites sp verrucatosporites usmensis 5 fresh water anacolosidites lutoides bombacaeae cycadopites gothanipollis gymnospermae ixonantes type lycopodium cernuum lycopodium phlegmaria magnastriatites howardi margocolporites vanwijhei matonia sp monoporites annulatus osmundacidites palmae undet polygonum protecidites verrucatosporites spp retistephanocolpites wiliamsi laevigatosporites freshwater algae 6 upland element cedripites podocarpidites winantris et al./ jgeet vol 02 no 02/2017 115 table 2. age relative based on pollen and spore marker 4.2. relative age some importance fossils have been obtained which can be used to determine relative age tanjung formation particularly in the research area as follow: proxapertites cursus, proxapertites operculatus, palmapollenites kuthensis (iguanurinae), verrucatosporites usmensis, magnastritatites grandiosus/magnastriatites howardii, retistephanocolpites . both proxapertites operculatus and proxapertites cursus, those fossils existed in the kalimantan until the late eocene, although the first appearance was not explicitly described (morley, 1991). magnastritatites howardi recorded appeared in the border of late eocene early oligocene (morley.1998), the appearances of verrucatoporites usmensis approaching the middle-late eocene border. palmapollenites khutcensis existed since eocene until oligocene, and retistephanocolpites wiliamsi appeared in the middle eocene and disappeared in the late oligocene. based on those taxa the establishment process of coal in the study area during late eocene (fig 4). 5. conclusions the results showed that the tanjung coal formation in the barito basin was formed at lateeocene. this is different from previous research that said tanjung formation in the muara teweh the age relative was early eocene. the dominance of pollen which derived from swamp habitat indicates that the process of coal sedimentation occurred in the swamp environment with marine influence. acknowledgements we are grateful to rector of padjadjaran university who have suport this research through academic leadership programme (alg). references anonim, 2016. swamp, bog, and wetland. national geographic society belkin, h.e, and tewalt, s.j, 2007. geochemistry of selected coal samples from sumatra, kalimantan, sulawesi, and papua, indonesia. usgs. science for changing the world. gower,d; johnson, k; richardson,j; rosen, b;rüber, l; williams, s; 2012.biotic evolution and environmental change in southeast asia. cambridge university press. friederich, m; esterle,j; moore,t; and nas, ch, 2009. variations in the sedimentological characteristics of tertiary coals in se asia; and climatic influences on tertiary coals and modern peats. heryanto r dan sanyoto p. 1994. peta geologi lembar amuntai , kalimantan selatan. lee kong chian 2016. freshwater swamp natural, history museum. all rights reserved. morley, 1998. biogeography and geology evolution of se asia pp 211-234, backhyusp ublisher, leiden, netherlands. morley rj .2012. a review of the cenozoic palaeoclimate history of southeast asia. biotic evolution and environmental change in southeast asia, eds gower dj, et al.(cambridge university press, cambridge, uk), pp 79-114. nas, ch and hidartan 2010. the quality of central kalimantan coocking coals, proceeding mgeiiagi. balikpapan kalimantan. nas, ch and hindartan, 2010. kalimantan coal and mineral resources. proceeding mgei-iagi,2930 march 2010, balikpapan, kalimantan indonesia 116 winantris et al./ jgeet vol 02 no 02/2017 satyana, a.h., idris, r., 2006. chronology and intensity of barito uplifts, southeast kalimantan: a geochemical constraint and windows of opportunity: abstract 2006. satyana, a.h., silitonga, p.d., 1994. tectonic reversal in east barito basin, south kalimantan: consideration of the types of inversion structures and petroleum system significance. proc. indones. pet. assoc. twenty-third annu. conv. oct. 1994 57 74. witts, d., hall, r. morley, r.j. and boudagherfadel, m. k. 2011. stratigraphy and sediment provenance, barito basin, southeast kalimantan. proceedings indonesian petroleum association, 35th annual convention, ipa11-g-054 1-18. witts, d., hall, r; nichlos,g and morley, r.j. 2012. a new depositional and provenance model for the tanjung formation barito basin,se kalimantan indonesia. journal of asian earth sciences 56 (2012) 77 104. 1. introduction 2. stratigraphy bariro basin 3. material and methods 4.result and discussion 4.1.paleoenvirnment 4.2. relative age 5. conclusions acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 zafar, sumaira et al./ jgeet vol 02 no 04/2017 235 development of goverment schools based on gis: a case study of orangi town, karachi sumaira zafar 1 *, maha qaisar 1 , zainab sohail 1 , arjumand zaidi 2 1-2 department of remote sensing and gisc, institute of space technology (ist)-karachi, 2 usaid advance center for water studies, mehran university of engineering and technology-jamshoro * corresponding author : sumaira.zafar_ncrg05@ist.edu.pk tel.:+92-21-34650765 ext 2296 received: june 6, 2017. revised : sept 18 2016, accepted: oct 09, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.348 abstract the primary school system in pakistan needs improvement in order to provide the basic right of education to all. government schools are not enough to cater the needs of increasing population of the country. the main goal of this study was to present a methodology for the development of government schools based on geographical information system (gis) through a case study of orangi town in karachi. in this study, first the adequacy of government schools in the study area was evaluated and then the need for additional schools with their suitable locations were identified. data regarding school locations and students enrollments were collected from sindh basic education program of a non-profit ngo immap. school building footprints were digitized from 2001 and 2013 google earth archived images. population in 2013 was estimated by projecting 1998 census data downloaded from the website of the census bureau of pakistan. an educated assumption of 20 % of the total population of orangi town was used to calculate number of primary school-aged children. study results showed that schools existed in 2013 were not sufficient to serve all these children. this study also revealed that new schools were built during this time period, but the population growth rate was much higher than the growth rate of schools that created a big supply-demand gap. the most progressive union council (uc) of orangi town was haryana colony where 17 new schools were constructed between 2001 and 2013 though the required number of schools still fall short. new sites for schools analysis. keywords: education, gis, proximity analysis, schools, temporal analysis 1. introduction education is the basic human right that should be available to all people belonging to any socioeconomic class. it is not only the requirement of an individual but the successful human societies around the world have high literacy rates. pakistan is a developing country with high population growth rate and the reported literacy rate of pakistan is 57.7 % (rehman et al., 2016). the people belonging to the lower and lower middle classes can only afford government schools for their children because of their minimal tuition fees. the population growth rates in these two classes is higher than the growth rate of government schools accessible to them. before the situation gets further worse, there is an urgent need to improve the education facilities and make it possible for every child in the country to avail this opportunity. every good governance is expected to take up the responsibility of facilitating its peoples in acquiring quality education. in pakistan, there are two types of school systems; the government schools where education is almost free, and the private schools that charge extraordinarily high fees for providing education. the existence of parallel educational systems in pakistan and their limited accessibility to the majority of the population is even a bigger dilemma. the underprivileged children can only study at government schools and most of these schools not only have an insufficient number of teachers and limited educational facilities but lack proper curriculum to compete (alderman et al., 2001). parents, who may afford higher tuition fees, send their children to private schools. the medium of teaching is also different in both private and public school systems. this disparity is not only promoting a class difference between the masses and the elites of our society, but it is also causing restlessness among people who are deprived of their basic education right. gender imbalance at school level is also evident from the prevailing ratio of 10 boys to 4 girls (qureshi, 2012). one of the reasons for this unfortunate situation is the low allocation of funds in the education sector coupled with unsuitable sites selection for schools. in 2014 national budget, financial allocation for education is around 1.5 % to 2 % of the total national gross domestic product (gdp) which is way too low compared with the global standard of 4 % (ministry of finance, n.d.). poverty and its consequence in the form of child labour are also some major factors that mailto:sumaira.zafar_ncrg05@ist.edu.pk 236 zafar, sumaira et al./ jgeet vol 02 no 04/2017 prohibit parents to send their children to schools (ray, 2000). these problems contribute to low literacy rate in the country which in turn causes economic crises in terms of increasing number of unemployed people. taking all these factors into account, it was felt necessary to evaluate government schools and their growth in the past decade taking orangi town as a test case (taki and lubis, 2017). although one of the five programs run by the renowned orangi pilot project since 1980 in the same area was education which has upgraded and improved the academic standards of the private schools in orangi town (hasan arif, 2006). however, the need for upgradation of government schools still exists. in this study, a geodatabase of the existing schools in the study area was built that was further utilized to derive valuable information regarding the adequacy of the current school system serving orangi town residents. it is an agreed upon fact that planning and development in any sector including education can be done more efficiently if these are managed through geodatabases. in this study, sites for building new government schools were also proposed in areas where the existing system failed to cater the educational needs of the people. emerging technologies of geographical information system (gis) and remote sensing (rs) were utilized for this purpose (audet and paris, 1997)(agrawal and gupta, 2017)(huang and jiang, 2017). 1.1 study area orangi town is a densely populated town in the northwestern part of karachi covering an area of 60 sq.km. it shares borders with new karachi town in the north, gulberg town in the east, liaquatabad town in the south, and site town in the west (fig. 1). orangi town has 13 union councils 1 (ucs) with a total population of 919,995 people out of which 183,999 are children of 4-5 years age group. the town consists of 86 informal settlements or katchi abadis which account for over 70 % of its population. it has 104,917 houses in 7,256 lanes which make on average around 9 people per house (hasan arif, 2000). several ethnic groups are residing in orangi town including muhajirs, punjabis, sindhis, kashmiris, seraikis, pakhtuns, balochis, memons, bohras, ismailis, and others. orangi town was selected for this study because of its critical condition with respect to population, economic status, urban sprawl, and an insufficient number of government schools. orangi residents merely get enough money to make both ends meet, so it is quite hard for them to send their children to private schools of the area where tuition fees are higher than what they can afford. 1 administrative units at city level. fig 1. study area government schools are not only insufficient in number, but their defective and inadequate infrastructure, larger class sizes, and unstable enrollments are making these systems less efficient and unattractive for the residents of orangi town. 2. methodology this study has three major objectives as described below. 1. to report temporal changes in number of schools over a span of 12 years from 2001 to 2013 using google earth archive images to evaluate their growth in orangi town. 2. to calculate the ratio between primary school aged children and number of schools to access the adequacy of existing schools in the study area. 3. to analyze the proximity of schools from the population being served and suggest new school locations for orangi town children with easy access to serving schools. 2.1 data collection for mapping of schools, it was necessary to collect school location data. the existing school data used in this study were acquired from usaid nonprofit organization immap pakistan (broda and baxter, 2003). the immap had earlier conducted a survey with the objectives to reconstruct and rehabilitate schools in five (5) towns of karachi. other data and their sources are listed below. zafar, sumaira et al./ jgeet vol 02 no 04/2017 237 1. union council map of orangi town of karachi metropolitan corporations. 2. google earth archive maps to find out the temporal changes in the number of schools over the span of 12 years (al-hanbali et al., 2003). 3. union council (uc) wise population data of orangi town from the census bureau of pakistan (mahmood, 2011). 2.2 data processing several data processing steps were performed to achieve the objectives of the study. the following are the sequence of these steps including gis and remote sensing techniques. fig. 2 shows the methodological framework of the study. fig. 2. methodological framework 1. geo-referencing: maps of orangi town, acquired from karachi metropolitan corporation (kmc), were scanned and georeferenced using ground control points identified at google earth images. 2. digitization: digitization of uc level maps and school location data were done to prepare geodatabase and gis maps. 3. data manipulation: information from raw data was derived. details of data analysis are 4. estimation of future population: the available population fig.s, when this study was conducted, were from 1998 census. population growth model (eq. 1) was used to estimate the population of orangi town in 2013 (p) using 2 % population growth rate (r) described in the current account balance of pakistan . p = po e rt eq.1 where; po = population in 1998 (723,694 people); r = 0.02; t = time span for estimation which was 15 years in this study. population of 2013 was calculated as; p (2013) = 723,694 e 0.02*15 = 976,884 people 3. data analysis and results 3.1. temporal change in number of schools from 2001 to 2013 as discussed earlier, the primary education in a country should be the responsibility of its government. to assess the initiatives taken by the city government of karachi in its highly populated town of orangi, the number of government schools, their growth to cater increasing population of the town, and their serving capacities to address the need of the residents were analyzed. it was believed that with an increase in population there should be a corresponding increase in the number of schools. using immap data and google earth archive maps, schools that existed in 2001 were digitized first. tabel 1. number of schools in 2001 and 2013 similarly, the school's footprints in 2013 were digitized. the difference between 2013 and 2001 schools was the change in number of schools in orangi town over the span of 12 years. few pieces of evidence were drawn from the following maps and tables (1-2) that are discussed in this section. name uc. no. school (2001) school (2013) new school in 12 years azad nagar 1 6 14 8 haryana colony 2 0 17 17 hanfiabad 3 4 11 7 muhammad nagar 4 8 13 5 madina colony 5 1 5 4 ghaziabad 6 2 4 2 chushti nagar 7 0 5 5 bilal colony 8 3 3 0 islam chowk 9 4 4 0 gabol colony 10 3 5 2 data nagar 11 9 9 0 mujahidabad 12 2 12 10 baloch goth 13 8 8 0 238 zafar, sumaira et al./ jgeet vol 02 no 04/2017 fig.s 3 and 4 illustrate the number of schools in ucs of orangi town in 2001 and 2013 respectively. fig. 5 is a density map for 2001 developed by dividing the number of schools in each uc by its area in sq.km. the density of schools was more in regions with darker shades in the map. baloch goth had 11 schools, data nagar 6 to 10 and muhammad naqar had 4 to 5 schools per sq.km. fig. 3. schools in 2001 fig. 4. schools in 2013 in 2013, the highest densities of schools were found in baloch goth and mujahidabad, and high densities in haryana colony, hanifabad and muhammad nagar (fig. 6). fig. 5. 2001 schools density map fig. 6. 2013 schools density map fig. 7. uc-wise increase in schools (2001-2013) fig. 7 shows the temporal changes in number of schools in each uc. haryana colony had the maximum increase of 17 schools during the study table 2. uc-wise population of orangi town name uc no. population 1998 estimated population 2013 azad nagar 1 56,160 75,808 haryana colony 2 64,570 87,160 hanfi abad 3 54,372 73,394 muhammad nagar 4 63,753 86,057 madina colony 5 49,998 67,490 ghaziabad 6 59,402 80,184 chushti nagar 7 58,582 79,077 bilal colony 8 64,776 87,438 islam chowk 9 62,248 84,026 gabol colony 10 56,121 75,755 data nagar 11 56,964 76,893 mujahidabad 12 51,866 70,011 baloch goth 13 24,882 33,587 total 723,694 976,884 zafar, sumaira et al./ jgeet vol 02 no 04/2017 239 period. gabol colony and hanfiabad also had new schools built during this time period. this information helped in deducing government initiatives and it was concluded that government had paid some, although not sufficient, attention to the education system of orangi town. to improve education standards in the town, the government ought to plan more schools in the union councils that have unserved population of school-aged children. 3.2. population to school ratio population to school ratio in each uc was calculated by dividing the uc population with the number of schools in that uc. the purpose of this analysis was to ascertain, on average, the population being served by a single school. fig. 8 and 9 show population to school ratios at uc level in 2001 and 2013 respectively. in these fig.s, the darker regions illustrate the severity level of these union councils bearing dense population with the scarcity of schools. fig. 8. population and school ratio (2001) fig. 9. population and school ratio (2013) 3.2.1. ratio between 5-9 years age group population and schools according to the estimated population of sindhpakistan, 15.47 % are 5-9 years age group children (distribution of population, 2012). the same percentage was used to calculate population between 5-9 years in each uc. table 3. uc-wise population of 5-9 years age group name uc no pop 1998 estimate d pop 2013 population between 5-9 years of age azad nagar 1 56,160 75,808 11,727 haryana colony 2 64,570 87,160 13,484 hanfiabad 3 54,372 73,394 11,354 muhammad nagar 4 63,753 86,057 13,313 madina colony 5 49,998 67,490 10,441 ghaziabad 6 59,402 80,184 12,404 chishti nagar 7 58,582 79,077 12,233 bilal colony 8 64,776 87,438 13,527 islam chowk 9 62,248 84,026 12,999 gabol colony 10 56,121 75,755 11,719 dada nagar 11 56,964 76,893 11,895 mujahidabad 12 51,866 70,011 10,831 baloch goth 13 24,882 33,587 5,196 total 723,69 4 976,884 151,124 fig. 10 represents the population of primary school going children in 5-9 years age group in 2013. each union council had more than 5,000 children between 5-9 years of age. map regions with intense shades represent the ucs having more children of this age as compared to the ucs with lighter shades. in fig. 10, it is also evident that number of students enrolled in the government schools of haryana colony was maximum among all other ucs. the number of enrollments in this uc was 2,600, whereas, the school-aged children of this uc were around 16,000 in 2013. this implies that majority of the school-aged children were not getting school education. 240 zafar, sumaira et al./ jgeet vol 02 no 04/2017 fig. 10. population of 5-9 years age group (2013) fig. 11. 5-9 years age group and schools ratio (2013) fig. 11 shows union councils with dark shades representing less number of schools for children between 5-9 years of age. as the shade goes lighter, the number of schools for the primary level going children increases. in fig. 12, it can be observed that a small number of students were enrolled in government schools in 2013. this can also indicate another problem of the area where not only the sufficient number of schools were not present to serve the population but the residents themselves were not aware of the importance of educating their children. 3.3. proximity of school to serving population orangi town comprises of low-income group residents that can barely afford educational expenses of their children. it is presumed that people living far from schools will hesitate to send their children with an additional conveyance cost. gis proximity tool based on euclidean distance was used to visualize the distances of current schools from the settlements of the orangi town (lisa aultman-hall et al., 1997) (falb et al., 2007). for proximity analysis, a maximum threshold of 500 meters was considered as a convenient walking distance for children living nearby. proximity analysis was done to evaluate if these schools were within this convenient distance from the population being served? new schools were proposed where people were living far from schools at a distance more than 500 m. fig. 13. proximity from existing schools in fig. 13, the served areas are presented by the innermost circles (in yellow colour) with 500 meters radius around each school. fig. 13 also illustrates the distance of each school from adjoining population. from this fig., an urgent need can be highlighted for establishing new schools in the areas with deep orange shade representing areas farther than 500 m from any serving school in orangi town. the gis tools can be used to suggest new school sites based on an easily accessible distance between schools and people being served by these schools. following this approach, fig. 14 represents proposed new schools sites in ghaziabad, bilal colony, medina colony, chisti nagar, islam chowk, gabol colony, azad nagar, and haryana colony. fig. 14. easily accessible proposed school sites 4. conclusions in this study school data of 2013 were compared with the school footprints on 2001 archive google earth image to analyze schools growth during study period in a heavily populated town of karachi named orangi town. the school growth was also compared with the population growth of orangi town within that time frame. as expected, the population growth was much higher than the increase in number of schools. the existing schools were found to be insufficient in number to cater the zafar, sumaira et al./ jgeet vol 02 no 04/2017 241 educational needs of the area. this situation is very alarming and many social issues such as unemployment, crime, poverty, and others can emerge due to increase in illiterate population. the school going population in each uc was divided by the number of schools present in that uc to find out the number of children that could be served by a single school. few ucs that were densely populated had very high children to school ratio which indicated that the existing schools in 2013 were not enough and more schools were needed in these areas. in this study, the proximity of schools from the population to be served was also analyzed considering a maximum threshold of 500 meters as an acceptable walking distance for children living nearby. this proximity analysis revealed that there were some unserved settlements in the northern parts of orangi town. the gis proximity analysis also helped in identifying sites for the construction of new school buildings in unserved areas of ghaziabad, bilal colony, medina colony, chisti nagar, islam chowk, gabol colony, azad nagar and haryana colony. this is also important to mention here that this study was based on quantitative assessment of primary school systems in orangi town that is not a sufficient indicator to evaluate an overall adequacy of any education system. not only the construction of school buildings should be the prime concern but maintaining it further is essential for the sustainability of the educational system. therefore, it is proposed as a future research task, to evaluate the quality of school system in orangi town to augment the finding of this study. till then, the results of this study can help the government to step forward and strengthen educational system through establishing new schools in areas that are still unserved. only then the limited education budget can be optimally utilized and people at orangi town may get primary education within walking distances from their homes and at an affordable cost. references agrawal, s., gupta, r.d., 2017. application of image analysis in land-use and land-cover assessment around schools for planning and development, in: proceedings of the computer graphics international conference. p. 4. al-hanbali, n., al-kharouf, r., bilal, m., 2003. integration of geo imagery and vector data into school mapping gis datamodel for educational decision support system in jordan. alderman, h., orazem, p.f., paterno, e.m., 2001. school quality, school cost, and the public/private school choices of low-income households in pakistan. j. hum. resour. 304 326. audet, r.h., paris, j., 1997. gis implementation model for schools: assessing the critical concerns. j. geog. 96, 293 300. broda, h.w., baxter, r.e., 2003. using gis and gps technology as an instructional tool. soc. stud. 94, 158 160. doi:10.1080/00377990309600199 distribution of population, 2012. falb, m.d., kanny, d., powell, k.e., giarrusso, a.j., 2007. estimating the proportion of children who can walk to school 33, 269 275. doi:10.1016/j.amepre.2007.05.005 hasan arif, 2006. orangi pilot project  : the expansion of work beyond orangi and the mapping of informal settlements e n v i r o n m e n t & u r b a n i z at i o n 18, 451 480. doi:10.1177/0956247806069626 hasan arif, 2000. scaling up of the orangi pilot project programmes  : successes , failures and potential. huang, g., jiang, y., 2017. urbanization and socioeconomic development in inner mongolia in 2000 and 2010: a gis analysis. sustainability 9, 235. lisa aultman-hall, roorda matthew, w. baetz brian, 1997. using gis for evaluation of neighborhood pedestrian accessibility _ journal of urban planning and development _ vol 123, no 1. j. urban plan. dev. 123. mahmood, n., 2011. the demographic dividend  : effects of population change on school education in pakistan. ministry of finance, n.d. highlights of pakistan economic survey 2013-14. qureshi, m.g., 2012. the gender differences in school enrolment and returns to education in pakistan. pak. dev. rev. 219 256. ray, r., 2000. child labor, child schooling, and their interaction with adult labor: empirical evidence for peru and pakistan. world bank econ. rev. 14, 347 367. rehman, a., jingdong, l., hussain, i., 2016. paci fi c science review b  : humanities and social sciences the province-wise literacy rate in pakistan and its impact on the economy. pacific sci. rev. a nat. sci. eng. 1, 140 144. doi:10.1016/j.psrb.2016.09.001 taki, h.m., lubis, m.z., 2017. gis modeling accessibility of community facilities: a study case of depok city, indonesia. geospatial inf. 1. 1. introduction 1.1 study area 2. methodology 2.1 data collection 2.2 data processing 3. data analysis and results 3.1. temporal change in number of schools from 2001 to 2013 3.2. population to school ratio 3.3. proximity of school to serving population 4. conclusions references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 213 research article interpretation of 2d-subsurface resistivity data in the iron ore prospect area of eastern binangun coastal, regency of cilacap, central jawa sehah 1, *, sukmaji anom raharjo 1 , fajar destiani 1 1 department of physics, jenderal soedirman university, jl. dr. suparno no. 61 purwokerto, central java, indonesia * corresponding author : sehah.geophysics@gmail.com tel.:081-327-507517; fax: 0281-638793 received: september 20, 2018; accepted: november 31, 2018. doi: 10.24273/jgeet.2018.3.4.2139 abstract interpretation of 2d-subsurface rock resistivity data has been carried out in the iron ore prospect area of eastern binangun coastal in cilacap regency, central java. the background of this research is the potential for abundant iron sand in this area that prospects to be exploited. the research was conducted using a magnetic method in 2017 to map the distribution patterns of the local magnetic anomalies that were interpreted to originate from the distribution of iron ore in the subsurface. in 2018, the research continued using the 2d-resistivity method to find out the lithology section in the subsurface of research area. 2dresistivity data acquisition is carried out on four tracks consisting of bng-01 to bng-04. the resistivity data modeling have produced the true resistivity value for each track in the form of the subsurface resistivity section, which including the bng-01 track is 2.27 bng-02 track is 4.5 bng-03 track is 6.37 bng-04 track of 4.98 interpretation process, some models of subsurface rocks lithology section is obtained under the four trajectories. ore grains (28.2 ter main part of the coastal aquifer so that exploitation of iron sand has the potential to reduce aquifer function in storing and flowing of groundwater and causing of abrasion in the eastern binangun coastal area rivers. keywords: 2d-resistivity data, iron ore, subsurface lithology section, binangun coastal 1. introduction 1.1 research background one of the natural resources found in the south coast of java island in indonesia is iron sand. iron sand is a rock fragment measuring between gravel and silt or 0,0625 2 millimeter on the wentworth-udden scale (a scale which distinguishes sedimentary rocks based on their size). based on the information from the oregon department of geology and mineral industries (dole, 2006), iron sand consists of opaque mineral mix with non-metallic minerals, such as feldspar, calcite, biotite, amphibole, tourmaline, pyroxene, and others. while the iron ore minerals consist of magnetite, titaniferous magnetite, ilmenite, limonite, and hematite. titaniferous magnetite is an important part, which is a change from magnetite and ilmenite. especially the iron ore minerals come from the basaltic and the andesitic volcanic rocks. regency of cilacap, that located at the south coast of java island has abundant natural resources of iron sand. one of them is the eastern binangun coastal. this area is located in the eastern of cilacap city with a distance is about 35 km. the iron ore reserves in this area have not been officially exploited. according to the cilacap regency official website (2013), the total area which prospect of iron ore is more than 500 hectares, with a magnetism degree of 12.20% and iron (fe) content of more than 53%. the coastal area which prospect contains iron ore stretches from the village of welahan wetan district of binangun to the village of jetis district of nusawungu with reserve is about 744,678.85 tons. the dominant iron ore mineral in the binangun coastal is magnetite (fe3o4) (jatmika et al., 2012). geologically, the research area is composed of the alluvium formation and coastal sediments (asikin et al., 1992). the alluvium deposits that occupy the northern of the research area consist of silt, clay, sand, gravel, gluttony; and rocks material resulted from erosion of karangbolong ancient volcano that deposited through the flow of several rivers into the research area (asikin et al., 1992). while the coastal deposits that occupy the southern part of research area consist of very loose sand that shows the impression of layering where iron sand resource is found (herman, 2005), based on the results of research which performed by sehah et al. (2017), the sediment rock was obtained. these rocks http://journal.uir.ac.id/index.php/jgeet mailto:sehah.geophysics@gmail.com 214 sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 are interpreted as sand containing iron ore inserted with clay, silt, and gravel from the alluvium formation with depth of 1.709 11.966 meters. the magnetic susceptibility value of these rocks is estimated about 0.0093 cgs unit. the coastal aquifer is the groundwater sources that potential in the eastern binangun coastal area, such as for drinking, bathing, and other necessities of human life. the coastal aquifers are an important water source to meet the needs of freshwater, especially in areas that develop along the coast ( ). many areas on the coast which many populations, causing increased demand for freshwater. also, in this area usually there is the interface zone as a barrier between saltwater and freshwater (supriyadi et.al, 2017). therefore, this area around the coastal requires a special attention and management to overcome it. moreover, this area is the prospect of iron ore which potential to be exploited. 1.2. basic theory to determine the characteristics of coastal aquifers in the iron ore prospect area, the geophysical research is carried out. the method used in this research is the 2d-resistivity. the 2d-resistivity method is one of methods in the geoelectric survey which used to research subsurface conditions by studying the nature of electricity in the subsurface rocks. generally, the resistivity method is used for shallow exploration, that is around 300 500 meters (nurhidayat, 2016). the resistivity method can be used for exploration in several fields, such to interpret subsurface stratigraphical structure, distribution of mineral deposits, accumulation of petroleum in the shallow reservoir layer, groundwater aquifers, geothermal reservoirs, and fluid contact between oil and water (hersir, 2015). this research aims to obtain the 2d-resistivity cross section in the subsurface of eastern binangun coastal area based on the resistivity data from the acquisition. the subsurface resistivity profile that obtained is interpreted to obtain the subsurface rocks lithological profile in this area including the coastal aquifer and iron sand deposits so that its physical characteristics can be evaluated early. the 2d-resistivity method is suitable for this purpose because its working principles are based on the changes of the subsurface rocks resistivity values in two dimension, which easy to detect (kumar et.al., 2015) data acquisition technique in the 2d-resistivity can be done by injecting the dc electric current into the rock of the earth's crust through two current electrodes; c1 and c2. the dc electric current which injected will spread evenly to all rocks medium as shown in fig. 1. the electrical polarization that occurs in the subsurface rock is measured by two voltage potential electrodes, namely p1 and p2. after the current and voltage values are measured, then the apparent resistivity value of the subsurface rock can be calculated using a simple equation (telford et.al., 1990). i v k a   (1) where ρa is the apparent resistivity, k is the geometrical factor, v is the voltage (mv) and i is the current (ma). the calculated resistivity is generally expressed in ohm fig. 1. the scheme of geo-electrical resistivity data acquisition the geometrical factor in the equation (2) will give a certain value for a used electrode spacing. and for wenner configuration, all inter-electrode spacing are equal to a constant value, i.e. a. thus, the geometrical factor can be written as a cppccppc k   2 1111 2 22212111                    (2) the advantage of the wenner configuration is that the accuracy of voltage readings on p1p2 electrodes is better because the p1p2 electrodes are relatively close to the c1c2 electrodes as if using the multimeter measuring instrument with a relatively smaller impedance. the subsurface rocks as a medium also have different resistivity properties according to its type. therefore, by utilizing the differences in the resistivity properties of the rocks, then it can be seen how the subsurface geological conditions. in this research, the 2d-resistivity method has used to investigate and interpret the subsurface geological structures. the variation in rocks resistivity depends on the types of rocks and minerals, porosity, fluid content in the pores of the rock (can be in the form of petroleum, gas, or water), and others (saad et.al., 2012) 2. research method the acquisition of 2d-resistivity data using wenner configuration has been carried out in eastern binangun coastal area regency of cilacap, as shown in fig. 2. data processing, data modeling, and interpretation were carried out in the geophysical laboratory; faculty of mathematics and natural sciences, jenderal soedirman university, purwokerto, central java. this research has been conducted for six months; from march to august 2018. the main equipment that used is resistivity meter with nrd-300 type, which equipped with supporting components. also, the other equipment also used, such the global positioning system (gps), the geological maps, the google earth applications, and others. the research begins with the determination of the location of trajectory for 2d-resistivity data acquisition. sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 215 fig. 2. the research location; the eastern nusawungu coastal in cilacap regency first, the entire of electrodes is positioned on the left of the trajectory with the same distance, that is equal to a. next, be measured some variable, i.e. current (i), voltage (v), and distance between electrodes (a). moreover, then all electrodes are moved to the right as far as a, where c1 is moved to p1, p1 is transferred to p2, and p2 is moved to c2, then those physical variables are measured again. the measurements are carried out continuously until the entire of research area can be covered. to obtain the 2d-resistivity section under a particular trajectory, the resistivity data acquisition on a trajectory is repeated up to n times of measurements; where each the repeating, the distance between electrodes is always widened to 2a, 3a, 4a, 5a, 6a and so on, as shown in fig. 3 (saad, 2012). but the electrode movement distance to the right is made fixed, that is equal to a. the obtained resistivity data from the acquisition on each track, then processed and modeled in inversion. the obtained result is the 2d-resistivity cross section of subsurface rock. based on the geological information of the research area and the supporting of research data, then be conducted interpretation to the 2d-resistivity cross-section, so obtained the subsurface lithological profile of the research area. based on this subsurface lithological profile, iron sand deposits and their exploitation effects on the research area can be interpreted, especially for the coastal aquifers. 3. result and discussion the 2d-resistivity data acquisition with the wenner configuration has been conducted over four trajectories which placed in the iron ore prospect area, based on the local magnetic anomaly map from the research by sehah et al. (2017). the position of each trajectory is shown in fig. 4. the data which obtained in the field for each trajectory consists of electric current (i), voltage (v), and distance between electrodes (a). based on these data, the geometrical factor (kwen) and the apparent resistivity (ρa) values for each array can be calculated. then the datum point value for each n of measurement can be determined based on the distance value between electrodes in the wenner configuration. fig. 3. the resistivity data acquisition technique uses the wenner configuration. the apparent resistivity, the datum point, and distance between electrodes for each n data in the trajectory are then modeled to result in 2d-subsurface resistivity profile. the 2d-subsurface resistivity profile that generated from modeling for the bng-01 to bng-04 trajectories is shown in fig. 5 to fig. 8. while its lithological interpretation results are shown in table 1 to table 4. the length of each data acquisition trajectory is 200 meters. the obtained results showed that the trend of subsurface rocks resistivity value changed downward; where the value is getting smaller. 216 sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 the 2d-subsurface resistivity profile which obtained is interpreted so that known the types of its constituent rocks, including iron sand deposits and coastal aquifer. the interpretation results are designed using the res2dinv 3.54 software, so that it can obtain the 2d-subsurface lithological profile in the research area as shown in appendix 1. this design is based on the 2d-resistivity profile and the results of its interpretation. then, the resistivity values of some objects having similar interpretation are grouped into one type of rock. example fine sand, sandy clay, clayey sand, sand containing iron ore, and others. fig. 4. location of 2d-resistivity data acquisition on the magnetic anomaly map of eastern binangun coastal area in cilacap regency fig. 5. the 2d-subsurface rocks resistivity profile of modeling results using res2dinv 3.54 in the bng-01 trajectory fig. 6. the 2d-subsurface rocks resistivity profile of modeling results using res2dinv 3.54 in the bng-02 trajectory fig. 7. the 2d-subsurface rocks resistivity profile of modeling results using res2dinv 3.54 in the bng-03 trajectory fig. 8. the 2d-subsurface rocks resistivity profile of modeling results using res2dinv 3.54 in the bng-04 trajectory 109.270 109.275 109.280 109.285 109.290 109.295 longitude -7.700 -7.695 -7.690 l a ti tu d e -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 contour interval of 50 nt nt the eastern binangun coastal iron ore prospect area coastal sand deposits area location of data acquisition of res2d bng-01 bng-02 bng-03 bng-04 sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 217 table 1. the interpretation results to the 2d-resistivity profile contour of the bng-01 trajectory. resistivity ( interpretation lithology hydrology < 5.29 5.29 12.4 12.4 28.8 > 28.8 fine sand sandy clay clayey sand sand containing iron ore grains deep aquifer semi impermeable semi aquifer shallow aquifer the subsurface rock resistivity section in the bng-01 track shows that the deep aquifer is estimated been intruded by saltwater. this estimation is based on the small resistivity value for the coastal aquifer. according to the literature, the layers that saturated with saltwater and dissolved solids have resistivity values of 8 50 (satriani, 2011). this is also supported by information from the map of groundwater potential indication and irrigation area which issued by the ciptakarya general directorate (2003). the iron ore is estimated to be in the sand with a resistivity value of surface. the range of its resistivity values is relatively small and according to the high magnetic anomaly value, which shows a high iron ore content (saad et.al., 2012). table 2. the interpretation results to the 2d-resistivity profile contour of the bng-02 trajectory. resistivity interpretation lithology hydrology < 6.49 6.49 13.5 13.5 28.2 28.2 58.6 > 58.6 fine sand sandy clay clayey sand sand containing iron ore grains sand inserted with gravel deep aquifer semi impermeable semi aquifer shallow aquifer non aquifer based on the modeling results as shown in fig. 2, the deep aquifer in the bng-02 track is interpreted to have also been intruded by saltwater. this is based on the very small resistivity value, that is less than 6.49 . while the shallow aquifers are mostly estimated not to be intruded by salt water, sand that contains iron ore is estimated to be present on the surface of research area. the interval of rocks resistivity values in this trajectory is 6.49 58.6 . the rocks with relatively high resistivity values (more than dominant and only localized in the north. the rocks are interpreted as sand inserted with gravel, but estimated contains small amounts of iron ore. table 3. the interpretation results to the 2d-resistivity profile contour of the bng-03 trajectory. resistivity interpretation lithology hydrology < 6.37 6.37 12.3 12.3 32.9 32.9 63.4 > 63.4 fine sand sandy clay clayey sand sand containing iron ore grains sand inserted with gravel deep aquifer semi impermeable semi aquifer shallow aquifer non aquifer the results of modeling on the 2d-resistivity profile in the bng-03 track is similar to the bng-02 track, both its resistivity value and its interpretation result. then, in this trajectory, there is also sand deposite which interpreted to contain iron ore grains. the range of rock resistivity values in the bng-03 track is relatively higher than bng-02 track, which is 6.37 63.4 m. rocks with a higher resistivity value (more than 63.4 m) are very few, only localized at three places. those rocks are interpreted as sand that inserted with gravel and may to still contain small amounts of iron ore. the rocks may contribute as one of the negative anomalous sources in the magnetic anomaly map, as shown in fig. 4. this is related to low iron ore mineral content in it. table 4. the interpretation results to the 2d-resistivity profile contour of the bng-04 trajectory. resistivity ( interpretation lithology hydrology < 4.98 4.98 11.1 11.1 24.9 24.9 83.3 > 83.3 fine sand sandy clay clayey sand sand containing iron ore grains sand inserted with gravel deep aquifer semi impermeable semi aquifer shallow aquifer non aquifer the range of resistivity values for the bng-04 track is the highest, which is 4.98 with gravel (located at the upper right on fig. 8) is thought to contribute to this. in addition, this trajectory is relatively far from the magnetic anomalies closures center as shown in fig. 4, so the iron sand deposits in this research area are not expected to be much, such as previous trajectories. this also produces high resistivity value in this area. in general, the results of lithological interpretation on the bng-04 track is same as the others tracks. this is related to the changes of the subsurface resistivity values which almost same in the all research areas. it indicates that the research area has the same subsurface rock stratigraphy. based on the results of 2d resistivity data modeling on trajectories throughout the research area, it is known that the research area is dominated by rocks which have relatively small resistivity values (<100 m). the rocks are defined as sedimentary rock, especially the alluvium and coastal deposite. sedimentary rocks generally have low resistivity values because it has high water content and greater porosity than igneous and metamorphic rocks. this is consistent with the geological information that the dominant rocks in the research area are coastal deposits and alluvium, where iron ore resource is found (herman, 2005). according to some residents, the iron sand can be observed clearly when they dig wells with an average depth of about 5 meters. in some locations, iron sand is often found on the surface of research area as shown in fig. 9. most of the iron ore grains have been mixed with sand, gravel and surface soil. because of enough prospects, in this area iron ore mining was carried out by the local company. but this business was stopped, because it was opposed by the community 218 sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 fig. 9. iron ore grains are found on the surface of the research area in the eastern binangun coastal the fact that shallow aquifers in the research area are not intruded by saltwater is supported by the results of testing the electrical conductivity of water samples. all water samples are taken from the wells around the resistivity data trajectories. the complete testing results of electrical conductivity of several well water samples can be seen in table 5. table 5 shows that well water sourced from shallow aquifers in this area may not have been intruded by salt water, like the results of hydrological interpretation. according to hendrayana (2002) the limit of the electrical conductivity value for freshwater is less than 1.500 si per cm, so that all well water samples in this coastal area are freshwater. the electrical conductivity in minerals and solutions takes place by the movement of electrons and ions (porretta and bianchi, 2016). the electric conduction in the rocks, in many cases through water contained in the rock pores and along the interface layer of the rock and solution (kebede, 2001). table 5. the electrical conductivity of several water samples from measurements taken around the trajectories. water samples average electrical conductivity (µsi/cm) distance from the sea (m) bng 01 bng 02 bng 03 bng 04 425,00 456,67 608,99 394,33 1396,69 1297,49 1305,71 654,36 water samples were taken from 2 3 wells for each trajectory. fig. 10. the subsurface rocks lithological profile of interpretation results using res2dinv 3.54 on the bng-01 trajectory fig. 11. the subsurface rocks lithological profile of interpretation results using res2dinv 3.54 on the bng-02 trajectory fig. 12. the subsurface rocks lithological profile of interpretation results using res2dinv 3.54 on the bng-03 trajectory sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 219 fig. 13. the subsurface rocks lithological profile of interpretation results using res2dinv 3.54 on the bng-04 trajectory 4. conclusion the geoelectric-resistivity survey has been done in the iron ore prospect area of eastern binangun coastal in cilacap regency central java indonesia with purpose to interpret the subsurface rock structure. this research was conducted for six months; from march to august 2018. data acquisition of the 2d-resistivity in the field has been carried out on four tracks consisting of bng01 to bng-04 using the wenner configuration. those data trajectories is placed in the iron ore prospect area based on the local magnetic anomaly map of research area. based on the results of 2d-resistivity data modeling, the true resistivity value can be obtained for each track in the form of subsurface resistivity cross-section, which includes the bng-01 track of 2.27 bng-02 track of 4.5 bng-03 track of 6.37 bng-04 track of 4.98 83. after interpretation, then obtained the subsurface lithological profile, consisting of several rocks. those rocks consists of sand which inserted with gravel (> 83.3 sandy clay (4.98 the sand which contains iron ore is main part of the coastal aquifer. the exploitation of iron sand massively causes sand and other subsurface rocks to disappear or decrease. therefore, this exploitation activity has the potential to reduce the aquifer function in storing and flowing of groundwater. furthermore, this activity also can trigger the coast abrasion and seawater intrusion into coastal aquifers in the research area. acknowledgements thank to the ministry of research, technology, and higher education of the republic of indonesia for the research funds provided. thank to the chairman of the research and community service institute, jenderal soedirman university for the support given. thank to the head of the geophysical laboratory of jenderal soedirman university for the equipment facilities provided, especially the geoelectric equipment i.e. the resistivity meter naniura nrd-300. thank also to all research teams, especially students who have collaborated in data acquisition in the field, with good cooperation. references asikin, s., handoyo, a., prastistho, b., 1992. peta geologi lembar banyumas, jawa. pusat penelitian dan pengembangan geologi (pppg) bandung. direktorat jenderal cipta karya, 2003. peta potensi indikasi air tanah dan daerah irigasi kabupaten cilacap, propinsi jawa tengah. departemen pekerjaan umum republik indonesia. dole, h.m., 2006. a description of some oregon rocks and minerals. oregon department of geology and mineral industries. oregon state university. hendrayana, h. 2002. intrusi air asin ke dalam akuifer di daratan. yogyakarta: universitas gajah mada press. herman, d.z., 2005. kegiatan pemantauan dan evaluasi konservasi sumberdaya mineral daerah kabupaten cilacap, propinsi jawa tengah. (kolokium hasil lapangan). hersir, g.p., 2015. resistivity surveying and electro-magnetic methods. presented at short course vii on surface exploration for geothermal resources organized by unugtp and lageo, in santa tecla and ahuachapán, el salvador, march 14 22, 2015 jatmika, j., widanarto, w., effendi, m., 2014. pengaruh suhu sintering terhadap struktur dan sifat magnetik material mn-zn ferit. prosiding pertemuan ilmiah xxviii hfi jateng dan diy. 26 april 2014. kebede, y., 2001. application of the resistivity method in the krísuvík geothermal area. geothermal training programme. reykjanes peninsula, sw-iceland. kumar, n.t., rao, r.p., naganjaneyulu, k., 2015. electrical resistivity imaging (eri) using multi-electrodes for studying subsurface formations in cauvery plains. advances in applied science research 6 (5), 47 53. http://www.pelagiaresearchlibrary.com of saline-water intrusion on the lives and livelihoods of gambian rice growing farmers. research & reviews: journal of ecology and environmental sciences. 2018; 06 (1): 1 7. nurhidayat, 2017. survei pasir besi dengan metode geolistrik di pantai marina bantaeng. (skripsi). porretta r and bianchi f. 2016. profiles of relative permittivity and electrical conductivity from unsaturated soil water content models. annals of geophysics 59 (3), 1 11. doi: https://doi.org/10.4401/ag-6990 saad, r., adli, i., mohamad, a.s., 2012. the study of iron ore prospect using 2-d resistivity and induced polarization (ip) method. electronic journal of geotechnical engineering (ejge) 17, 2981 2988. http://www.ejge.com/2012/abs12.276.htm saad, r., nawawi, m.n.m., mohamad, e.t., 2012. groundwater detection in alluvium using 2-d electrical resistivity tomography. electronic journal of geotechnical engineering (ejge) 17, 369 376. http://www.pelagiaresearchlibrary.com/ https://doi.org/10.4401/ag-6990 http://www.ejge.com/2012/abs12.276.htm 220 sehah,. raharjo, s.a,. destiani,f./ jgeet vol 03 no 04/2018 http://www.ejge.com/2012/abs12.035.htm satriani, a., loperte, a., imbrenda, v., lapenna v., 2012. geoelectrical surveys for characterization of the coastal saltwater intrusion in metapontum forest reserve (southern italy). international journal of geophysics. volume 2012, article id 238478, 8 pages. doi: http://dx.doi.org/10.1155/2012/238478 sehah, raharjo, s.a., muntiqoh, s., 2017. pemetaan sebaran dan potensi bijih besi berdasarkan data anomali magnetik dan data resistivitas di pesisir timur kecamatan binangun kabupaten cilacap. prosiding seminar nasional dan call kearifan lokal berkelanjutan vii 17-18 november 2017, purwokerto. sehah, raharjo, s.a., andriyanto, i., 2017. exploration of iron sand at the eastern coastal of binangun in the cilacap regency using magnetic survey. indonesian journal of applied physics (ijap) 7 (2) 71 81. doi: http://dx.doi.org/10.13057/ijap.v7i2.13700 supriyadi, khumaedi, and putro asp. 2017. geophysical and hydrochemical approach for seawater intrusion in north semarang, central java indonesia. international journal of geomate. 12 (31), 134 140. http://www.geomatejournal.com/user/download/622/13 4-140-50405-supriyadi-march-2017-g1.pdf telford w.m., geldart l.p., sheriff r.e., 1990. applied geophysics. melbourne: cambridge university press. https://doi.org/10.1017/cbo9781139167932 website resmi pemerintah kabupaten cilacap. pasir besi di cilacap. tambang pasir besi di kesugihan cilacap. url http://denisugandi.com/2015/05/ (accessed 09.15.18). © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc bysa license (http://creativecommons.org/licenses/by-sa/4.0/). http://www.ejge.com/2012/abs12.035.htm http://dx.doi.org/10.1155/2012/238478 http://dx.doi.org/10.13057/ijap.v7i2.13700 http://www.geomatejournal.com/user/download/622/134-140-50405-supriyadi-march-2017-g1.pdf http://www.geomatejournal.com/user/download/622/134-140-50405-supriyadi-march-2017-g1.pdf https://doi.org/10.1017/cbo9781139167932 http://denisugandi.com/2015/05/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ interpretation of 2d-subsurface resistivity data in the iron ore prospect area of eastern binangun coastal, regency of cilacap, central jawa 1. introduction 1.1 research background 1.2. basic theory 2. research method 3. result and discussion 4. conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 novriyanti et al./ jgeet vol 02 no 02/2017 133 kick-off point (kop) and end of buildup (eob) data analysis in trajectory design novrianti 1 , rycha melisa 1 , rafhie adrian 1 1 department of petroleum engineering, universitas islam riau, jln. kaharuddin nasution no. 113, pekanbaru, riau abstract well x is a development well which is directionally drilled. directional drilling is choosen because the coordinate target of well x is above the buffer zone. the directional track plan needs accurate survey calculation in order to make the righ track for directional drilling. there are many survey calculation in directional drilling such as tangential, underbalance, average angle, radius of curvature, and mercury method. minimum curvature method is used in this directional track plan calculation. this method is used because it gives less error than other method. kick-off point (kop) and end of buildup (eob) analysis is done at 200 ft, 400 ft, and 600 ft depth to determine the trajectory design and optimal inclination. the hole problem is also determined in this trajectory track design. optimal trajectory design determined at 200 ft depth because the inclination below 35º and also already reach the target quite well at 1632.28 ft tvd and 408.16 ahd. the optimal inclination at 200 ft kop depth because the maximum inclination is 18.87º which is below 35º. hole problem will occur if the trajectory designed at 600 ft. the problems are stuck pipe and the casing or tubing will not able to bend. keywords: directional drilling, trajectory, kick of point, end of buildup, minimum of curvature 1. introduction directional drilling is a technique to deflect the wellbore and then directed to desired target in the formation also not located vertically below the well. in the beginning, directional drilling is used to correct the turn that occured at the vertical hole. (grace bs, widrajat, ak, 2015) (adams, 1985) (rubiandini, 2012). actually in drilling always desirable a vertical hole because of the operation cost is cheaper and easier to implement. but not all drilling can be done vertically certain reasons, so it should be directional drilling.(grace bs, widrajat, ak, 2015) there are causative factors in directional drilling: (bourgoyne, at, 1991)(inglis, 2005) 1. topograph factor a. productive formation is located below the lake or river. b. productive formation is located below the buildings. 2. geological factor a. salt dome b. faults 3. economic factor a. land acquisition fee b. equipment removal c. waste treatment 4. multi-lateral cluster system 5. cluster system 6. blowout prevention by relief well. 7. sidetracking there are 3 common types of track in directional drilling: (rabia, 2002),(adila, maruti tiffani, 2015) (mitchell, 1995)(omar farah, 2013)(mitchell and miska, 2011). a. build hold the turning point depth in kick-off point located not to far from the surface (shallow). the deflection of hole is done by increasing the slope and corresponded to buildup rate (bur) that has been planned. kick of point (kop) is the point or depth where the well track will be distorted until it reaches the specified inclination angle. (hamid and setiawan, 2015) b. build hold and drop this type is used in certain condition, for example at salt dome or while sidtracking. the deflection of hole is done far from the surface casing, and the the slope is mainatained until reach the target. the well with the deep turning point or kick-off point (kop) have certain deficiency, there are: 1. the formation may be harder and is hard to deflect. 2. tripping will be more often to replace bottom hole assembly (bha) while turning. 3. buildup rate will be uncontrolable. c. build hold partial drop and hold first, it will be same with the deflection in the shallow depth but then it will be deflected * corresponding author : novrianti@eng.uir.ac.id tel.:+81-22-2000489 received: may 2, 2017. revised : may 25, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.302 mailto:novrianti@eng.uir.ac.id 134 novriyanti et al./ jgeet vol 02 no 02/2017              2 tan 2 dl dl rf again into vertical. as for the selection for the type of drilling based on coordinate between sufrace location and the target location or the desired formation. after the plan and the drilling operation is done, the measurement of slope for each depth and the direction of borehole (survey) are executed. if the points are deviated, borehole will be directed to the point that already set before. there are many methods that can be used to determine suface point coordinates, tangential, balance tangential, average angle, radius of curvature, minimum of curvature, and mercury method (inglis, 2005)(zaremba, 1973) (wilson, 1968)(sawaryn and thorogood, 2005). the calculation of each methods based on measurement of 3 kinds of parameter. there are, depth of well (md), the alteration of slope (i), and the direction angle (a) which are written on the survey equipment. the first reference to the minimum curvature directional survey calculation method is credited to mason and taylor in 1972.(sawaryn and thorogood, 2005)(taylor and mason, 2013) minimum of curvature method seperate 2 intervals where the upper interval and lower interval. for the upper interval, inclination angle and azimuth is being used at the initial point. for the lower interval, inclination angle and azimuth is being used at the end of point. minimum of curvature method can be seen in the fig. 1 below: fig 1. minimum of curvature method in this study, minimum of curvature method is used in the calculation of well track plan in well x. this method is used because it will gives the lower error than other method. besides that, to determine the trajectoory design and optimal inclination analysis for the kick-off point (kop) and end of buildup (eob) is done by using 3 type of sesitivities based on depth, there are 200 ft, 400 ft, and 600 ft depth. 2. material and methods in well trajectory design, the maximum inclination angle, target distance, bur, and azimuth must be determined in the first place. the formulas used are : a. target direction c b d 1 tan   (1) b. target distance (d2) 22 222 cba cba   (2) c. build radius bur r r bur 58,5729 58,5729   (3) d. maximum inclination         do dc doc 1 tan (4) doc do oc   cos (5) oc r boc 1 cos   (6) docbocbod  (7) bod 90 (8) e. eob md eob md =        1001 x bur v  (9) trajectory design parameters are calculated by using minimum of curvature method. the formulas are : (10) a.      122112 cos1sinsincos aaiiiidl  (11) b.  rfii md tvd 21 coscos 2    (12) c . measured depth (ft) bur nainklinationbinklinatio  (13) d. closure distance = 2 2 en  (14)  rfaiai md n 2211 cossincossin 2    (15)  rfaiai md e 2211 sinsinsinsin 2    (16) novriyanti et al./ jgeet vol 02 no 02/2017 135 trajectory design and optimal inclination is done by analyze the kick-off point (kop) and end of buildup (eob) at 200 ft, 400 ft, and 600 ft depth. the profile data of well x that being used in trajectory and incliatnin design can be seen in the table 1. table 1. well profile 3. results and discussion the coordination of target, target distance, and azimuth that used in drilling track design in well x can be seen in fig. 2. below : fig 2. plan view fig 3. target coordinate azimuth which is the direction of drilling it self. a is the horizontal displacement, b and c is the drilling target coordination and d is the azimuth value and drilling direction. trajectory design of well x at 200 ft kop fig 4. trajectory design at 200 ft kop fig 5. vertically track direction in the drilling track design catogory, the good track with 200 ft kop already assumed as good criteria because the inclination is 18.87º , which is the suitable value when the inclination in drilling opration si less than 35º because in other well data if the inclination is more than 35º will caused the casing is unable to bend or the it will caused casing failure because the casing will break. the result in the 200 ft kop are 1632.28 ft tvd and 408.16 ft ahd, when with the 200 ft kop it will reach the.target well because the desired target is 1632.3 ft and 408.75 ft ahd. fig 6. trajectory design at 400 ft kop location name sumur ra classification development tipe well directional total depth 2000 ft md coordinate target target formation coordinate surface 136 novriyanti et al./ jgeet vol 02 no 02/2017 fig 7. direction of vertical track kick-off point determinated at 400 ft depth in well x has 23.62º inclination, the target depth reached at 1632.41 ft tvd and 407.92 ft ahd. the good criteria is at 400 ft kop because the inclination is below 35º fig 8. trajectory design at 600 ft kop fig 9. direction of vertical track at 600 ft kop the maxumum inclination angle is 35.26º, the target depth at 1632,43 ft tvd and 407.99 ft ahd. this depth has large the maximum incliation angle and its capability to reach the target will not be at maximum effort and if the kop is too deep it will be reach the hard formation so the track will be hard to deflect, then it will be caused stuck pupe when tripping out because the inclination is too large. when the maxumum inclination angle is too large it also cause casing failure or tubing failure when installation, and the inability to maintain when bent. because when a drillstring need to be bent or deflected at 600 ft sharply to reach desired target. because in drilling track design must consider the probability of the drillstring to be bent. if the drillstring passed its limit to be bent, the drillstring will be break. 4. conclusion acccording to the drilling track design to the effect of kop and eob depth selecton in well x, the conclusion are: 1. optimal trajectory design at 200 ft kop because it gives the inclination below 35º and it will reach the target very well at 1632.28 ft tvd and 408.16 ft ahd. 2. optimal inclination at 200 ft kop because the maximum inclination angle is 18.87º, which is good. 3. hole problem that will occured if the trajectory design at 600 ft are stuck pipe and inability of drillstring to be bent. references adams, n.j., 1985. drilling engineering. tulsa. adila, maruti tiffani, w.a., 2015. perencanaan lintasan dan analisis pembebanan pada lubang 81/2 sumur fa 12 lapangan a. semin. nas. cendikiawan 267 275. bourgoyne, at, k.m.m., 1991. drilling engineering. grace bs, widrajat, ak, h., 2015. perbandingan lintasan pemboran berarah dengan berbagai metode perhitungan pada sumur g12 lapangan g i, 446 454. hamid, a., setiawan, a., 2015. evaluasi lintasan pemboran berarah dengan metode minimum of curvature pada sumur x lapangan y petrochina internasional 58 64. inglis, t., 2005. directional drilling, encyclopedia of hydrocarbons volume i. doi:10.2118/7835ms mitchell, r.f., miska, s.z., 2011a. fundamentals of drilling engineering. mitchell, r.f., miska, s.z., 2011b. fundamentals of drilling engineering, society of petroleum engineers journal february. mitchell, wi., 1995. oil well drilling engineering handbook, 10 th edit. ed. usa. omar farah, f., 2013. directional well design , trajectory and survey calculations , with a case study in fiale, asal rift, djibouti. rabia, h., 2010. well engineering & construction 248. rubiandini, r., 2012. teknik operasi pemboran i.pdf. bandung. sawaryn, s.j., thorogood, j.l., 2005. a compendium of directional calculations based on the minimum curvature method. spe drill. complet. 20, 24 36. doi:10.2118/84246-pa taylor, h.l., mason, m.c., 2013. a systematic approach to well surveying calculations. soc. pet. eng. j. 12, 474 488. doi:10.2118/3362-pa wilson, g.j., 1968. an improved method for computing directional surveys. j. pet. technol. 20. doi:10.2118/1992-pa e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 117 geology structure identification using pre-stack depth migration (psdm) method of tomography result in north west java basin sudra irawan 1, *, muhammad zainuddin lubis 1 1 geomatics engineering politeknik negeri batam, batam kepulauan riau, indonesia, 29461 . abstract north west java basin is a tertiary sedimentary basin which is located in the right of the western part of the java island. north west java basin is geodynamic where currently located at the rear position of the path of the volcanic arc of java that is the result of the india-australia plate subduction to the south towards the eurasian plate (explanation of sunda) in the north. geology structure observation is difficult to be conducted at quaternary volcanicfield due to the classical problem at tropical region. in the study interpretation of fault structures can be done on a cross-section of pre-stack depth migration (psdm) used prayer namely hardware key device, ie central processing unit: redhat enterprise linux as 5.0, prayer monitor 24-inch pieces, server: sgi altix 450/suse linux enterprise server 9.0, 32 gb, 32 x 2,6 ghz procesor, network: gigabyte 1 gb/s, and the software used is paradigm, product: seismic processing and imaging. the third fault obtained in this study in accordance with the geological information derived from previous research conducted by geologists. the second general direction is northwest-southeast direction represented by baribis fault, fault-fault in the valley cimandiri and gunung walat. this direction is often known as the directions meratus (meratus trend). meratus directions interpreted as directions that follow the pattern of continuous arc cretaceous age to meratus in kalimantan. keywords: north west java, geology structure, pre-stack depth migration (psdm), fault. 1. introduction geological structure observation is difficult to be conducted at quaternary volcanicfield due to the classical problem at tropical region such as intensive erosion, dense vegetation covers, and rough terrain (pradipta & saepuloh, 2016). north west java basin is a tertiary sedimentary basin which is located in the right of the western part of the java island (fig 1). proven can produce hydrocarbons, such as field jatibarang. this basin has a distribution of land and offshore serang in west stretches eastward to cirebon and consists of several sub-basins (noble et al., 1997). research on seismic previously performed using side scan sonar instruments for identification seabed for introduction of seismic (lubis et al., 2017). north west java basin is geodynamic currently located at the rear position of the path of the volcanic arc of java that is the result of the india-australia plate subduction to the south towards the eurasian plate (explanation of sunda) in the north. several tectonic events that have occurred since the tertiary affect the formation of the structure and patterns of sedimentation in the basin. during the period of late cretaceous to early eocene, ongoing subduction known as the meratus subduction on the southern boundary of the sunda shelf with fire mountain trails pass through the north west java basin (arpandi & patmosukismo, 1975). the meratus subduction affects the state geological basin (gresko et al., 1995). the occurrence of regional metamorphism in the late cretaceous, the paleocene deformation, and volcanism until the early oligocene estimated of maratus subduction-related activities. metamorphism and magmatism that took place resulted in metamorphic and igneous intrusions are then compiled bedrock in north west java basin, while the deformation caused erosion on the appointment and kala paleocene. regional stratigraphy basin of north west java are presented in fig 2. * corresponding author : sudra@polibatam.ac.id tel.:+6257-4341-9535; office: 778-469856 ext: 2510; fax: +62-778-463620 received: mar 29, 2017. revised : 2 may 2017, accepted: may 28, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.297 mailto:sudra@polibatam.ac.id 118 irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 fig. 1. north west java basin (noble et al., 1997). interpretation of fault structures can be done on a cross-section of pre-stack depth migration (psdm) the result of improved velocity model with methods horizon based tomography. the horizon tomography is a method to correct the error the travel time of seismic waves along the horizon analyzed (natasia et al., 2016). improvement in seismic wave propagation time error, then there will be an improvement on the depth error. these improvements are expected to provide the correct information about the subsurface geological conditions (sudra et al., 2014). psdm results obtained in the last iteration of process tomography (accurate velocity models result of improvements) can be used for further seismic activity, namely the interpretation. subsurface fault identification, estimation of reservoir thickness distribution, and calculation of hydrocarbon reserves is some process of interpretation that can be done on a cross-psdm. fig 2. regional stratigraphy basin of north west java (adnan et al., 1991) irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 119 continuity of reflectors are sharper and can reduce the effects of an excess pull-up imaging resulting from the process psdm. image of psdm results more present than the actual geological model generated imaging pstm process. the process will be easier because the interpretation of the subsurface domain is already in depth (depth). fault or the fault is a fracture zone in the rock that has undergone a shift both vertically and rotated so that the displacement between the parts that deal. the shift of these rocks occur along a surface called the fault plane. fault was caused by unequal pressure on a layer of rock. the rock will undergo deformation when passing the threshold power of elasticity, these rocks will experience a fault or faults. fig 3. fault structure (sheriff & geldart, 2002) components of fault according to the sheriff and geldart (2002) as shown in fig. 3, consists of: (1) slip is a movement distance relative to one side against the other, (2) throw a vertical component in the field of separation of fault, (3) heave a horizontal component in the field of separation of fault, (4) dip is the angle between the fault plane with the horizontal plane, (5) hade an angle between the fault plane to the vertical plane, and (6) fault trace a fault line on a surface. in principle, any fault on the seismic data indicated by the loss of the seismic event, diffraction, dip changes, and changes in the pattern of events that pass through fault. 2. materials and method in the study used prayer namely hardware key device, ie central processing unit: redhat enterprise linux as 5.0, prayer monitor 24-inch pieces, server: sgi altix 450/suse linux enterprise server 9.0, 32 gb, 32 x 2,6 ghz procesor, network: gigabyte 1 gb/s, and the software used is paradigm, product: seismic processing and imaging, with details: (1) software geodepth velocity modeling (epos 41), geodepth, to perform map-making 3d models and manufacturing rms velocity and interval velocity model improvements. (2) software geodepth migrations (epos 41) (3d k. pstm (16 cpus), to run processes and 3d pstm k. psdm (fermat / eikonal) to run the process psdm), (3) software geodepth 3d tomograpy (epos 4.1) to make the process tomography. the data consists of two types of seismic data and well data. the seismic data consists of cdp gathers dan rms velocity and the well data covering: sonic log, density log, resistivity log, gamma log ray (gr), and neutron log. the log data is used to calculate the estimation of hydrocarbon reserves. the data in this study consists of three main activities, namely to make the map a 3d model rms velocity as in fig. 3, making and repairing interval velocity model, and identify subsurface structure of the final psdm results (fig 4). fig 4. flow diagram to create 3d model rms velocity maps start cdp gathers vrms 3d pstm time migrated section picking horizon gridding, smoothing ekstrapolasion time migration horizon maps verticalfunction extract vrms volume 3d model vrms maps 120 irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 identification of the structure in this research focused on the structure of the fault or faults. sufficient geological knowledge, especially knowledge is the basis of geological structure in identification of the fault. faulting of psdm cross section that has been identified, the next dipicking fault, then in the grid so it looks fault field. fig 5. flow diagram to create and refine the interval velocity model and identify fault structures from final psdm result. 3. result and discussion there are three pieces of fault that has been identified from the results of the last tomographic psdm sesarnya fields (red, blue and purple) shown in fig 6. fault-fault produced already in the depth domain, meaning there are in the depth of the actual fault. 3 pieces fault determination is based on the components of the fault in general that fault plane, tactics (strike) fault, the slope of the fault, the hanging wall, foot wall, slip net (includes trike slip and dip-slip). fig. 6. the three areas of faults were identified in the study area, is included in the third fault normal fault. the blue color is the fault plane which includes normal fault type (normal fault). normal fault is a major fault which has a strike direction southwest-northeast. the slope of the fault is estimated at 65 o , with the hanging wall and foot wall of fault is shown in fig. 7. the net value is estimated at around 73 meters slip. part of the net slip, the strike slip and dip-slip hard to identify from fig 7. the red color (fig 8) is the fault plane of the type of normal faults that have the same strike direction as the major fault is southwestnortheast. this fault means that minor faults included in this fault follows the major fault (main). the slope of the fault is estimated at 75 o , steeper than the main fault. the part of hanging wall and foot wall of this fault is shown in fig 8. the net value is estimated in around 10 meters slip. the purple color in fig 9 is a normal fault of the fault plane which has a strike direction of northwest-southeast, opposite the main fault strike. fault is also included in a minor fault with a slope of approximately 75 o . the part of hanging wall and foot wall of this fault is shown in fig 9. the net value is estimated at around 10 meters slip. dix transform 3d model vrms maps time migrated horizon maps cdp gathers vrms maps image ray migration depth migration maps psdm inisial vinterval stack gathers inisial psdm stack inisial picking residual moveout gridding, filtering, smoothing, ekstrapolasion 3d model residual depth maps horizon based tomography depth maps tomography velocity maps tomography vinterval tomography volume psdm tomography no yes psdm final picking and gridding faults picking and gridding mmc top-bottom finish gathers flat? irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 121 fig. 7. the appearance of the hanging wall and foot wall on a normal fault (blue) at the cross end psdm. fig. 8. the appearance of the hanging wall and foot wall on a normal fault (red) in the sectional final psdm. 122 irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 fig. 9. the appearance of the hanging wall and foot wall on a normal fault (purple) in the sectional final psdm fig. 10. general pattern structures in north west java basin (martodjojo, 2003) the third fault obtained in this study in accordance with the geological information derived from previous research conducted by geologists. according to martodjojo (2003), in general faults and folds in the basin of north west java is divided into three main directions (fig 10). the first direction is southwest-northeast, which is represented by cimandiri fault, reverse fault and fault-rajamandala other faults in the area purwakarta. this direction is often known as the directions meratus (meratus trend). the meratus direntions were interpreted as directions that follow the pattern of continuous arc cretaceous age to meratus in kalimantan (katili, 1978 and setiawan et al., 2015). fault corresponding to the first direction in this study is a normal fault in blue and red (fig 7 and 8). the second general direction is northwestsoutheast direction represented by baribis fault, faults in the cimandiri valley and mount walat. this direction is known as directions sumatra (sumatra trend), as a parallel to the direction of the bukit barisan mountains. fault that has been identified in accordance with the direction this is normal fault purple color (fig. 8). the third general direction is north-south direction. these directions are on-mountain ciletuh straightness thousand (fault cidurian, block leuwiliang). but in the sunda shelf, off the northern coast of west java, the pattern of this fault is a major pattern. irawan, s and lubis, m. z./ jgeet vol 02 no 02/2017 123 4. conclusion research in north west java basin have third general direction is north-south direction. the third fault obtained in this study in accordance with the geological information derived from previous research conducted by geologists. references adnan, a., sukowitono, dan suprianto., 1991, jatibarang sub basin a half graben model in the onshore of northwest java, proceedings of indonesian petroleum association, 20th annual convention. arpandi d., dan patmosukismo, s., 1975, the cibulakan formation as one of the most prospective stratigrahpic units in the north west java basinal area, proceedings of indonesian petroleum association, 4th annual convention. gresko, m., suria, c. and sinclair, s., 1995. basin evolution of the ardjuna rift system and its implications for hydrocarbon exploration, offshore northwest java, indonesia. katili, j.a., 1978. past and present geotectonic position of sulawesi, indonesia. tectonophysics, 45(4), pp.289-322. lubis, m. z., anurogo, w., khoirunnisa, h., irawan, o. g., & roziqin, a. 2017. using side-scan sonar instrument to characterize and map of seabed for identification target in punggur sea of the riau islands. jgeet (journal of geoscience, engineering, environment, and technology), 2(1). martodjojo, s., 2003. evolusi cekungan bogor jawa barat. penerbit itb bandung. natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field ,north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. noble, r.a., pratomo, k.h., nugrahanto, k., ibrahim, a.m., prasetya, i., mujahidin, n., wu, c.h. and howes, j.v.c., 1997. petroleum systems of northwest java, indonesia. pradipta, r. a., & saepuloh, a. 2016. geology structure identification based on polarimetric sar (polsar) data and field based observation at ciwidey geothermal field. in iop conference series: earth and environmental science (vol. 42, no. 1, p. 012008). iop publishing. setiawan, n. i., osanai, y., nakano, n., adachi, t., & garnet-bearing epidote-barroisite schist from the meratus complex in south kalimantan, indonesia. indonesian journal on geoscience, 2(3), 139-156. sheriff, r.e., 2002. encyclopedic dictionary of applied geophysics. society of exploration geophysicists. sudra irawan, sismanto, & adang sukmatiawan.2014. applying the horizon based tomography method to update interval velocity model, identify the structure of prestack depth migration 3d and estimate the hydrocarbon reserve in sbi field of north west java basin. jurnal teknologi,69(6), 53-58. 1. introduction 2. materials and method 3. result and discussion 4. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02 2023 nurdin et al./ jgeet vol 8 no 2/2023 131 research article model for optimizing land use to support sustainable environmental economic strengthening in the upper kampar river basin nurdin 1, imam suprayogi1, ermiyati1, syafridatul audah1, zaflis zaim2 1 civil engineering department, engineering faculty, riau university, pekanbaru, indonesia. 2 urban and regional planning engineering department, engineering faculty, riau islamic university, pekanbaru, indonesia * corresponding author : nurdin@lecturer.unri.ac.id tel.:+62-812-7579-103 received: may 22, 2023; accepted: jun 26, 2023. doi: 10.25299/jgeet.2023.8.2.12906 abstract simple and complex agroforestry systems can be implemented simultaneously in the cultivation area within the upper kampar river basin. based on the arcswat simulation results, the surface runoff (qsurf) was estimated to be 37.20 mm, which is significantly lower than the existing land use runoff in 2014, which was 102.12 mm. this forms the basis for implementing simple agroforestry and complex agroforestry systems in the upper kampar river basin. the plant species that can support these agroforestry systems are selected based on the principles of land conservation and the suitability of local plants in the upper kampar watershed environment. four types of filler plants are considered: coffee and cocoa for the simple agroforestry system, and gambier and ambon bananas/kepok bananas for the complex agroforestry system. these plant species are the most dominant filler plants in the upper kampar watershed. to optimize the land with these filler plant species, analysis is conducted using quantitative methods (qm) for windows 4 software based on objective functions and constraint functions. the analysis determines that coffee is suitable for the simple agroforestry system, while gambier is suitable for the complex agroforestry system. before land optimization with the planting of coffee, cocoa, gambier, and ambon bananas/kepok bananas, the net profit is estimated to be idr. 359,113,963,811.06. after optimizing the land and developing it with the suitable filler plant species, only coffee and gambier are planted, while cocoa and ambon bananas/kepok bananas are planted according to the available area. as a result, the net profit increases to idr. 951,426,300,000, with an economic value increase of idr. 592,312,336,188.94 per year. keywords: scenario, land use, runoff reduction, cover crops, land optimization. 1. introduction the upper kampar watershed is located in three regencies, namely kampar regency covering an area of 73,506.46 hectares (22.25%), pasaman, and lima puluh kota with an area of 256,816.96 hectares (77.75%). referring to nurdin et al.'s study in 2019, based on the land use map of 2014, the upper kampar watershed has a forest area of 142,160.07 hectares (44.431%) and a cultivation area of 177,799.41 hectares (55.569%). in the pasaman regency, the upper kampar watershed is located in the south mapat tunggul subdistrict with a population growth rate of 1.56%. in lima puluh kota regency, it is found in kapur ix subdistrict with a population growth rate of 1.02%, bukit barisan subdistrict with a population growth rate of 0.85%, and pangkalan koto baru subdistrict with a population growth rate of 0.82%. in kampar regency, it is found in the xiii koto kampar subdistrict with a population growth rate of 1.48% and koto kampar hulu subdistrict with a population growth rate of 3.81%. according to (suasti et al., 2012) the increasing population growth has led to rapid development, resulting in changes in land use patterns. built-up areas are expanding and encroaching upon natural spaces, causing them to change their functions. agroforestry is a land use system that involves various technologies and utilizes annual crops, perennial crops, and/or livestock simultaneously or in rotation over specific periods, resulting in ecological, social, and economic interactions. agroforestry systems have more advantages compared to other land use systems. one of the advantages of this system is its suitability for steep sloping land. multistrata agroforestry systems can prevent soil erosion by building organic matter in the soil, improving soil structure, and making the soil more stable (rendra et al., 2016). the use of arcswat 2012 has simulated three scenarios regarding land use in the year 2014 and has provided the best results in scenario iii. scenario iii involves the combined implementation of simple agroforestry patterns and complex agroforestry, simultaneously applied to a cultivation area covering 175,881.45 hectares (54.94%) of the total land area of the upper kampar watershed (330,240.36 hectares). this land use pattern has the potential to reduce surface runoff from the existing qsurf value of 102.12 mm to qsurf as low as 37.20 mm (nurdin et al., 2019). quoting from (jong jek siang, 2011), mathematical programming techniques in operations research are useful for finding the optimal values of a multi-variable function that satisfies a set of constraints. some models involving calculus and numerical methods are used to solve these problems. the models that fall under this technique include: calculus methods, nonlinear programming, geometric programming, quadratic programming, linear programming, dynamic programming, integer programming, network methods: cpm and pert, game theory, separable programming, multi-objective programming, etc. the land use in scenario iii in the cultivation area of the upper kampar watershed has been simulated by (nurdin et al., 2019) using the arcswat 2012 application. the simulation resulted in lower surface flow, as indicated by the value of qsurf. however, the suitable and optimal use of filler crops in simple agroforestry and complex agroforestry patterns to provide economic value to the communities around the upper kampar watershed is not known yet. http://journal.uir.ac.id/index.php/jgeet 132 nurdin et al./ jgeet vol 08 no 02/2023 to determine the optimal land use for filler crops in simple agroforestry and complex agroforestry patterns, the software program "quantity method (qm) for windows" can be used. quoting from (harsanto, 2011), qm for windows is user-friendly software developed to accompany operations management textbooks. it assists in the technical calculation process for quantitative decision-making. 2. methods 2.1. research sites the research location is located within the upper kampar watershed, in the mapat tunggul selatan subdistrict, kapur ix subdistrict, bukit barisan and pangkalan koto baru in west sumatra province, and the koto kampar hulu and xiii koto kampar subdistricts in riau province. the administrative map of the subdistricts within the upper kampar watershed is presented in figure 1. fig 1. administrative map of the upper kampar watershed 2.2. work steps for implementing a linear program a. determination of agroforestry pattern areas the implementation of agroforestry patterns in the best scenario for the upper kampar watershed is in scenario iii, specifically in the agricultural cultivation area covering an area of 175,881.45 hectares (54.94%) of the total land area within the upper kampar watershed, which is 330,240.36 hectares. according to nurdin et al. (2019), hydrological analysis using the acrswat application can reduce surface runoff (existing qsurf) from 102.12 mm to qsurf = 37.20 mm. this pattern involves the implementation of simple and complex agroforestry simultaneously in the cultivation area within the upper kampar watershed. this agroforestry pattern serves as the basis for implementing a sustainable land use program in the future in the upper kampar watershed. according to (lensari et al., 2022) have optimized land use through an agroforestry system by assisting a group of women farmers in planting home gardens, resulting in environmental and economic benefits for the community. b. types of filling plants in agroforestry patterns. the concept of filler plants in agroforestry patterns is derived from the source of (bps kabupaten lima puluh kota, 2017), with an area of 100% in the upper kampar watershed. the three districts used as benchmarks for predicting the extent and productivity of existing filler plant species are bukik barisan district, kapur ix district, and pangkalan koto baru district in lima puluh kota regency. these districts are used as references for predicting the extent and productivity of existing filler plant species. as for other supporting data, especially in determining selling prices that are not available in the central statistics agency of lima puluh kota regency, reliable sources such as journals from various publications and other books are used. c. use of linear programs in optimization linear programming, as referred to in this case, follows several previous authors such as (niswarni, 2016), (nasution et al., 2015), (rotinsulu et al., 2020), and (rumetna et al., 2021). it aims to find the combination of land areas for different filler crops in simple and complex agroforestry patterns, in order to nurdin et al./ jgeet vol xx no xx/20xx 133 optimize income based on the production prices of each crop. both simple and complex agroforestry patterns involve planting more than one type of filler crop, which mathematically forms a set of variables xs1, xsn, xc1, and xcm representing the area of each filler crop as parameters in the agroforestry patterns. furthermore, the objective function and constraint function can be formulated in mathematical expressions to determine the objective and constraint functions ; objective function the goal to be achieved is to maximize profit (z), which is stated in the following equation: max z = ps1xs1+psnxsn+pc1xc1+pcmxcm (1) where z = net profit optimization results xs1, xsn = the variables represent the area of each type of filler crop 1 to n in simple agroforestry. xc1, xcm = variables in the form of the area of each type of filling plant 1 and to m complex agroforestry ps1, psn = arameters in the form of net profit/ha for each type of filler plant 1 and to n for a simple agroforestry pattern pc1, pcm = parameters in the form of net profit/ha for each type of filler plant 1 and to the m agroforestry complex constraint function the limitations that exist are the constraints in conducting optimization analysis. this analysis is performed by considering the constraints : a. first obstacle a simple agroforestry land area limit can be formulated: xs1 + xsn ≤ as (2) where, as = area of simple agroforestry land suitable for planting b. second obstacle limits of complex agroforestry land area can be formulated: xc1 + xcm ≤ ac (3) where, ac = area of complex agroforestry land suitable for planting c. the third to sixth constraints limiting the area of each simple agroforestry and complex agroforestry land types can be formulated : xs1 ≥ as1 (4) xsn ≥ asn (5) xc1 ≥ ac1 (6) xcm ≥ acm where, (7) as1, asn = minimum area limits for each type of filler plan on seder agroforestry ac1, acm = minimum area limits for each type of filler plant complex agroforestry patterns. the value of the net profit/ha for each type of plant including the type of filler considered, the area of simple and complex agroforestry land that is suitable for planting, and the minimum area of each type of filler considered for simple and complex agroforestry is entered into the form of a linear equation. furthermore, these new equations are input into the quantitative methods (qm) for windows 4 program, and will obtain the optimal area of each type of infill plant on simple and complex agroforestry patterns. 3. results and discussion 3.1. determination of agroforestry pattern areas the upper kamkar watershed the implementation of simple and complex agroforestry patterns simultaneously in the cultivation areas within the upper kampar watershed. these cultivation areas include dryland farming, plantations, paddy fields, open land, dryland farming mixed with shrubs, shrubs/brushes, covering a total land area of 175,881.45 hectares (54.94%) out of the total land area of the upper kampar watershed, which is 330,240.36 hectares (nurdin et al., 2019). according to (rianse, 2010), in the simple agroforestry pattern, trees are intercropped with various annual crops. high-value economic tree species such as coconut, rubber, cloves, teak, as well as low-value economic tree species such as dadap, lamtoro, kaliandra, are planted, along with annual crops such as rice, corn, soybeans, legumes, cassava, vegetables, and other grasses. in the complex agroforestry pattern, fruit trees such as durian, rambutan, and banana, as well as shrubs like gambier, are cultivated. the implementation of these agroforestry patterns aims to reduce surface runoff (existing qsurf = 102.12 mm) to qsurf = 37.20 mm. this can contribute to the reduction of surface water flow, leading to better water management and conservation in the upper kampar watershed. 3.2. types of filling plants in agroforestry patterns. three sub-districts that have their administrative areas 100% within the upper kampar watershed are bukit barisan, kapur ix, and pangkalan koto baru in lima puluh kota regency. these sub-districts are used as a benchmark to predict the extent and productivity of existing filler crops within the upper kampar watershed because some of the land already has perennial lowland crops such as coffee, ambon/kepok bananas, cocoa, gambier, bitter beans, rambutan, sapodilla, starfruit, guava, water guava, papaya, soursop, and others. in accordance with land conservation principles, the cultivation of lowland crops in the cultivation areas can serve as erosion prevention, but due to their irregular distribution, planned cultivation patterns need to be implemented, prioritizing local plant species that meet the priorities of the local community. in line with this (p and meydianawathi, 2014) implemented an agroforestry program by intercropping cassava, peanuts, and corn among the trees, but it can still be optimized by encouraging farmers to cultivate understory plants such as ginger, turmeric, and galangal. the strategy implemented to ensure the simultaneous implementation of simple and complex agroforestry patterns in the upper kampar watershed is by analyzing the optimal land area for each type of filler crop. the designated land area for simple/complex agroforestry patterns in three districts of upper kampar watershed already consists of 20,004.52 hectares (17.79%), approaching 20% of the total area. assuming that the effective land area for perennial crops is only 50% of the total agroforestry area and deducting the already planted perennial filler crops by 20%, there is still room to insert 30% of perennial crops. hence, the total land area available for planting is 52,734.43 hectares out of the 175,781.44 hectares of land allocated for simple and complex agroforestry in das kampar hulu. this consists of 31,082.50 hectares for simple agroforestry and 21,651.93 hectares for complex agroforestry. 3.3. use of linear programs in optimizing land use linear programming, in this case, refers to finding the optimal combination of land areas for filler crops in a simple and complex agroforestry pattern, in order to generate optimal income based on the respective production prices of each crop. based on data from (bps kabupaten lima puluh kota, 2017), the dominant filler crops in three sub-districts, with 100% land area in the upper kampar watershed, that align with the conservation concept for simple agroforestry patterns are coffee and cocoa. in 134 nurdin et al./ jgeet vol 08 no 02/2023 addition, for complex agroforestry, the dominant crops are gambier and ambon/kepok bananas. according to (ukrita, 201ad), the export of coffee from west sumatra is still low due to the limited export volume caused by the insufficient quality required for export purposes. meanwhile (p and meydianawathi, 2014) state that cocoa beans are relatively expensive, primarily used for export purposes. indonesia is one of the world's cocoa exporters, with west sumatra being a major supplier of cocoa in western indonesia. the complex agroforestry system involves the cultivation of gambier plants and ambon/keppok bananas among existing and new tall plants. according to (nasution et al., 2015) and (hendri et al., 2021), indonesia is the largest producer of gambier in the world, with a significant portion coming from the limapuluh kota regency in west sumatra. according to (fairuzi, 2008) states that ambon/keppok bananas are not only needed for domestic purposes but also for markets in pekanbaru and jakarta, where they are used in various products. the predicted harvest areas for four types of filler crops in the upper kampar watershed are based on the harvest areas in three districts as shown in table 1. the respective ratios for each crop type with simple and complex agroforestry areas are 0.40% for coffee, 0.89% for cocoa, 28.43% for gambier, and 0.12% for ambon bananas. these ratios result in the following harvest areas in the kampar hulu watershed: 419.01 hectares for coffee, 925.67 hectares for cocoa, 20,519.50 hectares for gambier (the largest area), and 83.20 hectares for ambon bananas. based on the harvested area of each filler crop in the upper kampar watershed and the productivity in three districts for coffee at 1.30 tons/ha, cocoa at 0.81 tons/ha, gambier at 0.74 tons/ha, and ambon banana at 39.04 tons/ha, these figures are used to estimate the production of the four types of filler crops in the upper kampar watershed. the estimated production is as follows: 545.30 tons of coffee, 747.46 tons of cocoa, 15,093.90 tons of gambier, and 3,248.03 tons of ambon banana. based on the estimated production, the gross income in the upper kampar watershed for each filler crop is calculated using the following production prices: coffee at idr 23,500,000/ton, cocoa at idr 32,083,333/ton, gambier at idr 27,500,000/ton, and ambon banana at idr 2,404,186.11/ton. the estimated gross incomes for each crop are as follows: idr 12,814,569,762.95 for coffee, idr 29,698,713,417.78 for cocoa, idr 564,280,646,653.35 for gambier, and idr 200,027,286.55 for ambon banana. the cost of production for four types of crops, coffee, cocoa, gambier, and ambon banana, is referenced from several research findings. according to (listyati et al., 2017), the net profit from coffee sales is idr 11,417,600, derived from the gross profit of idr 18,059,500 minus the production cost of idr 6,641,900, with a net profit to gross profit ratio of 63.22%. for cocoa crops, referring to the findings of (rusdiana and martono, 2014), the net profit is idr 12,225,000, derived from the gross profit of cocoa sales of idr 21,630,000 minus the production cost of idr 9,105,000, with a net profit to gross profit ratio of 57.91%. regarding gambier crops, referring to (a.f and rosmeilisa, 2001), the net profit is idr 11,642,500, derived from the gross profit of gambier sales of idr 19,687,500 minus the production cost of idr 8,045,000, with a net profit to gross profit ratio of 59.14%. finally, based on the research conducted by widowati et al. (2015), the net profit from ambon bananas is idr 6,278,350, derived from the gross profit of banana sales of idr 12,750,000 minus the production cost of idr 6,471,650, with a net profit to gross profit ratio of 49.24%. by applying these net profit to gross profit ratios, the net earnings for coffee are calculated to be idr 8,101,371,004.14, for cocoa idr 17,198,524,940.23, for gambier idr 333,715,574,430.79, and for ambon banana idr 1,183,821.24. the total net profit (existing) for one year amounts to idr 359,113,963,811.06. optimizing land use with four types of filler crops, namely coffee and cocoa for simple agroforestry patterns, gambier and ambon banana for complex agroforestry patterns, can be conducted and analyzed using the software quantitative methods (qm) for windows 4 based on the objective function and constraint function. the mathematical formulation consists of four variables: two variables, xs1, indicating the area of land for simple agroforestry planted with coffee, xs2, indicating the area of land for simple agroforestry planted with cocoa, two variables, xc1, indicating the area of land for complex agroforestry planted with gambier, and xc2, indicating the area of land for complex agroforestry planted with ambon banana. tabel 1. estimates of the benefits of coffee, cocoa, gambier and ambon/kepok bananas in the upper kampar watershed description types of filler plants coffee cocoa gambier ambon banana calculations within 3 districts harvest area (ha) 282,00 623,00 12.139,00 49,22 production (tonnes) 367,00 503,06 8.929,39 1.921,50 productivity (tonnes/ha) 1,30 0,81 0,74 39,04 area of as (ha) 69.730,79 area of ac (ha) 42.696,85 harvested area ratio/area fo as (%) 0,40 0,89 harvested area ratio/area fo ac (%) 28,43 0,12 estimates within the upper kampar river basin area of as (ha) 103.608,34 area of ac (ha) 72.173,11 harvest area (ha) 419,01 925,67 20.519,30 83,20 production (tonnes) 545,30 747,46 15.093,90 3.248,03 price (idr/tonnes) 23.500.000,00 32.083.333,50 27.500.000,00 2.404.186,11 gross income (idr) 12.814.569.762,95 29.698.713.417,78 564.280.646.653,35 200.027.286,55 net income/gross income (% 63,22 57,91 59,14 49,24 net income (idr/ha) 19.334.783,33 18.579.458,43 16.263.500,00 1.183.821,24 net profit (idr) 8.101.371.004,14 17.198.524.940,23 333.715.574.430,79 98.493.435,90 total net profit (idr) 359.113.963.811,06 source : (listyati et al., 2017), (rusdiana and martono, 2014), (rizal et al., 2015), (a.f and rosmeilisa, 2001), (bps kabupaten lima puluh kota, 2017) and processing and analysis results so that the net profit value/ha for each type of coffee plant is idr 19,334,783.33/ha and cocoa is idr 18,579,458.43/ha, for this type of gambier plant it is idr 16,263,500/ha and for the type of ambon banana plant is and idr 1,183,821.24/ha, so the nurdin et al./ jgeet vol xx no xx/20xx 135 goal is to maximize net profit (z) which can be described in the equation: maximize z = 19,334,783.xs1 + 18,579,458.xs2 + 16,263,500.xc1 + 1,183,821.xc2 the first obstacle is the maximum area of simple agroforestry land suitable for planting with coffee filling plants covering an area of 31,082.50 ha. second obstacle is the maximum area of complex agroforestry land that is suitable for planting gambier and ambon banana fillers with an area of 21,651.93 ha. the third to sixth obstacle is the minimum limit of simple and complex (existing) agroforestry land, where coffee plants cover an area of 419.01 ha, cocoa cover an area of 925.67 ha, gambir cover an area of 20,519.30 ha and ambon bananas cover an area of 83.20 ha. based on the variables xs1, xs1, xc1 and xc2 which are non-negative variables having values greater than zero, which form the equations as input to the qm for windows 4 auxiliary program to solve linear programs, with a set of linear programming mathematical formulas: maximum z = 19,334,783.xs1 + 18,579,458.xs2 + 16,263,500.xc1 + 1,183,821.xc2 with delimiter: xs1 + xs2 ≤ 31.082,50 xc1 + xc2 ≤ 21.651.9 xsi ≥ 419,01 xs2 ≥ 926,67 xc1 ≥ 20.519,30 xc2 ≥ 83,20 the results of optimizing simple agroforestry land with coffee and cocoa filler species and complex agroforestry land with gambir and ambon banana filling plants in the qm for windows 4 linear program application are in the form of the area of each type of filler plant: a. xs1 coffee plantation area = 30,155.83 ha b. xs2 cocoa plantation area = 926.67 ha c. gambir xc1 = 21,568.73 ha d. ambon banana plantation xc2 = 83.20 ha e. the net profit value z = idr. 951.426.300.00. the minimum limit of land input for coffee filling plants is as large as coffee plants in the upper kampar watershed, namely, 419.01 ha, where the maximum limit for agroforestry land is 31,082.50 ha, with an optimized land area for coffee plants of 30,155 .83 ha. the remaining simple agroforestry land is only 926.67 ha, which is equal to the minimum area of land for planted cocoa plants as well as the area of output cocoa plants in the qm for windows 4 model. to obtain optimal land use, the area of coffee land that can be developed area of 29,736.82 ha, cocoa plants are not feasible to develop. gambier filler plants with a minimum land area of 20,519.30 ha, with a maximum limit of 21,651.93 ha for complex agroforestry land. of the 21,568.73 ha of optimized land area for gambier plants, only 83.20 ha of complex agroforestry land remains, the same as the minimal ambon banana land area. the optimal area of gambier land that can be developed is 1,049.43 ha, while the ambon banana land is not feasible for development. if before optimizing the area planted with coffee was 419.01 ha, cocoa was 925.67 ha, gambir was 20,519.90 ha, and ambon banana was 83.20 ha, then a net profit of idr. 359,113,963,811.06. after the land was optimized, it was found that the area for the development of fill land with coffee plant types was 29,736.82 ha, and 1,049.43 ha for gambier plantations, so from the addition of the development area, a net profit of idr 951,426,300,000. in other words, after optimizing the land, the amount of increase in economic value for the people around the upper kampar watershed is idr 592,312,336,188.94 as presented in table 2. a map of the distribution of agroforestry land for simple and complex patterns is presented in figure 2. fig 2. map of the distribution of agroforestry land in the upper kampar watershed 136 nurdin et al./ jgeet vol 08 no 02/2023 table 2. net profit before and after land optimization plant type planting area before optimization (ha) net profit before optimization (idr) planted area after optimization (ha) net profit after optimization (idr) economic improvement after optimization (idr) coffee 419,01 8.101.371.004,14 30.155,83 544.604.803.108,46 536.503.432.104,32 cacao 926,67 17.198.524.940,23 926,67 17.198.524.940,23 ambon banana 20.519,30 333.715.574.430,79 21.568,73 389.524.478.515,41 55.808.904.084,62 gambier 83,20 98.493.435,90 83,20 98.493.435,90 359.113.963.811,06 951.426.300.000,00 592.312.336.188,94 source : output results qm for windows if the number of farmers is 35,899 people, then the existing net profit before land optimization is idr. 359,113,963,811.06, or each farmer gets a profit of idr. 10,003,453.13 for one year or idr. 833,621.09 / farmer every month. while the net profit after optimization is idr. 951,426,300,000, so that each farmer gets a net profit of idr. 26,502,863.59 for one year or idr. 2,208,571.966/farmer every month. it can be said that there has been an increase in the economic value for each farmer of idr. 16,499,410.46/year or idr. 1,374,950.87/month. 4. conclusion 1. the use of quantitative methods (qm) for windows 4 in optimizing land in the upper kampar watershed with coffee filler types for simple agroforestry patterns and gambier for complex agroforestry patterns can increase the social and economic value of the community. 2. in the condition of the land prior to optimization by planting coffee, cocoa, gambier and ambon bananas, the net profit was only idr. 359,113,963,811.06. the results of optimizing the development of infill land that are feasible to develop are only for coffee and gambier plants, while for cocoa and ambon bananas only according to the existing area, so that a net profit of idr. 951,426,300,000 with an increase of idr. 592,312,336,188.94 for one year. 3. the simple and complex agroforestry patterns implemented in the upper kampar watershed can increase the economic value of idr. 16,499,410.46/year/farmers or idr. 1,374,950.87/month/farmers. acknowledgements thank you is conveyed to the editor of the journal of geoscience, engineering, environment, and technology for publishing this article in an accredited journal with sinta 2 ranking, as well as to all parties who have contributed data and ideas to this writing.. references a.f, e., rosmeilisa, p., 2001. analisis usahatani gambir di sumatera barat (studi kasus kecamatan harau, kabupaten 50 kota). j. littri 7, 67–71. bps kabupaten lima 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linear dan software pom-qm 09, 42–49. rusdiana, s., martono, b., 2014. analisis finansial diversifikasi usaha perkebunan. sirinov 2, 157–170. suasti, y., hermon, d., ahyuni, 2012. dampak pertambahan penduduk terhadap konversi lahan di kota padang. pusat penelitian kependudukan dan lingkungan hidup (pklh) universitas negeri padang, padang. ukrita, i., 201ad. keunggulan komparatif kopi sumatera barat di pasar domestik. j. penelit. lumbung 12. © 2023 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 arisona, a et al./ jgeet vol 02 no 01/2017 31 evaluation study of boundary and depth of the soil structure for geotechnical site investigation using masw a. arisona 1,2 *, mohd.nawawi 1 , amin e. khalil 1,3 , u.k nuraddeen 1 , mohd. hariri 1 , m.a. fathi 1 1 geophysics program, school of physics, universiti sains malaysia. 2 geophysical department, haluoleo university, kendari,indonesia. 3 geology dept., faculty of science, helwan university, egypt, mesir. * corresponding author : arisona1972@hotmail.com tel.: +60 164607608 abstract this study reviews the correlation between the experimental rayleigh dispersion curve and the vp & vs ground model versus depth. six samples of stations a , b , c , d , e and f were used in the experiment.the geophone spacing used was set 1 m and total length of each line was 23 m. the result shows positive significance (best fit) of r2 that ranges from 0.80 to 0.90. the fk (frequency-wave number method) dispersion curves analysis confirmed that the soil structure investigated is divided into three zones: (1) unsaturated soil zone (clay soil), in which the layer is dominated by soil with typically alluvial clayey silt and sand. the vp ranges from 240 m/s to 255 m/s at a depth of 2 to 8 m. (2) the intermediate zone (stiff soil), in which the layer is dominated by sand, silt, clayey sand, sandy clay and clay of low plasticity. this structure is interpreted as partially saturated soil zone, the soil is typically very dense. it contains soft rock typically fill with cobble, sand, slight gravel and highly weathered at depth of 18 to 30 m with vp of 255 to 300 m/s. (3) saturated soil zone at a depth of 8 to 18 m with vp of 300 to 390 m/s. there is a very good agreement between wave-number (k) and phase velocity (vw) produced. both the two parameters shows similar pattern in the topsoil and subsurface layer, which constitute boundary field of soil structure. moreover, relationship between phase velocity versus wave-length shows best fit of model from inversion with measured value (observed) in implementation of the boundary and depth of each layer. keywords: masw, dispersion curve, phase velocity, wave number, wavelength. 1. introduction multichannel analysis of surface wave (masw) survey is gaining popularity in geophysical/ geotechnical investigation due to the fact that it is non-destructive and provides accurate means of site characterization. it has been applied to delineate boundaries and depth of the target structure for geotechnical site investigation. blake (2009) used masw to define the velocity of the structure and depth to bedrock. this survey gives information of sub surface structure, thickness of layers, wave velocity of a body, and soil amplification parameters like vs30; all of which are important in earthquake engineering. the utilization of masw for soil characterization originates from the inherent nature of this kind of wave. tran (2008) studied surface wave propagation along a free surface and associated motion, important information about the mechanical properties of the medium is revealed. the objective of this study is to characterize the boundary and depth of the soil structure using masw technique that substitute core drilling of sample (which is very expensive to perform), so necessitating geophysical technique as alternative means. basically, geophysical method involve measuring the physical properties of the ground (or structure) and determining variations or keary, et al.,2002). furthermore, the occurrence of anomalies can indicate the presence of features or changes in a material composition (keary, et al.,2002). dey (2015) reveals that unlike conventional borehole sounding test, geophysical method is less expensive and it provides the benefit of precision to estimate the subsurface compression and shear wave velocity profile over a large area. it has been found to be better in some aspect compared to the other non-invasive methods such as the ground penetrating radar (gpr) and nuclear magnetic resonance (nmr) techniques. a significant application of geophysical method in geotechnical engineering practice is determination of boundary, depth layer and insitu characterization of soil (grandjean, 2009 and hiltunen et al., 2012). critical analysis of the modeling observes whether geophysical signatures can characterize the physical properties that affect the saturation of soil. received: feb 1, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017. doi: 10.24273/jgeet.2017.2.1.21 mailto:arisona1972@hotmail.com 32 arisona, a et al./ jgeet vol 02 no 01/2017 this analysis focuses on the dispersion of surface waves using masw method (the fact that wavelengths with different frequencies travel at different speeds). the basic principle is quite simple, the various components (frequencies) of the seismic signal travel at a speed that depends on the characteristics of the medium (dey, 2015). to determine accurate dispersion information, multichannel data processing methods are required to discriminate against noise and enhance rayleigh wave signals (tran, 2008 and chik et al., 2011). the pattern of the relantionship of the layers can be formulated mathematically as: 𝒌𝒎(𝝎) = 𝝎 𝑽𝑹𝒎(𝝎) = 𝝎𝑷𝒎 (𝝎) (1) where the wavenumber (km) generated by equation (1) is inversely proportional to phase velocity (vrm) or equivalently proportional to the slowness pm(). for a given frequency, surface waves have uniquely defined wavenumbers k0(f), k1(f), k2(f) for different modes of propagation. in other words, the phase velocities vrm = ω/km are fixed for a given frequency. the f-k transform allows separation of the modes of surface waves by checking signals at different pairs of f-k. the masw method uses this dispersive property to estimate p and s wave velocities. it was reported by roy (2013) that the masw method has been developed with the assumption that the subsurface is vertically heterogeneous and laterally homogeneous (i.e. a layer-cakemodel). the masw used phase information of high-frequency rayleigh waves recorded on vertical component geophones to determine near-surface s-wave velocities (tran, 2008). the differences between masw results and direct borehole measurements are approximately 15% or less. studies show that inversion with higher modes and the fundamental mode simultaneously can increase model resolution and depth of investigation (xia , 2014). the maximum depth of penetration is determined by the longest wavelength of the surface waves. the longest wavelengths generated depend on the impact power of the source and physical properties of the subsurface (pei,2007). the greater the impact power, the longer the wavelength and the greater will be the depth of penetration. although the impact of the source such as a heavy weight drop can generate a longer wavelength of surface waves, they are very costly and not convenient for field operation. therefore, a controlled type of seismic source such as a sledge hammer is used in an active survey (dey, 2015). the penetration depth of rayleigh waves is about 0.4 times the longest wavelength (schuler, 2008). therefore, the depth of investigation can be estimated by using the dispersion curve. since wavelength is equal to velocity divided by frequency we can estimate the depth of penetration using the equations: d = 0.4 √⌈ vr f ⌉ 2 and λ = vr f ( 2) where  is wavelength (m) ; d is depth of penetration (m), vr is rayleigh wave velocity (m/sec) and f is frequency (hz). on the other hand, the dispersion curve is an interpretation of the different modes or harmonics of the surface wave as it propagates through a given media. 2. site description and geology the study was carried out in pedas, negeri sembilan, peninsular malaysia (figure 1). this area has a distinctive and unique geology than the surrounding areas because of the presence of hot springs. hot spring is allegedly originates from the host rock, it is then migrated through the grounds and surrounding rock (limestone and sandstone) impregnated. figure 1. geology map of negeri sembilan, peninsular malaysia (modified from jmg, 2014). the location of the study areas in the geological map is showing presence of hot spring. pedas is located in the vicinity of seremban fault zone that lies within the west belt granite intrusion. alexander (1968) revealed that the structural geology in the igneous rock of pedas area was dominated by granites with typically medium to coarse grained rocks, often porphyritic. based on the negeri sembilan geological map, the location of site investigation is part of the main fault zone that is controlled by meta-sediment and granite rocks. soil structure around hot spring with typically saturated soil. it comprises of sandstone, silty sandy gravel, and granite (bedrock), as was confirmed by hamizah (2016) on the study of electrical resistivity imaging (2d and 3d) and geochemical study in the hot spring area in pedas. soil type depends on the parent rock type of the basin, although variations may occur over small distance due to differences in local condition. the bed rock in the study area is overlain by alluvial deposits of red and yellow lateritic clay, sand and arisona, a et al./ jgeet vol 02 no 01/2017 33 gravel. the alluvium is quite deep in certain areas especially along the hills due to aggregation and tin mining activities. the alluvial deposits, especially along the rivers are composed of gray clay and peat. more areas under laterite are found along the southwestern coast of the state (nather khan and mustafa, 2010). geological genesis of hot spring formation at pedas is still studied by experts. 3. experimental work the masw measurements were carried out along 52 stations in the study area. the stations were selected based on data picking and frequencies to obtain best a curve fit. in this study, six samples were collected for use in masw dispersion inversion. figure 2 shows the arrangement of 24 channels geophones using the spacing of 5 m and set 1 m inter-distance is used for recording data and the total length was 23 m. the energy source was set at 15 m offsets. the data were recorded using the sampling rate of 1 ms. the data were recorded by commercial instruments (terra look mk-8). there are two main procedure involve in masw data processing technique adopted in this study : generation of dispersion curves (frequency vs. phase velocity plots), and inversion of dispersion curves to estimate s-wave velocities (roy , 2013). figure 2. masw field setup and recorded data on 24 channel at the site the theoretical dispersion curve is calculated from random parameters given by the na (forward problem) and then the number of layers to invert is chosen. there are four parameters to invert: p-wave velocity (vp), poisson ratio, s-wave velocity (vs) and depth. density was held constant at 2000 kg/m3 (table 1). it was found that the choice of vp did not have much influence on the inversion process. through trial-and-error, a three-layer model appeared to provide best fit to the data set. finally, the misfit between the theoretical dispersion curve and recorded data is evaluated. the depth to soil layer value is determined for each site as the depth to the boundary of layer 1 and layer 2. the best fit model of dispersion inversion for this study comprises of 3 layers (as seen in table 1). layer 1 and 2 of the model fit to the geological setting of soil structure around hot spring with typically saturated soil, comprises of sandstone, silty sandy gravel, and granite (bedrock). all model inversions were conducted using geopsypack win32 v. 2.10.1. a neighbourhood algorithm applied in dinver software is used to different models and finding the misfit of each one compared with the experimental dispersion curve. active-source experiments are processed with a fk technique. at the same location, the various shots available are stacked together with time. the various shot locations are combined to get standard deviations on dispersion curves usually picked without error estimates (wathelet, 2014). these uncertainties are analogous to those derived from ambient vibrations (stationary in time viewed as a random variation of source locations). 4. result and discussion figure 3 shows that each dispersion curve have a chance in source effects of surface waves. the signal to noise ratio is a measure of high amplitude wave energy at a given frequency, which assists in dispersion curve picking. the picking is automatically adjusted to the maximized the fk output. by selecting the lowest frequency on dispersion curve at six stations (figure 3), this survey estimated approximately 15 to 59 m deep accurately (based on the equation 2) and the estimated results are shown in table 2. figures 4a and 4b shows linearity dispersion curve (relationship wave number k with depth d and phase velocity vw), which caused by the homogeneity of the material beneath the surface, both the profiles above shows similar patterns. this can be observed when we compare the upper soil layers (top soil) with lower layer (bedrock). in addition, the curve which gives the best fit to the measured data can provides information regarding maximum depth, and also interpretation at boundary inter-layers. moreover, both profiles showed a significant correlation with r2 of each 0.954 and 0.939, in which the curve gives the best fit to the measured data to determine the boundary and depth of each layers. moreover, it indicates that the similarity of material, specifically a soils layer around the survey area. the dependence phase velocity and depth distribution on wavenumber has been conducted by chik et al. (2011). it shows the linearity of frequency and phase velocity versuswave-number relationship. the theoretical dispersion reveals consistent shear wave velocity profile in the evaluation of near surface soil properties. specifically to implement a wide variety of geotechnical investigations, including pavements, solid waste landfills, and sea beds profile. 34 arisona, a et al./ jgeet vol 02 no 01/2017 table1 . ranges used in parameters for the masw dispersion inversion layer compression-wave velocity (vp) m/s poisson’s ratio shear-wave velocity (vs) m/s density kg/m3 min max min max min max max 1st 2nd 3rd 200 5000 0.2 0.5 150 3500 2000 figure 3. dispersion curves from stations a, b, c, d, e and f with a 15 m source offset table 2 estimates of soil structure depth station a b c d e f frequency (hz) 6.16 7.29 6.07 6.56 7.3 7.4 velocity (m/s) 440.18 350.88 900 420.36 471.89 285.59 depth (m) 28.58 19.25 59.31 25.63 25.86 15.44 table 3. regression analysis of dependence of phase velocity (vm/s) on wave length (m), linear model ( 95 % higher confidence level ). station label correlation coefficient ( *r2) equation of the fitted model standar errors of estimate (%) a b c d e f 0.918 0.904 0.867 0.855 0.915 0.945 = 0.221v 27.57 = 0.227v 30.04 = 0.185v23.13 = 0.220v 24.70 = 0.177v 18.27  = 0.187 v19.37 3.29 3.81 3.82 3.36 3.14 3.10 *significantly level is 0.05 arisona, a et al./ jgeet vol 02 no 01/2017 35 figure 4. combined raw dispersion curves by active fk (requency-wavenumber method) masw techniques that was adopted from six station at site test a) stations a,b and c b) stations d, e and f. plotted graph have extracted result from figure 4 by using equation 1. figures 5a, 5b and 5c shows fk dispersion curve relationship between phase velocity versus frequency and vp & vs versus depth. the models have a misfit lower than 0.4, in which colour code shows the misfit of each model. figure 5. joint inversion of fk dispersion curve analysis. (a) extracted dispersion curve by phase velocity versus frequency at station a ( as a comparison for estimates of depth and boundary / layer) . (b and c). a view of the parameter space using the vp and vs profiles for two layer of soil synthetic data. soil zone characterized based on figure 1b. the black line represents the shear-wave velocity model with minimum misfit. based on the refraction survey, dispersion curve (figure 5a) shows the wave velocity range from 255 m/s to 300 m/s in the unsaturated soil zone at the depth of 8m (water table level). below the water table, the wave velocity continues to decrease till the depth of 18.0 m, due to the effect of critically refracted waves. in the transition zone which is located below the water table, the velocity refers to an apparent velocity as was studied by godio et al. (2010). the data in joint inversion of fk analysis shows three different soil zones : the upper part of the unsaturated soil zone at a depth of 2 to 8 m with vp of 240 to 255 m/s, saturated soil zone at a depth of 8 to 18 m with vp of 255 to 300 m/s and in the intermediate zones (estimated as partially saturated soil zone) at a depth of 18 to 30 m with vp of 300 to 390 m/s. in intermediate zone the response is very sensitive to different saturation conditions due to the groundwater fluctuation and the different distribution of the water below the water table level. the model (figure 5b) shows a constant layer for at least 2 meters deep with phase velocity (vp) of 255 m/s. in addition, figure 5c agrees with a constant first layer up to around 8 meters deep. an increase in the depth of the shear wave velocity dispersion curves, particularly at a depth of 8 meters is caused by the presence of water table level and solid layers. cross-section in figure 5b shows overlapping of profile lines, this is due to noise interference around the survey area. the two layers for pand s-wave velocities (figures 6) of the inverted profile fit the model indicated by red colours. the possible parameter range is indicated by the region that is covered by models. the corresponding depth models are plotted in figures 5 and 6. the compressional wave velocities reach 500 m/s to 2000 m/s with a velocity at depths of 20 m. discontinuity zone is found at about 30m deep. while, shear wave velocities range from200 m/s to 600 m/s and as well as at depths of 36 arisona, a et al./ jgeet vol 02 no 01/2017 approximately 20 m to 30 m, this is interpreted as a discontinuity zone. at depth of 30 m up to lower layer shows constant velocity, either vp or vs. these indicates that both vp and vs profiles has materials of homogeneities at depth down of 30 m. figure 6. depth against vp and vs profile with best misfit scale thatwas obtained in station d. the black line indicates the reference model (true dispersion curve) used as target curve inthe inversion process. the corresponding depth of models are plotted, the maximum depth is 50 m. figure 7a and 7b shows joint inversion of slowness and ellipticity h/v (slowness indicates frequency dependent group and phase velocity) and ellipticity curves are then simultaneously inverted to get the shear wave velocities. extracted ellipticities provided information within the frequency band from 6 to 40 hz, shear-wave velocities are better constrained over larger depths than by using inversion of dispersion curve alone. however, even though such joint inversion provides the general shape of shear-wave velocity structure within sediments, bedrock depth is not constrained. in addition, the true ellipticity may also contain a smooth peak in case of gradual increase of the velocity with depth. figure 7a shows slowness drastically increase with frequency, particularly at frequency of 20 hz. this relationship indicates the presence of lowervelocity layers overlying a zone with a significant velocity decrease with depth. an additional contribution to the analysis can be provided by the inversion of the ellipticity curve obtained as the result of the seismic noise analysis by using the tool dinver available in geopsy package. the important assumption of this technique is that the analyzed wave field is mainly characterized by rayleigh waves. the fundamental and first higher mode in figure 7b could be consistently explained with a common mode. nguyen et al, 2009 opined that interpretation of the first higher mode is correct, since other associations to even higher modes could not be consistently fitted. , generally is connected to deep penetration. as it was reported by babuska and cara (1991) that longer wavelengths penetrate deeper than shorter wavelengths for a given mode, generally exhibit greater phase velocity, and are more sensitive to the elastic properties of the deeper layer. shorter wavelengths are sensitive to the physical properties of surficial layers. correlation was conducted in the wavelength rather than frequency domain, because wavelength is related more closely to depth of interest (martin and diehl , 2004). figure 7 a) contain the distribution curves for the fundamental rayleigh mode and inversion results at array station d b) of the ellipticity inversion that is adopted from station d. observed curves used in the inversion are in black and the colour distinguishes the misfit value. red and yellow colours represent optimal models with smallest misfits. arisona, a et al./ jgeet vol 02 no 01/2017 37 figure 8 shows the masw rayleigh dispersion curve obtained for stations a to f as function of the phase velocity and the wavelength; as the wavelength reflects more closely at the depth of penetration. curve of the model analysis in the phase velocity to wave length could be a suitable approach to estimate the geometric specifications of the soil layers, especially for the soil layers with a clear contrast between the sedimentary cover (top soil) and bedrock. these allegation was very strong with the results of the correlation coefficient (r2) of a six stations by high significantly values which are 0.918, 0.904 ,0.867, 0.855 , 0.915 and 0.945, respectively. the results obtained from the regression analysis are in agreement with dispersion curve interpretation in test site with low percentage error as shows in table 3. moreover, the similarities between the equations in the studied sites are good evidence for the utilization of this method in the geotechnical site investigation. correlation between the experimental rayleigh dispersion curve (phase velocity versus wavelength) and the vs ground model (shear wave velocity versus depth) estimated from rayleigh dispersion inversion was observed, and they confirm that these non-invasive techniques are useful in evaluating the vs ground profile. 5. conclusion from the overview above, the masw dispersion curves have successfully applied on characterizing and evaluating boundaries and depth that have significant implication in both geotechnical and engineering applications. particularly in comparison with conventional drilling, it is cheap and provides the benefit of precision. it is suitable for estimating the subsurface shear and compression wave velocity profile over a large area. the utilization of linear regression of two explicit empirical relationships for wavelength phase velocity and wave number versus depth and phase velocity has a good matching (best fit curve) and both relationships were recommended for correcting and estimation rayleigh dispersion curve of soil structure due to the higher value of r2. this confirms that relationship pattern of fk (frequency wave number) dispersion curves is a good interpretation method for understanding the soil layers of the investigated area. figure 8. representation of dispersion curve (a,b,c,d,e and f) of the model analysis in the phase velocity versus wave length obtained for stations a, b, c, d, e and f at test site in the study area (red dots are measured values and lines are best fit model) and correlation coefficients (r2) by each station. 38 arisona, a et al./ jgeet vol 02 no 01/2017 acknowledgements first of all we thank to the directorate general of higher education (dghe) of indonesia who has giving us scholarship. the field support from colleague of postgraduate student and technical staff of geophysics programme, school of physics, universiti sains malaysia is highly appreciated. references alexander, j. b.,1968. the geology and mineral resources of the neighbourhood of bentong, pahang and adjoining portions of selangor and negeri sembilan. journal of mal. geol. survey mem. (ns) 8: 1-250. babusk,v. and cara, m. ,1991. seismic anisotropy in the earth , modern approaches in geophysics, volume 10 , isbn: 978-94-010-5596-3, springer science & business media. blake, d.r., 2009. surface layer thickness and velocity determined using the multi channel analysis ofsurface waves (masw) method compared with microtremor resonance analysis federal road, greene county, ohio, (thesis). chik,z., islam, t., and taha, m.r., 2011. implemented in awide variety of geotechnical investigations, including pavements, solid waste landfills, and sea beds profile, tamkang journal of science and engineering, vol. 14, no. 2, pp. 107-114. dey,a.,2015.subsurface profiling using masw: aspects of data acquisition,dispersion and inversion analyses (rep.). https://www.researchgate.net/publication/2820029 61) (accessed 08.12.15) grandjean ,g.,2009. from geophysical parameters to soil characteristics (rep.). http://eusoils.jrc.ec.europa.eu/public_path/digisoild2.1 (accessed 11.12.15) godio,a., bastani, m., french, h., bloem, e., foti, s., arato, a., and pedersen, l. , 2010. optimisitaion of geophysical field methods (rep.) http://www.bioforsk.no/ikbviewer/content/71116/ version=1/soilcam_deliverable_d1.2 (accessed 07.09.16) hiltunen,d.r.,hudyma,n.,tran,k.t., and sarno,a.i., 2012.geophysical testing of rock and its relationthips to physical properties (rep.). http://www.fdot.gov/research/completed_proj/su mmary_smo/fdot_bdk75_977-01_rpt(accessed 04.06.16) hamizah binti mohamad, 2016. the study of electrical resistivity imaging ( 2d and 3d) and geochemical in the hot spring area at pedas (rep.) kearey, p., brooks, m., and hill , i., 2002. an introduction to geophysical exploration , third edition, blackwell science publications. martin,a.j. and diehl,j.g.,2004. practical experience using a simplified procedure to measure average shearwave velocity to a depth of 30 meters (vs30), 13 th world conference on earthquake engineering, vancouver,b.c., canada, august 1-6, 2004, paper no. 952. https://www.researchgate.net/publication/282002961 https://www.researchgate.net/publication/282002961 http://eusoils.jrc.ec.europa.eu/public_path/digisoil-d2.1 http://eusoils.jrc.ec.europa.eu/public_path/digisoil-d2.1 http://www.bioforsk.no/ikbviewer/content/71116/version=1/soilcam_deliverable_d1.2 http://www.bioforsk.no/ikbviewer/content/71116/version=1/soilcam_deliverable_d1.2 http://www.fdot.gov/research/completed_proj/summary_smo/fdot_bdk75_977-01_rpt http://www.fdot.gov/research/completed_proj/summary_smo/fdot_bdk75_977-01_rpt 1. introduction 2. site description and geology 3. experimental work 4. result and discussion 5. conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet http://journal.uir.ac.id/index.php/jgeet . http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 139 case study adaptation to the climate change impact through community participation on customary land use zaflis zaim 1, * imam buchori 2 1 urban and regional planning department, universitas islam riau indonesia 2 urban and regional planning department, universitas diponegoro semarang . * corresponding author : zaflis@eng.uir.ac.id received: jan 1, 2019; accepted: mar 30, 2019. doi: 10.25299/jgeet.2019.4.2.2777 abstract climate change and global warming have brought some policy to reduce the impacts by adaptation and mitigation strategies. one adaptation strategy is to increase land use size in agriculture area base on community participation. on the other hand, sustainable development needs cooperation mainly on common investment. the aim of the study is to identify the land utilization process, role model and level of participation on customary land. we use observation and deep interview method to analyze this study. the result shows that the customary land utilization process has realized through public deliberation with local fig.s. the agriculture programs operated with wanatani concept or agro-forestry by housewives where multi-level strategy is mutually beneficial. around 30 housewives have been participating in producing agriculture products, i.e., coffee, milk candy, palm sugar, and ginger powder. the level of participation especially for female farmers at rw 01, which shows a percentage of 16.6%. generally, community participation has encouraged the gotong-royong model while has to contribute in their time, tools and materials to develop the communal shed. in conclusion, the land tenure system has taken with sharing benefits between local government & farmers. the customary tenure has recognized as one of the tenure systems in indonesia, especially on adat land management. keywords: climate change, development, participation, adat land, investment. 1. introduction 1.1 background it has been important in the issues concerning climate change and global warming caused by the increasing concentration of greenhouse gases (ghg) in the atmosphere in every country. it has been producing the volume of sea and sea level increase significantly every year (bellard et al, 2013). the phenomenon also has been gave an impact such as inundation at many coastal city like semarang (buchori et al, 2018). on the other hand, semarang regency contributed around 1.7 million tons of co2e in 2009, and it was predicted to increase to 2.9 million tons of co2e by 2020 (klh, 2009). mostly, the emissions are from the use of fossil energy for electricity and transportation with a total contribution of about 49.77% of the total emissions. fig. 1 and 2 describes greenhouse gases emission projection from government and community activity. indonesia seeks to implement a policy of reducing greenhouse gas emissions by 26% from business as usual through the implementation of presidential regulation number 61/2011. according to the regulation, the government of semarang regency is required to reduce ghg emissions through mitigation efforts. in the aspect of mitigation, the planning of the action program is expected to contribute to reducing emissions by 3.71% by 2020. climate change mitigation is an effort to reduce the production of greenhouse gases to minimize global warming. meanwhile, the adaptation of climate change is an effort to adjust to climate change aimed at reducing risk and increasing resilience. an integrated climate strategy implemented through an action plan that is integrated into the development planning process, including expanding the area of land cover; carry out conservation & management of water resources; and management of domestic and industrial wastes (blh, 2014). the activities conducted at the effort to expand the area of land cover include planting trees suited to the climate & humidity conditions in the region. domestic waste management through the development of biogas facilities from livestock manure, building the septic tank and producing organic fertilizer. meanwhile, the conservation & management of water resource is performed through the construction of reservoirs, infiltration wells, and water reservoirs. these activities are conducted through community efforts based on community participation, especially in 5 villages, including lerep, pagarsari, branjang, gogik, and nyatnyono. through http://journal.uir.ac.id/index.php/jgeet 140 zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 the joint commitment, community participation has been encouraged and significantly improved in addressing issues and reducing the impact of climate change by utilizing private, state-owned (plantations) and village-owned lands, among others: allocated land (bengkok land), village-owned properties, and community forests. fig 1. greenhouse gases emission projection from government activities, the year 2010-2020 fig 2. greenhouse gases emission projection from community activities, the year 2010-2020 (source: integrated climate change strategy semarang regency, 2014) fig.3. monthly rainfall 1991 to 2000 at semarang regency (source: processed from monthly rainfall data distanbunhut semarang regency, 2014). zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 141 fig.4. monthly temperature average, the year 1991 to 2000 at semarang regency. (source: processed from monthly temperature average distanbunhut semarang regency, 2014) 1.2 objectives and focus of the research this study aims to identify the process of land use, especially for village-owned land, to map the participation model and measure the level of community participation that develops during the village-owned land planning & utilization process. village-owned land as the object of research was focused on the distribution of allocated land (bengkok land). the utilization of village-owned land is inseparable from government policies and programs in adapting and reducing the impact of climate change, especially in semarang regency. the study was centralized at lerep village as one of the villages that realizes the climate changes mitigation programs. there are 2 kind of adat land such as bondo desa and bengkok land (see fig. 5). this research will focus on: settlement problem that encouraged participation, number of local fig.s who have actively communicated to the participation process, the duties or tasks of the fig., type of land use and the allocation of village-owned land, the periodization of the land planning process, the type of plants in mitigation/adaptation programs, the developed agricultural or livestock derivative products. the object or focus of this research can develop according to the facts and conditions at the research location. 2. literature review 2.1 community participation and planning process community participation can be defined as the participation of all or some members of society in solving problems that occur in the community life (indonesia dictionary, 2001). glass (1979) defined citizen participation as providing citizens with opportunities to take part in governmental decision or element in the planning process so that it can be seen from the reality that there is a very relationship between community participation and the planning process. fig.5. kind of adat land in lerep village and research focus planning requires input that, on the one hand, to success the process, and on the other hand, it can not provide other inputs (day, 1997). the weaknesses in terms of resources (place, energy & money) and time limitations (deadline) are common in the planning process that can reduce the effectiveness of community participation (day, 1997). transactive planning finds the knowledge transformation resulted from the communication between professionals and community members in action (friedman, 1973). thus, collective learning is a process conducted with the community by learning from each other by listening, respecting, and being open to each other. community participation in the planning process can provide benefits for the community and local government. therefore, burby (1997) states that the clarity and specific management of the growth of a country growth can improve the quality of urban planning. a study conducted by dawkins & nelson (2003) proved the existence of the relationship between growth and development management programs. they found that cities with interesting growth management programs would attract new construction activities to be more frequently (dawkins and nelson, 2003). the planners must also target stakeholders and groups that have some interests so that they are base on contributions they can make during the planning process. some theories explain opinions with the techniques or methods used are emphasized to get kind of adat land in lerep village bengkok land allocation (head of the village, secretary, dept head, sub-village head, bayan, mudin) bondo land 142 zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 attention and increase the level of community participation. a scientific group has also proven that the methods used by the planners in choosing the community participation processes (e.g. hearing, open house, surveys) will also have some effect on the level of participation (brody, godschalk and burby, 2003). 1.1. the required parties to participate a component of a community chooses to participate on different issues or problems. groups with different backgrounds may choose to participate at different stages of the process, especially for big projects. so that the number and type of participants can change during the planning process (sanoff, 2000). the community is also not pleased or finds difficulties to accept a decision made by someone. therefore, to present an agreement, they must feel that they have an idea or to take part in the decisionmaking process (fisher & ury, 1981). this is cause the characteristics of each person are different based on their natural conditions. the public or the community prefers to participate in the process if they can see how their inputs or suggestions can change a decision or if the decision can affect their lives in the present and the future (brody, godschalk and burby, 2003). according to creighton (1994 in sanoff), people also choose to participate if: a. they perceive themselves as being influenced by an issue because of a threat that may present or of the benefits of the proposed facility; b. they have economic interests, especially for the results of a decision; c. they need protection to get increased access to the use of a facility or public service and other conditions or motivations. the community will participate according to their level of expertise, interest or intention in a condition and life problem (maier, 2010). these are becoming a variable level of involvement that depends on differences in technical expertise, roles in society, and willingness to provide time and energy. so, the number, composition or type of participants can change & differ during the decision making and the planning processes (creighton, 1994; sanoff, 2000). the number of people involved in the direct process can also influence the duration of the process (stewart & sinclair, 2007). 1.2. land tenure system land tenure generally refers to an understanding of land position so that someone can use land under a legal utilization system which regulated in government regulation in the community recognized by the state. below are some definitions of land tenure from some sources: community to use specific pieces of land and associated resources in a certain period and for (choudhury and jansen, 1997). individuals or groups have to land and the resulting (werhmann, in rudiarto 2006). and established institutional arrangements in society that govern how land & resources are allocated, used (nichols, 1993). from the definitions above, there are some elements related to land tenure, including regulation, land access, land utilization control, ownership, land utilization type and social relation in the community. the combination of the elements forms the land tenure system, which is an interpretation of ownership of property in general. land tenure system then creates a condition where available land is connected with a physical object and was realized as construction on the owned property or asset. the strength of a land status depends on the certainty of land use. therefore, land tenure is very vital on planning and development of land in a location. the strength of land status depends on the legal and social aspect of someone in utilizing the land. the legal aspect contains legal recognition of land ownership while the social aspect contains reality land. both aspects can reinforce the position of land ownership, so that tenure security is also very important in land planning and development. legal recognition and the fact of land status also demand thoughts, concept, and strategy for land legitimacy or legalization (rudiarto, 2006). legalization will strengthen and give trust to a local community in planning, management, and optimization of land use. according to payne (2002), there are five types of land tenure system: a. customary land. the system considers land to be community asset managed and protected for current and future generations. the allocations, transfers, usages are determined by a community leader. b. private tenure. the system views individual and gives complete freedom in owning and managing their land asset. the condition was concentrated in the urban area. c. public tenure. the system exists due to reaction to a limitation of individual ownership and grows in public needs. d. religious tenure. the system is often found in islamic countries where charity agencies are appointed to manage certain lands. e. non-formal tenure. the system is land ownership which is closely related to legality and illegality. the system is often found in lower social class society. zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 143 3. research method. 3.1 research tool and material this study used secondary and primary data in the form of maps, interviews, observation or photo documentation. the secondary data comes from village office of lerep, bps/statistical center bureau, public works agency and environmental board (blh) of semarang regency. to support the mapping, the arcgis application, mobile mapper and remote sensing drone were used as the inputs for research data. other tools were used the interview guides, recording devices, and cameras. 3.2 analysis the research approach was conducted by using an observation method on the observed object according to the research objectives. descriptive-qualitative analysis techniques explain the level of participation and the planning process of the utilization of villageowned land. meanwhile, the community participation model is explained through the chart of the land planning process along with a description of the duties/responsibilities of each key personnel or local fig.s who play some roles. the interview conducted with the informants was used to get a more detailed explanation of environmental conditions and phenomena. meanwhile, the spatial data overlay was used for obtaining the overview of land development from the early until the recent period. 4. results lerep village covers an area of 682.24 hectares (bintari & foe, 2012). the results of observation showed that the dominant land use functioned as agricultural land with the biggest use for plantations or fields, covering the total area of 166.18 hectares (24.3%), followed by the state-owned plantation (22.2%), and irrigated rice fields (19.9%). while the area of non-agricultural land is 183.11 hectares or 26.8%. from the results of interviews & observations, it is known that lerep village has widely distributed village-owned properties & lands as customary lands. planning and utilization of land are under the authority of the village head and his sub-ordinates elected by the community. the distribution & area of land use in lerep village can be sawed in the fig. 6 and 7 below. before 2006, most of these lands were used by residents for rainfed lowland agriculture and less productive dry land (results of interview sgt, 2018). the shift in the use of village-owned land began in early 2006 when a health care officer in west ungaran saw environmental hygiene problems, especially for residential areas. at that time, the healthcare officer assessed the existence of unhealthy residential problems due to the location of livestock pens close to community residential area. besides, livestock manure produces a bad smell, cleanliness problems, and poor sanitation. therefore, the healthcare officer began taking steps to communicate and socialize with the village head by inviting local fig.s to find solutions to the environmental problems in the community settlements. the communication, coordination and community consultation processes can be seen in the fig. 8 below. fig 6. type and size of land use in lerep. fig. 7. map of land use in lerep village (source. mitigation risk disaster based on community, dpu and mci 2018) community participation began to be conducted intensively and reached a peak through deliberation at the sub-village level. this activity was pioneered by the health care officer and driven by the role of village officials. given the existence of environmental problems above, the main objective of sub-village deliberation was to discuss the issues of cleanliness and environmental health due to the presence of livestock pens in every house. the final process of the deliberation resulted in an agreement between the community and the village officials to build a shared cattle shed on the allocated land (bengkok land). the results of the community meeting/deliberation also decided the plan to use the allocated land, especially for bengkok bayan, as the location for the construction of livestock pens. considering that there were no people assigned in indrokilo sub-village and assigned as bayan (the vice head of sub-village), the village head wanted to allocate bengkok-bayan land for the development plan. from the results of the interview, it knows that the right of bengkok-bayan 27% 3% 24% 22% 2% 20% 2% type and percentage of land use in lerep house/building & yard road, river, cemetery garden plantation village forest irrigated agricultural land rainfed rice field 144 zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 land management in lerep village is on the authority of the village head (interview with sgt and atn, 2018). the result of the agreement made between the community, healthcare officer and village officials was a recommendation that every cattle breeder can relocate their livestock pens to the communal livestock pens. the construction process of communal livestock pens was started in late 2007 through cooperation, both in terms of labor, tools and times. after constructing the communal livestock pens, the village officials asked the residents to move their cattle to the agreed location and to be relatively far from their houses. the condition of communal sheds can be seen in fig. 11. the role model of every local fig. can be seen in the fig. 9. fig 8: initial process of proposal & the parties involved in discussion of bengkok land utilization planning fig 9. distribution of bengkok land management for village & sub-village officials & their obligations furthermore, the assistance received from the local government was in the form of biogas tank facilities for processing manure into gas for household needs. at almost the same time, the domestic and foreign ngos also assisted in the form of plant seeds planted on village-owned land, community forests and other types of land. this effort was intended to reduce the impacts of climate change, especially in semarang regency, while encouraging the community participation in increasing the area of land cover. types of plant seeds provided by ngos to villagers include albizia chinensis, clove, mahogany, avocado, durian, arenga pinnata, longan, and coffee (interview with bintari staff, 2017). based on the topography, rainfall and climate data in the fig. 3 and 4, the types of plants were suitable to be planted in locations with altitudes of more than 600 meters above sea level they are providing public services and government administration at the village level or in the administrative area of the village. the bengkok land can be cultivated as a wage for their services. helping village government through public & community services for sub-village residents. bengkok land as wage for their services. helping the sub-village head in public services for residents. bengkok land can be cultivated as a wage. helping the sub-village head is socialreligious issues for residents. bengkok land can be cultivated as a wage for their services for the sub-village residents. bengkok of village head and secretary bengkok of subvillage head bengkok of bayan bengkok of dept head & officials bengkok of mudin bengkok land distribution 1. sub village head 2. bayan 3. group of farmers l a n d u se u tiliz a tio n a g re e m e n ts o n b e n g k o k l a n d sub village deliberation (musrenbangdusun) farmer’s aspiration village head sub village residents the year 2006 2006-2007 socialization from health orderly oct 2007now zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 145 with fairly cold temperatures. the results of the topography mapping can be seen in the fig. 10. based on observations, the processed agricultural products include palm sugar, coffee powder, milk candy, soap, crackers, ginger powder, boiled aren nut, honey, cloves, albizia chinensis powder, and cow's milk (see fig. 13). in addition to reducing the impact of climate change, the types of crops above also provided added value for improving the household economy compared to paddy. based on the results of interviews, it was found that there were 180 families in the rw-01 (community association) of lerep village with a total of 4 rt (neighborhood association). mostly, the residents work as farmers of horticultural crops, perennial crops, and breeders (cows & sheep). in addition to agricultural products, farmers also make processed products from plants grown in the village. the farmers divided into two groups, namely: wanita tani and ngudi makmur. wanita tani is a group of female farmers with 22 active member of 30 members, while ngudi makmur is a farmer group consisting of 32 male farmers. fig 10. map of topography in lerep village. (source: mitigation risk disaster base on community, dpu and mci 2018) fig 11. land use condition and communal sheds fig 12. tank installation of biogas & communal sheds 146 zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 fig 13. coffee product, ginger, crackers, and honey from agriculture farm table 1. name, number of farmers group & their activity no farmers group name focus/activities number of group members (person) 1 ngudi makmur livestock 32 2 mangger lestari products of agriculture farm. 30 total 62 the allocated land is used for, among others, agricultural activities, cattle breeding, and social facilities, such as education and healthcare facilities. also, there are also sanitation facilities built, such as biogas tanks or wells that process cow manure from communal sheds into gases (see fig. 12). the gas products are then supplied to five houses around the allocated land. at the initial stage of operation, it was known that the biogas tanks could function properly. however, there were some constraints in the operation of the installation such as the high costs of maintenance, material, expert & technical maintenance of the installation. in general, the management of the village-owned land requires agreement, memorandum of understanding and commitment during its utilization and requires the clarity of collective investment patterns from the community. therefore, it is not surprising that investment factors play a major role in sustainable land management. hartshon, in adnyana (2002) argues that land investment encourages land use change for several reasons: economic/profit motives; preferences; comfort; values & perceptions (hartshon., et al. 1992). village-owned land in the form of crooked land certainly has a value in the form of a permanent position on the status of the land, so that it affects the perception of the community in its utilization or management. the number of farmers who are actively involved in managing village-owned land and their processed products can be sawed in the table 1 below. the table also explains the level of community participation in village-owned land management especially for rw 01, which shows a percentage of 16.6% for female farmers). 5. discussion in general, the management of the village-owned land requires agreement, memorandum of understanding and commitment during its utilization and requires the clarity of collective investment patterns from the community. therefore, sustainable investment in village land management is influenced by factors: technical, physical, socio-economic, cultural and institutional factors. however, the actual influence of these factors differs in time and space (nyanga, aad kessler & albino; 2016). regarding socio-economic factors, other researchers showed the influence of motivation to invest in land management namely: personal characteristics, availability of resources, participation in past programs, conditions & market access and development strategies (adimassu et al., 2012; bamlaku, 2011; kessler, 2006; paudel and thapa, 2004; tenge at al., 2004). the personal characteristics of farmers in terms of the education level of the head of the household are urgent and influential on land conservation in nepal (paudel and thapa, 2004). whereas in ethiopia, the characteristic is a combination between several factors, such as the contribution of resources, the experience of the head of the household, knowledge, and access to information that explains the decision of farmers for how much & where to invest in land management (adimassu et al, 2012). therefore, the key socio-economic factors for investment patterns in the land cultivation system, need to get more attention through research. land conversion occurs in unplanned settlements, especially the use of customary land in lerep village which has been less productive and has changed its function to become more productive land for zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 147 agricultural activities, livestock and social activities. dynamics and variations in agricultural activities are pursued through collective investment efforts from farmers who are driven by climate change mitigation & adaptation programs. however, the low level of farmer participation in investing in village land, limited information & funds and the stagnation of sanitation programs require observation and deepening of studies using appropriate methods. on the other hand, the existing land management investment theories are only suitable for investment in private land. according to literature review and observation, the customary land is the state-owned land with usufructuary status, but not all farmers who have management rights beside the breeders. this condition have decrease a chance to other residents (farmers) on bengkok utilization. so, it was semipublic on management system while actualized. 6. conclusion the climate change mitigation & adaptation programs have encouraged the growth of community participation via the use of village-owned land. although the level of participation that has developed is not high enough, the agricultural & livestock activities with agroforestry systems with adjustments to climate conditions and crop types have been able to increase the income of the community in lerep. this research only focused on the utilization and management system of village-owned land. therefore, the researchers suggested that observations on the level of community participation in climate change mitigation or adaptation programs can also observe in other types of land use, especially on the plantation and community forests as the widest land in this village. also, the influencing factors of the investment in land management in the utilization of villageowned land need to be a review. the scope of the study area can be expanded to others sub-district from lerep village. this intended to achieve and develop to land information system in the land parcel that is more informative and integrated between the government institutions. the spatial data system will give some advantages on land registration, status transformation, permit extension, spatial planning process up to legalization phase. acknowledgements we say thanks lpdp (educational fund management agency) for the research cost assistance, the rector of universitas islam riau and semarang regency government for the survey and permission. we also would like to thank farmers group, research assistant and local actors for their contribution and attentions. references adnyana, i ketut puspa, 2002. perubahan pemanfaatan ruang dalam perspektif masyarakat adat bali, studi kasus padangsambian denpasar, disertasi-tidak dipublikasi, pps-universitas gadjah mada, yogyakarta. adimassu, z., kessler, c.a., hengsdijk, h., 2012. exploring management in the central rift valley of ethiopia., j.applied geography. 35, 191 198. bamlaku, a., 2011. the impact of poverty, tenure security & risk on sustainable land management strategies in northcentral ethiopia: analysis across three agro-ecological zones, j. sustain. dev. afr. 13, 227 240. bellard, c. leclerc, f. courchamp., 2013. potential impact of sea level rise on the french islands worldwide, nat. conserv. 5, 75 86. bintari dan friend of earth., 2012. kerangka konsep pendidikan lingkungan hidup: studi kasus masyarakat indrokilo desa lerep kecamatan ungaran barat, yayasan bina karta lestari, semarang, p.19. brody, s., godschalk, d., and burby, r., 2003. mandating citizen participation in plan making six strategic planning choices; apa journal, 69 (3), 245262. buchori, i., a.sugiri, mussadun et al., 2018. a predictive model to assess spatial planning in addressing hydrometeorological hazards: a case study of semarang city, indonesia, international journal of disaster risk reduction, 27, 415-426. burby, r.j., and p.j. may., 1997. making governments plan: state experiments in managing land use, baltimore: johns hopkins university press. choudhury, k and jansen louisa j.m., 1997. terminology for integrated resources planning and management, fao, rome. day, d., 1997. citizen participation in the planning process: an essentially contested concept, journal of planning literature, 11(3), 421-433. fisher, r., and ury, w., 1981. getting to yes, houghton mifflin company boston, usa. friedmann, j., 1973. retracking america. a theory of transactive planning, anchor press/doubleday. garden city, ny. dawkins, c. j., and nelson, a. c., 2003. state growth management programs and central city revitalization, journal of the american planning association. 69(4): 381396. glass, j.j., 1979. citizen participation in planning: the relationship between objectives and techniques, journal of the american planning association, 45, pp.180 189. kessler, c.a., 2006. decisive key-factors influencing farm j.appl. geogr. 26, 40 60. maier, karel., 2010. citizen participation in planning: climbing a ladder? publisher: routledge. http://dx.doi.org/10.1080/713666506. nichols, s., 1993. land registration: managing information for land administration., phd dissertation, department of surveying engineering, technical report no.168., university of new brunswick, fredericton, new brunswick, canada., 340pp. nyanga, aad kessler, and albino tenge., 2016. key socioeconomic factors influencing sustainable land management investments in the west usambara highlands, tanzania, land use policy, 51, 260 266. paudel, g.s., and thapa, g.b., 2004. impact of social, institutional and ecological factors on land management 148 zaim, z. & buchori,i ./ jgeet vol 04 no 02/2019 practices in mountain watersheds of nepal, appl. geogr. 24, 35 55. payne, g., 2002. land rights, and innovation: improving tenure security for the urban poor, itdg, london. rudiarto, i., 2006. land tenure & tenure security dalam pemanfaatan lahan permukiman kota (permasalahan, konsep pendekatan dan manfaat), j. tata loka, vol 8, undip semarang. sanoff, henry., 2000. community participation methods in design and planning, john wiley & sons inc, canada. stewart, j. m., & sinclair, a. j., 2007. meaningful public participation in environmental assessment: perspectives from canadian participants, proponents, and government; journal of environmental assessment policy and management, 9 (2). retrieved from http://www.worldscientific.com/doi/pdf/10.1142/s14643 33207002743. tenge, a.j., de graaff, j., hella, j.p., 2004. social and economic factors affecting the adoption of soil and water journal land degrad. dev. 15, 99 114. --------------, 2018. pengurangan resiko bencana berbasis komunitas, program global resilience partnership transform, dinas pekerjaan umum kabupaten semarang dan mci. ----------------2014. integrated climate change strategy semarang regency strategi year 2015-2020, semarang regency government, blh. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://www.worldscientific.com/doi/pdf/10.1142/s1464333207002743 http://www.worldscientific.com/doi/pdf/10.1142/s1464333207002743 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 1.1 background 1.2 objectives and focus of the research 2. literature review 2.1 community participation and planning process 3. research method. 3.1 research tool and material 3.2 analysis 4. results 5. discussion 6. conclusion http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 usman, d.n. et al./ jgeet vol 03 no 04/2018 231 research article gold-silver mineralization in the neo-tectonism of honje formation and cipacar formation, in cibaliung block, banten province dudi nasrudin usman 1,2, nana sulaksana 1 , febri hirnawan 1,2, iyan haryanto 1 1 faculty of geological engineering, padjadjaran university, jln. raya jatinangor km. 21 bandung, indonesia 2 mining engineering program, faculty of engineering, islamic university of bandung, jln. tamansari no. 1 bandung 40116 * corresponding author : dudi13001@unpad.ac.id received: july 18, 2018; accepted: november 11, 2018. doi: 10.24273/jgeet.2018.3.4.1852 abstract the gold ore mineralization region is a zone of mineralization which is inseparable from the role of geological structures, one of which is fracture. the cibaliung and surrounding areas are epithermal gold mineralization zones, in this region there are two main mineralized zones, namely cibitung zone and cikoneng zone. it has almost the same characteristics where the fractures formed are quite large so that it influences the class of rock mass, but the other side is the presence of many fractures which make it easier for scattered mineralization to fill the fracture so that the formed vein is thick enough. this study aims to analyze the relationship of rock mass rating (rmr) and rocks quality design (rqd) to tectonic movements in the region to prove the neo-tectonic phenomena in the honje formation and cipacar formation using surface mapping methods. the methods used are rock type mapping, rock structure mapping, mapping and rqd measurements, rock descriptions and rock sample collection. all the data obtained are then verified and validated before processing and statistical tests. statistical tests are carried out to ensure an analysis with a basis that is recognized by all parties. both formations above have different ages, which is for the honje formation (andesite lava) with the final miocene age and cipacar formation (tuff) at the age of pleistocene. the findings of this study are the two formations measured by rqd and rmr on rock cracks and surrounding conditions; the rmr observation station made around 125 points in the honje formation and 117 points in the cipacar formation. the r2 value of the rmr value of the honje formation and the cipacar formation shows a positive relationship of 67%; the biggest rmr value is in tuff rock. in addition, the relation between rmr andesite lava value and rmr tuff value is done with t-test between andesite lava and tuff where the result shows no difference of mean between rmr andesite lava and rmr tuff value. therefore, the tectonic processes that occur in the honor andesite lava unit of honje formation with the preceding position are formed, and the older age at the end of the miocene age that is blocked by the field of unconformity experienced continuity on cipacar formation tuff unit with the upper position that is formed after honje formation and younger age in pleistocene. the continuation of the tectonic process proves the existence of active tectonic activity better known as neo-tectonic. keywords: neo-tectonic, gold mineralization, andesite lava, tuff, low sulfide 1. introduction the magmatism pathway characterized by a row of intrusion stones along the sumatra axis parallel to the subduction zone is a path formed by the collision of two tectonic plates of the indian ocean australia and asia eurasia. the line spreads stretching from north sumatra to java and bali, then connected to nusa tenggara to sulawesi and maluku islands to the philippines. the process of forming the magmatism pathway occurs as a result of the drive of the oceanic tectonic plates forming the rising fault zones, paralleled along the subduction zone. the rising faults are the weakness zones that facilitate the hydrothermal breakthroughs of the magma to reach the top of the earth's crust. this process is followed by chemical reactions between the hydrothermal solution and the surrounding rock which produces mineral zones starting from porphyritic, mesothermal and epithermal according to their respective regions. the geological structure found in the research area is straight normal fault toward northeast-southwest. (sudana et al,1992) states where it is suspected that there is a connection of the structure with the zone of the krakatau area in the sunda strait which is a depression of tectonic volcanic activity (zen, 1983 in sudana, et al., 1992). this study wishes to convey the purpose by which tectonic movement and activity can be demonstrated by rmr and rqd values of two different formations, in which case the two formations are the honje formation (andesite lava) and the cipacar formation (tuff). to support and respond to the desired objectives in this paper, a method of mapping the surface geology is applied to obtain an overview of the pattern and http://journal.uir.ac.id/index.php/jgeet mailto:dudi13001@unpad.ac.id 232 usman, d.n. et al./ jgeet vol 03 no 04/2018 distribution of cracks from 2 different formations, observations and rmr measurements in the field, which is then assisted by verification and validation of data as evidenced by data processing through correlation regression analysis method. 2. geology setting volcanism during paleogene to neogene is recorded both in several basins on java and sumatra, such as the sibolga basin, bengkulu basin and the basin of south sumatra. paleogene and neogene volcanism in java are characterized by the presence of jatibarang formation (paleogene) and merawu (neogene). the pliocene-quarter vollitism phase is characterized by a change in the transgressive cycle into a regressive cycle to the end of tertiary. recent field data shows the presence of early tertiary volcanic rocks in southern sumatra kikim formation and lahat formation (adiwidjaja, et al., 1973; pulunggono, et al., 1984 in soeria-atmaja, 1997) and the northern coast of java is jatibarang formation (martodjojo, 1984 in soeria-atmaja, 1997)). the presence of early tertiary volcanic rocks in java and sumatra has shown the magnitude of the magmatic arc. the jatibarang formation is known to be 29.0 million years ago (martodjojo, 1984 in soeriaatmaja, 1997), not done dating on kikim formation and lahat formation. however, stratigraphically both are under the oligocene talangakar formation. the jatibarang formation, kikim formation, and lahat formation exhibit similar characteristics, including a thickness of tuff in addition to the presence of volcanic breccia and lava flows. tertiary old-age volcanic rock outcrops are also found in the western regions of sumatra (age k-ar 65 million years ago), natal (sutanto, 1997 in soeria-atmaja, 1997), and sibagindar (west aceh). based on the evidence in the field, it can be concluded that the dispersal of early tertiary volcanic rocks is wider than previously thought. early tertiary volcanic rocks were also found in southern java. outcrop can be found in west java (jampang formation), central java (old andesite lava formation) and east java (besole formation). the jampang formation is 17.9-32.3 million years ago in soeria-atmadja, et al, (1994) and can be compared to the oligo-miocene old andesite lava formation. volcanic rocks did not appear in southern bali, but were reopened in lombok, flores, and sumba. in the lombok region, early tertiary volcanic rocks are represented by early oligocene-miocene collector formations. the continuity of early tertiary volcanic rocks in northern java is still not known with certainty. hamilton (1979) and martodjojo (1984) assume that the manunggul formation in southern borneo (meratus area) is a continuation of the jatibarang formation. nevertheless, the results of k-ar age calculations show the age range of 72.2-86.9 millions years ago (sumarso, 1985 in soeria-atmaja, 1997), much older than the jatibarang formation. arpandi, et al (1975) in soeria-atmaja (1997) state that volcanic rocks in the bengkulu area (between bengkulu and palembang), southern sumatra and northern java range from 50-60 millions years ago, older than the magmatic arc tertiary beginning in southern java. the magmatic bows represented by kikim formation, lahat formation and jatibarang formation are suspected to be continuous and related to the presence of melange in luk ulo (central java) and ciletuh (west java). tertiary magmatic activity is expected to begin in the north on limestone to shift south after experiencing "dormancy" in the eooligocene. the alteration of the magmatic arc corresponds to the sumba microcontinent docking (sumba, east java, paternoster) (fig. 3). 2.1 structure and tectonic regional the tectonic activity of the study area is the western part of java island where geologically the area is included in banten block. bemmelen (1949) mentions this area as banten block with a line boundary extending south-north from pelabuhan ratu bay to jakarta bay including geological boundaries. tectonic java sumatra experienced many developments through the latest scientific publications in particular. the orientation of java island has similarities with the island of sumatra. both islands are separated since the mio-pliocene. java island has changed its direction anti-clockwise while the island of sumatra is rotated in a clockwise impact on the widening of the sunda strait towards the south like a triangle zone. geologically, the similarity of java island and sumatera island can be described as the existence of segmented basements in banten and lampung with north-south direction. the discovery of horst graben systems as in ujung kulon high ujung kulon low honje high west malingping low. fig 1. tectonic development of transitional zone between sumatera and java. (handayani, 2008) the existence of the horizontal fault of sumatera is active in the form of dextral and ujung kulon horizontal fault (off the southwest coast of pelabuhan ratu) with step-over position, such as in order from sumatera fault to ujung kulon fault. other evidence that gives the belief that during the time of sumatra island and java island is one that is the existence of synthetic faults are releasing, both in lampung and banten, implicate "basal lava flood" in lampung and banten because of these faults to encourage the release of magma rise to the surface. the subduction model suryadi, a. et al./ jgeet vol 03 no 04/2018 233 that occurs in the sunda strait region is the convergence between the indian plate and the eurasian plate causing changes in the movement of the surrounding plates. one of the expected changes due to the collision is the change in the direction of the indoaustralian plate convergence of the eurasian plate (fig. 1) 3. materials and methods the area of cimanggu as one of the areas that is part of bayah dome is geologically strongly influenced by the presence and presence of the western java plate meeting, and closely related to the presence of mount krakatau in the sunda strait. mount krakatau as part of the meeting plate in the sunda strait provides very important information to be able to describe how the plate activity. in addition to the existence of mount krakatau as evidence of the encounter and movement of western java plate, other phenomena present such a fairly complex rock types with different each of age, the presence of other mountains in the land area of the cibaliung region and surrounding areas, as well as the findings the presence of mineralized zones as part of tectonic activity in the region. the geologic structure that developed in the research area is stocky with dominant south-western direction. stump is generally filled with quartz veins with varying thickness, 0.5 to 5 cm. evidence of fault structures in the fault section, scratch lines, and traces of other structures that can be found in the field. faulting is indicated from the river straightening pattern that can be observed on topographic maps, dem srtm images, and landsat images. it is estimated that the fault developed in the study area is a northwest-southeast trending shear fault. observation and measurement activities other than rock outcrop dimensions also performed solid measurements. measurement results obtained data direction and stance of varying heavily. the data are then sorted and separated into shear joints and extensional joints. the crusher has an azimuth range of n 0 90° e and n 180 270° e, while the tensile strength has an azimuth range of n 90 180° e and n 270 360° e. the rash is present in pairs and the fracture part is not filled with secondary minerals. tensile strength tends to be solitary, has a relatively uniform stance, and is filled with secondary minerals which then form quartz veins (quartz veins). the result of the stout dynamical analysis shows that the main emphasis (σ1) in the research area tends to be s-sw and sw-w oriented. the main emphasis has a steep slope, while the smallest tendency tends to slope. this indicates that the geological structures in the research area, especially stocky are dominated by extensional activity. the strain force acting on the rocks produces tensile strengths that have northwest-southeast direction and are relatively perpendicular to the direction of the main firm. handayani (2008) writes in his writing that the sunda strait area is a transitional area between the subduction of the western oblique of sumatra island and the south-western subduction of java island that began in kala oligocene. the fault of sumatra that moved horizontally causes the sunda strait facial area to experience strain activity. the stretching activity then forms the normal and coarse-trending faults of the north-south and northeast-southwest direction. stretching activities in the sunda strait face continued to this day (handayani, 2008) fig 2. the results of the robust static analysis show that the main emphasis (σ1) in the research area tends to be s-sw and sw-w. the strain force in the research area is thought to be the main geological structure of the mineralization controller. this is evidenced by the presence of quartz veins that have a thickness of more than 30 cm directed n-w and n-nw. tensile strength is the primary opening zone for which the hydrothermal solution of metallic mineral elements, such as gold (au), silver (ag), lead (pb), and zinc (zn), rises to the surface and is concentrated. mineralization occurs in the late miocene honje formation (fig. 3). fig. 6. above provides an overview of the interpretation of the western java structure interpreted by haryanto, 2013 where there are many geological structures with varying sizes and directions. the conditions are grouped into 4 directions of the fault line that is westeast, northeast-southwest, northwest-southeast and north-south (haryanto, 2013). the above matter when considering the interpretation based on landscapes 8 (ldcm) 8 rgb567 especially for the location of study where in the west and east is a high altitude while in the middle is a low so that the grouping for the general direction of the structure alignment is divided based on the height direction of the main strike ; 1 : 510, n 510 e 2 : 390, n 2330e 3 : 20, n 1390e 234 usman, d.n. et al./ jgeet vol 03 no 04/2018 difference where the western block has a direction general 154 0 , the eastern block has a general direction of 154 0 , and the middle block has a general direction of 153 0 . so the pattern of structure that develops in this area is directed 154 0 . (fig. 4). fig 3. structural interpreted through topography (haryanto, 2013) fig 4. structural alignment interpreted through satellite image imagery landsat data continuity mission (ldcm) 8 rgb567 acq: july 5, 2015 (landscape image map 8: geological survey center, 2015). 3. result tectonic activity as an underlying geological process for subsequent geological products such as earthquakes, volcanology and ground motion. the effect of the geological product is one of them is the formation of mineral (mineralization). the presence of mineralization is closely related to the formation of fractures in the rocks caused by tectonic activity. the formation of fractures hence facilitate the process of mineralization itself, the more formation of fractures in the rocks the mineralized zone will be wider and thicker the veins are formed, but vice versa, if a little fracture is formed then the mineralized zone, is small. the presence of fractures in rocks can also provide an overview of tectonic activity in the region. at the study site, the presence of fractures can be observed and measured either directly or using secondary data such as images satellite. however, to obtain fracture data related to rmr value then it must be done directly in the field. the research location is divided into 2 rock formations with different ages, namely; 1. honje formation with final miocene age 2. cipacar formation with pleistocene age result of geological observation and mapping of both rock and structure, then got data that is identified there are 2 rocks that can be mapped and measured fracture, that is; 1. andesite lava as part of the honje formation 2. tuff as part of cipacar formation the lithology of the study area is divided into 2 units of unofficial lithostratigraphy, the units of andesite lava and tuff units. a. units of andesite lava andesite lava units cover 90% of the research area. in general, the lithology of the andesite lava unit has the characteristics of rock outcrops in dark gray, massive structure, degree of hypocrystalline crystallization, uniformity of inequigranular crystal grains, porphiroafanitic texture, composed of 3% biotite minerals, hornblenda 3% and aphanitic base mass 94%, name of andesite lava rocks. the size of the crystal grains which tend to be smooth indicates that andesite lava comes from lava flows. weather conditions are 10% rocky. (fig. 5). locally encountered andesite lava with a similar texture but has a color tends to be black, allegedly andesite lava basaltic. this andesite lava unit belongs to the roct unit honje formation. fig 5. andesite lava outcrop in st-8 citeluk river fig 6. quartz veins on andesite lava at st-54 citeluk river andesite lava is subject to prophylitic and argillic alteration. prophylitic alteration is evidenced by the emergence of chlorite minerals as a result of alteration of amphibole minerals, as in observations at station observations 26 and 28. the argillic alteration is characterized by the presence of kaolin minerals, as observed in observation vein suryadi, a. et al./ jgeet vol 03 no 04/2018 235 stations 29, 35, and 42. hydrothermal alterations occurring in andesite lava also form tightly packed quartz veins with a thickness of 0.5 to 5 cm (fig. 6). quartz veins can be clearly observed in the outcrops at st 14.1, 15.2, 17-i, 18-i, and vein. the andesite lava is thought to originate from the freezing of lava flows. this is evidenced by the existence of brecciating structure in observation stations 4.4, and 5.2. brecciated is a structure commonly found in extrusive igneous rocks. in addition, the size of the constituent andesite lavaic minerals that tend to be smooth indicates a fast magma freezing process on the surface of the earth. b. tuff unit tuff units cover 10% of the research area. in general, lithology in tuff units has a characteristic gray whitish color, tuff grain size (> 2 mm), good sorting and closed packing. tuff consists of 5% biotite minerals and 95% of volcanic glass (fig. 7). the tuff unit belongs to the pliocene cipacar formation, unconformity with the andesite lava unit. judging from its texture and composition, tuff rock units are thought to be formed from volcanic eruptions which then form deposits of volcanic deposits. fig 7. brecciation andesite lavas in st-5.2 citeluk river fig 8. outcrop tuff in st-5 citeluk river based on the data, data processing is performed statistically (fig . , which must meet the requirements of data normality testing, from 125 (table 1) and 117 data (table 2.) related to the rmr value as the data population, sampling is carried out as many as 35 data, after that simple linear regression analysis to get the relationship and influence between the rmr values for each rock unit in different formations. to see the extent between the rmr andesite lava value and the rmr tuff value then a differential t-test between andesite lava and tuff is performed as below; t arithmetic <t table, then h0 is accepted, that x1 and x2 are equal, there is no average difference between the variables x1 and x2. the result of the mean difference test above where h0 is accepted with the understanding between x1 and x2 is equal, so there is no mean difference between the two between rmr andesite lava value and rmr tuff value. it shows that the tectonic process that occurs in andesite lava unit of formation honje with an earlier position is formed and older age at the end of the miocene age is blocked by the field of unconformity experienced continuity on formation cipacar with a higher position that is formed after honje formation and younger age that is in pleistosene. the continuation of the tectonic process proves the existence of active tectonic activity better known as neo-tectonic. fig 9. rmr value of all lithology at honje and ciracas formation table 1. the value of rmr lava andesite lava honje formation no. lithology rmr valu e rocks classificatio n 1 lava andesite lava 65 good rock 2 lava andesite lava 66 good rock 3 lava andesite lava 68 good rock . . . . . . . . . . 123 lava andesite lava 71 good rock 124 lava andesite lava 79 good rock 125 lava andesite lava 58 good rock source: field observation results, 2016 236 usman, d.n. et al./ jgeet vol 03 no 04/2018 description: g. rock = rock class good rocks table 2. rmr tuff value of cipacar formation no. litholog y rmr value rocks classification 1 tuff 70 good rock 2 tuff 69 good rock 3 tuff 68 good rock . . . . . . . . . . . . 115 tuff 80 good rock 116 tuff 76 good rock 117 tuff 75 good rock source: field observation results, 2016 description: g. rock = rock class good rocks 4. conclusion the tectonic activity in the study area is active tectonic activity, based on the similarity of the mean value of rmr between the average value of rmr andesite lava of honje formation with the final miocene age with the average value of rmr tuff of cipacar formation with tcount = 0.555 <ttabel = 1.995, which means that there is no difference in the mean value of the two units of the rock. the same rock mass classification as evidence that there is tectonic movement in the region continues to work from the old rock formations to the young formations constrained by the field of noncausal affecting against 2 different rock types. references ahmad fajriyanto, armijon, and eko rahmadi, 2012, potential dangers of earthquake and strain analysis in the sunda strait based gps (global positioning system), journal of engineering, 16,. angeles, ciceron a, et al. 2002. geology and alterationmineralization characteristics of the cibaliung epithermal gold deposit, banten, indonesia. resource geology. 52, 4. lina handayani and hery harjono, 2008, development of regional tectonics bow front sunda strait and its relationship with sumatra fault zone, geology and mining research journal., 18, 2, 31-40. hall, robert et. al., 2007. structure, proceedings, indonesian petroleum association, thirty-first annual convention and exhibition, may. haryanto, iyan., 2013. fault structure in west java island based on geological interpretation results, bulletin of scientific contribution. 11, 1, 1 10. hamilton, w., 1979. tectonic of the indonesian region, u.s.g.s. prof. paper 1078. hirnawan, febri., 2009. a measure of intense in west and central java through manifestation of river basin morphometry development on quartenary volcanic deposits. jurnal geologi indonesia. 4 , 4, 285 300. katili, j.a., 1973. volcanism and plate tectonics in the indonesian island arc. tectonophysics, 26, h. 165-188. martodjojo, s., 1984, evolution basin bogor, west java: doctoral thesis, institut teknologi bandung pulunggono and martodjojo, s., 1994, tectonic changes paleogene-neogene is the most important event in java, proc. geology and geotektonik p. java since the mesozoic end until the quarter, yogyakarta, p. 37-50 sudana, d., dan santosa, s., 1992. geology of the cikalang quadrangle, java: geology research development centre. bandung. soeria-atmaja, r., maury, r. c., bellon, h, pringgoprawira h, polves, m dan priadi, b., 1994. tertiary magmatic belts in java. journal of southeast asian earth sciences. 9, ½, 1327. soeria-atmaja, r., s. suparkat., chalid abdullah., dardji noeradi., sutanto. 1997. magmatism in western indonesia, the trapping of the sumba block and the gateways to the east of sundaland. journal of asian earth sciences, 16, 1, 1 -12, soeria-atmaja, r., dan dardji noeradi. 2005. distribution of early tertiary volcanic rocks in south sumatra and west java. the island arc. 14, 679 686. received 22 june 2004; accepted for publication 7 august 2005. v. ispolatov, b. lafrance, b. dubé, r. creaser, m. hamilton, 2009. geologic and structural setting of gold mineralization in the kirkland lake-larder lake gold belt, ontario, doi: 10.2113/gsecongeo.103.6.1309 published on september 2008, first published on january 08, 2009 van bemmelen, r.w., 1949. the geology of indonesia. © 2018 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc bysa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geology setting 2.1 structure and tectonic regional 3. materials and methods a. units of andesite lava b. tuff unit 4. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 116 egbelehulu.p/ jgeet vol 04 no 02/2019 research article assessment of the leachate contamination level of groundwater resource at a dumpsite, in minna, north central, nigeria using resistivity method priscillia egbelelulu 1 , taiwo adewumi 3, *, emmanuel e. udensi 2 , naeem abdulsalam 1 , oke i. okwokwo 1 1department of physics, university of abuja, abuja 2 department of physics, federal university of technology minna. 3 department of physics, federal university lafia, nasarawa state * corresponding author : tydon4real@yahoo.co.uk, taiwo.adewumi@fulafiaphysics.org received: sept 24, 2019; accepted: may 20, 2019. doi: 10.25299/jgeet.2019.4.2.2159 abstract this research work focused on the use of direct current resistivity method to analyse data collected from refuse dumpsite orth central nigeria. vertical electrical sounding was carried out on the dumpsite with the aim of delineating the leachate contaminant plumes using resistivity method. nine electrical resistivity profiles were measured on the site. six transverse profiles was conducted on the dumpsite with thirty six vertical electrical sounding (ves) point, three transverse profiles was also conducted on the control site which is 100 meters away from the dumpsite having nine vertical electrical sounding (ves) point and a dimension of 40m x 40m. the resistivity data obtained was analysed using winresist software. the data obtained from the study area revealed three underlain layer they are the top soil, fractured basement and fresh basement. the dumpsite was typified by a-types and h-types of curve and the control site was typified by h-type of curves. iso resistivity maps at various depths were observed, at surface, 3m, 5m,7m and 10m for the dumpsite and the control site. it can therefore be inferred from this study that the depth of contamination is 7 meter and aquifer found within this depth are most likely to be contaminated by leachate and water bearing formation beyond the depth of 7m is safe from contamination. the rate of contamination of the study area is approximately 1.0 meter per year. keywords: contaminant, dumpsite, electrical resistivity, leachate and plumes 1. introduction as a result of fast growing rural and industrial volume of solid waste worldwide despite the current level of global technological advancement and industrialization. dumpsite serves as the ultimate recipient of solid waste. industrial development and uncontrolled increase of rural-urban migration have also resulted in an increased production rate of different types of wastes ranging from municipal to industrial, which have adverse effects on human health through groundwater quality (ramakrishnaiah et al., 2009, and omolayo et al., 2014). the challenge is worsened by the fact that there are inadequately trained waste disposal personnel and equipment, poor waste collection, sorting and disposal methods, and location of this disposal site without regards to the local geology and hydrogeology of the area (jatau and ajodo, 2006). groundwater contamination from landfills often results from leaking leachate water that has percolated through waste and accumulated various ions in solution (capenter et al., 2012). the leachates become part of the groundwater flow system immediately they reach the water table. the extent of pollution is greater in high rainfall area than less humid and arid areas (alyaqout et al.,2003). this situation is not any way different in minna, where numerous dumpsites are distributed at almost every area within the metropolis. the locations of these dumpsite such as that of the study area causes environmental pollution which may eventually lead to environmental hazards if nothing is done about it. these wastes discarded into landfills and dumpsite undergoes decay, oxidation, and corrosion which result to the releasing of metal ions causing potential risk to the soil, groundwater and community health (soupios et al., 2007). the dump site used for this research was chosen because of the uniqueness of the kind of wastes deposited there. apart from domestic waste dumped in this area, there is also a considerable large amount of http://journal.uir.ac.id/index.php/jgeet egbelehulu.p./ jgeet vol 04 no 02/2019 117 clinical waste present on the site this is as a result of a pharmaceutical company (dana pharmaceutical) few kilometres from the dump site. although the area is sparely populated, there is a likely hood of future settling of people in the area since the dump site is not a legal site and the land belongs to nigeria union of teachers (n.u.t) who intends commencement of housing project in the area. the major sources of water in the community are wells and bore hole. as a result of the imminent impact of solid waste on the environment, it is of necessity to carry out research of this magnitude to investigate the potential for the contamination of soil and groundwater around the dumpsite. electrical resistivity method was used to carry out this research because the method is the most used method in hydrogeological studies as relevant data can be provided on lithologies and subsurface water resources without the large cost of an extensive programme of drilling (kearey, 2002). it is also a useful tool for investigation of the subsurface of an area as it can provide information on the spatial variation in lithology, subsurface integrity with respect to the evaluation of the protective capacity of the area and the direction of groundwater flow and hence, direction of the contaminant plume. ( aweto and mamah 2014) 2. geology and location of the study area the study area lies within the basement complex rocks in the north-western nigeria basement bounded central portion of the nigerian basement complex. the basement complex is one of the three major lithopetrological components that make up the geology of nigeria (figure 1). the nigerian basement complex forms a part of the pan-african mobile belt and lies between the west african and congo cratons and south of the tuareg shield (black, 1980 as cited by obaje, 2009 ). the minna area comprises of meta-sedimentary and meta-igneous rocks which have undergone polyphase deformation and metamorphism (amadi et al., 2011). total area covered for the study is 100m x100m north-eastern part of minna along eastern bye pass after serikin power road maitunbi off kaduna express road minna niger state. this dumpsite (figure state although is not an official dumpsite used by niger state. fig 1. geological map of the study area (adapted from amadi et al, 2011). 118 egbelehulu.p./ jgeet vol 04 no 02/2019 fig 2.the dumpsite the study area. 3. methodology 2d electrical resistivity was carried out within one of the popular dump site in minna using terameter. the area of study under investigation was first inspected and gridded into profiles. the length of the profile is 100 x100m. six profiles were taken on the dump site with distance of 20 meters apart. a control site situated 100m away from the dumpsite was measured and gridded with a profile length of 40mx 40m having three profiles and an interspacing between each profile of 20m. since the aim and objective of this study is to assess leachate contamination of ground water the most suitable electrical method to be adopted would be vertical electrical sounding (ves) schlumberger method this is because it is most suitable in revealing variations in apparent resistivity with depths. vertical electrical sounding (ves) was carried out on the gridded profile which has thirty-six (36) ves points marked with pegs using schlumberger method of electrode configuration spread. the control site is also gridded with nine (9) ves points marked with pegs. schlumberger configuration is also used to measure its apparent resistivity with depth. 4. field procedure schlumberger array was used for ves survey by keeping the potential electrodes fixed at one location while the current electrodes are expanded about a centre point. only when the current electrodes become relatively distant does the potential electrode spacing need to be expanded in order to have measurable potential. the potential electrodes are moved only when the signal become too weak to be measured. by using schlumberger array method, features with electrical properties different from those of the surrounding material may be located and characterized in terms of electrical resistivity, geometry and depth of burial. the electrical resistivity data are collected using a terrameter (computer-controlled measurement systems connected to multi-electrode arrays). the data acquisition process is totally controlled by the computer software which checks that all the electrodes are connected and properly grounded before measurement starts. after adequate grounding is achieved the software scans through the measurement protocol selected. 5. data collection the dimension of the area of study was measured to be 100m by 100m and was gridded with an interspacing of 20m (i.e. between each ves point is 20 m) with six profiles and a control site of 40m by 40m gridded with an interspacing of 20m with three profiles represented by figure 3a and figure 3brespectively. vertical electric sounding were required at thirty-six stations along the six profile on the dumpsite and nine points on the control site which was taken azimuthally north-east direction for all the profiles. at each point, the maximum current electrode spacing was 100 m. egbelehulu.p./ jgeet vol 04 no 02/2019 119 fig 3a. layout of the field procedure on the dumpsite. fig 3b. layout of the field procedure on the control site. 6. results and discussion 6.1 results the analysis of leachate contamination over a dump site in eastern bypass, minna, niger state was successfully investigated. six (6) profiles were taken in this study with the total number of forty five (45) ves points. for the purpose of this paper, three profiles (c, d and f) will be taking into consideration because the profiles show the extent of the leachate in the subsurface. the summary of the analysis on ves points along profile c shows that the profile is underline by three basic layers; these are the topsoil, the fractured basement and the fresh basement (table 1). the resistivity value for the first layer of this profile ranges from 13.4 447.9 ohms-meter which is the topsoil and it percolates into the subsurface with a relative thickness of 0.7 to 6.6 meters. and the analysis on ves points along profile d (table 2) reveals that the profile is also underline by three basic layers, these are the topsoil, the fractured basement and the fresh basement. the resistivity values for the first, second and the third layer of this profile ranges from 31.7 333.6 ohms-meter with relative thickness of 0.6 6.8 meters, 99.4 725.5 ohm-m with relative thickness of 3.4 9.0 meters and 1036.8 25164.6 ohm-m with infinite relative thickness respectively. the analysis on ves points along profile f (table 3) shows that the profile is underline by three basic layers, these are the topsoil, the fractured basement and the fresh basement. the resistivity value for this profile ranges from 23.1 to 316.9 ohms-meter for the first layer which is the topsoil which percolates into the subsurface with a relative thickness of 0.4 to 9.0 meters. the second layer has a resistivity value which ranges from 35.4 to 709.9 ohm-m which is fractured basement made of granite, with a thickness range of 2.3 to 5.7 meters. the third layer has resistivity value ranging from 1948.0 to 10169.1 ohm-m which is fresh basement and has infinite thickness. 120 egbelehulu.p./ jgeet vol 04 no 02/2019 table 1. summary of ves analysis along profile c (dumpsite). ves point layers thickness (m) depth (m) curve type c1 1 32.8 1.0 0.0 ρ 1< ρ 2< ρ3 a 2 332.4 2.6 1.0 3 7439.8 3.6 c2 1 13.4 1.9 0.0 ρ 1< ρ 2< ρ3 a 2 177.6 2.7 1.9 3 1103.0 4.6 c3 1 13.5 1.9 0.0 ρ 1< ρ 2< ρ3 a 2 177.7 2.7 1.9 3 1109.4 4.6 c4 1 118.0 1.5 0.0 ρ 1< ρ 2< ρ3 a 2 339.5 3.5 5 3 1232.3 8.5 c5 1 60.6 6.6 0.0 ρ 1< ρ 2< ρ3 a 2 280.9 3.6 6.6 3 2358.8 10.2 c6 1 447.9 0.7 0.0 ρ 1>ρ 2< ρ3 h 2 373.4 19.2 0.7 3 3110.3 19.9 table 2. summary of ves analysis along profile d (dumpsite). ves point layers thickness (m) depth (m) curve type d1 1 31.7 6.8 0.0 ρ 1<ρ 2< ρ3 a 2 1732.1 6.3 6.8 3 25164.6 13.1 d2 1 43.6 2.1 0.0 ρ 1<ρ 2< ρ3 a 2 129.8 5.8 2.1 3 1036.8 7.9 d3 1 1458.2 0.6 0.0 ρ 1>ρ 2< ρ3 h 2 99.4 5.4 0.6 3 1503.9 6.0 d4 1 277.9 0.9 0.0 ρ 1<ρ 2< ρ3 a 2 344.6 9.0 0.9 3 5666.2 9.9 d5 1 139.9 2.1 0.0 ρ 1<ρ 2< ρ3 a 2 478.5 3.4 2.1 3 2376.8 5.5 d6 1 333.6 4.0 0.0 ρ 1<ρ 2< ρ3 a 2 725.5 8.2 4.0 3 1532.5 12.2 table 3. summary of ves analysis along profile d (dumpsite). ves point layers thickness (m) depth (m) curve type f1 1 23.7 1.6 0.0 ρ 1< ρ 2<ρ3 a 2 709.9 2.3 1.6 3 6394.4 3.9 f2 1 23.1 4.6 0.0 ρ 1< ρ 2<ρ3 a 2 847.0 5.7 4.6 3 6781.8 10.3 egbelehulu.p./ jgeet vol 04 no 02/2019 121 ves point layers thickness (m) depth (m) curve type f3 1 93.3 9.0 0.0 ρ 1< ρ 2< ρ3 a 2 244.4 5.1 9.0 3 3378.1 14.1 f4 1 71.0 2.2 0.0 ρ 1< ρ 2< ρ3 a 2 507.6 4.9 2.2 3 1948.0 7.1 f5 1 316.9 0.4 0.0 ρ 1>ρ 2<ρ3 h 2 35.4 3.7 0.4 3 8879.6 4.1 f6 1 66.5 6.6 0.0 ρ 1< ρ 2<ρ3 a 2 458.7 4.0 6.6 3 10162.1 10.6 fig. 4 (a) subsurface geoelectric section along profile c, (b) subsurface geologic section along profile c. 6.2 discussion the analysis made from the above (tables 13) makes it easier to draw a number of deductions regarding the thickness of the leachate plume and zone of water saturation (aquifer). by correlating the two, we can deduce if the aquifer is affected by leachate which is among the objectives of this research. the deductions and correlations shall be made from iso resistivity maps at some depths of interest, geologic sections with their range in resistivity value and geo-electric sections. the delineation of the water tables that are likely affected by leachate shall be based on the thickness of the leachate plumes, geologic sections in succession and maximum weathering depth from the surface. the geo-electric section and the subsurface geoelectric section of profile c (figure 4a and 4b) shows that the profile is underlain by three layers. the first is the topsoil with average resistivity of 114.4 ohm-meter and a maximum depth of 6.6 meter. it has the best 122 egbelehulu.p./ jgeet vol 04 no 02/2019 water bearing formation on this profile at c5. the second layer has an average resistivity value of 280.25 ohm-meter which is the fractured basement. the best water bearing formation in this layer is c6 having a resistivity of 373.4 with a depth of 19.9 meter. the third layer is the fresh basement with an average resistivity of 2725.6 ohm-meter. the geo-electric section and the subsurface geoelectric section of profile d (figure 5a and 5b) reveals that the profile is also underlain by three layers. the first is the topsoil with average resistivity of 380.8 ohmmeter and a maximum depth of 6.8 meter. the second layer has an average resistivity value of 580.9 ohmmeter which is the fractured basement, the best water bearing formation for this profile is at d4 at the depth of 9.9 meter. the third layer is the fresh basement with an average resistivity of 6213.5 ohm-meter. the geoelectric section and the subsurface geo-electric section of profile f (figure 6a and 6b) shows that the profile is underlain by three layers. the first is the topsoil with average resistivity of 109.4 ohm-meter and a maximum depth of 9.0 meter, the best water bearing formation on this layer is at ves f3 having a resistivity of 93.3 and at the depth of 9.0 meter. the second layer has an average resistivity value of 357.55 ohm-meter which is the fractured basement. its best water bearing formation is at f3 having a resistivity of 244.4 having a depth of 14.1 meter. the third layer is the fresh basement with an average resistivity of 6256.81 ohm-meter. the extent at which the leachate has gone into the subsurface is more pronounced in this profile and this indicate that this region is prone to groundwater contamination. fig. 5 (a) subsurface geoelectric section along profile d, (b) subsurface geologic section along profile d egbelehulu.p./ jgeet vol 04 no 02/2019 123 fig. 6 (a) subsurface geoelectric section along profile f, (b) subsurface geologic section along profile f fig. 7 (a) subsurface geoelectric section along profile a 124 egbelehulu.p./ jgeet vol 04 no 02/2019 the subsurface geo-electric and geologic section of the control site are presented in the figures 7-9. figure egbelehulu.p./ jgeet vol 04 no 02/2019 125 7a and 7b shows the geo-electric and geologic section of control site profile a and it reveals that the profile is underlain by three layers; topsoil, fractured basement and fresh basement. the top soil has an average resistivity of 757.5 ohm-meter and a maximum depth of 2.5 meter, the second layer has an average resistivity value of 250.2 ohm-meter with a depth of 30 meters which is the fractured basement, thus it best water bearing formation on this layer and on the profile having a resistivity of 350.7 ohm-meter. the third layer which is the fresh basement has an average resistivity of 1545.6 ohm-meter. figure 8a and 8b shows the geo-electric and geologic section of control site profile b. it shows that the profile is underlain by three layers; topsoil with an average resistivity of 417 ohm-meter and a maximum depth of 1.3 meter, fractured basement with average resistivity value of 165.6 ohm-meter and maximum depth of 29.4 meter it also confined it best water bearing formation on this layer and on the profile. the third layer which is the fresh basement has an average resistivity of 1194.4 ohm-meter.figure 9a and 9b also shows the geo-electric and geologic section of control site profile c and it reveals that the profile is underlain by three layers; topsoil with an average resistivity of 1790.7ohm-meter and a maximum depth of 2.8 meter, fractured basement with an average resistivity value of 144.4 ohm-meter. its maximum depth is 13.1 meter at -meter. and the fresh basement with an average resistivity of 8456 ohmmeter. figure 10 12 is the iso-resistivity contour maps produced by contouring resistivity values obtained from the study area at depths of interest (3m, 5m, 7m and 10m) using surfer 8 software package. the contour maps (figure 10 12) of all the ves point on the refuse dump site were produced and contour maps for the control site were also taken at the same depths. the purpose of these maps is to correlate the two maps produced and to observe the variation in conductivity of the earth material at different depths to delineate the extent of contamination. figure 10a and 10b shows the iso-resistivity contour maps of dumpsite and control compared to the resistivity values of the control site this shows that the dumpsite is very conductive at the surface this is because of the presence of leachate and surface water. figure 11a and 11b shows the isoresistivity contour maps of dumpsite and control site at respectively. these maps are produced to examine the extent of contamination at this depth by correlating the two maps. the resistivity values of the dump site dump site is slightly higher than the control site. it can thus be inferred that the leachate contamination has a minimal effect at this depth this is because of the granitic intrusion at the dump site. however because of the low range, contamination is still visible. figure 12 a and 12b also shows the iso-resistivity contour maps of dumpsite and control site at depth of 7m contoured at 20 resistivity value at the dump site is very similar to that of the control site thus the dump site is less conductive. it can therefore be inferred that the leachate contamination has no effect at this depth. fig 10a. dumpsite site iso-resistivity map at depth of 3m fig10b. control site iso-resistivity map at depth of 3m . 126 egbelehulu.p./ jgeet vol 04 no 02/2019 fig11a. dumpsite iso-resistivity map at depth of 5m. contour fig11b. control siteiso-resistivity map at depth of 5m. contour fig 12a. dumpsite iso-resistivity map at depth of 7m. contour fig 12b. conrol iso-resistivity map at depth of 7m. contour 7. conclusion the analysis of leachate contamination over a dump site in eastern bypass, minna, niger state was successfully investigated. results suggest leachate contamination in the subsurface which is supported by vertical electrical sounding made on the dump site. three distinct geologic sections were delineated at the dump site they are; top most layer which consist of the contaminated area, followed by fractured basement which is granitic followed by fresh basement. it can be inferred from this study that the depth of contamination is 7 meter, aquifer found within this depth are most likely to be contaminated by leachate and water bearing formation beyond the depth of 7 m is safe from contamination. the rate of contamination of the study area is approximately 1.0 meter per year. references amadi, a. n., nwanwulu, c. d., unuevho, c. i., okoye, n.o., okunlolo, i. a., ako, t. a., & alkali, y. b. (2011). evaluation of the groundwater potential in pompo village, gidan kwano, minna using vertical electrical resistivity sounding. british journal of applied science and technology, 1(3), 53 66 al-yaqout, a., & hamoda, m. (2003). education of landfill leachate in arid climate: a case study. environmental. international, 29, 593 600 aweto, k. e & mamah, l. i (2014). application of resistivity method to groundwater protection studies in niger delta. international journal of environment protection. 4( 3), 27-35 black r. (1980). precambrian of west africa. (4)3 8 carpenter, p. j., ding, a., & cheng, l. (2012). identifying groundwater contamination using resistivity surveys at a landfill near maoming, china. nature education knowledge 3(7), 20 21 jatau, b. s., & ajodo, r. o. (2006). preliminary geoenvironment evaluation of part of kaduna north metropolis, kaduna, nigeria. a paper presented at egbelehulu.p./ jgeet vol 04 no 02/2019 127 nigeria association of hydrogeologists (nah) 18th annual national conference asaba, 1-2. kearey, p, brooks, m., & ian, h (2002). an introduction to geophyscial exploration. third edition blackwell publishing. obaje n.g (2009). geology and mineral resources of nigeria.springer dordrecht heidelberg london new york pg. 13-19. omolayo, d., & fatoba, j.t. (2014). 2d electrical imaging surveys for leachate plume migration at an old dumpsite in ibadan south western nigeria. international journal. geophysics, 530, 1 6. rahaman, m.a., & ocan o. (1978). reletionships in precambrian migmatite gneissess of nigeria. nigeria journal mineral geology. 15, 23 32. soupios, p. papadopoulo, s. i, kouli, .m, georgaki, i, vallianatos, f &kokkinous, e. (2006). environmental geology 7, 418 © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geology and location of the study area 3. methodology 4. field procedure 5. data collection 6. results and discussion 6.1 results 6.2 discussion 7. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 40 siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 research article hydrogeochemical and groundwater assessment for drinking purpose at itera campus area and its surroundings luhut pardamean siringoringo 1, *, reza rizki 1 , janner nababan 2 1 institut teknologi sumatera, jl. terusan ryacudu, kecamatan jati agung, lampung selatan 35365, indonesia. 2 balai konservasi airtanah, badan geologi, kementerian energi dan sumber daya mineral, indonesia. * corresponding author : luhut.pardamean@gl.itera.ac.id received: des 26, 2018; accepted: feb 20, 2019. doi: 10.25299/jgeet.2019.4.1.2478 abstract the total population around itera has increased every year as students acceptance every year. to anticipate this, it needs to be done a research at itera campus and its surrounding about the quality of groundwater for drinking purpose and the hydrogeochemical of groundwater to know the controlling factors which are dominant. the methods are integrating piper diagram plotting result, x-y plotting result for some cations and anions, and gibbs diagram plotting result. it is for hydrogeochemical analysis. groundwater assessment for drinking purpose referred to peraturan menteri kesehatan republik indonesia no. 492/menkes/per/iv/2010. there were 14 samples that were taken from nine dig wells and five drill wells. the groundwater facieses were dominated by facies na-hco3-cl (35,71%) followed by facies na-cl (21,43%), facies na-hco3 (21,43%), facies na-so4-cl (14,29%), dan facies ca-mg-hco3 (7,14%). groundwater hydrogeochemical of research area shows that groundwater chemistries are controlled by minerals weathering, evaporation, and precipitation. there are eight wells that not proper for drinking and six wells that proper for drinking. integration lab result, stratigraphic analysis, and depth aquifer show that groundwater that proper for drinking comes from confined aquifer while that not proper for drinking comes from unconfined aquifer. keywords: facies, gibbs, hydrogeochemical, piper 1. introduction itera is a first new state technology institute at sumatera. itera from 2014 till 2018 has been lecturing for about five thousand students. this number will be increasing as long as new students acceptance every year. the additional of amounts students will trigger economic growth, especially at campus surroundings. to anticipate economic growth in the future, research is very important to be done to understand groundwater hydrogeochemical characteristic of the research area and its proper to all needs especially for drinking water purpose (chang and wang, 2010; wen et al., 2005). it is based on that water is the most important element in human health. groundwater chemistry composition depends on hydrogeochemical process that groundwater pass. groundwater chemical compositions are integration natural and anthropogenic factors such as precipitation, oxidation-reduction between groundwater and mineral aquifers, geological structures, cation exchange, mineral dissolution, water mixing, fertilizer leaching, biology process, and human activities. all these interactions result in variations of groundwater type (yang et al., 2016). thus, hydrogeochemical study what types of process that control groundwater hydrochemistry (jeevanandam et al., 2007). the objects of research including groundwater from dig well, that could be called as groundwater from unconfined aquifer and groundwater from drill well, that could be called as groundwater from confined aquifer. the research purposes are to interpret hydrogeochemical processes that control groundwater chemistry composition and groundwater assessment for drinking purpose. this research might be the first research that ever been done at this research area. hopefully, this research result could help local government to make policies about development area in the future. 2. geology and hydrogeology research area is included within tanjungkarang sheet regional geology map scale 1:250.000 (mangga, s.a; amirudin; suwarti, t ; gafoer, 1993). the area is composed of lampung formation of quaternary age (fig 1). the lampung formation is composed of pumice tuff, rhyolitic tuff, tuff unified tuffit, tuffaceous claystone, and tuffaceous sandstone. from this, all lithologies are volcanic activities associated. lampung formation is deposited unconformity above of andesite of tertiary age. at above of lampung formation is deposited unconformity young volcanic deposits (lava andesitebasalt, breccia, and tuff). geological structures that have been developed so little or still unidentified. http://journal.uir.ac.id/index.php/jgeet siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 41 according to kepres no 26, the year 2011, the research area is included within metro-kotabumi groundwater basin. it can be known from the location of research area within south lampung sub-province administratively. from hydrogeology perspective, research area is composed of tuff aquifer that locally productive (setiadi, h., ruhijat, 1993). it means not whole research area has high productivity to release water (low-medium break out). 3. research methods the preliminary step in this research was prepared topless glass 2000 ml which had been washed with liquid soap, motionless for several minutes, shaken, rinsed with sanitary water, dried, and if residual water still exists then be drained by dry tissue. these treatments also be used for 1000 ml polypropylene bottles as temporary storage media before groundwater samples were analyzed at lab (badan standarisasi nasional, 2008). the topless glass only be used to took sample from dig well. furthermore, the bottles were filled by this sample. if the samples were taken from drill well, the treatment would not use topless glass. in detail, the samples were directly taken using polypropylene bottles one minute after the faucet be opened. this treatment was done for throwaway samples were sent to laboratorium kualitas air fakultas teknik sipil dan lingkungan itb then be analyzed with standard methods for the examination of water and wastewater 22 nd edition 2012 (apha). figure 1 shows the geological of research area is composed by lampung formation at the surface. the formation is composed of pumice tuff, rhyolitic tuff, tuff unified tuffit, tuffaceous claystone, and tuffaceous sandstone. it means the majority rocks were silicate rocks. this profile could be impacted to the chemical of groundwater, especially addition of na and k ion to groundwater (meybeck, 1987). the method to analyze how much geology and non geology aspects has been impacted to groundwater is integrating piper diagram, x-y plotting (ca+mg / hco3, na+k / ca+mg, na/cl, and na+cl / hco3+so4+ mg-ca) and gibbs plot (na/(na+ca) / tds, cl/(cl+hco3) / tds). groundwater assessment for drinking purpose using indonesia healthy ministry regulation standard no. 492/menkes/per/iv/2010. the parameters are smell, flavor, colour (pt.co), muddiness (ntu), ec (µs/cm), tds (mg/l), temp (⁰c), fe (mg/l), f (mg/l), ph (mg/l), mn (mg/l), no3 (mg/l), no2 (mg/l), cl (mg/l), so4 (mg/l), na (mg/l), caco3 (mg/l caco3), and pb (mg/l). fig. 1. geological map of research area (modified from mangga, 1993). 42 siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 4. result and discussion 4.1 hydrogeochemical study the groundwater observations had been conducted on 14 wells including nine dig wells and five drill wells (fig 2). all of nine dig wells having range water depth between 0,2 m-8,2 m which can be classified into unconfined aquifer (table 1). while other five drill wells having well depth about 40 m and 80 m which can be classified into confined aquifer. it is also supported by previous research result that had been conducted at campus itera in 2017. the previous research was purposed to detect type of aquifer and its depth with schlumberger configuration-geoelectrical method. this research concluded, stratigraphically, the rocks from younger to oldest are siltstone, claystone, sandstone, and claystone with depth aquifer at more than 25 m (setiawan et al., 2017). if observed from rocks ability to storage, to release water and also connected to its position to upper rock layer and lower rock layer, then can be concluded that sandstone is confined aquifer. piper diagram is one of the most effective graphic representation in the study of the groundwater quality, which helps to understand the groundwater geochemical characteristics (yang et al., 2016). based on plotting data of cation and anion into piper diagram, there are five hydrochemical facieses, they are nahco3-cl (35,71%), na-cl (21,43%), na-hco3 (21,43%), na-so4-cl (14,29%), and ca-mg-hco3 (7,14%) (fig 3). 4.2 groundwater assessment for drinking purpose groundwater assessment for drinking purpose at research area is according to indonesia healthy ministry regulation standard no. 492/menkes/per/iv/2010 (table 2). there are 18 parameters which be used as references for this research. the 18 parameters including 7 physics and 11 chemical data. laboratory analysis result shows there are value differences which very contrast on some parameters. the parameters are colour, muddiness, tds, fe, ph, mn, and no3 (table 3 and table 4). these contrast differences in value are evidently out of standard range which had been set. these are occurred on some samples were a1, a2, a3, a4, a5, a7, a8, a9 (table 5). x y plots are used to assess relative abundances of major cationic and anionic species present in different water environments (pazand et al, 2018). there are four x-y plots that will be used for analyzing the effect of rocks to groundwater. they are na/cl, na+k / ca+mg, ca+mg / hco3, and na+cl / hco3+so4+mg-ca (meq/l) graphic. fig. 2. the research area includes wells. siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 43 table 1. the aquifer types of research area based on integration with previous research. fig. 3. piper diagram of ionic compositions of groundwater in research area. samples code wells type water depth aquifer type a1 dig 3 unconfined aquifer a2 dig 5,45 unconfined aquifer a3 dig 5,6 unconfined aquifer a4 dig 0,2 unconfined aquifer a5 dig 0,7 unconfined aquifer a6 dig 1 unconfined aquifer a7 dig 1,1 unconfined aquifer a8 dig 0,2 unconfined aquifer a9 dig 8,2 unconfined aquifer b1 drill 40 confined aquifer b2 drill 40 confined aquifer b3 drill 80 confined aquifer b4 drill 80 confined aquifer b5 drill 80 confined aquifer 44 siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 na/cl graphic is used to identify the mechanisms for acquiring salinity and saline intrusions in semiarid regions (yang et al, 2016). na/cl ratio is >1, indicating that weathering of silicate rocks such as granodiorite, andesite, rhyolite and tuff was the primary process responsible for the release of na + into the groundwater. na/cl ratio is <1, the ion exchange and/or evaporation were dominant process resulting in the addition of cl in the groundwater (meybeck, 1987). based on ion na and cl plotting into na/cl graphic (fig 4a), could be known that the ratio is >1. this result shows that the ion na comes from the weathering of silicate rocks. the (ca 2+ +mg 2+ ) / hco ratio is used to define the sources of ca 2+ and mg 2+ in groundwater (fig 4b). if ca 2+ , mg 2+ and hco in waters are derived from carbonate minerals, the ratio of (ca 2+ +mg 2+ ) / hco should equal to 1 (zhang et al, 2015). fig 4b shows that the ratio was not equal to 1, so can be known that the source of ca 2+ and mg 2+ come from another source. fig 4c shows that na + and k + are relatively more abundant than ca 2+ and mg 2+ . it was associated with volcanic terrain and sourced from the weathering of k-feldspar and plagioclase. na+cl / hco3+so4+mg-ca graphic used to identify the mechanisms for obtaining cation exchange and adsorption. if there are cation exchange and adsorption, the point is close to the 1:1 line (pazand et al, 2018). fig 4d shows r 2 =0,8126 indicating there are different degrees of cation exchange adsorption in study area. gibbs plot shows as a function of the tds that has the ability to provide information about the relative importance of the major natural mechanisms controlling groundwater chemistry and is extensively used to assess the functional sources of dissolved chemical constituents, such as precipitation dominance, rock dominance, and evaporation dominance (pazand et al, 2018). fig 5 shows that groundwater chemistry is mainly controlled by rock weathering and balance of evaporation-precipitation condition. the chemical of groundwater including ion changing or chemistry reactions can be changed as time goes by. next research needs to be done to know this changing in a certain period. 4.2 groundwater assessment for drinking purpose groundwater assessment for drinking purpose at research area is according to indonesia healthy ministry regulation standard no. 492/menkes/per/iv/2010 (table 2). there are 18 parameters which be used as references for this research. the 18 parameters including 7 physics and 11 chemical data. laboratory analysis result shows there are value differences which very contrast on some parameters. the parameters are colour, muddiness, tds, fe, ph, mn, and no3 (table 3 and table 4). these contrast differences in value are evidently out of standard range which had been set. these are occurred on some samples were a1, a2, a3, a4, a5, a7, a8, a9 (table 5). fig. 4. ions scatter diagram of groundwater in the study area. siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 45 fig. 5. relationships between ion concentrations for na + , ca 2+ , cl , hco 3 with tds. colour and muddiness have straight correlation according to data. the samples which had very high value for colour are a4 (10 pt. co), and a8 (20 pt. co). the colour for a4 is yellow to red, it is affected by iron contamination and the colour for a8 is yellow to brownish it might be affected by iron mixing with organic matter. this result also occurred for muddiness parameter. both samples also had high muddiness above standard, a4 (29,7 ntu) and a8 (65,4 ntu). besides that, a7 (15,7 ntu) and a9 (7,66 ntu) also has high value but not higher than a4 and a8. tds depends mainly on the concentration of major ions such as hco3 , so4 2, cl , mg 2+ , and na + (chang and wang, 2010). the high value above standard for tds parameter come from a3 (526 mg/l) and a5 (525 mg/l). these results are affected because of cl and so4 2 ions that its source from tuff as volcanic deposits and/or anthropogenic contamination. the rise in iron contamination in natural water sources is linked to various processes, which including oxidation-reduction reactions from weathering of iron rich minerals, microbiological activities, and anthropogenic iron contaminations (sarkar and shekhar, 2018). there are two samples that have high value of fe, a4 (1,04 mg/l) and a8 (0,581 mg/l). these only about 14% of all samples. this percentage shows that this as a local phenomenon because of uncovering all area. this phenomenon shows the high value of fe is effected by anthropogenic iron contaminations. the presence of mn as same as with fe. both presence due to either natural or anthropogenic sources (corniello and ducci, 2014). natural sources come from weathering of minerals (pyroxenes, amphiboles, biotite, magnetite and in particular, olivine). while, anthropogenic sources come from wastewater discharge, dust and aerosols during metallurgical processing, coal combustion, corrosion of water pumping infrastructure and transport of minerals or contamination associated with mining activities (esteller et al, 2017). the main factors controlling the presence of these elements in water are ph, redox conditions and presence of organic or inorganic ligands (corniello and ducci, 2014). an acidic ph indicates that both ions are mobile, while a more neutral ph indicates that mobility is determined by redox conditions (esteller et al, 2017). the table 4 shows that a2 and a5 have direct correlation with ph value (acid) so could be concluded that mn source comes from anthropogenic not by redox conditions. typical sources of nitrate in groundwater are mainly related to agricultural and domestic wastewater discharges (andersen and kristiansen, 1983). there were three samples which had higher result than standard, a2 (59,8 mg/l), a3 (55,7 mg/l), and a5 (114 mg/l). these covered about 21% of all samples. these results might be had direct correlation with research area that mostly was covered by agriculture about 60%. the samples which contain ph out of standard are a1, a2, and a5. all of them contain ph under 6. a2 and a5 might be affected by dominance the presence of mn and fe. a1 might be affected by intake co2 from atmosphere. table 5 shows that almost all samples especially which are taken from dig wells cannot be used for drinking water but samples which are taken from drill wells can be used for drinking purpose. this result also gives information that groundwater from unconfined aquifer is not good for drinking purpose but groundwater from confined aquifer is good for drinking purpose. a b 46 siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 table 2. the groundwater physics and chemistry standard for drinking purpose based on no. 492/menkes/per/iv/2010. table 3. the physical data of all samples at research area. samples code wells type smell taste colour (pt. co) muddiness (ntu) ec (µs/cm) tds (mg/l) temp (⁰c) a1 dig no no 5 2,41 433 259 25,7 a2 dig no no 5 0,07 365 219 25,8 a3 dig no no 5 1,51 752 526 25,7 a4 dig yes yes 10 29,7 248 149 25,7 a5 dig no no 5 4,94 778 545 25,7 a6 dig no no 5 2,48 222 155 25,7 a7 dig no no 5 15,7 535 375 25,7 a8 dig yes yes 20 65,4 138 83 24,8 a9 dig no no 5 7,66 326 228 25,7 b1 drill no no 5 0,79 435 304 25,9 b2 drill no no 5 1,14 311 187 25,8 b3 drill no no 5 0,81 339 203 25,8 b4 drill no no 5 2,3 423 253 24,7 b5 drill no no 5 0,84 261 157 25,8 parameters standard smell no smell flavour no flavour colour (pt.co) 15 muddiness (ntu) 5 ec (µs/cm) no information tds (mg/l) 500 temp (⁰c) ± 3 ⁰c fe (mg/l) 0,3 f (mg/l) 1,5 ph 6,5-8,5 mn (mg/l) 0,4 no3 (mg/l) 50 n02 (mg/l) 3 cl (mg/l) 250 so4 (mg/l) 250 na (mg/l) 200 caco3 (mg/l caco3) 500 pb (mg/l) 0,01 siringoringo, p.,s. et al./ jgeet vol 04 no 01/2019 47 table 4. the chemistry data of all samples which taken at research area. samples code well s type fe (mg/l ) f (mg/l ) ph mn (mg/l ) no3 (mg/l ) n02 (mg/l ) cl (mg/l ) so4 (mg/l ) na (mg/l ) caco3 (mg/l caco3 ) pb (mg/l) a1 dig 0,01 0,543 5,86 <0,2 45,2 0,3 57,7 15,9 43,5 50,5 < 0,001 a2 dig 0,01 0,063 5,3 0,458 59,8 0,006 58,6 2,76 47,1 42 < 0,001 a3 dig 0,045 0,273 7,1 <0,2 55,7 0,004 70,6 48 78 110 < 0,001 a4 dig 1,04 0,123 6,43 <0,2 7,41 0,004 22,9 17,8 24,9 59 < 0,001 a5 dig 0,01 0,255 5,54 1,11 114 0,665 133 35,7 77,4 126 < 0,001 a6 dig 0,01 0,162 6,53 <0,2 6,85 0,004 12,9 7,89 20 59 < 0,001 a7 dig 0,232 0,255 6,5 <0,2 22,7 0,117 53,9 38,8 41,9 118 < 0,001 a8 dig 0,581 0,233 6,64 <0,2 5,45 0,004 16,6 21,5 13,9 19 < 0,001 a9 dig 0,01 0,181 6,58 <0,2 25,9 0,073 27,8 30,3 38,9 61 < 0,001 b1 drill 0,01 0,409 7,06 <0,2 3,88 0,004 35,5 29,8 78,8 12,5 < 0,001 b2 drill 0,01 0,103 6,33 <0,2 16,9 0,004 21,9 41 29,6 46,3 < 0,001 b3 drill 0,172 0,457 7,15 <0,2 2,93 0,004 19,9 1,93 70,7 17 < 0,001 b4 drill 0,01 0,574 7,38 <0,2 2,29 0,391 9,58 1 81,4 19 < 0,001 b5 drill 0,01 0,291 6,83 <0,2 2,09 0,004 11,9 1,41 51,0 18 < 0,001 table 5. list of samples out of standard 5. conclusions from research at itera campus area and its surroundings then can be concluded as follow: a. groundwater consist of five groundwater facieses, they are facies na-hco3-cl (35,71%), facies na-cl (21,43%), facies na-hco3 (21,43%), facies na-so4cl (14,29%), and facies ca-mg-hco3 (7,14%). b. x-y plots show that na + and k + at research area come from weathering of silicate minerals. gibbs plot shows that there is another factor that controls groundwater chemistry in addition to effect from rocks weathering. the factor is a balance of evaporation-precipitation condition. c. groundwater which comes from unconfined aquifer (dig wells) is not proper for drinking purpose because it has been polluted by effect of human activities. besides that, well 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journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1016/j.gsd.2018.01.008 https://doi.org/10.1016/j.gsd.2018.01.008 https://doi.org/10.1016/j.gsd.2018.01.008 https://doi.org/10.1016/j.gsd.2018.01.008 https://doi.org/10.1016/j.gsd.2018.01.008 https://doi.org/10.1016/j.gsd.2017.12.011 https://doi.org/10.1016/j.gsd.2017.12.011 http://journal.itera.ac.id/index.php/jsat/article/view/64 http://journal.itera.ac.id/index.php/jsat/article/view/64 http://journal.itera.ac.id/index.php/jsat/article/view/64 http://journal.itera.ac.id/index.php/jsat/article/view/64 https://doi.org/10.1007/s00254-005-0001-7 https://doi.org/10.1007/s00254-005-0001-7 https://doi.org/10.1007/s00254-005-0001-7 https://doi.org/10.1016/j.envpol.2016.08.017 https://doi.org/10.1016/j.envpol.2016.08.017 https://doi.org/10.1016/j.envpol.2016.08.017 https://doi.org/10.1016/j.envpol.2016.08.017 https://doi.org/10.1016/j.envpol.2016.08.017 https://doi.org/10.1016/j.gexplo.2015.08.010 https://doi.org/10.1016/j.gexplo.2015.08.010 https://doi.org/10.1016/j.gexplo.2015.08.010 https://doi.org/10.1016/j.gexplo.2015.08.010 https://doi.org/10.1016/j.gexplo.2015.08.010 https://doi.org/10.1016/j.gexplo.2015.08.010 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ hydrogeochemical and groundwater assessment for drinking purpose at itera campus area and its surroundings 1. introduction 2. geology and hydrogeology 3. research methods 4. result and discussion 4.1 hydrogeochemical study 4.2 groundwater assessment for drinking purpose 4.2 groundwater assessment for drinking purpose 5. conclusions acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 20 sheroy, m. m/ jgeet vol 02 no 01/2017 atterberg limits prediction comparing svm with anfis model mohammad murtaza sherzoy 1, * 1 academy of sciences of afghanistan, sher ali khan watt, shari-e-naw, kabul, pobox 894,afghanistan abstract support vector machine (svm) and adaptive neuro-fuzzy inference systems (anfis) both analytical methods are used to predict the values of atterberg limits, such as the liquid limit, plastic limit and plasticity index. the main objective of this study is to make a comparison between both forecasts (svm & anfis) methods. all data of 54 soil samples are used and taken from the area of peninsular malaysian and tested for different parameters containing liquid limit, plastic limit, plasticity index and grain size distribution and were. the input parameter used in for this case are the fraction of grain size distribution which are the percentage of silt, clay and sand. the actual and predicted values of atterberg limit which obtained from the svm and anfis models are compared by using the correlation coefficient r 2 and root mean squared error (rmse) value. the outcome of the study show that the anfis model shows higher accuracy than svm model for the liquid limit (r 2 = 0.987), plastic limit (r 2 = 0.949) and plastic index (r 2 = 0966). rmse value that obtained for both methods have shown that the anfis model has represent the best performance than svm model to predict the atterberg limits as a whole. keywords: atterberg limit, support vector machine (svm), adaptive neuro-fuzzy inference system (anfis), sand, clay, silt. 1. introduction the atterberg limits can be used to distinguish between sand, silt and clay, and it can distinguish between different types of sand, silt and clays. these limits were created by albert atterberg, a swedish chemist. they are then refined by arthur casagrande. knowledge of the grain size distribution is very important for the behavior of soil under load and soil that come in contact with water can be identified. water is also a part of the soil component, and its presence reduces the strength of the soil (ali, 2011). if a particular soil grain size distribution is known, an accurate prediction of how the soil when acting as a basis for or a component of the structural works such as buildings, dams, and roads and other can be made. once you know how to soil tend to behave, engineers can design and estimate the best foundation to support an initiatory safer and more durable. previously, the study of the grain size distribution and geological characteristics of the other soil has been done, for example, (berbenni 2007) conducted a study on the impact of the size distribution of soil to the yield stress. reproduction of his results showed a yield stress decreased with increasing grain size distribution. however, in this study, the grain size distribution of soil fractions and percentages will be used to predict the atterberg limits using analytical methods support vector machine (svm) and adaptive neurofuzzy inference system (anfis). considering the main objective and aim of this work the prediction of the atterberg limits, it is convenient to review fundamental principles related to the comparing a support vector machine (svm) model with adaptive neuro -fuzzy inference system (anfis). the atterberg limits are a convenient means to describe the plastic type properties of a soil. they are defined by limits on different types of behavior, and are expressed as a water content for a detailed description. svm is generally utilized in classification and regression problems (chen et al. 2010). svms have the ability to enable a learning machine to generalize well to unseen data with their strong statistical learning theory grasp and very promising in empirical performance (lin & yeh 2009). there are a wide number of applications that can be utilized by using svms such as regression, pattern recognition, bioinformatics and artificial intelligence (tripathi et al. 2006). support vector machine is a machine learning method that is widely used for data analyzing and pattern recognizing. the algorithm was invented by vapnik and the current standard incarnation corresponding author: murtaza_sherzoy2000@yahoo.com phone: +93780151633 received: jan 15, 2017. revised : 18 jan 2017, accepted: feb 20 , 2017, published: 1 march 2017 doi:10.24273/jgeet.2017.2.1.16 mailto:murtaza_sherzoy2000@yahoo.com sheroy, m. m/ jgeet vol 02 no 01/2017 21 was proposed by (cortes and vapnik 1995). this application note is to help understand the concept of support vector machine and how to build a simple support vector machine using matlab. the anfis has the ability to learn from data, such as that owned by an artificial neural network. anfis models can also quickly achieve optimal results even if the target is not given. additionally, there is no ambiguity in the anfis, unlike in a neural network. because anfis combines both neural networks and fuzzy logic, it can handle complex problems and non-linear problems. 2. material and methods a. data distribution the distribution of the sample can be divided into two areas, area 1 (fig 1) and area 2 as shown in (fig 2). the first sample was taken around the state of pahang, while in the second, the distribution of the sample is in the state of johor. in this study, all sample data for the grain size distribution were prepared by ikram and tests of soil classification and testing the limits atterberg has been obtained from the results of laboratory tests. all distributions of soil samples taken as casual as the distance between the distributions of samples is almost 400 km. a total of 54 soil samples taken in the neighbourhood of the peninsular malaysian and its distribution is shown in table 1. b. revision of area the atterberg limits value and grain size distribution were obtained through laboratory test carried out by (ikram) the malaysian institute of public works. the anfis and svm models were then examined by applying 54 data records collected from these tests, the actual data value compared with the predicted atterberg limit values. for use as a training data set the anfis and svm models need a set of input and output data. the grain size distribution was employed for the purpose of this study, as input parameters in the development of the anfis and svm models for the prediction of atterberg limit values. table 1. distribution area sample data collection peninsular malaysia (ikram, 2011) no area location total sample 1 2 3 4 5 6 7 8 1 1 1 1 1 1 1 2 genting sempah, pahang gua tempurung, perak lentang, pahang simpang pulai, perak kuala kubu baru, selangor fraser hill, pahang logging, pahang 9 3 4 10 7 10 1 gunung pulai, johor total 54 fig 1. distribution of sample data (area 1) peninsular malaysia (ikram, 2011) 22 sheroy, m. m/ jgeet vol 02 no 01/2017 fig 2. distribution of sample data (area 2) peninsular malaysia (ikram, 2011). the soil sample data were taken based on the occurrence of debris flow event across peninsular malaysia, as recorded in table 1. fig 1 presents the location of the grain size distribution sample used in the study. the sampling area can effectively be divided into two areas, including the state of perak and pahang (area 1) and johor (area 2), respectively. all the 54 soil samples were collected and for different parameters tested, including grain size distribution, liquid limit (ll), plastic limit (pl), plasticity index and grain size distribution. methods of data collection for this study is to gather existing data for analysis svm and anfis method. both input and output parameters such as soil grain size distribution, liquid limit (ll), plastic limit (pl) and plasticity index (pi) will be identified and studied. the methodology was established for comparing the output parameters will be analyzed based on the two methods mentioned svm and anfis. c. support vector machine (svm) model support vector machine (svm) is a technique valuable for data classification, regression and prediction. svms are a set of learning methods that analyses data and recognize patterns, the first introduced in computer science. svm algorithm is the current standard proposed by (cortes and vapnik 1995). svm has originated from statistical learning theory pioneered by (boser et al. 1992). since svm is a relatively new technique, a brief explanation of how it works is given below. more detail can be found in many publications. the second learning technique uses the support vector machine (svm) that is firmly based on the theory of statistical learning theory, uses regression method. the svm developed to predict the plastic limit (pl), liquid limit (ll) and plastic index (pi). further, an attempt has been made to simplify the models, requiring only three parameters plastic limit, liquid limit and plastic index as input for prediction. fig 3. architectural graph of support vector machine (lin et al, 2009). sheroy, m. m/ jgeet vol 02 no 01/2017 23 d. kernel function once applying the svm to linearly separable data we have started by generating a matrix h from the dot product of our input variables: the k (xi; xj) is an example of a family of functions in the above equation, called kernel functions being known as a linear kernel). the set of kernel functions is composed of variants of (2) in that they are all based on calculating inner products of two vectors. this means that if the functions can be recast into a higher dimensionality space by some potentially non-linear feature mapping function . only inner products of the mapped inputs in the feature space need be determined without us needing to explicitly calculate . one of the reason that this kernel trick is valuable is that there are many regression and classification problems that are not linearly regress able and separable in the space of the inputs x, which might be in an advanced dimensionality feature space given a suitablemapping.. g. the kernel function can be defined as in equation (2) if we define our kernel to be: (2) as show in the left side of the fig 5 the data set that is not linearly separable in the two dimensional dataspace x could be separable in the nonlinear feature space, which is on the right hand of fig 5. because the data set defined implicitly by this non-linear kernel function is known as a radial basis kernel e. adaptive neuro fuzzy interference system (anfis) model the proposed neuro-fuzzy model of anfis is a multilayer neural network-based fuzzy system. its topology is shown in fig. 5, and the total of the the input and output nodes represent the training values and the predicted values, respectively, and in the hidden layers, there are nodes functioning as rules and membership functions (mfs). this disadvantage of a normal feed forward multilayer er to modify or understand the network. for simplicity, we assume that the examined fuzzy inference system has two inputs x and y and one output. for -order surgeon fuzzy model, a common rule set with two fuzzy if fig 5. (a) firstorder sugeno fuzzy model; (b) equivalent anfis architecture, (jang,1993) 24 sheroy, m. m/ jgeet vol 02 no 01/2017 fig 5 (a) graphically illustrated mechanism fuzzy reasoning to get a f output from a given input vector [x, y]. that w1 and w2 shoot strength usually obtained as a result of grade of membership in the premises, and output f is the weighted average of each rule`s output. to fascinate learning (or adaptation) surgeon fuzzy model, it is easy to put into the framework of fuzzy model adaptive network that can compute the gradient vector in a systematic manner. resultant network architecture, called anfis (adaptive neuro-fuzzy inference system), and shown from fig. 1b, different layers of anfis have or adaptive (jang, 1993). different layers with their associated nodes are described below: f. performance avaluation this part is important to have a fair comparison of the predicting result obtained from anfis and svm. addition, there are a lot of criteria included in the models which will prove difficult to perform simply by using conventional mathematic formula. data obtained from both svm and anfis parameters compared to see the difference. this is to see the effect of changes to the output and error when various renovations g. root mean square error (rmse) the correlation coefficient (r), root mean squared error (rmse) was used to evaluate the performance of the proposed models. by this formula determines the residual value between the actual and predicted atterberg limits. the effect on coefficient is more obvious by larger error in predicted values than the smaller ones. the best fit can be seen when the value of rmse is zero. the formula for rmse can be calculated using equation (5). (5) where n is amount of data, hi is observed value, ti is the predicted value. h. correlation coefficient (r) generally, this formula is the root of ratio between the explained variations where it range between the actual value and the predicted value. this formula is best shown by equation (6). (6) where n is amount of data, hi is observed value, ti is the predicted value, ͞h ͞i and t͞i are the average of the observed and predicted values respectively. correlation coefficient r 2 indicates the strength of the linear relationship and the relationship of those variables. r 2 value closer to 1 indicates the efficiency of a model. 3. result and discussion comparison of both svm and anfis methods of analysis necessary to determine the best methods of both, and to calculate the uncertainty for both these models. determination of the best and efficient analysis is important that the accurate method can be used for a reference primarily associated with atterberg limits or engineering properties of soil in the future. for svm analysis method, two criteria are discussed modification of renovation and modification of the input training data set. as for the method of analysis anfis, modification total input will be carried out for comparison purposes. all data obtained were analysed and a comparison is made through tables and graphs. fig 6 shows a comparison of the predictive values of the liquid limit for svm and anfis models. from the fig, it was found that the anfis model is represented by the red line is closer to the actual value compared with the svm predictions that indicate by green line. fig 7 also clearly shows the red line representing the results of the anfis model predictions are seen getting closer to the actual value of the plastic limit is represented by the green line ( svm model ). fig 8 anfis prediction is seen closer to the actual value than the svm for analysis of plasticityc index. in terms of observations on all of these figs, it is seen that the results of anfis prediction closer to the experimental data for the analytical testing laboratory liquid limit, plastic limit and plasticity index analysis where revenue forecasts anfis model is closer to the actual value. sheroy, m. m/ jgeet vol 02 no 01/2017 25 fig 6. predicted and actual liquid limit values using svm and anfis models with 3 input fig 7. predicted and actual plastic limit values using svm and anfis models with 3 input 4. comparison of svm and anfis best models rmse and r of 3 input in this study, the performance of both anfis and svm model can be assessed by looking at the difference between the values predicted by the correlation coefficient, r 2 and root mean squared error rmse. the r 2 value closer to 1 indicates the efficiency of such a model. the smaller rmse values indicate smaller errors produced by the model. comparison of r 2 values for the two models are briefly described by table 2 referring to table 2 the value of r 2 obtained results anfis is better than svm model for the liquid limit, plastic limit and plasticity index. however, the results indicate that anfis is more accurate the svm model. in this study comparison of the root mean square error or rmse will be conducted. rmse is a mathematical method for measuring the magnitude of the average error. the lower the rmse value of a data means more accurate predictions. table 3 shows the rmse values obtained for the three analyzes the atterberg limits. the results show that the low rmse values obtained by anfis model for all liquid limit,plastic limit and plasticity index analysis. meanwhile, finally the anfis model shows the rmse is lower than svm. in conclusion, the three atterberg limits tests conducted, three tests that test the liquid limit plastic limit and plasticity index, anfis models give a more accurate prediction of the actual value compared with the svm model. 26 sheroy, m. m/ jgeet vol 02 no 01/2017 fig 8.predicted and actual plasticity index values using svm and anfis models with 3 input table 2. comparison of correlation coefficient values, r 2 for svm and anfis models no. parameter svm anfis 1 liquid limit 0.835 0.987 2 plastic limit 0.578 0.949 3 plasticity index 0.831 0.996 table 3. comparison of rmse values for svm and anfis models no. parameter svm anfis 1 liquid limit 3.378 0.957 2 plastic limit 1.798 0.615 3 plasticity index 2.776 0.421 5. modification of svm model to find out how the number of total input can change the outcome of the prediction by the svm model, the model is analyzed by carrying out modifications for the amount of inputs used. the amount of inputs used for both models are modified from two inputs to the three inputs by using the percentage of silt and clay fraction was then added to the three inputs of the percentage of sand, silt and clay. these modifications are briefly described in table 5 below. a. total input svm to find out how the number of total input can change the outcome of the prediction by the svm model, the model is analyzed by carrying out modifications for the amount of inputs used. the amount of inputs used for both models are modified from two inputs to the three inputs by using the percentage of silt and clay fraction was then added to the three inputs of the percentage of sand, silt and clay. fig 9, 10 and 11 show the results of the svm model predictions for the three tests atterberg limits on the amount of inputs used. as shown in fig 4.16, the svm model predictions for the liquid limit test that uses three input be represented by the red line is closer to the actual data (green lines) than the two input be represented by yellow line. large errors also occur in most of the samples as an example, the samples 2, 4, 6,7, 15, sheroy, m. m/ jgeet vol 02 no 01/2017 27 16, 17, 25, 26, 27,30,36, 43, 44, 53, 54 for the twoinput svm model predictions away from the true value. similarly in fig 10 below shows the results of the predictive value of the plastic limit of the svm model that uses three input a little bit accurate than using two input model. the difference between the svm prediction model that uses two input too much away from the actual value. in conclusion, based on fig 9, 10 and 11, the results of svm model predictions indicate that the modifier amount of inputs used by the model is related to the value of output produced. this is evidenced also by the r 2 obtained as a result of the analysis. table 5 below shows the value of the coefficient r 2 obtained after doing an analysis of both models. comparison of the coefficient r 2 obtained from svm model are shown in table 5 below. table 5.modification total input total input percentage (%) output 2 input clay and silt liquid limit plastic limit plasticity index 3 input sand, clay and silt fig 9.comparison of results for liquid limit prediction model based on svm total input fig 10. comparison of result for plastic limit prediction model based on svm total input 28 sheroy, m. m/ jgeet vol 02 no 01/2017 fig 11.comparison of results for plasticity index forecast based on svm model total input table 5. comparison of r 2 values for svm model based on total input no. parameter svm model 2 input (clay and silt) 3 input (sand, clay and silt) 1 liquid limit 0.830 0.835 2 plastic limit 0.538 0.578 3 plasticity index 0.827 0.831 the results show that the higher the number the more accurate the inputs used for the prediction model. this is evidenced by the difference in the coefficient r 2 obtained for the svm model with the input of more than the number of inputs. the three tests of the liquid limit, plastic limit and plasticity index indicate that by using more number of inputs, the higher the performance of the svm model. the results of the comparative value of rmse of the amount of inputs used are shown in table 6 below. referring to table 6, the svm model performed better when using more inputs for the three tests atterberg limits are. lower rmse values obtained when using three input than two inputs. 6. modification of anfis model anfis model has also been modified in this study for comparison and does not respond to the modification of the model studied. the modification is done in terms of modification of the input. a. total input anfis the amount of inputs used for both models are modified from two inputs to the three inputs by using the percentage of silt and clay fraction was then added to the three inputs of the percentage of sand, silt and clay. the results and the prediction of anfis model for the three values of atterberg limits are shown in figs 12, 13 and 14 anfis prediction that uses three input is represented by the blue line, while the anfis predictions for the two input lines are represented in pink. for liquid limit test, it was found that using the anfis model predictions of three input is closer to the true value compared to the analysis using two inputs similarly, the analysis of plastic limit testing and plasticity index indicate that the anfis prediction for the three inputs closer to the true value than two inputs. table 6. comparison rmse values for svm model based on total input. no. parameter svm model 2 input (clay and silt) 3 input (sand, clay and silt) 1 liquid limit 3.425 3.378 2 plastic limit 1.876 1.798 3 plasticity index 2.824 2.776 sheroy, m. m/ jgeet vol 02 no 01/2017 29 fig 12 comparison of results for liquid limit prediction based on anfis model total input fig 13. comparison of result for plastic limit prediction based on anfis model total input fig 14. comparison of result for plasticity index prediction based on anfis model total input 30 sheroy, m. m/ jgeet vol 02 no 01/2017 table 1. comparison of the r 2 value for anfis model by total input no. parameter anfis model 2 input (clay and silt) 3 input (sand, clay and silt) 1 liquid limit 0.838 0.987 2 plastic limit 0.636 0.949 3 plasticity limit 0.835 0.996 table 2. comparison of rmse values for anfis model based on total input no. parameter anfis model 2 input (clay and silt) 3 input (sand, clay and silt) 1 liquid limit 3.345 0.957 2 plastic limit 1.647 0.615 3 plasticity index 2.739 0.421 comparison of the total input anfis model is also reflected in the value of r 2 obtained as shown in table 7 r 2 values obtained for anfis model that uses two inputs for limit liquid testing is 0.838 increasing to 0.987 for the model using three inputs. similar results were also obtained for analysis of plastic limit testing and plasticity index of the value of r 2 is also increased when the input is increased from two to three input. referring to table 8 the results for the low rmse also obtained by anfis model for the analysis of the three liquid limit, plastic limit and plasticity index when the three inputs used rmse values for liquid limit decreased from 3.345 to 0.957 similarly, the plastic limit testing rmse values decreased from 1.647 to 0.615 the index test plastic, the rmse values obtained decreased from 2.739 to 0.421 thus, we can conclude that, the rmse obtained was dependent on the modification of the number of inputs used in the anfis model. conclusion from the results obtained, it can be concluded that the prediction by anfis method shows higher accuracy than the svm method for the liquid limit plastic limit and plasticity index. r2 coefficient and rmse values obtained for both methods also showed anfis model performed better than the svm model in predicting the atterberg limits as a whole. the outcome of the study show that the anfis model shows higher accuracy than svm model for the liquid limit (r 2 = 0.987), plastic limit (r 2 = 0.949) and plastic index (r 2 = 0966). rmse value that obtained for both methods have shown that the anfis model has represent the best performance than svm model to predict the atterberg limits as a whole. modifications of svm and anfis models have been done in order to evaluate the response of the output to the modification and the efficiency of the model. references ali, t.y., 2011. effect of fine particles on shear strength parameter of sand (thesis). faculty of civil engineering. berbenni , s., favier , v., berveiller , m., 2017. impact of the grain size distribution on the yield stress of heterogeneous material. impact of the grain size distribution on the yield stress of heterogeneous material 23, 114 142. boser, b.e., guyon, i.m., vapnik, v.n. 1992 a training algorithm for optimal margin classifiers. in: in d. haussler, editor, 5th annual acm workshop on colt, pages 144152, pittsburgh, pa, acm chen, s.t., yu, p.s& tang, y.h. 2010. statistical downscaling of daily precipitation using support vector machine and multivariate analysis. journal of hydrology. 385: 13-22 cortes, c. and vapnik, v. 1995. support-vector networks. machine learning. volume 20, number 3. pp 273-297 fletcher, t. 2009. support vector machine explained (online) http://www.tristanfletcher.co.uk/ svm%20explained.pdf (22deceber2011) ikram 2011. report of study on debris flow controlling factor and triggering system in peninsular malaysia. institute of public work. malaysia jang, j.s.r. 1993. anfis: adaptive network based fuzzy interference system. ieee transaction on system, man, and cybernetic, 23(03):665-685 lin, h.j. & yeh, j.p. 2009. optimal reduction of solution for support vector machines. applied mathematics and computation. 214: 17-29 tripathi, s., srinivas, v.v. & nanjundiah, r.s. 2006. downscaling of precipitation climate change scenarios: a support vector machine approach. journal of hydrology. 330(3-4): 621-640 vapnik, v.n 1995. the nature of statistical learning theory. new york: springer verlag. 1. introduction 2. material and methods a. data distribution b. revision of area c. support vector machine (svm) model d. kernel function e. adaptive neuro fuzzy interference system (anfis) model f. performance avaluation g. root mean square error (rmse) h. correlation coefficient (r) 3. result and discussion 4. comparison of svm and anfis best models rmse and r of 3 input 5. modification of svm model a. total input svm 6. modification of anfis model a. total input anfis conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 04 2018 208 ujjania, n.c, et al./ jgeet vol 03 no 04/2018 research article festivals and deterioration of aquatic environment: a case study of idol immersion in tapi river, india n.c.ujjania 1 , azahar a. multani 1 , chaitali a. mistry 1 , mitali s. patel 1 1 department of aquatic biology, veer narmad south gujarat university, udhana magdalla road, surat (gujarat) 395007 * corresponding author : ncujjania@vnsgu.ac.in received: august 30, 2018; accepted: november 14, 2018. doi: 10.24273/jgeet.2018.3.4.2088 abstract in the civil society different festivals are celebrated, these are the integral part of human life and many of festivals are religious, seasonal change and culturally important. the present study elucidated the environmental impact of ganesh idol immersion on water quality of tapi river and for this purpose water samples were collected during different durations (pre immersion, during immersion and post-immersion) from selected sampling stations or idol immersion points of tapi river. the important water quality parameters like ph, temperature, dissolved oxygen, free carbon dioxide, total hardness, total alkalinity, biological oxygen demand, chemical oxygen demand, oil & grease, and total calcium were analyzed for the study. result shows that dissolved oxygen was depleted while remaining parameter was increased during the idol immersion and it was concluded that aquatic ecosystem of tapi river was deteriorated and pollution and nutrient load were increased due to these religious activities. the celebration of festivals and these religious activities cannot stop but pollution can reduce to save the river. keywords: pollution, idol immersion, ganesh festival, tapi river, water quality 1. introduction in india, different types of festivals and rituals are celebrating and it is the rich and diverse cultural heritage. these festivals and rituals are the integral part of human life and many of these are religious, seasonal change and heaving cultural importance. in india subcontinent, many festival like holi, ganesh chaturthi, durga puja, deepawali, eid and tazia are celebrated for enjoyment but these festivals may cause of different types of pollution like water, air, noise, soil etc. (shukla, 2004; gupta et al., 2011; mehta, 2013; shivhare and rastogi, 2016 and bhatnagar et al., 2016). the ganesh chaturthi is one of the important festivals of the hindu religion which celebrating in the bhadrapad month of the hindu calendar and during this festival ganesh idols are worshiped for number of days and immersed in different water bodies (reddy and kumar, 2001). ganesh chaturthi festival culminates in the immersion of idols and it is observed that abour 160,000 idols in mumbai and about 60000 different sized idols were worshiped and immerse in surat city (anon, 2018). these idols were constructed by different components (biodegradable and nonbiodegradable substances) like plaster of paris, clay, cloths, small iron rods, bamboo and decorated with different paints such as varnish, water colors etc. and when these idols immersed in the water body, these components lead to significant deterioration in the water quality (dhote et al., 2001; reddy and kumar, 2001; bajpai et al., 2002; mukerjee, 2003; swain et al., 2005; vyas et al., 2006; vyas et al., 2008; vyas and bajpai, 2008; dhote and dixit, 2011; bhat et al., 2012, kaur, 2012 and bhattacharya et al., 2014). the inputs of immersed idol may cause of the changes in water quality and increase the siltation in water body (malik et al., 2010; variya, 2010; varsani, 2010; ujjania and azahar, 2011; malik et al., 2012 and ujjania and mistry, 2012). the biodegradable components released through the idol immersion in the water body result in eutrophication (leland, 1991). water pollution by the ganesh idol immersion were studied by reddy and kumar (2001) in hussainsagar lake (hyderabad), billore and dandwate (2015) in kakerpura lake, mhow (mp), naphade et al., (2016) in rajalwadi reservoir, aurangabad (maharashtra) and watkar and barbate (2017) in chandrabhaga river, nagpur (maharashtra). the present paper elucidates the impact of festivals on the aquatic environment with reference to ganesh idol immersion in tapi river and its management practices. 2. material and methods water samples for the current study were collected from the pre-selected 3 sampling stations (ashwani kumar ovara, nanpura ovara and pal ovara) on the tapi river on the basis of idol immersion intensity (fig. 1). these samples were collected during the ganesh festival 2011 at different intervals i.e. pre-immersion (30th august to 20th september 2010), immersion (22nd to 24th september 2010) and post-immersion (4th to 18th october 2010) of ganesh idol period. these water samples were used to analyze the important http://journal.uir.ac.id/index.php/jgeet ujjania, n.c, et al./ jgeet vol 03 no 04/2018 209 physico-chemical parameters (ph, temperature, dissolved oxygen, free carbon dioxide, total hardness, total alkalinity, biological oxygen demand, chemical oxygen demand, oil and grease and total calcium) to follows the methods of trivedi and goyal (1986) and apha (2005). temperature measurement and fixation of dissolved oxygen was done in situ and collected samples were transferred to the research laboratory of department of aquatic biology, vnsgu (surat) for further analysis of remaining parameters. 3. result and discussion the findings of present study presented in table 1 and fig. 2 (a, b, c, d, e, f, g and h) and these data indicate the significant deterioration in water quality of the aquatic environment of the tapi river during the study period. the hydrogen ion concentration (ph) is important parameter of water because it deals with solubility of nutrients. study shows that water of tapi river was high 6.91-7.92 (7.62 ± 0.10) during the immersion period whereas ph values was comparatively low 6.80 -7.91 (7.30 ± 0.08) and 6.98 7.91 (7.51 ± 0.11) during the pre-immersion and post-immersion period respectively (table 1 and fig. 1). kalita et al. (2006) and malik et al. (2012) reported acidic nature of water due to idol immersion in in beel water of assam and different rivers of south gujarat. nag and pande (2015) were also reported increase in acidic nature due to idol immersion in yamuna river. these changes in ph of water may be due to addition of organic matter and biodegradable materials (dubey and ujjania, 2015) which was used in the preparation of ganesh idols. the temperature of water surface was analysed in situ and significance variation was observed during the study period. the range of temperature during the preimmersion 27.00 31.00 0c (28.79 ± 0.43), immersion 28.00 31.00 0c (29.67 ± 0.40) and post-immersion 28.00 30.50 0c (29.37 ± 0.30) was observed and described in table 1 and fig. 2. the increasing trend in temperature enhance the chemical reaction and biological activity (jayalakshmi and balagani, 2005) which affect the solubility of gases in water (murugesan et al., 2004). similar findings were also reported by desai and tank (2010) and nag and pande (2015). fig. 1. map of study area (1) ashwanukumar ovar, (2) nanpura ovara and pal ovara 210 ujjania, n.c, et al./ jgeet vol 03 no 04/2018 dissolved oxygen (do) is considered important water quality parameters which influence the physical and biological process in the waterbody and it is one of the important parameter for the assessment of the suitability of aquatic resources for the survival of fauna and flora. the result shows that during the idol immersion it was low 2.80 to 7.60 (4.76 ± 0.52) mg/l whereas it was high during the pre-immersion 4.80 6.80 (6.27 ± 0.17) mg/l and post immersion 2.8 6.80 (4.84 ± 0.47) mg/l (table 1 and fig. 1). the decrease trend in do was cumulative effect of idol immersion activities (desai and tank, 2010, ujjania and azahar, 2011 and malik et al., 2012) in different rivers of southern gujarat including tapi. fig 2. graphical presentation of water quality parameters during pre-immersion (1), immersion (2) and post-immersion (3) 6,80 7,00 7,20 7,40 7,60 7,80 1 2 3 p h 27,50 28,00 28,50 29,00 29,50 30,00 30,50 1 2 3 t e m p e ra tu re ( o c ) 0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 1 2 3 d is so lv e d o x y g e n ( m g /l ) 12,50 13,00 13,50 14,00 14,50 15,00 15,50 1 2 3 f re e c o 2 (m g /l ) 0 50 100 150 200 1 2 3 t o ta l h a rd n e ss ( m g /l ) 0 50 100 150 200 250 300 350 400 1 2 3 t o ta l a lk a li n it y ( m g /l ) 0,0 1,0 2,0 3,0 4,0 5,0 1 2 3 b o d ( m g /l ) 0,0 10,0 20,0 30,0 40,0 50,0 60,0 1 2 3 c o d ( m g /l ) 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1 2 3 o il & g re a se ( m g /l ) 0 20 40 60 80 100 120 140 1 2 3 t o ta l c a lc iu m ( m g /l ) ujjania, n.c, et al./ jgeet vol 03 no 04/2018 211 table 1. water quality parameter of tapi river during the ganesh festival parameters unit pre immersion immersion post immersion min. max. mean se min. max. mean se min. max. mean se ph 6.80 7.91 7.30 0.08 6.91 7.92 7.62 0.10 6.98 7.91 7.51 0.11 temperature 0 c 27.00 31.00 28.79 0.43 28.00 31.00 29.67 0.40 28.00 30.50 29.37 0.30 dissolve oxygen mg/l 4.80 6.80 6.27 0.17 2.80 7.60 4.76 0.52 2.80 6.80 4.84 0.47 free co2 mg/l 7.04 19.36 14.67 1.00 10.56 21.12 14.67 1.17 8.80 21.12 13.69 1.34 total hardness mg/l 110.00 168.00 125.67 4.93 144.00 178.00 165.22 4.07 120.00 170.00 143.33 6.84 total alkalinity mg/l 220.00 290.00 258.33 7.26 280.00 380.00 327.78 11.64 230.00 310.00 273.89 8.07 bod mg/l 3.20 6.00 4.37 0.20 2.40 6.00 4.31 0.39 2.40 5.20 3.60 0.32 cod mg/l 19.42 43.42 30.61 2.27 40.57 49.14 45.01 1.04 14.00 42.28 35.11 2.81 oil & grease mg/l 0.33 0.90 0.59 0.04 0.69 1.30 0.98 0.07 0.33 0.82 0.64 0.05 total calcium mg/l 60.00 112.00 83.67 4.00 82.00 140.00 116.67 7.36 76.00 128.00 93.56 6.70 bod biological oxygen demand, cod chemical oxygen demand and se standard error the free co2 was generated from the microbial activities and it required for the photosynthesis which affect the algal growth. in present study the high value of carbon dioxide 12.32 14.08 (12.907 ± 0.587) mg/l were observed during the immersion period while 7.04 15.84 (12.320 ± 2.156) mg/l and 8.8 14.08 (11.147 ± 1.552) mg/l were observed during pre-immersion and post-immersion period respectively (table 1 and fig. 1). ujjania and azahar (2011) and bhattacharya et al. (2014) also reported the similar finding in tapi river of gujarat and chhatri lake, amarawati (maharashtra) respectively. total hardness is the important water quality parameter which deals with the uses for different purposes. in present investigation, it was high 144.00 178.00 (165.22 ± 4.07) mg/l during immersion period whereas it was comparatively low 110.00 168.00 (125.67 ± 4.93) mg/l and 120.00 170.00 (143.33 ± 6.84) mg/l during pre-immersion and during postimmersion respectively (table 1 and fig. 1). idol constructive components are responsible for increasing hardness and high value of total hardness was observed during the idol immersion activity. vyas et al. (2008) reported low value of total hardness (72.00 mg/l) while it was increased (149.00 mg/l) due to idol immersion in upper lake of bhopal (mp). bhattacharya et al. (2014) reported the effect of idol immersion on hardness (116.33 mg/l pre immersion and 136.74 mg/l during the immersion) in ganga river which was moderately similar findings of present investigation. malik et al. (2012) also reported high value (347 ppm) of total hardness during immersion period in tapi river. the alkalinity is the water buffering capacity and it was increases due to various religious activities and domestic waste specially soap and detergents (patil, 2003). in present study it was found high 280.00 380.00 (327.78 ± 11.64) mg/l during immersion period compare to pre-immersion and post-immersion period 220.00 290.00 (258.33 ± 7.26) mg/l and 230.0 310.0 (273.89 ± 8.07) mg/l respectively (table 1 and fig. 1). the amount of total alkalinity was related to carbonates and bicarbonates concentration and its increasing value was fluctuated due to idol immersion (waikol and patil, 2009). desai and tank (2010) reported high value of alkalinity (320 mg/l) during the idol immersion in tapi river which is similar to the findings of current study. the result of present study is evident of the study reported by gupta et al. (2011) regarding religious activity in ponds of varanasi. ujjania and azahar (2011) and ujjania and mistry (2012). biological oxygen demand (bod) is indicate the organic pollution load in the water body and it was 2.40 6.00 (4.31 ± 0.39) mg/l during the immersion period which was significantly high compare to preimmersion 3.20 6.00 (4.37 ± 0.20) mg/l and postimmersion period 2.40 5.20 (3.60 ± 0.32) mg/l (table 1 and fig. 1). the values of bod is directly related to the nutrient level in the water body (mccoy and olson, 1986) which was affected by the immersion activity. the similar results were also observed by desai and tank (2010), ujjania and azahar (2011) and ujjania and mistry (2012) in the tapi river. chemical oxygen demand (cod) is an important pollution indicating parameter and in present study it was high 40.57 49.14 (45.01 ± 1.04) mg/l during the idol immersion period while it was low 19.42 43.42 (30.61 ± 2.27) mg/l and 14.00 42.28 (35.11 ± 2.81) mg/l during pre-immersion and post-immersion period (table 1 and fig. 1). similar finding of cod (21.14 49.1 and 47.4 52.8 mg/l) during the idol immersion activity were reported in tapi river by ujjania and azahar (2011) and malik et al. (2012) respectively. 212 ujjania, n.c, et al./ jgeet vol 03 no 04/2018 the oil and grease (og) is an important parameter for water quality and safety whcih can cause surface films and shoreline deposits leading to environmental degradation and human health. the important sources of og in aquatic resource are the automobile industrial discharges, oil paints of idol, worship contents etc. during the study, oil and grease was comparatively high 0.69 1.30 (0.98 ± 0.33) mg/l and 0.33 0.92 (0.64 ± 0.05) mg/l during idol immersion and postimmersion period respectively, whereas, it was low 0.33 0.90 (0.59 ± 0.04) mg/l during the pre-immersion of idol (table 1 and fig. 1). the results of present study evidenced by vyas et al. (2006), ujjania and azahar (2011), ujjania and mistry (2012) and bhattacharya et al. (2014). calcium is naturally present in water from dissolution of rocks and idol construction components also one of the important source. in present study the total calcium was observed 60.0 112.0 (83.67 ± 4.00) mg/l, 82.00 140.0 (116.67 ± 7.36) mg/l and 76.0 128.0 (93.56 ± 6.70) mg/l during pre-immersion, immersion and post immersion period respectively (table 1 and fig. 1). results depicted that total calcium was comparatively high during the idol immersion period. reddy and kumar (2001) reported high concentration of calcium after the idol immersion in the hussainsagar lake, andhra pradesh. ujjania and azahar (2011) and ujjania and mistry (2012) also reported similar findings in tapi river. 4. conclusion celebration of various festivals in societies playing important role in deterioration of aquatic environment and ganesh festival is equally responsible to damage of tapi river ecosystem because idols of ganesh which were constructed by different degradable and nodegradable components like plaster of paris, clothes, small iron rods, chemical colours, varnish, paints and decorative components immersed in it. religious activities and aquatic resources are related to human sentiments but scientifically these activates are responsible for aquatic pollution which affect the natural, chemical and biological processes and produce undesirable situations for aquatic biota. the idol immersion and similar religious activities are concern of environmental issue and need to the protection of aquatic resources. administrative remedial measures are not enough to conserve the water ecosystems but well-designed awareness programmes for people may also be required. the conservative approach like use of eco-friendly idols made of natural clay, immersion of idols in artificial water tank or in the water pot at home, remove the idol accessories with toxic paints of idol before immersion into river. use of permanent idols made of stones or metallic components be yet another eco-friendly way to handle this issue. it is concluded that water quality parameters of tapi river determined during ganesh idols immersion activity indicated significant changes during pre-immersion and immersion of idols and there is need of application and adoption of appropriate conservative measures. acknowledgement authors extend sincere regards to prof. dr. shahid naseem, chairman, department of geology, for providing the analytical facilities. mr. wasi haider is acknowledged for his technical support to analyze the samples. ms. sumera asif khan is also thanked for her help in statistical analysis. references anon, 2018. www. redorbit. com / news/ science/ 1524819/ hindu_ festivals_ bring_ pollution_ to_ indias_ waterways apha, 2005. standard methods for examination of water and waste water, american public health association, washington, dc bajpai, a., pani, s., jain, r.k. and mishra, s.m., 2002. heavy metal contamination through idol immersion in a tropical lake. ecology and 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(http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ festivals and deterioration of aquatic environment: a case study of idol immersion in tapi river, india 1. introduction 2. material and methods 3. result and discussion 4. conclusion acknowledgement references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 hamimu, et al./ jgeet vol 04 no 03/2019 149 research article analysis of the sub-surface distribution of graphite minerals using the geoelectrical resistivity method in the sabilambo village, kolaka regency, southeast sulawesi province la hamimu 1 *, l.o ngkoimani 2 , jahidin 1 , suryawan a 2 , usmardin 1 1 halu oleo university, geophysics engineering department 2 halu oleo university, geology engineering department *corresponding author: suryawan_tambang@uho.ac.id tel : +62 812 4580 6864 received : mei 27, 2019; accepted: jun 19, 2019. doi : 10.25299/jgeet.2019.4.3.2406 abstract southeast sulawesi province is one of the regions in indonesia that has abundant mineral resources, the availability of several types of minerals is strongly influenced by the diversity of rock formations that make up the area. the metamorphic complex is one of the rock formations in the southeast sulawesi province. where the rock complex is divided into 2 (two), namely: pompangeo complex and mekongga complex, the distribution area of this metamorphic rock is estimated around 50% of the total land area of southeast sulawesi province. this rock complex is very possible to contain mineral deposits, one of which is graphite mineral deposits. however, the problem that is now is the identification of the potential for subsurface distribution of graphite excavated material has not been carried out. therefore, this research was conducted to determine the potential for subsurface distribution of graphite mineral deposits is using geoelectrical resistivity method where is using wenner-schlumberger configuration, this research activity was conducted in the sabilambo village in kolaka regency, where most of the research area is metamorphic complex. based on the result of the resistivity analysis, subsurface distribution of graphite mineral deposits in the study area can be found on the surface to a depth of 33.5 meters below ground level, with keywords: graphite, sub-surface, distribution, geoelectrical resistivity method. 1. introduction south east sulawesi is one of province that has resources minerals which is quite an abundance and varied for example laterite nickel contained in kolaka district, north konawe district, south konawe district and bombana district (nukdin, 2012), (tonggiroh et al., 2012), (kamaruddin et al., 2018), (irzon and baharuddin, 2016), besides that there are also deposits of gold minerals in the region bombana district in associated with metamorphic complex (setiawan et al., 2012), (idrus et al., 2011), (surono and a. tang, 2009), (fadlin et al., 2016), (hasria et al., n.d.), (idrus et al., 2016), (hasria et al., n.d.). besides that, heavy metal enrichment is also found in mn, co, and cr (irzon, 2017). the existence of abundant minerals resources in the southeast sulawesi province, one which in influenced by the diversity of rock formations found on the surface, the arrangement of the south east sulawesi arm stratigraphy is formed by the meeting of two plates, namely the indo-australia continental plate and the pacific ocean plate. in general, the stratigraphic arrangement in the southeast sulawesi arm consists of microcontinent fragments (low to high-grade schist), ophiolite complexes, and sulawesi molasses. (surono, 2010), (rusmana et al., 1993), (simandjuntak et al., 1993) (fig. 1). the pieces of the sulawesi continent are composed of several types of rock formation, including the complex of pompangeo and the complex of mekongga. the oldest rock of these two rock formation in metamorphic rock which occupies the middle part of the southeast arm of sulawesi which forms the mendoke mountains and the southern part forms the rumbia mountains with rock types consisting of schist, quartzite, slate and marble (surono, 2010), (rusmana et al., 1993), (simandjuntak et al., 1993). based on geological aspect combined with geographic aspect where the metamorphic rock complex is estimated to have a fairly widespread of about 50% of the total land area of southeast sulawesi province with include bombana district, kolaka district, north kolaka district, konawe district, south konawe district, north konawe district, and kendari city (rusmana et al., 1993), (simandjuntak et al., 1993). the existence of this vast rock complex has brought valuable mineral deposits, one of which is the potential of graphite mineral deposits. the presence of graphite minerals is found in the complex area of the pompangeo and mekongga mountain ranges. where in the alteration zone found in the mendoke mountains associated with http://journal.uir.ac.id/index.php/jgeet mailto:suryawan_tambang@uho.ac.id hamimu, et al./ jgeet vol 04 no 03/2019 150 metamorphic rocks there is a carbonization process which is the initial stage of the formation of graphite minerals which are in quartz veins and alteration of mica schist (hasria et al., 2017). the research area is in district kolaka, based on the geological aspect mostly composed of metamorphic rocks from the mekongga complex and pompangeo complex. (simandjuntak et al., 1993), (rusmana et al., 1993) (fig. 2). based on the above assumptions, the kolaka district is one of the regions with the potential for graphite mineral deposits, with a widespread of rocks then it is possible to allow deposits of graphite minerals to be found in such a large distribution. however, the problems that arise to this day are the identification of the subsurface distribution of graphite mineral deposits that have not been carried out. in this study, we will identify the subsurface distribution of graphite mineral deposits with subsurface geophysical mapping method using geoelectric rock type resistivity. this research as part of the development of southeast sulawesi province as an advanced area of potential aspects of minerals, so that the utilization of minerals can be carried out optimally for the development of future industries that prioritize environmental aspect. fig. 1. the geological setting of the southeast arm of sulawesi which consists of the microcontinent fragment, ophiolite complex, sulawesi molase and location of the researched area (squared area), in kolaka regency, southeast sulawesi. (modified from surono, 2010, rusmana et al., 1993 and simandjuntak et al., 1993). fig. 2. the regional geological map that shows the position of the mekongga complex dan pompangeo complex in the kolaka regency. (modified from simandjuntak et al., 1993, and rusmana et al., 1993). research area hamimu, et al./ jgeet vol 04 no 03/2019 151 2. setting geology 2.1 geomorphology research area southeast sulawesi arm consists of 5 (five) morphological units, namely mountain morphology, high hill morphology, low hill morphology, flat morphology, and karst morphology. mountain morphology units occupy a larger area among all existing morphological units (surono, 2013). if the kolaka regency is specifically seen, it can be divided into 3 (three) morphological units. the distribution of morphological relief is based on the classification of relief according to van zuidam, 1985 (setyawan et al., 2017). the division of the morphological unit of the study area consists of mountains, hills and plain. (fig. 4a and 4b) the mountainous morphology units in the study area are part of the mekongga mountain range. the highest peak in the mekongga mountain range is mount mekongga which has a height of 2.790 mdpl. the mountain range in this unit has a pattern that is almost parallel to the northwest-southeast. this direction is parallel to the pattern of regional fault structures in the region. this pattern indicates that the formation of mountain morphology is closely related to regional faults. unit the mountain morphology is formed/ composed by metamorphic rocks and as thick as ophiolite rocks. mountain units formed by metamorphic rocks have a mountain that is cut short by an uneven slope despite sharp angles, whereas mountain units composed of ophiolite rocks have long and straight ridges with relatively flat slopes. the hilly morphological unit dominates in the southern part especially in pomalaa subdistrict, the altitude of the area in this morphological unit reaches 500 mdpl, with the formation of constituent rocks in the form of ultramafic complex, langkowala formations, and tokala formations and continental pieces. (rusmana et al., 1993), (simandjuntak et al., 1993), and (surono, 2010). the plain morphology units are generally in the west and dominate the urban areas of kolaka regency along the makassar strait. this morphological unit is composed of several collections of rock formations, among others: alluvium, ultramafic rock complex, and metamorphic rock complex. based on the relief classification according to van zuidam, 1985. where the morphology of the study area consisted of 2 (two) morphological units, namely: hills, and plains. hills morphology unit is a dominant morphological unit found in the study area (fig. 4c) fig. 3. the morphological form of the southeast sulawesi scale 1: 250,000 which is modified based on. (surono, 2013) hamimu, et al./ jgeet vol 04 no 03/2019 152 fig. 4.(a) the morphological form of the kolaka regency area is seen using dem (digital elevation model) which is overlaid on the geological map of the kolaka sheet (rusmana et al., 1993), (simandjuntak et al., 1993) and (surono, 2010). (b). vertical cross-section of the morphology of the kolaka regency. (c). morphology unit in the research area. 2.2 stratigraphy research area the rock formations of the kolaka regency region are sorted from the youngest which consists of alluvium (qa) composed of mud, clay, sand and gravel, the alangga formation (qpa) is composed of conglomerates and sandstones; the buara formation (ql) is composed of coral reefs, conglomerates, and sandstones; langkowala formation (tml) is composed of sandstone, shale, and conglomerates; the pompangeo complex (mtpm) is composed of various types of schist including mica schist, chlorite schist, graphite mica schist, quartz mists, glaucophane schist, schist yakut-amphibolite, genes, hornfels, and eclogite. the ultramafic complex (ku) is composed of harzburgite, dunite, wherlite, serpentinite, gabbro, micro gabbro, basalt, dolerite, rodingites and spot gabbro malih and amphibolite; tokala formation (trjt) is composed of white limestone, marble, and phyllite; and the mekongga complex (pzm) is composed of schist, genes, and quartzite (rusmana et al., 1993) (simandjuntak et al., 1993) (fig. 6) the research area lithology is dominated by metamorphic rocks with slate rock types. show the fresh colors of rocks in the form of back, weathered brown color, the texture of lepidoblastic rocks and show the existence of slaty structures. in this slate rock, foliation was also found with the direction of foliation n100 0 e 355 0 e and the foliation slope between 12 0 53 0 . (fig. 5) spread from the new area covers the northern to the western part of the study area, most of these rocks have been disrupted due to the development of the geological structure. fig. 5. the lithology of the research area is dominated by the type of slate and is part of the metamorphic complex mekongga (mtpm). plains research area 4 (a) hamimu, et al./ jgeet vol 04 no 03/2019 153 geological age symbol litostratigrafi era kala quarternar y holocene alluvium: mud, clay, sand, and gravel. buara formation: coral reef, conglomerate dan sandstone pleistocene alangga formation: conglomerate, sandstone tertiary miocene langkowala formation: sandstone, shale, and conglomerate paleocene pompangeo complex: mica schist, chlorite schist, graphite mica schist, quartz-mica schist, glaucophane schist, yakut-amphibolite schist, genes, hornfels, and eclogite. cretaceous ultramafic complex (ku): hazburgite, dunite, wherlite, serpentinite, gabbro, micro gabro, basal, dolerite, rodingsit, meta gabbro, and amphibolite triassic tokala formation (trjt): meta limestone, pualam and phyllite; mekongga complex (pzm) composed of schist, genes, and quartzite carbon mekongga complex (pzm): schist, genes, and quartzite. fig. 6. the stratigraphic column of the kolaka regency area, (modification from rusmana et al., 1993), (simandjuntak et al., 1993). 2.3 structural research area in the southeast sulawesi arm, the main structure formed after the collision was the shear sliding fault, including the matarombeo fault, the lawanopo fault system, the konawe fault system, the kolaka fault, as well as many other faults and lines. the geological structure found in the research location is the kolaka fault, which is formed between kolaka subdistrict and wundulako subdistrict, kolaka regency, besides that in the study area there is also an anticline fold. 3. research method measurement of the subsurface distribution of graphite mineral deposits in the study area was carried out using the resistivity method of the wenner-schlumberger configuration. measurements were made on 4 location, namely the kali merah block, block km12, blok sabilambo, and the lakandole block. determination of measurement path location based on the geological conditions of the study area, such as the presence of surface outcrops of graphite mineral deposits. 2d resistivity cross-section model which illustrates the distribution of subsurface graphite mineral deposits obtained through processing data using res2dinv software. the potential is determined by using the following eqn. 1 : (ngkoimani et al., 2015) 𝑽 = − ∫ 𝝆𝟎𝑰 𝟐𝝅𝒓𝟎 𝒅𝒓𝟎 = 𝝆𝟎𝑰 𝟐𝝅𝒓𝟎 ∞ 𝟎 (1) four electrodes were injected into the soil surface along a straight at pre-determined distances (a) (fig. 5). the electrical potential of current flow was measured between a pair of inner electrodes (p1 and p2) (fig. 5) while electrical current flowed was measured between a pair of outer electrodes (c1 and c2) (fig. 7). fig. 7. schematic of wenner array and schlumberger array (ngkoimani et al., 2015) the resistivity measurement of line 1 has 100 meters in length with electrode space about 5 meters. line 2 has 150 meters in length with electrode space about 5 meters, line 3 has 100 meters in length with electrode space about 5 meters, and line 4 has 200 meters in length with electrode space about 5 meters. (fig. 8) qa q l tml mtpm ku trjt pzm qpa hamimu, et al./ jgeet vol 04 no 03/2019 154 fig. 8. map of the location of the research area in sabilambo subdistrict, kolaka regency, southeast sulawesi province. 4. distribution sub surface graphite minerals 4.1 line 1 (04 0 s and 121 0 e) at line 1, resistivity measurements are carried out in a 100 m long track and cut the river. the measurement path passes through the surface outcrop of graphite mineral deposits at the riverbed. the crosssection model of 2d resistivity of line 1 is shown in fig 9. based on the resistivity cross-section model in fig. 9 above, it can be seen that the subsurface resistivity varies which is characterized by colour variation. variations in resistivity values indicate that subsurface lithology conditions vary. it is suspected that the presence of subsurface graphite mineral deposits is characterized by a blue layer with a resistivity value of estimation of the subsurface distribution of graphite mineral deposits based on the resistivity cross-section model above can be explained as follows: • graphite mineral deposits are found at a depth of 0-1.25 meters (electrodeposition 60-65 meters) with a thickness of 1.25 meters. this estimation is strengthened by the outcrop of the graphite mineral layer on the surface of the riverbed. • graphite mineral deposits are also found at a depth of 3.8 meters. this layer is spread far to reach a depth of 19.8 meters with a thickness of 16 meters. 4.2 line 2 (04 0 0 at line 2, resistivity measurements are carried out in a 150 meters track. around the measurement path, there is a surface outcrop of graphite mineral deposits. the cross-sectional resistivity model of line 2 is shown in fig 10. based on the resistivity cross-section model in fig. 10 above, it can be seen that the subsurface resistivity varies which is characterized by colour variation. variations in resistivity values indicate that subsurface lithology conditions vary. it is suspected that the presence of subsurface graphite mineral deposits is indicated by a blue layer with a resistivity estimation of the subsurface distribution of graphite mineral deposits based on the resistivity cross-section model above can be explained as follows: • graphite mineral deposits are found at a depth of 6.38 meters to reach a depth of 19.8 meters (thickness of 13.42 meters). • graphite mineral deposits are also found at a depth of 12.4 meters to reach a depth of 28.7 meters (thickness of 16.3 meters). fig 9. 2d resistivity cross-section model at line 1. graphite hamimu, et al./ jgeet vol 04 no 03/2019 155 fig 10. 2d resistivity cross-section model at line 2. 4.3 line 3 (04 0 , s and 121 0 e) at line 3, resistivity measurements are carried out in a 100 meters long track. around the measurement path, there is a surface outcrop of graphite mineral deposits on the river bank. on this track, measurements are made on the banks of the river in the direction of the river flow. the 2d resistivity crosssection model of line 3 is shown in fig 11. based on the resistivity cross-section model in fig. 11 above, it can be seen that the subsurface resistivity varies which is characterized by colour variation. variations in resistivity values indicate that subsurface lithology conditions vary. it is suspected that the presence of subsurface graphite mineral deposits is indicated by a blue layer with a resistivity value of estimation of the subsurface distribution of graphite mineral deposits based on the resistivity cross-section model above can be explained as follows: • graphite mineral deposits are found at a depth of 6.38 meters to reach a depth of 12.4 meters (thickness of 6.02 meters). • graphite mineral deposits are also found at a depth of 9.26 meters to reach a depth of 19.8 meters (thickness of 10.54 meters). 4.4 line 4 (04 0 0 at line 4, resistivity measurements are carried out in a 200 meters long track. around the measurement path, there is a surface outcrop of graphite mineral deposits on the edge of the road. on this track, measurements are made on the edge of the highway and parallel to the highway. the 2d resistivity crosssection model of line 4 is shown in fig. 12. based on the resistivity cross-section model in fig. 12 above, it can be seen that the subsurface resistivity varies which is characterized by colour variation. fig 11. 2d resistivity cross-section model at line 3. 000 fig 12. 2d resistivity cross-section model at line 4 graphite graphite graphite hamimu, et al./ jgeet vol 04 no 03/2019 156 variations in resistivity values indicate that subsurface lithology conditions vary. it is suspected that the presence of subsurface graphite mineral deposits is indicated by a blue layer with resistivity values of 14.9 surface distribution of graphite mineral deposits based on the resistivity crosssection model above, it can be explained that the graphite mineral deposit layer is found at a depth of 6.38 meters to reach a depth of 33.15 meters (thickness of 26.77 meters). 5. conclusion identification of the subsurface distribution of graphite mineral deposits in kolaka district, kolaka regency was carried out using the wennerschlumberger (ws) configuration resistivity method. resistivity measurement was carried out in 4 (four) line measurement, namely the lin 1, line 2, line 3. and the trajectory of line 4. based on resistivity analysis, the subsurface distribution of graphite mineral deposits in the study area can be found on the surface to reach a depth of 33.15 meters with a thickness ranging from 1.25 meters to 26.77 meters and having resistivity acknowledgements we would like to thank the halu oleo university for funding support for the implementation of this study with the 2018 higher education internal basic research scheme. references fadlin, idrus, a., warmada, i.w., 2016. studi kimia fisika fluida hidrotermal endapan emas orogenik daerah wububangka, kabupaten bombana, sulawesi tenggara. din. rekayasa 12, 30 36. 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pp. 32 34. surono, a. tang, h., 2009. kemungkinan keterdapatan endapan emas primer di kabupaten bombana, sulawesi tenggara. j. teknol. miner. dan batubara 5, 163 170. tonggiroh, a., suharto, muhardi, m., 2012. analisis pelapukan serpentin dan endapan nikel laterit daerah pallangga kabupaten konawe selatan sulawesi tenggara, in: prosiding 2012. pp. 978 979. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ hamimu, et al./ jgeet vol 04 no 03/2019 157 analysis of the sub-surface distribution of graphite minerals using the geoelectrical resistivity method in the sabilambo village, kolaka regency, southeast sulawesi province 1. introduction 2. setting geology 2.1 geomorphology research area 2.2 stratigraphy research area 2.3 structural research area 3. research method 4. distribution sub surface graphite minerals 4.1 line 1 (04003’36,23” s and 121041’58,10” e) 4.2 line 2 (04004’18,07” s and 121040’35,23” e) 4.3 line 3 (04004’44,34” s and 121039’26,90” e) 4.4 line 4 (04004’81” s and 121038’90”) 5. conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 93 research article tidal ellipses analysis based on flow model hydrodynamic data acquisition in mandeh bay, west sumatera ulung j. wisha 1 *, ruzana dhiauddin 2 , and wisnu a. gemilang 3 1 research institute for coastal resources and vulnerability, ministry of marine affairs and fisheries, indonesia * corresponding author : ulungjantama@kkp.go.id tel.: +62 751 751458; fax:+62 751 751458 received: mei 06, 2019; accepted: jun 19, 2019. doi: 10.25299/jgeet.2019.4.2.3115 abstract mandeh bay is threatened by sedimentation issue caused by the rapid development of marine tourism area which strongly impacts to the environmental degradation. due to the semi-enclosed area of mandeh bay, the tidal current has a significant role in triggering vertical and horizontal transports within the bay. this study aimed to determine the characteristic of tidal current during the southwest monsoon. we developed a hydrodynamic model based on navier-stokes equations using a flexible mesh and tidal forecast in which the validation is performed by adcp data. the simulation results will be used as the basic data to develop a model which depicts the elliptical pattern of tidal current constituents. offshore rotary tidal currents which are originally semidiurnal reiterate the elliptical pattern every 6 hours and 12 minutes. the strongest semidiurnal current speeds are observed in the bay mouth ranged from 0.1-0.5 m.s-1. the tidal constituent ellipses are oriented more meridionally and in several areas oriented zonally. the current speed of m_2 is the highest at all which the s_2 speed is averagely one third of m_2 magnitude. while, the two main diurnal tidal constituents (k_1 and o_1) have the maximum speeds approximately one fifth of m_2 magnitude. thus, the domination of semidiurnal constituents may trigger sediment distribution and accumulation within the bay because of its twice tidal oscillations entering the bay. keywords: tidal current, mandeh bay, southwest monsoon, hydrodynamic model, tidal current ellipses 1. introduction west sumatera is one of the provinces that has potential marine ecotourism enhancing local income (hermon, 2016).the rapid development of west sumatera has a role in inducing environmental degradation. several coastal damages, caused by mass-tourism, discrepant land-use, and industrial activities, have been occurring. this may enhance the sedimentations, pollutions, marine litters issues, and coastal vulnerability as well (duhec et al., 2015). according to its positions, west sumatera waters are tremendously strategic which are directly bordered by the indian ocean. this condition contributes to the generation of local water mass movement related to sedimentary behavior (hanebuth et al., 2015). one of the significant areas in the west sumatera experiencing dramatic sedimentation issues is mandeh bay. in mandeh bay, the existence of several new ports and settlements is the main problems of ineffective development. due to the rapid development that has been occurring, sedimentation issue strongly threats the condition within the bay which induces the high level of turbidity and water quality degradation as well. mandeh bay is a semi-enclosed water area which depends on hydrodynamic regime such as tidal current (hidayat and rozamuri, 2016). water mass movement is a complex phenomenon which is related to the controlling factors variation generating sea current, so that the regime of tidal current is essential to study because it is the main factor triggering transport mechanism (chen et al., 2015), especially for mandeh bay where the water mass movement tends to be weak due to its semi-enclosed water area. this may cause sedimentation. sediment sourced from estuaries and rivers will take place triggering the higher suspended sediment concentration in water (bábek et al., 2015). the study about current pattern correlated with the tidal regime is a significant way to depict the water circulation within a bay. in the narrowed and semi-enclosed water area, tidal is the primary factor inducing water mass circulation (wang et al., 2018). tidal current is a physical factor that always changes depending on the monsoon conditions (rath et al., 2017). it is obvious why tidal current characteristics in mandeh bay is necessary to determine the transport mechanism and water dynamics for better development in the future. moreover, this study may helpful for fisheries and shipping activities in term of sea current dynamics. one of the ways to fig. out the tidal current pattern is model approach using numerical simulation. this approach can illustrate vastly the study area that may be uncovered by http://journal.uir.ac.id/index.php/jgeet 94 wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 observation. this study aimed to determine the tidal current condition during the southwest monsoon. 2. materials and methods 2.1 field measurement and flow model simulation field observation was conducted in june 2018. we used adcp (acoustic doppler current profiler) to collect current, and tidal data which those data will be used for validating the simulation results. unfortunately, due to a technical problem, adcp data cannot be retrieved. so, we decided to use the older adcp data that were obtained from another survey project of the research institute for coastal resources and vulnerability (ricrv) in june 2015. bathymetry data obtained from the single-beam echosounder survey and global tide prediction data were applied as the model input. simulation results will illustrate as a tidal current pattern for four extreme tidal conditions which those results will be validated using field observation data. to evaluate the simulation results, we employed a root mean squared error (rmse) formula as follows: 𝑅𝑀𝑆𝐸 = √ 1 𝑛 ∑ (𝑦 − 𝑦𝑖)2𝑛𝑖=1 (1) where: n = total data validated y = model result data yi = observation data flow model flexible mesh was employed to simulate the tidal current pattern in the form of a two-dimensional hydrodynamic model. the model is based on the solution of incompressible reynolds which is averaged by navier-stokes equations consist of continuity and momentum equations. the local continuity equation is formulated as follows: 𝜕𝑢 𝜕𝑥 + 𝜕𝑣 𝜕𝑦 + 𝜕𝑤 𝜕𝑧 = 𝑆 (2) the two horizontal momentum equations for x and y components are generally written by the following discretization: 𝜕𝑢 𝜕𝑡 + 𝜕𝑢2 𝜕𝑥 + 𝜕𝑣𝑢 𝜕𝑦 + 𝜕𝑤𝑢 𝜕𝑧 = 𝑓𝑣 − 𝑔 𝜕𝜂 𝜕𝑥 − 1 𝜌𝑜 𝜕𝑃𝑎 𝜕𝑥 − 𝑔 𝜌𝑜 ∫ 𝜕𝜌 𝜕𝑥 𝜂 𝑧 𝑑𝑧 − 1 𝜌𝑜ℎ ( 𝜕𝑆𝑥𝑥 𝜕𝑥 + 𝜕𝑆𝑥𝑦 𝜕𝑦 ) + 𝐹𝑢 + 𝜕 𝜕𝑧 (𝑣𝑡 𝜕𝑢 𝜕𝑧 ) + 𝑈𝑠 (3) 𝜕𝑣 𝜕𝑡 + 𝜕𝑣2 𝜕𝑦 + 𝜕𝑢𝑣 𝜕𝑥 + 𝜕𝑤𝑣 𝜕𝑧 = −𝑓𝑢 − 𝑔 𝜕𝜂 𝜕𝑦 − 1 𝜌𝑜 𝜕𝑃𝑎 𝜕𝑦 − 𝑔 𝜌𝑜 ∫ 𝜕𝜌 𝜕𝑦 𝜂 𝑧 𝑑𝑧 − 1 𝜌𝑜ℎ ( 𝜕𝑆𝑦𝑥 𝜕𝑥 + 𝜕𝑆𝑦𝑦 𝜕𝑦 ) + 𝐹𝑣 + 𝜕 𝜕𝑧 (𝑣𝑡 𝜕𝑣 𝜕𝑧 ) + 𝑉𝑠 𝑆 (4) where: t : time x, y, z : cartesian coordinate 𝜂 : surface elevation 𝑑 : still water depth u, v, w : velocity components in the x, y, and z direction f : 2ω𝑠𝑖𝑛𝜙 (coriolis parameter) 𝑔 : gravitational acceleration 𝜌 : density 𝑆𝑥𝑥, 𝑆𝑥𝑦, 𝑆𝑦𝑥, 𝑆𝑦𝑦 : components of radiation stress tensor 𝑣𝑡 : vertical turbulent or eddy viscosity 𝑃𝑎 : atmospheric pressure 𝜌𝑜 : reference density 𝑆 : magnitude of discharge due to point sources (𝑈𝑠,𝑉𝑠 ) : velocity by which the water is discharged into the ambient water field measurement points of adcp surveys are positioned within mandeh bay next to cubadak island (fig. 1). adcp was deployed for 30 days on june-july 2018 at 10 meters depth. we used adcp nortek that can record several physical parameters such as currents, tidal, and temperature data. after the acquisition stage has done, the data must be sorted using surge software to delete the bias data. current data is recorded in several depth-cells data, we only used the uppermost data adjusted with the simulation built. thus, between model and field data can be well compared to evaluate the error resulted from the simulation. the simulation was running once for 15 days that represents 2 phases of tidal (neap and spring). we used tidal forecast data as the boundary conditions which are obtained from naotide execution and three boundaries which represent north, west, and south tidal condition in the mesh file (fig. 2). model results will be shown spatially in the form of hydrodynamical maps for four extreme tidal conditions. the model setup is shown in table 1. fig. 1. study area of mandeh bay. wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 95 fig. 2. boundary condition and mesh file of hydrodynamic model. table 1. model set-up for hydrodynamic simulation parameter implemented in the simulation time of simulation number of time step = 384 time step interval = 3800 sec simulation start date = 10/06/2018 12.00 am simulation end date = 26/06/2018 12.00 am mesh boundary bathymetry = hydrography and oceanography center, indonesian navy bathymetry map digitation flood and dry drying depth = 0.005 m flooding depth = 0.05 m wetting depth = 0.1 m wind forcing format = varying in time, constant in domain neutral pressure 103 hpa soft start interval = 0 sec boundary condition type = specified level format = varying in time, constant along boundary time series = tide forecasting with coordinates below: 1. longitude: 100.38600, latitude: -1.2578 2. longitude: 100.36669, latitude: -1.2388 3. longitude: 100.37596, latitude: -1.1812 2.2 tidal harmonic and ellipses analysis due to the limited adcp measurement (only one instrument mounted), we developed a tidal current model to analyze the tidal current using tidal ellipse parameters which can sufficiently cover the study area. it is important to be able to extract the harmonic components of the current associated with the tide. because of tidal current periodic nature, it can be separated into basic harmonic constituents. the longer the time series, the better the results will become, as the closely spaced can be more properly separated. the harmonic analysis is based on a least-square fit of the observation area. this methodology essentially allows for the determination of the barotropic tide at any time at any location within the study area. the velocity components are represented by a mean current and sum of harmonic current constituents as follows: 𝒖(𝒓, 𝒕) = (𝒓) + ∑ [𝒂𝒊(𝒓)𝒄𝒐𝒔(𝝎𝒊𝒕) + 𝒃𝒊(𝒓)𝒔𝒊𝒏(𝝎𝒊𝒕)] 𝑵 𝒊=𝟏 (5) where, u_o is the mean current, r(x,y) is the position vector, a_i and b_i are amplitudes, t is time, ω_i is the frequency of a given constituent, and n is the number of constituents. before executing the least square fit, the data are multiplied with gaussian weighting function on the form: 𝜙(𝑟, 𝑟𝑗 )~𝑒𝑥𝑝 {− [ (𝑥−𝑥𝑗) 2 𝜎𝑥 2 + (𝑦−𝑦𝑗) 2 𝜎𝑦 2 ]} (6) where, r_j (x_j,y_j) are the positions of the knot points and σ_x and σ_y are decay parameters that control the shape of gaussian curve. in this study, we used isotropic decay parameter with σ_x= σ_y= 55.5 km, which is equivalent to the length of half a degree latitude. the tidal constituents that have been extracted, six principal constituents and three over-tides are shown 96 wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 in table 2. results of extracted tidal currents are depicted in the form of tidal ellipse parameters which consist of semi-major and semi-minor axes representing maximum and minimum current speeds respectively, the inclination is the counterclockwise angle between the east direction and the semi-major axis. the ellipse parameters are illustrated using a concept of greenwich phase lag by appointing each tidal constituent which the fictitious star will travel around the equator with an angular speed as its corresponding constituent (fig. 3). table 2. tidal constituents used in the harmonic analysis. period is given in hours and frequency in cycles/day name of constituent symbol period frequency diurnal luni-solar 𝐾1 23.83 1.00 principal lunar 𝑂1 26.78 0.93 semi-diurnal smaller lunar elliptic 𝐿2 12.19 1.97 principal lunar 𝑀2 12.41 1.93 larger lunar elliptic 𝑁2 12.69 1.90 principal solar 𝑆2 12.01 2.00 higher harmonics shallow water over-tides of principal lunar 𝑀4 6.21 3.86 𝑀6 4.14 5.80 𝑀8 3.11 7.73 fig. 3. illustration of a clockwise rotating tidal current ellipse and its parameters. modified from (foreman, 1978) and (vindenes et al., 2018). 3. result and discussion 3.1 sea current profiles in mandeh bay the dominance of current speed and direction is shown in the form of current rose (fig. 4). acdp was set for five cells measurement which each cell is representing the water column with specified depth (1.5 m, 3.5 m, 5.5 m, and 7.5 m from the surface). in the uppermost cell (1.5 m) near the surface, the dominance current flows southwestward (16%) and northeastward (12%) which the predominant current speed ranged from 0-0.1 m.s-1. higher speed is also observed only ranged between 0.1-0.2 m.s-1 (2 %) and 0.2-0.3 m.s-1 (0.1%) respectively with the same direction domination. the deeper layer (3.5 m from the surface) shows the same current direction domination that is flowing southwestward (15.5 %) and northeastward (12.1 %). the current speed <0.1 m.s-1 is still dominant which the higher speed (ranging from 0.2-0.3 m.s-1) is observed flowing southwestward (0.1 %) while the current speed ranging from 0.1-0.2 m.s-1 is also identified in the same direction (0.5-1 %). at 5.5 m depth, the dominant current direction is oppositely changed in which the sea current flows predominantly northeastward (14 %) and southwestward (6 %). the current speed <0.1 m.s1 is frequently identified in all directions and the higher speed (ranging from 0.2-0.3 m.s-1) is observed less than 1 %. the same condition is identified at 7.5 m depth which is the surface bottom. the current flows predominantly northeastward (17.5 %) and southwestward (12 %) which the current speed ranges between 0-0.2 m.s-1. from the results above, it is interpreted that the current speed in the surface layer is the strongest which gradually becomes weaker in accordance with the increasing depth. this mechanism is common because, in the surface, the energy transfer from winds takes place generating higher speed in the surface while in the deeper layer, the wind force is gradually reduced by the detention of bottom friction and density so that the speed becomes weaker in the surface bottom. the opposite condition between the surface and bottom layers shows the influence of spiral ekman regime in which the current direction rotates counterclockwise in the southern hemisphere. the effect of the spiral ekman results from coriolis and wind forces which gradually forms spiral toward the bottom of waters and decreases speed. this event is the main factor triggering vertical transport in the ocean floor. mandeh bay becomes the area impacted this regime which the transport mechanism is following spiral ekman mechanism, furthermore, the other physical factors also take place such as tidal, density, waves, bottom friction etc. vertical profiles of sea current are shown in fig. 4 which are obtained from east velocity (x-direction), north velocity (y-direction) and up velocity (zdirection) of current. the negative velocity is representing the westward direction while the positive value is showing the eastward direction. from fig. 5, sea current flows dominantly westward with the speed ranged 0-0.12 m.s-1. north velocity profile is showing the dominant direction which is southward with the current speed ranged 0-0.13 m.s1. up velocity profile tends to be stable along the decreasing depth with the weakest velocity ranged from 0-0.08 m.s-1. furthermore, between 4.5-8.5 meters depth, the water mass moves averagely toward the bottom. vertical profile of current is also reflecting the vertical transport mechanism in the mandeh bay. wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 97 fig. 4. current rose for four depth layers based on adcp measurement. 3.2 model validation the model validation is performed by comparing adcp data and model result. in this study, we validated the surface elevation and velocity components (u and v) in the form of elliptical analysis. the comparison between field measurement data (red line) and the model result (blue line) shows the same surface elevation phases (fig. 6). the rmse calculated is 17.76 % which shows a slight error identified from the model developed. based on the tidal measurement, the tidal type of mandeh bay is mixed tide prevailing semidiurnal, it was also determined by (mukhtar et al., 2016). there are some different phases according to model validation in fig. 5 where the elevation is not uniform at the neap tidal condition (green ellipses). during the neap conditions, the astronomical forces become weaker than the spring conditions, resulting in the external forces predomination. that is why 98 wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 during the neap tidal conditions, the fluctuation is more erratic (qarnain et al., 2014). fig. 7 depicts the current velocity components comparison between the model result and field measurement in the form of vector magnitude and direction. the current velocity ranged from -0.2 up to 0.28 m.s-1 and from -0.1 up to 0.12 m.s-1 for field measurement and model result respectively. the direction differentiation approximately 15 degrees predominates east-northeastward and westsouthwestward. the ellipsoid velocity components analysis is also depicting that the tidal current is a rotary cycle which it rotates continuously 360 degrees during the tidal period. the rotation of tidal current is caused by the depended on its location, inducing the different current speed as the tidal regime takes place (poulain, 2013). moreover, the local factors also have a role in triggering the current speed formed. the rotary current is shown in fig. 6 which shows a series of arrows representing the current direction and speed at each hour. offshore rotary currents which are originally semidiurnal reiterate the elliptical pattern every 6 hours and 12 minutes. furthermore, there are clear relationship times of currents and times of tides in the locality (antony and unnikrishnan, 2013; boon, 2004). fig. 6 model verification using surface elevation data fig. 7 model verification using elliptical velocity component analysis. wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 99 3.3 tidal current simulation during neap tidal conditions (fig. 8), the current speed ranged from 0-0.023 m.s-1 and 0-0.024 m.s-1 for flood and ebb respectively. at high neap tidal condition, the current flowed from southward and rotated in the bay mouth followed by the increasing speed (ranging from 0.007-0.023 m.s-1) due to narrowed area and the existence of several isles. the direction rotates almost 180 degrees within the bay. furthermore, the water masses flowed from northward via cubadak strait ranged from 0.0070.012 m.s-1 become weak after passing the narrowed strait, resulting in the low current speed within the bay. at low neap tidal condition, the current direction predomination flowed toward the southwest. due to the changes in surface elevation during the replacement of tidal condition, the tidal current flows outer ward the bay through straits around cubadak island. the highest speed during ebb tide ranged from 0.004-0.013 m.s-1 right in the bay mouth and cubadak strait (fig. 8). the current speed is slightly different between flood and ebb during neap tidal condition. the current direction within the bay is oppositely rotated almost 180 degrees during the replacement of tidal condition showing that the influence of tidal ellipse parameters takes place. this regime is strongly related to transport mechanism occurred within the bay supported by the bottom morphology creating variations of current speed propagation. at spring high tidal condition (fig. 9) the current speed ranged from 0-0.04 m.s-1 which the current direction dominantly towards the northeast. the current flows from sea to inner bay via the straits around cubadak island. tidal current from south and west enter the bay significantly suffering deformation of speed and direction. the rendezvous of two sources of water mass occurred within the bay where the mixing of two water masses takes place. the opposite condition happened during low spring tidal condition which the current speed becomes higher ranged from 0-0.05 m.s-1. tidal current flows separately towards the southwest (out of the bay) due to elevation change. the highest speed is observed in the bay mouth ranged from 0.017 0.05 m.s-1. during the neap tidal condition, the flow velocity is mostly weaker than spring condition because of the moon, sun, and earth gravity forces which are upright resulting in the weakened current generation (bayhaqi et al., 2018; lazure et al., 2009; van rijn, 2011). the long tidal wave from the deeper ocean will propagate and release the energy in the shallower waters, resulting in the tidal dominated coastal. in the semienclosed area of mandeh bay, tidal regime takes place which rotates as the elevation changes caused by earth rotation and astronomical forces alteration. the rotation is reiterated according to the tidal type which will move in and out of the bay. this strongly influences turbulence, mixing, and water mass dynamic as well (bayhaqi et al., 2018). tidal current penetrates deeper during ebb than flood tide which causes a significant variation of distributed materials over the ebb-flood tidal cycle, resulting in the insignificant residual changes. this shows that at low tidal condition both neap and spring the transport mechanism is maximally supported by the higher current speed. the strongest currents are observed in the bay mouth where the tidal current patterns are topographically influenced by the shallow subtidal delta platform (the existence of sutan, sironjong gadang, and sironjong ketek islands). consequently, local differences in tidal current pattern and drift velocities contribute to the residual sediment transport within the bay. this is obvious why sedimentation issues are the main problem occurred in mandeh bay that directly disrupt the fisheries and marine tourism activities. tidal current propagations are strongly influenced by the bathymetry profile. mandeh bay categorized into shallow water area which the morphology is uneven ranged from 0-214.54 meters depth. this uneven profile induces the variability of bottom friction which has a big role in hampering the surface current flow. bottom friction also controls the magnitude of velocity components which it varies over the seabed depended on the bathymetry profile (ffield and gordon, 2002). when the surface elevation decreased and the current speed enhanced, bottom friction becomes stronger triggering turbulence and mixing in the water column. 3.4 tidal current ellipse parameters analysis fig. 10 depicts the two major semidiurnal and the two major diurnal tidal constituents from our harmonic analysis of tidal current simulation. the reference ellipse for two major semidiurnal tidal constituents has 0.1 m.s-1 radius, while for two major diurnal tidal constituents the radius only 0.05 m.s-1. the predominant constituent is m_2 which is the principal lunar semi-diurnal tidal constituent. overall, m_2 semi-minor axes are primarily negative which most ellipses rotate clockwise. the counterclockwise rotated m_2ellipses are very narrow with semi-minor axes not exceeding 0.01 m.s-1. the maximum phase of tidal current m_2 ranges from 109-117 degrees within the bay and 118-181 degrees in the bay mouth. there is a general increase of the phase values eastward, with several exceptions at some of the southernmost ellipses within the bay and in the bay mouth, where the pattern is fickler. this condition probably is influenced by the bottom morphology and the other physical factors taking place locally such as internal tides that possibly occurred due to the existence of several basins and trenches in the surrounding (mller et al., 2012). the second most obtrusive constituent is s_2 which is the principal solar semi-diurnal tide. the maximum s_2current speed approximately one third the speed of m_2. the highest speeds of s_2 have also observed in the bay mouth reached 0.24 m.s-1. the semi-major axes of the s_2ellipses within the bay (excluding the northernmost ellipses) are oriented more/less zonally. the southernmost ellipses beside mandeh peninsula are oriented more meridionally. in the bay mouth, the ellipses are oriented along the channel. 100 wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 fig. 8. tidal current pattern during neap high tidal condition (left) and neap low tidal condition (right) fig. 9. tidal current pattern during spring high tidal condition (left) and spring low tidal condition (right). wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 101 the phase of s_2 tidal current is quite variable, showing the unclear propagation pattern compared to that we see in the phase of m_2 tidal current, this is also defined by stanton et al. (2001). however, values in the bay mouth and within the bay ranged from 105 to 283 degrees. the two main diurnal tidal constituents k_1 and o_1 have the maximum speeds approximately one fifth of m_2 magnitude. due to the low magnitudes of diurnal tidal constituents, the phase and orientation cannot be well interpreted the tidal current ellipse fluctuations where the accuracy of the derived tidal ellipse parameters decreased as the constituents become weaker (stanton et al., 2001). the orientation of the ellipses of the diurnal constituents is quite erratic within the bay. in the cubadak strait and within the bay beside mandeh peninsula, the diurnal ellipses are oriented more meridionally. however, we did not observe the maximum current speeds which tend to be uniform. the maximal tidal current speeds of n_2 and l_2, the larger lunar elliptic and smaller lunar elliptic constituents, are approximately one fourth and one sixth of the maximal average speed of m_2. the higher harmonic tidal constituents are all relatively weak which the maximal current speed for m_4, m_6, and m_8 are respectively one ninth, one twelfth, and one fifteenth of m_2 magnitude. fig. 10. tidal ellipses of the two main semi-diurnal tidal constituents (𝑀2 and 𝑆2) and the two main diurnal constituents (𝐾1 and 𝑂1). black ellipses rotate clockwise, and red ellipses rotate counter clockwise. 102 wisha, u.j., dhiauddin, r., and gemilang, w. a./ jgeet vol 04 no 02/2019 4. conclusion the current speed observed is higher in the surface which gradually rotates clockwise bottomward due to the influence of spiral ekman. the vertical profile of current is reflecting the vertical transport mechanism in mandeh bay where the north, east, and up velocity have a special influence of vertical water mass movement. offshore rotary tidal currents which are originally semidiurnal reiterate the elliptical pattern every 6 hours and 12 minutes which it penetrates deeper during ebb than flood tide causing a significant variation of distributed materials over the ebb-flood tidal cycle, resulting in the insignificant residual changes. the strongest current speeds are observed in the bay mouth where the tidal current patterns are topographically influenced by the shallow subtidal delta platform (the existence of sutan, sironjong gadang, and sironjong ketek islands). this condition also affects the elliptical variation of tidal current constituents where mandeh bay is predominated by semidiurnal constituents (m_2 and s_2). the current speed of m_2 is the highest at all which the s_2 speed is averagely one third of m_2 magnitude. thus, this may trigger a higher sediment distribution and accumulation within the bay because of the twice tidal oscillations entering the bay. this study will be more appropriate if the adcp measurement is fully covering the bay by which the vessel moored adcp survey is possible to be conducted. the estimated tidal constituents which have relatively high uncertainties, lead us 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h., wehde, h., 2018. analysis of tidal currents in the north sea from shipboard acoustic doppler current profiler data. cont. shelf res. 162, 1 12. https://doi.org/10.1016/j.csr.2018.04.001 wang, a. jun, ye, x., xu, x. hui, yin, x. jie, xu, y. hang, 2018. settling flux and origin of particulate organic carbon in a macro-tidal semi-enclosed embayment: luoyuan bay, southeast china coast. estuar. coast. shelf sci. https://doi.org/10.1016/j.ecss.2017.03.023 yanagi, t., shimizu, m., nomura, m., furukawa, k., 2003. spring-neap tidal variations of residual flow in tokyo bay, japan. cont. shelf res. https://doi.org/10.1016/s02784343(03)00102-x © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. materials and methods 2.1 field measurement and flow model simulation 2.2 tidal harmonic and ellipses analysis 3. result and discussion 3.1 sea current profiles in mandeh bay 3.2 model validation 3.3 tidal current simulation 3.4 tidal current ellipse parameters analysis 4. conclusion acknowledgment references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 47 spatial statistical analysis for potential transit oriented development (tod) in jakarta metropolitan region herika muhamad taki 1, *, mohamed mahmoud h. maatouk 1,2 1 department of urban and regional planning, fed, king abdulaziz university, jeddah, 21589, saudi arabia 2 department of architecture, minia university, egypt * corresponding author : htaki0001@stu.kau.edu.sa tel.:+6285780173756; +966543591911 received: jan 11, 2018. revised : feb 2, 2018, accepted: feb 25, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.1091 abstract spatial planning on transit oriented development (tod) concerns with the integration between land use and transportation aspects. however, in some places, public transport management based on transit nodes such as train services which are not wellintegrated, and causing spatial chaos, especially surrounding station areas. it is essential to prepare a public transportation plan by maximizing regional potential capacity with tod model. the purpose of this paper is to identify and prioritize potential areas for tod using spatial statistical analysis with combined models of geographic information system (gis) and analytical hierarchy process (ahp) for jakarta metropolitan regional (jmr), indonesia. this paper employed two major indicators: mainand sub-indicators depending on relevant references. the weight of each indicator was determined by chosen experts. the result showed that some of the metro areas of jakarta were highly suitable for tod the potential location of tod and was applicable to other areas within the same geographical conditions. keywords: transit oriented development (tod), geographic information system (gis), analytical hierarchy process (ahp), spatial statistical analysis, jakarta metropolitan region (jmr). 1. introduction the use of public transportation such as railway is one of the important characteristics of urban growth (mohajeri and amin, 2010; taki, 2017). many urban planning in the world relates to public service based transportation facilities that defined as compliance in the needs of present and future generations (javadian et al., 2011; m z lubis et al., 2017). moreover, rapid population growth and migration require the provision of public transport facilities as a primary need. however, in some places, the transportation management of the railway is not well integrated resulting inconveniences of city life, especially the surrounding area of the station. for example, traffic congestion, environmental pollution, unnecessary longer travel time, high fuel consumption. for this reason, it is very important to plan a public transportation such as railway that move fast by carrying maximum number of passengers to reach the maximization of the potential area (sunarto, 2009; taki et al., 2017a). this is the part of the city development in the transportation sector, especially the renewal of stations or rail networks in accordance with the transit oriented development (binglei and chuan, 2013; feudo, 2014; galelo et al., 2014). tod is a city development concept where attempts are made to incorporate various functional activities (mixed-use) in the area around the transit station to the extent of a pedestrian reachable radius (i.e. ± 400-800 m or equal to mileage on foot for 10 minutes). tod has the goal of creating a green environment that is comfortable, safe, pleasant and sufficient for pedestrians (walkable environment). by mixing the various functions of the activities, the needed traveling can be combined to be shorter and faster. these functions are central to commercial areas, offices, retail, service, density to medium density as well as public open space. (hasibuan and soemardi, 2014) consider tod emphasizes the integration of area-based transits, renewing individualist community and living structures. this study has two objectives. first was to develop a method of spatial statistical analysis using ahp techniques (nguyen et al., 2015; lubis et al., 2017). this approach, integrating various assessment criteria from experts including the criteria of transport facilities, urban environment, and economic performance. this research helped identify the most potential sites for tod. second objective was to apply this method in the context of gis by conducting case studies in the metropolitan area of jakarta. the spatial statistical analysis was employed to obtain a land suitability grouping for specific uses. the spatial statistical classification in one area may differ with other areas depending on the land use under mailto:htaki0001@stu.kau.edu.sa 48 taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 consideration. spatial analysis for tod using gis and ahp was a geographical process used to determine the feasibility of area (whether it was potential or not) for the use of tod. 1.1 study area jakarta metropolitan region (jmr) or called jabodetabek located in java island, indonesia (fig. 1). the region of jmr includes jakarta-bogordepok-tangerang-bekasi municipality. jmr is an integrated urban area between jakarta and its surrounding area, one of the top ten metropolitan areas in the world and the largest metropolitan area in southeast asia. based on data from bps (statistik, 2011) shows that jmr in 2010 has a population growth of 27 million people and 7.5 million units of motor vehicles. the number of trips from botabek to jakarta can be quantified as much as 1.1 million trips/day. percentage of transportation mode used: private vehicle, 62.2% (private cars and motorcycles) and public transportation 12.9% (buses and trains). the commuters from botabek to jakarta are highly dependent on the railway and highway network facilities. 2. methods 2.1 data sources data collected in this study derived from the ministry of transportation, ministry of agrarian and spatial planning, central bureau of statistics, geospatial information agency. the range of data between 2010-2016 and the type of data was; first, ahp data were the primary data from interviews and questionnaires answered by 12 experts of various scientific fields related to this research for giving weight value of each indicator and subindicator. secondary data in the form of gis spatial data and attribute data, consisting of population statistic data, administrative boundary, land use, and transportation. 2.2 determination of selective criteria determination of the criteria and sub criteria of the land suitability assessment for tod was carried out by selecting and seeking for the appropriate criteria and sub criteria. it obtained from previous research and interviews by experts. these criteria and their references were; transport related (mohajeri and amin, 2010; taki et al., 2017b; atkinson-palombo and kuby, 2011), facilities services (olaru et al., 2011; ratner and goetz, 2013; vale, 2015), urban environment (binglei and chuan, 2013; black et al., 2016; prasertsubpakij and nitivattananon, 2012) and economic performance (fard, 2013; singh et al., 2014; taki and lubis, 2017) 2.3 methodology overview the applied methodology was a combination of ahp and gis technique involving the following major steps (fig. 2): fig. 1 the metropolitan region of jakarta taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 49 fig. 2 methodological framework of tod 2.4 ahp pairwise comparison ahp provides steps to ensure the credibility of relative significance used mathematically. the consistency ratio index (cr) in equation 2 can be calculated based on the nature of the reciprocal matrix. according to saaty (1990) that if cr <0.10, it indicates that the matrix of pair-wise comparison has acceptable consistency. hence, the weighting value is valid. however, if cr > 0.10, this means that the pairwise ratio shows a lack of consistency or the matrix in which it should be modified. 𝑐i = 𝜆𝑚𝑎𝑥 − 𝑛/𝑛 − 1 (1) where; 𝑐i = consistency index n = the number of items being compared in the matrix 𝜆𝑚𝑎𝑥 = the largest eigen value 𝑐r = 𝑐i/𝑟i (2) where; 𝑐r = consistency ratio index 𝑟i = random consistency index table 1. 𝑟i for n = 10 (saaty, 1990)(saaty, 1990) 2.5. standardized criteria using z-score z score is a standard score of the distance of a value of the sample or population in the standard deviation unit. it is generally used to change raw scores obtained from the different types of measurements. the z-score also tells how much distance the score itself with mean. the formula for calculating the standard score is given on equation 3 below: z = (x-µ) / σ (3) where; x = score, µ = mean, σ = standard deviation 2.6. land suitability assessment land suitability evaluation of the food and agriculture organization (fao, 1976) was adopted for land suitability assessment of potential tod in which the fao's classifications proposed 'appropriate' (s) and 'unsuitable (n) classes. the equation 4 was used to combine evaluation criteria (factor) according to weighted linear combination method. where; wi = the result of multiplication of all related weights in the factor hierarchy level ri = the standard assessment of each pixel assigned to the class on the criteria map n = the number of criteria under element 2.7. spatial statistical analysis spatial data used in this analysis are coordinated grids on the map or pixels form from 50 taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 the satellite image. thus, the spatial statistical analysis is presented in the form of a thematic map. spatial distribution patterns are generally divided into three groups (random, uniformed, and clustered). 2.7.1. spatial autocorrelation analysis (global moran's i statistic) for identifying existence of spatial clusters autocorrelation measurement that can be applied at intervals related to a point or area. for area data, the coefficient equation of moran (equation 5) is as follows: (5) where, n is the number of cases. x is the mean of the variable. xi is the variable value at a particular location. xj is the variable value at another location. wij is a weight indexing location of i relative to j. 2.7.2. hot spot and outlier analysis (getis-ord gi* and anselin local moran's i statistics) for mapping spatial clusters hot spot analysis (getis-ord gi *) is contained in the mapping cluster set to identify statistically and formulated as equation 6 follows: (6) where, wij is a spatial weight matrix element and (d) is the spatial object spacing element, while xj is the attribute value for feature j in distance d. 3. results 3.1. classification of assessment criteria this study identifies the following criteria (table 2) as an indicator of suitability assessment in the selection of potential sites for the development of tod. the assessment for this location is based on four main-criteria and 20 subcriteria selected. table 2. classification of assessment criteria taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 51 3.2. criteria maps for tod suitability analysis the map of potential tod's assessment criteria is compiled based on a gis database of 20 subcriteria (fig. 3-6). the process of map analysis conducted using overlay technique is to unite all layers of the map into a joined and comprehensive layer. hence, it presents a result map that shows a potential suitability map of potential tod in the final stage. fig. 3 transportation-related fig. 4 facilities services fig. 5 urban environment fig. 6 economic performance 3.3. c alculation of criteria weight by ahp this study uses the opinion of experts in their fields to assess the relative importance of the selected criteria. there were 12 experts and they were required to answer and submit their opinions through a set of questionnaires, which consist of contained pairwise comparisons of the 4 main criteria and 20 sub criteria (table 3 and 4). table 3. the weight of criteria from 12 experts and calculation of weight e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 terminal 0.22 0.21 0.29 0.22 0.19 0.41 0.41 0.41 0.13 0.13 0.13 0.40 3.16 0.26 1 transportation facility 0.09 0.08 0.14 0.33 0.32 0.16 0.16 0.16 0.41 0.41 0.41 0.25 2.89 0.24 2 main road 0.12 0.13 0.14 0.09 0.10 0.21 0.21 0.21 0.11 0.11 0.11 0.10 1.65 0.14 3 airport and seaport 0.28 0.33 0.09 0.08 0.10 0.10 0.10 0.10 0.15 0.15 0.15 0.12 1.74 0.14 4 busway shelter 0.18 0.15 0.24 0.17 0.16 0.07 0.07 0.07 0.13 0.13 0.13 0.07 1.58 0.13 5 tollgate 0.11 0.11 0.11 0.12 0.14 0.05 0.05 0.05 0.07 0.07 0.07 0.06 0.98 0.08 6 inconsistency 0.09 0.09 0.08 0.08 0.09 0.03 0.03 0.03 0.06 0.06 0.06 0.09 population density 0.45 0.41 0.34 0.40 0.29 0.46 0.46 0.46 0.44 0.44 0.44 0.23 4.82 0.40 1 cbd 0.35 0.24 0.25 0.27 0.18 0.25 0.25 0.25 0.21 0.21 0.21 0.19 2.85 0.23 2 industrial 0.14 0.11 0.14 0.20 0.33 0.15 0.15 0.15 0.18 0.18 0.18 0.23 2.15 0.17 3 commercial and business 0.23 0.19 0.18 0.05 0.08 0.07 0.07 0.07 0.06 0.06 0.06 0.13 1.25 0.10 4 real estate 0.08 0.06 0.09 0.07 0.11 0.07 0.07 0.07 0.11 0.11 0.11 0.23 1.18 0.10 5 inconsistency 0.09 0.08 0.06 0.05 0.08 0.04 0.04 0.04 0.01 0.01 0.01 0.09 school 0.08 0.05 0.08 0.09 0.23 0.59 0.59 0.59 0.50 0.50 0.50 0.24 4.06 0.34 1 education and public facility 0.48 0.53 0.42 0.41 0.52 0.20 0.20 0.20 0.23 0.23 0.23 0.14 3.78 0.32 2 recreation facility 0.25 0.28 0.33 0.38 0.16 0.08 0.08 0.08 0.08 0.08 0.08 0.36 2.26 0.19 3 hospital 0.20 0.14 0.16 0.12 0.09 0.13 0.13 0.13 0.19 0.19 0.19 0.26 1.90 0.16 4 inconsistency 0.05 0.06 0.08 0.09 0.06 0.02 0.02 0.02 0.01 0.01 0.01 0.08 far 0.07 0.11 0.09 0.49 0.49 0.48 0.48 0.48 0.28 0.28 0.28 0.48 4.03 0.34 1 bcr 0.36 0.33 0.21 0.31 0.31 0.10 0.10 0.10 0.11 0.11 0.11 0.13 2.28 0.19 2 formal housing 0.18 0.18 0.22 0.06 0.06 0.17 0.17 0.17 0.21 0.21 0.21 0.16 2.00 0.17 3 informal housing 0.13 0.14 0.17 0.09 0.09 0.12 0.12 0.12 0.26 0.26 0.26 0.13 1.90 0.16 4 park 0.26 0.24 0.31 0.05 0.05 0.13 0.13 0.13 0.13 0.13 0.13 0.11 1.78 0.15 5 inconsistency 0.09 0.09 0.06 0.09 0.09 0.07 0.07 0.07 0.05 0.05 0.05 0.01 iv urban environment 0.13 ii economic development 0.31 iii facilities services 0.17 sum weight ranking i transportationrelated 0.40 no main-criteria weight sub-criteria experts 52 taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 table 4. (cont.) the weight of criteria from 12 experts and calculation of weight 3.4. land suitability map for potential tod all criteria values were standardized by the zscore method using arcgis software (fig. 7-8). each main-criteria had a different land suitability pattern. the highest index was found in the urban environment (4.0) and the lowest index was found in transportation related (0.0033). variations pattern of land suitability map consisted of the spread points (facilities services and urban environment), area-polygon (economic development) and line buffer (transportation related). the red color showed the altitude value of the suitability, otherwise the blue colour indicated the lowness of land suitability value. fig. 7 criteria map fig. 8 suitability map for potential tod 4. discussion 4.1. the distribution of potential tod using suitability analysis result based on the suitability map (fig. 8) of potential tod, suitability analysis conducted a comparative class analysis based on percentage and proportion of the study area (table 5). it is permanently not suitable class (n2) has the biggest percentage (36,4%) with wide area about 7609.97 ha. the highly suitable class (s1) only has 2.3% of the study area with wide area about 74.69 ha. thus, tod planning is focused in areas with highly suitable categories. taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 53 table 5. the distribution of potential tod based on percentage and area 4.2. descriptive statistical analysis table 6 of descriptive statistical analysis indicated mean and standard deviation values for each main criteria and potential tod index. the highest of mean (2.17) and standard deviation (1.04) was facilities services, while the lowest of mean (0.00) and standard deviation (0.00) was transportation related. all the indexes were positive, indicating high index value. otherwise, there were no low negative index. table 6. the descriptive statistics of main criteria. 4.3. spatial statistical analysis 4.3.1. spatial autocorrelation using global moran-i the calculation results of global moran's i statistic can be seen that the value of z-score = 4,838 > z0.99 = 2.58. therefore, h0 is rejected or the conclusion that there is spatial autocorrelation. the moran index is 0.247 in the range 0 < i indicates a positive spatial autocorrelation. it concluded that inter area each other have similarity values or indicate that data in the clustered (fig. 9). fig. 9 the standard normal distribution. 4.3.2. high/low clustering using getis-ord general g analysis result of high/low clustering using getis-ord general g shows that the z-score value of 19.6713 with p-value 0. based on the result can be stated that the spatial tod index in the region has a global pattern or a clustering trend or highs cluster because there are no spatial clustering feature values. this happens because the p-value is small and statistically significant, so the value of the z-score becomes important. if the z-score is positive, it shows high value clustered in the research area (high cluster). conversely, if the zscore is negative, it shows low values clustered in the study area (low cluster). 4.3.3. cluster and outlier using anselin local moran's i cluster area based on a difference global moran's tod index is a measure that has not been able to show in the area where cluster occurs. therefore, the test continues using moran scatterplots (fig. 10 and 11). the results show that most areas are in the lh (low-high) and hl (highlow) quadrant, which has a high index and is surrounded by low neighbouring areas and vice versa. fig. 10 moran scatterplot fig. 11 mapping cluster 4.3.4. hot spot and cold spot analysis using getis-ord gi* based on hot spot results map using getis-ord gi * statistic in fig. 12, there are 7 groups of interval classes in each class distribution describing distinct colour intensity levels in each color. the higher intensity of color indicates that the area has a high spatial concentration, also with the surrounding area (for areas with hot spot status), in contrast with areas that have cold spot status (blue color). 54 taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 fig. 12 mapping hot spot 4.3.5. the statistically significant hot spots fig 13 show some areas in red color. it means that the area being the centre of the hot spot of the potential tod index. statistically significant hot spots have been identified at a 99% confidence. the significant hot spots cluster in fig 14 indicates that the area has a high value and is surrounded by high-value areas. those areas in this cluster are the capital of jakarta, tangerang city, depok city, and the city of bogor. fig. 13 potential tod based on moran i (above) and getis gi* (below) fig. 14 potential tod index based on the statistically significant hot spots taki, h.m & maatouk, m.m.h/ jgeet vol 03 no 01/2018 55 4.3.6. policy directives in accordance with the results of the abovementioned analysis, some development directives can be compiled as an internal policy election potential area of tod in jakarta metropolitan region. first, the policy of making land zoning of each sub-district on a more detailed scale, so there should be comprehensive regulation on the land allocation to the developed area. second, the building permit regulation/policy in areas classified as hot spots to keep the tod area around the station from disordered land use. 5. conclusion based on the analysis of research on spatial statistical for potential tod area in jakarta metropolitan region (jmr), it can be concluded that there is spatial regularity of tod area class in the study area. where area with high tod index tend to concentrate in the middle of city, while area class with low tod index tend to show spatial spread patterns. central jmr especially the capital of jakarta along with tangerang city, depok city, and bogor city have a tod distribution pattern that belongs to highs cluster. the pattern of tod distribution in the territory of the region has a strong relationship with the level of urban development and regional economy in accordance with the selected research criteria. this indicates that there is a higher development of the city and the economy of the region compared to the surrounding area. spatial planning that can be done to organize this tod area is by directing the arrangement of the developed region according to the allocation of land use, regulate the built area and the supporting policies contained in the regulation. the use of the spatial autocorrelation method using gis and combined with ahp in the planning of potential areas of tod has advantages because it can give the description of the high significance level and spatial clustering of hot spots among criteria to provide sharper spatial analysis. references atkinson-palombo, c., kuby, m., 2011. the geography of advance transit-oriented development in metropolitan phoenix, arizona, 2000 2007. j. transp. geogr. binglei, x., chuan, d., 2013. an evaluation on coordinated relationship between urban rail transit and landuse under tod mode. j. transp. syst. eng. black, j., tara, k., pakzad, p., 2016. planning and design elements for transit oriented developments/smart cities: examples of cultural borrowings. procedia eng. fao, 1976. a framework for land evaluation, fao soils bulletin n.32. doi:m-51 fard, p., 2013. measuring transit oriented development: implementing a gis-based analytical tool for measuring existing tod levels. fac. geoinformation sci. earth obs. univ. twente. feudo, f., 2014. how to build an alternative to sprawl and auto-centric development model through a tod scenario for the north-pas-de-calais region? lessons from an. transp. res. procedia. galelo, a., ribeiro, a., martinez, l., 2014. measuring and evaluating the impacts of tod measures searching for evidence of tod characteristics in azambuja train line. procedia-social behav. hasibuan, h., soemardi, t., 2014. the role of transit oriented development in constructing urban environment sustainability, the case of jabodetabek, indonesia. procedia environ. javadian, m., shamskooshki, h., momeni, m., 2011. application of sustainable urban development in environmental suitability analysis of educational land use by using ahp and gis in tehran. procedia eng. 21, 72 80. doi:10.1016/j.proeng.2011.11.1989. lubis, m.z., anurogo, w., gustin, o., hanafi, a., timbang, d., rizki, f., saragih, d.a., kartini, i.i., panjaitan, h.c., yanti, m.t., 2017. interactive modelling of buildings in google earth and gis: a 3d tool for urban planning (tunjuk island, indonesia). j. appl. geospatial inf. 1, 44 48. lubis, m.z., taki, h.m., anurogo, w., pamungkas, d.s., wicaksono, p., aprilliyanti, t., 2017. mapping the distribution of potential land drought in batam island using the integration of remote sensing and geographic information systems (gis), in: iop conference series: earth and environmental science. iop publishing, p. 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development, integration of land use and transport, and pedestrian accessibility: combining node-place model with pedestrian shed ratio to evaluate. j. transp. geogr. 1. introduction 1.1 study area 2. methods 2.1 data sources 2.2 determination of selective criteria 2.3 methodology overview 2.4 ahp pairwise comparison 2.5. standardized criteria using z-score 2.6. land suitability assessment 2.7. spatial statistical analysis 2.7.1. spatial autocorrelation analysis (global moran's i statistic) for identifying existence of spatial clusters 2.7.2. hot spot and outlier analysis (getis-ord gi* and anselin local moran's i statistics) for mapping spatial clusters 3. results 3.1. classification of assessment criteria 3.2. criteria maps for tod suitability analysis 3.3. c alculation of criteria weight by ahp 3.4. land suitability map for potential tod 4. discussion 4.1. the distribution of potential tod using suitability analysis result 4.2. descriptive statistical analysis 4.3. spatial statistical analysis 4.3.1. spatial autocorrelation using global moran-i 4.3.2. high/low clustering using getis-ord general g 4.3.3. cluster and outlier using anselin local moran's i 4.3.4. hot spot and cold spot analysis using getis-ord gi* 4.3.5. the statistically significant hot spots 4.3.6. policy directives 5. conclusion references 403 forbidden<br> http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 56 heriyanto et al./ jgeet vol 04 no 01/2019 research article regression model in transitional geological environment for calculation farming and production of oil palm dominant factor in indragiri hilir riau province heriyanto 1, *, detri karya 2 , tiggi choanji 3 , asrol 1 , djaimi bakce 1 , elinur 4 1 department of agribussines, universitas islam riau, jl. kaharuddin nasution no.113 pekanbaru, 28284. indonesia. 2 department of economics, universitas islam riau, jl. kaharuddin nasution no.113 pekanbaru, 28284. indonesia. 3 department of geological engineering, universitas islam riau, jl. kaharuddin nasution no.113 pekanbaru, 28284. indonesia. 4 department of agribussines, universitas riau, jl. bina widya km 12,5 simbang baru. pekanbaru, 28293. indonesia. * corresponding author : heriyanto@agr.uir.ac.id tel. 082388011877 received: january 1, 2019; accepted: february 20, 2019. doi: 10.25299/jgeet.2019.4.1.2600 abstract palm oil commodity is plantation sub-sector commodity which can increase the income of farmers and communities, providers of raw material processing industries that create added value. cultivated by smallholders self consists of land area, peatlands tidal, coastal peatlands and coastal lands. differences typology of this land will contribute to the different productions. generally, this study aimed to analyze the factors of production and farming oil palm, according to the typology of land specifically aimed to analyze the production and cultivation of oil palm as well as the dominant factor affecting the production kalapa smallholders' according to the typology of the land and to formulate policy implications of oil palm development patterns of the people in indragiri hilir in riau province. to answer this research analyzed with descriptive statistics and build a multiple regression model with dummy variables ordinary least square method (ols). memperlihatan research results that palm oil production and farming on land typology highest compared with tidal peat, peat coast, and coastal lands. oil palm farming income on a non-pattern land typology best compared with other lands (peat tides, coastal peatlands, and coastal land). the dominant factor affecting the production of palm oil in indragiri hilir is the amount of fertilizer, labor, plant age, herbicides, and soil typology dummy land. policy implications development of oil palm plantation in indragiri hilir in order to increase production, productivity and farm income oil palm can be through the construction of roads production, provision of means of production and palm oil processing industry to shorten the distance and shorten the time of transport that tbs of oil palm plantations to the factory. furthermore, the use of fertilizers, labor and land typology is very responsive to tbs production. therefore, in the farming of oil palm cultivation should follow the recommended technical. keywords: dominant factor, palm oil, farm, land typology, geological transitional environment 1. introduction development in the plantations directed to further accelerate the pace of production growth both from estates, private and state plantations and nucleus estates of the people as well as plantations that are managed independently to support the construction industry, as well as improving the use and preservation of natural resources in the form of land and water , the role of such a large plantation sector to the increased use of farmers and provision of raw materials for the domestic industry as well as a source of foreign exchange (heriyanto, 2017). sub particularly palm oil plantation sector has a tremendous opportunity to be a mainstay on exports as a source of foreign exchange, increase the income of farmers and communities, providers of raw material processing industries that create added value. also, oil palm plantations are also a significant source of food and nutrition in the menu of the population, so that their scarcity in the domestic market was highly significant in the economic development and welfare of the community (laelani, 2011). riau province as one of the provinces that have the most significant oil palm plantations in indonesia, in 2017 extensive farming area reached 2.7765 million ha with a production of 9.0714 million tons spread over twelve districts and the city (badan pusat statistik, 2017). the plantations are managed in the third form of business entity are: (1) large estates managed by the state-owned enterprises which is managed by pt. perkebunan nusantara v, (2) national estate plantations managed by large private companies, and (3) community plantations managed by households in the form of individual businesses or generated independently. http://journal.uir.ac.id/index.php/jgeet heriyanto et al./ jgeet vol 04 no 01/2019 57 oil palm plantation in indragiri hilir keep fifth place in riau province. according to the statistic plantations of oil palm in indragiri hilir in 2013 covering an area of 109 017 ha with a production of 249 604 tonnes and in 2017 increased to an area of 117 820 ha with a production of 721 084 tonnes grown by 79 545 heads of families spread across the region indragiri hilir and supported by 12 palm oil mills (pks). district which has the largest oil palm plantation is the district-wide kemuning with 39.388 ha with a production of 117.243 tons of which are managed by 34 363 heads of households, while the district has an area of oil palm plantation is the smallest sub-district of kuala indragiri 39.00 ha area with production 57.00 ton managed by the 35 heads of households (badan pusat statistik, 2016a, 2016b). it is based overlaying (overlay) spatial plan map riau province sk. 673 dated 29 september 2014 primarily to map spread plantation that the spread of plantations folk/self-help in indragiri hilir is in the status of forest and non-forest. in the non-forested area that is in the tutorial use other, the which is an area that is free to use, while in forest areas items, namely in the area of conversion forest and production forest the use of the which is governed by forest legislation is so difficult, getting legality or proof of ownership of land. problems faced by oil palm farmers self-help in indragiri hilir is a matter of technical and socioeconomic problems. technically oil palm plantation development in wetland areas, especially land is wetlands including marginal land, the land synonymous with acid sulfate, has the nature of physics, chemistry and biology are worse than the mainland. constraints on the development of wetlands, among others, land conditions are not uniform and dispersed locations, making it difficult to control pests and diseases as well as control the pattern of water. wetlands have lower productivity and extremely low compared to the mainland (tim ipb, 1192; hardjoso dan darmanto, 1996 in noor, 2004). socially and economically that the cost of development and maintenance of the garden in a swamp area is more significant than in the mainland, in a swamp area is identical to the high cost of transport for the transport rely on water, high prices of inputs of production factors, the high cost of care and maintenance as well as the inexpensive price of fresh fruit bunches of oil palm independent smallholders. the factors of production influence production of palm oil, the optimal use of production factors will provide the optimal production. oil palm plantations is different from other commodities, because it requires the plant close to farmers, so that the fruit produced can be immediately sent to a factory (within ± 24 hours) so that the quality of the oil does not contain a high fatty acid (gatto et al., 2017; harahap et al., 2017). the existence of palm oil mills in indragiri hilir not fully able to be reached by the farmers, the majority of factories are in the typology of land so that farmers typology of wetlands (peat tides, coastal peat and coastal), which still relies on water transportation and land takes longer and greater costs. as for the factors of production in oil palm farming consists of: natural or land, means of production and labor. cultivated by smallholders self consists of land area, peatlands tidal, coastal peatlands and coastal lands. the typology of this land will contribute to a different production to the unquestionable factors that influence the pattern of non-oil palm production. based on the review above in general, this study aims to farm and dominant factor production on environmental conditions precipitation geological transitions in indragiri hilir riau province specifically aimed to analyze production and farming oil palm, the dominant factors affecting the production of oil palm according to the typology of land and formulate policy implications of oil palm development patterns of the people in indragiri hilir riau province. 2. plantation development and land typology 2.1 plantation development concept the concept of agricultural development includes land resources, plasma nuftah, water, technology, and finance and human resources. agricultural development aims to improve the income and welfare of farmers through increased agricultural production. besides increasing agricultural production to meet the raw material in the domestic industry that continues to grow also aims to increase foreign exchange earnings from agricultural exports. as one of the steps that can be done to enhance the contribution of agriculture sector is the plantation crop production (soekanda, 2001). development in agricultural covering several developmental stages, namely: (1) traditional agriculture, ie agriculture is still extensive and not maximizing current input (2) agriculture transitional, which is a step in the transition from traditional agriculture (subsistence) to agriculture modern and (3 ) dynamics agriculture (modern) agriculture is already doing specialization of certain plants using capital intensification, with the production of labor-saving technologies pay attention to economies of scale (economies of scale), i.e. with how to drink it cost to get certain advantages. 2.2. land typology concepts land can be defined as an area on the surface of the earth, covering all components of the biosphere that could be considered permanent or cyclical located above and below the region, including the atmosphere, soil, parent rock, relief, hydrology, plants and animals, as well as any consequences caused by human activity in the past and now all of which affect the land use by humans in the present and future (brinkman and anthony, 1973; champ and charles edward date, 1976). the land could be seen as a system composed of (i) the structural components are often called land characteristics, and (ii) a functional component that is often called the land quality. land quality is essentially 58 heriyanto et al./ jgeet vol 04 no 01/2019 a group of elements of land (multiple attributes) that determine the level of capabilities and suitability. the use of land for agriculture, in general, can be divided into land use annuals, annual, and permanent. land use seasonal crops mainly for seasonal crops in the rotation pattern can be with or intercropping and harvest each season with a period typically less than one year. the annual cropland use is the use of longterm crop as the results of the plant are the no longer productive economy, such as in plantation crops. directed permanent land use on land that is not cultivated for agriculture, such as forests, conservation areas, urban, rural and ingredients. agricultural land according to the physical form and its ecosystem can be divided into two major groups, namely wetlands and dry land. 2.2.1 dryland dryland is land that is used for agricultural business using limited water and usually expects from rainfall. this land has diverse agro-ecosystem conditions, generally sloping with conditions of land stability that are less or sensitive to erosion, especially if processing does not pay attention to the principles of soil conservation. dryland is generally in the highlands (mountainous areas) which are characterized by undulating topography and are recipients and infiltrants of rainwater which are then channeled into a low level, either through the surface of the land (river) or through the earth's groundwater network. dryland farming according to physical conditions can be distinguished: a. the fields, the fields are dry farming land that is moving. the fields can be concluded in the fields of land a farmer has not made the preservation of soil fertility. the increase in land productivity occurs naturally only, therefore if productivity returns are not going well, then generate grassland widely. farming business system (shifting cultivation) this is one attempt waste of natural resources of land b. upland, the moor is a continuation of the farming system; this happens if the forest that may be opened for agricultural business activities is no longer possible. the upland farming properties are already settled. c. gardens, gardens are permanent farms/farms, which are planted permanently / permanently, both in kind and in mixed. d. the yard, the yard is a piece of farming land that is around the house which is limited by a live hedge or dead fence. e. ponds, ponds are one of the wet business fields but are in dry environments. ponds can be divided into two types, namely a pool of still water and running water. farming in ponds is usually carried out continuously with a production period of around 36 months. fish farming in ponds is commercial and there are also only for family purposes. 2.2.2 wetlands wetlands or lowlands are areas where the soil is saturated with water, either permanent or seasonal. according to (noor, 2004), wetlands or lower lands are a swamp, brackish, peat, or other water bodies either naturally or artificially whose water flows or is inundated are fresh, brackish, saline including marine areas which are low in water at low tide no more than six meters. within the limits of the ramsar convention that reservoirs, ponds and rice fields are included in the wetland group. according to (noor, 2004) which is included in the wetland group is: a. swamp swamp/marsh is a wetland area that is always flooded naturally because the drainage system is not good or is located lower than the surrounding area. swampland, scientifically continuous or seasonal stagnant water either naturally or manmade, including marine areas that are less than 6 m in water during low tide, namely swamps and tidal land). b. peatlands according to the epistemology, peat is a type of material or organic material that is naturally buried in a wet or saturated state. pedologically, peat is a form of terrestrial land whose morphology and characteristics can be influenced by organic matter (ananto, 2017; ananto and pasandaran, 2007; ardi and teddy, 1992; daryono, 2009; noor, 2010; safriyani et al., 2016; sodik et al., 2016; sulaeman and abdurachman, 2002; suriadikarta, 2009, 2012, 1969; yuliani and selatan, 2014; zurich and purba, 2014). technically and practically, peatlands can be used as agricultural land, plantation land, mining materials, swamp forests, and industrial materials and materials. peat is a type of wetland ecosystem that has various functions and benefits, especially hydrological functions. naturally, the peat ecosystem is always in a state of waterlogging, has a low ph (acid), and nutrient poor. c. coastal land the coastal area is a meeting area between land and sea, towards the land covering parts of the land which are still influenced by the characteristics of the sea such as tides, sea breeze and salt intrusion, while towards the sea covers the sea which is still influenced by natural processes in land such as sedimentation and freshwater flow and areas affected by human activities on land. the above shows that there are no real boundaries so that the boundaries of coastal areas are only imaginary lines which are determined by local circumstances. 2.3. farming concept farming is one of the activities of organizing or managing assets and natural way of farming. farming is a business activity of man to cultivate the land to obtain the results of plant or animal without causing a reduction in the ability of the land in question to obtain further results. farming can also be interpreted as an activity which organizes agricultural inputs and technologies in a business related to agriculture, in farm income, there are two elements have used that element of the income and expenditure of the farm. acceptance is the result of multiplying the number of heriyanto et al./ jgeet vol 04 no 01/2019 59 products in total with the unit selling price, while the expenditure or costs intended as the value of the use of production facilities and others issued in the production process (ahmadi, 2001). production is related to revenue and production costs, the acceptance is received by farmers because it still has to be reduced by production costs, namely the overall costs used in the production process. reception on agriculture is a production that is expressed in the form of money before deducting expenses for farming activities (mosher, 2002). next (suratiyah, 2008), income is derived from the proceeds less the total cost, with the following formula: i=tr tc (4) where: i = income (rp), tr = total revenue (rp), dan tc = total cost (rp) farming costs are all expenses that are used in farming. costs of farming are divided into two, namely fixed costs and variable costs. fixed costs are costs that magnitude does not depend on the size of the production that will be produced, while variable costs are the costs that the size is influenced by production volume. oil palm farm income analysis is done by calculating the cost of investment in fixed costs, variable costs, production, gross price revenue, and net revenue farming. interest expense, income tax expense, and the rent would be calculated if the cost of farming has been set. analysis of farming using the formula (soekartawi, 2005): tr=q x p (5) where : tr = total revenue (rp.) q = the resulting total production (kg) p = price (rp.) π = tr vc fc (6) where : π = profit (rp) tr = total revenue (rp) vc = variable cost (rp) fc = fixed cost (rp) mathematically to calculate farm income can be written as follows: =y.py σxi.pxi btt (7) where : = income (rp) y = production result (kg) py = prices of production (rp) xi = factors of production pxi = the price of production factors to-i (rp) btt = total fixed costs (rp) 2.4. dominant factors affecting productivity palm oil there are several factors that affect the productivity of oil palm plantations, the climate, the shape of the area, soil conditions, planting materials, and cultivation techniques (pusat penelitian kelapa sawit, 2006). growth and palm productivities influenced by many factors both factors that influenced natural or humaninfluenced factors. table 1. total sample oil palm farmers governmental according to land and rural typology in indragiri hilir factors that affect the productivity can be grouped into three factors, environmental factors, factors of plant material and technical culture action factor (risza, 2009). these three factors are interrelated and mutually influence each other. (risza, 2009) adding that the age of the plant, a population of plants per hectare, land preservation system, pollination system, the coordinate system of harvest-haul though, security systems of production and harvest a premium system also affects the productivity of oil palm. premium system can provide motivation for workers to increase manpower resources to achieve the expected premium target. therefore, by increasing the premiums granted an impact production increased due to the addition of labor. from the description that the factors that affect the productivity of oil palm are (1) land (topography), (2) the use of fertilizers (3) labor (4) the age of the plant no land typology subdistrict village samples 1 mainland region kemuning sekara 10 kemuning muda 11 limau manis 9 tuk jimun 2 keritang pancur 2 2 peat region tidal kemuning limau manis 1 lubuk besar 3 keritang sencalang 6 pancur 1 kempas rumbai jaya 3 harapan jaya 4 harapan tani 4 pekan tua 4 tempuling tempuling 2 karya tunas jaya 4 3 coastal peat region enok syuhada 2 tempuling sungai salak 2 batang tuaka tanjung siantar 2 reteh sungai undan 2 sungai terab 2 sanglar 3 gaung anak serka rambaian 2 sungai empat 2 4 coastal areas pulau burung pulau burung 3 pelangiran tanjung simpang kateman 4 concong kampung baru 2 total sample 92 60 heriyanto et al./ jgeet vol 04 no 01/2019 (5) the number of plant population per hectare (6) types of seed (7) the cropping pattern. fertilizer is an addition and complement to the availability of nutrients in the soil. fertilization actions are affecting levels of productivity. fertilization should pay attention to more important things, such as soil type, the age of the plant itself and weather factors that fertilization delivers maximum results. fertilization which includes fertilizers, fertilizers, manner, time and frequency of fertilization. the key to successful fertilization refers to a 5 right that is timely, appropriate dose, the right type of fertilizer, the right way and the right application where the application. the age composition of productive plants (10-15 years) compared to non-productive will lead to the fall of the productivity of oil palm. according to risza (2009) oil palm crop productivity also depends on the age composition of the plant. the wider the age composition of juvenile plants and older plants, the lower the productivity per hectare. the age composition of this plant changes every year and therefore contributes to the achievement of productivity per hectare per year (risza, 2009). 3. research methods this research was conducted in indragiri hilir riau province because it has tipology types of land, peat tides, coastal peat and coastal lands. research using multistage sampling methods sampling area concerning the spatial maps of the districts used to elect a representative (independent smallholders) in indragiri hilir can be seen in table 1 below: samples taken are subdistrict of kemuning, keritang, kempas, gaung and tempuling represent sub-district high category. district of reteh, batang tuaka and gaung anak serka representing the subdistrict and district enok medium category. kateman, pulau burung, and concong represent districts with oil palm acreage lower category. according to the typology of the village and field observations set 20 sample villages in 11 districts with a total area of a sample of 92 respondents. 3.1 data analysis to analyze the production of palm oil according to the typology of land use descriptive statistics analysis. furthermore, to analyze the dominant factors affecting the production of oil palm in indragiri hilir based typology of land use models dummy regression variable multiple ordinary least square method (ols). mathematical function regression model is as follows: y = b0 + b1 x1 + b2 x2 + b3 x3 + b4 x4 + b5 x5 + b6 d1 + b7 d2+ b8 d3 + b9 d4 + u where: y = production of palm oil (kg/year) x1= number rod (rod / ha) x2= total fertilize (kg/ha) x3= labor (hok/ha/year) x4= age plants (year) x5= herbicide (ltr/ha) d1= land type d1=0 coastal land d1=1 in addition to land peisir d2= land type d2=0 tidal peatland d2=1 peat lands addition tidal d3= land type d3=0 mainland d3=1 in addition to the mainland d4= seed type d4=0 superior d4=1 winning is not b0= intersep b1...b7= regression coefficient u= error term before the estimation of multiple regression model, the data used should be ensured free of irregularities classical assumptions for multicollinearity, heteroskedasticity, and autocorrelation (gujarati, 2008; intriligator, 1978; pindyck and rubinfeld, 2014; thomas, 1997; verbeek, 2017a, 2000). the classic test can be regarded as an econometric criterion to see if the results meet the basic classical linear estimation or not. with the fulfillment of these classical assumptions then the estimator ordinary least squares (ols) regression coefficient of linear bias is not the best estimator blue (best linear unbiased estimator) (gujarati, 2011, 2008, 2003; pindyck and rubinfeld, 1998; thomas, 1977; verbeek, 2000), that phase estimate obtained correctly and effectively. one of the assumptions that must be met to satisfy blue properties are homoskedasticity when assumptions are not met, then the opposite is true, which means that heteroskedasticity error variance is not constant. variance this constant error that does not lead to the conclusion reached is invalid or bias. in order to provide valid results in econometric necessary to test some of the assumptions of normality econometrics covering detection, multicollinearity, heteroscedasticity and autocorrelation of the equation in the regression model (gujarati, 2011, 2008, 2003; pindyck and rubinfeld, 1998; thomas, 1977; verbeek, 2000). detection of normality was conducted to determine whether the variable or normal distribution using the shapiro-wilk by the following formula (intriligator, 1978; pindyck and rubinfeld, 1998; thomas, 1977; verbeek, 2017b, 2000): w = [∑ 𝑎𝑛 ℎ 𝑖 (ẽ(𝑉−1+1)−ẽ(𝑖))] 2 ∑ (ẽ𝑖−ẽ) 2ℎ 𝑖=1 v = t k nj h = n/2 for even numbers or the (n-1) for an odd number, where: v = degrees of freedom; t = number of observations; k = number of variables; a,i n = parameters of the shapiro-wilk statistical. multicollinearity test is used to determine whether there is a correlation between the independent variables in the regression model. to detect mul multicollinearity tikolinieritas in a model made by looking at variance inflation factor (vif) to the equation, as follows (gujarati, 2008, 2003; thomas, 1977): variance inflation factor = 1/ tolerance multicollinearity problems become very serious if the variance inflation factor of greater than 10 while the multicollinearity problem is not considered serious heriyanto et al./ jgeet vol 04 no 01/2019 61 if the value is smaller variance inflation factor equal to 10. heteroskedasticity detection is used to determine whether a variant of the confounding variable is not constant for all observations. heteroscedasticity problem detection using the breusch-pagan test (pindyck and rubinfeld, 1998; thomas, 1977; verbeek, 2017b) with the following formula:   12 i 2 i zh where: h = unknown elements, which is a function derived continuously (does not depend on i) that h (.)> 0 and h (0) = 1. s = variance z = variables that affect terms disturbance variance. value statistics bruesch-pagan insignificant showed no problems heteroskedasticity. autocorrelation used to determine whether a linear regression model there is a correlation between the member observation one other observation moved at different times. to test for autocorrelation using durbin watson, with the following formula (pindyck and rubinfeld, 1998; thomas, 1977; verbeek, 2017b): d = [∑ (ê𝑡−ê𝑡−1) 𝑡=𝑛 𝑡=1 ] ∑ ê𝑡 2𝑡=𝑛 𝑡=1 where d = coefficient of durbin-watson; t = t; n = sample; e = residual. the d value obtained from comparation of du and dl value, if 0 <d <dl or 4 dl <d <4 means there is autocorrelation, when the value of d lies between dl <d <du or 4 du <d <d <dl means cannot be ensured autocorrelation, when du <d <4 du means no autocorrelation positive / negative. 4. results and discussions 4.1. palm oil production and farming peoples based typology of land production of palm oil is the result obtained by the farmers of the results of the processing of palm oil or farm management. the production is a determining factor for the amount of revenue that the farmers in addition to the price. the higher production of palm oil the higher revenue that the farmer, if the fixed price. therefore oil palm growers seek to obtain maximum production production of oil palm (non pattern) generated by each typology of different land in indragiri hilir. to determine the production of oil palm land typology can be seen in fig. 1. the table shows that the average production of palm oil self-generated patterns highest to lowest in a row on a land area of 11351.7 kg / ha / year next on peat tidal amounted 9.703,2kg / ha / year, production on peatlands discuss coast of 9344.9 kg / ha / year and the typology of coastal land for coastal 7250.5 kg / ha / year. comparison of production can be seen in fig. 1. referring to fig. 1 shows that the high production on tbs on mainland soil typology is influenced by the type of land, seed varieties, fertilizer applications, maintenance by spraying herbicides and by way of slashing. fig. 1. average production tbs based typology of land farmers on the land typology entirely land use types of seeds kind of topaz, marihat, and lonsum. while on the other land typology there that use this type of seed is not clear. on the land typology majority of farmers, land applies cropping pattern equilateral triangle, while the majority of farmers other land typologies apply to crop patterns and irregular quadrangle. at the time of planting oil palm farmers on land typology land use fertilizer as much as 52.94%, while the peat tidal typology as much as 43.75%, coastal peat as much as 29.41% and 33.33% as much coastal land.in tm-time farmers fertilizing the soil typology of land as much as 88.24%, on peatlands tidal typology as much as 18.75%, on the typology of the coastal peatlands as much as 76.47% and the typology of coastal land wholly or 100% use of fertilizers. fig. 2. palm oil production costs based typology farming land fig. 2 shows the cost of production of oil palm on peat highest tides, the next is the cost of production on the land mainland and coastal lands. the lowest production costs, namely farming coastal land peat. the high cost of farm production of palm oil on peatland tidal due to farmers on this land typology other than extraction costs also incurred costs for maintenance on the plants produce ranging from slashing weeds manually and by spraying herbicides, fertilizers, disposal and cleaning disc midrib while farmers in the typology of coastal land clearing are not spending it manually and only clear land by spraying herbicides. the high cost of labor in peatlands and coastal tidal because the distance from the house to the garden and orchard conditions, where the farther the distance from the house to the garden, the cost will increase and the higher grass or weeds growing wages. net income based typology oil palm farming land can be seen in fig 3. 62 heriyanto et al./ jgeet vol 04 no 01/2019 fig. 3. net income based typology oil palm farming land oil palm farmers' incomes are highest on mainland soil typology rp. 5,939,517.51, followed the next while on peat tidal rp. 559,143.50, coastal land rp. 350.000, and coastal peat rp. 215000. the low income of oil palm farmers self-supporting patterns caused due to the high prices of inputs and outputs as well as the length of the inexpensive price of tbs journey from the ground to the shelter (mcc) over 12 hours which resulted in the release tbs experiencing the fruit from the stalk or quote affect the selling price and additional costs to be borne by farmers. oil palm growers in the typology of the coastal peatlands did not feel the losses; this was due to revenues from the sale of tbs real wages of the work performed and the cost of depreciation of plants considered as revenue instead of an expense. net income of non-oil palm farmers in the land pattern mainland high compared to net income of oil palm on peat land tides, coastal peatlands and coastal lands. net income of farmers on the mainland average of 10.6 times higher than net income in peatland tidal and net income in land application mainland average of 116.3 times higher than the net income of farmers in coastal land. the high net income of farmers on the mainland than in other lands because (1) production of ffb in mainland land is higher than production in peatlands tidal peat production in coastal areas and coastal land; (2) the selling price of land tbs in the mainland is also higher than the selling price of ffb in peatland tides, production in the coastal peatlands and coastal lands. the high oil palm farmers' net income in the coastal area than the income of farmers in the coastal peatlands plug because the cost of production in the coastal area is relatively lower than the cost of production on peatlands coastal. 4.2. dominant factors affecting production of palm oil the results of the model estimation palm oil production factor in this study is very good as where the look of the coefficient of determination (r 2 ) is 0.6809. this shows that 68.09 percent of the variable amount of production can be explained by the variable of the principal amount, the amount of fertilizer, labor, plant age, herbicides, coastal land dummy, dummy peatland tidal land dummy land and seed type. while 31.01 percent is influenced by other variables that are not included in the model. this variation is significant at the 1 percent significance level visits of f count equal to 19.2 and probability <0.0001. results of statistical test for normality using the shapiro-wilk statistical calculations show that the results of the shapiro-wilk for palm oil production of 0.05. the value is significant at the 10 percent significance level. multicollinearity test vif value for all independent variables (number of plants, the amount of fertilizer, labor, age plants, herbicides, coastal land dummy, dummy peatland tidal land dummy land and dummy type of seed) has a value less than 10. test results heteroskedasticity show breusch-pagan statistics at 30.95 zero value on the real level of 10 percent. value durbin-watson (dw) on models built in the amount of 1.808 at n = 92 and k = 8 from table distribution dw with the real level of 1 percent was obtained dl value by 1.336 and du amounted to 1,714. his indicates that the normally distributed data, multicollinearity does not occur, not happening and not happening heterokedasity autocorrelation. regression coefficients in the model production functions are each variable independently (number of plants, the amount of fertilizer, the amount of labor, plant age, herbicides, dummy coastal land, dummy peatland coast, dummy land mainland, and dummy types of seeds) as presented in table 1. based on the table can be created multiple linear regression equation as follow: y = -3.695,122 + 31,34824 x1 + 5,9176 x2 + 28,35857 x3 + 800,2312 x4 + 138,0101 x5 -1.931,714 d1 572,7889d2 + 2.033,881 d3 -1.554,361d4. faktor dominan yang mempengaruhi produksi kelapa sawit rakyat di kabupaten indragiri hilir dapat dilihat dari hasil pendugaan model faktor dominan yang mempegaruhi produksi usahatani kelapa sawitt dapat dilihat pada tabel 2. the dominant factor affecting oil palm production in indragiri hilir can be seen from the results of the estimation model of the dominant factors affect oil palm coconut farm production can be seen in table 2. * significant at the 10 percent significance level based on the model estimation results in table 2 that there are five variables that significantly affect people's production palm oil, the amount of fertilizer, labor, plant age, herbicides and land dummy land. whereas the principal amount of plants, peat tidal parameter standard variance estimate error inflation intercept -3.695,12 4.369,68 -0,85 0,4003 0 number rod (rod / ha) 31,34824 32,61984 0,96 0,3394 1,12891 total fertilize (kg/ha) 5,9176 2,6101 2,27 0,026* 1,15698 labor (hok/ha/year) 28,35857 7,35175 3,86 0,0002* 1,16492 age plants (year) 800,2312 138,6076 5,77 <.0001* 2,08768 herbicide (ltr/ha) 138,0101 82,9744 1,66 0,1001* 1,05036 coastal land -1.931,71 1.326,81 -1,46 0,1493 1,17724 tidal peatland -572,789 889,2131 -0,64 0,5213 1,33265 mainland 2.033,88 1.060,90 1,92 0,0587* 1,952 seed type -1.554,36 1.159,24 -1,34 0,1837 1,15437 r2 =0.6809, fhitung =19.2, pr > f <0.0001, dw = 1.808 variable t value pr > |t| heriyanto et al./ jgeet vol 04 no 01/2019 63 dummy, dummy coastal land and seed type did not affect the production of oil palm in indragiri hilir. next table 2 above shows that the variables, while the number of plants, peat tidal dummy, dummy coastal land and seed type is not significant or not significant to the variable of palm oil production. the not influential factor of the number of plants for oil palm farmers self-pattern (people) in indragiri hilir applies cropping pattern and the number of plants that vary between 70-300 stems / ha, whereas the ideal number of plants between 128-143 stems/ha. this means that the addition of the principal amount of palm oil plants will not significantly affect production. coastal land also did not significantly affect production compared with another land, this is due to that the coastal land characteristics not significantly different from other land (peat tidal and inland). next peatland tidal no real effect on production compared with another land (coastal and inland), this is due to that as previously described that have almost the same characteristics the land is located between the coastal and inland area. it is also due to the manufacture of dikes, canals, sluice and the production are largely not well established, subsequent transport oil palm production in the district is largely the indragiri downstream through water transport. while these types of seedlings did not affect the production of palm oil in indragiri hilir caused difficult to distinguish between quality seeds and not superior. of seeds by farmers do not have a legal, because farmers buy seed is not a direct superior of breeding seeds but from retailers in the form of sprouts and seedlings so. viewed from the aspect of the prevailing price is still far below the price of seeds are certified. while the factors of production that have a real effect on the production are the use of fertilizers, labor, the age of the plant, pesticide and land dummy land. these five factors are outlined as follows: a. total fertilize the estimation results in the can show that data on the use of fertilizers has a positive influence on the amount of palm oil production and significantly different from zero at the 10 percent significance level so h0 is rejected and ha accepted hypothesis. this means that if the amount of one kilogram of fertilizer plus it will increase the production 5.9176 kilograms. fertilizer production facilities that have an important role in the growth of palm oil; the study was in line with (heriyanto et al., 2018; mustofa et al., 2010). growth in oil wellhead will provide palm oil production. additionally, fertilizer is a nutrient for plants that do not all provided by nature or provided by nature is not sufficient for the plant to be absorbed for the growth and the production of palm oil. given that oil palm farm in indragiri hilir majority is on marginal land. b. labor the estimation results in the data may indicate that the number of workers has a positive influence on the amount of palm oil production in indragiri hilir and significantly different from zero at the real level of 1 percent, so h0 is rejected and ha accepted hypothesis. this means that if the number of labor increases by one hok then production will also increase 28.35857 kilograms. c. mainland results obtained estimates that mainland land positive effect on the production of oil palm in indragiri hilir and significantly different from zero at the 1 percent significance level so that h0 hypothesis is rejected and ha accepted. this means that if farmers are farming oil palm on the land area of production is higher compared to another land (peatland tidal and coastal land) amounted to 2033.881 kg. this is due to that land area is the most suitable land for oil palm because it can affect the production of 14:56% and purba, 2001). d. age plants the estimation results in the data may indicate that the age of the plant positive effect on the amount of palm oil production and significantly different from zero at the 10 percent significance level so h0 is accepted and hypothesis ha rejected. this means that if the age of the plant increases, the amount of production will increase. coefficient age of the plant has a positive sign that is equal to 800.2312 which means that every increase of 1 year age of the plant will increase production amounted to 800.2312 kg/ha. it can be concluded that in the case of oil palm age in indragiri hilir are largely still in their productive age. 4.3. policy implications to achieve agricultural development policy in the plantation sector subset out in the strategic plan of the directorate general of plantation year 2015-2019, drafted a policy which consists of a common policy and technology policy. general policy aims to synergize all the resources of the estate in order to increase the competitiveness of the plantation business, value added, productivity and quality of farm products through the active participation of the community estate, and the application of modern organization which is based on science and technology and is supported by governance good. technical policy estate development aimed at improving production, the productivity of oil palm plantations. to increase the production and productivity of oil palm plantations in the governmental pattern indragiri hilir can be done in the following way: first: the expansion of the plant is done by planting oil palm on vacant land or new land by applying the latest technological innovations and adapted to the soil conditions. the development of oil palm plantations in indragiri hilir done on the typology of tidal peat, peat coast and in the coastal area. both the use of quality seeds to increase production of palm oil and palm oil productivity of the people by the pattern of nonrecommended or recommended are the type marihat, topaz, socfin and lonsum. 64 heriyanto et al./ jgeet vol 04 no 01/2019 increased production and productivity of oil palm patterns on non-productive plants in indragiri hilir be done by improving the maintenance of plants ranging from planting to produce crops to devote more manpower for maintenance by way of slashing or spraying with herbicides. furthermore, the provision of fertilizer from the time of planting to produce crops by the recommendation or suggestion that serve as additional nutrients not provided by nature and to neutralize the soil. as well as the construction of the water system as a trio of water circulation and keep the water level and avoid the intrusion of sea water. the infrastructure development of oil palm plantations can support the cultivation, post-harvest and marketing. 4.4. fertilize the estimation results in the can show that the herbicide positive effect on the amount of palm oil production and significantly different from zero at the 10 percent significance level that the hypothesis h0 is accepted and ha rejected. this means that if the herbicide increased one liter / ha, the number of production will increase. herbicides coefficient has a positive sign that is equal to 138.0101 which means that every increase of 1 liter / ha of herbicide will increase palm oil production amounted to 138.0101 kg / ha. it can be concluded that largely oil palm in indragiri hilir district, there are still palm pest weeds that have an impact on the production of palm oil. 5. conclusion based on the analysis and discussion of the conclusions of this study as follows: 1. production and productivity of land, farming land of palm oil on the mainland highest compared with peat typology tidal, coastal peat and coastal lands. oil palm farming income on a non-pattern land typology best compared with another land (peat tides, coastal peatlands and coastal area) 2. the dominant factor affecting the production of palm oil in indragiri hilir is the amount of fertilizer, labor, plant age, herbicides and soil typology dummy land. 3. policy implications development of oil palm plantation in indragiri hilir in order to increase production, productivity and farm income oil palm can be through the construction of roads production, provision 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http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. plantation development and land typology 2.1 plantation development concept 2.2. land typology concepts 2.2.1 dryland 2.2.2 wetlands 2.3. farming concept 2.4. dominant factors affecting productivity palm oil 3. research methods 3.1 data analysis 4. results and discussions 4.1. palm oil production and farming peoples based typology of land 4.2. dominant factors affecting production of palm oil 4.3. policy implications 4.4. fertilize 5. conclusion acknowledgment references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 1 2020 khoirunnisa, h. et al./ jgeet vol 5 no 1/2020 32 research article the role of decadal kelvin wave in the western of sumatra and along the south coast of java using frequency-wavenumber 2d spectral analysis hanah khoirunnisa 1,*, reno arief rachman1, nining sari ningsih2, fadli syamsudin1 1 agency for the assessment and application of technology (bppt), jakarta, indonesia 2bandung institute of technology, bandung, indonesia * corresponding author : hanah.khoirunnisa@bppt.go.id tel.: +62 85760378214; fax: +62 85742319887 received: oct 2, 2019; accepted: feb 24, 2020. doi: 10.25299/jgeet.2020.5.1.3889 abstract this study observed the decadal variability of the sea surface height anomaly (ssha) and identified the decadal kelvin wave p ropagation along west-sumatra and south coast of java. ssha data and the vertical distribution of sea temperature for 64 years based on hybrid coordinate ocean model (hycom) model resulted has already used in this research. there are several methods to identify the propagation of decadal kelvin wave. these methods were low-pass filter by cut-off 1 and 8 years, visual analytic by using hovmӧller diagram method, and frequency-wavenumber 2d spectral analysis to identify the kelvin wave propagation and its period. the decadal kelvin wave could be observed in west coast of sumatra and along south coast of java. there are three propagations of decadal kelvin wave and their velocities were 1.029x10-3 m/s (1974 – 1976), 0.21 m/s during 1985 – 1986), and 6.86x10-4 m/s for 1998 to 2001 trough west sumatra and southern java. the frequency-wavenumber 2d spectral analysis produced the improvement of kelvin wave and it has the period of 7.25 years. the occurrence of the kelvin wave has a relation to iod index. the average of the iod index when the decadal kelvin wave was occurring must be the negative value, its value was a -0.21. keywords: decadal variability, sea surface height anomaly, kelvin wave, frequency-wavenumber 2d spectral analysis 1. introduction there were several forms of variability in the indian ocean. they should be named as intra-seasonal, seasonal, inter-annual, decadal, and inter-decadal. the inter-annual variability of sea level change has been observed in the western indian ocean and also it was influenced by climate phenomenon (mahongo et al., 2014). the pacific decadal oscillation (pdo) was an example of the decadal variability has ever been observed. pdo is described as a form of el nino on climate variability in the pacific ocean. they have two-phases, it should be named as the cold and warm phase. it has a spatial and temporal scale. technically, the observation of pdo has been done in the last of the 20th century (mantua and hare, 2002). decadal variation is strongly influenced by the meteorology condition (mahongo, et al 2014). nowadays, there were three scales the seaatmosphere interaction has been known, it was named as: interannual (3 to 7 years), decadal (10 to 11 years), and inter-decadal (16 to 18 years) (mann and park, 1996; park et al, 2000). correspondingly, the indian ocean has also the decadal variability. there were inter-annual and inter-decadal variability on the ocean-atmosphere interactions in a large basin of the indian ocean. it was determined by the monthly of sst and surface wind (qian et al., 2001). the interannual variability indian ocean dipole (iod) has also the period of decadal. the decadal modulation of the iod has influenced the global climate (yuan et al., 2008). additionally, sea level anomalies along south coast of java have the decadal period (khoirunnisa, 2015). there is a correlation between thermocline depth variation and iod index (ashok et al., 2004; schott et al., 2009). the iod index was a range of the both pressures, between western of sumatra and the eastern of africa. it can be influenced the sea surface height anomaly around the india ocean (saji et al, 1999; susanto et al, 2001; khoirunnisa, 2015). the sst anomalies occur near the south coast of java and western sumatra and declining in the long term around ± 3°c (saji et al, 1999; yuan et al, 2008; sambodho et al, 2017; and wisha and khoirunnisa, 2017). similar with the iod, the sea surface height (ssh) in the indian ocean has also the decadal variability. it was observed in the year of 1992 to 2001, as well as in the period of 2001 to 2008 (church et al., 2004 in han et al., 2008). in addition to ssh data, the north indian ocean and the south indian ocean have been first observed the decadal variability of the ssta over the period of 1961 2000 (han et al., 2008). tropical indian ocean region has an important role on climate. han et al. (2008) points out that there was a decadal variability of the thermocline depth and the heat content in the tropical indian ocean during 1992 to 2008.in the indian ocean have observed a link between atmospheric circulation and monsoon or the precipitation anomalies (qian et al., 2001). this study aims to assess the existence of the decadal kelvin wave and their influence on the thermocline in the west coast of sumatra and southern java. the used methods were the visual analysis with hovmӧller diagram and frequencywavenumber 2d spectral analysis to prove the existence of the kelvin wave. 2. data and methods the data will be used is the ssha and temperature per depth along the western coast of sumatra and southern java (figure 1). these were a result of three-dimension hydrodynamic model called the hybrid coordinate ocean http://journal.uir.ac.id/index.php/jgeet khoirunnisa, h. et al./ jgeet vol 5 no 1/2020 33 model (hycom) for 64 years with a range of years from 1950 to 2013 conducted by ningsih et al. (2012). in addition, we also used the monthly indian ocean dipole (iod) index at the year of 1958 to 2010. fig.1.the research area along the western of sumatra and southern of java and lesser islands was marked up by a – h point. there are several methods to determine the decadal variability of the ssha and kelvin wave. they were the lowpass filter, hovmӧller diagram, and 2d frequency-wavenumber spectral analysis (dispersive diagram). the low-pass filter was applied by a year cut-off to remove the seasonal variability. as well as 6 and 8 years cut-off was applied to catch the decadal period of the ssha. the next method was the frequencywavenumber 2d spectral analysis (diagram dispersive) to identify the existence of kelvin wave propagation. 2.1 frequency-wavenumber 2d spectral analysis frequency-wavenumber 2d spectral analysis was used to identify the presence of kelvin wave propagation in the southern of java. it was described with a curve that was often called the dispersion curve. the kelvin wave was identified by the line of the theoretical kelvin wave. the lines can be obtained by the linear phase velocity of the kelvin wave. the dispersion relation of the wave equation can be stated as an equation 1: 𝜔2 = 𝑔𝑘 tanh (𝑘𝐻) (1) for the shallow water, 𝑘𝐻 → 0, sotanh(𝑘𝐻) = 𝑘𝐻, then equation 2 become: 𝜔 = 𝑘√𝑔𝐻 (2) in addition, the phase speed equation of the kelvin wave can be written: 𝑐 = 𝜔/𝑘 (3) where: 𝜔 : the angular frequency 𝑘 : wavenumber the equation 3 can be written again become: 𝑐 = √𝑔ℎ (4) 𝜔 𝑘 = √𝑔ℎ (5) 𝑡𝑎𝑛 ∝ = √𝑔ℎ (6) where: ∝ : the angle between𝜔 and𝑘 𝑔 : the gravitational acceleration (𝑚/𝑠 2) ℎ : the average of depth (m) c :the phase velocity (m/s) table 1. the parameters that be used in the frequency-wavenumber 2d spectral analysis. parameter value description h 0.4 km thickness of fluid layer (m) g’ 4.89 x 103 km/𝑠2 reduced gravity (m/s2) f’ 2.28 x 105 second the coriolis parameter (rad/s) at the 9os 𝑅 = √𝑔′ℎ/𝑓 1939.7 km deformation of rossby radius (m) the value of thickness of fluid layer and reduced gravity had been got from national program of the indonesian government (np), joint indonesia german indian ocean expedition (jgie), and volunteer observing ship – japanese global ocean observing system (vos-jgoos). based on roisin and jean (2008), the thickness of fluid layer was a thickness of uniform density of fluid layer. its equation can be written by:      z h (7) where: ℎ : thickness of fluid layer (m)  : density gradient(kg/m 3)  z :the change of the depth into density (m4/kg) the reduced gravity was the acceleration in the depth which has the different between its gravitational acceleration and the surface gravitational acceleration. the reduce gravity has an equation as bellows: 0 /'  gg (8) where:  : the density gradient (kg/m 3) g : the gravitational acceleration(m/s2) g′ : the reduced gravity (m/s2) 0  : the reference of density (kg/m3) 3. results and discussion 3.1 hovmӧller diagram figures 2 and 3 have shown the ssha variation along the west coast of sumatra and south coast of java during 1950 to 2013 (64 years). the right side of the figure 2shows the variation of the ssha by low-pass filter 8 years cut-off. it presents the eastward propagation of the decadal variability of the ssha with the range of 11 and 14 years. the eastward propagations were illustrated in figure 3. the eastward propagation is indicated as a decadal kelvin waves. furthermore, to make itto be sure, the last method was applied and it was called by the frequency-wavenumber 2d spectral analysis (dispersive diagram). there are three times of the eastward propagations along western sumatra and southern java. they had occurred at the year of 1974 to 1976, 1985 to 1986, and 1998 until 2001. these phase speed were1.029x10-3 m/s; 0.21 m/s; and 6.86x10-4 m/s (figure 3). fig 2. the sea level anomaly visualization has been applied by hovmӧller diagram. the raw data (up) and the low-pass filter data by 8 years cut-off (bottom right-side) and the iod index (bottom leftside). there was the relation between the occurrence of the kelvin wave and the iod index. table 2 shows that the decadal kelvin was occurred as well as the negative iod. the average of iod index when the decadal kelvin wave was occurring is a -0.21. 34 khoirunnisa, h. et al./ jgeet vol 5 no 1/2020 table 2. the relation between the indian ocean dipole (iod) index and the occurrence of the decadal kelvin wave the iod index the occurrence of decadal kelvin wave 0.035 1974 – 1976 -0.5 1985 – 1986 -0.19 1998 – 2001 2.2 frequency-wavenumber 2d spectral analysis results there was an assumptionof the decadal kelvin wave existence as well as in figures 4 and 5. nevertheless, it should be proven by some methods. it was a frequency wavenumber 2d spectral analysis. when the black linear lineis wedged by the energy spectrum, it shows the kelvin wave propagation. figure 4 is the result of dispersive diagram for non-filter data. it was reflecting the kelvin wave propagation. as well as figure 5 is the result of dispersive diagram for the low-pass filter data by 3 years cut-off. both of pictures stated that there was the existence of the decadal kelvin wave. kelvin waves which were detected by the method of frequency-wavenumber 2d spectral analysis (figures 4 and 5) have the variety period, which was 19.25 years (inter-decadal), 11 years (decadal), and 6.55 years (inter-annual). so, the eastward propagation in figure 2,could be indicated as a decadal kelvin wave propagation which has a period of 11 years. fig 3. the visual analytic byhovmӧller diagram of the low-pass filter data by 8 years cut-off of the ssha data in the western of sumatra and southern of java during 1950 to 2013. there were three eastward propagations that indicated as a decadal kelvin wave fig 4. the energy spectrum plotted by using frequency-wavenumber 2d spectral analysis (dispersive diagram) for raw data. these were several the kelvin wave energy spectrums we had proven the existence of the decadal kelvin wave trough the dispersive diagram of the ssha data. moreover, trough the energy spectrum of the temperature, the existence of the kelvin wave can be observed too. figures 6 to 9 are the plot of the energy spectrum of the temperature at a depth of 10, 80, 150, and 220 m by using frequency wavenumber 2d analysis. based on that, there were several energies that coincide to the black lines. it proves that by the energy spectrum of temperature plot could show the existence of the kelvin wave propagation. the kelvin wave was identified with a period of 3.43 and 7.3 years by dispersive diagram. meanly, it proves that in the western of sumatra and along the southern of java have the decadal of kelvin wave. in figures 6 to 9 was indicated by thedecadal kelvin wave propagation with a period of 7.3 years at depths of 10, 80, 150, and 220 m. as well as figures 6 to 9, the decadal kelvin wave has also identified with a period 0f 7,25 years by using dispersive diagram of the ssha data. fig 5. the energy spectrum plotted by using frequency-wavenumber 2d spectral analysis (dispersive diagram) for 8 years low-pass filter data. these were several the kelvin wave energy spectrums. fig 6. the energy spectrum plotted by using frequency-wavenumber 2d spectral analysis (dispersive diagram) for the depth temperature of 10 m. these were several the kelvin wave energy spectrums. fig 7. the energy spectrum plotted by using frequency-wavenumber 2d spectral analysis (dispersive diagram) for the depth temperature of 80 m. these were several the kelvin wave energy spectrums. khoirunnisa, h. et al./ jgeet vol 5 no 1/2020 35 fig 8. the energy spectrum plotted by using frequency-wavenumber 2d spectral analysis (dispersive diagram) for the depth temperature of 150 m. these were several the kelvin wave energy spectrums. fig 9. the energy spectrum plotted by using frequency-wavenumber 2d spectral analysis (dispersive diagram) for the depth temperature of 220 m. these were several the kelvin wave energy spectrums. 4. conclusion the decadal kelvin wave has been identified in the western of sumatra island and along the southern of java with a period of 19.25 (inter-decadal) and 11 years (decadal) by using the hovmoller diagram and proven by frequency-wavenumber 2d spectral analysis (dispersive diagram). thesehave phase speed (propagation velocity) as well as 1,029x10-3 m/s (1974 to 1976) and0.21 m/s (1985 – 1986). in the other way, the kelvin wave propagation can be showed by dispersive diagram of depth temperature, and its period was a 7.25 years. the occurrence of the kelvin wave has a relation to iod index. the average of the iod index when the decadal kelvin wave was occurring must be the negative value, its value was a -0.21. references clarke, c. o., p. j. webster, and j. e. cole. 2003. inter-decadal variability of the relationship between the indian ocean zonal mode and east african coastal rainfall anomalies. journal of 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(2008). decadal and interannual variability of the indian ocean dipole. advances in atmospheric sciences, 25(5), 856-866. © 2016 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 anukwu et al./ jgeet vol 02 no 02/2017 95 soil structure evaluation across geologic transition zones using 2d electrical resistivity imaging technique geraldine c. anukwu 1,2, *, a. f. adebara 1 , t.k. abodunrin 3 , a. p iwakun 3 1 department of geosciences, university of lagos, akoka, lagos, nigeria. 2 geophysics program, school of physics, universiti sains malaysia, pulau pinang. 3 department of physics, olabisi onabanjo univsersity, ago-iwoye, nigeria. abstract this study utilizes the electrical resistivity values obtained using 2-d electrical resistivity imaging (eri) technique to evaluate the subsurface lithology across different geological units. the primary objective was to determine the effect of subsurface lithology on the integrity of a road pavement, which had developed cracks and potholes at various locations. the dipole-dipole configuration was utilized and a total of nine traverses were established in the study area, whose geology cuts across both the basement and sedimentary complexes. the inverted resistivity section obtained showed significant variation in resistivity along established traverses and also across the different rock units, with the resistivity value ranging from about 4 ohm-m to greater than 7000 ohmm. the lithology as interpreted from the resistivity section revealed the presence topsoil, clay, sandy clay, sand, sand stones/basement rocks, with varying vertical and horizontal arrangements to a depth of 40m. results suggest that the geologic sequence and structure might have contributed to the observed pavement failure. the capability of the 2d eri as an imaging tool is observed, especially across the transition zones as depicted in this study. the study further stressed the ability of this technique if properly designed and implemented, to be capable of providing a wealth of information that could complement other traditional geotechnical and geologic techniques. keywords: electrical resistivity imaging, transition zone, ago-iwoye, nigeria 1. introduction 1.1 sub introduction as a means of ensuring the continuous integrity of engineering structures long after their completion, it is important that the subsurface on which such structures are built upon is properly considered. the presence of potholes, cracks, bulges/and or depressions are common occurrence along roads in southern part of nigeria. various factors have being attributed to the probable cause of failure which include poor quality construction, improper design and specification, poor drainage and improper usage, poor soil properties (onuoha et al 2014). most times, adequate attention is not given to the fact that the subsurface that provides the needed support for the road can be a major cause of failure. research have however shown that there is need to put into consideration the geology and geomorphology of the underlying earth materials as they can greatly affect the integrity of any road (ajayi, 1987; olorunfemi and meshida, 1987; momoh et al 2008 and adiat et al 2009; ayolabi and adegbola, 2013, igwe, 2015). to obtain a proper understanding of the characteristics of the underlying earth materials, various approaches can be adopted; one of such is the geophysical techniques. the advantages offered by the geophysical techniques is that they are generally non-invasive, non-destructive and of better spatial coverage (sobreira et al 2010, emujakporue, 2012). some of the geophysical techniques that can be employed to achieve the desired information for investigating subsurface conditions are: seismic refraction, seismic reflection, masw, remi, ground penetrating radar; electromagnetic method; electrical resistivity, magnetic, (wightman et al 2004; anderson, 2008). electrical resistivity techniques have been successfully applied in characterizing the subsurface for many years with applications ranging from hydrogeological, archeological, environmental and engineering studies (adepelumi and olorunfemi, 2000; rizzo et al 2005; alaia et al 2007; ariyo and adeyemi, 2012).the electrical method makes use of the response of the subsurface to current introduced into the ground via electrodes. the measurements obtained can be used to obtain apparent resistivity of the subsurface materials, from which the true resistivity can be implied. the resistivity distribution observed thus forms the basis for identifying the earth materials present in such geologic environments. resistivity * corresponding author : geraldineijeoma@gmail.com received: 11 april, 2017. revised : 2 may 2017, accepted: 31 may, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.195 mailto:geraldineijeoma@gmail.com 96 anukwu et al./ jgeet vol 02 no 02/2017 methods applied in road investigation has been reported by quite a number of researchers (momoh et al 2008; oladapo et al 2008; adiat et al 2009; emujakporue, 2012). these authors in their works utilized 1d resistivity measurements (vertical electrical sounding and/or profiling) to characterize the subsurface as well as identify faults and other geologic units that were detrimental to the integrity of the road. advances in instrumentation and computer algorithm has led to the development of 2d, 3d electrical imaging technique using multi-electrode resistivity systems which is more cost-effective and capable of providing a better representation of the subsurface (loke, 2004; kumar, 2012; metwaly and alfouzan, 2013). in the 2-d electrical imaging method, resistivity changes in both vertical and horizontal direction along the survey line are accounted for. here, the implementation of the technique involves the use of a large number of electrodes (>25). these electrodes are connected by means of a multi-core cable, which is in turn connected a switching unit (electrode selector) and to the resistivity meter. the electrode selector is capable of automatically selecting four electrodes as needed for each measurement. the study therefore aims to employ 2-d eri with its inherent advantages when compared to 1-d resistivity measurements to determine the effect of subsurface lithology on the integrity of the pavement along ago-iwoye to ishara road, which had developed cracks and potholes at various locations. as the study spans through a geological transition zones, the results presented can also serve as a guide to aid the proper deployment of techniques and solutions that can guide against the occurrence of such failures along the studied road and places with similar geological settings. 2. geological setting the study area is located between longitude n 060 57.0711 n 070 00.3811 and latitude e 0030 54.7721 e 003042.2711 respectively with an average elevation of 71 meters. the road investigated in this study is the asphalt pavement roadway from ago-iwoye to ishara passing along okegbe and imagbon villages, all in ogun state (fig.1.). the road serves as a link between the university (olabisi onabanjo university) town of ago-iwoye and another town ishara which then connects to other major cities in the southwest these includes abeokuta, lagos and ibadan. as at the time this study was conducted, the road had undergone major failures on some portion, which necessitated this study to determine the effect of the subsurface conditions on the failure of the road. rocks in the study area falls in both the basement and sedimentary complexes of sourth western nigeria, with the northwestern part (agoiwoye axis) comprising of basement complex rocks and the sourthern part (ishara axis) having sedimentary rocks. somewhere in between lies the contact between both geological zones (fig. 1.). extensive studies have been done by several authors on the geology of the southwestern nigeria, describing both rock types. the basement complex of nigeria show four distinct lithologies: etrologicgneiss complex, metasedimentary and metavolcanic rocks (the schist belts), the panafrican granitoids (the older granites), and the undeformed acid and basic dykes of the study area belongs to the schist (rahaman, 1989). fig. 1. map of the study area showing traverses and geologic boundary anukwu et al./ jgeet vol 02 no 02/2017 97 the basement rock type of the study area falls under the schist belt lithology and is made up of low grade, metasediment-dominated belts occupying n-s trending synformal troughs. they are infolded into the older migmatite-gneiss complex. on the other hand, the sedimentary part belongs to the abeokuta group, of which the following formations have been esablished: ise, araromi and afowo (omatsola and adegoke, 1981). lithologies identified in these formations include: sandstones, grits, siltstones, limestones, shales and sands. 3. materials and method the 2d electrical imaging involved the establishment of nine traverses in the study area utilizing the dipole-dipole configuration (fig. 1.). the nine traverses were along the north east direction of the expressway starting from the agoiwoye axis of the road. resistivity measurements were obtained using the supersting r8/ip 8 resistivity meter system, developed by the advanced geosciences inc., (agi). a total of 84 electrodes were deployed along a linear arraywith an electrode spacing of 2m. the acquired data can generally be displayed as pseudosections, which provide an approximate estimate of the subsurface resistivity variation. in order to obtain a true picture of the subsurface, an inversion of the data needs to be done. for our study, the res2dinv software was used to analyze the data i.e. plotting the 2d pseudosection and inversion. loke (2004) describes the algorithm used by the program for inversion, which is based on a smoothness constrained least squares approach. as a means of comparing and validating results, one of the traverses was done on the stable portion of the road which had no visible cracks and potholes as at the time of this study. the resistivity signature from this portion was compared to the others in order to confirm the resistivity signatures obtained from the subsurface. 4. results and discussion the result of the inverted resistivity sections for all traverses and their corresponding interpretation are presented in table 1. the lithological sequence inferred from the resistivity values for all the traverses shows variation in the depth to bedrock and structure which is dependent on the rock type that characterizes the location (table 1). the lithology sequence ranges includes topsoil, clay, clayey sand/sand (saturated unit), fresh bedrock. the thickness of the layers varies along the traverse, however, the maximum depth of investigation obtained is 40 m. as the traverses cuts across different geological boundaries, it is expected that the resistivity signature will vary as the resistivity value is a function of the composition amongst many other factors. the range of values obtained from the measurements, as we traverse north-eastwards toward the sedimentary boundary is presented in table 2. it is observed that the val with , the resistivity value only one of the traverses (traverse 8) falls on the sedimentary complex, as observed on the geological map (fig. 1.). the basement complex rock type ranges from migmatite, banded gneiss, porphyroblastic gneiss and granite gneiss. the highest resistivity values obtained for the basement complex rocks corresponds to that reported by olayinka and sogbetun, 2002. the relatively low resistivity ranges obtained for traverses 2, 4, 3 and 9 can be as a result of the structural features observed along the profile ranging from possible faulting and depressions. the complex interplay of lithology, even within similar geological formation is as such a paramount reason that should necessitate adequate site investigation for any infrastructure development. critical observation of the resistivity sections for possible causes of pavement failure is presented as follows. fig. 2. shows the resistivity sections of traverses 1 and 2. these traverses both fall on the basement complex, with varying degree of pavement failure. field observation revealed the presence of potholes on the road at distances 112 m to 168 m along traverse 1, while the frequency of the potholes where higher on traverse 3. the second lithologic layer exhibits a relatively low resistivity of about 64.5 ohm-m to 9.58 ohm-m for both traverses. this low resistivity layer we have inferred as clay (ariyo and adeyemi, 2012). igwe (2015) reported that the presence of large expanse of clay as one of the probable causes of pavement failure, as it might lead to differential settlement. the presence of potholes at the observed positions on traverse 1 coincides with the observed low resistivity at these positions. this low resistivity layer stretches almost all through traverse 2, a possible cause of the higher frequency of potholes along this traverse. the basement geometry for both of the traverses show marked variations. the maximum obtained resistivity for traverse 2 is far lower than that of traverse one (table 2). the resistivity of the fresh bedrock as interpreted is greater than 1000 ohm-m. the resistivity value of more than 1000 ohm-m was used as the cut off for the basement for the traverses that fall on the basement complex as has been reported in other research work in the study area (omosanya et al 2012; ariyo and adeyemi, 2012). unlike in traverse 1, in which the basement is seen to run all through the traverse, a bedrock depression is observed. ariyo and adeyemi (2012) also reported that such bedrock depressions characterize the study area, which can also be seen in on the resistivity section. also, the presence of a high resistivity material line positions 36 72m and 94 100 m; at depths of 10 20 m and 5 10 m respectively. this high resistive material we have identified as possible boulders. the resistivity values surrounding these features show values that suggests possibly saturated layers (269 698 ohm-m). the closeness of such saturated layer to the surface can lead to failure as the presence of moisture at the base/sub-base can decrease the strength of the road (igwe, 2015). 98 anukwu et al./ jgeet vol 02 no 02/2017 table 1. geoelectric layer for traverse 1 table 2. apparent resistivity range across the study area traverse layer resistivity(ωm) depth inferred lithology 1 64.5 – 167 0-2 topsoil 2 < 64.5 2 10 clay 3 167 – 699 5 – 12 sandy clay /sand 4 >1125 > 12 fresh basement 1 <1125 0-2 topsoil 2 <64.5 2 10 clay 3 167-434 10 – 40 sandy clay /sand 4 > 1125 > 12 fresh basement 1 64.5 1125 0-5 topsoil 2 9.58 – 104 2 15 clay 3 167 – 434 10 25 sandy clay /sand 4 > 1125 12 40 fresh basement 1 167 – 1812 1 10 topsoil 2 104 – 698 10 32 sandy clay/sand 3 > 1125 32-40 fresh basement 1 >167 0-5 topsoil 2 9.58 – 698 5 12 clay/clayey sand/sand 3 >1125 5 40 bedrock (sandstones) 1 9.58 – 1125 0-5 topsoil 2 9.58 – 103 3 25 clay 3 167 698 12 35 sandy clay/sand 4 > 1125 7 – 40 bedrock (sandstones) 1 64.5 – 1125 0-1 topsoil 2 9.58 – 103 1 10 clay 3 167 – 698 5 10 sandy clay/sand 4 > 1125 10 40 bedrock (sandstones) 1 103.8 – 434 0-5 topsoil 2 167 – 1182 5 10 sandy clay/sand 3 < 104 8 25 clay 4 167 – 698 25-35 sandy clay/sand 5 > 1125 31-40 bedrock (sandstones) 1 269-1125 0-2 topsoil 2 <104 2 35 clay 3 269 – 434 10 40 sand 7 8 9 1 2 3 4 5 6 geological setting traverse lowest apparent resistivity (ohm-m) highest apparent resistivity (ohm-m) rock type 1 7.55 24920 migmatite 2 3.9 2917.8 4 91.9 3156.9 banded gneiss 3 8.67 3460.3 6 6.77 22752 5 6.72 25840 7 3.45 18241 porphyroblastic gneiss 9 2.28 1723.9 granite gneiss sedimentary complex 8 12.07 1793.5 abeokuta formation basement complex anukwu et al./ jgeet vol 02 no 02/2017 99 fig. 2. inverted resistivity section (a) traverse 1 (b) traverse 3. traverse 4 was taken as control for other traverses, for as at the time of this study, this traverse length showed no visible crack or any form of failure. the lowest resistivity value is 91.90 ohmm with the inverted resistivity section of this traverse (fig. 3.) showing a relatively higher resistivity value for approximately the top 10m (weathered layer). the lithology of this traverse comprises of four layers. the first is the topsoil, followed by high resistivity layer, which we have inferred as probably sandstones. the third layer shows a resistivity of less than 537 ohm-m, this is we have inferred to be the saturated unit, while the basement closely follows at a depth of occurrence of 38m and resistivity value of about 1875 ohm-m. the stability of the pavement along this traverse is attributed to the absence of an expansive low resistivity zone and possible deep occurrence of the weathered layer. the resistivity section for the traverse that falls on the sedimentary complex (traverse 8) is shown in fig. 4a, with an inferred five layer lithology (table 1). it can be observed on the section that the layering, as expected for sediments is seen, which is absent from previous resistivity sections. from the surface to a depth of about 10m, a resistivity value above 100 ohm-m is observed, followed by an approximately 20m thick low resistivity zone (less than 25 ohm-m). this layer can be inimical to the stability of structures, as field observation of the pavement revealed the presence of potholes along this section of the road. below this layer are layers with resistivity values greater than 400 ohm-m an indication of a sandy/sandstone materials (table 1). as part of the objective of this study is to have a better understanding of the geology of subsurface, the 2-d eri was capable of imaging the lithological sequence as we transit from the geological formation to the next. although quite a number of variables are responsible for any resistivity signature observed, this study has shown that the technique is capable of distinguishing between geologies, especially as we observed a progressive decrease in bedrock resistivity as we approached the sedimentary complex boundary. the bedrock structures is clearly imaged by this technique and it can provide a potent way by which the bedrock, as well as geological boundaries can be effectively mapped. fig. 3. inverted resistivity section of traverse 4 (stable segment of the road). 100 anukwu et al./ jgeet vol 02 no 02/2017 fig. 4. electrical imaging section of traverse 8 (on the sedimentary complex). 5. conclusion and recomendation in order to understand the subsurface geology and its effect on the integrity of the ago-iwoye to ishara road of ogun state, south western nigeria, a 2-d electrical imaging (2-d eri) study was carried out. the effectiveness of the electrical survey technique is based on its ability to relate the obtained geoelectrical heterogeneity to lithological variations in the subsurface. for our study area, the number of lithogical layer inferred for traverses on the basement complex ranged from 3 to four with inferred lithology of topsoil, clay, clayey sand/sand and fresh basement. that for traverse on the sedimentary complex ranged from three to five layers, ranging from clay, clayey sand, sand, bedrock. from our study, we have identified two basic lithological sequences that could compromise the integrity of the pavements: 1. the presence of relatively very low resistivity zones as was identified on almost all the traverses, except on traverse four which as at the time of this study had no visible crack/pothole on it. the closeness of this layer to the surface, its thickness and extent can lead to differential settling, which may result in the loss of pavement integrity. 2. geological features such as basement/bedrock depression as identified on some profiles are inimical to the integrity of the subsurface as they can lead to the accumulation of water, which in turn can lead to pavement failure. furthermore, the 2-d eri was able to effectively characterize the change in lithologic sequence as we traverse from basement complex rocks to the sedimentary complex rocks. this makes the 2d eri a tool capable of providing a cost-effective and rapid view of the subsurface. in view of the possible heterogeneous nature of the subsurface, as depicted by this study, along various traverses, it is important that geophysical survey be included as one of the techniques for site investigation, prior to any construction. this is particularly paramount for structures that traverse transition zones such as this study area, as the result if properly designed and implemented can provide a wealth of information that would complement other traditional geotechnical and geologic techniques. references adepelumi, a., & olorunfemi, m. 2000. engineering geological and geophysical investigation of the reclaimed lekki peninsula, lagos, south west nigeria. bulletin of engineering geology and the environment, 582, 125-132. adiat, k., adelusi, a., & ayuk, m. 2009. relevance of geophysics in road failures investigation in a typical basement complex of southwestern nigeria. pacific journal of science and technology, 51, 528-539. ajayi, l. 1987. thought on road failures in nigeria. the nigerian engineer, 221, 10-17. alaia, r., patella, d., & mauriello, p. 2007. application of geoelectrical 3d probability tomography in a test-site of the archaeological park of pompei naples, italy. journal of geophysics and engineering, 51, 67. anderson, n. l., croxton, n., hoover, r., & sirles, p. 2008. geophysical methods commonly employed for geotechnical site characterization. transportation research e-circulare-c130. ariyo, s., & adeyemi, g. 2012. geo-electrical characterization of aquifers in the basement complex/sedimentary transition zone, southwestern nigeria. international journal of advanced scientific research and technology, 21. ayolabi, e., & adegbola, r. 2014. application of masw in road failure investigation. arabian journal of geosciences, 710, 4335-4341. emujakporue, o. 2012. geophysical investigation of the causes of highway failures in niger delta sedimentary basin a case study of the eastern part of east-west road, nigeria. scientia africana, 111, 143-152. igwe, o. 2015. the causes and mechanisms of raininduced highway and pavement collapse in obolo-eke, southeast nigeria. arabian journal of geosciences, 811, 9845-9855. k.o, o. 2012. combination of geological mapping and geophysical surveys for surface-subsurface structures imaging in mini-campus and methodist ago-iwoye ne areas, southwestern nigeria. journal of geology and mining research, 45. doi:10.5897/jgmr12.001 anukwu et al./ jgeet vol 02 no 02/2017 101 kumar, d. 2012. efficacy of electrical resistivity tomography technique in mapping shallow subsurface anomaly. journal of the geological society of india, 803, 304-307. loke, m. 2004. tutorial: 2-d and 3-d electrical imaging surveys, 2004 revised edition. metwaly, m., & alfouzan, f. 2013. application of 2d geoelectrical resistivity tomography for subsurface cavity detection in the eastern part of saudi arabia. geoscience frontiers, 44, 469-476. momoh, l., akintorinwa, o., & olorunfemi, m. 2008. geophysical investigation of highway failure-a case study from the basement complex terrain of southwestern nigeria. oladapo, m. i., obafemi, m., & ojo, s. 2008. geophysical investigation of road failures in the basement complex areas of southwestern nigeria. research journal of applied sciences, 32, 103-112. olayinka, a., & sogbetun, a. 2002. laboratory measurement of the electrical resistivity of some nigerian crystalline basement complex rocks. african journal of science and technology, 31. olorunfemi, m., & meshida, e. 1987. engineering geophysics and its application in engineering site investigations case study from ile-ife area. the nigerian engineer, 222, 57-66. omatsola, m., & adegoke, o. 1981. tectonic evolution and cretaceous stratigraphy of the dahomey basin. journal of mining and geology, 181, 130-137. onuoha, d. c. o., s. u. and obienusi, e. a. 2014. evaluating the causes of the road failure of onitsha-enugu expressway, southeastern nigeria. civil and environmental research issn 2224-5790 paper issn 2225-0514 online vol.6, no.8, pp. 1118-130. rahman, m. 1989. review of the basement geology of southwest. nigeria. geol. nigeria, 943-959. rizzo, e., chianese, d., & lapenna, v. 2005. integration of magnetometric, gpr and geoelectric measurements applied to the archaeological site of viggiano southern italy, agri valley-basilicata. near surface geophysics, 3, 13-19. sobreira, j. f. f., lipski, m., carvalho, l. a., & márquez, e. 2010. geotechnical characterization based on seismic data approaches applied in campos basin, southeastern brazilian margin. the leading edge, 297, 842-846. wightman, w., jalinoos, f., sirles, p., & hanna, k. 2004. application of geophysical methods to highway related problems. retrieved from www.cflhd.gov/agm/index.htm. 1. introduction 1.1 sub introduction 2. geological setting 3. materials and method 4. results and discussion 5. conclusion and recomendation references adepelumi, a., & olorunfemi, m. 2000. engineering geological and geophysical investigation of the reclaimed lekki peninsula, lagos, south west nigeria. bulletin of engineering geology and the environment, 582, 125-132. adiat, k., adelusi, a., & ayuk, m. 2009. relevance of geophysics in road failures investigation in a typical basement complex of southwestern nigeria. pacific journal of science and technology, 51, 528-539. ajayi, l. 1987. thought on road failures in nigeria. the nigerian engineer, 221, 10-17. alaia, r., patella, d., & mauriello, p. 2007. application of geoelectrical 3d probability tomography in a test-site of the archaeological park of pompei naples, italy. journal of geophysics and engineering, 51, 67. anderson, n. l., croxton, n., hoover, r., & sirles, p. 2008. geophysical methods commonly employed for geotechnical site characterization. transportation research e-circulare-c130. ariyo, s., & adeyemi, g. 2012. geo-electrical characterization of aquifers in the basement complex/sedimentary transition zone, southwestern nigeria. international journal of advanced scientific research and technology, 21. ayolabi, e., & adegbola, r. 2014. application of masw in road failure investigation. arabian journal of geosciences, 710, 4335-4341. emujakporue, o. 2012. geophysical investigation of the causes of highway failures in niger delta sedimentary basin a case study of the eastern part of east-west road, nigeria. scientia africana, 111, 143-152. igwe, o. 2015. the causes and mechanisms of rain-induced highway and pavement collapse in obolo-eke, southeast nigeria. arabian journal of geosciences, 811, 9845-9855. k.o, o. 2012. combination of geological mapping and geophysical surveys for surface-subsurface structures imaging in mini-campus and methodist ago-iwoye ne areas, southwestern nigeria. journal of geology and mining research, 45. doi:10.5897/jgmr12.001 kumar, d. 2012. efficacy of electrical resistivity tomography technique in mapping shallow subsurface anomaly. journal of the geological society of india, 803, 304-307. loke, m. 2004. tutorial: 2-d and 3-d electrical imaging surveys, 2004 revised edition. metwaly, m., & alfouzan, f. 2013. application of 2-d geoelectrical resistivity tomography for subsurface cavity detection in the eastern part of saudi arabia. geoscience frontiers, 44, 469-476. momoh, l., akintorinwa, o., & olorunfemi, m. 2008. geophysical investigation of highway failure-a case study from the basement complex terrain of southwestern nigeria. oladapo, m. i., obafemi, m., & ojo, s. 2008. geophysical investigation of road failures in the basement complex areas of southwestern nigeria. research journal of applied sciences, 32, 103-112. olayinka, a., & sogbetun, a. 2002. laboratory measurement of the electrical resistivity of some nigerian crystalline basement complex rocks. african journal of science and technology, 31. olorunfemi, m., & meshida, e. 1987. engineering geophysics and its application in engineering site investigations case study from ile-ife area. the nigerian engineer, 222, 57-66. omatsola, m., & adegoke, o. 1981. tectonic evolution and cretaceous stratigraphy of the dahomey basin. journal of mining and geology, 181, 130-137. onuoha, d. c. o., s. u. and obienusi, e. a. 2014. evaluating the causes of the road failure of onitsha-enugu expressway, southeastern nigeria. civil and environmental research issn 2224-5790 paper issn 2225-0514 online vol.6, no.8, pp. 1118-130. rahman, m. 1989. review of the basement geology of southwest. nigeria. geol. nigeria, 943-959. rizzo, e., chianese, d., & lapenna, v. 2005. integration of magnetometric, gpr and geoelectric measurements applied to the archaeological site of viggiano southern italy, agri valley-basilicata. near surface geophysics, 3, 13-19. sobreira, j. f. f., lipski, m., carvalho, l. a., & márquez, e. 2010. geotechnical characterization based on seismic data approaches applied in campos basin, southeastern brazilian margin. the leading edge, 297, 842-846. wightman, w., jalinoos, f., sirles, p., & hanna, k. 2004. application of geophysical methods to highway related problems. retrieved from www.cflhd.gov/agm/index.htm. http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 1 2020 sehah, et al./ jgeet vol 5 no 1/2020 37 research article a geophysical survey with magnetic method for interpretation of iron ore deposits in the eastern nusawungu coastal, cilacap regency, central java, indonesia sehah 1,*, sukmaji anom raharjo 1, azmi risyad 1 1 department of physics, jenderal soedirman university, street of dr. suparno no. 61 purwokerto, central java, indonesia. * corresponding author : sehah.geophysics@gmail.com tel.: 081-327-507517; fax: 0281-638793 received: jan 4, 2019. accepted: mar 30, 2020. doi:10.25299/jgeet.2020.5.1.2934 abstract geophysical survey with magnetic method to interpret the iron ore deposits in the eastern nusawungu coastal, cilacap regency, central java, indonesia was carried out during six month, i.e. march –august 2017, covering the area in the geographical position of 109.3462 – 109.3718 e and 7.6958 – 7.7098 s. this survey has produced total magnetic field strength data at each measuring point in the research area. the magnetic field strength data which have been obtained, then be processed, corrected, and mapped so that the local magnetic anomaly contour map can be obtained. the local magnetic anomaly contour map shows the distribution of magnetic anomalous sources in the subsurface of research area. the 2d-modeling of magnetic anomalies data has been carried out along the ab trajectory extending on the local magnetic anomaly contour map from the position of a(109.3463e and 7.7023s) to b (109.3688e and 7.7053s), so that some subsurface anomalous objects is obtained. the modelling results of magnetic anomalies data show that the research area is estimated to have the potential of iron ore deposits. the subsurface rocks deposits containing iron ore are estimated to be located below the ab trajectory with a length about of 164.85 meters, a depth ranging of 1.709 – 31.909 meters, and a magnetic susceptibility value of 0.0122 cgs unit. these rocks are interpreted as sand deposits which coexists with silt and clay containing iron ore grains from the alluvium formation. further, iron ore is also estimated to be present in the rocks deposits below the ab trajectory which have a depth of 24.405 – 49.809 meters and 3.989 – 11.111 meters, with the magnetic susceptibility values of 0.0093 and 0.0073 cgs units. keywords: geophysical survey, magnetic method, iron ore, eastern nusawungu, cilacap regency 1. introduction 1.1 background of research along with the increasing human needs, currently the exploration technology of natural resources to be developed, especially the subsurface natural resources. one method that is quite well used for exploration of subsurface natural resources is the magnetic method. this method is suitable used for exploration, especially for metallic ores and minerals (ahnin et.al. 2013 and ba dai et.al., 2014). the basic of the magnetic method is to utilize the variation of the subsurface rocks magnetic susceptibility thatmeasured on the earth's surface to interpret the geological structure or subsurface rocks physical model thatbe the target of the research. some types of subsurface rocks or geological structures that can be interpreted using the magnetic method are fold, fault,igneous rock intrusion, metallicores, geothermal reservoir,and others. one type of metallicoreswhich is commonly explored using the magnetic method is iron ore(amigun e.al., 2012 and vincent et.al., 2013). the coastal of cilacap regency have the potential of abundant iron ores. the mining activity in this area (i.e. the western coastal of cilacap regency) have produced about of 300,000 tons of iron ore concentrates per year (herman, 2005). iron ore mining which carried out over several years has resulted in decline in iron ore reserves along the coastal of cilacap regency. according to the mining and energy office of cilacap regency, currently the remaining iron ore reserves are estimated to be only 600,000 tons with iron (fe) content is less than 50%, sothat less prospect. although the large-scale mining has been closed and the former mining area was reclaimed, but the minings in small-scale still continueto this now time (antaranews.com, 2007). one area which is estimated still to store iron ores reserves is the easterncilacap regency coastal. this area include of binangun and nusawungu coastal. iron ores reserves in these areas have not been mined,with thetotal areas of more than 500 hectares, degree of magnetism is about of 12.2% and the iron (fe) content is more than 53%. overall, the iron ore reserves which have not been mined in these coastal are spreading from the welahan wetan village in binangun district to the jetis village in nusawungu district, with estimation are about 744,678.85 tons of reserves (anonim, 2015). the magnetic survey has been conducted in these coastal areas, including the widarapayung coastal (sehah et.al., 2016), the eastern coastal of binangun (sehah et.al., 2017), the western coastal of nusawungu (raharjo and sehah, 2017), and eastern coastal of nusawungu. this paper is focused to publish the results of the magnetic survey in the eastern coastal of nusawungu only. iron metal is an important raw material which has been used by almost all industries for centuries to the present. http://journal.uir.ac.id/index.php/jgeet 38 sehah, et al./ jgeet vol 5 no 1/2020 some of the uses of ferrous metal is materials for concrete construction, bridges, transportation such as trains, cars, motorbikes, and so on. aside from being a raw material for the steel industry, the nano-sized iron sand is also used as a mixture of cement, laser printer, and dry ink (toner). given the importance of the iron sand contribution in the industrial world, so necessary to investigate the potential and distribution of the iron ores which is buried in the coastal of cilacap regency, especially the areas which have not been exploitedlike the eastern coastal of nusawungu (anonim, 2015). the objective of this geophysical survey is to model the subsurface anomalies sources which are thought to contain iron ore in the nusawungueastern coastal area. one of method in the geophysical survey which suitable for exploration of anomalies sources which are thought to contain iron ore is magnetic method. the magnetic method is a geophysical exploration methodbased on the measurements of magnetic field variations on the earth surface which arise due to the distribution of nonhomogeneous magnetized rocks andminerals in the subsurface (adagunodo et.al. 2015; waswa et.al. 2015). the basic principle of the magneticmethod is to utilizevariation of measurable magnetic field valueto model subsurface anomalous objects based on their magnetic susceptibilities values. the magnetic method is suitable be used for the iron oreexploration and other metallic ore, because their magnetic susceptibilityare generally very large, so that it can be detected easily (grandis and sumintadireja, 2018). 1.2. basic theory a volume of objects such as subsurface rocks that consist of magnetic materials or magnetic minerals can be considered as magnetic dipoles as shown in figure 1 (telford et.al., 1990). the magnetization that occurs on the object depends on its track record as long as it is in the main magnetic field of the earth, or in other words depends on the magnetic induction that received from the main magnetic field of the earth. the magnitude of the magnetic potential contained at a point in the rock can be written with the equation (telford et.al., 1990).       m m 2 1 mcosθ v =-c m• =c r r (1) fig. 1. magnetic anomalies from rocks or magnetized objects in the subsurface of the earth. by integrating the equation (1) and changing the variables slightly, the magnetic potential quantity of all rock volumes can be calculated using the equation            0 m 0 1 v r =-c m r • dv r -r (2) where )(rm  in equation (2) is the dipole moment per unit volume and cm is a constant. if )(rm  is fixed and has a fixed direction, then the magnetic induction of all rock volumes can be calculated through an integration process which can be expressed by the equation             0 m 0v 1 b r =c m r • dv r -r (3) the magnetic induction field such as equation (3) is referred to as magnetic anomaly that superposed with the earth's main magnetic field (b0) at all points on the surface. thus, the total magnetic field value recorded in the magnetometer apparatus at a point on the surface is combination of the main magnetic field and magnetic anomaly (br0), with assuming that the external magnetic field is ignored. this formulation can be expressed with simple equations  t 0 0b =b +b r (4) but in reality to get the total magnetic anomaly, it is necessary to correct to the total magnetic field data that measured at each point on the surface, which includes daily correction (bd), topographic correction (bto), and main magnetic field or igrf correction (b0). if the total magnetic anomaly is denoted as b, the equation of the correction can be expressed by (stella et.al., 2015) 0 bbbb dt  (5) igrf is stands for the-international geomagnetic reference field which is the main magnetic field of the earth. the igrf value on the surface is not constant, but changes according to latitude position and time. the effect of magnetic value variation in igrf is anticipated by updating and setting igrf values regularly, i.e. every five years (macmillan and maus, 2005). 2. research method magnetic survey for exploration of buried iron ore deposits in the eastern nusawungu coastal area of cilacap regency has been carried out in march august 2017 with the location as shown in figure 2. magnetic data acquisition has been conducted covering the area in the geographical position of 109.3462 – 109.3718e and 7.6958 – 7.7098s. then processing, modeling, and interpretation of obtained magnetic anomaly data have been carried out at the geophysical laboratory, faculty of mathematics and natural sciences (mipa), jenderal sudirman university, purwokerto. several equipment which is used for magnetic surveying consists of proton precession magnetometer, global positioning system, compass, surfer 7, mag2dc 2.11 for windows software, and several other supporting equipment. the research begin with magnetic data acquisition. after the total magnetic field strength dataare obtained, then several corrections which include daily and igrf corrections are applied, so that the total magneticfield anomalies data can be obtained. the total magnetic field anomalies data is spreaded on the topographic surface, so must be reducedto horizontal surface. it is because those magnetic anomalies data cannot be processed in the next, if not distributed on the horizontal surface (blakely, 1995). then the magnetic anomalies data are corrected from the effects of regional magnetic anomaly so that the local magnetic field anomalies data can be obtained (telford et.al, 1990; mariita, 2008). sehah, et al./ jgeet vol 5 no 1/2020 39 fig. 2. the research location; the eastern nusawungu coastal in cilacap regency. the total magnetic anomalies data in equation (5) are still spreaded on the topographicsurface, so that it is a function of longitude (x), latitude (y), and altitude (h). further, the anomalies data is reduced to horizontal surface (h0) from topographic using the taylor series approximation, which can be written as equation (6). equation (6) can be written in an iterative form, where b(x,y,h0)that is a magnetic anomalies data distributed in a flat surface an be estimated through an approach;b (x,y,h0) obtained from i-thiterations can be used to obtain the value of b (x,y,h0) in the (i + 1)-thiteration. the iteration process is done sufficiently, so that the value of b(x,y,h0)which obtained shows convergence (blakely, 1995).          i n n n n i hyxb zn hh hyxbhyxb 0 0 01 0 ,, ! ,,,,         the magnetic anomalies data that have been spread in the horizontal surface is still affected by the effects of the regional magnetic anomalies. therefore the regional magnetic anomalies data must be reduced because the target of this research is a local geological structurelike iron ore deposits. the regional magnetic anomalies data is obtained through upward continuation of magnetic anomalies data which have distributed in the horizontal surface to a certain height (h0 + h), so that changing in anomalous data show a subtle trend. the equation of upward continuation for anomalies data is taken from the 2ndidentity of green theorems (blakely, 1995), whose formulation can be expressed asequation (7)      dydx hyyxx hyxbh hhyxb          2/3 222 0 0 '' ),,( 2 ),','(  (7) b (x’,y’,h0 + h) is a regional magnetic anomalies data, which is then corrected to the total magnetic anomalies data which have distributed in the horizontal surface, using the following equation (8) (stella et.al., 2013) ),','(),,( 00 hhyxbhyxbb local  (8) the local magnetic anomalies data which obtained are magnetic anomalies data that represents the subsurface conditions that are shallow (in the crust near surface). 3. results and discussion the results which obtained in this research include the results of data acquisition, the results of magnetic anomalies data processing, and the results of modeling and interpretation. 3.1. results of data acquisition and processing acquisition of the total magnetic field data has been carried out in the eastern nusawungu coastal area of cilacap, covering the area in the geographical position of 109,3462e – 109,3718e and 7,6958s – 7,7098s, with the location map as shown in figure 3. the results whichobtained are total magnetic field data (bt) at each measurement point with values ranging of 44,384.28 – 45,291.84 nt. to get the total magnetic anomaly data, thenseveral corrections and reduction were carried out as explained in the research method section. the data corrections which has been performed including of the daily correction and the igrf correction. fig. 3. the location map from google earth of research area (eastern nusawungu coastal area) which completed with the measurement points position. the daily correction is performed using the looping technique, where looping is done every two hours. and igrf correction is done using online calculations from services provided by national geophysical data center (https://www.ngdc.noaa.gov/geomag/calculators/magcal c.shtml). the results of online calculation show that the igrf value for this area is 44,998.5 nt. after apply several corrections, then the total magnetic anomalies data are obtained. these anomalies data is distributed on the topography with values ranging from -612.55 – 296.29 nt, as shown in figure 4. fig. 4. the total magnetic anomaly contour map; distributed above the topographic surface. then the total magnetic anomalies data are reduced from the topographic surface to the horizontal surface using taylor series approximation like equation (6), so the anomalies data can be processed in the next stage. the horizontal surface has been chosen at the height of average topographic,i.e. 25.63 meters above a reference spheroid, so that the iteration process to calculate the magnetic anomalies value sreach convergence quickly (blakely, 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) -600 -500 -400 -300 -200 -100 0 100 200 contour interval is 50 nt nt (6) https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml 40 sehah, et al./ jgeet vol 5 no 1/2020 1995). the magnetic anomalies data obtained from this calculation process have ranging of -478.77 – 221.62 nt with a contour map is shown in figure 5. the ranging between maximum and minimum anomalies data is relatively smaller than the ranging of anomalies data when still above the topography. this shows that the iteration process in the taylor series calculations has reached convergent, so that anomalies data which obtained is considered to have been distributed on the horizontal surface (blakely, 1995). the research target is near surface objects, i.e. iron sand deposits, so magnetic effects from deep and wide sources must be reduced. this magnetic effect is called as regional magnetic anomaly. those regional magnetic anomalies data were found through process of upward continuation of the total magnetic anomalies data which distributed on the horizontal surface to a certain height, so the ranging of anomalies data has shown a very small value and its contour map tends to remain (mastellone et.al., 2013). upward continuation process of anomalies data is done step by step; where for each upward step is equipped with anomaly contour image, as can be seen in appendix 1. visual observation is done to determine; whether anomaly contour pattern has shown regional anomaly pattern. based on this criteria,the anomaly contour as show in figure 6 isdesignated as the regional magnetic anomaly contour map, because it has shows regional pattern (ganiyu et.al., 2013). this contour has been obtained from upward continuation process at height of 2,250 meters above the reference spheroid. fig. 5. the total magnetic anomaly contour map; distributed above the horizontal surface (average topographic). fig. 6. the regional magnetic anomaly contour map which has beenupwarded to a height of 2,250 metersabove the references pheroid. the regional magnetic anomalies data that obtained then corrected to the total magnetic anomalies data that has been spread above the horizontal surface, so that the local magnetic anomalies data are obtained. thes edata have values ranging of -498.66 – 201.73 nt. the local magnetic anomaly contour map completely can be seen in figure 7. the local magnetic anomaly contour represents a geological condition near surface including the iron ore deposits in the research area. based on the results of previous research (sehah et.al., 2017) and the geological information (herman, 2005), that the cilacap regency coastal is dominated by iron sand, including the nusawungu coastal area. therefore, the magnetic anomaly contour pattern which resulted has a strong correlation with the content of iron ore in it. the local magnetic anomaly contour map obtained show several pairs of magnetic dipoles which located in the middle relatively towards the west. the objects that are sources of magnetic anomalies are estimated to be located below this zone, one of which is iron ore. this coastal area is the most eastern area of the whole area that have prospect of iron sand in cilacap regency. it is based on the geophysical survey results using magnetic method (sehah and raharjo, 2017). the research result shows that the binangun and nusawungu coastal areas are iron ore prospective areas, especially the eastern binangun and the western nusawungu coastal. while the potential of iron ore in the eastern nusawungu coastal is estimated not be as large as both areas. fig. 7. the local magnetic anomaly contour map at theaverage topographic height of research area. 3.2. results of modeling and interpretation to explore the distribution of iron ore deposits in the eastern nusawungu coastal area, anomalous object modeling has been carried out in two dimension (2d). the 2d-modeling begins by making the trajectory above the local anomaly contour through several anomalous closures which indicate dipoles pairs (lino et.al., 2018). this area is estimated to contain iron ore deposits. the 2d-modeling is done on the local magnetic anomalies data which extracted from the ab trajectory, as can be shown in figure 8. fig. 8. the ab trajectory which is placed on the local magnetic anomaly contour map with a direction of 7.73 n-w. the ab trajectory has a length about of 2,345.10 meters and stretching from position of 109.3463e and 7.7023s to 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) -500 -400 -300 -200 -100 0 100 200 contour interval is 50 nt nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) 19.83 19.85 19.87 19.89 19.91 19.93 19.95 contour interval is 0.01 nt nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) -500 -400 -300 -200 -100 0 100 200 contour interval is 50 nt nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) -500 -400 -300 -200 -100 0 100 200 contour interval is 50 nt nt a b (109.3463 e and 7.7023 s) (109.3689 e and 7.7053 s) 7.73 deg sehah, et al./ jgeet vol 5 no 1/2020 41 109.3689e and 7,7053s. the magnetic anomalies data which extracted from the ab trajectory, then referred to as observation anomalies data in the form of a curve. the modeling on the local magnetic anomalies data is done using the curve matching techniques between the observation anomaly curve versus the calculation anomaly curve. the observation anomaly curve is taken from the local anomalies data that extracted along the ab trajectory. after two curves reach a match, then eight anomalous objects are obtained in the subsurface. all objects can be interpreted as the subsurface rocks of the research area as can be shown in figure 9, including the iron ore deposits. before 2d-modeling is done, several model parameters are needed. several parameters that used in the modeling are igrf values, inclination angle, and declination angle of the research area as can be seen in table 1. the parameter values can be accessed online easily and completely through the website at: https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml table 1. the parameters which used in the 2d-modeling of the local magnetic anomalies data no parameter value 1 main magnetic field (igrf) 44.996,30 nt 2 inclination angle -32,441 3 declination angle 0,853 to interpret the subsurface anomalous objects that obtained, the average magnetic susceptibility value for the rocks in the research area must be estimated firstly based on the geological information. geologically, this research area is composed of alluvium formations and coastal sand deposits. the alluvium is composed of silt, clay, sand, and gravel containing iron ore grains;while the coastal sand deposits consist of loose sand grains which intersect with iron ore (herman, 2005). below the two rock formations is the halang formation which is composed of claystone, sandstone, marl, and tuff with breccia inserts (asikin et.al., 1992). the geological map of the research area is shown in figure 10. based on the geological information supported by simple calculation, the average magnetic susceptibility value of rocks in the research area is estimated as0.0080 cgs unit (sehah et.al., 2017). while the magnetic susceptibility value of each subsurface object can be obtained by summing the average magnetic susceptibility values of rocks to the magnetic susceptibility contrast value of each anomaly object, as be shown in table 2. based on the magnetic susceptibility values of each subsurface object which supported by the geological information of the research area, then lithological interpretation can be conducted. the results of interpretation for each anomaly object has been shown in table 2. generally, the iron ore are thought to occur in the alluvium rocks deposits near the surface (hikmatyar, 2016) such as object 1, object 2, and object 3. fig. 9. the result of 2d-modeling on the local magnetic anomalies data along the ab trajectory using the mag2dc for windows. fig. 10. the geological map of the research area which is part of geological map – sheet of banyumas central java indonesia. this research area are covered by alluvium deposits which is composed of silt, clay, sand, gravel; and coastal sand deposits consisting of loose sand grains which intersect with iron ore grains (asikin et.al., 1992). https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml 42 sehah, et al./ jgeet vol 5 no 1/2020 table 2. the results of the calculation of the magnetic susceptibility value of each anomalous object and its interpretation no. anomaly object depth (meter) magnetic susceptibility (cgs) results of interpretation top bottom   1 object 1 3.989 11.111 -0.0007 0.0073 alluvium deposits; composed of sand, silt, clay, and gravel containing iron ore grains 2 object 2 1.709 31.909 0.0042 0.0122 alluvium deposits; sand inserted with silt and clay containing iron ore grains significantly 3 object 3 24.405 49.809 0.0013 0.0093 alluvium deposits; composed of sand, silt, clay, and gravel containing iron ore grains 4 object 4 19.140 193.477 -0.0050 0.0030 the rocks from halang formation; composed of sandstone, claystone, marl, tuff, and other 5 object 5 32.289 77.842 -0.0050 0.0030 6 object 6 87.179 134.188 -0.0014 0.0066 7 object 7 94.017 285.470 -0.0066 0.0014 8 object 8 142.735 255.556 0.0096 0.0176 the rocks from halang formation; composed of sandstone, claystone, marl, tuff and other with inserted by breccia the modelling result of the local magnetic anomaly data indicate the presence of anomalous objects in the subsurface which estimated to have iron ore prospects. the anomaly object is interpreted as sand that inserted with silt and clay containing iron ore from the alluvium formation (object 2). this rock deposit has a length of about 164.850 meters, a depth of 1.709 – 31.909 meters, and the magnetic susceptibility value of 0.0122 cgs unit. this rock is located below the largest magnetic dipole pair, which indicates the large magnetic susceptibility value such as iron ore (siregar & budiman, 2015; joshua et.al., 2017). iron ore is also estimated be present in other anomaly object, that interpreted as alluvium deposit consisting of sand, clay, and gravel containing of iron ore grains (object 3). this rock deposit has length about of 376.281 meters, depth ranging of 24.405 – 49.809 meters, and susceptibility is 0.0093 cgs unit. the iron ore grains are also estimated to be found near the surface although not dominant, that are interpreted as clay, sand, silt, and gravel containing iron ore granules (object 1). this interpretation is based on its magnetic susceptibility value which relatively large (i.e. 0.0073 cgs unit) and supported by direct observation in the field. this rock stretches below the ab trajectory with a depth of 3,989 – 11,111 meters and have an important role as a buffer rocks in the coastal area. the modelling results show that the iron ore which be estimated to be present in the rocks (object 2) has formed a elongated deposits. generally iron ore grains are found along the coastal, which be formed due to the destruction of the host rock from volcanic eruptions by weather and water in the surface. the destruction rock process occurs due to heat and rain, resulting in iron mineral granules detached from the rock. furthermore, iron ore and other materials from the destruction are transported and deposited along the coastal. certain waves of sea water have sorted and accumulated these deposits into iron ore grains. most iron ore which has a large density will be deposited over the coastal, while iron ore which has a light density will be carried back by waves into the sea. this happens continuously so as to form iron sand deposits in the coastal (kurnio, 2007 and hilman et.al., 2014) as results which obtained from the modeling in this research. figure 11 shows the iron ore grains which spread unevenly in the alluvium deposits on the research area surface. most of the iron ore mineral resources in coastal are from volcanic rocks, namely andesite and basaltic rocks. geographically the research area is about 60 kilometers from slamet volcano central java, indonesia. possibility of the material from volcanic eruptions containing iron ore minerals carried by the river flows to this coastal areas, as explained before. in addition, there is a gabon formation in the eastern research area, which is often found volcanics rocks intrusion as can be shown in the geological map in figure 10. the intrusion rock material that eroded and carried by river water flow in this area is also estimated to contribute to the formation of iron ore deposits. this gabon formation is located in the karangbolong mountains which is thought to be an ancient volcano that has been lost. geographically, this area is located in kebumen district, central java. fig. 11. iron ore grains which spreaded in the alluvium deposits on the surface of the research area unevenly (source: personal documentation). exploitation of iron sand which is likely to be carried out in this research area is feared to cause rock or sand material to be reduced, so that the surface will decrease. the surface decrease results in environmental damage and increases the potential for sea water intrusion. the seawater which have large density and higher pressure becomes easier push groundwater and interface zones in the aquifer, so that intrusion can occur. in addition, the exploitation of iron sand in the coastal is also feared to result in abrasion. moreover, naturally abrasion has occurred in this region, as shown in figure 12. fig. 12. abrasion of the alluvium deposits in the nusawungu coastal area which has occurred due to the sea water waves (source: personal documentation). sehah, et al./ jgeet vol 5 no 1/2020 43 4. conclusion geophysical exploration with a magnetic method to investigate the iron ore deposits in the eastern coastal area of nusawungu, cilacap regency, central java has been carried out. based on the results of research which has been obtained can be concluded: a. the research area has the iron ore potential which is estimated to be localized below the ab trajectory with a length of 164.85 meters, a depth ranging of 1.709 31.909 meters, and magnetic susceptibility value of 0.0122 cgs unit which interpreted as sand inserted with silt and clay containing iron ore grains significantly from the formation alluvium. b. iron ore deposits are also estimated to be found in the alluvium at a depth of 24.405 – 49.809 meters with magnetic susceptibility value of 0.0093 cgs and at a depth of 3.989 – 11.111 meters with magnetic susceptibility value of 0.0073 cgs unit. c. in addition to alluvium formation, other rocks that obtained from modeling are subsurface rocks from the halang formation, with magnetic susceptibility value ranging of 0.0014 – 0.0176 cgs unit, which is composed of sandstone, claystone, marl, tuff, and other with inserted by breccia. acknowledgments thank to the ministry of research, technology, and high education republic of indonesia and the general director of high education for the research funds that provided. thank to the rector and the chairman of the research and community service institute of jenderal soedirman university for the support given. thank to the head of the geophysics laboratory of jenderal soedirman university for equipment facilities provided especially proton precession magnetometer (ppm) and other supported tools. thanks also to all the research teams, especially the students who have collaborated well and compactly in data acquisition in the field. appendix 1 (a) upward to height of 500 meters (b) upward to height of 1000 meters (c) upward to height of 1500 meters (d) upward to height of 2000 meters (e) upward to height of 2.250 meters (f) upward to height of 2500 meters appendix 1. several magnetic anomaly contour resulted from upward continuation process of the total magnetic anomalies data. the magnetic anomalies data is upwarded from a height of 500 meters up to 2500 meters above the reference spheroid. initially upward continuation process of the total magnetic anomalies data is carried out every 500 meters. however, after approaching regional conditions, the upward process is carried out every 50 meters to reach a certain height which shows a fixed contour pattern with interval anomalies values is very small. this contour map is considered to have shown regional magnetic anomalies (ganiyu et.al., 2013), as shown in part (e). 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) contour interval of 1 nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) contour interval of 0.2 nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) contour interval of 0.05 nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e contour interval of 0.02 nt 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e ( d e g ) contour interval of 0.01 nt contour has shown a regional patterns 109.350 109.355 109.360 109.365 109.370 east longitude (deg) -7.708 -7.706 -7.704 -7.702 -7.700 -7.698 -7.696 s o u th l a ti tu d e contour interval of 0.005 nt the contour pattern starts to break 44 sehah, et al./ jgeet vol 5 no 1/2020 references adagunodo, t.a., sunmonu, l.a., adeniji, a.a., 2015. an overview of magnetic method in mineral exploration. journal of global ecology and environment (jogee) 3 (1) 13 – 28. ahnin, w.m., susilo, a., sunaryo, 2013. mapping of manganese ore deposits by using geomagnetic method in aceh jaya district, nangro aceh darussalam province, indonesia. international refereed journal of engineering and science (irjes) 2 (10) 12 – 20. amigun, j.o., afolabi, o., ako, b.d., 2012. application of airborne magnetic data to mineral exploration in 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accepted: jun 19, 2019. doi: 10.25299/jgeet.2019.4.2.3171 abstract this research aimed to reveal the petrogenesis of granitic rocks of bayah complex starting from magma differentiation to exposing event, this research also intended to determine the tectonic environment. the methods carried out in this research include field observation, petrographic analysis using polarized light microscopy, and geochemical analysis using x-ray fluorescence (xrf) and inductively coupled mass spectrometry (icp-ms). petrographic analysis shows that bayah granitic rocks are composed of quartz, plagioclase, and k-feldspar while the rest are amphibole, biotite, sericite, chlorite, epidote, and opaque. based on its major oxide concentrations, bayah granitic rocks classified as granite and diorite-quartz which have high-k calc-alkaline magma. 4 samples of granitic rocks showed the a/n+k+c > 1 molar ratios belonging to the peraluminous s-type granite index while the remaining 1 sample showed a molar ratio of a/n+ k+c < 1 and a/n+k > 1 which classified as metaluminous i-type granite. accordingly, bayah granitic rocks are s-type granite which crystallized from sediment-derived magma, the sediments itself estimated sourced from continental especially malay peninsula, indonesian tin island, and schwaner mountains. during differentiation, the magma undergone crustal contamination reflected by the increase in both sio2 0.51 wt% and al2o3 1.95 wt%, and decrease in fe2o3 + mgo 0.61 wt% from the pure composition of sediment-derived magma. furthermore, the occurrence of crustal contamination also recognized from high concentrations of rb and ba which indicate the interaction of magma with the materials of continental crust. regard to the exposing event, bayah granitic rocks approximated to be exposed due to regional tectonic activity which caused orogenesa i in the early oligocene to the late oligocene. moreover, based on the plot of trace elements especially rb, y, nb, ta, and yb on harker and tectonic discriminant diagrams, bayah granitic rocks are formed on volcanic-arc active continental margins in accordance with regional tectonic setting. keywords: volcanic-arc, petrogenesis, s-type granite, magma differentiation, bayah complex. 1. introduction the presence of granitic rocks such as granite, monzonite, granodiorite and tonalite are closely related to magmatism. one of the most recognized magmatism activity in western java island is bayah magmatism which formed the bayah dome in the oligocene. the discovery of granitic rocks in bayah itself was first reported by koolhoven (1933) which later discussed also by van bemmelen (1949); sujatmiko & santosa (1992), sukarna et al. (1993), and hartono et al. (2008) known as granodiorite cihara. however, only sukarna et al. (1993) and hartono et al. (2008) discussed the geochemical signature of these granitic rocks. this research aimed to reveal the petrogenesis and environment of bayah granitic rock based on field observation, petrography, and geochemistry analyses. field data was taken from the cigaber and cisanun stream, lebakpeundeuy village, cihara district, lebak regency, banten. the location of the study itself is known as bayah complex due to the discovery of various type of rocks in the same area (patonah & haryadi, 2018; ahnaf et al., 2018). in addition, the research area also has a complex structural pattern affected by the collision of the indoaustralian plate with eurasia which at least occurred in the late cretaceous (sukarna et al., 1993; ahnaf et al., 2018). regional tectonic activity also triggers orogenesis which also contribute to complexity bayah geological setting. http://journal.uir.ac.id/index.php/jgeet ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 105 fig. 1. modified geological map of the research area after sujatmiko & santosa (1992). 1.1 geology setting the regional geology of the research area has been reported in detail by sujatmiko & santosa (1992) in the leuwidamar regional geological map and the explanatory notes. some of the rock formations located at the research area i.e. metamorphic rock, bayah formation, cikotok formation, and cihara granodiorite, whose distribution shown in fig. 1. compilation of several sources regarding the regional geology of the study area is presented as follows: metamorphic rocks: this rock group consisted of schist, quartzite, and amphibolite which can be found in the cisanun and cigaber stream. sujatmiko & santosa (1992) consider these rocks to have the age of the early oligocene to the late oligocene which in its formation related to contact metamorphism due to granodiorite intrusion which also occurs at the same age. however, the latest research e.g. patonah et al. (2014); widiaputra et al. (2016); patonah & haryadi (2018); ahnaf et al. (2018) stated that metamorphic rocks estimated to be the oldest rocks in bayah complex aged as pre-tertiary to the early eocene. furthermore, patonah & haryadi (2018) explained that metamorphic rocks found at this location reached epidote-amphibolite to amphibolite facies from the discovery of garnet and hornblende minerals which indirectly stated that these rocks formed in the regional metamorphism rather than local metamorphism due to intrusion. these metamorphic rocks come from protolith pelitic to psammite sediments and mafic igneous rocks. bayah formation: this formation divided into limestone members (tebl), claystone members (tebm), and conglomerate members (teb) (sujatmiko & santosa, 1992). around the research area, the bayah formation found to be claystone member (tebm) which consists of calcareous claystone, black claystone, shale, and sandstone. the bayah formation clearly exposed in south bayah, cimandiri, and banten beach (sukarna et al., 1993), while around the research area these rocks easily found on the cipager, cisanun, and cimuncang stream. based on the radiometric determination of u-pb, these rocks estimated to be of the middle eocene whose materials sourced from malay peninsula, indonesia tin island, and schwaner mountains (clements & hall, 2008). furthermore, bayah formation estimated that this formation 106 ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 deposited in the neritic-paralic environment and influenced several times by tectonic activity which is represented by the presence of reverse faults (sujatmiko & santosa, 1992; koolhoven, 1933; sukarna et al., 1993). cikotok formation: this formation also known as old andesite formation (oaf) (e.g. koolhoven, 1933; sukarna et al., 1993). this formation consists of volcanic breccia, andesite, basalt, and tuff. rocks from this formation exposed on the ciguling, cihara, and cimuncang stream. this formation is the oldest volcanic product that occurred in the research area (ahnaf et al., 2018) which has the age of the late eocene to the late oligocene (sujatmiko & santosa, 1992). furthermore, sukarna et al. (1993) divided this formation into lower sequence and upper sequence. the lower sequence estimated to be formed in eocene to early oligocene and has interfingering contact to bayah formation while the upper sequence formed in late oligocene to early miocene and has contact to cijengkol formation and citarate formation. this formation is quite thick and inserted with sedimentary rocks that are eocene, oligocene, to miocene aged (hutabarat, 2016). in some way this formation especially andesite and basalt are related to hydrothermal activity that led to the alteration and mineralization with low intensity. granodiorite cihara: this group of rocks composed of granodiorite, porphyry granodiorite, granite, porphyry dacite, gabro, and apalite which have the age of the early oligocene to the late oligocene (sujatmiko & santosa, 1992). this group easily recognized because it has a fairly wide distribution and easily found on the cigaber, cisanun, cipeusing, cibayawak, and cikahuruan stream. based on ahnaf et al. (2018), granodiorite cihara lifted due to orogenesis which then breaks through rocks that already exist on it. in another report, sukarna et al. (1993) assumed that this group have a younger age i.e. miocene which then known as miocene plutonic and volcanic rocks (mpv). these granitic rocks have widespread and estimated to be present in the form of batholite (hartono et al., 2008). this rock is known by van bemmelan (1949) as the bayah dome due to its intrusive shape that resembles a dome. similar to the cikotok formation, some of these rocks have been altered and mineralized in moderate intensity. 2. material and method in this research, data acquisition including field observation, petrographic analysis, and geochemical analysis. the geochemical data as primary data in this research used for determining the characteristics of magma and rock tectonic environment while petrographic data used for identifying the content, texture and paragenesis of minerals. in addition, field data useful for determining the position of granodiorite cihara rocks among other rocks around it. granitic rock samples were taken from two streams i.e. cigaber and cisanun which is represented granitic rocks in the field. a drill and geological hammers used to obtain fresh samples during sampling. these samples then sorted according to the level of oxidation, alteration and mineralization which then fresh samples of rock brought to the laboratory for petrographic and geochemical analysis. petrographic preparation and analysis carried out in the lab. petrology and mineralogy ftg at padjadjaran university, sample preparation including cutting to polishing the samples into thin sections which then analyzed under polarized light microscopy. the preparation and geochemical analysis carried out at intertek jakarta and the bandung geological survey center, this geochemical analysis used x-ray fluorescence (xrf) to obtain major oxide concentrations and inductively coupled plasma mass spectrometry (icp-ms) to obtain major and minor elements concentration including trace elements and rare earth elements (ree). 3. result and discussion 3.1 field observation field data was taken from the cigaber and cisanun stream which represented the research area because of their complete lithology including metamorphic rock, bayah formation, cikotok formation, granodiorite cihara, and quaternary volcanic rocks. as seen in fig. 2, rock outcrops found on the cisanun stream include claystone, diorite, granodiorite, amphibolite (exitu), schist, and phyllite. while from the cigaber stream consisted of volcanic breccia, andesite, granodiorite, and schist. the lithostratigraphic correlation between the two stream showed that the position of metamorphic rock is at the bottom which is then followed by the cihara granodiorite, bayah formation, cikotok formation, and quaternary volcanic rock same as stated by ahnaf et al. (2018) and patonah & haryadi (2018). the granodiorite position showed intrusions that break through the rock above such as the cikotok formation and metamorphic rock. granitic rocks (granodiorite cihara) that found on the cisanun and cigaber stream have thicknesses vary from a few meters. besides on the river, these rocks are also found on the hill. these rocks are easily recognized because of its rough texture, quartz in these rocks have size more than 2 mm which is able to observed directly. megascopic characteristics of these granitic rocks are still the same, which have medium gray in color, coarse texture, leucocratic color index, phaneritic grains, subhedral crystalline form, panidiomorphic to hypidiomorphic mineral form, sub-equigranular crystalline relationship, and hard. minerals those are identified megascopically i.e. quartz and feldspar. some of these rocks are altered and mineralized with low to moderate intensity, alteration minerals appeared including clay and chlorite while mineralization in the form of pyrite and chalcopyrite. the appearance of rock outcrops and rock handspecimen samples presented in fig. 3. ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 107 fig. 2. trajectoray of exposed rocks from cisanun and cigaber strea. fig. 3. exposed granitic rock (granodiorite) and hand specimen sample. 108 ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 fig. 4. photomicrograph of granodiorite thin section. a-b showed sample jsa-142, c-d showed sample jsa-151, e-f showed chloridized-amphibole and sericited plagioclase from sample jsa-151. identified primary minerals i.e. quartz (qz), plagioclase (pl), muscovite (ms), and amphibole (amp) while secondary quartz, chlorite (chl), and sericite (ser) appeared as secondary minerals. 3.2 petrography petrographic samples taken for analysis came from the cisanun stream (jsa-142) and cipeusing stream(jsa-151) where the cipeusing streamable to represent the cigaber stream because of its adjacent location. photomicrograph of a thin section of the rocks showed in fig. 4. jsa-142: this thin section is colorless in color, showing porphyritic to phaneritic texture, subequigranular relationship minerals, subhedral to anhedral crystals form, hypidiomorphic minerals form, primary minerals of this rock i.e. quartz, plagioclase, kfeldspar, and muscovite, while sericite, chlorite, carbonate, and opaque minerals appeared as minerals secondary. this thin section also refers to the poikilitic texture in which large mineral such as plagioclase surrounded by smaller minerals such as the quartz groundmass. the rock seems undergone alteration. this rock is ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 109 composed of 60% phenocryst and 40% groundmass. quartz, plagioclase, k-feldspar, and muscovite appeared as phenocryst while secondary/ smaller quartz and sericite as groundmass. quartz phenocryst have size of 150 microns and more, colorless, elongated to spherical subhedral, found in almost all parts of the thin section. plagioclase have size of 100 microns, colorless, tabular subhedral, some of these minerals altered into sericite, plagioclase type ranged from oligoclase to andesine. k-feldspar have size of 50 to 100 microns, colorless, tabular with subhedral to anhedral crystals, found in small amounts. jsa-151: this thin section is colorless in color, showing phaneritic texture, sub-equigranular relationship minerals, euhedral to subhedral crystals form, panidiomorph to hypidiomorphs minerals form, primary minerals making up these rocks are quartz, plagioclase, k-feldspar, biotite, amphibole while secondary minerals are present in the form of chlorite, sericite, and opaque minerals. this thin section shows indistinct perthite texture. this thin section also shows mineral alteration in weak intensity. this rock is composed of 75 % phenocryst and 25 % groundmass. quartz, plagioclase, k-feldspar, biotite and amphibole appeared as phenocryst while smaller porphyritic quartz appeared as groundmass. phenocryst quartz have size 300 microns and more, colorless, spherical subhedral, found in all parts of the thin section. plagioclase have size of 400 microns and more, colorless, tabular euhderal, some of this mineral altered into sericite, plagioclase show extinction angle ranged from 20-25 o classified as andesine. k-feldpsar have size of 50 to 200 microns, colorless, tabular subhedral, these minerals are difficult to identify because their small amount and lack of twins. this thin section also shows alteration in the presence of chlorite seen to change amphibole and sericite to change plagioclase. 3.3 geochemistry there are 5 granitic rock samples to be discussed in geochemistry scope. 3 samples from this study were from the cisanun stream (jsa-142 and jsa 141) and cigaber stream (jsa-126), while 2 other samples were from hartono et al. (2008). previous studies of granitic rocks in bayah have been discussed by hartono et al. (2008), but out of the 8 samples discussed only 2 of them were granitic rocks which in this research named uh-01 and uh-02 while the other 6 samples were volcanic rocks such as andesite, basalt, rhyolite, dacite and some of them are part of the cikotok formation. the results of xrf and icp-ms geochemical analysis from these samples listed in table 1 and table 2. 3.3.1 magma series and rock name based on the relationship between n2o + k2o (a), feot (f), and mgo (m) represented by the afm ternary diagram after irvine & baragar (1971) (fig. 5a), rocks in the study area belong to the calc-alkali magma series. due to high content of k2o, magma origin of these rocks are specified as the high-k calc-alkaline series as shown in fig. 5b. according to yuwono (2004), calcalkali series typically found in subduction/ orogenic setting, furthermore, this calc-alkaline magma could be found in island arc or active continental margin tectonic setting. table 1. major oxides in wt% and cipw norm of bayah granitic rocks. besides it also supported by typically volcanic arc with low tio2 content. 4 out of 5 samples showed very low tio2 at 0.009-0.14 wt% and one sample (uh-01) showed slightly higher tio2 at 0.56 wt%. in addition, granitic rocks in the study area have high sio2 and k2o content where sio2 ranged from 67.38-75.68 wt% with an average of 72.51 wt% and k2o ranged from 3.10-5.66 wt% with an average of 4.28 wt%. thus, based on the rock classification diagram (fig. 6), jsa-142, jsa-126, jsa-141, and uh-02 belong to granite rocks (cox et al., 1979) or more precisely monzogranite (streckeisen, 1976), while uh-01 is diorit-quartz (cox et al., 1979) which is also called granodiorite (streckeisen, 976). classification of rocks cox et al. (1979) is based on the content of sio2, k2o, and na2o while streckeisen (1976) emphasized the mineral content of quartz (q), k feldspar (a), and plagioclase (p) which in this paper determined from the cipw norm. 3.3.2 granite type and magma origin over the past two decades there have been two types of determinations of granitic rocks i.e. chappell & white (1974) and pearce et al. (1984). although they same determined the rocks based on geochemical data, there are advantages and disadvantages of the two types of determination. for example, determination based on chappell & white (1974), granitic rocks divided into i-type and s-type which are then also mtype (white, 1979) and a-type (collins et al., 1982), this classification able to represent its petrogenesis such as magma origin and indication for tectonic jsa-142 jsa-126 jsa-141 uh-01* uh-02* oxide sio2 75.55 74.28 69.68 67.38 75.68 tio2 0.11 0.14 0.105 0.56 0.009 al2o3 12.52 13.64 14.64 15.56 13.39 fe2o3 2.41 2.75 2.47 3.93 1.56 mno 0.14 0.06 0.124 0.07 0.04 mgo 0.45 0.36 0.91 1.66 0.49 cao 0.39 0.35 0.38 3.55 1.43 na2o 1.97 2.71 2.20 3.87 3.76 k2o 4.82 4.31 5.66 3.1 3.52 p2o5 0.035 0.049 0.05 0.21 0.17 cr2o3 0.02 0.02 0.01 loi 1.58 1.16 2.86 total 100.00 99.83 99.09 99.89 100.05 mineral quartz 43.31 39.89 32.25 22.46 36.41 plagioclase 18.34 24.34 20.17 48.68 37.8 orthoclase 28.48 25.47 33.45 18.32 20.8 corundum 3.45 4 4.32 1.2 diopside 0.25 hypersthene 3.19 3.06 4.34 6.47 2.56 ilmenite 0.21 0.27 0.21 1.06 0.02 magnetite 3.49 3.99 3.58 5.7 2.26 apatite 0.09 0.12 0.12 0.49 0.39 cipw norm wt% wt% 110 ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 environments. however, the determination of the tectonic environment still less convincing because only based on major elements that are relatively less sensitive in geochemistry than trace elements. table 2. minor elements concentration of bayah granitic rocks. nevertheless the advantage of this determination is the prediction of magma origin such as i-type derived from igneous rock, s-type from sedimentary rock, mtype from mantle, and a-type from anorogenic setting. in contrast, pearce et al. (1984) divide the type of granitic rock based on trace elements which is very useful in determining tectonic environments. in its division pearce et al. (1984) divided the granitic rock environment into ocean ridge granites (org), volcanic arc granites (vag), within plate granites (wpg), and collision granites (colg). thus, in this paper the two determinations of granitic rocks used where the determination based on chappell & white (1974) used to estimate magma origin while pearce et al. (1984) used to determine tectonic environments. the molar concentration of al2o3 (a), na2o (n), k2o (k), and cao (c) used to determine shand's index (shands, 1951) and the granite type chappel & white (1974). as shown in table 3, sample jsa-142, jsa-126, jsa-141, and uh-02 have molar a/cnk ratio > 1.0 and classified as peraluminous index (shands, 1951; maniar & piccoli, 1989) which also classified as s-type granite. whereas the remain sample uh-02 has a molar a/cnk ratio of <1.0 and a/nk > 1.0 and classified as a metaluminous index of i-type granite (shands, 1951; maniar & picolli, 1989). s-type granite rocks in the study area also have low na2o characteristics which are <3.2 wt% (except uh-02), corundum > 1%, and high sio2 content similar to those described by chappel & white (2001), as well as i-type granite containing na2o > 3.2 wt% and corundum < 1%. in addition, all rock samples analyzed were classified as peacock's index calcic because they contained sio2 > 61 wt% (peacock, 1931; maniar & picolli, 1989). thus the magma origin of granitic rocks in the research area estimated largely derived from sediment. however, hartono et al. (2008) reported that 3 granitic rock samples in bayah were more likely to be i-type than s-type, whereas one sample of them is peraluminous s-type granite (uh02). the results of combining data from this research and hartono et al. (2008), granitic rocks are more likely to be s-type although there is one i-type sample. accordingly the discussion of the original magma will be different from with hartono et al. (2008) that stated the origin of the granitic rocks magma is the same as cikotok formation. 3.3.3 tectonic environment determination of tectonic environments based on trace elements in accordance with those recommended by pearce et al. (1984). as shown in the harker diagram at y, rb, nb vs. sio2 in fig. 7, all rock samples have depleted y concentration of 11.00 ppm to 16.30 ppm with an average of 13.69, this low y content identical to the volcanic arc granites (vag) environment or collision granites (colg) because high y or yb commonly found in oceanic ridge granites (org) and within plate granites (wpg) (pearce et al., 1984). similar to y, the rb concentration of granitic rock samples also quite low at 42.00 ppm to 105.00 ppm with an average of 83.78 (<100 ppm). rb concentration able distinguish vag with syn-collision granites (syncolg), where rb <150 ppm more likely to be found in the vag than syncolg. the nb concentration also shows depleted trend of 3.00 ppm to 5.20 ppm with an average of 4.50 ppm, this depleted nb usually found in the vag and org. taking into account the concentrations of y, rb and nb, granitic rocks in the research area are located in the volcanic arc granites (vag) environment. furthermore, trace elements rb, y, nb, ta, and yb are plotted in the discriminant diagram after pearce et al. (1984) in fig. 8, where the plot results of each discriminant diagram show that the granitic rocks are located in the volcanic arc granites (vag) correspond to the harker diagram in fig. 7. in detail, vag divided into oceanic-thoelitic, oceanic calc-alkaline, and active continental margin type. regard to these three vag types, vag oceanic thoelitic likely not possible since all granitic rocks in this research are calc-alkaline to high-calc alkaline as shown in fig. 5. jsa-142 jsa-126 jsa-141 uh-01* uh-02* rb 115.00 108.00 109.90 42.00 44.00 sr 56.80 83.20 73.94 77.00 173.00 cs 1.70 2.00 1.52 ba 431.00 346.00 590.00 213.00 221.00 v 5.00 6.00 5.94 cr 5.00 5.00 87.00 6.00 co 2.00 2.00 ni 5.00 2.00 146.00 zn 32.00 29.00 33.00 ti 655.00 791.00 629.00 y 16.30 15.60 12.55 11.00 13.00 zr 2.30 3.00 0.01 45.00 nb 5.20 5.20 4.10 3.00 5.00 hf <0.1 0.20 ta 0.47 0.45 1.36 pb 8.00 6.00 6.75 th 7.10 6.98 6.32 4.00 5.00 u 1.25 1.11 1.15 la 15.00 17.10 12.23 10.13 9.33 ce 33.00 35.50 29.04 21.71 22.34 pr 4.15 4.38 2.41 1.98 2.59 nd 15.70 16.70 13.85 8.98 5.28 sm 3.50 3.60 2.76 2.01 2.18 eu 0.40 0.60 0.64 0.01 0.27 gd 3.20 3.20 1.85 1.50 2.24 tb 0.49 0.47 0.31 dy 2.90 2.80 1.71 1.87 2.22 ho 0.60 0.60 0.20 er 1.50 1.70 0.70 0.61 1.50 tm 0.30 0.20 0.08 yb 1.60 1.70 0.97 0.76 1.69 lu 0.26 0.27 0.06 total ree 82.60 88.82 66.80 49.56 49.64 ree incompatible/ transition hfse lfse-lile ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 111 fig. 5. (a) afm diagram (irvine & baragr, 1979) and (b) k2o vs sio2 diagram (peccerillo & taylor, 1976). fig. 6. plutonic rock classification, (a) qpa diagram (streckeisen, 1976) and (b) na2o+k2o vs sio2 dragram (cox et al., 1971). table 3. acnk content in molar%, shand's index, and granite type of bayah granitic rocks. vag oceanic calc-alkaline also not likely become the environment of the rocks considering high content of al2o3 (12.42-15.56 wt%) and low yb (0.76-1.70 ppm) which represent continental than oceanic rocks. thus, granitic rocks of bayah complex are formed in the vag active continental margin. this tectonic environment also supported b of high calc alkaline. referring to the regional tectonic setting, the bayah complex on java island is a part of the volcanic island arc thta highly affected by the collision between indoaustralian oceanic plate and sunda continental plate (part of the eurasian plate) (sukarna et al. 1993; clements et al., 2009). the collision resulted volcanism and magmatism activities, including magmatisme in bayah complex. the geochemistry of granitic rocks represented by the tectonic discriminant diagrams after pearce et al. (1984) show the suitability rock environment with the regional tectonic setting i.e. the volcanic arc. furthermore, the sunda plate is the most southeastern margin of the eurasian plate which moves south in contrast to the indo-australian plate which moves north, both plates are at least collided in the late cretaceous (sukarna et al., 1993; ahnaf et al., 2018). al2o3 (a) cao (c) na2o (n) k2o (k) jsa-142 8.184 0.464 2.153 3.410 1.358 1.471 peraluminous s type jsa-126 8.945 0.417 2.972 3.059 1.387 1.483 peraluminous s type jsa-141 9.919 0.467 2.492 4.151 1.395 1.493 peraluminous s type uh-01 10.118 4.197 4.208 2.182 0.956 1.584 metaluminous i type uh-02 8.535 1.657 4.007 2.428 1.055 1.326 peraluminous s type granite type molar % sample a/(n+k+ c) a/(n+k) shand's index 112 ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 thus it is very fitted because geochemically the granitic rocks show volcanic arc active continental margin. the southeast region of the eurasian plate known as one of the most seismically active and has a complex tectonic setting, it is not surprising that volcanism and magmatism activity have been running from late cretaceous untill the present time. 3.4 formation of grantic rocks 3.4.1 sediment source as discussed earlier, the s-type granite magma in the research area originated from sediments. by regard to regional geology, this granitic rocks known as the granodiorite cihara was formed in the early oligocene to the late oligocene (sujatmiko & santosa, 1992). by this, it could be assumed that the sediment sources are older than the early oligocene. there are only sedimentary rocks from bayah formation and cijengkol formation which are older than these granitic rocks therefore one or both of these rock formations have the same source as granitic rocks. fig. 7. harker diagrams of y, rb, and nb vs sio2 after pearce et al. (1984). fig. 8. tectonic discriminant diagrams of rb, y, nb, and ta after pearce et al. (1984). ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 113 based on the u-pb dating of zircon minerals from both formations, clements & hall (2008) stated that these two formations show similar zircon age signatures i.e. early cretaceous to middle cretaceous for bayah formation and jurassic to cretaceous for the cijengkol formation which originated from the schwaner mountains. furthermore, other zircons still from the same two formations also show similar age clusters i.e. pemian-triassic originating from the granitic rocks of the malay peninsula and indonesian tin island. thus, the bayah formation and cijengkol formation sourced from several same sources, namely the schwaner mountains, malay peninsula, and indonesian tin island which also as source for granitic rock magma in bayah complex. this statement also supported by composition of granitic rocks that geochemically originated from continental. 3.4.2 sediment accumulated, metamorphosed, melted clastic sediments from eurasia accumulated in the marine, terrestrial, and oceanic trench at the subduction between the indo-australian plate and the sunda plate. sediments accumulated in the shallow marine to terrestrial formed the bayah formation in the middle eocene and the cijengkol formation in the early oligocene while the sediments in trench are metamorphosed in various depths as metasediment rocks. metasediments those fill the shallow part then exposed in eocene as metamorphic rocks whereas those fill the deep part melted as magma through partial to complete melting. melting from metasediments according to chappell & white (1984); chappell & white (1992) occurred at 800 o c although some researchers such as clemens & watkins (2001) and johnson et al (2001) stated higher temperature at 850 o c. the pure composition of this melt is unknown because direct observation is very unlikely. however, experiments have been carried out regarding the general composition of the melting of the metasediments. montel & vielzeuf (1997) in villaros (2010) stated that the nature of magma from melting is always leucocratic with feo + mgo below 4.00 wt%, sio2 72.00 wt%, and al2o3 12 wt%. in addition, from high field strength elements ( hfse), light rare earth elements (lree), and lithophile elements (lile) in melt metasediments able to indicate the process of magma differentation. 3.4.3 magmatic differentiation-crystallization the average composition of granitic rocks from bayah complex showed sio2 72.51 wt%, al2o3 13.95 %, and fe2o3 + mgo 3.39 wt %. by comparing the composition to pure sediment-derived magma from experimental after montel & vielzeuf (1997), bayah granitic rocks have increased in sio2 0.51 wt% and al2o 3 1.95 wt%, and decreased in fe2o3 + mgo 0.61 wt%, this difference in other words stated that magma have undergone changes in composition (differentiation). villaros (2010) explained that there are 4 types of differentiation in s-type granite magma namely magma mixing, crystal fractionation, entrainment of source material, and crustal contamination/assimilation. by considering the composition of major and minor elements in granitic rocks it seems that magma mixing and crystallization fraction not significantly occurred. white & chappell (1988) stated that basalt mixing occurs when the content of cao and na2o are higher than the sediment-derived magma while bayah granitic rocks only show an average value of cao 1.22 wt%, and na2o 2.90 wt%. in addition villaros (2010) stated that that magma mixing usually characterized by low lile concentration while bayah granitic rocks show fairly to high lile such as rb 42.00-115.00 ppm with an average of 83.78 ppm, sr 56.80-173.00 ppm with an average of 92.79 ppm, ba 213.00-590.00 ppm with an average of 360.20 ppm, consequently the mixing mechanism not likely occurred. crystal fractionation typically has more felsic and high hfse concentration magma residues, bayah granitic rocks are indeed more felsic than pure sediment-derived magma but have ow average hfse concentration such as zr 12.58 ppm, hf 0.20 ppm, nb 4.50 ppm, ta 0.76 ppm, and th 5.88 ppm so that crystal fractionation also not significant occurred. remaining 2 types of differentiation, namely entrainment of source material and crustal contamination, it seems that crustal contamination more likely possible because there are increase in sio2 0.51 wt % and al2o3 1.95 wt %, and a decrease in fe2o3 + mgo by 0.61 wt %. the continental composition which is rich in sio2 and al2o3 automatically enriching magma in both sio2 and al2o3 and conversely reducing fe2o3 + mgo, moreover this crustal contamination also implied by high rb concentration (average 83.78 ppm) and ba (average 360.20 ppm) which usually enriched due to interaction with crustal. after the magma differentiated, as it gets closer to the surface, the temperature will be lower and the magma slowly crystallized as plutonic rocks. 3.4.4 batholite exposed granitic rocks are exposed on the surface as batholite (sujatmiko & santosa, 1992; hartono et al., 2008) which became known as the bayah dome by van bemmelen (1949). the batholite exposing is related to global tectonic events, sribudiyani et al. (2003) and ahnaf et al. (2018) stated that there were continental fragments detached from godwana moving north near subduction zone of the indo-australian and sunda plate. as a result, orogenesa occured several times and led to the uplifting. orogenesis in the bayah complex divided into 3 stages i.e. orogenesa i in the early oligocene, orogenesa ii in early to middle miocene, and orogenesa iii in middle miocene to pliocene (van bemmelen, 1949; ahnaf et al. 2018). associated with the age of granitic rocks (granodiorite cihara) which showed the early late oligocene, this batholite is estimated to be exposed during orogenesa i in the oligocene. after batholite exposed, there are also small follow-up intrusions that occurred afterwards such as dacite and quartz diorite in the miocene. field data showing contact between granitic rocks with metamorphic rock and cikotok formation, thus, it is interpreted that the batholite break through these two 114 ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 formations to form a dome. after that, hydrothermal process occurred and resulted in alteration and mineralization in batholite body. 4. conclusion bayah granitic rocks are exposed on the cisanun and cigaber stream along with metamorphic rocks, bayah formations, and cikotok formations. by petrographic analysis, these rocks composed of phenocrystalline quartz, plagioclase, k feldspar and other minerals such as biotite and amphibole with secondary quartz groundmass. based on the mineral content of cipw norm, granitic rocks classified as monzogranite and granodiorite whereas based on the content of sio2, k2o, and n2o these rocks classified as granite and quartz-diorite formed from high k calcalkaline magma. based on the molar ratio of al2o3, cao, na2o, and k2o, the rocks are mostly classified as peraluminous index, furthermore, granitic rocks also classified as s-type granite. the s-type granite magma are sourced from the same clastic sediment of the bayah formation and the cijengkol formation. these sediments are thought to originate from continental especially malay peninsula, indonesian tin island, and schwaner mountains. oxide compositions of granitic rocks have increased in sio2 and al2o3 and decreased in fe2o3 + mgo from pure composition of sedimentderived magma due to magma differentiation in the form of crustal contamination. the occurrence of crustal contamination also reflected by high concentration of rb and ba caused by interaction with the materials of continental crust. bayah granitic rocks are estimated to be exposed due to regional tectonic activity that caused orogenesa i in the early late oligocene, the rocks intruded cikotok formation and metamorphic rocks and formed the bayah dome. based on the trace element concentration, especially rb, y, nb, ta, and yb, bayah granitic rocks are formed on a volcanic-arc active continental margin in accordance with the regional tectonic setting. acknowledgments the authors would like to thank colleagues in geological engineering faculty, padjadjaran university and geotechnology center, indonesia institute of sciences for valuable discussion especially for regional geology setting and geochemistry interpretation. we also thank mr. sangsang and family in lebakpeundeuy, lebak, banten for their help during field observation. this research is also partially funded by padjadjaran university, we thank to everyone in charge for the fund support in this research. references ahnaf, j.s., patonah, a., permana, h., 2018. structure and tectonic reconstruction of bayah complex area, banten. journal of geoscience, engineering, environment, and technology 03 (02), 77-85. chappell, b.w., white, a.j.r., 1974. two contrasting granite types. pacific geology 8, 173 174. chappell, b.w., white, a.j.r., 1992. i-and s-type ranites in the lachlan fold belt. earth and environmental science transactions of the royal society of edinburgh 83(1-2), 126. clemens, j., watkins, j.m., 2001. the fluid regime of hightemperature metamorphism during granitoid magma genesis. contributions to mineralogy and petrology, 140(5), 600-606. clements, b., hall, r., 2008. u-pb dating of detrital zircons from west java show complex sundaland provenance. proceeding of 32nd indonesia petroleum association annual convention. clements, b., hall, r., smyth, h.r., and cottam, m.a. 2009. thrusting of a volcanic arc: a new structural model for java. petroleum geoscience 15, 159-174. collins, w.j., beams, s.d., white, a.j.r., chappell, b.w., 1982. nature and origin of a-type aranites with particular reference to southeastern australia. contributions to mineralogy and petrology 80(2), 189-200. cox, k.g., bell, j.d., pankhurst, r.j., 1979. the interpretation of igneous rocks, george allen and unwin. hartono, u., syafri, i., ardiansyah, r., 2008. the origin of cihara granodiorite from south banten. jurnal geologi indonesia 03 (02), 107-116. hutabarat, j., 2016. geokimia batuan vulkanik formasi cikotok di segmen utara kubah bayah, banten. bulletin of scientific contribution 14 (02), 195-204. irvine, t.n., baragar, w.r.a. 1971. a guide to the chemical classification of the common volcanic rocks. canadian journal of earth science 8, 523-548. johnson t. e., hudson n. f. c., droop g., 2001. partial melting of the inzie head gneisses: the role of water and a petrogenetic grid in kfmash applicable to anatectic pelitic migmatites. j. metam. geol. 19, 99-118. koolhoven, w.c.b., 1993. geological map of java, scale 1:100.000. explanatory notes to sheet 14 (bajah), 42p. bandung: geological research and development centre (unpubl). maniar, p.d., piccoli, p.m., 1989. tectonic discrimination of granitoids. geological society of america, bulletin 6, 129198. montel, j.m. , vielzeuf, d., 1997. partial melting of metagreywackes, part ii. compositions of minerals and melts. contributions to mineralogy and petrology 128(23), 176-196. patonah, a., permana, h., 2018. basement characteristic western part of java, indonesia: case study in bayah area, banten province. international journal on advanced science engineering information technology 08 (05), 2135-2141. patonah, a., syafrie, i., ayasa, h., 2014. new perspective on high-grade metamorphic regional in bayah complex, banten province, indonesia. proceeding 1st international conference geoscience for energy, mineral resources and environment. peacock, m.a., 1931. classification of igneous rock series. the journal of geology 39(1), 54-67. pearce, j.a., harris, n.b.w., tindle, a.g.w., 1984. trace element discrimination diagrams for the tectonic interpretation of granitic rocks. journal petrology 25, 956-983. peccerillo, a. and taylor, s.r., 1976. geochemistry of eocene calc-alkaline volcanic rocks from the kastamonu area, northern turkey. contribution to mineralogy and petrology 58, 63-81. shand, s.j., 1951. eruptive rocks. j. j. wiley, new york. sribudiyani, muchsin, n., ryacudu, r., kunto, t., astono, p., prasetya, i., sapiie, b., asikin, s., harsolumakso, a.h., yulianto, i., 2003. the collision of the east java microplate and its implication for hydrocarbon occurrences in the east java basin. proceeding of 29th indonesian petroleum association annual convention. streckeisen, a., 1976. to each plutonic rock its proper name. earth-science reviews 12(1), 1-33. sujatmiko, santoso, s., 1992. regional geology map quadrangle leuwidamar. geological development and research center, bandung. ahnaf.j.s & et al./ jgeet vol 04 no 02/2019 115 sukarna, d., mangga, s.a., brata, k., 1993. geology of the bayah area: implication for the cenozoic evolution of west java, indonesa. geology society of malaysia 33, 163-180. van bemmelen, r.w., 1949. the geology of indonesia. martinus nijhoff, den haag. villaros, a., 2010. petrogenesis of s-type granite with particular emphasis on source processes: the example of the s-type granite of the cape granite suite (doctoral dissertation, dissertation. stellenbosch university). white, a.j.r., 1979. sources of granite magma. geological society of america program with abstracts 11, 539. widiaputra, t., patonah, a., 2016. metamorphic rocks in bayah complex, banten province: a study in tectonic environment. proceeding of geosea xiv and 45th iagi annual convention 2016 ikatan ahli geologi indonesia ( iagi ), 885-939. yuwono, y.s., 2004. diktat pengantar petrogenesis. geological engineering department. fitb, bandung institute of technology, bandung. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 1.1 geology setting 2. material and method 3. result and discussion 3.1 field observation 3.2 petrography 3.3 geochemistry 3.3.1 magma series and rock name 3.3.2 granite type and magma origin 3.3.3 tectonic environment 3.4 formation of grantic rocks 3.4.1 sediment source 3.4.2 sediment accumulated, metamorphosed, melted 3.4.3 magmatic differentiation-crystallization 3.4.4 batholite exposed 4. conclusion acknowledgments references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 158 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 research article the use of disintegration ratio in evaluating rock durability in selected mudrock samples in indonesia misbahudin 1, *, imam achmad sadisun 2 1 geological engineering, faculty of exploration and production technology, pertamina university, jl. teuku nyak arief, kawasan simprug, kebayoran lama, jakarta selatan 12220, indonesia 2 engineering geology research division, geological engineering study program, faculty of earth sciences and technology, institut teknologi bandung, jalan ganesha no. 10 kota bandung 40132, indonesia * corresponding author : misbahudin.mt@gmail.com tel.: +62-858-1143-5418 received: oct 11, 2018; accepted: july 31, 2019 doi: 10.25299/jgeet.2019.4.3.2331 abstract characterization of durability of mudrocks is important regarding its slaking behaviour within a short time when exposed to and or interact with water. some relevant cases that occurred due to slaking are damage to roads and slope failures along the cipularang and cipali toll road. current engineering activities related to the presence of mudrocks are being and will be held in several locations in indonesia such as the construction of the cisumdawu toll road in ujungjaya district, sumedang and building the national observatory in timau district, kupang. this research is useful for providing engineering considerations related to those activities. the methods used in this research included x-ray diffraction to obtain mineralogy of mudrock, laboratory testing of physical properties of rocks such as dry density, water content, porosity, absorption and mudrocks durability tests. durability of rocks was determined by disintegration index test. testing was carried out by wetting and drying of rock samples. test results showed that the average disintegration ratio of claystones, shales, mudstones and siltstones are 0.1035, 0.2183, 0.4942 and 0.9900. slaking mode occurs to claystones, mudstones and shales is body slaking while dispersion slaking occurs to siltstones. evaluation of the durability of mudrocks in this research indicates that siltstones have the highest durability characterized by very slow disintegration, followed by mudstones, shales and claystones at the lowest with very quick disintegration. disintegration ratio from the disintegration index test characterizes the durability of mudrocks in more details. it can be concluded that porosity and absorption are incorporated into the main factors affecting the durability of mudrocks. keywords: disintegration index test, disintegration ratio, durability, mudrocks 1. introduction in some engineering activities, mudrocks often have a negative impact. this is related due to its characteristics of easily slaked when exposed and or interacting with water in a short time. some adverse effects that can be caused by the presence of these rocks are cases of slope failure, road damage, landfill problems, land subsidence, tunnel loading and instability in building foundations. several types of rocks in mudrocks can consist of siltstones, mudstones, shales and claystones (dick and shakoor, 1992; gautam, 2013). cases of failure or poor engineering buildings take place in several locations in indonesia, such as the cikampek-purwakarta-padalarang toll road (cipularang), often found in landslides or subsidence both on the slopes and on the sides of roads. the cikampek-palimanan (cipali) toll road also began to show similar characteristics on several sides of the road. the training center for education and the national sports school (p3son) hambalang has a disturbed foundation because of the shrinking nature of the material associated with mudrocks. other cases that could potentially be affected by the presence of mudrocks is the plan to make the cileunyi-sumedang-dawuan toll road (cisumdawu) which will be connection access between regions around bandung and cirebon. this road will pass through the subang formation in the ujungjaya-legok section. the subang formation has distinctive properties which are often found in conditions slaked in a short time when exposed to the atmosphere and or when wet by water, triggering several significant problems in engineering activities (sadisun et al., 2005; misbahudin and sadisun, 2018). besides the claystone of the subang formation, there are also several rock formations with similar properties such as the bobonaro formation. the timau national observatory, kupang, east nusa tenggara is planned to be built on this formation. meanwhile, the batuasih formation in the form of shales was allegedly the cause of damage to some parts of the saguling dam (misbahudin, 2017). http://journal.uir.ac.id/index.php/jgeet misbahudin and sadisun, i.a. / jgeet vol 04 no 03/2019 159 the vulnerability of rocks to disintegration is related to the low durability that rocks have. rock durability is often measured by a test of slakedurability. this test was standardized by the international society of rock mechanics (isrm, 1981). slake durability tests are widely used to assess physical changes as a result of wetting-drying processes (franklin and chandra, 1972; koncagul and santi, 1999; gokceoglu and aksoy, 2000). some researchers developed static durability tests through wetting-drying process. sadisun et al. (2005) made a static slaking index test, then erguler and ulusay (2009) develop the method called the disintegration index test. regarding durability testing, some researchers characterize the reference material that is retained on a 2 mm (mesh no. 10) sieve as durable material. it should be noted that when rocks are disintegrated, rocks will be slaked or split into fragments that have different size ranges. this will depend on the type of rock itself. these rocks will differ in terms of mineralogical content and physical properties of rocks. based on the explanation above, the characterization of mudrocks durability to the process of disintegration by both weathering and other natural deterioration processes is important. this is useful for providing engineering considerations in the construction activities that will take place as well as those that have already been built. 1.2 location and geological condition the research locations are in warungkiara, sukabumi, ujungjaya, sumedang, west java and timau, kupang, east nusa tenggara regions as shown in fig. 1. the rock formations are related to the research focus on mudrocks in the sukabumi area consisting of rajamandala formation (sukamto, 1975). martodjojo (2003) called it batuasih formation for rocks in this area. subang formation and kaliwangu formation cover the research area in ujungjaya, sumedang. meanwhile, in timau area, kupang main rock formation is bobonaro formation (fig. 2). based on djuri (1973), subang formation in the study area consisted of claystone containing limestone layers, dark grey; sometimes there are intercalation of green glauconite sandstones. according to martodjojo (2003) this formation consisted of blackish claystonesandstone interbedding and claystone deposited in tidal plains environment. kaliwangu formation contains clay intercalation of tuffaceous sandstones, conglomerates and sometimes found sandstones and calcareous sandstones (djuri, 1973). this formation consists of sandstone and clay, tufaceous and is black grey with lignite intercalation. the most important characteristic is that it is rich in mollusca fossil, conglomerates are often found as intercalation and depositional environments are the uppermost tidal environment (martodjojo, 2003). fig. 1. the sampling location for the study is in three areas, sukabumi and sumedang, west java and kupang, east nusa tenggara. 160 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 fig. 2. the geological map of sampling location (djuri, 1973; sukamto, 1975; and rosidi et al., 1996) batuasih formation consists of stiff, dense and often wet clays. several thin intercalations of sandy silt were also found and sometimes sand was also found. this sandy silt generally consists of quartz and chert; does not contain volcanic fragments. pyrite is common. the upper part, especially more calcareous; many contain fossils of foraminifera and gastropods besides echinoid and bryozoa fragments. the colours are generally blackish-grey, brittle and shaly. baumann (1972) op cit. martodjojo, 2003 considers that batuasih formation is an oceanic facies of upper bayah formation. deposition environment of batuasih formation is a transitional sea with reduced conditions at the bottom. rosidi et al. (1996) suggested that bobonaro formation in this study was miocene, consisting of fragments of boulder size with clay matrixes containing different types of foraminifera. the lithology consists of two main parts, namely scaly clay with soft consistency, dark red, greenish, greyish green, brownish-red and grey. this scaly clay is a matrix of exotic blocks that originate from older rock formations. these blocks have a variety of sizes derived from cablac formation limestones, chert, ultrabasic rocks, pillow lava, chrinoide limestone of maubisse formation and rocks from the mutis complex. 2. methods 2.1 rock sampling in general, the sampling process follows the procedure made by clayton et al. (1987). mudrocks samples are taken as undisturbed samples. this is related to the release potential of stress from the overburden stress received by the sample during the deposition process. this release of stress can cause disintegration of the sample earlier. therefore, sampling is carried out first with a depth of 0.5 1 m or up to the depth of the sample which does not show any symptoms of cracking due to stress release. samples are then carefully formed into dimensions of 20 cm x 20 cm x 20 cm and as soon as possible coated with wrap plastic and aluminium foil. this layer aims to avoid samples from changes in natural water content and temperature as well as maintain the natural conditions of the sample. after being coated with the material, the sample is put into a sample box arranged from the multiplex slab and guarded against mechanical shocks using bubble wrap or other damper material. misbahudin and sadisun, i.a. / jgeet vol 04 no 03/2019 161 2.2 laboratory examination 2.2.1 disintegration index test wetting-drying tests are referred to as disintegration index tests following static durability tests on mudrocks carried out by erguler and ulusay (2009). this test also takes into consideration the research that has been done by sadisun et al. (2005). the main procedure for disintegration index test is preparation of rock samples weighing 450 550 g which are dried in the oven for 24 h at 105 °c. after being cooled at room temperature, the sample is then immersed in a container filled with water for 24 h (fig. 3). most rock samples will experience physical disintegration into small fragments because of the interaction between rock samples with water. fig. 2. (a) preparation of testing samples (b) samples immersion as a wetting process. fig. 3. wet sieving with varying opening sizes. the durability index produced from the disintegration index test is total disintegration index declared through eqn. (1). 𝑫𝒊𝒕 = 𝑾𝒕 𝑾𝒐 × 𝟏𝟎𝟎 (1) with, 𝑫𝒊𝒕 as total disintegration index (%), 𝑾𝒕 as the sample dry weight retained on the sieve 2 mm (g) and 𝑾𝒐 as the initial dry weight of the sample (g). fragment size analysis and disintegration ratio fragment size analysis was carried out to determine the fragment size distribution of the disintegration material. wet sieving is used in conducting material distribution on each sieve (fig. 4). the wet sieve is done manually so there is no disintegration mechanics during the sieving process. the size of the sieve used is maintained to remain consistent during the implementation of testing. the sieves used have an opening size of 76.2 mm, 38.1 mm, 25.4 mm, 19 mm, 13.4 mm, 9.5 mm, 6.35 mm, 4.76 mm and 2 mm. in order to present characteristics that are more responsive to disintegration material, disintegration ratio is used following the research conducted by erguler and shakoor (2009). disintegration ratio defined follows eqn. (2). 𝑫𝑹 = 𝑨𝒄 𝑨𝒕 (2) with, 𝑫𝑹 is disintegration ratio, 𝑨𝒄 as area under the sample fragment size distribution curve and 𝑨𝒕 as overall area of the fragment size distribution curve that covers all samples. identification of clay mineral x-ray diffraction (xrd) is a method often used to identify clay minerals. particles smaller than 0.002 mm are used for this analysis. preparation of samples includes use of glass or ceramic for that sample oriented. a coarse powder sample is prepared on a metallic glass to extract clay material. characteristics of diffraction peaks and relative intensity were used to identify clay minerals. the mineral standard used in this identification follows international center for diffraction data (icdd, 2002). 2.2.2 physical properties of rocks based on dick et al. (1994) rock durability can have a high value because it is related to degree of induration of rocks is high and is reflected by the value of dry density and void ratio whereas low durability is related to the size of the expansive mineral content such as the smectite group indicated by the value of absorption and specific gravity. therefore, to evaluate characteristics disintegration by the physical properties of rocks carried out a series of tests following the testing standards of isrm (2007). this standard is used to determine natural water content, dry density, porosity and absorption of rock. the standard for determining porosity and absorption passes through the immersion process in water. when the immersion test continues, the mudrocks sample will split into small fragments. to avoid these conditions, immersion liquid is replaced with ethylene glycol in order to minimize deteriorate interactions between rocks and water. 3. results and discussion 3.1 characteristics of mudrocks in field 3.1.1 claystones and mudstones of subang formation subang formation outcrops have weathering levels from fresh rock to residual soil. fresh rocks are widely exposed which are found on river slopes. description of claystones is color of grey to blackish grey, clay grain size and found several sizes of silt, low-medium compactness, brittle, locally present pyrite, iron oxide concretion and conchoidal texture with flaked surface. claystones are prone to cracks in a short time when exposed. cracks that occur can take place naturally and rapidly. cracks show an orientation that is relatively parallel to the direction of rock bedding (fig. 5). 162 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 fig. 4. (a) kaliwangu formation claystone show mollusca fossil (b) natural crack not well developed. 3.1.2 claystones of kaliwangu formation the outcrop of kaliwangu formation has a narrow spread. at the study site, rock outcrops were only found on one river which is a small valley between two hills. most of the outcrops are fresh. description consists of greenish-grey colour, soft consistency, there are abundant fossils of mollusca with a size of 0.1 2 cm, low compactness and locally limestone nodules. outcrops of claystones are generally found in a fresh rocks and undergo a process of wetting which is quite intensive. rocks are sticky if peeled. some cracks are filled with weathering soil. cracks that occur due to disintegration are not well developed in a short period. however, it can be observed that there is a natural crack orientation following the rock bedding (fig. 6). 3.1.3 siltstones and mudstones of bobonaro formation rock outcrops are found on hill slopes with the appearance of rocks slaked. outcrops are generally found in fresh conditions with some parts experiencing slightly to moderate weathering. river flows that pass through rocks cause gully erosion. description of these rocks is siltstone, grey to white color, silt grain size and high compactness (fig. 7). mudstones, a mixture of sizes of silt and clay with medium compactness. in the claystones, found a scaly structure with a darker color. at the time of observation, no natural cracks that are formed or are difficult to find when exposed to the surface, the existing cracks are oxidized and there are limestone boulders. 3.2 characteristics of mineralogy of mudrocks samples x-ray diffraction (xrd) is useful for identifying mineral compositions from rocks that have fine grain size. xrd test was carried out on 13 samples. table 1 summarizes the semi-quantitative analysis result of clay minerals identified through xrd test. the table shows that claystones have varying amounts for illite, kaolinite and montmorillonite. quartz, plagioclase and calcite are the most common minerals for each rock samples with a percentage of 28.0 %, 11.5 %, and 10.3 % of the overall composition of the samples. siltstones contain a maximum of quartz minerals of 67.0 %. 3.3 physical properties of rocks table 2 shows a summary of the physical properties of mudrocks samples consisting of natural water content, dry density, porosity and absorption. natural water content ranges from 2.26 % to 32.71 % for all samples. claystones have the highest natural content with an average value of 20.19 % and siltstones have the lowest natural water content with an average value of 4.18 %. mudstones and shales have an intermediate value for average water content. natural water content of mudrocks is a reflection of the clay content and composition of clay minerals. mudrocks which have a percentage of clay content and expansive clay minerals will have a large value for higher natural water content. it should also be noted that natural water content can vary depending on season or weather conditions (gautam, 2013). dry density ranges from 1.77 % to 3.02 % for all samples. claystones have the lowest average dry density value of 1.88 % and the highest porosity value with an average of 31.48 %. this indicates the low degree of compacting and induration of claystones. the average dry density for siltstones, mudstones and shales are 2.39 %, 2.19 % and 2.20 % respectively while average porosity values for these rocks are 7.07 %, 16.80 % and 20.87 % respectively. the average absorption value is 18.63 % for claystones, 8.26 % for mudstones, 3.41 % for siltstones and 11.08 % for shales. claystones have the highest average absorption value and siltstones have the lowest one. the average absorption value of all samples is 12.31 %. mudstones and shales have varying absorption values. high absorption values indicate low degree of induration and abundance of clay material (gautam, 2013). 3.4 characteristics of mudrocks durability with disintegration index test 3.4.1 visual observation of mudrocks after going through the disintegration index test, claystone shows cracks and intensive fragmentation. after the drying process, through the oven, cracks develop well in almost all claystone samples. when the wetting process through immersion for 24 hours can be observed symptoms of body slaking on claystones (fig. 8). this occurs in all claystones samples. some fragments on the edge of the samples begin to fall after being preceded by grains of sand and mud falling. misbahudin and sadisun, i.a. / jgeet vol 04 no 03/2019 163 table 1. semi-quantitative analysis result of x-ray diffraction test. slightly different conditions occurred in the kc-02 and kc-03 sample which showed slightly more intensive of dispersion slaking before forming a body slaking. the results of body slaking are rock breakdown in all rock bodies for kc-02 and kc-03 sample and also have larger disintegrated fragments than other samples. fig. 9 shows the difference in disintegration fragments for both samples as a comparison. mudstones show hairline cracks and other samples have experienced cracks and intensive fragmentation such as claystones. when the oven drying process is complete, the bm-03 sample shows a fairly large crack formation along the horizontal plane of the layer. these cracks then continue to become more open during the wetting process. some muds are dispersed and there are few broken and falling rock fragments (fig. 10). sample sm-02 and sm-08 show different characteristics with bm-03 sample. sample sm-02 and sm-08 showed symptoms of body slaking as the final result of the wetting process as is the case with claystone samples. this is estimated due to the clay mineral content in the sm-02 and sm-08 sample which are relatively higher compared to other mudstone samples. when going through the process of wetting the water can interact with clay minerals and urge the air in the pore to produce stresses that deteriorate rocks (gautam, 2013). shales with the dominant lamination tend to disintegrate following fissility. water entering along the lamination plane is a way for the development of cracks and disintegration of rock. all shales samples in the disintegration index test show similar characteristics. after going through drying process, samples showed no significant change. some hairline cracks are formed apart from the shales fissility. in this condition, the sample still shows the appearance of rocks with high compactness. different things are shown when the sample begins to be immersed in water. the sample disintegrated into small fragments with the appearance of body slaking. this disintegration takes place following fissility. other fine cracks formed are not as dominant as their effects on disintegration compared to fissility of shales which are the main triggers for water to deteriorate rocks. fig. 11 shows the state of shale samples after drying and during immersion. siltstones show a characteristic that is difficult or absent from disintegration. bs-02 sample after going through drying process shows formation of hairline cracks while other samples do not show crack formation. bs-02 sample was then slaked and did not show significant disintegration. some mud may be dispersed even though it is difficult to observe and no fragments on the edge of the samples. fig. 12 displays bs-02 samples after drying and immersion in water. 3.5 mudrocks durability parameters the characteristics of mudrocks durability in this study can be represented as a whole through the fragment size distribution curve. fig. 13 shows the fragment size distribution curve for all samples. on the curve, it can be seen that each sample has a different percentage of material retained in each sieve. in evaluating the mudrocks durability characteristics of the fragment size distribution curve, two durability indices are used. table 3 summarizes disintegration index test data. 3.5.1 total disintegration index (dit) total disintegration index (dit) shows the percentage of material retained in a 2 mm sieve. based on average value of dit for all rock samples, siltstones are the most durable rock compared to other rock samples. siltstones have an average dit of 99.42 % while claystones have an average value of 36.75 %. some claystones are completely disintegrated after undergoing a process of wetting and drying. shales and mudstones show degree of intermediate deterioration with average value of dit 51.19 % and 83.99 % respectively. mineral samples code bobonaro fm. subang fm. kaliwangu bs-01 bs-02 bm-03 sm-02 sc-03 sc-04 sc-05 sc-06 sc-07 sm-08 sc-09 kc-02 kc-03 quartz 67 31 8 24.4 19.6 30.2 23.5 24 30.7 37 33.4 21.3 14.8 montmorillonnite 24 8.3 11.1 8.6 4.4 10.4 9.3 3.1 7.2 5.5 3.3 kaolinite 4.3 2.5 23.5 26 28.8 24.3 16.9 16.6 10.7 11 17.7 4.8 illite 8 19 21 18.9 20 20.4 26.2 24.9 28.9 35.8 53.3 pyrite 6.4 5.2 3.4 4.4 4.5 4.6 2.8 5.7 1.8 siderite 0.6 3.8 2.7 2.1 3.6 2 3.6 2.5 1.9 calcite 8.1 2.2 43.5 18.4 10 5.6 7.6 15.5 8.5 6.8 7 6.2 10.6 plagioclase 7.1 38 14.5 12.4 6.9 6.6 6.2 7.4 6.7 8.1 6.6 10.7 3.2 nontronite 2 4.2 8.3 beidellite 8.2 164 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 table 2. data of physical properties of mudrock samples table 3. the parameters resulted from disintegration index test. lithology formation samples code natural water content (%) dry density (g/cm 3 ) absorption (%) porosity (%) claystone kaliwangu kc-01 30.43 2.43 6.70 14.66 claystone kaliwangu kc-02 29.10 1.58 34.10 48.68 claystone kaliwangu kc-03 32.71 1.61 34.92 50.72 claystone kaliwangu kc-04 21.58 1.97 5.15 9.16 claystone subang sc-01 14.62 1.80 17.87 29.00 claystone subang sc-03 16.39 1.72 18.89 29.33 claystone subang sc-04 17.02 1.95 24.67 43.38 claystone subang sc-05 18.09 1.79 23.37 37.64 claystone subang sc-06 15.10 1.95 22.99 40.34 claystone subang sc-07 16.41 1.81 19.27 31.33 claystone subang sc-09 15.27 1.70 18.34 28.09 claystone subang sc-10 15.57 1.91 17.57 30.23 mudstone bobonaro bm-03 15.70 2.20 1.63 3.23 mudstone bobonaro bm-06 6.76 1.77 7.49 11.92 mudstone subang sm-02 12.85 2.48 15.10 33.80 mudstone subang sm-08 7.47 2.29 8.82 18.23 shale batuasih ash-01 6.98 2.13 10.17 19.50 shale batuasih ash-02 4.43 2.43 6.40 14.01 shale batuasih ash-04 2.26 2.46 4.63 10.25 shale batuasih ash-06 14.66 1.96 17.50 30.95 siltstone batuasih asl-03 5.28 2.62 2.22 5.25 siltstone batuasih asl-05 2.45 2.08 4.17 7.79 siltstone batuasih asl-07 27.82 1.54 36.88 51.10 siltstone bobonaro bs-01 3.95 3.02 1.84 5.02 siltstone bobonaro bs-02 7.23 2.19 5.25 10.37 siltstone bobonaro bs-04 2.27 2.17 3.97 7.78 siltstone bobonaro bs-05 3.90 1.91 11.20 19.32 lithology formation samples code total disintegration index, dit (%) disintegration ratio, dr claystone kaliwangu kc-01 0.17 0.0031 claystone kaliwangu kc-02 62.98 0.4462 claystone kaliwangu kc-03 27.50 0.1552 claystone kaliwangu kc-04 13.41 0.0152 claystone subang sc-01 68.08 0.1077 claystone subang sc-03 64.09 0.1692 claystone subang sc-04 1.04 0.0031 claystone subang sc-05 1.34 0.0038 claystone subang sc-06 8.23 0.0154 claystone subang sc-07 58.94 0.0769 claystone subang sc-09 54.57 0.0769 claystone subang sc-10 80.58 0.1692 mudstone bobonaro bm-03 98.60 0.9688 mudstone bobonaro bm-06 92.56 0.9242 mudstone subang sm-02 60.33 0.1231 mudstone subang sm-08 84.49 0.2154 shale batuasih ash-01 71.18 0.3077 shale batuasih ash-02 74.72 0.2308 shale batuasih ash-04 62.62 0.2879 shale batuasih ash-06 32.84 0.0758 shale batuasih ash-07 14.60 0.0769 siltstone batuasih asl-03 99.05 0.9846 siltstone batuasih asl-05 99.62 0.9970 siltstone bobonaro bs-01 99.55 0.9844 siltstone bobonaro bs-02 98.63 0.9844 siltstone bobonaro bs-04 99.78 0.9924 siltstone bobonaro bs-05 99.86 0.9970 misbahudin and sadisun, i.a. / jgeet vol 04 no 03/2019 165 3.5.2 disintegration ratio (dr) disintegration ratio (dr) represents the level of durability of mudrocks. based on erguler and shakoor's research (2009), dr value about 0 indicates low rock durability and high value represents high durability. claystones have lowest average dr of 0.1035 while siltstones have highest value with an average value of 0.9900. dr for mudstones and shales are at an average value of 0.5579 and 0.1958. when claystones interact with water, rocks will rapidly disintegrate because existing clay tends to absorb water. in siltstones, influence of water which causes disintegration is not significant if it takes place in a short time. 3.5.3 relationship between total disintegration index and disintegration ratio the bivariate analysis between total disintegration index (dit) and disintegration ratio (dr) indicates a statistically significant relationship. the relationship between dit and dr follows an exponential curve (fig. 14). small changes in dit value can make drastic changes to dr values. in this curve, it can also be concluded that rocks with a high value of dit can have a low dr value. this is related to size distribution of fragments through process of wetting and drying. as a representation, sample sm-02, sc-03, kc-02 and ash-04 have a relatively similar or dit value but dr is different (fig. 15). this can also be drawn from fragment size distribution curve of these samples with curves at 2 mm sieve having same percentage of retained material but overall curve area is different (fig. 13). in general, claystones have low total disintegration index and disintegration ratio contrast with siltstones. fig. 5. (a) iron oxide concretion in subang formation claystones (b) natural crack on surface as a slaking process. fig. 6. disintegration appearance and cracks on surface of bobonaro formation siltstone. fig. 7. disintegration on mudstones samples, dispersion with crack (left) and body slaking result (right). fig. 8. the difference of disintegration fragment size between kc-02 (kaliwangu fm.) and sc-03 (subang fm.) sample. 166 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 fig. 9. body slaking on claystones sample. fig. 11. body slaking on shales sample. fig. 12. hairline cracks that formed on siltstones sample, no significant disintegration. misbahudin and sadisun, i.a. / jgeet vol 04 no 03/2019 167 fig. 13. fragment size distribution curve resulted from disintegration index test. fig. 14. correlation between total disintegration index and disintegration ratio. y = 0.0081e0.0479x r² = 0.862 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 10 20 30 40 50 60 70 80 90 100 d is in te g ra ti o n r a ti o , d r total disintegration index, dit (%) 168 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 fig. 15. samples showing similar dit values but different dr. 3.6 influential factors on durability of mudrocks the characteristics of mudrocks durability to the disintegration process represented by the wetting and drying process are influenced by variations in geological and engineering factors (dick et al., 1994 and gautam, 2013). the two variable regression method is applied to identify factors that affect durability. regression analysis is the method most often used to determine the tendency of changes in two variables (davis, 1973 and czajka, 1994). through deterministic coefficients (r 2 ) it can be determined how strongly the influence of independent variables on the dependent variable. the independent variables in this analysis are clay mineralogy of smectite group: montmorillonite, beidellite, nontronite, saukonite, hectorite, saponite (chamley, 1989), physical properties of rock which include natural water content, absorption, dry density and porosity while the dependent variable is disintegration ratio. the independent variable plotted as the x-axis is rock mineralogy and physical properties of rocks while the dependent variable is plotted as the y-axis is disintegration ratio (dr ). table 4 displays the deterministic coefficient value (r 2 ) for regression variables. fig. 16 shows selected plots based on the results of regression analysis of two variables for absorption, porosity, natural water content, dry density, and smectite group clay minerals. the plots show that absorption and porosity have a better correlation with dr than natural water content, dry density and the percentage of smectite group clay minerals. fig. 16 shows the condition of rocks with porosity of less than 20 % will have value of dr greater than 0.2. when rock porosity has a value of less than 20 %, there is a drastic increase in dr. in line with absorption of rocks is more than 10 %, dr has a value of less than 0.2. if absorption is less than 10 %, there is a drastic increase in dr value. high value of r 2 = 0.7894 indicates a strong influence of porosity on changes in dr values. the relationship between porosity and dr follows a negative exponential curve. a small change in the porosity value will cause a drastic change in dr value. absorption versus dr for rock samples has a value of r 2 = 0.7759 which indicates that absorption has a strong influence on changes in dr value. claystones with a greater value of absorption variable has a larger pore space. when pores are filled with water, it produces pressure against grains, develops cracks or progressively deteriorates rocks (olivier, 1979; dick et al., 1994; czerewko and cripps, 2001). siltstones have lower absorption, high dry density and higher durability. rocks with large porosity are positively related to high absorption values. both of these variables are negatively related to the amount of disintegration. analysis of two variables for the percentage of smectite group clay minerals, dry density and natural water content was correlated and had a moderate to weak influence on dr. although the relationship of each variable to dr follows a certain trend curve, namely logarithmic for natural water content and percentage of smectite group clay minerals and exponential curves for dry density, the influence is weak. the value of r 2 = 0.4325 for the relationship of natural water content and dr indicates the condition of 43.25% variability in dr value can be explained by the presence of natural water content variables but the remainder is influenced by other variables. the same is true for dry density and the percentage of smectite group clay minerals with values of r 2 = 0.2759 and 0.0145 respectively. fig. 16. correlation between porosity and absorption with disintegration ratio. samples code sm-02 sc-03 kc-02 ash-04 total disintegration index (%) 60,33 64,10 62,98 62,62 disintegration ratio 0,1231 0,1692 0,4462 0,2879 fragment of disintegration y = 2.6135e-0.132x r² = 0.7894 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 10 20 30 40 50 60 70 80 90 100 d is in te g ra ti o n r a ti o , d r porosity (%) y = 2.0385e-0.214x r² = 0.7759 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 10 20 30 40 50 60 70 80 90 100 d is in te g ra ti o n r a ti o , d r absorption (%) misbahudin and sadisun, i.a. / jgeet vol 04 no 03/2019 169 table 4. deterministic coefficient value (r 2 ) for correlation between disintegration ratio with physical properties and rock mineralogy. 4. conclusion disintegration index test can evaluate durability characteristics of mudrocks with qualitative and quantitative data. visual observation and durability parameters can be obtained representatively. the total disintegration index and disintegration ratio have high variations of value for different types of mudrocks. claystones are found to be the lowest durability rock, while siltstones are the highest durability one. the average disintegration ratio for claystones, shales, mudstones and siltstones is 0.1035, 0.1958, 0.5579 and 0.990, respectively. claystones disintegrate rapidly become small fragments while siltstones disintegrate slowly and remain as larger fragments. the relationship between total disintegration index and disintegration ratio is the exponential curve. this relationship indicates that rocks with a high total disintegration index can have a low disintegration ratio based on the fragment size distribution. based on regression analysis of two variables, porosity and absorption have a strong influence on changes in disintegration ratio values. both variables are related in the form of negative exponential curves. small changes in the value of porosity and absorption will have a drastic effect on the value of the disintegration ratio. regarding this study, the characteristics of mudrocks in indonesia have different durability properties. mudrock with low durability and rapid disintegration can have a detrimental effect on engineering activities such as causing slope failure or foundations in road and building construction. on the other hand, there are also mudrocks with different characteristics with high durability and slow disintegration which, in a longer period of time, can only be seen to interfere with engineering activities. acknowledgement the author would like to thank for the help and support of laboratory of metallurgy itb in conducting the disintegration index test. in addition, thank you also to laboratory of hydrogeochemistry itb for conducting x-ray diffraction testing. references chamley, h., 1989. clay sedimentology, springer-verlag berlin heidelberg, new york. clayton, c.r.i., matthews, m.c., simons, n.e., 1987. site investigation. department of civil engineering, university of surrey. czajka, r., 1994. determination of variability of physical properties in a selected layer (from the baltic cliff) using statistical methods. bull. int. assoc. eng. geologists 49, 33 39. doi: 10.1007/bf02594998 czerewko, m.a. cripps, j.c., 2001. assessing the durability of mudrocks using modified jar slake index test. quarterly journal of engineering geology and hydrogeology 34, 153 163. doi: 10.1144/qjegh.34.2.153 davis, j.c., 1973. statistics and data analysis in geology. john willey & sons, new york. dick, j.c., shakoor, a., 1992. lithologic controls of mudrock durability. quarterly journal of engineering geology 25, 31 46. doi: 10.1144/gsl dick, j.c., shakoor, a., wells, n., 1994. a geological approach toward developing a mudrock-durability classification system. can. geotech. j. 31, 17 27. doi:10.1139/t94-003 djuri, 1973. geological map of arjawinangun, java quadrangle, scale 1:100.000. center of research and development of geology, bandung. erguler, z.a., shakoor, a., 2009. relative contribution of various climatic processes in disintegration of claybearing rocks. eng. geol. 108, 36 42. doi:10.1016/j.enggeo.2009.06.002 erguler, z.a., ulusay, r., 2009. assessment of physical disintegration characteristics of clay-bearing rocks: disintegration index test and a new durability classification chart. eng. geol. 105, 11 19. doi:10.1016/j.enggeo.2008.12.013 franklin, j.a., chandra, r., 1972. the slake-durability test. int. j. rock mech. min. sci. 9, 325 328. doi:10.1016/01489062(72)90001-0 gautam, t.p., 2013. an investigation of distribution behavior of mudrocks based on laboratory and field tests. kent university, usa (dissertation). gautam, t.p., shakoor, a., 2013. slaking behavior of claybearing rocks during a one-year exposure to natural climatic conditions. eng. geol. 166, 17 25. doi:10.1016/j.enggeo.2013.08.003 gokceoglu, c., aksoy, h., 2000. new approaches to the characterization of clay-bearing, densely jointed and weak rock masses. eng. geol. 58, 1 23. doi:10.1016/s0013-7952(00)00032-6 icdd, 2002. the power diffraction file pdf2 database. international centre for diffraction data, usa. isrm, 1981. isrm suggested methods: rock characterization, testing and monitoring. brown, e.t. (ed.), london. isrm, 2007. the complete isrm suggested methods for rock characterization, testing and monitoring: 1974 2006 in ulusay, r., hudson, j.a. (eds.). suggested methods prepared by the commission on testing methods, international society for rock mechanics (isrm), ankara, turkey. koncagu, e.c., santi, p.m., 1999. predicting the unconfined compressive strength of the breathitt shale using slake durability, shore hardness and rock structural properties. international journal of rock mechanics and mining sciences 36, 139 153. doi: 10.1016/s01489062(98)00174-0 martodjojo, s., 2003. evolusi cekungan bogor, jawa barat, itb press, 238. misbahudin, m., 2017. characterization of the durability of mudrocks using disintegration index test. institut teknologi bandung (thesis) misbahudin, m., sadisun, i.a., 2018. durability analysis of subang formation claystones in ujungjaya area and surroundings, sumedang regency, west java. bull. geol. 2, 163 174. doi:10.5614/bull.geol.2018.2.1.3 olivier, h.j., 1979. a new engineering-geological rock durability classification. engineering geology 14, 255 279. doi: 10.1016/0013-7952(79)90067-x porosity absorption water content dry density % smectite group clay dr 0,7894 0,7759 0,4325 0,2759 0,0145 170 misbahudin and sadisun i.a., / jgeet vol 04 no 03/2019 rosidi, h.m.d., tjokrosapoetro, s., gafoer, s., 1996. geological map of kupang-atambua, timor quadrangle, scale 1:250.000. center of research and development of geology, bandung. sadisun, i.a., shimada, h., ichinose, m., matsui, k., 2005. study on the physical disintegration characteristics of subang claystone subjected to a modified slaking index test. geotech. geol. eng. 23, 199 218. doi:10.1007/s10706-003-6112-6 sukamto, r.a.b., 1975. geological map of jampang and balekambang, java quadrangle, scale 1:100.000. center of research and development of geology, bandung. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ the use of disintegration ratio in evaluating rock durability in selected mudrock samples in indonesia 1. introduction 1.2 location and geological condition 2. methods 2.1 rock sampling 2.2 laboratory examination 2.2.1 disintegration index test 2.2.2 physical properties of rocks 3. results and discussion 3.1 characteristics of mudrocks in field 3.1.1 claystones and mudstones of subang formation 3.1.2 claystones of kaliwangu formation 3.1.3 siltstones and mudstones of bobonaro formation 3.2 characteristics of mineralogy of mudrocks samples 3.3 physical properties of rocks 3.4 characteristics of mudrocks durability with disintegration index test 3.4.1 visual observation of mudrocks 3.5 mudrocks durability parameters 3.5.1 total disintegration index (dit) 3.5.2 disintegration ratio (dr) 3.5.3 relationship between total disintegration index and disintegration ratio 3.6 influential factors on durability of mudrocks 4. conclusion acknowledgement references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 3 2021 hadian et al./ jgeet vol 6 no 3/2021 127 research article groundwater conservation strategy based on water balance at muarabungo groundwater basin, indonesia mochamad nursiyam barkah1, fauziyah hani2 , bombom rachmat suganda1, munib ikhwatun iman3, cecep yandri sunarie 1, mohamad sapari dwi hadian1* 1water center geology faculty, padjadjaran university, jatinangor 45363, indonesia. 2magister program, fakulty of geology, padjadjaran university, jatinangor 45363, indonesia. 3center for groundwater and environmental geology, geological agency memr, bandung, indonesia. * corresponding author : sapari@unpad.ac.id tel.: +62-81321102268; fax: +62-22-7796545 [tel./fax] received: oct 16, 2019; accepted: jun 20, 2021. doi: 10.25299/jgeet.2021.6.3.3976 abstract muarabungo groundwater basin,is locateed in jambi and west sumatra province. based on the four rainfall stations in muaratebo, dusun rantau pandan, sungai bengkal and komplek pengairan pu station recorded in 2008 to 2011, the precipitation (ppt) in study area is 1799.09 mm/year. value of evapotranspiration (evpt) in the study area is equal to 1261.26 mm / year (70.1%). groundwater basin of muarabungo has an infiltration debit of 2,516,791,750 m3 / year and run-off debit (ro) of 798 042 638 m3 / year. rock composer in the muarabungo groundwater basin are dominated by alluvium deposition, quaternary rocks, and also the surrounding areas are composed by igneous and metamorphic rocks. aquifer with a good productvity can be found on alluvium and sedimentary rocks such as tuff sandy, whereas region without exploitable groundwater are composed by igneous rocks and metamorphic rocks. based on groundwater quality, groundwater basin is divided into 13 facies, namely ca; cl, mg; cl, na + k, cl, ca; hco3, mg; hco3, na + k; hco3, ca; no. dominant type, mg; nodominan type, na + k; no. dominant type, no. dominant type; cl, no. dominant type; hco3, nodominan type; so4, and no. dominant type; no. dominant type. the result of water balance measurement in research area is used to show the areas for crisis and secure area. the water balance calculation and determining recharge and discharge areas are needed for developing conservation strategy. keywords: groundwater basin, water balamce, aquifer, conservation, muarabungo 1. introduction the population in indonesia increased each year, including the jambi province. this in turn drive the high demand for clean water sourced from ground water. for ground water utilization, it must be known in advance the potential of ground water in the muarabungo basin, both based on quantity and quality. due to the groundwater use, groundwater basin potential must be balance with conservation efforts in order that optimal utilization and prevent environmental disaster such as groundwater depletion, flood in rainy season, and drought in dry season. therefore, the potential of groundwater in each region is very important to know both the quantity and quality in determining an effective groundwater conservation strategy so that the sustainability of groundwater utilization will be guaranteed in the future. 2. research method the research method uses primary data supported by secondary data. the data comes from government agencies such as water resources research center and development (pusair), statistic center agency (bps), literature studies, and the geological agency. these data include, geological maps, hydrogeological maps, topographic maps, land use maps, rainfall data, climatology data, water use data, and population data. in addition there are data on the physical and chemical properties of groundwater in the study area. from the available data, the water balance is calculated using the ffolliott method and groundwater quality is also determined from an analysis of the physical and chemical properties of the groundwater (folliott, baker, tecle, & neary, 2003). from the quantity and quality, the conservation strategy is determined at an altitude of 42 133 meters. in general, groundwater is relatively acidic, possibly due to various factors. it could be due to water contact with the rocks that pass through it namely rocks from the kasai formation which consists of tidal rock rocks are acidic, tuff sandstones, with bentonite inserts and little lignite or due to acid rain due to air waste from coal mining. the following results of the analysis of the physical properties of groundwater in muarabungo groundwater basin: table 1. analisys of physical properties results of water in muarobungo groundwater basin area physical properties measurement result notes water temperature 26.2oc – 31.7oc ph 4.2 8.8 poor – good quality (dephut, 2009) electrical conductivity 0 – 340 µs/cm fresh groundwater (mandel, 1981) dissolved solids total 0 – 150 mg/l fresh groundwater (freeze & cherry, 1979) groundwater chemical analysis was carried out at 54 points of interest. groundwater quality was determined based on pp ri no. 20 of 1990 concerning water quality criteria and sk. men klh no: kep-02 / menklh / i / 1988 concerning water http://journal.uir.ac.id/index.php/jgeet about:blank 128 hadian et al./ jgeet vol 6 no 3/2021 quality standards for water resources and groups a and b and based on the republic of indonesia ministerial regulation number 492 / menkes / per / iv / 2010 concerning drinking water quality requirements. here are the results of measurements of water samples: (m. s. d. hadian & rahmat, 2015) table 2. comparison of water quality based on standards of quality standards and field conditions element measurement result max. water quality standard notes ca 0 – 26.7 mg/l 200 mg/l good quality mg 0.03 – 10.835 mg/l 150 mg/l good quality na 0.33 14.55 mg/l 200 mg/l good quality cl 0.97 18.5 mg/l 250 mg/l good quality so4 0 14.46 mg/l 100 mg/l good quality hco3 2.49 – 112.7 mg/l k 0.1 – 9.86 mg/l 3. groundwater facies based on groundwater chemical data, groundwater facies were determined the study area development. the data is plotted to the piper diagram (figure 1). plotting data into piper diagrams is assisted with rockworks15 software. from the results of the analysis of groundwater facies in the study area can be divided into 13 groundwater facies, namely the facies of ca; cl, mg; cl, na + k; cl, ca; hco3, mg; hco3, na + k; hco3, ca; no dominant type, mg; no dominant type, na + k; no dominant type, no dominant type; cl, no dominant type; hco3, no dominant type; so4, and no dominant type; no dominant type. (m. s. d. hadian, prayogi, & azy, 2012) fig 1.results of groundwater chemical data plots into the piper diagram 4. discussion groundwater conservation is an effort to protect and maintain the condition and environment of the groundwater in order to maintain the sustainability or continuity of the availability in adequate quantity and quality, for the sake of the continuity of its functions and benefits to meet the needs of living things , both now and in future generations (danaryanto & darmawan, 2004, kodoatie, robert j. & syarief, 2010). groundwater conservation efforts that can be done at the muarabungo groundwater basin include: 4.1 groundwater preservation groundwater preservation means groundwater extraction is limited to a safe amount, where the water uptake must be adjusted to the potential of available water and also does not cause negative impacts on the environment, such as the impact of groundwater level degradation 791,750 m3 / year. however, not all the potential water available can be extracted and used for daily needs. therefore infiltrated water below the surface not only fill the aquifer, but also fill the unsaturated zone (unsaturated water) and the saturated zone (saturated water). fig 2. population growth in muarabungo groundwater basin hadian et al./ jgeet vol 6 no 3/2021 129 specific yield is the ratio in percent (%) of the volume of water that can be taken from a soil or rock that is saturated with water compared to the total volume of rock or soil. this specific yield is a large amount of water available for human use. according to todd (1980), sy alluvium which consists of clayrich material is 3 28%, sy sandstones 21-27%, and sy tuff 21%. the muarabungo groundwater basin is dominated by alluvium and sandy tuff / sandstone tuff, so that each region is not permitted to use water exceeding 28% of the total water potential that is equal to 704,701,690 m3 / year. fig 3. estimated groundwater use lines based on the figure 3, the amount of water usage (domestic water demand), predicted to reach a critical figure around 2030, assumed based on the average population growth results in 2008-2013 (source: bps) which is 5.5%. the critical limit for water use is 28% of the potential water available. the amount of water used is only based on domestic water needs. this projection is only based on population growth, not yet projected by the influence of land use change. if the amount of groundwater use coupled with industrial and commercial needs and the effect of increasing runoff water coefficients are included, it is possible that critical water estimates will occur before 2033. therefore, to avoid this happening, conservation must continue. 4.2 determination of groundwater catchment areas the determination of groundwater catchment areas is intended to be designated as a protected area by the local government. in accordance with law number 24 of 1992 concerning spatial planning and presidential decree number 32 of 1990 concerning the protection of protected areas is explicitly stated that water catchment areas are designated as protected areas where any cultivation activities are prohibited in those areas unless they do not disturb the protection function (m. hadian, mardiana, abdurahman, & iman, 2006). the function of water catchment areas is to supplement groundwater reserves. in this study, the water catchment area was determined based on buckling slopes (boundary morphology of the land with hills), the position of the emergence of springs, depth of ground water level, ec and tds values. fig 4. recharge and discharge zone map 4.3 addition of groundwater recharge (artificial recharge) if groundwater utilization is increased, the groundwater refilling capacity can be artificially enlarged. addition of groundwater recharge can be done by making rainwater collection ponds or catchment wells. the addition of groundwater recharge such as recharge wells generally can be applied to areas with high groundwater uptake with high population density areas from the surrounding area namely kec. pasar muarabungo with a density of 2,631.13 inhabitants / km2 (bps bungo district, 2013). wells infiltration aim to increase water infiltration in open areas such as fields, parking lots, yards and so on. furthermore the construction and depth adapted to local soil conditions. rainwater collection ponds are ponds or containers used to collect rainwater. this method can be applied in the area around the muaratebo station and bengkal river because it is noted that the rainfall in this area is smaller than other stations it can be seen in figure 2. the main objective is to raise the groundwater level, and also to store excess water reserves when it rains , so that there are water reserves during the dry season. this method has a direct effect on free groundwater in the shallow aquifer layer, and is effective for replenishing water into the deep aquifer layer. 4.4 public outreach some people's misunderstanding about all matters relating to groundwater sometimes makes groundwater users not pay 130 hadian et al./ jgeet vol 6 no 3/2021 attention to the conservation of groundwater, such as disposal of household waste and disposal of sewage (feces) that do not meet the requirements and that can pollute groundwater. therefore the understanding of groundwater resources and the proper use of groundwater needs to be socialized to the community in this groundwater conservation effort. 5. conclusion based on water balance calculations, all areas in the muarabungo groundwater basin are still in a safe zone, there are no crisis areas. this area has underground water potential of 2,516,791,750 m3 / year and surface water of 798,042,638 m3 / year. the assumption of water use in the muarabungo groundwater basin is 29,565,821.25 m3 / year. based on the physical and chemical properties of groundwater, groundwater quality in the muarabungo groundwater basin is quite good. it's just that the ph value in some places is quite acidic. conservation strategies that can be carried out include: • groundwater preservation intake of water must be adjusted to the potential of available water. potential water availability is 768,476,816.75 m3 / year • determination of groundwater absorption areas based on the analysis results, the recharge area is estimated to be in kec. punjung island, tabah,. padang laweh, jujuhan, tanah tumbuh, tanah sepenggal, maro sebo ulu, and muara tabir. • addition of groundwater additives (artificial recharge) addition of groundwater recharge can be done in areas with high population density. the highest population density in the study area is in pasar muarabungo district, which is 2,631.13 people / km2 (bps bungo district, 2013). • community outreach this is done so that the community understands about all matters relating to groundwater so that in the implementation of groundwater utilization so that the community can pay attention to the conservation of groundwater. acknowledgement the authors thank the unpad postgraduate school dean prof. dr. hendarmawan, m.sc, head of the environmental geology laboratory, faculty of geological engineering, padjadjaran university, rudi suhendar head of the geology agency who has facilitated all needs and provided the data needed for the purposes of this research. references danaryanto, s., & darmawan, h. (2004). air tanah di indonesia dan pengelolaannya. [jakarta]: departemen energi dan sumber daya mineral indonesia. ffolliott, p. f., baker, m. b., tecle, a., & neary, d. g. (2003). a watershed management approach to land stewardship. journal of the arizona-nevada academy of science. hadian, m., mardiana, u., abdurahman, o., & iman, m. . (2006). sebaran akuifer dan pola aliran air tanah di kecamatan batuceper dan kecamatan benda kota tangerang, propinsi banten. indonesian journal on geoscience, 1(3), 115–128. https://doi.org/10.17014/ijog.vol1no3.20061 hadian, m. s. d., prayogi, t. e., & azy, f. n. (2012). groundwater quality assessment for suitable drinking and agricultural irrigation using physico-chemical water analysis in the rancaekekjatinangor district, west java, indonesia. international proceedings of chemical, biological and environmental engineering. hadian, m. s. d., & rahmat, b. (2015). manajemen air tanah pada endapan aluvium geologi dan hidrogeologi daerah rawa lakbok, jawa barat. bulletin of scientific contribution, 13, 192–201. kementrian kehutanan. 2013. peta penggunaan lahan indonesia tahun 2012, lembar 0814, painan, provinsi sumatera barat. kementrian kehutanan kementrian kehutanan. 2013. peta penggunaan lahan indonesia tahun 2012, lembar 0815, solok, provinsi riau. kementrian kehutanan kementrian kehutanan. 2013. peta penggunaan lahan indonesia tahun 2012, lembar 0914, m. bungo, provinsi jambi. kementrian kehutanan kodoatie, robert j. & syarief, r. (2010). tata ruang air tanah. yogyakarta: andi press. purwanto, dkk., 1983. peta hidrogeologi indonesia lembar 0815 solok. badan geologi. bandung rosidi, dkk., 1996. peta geologi lembar panian dan bagian timur lembar muarasibeurit, sumatera setiawan, dkk., 2013. peta hidrogeologi indonesia lembar 0914 muarabungo. badan geologi. bandung simandjuntak, dkk. 1994. peta geologi lembar muarabungo, sumatera. badan geologi. bandung soetrisno, dkk., 1987. peta hidrogeologi indonesia lembar 0714 muarasibeurit sebagian lembar 0814 painan. badan geologi. bandung sosrodarsono dan takeda. 2003. hidrologi untuk pengairan. jakarta : paradnya paramita todd, d. k. (1980). groundwater hydrology. (j. willey, ed.) (2nd editio). wiley, new york. https://doi.org/10.1002/gj.3350170407 © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). about:blank http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 4 no 4 2019 khan, a. et al./ jgeet vol 04 no 04/2019 227 research article soil minerals serving as source of arsenic in alluvial aquifers of holocene: a case study from indus delta, sindh, pakistan adnan khan1*, suhail anjum2, viqar husain1 1department of geology, university of karachi, karachi, pakistan 2department of geology fuuast, karachi, pakistan * corresponding author : adkhan@uok.edu.pk telp.:+92-300-3635848 received: oct 1, 2016; accepted: nov 20, 2019. doi: 10.25299/jgeet.2019.4.4.3077 abstract: groundwater arsenic contamination is recently reported in the alluvial aquifers of indus deltaic plain. since the source of a rsenic is believed to be natural as widely reported in other deltaic aquifers of same age (holocene), it is imperative to evaluate the soil characteristics for identifying the sources of arsenic and its mobilization mechanism. for this purpose, 49 soil samples were collected from near aquifer sites in all three talukas of tando muhammad khan district. visual analysis revealed that soil is light grey in color with fine texture ranging from silt to silty-clay. the xray diffraction study reveals the occurrence of quartz, mica and clay minerals in all collected soil samples. plagioclase feldspar is second dominant mineral group in the order of albite (calcian) >albite>albite (disordered) = anorthite > anorthite (sodian) = anorthite (disordered). calcite is major carbonate mineral which is detected in 40 out of total 49 soil samples. the occurrence of other occasional minerals includes amesite, nitro-calcite, rutile and zinnwaldite. the frequency of micaceous minerals in collected samples is in the order of clinochlore> polylithionite> biotite > phlogopite> muscovite. polylithionite is found in about half of the total soil samples, where most of the aquifers contain arsenic >20 μg/l (khan, 2014). phlogopite is observed in seven soil samples which are also associated with clinochlore. on the other hand, biotite is found in 14 sediment samples collected from tando muhammad khan and bhulri shah karim talukas and muscovite occurs in three soil samples of tando muhammad khan taluka. it can be concluded from present study that fine-grained phyllosilicates have strong affinity for arsenic retention. these sediments are important source of arsenic indus delta and other deltaic plains of the world. keywords: arsenic, sediments, alluvial aquifers, holocene, indus delta, pakistan. 1. introduction arsenic is widespread contaminant in the environment and its adverse health effects are a global concer(who, 2010). there are two major sources of arsenic which includes weathering of minerals (bhumbla and keefer, 1994; yan-chu, 1994; mandal and suzuki, 2002; foley and ayuso, 2008; mailloux et al., 2009) and anthropogenic activities like mining activities, industrial wastes and agricultural in puts (chilvers and peterson, 1987). chronic application of pesticides and herbicides also results in substantial accumulation in soils (hiltbold, et al., 1974)mineralogy is one of the important research approaches for disclosing the mechanism of environmental contamination (akai et al., 2004; akai and anawar, 2013). the geogenic as is of serious concern in countries like bangladesh, india, and vietnam. high concentration of as in soil and water has also been noted in developed countries, e.g., us (peryea and creger, 1994)and south australia and tasmania (merry, et al., 1983) it is widely believed that high concentration of arsenic (as) is mainly confined to the sedimentary aquifers of holocene age (bhattacharya, et al., 1997; ishiga, 2000; anawar et al., 2002, 2003)high levels of arsenic in groundwater mainly result from natural contamination(chowdhury, et al., 1999; acharyya et al., 2000; nicksonet al., 2000; mcarthur and ravenscroft, 2000; anawar et al., 2002; polizzotto and harvey, 2005; rabbani et al., 2017).various theories have been put forward regarding the modes of arsenic release, ranging from oxidative or reductive degradation of arsenic-bearing solids to competitive ligand displacement by phosphate(chakrapani et al., 1995; bhattacharya, et al., 1997; acharyya et al., 2000; nickson et al.,2000; mcarthur and ravenscroft, 2000). major as minerals occurring in nature are niccolite, realgar, orpiment, cobaltite, arsenopyrite, tennatite, enargite, arsenolite, claudetite, scorodite, annabergite, hoernesite, haematolite, conichalcite and pharmacosiderite (smedley and kinniburgh, 2002)these minerals originate in hydrothermal veins, hot springs, secondary minerals deposited oxidation products of associated as minerals. these mineral deposits are typically associated with orogeny where volcanic activity and metamorphism are quite common. hence, the occurrence of as in himalayan river basin is rational. all the rivers deposit fine to very fine textured sediments in deltaic region due to low energy and very high suspended load. these fine sediments are mainly comprised of minerals like quartz, feldspar and biotite which contains as concentration in the range of 0.4-1.3, 0.1-2.1 and 1.4 mg/kg respectively (garlick and wedepohl, 1969). on the other hand, calcite and dolomite contains arsenic in the range of 1-8 and <3 mg/kg respectively. beside arsenic speciation and toxicity in the soil, several studies have documented relatively higher as concentration in the soil as compared to the aquifer materials (onken and hossner, 1995; swartz et al., 2004; polizzotto et al., 2006).it is due to the fact that arsenic compounds are absorbed strongly onto soil, and therefore transported only over short distances in surface and groundwater (manning and goldberg, 1997).solid phase as and fe becomes more reduced with depth (0.5-3.6 m) in the soil and released via redox cycling in surface soils/sediments into the sandy aquifer (polizzotto et al., 2008). http://journal.uir.ac.id/index.php/jgeet mailto:adkhan@uok.edu.pk 228 khan, a. et al./ jgeet vol 4 no 4/2019 keeping in view these facts, it is likely that the constituent minerals in the alluvial deposits of tando muhammad khan district (part of indus deltaic flood plain)are probable source of as-enriched groundwater, similar to other highly as enriched groundwaters of (anawar et al., 2003; polizzotto et al., 2006) west bengal (nath et al., 2008; hery et al., 2010; nath et al., 2011)vietnam(berg et al., 2008) china (xie et al., 2009) and spain (garcia-sanchez et al., 2005).substantial work has been carried out by various workers on the groundwater of tando muhammad khan to explain the arsenic contamination(husain et al., 2012; khan et al., 2014, 2017) however, sediment characteristics have not yet been studied to explain the possible source/host of arsenic responsible for high arsenic groundwater in study area. therefore, present study is aimed at characterizing the near aquifer site sediments in terms of mineral composition and chemical characteristics to link with the hydrogeochemical characters of the corresponding groundwater in order to complete the picture of arsenic release mechanism in study area. 2. material and methods 2.1. study area indus basin is topographically a plain area, characteristically devoid of any well-defined natural surface and subsurface drainage (qureshi et al., 2008)it covers an area of 2600 sq. km covering the whole hyderabad division comprising of tando mohammad khan, tando allayar and matiari districts. geology of tando muhammad khan district is very simple where the holocene fine sediments cover the surface and indus river flows on the western margin of the basin (fig.1). surface soil comprises fine textured sediments dominated by silt and clay with subordinate sand (kazmi, 1984). the entire study area is covered with marsh peat, micaceous silt and clay units similar to bangladesh (shamsudduha et al., 2008). 2.1.1. quaternary sediments quaternary sediments of late holocene have carpeted the surface geology of study area that are brought by the indus river (kazmi, 1984; mehmood et al., 2009). deposition of such young sediments is mainly controlled by orogenic movement of himalayas which incepted in the early pleistocene time (gill, 1952). this phase of orogeny was the strongest of all stages where major structural and tectonic events took place in terms of folding, faulting and uplift. this was the time when thick deposition of sediments in all parts of himalayan basin occurred including deltaic part of indus basin. (acharyya, et al., 2000; polizzotto et al., 2006; alizai et al., 2012). interestingly, holocene aquifers are the host of high arsenic groundwater worldwide.(acharya, 2005). similar is true about alluvial deposits of tando muhammad khan district and adjoining areas where more than 600 ppb arsenic is reported in shallow alluvial aquifers (husain et al., 2012). these flood plain deposits of study area have been classified in table 1 out of which two are described below due to the fact that only these two comprises the surface geology of study district. fig. 1 geological map of tando muhammad khan district and adjoining areas. fig. 2 map showing the arsenic distribution in groundwater of study area. 2.1.2. surficial deposits of alluvium the surficial alluvial deposits in study and adjoining areas consists of fine sand, silt and clay transported and deposited by the streams resulting in the formation of cultivable land. khan, a. et al./ jgeet vol 4 no 4/2019 229 2.1.3. extinct streams deposits extinct streams deposits carve the surface geology of tando muhammad khan district (table 1). these sediments form the flood plain deposits overlain by the river channel and meander belt deposits. the sediments of lower indus flood plain comprise of greenish grey to grey clay and silt followed by fine sand. sporadically these deposits are interlayered with some sticky, black and calcareous clay. these sediments can be characteristically seen in shallow depressions formed by the chocked estuaries and surrounded by salt at some places, interlayered with sticky black calcareous clay. these are characterized by long shallow depressions formed by choked estuaries and occupied by salt deposits. the meander belt and stream bed deposits show imprints of older meander belts traces. these deposits are the admixture of poorly sorted sediments of fine sand with subordinate silty clay. these sediments are directly overlying the deltaic alluvium (akhtar et al., 2012). table 1 stratigraphic units of holocene in tando muhammad khan district and adjoining areas (after (akhtar et al., 2012). period epoch deposit / formation sub units lithological description quartenary holocene stream bed deposits floodplain deposits low lying areas along river, frequently inundated during high floods. these are flat and relatively even surfaces stream bed and meander belt deposits deposits characterized by river meanders, cut off, oxbow lakes, abandoned channels numerous point bars, swales, and sand ridges. surficial alluvium deposits unconsolidated surficial deposits deposit consist of sand, silt and clayey material brought by streams deposits of extinct streams stream bed and meander belt deposits poorly sorted fine to medium grained sand, silt, and least aboundant clay floodplain deposits (lower terraces) consist of greenish gray to gray silt and clay with subordinate fine sand, occasionally intercalated with sticky black clay 2.2. soil sampling for mineralogical analysis forty-nine representative soil samples (about 0.3 meters depth) near aquifer sites were taken from various parts of study area. sample location was marked on the map using global positioning system. the soil samples were collected using hand shovel in the plastic bags. the physical properties (i.e. color, texture) of the collected samples were also documented in the field. the samples were air dried for about 2 days at room temperature and subsequently oven dried at 105°c. the dried sample was ground to very fine mesh and sieved through 2 mm screen to eliminate the coarse particles and other deleterious material. table 2. minerals identified in the soil collected from various localities of tando muhammad khan taluka. s.no. sample code union council coordinates arsenic μg/l identified minerals lat. ºn long. ºe 1 tmk-1 uc-1 250753 683201 80 quartz, calcite (magnician), albite (calcian), clinochlore, biotite 2 tmk-2 uc-2 250743 683209 400 quartz, albite (calcian), dolomite, clinochlore, muscovite 3 tmk-4 uc-3 250732 683150 30 quartz, calcite (magnician), albite (calcian), biotite, rutile, amesite 4 tmk-5 uc-2 250715 683145 40 quartz, calcite (magnician), clinochlore, biotite 5 tmk-6 uc-1 250719 683234 5 quartz, , clinochlore, albite (calcian), biotite 6 tmk-7 uc-1 250725 683212 20 quartz, , calcite, clinochlore, albite (calcian), biotite 7 tmk-13 tandosaindad 250752 683240 30 quartz, , clinochlore, albite (calcian), biotite 8 tmk-16 uc-1 250750 683316 400 quartz, albite (calcian), calcite (magnician), clinochlore, biotite 9 tmk-18 uc-1 250740 683338 150 quartz, anorthite, polylithionite, clinochlore 10 tmk-19 tandosaindad 250926 683433 150 quartz, albite, calcite, chlorite (serpentinite), muscovite 11 tmk-23 tandosaindad 251138 683352 300 quartz, calcite (magnician), albite (calcian), biotite, clinochlore 12 tmk-24 tandosaindad 251152 683925 30 quartz, calcite (magnician), anorthite, phlogopite, clinochlore 13 tmk-26 tandosaindad 250931 683256 10 quartz, calcite, clinochlore, albite, phlogopite 14 tmk-41 tandosaindad 250708 683402 80 quartz, albite (calcian), phlogopite, clinochlore 15 tmk-42 tandosaindad 250707 683410 500 quartz, calcite, albite (calcian), phlogopite, clinochlore 16 tmk-71 lakhat 250018 683109 250 quartz, calcite, albite, dolomite, clinochlore, biotite 17 tmk-86 lakhat 250018 683422 0 quartz, calcite, albite (calcian), phlogopite, clinochlore 18 tmk-87 uc-1 250743 683351 5 quartz, polylithionite, calcite (magnician), albite (calcian). clinochlore 19 tmk-88 tandosaindad 250737 683418 200 quartz, albite (calcian), phlogopite, nitro calcite, clinochlore 20 tmk-89 tandosaindad 250811 683341 80 quartz, polylithionite, calcite (magnician), clinochlore, albite 21 tmk-90 tandosaindad 250834 683326 20 quartz, polylithionite, calcite, anorthite (sodian) 22 tmk-91 tandosaindad 250839 683343 10 quartz, polylithionite, calcite (magnician), albite (disordered), clinochlore 23 tmk-92 tandosaindad 250946 683331 60 quartz, polylithionite, albite (calcian), calcite, clinochlore 24 tmk-93 tandosaindad 250838 683220 60 quartz, , albite (calcian), calcite, polylithionite 25 tmk-95 uc-1 250806 683214 0 quartz, polylithionite, albite (calcian)., calcite, clinochlore 26 tmk-97 uc-1 250721 683311 60 quartz, polylithionite, albite (calcian). clinochlore 27 tmk-98 uc-2 250636 683325 300 quartz, albite (calcian), calcite, clinochlore 230 khan, a. et al./ jgeet vol 4 no 4/2019 28 tmk-99 uc-1 250627 683349 80 quartz, polylithionite, calcite (magnician), albite (calcian) 29 tmk-100 uc-2 250557 683405 100 quartz, calcite (magnician), anorthite (disordered), biotite 30 tmk-108 tandosaindad 250808 683503 0 quartz, calcite (magnician), anorthite (sodian), muscovite 31 tmk-110 tandosaindad 250835 683640 30 quartz, polylithionite, anorthite (disordered), clinochlore 32 tmk-112 lakhat 250831 683534 100 quartz, calcite (magnician), albite (disordered), zinnwaldite, clinochlore 33 tmk127 lakhat 250334 683219 5 quartz, polylithionite calcite (magnician), albite (disordered), zinnwaldite, clinochlore 34 tmk129 lakhat 250309 683259 30 quartz, calcite(magnician), albite (calcian), polylithionite, clinochlore 35 tmk-135 lakhat 250008 683134 60 quartz, calcite, anorthite, biotite, clinochlore 36 tmk-136 lakhat 250004 683117 80 quartz, polylithionite, calcite(magnician), albite (calcian), clinochlore 37 tmk-138 lakhat 250056 683111 40 quartz, polylithionite, calcite(magnician), albite (calcian), clinochlore 38 tmk-141 uc-1 250815 683317 20 quartz, polylithionite, calcite(magnician), albite (calcian), clinochlore 39 tmk-145 uc-2 250644 683244 80 quartz, polylithionite, calcite(magnician), albite (calcian) 40 tmk-153 tandosaindad 251056 683603 60 quartz, albite (calcian), calcite sample weighing 100 grams (n = 49) was sent to the laboratory for xrd analysis for mineral identification. 2.3. sediment analysis soil samples were analyzed by a widely used technique of x-ray diffraction (bish and post, 1989; moore and reynolds, 1997) to determine the crystalline phase of the same. all the samples were scanned through a range of 2θ angles. variable orientation of the powdered soil provided all possible diffraction directions. the d-spacing of each peak was subsequently obtained by the conversion of diffraction peaks. the conversion of peaks into d-spacing indicated a specific mineral due to the fact that every mineral manifest a distinct set of differing d-spacing. at the end, the d-spacing was compared with standard reference pattern. 3. results and discussion 3.1. mineralogical characterization of near aquifer sediments forty-nine representative soil samples were collected from near well sites in three talukas of tando muhammad khan district, where arsenic in groundwater occurs in the range of 10-500 μg/l (fig. 2). in tando muhammad khand taluka, arsenic varies between 10-500 μg/l in groundwater where about 80% of the wells have arsenic above who recommended value (10μg/l) for drinking purpose. on the other hand, 4 out of 6 wells in bhulri shah karim taluka shows arsenic content in the range of 10-200 μg/l. likewise, all 3 samples of water from bhulri shah karim exceed the who guideline value (50-300 μg/l). soil samples were collected from near these sites where groundwater exhibited the variable content of arsenic. mineralogical study was carried out using xrd technique which revealed the occurrence of quartz, mica and clay minerals as major components in all collected samples (table 1-3). table 3. minerals identified in the soil collected from various localities of bhulri shah karim taluka. s. no. sample code union council coordinates arsenic μg/l identified minerals lat. ºn long. ºe 41 tmk-39 mullakatyar 250633 681808 0 quartz, calcite, albite (calcian), phlogopite, clinochlore 42 tmk-58 bhulri shah karim 245204 682003 150 quartz, calcite (magnician), biotite, clinochlore, albite (calcian) 43 tmk-66 allayar turk 245814 682410 200 quartz, calcite, biotite, clinochlore, albite (calcian) 44 tmk-118 mullakatyar 245954 682244 10 quartz, albite (calcian), polylithionite, clinochlore 45 tmk-121 jhannansoomro 245622 682036 60 quartz, calcite (magnician), albite (calcian), polylithionite 46 tmk-122 jhannansoomro 245625 682017 80 quartz, calcite, albite (calcian), biotite table 4. minerals identified in the soil collected from various localities of taluka tando ghulam hyder. s. no. sample no. union council coordinates arsenic μg/l identified minerals lat. ºn long. ºe 47 tmk-105 nazarpur 250354 683622 300 quartz, calcite,polylithionite, albite (calcian), clinochlore 48 tmk-106 nazarpur 250302 683712 100 quartz, calcite (magnician), albite (calcian), polylithionite, clinochlore 49 tmk-107 nazarpur 250252 683745 50 quartz, polylithionite, calcite (magnician), albite (calcian), clinochlore quartz occurred in all the collected samples while plagioclase feldspar is second frequent mineral group in the order of albite (calcian) >albite>albite (disordered) = anorthite>anorthite (sodian) = anorthite (disordered). calcite is another dominate member among carbonate minerals which is detected in 40 out of total 49 soil samples. on the other hand, micaceous minerals span between frequency range of 3-38 samples in fine textured soil (silty-clay). these platy minerals varied in the order of clinochlore > polylithionite > biotite > phlogopite > muscovite in the study area. other rare minerals include amesite, nitrocalcite, rutile and zinnwaldite. these minerals occurring in the sediments of tando muhammad khan district are mainly derived from western himalayas during holocene period (giosan et al., 2006). the source of these minerals is basic igneous and metamorphic rocks. such micaceous minerals are possible source of fe and arsenic in the sediments of study area. interestingly, arsenic occurs in the range of 5-600 μg/l in groundwater samples collected from aquifers near to these micaceous sediments (table 2-4). a study carried out by seddique et al. (2008) in bengal deltaic plain explained that arsenic is mainly fixed in silicate minerals as compared to fe and mn oxides which host only 5% as. it implies that the silicate minerals are main source of arsenic in the deltaic sediments. 3.1.2. clinochlore clinochlore is a member of chlorite group and is one of the better-known members. a study carried out by nath et al., (2009)has shown the occurrence of clinochlore in the aquifer khan, a. et al./ jgeet vol 4 no 4/2019 231 sediments of bengal basin which is also drained by ganges, brahmaputra and meghna rivers from himalayas. clinochlore seems to play a vital role in elevated concentration of arsenic and iron via desorption process in the groundwater of tando muhammad khan district, where its occurrence is more prevalent than biotite and other phyllosilicates (table 2-4). the occurrence of clinochlore in 36 soil samples from all three talukas of tando muhammad khan district can have substitution of fe in the cationic sites in the form of fe+2 and /or fe+3, where a wide range of arsenic (5-500 μg/l) occurs in the groundwater(mosaferi et al., 2014) 3.1.3. polylithionite about half of the collected samples contain polylithionite mineral where most of the aquifers contain arsenic > 20 μg/l (table 3). polylithionite is also reported in the sediments of chandpur district, bangladesh where almost all the shallow hand tube wells water is highly arsenic contaminated (ahmed et al., 2008). this mineral is one of the lithium rich mica which is not a better-known mica mineral but its high occurrence in the sediments of indus delta clued about its less chemical reactivity and abundance in the source area. the occurrence of objectionable arsenic concentration in the aquifers overlying the polylithionitic soil suggests a strong affinity with arsenic with this mineral. 3.1.4. biotite-phlogopite biotite occurred in the fourteen collected sediment samples from tando muhammad khan and bhulri shah karim talukas and muscovite occurs in three soil samples of union council-2 and tando saindad. the role of phyllosilicates to serve as asfixing phase has been pointed out in previous studies (foster et al., 2000; breit et al., 2001; (pal et al., 2002; ahmed, 2004). biotite shows more reactive site for arsenic adsorption as compared to muscovite. likewise, silty mica as compared to sand size provide more effective site for arsenic adsorption. there is an effective role of ph on arsenic adsorption on micas. studies carried out by chakraborty et al., (2007) and pal et al., (2002) revealed that silt-sized biotite retained 214 mg/kg of arsenate in circum neutral ph (6.5–7.5). conversely, silt sized. it can be inferred from these studies that flood plain soil is more prone to retain arsenic as compared to aquifer sediments. similar pattern is observed in the study area where surface sediments comprises micaceous minerals (muscovite biotite and phlogopite) which are thought to be the good absorbents of metals (ansari, 1997; sing et al, 2005; datta and subramanian, 1997). these minerals absorb as into surface fe(iii) and as rich precipitates (charlet et al, 2002). dissolution and alterations in biotite and muscovite within acidic to alkaline ph region have been investigated by various workers (kalinowski and sachweda, 1996; malmstrom et al., 1996; turpault and trotignon, 1994; samson et al, 2005). interestingly, biotite provides more reactive surface as compared to muscovite (farquhar et al, 1997). moreover, edges of freshly cleaved muscovite surface are more reactive site than crystal face (zhang and bailey, 1998; johnsson et al, 1992). however, the accumulation of arsenic both on edges and to lesser extent on the basal pinacoid of mica is reported by charlet et al, (2005). beside iron sulfides and other primary fe-bearing minerals, iron (hydro) oxides are pressured to be derived from weathering of micas(polizzotto et al., 2006). it was observed by chakraborty et al., (2007)in an experiment that biotite dissolution starts from the crystal’s edges inward. moreover, secondary minerals such as fe oxides are precipitated mostly at the edges relative to basal surfaces (murakami et al., 2003). .nath et al., (2008) shows that top soils are enriched in arsenic with low fe-oxyhydroxides that can be compared with the findings of métral et al. (2008). chakraborty et al. (2007)explained that fe(oh)3 is presumed to be derived from the weathering of mica, iron sulfide and other primary fe-bearing minerals in the holocene aquifer sediments where highest arsenic concentrations are reported. phlogopite is fourth important micaceous mineral reported in the soil of study area where it is reported in seven soil samples. it is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. phlogopite is also known as magnesium mica which is the magnesium end member of the biotite solid solution series, with the chemical formula kmg3alsi3o10(f, oh)2. 3.1.5.chlorite the chlorites are a group of phyllosilicate minerals. chlorite is major detrital mineral transported through rivers which have been originated from himalayas (chakrapani et al., 1995)this mineral is the product of physical weathering which prevails in cold climate (bockheim, 1982; campbell and claridge, 1982)since the sediments have been sourced from himalayan region (alpine glacier) and transported through indus river to reach the deltaic setting, the occurrence of chlorite in high proportion is rational. contrary to this, kaolinite (indicator of intense chemical weathering) was not detected in any soil sample (table 2a-c). it implies that monsoon climate was weakened gradually since mid-holocene and physical disintegration of rocks dominated over chemical weathering (alizai et al., 2012)a study carried out by (rasool et al., 2016) in upper reaches of indus basin (punjab plain) determined the occurrence of high arsenic groundwater in aerobic aquifers where sediments showed linear relationship to xrd intensity of chlorite. a study carried out in bengal delta revealed that grey soft clay constitutes chlorite beside other minerals(pal and mukherjee, 2009) 3.1.6. calcite calcite is reported to occur in 40 sediment samples (n =49) which is expected to be derived by the weathering of limestone beds of eocene age which are cropping out in ganja hills located on the western bank of river indus near study area. moreover, calcitemagnesiun occurs more frequently as compared to calcite which is attributed to one of the important magnesium sources in the aquifers of tando muhammad khan district. nitro calcite is found in a sample collected from an irrigated well in agricultural land of tando saindad union council, where groundwater contained 200 μg/l arsenic. although dolomite is reported only in two samples of uc-2 and lakhat but a good correction has been observed with aqueous arsenic where groundwater contains 400 and 250 μg/l arsenic respectively. calcite is the major carbonate mineral in study area which suggests its proximal source due to the fact that carbonate minerals are less resistant against chemical weathering (garrison, 1981)as a result, the transportation of calcite as residual grain from himalayas to the indus deltaic plain is not possible. hence, the source of calcite is weathering of laki limestone occurring in the proximity of indus river in study area. the calcite contains 1-8 mg/kg of arsenic in it whereas dolomite host as < 3 mg/kg (boyle and jonasson, 1973). likewise, limestone hosts about 2.6 mg/kg of arsenic (baur and onishi, 1969). hence, these carbonate minerals are serving as potential minerals to adsorb as in calcareous soils, 232 khan, a. et al./ jgeet vol 4 no 4/2019 where calcite plays a vital role in retention and solubility of arsenic (mehmood et al., 2009). 4. conclusion present study has revealed the occurrence of large number of phyllosilicates which are also reported from bengal delta plain in the fine fractions of the soil. these minerals included clinochlore, polylithionite, biotite and phlogopite as major platy minerals. these fine silicates are serving as main source of arsenic in the deltaic setting either by sorbing the arsenic or hosting this metalloid into their structure. upon prevalence of anoxia caused by bacteria mediated organic matter decay, these minerals release their sorbed or structural arsenic into the water which reaches the aquifer depth upon infiltration. calcite is major carbonate mineral which is serving as arsenic host. further studies are required to assess the chemistry of soil and aquifer sediments to better explain the source and mechanism of arsenic mobilization in shallow alluvial aquifers of the deltaic system. 5. acknowledgement present study was carried out with the financial support of higher education commission (hec) on project titled “geochemical and geo-microbiological investigations of groundwater arsenic contamination in district tando muhammad khan, sindh: impact of human health and mitigation options”. authors are highly indebted to geoscience advanced research laboratory, islamabad for providing the facility to analyze the sediment samples. 6. references acharyya, s. 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(1994) ‘arsenic distribution in soils. in “arsenic in the environment, part i: cycling and characterization”(jo nriagu, ed.)’. © 2016 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 nasution f and nalendra s / jgeet vol 02 no 03/2017 203 characterization of coal quality based on ash content from m2 coal-seam group, muara enim formation, south sumatra basin frillia nasution 1* , stevanus nalendra 1 1 geology study program, engineering faculty, sriwijaya university. * corresponding author: nasutionfrillia@gmail.com tel.:+62-852-7329-9464; received: may 22, 2017. revised : july 5, 2016, accepted: aug 5, 2017, published: 1 sept 2016 doi : 10.24273/jgeet.2017.2.3.292 abstract muara enim formation is well known as coal-bearing formation in south sumatra basin. as coal-bearing formation, this formation was subjects of many integrated study. muara enim formation can be divided into four coal-seam group, m1, m2, m3, and m4. the m2 group comprising of petai (c), suban (b), lower mangus (a2), and upper mangus (a1). depositional environments of group m2 is transitional lower delta plain with sub-depositional are crevasse splay and distributary channel. the differentiation of both sub-depositional environments can be caused the quality of coal deposit. one of quality aspects is ash content. this research conducted hopefully can give better understanding of relationship between depositional environments to ash content. group m2 on research area were found only seam c, seam b, and seam a2, that has distribution from north to central so long as 1400 m. coal-seam thickness c ranged between 3.25-9.25 m, seam b range 7.5413.43 m, and seam c range 1.53-8.37 m, where all of coal-seams thickening on the central part and thinningsplitting to northern part and southern part. the ash content is formed from burning coal residue material. ash contents on coal seam caused by organic and inorganic compound which resulted from mixing modified material on surrounded when transportation, sedimentation, and coalification process. there are 27 sample, consists of 9 sample from seam c, 8 sample from seam b, and 10 sample from seam a2. space grid of sampling is 100-150 m. ash content influenced by many factors, but in research area, main factor is existence of inorganic parting. average ash content of seam c is 6,04%, seam b is 5,05%, and seam a2 is 3,8%. low ash content influenced by settle environment with minor detrital material. high ash content caused by oxidation and erosional process when coalification process. ash content on coal in research area originated from detritus material carried by channel system into brackish area or originated from higher plant in brackish area. the high ash content also can be caused by after the coal deposited. it had originated from overburden horizon which infill in cleat of coal seam. keywords: muara enim formation, group m2, transitional lower delta plain, ash content. 1. introduction 1.1. background muara enim formation is well known as coalbearing formation in south sumatra basin. as coalbearing formation, this formation was subjects of many integrated study, such as sedimentology, depositional environment, paleogeography, structure geology, tectonic evolution, depositional history, and many more (de coster, 1974). muara enim formation consists of sandstone, claystone and coal. coal in bottom part of middle palembang formation in southern part of this basin often used as stratigraphy marker. muara enim formation can be divided into four coal-seam group, m1, m2, m3, and m4. (de coster, 1974) interpreted this formation deposited in late miocene-pliocene. the m2 group is comprising of petai (c), suban (b), lower manggus (a2), and upper manggus (a1). group m2 consists of intercalated of claystonesandy claystone, fine-medium sand, coal in bottom part. coal seams in group m2 have limited distribution. it caused by depositional environment from this unit. depositional environment of group m2 is transitional lower delta plain with subdepositional are crevasse splay and distributary channel. the differentiation of both sub-depositional environments can be caused the quality of coal deposit. one of quality aspects is ash content. this research conducted hopefully can give better understanding of relationship between depositional environments to ash content. mailto:nasutionfrillia@gmail.com 204 nasution f and nalendra s / jgeet vol 02 no 03/2017 1.2. description of the research area the work is conducted in the bukit kendi coalfield that has been mined since 1996, and nowadays the mine concessions is under the management of the state-owned company of baramulti group. in recent times, the area becomes a mining area, this can have a positive impact on research because it can find outcrops such as on the mine wall, on the cliffs of hauling roads, and some rivers. the region is administratively included within pullo panggung district, tanjung lalan district, and sleman district of muara enim regency of south sumatra province. geographycally, muara enim located on between 4⁰-6⁰ls and 104⁰-106⁰bt (fig. 1). research area can be accessed using light vehicle for five hours from palembang city. the purpose of this research is to identified coal quality in pullo panggung area, and objectives of this research is to mapping the coal distribution based on ash content. fig. 1. research area (pemerintah kabupaten muara enim, 2012). 2. an overview of geology 2.1. tectonic framework south sumatra basin formed in early tertiary (eocene-oligocene) when graben series develops as oblique subduction system between hindia oceanic plate beneath asian continental plate (de coster, 1974). there are three orogeny episode which formed structure framework of south sumatra basin, they are middle mesozoikum orogeny, late cretaceous-early tertiary and plio-pleistosen orogeny (de coster, 1974),. first episode, paleozoikum and mesozoikum metamorphosed deposit, folded and faulted into structural boudine and intrusion by granite batholith and also formed basement structural style. (pulunggono et al., 1992), this phase formed transform fault with nw-se trend (fig. 2). second episode, in late cretaceous there are extensional phase which resulted tensional movement and formed graben and horst with n-s dominant trend. combined with mesozoikum orogeny and pre-tertiary weathered rocks, those tensional movement formed old structure which controlled pre-talang akar formation development. fig. 2. south sumatra tectonic framework (pulunggono et al., 1992). third episode are compressional phase in pliopleistocene which caused depositional pattern changed to regression and influenced to formed recent fold and fault structural style. on this tectonic period, there also uplifted of bukit barisan mountains which resulted semangko strike-slip fault along bukit barisan mountains. horizontal movement began from early pleistocene until now which influence the south sumatra basin and central sumatra basin condition. this condition caused newly faults have development trend parallel with semangko faults. due to this horizontal movement, orogeny in plio-pleistocene resulted folds with nw-se but the faults have nesw oriented. faults which formed in this basin are thrust fault, strike-slip, and normal fault. dominant structures are structures with nw-se trend which resulted from plio-pleistocene orogeny. as patterns, structures can be divided into old pattern with n-s oriented and younger pattern with nw-se trend which parallel with sumatra trend. 2.2. physiography physiographically, (bemmelen, 1949), divided sumatra into six physiography zone (fig. 3). they are a) barisan range, b) semangko zone, c) tigapuluh mountains zone, d) outer island arc zone, e) sunda shelf, and f) lowland and undulating zone. based on (bemmelen, 1949) classification, research area located on lowlands and undulating zone (orange square). 2.3. regional stratigraphy regional stratigraphy of south sumatra basin well known as megacycle which consists of transgression and followed by regression phase (adiwidjaja and de coster, 1973). formations nasution f and nalendra s / jgeet vol 02 no 03/2017 205 deposited on transgression phase are telisa group (talang akar fm., baturaja fm., and gumai fm.). on other side, regression phase deposited palembang group (air benakat fm., muara enim fm., and kasai fm. older formations (lemat fm. and older lemat fm. deposited before main transgression phase. stratigraphy unit of south sumatra basin from oldest to youngest (de coster, 1974), are pretertiary group, kikim fm., older lemat fm., lemat muda fm., talang akar fm., baturaja fm., telisa fm., gumai fm., lower palembang fm., middle palembang fm., and upper palembang fm. (fig. 4). fig. 3. physiography zone of sumatra (bemmelen, 1949). fig. 4. regional stratigraphy of south sumatra basin (sutriyono et al., 2016). muara enim formation is coal-bearing formation in south sumatra basin. muara enim formation can divided into four coal-seam group (ilyas, 1999), accordingly from bottom to top are m1, m2, m3, and m4 (fig. 5). the m2 group have found in research area. group m2 contains majority of coal resources in tanjung enim area. the m2 consists of three major coal unit (from top to bottom); mangus, suban and petai (amier, 1991). recognized these unit locally split into two seams as follows: mangus unit (a1 and a2 seams), suban unit (b1 and b2 seams), and petai unit (c1 and c2 seams) fig. 5. stratigraphy of muara enim formation (modified (a.d.tarsis, n.d.)). pulunggono, 1986 interpreted muara enim formation deposited in shallow marine to parallic and non-marine environments. this formation consists of claystones and shales intercalated by sandstone and coal layer. on other hand, based on analysis of well and seismic data, divided muara enim formation into two depositional packages: lower and upper muara enim formation (muksin et al., 2012),. these two depositional packages consists of three subenvironment, they are tidal mud flat, tidal mixed flat and tidal sand flat environment. 3. research method research method was conducted on this study are:  field observation, including observation of relationship coal layer to other layers (bottom and top) and also the condition which influenced the layers.  quality analysis of coal layer to identified distribution of coal layer and geology factors.  research were conducted by reconnaissance through study literature and field observation, analyses phase (primary analysis and secondary analysis), and conclusion phase (result). group m2 on research area were found only seam c, seam b, and seam a2, that has distribution from north to central so long as 1400 m (fig. 6). 206 nasution f and nalendra s / jgeet vol 02 no 03/2017 coal-seam thickness c ranged between 3.25-9.25 m, seam b range 7.54-13.43 m, and seam c range 1.538.37 m, where all of coal-seams thickening on the central part and thinning-splitting to northern part and southern part. the ash content is formed from burning coal residue material. ash contents on coal seam caused by organic and inorganic compound which resulted from mixing modified material on surrounded when transportation, sedimentation, and coalification process. there are 27 sample, consists of 9 sample from seam c (table 1), 8 sample from seam b (table 2), and 10 sample from seam a2 (table 3). space grid of sampling is 100-150 m. the coal quality analysis discussed throughout this research were analyzed on air dried basis (adb.). table 1. ash value of seam c. tabel 2. ash value of seam b. table 3. ash value of seam a2. fig. 6. outcrops of seam a2, seam b, and seam c. sample code seam ash value (adb) fr-01 b 5,63 fr-08 b 8,04 fr-02 b 5,61 fr-12 b 6,4 fr-10 b 3,07 fr-05 b 4,95 fr-14 b 3,69 fr-07 b 3,05 sample code seam ash value (adb) fr-01 a2 3,03 fr-08 a2 1,71 fr-02 a2 2,48 fr-03 a2 3,39 fr-09 a2 2,59 fr-04 a2 3,28 fr-10 a2 3,24 fr-05 a2 2,71 fr-07 a2 6,85 fr-06 a2 9,56 sample code seam ash value (adb) fr-11 c 4.66 fr-15 c 8,13 fr-12 c 6 fr-16 c 7,45 fr-17 c 7 fr-10 c 4,73 fr-05 c 5,59 fr-14 c 7,24 fr-07 c 2,23 nasution f and nalendra s / jgeet vol 02 no 03/2017 207 4. result and discussion the ash contents for all samples varies slightly, with average ranging from 1.71-9.56 adb.%. 4.1. ash content analysis of seam c seam c on research area have thickness around 3.25-9.25 m, where divided into 5 body with 4 parting with various thickness between 5-30 cm. stratigraphic profile of seam c can be seen on fig. 7. fig. 7. coal profile of coal-seam c in northern (left), central (middle), and southern (right) of research area. based on ash content on seam c (fig. 8), showed highest ash content located on central part of research area, besides that northern and southern part have low ash content. it can be caused by northern and southern part are depocenter of basinal area. this condition made coal layer on this part have thick layer and less of parting. the highest ash content located on central part of research area, it indicated that coal deposited in edge of basinal area. this part could influenced by terrestrial material. this condition indicated why ash content on edge of basinal have ash content higher than depocenter of basinal area. fig. 8. iso ash map of seam c. 4.2. ash content analysis of seam b seam b on research area have thickness around 7.54-13.43 m, where divided into 5 body with 4 parting with various thickness between 4-20 cm. stratigraphic profile of seam c can be seen on fig. 9. fig. 9. coal profile of coal-seam b in northern (left), central (middle), and southern (right) of research area. based on ash content on seam b (fig. 10), showed ash content increased to northern part. that analysis indicated that coal seam b in northern part deposited in edge of basinal area. this part could influenced by terrestrial material. this condition indicated why ash content on edge of basinal have ash content higher than depocenter of basinal area. fig. 10. iso ash map of seam b. 4.3. ash content analysis of seam a2 seam a2 on research area have thickness around 1.53-8.37 m, where divided into 3 body with 2 parting with various thickness between 5-10 cm. stratigraphic profile of seam c can be seen on fig. 11. fig. 11. coal profile of coal-seam a2 in northern (left), central (middle), and southern (right) of research area. 208 nasution f and nalendra s / jgeet vol 02 no 03/2017 based on ash content of seam a2 (fig. 12), showed ash content increased to southern part. it caused by southern part is edge of basinal area. coal which deposited in edge of basinal area mainly influenced with terrestrial material. it resulted coal in this area have higher ash content than central part. the low ash content in central part was assumed that minor terrestrial content. it indicated the area is depocenter of basinal area. fig 12. iso ash map of seam a2. 4.4. interpretation of depositional environment depositional environment of group m2 in research area is transitional lower delta plain by using horne, 1978 classification of depositional environment based on coal characteristic. it indicated by lithology changed and repeated lithology as characteristics of depositional processes influenced by tidal (thomas, 2013) (fig. 13). parting occurence on coal seam in research area caused by in depositional processes of coal there are flooding phase or formed by tidal process which caused fine grain sediment also deposited coincided with coalification process. but fine grain sediment was not continuous deposited because the limited source of this material. the depositional process still occupied to deposit peat material and coalification process. this process can be caused occurrence of parting in coal seam. ash content on coal seam in research area originated from detritus material which brought by channel system into brackish area or originated from higher plant in brackish area. the high ash content also can be caused by after the coal deposited. it can origin from overburden horizon which infill in cleat of coal layer. in research area, coal seam have found with various thickness (thick and thin). it influenced by two processes: process when depositional takes place and process after deposited. first process is basin subsidence, if there are rapid subsidence it could made thick coal seam. second process is erosional process by channel changing. it could be caused thinning on edge of coal seam. on other hand, various coal thickness can also influence by different of rate of peat growth. if rapid peat growth rate, it caused thick coal layer, but if slow peat growth rate, it caused thin coal seam. 5. conclusion coal-seam group of muara enim formation in research area occurred on group m2 unit which consists of seam c, seam b, and seam a2. group m2 have various thickness. thickness of seam a2 is around 1.53-8.37 m. seam b between 7.54-13.43 m, and seam c have thickness is 3.25-9.25 m. all of seam have thickening geometry in central part and thinning in both of edge part (northern and southern part). based on sedimentation characteristic, group m2 in research area deposited in transitional lower delta plain with sequence interburden characteristics, intercalated of fine-coarse grain with fining upwards and coarsening upwards, thick coal seam with continuous distribution. ash content influenced by many factors, but in research area, main factor is existence of parting. average ash content of seam c is 6.04 adb.%, seam b is 5.05 adb.%, and seam a2 is 3.8 adb.%. low ash content influenced by settle environment with minor detrital material. high ash content caused by oxidation and erosional process coincided with coalification process. fig. 13. measuring section model compared to depositional environment of group m2. nasution f and nalendra s / jgeet vol 02 no 03/2017 209 acknowledgements this research was funded by the sriwijaya university undergraduate geology study program. the authors would like to gratefully acknowledge pt. prima mulia sarana sejahtera (baramulti group) for the support during field session and for providing some coal analysis. references a.d.tarsis, n.d. penyelidikan batubara bersistem dalam cekungan sumatera selatan di daerah benakat minyak dan sekitarnya, kabupaten muara eim propinsi sumatera selatan. jakarta. adiwidjaja, p., de coster, g.l., 1973. pre-tertiary paleotopography and related sedimentation in south sumatra. proc. indones. pet. assoc. 89 104. amier, r.i., 1991. coals, source rocks and hydrocarbons in the south palembang sub-basin, south sumatra, indonesia. bemmelen, van, 1949. geology of indonesia, vol. ia. ed. goverment printing office, the hague. de coster, g.l., 1974. the geology of the central and south sumatra basins. proc. indones. pet. assoc. third annu. conv. june 1974 77 110. horne, j.., ferm, j.., caruccio, f.., baganz, p., 1978. depositional models in coal exploration and mine planning in appalachian region. am. assoc. pet. geol. bull. 62, 2379 2411. ilyas, s., 1999. pengkajian cekungan btubara di daerah talang ubi, kabupaten musi banyuasin dan muara enim, provinsi sumatera selatan. pemaparan has. kegiat. lapangan dik-s batubara, dsm 1 6. muksin, n., yusmen, d., waren, r., werdaya, a., djuhaeni, d., 2012. regional depositional environment model of muara enim formation and its significant implication for cbm prospectivity in south sumatra basin , indonesia * 80272. pemerintah kabupaten muara enim, 2012. peta administrasi wilayah kabupaten muara enim. pulunggono, a., 1986. tertiary structural features related to extensional and compressive tectonics in the palembang basin, south sumatra. proc. indones. pet. assoc. pulunggono, a., s. haryo, a., kosuma, c.g., 1992. pretertiary and tertiary fault systems as a framework of the south sumatra basin; a study of sar-maps. proc. indones. pet. assoc. 21, 92 11.37. sutriyono, e., wiwik, e., hastuti, d., susilo, b.k., 2016. geochemical assessment of late paleogene synrift source rocks in the south sumatera basin. int. j. geomate 11, 2208 2215. thomas, l., 2013. coal geology, second edi. ed, coal geology. a john wiley & sons, ltd.,. doi:10.1002/9781118385685 1. introduction 1.1. background 1.2. description of the research area 2. an overview of geology 2.1. tectonic framework 2.2. physiography 2.3. regional stratigraphy 3. research method 4. result and discussion 4.1. ash content analysis of seam c 4.2. ash content analysis of seam b 4.3. ash content analysis of seam a2 4.4. interpretation of depositional environment 5. conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 fatriadi, r. et al./ jgeet vol 02 no 01/2017 53 effectiveness of the national program for community empowerment (pnpm) for infrastructure development accelerated and geoplanology in district of marpoyan damai, pekanbaru riry fatriadi 1, , febby asteriani 1 , catur cahyaningsih 2, * *1 planology department, universitas islam riau, jl. k.h nasution no. 113 marpoyan, 28284, pekanbaru, indonesia. 2 department of geological engineering, universitas islam riau, jl. k.h nasution no. 113 marpoyan, 28284, pekanbaru, indonesia abstract since 2007 pnpm urban realize that poverty is a structural problem and multi-dimensional. in pnpm urban perspective , the complexity of the various dimensions of poverty -related social , political , economic , and asset . this research aim is to know the effectiveness of the national program for community empowerment for infrastructure development accelerated. in this research , the authors use an explanatory survey research methods . selected number of samples in the analysis of the effectiveness of pnpm urban infrastructure improvements are stakeholders involved in pnpm urban population in the research area of all stakeholders involved in pnpm urban in district marpoyan damai , the authors take purposively respondents who meet the criteria and are associated with research. the results showed that increasing road infrastructure with the pnpm mandiri. the average improvement of road infrastructure after the pnpm urban amounted to 35.8 %. the average increase in the quality of infrastructure before the pnpm urban program is only at 4.4 % per year . this indication shows that roads infrastructure and the quality of the road surface to be increased significantly in the presence of the pnpm urban marpoyan damai in the district . from interviews with relevant stakeholders pnpm urban, respondents said pnpm urban was very effective against the improvement of infrastructure in district marpoyan damai . respondents argue that any proposed activity in infrastructure always realized by pnpm urban . geological condition of study consists of alluvium sand, gravel, clay, peat swamp, plant remain in quaternary age. there are two anticline in this area that is part western and southern and fault inferred direction northwest-southeast in the middle area of research so that the topography of the area of research a bit wavy and faulted that need observation on landuse planning such as drainage, airport, residential and availability of clean water.. keywords: poverty, effective, geology, land use planning 1. introduction poverty is a cross sectors problems, cross area and cross generation problem, so to handle an integrated comprehensive and sustainable approach is required. in pnpm urban perspective, the complexity of poverty related to various dimensions of social, political, economic, and assets. birds should start from the social aspect of humanity fundamentally. root causes of poverty are not solely economic issues and more on the issue of inequality, due to the collapse of human values and the neglect of governance principles good governance becomes the basis for pnpm urban to build social capital and start a social change on an ongoing basis (kuncoro, 2004; suryono, 2001 & tri wahyu, 2011). weak social capital also encourages a shift in public behavior that is farther away from the spirit of independence, solidarity and concern to solve the problem together. institutional conditions led people who are not rooted and can not be trusted are generally thrives in situations where the general public is not helpless. the powerlessness of society in addressing and cope with situations in their environment, which in turn encourages indifference, do not care, do not believe in themselves, relying on outside help to overcome the problems faced, not independent, as well as waning orientation of moral and values sublime in the society, especially the sincerity, fairness and honesty. (arikunto, 1998; ministry of national education, 2003; george odunga, 2013; nawawi, 1998; sedarmayanti, 2001; todaro, 2000; wahab, 2004) geology and regional planning is required to determine the rocks composition of rocks in the research area. (cahyaningsih, 2016); (mairizki and * corresponding author : caturcahyaningsih@eng.uir.ac.id tel: +62-82284013121 received: feb 1, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017 doi: 10.24273/jgeet.2017.2.1.30 mailto:caturcahyaningsih@eng.uir.ac.id 54 fatriadi, r. et al./ jgeet vol 02 no 01/2017 cahyaningsih, 2017); (putra and choanji, 2016), (suryadi, 2016) & (yuskar, 2016). 2. aim the purpose of this study was to examine the effectiveness of pnpm urban pekanbaru to accelerate infrastructure development and regional geology planning in the district marpoyan, pekanbaru. 3. methods explanatory survey research methods using for this research. survey research is an investigation conducted to obtain the facts from existing symptoms and seek explanations are factual and explanatory means explaining events or circumstances right now, and explain events or circumstances that would come. 3.1 research variables the variables of research can be seen in table 1. 3.2 sampling technique the samples were selected in the analysis of the effectiveness of pnpm urban against improvement of infrastructure are stakeholders involved in pnpm urban at the study site from the population of all stakeholders involved in pnpm urban in the marpoyan damai peace. number of ksm (self help groups) that consists of community groups and stakeholders directly involved in pnpm urban is 80 ksm. in conducting the sample size calculation was based on an error of 5%. using tables (sugiyono, 2000). from the table it can be determined the number of samples taken in the district. marpoyan damai damai with a population of 80 is 66 samples (table 2). ksm determination on each mfi usingtechnique, simple random sampling meaning that researchers sampled randomly from the ksm amount in an mfi. 3.3 geological analysis regional geological map sheets pekanbaru no 0816 from coordinating surveys and mapping agency (bakosurtanal) was used to analyze rock composition of age of rocks. this analysis is done in of geological basic laboratory universitas islam riau. 4. result 4.1 analysis of public participation in the urban pnpm in district marpoyan damai pnpm urbanis a process of learning communities to alleviate poverty. the learning process is actually a process of education, meaning that changes can occur through a process of education, accompanied by a facilitator in the village / village goals. the stages of pnpm urban cycle can be seen in table 3. in district marpoyan damai, community participation in the implementation of pnpm urban cycle is very high. be it in the citizen readiness rembug socialization, fgd (focus group discussion) rk (reflection poverty), mapping governmental (ps), election of members of the mfi base level, pnpm volunteers, as well as in the preparation of the medium term plan poverty reduction program (pjm pronangkis). every society, both men and women play together to solve the problem of poverty. community participation in the district of marpoyan damai each village can be seen in table 4. table 1 . effectivity variable of pnpm mandiri at city on acceleration of infrastructure development variable indicator sub indicator infrastructure ● society participation ● improving the quality of infrastructure development ✓ public participation in pnpm mp ✓ improvement of quality of infrastructure development ✓ contributions of public funds on infrastructure development financing table 2. number of sampling no. microfinance ksm total sample 1 tangkerang west makmur 19 16 2 damai indah makmur 17 14 3 jaya woner 14 11 4 maharatu makmur 8 7 5 east sidomulyo sorcerer 22 18 total 80 66 source: observation and analysis in 2011 fatriadi, r. et al./ jgeet vol 02 no 01/2017 55 table achievement of participation of the population in the district of marpoyan damai above can be seen that, every activity on theof stages pnpm urban cycle performed with indicators set every village in the district marpoyan damai has been reached, even enthusiastic residents in participating in every activity is high enough, it can be seen in table 4 that any activities carried out in excess of the specified indicators. every citizen of both men and women have equal rights. they jointly play an important role for the implementation of each activity of pnpm urban in district marpoyan peace. the education process is conducted in the district of marpoyan damai has an impact on public awareness. so grows the critical consciousness of society, such as in the implementation of the poverty reflection (rk) which foster the values of justice, equality, mutual understanding, and mutual care to the problems of others. district of marpoyan together to learn to identify, analyze patterns of relationships (interactions) they are in social life, causing equal and equitable relationship. integrated policy and the provision of appropriate information can stimulate the development of infrastructure, increase community participation, creating community awareness. social relationships in a fair, people in the district of marpoyan damai has grown values appreciate each other, give each other, understand each other so that they are empowered to selfreliance in poverty reduction. through this learning process, it is expected the public is able to change the mindset and attitude as human behavior is responsible for running his nature as a human, that human beings are capable of providing the potential that exists within him for the welfare of themselves and their surroundings. table 3. pnpm urban cycle stages cycle what is learned? principles of community values mindset rembug community preparedness (rkm) participation: learning communities decide consciously efforts to solve the problems they need justice and equality: all layers of society has the right to obtain information and make decisions society merupaka subject of development and reserve the right to determine their own destiny without coercion from outside parties, but based on their critical kesanadan reflection poverty (rk) participation: engagement to determine the main problems of poverty justice and equality, mutual understanding and mutual care for the problems of others. honesty to acknowledge the problem the main causes of poverty: the erosion of human values, all parties are responsible in solving the problem of poverty. people able to analyze the causal problem of poverty mapping governmental (ps) participation, transparency of information in exploring the potential and problems together caring about the problems of the poor, mutual respect, mutual understanding, equality in the activities of the community were able to conduct a study and penelitiah simple view of the problems in the region development bkm democracy, participation, decentralization in the institutional development of representative honesty, fairness, equality, volunteerism becomes a commitment to all citizens people were able to organize themselves in determining who should lead pjm pronangkis (participatory planning) participation, transparency, democracy in the learning process preparing plans to meet community needs justice, honesty and togetherness in an effort to meet the need to address the issue of poverty can be tackled society was able to plan the program. society has the responsibility for planning. ksm organizing participation, democracy, accountability, within the group as social capital justice, honesty, equality, mutual care among group members, mutual understanding, mutual respect and mutual trust society capable of organizing itself in society source: module review the implementation cycle pnpm urban 56 fatriadi, r. et al./ jgeet vol 02 no 01/2017 table 4. achievement participation residents in the district marpoyan damai village event achievementparticipation & women's adult population total population adult indicator 10% (pa mfi 40%, pjm 5%) realizatio n (+ / -) achieve ment percentage of accomplish ment participatio n population adult indicator 40% of women (tim ps 50%) realized (+ / -) achieve ment percentage achievemen t of women's participatio n tangkerang barat socialization and rkm 1326 1409 13257 83 achieved 11% 530.28 586 56 achieved 42% volunteers 1175 1194 11751 19 reached 10% 470.04 494 24 achieved 42% fgd rk 1225 1295 12253 70 achieved 11% 490.12 533 43 achieved 42% ps 1225 1307 12253 82 achieved 11% 490.12 547 57 achieved 42% tim ps 1225 1249 12253 24 achieved 10% 631 613 18 achieved 51% election of members of the mfi 4901 4945 12253 44 achieved 40% 1960.48 2000 40 achieved 41% preparation of pjm 613 641 12253 28 achieved 5% 245.06 277 32 achieved 44% tangkerang tengah socialization and rkm 31 417 3142 3210 68 achieved 10% 1257 1312 55 achieved 41% volunteers 3142 3211 31417 69 achieved 10% 1256.68 1317 60 achieved 42% fgd rk 3267 3307 32667 40 achieved 10% 1306.68 1352 45 achieved 41% ps 3267 3307 32667 40 achieved 10% 1306.68 1363 56 achieved 42% tim ps 3267 3300 32667 33 achieved 10% 1633 1674 41 completi ons 51% election of members of the mfi 13067 32667 13099 32 achieved 40% 5226.72 5261 34 reached 40% preparation of pjm 1633 1670 32667 37 achieved 5% 653.34 693 40 achieved 42% fatriadi, r. et al./ jgeet vol 02 no 01/2017 57 table 5. continued village activity populationparticipation achievement adult & women total population adult indicator 10% (pa mfi 40%, pjm 5%) realiz ation (+ / ) achieveme nt percentage of accomplishme nt participation population adult indicator 40% of women (tim ps 50%) realize d (+ / ) achievem ent percentage achievement of women's participation wonorejo socialization and rkm 634 817 183 6337 achieved 26% 253.48 345 92 achieved 44% volunteers 607 647 6067 40 achieved 11% 242.68 270 27 achieved 43% fgd rk 616 649 6157 33 achieved 13% 246.28 264 18 achieved 41% ps 616 661 6157 45 achieved 15% 246.28 272 26 achieved 42% tim ps 616 631 6157 15 achieved 10% 776 468 308 achieved 53% election of members of the mfi 2463 2498 6157 35 achieved 40% 985.12 1135 150 achieved 72% preparation of pjm 308 370 6157 62 achieved 7% 139.34 173 34 achieved 45% maharatu socialization and rkm 15 070 1507 1835 328 achieved 12% 602.8 166 769 achieved 42% volunteers 1507 1636 129 1507 0 achieved 12% 602.8 682 79 achieved 42% fgd rk 2240 2282 15470 42 achieved 15% 937 896 41 achieved 42% ps 1627 1671 16270 44 achieved 11% 650.8 730 79 completio ns 43% tim ps 1627 1665 16270 38 achieved 10% 848 814 34 achieved 51% election of members of the mfi 6508 6538 16270 30 achieved 40% 2603.2 2645 42 achieved 41% preparation of pjm 814 855 16270 41 achieved 5% 325.4 371 46 completio ns 46% sidomulyo timur socialization and rkm 18 671 1867 1893 26 achieved 10% 746.84 786 39 achieved 42% volunteers 1525 1534 15251 9 achieved 10% 610.04 616 6 reached 40% fgd rk 1639 1688 16391 49 achieved 10% 655.64 694 38 achieved 42% ps 1635 1657 16351 22 achieved 10% 654.04 679 25 achieved 41% tim ps 1635 1658 16351 23 achieved 10% 839 818 21 achieved 51% election of members of the mfi 6540 6560 16351 20 achieved 40% 2616.16 2637 21 achieved 40% preparation of pjm 818 839 16351 21 achieved 5% 327.02 347 20 achieved 42% 58 fatriadi, r. et al./ jgeet vol 02 no 01/2017 4.2 analysis quality improvement of infrastructure development the implementation of community-based infrastructure in the district of marpoyan damai is 55.75% compared with those not based society. this means that any activities undertaken mainly pnpm urban infrastructure activities are much cheaper because of the community-based, in addition to utilizing public funds blm also contribute in terms of the funds that is self funding from the public. besides the quality of his work is much better results, because the people themselves who do the infrastructure work ranging from planning, implementation, monitoring and evaluation. in district of marpoyan damai, the proposed infrastructure activities so much from the beginning of blm fund budget in 2009 until 2010. this type of infrastructure activities proposed in the form of environmental quality improvement activities, such as: 1. roads, which consists of a dirt road, the concrete road paving blocks, cementing and stockpiling gravel. 2. drainage, consisting of tertiary channel and the environment, household waste, including of rehabilitation and improvement. 3. bridge, such as construction of box culvert and bridge. 4. health facilities: development posyandu 5. clean water, forming of a wellbore number of proposed infrastructure development activities in the district of marpoyan the peace , proved the level of the needs of society in terms of the environment is very high. each proposal submitted community activities directly realized by pnpm urban as a facilitator of each activity. of 2008 before the pnpm mandiri in district marpoyan peaceful, just society as an object and not directly involved in the development process in his village. from 2009 until now the community has been the subject of such development. communities in the district of marpoyan damai directly involved in the overall development process. with pnpm urban was shown to accelerate the development of infrastructure for bebasis community and in accordance with the needs of the community itself.in addition, the presence of pnpm urban can foster social capital of the community capital (mutual cooperation, caring, self-reliance and others) in the district marpoyan damai. 4.3 contributions community fund on financing for development infrastructure effectiveness pnpm urban to accelerate infrastructure development can be seen in terms of funding. in this case will be compared between "financing capabilities through blm (apbn and apbd) with the ability to finance the allocation of public funds to infrastructure development". based on the theory of effectiveness, the ability of the funds will be directly proportional to the achievement of objectives (wahab, 2004). in this case the goal is defined pnpm urban mean acceleration of infrastructure development. comparison between expenditure on infrastructure financing between blm pnpm urban with governmental funds people in the district of marpoyan damai can be seen from figs 1 and 2. graph shows the contribution of blm and nongovernmental funds to finance infrastructure in the district of marpoyan damai. blm is a stimulant of government funds donated to the community to improve the human development index (hdi) so that people become self-reliant so that they can overcome poverty. with this stumulan funds can raise awareness and public concern that arise volunteers from each village. contributions from the community in the form of self-help funds donated in support of community development programs of pnpm urban. graph in 2009 until 2010 funds blm stimulant proven to increase public awareness, it can be seen from the number of self-donated funds public infrastructure development. comparison of blm with funds nongovernmental in 2009-2010 can be seen in fig 3. from a comparison chart of the infrastructure financing can be seen that the government has been successful in the last 2 years through pnpm urban in the district of marpoyan damai to raise public awareness of development so that makes a society that previously powerless (poor) become more empowered to independent society. in this case the non-governmental funds increased in 2010. for example, in the construction of road infrastructure, non-governmental funds in 2009 reached 14% of the blm. in 2010 the fund comes community towards road infrastructure increased by 31% from government funds budgeted blm. the average increase in funding nongovernmental year from 2009 to 2010 of 22.5%. pnpm urban is divided into 3 activities (tridaya) that environmental activities / infrastructure, social as well as economic. blm initiated the distribution of funds for infrastructure projects, ie by 70%, 20% and socially productive economy rolling by 10%. actual construction of infrastructure in district of marpoyan damai of blm fund is equal to 70% coupled with an average improvement of community self-help funds of 22.5% was 92.5%. this means the realization of infrastructure development in the district of marpoyan damai is 92.5% with the national community empowerment program (pnpm) urban. these indications show that pnpm urban can realize the proposed activities of the public infrastructure. from table 5 and table 6 infrastructure improvement can be seen as an example of the road network, before their pnpm urban (2006-year of 2007) compared to after the pnpm urban (2009year of 2010). from fig 4 can be seen an increase in the road infrastructure in the district marpoyan peace. the condition of paved roads increased by 13.2%, paved fatriadi, r. et al./ jgeet vol 02 no 01/2017 59 roads and dirt roads no increase (0%). the average increase in the road before their pnpm urban in district marpoyan damai is 4.4%. from fig 5, it can be seen that the road infrastructure is increasing with the pnpm mandiri. the condition of paved roads increased by 19.4%, the condition of roads paved roads increased by 28.8% while the ground to be drastically reduced in the amount of 59.2%. the average increase in the quality of infrastructure before the pnpm urban program is only 4.4% per year, after the pnpm urban average increase in the quality of infrastructure to 35.8%.this indication shows that infrastructure as a sample of road infrastructure, the quality of the road surface be toincreased significantly by the pnpm urban is in district marpoyan peace. results of interviews with stakeholders relevantpnpm urban which consists of ksm, pnpm urban consultant, member of mfis, with a sample of 66 samples. can be seen in table 7. fig 1. graph of infrastructure financing in 2009 fig 2. graph infrastructure financing in 2010 fig 3. comparison chart infrastructure financing through blm with governmental funds. 60 fatriadi, r. et al./ jgeet vol 02 no 01/2017 table 5. length of road by type of surface (km) in district marpoyan damai 2006-2007 village year 2006 year 2007 asphalt compaction land asphalt compaction land tangkerang tengah 24 10 41 29 10 41 tangkerang barat 22 12 27 28 12 27 maharatu 16 23 29 16 23 26 sidomulyo timur 8 21 22 8 21 19 wonorejo 9 18 21 9 18 21 total 55 130 129 55 130 112 table 6. length of road by type of surface (km) in the district of marpoyan damai year 2007-2010 village of the year 2007 year 2009 year 2010 aspha lt hardened land aspha lt hardened land asphalt hardened land tangkerang tengah 29 10 41 38 18 16 38 18 26 tangkerang barat 28 12 27 33 16 16 33 16 16 maharatu 29 16 23 38 17 16 38 17 16 sidomulyo timur 8 21 31 13 19 31 22 13 19 wonorejo 21 9 18 28 13 3 0 28 14 total 129 55 130 168 77 67 168 168 78 table 7. interviews results of respondents respondents rate the effectiveness of the infrastructure improvement seen from the realization of development not effective (<20%) effective enough (20% -40%) effective (40% 70%) very effective (> 70%) mfi 2 4 10 ksm 5 9 32 consultants pnpm mp 4 total 7 13 46 fig 4. graph improving the quality of road infrastructure in sub marpoyan peace before pnpm urban source: district of marpoyan damai in 2006, 2007 source: district of marpoyan damai in 2007 until 2010 source: analyse result in 2011 fatriadi, r. et al./ jgeet vol 02 no 01/2017 61 fig 5. graph improving the quality infrastructure in the district of marpoyan damai after pnpm mp. 4.4 geology and regional planning geological condition of research area consist of alluvium sand, gravel, clay, peat swamp, plant remain in quaternary age. there are two anticline in this research area, those western section cut sidomulyo timur, around the area beringin indah and in the south of maharatu. there is an inferred fault with direction northwest-southeast in the middle area of research area cut of sidomulyo timur and maharatu. fig 6 shows a map of geological research area. stream-flow patterns that developed in the study dominated parallel type. this flow pattern is generally formed on a slightly steep topography caused by the presence of anticline in the region. fig 7 shows a map of the study area drainage patterns. undulating topography of the research area cause by anticline and fault need special observation for land-use planning, drainage, airports, water supply and urban area. fig 8 shows a map of land use and administration of research area. fig 6. geological regional map of research area. deposition old alluvium, sand, gravel, clay, plant remain and peat swamp regional geological map of marpoyan damai district riau province 62 fatriadi, r. et al./ jgeet vol 02 no 01/2017 fig7. drainage pattern map of the study area fig 8. land use use and administration map of research area. drainage map of marpoyan damai district riau province fatriadi, r. et al./ jgeet vol 02 no 01/2017 63 5. conclusion pnpm urban highly effective against the increase in infrastructure development in the district of marpoyan damai pekanbaru. it can be seen from the realization of infrastructure development with pnpm mp 92.5%. these indications show that any proposed development of the public infrastructure can be realized by pnpm urban. improved infrastructure is quite significant with the pnpm urban compared to before the program is running. the quality of the road surface before the pnpm mp (2006-2007) average increase in the quality of the road is only 4.4%. after the pnpm mp (2009-2010), the average increase in the quality of the road surface of 35.8%. in addition, the implementation of community-based infrastructure proved cheaper 55.75% compared with those not based society. with pnpm urban was shown to accelerate the development of infrastructure for community-based and according to the needs of society itself. undulating topography of the research area cause by anticline and fault need special observation for land-use planning, drainage, airports, water supply and urban area. references rainwater harversting effectiveness as an 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(2): 2010 11. putra, dewandra bagus eka, and tiggi choanji. 2016. engineering, environment, and technology 1 (1): 41 44. deformation history of kubang pasu formation at south of unimap stadium hill, ulu pauh, engineering, environtment, and technology 1 (1): 1 6. -tourism potential of geoscience, engineering, environment, and technology 1 (1): 59 62. arikunto, suharsimi., 1998. manajemen penelitian, edisi baru. penerbit rineka cipta. jakarta. depdiknas., 2003. kamus besar bahasa indonesia, edisi ketiga. penerbit balai pustaka. jakarta. effendy, onong uchjana., 2003. ilmu,teori dan filsafat komunikasi. pt.citra aditya bakti. bandung. george odunga obare., 2013. strategic positioning of marketplaces and learning institution as digital village centres for rural empowerment and development in bondo district, international journal of business and social research vol. 3 no. 9 uday tower gulshan-1 dhaka-1212, bangladesh. kuncoro, mudrajad., 2004. otonomi dan pembangunan daerah. penerbit pt. erlangga, jakarta. nawawi, hadari. 1998. metode penelitian bidang sosial. gadjah mada university press. sedarmayanti., 2001, sumber daya manusia dan produktivitas kerja; bandung: cv. mandar maju. sugiyono., 2006. statistika untuk penelitian. penerbit cv. alfabeta. bandung. sumaryadi, i nyoman., 2005. perencanaan pembangunan daerah otonom dan pemberdayaan masyarakat. penerbit citra utama. jakarta. suryono, agus., 2001. teori dan isu pembangunan. malang, universitas malang press. todaro, michael, p., 2000. pembangunan ekonomi di dunia ketiga, erlangga, jakarta. tri wahyu rejekiningsih., 2011. identifikasi faktor penyebab kemiskinan di kota semarang dari dimensi kultural, jurnal ekonomi pembangunan vol.12 no.1, ums surakarta. wahab, solichin abdul., 2004. analisis kebijaksanaan : dari formulasi ke implementasi kebijaksanaan negara. penerbit bumi aksara. jakarta. 1. introduction 2. aim 3. methods 3.2 sampling technique 3.3 geological analysis 4. result 4.1 analysis of public participation in the urban pnpm in district marpoyan damai table 1 . effectivity variable of pnpm mandiri at city on acceleration of infrastructure development 4.2 analysis quality improvement of infrastructure development 4.3 contributions community fund on financing for development infrastructure 4.4 geology and regional planning 5. conclusion references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 128 cahyaningsih, c. et al./ jgeet vol 03 no 02/2018 lithofacies and depositional analysis environment of west section kolok nan tuo, sawahlunto, west of sumatera catur cahyaningsih 1 , anjas latif ritonga 1 , shaury aldila 1 , zulhikmah 1 1 department of geological engineering, universitas islam riau, pekanbaru-riau, 28284, indonesia * corresponding author : caturcahyaningsih@eng.uir.ac.id tel.:+81-72-867-1686 received: 2 june, 2017. revised : 24 may, 2018, accepted: 30 may, 2018, published: 1 june 2018 doi: 10.24273/jgeet.2018.3.2.340 abstract study areas were located to the west of kolok nan tuo village. geographically this area is located at coordinates 00° 36' 57,85'' 00° 37' 56,89'' latitude and 100°42' 10,08 '' 100°43' 47,28" longitude. the methods used in research is geological mapping. based on the results of stratigraphic research area is divided into three units: crystalline limestone unit (sbgk) consisting crystalline limestone of and mudstone lithofacies, conglomerate units (sk) consists of polymic conglomerate and sandstones greywacke lithofacies while claystone unit (sbl) lithofacies consists of claystone with sedimentary flake structures. result of research suggested that depositional environment based on type of lithofacies include of grain size, sedimentary structures and content of fossils. sbgk interpreted as basement of basin, sk depositional environment was debris unit limestones, which can be seen from fragments of conglomerates that consist of crystalline limestones and mudstone that deposited in alluvial fan (deposition surface). clay lithologies where mudstone generally deposited in current flow that form flake structures and calcareous, that interpreted deposited in neritic environment. keywords: ombilin basin, geological mapping, lithofacies, kolok nan tuo 1. introduction the geological process is a process associated with the formation of the earth regarding both tectonic and regarding its constituent rocks. while the field study conducted by researchers intend to map the distribution of rocks in the west section of kolok nan tuo (fig. 1), which will be grouped based on the lithology of their respective characteristics and the depositional environment is also different. so that the results of these studies will produce a geological map. 2. basic theory many experts define different facies. however, they generally agree that the facies is characteristic of sedimentary rock units. according to selley (walker, 1985 and james 1992) facies sediments is a body of rock that can be identified and differentiated from other rock units by geometry, lithology, sedimentary structures, fossils, and the pattern of their ancient stream. armed with the physical, chemical, and biological environments can be reconstructed in the deposition of sedimentary rock sequences and are called facies analysis. while lithofacies based on characteristics of the composition, physical, and chemical at a rock. geologically of study area, west section of kolok nan tuo belongs to the ombilin basin. ombilin basin is divided into several formations which are distinguished by lithofacies and the depositional environments (koesomadinata and matasak, 1981): fig. 1. administrative map of study area cahyaningsih, c. et al./ jgeet vol 03 no 02/2018 129 2.1. pre-tertiary rocks the pre-tertiary rock is a rock the underlying basin ombilin. these rocks are exposed at the western and eastern parts of basin. pre-tertiary rocks exposed in the western part of the basin consists of (koesomadinata and matasak, 1981): silungkang formation, composed of coral limestone lithology of volcanic rocks. rock consists of andesitic volcanic lava, as well as the basaltic tuffs. age formations are the pleistocene-carbon content of fossil fussulinid in limestone. tuhur formation, consisting of lithology slate, shale members and limestone members. this formation was triassic age. 2.2. tertiary rock 2.2.1 brani formation brani formation consists of conglomerates with fresh color is purplish brown, grain size is gravel, with a wide variety of fragments such as andesite, limestone, slate, argillite, granite, quartzite, arkose with coarse-grained, massive and generally not plated. this age formation is based on relationship with sangkarewang formation which allegedly paleocene to eocene. the formation was deposited as a precipitate brani estimated alluvial fan (koesomadinata and matasak, 1981). 2.2.2 sangkarewang formation according koesomadinata and matasak (1981), consists of shale formations sangkarewang layered thin dark gray-brown to black, plastic, containing calcareous carbon material, mica, pyrite, and the rest of the plant. these formations have inserts in the form of layers of sandstone with thick are generally less than 1 m, there are fragments of quartz and feldspar, calcareous gray to black, clay matrix disaggregated mica and carbon-containing material and the presence of slump structures. inset these sandstones show a pattern fining upwards. based on pollen analysis estimated age of this formation or pre-eocene eocene. formation sangkarewang estimated deposited at lake environment. 2.2.3 sawahlunto formation according to koesomadinata and matasak (1981), this formation consists of shale sequences gray-brown, silty shale and siltstone with quartz sandstone inserts gray-brownish and characterized by the presence of coal. generally carbonaceous shale. sandstone has a characteristic sequence of fining upwards, has a layered sedimentary structures crossmaze, ripple lamination and firm base erosion that shows a sequence of point bar. coal interspersed with the generally gray siltstone and carbonaceous clays. this sawahlunto formation eocene based on the analysis of pollen shows paleocene to eocene age. the presence of carbonaceous shale, coal, particularly sandstonetype point bar shows the depositional environment of formation. this is a floodplain with a winding river where coal is deposited. 3. methodology the research method used is the analysis of maps and field studies (mapping). map analysis is used to determine the state of the landscape and slope (putra and choanji, 2016; suryadi, 2016) as supporting activities to facilitate field research activities. the field research aimed at obtaining more field data according to research materials to be analyzed. at this stage, do some work done, including determining the location of the observations and the observations of outcrops. at every outcrop, observations do plotting observation station location on the map and delineate the megascopic framework outcrop. outcrop observations include:  measurement outcrop dimensions, fig.graphs, and sketches.  description lithology, strike-dip, coating thickness, and sedimentary structures.  sampling. after the field data obtained is then performed the data analysis stage so characteristic lithological types and lithologies in the study area can be determined. 4. result based on field data, the rocks in the study area can be classified into three rock units:  limestone crystalline unit  conglomerate unit  claystone unit lithologies as each have a different lithofacies, crystalline limestones facies units composed of limestone crystalline and mudstone, conglomerate unit consists of a conglomerate facies and facies greywacke sandstone and mudstone facies units consist of claystone facies which sometimes contained in the form of thin layered sandstones. 5. discussion based on the results of the analysis of field data, lithologies in the area of research can be grouped into three lithologies. 5.1 crystalline limestones unit unit crystalline limestones located in the eastern part of the study area. crystalline limestones unit is composed of crystalline limestone and limestone. mudstone referring to the regional geology, rock units is comparable to the old silungkang formation permian-carbon era. crystalline limestones unit is marked in blue on a geological map of the study area. lithology on this unit are: cahyaningsih, c. et al./ jgeet vol 03 no 02/2018 130 5.1.1 crystalline limestone facies crystalline limestones facies are dominant in the eastern part of the study area. description detailed crystalline limestones have weathered gray color and a fresh color white whitish-grey. with component binder matrix deposition and grains have crystallized so that no fossils of both types of macro and micro. (fig. 1) fig. 1. crystalline limestones with directions n65°e 5.1.2 limestone mudstone facies limestone mudstone facies are dominant in the southeast area of research. description limestone mudstone a detailed have weathered blue-white color and a fresh color bluish grey because it is a carbonate rock. according to the classification of this rock called dunham, mudstone because it has granules of less than 10% and this rock was not found fossilized. the texture of this rock is noncrystalline, amorphous because the constituent mineral crystal and type of compactness is quite loud. (fig. 2). 5.2. greywacke sandstone facies facies lithic sandstones greywacke dominant is in the southern part of the study area. in the flow of the river, malakutan discovered sedimentary layering structure. description sandstones greywacke lithic in detail which has a color weathered gray dark and fresh colors gray, grain size medium kind of well rounded, medium sorted, permeability moderate, compactness bit loud, for component grains were observed in macroscopic using loops consist of 40% quartz, 30% feldspar and debris 30%. matrix percentage is more than 15%. (fig.. 4) fig. 2. limestone mudstone with directions n84°e fig. 3. conglomerates with fragments of limestone crystalline and limestone mudstone with direction n246ºe cahyaningsih, c. et al./ jgeet vol 03 no 02/2018 131 fig. 4. greywacke lithic sandstones with fig. directions n125°e for classifying the sandstone use classification of pettijohn, 1986. (fig. 5). facies sediment may have formed tectonically unstable when appointed by poorly sorted, and sedimentary structures indicate that the slow lorises rock units are the result of the silungkang formation debris deposited on the environment precipitation inland. (fig 6). fig. 5. triangular sandstone classification (pettijhon, 1975) fig. 6. an illustration of formation of conglomerate rock units as a result of debris and forming alluvial fan. 5.3 claystone unit claystone is in the central part of the study area that spreads from north to south. these lithologies of claystone and sometimes there is a fine sandstone insert. members of this unit included into the lower formation ombilin old when late oligocene-early miocene. this unit is marked in green on a geological map of the study area. the lithofacies on this unit are: 5.3.1 mudstone facies clay facies predominantly located in the southern part of the study area. description claystone detailed flake has weathered grey color and a fresh color grey-brown, clay 1/256 mm grain size, very well rounded, closed containers, thin laminated sedimentary structures, low permeability, well sorted, indicating that environmental carbonate deposition on this rock is in the form of land environment, the type of soft compactness. (fig.. 7) fig. 7. claystone unit with flakes structures with photo directions n 125° e n 305°e for facies sedimentary depositional environments is deposited in neritic environment which can be seen from flake structure of the sediment, indicating that the current relatively quiet and nature carbonate facies sediments showed that the sedimented on the marine environment. (fig. 8). 6. conclusion in kolok nan tuo area there are five lithofacies are: crystalline limestone, mudstone limestone, conglomerates, sandstones greywacke lithic, and claystone that can be grouped into three lithologies are limestone lithologies crystalline which is a basement in the basin the conglomerate unit formed on alluvial fan and it is resulted cahyaningsih, c. et al./ jgeet vol 03 no 02/2018 132 fig. 8. an illustration of the state of environmental change precipitation to claystone unit from debris unit of limestone crystalline which can be seen on the number of fragments of limestone crystalline and limestone mudstone in facies conglomerates which deposited on terrestrial environments (fluvial) as an alluvial fan. clay lithologies interpret deposited in neritic condition which can be seen from the content of which is the identifier sediment carbonate marine environment on clay facies. (fig. 4.) fig. 9. geological map of the study area acknowledgment thanks to laboratory of geological engineering department, faculty of engineering, universitas islam riau who has helped the data collection and analysis in finish writing this article. references putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geosci. eng. environ. technol. 1, 41 44. doi:10.24273/jgeet.2016.11.5 cahyaningsih, c. 2016. carbonate microfacies and diagenesis of langgun island, langkawi kedah province, malaysia dunham, rj. 1962. spectral subdivision of limestone type. in we ham (ed), classification of carbonate rocks, am.assoc.pet.mem, 1, p 62 -84. yeni, yulia f., 2011. development of sedimentation brani formation, formation sawahlunto and ombilin formation seen from provenance and composition sandstone basin ombilin. napier: the 36th hagi and involvement 40th annual convention and exhibition. koesoemadinata, rp & matasak, t., 1981. stratigraphy and sedimentation of ombilin cahyaningsih, c. et al./ jgeet vol 03 no 02/2018 133 basin, central sumatra, proceedings of the 10th annual conference, indonesia petroleum association, jakarta, siregar, i.m., 2015. potential of sandstone karbonatan as minerals c kampung sulitair regional, district of solok, west sumatra province. pekanbaru -riau. margaesa, d., 2014. precipitation facies analysis of coal seam x25 based log inside casing in balikpapan formation as correction correlation litho. bandung: pt. sinergy consultancy services. pettijohn, fj, pe potter, r. siever., 1986. sand and sandstone, second edition, springer-verlag new york inc. prayitno, b., 2016. limnic condition in rheotrhopic peat type as the origin of petai coal, central sumatra basin, indonesia. j. geosci. eng. environ. technol. 2, 145 -149 . saraev. sv., 2014 lithologic and facies characteristics of the lower cambrian usolka formation and its age analogs in the cisyenisei sedimentary basin, west siberia. russia. selley., 1988. applied sedimentology, academic press, london. suryadi, a., 2016. fault analysis to determine deformation history of kubang pasu formation at south of unimap stadium hill, ulu pauh, perlis, malaysia. j. geosci. eng. environ. technol. 1, 1 6. doi:10.24273/jgeet.2016.11.1 van bemmelen, rw., 1949. the geology of indonesia, vol. ia, general geology, the hageu martinus nijhoff. yuskar, y., 2016. geo-tourism potential of sand bars and oxbow lake at buluh. j. geosci. eng. environ. technol. 1, 59 62. yuskar, y., putra, d.b.e., suryadi, a., choanji, t., cahyaningsih, c., 2017. structural geology analysis in a disaster-prone of slope failure, merangin village, kuok district, kampar regency, riau province. j. geosci. eng. environ. technol. 2, 249 254. 1. introduction 2. basic theory 2.1. pre-tertiary rocks 2.2. tertiary rock 2.2.1 brani formation 2.2.2 sangkarewang formation 2.2.3 sawahlunto formation 3. methodology 4. result 5. discussion 5.1 crystalline limestones unit 5.1.1 crystalline limestone facies 5.1.2 limestone mudstone facies 5.2. greywacke sandstone facies 5.3 claystone 6. conclusion references author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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fax: +91-5102321667 received: dec 17, 2018; accepted: feb 22, 2019. doi: 10.25299/jgeet.2019.4.2-2.2441 abstract the major part of uttar pradesh (u.p.) is covered by gangatic alluvium in the north whereas the southern part is covered by peninsular terrain. the peninsular part of uttar pradesh is covered by the rocks of archean to mesozoic age. this peninsular part covered by the bundelkhand craton, its nuclei mostly composed of archean granitoids show heterogeneity in texture and composition, intruded by later phase of magmatic activity. the oldest unit, bundelkhand gneissic complex (bgc) is exposed in the south and southwestern part of uttar pradesh, whereas the comparatively younger unit dudhi gneissic complex (dgc) exposed in south and southestern part of uttar pradesh, which overlies by the mahakoshal group in sonbhadra and mirzapur district. the mahrauni group occurs as sliced unit between bgc and bijawars and has the thrusted contact with bgc. the exposures of the rocks of mahrauni group are very scanty and exposed around girar, manpura and rajaula areas of mandawra block in lalitpur district. the bijawar group is exposed around sonrai area district lalitpur of uttar pradesh. the rocks of ajabgarh group rocks are exposed in mathura district. these groupsbijawar, mahakoshal and ajabgarh are metasedimentary/metavolcanics unit and belong to delhi supergroup, which is capped by the sedimentary units of vindhyan supergroup, and exposed mainly in the southern part of uttar pradesh and a very few exposures in the west. the comparatively younger unit, gondwanas is exposed only in south and southeastern part of u.p. mainly in sonbhadra. the few exposures of deccan trap are also traced in lalitpur district in the south of u.p. the northern part of u.p. is alluvium covered which belongs to quaternary period. these quaternary sediments are classified in to older alluvium, newer alluvium and aeolian younger sediments of upper pleistocene-holocene age. these sediments unconfomably lies over and undulating basement of the rocks of delhi supergroup of proterozoic age. the older alluvium comprises fine grained, well compacted and more mature sediments occupying extensive stretches at relatively higher elevations. the older alluvium is classified in to banda older alluvium and vanarasi older alluvium. banda older alluvium (boa) exposed around the rivers flowing. varanasi older alluvium (voa) exposed beyond the river basinal margins. the drainage pattern in region is subdendritic to dendritic type formed by hills and nalas flowing over the soil cover. economically, the south and southwestern uttar pradesh is more significant for their economic mineral environment for the minerals of iron, gold, diamond, calcite, platinum, phasphorite, clay, graphite, bauxite, copper, silica sand, potash etc. keywords: bundelkhand greenstone belt, dudhi gneissic complex, mahakoshal group, bijawar group, ajabgarh, vindhyan supergroup 1. introduction the state of uttar pradesh (u.p.) bounded by 23°52 to 31°25 n latitude and 84°39 to 77°03 e longitudes which comprise about 2,40,928 km 2 area is made up of distinct rock types which extends from oldest archean metamorphites to the youngest quaternary alluvium. statigraphically, this state is mostly covered by the alluvium of ganga plain which separates the himalaya or extra peninsula and the peninsula india. the peninsular part of u.p. is exposing rocks of archean to mesozoic period. the ganga, yamuna, ramganga, gomti, ken, betwa and ghaghra are the major rivers signify drainage of uttar pradesh. medlicott (1859) was possibly the first to study the rocks of the bundelkhand region. hacket (1870) made geological report of gwalior and its adjoining areas. heron (1935) studied the rocks from various parts of bundelkhand region and referred these rocks as erpreted the trends of mineral lineation as suggestive of direction of flow of granitic fluids. jhingran (1958) suggested that the pink granite is younger than the grey ones. on the basis of grain size, colour of feldspar and presence or absence of ferromagnesian minerals, he distinguished ten types of granites within the great batholithic massif. he also reported gneisses, quartz-reefs, basic dykes and tuffaceous serpentinite rocks in the craton. saxena (1961) stated that the bundelkhand granitic activity as an http://journal.uir.ac.id/index.php/jgeet mailto:email-gkdinkar@rediffmail.com 52 dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 equivalent to the closepet granite of dharwar craton of south india. prakash et al. (1975) stated that the mehrauni group rocks are oldest unit of the southwestern part of bundelkhand massif. mishra and sharma (1975) made a systematic study of the stratigraphic setting of the bundelkhand complex. sharma (1982) made a detailed lithostratigraphic, structural and petrological study of the kuraicha formation and bundelkhand group. bhattacharya (1985) estimated tectonic strain for the rocks of the bundelkhand massif and has shown that the mineralogical behaviour of the rocks has controlled the deformation patterns of the massif. basu (1986) carried out extensive field investigations and mapped the entire area of the bundelkhand craton. bhattacharya (1986) developed a semi-quantitative method for identifying different fold episodes of deformed terrains. sarkar et al. (1989, 1995, 1997) presented a detailed account of the geochronology and petrology of various rock types of the bundelkhand complex. basu (2001) presented a model for the evolution of the continental crust, considering the geological, structural, geophysical data, and mineralization aspects, of the bundelkhand craton. pati and raju (2001) studied petrochemistry of the pillowed metabasalts of bijawar group, as exposed in a few parts of the sonrai area in lalitpur district of uttar pradesh. mondal et al. (2002) dated the gneissic and granitiod rocks of the bundelkhand massif by ion-microprobe 205 pb/ 206 pb (zircon age) methods. farooqui and singh (2006)and farooqui and singh (2010), kaur et al. (2014, 2016); verma et al., (2016); saha et al. (2016); and nasipuri et al. (2019) discuss the geochronological aspects of bundelkhand granitoids in detail. bhattacharya and singh (2013) described the proterozoic crustal scale shearing in the bundelkhand massif with special reference to quartz reefs. recently singh and slabunov (2015a, 2015b, 2016), slabunov et al. (2017), and slabunov and singh (2018) discussed the geology and geochronology of the supracrustal rocks of bundelkhand craton and first to establish two greenstone complex i.e., central and southern bundelkhand. further studies suggest that the entire area was subject to two major phases of sedimentary-volcanic process before regional granitisation during the archean. granitisation, in preferred tectonic block, led to the development of an intra-cratonic belt controlled between lineaments, within which the younger bijawar-vindhyan basins developed. the rocks of the archean basement complex and the overlying sedimentary sequences in the bundelkhand craton occur in southern uttar pradesh and adjoining madhya pradesh, within which broad but distinct stratigraphic units are recognized and classified (fig. 1) and discussed in detail in following section. 2. geology of southern part of uttar pradesh and adjoining area the peninsular part of uttar pradesh is covered by the rocks of areachen to mesozoic ages (fig. 1). the hard rocks are mainly igneous and metamorphic rocks and are exposed as isolated hills. the basement of the peninsular belongs to bundelkhand granitoids intruded by later phase of magmatic activity. the rocks exposed in the southwest and south part of state are dominantly granitic, consist bundelkhand craton and those in the sonbhadra area in the east are dominantly gneissic rocks, comprise mahakoshal belt (fig. 1). the bundelkhand craton mostly contains a wide variety of plutonic and hypabyssal rocks dominated by porphyritic granite of several generations, gneisses, migmatites, and lucogranites (geological survey of india, 2012). migmatites, different types of granite, basic intrusive dykes and quartz reefs have been identified and assigned to various types. it is generally agreed that the enclaves of metabasics and metasedimentary are older than the granitoids. the bundelkhand granitoids display heterogeneity in texture and composition and are pegmatitic in some places (dinkar, 2016; dinkar et al., 2018). the detailed geology of central bundelkhand greenstone complex is given by singh and slabunov (2015a) and slabunov and singh (2018), so we don t discuss here. the southern bundelkhand greenstone complex exposures of the rocks belonging to mehroni group are very scantly and can be observed around girar, manpura and rajaula areas in mandawra block of lalitpur (prakash et al., 1975; singh and slabunov, 2016; slabunov et al., 2017; dinkar et al., 2018 and references therein). in sidhi (son valley) area, the older metamorphics and granite gneiss are exposed as a linear belt south of mahakoshal belt and in rihand reservoir area bordering mirzapur district, uttar pradesh. the gneissic complex associated with high grade meta-sedimentary and meta-volcanics including mafic and ultramafic schist. these include sillimanite-garnet gneiss, garnet-sillimanite-corundum schist, staurolite-garnet-biotite schist, garnetiferous grunerite-magnetite quartzite, quartz sericite schist, quartzite, marble and calc-silicate rocks, talcchlorite schist, amphibolites and hornblende granulite (geological survey of india, 2012). the dudhi gneissic complex (dgc) composed of mainly granitic gneiss, migmatites, and nonfoliated massive granite with enclaves of metamorphites and veins of pegmatite, aplite and quartz (geological survey of india, 2012). the rocks of this group are exposed in mirzapur and sonbhadra areas in uttar pradesh. the mahrauni group occurs as sliced unit between bgc and bijawars and has the thrusted contact with bgc in southern lalitpur. the exposures of the rocks of mahrauni group are very scanty and exposed around girar, manpura and rajaula areas of mandawra block in lalitpur district. the rocks of mahakoshal group in the uttar pradesh are the eastward extension of similar rocks of madhya pradesh inferred to have paleoproterozoic age to the group includes metasediments with interlayered metavolcanics and granitic bodies intruding it (geological survey of india, 2012). roy and devarajan (2000) classified this group into three formations. the youngest one is dudhmaniya formation composed of impersistent banded iron formation, chlorite phyllite and greywacke underlain by an argillite-predominently faciesthe parsoi formation, and oldest one is agori formation characterized by the argillite-arenite facies with chemogenic rocks (bif). parsoi formation characterized by andalusite is developed in the phyllite. the basal part dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 53 of agori formation is characterised by proliferation of the basic and ultrabasic volcanic rocks. the upper part of the agori formation contains bif, phyllite, acid volcanic and calcareous and chert bands. the bijawar group (metasedimentary sequence) characterized by ferruginous quartzite, carbonate, phosphorite, sandstone and tuffaceous rocks rest over unconformably on the southern part of bundelkhand craton. the rocks of this group are exposed in sonrai area in the southern part of lalitpur district. the classification of the bijawar group into sonari formation, solda formation and kurrat flow is in ascending order. the sonari formation is consisting of carbonate, arenite, argillite sequence and phosphorites horizons. the solda formation characterized by ferruginous quartzite, shale and tuffaceous rocks, is the youngest formation (absar et al., 2009). the small exposures of ajabgarh group characterized by purple and white quartzite interbedded with phyllite and slate occur in mathura district. this sequence traversed by quartz veins is grouped under barsana formation. the barsana formation in the uttar pradesh is northeastward extension of the ajabgarh group of paleoto meso-proterozoic age. the bundelkhand craton is capped by the sedimentary units of vindhyan supergroup in southern and western side. the rocks of this unit occur as mounds and small hillocks. these are structurally controlled by e-w and ne-sw trending lineaments. this supergroup is subdivided unconformably into a lower sequence (semri group) and an upper sequence (kaimur, rewa and bhander groups). the semri group includes carbonate, tuff, green silicious shale and minor glauconitic sandstone and dolomitic limestone, with conglomerate bands in the basal part. the shale sequence is composed of alternate green bands of shale, mudstone and siltstone. this is exposed along the margins of the basin and is well developed in the son valley, rewa and katni area and along the northern limit of the vindhyan terrain in the bundelkhand region in part of the satna, panna, chhatarpur and damoh district of madhya pradesh (ramakrishnan and vaidyanadhan, 2010). the kaimur group are consists of sandstone and overlying quartz arenite containing silica sand as lenses in the arenite. these conglomerate lenses occur in the basal part of the sequence. the kaimur sandstone transgresses the semri rocks towards the north and west directly overlies the bundelkhand granite and bijawar rocks. however the southern margin, the contact between kaimur and underlying semri groups appears to be without any break in sedimentation, although, a few conglomerate bands are recorded. the overlying sequence of the rewa group consist thick alternating sequence of argillaceous lithounits with interbedded diamondiferous conglomerate horizons conformably overlying the kaimur rocks with a gradational contact. this group is divided into panna shale, lower rewa sandstone, jhiri shale and upper rewa sandstone. generally, limestone is absent except for a restricted occurrence in the lower most paisuri formation of the group and occurs mainly in northern part of satna district and further east. fig.1: geological map of southern part of uttar pradesh and adjoining area (modified after geological survey of india, 2012). 54 dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 bhander group occupies the central part of the basin in rewa, satna, damoh, sagar and bhopal. the bhander group chiefly represents a basal argillaceous unit passing into arenaceous units and algal stromatolitic calcareous unit (satna-rewa-nagod-amanganj-hatta area.) non-stromatolitic limestone is recorded in bhopal. this group has been divided into ganurgarh shale, nagod limestone, sirbu shale and maihar (upper bhander) sandstone. the vindhyan group is unconformably overlain the bijawars. a few outcrops of lameta bedds and deccan trap occur in the southern part this state. one outcrop of deccan trap relatively large in size trending in almost n-s. these outcrops are smaller in size and extend for a few tens of meters only. the deccan trap occurs as flat cap rocks in the area. the deccan trap is mainly constituted of basaltic rocks. most of the basaltic rocks show highly weathered and irregular surfaces as well as lateritic soil and black alluvium soil cover. the presence of characteristic black cotton soil cover marked by extensive gully stratigraphic successions of southern part of uttar pradesh are summarized in table 1. table 1: generalized stratigraphic succession of southern part of uttar pradesh (after geological survey of india, 2012). sr. gr. group formation member/lithology newer alluvium channel alluvium/ colluvium grey micaceous fine to coarse grained sand, silt and clay terrace alluvium cyclic sequence of grey micaceous sand, silt and clay fan alluvium/ bhat alluvium/ ramnagar alluvium light grey to khaki, silt-clay and cross bedded fine sand with gravel and pebbles older alluvium varanasi alluvium polycyclic sequence of oxidized khaki to brown silt-clay with kankar and brown to grey fine to medium micaceous sand gravel (divisible into silt-clay sandy and rudaceous facies) banda alluvium reddish to deep brown quartzo-feldspathic sand with gravel lenses, silt and clay laterite gravel and pebble of laterite and bauxite with deep cherry red to brownish black lithomarge clay deccan trap basic rocks, dolerite and basalts lameta bed silty shale and clay gondwana damuda barakar coarse, ferruginous sandstone intercalated with coal seams and shale talchir green shale and diamictite boulder bed green shale, boulder shale and diamictite post delhi intrusive granite and granite gneiss, pegmatite, quartz vein and amphibolite vindhyan bhander maihar/ tantpur ≡ upper bhander sandstone white to purple quartz arenite, medium to fine grained purple and reddish spotted and laminated sandstone with intermitted partings of shale and siltstone and occasional shale and pebble conglomerate sirbu shale alternating splintery, ferruginous chocolate shale, greenish shale lower bhander sandstone sandstone with subordinate siltstone nagodi/lakheri ≡ upper bhander sandstone grey-greyish blue stromatolite limestone with greenish grey shale intercalation ganurgarh ≡ simrawal shale brick red to purple brown evenly bedded shale with gypsum partings rewa taragarh/ govindgarh; ghadara; chauri≡upper rewa jhiri shale/jhiri ≡ kokah shale reddish brown to purple massive current bedded sandstone greenish grey shale with siltstone and sandstone interbeds itwa/ asan/ kopar ≡ lower rewa sandstone greenish glauconitic medium to fine grained current bedded sandstone with diamondiferous conglomerate panna greenish grey white to purple shale and quartz arenite dhandraul/drummondganj ≡ mangesar/ bhouri/ dudauni sandstone milky white, compact, medium to fine grained sandstone and orthoquartzite dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 55 vindhyan kaimur scarp ≡ mangesar/ bhouri/ dudauni sandstone red, pink, compact, blocky sandstone, khaki and greenish grey, micaceous sandstone and siltstone bijaigarh grey micaceous siltstone, red and yellow ochre shale and siltstone, black carbonaceous shale and ferruginous sandstone markundi light greyish white, medium to fine grained silicified sandstone and arkosicsandstone susnai breccia ≡ koh autoclastic breccia with angular fragment of porcellainitic shale interbedded in gritty to sandy matrix ghurma black carbonaceous, micaceous, yellow braown and light grey porcellainitic shale and thin bands of sideritic ironstone ghaghar ≡ sasaram coarse to medium grained pinkish sandstone semri rohtasgarh ≡ tirohan/ breccia alaur member: thin bedded limestone with argillaceous and cherty intercalations rudauli member: fine laminated black porcellainitic shale with cherty limestone nodule kurail member: very fine grained limestone, dolomitic at base with sand and mud dykes basuhari ≡ glauconitic, rampur pandwafall sandstone khandura member: fine laminated flaggy greenish shale and porcellainitic shale mungadih member: greenish glauconitic medium grained sandstone bargawan ≡ fawn and salkhan limestone nauka tola member: fawn to yellow brown cherty dolomitic limestone kheinjua ≡ koldaha shale, olive shale olive to greenish grey, khaki, splintery shale with calcareous interbeds and partings chopan ≡ deonar light grey, greenish porcellainitic shales agglomeratic beds and arkosic sandstone kajrahat siliceous, cherty, dolomitic limestone, blocky and slabby limestone with argillite interbeds arangi leached purplish porcellainitic shale and black calcareous shales phaterwar (≡ basal conglomerate, deolond) gritty to pebbly sandstone, medium grained sandstone, siltstone and basal conglomerate delhi jungel (west of son river) panchperi hard compact sandstone purple thin laminated shale conglomerate and sandstone with impersistent shale baharadand basal, dolerite, tuff, aggolomerate and serpentinite ajabgarh tasing slate, phyllite, minor schist with quartzite laminations asarwas phyllite, slate, limestone, quartzite intercalated with phyllite and schist thanagazi carbonaceous phyllite and tuff deota-dantal brecciated quartzite, minor phyllite and schist bijawar solda ferruginous quartzite and shale, bhq, chloritic schist and calcareous sandstone sonari calcareous sandstone, grey shale, grit with lenses of phosphoriteand banded sulphide kurrat lava basaltic flows of tholeiitic composition mahakoshal dudhamaniya phyllite, quartzite, shale/slate, mica schist with younger intrusives parsoi variegated phyllite, greywacke, quartzite, metabasics and dolerite dykes and quartz vein agori shale, siltstone, sandstone, bif, basic and ultrabasic rocks dudhi granitoid complex jhirgadandi, baghisoti dumar, asnadohar and sirpalia granite two mica granite, diorite, porphyritic granite, mesocratic granite and pink leucogranite dudhi granitoid porphyoblastic gneiss dudhi gneisses banded gneiss, migmatite and biotite gneiss basic-ultrabasic intrusives dolerite, lamprophyre, olivine basalt, kersanite, gabbro 56 dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 bundelkhand granitoids acid intrusives aplite, pegmatite, quartzofeldspathic vein, quartz reef/ vein, pyrophyllite porphyries granite, rhyolite, diorite, dacite granite coarse grained; medium grained; and fine grained grey, and pink granite. porphyritic coarse grained and porphyritic grey, and pink granite. fine grained and medium grained leucogranite. gneisses augen gneiss, granite gneiss, porphyritic granite gneiss, migmatite. 3. geology of soil covers of uttar pradesh geologically, uttar pradesh is covered by alluvium in the north whereas the southern part is covered by peninsular terrain. the alluvium of gangatic plain extends from aravalli-delhi ridge in the west to rajmahal hills in the east. this alluvium sediment belongs to holocene period. the ganga foredeep sediments extend much to south of depositional boundary of the siwalik foredeep and rest over the cratonic rocks of precambrian age. the peninsular uplands also contribute to a significant volume of sediments. the different lithology coupled with depth of weathering of these two regions is reflected in the lithology of holocene sediments, is mainly dominated by voa sediments exposed beyond the river basinal areas and boa sediments exposed around the rivers flowing. the sediments of voa consisting of polycyclic sequences of brownish silt clay and micaceous sand with small calcrete horizons overlies the boa sediments. the sediments of varanasi alluvium were derived from himalayan provenance. these sediments show progressively finer characteristics away from provenance. banda older alluvium is exposed in the area south of the yamuna river bordering the peninsular upland and it rests over the precambrian rocks. these older alluvium comprises finer grained, well compacted and more mature sediments occupying extensive stretches at relatively higher elevations. these sediments, related to some earlier fluvial episodes, have been at most places stabilized by vegetation and majority of the badlands are sculptured within it. these sediments characteristically display red brown colour and are richer in ferruginous content. the drainage pattern in the region is subdendritic to dendritic type formed by hills and nalas flowing over the soil cover. the southern part of the state mainly drained by betwa a tributary of yamuna river basin. betwa is feeding by its tributaries dhasan, kane river etc. 4. mineral significance in southern part of uttar pradesh the minerals found in uttar pradesh include limestone, dolomite, glass-sand, marble, bauxite, non-plastic fireclay, and uranium. besides, barytes and andalusite are found in the districts of mirzapur and sonbhadra. sand-stone, pebbles, reh, salt punter, maurang, sand and other minor minerals are also found in the state. the following types of minerals which occur in the uttar pradesh (geological survey of india, 2012) discussed below. iron: an outcrop of banded hematite quartzite (bhq) in the berwar formation of the mehroni group found in the west of dhasan river between berwar and girar. the lithology comprises meta-sedimentary rocks associated with metavolcanics. detailed work by directorate of geology and mining,u.p. in the solda area of lalitpur district iron ore is associated with the rocks of bijawar group and iron ore occurs in small pockets of enriched secondary crystalline haematite within bijawar group of rocks around sonrai area in lalitpur district. in the sonbhadra district, south of dudhi near migrarasni, the bhq contains iron ore with pockets of rich specularite occurs within mahakoshal group around parsoi area. diamond: in sonbhadra, jungel valley exposes volcanic suite of rocks consisting of different types of basaltic flow agglomerates intruded by ultramafic plugs. detail exploration has revealed five plugs in the area. two diamonds have been found from one of the plugs at a depth of 4.5 m. in banda, around kalinger three diamond crystals were recovered from the palaeo-channel of baghein river, during the exploration for placer diamonds by directorate of geology and mining, u.p. gold: placer gold is reported from the sona nadi near kalagarh in nagina tehsil of bijnor as reported by directorate of geology and mining, u.p. in gonda, auriferous gravel beds occur in channel bars, point bars and younger terraces of dara, dhobha, kowali and bhambher river around jhorwa. in barabanki, beharaich, faizabad, ambedker nagar auriferous gravel beds occur in channel bars, point bars and younger terraces of sand in ghagara river as reported by directorate of geology and mining, u.p. in lalitpur placer gold is found in second and third terraces along the sukharwah river around patha as reported by directorate of geology and mining, u.p. and also in dhasan river in girar. primary gold is reported in lalitpur, from quartzofeldspathic and quartz veins associated with mafic dykes in the bgc and banded iron formation (bif) around girar as reported by directorate of geology and mining, u.p. silicified/cherty bands and smoky quartz veins occurring at girar and bhikampur have gold bearing. in sonbhadra, gold associated with rocks of mahakoshal group, represented by the metamorphic volcanic rocks inter-bedded with phyllite, lenticular chert and limestone, banded iron formation (bif), quartzite and metagreywacke. dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 57 platinum: in lalitpur, platinum and palladium mineralization is recorded in the eastern part of mandawra as reported by directorate of geology and mining, u.p. antimony: in sonbhadra, antimony values have reported from amriniya area. mineralization is observed in the form of veins and pockets of stibnite, associated with the quartz vein in dudhkhamba and dandakhan localities of mahakoshal area. arsenic: in sonbhadra, arsenopyrite and scorodite mineral occur in association with the gold occurrences in the rocks of mahakoshal group around gulaldih, bihwa, amriniya and parsoi. copper: in lalitpur, the mineralization of copper occurs around sonrai area. the mineralization is confined to a zone of black shale, chert and breccia within the bijawar group as reported by directorate of geology and mining, u.p. in sonbhadra, the mineralization is associated with the fawn limestone of semri group and the mahakoshal group. bauxite: in chittrakut, the directorate of geology and mining, u.p., explored bauxite deposit in rajahuan area and its surrounding. in this area, the bauxite horizon is 2-5 m thick. in lalitpur, bauxite occurring as capping over the dhandraul quartzite (kaimur group of the vindhyan supergroup) is located in pathrai, north of imlia tal, south of bigori area. in varanasi, bauxite occurrence has been reported in laterite capping in chandraprabha area. the laterite profile developed over the rocks of kaimur group is marked by ferruginous quartzite at base, clay and lithomarge in the middle part and laterite with bauxite horizon at top. molybdenum: in sonbhadra, the tungsten mineralization occurs to north of wyndhamganj, sonbhadra. the mineralization occurs in the rocks of the parsoi formation of mahakoshal group and also within the intrusive granite and quartz veins. in hamirpur, geochemical survey carried out by geological survey of india reported tungsten in bilkhi of hamirpur district. agate: in banda, it is found in quaternary gravels of ken river. moss agate contains small dendrites made up of manganese/iron-oxide. andalusite: in sonbhadra, andalusite occurrences have been located near wyndhamganj and bagarwa. it occurs as porphyroblasts in phyllite of parsoi formation, mainly confined to its contact with the granite and also in quartz and pegmatite veins traversing the phyllite. calcite: in sonbhadra, a small lenticular occurrence of calcite is known within the rocks of sidhi group, near parsoi. clay: in banda, lithomargic clay occurs in lateritic profile in lakhanpur area. the lateritic profile is developed over the rocks of the vindhyan supergroup. in sonbhadra, clay pockets are associated with rocks of the gondwana supergroup, vindhyan supergroup and dudhi gneissic complex in different areas. in varanasi, clay is associated with the bauxite profile in chandraprabha area at lorha. bauxite profile is developed over the dhandraul sandstone of the vindhyan supergroup. feldspar: in jhansi district of the uttar pradesh, feldspar bearing pegmatite veins are intrusive into the bundelkhand granitoids occurs near bijauli. graphite: in hamirpur, a lenticular body of graphite occurs in the bundelkhand granitoids near pathnauri and rath as reported by directorate of geology and mining, u.p. gypsum: in jhansi, gypsum occurrences are similar to those of hamirpur district. selenite is reported from gonti, gokal, dhanora, parsua, siya and malheta areas. limestone/dolomite: in banda region, tirohan limestone, a dolomitic limestone is exposed along the base of vindhyan scarp and is overlain by the quartzite and sandstone of the semri group of vindhyan supergroup. the limestone has invariable a high mgo content and is therefore, unsuitable for manufacture of cement. in sonbhadra, limestone bands occur within the semri group of vindhyan supergroup. the deposits of limestone are confined to kajrahat and rohtas formation of semri group as reported by directorate of geology and mining, u.p. marble: in sonbhadra, the deposits occur around kauria hill is the extension of ningha deposit. this deposit is associated with the rocks of agori formation of mahakoshal group (geological survey of india, 2012). the lithology of agori formatiom is completely sedimentary in nature with basic and ultrabasic rocks, whereas the marble is metamorphic in nature. and the rocks of agori formation do not attained the metamorphic grade, so on the basis of metamorphic grade it can be said that this marble will not be of agori formation. as per gsi, 2012 the marble unit occurs in golwa gangutana formation of alwar group in stratigraphy, but this alwar group is not exposed in sonbhadra. hence, it can be said that this marble can belongs of alwar group of delhi supergroup? phosphorite: in lalitpur, rock phosphates occur near sonrai and jetupura area. the phosphorite is associated with the rocks of jamini and rohni member of the sonrai formation. in sonbhadra, incidences of phosphorite are also reported from stromatolitic limestone bands of the kajrahat limestone formation around bari and sindhuria in sonbhadra district. potash: in banda, glauconite bearing panna shale of rewa group is exposed around patin, itwah and kumsi. in sonbhadra, the potash bearing glauconite is associated with shale and sandstone of kheinjua formation of the semri group and exposed around newari and basuhari area. pyrophyllite and diaspore: in jhansi, the deposits are located around palar, gorhari and bawal tanda. in lalitpur, pyrophyllite and daispore are occurring in several localities near rajghat dam. in hamirpur, the pyrophyllite and diaspore deposits found at gaurhari, pahari, garhi and tori area. 58 dinkar, g.k. et al./ jgeet sp vol 04 no 02-2/2019 silica sand: in prayagraj (allahabad), silica sand occurs around shankargarh. it is associated with dhandraul sandstone of the kaimur group. pratappur member of the dhandraul sandstone contains thick silica sand horizon. in banda, silica sand deposit occurs around baragarh. this deposit is an extension of the shankargarh deposit of allahabad district. in chandauli, silica sand deposits also reported from several localities. the silica sand derived from the weathering of dhandhraul sandstone of the kaimur group. sillimanite: in sonbhadra, sillimanite mineralization occurs in chipia village in quartz biotite schist. uranium: in lalitpur, the uranium in the form of coffinite occurs with hard bitumen within the zones of decollement, as well as in the brecciated bandai sandstone of sonrai fromation. in sonbhadra, surface indicators of uranium mineralisation associated with ferruginous brecciated rocks is traceable intermittently, exposed along the jamual-markundi, fault at tectonic contact of neoto meso-proterozoic vindhyan supergroup and paleoproterozoic mahakoshal group between gurdha and mohariya, sonbhadra district. acknowledgements gkd extends his thanks to the director, directorate of geology and mining, u.p., for granting 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u pb geochronology of granitic rocks from the central bundelkhand greenstone complex, bundelkhand craton, india. j. of asian earth sci. 118, 125 137. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. geology of southern part of uttar pradesh and adjoining area 3. geology of soil covers of uttar pradesh 4. mineral significance in southern part of uttar pradesh acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 1 2020 8 fadlin, et al./ jgeet vol 5 no 1/2020 research article geosite assessments at the southern part of karangbolong dome: new insight to geotourism potential in kebumen, central java, indonesia fadlin1,*, gentur waluyo1, yohanes iwan1, nita ariyanti2, and nanda ajeng nurwantari3 1geological engineering department, jenderal soedirman university, purbalingga 53371, indonesia. 2geological engineering department, sepuluh nopember institute of technology, surabaya 60111, indonesia. 3earth resource science department, akita university, akita city 010-8502, japan *corresponding author : fadlin.unsoed@gmail.com, fadlin@unsoed.ac.id tel:+62-81225570901; office tel: +62281-6596700 received: march 19, 2019; accepted: march 23, 2020. doi: 10.25299/jgeet.2020.5.1.2874 abstract karangbolong is a morphological dome in the kebumen area that has a high geological diversity and has a lot of tourism potential. still, it has not been developed optimally as a geotourism potential based on conservative and educative aspects, especially the existence of ancient volcano of menganti, the quite interesting from a geological point of view, so in this case, an inventory of a geological diversity required. this study aims to understand the geological conditions and conduct an assessment of the feasibility of geodiversity in the ancient volcano complex of menganti. the methodology for this research is a direct observation in the field based on the surface geological mapping, rock sampling for petrology study of rocks for supporting the quantitative assessment of genocide in the research area. the research area has 2 (two) landscape models, i.e.,ex-volcanic landscape, in this case occupying 95% of the research area and then the karst landscape, holding 5% of the research area. stratigraphy of the research area can be divided into five units from old to young, that is basaltic lava of menganti, the pyroclastic flow of menganti, which is interfingering with andesitic lava of karangduwur, andesite-basalt intrusion unit, and limestone of agropeni. this menganti volcanic filed has prospective value for tourism developments. this site can develop as a geological tour (geosite) that reviews the paleo-volcanism activities and cave genetic activity. based on field investigation, the research area has 27 geosite objects that can be developed as geotourism potential, covering three geomorphological sites, seven lithology sites, nine cave karst sites, five beach sites, and two waterfall sites. based on the results of a quantitative assessment of geosites in the research area with accessibility, state of preservation, scientific wort, and educational significance parameters, the research area has a geodiversity index from 19 until 24, in this case, the research area has good until very good grade to be developed as a geotourism potential base on educative and conservative, to improve the economic value of local communities. keywords: qualitative assessment, geodiversity, geotourism, kebumen. 1. introduction indonesia is one of the big countries in terms of nature tourism in this world, especially volcano tourism because indonesia is one of the states in the asia-pacific rim, which is being passed by the ring of fire. approximately 127 active volcanoes have occurred in indonesia until now. generally, that condition formed by the subduction of the earth crust, and that why this country has so many volcanoes diversity. some of them are famous as a tourism object such as batur volcano in bali island, rinjani volcano in lombok island, tambora volcano in sumbawa island, and also volcano complex of dieng highlands in central java, and many more. not only a recent volcano (active volcano) has a tourism value but also the ancient volcanoes and, in advance, can be developed by the geotourism approach. indonesia is also rich in a landscape of morphological karst diversity such as maros karst in sulawesi, southern mountain karst in yogyakarta, and raja ampat archipelago in west papua. there are many more places that have not been exposed to and developed in indonesia. the geological processes produce unusual phenomena with an extraordinary uniqueness of natures in indonesia with the high complexity of the controlling of tectonic setting. in this case, indonesia is the meeting point of three main plates in the world, which eurasia, indo-australia, and pacific plates. and also, tropical climate influence is indirectly made indonesia one of the countries with a high geological diversity in the world, which made it worthy of developing it as geotourism potential at the national level or international level. geotourism is a form of nature tourism that specifically focuses on landscape and geology to encourage tourism development that prioritizes conservation of geosite or geodiversity and biodiversity, as well as an understanding of earth sciences through appreciation and learning. this activity achieved through independent visits to geological features, use of geo-trails and viewpoints, guided tours, geo-activities, and patronage of geosite visitor centers (newsome and dowling, 2010). geotourism is an emerging trend that will endure. sustaining the local environment or bringing in a bit of the local color can mean the difference between a discounted rate or a higher rate, which can develop increased seasonal traffic and spur local tourism (stokes et al., 2003). geotourism follows advanced principles; this concept is introduced openly in 2002 and reported by american travel industry association and national geographical tourists (tourtellot, 2010). in this aspect, tourism activities based on natural earth objects such as volcano, river, valley, beach, waterfall, lake, spring, rocks, and others. geotourism is advanced tourism with the main focus on geological features, which promotes understanding, culture, and environmental appreciation, as well as conservation (dowling, r. & http://journal.uir.ac.id/index.php/jgeet mailto:fadlin.unsoed@gmail.com mailto:fadlin@unsoed.ac.id tel:+62-81225570901 fadlin, et al./ jgeet vol 5 no 1/2020 9 newsome, 2006). the research area (karangbolong dome) has a unique and variety of geological features, and this can have seen in the morphological character as well as some pattern, which is relatively different from the surrounding patterns. karangbolong dome administratively belongs to kebumen regency, in the eastern part of south serayu mountains, which is a form of the tertiary back-arc basin due to an interaction between the indian ocean plate, which thrusts to the northern direction under the asian plate (van bemmelen, 1949). based on the geological map of banyumas with 1:100.000 scale (asikin et al., 1992). karangbolong dome mostly consists of the tertiary rocks, in this case, is the gabon formation (tmog), which consists of volcanic breccia, lapilli tuff, agglomerate which is intruded by early miocene andesitediorite rocks as well as andesitic lava flow on top. this formation’s age is oligocene-miocene (ansori, 2010). kalipucang formation (tmk), consists of coral and crystallized limestone, white-yellowish in color, contain coral fossil, foraminifera, and mollusca shell fragments. in the same place clastic pumice and in the bottom part shale bitumen is deposited, and the youngest is the halang formation (tmph), lithology consists of (interlayer) sandstone, limestone, napal, and tuff, there is also a breccia insertion which is influenced by turbidity current and undersea landslide (ansori, 2010). the various geology conditions made it significant to develop it into a real geotourism area, which is massive and integrated as well as educational and conservative-oriented. the long-term development target is development at the local or national level. in this aspect, we able to protect and keep nature sustainability as well as increase the economy of the locals. the research area focused on the southern part of karangbolong dome. administratively, the research area is a part of the ayah district, kebumen regency, province of central java (figure 1). the research area has quite a high geodiversity and keeps many tourism potentials. however, it has not been developed in general as potential geology and public tourism, which is based on education and conservation, especially the existence of menganti paleo-volcano, which then geological site inventory is needed to do a good and correct assessment towards geosite in the region. the goal of this study is to understand the geological condition as well as to give value towards the geology diversity (geodiversity) worthiness in the menganti paleo-volcano complex to develop the target into geotourism of paleo-volcano. fig 1. location of research area (southern part of karangbolong dome), source:(googlemap) 2. methodology method of this research became a literature study of the past researcher, which is related to the object or topic research, then do observation in the field based on geological surface mapping concept with topographic base map scale1:25.000 with the output as a geological map as well as geodiversity distribution. field observation activity, including the random sampling of the rocks for petrographic analysis using the polarization microscope to understand the minerals composition of the rocks. quantitative assessment towards geosite is based on (table 1)assessment criteria for geosite inventory and geomorphological site (solarska and jary, 2010), which is hoped that by this quantitative assessment, it can reduce the subjectivity which is related to the evaluation of the procedures. table 1. assessment criteria for geosite inventory and geomorphological sites (solarska and jary, 2010). criteria traits points accessibility the site clearly visible, located directly on the touristic trail or nature's path 5 the site clearly visible, located on the road or path 4 the site barely visible, located more than 250 m away from the path or road 3 site difficult to access for tourist 2 site unavailable for tourists 1 state of preservation a well-preserved site with no visible signs of degradation 5 site in slight violation of its structure 4 partially destroyed 3 the site heavily modified by human 2 site destroyed-loss character of geosite 1 scientific worth very high: one site in the region, unique to a wider scale 10 high: very important for regional studies 8 average: significant for regional research 6 low: common site with average values 4 very low:no particularly distinctive features 2 educational significance very high: number of represented issues = 5 and more 10 high :number of represented issues = 4 8 average :number of represented issues = 3 6 low :number of represented issues = 2 4 very low :number of represented issues = 1 2 3. result and discussion 3.1. geology of research area the different and unique shapes of the earth’s morphology made into an attraction of its own for those who see it. irregular and different reliefs could identify different lithology as well (brahmantyo and bandono, 2006). generally, the research area has 2 (two) geomorphology characters which are volcanic remains morphology and the karst morphology (brahmantyo and bandono, 2006), in this case, the volcanic remains morphology occupies 95% of the research area, consisting of research area 10 fadlin, et al./ jgeet vol 5 no 1/2020 volcanic products like lava, intrusion until pyroclastic rocks. this morphology dividedinto four units of geomorphology, which are volcanic cone of menganti, lava flowsof karangwudur, pyroclastic rocks of menganti, lava flow of menganti, while the karst morphology occupies 5% of the research area. this karst morphology is divided into two geomorphology units which are karst cone hills and karst valley unit, this morphology consists of limestone. based on surface geological mapping as well as lithological data as well as the forming characteristic of research area can be divided into five units from oldest to youngest are menganti basaltic lava unit, menganti pyroclastic flow unit (interfingering) with karangduwur andesite lava flow unit, andesite-basalt intrusion unit and agropeni limestone unit (figure 2). based on volcano stratigraphy towards the paleovolcanism, then it is divided into one crown (karangbolong),which consists of 2 (two) hummocks, namely gadung hummock and menganti hummock (figure4) with a geological alignment lineation pattern is relatively towards north-south. based on a petrology of ancient lava basalt menganti area, that rock sample is petrographically dark gray on parallel nikol, has a poikilitic texture, intersertal, euhedralsubhedral crystals, with a relatively equal mineral composition of plagioclase (bytownite an78-an71) labradorite (an68an62)), pyroxene, hornblende, with the addition of "opaque mineral" gangue mineral, it indicates that the crystallization process takes place on a saturated aqueous environment, thus forming a hornblende mineral (mulyaningsih et al., 2016). from the results of the petrographic analysis can also be interpreted that the activity of primary magma evolution from the magma basalt rich (olivine) to pyroxene-rich basalt magma with magma affinity magma tholeiitic, it can also be explained from fractionation plagioclase type bytownite to labradorite and also if petrological results are not observed the appearance of k-feldspar and quartz mineral in basalt igneous rocks samples, this indicates that these rocks have not been fractionated (fadlin et al., 2018). based on that samples, the texture of zoning in plagioclase minerals indicates that the process of magma mixing and assimilation causes rocks to become unstable and dissolved, marked by the presence of sieve texture(gill, 2013)(figure 3). sieve texture is a texture often include combinations of intricate zoning patterns and resorption feature in plagioclase e that record changing physical conditions in the magmatic system. based on dominant mineral composition, in this case, plagioclase and pyroxene minerals can be classified as pyroxene basalt (travis, 1955). the columnar joint of lava basalt outcrop is one of the highest-level geodiversity sites in terms of accessibility, state of preservation, scientific worth, excellent educational significance (table 2), in addition, this site also has a fairly high phenomenon value the shape is neatly arranged like a placemat. geodivesity is interpreted as the center of the ancient volcanic eruption of menganti and is considered as the center of the first (oldest) eruption in terms of relationships in volcano-stratigraphy (pendi et al., 2018). fig 2. outcrop of menganti basaltic lava unit, showing the columnar joint structure(a).outcrop of menganti pyroclastic flow unit, showing the fragment interlocking relationship(b). the outcrop of the karangduwurandesitic lava unit has been altered(c). outcrop of andesite-basalt intrusion unit (d). outcrop of agropeni limestone unit, showing the stalactite in the rooftop of the cave(e). a b c d e fadlin, et al./ jgeet vol 5 no 1/2020 11 fig 3. photomicrograph of basaltic lava (columnar joint), showing sieve texture, consists of plagioclase (plag), which dominated by mafic plagioclase, pyroxene (px), and opaque minerals as secondary mineral (opak=opaque). (a)parallel nikol, (b) cross nikol. fig 4. geology map of the research area 3.2. geodiversity site inventory geodiversity is a description of the diversity of geological components found in an area, including its existence, distribution, and condition so that it can represent the geological evolutionary process of the area (kementrian esdm, 2020). geodiversity also has another meaning is an image of diverse geological components that exist in an area, including occupation, distribution, and condition so that it could represent the geological evolution of the area such as rocks, minerals, fossils, soil, and landforms is an integral part of nature (gray, 2004). geodiversity assessment argued to be a potentially effective tool for supporting decision-making processes with regards to management and conservation of natural areas or regions at different scales, be these local or regional. further, geodiversity is seen to be a complementary resource to natural heritage and as such can be an asset of environmental, scientific, educational, cultural or economic interest in need of effective management (serrano and ruiz-flaño, 2007), so that is very important to do a quantitative assessment about geodiversity in the research area for supporting the geotourism development. the research area has those diversity aspects which are geomorphology diversity which consists of 3 geosites (structural valley, karangbata cape and karangduwur peak), lithology diversity consists of 7 geosites (pyroclastic fall deposit, pyroclastic flow deposit, primary hyaloclastic breccia, secondary hyaloclastic breccia, columnar joint of basaltic lava, sheet joint of basaltic lava and pillow texture of basaltic lava), karst cave diversity consists of 9 geosites (sawangan, siwowo, campur, sarangburung, payung, surupan, upas, celeng, and sikidang), beach diversity consists of 6 geosites (karangagung, sawangan, menganti, lampon, pecaron, and pasir)as well as waterfall diversity consists of 2 geosites (sawangan rainbow waterfall and ketep widodari waterfall) (table 2). there are 27 geosites which are spread throughout the south-west region of the research area (figure 4), which can develop as a geotourism potential. a b 12 fadlin, et al./ jgeet vol 5 no 1/2020 table 2.geodiversity site based on incentivization result (distribution on map) site geodiversity geomorphology: karst cave: beach: 1. structural valley 11. sawangan 20. karangagung 2. karangbata foreland 12. siwowo 21. sawangan 3. karangduwur peak 13. campur 22. menganti lithology: 14. sarangburung 23. lampon 4. pyroclastic fall deposit 15. payung 24. pecaron 5. pyroclastic flow deposit 16. surupan 25. pasir 6. primary hyaloclastic breccia 17. upas waterfall: 7. secondary hyaloclastic breccia 18. celeng 26. pelangisawangan 8. basaltic lava columnar joint 19. sikidang 27. ketepbidadari 9. basaltic lava sheetet joint 10. basaltic lava pillow texture fig 5. distribution map of geodiversity site based on inventory result 3.3. quantitative assessment of geosite the assessment of geosite, which occurs in the research area, is hoped to be able to reduce objectivity towards the geology diversity evaluation process that occurs in the research area. the result from the assessment value evaluation towards the geosite shows a diverse geodiversity index with a total grade index from the four variables are around 19-24 for each geosite (table 3). qualitatively the research area has a geodiversity index in a varying level, starting from the highest score (very good) until the middle score (good), in this case, the highest grade is in the south-western part of the research area, the middle score (good) is in the central part of the research area while the lowest score (satisfactory) is in the north-eastern part of the research area wherein that part there are not many geosite occurrences which is potential to be developed (figure6). fadlin, et al./ jgeet vol 5 no 1/2020 13 table 3. identification and assessment quantitatively of geosite occurrence in the research area based on (solarska and jary, 2010), modified by the researcher in this paper. no geosite description score index level a geomorphology 1. structural valley 2. karangbata foreland 3. karangduwur peak this morphology is formed by tectonic activity, generally in the form of fracture, with a triangular facet appearance; this valley is generally composed of volcanic breccia lithology, with land use as forest and plantation by perhutani. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: the site is well groom, signs of degradation have not yet been seen (5) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 3 (6) this potential can be used as a geotracking location, for tracking tours or walking along the valley with length ± 4 km, or for special interest tours, as a place of study of earth sciences such as geological structure and geomorphology. this morphology is formed by the volcanic activity of ancient volcanoes that occur in the region menganti, in this case, composed of the lithology of basalt lava. a. accessibility: accessible on foot, approximately 250 meters from the main road (3) b. state of preservation: the site is well groom, signs of degradation have not yet been seen (5) c. scientific worth: high, very important for regional study (8) d. educational significance: high, the number of problems represented = 4 (8) this potential can be used as a camping site for the pleasure of enjoying the expanse of the sea and sunset just spoil the eyes, as a place of study of earth science such as understanding the morphology, the process of erosion and abrasion. this morphology is a height built by reef limestone units that have sufficiently intense karstification. the limestone units are riding in an uncomfortable manner with volcanic rocks of lava. a. accessibility: the site looks clear, there is a way to the site (4) b. state of preservation: the site is well preserved, the degradation mark has not yet been seen (5) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) this potential can be used as a camping site, tourism substation view, spot climbing, and also very good to enjoy the sunset, and as a place of study of earth science such as understanding the geomorphology, erosion, abrasion and karstification process. 21 24 23 good very good very good b lithology 1. pyroclastic fall deposit 2. pyroclastic flow deposit 3. primary hyaloclastic breccia) this falling pyroclastic was an eruption product of the ancient volcanic, composed of pyroclastic breccia, with andesite fragment composition, a tuffaan sand matrix, with a vertical thickness of ± 50 meters, with a relatively steep morphological slope (90°) generated from its collapse wall near the eruption center. a. accessibility: accessible on foot, approximately 250 meters from the main road (3) b. state of preservation: site slightly changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 3 (6) this potential can be used as a climbing location, or cable train, or flying fox, as well as a place of study of earth science such as understanding the product rock as a volcanism activity of the ancient. this pyroclastic flow deposit is a product of ancient volcanic eruption, transported by river and composed of an epiclastic breccia with andesite fragment composition, a tuffaan sand matrix, with a vertical thickness of ± 20 meters, with a relatively steep slope of morphology (80 °) resulting from tectonic activity. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: site slightly changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 3 (6) it can be developed as a place or stopsite for learning of earth science, such as understanding the product rock as an ancient volcanism activity. this hyaloclastic breccia was formed by past volcanic activity under the sea. a. accessibility: accessible on foot, approximately 250 meters from the main road(3) 19 20 21 good good good 14 fadlin, et al./ jgeet vol 5 no 1/2020 no geosite description score index level 4. secondary hyaloclastic breccia 5. basaltic lava columnar joint 4. basaltic lava (sheeted joint) 5. basaltic lava (pillow texture) b. state of preservation: the site has changed little (4) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 4 (8) it can be developed as a place or stopsite for learning of earth science, such as understanding the product rock as the activity of the past / ancient volcanism, due to havinga phenomenal value that can be patented as geoheritage. this hyaloclasticbreccia was formed by past volcanic activity under the sea but as a secondary product, with the presence of a carbonate clay matrix. a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: the site is well-preserved, has not seen the appearance of degradation (5) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 3 (6) this location can be developed as marine tourism to enjoy the beach or sunset or dusk, also very worthy as a place or stopsite for learning of earth science such as understanding the product rock as the activity of the past / ancient volcanism, due to have phenomenal value can be patented as geoheritage. these igneous rocks are produced from the cooling of magma on the activity of underwater volcanoes in the past with a unique structure resembling a brick or otherwise known as a columnar joint. a. accessibility: the site is clearly visible, located on the tourist track (5) b. state of preservation: the site is well-preserved, yet visible signs of degradation (5) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 3 (6) this location can be developed as marine tourism to enjoy the beach or sunset or dusk, also very worthy as a place or stopsite for learning of earth science such as understanding the product rock as the activity of the past / ancient volcanism, due to have phenomenal value can be patented as geoheritage. these igneous rocks were produced from the magma cooling process of past underwater volcanic activity with a unique structure resembling a brick head or known as a sheeted joint structure. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: site slightly changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) this location can be developed as marine tourism to enjoy the beach or sunset or dusk, also very worthy as a place or stopsite for learning of earth science such as understanding the product rock as the activity of the past / ancient volcanism, due to have phenomenal value can be patented as geoheritage. these igneous rocks are produced from the cooling of magma on the underwater volcanic activity of the past with a unique structure resembling a brick or otherwise known as a pillow joint. a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: the site is well-preserved, yet visible signs of degradation(5) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 3 (6) this location can be developed as marine tourism to enjoy the beach or sunset or dusk, also very worthy as a place or stopsite for learning of earth science such as understanding the product rock as the activity of the past / ancient vulcanism, due to have phenomenal value can be patented as geoheritage 20 22 22 20 good very good very good good c karst cave 1. sawangancave sawangan cave is one of the karst cave in the research area, formed by the activity of limestone solubility (karstification), the flow of water below the surface directly flow to the beach, and this cave has its own uniqueness, there are igneous rocks of volcanic lava at the basement of the river. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: little sites have changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. this location also offers a waterfall tour exactly at the mouth of the cave. in addition to these two things in geosite, it is very feasible as a place or stopsite for the study of earth science to understand the carbonate rock and karstification process that works. 22 very good fadlin, et al./ jgeet vol 5 no 1/2020 15 no geosite description score index level 2. siwowocave 3. campur cave 4. sarangburung cave 5. payung cave 6. surupan cave 7. upas cave this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: little sites have changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. this location also offers a waterfall tour exactly at the mouth of the cave. in addition to these two things in geosite, it is very feasible as a place or stopsite for the study of earth science to understand the carbonate rock and karstification process that works. this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: little sites have changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. this location also offers a waterfall tour exactly at the mouth of the cave. in addition to these two things in geosite, it is very feasible as a place or stopsite for the study of earth science to understand the carbonate rock and karstification process that works. this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: little sites have changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. geosite is also very feasible as a place or stops site for the study of earth science to understand the carbonate rock and karstificationprocess that works. this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: little sites have changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. geosite is also very feasible as a place or stops site for the study of earth science to understand the carbonate rock and karstificationprocess that works. this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: little sites have changed (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. geosite is also very feasible as a place or stops site for the study of earth science to understand the carbonate rock and karstificationprocess that works. this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: the site has changed little (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) that potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. geosite is also very feasible as a place or stops site for the study of earth science to understand the carbonate rock and karstificationprocess that works. 21 21 21 21 21 22 good good good good good very good 16 fadlin, et al./ jgeet vol 5 no 1/2020 no geosite description score index level 8. celeng cave 9. sikidang cave this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: the site has changed little (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) the potential that can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave while enjoying the ornaments in the cave. geosite is also very feasible as a place or stops site for the study of earth science to understand the carbonate rock and karstificationprocess that works. this cave is a karst cave that is formed from limestone dilution activities (karstification). a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: the site has changed little (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) the potential can be developed in geosite location is, of course, the most interesting is the caving tour or down the cave, while enjoying the ornaments in the cave. geosite is also very feasible as a place or stops site for the study of earth science to understand the carbonate rock and karstificationprocess that works. 21 21 good good d beach 1. karangagung beach 2. sawangan beach 3. menganti beach 4. lampon 5. pecaron this beach is a coast with a relatively steeply coastal line, which is formed as a result of the abrasion process. a. accessibility: be on the tourist path or the path(5) b. state of preservation: site has been changed slightly (4) c. scientific worth: high, very important for regional studies(8) d. educational significance: average, the number of problems represented = 3 (6) this potential can be developed for beach tourism potential to enjoy the natural scenery while enjoying the sunset or sunset. this geosite is also very feasible as a place or stopsite for learning geography to understand the process of coastal formation associated with abrasion and erosion. this beach is a coast with a relatively steeply coastal line, which is formed as a result of the abrasion process. a. accessibility: be on the tourist path or the path(4) b. state of preservation: site has been changed slightly (4) c. scientific worth: average, scientific worth (6) d. educational significance: high, the number of problems represented = 4 (8) this potential can be developed for beach tourism potential to enjoy the natural scenery while enjoying the sunset or sunset. this geosite is also very feasible as a place or stopsite for learning geography to understand the process of coastal formation associated with abrasion and erosion. this beach is a coast with a relatively flat coastal line, with white sand, which formed due to the abrasion process. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: site has been changed slightly (4) c. scientific worth: high, very important for regional studies(8) d. educational significance: high, the number of problems represented = 4 (8) this potential can be developed for beach tourism potential to enjoy the natural scenery while enjoying the sunset or sunset. this geosite is also very feasible as a place or stopsite for learning geography to understand the process of coastal formation associated with abrasion and erosion. this beach is a coast with a relatively steeply coastal line, which is formed as a result of the abrasion process. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: site has been changed slightly (4) c. scientific worth: high, very important for regional studies(8) d. educational significance: high, the number of problems represented = 4 (8) this potential can be developed for beach tourism potentialto enjoy the natural scenery while enjoying the sunset or sunset while understanding the process of coastal formation associated with abrasion and erosion, as well as volcanic rocks in the location. this beach is a coast with a relatively flat coastal line, with white sand, which formed due to the abrasion process. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: site has been changed slightly (4) c. scientific worth: high, very important for regional studies(8) d. educational significance: high, the number of problems represented = 4 (8) 23 22 22 24 24 very good very good very good very good very good fadlin, et al./ jgeet vol 5 no 1/2020 17 no geosite description score index level 6. pasir this potential can be developed for beach tourism potentialto enjoy the natural scenery while enjoying the sunset or sunset while understanding the process of coastal formation associated with abrasion and erosion, as well as volcanic rocks in the location. this beach is a coast with a relatively flat coastal line, with white sand, which formed due to the abrasion process. a. accessibility: accessible on foot, approximately 250 meters from the main road(3) b. state of preservation: site has been changed slightly (4) c. scientific worth: high, very important for regional studies(8) d. educational significance: high, the number of problems represented = 4 this potential can be developed for beach tourism potential to enjoy the natural scenery while enjoying the sunset or sunset while understanding the process of coastal formation associated with abrasion and erosion, as well as volcanic rocks in the location. 19 good e waterfall 1. pelangi sawangan waterfall 2. ketep bidadari waterfall this waterfall is formed due to morphological cuts in the flow of the underground river that flows down to the beach. this waterfall will also have a considerable water discharge in the rainy season. a. accessibility : site looks clear, there is a way to the site (5) b. state of preservation: site is well-maintained, no degradation has been seen (5) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 4 (8) the potential can be developed for waterfall tourism while studying carbonate and volcanic rocks, as well as the process of submarine rafting. this waterfall is formed due to fault slide down on the steep morphology in the menganti area, has a large enough water discharge in the rainy season. a. accessibility: site looks clear, there is a way to the site (4) b. state of preservation: terawatt good site, has not seen any degradation (5) c. scientific worth: average, scientific worth (6) d. educational significance: average, the number of problems represented = 4 (8) the potential can be developedfora waterfall tour while studying volcanic rocks. 24 23 very good very good fig 6. geodiversity anomaly map index of the research area, which shows high to low score diversity index (red: high index/very good, green: middle index/good and blue: low index/satisfactory).1. structural valley; 2. karangbata foreland; 3. karangduwur peak; 4. pyroclastic fall deposit; 5. pyroclastic flow deposit; 6. primary hyaloclastic breccia; 7. secondary hyaloclastic breccia; 8. basaltic lava columnar joint; 9. basaltic lava sheetet joint; 10. basaltic lava pillow texture; 11. sawangan cave; 12. siwowo cave; 13. campur cave; 14. sarang burung cave; 15. payung cave; 16. surupan cave; 17. upas cave; 18. celeng cave; 19. sikidang cave; 20. karangagung beach; 21. sawangan beach; 22. menganti beach; 23. lampon beach; 24. pecaron beach; 25. pasir beach; 26. pelangisawangan waterfall; 27. ketepbidadari waterfall. 18 fadlin, et al./ jgeet vol 5 no 1/2020 4. conclusion the research area has two landform models, which are volcanic mountain landform; in this case, it occupies 95% of the research area and karst hills landform, which occupies 5% of the research area. stratigraphy of the research area can be divided into 5 units from oldest to youngest are menganti basalt lava flow unit, menganti pyroclastic flow unit, which (intercorrelated) with karangduwur lava flow unit, andesitebasalt intrusion unit and agropeni limestone unit. menganti volcanic filed has prospective value for tourism developments. this site can develop as a geological tour (geosite) that reviews the paleo-volcanism activities and cave genetic activity. based on field observation, the research area has 27 geosite objects, which could be developed as geotourism potential, including three geomorphology sites, seven lithology sites, nine karst cave sites, fivebeach sites, and two waterfall sites. the research area has various geodiversity index. thereforethis geositecan develop into good geodiversity. from total scoringfrom every single site has an average score of about 19-24. in this case,it has a good index level. therefore it needs development so that it is possible to develop into geotourism potential, which based on educative and conservative in the hopes of increasing the welfare of the local economy. acknowledgments the author is also thankful to eko bayu purwasatrya, st., m.si (research group of geological central java) for a piece of good advice and discusses this study. lppm jenderal soedirman university fully funded this study. sincere gratitude goes to head of lppm unsoed and staff member at lppm. references ansori, c., 2010. potensi dan genesis mangan di kawasan kars gembong selatan berdasarkan penelitian geologi lapangan, analisis data induksi polarisasi dan kimia mineral. buletin sumber daya geologi 5, 1–9. asikin, s., handoyo, a., prastistho, b., gafoer, s., 1992. peta geologi lembar banyumas, jawa tengah, skala 1:100.000. pusat penelitian dan pengembangan geologi, bandung. brahmantyo, b., bandono, 2006. klasifikasi bentuk muka bumi. geoaplika 1, 71–79. dowling, r. & newsome, d., 2006. geotourism: sustainability, impacts, and management. elsevier, oxford. fadlin, saban, g., hamzah, w.n., 2018. magmatisme tholeitik pada active continental margin (acm) di serayu bagian utara dan selatan – banyumas, jawa tengah. geologi dan sumberdaya mineral 19, 15–30. gill, r., 2013. igneous rocks and processes. a practical guide, first. ed, wiley-blackwell. chicester-uk. https://doi.org/10.1017/cbo9781107415324.004 googlemap, https://www.google.co.id/maps [www document]. (accessed 2018-05-22). gray, m., 2004. geodiversity: valuing and conserving abiotic nature. john wiley & sons, ltd, london. kemeterian energi dan sumber daya mineral (esdm), 2020. peraturan menteri energi dan sumber daya mineral republik indonesia, nomor 1 tahun 2020, tentang pedoman penetapan arisan geologi (geoheritage) mulyaningsih, s., hidayat, s., rumanto, a., 2016. seminar nasional ke-iii. fakultas teknik geologi universitas padjadjaran, in: peran geologi dalam pengembangan pengelolaan sumber daya alam dan kebencanaan. newsome, d., dowling, r.k., 2010. geotourism: the tourism of geology and landscape. goodfellow publisher, oxford. serrano, e., ruiz-flaño, p., 2007. geodiversity. a theoretical and applied concept. geographica helvetica 62, 140– 147. https://doi.org/10.5194/gh-62-140-2007 solarska, a., jary, z., 2010. geoheritage and geotourism potential of the strzelin hills (sudetic foreland, sw poland). geographica pannonica 14, 118–125. stokes, a.m., cook, s.d., drew, d., 2003. geotourism: the new trend in travel, national geographic traveler. travel industry association of america, am. tourtellot, j.b., 2010. geotourism for your community. national geographic. travis, b.r., 1955. classification of rocks, russell b. ed, quarterly of the colorado school mines. colorado school of mines, colorado. van bemmelen, r.w., 1949. the geology of indonesia. general geology of indonesia and adjacent archipelagoes, first. ed. government printing office, hague. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 iswahyudi, et al./ jgeet vol 5 no 4/2020 181 research article origin of geothermal water around slamet volcano, paguyangan, cipari, central java, indonesia sachrul iswahyudi1*, indra permanajati1, rachmad setijadi1, januar aziz zaenurrohman1, muhamad afirudin pamungkas1 1department of geological engineering, jenderal soedirman university, purwokerto, indonesia. * corresponding author : sachrul.iswahyudi@unsoed.ac.id tel.:+62-81392331997 received: nov 25, 2019; accepted: nov 18, 2020. doi 10.25299/jgeet.2020.5.4.4112 abstract the existences of several hot springs between slamet volcano, paguyangan, and cipari districts raised questions regarding their origin. several studies have been conducted related to the hydrothermal system at the location. subsequent studies are needed to understand the hydrothermal system at the research site for the sustainability and conservation of geothermal natural resources. this research has reviewed several previous studies plus the latest information on the origin of hot spring water with the help of deuterium (2h) and 18o isotopes. this study used geochemical analysis of hot springs (geothermal) and local meteoric water to obtain information on isotope values. this was used for the interpretation of the origin of geothermal water. this study also used regional geological analysis methods for the interpretation of the mechanism for the emergence of these hot springs. the results of the analysis informed that the origin of hot water was local meteoric water. the geological structure was weak enough to allow water from the geothermal reservoir to reach the surface and meteoric water into the reservoir. keywords: slamet volcano, paguyangan, cipari, geothermal water 1. introduction 1.1 background there are several hot springs in the area between slamet vulcano, paguyangan and cipari central java. the distribution of these hot springs raises the question: what is the origin of the geothermal springs at this location? it is important to understand more about the possibility of the existence of several geothermal systems that control the distribution of some of these hot springs. several studies on hot springs at the research sites have been carried out previously with several different research methods (juhri and harijoko, 2016; sumaryadi, 2014; permana dan mulyadi, 2018; kastowo, 1975). further studies need to be carried out continuously to get more complete information about the developing hydrothermal system. it is expected to be able to provide more useful information for the management and development of geothermal and renewable energy. 1.2. literature reviews regional geology : the geological conditions of the study area can be seen from several aspects such as the stratigraphic arrangement and control of geological structures. from old to young, the stratigraphy of the study area is composed of 5 different rock formations. the first formation of the miocene age is the pemali formation which is composed of marl with the insertion of tufan sandstones and limestones. the second formation formed is the rambatan formation with the dominance of sandstones in it. above the rambatan formation there is the halang formation which is composed of tuffaceous sandstones, conglomerates, marl and claystone (kastowo, 1975). on top of the three formations of tertiary ages, there are two rock formations which are the result of the eruption of slamet volcano, namely slamet compacted volcanic rock and lava of slamet volcano (djuri et al, 1996). the existence of a geological structure in the form of a fault that extends from the northwest to the southeast represents control of the geological structure in the study area.the fault structure that controls slamet volcano geothermal system consists of one main normal fault and three strike-slip faults. the main normal fault of slamet is very influential in the appearance of the volcanic cone of the slamet muda volcano. the presence of a normal fault is very important as a controller of rock permeability in the reservoir (direktorat panas bumi, 2017). geothermal water : water in geothermal systems come from several sources, including surface (meteoric) water, formation water (connate waters), metamorphic waters and juvenile waters (nicholson, 1993). ellis and mahon (1967) also explained that geothermal fluids can be produced from reactions between meteoric groundwater and host rock. experiments on the origin of water in geothermal water conducted by craig (1963) stated that geothermal water shows similarities to local meteoric water. this is based on the meteoric waterline model that was also proposed by craig in 1961.several studies on the origin of geothermal water have been carried out. lu et al (2018) used the 18o and 2h methods to determine the origin of geothermal water. the study concluded that geothermal water at the study site came from local meteoric water. chatterjee et al (2017) also uses isotopes 18o and 2h to determine the origin of geothermal water. this study concludes the origin of geothermal water comes not from meteorics water but formation water that is stored long in rock layers. 1.3. location research location is located in the area around slamet volcano, paguyangan, bantarkawung, and cipari, central java. the location is limited by the geographical coordinates of http://journal.uir.ac.id/index.php/jgeet mailto:sachrul.iswahyudi@unsoed.ac.id 182 iswahyudi, et al./ jgeet vol 5 no 4/2020 108.70° 109.26° east longitude and 7.01° 7.52° south latitude, which can be reached from the nearest cities (purwokerto, cilacap) using two-wheeled vehicles or fourwheeled vehicles (fig 1). fig 1. research location 2. methods this research was conducted based on geochemical analysis of geothermal isotopes and geological analysis. the first step is to observe geothermal manifestations and then take geothermal and meteoric water samples. then the obtained water samples were analyzed in the laboratory to obtain information on deuterium (2h) and 18o isotopes of geothermal and meteoric water. the laboratory analysis was carried out for the interpretation of the origin of geothermal water (meteoric, magmatic, or others). geochemical analysis of geothermal water was carried out on samples from springs and hot spring or geothermal pools from paguyangan, buaran, bantarkawung, saketi, and cipari districts. geothermal isotope data were obtained from laboratory analysisand from previous research, namely: pancuran-3, pancuran-7, guci, cahaya, sigedong (sumaryadi, 2014). the results of the analysis of deutrium and 18o isotopes were then analyzed for the interpretation of the origin of the geothermal water and hydro geochemical processes that accompanied its appearance on the surface. geological analysis was carried out to estimate the locations where meteoric water came into the reservoir and where the geothermal water came out to reach the surface. 3. result and discussion 3.1. distribution of geothermal manifestations manifestations of geothermal systems area between slamet volcano, paguyangan, bantarkawung, and cipari is spread over a range of more than 50 kilometers from the slametvolcano crater. in the east, there is a collection of hot spring manifestations around slamet volcano, namely the hot springs of pancuran-3, pancuran-7, guci, cahaya, sigedong, and saketi. in the central part of the research location there are several hot springs, namely paguyangan, buaran and bantarkawung hot springs. whereas in the south-west there are cipari hot springs (fig 2). 3.2. chemistry data of hot and cold water laboratory analysis of water from hot and cold spring samples has been carried out by several previous studies. observations and sampling that did not have laboratory analysis data were carried out on the manifestations of hot water and cold water at the study site. the water samples were then analyzed to determine the isotopic content of 2h and 18o (table 1). fig 2. distribution of hot springs at the study site 3.3. origin of geothermal water the interpretation of the origin of geothermal water in the study location was based on the calculation and ratio of deutrium and 18o isotope components. plotting of deutrium and 18o water isotope data laboratory analysis of geothermal and cold water at the study site reveals several trends, namely: a. plotting of deutrium and 18o isotopes data of local cold water samples shows consistent with global meteoric water lines. both the local and global meteoric water lines arealmost coincidental. variations in local and global deuterium and 18o isotopes values are controlled by temperature, geographic location, rainfall, distance relative to the sea, and elevation. table 1. deutrium and 18o water isotopes analysis result no. location code del 8o del d hot springs 1 paguyangan lp1 * -5,2 -27,5 2 buaran lp3 * -5,8 -31,0 3 bantarkawung( lp5 * -5,4 -30,9 4 cipari lp7 * -3,7 -22,5 5 pancuran 3 p3 ** -6,4 -39,1 6 pancuran 7 p7 **** -7,9 -51,4 7 guci gu ** -6,9 -44,7 8 cahaya ca ** -6,1 -41,1 9 sigedong si ** -6,6 -41,0 10 saketi sa 11 cipari cp2 *** -3,2 -21,8 springs/wells 1 kalipagu kp ** -7,5 -44,3 2 sigedong sg ** -7,8 -48,0 3 cipari lp8 * -5,8 -33,7 4 bantarkawung lp6 * -5,8 -35,7 5 paguyangan lp2 * -5,3 -30,6 6 buaran lp4 * -6,5 -38,9 notes: * : laboratory analyses ** : sumaryadi (2014) *** : permana dan mulyadi (2018) **** : iswahyudi, et al (2015) b. plotting of deutrium and 18o isotopes hot water samples data generally similiar to global and local meteoric water lines even though there are varied deviations in each plotting point in all locations of hot water manifestations. iswahyudi, et al./ jgeet vol 5 no 4/2020 183 deviation in the values of deutrium and 18o values (shift) are interpreted to occurs because of the enrichment of these isotopes, and related processes of interaction of geothermal water and rocks (enrichment of 18o) and evaporation on the surface (enrichment of deutrium). c. plotting data on samples of hot and cold water in the bantarkawung area almost coincided at the same point. it is interpreted that, the origin of bantarkawung geothermal water came from a relatively very close location. the similarity of plotting can also be caused by the close circulation of meteoric and geothermal fluids that have reached a relatively perfect balance. d. in general, the geothermal water of the study site came from the local meteoric water. this is indicated by the position of plotting data of deutrium and 18o isotopes which tend to correspond to local and global meteoric water lines even though there are enrichments of both of these water isotopes. the analysis of the origin of the geothermal water described above is shown in fig 3 below. 3.4. hot springs existence mechanism interpretation the emergence of hot springs is closely related to existing geological conditions. based on the geological map data around the study site, the lithology consists of tertiary-aged sedimentary rocks and quarter-age volcanic rocks (fig 4). tertiary-aged sedimentary rocks are folded, fractured and faulted in several places. those places are weak zones that allow geothermal water from the reservoir to reach the surface or close to the surface. it is confirmed that almost all hot springs that appear on tertiary sedimentary rocks are located in the fracture or fault zones. these fractures and faults also allow meteoric water to enter into geothermal and heated reservoirs (fig 4). some hot springs appear in quarter-age volcanic rocks that do not have fracture or fracture indications. it was interpreted that the appearance of several hot springs was also caused by geological structures in the form of fractures or faults covered by volcanic lithology from quater-age volcanic eruptions (fig 4). fig 3. interpretation of the origin of geothermal water at the study site. fig 4. geological map that shows the geological structure density (fracture or fracture) of the research location (kastowo, 1975). 184 iswahyudi, et al./ jgeet vol 5 no 4/2020 4. conclusion geothermal water from samples of paguyangan, buaran, bantarkawung, cipari, pancuran 3, pancuran 7, guci, cahaya, sigedong, saketi, cipari comes from local meteoric water. in general, enrichment values of 18o and 2h occur in geothermal water from values of 18o and 2h of local meteoric water. this is interpreted because of interaction of geothermal water and rock and surface evaporation. the enrichment of the value of 18o geothermal water from the sigedong, cahaya, pancuran 3 and pancuran 7 regions indicates more intensive processes of geothermal water rock interactions than those that occur in other regions. differences of the local meteoric water lines of the study area and global meteoric water line occur because of differences in geographical latitude and distance from the sea where the water samples are taken. hot springs at the study site coincide with the locations of geological structures in the form of faults, fractures and folds. it is interpreted that, these locations are weak zones that allow geothermal water from the reservoir to reach the surface and meteoric water can enter the reservoir. acknowledgements our gratitude goes to the research and community service institute (lppm) jenderal soedirman university, geological engineering teaching staff and those who helped provide support and assistance so that this paper was published. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51–58. chatterjee, s., ansari, m. a., deodhar, a. s., sinha, u. k., & dash, a. 2017. a multi-isotope approach (o, h, c, s, b and sr) to understand the source of water and solutes in some the thermal springs from west coast geothermal area, india. arabian journal of geosciences, 10(11). https://doi.org/10.1007/s12517017-3022-0. craig, h. 1963. the isotopic 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(2018). geochemical and isotopic evidence on the recharge and circulation of geothermal water in the tangshan geothermal system near nanjing, china: implications for sustainable development. hydrogeology journal, 26(5), 1705–1719. nicholson, k. 1993. geothermal fluids, chemistry and exploration techniques. springer verlag inc. permana, l.a. and mulyadi, e. 2018. studi geokimia panas bumi jawa tengah bagian selatan, provinsijawa tengah, pusat sumber daya mineral batubara dan panas bumi. http://psdg.bgl.esdm.go.id/kolokium/2015/pabum/4.pdf. surmayadi m., 2014, geokimia panas bumi gunung slamet jawa tengah, proceeding seminar nasional, bandung 24 mei 2014, © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1007/s12517-017-3022-0 https://doi.org/10.1007/s12517-017-3022-0 http://ebtke.esdm.go.id/post/2017/09/25/1751/buku.potensi.panas.bumi.2017 http://ebtke.esdm.go.id/post/2017/09/25/1751/buku.potensi.panas.bumi.2017 http://psdg.bgl.esdm.go.id/kolokium/2015/pabum/4.pdf http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 sari, s. l. et al./ jgeet vol 02 no 03/2017 183 impact of sulphur content on coal quality at delta plain depositional environment: case study in geramat district, lahat regency, south sumatra siska l. sari 1, *, m.a rahmawati 1 , a.triyoga 1 , idarwati 1 1 geological study program, sriwijaya university, jl. srijaya negara, bukit besar, ilir barat i palembang 30139 * corresponding author : siskalindasarii@gmail.com. tel.:+82-18-695-6119; received: may 25, 2017. revised : july 1, 2017, accepted: aug 9, 2017, published: sept 1, 2017 doi : 10.24273/jgeet.2017.2.3.301 abstract the research was conducted in geramat district of lahat regency, south sumatra. an evaluation of the geological condition of the research area shown that the coal deposits were found in muara enim formation as a coal-bearing formation. the method used was literature study, field observation and the laboratory work includes proximate and petrography analysis. the aim of this research is to determine the environmental condition of coal based on the change of total sulphur content and to know the relation between ash content to calorific value. as the result of proximate analysis conducted on five samples of coal, the research area obtained total sulphur (0,21-1,54% adb), ash content (3,16 71,11% adb) and gross calorific value (953 5676 cal/g. adb). based on the result of maceral analysis showed the maceral percentage of coal in research area composed by vitrinite (77,8-87,4 %), liptinite (0,6 %), inertinite (8,0 17,6 %) and mineral matter concentration in the form of pyrite (1,6-4,6 %). the average reflectance value of vitrinite (rv) of coal in the research area (0.54%). the results analysis shows that the coal in muara enim formation on the research area is in the transitional lower delta plain depositional environment phase. any changes in the sedimentary environment affected by sea water will be followed by changes in total sulphur and the higher ash content, on the contrary, the lower calorific value of the coal.. keywords: coal, depositional environment, delta plain, sulphur, geramat district. 1. introduction sulphur content, thus affecting the quality of coal. this condition resulted in the coal is in demand in the world market, considered as an environmentalfriendly coal. the establishment of sulphur presence in coal and peat such as (1) low sulphur content coals (<1%), contains more organic sulphur than pyritic sulphur. conversely, high sulphur content coals contains more pyritic sulphur than organic sulphur. (2) high sulphur content coals are usually associated with cap rock derived from the marine environment (3) the highest sulphur content in coal is usually on the roof and floor part (casagrande, 1987). sulphur is one of an important factors associated with the depositional environment of coal. the sulphur content contained in coal is expected to be minimal due to causing of air pollution. sulphur occurs in peat, associated with sea water generally contains higher level of sulphur than fresh water peat. the characteristic of coal depositional are divided in to five categories which are distinguished based on moisture factor, ph, hydrogen ion concentration, food supply and bacterial activity. according to diessel (1992) three of them are topogenic peat swamps, which are divided into acid high water-table conditions, neutral high watertable condition and variable water-table condition. the other two are ombrogenic peat swamps, divided into continuously wet and intermittently dry (fig 1). fig. 1. modified sketch of depositional environment and peat-accumulated condition (diessel, 1992) determination of coal quality based on depositional environment is related to total sulphur 184 sari, s. l. et al./ jgeet vol 02 no 03/2017 content, ash content and calorific value. the higher level of sulphur content in coal indicates its sedimentation in the marine environment while lower sulphur content in coal indicates the depositional environment relatively in land environment. the higher level of ash, the smaller calorific value of coal and vice versa. the percentage of sulphur content and ash content in coal effects the calorific value and quality of coal (cook,1999 in sulistyana, 2012). this research aims to determine the relationship of sulphur content and ash content along the calorific value and to perform a depositional environment analysis towards organic material. the study was located in geramat district, lahat regency south sumatera as a part of south sumatera basin. the local stratigraphy of research area consist of air benakat formation, muara enim formation, kasai formation and andesit unit (fig. 2). 2 regional geology south sumatera basin is a back-arc sedimentary basin bounded by barisan mountains in the southwest, sunda shelf in the northeast, lampung high in the southeast and tigapuluh mountains splitting the basin from the central sumatera basin. the regional stratigraphy of south sumatra basin began from eocene to quartenary (de coster,1974). regional strati basin can be seen in (fig 3). (a) basement rocks the basement rocks of south sumatra basin is a complex of mesozoic igneous rock along with paleozoic and mesozoic metamorphics and carbonates. the paleozoic and mesozoic metamorphic and sedimentary rocks were sustained intensely by the tectonism stress resulted in the rocks to be folded and faulted and were intruded by igneous rocks during the middle mesozoic orogeny. (b) lahat formation lahat formation deposited in early tertiary, in the late eocene to the early oligocene. it was considered as an initial deposition and was deposited on the pre-tertiary unconformity surface. lahat formation consisted of tuffaceous sandstone, conglomerate, breccia and claystone. these rocks are product of continental sedimentation and volcanism in early tertiary tectonism. (c) talang akar formation talang akar formation has been dated in late oligocene to early miocene by its stratigraphy position beneath the well dated basal telisa limestone member. it consisted of sandstone and claystone, deposited in delta environment. fig. 2. geology map of lahat sheet and research area map (gafoer et al, 1986) sari, s. l. et al./ jgeet vol 02 no 03/2017 185 fig. 3. regional stratigraphy of south sumatra basin (de coster, 1974 and gafoer 1986 in barber et al., 2002). (d) baturaja formation following by deposition of talang akar, there apparently was reduction in amount of clastics material being transported to the basin. this factor affected the depositional environment of the basalt telisa limestone (equivalent to baturaja formation). in the early stage, extensive platform or bank limestone deposits were form shelfal, and platform portions of the basin. in the later stage, further buildups of detrital, reefal and bank limestone were formed on top of these banks in restricted localities. the deposition of these limestones probably ended when marine transgression resumed. the basal telisa limestone occurs only on the broad shelf and platform areas within the basin. (e) gumai formation gumai formation was deposited during the maximum transgression phase and progresses well throughout the whole basin, in the early miocene to the middle miocene. the gumai consisted of fossilliferous marl, the minor amount of sandstone, thin limestone, shale and siltstone. (f) air benakat formation towards the late miocene the seawater level was no longer increasing, rather it occurred the decreasing of seawater level globally (regression phase). air benakat formation was deposited in this new phase, laid conformably above the gumai formation, it consisted of shale, sandstone, claystone and thin layer of limestone, with a shallow marine environment. (g) muara enim formation as the main coal bearing formation in south sumatera basin, the muara enim formation turn out to be the main focus of the study. the formation was composed of sandstone, claystone, shale and coal. most of the coal is in sub bituminous stage (low rank coal), only in the certain spots (alongside the intrusion of andesite) it turned into high rank coal. the muara enim was deposited on the late miocene to the pliocene, in the shallow marine to brackish environment (at the bottom) and delta plain to non-marine environment. (h) kasai formation the deposition of kasai formation considered as the final sedimentary deposition in south sumatera basin. it was resulted of the erosion of volcanic products of the barisan and tigapuluh mountains at the pliocene to the pleistocene. the lithology of this formation consists of tuffaceous sandstone, gravel, clay and thin layer of coal. 3. methods the research was conducted through three stages such as (1) collaborative literature study; (2) field observation; (3) laboratory analysis. collaborative literature study conduct before going directly to the field, mainly through the scientific papers that have been published by previous researchers. it aims to provide an overview of the general geological condition of the research area. meanwhile field observation conducted by doing geological mapping within an area of 25 km 2 . the geological mapping was done to determine the distribution of coal and also the correlation to other rock units obtained in the research area. as for the laboratory analysis, the first thing we should do was sorting the coal samples that previously collected from the field (fig 10). the next step is working on coal proximate analysis to find out the percentage of ash content and total sulphur along with the calorific value contained in the samples. based on the results of the analysis, the depositional environment of the research area can be determined by the consisting of ash content, sulphur content and the calorific value. for coal maceral analysis conducted by showing the relationship value of tissue preservation (tpi) 186 sari, s. l. et al./ jgeet vol 02 no 03/2017 and gelification index (gi) in the research area. tpi = 𝑇𝑒𝑙𝑖𝑛𝑖𝑡𝑒 + 𝑇𝑒𝑙𝑜𝑐𝑜𝑙𝑙𝑖𝑛𝑖𝑡 + 𝑃𝑠𝑢𝑑𝑜𝑣𝑖𝑡𝑟𝑖𝑛𝑖𝑡 + 𝑆𝑒𝑚𝑖𝑓𝑢𝑠𝑖𝑛𝑖𝑡 + 𝐹𝑢𝑠𝑖𝑛𝑖𝑡 𝑉𝑖𝑡𝑟𝑜𝑑𝑒𝑡𝑟𝑖𝑛𝑖𝑡𝑒 + 𝐷𝑒𝑠𝑚𝑜𝑘𝑜𝑙𝑖𝑛𝑖𝑡 + 𝐼𝑛𝑒𝑟𝑡𝑜𝑑𝑒𝑡𝑟𝑖𝑛𝑖𝑡 gi = 𝐻𝑢𝑚𝑖𝑛𝑖𝑡𝑒 + 𝐺𝑒𝑙𝑜𝑣𝑖𝑡𝑟𝑖𝑛𝑖𝑡 𝐼𝑛𝑒𝑟𝑡𝑖𝑛𝑖𝑡 4. result and discussion according to the measuring section analysis performed at several spots of research area, there are claystone, coal and sandstone along with the occurrence of some evolved sedimentary structures such as cross bedding, and graded bedding. generally, the physical features of coal around the geramat district were black-colored, dull luster, black stretch and massive compaction, with some additional materials such as resin and pyrite. the result of the proximate analysis represented the percentage value of total sulphur content, ash content and calorific value of coal (table 1). 4.1 depositional environment coal deposition environment analysis according to the horne (1987) model of the study area classified in the transitional lower delta plain depositional environment. the results of lithologic analysis shown that the sandstone is gradually coarsening-fining upwards, supported by the measuring section data which has the same pattern as the depositional environment model (fig 4). one of the components in determining the deposition environment is based on the lithology of coal-bearing rocks and sedimentary structures in the stratigraphy sequence. fig 5 explain comparison between the environmental model of coal deposition in a transitional lower delta plain environment based on horne (1986) with a stratigraphic measuring section conducted at the point of the study area indicating the compatibility of the constituent lithology so as to interpret the environmental conditions of the coal depositional in the research area. as seen from the sedimentary environment model, it shows the lithologic uptrend from bottom to top. the transitional lower delta plain environment shows finer grain-size lithologic characteristics than upper delta plain ones, this zone contains brackish water to marine. such deposition environments are more extensive swamp development in nearly complete filling of interdistributed bays. the subsidence is one of the factors affecting the depositional environment and also the characteristics of the distribution and the quality of coal seams, especially the sulfur content in the research area. the subsidence occurred at a relatively faster velocity resulting in a slower process of precipitation in the sedimentary environment influenced by tectonic activity compared to more stable environments without the effect of subsidence. the former subsidence caused the the transitional lower delta plain environment has a somewhat lower sulphur content whereas in the upper delta plain environment it has a higher sulphur content. based on the outcrop profile analysis the research area it is located in the transitional lower delta plan environment with the sub-environment such as crevasse splay, indistributary bay, levee and channel. the sediment deposited in crevasse splay deposits are derived from deposition of floods that erode the levee, allowing water to flood into the floodplains around the stream and form crevasse splays deposits. this crevasse will form a pattern and a separate channel system. based on the stratigraphic cross-sectional measurements in the study area showed the presence of fine grained and massive sandstones layer indistributary bay is characterized by claystone and sandstone lithologic with fine grain size. levee depositts are characterized by the appearance of gray claystone and coarse-grained brown sandstones. channel sediments deposited on the facies are coarse-grained deposits and is strongly influenced by the rapid river flow (bedload). channel deposits consist of river wall debris due to erosion by current flow (walker and cant, 1979). the channel deposits is always in motion and on the river base precipitated the coarse grained granules. characteristics of channel deposits in the study area are seen in stratigraphic cross-sectional measurements in geramat area which have coarsegrained sandstone lithology composition with cross bedding sedimentary structure. . table 1. percentages data of total sulphur, ash content and calorific value from five samples. no lab no. sample marks ash % adb total sulphur % adb gross calorific value cal/g. adb 1 1443/17 lp 109 71,11 0,27 953 2 1444/17 lp 24 63,45 0,22 2,520 3 1445/17 lp 49 3,16 0,21 5,645 4 1448/17 lp 8 3,72 0,35 5,676 5 1449/17 lp 34 10,88 1,54 5,325 sari, s. l. et al./ jgeet vol 02 no 03/2017 187 fig. 4. depositional environment of research area based on horne (1987). fig. 5. identification of transitional lower delta plain (1978) based on the depositional environment, it is known that the research area contains low sulphur content because it was not influenced by an intensive sea deposits. it is also proven by the results of data analysis performed wherein total sulphur content con flooding peat is an important factor in determining the sulphur content within the coal as seen in lp 8 (fig 6) and lp 24 (fig 7). 4.2 the relationship of coal quality with ash content and calorific value the result of proximate analysis shows the percentage value of ash content and calories that can be seen in table 1. from the data it can be seen value, the higher the calorific value. the example is in lp 109 sample (fig 8). fig. 6. coal outcrop contains low sulphur content on lp 8. fig. 7. coal outcrop contains low sulphur content on lp 24. 188 sari, s. l. et al./ jgeet vol 02 no 03/2017 fig. 8. coal outcrop of lp 109 with high ash content. fig. 9. coal outcrop contains low ash content lp 49. the analysis conducted on outcrop lp 49 (fig 9) resulted in high ash content, based on its acidic depositional environment wherein the presence of mineral matter quite excessive. it caused the high percentage of ash content as 71.11% adb and low caloric value 953 cal/g, so that the coal on the outcrop is not economically prospect for mining project. as for the lp-s49-ap coal outcrop has low ash content such as 3,16% adb and high calorific value 5,645 cal/g, indicating the mineral content of the coal outcrop is rather low . the coal cropline can be seen on fig 10. 4.3 depositional environment interpreted from maseral from the calculation obtained the value of tpi and gi on coal shown in table 2. the tpi value shows a ranging value between 0,15 6,67. the tpi value indicates a change in plant composition and peat type in the study area caused by condition changes in the depositional environment. as for the gi value is high enough to indicates that the oxidation process is not dominant with low inertinite content. to interpret the coal depositional environment of the research region, the value of tpi and gi is plotted in the diagram according to lamberson et al. (1991). the results shows transitional lower delta plain as the coal depositional environment. the transitional lower delta plain environment formed in limnic sub-environment. fig. 10. coal cropline map at geramat district, lahat regency sari, s. l. et al./ jgeet vol 02 no 03/2017 189 table 2. calculation result of tpi and gi no. code sample tpi gi 1 lp 38 0,130 7,31 2 lp 8 0,376 4,927 3 lp 24 6,67 4,42 4 lp 49 0,15 10,925 the transitional lower delta plain environment shows low tpi values and relatively high gi values dominated by the detrovitrinite maceral subgroup. this sedimentary environment is dominated by shrub plants compared to timber plants therefore the value of tpi is low. the combination of tpi and gi can be used to determine the degree of decomposition and plants accumulation rate (lamberson et al., 1991). interpretation of the variations in the value of tpi and gi can be seen in (fig 11). fig. 11. the interpretation results diagrams in the research area. from the results of the diagram analysis, it is seen that the gi value of coal in the research area is relatively high indicating the depositional environment was in humid or wet conditions in the swamp environment so that the formation of vitrinite will be intensified, with the lack of sea water effect causing the sulphur content in the research area is low. unlike the coal outcrop in lp 24 which has a value of tpi reaching 7 this is due to the location of coal is experiencing andesit intrusion that causes coal in this condition is in the non-marine environment with high coal quality, due to the influence of intrusion the pyrite impurity mineral is more dominant than other research sites. 4.4 coal quality the analysis of 5 coal samples referring to the american society for testing and materials (astm) (1981) suggests that geramat's coal quality as follows: according to the data percentage value of s109 ash content 71 (% adb), total sulfur 0.24 (% adb), calorific value 953 (cal/g), s24 ash content 63.4 (% adb), total sulfur 0.2 (% adb), calorific value 2.520 (cal /g), s49 ash content 3.72 (% adb), total sulphur 0.21 (% adb), calorific value 5,645 (cal/g), s8 ash content 3.72 (% adb), total sulfur 0.35 (% adb), calorific value 5.676 cal/g), s34 ash content 10.88 (% adb) total sulfur 1.54 (% adb), calorific value 5.325 (cal/g).the coal quality of research area is classified in low rank coal with caloric value ranged between 9535675 (cal/g). based on the maceral analysis, showing the maximum vitrinite reflectance value (% rv max) ranged from (0.33 0.54%) as seen in table 3, based in ward, 1984 the coal rank included in subbituminous high volatile bituminous b . 4. conclusions based on this research, it can be concluded as follows : (a) the research conducted in geramat district, lahat regency, south sumatra with muara enim formation as a coal-bearing formation. (b) the sedimentary structures observation at the several outcrops in the field shows that the deposition environment of the research area is in the transitional lower delta plain phase, telematic sub-environment with low sulphur content. (c) organic materials developed in the research area in the form of shrubs with significant vitrinite maceral content in humid or swamp environments. (d) the coal quality contained in geramat district shows a high ash content of 71.11 (% adb) with low sulphur content generally <1% and a calorific value of 5,676 (cal/g) which belongs to suba bituminous high volatile bituminous b. 5. acknowledgements the acknowledgments primary addressed to mrs. idarwati, s.t., m.t as a supervising lecturer who is kindly assisted, provided support and gave direction and also big thanks to our friends in the class who helped in discussing and determining the work components on this paper. 190 sari, s. l. et al./ jgeet vol 02 no 03/2017 table 3. result of muara enim formation maceral analysis in the research area. references astm. 1981. annual book of astm. philadelphi, united states of america. barber, a.j., crow and milsom j.s. 2005. sumatra : geology, resources and tectonic evolution. the geological society. london. casagrande, d.j. 1987. sulphur in peat and coal, in : scott, a.c. (ed.) coal and coal-bearing strata : recent advances, geol. soc. spec. publ., no.32, p 87-105. de coster g. l. 1974. the geologi of central sumaatera and south sumatera basins. proceeding indonesian petroleun assoc, 4th annual convention. diessel, c.f.k., 1992, coal bearing depositional system, spinger verlag berlin. (hal. 423-430). gafoer.s, burhan. g, dan purnomo.j. 1986. laporan geologi lembar palembang, sumatera., skala 1 : 250.000. pusat penelitian dan pengembangan geologi. horne, j.c., ferm, j.c., caruccio, f.t., baganz, b.p. 1978, depositional models in coal exploration and mining planning in appalachian regioan, aapg bulletin 62 p: 2379 2411, america. lamberson, m.n., bustin, r.m., kalkreuth, w. (1991). lithotype (maceral) composition and variation as correlated with paleowetland environments, gates formations, northeastern british columbia. canada; international journal of coal geology 18. p. 87 124 sulistyana b., waterman., and saputra, dean. 2012. analisis pengaruh lingkungan pengendapan batubara terhadap kandungan sulfur batubara. proceeding simposium dan seminar geomekanika ke-1 tahun 2012. ward, c.r. (1986). review of mineral matter in coal, australian coal geology,geol.soc. of australia, vol. 6 pp. 87-107. walker, r. g., and cant, d. j. (1979). facies models 3. sandy fluvial systems, in walker, r. g. (ed.), facies models: geoscience canada reprint ser. 1 , p. 23-31. d t s f sc i a de pyrite (%) 1 lp 34 bb 0.33 0.30-0.37 0.02 100 79.4 5.4 4.0 1.0 6.6 0 0 0 3.6 2 lp 8 bb 0.37 0.34-0.40 0.01 100 66.4 15.4 8.0 1.6 7.0 0 0 0 1.6 3 lp 24 bb 0.54 0.51-0.59 0.02 100 11.4 66.4 7.0 0 10.6 0 0 0 4.6 4 lp 49 bb 0.44 0.31-0.37 0.02 100 77.0 10.7 4.6 0 3.4 0 0 0 4.0 informations : bb = coal d = desmocolnite i =inertodetrinite n = total measurement t = telecolinite a =atrinite v = vitrinite s = semifusinite de =densinite i = inertinite f = fusinite pyrte =mineral pyrite h = huminite sc = sclerotonite n material mineral (%) v i h maceral component (%) no no samples lithology mean reflectance vitrinite (% rv random) range (%) standard deviation 1. introduction 2 regional geology 3. methods 4. result and discussion 4.1 depositional environment 4.2 the relationship of coal quality with ash content and calorific value 4.3 depositional environment interpreted from maseral 4.4 coal quality 5. acknowledgements references e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 4 no 4 2019 248 ojo, o. et al./ jgeet vol 04 no 04/2019 research article integrated approach in geophysical investigation of road failure in crystalline basement environment in south-western part of nigeria. olabanji ojo1*, victor adejumo2, obaromi olubunmi2 1department of geological sciences, osun state university, osogbo, osun state, nigeria. 2zibronel geosciences, akure, ondo state, nigeria * corresponding author : adeolu.ojo@uniosun.edu.ng tel.:+2348035626912. linkedin: olabanjiojo. received: oct 1, 2016. accepted: nov 20, 2019. doi: 10.25299/jgeet.2019.4.4.2590 abstract the result of the geophysical investigation carried out to access the cause of road failure and remediation measures along ilesha-osogbo expressway, osun state, south-western nigeria is presented. the study involved integrating the dipole-dipole technique of electrical resistivity method with the ground penetrating radar (gpr) method. two dipole-dipole traverses, one long and 20 short gpr profiles were established across the failed section of the road. the dipole-dipole data were interpreted using the diprowin software to produce the pseudosection while the gpr data were interpreted using the radprowin to produce the radargram. the result revealed that the failed road exhibit incompetent layer of resistivity values ranging between 17 ωm to 171 ωm lying between two competent layers of resistivity values greater than 200 ωm. a combination of the dipole-dipole technique and the gpr techniques revealed the depth extend to failure to about 4.5 meters to 5 meters deep which overlie a basement rock of undifferentiated gneiss, a rock that is easily prone to weathering. the water level was observed to occur at shallow depth of about 2 meters and infiltrates the entire weathered layer. the shallow groundwater level coupled with the water-logged clayey layer derived from the weathered materials from basement rock were found responsible for the failure of this section of the road. the study recommends the excavation of the waterlogged clayey layer to a depth of about 5 to 6 meters deep into the subsurface and replacement first with heavy boulders of granitic materials and later overlaid with a thick layer of highly resistive landfill materials such as laterite. the result of the two techniques used in this work have proved to be supportive due to the integration of the double dipole technique with the gpr technique, a relatively new technique recently being introduced into road failure mapping. keywords: geophysical, road, failure, idominasi, groundwater, clay 1. introduction failed roads generally constitute one of the major challenges to transportation especially in most developing nations of the world. it has been described as next to power supply in nigeria (ifabiyi and kekere, 2013) and has been a major setback to growth and development other countries. not only has it causes deaths of several thousands of people worldwide, it has also resulted to loss of properties worth millions of dollars annually. a greater percentage of developing nations are located in africa and asia. in nigeria, this challenge is beginning to gain government attention due to concerted effort towards to putting an end to this menace. reports show that out of 192 countries of the world, nigeria rank 191 (frsc, 2011) in terms of unsafe roads. hence, death toll due to road crashes has been put at 162 deaths per 10,000 populations. road failures in nigeria come in form of bulges, potholes, cracks and depression, all of which makes road non-pliable for road uses who are involved in day to day delivery of goods and services. governments at all the three tiers of government are coming up with concerted effort towards resolving these situations in the country. roads in nigeria has been classified into three. these include trunk a road which are highways that link state capitals together or dual carriage ways that link one part of the country to another. they constitute about 17% of the total national road network and the management of these types of road has been the responsibility of the federal government. the second, the trunk b roads which are intra-state roads which are managed by state governments constitute about 16% of the total road network of nigeria (ebhohimen and luke, 2014) while the third, trunk c roads are locally constructed road that link the local communities together and serve the purpose of means of transportation for rural dwellers to move locally made goods and services from the rural area to urban markets. they constitute about 67% of the total road network in the nation. these types of roads are under the management of the third tier of the government, the local governments. the construction and ultimate maintenance of all nigerian roads are sole responsibilities of these three tiers of government in nigeria. most of these roads do fail while construction is ongoing stage and also after the completion of the project. investigation indicated that lapses exists at the design and construction level. it is unfortunate to note that most contractors fail to take into consideration a 249 ojo, o. et al/ jgeet vol 04 no 04/2019 number of factors during the design and construction of roads. these include geologic factors such as nature of soil and the near-surface geologic sequence, existence of geological structures such as fractures and fault, presence of cavities, existence of an ancient stream channels and shear zones. these concealed subsurface structures and zones of weakness are controlled by regional fractures and joint systems and in conjunction with leaching of silica could result in rock deficiency are known to contribute to failure of highways and rail tracks (nelson and haigh, 1990). geomorphological factors have been related with the relief and surface/subsurface drainage systems which can be mapped by a combination of two or more geophysical and geotechnical methods (olorunfemi et al., 1986; olorunfemi and mesida, 1987; ojo and olorunfemi, 1995). biological factor such as the presence of surficial materials such as buried organics within the subsurface especially in locally made roads. adegoke-anthony and agada (1980) as well as ajayi, (1987) observed that road failure usually prevalent in basement complex of nigeria are not only attributed to the design, construction and usage of the roads alone but also to lack of understanding of the role of the influence of geomorphology and geology during the design and construction phases. it also has to do with inadequate knowledge characteristic nature of residual soils underlying the roads. as a result, some roads are not capable to withstand stresses. highway and road failure have become most noticeable almost all parts of nigeria especially in the western part of nigeria seating on soils derived weathered materials from the migmatized and unmigmatized granite, schist, and rocks of the pre-cambrian basement complex rocks. it is also prevalent in the eastern part of the country sited in fairly competent and incompetent subsurface earth materials where intense erosion has washed away. this has serious obstructions and have been constituting serious economic setbacks to communities where they occur. the present study desire to integrate the use of electromagnetic method and electrical method in geophysics using the ground penetrating radar (gpr) and the dipole-dipole array spread to unravel the causes, characteristic nature of road failure in idominasi community, along ilesha-osogbo expressway and to proffer a solution to the way out of the problem associated with the failed portion of the road. this community lies within the crystalline basement complex of south western nigeria. this is necessary because it is the only road that links the state capital, osogbo with the industrialized ilesha township. the road is a very important commercial pathway that links the economy of these two communities. the integration of these two methods becomes very necessary because the gpr technique would provide detail information depth to the failure, cause of the failure and the internal stratigraphy of the studied area. the dipoledipole survey of the other hand would provide information about the resistivity variation of the subsurface rock of the study area. the results from these two methods would provide comprehensive information that is needed for tangible conclusions about the nature, the extent as well as probable remediation techniques needed in this failed portion of ilesha osogbo expressway. 2. location and accessibility of the study area the study area, idominasi, lies between ilesha and osogbo, two major towns in osun state approximately between latitude 4° 40’e and 4°45’eand between latitudes 7° 40’n and 7° 44’n north of the equator. the study area is surrounded by the following villages: ijowa, ibala, iragun and ipoye. geologically, the study area is part of the ilesha schist belts in south western nigeria. rocks within the area include undifferentiated gneiss, granite gneiss andbanded gneiss (see figure 1). structurally, the area is divided into two; the iwaraja faults to the eastern and ifewara to the western part (folami, 1992, elueze, 1988). to the west of the fault is mostly amphibolites, amphibole schist, meta-ultramafites, and meta-pelites while to the east are units with minor meta-pelite, a major component of quartzites and quartz schist. olusegun et al.,(1995) and rahaman, (976) observed that “these entire assemblages are associated with migmatitic gneisses and are cut by a variety of granitic bodies”. the local geology of the study area is typical of the basement complex rock assemblage broadly grouped into gneiss-migmatite complex, mafic-ultramafic suite (or amphibolite complex), intrusive suite of granitic rocks and meta-sedimentary assemblages. a variety of minor rock types are also related to these units. the study area is made accessible by a network of roads that runs from ilesha to osogbo. another road joins the expressway from idominasi township. a major river (river ora) running fig. 2: gpr profile orientations along and across the failed portion of the road 250 ojo, o. et al./ jgeet vol 04 no 04/2019 from east to the west and meandering southwards drains the entire area under study. smaller river channels in the study area drains into river ora. this study area possesses is a typical tropical climate having more wet season months than the dry season months. the wet season commences in april till october while thedry season commences from november to march. the köppen-geiger climate classification consider the climate around the study area as aw. the average annual temperature in ilesa is 25.6 °c. the average annual rainfall is 1317 mm. the least amount of rainfall occurs in january but precipitation reaches its peak every september with an average of 222 mm. on the average, the highest temperature is about 28.6 °c around march while the coldest month is about 23.9 °c on average around august every year. 3. materials and methods the ground penetrating radar (gpr) gssi sir 3000 monostatic equipment and the abem sas 1000 resistivity meter were used for the exercise. initial reconnaissance survey was carried out to map the geology and study the topographic layout of the studied area. this is followed by the establishment of a long traverse along the failed road using the global positioning system (gps). two dipole-dipole method of electrical resistivity technique were carried out along the failed portion of the road using abem sas 1000 resistivity meter (terrameter). results from this were interpreted using the diprowin software to produce two pseudo-sections along the failed portion of the road. zones of highly resistivity and low resistivity as well as depth to failure were identified from the pseudo-section. also the electromagnetic wave was beamed into the subsurface using the (gpr sir 3000) in order to view the subsurface depth extent to failure. the beginning and the end of the traverse were properly georeferenced. the gpr instruments was used to make 20 parallel traverses across the failed portion of the road. the operation was carried out using the geologic scan preset parameters configured into the terrasirch mode as shown; t-rate = 100, rate = 80, range = max, gain = 5 point auto, survey wheel calibration = 1024 sample per scan), frequency = 400 mhz, collection mode = distance, sample per scan format = 16 bit (default).radargram obtained from these activities were interpreted for the possible cause to road failure, depth to road failure, stratigraphy of the study area. the depth to water level and mud were computed from the analysis and subsequently used to construct a 3d model of the depth to ground water and depth to weathered layer/basement interface. results from the two techniques were compared and inferences from these were used to proffer solution towards remediating the problem. 4. results and discussions figure 2 shows the gpr profile orientations along failed road segment while figure 3 shows the pseudo-section obtained using the dipole-dipole electrical method. figure 4 to 15 shows the radargram obtained from gpr profiles. figure 16 and 17 is the pictorial situation of the failed portion of the road. fig. 2: gpr profile orientations along and across the failed portion of the road the results obtained from the dipole-dipole investigation reveals that the first part of the road is relatively stable (indicated in red colour in figure 3) around idominasi junction but progressively becomes unstable towards the south eastern direction (indicated in blue colour). this is exemplified by the low resistivity values obtained within the middle portion of the traverse. the earlier part is underlain with thick lateritic material of about 20 meters’ thickness with rubble of unweathered quartzite having resistivity values of between 325 ωm and 621 ωm. as the profile continues, failure begins to be prominent and the resistivity begin to reduce to as low as between 17 ωm to 46 ωm (figure 3) the 2-d resistivity pseudosection reveals relatively low resistivity values in the range of 46 and 69 ωm at a depth range between 0.6 and 5.0 m typical of clay material. the extent of the failure is prominent at the top 5 m while, the failure reduces gradually at relatively deeper depth. however, at about 10 m depth, the effect was not noticeable. as shown in figure 3, the depth to failure is about 2 m deep while beyond this depth, there seem to be a relatively competent layer underlying the muddy interval. stratigraphically, the area under investigation is underlain by clay to a depth of about 4 m to 44 m and basement below the strata. within the failed portion, the entire basement is almost weathered and almost lacking as the resistivity is as low as 17-117 ωm. about 20 short gpr profiles were established during the course of the survey with the aim of revealing the water level, subsurface stratigraphy and the disturbed layer. analysis of the gpr profiles (figures 4-15) reveal that the cause of the failed portion of the road is the closeness of the water level to the surface coupled with the low resistivity clay material. this extends to a depth of about 0 to 4.5 or 5 meters. this result is similar to that obtained using the dipole-dipole technique. the material that constitute the overburden is rich in clay and varies in thickness from about 4 – 5 meters. the depth to the water level also varies from 1.40 meters in figure 4 to 2.0 m in figure 5. this result is also confirmed in the dipole-dipole that was run in the area which reveals the depth of 4.5 to 5 meters to the incompetent less resistive layer having resistivity values of 46 and 89 ωm in figure 4 and resistivity values of 14 and 171 ωm in figure 5. this observation is also obtained in figures 6 to 15. 251 ojo, o. et al/ jgeet vol 04 no 04/2019 fig. 3: pseudosection of the failed portion of the from north to south. (red = competent highly resistive layer; blue = low resistivity incompetent failed portion) fig. 4: gpr radargram for profile 1 fig. 5: gpr radargram profile 2 252 ojo, o. et al./ jgeet vol 04 no 04/2019 fig 6: gpr profile traverse 3fig 7: gpr profile traverse 4 fig 8: gpr profile traverse 5 fig 9: gpr profile traverse 6 fig 10: gpr profile traverse 7 fig 11: gpr profile traverse 8 253 ojo, o. et al/ jgeet vol 04 no 04/2019 fig 12: gpr profile traverse 9 fig 13: gpr profile traverse 10 fig 14: gpr profile traverse 11 fig 15: gpr profile traverse 12 figure 16 and 17 shows the ongoing geophysical investigation using the gpr instrument as well as the dipole-dipole electrical resistivity instrument respectively. figure 16: picture of the failed portion of the road and investigation using the gpr instrument figure 17: picture showing ongoing dipole-dipole geophysical survey on the failed portion of the road table 1: table showing first dipole-dipole array field data 254 ojo, o. et al./ jgeet vol 04 no 04/2019 traverse one resistivity field record (dipole-dipole array) date: observer: instrument used: abem sas 1000 terrameter traverse azimuth traverse no. one (1) electrode spacing: 5 site description: number of n = 5 electrode position c1 c2 p1 p2 geometric factor (k) resistance r (ω) apparent resistivity (ω) 0 1 2 3 94.2478 4.3446 409 3 4 376.9911 1.0698 403 4 5 942.4778 0.38497 363 5 6 1884.9556 0.16367 309 6 7 3298.6723 0.098464 325 1 2 3 4 94.2478 4.5423 428 4 5 376.9911 1.0976 414 5 6 942.4778 0.34256 323 6 7 1884.9556 0.17121 323 7 8 3298.6723 0.11068 365 2 3 4 5 94.2478 3.6199 341 5 6 376.9911 0.71980 271 6 7 942.4778 0.27639 260 7 8 1884.9556 0.14664 276 8 9 3298.6723 0.092391 305 3 4 5 6 94.2478 2.4770 233 6 7 376.9911 0.58185 219 7 8 942.4778 0.25172 237 8 9 1884.9556 0.14695 277 9 10 3298.6723 0.11324 374 4 5 6 7 94.2478 2.3010 217 7 8 376.9911 0.48245 182 8 9 942.4778 0.17720 167 9 10 1884.9556 0.10213 193 10 11 3298.6723 0.070471 232 5 6 7 8 94.2478 2.0330 192 8 9 376.9911 0.38671 146 9 10 942.4778 0.14869 140 10 11 1884.9556 0.083077 157 11 12 3298.6723 0.051189 169 6 7 8 9 94.2478 1.4265 134 9 10 376.9911 0.30677 116 10 11 942.4778 0.12170 115 11 12 1884.9556 0.062223 117 12 13 3298.6723 0.035221 116 7 8 9 10 94.2478 1.3773 130 10 11 376.9911 0.30058 113 11 12 942.4778 0.12363 117 12 13 1884.9556 0.065282 123 13 14 3298.6723 0.046602 154 8 9 10 11 94.2478 1.2367 117 11 12 376.9911 0.25734 97 12 13 942.4778 0.065953 62 13 14 1884.9556 0.048762 92 14 15 3298.6723 0.035587 117 9 10 11 12 94.2478 1.45220 137 12 13 376.9911 0.25038 94 13 14 942.4778 0.10360 98 14 15 1884.9556 0.065972 124 15 16 3298.6723 0.043294 143 10 11 12 13 94.2478 1.2113 114 13 14 376.9911 0.22586 85 14 15 942.4778 0.11383 107 15 16 1884.9556 0.071055 134 16 17 3298.6723 0.054921 181 11 12 13 14 94.2478 1.0519 99 14 15 376.9911 0.22983 87 15 16 942.4778 0.11715 110 16 17 1884.9556 0.080555 152 17 18 3298.6723 0.07866 259 12 13 14 15 94.2478 0.81797 77 15 16 376.9911 0.15770 59 16 17 942.4778 0.077111 73 17 18 1884.9556 0.053673 101 18 19 3298.6723 0.043151 142 13 14 15 16 94.2478 0.72319 68 16 17 376.9911 0.16589 63 17 18 942.4778 0.087615 83 18 19 1884.9556 0.063142 119 19 20 3298.6723 0.039343 130 14 15 16 17 94.2478 0.67862 64 17 18 376.9911 0.18749 71 18 19 942.4778 0.10817 102 19 20 1884.9556 0.060088 113 20 21 3298.6723 15 16 17 18 94.2478 0.71850 68 18 19 376.9911 0.19061 72 19 20 942.4778 0.089627 84 20 21 1884.9556 21 22 3298.6723 16 17 18 19 94.2478 0.91152 86 19 20 376.9911 0.20725 78 20 21 942.4778 21 22 1884.9556 22 23 3298.6723 17 18 19 20 94.2478 1.3760 130 20 21 376.9911 21 22 942.4778 22 23 1884.9556 23 24 3298.6723 table 2: table showing second dipole-dipole array field data traverse two resistivity field record (dipole-dipole array) date: observer: instrument used: abem sas 1000 terrameter traverse azimuth traverse no. two (2) electrode spacing: 5 site description: number of n = 5 electrode position c1 c2 p1 p2 geometric factor (g) resistance r (ω ohm) apparent resistivity (ω ohm) 0 1 2 3 94.2478 0.69290 65 3 4 376.9911 0.22664 85 4 5 942.4778 0.014776 14 5 6 1884.9556 0.061431 116 6 7 3298.6723 0.050204 167 1 2 3 4 94.2478 0.45880 43 4 5 376.9911 0.13538 51 5 6 942.4778 0.087540 83 6 7 1884.9556 0.063269 119 7 8 3298.6723 0.088032 290 2 3 4 5 94.2478 0.51966 49 5 6 376.9911 0.16736 63 6 7 942.4778 0.12739 120 7 8 1884.9556 0.15163 286 8 9 3298.6723 0.13716 452 3 4 5 6 94.2478 0.39549 37 6 7 376.9911 0.26276 99 7 8 942.4778 0.25160 237 8 9 1884.9556 0.25199 475 9 10 3298.6723 0.52869 1744 4 5 6 7 94.2478 1.0900 103 7 8 376.9911 5.2541 1981 8 9 942.4778 0.34672 327 9 10 1884.9556 2.8150 5306 10 11 3298.6723 0.13563 447 5 6 7 8 94.2478 1.0305 97.1 8 9 376.9911 0.37437 141 9 10 942.4778 1.2457 1174 10 11 1884.9556 0.096081 181 11 12 3298.6723 0.066031 218 6 7 8 9 94.2478 1.2515 118 9 10 376.9911 3.6771 1386 10 11 942.4778 0.29211 275 11 12 1884.9556 0.18016 339.6 12 13 3298.6723 0.045060 149 7 8 9 10 94.2478 0.014504 1.41 10 11 376.9911 0.88606 334 11 12 942.4778 0.43357 409 12 13 1884.9556 0.12729 239.9 13 14 3298.6723 0.10456 345 8 9 10 11 94.2478 1.9173 181 11 12 376.9911 0.68693 259 12 13 942.4778 5.6166 5294 13 14 1884.9556 0.097445 184 14 15 3298.6723 0.088045 290 9 10 11 12 94.2478 7.5819 715 12 13 376.9911 1.5697 592 13 14 942.4778 0.60218 568 14 15 1884.9556 0.51181 965 15 16 3298.6723 0.39240 1294 10 11 12 13 94.2478 1.1978 113 13 14 376.9911 0.17760 67 14 15 942.4778 0.11088 105 15 16 1884.9556 0.079292 149 255 ojo, o. et al/ jgeet vol 04 no 04/2019 16 17 3298.6723 0.074019 244 1112 13 14 94.2478 0.34964 113 14 15 376.9911 0.17750 67 15 16 942.4778 0.098327 93 16 17 1884.9556 0.068025 128 17 18 3298.6723 0.058611 193 1213 14 15 94.2478 1.1306 107 15 16 376.9911 0.19492 73.5 16 17 942.4778 0.083223 78 17 18 1884.9556 0.077026 145 18 19 3298.6723 0.044675 147 1314 15 16 94.2478 0.49428 47 16 17 376.9911 0.11667 44 17 18 942.4778 0.085506 81 18 19 1884.9556 0.046120 87 19 20 3298.6723 0.043888 145 1415 16 17 94.2478 0.38620 36 17 18 376.9911 0.20279 76 18 19 942.4778 0.10907 103 19 20 1884.9556 0.10323 195 20 21 3298.6723 1516 17 18 94.2478 0.45114 43 18 19 376.9911 0.17232 65 19 20 942.4778 0.15002 141 20 21 1884.9556 21 22 3298.6723 1617 18 19 94.2478 0.44504 42 19 20 376.9911 0.23666 89 20 21 942.4778 21 22 1884.9556 22 23 3298.6723 1718 19 20 94.2478 0.60064 57 20 21 376.9911 21 22 942.4778 22 23 1884.9556 23 24 3298.6723 highway structures constructed on top of subgrade soils are supposed to be strong enough to support heavy loads on them. (momoh, et. al., 2008) observed that subgrade soils underlying a stable highway should possess highly resistive and sufficient geotechnical strength to withstand stress. such soil must have good drainage and permeability characteristics and not shrink or swell excessively (adeleye, 2005, oladapo, 1998). however, the result obtained from this work does not conform to the ideal due to the fact that the soil underlying the study area has been affected by the presence of water such that they could shrink and swell at any time. probably, the study area is underlain by typical expansive clay materials. the stable segment which also falls within the earlier part within the first pseudo-section is underlain by weathered basement that is not waterlogged. hence, there exist no failure in this segment and this segment is devoid of any geological features or structures that could aid and abet failure. the top soil and the subgrade soil here is purely lateritic with a significant thickness of about 20 meters. this means this area is thick enough to support any impose wheel load. as the traverse progresses, failure begin to be noticeable due to the presence of water level located closer to the surface, coupled with the fact that the section is made up of weathered incompetent layers made up of mud/clay materials. 5.0 conclusion and recommendation this research has been carried out in order to investigate the cause of road failure at idominasi, along ilesha-osogbo expressway using an integrated approach that combines the use of the dipole-dipole technique of electrical resistivity method with the electromagnetic ground penetrating radar (gpr) method. the cause of the road failure was found to be the presence of a low resistivity (weak and incompetent) lithology localized and sandwiched between two competent layers. the water level was observed to be located very close to the surface. the combination of these two has been the root cause of the failed portion of the road. in order to proffer a solution to the problem on ground, the depth to water table and the depth to mud were extracted from the gpr radargrams for each profile of the radargram carried out in the study area. from the results obtained, since the clay is localized within a small portion of the road sandwiched within competent lateritic layers, towards the north western side and towards the south eastern part, the possible solution to the problem is to excavate the entire clayey layer in the study area, and replace with landfill material which can resist and withstand imposed wheel load. excavation would be done to a depth of about 6 m to 7 m deep. landfill materials to be used should be composed of homogenous and highly resistive lateritic material which is devoid of any significant geological features that could aid the development of swells and shrinking. this will go a long way to resuscitate the road and support heavy wheel load imposed on it. 6. acknowledgement the authors would like to say that this work was funded by research grant award by the tetfund. we wish to appreciate the effort of members of staff of geological sciences of osun state university, osogbo during the field work as well as the university needs assessment fund for the purchase of the gssi sir 3000 machine. we also wish to appreciate all the anonymous reviewers for their contribution towards the review of the manuscript. we are highly indebted to all. 7. references adegoke-anthony, wc.and o.a. agada, 1980. geotechnical characteristics of some residual soils and their implications on road design in nigeria. technical lecture. lagos, pp:1-16. adeleye,a.o.,2005.geotechnical investigation ofsubgrade soil along sections of ibadan-ife highway unpublished m.sc. project, obafemi awolowo university, ile-ife,pp: 181 agada, o.a. and adegoke-anthony, w c. 1980 geotecnical characteristics of some residual soils and their implications on road design in nigeria. technical lecture. lagos, pp:1-16. ajayi, l.a, 1987. thoughts on road failures in nigeria. nigerian engineer. 22(1): 10-17 ebhohimen and luke, 2014: ”geophysical investigation of road failure the case of opoji in nigeria”.international journal of scientific & engineering research, volume 5, issue 1, january2014 elueze, a. a. (1988): geology of the precambrian schist belt in ilesa area, southwest nigeria. precambrian geology of nigeria. geological survey of nigeria publication. pp77-82. federal road safety corps (frsc, 2011) united nation decade of action on road safety, benin city, nigeria. o’flaherty c.a (1979) highway engineering, edward arnold – london. 256 ojo, o. et al./ jgeet vol 04 no 04/2019 folami, s.l., (1992). interpretation of aeromagnetic anomalies in iwaraja area, southwestern nigeria. journals of mining and geology, 28(2), 391-396. ifabiyi p.i. and kekere, a.a 2013: geotechnical investigation of road failure along ilorin-ajase – ipo road kwara state, nigeria. journal of environment and earth science,vol. 3, no.7, 2013 nelson, r.g. and j.h. haigh.(1990). geophysical investigation of in lateritic terrain. geotechnical and environmental geophysics. ward, s.h. (ed), (geotechnical), seg, tulsia. 2: 133 – 154 mohamed and noha, 2016. ground magnetic, gpr, and dipole-dipole resistivity for landfill investigation momoh, l.o., akintorinwa, o., and olorunfemi, m.o., (2008): geophysical investigation of highway failure a case study from the basement complex terrain of southwestern nigeria. j. appl. sci. res., 4(6): 637648. olorunfemi, m.o., ojo, j.s., sonuga, f.a., ajayi, o., and oladapo, m.i., “geoelectric and electromagnetic investigation of the failed koza and nassarawa earth dams around katsina, northern nigeria”. j. min. geol., vol. 36, no. 1, pp 51-65, 2000a. oladapo m. i. (1998), “geophysical and geotechnical investigation of road failure in the basement complex areas of southwestern nigeria”, (unpublished m.sc. thesis), department of applied geophysics, federal university of technology, akure. olorunfemi, m.o., ojo, j.s., sonuga, f.a., ajayi, o., and oladapo, m.i., “geoelectric and electromagnetic investigation of the failed koza and nassarawa earth dams around katsina, northern nigeria”. j. min. geol., vol. 36, no. 1, pp 51-65, 2000a © 2016 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 syaifudin m./ jgeet vol 1 no 1/2016 27 organic geochemical characteristic of crude oils from orange graben, south sumatra basin m. syaifudin 1, * 1 geology corresponding author: syaifudin_muhammad@yahoo.com tel.: 0812-2793-352 received: oct 1, 2016. revised : nov 15, 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.3 abstract lemat formation in the orange graben in the south sumatra basin has been considered as syn-rift sediments consist of fluvio-lacustrine sediments, create source rock with fluvio-lacustrine characterize. based on existing publications, showing that the oils from orange graben have fluvio-deltaic characterization and generated by source rock from talangakar formation with fluvio-deltaic depositional environment. this paper emphasizes geochemistry methods. source rock analysis, consist of 26 samples for carbon isotope and 14 samples for biomarker, while oil analysis, consist of 15 samples for carbon isotope and 19 samples for biomarker. characterization has been based on qualitative and quantitative data. qualitative data comprise evaluation based on chromatograms and mass-fragmentograms, whereas quantitative data consists of a series of cross-plots, eg. cross plot of carbon isotope δ 13 c saturates aromatics, distribution of c27-c28-c29 sterane, pr/nc17-ph/nc18, pr/ph-pr/nc17, carbon isotope δ 13 c saturates-pr/ph, pr/ph-total hopane/total sterane, and ratio of c26/c25 (tricyclic). based on geochemical result of analysis, source rocks of lemat formation in the orange graben interpret as source rock with fluvio-deltaic characterize, have terrestrial influence while talangakar formation in the orange graben interpreted as source rock with deltaic characterization, having marine and terrestrial influence. both of them , consist of humic kerogen. whereas, oil samples in the orange graben interpreted as oilwhich is generated by source rock with fluvio-deltaic characterization, having terrestrial influence, in anoxic-suboxic-oxic conditions, consisting of humic kerogen. correlation result between source rocks and oils in the orange graben, indicating that fluvio-deltaic oil type in the orange graben are correlate with not only the source rocks of talangakar formations but also with source rock of lemat formation. key words: geochemistry, crude oil, biomarker, carbon isotope, fluvio-lacustrine-deltaic. 1. introduction south sumatra basin is a potential and mature basin for hydrocarbon source. there are a number of sub-basins which is potential as the hydrocarbon source in this basin. orange graben is one of sub-basin on the south palembang subbasin, formed in upper cretaceous to lower tertiary, in extensional phase, this is the beginning of sedimentation in this area. lemat formation in orange graben has been considered as syn-rift sediments consist of terrestrial sediment (fluvio-lacustrine), creating source rock with fluvio-lacustrine characterization. while based on existing publications, showing that oil from orange graben have fluvio-deltaic characterize and generated by source rock from talangakar formation with fluvio-deltaic characterization. this is interesting to study further, especially about possibility of source rock with fluviolacustrine characterization in research area. this study emphasized to source rocks of lemat and talangakar formation in orange graben, south palembang sub-basin, south of sumatra basin. 2. location of study area the study area located in orange graben, south of sumatra (figure 1). 3. research methods the basic source rock analyses comprise screening, kerogen typing, and maturation. further analysis, such as correlation between source rock and crude oil as well as crude oil to crude oil, has been done by using more sophisticated techniques, i.e. carbon isotope and biomarkers. source rock analysis, consist of 26 samples for carbon isotope and 14 samples for biomarker, while oil analysis, consist of 15 samples for carbon isotope and 19 samples for biomarker. characterization has been based on qualitative and quantitative data. qualitative data comprise evaluation based on chromatograms and mass-fragmentograms, whereas quantitative data consists of a series of cross-plots, eg. cross plot of carbon isotope δ 13 c saturates-aromatics, distribution of c27 c28 c29 sterane, pr/nc17 ph/nc18, pr/ph pr/nc17, carbon isotope δ 13 c saturates pr/ph, pr/ph total hopane/total sterane, and ratio of c26/c25 (tricyclic). 28 syaifudin m./ jgeet vol 1 no 1/2016 fig 1. location map of the study area and data of source rocks in orange graben. the results of this study expected could explain the character of source rocks and oil in the orange graben, also to find out the possibility of lacustrine source rock existence and determine the correlation between source rocks and oils in this area, so can be known whether lemat formation source rocks also have contributed to produce oil in this area or not. in addition, to provide a new opportunity in the exploration of hydrocarbons in the orange graben which considered as a mature and potential basin for hydrocarbon. 4. regional geology the evolution of the south sumatra basin started in the mesozoic era (pulunggono et al., 1992) (25) as a back-arc basin (figure 2). back-arc basins in indonesia are generally hydrocarbon prolific basins. the mechanism involved in the basin formation is general rifting, which formed a graben or half graben. this basin was formed in two phases, i.e. the rifting phase occured during the paleogene and the sagging during the neogene. the rifting phase is characterized by the thinning of crust forming graben or half graben, whereas the sagging phase is characterized by stable tectonics, and even a change in tectonic compression, which finished with volcanic activities that are shown by the occurrence of tuff that appeared in the air benakat formation. the rifting phase was filled by the lahat group that is comprised of the benakat and lemat formations, whereas the sagging phase was filled with sediments from the talangakar formation up to the youngest formation, i.e. kasai formation (figure 3). 5. characterization of source rocks and oils in orange graben 5.1. quantitative method pristane/phytane (pr/ph) ratios have been used to assess the redox potential of the depositional environment and source of organic matter (didyk et al., 1978 (10); tissot and welte, 1984 (31); zhang and huang, 2005 (38); peters et al., 2005 (22); duan et al., 2008 (11); hao et al. 2011 (18); cheng et al., 2013 (7) and tao et al., 2015 (9) or reflect the relationship between contributing organisms and the chemistry of the environment (mello and maxwell, 1990) (20). figure 4 shows a cross plot pr/nc17-ph/nc18 as proposed by connan and cassou (1980) (8) and pr/ph pr/nc17, source rocks of lemat and talangakar formations, and oils in orange graben. this image shows both source rocks of lemat and talangakar formation and oils, consists of humic kerogen in suboxic-anoxic until oxic conditions, but mostly in oxic conditions. waples, 1985 (35) stated that on the average, the stable carbon isotope values of the saturated more negative (lighter) than kerogens. a plot of the stable carbon isotope values of the saturated and aromatic hydrocarbons in the source rocks of lemat and talangakar formations and oils in orange graben as proposed by sofer (1984) (27) is shown in figure 5. this figure shows source rocks of lemat and talangakar formations and oils consists of terrestrial and mixed material, in anoxic suboxic to oxic conditions, but mostly in oxic conditions. figure 6 shows a cross plot of pr/phhopane/sterane and sterane distribution c27, c28, syaifudin m./ jgeet vol 1 no 1/2016 29 fig 2. tectonic evolution of the south sumatra basin from upper jurassic-now (pulunggono et al., 1992). fig 3. regional stratigraphy of the south sumatra basin (modified from ryacudu, 2008). 30 syaifudin m./ jgeet vol 1 no 1/2016 fig 4. cross plot of pr/nc17-ph/nc18 and pr/ph pr/nc17, source rocks of lemat and talangakar formation, and oils in orange graben. fig 5. cross plot of carbon isotope 13 c saturates 13 c aromatics and carbon isotope 13 c saturates pr/ph, source rocks of lemat and talangakar formation, and oils in orange graben. syaifudin m./ jgeet vol 1 no 1/2016 31 and c29, source rocks of lemat and talangakar formations and oils in orange graben. from this picture it appears that the source rocks of lemat and talangakar formations and oils affected by terrestrial material in anoxic suboxic until oxic conditions, but mostly in high oxic conditions. it is usually believed that c27 steranes derive mainly from phytoplankton and metazoa, whereas c29 steranes mainly originate from terrigenous higher plants (huang and meinschein, 1979 (19); volkman, 1986 (33)). from the cross plot of sterane distribution c27, c28, and c29, show lemat formation derived from estuarine to terrestrial environments, whereas talangakar formation and oils derived from marine, estuarine, and terrestrial environments. fig 6. cross plot of pr/ph-hopane/sterane and sterane distribution c27, c28, and c29, source rocks of lemat and talangakar formation, and oils in orange graben. fig 7. comparison of biomarker characterization qualitatively between source rocks of lemat and talangakar formation, and oils in orange graben 32 syaifudin m./ jgeet vol 1 no 1/2016 5.2 qualitative method figure 7 is a comparison of biomarker characterization qualitatively between source rocks of lemat and talangakar formation and oils in orange graben. from this picture it appears that source rocks of lemat and talangakar formations and oils, according to ten haven and schiefelbein (1995) (30); peters et al. (2005) (22); syaifudin et al. (2015) (28) and tao et al. (2015) (29), is not lacustrine sediments because has c26/c25 (tricyclic) smaller than 1. based on tricyclic data, according to price et al. (1987) (24), lemat formation and oils show terrestrial pattern, whereas talangakar formations show marine and terrestrial pattern. terrestrial is characterized by high c19 and c20 tricyclic (philp and gilbert, 1986 (23); peters and moldowan, 1993 (21), hanson et al., 2000 (16); grice et al., 2001 (14); george et al., 2004 (12); volk et al., 2005 (32); zhang and huang 2005 (38); peters et al., 2005 (22); hao et al., 2009 (17); hao et al., 2011 (18); asif et al., 2011 (4); adedosu et al., 2012 (1); tao et al., 2015 (29); wang et al., 2015 (34)). lemat, talangakar formation and oils show c19 and c20 tricyclic are more abundant. c23 tricyclic is often the dominant in crude oils of a marine source (aquino neto et al., 1983 (2); zumberge, 1987 (40); burwood et al., 1992 (6); hanson et al., 2000 (16); zhang and huang, 2005 (38); hakimi et al., 2011 (15); tao et al., 2015 (29)). talangakar formation besides show c19 and c20 tricyclic dominan, also c23 tricyclic dominan. these data indicate lemat formation interpreted as fluvio deltaic sediment, whereas talangakar formation having more marine characterization than lemat formation. based on data of 29h and 30h (hopane) distribution, the pattern of 29h <30h indicate marine clastic sediments, while 29h>30h is evaporates-carbonate sediment (zumberge (1984) (39); connan et al. (1986) (9); price et al. (1987) (24); waples and machihara (1991) (36); peters et al. (2005) (22); hakimi et al. (2011) (15); xiangchun et al. (2013) (37); syaifudin et al. (2015) (28), and wang et al. (2015) (34). the source rocks of lemat formation and oils shows 29h <30h, while talangakar formation not only show 29h<30h but also show 29h>30h. from data of homohopana distribution which decreased regularly from c31 to c35, interpreted as depositional environment which associated with clastic sediments (waples and machihara, 1991 (36)) or more oxidizing conditions (peters and moldowan, 1993 (21); hakimi et al. (2011) (15). the source rock of lemat, talangakar formations, and oils in orange graben interpreted as depositional environment which associated with clastic sediments. based on these data, oil in the orange graben interpreted originated from fluvio-deltaic source rocks and has a correlation with lemat and talangakar formations in orange graben. 6. conclusion source rocks of lemat and talangakar formations and oils in orange graben consists of humic kerogen and terrestrial and mixed material. source rocks of lemat and talangakar formations and oils in orange graben, is not derived from a lacustrine sediments, affected by terrestrial material in anoxic -suboxic until oxic conditions, but mostly on high oxic conditions. besides, its also looks like lemat formations derived from estuarine to terrestrial environments, whereas talangakar formation and oils in orange graben derived from marine, estuarine, and terrestrial environments. lemat formation and oils in orange graben show terestrial pattern, whereas talangakar formations show marine and terrestrial pattern. these data indicate lemat formation interpreted as fluvio-deltaic sediment, whereas talangakar formation having more marine characteriztion than lemat formation. oils in the orange graben interpreted originated from fluvio-delta source rocks, has a correlation with lemat formation and talangakar formation in orange graben. acknowledgements we would like to thank the management of directorate general of oil and gas and medco ep for their permission to publish this paper. references [1] t.a. adedosu, o.o.sonibare, j.tuo, o.ekundayo, 2012. biomarkers, carbon isotopic composition and source rock potentials of awgu coals, middle benue trough, nigeria, journal of african earth sciences, 66 67, elsevier, p 13 21. 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[40] j.e.zumberge, 1987. terpenoid biomarker distributions in low maturity crude oils. journal organic geochemistry 11, elsevier, p 479 496. http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 178 iqbal, m. et al./ jgeet vol 04 no 03/2019 research article hydrogeochemistry of natar and cisarua hot springs in south lampung, indonesia mochamad iqbal 1, *, bella restu juliarka 1 , wijayanti ashuri 1 , bilal al farishi 1 1 geology research group, institut teknologi sumatera, jalan terusan ryacudu, way huwi 35365, lampung selatan, lampung. * corresponding author : mochamad.iqbal@gl.itera.ac.id tel.: +62 896 5711 4572; fax: +80-65-711-4572 received: apr 06, 2019; accepted: jun 19, 2019. doi: 10.25299/jgeet.2019.4.3.4070 abstract natar hot spring is one of the geothermal manifestations that is located in lampung province, indonesia. about 6 km to the east, another hot spring appears with temperature around 40°c with neutral ph called cisarua hot spring. the natar hot spring itself having temperature 47-54°c with 6.23 ph. based on the geologic map, the appearance of these hot spring is caused by lampung-panjang fault which trending northwest-southeast. morphology of the research area is showing a flat terrain topography which composed of quaternary volcanic rock and metamorphic rock in the basement. the nearest volcano that expected to be the heat source of the geothermal system is the quaternary extinct volcano called mt. betung which is located about 15 km to the southwest. the aim of the study is to analyze the geochemistry of the manifestations and calculate the reservoir temperature. geochemistry analysis result shows both manifestations are bicarbonate which is formed as a steam-heated water or steam condensates. geothermometer calculation shows that the geothermal reservoir has temperature 150-160°c with approximately 300 m in depth. all manifestations are originated from meteoric water according to stable isotope analysis d and δ18o data and interacting with carbonate-metamorphic rock beneath the surface based on 13c isotope value. a further geophysics study is needed to determine where the heat comes from. keywords: geochemistry, hot spring, natar, cisarua, lampung, isotope, geothermometer. 1. introduction indonesia has abundant of geothermal resources, until 2014, it is recorded that total potential of geothermal energy in indonesia exceeds 28,9 gwe (girianna, 2014). one of the areas which have geothermal spot is located in south lampung regency, lampung province, indonesia. its existence is well-known because of the presence of geothermal surface manifestation in the form of hot spring which used as a bathing place. there are two groups of hot spring in the research area, i.e. natar hot spring and cisarua hot spring. both are located in natar district, precisely 4 km in the east of natar city and 15 km in the north of bandar lampung city. preliminary research at cisarua hot spring has been conducted by (suharno et al., 2012) and measured that the hot spring was 50°c with discharge about 20 l/s. additionally, travertine deposit was found surrounding the discharge (suharno et al., 2012). the study of recharge area by analysing dem/topographic map is also been done by iqbal et al. (2018) which shows that the recharge area of natar and cisarua are lied at the southern part of metro-kotabumi groundwater basin and around mt. pesawaran, mt. betung, and panjang. the aim of this research is to identify and understand the characteristic of the geothermal fluid at natar and surrounding area. geothermal manifestations in the research area appear at the flat terrain topography which makes it interesting to be studied. its appearance can be an initial deduction to determine the relation between natar with the nearest geothermal system (e.g.: ulubelu and way panas) which act as the outflow or natar geothermal system is an independent system with flat topography without any influence from the volcano (non-volcanic geothermal system). 2. methods this research analyzes geochemistry aspect from several samples which are taken from the hot spring and groundwater (well). thermal water samples are taken from natar and cisarua hot spring with total 4 samples. meanwhile, groundwater sample is taken from the local well near cisarua hot spring. these samples are then analyzed at pair-batan laboratory jakarta to determine the cation-anion content, (li+, na+, k+, ca2+, mg2+, cl-, f-, so42+, hco3-), stable isotope d, 18o, tritium, and 13c. the results of this analysis will be plotted on several ternary diagrams i.e. cl-so4-hco3 (csh), cl-li-b (clb), and na-k-mg (nkm) for further interpretation. csh diagram is used http://journal.uir.ac.id/index.php/jgeet iqbal, m. et al./ jgeet vol 04 no 03/2019 179 to determine the type of thermal waters, clb diagram used to determine the similarity of the reservoir, and nkm diagram is used as geoindicator for mixing fluid with groundwater. another aspect that can be obtained from geochemistry data is the estimated reservoir temperature using a geothermometer (na/k, k/mg, na-k-ca, etc.). by knowing the reservoir temperature, the reservoir depth can be estimated using statistical data on geothermal field drilling in indonesia (hochstein and sudarman, 2008). 3. geological setting geology of the research area already mapped by mangga et al. (1993) in tanjungkarang quadruple with scale 1:250.000 (fig. 1). the morphology of the research area is composed of the terrain and the foot of mount betung in the southern region (fig. 1). local stratigraphy in natar and cisarua map areas consists of young volcanic deposits (qhvp) and lampung formation (qtl). in addition, there are also metamorphic rocks of trimulyo marble (pzgm) and igneous rocks of branti granodiorite (kgdb). mangga et al. (1993) described these formations as follows (oldest to youngest): trimulyo marble (pzgm) consists of marble with schists intercalation. grey-white marble, in some places greenish-grey which is composed of calcitedolomite with granoblastic texture, massive and hard. this formation is metamorphosed regionally and is considered to be the core rock of sumatra's metamorphic rocks. branti granodiorite (kgdb) consists of granodiorite and diorite from early cretaceous (87 ± 3 million) with medium grain, white-pink grey in color, granitoid with subhedral biotite. this unit is an intrusive rock in the form of small plutons but does not show contact with the wall rock which are located approximately 25 km north of tanjungkarang. lampung formation (qtl) is deposited in the fluvial-terrestrial environment has a pliocenepleistocene age which is composed of rhyolite -dacite tuff, pumiceous tuff, and tuffaceous sandstone. tuff is rhyolite-dacite in composition, white to brownish, volcanoclastic rock, and fractured. pumiceous tuff, yellowish grey to greyish-white, medium-coarse grains, poorly sorted, composed of pumice and rock fragments. tuffaceous sandstone, yellowish-white, medium-fine grains, poorly sorted, sub-rounded, pumiceous in some places, showing a crossbedding, generally composed by dacite. this formation has a thickness of about 200 m. young volcanic deposit (qhvp) is composed of andesite-basalt lava, breccia, and tuff. the lava is pleistocene and holocene in age, blackish grey, aphanitic and porphyritic with plagioclase and augite phenocryst in the glass groundmass, with a little olivine. breccia with blackish-grey colour, poorly sorted, angular, pebble-boulder size. tuff is graybrownish-brown in colour, composed of lava, glass and carbonaceous. the geological structure in the research area is dominated by lineament trending northwestsoutheast (fig. 1) which is thought to be the cause of the emergence of geothermal discharge in the form of hot springs in natar and cisarua. fig. 1. geologic map in natar and surroundings (mangga et al., 1993). 180 iqbal, m. et al./ jgeet vol 04 no 03/2019 4. result generally, the manifestations in natar geothermal system are classified as warm-hot springs with temperatures ranging from 40-54°c and ph close to neutral. the description of manifestations is presented in table 1. the results of water chemistry analysis in several samples are presented in table 2 while table 3 presents the results of stable isotope analysis. in general, all samples have the highest content in hco3 with the content ranging from 208-396 ppm. cl content in cold water is smaller than the sample of hot water while the mg value in all samples is classified as similar. in general, the results of the isotope analysis show differences in values that are not too significant at δ18o, δd, δ13c, and t (tritium). the differences in the 18o and d isotope values in each sample of thermal and cold water only ranged from 2.61 and 13.2 respectively (table 3). whereas at 13c and tritium the value difference is smaller so that it can be classified still in the same group. table 1. hot spring characteristics in the research area. no. sample sampling date debit t water t air ph description l/s °c °c 1 apn1 15 april 2018 ~1 54 32 6,23 clear, a little smell of sulfur, tasteless, there are bubbles of great intensity, manifestations concentrated in wells, appearance around manifestations in the form of organisms (mosses) that are on the walls of wells and orange well edges (fig. 2a). 2 apn2 30 september 2018 ~0,03 50 32 ~7 clear, odourless, tasteless, there are bubbles of great intensity, manifestations concentrated in 50 cm holes, appearance around manifestations in the form of organisms (mosses) and yellowish deposits around the manifestation hole (fig. 2b). 3 apn3 30 september 2018 ~0,12 47 32 ~7 clear, odourless, tasteless, there are bubbles of small intensity, manifestations are concentrated in wells, wells are right in the middle of a hot water bath, the appearance around the manifestation is an organism (moss) that is on the well wall (fig. 2c). 4 apc 30 september 2018 ~1 ~40 32 ~7 clear, the smell of sulfur, brackish, there are 3 bubbles with moderate intensity concentrated in the well, the appearance around the manifestation is yellowish deposits (fig. 2d). table 2. water chemistry result. no sample location code sample type temperature ph li + na + k + ca 2+ mg 2+ cl f so4 2+ hco3 °c ppm 1 natar apn thermal water 54,3 6,23 0,03 97,72 6,92 3,86 12,55 40,33 2,12 23,81 337,18 2 natar apn2 thermal water 50 ~7 0,02 120,11 3,81 44,79 15,93 35,33 2,26 20,81 396,36 3 natar apn3 thermal water 47 ~7 0,02 93,24 8,12 4,38 15,03 46,12 2,91 20,57 314,29 4 cisarua apc thermal water ~40 ~7 0,02 98,43 5,29 15,77 15,42 38,90 2,47 20,11 330,16 5 cisarua adc cold water nm ~7 0,04 26,86 2,46 28,11 15,55 5,19 0,58 35,66 208,24 nm: not measured. table 3. stable isotope analysis result. sample location code δ 18 o δd δ 13 c tritium tu natar apn -4,97 -40,4 -5,18 2,86 natar apn2 -2,65 -27,2 nm nm natar apn3 -5,18 -37,4 -4,27 2,77 cisarua apc -5,26 -40,1 -4,02 2,83 cisarua adc -3,27 -35,4 nm 2,37 nm: not measured. iqbal, m. et al./ jgeet vol 04 no 03/2019 181 (a) apn1 (b) apn2 (c) apn3 (d) apc fig. 1. geothermal manifestation in the research area (apc: cisarua, apn: natar). 5. discussion 5.1 geoindicator the csh ternary diagram is used to classify geothermal water types. samples of cold water and thermal water are then plotted on the diagram. from several samples that have been taken and analyzed, all of the samples are classified as bicarbonate water (fig. 3). this type of bicarbonate water is formed by condensation of steam and geothermal gas into groundwater near the surface (nicholson, 1993). it can be seen that the cold-water point is located lower than the hot water point (fig. 3) which indicates that cold water has a higher so4 content, lower cl, and higher hco3 compared to the thermal water. geothermal fluids (steam and water) that rise to the surface have content of cl (in the liquid phase) and co2 (in the vapour phase) and then heated the groundwater near the surface and form steam-heated waters/steam condensates. cl element which is carried from the reservoir adds cl element which is in groundwater when mixed near the surface so that the cl content in hot water is higher than cold water. the co2 vapour that rises to the surface adsorbs h2o in groundwater and forms bicarbonate ions so that the content increases in the thermal water. while the higher so4 content of cold water compared to hot water is caused by oxidation of the soil which contains many elements of sulfur (miljević et al., 2013). fig. 3. csh (cl-so4-hco3) diagram to classify the type of water. 182 iqbal, m. et al./ jgeet vol 04 no 03/2019 the clb ternary diagram (fig. 4) is used to identify reservoir similarities by comparing the conservative elements (cl, li, b, br, as, cs). conservative or nonreactive elements tend to be in solution when the element is dissolved (nicholson, 1993). in this study, boron content was not measured so that to determine the similarity of the reservoir only a comparison of cl/li elements was used. the four samples have similar cl/li ratios (fig. 4) so that all manifestations come from the same reservoir/aquifer. fig. 4. clb (cl-li-b) diagram to identify the similarity of the reservoir. the content of mg in geothermal reservoir fluids is relatively low, which is around 0.01-0.1 mg/kg (nicholson, 1993), while the value of mg in groundwater tends to be high. thermal water samples in the study area belong to immature waters (fig. 5) with relatively high mg content which indicates that hot water samples have been mixed with the groundwater. plotting on the piper diagram (fig. 6) based on the concentration of dissolved ions in the samples adn, apc, apn1, apn2, and apn3 shows two types of water types, namely ca/mg hco3 and na+k hco3. based on clark (2015), natar cold water (adn) which has a type of water ca/mg hco3 indicates that the water is originating from shallow aquifers. in contrast to the thermal waters at apc, apn1, apn2, and apn3 which has a type of water na+k hco3 which indicates that there has been a change between the alkali element and alkaline earth. this indicates the presence of water-rock interactions and different aquifer/reservoir layers between cold water (adn) and thermal water (apn1, apn2, apn3, and apc). 5.2 temperature and reservoir depth the reservoir temperature is estimated by using several geothermometers such as na/k (fournier, 1979; giggenbach, 1988; nieva and nieva, 1987; tonani, 1980; truesdell, 1975), na-k-ca (fournier and truesdell, 1973) and k/mg (giggenbach, 1988). from several calculations using the geothermometer, the authors conclude that the reservoir temperature in the natar geothermal system is 120-140°c. the estimation of the reservoir depth is calculated by using statistical geothermal drilling wells in indonesia proposed by hochstein and sudarman (2008). from the drilling data, iqbal et al. (2016) obtained a quadratic regression trendline to see the relationship between the reservoir temperature and the reservoir depth (fig. 7) and acquire the following equation: h = 0,0257 t 2 + 0,4446 t + 31,248 (1) where h is reservoir depth and t is reservoir temperature. by using reservoir temperature data that has been calculated previously, the calculation using eqn. 1 produces a reservoir depth in the natar geothermal system which is 285-400 m. seeing from the regional geological map (fig. 1), the natar geothermal system is covered by the lampung formation which is dominated by tuff with a thickness of about 200m (mangga et al., 1993). lampung formation was deposited above the unconformity of metamorphic rock which acts as a basement in the regional geology of sumatera. therefore, the natar geothermal reservoir is thought to lie in the metamorphic rock (basement) which support by 13c isotope data from hot water samples which show that the hot water has undergone interaction with metamorphic-carbonate rocks (trimulyo marble unit) under the surface (fig. 8). fig. 5. nkm (na-k-mg) diagram. fig. 6. piper diagram. iqbal, m. et al./ jgeet vol 04 no 03/2019 183 fig. 2. estimation of the reservoir depth using statistical data of geothermal field in indonesia (hochstein and sudarman, 2008; iqbal et al., 2016). fig. 3. range of 13 c isotope values. 13 c isotope values of thermal water samples in the study area indicate that the thermal water has undergone interaction with metamorphic-carbonate/marble rocks (clark, 2015). 5.3 the origin of thermal waters interpretation of stable isotope values d and 18o is carried out to determine the origin of the geothermal fluid. plotting sample isotope values in the study area show that all samples are originated from meteoric water (fig. 9). these data also support that the hot springs come from the groundwater that heated by the geothermal steam or steam-heated water because it has relatively similar isotope values. tritium analysis was carried out in the research area to measure the residence time of water since infiltrate until it discharges to the surface. tritium analysis was carried out on four samples, namely; apn1, apn3, apc, and adc. the tritium value of thermal water ranges from 2.77 tu (apn3) to 2.86 tu (apn1) while in cold water tritium value is 2.37. based on pujiindiyati (2007), the value of 2-8 tu tritium in areas with low latitude indicates that the water is modern groundwater which has only permeated <5 to 10 years 184 iqbal, m. et al./ jgeet vol 04 no 03/2019 ago. tritium value in cold water is lower than hot water which indicates that the residence time of thermal water in aquifers/reservoirs below the surface is relatively longer than cold water (groundwater). fig. 9. d and 18o isotope values of thermal and cold water in the study area. meteoric water lines using global values (gmwl/global meteoric water line) refer to (craig, 1961). the range of isotope values of magmatic water is proposed by (white, 1974). 6. conclusion this research obtains several conclusions as follows: 1. natar and cisarua hot springs are bicarbonate type hot springs which are formed due to steam-heated waters. 2. both hot springs come from the same reservoir, namely natar reservoir which has a temperature of 120-140°c with a depth of 285-400 m. 3. geothermal discharge in natar has undergone water-rock interaction with metamorphiccarbonate/marble under the surface. 4. further research is needed to find the heat source from the natar geothermal system by using geophysical methods such as gravity or magnetotelluric methods. acknowledgements the authors would like to thank institut teknologi sumatera for providing the research grant through references clark, i., 2015. groundwater geochemistry and isotopes. crc press. craig, h., 1961. isotopic variations in meteoric waters. science 133, 1702 1703. https://doi.org/10.1126/science.133.3465.1702 fournier, r.o., 1979. a revised equation for the na/k geothermometer. us geol. surv. 3. fournier, r.o., truesdell, a.h., 1973. an empirical na-k-ca geothermometer for natural waters. geochim. cosmochim. acta 37, 1255 1275. https://doi.org/10.1016/0016-7037(73)90060-4 giggenbach, w.f., 1988. geothermal solute equilibria. derivation of na-k-mg-ca geoindicators. geochim. cosmochim. acta 52, 2749 2765. https://doi.org/10.1016/0016-7037(88)90143-3 girianna, m., 2014. geothermal handbook for indonesia. bappenas, jakarta. hochstein, m.p., sudarman, s., 2008. history of geothermal exploration in indonesia from 1970 to 2000. geothermics, indonesian geothermal prospects and developments 37, 220 266. https://doi.org/10.1016/j.geothermics.2008.01.001 iqbal, m., ashuri, w., juliarka, b.r., farishi, b.a., harbowo, d.g., 2018. delineation of recharge and discharge area for geothermal energy in natar. presented at the international conference on science, infrastructure technology, and regional development, south lampung. iqbal, m., herdianita, n.r., risdianto, d., 2016. characteristic of geothermal fluid at east manggarai, flores, east nusa tenggara. iop conf. ser. earth environ. sci. 42, 012016. https://doi.org/10.1088/1755-1315/42/1/012016 mangga, s.a., amirudin, suwarti, t., gafoer, s., sidarto, 1993. peta geologi lembar tanjungkarang, sumatera skala 1:250.000. miljević, n., boreli-zdravković, d., veličković, j., golobočanin, d., mayer, b., 2013. evaluation of the origin of sulphate at the groundwater source ključ, serbia. isotopes environ. health stud. 49, 62 72. https://doi.org/10.1080/10256016.2013.729509 nicholson, k., 1993. geothermal fluids. springer berlin heidelberg, berlin, heidelberg. nieva, d., nieva, r., 1987. developments in geothermal energy in mexico part twelve. a cationic geothermometer for prospecting of geothermal resources. heat recovery syst. chp 7, 243 258. https://doi.org/10.1016/0890-4332(87)90138-4 pujiindiyati, r., 2007. tritium (3h) untuk identifikasi dan penanggalan air tanah modern. j. teknol. pengelolaan limbah 10. suharno, aritonang, r.b., zainudin, a., rustadi, 2012. sistem panas bumi cisarua natar, lampung selatan. presented at the the 12th annual indonesian geothermal association meeting & conference, bandung. tonani, f.b., 1980. some remarks on the application of geochemical techniques in geothermal exploration, in: strub, a.s., ungemach, p. (eds.), advances in european geothermal research. springer netherlands, pp. 428 443. truesdell, a.h., 1975. summary of section iii: geochemical techniques in exploration, in: second united nations symposium on the development and use of geothermal resources. lawrence berkeley laboratory, berkeley, california. white, d.e., 1974. diverse origins of hydrothermal ore fluids. econ. geol. 69, 954 973. https://doi.org/10.2113/gsecongeo.69.6.954 © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ iqbal, m. et al./ jgeet vol 04 no 03/2019 185 hydrogeochemistry of natar and cisarua hot springs in south lampung, indonesia 1. introduction 2. methods 3. geological setting 4. result 5. discussion 5.1 geoindicator 5.2 temperature and reservoir depth 5.3 the origin of thermal waters 6. conclusion references e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 96 winarno et al./ jgeet vol 5 no 2/2020 research article effect of porphyritic andesite intrusion on the formation of contact metamorphism aureole in selo gajah hill clastic limestone, bojonegoro regency, east java, indonesia tri winarno 1,*, jenian marin 1, wisnu wijaya jati 1 1department of geological engineering, diponegoro university, semarang, central java, indonesia corresponding author : triwingeo@gmail.com telp :+62 857-4006-6835 received: nov 18, 2019, accepted: jun 25, 2020.) doi 10.25299/jgeet.2020.5.2.4098 abstract at selo gajah hill, jari village, gondang sub-district, bojonegoro regency, east java there are limestone intruded by porphyritic andesite. the intrusion produces contact metamorphisms in the wall rocks. it is very interesting to study the protolith rock, facies of metamorphism and the zonation of contact metamorphism aureole. this research uses field observation method and laboratory analysis i.e. petrographic analysis. field observation is conducted by doing geological mapping in the bukit selo gajah area and rock sampling for petrographic analysis. petrographic analysis aims to describe the texture of the rocks and the percentage of minerals, which will be used to determine the protolith rock, metamorphism facies and the determination of contact metamorphism zone. the lithology found in mount selo gajah from oldest to youngest are clastic limestone with intercalation of marl, marl with intercalation of sandstone, porphyritic andesite intrusions, hornfels, and pyroclastic breccia. metamorphic rocks on selo gajah hill is the product of contact metamorphism of carbonate rock which was intruded by porphyritic andesite intrusion. the metamorphism facies found in the research area are hornblende hornfels and pyroxene hornfels with the protolith rock is carbonate rocks. metamorphism zone in selo gajah hill is divided into two zones: the zone closest to the intrusion body is vesuvianite zone or idiocrase zone with a radius of 40-140 m from the outer part of the intrusion body and the monticellite zone with radius ranging from 25 to 75 m from the outside of the vesuvianite zone. keywords: bukit selo gajah, hornfels, contact metamorphism zone, andesite intrusion 1. introduction the research is held in bukit selo gajah, jari village, gondang district, bojonegoro regency, east java province. in regional geology, the research area is included in the regional geological maps of bojonegoro sheet 1508-5 (pringgoprawiro and sukido, 1992). based on the regional geological map, the lithology found in bukit selo gajah are limestone intruded by porphyritic andesite. the intrusion produces contact metamorphism in the limestone. from the standpoint of petrology, the essence of metamorphism is the chemical reaction among minerals and fluid (ferry et al., 2011). previous work on contact metamorphism of sedimentary rocks has demonstrated that 1) pure carbonates recrystallize without significant devolatilization, 2) limestones and marlstones are characterized by calc‐ silicate formation during heating, releasing co2‐ dominated and h2o‐ bearing fluids (aarnes et al., 2011a) (aarnes et al., 2011b). experimental studies show that carbonates partially melt at relatively low temperature, but natural examples of such melting are rare (ganino et al., 2013). contact metamorphism of igneous rocks will cause metamorphic zones distinguished by mineral assemblage, depend on initial rock composition (deer et al., 2013). the purpose of this research is to study the distribution of lithology, stratigraphy and facies of metamorphism in bukit selo gajah and surrounding areas. 2. regional geology based on the division of physiographic zone according to (van bemmelen, 1949), the study area is a part of the quaternary volcanic zone and kendeng antiklinorium. this zone is adjacent to the central depression zone in the south and randublatung zone in the north in fig.1.the stratigraphic condition of the research area consists of three formations, they are kalibeng formation, andesite intrusion, and pandan breccia which can be seen in fig. 2. the kalibeng formation consists of a rich fossilgreenish grey marl interbedded with tuff. this sediment is deposited in the bathyal environment. the upper part of the kalibeng formation (atasangin member) consists of finecoarse tuffaceous sandstone, tuff, and volcanic breccia. this sediment is deposited by the turbidite mechanism (pringgoprawiro and sukido, 1992). this formation is of late miocene – pliocene (fig. 2). pyroxene andesite is an intrusion of porphyritic andesite with a high content of pyroxene. this formation is of pleistocene age. pandan breccia is a pleistocene pyroclastic breccia. study area is part of pandan volcanic complex, consist of nangka volcano, lawang volcano, and pandan volcano. this complex is characterized by andesitic rocks as pyroclastics and intrusions (arhananta et al., 2018). selo gajah hill located in the north of the main pandan volcano. winarno et al./ jgeet vol 5 no 2/2020 97 fig. 1. physiography of eastern part of java (van bemmelen, 1949) fig. 2. the stratigraphy of kendeng zone (pringgoprawiro and sukido, 1992) 3. research methods this research is conducted by doing literature study, field observation, laboratory analysis and data analysis. the laboratory analysis used in this research is petrographic analysis to find out the structure, texture, and mineral composition in rocks. the data of petrographic analysis is used to determine the protolih rock, the facies of metamorphism and the contact metamorphism aureole zonation. 4. results and discussion 4.1 stratigraphy from the geological mapping in the research area, there are five units of lithology found in the research area. those lithology from oldest to youngest are clastic limestone, marl (carbonate claystone), porphyritic andesite, hornfels (metamorphic rock), and pyroclastic breccia (fig. 3-4). the explanation of each lithology unit is as follows. clastic limestone the oldest lithology unit in the research area consists of clastic limestone with intercalation of marls (fig. 5). the rock color is generally blackish gray. in megascopic appearance, there are found some cavities which are the result of dissolution. based on petrographic analysis,the rock composition consists of 10% shell of the organism, 30% algae which part of the body has been replaced by calcite mineral, 30% brown rock matrix/ micrite and light brown sparite, and 30% porosity which is the result of dissolution. based on the composition, this rock is floatstone (embry and klovan, 1971). fig. 3. geological map of selo gajah hill, jari village, gondang sub-district, bojonegoro 98 winarno et al./ jgeet vol 5 no 2/2020 fig. 4. geological cross section of jari village, gondang sub-district, bojonegoro district fig. 5. (a) the outcrop of clatic limestone at sta 32. (b) handspeciment of clastic limestone, (c) petrographic appearance of clastic limestone marl (carbonate claystone) this lithology unit consists of marls with the intercalation of carbonate sandstones (fig. 6). in general, the rocks have the strike direction of east-west with the strike/dip direction n 280°e/58°. fig. 6. (a) the outcrop of marls at sta 28 (b) handspeciment of marls (c) petrographic appearance of marls porphyritic andesite the unit of porphyritic andesite intrusion is a lithology that is unconformably intruded the lithological units of clastic limestone with intercalation of marls and marls with intercalation of carbonate sandstone. because of the intrusion the areas near the intrusive body underwent contact metamorphism (fig. 7). fig. 7. (a) the contact of porphyritic andesite intrusion (and) and hornfels (hfl) at sta 9 (b) handspeciment of porphyritic andesite (c) petrographic appearance of porphyritic andesite the rock color is generally gray. in megascopic appearance, the rock structure is massive with the rock texture is porphyritic. in microscopic appearance, the rock composition consists of 50% plagioclase (andesine) as phenocryst and groundmass,10% pyroxene as a groundmass, 15% hornblend as phenocryst and groundmass,5% sanidine as base mass, and quartz at 5% as groundmass. based on the composition, the rock has the name porphyritic andesite (thorpe and brown, 1985). hornfels the lithology unit of hornfels metamorphic rock consists of sedimentary rock which is transformed to metamorphic rock due to the influence of andesite porphyritic intrusion (fig. 8). in general, the rocks have winarno et al./ jgeet vol 5 no 2/2020 99 the strike direction of east-west with the strike/dip direction 270°e/77°. in general, the color of the rocks is bright white and blackish gray. in megascopic appearance, there are found some cavities which are the result of dissolution. in microscopic appearance, the thin section of rock shows hornfelsic/ granulose structure and granoblastic textures while the special textures are crystalloblastic and decussate. the composition of the rocks consist of wollastonite minerals (15%), vesuvianite (30%), spurrite (25%), calcite (15%), and monticellite (15%). based on the composition, the rock is metacarbonate-rock (robertson, 1999) and marble (huang, 1962). fig. 8. (a) the outcrop of hornfels at sta 30 (b) handspeciment of hornfels (c) petrographic appearance of hornfels pyroclastic breccia the lithology unit of pyroclastic breccia is unconformably deposited above the andesite porphyritic intrusion. this can be seen through the appearance of rock contacts in the field at sta 15 and sta 24. pyroclastic breccia covers porous andesite intrusions. the appearance of pyroclastic breccia can be seen in fig. 9. in general, this rock found in the field is weathered.in megascopic appearance, the color of rocks is generally grayish brown with a massive structure. the fragments of the breccia are composed of andesite with the matrix is tuff-lapilli. fig. 9. (a) the outcrop of pyroclastic breccias at sta 30 (b) handspeciment of pyroclastic breccia 4.2 mineralogy rock sampling is conducted systematically, based on three types of rocks: sedimentary rock as protolith rock of hornfels, igneous rocks as intrusion rocks, metamorphic rocks as a product of contact metamorphism. the rock sampling location can be seen at figure 10. there are 19 rock samples were taken, consist of 8 sedimentary rocks (table 1), 5 igneous rocks (table 2), 6 metamorphic rock (table 3). those samples then will be analysed with petrographis analysis. petrographic analysis includes observations of rock and mineral textures, and mineral composition of rock constituents. following are the observations of rock mineralogy in each sample. 100 winarno et al./ jgeet vol 5 no 2/2020 fig. 10. tracking map of selo gajah hill, jari village, gondang sub district, bojonegoro district table 1 shows the minerals which compose the sedimentary rock in the research area. sedimentary rock in the research area near the intrusion body is considered to be a protolith in the research area. these mineral were used to indicate the type of sedimentary rock in the research area to support the research. the determination of rocks is based on the classification of (embry and klovan, 1971). the embry and klovan classification (1971) considers the composition of the constituents in rocks and the size of fragments in carbonate rocks. based on the composition, the carbonate rocks in the research area consists of wackestone, packstone and floatstone. table 2 shows the minerals which compose the igneous rock in the research area. these minerals were used to indicate igneous rock types in the research area to support the research. the determination of rocks is based on the classification of (thorpe and brown, 1985) by considering the composition of the constituent minerals in the rocks. based on the composition of minerals in igneous rocks, the rock is classified as porphyritic andesite. table 3 shows the minerals which compose the metamorphic rock of the research area. these minerals were used to determine metamorphic rock types in the research area to support the research. the determination of rocks based on the classification of (robertson, 1999) and (huang, 1962) by considering the composition of the constituent minerals in rocks. based on the composition of minerals in metamorphic rocks , the rock is classified as metacarbonate-rock (robertson, 1999) and marble (huang, 1962). table 1. the mineralogy of sedimentary rock at research area sample sta composition (%) rock name alg for skel mat cal por wp-04 sta 44 15 35 50 packstone wp-07 sta 33 30 10 30 floatstone wp-13 sta 13 10 30 20 15 20 floatstone wp-15 sta 09 35 10 55 floatstone wp-16 sta 21 35 10 55 wackestone wp-17 sta 31 40 10 30 20 floatstone wp-18 sta 34 30 10 60 wackestone wp-19 sta 37 20 10 70 wackestone note: alg : algae, for : foraminefera, skel : skeletal grain, mat : matrix, cal : calcite, por: porosity table 2. the mineralogy of igneous rock at research area, all rocks are porphyritic andesite sample sta composition (%) pl san px lit qz hb opq wp-02 sta 13 50 5 10 10 5 15 5 wp-05 sta 09 50 5 10 10 5 15 5 wp-06 sta 02 55 5 10 5 20 5 wp-10 sta 25 50 5 10 5 25 5 wp-11 sta 05 50 5 10 10 5 15 5 note: pl : plagioclase, lit : lithic, qz : quartz, hb: hornblende, opq : opaque mineral, san : sanidine, px : pyroxene table 3. the mineralogy of metamorphic rock at research area sample sta mineral composition (%) wol ves spu fos cal mon tre opq til wp 011 1 30 20 25 10 15 10 wp 012 1 25 40 25 5 5 wp 013 1 15 25 15 5 10 15 10 wp 03 4 20 25 30 5 25 wp 08 30 15 30 25 15 15 wp 09 6 10 15 65 10 wp 12 45 35 35 15 15 wp 14 31 15 15 55 5 10 note: wol : wollastonite, ves : vesuvianite, spu : spurrite, fos : foshagite, cal : calcite, mon : monticellite, tre : tremolite, opq : opaque mineral, til : tilleyite 4.3. the metamorphic facies and the protolith rock at selo gajah hill the determination of metamorphic facies is determined by looking at the mineral composition in metamorphic rocks. calcite is one of mineral that can form metamorphic minerals. calcite has a chemical formula of caco3. wollastonite is formed by the loss of carbon dioxide which is then replaced by silica. the chemical reaction of wollastonite formation is: caco3 + sio2 → casio3 + co2 wollastonite is formed at a temperature of 600°-700° c with a pressure of 0.2 gpa according to (deer et al., 2013)tremollite is formed at a temperature of 600°-700° c with a pressure of 0.5 gpa (bucher and grapes, 2011). the chemical reaction of tremollite formation is: winarno et al./ jgeet vol 5 no 2/2020 101 5camg(co3)2 + 8sio2 + h2o → ca2mg5si8o22(oh)2 + 3caco3 + 7co2. spurrite has chemical formula of ca5(sio4)2(co3). according to deer et al. (1998) spurrite formed due to the intrusion of andesitic to basaltic rocks to the carbonate rocks s with temperatures of 600°-800° c. according to (winkler, 1979) spurrite can be formed due to the release of co2 by tilleyite at the highest temperature of 900° c. foshagite has the chemical formula of ca4si3o9 (oh)2. the temperature and pressure of foshagite formation are the same with wollastonite, but in the foshagite formation, there is hydrogen enrichment by water. monticellite has the chemical formula camgsio9. monticellite formed due to the intrusion of granitic to basaltic to the carbonate rocks.vesuvianite has the chemical formula of ca19(al,fe)10(mg,fe)3[si2o7]4[sio4]10(o,oh,f)10. vesuvianite formed in areas closest to intrusion bodies with the protolith rock rich in carbonate minerals. the type of intrusion also determines the facies and minerals resulted from the metamorphism. in the research area, the type of intrusion is included in the porphyritic andesite. according to (winkler, 1979) the presence of minerals of monticellite, melilite, larnite, merwinite, wollastonite and spurrite are minerals resulted from contact metamorphisms with high temperatures and formed in shallow intrusions with rapid cooling. the presence of spurrite, wollastonite and monticellite according to (winkler, 1979) suggests that it is classified as sanidinite facies. based on the mineral composition showing the temperature and pressure formation and the presence of minerals that show the facies of sanidinite, the facies of metamorphism can be determined as hornblende hornfels sanidinite hornfels which can be seen in fig. 11. fig. 11. the facies of metamorphism at selo gajah hill, jari village, gondang sub distric, bojonegoro 4.4.the zonation of contact metamorphism at selo gajah the determination of contact metamorphism zonation on limestones uses a model made by (burnham, 1959). this model will be modified according to the conditions in the research area. the determination of this zone is based on mineral composition in the research area. the minerals used in the determination are minerals on metamorphic rocks. the location of metamorphic rock sampling for petrographic analysis can be seen in fig. 12. the metamorphic zonation map is arranged based on mineral composition in rock samples (table 3), lithology unit boundaries and structural geology. based on mineralogy, metamorphic zone can be divided to three zone. from the inner to outer are: unaffected zone, monticellite zone, and vesuvianite zone. the map of influence of contact metamorphism can be seen in fig. 12. figure 12. hornfels sampling map at selo gajah hill, jari village, gondang sub district, bojonegoro 102 winarno et al./ jgeet vol 5 no 2/2020 this zonation map (fig. 13) can provide information the radius effect of metamorphism experienced by carbonate sedimentary rocks. the zone closest to the intrusion body is the vesuvianite or idocrase zone. the radius of vesuvianite zone ranges from 40 to 140 meters from the outside of the body of the intrusion. the zone outside of the vesuvianite zone is the monticellite zone. the montizellite zone radius ranges from 25 to 75 meters from the outside of the vesuvianite zone (fig.14). figure 13. metamorphic zonation map at selo gajah hill, jari village, gondang sub district, bojonegoro figure 14. the vertical cross section of contact metamorphism effect zonation at selo gajah hill, jari village, gondang sub distric, bojonegoro the zones outside of the vesuvianite zone and monticellite zone is a zone that does not experience the effect of metamorphism so the rock is not changed. the forsterite zone and garnet zone were not found in the research area due to the absence of identifier minerals such as grossular, klinohumite, forsterite, and clintonite. 5. conclusion metamorphic rocks in the selo gajah hill are the result of contact metamorphism from carbonate sedimentary rocks that are intruded by porphyritic andesite intrusion.the facies of metamorphism in selo gajah hill are hornblend hornfels sanidinite hornfels with the protolith rocks came of carbonate sedimentary rocks. the zonation of metamorphism in selo gajah hill is divided into two zones, they are the zone closest to the intrusion body is the vesuvianite or idocratic zone with a radius of 40-140 meters from the outside of the intrusion body and the monticellite zone with a radius ranging from 25 75 meters from the outside of the vesuvianite zone. acknowledgements the author would like to thank all the people in jari village who have accepted the author during the research, winarno et al./ jgeet vol 5 no 2/2020 103 and to the geological department, diponegoro university who have given the opportunity to do this research. references aarnes, i., fristad, k., planke, s., svensen, h., 2011a. the impact of host-rock composition on devolatilization of sedimentary rocks during contact metamorphism around mafic sheet intrusions. geochemistry, geophys. geosystems 12, n/a-n/a. https://doi.org/10.1029/2011gc003636 aarnes, i., svensen, h., polteau, s., planke, s., 2011b. contact metamorphic devolatilization of shales in the karoo basin, south africa, and the effects of multiple sill intrusions. chem. geol. 281, 181–194. https://doi.org/10.1016/j.chemgeo.2010.12.007 arhananta, arina, i., purwanto, j., mendel, j., setiawan, j., 2018. kinematik struktur geologi daerah atasangin, kecamatan sekar, bojonegoro, jawa timur dan implikasinya terhadap aktivitas magmatisme gunung pandan, in: seminar nasional kebumian ke-11. universitas gadjah mada, yogyakarta. bucher, k., grapes, r., 2011. petrogenesis of metamorphic rocks. springer berlin heidelberg, berlin, heidelberg. https://doi.org/10.1007/978-3540-74169-5 burnham, c.w., 1959. contact metamorphism of magnesian limestones at crestmore, california. geol. soc. am. bull. 70, 879. deer, w.a., howie, r.a., zussman, j., 2013. an introduction to the rock-forming minerals. mineralogical society of great britain and ireland. https://doi.org/10.1180/dhz embry, a.f., klovan, j.e., 1971. a late devonian reef traction on northeastern banks island, n.w.t.1. bull. can. pet. geol. 19, 730–781. https://doi.org/https://doi.org/10.35767/gscpgbull.1 9.4.730 ferry, j.m., ushikubo, t., valley, j.w., 2011. formation of forsterite by silicification of dolomite during contact metamorphism. j. petrol. 52, 1619–1640. https://doi.org/10.1093/petrology/egr021 ganino, c., arndt, n.t., chauvel, c., jean, a., athurion, c., 2013. melting of carbonate wall rocks and formation of the heterogeneous aureole of the panzhihua intrusion, china. geosci. front. 4, 535– 546. https://doi.org/10.1016/j.gsf.2013.01.012 huang, w.t., 1962. petrology. mcgraw-hill education, new york. pringgoprawiro, h., sukido, 1992. peta geologi regional skala 1:100.000 lembar bojonegoro. bandung. robertson, s., 1999. bgs rock classification scheme volume 2: classification of metamorphic rocks. nottingham. thorpe, r., brown, g., 1985. the field description of igneous rocks. open university press, university of california, california. van bemmelen, r.w., 1949. the geology of indonesia. vol.ia: general geology of indonesia and adjacent archipelagoes. government printing house, the hague, netherlands. winkler, h.g.f., 1979. petrogenesis of metamorphic rocks. springer new york, new york, ny. https://doi.org/10.1007/978-1-4757-4215-2 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ p-issn. 2503-216x e-issn. 2541-5794 volume 4 no 1 march 2019. p. 1-65 an analysis of the accuracy of time domain 3d image geology model resulted from pstm and depth domain 3d image geology model resulted from psdm in oil and gas exploration sudra irawan, yeni rokhayati , satriya bayu aji page 1 list of content journal of j eetgeoscience engineering environment and technology journal of geoscience, engineering, environment and technology uir press publisher assessment of geothermal potentials in some parts of upper benue trough northeast nigeria using aeromagnetic data abdulwahab mohammed, taiwo adewumi, salako a kazeem, rafiu abdulwaheed, abbass a. adetona, and alhassan usman page 7 saltwater intrusion zone mapping on shallow groundwater aquifer in selat baru, bengkalis island, indonesia dewandra bagus eka putra, yuniarti yuskar, husnul kausarian, wan zuhairi wan yaacob, mohamad sapari dwi hadian page 16 correlation between fracture azimuth, surface lineaments and regional tectonics: a case study from belik district, central java, indonesia reza syahputra , felix m. h. sihombing, octria a. prasojo page 22 age and paleobathymetry of salodik group in poh–pagimana section, east arm of sulawesi based on foraminiferal assemblages rakhmat fakhruddin, dedy kurniadi page 30 hydrogeochemical and groundwater assessment for drinking purpose at itera campus area and its surroundings luhut pardamean siringoringo, reza rizki, janner nababan page 40 the key parameter effect analysis of the polymer flooding on oil recovery using reservoir simulation tomi erfando, novia rita, romal ramadhan page 49 regression model in transitional geological environment for calculation farming and production of oil palm dominant factor in indragiri hilir riau province heriyanto, detri karya, tiggi choanji, asrol, djaimi bakce, elinur page 56 p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually our journal has accredited as a scientific journal (s2) by the ministry of research, technology, and higher education no 30./e/kpt/2018 period : 2017 2021 scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. sabah a. ismail (iraq) editorial member dr. kurnia hastuti (indonesia) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. eng. takahiro miyazaki (japan) dr. mursyidah, m.sc. (indonesia) dr. sapari dwi hadian mt (indonesia) dr. emi sukiyah st., mt (indonesia) bambang setiadi ph.d (indonesia) dr. vijaya isnaniawardhani (indonesia) dr. anas puri s.t, m.t (indonesia) mirza muhammad waqar, m.sc (pakistan) good fried panggabean, s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) yuta izumi m.eng (japan) kageaki inoue, m.eng (japan) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) yuta izumi, m.eng (japan) yuniarti yuskar s.t, m.t (indonesia) muhammad zainuddin lubis s.ik m.si (indonesia) nur islami (indonesia) pakhrur razi, s.si, m.si (indonesia) babag purbantoro, s.t, m.t (indonesia) budi prayitno s.t, m.t (indonesia) joko widodo, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 04 no 01 2019. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content an analysis of the accuracy of time domain 3d image geology model resulted from pstm and depth domain 3d image geology model resulted from psdm in oil and gas exploration ............................................................ 1 assessment of geothermal potentials in some parts of upper benue trough northeast nigeria using aeromagnetic data .................................................. 7 saltwater intrusion zone mapping on shallow groundwater aquifer in selat baru, bengkalis island, indonesia ....................................................... 16 correlation between fracture azimuth, surface lineaments and regional tectonics: a case study from belik district, central java, indonesia ............... 22 age and paleobathymetry of salodik group in poh–pagimana section, east arm of sulawesi based on foraminiferal assemblages ............................ 30 hydrogeochemical and groundwater assessment for drinking purpose at itera campus area and its surroundings ....................................................... 40 the key parameter effect analysis of the polymer flooding on oil recovery using reservoir simulation ............................................................................. 49 regression model in transitional geological environment for calculation farming and production of oil palm dominant factor in indragiri hilir riau province ......................................................................................................... 56 page 1 page 2 page 4 page 1 page 2 page 3 page 4 page 1 page 2 page 3 page 4 e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 herawarti, ira et al./ jgeet vol 02 no 01/2017 69 analyzing the statistics function for determination of oil flow rate equation in new productive zone ira herawati 1, *, novia rita 1, *, novrianti 1 , rosalia m taufand 1 1 petroleum department, faculty of engineering, islamic university of riau, riau, 28284,indonesia abstract oil rate will be decline at production time in a well. so, we have to produce in another layer who assume have a potential. before we produce another layer who assumed have a potential, we need to predict oil rate to known how much oil gain. in this field research oil rate prediction in new productive zone was determine following by analogical data and near well references. in this method there is a difference determine of oil rate for each people. cause of that, in this research using analysis statistical for oil rate predicting in new productive zone based on linear function for productivity index (pi) and polynomial function for watercut. determining equation of linear and polynomial functions for oil rate prediction measuring by production and logging data for each well who assumed productive zone in area x field rmt. based of statistically analysis for linear function known that coefficient determination (r 2 ) = 0.9964 and polynomial function known that coefficient determination (r 2 ) = 0.9993. this result indicated that we can use both of the functions for oil rate prediction in new productive zone in area x field rmt. after that, based on both of functions calculate oil rate prediction each wells in area x field rmt. so, known differences in oil rate prediction between oil rate data in area x field y known is 28.13 bopd or 0.78%. keywords: oil rate, statistical analysis, coefficient determination , productivity index, watercut 1. introduction the decline of oil flow rate in an oil field becomes a problem that have to be faced during the production period. one of several ways to solve the declining oil flow rate problem is by producing a new zone. previously, oil flow rate determination in the new zone that have not been producing at a potential reservoir is determined from the logging data and wells near by reference (gollan, michael. whitson, curtis h,1996). this method focuses on the analogy of the existing data. by using these methods, several parameters that become the benchmark of oil flow rate estimation have an uncertainty factor. in this case, everyone has the different determination of an oil flow rate with the same parameters. it makes this research needs to be done to determine that uncertainty factor. potential reservoir which is the becomes the object in this research shall be referred to the productive zone (kelkar, 2002). productive zone in this study is the layer that has never been in produces by a well, so it becomes a backup for the well. this occurs because the well was still quite good producing from another layer or from wells that are still relatively new, so there arecertain zone that has never been produced. when production wells down then, can be done to increase production by opening new layers that are considered productive. (ariadji, tutuka. radjes, 2012) in the case of management and these issues , it is often found some forecasting activity, prediction, estimation and more. one method that can be used to solve the problem is statistical methods. the used of statistical method sare very dependent on the structure of the data or the number of variables (stroud k.a and j. dexter, 2003) . one of the method that is used for one variable or more than one variable is the regression analysis (stroud k.a and j. dexter, 2003) . regression analysis is a statistical methodology to predict the value of one or more response variables (variable dependen) from the collection of predictor variable value (variable independen) . this analysis can also be used to predict or forecast the effect of the predictor variable (independent variable) on the response. in regression analysis , it is learn how does these variables relate and expressed in a mathematical function.this research is done by using regression analysis, to determine the function representing the approximate flow rate of oil in the productive zone (jothikumat, 2004). the objective of this paper is to determine the coefficients and function of linear regression of the permeability and thickness of the perforation of * corresponding author : iraherawati@eng.uir.ac.id, noviarita@eng.uir.ac.id tel.:+81-72-867-1686; fax: +81-72-867-1658 [tel./fax of the corresponding author] received: feb 1, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017 doi: 10.24273/jgeet.2017.2.1.34 mailto:iraherawati@eng.uir.ac.id mailto:noviarita@eng.uir.ac.id 70 herawarti, ira et al./ jgeet vol 02 no 01/2017 the productivity index and regression function at the polynomial correlation to the water saturation of the watercut. at the end we could to estimate the flow rate of the oil in the productive zone using a regression function and evaluation of oil flow rate estimates based on the function of the oil flow rate based on the data. 2. material and methods productive zone in this study is a new zone that has not been produced and has potential if seen from the data logging. this study uses data of each well log consisting of log gr (gamma ray), log sp (spontaneous potential), caliper logs, resistivity logs, neutron and density logs. based on the gr deflection curve at minimum value, indicates that the area with the curve approaching the minimum value may be a reservoir layers because of thenonshale (permeable) rock type whichin this case, the sandstone type, the reservoir rock type in general. mean while, if the deflection curve leads to a maximum value then the rock type may be shale (impermeable). on the log resistivity deflectioncurve with a great value indicates the potential for hydrocarbons contained therein, on the contrary if the deflection curve with a small resistivity values indicates the potential non-hidrokarbon (water zone). from the results of neutron log that has a deflection at a great value, it can be seen that these rocks have a large porosity. in the productive reservoir layers, the neutron-density log curves will intersect and form of separation. this indicates the exist of permeable layer and a reservoir layer. this both curvesshows the formation of separation column (cross over). the small cross over indicates the type of fluid is oil. at the gas zone, these two curves show the formation of the separation column. a large cross over, gas zone is also characterized by neutron porosity price that is far less than the price of porosity, so it would show the existence of a larger separation. in this research, to determine the flow rate of oil in the productive zone, it would require some data from wells located in an area that is not separated by any fault (fault). a layer of sand that is used as data in this study is the same sand layer. this is done because the consideration of the physical properties of rock and fluid at the same sand tends not much different when compared to the physical properties of fluids and rocks on different sand. in areas 1 and 3 there are 614 wells candidates which are productive zones that have been produced. however, this research is limited to areas that are not separated by their fault, so the area that it is included into non-separated by fault area is area 1with focus area 1, 2, 3 and area 3 with focus area 5 there are only 104 wells. after determining the candidate wells that are included in the areas relevant to the objectives of this study, furthermore, pick the same sand layer seen in a predetermined area. in this study, a-1 sand layer chosed. of the 104 wells which are reviewed there were 21 wells that have a productive zone a-1. furthermore in this study, the 21 well candidates is reviewed as productive zones to estimate the oil flow rate. permeability and saturation datain the productive zone which is used as a candidate in this research was determined from logging data to the log attached. while the thickness of the zone productive in this study is the interval thickness of each well perforations known by looking at the production history of candidate wells which is about to be examined and retrieve perforation data (top perforation and bottom perforation), the watercut data and production flow rate on the candidate wells in this research. 1. result and discussion calculations of permeability, saturation and resistivity well rmt-01 is done by the sameway to each well. result of pi calculation as shown at table 1. if the khp value is plotted against pi from the calculation, it can beshown by the fig 1. table 1. result of pi calculation well k (md) hperfo (ft) k.hp re (ft) wc (%) µ (cp) pg (psi/ft) pi (stb/d/psi) rmt-01 499 10 4990 393.29 97.2 0.36512 0.3651 14.29 rmt-02 752 6 13320 274.39 93.22 0.42356 0.4236 34.81 rmt-03 1849 3 5547 417.68 96.7 0.37246 0.3725 15.43 rmt-04 4370 2 8740 533.54 96.3 0.37833 0.3783 23.07 rmt-05 2102 8 16816 554.88 98 0.35337 0.3534 47.26 rmt-06 2403 8 19224 481.71 97.23 0.36468 0.3647 53.46 rmt-07 810 8 6480 295.73 95.8 0.38568 0.3857 18.37 rmt-08 3721 5 18605 554.88 98.4 0.3475 0.3475 53.17 rmt-09 1770 2 3540 609.76 98.7 0.34309 0.3431 15.82 rmt-10 3322 12 39864 442.07 98.03 0.35293 0.3529 116.02 rmt-11 1243 3 29820 329.27 99.68 0.32877 0.3288 97.5 herawarti, ira et al./ jgeet vol 02 no 01/2017 71 fig 1. pi plot againts khp based on the khp and pi data in table 1 and after the regression done, it resulting linest function outputs in excel shown in tabel 2. from the function linest output in table 2, it is generated a linear function to estimate the pi (morrison, 2015) is as follows: pi = 2.94 x 10−3khp − 1.22 (1) from the linest functions output above, do the t value and f value calculation to determine whether the function of the resulting statistics can be accepted. calculation of pi' based on linear functions to absolut delta pi performed to determine the percentage of pi errors and differences of each well, so the results got in table 3. table 2. linest function to estimate pi rmt-12 1404 10 14040 204.27 93.92 0.41333 0.4133 39.49 rmt-13 6167 3 18501 375 98.7 0.34309 0.3431 56.8 rmt-14 751 14 10514 554.88 96.6 0.37393 0.3739 27.93 rmt-15 1166 6 3708 480.18 91.9 0.44295 0.4429 8.49 rmt-16 2210 6 2352 161.59 83.47 0.56674 0.5667 5.03 rmt-17 841 4 3364 0 97.84 0.35572 0.3557 0 rmt-18 2705 9 9045 210.37 90.8 0.4591 0.4591 8.49 rmt-19 7128 4 1576 326.22 88.8 0.48847 0.4885 3.47 rmt-20 810 12 1692 539.63 85.49 0.53712 0.5371 3.14 rmt-21 2060 14 2282 475.61 88.79 0.48862 0.4886 4.74 kh bo coefficient 2.94 x10 -3 -1.22 standard error (seb) 4.37 x 10 -6 0.71 coefficient of determination (r 2 ) 0.9976 1.51 standard error y (sey) f-value 4507.63 11 degrees of freedom denominator(dfd) regression sum of square (ssreg) 10215.74 24.93 regression sum of residual (ssres) t-value 67.14 1.72 72 herawarti, ira et al./ jgeet vol 02 no 01/2017 table 3. well pi (stb/d/ psi) pi' (stb/d/ psi) delta pi (stb/d/ psi) abs delta pi(stb/d /psi) %error pi abs %error (%) rmt-01 14.29 13.21 1.08 1.08 7.54 7.54 rmt-02 34.81 37.69 -2.89 2.89 -8.29 8.29 rmt-03 15.43 14.85 0.58 0.58 3.76 3.76 rmt-04 23.07 24.23 -1.16 1.16 -5.02 5.02 rmt-05 47.26 47.97 -0.7 0.7 -1.49 1.49 rmt-06 53.46 55.04 -1.59 1.59 -2.97 2.97 rmt-07 18.37 17.59 0.78 0.78 4.25 4.25 rmt-08 53.17 53.22 -0.05 0.05 -0.09 0.09 rmt-09 15.82 14.83 0.99 0.99 6.25 6.25 rmt-10 116.02 115.7 0.33 0.33 0.28 0.28 rmt-11 97.5 86.18 11.32 11.32 11.61 11.61 rmt-12 39.49 39.81 -0.32 0.32 -0.8 0.8 rmt-13 56.8 52.92 3.88 3.88 6.84 6.84 rmt-14 27.93 29.45 -1.52 1.52 -5.45 5.45 rmt-15 8.49 9.45 -0.95 0.95 -11.23 11.23 rmt-16 5.03 5.46 -0.44 0.44 -8.67 8.67 rmt-17 6.02 8.44 -0.48 0.59 -10.12 10.12 rmt-18 8.49 9.45 -0.95 0.95 -11.23 11.23 rmt-19 3.47 3.18 0.29 0.29 8.41 8.41 rmt-20 3.14 3.52 -0.38 0.38 -12.12 12.12 rmt-21 4.74 5.26 -0.51 0.51 -10.77 10.77 the following fig 2 is a plot between the pi againts khp based on data and a linear function to estimate the value of pi', and khp againts based on hypothetical data. calculation of wc function (watercut) meanwhile, water saturation (sw) was determined from log data interpretation that is determined based on the average price of saturation. the watercut data and water saturation (sw) are plotted on a scatter , then it will form the fig 3 as follows. from the field data can be conducted to determine the regression coefficients, to obtain the correlation polynomial to predict wc with linest function as shown in table 4. herawarti, ira et al./ jgeet vol 02 no 01/2017 73 fig 2. pi vs khp fig 3. plotted between sw and wc at trend linear tabel 4. linest function to estimate wc using actual data sw 3 sw 2 sw intercept coefficient 332.02 -735.14 553.45 -48.28 standard error (seb) 122.52 215.99 106.11 10.59 coefficient of determination (r 2 ) 0.9598 4.38 #n/a #n/a standard error y (sey) f-value 151.04 19 #n/a #n/a degrees of freedom denominator (df deno regression sum of square (ssreg) 8692.26 364.47 #n/a #n/a regression sum of residual (ssres) t-value 2.71 3.4 5.22 4.56 0,00 20,00 40,00 60,00 80,00 100,00 120,00 140,00 p i ( s t b /d /p si ) khp fungsi data kolinear 0 10 20 30 40 50 60 70 80 90 100 0,00 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00 w a te rc u t ( % ) sw data linear (data) 74 herawarti, ira et al./ jgeet vol 02 no 01/2017 from the linest function output in table 4 generated the polynomial function to estimate wc is: wc′ = 553.45sw − 735.14sw2 + 332.02sw3 − 48.28 from the linest function output above, calculate the t value and f value to determine whether the function of the resulting acceptable statistically. fig 4 is a plot between sw against watercut based data, the actual equation and the equation based on the data adjusted to the data hypothetical in making the regression line. determination of oil flow rate calculation was performed on each well to get the oil flow rate with a linear function of khp regression of the productivity index and polynomial functions for swregression against watercut generated at the output function linest, so it can be tabulated as shown in table 5. plot betweenqo and qo 'to each well, can be seen in fig 5. where, qo : oil flow rate data (bopd) qo' : oil flow rate calculation based functions fig 4. swvs wc againts the equation table 5. q and q calculation 0 10 20 30 40 50 60 70 80 90 100 0,00 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00 w a te rc u t (% ) sw persamaan data kolinear adjust data herawarti, ira et al./ jgeet vol 02 no 01/2017 75 fig 5. plot qo and qo 'in each well based on the calculations performed to estimate the oil flow rate based on function, then from the twenty-one (21) wells studied,it is known the total of oil flow rate is 3633.68 bopd. while from the data is known that oil flow rate total of twenty-one well studied is 3605.55 bopd. from these results, note the difference oil flow rate based on the data of the oil flow rate based function is 28.13 bopd. the percentage error of both oil flow rate is 0.78%. after assessing the watercut from water saturation data and productivity index from permeability data, the thickness of the perforation of each well, then performed the calculations of oil flow rate using both equation for estimating the flow rate of oil in new productive zones. 4. conclussion based on the research are: 1. estimated oil flow rate can be multiplied by the thickness of the perforation permeability parameters (k.hp) to determine the productivity index with r 2 = 0.9964. while water saturation parameters can be used to determine watercut of polynomial functions with r2 = 0.9993 2. the regression coefficient for k.hp known by using linest function in excel is 2.92x10-3, intercept is 1,49 while the sw regression coefficient is 397.83, sw 2 is (-5402.47), sw 3 is 140.53 intercept is (-35). the function equation for estimating productivity index is pi = 2.94 x 10−3khp − 1.22 and polynomial equations to estimate water cut is wc = 397.83sw − 402.47sw2 + 140.53sw3 − 35.90 3. oil flow rateestimation based on the function is 3633.68 bopd while the oil flow rate data is 3605.55 bopd, the difference is 28.13 bopd with a percentage of 0.78% error. while the percentage of the average absolute error for each of the wells 5.47% references ariadji, tutuka. radjes, muhammad tities. 2012. lapangan secara terintegrasi surface dan subsurface dengan menggunakan desain ariadji, tutuka. radjes, m.t., 2012. kuantifikasi ketidakpastian pengembangan lapangan secara terintegrasi surface dan subsurface dengan menggunakan desain eksperimenta. iatmi. jothikumat, e. al., 2004. ap ® statistics. kelkar, 2002. applied geostatistics for reservoir characterization.pdf. morrison, f.a., 2015. obtaining uncertainty measures on parameters of a polynomial 7. stroud k.a and j. dexter, 2003. advancedengineering-mathematics-4th. schmuller, joseph. 2013. statistical analysis with excel third edition. hoboken, new jersey stanley, l.t. 1973. practical statistic for petroleum engineers. petroleum publishing company. tulsa tang, hong. 2007. using production data to mitigate reservoir connectivity uncertainty. lousiana state university. international petroleum technology. 0 50 100 150 200 250 300 350 400 450 500 la ju a li r m in ya k (b o p d ) sumur qo qo' 1. introduction 2. material and methods 1. result and discussion calculation of wc function (watercut) determination of oil flow rate author guideline journal of geoscience, engineering, environment, and technology 1. paper title attention. remember that readers are the potential authors who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequentlyused abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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doi:10.1016/b0-12-369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 171 reviewing the use of geographic information system (gis) to measure sustainable urban transport performance puji adiatna nadi 1, *, abdulkader murad 1 1 king abdulaziz university, department of urban and regional planning, faculty of environmental design, jeddah, saudi arabia. abstract the purpose of this paper is to show how geographical information systems (gis) used to measure the performance of urban transport sustainability. the first, this paper discusses about understanding about transport performance and how to measure it. the second, explore about sustainability in urban transport. the third, defines gis and its possible uses in the sustainable urban transport performance. the relevant gis functions have also been explained. the gis models are explored to assist urban transport planner to measure sustainability in urban transport. keywords: sustainable urban transport, gis, performance 1. introduction the natural environment is a human dwelling to live in the world as inherit the past and will be inherited to the future. the existence of a comfortable habitat necessary to establish events life for the residents. their events characterized by movement in the form of transport as the backbone of community activities. transport as vital role in making human activities, so need attention in supporting the sustainability. trends in rapidly growth of urban population in all countries in the near future. therefore, the attention in sustainability development becomes important. the increase of urban population is directly proportional to the increase in needs of the movement in urban transportation. the performance of urban transport should be measured in effort to prepare future community. several analytical techniques to assess relationship between land use (urban form) and transport i.e. descriptive statistics (exploratory and graphical methods), spatial mapping, spatial statistics, travel preference functions, regression analysis, selection of suitable predictive models based on-time series census data and application of travel models scenarios for land use distribution (black et al., 2002). while, this study will be explore the use of geographical information system (gis) as a tool to analyze the performance of urban transport to be sustainable. trends issues in sustainability and urban transport become most popular in rapidly growth city, especially developing countries which have bigger population in middle-income and vehicles ownership is more in rates. the purpose of this paper to review the use of gis for measuring sustainable urban transport performance. to achieve purpose of the research objective, start with improve the research questions; what are the trends of use of gis for measuring urban transport performance and sustainability in current practices? the issue of sustainable development is affecting a paradigm in urban transport in recent time. the urban transport performance is driven towards development reflects sustainability efforts. therefore, this objective study is to describe the use of gis in measuring sustainable urban transport performance studies. 2. methodology 2.1 literature search procedure survey based on international journal studies, include doctoral dissertation, master thesis, books, unpublished working papers and conference proceeding papers. the journals select through electronic search topics on the field. during searched in electronic search, the authors used some key words or terms: gis and urban transport, sustainable urban transport, and sustainable urban transport performance. the first term is utilized to generate all papers that treat the relationship topic between gis approach and urban transport sector, including papers referring to this subject in different methods and techniques used. the second term aims to find all papers related sustainable urban transport studies, this attempt to delimit papers that related * corresponding author : padiatna@stu.kau.edu.sa tel.:+966-54-678-3750 received: may 15, 2017. revised : may 25, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.345 mailto:padiatna@stu.kau.edu.sa 172 nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 in transportation sector. finally, the last term are adopted to generate more specific search result about how to measure the performance of sustainable urban transport. the electronics sources that authors used through explore science direct, springer link, jstor, and scholar google. also the authors examine some references cited in each relevant literature source to obtain additional sources of knowledge. the research covers a period of more than twenty years between 1996 and 2016. next step, authors exclude all papers that are not related to the gis approach and urban transport sector, through identification on the title of journals, abstract and introduction section. as the result, the papers with only specific in gis approach and urban transport performance analysed in this study. 2.2 classification methods in this stage, the authors used literature review and research in the field gis approach and sustainable urban transport. the paper is classified into two major categories: (i) gis application and objectives in transport performance and (ii) gis tools and functions for analysis of transport performances. a. gis application and objectives in urban transport performance the papers is classified as main topic of gis application in urban transport research. as the urban transport knowledge very large, especially how to measure its performance, the authors filtered of the papers in main objects of the studies and what is depend on. each papers also consist of several objective to describe the urban transport performance. b. gis tools and functions for of urban transport performance according this criterion, the papers is classified based on gis tools was used in research to analyse urban transport performance. the gis has many type of tools as instrument to be used in analysis process of the research. the function of gis tools in each research according focus of the object research. each function have unique function depend on creativity of the researchers to measure performances of urban transport. 3. results and discussion in gis has several spatial analysis tools that can be applied to measure performance of sustainable urban transport. these applications vary from accessibility, air pollution (emission), noise pollution, energy consumption, public transport, transportation network, traffic, and transportation infrastructure. one of the important issue is to define the sustainability of transport performance in urban area. gis as tools can great to assist for researcher to measure the level of sustainability in urban transport performance. there are many of gis analysis in transport performance studies in previous research. 3.1 classification by gis application and objectives to measure transport performances a. accessibility one main topic to present the transport performance is about accessibility. this topic described through (paudel et al., 2009) which used arcmap-gis software in his research to identify dairy manure transportation routes that minimized costs relative to environmental and other constraints with using tools analysis: network analysis. similarly, a study by (gutiérrez et al., 2010) used arcgis with network analysis tools in order to calculate and map regional spillovers, economic potential values are computed using network routines. furthermore, (mavoa et al., 2012) used gis through network analysis to measure of accessibility aggregate and accessibility measures. network analysis also used to define the health care locations in order to determine the levels of accessibility (murad, 2005), as versatile tool to integrate land use and transport system components in an accessibility metric (ford et al., 2015), to measure the accessibility to transit network for households and cars (chapleau and morency, 2005), to know how far patients live from their nearest health centers (murad, 2004). buffer analysis also to measure distance from each dairy farm to receiving farmlands (paudel et al., 2009), to measure geography framework 2000), to define the retail center catchment (murad, 2003), to evaluate the accessibility to health care facilities (a. a. murad, 2014) and the dynamic measure of relative accessibility of households to the nearest bus stops (chapleau and morency, 2005). for overlay analysis used to having a gis layer with patient data and facilities catchment area (murad, 2004), to find out health centers with a large number of physicians but without any dentists or with fewer servants (murad, 2011), designated as city accessibility, previous researchers used network analysis, but several studies used buffer analysis and overlay analysis. the use of gis tools in reviewed paper found tools in single form such as just network analysis or mix with buffer analysis, overlay analysis and classifications analysis. b. air pollution (emission) measuring of air pollution as effect traffic network in the whole area serviced to estimate the various pollutant level (brown and affum, 2002) become as a part of sustainable urban transport. this study used network analysis in gis to estimate the main pollutants from road network and environmental consequences. likewise, (paudel et al., 2009) used networks analysis to identify transportation routes that minimized costs relative to environmental constrain. gis also used to applied in geo-code trip origins and destinations to calculate the emission in transportation activity (armstrong and khan, 2004). gis also used to develop the spatial information, urban road nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 173 network and distribution of pollutants in the atmosphere (lin and lin, 2002). dynamic simulation models in gis was developed to describe traffic flows, the emission from traffic and resulting air quality (fedra, 1999);(gualtieri and tartaglia, 1998). with quintile analysis and thematic maps, gis used to model air pollution and ghg emission from vehicles through transport add-on environmental modelling system (traems) (gharineiat and khalfan, 2011). similarly, (alshuwaikhat and aina, 2006) points to gis with network analysis and buffer analysis to assessment an unacceptable level of air pollutant by citizens. emission modeling and evaluation of environmental impacts have analysed using network analysis in gis to estimate and reproduce traffic behavior and calculate pollutant emissions. based on these previous research as commonly the researchers measure air pollution or emission as effect of urban transport activity used network analysis and buffer analysis in gis environment. it used to describe the influence of pollutant of environmental consequences. c. noise pollution heavy traffic road resulting the noise pollutant as challenge for urban transport planners to manage and solve the problems. (li et al., 2002) used fhwa model as integrated system to calculate noise in traffic road then translates it into a syntax that arcviewgis understand in spatial and non-spatial data. whereas, (brown and affum, 2002) used traems model to measure noise pollution with three main methods: embedding in gis tools, implementing the models in gis and interface approach. using siam methods, (antunes and santos, 2001) assess noise impacts of traffic network in gis environment to generate, storage, data management, overlay, classification, aggregation analysis, trend analysis and display of the thematic information. noise pollutant become trends topic in a part of sustainable transportation as rapidly growth of private vehicle ownership in urban citizen. road load not just affected in construction and air pollution, but also in the increasingly of noise as vehicle machine effect. the previous researchers used statistics calculations and gis approach to describe the phenomena thoroughly network analysis, buffer analysis, and classification analysis. d. energy consumption energy consumption in traffic assignment, explored by (arampatzis et al., 2004) with gis utilization for policy definition, traffic simulation and analysis, energy consumption and pollutant emission modelling, and evaluation of environmental impacts and its scenarios. gis tools was implemented according to a three-stage: the database, mathematical models for traffic assignment, the presentation in thematic maps, figures and diagrams. similarly, (gharineiat and khalfan, 2011) used gis as tools to make energy efficiency planning in traffic vehicles. issues efficiency of the use of energy as interesting point in sustainability studies. energy sources become limited, whereas the energy use more excessively. previous researchers used gis to analysis and present energy consumption in traffic road network, calculate the effect with spatial indicators approach. e. public transport one issue about sustainable urban transport is to encourage the u daily life. gis approach also used by transport planners to measure the performance of public transport in studies area to know level of services, accessibility and catchment area from the stations. according (miller and storm, 1996) that gis design have several key features as advantages in public transport studies, such as: accurate illustration of the multi-modal transport network, flexible in updating database, user friendly in interfaces and proficient in implementations. his research used network equilibrium-based travel demand as methods and network analysis in gis application. isochrones methods used by ( t al., 2000) in measuring public transport performance with two approaches, such as accessibility measures and the space-time geography framework through gis tools with network analysis and buffer analysis. catchment area methods (abosuliman et al., 2011) and classification methods (aljoufie, 2016a) are used gis with analysis network to present public transport network. similarly, (abreha, 2007) used network analysis to assess the level of service of the existing public transport system and to identify deficient network elements. also, used buffer analysis to buffer distance from bus route and overlay analysis in network and land-use with classification method. gis applications have some advantages to analyse the public transport studies accordingly with good illustration in transport network, flexibility for updating data, and simple in operations and good in implementation. beside network analysis, the researcher also using catchment area methods, buffer analysis and classification analysis. buffer analysis used to describe the level of accessibility of households to reach the nearest station. f. traffic and road network reference (miller and storm, 1996) used network analysis as a tools in gis to represent the multi-modal transportation network to support network equilibrium-based travel demand models. gis-t become popular in transport studies especially in network analysis because it has several advantages in data modelling, data manipulation, and data analysis that are not achieved by previous gis (chen et al., 2011; thill, 2000) studied to design and implemented a gis-t data model to representation modal urban transportation network. gis-t provides several functions and 174 nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 evaluations to representation of multiple data, identification the shortest-path, coverage of service, route planning, and transportation network analysis ( ). network analysis in gis also used by (zhang et al., 2016) to analyse the model results, the factors shortest distance and study by (aljoufie, 2014) used network analysis in gis to present the simulated pattern of traffic flow and the characteristics of transport system. furthermore, (yigitcanlar et al., 2010) used the sustainable infrastructure, land-use, environment and transport model (silent) as advanced gis and indicator-based urban sustainability indexing model. whereas, the gis system produces a set of indices in five comparative sustainability levels: low, medium-low, medium, medium-high, and high. then, (abreha, 2007) used network analysis to identify deficient network elements. the research work conducted by (al-ali, 2016) state network analysis in gis has could be used in establishing urban cycling routes in preventing traffic accidents, designing the road traffic safety evaluation system, road networks, road accident analysis and real-time monitoring, the analysis of the impact of traffic congestion on road accidents, decision analysis in public resource administration and the analysis of causes and consequences of road traffic crashes. the work by (fedra, 1999) has integrated spatial and gis parameters and indicators and demonstrated the possible capabilities and applicability of gis as tools in assessing performance of the transportation system. whereas (wang, 2005) explored the integrating of gis as spatial analysis simulation models to add a temporal dimension and computer visualization to add more options for presentation, all works to support planning process. gis with overlay analysis used traffic safety by mapping accident location data, performing kernel density analyses and combining the results (machado et al., 2015). the domination of network analysis of gis approach in traffic and road network seen from previous research. although supported by methods variation such as silent but core of the research still using network analysis in gis or gis-t and also classification analysis commonly used in several previous studies. g. transportation infrastructure a study by (dalumpines, 2008) explores the extraction of urban form/land use information in developing indicators to support transport ecological footprint (tef) analysing using remote sensing and gis. the useful of gis in this study to supports handling of spatial data from remotely sensed imagery and integrates it with other images and ancillary data from different sources. gis also used in overlay analysis between neighborhood and connectivity functions to delivered tef-linked indicators and used buffer analysis to proximity index 1 km distance from the public road network. similarly, a study described public transport infrastructure using gis to present eco-efficiency for public transport infrastructure (aljoufie and tiwari, 2016). it is calculated from length of public transport routes in meters divided by geographical area of district in hectares. then, the paper by (lopes et al., 2014) used gis based to spatial regression models to forecast travel demand in correlation with transportation infrastructure supply, also used gis-t software to analyse the changes produced in the models with the inclusion of spatial variables. performances of transportation infrastructure also as main factor which affected the sustainable urban transport. some calculation combined with classification analysis used in this analysis. buffer analysis is correlated with index impact of transport infrastructure. table 1 show the matrix of topic research classification based on gis approach as previous discussion. table 1 the matrix of topic research classification based on gis approach topic objective authors accessibility to identify transportation routes to calculate and map regional spillovers, economic potential values to measure of accessibility aggregate to define nearest location (paudel et al., 2009), (gutierrez et al., 1998), (mavoa et al., 2012), (murad, 2003), (murad, 2004), (murad, 2005), (murad, 2008), (murad, 2011), (a. murad, 2014), (chapleau and morency, 2005), (ford et al., 2015) noise pollution to calculate noise pollution area to model the environmental impacts of different road traffic scenarios. (li et al., 2002), (brown and affum, 2002), (antunes and santos, 2001), (valdes et al., 2016) energy consumption to calculate energy consumption (arampatzis et al., 2004) public transport to representation of the multimodal transportation network to presented data in spatial analysis to presented road network to assess the level of service of the existing public bus transport system to identify deficient network elements. (miller and storm, 1996), (mavoa et al., 2012), (abosuliman et al., 2011), (aljoufie and tiwari, 2016), (li et al., 2002), (valdes et al., 2016) nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 175 topic objective authors traffic and road network to representation of the multimodal transportation network be realistic to model road network multiple data representations, shortest-path identification, service coverage, route planning, and transportation network aided analysis to present the simulated pattern of traffic flow and the characteristics of transport system to assess the level of service of the existing public bus transport system to identify deficient network elements. to analyse the impact of traffic congestion on road accidents to analyzed traffic safety for vulnerable road users by mapping accident location data performing kernel density analyses and combining the results (miller and storm, 1996), (thill, 2000), (chen et al., 2011), (mavoa et al., 2012), (zhang et al., 2016), (aljoufie, 2014), (yigitcanlar and dur, 2010), (abreha, 2007), (al-ali, 2016), (fedra, 1999), (wang, 2005), (machado et al., 2015), (valdes et al., 2016) transport infrastructure as presentation tools to presented result of analysis, with classification analysis supports handling of spatial data from remotely sensed imagery and integrates it with other images and ancillary data from different sources to forecast travel demand in collaboration between gis based and spatial regression models (dalumpines, 2008), (aljoufie and tiwari, 2016) the research topic in sut performance is dominantly by traffic and road network and accessibility. then, the average papers about noise pollution, public transport and transport infrastructure. topic about energy consumption is a few. fig. 1 shows the papers number used gis approach in transport performance studies. fig. 1. number of papers using gis in transport performance 3.2 classification by gis tools and functions to measure transport performances a. geocoding geocoding denotes to the representation of a be indexed spatially. for instance, a valid street address can use reverse geocoding converts x, y coordinates. this function allows the address of a mobile user to be displayed once their phone has been located via gps or cell tower triangulation (shekhar and xiong, 2008). in his research, (murad, 2004) used geocoding in his studies to identify the location health care needs as the data gathered non digitized format. also, used geocoding to create points on a map from a table of addresses. b. network analysis network analysis include the basic functions of a gis. this gis tools used to measure of accessibility aggregate , to define the locations to determine their levels of accessibility (murad, 2005), to calculate the length of each network link from geometry (ford et al., 2015), to estimate the main pollutants from road networks (brown and affum, 2002), traffic model for traffic flows mapping (gualtieri and tartaglia, 1998), traffic simulation and analysis (arampatzis et al., 2004), presenting road network (aljoufie, 2016b);(valdes et al., 2016), to assess the level of service of the existing public bus transport system and to identify deficient network elements (abreha, 2007). c. buffer anaysis the function of buffer in gis denote to finding spatial objects that are within a certain distance of an area (shekhar and xiong, 2008). also, buffer analysis used to representation the space-time geography framework isochrones (lines of equal travel time) are a natural way 2000), to define the object area based on a defined distance from other object (murad, 2003), to evaluate the accessibility of any location according to the factor of distance (a. a. murad, 2014). d. thiessen function as a part of gis analysis, thiessen function used to have polygon feature data where the area inside the polygon is closer to the point than to any other point (murad, 2003) created around the points to form an exhaustive landscape, with those polygons inheriting all of the (shekhar and xiong, 2008). e. straight-line allocation function (sla) this tools to develop techniques for the optimal location of such central facilities such as schools, fire stations and retail stores (shekhar and xiong, 176 nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 2008). also, several functions of straight-line allocation function (sla) i.e. to identify customers/clients served by a service or stores, to identify the closest hospital or health center, to find areas with a shortage of fire hydrants, to locate areas not served by a chain of supermarkets (murad, 2008). f. classification methods objects with similar attribute structure can categorized into classes by this method. for instance, classification method used to identify level of accessibility to health care facilities (a. murad, 2014) and to identify level of accessibility to health care facilities (lopes et al., 2014). table 2 show the matrix of classification gis tools in previous studies as discussed at below. the use of gis tools in reviewed papers is dominantly by network analysis. on regular is using the buffer analysis, overlay analysis and sla. while, paper number just a few in thiessen function, quintile analysis and classification methods as shows in fig. 2. fig. 2. proportion of paper used gis tools to measure urban transport performances table 2 the classification gis use by tools in transport performance studies gis tools function authors geocoding to identify the location of place in the map. to create points on a map from a table of addresses (murad, 2004) network analysis to define the locations to determine their levels of accessibility. to calculate the length of each network link from geometry. to estimate the main pollutants from road networks. traffic model for traffic flows mapping traffic simulation and analysis presenting road network to assess the level of service of the existing public bus transport system to identify deficient network elements (paudel et al., 2009), (gutiérrez et al., 2010), (mavoa et al., 2012), (murad, 2005), (chapleau and morency, 2005), (ford et al., 2015), (miller and storm, 1996), (thill, 2000), (chen et al., 2011), (mavoa et al., 2012), (zhang et al., 2016), (aljoufie, 2016a), (yigitcanlar and dur, 2010), (abreha, 2007), (al-ali, 2016), (fedra, 1999), (wang, 2005), (machado et al., 2015), (brown and affum, 2002), (armstrong and khan, 2004), (gualtieri and tartaglia, 1998), (arampatzis et al., 2004), (brown and affum, 2002), (miller and storm, 1996) buffer analysis the space-time geography framework. isochrones (lines of equal travel time) are a natural way. to define the object area based on a defined distance from other object to evaluate the accessibility of any location according to the factor of distance (mavoa et al., 2012), (murad, 2003), (a. a. murad, 2014), (chapleau and morency, 2005), (abreha, 2007), (antunes and santos, 2001), (alshuwaikhat and aina, 2006), (gualtieri and tartaglia, 1998), (paudel et al., 2009), (chapleau and morency, 2005), (murad, 2008), (murad, 2011) thiessen functions to have polygon feature data where the area inside the polygon is closer to the point than to any other point (murad, 2003) straight-line allocation function (sla) to identify customers/clients served by a service or stores; to identify the closest hospital or health center; to find areas with a shortage of fire hydrants; to locate areas not served by a chain of supermarkets (murad, 2008) overlay analysis to have a gis layer that have patient data and facilities catchment area, to get a layer that have district data such as population size and proximitst health centres. (murad, 2003), (murad, 2004), (murad, 2008) nadi. p.a. and murad, a./ jgeet vol 02 no 02/2017 177 gis tools function authors catchment areas classification methods to identify level of accessibility to health care facilities to present multiple regression model of spatial distribution (a. a. murad, 2014), (lopes et al., 2014) 4. conclusion this paper aims to review of the literature on the use of geographic information system (gis) for measuring sustainable urban transport performance. the paper introduce an approach based on classification scheme technique where research journals in this field are collected, classified and results are interpreted. a comprehensive literature study done through a classification model adoption. the gis application in urban transport performance studies consist of seven classifications: accessibility, air pollution (emission), noise pollution, energy consumption, public transport, traffic and road network. this paper shows the use of gis in sustainable urban transport (sut) performance is dominantly on traffic and road network studies while the usage gis tools is dominantly by network analysis. based on these studies, classification and analysis of the journals, some idea for next research are founded. assessment of urban transport in previous research mostly not involve the sustainability paradigm in measuring its performance and the concern in urban transport sustainability using comprehensive indicators is still rare. therefore, it is interesting that how to know gis as quantitative research could be use measure performance of sustainable urban transport to be more comprehensive with involve its indicators and other aspects such as: data, people, software and hardware. references abosuliman, s.s., kumar, a., alam, f., rasjidin, r., 2011. the conceptul design of monorail system in jeddah city, saudi arabia. abreha, d.a., 2007. analysing public transport performance using efficiency measures and spatial analysis; 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(eds.), 2008. encyclopedia of gis. springer, new york. thill, j.c., 2000. geographic information systems for transportation in perspective. transp. res. part c emerg. technol. 8, 3 12. doi:10.1016/s0968-090x(00)00029-2 valdes, c., monzon, a., benitez, f.g., 2016. sustainable urban transportation strategies: searching for synergies. ksce j. civ. eng. 20, 1066 1075. doi:10.1007/s12205-016-0685-0 wang, x., 2005. integrating gis , simulation models , and visualization in traffic impact analysis 29, 471 496. doi:10.1016/j.compenvurbsys.2004.01.002 yigitcanlar, t., dur, f., 2010. developing a sustainability assessment model: the sustainable infrastructure, land-use, environment and transport model. sustainability 2, 321 340. doi:10.3390/su2010321 yigitcanlar, t., sipe, n., evans, r., pitot, m., yigitcanlar, t., sipe, n., evans, r., pitot, m., 2010. a gis-based land use and public transport accessibility indexing model a gis-based land use and public transport accessibility indexing model. aust. plan. 3682. doi:10.1080/07293682.2007.9982586 zhang, y., brussel, m., bosch, f. van den, grigolon, a., maarseveen, m. van, 2016. a gis based bicycle level of service route model, in: ddss. 1. introduction 2. methodology 2.1 literature search procedure 2.2 classification methods 3. results and discussion 3.1 classification by gis application and objectives to measure transport performances 3.2 classification by gis tools and functions to measure transport performances 4. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 4 no 4 2019 236 nur islami / jgeet vol 4 no 4/2019 research article the weak soil investigation at the slope zone in the hot spring area, rokan hulu, indonesia 1nur islami 1physics pmipa, universitas riau, jl. hr. soebrantas, pekanbaru, 28293, indonesia corresponding author: nurislami@lecturer.unri.ac.id tel.:+6281363888549 received: jul 1, 2019; accepted: aug 28, 2019. doi: 10.25299/jgeet.2019.4.4.4258 abstract the slope failure can occur due to the soil on the slope area is relatively porous and the surface water is easily to move in the soil. the zone of the weak zone of the soil should be detected early to avoid the ground mass movement on the slope area. this study is to investigate the weak zone of the soil on the slope area of the hot spring tourism location using geoelectrical resistivity and soil property analysis methods. the wenner configuration with a total of 40 electrodes has been employed at each four resistivity survey lines. the electrode spacing was adjusted to be 2 – 5 meter in order to get relatively higher resolution of the resistivity data. soil samples were collected at several site to measure the soil characteristics of the study area. the soil analysis results show that the study area consist of gravel, sand, clay, silt and weathered metasediment. the geoelectrical resistivity model shows the relatively low resistivity value of about 30 ohm.m at the slope zone which is indicating that the soil has higher porosity.generally only a few locations with the weak soil zone detected in the slope of the hot spring area, however, it is not potential for the ground mass movement due to the soil is relatively thin. keywords: geoelectrical resistivity, rokan hulu, slope failure, soil 1. introduction in the undulation ground zones, the mass movement are often becoming a disaster that can cause loss of the wealth and threat the safety of the human (federico et al., 2018). landslides are a type of natural disaster that often occurs in indonesia. generally, the movement between plates in the subduction zones causes the ground surface morphology varies from lowland to high mountains (satoru et al., 2015). furthermore, as a country on the equator, indonesia has climatological conditions with high rainfall. high rainfall can soften the soil which can cause dynamic forces resulting in slope instability (shuai et al., 2016). the study of landslide has been conducted using various method in the worldwide.zbigniew (2018) identified the landslide triggers bythe ‘nearly real-time’ observing methods in the carpathian mountains. this area is one of the largest landslide zones in europe.jie et al., 2018, detected and characterized the displacement of the landslides by employing multi temporal satellite, in the dadu river, danba county. the research shown the potential landslides are detected from the several sites. they suggested the guidelines on insar applied in the study area. the successive landslide of dam formation has been analysed using dissimilar triggering mechanisms in tangjiawan landslide, china (xuanmei et al., 2018). the high intensity of earthquakes and greattypical uplifting rate were inferred as the contribution of succeeding damming events.the runout simulations (margherita et al., 2018) was used to investigate the cima salti landslade in italy. in their research, the landslide was predicted travelled transverselymotionless ice throughout the lateglacial period. then, the simulations were used as aninstrument in predicting valley growth and also the natural risks. geoelectrical resistivity method has been used widely to investigate the subsurface condition. the geoelectrical resistivity method was also can be used to detect the thickness of the peat soil and to predict the potential of groundwater resources in the coastal area (islami et al., 2018a). the method was successfully employed to investigate the heavy metal zone in the groundwater system. the zone of heavy metal can be delianiated and mapped using this method (islami et al., 2018b). the geoelectrical resistivity also was success to monitor the nitrate in the the shallow depth at the sandy soil area (islami, 2017). the nitrate movement direction was clearly seen when it observed using the time lapse geoelectrical resistivity monitoring. in this research, the use of geoelectrical resistivity and combined with the soil analysis method were used to investigate the weak soil zone in the hot spring tourism area of rokan hulu, indonesia. the interpretation of geoelectrical resistivity model was improved by the direct resistivity measurement and soil analysis result, so that the weak zone of the soil in the slope area can be detected well. 2. the study area the study area is located in the hot spring tourism location, rokan hulu, indonesia. the study area is mainly surrounded by the thick secondary forest. figure 1 shows the location of study area that was obtained from google earth. in the figure, the thick secondary forest is clearly surrounding the pool of hot spring. the secondary thick forest situation can be seen in the fig. 1 (bottom). http://journal.uir.ac.id/index.php/jgeet nur islami / jgeet vol 4 no 4/2019 237 fig. 1. the google map and the situation in the study area. the study area consists of the sihapas formation. the sihapas formation comprising carbonaceous shale, clean quartz sandstones, conglomerate, and siltstones. the telisa formation also can be found in the study area. it is containing of silty sandstone, calcareous to carbonaceous siltstones, and shale. a very massive intrusion is also found in the study area such consists of a cassiterite-bearing intrusion, granites, and also some granodiorites with zones of cataclasis. the age of intrusions are predicted of around the jurassic zone. the in trusion are bring into being about 2.2 km after the hot spring to the south east path (rock et al., 1983). 3. methodology the combination of three methods have been employed in this research. they were the geoelectrical resistivity survey, direct surface resistivity measurement and soil property analysis methods. 3.1. geoelectrical resistivity survey the geoelectrical resistivity survey was used in this research. four lines of two dimension of geoelectrical resistivity with the wenner configuration was employed for each survey lines. the home-made resistivity equipment was used in the survey. the total data reading for each line is 190 data which the reading was measure until the twelve layer measurement (n=12). the geoelectrical resistivity data then processed using the res2dinv software. in this software the real resistivity data was obtained and calculated based on the model that is built based on the measured data (geotomo, 2007). fig. 2 is the design of the geoelectrical resistivity survey. for the each survey line, the first measurement was conducted for the first layer data (n=1), which is the electrode spacing is equal to a. then, the second layer measurement is the second layer data (n=2). the measurement was continued until the twelve layer (n=12). fig. 2. the design of geoelectrical resistivity measurement. in this figure, total of the electrode is 19 with the n equal to 6 (adapted from geotomo, 2017) 3.2. surface direct resistivity measurement direct resistivity measurement on the surface with small electrode spacing was used for the improvement of the resistivity interpretation. this measurements were done in several sites with certain soil and rock condition. the data from these measurement were used to help in the geoelectrical resistivity model interpretation. 3.3 grain size soil analysis soil samples were obtained from several location in the study area, especially at the location where the direct surface resistivity measurement was done. the soil was taken using hand auger if the target of the soil was at the depth more than 20 cm. the soil sample then dried and measure it grain size distribution and grouped based on gravel, sand, clay and silt. 4. result and discussion 4.1 the morphology of the study area 100.2685 100.269 100.2695 100.27 100.2705 100.271 100.2715 100.272 longitude 0.8285 0.829 0.8295 0.83 0.8305 0.831 0.8315 l a ti tu d e n 100 m 238 nur islami / jgeet vol 4 no 4/2019 fig. 3 shows the contour map of the study area. in the figure, it is clearly seen that the hot spring is situated on the surface of about 82 m above sea level. the hot spring is surrounded by the hill at the south part, the slope is relatively step. fig. 3. the elevation contour of the study area as seen in fig 4, the hot spring is situated at the lower part of the hill. the hill should be assessed in term of the possibility of it weak zone. it is very important as the hot spring is very attracting the domestic tourist. fig. 4. the 3d shape of study area 4.2 geoelectrical resistivity survey the map of the resistivity survey location can be found in the fig. 5. a total number of four resistivity survey was conducted on the slope zone of the hill at the south and north side of the hot spring location. in the map, the line survey is indicated with the line colour yellow. the survey was conducted at the thick secondary forest with relatively step of the slope gradient. fig. 5. the geoelectrical resistivity survey location in the. the result of geoelectrical resistivity survey model is given in the fig 6. fig. 6, the resistivity value for all resistivity line survey has the range of about 60 ohm.m until more than 3000 ohm.m. this is indicating the subsurface consists of a wide range of resistivity value. the resistive material such as methasediment can be predicted occur at the subsurface such as in res line 2, res line 3. the dark colour of brown-red is indicating the resistive material. however, on the surface at the several zone, the higher resistivity is also appeared. these value, besides the hard rock material, it is also possible due to the occurrence of the dried soil. in the line 4, it can be seen that relatively low resistivity value can be observed at the surface, while the higher resistivity value of more than 3000 ohm.m can be found at the depth of 4 meter below the surface. this value may indicate that the hard rock is available at the depth 4.3. direct resistivity measurement table 1 is the direct resistivity data measurement that was obtained from the selected surface at the study area. the measurement was done with 5 cm electrode spacing to make sure that the soil is homogeneous. consequently the amount gotten is the real resistivity value with assumption that inside a range of 5 cm, the measured material is similar (telford et al., 1990). table 1 displays that comparative dry soil has an average resistivity of 562.1ohm.m. the medium when saturated by water, the soil resistivity declinesvividly to 83.7ohm.m. the fresh methasediment has resistivity valueof 3286.1 ohm.m on average. whereas it is in wet condition, the resistivity become 1632.6ohm.m. based on these data, the zone with the relatively higher water content will be ranging from 28.7-168.3 ohm.m. 100.2685 100.269 100.2695 100.27 100.2705 100.271 100.2715 100.272 longitude 0.8285 0.829 0.8295 0.83 0.8305 0.831 0.8315 l a ti tu d e n 100 m 70 75 80 85 90 95 100 105 110 115 120 elevation (m) hot spring hot spring 76 78 80 82 84 86 88 90 92 94 96 98 100 102 104 106 108 110 112 114 elevation (m) 100.2685 100.269 100.2695 100.27 100.2705 100.271 100.2715 100.272 longitude 0.8285 0.829 0.8295 0.83 0.8305 0.831 0.8315 l a ti tu d e n 100 m line 1 line 3 line 4 line 2 nur islami / jgeet vol 4 no 4/2019 239 fig. 6. geoelectrical resistivity model of line 1, line 2, line 3 and line 4 table 1. direct resistivity measurement for small electrode spacing material number of samples range of resistivity (ohm.m) average resistivity (ohm.m) dried soil (relatively) 8 310.8-896.6 562.1 water-filled soil 8 28.7-168.3 83.7 fresh methasediment 8 2621.5-4328.5 3286.1 wet methasediment 8 1376.2-3842.3 1632.6 4.4 soil grain size distribution table 1 shows the grain size distribution of the soil sample in the study area. the soil sample was taken at the interested zone. the interested zone was defined from the result of resistivity survey. the soil sample was taken mainly in the low resistivity value in the geoelectrical resistivity survey. based on the data given in the table 1, there is no specific trend can be recorded. however, in the low resistivity zone, the sand content is relatively higher if compare to the another location. the resistivity survey was conducted where the rainfall occur at the night before the survey. so that why the resistivity value at the higher sand content resulting the relatively low resistivity value. 240 nur islami / jgeet vol 4 no 4/2019 table 2. grain size soil distribution obtained from the surface and depth of less than 1 m sample id latitude longitude depth (cm) gravel (%) sand (%) clay and silt (%) soil 01 0.8291051 100.26992 0 0 26.2 73.8 soil – 02 0.8296326 100.26996 15 0 23.1 76.9 soil – 03 0.8306599 100.27042 40 1.2 32.1 66.7 soil – 04 0.8297298 100.27044 60 2.5 31.4 66.1 soil – 05 0.8294105 100.27077 15 2.1 30.9 67.0 soil – 06 0.8296326 100.27146 80 4.2 32.1 63.7 soil – 07 0.8298407 100.27123 40 4.1 32.2 63.7 4.5 the weak soil zone on the slope area based on the geoelectrical resistivity data in fig. 6, and supported by direct surface resistivity measurement in table 1, and grain size distribution in table 2, the weak soil zones can be detected in the zone of low resistivity value as indicated in the fig 6. the low resistivity value in the fig 6 due to the occurrence of the water in the pore of the soil. however, the higher resistivity value in the fig. 6 is due to the hard rock. in the res line 1, the weak zone can be found below the 32 m mark in the depth of 82 meter. however, this weak zone cannot cause the possibility of the ground movement. it is due to the zone is not available at the slope furthermore the zone elevation is lower than the lowest surface there. when the rainfall occur in the area, the weak zone detected in the resistivity data will save the water. as the result, the weight of the ground mass will increase drastically due to the present of water in the pore. in wet climates, such as in the study area, the climate factor that affects landslides is rain. the amount of rainfall, intensity and distribution of rain determine the strength of the dispersion (shuai et al., 2016; loredana, et al., 2017; ) in the res line 2, the resistivity shows that there is no possibility of the weak soil zone, infat the relatively higher resistivity value can be found at the depth below than 75 m above mean sea level. in the res lone 3, relatively low resistivity value of about 300 ohm.m is the possibility of weak soil zone. however the thickness of the soil is just less than 2 meter. that means, the possibility of weak zone is also can not be found here. in the geoelectrical resistivity survey of line 3, the resistivity model shows a relatively lower resistivity value at the surface until the depth of less than 2 meter from the surafce. below that, the resistiity value is relatively higher that is indicating the hard rock material. generally in this resistivity line 3 model, the slope is relative stabil and there is no indication of the weak soil zone. in the resistivity survey of line 4, almost of all zones are the low resistivity at the surafce and until 2 meter depth. the soil grain size distribution data shows that the low resistivity value consits clay and silt. however, at this zone, the sand is highest value if compare than the other lower resistivity value in all the soil sample. however, based on the height of the slope, the slope is quite gentel, so that the possibility of the weak zone can cause the landslide is almost impossible. 5. conclusion the investigation of theweak soil zone has been successfully done in the slope area of the hot spring tourism location, rokan hulu, indonesia. the geoelectrical resistivity models show that there are some zones with relatively low resistivity value. the low resistivity value is indicating that the soil has the relatively porous so that it is possible to accommodate water. the weak zone has been found in all the geoelectrical resistivity models. however, the thickness of the weak soil zone is relatively thin taht are laying on the hard rock material. thus, these weak soil zone are predicted can not cause any ground movement in the future. acknowledgment this research is part of the geothermal investigation research funding under drpm decentralization of institute of research and community services universitas riau. thank you to all the crew members that have helped in the data acquisition. references federico, d.t., teresa, n., andrea, c., lorenzo, s., 2018. tracking morphological changes and slope instability using spaceborne and ground-based sar data. geomorphology, 300, 95-112. doi: 10.1016/j.geomorph.2017.10.023 geotomo, 2007, rapid 2-d resistivity & ip inversion using the least-squares method. geotomo software res2dinv ver. 3.56. malaysia. www.geoelectrical.com islami, n., irianti m., nor m., 2018a. geophysical survey for groundwater potential investigation in peat land area, riau, indonesia. iop conference series: earth and environmental science. 144 (1), 012001. doi: 10.1088/1755-1315/144/1/012001 islami, n., taib, s.h., yusoff, i., ghani, a.a., 2018b. integrated geoelectrical resistivity and hydrogeochemical methods for delineating and mapping heavy metal zone in aquifer system. environmental earth sciences, 77 (10), 383. doi: 10.1007/s12665-018-7574-4 jie, d., mingsheng, l., qiang, x., lu, z., minggao, t., jianya, g., 2018. detection and displacement characterization of landslides using multi-temporal satellite sar interferometry: a case study of danba county in the dadu river basin. engineering geology, 240, 95109. doi: 10.1016/j.enggeo.2018.04.015 loredana, a., roberto, c., francesco, d.p., francesco, m., 2017. geo-hydrological risk perception: a case study in calabria (southern italy), international journal of disaster risk reduction, 25, 301-311. doi: 10.1016/j.ijdrr.2017.09.022 margherita, c.s., andrea, w., vincenzo, p., lisa, b., anne, m., monica, g., 2018. forensic investigations of the cimasalti landslide, northern italy, using runout simulations. geomorphology, 318, 172-186. doi: 10.1016/j.geomorph.2018.04.013. rock, n.m.s., aldis, d.t., aspden, j.a., clarke, m.c.g., djunuddin, kartawa, w., miswar, thompson, s.j., whandoyo, r., 1983. geologic map of the lubuksikaping quadrangle, sumatra. geological research and development center, indonesia. satoru, k., hidehisa, n., sei-ichi, y., naoya, i., tomoyuki, o., 2015. large deep-seated landslides controlled by geologic structures: prehistoric and modern examples in a jurassic subduction–accretion complex on the kii nur islami / jgeet vol 4 no 4/2019 241 peninsula, central japan. engineering geology, 186, 44-56. doi: 10.1016/j.enggeo.2014.10.018 shuai, z., qiang, x., zeming, h., 2016. effects of rainwater softening on red mudstone of deep-seated landslide, southwest china. engineering geology, 204, 1-13. doi: 10.1016/j.enggeo.2016.01.013 telford, w.m., geldart, l.p., sheriff, r.e., 1990. applied geophysics, 2nd edition, cambridge university. xuanmei, f., weiwei, z., xiujun, d., ceesvan, w., qiang, x., lanxin, d., qin, y., runqiu, h., hans-balder, h., 2018. analyzing successive landslide dam formation by different triggering mechanisms: the case of the tangjiawan landslide, sichuan, china. engineering geology, 243, 128-144. zbigniew, b., 2018. identification of flysch landslide triggers using conventional and ‘nearly real-time’ monitoring methods – an example from the carpathian mountains, poland. engineering geology, 244, 41-56. doi: 10.1016/j.enggeo.2018.07.012. © 2016 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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accepted: jun 8, 2021. doi: 10.25299/jgeet.2021.6.2.4127 abstract mount iyang-argopuro is one of the geothermal working areas in the east java. mount iyang-argopuro has the potential of 185 mwe of reserves and 110 mwe of resources. it is estimated to have a liquid dominated reservoir with temperature up to 250-275 oc. an early 3d natural state numerical model of mount iyang-argopuro field is created using tough2 simulator in order to identify the undisturbed condition of reservoir and resource assessment. since mount iyang-argopuro geothermal area is still in the exploration stage, the model created based on based on geological, geophysical, and geochemical data. the model has an area 14 km x 8.2 km and 9180 m in thickness. the model consists of 7410 of rectangular cell blocks with the roughest cell size is 1000 m x 1000 m and the finest is 200 m x 500 m. the model is verified by matching the model temperature and pressure profiles to the calculated geothermometer temperature and pressure, which shows good match enough. keywords: mount iyang-argopuro; natural state; reservoir simulation; tough2 1. introduction mount iyang-argopuro geothermal system of is one of indonesia’s geothermal prospect area which located in bondowoso region, jember region, probolinggo region, and situbondo region, east java province. fig 1. mt. iyang-argopuro geothermal area location map mount iyang argopuro is currently in exploration stage based on sk wkp no 2067 k/30/mem/2012 since 2012 by ministry of energy and mineral resources (memr). the prospect area is 106.500 ha and estimated to have water-dominated reservoir (memr, 2017) since no model of reservoir mount iyang-argopuro are developed, this study aims to create a numerical model of mount iyang-argopuro which represent the undisturbed condition or natural state condition of subsurface reservoir structure, heat and fluid flow inside the system, by integrating early obtained or exploration data. numerical model is usually built using geoscience, well, and reservoir data (di pippo, 2012). however, in this study, the geoscience surveys are used as the main database to determine surface and subsurface conditions of the area since no deep hole has been drilled yet. the reservoir model has been created using petrasim tough2 simulator. natural state condition is reached by matching the pressure and temperature parameter of simulation model to actual based on normal hydrostatic pressure and geochemical geothermometers. the numerical model model can be used for further research. numerical modeling aslo useful for reservoir resources assessment and future production performance prediction (axelsson, 2012). 2. methodology the 3d numerical model is built based on geosciences data and conceptual model of the system. the grid-blocks system is created tough2 simulator (pruess et al., 2012). mount iyang-argopuro geoscience geothermal data is collected, such as conceptual models, geological, geophysical and geochemical data. these data are processed to obtain input simulator data in the tough2 simulator. after model is created and initial condition of the model is assigned. the model is simulated in unlimited time untill it reaches the steady state condition. the minimum time required is 1 million years in order to reach natural state condition (vereina, 2005). the model validation is done by matching the pressure and temperature profile from simulation results to calculated geothermometer and pressure gradient. if it does not shows a good match enough, an iterative calibration of input parameter should be done until it shows a good match. http://journal.uir.ac.id/index.php/jgeet 114 asmorowati et al./ jgeet vol 6 no 2/2021 start creating a resevoir model conceptual model, geosciences and reservoir data natural state simulation natural state matching iterative calibration and refinement of the input parameter natural stated model no match stop figure 2. research flowchart 3. geoscience data 3.1 regional geology and geological structure mount argopuro is located at iyang mountains but actually, it is in bigger mountains, kendeng mountains. it is streched from west to east of eastern java. this mountain range is biting with other mountains such as: mount semeru, lawu, bromo and mount raung (purwanto et al., 2017) the mount iyang argopuro geothermal area consists of nature reserve (0.02%), wildlife reserves (12%), protected forests (around 38.5%) , permanent production forests (18.4%), and other use areas (31%) (memr, 2017). the argopuro iyang region consists of volcanic rocks obtained by quaternary activity results of old mount iyang-argopuro and young mount iyang-argopuro. the evolution of volcanic activity shifts relative to the west, starting from old mount iyang argopuro (mount gilap and mount jembangan) to young mount iyang-argopuro (mount argopuro, mount semen and mount pandu) (memr, 2017). the geological structure of the iyang-argopuro area consists of normal faults shear directed towards ne-sw, nw-se and n-s. which controlling the appearance of the manifestation, such as solfatara in the crater of cikasur, cisentor, and rengganis. hot-warm springs in cisentor, tiris and rabunan (memr, 2017). according to nainggolan et al. (2015), old argopuro deposition grouped into seven rock units, those are lava and pyroclastic unit mount gilap (qlpg), lava and pyroclastic unit cemorokandang (qlpck), lava and pyroclastic unit mount gendeng (qlpgd), lava and pyroclastic unit mount patrol (qlpp), lava and pyroclastic unit mount malang (qlpm), lava and pyroclastic unit mount siluman (qlps) and lava and pyroclastic unit mount berhala (qlpb). this arrangement is sorted from old to young, with lava and pyrocatstic unit mount gilap (qlpg) is the oldest one, while the lava and pyroclastic unit mount berhala (qlpb) is the youngest. these unit are composed by basaltic andesite lava and the volcanic breccia. basaltic andesite are dominant in all rocks unit than the volcanic breccia, except at lava and pyroclastic unit mount malang (qlpm) young argopuro deposition grouped into three rock units, those are lava pyroclastic unit taman hidup (qlpth), lava and pyroclastic unit jambangan (qlpj) and lava and pyroclastic unit argopuro-dominant rengganis (qlpar). all three of these units can be equal with post caldera iyang / argopuro group. figure 3. mount iyang-argopuro geological map (nainggolan et al., 2015) argopuro volcanic rocks consist of andesites basaltic, porphyry basalt, trachy basalt, and sometimes attractive altered breccia breccias, and micro-microbials suspected of breaking through volcanic rocks from mount argopuro products (indarto, fauzi, gaffar, abdullah, & utara, 2011) 3.2 geophysical data a. gravity according nainggolan et al. (2015) gravity anomaly colored in red indicating a volcanic neck of mount iyang asmorowati et al./ jgeet vol 6 no 2/2021 115 argopuro which estimated to be the heat source of the system. fig 4. gravity anomaly of mount iyang-argopuro (nainggolan et al., 2015) low anomaly in peak of mount iyang argupuro indicating that crater area is a prospect area. this statement is supported by the appearance of surface manifestations and alteration in the location. b. magnetotelluric (mt) according to (singarimbun et al., 2017) the system structure of mount iyang-argopuro geothermal prospect is identified by four components by different range of resistivity distribution. mineral alteration is identified by the resistivity of less than 8 ohm-m at depth of 2000 m. the lateral resistivity value distinction indicating fault structure. the resistivity distribution value over than 8 ohm-m is identified as reservoir rocks which located at depth of 2000 m – 5000 m. meanwhile, the resistivity distribution of over than 1024 ohm-m is identified as the heat source is located at 8000 m depth. the mt data from mount iyang-argopuro is shown in figure 5 below fig 5. the mt line and inversion results of mount iyang-argopuro (singarimbun et al., 2017) c. geochemical data geothermal manifestations of mount iyang-argopuro are hot spring in the rabunan area, hydrothermal alteration, and fumarole. based on the results of geochemical analysis by indarto, et al., (2011) sio2 (106.50 108.17) mg / l, hco3 (464.80 484.05) mg / l, cl (19.5024.94) mg / l, so hot water is interpreted as a type of bicarbonate. therefore the 116 asmorowati et al./ jgeet vol 6 no 2/2021 hot spring of this area is estimated to be an outflow zone due to the type of water indicated. the alteration minerals indicate that in the rabunan geothermal system at that time there is a change in temperature (indarto et al., 2011) fumarole appears in the peak of mount iyangargopuro. the gas geotthermometer analysis (carhar) indicated that the reservoir temperature is approximately 275 oc. the fomarole are identified to be upflow zone of the system. the gas component ratio (h2/ar, h2s/ar, co2/h2, h2s/h2) are indicating the reservoir temperature is 250 oc – 275 oc. fig 6. gas geothermometer (car-har) (memr, 2017) 4. conceptual model the basis for constructing the conceptual model is the analysis of geological, geochemical, and geophysical information, temperature and pressure data, information about reservoir properties and information about the chemical content of reservoir fluids (axxelson, g., 2013) the conceptual model of mount iyang-argopuro is shown in figure 7. fig 7. conceptual model of mt. iyang-argopuro geothermal system, east java province (memr, 2017) upflow zone located in peak of mount iyangargopuro which is indicated by the appearance of solfatar and mineral alteration. the hot rock of the system also identified underneath mount iyang-argopuro. the system is bounded by sumbermalang fault in the east, cemara lima in north. 5. model description 5.1 reservoir boundary this model is created using a 12 x 6.2 km reservoir area and addition of 1 km boundary in every side of model. the east and west reservoir boundaries use the consideration of magnetotelluric data (mt) cross-section ac (a from west to c from the east), the northern boundary of the reservoir area using consideration of the location of the manifestation of the hot spring shown in the figure 8. while the southern boundary is the limitation of this research problem. this southern boundary does not have any data yet, that can be used as consideration for determining the side boundary of the 3d model, so the assumption uses gravity data from the top view (in figure 2a). fig 8. reservoir boundary determination based on mt, gravity, and manifestation data (modified from gaffar et al., 2012; indarto et al., 2011; nainggolan et al., 2015) 5.2 reservoir thickness reservoir thickness is identified from the mt survey, the vertical area has medium resistance about 30 ωm – 1000 ωm. it is interpreted as a reservoir with 1000 m 3000 m depth. (ghaffar, indarto, & sudrajat, 2012) 5.3 grid system asmorowati et al./ jgeet vol 6 no 2/2021 117 the 3d numerical model has of 14000 m in x-axis, 8200 m in y-axis, and 9180 m to z-axis. the model consists of 7410 of rectangular cell blocks with the roughest cell size is 1000 m x 1000 m and the finest is 200 m x 500 m. this model has 19 layers with different layer thickness depending on the region. several regions such as reservoir need to be fine in order to obtain accurate calibration. generally, the model has thickness of 500 m in each layer, except at first layer (200 m) and the second layer (480 m). table 1. layer thickness of the model layer thickness (m) atm 200 m layer 2 480 m layer 3-19 500 m the grid-blocks scheme of mount iyang-argopuro numerical model are shown in figure 9 below. fig 9. 3d grid blocks gor numerical model of mt. iyangargopuro field 5.4 rock properties assign rock properties in each zone is the next step after creating a grid system. the rock properties consist of density, porosity, permeability (x,y,z direction), thermal conductivity and specific heat. the most important parameter in a natural state is permeability which can control the fluid flow in geothermal system. 5.5 top boundary the top boundary is made into an atmospheric condition. it is assigned at the top surface with 1 bar for pressure and 25 oc for temperature. the top boundary is assigned to have a huge volume factor to ensure the atmosphere does not affected by reservoir condition (firdaus, sutopo, & pratama, 2016). 5.6 side boundary all side boundary is set to be a no-flow boundary which means the boundary has a very low permeability. the model is designed to make sure that no flow of mass or heat from and into the system from the lateral side. 5.7 bottom boundary the bottom boundary is the heat source. it is set for 350 oc of temperature and 7.2e07 of pressure. the heat source volume factor is set at 1.0e36 to ensure the pressure and temperature of heat source have a proper influence in the system. 5.8 initial condition to accelerate the modeling process, we have to create an initial condition to assign pressure and temperature value each grid blocks. in this model, we will use linear pressure and temperature gradients. for temperature, thermal gradient of 3oc/100m is used in this this model. and for pressure, hydrostatic gradient of 0.0979 bar/m. both gradients applies to every depth from the surface. table 2. material properties layer permeability (m3) horizontal vertical atm 1.0e-13 1.0e-13 capr 1.0e-18 1.0e-18 res 1 8,0e-15 4,0e-15 res 2 1,0e-14 5,0e-15 altr 1,0e-14 5,0e-15 hs 3,0e-15 1.0e-15 bond 1.0e-18 1.0e-18 the material is assigned to the model based on the distribution of rock properties derived from mt survey. the distribution of material in the model is shown in the figure 10. the top material is atmosphere to represent the earth surface condition. the atmosphere is assigned in top layer to layer 6. followed by thick clay cap rock layer which is lies varies from layer 2 to layer 13. beneath the cap rock, lies the main reservoir which has average thickness of 1000 m. then followed by hot rocks which in this model is stated as reservoir 3 or altr. the heat source is assigned to 9 blocks at the bottom of model at depth of 8000 m. fig 10. distribution of rock types in layers 6. result and discussion natural state condition is the initial condition of unexploited geothermal system and before any production. natural state validation in this model done by temperature matching between the model temperature and geothermometer estimation. since no deep hole well drilled yet. a synthetic well is made in the model in order to measure the model temperature and pressure. the sintetic well located at model coordinate x,y (9250,4450). this well has a depth of 4500 m from the surface to the reservoir zone. hot mass is injected through 9 blocks of heat source with the total mass flow of 5 kg/s. then the model is simulated. after the simulation, the recorded temperature and pressure is subject to later matching with the calculation of geothermometer and pressure gradient. mount iyangargopuro numerical model reaches the natural state and steady-state condition after 2,23 billion years of simulation. 118 asmorowati et al./ jgeet vol 6 no 2/2021 fig 11. temperature and pressure result from the figure 11, the identical trendline is shown beetwen model and actual for both temperature and pressure. the temperature recorded in the reservoir is 260270 oc, which shows a good match enough between model and the geothermometer calculation which is around 275 oc. the heat transfer from the top of reservoir, along the cap rock, to the surface is identified as a conduction heat flow as the temperature gradient is relatively slant. while convective heat flow is identified in the reservoir from the vertical temperature gradient of fluid. besides matching the temperature and pressure, it is important to identify the mass and heat flow from heat source to the entire system. based on simulation results in figure 12 and figure 13, the hot mass from the bottom of mt. argopuro is flowing upward, toward the peak of mt. argopuro. this phenomenon is identified as upflow zone which is correspond to the existence of surface manifestation in the form of fumarole at rengganis peak. fig 12. model heat flow compared to conceptual model fig 13. model heat flow in horizontal cross section the hot mass then filling the reservoir zone through the system faults (ne-sw) towards west following the clay cap distribution. a portion of mass also flows towards north and south which is indicated by the emergence as hot water manifestation in rabunan and cisentor. these phenomena are the outflows of the system such as in figure 12 and 13. the cold water, which is identified as recharge water is flowing throgh western part of the system and then flows downward through the geothermal fault system and eastward into the system heat source and reservoir. this phenomenon is match to the prediction of recharge zone in the conceptual model of the system. 7. conclusions the 3d natural state numerical model model of liquiddominated reservoir of mount geothermal area has been developed based on geosciences data since limited petrophysical data available. asmorowati et al./ jgeet vol 6 no 2/2021 119 the model is validated by matching the model temperature and pressure to the calculation of geothermometer and pressure gradient after being simulated for 2.23 billion years. the reservoir temperature reaches 260-270 oc and shows a good match to the gaothermometer calculation. the mass and heat flows in the model are similar to the conceptual model where the hot mass is flow upward into peak of mt argopuro and filling the reservoir into west direction. acknowledgement the authors would like to thank the directorate general of renewable energy and energy conservation (dg ebtke) and the ministry of energy and mineral resources (memr) for supporting this research, providing mt. iyang argopuro exploration data which is consent for publication. references axelsson, g. 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(2005). numerical modelling of the natural state of the mutnovsky geothermal reservoir (kamchatka, russia). proceedings world geothermal congress 2005, (april), 1–8. https://doi.org/10.1134/s002449020706003x © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at which the author did the work must be retained as the main, affiliation address.start by adding an asterisk (*) and then email, phone number, font gulliver 7pt. 3. abstract summary of the all research (aim, scope, result and conclusion) with maximum 300 words, justified, 8 point, and line spacing : single. for keywords wrote in italic and then separated using symbol (,) with maximum are 6 words. 4. introduction in introduction, authors should state the objectives of the work at the end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type area. the structure of manuscripts should follow the following order; 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(do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 224 aditya a. / jgeet vol 02 no 03/2017 mataloko geothermal power plant development strategy in order to maintain the sustainability of supply and demand electric energy in kupang, east nusa tenggara (a system dynamics framework) addin aditya 1 * 1 department of information system, sekolah tinggi informatika dan komputer indonesia, jl. raya tidar no. 100 malang 65149, indonesia * corresponding author : addin@stiki.ac.id tel.:+6282335137337 received: july 28, 2017. revised : aug 4, 2017, accepted: aug 5, 2017, published: 1 sept 2017 doi : 10.24273/jgeet.2017.2.3.488 abstract region. in 2015, the electrification ratio in kupang is 58.67%. this figure is far below from indonesia electrification ratio, which is 88.3%. at present, people of kupang get their electricity supply from fuel energy power system, which is costly and has a bad impact for environment. furthermore, indonesia has many renewable resource that has not been fully utilized and this condition in line with acceleration program of electricity infrastructure development in indonesia, considering that kupang has a geothermal potential in mataloko. this research aims to develop a dynamical model of mataloko geothermal power plant 1 x 2.5 mw development strategy in kupang, east nusa tenggara from technical and economical aspect. we used system dynamics to modelling the existing electricity condition in kupang as a base model to develop scenarios. we hope this scenario can be taken as consideration to develop a renewable resource power plant in order to fulfill the electricity demand. the result shows that geothermal potential in mataloko is feasible to generate an electricity. keywords: geothermal power system, renewable resource, electrification ratio, supply and demand, system dynamics 1. introduction electricity energy has become a primary needs for all people in indonesia. in line with the rapid growth of economics, industrial and information technology, then electricity demand will raise (rahawuryan, et al., 2015). nowadays, indonesia has unequal electrification ratio caused of production of electricity was not enough to fulfill the demand. east nusa tenggara is an archipelago province with 1.192 number of islands, 432 islands with name and 44 inhabitants island. big islands in ntt usually called flobarmorata (flores, sumba, timor, alor and lembata). the area of ntt is 47.931,54 km 2 . administrative area of ntt divided to 21 regency and 1 city. the largest area is sumba timur regency with 7.005 km 2 (14.61%) and kupang regency with 5,525.83 km 2 (11.53%). the smallest area in ntt is kupang city with 180.27 km 2 (0.38%) and sabu raijua regency with 460.47 km 2 (0.96%). astronomically, ntt province is located between 8 0 120 0 south latitude and between 118 0 125 0 east latitude. in terms of geographic position, ntt province has boundaries as follows: north flores sea, south indian ocean, west nusa tenggara barat, east-timor leste (bps_ntt, 2016). at present, the electrification ratio of east nusa tenggara is 58.67%. this figure is still far below the indonesia electrification ratio, which is 88.3%. has an acceleration program of 35,000 mw electricity development and kupang has a renewable resource that in line with it. we hope with the existence of this geothermal energy, can fulfill the electricity demand of kupang and also increase the electrification ratio in it. 2. basic theory 2.1 geothermal energy geothermal energy is energy contained within the high temperature mass of the earth crust, mantle and core (toth & bobok, 2017). since the earth interior is much hotter than its surface, energy flows continuously from the deep, hot interior up to the surface. this is the so-called terrestrial heatflow. with depth in accordance with fo heat conduction. thus the energy content of a unit of mass also increases with depth. nowadays, geothermal energy production is mainly achieved from hot water steam production via boreholes. another rapidly growing production aditya a. / jgeet vol 02 no 03/2017 225 technology involves exploiting the energy content of near-surface regions by using shallow boreholes heat exchangers and heat pumps. it is likely that the natural heat of volcanoes and other geothermal resource were already being used in the remote of paleolithic era, but concentrate evidence only 8000 to 10000 years ago. we are therefore forced to use earliest relationship with geothermal phenomena the geothermal field is a geographical notion such surface manifestation as geysers, fumaroles or boiling mud-ponds indicate an active geothermal domain underground. these phenomena are characteristic of active volcanic regions. where geothermal fields exist but have no spectacular surface manifestation, high terrestrial heat-flow and above-average geothermal gradient show that geothermal energy production would still possible (boldizàr, 1943). fig 1. struc (toth & bobok, 2017) 2.3 geothermal power plants principally, the work of geothermal power system is same as steam power plant, only steam power plant using boiler to make a steam while steam for geothermal power plant was from geothermal reservoir (hanindhito, et al., 2011). geothermal power plant development method were divided in three ways: 1. dry steam power plant this is the first method to develop geothermal power plant. steam from geothermal resource run directly by pipes that connected with generator. then hot steam from steam turbine is cooled in condenser unit and after that it injected to the geothermal reservoir. 2. flash steam power plant steam from geothermal resource is separated from water particle in separator unit. hot steam will flow to turbine for spin it. after that, temperature of steam will decreased through direct contacts condenser or heat exchanger type condenser. mainly steam will turn into water and injected to the geothermal reservoir or can be used to another needs. 3. binary steam power plant this method will be implemented if fluid temperature of geothermal is in low level. fluid from geothermal resource ran directly to exchanger unit that will heat up the organic fluid until it produce steam. this steam will be used to spinning the turbine that connected with generator. after it used to spinning the turbine, steam will turns into fluid element and it used to exchanger unit again. fluid from geothermal resource through exchanger unit will be injected to the geothermal reservoir after cooling process. 2.3 model and simulations model is a represent from the real system. it called good model if its behaviors mostly represent the system in the real world with no breaking the basic rules of system thinking. building a model is influencing by person subjectivity or organizations, then we need perfection to do continuously with digging a relevant potential and information (winardi, 1989). there are several advantages using modelling in research with system approach (barlas, 1996), such as: 1. allow us to do many kind of research without limitation of research areas 2. allow us to do experiment to system without breaking the real system 3. could determining the objectivity of maintenance system activity 4. can use to predicting the next behavior and condition system to develop system dynamics model, firstly we understand system with it problems and connecting each other so it will make a loop / causal loop (suryani, 2006) fig. 2. modelling research problem with system dynamics commonly, modelling research with system dynamics using special software. such as vensim, powersim, stella and dynamo. a model can be made 226 first author et al./ jgeet vol xx no xx/20xx with drawing variables and its connection through those software. structure and behavior will be important things that must concern to building system dynamics models. structure is an element that forming a phenomena. relevancy between elements (see fig 3) are depended by: fig 3. variables in system dynamics level define as a condition in system every several times. level is accumulation in a system. equation in rate variable is decision structure that explain how and why a decision made based on information system. auxiliary is formulation from variables to fulfill stock and flow. source is components that has no related with system. to ensure that model represent the real system, validation is necessary (forrester, 1968) two ways to measure model validity: a. mean comparison 𝐸1 = |𝑆−𝐴| 𝐴 (1) where: s = mean of simulation a = mean of data model valid if e1 ≤ 5% b. error variance 𝐸2 = 𝑆𝑠−𝑆𝑎 𝑆𝑎 (2) where: ss = standard deviation of model sa = standard deviation of data model valid if e2 ≤ 30% 3. data and methods 3.1 data all data in this research obtained through survey and interview with pt pln (persero). in addition, books and journals review is necessary to adding some information about geothermal energy. also data number of electricity customer, number of household and geographical condition from statistic center (bps). these data will formed to model so that can be a basic model to determining policy scenarios. several data that accomplish to collect is: 1. data of ntt electricity customer 2. data of ntt peak load 3. electricity demand growth 4. geographical condition of mataloko field 3.2 conceptual model next step is building a conceptual model. in terms of system dynamics, conceptual model often called as causal loop diagram. this diagram represent variables that related each other and it forming a loop diagram (fig 4). fig 4. causal loop diagram 4. result and discussion 4.1 base model firstly, to build base model we need to identify what kind of variables that related to the main system. in this case, electricity demand and rate of demand are main variable that influence the electrification ratio in ntt (fig 5). fig 5. base model of electricity demand fig 6. simulation result of ntt electricity demand aditya a. / jgeet vol 02 no 03/2017 227 4.2 validation validation to base model is necessary with using mean comparison and error variance. the result shows that base model is already represent the real system (table 1). table 1 validation of base model variable valid e1 ≤ 5% valid e2 ≤ 30% ntt electricity demand 1 % 7% 4.3 model scenario there are two ways to build a model scenario, parameter scenario and structure scenario. in this case will use structure scenario, which is adding some model scenario. such as capacity planning sub model, fulfillment ratio sub model, power plant utilization and economical aspect sub model. 4.3.1 power plant capacity planning there are several factors that must be concerned to modelling power plant capacity. such as, total of electricity demand in an area and reserve margin. reserve margin is power spare of power plant to peak load and represent by percent (%). based on electricity demand in fig 5 and add reserve margin about 20% (pln, 2016) then sub model of power plant capacity planning can be built. from the result of simulation can be seen that need 86.4 mw fulfill the electricity demand in ntt province. fig 6. ntt power plant capacity planning 4.3.2 technical aspect of geothermal power plant this model built in order to identify what kind of variable that have to be concerned in planning and developing geothermal power plant and estimating how much power that can be produce to fulfill the electricity demand. fig 7. fulfillment ratio of geothermal power plant variables that has to be concerned in order to develop geothermal power plant is geothermal work space, constants, under surface temperature and cut off temperature (tama, 2012). here is the equation model of geothermal potential: q = 0.115858 * a * (tres tcut off) 0 c (3) with: q : geothermal potential (mwe) a : geothermal work space (km 2 ) tres : under surface temperature ( 0 c) tcut off : cut off temperature (120 0 c) fig 8. simulation result of geothermal power plant fulfillment ratio 4.3.3 geothermal power plant utilization utilization is the primary method by which asset performance is measured and business success determined. in power plant development, utilization is necessary to calculating how much the utilization of geothermal energy to meet the electricity demand in a region. this following picture shows a model scenario of power plant utilization. from the simulation result shows that in 2030, the utilization of geothermal power plant is 75%. 228 first author et al./ jgeet vol xx no xx/20xx fig 9. model scenario of power plant utilization fig 10. simulation result of power plant utilization 4.3.4 power plant economical aspect in developing of geothermal power plant is determined by investment cost. such as wells exploration, wells injection, wells production and wells make up (santoso, 1997). and also piping cost, operational and maintenance cost and separator. investment cost of geothermal power plant development is idr 139,039,920,00 detail of geothermal power plant development investment. table 2. cost description of power plant development (pln) no description cost (idr) 1 wells exploration cost 95,889,600,000 2 wells injection cost 19,977,000,000 3 operational and maintenance 23,173,320,000 total 139,039,920,000 based on table 2 and calculation on fig 11 then can be concluded geothermal development payback time is 16 years and income projection per year is idr 731,727,424. fig 11. economical aspect of geothermal power plant development fig 12. simulation result of geothermal power plant payback fig 13. income projection per year of geothermal power plant development 5. conclusions in this research can be concluded that: 1. geothermal power plant development planning is very necessary in order to ensure the sustainability of electricity supply and demand in ntt. furthermore, this research is also support the government program in using renewable resource as a main energy. 2. technical aspect that must to be concerned in developing geothermal power plant are geothermal workspace area, under surface temperature and cut off temperature. 3. payback time of geothermal power plant investment is 16 years after it operation. based on this results are proven that mataloko field is feasible to develop a power plant. aditya a. / jgeet vol 02 no 03/2017 229 references barlas, y., 1996. multiple test for validation os system dynamics type of simulation model. turkey: s.n. boldizàr, t., 1943. aspect of geothermal gradient in mining industry (in hungarian). budapest: bkl 20. bps_ntt, 2016. nusa tenggara timur province in figures. nusa tenggara timur: bps-statistics of nusa tenggara timur. forrester, j. w., 1968. principle of system. massachusettss: wright-allen press inc.. hanindhito, s., mahmudsyah, s. & yuwono, t., 2011. studi pembangunan pltp guci 1 x 55 mw jawa tengah berdasarkan aspek teknis, ekonomi dan lingkungan. pln, 2016. [online] available at: http://www.pln.co.id rahawuryan, f., marsudi, s. & purwati, e., 2015. studi kelayakan perencanaan plta kesamben kabupaten blitar jawa timur, s.l.: s.n. santoso, p., 1997. kajian keekonomian dan kebijakan pengusahaan sumber daya energi panas bumi untuk pembangkitan listrik skala kecil di indonesia. suryani, e., 2006. pemodelan dan simulasi. yogyakarta: graha ilmu. tama, r. g., 2012. studi pengembangan pembangkit listrik tenaga panas bumi (pltp) di jailolo untuk memenuhi kebutuhan listrik di maluku utara. proceeding seminar tugas akhir jurusan teknik elektro fti-its. toth, a. & bobok, e., 2017. flow and heat transfer in geothermal systems. miskolc: elsevier. winardi, 1989. pengantar tentang teori sistem dan analisis sistem. bandung: mandar maju. 1. introduction 2. basic theory 2.1 geothermal energy 2.3 geothermal power plants 2.3 model and simulations 3. data and methods 3.1 data 3.2 conceptual model 4. result and discussion 4.1 base model 4.2 validation 4.3 model scenario 4.3.1 power plant capacity planning 4.3.2 technical aspect of geothermal power plant 4.3.3 geothermal power plant utilization 4.3.4 power plant economical aspect 5. conclusions references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 66 sari. r.a.p et al. / jgeet vol 04 no 02/2019 research article depositional environmental changes of cimanceuri formation based on mollusk fossil assemblages in bayah, banten province rahajeng ayu permana sari 1 *, winantris 2 , lili fauzielly 3 , anita galih ringga jayanti 4 , aswan 5 , unggul prasetyo wibowo 6 1 faculty of geology, universitas padjadjaran , jl. raya bandung sumedang km.21, kabupaten sumedang, west java 45363, indonesia. 2 geological museum, geological agency, jl. diponegoro no. 57, bandung 40122, indonesia. 3 geology department, faculty of earth sciences and technology, institut teknologi bandung, jalan ganesa 10 bandung, indonesia. * corresponding author : r.ayupermanasari@yahoo.com tel.: +6281332075501 received: apr 5, 2019; accepted: jun 19, 2019. doi: 10.25299/jgeet.2019.4.2.2986 abstract bayah is located in lebak regency, banten province. this location is chosen due to its abundant mollusk fossils which exposed along the outcrops. the aim of this research is to determine depositional environmental changes using mollusk fossil assemblages. data obtained from a measured stratigraphic section of cimanceuri formation. it is dominated by very fine-fine sandstones with claystone intercalation. a total thickness of measured stratigraphic section is 4.2 meters. there are at least seventeen mollusk associations (bottom-top) consisting of 1) ringicula arctatoides olivella tomlini were obtained. 2) ringicula arctatoides marginella (cryptospira) ventricosa sangiranensis. 3) olivella tomlini, 4) ringicula arctatoides olivella tomlini, 5) ringicula arctatoides, 6) turritella (turritella) bantamensis scapharca (scapharca) gedinganensis, 7) polinices aurantius marginella (cryptospira) ventricosa sangiranensis, 8) scapharca (scapharca) gedinganensis, 9) scapharca (scapharca) multiformis timoclea bataviana, 10) turritella (turritella) bantamensis tjicumpaiensis ringicula arctatoides, 11) turritella (turritella) bantamensis ringicula arctatoides, 12) turritella (turritella) bantamensis tjicumpaiensis turritella (turritella) bantamensis, 13) turritella (turritella) bantamensis tjicumpaiensis ringicula arctatoides, 14) turritella (turritella) bantamensis architectonica sp., 15) turritella (turritella) bantamensis tjicumpaiensis, 16) turritella (turritella) bantamensis turritella (turritella) bantamensis tjicumpaiensis, and 17) turritella (turritella) bantamensis. the condition with the most stable ecosystem is the association of turritella (turritella) bantamensis tjicumpaiensis turritella (turritella) bantamensis (association 12). at least there are seven depositional environmental changes that occur in this research area with two shallowing deepening cycles : 1) open shallow marine, 2) subtidal open shallow marine, 3) open shallow marine, 4) open shallow marine subtidal, 5) subtidal, 6) subtidal open shallow marine, and 7) open shallow marine. keywords: mollusk, depositional environment, bayah, cimanceuri formation 1. introduction mollusks are one of the phylum with a very abundant number of organisms, so it is potential to be used as an indicator to interpret the depositional environment. in addition, the environmental distribution of mollusks is wide ranging from marine to terrestrial. bayah region has many marine sediment outcrops. bayah region is chosen for studying due to its abundant mollusk fossils which exposed along the outcrops. in this location, foraminifera fossils that commonly used for interpretation of depositional environments is rarely found. based on this condition we propose the mollusk fossils to be used as indicators of depositional environment interpretation. bayah is located in lebak regency, banten province (fig. 1.). the details location have found in cikumpay river with coordinates 106° 14' 18,282" bt; 6° 54' 48,963" ls and 106° 14' 18,084" bt; 6° 54' 49,987" ls coordinates 106° 14' 0,582" bt; 06° 55' 8,776" ls (fig. 2 and 3) the assembly of fossils which was found in the cimanceuri formation is deposited in terrestrialfluvial to littoral. its lithology is very fine to finegrained carbonate sandstones with claystone intercalation and contains of mollusk fossils in several places, at the top of this formation there is a coquina (sujatmiko, et al., 1992). mollusk and foraminifera fossils which found in cimanceuri formation shows early pliocene (koolhoven, 1933 in sujatmiko, et al., 1992). based on neogen stage of java (oostingh, 1938 and shuto, 1975), cimanceuri formation are known belong to the sondean stage with turritella bantamensis tjicumpaiensis and scapharca gedinganensis as its fossil index. these fossil index are come from pliocene / n19-n20. (sufiati, et al., 2014). 2. material and method twenty-two rock samples were obtained from 3 measured stratigraphic sections in cikumpay and cikuya rivers (fig. 3.). systematically rocks sampling http://journal.uir.ac.id/index.php/jgeet sari. r.a.p et al. / jgeet vol 04 no 02/2019 67 are carried out with an interval of ±20 cm at each layer. description and measurement of sediment thickness were carried out in the field. afterwards, the samples then prepared. the preparation process aims to clean up the remaining sediment until the fossils ready to be identified. fig. 1. research area, bayah, lebak regency, banten province (source: google maps). fig. 2. sampling location map bayah, lebak regency, banten province. 68 sari. r.a.p et al. / jgeet vol 04 no 02/2019 fig. 3. the outcrop of cky 3 in research area. a binocular microscope is used to identify microsized mollusks. the references to identification and determination refer to martin (1879,1880), oostingh (1933), leloux (2009), and sufiati (2012), while for the ecological determination of each species refers to abbott (1991), okutani (2000), aswan (2006), and prasetyo et al. (2012). species that have been identified are then used for determine mollusk associations of each layer. the mollusk association zone is used to indicate mollusk fossil assemblages that live in similar habitats associated with certain lithologies. classification of depositional environment refers to fan (2012) (fig. 4.). the name of mollusk fossils association is based on insitu and abundant mollusk fossils, whether one or more species appear (prasetyo et al., 2012). the result of these associations are used for interpretation of depositional environmental changes in cimanceuri formation. the mollusk fossils obtained from bayah are stored at bandung geological museum. shannon-wiener diversity index is used to identified the condition of ecosystem in research area, (bakus, 2007): (1) where : = diversity index s = number of species ʃ = sum pi = 𝑛𝑖 𝑁 𝑛𝑖 = number of individuals of species i n = the total number of individuals of all species low diversity (h'<1) indicates that ecosystem conditions are unstable or disturbed, moderate diversity (1<h'<3) indicates a fairly stable ecosystem, and high diversity (h'>3) indicates a stable ecosystem condition (jurnaliah, 2011). the shannon diversity index is calculated using microsoft excel. 𝐻′ = − 𝑃𝑖 𝑠 𝑖=1 𝑙𝑜𝑔 𝑃𝑖 sari. r.a.p et al. / jgeet vol 04 no 02/2019 69 fig. 4. classification of tidal zone (modified from fan, 2012). fig. 5. determination diagram of mollusk cky 1. fig. 6. diagram determination of mollusk cky 2. 70 sari. r.a.p et al. / jgeet vol 04 no 02/2019 fig. 7. diagram determination of mollusk cky 3. sari. r.a.p et al. / jgeet vol 04 no 02/2019 71 3. result and discussion based on this research, 2373 mollusk fossils were obtained from 22 samples which is taken from cikumpay and cikuya rivers. its consist of 222 species (56 bivalves, 164 gastropods, and 2 scaphopods). the data of dominant mollusk fossil species in cky 1, cky 2, and cky 3 showed by graphic (fig. 5,6, and 7). the dominant mollusk fossils are used to determine depositional environmental. lithology and mollusk fossils association in cky 1 and cky 2 shows similarities so they are interpreted as the same layer. based on the strike / dip measurements, cky 3 is interpreted to be younger than cky 1 and cky 2. total thickness of measured stratigraphic section is 4.2 meters. the lithology is dominated by very fine-fine grained calcareous sandstones with non-calcareous claystone intercalation. at the top, there is a coquina sandstone with abundant mollusk fossils (fig. 8.). the results of determination represents 17 mollusk associations with 10 species variations. from these associations, it can used to analyze the depositional environmental changes from old to young layers which are correlated with local sea level changes. classification of the depositional environmental is divided into 3, namely: intertidal, subtidal, and open shallow marine. at least there are seven depositional environmental changes that occurs in this research area, there are: open shallow marine environments that change slightly to open shallow marine subtidal environment and then back to open shallow marine environment. furthermore, the environment will revert gradually to subtidal, then slowly deeper into open shallow marine environment. the diversity index value of the samples which is taken from this study ranged from 1,095 3,182 (table 1.). the highest diversity index value is at cky3 l5a, while the lowest diversity index value is at cky3 l6. this can be interpreted that the research area is a medium high productivity area and has a fairly stable stable ecosystem. based on the mollusk fossil associations, two shallowing-deepening sea level local cycle was occurred at the cimanceuri formation (fig. 8). start from association 1 (cky1 l1), it is an open shallow marine environment characterized by association of ringicula arctatoides olivella tomlini (fig.9). in association 2 (cky1 l3) there are still abundant ringicula arctatoides but it is also followed by the abundance of marginella (cryptospira) ventricosa sangiranensis (fig.10). these fossils has an intertidalsubtidal environment. it can be interpreted that sea level becomes shallow and returning to open shallow marine environment on the layer above it. its showed by associations olivella tomlini, ringicula arctatoides olivella tomlini, and ringicula arctatoides (association 3,4,5) respectively. in association 6 (cky3 l1b) the environment returns to shallow again. it is showed by an abundance of turritella (turritella) bantamensis scapharca (scapharca) gedinganensis at the same time. furthermore, in associations 7 and 8 (cky3 l1c & l1d) is getting shallowing until subtidal environment, which is characterized by the abundant of polinices aurantius marginella (cryptospira) ventricosa sangiranensis and scapharca (scapharca) gedinganensis associations. the environment has changed back into an open shallow marine slowly which is indicated by the abundant presence of intertidal-subtidal mollusk fossils, scapharca (scapharca) multiformis and the abundance of open shallow marine environment fossils, timoclea bataviana (association 9). hereafter, the sea level was becomes deeper with consecutively association of turritella (turritella) bantamensis tjicumpaiensis ringicula arctatoides, turritella (turritella) bantamensis ringicula arctatoides, turritella (turritella) bantamensis tjicumpaiensis turritella (turritella) bantamensis, turritella (turritella) bantamensis tjicumpaiensis ringicula arctatoides, turritella (turritella) bantamensis architectonica sp., turritella (turritella) bantamensis tjicumpaiensis, turritella (turritella) bantamensis turritella (turritella) bantamensis tjicumpaiensis, and turritella (turritella) bantamensis (association 10-17). table 1. table diversity index in this study location total number of individuals number of species diversity index cky3 l6 22 6 1,095 cky3 l5b 13 8 1,567 cky3 l5a 74 37 3,182 cky3 l4b 43 28 3,144 cky3 l4a 29 17 2,375 cky3 l3f 51 29 2,957 cky3 l3e 45 16 2,282 cky3 l3d 26 16 2,548 cky3 l3c 25 11 1,942 cky3 l3a 50 31 3,07 cky3 l2 65 23 2,613 cky3 l1d 13 8 1,738 cky3 l1c 36 24 2,869 cky3 l1b 44 28 3,036 cky3 l1a 9 6 1,677 cky2 l4 15 12 2,338 cky2 l3 455 61 2,98 cky2 l1 499 57 2,847 cky1 l5 387 45 2,689 cky1 l4 138 38 2,969 cky1 l3 287 45 2,963 cky1 l1 47 19 2,392 total 2373 72 sari. r.a.p et al. / jgeet vol 04 no 02/2019 figure 8. composite stratigraphic coloumn and local sea levelchanges in research area (getting to the right → deeper). sari. r.a.p et al. / jgeet vol 04 no 02/2019 73 fig. 9. the examples of macro-mollusk fossils in this study (gastropods, a: ventral view, b:dorsal view; bivalvia, a:internal view, b:eksternal view, c: dorsal view). 74 sari. r.a.p et al. / jgeet vol 04 no 02/2019 fig. 10. the examples of micro-mollusk fossils in research area (a: ventral view, b:dorsal view in summary, the whole mollusk fossil association assemblages above are interpreted as sea level rise. similar results also stated in several previous research: martodjojo (2003) explained banten in pliocene, remains in the south where the environment is transitional environment (cimanceuri formation). the bogor basin environment in pliocene is divided into two parts. most of the bogor basin environment is terrestrial occupied by volcanic arc but southern mountains region has subsidence and transgression, according to zhong et al (2004) the history of eustatic sea level change since the pliocene began with a rapid rise from 5.33 to 5.1 ma. the sea level at highstand between 5.1 and 3.7 ma, roza et al (2015) reported fluctuations began to occur during the middle pliocene where sea level tended to increase (transgression) and fell back to the late pliocene, and morley et al (2016) stated that major transgression occurred across the sunda shelf at the beginning of the pliocene. 4. conclusion there are seven depositional environmental changes that occur in this study with two shallowing deepening cycles. depositional environmental changes (bottom-top) consist of: 1) open shallow marine, 2) subtidal open shallow marine, 3) open shallow marine, 4) open shallow marine subtidal, 5) subtidal, 6) subtidal open shallow marine, and 7) open shallow marine. this result similar to several previous research that stated in pliocene sea level tended to rise. in this area 17 mollusk fossils associations were obtained, namely 1) ringicula arctatoides olivella tomlini. 2) ringicula arctatoides marginella (cryptospira) ventricosa sangiranensis. 3) olivella tomlini, 4) ringicula arctatoides olivella tomlini, 5) ringicula arctatoides, 6) turritella (turritella) bantamensis scapharca (scapharca) gedinganensis, 7) polinices aurantius marginella (cryptospira) ventricosa sangiranensis, 8) scapharca (scapharca) gedinganensis, 9) scapharca (scapharca) multiformis timoclea bataviana, 10) turritella (turritella) bantamensis tjicumpaiensis ringicula arctatoides, 11) turritella (turritella) bantamensis ringicula arctatoides, 12) turritella (turritella) bantamensis tjicumpaiensis turritella (turritella) bantamensis , 13) turritella (turritella) bantamensis tjicumpaiensis ringicula arctatoides, 14) turritella (turritella) bantamensis architectonica sp., 15) turritella (turritella) bantamensis tjicumpaiensis, 16) turritella (turritella) bantamensis turritella (turritella) bantamensis tjicumpaiensis, and 17) turritella (turritella) bantamensis. the most stable ecosystem condition is the association of turritella (turritella) bantamensis tjicumpaiensis turritella (turritella) bantamensis (association 15/cky l5a) with the value of diversity index is 3,182. acknowledgements we would like to say thanks to geological museum, geological agency, ministry of energy and mineral resources and universitas padjadjaran for the permission to use the facilities during the research project. we also say thanks to desty kistiani, s. pd, agustina, s.t., and staff of documentation and conservation section for the support so this research can be completed properly. references abbott, r.t. & dance, s.p. 1986. compendium of seashells. melbourne: american malacologists inc. aswan, ozawa, t., 2006. milankovitch 41000-year cycles in lithofacies and molluscan content in the tropical middle miocene nyalindung formation, jawa, indonesia. palaeogeogr. palaeoclimatol. palaeoecol. 235, 382 405. https://doi.org/10.1016/j.palaeo.2005.11.004 aswan, sufiati, e., rudyawan a., kistiani d., and thaw zin oo. 2018. depositional environmental evolution of kalibiuk formation based on paleontological molluscan study, cisaat river section, bumiayu, central java, indonesia. iop conf. series: earth and environmental science 162 (2018) 012033. doi:10.1088/1755-1315/162/1/012033 https://doi.org/10.1016/j.palaeo.2005.11.004 sari. r.a.p et al. / jgeet vol 04 no 02/2019 75 bakus, g.j., 2007. quantitative analysis of marine biological communities: field biology and environment. john wiley & sons, inc., hoboken, nj, usa. https://doi.org/10.1002/0470099186. fan, d. 2012. open-coast tidal flats. principles of tidal sedimentology, 187 229. springer science & business media jurnaliah, l. 2011. diversitas foraminifera bentonik kecil di daerah perairan semarang (lembar 1409) jawa tengah (diversity small benthonic foraminifera in semarang sea). bulletin of scientific contribution, vol.9, desember 2011: 121-124 leloux, j. and wesselingh, f. p. 2009. types of cenozoic mollusca from java in the martin collection of naturalis. nnm technical bulletin, 11: 1-765, leiden. martin, k. 1879-1880. die tertia rschicten auf java. nach den entdeckungen von f. junghuhn. paleontologischer theil. geologische-reichsmuseum, leiden. ix+164+51+6. martodjojo, s. 2003. evolusi cekungan bogor jawa barat. penerbit itb bandung. morley, r. j., morley, h. p. and swiecicki, t. 2016. miopliocene palaeogeography, uplands and river systems of the sunda region based on mapping within a framework of vim depositional cycles. proceedings, indonesian petroleum association fortieth annual convention & exhibition. okutani, t., 2000. marine mollusks in japan. tokyo: tokai university press. oostingh, c. h. 1938. mollusken als gidsfossielen voor het neogeen in nederlandsh indie (surabaya: handelingen van het achtste nederlandsch indisch natuur wetenschappelijk congres). prasetyo u., aswan, zaim, y. & rizal, y., 2012, perubahan lingkungan pengendapan pada beberapa daerah di pulau jawa selama plio-plistosen berdasarkan kajian paleontologi moluska. (depositional environmental changes in java during plio-pleistocene based on paleontological mollusk). jurnal teknologi mineral (jtm), xix, 173-180, bandung. roza, s. e. v, abdurrokhim. 2015. penentuan perubahan ketinggian air laut berdasarkan analisis foraminifera bentonik. seminar nasional ke-ii fakultas teknik geologi universitas padjadjaran shuto, t., 1975. preliminary correlation of the neogene molluscan faunas in southeast asia. contributions to the geology and palaeontology of southeast asia, clv. geology and palaeontology of southeast asia, 161 173. sufiati, e., prasetyo, u., kistiani, d., aripin, dan irman. 2014. penelitian fosil moluska di kecamatan bayah, kabupaten lebak, propinsi banten. laporan kegiatan lapangan museum geologi bandung, unpublished. sujatmiko & santosa s. 1992. peta geologi lembar leuwidamar, jawa (geological map of leuwidamar quadrangle, java). bandung: pusat penelitian dan pengembangan geologi. zhong, g., geng, j., wong, h. k., ma, z., and wu, n. 2004. a semi-quantitative method for the reconstruction of eustatic sea level history from seismic profiles and its application to the southern south china sea. earth and planetary science letters 223 (2004) 443 459. doi:10.1016/j.epsl.2004.04.039 © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. material and method 3. result and discussion 4. conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 217 the metamorphic rocks-hosted gold mineralization at rumbia mountains prospect area in the southeastern arm of sulawesi island, indonesia hasria 1,2* , arifudin idrus 1 , i wayan warmada 1 1 department of geological engineering, universitas gadjah mada, indonesia 2 department of geological engineering, halu oleo university, indonesia *corresponding author : hasriageologi@gmail.com telp. +62 852-4185-7853 received: july 8, 2017. revised : aug 13, 2017, accepted: aug 20, 2017, published: 1 sept 2017 doi : 10.24273/jgeet.2017.2.3.434 abstract recently, in indonesia gold exploration activities are not only focused along volcanic-magmatic belts, but also starting to shift along metamorphic and sedimentary terrains. the study area is located in rumbia mountains, bombana regency, southeast sulawesi province. this paper is aimed to describe characteristics of alteration and ore mineralization associated with metamorphic rock-related gold deposits. the study area is found the placer and primary gold hosted by metamorphic rocks. the gold is evidently derived from gold-bearing quartz veins hosted by pompangeo metamorphic complex (pmc). these quartz veins are currently recognized in metamorphic rocks at rumbia mountains. the quartz veins are mostly sheared/deformed, brecciated, irregular vein, segmented and relatively massive and crystalline texture with thickness from 1 cm to 15.7 cm. the wallrock are generally weakly altered. hydrothermal alteration types include sericitization, argillic, inner propylitic, propylitic, carbonization and carbonatization. there some precious metal identified consist of native gold and ore mineralization including pyrite (fes2), chalcopyrite (cufes2), hematite (fe2o3), cinnabar (hgs), stibnite (sb2s3) and goethite (feho2). the veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18.4 ppm. based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposit type. the orogenic gold deposit is one of the new targets for exploration in indonesia. keywords: alteration, ore mineralization, metamorphic rocks, gold deposits, rumbia mountains, southeast sulawesi. 1. introduction gold is one of the most malleable, ductile, dense, conductive, nondestructive, brilliant, and beautiful of metals. this unique set of qualities has made it a coveted object for most of human history in almost every civilization, and there have been active gold markets for over 6000 years (green, 2007 in et al., 2015), so many research and mining companies are trying to find economical gold reserves to explore. currently, gold exploration activities in indonesia are focused on volcanic-hosted hydrothermal deposit. several gold deposits were discovered are erstberg, kucing liar, deep ore zone (doz) in papua including skarn type; batu hijau in sumbawa island (idrus et al., 2007; imai & ohno, 2005) and grasberg in papua including porphyry type ; pongkor in west java (warmada, 2003), gosowong in halmahera island including epithermal type. in sulawesi island, gold is also predominantly related to volcanic rocks, which are extended along western and northern neogene magmatic arcs of the island (idrus, 2009) (fig. 1). however, were recently in indonesia gold exploration activities are not only focused along volcanic-magmatic belts, but also starting to shift along metamorphic and sedimentary terrains. many current discoveries of placer (secondary) and primary gold mineralization genetically occur in association with metamorphic rocks, for instance, langkowala area and wumbubangka mountaints, bombana in southeast sulawesi (idrus & prihatmoko, 2011; idrus, et al., 2011; idrus et al., 2012), awak mas in south sulawesi (querubin & walters, 2011 in idrus et al., 2014); poboya ls-epithermal in central sulawesi (wajdi et al., 2011 in idrus et al., 2014) and gunung botak in buru island, mollucas (idrus et al., 2014). gold-bearing quartz veins are also recognized in derewo metamorphic belt at northern and northwestern part of central range papua. some exploration reports categorized the derewo metamorphic-related quartz veins into mesothermal gold deposit type (idrus et al., 2014). the gold mineralization genetically occur in association with sedimentary rocks is paningkaban, banyumas regency, central java (idrus et al., 2015). rumbia mountaints (fig. 2) is one of the location having a potential of mineral resources gold has been found in southeast sulawesi. the gold is not associated with volcanic rock-related gold deposits but associated with metamorphic rocks. this mailto:hasriageologi@gmail.com 218 hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 research aims to explore the characteristics of hydrothermal alteration and mineralization hosted by metamorphic rocks at rumbia mountains by the aplication petrography, ore microscopic, (x-ray diffraction) and fa-aas (fire assay-atomic absorption spectrophotometry) analyses. this study is an important stage for the next exploration of gold in the area or other areas that have an identical setting of geology. metamorphic rockhosted gold deposits could represent the new targets for gold exploration particularly in indonesia. fig. 1. geological setting of sulawesi island and location of the researched area in rumbia mountains (squared area), southeast sulawesi (modified from surono, 2013). fig. 2. geological geological map of rumbia mountains area occupied by paleozoic metamorphic rocks (pompangeo complex; mtpm) (modified from simandjuntak et al., 1993). squared area indicates the location area of this study. hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 219 2. geological setting the stratigraphy in the southeastern arm of sulawesi consists of three constituent rocks are sulawesi molasse composed of clastic sediments and carbonate, ophiolite complex are dominated by mafic and ultramafic rocks and continental terrain composed of metamorphic rocks. contaccts between the ophiolite complex and continental terrain, including their basement rocks are faulted. the sulawesi mollase uncorformably overlies both the ophiolite complex and continental terrain (surono, 2013). the mountains rumbia is a part of continental terrain is subsequently occupied by metamorphic rocks (pompangeo complex, mtpm) consisting of mica schist, quartzite, glaucophane schist and chert. the continental terrain, which were firstly described by surono, 1994. the metasediments and metamorphic rocks are of permian-carboniferrous in age and occupy the mendoke and rumbia mountains. mica schist and metasediments particularly meta-sandstone and marble are commonly characterized by the presence of quartz veins various width up to 2 meters, containing gold in some places (idrus et al., 2011). the langkowala formation is unconformably underlain by paleozoic metasediments and metamorphic rocks (pompangeo complex, mtpm) and conformably overlain by the eemoiko formation (tmpe), which is composed of corraline limestone, calcarenite, marl and sandstone; and boepinang formation (tmpb), which is composed of sandy claystone, sandy marl and sandstone. the eemoiko and boepinang formations were reported having pliocene age (surono, 2013). 3. research methods field investigation was carried out in rumbia mountaints area of southest sulawesi. the samples consist of altered rock, veins and clay samples collected from different hydrothermal alteration zones and ore samples. this study is conducted in four stages including field work, laboratory analyses, data analyses and interpretation. fieldwork includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rock types, altered rocks and gold bearing veins. laboratory work includes slab, vein textural dan structural analyses and mineralogy (petrography, ore microscopy and xrd (x-ray diffraction) and ore geochemistry. mineralogical analysis was conducted at department of geological engineering, gadjah mada university and ore geochemistry was done at aas laboratory, als canada ltd in canada and pt. intertek utama services jakarta. 4. the quartz vein the quartz veins in the study area consist three generations. the first is parallel to the foliations, the second crosscuts the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage (fig. 3). gold grades in the second and third veins are relatively higher than that in first veins (table 1). characteristics of quartz veins are mostly sheared/ deformed, irregular vein, brecciated, and relatively massive with thickness from 1 cm to 15.7 cm. based on data shows that gold-bearing quartz (qz) veins/veinlets have been discovered in association with paleozoic metamorphic rocks particularly mica schist, actinolite schist (green schist), phyllite and metasandstone. fig. 3. characteristics of quartz vein : (a). brecciated, sheared/deformed quartz vein (first generation) parallel to the foliation, b) massive, crystalline of quartz vein, (first generation) which is parallel to the foliation, c) brecciated, sheared/ deformed quartz vein (second generation) d). irregular vein, sheared/segmented of quartz vein cross cutting foliation (second generation), (e) a cluster of sheared/deformed laminated quartz vein (third generation), (f) laminate quartz vein (third generation). 220 hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 in addition, as observed by prihatmoko et al. (2010), druzy/sugary and some pseudomorph bladed carbonate textures have also been recognized associated with quartz veins/reefs cross cutting foliation. in the onggomate hill the veins formed a breccias zone composed of quartz as matrix, massive to crystalline, crackle to mosaic, with mica schist and phyllite fragments. in the roko-roko hill quartz veins (1-30 cm) hosted by mica schist and metasediment are commonly massive to crystalline quartz (druzy textures) with pseudomorph bladed carbonate textures. therefore, at least 2 later stages of veinings (after the first generation veinings) could be identified, including (1) vein breccias and (2) later quartz veinlets, 1-10 mm, which are commonly crystalline and containing native gold (prihatmoko et al., 2010 in idrus et al, 2012 ). 5. hydrothermal alteration hydrothermal alteration and mineralization underlie within all lythologic units found in the research area. widespread zones of hydrothermal alteration are found on the surface. alteration is typically pervasive and selective pervasive with intensity ranges from weak to strong, so it is very rare to observe good outcrops in the area. in general, the wallrocks are weakly altered. strong alteration zone is only restricted surrounding quartz veins (like halos/selvage). there are six main alteration zones that are indentified, namely sericitization, argillic, inner propylitic, propylitic, carbonatization and carbonization alterations. sericitization is characterized by the presence of sericite (or muscovite), chlorite and quartz while argillic alteration is typified by montmorilonit-kaolinite, chlorite and quartz. inner propylitic alteration is characterized by actinolite, chlorite, quatz and epidot, while propylitic alteration is typified epidote and/or chlorite and calcite. carbonization is probably represented by (rare) occurrence of graphite with commonly black in colour in the quartz vein and altered mica schist and carbonatization altera¬tion is typified by the presence of calcite veinlets/stringers while (fig. 4). ore mineralization is closely associated with seritisization, argillic, inner propylitic, propylitic and weak carbonation alterations. the carbonization is considered to be one of the alteration type characteristics, associated with orogenic/ metamorphic-hosted gold deposit (idrus, et al., 2012). idrus et al. (2012) also reported the presence silicification alteration is represented by silicified metasediment and mica schist mostly present surrounding quartz veins or along structural zones. the presence of narrow clay-sericite alteration halo (tens cm to 1 m) around the quartz veins in the rokoroko hill (prihatmoko et al., 2010 in idrus et al., 2012). fig. 4. hyrdothermal alteration types : (a). sericitization, (b). argillic, (c). inner propylitic, (d). propylitic, (e). carbonization,(f carbonatization alteration. the scale bar without expression in each of photomicrograph on this paper indicates 1 mm. xnicol 40x. opq= opaq, ms= muscovite, ser= sericite, qz= quartz, rt= rutil, gln= glaucophane, mnt-kln= montmorilonitekaolinite, chl= chlorite, ep= epidote, act= actinolite, hbl= hornblende, grt= garnet, gr= graphite, cal= calcite. hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 221 6. ore mineralization based on field relationship, ore microscopy, electron microprobe analyses, there some precious metal identified consist of native gold and ore mineralization including pyrite (fes2), chalcopyrite (cufes2), hematite (fe2o3), cinnabar (hgs), stibnite (sb2s3) and goethite (feho2). idrus et al. (2012) also reported the presence tripuhyite (fesbo4) and rare arsenopyrite (feass2) are present in the quartz veins and silicified metamorphic wallrocks. pyrite, hematite, cinnabar and stibnite are present abundantly in the primary mineralization gold deposits, present in the quartz veins and wallrocks; and commonly present at alteration rocks (fig. 5). pyrite occurs as isolated idiomorphic crystals, angular fragmens,, strongly brecciated fragments, anhedral shape, medium reflectance and isotropic. some pyrite grains are partly enclosed by hematite, chalcopyrite and possibly stibnite. fractures and brittle cavities in pyrite are often filled by hematite and chalcopyrite. hematite is typically pinkish orange in color and commonly present in altered rocks, internal purple reflections, subhedral-anhedral crystals, present as sulfide mineral interactions with oxygen causing the oxidation of sulphide minerals, especially pyrite. hematite is looked replacing pyrite. chalcopyrite is associated with pyrite while cinnabar is typically pinkish red in color and commonly occurred in the form of mineralized layers along foliations of the metamorphic rocks. pyrite, hematite, cinnabar and stibnite are genetically closely related to gold mineralization. graphite (gr) is present as a result of carbonization and associated with stibnite minerals. those sulfides could be pathfinder minerals for the exploration of the metamorphic-hosted gold deposit. in general, gold is very fine-grain, but occasionally native gold is visible in quartz veins. bulk-ore chemistry analyzed by aas (atomic absorption spectrometry) indicates a very broad and erratic variation of gold grade ranging from below detection limit <0.0002 ppm to 18.4 ppm au (table 1). fig. 5. ore minerals in study area. a. aurum? (gold?), pyrite and chalcopyrite. b. hematite is looked replacing pyrite. c and f. the present of abundantly cinnabar in mineralization of hydrothermal gold deposits. d. graphite as a result of carbonization and associated with stibnite. e. goethite. the scale bar without expression in each of photomicrograph on this paper indicates 1 mm. au= aurum (gold), py= pyrite, ccp= chalcopyrite, hem= hematite, cin= cinnabar, stb= stibnite, gth= goethite, qz= quartz,chl= chlorite.. 222 hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 table 1. ore geochemistry of metamorphic-hosted gold quartz veins/reefs from rumbia mountains, bombana (in ppm). samples code elements (ppm) au ag as cu hg pb sb zn dhr 11 0.0007 1.170 0.69 17.15 0.007 29.9 3.86 45.2 dhr 15 0.0007 0.232 2.53 45.1 0.021 8.22 0.975 56.1 dhr 16 <0.0002 1.620 4.22 71.8 <0.004 29.3 7.33 66.8 dhr 20 <0.0002 0.138 3.85 31.7 0.072 13.20 0.675 47.1 dhr 24 0.0004 1.420 5.38 28.1 0.013 48.2 6.85 87.9 dhr 25 0.0008 0.161 5.35 13.75 0.005 8.18 1.285 12.7 dhr 34 0.0048 0.619 27.800 123.50 0.015 24.40 2.460 34.7 dhr 35a 0.0779 0.093 194.500 7.70 0.577 4.22 19.600 4.3 dhr 50 0.0017 0.650 1810.00 43.00 1.375 83.00 6170.000 109.5 dhr 55 0.0124 0.014 49.100 61.90 0.287 11.15 1.795 59.5 dhr 62 0.0049 0.405 17.500 7.79 0.065 11.40 28.000 12.3 dhr 66 0.0071 0.191 160.00 708.00 0.085 10.10 3.210 138.5 dhr 74b 0.0009 0.491 2.52 4.70 0.010 19.45 5.060 10.8 dhr 76a 0.0009 0.103 3.23 17.70 0.076 19.35 0.733 48.4 dhr 81a 0.0014 0.564 32.4 179.00 0.014 9.10 2.060 61.3 dhr 85a 0.0024 3.100 2.44 1505.00 0.020 3.99 0.739 59.4 dhr 87 0.0002 0.281 2.88 1150.00 0.010 8.44 6.300 11.8 dhr 87a 0.0015 0.112 4.11 30.80 0.032 24.4 0.635 27.9 dhr 97a <0.0002 0.041 4.48 51.00 0.011 4.68 1.835 39.9 dhr 101 0.7200 0.300 1840.00 43.00 0.080 6.00 21.000 53.0 dhr 103 0.0800 0.100 69.00 26.00 0.210 2.00 2.000 14.0 dhr 104 18.4000 0.300 192.00 44.00 0.310 27.00 62.000 52.0 dhr 105 0.9800 < 0.010 292.00 23.00 0.150 28.00 17.000 49.0 dhr 107 3.7600 0.100 852.00 25.00 0.340 11.00 37.000 42.0 dhr 108 0.2600 0.100 201.00 44.00 0.440 9.00 148.000 57.0 dhr 109 0.6300 < 0.100 118.00 28.00 0.070 9.00 32.000 53.0 dhr 110 0.1500 0.300 279.00 43.00 0.290 18.00 160.000 77.0 dhr 111 0.2200 0.100 75.00 45.00 0.080 11.00 34.000 20.0 dhr 113 < 0.0100 0.100 18.00 15.00 0.430 < 2.00 7.000 11.0 7. conclusion the primary gold grains hosted by rumbia mountains are evidently derived from sheared and segmented, partly brecciated, relatively massive, laminated gold-bearing quartz±calcite veins/reefs with thickness from 1 cm to 15.7 cm hosted by pompangeo metamorphic complex (pmc). the pmc particularly consists of mica schist (dominant rock type), actinolite schist, phyllite and metasedimen. mica schist is abundantly composed of muscovite, chlorite quartz, actinolite, epidote with a small amount of, sericite, rutile, kyanite and opaque minerals. hence, the metamorphic rock is categorized into green schist facies, which is noted as an important host rock facies for orogenic gold deposit worldwide the metamorphic rocks are strongly weathered, however trenching program has opened up the soil cover and exposes the hydrothermal alteration zones. in general, the wallrocks are weakly altered. hydrothermal alteration types include sericitization, argillic, inner propylitic, propylitic, carbonatization and carbonization. the veins contain erratic gold in various grades from below detection limit limit <0.0002 ppm to 18.4 ppm. mineralogically, gold is genetically related to consist of pyrite (fes2), chalcopyrite (cufes2), hematite (fe2o3), cinnabar (hgs), stibnite (sb2s3) and goethite (feho2). idrus et al. (2012) also reported the presence tripuhyite (fesbo4) and rare arsenopyrite (feass2) are present in the quartz veins and silicified metamorphic wallrocks. gold is mainly identified in the form of 'free gold' among silicate minerals particularly quartz. based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposit type (cf. groves et al., 1998; 2003 and goldfarb et al., 2005). the orogenic gold deposit is one of the new targets for exploration in indonesia. acknowledgements this study was funded by ristekdikti research grant 2017 awarded to the author. fieldwork was partly supported by pt. panca logam makmur (plm) which has given us permission to do this research in the wumbubangka prospect area and its vicinity. special thanks to my students from department of geological engineering, halu oleo university for their assistance during the fieldwork. we also would like to thank the head and staff the geological engineering hasria, idrus, a., and warmada, i.w./ jgeet vol 02 no 03/2017 223 department, faculty of engineering, gadjah mada university who gave me permission to access to the laboratories. references goldfarb, r.j., baker, t., dube, b., groves, d.j., hart, c.j.r., and gosselin, p., 2005. distribution character and genesis of gold deposits in metamorphic terrains. in: hedenquist, j.w., thompson, j.f.h., goldfarb, r.j., richards, i.p (eds.), economic geology. one hundred th anniversary volume, p. 407-450. groves, d. i., goldfarb, r. j., and robert, f., 2003. gold deposit in metamorphic belts: overview or current understanding, outstanding problems, future research, and exploration significance. economic geology, 98, p.1-29. groves, d. i., goldfarb, r. j., gebre-mariam, m., hagemann, s. g., and robert, f., 1998. orogenic gold deposit: a proposed classification in the context or their crustal distribution and relationship to other gold deposit types. ore geology review, 13, p.7-27. idrus, a., 2009. potensi sumberdaya mineral bijih pada busur magmatik sulawesi bagian barat dan utara, invited speaker on national seminar geologi sulawesi dan prospeknya oktober 2009, 26pp. idrus, a., fadlin., prihatmoko, s., warmada, i.w., nur, i., and meyer, f.m., 2012. the metamorphic rockhosted gold mineralization at bombana, southeast sulawesi: a new exploration target in indonesia. jurnal sumber daya geologi, (22) 1: 35-48. idrus, a., hakim, f., warmada, i.w., aziz, m., kolb, m and meyer, f.m., 2015. geology and ore mineralization of neogene sedimentary rock hosted ls epithermal gold deposit at paningkaban, banyumas regency, central java, indonesia.journal of southeast asian applied geology,volume 7(2), pp. 73-79. idrus, a., kolb, j., and meyer, f.m., 2007. chemical composition of rock-forming minerals in coppergoldbearing tonalite porphyry intrusions at the batu hijau deposit, sumbawa island, indonesia: implications for crystallisation conditions and fluorine-chlorine fugacity, special issue. resource geology, 57 (2), p.102-113. idrus, a., nur, i., warmada, i w., and fadlin., 2011. metamorphic rock-hosted orogenic gold deposit type as a source of langkowala placer gold, bombana, southeast sulawesi. jurnal geologi indonesia, (6) 1: 43-49. idrus, a., prihatmoko, s., hartono, gh., idrus., ernowo, franklin, moetamar, setiawan, i., 2014. some key features and possible origin of the etamorphic rock-hosted gold mineralization in buru island, indonesia. indonesian journal on geoscience, 1, p. 9-19. imai, a. and ohno, s., 2005. primary ore mineral assemblage and fluid inclusion study of the batu hijau porphyry cu-au deposit, sumbawa, indonesia. resource geology, 55, p.239-248. o'connor, f.a., lucey, b.m., batten, j.a., and baur, d.g., 2015. the financial economics of gold-a survey. international review of financial analysis, 1-20p. simandjuntak, t.o., surono, and sukido., 1993. peta geologi lembar kolaka, sulawesi, skala 1 : 250.000. pusat penelitian dan pengembangan geologi, bandung. surono., 2013. geologi lengan tenggara sulawesi. badan geologi, kementerian energi dan sumber daya mineral. bandung, 169p. wadji, m.f., santoso, s.t.j., kusumanto, d., and digdowirogo, s., 2011. metamorphic hosted low sulfidation epithermal gold system at poboya, central sulawesi : a general descriptive review, proceedings of the sulawesi mineral seminar, manado 28-29 november 2011, p. 201-210. warmada, i w., 2003. ore mineralogy and geochemistry of the pongkor epithermal goldsilver deposit, indonesia. dissertation. papierflieger, clausthal-zellerfeld. isbn: 3-89720658-7. 1. introduction 2. geological setting 3. research methods 4. the quartz vein 5. hydrothermal alteration 6. ore mineralization 7. conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 30 fakhruddin, r & kurniadi, d./ jgeet vol 04 no 01/2019 research article age and paleobathymetry of salodik group in poh pagimana section, east arm of sulawesi based on foraminiferal assemblages rakhmat fakhruddin 1, *, dedy kurniadi 2 1 pusat survei geologi, badan geologi, jl. diponegoro 57, bandung, indonesia. 2 lemigas r & d centre for oil and gas technology, jl. ciledug raya, kav. 109, cipulir, kebayoran lama, 1089/jkt, south jakarta, indonesia * corresponding author : rakhmat.fakhruddin@esdm.go.id tel.:+62-22-7203205; fax: +62-22-7202669 received: jan 20, 2019, accepted: feb 20 , 2019, published: march 1, 2019 doi: 10.25299/jgeet.2019.4.1.2751 abstract planktonic and benthic foraminiferal assemblages were used for age and paleobathymetry analysis of outcropping carbonate succession of the salodik group in poh pagimana section, east arm of sulawesi. twenty spot samples of carbonate rocks were collected from cut slope along the road between poh and pagimana. age analysis conducted for each sample by its planktonic foraminifera assemblages and group into their age interval. the age range from early eocene to pliocene. benthic foraminiferal assemblages indicate paleobathymetry ranging from middle shelf to upper bathyal settings. age analysis of the studied section show an older sediments (early middle eocene) overlie younger sediment (early miocene). this is interpreted as the evidence of thrust fault in the poh pagimana section as part of thrust sheets of batui thrust complex which imbricated on deformation zone. the youngest sediment which have suffered deformations shown by disordered age sequence is pliocene in age (n20-21). the eocene to pliocene carbonate succession in the studied section was deposited relatively in the more basinward position compared to the carbonate-dominated sediments in the tomori area which was deposited in the more landward position. keywords: salodik group, poh pagimana section, east arm of sulawesi, early eocene to pliocene 1. introduction paleogene to neogene carbonate-dominated succession outcropping in the east arm of sulawesi, in named of salodik dan poh formations (rusmana et al., 1993; surono et al., 1993). the name of salodik and poh formations have been redefined by simandjuntak (1986) as salodik limestones, and as salodik group by handiwiria (1990). the salodik group is deformed and imbricated with total thickness of this unit in the range of 1000 to 1200 metres (simandjuntak, 1986). several previous paleontological work have been conducted in the salodik group. simandjuntak (1986) with his work in biak poh section, balantak section, nambo river, and kolo atas area concluded that salodik group is early eocene to early middle miocene (zones p7 to n12 13). it was deposited as carbonate platform of an open shelf in eocene times and in deepening shelf environment through oligocene to middle miocene times. furthermore, simandjuntak (1986) divided this carbonate succession into boundstone, grainstone, packstone, and wackestone facies. larger foraminifera analysis of the salodik group from poh locality give age of middle lutetian to bartonian (zones ta3 tb), middle eocene (renema et al., 2002). the salodik and poh formations is dated early eocene to middle miocene in age (husein et al., 2014). depositional environment of salodik formation varied from reef to shallow marine whilst poh formation was deposited in lagoon and neritic to bathyal setting (husein et al., 2014). the simple aim of this paper is to determine the age and paleobathymetry of salodik group in poh pagimana section (fig. 1) based on its foraminifera assemblages to better understand the stratigraphy of the east arm of sulawesi carbonate succession. 2. stratigraphy the study area is located in the luwuk banggai basin (badan geologi, 2009). two stratigraphic sequences are imbricated together in the east arm of sulawesi fold-and-thrust belt: a parautochthonous sequence (banggai sula microcontinent); and an allochthonous sequence (east sulawesi ophiolite/eso) (charlton, 1996). the oldest banggai sula microcontinent sedimentary rocks are of triassic age, and consist of deep water limestone and marl with shale intercalation (tokala formation/lemo beds), and terrestrial to marginal marine shale and sandstone of meluhu formation (simandjuntak, 1986; rusmana et al., 1993; surono et al., 1993; charlton, 1996; milsom, 2000milsom). http://journal.uir.ac.id/index.php/jgeet mailto:rakhmat.fakhruddin@esdm.go.id fakhruddin, r & kurniadi, d./ jgeet vol 04 no 01/2019 31 fig. 1. geological map of the study area, modified from rusmana et al. (1993). black box indicate the study location. early jurassic sediment represented by inner shelf deposit of quartz-rich dominated sandstone with coal and conglomerate intercalation of kapali beds/nanaka formation (simandjuntak, 1986; rusmana et al., 1993; surono et al., 1993). these are succeeded by middle upper jurassic limestone and marl with belemnite and ammonite, interpreted to be deposited in middle to outer shelf setting (nambo formation/sinsidik beds) (simandjuntak, 1986; rusmana et al., 1993; surono et al., 1993; charlton, 1996; hasibuan and kusworo, 2008). during the drifting of the banggai sula microcontinent in the cretaceous and into the cenozoic, passive margin sedimentation took place and deposited syn-drifting carbonates (satyana and zaitun, 2016). sediments of the cretaceous was deposited in relatively deep-water low energy sedimentary environment with carbonate-shale-chert sequences known as luok beds (more proximal facies) and matano formation (more distal facies) (simandjuntak, 1986; rusmana et al., 1993; surono et al., 1993; charlton, 1996). in the early eocene to early middle miocene, carbonate-dominated succession (salodik group) was deposited in shelf carbonate platform setting (simandjuntak, 1986; rusmana et al., 1993; surono et al., 1993). the carbonate-dominated succession of salodik group (tomori, matindok, and minahaki formations) in tomori area is dated as late eocene to late miocene, and was deposited in shallow water carbonate platform (davies, 1990; handiwiria, 1990; charlton, 1996; satyana and zaitun, 2016). the allochthonous sequence of eso comprised of gabbro, basalt, serpentinite, dolerite, peridotite, and minor of phyllite and schist, and was dated to be ranged from middle cretaceous to late oligocene (rusmana et al., 1993; kadarusman et al., 2004; husein et al., 2014). the collision between banggai sula microcontinent and eso is probably took place from late middle miocene to pliocene in submarine and open sea tectonic setting (simandjuntak, 1986; garrard et al., 1988; satyana and zaitun, 2016). subsequent to the collision, formation and development of the melange occurred since the late middle miocene continued into pliocene, named as kolokolo melange (simandjuntak, 1986). it is consist of mixed fragments and blocks in sheared matrix of scally clay and marly mudstone (simandjuntak, 1986; surono et al., 1993). post-orogenic sediments derived from erosion of the obducted ophiolite is known as batui group and sulawesi group/celebes molasse. the batui group is dated as late miocene to pliocene in age, and consist of deep water quartz-rich sandstones associated with pebbly mudstones (kolo beds), molasse type sediments conglomerate dominated coarse clastic rocks (biak/bongka formation), and volcaniclastic sediments which do not contain material derived from the collision complex (lonsuit turbidites) (simandjuntak, 1986; rusmana et al., 1993; surono et al., 1993). the sulawesi group (early pliocene to pleistocene) comprise of flysch facies sediments of the kintom formation and molasse type sediments of biak and kalomba formations (abimanyu, 1990; rusmana et al., 1993; surono et al., 1993; hasanusi et al., 2004). pleistocene to present-day sedimentation is represented by carbonate sequence dominated of quaternary coralline reefs named as luwuk formation (simandjuntak, 1986; abimanyu, 1990; rusmana et al., 1993; surono et al., 1993; hasanusi et al., 2004). 3. materials and methods twenty spot samples of carbonate rocks along the road between poh and pagimana were sampled from the salodik group for foraminifera analysis. the 32 fakhruddin, r. & kurniadi, d./ jgeet vol 04 no 01/2019 location of each of these samples is shown in fig. 2. foraminifera analysis have been carried out at the geollabs, pusat survei geologi, bandung. the outcrop in the studied section was not continuous leading to the difficulty to determine stratigraphic position and to perform age analysis by biostratigraphic zonation. age analysis conducted for each sample by its planktonic foraminifera assemblages and group into their age interval. identifications of foraminifera were done based on barker (1960) and marcelle (2015). age interpretation was based on planktonic zonation proposed by marcelle (2015). paleobathymetry interpretation of the studied samples using benthic foraminifera analysis was based on rauwerda et al. (1984) and holbourn et al. (2013). 4. results and discussions 4.1 lithology the studied sediment comprised of interbedded of limestone and marl. the limestone is grey in colour, partly well-bedded, containing foraminifera, mollusc, and coral. marl is white to grey, soft, contain abundant foraminifera. khorniawan (2013) divided sediment in the studied section by petrographic analysis into 13 types of carbonate: large bioclast packstone forams, bioclast planktonic forams packstone, bioclast planktonic forams packstone with quartz, red algae bioclast wackstone, bioclast red algae grainstone, packstone with dolomitization, ooid grainstone, ooid packstone, bioclast coral rudstone, bioclast miliolids grainstone, bioclast planktonic forams packstone with microspar, indeterminate bioclast packstone, and bioclast red algae packstone with microspar. as general, carbonate rocks in the studied section are able to group into four type: packstone, wackstone, grainstone and rudstone. field photographs represent each of age interval of the studied section is provided in fig. 3. 4.2. age analysis foraminifera analysis indicate that the salodik group in poh pagimana section is early eocene to pliocene. details of the foraminifera identified in each sample are presented in table 1. the age range of each of the analyzed samples are summarized in fig. 4. in addition, indication of reworked foraminifera was found in twelve samples (ppg03, ppg04, ppg07, ppg08, ppg09, ppg10, ppg11, ppg13, ppg14, ppg15, ppg18, and ppg19). fig. 2. detailed map of the study area (above) and interpretation of geological cross-section (bottom). black dots indicate sample localities. see text for further explanation of the age range for each sample. fakhruddin, r & kurniadi, d./ jgeet vol 04 no 01/2019 33 it is interpreted by the occurrence of older foraminifera in younger foraminifera assemblages (red cross marks in table 1). based on planktonic foraminifera assemblages for each sample, the studied section is able to divide into four age interval: 4.2.1. early middle eocene foraminifera assemblages yielded an early to middle eocene age are found in ppg09, ppg10, ppg11, ppg12, ppg13, and ppg14. sample ppg09 contains igorina anapetes and morozovella lensiformis, suggesting zones p9 10, early middle eocene. the presence of morozovella aragonensis and morozovella formosa in ppg10 indicate early eocene age, zone p7. based on the appearance of morozovella aragonensis and morozovella subbotinae, sample ppg11 is designated to zone p7, early eocene. sampel ppg12 yielded a middle eocene age, zone p11, based on the occurrence of morozovella aragonensis and morozovella lehneri. early to middle eocene age (zones p9 10) interpretation in sample ppg13 is inferred as shown by the presence of morozovella caucasica. sample ppg14 is appointed to zone p11, middle eocene, based on findings of igorina anapetes and truncorotaloides rohri. 4.2.2. oligocene early miocene seven samples of foraminifera-bearing carbonate (ppg07, ppg08, ppg15, ppg16, ppg17, ppg18, and ppg19) from the studied section have oligocene early miocene age. the occurrence of globigerinoides sacculifer and globoquadrina binaiensis in sample ppg07 indicates an early miocene age, zone n5. sample ppg08 is inferred as zone n4, early miocene, as shown by the presence of globigerinoides primordius and paragloborotalia kugleri. sample ppg15 is interpreted as zone p22 n4, late oligocene early miocene, based on findings of globigerina ciperoensis and paragloborotalia mayeri. the appearance of globigerina sellii and paragloborotalia obesa suggests late oligocene age, zone p21 22, for sample ppg16. an oligocene age, zone p19 21, is designated to sample ppg17 based on the presence of globigerina ciperoensis and globoturborotalita ouachitaensis. sample ppg18 yielded a late oligocene early miocene age, zones p21 n5, suggested by the appearance of paragloborotalia nana and paragloborotalia obesa. sample ppg19 contains paragloborotalia obesa and dentoglobigerina tripartita indicates zone p21 22, late oligocene. 4.2.3. middle miocene foraminifera analysis indicate that three samples (ppg04, ppg05, and ppg06) are middle miocene in age. sample ppg04 contains globigerinoides bollii and paragloborotalia peripheroacuta suggesting a middle miocene age, zone n12. sample ppg05 yielded a middle miocene age, zone n10 11, based on findings of paragloborotalia peripheroacuta and paragloborotalia peripheroronda. the appearance of paragloborotalia peripheroacuta in sample ppg06 indicate zone n10 12, middle miocene. fig. 3. field photographs of several outcrops of the salodik group in poh pagimana section., a. bedded limestone with marl intercalation (ppg20)., b. unbedded marl (ppg08)., c and d. limestone with no visible bedding (c: ppg19; d: ppg12). 34 fakhruddin, r. & kurniadi, d./ jgeet vol 04 no 01/2019 4.2.4. late miocene pliocene late miocene to pliocene age range in the studied section is represented by samples ppg01, ppg02, ppg03, and ppg20. the presence of globorotalia merotumida and globorotalia plesiotumida in ppg01 suggest a late miocene age, zone n17 18. sample ppg02 contains globorotalia plesiotumida, also provided a late miocene age, zone n17 18. in sample ppg03 and ppg20, similar foraminifera assemblages of globorotalia margaritae and sphaeroidinellopsis seminulina was found, and designated these samples to pliocene age, zone n19 20. table 1. list of foraminifera identified in the samples studied. black cross = in situ foraminifera and red cross = inferred reworked planktonic foraminifera. fakhruddin, r & kurniadi, d./ jgeet vol 04 no 01/2019 35 table 1. (continued). 4.3. paleobathymetry in early eocene (zone p7), sediments in the studied section was deposited in middle shelf environment as shown by the presence of cibicides sp., lenticulina sp., nodosaria sp., and nonion sp. in sample ppg10, and based on the appearance of bolivina sp. and lenticulina sp. in sample ppg11. paleobathymetry at zone p9-10 (early to middle eocene) was in the outer shelf as shown by the occurrence of eponides sp., lenticulina sp., nodosaria sp., and planularia sp. (ppg09), and in the middle shelf environment based on the presence of amphistegina sp., bolivina sp., and lenticulina sp. (ppg13). in zone p10 11 (middle eocene), paleobathymetry then changed into upper bathyal setting based on the findings of cibicides sp. and 36 fakhruddin, r. & kurniadi, d./ jgeet vol 04 no 01/2019 karreriella sp. in sample ppg12. in zone p11 (middle eocene), sample pg14 mark the shifting of paleobathymetry into outer shelf, interpreted by the appearance of eponides sp., gyroidina sp., and lenticulina sp. in zone p19 21, early oligocene, the occurrence of bolivina sp., cibicides sp., eponides sp., karreriella sp., dan pullenia sp. in sample ppg17 indicate upper bathyal setting. in zone p21 22, late oligocene, sampels ppg16 and ppg19 represent upper bathyal and middle shelf environment appointed by the presence of cibicides sp., eponides sp., and pullenia sp. (upper bathyal; ppg16) and the appearance of cibicides sp. and nonion sp. (middle shelf; ppg19). the presence of bolivina sp., dentalina sp., globobulimina sp., lenticulina sp., and uvigerina sp. in sample ppg18 (zones p21 n5, late oligocene early miocene) indicate middle shelf environment. in zone p22 n4, late oligocene early miocene, sample ppg15 yielded benthic foraminifera of bulimina sp., gyroidina sp., and karreriella sp. suggest upper bathyal setting. in zone n4, early miocene, upper bathyal environment is inferred based on the findings of cibicides sp., gyroidina sp., karreriella sp., and pleurostomella sp. in sample ppg08. in zone n5, early miocene, paleobathymetry was also in upper bathyal environment as shown by the presence of eggerella sp., eponides sp., gyroidina sp., karreriella sp., and uvigerina sp. in sample ppg07. paleobathymetry at zones n10 11 (middle miocene) was in upper bathyal environment, based on the appearance of eponides sp., karreriella sp., planulina sp., and pullenia sp. in sample ppg05. sample ppg06 with the age of middle miocene (zones n10 11) contains bolivina sp. and planulina sp., is also designated to upper bathyal environment. in zone n12 (middle miocene), paleobathymetry was change into middle shelf as suggested by the occurrence of amphistegina sp., dentalina sp., and lenticulina sp. in sample ppg04. sediment of the studied section in the late miocene (zone n17 18) was deposited in middle shelf environment based on the findings of dentalina sp., elphidium sp., and lenticulina sp., in sample ppg01, and was deposited in upper bathyal environment as shown by the occurrence of cibicides sp., eponides sp., and gyroidina sp. in sample ppg02. pliocene time (zone n19 20) of the studied section represented by sediment which was deposited in middle shelf and upper bathyal environment. middle shelf setting indicated by the presence of bolivina sp. and nodosaria sp. (sample ppg20), whilst upper bathyal environment interpretation indicated by the appearance of karreriella sp. and planulina sp. in sample ppg03. 4.4. thrust fault identification age analysis of the studied section show an older sediments (sample ppg09, early middle eocene) overlie younger sediment (sample ppg08, early miocene). this is interpreted as the evidence of thrust fault in the poh pagimana section. the thrust fault is part of thrust sheets of batui thrust complex which imbricated on deformation zone resulted from collision of banggai sula microcontinent with the east sulawesi ophiolite (davies, 1990; kadarusman et al., 2004; satyana and zaitun, 2006). the chaotic order of the age sequence of the studied sample (ppg09 ppg14; ppg15 ppg19; ppg03 ppg01; fig. 4) is interpreted as the result of deformation structure. the youngest sediment which have suffered deformations shown by disordered age sequence is pliocene in age (n20-21). this indicate that the thrusting associated with the tectonic event in studied section was still took place after n20-21, probably at n22 (villeneuve et al., 2000; husein et al., 2014). 4.5. correlation with tomori area lower part of tomori formation, aged late eocene early oligocene, was deposited in inner sub-littoral (davies, 1990; handiwiria, 1990). in eocene early oligocene, salodik group at the studied section was deposited in the marine environment with paleobathymetry ranging from middle shelf, outer shelf to upper bathyal. upper part of tomori formation, (early oligocene middle miocene) was deposited in littoral to inner sublittoral with interval of supra-littoral environment (davies, 1990; handiwiria, 1990). tiaka member is found in upper part of tomori formation with lithology of limestone, coal, and dolomite. tomori formation is overlay by matindok formation (middle miocene) with depositional environment in littoral to inner sublittoral (davies, 1990; handiwiria, 1990). in the poh pagimana section, late oligocene to middle miocene salodik group was deposited in the marine environment vary from middle shelf to upper bathyal. in tomori area, minahaki formation at middle to late miocene time was deposited in supra-littoral and inner to outer sub-littoral environment (davies, 1990; handiwiria, 1990). mantawa member of minahaki formation, late miocene in age was a carbonate pinnacle reef deposited in inner sub-littoral (handiwiria, 1990; gutteridge et al., 2017). at late miocene to pliocene time, salodik group in the studied section, was deposited in the middle shelf to upper bathyal setting. from the above description, it is inferred that the early eocene to pliocene carbonate succession (salodik group) in the studied section was deposited in relatively deeper paleobathymetry compared to the salodik group (tomori, matindok, and minahaki formation) in the tomori area. in the other words, from eocene to pliocene, paleobathymetry in the studied section was relatively in the more basinward position compared to the sediments in tomori area which was deposited in the more landward position. simplified cross section scheme between the studied section and tomori area is provided in fig. 5. fakhruddin, r & kurniadi, d./ jgeet vol 04 no 01/2019 37 fig. 4. summary diagram of the age range and paleobathymetry of the samples studied. planktonic zonation from boudagherfadel (2015). abbreviation: ms=middle shelf, os=outer shelf, and ub=upper bathyal. 38 fakhruddin, r. & kurniadi, d./ jgeet vol 04 no 01/2019 fig. 5. simplified cross section scheme between the studied section and tomori area (modified from gutteridge et al., 2017). 5. conclusion twenty spot samples of carbonate succession of the salodik group were collected along the road between poh and pagimana for foraminiferal analysis. planktonic foraminifera suggest an early eocene to pliocene age whilst benthic foraminiferal assemblages indicate paleobathymetry ranging from middle shelf to upper bathyal settings. age analysis of the studied section show an older sediments (early middle eocene) overlie younger sediment (early miocene), and interpreted as the evidence of thrust fault in the poh pagimana section as part of thrust sheets of batui thrust complex which imbricated on deformation zone. in addition, the eocene to pliocene carbonate succession in the studied section was deposited relatively in the more basinward position compared to the carbonatedominated sediments in the tomori area which was deposited in the more landward position. acknowledgements this study was financially supported by pusat survei geologi, badan geologi, kesdm. we thank alexander limbong and supriadi for their support during the fieldwork. we are indebted to rukman and m. agus rozak for their helps during the laboratory process. we are grateful to anonymous reviewers for their helpful comments the manuscript. references abimanyu, 1990. the stratigraphy of the sulawesi group in the tomori psc, east arm of sulawesi. proceedings pit xix ikatan ahli geologi indonesia, bandung. badan geologi, 2009. peta cekungan sedimen indonesia. badan geologi, bandung. barker, r.w., 1960. taxonomic notes on the species fig. d by h.b. brady in his report of the foraminifera dredged by hms challenge society of economic paleontologists and mineralogists, 9, 10238, charlton, t.r., 1996. correlation of the salawati and tomori basins, eastern indonesia: a constraint on left-lateral displacements of the sorong fault zone. geol. soc. london, spec. publ. 106, 465 lp-481. https://doi.org/10.1144/gsl.sp.1996.106.01.29 davies, i.c., 1990. geological and exploration review of the tomori psc, eastern indonesia. proceedings of the indonesian petroleum association, 19 th annual convention, 41 67. garrard, r.a., supandjono, j.b., and surono, 1988. the geology of the banggai sula micro-continent, eastern indonesia. proceedings of the indonesian petroleum association, 17 th annual convention, 23 52. gutteridge, p., garland, j., vincent, b., thompson, s., morgan, j., turney, j., and jerram, d., 2017. southeast asian carbonate systems and reservoir development: an up-to-date synthesis, 2017, (rep.). cambridge carbonate ltd. handiwiria, y.e., 1990. the stratigraphy and hydrocarbon occurrences of the salodik group, tomori psc area, east arm of sulawesi. proceedings pit xix ikatan ahli geologi indonesia, bandung. hasanusi, d., abimanyu, r., artono, e., and baasir, a., 2004. prominent senoro gas field discovery in central sulawesi. proceedings of the indonesian petroleum association, deepwater and frotier exploration in asia & australasia symposium. hasibuan, f. and kusworo, a., 2008. umur formasi nambo di sulawesi tengah dengan acuan khusus fosil moluska. jurnal sumber daya geologi, xviii, 43 54. http://dx.doi.org/10.33332/jgsm.2008.v18.1.43-54 holbourn, a., henderson, a.s., and macleod, n., 2013. atlas of benthic foraminifera. wiley-blackwell, natural history museum, london, england. doi: 10.1002/9781118452493 husein, s., novian, m.i., 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10.1016/s1367-9120(00)00035-3 rauwerda, p.j., morley, r.j., and troelstra, s.r., 1984. assessment of depositional environment and stratigraphy on the basis of foraminifera palaeoecology (rep.). robertson research (singapore) private limited. renema, w., racey, a., and lunt, p., 2002. paleogene nummulitid foraminifera from the indonesian archipelago: a review. cainozoic research, 2, (1-2), 23 78. rusmana, e., koswara, a., and simandjuntak, t.o., 1993. geological map of the luwuk sheet, sulawesi. 1:250.000. https://sedimentary-geology-store.com/catalog/book/taxonomic-notes-species-hb-brady-his-report-foraminifera-dredged-hms-challenger https://sedimentary-geology-store.com/catalog/book/taxonomic-notes-species-hb-brady-his-report-foraminifera-dredged-hms-challenger https://sedimentary-geology-store.com/catalog/book/taxonomic-notes-species-hb-brady-his-report-foraminifera-dredged-hms-challenger 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http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ age and paleobathymetry of salodik group in pohpagimana section, east arm of sulawesi based on foraminiferal assemblages 1. introduction 2. stratigraphy 3. materials and methods 4. results and discussions 4.1 lithology 4.2. age analysis 4.2.1. early–middle eocene 4.2.2. oligocene–early miocene 4.2.3. middle miocene 4.2.4. late miocene–pliocene 4.3. paleobathymetry 4.4. thrust fault identification 4.5. correlation with tomori area 5. conclusion acknowledgements references author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 4 no 4 2019 242 alexander, o., et al./ jgeet vol 04 no 04/2019 research article evaluation of the hydrocarbon potentials of shale exposures at okpekpe in edo north ogbamikhumi alexander1,*, igbinigie nosa samuel1, odokuma-alonge ovie1 1department of geology, faculty of physical sciences, university of benin, nigeria * corresponding author : alexander.ogbamikhumi@uniben.edu tel.: +2348032722203 received: oct 1, 2016. accepted: nov 20, 2019. doi: 10.25299/jgeet.2019.4.4.2807 abstract this study evaluates the source rock characteristics of rock exposures along a newly exposed road cut in okpekpe. an integrated technique of organic geochemical analysis and biostratigraphy evaluation were adopted to determine the source rock quality, maturation index, kerogen types, depositional environment andsediment age. results of organic geochemistry gave total organic carbon (toc) value between 0.81 to 3.04 w.t% (2.08wt.% average) indicative of a good source potentials. the plot of total sulphur content (tsc) against toc suggests a transitional depositional environment for the samples while the plot of hydrogen index (hi) against oxygen index (oi) shows that the samples are capable of generating mixed type ii/iii kerogen. palynological analysis revealed that the basal section of the exposure is characterized by the occurrences of typical and moderately rich late cretaceous – early tertiary palynomorphs. while the upper section is poorly rich in palynomorph abundance but with spot occurrences. the palynomophs asssemlages is of late maastrichtian early paleocene and the outcrop is characterized by the presence of terrestrial pollens and spores indicating a continental to transitional depositional environment, typical of the mamu formation of the anambra basin. keywords: organic-geochemistry, biostratigraphy, source-rock, okpekpe, anambra-basin 1. introduction katz (1995) described source rock as fine grained argillaceous deposits, rich enough in organic matter and capable of generating hydrocarbon. prospectivity for hydrocarbon is dependent on various factors such as the presence of viable structures and a viable petroleum system, of which the presence of source rock is a key component. understanding the characteristics of the source rock shed light on its quality and hydrocarbon generating potentials (ogbamikhumi et al., 2017). in localities where the formation of the study source rock needed to be tied to regional geology, biostratigraphy characteristics play a major role in age and environment of deposition determination, which will ultimately help in correlating the rock exposure to it corresponding regional equivalent when compared to literature. only few documented reports are available on this region of the anambra basin. (edegbai and emofurieta 2015; ogbamikhumi and igbinigie, 2017), most recorded work of the anambra basin are restricted to the center of the basin (burke et al., 1972; ladipo, 1988; nwajide and reijers, 1996; nton and bankole, 2013; ola and adeoti 2017). hence the motivation behind this study; which intends to characterize the encountered shale exposures to understand its hydrocarbon generation potential and define its regional equivalent by comparing analytical result obtained with recorded literatures. the study area is located in okpekpe community, edo north at coordinates n07° 11’ 02.0’’ and e006° 28’ 06.5’’. it is situated within the anambra basin, specifically at the benin flank of the basin (figure 1). generally, the sediment of this region includes extension of the ajali formation, the transgressive nkporo group and the regressive coal measures of the late cretaceous sea (nwajide, 2005). 2. materials and methods five outcrop samples were obtained from the study area and subjected to both organic geochemical analysis and palynological evaluation after sample preparation in the laboratory. the slide preparation method for palynological study was in accordance with standard methods as described in literature (traverse, 1988; wood et al., 1996). a frequency count of stratigraphically important forms was determined for each of the samples. necessary photomicrographs of important structures and forms were taken using a digital camera attached to the microscope for detailed study and identification of the fossils forms and characteristic. the organic geochemical evaluation technique adopted include: turbidimetrically barium sulphate precipitate for total sulphur content determination (tsc), the walkley black wet oxidation method using a soxhlet extractor, for total organic carbon (toc) estimation and the rock-eval pyrolysis technique. the rock-eval pyrolysis technique is used for the anhydrous pyrolysis of source rocks that enables the chemical composition of kerogen, and hence its hydrocarbon potential to be determined (espitalie mailto:alexander.ogbamikhumi@uniben.edu alexander, o., et al./ jgeet vol 04 no 04/2019 243 et. al., 1985; peters, 1986). parameters estimated mathematically from results of the pyrolysis process for further evaluation include; tmax ,s1, s2, s3, , hi, pi and oi. fig. 1. geological map of nigeria showing the anambra basin and the study area (abubakar, 2014). 3. results the geochemical analysis results of the samples are presented in the table 1. toc is the total amount of insoluble organic material or kerogen present in the rock, and it is expressed as a percentage in weight (toc wt.%). it is a source quality index that qualifies a rock sample as either being a potential source of hydrocarbon or not. tsc represent the total amount of sulphur in the sample. the sulphur content in a rock sample is associated with fauna abundant as we move from the continent to the deep marine. therefore, it can be used as an index to predict the environment in which the sample was deposited. the som represent the extractable organic constituent in the sample. s1 captures the free hydrocarbon constituent in the analyzed samples i.e the organic matter that has been completely transformed to hydrocarbon. s2 is defined by the generated hydrocarbon that are released by thermal cracking of nonvolatile constituent of organic matter, which give an insight to the potential amount of producible hydrocarbon in the rock if sediment burial and maturation continues.s3 is the total quantity of generated co2, that account for the oxygen richness of kerogen, and is rely upon to estimate the oxygen index. tmax is the temperature at which the greatest amount of hydrocarbon is released from kerogen during the pyrolysis process. this happens at the top of s2 peak, and it is an index of sediment maturity, which is dependent on the kerogen type. hi is the ratio of s2 hydrogen to toc in grams. hi is a source rock hydrocarbon richness index. oi is the ratio of s3 hydrogen to total organic carbon. gp represent the total free hydrocarbon generated from pyrolysis of the samples and the existing hydrocarbon in the samples. pi represent the ratio of the free hydrocarbon to the potential hydrocarbon yield. this parameter is an index that account for organic matter evolution. table 1 results of the geochemical analysis toc, tc, ts and som are in (wt. %), s1, s2, s3 and hi are in mghc/g som – soluble organic matter tmax – maximum temperature (0c) toc – total organic carbon mghc/g – milligram hydrocarbon per gram pi – production index hi – hydrogen index wt% weight percent oi – oxygen index (mgco2/g) tsc – total sulphur content mgco2/g – milligram carbon dioxide per gram samples toc s1 s2 s3 tsc tmax gp pi hi oi som 1 1.82 0.29 3.37 0.91 0.36 424 3.66 0.08 185 50 1050 2 3.04 0.56 12.82 1.25 0.39 417 13.38 0.04 422 41 1330 3 2.44 0.32 3.34 1.43 0.67 418 3.66 0.09 137 59 1870 4 0.81 0.08 0.25 1.09 0.81 470 0.33 0.24 31 135 2960 5 2.30 0.49 4.10 1.42 0.79 421 4.59 0.11 178 62 2840 e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 4 no 4 2019 244 alexander, o., et al./ jgeet vol 04 no 04/2019 fig 2. hydrogen index versus oxygen index plot showing the type of organic matter. modified from van krevelen diagram (after akande, 2012) fig 3. plot of tsc against toc indicating various aquatic conditions of deposition (modified from leventhal, 1983) fig 4. palynomorphs distribution chart table 2 summary of palynostratigraphic zonation, age and environment of deposition. sample no elevation (m) zonation (after evamy et al., 1978) characteristics age depositional environment 5 155 palynozone 200 spot occurrences of cyathidites minor, rugulatisporites caperatus, lycopodium sp, monocolpollenites sphaeroidites early paleocene 4 154 3 151 2 148 palynozone 100 occurrence of foveotriletes margaritae, proxapertites operculatus, longapertites marginatus, buttinia andreevi late maastrichtian continental 1 146 alexander, o., et al./ jgeet vol 04 no 04/2019 245 the plot of hydrogen index versus oxygen index is a graphical means of highlighting the hydrocarbon type the source rock is expected to generate (figure 2). the hydrogen index is dependent on the kerogen type present in a source rock i.e the higher the hydrogen index, the greater the tendency for the source rock to yield oil and vice versa for gas. figure 3 present the graphical plot of total sulphur content against total organic carbon. this plot is a means of interpreting the possible environment of deposition of the analyzed rock sample. the results of palynological analysis is presented in figure 4 and summarized in table 2. 4. discussions 4.1 source quality and kerogen type tissot and welte (1984) and hunt (1979), proposed 0.5wt% as the minimum threshold value for a rock to be regarded as a petroleum source rock. as presented in table 2, the toc of the samples ranges from 0.81 to 3.04 w.t% (2.08wt.% average), which exceeds the threshold value of 0.5wt.%. this suggests that the samples are good to very good source rocks and is similar to report of earlier workers that study the source potentials of the mamu formation and the nkporo shales (babatunde, 2010). source rocks genetic potential that is below 2mghc/g are indicative of minor oil content but with some potential gas, while those with genetic potential of 2 – 6mghc/g have some reasonable oil potential (tissot and welte, 1987; akande et. al., 2005). the genetic potential values for the samples ranges from 0.33 to 13.38 mghc/g (5.12 mghc/g average), which indicates that they have infinitesimal oil but some gas potential. the kerogen type present in a source rock determines its hydrogen index. many organisms contribute to the organic matter present in petroleum source rocks and they differ in their organic matter and total hydrogen contents. the preserved organic matter exhibits parallel diversity that are further modified overtime into gas or oil (dow, 1977). laughrey (2009) proposed that source rocks with hi greater than 600 mghc/g will generate oil, while those with hi between 200 and 600 mghc/g will generate wet gas (oil and gas). rocks with hi values between 50 and 200 mghc/g will generate gas and those with hi values less than 50 mghc/g are inert. the hi value for the studied samples ranges from 31 to 422 mghc/g (190.6 mghc/g average) suggesting that the source rock is gas and oil prone. the plot of hi against oi in the modified van krevelen diagram in figure 2, also reveals that studied samples are predominantly type iii/ii kerogen. this implies that the samples are majorly oil-gas prone source rocks and is similar to reports of akaegbogbi (2000). 4.2 source rock maturation maturation is the process of chemical change in sedimentary organic matter due to burial, i.e. the action of increasing temperature and pressure over geological time (miles, 1989). the concentration and distribution of the hydrocarbon contained in a particular source depends on both the type of the organic matter and its degree of thermal maturation. peter and cassa (1994) proposed that source rocks with tmax values of less than 435oc are immature, while those with tmax value of between 435470oc are mature and those above 470oc are post mature. for the studied samples, the value ranges from 417 to 4700c (430oc average). this suggests that majority of the samples are immature and are similar to the report of ogala (2011) for the maastrichtian mamu formation of the anambra basin. 4.3 paleo-environment interpretation the paleo-depositional environment of a rock can be determined by the abundance of ancient life forms recoverable from sample analysis, believed to have thrived in the same environment where the rock was deposited. from the palynological evaluation results (figure 4 and table 2, the outcrop sediments were predominantly dominated by land derived pollens and spores. according to schrank (1984), an assemblage of palynomorph with a high content of pollens and spores indicates a terrestrial influence and vice versa. based on this observation, the outcrop was characterized by the presence of terrestrial pollens and spores such as longapertites vaneendenburgi, foveotriletes margaritae, echitriporites trianguliformis, cingulatisporites ornatus, erecipites sp., longapertites sp., liliacidites sp., lycopodium sp, cyathidites minor, echitriporites trianguliformis, cupaniedites sp indicates continental environment. this depositional environment is also supported by the paucity of foraminiferal species over these samples. the nonrecovery of foraminifera is also attributable to the lithology of the samples, deposited in a continental environment where bottom conditions were not conducive for the preservation of foraminiferal species. the cross plot of tsc versus toc parameters derived from the organic geochemical analysis in figure 3, exclusively shows a normal marine depositional environment for the samples, which tends towards a terrestrial environment. both results from palynological and geochemical analysis is suggestive of the proximal end of the transitional depositional environment for the studied samples. 4.4 biozonation and age determination from the results in figure 4 and table 2, two palynozone were defined; 4.4.1 palynozone 100 / assemblage zone: iii this zone was defined within the intervals 145 – 148 m. it is the oldest assemblage zone recognized in the analyzed portion of the outcrop. the preponderance of typical late maastrichtian forms such as syncolporites sp, rugulatisporites caperatus, foveotriletes margaritae, proxapertites operculatus, longapertites sp., mauritidites crassibaculatusi, longapertites marginatus, buttinia andreevi, longapertites vaneendenburgi, monocolpites marginatus recovered within this section confirms this assemblage zone assignment which is dated late maastrichtian. 4.4.2 palynozone 200 / assemblage zone iv the zone is defined within the interval 148 – 155 m. recorded at interval are spot occurrences of cyathidites minor, rugulatisporites caperatus, lycopodium sp, monocolpollenites sphaeroidites, monocolpites marginatus and longapertites marginatus, suggest an early paleocene age. the age assignment follows the informal assemblage zones classification of palynozone 100-200 by evamy et al (1978), this zone is equivalent to the zone iiiiv of legoux (1978). the studied sections of the outcrop ranges in age from late maastrichtianearly paleocene and the predominance of terrestrial pollen and spores, paucity of dinocysts and forams indicates that the paleo-depositional environment is continental to transitional. this corresponds to the depositional environment established in literature of the mamu formation (obaje, 2009). 246 alexander, o. et al./ jgeet vol 4 no 4/2019 5. conclusion the results of organic geochemical and palynological evaluation of the source potentials of the studied exposure in okpekpe revealed that the shales have a good to very good source potentials and are typically made of a type iii/ii kerogen constituent capable of generating gas and oil when attained maturation. both analysis results revealed that the rock was most likely deposited close to the terrestrial end of a transitional environment. palynological evaluation showed that the studied rock exposure ranges in age from late maastrichtianearly paleocene. this was based on index spores, pollens and dinoflagellates. these include longapertites marginatus, cingulatisporites ornatus, proxapertites cursus, echitriporites trianguliformis, cyathidites minor, rugulatisporites caperatus, all of which are dated to be of maastrichtian – paleocene age which agrees with the age of the mamu formation in the anambra basin. references abubakar, m.b., 2014. petroleum potentials of the nigerian benue trough and anambra basin: a regional synthesis. natural resources scientific research 5(1), 25-58. akaegbobi, i. m., 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for evaluating petroleum source rock using programmed pyrolysis.american association of petroleum geologists, bulletin. 70(3), 318 – 329. peters, k. e., cassa, m. r., 1994. applied source rock geochemistry. in: the petroleum system – from alexander, o., et al./ jgeet vol 04 no 04/2019 247 source to trap aapg memoir, 60, tulsa, ok, 93-117 shrank, e., 1984. organic geochemical and palynological studies of dekhia shales profile (late cretaceous) in southern egypt. berliner geowiss, abh., 50, 189-207. tissot, b., welte, d., 1984. petroleum formation and occurrence (2nd ed.): springer-verlag, berlin. traverse, a., 1988. palaeopalynology: unwin hyman, london. wood, g.d., gabriel, a.m., lawson, j.c., 1996. palynological techniques—processing and microscopy. in: palynology: principles and applications. american association of stratigraphic palynologists foundation, dallas 1, 29–50. © 2016 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 178 erfando, t. and herawati, i./ jgeet vol 02 no 02/2017 reviewing analysis of petroleum downstream industry potential in riau province tomi erfando 1, *, ira herawati 1 1 petroleum engineering department, universitas islam riau abstract petroleum downstream industry in riau province is still not optimal. the data shows that from 98,892,755 barrels lifting oil each year only 62,050,000 barrels could be processed in refinery unit ii dumai operated by pt pertamina. there is a potential of 35-40% of downstream industry. indonesian government through the ministry of energy and mineral resources declared the construction of a mini refinery to boost oil processing output in the downstream sector. a feasibility study of development plan mini refinery is needed. the study includes production capacity analysis, product analysis, development & operational refinery analysis and economic analysis. the results obtained by the mini refinery capacity is planned to process crude oil 6000 bopd with the products produced are gasoline, kerosene, diesel and oil. investment cost consist of is capital cost us $ 104419784 and operating cost us $ 13766734 each year with net profit earned us $ 12330063/year and rate of return from investment 11.63% keywords: petroleum, downstream industry, riau, mini refinery 1. introduction riau province is one of the biggest oil and gas producers in indonesia. the oil and gas comes from several operational areas spread in bengkalis regency, siak regency, pelalawan regency, indragiri hulu regency, kampar regency, rokan hulu regency, rokan hilir regency and meranti islands regency. based on the official report released by the ministry of energy and mineral resources (lifting.migas.esdm.go.id), riau province's crude oil lifting for 2016 reached 98,892,755.93 barrels, this production is the highest in indonesia. meanwhile, natural gas production is estimated at 18,814,803.69 mmbtu. the large potentials in the oil and gas sector should be developed to increase local and national revenues. oil and gas can be used as basis for regional economic development, so that oil and gas activities can be used as a stimulus to move the local economy (murbuni, 2001). in the upstream sector (exploitation), some fields in riau province have entered on tertiary recovery or enhancing oil recovery. meanwhile, in the downstream sector, it can be said that it is not optimum yet because in riau province there is only one petroleum refinery unit ii managed by pt pertamina in dumai city. the refinery has an installed capacity of 170,000 barrels per day (risdiyanta, 2015). if we calculate a year only able to process 62.05 million barrels of oil produced from oil and gas fields in riau. there are still 35-40% unprocessed oil production. one of the efforts to improve performance in the downstream sector of oil and gas is to encourage the development of industries based on the processing of oil and natural gas (directorate general, oil and gas, ministry of energy and mineral resources 2015). this is stated in uu no. 3 tahun 2014 on industry, the role of government in pushing forward industrial sector forward done in a planned and arranged systematically in a planning document. the plan set by indonesia government for riau province in the downstream sector is constructing of a mini refinery with a capacity of less than 20,000 barrels per day. regulation of the minister of energy and mineral resources of the republic of indonesia number 22 of 2016 concerning the implementation of small-scale oil refinery (mini refinery) where there are two development mini refinery plans, cluster ii selat panjang covering emp melacca strait and petroselat and cluster iii riau covering tonga, siak, langgak, west area and kisaran. the construction of a mini refinery has several considerations which are required lower cost and shorter time than building a large refinery, increasing fuel demand, close proximity to oil production wells that will save transport shipping cost and environmentally friendly minimum water and solid waste or air pollution (sulistyaningrum, 2015). a preliminary analysis of development plans is required to provide a clearer picture of the technical and economic aspects of the project. this research is also expected to be a reference by stakeholders in taking policy. the policies are * corresponding author : tomierfando@eng.uir.ac.id received: may 15, 2017. revised : may 25, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.304 erfando, t. and herawati, i./ jgeet vol 02 no 02/2017 179 expected to increase local revenue from not optimized yet oil and gas production. 2. methodology this study is a descriptive research, which will provide an overview of the potential of downstream industries in riau province. the problem identification is viewed from the not optimal processing of petroleum production in the downstream sector. currently downstream capacity is only capable of processing 60-65% of petroleum production through the presence of pertamina refinery in dumai and reviewing the plan issued by the government for the construction of a mini refinery as one of the upgrading efforts in the downstream industry. focus of the research is cluster ii covering tonga, siak, pendalian, langgak, west area and kisaran. one of the oil samples taken from siak field, sumatran light crude (slc). testing of distilled point is done in the petroleum engineering laboratory of universitas islam riau. the data used are primary data from the laboratory test results for the distillation point and secondary data from several sources such as production data from the lifting report of the ministry of energy and mineral resources, legal products applicable in indonesia in the form of laws, government regulations and minister regulations. other secondary data are obtained from a variety of sources that can be trusted for its validity. the analysis undertaken to get conclusions are as follows the first assessment of the ability of the supply of raw materials to determine the production capacity in the downstream industry. the second determination of the product type (fraction) generated through the sample test. the third determination of the amount of costs required in the construction of a mini refinery, the cost will be grouped into two namely the cost of capital and operating costs (non-capital). the calculation method for the payment of capital costs by using linear depreciation over several years of production. the fourth economic analysis of the project involves adding value from raw materials to processed products and return on investment. the oil and gas sector comprises three business groups: upstream, intermediate and downstream. the upstream sector is getting mining permits, exploration and exploitation. refining, processing, and marketing activities are downstream oil and gas industry activities (nugroho, 2004). in this research will focus on the downstream industry of oil and gas is refining/ processing of petroleum. processing flow in mini refinery operations has many configurations that match the needs and desired output product (mcguire, 2012). this is an example of a processing flow on a mini refinery fig. 1. operating processes at oil refineries can be classified into 5 stages (risdyanta, 2015), as follows: 1. distillation process, is a distillation process based on the difference of boiling point; this process takes place in the atmospheric distillation column and the vacuum distillation column. vacuum distillation process is a second phase of the crude oil processing (ocic et al, 2000). 2. the conversion process, which is a process for changing the size and structure of hydrocarbon compounds. included in this process are: a. decomposition by thermal cracking and catalyst (thermal and catalytic cracking) b. unification through alkylation process and alteration polymerization through fig. 1. example of processing flow on a mini refinery (mcguire, 2014) 180 erfando, t. and herawati, i./ jgeet vol 02 no 02/2017 isomerization process and catalytic reforming. 3. treatment process. this is intended to prepare the hydrocarbon fractions for further processing, also to be processed into the final product. 4. formulation and mixing (blending) process, is the process of mixing hydrocarbon fractions and addition of additive to obtain the final product with certain specifications. 5. other processes include waste treatment, sour-water stripping, sulfur recovery, heating, cooling, hydrogen-making and other supporting processes. the implementation of the economic feasibility study for modern oil and gas projects is divided into main scopes (shaallan, 2012): 1. economic feasibility study 2. petroleum industry 3. risk and uncertainty analysis 4. use of software 5. contract of oil and gas 6. case study in this study only discussed about economic feasibility studies and case studies on the downstream oil and gas industry. 3. result and discussion 3.1 production capacity analysis supply of raw materials becomes one of main factors in the consideration in development of downstream industry of oil and gas sector. the raw material is the availability of crude oil and natural gas in the operating area that goes into the planning. based on the policy issued by the ministry of energy and mineral resources of the republic of indonesia there are 2 clusters which become development planning in riau province, namely cluster ii and iii. cluster ii in strait panjang covers the work area of emp melacca strait and petroselat and cluster iii riau covers the work area of tonga, siak, pendalian, langgak, west area and kisaran. in this research will focus on cluster iii riau. samples tested in the petroleum engineering laboratory of islamic university of riau. production capacity of each working area in cluster iii, as shown in the fig. 2 below: fig. 2. production capacity of each working area in cluster iii mini refineries offer the possibility of phased construction and the flexibility of quick and easy upgrade to reflect changes in product demand (mama, 2015). total production for mini cluster ii refinery work area is 6300 bopd. the details are tonga 1200 bopd, siak 1500 bopd, langgak 400 bopd, pendalian 900 bopd, west area of 1000 bopd and kisaran estimated production will reach 1300 bopd. the ability of raw material supply in the form of crude oil is a reference in the development of production capacity for mini refinery development in cluster iii which is 6000 bopd. this figure considers the condition in the future, whereas principle oil production will decrease (decline) if special treatment has not done in the form of addition of production well, secondary and tertiary recovery. in the other side, 3.2 refinery products analysis based on the official report released by the ministry of energy and mineral resources (2016) the type of oil produced in riau is generally sumatran light crude or slc. one of the slc samples taken directly in the field was tested by crude oil destilation. this test aim to determine fractions generated from crude oil. however, limitation of the testing equipment it is not being used to obtain the distilled distillation result but rather the combination of all the distillates which are the refluxable feedstock to obtain the fractionated fuel. the table below test results of table 1. distillation test results one of slc sample weight of crude oil (gr) crude oil density (gr/cc) bubble point temper ature ( o c) initial boiling point temper ature ( o c) o api resi dua l wei ght (gr) 79.11 0.791 180 185 47.6 68 in this experiment to get the distillation result from crude oil, the crude oil sample was heated by using electric heater and crude oil destilator. before getting the distillation results, the sample will pass the bubble point. it is the temperature at which the gas phase begins to release from the oil, marked by appared bubble burst first time. after passing the bubble point the sample will reach the boiling point core, it is the temperature at which the first droplet of the distillation. after reaching the initial boiling point the sample will continue to produce the distillate until it reaches the end boiling point, it is the temperature at which the sample no longer produces the distillate and only residual remains. based on our experiment the bubble point temperature obtained is 180 ° c, the initial boiling point temperature obtained 185 ° c and the boiling point end temperature obtained is 250 ° c. additional data is required for test result to be divided into distillation fractions, the data obtained from the results published by emergency canada, 0 200 400 600 800 1000 1200 1400 1600 b o p d working area erfando, t. and herawati, i./ jgeet vol 02 no 02/2017 181 emergencies science and technology division (2006) divide into 5 main groups as follows: in mini refinery operations it is advisable to process petroleum into products with simple straightforward atmospheric distillation aimed at reducing costs. this simple distillation is diesel fuel and / or kerosene production with by-products of gasoline and naphtha. however, it is not possible to make a second phase vacuum distillation can filter components of fuel oil from the first atmospheric tower into clean diesel oil and heavy residual oil. fig. 3. fraction of slc distillation the addition of a secondary process can provide better value and quality for the final product to be produced (risdiyanta, 2015). the process will provide consequences required investment cost that will increase. these secondary processes include cracking, catalic reforming, polymerization and so on. in future, as for the quality of the refined products, specifications are no longer set by customers and vehicle manufacturers only, but also by environmental regulations. to reduce emissions from automobiles, reformulated gasoline and diesel fuel, with low sulfur and high cetane number, have (stanislaus, a., qabazard, h., & absi-halabi, m., 2000). 3.3 development & operational refinery analysis the refinery configuration refers to a study by jones (2004) who has prepared a mini refinery project plan with the same capacity of 6000 bopd. in the refinery development project the main component of cost are cash inflow and cash outflow (shaallan, 2012). cash inflow is derived from the proceeds from sale of product from the refinery. cash outflow (expenses incurred) consists of capital cost for building refineries, refinery operating cost and purchases of raw materials, state taxes to be paid on the based on agreed contacts. the cost of capital will include several working groups in construction of this mini refinery as follows: table 2. capital cost estimate scope cost (us$) engineering 6530832 site facilities 27061760 process units crude unit 8037680 naphtha hds 6324000 reformer 18228000 unicracker 16120000 other infrastructure 1987720 contingency 13108499 working capital 7021293 total project cost 104419784 fig. 4. percentage capital cost in table 2 and fig. 4, the greatest cost is required for construction of process unit (crude unit, naphtha hds, reformer, unicracker) of us $ 48709680 or 48% of total capital cost. construction of site facilities have a percentage of 26% equivalent to us $ 27061760. project work has aspects of uncertainty especially the price of raw materials in the market for it needs to be taken into account unexpected costs in the mini refinery work, the unexpected cost is the third largest cost group to be spent in capital investments worth us $ 13108499 (13% of total capital cost). the cost of mini refinery work is estimated to be 7% of the total capital cost or us $ 7021293. engineering design in feasibility study will cost us $ 6530832, this cost has a 6% percentage of the cost of capital. the last group is the cost of operating support facilities such as communication networks, security systems, monitoring and others costing us $ 1987720 only 2% of the cost of capital. table 3. daily operation cost scope cost (us$) natural gas 15195 electricity 2702 water 211 chemical 8859 labor 9759 maintenance supplies 992 total operation cost 37717 light naphtha 3% heavy naphtha 9% kerosene 11% gas oil 20%reduced crude 57% engineering, 6% site facilities, 26% process unit , 47 % other infrastruct ure, 2% contingency, 13% working capital, 7% 182 erfando, t. and herawati, i./ jgeet vol 02 no 02/2017 fig. 5. daily operation cost after the refinery is built, it is expensive to operated. fixed cost include personnel, maintenance, insurance, administration and depreciation. variable cost include crude feedstock, chemicals and additive, catalysts, maintenance, utilities and purchased energy (such as natural gas and electricity). to be economically viable, the refinery must keep operating costs such as energy, labor and maintenance to a minimum (canadian fuels association, 2013; jones & pujado, 2006) table 3 and fig. 5 show the amount of operating costs consisting of purchasing natural gas as the main energy source, electricity, water, chemicals, labor and supply management needed per day. in the operation of mini refineries would require a considerable energy, certainly can not depend on electricity supply from pln for it needs to be allocated gas purchase costs for the plant. gas can come from existing fields in the operating area, the cost of which is set at us $ 15195 or 40% of operating costs. electricity needs are still supported by electricity coming from pln where the allocation is not large, the funding for electricity originating from pln is estimated at us $ 2702. labor cost is the second highest persentage of 26% or us $ 9759. chemicals as a supporter of processing raw materials daily cost us $ 8859 (23%). maintenance supplies and water are not significant at only 3% (us $ 992) and 1% for us $ 211 of operating cost on a daily basis. if the operating expenses are calculated within a year then total operating cost is us $ 13766734. 3.4 economic analysis the most widely used measure economic performance in the refining industry is return on investment (roi) (pirog, 2007). this section will focus on that parameter. the calculation can certainly be a consideration for investors and governments in taking policy towards the project. the following shows the calculation results of the details of investment components. table 3. rate of return investment item(s) amount (us $) total project cost 104419784 total operation cost (13766734) raw material (131400000) depreciation (6526236) product added value 163834448 net profit 12330063 rate of return 11.63% increase of product value is obtained from sale of processed products in this case gasoline, kerosene, diesel and oil with total sales of us $ 163834448. the production capacity of mini refinery to be built is 6000 bopd operational time in a year 365 days then the need for raw materials is 2190000 barrel assuming average world oil price of us $ 60 / barrel then the total expenditure for raw materials is us $ 131400000. depreciation (straight line method) from mini refinery is us $ 6526236 / year, the value is the capital cost divided by the estimate mini refinery project time, that is assumed to be 16 years (jones, 2004). net profit is derived from the total value added of the product produced minus cost of raw materials, operating cost, and depreciation. the addition of the value of each barrel final product generated amounted to us $ 15.85. the rate of return on investment of 11.63%, this value is low in oil and gas projects usually set a return of investment of 30%. the low rate of return on this investment can be concluded that the construction of a mini refinery is not economical (utami, 2013). the economic feasibility of a project is not the only factor to decide whether to build or not but must look to local need of a region (mcguire, 2012). during the construction, commissioning and operation of the refinery, massive labour employment, both skilled and unskilled was generated in the market. this project also generated the secondary employment for other business like transport, manufacturing, power, market for the daily consumption by the labour, housing & construction in the project location (chaudhuri & ray, 2016) 4. conclutions based on review for , the conclusion reach as follow: 1. the production capacity of mini refinery is 6000 bopd 2. types of final product from mini refinery are gasoline, kerosene, diesel, and oil 3. total capital cost of mini refinery development is us $ 104419784 and annual operating cost is us $ 13766734 4. total annual net income is us $ 12330063 and return on investment 11.63% natural gas 40% electricity 7% water 1% chemicals 23% labor 26% maintanance supplies 3% erfando, t. and herawati, i./ jgeet vol 02 no 02/2017 183 references chaudhuri, s. & ray, s., 2016. social and economic impact analysis of vadimar refinery of essar oil : the case of a mega refinery p.17. indira gandhi institute of development research (igidr). mumbai cross, p., desrochers, p. & shimizu, h., 2013. the economic of petroleum refining understanding the business of processing crude oil into fuels and other value added product. canadian fuels association. directorate general, oil and gas, ministry of energy and mineral resources, 2015. status sumber daya alam migas di indonesia: cadangan, produksi dan outlook jangka menengah dan jangka panjang. presented at public discussion for essential services reform (iesr), jakarta, 23 september. environment canada, emergencies science and technology division, 2006. sumateran light. http://www.etccte.ec.gc.ca/databases/oilproperties/pdf/web _sumatran_light.pdf jones, d.s.j. & pujado, p.r. (ed), 2006. handbook of petroleum processing. springer. aa dordrecht, netherlands. jones, j.d., 2004. feasibility study for a petroleum refinery for the jicarilla apache (rep.), final project technical narrative. ministery of energy and mineral resource, 2016. peraturan menteri energi dan sumber daya mineral no. 22 tahun 2016 tentang pembangunan kilang mini. http:// jdih.esdm.go.id/view/download.php?page=p eraturan&id=1542 ministery of energy and mineral resources, 2016. perhitungan realisasi alokasi lifting minyak mentah kumulatuif s/d triwulan iv. http://lifting.migas.esdm.go.id mama, c. k., 2015. analysis: mini refining investment oppurtunities in nigeria. africa's barrel equations p.8. mcguire, dan, 2012. mini-refinery feasibility overview. p.5. refinery equipment, texas. murbuni, sunoto, 2001. pemberdayaan potensi daerah dalam kegiatan operasi industri hulu migas nasional. proceeding simposium nasional iatmi, yogyakarta, 3-5 oktober. nugroho, h., 2004. pengembangan industri hilir gas bumi indonesia: tantangan dan gagasan. perencanaan pembangunan no. ix/september. ocic, o.j., gehrecke, s.k., & perisic, b.j., 2000. energy management in an oil refinery. world petroleum congress. pirog, robert, 2007. petroleum refining: economic performance and challenges for the future. crs report for congress risdiyanta, 2015. mengenal kilang pengolahan minyak bumi (refinary) di indonesia. 5(4): 46-54 shaallan, h. y., 2012. economic feasibility study for petroleum project (practical aspects). journal of petroleum research & studies. 5: 26-47 sulistyaningrum, eny, 2015. peranan industri pengolahan minyak bumi melalui pembangunan kilang mini dalam meningkatkan perekonomian. dipaparkan pada pertemuan ikatan sarjana ekonomi indonesia cabang surabaya. stanislaus, a., qabazard, h., & absi-halabi, m., 2000. refinery of the future. world petroleum congres. undang-undang no. 3 tahun 2014 tentang perindustrian. http://peraturan.go.id/inc/view/11e44c4e40b 02a40a365313231323530.html utami, d.s. & kamila, i. 2013. darurat pembangunan kilang baru. corporate communication sekretaris perseroan pt pertamina. jakarta. juli. hlm. 19 http://lifting.migas.esdm.go.id/ 1. introduction 2. methodology 3. result and discussion 3.1 production capacity analysis 3.2 refinery products analysis 3.3 development & operational refinery analysis 3.4 economic analysis 4. conclutions references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 102 hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 urban green space development strategy reconverting gas station to public parks in the city of surabaya, indonesia valid hasyimi 1 *, djoko santoso abi suroso 2 1 urban planning, faculty of environmental design, king abdulaziz university. 2 regional and rural planning, school of architecture, planning, and policy development, itb. . abstract urban green space development has become a challenging task for city governments especially in indonesia, due to high prices of land around urban centers. on the other hand, there are inconsistencies between land use and land allocation within the city planning. in surabaya city, quite a lot of gas stations were built on areas which are originally intended for green open spaces. surabaya city municipality is strongly committed to reconvert gas station areas to green open spaces as determined in the plan. innovative strategies have enabled the city government to reconvert 13 gas stations to public parks. this paper analyzes the implementation process of the urban green space reconversion policy, describing the historical details of the issues, the taking over of land from gas station owners, and the park development and campaigning. discussion also includes the most influential factors in this success story. keywords: reconversion, gas station, urban green space, policy 1. introduction high urban growth is identified as the main reason of the lack of urban green space in the center of city, whereas city growth must consider the economic and environmental balance. urban planning without considering environmental aspects will cause eco-living degradation like pollution, increased urban heat, higher vulnerability to disasters, etc. the amount of green space close to where people live has a significant relation with their perceived health (maas et al., 2006). green space is suggested to promote health by providing the means for restoring the mind from mental fatigue (kaplan, 2001), serving as a resource for physical activities (björk et al., 2008). furthermore, various studies have labeled urban green space as a resource that helps reduce stress level, e.g. (grahn and stigsdotter, 2003; nielsen and hansen, 2007; ulrich, 2006). the relation between green space and health is also becoming a visible political agenda (schipperijn et al., 2010). many recent national and local health policies, as well as city planning policies, are mentioning positive impacts of the use of urban green space. however, translating these aims into concrete actions for city planning or urban green space management is challenging while documentation and knowledge on how to implement this agenda is scarce to be found in any paper. so the question is how to effectively increase urban green space areas in city centers in an innovative way? what is the most influential factor that influence the success of such projects? 1.1 surabaya city success story surabaya has experienced the worst environmental issues in 1990 when significant increase in air pollution and urban heat had made the city no longer comfortable for living. high urban development without considering the environmental effects had impacted the living quality of the residents. in facing the issues, the municipal government had decided to evaluate the city plan implementation and found out violations. many commercial activities, mostly gas stations, were carried out on land that were supposed to function as green areas. to reconvert gas stations to their original land allocation, the municipal government had to deal with the facts that these gas stations have very high economic value because of their strategic location, and the land generally has lost its fertility to grow plants because of the concrete hardening and the pollutants caused by rusting or leaking tanks underneath. this success story, policy, innovation, and the implementation process of how surabaya increased its urban green spaces in city centers needs to be well documented for reference and good lesson to learn. * corresponding author : valid.hasyimi@ymail.com tel.:+966582 969095 received: 2 may 2017. revised : 25 may 2017, accepted: 31 may 2017, 2016, published: 1 june 2017 doi: 10.24273/jgeet.2017.2.2.306 mailto:valid.hasyimi@ymail.com hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 103 the objectives of this research are: a. to analyze land use reconversion process from gas station to urban green space. b. to analyze public green parks development from dismantled gas station and its impact to the environment. c. to determine the most influential factor that influence successful implementation of reconversion policy in surabaya city. 2. literature review public policy is a proposed course of action of a person, group, or government within a given environment providing obstacles and opportunities which the policy was proposed to utilize and overcome in an effort to reach a goal or realize an objective or a purpose. based on theories defined by experts, there are 7 factors that influence successful policy implementation: policy content & purpose, policy actor, communication, organization, supporting resources, leadership, and socialeconomy-political condition. urban green space is defined as all publicly owned and publicly accessible open space with a high degree of cover by vegetation, e.g. public parks, woodlands, nature areas and other green spaces (schipperijn et al., 2010; thaiutsa et al., 2008). public parks in this paper is defined as urban green space that can be used for recreational purposes or outdoor activities, where 60% of its total area must be covered by vegetation (municipal regulation of surabaya no. 7/2002). based on fig. 1, the seven influential factors are synthesized into four new factors/indicators that are considered as the most influential factors in the implementation of reconversion. a) background issue and policy purpose a well defined issue serves as an important background/reason for decision makers in creating a policy that can effectively solve the said problem in the society. b) leadership the role of a leader in the implementation of the policy, in this context is the major of surabaya, is to act as initiator, resources manager, and value keeper. c) municipal internal factor the success of the implementation is also influenced by the support of the city communication pattern, and its resources. d) municipal external factor planning and implementing a policy needs political and public support, and to ensure maximum public benefits these parties must also monitor the implementaion. socioeconomic-cultural aspects are also considered in the external factors. these four factors above will be further synthesized to obtain specific parameters that are used as analysis benchmark. the city regulation no.7/2002 about urban green space management stated that the municipal government shall stop any permit of the use of urban green space area for any non-urban green area use and shall commit to expand urban green space. 3. methods 3.1 study area the study area in this research is the whole surabaya city administrative region, which administratively is the capital city of east java province. this research specifically will focus on 13 urban green spaces in surabaya that were created from dismantled gas stations, of which 6 of them were developed as public parks. the substantial scope of this research will cover: a. issues that encourage municipality government to reconvert gas stations to public green spaces. b. reconversion implementation strategy; starting from decision making process, reconverson process, to development process of the parks so that they are ready to use. c. influential factors in the surabaya successful implementation of its reconversion policy. d. impacts of the reconversion from socioeconomic and environmental aspects. fig 1. synthesis of influential factors in policy implementation process. 104 hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 3.2 data collection to achieve the research goal, data was collected through primary survey using in-depth interview and observation. secondary survey in the forms of literature study and institutional survey was performed to complete the overall data. literatures reviewed in this research include books, regulations, and other references to develop the necessary theories/hypothesis and to gain understanding of the regulations before the primary survey was conducted. survey was also carried out to institutions that have direct relation with the activities in this reconversion implementation. in social sciences, triangulation is often used to indicate that two (or more) methods are used in a study in order to check the results of one and the same subject. the purpose of triangulation in qualitative research is to increase the credibility and validity of the results. there are several types of triangulation (denzin, 1978) where in this research actor triangulation (government ngo business owners) and methodological triangulation (in depth interview, documents, and observation) were used. in-depth interview was arranged with stakeholders that have direct relation with this reconversion implementation. they were representatives from city government, former government, ngos, and experts. observations were made at the reconverted 13 urban green spaces to note the the physical condition and people activities in and outside the parks. 3.3 analysis method to achive the main objectives, this research used two types of qualitative analysis, which are descriptive-historic analysis to evaluate the development process from gas station to urban green space and analytic hierarchy process (ahp) to examine influential factors in surabaya successful reconversion implementation, see fig. 2. to analyze the development process of urban green spaces from dismantled gas stations using descriptive-historic analysis, every stage of the process is described by referring to the four synthesis factors that influence the successful reconversion. analytic hierarchy process (ahp) introduced by thomas saaty (1980) is used to determine the most influential factor. ahp helps to capture both subjective and objective aspects of a qualitative data by setting priorities and synthesizing the results (becker et al., 2017). it is a very flexible and powerful tool because the scores, and therefore the final ranking, are obtained on the basis of the pairwise relative evaluations of both criteria and the options provided by the user (han et al., 2016). the ahp can thus be considered as tool that is able to translate the evaluations (both qualitative and quantitative) made by any user into a multicriteria ranking. in addition, the ahp is simple because there is no need of building a complex ex knowledge embedded in it. the ahp can be implemented in three simple consecutive steps: a. computing the vector of criteria weights b. computing the matrix of option scores c. ranking the options with ahp, all factors that are influential to the successful implementation of this reconversion are ranked and one factor in the first rank is considered as the most influential. experts assign the cardinal scores using their own subjective judgments. according to previous studies, such as (wey, 2015) the ahp method is useful for quantifying these subjective judgments when it is combined with fuzzy theory. table 5 shows the result of ahp procedure for the determination of weights, which are estimated by expert based on each study criterion. for example, expert 1 makes pairwise comparisons to obtain weights for the four factors. moreover, we donate the matrix by wf where f is and index of weight for the criteria/factors and e for the expert, with each expert having different weights for each criteria, they have to reach concencus in the evaluation process. 4. results and discussions 4.1. public green park development from dismantled gas stations. the purpose of this analysis is to describe in chronological order the surabaya public parks reconversion stages from dismantled gas station. details of this historical descriptive analysis will cover analysis of background issues that affected the creation of public park policy, policy formulation phase, implementation phase, and the development of the parks with their impacts to society. the analysis is structured in such a way that the implementation process can be divided to 2 fig 2. research framework. hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 105 parts: land conversion process, and parks development process. land reconversion process this analysis consists of 5 phases, which is shown in fig. 3. they are the emergence stage of issue, discussion stage of issue, decision taking stage, trial stage, and success land reconvertion stage. here is the explanation of each step. table 1 describes the analysis in every stage based on the synthesis of influential factors. i. emergence stage of issue the main issue that is being evaluated in this research is land reconversion and not land-use violation. when the land was initially utilized for gas stations, the former owners had obtained proper legal permits from the local government. sanctioning of violations can only be imposed if goverment has issued non-renewable permit of the said land. former owners had rented the land for commercial activities for decades, and had paid retribution based on legal permit issued by the government who has the authority to renew any land use rights/contracts for 10-20 years. ii. discussion stage of issue an important step in ensuring successful implementation of reconversion policy is to gain approval from the concerned parties. the city government had started early in engaging representatives of the affected society, related governmental bodies, and several environmental non-governmental institutions (ngos) in a dialogue forum to formulate issues and priorities. the head of bappeda (the regional development planning agency) had been strongly supportive of the reconversion plan, and as a result the mayor of surabaya was also convinced of the project. the combined team defined alternatives for implementing the policy. iii. decision making stage regulation number 7/2002 about urban green space management in surabaya was enacted on the december 2, 2002, after which the municipal government has the legal right to stop business activites of any gas station that violate the regulation. announcement was made to gas station owners through municipal letter no. 540/2256/402.1.2/2002 issued on december 31, 2002. because city government was not to renew commercial permit for land intended for green spaces, gas station owners were given one year leeway to relocate their bussiness when their permit expires. iv. court trial stage thirteen gas stations examined in this research were specifically selected because the owners had violated the regulation by keeping the operation of the stations when the permit expired. for not being cooperative, the municipal government closed down these stations, took over the land, and started the development of urban parks. three of the gas stations were owned by the municipal cooperative (koperasi pegawai negeri sipil pemkot surabaya). owners of the remaining ten stations filed a lawsuit against the municipal government and the head of surabaya civil service (pamong praja). the plaintiffs also lodged an appeal to the supreme court who finally ruled that surabaya municipal government reserved the right to reconvert the land in dispute and the ten owners had to relocate their business. v. land use taking-over stage based on supreme court ruling, in 2006 the municipal government of surabaya took over the 13 gas stations and reconverted the land to public green spaces. each of the parks were developed with different settings:  taman flora (flora park)  taman lansia (senior citizen park)  taman buah undaan (undaan park)  taman korea (korean park)  taman persahabatan (friendship park)  taman pelangi (rainbow park)  kombes m. duryat park  ngagel jaya utara street manyar park  krembangan barat/timur park  indrapura tam kalongan park  jaksa agung suprapto park  dr. soetomo street raya darmo park  sikatan street veteran park park development process analysis the development of urban green parks on the reclaimed land were broken down into four stages, see fig. 4. they are collaboration phase, soil refertilization phase, park development phase, and maintenance phase. table 2 describes the analysis in every stage based on the synthesis of influential factors. emergence stage of issue discussion stage of issue decision making stage court trial stage land use taking over stage fig 3. land reconversion process. 106 hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 table 1. land reconvertion analysis, analyzing every stage of land reconvertion process with the synthesis influential factors in policy implementation process. table 2. park development analysis, analyzing every stage of park development process with the synthesis influential factors in policy implementation process. hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 107 i. partnership engagement stage given the limited regional government budget allocated for development of public parks, the municipal government decided to fund parts of the project through public private partnership. this solution was considered as a new innovation because such scheme of funding was not yet common at the time. the following funding options were applied to different types of parks:  municipal fund (municipal budget and selfmanagement) the municipal government allocates certain yearly budget for developing and maintaining parks. parks that are financed by regional budget are passive parks which means that these parks are to function as green belt.  public private partnership the municipal government offered partnership to private sectors for financing development of parks. the common term used by the municipal government is for private parks. foster fathers were expected to fund the development and maintenance of active parks, and jointly the government and foster father could assign a certain theme. active parks are to be used by local residents for activities according to its theme. companies and private organizations participated in this project as foster fathers are pertamina, bank jatim, and korean businessmen association in indonesia. ii. soil re-fertilization stage surabaya municipal government collaborated with agricultural experts and the department of environmental studies of bogor agriculture university to restore soil fertility. illustration of the re-fertilization process in parks constructed from dismantled gas stations can be seen in the fig. 5 below. fig 5. illustration of land re-fertilization process. iii.park development stage during the parks construction period in 2005, the mayor of surabaya assgined a former regional spatial development superintendent named mrs. tri rismaharini as head of environmental department of surabaya. she had brought innovative ideas to attract investors to invest in the development of the parks, as well as to encourage people to take advantage of the newly built green spaces; especially the active parks (see table 3). table 3. park list and status. no parks name status 1 taman flora active 2 taman lansia active 3 taman buah undaan active 4 taman korea active 5 taman persahabatan active 6 taman pelangi active 7 kombes m. duryat passive 8 ngagel jaya utara manyar passive 9 krembangan barat/timur passive 10 indrapura kalongan passive 11 jaksa agung suprapto passive 12 dr. soetomo jl. raya darmo passive 13 sikatan jl. veteran passive active parks were designed in such a way that local communities can perform various relaxing activities, recreation, and physical exercise. each park features 60-90% vegetation cover of its total area, while the remaining 10-40% were constructed for park facitilites, public square, pathways, and seating areas. passive park was created as urban green belt without any facility for public activities partnership engagement stage soil re-fertilization stage park development stage post development & maintenance stage fig 4. park development process. 108 hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 because 90-100% of its area is covered by vegetation. iv.post development & maintenance stage fig. 6 below shows increased budget allocation for green spaces maintenance for years 2010-2013. the city government has built more parks within this period, and the increased budget indicates that the municipal government is committed to keep public parks well maintained. during the first few years of operation, the municipal government deployed security officers to guard and protect parks from obstructions, vandalism, nuisance, and thieves stealing park facilities. reports showed that assignment of security guards were effective in reducing violations and criminal acts in the parks. existence of city parks enhances the natural beauty of urban areas and encourages people to care about the environment. parks can also facilitate change in social behaviour where residents are more willing to do outdoor activities in the park rather than going to malls; and they are more aware of the importance of taking care of public facilities. 4.2. analysis of factors influencing the successful implementation of reconversion. this analysis examines factors affecting public green park reconversion by identifying components collected in the interview and secondary data. the aim is to gather information of collaboration culture, which will be presented in a descriptive summary. four influential factors that are listed in fig. 1 are treated as factors, each with its designated numbers f1 to f4. the expert panel consists of 5 experts, first assigns scores/criteria weight to each factor. the four sets of scores / criteria weight are shown in table 4. the matrix of ahp result can be seen in table 5; and the final ranking of the criteria is shown in table 6. table 4. the fahp result: criteria weight (wid) estimation by five experts. factor i experts e1 e2 e3 e4 e5 f1 0.06 0.06 0.06 0.06 0.06 f2 0.31 0.26 0.56 0.56 0.56 f3 0.31 0.12 0.12 0.12 0.26 f4 0.31 0.56 0.26 0.26 0.12 table 5. matrix of ahp result related in between each factor. matrix f1 f2 f3 f4 f1 1/6 1/4 1/5 f2 6 1/8 3 1 5/7 f3 3 2/3 1/3 4/7 f4 4 5/6 4/7 1 5/7 table 6. summary result of ahp analysis, ranked from the most to least influential factors. factors weight rank f2 (leadership) 46.6% 1 f4 (municipal external factor) 29.0% 2 f3 (municipal internal factor) 18.2% 3 f1 (background issue & policy purpose) 6.1% 4 the most influential factor in this implementation process from ahp is leadership which has 46.6% weight from the others. the second is municipal external factor (29%), followed by municipal internal factor (18.2%), and background issue and policy purpose (6.1%). 5. conclusion surabaya municipality has succeeded in reconverting gas stations to public green spaces and at the same time in encouraging residents to visit public parks by creating different theme for every park. land conversion process was broken down into 5 stages, which are issue emergence stage, issue discussion stage, decision making stage, court stage, and land reconversion stage. based on municipal regulation about green space management, the mayor of surabaya issued instruction letter no 540/2256/402.1.2/2002 on december 31, 2002 about green space use permit. the letter clarified details of non-extendable land use permits for gas stations and the one year leeway for gas stations owners to relocate their bussiness park development process, based on the different activities involved, were broken down into four stages which are cooperation stage, refertilization stage, park development stage, and maintenance stage. 12 12,5 13 13,5 14 14,5 15 15,5 16 16,5 17 2010 2011 2012 2013 m il li o n s (r p ) fig 6. budget allocation for park maintenance. hasyimi, v. and suroso, d. s. a./ jgeet vol 02 no 02/2017 109 the most innovative way from this policy policy implementation is how the municipality of surabaya seek any opportunity from its limited land, by re-evaluating land use implementation in the city center. in this context, the municipality has legitimate public interest to increase its urban green space inside the city center. the municipality has strong commitment to reconvert the land that and gave interesting theme for every park to attract people. the surabaya municipal also engaged its residents and other external parties in every stage of the process. even the mayor himself and the head of park and cemetery department were directly involved in the planting of vegetations in the parks and actively joined the environmental campaign. today, these public green parks have become an important eco-life symbol of surabaya city and have set a precedent for many cities in indonesia and around the world. existence of public parks in urban areas have changed people behavior to be more care about eco-lifestyle and have increased community awareness in maintaining public facilities well. based on analytic hierachy process, factor that is regarded as the most influential in supporting implementation of public park policy is the leadership factor. this conclusion is supported with data obtained from media sources and the numerous numbers of leadership awards and accolades received by the mayor of surabaya during the period of 2002-2013. 6. recommendations municipality has a strategic role in increasing urban green spaces in the city. central government can develop an official documentation of the case in surabaya to be used as a reference for other municipalities in increasing urban green spaces. to balance urban growth with environmental sustainability, the indonesian government needs to create an independent institution to help central and local government enforcing environmental laws. in the us, the agency responsible for performing environmental inspection especially in urban and industrial areas is the united states environmental duties is reviewing the number and distribution of gas stations in urban areas. epa inspects and provides guidance for construction of gas stations to prevent faults in underground tank installation which could pollute soil and ground water. epa also offers technical advice on rehabilitation of gasoline contaminated soil. references becker, w., saisana, m., paruolo, p., vandecasteele, i., 2017. weights and importance in composite indicators: closing the gap. ecol. indic. 80, 12 22. doi:10.1016/j.ecolind.2017.03.056 björk, j., albin, m., grahn, p., jacobsson, h., ardö, j., wadbro, j., ostergren, p.-o., 2008. recreational values of the natural environment in relation to neighbourhood satisfaction, physical activity, obesity and wellbeing. j. epidemiol. community health 62, e2. doi:10.1136/jech.2007.062414 grahn, p., stigsdotter, u.a., 2003. landscape planning and stress. urban for. urban green. 2, 1 18. doi:10.1078/1618-8667-00019 han, r., tang, b.j., fan, j.l., liu, l.c., wei, y.m., 2016. integrated weighting approach to carbon emission quotas: an application case of beijing-tianjin-hebei region. j. clean. prod. 131, 448 459. doi:10.1016/j.jclepro.2016.05.001 kaplan, s., 2001. meditation, restoration, and the management of mental fatigue. environ. behav. 33, 480 506. doi:10.1177/00139160121973106 maas, j., verheij, r. a, groenewegen, p.p., de vries, s., spreeuwenberg, p., 2006. green space, urbanity, and health: how strong is the relation? j. epidemiol. community health 60, 587 592. doi:10.1136/jech.2005.043125 nielsen, t.s., hansen, k.b., 2007. do green areas affect health? results from a danish survey on the use of green areas and health indicators. heal. place 13, 839 850. doi:10.1016/j.healthplace.2007.02.001 schipperijn, j., stigsdotter, u.k., randrup, t.b., troelsen, j., 2010. influences on the use of urban green space a case study in odense, denmark. urban for. urban green. 9, 25 32. doi:10.1016/j.ufug.2009.09.002 thaiutsa, b., puangchit, l., kjelgren, r., arunpraparut, w., 2008. urban green space, street tree and heritage large tree assessment in bangkok, thailand. urban for. urban green. 7, 219 229. doi:10.1016/j.ufug.2008.03.002 ulrich, r.s., 2006. evidence-based health-care architecture. lancet 368, 38 39. doi:10.1016/s0140-6736(06)69921-2 wey, w., 2015. smart growth and transit-oriented development planning in site selection for a new metro transit station in taipei , taiwan. habitat int. 47, 158 168. doi:10.1016/j.habitatint.2015.01.020 1. introduction 1.1 surabaya city success story 2. literature review 3. methods 3.1 study area 3.2 data collection 3.3 analysis method 4. results and discussions 4.1. public green park development from dismantled gas stations. land reconversion process i. emergence stage of issue ii. discussion stage of issue iii. decision making stage iv. court trial stage v. land use taking-over stage park development process analysis i. partnership engagement stage ii. soil re-fertilization stage iii.park development stage iv.post development & maintenance stage 4.2. analysis of factors influencing the successful implementation of reconversion. 5. conclusion 6. recommendations references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 setyawan et al./ jgeet vol 5 no 2/2020 81 research article shale gas potential in jambi sub-basin, indonesia: insights from geochemical and geomechanical studies reddy setyawan1, edy ariyono subroto2, benyamin sapiie2, randy condronegoro3, beiruny syam3 1geological engineering, faculty of engineering, university of diponegoro, indonesia 2 geological engineering, faculty of earth sciences and technology, bandung institute of technology, indonesia 3exploration department petrochina international jabung ltd, jambi, indonesia * corresponding author : reddy@live.undip.ac.id tel.:+6281 325 435 420 received: dec 10, 2019 ; accepted: jun 19, 2020. doi 10.25299/jgeet.2020.5.2.4191 abstract jambi sub-basin, which is located in south sumatra, indonesia has enormous potential of shale gas play. yet, detailed geological studies are rarely undertaken to understand this relatively new hydrocarbon play concept. this paper presents a combination of geochemical and geomechanical studies with the aim to better understand: (1) the maturity level of source rock; (2) the mechanical properties of shale; and (3) the quality of hydrocarbon source rock. this research began with determination of wells that penetrate the talangakar and gumai formations that have shale in it. source rock analysis was done by using toc (total organic carbon), s1, s2, s3, tmax, and ro (vitrinite reflectance) data. geomechanical evaluation was done by using xrd and well logs data. brittleness index was obtained by using jarvie et al. (2007) formula, based on the xrd data. s-wave and p-wave are used to calculate the rock strength, young's modulus and poisson's ratio with ucs-to methods.source rock in the geragai belongs to the of moderate-to-good category because it has more than 0.5% toc and potentially forms gas because it has a type iii kerogen. jtbs-2 well is the only well in the geragai area which already mature and has been able to produce hydrocarbons, because it passed the oil and gas windows. source rock in the betara belongs to moderate-to-good category because it has more than 0.5% toc potentially forms gas because it has a type iii kerogen. most formations in the betara are not yet mature based on the value of ro and tmax. in wells that have not reached the oil window nor gas windows, the prediction line drawn on the petroleum source rock summary chart, estimated that they would p ass the gas window at lower talangakar formation or lahat formation at depth of more than 8000 feet. the results of xrd analysis showed that the betara had a high brittleness index with an average of 0.809. talangakar formation has a higher rock strength values than gumai formation, both in betara high and geragai deep. the principle that say the rocks which have high toc values will have a high value of bi can be proven in the study area, the rocks that have high ro will have a high value of bi, cannot be identified in the study area. with sufficient high value of rock strength and low abundance of clay minerals, the rocks at talangakar formation is good for hydraulic stimulation. keywords: gumai formation, talangakar formation, source rock, young's modulus, poisson's ratio, brittleness index 1. introduction 1.1 background the jambi sub-basin is part of the tertiary sedimentation basin of south sumatra, which is currently one of the locations for oil and gas exploration. in the jambi sub-basin there is a gumai formation which is composed of quite thick deep marine shale (salim et.al., 1995). the opportunity for shale gas exploration requires a better understanding of the geological, geophysical and geochemical aspects to get positive results.main object for this research are geragai deep and betara deep, which located in jambi sub-basin. those two deeps are two of four deeps in jambi sub-basin (figure 1). indonesia has started to develop shale gas since 2009. the potential for shale gas in indonesia is estimated to reach 574 tcf or greater than coal methane gas (cbm) 453.3 tcf and conventional gas 153 tcf. indonesia's shale gas reserves are located in sumatra, kalimantan, java and papua. studies related to shale gas have been carried out in the north sumatra basin and the central sumatra basin. the purpose of this study is to determine the level of maturity of the talangakar and gumai formations, to determine the mechanical properties of shale both of these formations, and to determine the potential of shale gas from the talangakar and gumai formations. table 1. list of abbreviation used in this article abbreviation meaning toc total organic carbon py potential yield ro vitrinite reflectance xrd x-ray diffraction s1 the amount of free hydrocarbons (gas and oil) in the sample s2 the amount of hydrocarbons generated through thermal cracking of nonvolatile organic matter s3 the amount of co2 (in milligrams co2 per gram of rock) produced during pyrolysis of kerogen tmax maximum temperature when s2 was obtained hi hydrogen index oi oxygen index pr pristane ph phytane nc17 carbon atom number 17 nc18 carbon atom number 18 las log ascii standard 1.2 geological setting and stratigraphical framework 1.2.1 geology of south sumatra basin http://journal.uir.ac.id/index.php/jgeet 82 setyawan et al./ jgeet vol 5 no 2/2020 the south sumatra basin is a northwest-southeast trending back-arc basin bordered by the barisan mountains and the semangko fault in the southwest, and the paparan sunda pretertiary rocks to the northeast, the duabelas mountains and the tigapuluh mountains to the northwest separating the south sumatra basin with the central sumatra basin; and lampung high in the southeast that separates the south sumatra basin with the sunda basin. sedimentation that occurred in the south sumatra basin took place in two phases (jackson, 1961): transgression phase: telisa group was deposited in this phase, which consisted of the lahat formation, talangakar formation, baturaja formation, and gumai formation. this telisa group deposited unconformably on pre-tertiary source rock (figure 1). regression phase: at this phase the sediment produced from the palembang group consisted of the airbenakat formation, muaraenim formation, and kasai formation. the rocks that form the base of the basin consist of metamorphic rocks and igneous rocks that are of mesozoic age (figure 2). according to salim et al. (1995), the south sumatra basin was formed during the early tertiary (eocene oligocene) when a series of graben developed as a reaction to the angular subduction system between the indian ocean plate under the asian continent plate. according to de coster (1974) and salim et al. (1995), it is estimated that there have been three episodes of orogenesis that form the structural framework of the south sumatra basin, that is central mesozoic orogenesis, late cretaceous late-tertiary tectonics and plio – pleistocene orogenesa. fig 1. location of jambi sub-basin fig 2. regional stratigraphy of south sumatra basin (ginger and fielding, 2005) 1.2.2 geology of jambi sub-basin the jambi sub-basin is part of the south sumatra basin located in the northern part of the south sumatra basin. in the northern part of the jambi sub-basin it is bounded by the dua belas mountains and bangko high, in the south and east are bordered by ketaling high, and in the west it is bounded by bukit barisan.the stratigraphy of the research location is slightly different from the regional stratigraphy, that is the lemat formation was not found. at the research location, above the lahat formation was deposited the talangakar formation (jabung regional study, 2005) fig 3. regional stratigraphy of jambi sub-basin (petrochina jabung, 2005) hydrocarbons in the south sumatra basin are in the form of oil and gas, which may originated from petroleum migration and followed by gas migration. the source rock comes from the lahat formation has a lacustrine depositional environment. in addition to the lahat formation, coal and shale in the talangakar formation are also a source of hydrocarbons in the south sumatra basin (clure, 2005). the gumai formation which is younger than the talangakar formation also acts as a source rock with a marine depositional environment, but has a smaller amount of organic material and has a lower maturity compared to some other parts of the south sumatra basin (figure 4). fig 4. petroleum system play of south sumatra basin (patra nusa data, 2006) lithology in the lahat and talangakar formations is dominated by coal facies and has an excellent source rock potential with a toc value greater than 3% and a hydrogen index value greater than 300 mghc / gtoc (patra nusa data, 2006). potential source rock facies are dominated by type ii / setyawan et al./ jgeet vol 5 no 2/2020 83 iii kerogens produced from higher plant material with a small amount of liptinite, algae, and excitites (patra nusa data, 2006). the mean geothermal gradient in the south sumatra basin is 2.89°f per 100 feet, so the average depth of the peak of the oil window is 1700 meters (5500 feet) and the peak of the gas window is 2300 meters (7500 feet). hydrocarbon generation in the lahat and talangakar formations began in the late miocene which resulted from increased heat flow associated with late miocene tectonics and entering the gas window at the age of the pliocene or late pliocene. early formed hydrocarbons may also have migrated due to the pliocene-pleistocene orogenesis. 2. material and method the study began with the determination of wells that penetrate the talangakar formation and the gumai formation which have shale layers in them. the source rock evaluation was carried out to determine the richness of organic material, the type of kerogen produced and to determine the maturity of the source rock. richness quality determination used waples (1985) classification. the data used were obtained using rock-eval pyrolysis analysis. in this study, the evaluation of the source rock focused on the gumai formation and talangakar formation, both the upper talangakar formation and the lower talangakar formation to determine the richness of organic material and maturity in shale lithology. the data used came from the geragai area, comes from scrg-1, lgcy-1, jtbs-1, jtbs-2, and dsco-1 well; as well as from the betara area are irzr-1, irzr-5, evnx-1, evnx-2, and vntr-1 well. analysis of the quality and quantity of source rock requires data on hydrogen index values (hi), s1, s2, and toc values which are then plotted into a graph of the relationship between toc and hi (figure 5) and graphs of the relationship between toc and hydrocarbon potential values ( py). the py value is obtained from the sum of s1 and s2 values. ro vs. depth graph is used to determine rock maturity and gas window limits. source rock maturity determination used table 2. source rock quality based on toc (waples, 1985) toc value source rock implication < 0.5% negligible source capacity 0.5%-1.0% possibility of slight source capacity 1.0%-2.0% possibility of modest source capacity >2.0% possibility of good to excellent source capacity table 3. kerogen type classification (peters and cassa,1994) kerogen type hi value (mghc/gtoc) product at peak mature type i >600 oil type ii 300-600 oil type ii/iii 200-300 oil & gas type iii 50-200 gas type iv <50 none table 4. source rock maturity based on ro (peters and cassa, 1994) maturity level ro tmax(˚t) immature <0.60 <435 early mature 0.60-0.65 435-445 peak mature 0.65-0.90 445-450 late mature 0.90-1.35 450-470 over mature >1.35 >470 the first analysis conducted was the evaluation of the source rock using toc, s1, s2, s3, tmax, and ro data (vitrinite reflectance). from the data of the wells, toc vs. s1 + s2 and toc vs hi graphs were made to determine the richness of organic material in rocks, tmax vs hi and oi vs hi graphs to determine the type of kerogen produced by parent rock. sedimentary environment analysis was carried out using data from all wells in the form of gc and gc-ms data. from the well data will be made pr / nc17 vs pr / ph graph to determine the condition of the depositional environment and the type of kerogen produced in the environment, and pr / nc17 vs ph / c18 graph to determine the origin of organic material and depositional environmental conditions. the second analysis was carried out to determine the geomechanical properties of rocks with xrd data and well logs. unavailability of core rock data and rock analysis, then carried out using the value of the brittlenessindex. the brittleness index was obtained by the method of jarvie et al. (2007) based on xrd data. geomechanical log modeling is done by inputting electrical log data such as gamma ray, resistivity, density, and sonic logs. s-waves and p-waves are used to calculate rock strength, my and pr by the ucs method (nations, 1974). the shale geomechanical property obtained from the log analysis, supported by petrophysical analysis, needs to be calibrated with the brittleness index previously obtained so that it is considered to represent the true shale geomechanical properties even without drill core data. table 5. availibility data used in this research well source rock xrd las log vpvs gr bhc rt scrg-1 √ √ √ √ x stra-27 √ √ √ √ x stra-35 √ √ √ √ x sprn-1 √ √ √ x lgcy-1 √ √ √ √ x mrcp-1 √ √ √ x mrcp-13 √ √ √ √ x irzr-1 √ √ √ √ x irzr-41 √ √ √ √ x irzr-42 √ √ √ √ x irzr-5 √ √ √ √ x irzr-7 √ √ √ √ x jtbs-1 √ √ √ √ √ jtbs-2 √ √ √ √ x jtbs-28 √ √ √ √ x evnx-1 √ √ √ √ √ x evnx-15 √ √ √ x evnx-2 √ √ √ √ √ x evnx-9 √ √ √ √ x vntr-1 √ √ √ √ √ x dsco-1 √ x trvg-1 √ √ √ √ in this study, a geomechanical evaluation was carried out as an initial review to determine the potential of shale gas that was focused on the gumai formation and the talangakar formation both in upper talangakar and lower talangakar. the data used came from the geragai area, namely wells scrg-1, sprn-1, lgcy-1, mrcp-1, mrcp-13, jtbs-1, jtbs-2, jtbs-13, and dsco-1; and batara areas namely wells stra-27, stra-35, irzr-1, irzr-5, irzr-7, irzr-41, irzr-42, evnx-1, evnx-2, evnx-9, evnx-15, vntr-41 -1 and trvg-1. geomechanical analysis is done by calculating young's modulus, poisson's ratio, and ucs values based on vpvs data; and the brittleness index calculation based on xrd data. 3. result 3.1 geochemical evaluation 3.1.1 geragai area in general, the organic material content in the gumai formation in the geragai area classified as moderate to good (waples, 1985) in shale lithology with values from 0.09% to 84 setyawan et al./ jgeet vol 5 no 2/2020 1.55% with an average of 0.77%. from the upper talangakar formation the average organic material content is higher than the organic material content of the gumai formation which is 1.26% with values from 0.08% to 7.17%. from the samples taken, the lower talangakar formation has the highest average of 1.84%, with values from 0.15% to 8.55%. samples from the gumai formation were obtained from scrg-1, lgcy-1, and dsco-1 well, while the upper and lower talangakar formations were obtained from wells jtbs-1, jtbs-2 and lgcy-1. the jtbs-2 well is the deepest well in the geragai area, but not yet penetrate the lahat formation or bedrock. determination of the quality of the source rock can also be seen from the py value obtained from the total value of s1 and s2. the py value then plotted into the cross plot of py and toc for the gumai formation, samples came from scrg-1, jtbs-1, jtbs-2, dsco-1, and lgcy-1 well. the analysis shows that the wells have an average py value from poor to moderate range, with a range of values of 1.11 mg / g in dsco1 to 3.39 mg / g in jtbs-2. however, in the dsco-1 there is no s1 value, so the py value in the dsco-1 is less accurate. the lowest py value after the dsco-1 well is a sample from the lgcy-1 well with a value of 1.20 mg / g. fig 5. crossplot of toc vs hi, showing source rock quality and capability to produce hydrocarbon in geragai. based on the hi value of gumai formation at scrg-1, jtbs-1, jtbs-2, dsco-1, and lgcy-1 have hi values less than 200 mghc/gtoc, except for jtbs-2 wells, so based on classification of peters and cassa (1994), these wells have the potential to produce gas. in jtbs-2, from all 28 samples, there were only three samples that has hi data. from these three data, samples from jtbs-2 wells have hi values ranging from 264 mghc / gtoc to 405 mghc / gtoc, so that rocks in these wells have the capability to produce a mixture of oil and gas. the same results are shown from the results of plotting and reading on cross plots between tmax and hi values, which show rocks in wells scrg-1, jtbs-1, dsco-1, and lgcy-1 produce type iii kerogen, which has the potential to form gas. the jtbs-2 well, based on the results of the cross-plot reading, also shows the same result, which has a type ii or ii / iii kerogen that has the potential to generate a mixture of oil and gas (figure 6). fig 6. crossplot of tmax vs hi to determine kerogen type in geragai area. the source rock maturity can be known from the tmaks and vitrinite reflectance value, but many samples from geragai were not analyzed for tmaks, so to understand the maturity can only be known from the ro values plotted into the cross plot between ro values and depth (figure 7). fig 7. crossplot of ro vs depth to determine maturity level of source rock in geragai area. from the cross plot reading, it is known that only samples originating from gumai formation of jtbs-2, upper and lower talangakar formation of jtbs-2, and lower talangakar formation from lgcy-1 have either matured or did not enter the initial maturity phase. samples are from setyawan et al./ jgeet vol 5 no 2/2020 85 scrg-1 wells from all formations, jtbs-1 from all formations, jtbs-2 baturaja formation, all formations in dsco-1, and all formations in lgcy-1, except the lower talangakar formation, have not surpass the maturity phase because they have ro value less than 0.6% (peters and cassa, 1994). samples from jtbs-2 wells from the gumai formation are mostly immature, but from a depth of ± 5790 feet have entered the initial phase of maturity with a ro value of more than 0.6%. in the upper talangakar formation, most of the samples have matured because they have a ro of more than 0.7%. at a depth of ± 8750 feet, rocks have exceed the oil window threshold with a value of 1.0% ro, so that from this depth the source rock is estimated to to produce oil. from the lower talangakar formation, rocks have entered the final maturity phase and at a depth of ± 9950 feet have entered the gas window, so that from this depth the parent rocks have been able to produce gas (figure 7). 3.1.2 betara area in general, the organic material content in the gumai formation is in the poor to excelent (wples, 1985) category with a range of values of 0.17% 8.00% with an average of 1.67% which belongs to the good category. the upper talangakar formation has a lower average compared to the gumai formation, which is 0.98%, with a range of values of 0.55% 4.96% (figure 8), so it categorized as moderate to very good. the talangakar bawah formation has the highest average of the three formations analyzed in the study area at 1.8% toc, so this formation categorized in the good category. the range of toc values in the upper talangakar formation is 0.07% 8.45%, so this formation has the longest toc range compared to other formations (figure 8). figure 8. crossplot of toc vs hi, showing source rock quality and capability to produce hydrocarbon in betara area. determination of hydrocarbon quality can also be obtained by calculating the value of py (potential yield) obtained from the total value of s1 and s2. the py value is then entered into the cross plot of the relationship between py and toc. in the gumai formation in the betara area, samples from irzr-5 well have the highest average py value of 21.07 mg / g, followed by samples from irzr-1 well with a value of 2.35 mg / g, and samples from vntr-1 well have the smallest py value with a value of 1.84 mg/g. in the upper talangakar formation, py analysis using samples from wells evnx-1, irzr-1, irzr-5 and vntr-1, withsamples from irzr-1 well has the highest average py value of 15.79 mg / g. the other three wells, including those with poor to moderate hydrarbon potential, have an average py value of less than 5.0 mg / g. samples from evnx-1 well have the smallest average value, which is 0.77 mg /g, then vntr-1 with an average of 1.02 mg / g and irzr5 with an average of 2.15 mg/g. determination of the kerogen type for the betara area can be done by plotting and reading the cross plot of tmaks and hi and the cross plot of oi and hi (figure 9). because wells in betara area have all the data, the determination of the kerogen type can be done with those two cross plots. in general, the five wells analyzed can be divided into three kerogen groups, which is kerogen type iii, kerogen type ii, and kerogen type ii / iii (figure 9). figure 9. crossplot of oi vs hi to determine kerogen type in betara area. figure 10. crossplot of ro vs depth to determine maturity level of source rock in betara area. the results of reading the two crossplots, the gumai formation and upper talangakar formation samples, from 86 setyawan et al./ jgeet vol 5 no 2/2020 evnx-1, evnx-1, irzr-1, irzr-5 and vntr-1 well have not entered the maturity phase, so the gumai and upper talangakar formations have not yet produce hydrocarbons. in the upper talangakar formation it looks a bit promising because samples from evnx-1, evnx-2 and irzr-5 have entered the initial phase of maturity as indicated by ro values greater than 0.6% and tmaks of more than 435°c (figure 10). a slightly different case is shown from samples from wells vntr-1, because the lower talangakar formation in this well has not yet entered the maturity phase, either based on ro or tmax values. 3.2 geomechanics evaluation in general, based on the results of bi calculations from 45 samples from nine wells collected from the gumai and talangakar formations, the bi values ranged from 0.417 in the irzr-42 well in the lower talangakar formation to 0.979 in the stra-27 well in the lower talangakar formation. the lower talangakar formation has an average bi value of 0.809 which indicates that the lower talangakar formation has a good agility level. figure 11. triangular diagram of xrd showing mineral distribution. based on the xrd analysis in the laboratory which is then plotted into a triangular diagram (figure 11), it is found that almost all samples have very high quartz content and very low clay and carbonate mineral content. the low clay content and high quartz content indicate that the wells are good enough to do artificial fracturing. high abundance of quartz, and low abundance of carbonates and clays, can occur in rocks that are not pure shale. results of cross plot of pr and ym (figure 12) and ym and ucs (figure 13), can be seen that the stra-27, stra-35, irzr-07, and evnx-2 samples have a range of brittleness low to moderate level. pr range from 0.285 to 0.33 and ym values from 7 gpa to 37 gpa, and ucs values from 17 mpa to 58 mpa. irzr-41 wells and vntr-1 wells have the lowest brittleness range (figure 12 and figure 13). among eight wells that have bi calculation, the irzr-42 well has the longest bi range, from low to high. the highest bi value in the irzr-42 well is at a depth of 6160 feet. evnx-9 has the highest brittleness value with pr value ranging from 0.26 to 0.28 and ym from 39.73 gpa to 47.31 gpa (figure 12). figure 12. crossplot of pr vs my of wells to has bi data. figure 13. crossplot of ucs vs my of wells that have bi data. 4. result 4.1correlation of geochemistry and geomechanics to understand the correlation of geochemistry, represented by the value of toc and ro, and geomechanics, represented by rock strength, can be done by make a cross plot of bi rocks and toc and bi rock and ro cross plots. to make the two cross plots, the ideal is to use bi, toc, and ro data from the same well. however, this cannot be carried out at the research location due to lack of ideal data. therefore, the toc and ro data are taken from the nearest well or field and the depth is almost the same as the data used for bi values. as the toc value increased, the rocks become more flexible, or rocks that have high toc value will have low rock strength. this happens because a high amount of organic material usually exists in clays or shale which make the rock become ductile. in figure 14 an ideal correlation can be seen between the value of bi and toc. figure 14. crossplot of bi vs toc showing positive correlation of those two parameters. setyawan et al./ jgeet vol 5 no 2/2020 87 rocks that have high ro value will ideally have a high bi value too or as it become more mature, it will become more rigid. this happens because as the rock become mature, the organic material will be converted into hydrocarbons due to heat and pressure, so the rocks will become denser compared to rocks at early depositional process. figure 15 shows an ideal relationship, which shows that the more mature the rock, the strength of the rock will also increase, although it is very small. figure 15. crossplot of bi vs ro showing positive correlation of those two parameters. 4.2 geomechanics discussion an anomaly which shows that the upper talangakar formation has higher rock strength than the lower talangakar formation can happen due to several things, one of which is due to overpressure. overpressure is a pore pressure condition that is larger than the hydrostatic pressure. according to swabrick and osborne (1998), the mechanism for the formation of overpressure is divided into two, due to loading and nonloading. overpressure mechanism associated with loading is caused by one or more main strains that work on the sediment. for example is caused by high sedimentation rate. mechanism associated with non-loading occurs due to increasing in the volume of fluid in the pore with the condition of the fluid can not be release from pore cavity. clay minerals diegenesis and hydrocarbon generation are examples of non-loading mechanisms. the transformation of smectite into illite and kaolinite to illite causes an increase in the volume of fluid in the rock pore cavity. transformation of smectite into illite causes changes in the size of clay minerals which contribute to the reduction in the value of effective stress (katahara, 2006). water that is bound in the smectite will come out into water that fill pore cavity (boles and franks, 1979). transformation of kerogen to hydrocarbons results in an increasing of fluid volume 75–140% at 70°c, which is the cause of overpressure (swabrick et al., 2002). hydrocarbon generation involves two processes, namely the transformation of kerogen into oil and gas, and oil into gas. kataren, 2014 stated that in geragai and betara there were zones of a non-loading overpressure mechanism in the upper talangakar formation caused by hydrocarbon maturity. geochemical analysis result support this statement, because source rock in geragai has surpass phase of maturity. due to the overpressure zone in the upper talangakar formation, this formation has rock strength greater than the lower talangakar formation. the upper talangakar formation at betara high does not experience anomalies like in geragai, because samples was from high area and not in the betara deep, which may not have a zone of overpressure in it because the rocks in the betara high have not surpass maturity phase. the inversion in the south sumatra basin could have an effect on rock strength. the burial history may affect rock strength because inversion started as the upper talangakar deposited. overburden pressure may also increase after baturaja and gumai formation deposited. 5. conclusion 1. source rock in geragai area have moderate to good category and has the potential to generate gas and a mixture of oil and gas. the jtbs-2 well is the only well in the geragai area that has surpass maturity phase and capable to produce hydrocarbons, because it has exceeded the oil window and gas window phases. 2. source rocks in the betara area are in the moderate to good category and have the potential to generate gas, and mixture of oil and gas. most of the well in the betara area have not surpass the maturity phase either based on ro or tmax values. the evnx-1 well is the only well in the betara area that has entered a maturity phase but cannot produce hydrocarbons yet. 3. in wells that have not yet exceed oil window or gas window, maturity can be estimated on average it will surpass the gas window in the lower talangakar formation or in the lahat formation with a depth of more than 8000 feet. 4. in general, gumai and talangakar formations at betara high have lower rock strength values than those in geragai. the upper talangakar formation within the geragai has higher rock strength compared to the lower talangakar formation due to the influence of overpressure in the upper talangakar formation within the geragai formation. 5. the ideal relationship between bi and toc values that indicate high toc values will have low rock strength can be proven at the study site. the relationship between bi and ro shows that the more mature the rock, the less flexible the rock will be, is not proven at the study site because most of the source rock has not yet entered the maturation phase of the hydrocarbon. 6. the geragai deep is more potential to produce shale gas compared to the betara high because the source rock inside geragai has mature and entered the gas window and the geragai deep has a higher rock strength compared to the betara high. acknowledgements the first author would like to thank prof. dr. ir. eddy ariyono subroto and ir. benyamin sapiie, ph.d. for all directions, guidance, advice, critics, input, assistance and advice provided during the study. the author also thanks randy condronegoro mt. and beiruny syam st., as a supervisor at petrochina international jabung ltd, for their time, opportunities, new sciences, and assistance during the author's research. references clure, j., 2005. fuel resources: oil and gas, 139-140 dalam barber, j., crow, m.j., milsom, j.s., sumatra: geology, resources and tectonic evolution, 302., the geological society, london-united kingdom. 88 setyawan et al./ jgeet vol 5 no 2/2020 de coster, g.l., 1974. the geology of the central and south sumatra basins, proceedings of the third annual convention and exhibition indonesian petroleum association, jakarta, indonesia, june, 77 110. ginger, d. dan fielding, k., 2005. the petroleum system and future potential of the south sumatra basin, proceedings of the thirtieth annual convention and exhibition indonesian petroleum association, jakarta, indonesia, august, 68 – 70. jackson, a., 1961: oil exploration – a brief review with illustrations from south sumatra, contributions from the departement of geology, institut teknonolgi bandung, 1-9. jarvie, d.m., hill, r.j., ruble, t.e., dan pollastro, r.m. (2007): unconventional shale-gas systems: the mississippian barnett shale of north-central texas as one model for thermogenic shale-gas assessment, bulletin of american association of petroleum geologist v.91 no.4, tulsa, oklahoma, usa, 475 – 499. katahara, k., 2006. overpressure and shale properties: stress unloading or smectite-illite transformation, 2006 society of exploration geophysicists annual meeting, new orleans, louisiana, usa. kataren, l.r., 2014. estimasi overpressure berdasarkan data log talikawat pada sub-cekungan jambi, cekungan sumatra selatan, tesis magister istitut teknologi bandung, 93-99. nations, j.f., 1974. lithology and porosity from accoustic shear and compressional wave transit time relationship, spwla fifteenth annual logging symposium, article q, 1 – 16. patra nusa data., 2006. indonesian basin summaries, patra nusa data, jakarta, 29 – 30. peters, k.e. dan cassa, m.r., 1994. applied source rock geochemistry, 93 – 100 dalam dow, w.g., magoon, l.b., the petroleum system – from source to trap, 639 hlm., the american association of petroleum geologists, tulsa, oklahoma, u.s. salim, y., djumhana, n., yustika, m.p., isjmiradi, sidjaja, m., dan fauzi, m., 1995. remaining potential of the south sumatra basin, technical study report, south sumatra ami study group, jakarta, indonesia, 29 – 48. swabrick, r.e. dan osborne, m.j., 1998. mechanism that generate abnormal pressure, american association of petroleum geologist memoir 70, tulsa, oklahoma, usa. swabrick, r.e., osborne, m.j., dan yardley, g.s., 2002. the magnitude of overpressure from generating mechanism under realistic basin condition, american association of petroleum geologist memoir 76, tulsa, oklahoma, usa. waples, d.w., 1985. geochemistry in petroleum exploration. international human resources development co., boston, 33-94.2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51–58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41–44. salim, y., djumhana, n., yustika, m.p., isjmiradi, sidjaja, m., dan fauzi, m., 1995. remaining potential of the south sumatra basin, technical study report, south sumatra ami study group, jakarta, indonesia, 29 – 48. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12-3693969/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://link.springer.com/book/10.1007%2f978-3-642-03608-8 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 136 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 research article identification of clay mineral content using spectral gamma ray on y1 well in karawang area, west java, indonesia. rahmat c. wibowo1*, alia puja pertiwi2, suci kurniati3 1*2,3.department of geophisycs engineering, engineering faculty, universitas lampung, lampung, indonesia. * corresponding author : rahmat.caturwibowo@eng.unila.ac.id tel; 081 327 507517 fax: 0281-638793 received: january 21, 2020; accepted: jul 7, 2020. doi : 10.25299/jgeet.2020.5.3.4504 abstract northwest java basin (nwjb) is one of the proven hydrocarbon basins in indonesia. the scope of this paper will focus onthe shales and sandstone interval within y1 well in karawang area, nwjb, indonesia.a cored interval from y1 well was chosen for an investigation of the clay minerology for the gamma-ray activity and with the purpose of determining how the spectral natural gamma (sng) log could be used as an indicator of source rock and reservoir quality. the th/u as a redox indicator is used to assert that the shales are of anoxic conditions of shallow marine environments. despite the relatively high insoluble th values (60-74.15) ppm, the presence of u in substantial amounts, which only occurs in reducing conditions where it is preserved as a lower insoluble valence (u4+) explains for the low th/u values ranging between (5.8-7.1) ppm/ppm. the overall th/u value of the evaluated shales remain less than 25, where th/u <25 is suggestive of marine sediments, whereas th/u <4 is indicative of marine black shales of reducing conditions. although no linear relationship was found between clay content and k, th, or u, the k content characteristic three discrete reservoir characteristic (rc). the rc-i has predicted a matrix-supported texture with the highest k signal, illite and illitised kaolinite are roughly equal in importance as source of k. the rc-ii has predicted a grain-supported texture with intermediate k content. k-feldspar, mica and illite as the main sources. the rc-iii has predicted have a low k content with grain-supported texture and most of the k is hosted in feldspar. overall, the laboratory measurements appear to be applicable to the log data, and, using sem or xrd, the detail facies subdivision can be extended throughout the source rock and reservoir section based on the sng log. keywords: clay minerals, sng, northwest java basin, source rock, reservoir 1. introduction natural gamma-ray wireline logging is commonly usedfor lithological, or more precisely mineral, identificationin boreholes. in sandstone reservoir sections, its mainpurpose is to obtain an indication of the clay contentand thus, reservoir quality. schlumberger (1982) hasdescribed two types of gamma-ray logs: the conventionalgamma ray log records the total natural gamma radiation in the borehole independent of the energy of thegamma rays, whereas the spectral natural gammaray(sng) probe measures the gamma-ray spectrum, i.e. theenergy distribution of the gamma rays. the gamma raysoriginate from the decay of radiogenic potassium (40k),thorium (232th) and uranium (238u), each of whichexhibit a characteristic energy spectrum. the measuredenergy spectrum is transformed into concentrations ofk, th and u (schlumberger 1982). the advent of various instrumentation such as the spectral gamma rays (sgr) detector has gained acceptance in the global energy industry as an important nondestructive, automated, rapid and inexpensive surveytool for petro-mineralogical and geophysical assessment using radio-isotropy as its mode of determination of clay content, evaluation of clay mineralogy, identification offissure zones, organic matter quantification, reservoir charac-terization, source rock evaluation and depiction of sedimentary conditions and processes which proves their wide acceptance in the areas of sedimentology and stratigraphy (ruffell et al., 2006; schnyder et al., 2006; klaja & dudek, 2016). in the y1 well of the karawang area, sng core analysis was performed in order todifferentiate micaceous sand from shale. the purpose ofthis study was to identify the radioactive minerals in the shale and sandstones, and to estimate their contribution to thegamma-ray spectrum. furthermore, the aim was to identify the gamma-spectral characteristics of intervals withdifferent source rock and reservoir quality. with these objectives, wesampled the cores of y1 and defined three reservoir characteristics (rc) based on sng log pattern. the three characteristics chosen are expected to havereservoir qualities. 2. northwest java basin nwjb area is part of backarc basin series in western part of indonesia. this basin is spreading in west toeast and have a boundary with sunda platform in southern area. nwjb have complex configuration fromstructure prespective. most of this basin is half graben structure that have north to south orientation. ingeneral, this basin is divide into four sub-basins; those are ciputat-kepuh sub basin, pasir bungur sub basin,cipunegara sub basin, and jatibarang sub basin (figure 1). nwjb is extensional basin formed in tersier; this basin is a part of sunda land (figure 2). this basin evolved intowrenched-induced pull apart basin during eoceneoligocene, this result in creation of faulted highs andhalf graben system. the structural trend of normal faulting is south to north and is known as thesunda faulttrend. during http://journal.uir.ac.id/index.php/jgeet wibowo, r.c., et al./ jgeet vol 5 no 1/2020 137 this stage, deposition of lacustrine andvolcanic (jatibarang formation) happened.the jatibarang formation considered as eocene-middle oligocene age, it consist of interbedded volcanicsmaterial including tuffs, lava, and breccia tuff. this deposition is overlain by deposition of fluvio deltaictalang akar formation during early to late oligocene. talang akar formation (taf) is divide into lower taf and upper taf. lower taf consist of silisiclasticrocks deposited in fluvial environment; consist of severalgood reservoir such as conglomeratic reservoirand fluvial sand reservoir. upper taf deposited in deltaic to shallow marine environment, consist ofintercalation shand-shale and clastical carbonate at upper part. batu raja formation (brf) deposited inpost-rift phase during early miocene, consist of bioclastic carbonate and reefal carbonates. this formationbecame one of the best reservoir in nwjb. the cibulakan formation deposit in shallow marine environment, it consist of mixture of clastic andcarbonate rocks mostly dominated by shale and thin bed ofsandstone. in the middle of this formation, reefalcarbonate deposit, many author called it mid main carbonate (mmc). in the upper part of this formationfacies changing happened, and mostly consist ofcarbonate rock, this is where parigi formation is deposite. parigi formation deposited in shallow marine platform, mainly formed as flat reef. in seismic section,this formation is easy to identifie. parigi formation consist of fine-grained limestone, shally, lime muds andpackstone-wackstone facies. this formation is mainly deposite in local high that have relative orientationof north to south. this formation is overlay by the cisubuh formation, which is the youngest formationin nwjb, dominated by carbonaceous shales and thin sandstone (bishop, 2000). fig 1. index map of northwest java basin province, indonesia (bishop, 2000). 3. geochemistry of potassium, thorium, and uranium hassan et al. (1976) examined the mineralogy and chemical composition of 500 samples of varying lithology from different environments of deposition. of particular relevance to this work, their data included k, th and u measurements. the following conclusions concerning the occurrence of these three elements are based on hassan et al. (1976) as well as schlumberger (1982), and nielsen et al. (1987). 3.1potassium (k) potassium is a major element in many rock-forming minerals. the radioactive isotope 40k constitutes 0.0118% of the total potassium in a mineral, and the gamma signal from the radioactive decay is an important indicator of mineralogical composition. the most common k-bearing minerals in sedimentary rocks are k-feldspar, mica and illite. k-feldspar and mica are more common in sandstones, illite in shales. k-feldspar and mica have a greater k content than illite, and thus the gamma-ray flux is only a measure of clay content in the absence of significant k-feldspar (cowan & myers 1988). glauconite can also be a significant source of k in sedimentary rocks. typical potassium contents of kbearing minerals are: illite, 4.5%; muscovite, 7.9–9.8%; plagioclase, 0.54%; k-feldspar, 10.9–14.0% (nielsen et al. 1987). engstrøm (1981) measured k, th and u in danish cenozoic strata (clay, silt and sand) and found results in accordance with the distributions and concentrations mentioned above. kaolinite is sometimes reported to contain minor amounts of k and th, but ideal kaolinite contains neither elements. straightforward relationships between k and clay content should not be expected. in miocene–pliocene shales from the north sea, berstad & dypvik (1982) found a positive correlation between k and the clay content. this was inferred to be mainly controlled by the illite of the clay fraction. on the contrary, in paleocene and eocene strata, radioactivity and clay content are negatively correlated. this is probably because the clay fraction is rich in a k-poor smectite, derived from basaltic volcanic material. 3.2 thorium (th) thorium is a common trace element in most geological environments. in weathering environments, it is practically insoluble and is thus commonly concentrated in residual deposits such as bauxite and clay. important quantities of thorium are found in the heavy minerals’ monazite, rutile 138 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 and zircon. zircon normally contains 100–2500 ppm th (nielsen et al. 1987), while monazite may contain substantially more. pure clay samples typically contain 5–30 ppm th (adams & weaver 1958). theoretical considerations indicate that th4+, with an ionic radius of 0.97 nm, cannot be accommodated in the layer structure of clay minerals, so that th in these minerals could be assumed to be fixed by adsorption (adams & weaver 1958). hurst & milodowski (1994) stated, however, that the origin of th in clay minerals is unclear, and proposed that it is caused by inclusions of clay-sized heavy minerals. in the samples of hassan et al. (1976), the th content correlated with the content of clay minerals, but it was not proven that the clays were responsible for the th enrichment. 3.3. uranium (u) under neutral ph conditions, the uranyl ion ((uo)2+) forms ionic complexes with carbonates, which control its dispersion and mobility in nature. the uranyl ion also forms numerous complexes with organic compounds (e.g. humic acids), which facilitate its fixation by organic and mineral matter. hassan et al. (1976) found that u shows a strong correlation with organic carbon, probably because uo2 precipitates under reducing conditions. factors other than the content of organic matter (such as the availability of u) may be important for the occurrence of u in sediments as exemplified by the data of berstad & dypvik (1982). in shales from the cenozoic of the north sea, these workers found no correlation between u and total organic carbon (toc). uranium also occurs as a trace element in accessory minerals (zircon contains 300–3000 ppm u; nielsen et al. 1987) and in colloidal fe-oxide/hydroxide coatings on mineral grains. uranium species may also be adsorbed onto clay minerals. fig 2. generalized stratigraphic columns for the northwest java basin province (bishop, 2000). 4. methods 4.1 borehole gamma-ray gamma ray log is a curve where the curve shows the amount of radioactive intensity that is in the formation. this log works by recording the natural gamma ray radiation of rocks, making it useful for detecting or evaluating deposits of radioactive minerals such as potassium (k), thorium (th), or uranium ore (u). in sedimentary rocks many radioactive elements are concentrated in shales and clays, so the size of the radioactive intensity will indicate the presence or absence of clay minerals. rocks that have high clay content will have high radioactive concentrations, so that the gamma ray value is also high, with deflection curves to the right. the main radioactive element is potassium which is commonly found in illites. on a clean permeable layer, a gamma ray log curve will show very low radioactive intensity, except if the layer contains certain minerals that are radioactive, or the layer containing saltwater containing dissolved potassium salts. radioactive elements are mostly contained in shale layers, so gamma ray logs are very useful for determining the size of flakes or clays. the gamma ray log records radioactive elements on an api (american petroleum institute) scale. the basic unit is cps (count per second) which is then converted to api after being calibrated with a formation that has known exactly the radioactive mineral content (u, th, and k). the uses of this gamma ray log include determining shale (vsh) content, clay content, determining permeable layers, evaluating radioactive ore minerals, evaluating non-radioactive mineral layers, and correlations between wells. clay content is one of the important parameters that affect source rock and reservoir properties by using a gamma ray log that records the amount of natural radioactivity of rocks. 4.2 laboratory gamma-ray determination of clay mineral content is limited to five typical minerals that are significant for the oil industry, namely chlorite, glauconite, illite, kaolinite and smectite. clay minerals formed in continental and marine environments influence variability with respect to chemical composition. the type of clay mineral produced is strongly influenced by environmental reactions of sediments and diagenesis. the dominant clay mineral type can be determined based on the thorium-to-potassium cross plot in figure 3. the correct grouping of plotted points makes it possible to eliminate several types of clay minerals. likewise, the results of conventional gamma logging, gamma ray spectral results can be influenced by the diameter of the borehole and drilling fluid and in the borehole casing by the pipe column and cement bond. evaluation of clay mineral types using boreholes so that after processing can be carried out which aims to determine the type of minerals by interpreting the cross plot, the interpretation includes determining the type of clay mineral based on a cross plot of potassium to thorium ratio, can be seen in figure 3. similar techniques can be used for laboratory measurements of gamma radiation from k, th and u in rock samples. laboratory measurements were obtained with nai crystals using three energy windows centred around the three most prominent gamma energy k, th and u peaks of the spectrum (figure 4). these measurements are in the high-energy part of the spectrum and thus less dependent on geometry, density and matrix influence. however, by using only counts from a fraction of the spectrum, longer counting times are needed. wibowo, r.c., et al./ jgeet vol 5 no 1/2020 139 fig 3. interpretation of mineral clay based on the thorium and potassium ratio (schlumberger, 1985). fig 4. natural gamma-ray spectrummeasured in the laboratory with a naicrystal. energy windows used forconcentration determinations are centredaround the three most prominent high-energy k, th and u peaks. (fabricius et al., 2003) 5. results and discussion 5.1 gamma-spectral analysis averaged data of shales and sandstonewas recorded (figure5). overall, the total count of gamma radiation follows a consistent pattern for all shales, where the highest radioactivity is th counts with intermediate u and lower k counts relatively. the response indicates that the decay of isotopes of these shales are of common shales (fertl, 1979). comparatively, the shales from the bottom part show close range of th, u and k decay. upper part shales also show similar radioactive emission, with generally generatinghigher radiation. potassium concentrations are low in rc iii samples (< 0.7%), higher in rc ii samples (0.6–2%),and highest in rc i (generally > 2% although one sample contains 1.2% k; figure 5). this differentiation of rc in terms of k content was not observed for the clay fraction. considering all the data, the k content of the clay component shows a weak decrease with increasing depth to around 2177.5 m; at greater depths, the data show considerable scatter but appear to broadly increase between 2177.5 and 2188 m (figure 5). the th and u concentrations of the total samples are variable in rc iii and ii, but uniformly high in rc i (figure 5). the th content in the clay fraction follows roughly the same pattern as the k content, while no pattern is apparent for the u content of the clay fraction (figure 5). for rc ii and i sample, roughly constant th/k ratios of 9 – 15 (ppm/%) were obtained, whereas rc iii sample show significant variation in this ratio (2 – 47 ppm/%). this is a consequence of rc i samples being low in k but having variable th and u contents; it is assumed that this variability is governed by the heterogeneous distribution of heavy minerals within the facies. fig 5. the natural spectral gamma-ray log over the coredinterval of y1. intervals in which the k content is < 0.7% are referred torc iii, those with 0.7–2% k are referred to rc iiand the sediments with > 2% k are assigned to rc i.the corresponding lithofacies of the core samples, as determined by laboratory measurements. 5.2 thorium and potassium ratio for clay type th/k ratio was computed using fertl (1979) clay type procedure as diagnostic for determination of the dominant clay minerals. the averaged th/k of all shales are predictive of mixed layer clays (th/k > 3.5 but < 10). the shales show high k values as compared to lower k. the shales thus tend to have higher th/k values and skew towards the smectite region of mixed layer clays whilst the bottom part shales skew into the illitic region of the mixed layer clays. predominance of clay minerals shown by the mineralogical plot (figure 6) by quirein et al. (1982) validate fertl (1979) as mixed layer clays. 5.3 discussion th/u is instrumental in evaluation of depositional environment as it functions as a redox indicator. u is geochemically mobile and more soluble than th thus prone to mobilization during leaching and clay mineral diagenesis. therefore, under reducing conditions u6+ takes on the lower valence as u4+ and becomes insoluble producing low th/u. on the contrary, oxidizing conditions are indicated by high th/u (schnyder et al., 2006; klaja & dudek, 2016). basically, as recorded (fig 5), th/u <25 for shales from all members is indicative of reducing conditions as discussed by (klaja & dudek, 2016) where th/u <25 is generally affiliated to marine depositional environments. although further distribution of th/u shows that, th/u <4 is of deep 140 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 marine depositional environments, and typical of black shales. th/u from radioactive decay in this paper shows an estimate of 78% of (th/u: <25 and >4) which is proposed by adams & weaver (1958) as of transitional environment, grey and green shales of shallow marine (klaja & dudek, 2016) and 22% of (th/u < 2) indicative of black shales. an overall assertion infers a marine depositional environment of the shales. clay mineralsare helpful in studying the hydrocarbon generation of theshales because a common coincidence exists between their temperatures for oil and gas generation. convincing evidence and research have proven that, mixed-layer clays are not a continuous solid solution, but mixtures of dioctehedral phases with very little compositional variations (aagaard & helgeson, 1983). the spectral gamma ray technique is unable to differentiate the evolution of mixed-layer i/s clays, although estimate projections are made from the mineralogical plot of th/k (ppm/%) (figure 6), bottom part shales may be considered as showing dominance illite in mixed-layer i/s clays whilst upper part shales are considered as dominant in smectite in mixed-layer i/s clays. mixed layer clays exist here as a geothermometer and indicator of thermal maturity based on the concept first applied in detailed studies of the gulf coast (hoffman & hower, 1979). the transformation of clay minerals during diagenesis is from montmorillonite to mixed–layer smectite/illite to illite (jiang, 2012). during earlydiagenesis, maturity of the source rock is relatively low and smectite favors the percentage of illite–smectite mixed layer clays. with time and thermogenic conditions, clay minerals lose water and at this point become oil generative until smectite are converted to more illites percentages of the mixed layer in order to favor the expulsion of dry gas (jiang, 2012). the progression of this activity produces a series of smaller hydrocarbon molecules of higher volatility and hydrogen content, thus favoring the culmination of methane gas. with evolving kerogen by thermal maturation, the chemical composition of the shale changes progressively with increasing carbonaceous content and reverse of hydrogen content (mccarthy et al., 2011). the upper part shales (2180 – 2181m) may thus be considered less diagenetically and geothermo-metrically mature (less gas prone) as relative to the bottom part (2182 – 2184m) shales of more progressive evolution (k rich). the illite favored mixed-layer clays are less expandable in contrast to the smectite favored mixed-layer clays. smectite has a large sorption capacity relative to illite, but the presence of moisture in its expandable structure can greatly reduce gas-sorption capacity. a high maturity gas window usually exists in shales which have most of the smectite content converted to illite (gasparik et al., 2013). the shales of the bottom part members are considered more gas viable with respect to clay mineral type inference of th/k. the samples ofthe three rc are most effectively separated onthe basis of the k content. thus grainsupported porous (clay-poor) (rc i) contain < 0.7%k, grain-supported, clay-rich quartz arenites (rc ii) contain 0.6–2% k whereas the matrix-supportedwackes of rc iii contain > 2% k. in figure 5,the distribution of these three rc is presented,calculated on the basis of (corrected) log data. rc ii occurs throughout the section but particularlydominates the uppermost interval where it is interpreted to represent a lower shoreface sedimentary environment.rc i, showing good reservoir properties, is common in the nwjb where it typically occurs within channel-fill sections of progradation shelf edge facies (ginanjar et al., 2019). the clay-dominated rc iii is mainlyfoundin the lower part of the studied section which is interpreted to represent an shallow marine sedimentary environment (ginanjar et al., 2019). schlumberger (1982) reported how the nsg tool candifferentiate between different types of sandstone. feldspathic sandstones or arkoses will typically have th/kratios less than 1 x 10-4, because of their low th and theirhigh k contents whereas micaceous sandstones have ath/k ratio close to 2.5 x 10-4 because of the presenceof th-bearing heavy minerals. the th/k ratios in clay-bearing sandstones are still higher. this is consistent withthe present clay-bearing samples (rc ii and i)which have th/k ratios of 9 – 15 (ppm/%). by contrast, this ratio varies widely in the rc iii samples (th/k: 2 – 47 ppm/%), depending on the feldsparand heavy mineral content. thus, high th/k ratios canbe found in mineralogically mature rc iii sandstones. the lithofacies as defined in this study are expectedto reflect the reservoir quality of the rock, but they cannot be predicted from the th/k ratio. hurst (1990) alsofound th/k cross-plots to be poorly suited to identifying and quantifying the clay mineralogy of sandstones. fig 6. a mineralogical chart of th/k ratio chart for dominant minerals wibowo, r.c., et al./ jgeet vol 5 no 1/2020 141 6. conclusion 1. neither gamma-spectral k nor th was found to bea measure of clay content, but the k concentrationprovides a method of recognising the three broadlithofacies adopted here. porous quartz arenites havek concentrations below 0.7%, grainsupported quartzarenities with pore-filling clay have k concentrationsbetween 0.6 and 2%, while matrix-supported wackesnormally have k concentrations above 2%. it is possible, therefore, to define the lithofacies on the basisof the k signal of the spectral natural gamma log. 2. the shales of the belaga formation are of marine depositional environments and typically range fromgrey to black shales and are interpreted as dominant in mixed-layer illite-smectite from th/k evaluation. perhaps, the more diagenetically mature layar, kapit and bawang shales from clay mineralogy perspective are more conducive to gas generation relative to the shales of the pelagus and metah shales. however, this method needs conjunctive mineralogical laboratory analyses to undoubtedly consider diagenesis as well as decipher if clays are detrital or authigenic. 3. organic matter is preserved under reducing conditionswhere u is concentrated. this relationship makes u a good indicator of organic matter. from previous studies, (u > 5) is usually considered as cut-off for black shale. generally higher u values than k of the all shales in this study may require a follow-up toc and rock-eval pyrolysis to support organic matter richness and maturity for gas generation. 4. the th/k ratio does not give an indication of the lithofacies in this study. clay-bearing samples (those oflithofacies ii and iii) have th/k ratios of 3 x 10-4 –10 x 10-4, whereas in the lithofacies i samples thisratio varies widely (th/k: 2 x 10-4 – 22 x 10-4) depending on the content of feldspar and heavy minerals. acknowledgements we would like to thank lemigas for allowing us to conduct research there. also we have gained a lot of knowledge from this research. references aagaard, p. & h. c. helgeson, 1983. activity/composition relations among silicates and aqueous solutions: ii. chemical and thermodynamic consequences of ideal mixing of atoms on homological sites in montmorillonites, illites, and mixed-layer clays. clays and clay minerals, 31(3), 207-217. adams, j.a.s. & weaver, c.e., 1958. thorium-to-uranium ratios as indicators of sedimentary processes: example of concept of geochemical facies. american association of petroleum geologists bulletin 42, 387– 430. berstad, s. & dypvik, h., 1982. sedimentological evolution and natural radioactivity of tertiary sediments from the central north sea. journal of petroleum geology 5, 77–88. bishop, m.g., 2000. petroleum systems of the northwest java province, java and offshore southeast sumatra, indonesia, usgs report, denver, 34. cowan, d.r. & myers, k.j., 1988. surface gamma ray logs: a correlation tool for frontier areas: discussion. american association of petroleum geologists bulletin 72, 634–636. fabricius, i.l., fazladic, l.d., steinholm, a., & korsbech u., 2003. the use of spectral natural gamma-ray analysis in reservoir evaluation of siliciclastic sediments: a case study from the middle jurassic of the harald field, danish central basin. geological survey of denmark and greenland bulletin 1, 349-366. fertl, w. h., 1979. gamma ray spectral data assists in complex formation evaluation. the log analyst, 20(05), 3-37. gasparik, m., a. ghanizadeh, y. gensterblum & b. m. krooss, 2013. "multi-temperature" method for high-pressure sorption measurements on moist shales. review of scientific instruments, 84(8), 085116. hassan, m., hossin, a. & combaz, a., 1976. fundamentals of the differential gamma ray log – interpretation technique. society of professional well log analysts 17th annual logging symposium, june 9–12, 1976. transactions, paper h, 18 pp. hoffman, j. & j. hower, 1979. clay mineral assemblages as low grade metamorphic geothermometers: application to the thrust faulted disturbed belt of montana, usa. sepm special publication, 26, 55-79. hurst, a., 1990. natural gamma-ray spectroscopy in hydrocarbon-bearing sandstones from the norwegian continental shelf. in: hurst, a., lovell, m.a., & morton, a.c. (eds): geological applications of wireline logs. geological society special publication (london) 48, 211–222. hurst, a. & milodowski, a., 1994. characterisation of clays in sandstones: thorium content and spectral log data. society of professional well log analysts 16th european formation evaluation symposium, october 11–13, 1994. transactions, paper s, 18 pp. jiang, s., 2012. clay minerals from the perspective of oil and gas exploration. in: marta valaskova (ed.), clay minerals in nature-their characterization, modification and application, intech open. https://doi.org/10.5772/47790. klaja, j. & l. dudek, 2016. geological interpretation of spectral gamma ray (sgr) logging in selected boreholes. nafta-gaz. mccarthy, k., k. rojas, m. niemann, d. palmowski, k. peters & a. stankiewicz, 2011. basic petroleum geochemistry for source rock evaluation. oilfield review, 23(2), 32-43. nielsen, b.l., løvborg, l., sørensen, p. & mose, e., 1987. gamma-ray analysis for u, th and k on bulk cutting samples from deep wells in the danish subbasin and the north german basin, 82 pp. unpublished report, risø national laboratory, denmark. quirein, j.a., gardner, j.s., & watson, j.t., 1982, combined natural gamma ray spectral/litho-density measurements applied to complex lithologies. society of petroleum engineers of the american institute of mining, metallurgical and petroleum engineers paper spe, 11143, 14 p. ruffell, a., j. mckinley, c. lloyd & c. graham, 2006. th∕ k and th∕ u ratios from spectral gamma-ray surveys improve the mapped definition of subsurface structures. journal of environmental & engineering geophysics, 11(1), 53-61. https://doi.org/10.5772/47790 142 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 schlumberger 1982: natural gamma-ray spectrometry. essentialsof n.g.s. interpretation, 69 pp. houston, texas: schlumbergereducational services. schlumberger. 1995. log interpretation charts. schlumberger wireline and testing : sugarland, texas. schnyder, j., a. ruffell, j.-f. deconinck & f. baudin, 2006. conjunctive use of spectral gamma-ray logs and clay mineralogy in defining late jurassic–early cretaceous palaeoclimate change (dorset, uk). palaeogeography, palaeoclimatology, palaeo-ecology, 229(4), 303-320. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 1 2022 mildawati, r. et al./ jgeet vol 7 no 1/2022 21 research article effects of corn stalks ash as a substitution material of cement due to the concrete strength of rigid pavement roza mildawati 1,*, anas puri1, m. zaky handayani1 1 universitas islam riau, civil engineering department, jl. kaharuddin nasution 113 pekanbaru, indonesia . * corresponding author: rozamildawati@eng.uir.ac.id tel.: +62 812-9085-1785 received: feb 27, 2020; accepted: feb 4, 2022. doi: 10.25299/jgeet.2022.7.1.4681 abstract cement is an adhesive material for concrete mixtures in addition to water, fine and coarse aggregates. one of the main ingredients of cement is silica (sio2) which is originated from the earth's crust. silica is also available in plants such as corn stalks. this research is aimed to utilize the corn stalk ash (csa) as an alternative substitution for some cement in concrete for the rigid pavement of road construction. according to the indonesian standard, the flexural tensile strength should be exceeded at least 4.5 mpa. the flexural tensile strength has also a correlation due to compressive strength. the concrete materials consisted of the coarse aggregate (river crushed stone) from kampar river and danau bingkuang sands from kampar district of riau province, and portland composite cement from semen padang. the csa was made by burning the dried corn stalks in a steel cylinder can over 24 hours. the content of csa was varied by 0%, 5%, 7% and 9%. the compressive strength design of concrete was 31,3 mpa. testing procedures were based on the indonesian standard for concrete. the tested specimens have consisted of cube specimens (150 mm x 150 mm x 150 mm) for compressive tests, and beam specimens (150 mm x 150 mm x 600 mm) for flexural strength tests. all specimens were tested on 28 days-age. the results show that csa can be used as a partial substitution of cement in concrete. the addition of csa tends to increase the compressive strength of concrete instead of its flexural tensile strength. the optimum content of csa was 7% and resulted in an 8.0% and 6.9% increase in compressive and flexural tensile strength due to design respectively. compressive and flexural tensile strength fulfilled the standard. flexural tensile strength is obtained by 15% of the compressive strength. cornstalk ash can be used as a substitution of cement for rigid pavement concrete. it can reduce the utilization of cement and will be potentially cost efficiency. keywords: compressive strength, flexural strength, optimum content, rigid pavement, cement substitution 1. introduction concrete is a mixture of water, portland cement or hydraulic cement, aggregate coarse and fine aggregates, with or without additives or mixtures (sni 03-2847-2013, 2013) . a concrete structure can be defined as a building located above the ground with or without reinforcement (aci 318-89-1990, 1990). concrete becomes one of the alternative materials in building construction, both in road construction and construction, in addition to the use of metal and wood, which has been known as one of the bad properties of concrete can be seen from the strength of the strength and flexural strength, increased strength and flexural strength so that the better concrete performance. where a concrete mixture consisting of coarse aggregate, fine aggregate, cement, fly ash and other addictive materials. one of the concrete mix materials is cement, while cement which is often used is portland cement. portland cement is one type of hydraulic cement, while the main ingredients in making portland cement are lime (cao), silica (sio2), alumina (al2o3), magnesia (mgo), and alkalis (mulyono, 2004). silica (sio2) is one of the important components in the composition of cement. silica is extracted from the earth's crust but can also be found in plants in large numbers. the shape of the silica plant that is found in the form of quartz or crystalline silicon (buol et.al, 1980). corn is one of the types of agricultural crops that have the largest yields. in addition to corn cobs, corn stalks are also waste from agriculture. in agricultural activities will produce 19.13% of waste obtained from stems and leaves. corn stalk ash has a silica content of 67.41%, the silica content of corn plants increased more than no other macros such as n, p, k, ca, mg and s (majedu, 2014). research about the utilization of corn bark ash for additional admixture in concrete has been done by chandra (2013) , and corn cob ash for substitution of some cement in concrete also done by oladipupo (2012). dewi, et.al (2019) also used corn stalk ash and sikament nn additive as a substitution of some cement in concrete. their research focused on the compressive strength of concrete especially concrete for general purposes. pekanbaru is one area that grows sweet corn and has the rest of the sweet corn stalks that are not used. then the researchers are interested in conducting research on the utilization of sweet corn stalk ash on compressive strength and flexural strength of concrete. this research is aimed to utilize the corn stalk ash (csa) as an alternative substitution for some cement in concrete for the rigid pavement of road construction. can the csa as a concrete http://journal.uir.ac.id/index.php/jgeet 22 mildawati, r. et al./ jgeet vol 7 no 1/2022 admixture and fulfill the minimum standard of the flexural tensile strength for rigid pavement material. 2. methodology 2.1 research methods the analysis carried out in the research on compressive strength testing on cylindrical objects and cube specimens refers to sni 03-2834-2000, while research on flexural tensile strength tests on beams refers to sni 03-4431-2011. research on the compressive strength of concrete for cylinder and cube specimens refers to sni 03-1972-1990. the first stage of the analysis consists of checking the material of the test object, namely checking aggregates, checking water content, checking specific gravity and material absorption, checking mud content, checking bulk density. then the second stage consists of checking the concrete including the results of the mix design, checking the slump value, checking the compressive strength and flexural strength of the concrete with the substitution of sweet corn stalk ash on the weight of cement. and the last stage consists of analysis of concrete testing. 2.2 concrete concrete is defined as a mixture of ingredients consisting of hydraulic materials (portland cement), coarse aggregate, fine aggregate, and water with or without the use of materials additional (sni 03-2847, 2013). as the age increases, the concrete will harden and will reach strength (f'c) at the age of 28 days. concrete has compressive strength that is good, therefore concrete is widely used or used for various types of structures, especially bridge and road structures. concrete has a high compressive strength but is weak against strength pull. high-strength concrete has a strength between 35-65 mpa (k400-k800) is generally used for prestressed concrete such as prestressed concrete piles, prestressed concrete girders, prestressed concrete slabs and the like (pd t-07-2005-b, 2005). 2.3 rigid pavement portland cement concrete road pavement or more often called rigid pavement or also called rigid pavement, consists of cement concrete slab portland and the foundation layer (maybe not present) above the subgrade. pavement stiff road and has a high modulus of elasticity, will distribute the load over a large enough land area, so that the largest part of the pavement structure capacity is obtained from the concrete slab themselves (sukirman, 2013). the advantages of rigid pavement over flexible pavement (asphalt) is how the load distribution is transmitted to the subgrade. rigid pavement because it has stiffness (stiffnes), will distribute the load on the area which is relatively wide in the subgrade, the concrete itself is the main part that bears the structural loads, while flexible pavements are made of materials that less rigid, then the spread of concrete is not as good as in concrete, so it requires a larger thickness (tenriajeng, 1999). 2.4 concrete strength the compressive strength of concrete is the magnitude of the load per unit area, which cause the concrete test object to crumble when loaded with a certain compressive force, produced by the press machine (sni 03-1974-1990, 1990). compressive strength of concrete begins by the maximum stress when the concrete has reached the age of 28 days. concrete designed must meet the requirements of the average compressive strength, which meets requirements based on standard deviation data from compressive strength test results for conditions and types the structure that is retained in the fourth sieve is called coarse aggregate and whose grains are smaller than 4.75 mm or pass through the sieve number four is called fine aggregate. flexural strength is the ability of a concrete block to be placed in two bearing to withstand the force in a direction perpendicular to the axis of the test object, which given to him, until the test object breaks, expressed in mega pascal (mpa) force per unit area (sni 4431-2011, 2011). 2.5 concrete material (1) portland cement portland cement which was originally discovered in near the city of dorset, england, is a commonly used material for these needs (dipohusodo, 1999). portland cement is made from fine powder crystalline mineral whose main composition is calcium and aluminum silicate. (2) water water is needed in the manufacture of concrete to trigger chemical processes cement, wets the aggregate and provides convenience in concrete work. (3) aggregate aggregate is material granular materials such as sand, gravel, crushed stone as a result of natural disintegration produced from the stone crushing industry which has the largest grain 0.5 mm for fine aggregate. while coarse aggregate has a grain size between 5 mm up to 40 mm (sni 03-2847-2002, 2002) (4) additional ingredients auxiliary minerals are currently being added to the mix concrete for various purposes, including to reduce the use of cement, reduce temperature due to hydration reaction, reduce bleeding or increase the workability of fresh concrete. how to use it is also different, as substitute or as an addition to the mixture to reduce use of aggregates (nugraha, 2007) . additional ingredients are ingredients added to the concrete mix at the time of or during mixing take place. the function of this material is to change the properties of the concrete to be more suitable for a particular job, or to save costs (mulyono, 2004). corn stalk ash is the ash produced by burning corn stalks pass filter no. 200. the components of old and readyto-harvest corn plants consist of: 38% seeds, 7% cobs, 12% bark, 13% leaves and 30% stems. corn is 17 one of the plants that have the largest waste in indonesia. apart from cob corn, corn stalks are also waste from agriculture. plant waste corn, mainly in the form of stems, leaves, skin, cobs or cob reaches 1.5 times the weight of the seeds means that if 8 tons of seeds are produced per hectare then all at once obtained 12 tons of waste made. the stems of corn plants are dense, the thickness of the corn stalk is about 2 – 4 cm depending on the variety. genetic have a high effect on plants. very tall plant this varied character is a very influential character in the classification character of corn plants (ervina, 2013). corn is plants containing silica. corn plants have silica content 20.6% which exceeds the macronutrients n, p, k, ca, mg and s (yuwono, 2001). mildawati, r. et al./ jgeet vol 7 no 1/2022 23 2.6 selection of material types the materials used in this research are outlined below. (1) coarse aggregate the coarse aggregate used is crushed stone from the kampar river. (2) fine aggregate the fine aggregate used is banau bingkuang kampar sand. (3) water the water used comes from bore wells from the faculty of engineering, riau islamic university, pekanbaru, pekanbaru city. (4) cement the cement used is portland pcc cement from pt semen padang. (5) additional ingredients the material used as a partial substitute for cement is corn stalk ash, specifically sweet corn. in this research, supporting equipment is needed. the equipment used in this research are outlined below. (1) grail this tool is used to place the test object before carrying out the previous test. the cup is made of heat-resistant aluminum. different sizes are used. (2) oven the oven used is onky heraeus which is equipped with a temperature setting. the temperature used in this study was 110±5◦ c. (3) awl rod the awl used is made of steel with a length of 60 cm and a diameter of 16 cm. (4) hammer hammer made of iron with wooden handle (5) ruler ruler used to measure diameter, slump drop made of steel. (6) sieve sieve used to sieve coarse aggregate and fine aggregate in order to obtain a sieve analysis. the filter sizes used are 11/2, ,3/8, no.4 (4.8 mm), no.8 (2.4 mm), no.16 (1.2 mm), no.30 (0 .6 mm), no.50 (0.3 mm), no.100 (0.15 mm), no.200 (0.075 mm) (7) container a cylindrical container made of steel with a height of 155 mm and a diameter of 158 mm. used for checking the density of fine aggregate and coarse aggregate. (8) scales the scale must have an accuracy of 0.3% of the weight being weighed or 0.1% of the maximum capacity of the scale. the scales used are manual scales with a capacity of 20 kg and automatic scales with a capacity of 2 kg. (9) pycnometer the pycnometer used is iwaki cte33 500ml, made of glass that has a pointer scale which will be used as a measuring tool. (10) slump uji test equipment this tool is made of conical steel with a thickness of 2 mm, an upper diameter of 100 mm and a lower diameter of 200 mm. (11) concrete mold the concrete mold is made of steel. in this study, the researchers used a cylindrical mold with a height of 300 mm and a diameter of 150 mm which was used to print concrete after mixing fresh concrete. (12) vibrating machine the vibrating machine functions to compact the fresh concrete that has been inserted into the mold and also to remove the air that is in the mold. (13) beheaded cone the truncated cone is used when testing the specific gravity of the fine aggregate, which is to check the dry state of the saturated surface of the fine aggregate. made of steel with a top diameter of 35 mm and a bottom 80 mm, a height of 70 mm and a thickness of 1 mm. (14) concrete compressive strength machine. the concrete compressive strength machine is used to test the compressive strength of concrete. the machine used is bt testing with manual dial. this tool is made of steel and has load control and regulation. (15) concrete bending strength machine (16) concrete mixer machine the concrete mixer used is tiger with a capacity of 125 liters. this machine is used to mix the ingredients for making concrete. (17) soaking tub the soaking tub serves to treat the concrete that has been printed, the concrete is soaked according to the planning day. (18) iron drum iron drums are used as a place to burn corn stalks to ashes. 2.7 concrete mix design in sni 03-2834-2000 the requirements for the planning method of sni 032834-2000 are as follows: 1. planning the required compressive strength (fc’) at the age of 28 days. the planned concrete must meet the requirements for average compressive strength (fc’r). 2. standard deviation (s). deviation measuring instrument is a measure of the quality level of the implementation of the manufacture (production) of concrete. standard deviation is the identification of deviations that occur in the data group in this case concrete production. this s value is used as one of the input data in the planning of the concrete mix. the formula for calculating the standard deviation is as follows (mulyono, 2004). s= √ ∑ (𝑥𝑖−𝑥)²𝑛𝑖=1 𝑛−1 (1) where: s = standard deviation xi = compressive strength of concrete used from each object test x = average concrete strength n = number of test objects as a result of inspection the following is the standard deviation to find the level of concrete quality control whether it is good or not. table 1. standard deviation value for indication of level of concrete quality control (mulyono, 2004) standard deviation concrete quality control level index 2,8 very satisfy 3,5 satisfying 4,2 good 5,6 enough 7,0 bad 8,4 without control 24 mildawati, r. et al./ jgeet vol 7 no 1/2022 3. added value (margin) the added value is calculated by the formula: m = k x s (2) where: m = value added margin (n/mm²) k = 1.64 is a statistical determination whose value depends on the percentage lower than fc'. in this case, 5% is taken, so the value of k = 1.64 s = standard deviation (n/mm²). after getting the added value of the margin, continue calculating the average compressive strength (fc’r). 4. calculation of the targeted average compressie strength (fc'r). the planned average compressive strength is calculated by the formula: fc'r = fc'+ m 3.20 (3) where: fc'r = average compressive strength (mpa) fc' = planned compressive strength of concrete (mpa) m = value added or margin (mpa) 5. determine the type of portland cement used. 6. determine the type of aggregate to be used. both fine aggregate and coarse aggregate. 7. determining the water cement factor (fas) water-cement factor is the ratio of the weight of water to the weight of cement used in the concrete mix. 8. determination of the maximum cement water factor (fas) this determination is based on the minimum amount of cement with the maximum water cement factor for various types of concrete mix designs. 9. determination of slump value. 10. determination of the maximum aggregate size. 11. free moisture content, to determine the free moisture content of the combined aggregate in the form of a mixture of a mixture of natural sand and gravel (crushed stone), the free moisture content must be calculated between 160190 kg/m³ (if the slump is 30-60 mm and the maximum size line is 30m. calculations can be done with the following equation: 2 3 wh + 1 3 wk (4) where: wh = water estimate for fine aggregate wk = water estimate for coarse aggregate 12. calculating the amount of cement in step 11, and step 8. amount of water/phase 13. maximum cement quantity is ignored if not specified. 14. determine the minimum amount of cement. the weight of cement obtained from step 11 must be greater than the minimum requirement. 15. determine the adjusted water-cement factor. 16. determine the number of fine aggregates, in accordance with the requirements of sk 03-2834-2000. 17. determine the percentage of fine aggregate to the mixture based on the slump value, water-cement factor and the maximum nominal aggregate. 18. calculating the relative density of aggregates bj. mixture = ( 𝑃 100 x bj fine aggregate) + ( 𝐾 100 x bj coarse aggregate) (5) where: p = percentage of fine aggregate to mixed aggregate (%) k = percentage of coarse aggregate to mixed aggregate (%) bj = specific gravity 19. determine the specific gravity of the concrete, based on the type of aggregate combined and the value of the free moisture content, step 11. 20. calculate the combined moisture content, i.e. the specific gravity of the concrete minus the cement content and moisture content, steps 19-15-11 21. calculate the fine aggregate whose magnitude is the combined aggregate content times the percentage of fine aggregate in the mixture, steps 20-16. 22. calculate the coarse aggregate content, combined aggregate minus the coarse aggregate content, steps 20 and 21. fig. 1: the relationship between the compressive strength of concrete and the water-cement factor of cylindrical specimens 150 mm x 300 mm (sni 03-2834-2000) estimated compressive strength (mpa) of concrete with a cement water factor of 0,5 and the type of coarse aggregate commonly used in indonesia table 2. estimated compressive strength (mpa) of concrete with a cement water factor of 0.5 and the type of coarse aggregate commonly used in indonesia cement type aggregate type rough compressive strength (mpa) at age (days) 3 7 28 91 test object shape portland cement type 1 or sulfate resistant cement type ii and iv unbreakable stone broken stone 17 23 33 40 18 27 37 45 cylinder unbreakable stone broken stone 20 28 40 48 23 32 45 54 cube portland cement type iii unbreakable stone broken stone 21 28 38 44 25 33 44 48 cube unbreakable stone broken stone 25 31 46 53 30 40 53 60 cube mildawati, r. et al./ jgeet vol 7 no 1/2022 25 this research was conducted at the laboratory of concrete, the faculty of engineering, universitas islam riau (uir). the materials used were the danau bingkuang sand, crushed stone of kampar river, portland composite cement (pcc) from semen padang, freshwater and corn stalk ash. the particle size distribution of sand is shown in fig.1 which fulfilled zone ii in indonesian standard. the maximum particle size of the crushed stone was 40 mm. the mud content and water content of all aggregate less than 1.0%. the compressive strength design of concrete was fc’ = 32 mpa. the minimum flexural strength of concrete for rigid pavement is 4.75 mpa. table 3 shows the result of a mixed design of concrete. the values were not yet corrected due to ssd (saturated surface dry) of aggregates. the w/c ratio was 0.37. the workability target was 60 mm – 180 mm. this research stage was the material preparation, testing material properties, mix design, concrete mixing, slump test, manufacturing the test specimens, conducting the concrete compressive strength and flexural tensile strength tests, data analysis, discussion of analysis results, reporting the research and publishing the articles. fig. 2: the particle size distribution of sand (zone ii categorized). the specimens for compressive strength tests were a cubic shape with dimension 15 cm x 15 cm x 15 cm and for flexural tensile strength, tests were a beam shape with dimension 15 cm x 15 cm x 60 cm. table 3. concrete mixture combinations for each m3. descriptions cemen (kg) water (ltr) sand ( kg ) crushed stone 2/3” (kg) crushed stone 1/2” (kg) each m3 528,571 185 575,522 313,154 469,731 each 1 zak of cement 50 17,5 54,441 29,622 44,434 each of mixture components 1 0,35 1,088 0,592 0,888 3. results and discussion 3.1 effects of csa due to the workability of fresh concrete the workability of fresh concrete was tested by the slump test method. the value of slump tests is shown in fig.3 and 4 for specimens test of compressive and flexural strength respectively. all slump values were not fulfilled the design target. slump values tend to decrease by increasing the csa. fresh concretes tend to difficult to be worked. similar results were found by dewi, et.al (2019). fig. 3: relationship of slump value and csa content for compressive strength test specimens. 3.2 effects of csa due to the compressive strength the addition of csa affected insignificantly the compressive strength of concrete (fig.5). the compressive strength increased only about 1.8% – 5.7% from the design value. the optimum content of csa was 7%. dewi, et.al (2019) also found that the csa has an insignificant effect on the compressive strength. based on these results, it is evident that the csa can substitute some of the cement content in the concrete. it is beneficial to use in the field. fig. 4: relationship of slump value and csa content for flexural tensile strength test specimens. fig. 5: effects of csa due to the compressive strength of concrete. 3.3 effects of csa due to the flexural tensile strength the effects of csa due to flexural tensile strength are similar to the compressive strength. the addition of csa affected insignificantly the flexural tensile strength of concrete (fig.6). the flexural tensile strength increased only about 2.9% – 6.9% from the design value (4.75 mpa.). the optimum content of csa was also 7%. based on these 0 10 20 30 40 50 60 70 80 90 100 0,1 1 10 100 p a ss o f p e r c e n ta g e ( % ) particle size (mm ) min max data 52,00 48,33 44,67 41 39,00 0 10 20 30 40 50 60 0% 3% 5% 7% 9% v a lu e o f s lu m p ( m m ) csa content 55,00 52,33 51 48 45,33 0 10 20 30 40 50 60 0% 3% 5% 7% 9% v a lu e o f sl u m p ( m m ) csa content 32,3 32,6 33,1 33,8 32,932,0 0 10 20 30 40 0% 3% 5% 7% 9% c o m p re ss iv e s tr e n g th ( m p a ) csa content 26 mildawati, r. et al./ jgeet vol 7 no 1/2022 results, it is evident that the csa can substitute some of the cement content in the concrete. the minimum standard of 4.75 mpa. flexural tensile strength for rigid pavement was fulfilled. it is beneficial to use in the field. csa can reduce the utilization of cement. since the prize of cement is cheapest compare to other concrete materials, substitution the cement content can reduce the cost of concrete. fig. 6: effects of csa due to the flexural tensile strength of concrete. the comparison between flexural tensile strength and compressive strength of concrete is shown in fig.7. the flexural tensile strength was about 14.7% 15.0% of the compressive strength. fig. 7: the comparison between flexural tensile strength and compressive strength of concrete. 4. conclusions according to the results, it can be concluded that the csa can be used as a partial substitution of some cement in the concrete. the addition of csa tends to increase the compressive strength of concrete instead of its flexural tensile strength. compressive and flexural tensile strength fulfilled the standard. flexural tensile strength is obtained by 15% of the compressive strength. cornstalk ash (csa) can be used as a substitution of cement for rigid pavement concrete and can increase the compressive strength of concrete instead of its flexural tensile strength. about 5%. csa can reduce the utilization of cement and will be potentially cost efficiency. acknowledgment authors to thanks for supporting by research institute and community services (lppm) with contract number 698/kontrak/lppm-uir/5-2019 and the laboratory of civil engineering of universitas islam riau. references aci 318-89, 1990. (1990). building code requirements for reinforce concrete, part i, general requirement, fitth edition. skokie, illinois, usa: pca. badan standardisasi nasional. (1990). sni 03-1974-1990 metode pengujian kuat tekan beton. sni 03-19741990. dipohusodo, i. (1999). struktur beton bertulang berdasarkan sk sni t15-1991-03. jakarta: pt. gramedia pustaka utama. ervina. (2013). isolasi silika dari tongkol jagung, tugas akhir, universitas pembangunan nasional, surabaya. et.al, b. (1980). food comotition and analysis, p.122123,avi publishing, new york. majedu, k. a., s. a. a. and i. o. l. (2014). the use of corn cob ash and saw dust ash as cement replacement in concrete works. the internasional journal of engineering and science (ijes) vol. 3 no. 4. federal polytechnic ede : osun state. mulyono, t. (n.d.). teknologi beton, edisi kedua, andi, yogyakarta. 2004. nugraha, a. dan p. (2007). teknologi beton. penerbit c.v andi offset, yogyakarta. pd t-07-2005-b. (2005). pelaksanaan pekerjaan beton untuk jalan dan jembatan. badan penelitian dan pengembangan pupr, 1–21. sukirman, s. 2003. (2013). persyaratan beton struktural untuk bangunan gedung. in bandung: badan standardisasi indonesia. sni 4431-2011, s. (2011). cara uji kuat lentur beton normal dengan dua titik pembebanan. tata cara perhitungan struktur beton untuk bangunan gedung. sni 03-2847-2002. (2002). sni 03-28472002, 251. tenriajeng. (1999). perkerasan kaku jalan raya 2013– 2015. yuwono, r. dan. (2001). kesuburan dan pemupukan tanah pertanian”, pustaka buana, bandung. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). 4,75 4,89 4,91 5,08 4,87 1 2 3 4 5 6 0 3 5 7 9 f le x u ra l t e n si le s tr e n g th ( m p a ) csa content (%) 0 10 20 30 40 0 3 5 7 9 c o n cr e te s tr e n g th ( m p a ) csa content (%) flexural tensile strength, fs' compressive strength, fc' http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 104 suryadi, a. et al./ jgeet vol 5 no 2/2020 research article geophysical survey on open dumping landfill for monitoring spread of leachate: a case study in pekanbaru, riau, indonesia adi suryadi1*, frezy ukhuah islami1, husnul kausarian1, dewandra bagus eka putra1 1department of geological engineering, faculty of engineering, universitas islam riau, pekanbaru, indonesia * corresponding author : adisuryadi@eng.uir.ac.id tel.:+62 822 8389 6947 ; fax: received: may 29, 2020; accepted: jun 20, 2020. doi 10.25299/jgeet.2020.5.2.5340 abstract pekanbaru is a city in indonesia with high population growth. the increasing amount of the population has a parallel relation ship with the increasing quantity of waste disposal. this study has been conducted on an open dumping landfill at pekanbaru that surrounded by residential areas. waste disposal produces leachate as a threat to surface water and groundwater resources. this study aims to investigate the contamination spread formed by leachate using the geophysical method. direct current resistivity (dcr) has been used to produce 2 d resistivity subsurface models. data acquisition has been done using multi-electrodes (32 electrodes) with spacing 2 m between electrodes. 2d resistivity model produced, a contaminant from leachate represented by low resistivity value 26.1 870 ωm. the deepest penetration of leachate that detected is around 3 m from the surface. it has been understood that leachate from the landfill of the study area is not contaminated groundwater yet. it confirmed by groundwater analysis at residential around the landfill area. by knowing the spreading of leachate, preventive action can be made to maintain the quality of groundwater resources. keywords: contamination, groundwater, landfill, leachate, pekanbaru, resistivity 1. introduction geo-electrical survey is a survey that looking the physical parameters which is resistivity value to differentiate subsurface material. recently, the interest of underground sources of water is increasing rapidly to fulfill the water demand. pekanbaru is a city that use groundwater as main source of clean water. parallel with increasing of population in pekanbaru, waste production also increasing. the study area is an open dumping landfill at marpoyan that have potential to produce leachate. as we known that open dumping landfill is a primitive way to dispose the waste without any technology to prevent the contamination through subsurface. the location of landfill become a big problem because it surrounded by residence area (figure 1). so the aim of this study is to detect the probability of groundwater contamination from leachate leaded by open dumping landfill. fig 1. study area is an open dumping landfill that. electrical resistivity imaging (eri) is the most common and successfully used especially in groundwater exploration and environmental problem like soil or groundwater contamination (azhar et al., 2016; hamzah et al., 2007, 2008; jumary et al., 2002; saad et al., 2012; adi suryadi et al., 2019) .by using eri, resistivity distribution of subsurface will be modelled into two-dimensional image. the model that resulted is showing the apparent resistivity value which can be interpreted as contaminant depend on the value (akankpo, 2011; n. nwankwo and o. emujakporue, 2012; okereke and harcourt, 2012; surface et al., 2011; a. suryadi et al., 2019). 2. methods abem sas1000 resistivity meter and abem lund es464 selector system is the equipment that used to collect the resistivity data. the survey employed 61 multi-electrodes with 5 m minimum electrode spacing. the line survey length is reach 400 m that arranged in a straight line. the selector system was connected with all electrodes through multi-core cable (figure 2) (hamzah et al., 2008; loke and barker, 1995; a. suryadi et al., 2019). in each measurement the resistivity meter only select four electrodes to activate. beside of that, coordinate of line survey must be recorded to correlate all the lines taken (kausarian et al., 2018; lubis et al., n.d.; suryadi, 2016). apparent resistivity (ρa) calculated by multiple of geometry factor (k) with voltage (v) and divided by current (i) injected. ρa = k v/i (1) geometry factor (k) is depend on configuration electrode that utilized. in this study configuration used id pole-dipole (figure 5) that k calculated with formula: k = 2π (b(a+b))/a (2) http://journal.uir.ac.id/index.php/jgeet suryadi, a. et al./ jgeet vol 5 no 2/2020 105 fig 2. equipment set up to acquisition resistivity data (loke and barker, 1995). fig 3. hand auger equipment to get shallow geological profile. the data collected processed by using inverse modelling software which is res2dinv. the result of inverse modelling will interpreted based on apparent resistivity and proven by drilling data. some supporting data also collected like subsurface condition using hang auger to get the real data of geology. the equipment hand auger is shown at figure 3. the depth maximum of hand auger only 10 m from the surface. else from hand auger, another supporting data taken is groundwater elevation and groundwater quality (figure 4). this data can prove that groundwater already contaminated or not. fig 4. equipment for groundwater quality analysis (ph, temperature, tds and conductivity). 3. results and discussion interpretation from 3 survey line shown that contamination from leachate only affected surface. based on resistivity value there are 3 types of layer (figure 5) which is low resistivity value (l1), moderate resistivity value (l2) and high resistivity value. low resistivity value is ranging from 26.1 – 870 ωm that interpreted as wet clay and sand. moderate resistivity value has value 269 – 3319 ωm that interpreted as dry clay. the highest resistivity value is 2276 – 91770 ωm interpreted as dry sand. from this interpretation dry clay (l2) become the preventer for penetration of leachate. that why in the beginning we mention that contamination only affect surface layer and not yet contaminate the groundwater. this statement also proven by result of hand auger that resulting there is clay layer at depth below 2 meters. the comparison between resistivity result and can be seen at table 2. fig 5. result of resistivity survey from survey line 1, 2 and 3 that shown there are 3 layers named as l1, l2 and l3. 106 suryadi, a. et al./ jgeet vol 5 no 2/2020 table 1. interpretation of resistivity results. table 2. comparison between resistivity result and hand auger results. resistivity interpretation log profile layer resistivityy value (ωm) depth (m) interpretation depth (m) material l1 26,1 – 870 0 – 3 top soil 0 – 0,9 wet clay and sand l2 269 – 3319 1 – 6 dry clay 0,9 – 2 grayish black clay l3 2776 – 91770 5 – 9,6 dry sand 2 – 3 brownish gray sand figure 6. hand auger result that shown geological profile of subsurface at study area. another supporting data that parallel with interpretation that state groundwater is not contaminated by leachate yet is groundwater quality. as the result from 6 wells sampling (figure 7) around the study area showing 5 wells is in normal condition at variable tds, ph, temperature dan conductivity (table 3). tds ranging from 35.0 – 81.0 mg/l, ph ranging from 3 – 7, temperature ranging from 29.4 – 30.20c and conductivity ranging from 58.6 – 135.5 μs/cm. the well that contaminated only well from landfill area. contamination clearly shown at variable tds and conductivity that has very high value (207.9 mg/l for tds and 344.3 μs/cm. based on groundwater flow we predict that contamination will migrate to northeast from study area. figure 7. location of groundwater sampling for groundwater quality analysis. table 3. groundwater quality result. no well no. coordinate tds (mg/l) ph temperature (0c) conductivity (μs/cm) 1 sm1 n 00 26' 56.53" / e 101 27' 53.58" 64.9 6.07 29.6 c 108.6 2 sm2 n 00 26' 55.35" / e 101 27' 48.04" 47.2 5.87 30.2 c 79.9 3 sm3 n 00 27' 03.12" / e 101 27' 55.05" 62.6 5.94 29.4 c 104.3 4 sm4 n 00 27' 00.64" / e 101 27' 49.53" 81.0 6.13 29.6 c 135.5 5 sm5 n 00 26' 55.91" / e 101 27' 51.35" 35.0 6.28 29.6 c 58.6 6 sm6 n 00 26' 57.81" / e 101 27' 51.93" 207.9 6.37 29.0 c 344.3 7 aquades 5.8 6.52 29.0 c 9.7 survey line layer resistivity value (ωm) depth (m) interpretation survey line 1 l1 26,1 269 0 – 3 top soil (wet) l2 269 – 2775 1 – 6 dry clay l3 2776 – 91770 5 – 9,6 dry sand survey line 2 l1 82,4 – 471 0 – 3 peat mixed with clay and sand l2 471 – 2687 2 – 5 clay l3 2687 – 36669 3 – 9,6 dry sand survey line 3 l1 228 – 870 0 – 3 peat mixed with clay and sand l2 870 3319 2 – 6 clay l3 3319 – 24713 3 – 9,6 dry sand suryadi, a. et al./ jgeet vol 5 no 2/2020 107 figure 8. groundwater elevation map that show the probability of contaminant migrate to northeast from study area. 4. conclusion technology of sustainable landfill must be apply to all landfill in pekanbaru to prevent the contamination of groundwater. it very important because majority of society in pekanbaru use groundwater as the main source of clean water. this study shown that contamination of leachate fortunately prevented by clay layer of study area. that layer is a impermeable media that can’t transfer fluid. beside that, the groundwater quality analysis also shown there is no contaminant detected at groundwater except well at landfill. the contamination of leachate represented by high tds and conductivity value. the probability of migration contaminant is predicted to northeast from study area. acknowledgements the authors would like to give an acknowledgment to department of research and community service as funder of this research with contract no. 670/kontrak/lppm-uir/52019. additional thanks to geology laboratory of uir that provide all the equipment of this study and lastly to all our studentsthat help us during data acquisition at field. references akankpo, o., 2011. monitoring groundwater contamination using surface electrical resistivity and geochemical methods. j. water resour. prot. 03, 318–324. https://doi.org/10.4236/jwarp.2011.35040 azhar, m.a., suryadi, a., samsudin, a.r., yaacob, w.z.w., saidin, a.n., 2016. 2d geo-electrical resistivity imaging (eri) of hydrocarbon contaminated soil. ejge ( electron. j. geotech. eng. 21, 299–304. hamzah, u., ismail, m.a., samsudin, a.r., 2008. geophysical techniques in the study of hydrocarbon-contaminated soil 54, 133–138. https://doi.org/10.7186/bgsm2008020 hamzah, u., samsudin, a.r., malim, e.p., 2007. groundwater investigation in kuala selangor using vertical electrical sounding (ves) surveys. environ. geol. 51, 1349–1359. https://doi.org/10.1007/s00254-006-0433-8 jumary, s.z., hamzah, u., samsudin, a.r., 2002. teknikteknik geoelektrik dalam pemetaan air masin di kuala ( mapping of groundwater salinity at kuala selangor by geoelectrical techniques ). kausarian, h., batara, putra, d.b.e., suryadi, a., lubis, m.z., 2018. geological mapping and assessment for measurement the electric grid transmission lines in west sumatera area, indonesia. int. j. adv. sci. eng. inf. technol. 8. loke, m.h., barker, r.d., 1995. least-square deconvolution of apparent resistivity psuedosection. geophysics 60, 1682–1690. lubis, m.z., irawan, s., anurogo, w., kausarian, h., pujiyati, s., n.d. equispaced unshaded line array method for target identification using side scan sonar instrument. n. nwankwo, c., o. emujakporue, g., 2012. geophysical method of investigating groundwater and sub-soil contamination – a case study. am. j. environ. eng. 2, 49–53. https://doi.org/10.5923/j.ajee.20120203.02 okereke, i.d., harcourt, p., 2012. electrical resistivity investigation of solid waste dumpsite at rumuekpolu in obio akpor l . g . a ., rivers state, nigeria 1, 631– 637. saad, r., nawawi, m.n.m., mohamad, e.t., 2012. groundwater detection in alluvium using 2-d electrical resistivity tomography (ert). electron. j. geotech. eng. 17 d, 369–376. surface, e.n., meeting, e., geophysics, e., kingdom, u., 2011. 3d electrical resistivity tomography to locate dnapl contamination in an urban environment naudet v., gourry j.-c., mathieu f., girard j.f., blondel a, saada a. brgm , 3 avenue claude guillemin, f45060 orleans, france 12–14. suryadi, a., 2016. fault analysis to determine deformation history of kubang pasu formation at south of unimap stadium hill , ulu pauh ,. jgeet (journal geosci. eng. environ. technol. 1, 1–6. suryadi, a., batara, amir, s.n., 2019. electrical resistivity imaging (eri) and induced polarization (ip) survey to solve water drought problem at alor gajah, melaka, malaysia, in: iop conference series: materials science and engineering. https://doi.org/10.1088/1757899x/532/1/012025 suryadi, adi, putra, d.b.e., kausarian, h., prayitno, b., fahlepi, r., 2019. groundwater exploration using vertical electrical sounding (ves) method at toro jaya, langgam, riau. j. geosci. eng. environ. technol.3,226.https://doi.org/10.24273/jgeet.2018.3.4.2 226 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 manyoe, i.n. et al./ jgeet vol 5 no 2/2020 75 research article subsurface shallow modelling based on resistivity data in the hot springs area of libungo geothermal, gorontalo, indonesia intan noviantari manyoe1,*, ronal hutagalung1 1geological engineering major, faculty of mathematics and natural science, universitas negeri gorontalo, gorontalo, indonesia. * corresponding author : intan.manyoe@ung.ac.id tel.: +62 81280023410 received: may 29, 2020; accepted: jun 18, 2020. doi 10.25299/jgeet.2020.5.2.5094 abstract volcano-tectonic events in libungo can be the cause of the presence of geothermal potential. there is no detailed research on shallow subsurface conditions in libungo that can show the distribution of subsurface fluids. this research aims to create a shallow subsurface model of the libungo geothermal area based on resistivity data. resistivity data collection was carried out in the libungo hot springs area. the electrode configuration used is the schlumberger configuration. the variation in resistivity values is calculated using current data, potential difference data and geometry factors. the results of the calculation of the resistivity values variation are plotted versus depth. variations of resistivity value versus depth are then displayed in the form of a single log, lithology distribution and 3d lithology model. the results showed that the shallow subsurface of the libungo geothermal area was composed of andesite, volcanic breccia, silty clay and clay. andesite in the research area has resistivity values ranging from 320 349 ωm, has slightly fracture and is andesite dry. volcanic breccia has a resistivity value of 177-198 ωm, has a well to slightly fracture and is a volcanic breccia moist. silty clay has a resistivity value of 3.25-37.99 ωm and is a wet to moist silty clay. clay has resistivity values in the range 1.56-2.78 ωm and is wet to moist clay. fluid distribution in the shallow subsurface area occurs in volcanic breccia, silty clay and clay. shallow subsurface fluids accumulate mostly in the northern part of the libungo geothermal area. keywords: fracture, fluids, thermal, lithology, schlumberger. 1. introduction geothermal potential in indonesia is one of the largest in the world. indonesia has abundant geothermal potential with 331 potentials spread from sabang to merauke (direktorat panas bumi, 2017). geothermal potential can be used directly or indirectly and has implications for improving the economic community. gorontalo is one of the provinces in indonesia, which has geothermal potential. all regencies in gorontalo have geothermal potential, but the greatest geothermal potential is accumulated in eastern gorontalo at suwawa area. suwawa area consists of the lombongo geothermal area, pangi geothermal area, libungo geothermal area, tulabolo timur geothermal area and hungayono geothermal area. various geothermal studies have been carried out in the suwawa area in terms of geology, geophysics and geochemistry (direktorat panas bumi, 2017; manyoe, 2019; manyoe and bahutalaa, 2017; tolodo et al., 2019). gorontalo, which is located in the north arm of sulawesi, eastern indonesia, is influenced by the macro and micro plates, namely eurasian, indian-australian and pacific-philippines (hall and wilson, 2000). the pacific and philippine plates move in the direction of wnw crashing into the eurasian plate at a speed of 9 cm/yr (hinschberger et al., 2005). banggai-sula microcontinent is located in the se part of the north arm of sulawesi. banggai-sula microcontinent is a fragment from australia (hall, 2002). banggai-sula move to the west because of the sorong fault movement. a collision occurred between banggai-sula microcontinent with north east arm sulawesi. this causes north arm sulawesi to rotate 20° clockwise and causes subduction in the sulawesi sea (hinschberger et al., 2005). the libungo geothermal area is a geothermal area in suwawa which has a high temperature of the hot springs among other geothermal areas in suwawa (manyoe, 2019; manyoe and bahutalaa, 2017; suleman and angsari, 2005; tolodo et al., 2019). the libungo geothermal area is composed of bilungala volcanics (tmbv), bone diorite (tmb), pinogu volcanics (tqpv), reef limestone (ql) and lake deposits (qpl) (apandi and bachri, 1997). bilungala volcanic arcs are formed below sea level. sula's micro fragment collide into an arc and stops the magmatisme associated with the bilungala arc. new volcanic activity occurs from different tectonic events and produces pinogu volcanics (hamilton, 1979; moore and silver, 1983; perelló, 1994). manyoe (2019)studies the libungo area based on geological conditions. suleman and angsari (2005)studied geochemistry in the libungo area while direktorat panas bumi (2017) investigated through geomagnetic, gravity, and electrical methods. the gradient thermal welldrilling in the geothermal area of libungo conducted by (nanlohi and risdianto, 2006). manyoe's research can show the surface lithology of the libungo area (manyoe, 2019). suleman and angsary's research can show reservoir fluid characteristics (suleman and angsary, 2005). directorate panas bumi (2017) research can show deep subsurface interpretations. however, there is no research in the libungo geothermal area that discusses the details of shallow subsurface conditions that can model the distribution of lithology in the shallow subsurface areas in libungo. shallow subsurface can be identified using the resistivity method (suryadi et al., 2018). resistivity methods have an important role in geothermal studies. circulation of hot fluid at subsurface affects the resistivity properties of geological http://journal.uir.ac.id/index.php/jgeet 76 manyoe, i.n. et al./ jgeet vol 5 no 2/2020 formations in geothermal areas (thanassoulas, 1991). the general resistivity method and the schlumberger configuration resistivity method that will be used by researchers can create shallow subsurface and deep subsurface models (chabaane et al., 2017; el-qady, 2006; islami, 2019; suryadi et al., 2018; teftae et al., 2019). volcano-tectonic processes in the libungo area can be the cause of the presence of geothermal potential. it is very interesting to examine shallow subsurface conditions in the research areathat are not explained in detail in previous studies. this research aims to create a shallow subsurface model in the hot springs area of the libungo geothermal based on resistivity data.this research is useful to show the media spread of the fluid in the shallow subsurface so that it can be the basis for the development of direct utilization of geothermal potential in the libungo around the hot springs area. 2. methods 2.1. research location data was collected in the libungo geothermal area. administratively, the libungo geothermal area is located in the south suwawa district, bone bolango regency, gorontalo province. the north of research area is bordered by the valley of the bone river. the south is bordered by the southern volcanic hills. east side is bordered by southern volcanic hillsides. the west is bordered by the southern volcanic hillsides. regionally, the research area is composed of volcanic rocks, plutonic rocks and sedimentary rocks (fig. 1). fig.1. regional geology of research location (apandi and bachri, 1997). bone diorite (tmb) is composed of granite, granodiorite and diorite. bilungala volcanics (tmbv) is composed of basalt, breccia, andesite lava, tuff, dacite and rhyolite. bilungala volcanics (tmbv) is entirely composed of volcanic rock. bone diorite (tmb) is interpreted as being comagmatic towards bilungala volcanics (apandi and bachri, 1997; bachri, 2006; perelló, 1994). pinogu volcanics (tqpv) is composed of breccias, tuffs and lava. reef limestone (ql) is composed of clastic limestone and reef limestone. lake deposits (qpl) is composed of claystone, sandstone and gravel (apandi and bachri, 1997; perelló, 1994). bilungala volcanics (tmbv) and bone diorite (tmb) formed in the middle miocene to early pliocene. pinogu volcanics (tqpv) are formed in late pliocene to early pliocene while reef limestone (ql) and lake deposits (qpl) are formed in plio-plistocene and uplift (bachri, 2006). 2.2 data collection resistivity data acquisition is carried out around the libungo hot springs, namely the libungo hot spring 1 and the libungo hot spring 2. the libungo hot spring 1 is at coordinates 0.5195°n and 123.1447°e. the libungo hot spring 2 is at coordinates 0.5213°n and 123.1448°e (fig. 2). fig.2. electrical station survey. gf1 till gf6 are electrical station point. lh1 and lh2 are libungo hot springs point. the instrument used for resistivity data acquisition is the ipmgeo-4200 resistivity meter. gf1 points are at coordinates 0.5212°n and 123.1445°e while gf2 points are at coordinates 0.5211°n and 123.1457°e. gf3 points are at coordinates 0.5195°n and 123.1439°e while gf4 points are at coordinates 0.5194°n and 123.1451°e. gf5 points are at coordinates 0.5189°n and 123.1437°e while gf6 points are at coordinates 0.5187°n and 123.1449°e. the electrode configuration used is the schlumberger configuration. a and b electrodes are current electrodes. m and n electrodes are potential difference electrodes. l is the distance of ab/2 and l is the distance of mn/2 (fig. 3). fig. 3. schlumberger electrode configuration (adapted from santoso, 2002). the direction of the array is east-west direction. electric current is injected into the subsurface through a current electrode and the distribution of the potential difference is measured by the potential difference electrode. the measurement starts from the middle of the array to both ends of the array by changing the distance between the electrodes. 2.2. data processing and interpretation data obtained from the results of the acquisition are current data (i) in units of ma and potential difference data (v) in units of mv. additional data used to determine variations in resistivity are geometric factors (k). current electrodes and potential electrodes have moved from the center to the end of the array during the data acquisition process. the removal of these electrodes follows the schlumberger electrode configuration. therefore, it is necessary to calculate the geometry factor to correct the manyoe, i.n. et al./ jgeet vol 5 no 2/2020 77 electrode configuration using eqn. (1). where l is the distance of ab/2 and l is the distance of mn/2. k = π (l 2 -l 2 ) 2l (1) after calculating the geometry factor, the calculation of the resistivity value (ρ) is then performed. calculation of the resistivity value by entering the data of current (i), potential difference (v) and geometry factors (k) using eqn. (2). ρ = k v i (2) the thickness of the subsurface layers is obtained by plotting variations of resistivity value versus depth in curve. based on variations of resistivity value versus depth, interpretation of subsurface layers using resistivity values by hunt (2005); mori (2003); telford w.m, geldart l.p (1990); wintolo et al., (2017) with regard to the geology of the research area (table 1). the results are displayed in the form of a single log, lithology fence and 3d lithology model using rockworks 16. table 1. resistivity value of materials (hunt, 2005; mori, 2003; telford w.m, geldart l.p, 1990; wintolo et al., 2017). no material resistivity (ωm) 1 silty clay 3 – 150 2 clay 1 – 100 3 sandstone 50 500 4 volcanic breccia 90 290 5 tuff 5 14 6 andesite 100 2000 7 granite 1000 10000 8 diorite 104 105 9 basalt 10 – 1.3 x 107 10 bedrock: well fractured to slightly fractured with moist material in cracks 150 300 11 bedrock : slightly fractured with dry material in cracks 300-2400 3. result and discussion the variation of resistivity versus depth is displayed in the form of single log, lithology fence and lithology model. single log displays lithology distribution based on depth at each resistivity data collection point. lithology fence displays lithology distribution patterns around the libungo hot springs. the lithology model displays a shallow subsurface model of the libungo geothermal region, an explanation of the physical properties of the subsurface of each lithology based on resistivity. lithology symbol and color by apandi and bachri (1997) and victorine (2008) used in single log, lithology fence and lithology models (fig. 4). fig.4. lithology simbols and colors (apandi and bachri, 1997; victorine, 2008). single log gf1 reaches a maximum depth of 20.61 m (fig. 5). single log gf1 consists of three layers, namely soil, silty clay and volcanic breccia. soil as the first layer, silty clay as the second layer and volcanic breccia as the third layer. the soil is at a depth of 0 0.84 m with a thickness of 0.84 m. silty clay is at a depth of 0.84 15.49 m with a layer thickness of 14.65 m. volcanic breccia is at a depth of 15.49 20.61 m with a thickness of 5.12 m. based on regional stratigraphy, silty clay is synchronized with lake deposits (qpl) and volcanic breccia is equivalent to pinogu volcanics (tqpv). single log gf2 reaches a maximum depth of 25 m (fig. 6). single log gf2 is near libungo hotspring 2. soil as the first layer is at a depth of 0 0.60 m with a thickness of 0.60 m. starting from a depth of 0.60 11.94 m, there are alternates between clay and silty clay. clay is at a depth of 0.60 0.71 m with a layer thickness of 0.11 m. the next layer is occupied by silty clay which is at a depth of 0.71 1.64 m with a thickness of 0.93 m. at a depth of 1.64 3.64 m, a layer of clay with a thickness of 1.99 m is found. the next layer is silty clay which is at a depth of 3.64 11.96 m with a thickness of 8.3 m. volcanic breccia in the next layer is at a depth of 11.94 25 m with a thickness of 13.06 m. based on regional stratigraphy, silty clay is synchronized with lake deposits (qpl) while volcanic breccia is equivalent to pinogu volcanics (tqpv). fig 5. single log gf1. fig 6. single log gf2. single log gf3 reaches a maximum depth of 20.41 m (fig. 7). single log gf3 consists of three layers, namely soil in the first layer, silty clay in the second layer and volcanic breccia in the third layer. the soil is at a depth of 0-1 m with a thickness of 1 m. silty clay is at a depth of 1 5.21 m with a layer thickness of 4.22 m. volcanic breccia is at a depth of 5.21 20.41 m with a thickness of 15.2 m. referring to regional stratigraphy, silty clay is equivalent to lake deposits (qpl) and volcanic breccia is equivalent to pinogu volcanics (tqpv). fig 7. single log gf3. the maximum depth that can be achieved in a single log of gf4 is 20.22 m (fig. 8). single log gf4 is near libungo hot spring 1. soil is at a depth of 0 1.03 m. there is clay at a depth 78 manyoe, i.n. et al./ jgeet vol 5 no 2/2020 of 1.03 3.23 m. silty clay is at a depth of 3.23 6.61 m. volcanic breccia is in the lower layer at a depth of 6.61 20.22 m. referring to regional stratigraphy, silty clay is equivalent to lake deposits (qpl) while volcanic breccia is equivalent to pinogu volcanics (tqpv). fig 8. single log gf4. single log gf5 reaches a maximum depth of 20.61 m (fig. 9). the soil was found at depth 0 1.61 m. under the soil layer, silty clay is found at a depth of 1.61 3.65. the next layer is volcanic breccia which is at a depth of 3.65 11.87 m. the lowest layer is andesite which is at a depth of 11.87 20.61 m. silty clay is equivalent to lake deposits (qpl) while volcanic breccia and andesite are equivalent to pinogu volcanics (tqpv). the equalization is based on the regional stratigraphy of the research area. single log gf6 reaches a maximum depth of 20.22 m (fig. 10). single log gf6 consists of four layers, namely soil in the first layer, silty clay in the second layer, volcanic breccia in the third layer and andesite in the fourth layer. the soil is at a depth of 0 1.23 m. silty clay is at a depth of 1.23 2.57 m. volcanic breccia is at a depth of 2.57 12.86 m with a thickness of 10.3 m. fig 9. single log gf5. andesite is at a depth of 12.86 20.22 m with a thickness of 7.36 m. andesite in the research area began to appear at the point of gf5 and at the point gf6. referring to regional stratigraphy, silty clay is synchronized with lake deposits (qpl). referring to regional stratigraphy, volcanic breccia and andesite are equivalent to pinogu volcanics (tqpv). fig 10. single log gf6. gf1 gf6 fence lithology shows the pattern of lithological distribution around the libungo hot springs (fig. 11). gf1 and gf2 are located in the north. gf3 and gf4 are located in the middle. gf5 and gf6 are located in the southern part. silty clay dominates the northern area around the libungo hot springs. volcanic breccia is identified in all areas stretching from north to south. volcanic breccia is getting thicker towards the south. in the south the gf5 and gf6 are marked by the appearance of andesite. silty clay, which at some point is in alternate with clay, is getting thicker to the north. this is influenced by the presence of the bone river in the north. the northern part of the research area, regionally also included in the lake deposits (qpl). the presence of clay and silty clay thickened to the north is interpreted to be influenced by these two things. volcanic breccia is getting thicker to the south. the appearance of andesite in the south can be explained by the presence of southern mountains which are mostly composed of quarternary volcanic rocks namely pinogu volcanics (tqpv). fig 11. litologi fence that shows lithology distribution of gf1 – gf6. according to nanlohi and risdianto (2006), shallow fractures due to tectonics around the libungo hot springs were not found. the heat from the reservoir is transmitted to the surface by the physical properties of porous and permeable rocks. shallow subsurface modeling can show the porous and permeable lithology distribution which is a way to heat and fluid to the surface. the lithology of the research area is composed of andesite, volcanic breccia, silty clay and clay (fig. 12). according to earle (2015), andesite is a volcanic rock which has fractures and does not have fractures. percentage of fractures in andesite are around 0-50%, start from unfracture andesite to fracture andesite.high resistivity in the libungo geothermal area is 320349 ωm. this high resistivity is interpreted as andesite. according to hunt (2005), the resistivity of 320-349 is a lithology that has a slightly fracture with dry material as a fracture filler. based on this classification, andesite in the libungo geothermal area is an andesite which has slightly fractures and is andesite dry. the fracture was not found in the shallow subsurface of the libungo area, according to nanlohi and risdianto (2006), but based on the resistivity value it was found that there was a fracture in andesites in the libungo geothermal area. andesites in the libungo geothermal area can transfer heat from the reservoir. heat transfer by shallow subsurface rocks is similar to research by nanlohi and risdianto (2006), manyoe, i.n. et al./ jgeet vol 5 no 2/2020 79 but based on the interpretation of resistivity, andesite cannot transfer fluid. volcanic breccia are rocks that composed of angular fragments and are the result of brecciation or depositional environments due to volcanic activity (bowes, 1989). volcanic breccia has good porosity and permeability (zou, 2013). medium resistivity in the libungo geothermal area is 177-194 ωm. this medium resistivity is interpreted as volcanic breccia. fig.12. lithology distribution models in the libungo hot springs. a) lithology model 3d; b) litology isopach 3d andesite; c) litology isopach 3d volcanic breccia; d) litology isopach 3d silty clay; e) litology isopach 3d clay; and f) litology isopach 3d soil. according to hunt (2005) resistivity 177-194 ωm is a lithology that has a well to slightly fracture with moist material as a filler. based on this, volcanic breccia in the libungo geothermal area has well to slightly fractures and is a volcanic breccia moist. volcanic breccia in the libungo geothermal area can transfer heat from the reservoir as researched bynanlohi and risdianto (2006). based on the resistivity interpretation, volcanic breccia can also transfer fluid to the surface because it has fractures. silty clay has a porosity of 36-79% (earle, 2015). silty clay has good porosity and permeability so that it can be a medium of heat and fluid to the surface in the libungo geothermal area. this is supported by the resistivity value of silty clay which is in the range of 3.25-37.9 ωm. according tohunt (2005), silty clay and lithology containing silty with resistivity values below 75 ωm have wet-moist physical properties. clay resistivity value in the research area is in the range 1.56-2.78 ωm. according to hunt (2005) the resistivity value in the range 1.56-2.78 ωm is the resistivity value for wet-moist clay. according toearle (2015), clay is a material that has good porosity but has poor permeability. therefore, clay in the libungo geothermal area has good porosity as evidenced by resistivity values that show wet-moist physical properties but cannot transfer fluids properly to the surface. based on the shallow subsurface model, the libungo geothermal area is composed of andesite, volcanic breccia, silty clay and clay. andesites are concentrated in the southern part of the libungo geothermal area, characterized by high resistivity. volcanic breccia spread from the north to the south of the research area. volcanic breccia is getting thicker to the south marked with a medium resistivity value. silty clay is spread from north to south of the research area. silty clay is getting thicker to the north marked by a low resistivity value. clay is scattered in the middle of the northern part of the libungo geothermal area characterized by very low resistivity. 4. conclusion the shallow subsurface of the libungo geothermal area is composed of andesite, volcanic breccia, silty clay and clay. andesite occupies the southern part of the study area. volcanic breccias occupy the northern to southern parts of the research area. silty clay occupies the entire research area. silty clay is getting thicker to the north and volcanic breccia is getting thicker to the south. clay occupies the middle of the north of the research area. the highest resistivity value in the research area is andesite resistivity values ranging between 320-349 ωm. the medium resistivity value is the volcanic breccia resistivity value which ranges between 177-198 ωm. low resistivity value is the resistivity value of silty clay which ranges from 3.25-37.9 ωm. the very low resistivity value is the clay resistivity value which ranges between 1.56-2.78 ωm. andesites in the research area have fractures, but andesites are not a fluid path to the surface. volcanic breccias have fractures. fractures in volcanic breccias provide fluid to the surface. clay and silty clay in the research area are wet to moist but only silty clay is able to transfer fluids properly to the surface. based on resistivity data, the accumulation of geothermal fluid in the libungo area is located in the northern part of the research area in volcanic breccia, silty clay and clay. therefore, direct use of geothermal in the hot springs area of libungo geothermal, it is recommended to be carried out in the northern part by considering the availability of fluid in the shallow subsurface. as for proving that the shallow subsurface fractures in andesite are due to the effects of tectonics, it is necessary to investigate the geological structure in the research area. acknowledgments the authors would like to thank to the research and community service 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environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 02 2019 lubis. m.z et al./ jgeet vol 04 no 02/2019 135 review article review : bathymetry mapping using underwater acoustic technology muhammad zainuddin lubis 1 *, sri pujiyati 2 , budhi agung prasetyo 3 , tiggi choanji 4 1 department of informatics engineering, geomatics engineering, politeknik negeri batam, batam kepulauan riau, 29461 indonesia. 2 marine science and technology, ipb university, indonesia 3 marine environmental science study program, department of science, institut teknologi sumatera , indonesia 4 department of geological engineering, jl. kaharuddin nasution no 113, universitas islam riau, 28125, indonesia. * corresponding author : zainuddinlubis@polibatam.ac.id tel.:+ 6281342578087, office : 778-469856 ext : 2510; fax: +62-778-463620 received: mei 25, 2019; accepted: jun 26, 2019. doi: 10.25299/jgeet.2019.4.2.3127 abstract the bathymetry mapping using underwater acoustic technology very important in indonesia waters. bathymetry is the result of measuring the height of the seabed so that the bathymetric map provides information about the seabed, where this information can provide benefits to several fields related to the seabed. in bathymetry mapping uses underwater acoustic technology where among them is using single beam echosounder and mbes (multibeam echosounder system), and multibeam echosounder (mbes) is acoustic equipment that is intensively used frequently in basic waters mapping. the advantage of using underwater acoustic technology is the acquisition and processing of data in real time, high accuracy and precision (correction of the bathymetry data was carried out with reference to the 2008 international hydrographic organization (iho), and cannot be a threat or damage to objects. retrieval of bathymetry data must use parallel patterns, namely: patterns with perpendicular sounding directions and tend to be parallel to longitudinal lines or in accordance with parallel sounding patterns. keywords: bathymetry, underwater acoustic technology, iho 2008 1. introduction bathymetry is the result of measuring the height of the seabed so that the bathymetric map provides information about the seabed, where this information can provide benefits to several fields related to the seabed, which greatly require bathymetric information such as shipping lanes for transportation and cargo vessels (morlighem et al., 2017). bathymetry information on a waters will experience changes without a certain time limit. changes in these conditions generally will have a causal factor, namely by several factors such as erosion of the coast by waves, sedimentation, land use in coastal areas, etc (riadi et al., 2014). bathymetry is the process of describing the basic waters since measurement, processing, and visualization (masrukhin et. al., 2014). the condition of bathymetry in the waters is very important in relation to the use of space in the coastal area (rampengan, 2009). measurement of bathymetry with conventional methods using the guesswork method, namely the seabed measurement system using cables equipped with ballast pendants whose mass ranges from 25-75 kg (febrianto et al., 2016). but along with the times and technology, the method has begun to be abandoned, especially in measuring the wide and deep waters. current technological developments in bathymetry mapping can be done with acoustic technology, namely by using sound waves so that the use of this technology is better because it does not damage the environment around the research (lubis et al., 2018 and lubis et al., 2017). in bathymetry mapping uses underwater acoustic technology where among them is using mbes (multibeam echosounder system) multibeam echosounder (mbes) is an acoustic equipment that is intensively used frequently in basic waters mapping, especially because this technology has more capabilities namely wide coverage and high resolution for acquisition of bathymetry data (anderson et al., 2008). mbes bathymetry is a process of mapping depth of water expressed in terms of depth or depth contours measured against a vertical datum. a bathymetric map generally displays basal reliefs with contour lines called depth contours or isobaths. mbes bathymetry is a process of mapping the depth of water expressed in terms of depth or depth contours measured against a vertical datum (adi et al., 2017). 2. theory of operation in theory, the use of underwater acoustic technology for bathymetric mapping by optimizing http://journal.uir.ac.id/index.php/jgeet 136 lubis. m.z et al./ jgeet vol 04 no 02/2019 the bathymetry survey will greatly depend on the speed of the ship in making a measurement. the maximum vessel speed in the cast (u) is allowed according to the standard of the ability of the equipment to reach 100% coverage of the seabed along the track direction, that is by using the value of the speed of sound (c), wide of fore-aft ϕ and the width of the vessel gap (2θ) from the existing radiation pattern, and the slope of the ocean floor α in the direction of the survey path (figure 1) and the maximum speed on the ship (figure 2). in the application of bathymetry mapping using underwater acoustic technology, there are factors of value and its relation to the speed of the ship when conducting activities in the waters. the values ϕ start from 0,5 ° until 2,66 °, which provides information that the speed of the ship is more than 12 knots (6 m / s) which can be achieved by front-rear position beamwidth 0,5 ° or larger for warships that have a basic slope up to 45 °. in casting activities, sea conditions or the condition of the ship's speed and the length of the track along the routine will be greater than 100%. fig 1. geometry ensonification on a sloping basis (moustier, 1988). fig 2. maximum boat speed (or 100% coverage with short or high frequency reflections) (moustier, 1988). each transducer used for seafloor mapping has a sending system that emits an acoustic pulse signal with certain characteristics or codes, so that the signal reflected from the bottom of the water is only received by each recipient transducer as shown in figure 3, and illustrated taking bathymetry data using a single beam and multibeam echosounder can be seen in figure 4. fig 3. geometry illustrations in bathymetry data extraction using the multibeam echo sounder. (a) (b) fig 4. (a). illustration of taking bathymetry data using single beam echosounder, and (b). illustration of taking bathymetry data using multi beam echosounder (mbes). 3. bathymetry data correction the level of accuracy obtained from data from the bathymetry result is the main thing that must be known, because there is a relationship with the value of accuracy or accurate level of data to provide information on the bathymetry value of the seabed actually in the water. with this, the data obtained is in accordance with predetermined standards, so it is necessary to control data quality in the form of correction of data on bathymetry data. correction of the bathymetry data was carried out with reference to the 2008 international hydrographic organization (iho). if correction of the bathymetry value after the data has been obtained, it will be corrected by bathymetry by calculating the deviation of depth at the point of lubis. m.z et al./ jgeet vol 04 no 02/2019 137 analysis, which is found at the intersection between the transverse and longitudinal paths expressed as the error (s) based on the equation as follows: s = dl db (1) information: s = depth error dl = depth of analysis point on transverse path db = depth of analysis point on longitudinal path. the magnitude of the error value of the bathymetry results in data collection in water will be limited based on the standards set by iho (2008), ie it cannot exceed the tolerance limit of 2σ. this provision has been based on the values of a and b contained in the minimum standard table for hydrographic survey activities (table 1). accuracy standards in measuring bathymetry activities using special order underwater acoustic technology must be used in critical water conditions, such as shallow waters with slurry bases which have muddy sediments; order 1a is a shallow water area that has a depth of the seabed that is less than 100 meters, with a distance below the keel of the ship which has been affected by a smaller critical area; order 1b is a shallow water area of less than 100 meters, ie the distance below the keel of the ship is not considered by the critical area again with factors including the expected surface type area; while order 2 will be applied to the depth of an aquatic waters more than 100 meters or deep waters (iho 2008). iho standards of hydrographic surveys is a standardization or technical reference issued by iho (international hydrographic organization). iho hydrographic surveys sp-44 in 2008 is the latest standardization that has undergone renewal (iho 2008). in this 2008 iho sp-44, measurements of depth tolerance were carried out. if the error value in different depth data is still within the tolerance limit obtained by calculating formula (i), then the quality of depth data goes into the tolerance limit which refers to the 2008 iho standards of hydrographic surveys sp-44. beyond tolerance, the depth of quality does not enter the tolerance limit. table 1 is the standard for accuracy of water depth measurements (iho 2008). table 1. standards for accuracy of water depth measurements. orde spesial 1a 1b 2 depth detail a = 0,25 m a = 0,5 m a = 0,5 m a = 1,00 m b = 0,0075 b = 0,013 b = 0,013 b = 0,023 the process of calculating the error limit or tolerance limit error in measuring bathymetry in a waters will refer to the iho standard (2008), which is mathematically using the equation: (2) where : a = constant constant error (m) b = non-permanent depth error factor d = measured depth (m) b x d = error in depth which is not fixed (m). correction of bathymetry data of water will determine the accuracy of the bathymetry data used to determine the position of a target or determine a ship's shipping lane. some of the depth points used in making corrections to the bathymetry data are determined based on the intersection point of the gridding milling path. this aims to be able to find out how much deviation or error detection is in the same position at different times. the error value of each water depth correction point does not exceed the tolerance limit set by iho (2008). 4. underwater acoustic technology underwater acoustic technology that will use the hydroacoustic method while this method has several systems, one of which is the single-beam echosounder system, which is an air enhancement measuring device that uses a single beam system to buy and receive sound signals (snellen et al., 2011). this system measures air depth directly from ship surveys (brouwer 2008). in general, singlebeam has a component transceiver on the hull or bearing side of the ship. transceiver transfers acoustic pulses with certain frequencies contained in the beam directly down the air column while in the pathway (lubis and anurogo, 2016; lubis and pujiyati, 2016). before carrying out oceanic mapping or bathymetry activities using underwater acoustic technology, the raw data obtained from sonar will be collected for each ping in a beamformed and the range of objects or bathymetry values detected (roman and singh, 20015). this range detection will be achieved by looking at each beam and making selections in the range of peak amplitude returned to the receiver from the transducer. to reduce the possibility of this error, which has a relationship with the return of very weak signals, the beam does not overwrite the bottom and other false detection with the range sent using the amplitude threshold value and median filter with neighboring beams, this can be seen in figure 5. the resolution owned by sonar has a maximum range value that will carry out a pulse transmission process with a fixed duration of time (τ) which is determined by the bathymetry axis as long as the reflected volume will be returned from individual reflections that cannot be distinguished, with the following equation: τ/2 (3) where c is the speed of sound, which will be considered with acoustic backscatter values obtained with various distances in bathymetry in the waters, illustration of the beam obtained in this case can be seen in figure 6. 138 lubis. m.z et al./ jgeet vol 04 no 02/2019 figure 5. sample single ping obtained from multibeam sonar which can be formatted and plotted as intensity images in 2d cartesian space. fig 6. dependence on the back scattering angle is spread out, with a sketch showing normal and grazing incidence. references adi, a. p., manik, h. m., & pujiyati, s., 2017. integrasi data multibeam batimetri dan mosaik backscatter untuk klasifikasi tipe sedimen. jurnal teknologi perikanan dan kelautan, 7, 1, 77-84. anderson, j. t., van holliday, d., kloser, r., reid, d. g., & simard, y. 2008. acoustic seabed classification: current practice and future directions. ices journal of marine science, 65, 6, 1004-1011. brouwer pai., 2008. seafloor classification using a single beam echosounder [tesis]. department of earth observation and space system cahir of acoustic remote sensing. delf, the netherlands. p 1. de moustier, c., 1988. state of the art in swath bathymetry survey systems. febrianto, t., hestirianoto, t., & agus, s. b. 2016. pemetaan batimetri di perairan dangkal pulau tunda, serang, banten menggunakan singlebeam echosounder. jurnal teknologi perikanan dan kelautan, 62, 139-147. international hydrographic organization., 2008. standards for hydrographic surveys. 5th ed. monaco fr: international hydrographic bureau publishing. lubis, m. z., & anurogo, w., 2016. fish stock estimation in sikka regency waters, indonesia using single beam echosounder cruzpro fish finder pcff-80 with hydroacoustic survey method. aceh journal of animal science, 12, 70-78. lubis, m. z., & pujiyati, s., 2016. detection backscatter value of mangrove crab scylla sp. using cruzpro fishfinder pcff-80 hydroacoustic instrument. j. biosens. bioelectron, 72, 2. lubis, m. z., anurogo, w., kausarian, h., choanji, t., antoni, s., & pujiyati, s., 2018, july. discrete equispaced unshaded line array method for target identification using side scan sonar imagery. in iop conference series: earth and environmental science vol. 176, no. 1, p. 012025. iop publishing. lubis, m. z., kausarian, h., & anurogo, w., 2017. seabed detection using application of image side scan sonar instrument acoustic signal. journal of geoscience, engineering, environment, and technology, 23, 230234. masrukhin, m. a. a., sugianto, d. n., & satriadi, a., 2014. studi batimetri dan morfologi dasar laut dalam penentuan jalur peletakan pipa bawah laut perairan laranganmaribaya, kabupaten tegal. journal of oceanography, 31, 94-104. morlighem, m., williams, c. n., rignot, e., an, l., arndt, j. e., bamber, j. l., ... & fenty, i., 2017. bedmachine v3: complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation. geophysical research letters, 4421, 11-051. rampengan, r. m., waters. j. perikanan dan kelautan, 53, 68-72. riadi, e., zainuri, m., & purwanto, p., 2014. studi kondisi dasar perairan menggunakan citra sub-bottom profiler di perairan tarakan kalimantan timur. journal of oceanography, 31, 26-35. roman, c., & singh, h., 2005. improved vehicle based multibeam bathymetry using sub-maps and slam. in 2005 ieee/rsj international conference on intelligent robots and systems pp. 3662-3669. ieee. snellen, m., siemes, k., & simons, d. g., 2011. model-based sediment classification using single-beam echosounder signals. the journal of the acoustical society of america, 1295, 2878-. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. theory of operation 3. bathymetry data correction 4. underwater acoustic technology references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 01 2019 16 putra, d.b.e., et al./ jgeet vol 04 no 01/2019 research article saltwater intrusion zone mapping on shallow groundwater aquifer in selat baru, bengkalis island, indonesia dewandra bagus eka putra 1, *, yuniarti yuskar 1 , husnul kausarian 1 , wan zuhairi wan yaacob 2 , mohamad sapari dwi hadian 3 1 department of geological engineering, faculty of engineering, universitas islam riau 2 department of geology, universiti kebangsaan malaysia 3 laboratory hydrogeology and environmental geology, faculty of geological engineering, universitas padjadjaran * corresponding author : dewandra.bagus@eng.uir.ac.id tel.:+62-819-5954-3306 received: jan 1, 2019; accepted: feb 1, 2019. doi: 10.25299/jgeet.2019.4.1.2672 abstract saltwater intrusion becomes a common problem in coastal area. northern coast of bengkalis island in riau, indonesia that contiguously to malacca strait is experiencing the problem particularly in selat baru area which considered as developing area and most of the people live close to the sea. dug well is the main source of groundwater that had been used by the population in selat baru and as the increasing of land occupation, the demand of clean water is rising up followed by the number of dug well. a study of groundwater monitoring was conducted to identify the zone of saltwater intrusion. field observation had done by measuring the water level and physical parameters of groundwater such as taste, ph, electrical conductivity (ec) and total dissolved solid (tds) from 110 existing dug wells. some conus feature had found from groundwater elevation map which indicated lower water level caused by excessive groundwater pumping. generally, ph shows values from 6-8 that was still in range of water quality standard, but there are 20 wells (18%) that have ph below the water quality standard (slightly acidic water). similar pattern had been observed from electrical conductivity (ec) and total dissolved solid (tds) map, higher value of ec and tds was dominant in the northern part of study area and lower value in the south. groundwater taste map also revealed the identical condition with ec and tds map which dominated by brackish and saline water in the northern part. therefore, the study area had been divided into two zones of groundwater saline water zone possibly caused by the saltwater intrusion in the northern part and freshwater zone from the center to the southern part. keywords: coastal groundwater, groundwater quality monitoring, saltwater intrusion, groundwater physical parameters 1. introduction groundwater is an essential and valuable water resource in many developing countries (taufiq et al., 2018), the number of societies facing water shortages is increasing as the level of the groundwater table decreases as a consequence of excessive usage and the level of pollution of surface and groundwater resources increases due to environmental impacts. for this reason, there have been many studies on water quality in various parts of the world ((gültekin et al., 2013); (srivastva et al., 1988); (baykal et al., 2000); (mladenov et al., 2007); (jaji et al., 2007); (tayfur et al., 2013)). there are many benefits of groundwater for the survival of living beings. present land use activities had large contribution for the change of water quality (karanam et al., 2019). for humans the groundwater used to meet daily needs. intensive irrigated agriculture substantially modifies the hydrological cycle and often has major environmental impacts (foster et al., 2018). during recent decades, the agricultural exploitation of water has been strongly reinforced, causing an over-pumping of the groundwater resources accompanied by an intrusion of seawater (chabaane et al., 2018). groundwater is the main source of drinking water for the people of indonesia (sapari et al., 2017). saltwater intrusion became an important issue in coastal region because it can affect the freshwater quality in surrounding areas (putra et al., 2017). climate change-induced sea level rise on multiobjective saltwater intrusion management strategies in coastal aquifers (kumar and bithin, 2018) (hamed et al., 2018). the salinity of water resources is an important problem that the world population suffers. this salinity has been studied intensively during the past decades, particularly in coastal aquifers (bahir et al., 2018). in environmental management, at first the human relationship with the environment running in a spirit of harmony that humans become an integral part of nature so that its behavior in tune and in harmony with the rhythms of nature and nature conservation in these conditions can be maintained (suhartono et al., 2015). the use of natural resources was massive and uncontrolled and ignore the environmental http://journal.uir.ac.id/index.php/jgeet mailto:dewandra.bagus@eng.uir.ac.id putra, d.b.e., et al./ jgeet vol 04 no 01/2019 17 equilibrium will result in a variety of negative effects will be felt in relatively quick time in both the acute and the condition of chronic conditions in the long term. environmental damage in coastal areas triggered by ecological conditions of coastal areas that can meet the economic needs of human beings through some important activities such as industry, fisheries and services 2. study area selat baru is a small area located in the northern coast of bengkalis island, riau, indonesia and contiguously to malacca strait. the strait of malacca is located between the east coast of sumatra island in indonesia and the west coast of peninsular malaysia, and is linked with the strait of singapore at its southeast end ((thia-eng et al., 2000); (yuskar et al., 2018)). the study area was found to have brackish water in its river owing to a certain amount of salt water mixing ((putra et al., 2017); (putra and yuskar, 2016)). the study was initiated from the result of water quality analysis in the western area of bantan tua, jangkanng and deluk village which adjacent directly to selat baru village (fig. 1). the people of selat baru area, use groundwater for domestic purpose. they normally get their water supply from the shallow aquifer through traditional hand-dug wells as well as from the surrounding rivers. even though, there is no official report about saltwater intrusion but it is very important to have proper planning and management of the groundwater exploitation in the coastal area of north bengkalis island especially selat baru village. the effect of an excessive withdrawal, especially during dry season, must be taken into account in order to avoid risk of saltwater intrusion into the groundwater aquifers (samsudin et al., 1997). stratigraphy of the study area (fig.2) are composed of rocks that include surface deposits which are young superficial deposit (qh), and older superficial deposit (qp) (cameron, 1983). young superficial deposit consists of clays, silts, clean gravel, vegetation rafts, peat swamps and older superficial deposits consist of clays, silts, clayey gravels, vegetation rafts (yuskar et al., 2018). 3. methodology the research had been conducted by measuring 110 dug wells in selat baru beach and the surrounding area. shallow groundwater depth measured using manual and simple tools such as rope, stone and tape rule. elevation and coordinate of each dug well position had been acquired using gps. the physical parameters of water samples measured in the field are color, taste, temperature, ph, electrical conductivity (ec) and total dissolved solid (tds). those parameters divined using ysi pro-1030 water quality instrument. fig. 1. location of study area, selat baru area and surrounding bengkalis island riau indonesia (source: google earth 2018). 18 putra, d.b.e., et al./ jgeet vol 04 no 01/2019 fig. 2. regional geological map of study area. 4. result and discussion the data of each dug well being processed to produce shallow groundwater isopach map (fig. 3), ec and tds map (fig. 4 & 5) and groundwater taste map (fig. 6). physical parameters such as temperature, ph, ec, and tds had been used as a comparison to water quality assessment. 4.1 groundwater contour map groundwater contour isopach map had been produced from the measuring the elevation of groundwater level in each well. groundwater elevation is in range from 0.5-13.35 m.a.s.l. groundwater elevation map shows some conus feature (a, b, d, d and e) that indicating deeper water level possibility caused by the excessive use of groundwater (fig. 3). 4.2 ph and temperature in general, ph condition of groundwater is in normal value, in range of 6-8 and average 6.84. only 20 wells (18%) that have ph value below the water quality standard (slightly acidic type of water). the temperature of groundwater also shows the normal value with average 27.26 o c and in range of 25.730.6 o c which meet the values of water quality standard. 4.3 electrical conductivity (ec) and total dissolved solid (tds) ec and tds values show similar pattern (fig.4 and 5), dominated by higher in the northern part of the study area and lower in the south. ec has average value of 1500.3µs/m and in range of 125.8-11485µs/m while tds has average value of 947.93mg/l and in range of 76.5-7214mg/l. those value represented by the taste of groundwater that more saline in the northern wells. fig. 3. groundwater elevation map shows the occurrence of some conus features that indicated by dark blue color (a, b, c, d and e). from the map, freshwater was shown by bright and dark green color (tds 0-2000mg/l; ec 0-1000µs/m) and brackish water shown yellow and brown color (tds 2000-4000mg/l; ec 1000-7000 µs/m), and saline water shown by blue color (tds >4000mgl/l; ec >7000 µs/m). putra, d.b.e., et al./ jgeet vol 04 no 01/2019 19 4.4 groundwater taste map groundwater taste map shows the majority of water in the research are is freshwater (fig. 6). however, in the northern area, the groundwater taste had become more saline towards the coastline. in total, 24 wells had brackish taste water (21.8%), four wells had salty taste water (3.6%) and the remaining 82 wells had tasteless water (74.6%). several wells in the central part of the study area around the conus a and e (sbd 10, 32 and 33) have brackish water and proven by the ec and tds value of the water (consecutively 3993µs/m & 2517mg/l; 4449µs/m & 2752mg/l; 1594µs/m & 1002mg/l), those areas interpreted as the area that suffered from intrusion event due to excessive use of groundwater. fig. 4. groundwater ec map that shown higher value in the northern part and lower value in southern part with several locations in central part have high value. fig. 5. groundwater tds map that shown similar pattern to groundwater ec map. 20 putra, d.b.e., et al./ jgeet vol 04 no 01/2019 fig. 6. groundwater taste map that divided the groundwater zone into two, brackish water zone in the north and freshwater zone in the south. 5. conclusion in conclusion, the study area was divided into two zones of groundwater, brackish water zone possibly caused by the saltwater intrusion in the northern part and freshwater zone from the center to the southern part. some wells in the southern part had higher ectds value and located in the conus feature regions; this might be a result of saltwater intrusion that reached those areas. however, advance study needs to be carried out to ensure the impact of saltwater intrusion to the groundwater and to determine the subsurface saltwater-freshwater boundary in study area. acknowledgment thank you to aldila and anang putranto that help authors to collect the field data and to lembaga penelitian dan pengabdian masyarakat (lppm) universitas islam riau for the research funding. references bahir, m., ouhamdouch, s., carreira, p.m., 2018. geochemical and isotopic approach to decrypt the groundwater salinization origin of coastal aquifers from semi-arid areas (essaouira basin, western morocco). environ. earth sci. 77, 485. 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https://doi.org/ttps://doi.org/10.1007/978-981-108471-3_90 © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.24273/jgeet.2017.2.4.578 https://doi.org/10.24273/jgeet.2017.2.4.578 https://doi.org/10.24273/jgeet.2017.2.4.578 https://doi.org/10.24273/jgeet.2017.2.4.578 https://doi.org/10.24273/jgeet.2017.2.4.578 https://doi.org/10.1016/j.proenv.2015.01.017 https://doi.org/10.1016/j.proenv.2015.01.017 https://doi.org/10.1016/j.proenv.2015.01.017 https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10040-018-1728-z https://doi.org/10.1007/s10661-007-0068-6 https://doi.org/10.1007/s10661-007-0068-6 https://doi.org/10.1007/s10661-007-0068-6 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 https://doi.org/ttps:/doi.org/10.1007/978-981-10-8471-3_90 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ saltwater intrusion zone mapping on shallow groundwater aquifer in selat baru, bengkalis island, indonesia 1. introduction 2. study area 3. methodology 4. result and discussion 4.1 groundwater contour map 4.2 ph and temperature 4.3 electrical conductivity (ec) and total dissolved solid (tds) 4.4 groundwater taste map 5. conclusion acknowledgment references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 taufan, y.a., et al./ jgeet vol 5 no 3/2020 113 research article resistivity models of pantar island geothermal system east nusa tenggara, indonesia y.a. taufan 1,*, i. syafri1, a.agus nur1, d. risdianto2, a. zarkasyi2, t.rahadinata2, w. awaludin2 1department of geological enginerring, padjadjaran university, , bandung, indonesia. 2department centre for minerals, coal, and geothermal resources, geothermal group, bandung, indonesia. * corresponding author: yoqie.taufan@gmail.com tel : +628179189958 received : june 5, 2020; accepted : july 24, 2020. doi : 10.25299/jgeet.2020.5.3.5115 abstract the subsurface geological conditions of a geothermal system are vital objects to be considered in geothermal exploration. the magnetotellurics survey was conducted to explore for geothermal potential in pantar island. this is to achieve deeper penetration compared to our previous study that adopted resistivity method to determine reservoir zones based on rock resistivity models. the difference in rock resistivity in geothermal systems provides subsurface geological information in the form of low resistivity that associated the clay cap zones (high conductive), the medium resistivity zones associated with the reservoir zones, and high resistivity associated with a heat source. the results of 2d and 3d models from mt data show that the low resistivity value (<20ωm) as a clay cover zones, this layer from the surface to -1000 meters. medium resistivity values (20-100 ωm) starting from depths -1000 meters to -2000 meters associated with reservoirs zones, high resistivity values (> 200 ωm) starting from depths of -2000 meters are considered as heat source from the pantar geothermal system. keywords: magnetotellurics, resistivity models, geothermal system 1. introduction 1.1 background of research indonesia has a large geothermal potential in the world (merry et al., 2017), with a potential resource of 11,073 mw and reserves of 17,506 mw (ministry of energy and mineral resources., 2017) but only a few regions have produced (maryanto et al., 2017). the existence of geothermal energy consists of exploration activities to find potential energy sources. required geological conditions that have geothermal system criteria, this system is indicated by the presence of clay cover, reservoir where liquids accumulate, heat sources, geological structures that are generally in the form of fractures, and fluids that act to deliver heat from the reservoir to the surface. (moeck, 2014) the existence of a geothermal system in an area will not exist if the components of the geothermal system are not met. (carlson and plumer, 2008). the existence of reservoir information is an important part of the next stage of geothermal exploration. geothermal energy is formed naturally through the interaction of rocks and heat flowing beneath the earth's surface (zobin, 2017). the geothermal conditions require an effort to find energy potential as an exploration activity. traditional geological methods have difficulty identifying geothermal reservoirs that are buried deep because they only depend on the availability of point measurements, including hot spots, and analysis of water samples. geophysical methods with deep penetration for reservoir detection are the key to geothermal energy exploration (lan fang et al., 2016). geophysical investigation with gravity method and amt (audio-frequency magnetotellurics) method for geothermal potential on pantar island was conducted in 2015. this investigation was aimed at finding out the geothermal system on pantar island (figure 1). the results of the investigation with 2 (two) methods are still limited to the depth of subsurface geological information (rahadinata and taqodama, 2015). geophysical investigation using magnetotellurics (mt) method was carried out as a follow-up. (nainggolan et al., 2015). this method has the advantage of deeper penetration (aboud, 2014) with better accuracy compared to previous investigations. the mt method is one of the most widely used geophysical methods in geothermal exploration (lowrie, 2012), (reynolds, 2011) because of its ability to detect relatively deep subsurface conditions. this method is one of the passive geophysical exploration methods which record the magnitude of the earth's electromagnetic field (em), in order to determine the subsurface geological conditions with resistivity and conductivity parameters (bera and rao, 2012). difference in rock resistivity geothermal systems can provide subsurface geology in the study area, including determining reservoir zones (panjaitan, 2010). the purpose of this research is to study the geothermal reservoirof pantar island, and obtain 2d &3d subsurface models based on the resistivity parameters generated from magnetotellurics (mt) which is continuation of the method from previous studies. 1.2 location http://journal.uir.ac.id/index.php/jgeet 114 taufan, y.a., et al./ jgeet vol 5 no 3/2020 the location of this research is in geothermal area, of mount sirung, pantar island. located in alor regency, east nusa tenggara province, indonesia. located at coordinates 9059000 9073000 mu and 621000 633000 mt on the utm system, 51 s zone. fig 1. the research location, pantar island, east nusa tenggara, indonesia (adapted from hadi and kusnadi., 2015) 1.3 regional geology the rocks that occupy the north and east coasts are sedimentary rocks, which are limestone reefs, in the middle there are the oldest rocks formed at the end of tertiary namely kongmewas rocks and kalondama volcanic rocks with a geological structure directed north which separates the two old volcanic products. volcanic products in the form of old sirung products occupy the middle to the eastern part of beang beach, while the sirung pre-caldera formation is filled with boyali volcanic products, and mauta is in the south. in the middle between the peaks of sirung tua and boyali, a large explosion process occurs which produces pyroclastic and basal lava. the old sirung pyroclastic product and the material that came out was the result of a large eruption which caused a mass vacuum in the middle to collapse and form the sirung caldera. volcanic activity appears next to the collapsed caldera wall forming sirung's lava body and outside the caldera forms beang hill. the young sirava lava in the middle of the sirung crater is the youngest product of the sirung complex. the geological structure that developed in the field of investigation is dominated by the north-south direction relatively as a major internal fault. this pattern is related to the regional tectonic direction that is developing in the pantar area (figure 2). in this area there are volcanic structure patterns such as caldera, allegedly formed by a massive eruption that exploded from the eruption of the mount sirung complex resulting in a mass vacuum and collapsed to form a caldera and a crater. the volcanic structure pattern of sirung volcanic caldera formed around the summit of mount sirung forms linear with diameters starting from 2 km (hadi and kusnadi, 2015). fig 2. geological map of research location, pantar island, east nusa tenggara, indonesia (hadi and kusnadi, 2015) taufan, y.a., et al./ jgeet vol 5 no 3/2020 115 2. method 2.1 basic theory of mt the electric-magnetic phenomenon affecting electrical properties (unsworth, 2006), especially the conductivity of the medium (earth) can be exploited for exploration purposes using the mt method. this is done by simultaneously measuring variations in the electric field (e) and magnetic field (h) as a function of time. information about conductivity or resistivity contained in mt data can be obtained using the maxwell equation (telford et al., 1990) using a relatively simple model. mt measurement can produce resistivity information as a function of frequency and then can produce true resistivity to depth (m). mt measurements in this area have scattered observation points so that can be used as resistivity models on the west-east path. the results of the field data are then processed by fourier transforming the data into a 2d inversion process, then visualizing the 3d model for analysis into subsurface geological information. the differential form, maxwell's equation (telford et al., 1990) in the frequency domain can be written in the following equation: t b xe    (1a) t d jxh    (1b) qd  (1c) 0 b (1d) h is the magnetic intensity, j is the current density, e is the electric field, b is the magnetic field induction, d is the shift of electricity, and q is the electric charge. equation (1a) is derived from faraday's law which states that changes in magnetic flux cause an electric field with an electromotive force opposite to the variation of the magnetic flux caused by the electric field. equation (1b) is a generalization of ampere's theorem by calculating the law of conservation of charge enhanced by maxwell. the equation states that the magnetic field will be generated as a result of the current density and fluctuating electric current movement. equation (1c) states that gauss's law is the transfer of electricity in a space in proportion to the density of the electric charge in that space. while equation (1d) which is identical to equation (1c) applies to magnetic fields, but in magnetic flux or induction there is no magnetic monopoly. generally, the skin depth equation is written as inequation (2), ff     1 500 (2) equation (2) explains the value of skin depth is inversely proportional to frequency and directly proportional to wavelength. every time in mt measurements in the field, the desired object is at a height that can be inside, then the em waves needed are waves that have a small frequency or a large wavelength (naidu, 2012) 2.2 research stages the research method consists of data acquisition, data processing, and data interpretation. mt survey has been carried out in april2017. mt data acquisition has beencovering the area geothermal prospects. location of the mt measurement is shown in black dots (figure 3). thedistance between measurement points is about 1-1.5 km. the data processing, modeling, and interpretation ofobtained mt anomaly data have been carriedout at the centre for minerals, coal, and geothermal resources, geothermal group, bandung. fig 3. research location map with 4lines mt (adapted from rahadinata and taqodama, 2016) modeling for this research uses the inversion process, which is a modeling process by processing field data using mathematical and statistical parameters to obtain subsurface model information based on physical properties distribution (meju, 1994). in the inversion process, an analysis of field measurement data is carried out by performing curve fitting between the mathematical model and the field measurement data. the purpose of the inversion process is to determine the physical parameters of subsurface rocks that were not previously known. 116 taufan, y.a., et al./ jgeet vol 5 no 3/2020 fig 4. inversion modelling flow (meju, 1994) 3. result and discussion the results which obtained in this research include the results of modeling and interpretation. 3.1 result of resistivity model the model results in the study area are designed to be representative of all regions that are thought to have geothermal prospects based on the results recommended by previous studies. vertical models in the study area are displayed as many as 4 (four) line strajectories representing the study area. the results of the 2d and 3d models displayed provide combined information in the study area (figure 3). the results of this study obtain a subsurface model that is produced deeper than the previous resistivity method (vozoff, 1991), thus providing heat source zone information on the geothermal system on pantar island. the resistivity distribution is displayed in various color scales. blue indicates low resistivity (conductive), and red represents rocks with high resistivity values. the zone of low value ≤ 20 ωm from the surface to a depth of -700 m and detected to a deeper depth that is a depth of -1000 m at other locations, is generally spread over most of the investigation area. low zone around the manifestation of geothermal is thought to be related to hydrothermal activity in the form of alteration rocks which are found around the emergence of hot and hot water, tuff, breccia, polymic breccia, and pyroclastic. the results of the study also carried out a structural interpretation of the results of 2d resistivity model from this mt data. the 2d model is displayed in a vertical cross section that describes the vertical resistivity distribution of rocks (singarimbun et al., 2017). 3.2 discussion 3.2.1. 2d model the modelling results show rock resistivity values from 0 ωm to ≥ 250 ωm. line a (figure 5), the uppermost layer with a low resistivity value (0-20 ωm) shown by the blue layer, this layer continues from the surface to a depth of -1000 m in the west and the east of the line, while in the middle of the line has a depth of -750 m. the low resistivity zone on this path is thought to be the response of the hydrothermal activity product rock in the form of alteration rocks and volcanic sedimentary rocks, this zone is thought to be a clay cap in this geothermal system (weldeyohannes, 2018). the green-yellow, has a resistivity value of 20-100 ωm, this zone starts to appear at a depth of -750 m which is in the middle of this path, in the west starts from a depth of -1000 m, and the east of this layer starts at a depth -1200 m. this layer is thought to be a transition zone between alteration rock and reservoir. rock layers with moderate resistivity values are found along this path extending from west to east. rock resistivity with a value of 20-100 ωm starting from a depth of -1000 meters is thought to be a reservoir. this zone is thought to be the top of the reservoir of the pantar island geothermal system. rock resistivity zones with high values (> 200 ωm) are shown by layers with a redpink color starting to appear at depths approaching -2000 m. this high resistivity zone is thought to be a heat-bearing rock from the pantar island geothermal system. (parnadi et al., 2014) fig 5 : 2d model resistivity line a the results (figure 6) show a medium-high resistivity value (> 20 ωm) on the surface which is thought to be a response from volcanic rock units in the form of lava. underneath is a low resistivity value (<10 ωm) that extends from the west to the east. the low resistivity (the blue layer) in the west is thought to be the response of alteration rocks resulting from hydrothermal, tuff, breccia, polymic breccia, and pyroclastic. while the low resistivity value in the east is thought to be the influence of sea water intrusion. to the east of this interesting zone there is a contrast value of resistivity, indicating the existence of a structure that is a barrier of the prospect zone of this area. this structure is a depiction of the pintumas fault shown on the geological map (hadi and kusnadi, 2015). the low resistivity value that is thought to be closely related to hydrothermal activity is in the middle of this passage and passes through several geothermal manifestations. the shape of the zone of low resistivity value in this section is assumed to be the closing zone of the geothermal system of the island of pantar. after the low resistivity zone, there is a rock layer with a medium resistivity value (20-100 ωm) from a depth of -1000 m to -2000 m, which is assumed to be a reservoir in the form of a graben. rock resistivity zones with high values (> 200 ωm) are shown by layers with a red-pink color starting to appear at depths approaching -2000 m. this high resistivity zone is thought to be a heat source rock from the pantar island geothermal system. fig 6. 2d model resistivity line b 3.2.1. 3d model the results from 3d model (figure 7) show that the first layer of this area has rock resistivity with a resistivity value of ≤ 20 ωm that occupies the entire investigation area at the surface to a depth of -1000 m. the low resistivity value in this area is thought to be the response of the alteration zone which taufan, y.a., et al./ jgeet vol 5 no 3/2020 117 is a product of hydrothermal activity and the response of tuff, breccia, polymic breccia, and pyroclastic breccia. it is suspected that this zone is a clay cap (zone in the pantar geothermal system. fig 7. 3d geothermal syatem based on resistivity model at a depth of -750 m, a low-moderate resistivity value (20 50 ωm) is suspected. it is assumed that the low-moderate restivity value is a response from the lava lithology that spreads almost in most areas of investigation. this low-moderate resistivity value is thought to be a transition zone between the alter rock and the reservoir. at a depth of -1000 meters the resistivity zone is expanding and forming a closed closure covering almost all of the manifestations around mount sirung. this medium resistivity value at a depth of -1000 m is thought to be the peak of the reservoir of the pantar island geothermal system. at depths of more than -1000 meters the expansion of the resistivity value of 20-100 ωm is seen, this shows that the geothermal system in pantar is located along the emergence of geothermal manifestations starting from mount sirung to the northeast to the airmama heat. the rock zone with a resistivity of 20-100 ωm at a depth of -1000 meters is thought to be a reservoir zone in the pantar geothermal system. at depths of 1500 m the presence of rocks with moderate resistivity (20-100 ωm) leads to groups of rocks with higher resistivity values (> 100 ωm). in the east there is a low resistivity value, it is suspected that this is not related to hydrothermal activity, this low resistivity value is a response from limestone and also the response from sea water intrusion. this is due to its location in the eastern regions directly adjacent to the sea. at depths of -2000 m, visible rocks with a high resistivity value> 200 ωm are located just below the medium resistivity value at the previous depth. this high resistivity value is thought to be the heat-bearing rock (heat source) of the pantar island geothermal system (rahadinata and taqodama, 2015). 4. conclusions the reservoir zones of the pantar geothermal system are shown by resistivity of 20-100 ωm, this layer is at a depth of 1000 m to -2000 m and in some areas began to appear at shallower depths. this reservoir zone is closed by clay cap with resistivity values <20 ωm which are considered as alteration, tuff, breccia, polymic breccia, and pyroclastic. the presence of geothermal fluid is suspected in this reservoir zone so that it becomes important information for the next exploration stage. acknowledgements the authors thank the research team of the centre for coal, minerals, and geothermal resources, the geothermal field group, for helping and authoring the writing of this paper. references aboud, e., saud, r., asch, t., aldamegh., k.,mogren, s., 2014. water exploration using magnetotelluric and gravity data analysis; 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(text in indonesian). unsworth.,m., 2006. electromagnetic and potential field method geophysics. university of alberta. vozoff, k., 1991. the magnetotelluric method in nabighian, electromagnetic method in applied geophysics, vol. ii, part b: society of exploration geophysicists. tulsa oklahoma, 641-711. weldeyohannes., h., 2018.magnetotelluric methods in geothermal exploration at aluto langano ethiopia.proceedings, 7th african rift geothermal conference kigali, rwanda. zobin, v.m., 2017. introduction to volcanic seismology (third edition). elsevier. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://www.sciencedirect.com/science/article/pii/b9780444636317000200 https://www.sciencedirect.com/book/9780444636317 https://www.sciencedirect.com/book/9780444636317 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 putra, a.y., et al./ jgeet vol 5 no 3/2020 151 research article groundwater quality assessment for drinking purpose based on physicochemical analysis in teluk nilap area, rokan hilir, riau, indonesia. arief yandra putra1,*, fitri mairizki2 1 department of chemistry education, faculty of teacher training and education, universitas islam riau, pekanbaru, indonesia 2 department of geological engineering, faculty of engineering, univeristas islam riau, pekanbaru, indonesia. * corresponding author : ariefyandra0811@edu.uir.ac.id tel.:+62-813-7456-7116 received: august 1, 2020; accepted: august 27, 2020. doi: 10.25299/jgeet.2020.5.3.5488 abstract groundwater is water resource that widely used for domestic purposes, including for drinking. however, the industrial and population growth causes the quality and quantity of groundwater to decline. in this case, the quality of drinking water in indonesia must meet the requirements according to health minister regulation no.492/menkes/per/iv/2010. this study aims are to determine the quality of groundwater in the research area based on physicochemical parameters and its evaluation for drinking water. groundwater samples were taken from dug wells in teluk nilap area, rokan hilir, riau. groundwater samples have temperature average 30oc, tds average 312,5 mg/l and ph average 5,6. groundwater contain sulfate and nitrate with average value 48,8 mg/l and 11,86 mg/l, respectively. groundwater water also have iron and lead metal above the permitted standard with average value 2,57 mg/l and 0,022 mg/l. groundwater in the study is not recommended as drinking water. keywords: groundwater, physical, chemical, drinking water 1. introduction groundwater is one of the basic necessities for humans. groundwater is a natural resource that needs to be preserved and it has various functions to support human life. groundwater is the main water resource that used for drinking water by community. groundwater has many advantages compared to the other water resource such as : groundwater quality is better than surface water quality, groundwater quality does not depend on the season, there is a large amount of groundwater reserves and easy to obtain. however, population and industrial growth have caused the quality and quantity of groundwater to decline. one of the contributing factor is the presence of pollutants from garbage disposal area (satrio, et al., 2017), industrial activities (naslilmuna, et al., 2018) and domestic waste, both liquid and solid waste (sasongko, 2014). the use of groundwater for domestic purposes including for drinking must meet the requirements determined by national and international regulations. in this case, the quality of drinking water in indonesia must meet the requirements for physical, chemical, and biological parameters according to the health minister regulation no. 492/menkes/per/iv/2010. drinking water must be free from harmful bacteria and chemical impurities. drinking water also must be clean and clear, odorless and colorless, have no suspended matter or turbidity (risky, d.p., et al., 2017). it is necessary to monitor the quality of groundwater intensively and continuously to ensure that the groundwater used is suitable and safe for consumption. for this reason, a lot of research has been carried out on monitoring groundwater quality which used as a source of drinking water in various countries (siringoringo, et al., 2019) ; (ibrahim, m.n., 2019) ; (khan, a., khan, m.a., 2018) ; (lalitha, b.v., 2016) ; (annapoorna, h., janardhana, m.r., 2015). therefore, the aims of this research are to determine groundwater quality in study area based on physicochemical parameters and groundwater assessments for drinking purpose. 2. study area teluk nilap is one the villages located in kubu babussalam subdistrict, rokan hilir, riau. topographically, teluk nilap is low land with altitude about 6-10 m from sea level. the people of teluk nilap use groundwater for domestic purpose. however, at this time, the people in the study area feel a change in environmental condition including the decrease of groundwater quality. the groundwater looks brownish, oily, sticky to the skin and does not foam when given soap. based on the regional map, stratigraphy of research area composed by young superficial deposits (qh) and older superficial deposits (qp) (fig.1). the rocks in young superficial deposits are clays, silts and clean gravels, vegetation rafts and peat swamps. on the other hand, the older superficial deposits consist of clays, silts and clayey gravels, vegetation rafts. http://journal.uir.ac.id/index.php/jgeet mailto:ariefyandra0811@edu.uir.ac.id 152 putra, a.y., et al./ jgeet vol 5 no 3/2020 fig. 1. regional geological map of study area 3. methodology the groundwater samples were taken from dug wells in teluk nilap area with random sampling method. all samples were examined for physicochemical analysis in the industrial research and standardization laboratory, padang. the temperature, tds and ph of collected samples were determined by using thermometer, tds meter and ph meter, respectively. sulfate and nitrate concentrations were determined by using spectrophotometer. iron and lead concentrations were determined by using atomic absorption spectrophotometer. the quantitative data on physicochemical parameters obtained then compared with the drinking water quality standards based on health minister regulation no.492/menkes/per/ iv/2010. 4. result and discussion 4.1 temperature in general, temperature condition of groundwater is normal value, in range 27-31oc and average 30oc which meet the drinking water quality standard. the temperature standard permitted by health minister regulation is air temperature ±3oc. the research area is belongs to the tropical climate. water temperature can be affected by season, latitude, altitude, cloud cover, flow and depth of water. the large amounts of dissolved chemicals (phenol, sulfur) and decomposition of organic matter by microorganism can also cause groundwater temperature value will be above standard limit (mairizki, f., cahyaningsih, c., 2016). 4.2 total dissolved solid (tds) tds values of groundwater also show the normal value with average 312,5 mg/l in range 101-809 mg/l. tds standard permitted by health minister regulation is 500 mg/l. only 3 groundwater (20%) that have tds value over the drinking water quality standard (fig.2). all groundwater were classified as fresh water (tds 0-2000 mg/l) (putra, d.b.e., et al., 2019). fig 2. total dissolved solid value of groundwater tds consist of soluble organic or soluble inorganic compounds, minerals and dissolved gases. salts that dissolve in groundwater which contain magnesium, sodium, sulfate or chloride ions also increase the amount of dissolved solids in groundwater. the presence of tds such as sodium sulfate and magnesium sulfate can cause a change in groundwater taste. in addition, the high concentration of total dissolved solids affect the clarity, groundwater color and hardness (firdaus, et al.,2017). 4.3 ph ph condition of groundwater in range 2,8-6,6 and average 5,6. ph standard permitted by health minister regulation is 6,5-8,5. almost all groundwater are acidic and do not meet drinking water quality standard (fig.3). this is due to geological factors such as soil conditions. the study area is dominated by peat. ph value will determine the corrosion properties. the properties of corrosion will be higher at low ph. water with low ph also will easily dissolve the fe metal that form ferrous and ferric ions which can cause the water become colored, smelly and have a taste (putra, a.y., mairizki, f., 2019). putra, a.y., et al./ jgeet vol 5 no 3/2020 153 fig 3. ph value of groundwater 4.4 sulfate sulfate condition of groundwater show the normal value with average 48,8 mg/l in range 11,76-118,73 mg/l. sulfate standard permitted by health minister regulation is 250 mg/l. all groundwater meet the drinking water quality standard (fig.4). fig 4. sulfate value of groundwater the presence of sulfate in groundwater can be influenced by the type of rock that the groundwater passes through. sulfates are found in sedimentary and igneous rocks as sulfides metal. sulfate is found in igneous rocks as feldspatoid, and also found in many evaporite sedimentary rocks as gypsum, anhydrite and barite. in weathering, sulfur is oxidized to produce sulfate ions which are carried by groundwater (mutianto, h., 2010). 4.5 nitrate nitrate condition of groundwater also show the normal value in range 1,828-20,852 mg/l and average 11,86 mg/l. nitrate standard permitted by health minister regulation is 50 mg/l. all groundwater have nitrate value below the drinking water quality standard (fig.5). the presence of nitrate in high amounts at groundwater indicated the decomposition of organic compounds through biological processes with very low dissolved oxygen. nitrate content in groundwater can also come from agricultural materials such as nitrate fertilizers. nitrate residue will be carried by rainwater into the soil which increasing nitrate values in groundwater (sudaryanto, suherman, d., 2008). fig 5. nitrate value of groundwater 4.6 iron most groundwater have high concentration of fe metal with average 2,57 in range 0,18-6,87 mg/l. fe standard permitted by health minister regulation is 0,3 mg/l. only 1 groundwater (6,67%) has fe value below the drinking water quality standard while the others have high fe metal content above the quality standard (fig.6). fig 6. fe value of groundwater heavy metals are naturally present in trace amounts in groundwater. the concentration of heavy metals in groundwater depends on the soil properties, the type of rock that the groundwater passes through and the influence of environmental pollution around the groundwater source. high concentration of iron metal will cause groundwater color will be yellowish, corrosion of metal objects, deposition of water pipe walls and accelerate the growth of fe bacteria in groundwater (rahadi, b., lusiana, n., 2012). 4.7 lead lead content in groundwater in range 0,0026 mg/l0,1316 mg/l and average 0,022 mg/l. lead standard permitted by health minister regulation is 0,01 mg/l. 6 groundwater (40%) have pb value above the drinking water quality standard while the others still have pb metal content below the quality standard (fig.7). this must be a concern because pb can accumulate and pollute groundwater. the heavy metal content cannot be removed and it is toxic and carcinogenic. in humans, heavy metal can disrupt health depend on the part which are exposed of heavy metals. heavy metal can cause cancer, allergies and at high dose can cause death (yandra, a.p., mairizki. f., 2020). 154 putra, a.y., et al./ jgeet vol 5 no 3/2020 fig 7. pb value of groundwater 5. conclussion groundwater samples were taken from dug wells in teluk nilap area, rokan hilir, riau. all groundwater meet the requirements for drinking water quality according to the health minister regulation no.492/menkes/per/iv/2010 in terms of physical parameters with temperature average 30oc and tds average 312,5 mg/l. however, almost all groundwater does not meet the drinking water quality requirements based on its chemical parameters. all groundwater are acidic with ph average 5,6, containing sulfate and nitrate with average value 48,8 mg/l and 11,86 mg/l, respectively. groundwater water also have iron and lead metal above the permitted standard with average value 2,57 mg/l and 0,022 mg/l. therefore, groundwater in research is not recommended as drinking water. acknowledgements the authors would like to give an acknowledgment to universitas islam riau and the ministry of education and culture for providing research fund. additional thank you for all students that help authors to collect data at field. references annapoorna, h., janardhana, m.r. 2015. assessment of groundwater quality for drinking purpose in rural areas surrounding a defunct copper mine. aquatic procedia 4, 685-692. https://doi.org/10.1016/j.aqpro.2015.02.088. firdaus, a.r., paenrongi, a.v., safira, b., pertiwi, d.a., aqsha, e.s., beloratte, j., asadullah, m., syilvana, p.p. 2017. analisis kualitas airtanah berdasarkan parameter kekeruhan, tds (total dissolved solid), ph, dan zat organik di wilayah bukit batu putih, samarinda, kalimantan timur. jurnal teknologi mineral, 5(2), 1-4. ibrahim, m.n. 2019. assessing groundwater quality for drinking purpose in jordan : application of water quality index. journal of ecological engineering, 20(3), 101-11. https://doi.org/10.12911/22998993/99740. khan a., khan m.a. 2018. groundwater assessment for drinking purpose in gulistan-e-johar town, karachi, pakistan. journal of geoscience, engineering, environment, and technology, 3(4), 200-207. doi: 10.24273/jgeet.2018.3.4.2086. lalitha, b.v., teja, v.s., rajesh, v. 2016. a study on assessment of groundwater quality and its suitability for drinking in shivajipalem area visakhapatnam, a.p. international journal of engineering development and research, 4(2), 6181621. mairizki, f., cahyaningsih, c. 2016. groundwater quality analysis in the coastal of bengkalis city using geochemistry approach. international journal of engineering and high-end technology, 1(2), 82-87. mutianto, h. 2010. studi kualitas airtanah untuk pengembangan di kawasan parangtritis, bantul, daerah istimewa yogyakarta. jurnal geografi gea, 10(2). https://doi.org.10.17509/gea.v10i2.1075. naslilmuna, m., muryani, c., santoso, s. 2018. analisis kualitas air tanah dan pola konsumsi masyarakat sekitar industri kertas pt jaya kertas kecamatan kertosono kabupaten nganjuk. jurnal geoeco, 4(1), 51-58. https://doi.org/10.20961.ge.v4i1. 19176. putra, a.y., mairizki, f. 2020. analisis logam 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sasongko, e.b., widyastuti, e., priyono, r,e. 2014. kajian kualitas air dan penggunaan sumur gali oleh masyarakat di sekitar sungai kaliyasa kabupaten cilacap. jurnal ilmu lingkungan, 12(2), 72-82. doi:10.14710/jil.12.2.72-82. satrio, pujiindiyati, e.r. 2017. karakteristik air tanah akuifer dalam sekitar tempat pembuangan sampah terpadu (tpst) bantar gebang-bekasi, jawa barat. jurnal teknologi lingkungan, 18(1), 96-103. https://doi.org/10.29122/jtl.vl8il.48. siringoringo, l.p., rizki r., nababan j. 2019. hydrogeochemical and groundwater assessment for drinking purpose at itera campus area and its surroundings. journal of geoscience, engineering, environment, and technology, 4(1), 40-48. doi:10.25299/jgeet.2019.4.1.2478. sudaryanto, suherman, d. 2008. degradadi kualitas airtanah berdasarkan kandungan nitrat di cekungan airtanah jakarta. jurnal geologi dan pertambangan, 18 (2), 6168. doi:10.14203/risetgeotam2008.v18.17. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). https://doi.org/10.1016/j.aqpro.2015.02.088 https://doi.org/10.12911/22998993/%2099740 https://doi.org/10.12911/22998993/%2099740 https://doi.org.10.17509/gea.v10i2.1075 https://doi.org/10.20961.ge.v4i1.%2019176 https://doi.org/10.20961.ge.v4i1.%2019176 http://doi.org/10.22216/jk.v5i1.5277 http://doi.org/10.22216/jk.v4i1.4024 https://doi.org/10.29122/jtl.vl8il.48 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 268 hadian, m.s.d, et al./ jgeet vol 02 no 04/2017 hydro chemistry and characteristics of groundwater: case study water contamination at citarum river upstream mohamad sapari dwi hadian 1 ; t. yan waliyana 1 ; nana sulaksana 1 , dewandra bagus eka putra 2 , yuniarti yuskar 2 1 faculty of geology, universitas padjadjaran, jatinangor, indonesia 2 department of geological engineering, universitas islam riau, jl. kaharuddin nasution, pekanbaru 28284, riau, indonesia * corresponding author : sapari@unpad.ac.id tel.:+6281321102268 received: aug 11, 2017. revised : sept 1, 2017, accepted: nov 30, 2017, published: 1 dec 2017 doi :10.24273/jgeet.2017.2.4.578 abstract rancaekek and sayang, west java, are the area where many industrial factories are located. thus, the region becomes the targeted destination for industrial development. the population in the area is rising due to the growth of industries causing the regional development becomes uncontrollable. in addition, the constant increment of waste and also poor-coordinated disposal systems may result in groundwater contamination in the areas. the rapid growth of the area increases the need for groundwater as well as the need for more research about contamination at rancaekek and sayang. the research aims to explore the spread of groundwater contamination in the area. the research method is carried out based on the analysis of geological mapping, hydrogeological mapping and chemical characteristics of the groundwater in the area. chemical analyses of the groundwater were conducted through laboratory test of groundwater samples at specific spots of dug wells. the lab test results were further analyzed to determine the contamination zone. the findings reveal that the distribution of contamination in the area follow the shallow groundwater flow patterns, the water contamination contains heavy metal and there is degradation of soil fertility. the findings suggest the stakeholders delineate the contaminated area, and increase the dissemination of environmental awareness. keywords: contamination, groundwater, hydrogeology 1. background water has an important role for human survival. water is one of the basic needs for the development of human welfare. therefore, the need for water is a vital requirement to accessible and available for the community. rancaekek and sayang, west java, have been a central area of industrial development. this makes the population in the area has been increasing and growing from year to year. accordingly, the need for water for daily need as well as for industrial purposes have been increasing rapidly. depression of groundwater level is considered to be related to the natural shape of the aquifer as lenses. however, it was possible to be caused by overpumping in this zone. (hadian et al., 2006, 2014, 2016) in addition, in line with the rapid industrial development in the area, the amount of waste is also increasing. thus, it has influenced the potential and quality of the groundwater in the area. therefore, research on groundwater quality in the area, especially regarding groundwater contamination is indispensable (hem, 1991; azy & hadian, 2016). 2. research method to determine the level of contamination of groundwater, this research collected several data such as lithology, groundwater chemical, and land use in the area. the lithologic data was retrieved by geological mapping. the groundwater chemical data was obtained from laboratory test of the groundwater samples taken from certain observation spots. specific chemical parameters in this study are ca 2+, mg 2+, na + and k +, hco3-, no32-, so42and cl(kumaresan & riyazuddin p., 2006). the land use data was taken from literature research. the analysis used in this study was the spatial approach based on certain parameters and presented in the form of thematic maps. the results of this study are expected to be used for hydrogeological studies specifically to indicate the level of groundwater contamination in the area (hadian et al., 2014; prayogi, 2015). 3. result and discussion 3.1 geological mapping of rancaekek and sayang the area is composed of lithology derived from the volcanic eruption and lacustrine which age has hadian, m.s.d, et al./ jgeet vol 02 no 04/2017 269 reached the quarter. the area is composed of three lithologies: volcanic breccia unit (qbv), andesitic lava units (qa) and tuffaceous clay units (ql). the breccias unit is composed by breccias characterized by a light-coloured blackish grey, weathered brownish black, monomic, components of igneous rock in the size of pebble-lump with angled shape and matrix tuf with gray light beige and weathered beige brown colour, open pack, well permeability, medium sorting, and compact. these units are scattered in the north, northeast and southeast areas of the studied area. andesitic lava is composed by andesite characterized by a light-coloured bluish grey, weathered grey-black, porphyritic, the degree of crystallization hypocrystalline, subhedral crystalline form, compact, mineral quartz content, pyroxene and feldspar. these units are spread in the northern part of the studied area. tuff clay unit is composed of clay loam tuff characterized by weathered blackish brown colour, ground lustre, soft. these units are spread out in the area dominating from the middle through the southern area (silitonga, 1973; soetrisno, 1983) . based on the geological data above (fig. 1), the findings could not reveal any geological factors that caused the groundwater contamination in the area. (hadian et al., 2014, 2015; satrio, 2015, 2017; barkah, 2015). fig 1. lithology mapping of the area (no scale) 3.2 soil flow pattern observations and acquisitions discharge from the position of the wells and springs as well as the depth of the groundwater table elevation contours can describe the unconfined groundwater table or isofreatic in the area (fig. 2). the isofreatic map above shows that, in general, under normal conditions, the pattern of the groundwater flow tends to flow along the slope. however, there are conical pattern of the groundwater flow in some places caused by excessive groundwater retrieval exceeding the normal limit, which causes the groundwater level drops drastically and makes the land flow pattern becomes irregular. the condition is more common in the area around rancaekek. fig 2. rancaekek isofreatic mapping (no scale) 3.3 groundwater chemical of the area facies grouping of the groundwater in the areais based on the result of piper diagram analysis using converted water chemical laboratory data. fig 3. piper diagram of the groundwater facies in rancaekek based on the analysis using the piper diagram above (fig. 3), the chemical facies in the area can be grouped into 3 (three) facies, namely facies ca, mg hco3 (calcium, magnesium bicarbonate), facies mg, na hco 3 (magnesium, sodium bicarbonate) , facies na, mg hco3 (sodium, magnesium bicarbonate) (hadian, 2014). the trilinear diagram is used to identify the groundwater contamination based on water chemicals in the area. the diagram is used to find out the grouping, similarities or trends of the water sample by measuring the chemical elements of the water from a major element in the area so as to identify anomalies that do not follow the patterns of the trends of each element in each cross-section of the tdi (total dissolved ions) where the anomaly itself is further used as an indication of groundwater contamination (fig. 4-9). 270 hadian, m.s.d, et al./ jgeet vol 02 no 04/2017 fig 4. the graphic of cl toward tdi fig 5. the graphic of hco3 toward tdi fig 6. the graphic of mg toward tdi fig 7. the graphic of na toward tdi fig 8. the graphic of no3 toward tdi fig 9. the graphic of so4 toward tdi from the data analysis, there are six spots of observation that have been contaminated: station w14, w15, w16, w38, w39 and w41. those findings were identified based on the anomalies that occur in the diagram mg 2+, na +, no32-, so42and cl-. according to the analysis of these anomalies as well as the analysis of the land use planning of the area, the groundwater contamination in the area of research was caused by public waste. this is evident from the fact that the spots of contamination are located around the settlement. the groundwater contamination was caused by household waste such as soapy water found from anomalies in the elements na +, waste fertilizer pat found from anomalies in no32-, and industrial waste found from anomalies in mg 2+, so42 and cl. 4. conclusion geological conditions in the study area showed the absence of geological factors that cause groundwater contamination. instead, based on chemical analysis of groundwater, there are indications of groundwater contamination from waste society such as household waste, fertilizers waste and industrial waste. therefore, groundwater quality management in the area is required so that the potential of the groundwater can be improved to meet the needs of the surrounding people for their life and welfare. hadian, m.s.d, et al./ jgeet vol 02 no 04/2017 271 fig 10. contaminated spots overlay using land use map 5. acknowledgement gratitude is given to the researchers: dr. bombom, prof. dr. hendarmawan, moch. nursiyam barkah st., mt, environmental geology and hydrogeology laboratory padjadjaran university for their support and suggestions toward the research and the writing of this article. references azy, f. n., & hadian, m. s. d., 2016. groundwater characterization of cihaur watershed basin, batujajar and adjacent, west bandung district, west java, indonesia. iop conference series: earth and environmental science 29 (1), p. 012027. iop publishing barkah, m. n., setiadi, d. j., hadian, m. s. d., 2015. perhitungan potensi air tanah di kawasan kampus unpad jatinangor dengan metode numerik. bulletin of scientific contribution 13(3). rifai, a., hadian, s. d., mufti, i. j., fathoni, a. r., azy, f. n., jihadi, l. h., 2017. analysis of potential flooding in the education jatinangor based approach morphology, land cover, and geology. aip conference proceedings 1857 (1), p. 100008. aip publishing hadian, m. s. d., azzy, f. n., & sophian, r. i., 2016. geohazard and geological condition overview of sekeloa-bojongkoneng, bandung, west javaindonesia. aip conference proceedings 1730 (1), p. 040001. aip publishing. hadian, m s d., 2014. the role of volcanic facies ground water system based on water chemical and stable isotopes, dissertation at postgraduate geology universitas padjadjaran. hadian, m. s., mardiana, u., abdurahman, o., iman, m. i., 2006. sebaran akuifer dan pola aliran air tanah di kecamatan batuceper dan kecamatan benda kota tangerang, propinsi banten. indonesian journal on geoscience 1(3), 115-128, http://dx.doi.org/10.17014/ijog.vol1no3.20061 hadian, m. s. d., yuliwati, a. k., pribadi, k. n., 2016. increasing community environmental awareness through geodiversity conservation activities at ciletuh, sukabumi, west java. journal of environmental management & tourism 7(2 (14)), 334 hadian, s. d., rahmat, b., 2015. manajemen airtanah pada endapan aluvium rawa lakbok, jawa barat. bulletin of scientific contribution 13(3). hadian dkk., 2013. penentuan zona resapan dan umur air pada endapan vulkanik di kawasan jatinangor dengan mengunakan metoda isotop stabil. buletin geologi tata lingkungan 23(3). issn 1410-1696. hem, j.d., 1991. study and interpretation of chemical characteristics of natural waters u.s. geol. surv. water supply paper 2254. kumaresan m., riyazuddin p., 2006. major ion chemical of environmental samples around suburban of chennai city. current sci., 91(12), 1668 1677. prayogi, tantowi e. 2014. fasies air tanah gunung geulis daerah cisempur dan sekitarnya, kecamatan jatinangor rancaekek, kabupaten sumedang bandung propinsi jawa barat. skripsi pada fakultasteknik geologi universitas padjadjaran. satrio, prasetio, r., hadian, m. s. d., syafri, i., 2017. stable isotopes and hydrochemistry approach for determining the salinization pattern of shallow groundwater in alluvium deposit semarang, central java. indonesian journal of geoscience, 4(1), 1-10 silitonga, p.h., 1973. peta gelogi regional lembar bandung. soetrisno, s., 1983. peta hidrogelogi regional lembar bandung. 1. background 2. research method 3. result and discussion 3.1 geological mapping of rancaekek and sayang 3.2 soil flow pattern 3.3 groundwater chemical of the area 4. conclusion 5. acknowledgement references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 2 2021 120 suganda et al./ jgeet vol 6 no 1/2021 research article shallow aquifer groundwater facies at multiple landuse sites in manglayang volcanic area, jatinangor and surroundings, indonesia bombom rachmat suganda1,3*, wahyudi yusuf 2, mochamad nursiyam barkah2, cecep yandri sunarie2, m. sapari dwi hadian2 1environment hydrogeology and geology laboratory, padjadjaran university, jatinangor 45363, indonesia 2geological engineering, padjadjaran university, jatinangor 45363, indonesia 3water and energy center padjadjaran university, jatinangor 45363, indonesia * corresponding author : bombom.rachmat.suganda@unpad.ac.id tel.:+62-877-7110-0044 received: oct 16, 2019; accepted: jun 20, 2021. doi: 10.25299/jgeet.2021.6.2.3315 abstract manglayang mountain is generally composed by old and young volcanic materials. older rocks are located around the northern part of mountain peak, in medial and distal parts. in the southern and southeastern parts composed by relatively young volcanic rocks starting from the proximal, medial to distal. these geologic conditions produce diverse aquifer systems. these differences in land use environments contribute to water quality conditions in local shallow aquifers. the research is therefore carried out in order to the effect of difference in land use environments on groundwater facies by dividing the area based on each land use. land use in the research area is dominated by allotment of agricultural land, settlement, and industry. the study was conducted from the medial area to distal to the southern part of manglayang mountain, administratively including sukasari, jatinangor, and rancaekek districts. to observe the groundwater conditions in the aquifer from the study area, physical and chemical parameters were tested. chemical parameter test results were plotted using piper diagrams and durov diagrams as a method that can illustrate the condition of groundwater facies. physical characteristics of groundwater may reflect groundwater interactions with rocks. measurable tds concentrations of 48 299 mg / l and measured ec 100 1020 μmhos / cm, show different interaction conditions between groundwater with rocks or have received different material subsidies. similarly, the occurrence of temperatures that vary considerably between air and water indicates the distance of groundwater sources with various water bodies. the groundwater facies that developed in the research area are generally dominated by ca, hco3 in the agricultural land use area, mg, hco3 in the settlement area, and in some cl-facing evolving places in the industrial land use zones. in addition, there are also indications of mixing of anions and cations in groundwater samples in all three land use areas. this indicates that there has been a change in groundwater characteristics in some areas of land use utilization in the research area keywords: volcanic aquifer, manglayang mountain, landuse, groundwater facies 1. introduction bandung geological map sheet describes the geology of regional research area, the rocks exposed in the research area consisted of only one geological unit, young volcanic product (qyu), which is an indivisible young volcanic sediment. this unit consists of sand tufa, lapilli, breccia, lava, and agglomerated stone. the rocks in this region form small plains and flat parts with low hills covered by yellowgray and reddish soil. these rocks belong to the quaternary volcanoes seen between sumedang and bandung (silitonga, 2003). volcanic rock compiler of jatinangor area resulted from mount tampomas and mount tangkuban perahu sediment. endogenous processes in the form of tectonic activity result in deformation of geological structures such as stocky and cesarean, while the exogenous process is influenced by various aspects such as wind, climate, temperature, rainfall, physical, chemical and biological. the geological conditions of the study area are formed by the volcanic releases of volcanic materials, loose, volcanic breccia, and lava known as strato type volcanoes, such conditions form a graded aquifer system from high elevation to low elevation. (hadian, 2013). based on the distribution, the rock units in the study area can be divided into 8 units of volcanic rock products, which are intrusion andesite, old volcanic pyroclastic product i, old volcanic pyroclastic product ii, young volcanic pyroclastic product i, young volcanic pyroclastic product ii, young volcanic product and young lake sediment (mardiana, 2013). jatinangor is located in the southern part of manglayang mountain which has various land use activities such as agriculture, housing, trade and industry services. education and industrial areas in jatinangor experiencing rapid physical development, many farming areas in jatinangor change its function into rent for students or shopping areas; so, jatinangor has 80% urban area characteristics (bappeda kabupaten sumedang, 2009). groundwater conditions in jatinangor region show a decreasing level, especially groundwater levels in shallow aquifers, allegedly due to an imbalance between the number of groundwater catchments and the amount of water absorbed into the soil. increased demand for groundwater has led to a sharp increase in groundwater consumption so that shallow ground water conditions have always declined, especially near production wells. exploited groundwater exceeds the amount of recharge and will reduce the volume suganda et al./ jgeet vol 6 no 1/2021 121 that will be seen in reducing groundwater levels or decreasing groundwater pressure (hadian et al., 2013). if this condition continues, it leads to a breakthrough or inclusion of surface water into the water system into the groundwater (takeda & sosrodarsono, 2003) the purpose of this study was to illustrate and analyze the various aspects of hydrogeochemical (groundwater quality) of manglayang-shallow aquifer in various land use sites. 2. research methods groundwater samples were collected from springs and wells in residential areas on 15 different land use such as agricultural areas, residential areas, and industrial estates. samples were collected repeatedly during the dry and wet seasons and analyzed in pdam bandung laboratory referring to standard methods for water and wastewater inspection, 2012. concentrations expressed in units of mg / l, converted to meq / l. value of the concentration then plotted in piper trilinear diagram to determine the type of groundwater facies. the values were also plotted in durov diagrams to identify groundwater facies processes and groundwater mixing process in groundwater chemical evolution. the research method is presented in the following chart. fig 1. research methods flowchart 3.1 geology and hydrogeology condition the study area covers the southern part of the manglayang mountain. the altitude of this area is 1220 meters above sea level in the north and 696 meters above sea level in the south. based on the slope theme (van zuidam, 1985 in bermana, 2006), there are 4 geomorphological, oblique and steep units in this area, whereas based on rock distribution, the study area includes rock units of young volcanic products, young volcanic pyroclastic product, young volcanic pyroclastic product 2, old volcanic pyroclastic product 1, old volcanic pyroclastic product 2 and groundwater of young lake (hadian et al, 2013; mardiana, 2013). the study area consists of unravel volcanic sediment deposits, generally, a young volcanic sediment consisting of a mixture of loose and solid volcanic sediment with low to medium permeability. some of the study area are productive aquifers with various transmissivity. groundwater in this region is not widely utilized because of its deep groundwater level, in some area a plasterable spring is found. this area occupies ± 20% in the northwest and southeast of the study area. the aquifer with moderate productivity is widespread. transmissivity is very diverse, groundwater level is usually deep and have less than 5 liters / sec water discharge. this region occupies ± 55% (middle, west, east and north) of research area. and also rare groundwater areas occupy ± 3% in the southwest and southeast, and lake sediment in the form of tuff clay, tufan sandstone, medium to high permeability with widespread transmissivity, various groundwater level and generally less than 5 liters / sec water discharge. this area occupies ± 22% in the southern part of the study area (soetrisno, 1983, processed 2018). the study area is limited by the cibeusi watershed at west and the cikeruh watershed at east, from the spring to the upstream each. 3.2 landuse condition based on the indonesian landscape map of cicalengka sheet, 2001, the study area is grouped into the agricultural landuse (± 80.61%), settlements (± 17.28%) and industry (± 2.10%). the agricultural landuse consists of irrigated rice fields, rainfed rice fields, plantations, and fields, occupying medial to distal area. generally, lithology in this area is composed by a matrix-supported breccia up to tuf on the distal and grain supported breccia in the medial part. groundwater flow is generally aligned with the topography and river flow that is directed from the peak (proximal) to the southeast. rainfed rice fields are generally located in agglomerates units in the north with a rather tightly textured topography relief. the plantations and the fields are on the matrix-supported breccia rocks (loose). irrigated rice fields are generally located around cikeruh, cileles and cibeusi river. the settlements landuse consists of houses, offices, etc are spread over the distal points of the entire study area. the lithology of the settlement landuse are various from matrix supported breccia up to tuff. ground water flow is generally aligned with the topography and river flow that is pointing from the top (proximal) to the southeast. the industrial landuse consist of process industry, 122 suganda et al./ jgeet vol 6 no 1/2021 manufacturing and also service, are located in the lakes sediment with flatland morphology. composite lithology consists of partial sandstone tuff and matrix-supported breccia. the river flows from east to west-northwest. in this section generally, flow path engineering (irrigation) has been created so that the natural flow is difficult to know. groundwater flow in the industrial part is divided between the west and the east. this condition occurs due to excessive groundwater extraction in industrial activities so that the flow of natural ground water divided partly to the west and east. based on google earth satellite imagery map digitization, there are indications of landuse change in the research area. these changes are the conversion of agricultural landuse into settlements and industrial land. in 2017 agricultural landuse decreased to ± 75.20%, while settlement landuse increased to ± 25.78% and industry (± 3.02%). 3.3 physical characteristics groundwater the groundwater flow pattern based on the groundwater level at the good sampling points shows that the groundwater flow pattern on the agricultural landuse are from the north to the south and from the northeast to the northwest. the flow pattern on the settlement landuse is from the northeast to the northwest and the flow pattern on industrial landuse from east to west, as shown in figure 5. the physical parameters both in water springs and wells groundwater observation are water temperature, ph (acidity degree), tds (dissolved solids) and electrical conductivity (ec). groundwater temperatures in the study area were below the air temperature at each observation point with a difference between 0-9 0c in the dry season and between 1 4 0c in the rainy season. the difference was caused by unequal measurement times (performed at 9 am – 4 pm wib), so the air temperature at midday will be higher than morning and evening, the condition of the research area is classified into hypothermal zone (matthes & harvey, 1982 in puradimaja, 2004). although the changes are relatively small, ph value measured at the research points changes in some locations which indicates groundwater interaction with the rocks it passes. tds value has increased from north to south both in the dry season and the rainy season, equal to the quite significantly increased electrical conductivity value. the increase in tds and dhl parameters from the north to the south (young volcanic to lake sediment) is suspected resulting the occurrence of spring water and rock interactions that are more easily soluble in groundwater flows, whereas based on landuse, tds and dhl parameters increase from agricultural landuse to industrial landuse are suspected due to material subsidies in the soil flow especially in the rainy season. insitu measurements and laboratory analysis on physical and chemical water in the research area are performed by multivariate analysis with 2 (two) season variables and 3 (three) variables of landuse as interpreted as follows. from the above analysis, that some parameters have significant variaton in different seasons and different landuses, but generally do not have significant interaction between seasons and different landuses. the piper and durov trilinear diagrams were used to conclude the hydrochemical facies in groundwater samples in the study area. the two diagrams were developed to classify groundwater by measuring the chemical element of water from its major elements. the result of the groundwater quality in the piper trilinear diagram presented in the following figure. table 1. the significance of in-situ measurement variables and laboratory analysis on physiscal and chemical water parameter results units significance of variables dry season rainy season season landuse season & landuse water temp 19-26 20-28 oc + + ph 5,38-7,45 5,53-7,89 tds 48 – 449 65 – 510 mg/l + dhl 100-1020 141,251003,27 µmhos/c m + na+ 9,11 28,11 2,4 65,8 mg/l + + k+ 6,11 26,6 0,2 – 10 mg/l + ca2+ 16 60,4 14 60,9 mg/l + mg2+ 2,16 35,96 14 60,9 mg/l + hco+ 76,8-157,15 52,3 125,8 mg/l + so4 28,80 58,60 2,8 102,4 mg/l + + cl4,88 86,76 1,6 148,8 mg/l + table 2. research sampling locations table no kode x (xd) x (xm) x (xs) y (yd) y (ym) y (ys) z (meters asl) landuse 1 ck 1 6 52 54,7 107 45 12,7 1226 agriculture / farming 2 ck 2 6 54 13 107 46 33,0 877 agriculture / farming 3 ck 7 6 56 5,6 107 47 14,1 731 agriculture / farming 4 cb 1 6 53 22 107 45 20,0 1074 agriculture / farming 5 cb 2 6 55 31,4 107 45 20,7 806 agriculture / farming 6 ck 4 6 54 52,56 107 46 37,92 821 settlements 7 ck 5 6 55 50,9 107 46 46,1 744 settlements 8 ck 6 6 56 21,4 107 46 58,1 694 settlements 9 ck 8 6 56 55,9 107 47 13,8 706 settlements 10 cb 3 6 56 4,4 107 45 20,7 760 settlements 11 ck 9 6 56 18,1 107 46 27,6 718 industry 12 ck 10 6 57 17,1 107 46 9,0 696 industry 13 cb 4 6 56 19,8 107 45 26,8 727 industry 14 cb 5 6 56 46,5 107 45 30,3 716 industry 15 cb 6 6 56 48,4 107 45 24,9 707 industry suganda et al./ jgeet vol 6 no 1/2021 123 fig 2. trilinier pipper diagram : dry season fig 3. trilinier pipper diagram : rainy season table 3. diagram trilinear piper plotting results dry season ca;hco3 ck-11) ck-21) cb-11) cb-21) mg;hco3 ck-62) mg;cl ck-103) cb-63) no dominan; hco3 ck-71) ck-42) ck-52) ck-82) ca no ; dominan cb-3 ck-93) mg no ; dominan cb-43) no dominan; cl cb-53) rainy season ca;hco3 ck-2 1) cb-1 1) cb-2 1) mg;cl cb-4 2) cb-5 2) cb-6 2) ca;cl ck-7 1) no dominan; hco3 ck-1 1) ca; no dominan ck-4 2) no dominan; cl ck-6 2) cb-3 2) no dominan ; no dominan ck-5 2) ck-8 2) ck-9 ck-10 annotation: 1) agricultural landuse 2) settlements landuse ; 3) industrial landuse 124 suganda et al./ jgeet vol 6 no 1/2021 from these figures, the research area has several different types of groundwater facies, as presented in table 3. based on the water chemical grouping using pipper diagram, the groundwater facies are grouped into 4 (four), namely cahco3, mghco3, cacl and mgcl. based on the result data plotting, the majority area is in the 5 and 6 area. based on the classification by lloyd & heathcote (1988), this indicates that groundwater falling on the field 5 indicates the mixing of several types of water on the aquifer at the site, as shown in figure 2. the mixing may also occur due to the supply of water from the surrounding water bodies entering the aquifer and the also aquifer leakage, thereby allowing the mixing of groundwater from different aquifers, whereas the water properties in the field 6 indicate that groundwater undergoes a process of exchange ions and ions that are dominantly involved are ca2 +, mg2+ and hco3 ions. fig 4. durov diagrams: dry season fig 5. durov diagrams: rainy season 4. discussion groundwater conditions in shallow aquifers in manglayang mountain have undergone changes in hydrogeochemical, from facies of cahco3, mghco3, to cacl and mgcl facies along its journey. the facies showed that in the eastern study area (cikeruh watershed) was found facies of cahco3, ca and hco3 in the northern to middle area (1,200 750 meters above sea level) which is present in the area of agricultural and settlement landuse, facies mghco3 in the middle of the research area (50 meters above sea level) in the settlement area of mgcl facies in the southern part of the research area (700 mdpl) in the industrial landuse. in the western study area (cibeusi watershed) was found cahco3, ca and hco3 facies in the north (1,025 750 meters above sea level) on agricultural landuse areas. mg, cl and mgcl facies are found in the central to southern part (<700 meters above sea level) in the industrial landuse area. the groundwater facies sampling in the research area is presented in the following figure. facial conditions in the study area indicate the difference of aquifer between the north and south regions, the discovery suganda et al./ jgeet vol 6 no 1/2021 125 of ca, hco3 indicates that the flow of groundwater in the center comes from the basin that is in the north. while the discovery of mg, cl in the middle to the south is thought to be groundwater coming from the local area or local system. fig 6. groundwater facies in the study area a-b cross section fig 7. groundwater facies in the study area a-c cross section 5. conclusion groundwater conditions in shallow aquifers in manglayang mountain have undergone hydrogeochemical changes, from facies of cahco3 in agricultural landuse areas and mghco3 in settlements landuse areas, then undergoing changes to cacl and mgcl facies in the industrial landuse areas on its journey. the study area hydrochemical analysis showed that the formation of groundwater facies is influenced by hydrogeochemical processes such as groundwater washing by percolation of rainwater, cation exchange, and surface water mixing, as well as the mixing and exchange of groundwater ions. acknowledgements much obliged to the head and staff of pdam tirtawening environmental quality control laboratory. much obliged also to the head, staff, and assistant of hydrogeology and environmental geology laboratory, faculty of geological engineering, padjadjaran university. we also express our gratitude to those who have been willing to give criticism and suggestions. references apha, 2012. standard methods for examination water and waste water. 21th edition washington dc, usa badan koordinasi survey dan pemetaan nasional, 2001. peta rupa bumi digital indonesia lembar cicalengka 2001. bappeda kabupaten sumedang, 2009. studi kelayakan kawasan jatinangor sebagai kawasan perkotaan. bermana, i. (2006). klasifikasi geomorfologi untuk pemetaan geologi yang telah dibakukan. bulletin of scientific contribution, 2(4). hadian dkk, 2013 penentuan zona resapan dan umur air pada endapan vulkanik di kawasan jatinangor dengan mengunakan metoda isotopstabil. buletin geologi tata lingkungan. issn 1410-1696 vol. 23 no. 3 desember 2013 lloyd, j. w., & heathcote, j. a. (1988). natural inorganic hydrochemistry in relation to groundwater: an introduction. clarendon press. mandel, s. dan shiftan, z.l., 1981, groundwater resources, academic press. mardiana, u. (2013). sistem akifer pada batuan vulkanik di lingkungan kampus unpad jatinangor sumedang, jawa barat. matthes, g., & harvey, j. c. (1982). the properties of e le va ti o n ( m a sl ) e le v a ti o n ( m a sl ) distance (km) distance (km) 126 suganda et al./ jgeet vol 6 no 1/2021 groundwater by g. matthes. wiley-interscience, 1981. no. of pages: 406. price: £34.00. geological journal, 18(4). https://doi.org/10.1002/gj.3350180413 piper, a.m., 1944, a graphic procedure in the geochemical interpretation of water analysis. trans. am. geophys. union, washington, d.c puradimaja, dj,. 2004. diktat kuliah hidrogeologi umum. fakultas ilmu kebumian dan teknologi mineral, itb. bandung silitonga, p.h., 2003, peta gelogi regional lembar bandung, pusat penelitian dan pengembangan geologi, badan geologi bandung. soetrisno, s., 1983, peta hidrogelogi regional lembar bandung, badan geologi bandung. takeda, k., & sosrodarsono, s. (2003). hidrologi untuk pengairan. editor sosrodarsono, s. pt pradnya paramita: jakarta. ©2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ about:blank e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 230 lubis, m. z., kausarian, h., and anurogo, w./jgeet vol 02 no 03/2017 review : seabed detection using application of image side scan sonar instrument (acoustic signal) muhammad zainuddin lubis 1, *, husnul kausarian 2 , wenang anurogo 1 1 department of informatics engineering, geomatics engineering, politeknik negeri batam, batam kepulauan riau, 29461 indonesia. 2 department of geological engineering,, universitas islam riau, jl. kaharudin nasution no. 113, pekanbaru, riau 28284, indonesia. * corresponding author : zainuddinlubis@polibatam.ac.id tel+6281342578087, office : 778-469856 ext : 2510; fax: +62-778-463620 received: aug 9, 2017. revised : aug 30, 2017, accepted: aug 30, 2017, published: 1 sept 2017 doi : 10.24273/jgeet.2017.2.3.560 abstract the importance of knowing the method for seabed detection using side-scan sonar images with sonar instrument is a much-needed requirement right now. this kind of threat also requires frequent sonar surveys in such areas. these survey operations need specific procedures and special equipment to ensure survey correctness. in this paper describes the method of observation and retrieval of marine imagery data using an acoustic signal method, to determine a target based on the sea. side scan sonar is an instrument consisting of single beam transducer on both sides. side scan sonar (sss) is a sonar development that is able to show in two-dimensional images of the seabed surface with seawater conditions and target targets simultaneously. the side scan sonar data processing is performed through geometric correction to establish the actual position of the image pixel, which consists of bottom tracking, slant-range correction, layback correction and radiometric correction performed for the backscatter intensity of the digital number assigned to each pixel including the beam angle correction (bac), automatic gain control (agc), time varied gain (tvg), and empirical gain normalization (egn). keywords: seabed detection, side scan sonar (sss), acoustic signal. 1. introduction the seabed is part of the earth whose territory has not been explored in its entirety, whether its breadth, depth, or potential. potential seafloor can be explored through several activities such as research, detection, sweeping, and determining objects located on the seabed. the acoustic signal has any function for: marine seismic, marine fisheries, determine the abundance of fish in marine fisheries (lubis and manik, 2017; lubis and wenang, 2016), echo processing and identifying surface and bottom layer (lubis et al., 2016). one of the effective and efficient methods used for marine exploration activities is using the hydroacoustic method. this method is often used to investigate columns and bottom waters efficiently and accurately (blondel 2009). hydroacoustic utilizes sound waves capable of propagating to the seafloor and several layers beneath which are then reflected back and accepted as the echo from target detection (lubis et al., 2017a; lubis and pujiyati, 2017). seabed identification using sonar system with the acoustic signal from side scan sonar c maxcm2 instrument in punggur sea in riau islands, indonesia, with the acoustic method according to (lubis et al., 2017a). side scan sonar is an instrument consisting of single beam transducer on both sides. side scan sonar (sss) is a sonar development that is able to show in two-dimensional images of the seabed surface with seabed surface conditions and targets simultaneously. side scan of high-frequency sonar is routinely used in qualitative seabed mapping with the main purpose of determining the location of features and objects on the seabed (lubis et al., 2017b). several outcomes (scanning) can produce mosaics, geology and sedimentological features that are easily recognizable and interpreted qualitatively so as to provide information about the dynamics of the seafloor (kenny et al., 2003). the advantage of the sonar scan side is being able to detect whatever is in the bottom of the waters so that shipwreck or other objects can be detected. this seafloor imaging technology provides a large area with high resolution. the greater the frequency value then the resulting data resolution will be higher but the coverage area is narrower (chang et al., 2016). generally research on side-sonar image scan is more directed to image processing, such as geometric correction on sonar side scan images (dzieciuch et al., 2017), side scan sonar imagery and seabed geologic interpretation (garcia et al. 2000), brightness and distance correction in side scan sonar image processing (rhinelander, 2016). mailto:zainuddinlubis@polibatam.ac.id lubis, m. z., kausarian, h., and anurogo, w./jgeet vol 02 no 03/2017 231 2. sonar scan side data correction the correction done on the sonar side scan image is divided into two, namely geometric and radiometric correction to the image of sea floor data side scan sonar (sss). geometric correction aims to establish the actual position in the sonar side scan pixel image, where as radiometrically is related to the intensity of back and digital numbers assigned to each pixel (chavez et al., 2002; milkert and fiedler, 2002). geometric correction is done in several processes namely bottom tracking, slant-range correction, and layback. the radiometric correction process is beam angle correction (bac), automatic gain control (agc), empirical gain normalization (egn), time varied gain (tvg). the bottom tracking phase of correction is done on the track line by digitizing the first return area or first return to the seabed and entering the speed of sound in the water. the bottom tracking correction stage is shown in figure 1.the slant range correction process is calculating the horizontal distance of an object on the seabed with the bottom of the sea under towfish. in this correction, an object is plotted to the left or right of towfish, so to obtain a slant range correction can be calculated using the phytagoras formula as follows (fig 2). 𝑎 2 = 𝑐 2 𝑏 2 (1) where: a = slant range correction b = high towfish to the seabed c = slant range the result of applying this slant range correction will remove the blind zone from each datum and move to the representative position of the actual seabed and remap the pixel from its position visible to its true position by computing the return time and height of the sonar rides. blind zone is the area that is in the middle of the sonar side scan image with low backscatter intensity. the width of the blind zone will correspond to the distance between the seafloor and the sensor. thus, the intensity of the sound waves contained in the blind zone will be affected by noise on the sensor and suspended particles in the water (burguera and oliver 2016) layback correction is a measure of the horizontal distance from the position of the gps antenna installed on the vessel against towfish position drawn behind the boat. the actual position of towfish can be known through the calculation of layback (fig 3). fig. 1. area first return (geometric correction) fig. 2. slant range correction plan 232 lubis, m. z., kausarian, h., and anurogo, w./jgeet vol 02 no 03/2017 fig. 3. layback correction calculation scheme the horizontal distance from the antenna to towfish can be calculated by summing the horizontal distance from the stern to the towfish with the antenna distance to the stern of the vessel, where a = horizontal distance from the stern of the vessel to the towfish, b = the depth of the towfish from the sea surface, c = towcable length, d = towfish from the seabed, and e = the horizontal distance from the gps antenna to the stern of the vessel. time varying gain correction (tvg) is performed on sonar side-scan data processing because the sonar system will produce beam coverage areas that have darker or lighter shades depending on the seabed texture type, so we get the equation: a= √𝑐2 − 𝑏2 (2) layback = a + e (3) in addition, it needs correction beam angle to correct the variation of beam intensity emitted towfish to the seabed. the overall backscatter energy variation is controlled by the return angle. the further away from the towfish, the energy will be reduced so that it takes correction beam angle on the sonar side-scan data processing. fig 4 shows characteristics of beam patterns of sonar side scan devices having radiant sonar intensity relative to different directions (hsueh, 2007). this beam pattern will produce strong enough noise at low slope angle beam (urick 1967). fig. 4. general beam pattern on side sonar scan instrument the empirical gain normalization (egn) correction stage is performed for normalized gain so that the backscatter sonar output is independent of the angle and can build normalized mosaics, providing good contrast and brightness to the sonar side scan data, followed by automatic gain control correction to normalize the reflection of the sonar so as not to be affected by the geometry of the seabed. 3. calculation of object length the long calculation is intended to find out how long an object located at the bottom of the sea that is seen from the image of side scan sonar. the trick is to compare the length of an object and the distance between fix in side scan sonar image with the distance between fix field, so we get the equation: (4) where: s1 '= the length of the object in the field s1 = distance between the fiks in the field (meters) s2 '= the length of the object in the image s2 = the distance between the fixes in the side scan sonar image (meter) 4. calculation of object width the width calculation is intended to find out how wide an object is in the field. the trick is the same as to find the length of the object, and we get the equation: (5) where: l1 = width of between fix in field (meter) l1 = width of object in field l2 = width of between fix in side scan sonar image (meter) l2 = the width of the object in the image 5. acoustic impedance and reflection coefficient in principle to calculate acoustic impedance can be seen in fig 4, which shows the state of a medium against sound waves and then reflects back. acoustic impedance z and reflection coefficient r are used to determine how big/ strong the value of the reflection of an object. the sea bottom acoustic impedance is a property that rules the backscattering strength, together with other sediment features such as slope and roughness. in this sense, sonar devices can be used to measure lubis, m. z., kausarian, h., and anurogo, w./jgeet vol 02 no 03/2017 233 the backscattering strength of a material lay up on the sea bottom and estimate the aforementioned sediment features. this is generally referred to as the acoustic impedance, and in the linear regime, this is independent of the amplitude of pressure fluctuation. this paper is concerned with the linear absorptive properties of a range of aperture geometries with bias flow in the presence of seabed incident waves. fig. 5. general beam pattern on side sonar scan instrument based on data ρ and c referring to lurton (2002) can be calculated impedance value, reflection coefficient. this is done because the substrate type is known through the grab sample. the impedance value, the reflection coefficient can be calculated by equation (6), (7) below: z = ρ x c (6) r = 𝑍1−𝑍2 𝑍1+𝑍2 (7) where: z1 = acoustic impedance of medium 1 z2 = acoustic impedance of medium 2, ρ = mass type (kg / m 3 ) c = sound speed (m / s). r = reflection coefficient the acoustic impedance is the ability of a material to be passed by acoustic waves. the acoustic impedance can be used to define the reflection coefficient, r is the measurement of the strength of the reflection by acoustic waves. acoustic backscatter that is reflected back to the sonar side scan transducer from the seabed is recorded for a certain period of time for a ping resulting in a time series data counter-amplitude. the backscatter of this amplitude can indirectly describe the object as well as the surface of the ocean floor reflecting the acoustic waves of the transducer. the backscatter values explain the response of the seafloor at the frequency used and for the specific conditions of the ensonification region (blondel 2009). sample figure of result backscatter can be seen in fig 6. fig. 6. acoustic backscatter image. the higher the amplitude value the more rough or hard a target is detected. similarly, the smaller the amplitude value, the level of roughness or violence of an object decreases. in addition to the roughness factor and roughness of an object, the sound frequency in the tool used and the grazing angle of the acoustic pulse can also be a factor affecting the value of backscatter in the bottom waters (burczynski, 2002). sample figure of sound velocity can be seen in fig 7. fig. 7. sample of sound velocity figure. 6. baseline substrate sample analysis of seabed sampling process of the substrate is done by using grab sampler equipment, then substrate sample will be taken to the laboratory to be analyzed texture of its substrate type. the method used to determine the type of bed-based substrate is by measuring the large diameter of the substrate grain (s), the substrate is saturated, before sieving the substrate sample is dissolved with hydrogen peroxide (h2o2) to remove the organic matter contained therein dried with an oven and weighed with an analytical scale, after the substrate sample was weighed and then dissolved (immersed) in water, to separate each grain size from 0.063 s / d 8.00 mm diameter sieves based on wenworth (1922). 234 lubis, m. z., kausarian, h., and anurogo, w./jgeet vol 02 no 03/2017 the sieve yield of each diameter was dried by means of a driven, and each diameter was measured by weight with an analytical scale, the remaining sieving results in the sludge were accommodated in a residual pan and by the pipette method. based on the diameter of the grains and the weight percentage of the substrate components are clay depth (diameter <0.004 mm), mud (diameter 0.004 0.063), sand (diameter 0.063 2.00 mm) and gravel (2-8 mm). references blondel p. 2009. the handbook of sidescan sonar. springer, praxis.chichester. burczynski j. 2002. bottom classification. biosonics, inc. www.biosonics.com. burguera, a., & oliver, g. 2016. high-resolution underwater mapping using side-scan sonar. plos one, 11(1), e0146396. chang, r., wang, y., hou, j., qiu, s., nian, r., he, b., & lendasse, a. 2016, april. underwater object detection with efficient shadow-removal for side scan sonar images. in oceans 2016shanghai (pp. 1-5). ieee. chavez p s jr., j isbrecht, p galanis, g l gabel, s c sides, d l soltesz, s l ross,m g velasco. 2002. processing,mosaicking and management of the monterey bay digital sidescan-sonar images. marine geology, 181: 305-315. dzieciuch, i., gebhardt, d., barngrover, c., & parikh, k. 2016. non-linear convolutional neural network for automatic detection of mine-like objects in sonar imagery. in international conference on applications in nonlinear dynamics (pp. 309-314). springer, cham. hsueh, d. y. development of sidescan sonar image mosaicing software. diss. master thesis, institute of applied marine physics and undersea technology, national sun yat-sen university, kaohsiung, taiwan, 2007. kenny, a. j., cato, i., desprez, m., fader, g., schüttenhelm, r. t. e., & side, j. 2003. an overview of seabed-mapping technologies in the context of marine habitat classification☆. ices journal of marine science, 60(2), 411-418. lubis, m. z., & anurogo, w. 2016. fish stock estimation in sikka regency waters, indonesia using single beam echosounder (cruzpro fish finder pcff-80) with hydroacoustic survey method. aceh journal of animal science, 1(2). lubis, m. z., & manik, h. m. 2017. acoustic systems (split beam echo sounder) to determine abundance of fish in marine fisheries. journal of geoscience, engineering, environment, and technology, 2(1), 76-83. lubis, m. z., & pujiyati, s. 2016. detection backscatter value of mangrove crab (scylla sp.) using cruzpro fishfinder pcff-80 hydroacoustic instrument. j biosens bioelectron, 7(205), 2. lubis, m. z., anggraini, k., kausarian, h., & pujiyati, s. 2017. marine seismic and side-scan sonar investigations for seabed identification with sonar system. journal of geoscience, engineering, environment, and technology, 2(2), 166-170. lubis, m. z., anurogo, w., khoirunnisa, h., irawan, s., gustin, o., & roziqin, a. 2017. using side-scan sonar instrument to characterize and map of seabed identification target in punggur sea of the riau islands, indonesia. journal of geoscience, engineering, environment, and technology, 2(1), 1-8. lubis, m. z., wulandari, p. d., mujahid, m., hargreaves, j., & pant, v. 2016. echo processing and identifying surface and bottom layer with simrad ek/ey 500. journal of biosensors and bioelectronics, 7(3), 1000212. lurton x. 2002. an introduction to underwater acoustic. springer, praxis.chichester. uk milkert, d., & fiedler, h. m. (2002). processing and mosaicking digital side scan sonar images: two examples from the western baltic sea. baltica, 15, 40-48. rhinelander, j. 2016. feature extraction and target classification of side-scan sonar images. in computational intelligence (ssci), 2016 ieee symposium series on (pp. 1-6). ieee. urick, r. j. 1967. principles of underwater sound for engineers. tata mcgraw-hill education. wentworth, c k. 1922. a scale of grade and class terms for clastic sediments. journal of geology 30: 377 392. 1. introduction 2. sonar scan side data correction 3. calculation of object length 4. calculation of object width 5. acoustic impedance and reflection coefficient 6. baseline substrate sample analysis of seabed references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 kausarian, h. et al./ jgeet vol 5 no /2020 89 research article settlement and capacity analysis of land support development on flyover in large city; pekanbaru, indonesia husnul kausarian1,*, evan trionaldi1, taufan khalif arrahman1, dewandra bagus eka putra1, batara1 1department of geological engineering, universitas islam riau, pekanbaru, riau 28284, indonesia. * corresponding author : husnulkausarian@eng.uir.ac.id tel.:+62-761-674674; fax: +62-761-674834 received: may 16, 2020; accepted: jun 19, 2020. doi 10.25299/jgeet.2020.5.2.5048 abstract the study area located on the street of soebrantas to soekarno hatta street, with the coordinate position of 0 ° 30 ' 0.79 "n 101 ° 24 ' 57.88 "e 0 ° 30 ' 0.16 "n 101 ° 24 ' 53.17 "e in pekanbaru city, indonesia. the development that will conduct flyovers in this area became the basis of this research. the main study of this research is to find out how an atterberg's boundaries, compressibility, and the likelihood of a ground decline in drill 1 use the value of n spt to match with the purpose of this study. which is (1) to know the large grain size of soil samples, (2) knowing the value of the liquid limit, the plastic boundary, and the plastic index of the soil samples, (3) knowing the possibility of land degradation in the research area, (4) power capacity analysis of ground support (5) knowing the decline of modeling using the plaxis 2d method (6) knows the relationship of decreasing values based on nspt and plaxis (7) knowing the relationship of sieve analysis and attaberg limit with decreased results. methods of data retrieval have done with soil testing in the field and soil testing in the laboratories. a comprehensive analysis of the grain has done with sieve analysis. plastic boundary, liquid, and plastic boundary indices with method attaberg limit. decreased analysis and power capacity analysis of ground support with nspt value tests. keywords: sieve analysis, atterberg limit, the capacity of soil support and settlement, n-spt, plaxis 2d modelling, flyover 1. introduction to support the economic growth activities of the government of indonesia, planning various infrastructure development programs ranging from the construction of toll roads, bridges, airports, docks, ports, canals, and so on (salim and negara, 2018; laksono et al., 2018; persada et al., 2018; hamid et al., 2018). the development of infrastructure increased the confortivity, and reduce the gap between each region. the need for development land continues to grow so that the construction is forcing to established on the area that is fewer conditions such as soft soil. construction of the flyover will be implemented in this area to be the basis of this research. to find out how the atterberg boundaries, compressibility, and likelihood of falling ground using the value of n spt count (wafi et al., 2018; kuzu et al., 2020; bautista et al., 2019; kumar et al., 2017). 2. study area and background based on regional geological map of sheet pekanbaru (clarke et al., 1982). the research area lies in the minas formation, precisely located at coordinates 0 ° 30 ' 0.79 "n 101 ° 24 ' 57.88 " e-0 ° 30 ' 0.16 "n 101 ° 24 ' 53.17 " e the minas formation is a quarter precipitate, precipitating in unaligned above the petani formation, the formation consists of a coating that is in the dominance of the batupasir and occasionally appears a thin layer of clay. the formation was from miocene to the plistosen and precipitated in the fluvial-alluvium environment. 3. methodology 3.1 research object to conduct all the research methodology, we summarize all the step of research follows: 1. the grain size of the ground (sieve analysis) is a test of filtering soil samples through a set of the sieve. 2. liquid limit (liquid limit) is the moisture content on the boundary between the liquid state and the plastic state. 3. plastic limit is the moisture content at the lower limit with plastic. 4. the atterberg limit relationship with carrying capacity. 5. modelling power support using plaxis 2d 3.2 sieve analysis sieve analysis (bardet, 1997; gupta et al., 2016; ubani et al., 2018; ruiz-martínez et al., 2016) aims to determine the type of soil that is graded poorly, graded uniform and graded well. at once to know the grain size on the ground. the formula of sieve analysis is as follows: 𝑅𝑛 = 𝑊𝑛 𝑊𝑡 × 100% [1] where: rn = amount of unloaded weight wn = weight wt = cup weight 3.3 atterberg limit the atterberg limit test is a method used to describe the nature of the fine-grained soil context on varying water levels. the soil has certain conditions, namely from liquid to frozen state (deng et al., 2017; rehman et al., 2019). http://journal.uir.ac.id/index.php/jgeet 90 kausarian, h. et al./ jgeet vol 5 no /2020 fig. 1. regional geological map of research area. 3.3.1 liquid limit the liquid limit is the groundwater level (chai et al., 2017) at the liquid limit, and the plastic boundary or the maximum moisture content where the soil has a minimum slide is at the 25th beat with the cassagrande tool. liquid boundaries defined as the lowest moisture content in which the soil is in a liquid state or a condition where the soil changes from liquid to plastic: ll = 𝑊−𝑃𝐿 𝐿𝐿−𝑃𝐿 [2] where: ll = liquid limit w = weight of soil samples pl = plastic limit 3.3.2 plastic limit plastic limits defined as the moisture content in the position between the plastic and semi-solid (hamzaban et al., 2019), which is% water content where the ground with a cylinder diameter of 3.2 mm begins to crack – cracks when rolled. the plastic boundary can be determined by simple testing by rolling several soils using the soil repeatedly into an ellipsoidal form. soil sample water content where the ground starts cracking – fractures are defined as plastic boundaries: ip = ll – pl [3] where: ip = plastic index ll = liquid limit pl = plastic limit 3.3.3 plasticity index the plasticity index demonstrates the nature of soil saturation. if the value of the pi is high, then the soil contains a lot of clay, then if the pi value is low, the soil contains muchsilt. the characteristic and nature of silt are with the moisture content that decreases minimal soil will dry. the plasticity index pi is the difference between the liquid limit and the plastic boundary of the soil. 3.4 capacity analysis for support and decrease soil if the soil is experiencing a load like a foundation burden, the soil will experience distortion or decline. if this burden is augmented, the reduction also increases. finally, at one time, there was a condition that, at a fixed load, the foundation suffered a considerable decline. this condition indicates that the support capacity has occurred. 3.5 analysisof n-spt (standard penetration test) methods carried out in conjunction with drilling to know both ground dynamic resistance and sampling, which is interrupted by the spt test. the technique consists of a thick cold-tube beating test into the ground, accompanied by a measurement of the number of strokes for inserting a deep-side tube 300mm vertically. 3.6 soil reduction analysis the decreasing calculation stated based on bowles theory (1977). the bowles theory is the result of the modifying of the meyerhoff theory. bowles considers the meyerhoff theory to be overly cautious, resulting in considerable decline. so bowles recommend for better improvement is as follows: [4] [5] where: si = lower foundation (inch) q = load intensity (kip/ft2) n = number of spt test punch b = width of foundation (ft) 3.7 analysis of power capacity supports depth of land (meyerhof 1956 – 1974) with qa is the capacity to support net permit in kn/m2, for a decrease of 2.54 cm. the meyerhof suggests the value of “n” taken an average value from a distance of 0 to b under the base of the foundation. a. qa = 12 n; for width b ≤ 1.2 m [6] b. qa = 8 n ((b + 0.3)/b) ^ 2; for width b > 1.2 m [7] where: qa = maximum support power n = n-spt b = foundation width 3.8 analysis of power capacity to support clay (meyerhof 1956 – 1974) for the foundation load in the form of squares, circles, and elongated foundations that lie in the soil of the clay, capacity supports the ultimate by observing the depth factor of the foundation, as follows: 𝑞𝑢 = 𝑐𝑢𝑁𝐶 + 𝐷𝑓 𝛾 [8] and the capacity for net ultimate: kausarian, h. et al./ jgeet vol 5 no /2020 91 𝑞𝑢𝑛 = 𝑐𝑢𝑁𝐶 [9] where: qu = capacity to support ultimate (kn/m2) qun = capacity to support net ultimate (kn/m2) df = depth of foundation (m) γ = weight of the soil volume (kn/m3) cu = cohesion in undrained condition (kn/m2) 3.9 analysis of power capacity to support the sand (meyerhof 1956 – 1974) granular soil types do not have cohesion (c) or have little cohesion. this granular soil usually forms a supporting capacity, especially by relative density (df). groundwater position against the foundation. for granular or sandy soils, because cohesion c = 0 the equation of soil buffer capacity for elongated shaped foundations is as follows: qu = ydnq + 0.5 byny[10] where: y = weight unit d = depth of foundation b = foundation diameter nq + ny = factor – support capacity factor 3.10 analysis of plaxis 2d data the plaxis 2d is a two-dimensional element program developed for the analysis of deformation, stability, and groundwater flow in geotechnical engineering (brinkgreve et al., 2016; vickneswaran and ravichandran, 2020; jadid et al., 2020; vali et al., 2018). plaxis 2d geometry models can be easily defined in-ground and structure modes after an independent solid model can automatically be cut and fused. the staged construction mode enables to simulate the construction and digging processes by enabling and disabling ground clusters and structural objects. 4. result and discussion 4.1 sieve analysis 4.1.1 drill sample 1 (depth 4.50 – 5.00 m) calculation of sieve analysis on drill sample 1 (depth 4.505.00 m) (table 1) shows the result as below. table 1. calculation tables of sieve analysis on drill sample 1 (4.505.00) m. filter size heavy restraine d amoun t of weight held percentage mm inch stuc k escape 9,5 3/8 0,00 0 0 100,000 4,75 no # 4 0,00 0 0 100,000 2,36 no # 10 8 8 3,186 96,814 1,18 no # 20 118,30 126,3 50,302 49,698 0,6 no # 40 80,90 207,2 85,522 17,478 0,3 no # 80 27,90 235,1 93,634 6,366 0,15 no # 100 1,70 236,8 94,311 5,689 0,075 no # 200 4,90 241,7 96,263 3,737 the sieve size 3/8 in getting weight-held in 0.00, which indicates no samples restrained at the size of this 3/8 sieve with a percentage of escaping 100%. the sieve size no. 4 in the weight is 0.00 which indicates that there is no sample held on the size of the sieve no. 4 with a percentage of a breakout of 100%. size of filter no. 10 obtained weight 0.00 which indicates that no sample is held at the size of this no. 10 sieve with a percentage of a breakout of 100%. size of filter no. 20 obtained 26 gr held weight with a percentage held at 17.35% and the percentage of rp 82.641%. size of filter no. 40 was obtained the weight of 51.30 gr with the amount of weight held to be 77.3 gr. percentage held at 51.61% and percentage escaped by 48.350%. 55.80 gr held the size of filter no. 80 obtained weight with the amount of weight held to be 133.1 gr. percentage held at 88.86% and percentage escaped by 11.134%. size of filter no. 100 obtained weight was held by 2.50 gr with the amount of weight held to be 135.6 gr. percentage held at 90.53%, and percentage escaped by 9.465%. the size of the filter no. 200 is obtained by the weight of 7.60 gr with the amount of weight held to be 143.2 gr. percentage held at 95.610% and percentage escaped by 4.390%. the result of the projection of the calculation value in the analysis sieve graph (figure 2) obtained a group 1 curve shape that is categorized as medium-size sand with poor gradation according to the cu and cz values that can be because the sand has a uniform grain size. based on the test of the sieve analysis that is done, get results on the 200 no sample of soil type that passes by the amount of < 50%. based on uscs category, in this case, samples are included in the s (sand) types, according to the sample in the analysis. according to the uscs criteria for poorly graded soil, if it has a smaller cu of 5 and has a cz between 0.5 to 2.0 indicating well-graded soil, it can be concluded that the soil is well graded. good gradated soil will have cu > 4, and cc between 1 and 3 for gravel land and sand has cu > 6 with cc between 1 and 3. fig. 2. graph sieve analysis on drill sample 1 (4.50-5.00) m. 4.1.2 drill sample 2 (depth 8.00 – 8.50 m) calculation of sieve analysis on drill sample 1 (depth 8.008.50 m) (table 2) shows the result as below. table. 2. calculation of sieve analysis on drill sample 2 (depth 8.008.50 m). filter size heavy restraine d amoun t of weight held percentage mm inch stuc k escape 9,5 3/8 0,00 0 0 100,000 4,75 no # 4 0,00 0 0 100,000 2,36 no # 10 0 0 0,000 100,000 1,18 no # 20 26 26,0 17,359 82,641 0,6 no # 40 51,3 77,3 51,610 48,390 0,3 no # 80 55,8 133,1 88,866 11,134 0,15 no # 100 2,5 135,6 90,535 9,465 0,075 no # 200 7,6 143,2 95,610 4,390 the size of the sieve 3/8 to get a weight held in 0.00 which indicates that no samples were restrained at the size of this 3/8 sieve with a percentage of escaping 100% the size of sieve no. 4 in weight is 0.00, which indicates that there is no sample held on the size of the sieve no. 4 with a percentage of a breakout of 100%. 92 kausarian, h. et al./ jgeet vol 5 no /2020 size of filter no. 10 obtained weight held by 8 gr with a percentage held at 3.186% and the percentage of rp 96.814%. size of filter no. 20 was obtained weight was held at 118.30 gr with the amount of weight held to 126.3 gr percentage was held by 50.302% and the percentage passed by 49.698% size of filter no. 40 was obtained the weight of 80.90 gr with the amount of weight held to be 207.2 gr. percentage held at 82.52% and percentage escaped by 17.478% 27.90 gr held the size of filter no. 80 obtained weight with the amount of weight held to be 235.1 gr. percentage held at 93.634% and percentage escaped by 6.366% size of filter no. 100 obtained weight was held by 1.70 gr with the amount of weight held to be 236.8 gr. percentage held at 94.311% and percentage escaped by 5.689% the size of the filter no. 200 is obtained by the weight of 4.90 gr with the amount of weight held to be 241.7 gr. percentage held at 96.263% and percentage escaped by 3.737%. results of projection of calculation value on graph sieve analysis (figure 3), obtained form the class 1 curve is categorized as a medium-size sand with poor gradation according to the cu and cz values that can be because the sand has a uniform grain size. fig. 3. graph sieve analysis on drill sample 1 (8.00-8.50) m. according to the uscs criteria for the soil to graded well when it has a cu greater than 5 and has a cz between 0.5 to 2.0 indicating good graded soil, it can be concluded that the soil is a bad gradation. well graded soil will have cu > 4 and cc between 1 and 3 for gravel soil, and sand has cu > 6 with cc between 1 and 3. 4.1.3 calculation of sieve analysis on drill sample 3 (depth 8.00-8.50 m) the size of the sieve no. 3/8 (table 3), the weight of soil is 0.00 gr, which is that no grain is stuck on this filter, and the amount of the weight of the rate is 0gr. while the percentage of grain size is 0.000% and the percentage of escaped is still 100,000%. size of sieve no. 4 weight of the soil is 0.00 gr, which is that no grain is stuck in this filter, and the amount of weight is the rate of 0gr. while the percentage of the size of the weighted grain is 0.000%, and the percentage escaped is still 100,000%. size of sieve no. 10 weight of the soil is 0.40 gr, which is the details that are held disaringan. this is included in the fine grain, and the amount of the weight of the rate is 0.4 gr. while the percentage of the size of the weighted grain is 0186%, and the percentage passes the size of 99,814%. size of sieve no. 20 weight soil is 46.30 gr, which is the details that are held disaringan. this is included in the fine grain-medium and the amount of the weight of the 46.7 gr. while the percentage of the size of the weighted grain is 21,763%, and the percentage passes the size of 78,237%. the size of the sieve no. 40 the soil weight is 97.40 gr, which is the details that are held in the sieve. it is included in coarse grain, and the current amount weight is 144.1 gr, while the percentage of the size of the grain measure is 67,154%, and the percentage passes by 32,846%. size of sieve no. 80 the soil weight is 54.40 gr which is the details that are held disaringan is included in the fine grainmedium, and the amount of the weight of the 198.5 gr. while the percentage of the size of the weighted grain is 92,505%, and the percentage passes the size of 7,495%. size of sieve no. 100;soil weight is 2.20 gr.fine-grain restrained in the sieve with the weight amount of 200.7 gr. the grain weight size percentage is 93,530%, and the pass size percentage is 6,470%. size sieve no. 200 the soil weight is 5.10 gr which is the details that are held in the sieve included in the fine-grain and the amount of the weight of the 205.8 gr. while the percentage of the weighted grain size is 95,907% and the percentage passes the size of the grain 4,093%. uniformity coefficient (cu) samples of the soil are 3,714, which is included in the poor gradation category, which is smaller than 5. while the gradation coefficient (cz) sample of the soil is 1.2363 (figure 4). the value of the resulting chart derived from d60, d30, and d10 data, where the maximum of the d60 is the diameter passed at 60mm sieve size, as well as the d30 is the diameter passes at a 30mm sieve size, and the d60 is diameter qualified at 10mm sieve size. table. 3. calculation of sieve analysis on drill sample 3 (depth 8.008.50 m). filter size heavy restraine d amoun t of weight held percentage mm inch stuc k escape 9,5 3/8 0,00 0 0,000 100,000 4,75 no # 4 0,00 0 0,000 100,000 2,36 no # 10 0,40 0,4 0,186 99,814 1,18 no # 20 46,30 46,7 21,763 78,237 0,6 no # 40 97,40 144,1 67,154 32,846 0,3 no # 80 54,40 198,50 92,505 7,495 0,15 no # 100 2,20 200,7 93,530 6,470 0,075 no # 200 5,10 205,8 95,907 4,093 according to the criteria from uscs, the soil is well-graded if it has a cu greater than five and has a cz between 0.5 to 3.0, indicating well-graded soil. it can then conclude the soil in the drill holes 8.00 – 8.50 meters have a poor gradation because there are smaller cu of 5 and have a good cz because it has a gradation of not more than 3.0 mm. fig. 4. graph sieve analysis on drill sample 3 (8.00-8.50) m. 4.2 atterberg limit the first experiment had a water content of 32.8% with a low number of 11 times. the second attempt has a water content of 30.5% with a low number of 19 times. the third test has a water content of 27.9% with a blow count of 28 times. the kausarian, h. et al./ jgeet vol 5 no /2020 93 fourth experiment had a water content of 26.2% with a low number of 38 times (table 4). from the experiments that have been carried out so that the average value of water content is 28.65 grams. with the number of beats averaging 24 times the tap. 4.3 standard penetration test (n-spt) 4.3.1analysis power capacity calculation for soil support through spt test the test for power capacity is necessary, and then it can be deduced increasingly in the drilling that is done then the type of soil gained will be more distinct-different and also the level of consistency is different so that at the time of test n-spt on soil that has a hard consistency will be done as much as 60 times the punch and on the soil that has a soft consistency feeding the amount of blow its spt under 50 based on the calculation of land support capacity through n-spt test. table 4. atterberg limit bore hole 3at the depth 22.00-22.50 m. number of blows n 38 28 19 11 plastic limit wet soil weight + cruss gr 27,8 32, 7 28, 5 33,39 2 14,1 13,1 dry soil weight + cruss gr 25,1 28, 8 25, 3 28,8 13,2 12,4 water weight gr 2,7 3,9 3,2 4,592 0,9 0,7 heavy cruss gr 14,8 14, 8 14, 8 14,8 9,6 8,7 heavy dry soil gr 10,3 14 10, 8 14 3,6 3,7 moisture content % 26,2 27, 9 30, 5 32,8 25,0 0 18,92 atterberg limit result liquid limit (ll) 28,65 plasticity index (pi) 6,69 plastic limit (pl) 21,96 unified soil clasification land type name inorganic clay, with plasticity of low or medium, gravel clay, sandy clay, berlanau, thin clay (lean clays) table 5. calculated result of land support power capacity through test n-spt in bore hole 3. no depth soil type nspt b meyerh of qa = 12 n consistenc y 1 1,00 sand clay 2 1 24 very soft 2 3,00 fine sand 8 1 96 soft 3 5,00 fine sand 10 1 120 soft 4 7,00 fine sand 15 1 180 medium 5 9,00 fine sand 16 1 192 medium 6 11,00 fine sand 20 1 240 medium 7 13,00 fine sand 24 1 288 medium 8 15,00 sand 60 1 720 very hard 9 17,00 sand 60 1 720 very hard 10 19,00 sand 60 1 720 very hard 11 21,00 sand 60 1 720 very hard 12 23,00 clay 22 1 264 very hard 13 25,00 clay 26 1 312 very hard 14 27,00 clay 31 1 360 hard 15 29,00 clay 21 1 252 very hard 16 31,00 clay 35 1 420 hard 17 33,00 sand 37 1 444 hard 18 35,00 sand 58 1 696 very hard 19 37,00 sand 60 1 720 very hard 20 39,00 sand 60 1 720 very hard 21 41,00 sand 60 1 720 very hard if the value of n-spt obtained is big then the capacity to support the land will be greater and vice versa if the value of nspt is small, the capacity of the supporting power is smaller so that when implanted the foundation of the small n-spt value bridge pole will multiply a large decline, so it can be concluded that the value of nthe soil type that has a small n-spt value is the clay and silt soils and the type of soil that has a large nspt value is the sandy soil because the sandy soil does not have a liquid boundary and a plastic boundary so that the sand can not keep the water and the sand soil also has bad porosity. then in the land of clay and silt has a liquid boundary and a plastic boundary so that the soil type of clay and silt has soil properties that can stray water. if the foundation of the pole is implanted in the soil of the clay and eat water will occur a large decline because the clay and silt can not withstand a large burden, then if the foundation to be implanted bridge pole should be implanted on the type of sand soil because this type of sand soil can withstand a large burden because the greater the burden received by the sand to lowing the land. 4.3.2 calculation of n-spt test on sand soil on the depths of the 08.00 – 08.50 meters (table 5), deep sand can support large soils. so that at the time of the foundation of the sand-covered soil, then the decline is very small because the sand can support a strong soil to withstand the burden it receives, it is advisable to plant the foundation of the bridge pole preferably in the sandy soil because the sand has the capacity of large soil support and when the drilling is done at sufficient depth in the advisable to obtain the then for the sand can support a large license, because the sand can support permit up to 200 which means good enough if implanted the foundation of the bridge pole. table 6. calculation of n-spt test on sand soil. 4.3.3 calculation of n-spt test on clay the soil of the clay depth 22.00 – 22.50 meters has the capacity of small soil so that when planted the foundation of the clay soil in the field, there will be a decline due to heavy loads will affect the condition of the land strength at the time of the burden that is working. so to plant a foundation in the clay land is not advised even if done deep drilling, the clay will not be strong withstand the burden received and the capacity of the land support the clay is very small, and consistency in this layer of clay is soft to medium. table 7. calculation of n-spt test on clay soil. depth soil layer large angel (ф) = nc cu (kn/ m2) unit weight (kn/m2) meyerhof qu = kn/m2 22.00 – 22.50 silty clay nc = 14,83 72,60 kn/m 2 1,799 kn/m2 66,248 kn/m2 the depth of sand soil type 08.00 – 08.50 meters have the value of the capacity of the large soil support with a value of 200,123 kn/m2 so that at this depth the decline is small and at a depth of 22.00-22.50 meters acquired soil type is the form of clay and silt which has the value of capacity of small soil support that will cause the decline will be greater. then it is recommended to embed the foundation of the bridge pole should have the value of the capacity of the large land support 94 kausarian, h. et al./ jgeet vol 5 no /2020 to be exposed to the burden on the foundation of the bridge pole decline that occurs in the land will be smaller. 4.4 plaxis modelling 4.4.1 plaxis modelling power capacity to support land increasingly in the drill done and large loads received by the soil, then the capacity of land support will influence on the foundation of the pole so that it can cause the slope of the pole foundation (figure 5). the greater the nspt value that can be, then the smaller the decline that occurs, so too, the smaller the nspt value that can be, then the greater the decline that occurs. the depth of 00-01.00 m is obtained by a large reduction of nspt value of 10 with the lithology of flared-sand and smooth consistency with the loose grain. fig. 5. plaxis modelling power capacity to support land. depth of 3-7 meters is ground domination with fine sand granules with nspt value of 11-30 so that the soil at this depth categorized as soil with medium consistency. the depth of 9-13 meters is ground domination with finegrained sand grains with an nspt value of 31-50 so that the soil at this depth is categorized as ground with stiff (rigid) consistency with dense density. depth of 13-15 meters is ground domination with fine sand grains with an nspt value of > 50 so that the soil at this depth is categorized as ground with a very stiff consistency (very rigid) – hard (hard) with a relatively dense. depth of 15-35 m is ground domination with granular sand – loam with nspt value of < 60 and > 10 so that the soil at this depth is categorized as soil with medium-stiff consistency (rigid) with medium-dense relative density (dense). based on the calculations, it can be seen a large nspt value as well as large impairment value occurs in drill 1 holes with soil type contained in each depth, and also the consistency of each at any depth. from these two charts can be concluded the greater the value of nspt that canbe, then the smaller the decline in the value of each depth, n-spt values that can relate to the soil type and also the consistency of each depth.sand has a large n-spt value because it has no liquid and plastic properties, which sand can drain the water more easily. after all, it has pores, and the loam or silt usually has a relatively large n-spt value because the clay or silt has soft soil properties that have plastic boundaries and liquid boundaries, which are not able to pass the water. but the type of soil that can be sometimes unbiased to be a reference for the value of n-spt that is found, for example, can be seen at a depth of 5 meters, which has a relatively small n-spt value and a large decline, which affects the depth of this is the groundwater face. because the groundwater in bor 1 is at a depth of 4 meters. 4.4.2 plaxis modeling on declining soil the first image in getting deformed mash land drop profile. this deformed function to show a large decrease in the land that occurs can be seen in the soil that decreases. the decline occurred at a depth of 00.00 – 03.00 meters, on the layer of piles of soil material.the decline was shown by the direction of the blue-colored arrow that leads vertically. the load point is given in the center of the layer. the second image is for getting a displacement vertical land drop profile. the vertical image shows the direction of pressure or stress and the load given on the ground at the center of the soil layer and gets red stripes on the layer, which means the soil obtains the pressure of the ground.on the upper part receives a pressure greater than the bottom, which means from top to bottom is decreased pressure gained on the ground. the decline occurs as deep as 20.77 x 10-3 m. or 2.077 cm (figure 6). fig. 6. plaxis modeling on declining soil. 5. conclusion the calculation of the filter analysis in drill with depth (4.50-5.00) and (8.00 – 8.50) meters, it indicates that the sample is categorized as fine soil has poor grain uniformity, because in the sample (4.50-5.00) the meter has a value of cu 3.714, and in the sample (8.00 -8,50) meter has a value of 4. included in the category of bad graded soil. all the tests comply with astm, aashto, and uscs standards. at the depth (22.00 – 22.50) at a rate of water at an average of 18.92 grams. with an average beat amount of 24 beats. the average value of the plastic sample rate at this depth is 21.96%, and the value of the plastic index at this depth is 6.69%. plastic indices get through the calculation of liquid limit – plastic limit. the decline also influenced by the value of nspt that can, if the soil type is sandy but has a small nspt value then the decline is also greater and vice versa. based on the results of the sieve analysis and atterberg connection limit on the capacity of the land support, it can be kausarian, h. et al./ jgeet vol 5 no /2020 95 conditioned for the foundation strength of the pole. it should be implanted at depth to obtain the type of soil that does not have a plastic boundary and liquid boundaries that the plastic boundary and liquid limits save water content that will affect the foundation of the pole. references bardet, j.p., 1997. experimental soil mechanics (p. 582). upper saddle river, nj: prentice hall. bautista-de castro, á., sánchez-aparicio, l.j., carrascogarcía, p., ramos, l.f. and gonzález-aguilera, d., 2019. a multidisciplinary approach to calibrating advanced numerical simulations of masonry arch bridges. mechanical systems and signal processing, 129, pp.337-365. brinkgreve, 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engineers. wafi, a., sasmito, p., rizki, m.a. and rahman, a., 2018, april. comparison analysis of subsurfaces survey between geophysics method (geoelectric/ert) and geotechnical method (standard penetration test (spt) at kaima overpass manado-bitung toll road. in eage-hagi 1st asia pacific meeting on near surface geoscience and engineering (vol. 2018, no. 1, pp. 1-6). european association of geoscientists & engineers © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 5. no 4. december 2020 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 05 no 04 2020. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content stream sediment geochemical survey on metamorphic rock, kolaka, southeast sulawesi, indonesia.................................................................................................... 164 raster-based model for mass movement in malang regency, east java, indonesia ........................................................................................................................................ 169 analysis of the surface subsidence of porong and surrounding area, east java, indonesia .............................................................................................................................. 175 origin of geothermal water around slamet volcano paguyangan cipari, central java, indonesia. ............................................................................................................... 181 investigation of groundwater potential using electrical resistivity method and hydraulic parameters in lam apeng, aceh besar, indonesia .............................................. 185 disaster mitigation for palu city residents in dealing with liquefaction disasters in accordance of spatial patterns of palu city, central sulawesi province, indonesia ...................................................................................................................... 191 simulation of time-lapse resistivity method on sandbox model to determine fluid changes and desaturation ............................................................................................... 198 assessment of groundwater quality for drinking purpose in an industrial area, dumai city, riau, indonesia ............................................................................................. 204 determining groundwater potential using vertical electrical sounding method in manggar, balikpapan city, indonesia ...................................................................... 209 page 1 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 darisma, et al./ jgeet vol 5 no 4/2020 185 research article investigation of groundwater potential using electrical resistivity method and hydraulic parameters in lam apeng, aceh besar, indonesia. dian darisma1*, ferdy fernanda1, muhammad syukri1,2* 1department of geophysical engineering, faculty of engineering, universitas syiah kuala, aceh, indonesia. 2department of physics, faculty of mathematics and natural sciences, universitas syiah kuala, aceh, indonesia. * corresponding author: diandarisma@unsyiah.ac.id, m.syukri@unsyiah.ac.id. tel.:+62-852-6097-1289 received: aug 24, 2020; accepted: sept 22, 2020. doi : 10.25299/jgeet.2020.5.4.5501 abstract lam apeng is a village with a majority of people living as farmers, which causes the need of water for agriculture is increasing. the water demand in this area continues to increase as the population increases, for various purposes. the objective of this study is to determine the distribution of the groundwater layer using the electrical resistivity method and to determine groundwater potential using hydraulic parameters. this research is conducted using 2 measurement line with a length of each line is 112 meters and distances of each electrode is 2 meters. the data invert using res2dinv software to obtain 2d subsurface lithology subsurface. at line 1, the aquifer (sand) layer is located in the second layer with a rock resistivity value of 12 ωm 18.6 ωm at a depth of 8 m 18 m. at line 2, the aquifer (sand) layer is also located in the second layer with a resistivity value of 4.6 ωm 18 ωm at a depth of 5 m – 12 m. based on the interpretation of the two measurement lines, it can be concluded that the type of aquifer in the research site is a semi unconfined aquifer. in this study, hydraulic parameters (hydraulic conductivity, longitudinal conductance, transverse resistance, and transmissivity) was calculated based on the resistivity value and the thickness of the aquifer layer. the average resistivity of the aquifer layer used is 15.3 ωm and 11.3 ωm, respectively for line 1 and line 2, indicating that the aquifer was moderately corrosive. longitudinal conductance values are 0.65 ω-1 and 0.62 ω-1 which indicated moderate protective capacity. the transmissivity values are 6.78 m2/dayand 4.77 m2/day, which indicates that the designation in this area is low and the groundwater potential is local or only for personal consumption. keywords: groundwater, electrical resistivity, hydraulic parameter, lam apeng. 1. introduction water is an essential element for all life forms on earth. water covers nearly 71% of the earth's surface which is in the form of liquid, ice,and gas. based on the place of origin, water is divided into 2 types, namely water that is on the surface and water that is below the surface. groundwater is water that is found in the soil or rock layers below the surface. according to fetter (2001), soil and rock pores become saturated with water at a certain depth. the uppermost saturated zone is called the watertable. water stored in the saturated zone is called groundwater, which then moves as groundwater flow through rocks, or seepage (aquifer) and collects in ponds, lakes, rivers, and sea. davis and de wiest (1966) define water entering freely into the well, either unconfined or confined. the potential of groundwater depends on the porosity and ability of rocks to discharge water. the use of groundwater it self as a means of life is gradually increasing for industrial and household needs (chandra et al., 2010; suryadi et al., 2018). the existence of continuous extraction of groundwater can exceed the capacity of an aquifer. so that new aquifer sources are needed. 2. geological setting lam apeng village is located in seulimum subdistrict, aceh besar. the topography in the northern area of the study tends to be flat and continues to rise to the south towards seulawah agam volcano. the majority of the land is used as agricultural land and part of the land is still forest area. based on the regional geological map of aceh besar, lam apeng village is in the branching zone of the sumatra fault segment so that there are many local faults. the geological structure of the lam apeng area is dominated by rocks originating from boulders of volcanic eruptions, namely the lam teuba volcanic rock formations. this formation consists of volcanic rocks from andesite to dacite, pumice breccia, tuff, sandstone, and young volcanic deposits, including tuff, lava, breccia, and lava andesite to basalt. the tuff rocks are light brown to light gray, slightly hard, silt grain size to fine sand, which can be seen in fig 1. dacite rock is dark gray, hard, vesicular structure, large fine crystal grains: aphanitic, hypocrystalline, in equigranular, glass mineral, muscovite, and quartz. volcanic breccia rock consists of fragments of volcanic material, namely dacite andesite rock, glass mixed in one volcanic deposit which is included in volcanic rock. (barber et al., 2005). lam apeng is a village that has extensive agricultural and plantation land. as a result of these plantations and agricultural activities, water reserves are needed for these lands, where almost all of these communities work as farmers. in this area, the farmers use the river flow to meet the needs of their plantations, wherein the dry season the water discharge in the river has decreased due to the absence of rain in the upstream http://journal.uir.ac.id/index.php/jgeet mailto:diandarisma@unsyiah.ac.id mailto:m.syukri@unsyiah.ac.id 186 darisma, et al./ jgeet vol 5 no 4/2020 river and also difficult access to get the water. therefore, research is needed to identify the location of groundwater aquifers that can meet these needs. there are several ways to research and find groundwater reserves using geophysical methods and one of the methods that can be used is the electrical resistivity method (alfadli and natasia, 2017; syukri and saad, 2017). the electrical resistivity method is a very suitable method for groundwater exploration because of hydrogeological properties such as porosity and permeability, which are directly related to the resistivity value. this method can measure the resistivity of the subsurface rocks which can identify rock layers, structures, and also the groundwater layer (mohamaden et al., 2016; muchingami et al., 2012). the configuration used in this study is wennerschlumberger configuration. this configuration is a combination of the wenner and schlumberger configurations to identify changes vertically and horizontally. there are several studies conducted to determine groundwater sources using geoelectric methods (bayewu et al., 2018; metwaly et al., 2010; mohamaden and ehab, 2017). based on some of these studies, it proves that the geoelectric method is quite good and very effective for finding groundwater. the resistivity and aquifer thickness values from the inversion of electrical resistivity data were used to determine aquifer parameters (soil corrosivity, protective capacity, and designation).usually, the conventional way to estimate these parameters is through a pumping test and grain size analysis(fetter, 2001). but the test takes longer time and is not economical (perdomo et al., 2018; soupios et al., 2007). therefore, a geophysical approach (electrical resistivity method) can be used to determine hydraulic parameters (abdulrazzaq et al., 2020; hasan et al., 2020). fig. 1. geological map of aceh besar (modified from bennet et al., 1981) 3. methodology 3.1 electrical resistivity method the electrical resistivity method is a geophysical method that utilizes electric currents to determine subsurface conditions. the results of electrical resistivity measurements cannot be used with certainty considering the many factors that influence conductivity and resistivity. even so, the method can provide information about rock layers that contain water (aquifers). the resistivity value of rock layers containing water will be lower. the resistivity value obtained at the beginning of the measurement is not the actual resistivity value, but the resistivity value which is usually called apparent resistivity (ρa), which is shown by the following equation: i v k a   (1) where k is the geometric factor, δv and i are the potential difference and the injected current, respectively. the measurement of the resistivity value is obtained by placing the electrodes, which is known as the electrode configuration. the different configurations used can cause different geometric factors. the geometry factor is a correction value for the potential electrode and the current electrode. some of the configurations that are often used for geo-electrical surveys include wenner, pole-pole, and pole-dipole. in this study, the configuration used is the wenner-schlumberger configuration (fig. 2). fig. 2. electrode configuration of wenner-schlumberger (telford et al., 1990). the wenner-schlumberger configuration is a combination of the wenner and schlumberger configurations (dahlin, 2001). in this configuration, the distance between the electrodes p1 and p2 is a while the distance between c1 and p1 and p2 and c2 is na. the distance between the electrodes remains constant, covers well horizontally and deep penetration vertically. the result of the combination of wenner and schlumberger results in the value of k also changing according to the following equation: annk )1(   (2) darisma, et al./ jgeet vol 5 no 4/2020 187 data measurement in the field using the supersting r8/ip tool with the wenner-schlumberger configuration. the measurement path is in the form of two parallel straight lines. the length of line 1 is 112 m with 2 m spacing and line 2 is 112 m with 2 m spacing (fig. 3). fig. 3 design of measurement line in lam apeng the resistivity data obtained in the field will be processed using the res2dinv software to obtain a resistivity crosssection. the program is based on the smoothness constrained least square approach (degroot hedlin and constable, 1990; sasaki, 1992; darisma and marwan, 2019) which generates subsurface models into rectangular blocks which then determines the optimum inversion parameter. then the apparent resistivity value is calculated from the block model based on the finite difference or finite element method which is compared with the measurement data. this iteration processcontinues until the calculated apparent resistivity value matches the measurement value (loke and barker, 1996). 3.2 hydraulic parameters the electrical resistivity method is a powerful method for groundwater exploration and water flow modeling. the result of the electrical resistivity inversion is the thickness of the aquifer h and the resistivity ρ which is used to calculate the hydraulic parameters. these parameters are the longitudinal conductance s, transverse resistance r, hydraulic conductivity k, and transmissivity t (maillet, 1947). the relationship of these parameters with thickness h and resistivity is shown by the following equation,  h s  (3) hr  (4) 0013.06 108   exk (5) kht  (6) the hydraulic conductivity k and resistivity are an indirect relationship as seen in eq. 5. however, this relationship will be linear at low resistivity (fetter, 2001). the hydraulic parameters are then used to determine the soil corrosion, protective capacity, designation, and groundwater potential. soil corrosivity is caused by iron content which can be predicted based on the resistivity value of the aquifer (table 1) (baeckmann et al., 1997). the protective capacity rating is inferred based on the longitudinal conductance value (table 2). the rating is used to predict how safe a layer if a layer collapse when the water pump out from the aquifer (henriet, 1976). low transverse resistance shows that the rock has weathered, while high traverse resistance indicates that the rock is fresh and massive bedrock.the designation is used to predict the ability of a layer to drain fluid while the groundwater supply potential is to estimate the potential groundwater that can be extracted (krásný, 1993). designation and groundwater supply potential are predicted based on the transmissivity value (table 3) table 1. classification of soil corrosivity. soil resistivity (ωm) soil corrosivity <10 very strongly corrosive 10-60 moderately corrosive 60-180 slightly corrosive ≥ 180 practically noncorrosive 4. results and discussion 4.1 two-dimensional resistivity model the results of data processing of the wennerschlumbergerconfigurationresistivity method can be seen in fig. 4 and 5. the results of the 2d model inversion show that at line 1 (fig. 4) there are 3 layers. the rms value obtained was 12.3%. the top layer is interpreted as an alluvial rock layer with resistivity values ranging from 70 ωm 109 ωm at a depth of 0.5 m 8 m. the lower layer is interpreted as a tuff rock layer which has a resistivity value of 25 ωm 60 ωm with a depth greater than 18 m. table 2. classification of protective capacity. longitudinal conductance (mho) protective capacity rating >10 excellent 5-10 very good 0.7-4.9 good 0.2-0.69 moderate 0.1-0.19 weak <0.1 poor 188 darisma, et al./ jgeet vol 5 no 4/2020 table 3. classification of groundwater supply potential. transmisivity (m/day) designation groundwater supply potential 1000 very high withdrawal of great regional importance 100-1000 high withdrawal of lesser regional importance 10-100 intermediate withdrawal of local water supply (small community, plant etc) 1-10 low smaller withdrawal for local water supply (private consumption) 0.1-1 very low withdrawal for local water supply (private consumption) <0.1 impermeable sources for local water supply are difficult from the model (fig. 4), it shows that the aquifer layer is in the middle layer at a depth of 8 m 18 m with the carrier layer interpreted as sand with a resistivity value of 12 ωm 18.6 ωm. because of its ability to store and drain large amounts of water, this layer is conductive. the aquifer layer at line 1 is predicted to be 10 m thick. the interpretation of rock lithology at line 1 can be seen in table 4.the interpretation of rock lithology at line 2 can be seen in table 5. fig. 4. resistivity model of line 1. fig. 5.resistivity model of line 2. the results of the inversion at line 2 can be seen in fig. 5 which shows that 3 rock layers are similar to the model at line 1. this confirms that the inversion model at line 1 and line 2 is connected. the rms value obtained is 1.4%. the top layer consists of alluvium rocks with resistivity values ranging from 62.9 ωm 861 ωm and has a depth of 0.5 m 5 m. the lower layer consists of tuff rock where this rock is also found at line 1 which has a resistivity value of 26.3 ωm 100 ωm with a depth of a greater than12 m. table 4. interpretation of lithology line 1. layer depth (m) thickness (m) resistivity (ωm) interpretation 1 0.5 – 8 5 70 109 sand, clay,gravel 2 8 18 10 12 18.6 sand (aquifer) 3 >18 25 60 tuff based on the inversion model at line 2, the aquifer layer is in the middle layer at a depth of 5 m 12 m. the carrying layer is sand with a resistivity value of 4.6 ωm 18 ωm. the aquifer layer at line 2 is 7 m thick from the two inversion models at line 1 and line 2, it can be concluded that the aquifer is semi unconfined. this groundwater is in the layer above the watersaturated layer or tuff and under the alluvial layer that water can pass through and can also hold water. table 5. interpretation of lithology line 2. layer depth (m) thickness (m) resistivity (ωm) interpretation 1 0.5 5 4.5 62.9 861 sand, clay, gravel 2 5 12 7 4.6 18 sand (aquifer) 3 >12 26.3 – 100 tuff 4.2 estimation of aquifer potential based on the results of the inversion of electrical resistivity data in lam apeng area, the thickness of the aquifer at line 1 and line 2 is 10 m and 7 m, respectively. the resistivity value darisma, et al./ jgeet vol 5 no 4/2020 189 used is the average resistivity for each line. line 1 has a resistivity of 15.3 ωm and line 2 has a resistivity of 11.3 ωm. the resistivity value at each line was then used to determine the level of corrosivity in the lam apeng area based on table 1. the level of corrosivity in this area is classified as moderate. furthermore, longitudinal conductance and transverse resistance values are calculated based on eqn. 3 and eqn. 4. the longitudinal conductance value on each line is 0.65 ω-1 and 0.62 ω-1, which indicates that the safety of this layer if a layer collapse is classified as moderate (table 3).for the transverse resistance value, it generally correlates with the transmissivity value. after ward, hydraulic conductivity and transmissivity are calculated using eqn. 5 and eqn. 6. hydraulic conductivity at line 1 and line 2 is 0.678 m/day and 0.681 m/day, respectively. meanwhile, the transmissivity is 6.78 m2/day and m2/day for layer 1 and layer 2, respectively (table 6).this shows that the fluid flow in this aquifer is very low. aquifer properties based on hydraulic parameters are shown in (table 7). table 6. hydraulic parameter of the aquifer in lam apeng. line h (m) ρ (ωm) s (ω1) r (ωm2) k (m/day) t (m2/day) 1 10 15.3 0.65 153 0.678 6.78 2 7 11.3 0.62 79 0.681 4.77 table 7.aquifer properties based on hydraulic parameters. line soil corrosivity designation protective capacity groundwater supply potential 1 moderately corrosive low moderate smaller withdrawal for local water supply (private consumption) 2 moderately corrosive low moderate smaller withdrawal for local water supply (private consumption) 5. conclusions the electrical resistivity method can map the presence of water layers (aquifers) well. based on the results of the study, it can be interpreted that at line 1 and 2 has 3 layers. at line 1, the aquifer has a resistivity value of 12 ωm 18.6 ωm with a depth of 8 m -18 m, with a sand carrier layer. at line 2, the aquifer has a resistivity value of 4.6 ωm 18 ωm with a depth of 5 m 12 m, with a sand carrier layer. from the inversion model, it shows that the distribution of aquifer is evenly distributed in the middle layer which has a depth of up to 20 m. the aquifer type is a semi unconfined aquifer. based on the calculated hydraulic parameters, the longitudinal conductance values in this area are 0.65 ω-1 and 0.62 ω-1, respectively for line 1 and line 2, which indicates that the ability of a layer to survive if the aquifer layer collapse is in the moderate category. the soil corrosivity level of the aquifer layer in this area is moderate with an average resistivity value of 15.3 ωm and 11.3 ωm. the transmissivity value in this area is 6.78 m2/day for line 1 and 4.77 m2/day for line 2 which indicates that the ability of the aquifer layer to drain fluid is low. it can be concluded that the groundwater potential in this area is small or local where it is only sufficient for personal consumption. acknowledgment the authors would like to thank the students and 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https://doi.org/10.1016/j.nrjag.2017.04.001 telford, w.m., geldart, l.p., sheriff, r.e., 1990. applied geophysics, 2nd ed. cambridge university press. https://doi.org/10.1017/cbo9781139167932 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 01 2017 lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 76 review : acoustic systems (split beam echo sounder ) to determine abundance of fish in marine fisheries muhammad zainuddin lubis 1, *, henry m manik 2 1 department of informatics engineering, geomatics engineering batam polytechnic, batam kepulauan riau, 29461indonesia 2 department of marine science and technology faculty of fisheries and marine sciences bogor agricultural university kampus i pb dramaga bogor, indonesia * corresponding author : zainuddinlubis@polibatam.ac.id tel+62-778-469856 ext : 2510; fax: +62-778-463620 received: jan 23, 2017. revised : 15 feb 2017, accepted: feb 20, 2017, published: 1 march 2017 abstract acoustic waves are transmitted into the subsurface ocean will experience scattering (scattering) caused by marine organisms, material distributed in the ocean, the structure is not homogeneous in seawater, as well as reflections from the surface and the seabed. estimation of fish stocks in the waters wide as in indonesia have a lot of them are using the acoustic method. the acoustic method has high speed in predicting the size of fish stocks so as to allow acquiring data in real time, accurate and high speed so as to contribute fairly high for the provision of data and information of fishery resources. split beam echo sounder comprises two aspects, and a transducer. the first aspect is the high-resolution color display for displaying echogram at some observations and also serves as a controller in the operation of the echo sounder. the second aspect is transceiver consisting of transmitter and receiver. the echosounder divided beam first inserted into the es 3800 by simrad beginning of the 1980s and in 1985 was introduced to fishermen in japan as a tool for catching up. split beam transducer is divided into four quadrants. factors that contribute affect the value of target strength (ts) fish strength target can generally be influenced by three factors: a target factor itself, environmental factors, and factors acoustic instrument. factors include the size of the target, the anatomy of fish, swim bladder, the behavior of orientation. keywords: acoustic systems, estimation of fish stocks, split beam echo sounder, simrad, target strength 1. introduction acoustic waves are transmitted into the subsurface ocean will experience scattering (scattering) caused by marine organisms, the material distributed in the ocean, the structure is not homogeneous in seawater, as well as reflections from the surface and the seabed. part of the initial acoustic energy on an object and is reflected back to the source called backscattering (maisonhaute et al., 2002). according to (benoit-bird and whitlow, 2001), a good fisheries resource management must control the number of catches in conjunction with the number of stocks that can be exploited. it required an estimate of the number of fish stocks at the time and acoustic survey techniques can be used to estimate the abundance of fish at a time and under certain conditions. the use of echo sounder and echo integrator for the purposes of exploration of fishery resources today are growing rapidly. hardware echo integrator aims to get the echo signal integration. the accuracy of this method is very high so it can be applied to estimate the abundance of fish in the waters (benoit-bird and whitlow, 2001),. according to (lubis and pujiyati, 2016), the hydroacoustic method with detection backscatter value of mangrove crab (scylla sp.) using cruzpro fishfinder pcff-80 hydroacoustic instrument. according to (pujiyati, 2008) hydroacoustic method is an underwater detection method that use acoustic devices, among others: echosounder, fish finder, sonar, and acoustic doppler current profiler (adcp). fig 1. working mode of hydroacoustic tool according to (maclennan and simmonds, 1992) a good fisheries resource management must control the number of catches in conjunction with the number of stocks that can be exploited. it required mailto:zainuddinlubis@polibatam.ac.id lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 77 an estimate of the number of fish stocks at the time and acoustic survey techniques can be used to estimate the abundance of fish at a time and under certain conditions. the use of echo sounder and echo integrator for the purposes of exploration of fishery resources today are growing rapidly. hardware echo integrator aims to get the echo signal integration. the accuracy of this method is very high so it can be applied as an estimate abundance of fish in the waters (benoit-bird and whitlow, 2001). estimation of fish stocks in the waters wide as in indonesia have a lot of them are using the acoustic method. the acoustic method has high speed in predicting the size of fish stocks so as to allow acquiring data in real time, accurate and high speed so as to contribute fairly high for the provision of data and information of fishery resources (maclennan and simmonds, 1992) in fig 3 and 4. the second aspect is transceivers consisting of transmitter and receiver. the echosounder divided beam first inserted into the es 3800 by simrad beginning of the 1980s and in 1985 was introduced to fishermen in japan as a tool for catching up. split beam transducer is divided into four quadrants (foote, 1987) in which the transmitting wave conducted by the merger of four full beam. the signal reflected by the target is received by each quadrant and reassembled to form a full beam. the direction on the ship split beam is divided into four (4) ie fore, aft, port, and starboard. while in principle split beam is divided into four quadrants that fp.fs.ap and as in fig 2. fig 2. split beam transducer, source in (maclennan and simmonds , 1992). fig 3 split beam shape and a full beam transducer, source in (maclennan and simmonds, 1992) fig 4. geometry targets in split beam transducer. towards the target defined by the θ1 and θ2 angle, source in (maclennan and simmonds, 1992). in fig 3, split beam echo sounder has the function of time varied gain (tvg) in acoustic data acquisition system serves as a reliever tvg attenuation (amplifier) whether caused by geometrical spreading and absorbs noise as it propagates into the water. there are two types of functions, namely tvg function that works to echo a single fish called tvg 40 log r and a function for a group of fish that tvg 20 log r. fig 5. block diagram of the receiver split beam echo sounder, source in (arnaya, 1991). 78 lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 fig 6. the working principle of split beam on detecting fish echo sounder, source in (arnaya,1991). in (figure 6) by simrad, fish axis a located right above the maximum transducer gain, while fish b is located at the end (edge) transducer beam where the gain is lower. a fish echo thus more likely to result stronger than the backscattered echo in fish b. although both of these fish are at the same depth and the same size. to determine the size of the fish from the echo strength alone is not enough, however, knowledge about the pattern beam transducer and the fish in the beam position is very important to correct transducer gain strength and determining the target value of real fish. an estimate obtained approximate angle of incidence and factors beam pattern in the acoustic signals can be obtained by using a processor of the split beam which has a signal source x leads to phase detection and will produce energy or power by means of calculating the results of input and will generate output waveform display in fig 8. fig 7. split beam processor to obtain estimates of the incidence angle and the beam pattern factor, source in (ehrenberg, 1979) fig 8. diagram of a dual beam transducer / split beam, showing the location of the various segments described in the text and the shape of each beam used in the split reception beam or dual beam, source in (foote, k.g & traynor, 1988) table 1. beam descriptiont, tvg, used, and signal in split beam echo sounder beam descriptions tvg used signal a+c 40 logr+2 αr split-beam phase measurements 10 khz b+d 40 logr+2 αr split-beam phase measurements 10 khz a+b 40 logr+2 αr split-beam phase measurements 10 khz c+d 40 logr+2 αr split-beam phase measurements 10 khz e 40 logr+2 αr amplitude dual beam, split beam detected a + b + c + d +e 40 logr+2 αr integration echo detected lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 79 2. target strength target strength (ts) is the ability of the target to reflect a sound about it. based domain is used, the target strength is defined into two, namely in the form of target strength intensity (tsi) and energy target strength (tse). target strength (ts) can be defined as the quotient between the value of the intensity of the noise coming about the target and multiplied by the number of ten (10) in (maclennan et al., 2002) is : tsi =10 log 𝐼𝑟 𝐼𝑖 (1) tse =10 log 𝐸𝑟 𝐸𝑖 (2) information : tsi : intensity target of strength ii : intensity of sound on targets ir : reflected sound intensity targets tse : energy target strength ei : energy sound on targets er : energy reflection sound at a distance of 1 meter from the target according to (maclennan et al., 2002) stated that the target strength (ts) is a measure decibel sound that is returned by the target as measured by a standard distance of 1 meter from the acoustic center of the target is located, relative to the intensity of sound that hit the target. a simple model to estimate the backscattering cross section based on the size of fish referred by (maclennan and simmonds,1992): 𝜎𝑏𝑠 = 𝑏0𝐿 2 (3) ts = 20 log l+ 𝑏0 (4) then according in (love, 1997) introduced the equation which connects the backscattering cross section (𝜎𝑏𝑠 ), fish length (l) and wavelength (λ) by the following equation: 𝜎𝑏𝑠 / λ 2 = a(l/ λ) 𝑏 (db) where a and b are constants that depend on the anatomy, fish size, and wavelength. equation (4) can be converted into a logarithmic form becomes: ts = a log(l) + b log (f) + 𝑏0 (5) information : ts = target strength (ts) f = sound frequency a, b = constant then obtained the possibility of the average best performing measurements on the measurement of the target strength of the dorsal aspect: 𝑇𝑆𝐷 = 19,1 log (l) 0,9 (f) 62 (6) but according to (natsir et al., 2005) explains more about the similarities that show no difference in the comparison of results of different frequencies. furthermore, the equation (foote and traynor , 1988) to formulate relationships ts (target strength) to the length of the fish, namely: ts= 20 log (l) 68 (db) (7) conversions strength target value into a length (l) for pelagic fish used equation ts = 20 log l-73.97 (natsir et al., 2005). relations targets strength and obs (backscattering cross-section, m 2 ) is calculated based in [6] with equation: ts=10 log óbs (8) equation for densitas ikan (ña, ind./𝑛𝑚𝑖2) is : ña=sa /óbs (9) fish length (l) associated with óbsis: óbs=a𝐿𝑏 (10) associated of target strength and l is: ts=20 log l+a (11) where : a = the value of the target strength to 1 cm long fish (normalized target of strength) conversions strength target value into a length (l) for pelagic fish used equation: ts = 20 log l-73.97 (natsir et al., 2005) . according in (effendie, 2001) the relationship length (l) and weight (w) of a species of fish that is: w=al 𝑏 (12) in addition (natsir et al., 2005) has a long and weighs equation to convert length into weight alleged allegations are as follows: wt=a{∑ .𝑖11 ni(li+äl/2). b+1 (li-äl/2) .b+1}/{(b+1)äl}} (13) information : wt : total weight (g) al : class interval length (cm) li : the midpoint of the long-th grade (cm) ni : number of individuals in the i-th grade a, b : constants for certain species factors that contribute affect the value of target strength (ts) fish strength target can generally be influenced by three factors: a target factor itself, environmental factors, and factors acoustic instrument. factors include the size of the target, the anatomy of fish, swim bladder, the behavior of orientation (priatna. a & wijopriono, 2011). factors such targets are: 1. size of fish: there is a relationship between the size of the fish with a value of ts, but the relationship varies greatly depending on the species. generally, for fish species, the larger the fish the greater its value ts. this is especially true for the region of the graph geometrical relationship between the size of the target and ts, for the region, resonance, resonance region and the transition region, the 80 lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 tendency of the relationship is not valid (maclennan et al., 2002). anatomy such as the head, body, tail and fins have different sound reflections. likewise, stomach, intestine, liver, bones, flesh and gills have a specific gravity = (ρ) and the speed of sound = (c) different so acoustically will have the ability to reflect a different sound. 2. swim bladder of fish: acoustically fish and marine organisms are divided into two major groups, namely bladder fish (have a swim bladder). fish that have a swim bladder generally do not have the right maximum ts on the dorsal aspect, while fish that do not have a swim bladder with a maximum value of ts is generally right on the dorsal aspect. ts value of fish that have a swim bladder (furusawa, 1998 in manik et al., 2006). with deformed-cylinder model (dcm) with approximation of> 5 and the value of tilt angle was not until (<40 °) according to (yasuma et al., 2003). results from the resultant corner of a fish that has swim bladder that is: fig 9. swim bladder geometry for soft spheroid models, source in to (yasuma et al., 2003). 3. behavior / orientation fish: results of a previous study conducted by (henderson et al., 2008 and fässler et al., 2008) states that the value of target strength (ts) is determined by the orientation of the fish, especially the slope of the body to a line connecting between the head and tail. fish orientation will include tilting, yawing and rolling along. yawing no effect because generally spherical transducer position so that the fish does not cause changes in the angle when viewed from the transducer, for rolling no real effect because the fish have a swim bladder due partly reflected energy is derived from the swim bladder did not come from the dorsal aspect. tilting lead to a change in angle-position transducer is good for fish that have a swim bladder or not (arnaya, 1991). 4. instrumental factor: the small big factor value beam pattern depending on the extent of the transducer will be greater the beam angle of the transducer, and vice versa. large beam angle changes cause ts great value, separately it is better to use a relatively narrow beam. acoustic reflections of fish and plankton that are returned in the form of echo are detected by the receiver has an appeal. estimation of biomass can be seen from how much force the target and how to interpret it. ts plankton is numbers that indicate the size of the echo. the larger the value, the greater echo energy is returned to the receiver by the target. unit of measure standard international (si) for the ts expressed in decibels (db). a decibel is a logarithmic form of a comparison or ratio of the two intensities due to the values involved can be very large or very small. according to (lurton, 2002) ts formulated as backscattering cross-section of the target which returns a signal and is expressed in the equation: ts = 10 log ( σ (14) then the value of ts theoretical spherical object is: ts = 10 log 𝑎2 4 (15) where σ = target strength individual or backscattering cross-section (σ bs ) with ts according to (decino and willette, 2014 in lurton, 2002) with equation : ts = 10 log σ bs (16) 3. volume backscattering strength (sv) volume backscattering strength (sv) is defined as the ratio between the intensity reflected by a group of single targets (target located at a water volume of certain invocation of instantaneously measured at a distance of 1 m from a target with the intensity of sound that hit the target. definition volume backscattering strength (sv) has the same meaning as the target strength for a single target, while volume backscattering strength (sv) for a group of fish. each individual targets is the source of the reflected sound wave, so that the output of the integration will be proportional to the quantity of fish in the group. echo integration methods used to measure volume backscattering strength (sv) based on the measurement of the total power backscattered on the transducer (arnaya 1991). volume backscattering strength (sv) is the ratio between the intensity reflected by a single group target where the target is located at a water volume (xie and jones, 2009). this is similar to the definition of ts where ts value is the result of the detection of a single organism, while sv is the value for detection organism groups in (kaartvedt and aksnes, 2012) states sv is defined as the equation: sv = 10 log (i s i / i) (17) information : is : intensity scattering volume measured 1 m from the center of the acoustic waves. ii : scattering intensity emitted 4. fish density (abundance fish) to date research on fish stock estimates done by cruise track using a simrad ek 60 scientific split beam echo sounder system with a frequency of 70 khz and acoustic data acquisition is performed continuously during the day and night during the lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 81 period boat cruise at speeds ranging between 78 knots. trails include a data acquisition area of an area that allows the analysis of spatially made with the zig-zag shape according to (maclennan and simmonds, 1992 in (diez et al., 2016, jurvelius et al., 2016) with the length of each transect approximately 12 nmi of bounds islands outwards. density values for fish processing performed on ms. excel. the treatment may be carried out after the integration process sv and ts. density is generated by using the formula (lubis and anurogo, 2016). sv (db) = 10 log (n τbs) = 10 log n + ts (18) assuming the numerical density is proportional to the density of individuals, then the equation (1) can be rewritten as follows: sv (db) = 10 log ρ + a (19) where: sv : volume strength (db) ρ : abundance / density of organisms (ind / m3) a : target average strength (db) references arnaya, i.n. 1991. akustik kelautan ii. proyek peningkatan perguruan tinggi. institut pertanian bogor. bogor. benoit-bird, k. j., & au, w. w. 2001. target strength measurements of hawaiian mesopelagic boundary community animals. the journal of the acoustical society of america, 110(2), 812-819. decino, r. d., & willette, t. m. 2014. susitna drainage lakes pelagic fish estimates, using split-beam hydroacoustic and midwater trawl sampling techniques, 2005 2009. alaska department of fish and game, fishery data series, (14-47). diez, m. j., cabreira, a. g., madirolas, a., & lovrich, g. a. 2016. hydroacoustical evidence of the expansion of pelagic swarms of munida gregaria (decapoda, munididae) in the beagle channel and the argentine patagonian shelf, and its relationship with habitat features. journal of sea research, 114, 1-12. effendie, m. i. 2002. biologi perikanan. yayasan pustaka nusatama. 163 pp. ehrenberg e. john, 1979. a comparative analysis of in situ methods for directly measuring the acoustic target strength of individual fish ieee journal of oceanic engineering, vol. oe-4, no. 4. http://dx.doi.org/10.1109/joe.1979.1145 434. fässler, s. m., gorska, n., ona, e., & fernandes, p. g. 2008. differences in swimbladder volume between baltic and norwegian springspawning herring: consequences for mean target strength. fisheries research, 92(2), 314-321. foote, k.g & traynor, j.j. 1988. comparison of walleye pollock target strength estimates determined from in situ measurements and calculations based on swimbladder form. j.acoust.soc.am. 83(1). http://dx.doi.org/10.1121/1.396190. foote, k.g. 1987 . introduction to the use of sonar system for estimating fish biomass. fao. fisheries technical paper no 199 revision 1. furusawa, m. 1998. prolate spherodial model for predicting general trends of fish target strength. j.acoust.soc.am page 13-24. hannachi, m. s., l. b. abdallah, & o. marrakchi. 2004. acoustic identification of small pelagic fish species: target strength analysis and school descriptor classification. medsudmed technical documents no.5. henderson, m. j., horne, j. k., & towler, r. h. 2008. the influence of beam position and swimming direction on fish target strength. ices journal of marine science: journal du conseil, 65(2), 226-237. jørgensen, r. 2003. the effects of swimbladder size, condition and gonads on the acoustic target strength of mature capelin. ices journal of marine science: journal du conseil, 60(5), 1056-1062. jurvelius, j., marjomäki, t. j., peltonen, h., degtev, a., bergstrand, e., enderlein, o., & auvinen, h. 2016. fish density and target strength distribution of single fish echoes in varying light conditions with single and split beam echosounding and trawling. hydrobiologia, 1-12. kaartvedt, s., staby, a., & aksnes, d. l. 2012. efficient trawl avoidance by mesopelagic fishes causes large underestimation of their biomass. marine ecology progress series, 456(1), 1-6. love, r.h. 1997. target strength of an individual fish at any aspect . j.acoust. soc. am, (62) : 13971403. http://dx.doi.org/10.1121/1.38167 2. lubis, m. z., & pujiyati, s. 2016. detection backscatter value of mangrove crab (scylla sp.) using cruzpro fishfinder pcff80 hydroacoustic instrument. j biosens bioelectron, 7(205), 2. lubis, m. z., & anurogo, w. 2016. fish stock estimation in sikka regency waters, indonesia using single beam echosounder (cruzpro fish finder pcff-80) with hydroacoustic survey method. aceh journal of animal science, 1(2). lurton, x. 2002. an introduction to underwater acoustic. principles and applications. praxis publishing ltd. chincester. uk. maclennan, d. n dan e. j simmonds. 1992. fisheries acoustic. chapman and hall. london. http://dx.doi.org/10.1109/joe.1979.1145434 http://dx.doi.org/10.1109/joe.1979.1145434 http://dx.doi.org/10.1121/1.396190 http://dx.doi.org/10.1121/1.381672 http://dx.doi.org/10.1121/1.381672 82 lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 maclennan, d. n., fernandes, p. g., & dalen, j. 2002. a consistent approach to definitions and symbols in fisheries acoustics. ices journal of marine science: journal du conseil, 59(2), 365-369. maclennan, d. n dan simmonds, e. j. 2005. fisheries acoustic. chapman and hall. oxford : blackwell science. decino, r. d., & willette, t. m. 2014. susitna drainage lakes pelagic fish estimates, using splitbeam hydroacoustic and midwater trawl sampling techniques, 2005 2009. alaska department of fish and game, fishery data series, (14-47). maisonhaute, e., prado, c., white, p. c., & compton, r. g. 2002. surface acoustic cavitation understood via nanosecond electrochemistry. part iii: shear stress in ultrasonic cleaning. ultrasonics sonochemistry, 9(6), 297-303. manik, h. m., furusawa, m., & amakasu, k. 2006. measurement of sea bottom surface backscattering strength by quantitative echo sounder. fisheries science, 72(3), 503-512. natsir, m., b. sadhotomo, & wudianto. 2005. pendugaan biomassa ikan pelagis di perairan teluk tomini dengan metode akustik bim terbagi. jurnal penelitian perikanan indonesia. 11 (6): 101-107. priatna. a & wijopriono. 2011. estimasi stok sumber daya ikan dengan metode hidroakustik di perairan abupaten bengkalis. j. lit. perikan. ind. vol.17 no. 1 pujiyati, s., hestirianoto, t., wulandari, p. d., & lubis, m. z. 2016. fish stock estimation by using the hydroacoustic survey method in sikka regency waters, indonesia. j fisheries livest prod, 4(193), 2. pujiyati, s. 2008. pendekatan metode hidroakustik untuk analisis keterkaitan antara tipe subsrat dasar perairan dengan komunitas ikan demersal. disertasi. sekolah pasca sarjana. institut pertanian bogor. bogor. widodo, j. 1992. prinsip dasar hidroakustik perikanan. oseana. xvii (3): 83-95. xie. j dan jones. i. s. f. 2009. a sounding scattering layer in a freshwater reservoir. marine study center university of sydney. australia. http://dx.doi.org/ 10.4319/lo.1994.39.2.0443 yasuma, h., sawada, k., ohshima, t., miyashita, k., and aoki, i. 2003. target strength of mesopelagic lanternfishes (family myctophidae) based on swimbladder morphology. ices journal of marine science, 60: 584_591 http://dx.doi.org/10.1016/s10543139(03) 00058-4. lubis, m.z and manik, h.m/ jgeet vol 02 no 01/2017 83 1. introduction 2. target strength 3. volume backscattering strength (sv) 4. fish density (abundance fish) references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 204 mairizki, et al./ jgeet vol 5 no 4/2020 research article assessment of groundwater quality for drinking purpose in an industrial area, dumai city, riau, indonesia fitri mairizki1*, risti putri angga2, arief yandra putra3 1,2department of geological engineering, faculty of engineering, univeristas islam riau, pekanbaru, indonesia. 3department of chemistry education, faculty of teacher training and education, universitas islam riau, pekanbaru, indonesia. * corresponding author : fitrimairizki@eng.uir.ac.id tel.: +62-853-7897-3771; received: dec 6, 2020; accepted: dec 22, 2020. doi 10.25299/jgeet.2020.5.4.5983 abstract groundwater is the main water resource especially for daily water needs. population growth and urbanization have increased demand for water while the availability of groundwater has decreased both in quality and quantity. various human activities also produce industrial, agriculture and municipal waste that can pollute groundwater through leaching process. the purposes of this study are to determine the quality of groundwater around tofu industrial factory and its evaluation for drinking water based on health minister regulation no.492/menkes/per/iv/2010 and government regulation no.82 2001.the temperature, ph, total dissolved solids (tds) and electrical conductivity (ec) were measured by using ysi-pro. chemical oxygen demand (cod) and biochemical oxygen demand (bod) were measured based on sni 06-6989.2.2009 test method and sni 06-698.72.2009 test method, respectively. physically, groundwater had temperature average 28,60c, tds 243 mg/l and ec 396 µs/cm. almost all groundwater were acidic with ph average 5,6 and did not meet the drinking water quality requirements. groundwater had cod average 78 mg/l, bod average 36 mg/l and it were classified into moderate-heavy pollution. it indicated that groundwater may have been contaminated by organic material from tofu industrial wastewater. therefore, groundwater should not be used as a source of drinking water. keywords: groundwater, industrial area, drinking water, cod, bod. 1. introduction clean water is a basic human need that has a direct impact on the physical, social and economic well-being of community. in indonesia, generally clean water comes from water surface, groundwater, and rain water. the availability of fresh water is very limited while sea water cannot be used directly because it contains salt in high concentration (nurhalisaetal., 2017). groundwater is the main water resource especially for daily water needs. groundwater has many advantages compared to other water resources. groundwater is not affected by the season and relatively easy to obtain. although water is a renewable natural resource, it is limited depending on space and time. population growth and urbanization have increased demand for water while the availability of groundwater has decreased both in quality and quantity. various human activities also produce industrial, agriculture and municipal waste that can pollute groundwater through leaching process. pollutants can be in the form of heavy metals, organic substances and suspended solids which are under certain concentration endanger the environment and human health directly or indirectly. groundwater pollution due to industrial activities has become a concern of various countries in the world (sharma et al., 2016); (rout and baldev, 2018); (samira et al., 2019); (durgasrilaksmih., 2019). groundwater is suitable for consumption if it meets the requirements set out by international and national regulations. these requirements consist of mandatory and additional parameters including physical, chemical and biological components. physically, drinking water must be clear, tasteless and odorless. drinking water must also be free from impurities in chemicals and organic materials. (risky d.,p., et al., 2017). the study about groundwater quality as drinking water have been carried out by many researchers (annapoorna and janardhana, 2015); (lalitha, b.v., teja, v.s., rajesh, v., 2016);(khan a., and khan m.a., 2018); (naslilmuna, m., muryani, c., santoso, s., 2018); (ibrahim, 2019); (putra, a.,y., and mairizki, f., 2020). the study area is area around tofu industrial factory whose liquid waste is directly disposed of into environment without prior treatment. tofu industrial liquid waste contains a lot of organic compounds that can cause contamination of groundwater used by the surrounding community. it is important to monitor the groundwater quality regularly and continuously to ensure that groundwater free from contaminants and suitable for consumption. therefore, the research aims are to determine the quality of groundwater around tofu industrial factory and its evaluation for drinking water based on health minister regulation n0.492/menkes/per/iv/2010 and government regulation no.82 2001. 2. study area bukit batrem area is located in east dumai district, dumai city, riau. based on regional geological map, dumai is located in the central sumatra basin which composed by two formations, young superficial deposits (qh) and older superficial deposits (qp). stratigraphy of the study area consist of old superficial deposits (qp) with plistocene-aged rocks. rocks in the research area are clay, silt, clay gravels and vegetation rafts (fig.1). groundwater samples were obtained from 25 dug wells around the tofu industrial factory (fig.2). physically, groundwater are cloudy-browns and smells. liquid waste from tofu factory is immediately disposed of without treatment. therefore, it is feared that the liquid waste can contaminate the http://journal.uir.ac.id/index.php/jgeet mailto:fitrimairizki@eng.uir.ac.id mairizki, et al./ jgeet vol 5 no 4/2020 205 environment including groundwater that used by community around the area. fig. 1. regional geological map of research area fig 2. groundwater flow direction map of research area 3. methodology the groundwater samples were taken from 25 dug wells around tofu industrial factory in bukit batrem area, east dumai district, dumai city, riau. physical parameters were examined in the geological engineering laboratory universitas islam riau, while chemical parameters were examined in the industrial research and standardization laboratory padang. the temperature, ph, total dissolved solids (tds) and electrical conductivity (ec) were measured by using ysi-pro. chemical oxygen demand (cod) and biochemical oxygen demand (bod) were measured based on sni 06-6989.2.2009 test method and sni 06-698.72.2009 test method, respectively. the results then compared with the health minister regulation n0.492/menkes/per/iv/2010 about drinking water quality requirements and government regulation no.82 2001 about water quality management and water pollution control. 4. results and discussion 4.1 geological condition of study area in the research area, there were 25 dug well stations and 3 tofu factories that located in the middle of the research area. the geological condition of study area was dominated by peat soil. peat is a type of soil that formed through the accumulation of semi decomposed plants. this causes the color of groundwater to be yellow-brown and had an acidic ph. poor drainage and 206 mairizki, et al./ jgeet vol 5 no 4/2020 the distance between wells and drainage that does not meet the requirements also causes groundwater in study area to smell. 4.2 temperature the groundwater temperature in the research area ranges from 26-30oc with average 28.6oc and still meets the standard. drinking water temperature standard based on health minister regulation was the air temperature ± 3oc. water temperature greatly influences the chemical, physical and biological processes that occur in the water. high water temperature indicates the decomposition of organic compounds or the dissolution of chemical compounds such as phenols and sulfur (mairizki, f., and cahyaningsih, c., 2016) water temperature can be affected by several factors such as season, latitude, altitude, cloud cover, water flow and depth. 4.3. ph almost all groundwater ph values (96%) were less than 6,5 with average 5,6. groundwater ph standard according to health minister regulation was 6,5-8,5. groundwater in research area were acidic. this can be due to the geological conditions in that area and dissolving result of weathering rocks in tropical area rarely produce water ph above 7. changes in the ph of water can cause changes in smell, taste, and color. drinking water should be neutral, not acidic/alkaline, to prevent dissolution of heavy metals and corrosion of drinking water distribution network. groundwater with a low ph can dissolve iron metal, causing the groundwater to turn yellowish (putra, a.y., and mairizki, f.,2019) 4.4. total dissolved solid (tds) tds value of groundwater ranges from 30-350 mg/l with average 243 mg/l. all groundwater had tds value below 500 mg/l and meet the standard according to health minister regulation. all of groundwater also included in freshwater (tds 0-1000 mg/l) (putra, d.b.e et al., 2019). dissolved solids can be derived from organic or inorganic compounds that are dissolved in water such as sulfate, chloride and magnesium salts. dissolved solids can also from tofu industrial wastewater around research area. the presence of tds can change the taste of water (firdaus et al., 2017). fig 3. groundwater tds distribution map from fig.3, it can be seen that the higher tds values were scattered towards on the north of study area. this was because swampy areas or peat lands contain many chemical elements that can increase dissolved solids in groundwater. lower tds values were scattered towards on the south of study area. sandy areas can be useful as groundwater filtering materials that can reduce dissolved solids. 4.5. electrical conductivity (ec) ec value of groundwater ranges from 39-1188 µs/cm with average 396 µs/cm. ec value was a function of temperature, type and concentration of dissolved ions. ec value reflects the concentration of dissolved ions in water. the high concentration of dissolved ions in water causes its ec value to be higher. from fig.4, it can be seen that higher ec values were scattered towards on the north, while lower ec values were scattered towards on the south of study area. this was because tds values of groundwater in the north of study area were greater than tds values of groundwater in the south of study area. this showed that the ec value was directly related to the tds value. fig 4. groundwater ec distribution map 4.6 chemical oxygen demand (cod) cod is the amount of oxygen that needed to oxidize the substances in the water. a high cod value will reduce the dissolved oxygen content in water. based on government regulation, cod concentration < 5 mg/l (very light pollution), cod 6-9 mg/l (light pollution), cod 10-15 mg/l (moderate pollution), cod > 10-15 mg/l (heavy pollution) (putra,a.y., and yulis, p.a.r., 2019.). cod value in study area range 35162,13 mg/l with average 78 mg/l (fig.5). it can be concluded that groundwater was classified into heavy pollution category. the high cod value of groundwater was due to the location close the tofu factory, where the liquid waste was immediately disposed without treatment, causing contamination. it also indicated that groundwater has been contaminated by organic material which can come from tofu industrial wastewater. excessive cod content also will reduce groundwater ph (endang, s., ria, a.,t., n., anindya, p., f., 2017). it can be seen from groundwater ph value that almost entirely less than 6,5. mairizki, et al./ jgeet vol 5 no 4/2020 207 fig 5. cod value of groundwater 4.7. biochemical oxygen demand (bod) bod is the amount of oxygen that required by microbiologist to oxidize substances in water. based on government regulation, bod concentration < 1 mg/l (very light pollution), bod 1-3 mg/l (light pollution), bod 3-6 mg/l (moderate pollution), bod > 6 mg/l (heavy pollution) (putra,a.y., and yulis, p.a.r., 2019). bod value in study area range 3,5-117 mg/l with average 36 mg/l (fig.6). it can be concluded that groundwater sample classified into moderateheavy pollution. the very high bod value in some groundwater samples indicated the possibility of contamination due to the location close the tofu factory. the groundwater has been contaminated by tofu industrial liquid waste which contains various kinds of organic materials. in addition, the high bod content showed the high level of microorganism in decomposing organic matter contained in groundwater. excessive bod content will also reduce ph value as same as cod (endang, s., ria, a.,t., n., anindya, p., f., 2017). fig 6. bod value of groundwater 5. conclusion groundwater samples were obtained from dug wells located around tofu industrial factory. physically, groundwater had temperature average 28,60c, tds 243 mg/l and ec 396 µs/cm. almost all groundwater were acidic with ph average 5,6 and did not meet the drinking water quality requirements according to health minister regulation no. 492/menkes/per/iv/2010. groundwater had cod average 78 mg/l and bod average 36 mg/l. based on government regulation no.82 2001, groundwater in study area were classified into moderate-heavy pollution. it indicated that groundwater may have been contaminated by organic material from tofu industrial wastewater. therefore, groundwater should not be used as a source of drinking water. acknowledgements the authors would like to give an acknowledgment to the geological engineering laboratory universitas islam riau and the industrial research and standardization laboratory padang for their cooperation in conducting this research. additional thanks to all students who help authors to collect data. references annapoorna, h., janardhana, m.r. 2015. 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http://creativecommons.org/licenses/by-sa/4.0/ uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 5. no 2. june 2020 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, 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(indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 05 no 02 2020. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content impacts of population density for landuse assessment in cengkareng, west jakarta ................................................................................................................................................... 45 rock physics formula and rms stacking velocity calculation to assist acoustic impedance inversion that constrain well data ........................................................ 56 analysis of ultramafic rocks weathering level in konawe regency, southeast sulawesi, indonesia using the magnetic susceptibility ........................................................... 59 simultaneous equation model for economic calculation of households of independent rubber farmers in mineral land in kampar regency, riau province ................................................................................................................................................ 67 subsurface shallow modelling based on resistivity data in the hot springs area of libungo geothermal, gorontalo ..................................................................................... 75 shale gas potential in jambi sub-basin, indonesia: insights from geochemical and geomechanical studies .......................................................................................................... 81 settlement and capacity analysis of land support development on flyover in large city; pekanbaru, indonesia ................................................................................................... 89 effect of porphyritic andesite intrusion on the formation of contact metamorphism aureole in selo gajah hill clastic limestone, bojonegoro regency, east java ............................................................................................................................. 96 geophysical survey on open dumping landfill for monitoring spread of leachate : a case study in pekanbaru, riau, indonesia ........................................................... 104 page 1 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 heriyanto et al./ jgeet vol 5 no 2/2020 67 research article simultaneous equation model for economic calculation of households of independent rubber farmers in mineral land in kampar regency, riau province, indonesia heriyanto 1,*, asrol2 1,2departemen of agribussines, universitas islam riau, pekanbaru, 28284. indonesia . * corresponding author : heriyanto@agr.uir.ac.id telp ; 082388011877 received: sept 14, 2019; accepted: may 5, 2020. doi 10.25299/jgeet.2020.5.2.3791 abstract rubber is a plantation crop which is mostly a source of community income in kampar district. as a source of household income, rubber farming is managed by households independently. this study generally aims to design models and government policy strategies in the development of smallholder rubber plantations on land typology mineral land conditions on the economic decision making of rubber farmer households. specifically, this study was conducted with the aim of analyzing the characteristics of independent smallholders and internal and external dominant factors that influence the allocation of working time, income and household expenses of rubber farmers. this research was conducted using a survey method located in kampar district. the data used in this study consisted of primary data obtained using the interview method. samples were taken by simple random sampling method with 60 rubber farmers. descriptive analysis and economic decision model of rubber farmer households using the simultaneous equation model approach with the two stages least square (2sls) analysis method were performed to answer the research objectives. the results showed that only internal factors of farm households are responsive to household economic decisions. there are no external factors included in the model that are responsive to the economic decisions of rubber farming households in kuantan singingi regency regarding the aspects of production, working time allocation, income and expenditure of rubber farming households. from the aspec t of production, no responsive internal or external factors were found, but the biggest effect was the number of productive rubber stems. from the aspect of work time allocation, internal factors that are responsive to influence are the total outpouring of farmer work, outpouring of farm family work in businesses and the workforce of farmer households. furthermore, from the aspect of farmer's household income the responsive internal factors that influence it are the farmer's household income in the business. then what influences household expenditure is outflow of work in business, farmer education, wife education and total rubber farmer income. the policy implications of increasing rubber prices and outpouring of family work in the business have the most positive impact. while the increase in wages for workers outside the family has a negative impact on the household economy. keywords: household economy, dominant factors, rubber. 1. introduction the agricultural sector in indonesia continues to be demanded to play a role in the national economy through the formation of gross domestic product (gdp), foreign exchange earnings, supply of food and industrial raw materials, poverty alleviation, employment provision and increasing community income. at the provincial level, riau does not differ greatly from the national level. in 2016, the area of rubber was ranked second after oil palm with an area of 504,553 ha. in the last five years (2012-2016), the total area, production and number of farmers cultivating rubber plants in riau province tended to decrease. in 2012, the area of rubber plantations was 128,520 ha with a production of 392,781 tons, decreasing to 90,877 ha with a production of 333,155 tons. the number of farmers cultivating rubber plants also declined from 276,210 households to 244,560 households (badan pusat statistik, 2017b). at the level of kampar regency, it is not much different from the provincial level. in 2012 the largest plantation area was occupied by oil palm plants with an area of 190,486 ha. while the rubber plant is in second place with an area of 92,509 ha. in the period 20122016 the area of rubber plantations decreased. in 2012 the area of rubber plantations was 91,328 hectares and in 2016 the area of rubber plants was 91,143 hectares (badan pusat statistik, 2017a). the decreasing area and production of rubber plants, as well as farmers who are working on rubber plants are thought to be due to the conversion of rubber land to oil palm. development in the plantation sector is directed to further accelerate the rate of production growth both from large plantations, private and state plantations and community nucleus estates as well as self-managed plantations to support industrial development, as well as increase the utilization and preservation of natural resources (sda) in the form of land and water . the role of the plantation sector is so great for increasing the use of farmers and supplying raw materials for the domestic industry and as a source of foreign exchange (heriyanto, 2017). various problems that occur will affect production acquisition, allocation of work time, income, and the level of welfare of farmers. the level of welfare of farmers can be seen from the expenditure of household consumption. in other words, households are faced with the problem of allocating work time, income and expenses. the economic decisions of rubber farming households in relation to the allocation of work time, household income and expenditure, are theoretically influenced by internal and external factors. a rubber farming household that uses labor from outside the household expects workers with high productivity, but with low wages. instead a worker tends to expect a job with a high level of wages. about:blank 68 heriyanto et al./ jgeet vol 5 no 2/2020 comparison between the price level of rubber also determines the decision of rubber farmers to keep doing rubber plantation business or not. if the price of rubber products produced is quite high while the price of inputs is relatively cheap, so that production costs are less than the gross income obtained, then the business is profitable. the higher the level of profits obtained, the rubber plantation business will increasingly develop. various external shocks that affect the production process will affect the allocation of work time, will further affect the acquisition of income and ultimately will affect the amount and pattern of household expenditure. based on the background description and problems above, in general this research objective is to analyze the household economy which includes the allocation of working time, income and expenditure of rubber farmer households on mineral land. specifically the purpose of this study is to analyze the characteristics of rubber farmers and internal and external dominant factors that affect the allocation of work time, income and household expenditure. 2. literature review 2.1. agricultural development concepts some economists claim that agricultural development is believed to be able to drive economic growth while at the same time helping to reduce income inequality, poverty and unemployment (poonyth, d, r. hassan & calcaterra, 2001; romeo, m, 2000, 2001; warr, 2006). some agricultural development strategies that are expected to achieve this are agricultural-led growth strategies (poonyth, d, r. hassan & calcaterra, 2001), stategi agriculture-based development by (poonyth, d, r. hassan & calcaterra, 2001; romeo, m, 2000, 2001), and stategi agricultural demand led industrialization (adli) by (adelman, 1984;julia,2016). the concept of agricultural development includes land resources, nuftah plasma, water, technology, financing and human resources (hr). agricultural development aims to increase farmers' income and welfare through increasing agricultural production. this increase in agricultural production in addition to meeting domestic industrial raw materials that continue to grow also aims to increase foreign exchange from exports of agricultural products. one of the steps that can be taken to increase the contribution of the agricultural subsector is the production of plantation crops (soekanda, 2001). strategi agricultural-led growth (poonyth, d, r. hassan & calcaterra, 2001) emphasized that the agricultural sector as a leading sector in economic development because the agricultural sector is a driver for economic growth. therefore the agricultural sector needs to get the main attention compared to other sectors because of its potential in driving economic growth and job creation. development of a productive agricultural sector and better rural areas is the key to the growth of the agricultural sector and is a precondition for successful economic development. strategi agriculture-based development (romeo, m, 2000, 2001), based on the consideration that in many lowincome countries the majority of the population is in rural areas, where the agricultural sector is the main source of life. this strategy is more effective than the import substitution strategy or the export-led industrialization strategy, based on the consideration that it provides opportunities for income generation, directly or indirectly, for rural populations. through this strategy public resources are increased to be allocated to the agricultural and rural sectors and is expected to increase agricultural productivity and income of rural populations. the role of the agricultural sector in economic development includes: (1) increasing the availability of food or food surplus for domestic consumption, (2) releasing excess labor to the industrial sector, (3) being a market for industrial products, (4) increasing domestic savings, ( 5) increasing trade (sources of foreign exchange), and (6) improving the welfare of rural people (jighan, 1994). research on the household economy of farmers has been done by researchers, such as the household economy of rice farmers. households in paddy farming in production are determined by labor in the family, the amount of seeds, fertilizers and pesticides. the difference between households is that households of paddy rice farmers use more labor in the family (elinur, asrol, & heriyanto, 2017; heriyanto,2018). next heriyanto (heriyanto, 2017), has conducted research on the analysis of the efficiency of rubber production factors in kampar regency, riau province. the results of his study showed that the dominant factors affecting rubber production in kampar district were the number of plants, age of plants, number of workers and investment. the production factor is the number of plants, and the number of workers is technically inefficient, allocative, and economically. the use of fertilizers tends to be technically and economically efficient, butallocativelyinefficient. rubber farm house hold economic research analyzes from the aspects of production, farm household work time allocation, the use of non-family labor, non-farm income, and household expenditure that includes food and non-food expenditure. this research will produce a comprehensive economic model of smallholder farmers' households that have not been studied by researchers before. this study also recommends policies relating to the development of smallholder rubber in the context of increasing the household income of rubber farmers. 2.2. household economy understanding farm households is very important because the characteristics are very unique and complex. in this case the household has resources that can provide satisfaction and can be shared among household members. in addition, households in increasing their satisfaction must have alternatives so that households have many choices. household economic activities such as production activities as a farming company, consumption activities as consumers and as labor providers. in carrying out these activities the household carries out the principle of utility maximization with budgetary or resource constraints (nakajima, 1989). farmer house hold as an economic unit that acts as a producer and consumer. households as producers carry out production activities and as consumers carry out consumption activities simultaneously. this will be different from the company's activities. companies as economic units only carry out the activities of producing goods and services to achieve maximum profits. (becker, 1965) formulating an agricultural household model (economic model of agricultural households) that integrates production and consumption activities as a whole and the use of labor in the family is preferred. this household economic model uses a number of assumptions, namely: first, household satisfaction in consuming is not only determined by the goods and services obtained in the market, but also is determined by various commodities produced in the household. second, the element of satisfaction is not only goods and services, but includes time. third, time and goods or services can be used as factors of production in household production activities. and fourth, households act as producers as well as consumers. meanwhile, (barnum & squire, 1978) revealed that the household economic model can be used to analyze the economic behavior of agricultural companies which all use paid labor and sell all products produced to the market. unlike subsistence agriculture which relies on family labor, so there is no market surplus. (singh, i. & strauss, 1986)arrange the agricultural household economic model as a basic model of the household economy. in the model stated that household utilities are heriyanto et al./ jgeet vol 5 no 2/2020 69 determined by consumption of goods and services produced by households, consumption of goods and services purchased in the market, and consumption of leisure (leisure time). households include activities of production, consumption and allocation of labor in the family carried out simultaneously with more complex estimation techniques. estimation of the model uses two stage least squares (3sls) or three stage least squares (3sls) estimation techniques. rice farm household economics studies using 2 sls estimation techniques were carried out by (faradesi, 2004; rochaeni & erna m, 2005) in cianjur regency and bogor city. economic research on farm households is also applied to farm households in plantation crops, such as rubber and oil palm farm households, research conducted by (elinur & asrol, 2015a; husin & dwi wulan, 2011; khaswarina, 2017). rice farm household economics research analyzes the allocation of work time in farming, production and household expenditure. the allocation of work time consists of the equations of outpouring of family labor in lowland rice farming, outpouring of non-farm family labor. the production equation is influenced by the use of rice production factors. equation of rice farmers household expenditure consists of food and nonfood expenditure. however, this research has not accommodated household expenditure in terms of health, education and leisure time (leaisure) (faradesi, 2004; rochaeni & erna m, 2005) the economic research of rubber farmer households consists of a flow of farmer's household working time on rubber farming and non-farming. household income consists of income from rubber, non-rubber and non-farming farming. rubber farmer household expenses consist of food, non-food expenditure, education expenditure, farm investment and farmer household savings. the model does not yet accommodate the demand for workers outside the family and clothing, housing and health and leisure expenses. this research is still in the village scope (husin & dwi wulan, 2011; khaswarina, 2017;heriyanto et al., 2019; ningsih et al., 2020). the economic research of the oil palm farmer household builds a model consisting of the equal allocation of farm household work time, oil palm production, labor demand outside the farmer's family, farmer's household income and farmer household expenditure. the study of the household economics of oil palm farmers includes four aspects: first, the demand for labor is distinguished from labor within the family and outside the family. second, include outflow of family work outside the business and income from outside the oil palm farm. third, include business investment, education investment and household savings, i.e. saving money in financial institutions on the household expenditure side. and fourth, house hold consumption consists of food, non-food consumption and recreation (elinur & asrol, 2015a; heriyanto & asrol, 2019; karya, heriyanto, & asrol, 2019). this economic study of rubber farming households combines the economic models of rice farming households and rubber and oil palm farming households. the economic model of rubber farming households consists of complex equations that accommodate household expenditure that are in accordance with household economic phenomena, among others: first, the rubber production equation is influenced by production factors consisting of the amount of crops, fertilizers, pesticides and internal labor. second, the equality of household time allocation for rubber farmers from the allocation of working time for households in farming and outside farming. third, household income from rubber farmers consists of rubber farming income, non-rubber farming income and non-farming income. fourthly, the household expenditure of paddy farmers consists of food expenditure, clothing expenditure, education expenditure, health and recreation expenses. fifth, the rubber farming household economic model also includes expenditures for farming investment, because in general rubber farmers in the study area set aside their income for the farming. from several farmer household economic studies, this study has similarities and differences with previous farmer household economic research. the similarity is that this research has accommodated all farm household household economic activities which include production, consumption and work time allocation aspects. the advantage of this research is that it includes clothing and health and recreation expenses, which have not been accommodated by previous studies. 2.3. review of previous studies on home economics studies of the household economy have been carried out both partially and simultaneously such as, (chuzaimah, 2006; elinur, 2004; heriyanto, 2017; husin & sari, d, 2011; koestiono, 2004; siti & erna, 2005) analyzing policy simulations of the household economy of agriculture. the results of the policy simulation imply that the policy of increasing output prices is not effective in increasing the amount of production that can be sold to the market. this is due to additional benefits due to rising prices of agricultural output and technological improvements are more allocated as labor costs. (priyanti, b.m, y.syaukat, & s.u, 2007) conducting a farmer household economy model study on crop-livestock integration systems. the results of the study that the farm household household economic model is able to explain reciprocal farm household income obtained from maximizing satisfaction with production constraints, time allocation and income distribution. this includes aspects of production, allocation of use of family labor, use of inputs and production costs, income and income as well as farm household expenses. this model is very useful to identify the factors that influence the decisions of farm households, especially in increasing income simultaneously and integrated between crop and livestock businesses. (husin & sari, d, 2011), conducted a study on the economic behavior of rubber farmer households in prabumulih in workforce allocation, production and consumption with the result that the behavior of farm household household time allocation behavior was influenced by total household expenditure, rubber land area, non-rubber farm land area, rubber farming income and number of children under five. farmer household production behavior is influenced by the area of rubber land, non-rubber farming land area, outpouring of family labor on rubber farming, the use of fertilizers and pesticides. farmer household consumption behavior is influenced by total household income, time spent working by household members on rubber farming and number of household members. several variables that were responded to elasticly by the variable of work time spent were rubber farming income, total household expenditure and non-rubber farming land area. whereas the variable which is responded elasticly by household expenditure is total household income and expenditure for food consumption. research conducted by (elinur & asrol, 2015b) about the economic decisions of oil palm farmer households in the village of indra sakti kecamaan tapung, kampar regency the economic model of the household that he built includes aspects of production, location of work time, use of labor within and outside the family, household expenses consisting of food and non-food expenditure. the research has not included expenditure on clothing, housing, education, health, and recreation. overall expenditure is aggregated in food expenditure. this research is still in the scope of the village. (khaswarina, 2017; wahyudy, 2019), conducting research on the household economics of ex-upp tcsdp rubber farmers in koto damai village, kampar district. the economic model of the constructed household has included the production equation, allocation of work time, income in and out of farming, and food expenditure, education expenditure, non-food and 70 heriyanto et al./ jgeet vol 5 no 2/2020 household savings. the model does not yet accommodate the demand for workers outside the family and clothing, housing and health and leisure expenses. this research is still in the village scope. 3. research methods the location of the study was determined proportionally, namely in the kampar district the kampar district was chosen with consideration that the kampar regency was the second largest rubber plantation area after kuantan singingi regency in riau province. to achieve optimal results, this research is expected to be funded within one year. fig 1. number of rubber farmers samples in kampar district sampling in this study was conducted using a multy-stage purposive sampling method with criteria having an area of 1-3 ha with a rubber plant age of 13-25 years. samples were taken in 3 districts, namely kampar kiri hulu subdistrict, kampar kiri hilir subdistrict and xiii koto kampar subdistrict, because the three districts are rubber production centers in kampar regency. each sub-district took 20 rubber farmers and a total sample of 60 rubberfarmers.a clearer scheme for rubber farming household sampling ispresented in the figure above. the type of data collected is cross section data. primary data were obtained from direct interviews with respondents, namely rubber farming households using a prepared questionnaire. besides that, secondary data from a number of related institutions were also collected, such as: the plantation agency, the central statistics agency and other sources. secondary data are used to sharpen and support the analysis in this study. 4. data analysis to answer the objectives of the characteristics of independent rubber farmers the study was analyzed using descriptive analysis. with the tabulation method focused on explaining the pattern of work time allocation, income contribution and household expenditure patterns. the description of the pattern of rubber farm household household work time allocation includes the length (percentage) of work time allocated to businesses within and outside the rubber plantation business. furthermore, the allocation of working time can be disaggregated according to household members (husband, wife and children). meanwhile, the descriptive analysis of income contribution is intended to get a picture of the amount of income contribution in the business and outside the rubber plantation business to the total income of rubber farmer households. next the descriptive analysis of household expenditure patterns is focused on looking at the amount of income allocation that is reinvested in the rubber plantation business, consumption expenditure, savings, investment and leisure. the pattern of household consumption expenditure is further broken down according to commodity groups, namely food and non-food consumption. in addition, a descriptive analysis was also carried out relating to the general description of sample identity (age, education, number of family members and work experience). fig 2. frame work for economic analysis of rubber farmer house holds in kampar district analyzed with the simulatan equation model econometry with 2sls estimation method. furthermore, the household economic model that analyzes internal and external dominant factors that affect the allocation of work time, household income and expenditure and the impact of changes in government policy on household kampar district kampar kiri hulusubdistrict kampar kiri subdistrict koto kampar hulu subdistrict 20 samples 20 samples 20 samples heriyanto et al./ jgeet vol 5 no 2/2020 71 economic decision making are analyzed using the simultaneous equation approach with the two stages least square (2sls) analysis method. the data analysis process was carried out using the help of the statistical analysis system econometric time series (sas / ets) program version 9.4. frame work for economic analysis of rubber farmer house holds in kampar district analyzed with the simulatan equation model econometry with 2 sls estimation method can be seen in the figure below. 4. results and discussions 4.1. characteristics of independent rubber farmers the profile of rubber sample households (hereinafter referred to as rubber farm households) can be seen in table 1. based on table 1, it can be seen that the average age of heads of rubber farmer families is 48 years, thus it can be said that the average rubber farmers are at productive age . the average rubber farmer starts a rubber gardening business at the age of 32 years. thus the average rubber farmer has been in business for 16 years, so it can be said that these rubber farmers have enough experience in running a rubber farming business. table 1. characteristics of rubber farmer households no. description unit amount 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. number of household respondents from rubber farmers gender: a. men b. women the average age of rubber farmers the average length of education of rubber farmers the average length of education of a rubber farmer's wife average rubber farmer work experience average household member is a rubber farmer average household workforce of rubber farmers average household student is a rubber farmer household average area of rubber farmers origin: a. respondents were from kampar regency b. respondents came from outside kampar district person person person year year year year person person person hectare person person 60 58 2 48 9 9 16 6 4 2 2 57 3 table 2 shows that the formal education of rubber farmers and wives of rubber farmers, respectively 10 years and 9 years. thus it can be said that the education of rubber farmers and their wives is still low, ie only graduated from junior high school. the average rubber farm household member is 6 people, including 4 people belonging to the labor force and 2 school children. in general, the household workforce of rubber farmers works both inside and outside the rubber farming business. the majority of rubber farming households are from kampung kabuapten, as many as 57 households. only 3 rubber farmer households come from outside kampar district. this indicates that the rubber farming business is dominated by people from within kampar distric. farmers who are working on this rubber have an average of 2 hectares of garden area. rubber plantation land is own property with an average pattern of rubber plantation exploitation by rubber farmers and their families 4.2. internal and external dominant factors that affect working time allocation, income and expenditures of rubber farmer households table 2 shows the results of the estimation of the rubber production equation that rubber production is not responsive to the outflow of household work in the business (positive) and the number of productive rubber rods (positive). although the elasticity values are not responsive, rubber production is more sensitive to changes in the number of productive rubber stems thanchanges in the flow of rubber farm family work in the business. variations in the work flow of rubber farming families in the rubber farming business, labor outside the family and the number of productive rubber stems have a positive effect on production. this illustrates that if the outflow of rubber farming family work in the rubber farming business, labor outside the family and the number of productive rubber stems increases, then rubber production will tend to increase. table 2. internal and external dominant factors that affect the allocation of working time, income and expenditure ofrubberfarmerhouseholds note: significant at 10 percent level variabel parameter estimate t value pr > |t| elasticity intercept -3481.0400 -2.6600 0.0100 workflow in business 1.6465 3.9400 0.0002 0.4018 external family labor 1.4665 0.9600 0.3404 number of productive rubber stems 10.9694 21.5900 <.0001 0.9356 intercept 1917.9570 6.6000 <.0001 rubber farm household income in the business 0.0000 3.4500 0.0011 0.2279 outflow of work outside the business -0.6661 -5.4400 <.0001 -0.2162 rubber farm household work force 118.2826 1.3100 0.1956 intercept 313.7619 3.5700 0.0008 rubber farmers household income outside the business 0.0000 11.7200 <.0001 0.6274 t he total outpouring of farmers' work -0.0617 -1.8900 0.0634 -1.4268 rubber farm household work force -13.6572 -0.8400 0.4023 rubber farmer work experience -1.2138 -0.4600 0.6476 intercept 1486.3600 1.7500 0.0852 workflow in business -0.8648 -3.5500 0.0008 -2.6644 rubber farm household work force 369.6034 3.2000 0.0023 1.7351 intercept 6229224.0000 3.5500 0.0008 rubber farm household income in the business -0.0520 -4.0200 0.0002 -2.0195 outflow of work outside the business 4300.1760 5.0000 <.0001 1.0484 intercept 9100771 10.58 <.0001 t otal income of rubber farmer household 0.0009 0.2600 0.7947 number of family members 1159123.0000 7.3000 <.0001 0.3642 recreational expenditure of rubber farmers' households 4.8413 5.9000 <.0001 0.0979 wife's education -204663.0000 -2.0800 0.0426 -85103.4607 intercept -219881.0000 -0.3000 0.7622 t otal income of rubber farmer households 0.0030 1.3900 0.1714 number of family members 841287.8000 5.2900 <.0001 0.9657 farmer education 38506.8700 0.7800 0.4366 wife's education 70762.1500 1.4600 0.1504 intercept 274738.0000 0.2600 0.7948 t otal income of rubber farmer households 0.0024 0.4900 0.6256 number of school children 2749502.0000 10.9600 <.0001 0.8670 wife's education 17597.3800 0.1900 0.8495 intercept 48000314.0000 1.8000 0.0768 t otal income of rubber farmer households 0.3015 2.4000 0.0197 0.2623 workflow in business 9396.2280 0.9100 0.3684 number of school children -3478493.0000 -0.6400 0.5249 business scale 56847237.0000 4.4900 <.0001 0.2945 intercept 578960.6000 1.5000 0.1399 t otal income of rubber farmer households 0.0009 0.8300 0.4079 workflow in business -541.0220 -3.4300 0.0012 -4.7125 outflow of work outside the business -310.4160 -3.1100 0.0030 -0.8776 farmer education 50376.3100 2.5500 0.0135 1.8117 wife's education 63828.4600 3.4500 0.0011 1312289.7143 intercept -6376491.0000 -1.8600 0.0688 t otal income of rubber farmer households 0.0754 10.4900 <.0001 1.5748 t otal consumption of rubber farmers -0.1290 -0.5800 0.5643 interest rate 2657819.0000 5.2700 <.0001 0.8489 11. savings r2 =0.7665, fvalue=61.28, pr > f <.0001, dw =1.300045 r2 =0.91199, fvalue =193.44, pr > f <.0001, dw = 1.929889 8. educational investment 9. business investment r2 =0.76172,fvalue =59.67, pr > f <.0001, dw = 1.522326 r2 =0.47231, fvalue =12.31, pr > f <.0001, dw =1.426565 10. recreational expenditure of rubber farmers' households r2 =0.55386, fvalue =13.41, pr > f <.0001, dw =1.605136 5. rubber farmers household income outside the business r2 =0.38478, fvalue =17.82, pr > f <.0001, dw = 1.558858 6. rubber farm household food consumption r2 =0.68107, fvalue =29.36, pr > f <.0001, dw =1.342588 7. non-food consumption of rubber farming households r2 =0.41041, fvalue =7.52, pr > f <.0001, dw = 1.554068 2. workflow in business r2 =0.47965, fvalue =17.21, pr > f <.0001, dw = 1.923857 3. external family labor r2 =0.47965, fvalue =17.21, pr > f <.0001, dw = 1.923857 4. outflow of work outside the business r2 =0.4022, fvalue =19.18, pr > f <.0001, dw = 1.650385 1. prodution 72 heriyanto et al./ jgeet vol 5 no 2/2020 from the aspect of work time allocation shows that the outflow of family work in the business is not responsive to household income in the business (positive) and outflow of family work outside the business (negative). furthermore outflow of family work outside of business is responsive to outflow of household work outside the business (negative) and the number of household workforce (positive) (table 2). the results of the estimation of the equation of the use of workers outside the family show that the use of workers outside the family is not responsive to changes in household income of rubber farmers outside the business (positive). however, the use of labor outside the family of rubber farmers in an effort is responsive to changes in the total outpouring of farmer work (negative). furthermore, the estimation results of the household income equation can be stated that the household income of rubber farmers outside the business is responsive to changes in household income of rubber farmers in the business (negative). however, the household income of rubber farmers outside the business is not responsive to changes in the outflow of rubber farming families outside the business (positive) (table 2). furthermore, the results of estimating the expenditure of rubber farmer households shows that the food consumption of rubber farmer households is not responsive to changes in the number of rubber farmer family members (positive), rubber farmer household recreation expenses (positive) and the education of rubber farmer wives (negative). in the equation of non-food consumption of rubber farmer households shows that non-food consumption of rubber farmer households is not responsive to changes in the total income of rubber farmer households (positive), the number of rubber farmer family members (positive), education of rubber farmer wives (positive) and investment of farmer household education rubber (negative). table 2 shows the investment in education shows that the education investment of rubber farmer households is not responsive to changes in the number of school children of rubber farmer households (positive). several studies on farm household economics show that household education expenditure is significantly influenced by the number of school children and total household income of farmers. both variables are positively related to education expenditure (adevia, bakce, & hadi, 2017; asrol & heriyanto, 2019; husin & dwi wulan, 2011; khaswarina, 2017; putra, bakce, & rifai, 2012). thus the results of this study are in accordance with the results of previous studies. the equation of rubber farm household business investment it can be stated that the rubber farm household business investment is not responsive to changes in the total income of rubber farm households (positive) and the outflow of rubber farm family work in businesses (positive).research result (putra et al., 2012) shows the rubber farming investment variable is influenced by the total income of rubber farm households and the number of school children and is positively related. both variables are not responsive to investment in rubber farming. thus this research is similar (adevia et al., 2017; putra et al., 2012), where the income variable in farming is part of the total income of farm households. meanwhile, from the estimation results in the equation of rubber farmer household recreation expenditure it can be stated that the rubber farmer household recreation expenditure is responsive to changes in the outflow of rubber farm family work in businesses (negative), rubber farmer education (positive) and the education of rubber farmer wives (positive) , but not responsive to changes in the outflow of rubber rubber family work outside the business (negative). whereas based on the estimation results on the rubber farmer household saving equation it can be stated that the amount of rubber farmer household savings is responsive to changes in the total income of rubber farmer households (positive) but not responsive to changes in the total consumption of rubber farmer households (negative) and changes in interest rates (positive) 5. conclusion based on the results of the previous analysis and discussion, conclusions can be drawn. the conclusions of this research are: 1) characteristics of rubber farmers, the average age of rubber farmers at productive age (48 years), the length of education of rubber farmers 9 years, the education of the wife of rubber farmers 9 years, 16 years of farmer work experience, 6 household members, 4 farmers' labor force, number 2 school children, 2 hectares of land. 2) internal factors of farm households are responsive to household economic decisions. there are no external factors included in the model that are responsive to the economic decisions of rubber farming households in kuantan singingi regency regarding the aspects of production, working time allocation, income and expenditure of rubber farming households. from the aspect of production, no responsive internal or external factors were found, but the biggest effect was the number of productive rubber stems. from the aspect of work time allocation, internal factors that are responsive to influence are the total outpouring of farmer work, outpouring of farm family work in businesses and the workforce of farmer households. furthermore, from the aspect of farmer's household income the responsive internal factors that influence it are the farmer's household income in the business. then what influences household expenditure is outflow of work in business, farmer education, wife education and total rubber farmer income. acknowledgment the biggest thanks to all colleagues during thedata collection and the parties involved in this research and the universitas islam riau who permitted field observation, as well as the direktorat riset dan pengabdian masyarakat dirjen penguatan riset dan pengembangan kementerian riset, teknologi dan pendidikan. hopefully this journal can be useful as it should. references adelman, i. 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(2006). productivity growth in thailand and indonesia: how agriculture contributes to economic growth. in working papers in economics and development studies. bandung. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/http:/dx.doi.org/10.21082/jae.v23n2.2005.133-158 https://doi.org/http:/dx.doi.org/10.21082/jae.v23n2.2005.133-158 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 1 2020 ondara, k., et al./ jgeet vol 5 no 1/2020 25 research article hydrodynamics features and coastal vulnerability of sayung subdistrict, demak, central java, indonesia koko ondara1,*, ruzana dhiauddin1, ulung j. wisha1, guntur a. rahmawan1 research institute for coastal resources & vulnerability, ministry of marine affairs and fisheries, indonesia. * corresponding author : kornkoko@yahoo.com tel.:+628976929648 received: sept 19, 2019; accepted: march 20, 2020. doi: 10.25299/jgeet.2020.5.1.3996 abstract the sayung sub-district is an abrasion area in demak regency that is mostly affected by sea level rise. the purpose of this research is to determine the features of hydrodynamics and coastal dynamics occurrence in the sub-district of sayung.collecting field data/information and modeling approach (tides, waves, currents, weather and coastline changes) have been done in sayung, demak. the wave height in the eastern coast is the highest. the significant wave height in 2004 was greater than march 2016 showing that in 2004 the wind energy transfers were larger than 2016. the refraction coefficient in 2016 for all directions was the greatest from the west at the depth of 8 m and the smallest one was identified in the south. the refraction coefficient in 2004 for any direction yielded the largest value in the southwest at the depth of 2 m and the smallest onewas identified the south as well. during a cycle of tidal fluctuation, it occurs twice flood and ebb events. the maximum depth is 6.5 m located about 3.8 km from the coastline. the sediment thickness reached 564,886.39 m3. coastline changes occurred in 2003 andstarted to gain sedimentation in 2015. data and information produced can be useful as a basisfor further developments to mitigate abrasion andto create policy-briefin managing coastline affected abrasion even thoughsomeimprovement efforts have been made. keywords: hydrodynamics, abrasion, sedimentation, coastal vulnerability 1. introduction coastal development is taking place around the north coast of java (pantura)resulted in changed water conditions and coastlines around the north coast which is greater compared to the south coast. threats including tsunamis, tectonic earthquakes, the dynamics of large waters, and others will potentially take place. in addition, the north coast of java region is often used as the center of government and community activities such as jakarta, cirebon, tegal, pekalongan, semarang, surabaya, and others. sayung is one of the sub-districts in demak regency which experienced the worse tidal flooding compared to other subdistricts.the coastal areas in sayung sub-district affected by tidal flood reaching 0.25 meters are sriwulan, surodadi, bedono and timbulsloko village (desmawan and sukamdi, 2012a). a total of 83 slums affected by abrasion and almost 2,036 slums affected by inundation (marfai, 2012). the highest tidal flood occurs in the west season (widada, sugeng, baskoro rochaddi, 2012). during 1999-2009 in demak regency, sea level rose around 0.72 mm/year and 7.9 mm/year in relative sea level rise. the sea level rise inundated an area of 26.83 km² in 8 villages. significant coastline changes in wedung district resulted in the maximum accretion of 233,994 meters and maximum abrasion of 141,037 meters during 2012 2015 (dewi et al., 2016). this shoreline changes causes the settlements to draw closer to the sea, resulting in increased coastal vulnerability due to tidal flood events(wahyudi et al., 2012). abrasion that occurs in sayung subdistrict is influenced by waves that occur continuously (ondara and wisha, 2016) with the type of soil composed of silt and sandy silt and silt (subardjo, 2004) causing the population of people living in the area to decrease (damaywanti, 2013). due to frequent tidal floods and abrasion, the sayung subdistrict community supplies fresh water for daily activity from other areas (desmawan and sukamdi, 2012). fig. 1. administration map of demak, central java (source: bappeda demak,2010) this study aims to review the process of hydrooceanography and coastal dynamics in sayung, demak to determine the coastal vulnerability. data/information and model of this research can be useful as a basis in creating policy brief related to the further developments in the future. 2. material and method java sea semarang semarang regency grobogan regency pati regency kudus regency jepara regency http://journal.uir.ac.id/index.php/jgeet 26 ondara, k., et al./ jgeet vol 5 no 1/2020 the research was conducted during march august 2016 in the sayung coast which is administratively located in four villages that are sriwulan, bedono, timbulsloko, and surodadi. those four villages were chosen because of its susceptibility to the changes in settlement areas caused by abrasion and tidal flood inundation. this research begun with a comprehensive literature study from various previous-related research sources such as scientific journals, technical reports, proceedings and research reports carried out to identify coastal issues in the north coast of java especially in the sayung coast and surrounding. the secondary data and information were also employed consist of several aspects of gis, oceanography and coastal vulnerability. furthermore, data collection was conducted directly in the field to retrieve primary data as the basis for analysis and to validate the potential coastal resources and its threatening factors. characteristics of wind including magnitude and direction was analyzed. wind features were measured using an anemometer, a tool consisting of a spinning mug or blade. the average wind speed over a given period of time is calculated by counting the number of rounds over a given time period. conversion of wind speed can be made using shore protection manual 1984 or 1993 api formulation as follow: 𝑈𝑡 𝑈3600 = 1.2 + 0.2 ⋅ 𝑡𝑎𝑛ℎ {0.9𝑙𝑜𝑔10 ( 45 𝑡 )} ; 0< t < 3600 sec. (1) 𝑈𝑡 𝑈3600 = 1 + {3.0 + 𝑙𝑛 ( 3 𝑡 ) 0.6 }{0.15( 1 2 ) −0.125 } ; t  60 sec. (2) where: ut = wind speed with a duration of more than 3 seconds u3600 = wind speed with a duration of 1 hour wind data were used to hind cast significant wave heights and periods that will be corrected against elevation, stability, location effects and drag coefficient to obtain wind stress factor (ua). wind data used were the maximum monthly wind data that will induce the maximum wave height. wind stress factor (ua) was calculated using following equation: 𝑈𝑈 = 0,71𝑈𝑈𝑈1,23 (3) 𝑈𝑈 is the wind speed in the sea obtained from the equation: 𝑈𝑈 = 𝑈𝑈𝑈𝑈𝑈 (4) where𝑈𝑈 is the measured wind velocity and 𝑈𝑈 is the relationship between winds above sea and wind in the nearest land. to determine the maximum wave height and period that occurs basedon the depth change from 0.1 m to 10 meters, a relationship between maximum wave height and maximum wave period (10 years of input data) has been calculated using hindcasting method to obtain the equation from the correlationgraph which then used to calculate the period of wave in the deep ocean. to calculate the wavelength of the deep sea used a formula as follow: 𝑈0 = 1,56 𝑈2 (5) where l0is length between wave crests or troughs and t is time it takes a wave crest to travel one wavelength (units of time). the value of refraction coefficient (kr) is obtained using the equation as follow: kr = √ cos α0 cos α (6) the coefficient of shoaling is calculated by using the equation of: ks = √ n0l0 nl (7) where kr is the refraction coefficient, and ks is the coefficient of shoaling, 𝛼 is angle of incidence relative to the shoreline or some prescribed depth contour and n values varies from 0,5 for a deep-water wave up to 1.0 for a shallow-water wave. 3. result and discussion to facilitate the reading of wind data for 10 years, the wind rose diagram was created shown in figure 2. fig 2. wind rose in 2005 2015 the direction information of incoming wave is obtained by classifying the 2005-2015 wind data and grouped by the beaufort scale. it can be seen in figure 2 that the dominant and maximum waves are sourced from the southeast. this is because the eastern region is open water and topographically there is no obstacle factor hampering the wind blows and energy transfers. fig 3. the maximum daily wave chart on march 2016 fig 4. correlation graph of wave height and wave period for east direction after calculating the coefficient of refraction and shoaling, we obtained the new wave height value by using the following equation: 𝑈 = 𝑈0.𝑈𝑈.𝑈𝑈 (8) where h is representing the wave height at some coastal location, and hois the wave height at some offshore locations. ondara, k., et al./ jgeet vol 5 no 1/2020 27 table 1. shoaling coefficient calculation z (m) 6 4 2 0.1 n 0.4871 0.4194 0.2028 0.9258 ks 1.0129 1.089 1.5231 1.1464 h 0.042 0.0451 0.0631 0.0475 table 2. breaking wave calculation z (m) 6 4 2 0.1 h'o 0.0414 0.0414 0.0414 0.0414 h'o/gt2 0.0023 0.0023 0.0023 0.0023 according to the calculation of shoaling and refraction coefficients, it is obtained that the wave breaks at 0.04 meters with a depth of 6 meters. 3.1. bathymetry bathymetry data was measured directly using echo sounder. the depth of the horizontal waters is processed into the depth contours of the seafloor topography to show the depth variation. the maximum depth is 6.5 m which at about 3.8 km from the coastline. the result of bathymetry must be corrected using the existing the sea level adjusted with measurement time and the distance between surface and transducer sensor in order to obtain the actual depth (wisha and heriati, 2017). fig. 5.water depth contour map 3.3 tide fig 6. tidal data verification as one of the prerequisites of modelling, tidal data validation was done by comparing field data and model data (gao et al., 2009). as in figure 6, by using the root mean square error formula it was obtained the rmse of 0.3.figure 6 also shows that between the two surface elevation data, the same phase during the spring and neap tidal conditions is identified which is slightly different at the neap period might be caused by the influence of wave which affects the surface elevation formed (garrett and kunze, 2007). 3.2. sea current the result of current field data processing is depicted in the form of scatter plot, stick diagram, current rose, current velocity vertical profile, and hydrodynamic map which illustrate the features of currents in various depths. the current speed ranges from 0.06-0.5 m/s which predominantly moves towardsoutheast and northwest.according to (wisha et al., 2015), surface currents are influenced by monsoon winds. during the 1st transitional season, where the transition of the rainy season to the dry season took place, the wind blows from australia to asia. this theory corresponds to the current rose that the direction of the surface current shows the same pattern with the wind dominant direction. fig 7. the direction of the dominant current profile fig 8. vertical east velocity current profile to depth the current moves southeastward and northwestward with a speed of 0.056-0.44 m/s. furthermore, the currents patterns vertically vary at each depth. figure 8, 9 and 10 show in the current vertical profile results explaining that the deeper the water column, the weaker velocity observed, this is due to the influence of bottom friction and the role of density (wisha et al., 2016). during the high spring tidal phase, the current speed ranged from 0 0.05 m/s moving landward. while during the low tidal condition, the current flowed seaward with the speed of 0 0.08 28 ondara, k., et al./ jgeet vol 5 no 1/2020 m/s. this condition shows that the current speed id higher during ebb tides. this event is closely related to the transport mechanism in the coastal area where the water mass flowing toward the coast will be forwarded to the bottom of the waters (downwelling) and vice versa for the ebb event, where the water mass below the water level will rise to fill the void area in the surface. fig 9. vertical up velocity current profile to depth fig 10. vertical north velocity current profile to depth the deeper the water depth, the greater the density and the smaller the current speed. the movement of the insignificant currents is caused by the basic friction and density effects so that the energy generated by the ocean currents becomes weak which the inhibition of current movement makes it calmer. thus, the pattern and velocity of the current are more randomly and faster in the surface where the obstacle is reduced and the wind-energy transfer is maximum. according to wisha et al. (2016) the vertical profile of current velocity components is influenced by bottom topography, the dynamics of sea level pressure, bottom friction, density and winds. in the coastal areas of sayung, there are several permeable dams in the form of piles of wood and stone. the beach building was built with the aim to reduce the impact of abrasion by supporting mangrove growth around the coastal area (pribadi et al., 2010). the occurrence of vector accumulation around the permeable dam during high and low tidal conditions is shown in fig. 12. due to the narrow channel of permeable dam, the current flow passing the structures becomes more rapidly. however, the current velocity becomes weaker among the permeable dam. it can be seen from the graph of the current velocity in fig. 11. the current profile will be calmer around the structures and more rapidly in the estuary and tend to be stable offshore (cummins et al., 2012). fig 11. graph of ocean current velocity: front of permeable (black); between permeability and river (blue); between permeable (green); river mouth (light blue); open sea (red) based on the observation, during the high tidal condition, the oscillation of current toward the land and sea will bring the sediment into the permeable structure. however, during the low tidal condition, the water mass movement tends toward the sea, in this condition the sediment material will be trapped in the permeable structure. thus, the greater the mass of water entering the permeable structure, the larger the sediment material will betrapped. 3.4 sedimentation 3d map of field bathymetry measurements consists of channel 1 (high frequency) and channel 2 (low frequency), which was analyzed to obtain sedimentation volume in the study area. the result of sedimentation volume calculation (fig. 14) shows the suspension of suspended sediment is high within the bay. tidal current regime has a role in evoking the suspended sediment concentration. at the high tidal condition, the sediment concentration in the estuary will intensely accumulated. the cohesive sediment in sayung that is highly susceptible to salinity contributes to the higher suspended sediment inducing sedimentation. if salinity becomes high, the clumping process will take place, so sediment tends to be deposited(marfai, 2012). the result of overlapping channel 1 and channel 2 results in the figure of sediment thickness during bathymetry measurement. volume calculation was performed using the surfer software which the total volume of sediment is shown in table 3. table 3. comparison of sediment thickness volume equation volume (m3) trapezoidal rule 573.922.20 simpson's rule 564.886.39 simpson's 3/8 rule 587.137.34 ondara, k., et al./ jgeet vol 5 no 1/2020 29 fig. 12. simulation of ocean currents at high tide fig. 13. simulation of ocean currents at low tide fig 14. 3d bathymetry measurement map in sayung sub-district there are several rivers that carry suspended solids from the mainland. at the high tidal condition, the water masses moved from the sea toward the interior of the river, the mass of water will bring suspended solids from the sea into the river. during the spring tidal phase, the concentration of suspended sediment will be higher due to the higher astronomical energy transfer evoking the higher current speed and transport mechanism. the difference in surface elevation will cause massive movement of water masses. this is in line with the results of the study by wisha et al. (2015) which stated that the amount of sediment will increase during the low tidal condition because the sediments carried during flood tides will be settled down in the surface bottom. 3.5 geographic information system analysis the fig. 15 below shows the results of satellite image map analysis of 1999 and 2003 based on landsat-7 image obtained from usgs online data of usa. in the picture above shows that the coastline of 2003 experienced a change that leads to coastline retreat as seen in 30 ondara, k., et al./ jgeet vol 5 no 1/2020 the boxes 1 and 2 in fig. 2 above. the rate of change in these two regions can be seen in table 4 below. fig 15. coastline overlay 1999 (red line) and 2003 (blue line) table 4. coastline change between 1999 and 2003 no. the pace of change (m/year) information 1 6.83 abrasion 2 10.85 abrasion total 17.68 abrasion 3.6 shoreline changes in 1999 – 2015 the fig. 16 below shows the results of satellite image map analysis in 1999 based on landsat-7 image and landsat-8 2015 image obtained from usgs online data of usa. overlay of the coastline of 1999 and 2015 over landsat 7 satellite imagery (1999) shows several locations that have undergone significant changes over the past 16 years. white box shows a change of accretion while the blue box shows a shoreline retreat (abrasion). table 5.coastline change between 1999 and 2015 no. the pace of change (m/year) information 1 42.86 abrasion 2 57.20 abrasion 3 104.02 abrasion total 89.68 abrasion in general, from the two tables above, the rate of shoreline changes leads to the abrasion phenomenon, where coastlines tend to retreat from year to year. coastlines of 1999, 2003 and 2015 extracted from the imagery are then overlaid so that a map can be generated as shown in fig. 17. fig. 16. shoreline overlay 1999 (red) and 2015 (orange) fig. 17. map of coastline change in 1999, 2003 and 2015 from the picture above, it can be seen that most of the coastline continues to decline from year to year. however, there are also several accretion sites seen in the white circle on the map above, where coastline retreats occurred in 2003 but again progressed in 2015. changes that occur in this coastline can be caused by natural conditions such as sediment type of water base; aquatic dynamics; climate and weather and human ondara, k., et al./ jgeet vol 5 no 1/2020 31 activities such as land clearing, and over-exploitation of water resources. 4. conclusion the dominant and maximum waves that occurred in sayung district came from the southeast, northwest and north. the dominant current direction moved toward southeast and northwest. the wave is greater in the east part of study area. the significant wave height in 2004 was higher than on march 2016, indicating that in 2004 the wind blew larger than 2016. the largest refraction coefficient in 2016 is identified in the west at depth of 8 m and the smallest one is in the south. while, the largest refraction coefficient in 2004 in the southwest at the depth of 2 m and the smallest one is in the south. the maximum depth is 6.5 m around 3.8 km from the coastline. the sediment thickness reached 564,886.39 m3. coastline retreat occurred in 2003 but again progressed in 2015. changes that occur on this coastline can be caused by natural conditions such as sediment types baseline water; aquatic dynamics; climate and weather and human activities such as land clearing, and overexploitation of water resources. coastal protection buildings that can be used to protect the coastal areas of sayung sub-district arebreakwater, revetment, groynes and combinations. data/information and model of this research can be useful as a basis in creating policy brief related to the further developmentsin the future. acknowledgement gratitude is given to research institute for coastal resources and vulnerability (ricrv) for research funding in 2016 and for those who assisted in the completion of this work. references cummins, s.j., silvester, t.b., cleary, p.w., 2012. threedimensional wave impact on a rigid structure using smoothed particle hydrodynamics. int. j. numer. methods fluids. https://doi.org/10.1002/fld.2539 damaywanti, k., 2013. dampak abrasi pantai terhadap lingkungan sosial (studi kasus di desa bedono , sayung demak). pros. semin. nas. pengelolaan sumberd. alam dan lingkung. 363–367. desmawan, b.t., sukamdi, s., 2012a. adaptasi masyarakat kawasan pesisir terhadap banjir rob di kecamatan sayung, kabupaten demak, jawa tengah. j. bumi indones. desmawan, b.t., sukamdi, s., 2012b. adaptasi masyarakat kawasan pesisir terhadap banjir rob di kecamatan sayung, kabupaten demak, jawa tengah. j. bumi indones. 1. dewi, r.s., bijker, w., stein, a., marfai, m.a., 2016. fuzzy classification for shoreline change monitoring in a part of the northern coastal area of java, indonesia. remote lens. https://doi.org/10.3390/rs8030190 gao, j., lan, x., fan, y., chang, j., wang, g., lu, c., xu, c., 2009. cfd modeling and validation of the turbulent fluidized bed of fcc particles. aiche j. https://doi.org/10.1002/aic.11824 garrett, c., kunze, e., 2007. internal tide generation in the deep ocean. annu. rev. fluid mech. https://doi.org/10.1146/annurev.fluid.39.050905.11022 7 marfai, m.a., 2012. preliminary assessment of coastal erosion and local community adaptation in sayung coastal area, central java -indonesia. quaest. geogr. https://doi.org/10.2478/v10117-012-0028-2 ondara, k., wisha, u.j., 2016. simulasi numerik gelombang (spectral waves) dan bencana rob menggunakan flexible mesh dan data elevation model di perairan kecamatan sayung, demak. j. kelaut. indones. j. mar. sci. technol. https://doi.org/10.21107/jk.v9i2.1694 pribadi, k., diposaptono, s., agung, f., 2010. climate change and coastal zone management in indonesia: example of adaptation at demak coast, java island, indonesia. res. publ. serv. 1, 185–200. subardjo, p., 2004. studi morfologi guna pemetaan rob di pesisir sayung, kabupaten demak, jawa tengah. indones. j. mar. sci. 9, 153–159. https://doi.org/10.14710/ik.ijms.9.3.153-159 wahyudi, s.i., ni’am, m.f., le bras gilbert, 2012. problems, causes and handling analysis of tidal flood, erosion and sedimentation in northern coast of central java: review and recommendation. int. j. civ. environ. eng. widada, sugeng, baskoro rochaddi, and h.e., 2012. pengaruh arus terhadap genangan rob di kecamatan sayung, demak. bul. oseanografi mar. 1, 31–39. https://doi.org/10.14710/buloma.v1i2.11218 wisha, u.j., heriati, a., 2017. bathymetry and hydrodynamics in pare bay waters during transitional seasons (septemberoctober). omni-akuatika. https://doi.org/10.20884/1.oa.2016.12.2.98 wisha, u.j., husrin, s., prasetyo, g.s., 2016. hydrodynamics of bontang seawaters: its effects on the distribution of water quality parameters. ilmu kelaut. indones. j. mar. sci. https://doi.org/10.14710/ik.ijms.21.3.123-134 wisha, u.j., husrin, s., prihantono, j., 2015. hydrodynamics banten bay during transitional seasons (augustseptember) (hidrodinamika perairan teluk banten pada musim peralihan (agustus–september)). ilmu kelaut. indones. j. mar. sci. https://doi.org/10.14710/ik.ijms.20.2.101-112 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 208 dewi, s.h. et al/ jgeet vol 04 no 03/2019 research article benefits of adding corn stalk ash as a substitution of some cement against of compressive strength concrete sri hartati dewi 1* , roza mildawati 1 , tio perdana 1 1 department of civil engineering, universitas islam riau jalan kaharuddin nasution km. 11 no. 113 perhentian marpoyan pekanbaru 28284 * corresponding author : srihartatidewi@eng.uir.ac.id received: apr 4, 2019; accepted: jun 19, 2019. doi: 10.25299/jgeet.2019.4.3.2966 abstract concrete is a very important building material used in the world of construction services, and it is generally known that the good and bad properties of concrete can be seen from its compressive strength. concrete consists of portland cement (pc) or other hydraulic cement, fine aggregates, coarse aggregates, and water, with or without using additional materials. cement is one of the main mixtures of concrete constituents composed of natural resources such as lime (cao), silica (sio₃), alumina (al2o₃), little magnesia (mgo), and alkali. silica is also found in corn. according to (roesmarkam and yuwono, 2002) corn plants have a silica content of 20.6%. this study aims to determine the effect of utilization of corn stalk ash on compressive strength and modulus of elasticity of concrete. cornstalk ash is used as a partial substitute for cement, with a mixture composition of 2%, 4%, 6%, 8%, and 10%. this study uses sni 03-2834-2000 for mix design, with the added ingredient of 0.25% sikament nn. cylindrical test specimen size (150 mm x 300 mm), the specimen was treated and tested at 28 days. based on research using corn stalk ash 2%, 4%, 6%, 8%, and 10%. either without or using sikament nn the highest compressive strength at 8% is 20.8 mpa and 20.4 mpa, and decrease in usage of 10% corn stalk ash which is 18.2 mpa and 18, 4 mpa. the highest elastic modulus without or with sikament nn present in 8% ie 21656.14 mpa and 21607.52 mpa. modulus of elasticity value decreased in the use of corn stalks 10% ash is 20366.28 mpa and 20569.59 mpa. based on the research, corn stalk ash can replace the role of part of cement in construction using corn stalk ash 8%. keywords : concrete, cornstalk ash, compressive strength, modulus of elasticity, sikament nn. 1. introduction concrete is a very important building material used in the world of construction services, it is generally known that the good and bad properties of concrete can be seen from its compressive strength, the higher the compressive strength the better the concrete. cement that we often encounter on the market is portland cement, the main ingredient in making portland cement is lime (cao), silica (sio₃), alumina (al2o₃), little magnesia (mgo), and alkali. silica (sio2) is one of the important components in making cement. in addition to the silica crust also found in plants. indonesia is an agrarian country where the majority of the population works in gardening and farming, one of which is corn farming. corn is one type of agricultural crop that has the largest waste yield. based on roesmarkam and yuwono (2002) maize plants have silica content of 20.6%, so from this research was conducted by utilizing corn stalk ash as a partial substitute for cement in concrete mixtures. this is due to the presence of silica content where this content is also present in the cement content. corn stalk ash is the ash from the combustion of corn stalks that pass the filter no.200. the components of old and ready-to-harvest corn plants consist of 38% seeds, 7% cob, 12% skin, 13% leaves and 30% stems 2. literature review corn seed additive materials for addition to environmentally friendly lightweight concrete making". this study aims to determine the characteristics of lightweight concrete corn stalk ash and corn hump which includes weight, modulus of elasticity and compressive strength of concrete. the research was carried out by the experimental method, namely by making experiments in the form of specimens in the laboratory using corn stalk ash as an additive mixture of cement and corn cobs as a mixture of coarse aggregates in the manufacture of concrete. the results showed that 10% of the concrete with mixture of tebon corn with ash had lower compressive strength than ordinary concrete. the compressive strength at 7 days reached 92.43 kg / cm2, while at 14 days the concrete compressive strength reached 135 kg / cm2 and at 28 days, the concrete compressive strength reached 169.85 kg / cm2 or equivalent to 16.98 mpa. in the previous mix design calculation, the compressive strength of concrete at 28 days reached http://journal.uir.ac.id/index.php/jgeet dewi, s.h. et al/ jgeet vol 04 no 03/2019 209 25 mpa. compressive strength concrete with a mixture of 10% ash is less than ordinary concrete, but concrete mixes have a more economical and lighter value. ahmad, et al. (2017), "nature of eco-friendly concrete workability." this research was conducted at the material testing laboratory of the ptsm ftp department. this study aims to describe in detail the workability of concrete using waste instead of cement. fresh concrete specimens are made based on 20mpa concrete quality with fas of 0.45. the percentage of asp used is 0%, 5%, and 7.5% of the weight of cement. the results of this study indicate that the higher the percentage of asp, the slump value, the factor of density and bleeding is lower. decreasing the slump value for 5% asp specimens is 6.09% compared to the slump value for specimens that do not use asp. furthermore, 7.5% of the specimens experienced a significant decrease of 19.13% compared to the test object without asp. but despite the decline of almost 20%. the value of the density factor for the mixture without asp reached 0.996 cm which decreased to 0.987 cm and 0.982 cm respectively for 5% asp and 7.5% asp. the decrease in the value of bleeding for specimens 5% asp was 41.33% compared with the value of bleeding for specimens that did not use asp. furthermore, for 7.5% asp test specimens decreased significantly, which amounted to 58.67% compared to the test object without asp. chandra (2013), "study of stress strength and modulus of elasticity of concrete with addition of corn bark as additive". this study was conducted to determine the feasibility of corncob waste as an additive material in concrete mixtures for type i cement and how much influence the corn cobs ash influence on the strength of concrete pressure and modulus of elasticity in concrete. this study uses concrete mortar planning using aci 211.1-1991 with a cement water (fas) factor of 0.54 and a variation in the ratio of addition of corn cobs to the weight of cement 4%, 8% and 12%. the results showed that the concrete with hump ash had a high pressure compared to normal concrete. the results of the strong score urged 56 days at bn: 36.46 mpa; bj4%: 37.67 mpa; bj8%: 34.88 mpa; bj12%: 34.28 mpa. while the modulus of elasticity of corncob ash concrete is greater than normal concrete. the results of the modulus of elasticity of corncob ash concrete are 0%, 4%, 8%, and 12% respectively at 23634.61 mpa; 23886.83 mpa; 24407.83 mpa; 23653.23 mpa. oladipupo (2012), "strength properties of corn cob ash concrete". this study aims to increase the reduction of corn waste and reduce the cost of producing concrete by using locally available ingredients. compressive strength testing from this study shows that 10% of cca as a substitute for cement is satisfactory in compressive strength requirements for a concrete mixture ratio of 1: 2: 4 at 7 days. however, it does not meet the standard strength at 14, 21 and 28 days. the use of 20% cca for cement does not meet the strength requirements at all. cca can be used as a partial substitute for cement in highstrength concrete, but cca concrete will take longer to achieve the strength designed and needed. the results of the testing of compressive strength with the use of 10% cca at the age of 7 days, 14 days, 21 days, and 28 consecutive days amounted to 13.18 mpa; 15.41 mpa; 19.41 mpa; and 20.00 mpa. while for testing compressive strength with the use of cca 20% at the age of 7 days, 14 days, 21 days, and 28 consecutive days amounting to 9.18 mpa; 10.96 mpa; 12.74 mpa; and 13.78 mpa. novan (2010), "effect of concrete press strength with addition of sikament nn". this study aims to prove the effectiveness of the material added by sikament nn on the compressive strength of concrete. the results of the study show that the age of the concrete also affects the addition of concrete compressive strength with the addition of sikament nn at a dose of 1.5% of the weight of cement in a variation of 20% water reduction, i.e at 3 days there is an increase in concrete compressive strength of 3.3% of the concrete plan, the age of 14 days there was an increase in the concrete compressive strength of 28% of the planned concrete and the age of 28 days an increase of 48.13% of the concrete plan. thus the test results turned out that sikament nn with a dose of 15% at 28 days could reduce concrete compressive strength amounting to 48.13%. ramanuddin (2010), "effect of fineness and levels of rice husk ash on the strength of concrete with a compressive strength of 50mpa." this study aims to determine the effect of using rice husk ash on the strength of concrete with different levels of fineness and content. split was carried out with cylindrical specimens with a diameter of 100 mm and a height of 200 mm.the addition of rice husk ash in this study was 5, 10, 15, 20, and 25% of the weight of cement. the partial substitution of rice husk ash against cement was 5, 10, 15, 20 and 25% the optimum level of addition of rice husk ash is 10% of the weight of cement which results in a compressive strength of 47.82 mpa.the optimum partial substitution of rice husk ash is 10% of the weight of cement which results in a compressive strength of 51.71 mpa. optimum superplasticizer (structuro 335) of 1% of the weight of cement which produces a compressive strength of 51.71 mpa.the best size of fineness is rice husk ash which passes the filter no 200 which produces a compressive strength of 51.71 mpa. table 4.1 results of the percentage of fine aggregate escapes. 210 dewi, s.h. et al/ jgeet vol 04 no 03/2019 3. research methods fig. 1 flowchart 4. results and discussion 4.1 results of fine aggregate examination fine aggregate gradation is expressed by the percentage value of the amount of fine agate left or through a 4.8 mm filter arrangement. sand filter gradation analysis in sand area no.i, sand gradation boundary in sand area no.ii, sand gradation boundary in sand area no.iii, and sand gradation boundary in no.iv sand area. the results of filter analysis can be seen in table 4.2 below. from table 4.2 it can be seen that the percentage of fine aggregate escapes meets the zone ii fine gradation requirements. results can be seen in the size filter 0.15 mm the percentage of escape is 8.43%. filter size 0.3 mm the percentage of escape is 21.52%. filter size of 0.6 mm the percentage of escape is 39.76%. the 1.2 mm size filter passes the percentage of 59.88%. screen size of 2.4 mm the percentage of escape is 83.30%. screen size of 4.8 mm the percentage of escape is 99.95%. the size of the filter is 9.6 mm, the percentage is 100%, the size of the filter is 19 mm, the percentage is 100%, and the size of the filter is 38 mm, the percentage is 100%. data can be seen that the percentage of passing through the fine aggregate filter is between the smooth zone ii zone boundaries, namely the minimum and maximum limits for each filter size. table 4.2 results of the percentage of fine aggregate escapes. 4.2 results of rough aggregate examination the results of the pass percentage can be seen in table 4.2 and the results of filter analysis with a gradation limit for a maximum grain size of 40 mm. by using a combination of coarse aggregate size 2/3 as much as 65% and coarse size 1/2 size as much as 35%. the results of filter analysis can be seen in table 4.3 below. table 4.3 results of percentage pass rough aggregate 2/3 and coarse aggregate ½ from table 4.3 it can be seen that the percentage of rough aggregate passes with a 0.15 mm sieve has an escape percentage of 3.31%. the size filter 0.3 mm the percentage of escape is 4.05%. size filter 0.6 mm pass percentage of 4.28%. the 1.2 mm size filter passes the percentage of 4.43%. the 2.4 mm size filter passed the percentage of 4.67%. the size filter is 4.8 mm, the pass percentage is 5.84%. and for the filter size of 9.6 mm the percentage of escape is 16.66%. the 19 mm size filter passes the percentage of 96.69% and the size of the 38 mm filter the percentage passes by 100%. 4.3 inspection of specific gravity and material absorption. examination of specific gravity and water absorption of material is carried out to determine the saturated surface dry dry density and to obtain bulk density, and apparent density. the results of the examination can be seen in table 4.4 below. table 4.4 results of examination of specific gravity and material absorption. dewi, s.h. et al/ jgeet vol 04 no 03/2019 211 based on table 4.4 it can be seen that the saturated surface density of the coarse aggregate 2/3 is obtained 2.624, the saturated surface density of the coarse aggregate 1/2 is 2.582 and the density of the fine aggregate surface is 2.582. based on the value of the specific gravity of the material can meet the standard specifications for density, 2.58 to 2.83 gr / cm3 (tjokrodimuljo, 1995). the dry density of the saturated surface is a handle for obtaining the aggregate density of the mixture which will be used to determine the approximate weight of the concrete in m³. 4.4 results of checking mud levels examination of this sludge uses the aggregate addition method that passes filter # 200 (0.075) which is intended as a reference in the handle to carry out the test and to do the amount after washing the test material, the results of the examination can be seen in table 4.5 below. table 4.5 results of aggregate sludge examination results. based on table 4.4 it can be seen that fine aggregates and coarse aggregates of 2/3 contain the levels of sludge in a safe state used for mixture of concrete mixtures, which according to sni 03-68212002 for fine aggregate sludge content is 3.824% <5%, for coarse aggregate sizes 2/3 obtained 0.709% <1%, whereas for 1/2 size coarse aggregates in conditions that do not meet the conditions where the sludge content for 1/2 coarse aggregate is 2.581%> 1%, so coarse aggregate material 1/2 needs to be washed before use. 4.5 results of water content checks checking the water content aims to obtain a percentage of the water content contained in the aggregate, the results of the moisture content can be seen in table 4.6 below. table 4.6 results of aggregate water content checks. based on table 4.6 it can be seen that after conducting a material check, the highest water content is found in fine aggregate of 3.525%. while the lowest water content is roughly 2/3 aggregate of 0.951. 4.6 content weight check results content weight is the ratio between the weight of the dry aggregate and its volume. the results of the examination of the weight of material contents can be seen in table 4.7 below. table 4.7 results of weight content checks. based on table 4.6 it can be seen that after examining the material, the highest content weight in loose conditions and solid conditions is found in the coarse ½ aggregate material which is equal to 1.420 gr / cm3 for loose conditions and 1.584 gr / cm3 for solid conditions. whereas for the lowest content of weight is found in corn stalk ash which is equal to 0.312 gr / cm3 for loose conditions and 0.807 gr / cm3 for solid conditions. 4.7 results of concrete mixing inspections (sk sni 03-2834-2000) planning concrete mix (mix design) aims to determine the proportion of the mixture between cement, fine aggregate, coarse aggregate and water. the results of planning mix (mix design) concrete for each m3 before correction of moisture content can be seen in table 4.7. table 4.7 proportion of concrete mix (mix design) for each m3 after correction of ssd water content. based on table 4.7, it can be seen the use of cement, water, fine aggregate, and coarse aggregate in each m³, each 1 piece of cement and each mixture composition. after correction of water content, the proportion of concrete mixture for 3 cylindrical specimens can be seen in table 4.8. 212 dewi, s.h. et al/ jgeet vol 04 no 03/2019 table 4.8 proportion of concrete mixture (mix design) for 3 slinder specimens of size 15 cm x 30 cm after correction of water content based on table 4.8, it can be seen the proportion of concrete mixture used for 1 time stirring. this proportion is calculated according to the form and number of samples used. can be seen for 3 cylindrical specimens needed semen 7,509 kg; water 3,753 kg; coarse aggregate 2/3 15,243 kg; coarse aggregate ½ 8,209 kg; fine aggregate 14.124 kg; and sikament nn 0.0188 kg. 4.8 results and analysis of concrete slump values the results of the examination of the slump test are aimed at checking the change in water content in the concrete mixture, while the slump value is intended to determine the workability of the concrete in accordance with the conditions specified, the lower the slump value, the thicker the concrete and the process compaction or concrete work will experience difficulties and take a long time. meanwhile, the high slump value indicates that the concrete is runny, in the process of processing or compaction it is easier to implement and does not require a long time in the compaction process. the value of concrete slump with a mixture of corn stalk ash can be seen in table 4.9 and table 4.9. table 4.9 concrete slump value with corn mixture of corn without sikament nn using 0.51 cement water factor. based on the results of research data in table 4.9 graphs can be made as shown in 4.1. fig 4.2 graph of relationship of percentage of corn stems to slump value. from fig. 4.2, it can be seen that in normal concrete without mixture of corn stalk ash the slump value according to the requirements is 60 <146.7 <180, and it can be seen the higher the percentage of ash use, the smaller the slump value obtained, this proves that the use of ash corn stalk makes concrete stiff can be seen in the mixture of corn stalk ash slump value of 38.5. table 4.10 concrete slump value with mixture of corn corn + sikament nn using cement water factor 0.51. based on the results of the research data in table 4.10 a graph can be made as shown in fig 4.2. from fig. 4.2 it can be seen that the addition of 0.25% of nn to the weight of cement has a large effect on the concrete stress. can be seen in normal concrete without a mixture of corn stalk ash obtained slump value becomes very high beyond the normal limit, while for concrete with a mixture of 10% ash which previously has a value under the condition after given sikament nn has a slump value according to the requirements, namely 60 <96.7 <180. dewi, s.h. et al/ jgeet vol 04 no 03/2019 213 fig. 4.3 graph relationship percentage of corn rod + sikament nn to slump value. 4.9 results of concrete press strength analysis the concrete compressive strength test was carried out after the curing period of the 28-day old specimen, for each stirring of normal concrete and concrete with a mixture of corn stalk ash both with an additional 0.25% sikament nn to the weight of the cement and without sikament nn. table 4.12 strong concrete press test results with a mixture of corn rod corn. based on the results of research data in table 4.11 graphs can be made as shown in 4.3. fig. 4.4 relationship of percentage of corn stems against concrete compressive strength without sikament nn. each compressive strength is carried out at 28 days. it can be seen that the higher the percentage of the use of corn stalk ash, the higher the compressive strength obtained, but when the use of corn stalk ash is 10% the compressive strength decreases. can be seen in the graph that the compressive strength reaches the maximum value in the mixture of 8% corn stalk ash, and decreases again at 10%. this proves that the level of silica in 10% corn cannot replace the role of 10% cement in a concrete mixture. table 4.13 concrete press strength test results with mixture of corn corn + sikament nn. based on the results of research data in table 4.12 graphs can be made as shown in fig. 4.4. fig. 4.5 relation of percentage of corn stem ash to concrete strength + sikament nn. each compressive strength test was carried out at 28 days. it can be seen in the graph that the addition of 0.25 percent of nn to the weight of cement does not affect the concrete compressive strength. based on the graph the higher the percentage of the use of corn stalk ash, the higher the compressive strength obtained, but when the use of corn stalk ash 10% press decreased again. in table 4.12 the compressive strength of concrete reaches the maximum value also found in the mixture of 8% corn stalk ash which is 20.4 mpa, and has decreased again at 10%, which is 18.4 mpa. fig. 4.6 relationship of percentage of corn mixture concrete concrete without sikament nn with concrete mixture of corn corn + sikament nn. it can be seen that in the use of corn stalk ash in the concrete mixture using or not using sikament nn, the highest compressive strength was obtained by the 214 dewi, s.h. et al/ jgeet vol 04 no 03/2019 percentage of the use of ash 8%. to be more clear, can be seen in fig. 4.5. based on the picture, we can see that there is an increase in the quality of the percentage of 2% of the mixture of corn stalk ash to reach a maximum of 8% in the mixture of corn stalk ash. here we can see that the silica content possessed by corn can almost react as a substitute for the function of cement at 8%, but experiences a decrease in quality at 10% due to the high level of reduced cement content. however, the optimum value achieved at 8% of the use of corn stalk ash is still not able to reach the compressive strength of the 21 mpa plan. 4.10 results of modulus analysis of concrete elasticity. the testing of concrete elasticity modulus is carried out after the curing period of the 28-day-old test object, testing the elastic modulus is carried out simultaneously when testing the concrete compressive strength. table 4.14 elastiitas concrete modulus test results with a mixture of corn stems based on the results of the research data in table 4.13, a graph can be created like fig. 4.6. fig. 4.7 relationship of percentage of corn stems against modulus of concrete elasticity. it can be seen in fig. 4.6 that the higher the percentage of the use of corn stalk ash, the more rigid the concrete is obtained, but it can be seen in the use of corn stalk ash 10% the level of concrete stiffness decreases. based on the graph of the modulus value, the highest elasticity is found in the mixture of 8% ash, which is 21656.14 mpa and gets a minimum value of 10% mixture, namely 20366.28 mpa. table 4.15 modulus of concrete elasticity test results with mixture of corn corn + sikament nn. based on the results of the research data in table 4.14 graphs can be made as shown in 4.7. can be seen in the graph, the mixture of corn stalk ash with the addition of 0.25% sikament nn to the weight of cement has increased stiffness from the level of use of corn stalk ash 2% to 8% use of corn stalk ash, but the stiffness of concrete decreased on the use of corn stalk ash of 10 %. from this it can be seen that the optimum use of corn corn stem ash is at the level of 8%. based on the graph of the modulus value, the highest elasticity is found in the percentage of mixture of 8%, which is 21607.52 mpa and the minimum value is at the percentage of 10%, namely 20568.59 mpa. from table 4.13 and table 4.14 it can be seen that the use of sikament nn does not affect the modulus of elasticity of concrete. 4.11 research comparative results with previous researchers previous research that will be compared with this research is chandra (2013). the research that the authors do is that there are differences in the type of ash and the percentage of ash use, where previous researchers used corn cobs with a percentage level of 4%, 8%, and 12%. in addition there are differences where the previous researcher conducted a test of the strength of pressure and modulus of elasticity while testing this for compressive strength and modulus of elasticity. based on that, a comparison is made to test the concrete elastic modulus as in table 4.15. table 4.16 research comparative results with previous researchers. in this study and previous research (chandra, 2013) have differences in the quality of plans and materials used. the results of modulus of elasticity analysis in this study showed the highest value was found in the dewi, s.h. et al/ jgeet vol 04 no 03/2019 215 percentage of 8% use of corn stalk ash, namely 21656.14 mpa and decreased in the percentage of use of corn stalk ash 10%, whereas the analysis of modulus of elasticity in previous studies (chandra, 2013) the highest value was found in the percentage of 8% corn weevil ash use which was 24407.83 mpa and decreased in the percentage of use of corn weed ash 12%, it can be concluded from the results of this study with previous research (chandra, 2013) that the percentage of use of corn ash is good corn as well as corn stalk ash reached the maximum modulus of elasticity at 8%. 5. conclusions and suggestions 5.1 conclusions • based on the research, the higher the percentage of corn stalk use as a substitute for cement, the higher the compressive strength obtained, but the use of corn stalk ash 10% compressive strength decreased. can be seen in the use of 8% corn stalk ash concrete strength of 20.8 mpa and the use of 10% corn stalk ash compressive strength of 18.2 mpa. the silica content possessed by new corn can almost react as a function of cement at 8%, but experiences a decrease in quality at 10% due to too high levels of reduced cement content. it can be seen that the optimum level of use of corn stalk ash as a partial substitute for cement is at 8%. • based on research, the stiffness of concrete increased from the use of 2% corn stalk ash to 8% use of corn stalk ash, but decreased stiffness in the use of 10% corn stalk ash. can be seen in the use of 8% corn stems obtained modulus of elasticity of 21,656.14 mpa and the use of 10% of corn stalks obtained modulus elasticity value of 20,366.28 mpa. • the optimum compressive strength in this study was reached at the percentage mixture of 8%, with a compressive strength of 20.8 mpa. • it can be seen that corn stalk ash can replace the role of part of cement in a concrete mixture with a level of use of 8% corn stalk ash. 5.2 suggestions • further research is needed using corn stalk ash using a percentage level of between 7% and 9%. • for further research, it is recommended to do a detailed study of the chemical elements of corn stalks in order to determine a good percentage level. fig. 4.8 relationship of percentage of corn stems + sikament nn against modulus of concrete elasticity. 216 dewi, s.h. et al/ jgeet vol 04 no 03/2019 references ahmad, 2017. sifat workability beton ramah lingkungan, tugas akhir, universitas negeri makasar, makasar. antoni dan paul nugraha., 2007. teknologi beton. penerbit c.v andi offset, yogyakarta. chemical admixtures for concre astm standard, usa. buol et.al, 1980. food comotition and analysis, p.122-123,avi publishing, new york chandra, 2013. kajian kuat desak dan modulus elastisitas beton dengan penambahan abu bonggol jagung sebagai zat additive, tugas akhir, universitas atma jaya yogyakarta, yogyakarta. departemen pekerjaan umum, 2005. pedoman awal untuk perkiraan proporsi takaran campuran. dipohusodo, istimawan, 1999. struktur beton bertulang berdasarkan sk sni t-15-1991-03. jakarta: pt. gramedia pustaka utama. ervina, 2013. isolasi silika dari tongkol jagung, tugas akhir, universitas pembangunan nasional, surabaya. juwanto, 2017, pemanfaatan bahan addictive abu batang jagung dan bonggol jagung sebagai bahan tambahan pembuatan beton ringan ramah lingkungan, tugas akhir, universitas semarang, semarang. mulyono, t., 2004. teknologi beton, edisi kedua, andi, yogyakarta. oladipupo, 2012. strength properties of corn cob ash concrete, journal of emerging trends in engineering and applied sciences (jeteas) 3 (2). ramanuddin, 2010, pengaruh kehalusan dan kadar abu sekam padi pada kekuatan beton dengan kuat tekan 50mpa, tugas akhir, institut teknologi nasional bandung, bandung. roesmarkam dan yuwono, 2001. kesuburan dan pemupukan tanah pertanian, pustaka buana, bandung. subakti, 1999. teknologi beton dalam praktek, jurusan teknik sipil, fakultas tenik its, surabaya. samekto, w., 2001. teknologi beton, edisi kelima, kanisius, yogyakarta. sni 03-2834-2000, 2000, tata cara pembuatan rencana campuran beton normal, badan standarisasi nasional. sni 03-2847-2002, 2002, tata cara perhitungan struktur beton untuk bangun gedung, badan standarisasi nasional. sni 03-1974-1990, 1990, metode pengujian kuat tekan beton, badan standarisasi nasional. tjokrodimulyo, kardioyono, 1992. teknologi beton. biro penerbit, yogyakarta. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ 1. introduction 2. literature review 3. research methods 4. results and discussion 4.1 results of fine aggregate examination 4.2 results of rough aggregate examination 4.3 inspection of specific gravity and material absorption. 4.4 results of checking mud levels 4.5 results of water content checks 4.6 content weight check results 4.7 results of concrete mixing inspections (sk sni 03-2834-2000) 4.8 results and analysis of concrete slump values 4.9 results of concrete press strength analysis 4.10 results of modulus analysis of concrete elasticity. 4.11 research comparative results with previous researchers 5. conclusions and suggestions 5.1 conclusions 5.2 suggestions references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 210 the coherency and correlation between sea surface temperature and wind velocity in malacca strait: cross wavelet transform and wavelet coherency application hanah khoirunnisa 1, *, ulung jantama wisha 2 , muhammad zainuddin lubis 1 1 geomatics engineering department, state polytechnics of batam 2 research institute for coastal resources and vulnerability, ministry of marine affairs and fisheries * corresponding author : hanah.khoirunnisa@gmail.com tel.:+81-72-867-1686; fax: +81-72-867-1658 received: aug 1, 2017. revised : aug 15, 2017, accepted: aug 29, 2017, published: 1 sept 2017 doi : 10.24273/jgeet.2017.2.3.590 abstract this study tried to observe the correlation and coherency between sea surface temperature (sst) and wind velocity in the malacca strait at the year of 2015. the sst and wind velocity data with 6 hours interval step have been used in this study. s-transform, the cross wavelet transform, and the wavelet coherency were applied to observe the influence of the variation of sea surface temperature to the wind velocity in malacca strait. these methods could produce the phase lag and the time of occurrence between them. s-transform was used to show the spectrum energy of the sea surface temperature variation. the strongest correlation between them has the period of 32 days during july to august and october to november at each point with significance level of 95 %. the coherency of them has the range of 4 to 64 days at each point. the last result is the spectrum energy of sst variation that has the period of 5 to 50 days at each point. it was similar to the result of the correlation and coherence period between the wind velocity and the sst data. keywords: sea surface temperature, malacca strait, wind velocity, coherency, correlation. 1. introduction the malacca strait has been located in the coordinate of 96 to 106 e and 2 n to 8 s. it is directly connected to andaman sea and indian ocean (amiruddin et al., 2011). the indian ocean climate has influence to the malacca strait climate. monsoonal condition is the potential thing to affect the northern indian ocean condition (tomzcak, 2001). instead of that, the monsoonal condition can be shown by the wind reversing in two times a year, and also there are two conditions of monsoon climate, northeast monsoon (winter monsoon) and southwest monsoon (summer monsoon) (wyrtki, 1961; rao and sivakumar, 2000; and susanto et al., 2001). in the indian ocean, asian monsoon intensity has also influenced to control the basin-margin instability (lin et al., 2010). the malacca strait has been affected by the seasonal conditional. these were northeast monsoon and southwest monsoon (hii et al., 2006). it affect to several parameters in the malacca strait. the temperature and salinity in the malacca strait have the lowest condition at the winter monsoon and highest condition during summer monsoon (peralta and yusoff, 2014). in addition, the malacca strait has the shallow bathymetry. it was an average of 53.38 m (hii et al., 2006). and also, the malacca strait water mass has been influenced by the rivers in the west sumatra and west coast of peninsular malaysia (chua et al., 1997; hii et al., 2006; amiruddin et al., 2011). the water mass of the malacca strait has been moving southwesterly towards to the indonesian seas during southwest monsoon (amiruddin et al., 2011 and hii et al., 2006). in this study, we show an analysis about the variation and correlation of the sea surface temperature (sst) and wind velocity in the year of 2015 in the malacca strait. importantly, we also considered the influence of monsoonal condition. we also quantify the phase lag between them using cross wavelet transform and wavelet coherency. to show the variation of sst in malacca strait we were using the s-transform method. in addition, using these methods, we can identify the dominant period and its variation. 2. data and method this research used the gridded reanalysis era interim daily sst and wind velocity data in the malacca strait area in the year of 2015 by six hourlies interval step. they have the resolution as big as 0.125 o and 0.5 o , and it was downloaded by european centre for medium-range weather forecasts (ecmwf) in the region of 8 o n 2 o s and 96 o e 106 o e. it would be processed by the methods mailto:hanah.khoirunnisa@gmail.com khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 211 of s-transform to observe the dominant period of sea surface temperature, ocean data view as a visual analytic, cross wavelet transform, and wavelet coherency by morlet wavelet with significance level 95 % (grinsted et al., 2004). 2.1 s-transform the first method to observe the dominant period of sst is the s-transform. it was a window variable from short time fourier transform (stft) or it would be extension from wavelet transform (wt) (wang, 2010). the time series spectrum component could be shown by the fourier transform and only contains the information about the time series spectrum distribution at different frequencies. wavelet transform either to extract the data information in time and frequency domains. however, the wavelet transform is sensitive to noise. equation 1 shows the correlation between s-transform and stft. the stft equation to h(t) signal is shown in the below: 𝑆𝑇𝐹𝑇(𝜏, 𝑓) = ∫ ℎ(𝑡)𝑔(𝜏 − 𝑡)𝑒−𝑗2𝜋𝑓𝑡 𝑑𝑡 ∞ −∞ (1) where: 𝜏 : spectrum localization time 𝑓 : fourier frequency 𝑔(𝑡) : window function changing 𝑔(𝑡) value is the one of the way to determine s-transform with the gaussian function, such as: 𝑔(𝑡) = |𝑓| √2𝜋 𝑒 𝑡 2𝑓2 2 (2) from the equation 1 and 2, can be identified to stransform and it becomes the equation 3: 𝑆(𝜏, 𝑓) = 𝑆𝑇𝐹𝑇(𝜏, 𝑓) = ∫ ℎ(𝑡) |𝑓| √2𝜋 𝑒 (𝜏−𝑡)2𝑓2 2 𝑒−𝑗2𝜋𝑓𝑡 𝑑𝑡 ∞ −∞ (3) in the other words, the s-transform is the other form of stft with gaussian window. 2.2 wavelet coherence using wavelet coherence, the highest coherence between the correlated time series data can be observed in the time-frequency domain. torrence and webster (1998) in grinsted et al. (2004) have formulated the equations for the wavelet coherency as follows:             2 1 2 1 2 1 2 )(.)( ))(( )( swssswss swss sr y n x n xy n n (4) using s as a smoothing operator and its equation become: )))((()( swssws ntimescale  (5) the sscale is the notation of the smoothing along the wavelet scale and times is the smoothing in time. the smoothing operator which suitable to morlet wavelet as follows: s x t nstime cswws           2 2 2 1 *)()( ,   nnstime scswws )6,0(*)()( 2  (6) whereas 1 c and 2 c are used to normalization. using numerical method is one of the way to determine the normalization coefficient. to determine the confident level of wavelet coherence can be solved by monte carlo method. the squared of coherence is used to estimate the frequency. it has the range between 0 and 1 to indicate the correspondent of 𝑥 and 𝑦 value. the squared of coherence can be arranged as follows: )()( )( )( 2 fpfp fp fc yyxx xy xy  (7) whereas the )( fp xx and )( fp yy are the power spectral density of x and y data, and also the )( fp xy is the cross power spectral density of x and y data. 2.3 cross wavelet transform morlet wavelet shows a good relation between time and frequency localization. cross wavelet transform is the result of a band pass filter of a time series data (grinsted et al., 2004). the formulation for cross wavelet transform can be written as follows: ])'[(0)( 1' ' s t nnx s t sw n n n x n       (8) the )(sw x n value is a local phase and 2)(sw x n is a wavelet power. cross wavelet transform correlate two time series data, whereas can be defined as: *yxxy www  (9) so we can define which the value of xyw is a cross wavelet power and the value of xyw can be interpreted as a local relative phase between the value of nx and ny at time frequency domain. to determine the influence of the wind velocity to sst distribution, we decided to choose 3 sampling points, that is quite represent the research area, they are a, b, c point (fig.1). point a is located between northern of lhokseumawe and langkawi 212 khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 island, these point is still under the big influence from andaman sea, point b is located between eastern waters of medan and western of malaysia, and point c is located between bagansiapiapi waters and western of kuala lumpur, the coordinates of point a, b and c are shown at table 1. fig. 1. study area in malacca strait with a, b, and c point. table 1 sampling point coordinates point longitude latitude a 6 o 97 o b 4 o 99 o c 2 o 101 o 3. result and discussion 3.1 the variation of sea surface temperature and wind velocity fig 2. shows that the sst variation in the straits changed seasonally. in january, the highest temperature has the value of 303.36 k or 30.21 o c, whereas the highest temperature value in july is 304.28 k or 31.18 o c. it shows the sst is lower when the western monsoon (december-february) than the eastern monsoon (june to august). the condition of sst is depended on monsoon cycles, the change of monsoon is quietly influence the sst condition in malacca strait, specifically the change of the wind speed and direction significantly affect the distribution of sst that is come from heat waste and solar heating intensity, sst in the malacca strait is transported by the wind, surface current, wave, tide and the other physical factors (syamsul et al., 2012). the change of stt value in every monsoon condition is not too significant ± 1 o c (table 2). table 2. the maximum value of sst monsoon range of sst ( o c) northeast monsoon 31.18 33.06 northwest monsoon 31.51 34.29 southwest monsoon 32.20 34.14 southeast monsoon 30.81 33.58 fig 2. spatial sst distribution in the malacca strait (a) northeast monsoon (b) northwest monsoon (c) southwest monsoon (d) southeast monsoon. khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 213 fig. 3. spatial wind velocity distribution in the malacca strait (a) northeast monsoon (b) northwest monsoon (c) southwest monsoon (d) southeast monsoon fig. 4. the sst energy spectrum on the a, b, c point in the malacca strait using s-transform during 2015. 214 khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 table 3. the maximum value of wind velocity monsoon range of wind velocity (m/s) northwest monsoon 0.05 10.84 northeast monsoon 0.03 9.22 southeast monsoon 0.03 10.09 southwest monsoon 0.05 9.15 it suggests that seasonal factor affected the variation of sst in the malacca strait. the result of s-transform shows the variation of 5-50 days in sst at points a, b, and c does exist (fig 3). susanto (2000) said that the intra-seasonal variations have the period of 35 to 90 days. the influence of seasonal factors can also be seen from the changes in the malacca strait wind speed at different seasons. during western monsoon (december to february), the wind velocity in the southern of malacca strait is higher than the wind velocity in the northern of malacca strait. meanwhile, during the southeast monsoon, the condition of wind velocity in the southern of malacca strait is lower than the wind velocity in the northern malacca strait (fig 3). it shows that the wind velocity condition in the malacca strait is affected by monsoon conditions. based on table 3, during the eastern monsoon, the wind velocity has the highest condition, such as 13 m/s. it shows that the sst has the correlation to the wind velocity. 3.2 the correlation between the wind velocity and the sst fig 4. indicated that the correlation between sst and wind velocity has a period of 4-64 days at the points of a, b, and c. the strongest correlation occurred in july-august and october-november with a period of 32 days. these results are consistent with a dominant period of sst, which is 50 days. it proves that the variation of sst has influenced by wind velocity. the arrow indicates the phase lag between wind velocity and sst. in fig 5. is shown that the wind velocity and sst has a phase lag as long as 18 days in july-august and october-november at point c. while at points a and b, the wind velocity has a phase lag of 8 and 24 days. grinsted (2004) said that the calculation of the correlation between wind velocity and sst using cross wavelet coherency has a significance level greater than 95%. fig. 5. the correlation between the sst and wind velocity at the points of a, b, and c in the malacca strait using cross wavelet transform. khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 215 fig 6. the coherence of sst and wind velocity at the points of a, b, and c in the malacca strait using the wavelet coherency. 3.3 the coherence between the wind velocity and sst in the malacca strait fig 1. showed that the points of a, b, and c are the sample to observe the correlation and coherence of wind speed and sst. this study proves the coherence between the wind velocity and sst (fig 6). figure 6 provided the coherence between wind velocity and sst, it has the period of 4-64 days at the points of a, b, and c. these results illustrate that the sst variations with a period of 4-64 days is influenced by wind velocity. this proves that the intra-seasonal variation of the sst in the malacca strait is influenced by the local wind velocity. 4. conclusion the sst data in the malacca strait have a correlation and coherence to the wind velocity. it correlation has a period of 4-64 days. in addition, the strongest correlation occurred in july-august and october-november with a period of 32 days, and its confidence level is greater than 95%. the wind velocity and sst in the malacca strait has a phase lag of 8-24 days. in addition, there was a coherency between the wind velocity and the sst data with a period of 4-64 days at the points of a, b, and c in july-august and october-november. these correlation and coherence have a similar period with the variation of sst, i.e. 5-50 days. it should be the intra-seasonal variation. the strongest energy spectrum of sst occurred in july-august and october-november. it suggests that the intraseasonal sst variation (35-90 days) affected the wind velocity. 5. acknowledgment the authors gratefully acknowledge to the european centre for medium-range weather forecasts (ecmwf) since provided us the research data. so we had finished our research. references amiruddin a. m., z. z. ibrahim, and s. a. ismail. 2011. water mass characteristics in the strait of malacca using ocean data view. research journal of environmental sciences, 5(1):49-58. chua, t.e., s.a. ross and h. yu, 1997. malacca straits environmental profile. mpp-eas technical report 10. imo., quezon city, philipines, pp: 259. hii s. y., a. t. law, n. a. m. shazili, m. k. abdul rashid, h. mohd lokman, f. m. yusoff, and h. m. 216 khoirunnisa. h., wisha, u., and lubis m.z.,/ jgeet vol 02 no 03/2017 ibrahim. 2006. the straits of malacca: hydrological parameters, biochemical oxygen deman and total suspended solids. journal of sustainability science and management, 1(1):114. lin, y. n., k. sieh, and j. stock. 2010. submarine landslides along the malacca strait-mergui basin shelf margin: insights from sequencestratigraphic analysis. journal of geophysical research, 115: b12102. susanto, d. r., a. l. gordon, and q. zheng. 2001. upwelling along the coasts of java and sumatra and its relation to enso. geophysical research letters, 28: 1599 1602. grinsted, a., j. c. moore, and s. jevrejeva. 2004. application of the cross wavelet transform and wavelet coherence to geophysical time series. nonlinear processes in geophysics, 11: 561 566. rao, r. r. and r. sivakumar. 2000. seasonal variability of near-surface thermal structure and heat budget of the mixed layer of the tropical indian ocean from a new global ocean temperature climatology. journal of geophysical research, 105:995-1015. syamsul, r., d. peter, w. mulyadi, s. jurgen, i. yopie, i. taufiq, m. muhammad. 2012. general circulation in the malacca strait and andaman sea: a numerical model study. american journal of environmental sciences. 8(5): 479-488. tomczak, m., dan j. s. godfrey. 2001. regional oceanography: an introduction. permagon. tarrytown. new york. wang, y. h. 2010. the tutorial: s-transform. national taiwan university. roc. wyrtki, k. 1961. physical oceanography of the south-east asian waters. naga report 2. univ. calif scripps inst. ocean., la jolla, pp. 62-91. amiruddin chua 50339_b hii lin susanto grinsted rao syamsul tomczak wang wyrtki http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 alif, s.m., et al./ jgeet vol 5 no 3/2020 143 research article association between surface air temperature and land use on the campus scale satrio muhammad alif 1*, erwin yosua1 , adam irwansyah fauzi1 , bambang edhi leksono2 1department of geomatics engineering, institut teknologi sumatera, lampung, indonesia 2department of geodesy and geomatics engineering, institut teknologi bandung, bandung, indonesia. * corresponding author : satrio.muhammad@gt.itera.ac.id tel.:+62-818-0952-4852 received: june 25, 2020; accepted: august 13, 2020. doi: 10.25299/jgeet.2020.5.3.5187 abstract the increasing trend of global temperature is related to the land use change in the form of urbanization. the impact of land use change to surface air temperature in indonesia especially in smaller scope in indonesia have not researched yet. the study area is located on newly built campus and the development of land use change inside campus can be managed carefully. this research aim is to determine which land use affecting high-temperature by using multiple linear regression method with least square approach so that temperature increase can be controlled in which some land uses must be preserved in urbanization. land use data is interpreted from the photo map of 275 hectare campus. temperature data is measured by using the digital thermometer three times a day. the method idea is to obtain distinctive contribution of every land use to every temperature measurement point. the contribution follows the inverse distance weighted concept. surface air temperature measurement points are located with 150 meter interval and centroids of land use polygons are used for association calculation. temperature measurement shows values between 25.5oc and 35.4oc. land use with more anthropogenic activities and rubber plantation are the top contributors to high surface air temperature within a day. in the non-built-up land use category, water body increases the temperature in the daytime. anthropogenic activities and vegetation density within land use is the main factor in increasing the surface air temperature so that it is suggested to plant farm-like vegetation around every built-up land use. keywords: temperature, land use, multiple linear regression, least square 1. introduction surface air temperature which is temperature of the air near the surface of the earth shows increasing trends globally over the years (jones et al., 1999; shrestha et al., 2017; foster et al., 2017). the temperature increase can be significantly measured in global scale (hansen et al., 2006), country scale (li et al., 2020; fujibe, 2009; domroes and eltantawi, 2005; tang et al., 2010), or a city scale (rahman, 2011; ludwig et al., 2004; martinez-austria et al., 2016; sharovsky et al., 2004). the factors that affect the temperature are latitude, surface type, elevation, relationship to large bodies of water, and cloud cover (ackerman and knox, 2006). the temperature increase is affected by the change of those factors. in a smaller scale, one of the factors that lead to the temperature increase is surface type or land use (baldocchi and ma, 2013), vegetation characteristics, building spatial distribution, and surface material (bonan, 2000; stone and norman, 2006; middel et al., 2014). land use change — highly associated with urbanization (dadashpoor et al., 2019; alphan, 2003) — affect the temperature increase (kalnay and cai, 2003). it is associated with how well the land use or surface type in absorbing or reflecting solar energy such as grassland absorbs more energy than aluminium–based building which affects the temperature (frick and suskiyatno, 1998). the example of country with high urbanization is indonesia (equatorial region). the high intensity of urbanization in indonesia (rahmawati, 2020) affects the land use change and increase the temperature. the land use changes due to urbanization in indonesia are researched in many area such as banten (saifullah et al., 2017), central sulawesi (veldkamp et al., 2009), and jakarta (hutabarat, 2010). the association between surface air temperature and land use have been researched in global scale (rasul, 2020), country scale (yang et al., 2009; deng et al., 2015a; sadiqkhan et al., 2020; saavedra et al., 2020), and city scale (amorim et al., 2020; dissanayake, 2020). most of the researches involve large area (over 1000 hectare) and the temperature sampling method is in sparse interval. moreover, the specific impact of land use change to surface air temperature especially in indonesia have not researched yet. this research focuses on association between land use and temperature on the campus scale in indonesia the area of campus is 275 hectare (fig. 1) and it is good location to be researched since the campus is newly built campus (institut teknologi sumatera, 2013; alif et al., 2019a; alif et al., 2018) and the development of land use change inside campus can be managed carefully based the result of this research. smaller area means the sampling method is not sparse and factors that affect the temperature beside land use and elevation are neglected. this research aim is to determine which land use affecting high-temperature by using multiple linear regression method with least square http://journal.uir.ac.id/index.php/jgeet 144 alif, s.m., et al./ jgeet vol 5 no 3/2020 approach so that temperature increase can be controlled in which some land uses must be preserved in urbanization. (a) (b) (c) fig. 1. research location delineated by red lines (c) and is shown by red rectangle in (a) and (b). black lines connect figure (a), (b), and (c). 2. temperature and land use data land use data is interpreted from the photo map of 275 hectare campus. the the photo map is obtained from the photogrammetry measurement in 2019. the the photo map has 4.8 cm accuracy in 1:1000 scales. land use is interpreted visually using nine interpretation keys (hodgson et al., 2007) as follows: pattern, tone, texture, shadow, site, shape, size, association, and resolution). the classification is based on sni of land use classification (badan standardisasi nasional, 2014) resulting in 10 kinds of land use found on the area, delineated by polygons,and validated directly on site. those land uses are public facilities (canteen, sports field, and clinic), student and lecturer dormitory, classroom building, settlement, road network, vacant land, farm, rubber plantation, paddy field, and water body. the validation is conducted on every land use resulted in 91% overall accuracy. fig. 2. the digital thermometer used to measure surface air temperature. temperature data is measured by using the digital thermometer three times a day (fig. 2). the thermometer has a resolution 0.1oc and can measure temperature from -10oc until 50oc. the temperature is measured on april 11th, 2019 in monsoon transition (chang et al., 2005) with partly cloudy weather. the temperature is measured in the morning (06.30-07.30), noon (12.00-13.00), and afternoon (16.00-17.00) due to fluctuation of temperature in a single day (lakitan, 2002). the temperature is measured on point called in this research as temperature measurement points (tmp). elevation data is obtained from the digital elevation model processing resulted from campus the photo map. the elevation has 3 meter resolution with geoid as vertical datum. the elevation is classified into three classes (di gregorio, 2005; alif et al., 2019b): low, medium, and high. the elevation is taken into account as the other factor affecting surface air temperature besides land use. 3. association calculation method temperature data are overlaid with either land use data or elevation data to understand association among the parameters. the method idea is to obtain distinctive contribution of either every land use or every elevation class to every tmp. the contribution follows the inverse distance weighted concept (lu and wong, 2008) – the further the particular land use to the tmp, the less contribution the particular land use to the temperature on tmp. surface air temperature measurement points are located with 150 meter interval and centroids of land use polygons are used for association calculation. the numbers of tmp are 72 points based on number of minimum sample point formula for map with 1:1000 scales (badan informasi geospasial, 2014). the distribution of tmps is shown on fig. 3.there are total 99 land use points (lup) for association calculation derived from centroid of every land use polygons. the point samples of every elevation class (ecp) are located in ~150 meter interval and the number for every class depends on the area of every class. there are a total of 41 ecps used for association calculation. association calculation is conducted by applying distance from either lup or ecp to tmp into multiple linear regression method. the distance is twodimensional euclidean distance (johnson and wichern, 2002) by using universal transverse mercator coordinates of points as input. the distance is calculated from every tmp to every either lup or ecp. the distance value is used in multiple linear regression calculation. 400 m alif, s.m., et al./ jgeet vol 5 no 3/2020 145 fig 3. surface air temperature measurement point shown by orange dots. number mark close to every dot is the number of the measurement points. multiple linear regression method using least square approach is started by completing the mathematical equation of multiple linear regressions as shown on eqn. 1 (kahar, 2007). least square approach is usually used in calculating reference frame for topography mapping (kahar, 2007), statistics (pratomo and astuti, 2015), meteorology (estiningtyas and wigena, 2011), and transportation (cong et al., 2016; kresnanto, 2010; alif and silaen, 2020). least square approach is also used in surface air temperature or land use related research (kalota, 2017; marchetti et al., 2015; deng et al., 2015b; untari, 2012). 𝑎0+ 𝑎1𝑥11+ 𝑎2𝑥12+ 𝑎3𝑥13+ ... + 𝑎𝑢 𝑥1𝑢 = 𝑓1 𝑎0 + 𝑎1𝑥21 + 𝑎2𝑥22 + 𝑎3𝑥23+ ... + 𝑎𝑢𝑥2𝑢 = 𝑓2(1) ⁞ 𝑎0+ 𝑎1𝑥𝑛1+ 𝑎2𝑥𝑛2+ 𝑎3𝑥𝑛3 + ... + 𝑎𝑢 𝑥𝑛𝑢 = 𝑓𝑛 where a is association parameter of tmp and either lup or ecp which is the only independent variable in the equation, u is the number of either lup or ecp used in the equation, n is the number of tmp or equation used which is 72 equations, x is the inversion of distance between tmp and either lup or ecp, and f is the value of surface air temperature on every tmp. one mathematical equation from eqn. 1 describes one tmp which is the quantification of surface air temperature value and inversion of distance between tmp and either lup or ecp. eqn. 1or association calculation formula is used 11 times: one to calculate the association between temperature and elevation, 10 times to calculate association between temperature and every land use. the equation with those data can be calculated since the unknown parameters are always less than the known measurements (kahar, 2007) or 72 data. the association parameters of land use polygons are averaged to obtain the association parameter of land use. the association parameter of tmp and every land use compared with each other to understand the contribution of land use location to the temperature. eqn. 1 can be solved by converting the equation into matrices in eqn. 2 and the matrices are calculated in eqn. 3. b = [ 1 𝑥11 ⋯ 𝑥1𝑢 ⋮ ⋮ ⋱ ⋮ 1 𝑥𝑛1 ⋯ 𝑥𝑛𝑢 ] 𝐴= [ 𝑎1 ⋮ 𝑎𝑢 ]f = [ 𝑓1 ⋮ 𝑓𝑛 ](2) 𝐴 = (𝐵 𝑇 b) ‾¹𝐵 𝑇 f (3) where b is design matrix in multiple linear regressions, f is surface air temperature value matrix, and a is association parameter matrix used to understand the association between surface air temperature and either land use or elevation. 4. result and discussion land use polygon (fig. 4) and elevation class (fig. 5) are determined and validated before association calculation. the dominant land use in the area is farm and vacant land. the high elevation class in the area is located on the northwest which is dominated by farm and classroom building land use. fig. 4. land use polygon is shown by various colors with the legend inside the figure. before understanding the association between surface air temperature and land use, the contribution of elevation to the temperature is calculated. in a larger scale, the temperature is decreasing with height (anthony, 2015). from this research result with campus scale, it can be inferred that elevation is not on the line with the theory. in the morning, a high elevation class is the lowest contributor to the high-temperature. in the noon, low elevation class is the lowest contributor to the high-temperature. in the afternoon, the high elevation class is the lowest contributor to the high-temperature. temperature measurement in the morning shows values between 25.5oc and 26.1oc with the highest value located on the northern side of the campus. the area is close to the main road network connecting toll road entrance and the city. it is suggested that the traffic on 146 alif, s.m., et al./ jgeet vol 5 no 3/2020 the road contributes more to the highest temperature in the morning. the other area with high-temperature is located close to the southwest water body. on the contrary, the area with the lowest temperature located in central-eastern and which is on farm and rubber plantation land use with less anthropogenic activities in the morning. fig. 5. elevation class is shown by various colors with the legend inside the figure. red lines show the boundary of the campus. land use with the highest contribution to the temperature in the morning from the calculation is settlement. the contribution percentage of surface air temperature is shown in table 1. besides traffic that contributes more to the highest temperature, other land uses with anthropogenic activities contribute more than road networks which are: settlement, dormitory, public facilities. it is suggested that in the morning anthropogenic activities in those land uses especially settlement are more than anthropogenic activities in road network. top five high-temperature contributors in the morning are land uses with anthropogenic activities while the top six high-temperature contributors relatively have little vegetation. it is in line with the bottom four high-temperature contributors are land uses with relatively having much vegetation. table 1 contribution of land use to the surface air temperature in the morning rank land use percentage (%) 1 settlement 22.2 2 dormitory 22.1 3 public facilities 15.1 4 road network 12.3 5 classroom building 7.1 6 water body 6.7 7 vacant land 5.6 8 rubber plantation 4.2 9 paddy field 3.3 10 farm 1.4 temperature measurement in the noon shows values between 33.8oc and 35.4oc with the highest value located in the southwestern side of the campus close to the southwest water body. the location has various land uses that have little vegetation such as settlement, road network, water body, and vacant land. it is suggested in the southwest water body, the temperature of the solar is reflected by the water and increase the temperature of its surrounding, moreover, the land uses surrounding it relatively has little vegetation. on the contrary, the area with the lowest temperature located in the most north of campus in farm land use. it is highly suggested the absorption of solar energy at the noon in farm land use (frick and suskiyatno, 1998) is related to the temperature. land use with the highest contribution to the temperature in the noon from the calculation is dormitory. the contribution percentage of surface air temperature is shown in table 2. the typical land uses that contribute more to high-temperature in noon resembles morning results which are land uses with more anthropogenic activities except one thing. rubber plantation which contributes less in the morning contributes more to high-temperature more than public facilities and classroom building. it means — unlike the other vegetation — the vegetation in rubber plantation give bad impact on the local environment (majumder et al., 2014). the road network in the noon contributes more than itself in the morning. it is suggested that the traffic at the noon is more than the traffic in the morning including road network inside campus, especially road close to the southwest water body. water body contributes more than classroom building since it reflects solar energy into the surroundings. farm and paddy field is still the bottom two high-temperature contributors. temperature measurement in the afternoon shows values between 29.4oc and 30.3oc with the highest value located in the southwestern side of the campus close to the southwest water body similar to measurement in the noon. table 2 contribution of land use to the surface air temperature in the noon rank land use percentage (%) 1 dormitory 23.8 2 settlement 17.3 3 road network 15.2 4 rubber plantation 15.1 5 public facilities 9.0 6 water body 6.0 7 classroom building 5.8 8 vacant land 3.8 9 paddy field 2.3 10 farm 1.7 the other area with high-temperature is located east side of the campus in rubber plantation land use. on the contrary, the area with the lowest temperature scattered inside the campus which is mostly on farm land use with less anthropogenic activities in the afternoon. land use with the highest contribution to the temperature in the afternoon from the calculation is settlement. the contribution percentage of surface air temperature is shown in table 3. the land uses with more anthropogenic activities plus rubber plantation are the top six high-temperature contributors. moreover, rubber plantation bad impact on the local environment in the afternoon worse than its impact in the noon. water body land use in the afternoon contributes less than itself in the noon. table 3. contribution of land use to the surface air temperature in the afternoon alif, s.m., et al./ jgeet vol 5 no 3/2020 147 rank land use percentage (%) 1 settlement 23.3 2 rubber plantation 17.4 3 dormitory 16.7 4 road network 14.7 5 public facilities 10.8 6 classroom building 6.9 7 water body 4.2 8 vacant land 2.3 9 paddy field 2.1 10 farm 1.6 in a day, land use with more anthropogenic activities and rubber plantation are the top contributors to hightemperature in campus scale. the rank difference of those land uses from morning to afternoon is shown in fig. 6. built-up land use with more anthropogenic activities and less vegetation are the top contributors to high-temperature in all-time as well as rubber plantation in noon and afternoon. class building is the least contributor among built-up land use while water body is the biggest contributor after rubber plantation among non-built-up land use. it reflects the sunlight especially the one close to temperature highest peak hour (between noon and afternoon) (lakitan, 2002) and increases the temperature of its surrounding. settlement contributes more than dormitory at all times except at the noon. road network contribution to hightemperature depends on the traffic (ha et al., 2020). the traffic is less in the morning and more in the noon and the afternoon (alif and silaen, 2020) in the same boat with the road network ranking in all day. fig. 6. land use contributor rank to high-temperature in three measurement periods with legend inside the figure. built-up land use contributes to high surface air temperature depends on anthropogenic activities and its vegetation density (fauzi et al., 2019). it confirms that residential areas are the top contributors to hightemperature (ha et al., 2020). in brief, the built-up land uses have strong positive correlation with surface air temperature (rasul, 2020). the construction of new build up land use in campus development is suggested to be more vertical development than horizontal development. farm-like vegetation is the best land use to minimize the surface air temperature while water body is one of the worst. farm-like vegetation increase the temperature less than grass-like vegetation (yang et al., 2009). in this research, farm is the least contributor to high-temperature among non-built-up land use. the result confirms that water body increases the temperature in the daytime (ha et al., 2020; saavedra et al., 2020). water body is good in enhancing the beauty of the scenery but is bad in decreasing the surface air temperature. rubber plantation as discussed before is increasing the temperature though it is a type of vegetation. the conversion from non-built land use into build use in campus development will increase the temperature (sadiq khan et al., 2020) and it is suggested to plant more farm-like vegetation around the area without rubber-like vegetation or water body. 5. conclusion land use that contributes the most to hightemperature is settlement in built-up land use category and rubber plantation in the non-built-up land use category. the result is calculated by using multiple linear regression method with least square approach. anthropogenic activities and vegetation density within land use is the main factor in increasing the surface air temperature of its surrounding. in campus development, it is suggested to construct more vertical built-up land use than the horizontal one and plant farm-like vegetation around every built-up land use. this research which focuses on the association between land use and temperature shows the elevation difference on the campus scale does not 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use/cover types in china. science in china series d: earth sciences, 52(8), pp.12071215.doi: 10.1007/s11430-009-0085-0 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 3 2021 putra, d.f. et al./ jgeet vol 6 no 3/2021 131 research article a tracer streamline practice for re-evaluation waterflood pattern to introduce a cyclic water injection scheme dike fitriansyah putra1*, lazuardhy vozika futur 1, mursyidah umar1 1 department of petroleum engineering, islamic university of riau, jl. kaharuddin nasution no.113 pekanbaru 28284, indonesia * corresponding author : dikefp@eng.uir.ac.id tel.: +62-812-987-44099 received: nov 8, 2019; accepted: aug 30, 2021. doi: 10.25299/jgeet.2021.6.3.4064 abstract waterflood introduces in the oil field a couple of years ago. several waterflood schemes have been implemented in the fields to get the best incremental oil, such as peripheral injection, pattern waterflood, and etcetera. many waterflood schemes are not working properly to boost the oil recovery due to unpredicted and unexpected water tide array. then, the tracer practice started to be used for getting a better picture of the transmissibility reservoir as well as the direction of water pathway. this practice honors the parameters, such pressure, water cut, gor, and rates. the streamline modeling is used to map the tracer, and it concludes that the selection of location of the injector should be based on the highest oil recovery achieved. subsequently, the cyclic water injection method is one alternative. apparently, this approach yields a quantify incremental recovery. this research utilizes the pressure different approach to figure out the route of water in the formation. the inter-well tracer technique in this modeling study is a tool to review communication between injectors and producers in the existing pattern. many scenario should be tried to find the best options for the new pattern opportunities. in parallel, a innovative scheme of waterflood technique should be implemented too for escalating oil recovery. the stream pathway observes a new potential of the waterflood scheme. it is called "cyclic injection" scheme. the novelty of this approach is the ability to solve the poor sweep efficiency due to improper pathway of water influx in the oil bearing". keywords: tracer test, cyclic water injection, water-flood, streamlines 1. introduction the possibility of increasing oil productivity in the field is to utilize water injection to displace oil to producers. the water enters the formation and stimulate the production by increasing the amount of oil produced from the field (asadollahi, 2012). unfortunately, under improper pressure maintaining system as well as the higher offtake rate impact the decline of reservoir pressure. the water injection is the most popular method to boost oil production. notwithstanding many characteristics of the reservoir are favorable, there are also some characteristics of the reservoir that are detrimental, such as reservoir heterogeneity, especially the value of high permeability, it reflects poorly on water injection. the very high permeability can disturb the sweeping effect in the waterflood scheme (alhuthali et al., 2007). waterflood conformance control on reservoir heterogeneity is a common challenge in an oil field (thrasher et al., 2016). the study’s aim is to review the existing pattern performance by utilizing the inter-well tracer test as a tool. then, a streamline simulator is used to analyze the tracer test flow path. afterward, we discover the best scenario for the new pattern as well as a new scheme of waterflood to increase oil recovery. this study focuses on selecting the best scenario based on several parameters, including tracer time breakthrough, tracer production concentration, cumulative tracer production, and how the tracer flows in the streamlined model. in the petroleum industry, tracer tests are typically used to evaluate the communication between the injector and producer as well as the reservoir transmisibility. the tracer survey provides a variety of information about the heterogeneity of the reservoir, such as the fluid flow path and conformance problem. the flow path is defined as preferential pathways reservoir fluid to move from one point (injection wells) to the other point in the reservoir (production wells). this path is geologically homogeneous or highly heterogeneous due to layering, thief zones, natural fracturing, faulting, or flow-barriers. that means, it is necessary to establish flow paths using a fluid carrier containing various kinds of tracers (guan et al., 2005). the usefulness of the water injection tracer is to monitor the movement of water based on the assumption that the movement of the tracer reflects the movement of injected water. how true it depends on how closely tracer injection followed by formation water without a significant loss and delay. it depends how good a tracer chemical composition that is facing reservoir property (zemel, 1995), as a rule of thumb, 40% tracer must be produced to ensure the production well-effluent tracer profiles reliable analysis (hao et al., 2011). cyclic water injection (cwi) is a periodic water injection technique. this technique introduced in 1960 and aims to increase production in the field, which has a heterogeneous reservoir (yang et al., 2006). since then, the cyclic water injection has several times applied in some fields in the world, in china, the united states, and russia. those have shown positive results (shchipanov et al., 2008) cwi has a result that is not as good as other eor methods. because of a less incremental recovery when compared with other eor methods, the cwi is considered an advanced waterflood (rublev et al., 2012). cwi as a further development of conventional water injection based on two mechanisms (langdalen, 2014): 1. changing the water injection rate. http://journal.uir.ac.id/index.php/jgeet 132 putra, d.f. et al./ jgeet vol 6 no 3/2021 2. change the water injection pattern. basically, during cyclic water injection, the injection rate introduces alternately between the high rate and the regular rate or the low rate and stop the injection condition. the rate of water injection is directly proportional to the injection pressure. while the injection rate is high, then the pressure reservoir rises accordingly. oppositely, whereas low injection rate into the reservoir cause pressure drops significantly. once cyclic injection takes place, there should be a pressure pulse between the layers (shchipanov et al., 2008) as for some of the advantages of the application of cyclic water injection, including: 1. increase oil production (perez et al., 2014) 2. decrease water cut (perez et al., 2014) almost no cost incurred compared to conventional water injection (shchipanov et al., 2008) cyclic water injection based on two parameters: 1. pressurizing (half-cycle) water injects in high flow rates, and the hydrocarbons produced in the same flow rate. the high flow rate on continuous water injection, the reservoir pressure increase significantly even may exceed the initial reservoir pressure. the increasing of the pressure on the highpressure zone in the high permeability region can push water toward the low permeability region that is not swept yet by the scheme of continuous water injection. 2. depressurizing (half-cycle) water injection stops, the reservoir pressure is steppingdown, and then the water is sweeping away andreplacing hydrocarbons located in the lower permeability region. meanwhile, hydrocarbons that move away is heading from the high permeability zones towards the production wells. 2. methodology the streamline simulation is a numerical modeling that uses an implicit calculation for solving pressure equation as well as an explicit estimation for solving saturation/conservation equation (al-najem et al., 2012). the software simulator is petrel 2017 schlumberger; starting with several input data, then building 3d grid initially. it utilizes the finite difference approximation to derive pressure distribution for generating instantaneous velocity vectors perpendicular to the calculated pressure contours. the streamlines is traced by the velocity at the time of interest under a time varying-velocity (putra et al., 2021). the reservoir model is named plc field. it can be categorized as a vast reservoir with porosity range within 30% to 35%, and the average permeability is 800 md laterally. the current reservoir pressure is 310 bar, and the current temperature reservoir is 74oc. the datum point is in 1850 fttvd ss, and the oil gravity value is within 32-36oapi and gor value of 100 v/v. in this study, six scenarios are evaluated (table 1) and set by using a ratio of 1: 1 and 1: 2. fig 1 to fig 4 show the history matching stage conducted before the tracer streamline (putra, 2007) . fig 1. history matching of oil production (putra, 2007) fig 2. history matching of water production (putra, 2007) putra, d.f. et al./ jgeet vol 6 no 3/2021 133 fig 3. history matching of gas production (putra, 2007) fig 4. history matching of oil cumulative (putra, 2007) table 1. base case and six scenarios in the simulation model of cyclic water injection case injection duration (day) stop injection duration (day) injection rate (sm3) base case continuous 5,220 scenario #1 1 1 10,440 scenario #2 1 2 15,660 scenario #3 7 7 10,440 scenario #4 7 14 15,660 scenario #5 30 30 10,440 scenario #6 30 60 15,660 3. result 3.1 injection wells screening and selection in the plc field, there are two existing water injection wells; those are a-41bwat and a-41. two tracer injection tests conducted to screen the appropriate injector for a cyclic candidate well. a. tracer test in 41bwat in a-41bwat, tracer wn1 with 25.000 ppm concentrations is injected about 5,220 sm3 on july 1st, 2006, and continued until the end of the simulation run. the total tracer produced on production wells a-36 up to 1,816.29 sm3 or 34.795% of the injected tracer volume, a-40 up to 1,163.85 sm3 or 22.296% of the tracer injected, and b-39b is 470.59 sm3 or 9.015% of the injected tracer, the total data of reproduced tracer approximately 66.106% on injection applied to a41bwat. fig shows the flow pattern of a-41bwat toward production wells. if the water injected establishes flow pattern as fig , the water that passes through the flow path towards the a-36 well is 0.42 fraction, the water that passes through the flow path towards the a-40 well is 0.33 fraction, whereas the water passing through a flow path towards b-39b well is 0.25 fraction. fig displays the layout of the wells to a-41bwat as well as their distances. 134 putra, d.f. et al./ jgeet vol 6 no 3/2021 fig 5. tracer production concentration vs time (wn1) fig 6. the flow pattern of wells a-41bwat toward production wells fig 7. layout wells and their distances to the injector (a-41bwat) b. tracer test in a-41 well a-41, it has been injected tracer, wn2 with concentration 25.000 ppm, and volume about 5,220 sm3 on july 1st, 2006 and at the end of the simulation run, how much tracer has reproduced along with hydrocarbons is used as a benchmark to a-41bwat whether this well is worthy for injector that can sweep fluid and raise pressure around the production well. the total tracer produced on producer a-36 up to 1,949.89 sm3 or 37.354% of the tracer injected volume, a-40 is 1,180.546 sm3 or 22.616% of the tracer injected, and b-39b is 442.242 sm3 or 8.472% of the tracer injected, then the total volume tracer reproduced approximately 68.442% of volume injected. fig 9. shows the flow pattern of wells a-41 toward the production well. the water that passes through the flow path putra, d.f. et al./ jgeet vol 6 no 3/2021 135 towards a-36 is 0.45 fraction; the water flow towards a-40 is 0.32 fraction, whereas the water towards b-39b is 0.23 fraction. displays the layout of the wells to a-41 as well as their distances. fig 8. tracer production concentration vs. time (wn2) fig 9. the flow pattern of wells a-41 toward the production well fig 106. layout wells and their distances to the injector (a-41) 3.2 continuous water injection a benchmark between continuous water injection as a base case and water cycle injection as a study case is a comparison tool. the base case is continuous flowing injection at the rate of 5,220 sm3. fig 11 shows that without water injection at 5,220 sm3, reservoir pressure drops by 3.806 bar per year. therefore, it is necessary to perform the water injection to maintain reservoir pressure. fig 12 shows the performance of the production and injection since 2004. this scheme earned total oil and gas production amounted to 6,477,308 sm3 and 828,968,960 sm3, respectively. 136 putra, d.f. et al./ jgeet vol 6 no 3/2021 fig 117. pressure and injection rates base case fig 128. oil, gas, and water production rates field plc (continuous water) 3.3 cyclic water injection it is having selected the candidate injector for the water cycle well, which is a-41. the selection parameter is bottom hole pressure at the injectors when a-41bwat or a-41 serves as the injector. the bottom hole pressure in a-41bwat exceeds the fracture pressure of the formation. it can impact formation damage. fig 13 shows bottom hole pressure in the well a-41bwat reached 450.99 bar, while the fracture pressure of the formation is the plc field first segment is 357.6 bar. it is found in the research conducted by (bale, 2008). oppositely, the a-41 has a bottom hole pressure of 302.18 bar, which is still quite low from the fracture pressure limit. hence a-41 is appropriate and suitable to be the cyclic water injector. fig 139. bottom hole pressure in the well a-41 and a-41bwat (cyclic water injection) putra, d.f. et al./ jgeet vol 6 no 3/2021 137 fig 1410. incremental oil and gas production and watercut decline compare to base-case 3.4 the simulation result for each scenario table 2. displays the scenario with parameters, such as values cumulative oil production, cumulative production of gas, water cut average, and peak values of different bhp. the results table exhibits scenario #4 has a higher value of oil production cumulative and gas production cumulative. oppositely, scenario 4 has a decline water-cut, meanwhile bottom hole pressure at 347.729 bar. it is lower 10 bar than the fracture pressure limit. fig 1410. shows the incremental of oil up to 7.6% and gas up to 10.7%; meanwhile, water decline down to 5.45% from scenario #4. the oil & gas incremental trend of this study is close to the result of the field trial at the oil field of east unity, sudan, in the year 2012. according to research conducted by (musa and ibrahim, 2012) the east unity oil field can provide oil gains incremental within range 2 to 7%. the incremental of gas production is obtained up to 10.68%, while the water-cut drops down to 5.4%. another research has been conducted by (yang et al., 2006) in the gudao field, and the study obtained the water-cut reduction down to 0.2 to 3%. these phenomena show that the cyclic water injection scheme can be an opportunity to improve water-flood field performance. a. the influence of cyclic water injection to the flow rate of oil and gas the cyclic water injection scheme can alter the flow rate of oil and gas as well as the flow path. this phenomenon is impacted by pressurizing and depressurizing phase. the pressurizing phase pushes the water into the zone that has not reached yet by continuous water injection. the depressurizing phase has a reverse flow from the low permeability zone towards the high permeability zone. it impacts oil mobility from the trap sector due to sucking occurrence. indriecty, it improves production withdrawal to the producer. fig 15 show the up and down curves of scenario #4 compared to the base case in terms of oil and gas production. in the pressurizing phase, the production rate goes down because the water sweeps a high permeability zone. meanwhile, in the depressurizing phase, oil flow rate goes up because the reverse flow from the low permeability zone towards the high permeability zone carries residual oil in it. this phenomenon has been stated by (langdalen, 2014) that the increase of oil production in cyclic water flooding is provided within the depressurizing phase. table 2. parameters of oil and gas cumulative, water cut and peak bhp no. the model name oil production cumulative (sm3) gas production cumulative (sm3) water cut average (%) peak bhp (bar) 1 base case 6,476,550 828,900,224 0.954 283.896 2 scenario #1 6,493,495 830,278,336 0.949 301.997 3 scenario #2 6,510,715 831,706,432 0.947 322.526 4 scenario #3 6,542,294 836,500,480 0.943 315.692 5 scenario #4 6,588,822 843,135,168 0.939 347.729 6 scenario #5 6,570,901 846,228,480 0.940 340.375 7 scenario #6 6,587,363 859,280,960 0.939 400.018 fig 1511. the oil flow rate in the base case and scenario #4 138 putra, d.f. et al./ jgeet vol 6 no 3/2021 fig 1612. the gas flow rate of the base case and scenario #4 b. the influence of cyclic water injection on the reservoir pressure in addition to the sweeping effect, the cyclic water injection also affects the pressure in the reservoir. the reservoir pressure is dynamically up and down in pressurizing and depressurizing phases alternately. fig 17 shows the difference pressure trend between the base cases versus the cyclic water injection scheme. the base case falls steadily, while the pressure cyclic scenario #4 shows the up and down pressure trend that displays the pressurizing phase with the injection rate is 15.660 sm3 while the depressurizing phase at zero sm3. fig 16 exhibits both continuous water injection and cyclic water injection can withstand the reservoir pressure. it means cyclic water injection can maintain reservoir pressure as good as continuous. another author stated that the injection rate differences, such as cyclic water injection, cause pressure fluctuations reservoir (shchipanov et al., 2008) fig 1713. pressure reservoir in the base case and scenario #4 c. the influence of cyclic water injection to oil saturation cyclic water injection affects the sweeping flow path due to pressurizing and depressurizing period. fig 18 and fig 19 fig 15. show significant differences in oil saturation between continuous and cyclic water injection. some localized parts of the reservoir that are not swept yet by the continuous water injection can be flashed by cyclic water injection. up to 7.64% of un-sweep areas can be improved by cyclic water injection. (stirpe et al., 2004) stated that there are differences in localized effects of cyclic continuous water injection compare to continuous water injection. the difference lies in the zone that has low permeability fig 14. oil saturation 1 january 2013 (as seen from the west) putra, d.f. et al./ jgeet vol 6 no 3/2021 139 fig 15. oil saturation 1 january 2013 (seen from above) d. flow-path in scenario #4 fig 20 exhibits the dynamic flow path alteration in cyclic water injection, on july 24, 2006, while the injection is on, the streamline established a flow path through high permeability zone and continuous until the injection closed on july 31, 2006. once the injection is shut-in, the flow path changed dramatically towards the low permeability zone. the streamlined model shows flow path alteration differently until august 13, 2006, that has a different flow path. the water injection penetrates the low permeability zone during the depressurizing phase to sweep the residual oil and gas in that zone. fig 16. flow paths in scenario #4 4. conclusion based on the simulation study conducted, the conclusions derived from this study is the connectivity between both a41bwat and a-41 to the producers is the excellent one. the total tracer reproduced at the production wells reach up to 66.1% in a-41bwat and 68.44% in a-41 that above the 40% requirement for reliable tracer analysis. another conclusion is the cyclic water injection increase oil and gas production up to 7.64% and 10.68% respectively and decrease water-cut down to 5.45%. and finally, the cyclic water injection can sweep the oil and gas within inaccessible areas of continuous water injection. approximately up to 7.6 % un-sweep zone can be swept by cyclic water injection acknowledgements the authors are grateful to the lppm of the islamic university of riau (kontrak penelitian no.374/ kontrak/lppm-uir/4-2018) for the financial support as well as the petroleum engineering department of uir for their technical support, in this case, it is represented by the study centre of energy, data science, and numerical simulation. references al-najem, a.a., siddiqui, s., soliman, m., yuen, b., 2012. streamline simulation technology: evolution and recent trends. soc. pet. eng. spe saudi arab. sect. tech. symp. exhib. 2012 696–717. https://doi.org/10.2118/160894-ms alhuthali, a.h., oyerinde, d., datta-gupta, a., 2007. optimal waterflood management using rate control. spe reserv. eval. eng. 10, 539–551. https://doi.org/10.2118/102478pa asadollahi, m., 2012. waterflooding optimization for improved reservoir management. norwegian university of science and technology. 140 putra, d.f. et al./ jgeet vol 6 no 3/2021 guan, l., du, y., johnson, s.g., choudhary, m.k., 2005. advances of interwell tracer analysis in the petroleum industry. j. can. pet. technol. 44, 12–15. https://doi.org/10.2118/05-05-tn2 hao, c., shook, g.m., taimur, m., dwarakanath, v., smith, b.r., muhammad, s., masduki, a., mario, c.c., putra, k.a.d., 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y.a., ishimov, i.a., fedorov, k.m., 2012. predictions of cyclic water injection on urnenskoe oil field. soc. pet. eng. spe russ. oil gas explor. prod. tech. conf. exhib. 2012 3, 1878–1886. https://doi.org/10.2118/162015-ms shchipanov, a.a., surguchev, l.m., jakobsen, s.r., 2008. improved oil recovery by cyclic injection and production. soc. pet. eng. spe russ. oil gas tech. conf. exhib. 2008 2, 901–911. https://doi.org/10.2118/116873-ms stirpe, m.t., guzman, j., manrique, e., alvarado, v., 2004. cyclic water injection simulations for evaluations of its potential in lagocinco field. proc. spe symp. improv. oil recover. 2004-april. https://doi.org/10.2523/89378ms thrasher, d., nottingham, d., stechauner, b., ohms, d., stechauner, g., singh, p.k., lara angarita, m., 2016. waterflood sweep improvement at prudhoe bay, alaska. spe doe improv. oil recover. symp. proc. 2016janua. yang, y., dai, t., wang, c., 2006. the reservoir simulation research and extending application about cyclic water injection. int. oil gas conf. exhib. china 2006 sustain. growth oil gas 2, 1119–1128. https://doi.org/10.2118/104440-ms zemel, b., 1995. tracers in the oil field. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ cover front jgeet.cdr journal of geoscience, engineering, environment and technology volume 4. no 3. september 2019. p 149-226 issn (print) : 2503-216x issn (online): 2541-5794 uir press p-issn 2503-216x e-issn 2541-5794jgeet (journal of geoscience, engineering, environment, and technology) publish periodically four times annually our journal has accredited as a scientific journal (s2) by the ministry of research, technology, and higher education no 30./e/kpt/2018 period : 2017 2021 scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. sabah a. ismail (iraq) editorial member dr. kurnia hastuti (indonesia) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. eng. takahiro miyazaki (japan) dr. mursyidah, m.sc. (indonesia) dr. sapari dwi hadian mt (indonesia) dr. emi sukiyah st., mt (indonesia) bambang setiadi ph.d (indonesia) dr. vijaya isnaniawardhani (indonesia) dr. anas puri s.t, m.t (indonesia) mirza muhammad waqar, m.sc (pakistan) good fried panggabean, s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) yuta izumi m.eng (japan) kageaki inoue, m.eng (japan) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) yuta izumi, m.eng (japan) yuniarti yuskar s.t, m.t (indonesia) muhammad zainuddin lubis s.ik m.si (indonesia) pakhrur razi, s.si, m.si (indonesia) babag purbantoro, s.t, m.t (indonesia) budi prayitno s.t, m.t (indonesia) joko widodo, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) journal manager catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) journal of j eet geoscience engineering environment and technology preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 04 no 03 2019. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content research articles analysis of the sub-surface distribution of graphite minerals using the geoelectrical resistivity method in the sabilambo village, kolaka regency, southeast sulawesi province ........................................................................... 149 the use of disintegration ratio in evaluating rock durability in selected mudrock samples in indonesia ....................................................................... 158 ore forming fluid of epithermal quartz veins at cisuru prospect, papandayan district, west java, indonesia ..................................................... 170 hydrogeochemistry of natar and cisarua hot springs in south lampung, indonesia ........................................................................................................ 178 determination of priority regions as the direction of decision-making for land development of west kalimantan province ........................................... 186 mineralogy and geochemistry of gold ore low sulfidation-epithermal at lamuntet, brang rea, west sumbawa district, west nusa tenggara province ........................................................................................................ 198 benefits of adding corn stalk ash as a substitution of some cement against of compressive strength concrete .................................................................. 208 volcanism in the pre-semilir formation at giriloyo region; allegedly as source of kebo-butak formation in the western southern mountains ........... 217 1: front cover e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 02 2017 anis m. et al/ jgeet vol 02 no 02/2017 141 gis-based optimization method for utilizing coal remaining resources and post-mining land use planning: a case study of pt adaro coal mine in south kalimantan mohamad anis 1,2, *, arifudin idrus 2 , hendra amijaya 2 , subagyo 3 1 directorate general of mineral and coal, ministry of energy and mineral resources, republic of indonesia jl. prof. dr. soepom o, sh, no. 10, jakarta, 12870, indonesia, 2 department of geological engineering, gadjah mada university, yogyakarta, 55281 3 department of mechanical and industry engineering, gadjah mada university, yogyakarta, 55281, indonesia abstract coal mining activities may cause a series of environmental and socio-economic issues in communities around the mining area. mining can become an obstacle to environmental sustainability and a major hidden danger to the security of the local ecology. therefore, the coal mining industry should follow some specific principles and factors in achieving sustainable development. these factors include geological conditions, land use, mining technology, environmental sustainability policies and government regulations, socio-economic factors, as well as sustainability optimization for postmining land use. resources of the remains of the coal which is defined as the last remaining condition of the resources and reserves of coal when the coal companies have already completed the life of the mine or the expiration of the licensing contract (in accordance with government permission). this research uses approch of knowledge-driven gis based methods mainly analytical hierarchy process (ahp) and fuzzy logic for utilizing coal remaining resources and post-mining land use planning. the mining area selected for this study belongs to a pkp2b (work agreement for coal mining) company named adaro indonesia (pt adaro). the result shows that geologically the existing formation is dominated by coal bearing formation (warukin formation) which allows the presence of remains coal resource potential after the lifetime of mine, and the suitability of rubber plantation for the optimization of land use in all mining sites and also in some disposal places in conservation areas and protected forests. keywords: gis, optimization, remaining resource, post-mining planning, ahp 1. introduction coal is a nonrenewable energy resource that has been the primary energy resources and the most important in the world. coal resources play a strategic role in economic and social development in many industrialized countries (wang and zhang, 2008; liu et al., 2012). coal mining activities may cause a series of environmental and socioeconomic issues in communities around the mining area. mining can become an obstacle to environmental sustainability and a major hidden danger to the security of the local ecology (wang and zhang, 2008; liu et al., 2012; zhang et al., 2013). therefore, the coal mining industry should follow environmental protection principles for achieving sustainable development. the remaining of coal can be defined as coal remain resource (mainly measured and indicated) which are the remaining reserves from a coal mining activity (westman, 1999; watson, 2002 and rohrbacher et al., 2009). these remaining reserves are mainly measured after the mining companies have already completed contracts and their license granted by the government has already been expired. the remaining coal resources will be reevaluated with more complex parameters that can influence the sustainability of mining and sustainable development with reference to the recommended parameters of previous studies. this study analyzes the feasibility of continuing mining operations in terms of the possible environmental effects of the operation and by considering more dynamic and complex factors (westman, 1999; watson, 2002; rohrbacher et al., 2009; and cryanon, 2012). these factors include geological conditions, mining technology, land use, environmental sustainability policies and government regulations, the social economy (the community around the mine), and the post-mining land use sustainability. furthermore, we will generate a dynamic modeling that will also analyze the projected survival of remained coal resource for management and optimization purposes. the * corresponding author : email: mochanis@yahoo.com tel.:+62-81-31877-8374; fax: +62-27-463-1181 received: may 15, 2017. revised : may 25, 2017, accepted: may 31, 2017, published: 1 june 2017 doi: doi.org/10.24273/jgeet.2017.2.2.307 mailto:mochanis@yahoo.com 142 anis m. et al/ jgeet vol 02 no 02/2017 following is figure showing mindset of the research. in recent decades, there have been considerable improvements and empowerment in the area of computing software (schmitt, 2010). mathematical modeling techniques have been developed to predict the locality of point events of interest (schmitt, 2010). each technique can be regarded as a function that combines the various "predictor maps" to produce a map of the prospect (bonhamcarter, 1994). the method can be seen as generally fitting into one of two categories: knowledgedriven and data-driven. it is also possible to combine some features from both techniques. ahp (analytical hierarchy process) method has been widely used to assist in decision-making process. ahp helps the decision makers in finding the most appropriate decision with the purpose of an specific research and understanding an issues (saaty, 1980; isnain and juhari, 2013). it provides a comprehensive framework and rationale for structuring the problem to represent and measure things that are related to the overall objectives, and provide an alternative solution to this problem. ahp was introduced by thomas saaty in 1980 using mathematical methods and psychology concepts. since then this method evolved and improved over time. 2. sample and research methods there are several coal mining companies /pkp2b (contract of work) still active is in south kalimantan province (about 14 companies), among which pkp2b pt adaro indonesia was selected for this research. the company site is located in balangan and tabalong regency, south kalimantan province, which is approximately 220 km from banjarmasin city to the north and can be reached by road takes about 6 (six) hours. while the location of crushing (crushing plant) and the port of loading is in the village kelanis, in south barito regency, central kalimantan (fig. 2.). the total area of work agreement of pt. adaro indonesia is 35.800,80 hectares (directorat general of mineral and coal, 2014). pt adaro has been running the mining operation for 22 years, from the first approval of operation given by government. recently, pt adaro has been the biggest coal mining company in indonesia producing coal about 50 mt per years, but later it going to increase to 80 mt coal per year. it has total resources approximately 4 billion ton coal and total reserves of coal about 2,3 billion ton (directorat general of mineral and coal, 2014). fig. 1. mindset of the research there has not been planning to optimaze coal remaining resources optimation -based coal remaining resources legas basis  1945 constitution of the republic of indonesia;  law no. 4/2009 on minerals and coal;  law no. 26 /2007 on spatial planning regency  government regulation no. 24/2012 on mining operation;  other related goverment regulations subject  gov. of south kalimantan province  coal company  stakeholder threats  mis management of coal remaining resources  community resistance vs coal company  high operational cost opportunities  conservation of coal resources  conservation of post mining  community development with productivity of post mining object  potential of coal remaining resources  local/ regional ekonomi c social  environtment methodology gis modeling basedanalysis: optimation of coal remaining resources optimation of land use anis m. et al/ jgeet vol 02 no 02/2017 143 fig. 2. location of pt adaro mining site in indonesia 2.1 gis modeling method modeling activities to identify prospective mineral and coal are trying to describe the area that may be a major source of sediment formation zone (sutcu, 2012). this can be achieved through the process of defining the proof criteria, making evidentiary criteria maps (predictor maps) and weighting by combining these maps to produce final prospective map. interpretation maps of these prospects can be used to generate the target area to do exploration activities (bonham -carter, 1994 and harris, 2006). 2.2 ahp method this study uses a knowledge-driven approach integrated with gis (geographic information system), i.e. ahp or the analytic hierarchy process (saaty, 1980). 1. developing comparison matrix for each rank hierarchy, 2. calculate the relative weight and priority for each element in the hierarchy, and 3. calculate the ratio of consistency to assess the consistency of assessment, the application of the analysis is mainly determining the consistency (consistency analysis) performed after ranking order of each criterion. in terms of ensuring the accuracy of the assessment (weighting sequence of each of the criteria used in determining the eigen value) a consistent modeling equation is required and therefore consistency analysis was done using two main steps (saaty, 1980; isnain and juhari, 2013); a. calculate consistency index (ci): ci = λ max n (1) n 1 where λ max is the maximum value of the average that includes all the parameters / largest eigen values of matrix number n, n = is the number of characters / parameters used (i.e. n = 10) ci = is consistency index b. consistency ratio (cr) calculation: cr = ci / ri (2) where ri is random index cr is consistency ratio random index values (ri) are introduced by thomas saaty (1980). ri are shown in table 1 for n = 4. after the above steps then calculate the relative weight and priority for each element in the hierarchy. table 1. random index value (ri), saaty (1980) n 1 2 3 4 5 6 7 8 9 10 ri 0 0 0,58 0,9 1,12 1,24 1,32 1,41 0,46 1,49 144 anis m. et al/ jgeet vol 02 no 02/2017 table 2. matrix pair-wise features thematic map individual coal potential zone 2.3 gis-based optimization gis modeling approach method also allows an area known to be free from non-mining activities (eg land use settlements, highways, oil and gas pipelines, large rivers and other land). the analysis results can be known the extent of the potential area which is completely free and clean of surface activity, so that later would be known areas of optimization for continuous mining operations. the same thing can be determined by overlaying maps approaches related to the optimization of land use. surely must first set the initial criteria for the optimization of land suitability (fuzzy logic). this study uses a guide law no. 26 of 2007 on spatial planning district. optimization of the suitability of land / land use in this research is directed to the use of plantation/ agricultural and conservation areas, whereas the determination of the criteria optimization of land use can be seen in table 4. 3. data and analysis gis modeling approach also can be used to identify an area known to be free from non-mining activities (e.g. land use settlements, highways, oil and gas pipelines, large rivers and other land). the analysis results can be used to find the extent of the potential area which is completely free and clean of surface activity, so that later would be considered as areas of optimization for continuous mining operations. secondary data were taken from pkp2b (coal company) and related agencies (from the level of the central government and regional / prov. regency / city), located in the province of south kalimantan. retrieval of data from relevant government agencies was attained not only at the study area but also in government institution that support research data. secondary data obtained from the company and the institutions were the most recent data (for the past 5 years) and were in the form of either maps or tables related to the research objectives the collected data from various resources were uniform and there was no serious difficulties in data provision. this research will was conducted in several stages of analysis: a. analysis of the potential area coal remaining resource for optimization: b. analysis of the suitability of land for land use optimization. for gis modeling, arc gis 10.2 software was used to process ahp analysis. attribute determination analysis, such as polygon classification and weighting assessment was carried out to produce thematic maps of rainfall, lithology (rock formations), the distance from the geological structures (faults), slope and mining progress. 3.1 analysis of the coal resource remaining for optimization based on the analysis of this study the order/ranking of influential variables are as follows: 1. rock formations (fb); 2. condition of geology structure (ksg); 3. condition of coal seam (ksb); 4. land use (pl); 5. quality specification of coal calorie (kal); 6. quality specification of total sulfur (ts); 7. quality specification of total moisture (tm); 8. quality specification of ash content (ash); 9. slope (kl); 10. progress mine (kt). the next step is to develop the comparison matrix for each rank hierarchy. after the above steps then kriteria fb ks b pl ks g kal ts as h tm kl kt fb 1 2 3 4 5 6 7 7 8 10 ks b 0,500 1 2 2 4 5 6 6 7 8 pl 0,333 0,500 1 1 2 4 4 5 7 7 ks g 0,250 0,500 1 1 2 3 3 4 5 6 kal 0,200 0,250 0,500 0,500 1 2 3 3 3 4 ts 0,167 0,200 0,250 0,333 0,500 1 2 3 3 4 as h 0,143 0,167 0,250 0,333 0,333 0,500 1 2 2 3 tm 0,143 0,167 0,200 0,250 0,333 0,333 0,500 1 2 2 kl 0,125 0,143 0,143 0,200 0,333 0,333 0,500 0,500 1 1 kt 0,100 0,125 0,143 0,167 0,250 0,250 0,333 0,500 1 1 total 2,96 5,05 8,49 9,78 15,75 22,42 27,33 32 39 46 anis m. et al/ jgeet vol 02 no 02/2017 145 the relative weight and priority for each element in the hierarchy must be calculated. after the normal matrix obtained weighting value for each criterion should be defined (eigen value) to be used for calculating the coal potential by the following equation, psb = fb*b1 + ksb* b2 + pl* b3 + ksg*b4 + kal*b5 + ts*b6 + tm*b7 + ash * b8 + kl * b9 + kt * b10 psb = fb*0,29 + ksb* 0,20 + pl* 0,14 + kal* 0,11 + ksg * 0,08 + ts * 0,06 + ash * 0,04 + tm * 0,03 + kl * 0,02 + kt * 0,02 psb is potential coal area (see fig. 7) λmax = (2,96*2,98) + (5,05*2,04) + (8,49*1,37) + (9,78*0,16)+ (15,75*0,075) + (22,42*0,057) + (27,33*0,04) + (32*0,031) + (39*0,023) + (46*0,02) / 10 λmax = 8,819+10,327+11,637+11,326+11,768+12, 701 + 11,038 +9,943+8,779 8,952 / 10 λ max = 10,5289 ci = λ max n = 10,5289 10 = 0,059 n 1 9 cr = ci/ri = 0,059/1,49 = 0,039 cr values obtained from ci / ri (ri obtained from table 2 / random index value with n = 10) as the calculations showed that the value of cr is below / less from 0.1 and is 0.039, indicating that the value of cr is consistent and acceptable. the same stage is also carried out to count every sub criteria of its variable above. further, after spread potential of coal resources is identified, analysis of the coal resource remaining for optimization is conducted by gis modeling approach trough carrying out overlaying potential map with infrastructure one as shown at fig. 3. the analysis should first change spatial raster map into vector map to produce accurate optimization map. 3.2 analysis of the suitability of land for land use optimization the analysis of the suitability of land for land use optimization should base on condition of economic social of the community around the mining as well as result of the environmental management/ reclamation performance of the coal company. the result of analysis of the coal resource remaining for optimization is then overlaid with some supporting map, such as rainfall map and slope one considering criteria in accordance with the law no. 26/2007 about land pattern of the regency area (as guidance for analyzing fuzzy logic). in conducting analysis of suitability optimation or land utility, this research uses criteria map. some of the main criteria are mainly rainfall map around concession location of pt adaro and slope map give significant contribution of optimation decision of land suitability. analysis of gis modeling (fuzzy logic) of suitability optimation / land utility uses the criteria above and guidance of reference related to determining land utility which is accurate after post mining. base on the criteria include: 1. slope, in the research area is generally 0 25 % for plantation and over 25 % for conservation land; 2. rainfall, generally over 100 mm; 3. distance from street, close enough around about 1 km; 4. distance from settlement, close enough about 1 km; 5. distance from river, close enough about 1 km; from the consideration above, the analysis result would produce map of the suitability of land for land use optimization. the result is hope to return land to previous function that is rubber plantation area (fig. 4). it is in lane with the and lead to increase economic rank in the tabalong dan balangan regency. table 3. normal matrix obtained from the pair-wise matrix kriteria fb ks b pl ks g kal ts as h tm kl kt total avg bobot fb 0,338 0,396 0,354 0,409 0,317 0,268 0,256 0,219 0,205 0,217 2,98 0,30 0,30 ks b 0,169 0,198 0,236 0,204 0,254 0,223 0,220 0,188 0,179 0,174 2,04 0,20 0,20 pl 0,113 0,099 0,118 0,102 0,127 0,178 0,146 0,156 0,179 0,152 1,37 0,14 0,14 ks g 0,084 0,099 0,118 0,102 0,127 0,134 0,110 0,125 0,128 0,130 1,16 0,12 0,12 kal 0,068 0,049 0,059 0,051 0,063 0,089 0,110 0,094 0,077 0,087 0,75 0,07 0,07 ts 0,056 0,040 0,029 0,034 0,032 0,045 0,073 0,094 0,077 0,087 0,57 0,06 0,06 as h 0,048 0,033 0,029 0,034 0,021 0,022 0,037 0,063 0,051 0,065 0,40 0,04 0,04 tm 0,048 0,033 0,024 0,026 0,021 0,015 0,018 0,031 0,051 0,043 0,31 0,03 0,03 kl 0,042 0,028 0,017 0,020 0,021 0,015 0,018 0,016 0,026 0,022 0,23 0,02 0,02 kt 0,034 0,025 0,017 0,017 0,016 0,011 0,012 0,016 0,026 0,022 0,19 0,02 0,02 total 1,00 1,00 1,00 1,00 1,00 1,00 1,00 1 1 1 10,00 1,00 1,00 146 anis m. et al/ jgeet vol 02 no 02/2017 fig. 3. potential of optimation of coal remaining resources at location map of pt adaro fig. 4. optimized suitability land map at location of pt adaro potential of coal remaining resources optimation map pt adaro indonesia tabalong and balangan regency south kalimantan province scale 1 : 186.000 legend : regency boundary highway oil and gas pipeline river settlement very potential (10770 ha/30,2 %) potential (2371 ha/6,65 %) sufficent potential (7612 ha/21,3 %) less potential (7891 ha/22,1 %) not potential (6987 ha/19,6 %) potential of coal remaining resources regency of regency of balangan south kalimantan province scale 1 : 186.000 legend : area of conservation (0,08 %) area of plantation (97,7 %) not both area (1,466%) regency of regency of balangan south kalimantan province anis m. et al/ jgeet vol 02 no 02/2017 147 discussion table 4. the potential area zone of remaining coal resources the table above shows that from the initial area of pt adaro around 35.634 ha., the area that still has the potential to have coal resources is about 20,755.9 ha or 58.2%. while the area has the potential of remaining coal resources calculated based on the total area of pt adaro actively reduced by the area of infrastructure is about 14,878 ha or 48.2%. if subdivided areas of potential area contain potential coal resources remaining 10.772,9 ha or 30.23%, while the remaining area is categorized as very potential and potential. from the above conditions can be shown that the area of pt adaro indonesia is still very potential to be optimized and cultivated for sustainable mining (sm) is an area of 10,772.9 ha or 30.23%. another thing is to show that this mining company has an area of 9,983 ha or 28.8% which is still feasible to continue its mining activities even though the age of the mine will end in 8 years. this condition is also supported by the company's statistics that the remaining coal resource content of pt adaro's mine is still around 4 billion tons and reserves of about 2.3 billion tons and production rate of about 80 million tons. analysis of suitability optimation /land utility base on above criteria is that the research is propose when post mining activity pt adaro is finished. which is expected to be returned to the original function for rubber plantation area (pic. 4). this is in accordance with the social need and encourage economic level in tabalong and balangan regency where there has been rubber plantation processing plant. the result of this analysis shows that social-economic performance of the society is dominant enough. the result analysis also indicated that environment performance does not always affect directly because the performance of the processing surrounding of pt adaro is still in the early stage. where as this result has analyzed that plantation potential base on local statistic data plan give contribution significant enough out the mining sector. social-economically, it than be shown that plantation effort sector give contribution to sustainable development. therefore, the data of plantation sector criteria should be considered for arranging future reclamation planning of pt adaro (fig. 4.). the company also has an area of approximately 14,878 ha or 48.2% which is feasible and significant to be diverted to other sectors outside mining activities ie to achieve complete sustainable development above can be seen in the following fig. conclusion conclusions obtained from the analysis of this study showed that pt adaro have the potential resource area that has sufficient remaining coal of about 20,755.9 ha or 58.2%., (see fig. 3), so achieving sustainable mining after the lifetime of the mine is still possible. potential areas are generally located in the rock formations of warukin and dahor. infrastructure land is only a little less potential area. based on the criteria from reference land, and the existing land use in the area and around the mines, the land optimization recommended planning a rubber plantation area and a restricted area for conservation in the north of the concession area of pkp2b pt adaro (fig. 4). acknowledgements the authors acknowledge pkp2b pt adaro for the cooperation and providing data. the authors also appreciate the assistance for data collection and database creation from the private and governmental institutions, in particular the directorate general of mineral and coal. references agterberg, f.p., bonham-carter, g.f., wright, d.f., 1990. statistical pattern integration for mineral exploration. in: gaal, gabor, merriam, daniel f. (eds.), computer application sin resource estimation prediction and assessment for metals and petroleum. pergamon press, oxford. bonham-carter, g.f., 1994. geographic information system for geoscientis (modelling with gis), first ed. pergamon, new york. ontario, p.329 brundtland, 1987. our common future, world commission on the environment and development. carranza, e. j. m., 2009. geochemical anomaly and mineral prospectivity mapping in gis. handbook if exploration and environmental geochemistry; vol 11. elsevier, uk, 351 p. craynon, j. r., 2011. approaches and barriers to incorporating sustainable development into coal mine design, doctoral dessertation at the faculty of the virginia polytechnic institute and state university. de carvalho, j. j. a., koppe j.c., and costa, j. f. c. l., 2012. a case study application of linear programming and simulation to mine planning. the journal of the southern african institute of mining and metallurgy, vol. 112. friedrich, w. and becker-platen, j. d., 2007. global nonfuel mineral resources and sustainability, proceedings for a workshop on deposit modeling, mineral resource assessment, and their role in sustainable potential priority optimation large ( ha) % very potential i sm 10773 30 potential ii sm 2371 7 sufficient potential iii sm 7612 21 less potential iv sd 7891 22 not potential v sd 6987 19.6 35634 100 148 anis m. et al/ jgeet vol 02 no 02/2017 development, circular 1294, p. 1-16. hunt, j.w., 1988. sedimentation rates and coal formation in the permian basins of eastern australia. australian journal of earth sciences 35, 259 274. isnain, z. and juhari m. a., 2013, integrated remote sensing and gis based approach for mapping the groundwater potential in kota kinabalu, sabah, malaysia, ejdg, vol. 18 [2013], bund. q josé a. b, ronald r. g. and martin l. s., 2011. a methodological model to assist in the optimization and risk management of mining investment decisions, dyna, year 78, no. 170, pp. 221-226. kementerian esdm, 2009, undang-undang no. 4 /2009 tentang mineral dan batubara. kementerian esdm, 2006, perpres no. 5 /2006 tentang kebijakan energi nasional. liu h., changxie, y. e.; qi xin, 2012. study on developing coal resource with the socialeconomic influence in erdos city. crosscultural communication, vol. 8, no. 6, pp. 112-117. partington, g. a., 2009, commercial application of spatial data modelling with examples from north queensland, aig northern queensland exploration and mining conference 2009, townsville, australia, 3-8 june. rohrbacher, t. j., james a. l., osmonson, l. m., and carter, m. d., 2009. coal resource availability, recoverability, and economic evaluations in the united states a summary. the national coal resource assessment overview (usgs report). saaty, t. l. 1980. the analytic hierarchy process: planning, priority setting, resource allocation., mcgraw-hill, new york. setiabudi, b. t. dan hutamadi, r., 2003. kebijakan konservasi bahan galian dalam pengelolaan sumberdaya mineral di indonesia. kolokium hasil kegiatan inventarisasi sumberdaya mineral dim, p. 1-10. sikumbang n. dan heryanto r., 1994. peta geologi lembar banjarmasin 1712, kalimantan, sekala 1:250.000. pusat penelitian dan pengembangan geologi (p3g) bandung. sharma, p. d., 2011. bringing sustainability in coal mining operations is need-of-the-hour. schmitt, e., 2010, weights of evidence mineral prospectivity modelling with arcgis. eosc 448 directed studies, dec. 2010. shields, d. j., 2007. the contributions of geologic information to economic, social, and environmental sustainability, proceedings for a workshop on deposit modeling, mineral resource assessment, and their role in sustainable development. circular 1294, p. 17-18. standar nasional indonesia (sni), 2011. pedoman pelaporan, sumberdaya dan cadangan batubara. badan standardisasi nasional (bsn), 2011. sutcu, e., 2012, use of gis to discover potential coalfields in yatagan milas area in turkey, international journal of coal geology, 98 (2012) 95 109. suyartono, 2004. good mining practice: konsep tentang pengelolaan pertambangan yang baik dan benar. cetakan ke 2, studi nusa, semarang. wang l. p., 2008. countermeasures study on the sustainable development of coal industry in china. international journal of business and management vol. 3, no. 6. wang x. and zhang g., 2008. study on the sustainable development of henan coal industry under the guide of circular economy,international journal of business andmanagement vol.3, no.6. watson, d. w., 2002. gis assessment of remaining coal resources with high market potential, conference proceeding esri, san diego, ca. westman, e. c., 1999. a characterization and determination of the coal reserves and resources of southwest virginia, doctoral theses at the faculty of the virginia polytechnic institute and state university (dissertation). zhen w., yuanyuan, l., yan xu, 2008. the problems in sustainable development of resource orientated city and countermeasures, international journal of business and management. vol. 3, no. 6, june. yudi d., rina z., catur p., rini s., agus s. dan achmad m., 1999. studi regional cekungan batubara wilayah pesisir tanah laut kotabaru, kalimantan selatan. pemaparan hasil kegiatan lapangan dik-s bataubara, dsm, 1999. yufen h., yunxia w., sumei z., and lihong c., 2013. integrated evaluation of ecological sustainability of a mining area in the western region of china. international journal of environmental science and development. vol. 4, no. 2, april. _________, 2014. dokumen kegiatan tahunan (rkab dan rkttl) perusahaan pkp2b di prov. kalimantan selatan, direktorat jenderal mineral dan batubara, kesdm geology kalimantan selatan [www document], dinas energi dan sumberdaya mineral prov. kalsel, www.prov.kalsel.go.id (accessed 10.30.00). http://www.prov.kalsel.go.id/ 1. introduction 2. sample and research methods 2.1 gis modeling method 2.2 ahp method 2.3 gis-based optimization 3. data and analysis 3.1 analysis of the coal resource remaining for optimization 3.2 analysis of the suitability of land for land use optimization discussion conclusion acknowledgements references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 108 hasria, et al./ jgeet vol 5 no 3 /2020 research article characteristics of ultramafic igneous rock ofiolite complex in asera district, north konawe regency, southeast sulawesi province, indonesia hasria1*, erzam s. hasan2, deniyatno3, l m iradat salihin4 asdiwan1 1department of geological engineering, halu oleo university, kendari, indonesia 2 department of geophysical engineering, halu oleo university, kendari, indonesia 3 department of mining engineering, halu oleo university, kendari, indonesia 4department of geography, halu oleo university, kendari, indonesia * corresponding author : hasriageologi@gmail.com tel : +62 852-4158-7853 received: nov 25, 2019; accepted: apr 27, 2020. doi:10.25299/jgeet.2020.5.3.4113 abstract the research area is located in asera district, north konawe regency, southeast sulawesi province which has ultramafic rock lithology. the purpose of this study is to determine the characteristics of ultramafic igneous rocks using petrographic and geochemical analysis. petrographic analysis aims to determine the types and abundance of minerals present so that rock types can be determined based on the classification of travis (1955) and streckeisen (1976). the geochemical analysis aims to determine the oxide/major element so that it can determine the type of magma based on the afm classification according to irvine and baragar (1971) and the origin of the magma / original rock formation environment based on pearce (1977). petrographic analysis results showed that ultramafic rocks in the study area consisted of 2 types of rocks namely peridotite consisting of wherlit and lherzoite and serpentinite. the results of geochemical analysis indicate that the type of magma in the study area is thoellitic series and the origin of the magma/rock formation environment comes from the expansion of the oceanic floor or mid oceanig ridge (mor) which is ultramafic. keywords: asera, north konawe, ultramafic, petrography, geochemistry 1. introduction the opiolite and pelagic sedimentary rocks in the east and southeast arm of sulawesi are called the east sulawesi ophiolite belt. this belt consists of mafic and ultramafic rocks accompanied by pelagic and melange sedimentary rocks in several places. ultramafic is dominant in the southeastern arm, but the mafic rocks are dominant further north, especially along the north coast of the southeast arm of sulawesi. complete opiolite sequences are found in the eastern arm, including mafic and ultramafic rocks, pillow lava and pelagic sedimentary rocks which are dominated by deep sea limestone and layered cherry intercalation (surono, 2013). in the geological map of the kendari lasusua sheet with a scale of 1: 250,000 (rusmana et al., 1993), the asera district of north konawe regency, southeast sulawesi province (figure 1) is on the opiolite (ku) mandala line of eastern sulawesi in the lime age. the constituent rocks in the opiolite (ku) lane are harzburgite, lhezorlit, wehrlit, websterite, serpentinite, dunit, and gabro rocks. these rocks are rocks which, if weathered, can form nickel laterite in lateralization processes which are generally composed of mafic minerals with low silica (sio2) content of less than 45% (ahmad, 2002). the constituent minerals of ultramafic igneous rocks are olivine, pyroxene and hornblende which are in a fresh state is dark colour. decomposition of these primary minerals which causes the elements carried in the solution will then precipitate at a certain place. this process runs dynamically and slowly, so that the laterite profile is formed which is the development of the laterization stages. 2. research methods the method used in this study is divided into four stages namely: (1) desk study, (2) fieldwork (3) laboratory analysis and (4) data interpretation. 2.1. desk study at this stage secondary data collection and literature review of the results of previous studies were carried out relating to the geological conditions of the study area. 2.2. fieldwork field work includes surface geology observation and mapping and representative sampling, geomorphological observations and geological structures. 2.3. laboratory analysis this analysis includes petrography and geochemistry. petrographic analysis begins with sample preparation into thin sections, then analyzed using a nikon type polarization microscope. petrographic analysis aims to determine the types and abundance of minerals present so that rock types can be determined based on the classification of travis (1955) and streckeisen (1976). the geochemical analysis aims to determine the oxide / major element so that it can determine the type of magma based on the afm classification according to irvine and baragar (1971) and the origin of the magma / original rock formation environment based on pearce (1977). petrographic analysis was carried out at the geological engineering laboratory of the faculty of earth sciences and http://journal.uir.ac.id/index.php/jgeet hasria, et al./ jgeet vol 5 no 3/2020 109 technology of halu oleo university and geochemical analysis in the form of xrf (x-ray fluoresence) analysis was carried out at pt. minertech indonesia. 2.4. data interpretation the interpretation of the data in this study includes all relevant data from the results of field and laboratory work which are evaluated and compiled to produce research objectives. (a) (b) fig 1. (a) regional geology of the study area (modified from surono, 2013). (b) characteristics of ultramafic rocks in the study area. 3. results and discussion the number of stations in this study was 13 stations (figure 1b), but there were 8 representative samples analyzed by petrography. after petrographic analysis, geochemical analysis is then performed based on petrographic analysis. 3.1. characteristics of ultramafic rocks 3.1.1. ultramafic rock petrography petrographic analysis results showed that the characteristics of ultramafic rocks in the study area were divided into 2 groups of rocks (table 1), namely peridotite and serpentinit groups (travis, 1995) (figure 2). peridotite groups are divided into wherlite and lherzorlite which are characterized by the minerals olivine, orthopiroxen, and klinopiroksen, in these rocks and serpentine groups which are characterized by the presence of serpentine mineral (streckeisen, 1976) (table 2). table 1. characteristics of ultramafic rocks based on petrographic analysis rock group mineral content (%) rock name sample code ol (%) opx (%) cpx (%) srp (%) opq (%) peridotite 50 10 30 10 wherlit st_05 peridotite 45 20 25 10 lhezorlit st_02 peridotite 45 15 32 5 2 lhezorlit st_06 peridotite 43 35 15 7 lhezorlit st_07 peridotite 40 20 32 5 3 lhezorlit st_08 serpentinit 5 90 5 serpentinit st_01 serpentinit 95 5 serpentinit st_03 serpentinit 10 25 65 serpentinit st_04 a. peridotit group generally rocks in the study area are included in the peridotite group. based on the results of petrographic analysis, peridotite rock types are divided into 2, namely wherlit (st_05) and lhezorlit (st_02, st_06, st_7 and st_08) (streckeisen, 1976). the two rock types are distinguished by the presence of olivine, orthopiroxen and clinopiroksen minerals present in peridotite rocks. i). wherlit petrographic analysis results on st_05 showed that the mineral composition in rock samples consisted of 50% olivine minerals, 10% orthopiroxene minerals, 30% klinopiroxen and 10% opaque minerals (figure 2). fig 2. microscopic appearance of sample point st_05. olivine mineral (ol), orthopiroxen mineral (opx), klinopiroxen mineral (cpx) and opaque mineral (opq). opq ol opx cpx 110 hasria, et al./ jgeet vol 5 no 3/2020 the results of ploting using the streckeisen (1976) classification of mineral compositions (figure 2) show that the characteristics of ultramafic rocks at this station include wherlite rock types (figure 3). fig 3. classification of ultramafic rocks according to streckeisen (1976). ii). lhezorlit petrographic analysis results on st_02 showed that the mineral composition in rock samples consisted of 45% olivine minerals, 20% orthoproxene minerals, 25% klinopiroxen and 10% opaque minerals (figure 4). fig 4. microscopic appearance of sample point st_02. the mineral olivine (ol), ortho-pyroxene mineral (opx), clinopiroxen mineral (cpx) and opak mineral (opq). the results of ploting using the streckeisen (1976) classification of mineral compositions (figure 4) show that the characteristics of ultramafic rocks at this station include lherzoite rock types (figure 5). the same characteristics of ultramafic rock in the form of lherzoites are also found in st_06 st_07 and st_08 (table 2). fig 5. classification of ultramafic rocks according to streckeisen (1976). b. serpentinite group the serpentine group is based on the presence of abundant serpenitite minerals with a little extra mineral olivine and pyroxene and opaque minerals. the serpentine mineral is formed from the chemical changes of the olivine and pyroxene minerals so that it undergoes the serpentinization process. petrographic analysis results on st_01 showed that the mineral composition in rock samples consisted of 90% serpentine minerals, 5% olivine minerals and 5% opaque minerals (figure 6). fig 6. microscopic appearance of sample point st_01. serpentin (srp) mineral, olivine (ol), orthopiroxen mineral (opx), and opaque mineral (opq). figure 6 shows that the mineral serpentine with a 90% mineral percentage generally fills fractures in minerals due to the structure that works, and the effect of alteration that converts the minerals olivine and pyroxene into serpentine minerals. petrographic observations show that opaque minerals whose presence is around 5% are thought to be chromite minerals. the results of the analysis show that the rocks at this station have been serpentinized into serpentinic rocks. referring to the abundance of serpentine minerals in rocks, the characteristics of ultramafic rocks at this station include serpentine type ultramafic rocks (travis, 1955). serpentine type ultramafic rocks are also found in st_04 in the presence of 65% serpentine minerals, 10% olivine minerals and 25% clinopiroxen minerals (table 2). table 2. oxides/constituent elements of ultramafic rocks asera district north konawe regency southeast sulawesi province. elements rock name peridotite serpentinit sample code st_02 st_04 fe 6,281 (wt%) 6,027 (wt%) co 0,02 (wt%) 0,007 (wt%) ni 0,319 (wt%) 0,291 (wt%) al2o3 1,298 (wt%) 1,692 (wt%) sio2 37,82 (wt%) 38,119 (wt%) cao 1,79 (wt%) 2,114 (wt%) mgo 29,749 (wt%) 30,112 (wt%) cr2o3 0,243 (wt%) 0,451 (wt%) mno 0,159 (wt%) 0,219 (wt%) fe2o3 7,219 (wt%) 9,62 (wt%) na2 0,017 (wt%) 0,019 (wt%) al 0,208 (wt) 0,019 (wt) ca 0,627 (wt%) 1,694 (wt%) mn 0,033 (wt%) 0,068 (wt%) p 0,003 (wt%) 0,003 (wt%) s 0,038 (wt%) 0,013 (wt%) cr 0,269 (wt%) 0,236 (wt%) k2o 0,009 (wt%) 0,005 (wt%) c. determination of the types and origins of magma i). the main element of ultramafic rocks the determination of the oxide / main element of ultramafic rocks in the study area was carried out on 2 samples opx cpx ol opq opq srp ol srp hasria, et al./ jgeet vol 5 no 3/2020 111 representing rock units contained in the study area, namely the peridotite rock group and the serpentinite rock group that had been previously performed petrographic analysis to determine the mineral content contained in the rock. geochemical analysis is carried out to determine the oxides / main elements contained in these ultramafic rocks. the results of geochemical analysis showed that the oxide / element content in both samples was low sio2 with 37.82 (wt%) and 38.119 (wt%) content. the content of sio2, al2o3, and k2o is quite low while the content of mgo and feo and fe2o3 is quite high (table 2). the high content of mgo and the low content of sio2 are the characteristics of ultramafic rocks, where ultramafic rocks are rich in magnesium and iron minerals and low in silica (rollinson, 1993). following are the results of the analysis of the main elements carried out by pt. minertech indonesia (table 2). ii). types of magma based on the results of the geochemical analysis in the form of xrf, the types of magma plotted on the afm diagram (irvine and baragar, 1971) on the ultramafic rocks in the study area are included in the tholeiitic series (figure 7). this type is very common in tectonic settings in the form of ocean floor expansion zones or commonly referred to as mid ocenic ridge (mor) (wilson, 1989). this is characterized by low sio2 and k2o values and rich in ferromagnetic compositions such as mgo and feo (table 2). fig 7. plotting results in the classification of types of magma according to (irvine and baragar 1971). the types of magma consist of two groups, namely alkaline and subalkalin. these alkaline rocks are rich in alkaline and are usually not saturated with silica while subalkalin rocks are saturated with silica. this subalkalin group is divided into two groups namely thoellitic series and cal-alkaline series. thoellitic rocks are more rich in fe compared to mgo than cal-alkaline rocks and generally have less silica variation. the calc-alkaline group shows more silica and alkali enrichment. magma series describes the spatial variation of magma. the farther from the trench that is formed, the type of magma is transformed into thoellitic, then calc-alkaline is getting farther away becoming alkaline (wilson, 1989). the classification of magma types is based on the content of the main elements in rocks in the form of k2o + na2o, feo and mgo elements, which are plotted into the afm triangle (irvine and baragar, 1971) (figure 8), so based on these results and the results of petrographic and geochemical analysis, then the research area has a type of magma that is thoellitic series which is ultramafic. iii). origin of magma the origin of magma forming ultramafic igneous rocks in the study area can be determined using the pearce triangle diagram, 1977, which is based on the comparison of the main elements of ultramafic rocks in the form of feo, mgo, and al2o3 elements. based on the triangle diagram, the tectonic setting of ultramafic rocks in the study area is included in oceanic ridge and floor, or mid oceanic ridge (mor) (figure 8). based on the results of geochemical analysis on ultramafic rock samples in the study area, ultramafic rocks have a k2o value of less than 0.1 so it can be concluded that the type of mor that forms these rocks is the normal type (type n). type n or normal type mors are formed at shallow depths, which are between 60 80 km from the upper mantle (wilson, 1989). k2o value is used for this interpretation because the value of the element is at least in the mor. fig 8. results of ploting on the classification of the origin of magma according to (pearce, 1977). based on research conducted by several experts including surono 2013, robert hall, 2012 that opiolites in the southeast arm of sulawesi were formed in an ocean floor expansion environment (mor). by referring to this matter, which is supported by petrographic data and geochemical data, it can be interpreted that the research location was formed due to ocean floor expansion (mor). the formation process first takes place in the mid-ocean expansion, followed by the movement of material originating from the mantle in accordance with the movement of the expansion. based on the results of the withdrawal of absolute age by surono (2010) on pelagic sedimentary rocks in the eastern arm of sulawesi, the ultramafic rocks revealed in the east arm and southeast arm of sulawesi have late cretaceous age. based on these, the ultramafic rocks in the southeast arm of sulawesi might form in the late cretaceous which is marked by the rifting process. southeast sulawesi experienced a drift from the australian continent moving towards sulawesi's current position (hall, 2012). based on the reconstruction carried out (hall, 2012) shows that southeast sulawesi is part of the australian continent which is currently in the southeast part of sulawesi island. hall (2012) estimates that the expansion of the ocean floor that occurred in the late cretaceous caused rocks that characterize the oceanic floor to form. this process was followed by the movement of the australian continent towards eurasia / sundaland which was accommodated by india australia transform. the subduction process began at the beginning of paleocene on the edge of sundaland. this subduction caused the movement of the australian continent to move towards eurasia. in addition, the subduction also led to the formation of north sulawesi province which is an archipelago formed (hall, 2012). the subduction process stops 112 hasria, et al./ jgeet vol 5 no 3/2020 at the late oligocene and there is initial contact between sula spur and the north sulawesi archipelago bow. this subduction process continues and causes collision events in the early miocene which causes the ocean floor to rise to form the foreland basin. this collision event is often also referred to as soft collision. as a result of the continued subduction process, the second collision event occurred at the pliocene, known as a hard collision between the results of the first collision (sula spur and the north sulawesi archipelago bow) and eurasia / sundaland which formed sulawesi as seen today (hall, 2012). based on this concept and the results of petrographic and geochemical analysis, the rock area is ultramafic, with a type of magma thoellitic series and is formed in the oceanic ridge area (best, 2003; pearce, 1977 pearce et al, 1984), which is the ocean bloom zone (mor) originating from the australian continent which was exposed to the surface due to the collision process forming sulawesi as seen today (hall, 2012) 4. conclusions based on petrographic analysis that the characteristics of ultramafic rocks in the study area consisted of 2 groups namely peridotite groups consisting of wherlit and lherzoite and serpentinite groups. petrographic results supported by geochemical data indicate that the type of magma in the study area shows thoellitic series based on the percentage of the main elements in the form of feo, na2o + k2o and mgo plotted in the afm triangle. the origin of the magma / rock formation environment in the study area is the oceanic ridge and floor expansion (mor) based on the percentage of main elements in the form of feo, mgo, and al2o3. acknowledgements this study was made possible through the financial support from research institute of halu oleo university. the authors are very thankful to head research institute of halu oleo university forfacility assistance during field fieldwork. thanks to head asera district which has given permission to do.special thanks to my students from department of geological engineering, halu oleo university for their assistance during the fieldwork references ahmad, w., 2002, nickel laterites-a short course : chemistry, mineralogy, and formation of nickel laterites ( unpublished ), 98 p. best, m., g., 2003, igneous and metamorphic petrology 2nd edition, blackwell publishing company, australia. hall, r. 2012. late jurassic-cenozoic reconstruction of the indonesian region and the indian ocean. tectonophysics 570-571, 141. irvine, t.n and baragar, w.r.a., 1971. a guide to the chemical classification of the common volcanic rock. canadian journal of earth science 8,523-248. pearce t,h, 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global tectonic approach. chapman & hall. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 2 2021 kurnianto et al./ jgeet vol 6 no 2/2021 107 research article the geomorphological factors and its implications for the tidal energy installations in java, indonesia. fahmi arif kurnianto1*, fahrudi ahwan ikhsan1, bejo apriyanto1, elan artono nurdin1, tyas nisa fadilah2 1geography education study program, universitas jember, east java, indonesia. 2faculty of engineering, dian nuswantoro university, semarang, indonesia. * corresponding author : fahmiarif.fkip@unej.ac.id tel.:+62-85-745-115-207 received: oct 10, 2020; accepted: jun 2, 2021. doi 10.25299/jgeet.2021.6.2.5680 abstract this study aims to place the tidal energy installation effectively in indonesia based on geomorphological factors. the survey method was used to analyze the characteristics of beaches in indonesia. mathematical physics model was implemented to find the new formu las based on geomorphological factors. tides are the result of gravitational attraction and the centrifugal effect, which is the drive in the earth-moon system, tidal generating forces are the resultant forces that cause tides, namely: the earth-moon system (fs) centrifugal force and the moon's gravitational force (fb). fs works in the center of the mass of the earth-moon system whose mass point is located on the 3/4 radius of the earth. the style of tidal generator caused by the moon can be calculated by combining newton's universal gravitational law .the results of this study consist of f = m ac, where the style of the tidal generator caused by the moon can be calculated by combining newton's universal gravitational law in equation and newton's second law of motion in equation. the another results is tan = ℎ 𝑙 , where the formula takes into account constants (k) based on slopes. the last result is the constants (k) for each land form starting on 0,00 untill 1,00. the north coast of java is more suitable for tidal energy installations because the land form is dominated by alluvium plains of the quaternary age with a lower risk than the southern region of java. the effectiveness of tidal energy installation depends on the characteristics of the land form. in alluvial plains, the quaternary age of the alluvial plains is more suitable than the hill form volcanic quaternary, tertiary volcanic, and tertiary holokarst. keywords: geomorphological factor, tidal energy, indonesia 1. introduction most people in indonesia meet their energy needs by using conventional energy. conventional energy is energy that cannot be renewed (unrenewable) and when used continuously it will run out, such as petroleum, natural gas, and coal. conventional energy use not only has an impact on the crisis of energy shortages but also has an impact on the environmental crisis because its nature cannot be renewed (wardhani et al., 2016). during the next 40 years (2010-2050), national energy demand is predicted to increase by 3.21% per year from 1,082.33 million sbm in 2010 to 3,289.44 million sbm in 2050 (heyko, 2013). with the increasing need for energy, while fossil-based energy is certainly decreasing, there is a need for a substitution strategy for new and renewable energy sources. nre used is hydropower, solar power, waste, wind power, geothermal energy, and biomass. this ebt potential can in principle be renewed, because it is always available in nature. but in reality the potential that can be utilized is limited. the construction of a hydroelectric power plant (plta / mh) is constrained by the availability of land, water, environmental and social availability. the construction of solar power plants (plts) is constrained by low technological efficiency and requires extensive land. the use of wind power is constrained by wind speed and low wind continuity. the potential for waste utilization is limited to large cities like jakarta and surabaya with small capacity. meanwhile, other ebts are on average constrained by costs and are still being developed on a small scale. the limitations of the utilization of nre make the value of nre resources to date unable to replace the position of fossil energy resources as raw material for the production of electricity. this renewable energy is more appropriately referred to as additive energy, namely additional energy resources to meet the increase in electrical energy needs, and inhibit or reduce the role of fossil energy resources (pramudji, 2002). therefore there is still a need for more renewable energy, especially more predictable energy. indonesia is an archipelago with an area of about 60% of the territory of indonesia. there is a lot of potential from the sea that is unknown so that it cannot be utilized. indonesian people basically only know the potential of the sea in the form of various fisheries resources. the sea has a lot of potential for developing ebt. the sea can provide energy from the conversion of mechanical forces (wave energy and ocean current energy) or from potential forces (tidal / tidal energy and ocean heat). according to dronkers, (1969) sea tides is a phenomenon of the movement of the ups and downs of sea levels on a regular basis caused by a combination of gravitational forces and attractive forces of astronomical objects, especially by the sun, earth, and the moon. the influence of other celestial bodies can be ignored because the distance is further, and the size is smaller. the movement of water from tidal events can produce energy which can later be converted into electrical energy or http://journal.uir.ac.id/index.php/jgeet 108 kurnianto et al./ jgeet vol 6 no 2/2021 other useful forms of energy. the first country to carry out this experiment was france, namely in the city of la roche in 1966 (shaikh md. and shaiyek md., 2011). tides move large amounts of water every day and their utilization can produce relatively large amounts of energy. the basic principle of tidal power plants is the dynamics of the movement of turbines that are installed technically at the confluence of river and sea estuaries, the utilization of potential energy from tides to low tide and vice versa used to drive the turbine (sangari, 2012). even though the use of tidal energy is currently not done commercially and only a few countries use it, the future projection is not impossible anymore in all countries, especially indonesia. this can happen if all countries are able to see the potential in each region that can be used as an energy source for electricity generation (sleiti, 2015). geomorphological factors greatly influence the conservation of tidal zones (finotello et al., 2020). delta is a landform that is not found on all beaches, so it needs to be considered in tidal energy studies. geomorphological factors greatly affect vegetation around the coast (crotty and angelini, 2020). exploitation of tidal energy is very high, but consideration of geomorphological and ecological factors must be prioritized (catto, 2020). the conversion of coastal landforms is the main cause of environmental damage (xu et al., 2019). key factors related to coastal conservation are geomorphology and population density (van coppenolle and temmerman, 2019). the erosion and sedimentation patterns on the coast are strongly influenced by geomorphological factors (emery et al., 2019). there is a non-linear relationship between sea level rise, tides, and geomorphic changes (palmer et al., 2019). a few researchers focused on relationship among the geomorphological factors such as land form of beach, type of erosion, and type of depositon with a analysis of tidal energy installations. there have been limited studies concerned on impact of tidal energy to environment based on geomorphological factors especially in tropical region such as indonesia. therefore, this research intends to analyses a the geomorphological factors and its implication to tidal energy installations in indonesia. the development of tidal energy is strongly influenced by geomorphological factors. the geomorphological process between one place and another will be different. the difference consists of differences in intensity and differences in landforms (even with the same forming forces). the intensity of geomorphological processes and differences in landforms depend on (1) climate, (2) topography, (3) proximity to subduction, (4) lithology and (5) environmental changes. the influence of climate on land formation can be seen from weathering of rocks, soil color, depth of soil, and type of vegetation. weathering of rocks will often occur in landscapes that have high rainfall. this can be proven by the presence of rock outcrops that undergo structural changes in a short time (miocene to holocene period). climate greatly influences tidal dynamics on a beach. climate change will also deform the marine landform. the effect of topography on land formation is that there is a difference in geomorphological process patterns caused by high differences, slope and relief of a region. high differences between one place and another place will result in the two places having a causal relationship. a higher place is one of the causes of deformation of landforms for places located below it, for example the increase of floodplains in the downstream area is due to the increasing intensity of erosion in the upstream. the tidal region is associated with the deposition of material carried from the land. deposition dynamics will affect the presence of tidal energy.this study aims to place the tidal energy installation effectively in indonesia based on geomorphological factors. 2. methods the survey method was used to analyze the characteristics of beaches in indonesia. the beach sampling was conducted purposively by considering the distribution and similarity of lithological characteristics and watersheds. observation sheets are used as instruments to observe land around the coast. table 1 was used to identify topographic types, vegetation, and organic content.these 3 factors are associated with coastal vulnerability if used as a tidal energy installation. table 1. topographic types, vegetation, and organic content factor lower higher organic content highly organic low organic vegetation treed with groundcover no cover topography flat steep field observations are used to observe the geomorphological and stratigraphic processes of the region. furthermore, the mapping of areas related to the characteristics of watersheds is done using global mapper softwaretides are the result of gravitational attraction and the centrifugal effect, which is the drive towards the center of rotation. newton's gravitational law states that in a system of two masses m1 and m2 there will be an attractive force of f between the two which is proportional to the mass multiplication and inversely proportional to the square of the distance expressed by equation (2.1). 𝐹 = 𝐺 𝑚1𝑚2 𝑟 2 (2.1) where g is the general gravitational constant of magnitude 6,67 x 10-11 nm2/kg2 (abdjul, 2010). the gravitational force varies directly with mass, but is inversely proportional to the square of distance. in line with the law above, it can be understood that even though the mass of the moon is smaller than the mass of the sun but the distance of the moon to the earth is much smaller, so that the attraction of the moon to the earth has a greater effect than the sun on the earth. the gravitational pull draws seawater toward the moon and the sun and produces two gravitational tidal bulges at sea. the latitude of tidal protrusion is determined by declination, which is the angle between the earth's rotation axis and the moon and sun's orbital plane. the moon-pulling force causes the formation of a shared mass center system (barycenter), where the earth and moon surround the center of the mass. the revolution of the earth towards the center of mass causes the formation of a centrifugal force towards the outside of the rotary axis. in the earth-moon system, tidal generating forces are the resultant forces that cause tides, namely: the earth-moon system (fs) centrifugal force and the moon's gravitational force (fb). fs works in the center of the mass of the earth-moon system whose mass point is located on the 3/4 radius of the earth. the following are earth-moon-sun astronomical data: earth mass (me) = 5.98 x 1024 kg month mass (mm) = 7.35 x 1022 kg sun mass (ms) = 1.99 x 1030 kg the radius of the earth (re) averages = 6.37 x 106 m moon radius (rm) = 1,738 x 106 m sun radius (rs) = 6.96 x 108 m the distance of the earth the moon from the center to the center (dem) = 3.844 x 108 m earth distance sun from center to center (des) = 1,496 x 1011 m (tipler, 1998). kurnianto et al./ jgeet vol 6 no 2/2021 109 the center of mass of the earth-moon system (cm) can be calculated using equation (2.3) below : 𝐶𝑀 = 𝑚𝑚𝑥𝑒𝑚 𝑚𝑚+𝑚𝑒 (2.3) 𝐶𝑀 = (7,35 × 1022)(3,844 × 108) (7,35 × 1022) + (5,98 × 1024) 𝐶𝑀 = 28,2534 × 1030 605,35 × 1022 𝐶𝑀 = 0,04667 × 108 𝐶𝑀 = 4667 × 103𝑚 𝐶𝑀 = 4667 𝑘𝑚 so, the center of mass of the earth-moon system lies at a distance of 4667 km from the center of the earth. the style of tidal generator caused by the moon can be calculated by combining newton's universal gravitational law in equation (2.1) and newton's second law of motion in equation (2.4), so that the centripetal acceleration of ac can be obtained from equation (2.5) from the center of the earth in the earth system -month. f = m ac (2.4) 𝑀𝐸 𝑎𝑐 = 𝐺 𝑀𝐸 𝑀𝑀 𝑑𝐸𝑀 2 𝑎𝑐 𝐺 𝑀𝑀 𝑑𝐸𝑀 2 (2.5) the tidal generation force from the moon also considers the acceleration at a point close to the moon or called the sublunar point (p1) and the opposite point or called the antipode point (p2) as in figure 2.5. when the moon is at the apogee point and the earth is in its perihelion, the ratio of the force of this tidal generator becomes: moon apogee distance = 4.055 x 108 m moon perigee distance = 3,633 x 108 m the distance of the earth's perihelion = 1.470568 x 1011 m earth's aphelion distance = 1.515448 x 1011 m 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 𝑀𝑆 𝑀𝑀 𝑑𝐸𝑀 3 𝑑𝐸𝑆 3 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 1,99 × 1030 7,35 × 1022 (4,055 × 108)3 (1,470568 × 1011)3 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 1,99 × 1030 7,35 × 1022 (66,67646638 × 1024) (3,180206597 × 1033) 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 13,26861681 × 1055 23,37451849 × 1055 = 0,56 1 when the moon is at the perigee point and the earth is at aphelion, the ratio of the force of this tidal generator becomes: 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 𝑀𝑆 𝑀𝑀 𝑑𝐸𝑀 3 𝑑𝐸𝑆 3 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 1,99 × 1030 7,35 × 1022 (3,633 × 108)3 (1,515448 × 1011)3 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 1,99 × 1030 7,35 × 1022 (47,95083714 × 1024) (3,48035157 × 1033) 𝐹𝐷,𝑆 𝐹𝐷,𝑀 = 9,542216591 × 1055 25,58058404 × 1055 = 0,37 1 so, from the calculation above, it can be seen that the influence of the sun on tidal forces ranges from 37% to 56% of the force caused by the moon. 3. results and discussion the amount of energy available from tides is by using dams, depending on the volume of water collected.tidal dam scheme could be seen at the figure 1. fig. 1 tidal dam the collected water provides potential energy (ep) in equation (2.14) to drive a turbine or generator system. ep = m g h (2.14) where m is mass, g is the acceleration of the earth's gravity, and h is the change in altitude. if the water contained in the dam has a volume (v), density ( ) and mass (m), then m = v (2.15) and if the pool area is a and the maximum height (tidal range) is h, then the volume of dammed water is v = a h (2.16) the v value in equation (2.16) is substituted to equation (2.15), will produce m = a h (2.17) then equation (2.17) is substituted to equation (2.14), so that ep = a h g h (2.18) the stored sea water will decrease in height from h 'to 0. the average change in height is 0.5h. then the potential energy in equation (2.18) becomes: ep = a h g 0,5h ep = 0,5 g h2 (2.19) if it is assumed that the maximum tide occurs every 12.4 hours, and the turbine operates only when the water is released, the potential energy for 2 times per day is: ep total in 1 day = (24/12,4) 0,5 ρ a g h^2 =0,968ρ a g h^2 (2.20) if ρ seawater is 1025 kg m-3 and g = 9.81 n / kg, then: the total ep in equation (2.20) becomes ep total in 1 day = (0,968)(1025)(9,81) a h^2 =9731 a h^2 (2.21) because in 1 day there are 24 x 3600 seconds, and power = energy / time, then: power= (9731 a h^2)/((24) (3600)) power=0,113 ah^2 (2.22) from equation (2.22), it can be seen that power depends on the square tidal range (h^2). so the greater the range of tides, the greater the electric power that can be produced. table 2 show that the erosion that occurs on a beach will affect to the quantity of material carried by the river currents. these materials can threatening with the existence of tidal energy installations. a beaches with high erosion sensitivity will be affected by tidal energy damage. the formation of a landscape is largely determined by the geomorphological process. the geomorphological process is a process that is strongly influenced by the formation of the 110 kurnianto et al./ jgeet vol 6 no 2/2021 earth's surface. the power can be exogenous energy (wind, water, glaciers, or human intervention) and endogenous (tectonic and volcanic) power. every power, will cause a different influence on the land it forms. the formation of the land will affect the physical and natural economic conditions of the surrounding community. table 2. distribution of geomorphologcal process in java region topography geomorphological process organic content of soil vegetative cover (%) stratigraphy jakarta flat splash erosion low low mostly aluvium cirebon sloping sheet erosion high moderate mostly aluvium semarang steep slope sheet and riil erosion low low mostly aluvium surabaya steep riil erosion low moderate mostly sandstone carbonate yogyakarta very steep gully erosion low moderate carbonatealuvium situbondo flat splash erosion high moderate mostly sandstone carbonate jember flat and steep sheet erosion high moderate mostly aluviumvolcanic malang flat and steep sheet erosion high moderate mostly aluviumvolcanic cilacap flat and steep splash erosion high high mostly aluviumvolcanic sukabumi flat and steep splash erosion high high mostly aluviumvolcanic table 2 show that the distribution of beaches in indonesia with a various forms of beaches based on slopes is in desperate need of tidal energy installations. the lithology is the configuration of the host rock that is the foundation of a region. litology is very influential on various types of landform deformation because each type of rock has different characteristics. in addition, host rock is also an ingredient for soil formation. the lithology of each region varies, giving rise to different land forms, for example in areas with sedimentary rocks, the area will have a relatively sloping landform, flat and many floodplains. figure 2 shows that the northern part of java is an area that has the same geomorphological watershed characteristics. it also causes the same coastal geomorphological conditions. jakarta, cirebon, semarang, surabaya, situbondo are areas that are easy to exploit with flat landforms. surabaya and situbondo have similarities in stratigraphic aspects which are dominated by sandstone and carbonate. tidal energy installations in the north coast of java must consider aspects of conservation of landforms that characterize the region, including deltas and abrasion vulnerability.the geomorphological characteristics of the north coast are different from the south coast. jember, malang, yogyakarta, malang, sukabumi have land forms that are difficult to exploit, so the potential for damage to the region is lower. the dominant stratigraphy is old alluvium and volcanic with many active faults so that the land is more steep. delta landforms are generally not found, while the potential for abrasion is also low, so the tidal energy installation consideration in the south coast region is not the same as the north area. figure 2 shows that the entire northern coast of java has a flat topography. this is due to the dominance of the quaternary alluvium plains and anticlinal hills which are tertiary in age. fig. 2 north java topography the southern part of java is dominated by tertiary-aged landforms with a radius close to the subduction zone. this can be seen from the topography which is steeper than in northern java. therefore, the tidal energy installation is more in line with the characteristics of the north coast of java because the geomorphological characteristics are not at risk of deformation of the landform. in addition, the karst areas of the southern part of java and the tertiary volcanic mountains are areas that must be optimally conserved compared to the alluvium plains in the north. the topography of southern java can be seen in figure 3. during the high tide, the sea level is higher than the water level in the reservoir, its height is almost to the top of the dam, as shown in figure 1. the reservoir is filled with water from the ocean by passing through a tunnel in which there is a water turbine that is connected directly to the electricity generator. because of the flow of water that passes through the tunnel, the turbine in the tunnel will rotate turning the generator so that electricity is generated. this continues until the reservoir water level is almost the same as the water level outside the reservoir. figure 4 shows the very different distribution of coastal topography between northern java and southern java. kurnianto et al./ jgeet vol 6 no 2/2021 111 fig. 3 south java topgraphy fig. 4 map of coastal geomorphology tidal conditions in the waters of the archipelago are determined by tidal propagation from the pacific and indian oceans as well as coastal morphology, and complex aquatic bathymeries in which there are many shallow straits, troughs and seas, and deep seas. the condition of these waters forms a diverse tidal pattern. an area is said to be suitable for implementing tidal power plants if they meet a minimum tidal range of 2 m, a minimum current velocity of 2 m / s, and a sea structure that affects the magnitude of tides (sangari, 2012). changes in land use in coastal areas will affect the intensity of sedimentary transport, inducing stabilization of the landform, vegetation characteristics (marrero-rodríguez et al., 2020). the distribution of human activity in coastal areas is influenced by geomorphological factors (yi et al., 2020). preliminary observations of the coast must be carried out with the aim of maintaining environmental quality (scherelis et al., 2020). tidal energy site selection must consider the characteristics of coastal resources (mejia-olivares et al., 2020). the development of transportation in coastal areas is greatly influenced by geomorphological factors (oliveira et al., 2020). tidal energy could potentially slow down the sediment transport rate (deng et al., 2020). according to wyrtki (1961), tides in indonesia are divided into 4, namely: (1) single daily tides (diurnal tide), are tides which only occur once and one time recedes in one day. this type of tides is found in the karimata strait, (2) double daily tides (semi diurnal tide), are tides that occur twice and twice as lows, which are almost the same height in one day. this type of tides is found in the malacca strait to the andaman sea. (3) tidal mix of single daily inclines (mixed tide, prevailing diurnal), is a tidal which every day occurs one pair and one time recedes but sometimes with two pairs and two times low tide which is very different in height and time. this type of tides is on the south coast of borneo and the north coast of west java. (4) tidal mixture of double daily inclines (mixed tide, prevailing semi diurnal), is a tidal that occurs two pairs and twice recedes in a day but sometimes there is one tide and one time receding by having a different height and time. these types of tides are on the south coast of java and eastern indonesia. indonesia, with an area of almost 60% of the total area, has the potential to implement alternative tidal technologies. especially with the stretch of east-west along 5,150 km and the stretch of north to south 1,930 km has positioned indonesia as the country with the longest coastline in the world. in the rainy season, wind generally moves from the north west with the content of moisture from the south china sea and the bay of bengal. in the west season, sea waves rise from the usual around java. the territory of indonesia which is an archipelagic country has narrow straits that limit its islands. in addition, there are also quite a lot of bays and peninsulas which experience daily ups and downs that have the potential to be explored by energy. this makes it possible to utilize tidal power, as a renewable energy resource needed by humans. according to tidal recording data issued by the hydrooceanographic service of the indonesian navy (tni al), indonesia has 90 tidal stations spread from sabang to merauke. of the many tidal stations there are many tidal stations which have differences in tide and low tide exceeding 2.5 m. based on these conditions, it is possible for indonesia to utilize tidal power as a source of electricity generation. 4. conclusion the north coast of java is more suitable for tidal energy installations because the land form is dominated by alluvium plains of the quaternary age with a lower risk than the southern region of java. north java is an area that is still 112 kurnianto et al./ jgeet vol 6 no 2/2021 developing by the presence of exogenous forces on its alluvial plains, so that land rehabilitation can be carried out. the effectiveness of tidal energy installation depends on the characteristics of the land form. in alluvial plains, the quaternary age of the alluvial plains is more suitable than the hill form volcanic quaternary, tertiary volcanic, and tertiary holokarst. land forms in southern java are more suitable for conservation because of the high vulnerability of holokarst (underground river damage) and tertiary volcanic mountains where there is no pyroclastic (high weathering) deposition process. acknowlegdement thanks are conveyed to colleagues at the geography education study program, universitas jember for all the support given to the preparation of this article. references abdjul, t., 2010. pengaruh kerapatan sampel campuran sekam dan dedak pada koefisien refleksi dan koefisien transmisi gelombang kustik. sainstek 5. catto, n., 2020. atlantic canada’s tidal coastlines: geomorphology and multiple resources, in: world geomorphological landscapes. pp. 401–430. https://doi.org/10.1007/978-3-030-35137-3_18 crotty, 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rapid urbanisation of coastal zones: a case study of shenzhen. sustain. 12. https://doi.org/10.3390/su12062254 © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 04 no 03 2019 186 putri, r.f. et al./ jgeet vol 04 no 03/2019 research article determination of priority regions as the direction of decisionmaking for land development of west kalimantan province ratih fitria putri 1 *, aryana rachmad sulistya 2 1 department of environmental geography, faculty of geography, universitas gadjah mada, indonesia 2 master program of geography, faculty of geography, universitas gadjah mada, indonesia * corresponding author : ratihfitria.putri@ugm.ac.id tel.: +62-274-6492340 received: mar 26, 2019; accepted: june 21, 2019. doi: 10.25299/jgeet.2019.4.3.2908 abstract indonesia is an archipelago country consisting of large and small islands with a large number of approximately 17,508. some of the islands are among the border to neighboring countries. one of the islands is a border area of land that is found on the island of borneo, especially west kalimantan province. west kalimantan province is directly adjacent to malaysia. the identic character of the indonesian border area is largely a lagging region. determination of priority areas is certainly needed as an effective way of developing these border areas. the objectives of the research include (1) identification of the distribution of lagging priority areas in west kalimantan province, (2) give recommendations related to development of lagging priority areas. overlays of lagging region parameters and economic productivity are used to determine priority areas. the result of identification is known that bengkayang regency, kayong utara, and melawi are the lagging priority areas. recommendation given to the lagging priority regions are through regional development model and also based on determination of base sector. keywords: land development, priority region, economic land productivity. 1. introduction indonesia is an archipelagic country which consists of large and small islands with approximately reachs 17,508 islands. the existence of indonesia as an archipelago country had been recognized in the world through the marine law convention of pbb, unclos. some of the islands are the border islands with the neighboring countries. border areas of indonesia with the neighboring countries consist of both land and sea boundaries. land boundaries involve malaysia, papua new guinea, and timor leste. sea boundaries involve malaysia, singapore, philipine, papua new guinea, timor leste, india, thailand, australia and palau. one of the islands which hasland boundary area is located in kalimantan, especially west kalimantan. west kalimantan is directly adjacent to malaysia. border areas of west kalimantan province involve sambas regency, bengkayang regency, sanggau regency, sekadau regency, and kapuas hulu regency.west kalimantan province is one of the province in indonesia which consists of 14 regencies/cities and traversed by equator, precisely in pontianak city. the population density of west kalimantan province is always increasing in the period 2000-2017 (bps, 2018) (fig. 1). based on the newest data from west kalimantan barat province in figures 2017, the population of west kalimantan province amounted to 4,861,738 people. the population in west kalimantan province is concentrated in urban areas than in rural areas, especially in pontianak city and kubu raya regency. the background of the phenomenon is likely due to economic stagnation and limited employment in rural areas (kinggundu, 2014). existence of various and uneven population in each regencies/cities results the difference of condition of social, economy, resources management, infrastructure, etc. geographical condition, and potential of natural resources in each regencies/cities of west kalimantan province are able to impact the inequality of economic and human development. this condition is strengthen by data that was released by central agency on statistic of west kalimantan province about gini coefficient of west kalimantan province based on the expenditure data in 2016, its gini coefficient was amounted to 0.33 which means moderate inequality. development disparities among the regencies/cities of west kalimantan province in period of 2011-2015 relatively low, but it increases every year and 50% of west kalimantan province regions are included in the category of relatively underdeveloped regions, it counts 7 of total of 14 regencies/cities. main factors of social and economic inequality are the distance and quality of health services, population, and limited economic empowerment. another problems which also be a challenge for both central government and west kalimantan provincial government is the http://journal.uir.ac.id/index.php/jgeet putri, r.f. et al./ jgeet vol 04 no 03/2019 187 existence of region that directly adjacent to the other countries. the identical character of the borden regions in indonesia is most of them are the underdeveloped regions. the social-economic facilities and infrastructures in those regions commonly are more underdeveloped than the others in one region (province). those conditions are reinforced by opinion of nurdjaman and rahardjo (2005) in taena (2009) which the challenges of regional development in the regions that directly adjacent to the other countries, include geographical aspect, demography aspect, natural resource aspect, economic aspect, sosioculture aspect, etc. effort is needed in order to able developing those border regions effectively. concept about the underdeveloped region have not had the standard definition until now ( ). there are some sources which define and give the indicators about the classification of a region is categorized as a underdeveloped region. bps defined that the underdeveloped region as a region characterized by the low potential of its village, housing and environmental condition, and the less favorable demographic social position compared to the other regio putri (2013) defines the underdeveloped regions as the regions with their development average are relatively lower than the other regions. based on those definitions, it can be inferred that basically the concept of the underdeveloped region emphasizes on backwardness conditions of a region from physical, social, and economic aspect as a result from a less optimal development target in that region. various factors which are hipotized as the factors causing the underdeveloped regions are geographic factors, natural resources, human resources, facilities and infrastructures, disaster prone areas, conflicts, and development policies that applied in such regions. geographic factors become the causing factor because commonly the underdeveloped regions have a long distance and access which is difficult to reach by the transport and communication network, the existence of barrier in the form of hills, the coastal area, and the other geomorphological factors.natural resources have been a defining factor of the underdeveloped region because some regions do not have the potential of natural resources or perhaps they have the potential of natural resources, but it is only for conservation so they can not use it. education level, knowledge, and skills which are relatively low in the underdeveloped regions cause the human resources factor also becomes the indicator to determine the underdeveloped regions. limited facilities and infrastructures such as communication, transportation, irigation, clean water, and another access of facilities and infrastructures which commonly exist in the underdeveloped regions become the defining components that are neccessary in assessment of the regions. disaster prone areas, especially social disaster such as conflict prone areas and applicable development policies also contribute to give the assessment of the regions. mapping on determination of priority regions hopefully can be basic on decision-making, especially related to the development of the underdeveloped regions which prioritized to develope as soon as possible. determination of priority regions in development seems like have been an effective effort to fasten the development of the underdeveloped region because most of the government in some regions has limitation in many aspects such as finance, technologies, and quality of human resources. furthermore, the determination of priority areas is also expected to create synergism which can integrate between regions, thus obtaining better results than those obtained through the performance of each region (yunus, 2008 in giyarsih, 2017). approach which can be used to determine the underdeveloped regions is scoring method. this mehod give the score value on each paramaters that used in the determination of the underdeveloped regions. the value of scoring given in each parameters is based on the distribution of data. three major aspects that have had significant influence to bridge the gap are mainly investment in infrastructure, investment in human capital, and more exposed & vulnerable to natural hazard (khondkerand mazhab, 2015). in line with that, the parameters which used in determination of underdeveloped regions are mostly similar, according to pdt (2005), consist of (1) aspect condition (3) facilities and infrastructures (4) the ability of regional finance (5) access and regional characteristics (6) the underdeveloped region characteristics. those six parameters, further more, are not used overall in this research, but only parameter one, two and three which assumed have been enough to represent a region to be classified as a underdeveloped region. those three parameters will be combined with the economic productivity in each regencies/cities in west kalimantan province. overlay between the results of weighting and calculation of economic productivity is done to know the priority regions. the overlaying process results the priority regions classification map which shows that the priority regions are the regions which have the higher priority than the other regions in one region (province). further more, the result of mapping on priority region will help on formulating the policies that can be used to fasten the development of the regions. 188 putri, r.f. et al./ jgeet vol 04 no 03/2019 fig. 1 population densityin west kalimantan province. fig. 2 west kalimantan province. 2. study area and data 2.1 west kalimantan province area of study in west kalimantan province is one of the 4th largest province in indonesia, after papua, central kalimantan, and east kalimantan, which has 14 regencies/cities. astronomically, west kalimantan province is located between 2o08n-3005s and between 108o0w-114o10e (fig 2). geologically, west kalimantan province consists of schwaner mountain complex and melawi-ketungau basin. the percentage of schwaner mountain is the largest compiler in west kalimantan. schwaner mountain consists of three physiography, they are alluvial plains, mountains, and hills. alluvial plains are dominated by wetland in form of swamp, peat, tidal area, and large rivers or small rivers which are used as the main line for transportation in hinterland eventhough the road infrastructure have been able to reach most of the subdistrict in west kalimantan province. overall, the length of kalimantan area which is directly adjacent to the state of serawah, malaysia is approximately 1,200 km which 70,58% of it is located in west kalimantan or along more than 847.3 km and across 5 regencies, they are sambas regency, bengkayang regency, sanggau regency, sintang regecy, and kapuas hulu regency that involve 14 sub-districts, covering an area of 1,694 km2. 2.2 data acquisition data that used are secondary data obtained through badan pusat statistik (bps) in west kalimantan province publication in figures and each publication districting figures. inventory data parameters include data of the condition of human and economic resources in west kalimantan province. the data are furthermore synthesized graphically and analyzed descriptively. criteria (parameters) used for the determination of underdeveloped regions, according to the ministry of pdt (2005) consists of, (1) the economic aspect of society, (2) the condition of human resources, (3) conditions illustrated by poor population percentage indicators. human resource are described by labor conditions (unemployment rate), health conditions (malnutrition, infant mortality rate, and number of health infrastructure), and educational putri, r.f. et al./ jgeet vol 04 no 03/2019 189 conditions (the highest literacy rate and education of age 5+). meanwhile, infrastructure criteria (infrastructure) are represented by decent living standard conditions such as types of wall, roof, floor, toilet, cooking fuel, and home ownership status. additional parameters are also combined in determining the underdeveloped regions, the parameter of economic growth. the purpose of adding these parameters is to obtain more comprehensive results in accordance with conditions in the field. moreover, the addition of parameters is also done because of the limitations of indicators in the economic aspects (scoring method). 3. method 3.1. underdeveloped regions determination scoring the tiered quantitative approach method is weighted by providing scores and rate for each parameter determination of underdeveloped regions.the first step of assessment is scoring analysis. the scoring model is used to represent the degree of closeness, association, or severity of a particular impact on a phenomenon spatially. a score will be given in each input parameter and then summed to obtain the degree of relevancy.the last result of the scoring system is to classify the degree of linkage of output parameters (drobne and lisec, 2009). each parameter is given a score of 1-3, where score 1 is an advanced regions, score 2 is a developing regions and score 3 is underdeveloped regions. scoring scores are based on sturgess method. sturges formula is done by subtracting the maximum value with minimum value of parameters and divided by the desired interval. the weight given for each parameter corresponds with the magnitude of its effect on the underdeveloped regions. highest rate of 4 is given on the parameters of human resources with variables of unemployment rate, education, and health. other parameter economy which variable of percentage of the poor. lowest rate of 2 is given in the infrastructure parameters. the weight given on each parameter does not have a standard reference, but can be analyzed from the results of literature review and should be in accordance with the influence of determining underdeveloped regions. the parameters of human resources and economy has the same weight as the most influential because both parameters are the basic capital in building a region. if the human quality is good then the development of the regions will run quickly and that makes the regions more advanced. on the other hand, if basic human development capital is hampered, such as difficulty to access of education, high unemployment and disrupted health will result in a rise on the number of poor populations so that the regions can be left behind from other regions. parameters of infrastructure have the lowest weight because these parameters tend not to change much each year as well as the characteristics of living standards such as the form of houses in every regencies/cities in west kalimantan province are not much different. the weight value which is determined is multiplied with the score and classified by sturgess method toresult the analysis of advanced regions and underdeveloped regions. the classification of development regions is divided into three class, if the total value of excavation is high, it represents the underdeveloped regions, meanwhile the low total value shows the advanced regions and the total value between them is classified as the developing regions. the result of weighting is classified into three chategories used sturgess method. the three categories are advanced, developing, and underdeveloped regencies/cities. the calculation of economic productivity the calculation of economic productivity is affected by the rate of economic and population growth. the substraction between those two parameters results the degree of economic productivity in the region. mathematically, the calculation formula of economic productivity is explained by the following eq. (1): pk = lpe-lpp (1) where: pk : economic productivity lpe: economic growth rate lpp : population growth rate 3.2 weighted index overlay method on determiningthe priority regions the determination of priority regions is done by combining (overlay) between the three parameters in determining underdeveloped regions and the economic productivity. overlaying is done to strengthen the relation of parameters on the degree of regional development. there is no standars system on determining the underdevelope. regions from both of parameters and its techinal determination. it depends on the availability of data and the purpose of the research related to determination of regional okysari (2015) in the similar research also does the overlaying with the additional parameter, they are potential of village, housing and environmental condition, population condition, and additional variabel for the rural. overlaying from two classifications will result nine possibilities. the determination of priority regions from nine possibilities is done by the judgment based on the result of the further identification related to data that shows the regions are relevant to be classified as the priority regions to increased development. the following are nine possibilities as the result of overlaying (table 1). 190 putri, r.f. et al./ jgeet vol 04 no 03/2019 table 1. overlay scores result of lagging regions towards economic productivity 4. result and discussion 4.1 scoring determination of underdeveloped regions regency with the highest score is bengkayang regency with a total score of 82 (table 5). the position of the underdeveloped region with the second lowest score is melawi and kayong utara with 80 (table 5) as a total value, both are the results of regional expansion. other underdeveloped regions are landak and singkawang city (fig. 3). some of the reasons that may make the five regions being underdeveloped are due to human resources (represented by health and education conditions (table 3 and 4) and poor economic conditions (represented by poor percentage (table 2) of poor al score of 82). second lowest score of underdeveloped region is melawi and kayong utara with 80 as a total value, both are the result of regional expansion. other underdeveloped regions are landak and singkawang city.some of the reasons that may make the five regions being underdeveloped are due to human resources (represented by health and education conditions) and poor economic conditions (represented by poor percentage of poor people), where these two aspects have a same value and the highest among the total three parameters used. bengkayang is directly adjacent to malaysia in the north. accessibility in this region is still very limited, making it difficult to reach all areas of the region. it can also be the cause of the lack of facilities and affect the quality of human resources and the economy of the community. kayong utara and melawi are the result of regional expansion. melawi is one of the new region from the expansion of sintang in 2004, while kayong utara is an expansion of ketapang in 2007 (ppsp, 2013). it has not been a long time to have an administration and its own authority as a region is certainly a significant factor that causes both of them can't achieve a good development. beside, kayong utara is also an archipelagic area that causes difficult access and also many remote areas. in general, geographical conditionsbecome one of the dominant factor which makes many regions underdeveloped in west kalimantan province. table 2. poverty indexscoring result scoring result classification result of economic productivity overlaying result advanced high advanced developed moderate developed underdeveloped low underdeveloped advanced low low developed moderate developed underdeveloped high underdeveloped advanced moderate advanced developed low developed underdeveloped high underdeveloped regency poverty index (%) score weight result bengkayang 6,94 1 4 landak 13,51 3 12 mempawah 5,52 1 4 sanggau 4,57 1 4 ketapang 11,72 3 12 sintang 9,33 2 8 kapuas hulu 9,66 2 8 sekadau 6,5 1 4 melawi 12,57 3 12 kayong utara 9,84 2 8 kubu raya 5,22 1 4 pontianak city 5,22 1 4 singkawang city 5,76 1 4 putri, r.f. et al./ jgeet vol 04 no 03/2019 191 table 3. human resource parameter scoring result regency unemploymet education health weight result score lrs* sprs** bns*** imrs**** hcfs***** total score sambas 2 2 bengkayang 1 3 3 1 2 2 12 48 landak 2 2 2 1 1 2 10 40 mempawah 2 3 2 1 1 3 12 48 sanggau 2 2 3 1 1 2 11 44 ketapang 1 2 3 1 1 1 9 36 sintang 1 3 3 1 1 1 10 40 kapuas hulu 1 1 1 3 3 1 10 40 sekadau 1 2 2 1 2 2 10 40 melawi 1 3 3 1 1 2 11 44 kayong utara 1 3 1 1 2 3 11 44 kubu raya 2 1 2 1 1 2 9 36 pontianak city 3 1 1 1 1 3 10 40 singkawang city 2 3 3 1 2 3 14 56 *literacy rate score; **school participartion rate score; *** bad nutrient score; **** infant mortality rate score table 4. infrastructure parameters scoring result table 5. classification of developed region. regency total score classification sambas 70 developed bengkayang 82 underdeveloped landak 78 underdeveloped mempawah 70 developed sanggau 70 developed ketapang 74 developed sintang 72 developed kapuas hulu 74 developed sekadau 74 developed melawi 80 underdeveloped kayong utara 80 underdeveloped kubu raya 60 advanced kota pontianak 62 advanced kota singkawang 78 underdeveloped regency electricity (non pln) wall floor roof closet coocking fuel house ownership total score weight result ambas 1 2 1 3 1 2 1 11 2 22 bengkayang 2 3 3 2 2 2 1 15 30 landak 2 2 1 1 3 3 1 13 26 mempawah 1 1 1 1 3 1 1 9 18 sanggau 3 2 1 1 1 2 1 11 22 ketapang 3 2 2 1 1 3 1 13 26 sintang 3 3 1 1 1 2 1 12 24 kapuas hulu 3 3 1 1 2 2 1 13 26 sekadau 3 3 1 1 3 3 1 15 30 melawi 2 2 1 1 2 3 1 12 24 kayong utara 1 3 1 3 3 2 1 14 28 kubu raya 1 2 2 1 2 1 1 10 20 pontianak city 1 1 1 1 1 1 3 9 18 singkawang city 1 1 1 2 1 1 2 9 18 192 putri, r.f. et al./ jgeet vol 04 no 03/2019 fig. 3 map of lagging area determination in west kalimantan province. 4.2 calculation of economic productivity based on the calculation of economic productivity of west kalimantan province in 2015 that can be seen in fig. 4, economic productivity in each region of west kalimantan province is different. the area that has the lowest economic productivity is bengkayang with productivity value's only 1.49%, while the region that has the highest economic productivity is sanggau with productivity value reaches 7.3%. sanggau has the highest economic rate compared to other regions with value reachs 8.58% (table 5). the higher the rate of economy in a region, the process of increasing the area's output will be faster so that the prospects of regional development the better. according to reference todaro and smith (2004) in muta'ali, (2015), there are three main factors or components that affect economic growth, namely capital accumulation, population growth, and technological progress. bengkayang has the lowest economic growth rate compared to other regions in 2015, which is 3.96%. this shows that the growth of gdp of bengkayang is experiencing slow in the period of 2014 to 2015. the low economic growth rate causes the process of increasing output in bengkayang runs slowly so that the development prospect of bengkayang runs poorly. population growth rate becomes one of the factors that influences economic productivity in a region because if there's no productive human resources, economic productivity in the area will decrease and will increase poverty. bengkayang has the third highest population growth rate in west kalimantan province in 20142015 under singkawang and ketapang with a growth rate's 2.46%. sanggau has a relatively low population growth rate in west kalimantan province in 20142015, which is 1.27%. based on the condition of economic growth rate and population growth rate, bengkayang became the region with the lowest economic productivity, while sanggau has the highest economic productivity. overlay for land priority area determination classification of priority areas through overlay of regional development maps with economic productivity of each region in west kalimantan province resulted that bengkayang, melawi and kayong utara are classified as priority áreas (fig. 5).in general, these three regions are quite relevant if they are categorized into areas that are prioritized for improving development. bengkayang is a border area, while melawi and kayong utara are new regions from the expansion. table 6. economic productivity calculation result. putri, r.f. et al./ jgeet vol 04 no 03/2019 193 fig. 4 map of economic productivity in west kalimantan province. regencies/cities economic growth rate 2015 (%) human growth rate 20142015 (%) economic productivity result sambas 4,76 0,620904158 4,139095842 moderate bengkayang 3,96 2,464003985 1,495996015 low landak 5,11 1,334950425 3,775049575 moderate mempawah 5,62 0,903330782 4,716669218 moderate sanggau 8,58 1,276099446 7,303900554 high ketapang 5,53 2,532812611 2,997187389 low sintang 4,57 1,43194915 3,13805085 low kapuas hulu 4,66 2,324362547 2,335637453 low sekadau 5,75 0,831087035 4,918912965 moderate melawi 4,7 1,923026921 2,776973079 low kayong utara 5,03 2,125249317 2,904750683 low kubu raya 6,36 1,223796665 5,136203335 moderate pontianak city 4,99 1,591882253 3,398117747 low singkawang city 6,17 2,673148826 3,496851174 moderate 194 putri, r.f. et al./ jgeet vol 04 no 03/2019 fig. 5 . fig. 6 classification map of basis and non-basis sector in west kalimantan province based on lq method bengkayang regency is one of the underdeveloped regions located in north of and abutted with malaysia. accessibility in bengkayang province is limited while it makes complicated enough to reach each region and site in this regency. those problem are the one of the causal factor for less facility which influencing human resource capability and economy of society. the need to develop of underdeveloped region based on large numbers of isolated village, hilly topography condition which will minimize the access, and lots of swamp areas which needs more intense attention for development. bengkayang categorized as underdeveloped region with score of 82. indicators that contribute the most score come from human resource (health and education). the sub indicators of education are school participation rate and score of ability to read, both of those sub indicators have low score compared to other regency in west kalimantan putri, r.f. et al./ jgeet vol 04 no 03/2019 195 province. it has the same on health condition which represented by infant mortality rate and numbers of health facility. in addition, it has also low score for infrastructure condition. most of the society are living in the house of bamboo and using non pln electricity source. parameter of economic productivity shows the similarity. bengkayang regency has the lowest economic productivity among others in west kalimantan province with score of 1,49%. this low economic productivity influences low rate of economic growth and becoming one of the drop points it is categorized as priority to be developed region. kayong utara regency consist of 6 sub-districts which all of it in border with the sea (ppsp, 2013). kayong utara regency was unfoldmentarea from ketapang regency in 2017. in 2015, kayong utara was determined as the underdeveloped region in indonesia based on uu number 6 year 2007. parameters with bad score come from human resource indicator with the sub of parameter are education & health and infrastructure condition parameter. on the other hand, parameter for economic condition of society remains good.economic condition represented by percentage of poor society. it has score of 9.84% while the highest score is 13.51%. in role with this score, kayong utara regency positioned as the four highest percentage of poor society regency in west kalimantan. economic productivity of this regency has score of 2,905% and categorized above averages compared to other regency. this indicates that economic growth rate in sector is not lagged (ppsp, 2013). furthermore, kayong utara regency is archipelago type regency, each sub-district abuts on sea, hence it causing limited access to connect each sub-districts. limitation of the access is one important point causing the underdeveloped region. melawi regency included in the priority area because classified as lagging with economic productivity of 2,77%. melawi has low score on human resource and economic condition indicator. it is shown by rate of poor society and infrastructure positioned below other regencies. either of human resource or economic conditions indicator has the same bad score. infrastructure development can be done to improve the development of melawi district. on the other hand community-based development also needs to be done to improve the development of human resources in the region. development directional step for priority region. a. directional steps for priority region based on regional development theory determined that strategy to develop priority region in macro scope are using theory approach such as balances growth theory, growth pole/growth centre theory, import substitutions industrialization, exported growth and nucleus industries theory. importance and emphasize of those theory is about development region that has trickle effected to the lowest level by giving up stimulant in developing the region. application of this theory clustered in five basis groups ( ). those five basis groups divided to five aspects, which are spatial study, regional economy, development of investment and infrastructure, regional management, and society management. b. land development directional step for west kalimantan province based on basis sector recommended development directional step to strengthened economic development for each regency in west kalimantan can be done by lq analysis. lq method used to specialized basis sector and non-basis sector, basis sector named because the sector could meet the demand either inside the area or outside, otherwise non-basis sector named because that sector can only fulfil the demand inside the area. lq analysis also used as regional development indicator, for example is regional gross domestic products (tarigan, 2009). basic point of this analysis is economic base theory which mentioned that because of industry basis produces goods and services for markets either inside or outside the area, hence export of goods and services would give high revenue for those areas. this revenue flow will probably cause higher consumption and investment and finally increase revenue and create job opportunities (tarigan, 2005). increasing of the revenue would high up demand in basis and non-basis sectors that would push up investment.lq analysis used in three main sectors in west kalimantan province, which are agricultural, industries, and services sectors. by sector development would be more effective done by optimize on management in each sectors. based on calculation result of base sector determination of three priority area, bengkayang and kayong utaraare best in agricultural sector, while melawi are best in industrial sector. making specialization of basis products would increase productivity in the sector and help to increase regional economy. these methods and analysis hopefully would applicable enough to manage underdeveloped and priority regions in west kalimantan province. 5. conclusion identification of priority area determination through overlay of scores of lagging regions on the economic productivity of each region produced 3 districts covering bengkayang, kayong utara, and melawi. development guidance in the form of application of the theory concept of development of underdeveloped regions and development of base sector. calculation result of base sector determination of three priority area, bengkayang and kayong utara are best in agricultural sector, while melawi are best in industrial sector. making specialization of basis products would increase productivity in the sector and help to increase regional economy. both directions are expected to increase the development of priority area. acknowledgment the authors would like to acknowledge the great support of the department of environmental geography, faculty of geography, universitas gadjah 196 putri, r.f. et al./ jgeet vol 04 no 03/2019 mada who have provided suggestions for the improvement of this paper. references badan pusat statistik. 2015. indeks pembangunan manusia. available in: http://ipm.bps.go.id/page/ipm. accessed in 2 march 2019. dinas kesehatan. 2011. profil kesehatan kabupaten kayong utara tahun 2010. dinas kesehatan: sukadana. drobne, s. and lisec,a. 2009. multi-attribute decision analysis in gis: weighted linear combination and ordered weighted averaging: informatica. giyarsih, s.r. (2017). regional management of areas with indications of urban sprawl in the surrounding areas of universitas muhamadiyah yogyakarta, indonesia. indonesian journal of geography 49 (1), : 35-41. kementrian negara pembangunan daerah tertinggal. 2005. strategi nasional percepatan pembangunan daerah tertinggal. jakarta : kpdt. s khondker, bazlul h. and moogdhomim m. 2015. underdeveloped districts development: background study paper for preparation of the seventh five-year plan. kiggundu, a.t. 2014.constraints to urban planning and management of secondary towns in uganda. international journal of geography 46 (1):(12 21). yogyakarta: badan penerbit fakultas geografi ugm. perencanaan wilayah, tata ruang, dan lingkungan. yogyakarta: badan penerbit fakultas geografi ugm. tertinggal di kabupaten klaten. yogyakarta: fakultas geografi. ppsp. 2013. buku putih sanitasi kabupaten kayong utara. available in: https://ppsp.nawasis. accessed in 18 january 2019. ppsp. 2013. profil sanitasi kabupaten melawi. available in: http://ppsp.nawasis.info/dokumen/perencanaan/sanitasi/ pokja/ssk/revisi/kab.%20melawi/bab%20ii%20ssk%20new 1%20sdh%20di%20qa.pdf. accessed in 22 february 2019. putri, r.f., bayuaji, l., sumantyo, j.t.s., and kuze, h. 2013. terrasar-x dinsar for land deformation detection in jakarta urban area, indonesia. journal of urban and environmental engineering. vol 7(2), pp. 195-205. doi: 10.4090/juee.2013.v7n2.195205. tarigan, r. 2005. perencanaan pembangunan wilayah. bumi aksara: jakarta. tarigan, r. 2009. ekonomi regional teori dan aplikasi. pt. bumi aksara, jakarta. taena, werenfridus. 2009. kajian pengembangan ekonomi wilayah perbatasan kabupaten timor tengah utara dengan distrik enclave oekusi. thesis. graduate school program. institut pertanian bogor. © 2019 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ putri, r.f. et al./ jgeet vol 04 no 03/2019 197 1. introduction 2. study area and data 2.1 west kalimantan province 2.2 data acquisition 3. method 3.1. underdeveloped regions determination scoring 3.2 weighted index overlay method on determiningthe priority regions 4. result and discussion 5. conclusion acknowledgment references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 putri, r.f. et al./ jgeet vol 5 no 2/2020 45 research article impacts of population density for landuse assessment in cengkareng, west jakarta, indonesia ratih fitria putri1,*, aji wijaya abadi1, naufal fattah tastian1 1department of environmental geography, faculty of geography, universitas gadjah mada, indonesia * corresponding author : ratihfitria.putri@ugm.ac.id tel.: +81-90-403-7201; received: aug 28, 2019. accepted: march 17, 2020 doi 10.25299/jgeet.2020.5.2.3705 abstract economic development in jakarta has been influencing physical and social characteristics of urban area significantly. for recent years, burgeoning population growth occurs as a result of urban development and contributes to the landuse dynamics in a certain area. cengkareng, is one of the most developed urban areas in jakarta and has been experiencing such population and landuse dynamic s. its strategic location has turned this area becomen densely-populated. increasing population density increase land demand, shapes the settlement pattern, and changes the landuse of the area. a study conducted in cengkareng district has been done to describe h ow the population density impacts the landuse features for landuse assessment. the method implemented in this study combines quantitative and qualitative to process statistics and satellite imagery to produce data of population density, landuse change, and settlement pattern of the studied area. the study aims to determine the impact of increasing population density on determining the right landuse for urban areas. it can be use as the reference for the local government in designing regional spatial plans that are adjusted to the conditions of the population. the study resulted that cengkareng has experienced such significant landuse change which is dominantly converted into settlement and offices due to rising of population density. nucleated settlement pattern has taken more area regarding to increased land need over land supply. it becomes serious problem for cengkareng such aa slum settlements, flood problems, and land subsidence. keywords: landuse change; population density; settlement pattern 1. introduction jakarta used to be batavia, which was the capital of dutch east indies. massive development has been started in the colonial era and has led to rapid economic growth until nowadays. it turns batavia, which then become jakarta, as the center of economic and business activities beyond its role as the capital of indonesia. the economic growth of jakarta accelerates its development, mostly in networks and infrastructures. better networks have been stimulating better goods exchange and distribution as well as population mobility. the development has offered favorable condition as a living place with high quality of living standard and it can be seen by the increase of total population in jakarta from year to year as shown on table 1. table 1. population of jakarta 1970-2010 year population increase percentage 1971 4,576,009 1980 6,480,654 41,62 1990 8,227,746 26,95 2000 8,347,083 1,45 2010 9,607,787 15,10 the population increase encourages jakarta to become one of the metropolitan cities in the world. population increase is identified in demographic processes and its dynamics has been strongly influencing urban growth in jakarta. urban growth can not be separated from urbanization. urbanization is a terminology to define population movement, from non-urban area to urban area including socio-economic and physical feature change in the urban area (mcgranahan and satterthwaite, 2014). urbanization has both positive and negative impacts. the positive impact is the acceleration of economic growth which leads to better prosperity for the people. otherwise, the reverse impact is threat to urban sustainability since the city is growing physically and consuming land at a rate that exceeds population growth (belete, 2017). massive urbanization in jakarta has led to increase of land needs for buildings such as settlements, offices, and industries. uncontrollable urbanization triggers landuse change. most area in jakarta has been transformed into settlements. growing population is in harmony with increased settlements. it means there is rising population density as well as settlements density. cengkareng is one of jakarta’s district to experience landuse change due to urbanization (prasasti et al., 2015) cengkareng area extends 26.54 km2 in the western part of jakarta. its area consists of six sub-districts and the location is strategic. cengkareng has a close proximity to the international airport of soekarno-hatta in tangerang. its proximity to the airport reveals high mobility from and to the jakarta metropolitan area. it is also circled by jakarta outer ring road toll (jorr) which connects the entire province and the surrounding region. the presence of the airport and toll road correlate with positive population mobility. its presence opens wider accessibility to get in and out of the province. the economic activities are also supported along with its people’s mobility. it offers many opportunities for outsider to move http://journal.uir.ac.id/index.php/jgeet 46 putri, r.f. et al./ jgeet vol 5 no 2/2020 into the region, some of them settle along with locals and the rest becomes commuters. thus, there is increasing number of inhabitants live in cengkareng as shown on figure 1. fig 1. inhabitants of cengkareng.to prepare your paper, use directly this template and simply replace this text by your text. table 2. population growth of cengkareng 2009-2017 year population area (km2) population growth 2009 306,954 26.54 11,565.71 2011 468,918 17,668.35 2013 494,343 18,626.34 2015 500,145 18,844.95 2017 515,081 19,407.72 average of population growth 17,222.61 based on the figure 1, the population rises from 2008 until 2018. the data indicates that there is population growth and it results to increase in population density. admittedly, cengkareng is predicted to have rising population density and may experience more landuse change. by this means, a study is conducted to assess landuse change in cengkareng based on population density and settlement pattern. 2. materials and methods the research implements descriptive method in spatial context. this method integrates quantitative and qualitative analysis to describe the object of the study from a certain sample of a population. by this method, the collected data is used to explain the landuse change in the study area using population density variable through quantitative calculation and settlement pattern by qualitative analysis. 2.1 location the area studied in this research is cengkareng district, west jakarta. the area consists six sub-districts as shown on the figure 2. cengkareng district elevation is about 2 meters above mean sea level and this area is passed by three big rivers such as cisadane river, pesanggerahan river, and kali angke river which have been canalized but ironically the inundation still occurs in both rainy and dry season. the reason of choosing cengkareng as study area due to the rapid landuse change stimulated by urban growth. it is supported by the increasing number of population density due to high demand jobs in the industrial sector in cengkareng. it makes the migrants who have obtained employment tend to settle that cause increase the population density. population density increased from 11,471 inhabitants/km2 in 2011 be 18,769 inhabitants/km2 in 2015 that impact to the landuse change of settlement from 1825.84 ha in 2011 be 2087.61 ha in 2016 (putri et al., 2019). fig 2. administrative map of cengkareng district, west jakarta municipality 2.3 research design the research design is classified into three main steps as shown on figure 3. the first is determining population density from statistics of population. the second is gaining the landuse change percentage from statistics of landuse. the third is determining the population pattern by interpreting satellite imagery. later, the data are analyzed to describe the objective of the study. 306.954 468.918 494.343 500.145 515.081 0 100.000 200.000 300.000 400.000 500.000 600.000 2009 2011 2013 2015 2017 n u m be r of i n h ab it an t year number of inhabitants in cengkareng 2009 2017 number of inhabitants putri, r.f. et al./ jgeet vol 5 no 2/2020 47 fig 3. research flowchart 2.3.1 population density population density, refers to the objective of the study, is the arithmetic population density. it is the main parameter for landuse assessment. arithmetic population density represents the total inhabitants who live in a certain place and time per unit of area. the data needed for population density calculation is total population and area in a certain place and time which were obtained from the data recorded by indonesia central bureau of statistics. the use of population density data adapts the research of (li et al., 2015)which studies how population density related to landuse change in the western jilin province. the arithmetic population density uses the following equation. population = total inhabitants total area (agricultural + non − agricurtural area) the population density of each subdistrict in cengkareng then classified to categorize the class of the population density and processed by gis (geographic information system) software to produce population density map. 2.3.2 landuse change landuse change is the variable impacted by the dynamics of population. change in population density is analyzed from the landuse proportion from year to year. landuse proportion data were taken from the statistics of landuse published by the indonesia central bureau of statistics. landuse proportion of each subdistrict is visualized through graph for the analysis. 2.3.3 settlement pattern settlement pattern refers to the way of how house arrange each other which is primarily influenced by the variety of surrounding landscape, consists of physical landscape and cultural landscape. settlement pattern is relatively dynamic, following any development in urban area. settlement pattern can be classified into three different categories, forming nucleated pattern, dispersed pattern, and linear pattern. nucleated settlement formed as a lot of houses agglomerate creating a big clustered and mainly found in lowland area. dispersed settlement is a typical settlement where houses are spread out in different place, usually found in highland area. meanwhile, linear settlement is a settlement which develops in line and is adjacent to road, river, or shoreline. the settlement pattern can be investigated from satellite imagery. the satellite imagery using google earth as it can depict settlement, including other landuses. the image was through digitation process to produce settlement pattern map. the data resulted in this research are population density, landuse change in proportion, and settlement pattern. population density and landuse change data are used to identify how far population density influences the configuration of landuse in cengkareng while settlement pattern data is used to identify the settlement pattern in cengkareng regarding to the existing landuse proportion. from this analysis, it can be described the population density impacts for landuse assessment in cengkareng district. 3. result and discussion classifying and mapping population density population density map creating settlement pattern map determining population density google earth satellite imagery of cengkareng statistics of population in cengkareng population density data statistics of landuse in cengkareng classifying landuse type determining landuse change delineating landuse based on the interpretation identifying settlement pattern on each sub-district visualizing landuse change by graph or diagram landuse change data data analysis settlement pattern map impacts of population density for landuse assessment input process output annotation 48 putri, r.f. et al./ jgeet vol 5 no 2/2020 population dynamics can indicate urbanization. mainly, urbanization occurs as a result of urban growth. in developing country like indonesia, urbanization is a common phenomenon, characterized by high population increase in urban area. refers to urban growth, impacts of population assessment towards the surrounding environment, is easily identified through its spatial distribution of the population beyond emphasizing the population absolute number. spatial distribution of population can be described through population density. thus, population density becomes the most important demographic parameters involved in analyzing the impacts of population towards landuse change. population and its surrounding environment are influencing each other. as population changes dynamically, environment would get the impact. physical parameters such as landuse and landcover is well enough to represent the degree impacts of population dynamics. moreover, physical parameters are relatively easy to measure rather than socio-cultural parameters (arifin et al., 2018). cengkareng district has the most population among other districts in jakarta (bps 2018). with its small area, cengkareng also gets predicate as a district with high population density in jakarta. admittedly, a high total population in cengkareng is encouraged due to its strategic location which relatively close to the soekarnohatta international airport. obviously, the presence of the airport itself stimulates the growth of industrial activities, trade, and business. the growth of cengkareng can not be separated from the development in the jakarta metropolitan area. jakarta plays role as a big metropolitan area. in general, metropolitan area is divided into cbd (central business district) zone and outskirts zone. the cbd is a specialized zone in urban area, plays role as the center of urban population activities in the field of economic, capital, business, and financial (taubenbock et al., 2013). cbd becomes attractive due to its availability and accessibility to jobs, transportation points, as well as markets. its role as central location has turned the land becomes expensive and is intensively used. the investment in cbd also contributes in increasing economic benefit following land value. the intensive use in cbd encourage increase in land consuming and transform most of the land into built-up area, like what it looks like in jakarta recently. it also increases the population density in the center of metropolitan area. as population grows from time to time following metropolitan area development, the cbd becomes unfavorable for the residential area. hawley theory of human ecology states that metropolitan population growth would have two consequences. first, the population density should decrease rapidly with distance from the cbd. second, metropolitan population growth would increase population density in cbd since the shortage of available land. in shorts, there will be population deconcentration to the outskirts zone and changing in settlement pattern. this phenomenon can be identified clearly in jakarta, especially in cengkareng. population dynamics have resulted impacts to the landuse change occurred in cengkareng. 3.1 population density impact on landuse 3.1.1 subdistrict of duri kosambi subdistrict of duri kosambi located in the southern part of cengkareng district, occupies an area of 5.91 km2. according to its population density in 2009 to 2017, duri kosambi is known to have experienced significant increase of population density for the past few years as shown in figure 4. fig 4. population density in duri kosambi 2009-2017 population density grows from 9,020.30 inhabitants/km2 in 2009 to 14,568.02 inhabitants/km2 in 2017. the highest increased of population density occurred in 2009 to 2011 which is believed to be stimulated by high incoming migration. yet the population density of duri kosambi is relatively low, compared to other subdistricts of cengkareng. table 2 shows landuse of duri kosambi. landuse area can be converted into percentage unit to describe the proportion of the landuse. based on figure 5 that shows the landuse proportion of duri kosambi, 56 per cent of the area is used for settlement, 21 per cent is allocated for industrial area, 18 per cent for office building, the rest is for open space and other landuses. landuse proportion may represent the population dynamics as population correlate with land demand. when land demand rises over the population growth, it will give impact to the existing landuse. landuse may be transformed to another landuse or collide with the existing landuse as what has occurred in duri kosambi subdistrict. table 3. landuse of duri kosambi. type area (km²) settlement 3.29 industri 1.24 office 1.06 open space 0.10 other 0.22 fig 5. landuse proportion of duri kosambi 2017 according to bps (2017), duri kosambi has the largest industrial area among other subdistricts in cengkareng. 9.020,30 12.854,82 13.548,56 14.289,34 14.568,02 0,00 5.000,00 10.000,00 15.000,00 20.000,00 2009 2011 2013 2015 2017po p u la ti o n d en si ty ( p eo p le p er k m ²) year population density in duri kosambi 2009 2017 population density 56%21% 18% 1% 0% 4% landuse proportion of duri kosambi 2017 settlement industri office open space agricultural land others putri, r.f. et al./ jgeet vol 5 no 2/2020 49 along with increase of births, the presence of industrial area has resulted to increase of productive workers from incoming migration to jakarta(putri et al., 2019) and emerged population density in the area. rising in population density create problems in the landuse. the land needed for residential area is the major problem regarding to population growth. land consumption for residential area that exceeds the available land has brought impact to decline in open space and it becomes obstacle to improve the environment quality and the sustainability of community in duri kosambi. low-waged workers tend to settle adjacent to industrial area to prevent additional transportation cost. ironically, most settlement built by these workers is categorized as slum settlement. slum settlement promotes negative impacts such as pollution and social problems. river pollution is undergoing following the development of slum settlement as the community has been dispose their wastes in unproper way. less open spaces impact to unavailable temporary disposal site in duri kosambi which has led the bad behavior of the community to spread their waste to the river, road, and subsequently hampers flood management and the surrounding community will experience flood more often (aditianata, 2015). 3.1.2 subdistrict of rawa buaya rawa buaya subdistrict has an area 4.07 km2 and its area is adjacent to kali angke river. this subdistrict for the recent years has experienced population growth identified from its population density as shown on the figure 6. based on figure 6, rawa buaya is known to have highly increased population density in 2009 to 2011, which interspersed with some fluctuation from 2011 to 2017. population density have increased from 7,460.80 inhabitants/km2 in 2009 to 16,562.05 inhabitants/km2 in 2011 while the fluctuations occurred in 2011 to 2017 with a range of change about 300 to 500 inhabitants/km2. in 2017, the population density reached 17,383.14 inhabitants/km2. fig 6. population density in rawa buaya 2009-2017 table 3. landuse of rawa buaya. type area (km²) settlement 2.48 industri 0.60 office 0.92 open space 0.02 other 0.05 the increasing population density in rawa buaya has influenced the land arrangement. the landuse type in rawa buaya shown on table 3 which represents the landuse in unit of are. the data is also processed into unit of percentage to know the proportion of the landuse as shown on figure 7. in general, landuse in rawa buaya is dominated by settlement which occupies roughly twothird of the area, 15 per cent is covered by industrial area covering, office building uses 23 per cent of the area, and less than 3 per cent is used for open space the other landuses. apparently, landuse of rawa buaya does not change significantly from 2009 to 2017. in the past few years, the population density did not change significantly too which indicates slower development of settlement in this area probably because of less available land for housing. fig 7. landuse proportion of rawa buaya 2017 lack of available land for settlement has encouraged most of the low-waged workers from incoming migration to develop irregular settlement. eventually, the irregular settlement transforms into slum settlement. most of the settlement is adjacent to industrial area and on the riverbank, especially in the kali angke river. the mushrooming of slum settlement in the kali angke riverbank comes as a contabsequence of the local government’s failure to provide decent housing for lowwaged immigrants in the area of rawa buaya (asvada, 2013). the slum settlement is directly influencing the physical process of the river. the community in slum area disposes their waste to the river. the wastes worsen the water quality and the discharge of the river. later, it can cause more destructive flood and inundate the surrounding community. moreover, the existing slum area has been being obstacle for the local government in river normalization. it has shown that there is still conflict between the landuse for protection function and utilization function. the decreasing open spaces may occur due to the development of slum settlements. it can also be obstacle for the flood management. besides, open spaces can be designed and developed for artificial water retarding zone that may help to reduce the inundation. 3.1.3 subdistrict of kedaung kaliangke kedaung kaliangke subdistrict location is between two notoriously big river canals named kali kapuk and kali angke and has area of 2.81 km2, makes it as the smallest subdistrict by area in cengkareng districts. population dynamics which is represented by change in population density, has been influencing the landuse arrangement in this subdistrict. the population density in kedaung kaliangke has increased for the past few years as displayed on the figure 8. in 2009, the population density is on 9,531.19 inhabitants/km2 and dramatically change into 13,168.30 inhabitants/km2 in 2017. the increase of population density is inseparable from regional economic development which constantly attracts new immigrants who seek for better livelihood. but in fact, the population density results some problems towards landuse arrangement. 7.460,80 16.562,05 17.121,90 16.852,79 17.383,14 0,00 5.000,00 10.000,00 15.000,00 20.000,00 2009 2011 2013 2015 2017 p o p u la ti o n d en si ty ( p o p u la ti o n p er k m ²) year population density in rawa buaya 2009 2017 population density 61% 15% 23% 0% 0% 1% landuse proportion of rawa buaya 2017 settlement industri office open space agricultural land others 50 putri, r.f. et al./ jgeet vol 5 no 2/2020 table 4 describe the existing landuse in kedaung kaliangke. as shown on the table, it can be extracted the area of each landuse which can be derived into percentage unit as shown on figure 9. in 2017, the landuse in this subdistrict is dominated by three type of landuse. the first is settlement which approximately cover 64 per cent of the area, followed by office which occupies 21 per cent of the land, and industrial area for roughly 15 per cent. the open space is less than 1 per cent, which is quiet nonproportional compared to other subdistricts. from the landuse proportion, it can be described the landuse development in kedaung kaliangke. fig 8. population density in kedaung kaliangke 2009-2017 table 4. landuse of kedaung kaliangke. type area (km²) settlement 2.48 industri 0.60 office 0.92 open space 0.02 other 0.05 fig 9. landuse proportion of kedaung kaliangke 2017 population growth has shaped the development of landuse in kedaung kaliangke in the same pattern like the other subdistricts. the landuse is dominantly covered by settlement, office, and industrial area which depicts the relationship between population growth and land resources. settlement covers the most area as a result of the population increase encouraged by increasing birth and incoming migration. increase in incoming migration to the area has been caused by attraction of industry development which absorbs many workers. the presence of well-developed industries is due to the strategic location, close to international airport and the cbd of jakarta. by this means, population increase has been creating high demand on land need while jakarta’s available space for settlement is declining. instantly, there is some irregular settlement settled close to industrial sector or riverbank and develops to slum settlement. this slum community discharges their wastes directly to the river and disrupt the natural processes in the river. moreover, they contribute to the increase of pollution which eventually reduce the water quality. the presence of slum settlement also creates another problem for the local government policy in flood management since the settlement disrupts the flood fringe of the river. 3.1.4 subdistrict of kapuk kapuk subdistrict area is the second biggest in cengkareng. its area extends about 5.63 km2 and is directly adjacent to penjaringan district of north jakarta municipality. kapuk subdistrict known as the most densely populated subdistrict in cengkareng (saraswati 2000). recently, statistics shows the same condition as shown on figure 10. based on figure 13, it can be identified that there is increase in population density from 2009 to 2017. in 2009, the population density is 16,367.92 inhabitants/km2 and reaches 27,369.55 inhabitants/km2 in 2017. population density in kapuk is the greatest compared to other subdistricts in cengkareng. the population density increases dramatically which indicated high population growth. the increasing population in kapuk can be analyzed from the population dynamics and has brought impacts to the surrounding environment. fig 10. population density in kapuk 2009-2017 increasing population in kapuk is influenced by the development of its area as a strategic industrial center in the western jakarta. the presence of many factories near the airport has resulted in increasing demand of job. wider job opportunities attract many newcomers from the surrounding city or nearby province to leave their hometown and come to this area, work, and settle their house. mostly, the newcomers settle and build their house near the industry locations. as a consequence, there is rising in population as well as population density. population growth in kapuk has contributed to increase in land need for housing, public facility, and infrastructures hence subsequently results in landuse change. table 5 shows landuse of kapuk subdistrict. landuse area can be derived into percentage unit to describe the proportion of the landuse (figure 11). in 2017, the landuse is more dominated by settlement roughly 72 per cent of its area, industrial sector about 13 per cent, and office for 14 per cent. the landuse with small proportion are open space, agricultural land, and other landuse which only reach 1 per cent. mainly, the domination of settlement is caused by the development of industry. since the location is strategic, high capitals were invested here and the industrial sector has been well-developed. ironically, most of the settlement is located in slum area 9.531,19 13.059,53 12.693,09 12.882,89 13.168,30 0,00 5.000,00 10.000,00 15.000,00 2009 2011 2013 2015 2017p o p u la ti o n d en si ty ( p eo p le p er k m ²) year population density in kedaung kaliangke 2009 2017 population density 64% 15% 21% 0%0% 0% landuse proportion of kedaung kaliangke 2017 settlement industri office open space agricultural land others 16.367,92 24.510,38 26.682,48 26.337,71 27.369,55 0,00 10.000,00 20.000,00 30.000,00 2009 2011 2013 2015 2017 p op u la ti on d en si ty ( p eo p le p er k m ²) year population density in kapuk 2009 2017 population density putri, r.f. et al./ jgeet vol 5 no 2/2020 51 and forms slum settlements, turning kapuk subdistrict as the subdistrict in cengkareng with high presence of slumcategorized settlements (fitria et al., 2014). the development of settlement in kapuk has been disturbing the available land for conservation function. as stated in the local government regulation number 1 year 2014, kapuk subdistrict area is one of subdistricts designed for the development of flood management infrastructure such as polders and canals. the function can not run well while the slum settlements and industries create pollution as well as reduces the environment quality. moreover, little open spaces in kapuk subdistrict, especially green open spaces, can not support the environmental sustainability since it does not meet the minimum area. table 5. landuse of kapuk. type area (km²) settlement 4.06 industri 0.72 office 0.78 open space 0.02 other 0.05 fig 11. landuse proportion of kapuk 2017 3.1.5 subdistrict of cengkareng timur geographically, cengkareng timur subdistrict is adjacent to the jakarta outer ring road toll (jorr) in the west and its area extends approximately 4.52 km2. cengkareng timur also has experience population growth like other subdistricts in cengkareng. it is in figure 12 that shows rising in population density of cengkareng timur from 2009 until 2017. cengkareng timur is the third most densely populated subdistricts in cengkareng after kapuk and cengkareng barat. in 2009, the population density is 11,793.36 inhabitants/km2 and continuously increase until reaching 20,064.89 inhabitants/km2 in 2017. fig 12. population density in cengkareng timur 2009-2017 population density increase in cengkareng timur is more influenced by the incoming mobility to the area. incoming mobility is encouraged as the presence of wellconnected accessibility and road infrastructure. mostly, the newcomers come to look for job and expect for better prosperity. cengkareng timur is neighboring with kapuk and duri kosambi subdistrict which have the most industrial units among other subdistricts in cengkareng. it makes cengkareng timur so strategic for residential area. thus, there is increasing population density as the settlement develops. high demand of land for residential area has brought to high pressure towards existing landuse (table 6). landuse proportion of cengkareng timur has represented the landuse pressure as shown on figure 13. in 2017, cengkareng timur’s land use is used for residential area roughly 78 per cent, followed by industrial area with proportion as much as 11 per cent and office for about 6 per cent. small proportion is used for open spaces, agricultural land, and other landuses with only 5 per cent of total area. the current development of settlement occurs in different type of housing. first type is slum settlements which represents housing community with low quality of cleanliness, health, and sanitation as well as the environment. table 6. landuse of cengkareng timur. type area (km²) settlement 3.55 industri 0.49 office 0.27 open space 0.17 other 0.03 fig 13. landuse proportion of cengkareng timur 2017 it is resulted as not all workers can afford for better housing hence they create slum settlements which is mainly adjacent to industrial area or riverside. second type is the development of real estate, apartment, and such kind which is less-dominated by low-waged workers but high-class businessman. the last type is typical lowcost rent housing, commonly named as rusunawa (rumah susun sederhana sewa) and owned-simple flat housing or also known as rusunami (rumah susun sederhana milik). the second and third type housing is literally vertical housing which aims to accommodate more inhabitants and potentially increase population density. moreover, the development of rusunawa and rusunami can help to prevent any illegal land expansion for settlement by slum community and reduce any conflict with other landuses. the land consumption for housing is believed to have reduced the green open spaces in cengkareng timur. cengkareng timur should have minimum open spaces 1.56 km2 but in fact the existing 72% 13% 14% 0% 0% 1% landuse proportion of kapuk 2017 settlement industri office open space agricultural land others 11.793,36 17.900,78 19.234,55 19.419,93 20.064,89 0,00 5.000,00 10.000,00 15.000,00 20.000,00 25.000,00 2009 2011 2013 2015 2017 p op u la ti on d en si ty ( p eo p le p er k m ²) year population density in cengkareng timur 2009 2017 population density 78% 11% 6% 4% 0% 1% landuse proportion of cengkareng timur 2017 settlement industri office open space agricultural land others 52 putri, r.f. et al./ jgeet vol 5 no 2/2020 open spaces is only 0.8 km2(susilawati et al., 2018). declined open spaces worsen flood management and hamper flood problem solving that occurred in cengkareng timur. nevertheless, the existing open spaces is relatively wider compared to most of subdistricts. 3.1.6 subdistrict of cengkareng barat cengkareng barat, which has area about 3.61 km2, is located closer to the soekarno-hatta international airport and potentially encouraging population growth. the population density of cengkareng barat subdistrict shows the same trend like the other subdistricts in cengkareng as shown on figure 14. in 2009, the population density of cengkareng barat is at 13,620.73 inhabitants/km2 and increases significantly for upcoming years. in 2017, the population density becomes 20,685.54 inhabitants/km2 and makes cengkareng barat as the second most densely-populated subdistrict in cengkareng. fig 14. population density in cengkareng barat 2009-2017 the population density rises following economic development and have contributed in attracting many outsiders to come to the area. these outsiders create community and mostly decide to dwell in the area. obviously, it stimulates population density growth which is in harmony with increase in land need for housing, commercial building, and industrial area. the landuse type in cengkareng barat shown on table 7 which represents the landuse in unit of area. landuse area can be transformed into percentage unit to describe the proportion of the landuse. the existing landuse of cengkareng barat can be viewed on figure 15. in 2017, the land is most occupied by residential area as much as 81 per cent of its area. the presence of numerous housing unit can be found in this subdistrict. smaller area and more population than cengkareng timur, cengkareng barat is depicted as a densely-populated subdistrict in cengkareng. the more inhabitants in the area is dominated by newcomers who come from outside of jakarta. the more population in cengkareng barat has created landuse pressure also and caused any land conversion into settlements. it has depicted that the landuse arrangement in cengkareng, especially cengkareng barat is relatively bad. furthermore, the incoming migrants may potentially develop slum settlements which can reduce environmental quality, even worsen. the another landuse which is dominant in this area is office, about 11 per cent of cengkareng barat area. the industrial area in this subdistrict is lesser than the office. it indicates and builds understanding that cengkareng barat is specialized for residential zone rather than industrial zone. the open space proportion in the area is extremely small compared to duri kosambi and cengkareng timur subdistrict. the minimum open space may result problem in local climate, air circulation, and flood management as this area is designed for reduction of inundation. table 7. landuse of cengkareng barat. type area (km²) settlement 2.91 industri 0.09 office 0.40 open space 0.04 other 0.17 fig 15. landuse proportion of cengkareng barat 2017 3.2 general analysis population density in cengkareng district is highcategorized in the west jakarta municipality, even in jakarta province. increase population density has been occurring for several years as a result of urban development. it is believed that population density increase is the main factor that drives any land use change in cengkareng. land use in cengkareng district develops dynamically year by year and it indicates any land use change. most land use change occurs on settlement, office building, open space, and other land uses. figure 16 shows trend of land use change by proportion in cengkareng district from 2008 to 2014. residential area seems to have increased significantly from 64.72 per cent in 2009 into 68.60 per cent in 2014. increase in residential area land use is followed by decline in other landuses from 5.01 per cent in 2008 into 1.96 per cent in 2014. both office and open space has also decline with proportion less than 0.5 per cent. fig 16. landuse change in cengkareng district 2008-2014 increasing landuse proportion for residential area in the past few years is encouraged by highly increasing land demand following increase of incoming migrants in cengkareng district. rapid incoming migration has been caused by increase of worker demand since the growth of industrial area is significant. industrial area has occupied about 12.82 per cent of cengkareng area. land demand for residential area has resulted in changing other 13.620,73 18.875,73 19.383,79 20.239,61 20.685,54 0,00 5.000,00 10.000,00 15.000,00 20.000,00 25.000,00 2009 2011 2013 2015 2017 p op u la ti on d en si ty ( p eo p le p er k m ²) year population density in cengkareng barat 2009 2017 population density 81% 2% 11% 1% 0% 5% landuse proportion of cengkareng barat 2017 settlement industri office open space agricultural land others 0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00 settlement industri office open space others a re a p re se n ta ge (% ) landuse landuse change in cengkareng district 2008 2014 2008 2011 2014 putri, r.f. et al./ jgeet vol 5 no 2/2020 53 landuses such as agricultural land open space which would be converted into horizontal or vertical housing. growth of settlement or residential area has been stimulating the mushrooming of city village in urban area, which is unintendedly developed, creating city village community (darmawan, 2018). open space which is supposed to be utilized as place for the interaction and socialization of urban community has been an important need regarding to increase of population density. however, limited available space as well as increasing demand for housing has sacrificed most of open space and agricultural area to be developed as residential area. moreover, increasing population density means more population exist and may extract groundwater excessively, accelerating land subsidence due to decline in groundwater table. worse land subsidence has put cengkareng to experience serious flood, coastal flood, or inundation, severe damage for buildings and infrastructures, seawater intrusion, and destructing of local aquifers. the land subsidence evidence can be found in cengkareng in form of subsidence bowl with subsidence rate up to 260 mm/year (ng et al., 2012). another problem resulted from population density increase is the development of slum settlement that disrupts the flood management conducted by the local government. population density in cengkareng can be categorized statistically into three class which compares population density of a certain subdistrict among others, as shown on figure 17. subdistrict of duri kosambi, rawa buaya, and kedaung kaliangke are categorized as low denselypopulated subdistrict with population density less than 17,902.05 inhabitants/km2. subdistrict of cengkareng barat and cengkareng timur have moderate population density between 17,902.05 and 22,636.80 inhabitants/km2. meanwhile, kapuk subdistrict has the highest population density, more than 22,636.80 inhabitants/km2. but, another classification of population density done by the census of india has classified population density into five categories. based on census of india (2011) compiled in (kuchay, nissar a; bhat, sultan; shafi, 2016), population density which exceed 10,000 inhabitants/km2 is categorized high. it means, according to the general classification, population density in cengkareng is high. fig 17. population density map of cengkareng district, west jakarta municipality 2017 burgeoning population density has resulted not only in increase of land demand for settlement, but also shaped the pattern of urban settlement as displayed in figure 18. settlement area in cengkareng has nucleated pattern. it is due to its flat topography and availability of resources such as water, proximity to industrial area for job, and accessible road network. dense population has been influencing the settlement configuration or pattern. the more nucleated pattern, means the more compact settlement, which consists of both horizontal and vertical housing hence results in higher population density (table 8). in addition, nucleated pattern of settlement in cengkareng also consists of irregular settlement. the irregular shape settlement is found mainly in flat ground area due to difference between man-maderoad system and the nature lines, such as river lines (beny o.y. and khalimah, 2016). irregular settlement, along with nucleated settlement, would take greater land area rather than other landuses hence this settlement pattern may accelerate declining open space or agricultural land. 54 putri, r.f. et al./ jgeet vol 5 no 2/2020 table 9. measurement of velocity in every stations. subdistrict population density (inhabitants per km²) settlement pattern duri kosambi 14,568.02 nucleated rawa buaya 17,383.14 nucleated kedaung kaliangke 13,168.30 nucleated kapuk 27,369.55 nucleated cengkareng timur 20,064.89 nucleated cengkareng barat 20,685.54 nucleated fig 18. settlement pattern map of cengkareng district, west jakarta municipality 4. conclusion cengkareng district experiences progressive development from year to year. based on the data recorded by the indonesia central bureau of statistics, it can be identified significant population growth from 2009 to 2017 which results in increase of population density in every subdistrict. the population density increased drastically in year 2009 until 2011 and significantly in 2011 to 2017. increasing population density occurs with the same trend in duri kosambi, rawa buaya, kedaung kaliangke, kapuk, cengkareng timur, and cengkareng barat as a consequence of increasing births and incoming migration in cengkareng district. dynamics of population density has shaped the landuse arrangement in cengkareng. landuse change occurs in most land utilization type such as settlement, office building, open space, and other landuses. settlement dominates the landuse in all subdistrict with proportion more than 50 percent, followed by industrial area, and office building.the development of industrial area indicates high workers demand and stimulates development of irregular settlement nearby or adjacent to river such as the settlement in kali angke riverbank. it causes the mushrooming of slum community in the riverbank and disturbs the sustainability of the river. it becomes serious problem since its land has low topography and is passed by many big rivers. in short, regarding the population and landuse trend, the assessment of landuse shows that cengkareng district is best suited for settlement area thus the government can focus the development of the district for settlement area. some subdistricts such as duri kosambi, rawa buaya, kedaung kaliangke, and kapuk are dominated by industrial area and offices land utilization type. thus, the government consider those subdistricts for economic and business area. acknowledgements the writers express the most gratitude to the department of environmental geography, faculty of geography, universitas gadjah mada, which is directly involved in the making of the research and gives endless support to the development of this research, especially in demographical topic. references arifin, s., mukhoriyah, n., yudhatama, d., 2018. analysis of land use spatial pattern change of town development using remote sensing. int. j. remote sens. earth sci. 15, 93–102. 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taubenbock, h., klotz, m., wurm, m., schmieder, j., wagner, b., esch, t., 2013. delimiting central business districts a physical approach using remote sensing. jt. urban remote sens. event 2013, jurse 2013 1, 17–20. https://doi.org/10.1109/jurse#.2013.6550655 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 1 2020 kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 1 research article geomorphological assessment to tract the flow evolution of kali putih, srumbung district, magelang regency, central java, indonesia sari bahagiarti kusumayudha1*, i made oki sanjaya1, helmy murwanto1, sugeng raharjo1 1universitas pembangunan nasional veteran yogyakarta, yogyakarta, indonesia. * corresponding author : saribk@upnyk.ac.id tel.: +62 8122782595 received: nov 17, 2019. accepted: march 13, 2020. doi: 10.25299/jgeet.2020.5.1.4096 abstract kali putih (the white river) is located in srumbung district, magelang regency, central java, indonesia. it is originated from the upper slope of merapi volcano,flowing to the southwest direction. kali putih belongs to one of the most channels where frequently flowed by lahar of merapi volcano. based on geomorphological and geological traces found at the surrounding of modern kali putih channel, this indicated that the flow of kali putih has undergone displacement several times. the position of ancient river valley in the past has changed into the modern river valley in the present time. the existence of ancient kali putih is exhibitedby the presence of large dry valley morphology associated with volcanic blocks, gravels, and sand sized materials with various sorting, representing the characteristics of lahar and alluvial deposits. in the present time, the former river channelsare currently used by local people for agricultural and fisheries land.this researchwas conducted in order to analyse and determine the evolution of the ancient kali putih valleys, and the current river that acting as a collecting channel of lahars and pyroclastic avalanches of merapi volcano. by concerning to geological law of “the present is the key to the past”, results of this research can be used as a reference for studies related to volcanic disaster mitigation of the surrounding area. keywords: kali putih, flow evolution, geomorphology, lahar 1. introduction one of some volcanic products generatedby such an active volcano is lahar, that belongs to the strongest erosion forces, destructive, and capable of creating disaster. besides its high capacity of erosion and sedimentation, lahar flows also generally create a strong impact to the environment (lavigne, et.al, 2000). material deposits that exceed the capacity of such a river to hold, will bring environmental problems to downstream. problems caused by lahar sedimentation can be in the form of the closure of irrigation channels, siltation of the riverbed, and the buried of land around the river channel due to overflow of lahar which is not able to be accommodated by the river. changes in flow of the river's morphology caused by lahar include widening of the river channel, streamlining of the river flow, and silting of the riverbed (murwanto, et.al, 2013). in the research area, there is a river, namely kali putih (the white river) which often used by lahar as the secondary product of merapi volcano eruption to flow (murwanto, et.al, 2013). the river is located in srumbung district, magelang regency, central java province, indonesia (fig. 1), that belongs to an area with dense population. the local community mostly live in the adjacent of river flow, while the river itself is used to be threated by lahar. based on remote sensinganalysis using earth's map and google earth imagery, there are found straightness of river paths which interpreted as the former of kali putih flows. this indicates that kali putih has ever changed its flow due to natural processes. in order to derive geohistorical data and information on kali putih and lahar disaster in the past time, then the evolution of kali putih flow is needed to be traced with scientific assessment in the form of geomorphological and geological studies. this study aims to determine the evolution of the ancient kali putih valleys, and the current river that acting as a collecting channel of loose material, lahars or volcanic mud flows, and pyroclastic avalanches of the merapi volcano. fig. 1. location map of the research area 2. methods of the study method carried out in this study is descriptive, and analytic, combining with assessment on merapi volcanic http://journal.uir.ac.id/index.php/jgeet 2 kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 history and field observation by conducting geological and geomorphological mapping. data to be assessed including secondary and primary data. the secondary data were satellite imageries, peta rupa bumi indonesia (indonesian map of earth appearence) and regional geological map of merapi volcano, while primary data in terms of geomorphological and lithological characteristics were derived from field survey and mapping. field survey and mapping activities done in this research can be divided into several stages, including data acquisition, literature review, analyses on flow patterns, geomorphology, stratigraphy, geological structure, and petrology,and synthesis related to identification of the evolution of kali putih flows. 3. results and discussion 3.1 geomorphology in the present time kali putih flow is situated on the southwestern slope of merapi volcano. places flown by kali putih are cabe kidul, ngaglik, remame, jumoyo kidul, pendem, seloboro, tersangede, baturono. there are some ancient valleys that interpreted as the former kali putih flows.the first valleyis found in srumbung kidul, kemiren, jumoyo lor, pulosari, pendem, seloboro, and gajahan. the secondvalleyis discovered in srumbung, gempol, and seloboro. the valley of modern kali putih itself issituated in srumbung area, jumoyo, and seloboro. in order to study the evolution of kali putih flow, the geomorphology of the surrounding area needs to be analysed. however, landform has an important role to control erosion and flow of surface water. referring to setyawati & ashari (2017), the srumbung district is situated on the southwestern slope of merapi volcano, the landforms can be divided into volcanic food slope, volcanic footplain, and isolated hills (fig. 2). fig. 2.geomorphologic map of the southwestern slope of merapi volcano (setyawati & ashari, 2017). red box shows situation of the research area. field observation on the ancient kali putih channels was carried out to determine the position of the previous kali putih flow. this observation is related to geomorphology that consisting of assessment on morphology, morphometry (valley shape, valley width and valley length), passive morphostructure (lithology), and morpho-association. based on this study, the geomorphology of the research area can be devided into for geomorphic units, namely volcano footslope unit, rever channel unit, isolated hill unit, and isolated ranges unit. geomorphological map of the research area is displayed in fig.3. fig 3. geomorphological map of the research area 3.2 geology mainly, geology of the research area is influenced by merapi volcano activities. product of the volcanicactionscan be in the forms of primary yield as pysoclastics, and secondary creation as lahar. there are two kinds of merapi volcano pyroclastics,called fall pyroclastics, and flow or avalanche pyroclastics (kusumayudha, 2017). lahar is a debris and mud concentration formed from a mixture of water, particles, sand, and boulders (paripurno, 2009). the source of water can be rainfall, crater lakes,or melting of ice, while the particles come from pre-existing pyroclastic avalanches as well as material produced directly from eruptions. primary lahar occurs in volcanoes that there is a crater lakes. the base of its crateris impermeable so that a number of rainwater will be collected inside. if the volume of water in the crater is large enough, when an eruption occurs it can spill hot mud with temperatures reaching above 100oc (lavigne, et.al, 2000). rainy lahar (secondary lahar) or better known as cold lahar occurs when volcanic materials that have not been consolidated on peaks and slopes, at or after the eruption, then kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 3 mixed with rainwater.these pyroclastic materials will be transported and move downward as a high density of flow.(lavigne, et.al, 2000). lahar belongs to one of the strongest erosion forces. sedimentation by lahar flows that exceed the river's boundary limits generally brings environmental problems downstream,such as siltation of the riverbed, closure of irrigation channels, and buried of land around the river channel. it is due to the overflow of material lahar that can not be accommodated by the riverpassage. environmental changes due to lahar overflows include transformations in river flow morphology, such as channels widening, basins streamlining and siltation, and sedimentation characteristicschanging (thouret, et.al, 2000). lahar flow velocity is influenced by slope inclination, rainfall intensity, and material volume. the steeper the slope, the speed of the lahar flow will increase (thouret, et.al, 2000).genetically lahar is divided into two types, namely lahar of eruption (primary) and lahar of rainfall (secondary). based on characteristics of the dominant lithology, and refering to the regional stratigraphy according to wirakusumah, et al. (1989) and paripurno (2009), the rock units in the research area are determined as composed of gendol lava units, merapi lahar deposit 1units, merapi lahar deposit 2 units and alluvial deposits. referring to wirakusumah, et al. (1989) and camus et.al. (2000), the gendol lava unit belongs to the oldest old rock groupin srumbung area, it is tertiary geological age. the stratigraphic relationship between gendol lava units and merapi lahar deposit 1 unit is nonconformity.the stratigraphic relationship between the merapi lahar deposit 1unit and the merapi lahar deposit 2unit is aligned.the geologic map of the research area is shown in fig. 4. fig 4. gerological map of kali putih and surrounding area 3.3 merapi activity history before the year 1994, say 1960(s), 1930(s), 1900(s) etc eruptions of merapi volcano generally toward southwestern direction (kusumadinata, 1979). characteristics of the eruptions were variation of volcanian, pelean, and merapian types (kusumayudha, et.al, 2019). all of the types of eruption generally produced pyroclastics that deposited on the western flank of the volcano. when the deposits mixed with rain water to became more dense and heavy, then flowed downward lead by gravity, forming lahar (kusumayudha, 2017). because of this situation, the research area always passed by pyroclastic and lahar flows of that times. due to its role as the area of where always flown by lahar and pyroclastic, subsequentlythis area lithologically composed of pyroclastic and lahar deposits. kali putih is one of the rivers that flows to the southwest of mount merapi.the river is frequentlyaffected by rain lahar flows. based on the historical records, this river had been fed by lahar on november 21-25 1975, march 6, 1976, november 20-27, january 1993, july 1998 (lavigne, et.al, 2000), and in the end of 2010to 2011 (kusumayudha, et.al, 2019). the potential of lahar flow in the kali putih is still quite large. it is supported by the fact that there are still many materials in the upper slope, as well as the high potential for rainfall. this huge potential is a serious threat to changes the morphology of kali putih channel. by refering to “the present is the key to the past”, it can be strongly pressumed that kali putih has undergone such a flow evolution. there has been some ancient kali putih grooves, indicated bythe presence of a wide valley morphology with lahar deposits in the form of andesite blocks. the existence of a large valley and the presence of lahar deposits prove that the area was once a river channel that had been flowedby lahar. ancient kali putih grooves can be found in the srumbung area to salam. some of the former areas of the kali putih channel are used by the community as agricultural and fisheries land. as has been mentioned above, the existence of ancient kali putih in the research area can be observed based on geological and geomrophological aspects, including morphometric, morphogenesis, and morpho-association. results of the assessment pointed that kali putih was subjected toflow displacement three times. 3.3.1 kali putih evolution a. ancient kali putih 1 the ancient kali putih 1 is found in the areas of cabe kidul, ngaglik, babadan, remame, south jumoyo, pendem, seloboro, tersangede and baturono. the upper reaches of the river is in the northeast of lombok kidul (fig.5.). the geomorphological aspects are as follows: 4 kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 table 1. geomorphological aspects kali putih 1 morphography longitudinal valley, river terraces with flow direction from northeast to southwest, dammed by gendol hills, afterwardturn around the hills, and then turn back to flow to relatively southwestward direction (fig. 5, fig.6.). morphometry a. valley shape:“u” b. valley width: 30-60 meter active morphostructure lahar deposits and alluvial deposits (fig.7.). morphographic association volcanic food slope, volcanic food plain, isolated hills fig 5. ancient kali putih 1. dash lines show the old channel of ancient kali putih 1 (photo source: google earth). fig 6. old channel of ancient kali putih 1. fig 7.old lahar depositson the ancient kali putih 1 river bank. b. ancient kali putih 2 ancient kali putih 2 is found at villages of srumbung kidul, jamblang, kemiren, jumoyo lor, pulosari, pendem, seloboro and gajahan (fig. 8). the geomorphological aspects are as the following: table 2. geomorphological aspects kali putih 2 morphography longitudinal valley, river terraces with flow direction from northeast to southwest, dammed by gendol hills, afterwardturn around the hills, and then turn back to flow to relatively southwestward direction (fig. 8, fig.9.). morphometry a. valley shape: “u” b. valley width: 30-92 meter active morphostructure lahar deposits and alluvial deposits (fig.10.). morphographic association volcanic food slope, volcanic food plain, isolated hills fig 8. ancient kali putih 2. dash lines show the old channel of ancient kali putih 2 (photo source: google earth). kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 5 fig 9. old channel of ancient kali putih 2 at gajahan village fig 10. old lahar depositson the river bank of ancient kali putih 2 atpendem village (a); at gajahan village (b). c. ancient kali putih 3 ancient kali putih 3 is discovered in gempol village (fig. 11.). the geomorphological aspects are as the following: table 3. geomorphological aspects kali putih 3 morphography longitudinal valley and river banks with flow direction relatively northeast – southwest without colliding gendol hills (fig. 11, fig. 12.). morphometry a. valley shape: “u” b. valley width: 26-78 meter active morphostructure lahar deposits and alluvial deposits (fig. 13.). morphographic association volcanic food slope, volcanic food plain fig. 11. ancient kali putih 3.dash lines show the old channel of ancient kali putih 3 (photo source: google earth). fig. 12. ancient kali putih 3 at gempol village. fig. 13.old lahar deposits on the ancient kali putih 3 river bank at gempol village. d. modern kali putih modern kali putih can be found at salam, jumoyo, and srumbung areas (fig. 14.). the geomorphological aspects are as the following: table 4. geomorphological aspects modern kali putih morphography longitudinal valley of northeast – southwest direction (fig. 14, fig. 15.). morphometry a. valley shape: “u” b. valley width: 30-60 meter active morphostructure lahar deposit and alluvial deposit (fig.16.). morphographic association volcanic food slope, volcanic food plain 6 kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 fig14. modern kali putih.dash line shows the old channel of modern kali putih (source: google earth). fig 15. modern kali putih channel at pondok area (a);at karanggowang area (b). fig 16. lahar and pyroclstics (flow pyroclastic, glowing cloud) deposits on the river bank of modern kali putih at pondok area. based on the above analysis, it can be concluded that kali putih has undergone three times flow displacement, which started from the ancient kali putih 1, the ancient kali putih 2, the ancient kali putih 3, and become themodern kali putih. the displacement was due to the damming of the river channel by volcanic materials so that the river water requireda way out and formed a new river channel. the results of this study are a map of the evolution of kali putih in srumbung subdistrict, magelang regency, central java province which can be seen in fig.17. fig. 17. evolution map of the kali putih in srumbung subdistrict, magelang district, central java. the evidence of changes in river flow, the discovery of volcanic material, and the existence ofriver terracesreinforce the hypothesis on kali putih channel evolution. some informations from localcommunities,also further strengthens this hypothesis. the ancient kali putih 1 was estimated to be before 732 ad, as evidenced by the presence of the canggal inscription on wukir hill of 732 ad (murwanto, et al, 2013). ancient kali putih 2 is a subversionof the ancient kali putih 1 flow caused by the damming of the river by volcanic material so that the river water looks for a way out by creating the flow of the ancient kali putih 2. according to murwanto, et al. (2013), the ancient kali putih 3 in the gempol area was the previous kali putih which was moved by the dutch colonial kusumayudha, s.b. et al./ jgeet vol 5 no 1/ 2020 7 government to facilitate the construction of magelangyogyakarta connecting road. nowadays the ancient kali putih channels are used by the local people for farming and fisheries, while the modern kali putih flow is still potential of hit by lahars inthe future. due to the dense population of the surrounding area, in order for disaster mitigation, it is necessary to make serious efforts so that the river banks are not used as settlements.some embankments are need to be built along the riverbanks, and also need to pay attention to bridge constructions that pass through the river often flownby lahar. 4. conclusions based on the results of geological and geomorphologicalanalyses by using rbi map and google earth's imagesin this study, some conclusions can be summerized, as the following: 1. the geology and geomorphology of srumbung area are strongly influenced by merapi volcano activities and eruption producs, such as pyroclatics and especially lahars. 2. there is a river, called kali putih that its origin is from the upper part of merapi volcano. based on the historical records,kali putih that flows to the southwest, frequentlybe affected by lahar flows. 3. kali putih flow in srumbung areahas undergone three times flow displacement, which started from the ancient kali putih 1, the ancient kali putih 2, the ancient kali putih 3, and become themodern kali putih. 4. the displacement of kali putih cnannel was due to the damming of the river channel by volcanic materials so that the river water required a way out and formed a new river channel. 5. for disaster mitigation, the river banks are suggested not to be used as settlements.embankments need to be built along the riverbanks, and bridges that pass through the river often flown by lahar need such a special construction. references anonim, 2006-2013, google earth. camus, g., gourgaud, a., mossand-berthommier, p.c., vincent, p.m., 2000, merapi (central java, indonesia): an outline of the structural and magmatological evolution, with a special emphasis to the major pyroclastic events, journal of volcanological and geothermal research, vol 100, elsevier: 139-163, url: http://www.elsevier.nl/locate/jvolgeores kusumadinata, 1979,data dasar gunungapi indonesia (basic data of volcanoes of indonesia), departemen pertambangan dan energi r. i. kusumayudha, s.b. 2017, gunungapi aktif indonesia (active volcanoes of indonesia), adicita parama yogyakarta. kusumayudha, s.b, murwanto, h, sutarto, choiriyah, u, 2019, volcanic disaster and the decline of mataram kingdom in the central java, indonesia, 2nd geomeast international congress & exhibition proc., p 83 – 93, url: http://link.springer.com/chapter/10.1007/978-3030-02032-3_8#citeas lavigne, f., j.c. thouret, b. voight, h. suwa, a. sumaryono. 2000. lahars at merapi volcano, central java: an overview. journal of volcanology and geothermal research,423-456, url: http://www.elsevier.nl/locate/jvolgeores murwanto h., siregar d.a., purwoarminta, a. 2013. jejak erupsi gunung merapi di kabupaten magelang provinsi jawa tengah (the tracts of merapi volcano eruptions in magelang regency, central java). jurnal lingkungan dan bencana geologi. 135-147. paripurno, e.t. 2009, karakter lahar gunung merapi sebagai respon perbedaan jenis erupsi sejak holosen (the characteristics of merapi volcano lahar as the response of eruption type difference since holocene), universitas padjadjaran, bandung setyawati, s. & ashari, a. 2017. geomorfologi lereng baratdaya gunung api merapi kaitannya dengan upaya pengelolaan lingkungan dan kebencanaan (geomorphology of the southwest slope of merapi volcano related to environmental and disaster management). geomedia, vol 15, no. 1, doi: https://doi.org/10.21831/gm.v15i1.16235 thouret, j.c., lavigne, f., kelfoun, k., bronto, s. 2000, toward a revised hazard assessment at merapi volcano, central java, journal of volcanology and geothermal research, vol 100, elsevier: 479-502. wirakusumah, a. d., juwarna h., loebis h.. 1989. peta geologi gunungapi merapi, provinsi daerah istimewa yogyakarta & jawa tengah (geological map of merapi volcano, yogyakarta special territory and central java provinces). bandung: badan geologi. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://www.elsevier.nl/locate/jvolgeores http://link.springer.com/chapter/10.1007/978-3-030-02032-3_8#citeas http://link.springer.com/chapter/10.1007/978-3-030-02032-3_8#citeas http://www.elsevier.nl/locate/jvolgeores https://doi.org/10.21831/gm.v15i1.16235 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ author 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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accepted: may 28, 2021. doi 10.25299/jgeet.2021.6.2.6424 abstract the study area is located in north kabaena district, bombana regency, southeast sulawesi. this paper is aimed to describe characacristics of chromite deposits. this study is conducted in three stages, three stages including desk study, field work and laboratory analysis. desk study mainly covers literature reviews. field work includes mapping of surface geology and sampling of representative rocks types. laboratory analysis includes the petrologic observation of handspecimen samples, petrographic analysis of the thin section and ore microscopy for polished section. the results of petrographic analysis show that olivine minerals are generally replaced by minerals orthopyroxene and has been alterated by lizardite type serpentine veins with a fractured structure. the mineral oliv ine is also replaced by the mineral chrysotile as a secondary mineral with a fibrous structure. based on ore microscopy analysis show that chromite has generally experienced a lateritification process and has been replaced by magnetite, hematite and geotite minerals. chromite has experience process of weathering and alteration from its source rock caused by tectonics that occurred in the study area. the results shows that the characteristics of chromite deposits in north kabaena district chromite deposits has generally encountered in peridotite rock which have a grain size of 0.3-20 cm. furthermore, chromite deposits in the study area are also encountered in podiform deposits, distributed locally and shows podiform to tubular shape with the dimensions of 30-60cm. keywords: chromite, peridotite, serpentinite, olivine, podiform. 1. introduction podiform chromite deposits are an important source for chromite, which is the only ore for chromium, and they are the primary source for both high-chromium, lowluminum ore, used in metallurgical applications (mosier et al., 2012). based on this, many researchers and mining companies are trying to find chromite reserves to explore. chromite minerals are found in mafic and ultramafic rocks peridotite which is included in the ophiolite complex and metamorphic rocks such as serpentine, usually associated with olivine, talc, serpentine, uvavorite, pyroxene, biotite, magnetite, and anorthite. chromite can occur as primary deposits, namely stratiform and podiform deposit types (rasilainen et al., 2016), or as secondary deposits in the form of black sand and laterite soil. furthermore, podiform chromite deposits are small magmatic chromite bodies formed in the ultramafic section of an ophiolite complex in the oceanic crust. these deposits have been found in midoceanic ridge, off-ridge, and suprasubduction tectonic settings. most podiform chromite deposits are found in dunite or peridotite near the contact of the cumulate and tectonite zones in ophiolites (rasilainen et al., 2016; mosier et al., 2012. budi santoso and subagio (2016) have researched chromite minerals using the induced polarization (ip) method in the northern kabaena area, bombana, south east sulawesi results from primary chromite deposits and secondary chromite deposits. the primary chromite deposition is found in peridotite rocks with a charge ability value (221-320) msec and a resistivity value (900-6000) ohm. m, while the secondary chromite deposition is found in sand layers containing fragments of chunk and peridotite rock fragments with a charge ability value (203270) msec and resistivity value (296 -400) ohms. m. chromite has properties such as black, massif to a granular, crystalline form, octahedral crystals system, brown streaks, hardness 5.5 (mohs scale), and specific gravity 4.5 4.8. chromite minerals are thin, stable, and composed of small beads. the chromite chemical composition varies significantly because other elements influence it (santoso et al., 2016). based on research results of moe'tamar, 2005 in kabaena island show that distribution of chromite pumice (boulder) with a diameter (10-100) cm of solid black color, occasionally found chromite boulder fragments covered with quartz. 2. regional geological setting the stratigraphy in the southeastern arm of sulawesi consists of three constituent rocks are ophiolite complex are dominated by mafic and ultramafic rocks accompanied by pelagic and melange sedimentary rocks in several places; continental terrain composed of metamorphic rocks (pompangeo complex) consisting of mica schist, quartzite, glaucophane schist and chertand; and sulawesi http://journal.uir.ac.id/index.php/jgeet mailto:hasriageologi@gmail.com hasria et al./ jgeet vol 6 no 2/2021 95 molasse composed of clastic sediments and carbonate. contacts between the ophiolite complex and metamorphic rocks, including their basement rocks are faulted. the sulawesi mollase unconformably overlies both the ophiolite complex and continental terrain (surono, 2013). chromite deposits are encountered in kabaena utara district which is part of kabaena island in bombana regency, southeast sulawesi province (figure 1).the morphology of the study area consists of high hills to mountainous areas, caused by the geological structure it consists of shear fault thrust faults with irregular fault directions (simandjuntak et al., 1993).in the study area, there is also a sungkup fault following west-east direction. this fault shifts the ultramafic complex over the pompangeo complex and the kabaena metamorphosed sediment which is thought to have occurred in the mesozoic (moe’tamar, 2005). the formation indicated as a chromite-bearing formation is the ultramafic (ku) complex, which is cretaceous in which there are peridotite rocks consist of harsburgite, dunite, wherlite, serpentinite, gabbro, basalt, dolerite, diorite, mafic meta, ampybolite, magnesite. , and local rodingit (simandjuntak et al., 1993). ultramafic complex (ku), this formation comprises harzburgite, dunite, wherlite, serpentinite, gabbro, basalt, dolerite, diorite, meta mafic, amphibolite, magnesite, and local redingote. this unit is estimated to be cretaceous (simandjuntak et al., 1993) fig 1. kabaena geology and stratigraphy map (modification of simandjuntak et all., 1993) 3. research methods this study is conducted in four stages including fieldwork, laboratory analyses, data analyses andinterpretation. fieldwork includes mapping of surface geology, as well as sampling of representative rock types. laboratory work includes textural dan structural analyses and mineralogy analyses (petrography and ore microscopy analyses). the mineralogical analysis was conducted at department of geological engineering, hasanuddin university, indonesia. 4. results and discussions 4.1 characteristics of chromite the formation of ultramafic is by high-temperature mineral minerals which are magmatic deposits such as olivine, pyrexia, chromite, and hematite (purawiardi, 2014). this type of ultramafic rocksin research area has a brown weathered color and fresh dark green color, hypo crystalline, phaneritic, euhedral-subhedral and equigranular relationships. based on field observation can be seen the primary minerals such as olivine and pyroxene and secondary minerals are serpentine. based on the results of petrographic analysis, it shows that the abundant mineral olivine content is then replaced by orthopyroxene minerals and olivine minerals have been altered by lizardite-type serpentine veins with a fractured structure (fig. 2a). in figure 2b there is a chrysotile mineral with a fibrous structure as a secondary mineral that replaces the mineral olivine. the results of petrographic analysis (fig. 3) show that the antigorite mineral with a banded structure is present in the middle of the lizardite mineral with a granular structure. the appearance of lizardite minerals with a granular structure is formed due to the weathering process. in the thin section, the texture of the olivine mineral crystals has completely changed to the mineral serpentine (rasilainen et al., 2016). chromite is formed because of the crystallization process of magma at a temperature of 1200°c, found in metamorphic rocks such as serpentinite (robinson et al., 1997). 96 hasria et al./ jgeet vol 6 no 2/2021 fig 2. (a) thin section at x-nicol and parallel nicol of the serpentine-dunite; (b) thin section at x-nicol and parallel nicolof the serpentine-dunite with the mineral olivine which is replaced by orthopiroxen. chromite is field area partly in fresh conditions, but in some samples found to undergo a lateritification process that replaces chromite into mineral magnetite, hematite, and goethite. based on ore microscopy analyses, magnetite colour of bluish gray, measuring 50-250 μm, anhedral, has no pleochroism, isotropic and medium-high reflectance. fig. 3. thin section at x-nicol and parallel nicol of the serpentine-dunite which indicates the presence of antigorite minerals with a banded structure. podiform deposits are chromite bodies in the form of pockets up to tubular shape, usually related to the direction of magmatic stratification (robinson et al., 1997). the structure in the chromite body varies. solid chromite crystals in massive ore formations contain 75% to 85% percent chromite volume. spherical or speckled ores consisting of round chromite crystals 0.5-2 cm in diameter in the basic mass of silicates such as olivine, pyroxene, serpentine, are characteristic of chromite ore deposits. ribbon-shaped ore is closely related to massive ore, but it is richer in silicates and then forms links with mottled ores (fig. 4). based on ore microscopy analysis can be seen that the chromite found in the study area subsurface the process of its host rocks, likewise other minerals (fig. 5). it is caused by tectonic processes that occurs in the research area. from the results of the chromite host rock analysis of peridotite that has subsurface serpentinization consists of partially transformed olivine into serpentine, magnetite and chromite (robinson et al., 1997). fig. 4. the appearance of chromite nodules on peridotite rocks (a), appearance of chromite ore (b), podiform chromite with a diameter reaching 15 cm (c). olivin absorption colour is grayish-white, with the interference colour of the bluish-green type of oblique darkness, subhedral-anhedral shape, high relief, imperfect hemisphere (none), irregular fractions, and mineral size of 0.2mm to 0.5mm. the olivine mineral in the incision with a percentage of 30% shows the weathering process where around the body the olivine mineral has changed colour to brown and the mineral body of olivine has broken up into several parts caused by serpentine veins which intersect from two directions to form a mesh structure in the mineral olivine. lizardit white absorption color, white color interference, anhedral shape, medium relief, no hemisphere, low order double bias, mineral size from 0.20 to 0.250mm. types of tilting darkness. lizardite minerals present as veins with fractured structures that cut olivine and orthopyroxene minerals where serpentine veins cut hasria et al./ jgeet vol 6 no 2/2021 97 one another, indicating that the serpentine process has occurred in more than one phase. fig. 5chromite in photomicrograph (liz: lizardite, ol: olivine, chr: chromite, mag: magnetit). magnetite has mineral opaque, black interference color, opaque, high relief, high intensity and has a size (0.11.0 mm), granular euhedral crystal boundary shape. chromite has a physical characteristic of black colour, metal gloss, hardness 4.5-5.5, uneven shards, granularshaped, paramagnetic magnetics, and the properties in brittle. the observation of ore texture is carried out in a ore microscopy that shows the gray chromite, measuring 100-300 μm. the form of the euhedral-subhedral has no pleochroism, isotropic, brecciation fractions, high reflectance, bireflectance not observed. chromite deposits in the study area were found to have a grain size of 0.3-20cm asnodules or forming small pockets of peridotite that had subsurface serpentinization and were only localized (lintjewas, 2015). chromite analysis was performed by observing 4 petrographic samples and 4 mineragraphic samples under a microscope (fig. 6). fig. 6 (a) goethite secondary presence minerals; (b) secondary minerals such as goethite and hematite related chromite ore weathering processes,podiform chromite texture shown by using disseminated chromite ore on silicate minerals containing olivine; (c), and (d) magnetite is looked replacing chromite. chromite is generally partly observed in fresh conditions, but some samples have been found to undergo a lateritification process that replaces chromite into mineral magnetite, hematite, and goethite. bluish gray magnetite, measuring 50-250 µm, anhedral, has no pleochroism, isotropic medium-high reflectance, has no observed effect. blackish gray goethite, size <50 µm, anhedral form, weak pleochroism, anisotropic, moderate reflectance, bireflectance not observed. brown-colored hematite, <50 µm in size, euhedral-subhedral form, do not have pleochroism, isotropic, high reflection, bireflectance not observed (fig.4). goethite-colored blackish gray, measuring <50 μm, anhedral form, weak pleochroism, anisotropic, mediumreflectance, bireflectance not observed. it is a brown colour, measuring <50 μm, a euhedral-subhedral, with no pleochroism, isotropic, high reflection, unobserved bireflectance. magnetit has mineral opaque, black interference color, opaque, high relief, high intensity and has a size (0.1-1.0 mm), granular euhedral crystal boundary shape. hematit brown color, size <50 μm, euhedral-subhedral form, do not have pleochroism, isotropic, high reflection, bireflektansi not observed. 4.2 chromite mineralization type chromite ores in study areas are found inpodiform type (fig. 7) a podiform precipitate is a bag of chromic body-shaped to a tube or lens, usually associated with the direction of magmatic stratification (purawiardi, 2014). chromite deposits in the study area are also encountered in podiform deposits, distributed locally and shows podiform to tubular shape with the dimensions of 3060cm and along the circumference of the mountain (fig. 7).this precipitate can be found in the host rock, which is the constituent ultramafic rock (ibrahim et al., 2014) and upper coat which is commonly called the ophiolite sequence which supports this type of deposition, where the parent rocks in the peridotite and serpentinite research areas are included into the ultramafic rock of the coat. fig. 7 appearance of chromite pediform deposits on the research area chromite research areas include the type of chromite podiform deposits, these deposits are found on the stem rocks of ultramafic rock compilers of the ocean crust or commonly called fibonacci ophiolite. rocks associated with the type of podiform sediment are commonly referred to as alpine-type ultramafics and are found along the archipelago and on a volcanic belt that is always moving at a paleozoic or younger age (robinson et al., 1997; zhou and robinson, 1997). 98 hasria et al./ jgeet vol 6 no 2/2021 the formation of chromite minerals in the ofiolit sequin sequence rocks can be caused by partial melting and remobilization of rock differentiation at a certain depth due to fractional crystallization. chromite is eliminated because of the appointment process by regional tectonic (robinson et al., 1997 ; mosier et al., 2012 ;; robinson et al., 1997; mcclay, 1992) 5. conclusion chromite has experience process of weathering and alteration from its source rock caused by tectonics that occurred in the study area to cause changes in chromite mineralogy to magnetite, hematite, and goethite. sedimentary ores containing compounds fe2cr2o4 or feo (cr, al) 2o3 are always associated with magma breakthroughs. characteristics of chromite deposits in study area has generally encountered in peridotite rocks which have a grain size of 0.3-20 cm. furthermore, chromite deposits in the study area are also encountered in podiform deposits, distributed locally and shows podiform to tubular shape with the dimensions of 3060cm was encountered along the circumference of the use of the study area. acknowledgements the authors are very thankful to the head of north kabaena district for the research access and permission. authors also would like to thank to the head of the geological engineering laboratory, hasanuddin university, who gave me permission to use the laboratories. references ibrahim, m. a., rustandi, u., suryana, a. 2014. penyelidikan bitumen padat daerah pulau kabaena kabupaten bombana, provinsi sulawesi tenggara, in: proceeding pusat sumber daya geologi. pp. 1–10. lintjewas, l. 2015. tipe endapan kromit di daerah konawe utara propinsi sulawesi tenggara, pemaparan hasil penelitian geoteknologi 2015. mcclay, k. 1992. the mapping of geological structures. john wiley & sons, k. r. mcclay department of geology royal holloway and bedford new college universiry of london. moe’tamar 2005. inventarisasi dan evaluasi mineral logam di daerah kabupaten bombana dan kabupaten muna provinsi sulawesi tenggara. direktorat inventarisasi sumber daya mineral, bandung. mosier, l.m., singer, d.a., moring, b.c., galloway, j.p. 2012. podiform chromite deposits-data base an grade and tonnage models, u.s geological survey, reston, virginia. purawiardi, r. 2014. karakteristik bijih kromit barru, sulawesi selatan. j. ris. geol. dan pertamb. 18, 1. https://doi.org/10.14203/risetgeotam2008.v18.3 rasilainen, k., eilu, p., halkoaho, t., karinen, t., konnunaho, j., kontinen, a., törmänen, t. 2016. quantitative assessment of undiscovered resources in stratiform and podiform chromite deposits in finland, tutkimusraportti geologian tutkimuskeskus. robinson, p.t., zhou, m.f., malpas, j., bai, w.j. 1997. podiform chromitites.pdf. j. econ. geol. 20, 247–252. santoso, b., supriyana, e., wijatmoko, b. 2016. pendugaan mineral kromit dengan metode electricalresistivity tomography di daerah wosu-morowali sulawesi tengah. proceeding semin. nas. mipa 2016 27–28. simandjuntak, t., surono., sukido. 1993. peta geologi lembar kolaka , sulawesi, skala 1:250.000. pusat penelitian dan pengembangan geologi, bandung. surono, 2013. geologi lengan tenggara sulawesi. badan geologi, kementerian energi dan sumber daya mineral jl. diponegoro no. 57 bandung 40122 telp. 022-7215297, fax. 022-7218154. zhou, m.f., robinson, p.t. 1997, origin and tectonic enviroment of podiform chormite deposits: journal economic geology, 92, p. 259-26. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 2 2021 widiatama et al./ jgeet vol 6 no 2/2021 86 research article calcareous nanofossil of post-gondwana sequence in southern banda arc, indonesia angga jati widiatama1*, lauti dwita santy2, rikza nur faqih an nahar1, zulfiah3, winda eka mandiri puteri3, adrianus damanik3, rubiyanto kapid3 1geological engineering, institut teknologi sumatera, south lampung, 35365, indonesia. 2geological survey center, geological agency, ministry of energy and mineral resources, bandung, 40122, indonesia. 3 geological engineering, institut teknologi bandung, bandung, 40132, indonesia. * corresponding author : angga.widiatama@gl.itera.ac.id tel.:+62-856-0629-2290 received: jan 23, 2021; accepted: may 24, 2021. doi: 10.25299/jgeet.2021.6.2.6287 abstract the presence of calcareous nannofossils in samples of the post-gondwana sequences (kolbano and viqueque sequence) gives guidance about the relative age of the study area located in the outer banda arc, namely timor, rote, and sawu island. the study was carried out on six traverses, timor island traverse (baun and camplong), rote island traverse (termanu and central rote), and sawu island traverses (west sawu and east sawu). there is 29 outcrop sample prepared using the smear slide method and observed using a polarizing microscope with 1000x magnification. the results of the study showed the presence of cretaceous, paleogene, and neogen-quarternary calcareous nannofossil. there are 82 species from 14 families identified in the post-gondwana sequence. the results showed that the assemblage of calcareous nannofossil in cretaceous characterized by the presence of watznaueria fasciata, watznaueria cynthae, cyclagelosphaera brezae, orastrum campanensis, and micula concava. the assemblage of paleogene calcareous nannofossil characterized by the presence of coccolithus staurion, chiasmolithus solitus, discoaster minimus, tawelus (?) magnicrassus, chiasmolithus bidens, prinsius africanus, cyclicargolithus luminus, spenolithus elongatus, reticulofenestra umbilica, cruciplacolithus vanheckae, and helicospharea seminulum, and the assemblage of neogene calcareous nannofossil characterized by the presence of reticulofenestra pseudoumbilica, discoaster quinqueramus, helicosphaera princei, and discoaster pansus. quarternary calcareous nannofossil characterized by the presence of ponthospaera indooceanica. keywords: calcareous nannofossil, kolbano sequence, banda arc 1. introduction timor, rote, and sawu island are located in the outer banda arc formed by the collision between the edges of the australian continent and volcanic banda arc (m.g, 2004; villeneuve et al., 2004). timor island and its surrounding area litotectically divided into five major groups (fig. 1); (1) gondwana sequences, permian to jurassic, containing siliciclastic rocks deposited in the intracratonic basin, (2) kolbano sequence containing siliciclastic rock and pelagic carbonate from late jurassic to neogene, (3) banda terrain which is part of asia that has been uplifted due to collision during late neogen. (4) bobonaro melange contains melange with blocks in clay, broken formation, and mud domes formed during the collision in the late neogen, (5) viqueque sequence which is synorogenic deposits which are relatively undeformed (barber et al., 1977; carter et al., 1976; harris et al., 1998; m.g, 2004; villeneuve et al., 2004). kolbano sequence contains siliciclastic and pelagic carbonate consisted of the nakfunu, menu, ofu, and batuputih formation. while the viqueque sequence consists of the viqueque formation and quarternary deposits. the nakfunu formation (sawyer, 2018; suwitodirjo, 1996) is identical to the wai bua formation in timor leste (audley-charles, 1968) that the lithology consists of chert, claystone, calcilutite, shale, calcarenite, wackestone, and packstone. one of nakfunu formation characteristics is the consistency of layer thickness which ranges from 3 to 30 cm with sharp contact, flat to wavy. shale units can be thin or massive layers, black with iron and manganese nodules. sedimentary structures are rarely found in the nakfunu formation except for laminates. the nakfunu formation is deposited during marine transgression of early cretaceous in the distal continental rise or abyssal near or below the ccd (sawyer, 2018). sawyer et al. (2018) described menu formation consisting of cretaceous rocks from early to late cretaceous which have lithological characteristics in the form of red-pink to white calcilutite limestone layers. some layers are pelecypods wackestone, layered between 6 to 60 cm, the layer is sharp, there are also 1-2 cm red chert layers with an intensive joint. menu formation in rote island was exposed in several areas including baa, termanu, and papela. the dominant lithology of ofu formation is white to pink massive limestone concoidal-subconcoidal fractures and looks shiny like porcelain on a fresh surface. there are laminates and intensive pressure solutions resulted in calcite veins in stylolites and fractures. updated biostratigraphy from existing formations and distinguished three mapped units, boti, borolalu, and oeleu members. the lithology consists of pelecypods-foraminifera wackestone; quartz packstone or foraminifera packstone; and turbidite conglomerates layered with angular fragments from menu formation or ofu formation. the age of this widiatama et al./ jgeet vol 6 no 2/2021 87 unit is lutetian phase in the middle eocene to the early pliocene (sawyer, 2018). the plio-pleistocene series is aimed for syn-orogenic sediments known as viqueque sequence [8] or the batuputih formation (sawyer, 2018; suwitodirjo, 1996). this includes the equivalent of viqueque, batuputih, and noele formation in west timor. the lithology of batuputih formation mainly consists of white massive calcilutite or chalky limestone with light grey marl and often with plant fragments. this unit is soft to hard and the layer is less visible. the tuffaceous layer is very rare outside the type location even though vitric glass fragments are often found. coarse bioclastic and clastic allogens are found in the interlocking parts with noele formation. viqueque formation consists of coarsening upward from chalky limestone and calcilutite to sandstones covered by quaternary gravel and reef limestones. the viqueque formation appears in the central basin in west and south of the kolbano unit that was imbricated. the noele formation shows lithological variations reflected rapidly uplift and topographic variations in depositional environments. the lithology includes marl, carbonate claystone, tuffaceous marl, tuffaceous calcilutite, white-yellow glass tuffs, biocalcarenite, siltstone, sandy limestone, dark grey marl, and sandstone. as for differences with batuputih formation, calcilutite and chalky limestone are rarely found. fig 1. stratigraphy column of research area from various author 2. material and method the objective of this study is identify calcareous nannofossil in post-gondwana sequences (kolbano and viqueque sequence) and to determine the relative age based on calcareous nannofossil in islands around southern outer banda arc. field data collection carried out in the survey activities of the sawu basin included three islands, timor, rote, and sawu. the research conduct by the geological survey center, geological agency, ministry of energy, and mineral resources in 2014. the research data including six traverses (fig. 2) timor island traverse (baun and camplong), rote island traverse (termanu and central rote), and sawu island traverse (west sawu and east sawu). data collection includes stratigraphic measurements, descriptions of megascopic rocks, microscopic descriptions, and paleontology of calcareous fossils. there are 29 calcareous nanofossil samples prepared by the smear slide method and observed using a polarizing microscope with 1000x magnification. the age determination of cenozoic calcareous nannofossil based on martini’s zone (martini, 1970) while the mesozoic zone based on bown and cooper zonation (bown and cooper, 1998). fig. 2 map of research area (a) timor island traverse, (b) rote island traverse, and (c) sawu island traverse 88 widiatama et al./ jgeet vol 6 no 2/2021 3. geology research area 3.1 timor island there are two observation points of camplong traverse, 14ajw06, and 14ajw07 (figure 2a). the outcrop is on trans timor road near mina river bridge with a length of 50 meters and a height of 20 meters. lithology consists of a layering of tuffaceous limestone, chalky limestone, foraminifera grainstone, marl, and conglomerates. the measured section column is shown in figure 4a. the lower part of the outcrop consists of light white tuffaceous-chalky limestone layering, having intensive joint, 20-30 layer thickness, medium compacting with parallel lamination. the age is not older than burdigalian (nn4) to tortonian (nn 10), which characterized by the first appearance of the reticulofenestra pseudoumbilica until the first appearance of discoaster quinqueramus. the middle section consists of chalky limestone turning into intercalation of foraminifera grainstone-marl with an erosive layer contact (figure 3a). white foraminifera grainstone has medium compacting, bioclastic components, insitu planktonic foraminifera, and rework foraminifera, bivalves, juvenile mollusca, tuffaceous, with plagioclase and quartz as additional components. marl dominant forms of carbonate mud with planktonic foraminifera as the main bioclastic. marl and the foraminifera grainstone have erosional contact. fig. 3 post-gondwana sequence outcrop (a) intercalation of foraminifera grainstone and marl, (b) amonite limestone, (c) calcilutite and chert intercalation, (d) trace fossils of chondrites and planolites in calcilutite, (e) neogene orange calcilutite in rote island, (f) paleogene calcilutite in sawu island, (g) layer of foraminifera grainstone with flutecast at the lower part of the layer, and (h) calcilutite with fissile structure. based on calcareous nannofossil foraminifera grainstone is tortonian-messinian (nn 11) characterized by the presence of discoaster quinqueramus. the upper part of the outcrop is an unconformity between foraminifera grainstone -marl intercalation cut by conglomerates with quarternary matrix. based on nannofossil on the matrix shown nn20 zone or younger which characterized by the first appearance of ponthospaera indooceanica. there are three observation points of baun traverse, 14ls138, 14ls143, and 14ls145 (figure 2a) located in bihati river, baun is composed of broken formation of ammonite limestone, calcilutite, foraminifera grainstone, and basalt. the measured section columns are shown in figures 4a and 4b. ammonite limestone (figure 3b) is reddish-white, poorly sorted, high compaction, consists of ammonite sp., crinoid sp., halobia sp., and atomodesma sp. a distinctive characteristics of gondwana sequences of permo-triassic rocks that have a fault contact with a postgondwana sequence. the kolbano sequence consists of pale pinkish calcilutite and pale white calcilutite with parallel lamination and firm layer contact. late cretaceous nannofossil zone from the santonian-campanian (uc 11uc 15) characterized by first the appearance of the orastrum campanensis and micula concava in the lower part of the section until the last appearance of orastrum campanensis in the upper part of measured stratigraphy section. in the upper reaches of bihati river also found well-lamination of white foraminifera grainstone, consist of 20-30 layer thickness, medium compacting with parallel lamination. burdigalian-tortonian age (nn 4-nn 10) characterized by the first appearance of reticulofenestra pseudoumbilica appearance until the first appearance discoaster quinqueramus. these units are unconformity overlap of ammonite limestone and calcilutite with fault contact. 3.2 rote island termanu traverse consists of three observation points, 14ajw18, 14ajw19, and 14ajw20 in tanjung termanu (figure 2b). the measured section column is shown in figure 4d. outcrops consist of calcilutite, chert, and marl with radiolaria as the dominant bioclastic component. limestone is relatively thickening upward, while the chert is relatively thinning upward (figure 3c). based on calcareous nannofossil in the lower part of the tanjung termanu section, the age shows early cretaceous between berriasian and valanginian (nc2 nc3) is marked by the first appearance of cyclagelosphaera brezae, watznaueria fasciata, and watznaueria cynthae until the last appearance of cyclagelosphaera brezae. in the central part of the termanu traverse (14ajw20) above the intersection of calcilutite, chert, and marl, the chert layer tends to become more dominant calcilutite and marl, parallel lamination, consist of ichnofossil such as chondrites, planolites, and zoophycos (figure 3d). the age of rocks is early cretaceous, hauterivian to aptian (nc5 nc7) based on the last appearance of cyclagelosphaera brezae until the last appearance of watznaueria fasciata. the upper part of the termanu traverse is late cretaceous from albian to coniacian (nc 8-uc 10) marked by calcilutite characteristic changes of color from pink to orange. the lower part of this zone is marked by the first appearance of watznaueria fasciata, the upper part is marked by the first appearance of orastrum campanensis and micula concava. central rote traverse (figure 2b) located in central rote (14ajw16, 14ls130, and 14ls133) to papela beach (14ajw12). the outcrop on papela beach is characterized by calcirudite limestone with unoriented mollusca shell fragment as the main component and associated with manganese boulder and quartz sandstones. the outcrop consists of a broken formation, surrounded by the scaly clay mélange bobonaro. the presence of watznaueria fasciata widiatama et al./ jgeet vol 6 no 2/2021 89 indicates early cretaceous between berriasian and aptian (nc2-nc7). outcrops at the observation point 14ls130, 14ls133, and 14ajw16 can be divided into four zones. the lower part (zone 1) consists of red to orange foraminifera grainstone, well layered, 10-20 cm layer thickness, medium compacting, fissile structure, and parallel lamination, burdigali-tortonian age (nn4 nn 10) marked by the first appearance of the reticulofenestra pseudoumbilica until the first appearance of discoaster quinqueramus. the middle zone (zone 2) consists a layer of red to orange calcite limestone (figure 3e), with dominant foraminifera bioclastic component. the age shows tortonian-messinian age (nn 11) characterized by the first appearance of helicosphera princei and discoaster quinqueramus until the last appearance of the discoaster quinqueramus. conformable grayish-white grainstone foraminifera (zone 3) overlay zone 2, interspersed with layers of tuffaceous lapilli limestone and plant fragments, with medium compacting, the age indicated messinianzanclean (nn 12-nn 15) marked by the first appearance of discoaster pansus until the last appearance of the discoaster pansus. the upper part (zone 4) is foraminifera limestone with poorly lamination, medium compaction, overlay with foraminifera grainstone. the aged are pliocene-pleistocene (nn16 nn21) characterized by the last appearance of the discoaster pansus until the last appearance of dictyococcites productus and helicosphaera princei. the measured section column is shown in figure 4c. fig. 4 measured stratigraphic correlation and biozonation of calcareous nannofossil in timor island (a and b), rote island (c and d), and sawu island (e). 3.3 sawu island west sawu traverse (figure 2c) consists of four observation points (14sh103, 14sh104, 14sh108, and 14sh121). the west sawu traverse consists of the foraminifera grainstone at the lower part that gradually becomes calcilutite at the top. foraminifera grainstone is white, dominated by planktonic foraminifera, with minor benthonic foraminifera, erosional contact at some layer, graded bedding, flute cast, forming channel geometry, and lateral thinning layer. the aged are thanetian (np9) tagged by the first appearance of coccolithus staurion and chiasmolithus solitus to ypresian (np11) that labeled by the last appearance of discoaster minimus and tawelus (?) magnicrassus. it is also indicated by presence of foraminifera globigerinatheka sp. as paleogene marker. foraminifera grainstone gradually changed to red calcilutite with parallel lamination, 5-15 cm layer thickness. petrographically, calcilutite is a foraminifera wackestone to foraminifera mudstone. the age is from yalcian (np11) to lutetian (np15) marked by the first appearance of chiasmolithus bidens until the last appearance of coccolithus staurion and cyclicargolithus luminus. the measured section column is shown in figure 4e. east sawu traverse (figure 2c) consists of three observation points (14ls110, 14ls112, and 14ls113). the east sawu traverse consists of foraminifera grainstone at the lower part gradually becomes calcilutite at the top with implied chert (figure 3f). foraminifera grainstone characterized by an erosive contact with layer below it, layered 15 cm in thickness, graded bedding, parallel lamination, flute cast (figure 3g), and forming a channel geometry in lateral. foraminifera grainstone is danian (np2), which is tagged by the presence of prinsius africanus and also the presence of foraminifera globigerinatheka sp. as a marker of paleogene. 90 widiatama et al./ jgeet vol 6 no 2/2021 foraminifera on grainstone originates from foraminifera in situ and rework deposited. on top of foraminifera grainstone gradually turns into red calcilutite, the thin layer of 5-10 cm, with parallel lamination and scaly structures (figure 3h). based on the petrographic observations of calcilutite composed foraminifera wackestone to foraminifera mudstone. calcilutite indicated ypersian (np14) to lutetian (np15) based on the presence of spenolithus elongatus. in the east sawu travers, limestone characterized by the first appearance of the reticulofenestra umbilica and the last appearance of cruciplacolithus vanheckae, chiasmolithus solitus, and helicosphaera seminulum indicated age of middle eocene (lutetian to bartonian/np16), that overlapped with chert layer with bioclastic component like bivalve shells and radiolaria. 4. discussion correlations of measured section columns of timor, rote, and sawu showed in figure 4. the southern outer banda arc consist of 20 zones of calcareous nanofossil biostratigraphy (figure 5). gondwana and post-gondwana sequences are characterized by break-up unconformity that occurs in the early cretaceous (baumgartner, 1993). calcareous nanofossil of cretaceous kolbano sequences consisted of four families and 17 species (table 1). the watznaueriaceae family has the most species diversity with twelve species, holococcoliths with four species, family biscutaceae with one species, and polycyclolithaceae with only species. menu formation aged early cretaceous, nc2-nc3 zone with the first appearance of cyclagelosphaera brezae, watznaueria fasciata, and watznaueria cynthae in berriasian to the last appearance of cyclagelosphaera brezae in valanginian. late cretaceous (santonian/uc11) menu formation is characterized by the first appearance of orastrum campanensis and micula concava. late cretaceous nannofossil dominated by the calculites genus. cretaceous nanofossil showed in figure 6. fig. 5 biostratigraphy chart of calcareous nannofossil post-gondwana sequence in the banda arc. widiatama et al./ jgeet vol 6 no 2/2021 91 table 1. diversity of cretaceous calcareous nanofossil no calcareous nanofossil no calcareous nanofossil family biscutaceae 8 cy. deflandrei 1 discorhabdus ignotus 9 cy. margerelii family holococcoliths 10 watznaueria barnesiae 2 aspigolithus parcus 11 wz. biporta 3 calculites obscurcus 12 wz. britannica 4 calculites ovalis 13 wz. cynthae 5 orastrum campanensis 14 wz. fasciata family polycyclolithaceae 15 wz. fossacincta 6 micula concava 16 wz. manivitiae family watznaueriaceae 17 wz. ovata 7 cyclagelosphaera brezae fig. 6 cretaceous calcareous nannofossil, scale bar 5 μm.: (1) aspigolithus parcus; (2) calculites obscurcus; (3) calculites ovalis; (4) cy. brezae; (5) cy. deflandrei; (6) cy. margerelii; (7) discorhabdus ignotus; (8) micula concava; (9) orastrum campanensis; (10) wz. barnesiae; (11) wz. biporta; (12) wz. britannica; (13) wz. cynthae; (14) wz. fasciata; (15) wz. fossacincta; (16) wz. manivitiae; (17) wz. manivitiae; (18) wz.ovata. the paleocene to miocene sediment of the kolbano sequence is grouped in the ofu formation, in the form of a graded foraminifera grainstone into calcilutite. paleogene calcareous nannofossil of kolbano sequence consisted of eight families and 31 species (table 2). coccolithaceae family has fifteen species, noelaerhabdaceae as many as three species, sphenolithaceae has three species, prinsiaceae composes three species, pontosphaeraceae as many as two species, watznaueriaceae consist of two species, discoasteraceae has two species, and helicosphaeraceae as many as one species. prinsius africanus is an index fossil of the danian (np2). the beginning of the eocene started by the appearance of chiasmolithus bidens (ypresian / n11). eocene nannofossils dominated by coccolithus, chiasmolitus, and reticulofenestra genus. the upper limit of the eocene (eocene-oligocene transition) marked by the last appearance of ericsonia orbis and cruciplacolithus edwardsii. paleogene nannofossil selected showed in figure 7. table 2. diversity of paleogene calcareous nanofossil no calcareous nanofossil no calcareous nanofossil family coccolithaceae family helicosphaeraceae 1 chiasmolithus bidens 19 h. seminulum 2 ch. consuetus family pontosphaeraceae 3 ch. nitidus 20 p. cf. scisurra 4 ch. solitus 21 p. diamorphosus 5 coccolithus formosus family sphenolithaceae 6 co. hulliae 22 spenolithus cf. spiniger 7 co. pauxillus 23 s. radians 8 co. pelagicus 24 s. elongatus 9 co. staurion family watznaueriaceae 10 cruciplacolithus edwardsii 25 cy. reinhardtii 11 cr. primus 26 cy. luminis 12 cr. tenuis family prinsiaceae 13 cr. vanheckae 27 prinsius africanus 14 ericsonia orbis 28 p. tenuiculum 15 e. subpertusa 29 toweius magnicrassus family noelaerhabdaceae family discoasteraceae 16 reticulofenestra cf. ornata 30 discoaster minimus 17 r. dictyoda 31 d. barbadiensis 18 r. umbilica fig. 7 paleogene calcareous nannofossil in sawu island: (1) ch. bidens; (2) ch. solitus; (3) co. formosus; (4) co. hulliae; (5) co. staurion; (6) cr. edwardsii; (7) cy. luminis; (8) d. barbadiensis; (9) d. minimus; (10) e. orbis; (11) h. seminulum; (12) prinsius africanus; (13) r.umbilica; (14) s. elongatus; and (15) tawelus(?) magnicrassus. scale bar 5 μm. the ofu formation of kolbano sequence continued until miocene, that lithology predominantly contained the foraminifera grainstone with the insertion of calcilutite and tuff layers overlay by viqueque sequence which age is quarternary. neogene-quarternary calcareous nannofossil in the study area consisted of eight families and 33 species (table 3). the discoasteraceae family has the most species diversity with twelve species, noelaerhabdaceae with ten species, calcidiscaceae with three species, helicosphaeraceae with two species, sphenolithaceae with two species, coccolithaceae with two species, pontosphaeraceae with one species, and nannolith families inc sed with one species. the first appearance of the reticulofenestra pseudoumbilica becomes the lower boundary of the miocene age. miocene nannofossils are 92 widiatama et al./ jgeet vol 6 no 2/2021 dominated by discoaster, coccolithus, sphenolithus, and reticulofenestra genus. the upper miocene-pliocene boundary was marked by the first appearance of the discoaster pansus. quarternary sediment is marked by the appearance of ponthospaera indooceanica. quarternary nanofossil is dominated by the genus gephyrocapsa. neogene-quarternary nannofossil selected is shown in figure 8. integration of sedimentology and paleontology data provides a comprehensive understanding of depositional environments. the calcilutite and chert show that the similarity of the constituent bioclastic in the form of radiolaria showing the relationship between the menu formation which is calcilutite dominant and the nakfunu formation containing hemipelagic siliciclastic rocks. the similarity of the dominant radiolaria bioclastic component indicates depositional environment is in the upwelling area (bak, 2007; de wever et al., 2014, 1994). upwelling areas provide three conditions that increase the chances of preservation of silica-rich sediment deposits; (1) high nutrition in the upwelling area results in greater productivity of phytoplankton causing silica saturation due to the high productivity of radiolarian-rich deposits, (2) increasing the rate of organic material production below the upwelling zone implying a lower ratio of carbonate shelled organisms, (3) high organic components preventing dissolution of silica (de wever, 1989; de wever et al., 1994; 2014) the correlation among the central rote traverse in the form of pelagic mollusca deposited as turbidite carbonates turned into calcilutite supported by radiolarian on the termanu traverse indicated a change of depositional facies from slope to the basin floor. pelagic carbonate deposition continues until the late cretaceous is shown to be similar in thickness to the calcilutite facies. table 3. diversity of neogene-quarternary calcareous nanofossil no calcareous nanofossil no calcareous nanofossil family discoasteraceae 20 dy. antarcticus 1 discoaster asymetricus 21 r. minuta 2 d. berggrenii 22 r. pseudoumbilicus 3 d. broweri family calcidiscaceae 4 d. challengeri 23 calcidiscus leptoporus 5 d. deflandrei 24 hayaster sp. 6 d. hamatus 25 umbilicosphaera rotula 7 d. neohamatus family coccolithaceae 8 d. neorectus 26 coccolithus pelagicus 9 d. pansus 27 ericsonia cava 10 d. pentaradiatus family helicosphaeraceae 11 d. quinqueramus 28 helicosphaera princei 12 d. variabilis 29 h. kamptneri family noelaerhabdaceae family sphenolithaceae 13 dictyococcites productus 30 sphenolithus abies 14 gephyrocapsa ericsonii 31 s. neoabies 15 gy. oceanica family pontosphaeraceae 16 gy. carribeanica 32 p. indooceanica 17 reticulofenestra producta nannolith families inc sed 18 r. pseudoumbilicus 33 florisphaera profunda 19 dictyococcites productus sedimentary rock of the ofu formation in the paleocene to eocene show a change in pink and white. the character of the red limestone is identical to the widespread oceanic red bed (orb) deposit known as the low latency facies type in the tethys sea (cai et al., 2012; hu et al., 2005; scott et al., 2009). red limestone caused by the presence of iron (fe2+/fe3+). according to cai et al. (cai et al., 2012, 2009, 2008) an authigenic hematite formed in calcite crystals is it not only on the surface of the rock but also throughout the limestone. the typical characteristic sediment of ofu formation is indicated by the repetition of the deposition sequence in the form of a foraminifera grainstone to calcilutite. foraminifera grainstone deposited with a turbidite mechanism when decreasing the sea level, while calcilutite deposited during rising sea level to the maximum sea level. the sedimentary rocks of the ofu formation in the miocene-pliocene consist of a pink foraminifera grainstone that graded into white at the top. the dominance of the planktonic foraminifera indicates a more depositional environment towards the basin. the intersection of the foraminifera grainstone and marl indicates turbidity current control. the tuff and lapili components indicate the presence of explosive volcanism which become the source of volcaniclastic rocks originate from the banda arc. fig. 8 neogene-quarternary calcareous nannofossil in timor island, bar 5 μm.: (1) c. leptoporus; (2) hayaster sp.; (3) umbilicosphaera rotula; (4) co. pelagicus; (5) helicosphaera kamptneri; (6) h. princei; (7) dy. productus; (8) gy. ericsonii; (9) gy. oceanica; (10) r. producta; (11) r. pseudoumbilicus; (12) s. abies; (13) s. neoabies; (14) d. berggrenii; (15) d. neorectus; (16) d. broweri; (17) d. challengeri; (18) d. quinqueramus; (19) d. variabilis; (20) d. deflandrei; (21) d. neohamatus. scale fig. 9 depositional environment model of post-gondwana sequence in research area. widiatama et al./ jgeet vol 6 no 2/2021 93 pliocene-quarternary rocks are deposits of the viqueque sequences that form synorogenic in the collision between banda arc and australian passive margin. matrix supported conglomerates indicate formation due to mass flow. the depositional environment model of the study area is illustrated in figure 9. 5. conclusion calcareous nannofossil of kolbano sequence identified 82 species from 14 families consist of cretaceous, paleogene, and neogen age. the cretaceous calcareous nannofossil assemblage consists of 18 species (table 1) dominated by the watznaueria and cyclagelosphaera genus. the oldest index nanofossil in the kolbano sequence is berriasian based on the first appearance of cy. brezae. the paleogene calcareous nannofossil assemblage consists of 31 species (table 2) dominated by pontosphaera, cruciplacolithus, chiasmolithus, and coccolithus genus with index nannofossil is prinsius africanus, danian (np2). the beginning of the eocene started with the appearance of chiasmolithus bidens (ypresian/np11) and dominated by coccolithus, chiasmolitus, and reticulofenestra genus. the neogene-quarternary calcareous nannofossil assemblage consists of 33 species (table 3) dominated by discoaster, coccolithus, sphenolithus, reticulofenestra, and gepyrocapsa genus. r. pseudoumbilica becomes the marker of early miocene (nn4-nn10), nn11 zone marked by the existence of d. quinqueramus and d. berggrenii. quarternary (nn19 zone) characterized by the first appearance of p. indooceanica. acknowledgements we like to thank the geological agency, the indonesian ministry of energy and mineral resources for lending data, all members of the 2014 sawu basin team who have helped in data collection, and all parties who have made suggestions to make this paper better. references audley-charles, m.g., 1968. the geology of portuguese timoaudley-charles, m. g. 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section (central italy): a high-resolution transmission electron microscopy analysis. cretac. res. https://doi.org/10.1016/j.cretres.2011.11.016 cai, y., li, x., hu, x., chen, x., pan, y., 2009. paleoclimatic approach to the origin of the coloring of turonian pelagic limestones from the vispi quarry section (cretaceous, central italy). cretac. res. https://doi.org/10.1016/j.cretres.2009.06.002 cai, y., li, x., pan, y., hu, x., 2008. the color-causing mechanism of mn&lt;sup&gt;2+&lt;/sup&gt; and fe&lt;sup&gt;3+&lt;/sup&gt;: evidence from the italian cretaceous pelagic red limestones. acta geol. sin. carter, d.j., audley-charles, m.g., barber, a.j., 1976. stratigraphical analysis of island arc-continental margin collision in eastern indonesia. j. geol. soc. london. https://doi.org/10.1144/gsjgs.132.2.0179 de wever, p., 1989. radiolarians, radiolarites, and mesozoic paleogeography of the circummediterranean alpine belts, in: siliceous deposits of the tethys and pacific regions. 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engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 3 2021 manurung, p.l., et al./ jgeet vol 6 no 3/2021 147 research article total organic carbon (toc) value prediction in source rock potential at north east java basin, indonesia. paulus l. manurung1, ordas dewanto2, rahmat c. wibowo3* 1,2,3 department geophysical engineering, universitas lampung, bandar lampung, indonesia. * corresponding author: rahmat.caturwibowo@eng.unila.ac.id tel.:+6281 271 702 441 received: apr 5, 2021; accepted: aug 30, 2021. doi: 10.25299/jgeet.2021.6.3.6644 abstract this research aims to determine the potential of the source rock in the kujung and cepu formations in the north east java basin, using total organic carbon (toc). toc is calculated using the passey method. the passey method is used by overlaying the sonic log and the resistivity log and determining the baseline to get the separation of δlog resistivity, which is then used to predict the toc log by including the lom (level of organic maturity) variable obtained from the data of vitrinite reflectance. after the toc log value is obtained, a correlation is made with the toc core value. the prediction result of toc log in a pm-1 well is 2.16%, which means it has excellent quality. the prediction of toc log in a pm-2 well is worth 2.68%, which means it has excellent quality. the correlation value between the toc log and the toc core of the pm-1 well is 0.67, which means the correlation is strong. in pm-2 well, the correlation between the toc log and toc core is 0.92, which means that the correlation is robust. keywords: toc, correlation, passey method. 1. introduction the north east java basin is one of the most productive petroleum producing-basins in indonesia. in exploration and research, oil and gas exploration often focused primarily on evaluations of reservoirs and traps. in contrast, the evaluation of hydrocarbon charge includes evaluating hydrocarbon-producing source rocks. its migration was often simplified or underreported, even though this evaluation could answer the time (when) and the amount of oil formed in a hydrocarbon basin in indonesia (dewanto et al., 2017). shale hydrocarbon plays are one of the most popular hydrocarbons plays of the last five years. in shale hydrocarbon plays, source rock and reservoir rock are often the same rock. total organic carbon (toc), as a percentage of the total rock volume, is an important parameter in shale hydrocarbon play assessments and is also regarded as one of the key variables that directly affects the rock quality, shale hydrocarbon in place estimations, and hydraulic fracturing design. often the availability of toc data on shale as source rock are very limited. therefore, we need a method to predicting the toc of shale rock as the source rock. toc prediction will be validating with toc data, which is derived from core rocks of oil and gas wells (basyir et al., 2020). in general, the source rock is the rock that contains sufficient amounts of organic material, has reached a certain maturity, and is rich in the elemental content of carbon atoms obtained from fossil shells deposited in the rock to become the raw material for the formation of hydrocarbons. toc is the quantity of organic carbon deposited in the rocks. the higher the organic carbon value, the better the source rock will be, and also, the possibility of hydrocarbon formation will usually be higher. this study uses the δlogr methodology of passey et al., (1990) determines total organic carbon (toc) from the separation apparent when a properly scaled porosity log and resistivity log are overlain and a maturity factor applied. in water-saturated, organiclean rocks the two curves parallel each other because both respond to variations in formation porosity. in both hydrocarbon reservoirs and organic-rich non-reservoir rocks a separation between the curves, termed δlogr, is present. reservoir rocks are eliminated from the analysis by their gamma-ray response and by other well data such as the lithology from mudlog and well samples, where available. the toc of the source rock intervals is then calculated based on the δlogr separation measured in logarithmic resistivity cycles and thermal maturity expressed as lom (level of organic metamorphism) using the empirical relationships. in immature rocks the δlogr separation is due primarily to the response of the porosity log, e.g., the longer transit time of the sonic or acoustic log responding to the lower density organic matter. in thermally mature rocks the separation is also caused by longer transit times, but additionally by higher resistivity due to the presence of generated unexpelled hydrocarbons. we applied the method using the differential transit time log (dt), also known as the sonic or acoustic log, and the deep induction log (ild) as recommended by (passey et al., 1990). we used thermal maturity data from vitrinite, converted to lom (keller et al., 1999). 2. geology geologically (figure 1), the formation of the north east java basin is controlled by two fault systems, that is, the http://journal.uir.ac.id/index.php/jgeet 148 manurung, p.l., et al./ jgeet vol 6 no 3/2021 horizontal fault system trending northeast-southwest and east-west direction. this basin is formed by several main structural elements from south to north, namely: kendeng zone the madura strait is elongated in the east-west direction which is characterized by a fold structure, normal faults and many upward faults. south rembang zone and randublatung which are negative zones with east-west trending structural patterns characterized by folds. there is a dome structure that is associated with a fault structure. the north rembang zone and north madura, the anticlinorium structure that was elevated and eroded in plioceneplistocene associated with a horizontal fault system drifted in a continuous northeast-southwest direction to south kalimantan. fig. 1. regional geological map of the north east java basin (sribudiyani et al., 2003). fig. 2. geologic setting of east java basin (satyana, 2005). geologic setting of east java consisting of northern platform, central deep, and southern uplift (figure 2), and north east java basin is located on the southeastern margin of a stable sundaland micro continent. the basin is bounded by karimun java arch to the west, masalembo high to the north, doang high to the east and volcanic arc to the south. the basin was initiated at midcretaceous age by collision between microplates at the southeastern margin of sundaland. this collision created a suture zone between microplates and later on becomes a structural grain lineament of half and graben in north east java basin. the extensional phase that creates graben system in north east java basin began in paleogene to early neogene time. it is interpreted to be formed by slab roll-back system between australian to eurasia-sundaland plate subduction. the compressional phase has occurred during neogene to the present time as an implication of indian oceanic plate subduction to the south of java island, a westward stress due to buton-tukang besi and banggai-sula collision to the western part of sulawesi, and due to large sinistral strike slip rmks (rembang-madura-kangean-sakala fault. during the late oligocene, kujung formation carbonates were deposited over the ngimbang formation and on existing pretertiary basement highs with reefal build-ups developed throughout the east java area. patch reefs developed along the central basin edges with pinnacle-type reefs occurring in the isolated highs of deeper water area (satyana and purwaningsih, 2003). the petroleum system consists of important components, source rock is the main hydrocarbon parent rock in the east java basin originates from carbonate flakes derived from marginal marine, deltaic, and lacustrine environments. the ngimbang formation, mainly originating from the central deep basin (nainggolan, 2018) with kerogen types ii and iii so as to produce hydrocarbon (oil and gas). deep sea flakes at the bottom of the kujung formation are also potential as host rock. reservoirs are rocks with porosity and permeability that are good for storing and flowing hydrocarbons. the main reservoirs in this basin are the carbonate rocks of the ngimbang formation and the kujung interval i formation as well as the siliciclastic reservoir of the ngimbang formation, tuban formation and the ngrayong formation. hydrocarbon migration divided into primary migration is the transfer of hydrocarbon fluid from the host rock to reservoir rock and secondary migration is the movement of fluid in the reservoir through the trap. stone hoods have a role as non-permeable insulation such as claystone. the rock seals in this basin are shale of the ngimbang formation, tuban formation, wonocolo formation, and tongue formation. shale formation tuban is a covering rock that has a thickness of 500 ft – 1500 ft in the north east java basin (sribudiyani et al., 2003) the types of traps in all east java petroleum systems generally have similarities. this is due to tectonic evolution that occurs in all sedimentary basins along the southern boundary of the sunda plate so that the type of geological structure and trap mechanism become relatively similar. the structure traps that developed in the form of anticlines and faults and stratigraphic traps were found when the sandstone unit rested (onlap) and covered part of the bedrock heights (satyana and djumiati, 2003) the kujung formation was deposited after the ngimbang formation, a process of uplift and erosion accompanied by a decrease in eustatic sea-water resulting in a widespread regressive mid-oligocene event that explained the basis of the next kujung cycle (30 million years). although initially considered the eustatic event, some observations, both local (north east java basin) and regional suggested tectonic control. the end of the kujung cycle corresponded to the end of the initial carbonatedominated transgression. in most cases, this indicated the upper part of the early miocene limestone, the upper rock nature of the kujung cycle meant that the kujung cycle to the tuban cycle limit was often a misalignment due to the time it took for sequential to onlap the rest of the reef. in the late oligocene-early miocene, the kujung formation (figure 3.) was deposited with rocks that were dominated by limestone and marl with thin sandstone insertions and there were fossils of foraminifera, coral fragments, and algae in limestone. the kujung formation was widespread, covering the purwodadi area to the east of tuban and madura. the cepu formation (figure 3.) in the late miocene sedimentation in the madura basin clay, and silica sand. the structural process in the mid-miocene had stopped, then filled with cepu formation consisting of marl and limestone from deposition of planktonic and nanoplankton (nainggolan, 2018). 3. well logging method manurung, p.l., et al./ jgeet vol 6 no 3/2021 149 well logging is a method used to obtain more detailed drilling well record data which is depicted in the form of curves from the value of petrophysical parameters. the purpose of well logging is to obtain lithology information, porosity measurements, resistivity measurements, and fluid saturation. while the main purpose of using logs in this study is to determine the source rock zone and calculate the quantity of total organic carbon (toc). the principle of the gamma ray log is a record of the level of natural radioactivity that occurs due to three elements, namely uranium (u), thorium (th), and potassium (k) present in rocks. gamma rays are very effective in distinguishing between permeable and non-permeable layers, because radioactive elements tend to be concentrated in non-permeable shale, and are not abundant in carbonate rocks or sand is generally permeable. the resistivity log is a record of the formation resistivity when an electric current is passed, expressed in ohm-meters. sonic log is an acoustic log with the working principle of measuring the travel time of sound waves at a certain distance in the rock layer. for the working principle of this tool is sound at regular intervals emitted from a sound source (transmitter) and the receiver will record the length of time the sound propagates in the rock (δt) (schlumberger, 1989). 4. total organic carbon (toc) total organic carbon (toc) was a measure of organic wealth that described the amount of organic material in the source rock. toc was represented by the weight percent of organic matter relative to the total weight of the rock. in general, the source rock was classified as poor quality if the toc value was less than 0.5%; medium if the toc value was between 0.5% -1%; good if the toc value ranges from 1% -2%; and very good if the toc value ranges from 2% 4%; excellent if more than 4% (peters and cassa, 1994). according to keller et al., (1999) the source rock potential was determined by calculating a net organicrichness based on the δlogr toc profiles and then using maturity scaling factors applied to present-day thermal maturity from vitrinite reflectance using the methods of dembicki and pirkle, (1985). dembicki and pirkle, (1985) use "richness" to mean the thickness of an effective source rock times the average toc for that "effective" interval. we use "net richness" in the same way they used "richness" to distinguish it from richness as organic carbon concentration. we define net or effective source rock as the thickness of rock with ≥2 wt % toc for rocks with predominantly marine organic matter and ≥1 wt % toc for rocks with predominantly terrigenous organic matter. note that toc is not the only measure of source rock quality and is impacted by additional maturity caused by heat and/or burial. oil deposits in shale oil is quite high, estimated as relatively large reserves spread across several regions of indonesia. to determine the content of oil shale in the basin necessary to evaluate the condition of the reservoir, by determining and analyzing the reservoir parameters. determination and analysis of reservoir parameters is done by two methods, namely core analysis in the laboratory and log interpretation in the field. on the source rock, testing pyrolysis is used to determine the organic content (toc), the maturity of organic material, detecting the content of oil or gas produced and is also used to identify the type of some mixed material (mulyatno et al., 2018). fig. 3. stratigraphy column of kangean block (davies, 1989). 150 manurung, p.l., et al./ jgeet vol 6 no 3/2021 5. correlation correlation is an analysis technique that is included in one of the techniques of measuring association / relationship (measures of association). association measurement is a general term that refers to a group of techniques in bivariate statistics that are used to measure the strength of the relationship between two variables. the correlation coefficient is a statistical measure of the covariance or association between two variables. the magnitude of the correlation coefficient ranges from +1 to -1. correlation coefficient indicates the strength (strength) of the linear relationship and the direction of the relationship between two random variables. if the correlation coefficient is positive, then the two variables have a unidirectional relationship. to make it easier to interpret the strength of the relationship between the two variables, the authors provide the following criteria: a. 0 : no correlation b. > 0 0.25 : very weak correlation c. > 0.25 0.5 : fair correlation d. > 0.5 0.75 : strong correlation e. > 0.75 0.99 : very strong correlation f. = 1 : perfect correlation (sarwono, 2006). 6. methods analysis of total organic carbon (toc) in this study used two well data, which specifically carried out the research on the kujung formation (a pm-1 well) and cepu formation (a pm-2 well). the flow of this research was as follows: 1. performing a zone analysis of the source rock using gammaray log, resistivity log, and sonic log. 2. calculating the toc value of each source rock zone using log passey et al., (1990). with the following formula: toc = (∆log r) x 10(2.297−0.1688 x lom) (1) δlogr = log ( r rbaseline ) + 0.02 x (t − tbaseline) (2) with: toc = total organic carbon (wt%); lom = level of maturity; log r = curvature on overlay sonic/ resistivity logs; r = measured resistivity of the logging tool (ohms-m); t = measurement of transit time (μsec / ft); rbaseline = the same resistivity value as tbaseline when the baseline curve is in clayrich rocks (non source); 0.02 = based on the ratio at 50 μsec / ft per 1 resistivity cycle. 3. determine the correlation coefficient between the two toc core data and the toc log. 7. results and discussion in the pm-1 well sample (table 1), the average toc value of the 24 samples was 2.16%. the minimum toc value was 0.49% at a depth of 8254 ft and the maximum toc was 5.09% at a depth of 8848 ft. according to the toc classification system (peters and cassa, 1994), it could be classified that the source rock in this kujung formation study was a good in terms of organic richness because the average toc content varies in dominance between 1% and 2%. in the pm-2 well sample (table 2), the average toc value of the 14 samples was 2.68%. the minimum toc value was 0.58% at a depth of 6685 ft and the maximum toc was 6.49% at a depth of 5812 ft. according to the (peters and cassa, 1994) toc classification system, it could be classified that the source rock in the cepu formation study was a fairly good in terms of organic richness because the average toc content varied in dominance between 0.5% to 2%. table 1. the results of the quantification of the toc value in the pm1 well (kujung fm). depth (ft) lom toc log (wt%) 7010 5.7 4.84 7139 5.7 2.24 7248 5.5 1.65 7335 5.6 1.9 7447 5.5 0.67 7754 5.4 2.54 7967 5.4 3.49 8034 5.6 2.35 8142 5.7 3.11 8217 5.7 1.83 8254 5.8 0.49 8314 5.8 1.47 8538 5.9 4.4 8695 5.9 3.37 8848 6 5.09 8920 6.1 0.81 8960 6.1 1.55 9018 6.2 1.61 9093 6.1 1.64 9200 6.3 1.89 9366 6.4 0.8 9525 6.5 0.69 9828 6.7 1.03 9970 7.2 2.41 table 2. the results of the quantification of the toc value in the pm-2 well (cepu fm). fig. 4. correlation graph of toc log vs toc core on pm-1 and pm-2 wells. depth (ft) lom toc log (wt%) 5620 4.7 4.33 5812 4.9 6.49 5858 4.9 5.51 6129 5.1 2.72 6236 5.2 2.8 6347 5.4 2.59 6430 5.5 1.56 6532 5.6 3.3 6685 5.7 0.58 6784 5.8 2.18 6893 5.8 2.22 7016 5.9 0.72 7227 6 1.67 7385 6.1 0.86 manurung, p.l., et al./ jgeet vol 6 no 3/2021 151 fig. 5. graph of the relationship between toc and depth in the pm1 well. fig. 6. graph of the relationship between toc and depth in the pm2 well. 8. conclusion from the whole research process, conclusions could be drawn, namely: 1. quantitatively, from the 24 source rock zones of the pm-1 well, the average toc value of the source rock was 2.16%, and according to the toc classification of (peters and cassa, 1994) it could be defined as having very good quality. 2. from the 14 main rock zones in the pm-2 well, the average toc value of the source rock was 2.68%, and according to the toc classification of (peters and cassa, 1994) it could be defined as having very good quality. 3. the correlation between the value of toc core and toc log in the pm-1 well was 0.67 which meant that according to (sarwono, 2006), it was a strong criterion. 4. the correlation between the toc core and toc log values in pm-2 well was 0.92 which meant that according to (sarwono, 2006), it was a very strong criterion. acknowledgements the authors thank the esdm ministry for data access, and to the geophysical engineering, university of lampung as the authors institution. references basyir, a., bachtiar, a., and haris, a., 2020. total organic carbon prediction of well logs data: case study banuwati shale member fm., asri basin, indonesia. aip conference proceedings, 2256. doi: 10.1063/5.0014651. davies, j. r., 1989. generalized stratigraphy and hc existing of kangean block. gearhart geodata servises ltd. dembicki, h. jr., and pirkle, f. l., 1985. regional source rock mapping using a source potential rating index. american association of petroleum geologists bulletin, vol.69, no.4, pp. 567–581. dewanto, o., mulyatno, b. s., rustadi and wibowo, r. c. 2017. determining the temperature of shale material conversion into crude oil based on organic clay and organic carbonate test outside reservoir. international journal of mechanical and mechatronics engineering, ijmme, 17 (issn: 2077-124x (online), 2227-2771 (print)), pp. 84–89. keller, m. a., bird, k. j., and evans, 1999. petroleum source rock evaluation based on sonic and resistivity logs. menlo park, california: u.s. geological survey open-file report. mulyatno, b. s., dewanto, o., and rizky, s., 2018. determining layer oil shale as new alternative energy sources using core analysis and well log method. international journal of engineering & technology, 7(issn: 2227524x), pp. 941–949. nainggolan, t. b., 2018. dekomposisi spektral dengan transformasi wavelet kontinyu untuk deteksi zona hidrokarbon di perairan bali utara. jurnal pppgl, p. bandung. passey, q. r., creaney, s., kulla, j. b., moretti, f. j., and stroud, j., 1990. a pratical model for organic richness from porosity and resistivity logs. in aapg bulletin, pp. 74, 12, 1777–1794. peters, k. e., and cassa, m., 1994. applied source rock geochemistry, chapter 5, in aapg memoir 60, pp. 93– 120. sarwono, j., 2006. metode penelitian kuantitatif dan kualitatif. yogyakarta: graha ilmu. satyana, a. h., and djumiati, m., 2003. oligomiosen carbonates of the east java basin indonesia. in aapg (ed.) international conference. barcelona. satyana, a., 2005. petroleum geology of indonesia: current concepts (preconvention course). in indonesian association of geologists 34th annual convention proceedings. surabaya, indonesia. satyana, a. h., and purwaningsih, m. e. m., 2003. geochemistry of the east java basin: new observations on oil grouping, genetic gas type and trends of hydrocarbon habitats. in proc. int. conf. on indonesian petroleum association 29th ann. conv. jakarta. schlumberger, 1989. log interpretation principles / applications. schlumberger wireline & testing : texas. sribudiyani, m. n., ryacudu, t., kunto, p., astono, i., prasetya, b., sapie, s., and asikin, a. h., and harsolumakso, 2003. the collision of the east java microplate and its implication for hydrocarbon occurrences in the east java basin. in proceedings indonesian petroleum association 30th annual convention & exhibition. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 03 2017 zar a.t. et al./ jgeet vol 02 no 03/2017 191 geochemical characteristics of metamorphic rock-hosted gold deposit at onzon-kanbani area, central myanmar aung tay zar 1,3, *, i wayan warmada 1 , lucas donny setijadji 1 , koichiro watanabe 2 1 department of geological engineering, faculty of engineering, gadjah mada university, yogyakarta, indonesia 2 department of earth resources engineering, faculty of engineering, kyushu university, 744 motooka, nishi-ku, fukuoka 819-0395, japan 3 department of geology, pyay university, pyay, myanmar * corresponding author : aungtayzar99@gmail.com tel.:+62-81-329-747-974 received: june 16, 2017. revised : july 1, 2017, accepted: aug 20, 2017, published: 1 sept 2017 doi : 10.24273/jgeet.2017.2.3.410 abstract onzon-kabani area is located on the western border of generally n-s trending mogoke metamorphic belt. many artisanal and small-scale gold mines were noted sincelast three decades. gold mineralization is mainly hosted in marble and occasionally observed in gneiss.host rocks chemistry is mainly controlled by hydrothermal activities and regional metamorphism. the compatible elements of host rocks are relatively more mobile than incompatible elements during alteration and deformation. variety of plutonic rocks such as leucogranite, syenite and biotite granite are intruded into older metamorphic rocks. in acf diagram, leucogranite and syenite are placed in s-type granite field and biotite granite occupied in i-type granite field. mineralization is observed as fracture filling vein and less amount of disseminated nature in marble unit. mineralogically, gold areassociated with other base metal such as pyrite, galena, sphalerite, and chalcopyrite. hydrothermal alteration halos are developed as a narrow zone in the peripheral of hydrothermal conduits from proximal to distal; 1) silicic, 2) sericite-illite, and 3) propylitic alteration. in place, silicic altered zone is rich in sio2, al2o3, and k2o. moreover, concentrations of s, cu, zn, and pb are more than any other alteration zones. the cao is gradually increase to least altered zone where wt% of loss of ignition (loi)also increase significantly to least-altered samples (marble). some fluid boiling characteristics of vein textures and fluid inclusion petrography are also observed in hydrothermal system of research area. the homogenization temperature (th) of quartz vein samples are 159°c to 315°c and salinity are 0.88 to 12.51 wt% of nacl equivalent. this research focused to describe the geochemical characteristics of metamorphic rock-hosted gold deposit in onzon-kanbani area. keywords: mogok metamorphic belt, fracture filling vein, hydrothermal alteration, fluid boiling 1. introduction gold and associated base metal mineralization at onzon-kanbani areais located in thabeikkyin township, mandalay region, central myanmar. this area is west 85km faraway from well known mogok township (ruby land), myanmar. small scale local gold rush and abundant artisanal working were started since last thirty years ago. this area is alsoa part of mogok metamorphic belt(searle and haq, 1964)which famous for their precious and semiprecious gem stones production and distinct geological feature. mineralization is mostly hosted in marble unit and occasionally in gneiss.it is observed as fracture filling veins and minor disseminated nature in marble. generally, gold mineralization in mogok metamorphic belt is inferred as orogenic gold (mitchell et al., 2004) but locally epithermal and skarn gold mineralization are also spread along this belt (myint et al., 2014). the main objective of this paper writing is not onlyto describethe geochemical characteristics of metamorphic rock-hosted gold deposit but also to understand the deposit genesis of research area. 2. methods of study totally, fifty ofthin and polished sections of altered rocks and ore sampleswere conducted for mineralogical study by optical microscope and confirmed again by scanning electron microscopy with energy-dispersive x-ray (sem-edx). additionally, x-ray diffraction (xrd) analysis for the hydrothermal alteration minerals that were done for both bulk rock (random powder) and clay fraction. major and trace elements analyses were carried out on representative samples using xrf and inductively coupled plasma optical emission spectroscopy (icp-oes).moreover, quartz samples were collected from mineralization veins to conduct fluid inclusion study. double polished quartz wafers were prepared for these quartz veins where the thickness of wafers varied between 150 and 300µm. microthermometric measurements were done using linkam thmsg600 combined mailto:aungtayzar99@gmail.com 192 zar a.t. et al./ jgeet vol 02 no 03/2017 heating and freezing stage, attached to nikon petrographic microscope with axiovision software. all of these laboratory analyses were made in department of earth resource engineering, mineral resource lab, kyushu university, japan. 3. regional geologic setting myanmar is tectonically complex region and composed with micro plates such as sibumasu, west burma, and india. along a tectonic history is built by repeatedly occurring subduction, accretion and collision events. these events chiseled the geological landform and metallogenic provinces in myanmar. traditionally, the territory of myanmar is subdivided into (1) the india plate to the west, (2) burma microplate (west burma) in the central part and (3) shan mogok metamorphic belt is one of the distinct geological and metallogenic province in myanmar and located between central low-land (west burma) and shan-thai block (sibumasu). it is believed that southern continuation of himalaya (searle and haq, 1964)and formed by either collision (mitchell, 1979) or strike-slip movement (metcalfe, 2009). in this place, well-known right lateral strike-slip fault, sagaing fault (swe, 1972)is served as awestern boundary. alternatively, thestructural configuration of this area is closely related to this fault.mogok metamorphic belt is composed of paleozoic to mesozoic meta-carbonate rocks andmetapelite where avariety of cretaceouspalaeogene plutonic igneous rocks(barley et al., 2003; mitchell, 1979; mitchell et al., 2012)are intruded to older rocks. east of this belt, shan plateau (sibumasu) is a topographic high with anaverage elevation of about 1000m and mainly composed of a series of ordovician-triassic carbonate rocks and continental sedimentary rocks (jurassic?). the western margin of mogok metamorphic belt is juxtaposed with central lowland (west burma) which is filled by eocene to plioquaternary sediments. 4. geology of onzon-kanbani area onzon-kanbani area is a part of mogok metamorphic belt. therefore, mainly composed with metamorphic and igneous rocks which are exposed with differing areal coverage (fig.2).metamorphic rocks of research area such as avariety of marbles, calc-silicate rocks and gneiss are widely distributed in eastern and western part. the age of the protolith of metasedimentary was originally considered precambrian (bender, 1983), but permian fossils in marble near kyaukse (thein and win, 1969)indicate that carboniferous to triassic ageis more likely. alternatively, igneous units are generally covered the middle part of the research area and found as fitful. the older metamorphic rocks are intruded by granite and syenite. the main igneous intrusion of the research area is biotite granite metamorphic belt ranged that magmatism of leucogranite and syenite melt took place in eocene time during the regional metamorphism and then kabaing granite intruded the country rocks of the study area in miocene after regional metamorphism (barley et al., 2003). fig.1. map showing geologic setting of mogok metamorphic belt and its environ. modify after(barley et al., 2003) zar a.t. et al./ jgeet vol 02 no 03/2017 193 5. petrography the dominant metamorphic rocks in onzonkanbani area which is composed of meta-carbonate rocks (marbles and calc-silicate rock) and biotite gneiss. heterogeneous igneous intrusions are observed the middle part of the area where diopside calc-silicate rock occur along the margin of igneous intrusions (fig. 2). marble unit appears white (fresh) and dark gray to pale greenish (weathered) in color. the foliated nature also occurs in some marbles (thin foliated marble and diopside marble) and calc-silicate rock. gneiss unit is medium-crystalline, banded and gneissose with finer and coarser portion. weathered color light grayand dark gray of fresh surface indicate that abundance of biotite and hornblende in gneiss. in igneous rocks, leucogranite and syenite are observed as small intrusive bodies intruded to marble units. light to pinkish color appearance of outcrops arecharacteristic feature. biotite granite is a one of important plutonic rock in research area. it has dark grey to yellowish color weathered surface and light grey offresh surface. the exfoliation nature is common textural feature. microscopic observation shows a variety of minerals in marble and gneiss. in marble unit, diopside, phlogopite, calcite are main constituents whereas biotite, plagioclase and quartz are dominant in gneiss. some of the minerals are believed that the products of regional metamorphism related with india-asia collision. in syenite and leucogranite, felsic color minerals are mainly observed such as quartz, plagioclase, muscovite and nepheline. the common minerals of biotite granite are quartz, biotite, plagioclase and orthoclase. fig. 2. simplify geological map of research area with sample location. after myint lwin thein (thein et al., 1990) 6. petrochemistry 6.1 petrochemistry of host rocks the major and trace elements composition of host rocks (marble and gneiss) are given in table-1. the chemical characteristics of host rocks are mainly controlled by regional metamorphismas well ashydrothermal activities. basically, host rock marble is rich in cao and mgo whereas thenotable amount of al2o3 content showed that their mica content in marble. alternatively, gneiss samples are a high content of sio2 range from 45.983 to 49.672wt% where cao is not too much between 9.254 to 11.301wt.%.in order to evaluate the compositional change which accompanies deformation and hydrothermal alteration, the concentrations of elements of interest are compared to those of immobile such as zirconium. typically, zr is used as animmobile and incompatible element during hydrothermal alteration due to thevery high ionic radius where sio2 and some of themajor oxide elements cannot use because of alteration effect. in the case of chemically incompatible element zr versus compatible elements (zn and cr) regression lines which are considered to be mobile with each other in the marble and gneiss units during alteration and deformation. the compatible elements (zn and cr) are more mobile relative to zr (incompatible) during deformation and hydrothermal alteration as shown by their poor correlations in figure (fig. 3). but in thecorrelation between both of incompatible elements, zr vs (sr and ba) are considered to be immobile with each other in the marbles and gneiss unit while impacting alteration and deformation. the interelement correlation among the trace elements is significant which is consistent with their similar geochemical behavior. 194 zar a.t. et al./ jgeet vol 02 no 03/2017 6.2 petrochemistry of intrusive igneous rocks the chemical composition of plutonic igneous rocks at onzon-kanbani area was observed to identify the type of igneous rocks and their tectonic setting. the care during sampling was on fresh rocks, it intended to avoid metasomatic changes during hydrothermal alteration. results of major and trace elements of plutonic igneous rocks from onzon-kabani area are summarized in table-2. major element data and converted normative data (cipw norm) of plutonic rocks are used to plot on total alkalis-silica (tas) diagram as well as albiteanorthite-orthoclase triangular diagram to classify these plutonic rocks. according to total alkalis-silica (tas) discrimination diagram, the plutonic rocks of study area belong to acidic to intermediate rocks of granite and syenite (fig. 4). the ab-an-or discrimination diagram is intended to avoid the criticism that wt.% oxide data do not faithfully and to confirm plutonic rock classification. this triangular diagram also showed that plutonic rocks of research area are granite, syenite, and tonalite (fig. 4) respectively. all of these samples are pointed out as calc-alkaline type by afm diagram (fig. 4). moreover, acfdiagram also showed that most plutonic rocks of onzonperaluminous except two samples of biotite granite which fall in metaluminous. y versus nb and rb versus y+nb diagrams (pearce et al., 1984)were used to discriminate the tectonic environment of plutonic rocks in onzonkanbani area. these diagrams showed that most of plutonic rocks are in syn-collisional granite (syncolg) and within plate granite (wpg) except some samples which are placed in volcanic arc granite (vga) (fig. 5). table 1. major and trace element composition of least-altered -kanbani area sample id zyk1 (mb) zyk2 (mb) zyk3 (mb) gs (mb) gs-8 (mb) gk (mb) tma6 (mb) szyk3 (mb) gy-1 (gn) gy-9 (gn) zyk15 (gn) sio2 (%) 2.321 8.123 6.916 5.735 2.259 8.731 10.27 9 7.786 45.98 3 49.67 2 46.304 tio2 0.007 0.166 0.132 0.182 0.009 0.117 0.102 0.194 1.249 1.482 1.385 al2o3 0.41 1.912 1.856 1.888 0.36 1.826 1.933 2.449 16.73 9 15.37 3 16.274 feo 0.615 0.697 1.035 0.772 0.607 0.546 1.183 0.727 7.356 8.882 8.238 mno 0.029 0.031 0.033 0.035 0.037 0.023 0.102 0.03 0.136 0.199 0.173 mgo 6.222 1.982 1.881 1.996 6.626 1.489 2.222 1.765 6.416 7.676 7.029 cao 48.32 6 54.13 4 52.18 6 52.19 9 46.12 4 50.52 7 48.52 7 50.583 11.30 1 9.254 11.088 na2o 0.291 0.005 0.045 0.006 0.383 0.015 0.003 0.063 1.411 1.726 1.669 k2o 0.378 0.801 0.59 0.58 0.019 0.861 0.358 0.9 2.317 2.798 2.25 p2o5 0.003 0.012 0.01 0.011 0.001 0.013 0.006 0.012 0.738 0.224 0.833 loi 40.01 31.18 34.73 36.42 43.5 35.69 35.12 35.37 3.82 2.13 2.68 total 98.61 2 99.04 3 99.41 4 99.82 4 99.92 5 99.83 8 99.83 5 99.879 97.46 6 99.41 6 97.923 v(ppm) 5 9 13 22 3 12 15 13 298 334 329 cr 36 41 39 45 38 42 33 38 42 140 55 co 11 18 22 24 10 21 23 16 32 33 35 ni 21 25 24 27 19 22 26 28 48 74 51 cu 6 8 9 11 5 9 15 7 50 25 47 zn 21 29 31 33 18 39 66 38 113 148 124 pb 96 5 7 1 112 n.d 74 7 15 10 1 as n.d 7 4 7 n.d 10 6 5 13 6 16 mo 12 15 14 14 9 17 14 17 48 14 41 sr 181 481 477 473 179 473 495 548 3822 542 3324 ba n.d 81 105 84 n.d 180 24 115 1692 425 1532 y 6 7 11 9 4 10 6 14 20 48 21 zr 1 21 34 17 n.d 66 26 37 53 68 36 nb n.d 2 1 1 n.d 2 1 2 3 13 4 rb 4 38 30 29 3 36 18 53 57 182 56 note: total fe content expressed as feo(tot); n.d= below detection limit; major element and loi are weight percent; trace elements are in ppm zar a.t. et al./ jgeet vol 02 no 03/2017 195 fig..3 binary variation diagrams in cr, zn, sr and ba (all in ppm) for host rocks of onzon-kabani area whereas zn and cr are compatible elements, and zr, srand ba are incompatible elements fig.4. (a) classification diagrams of plutonic rocks using total alkaline versus sio2(middlemost, 1994), and (b) ternary plot diagram in normative ab-an-or for the plutonic rocks of the study area (o`connor, 1965), (c) afm diagram for determining sub-magma calc and (d) acf diagram determining i-type and s-type granitoid(hyndman, 1986) fig.5. position of onzon-kanbani plutonic sampleson y versus nb and rb versus y+nb diagram(pearce et al., 1984). abbreviations: org=oceanic ridge granite, vag=volcanic granite, wpg=within plate granite and syncolg=syn-collision granite 7. mineralization and associated hydrothermal alterations gold and base metal mineralization hosted by marble is closely associated with intense hydrothermal alteration. generally, mineralization is controlled by ne-sw trending faults within fracture and shear zones. open space fracture filling veins are common characteristicswith minor disseminated mineralization in marble. many kinds of vein textures are observed in mineralization vein such as massive vein, crustiform, banded, lattice, bladed carbonate, comb, and cockade. some of the texturesare diagnostic textures of boiling (lattice, bladed, banded, crustiform). they are indicated to boiling fluids of near neutral to alkaline ph condition (gregg and jaireth, 1995; simmons and christenson, 1994) (fig. 7). many local worksites are working on the narrow mineralization zones where the width of veins are generally 0.5 to 5 meters. wall rock alterations related with hydrothermal fluid are observed in onzon-kanbani area but not wide area scale. mostly, hydrothermal alteration halos are developed around mineralization veins as narrow zones. basically, hydrothermal alteration is overlapped to regional metamorphism. microscopic observation and x-ray diffraction patterns are used to identify the type of alterations which happen by hydrothermal impact. there are three distinct hydrothermal alteration zones from proximal to distal of hydrothermal conduct. silicic alteration zone or inner core of alteration halos, it is mainly composed of quartz, calcite, adularia and minor amount of illite and chlorite (fig.6). generally, this alteration is overlapped with mineralization vein but groundmass is strongly 196 zar a.t. et al./ jgeet vol 02 no 03/2017 silicified. gold and base metal mineralization are observed in massive and banded quartz veins. hydrothermal breccia is also frequently observed near this alteration zone. these breccia are characterized by a milled matrix of pyrite. some of the sulphides are oxidized because of deep weathering. sericite-illite alteration is observed as narrow zone next to silicic alteration zone. but this zone is not well developed in some alteration halos. the main constituents of minerals from this altered zone are sericite, illite, quartz, calcite and a minor amount of pyrite. sericite occurs as fine grained and spread out like dusty (fig. 6). propylitic alteration is an outer most zone of alteration and wild area coverage. this zone is characterized by the presence of chlorite, epidote,actinolite, smectite, and illite, (fig. 6). it is still preserve the primary texture of the original rock. it is believed that some part of propylitic alteration is not related to ore forming hydrothermal system (evans, 1987), overlapped to regional metamorphism. most of hydrothermal minerals from each altered zones showed that near neutral condition of ph (e.g. adularia, calcite, illite, sericite and chlorite). fig. 6. photomicrographs of (a & b) silicic alteration, (c & d) sericite-illite alteration zone, (e & f) propylitic alteration zone. abbreviations: calcite (cal), quartz (qtz), adularia (adl), sericite (ser), illite (ilt), epidote (epi), chlorite (chl) and opaque mineral (opq). 8. geochemistry of altered rocks the major and trace elements concentration of the altered rocks are varied depend on alteration intensity as well as the presence of a chemical ion exchange between wall rocks and hydrothermal fluids. the altered zonation reflects changes in the fluid composition with time and interaction of hydrothermal fluid and wall rocks (meyer and hemley, 1967). fig. 7. some of themineralization vein textures (a) lattice texture, (b) bladed calcite, (c) banded vein texture and (d) crustiform texture in onzon-kabani area,alteration zones are basicallyhosted in marble unit as narrow zonation. the major and trace elements of the least-altered rocks and altered rocks of each zones are shown in table 1 and 3. in this case each of the alteration zones has measured enrichment and depletion of major and trace elements relative to the leastaltered rock (fig. 8).the petrochemistry of zone 1 showed that silicic altered rocks are enriched in sio2, al2o3, k2o, and s indicating occurrences of abundant quartz, aluminium-bearing clay (illite), ± adularia and sulphides whereas any other elements such as feo, mgo, mno and cao are depleted. but in zone 2 of sericite-illite alteration zone, sio2 is quite reduced compared with silicic alteration zone. instead of sio2, cao is increased in remarkable amountbut still lowrelatively to least-altered rocks.moreover, al2o3, k2o, feo and mgo are also high because of abundant illite (sericite) and chlorite. propylitic alteration zone , cao shows high amount near least-altered rocks whereas al2o3 and k2o are depleted. locally enrichments of mgo, al2o3 and feo are indicated that the development of chloritization in propylitic alteration. the wt.% of loss of ignition (loi) increase significantly to least altered samples (marbles). this is due to dissociation of caco3 and dolomite camg (co3)2 that partially transform themselves into carbon dioxide gas at temperatures higher than 750° c. generally, high field strength elements of al, ti, and zr were assumed to be immobile elements during the alteration and deformation process. when plotting these minerals from least-altered and altered rocks in tio2 vs zr and tio2 vs al2o3 binary/bivariate diagrams, a general single trend of alteration is observed in both of diagrams but some of silicic and sericite-illite alteration samples are a little bit deficient from these lines (fig.9 ).it mean hydrothermal alteration of silicic and sericite-illite alteration is quite high intensity. zar a.t. et al./ jgeet vol 02 no 03/2017 197 fig.8 enrichment depletion diagram showing major oxides (wt%) and trace element (ppm) during alteration in different zones of hydrothermal alteration of onzon-kanbani area based on mean data of least-altered samples as a reference for calculations, (a) and (b) for silicic alteration zone, (c) and (d) for sericite-illite alteration zone, and (e) and (f) for propylitic alteration zone fig.9 binary diagrams zr-tio2 and tio2-al2o3 showing plot of the least-altered and altered rocks with alteration trend 198 zar a.t. et al./ jgeet vol 02 no 03/2017 table 2. major and trace element composition of plutonic rocks from onzon-kanbani area sample id zyki-2 (luc) zyki-3 (luc) zyk-5 (luc) zyk-9 (syn) zyk11 (syn) zyk12 (gr) zyk18 (luc) kb(gr) zyks-1 (luc) zyks-2 (syn) zyks-3 (luc) sio2(%) 74.27 75.4 75.49 78.85 73.73 79.77 61.51 79.07 75.63 75.51 71.53 tio2 0.03 0.27 0.03 0.07 0.38 0.26 0.2 0.01 0.05 0.34 0.33 al2o3 13.65 12.48 13.09 11.85 12.69 5.09 13.02 5.34 12.38 12.08 13.91 feo 0.23 2.43 0.21 1.21 3.1 1.73 1.8 0.55 1.77 1.18 2.56 mno 0.01 0.03 0.02 0.01 0.07 0.05 0.03 0.01 0.01 0.03 0.06 mgo 0.02 0.32 0.05 0.16 0.16 0.29 0.81 0.28 0.47 0.53 0.47 cao 0.28 0.89 0.57 3.13 1.17 7.52 6.88 9.57 1.08 1.26 1.42 na2o 1.14 2.78 1.2 2.76 2.44 1.15 2.82 2.65 2.42 2.51 1.99 k2o 9.68 5.03 8.78 0.78 5.51 2.35 8.86 2.12 5.48 5.25 6.32 p2o5 0.02 0.02 0.02 0.01 0.04 0.06 0.01 0.01 0.03 0.06 0.01 loi 0.5 0.22 0.31 0.63 0.48 0.51 3.3 0.32 0.61 1.2 1.12 total 99.83 99.87 99.77 99.46 99.79 99.78 99.24 99.93 99.23 99.15 99.72 v(ppm) 6 6 5 2 18 14 15 7 21 2 8 cr 22 24 24 27 20 30 22 20 19 24 23 co 21 9 10 13 2 7 12 4 2 17 4 ni 27 26 25 21 28 26 23 24 24 21 23 cu 3 4 7 8 9 6 50 7 5 7 8 zn 8 103 4 20 93 51 12 65 63 46 62 pb 20 27 35 11 25 25 43 28 35 25 21 as 5 8 8 6 10 6 10 9 8 5 9 mo 12 25 33 14 27 17 16 16 12 18 15 rb 437 296 336 27 291 165 359 187 281 378 308 sr 276 35 263 33 56 266 560 267 225 617 596 ba 644 211 660 11 214 1033 4552 1015 484 1246 1568 y 29 72 21 6 41 39 66 37 5 25 45 zr n.d 473 429 37 731 249 17 14 122 425 476 nb 2 14 1 1 9 15 32 22 14 12 3 note: total fe content expressed as feo(tot); n.d= below detection limit; major element and loi are weight percent; trace elements are in ppm table 3. result of xrf and icp-oes altered host rock from onzon-kanbani area, thabeikkyin township, mandalay region, myanmar silicic alteration sericite alteration propylitic least-altered gm-8 gm-9 gk-3 gk-5 chl1 gs1 gm11 mean (n=4) sio2 (%) 72.507 75.66 38.975 12.556 39.396 5.735 16.169 5.7737 tio2 0.25 0.117 0.497 0.184 0.36 0.182 0.009 0.1217 al2o3 12.582 13.649 10.708 3.127 5.428 1.888 0.51 1.5165 feo 0.796 0.347 5.789 1.003 2.03 0.772 0.469 0.7797 mno 0.027 0.001 0.202 0.129 0.049 0.035 0.105 0.032 mgo 0.697 0.212 3.242 0.994 11.675 1.996 8.134 3.0202 cao 2.269 0.703 18.791 45.956 22.449 52.199 39.786 51.7112 na2o 0.137 1.889 0.022 0.001 0.005 0.006 0.001 0.0867 k2o 6.521 5.587 3.033 0.609 0.542 0.58 0.003 0.5872 p2o5 0.032 0.02 0.09 0.022 0.099 0.011 0.002 0.009 s 0.4396 0.0127 1.8 0.0318 0.0377 0.0851 0.0108 0.0564 loi 3.55 1.62 16.06 35.31 17.82 36.42 34.76 35.585 zar a.t. et al./ jgeet vol 02 no 03/2017 199 total 99.8076 99.8177 99.209 99.9228 99.8907 99.9091 99.9588 99.2232 v(ppm) 11 6 163 17 32 22 n.d 12.25 cr 18 19 554 34 46 45 24 40.25 co 8 22 20 n.d 15 24 16 18.75 ni 24 24 194 24 27 27 19 24.25 cu 18 12 92 10 9 11 4 8.5 zn 88 71 535 68 67 33 18 28.5 pb 89 60 210 14 4 1 n.d 27.25 as 39.33 2.92 3267.87 n.d n.d 172.26 n.d 4.5 ba 866 1051 224 49 104 84 5 67.5 nb 14 9 4 6 8 1 n.d 1 rb 289 201 120 43 30 29 2 25.25 sr 124 248 317 367 199 473 199 403 y 9.32 5.81 17.67 6.43 8.42 n.d 2.78 8.25 zr 267 75 111 32 537 17 n.d 18.25 fig.10 ore microscopic images of selected samples (py=pyrite, gn=galena, sp=sphalerite, ccp=chalcopyrite, au=native gold and elt=electrum) 9. ore mineralogy and paragenetic sequence mineralogically, gold occurs as free grains or locked within pyrite, sphalerite, galena and gangue of au. electrum (<80 at %) is mostly observed as large grained in gold bearing quartz vein but native gold (>80 at %)is observed as fine grained in base metal quartz-carbonate vein and carbonate base metal sulphides vein (fig.11). other common ore minerals in research area are pyrite, marcasite, chalcopyrite, sphalerite, galena, arsenopyrite, chalcocite, covellite, hematite, and goethite. pyrite, galena, sphalerite, chalcopyrite, marcasite, and arsenopyrite are primary ore minerals whereas chalcocite, covellite, hematite, and goethite occur as late minerals, their occurrences reflect the oxidation of primary sulphides such as pyrite and chalcopyrite by circulation of surficial water. pyrite is the most abundant sulphide mineral in the ore body. it occurs over the entire period of mineralization as fine-grained massive aggregates to large euhedral grains. according to thevein and mineral structures and textures, there are three main paragenetic stages; 1) mineralization stage, 2) barren stage and 3) oxidation stage (table-4). in mineralization stage, the early formed quartz, pyrite, and minor calcite minerals are observed away from late phase 200 zar a.t. et al./ jgeet vol 02 no 03/2017 sulphides and quartz core vein. and also early formed pyrite and quartz minerals showed their euhedral crystal forms whereas anhedral sphalerite is younger than quartz and pyrite in order of deposition. some of theanhedral sphalerites are replaced along the boundary by later formed galena. moreover, disseminated chalcopyrite rods and small grainsoccur in sphalerite as exsolution texture (fig. 10). gold is mostly observed in quartz gangue, pyrite, sphalerite, galena and chalcopyrite ground mass as disseminated specks (fig. 10). actually, quartz, calcite, and pyrite are observed the entire period of mineralization as more or less amount. sericite and aminor amount of adularia are also found together with quartz at mineralization vein. after mineralization stage, veins are barren like a calcite or quartz vein with very minor amount of pyrite. subsequently, oxidation stage is going on by circulated meteoric water whereas hematite, goethite,and chalcocite are formed from primary sulphides. table 4. generlized paragenetic sequence of onzonkanbani area fig.11 back scatter image of electrum gold and native gold in mineralization vein (elt=electrum, au=native gold, sp=sphalerite, py=pyrite, qtz=quartz) 10. fluid inclusion study double polished quartz wafers were prepared for fluid inclusion study. from petrographic study, two-phase (liquid, vapor) fluid inclusions are dominant type of primary fluid inclusion. they are observed as two-phase liquid rich, two-phase coexisting of liquid-rich and vapor-rich and two phase vapor-rich fluid inclusions. moreover, microthermometry was carried out for primary fluid inclusions in quartz from gold and base metal mineralization veins. homogenization temperature th of fluid inclusion showed range from 159°c to 315°c where the boiling temperature was estimated to be 170°c. the histogram of homogenization temperature is shown in figure (fig. 12). salinities of the fluid inclusions were temperature tm (bodnar, 1993). the salinity range is low to moderate 0.88 to 12.51 wt% nacl equivalent. the plot diagram of homogenization temperature and salinity are showed negative trend (fig. 13). fig.12 homogenization temperatures of fluid inclusion in quartz from gold and base metal mineralization vein fig. 13. binary plot diagram ofsalinity vs. homogenization temperature th of fluid inclusions 11. discussion and conclusion gold mineralization in onzon-kanbani area ishosted in metamorphic rocks. the older metamorphic rocks are intruded by younger plutonic rocks. mineralization is commonly observed as fracture filling vein and disseminated nature hosted in marble unit. petrochemistry of host rocks is mainly controlled by regional metamorphism and hydrothermal activities. basically, host rocks are rich in cao and mgo whereas the notable amount of al2o3 content is showed their mica content in marble. of granitoid rocks are observed as intrusive bodies where most of the rocks are placed in the field of zar a.t. et al./ jgeet vol 02 no 03/2017 201 syn-collisional granite and within plate granite. hydrothermal alteration halos are developed as narrow zones beside of hydrothermal conduit or mineralization vein. they are silicic, sericite-illite and propylitic alteration zones from proximal to distal of hydrothermal conduits. hydrothermal alteration in onzon-kanbani area is regard as lowsulphidation epithermal system as indicated by the characteristic of alteration style and alteration mineral assemblages such as quartz, calcite, ±adularia, sericite, illite and smectite. these alteration minerals are showed that the temperature decreasing to the outer zone of alteration as well as indicated that the higher ph, near neutral condition of hydrothermal system. generally, hydrothermal alteration is overlapped to regional metamorphism. the geochemistry of each altered zone reflects changing of fluid composition and interaction of hydrothermal fluid and wall rock. according to immobile elements characteristics of least-altered and altered rocks, alteration intensity is higher to silicic and sericite-illite alteration. sio2 and cao content are inversely proportional in each altered zone. enrichments of s, pb, zn, and cu from silicic altered zone indicate that fracture filling vein mineralization is more common than disseminated mineralization. in ore mineralogy, hypogene ore mineral such as pyrite, sphalerite, galena, chalcopyrite and minor native gold and electrum are precipitated in mineralization stage. after this veins are barren by deposition of calcite or quartz at the end of mineralization stage. some of hypogenesulphide minerals are oxidized to supergene minerals during oxidation stage. according to fluid inclusions petrography whereas coexisting of liquid rich and vapor rich fluid inclusions as well as some of vein textures such as bladed, banded and lattice are strongly advocated that fluid boiling, iseffective on such a precipitation of ore minerals. moreover, homogenization temperature (159°c-315°c) and salinity (0.88 to 12.51 wt.% nacl equiv.) range are acceptable to say it formed in the epithermal environment. acknowledgements this research is supported by aun/seed-net (jica program).we would like to thank all of local companies and owners for permission to conduct research work in there and for helping during field investigation and general discussion. references barley, m.e., pickard, a.l., zaw, k., rak, p., doyle, m.g., 2003. jurassic to miocene magmatism and metamorphism in the mogok metamorphic belt and the india-eurasia collision in myanmar. tectonics 22, n/a-n/a. doi:10.1029/2002tc001398 bender, f., 1983. geology of burma, 293 p. gebrüder borntraeger, berlin and stuttgart. bodnar, r.j., 1993. revised equation and table for determining the freezing point depression of h 57, 683 684. evans, a.m., 1987. an introduction to ore geology, 2nd edn. ed. blackwell, oxford. gregg and jaireth, s.d.g. and m., 1995. quartz textures in epithermal veins, queensland; classification, origin and implication. econ. geol. 90, 1841 1856. hyndman, d.w., 1986. petrology of igneous and metamorphic rocks. geol. mag. 123, 88 89. doi:10.1017/s001675680002673x metcalfe, i., 2009. late palaeozoic and mesozoic tectonic and palaeogeographical evolution of se asia. geol. soc. london, spec. publ. 315, 7 23. doi:10.1144/sp315.2 meyer, c., hemley, j.j., 1967. geochemistry of hydrothermal ore deposits. holt, rinehart and winston, new york. middlemost, e.a.k., 1994. naming materials in the magma/igneous rock system. earth-science rev. 37, 215 224. doi:10.1016/00128252(94)90029-9 mitchell, a.h.g., 1979. guides to metal provinces in the central himalaya collision belt; the value of regional stratigraphic correlations and tectonic analogies. mem. geol. soc. china 3, 167--194. mitchell, a.h.g., ausa, c.a., deiparine, l., hlaing, t., htay, n., khine, a., 2004. the modi taung nankwe gold district, slate belt, central myanmar: mesothermal veins in a mesozoic orogen. j. asian earth sci. 23, 321 341. doi:10.1016/s1367-9120(03)00138-x mitchell, a.h.g., chung, s.-l., oo, t., lin, t.-h., hung, c.-h., 2012. zircon u pb ages in myanmar: magmatic metamorphic events and the closure of a neo-tethys ocean? j. asian earth sci. 56, 1 23. doi:10.1016/j.jseaes.2012.04.019 myint, t.a., than, t.n., min, a., 2014. precious and base metal mineralization in kwinthonzenweyon area, singu and thabeikkyin townships, mandalay region, myanmar. proc. sundal. resour. 2014 mgei annu. conv. 343 354. o`connor, j.t., 1965. a classification of quartz rich igneous rock based on feldspar ratios. us geol. surv. 525b, b79 b84. pearce, j.a., harris, n.b.w., tindle, a.g., others, 1984. trace element discrimination diagrams for the tectonic interpretation of granitic rocks. j. petrol. 25, 956 983. searle, d.., haq, b.t., 1964. the mogok belt of burma and its relationship to the himalayan orogeny. proc. int. geol. congr. 22, 132 161. simmons, s.f., christenson, b.w., 1994. origins of calcite in a boiling geothermal system. am. j. sci. doi:10.2475/ajs.294.3.361 swe, w., 1972. a strike-slip faulting in central belt of burma [abstr.]. reg. conf. geol. se asia, kuala lumpur. annex. geol. soc. malaysia newsl. 34, 59. thein, m., win, s., 1969. the metamorphic petrology, structures and mineral resources of the shantaung-u-thandawmywet range, 202 zar a.t. et al./ jgeet vol 02 no 03/2017 kyaukse district. burma res. congr. 3, 487 514. thein, m.l., myint, o., kyi, s., win, h.n., 1990. geology and stratigraphy of the metamorphosed early paleozoic rocks of the mogokthabeikkyinsingumadaya areas. yangon. 1. introduction 2. methods of study 3. regional geologic setting 4. geology of onzon-kanbani area 5. petrography 6. petrochemistry 6.1 petrochemistry of host rocks 6.2 petrochemistry of intrusive igneous rocks 7. mineralization and associated hydrothermal alterations 8. geochemistry of altered rocks table 4. generlized paragenetic sequence of onzon-kanbani area 10. fluid inclusion study 11. discussion and conclusion acknowledgements references e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 widyantama et al./ jgeet vol 1 no 1/2016 35 control structure of garba formation through petrography analysis in tanjung beringin, south oku regency, south sumatra ridho widyantama putra 1, *, frillia nasution 1 , nurlita putri 1 , rahmat alfath 1 1 university of sriwijaya, south sumatra. * corresponding author: widyantamaridho@gmail.com telp :+62822-9852-0185 received: oct 1, 2016. revised : nov 15, 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.4 abstract the study area is the village of tanjung beringin carefully situations, south oku regency, which is included within the subpalembang basin with the dominant lithology is granite. granite in this area has a diversity of grain size and mineral composition, in the southern part of the study area the size of the mineral feldspar is greater than the granite in the northern part, where the granite in this section contains plagioclase and quartz dominant, and it was bigger than the other minerals, granite on the area carefully situations are the result of the appointment that occurs due to the compression phase at the end of the late jurassic until late cretaceous. fracture growing on granite have a general direction northeast equivalent to tectonic compression miocene now, the presence of other directional sharpness is secondary sharpness formed by the collision between the rocks. fractures that develops is the path where the discharge of magma to the formation of granite with different characteristics. in petrographic analysis porphyritic texture is thriving and there are indications of alteration process in the presence of alteration minerals such as chlorite and quartz vein. keywords: granite, structure,basement, fracture, petrography. 1. introduction south ogan komering ulu regency geographically located between 103 0 2 104 0 21 longitude east and 04 0 14 04 0 55 latitude south. it has 549.394 ha width area. geologically, the location research arranged by three formation namely; garba formation, baturaja formation and talang akar formation. the vast majority of location area arranged by garba formation and lithology granite. granite is acid rock which formed by coagulation process of magma. particularly mineral component on granite is quartz, feldspar, plagioclase, and biotite . the aim of this research is studying petrography of granite rock in muara dua region, south oku in order to find out megascopic and microscopic granite rock. 2. regional tectonic according to suparman (1991), palembang basin is the southeastern part of south sumatera basin, located west and south of palembang. tectonic order in the research area which in the south sumatera basin has had northwestsoutheast tending linements that parallel to the according to de coster (1974), it has been estimated that 3 episode of orogenic which formed framework structure in region of south sumatera cavity that is orogenic mesozoic center, tectonic last lime first tertiary and orogenic plio plistocene. first episode, precipitates paleozoic and metamorphosed mesozoic, foldaway and broken into chunks structure and intrusion by granite batolith also has formed the basic pattern of cavity structure. in accordance with pulunggono (1992), this phase forming fault has an aim of nwe such as move faults. second episode on the last lime such as phase exstention which producing tencional moves which formed graben and horst in general has an aim of north south. combined with the result of orogenic mesozoic and rock weathering rock pra teriary, tenssional moves that forming old structure which controlling the formation forming of pra talang akar. third episode such as phase compression on plio plistocene that causing sedimentation pattern changing into regression and have a role in forming foldaway structure fault thus forming geologi configuration now. on this tectonic period also occur elevation of bukit barisan mountain which produce semangko fault level off that amend along bukit barisan mountain. horizontal 36 widyantama et al./ jgeet vol 1/2016 movement which occurred started from first plistocene until now influence south sumatera cavity condition and the center until the new faults formed on this region has development almost a line with semangko fault. caused by this horizontal movement, orogenic which occurred on plio plistocene produce foldaway which have an aim to north west south east however fault which has formed have an aim to north east south west and north west south east. the kinds of fault which exist on this cavity is ascend fault, level off fault and normal fault. the dominant visible structure is structure which have an aim to north west south east as a result of orogenesa plio plistocene. consequently structure pattern which occurred can be differentiated as old pattern which have an aim to north south and north west south east along with young pattern which have an aim to north west south east which is a line with sumatera island. fig. 1. south sumatera tectonic, pulonggono (1992). 3. regioal stratigraphy regional stratigraphy south sumatera cavity particularly known as megacycle which consist of phase transgression and following regression phase. formation group that precipitated in transgression phase constitute telisa group (talang akar formation, baturaja and gumai) whereas the precipitated one on regression phase constitute palembang group (air benakat formation, gumai and kasai) whereas lemat formation and older lemat precipitated before the main transgression phase. and sort of formation by old to young on south sumatera cavity according to de coster,1974 is group of pra-tertiary, kikim formation and older lemat formation, young lemat formation, talang akar formation, baturaja formation, telisa formation, gumai formation, lower palembang formation, middle palembang formation and upper palembang formation. fig. 2 stratigraphy chart of the south sumatera basin, adiwidjaja and de coster (1973). 4. research method the method that used on this research is : 1. data collection field by obtaining sample data granite rock. 2. carry out petrography laboratory analysis that take place at laboratorium dinamik and petrologi, department geological engineering, sriwijaya university, palembang. 5. result and discuss 5.1 physical characteristic granite existence in the research area is dominant compare to other lithology. physical characteristic of granite on research area in general, it has moldy dark brown color, fresh cream till white color, crystallinity holocrystaline texture, granularity phaneritic, composition of mineral is quartz, feldspar, plagioclase, and biotite (fig 1). on the physical evident is found mineral measurement which different with granite in the one location to another, this case is showing that the bigger than other mineral measurement so the more closer to the source and if the mineral measurement more smaller so the granite is getting far away from the source. granite on the research location constitute as product of intrusion on garba formation, beside that on the granite are exist squat tenssion and shear joint which formed by the cause of energy which struck the granite. the granite that controlled by many squat is showing that its granite is closer to tectonic activity and the other way if on the granite is less of the squat so the granite far from tectonic widyantama et al./ jgeet vol 1/2016 37 activity. and in some locations has squat which is contained by quartz mineral (quartz tendon). fig. 3. the exposure of granite outcrop in komering river. fig. 4. quartz vein on granite. 5.2 petrography analysis there exist 5 sample which reputed represent the granite that exist in the research location, in muara dua territory in order to analyzing petrography. the sample code is differentiate base on number that is; 1.l1, 1.l3,1l5,1.l6 and 1.l7. result analysis of petrography with using iugs classification, showing that mineral component which identification from granite sample has quartz percentage (20%-45%), plagioclase (10%30%), feldspar (10-20%), biotite (5-25%), opaque mineral (2%-5%) and clay mineral (5%-20%) with exist mineral difference that is chlorite (28%). table 1. percentage of mineral components on granite. mineral component sample code 1.l1 1.l3 1.l5 1.l6 1.l7 quartz 40% 30% 40% 42% 45% plagioclase 15% 10% 10% 20% 30% alkali feldsfar 15% 20% 10% biotite 5% 10% 25% 15% 5% opaque mineral 6% 2% 5% 5% 5% clay mineral 9% 20% 18% 5% chlorite 28% fig. 5. granite existence in a petrography analyze on the example of slices 1.l1. captured by polarization microscope magnification 40x. thin sectiom of igenous rock, silica mineral (alkali feldspar, quartz, and plagioclase) first formed at >400 0 c temperature, then accumulated alkali mineral (biotite), be found mineral difference on the thin section indicate that there is alteration process. fig. 6. granite existence in a petrography on the example of slices 1.l3. captured by polarization microscope magnification 40x. thin section granite rocks, silica mineral (alkali feldspar, quartz, and plagioclase) first formed at >400 0 c temperature, then accumulated by alkali mineral (biotite), be found mineral difference chlorite, indicated of alteration process propilitik (corbett and leach, 1996). fig. 7. granite existence in a petrography on the example of slices 1.l5. captured by microscope polasisari magnification 40x. thin section of granite rocks, silica mineral (quartz, and plagioclase) first formed at >400 0 c 38 widyantama et al./ jgeet vol 1/2016 temperature, then accumulated alkali mineral (biotite), be found mineral difference chlorite, indicated of alteration process propilitik (corbett and leach, 1996) fig. 8. granite existence in a petrography manner on the example of slices 1.l6. captured by microscope polasisari magnification 40x. thin section of igneous rock intrusion, silica mineral (quartz, and plagioclase) at first formed at >400 0 c temperature, then accumulated alkali mineral (biotite), in petrology description be found green clay mineral, mineral the clay result of difference mineral alkali feldspar and quartz. fig. 9. granite existence in a petrography manner on the example of slices 1.l7. captured by polarization microscope magnification 40x. thin section of granite rock silica mineral (alkali feldspar, quartz, and plagioclase) at first formed at >400 0 c temperature, then accumulated alkali mineral (biotite), be found clay mineral, as a result of difference from quartz mineral, granitic structure. 5.3 local structure analysis by the result of the range observation and doing the measurement toward the amend of fault ih granite. the data itself then being analyzed by using georose application in order to found out the particular direction of the fault which has amend so far. base on the fault analysis which has found main affirmation directionon north westsouth direction on north east south west. fig. 10. granite outcrop which has done measurement fault. fig. 11. the result of fault analysis by using rose diagram . fig.12. fault measurement on granite outcrop fig. 13. the result of fault analysis by using rose diagram widyantama et al./ jgeet vol 1/2016 39 fig. 14. fault measurement on granite outcrop. fig. 15. the result of fault analysis from rose diagram. fig. 16. fault measurement on granite outcrop. 6. conclusion granite megascopic appearance that is consist of plagioclase, quartz, feldspar and biotite mineral. there is a fault that working on it.s outcrop.the granite microscopic appearance is consist of quartz, plagioclase, feldspar, biotite, opaque mineral and clay mineral along with mineral change that is chlorite. the granite on this location is coat type that is the direct formed beside that its indicated from the size of granite fomation that is late cretaceous. on the four observation range which is obtained, direction ehich has dine on south west south east with affirmation style origin from north east south west, this case is showing that the origin tectonic which has done well-off on the thirds plio-pleistocene edge. references [1] a. pulonggono, a.haryo, c.g.kosuma. (1992). pre-tertiary and tertiary faults systems as a framework of the south sumatera basin; a study ofsar-maps. [2] de coster. 1974. the geology of the central and south sumatera basins. [3] p.adiwidjaja, de coster. 1973. pre-tertiary paleotopography and related sedimentation in south sumatera. [4] suparman. a., asseggaf. a. 1991. post convention field trip-garba mtn area south sumatera. http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 124 zamroni, a., et al./ jgeet vol 5 no 3/2020 review article the assessment of landslides disaster mitigation in java island, indonesia: a review akhmad zamroni 1,*, ayu candra kurniati2, haris nur eka prasetya3 1department of geological engineering, institut teknologi nasional yogyakarta, indonesia 2department of urban and regional planning, institut teknologi nasional yogyakarta, indonesia 3department of mining engineering, institut teknologi nasional yogyakarta, indonesia * corresponding author : akhmadzamroni@itny.ac.id tel.:+6285692988178 received:feb 24, 2020; accepted: jul 14, 2020. doi : 10.25299/jgeet.2020.5.3.4676 abstract the frequency of landslides and the fact that a large number of people live in the landslides-prone areas lead to a high death toll in java island, indonesia – over 1,112 people in the period between 1999 and 2005. indonesian national disaster management agency (badan nasional penanggulangan bencana [bnpb]) reported 2,766 landslides that occurred in java from 2014 to 2019, with 662 deaths. from its state, it looks as if indonesia 's disaster mitigation is still weak. it is very essential to a deep understanding of landslides disaster mitigation weakness in indonesia with the approach of governments, researchers, and local communities action. this research is a review of landslides disaster mitigation in java island with the approach of governments, researchers, and local communities action. furthermore, the purpose of this study is to highlight the driving forces of landslides disaster mitigation in java island, indonesia. from the assessment of each stakeholder (government, researchers, and local communities), the driving forces of landslides disaster mitigation in java island are the central government has commanding disaster management activities to local governments. however, the implementation of landslides disaster mitigation at the regional level has some obstacles such as the lack of residential development planning.many landslide research results have only become scientific papers but the landslides-prone areas have not been fully paid attention by the local government such as the absence of landslide danger warning signs.in addition, the level of preparedness and awareness among local communities is not constant at any given time. usually, community preparedness levels can be high following a disaster. it is likely, however, to diminish over time. keywords: landslides, mitigation, government, researcher, local community 1. introduction landslides are natural disasters that harm humans and the economy both from natural events and human activities. losses from landslides are often greater than other natural disasters such as windstorms, floods, and earthquakes (hadmoko et al., 2017). landslides in indonesia are often caused by earthquakes and high rainfall (cepeda et al., 2010). in addition, tropical climate conditions in indonesia are also a cause of high landslides in the area (faris and fathani, 2013). according to data from the geological agency of indonesia, landslides in indonesia caused 32 fatalities per incident. in addition, the annual frequency of landslides in indonesia from 1981 2007 was 49 times landslides per year. the total victims from indonesian landslides are sumatra (18%), sulawesi (24%), and java (52%). landslides in indonesia cause infrastructure damages such as roads and agriculture (cepeda et al., 2010). java is known as a volcanic island that produces materials from active or ancient volcanoes because of its location in the active boundary of two plates (smyth et al., 2005). subduction in java has effects on its geological history. oblique subduction in java is characterized by features such as displaced and fragmented terraces, major strike-slip faults, folding, and thrusting (hall et al., 2007). landslides often occur in java that has mountainous areas and a wet tropical climate. a number of factors supporting the occurrence of landslides in java are as follows: firstly, java has rugged terrain consisting of cliffs, hills, and mountains; secondly, from october to april, heavy rainfall is prevalent; thirdly, 36 of 129 indonesian volcanoes are located in java, producing highly weathered volcanic materials (christanto et al., 2009). the frequency of landslides and the fact that a large number of people live in the landslides-prone areas lead to a high death toll in java island, indonesia – over 1,112 people in the period between 1999 and 2005 (hadmoko et al., 2010). indonesian national disaster management agency (badan nasional penanggulangan bencana [bnpb]) reported 2,766 landslides that occurred in java from 2014 to 2019, with 662 deaths (http://bnpb.cloud/dibi/tabel1a). from its state, it looks as if indonesia 's disaster mitigation is still weak. geological information is of great importance given to public officials, politicians, business leaders, and the media or the general public.the geological disciplines that have a lot to do with society are the fields of disaster, where they should have the motivation of knowledge about disaster mitigation to reduce the occurrence of risks (stewart and gill, 2017). it is necessary to explore how social science can be integrated into geological disciplines like in disaster mitigation fields. disaster mitigation is a method to reduce the risk or effect of a disaster by preemergency or disaster acts. disaster mitigation is based on potential risks and impacts, and causes (human or natural factors) so that mitigation does not increase vulnerability to other risks (public safety canada, 2015). some previous studies about social sciences of landslides disaster mitigation in indonesia have been conducted in the last decade such as community-based risk reduction effort http://journal.uir.ac.id/index.php/jgeet http://bnpb.cloud/dibi/tabel1a zamroni, a., et al./ jgeet vol 5 no 3/2020 125 (karnawati et al., 2011), socio-technical approach for landslides risk reductionand disaster mitigation program (karnawati et al., 2013), driving factors of social vulnerability (siagian et al., 2014), the quantitative research of public perception of disaster landslides (suharini et al., 2014), and the communication problems between scientists and executives on the one hand and societies on the other (andreastuti et al., 2017). it is also very essential to a deep understanding of landslides disaster mitigation weakness in indonesia with the approach of governments, researchers, and local communities action. this research is a review of landslides disaster mitigation in java island with the approach of governments, researchers, and local communities action. furthermore, the purpose of this study is to highlight the driving forces of landslides disaster mitigation in java island, indonesia. 2. the stakeholders of landslides disaster mitigation in indonesia some stakeholders are involved in landslides disaster mitigation include the government or policymakers, practitioners, researchers, students, and the local community (margottini et al., 2013). the stakeholders of landslides disaster mitigation in this research focus on governments or policymakers, researchers, and local communities. policymaker in the landslides disaster mitigation is a member of a government department or organization that is responsible to establish of structural and or nonstructural mitigation, create a priority to protect important assets, and measure a cost-benefit ratio in the mitigation technique (samodra et al., 2018). within the scope of governments, the indonesian national disaster management agency (badan nasional penanggulangan bencana [bnpb]) is the main actor involved in providing direction, guidance, standards, and disaster management requirements (srikandini et al., 2018). bnpb's tasks include formulating and establishing disaster management policies and assisting refugees, and commanding disaster management activities. bnpb has a disaster management subagency at the regency or city and provincial level called the regional disaster management agency (badan penanggulangan bencana daerah [bpbd]) (bnpb, 2017). therefore, bpbd is responsible for supporting the efficacy of emergency recovery initiatives at the provincial and district level (karnawati et al., 2013). in the scope of researchers, the center for volcanology and geological hazard mitigation (pusat vulkanologi dan mitigasi bencana geologi [pvmbg]) is one of the units within the geology agency ministry of energy and mineral resources formed to conduct research, investigations, engineering, and services in the field of volcanology and geological disaster mitigation (kementerian energi dan sumber daya mineral badan geologi, 2016). in addition, universities are also involved in landslide disaster mitigation research. meanwhile, local communities in the landslides disaster mitigation are people who stay in the landslides prone areas that have opportunities to reduce landslide disaster through some actions such as observe weather or places conditions that are dangerous, land-use planning, or work together to repair damaged properties after landslides disaster (hewitt, 2010). global innovations occurred with shifts in disaster response from reactive to constructive, from singular to more systemic with an emphasis on disaster risk reduction ( drr), and from a state-centered model to forms of co-governance that understand the significance of the participation of non-state actors in disaster management and of community-based resilience and initiatives (srikandini et al., 2018). meanwhile, good disaster management should be shared by multiple state and non-state actors in a country to allocate the required resources, make disaster risk mitigation a political priority, ensure and enforce its implementation and delegate responsibility for deficiencies, and encourage the involvement of all relevant stakeholders (unisdr, 2004). the commitment of the local community and local government should increase disaster risk reduction. in addition, it is essential to conduct regular audits and analyses of the involvement of relevant stakeholders so that the landslides disaster mitigation system will be better (fathani et al., 2016). 3. the assessment of stakeholders action 3.1 governments action bnpb mostly works on a national scale mapping landslide areas. bnpb makes a guideline in determining of disaster risk assessment. the contents of the document are in determining disaster risk assessment must use three main parameters, namely the index of capacity, vulnerability, and hazard. the index of capacity is based on government preparedness in disaster preparedness, mitigation, disaster education, and early warning. vulnerability is based on physical, economic, social and environmental losses caused by disasters. while hazard is based on the potential and impacts resulting from disasters (basofi et al., 2018). in addition, one of bnpb’s policies is creating safe school disaster to increase student awareness so that they have a good plan during and after the disaster, and are always responsive in responding to disaster emergencies (husna and fauzi, 2019). based on literature reviews relating to bpbd conditions in several regions in java, in the scale of local government, bpbd conducted activities such as awareness-raising about the disaster and formed the formation of risk disaster reduction forum (forum pengurangan risiko bencana [fprb]) in the village-level whose members are man and woman citizens, village functionaries, and teenagers. bpbd cooperated with fprb conducted activities in disaster introduction, monitoring of treating disaster development, installing danger alerts, risk management, treating high-risk analysis, and disaster risk identification. the problem faced by fprb is limited funds because donations are only obtained from village funds and fprb only works waiting for direction from bpbd (wardani and putra, 2016). some weaknesses of bpbd in several regions in java such as bpbd did not install signs warning of landslide hazards in the landslides prone areas, bpbd did not oversee spatial planning activities and did not oversee building construction permits, bpbd did not make special building structures that function to prevent landslide impacts, bpbd did not relocate residents living in the landslides prone areas (suharini et al., 2014), and bpbd has not performed optimally to incorporate awareness, education, and creativity to create a culture of endurance and safety at all village levels (wardani and putra, 2016). however, bpbd also carried out repairs to infrastructure damaged because of landslides by using state budget, and bpbd has restored social-psychological conditions to eliminate the trauma of landslide victims (suharini et al., 2014). 3.2 researchers action the center for volcanology and geological hazard mitigation (pusat vulkanologi dan mitigasi bencana geologi [pvmbg]) has a landslides disaster mitigation sector that has the tasks of preparing technical policy, norms, standards, procedures, criteria, plans, reporting, mapping, technical 126 zamroni, a., et al./ jgeet vol 5 no 3/2020 recommendations for landslides disaster mitigation, research, investigation, engineering, monitoring and early warning, hazard modeling, and dissemination of landslides information (kementerian energi dan sumber daya mineral badan geologi, 2016). pvmbg determines the red zone area, which is an area that often occurs mass movement (iskandar et al., 2018). some universities use maps of estimated areas of landslides created by pvmbg for their research, for example, recently, the school of environmental science, universitas indonesia conducted a study about landslide vulnerability in residential areas, sawangan district, depok city (puspitasari and herdiansyah, 2019). in addition, many studies have been carried out by universities on landslides disaster mitigation such as; 1) researchers from the department of civil and environmental engineering and the department of geological engineering at gadjah mada university conducted a report on an integrated methodology to establish a framework for early warning landslide systems. they introduced a new model consisting of seven early warning sub-systems, namely the installation of monitoring and alert services, uniform operating procedures, the creation of an evacuation map, the establishment of a disaster preparedness and response team, distribution and communication, risk assessment and mapping, and local participation in the operation, and maintenance of all the program (fathani et al., 2016), 2) researchers from the department of environmental geography, gadjah mada university, and the graduate school of civil and structural engineering, kyushu university, conducted a report on the participatory mapping of landslide inventories. they mixed the conventional geomorphological field survey approach requiring active community engagement with the use of advanced technologies to locate and quantify the severity of past landslides, such as gps and laser range finder. participatory inventory mapping of landslides is a costeffective, reliable, and often the most feasible approach to use in a small data set, for example in indonesia. the strategy will endorse countermeasure tools to protect citizens, properties, buildings, and facilities from landslide hazards by developing effective land-use planning (samodra et al., 2018), 3) researchers from the institute of technology bandung, department of geophysical engineering conducted a study using the resistivity test in bandung, west java to define the possible ground movement as a landslide disaster mitigation strategy. the result was a possible landfill zone on jalan citra green, dago with a low resistivity region below the soil. (izzati et al., 2017). 3.3 local communities action community awareness is needed to reduce disaster risk in accordance with social, economic and local cultural conditions. continuing training and education programs on natural disaster mitigation can increase public awareness. this activity will increase community knowledge to prevent landslides and protect themselves if there are landslides in the future (fathani et al., 2016). local communities' actions are one of the factors causing landslides. these actions are not only the actions that they take in developing residential areas but also the lack of awareness of landslides disaster mitigation. residential areas have increased recently. many local communities build houses on the plains, surrounded by steep slopes. many settlements are built under roads or on hillsides. this condition will support the occurrence of landslides. it means that the construction of residential areas often does not consider the possibility of natural disasters such as landslides (wati et al., 2010). regional disaster mitigation landslides are more likely to save and evacuate activities. obstacles to community efforts to overcome landslides are limited early warning systems, limited funds for the construction of mitigation facilities, or limited land for making embankments, rainwater channels, and planting plants firmly rooted (suharini et al., 2014). the level of preparedness and awareness among local communities is not constant at any given time. usually, community preparedness levels can be high following a disaster. it is likely, however, to diminish over time.monitoring and alarm systems sustaining continue to be ignored as community awareness declines. all interested parties should develop early warning landslide systems that last not only for the short term (1–2 years) but also continuously. the development of the landslides disaster mitigation will not stop the landslide from occurring, but it does provide warnings to local communities. knowledge of local communities is expected to be increased, and as such people will be able to independently conduct mitigation (fathani et al., 2016). 3.4 the driving forces of landslides disaster mitigation in java island, indonesia from the assessment of each stakeholders (government, researchers, and local communities), the driving forces of landslides disaster mitigation in java island are the central government has commanding disaster management activities to local governments. however, the implementation of landslides disaster mitigation at the regional level has some obstacles such as the lack of residential development planning. it means there are still many settlements in landslides-prone areas. besides, there is limited training and education of landslides disaster mitigation for people living in landslides-prone areas. researchers have conducted a lot of landslide research that can be used as a landslide disaster mitigation. however, many research results are not applied for mitigation and are not disseminated to the public. many landslide research results have only become scientific papers. universities in indonesia have the task to conduct "tri dharma" which means three tasks that must be conducted by lecturers in the universities namely teaching, research, and charity. the lecturer also works as a researcher, some of the lecturers' research results can be applied to charity activities but there is no data that mentions how many the results of lecturer research that has been applied to the community. pvmbg as the units formed to conduct research, investigations, engineering, and services in the field of volcanology and geological disaster mitigation has conducted research activities in the field of landslides. pvmbg's website also recorded data on landslides-prone areas that can be accessed by the public. however, the landslides-prone areas have not been fully paid attention by the local government such as the absence of landslide danger warning signs. while there are still many casualties in each landslide disaster, it is estimated that public awareness of landslides disaster mitigation is still very low. in addition, there are still many local communities who live in landslides-prone areas because there are no regulations from the government regarding this matterand limited land to build landslide mitigation buildings such as embankments and rainwater channels. fig. 1. shows a diagram of the driving forces of landslides disaster mitigation in java island, indonesia. 127 zamroni, a., et al./ jgeet vol 5 no 3/2020 fig 1. shows a diagram of the driving forces of landslides disaster mitigation in java island, indonesia. 4. conclusions the driving forces of landslides disaster mitigation in java island, indonesia are; 1) the governmentsare still very limited in providing training and education of landslides disaster mitigation to local communities, 2) regulations regarding landslides disaster mitigation are still unclear, 3) the governments have limited funds and lack of overseeing spatial planning activities, 4) many landslides disaster mitigation studies are not applied, 5) public awareness of local communities to landslides disaster mitigation is low. acknowledgements the authors would like to appreciate to institut teknologi nasional yogyakarta, indonesia in providing the best place to conduct this research. references andreastuti, s., budianto, a. and paripurno, e.t., 2017. integrating social and physical perspectives of mitigation policy and practice in indonesia. in observing the volcano world (pp. 307-320). springer, cham. basofi, a., fariza, a. and safitri, e.i., 2018, november. landslide risk mapping in east java, indonesia, using analytic hierarchy process–natural breaks classification. in 2018 international seminar on research of information technology and intelligent systems (isriti) (pp. 77-82). ieee. bnpb,2017. natural disasters in indonesia. url http://bnpb.cloud/dibi/tabel1a(accessed 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2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 198 rizka, et al./ jgeet vol 5 no 4/2020 research article simulation of time-lapse resistivity method on sandbox model to determine fluid changes and desaturation rizka1*, beta arroma piskora1, soni satiawan1, hendra saputra2 1department geophysical engineering, institut teknologi sumatera, lampung selatan, indonesia. 2department geological engineering, institut teknologi sumatera, lampung selatan, indonesia. * corresponding author : rizka@tg.itera.ac.id tel. : +628-1322-10-9961 received: dec 16, 2019; accepted: dec 18, 2020. doi 10.25299/jgeet.2020.5.4.4266 abstract time-lapse resistivity method is an implementation of the resistivity method that is executed exactly at the same spot but with various in time. in this study, the technique uses to identify the dynamics of groundwater fluids. the application of the time-lapse resistivity method was carried out by performing a sandbox model simulation that contains layers of rocks with a fault structure. the rock layers consist of tuff, fine sandstone, shale, coarse sandstone, gravel that represents confined and unconfined aquifers. the simulation was achieved by applying the electrical resistivity tomography (ert) dipole-dipole configuration at the same place, and measurements with 3 different conditions, namely dry, wet conditions filled with 2.5% water and wet conditions filled with 5% water. data acquisition uses naniura resistivity meters with a track length of 96 cm. the first measurement results (dry conditions) obtained a range of resistivity values from 3.7 to 168.1 ω.m, the second measurement (wet conditions filled 2.5% water) obtained the range of resistivity values from 3.3 to 110.8 ω.m and the third measurement (wet conditions) filled with 5% water the resistivity values range from 1.7 to 91.2 ω.m. following the results of time-lapse inversion processing, a larger percentage change in the amount of 5.6% due to water absorption by the surface which then migrates into the inner layer. whereas the percentage of desaturation ranges is from -3.11 to 0.217 %, refer to archie’s law assumes conduction is caused by water content. keywords: time-lapse resistivity, electrical resistivity tomography, sandbox model 1. introduction the geo-electric resistivity technique is a geo-electric technique that studies the electrical resistivity properties of rock layers in the earth. in this method, an electric current is injected into the earth through two current electrodes then the response is received through two potential electrodes. based on the results of measurements of current and electric potential, variations in the resistivity value of the subsurface layer of the earth can be calculated. the difference in the variation in values obtained is the effect of different layers of the earth (telford et al., 1990). the geo-electrical methods used in this study are electrical resistivity tomography (ert) and time-lapse resistivity. ert measurement is done by injecting electric current to the subsurface of the earth to obtain resistivity pseudo section or a distribution model of resistivity value of subsurface material laterally and vertically (lowrie, 2007). the concept of the time-lapse resistivity method is basically a measurement of repeated resistivity at the same location. the time-lapse resistivity method can be applied to observe subsurface changes caused by fluid movements (williams et al., 2017), (loke et al., 2018), (kuswanto et al., 2018), (pratama et al., 2018), (comina et al., 2019), (inim et al., 2020), (rizka et al., 2020). in this study, a time-lapse resistivity was implemented by making simulations (physical modeling) on an aquarium container (sandbox model) that contains layers of rock with a fault structure. the purpose of this simulation is to determine the resistivity value in rock samples, determine the change in fluid changes and desaturation to the resistivity values (ρ), and to apply time-lapse resistivity inversion. 2. research method the time-lapse resistivity method consists of several activities that can be simplified into data acquisition, data processing and, data interpretation. data acquisition is done by making a model sandbox on an aquarium container made of glass with a length of 100 cm, width 20 cm, and a height of 13.5 cm. the aquarium container is filled with five layers. from top to bottom are tuff, fine sandstone, clay, coarse sandstone, and gravel (figure 1). tuff is a sample from the outcrops of the lampung formation taken on the itera campus. fine sandstone and clay are materials that have been sieved to obtain clean sandstone and clean clay. the fine sandstone is sand that passes sieve number 4 with a grain size of less than 4.75 mm and clay passed sieve number 100 with a grain size of less than 0.174 mm. the rock layers are made to resemble a confined and unconfined aquifer which sandstone is an aquifer. measurement of time-lapse resistivity in the sandbox model was obtained using the electrical resistivity tomography (ert) method with dipole-dipole configuration. physical measurement was conducted out under 3 conditions, namely dry condition (first condition) wet condition filled 2.5% water (second condition) and wet condition filled 5% water (third condition). http://journal.uir.ac.id/index.php/jgeet mailto:rizka@tg.itera.ac.id rizka, et al./ jgeet vol 5 no 4/2020 199 fig. 1 sandbox model measurements were made on rocks by sticking 4 nails that represent 4 electrodes (c2, c1, p1, and p2). furthermore, electrical current measurements (c1 and c2) and potential difference (p1 and p2) are measured by dipole-dipole configuration using naniura resistivity meters and multimeters. this configuration has another factor that represents the ratio of the distance between the electrodes c1 and p1, called n (figure 2). the smallest space (a) is 4 cm, the cross-section length is 96 cm, the number of n is 14 and the number of datum points is 217. fig 2. dipole-dipole configuration (everett, 2013) data processing was obtained based on the measurement results of the current value (i), potential difference (voltage, v), and spacing (n). then the geometry factor value is calculated using the equation k = n (n + 1) (n + 2) πa (1) so that the apparent resistivity value (ρa) is obtained with the formula ρa = k.r (2) based on ohm’s law, resistance (r) is calculated using the equation r = ∆v / i (3) then ρa = k.∆v / i in (4) the result of pseudo resistivity calculation is made by inversion modeling to get the true resistivity value and the actual subsurface model. then the time-lapse resistivity inversion was processed using res2dinv software to determine the change in the percentage of resistivity between the two sets of measurement data. time-lapse data is used to show the presence of additional data sets according to time measurements. this is done by calculating the difference between the measurement of condition two and condition one (first data set) and calculated the difference between the measurement condition three and two (second data set). the parameters used in data processing in this study can be seen in table 1. time-lapse inversion data processing uses the following parameters as follows:  no constraints. in no constraints, the change in subsurface resistivity value is determined by comparing the model resistivity value obtained from the inversion of the initial data set and the next time dataset.  simultaneous inversion. in a simultaneous inversion, the first inversion or reference data set is followed by the inversion of the next time data set in each iteration. because previously the authors chose "no constraints", the model obtained in the final iteration for the first data set is still used as the initial model for the next data set (geotomo software, 2010).  first data set, the model for the first data set is used as a reference model for the second data set, while the model for the second data set is used as a reference model for the third data set, and similarly for other data sets (geotomo software, 2010).  display percentage change in resistivity is a display of changes in the resistivity model obtained from the inversion of the time set data then compared with the reference model from the first data set inversion (geotomo software, 2010). table 1. parameter of processing parameter information electrode array dipole-dipole number of electrodes 4 number data points 217 electrode spacing (a) 4 cm separation factor (n) 14 length of transect 96 cm depth of investigation 13.5 cm mesh parameter finite mesh grid size 4 nodes mesh parameter finite-element method mesh refinement use normal mesh number of iterations 7 select times lapse inversion constrain no constraints simultaneous inversion first data set 3. results and discussion 3.1. dry condition model sandbox (first condition) in this model, tuff rock, fine sandstone, clay, coarse sandstone, and gravel are used. based on inversion modeling (figure 3), it can be seen that the resistivity value of each rock layer in the range of 3.7-168.1 ω.m. tuff has a resistivity value from 42.4 to 168.1 ω.m. fine sandstone has a resistivity value from 14.5 to 68.8 ω.m. clay has a resistivity value from 3.7 to 36.1 ω.m. coarse sandstone has a resistivity value from 4.5 to 14.8 ω.m. gravel rock has a resistivity value from 9.5 to 22.5 ω.m. 200 rizka, et al./ jgeet vol 5 no 4/2020 fig 3. pseudosection of resistivity models when dry condition 3.2. wet condition model sandbox filled with 2.5% water (second condition) the wet condition model sandbox filled with 2.5% (second condition) uses the same as the first condition. based on inversion modeling (figure 4), it can be seen that the resistivity value of each rock layer in the range of 3.3-110.8 ω.m. tuff has a resistivity value from 33.5 to 110.8 ω.m. fine sandstone has a resistivity value from 17.2 to 71.8 ω.m. clay has a resistivity value from 4.3 to 15.3 ω.m. coarse sandstone has a resistivity value from 3.5 to 13.0 ω.m. gravel rock has a resistivity value from 3.3 to 8.4 ω.m. fig 4. pseudosection of resistivity models when wet condition model sandbox filled with 2.5% water 3.3. wet condition model sandbox filled with 5% water (third condition) the model used in the third condition is the same as the first and second conditions. however, in condition two it is filled with 5% of the water from the volume of the sandbox. based on inversion modeling (figure 5), it can be seen that the resistivity value of each rock layer in the range of 1.7-91.2 ω.m. tuff has a resistivity value from 29.7 to 91.2 ω.m. fine sandstone has a resistivity value from 14.8 to 54.7 ω.m. clay has a resistivity value from 3.7 to 22.9 ω.m. coarse sandstone has a resistivity value from 2.6 to 17.3 ω.m. gravel has a resistivity value from 1.7 to 4.7 ω.m. fig 5. pseudosection of resistivity model when wet condition model sandbox filled with 5% water in the third condition is found a difference model with the previous condition because the rock sample has been filled with water which causes the rock resistivity to be small. moreover, utility conditions of electrode changes, samples in the third condition most mobile due to utility displacement. 3.4. comparison of resistivity values from different conditions based on experiments from first, second till third conditions, there is a difference in the true resistivity value which can be seen in table 2. based on the change in the true resistivity value, it can be seen that the true resistivity value gets smaller when the volume of water is added. so the resistance that the current passes through will be smaller. in figure 6, there are three graphs of resistivity values where the blue graph (first condition) is the highest true resistivity value from the other conditions. the red graph (second condition) is moderate resistivity values from the other conditions. while the green graph (third condition) is the lowest resistivity value from the other conditions. table 2. comparison of true resistivity values from different conditions no. rocks dry condition (first condition) wet condition model sandbox filled with 2.5% water (second condition) wet condition model sandbox filled with 5% water (third condition) interval (ωm) average (ωm) interval (ωm) average (ωm) interval (ωm) average (ωm) 1 tuff 42.4-168.1 94.6 33.5-110.8 68.5 29.7-91.2 59 2 fine sandstone 14.5-68.8 40.6 17.2-71.8 36.3 14.8-54.7 32.1 3 clay 3.7-36.1 14.5 4.3-15.3 8.4 3.7-22.9 7.6 4 coarse sandstone 4.5-14.8 9 3.5-13.0 6.1 2.6-17.3 4.4 5 gravel 9.5-22.5 13.3 3.3-8.4 5.2 1.7-4.7 3.4 rizka, et al./ jgeet vol 5 no 4/2020 201 fig 6. graph of comparison true resistivity value from different conditions the resistivity value is decrease influenced by the content of ions dissolved in water or electrolytic. arrhenius (1884) definite ions are electrically charged atoms or molecules. they are either positively charged (cations) or negatively charged (anions). arrhenius also noted the nature of electrolytes when dissolved in water, being to various degrees separated or dissociated into electrically opposing positive and negative ions. based on this definition, acids are substances that ionize in aqueous solutions to produce hydrogen ions (h+) while alkali produce hydroxide ions (oh-) in solution (heyrovska, 2011). so the chemical reaction of water (h2o) is as follows: (5) based on the arrhenius concept, water has acidic or alkaline. because the two potentials are balanced, each ion has the same potential difference (voltage) value. the equation for the value of the potential difference causes the electric current flowing in the water to be zero so the water resistance value is infinite (kurniawan et al., 2010) (figure 7). fig 7. flow chart of the relationship between the resistance value and the chemical composition of water (modified from kurniawan et al. (2010)) 3.5. time-lapse resistivity inversion modeling in this study, inversion modeling was also obtained using time-lapse resistivity inversion to see the percentage change in measurements of dry conditions (first condition), wet conditions filled with 2.5% water (second condition), and wet conditions filled with 5% water (third condition). data set changes were made twice, namely data set one (change in first and second condition) and data set two (change in second and third condition). based on the results of time-lapse inversion processing (figure 8), the average change in resistivity for the two data sets is almost the same at all measurement points, except on the length 20-24 cm, 48-60 cm, and 64-74 cm, which shows a change in percentage about 5.6%. this indicates a change in the resistivity value when measured under different conditions. this difference is due to the absorption of water by the surface which then migrates into the inner layer. another cause is because the layer is more compact after being pressed during the measurement. fig 8. (top) first data set model resistivity section, (middle) second data set model resistivity section, (bottom) percentage change in model resistivity in addition to producing a change in the percentage of resistivity, time-lapse inversion also produces a percentage of desaturation. desaturation is a decrease in the level of water saturation in the aquifer (namely the reduction in the fraction per unit volume of rock filled with water) (loke, 2004). desaturation can be attributed to archie's law which provides that the relationship between the resistivity of porous rocks and the fluid saturation factor applies to certain types of rocks and sediments, especially those with low clay content. in this case, electrical conduction is assumed through the fluid that fills the pores of the stone. archie's law is given by 202 rizka, et al./ jgeet vol 5 no 4/2020 (6) where  is the resistivity of the rock, w is the resistivity of the fluid,  is the fraction of the rock filled with fluid, while a and m. under certain special conditions, the equations (6) can be used to determine the change in fluid saturation or fluid resistivity with time. based on figure 9, it can be seen that the percentage value of desaturation shows an increase in the zone with a higher resistivity value with time due to water extraction. the decrease in the level of water saturation in the aquifer, or its desaturation value because archie's law assumes that conduction is due to water content. fig 9. (top) first data set model resistivity section, (middle) second data set model resistivity section, (bottom) percentage desaturation 4. conclusion time-lapse resistivity was obtained by making a simulation (physical modeling) on an aquarium container (sandbox model) which contains rock layers with a reverse fault structure, can find out the resistivity value in rock samples, determine fluid changes to the resistivity value (ρ) and measure time-lapse resistivity inversion. based on this research it can be concluded that: 1. there are some differences in the resistivity value from the first, second, and third conditions: a) in dry conditions (first condition), tuff has a resistivity value from 42.4 to 168.1 ω.m. fine sandstone has a resistivity value from 14.5 to 68.8 ω.m. clay has a resistivity value from 3.7 to 36.1 ω.m. coarse sandstone has a resistivity value from 4.5 to 14.8 ω.m. gravel rock has a resistivity value from 9.5 to 22.5 ω.m. b) in the 2.5% water filled condition (second condition), tuff has a resistivity value from 33.5 to 110.8 ω.m. fine sandstone has a resistivity value from 17.2 to 71.8 ω.m. clay has a resistivity value from 4.3 to 15.3 ω.m. coarse sandstone has a resistivity value from 3.5 to 13.0 ω.m. gravel rock has a resistivity value from 3.3 to 8.4 ω.m. c) in the 5% water filled from the volume of sandbox (third condition), tuff has a resistivity value from 29.7 to 91.2 ω.m. fine sandstone has a resistivity value from 14.8 to 54.7 ω.m. clay has a resistivity value from 3.7 to 22.9 ω.m. coarse sandstone has a resistivity value from 2.6 to 17.3 ω.m. gravel has a resistivity value from 1.7 to 4.7 ω.m. 2. the decrease in the resistivity value of each layer occurs due to the increase in the amount of water contained in each layer. the more water in the layer, the more electrolyte ions will be, so that the electric current that is injected will be easily flowed by the electrolyte ions. the electric current flows through a material either conductor or semiconductor that is able to conduct electric current properly. 3. based on the results of time-lapse inversion processing shows:  the percentage change is greater, namely 5.6%. this difference is due to the absorption of water by the surface which then migrates into the inner layer. another reason because the layer is more compact after being pressed during the measurement.  percentage of desaturation that shows an increase in the zone with a higher resistivity value with time due to water extraction. a decrease in the level of water saturation in the aquifer or its desaturation value because archie's law assumes that conduction is caused by water content. acknowledgment we want to thank the director of research and community service at the ministry of research, technology, and higher with contract number 009/sp2h/lt/drpm/2018 for providing the funding and also to geophysical engineering itera students to assist with acquisition data. references comina, c., giordano, n., 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jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 05 no 01 2020. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content geomorphological assessment to tract the flow evolution of kali putih, srumbung district, magelang regency, central java, indonesia .......................................... 1 geosite assessments at the southern part of karangbolong dome: new insight to geotourism potential in kebumen, central java, indonesia ............................... 8 gas saturated sandstone reservoir modeling using bayesian stochastic seismic inversion ........................................................................................................... 19 hydrodynamics features and coastal vulnerability of sayung sub-district, demak, central java, indonesia ............................................................................. 25 the role of decadal kelvin wave in the western of sumatra and along the south coast of java using frequency-wavenumber 2d spectral analysis ........................ 32 a geophysical surveywith magnetic method for interpretation of iron ore deposits in the eastern nusawungu coastal, cilacap regency, central java, indonesia ..................................................................................................................... 37 page 1 uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 6. no 2. june 2021 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 06 no 02 2021. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content resistivity data modeling for subsurface volcanostratigraphy construction of cibadak sub-watershed, bogor, west java, indonesia ........................................................ 74 feasibility study on the application of dynamic elastic rock properties from well log for shale hydrocarbon development of brownshale formation in the bengkalis trough, central sumatra basin, indonesia ..................................................... 81 calcareous nanofossil of post-gondwana sequence in southern banda arc, indonesia ........................................................................................................................................ 86 characteristics of chromite deposits at north kabaena district, bombana regency, southeast sulawesi province, indonesia ................................................................. 94 mapping of sediment on the waters around panjang island, banten bay, indonesia ........................................................................................................................................ 99 the geomorphological factors and its implications for the tidal energy installations in java, indonesia.................................................................................................... 107 3d natural state modeling of mount iyang-argopuro geothermal area, east java, indonesia .............................................................................................................................. 113 shallow aquifer groundwater facies at multiple landuse sites in manglayang volcanic area, jatinangor and surroundings, indonesia ...................................................... 120 e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 handoyo et al./ jgeet vol 1/2016 45 rock physics modeling and seismic interpretation to estimate shally cemented zone in carbonate reservoir rock handoyo 1, *, m rizki sudarsana 2 , and restu almiati 1 1 geophysical engineering, institut teknologi sumatera, south lampung, indonesia 2 geophysics, universitas padjajaran, west java, indonesia handoyo_1906@yahoo.com tel.:+6285295400039 received: oct 1, 2016. revised : 12 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.6 abstract carbonate rock are important hydrocarbon reservoir rocks with complex texture and petrophysical properties (porosity and permeability). these complexities make the prediction reservoir characteristics (e.g. porosity and permeability) from their seismic properties more difficult. the goal of this paper are to understanding the relationship of physical properties and to see the signature carbonate initial rock and shally-carbonate rock from the reservoir. to understand the relationship between the seismic, petrophysical and geological properties, we used rock physics modeling from ultrasonic pand swave velocity that measured from log data. the measurements obtained from carbonate reservoir field (gas production). x-ray diffraction and scanning electron microscope studies shown the reservoir rock are contain wackestone-packstone content. effective medium theory to rock physics modeling are using voigt, reuss, and hill. it is shown the elastic moduly proposionally decrease with increasing porosity. elastic properties and wave velocity are decreasing proporsionally with increasing porosity and shally cemented on the carbonate rock give higher elastic properties than initial carbonate non-cemented. rock physics modeling can separated zones which rich of shale and less of shale. keywords: elastic modulus, porosity, velocity, and shally-cemented. 1. introduction reservoir rocks possess certain characteristic which can be identified by several physical parameters. among many of the physical parameters are the porosity and permeability. according to [7], the characterization is a process of elaborating its characteristic qualitatively and quantitatively by using the available data. the characteristics provided as information regarding physical parameters from reservoir rock is very essential to understand the reservoir better. in this study, there will be rock physics modeling to differentiate zones which rich of shale and slight of shale. the study areas was located in java sea (figure 1). the purpose of this study is to : (1) knowing the characteristics of elastic rock paramameter; (2) predicting the mineral-rich shale zone as cement and a mineral-slight shale zone; (3) interpreting the existence of shale gas reservoir in the study area. 2. data and basic theory complex carbonate rocks is very difficult to be modeled. in addition to the types of minerals constituent of rock complex, carbonate rocks also have a variety of complex pore geometry. the only way to make rock physics modeling was using effective medium theory. illustration simplification model of carbonate rocks are shown by figure 2. lithology reservoir carbonate in research area was a carbonate wackestonemudstone which interspersed with mineral dolomite and calcite. the simple bounds for an isotropic linear elastic composite, defined as giving the narrowest possible range without specifying anything about the geometries of the constituents, are the simple effectif medium theory is the voigt bound (illustrated by figure 1). the voigt (mv) and reuss (mr) bound calculated effective elastic modulus, from the volum fraction n phase fi, and elastic modulus n phase fraction mi as follows [6]:       n n i i r n n iiv m f m mfm 1 1 1 (1) the velocities of various types of seismic waves in homogeneous, isotropic, elastic media are given by: 46 handoyo et al./ jgeet vol 1/2016        s p v k v 3 4 (2) jizba [5] studied the effect of cementation on rock physics properties of sandstones, avseth and mavko [2] showed that the scatter observed in velocity-porosity data can be decomposed into depth-lines, while dvorkin and nur [4] showed mathematically how cement could cause complexity in the velocity-porosity plane depending on cement location and mineral composition (figure 3). rock texture and lithology also greatly affect the observed scatter (e.g., bryant and raikes [3]; vernik [8]; anselmetti and eberli [1]). fig 1. the study area which located in java sea known as a carbonate rock reservoirs that produce gas. fig 2. simplification model to make the carbonate rock sample using effective medium theory. handoyo et al./ jgeet vol 1/2016 47 fig 3. the elastic-wave velocity versus porosity for quartzand clay cemented north sea sands, friable north sea sands (the north sea data and the models are discussed in dvorkin and nur, 1996), and hand-made ottawa sand and kaolinite mixture (data from yin et al., 1993). all data are for room-dry samples at 30 mpa differential pressure. the other bounds for an isotropic linear elastic composite, defined as giving the narrowest possible range without specifying anything about the geometries of the constituents, are the hashinshtrikman bounds. when there are only two constituents, the bounds are written as: )](5/[)2(2)( )()( 13 4 11111 1 12 2 1 1 13 4 11 1 12 2 1            kkf f kfkk f kk hs hs (3) 3. method the reservoir parameters were obtained from a cross-section of 2d seismic data and the welllogging borehole data. the well-logging data (well 01) is shown by figure 4. the r s flow chart shown by figure 5. characteristic of reservoir rock could be known from geological and seismic data input which could separated top and bottom of reservoir rock also its geometry. log data was used for making the crossplot with rock physics modelling. further this could separated zones which rich of shale and less of shale. figure 4. well-logging data of study area (well-01). 48 handoyo et al./ jgeet vol 1/2016 figure 5. flow chart of the research. 4. result and discuss 2d seismic interpretation of study area shown by figure 6. carbonate reservoir characterized by the geometry that resemble a built-up carbonate and the flatspot of sesimic response. in addition, figure 4 shown the top (1000 ms) and the bottom (1060 ms) of reservoir that characterized with the changes of contrast acoustic impedance, density, and p-wave velocity. also there is an exsistence of a very long fault structure near the reservoir (left side). figure 6. 2d seismic interpretation in study area. from well-01 data and seismic response, we could see that the geometry of carbonate reservoir shown by the existence of flatspot which resemble a built-up of carbonate rock. gamma ray crossplot and acoustic impedance shown by figure 7. the high gamma ray shown the influence of shally-cemented in carbonate rock. gamma ray data vs acoustic impedance separated zone of reservoir rock which rich of shale and less of shale. figure 7. gamma ray crossplot vs acoustic impedance. the high gamma ray shown the influence of shally-cemented in carbonate rock. rock physics modeling in reservoir rock used the effective medium theory voitgt, reuss and hashinshtrikman bounds. modeling of composite reservoir rock (figure 2) gave the result shown by curve in figure 8. elastic moduly (bulk moduly and shear moduly) decreasing proporsionally with increasing porosity value. the influence of shally-cemented in carbonate rock causing the high bulk moduly. figure 8c shown the reservoir rock zone which rich of shale and less of shale. handoyo et al./ jgeet vol 1/2016 49 figure 8. effective medium theory using voigt, reuss, and hashin-shtrikman bounds. figure 8a is bulk moduly, figure 8b is shear moduly, and figure 8c is prediction of shale-carbonate and initial carbonate zone. p-wave velocity values is decreasing proporsionally with increasing porosity value. according to figure 3, the effect of shallycemented in carbonate gave a higher p-wave velocity than the initial carbonate rock (figure 9). figure 9. effect shale-cemented in carbonate reservoir rock to p-wave velocities value. contact shale cemented in carbonate reservoir rock. shally cemented on the carbonate rock obtain the p-wave velocity higher than initial carbonate reservoir rock. 5. concluding remarks the conclusions from this paper are (1) geometry and top-bottom reservoir carbonate rock can be known from log data and seismic section, (2) the effect of shally-cemented on reservoir rock characterized by an enhancment in bulk moduly and p-wave velocity also a reduction in porosity, and (3) rock physics modeling and log data could separated the characteristic of reservoir rock which shally-cemented and its initial carbonate. acknowledgements thanks to the supporting partner in this research which was partly provided by lppm of institut teknologi sumatera and universitas padjajaran. references [1] anselmetti, f. s., and eberli, g. p., 1997, sonic velocity in carbonate sediments and rocks; in palaz, i., and marfurt, k.j., eds., carbonate seismology: soc. expl. geophys., tulsa, 53-74. [2] avseth, p., and mavko, g., 1995, the influence of diagenesis on the acoustic properties of grainsupported siliciclastic sedimentary rocks: annual meeting, stanford rock physics and borehole geophysics project, 58, paper b1. [3] bryant, s., and raikes, s., 1995, prediction of elasticwave velocities in sandstones using structural models: geophysics, 60, 437-446. [4] dvorkin, j., and nur, a., 1996, elasticity of highporosity sandstones: theory for two north sea datasets, geophysics, 61, 1363-1370. [5] jizba, d., 1991, mechanical and acoustical properties of sandstones and shales: ph.d.-thesis, stanford university. [6] mavko, g., and nur, a., 2009. the rock physics handbook, second edition tools for seismic analysis of porous media. cambridge university press the edinburgh building, cambridge cb2 8ru, uk [7] sukmono, s. 2002. seismic inversion and avo analysis for reservoir. program studi teknik geofisika itb. bandung. indonesia. [8] vernik, l., 1994, predicting lithology and transport properties from acoustic velocities based on petrophysical classification of siliciclastics. geophysics, 59, 420-427. e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 242 winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 pollen and foraminifera approaches to identify sediment sources in the river mouth mahakam east kalimantan winantris 1, *, and lia jurnaliah 1 1 faculty of geology, universitas padjadjaran, jl. raya bandung sumedang km.21, kabupaten sumedang, west java 45363 * corresponding author : win.oncos@gmail.com received: sept 1, 2017. revised : oct 1, 2017, accepted: nov 9, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.689 abstract the central role of mahakam river in the construction of mahakam delta is to supply sediment from terrestrial to the river mouth. the river upstream comes from mount camaru and the downstream part terminate at makasar strait. the surrounding area of the river is overgrown by wet tropical flora that produces pollen. the existence pollen in river sediments as an indicator that sediment came from terrestrial, and foraminifera as an indicator that sediment came from marine. the ratio changes of pollen to foraminifera show that there were differences of sediment source supply. the study was conducted at the river mouth. a shallow core, 200 cm depth, composed of sand and mud and sandy mud, from it taken vertically 11 samples to be analyzed pollen and foraminifera. sample preparation was using standard methods acetolysis. meanwhile, sample preparation of foraminifera using hydrogen peroxide method. pollen found in all samples, but foraminifera only found in 8 samples. the data indicating that sedimentation process in the mouth of a river not only gets sediment supplies from terrestrial but also from marine. the quantity of pollen and foraminifera varies vertically. the frequency of pollen much higher than foraminifera that indicates of source sediments dominance came from terrestrial which carried by mahakam river current. sonneratia caseolaris pollen continuously found in all samples. stictogongylus vandiemensis is species foraminifera the most common that followed by ramulina confossa, both of them come from the sea particularly from the shallow sea. keyword: pollen, foraminifera, sediment source, mouth of mahakam river 1. introduction the river mouth is the place where a river enters a lake, larger river, or the ocean is called its mouth (merriam-webster,1828). the mahakam river is an icon for the province of east kalimantan. mahakam river upstream rises in mount cemaru that empties into the makassar straits. the position of a river mouth in the upstream from mahakam delta. the main role of the mahakam river in the delta formation is supplying sediment to the estuary area. the province of east kalimantan, the place of mahakam river is located in the equatorial area (fig.1). the landscape along the mahakam river overgrown by various types of tropical flora. in the upstream section, there are hilly areas that inhabited by tropical rainforest that located in the district of mahakam hulu. mahakam river is generally covered by vegetation of lowland forest and mixed forest. entering the delta plains area there are swamp forests which dominated by nypa fruitcans and secondary mangrove plant, the true mangrove grows at the end of the delta plains, precisely in the area of mud flats (winantris, et.al 2013, fig.2). the existence of tropical forest plants along the river, makes sediments transported to the estuary filled with pollen which produced by forest plants. this is one reason why research is done. the study aims to identify the types of pollen found in sediments that before entering the mahakam delta. it is important to know the type of pollen that fills a river as a tool to identify the source of sediment deposited at the mouth of the river before entering delta area. benthic foraminifera classically used as an indicator of marine depositional environments, in particular, to detect the ocean depths (bathymetry), it is closely related to the way of living foraminifera are attached to the seabed. both pollen and benthic foraminifera have a similar function in this case for identifying the source of sediment.the mahakam delta is a mixed, river and tide-dominated delta (galloway, 1975). the delta characterized by a mixture of sediment from the river and the sea. furthermore, the delta is presently in a transgressive phase (salahuddin and lambiase, 2013). tide rise in mahakam delta winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 243 triggered by the waves that come from the makassar straits which cause water accumulation in the delta plain area (allen and chamber, 1998). high tides are also as transport media of sediment from the sea to the delta region evidence that the tide rise could encourage marine sediments towards the river mouth by looking for the presence of foraminifera in sediment. kind of foraminifera is an indicator of the marine bathymetry of the origin sediments. referring to the bathymetry and habitat classification of benthic foraminifera, it will be known the depth of sedimentary origin which is transported and deposited at the mouth of the river comes. likewise, the source of sediments that comes from upstream can be traced by the pollen data. pollen analysis is one of foundation for reconstructing past ecosystems, by fossil pollen preserved within accumulating sediment whose provenance can be identified back to the parent plant (lovett, et.al 2007). fig.1 location of mahakam river (duxbury, 2010) fig. 2 vegetation zone of mahakam delta (winantris, et.al.2013). 244 winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 2. material and methods a shallow core taken at the mouth of the mahakam river with a depth of 200 cm, from it taken 11 samples at intervals of 20 cm for the analysis of pollen and foraminifera, consist of: mr1 (0 cm), mr2 (20cm), mr-3 (40cm), mr-4 (60cm), mr-5 (80cm), mr-6 (100cm), mr-7 (120cm), mr-8 (140cm), mr-9 (160 cm), mr-10 (180cm) and mr-11(200cm). the position of sample location at mahakam river upstream from the delta (fig.3). sample preparation for the palynological analysis was done using acid treatment method. each sample was taken 10-gram dry weight for pollen analysis, and only 0,5 ml/slide from the residue of the sample that observed. identifying pollen used light binocular microscope under high magnification x100, 400x and 1000x, and scanning electronic microscopy. pole observation used lo analysis method. to get a clear pollen morphology the picture was taken under magnification 1000x. the same as pollen treatments, for the analysis of foraminifera are also using 10 gr dry weight/sample. processing sample of foraminifera used hydrogen peroxide method, and for observation using a binocular microscope. identification of foraminifera refers to lobliech & tappan (1994). meanwhile, the ocean depths refer to the classification of bathymetry (tipsword et al 1966), see fig 4. 3. pollen analysis the shallow core consists of sand and silt sediment, from a depth of 200 cm to 131cm consists of fine sand, medium and coarse sand. from the depths of 131cm up to the surface at position 0 cm composed of silts and clay. all samples which analyzed found the pollen. the total pollen sum of sand sediment only 30 to 70 grains in each sample, that include the poor to moderate category, and average just 51,2 grains/sample. different from silt sediment, pollens found more than in sand sediment. minimum pollen is 126 grains at mr-3 and maximum 256 grains at mr-4, pollen average reach 210,83 grains, it's belong rich category (table 1and fig.7). fig 3. spot location of study at mahakam river, kalimantan. winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 245 fig.4 classification of bathymetry (tipsword et. al,1966). table 1. pollen quantity sample code depth (cm) pollen (grains) mr-1 0 254 mr-2 20 232 mr-3 40 126 mr-4 60 256 mr-5 80 180 mr-6 100 217 mr-7 120 52 mr-8 140 52 mr-9 160 52 mr-10 180 70 mr-11 200 30 the data illustrate that there were a supplied of sediment from the mountains, surrounding the upstream area, besides from the lowland and the environment around the river mouth. the role of mahakam river as an agent to supply pollen from upland to downstream area. pollen of montane forest zone which found consist of altingia exelsa, arenga pinnata, celtis sp, dacrycarpus imbricatus, engelhardtia sp, erica sp, ilex sp,phyllocladus hypophyllus, pinnus sp, podocarp us neriifolius, quercus laurifolia, taxodium sp and vaccinium sp. pollen of altingia exelsa, arenga pinnata and celtis sp produced by vegetation of submontane forest zone that grows an altitude 10001500 m above sea level. dacrycarpus imbricatus, podocarpus neriifolius, quercus laurifolia, engelhardtia sp derived from lower montane forest zone which occupies an area at an altitude of 1400-1800 m above sea level. specifically, vaccinium sp and erica sp both are a type of pollen from the upper montane forest that occupies an area at an altitude of 2400-3000 meters above sea level (whitmore, 1975; stuijts, 1933). vegetation in the downstream area consists of lowland forest, mixed forest, swamp forest and mangrove forests, and in the upstream area, there are montane forests. based on the quantity of pollen can be known that the pollen from the vegetation in the downstream area is the most common. generally, there were mixed pollens which produced by mangrove, swamps, vegetation, lowlands and mountain vegetation (fig.5) pollen from lowland forest more various than from upland. the species that commonly found are eugeissona insignis, dipterocarpus sp. and cocos nucifera. sonneratia alba is the most mangrove pollen, while nypa fruit cans andoncosperma tigillarium are common pollen that comes from the delta plain. based on vegetation zone of mahakam delta, mangrove pollen which produced by mangrove plant came from mud flat area, that laid in the distal part of lower delta plain. the existence of mangrove pollen in the mouth of a river is indicated that there was a mobilisation of pollen from distally lower delta plain to the mouth of the river (fig .8). fig. 5. erica sp (1),.dacrycarpus imbricatus (2), cocos nucifera(3), oncosperma tigillarium (4), eugessona insignis(5), vaccinium sp (6). microscope magnification 1000x). 1 2 3 4 5 6 246 winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 4. foraminifera analysis small benthic foraminiferas were found in 8 (eight) sediment samples of 11 sediment samples from river mouth mahakam. based on foraminifera analysis there are 13 species and 56 specimens. the specimen, found in mr-9 sample with 160 cm species is 7 species, found in mr-11 sample with 200 cm depth. fig. 7 shows that the amount of foraminifera increased toward deeper core (table 2). table 2. quantity of foraminifera sample code depth (cm) species specimen mr-1 0 2 4 mr-2 20 2 2 mr-3 40 0 0 mr-4 60 0 0 mr-5 80 0 0 mr-6 100 2 2 mr-7 120 3 8 mr-8 140 3 3 mr-9 160 6 19 mr-10 180 2 3 mr-11 200 7 15 total 56 discover of small benthic foraminifera in the river mouth area are evidence of the energy came from sea direction. tidal wave have a role to encourage the sediment from the sea towards the downstream of mahakam river. (fig.6) the chart shows the quantity of foraminifera in the sand sediment is a significant differ from silt sediment. the quantity of foraminifera from sand more common than from silt sediment. inversely condition with mud sediments that showing the quantity of pollen is very high (fig.7). there are no benthic foraminifera in 40 cm-80 cm depth. lack of benthic foraminifera in those interval shows that the source sediment from terrestrial. this condition is significantly different from sand sediment in 120 cm-200 cm depth which is small benthic foraminifera is more common. it means that in deeper core the source sediment not only came from terrestrial but also came from marine (fig 8). the species of small benthic foraminifera in all sample sediments include shallow species such as reusoolina stellula and stictogongylus vandiemenensis, and deep species such as uvigerina bradyana. those foraminifera assemblages are evidence of sediment marine came from shallow sea and deep sea. the presence of benthic foraminifera in the river mouth sediment, possibly related to the transgressive phase in the modern delta area. salahuddin and lambiase (2013) found benthic foraminifera in the nypa swamp area which located on the delta plains, they said that the sediment of modern delta shows the transgression product. (1) (2) fig.6 reusoolina stelulla (1), stictogongylus vandiemenensis (2), (microscope magnification 56x) winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 247 fig 7. quantity of pollen (grains) and foraminifera (specimen) = mud = sand fig. 8. illustration of source of sediment which filled mouth of mahakam river based on origin of pollen and foraminifera 248 winantris & jurnaliah, l./ jgeet vol 02 no 04/2017 5. conclusions the sources of sediment that fills the mouth of the mahakam river dominated by terrestrial sediment and only a small portion of the sediment from marine. about 77, 23% samples who have observed, indicated that sediment supply from terrestrial and marine, and 27.27% samples the sediment supply only from terrestrial. the highest presence of foraminifera only 25 %, contrary to its pollen reaches 75% is the lowest presence of total pollen-foraminifera in the 200 cm depth. after that, the presence of foraminifera decrease and reaches minimum in 80-40 cm intervals by 0% so in the same intervals presence of pollen 100% while the sources of terrestrial sediment include from the delta and surrounding areas, lowlands and highlands.sediment from the ocean, covers shallow sea and deep sea. there were no benthic foraminifera at the interval 40 cm-80 cm depth it indicates that the source of sediment just comes from the mainland. the differences in the depth of sediment source that fills the mouth of the river indicate the strength of tidal waves was triggered by a wave of makassar strait also vary in the strength. acknowledgements we are particularly grateful for the assistance given by maria who help us in processing samples. references duxbury, m., 2010. borneo island, pacific ocean britannica. encyclopedia britanica inc. galloway, w. e., 1975. process framework for describing the morphological and stratigraphic evolution of deltaic depositional systems. deltas: models for exploration., september, 87 98. hidayat, h., vermeulen, b., sassi, m. g., f. torfs, p. j. j., & hoitink, a. j. f., 2011. discharge estimation in a backwater affected meandering river. hydrology and earth system sciences. https://doi.org/10.5194/hess15-2717-2011 lambert, b., 2003. micropaleontological investigations in the modern mahakam delta, east kalimantan (indonesia). carnets de géologie / notebooks on geology. https://doi.org/10.4267/2042/294 loeblich, a., & tappan, h., 1994. foraminifera of the sahul shelf and timor sea. cushman found. foraminif. res. spec. publ. retrieved from http://scholar.google.co.il/scholar?q=loeblich+and+t appan&hl=en&as_sdt=0,5&as_ylo=1994&as_yhi=199 4#1 lovet, j., rob, m., & barber, a. r. m. j., 2007. direct evidence for change. in r. . and r. m. h. hester (ed.), biodiversity under threat. royal society of chemistry., 167. rsc publishing. merriam-webster., 1828. mouth of river. merriamwebster. retrieved from www.merriamwebster.com/dictionary/mouth of the river salahuddin, & lambiase, j. j., 2013. sediment dynamics and depositional systems of the mahakam delta, indonesia: ongoing delta abandonment on a tidedominated coast. journal of sedimentary research. doi: 10.2110/jsr.2013.42 stuijts, i.-l. m., 1933. late pleistocene and holocene vegetation of west java, indonesia. modern quarternary research in southeast asia (first edit). rotterdam: a.a. balkema publisher. t. f. grimsdale and f. p. c. m. van morkhoven., 1955. the ratio between pelagic & benthonic foraminifera as a means of estimating depth of deposition of sedimentary rocks. in proceedings of the 4th world petroleum congress., 473 491. tipsword, h. l., f. m. setzer, and f. l. smith, jr., 1966. (n.d.). interpretation of depositional environment in gulf coast petroleum exploration from paleoecology and related stratigraphy: geological societies, 16, 119 130. whitmore t.c., 1975. tropical rain forests of the far east. oxford: clarendon press. winantris.s; adjat sudradjat; febri hirnawan; ildrem syafri., 2013. distribution and diversity pollen and spore, in recent mahakam delta, east kalimantan. sage. berlin. https://doi.org/10.5194/hess-15-2717-2011 https://doi.org/10.5194/hess-15-2717-2011 https://doi.org/10.4267/2042/294 http://scholar.google.co.il/scholar?q=loeblich+and+tappan&hl=en&as_sdt=0,5&as_ylo=1994&as_yhi=1994#1 http://scholar.google.co.il/scholar?q=loeblich+and+tappan&hl=en&as_sdt=0,5&as_ylo=1994&as_yhi=1994#1 http://scholar.google.co.il/scholar?q=loeblich+and+tappan&hl=en&as_sdt=0,5&as_ylo=1994&as_yhi=1994#1 https://doi.org/10.2110/jsr.2013.42 1. introduction 2. material and methods 3. pollen analysis 4. foraminifera analysis 5. conclusions acknowledgements references cover jgeet vol 5 no 3 september.cdr uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 4. no 4. december 2019 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 04 no 04 2019. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content soil minerals serving as source of arsenic in alluvial aquifers of holocene: a study case from indus delta, sindh, pakistan .......................... 227 the weak soil investigation at the slope zone in the hot spring area, rokan hulu, indonesia ............................................................... 236 evaluation of the hydrocarbon potential of shale exposures in endo north ............................................................................... 242 integrated approach in geophysical investigation of road failure in crystalline basement environment in south-western part of nigeria ........... 248 geotourism on xiii koto kampar: an approach for sustainable eco-geo system ............................................................................................. 257 geology and lamongan volcanic rocks case study at ranu pakis, klakah, lumajang, east java province, indonesia ............................................. 263 rock formation acid mine drainage in epithermal gold mineralization, pandeglang, banten province ........................................................................ 271 the hydrochemistry of groundwater in jambakan, klaten regency, central java province, indonesia .................................................................... 277 analysis of land cover changing and vegetation index at kuranji watershed in padang, west sumatera, indonesia ............................................ 286 page 1 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 1 2020 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 19 research article gas saturated sandstone reservoir modeling using bayesian stochastic seismic inversion rahmat catur wibowo1,*, ditha arlinsky ar1, suci ariska1, muhammad budisatya wiranatanagara2, pradityo riyadi2 1geophysical engineering department, engineering faculty, universitas lampung, lampung, indonesia 2lemigas r & d centre for oil and gas technology, jakarta selatan, indonesia * corresponding author : rahmat.caturwibowo@eng.unila.ac.id tel.:081-327-507517; fax: 0281-638793 received: jan 1, 2020, accepted: march 10, 2020 doi: 10.25299/jgeet.2020.5.1.4503: 10.24273/jgeet.2016.1.2.001 abstract this study has been done to map the distribution of gas saturated sandstone reservoir by using stochastic seismic inversion in the “x” field, bonaparte basin. bayesian stochastic inversion seismic method is an inversion method that utilizes the principle of geostatistics so that later it will get a better subsurface picture with high resolution. the stages in conducting this stochastic inversion technique are as follows, (i) sensitivity analysis, (ii) well to seismic tie, (iii) picking horizon, (iv) picking fault, (v) fault modeling, (vi) pillar gridding, ( vii) making time structure maps, (viii) scale up well logs, (ix) trend modeling, (x) variogram analysis, (xi) stochastic seismic inversion (ssi). in the process of well to seismic tie, statistical wavelets are used because they can produce good correlation values. then, the stochastic seismic inversion results show that the reservoir in the study area is a reservoir with tight sandstone lithology which has a low porosity value and a value of high acoustic impedance ranging from 30,000 to 40,000 ft /s*g/cc. keywords: seismic, geostatistic, stochastic inversion, bonaparte basin 1. introduction the bonaparte basin is mostly located off the coast of the arafura sea and has an area of about 270,000 km2. this basin is known as one of the basins that produces hydrocarbons in indonesia, especially hydrocarbons in the form of gases and condensates. the bonaparte basin is generally dominated by extensional fractures and very few fractures or compressional structures are found. (o'brien et al, 1993). according to barber et al (2003), lithological characters based on biostratigraphic data indicate that the depositional pattern in the bonaparte basin plover formation is dominated by the deposition of braided fluvial types in the south of the study area to the coastal environment which is influenced by waves (wave dominated shoreline) and in the wave dominated shoreline the northern part is formed in a shallow marine environment. the direction of deposition in the braided fluvial environment is relatively northwest-southeast. in the oil and gas exploration stage, the seismic method is one of the top choice geophysical methods that can provide better subsurface information by utilizing the seismic wave propagation properties. there is a technique commonly used in this seismic method, namely seismic inversion technique. seismic inversion is a method that can describe and estimate the physical properties of subsurface in the form of acoustic impedance values by utilizing seismic data as input and well data as control. well data here has detailed resolution on thin layer thickness. meanwhile, seismic data is strongly influenced by bandwidth which for thin layer thicknesses under tunning thickness cannot be resolved properly so as to cause high ambiguity problems in conducting inversions. therefore, to overcome these problems, an inversion technique with a geostatistical approach can be used which will result in high resolution inversion results. bayesian stochastic inversion seismic method is an inversion method that uses a geostatistical algorithm to obtain property models that have detailed resolution such as well data. in this study a mapping of sandstone reservoirs saturated with plover formation gas using stochastic inversion seismic methods in the "x" field in the bonaparte basin. 2. methodology in this research 3d post-stack time migration seismic data which is equipped with inline in the east-west direction totaling 300 lines (1100 1400) and xline in the north-south direction totaling 800 lines (1000 1800) with the distance between the lines which is 18.75 m. well data used in this study amounted to 4 wells named ar-1, ar-2, ar-3, and ar-4. there are also data markers, namely the top reservoir and base reservoir and checkshot data on each well. data processing conducted in this study consisted of qualitative and quantitative data processing for obtaining hydrocarbon prospect zones, log data sensitivity analysis, wavelet extraction, well seismic tie, picking horizon, picking fault, fault modeling, pillar gridding, time-map mapping structure map and depth structure map, isopatch map creation, ai scale-up log and trend modeling so that later stochastic inversion results will be obtained. stochastic seismic inversion is an inversion technique whose basic principle uses a random simulation algorithm and produces more than one acoustic impedance model that fills observational seismic data. more than one solution can overcome the problem of non-uniqueness and uncertainty in deterministic inversion, especially in the case of thin films. another advantage is that this method does not depend on the bandwidth of the seismic data used, but on the block size when simulating the impedance model so that the results of this http://journal.uir.ac.id/index.php/jgeet 20 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 stochastic inversion are less smooth than the deterministic inversion results. the basic principle of this stochastic seismic inversion is the bayesian principle. this principle uses the concept of probability which is interpreted as "a measure of a state of knowledge". this principle is a probability principle, where there is a prior probability model, which is then formulated with a likelihood probability function so as to obtain the output of the posterior probability model. this output model is the realization of the impedance model. the formulation of the bayesian principle is as follows (h. anders, 1998). σ(m)=k.ρ(m).l(m) where: σ(m) : posterior model ρ(m) : prior l(m) model l(m) : likelihood function k : constant bayes' theorem is the result of a combination of probability theory and conditional probability. probability theory states the likelihood of an event occurring with real numbers 0 to 1. meanwhile, conditional probability is an event a that occurs when it is known that event b has already occurred (wapole, 2000). 3. result and discussion 3.1 qualitative analysis in this study four data wells were used, namely ar-1 well, ar-2 well, ar-3 well, and ar-4 well. qualitative analysis is the first step in determining the hydrocarbon prospect zone. this qualitative analysis is performed by the quick look method where by looking at the response from the gamma ray log, resistivity log, neutron porosity log, and density log. this quick look method aims to interpret zones that are permeable, impermeable, lithological types, and hydrocarbon fluid content. in the ar-1 well contained in figure 1 it can be seen that the depth of the reservoir layer containing hydrocarbons is 3955 ft to 4275 ft which is marked with a dark blue box. in this layer it is known that the response of the gamma ray log curve shows a low response which ranges from 10 gapi to 60 gapi so that the layer can be said to be a permeable layer and has a sandstone or sandstone lithology type. then, the resistivity log curve response, the log lld, shows a very high response of more than 80 ohms. so the layer can be said to have a gas hydrocarbon fluid content. in addition, the separation of the log density and neutron porosity log also indicates that the layer is a hydrocarbon prospect zone. table 1. well data used in the study well data well name ar-1 ar-2 ar3 ar4 1 p-wave v v v v 2 gamma ray v v v v 3 resistivity(lld) v v v v 4 neutron porosity v v v v 5 density (rhob) v v v v 6 phie v v v v furthermore, the ar-2 well did not show any reservoir layers containing hydrocarbons. this is because in ar-2 well there is no separation between log density and log neutron porosity and is also dominated by high gamma ray log response. in addition, if seen from the response of the log resistivity curve, there is no contrast of high resistivity values. the qualitative analysis on ar-2 wells can be seen in figure 2. fig 1. qualitative analysis of ar-1 wells fig 2. qualitative analysis of ar-2 wells fig 3. qualitative analysis of ar-3 wells wibowo, r.c., et al./ jgeet vol 5 no 1/2020 21 then, in the ar-3 well contained in figure 3 it can be seen that the depth of the reservoir layer containing hydrocarbons is 4185 ft to 4492 ft which is marked with a dark blue box. in this layer it is known that the response of the gamma ray log curve shows a low response which ranges from 10 gapi to 60 gapi so that the layer can be said to be a permeable layer and has a sandstone or sandstone lithology type. then, the resistivity log curve response, the log lld, shows a high response of more than 80 ohms. so that the layer can be said to have a gas hydrocarbon fluid content. in addition, the separation of the log density and neutron porosity log also indicates that the layer is a hydrocarbon prospect zone. fig 4. qualitative analysis of ar-4 wells then, in the ar-4 well contained in figure 4 it can be seen that the depth of the reservoir layer containing hydrocarbons is 4220 ft to 4541 ft marked with a dark blue box. in this layer it is known that the response of the gamma ray log curve shows a low response which ranges from 10 gapi to 60 gapi so that the layer can be said to be a permeable layer and has a sandstone or sandstone lithology type. then, the resistivity log curve response, the log lld, shows a high response of more than 80 ohms. so that the layer can be said to have a gas hydrocarbon fluid content. in addition, the separation of the log density and neutron porosity log also indicates that the layer is a hydrocarbon prospect zone. 3.3. sensitivity analysis in the sensitivity analysis in the research, a cross-plot between the p-impedance and log porosity (phit) logs is used with a color scale of values in the form of a gamma ray log. this is done to see the sensitivity of these parameters in separating shale and sand lithology. in this research, sensitivity analysis is divided into two zones, namely the zone marked in yellow is identified as sandstone lithology or sandstone while the zone marked in blue is identified as shale lithology. based on the results of cross plots on each well it can be seen that the separation of lithologybetween sandstone (sandstone) and shale is considered sensitive because it can separate the boundary between sand and shale contained in the reservoir zone. lithology of sandstone or sandstone is indicated by an acoustic impedance value of 27.500 ft/s* /cc to 50.000 ft/s*g/cc where this is also indicated by a low gamma ray log value and a low porosity value caused by the study area consisting the reservoir with lithology in the form of tight sand. meanwhile, shale lithology is indicated by acoustic impedance values of 17.000 ft/s*g/cc to 25.000 ft/s*g/cc where this is also indicated by high gamma ray log values and relatively high porosity values as well. 3.3. time structure map time structure map making is done to see trends in the research area which will be used in making trend models or trend modeling in the stochastic inversion process. time structure map is obtained from the results of picking top reservoir and base reservoir so that it produces a map of the depth of the reservoir zone in the time domain. based on the results of the time structure map on the top reservoir and base reservoir, it is known that the area marked in red has shallow depth or the highest elevation area. meanwhile, the blue area has a fairly deep depth. on the structure map the top reservoir time is known to have a dominant time range of 1100 ms to -2100 ms. meanwhile, the base reservoir time structure map is known to have a range of -1200 ms to -2100 ms. from the two time structure maps above, it can be identified that the location of the four wells ison the anticline peak and it can be identified that the hydrocarbons in the study area migrated from the southeast to the northwest. this is indicated by the contour that represents the lowlands in the southeast and contours that represent the height in the northwest. fig 6. time structure map top reservoir fig 7. time structure map base reservoir 3.4. upscaling based on the results of acoustic impedance log scale up that has been done on ar-1 wells, ar-2 wells, ar-3 wells, and ar 22 wibowo, r.c., et al./ jgeet vol 5 no 1/2020 4 wells it is known thatthere are similarities from the acoustic impedance log data with the acoustic impedance log data that has been done upscaling. this is evident from the results of the histogram that shows similarities to each other so that it can be said that the upscaling process is correct. the acoustic impedance scale up log process is useful to assist in spreading the acoustic impedance values during a stochastic inversion process. fig 8. histogram analysis scale up the acoustic impedance log 3.5. trend modeling making trend modeling is done by using input in the form of acoustic impedance scale up log data and time structure map. the making of this trend model is done to describe the spatial distribution based on the value of the acoustic impedance scale up log with the trend direction based on the time structure map. the results of the modeling trend are shown in figure 9. fig 9. trend modeling based on the results of the trend modeling conducted, it is known that the acoustic impedance value in the study area has a range of values of 10,000 ft / s * g / cc to 50,000 ft / s * g / cc where the high acoustic impedance values are marked with red to green in around the ar-3 well and ar-4 well area, while the low acoustic impedance values are marked in purple to blue around the ar-1 well and ar-2 well area. 3.6. stochastic inversion in this study, stochastic inversion was carried out using the bayesian method approach with a total of 20. meanwhile, the variogram used was the cubic model. in doing this stochastic inversion seismic method is done by using input in the form of acoustic impedance scale up log data and trend models. the results of this stochastic inversion are in figure 10. based on the acoustic impedance distribution map using stochastic seismic inversion it is known that the area marked in red is an area that has a high acoustic impedance value with a range of values of 30,000 ft / s * g / cc to 40,000 ft / s * g / cc and is identified as reservoir with lithology in the form of tight sand saturated with hydrocarbons in the form of gas which is also supported by the results of interpretation of data wells that have been carried out in the previous process on ar-1 wells, ar-3 wells, and ar-4 wells that are identified as having a gaseous hydridarbon content. fig10. map of acoustic impedance acoustic impedance distribution fig11. cross-section of stochastic seismic inversion results 3.7. depth structure map depth structure map is obtained from the conversion of time structure map into depth domain. in doing time to depth conversion the stacking velocity method is used which is a method that can convert from time domain to depth domain using the speed model. making this depth structure map is very important because there are differences between the two domains that can cause ambiguity when interpreted where in fact conditions are domain depth, but seismic data has a time domain (twt). wibowo, r.c., et al./ jgeet vol 5 no 1/2020 23 fig 12. depth structure map top reservoir fig13. depth structure map base reservoir fig14. 3d map of the structure of the top reservoir depth based on the map of the depth structure of the top reservoir and base reservoir it is known that the prospect area of the four wells is identified to be in the height area in the southeast where it has a depth of 4000 ft to 4500 ft. in the prospect area there are two areas of height in the form of anticline which are in the southeast and northwest. this structure was formed because there is a fault that separates the two height areas. in the research area, there are three main faults namely faults that are southwest-northeast, faults that are east-west, and faults that are southeast-northwest where these three faults are identified as normal faults or normal faults. these faults can act as structural traps where hydrocarbons will migrate and are trapped in these structural traps so that hydrocarbons can accumulate in them. 3.8. isopach map isopach map making is done to describe the thickness of the reservoir layer where this map is made by subtracting the depth of the top reservoir from the base reservoir. based on the isopatch map that has been made it is known that in ar-1 wells, ar-3 wells, and ar-4 wells have a thick reservoir layer which is around 300 ft to 450 ft. meanwhile, the ar-2 well has a thinner reservoir layer which is around 210 ft. on the isopach map found in figure 14 it can be said that there was a depletion of the reservoir from the southeast to the northwest. fig 15. isopach map 4. conclusion this study showed that the bayesian stochastic inversion can produce better results than the deterministic inversion. because of the smoothness and average, the deterministic inversion was unsuitable for constraining reservoir models when this model was used for volumetric calculations, estimation of connectivity, and individualization of sand bodies or fluid flow simulation based on the results, it is known that the hydrocarbon prospect zone has a high acoustic impedance value ranging from 30,000 ft/s * g/cc to 40,000 ft/s * g/cc which is at a depth of 4,000 ft to 4,500 ft. this is due to the reservoir of the study area which is dominated by tight sandstone lithology which contains gas and has a low porosity value. 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18 1070–7. webster, r., dan oliver, m.a. 2007. geostatistics for environmental scientiests second edition. john wiley & sons ltd. inggris. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 sofwan, m., et al./ jgeet vol 5 no 3/2020 155 research article evaluation study of walkability index in central business district (cbd) area, pekanbaru city, indonesia muhammad sofwan 1,*, mira hafizhah tanjung1 1department urban and regional planning, faculty of engineering, universitas islam riau, pekanbaru, indonesia. * corresponding author : muhammad.sofwan@eng.uir.ac.id tel.: +62-812-2007-0060 received: dec 12, 2019; accepted: august 31, 2020. doi: 10.25299/jgeet.2020.5.3.4181 abstract walkable cities emphasize cities with high walkability values, where walkability can be defined as the degree to which the environment can be pedestrian friendly. walkable city is considered to be able to increase people's desire to walk so that it can make the environment more humanistic and can also help realize one of the objectives of sustainable transportation. the value of walkability can be viewed from the perspective of the urban form (macro level) of an area. the central business district (cbd) pekanbaru city walkability i ndex assessment uses the wai ipen project model that measures the form of the urban form. the walkability assessment process in the pekanbaru kota sub-district area (cbd) divides the study area into 6 grids. the analysis shows that there are 4 grids that have a negative walkability value. in the analysis of the walkability value pattern it can be seen that the area dominated by office activities has a lower walkability value compared to the area that has mixed land use. keywords: walkable city, cbd, wai ipen project 1. introduction a walkable city is a city planning concept supported by transportation planning that enables its citizens to walk in their daily activities. the concept of walkable city emphasizes cities that have high walkability where walkability is defined as the level of an area within walking distance of a building to its destination (pivo and fisher, 2011). walkability can be viewed from various perspectives such as in terms of urban design, transportation and urban form which are viewed from a more macro and close to the spatial layout. based on a survey conducted by urban mobility for indonesia, 12% of people choose to walk rather than using bicycles and traditional environmental transport such as pedicabs or delmans as non-motorized transportation when traveling (patsinai, 2013). related to this, the concept of walkability was introduced as one indicator of sustainable city development. by walking, traffic congestion and air pollution generated by motor vehicles can be reduced (forsyth, 2015; forsyth and southworth, 2008). more and more studies, especially from the united states (us) and australia, show that neighbourhoods walkability is an important correlate of physical activities such as walking behaviour, this suggests that creating a more walkable community may be a powerful and costeffective tool for promoting physical activity to population (ribeiro and hoffimann, 2018). previous studies have identified several correlations between neighborhoods development and physical activity, including the walk ability of the residential neighborhoods. walk ability reflects the comfort of the communities built for walking; the level of support based on three main component indexes; road connectivity, residential density, and mixed diversity of land uses. an environment characterized by many interconnected roads, high residential density and different diverse area uses is considered very easy to pass (van holle et al., 2014). geographic information systems (gis) can be used to measure artificial neighborhood features that can affect physical activity objectively. gis data has the potential to be used to build measures of neighborhoods attributes and to develop an index of walking ability for cities, regions, or local communities (leslie et al., 2007). the concept of walkable city emphasizes a city with a high value of walkability, walkability can be defined as the degree to which the environment can be pedestrianfriendly. the concept of walkable city is considered to be able to increase people's desire to walk so that it can make the environment more humanistic and can also help realize one of the objectives of sustainable transportation. the value of walkability can be viewed from the perspective of the urban form of an area. pekanbaru city is currently very intense in building pedestrian paths on several roads, one of them is jalan jenderal sudirman in pekanbaru kota sub-district. this sub-district is included in wp i as the primary center of pekanbaru city with its main function being the service and office trade area. as the primary center of the city, the pekanbaru kota sub-district is a strategic area that has a large economic, social and environmental influence in the local and regional scope. this condition certainly makes the pekanbaru kota sub-district as the central business district (cbd) of pekanbaru city. from the description of the condition of the central business district (cbd) of the city of pekanbaru above it http://journal.uir.ac.id/index.php/jgeet 156 sofwan, m., et al./ jgeet vol 5 no 3/2020 can be concluded that the condition of the pedestrian lane in the district of pekanbaru kota has been very good in terms of physical, but has not had a significant impact in increasing the number of pedestrians engaged in the city cbd pekanbaru. based on the above issues, this study aims to assess the pekanbaru kota sub-district as the central business district (cbd) of pekanbaru city based on the ipen project walkability index as a measure of the level of environmental friendliness of the pekanbaru city cbd towards pedestrians. 2. literature review (moura et al., 2017) defines walkability as a measure of the extent to which an urban environment can be friendly to pedestrians. by measuring it, planning experts might be able to improve the quality of the pedestrian environment, supporting strategies and interventions related to walking that are more objective, effective, and comprehensive.there are many different ways to consider "walkability." for example, in many developed countries, walkability discussions focus on encouraging modal shifts from motorized vehicles to non-motorized vehicles for short trips or promoting walking as a healthy recreational activity. in developing cities, walking is often considered in terms of providing mobility for the most impoverished population. some urban planners tend to think of walkability in terms of urban spatial planning, preferring to use mixed zones rather than separate land uses (krambeck and shah, 2006).(leslie et al., 2007) define walkability as '' the extent to which the characteristics of the built environment and land use are conducive for residents to walk either for recreation, sports or recreation, to access services, or to travel to work. walkability is a composite measure of four neighborhood attributes measured objectively: occupancy density, road connectivity, mixed land use, and net retail area ratio. several studies have found this environmental attribute to be consistently associated with walking behavior (owen et al., 2004; saelens et al., 2003). the walkability index was developed in the 2000s. the walkability index combines the main built environment features that encourage walking behavior such as road network connectivity, mixed land use, and residential density (ribeiro and hoffimann, 2018). (jun and hur, 2015) found some literature showing that physical environmental factors can be a tool to improve the social environment. these physical environment characteristics encourage more pedestrians to engage in activities on the road, present more opportunities for informal contact, and promote social cohesion as naturally. (lund, 2002) found that residents in traditional environments have a greater sense of community and are more likely to walk in their environment than people in modern suburban environments. (owens, 1993) argues that inadequate population density and mix-use settings allow people to walk more. some researchers also investigated the factors that classify each block group having "high" or "low" walk ability. the measured walk ability components include net occupancy density, junction density, land use mix, and retail floor area ratio (carlson et al., 2015; frank et al., 2010; saelens et al., 2012). many studies have identified differences in the types of walking and how the built neighborhood influences them: walking for transportation is related to neighborhood design, whereas recreational walking has not been proven to be influenced by neighborhood design (rodríguez et al., 2006). 3. methodology the development of the concept of walkability based on the ipen project in this study uses a combination of methods or mixed methods, where quantitative methods are carried out in the systematic calculation of urban form conditions, while qualitative methods are used in assessing the walkability of an area subjectively. this method is considered to be able to explain and describe the process and results to be achieved. from this conceptual framework, methodological indicators for evaluating walkability through gis-based and examining the road network are presented. it was applied to an area in lisbon, portugal, to assess the ease or difficulty that can be faced by various types of pedestrians in their walking activities and, potentially get information for intervention and improvement (moura et al., 2017). 3.1. walkability index the walkability index is obtained by adding up a partial index consisting of connectivity index, entropy index, far index, and household density index. all partial indices are calculated for each sub-district within an urban area to measure the comfort level of an urban environment in facilitating pedestrians. the walkability index uses the following formula (dobesova and krivk, 2012): wai=(2*con)+ent+far+hdens explanation : wai = walkability index con = connectivity index ent = entropy index far = floor area ratio (far) index hdens = households density index the value generated from the walkability index must indicate the physical activity of people in a certain area. an index value higher than the walkability index indicates that there is a greater likelihood that people will do more physical activity. 3.2. connectivity index the first partial index which is the input for the resulting walkability index is the connectivity index. connectivity is also called intersection density, which is calculated from the number of intersections per square kilometer of urban units. digital data input is a line of road geometry in a city. road crossing data obtained from aerial photographs that are still relevant to use in the past 5 years or satellite imagery in the latest year will be made into a road network map. while the highway is excluded from the input data because it is not suitable to be passed. in addition, the area of water bodies and rivers is reduced from the area of the city unit. calculating the index, each intersection is given a valence value. this value represents the number of roads that meet at a certain intersection. the "t" shaped crossroad has a valence value of three, an "x" shaped four. then, any crossroads that are too close, which means closer than 15 m, are combined and treated as one crossing. this intersection is then given a higher valence. knowing the connectivity index is calculated using a formula derived from (dobesova and krivk, 2012). 𝑐𝑜𝑛 = 𝛴 𝐶𝑟𝑜𝑠𝑠𝑟𝑜𝑎𝑑𝑠 1 𝑘𝑚2 sofwan, m., et al./ jgeet vol 5 no 3/2020 157 explanation : con = connectivity index 3.3. entropy index the entropy index shows how homogeneous or heterogeneous usage in a certain area. the higher the diversity of land uses, the higher the entropy index. the key to calculating the entropy index is high-quality land use polygon layers. types of land use in the entropy index assessment are divided into eight basic categories. table 1. basic categories of land use types category name mark living l commercial c services s industrial i institutional t recreational r other o water w 𝐻(𝑆) = −σ𝑖=1 𝑘 (𝑃𝑖 ). (𝑙𝑛𝑃𝑡) ln 𝑘 explanation : h(s) = entropy index pi = area ratio for each land use category to the total area of all categories k = number of existing land use categories 3.4. far (floor area ratio) index the far index represents the ratio of shop building area to all areas of land use categories that are commercially labeled. it is estimated that a high index indicates that the place has a significant percentage of smaller retail stores. such an area would certainly be more interesting to walk than others. when the far index has a low value, there may be more shops and shopping centers with large parking lots. therefore, it's easier to use the car to shop. to calculate floor area ratio (far) using a formula derived (dobesova and krivk, 2012). 𝐹𝐴𝑅 = ∑ 𝑇ℎ𝑒 𝑡𝑜𝑡𝑎𝑙 𝑓𝑙𝑜𝑜𝑟 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑟𝑒𝑡𝑎𝑖𝑙 𝑠𝑡𝑜𝑟𝑒𝑠 ∑ 𝑇ℎ𝑒 𝑡𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑐𝑜𝑚𝑚𝑒𝑟𝑐𝑖𝑎𝑙 𝑎𝑟𝑒𝑎 3.5. households density index in calculating the density of settlements, it is necessary to have information about each unit of the number of households in the city. the number of households is divided by the area designated for the urban settlement function. the data needed in the calculation of the household density index is the total area of the type of land use that is marked with l (living) and the total floor area of a house in an urban area. index values reflect life forms in urban areas. high values represent the high density of households. to calculate the settlement population index using the sourced formula (dobesova and krivk, 2012): ℎ𝑑𝑒𝑛 = ∑ 𝐹𝑙𝑜𝑜𝑟 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 ℎ𝑜𝑢𝑠𝑒 𝑏𝑢𝑖𝑙𝑑𝑖𝑛𝑔 ∑ 𝑆𝑖𝑧𝑒 𝑜𝑓 𝑟𝑒𝑠𝑖𝑑𝑒𝑛𝑡𝑖𝑎𝑙 𝑎𝑟𝑒𝑎 explanation : l (meter) : the total area of residential floor on one grid in meters l (acre) : the total area of residential floor on one grid in an acre la devider (constant) : the number of residential building blocks that exist on one grid hdens : h-dens index value (not standardized) average : the average value of the h-dens index (required in calculating the standard value of the h-dens index) 4. data and variables this study uses various data sources that can be divided into two types, namely primary data and secondary data that are qualitative and quantitative. there are several methods used in primary data collection, including the process of determining the characteristics of the problem, the data used is image data / aerial photographs taken using drones and after that the process of observing the interpretation of the results of the image / aerial photograph by correcting the results of interpretation in the field directly. other object data collection is done by observing and documenting pedestrian facilities, crossing roads, homogeneity of land use, activity functions on the ground floor and upper floors of each building. table 2. data and variable variable data connectivity number of intersections entropy types of land use area of each land use the lower zone land use per parcel land use upper zone per parcel characteristics of activities map of area blocks population density far (floor area ratio) shop building area extensive trading area building height (number of floors) households density building area of the house extensive residential area table 3. con value (z-value) grid junction count crossing count junction constant crossing constant junction score crossing score crossin & junction score con (z value) 1 30 13 3 4 90 52 142 -2,041483 2 47 14 3 4 141 56 197 6,941042 3 60 3 3 4 180 12 192 6,124449 4 35 6 3 4 105 24 129 -4,164625 5 36 10 3 4 108 40 148 -1,061571 6 37 2 3 4 111 8 119 -5,797812 total 927 average score 155 standard deviation 6,123 158 sofwan, m., et al./ jgeet vol 5 no 3/2020 5. discussion in theory, walkability has many concepts. in general, there are three approaches to walkability, namely from the transportation side, the urban design side and the urban form side. improved quality of walkability from all three sides of this approach greatly affects the walking behavior of urban communities. in this study assessing walkability from the urban form side. the urban form itself consists of variable housing density, diversity, land use, and environmental road patterns. the walkability approach is taken looks at the macro scale compared to the other two approaches. this approach is considered the most suitable way to get into spatial planning because it emphasizes land use that affects people's walking desires. from the urban form approach, the concept of walkability used in this study is the ipen project concept. this concept has four parameters in calculating the walkability index (value of walkability), namely the diversity of proportional area activities (entropy index), regional connectivity (connectivity index), the ratio of the floor area of commercial activities (far index), and occupancy density (h-dens). these four parameters are derived from three urban form variables. an area has a high walkability value when all four parameters are positive/high. 5.1. connectivity index analysis the connectivity index shows the number of intersections in the research area. the number of intersections is believed to make the area more connected. the ipen project states that the intersection in environmental blocks will make it easier for pedestrians to reach their destination because the intersection provides a more direct path to the destination (not circling). grids that have good accessibility are grid 2 (area around ahmad yani street with jalan hidayat street), grid 5 (area around an-nur great mosque), and grid 6 (the area around jalan diponegoro). in addition, there is also a positive value grid but because the result is close to 0 like grid 1 which can be said to be a normal accessibility condition. while grid 2 and negative value and can be interpreted that the number of intersections is small so that accessibility is low(table 3) (fig. 1). 5.2. entropy index analysis entropy index is a measure of the level of diversity of land use/function in the study area. the more diverse and equitable the function/land use of an area, the higher the level of walkability. areas that have high diversity are believed to have many destinations that can be chosen by residents. pedestrians will be more interested in walking in an environment that has many variantsof activity than those who have uniform uses because there is a lot they can do and further increase their reasons for walking. from the calculation results (table 4), it can be seen that the grid that has a high entropy index value is on grid 6, grid 5, and grid 4 (sorted by rank). meanwhile, the grid that has a low entropy index value is grid 1, grid 3, and grid 2. if further observed, the grid that has a high entropy index. table 4. h (s) region grid value grid h(s) z-score h(s) 1 0,374 -1,407 2 0,513 -0,643 3 0,497 -0,731 4 0,76 0,714 5 0,779 0,819 6 0,856 1,242 average 0.63 standard deviation 0.182 fig1. map of road network sofwan, m., et al./ jgeet vol 5 no 3/2020 159 fig 2. map of entropy index grid 1 fig 3. map of entropy index grid 2 fig 4. map of entropy index grid 3 fig 5. map of entropy index grid 4 fig 6. map of entropy index grid 5 fig 7. map of entropy index grid 6 160 sofwan, m., et al./ jgeet vol 5 no 3/2020 fig 8. legend of map entropy index grid 1, 2, 3, 4, 5, & 6. value is a grid that has a ratio of unequal land-use floor area. on-grid 6 (the area around jalan diponegoro) there are up to 6 types ofbuilding/use functions, where each type of function has an area that contrasts with the area measured. for grids that have the lowest entropy index values such as grid 1 (the area around jl. hos. cokroaminoto) is dominated by housing and trade uses. and also grid 3 (the area around bank riau kepri) is dominated by office and service activities. as well as grid 2 (the area around jalanahmad yani with jalan hidayat jalan jalan) whichis only dominated by the functions of trading 5.3. far analysis the existence of commercial areas is one of the important factors in encouraging people to walk. the commercial is a land use that has a high attractiveness because it offers many activities. the higher the value of the far index, the more diversity of commercial activities contained in the grid so that the more encouraging people to come to the place. conversely, the lower the diversity of the functions of commercial activities are spread in the grid and do not encourage people to walk in the region. from the results of calculations (table 5), half of all grids do not have high far values such as grids 3, 5, and 6. these grids show that the far value is still low to make the area have a good level of walkability. while the other half contained in grid 1 (the area around jl. hos. cokroaminoto), grid 2 (the area around jalan ahmad yani with jalan hidayat) and grid 4. the three grids do have a high variant of commercial activity, where this place is located tall buildings and have a wide variety of activities. grid 1 and grid 4 are the grids that have the most extensive commercial floor area compared to other grids. this grid also has a very high commercial density that allows people to carry out diverse activities in the region. grid 1, grid 4 and grid 2 are passed by jalan sudirman which is the main road in pekanbaru city. grid 1 and grid 2 are ramayana shops which are dense areas and vary in their commercial activities. in this research area, there is a grid that has the largest concentration of commercial activities, which is indicated by the presence of city-scale shopping centers. table 5. region grid far index value grid c sum c far far(z-score) 1 112.434 350.819 0,32 1,5 2 89.128 350.819 0,254 0,853 3 35.224 350.819 0,1 -0,657 4 95.721 350.819 0,273 1,04 5 10.324 350.819 0,029 -1,353 6 7.988 350.819 0,023 -1,412 average 0,167 standard deviation 0,102 fig 9. map floor area ratio (far) source sofwan, m., et al./ jgeet vol 5 no 3/2020 161 5.4. analysis of household density index the housing density is another important factor affecting the high level of the pedestrian in a city. the housing density is needed to provide the users needed to support transit, recreational and other facilities. these facilities tend to gather in densely populated areas. the lower the density of the house, the more distant facilities the communityneeds, so that the community will move far from its housing. the higher the density of housing the more dense housing units that have an impact on the high number of pedestrians and vice versa when the lower the density of housing the lower the number of pedestrians in the area. the results of the h-dens calculation show that not all grids have a good density to make the area pedestrianfriendly. grid 3, grid 4, grid 2 and grid 5 (in the highest order) have good housing density to encourage people to walk. while grid 1 and grid 6 have low h-dens index values and indicate the area is not pedestrian-friendly. grid 3, grid 4, grid 2, and grid 5 areas have high settlement densities and have many building blocks. while grid 1 and grid 6 are densely populated areas, the grid is dominated by trade and service activities. even along jalan sudirman, there is a dominance of office and service activities, especially on grid 6. table 6. district hdens grid value grid l (meter square) hdens (z-score) 1 76385 0,0736 2 200.579 0,1935 3 245.176 0,2365 4 231.115 0,223 5 189.653 0,183 6 93.765 0,09 average 1,1666 fig 10. housing density map 5.5. pekanbaru city cbd walkability index each parameter in the grid is added based on the data obtained in the previous calculation. from the results obtained for each index, the variable is very diverse, there is no one grid there is a positive value on each variable. the calculation of the pekanbaru kota sub-district walkability index which is divided into grids is as follows: (table.7) table 7. value of walkability index grid of cbd area in pekanbaru city grid z-con 2 x z-con z-ent z-far z-hdens walkability index 1 -2,041483 -4,082966 -1,407 1,5 0,0736 -3,916 2 6,941042 13,882084 -0,643 0,853 0,1935 14,286 3 6,124449 12,248898 -0,731 -0,657 0,2365 11,097 4 -4,164625 -8,32925 0,714 1,04 0,223 -6,352 5 -1,061571 -2,123142 0,819 -1,353 0,183 -2,474 6 -5,797812 -11,595624 1,242 -1,412 0,09 -11,675 162 sofwan, m., et al./ jgeet vol 5 no 3/2020 calculation results from the walkability index show that grid 2 (the area around ahmad yani street with jalan hidayat section) has the highest walkability index and then the highest value is also on grid 3 (the area around bank riau kepri). while grid 6 (the area around jalan diponegoro) has the lowest walkability index value of the six grids. of all the grids, there are four grids that have a negative walkability index value, namely grid 1, grid 4, grid 5 and grid 6. the negative value indicates an area that has a poor walkability value. the walkability index value in pekanbaru kota subdistrict has mixed results. the walkability index value in the cbd area of pekanbaru city which is not so high and there are still many negative value grids can be the basis for making conclusions that the level of walkability in general in pekanbaru kota sub-district is still relatively low. the area around ahmad yani street with the prince hidayat street (grid 2) has the highest walkability index value of all objects of the research area with an index value of 14,286. in this area, there are high trading and service activities, especially the ramayana shopping area which is used as a place to sell a variety of goods and basic needs of the community. the area has a high intensity of community movement. however, this value cannot be considered high enough to fully encourage the community to walk in the area. in fact the parameter that has a high value in the region is because the area has a good level of connectivity (connectivity index) and the number of commercial activities (far index), meanwhile, the value of other parameters such as regional diversity (entropy index) and housing density (hdens) has a negative value. as well as the area around other grids which has an unbalanced walkability index value among its parameters, some grids excel at the connectivity level but are low in the far index parameters and vice versa. to achieve a good walkability indexvalue, it is necessary to increase each of the parameters that make up the walkability. further analysis shows the pattern of walkability index values where areas that are dominated by office activities and services such as grid 1, grid 4, grid 5, and grid 6 have low walkability values. meanwhile, areas that are more mixed-use have higher walkability index such as grid 2 and grid 3. from the results of data processing shows areas that have high walkability values, tend to have a comparison of diverse activities such as housing, commercial, and the number of intersections, and many buildings with mixeduse functions are found. this pattern is not much found in areas that are not dominated by trade or housing activities. thus resulting in a low value of walkability, especially in areas that tend to be homogeneous activities. 5.6. evaluation of the walkability concept in the pekanbaru city sub-district area the ipen project walkability concept is a concept for assessing the walkability index of an area from the perspective of an urban form. the urban form perspective consists of three variables: population density, road network patterns, and land-use diversity. this theory emphasizes that the walkability of an area depends on land use and accessibility within the region. ipen project as a derivative concept from the urban form perspective evaluates the walkability of the number of intersections, proportional land use, commercial floor area population, and housing density. the findings of several studies indicate that the walkability index is highly correlated with walking trips for most non-work travel destinations, although sociodemographic characteristics also play a key role. in addition, households with more mobility choices are more sensitive to their environment than households with fewer mobility choices. this finding highlights the fact that the walkability index will not have the same correlation with travel behavior for all individuals or households (manaugh and el-geneidy, 2011). this concept has a tendency to prioritize the use of commercial and residential land compared to other land uses. in the theory of urban form, the intended land use is a variety of land uses without inclining to certain activities. pekanbaru kota subdistrict has a very diverse designation of areas such as commercial, offices, housing, government agencies, and other activities. the results of the assessment can be illustrated by the walkability index value of the cbd area of pekanbaru city which has different values in each region/grid. in general, the value of the walkability index in the pekanbaru city subdistrict has a negative average value, which means the environmental conditions of the pekanbaru city cbd area are still not friendly to pedestrians. this is indicated by the existence of four grids out of the six existing grids which have negative values. this condition allows for improvements related to some parameters that have a bad value. from some previous studies, there is a positive and stratified relationship between environmental walkability and the desire to walk. residents in more walkable environments present a higher percentage chance of walking in transportation compared to those who live in less walkable areas (ribeiro and hoffimann, 2018). the addition of commercial floor area is an action that is still possible, it does not significantly make the area walkable. but it is necessary to redesign the road network to improve the walkability index ideally. improving quality is difficult to do in areas that have been physically formed. although to improve walkability from the urban form side it is very difficult to implement. but it can still be done to improve the quality of the environment that is friendly to pedestrians in pekanbaru kota sub-district with development from another perspective, namely from the aspect of urban design (physical quality of the environment) or transportation (relations with other modes of transportation). 6. conclusion the walkability index value of pekanbaru kota subdistrict measured by using the wai ipen project model produces a variety of patterns of values based on the parameters measured. the area is divided into research which is divided into 6 grids to facilitate research in measuring the variables to be assessed. the results of the analysis show that grid 1, grid 4, grid 5, and grid 6 have negative walkability index values, whereas there are two regions that have positive results, namely grid 2 and grid 3. in the analysis of the walkability value patterns, it is seen that the area is dominated by agency activities/offices that have lower walkability values compared to dense residential areas with mixed-use patterns. besides that walkability throughout the research area is not so prominent. even so, the value of the walkability index in the study area still does not describe a friendly environment for pedestrians, so it is necessary to improve some forms of urban space in order to achieve the concept of a walkable city in the central business district (cbd) of pekanbaru city. acknowledgements sofwan, m., et al./ jgeet vol 5 no 3/2020 163 thank you to the survey team who helped the researchers in collecting data and to kemenristek dikti researchers also expressed their gratitude for the funding of this research. references carlson, j.a., saelens, b.e., kerr, j., schipperijn, j., conway, t.l., frank, l.d., chapman, j.e., glanz, k., cain, k.l., sallis, j.f., 2015. association between 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assessment method: a case study in lisbon. landsc. urban plan. 157, 282–296. https://doi.org/10.1016/j.landurbplan.2016.07.002 owen, n., humpel, n., leslie, e., bauman, a., sallis, j.f., 2004. understanding environmental influences on walking: review and research agenda. am. j. prev. med. 27, 67–76. https://doi.org/10.1016/j.amepre.2004.03.006 owens, p.m., 1993. neighborhood form and pedestrian life: taking a closer look. landsc. urban plan. 26, 115– 135. https://doi.org/10.1016/01692046(93)90011-2 pivo, g., fisher, j.d., 2011. the walkability premium in commercial real estate investments. real estate econ. 39, 185–219. https://doi.org/10.1111/j.15406229.2010.00296.x ribeiro, a.i., hoffimann, e., 2018. development of a neighbourhood walkability index for porto metropolitan area. how strongly is walkability associated with walking for transport? int. j. environ. res. public health 15. https://doi.org/10.3390/ijerph15122767 rodríguez, d.a., khattak, a.j., evenson, k.r., 2006. can new urbanism encourage physical activity? comparing a new urbanist neighborhood with conventional suburbs. j. am. plan. assoc. 72, 43–54. https://doi.org/10.1080/01944360608976723 saelens, b.e., sallis, j.f., black, j.b., chen, d., 2003. neighborhood-based differences in physical activity: an environment scale evaluation. am. j. public health 93, 1552–1558. saelens, b.e., sallis, j.f., frank, l.d., cain, k.l., conway, t.l., chapman, j.e., slymen, d.j., kerr, j., 2012. neighborhood environment and psychosocial correlates of adults’ physical activity. med. sci. sports exerc. 44, 637–646. https://doi.org/10.1249/mss.0b013e318237fe18 van holle, v., van cauwenberg, j., van dyck, d., deforche, b., van de weghe, n., de bourdeaudhuij, i., 2014. relationship between neighborhood walkability and older adults’ physical activity: results from the belgian environmental physical activity study in seniors (bepas seniors). int. j. behav. nutr. phys. act. 11, 1–9. https://doi.org/10.1186/s12966-014-01103 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 164 tonggiroh. a, / jgeet vol 5 no 4/2020 research article stream sediment geochemical survey on metamorphic rock, kolaka, southeast sulawesi, indonesia. adi tonggiroh department of geological engineering, hasanuddin university, gowa, south sulawesi, indonesia. * corresponding author :atonggiroh@gmail.com tel.:+81288269962 received: august 7, 2020; accepted: sept 10, 2020. doi: 10.25299/jgeet.2020.5.4.5433 abstract the aim of this research is to conduct surface geological mapping to determine the lithology that underlies the linear geochemical characteristics of ag, as, cd, co,cu, fe, mn, ni, pb, zn by using stream sediment data. furthermore, to know the distribution of these elements lithologically in the area. this study uses 10 sediment stream samples of 80 mesh up to 100 mesh which then chemical elements are analyzed with aas. alteration mineralization occcurs in quartz chlorite geneiss: quartz, epidote, chlorite, muscovite, sericite, calcite, monmorillonite, pyrite, sphalerite, bornite and chalcopyrite. based on linearity analysis elements are grouped into three according to the significant value of 0.3 to 0.9, which are significant elements ni, pb=cu=zn and as, abundant elements in lateralization and sulphide mineralization. the geochemical characteristics of the ni element reflect the associated distribution of ultramafic weathering which results are transported regionally and together with other elements as stream sediments. while pb, cu, zn are related to quartz veins in metamorphic or intrusive rocks. keywords: stream sediment, metamorphic rocks, kolaka. 1. introduction sediment stream is an exploratory geochemical method that may probability the source of heavy metals. stream sediments is one of geochemical technique used in this research, this method is widely used for various applications (rollinson, 2014). included as a conventional method is not efficient in determining a mineral deposit hidden deep beneath various types of covering layers (yilmaz et al., 2015) wich the layer begins with weathering of mineralized rocks and soil which then enters streams to form sediment, it is often difficult to determine the source of mineralization. such problems are typical of geochemical patterns (fletcehr, 1990, 2005). inefficiency of geochemical stream sediment method is due to the difficulty in determining mineral deposits that are hidden far below various types of bed layers. the difficulty in analyzing stream sediment data are based entily on variations in data sources that are unevenly distributed (farahbakhsha et al.,2019). various type, shapes and sizes of mineral grains can come from the river walls, headwaters or mineralization that is exposed far from rivers. however, its efficiency lies in the location of sampling point along river pattern. according to regional geology, the upstream of ulunggolaka river is located in the northern part of kolaka regency (not part of the study area) and flows over the metamorphic belt (pompangeo complex) predominantly composed of interbanded phyllitic marble, calcareous phyllite, graphitic schist and quartzite (parkinson, 1988) and ultramafic and metamorphic complex. pompangeo complex contains gold in quartz veins (mawaleda et al.,2017) which strongly indicate to have weathered, transported and settled as gold placer. strong indications of the placer gold deposits are results of surface processes and their formation in relation to the regional geomorphological evolution. many placer gold models (herail et al., 1989). the application of the geochemical sedimentary stream method around the ulunggolaka river is based on the terrigenous sediment texture which is controlled by transportation, the morphology of the temporary depositional environment and its mineralogical composition. the main goal of this study (1) geological surface mapping to determine the lithology that underlies the basic aim (2) to determine the linear geochemical characteristics of ag, as, cd, co, cu, fe, mn, ni, pb, zn by using stream sediment data. this study uses a statistical analysis approach to determine the environmental distribution of elements in which elements in heavy minerals can decompose and settle in stream sediments, so that interpreted geochemical data with statistics becomes more effective (ali et al., 2006) so the result of the elemental distribution can correlates to primary deposition. 2. location and accessibility the study area consists of mountaineous morphology composed of well-exposed schist and limestone unit. the study area covers about 4 km2 which is connected by brick roads from latambaga, kolaka regency, southeast sulawesi province and footpaths leading to the ulunggolaka river (figure 1). 3. regional geological setting research areas is situated at east sulawesi tectonic province which are characterized by ophiolite and metamorphic rocks (sukamto, 1982) and comes under geological map lasusua-kendari sheet (rusmana et al., 1993). it consists of the mekongga metamorphic complex (pzm), intrusive rocks (ptr (g)), tokala formation (trjt), ultramafic complex (ku), and alluvial (qa). intrusion rocks consist of aplite quartz, andesite, quartz latite (rusmana et al., 1993) and dacite (white et al, http://journal.uir.ac.id/index.php/jgeet tonggiroh. a, / jgeet vol 5 no 4/2020 165 2014) that intruded the metamorphic paleozoic rocks which are estimated to be of the perem age. fig 1. map of research area the distribution of metamorphic, limestone (figure 2) and ultramafic rocks is bordered by the kolaka sinistral shear fault which generally runs in the northwest-southeast direction which also contains dacite intrusion (white et al., 2014). the distribution of metamorphic, limestone (figure 2) and ultramafic rocks is bordered by the kolaka sinistral shear faut which generally runs in the northwest-southeast direction which also contains dacite intrusion (white et al., 2014). fig 2. (a) limestone outcrop (b) schist outcrop and oxydation. 4. methodology samples are taken from the composite river sediment layer at the top to the bottom, where the top is dominated by finesized fraction while the bottom is of coarse-sized fractions dominance. randomly the distance of the sample point takes into account the conditions of the river bed, topography and lithology, therefore at the sampling pont it is necessary to ensure that sufficiently sized fractions are available. if the river bed is dominated by coarse fractions, 80 mesh to 200 mesh sieves are required. a total of 10 samples were taken from stream sediments with metamorphic rocks dominance (ul 01, ul02, ul03, ul 04, ul05, ul06, ul07, ul08, ul09, ul10) at different geographical coordinates (figure 3). application of statistical linearity analysis to identify domains of the geochemical similarity and map the analyzed results to visualize the relationship between geochemical elements, mineralization and lithology at the study area. overall analysis of stream sediment composition data is used to obtain the amount of elements and its geochemical properties upon metamorphic rock domains. fig 3. geological map and coordinates of example of streams sediment. each sample is placed in a polyethylene bag to be dried by an oven at a temperature of 100oc (approximately 1 hour) then smoothed with a preparation machine at the laboratory of sedimentology dept of geological engineering. hasanuddin university. furthermore, each sample is divided into 2 bags, namely: one bag for grain size analysis and for chemical composition analysis with atomic absorption spectrometry (aas) including: ag, as, cd, co, cu, fe, mn, ni, pb, zn. 4 samples are taken from rock outcrops (2 samples at station ul01, ul08 and 2 samples at ul05, ul07) and then is prepared into a polish section to determine the texture of the metal minerals. and one thin section from metamorphic outcrop with a size of <0.03 mm for petrographic analysis. 5. results and discussions consentration of as, cd, co,cu, fe, mn, ni, pb, zn considering topographic factors, lithology, alteration mineralization, sediment grains and drainage patterns. 5.1 topography, drainage system and geological structure 166 tonggiroh. a, / jgeet vol 5 no 4/2020 the mountaineous topography of the study area is influenced by the regional geological structure namely; shear fault (sinistral fault) which act in northwest-southeast direction (rusmana, et al., 1993). the influence of the sinistral fault structure on the topography forms the denritic drainage pattern of the ulunggolaka river. and cause the exposer of the mineralized metamorphic complexes. identical topographic appearance of metamorphic rocks contacting with other lithology can be observed upstream of the ulunggolaka river, namely east and west (figure 4). fig. 4. (a) topography of ulunggolaka river. 5.2 lithology mapped rock outcrops are dominated by metamorphic rocks consisting of muscovite-quartz schist, quartz-chlorite gneiss, and unmapped outcrops namely limestone, serpentinite, andesite, wackestone. 5.3 mineralisation and alteration mineralization on quartz chlorite geneiss: quartz, epidote, chlorite, muscovite, sericite, calcite, monmorillonite, pyrite mineral, sphalerite, bornite and chalcopyrite. this mineral assemblage are grouped into four, namely: (1) epidote, chlorite, quartz (2) chlorite, muscovite, quartz (3) calcite, sericite, quartz (4) calcite, seirisit, montmorillonite. microscopic observation of the subhedral pyrite texture indicates a step of pyrite replacing sphalerite (figure 5). fig 5. photomicrgraph (a) pyrite (b) chalcopyrite (c) bornite (d) sphalerite. 5.4 characteristics of stream sediment grain the size distribution of sediment material consists o coarse sand to medium sand. these size variations are uneven, coarse sand size (ul01 to ul02), medium size sand (ul03-ul04), coarse to fine size sand (ul05,07,09,10) and sandy clay (ul06,08). this size variation is controlled by morphology, rock resistance to weathering and river currents. 5.5 elements statistic the results of chemical analysis of sediment samples from the study area show cu, zn, ni, pb, as have a fairly high concentration while the elements fe, co, ag have a low concentration. the tendency of positive skewness is low in cu, zn, pb, co and high in fe and as except ni. thus ni and as are elements that are in each group (table 1). table 1. stream sediment elements element detec. lim mean st.d max. min. skew cu 2 ppm 23.2000 7.6129 35.0000 12.0000 0.548 zn 2 ppm 65.3000 5.2926 75.0000 58.0000 0.734 ni 4 ppm 12.4000 3.1340 17.0000 7.0000 -0.22 fe (%) 0.01 2.7370 0.4261 3.6500 2.3000 1.352 pb 4 ppm 23.5000 7.7064 39.0000 13.0000 0.648 as 50 ppm 58.3000 22.1563 120.0000 49.0000 2.928 co 4 ppm 10.0000 1.8257 13.0000 8.0000 0.548 ag 1 ppm 0.0900 0.0000 0.0900 0.0900 5.6 linierity ni, as groups have other elemental variables with the same linearity. to classify variables, linearity analysis is performed on cu, zn, fe, pb, co, agby using ibm spss v.25 software. the following variables are obtained: (1) ni, and co, cu, pb, fe (2) zn, and pb, as, ni, cu (3) as, and cu, zn. the number of variables still requires reduction and with cluster analysis produces two regression groups and squared euclidean distance (sed), that is: 5.6.1. group ni and co cu pb fe ni linearity is very strong for co (y = 2.4x-13.2; sig = 0.318; df = 9.01), but is weak for cu, pb, fe. whereas co have strong linearity with fe (y = 1.333x + 0.5; sig = 0.996; df = 237) and pb have strong linearity with cu (y = 0.833x + 1.67). thus, there are two groups, namely (1) ni = co = fe, the ni component can be considered as an ultramafic content variable and a co controller. where the difference in co geochemical variables is strong with a single component, it is considered a measure of argillaceousness in sediments (kirkwood et al., 2016). (2) cu and pb, showed that the concentration enriched in the sedimentary fraction originating from intrusive rocks. sedimentary fraction originating from intrusive rocks. 5.6.2. group zn and pb as ni cu zn linearity is very strong for cu (regression y = 1.8x + 47; sed sig = 0.524; df = 19.33), pb (y = 3.2x + 8; sig = 0.128; df = 5.59) and as (y = 0.25x + 45; sig = 0.929; df = 19.33). but pb and cu (y = 0.833x + 1.67) showed two independent variables with similar strenght. thus, according to seds on three variables, namely: (1) ni (2) zn = pb = cu (3) as. the similarity of pb = cu is a strong indication of secondary sulfide formation which can also occur with zn, which is the intergrowth texture of the sphalerite. while the nature of as mobility in sediment flow can be tonggiroh. a, / jgeet vol 5 no 4/2020 167 accompanied by pb which is likely to substitute for sulfide. as and cu correlations (r2 = 0.11) support a positive indication that both are located in a hydrothermal deposition system. this reinforces the suspicion that primary sulfide traces are originated from as and pb (figure 6). fig 6. linieritas elements fig 7. elements distribution (a)west (b)east of ulunggolaka 5.7 distribution the variable elements ni, zn, pb, cu, as are used to determine the distribution with the statistical formula: 1 + 3.3 log n, n = the amount of data. obtained five groups of each element and based on the pattern of river straightness and the independent variables are equally strong, there are differences and similarities in anomalies in the western and eastern parts. in the western part, ni is broadly oriented in the northwest and pb, cu, zn is narrowly oriented spot. in the east, ni is broadly oriented to the northeast and pb, cu, zn is narrowly oriented. the general symptoms of ni anomalies indicate regional contact with metamorphic and utramafic rocks in the northern part of the study area. this is reinforced by the distribution of co. the elements pb, cu, zn have the same distribution character except as (figure 7). 6. conclusion surface geological mapping shows the study area being composed of muscovite-quartz schist, quartz-chlorite gneiss metamorphic rocks, where there are outcrops of limestone, serpentinite, andesite, wackestone. in metamorphic outcrops there are pyrite mineralization, sphalerites spread along the veins of quartz. the application of linearity analysis groups three elements according to significant values of 0.3 to 0.9, namely the significant elements of ni, pb = cu = zn and as, the abundant elements in lateralization and mineralization of sulfide. however, as is related to au mineralization (yang and blum, 1999a). the geochemical characteristics of the ni element reflect its association with the distribution of ultramafic weathering which are transported regionally together with other elements as stream sediments. where as pb, cu, zn are related to quartz veins in metamorphic or intrusive. references ali, k., cheng, q., li, w., chen, y., 2006. multi-element analysis of stream sediment geochemistry data for predicting gold deposits in south-central yunnan province, china. geochemistry exploration, environment, analysis 6, 341-348.doi : 10.1144/14677873/06-109 farahbakhsha, e., chandra, r., eslamkish, t., dietmar müllera, r., 2019. modeling geochemical anomalies of stream sediment data through a weighted drainage catchment basin method for detecting porphyry cu-au mineralization. geochemical exploration 204, 12–32. doi : 10.1016/j.gexplo.2019.05.003 fletcher, w.k., 1990. dispersion and behavior of gold in stream sediments, a contribution to the canada/british columbia mineral development agreement. open file, 1990-28. fletcher, w.k., muda, j., 2005. dispersion of gold in stream sediments in the sungai kuli region, sabah, malaysia. geochemistry exploration environment analysis 5(3), 211-214.doi: 10.1144/1467-7873/03-036 hérail, g., fornari, m.,rouhier, m. 1989, geomorphological control of gold distribution and gold particle evolution in glacial and fluvioglacial placers of the ancocala-ananea basin -southeastern andes of peru. geomorphology, 2, 369-383.doi : 10.1016/0169-555x(89)90021-4 kirkwood, c., everett, p., ferreira, a., lister, b.,2016.stream sediment geochemistry as a tool for enhancing geological understanding: an overview of new data from south west england. geochemical exploration 163,2840. doi :10.1016/j.gexplo.2016.01.010 mawaleda, m., suparka, e., chalid, i,a.,basuki, n.i, forster, m., jamal., kaharuddin., 2017. hydrothermal alteration and timing of gold mineralisation in the rumbia complex southeast arm of sulawesi indonesia.iop conference series earth and environmental science 71(1): 012030.doi : 10.1088/1755-1315/71/1/012030. parkinson, c.,1988.an outline of the petrology, structure and age of the pompangeo schist complex of central sulawesi, indonesia, the island arc 7,231-245.doi : 10.1046/j.1440-1738.1998.00171.x. 168 tonggiroh. a, / jgeet vol 5 no 4/2020 rollinson, h.r., 2014. using geochemical data: evaluation, presentation, interpretation. published by routledge. rusmana, e., sukido, sukarna, d., haryono, e., simandjuntak, t.,1993. peta geologi lembar lasusua-kendari, sulawesi skala 1: 250.000. white, l.t.,hall,r.,armstrong, r.a., 2014. the age of undeformeddacite intrusions within the kolaka fault zone se sulawesi indonesia. asian earth sciences 94,105-112. doi : 10.1016/j.jseaes.2014.08.014.13679120. yang, s.x., blum, n., 1999a. a fossil hydrothermal system or a source-bed in the madiyi formation near the xiangxi au-sb-w deposit, nw hunan, pr of china?. chemical geology 155, 151–169. doi : 10.1016/s00092541(98)00146-6 yilmaz, h.h., sonmez, f,n.,carranza, e.j.m.,2015. discovery of au–ag mineralization by stream sediment and soil geochemical exploration in metamorphic terrain in western turkey. geochemical exploration, 158,55–73. doi:10.1016/j.gexplo.2015.07.003 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 erawan, et al./ jgeet vol 5 no 3/2020 129 research article the permeability of granite weathering soil in tanjungpinang, bintan island, indonesia fery erawan 1,2, emi sukiyah3,*, johanes hutabarat3, adjat sudradjat3 1ministry of public works and human settlement, jakarta, indonesia. 2department of doctoral program of geological engineering, universitaspadjadjaran, bandung, indonesia. 3department of geoscience, universitaspadjadjaran, jatinangor, indonesia * corresponding author : emi.sukiyah@unpad.ac.id/ fery_erawan@yahoo.com tel.:+62818-0936-6959; fax: +227796545 received: jun 14, 2020; accepted: jul 15, 2020. doi:10.25299/jgeet.2020.5.3.5285 abstract bintan island is a part of riau islands province. on this island, the capital city is tanjungpinang. the compliance of public facilities such as landfill waste is a priority in this city. landfill design that suitable in this area is a sanitary landfill system. the soil layer uses to cover the waste in this landfill system. the closure did gradually avoid the disruption of waste processing. the type of soil for its landfill cover has to be able to control the leachate. it controlled by the permeability of the soil. the methods used in this study are the analysis of the physical and mechanical properties of soil. rock and soil samples are obtained systematically through trenching. sampling-based on changes in physical properties of soil that reflect its mechanical properties. a probabilistic approach used to solve the problems and to get accurate results. the geomorphology of the study area divided into four units. they are very flat terrain, flat terrain, slightly steep hills, and steep hills. the sample used for the study is undisturbed soil. analysis of the physical and mechanical properties of soil shows the types of soil, such as sw, gm, mh-oh, and ch. however, mh is the most dominant type of soil. each of the soil types represents a certain degree of weathering. the degree of weathering in the study area varies from the iii degree to vi degrees. rocks are weathering form clay mineral, which compiles the soil. clay mineral in the soil layer is varied from quartz, illite, kaolinite, gibbsite, goethite, and hematite—the impact of the swelling of clay. the swelling of clay in the study area ranged from low to high. the properties and composition of the soil are affected by the permeability value. keywords: permeability, granite, weathering, waste disposal site, riau islands 1. introduction the research area is in the tanjungpinang city region, which is the capital of the riau islands province, located on bintan island (fig.1). the population of this city in 2010 reached 187,359 people with a population density of 804 people per square kilometer (https://tanjungpinangkota. bps.go.id). in 2018, the population of the city will increase to 209,280, with a density of 1,387 people per square kilometer (susilowati et al., 2019). as an area with a relatively high population density and continues to increase compared to the surrounding area, the problem of waste becomes crucial and requires professional management.fulfillment of public facilities, the final processing site for domestic waste is a priority. appropriate design in areas with relatively high population growth and limited land, in general, is the sanitary landfill system (erawan, 2015). this kind of landfill requires suitable soil to cover landfills (fig. 2) periodically.soil with good permeability and suitability are needed so that leachate inflow into the channels that have been available under the garbage pile. the availability of soil needed needs to mapped to ensure the sustainability of waste management. 1.1. geological setting the riau islands region has many islands, one of which is bintan island. this area is located on the southeastern tip of the malay peninsula and is part of a tin route sourced from granite rocks, which includes bangka island and belitung island. some rocks on this island have experienced weathering and erosion processes that are sufficiently intensive and extensive so that it appears as a monadnock when viewed from the aspect of sundanese exposure (molengraaf & weber, 1921). bintan island is composed of pre-tertiary to quaternary rock formations (fig.3). the porphyry bedrock formed on perm-carbon. this rock formation can also compare to the pahang volcanic series formation of the malay peninsula. the berakit formation is a low-grade metamorphic rock of the perm-carbon age that can be found at the northern tip of bintan island and is the oldest rock in the region (kusnama et al., 1994). this bedrock is broken through by younger igneous rock. granite is widespread, occupies the northern, eastern, and southern coastal regions of bintan island and occupies a small portion of the western coast. this rock is triassic, exposed widely on bintan island to form the kawal granite pluton and intrusion into the older berakit formation (kusnama et al., 1994). andesite igneous rocks also found in the form of intrusions that breakthrough granite. irregular distribution forms hilly areas of bintan island, such as lengkuas mount and bintan besar hill. this rock formation thought to be of miocene age.the goungon formation is a tuff sandstone that also dominates the bintan island region and thought to be of plio-pleistocene http://journal.uir.ac.id/index.php/jgeet mailto:emi.sukiyah@unpad.ac.id 130 erawan, et al./ jgeet vol 5 no 3/2020 age. at the top of the goungon formation deposited alluvium. besides, also found conglomerate composed of granite gravel, metamorphic rocks, and sandstone, as well as swamps and coral sediment, uplifted. the geological structure in this area is in the form of folds, joints, and faults. some of them appear as geomorphological lineaments. they can see on bintan island and batam island. tectonically, the riau islands region included in the karimata lane, which lies east of the tin lane (kusnama et al., 1994). the landscape in granite rocks is bimodal because soils have not yet been formed completely and are side by side with arid rocks ranging from meter-sized lumps to mountain-scale domes (hutabarat et al., 2016; sudradjat et al., 2018). fig1. the research area, eastern tanjung pinang city. fig 2. a modern sanitary landfill (amadi et al., 2012) 1.2. research roadmap research that has carried out in the riau islands region is diverse, covering material aspects, territorial potential, and waters. erawan (2015) conducted a study on the valuation of geological aspects to assess the feasibility of selecting the location for the final processing site for domestic waste in the singkep islands, riau islands province. irzon et al. (2016) researched rare earth elements in soils produced by granite weathering on singkep island. hutabarat et al. (2016) discuss the core stone of granite, which is widely available in the eastern and northern bintan island. lubis et al. (2017) state that temperature and wind velocity characteristics associated with indian ocean dipole (iod) in batam waters have low sea surface temperatures. rizki et al. (2017) also did a mapping of vegetation and mangrove distribution levels in batam island using spot-5 satellite imagery. this region also owns geological potential in terms of mineral content, hydrocarbons and beautiful landscape, in addition to local history and culture (sukiyah et al., 2018). sudradjat et al. (2018) discussed the characteristics of soils in the riau islands concerning overburden landfills, where final waste has conducted from 2015 to 2018. heavy metals content and pollution in tin tailings from singkep island have also investigated by irzon et al. (2018). ahnaf et al. (2019) examined the granite's genetic makeup and its characteristics, but the study conducted in the bayah area, banten province. the results showed a variety of granite both the formation process and the time of its formation. however, research on granite weathering related to the nature of permeability in the riau islands has not yet found.therefore, the results of this study are significant for the solution to the problem of overburden at domestic landfills. erawan, et al./ jgeet vol 3 no 5/2020 131 fig.3 regional geology of bintan island and surroundings, riau islands (kusnama et al., 1994) 2. material and method materials needed in this research are digital earth indonesia map with a scale of 1: 50,000, geological map of tanjungpinang sheet of 1: 250,000 scale (kusnama et al., 1994), satellite imagery of bintan island and surrounding areas, thematic maps related to conditions territory, soil samples, and other supporting data. this research requires field survey equipment such as a compass, a geological hammer, measuring tape, tubes for soil samples, tubes for leachate samples, 4 mm, 0.063 mm, and 2 mm size sieves for grain size analysis, image processing software and gis (geographic information systems). the research subject is the physical-mechanical properties of the weathering results of rocks. the research objects include rocks, both fresh and weathered, landscape, domestic waste leachate, and rivers. the object of research is identified through field surveys as well as through satellite imagery and maps. soil samples pick using the trenching method. this method is one of the cheapest methods. however, it can still get a three-dimensional subsurface image so that the boundaries between weathering, cracking, and weathering in weak rocks can be identified (woodward, 2005). undisturbed soil sampling also carried out. the level of weathering rocks refers to the classification of the engineering weathering profile (mclean & gribble, 1979) which divides into six classes, namely (i) fresh rock, (ii) slightly weathered, (iii) moderately weathered, (iv) highly weathered, (v) completely weathered, and (vi) residual soil. the process of preparing rock-soil samples and testing done in a laboratory. analysis of soil physical-mechanical properties based on uscs. determination of soil type based on uscs classification as shown in the scheme in fig. 4 (briaud, 2013) variables of the physical and mechanical properties of the soil are often analyzed. they are water content, specific gravity, dry soil volume weight, saturation level, natural void ratio and natural porosity, liquid limit, plastic limit, grain size analysis, and permeability (kalinski, 2011). factors affecting permeability include pore ratio, pore distribution in grains, and degree of saturation (elhakim, 2016; gallage et al., 2013). permeability allows water to pass through the space between the pores (gupta et al., 2016). calculation of permeability using darcy's law: 𝒗 = 𝒌. 𝒊 (1) where v = flow velocity, k = permeability coefficient (cm/s or in/s), i = hydraulic gradient (h/l), l = slope length.all research data, both obtained in the field and analyzed in laboratories and studios, are considered in determining the type of overburden suitable for the final processing site for domestic waste in the riau islands region. s i n g a p o r e s t r a i t n a t u n a s e a north 10 km 132 erawan, et al./ jgeet vol 5 no 3/2020 fig.4. uscs modified from its classification flow chart (briaud, 2013). 3. result and discussion the results of observations at the waste final processing site of ganet, it is known that the problem that is still an obstacle is leachate.the liquid from the decay is sometimes unable to penetrate the soil cover at the bottom. leachate that has a strong odor sometimes runs out of control (fig.5). leachate flow control facilities are not optimal. it indicates that the soil cover at the bottom of the pile of waste is not functioning correctly. its permeability is incompatible with leachate characteristics. this liquid has different properties compared to water, where leachate has a higher viscosity than water. therefore, it is necessary to engineer this soil ofgranite weathering to obtain the appropriate permeability value. fig 5. black leachate in the ganet waste processing site seeps out of control. leachate is unable to penetrate the cover soil at the bottom of the waste landfill. erawan, et al./ jgeet vol 3 no 5/2020 133 fig.6 the observation location of the granite weathering profile in the tanjungpinang and surrounding areas. the dominant granite rocks make up the study area and both exposed as new rock and in weathered conditions with varying degrees. observations made at 24 survey sites (fig. 6). in general, granite weathered outcrops found in the study area have a reddish-brown to light-brown color, silt to sand particle size, brittle, if wet slightly plastic, weathering levels iv to vi (topsoil). outcrops of new granite rocks rarely found. field observations include measuring thickness at each weathering level (fig. 7). fig.7 field observation activities. (a, b, c) outcrop descriptions, thickness measurements in each weathering zone, undisturbed sampling. 3.1 the soil classification granite weathered soils in the tanjungpinang and surrounding areas classified as sw, gm, ch, mh-oh, where mh is dominant. variations in soil types in the study area represent the different depth and level of weathering. sw soil types represent weathering level vi (st24-a). gm soil types represent weathering levels of iv-v (st 03-a; st 24-b) wherein some locations, the level of chemical weathering, is relatively high, as seen from the cao and na2o content. the soil type ch represents the weathering level v (st 24-b). meanwhile, mh-type soils have weathered iii-iv (st 20) weathering levels, where this type of soil shows high chemical weathering. 3.2 the soil physical-mechanical characteristic the soil in the study area has a value of water content that varies in the low-moderate range—the lowest water content in st 24-c with a value of 6.24%. content weights obtained also vary, at st 10-b has the highest value of weight content of 2.67% and the lowest weight value of land owned at st 03-a with a value of 2.57%. the distribution of soil grain size that is fine on average, but in some locations shows the size of coarse grains including st 03-a at a depth of 3.50-4.80 m, st 14-b at a depth of 4.70-5.00 m, st 24-a at a depth of 0-0.3 m (fig. 7b), and st 24-c at a depth of 7.0-7.3 m.coarse soil particles are almost all gravel size, only soil particles at st 24 at a depth of 0-0.3 m are sand size. the sand-sized soil particles in st 24-a reach 90.70%. soil particles are passing through sieve no. 200 is less than 5% with different sizes, which reflected in the grain size (cu) uniformity coefficient that is more than 1 (fig. 8a). because the value of the curvature coefficient (cc) is <1 and> 3, it has a pattern of particle distribution decreasing and increasing. based on the uscs classification, the soil classified as sw (sand-well sorted).coarse gravel-sized soil spread on st 03-b at a depth of 3.50-4.80 m, st 14-b at a depth of 4.70-5.00 m and st 24-c at a depth of 7.0-7.3 m. 134 erawan, et al./ jgeet vol 5 no 3/2020 gravel-sized particles at these locations and depths have a percentage of 68.20%, 47.70%, and 50.90%, respectively. particles that passed the no.200 sieve test are more than 12%. at the three locations, the naming of soil particles then added to the results of the plasticity test. in the plasticity diagram for the three locations and depths, the material character position is below line a (fig. 8a). it indicates the type of mud soil. therefore, the naming of soil types in st 03-b, st 14-b, and st 24-c is gm (gravel mud). soil particles in st 2 with a depth of 0.6-1.0 m and 4.95-5.25 m; st 3 at a depth of 0-0.4 m; st 10 at depths of 0.5-0.8 m and 3.5-3.75 m; st 14 at a depth of 1.7-2.0 m; st 20 at a depth of 5.6-6.0 m; st 24 at a depth of 0.9-1.2 m; and st 29 at 0.5-0.75 m depth are fine grain size. the naming of the soil type based on the relationship between the plasticity index and the liquid limit (fig. 8b). soils with a liquid limit of <50% are categorized into soil type m (mud) while soil with a liquid limit> 50% included in the category of soil c (clay) or soil m-o (mud-organic). land at st02-a (depth 0.6-1.0 m); st 02-b (depth 4.95-5.25 m); st 03-a; st 10 a (0.5-0.8 m depth); st 10-b (depth 3,53,75 m); st 14-a (depth 1.7-2.0 m); st 20 (depth 5.6-6.0 m); st 24-b (depth of 0.9-1.2 m); and st 29 (0.5-0.75 m depth) is a fine particle soil and has a liquid limit of> 50%. land on st 03-a; st 14-a; and st 24-b located above line a, so the ground at this station is called ch (clay high plasticity). while the soil at st 02-a; st 02-b; st 10-a; st 10-b; st 20; and st 29 is below line a so that the soil at that location is called mh-oh (mud high plasticity-organic high plasticity) based on the uscs classification. fine particle size soils tend to be plastic. mh-oh type soil is the most dominant soil type at the study site. fig.8 relationship between plasticity index and liquid limit. dominant fine-sized soil particles are below line a 3.3. permeability permeability coefficient test on 13 soil samples is carried out in the laboratory (table 1). the permeability coefficient values range from 6.083 x 10-7 to 3.790 x 10-3. soil layers at locations st 14-a and st 20 have a permeability of 6.083 x 10-7 cm/s and 6,597 x 10-7 cm/s, respectively. the soil permeability value is valid to use as final cover soil for a sanitary landfill system. besides, the permeability range of the two layers of soil is relatively low so that it can withstand incoming water. permeability of other soil layers, namely soil in st 02-a; st 02-b; st 03 a; st 03-b; st 10-a; st 10-b; st 14-b; st 24a; st 24-b; st 24-c; and st 29 has a range of values of 1.517 x 10-3 cm/sec to 7.357 x 10-6 cm/sec which is quite high. high permeability indicates that this layer can hold and pass water quite effectively. so, this soil layer is sufficient to use as an intermediate soil cover. table1. the permeability coefficient of laboratory test no. sample code coefficient of permeability (cm/sec) 1. st 02-a 7.357 x 10-6 2. st 02-b 1.637 x 10-5 3. st 03-a 4.305 x 10-6 4. st 03-b 2.601 x 10-5 5. st 10-a 1.517 x 10-3 6. st 10-b 3.579 x 10-4 7. st 14-a 6.083 x 10-7 8. st 14-b 7.706 x 10-5 9. st 20 6.597 x 10-7 10. st 24-a 1.672 x 10-6 11. st 24-b 1.213 x 10-6 12. st 24-c 3.790 x 10-3 13. st 29 1.380 x 10-6 the grain size distribution of soil material is closely related to the value of the soil permeability coefficient. in general, uniform grain size distribution can form space between items so that the permeability value is high. if the grain size distribution is not uniform, the space between the grains that form closed pores (interlocking) results in a low permeability value. porosity is related to permeability. the greater porosity, the smaller the permeability coefficient value. in this study also found porosity values with permeability coefficients whose effects are not comparable. based on laboratory test results, there are different porosity values when compared with the coefficient of permeability. the value of porosity is low along with the low coefficient of permeability produced, but there is a portion of the value of porosity is low while the coefficient of permeability is high. therefore, in this study porosity and permebility do not affect each other less. this is due to the inhomogeneous soil conditions. 4. conclusion the treatment of leachate in the final landfills in tanjungpinang and surrounding riau islands province is not optimal. the relevant agencies have not fully supported the study of the overburden availability in the research area. the variation of physical and mechanical characteristics of soils resulting from granite weathering requires erawan, et al./ jgeet vol 3 no 5/2020 135 engineering in order to obtain a formula that is suitable for sanitary landfill cover. characterization of permeability of granite rock weathering results can be used as a reference for engineering and become input for sni to the land cover of domestic waste landfills. the permeability of granite weathered soil <10-7has fulfilled the standard of minister of public works regulation number 3, 2013. the regulation states that the permeability for the final cover is 1 x 10-7 cm/s. acknowledgments our gratitude goes to the leadership of unpad for research support through the 2015-2018 alg scheme. to the research team who helped a lot in the field activities, we would also like to convey our thanks. sincerity is all encouraging in further research in order to enrich the scientific treasury. references ahnaf, j. s., patonah, a., permana, h., 2019. petrogenesis of volcanic arc granites from bayah complex, banten, indonesia. j. geoscience, engineering, environment, and technology 4 (2), 104-112. doi: 10.25299/jgeet.2019.4.2.3171. amadi, a. n., olasehinde p. i., okosun e. a., okoye n. o., okunlola i. a., alkali, y. b., dan-hassan m. a, 2012. a comparative study on the impact of avu and ihie dumpsites on soil quality in southeastern nigeria. american journal of chemistry 2(1), 17-23. doi: 10.5923/j.chemistry. 20120201.05. briaud, jean-lous, 2013. introduction to geotechnical engineering: unsaturated and saturated soils. john wiley & sons, 998 p. elhakim, a.f. 2016. estimation of soil permeability. alexanfria engineering journal, vol. 55. pp. 2631 – 2638. erawan, f., 2015. geological valuation for the location of the final processing of domestic waste in singkep islands, riau islands province (abstract in english). 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china-sea), and its influence on the distribution of coral reefs and the land and freshwater fauna. proceedings of the section of sciences 23, 395-439. rizki, f., situmorang, a.d.l., wau, n., lubis, m. z., anurogo, w., 2017. mapping of vegetation and mangrove distribution level in batam island using spot-5 satellite imagery. j. geoscience, engineering, environment, and technology 2 (4), 264-267. doi: 10.24273/jgeet.2017.2.4.1002. sudradjat, a., sukiyah, e., haryanto, e.t., purnomo, d., 2018. karakteristik hasil pelapukan batuan di wilayah kepulauan riau dan jawa barat serta desain pemanfaatannya untuk tanah penutup tpa sampah domestik. laporan akhir alg, universitas padjadjaran. sukiyah. e., isnaniawardhani, v., sudradjat, a., & erawan, f., 2018. the geologic potentials of riau islands province and its development design. jurnal perspektif pembiayaan dan pembangunan daerah vol. 5. no.3: 181-190. susilowati, s.k., kapriaji, m. n., puspitasari, t.r., beti, mardayani, & rizqal, m., 2019. tanjungpinang municipality in figures. bps-statistics of tanjungpinang municipality. https://tanjungpinangkota.bps.go.id <download july 5, 2020>. woodward, john, 2005. an introduction to geotechnical processes. spon press. london & new york. 307 p. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved.this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 wibowo, et al./ jgeet vol 5 no 4/2020 169 research article raster-based model for mass movement in malang regency, east java, indonesia. sandy budi wibowo 1,*, franck lavigne2, siddiq luqman rifai3, rani rahim suryandari3, idea wening nurani4, st. dwi ermawan danas putra5, wahyu widi pamungkas5 1department of geographic information science, faculty of geography, universitas gadjah mada, yogyakarta, indonesia. 2institute de géographie, université paris 1 panthéon-sorbonne, paris, france. 3 cartography and remote sensing study program, faculty of geography, universitas gadjah mada, yogyakarta, indonesia. 4department of development geography, faculty of geography, universitas gadjah mada, yogyakarta, indonesia. 5laboratory of geographic information system, faculty of geography, universitas gadjah mada, yogyakarta, indonesia. * corresponding author : sandy_budi_wibowo@ugm.ac.id tel.:+62-274-6492334; fax: +62-274-589595 received: mar 31, 2020. ; accepted: sept 18, 2020. doi 10.25299/jgeet.2020.5.4.4737 abstract strengthening geospatial technology is very important in order to support disaster mitigation strategy, to manage vulnerable communities and to protectcritical environments. the main challenge in identifying disaster characteristics such as mass movements is the lack of direct observation during the event because it is too dangerous for researchers. geo-information technology as a product of geographic information science can be used as a solution in order to model the characteristics of mass movements. the purpose of this study is focused on identifying landslide processes from point of view of raster-based model. the method of this research emphasizes dynamic landslide model derived from time series raster calculation using massmov2d algorithm. the geographic database that was built for spatial modeling comes from pedogeomorphological and remote sensing survey outputs, especially topographic data, landforms and soil physical properties. the result shows that the relationship between pixels (neighborhood) is determined by the topology of the energy gradient line direction which allows to transfer the value between each pixel. the movement of landslide material starts from the toe. this decreases the stability of the landslide material in the main body of the landslide and generate progressive erosion. the raster-based model can finally reconstruct and identify the stages of initiation, transport and deposition landslide material. keywords: geo-information technology, raster-based models, landslides, mass movements. 1. introduction raster-based model is part of geo-information technology that can be applied for disaster studies, especially mass movements. it allows researchers to identify and reconstruct the process of mass movements, such as debris flows and landslides. this is very important because usually the identification of mass movement process is very limited. such identification is pretty dangerous to be done directly in the field during the event. the need for reconstruction and identification of mass movement processes becomes urgent and critical to minimize the number of victims which are often reported by mass media during the rainy season. therefore, strengthening geospatial technology for disaster studies is paramount, especially for supporting disaster mitigation strategy, for managing vulnerable communities and for protecting critical environments. various mass movement modeling techniques have been developed such as machine learning model (bui et al., 2020), deep learning neural network (dao et al., 2020), cellular automata (adamska-szatko and bała, 2010), statistical approaches (he et al., 2019) physical simulation (wibowo, 2011; wibowo, 2016, ran et al., 2018; weidner et al., 2019; marin and velásquez, 2020) and vibration simulation (katz et aharonov, 2006; chen et al. 2020). numerical model (raster) based on physical characteristics of materials is being developed as well such as dan and dan 3d based on the application of quantum mechanics to estimate the average depth of material of mass movements (hungr et mcdougall, 2009). another numerical model is mass mov 2d that uses raster data as a basis for calculating mass conservation and mometum of materials during the event (beguería et al., 2009). many alternative models are still being developed for mass movement, such as double layer-averaged two-phase flow model (yu et al., 2019; li et al., 2020; shen et al., 2020), smoothed-particle hydrodynamics (lin et al., 2019), unsupervised factor optimization (sameen et al., 2020), dem optimization (ville et al., 2015; sarma et al., 2020), evaluation of raster resolution (shirzadi et al., 2019; wang et al., 2020), spatial heterogeneity model (wang et al., 2020). however, the main obstacle still persists, i.e. the difficulty of obtaining data in the field during the event due to security reasons. therefore the purpose of this study is focused on identifying landslide processes, as one types of mass movements, from point of view of raster-based model. this would be important in providing one alternative solution to reconstruct landslide process for supporting disaster mitigation strategy, managing vulnerable communities and protecting critical environments. 2. methods 2.1 measurement of topography and physical characteristics of landslide rotational landslide in malang regency has been chosen as representative of mass movements. landslide geometry was measured from fixed observation point in front of landslide. we used laser rangefinder for measuring vertical and horizontal http://journal.uir.ac.id/index.php/jgeet 170 wibowo, et al./ jgeet vol 5 no 4/2020 distance (accuracy of 5 cm) and azimuth (accuracy of 1°) to produce point cloud with x, y, z coordinates. this allowed us to measure the geometry of the landslide in detail and to produce digital surface model as well. identification of soil physical properties was also carried out to determine the characteristics of landslide material. an outcrop of soil profile next to the landslide was investigated in order to have maximum similarity to the physical characteristics of landslide materials. soil horizons and their boundaries were used to determine the position of slip surface. 2.2 dynamic raster-based model data from topographic measurement and identification of physical characteristic of landslides werethen used as input for raster-based model. mass mov 2d algorithm was used by putting rheological parameters, viscosity, basal friction angle, internal friction, fluidization index and time. the output of the model was devoted to reconstruct the landslide process so that the mechanism of initiation, transportation and deposition of landslide materials could be identified. 3. results 3.1 topography and physical characteristics of the landslide the studied landslide was located in kemiri village, malang regency, indonesia. the type of mass movement was classified rotational landslide with a length of 78 m and a width of 27 m (figure 1 and figure 2). landslide geometry was measured using a laser rangefinder to produce 116 filtered x, y, z coordinates to eliminate improper coordinates other than ground (classification value number 2 in the lidar data classification). these coordinates were combined into a simple point cloud to build the digital surface model (dsm). based on this dsm, the slope of the surrounding area was 36° (or 72%) with a slightly convex form. fig. 1. map of study area. local population have reclaimed this landslide scar and turned it back into agriculture land. there is no new landslides recently. fig. 2. cross section of the landslide area showing topography before and after event. wibowo, et al./ jgeet vol 5 no 4/2020 171 soil in the study area was developed from weatheredquaternaryvolcanic parent materials from gendis mountains formation (qpg). the soil types was classified as alfisols, with brown topsoil (10 yr 4/3). the subsoil part including the endopedon had a dark brown color (10 yr 3/3). the soil texture was dominated by clay with lessivage/clay eluviation from topsoil to subsoil. the soil tended to be moistin field capacity condition. at depth of more than 228 cm, weathered pumice deposits with a diameter of 10-20 cm existed. the characteristics of landslide materials were closely related to the type of soil at the study site. bingham's viscous rheological law was suitable for alfisols with clay texture. i.e. rigid at low pressure, but can flow as thick fluid at high pressure. the friction between the landslide materials and the slip surface became smaller when it liquefied and reached saturation point, because the predominant soil texture in the soil profile was clay. its particle densities ranged from 2110 to 2280 kg/m3. dynamic viscosity was high enough for clay soils because of its resistance to external forces. however, the transformation from solid to liquid phase was rapid, especially in the contact area between the toe of the landslide and the slip surface. this was aggravated by the position of landslide of which the toe touched directly a creek. the characteristics of landslide materials are generally summarized in table 1. table 1. characteristics of landslide material used as input for rasterbased model parameter value unity rheology model bingham viscous density 2000 kg.m-3 yield stress 70 pa dinamic viscosity 300 pa.s basal friction 12 ° internal friction 14 ° fluidization rate 10 m.s-1 time 100 s 3.2 calculation of pixel values for dynamic raster-based model of landslides landslides were divided into pixels of 30 x 30 cm in two raster dataset: dsm before and after the event. based on cutand-fill analysis on these two dsm, the thickness of landslide materials was measured. dsm after the event expressed the elevation of slip surface as well. the floating point values of each pixel represented the elevation of slip surface and the thickness of the landslide material. determination of pixel value did not use the central point rule, but the largest share rule. it means the obtained pixel value is the most spatially dominant value within that pixel. changes in pixel values during the model run indicated the dynamics of mass movements. cohesive landslide material moveddownward the slope with constant changes in properties during mass movement, which was represented by the rate of fluidization. landslide materials moved because of the difference in potential values between pixels, from high to low. in every timestep (s), each pixel was always compared to its neighbors which had topology connection based on the direction of mass movement. the direction of the energy gradient line (egl) affected the direction of mass movement that can be devided into x and y axes (figure 3). in general, movement of landslide materials went to the lower pixel. this movement wasaccompanied by the sedimentationof material along the movement. it allowed sedimentation of cohesive materialsto occur. this avoided anexcessive accumulation of landslide materials in one pixel (convergence). weak stability of landslide material became the basis for performing repeated calculations (loops) until a stable condition is reached for every pixel. fig. 3. dynamics of spatial clasterization process of landslide material which produce spatial autocorrelation. this raster-based model showed the dynamics of the landslide movement which was characterized by progressive erosion. the movement of landslide material started from the toe of landslide which decreased the stability of the landslide material of the landslide body. consequently, this triggered movement on landslide body and followed by landslide crown.the mass movement of the landslide material was remarkably rapid at the beginning of the landslide, and slowed down during the sedimentation phase (figure 4). sedimentation of landslide material was accumulated at the bottom of the slope and clogged the creek underneath. fig. 4. dynamic raster-based model of landslide materials 4. discussion the importance of geo-information technology, affected to the fundamental needs of its development, both using technical approach and participatory approach (wibowo and nurani, 2019). this study shows that geo-information technology, with its technical approach on spatial aspect, can 172 wibowo, et al./ jgeet vol 5 no 4/2020 also be applied for mass movement studies. raster-based model allows to reconstruct mass movement in order to overcome common scientific issues, i.e. lack of direct observation during the real event due to security reasons. rotational landslides are one type of the most frequent mass movements (wibowo et al., 2014; wibowo et al., 2015; gob et al., 2016; cassel et al., 2018; samodra et al., 2018), especially in tropical region such as in indonesia (wibowo, 2010). given that rotational landslides often occur on complex terrain for which massmov2d algorithm has been designed (beguería et al., 2009), we decided to use it to build raster-based model. input data from point cloud that is acquired from laser measurement allows to build dsm and to measure the geometry of landslide. laser measurement, both laser rangefinder and lidar, provides high-resolution topographic data and very helpful for fieldwork in a remote and dangerous area (ville et al., 2015). another input data is physical soil properties of the landslide material that is acquired from soil profile next to the landslide area. this is aimed to have maximum similarity to soil properties of the landslide material. coupling between topographic data and physical soil properties of the landslide material is key parameter for dynamic raster-based model that we perform in this research. the process of this rotational landslide on clay dominant alfisols can be reconstructed and identified thanks to dynamic raster-based model. pixel values indicating elevation of landslide materials change over time. it means that landslide materials move dynamically during the event. the change of pixel values in the initiation process is much faster than in sedimentation process, showing that the movement of this landslide was extremely fast at the beginning (7.35 m/s). it rapidly slowed down to 1.02 m/s when the materials started to be deposited at foot slope. however, this velocity increased to 2.35 m/s at time step 11 s when the abundant accumulation of this sedimented materials started to flow downstream following the topography of creek. this velocity progressively slowed down until it reached stable condition at timestep 100 s. this phenomena is very common for subaerial mass movements on earth surface (wibowo et al., 2015; weidner et al., 2019; marin and velásquez, 2020; chen et al. 2020). the transfer mechanism of pixel value to neighbors follows the direction of egl, indicating that landslide materials shift downward with continuous alternating process between erosion and sedimentation during the transport phase (samodra et al., 2018). wet clay soils like alfisols tend to be sticky, so that this cohesive materials are easily sedimented, except if there is enough force erode it during the rapid movement of landslide. however, this alternance disappears when the movement weakens at the landslide toe (yu et al., 2019; li et al., 2020; shen et al., 2020). absence of transfer of pixel value at timestep 100 s indicates that the dynamic raster-based model stops when sedimented landslide materials reach its stability condition at downslope. the problematic of this research on lack of direct observation during the real event due to security reasons has been resolved, given that the raster-based model in this research is able to provide a detailed reconstruction and identification of mass movement process. 5. conclusion dynamic raster-based modelfor mass movement using the massmov2d algorithm allows to spatially reconstruct landslide in malang regency, indonesia. this landslide reconstruction helps the identification of initiation, transport and deposition process of material of landslide from spatial point of view. this landslide process is depicted on the change in value of each pixel. the relationship between pixel and its neighbors is determined by the topology of the energy gradient line direction. it allowsto transfer values between each pixel. the dynamics of a landslide movement characterized by progressive erosion. the movement of landslide material started from the toeof landslide which decreased the stability of the landslide material of the landslide body. the output of this research would provide one alternative solution to reconstruct landslide process, even without direct observation during the real event due to security reasons. this kind of landslide reconstruction would be important for supporting disaster mitigation strategy, for managing vulnerable communities and for protecting critical environments. acknowledgement this research was funded by hibah dosen mandiri from fakultas geografi, ugm. the authors acknowledge fibrian tri setyanto, anung aprian feriadi and dian hasimaiwan surya who were very helpful during the fieldwork. we also highly appreciate sri rahayu utami, ph.d., dr. sudarto, and widianto, m.sc. 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103421. https://doi.org/10.1016/j.advwatres.2019.103421 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.1016/j.apm.2019.11.031 https://doi.org/10.1016/j.compgeo.2019.103153 https://doi.org/10.1016/j.cageo.2019.104336 https://doi.org/10.1016/j.enggeo.2020.105523 https://doi.org/10.1016/j.enggeo.2019.105168 https://doi.org/10.1016/j.catena.2019.104425 https://doi.org/10.1016/j.advwatres.2019.103421 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 2 2020 jahidin et al./ jgeet vol 5 no 2/2020 59 research article analysis of ultramafic rocks weathering level in konawe regency, southeast sulawesi, indonesia using the magnetic susceptibility parameter jahidin1,*, lo. ngkoimani2, lm. iradat salihin3, hasria2, erzam s. hasan4, irfan ido5, suryawan asfar2 1geophysics engineering department, halu oleo university, kendari 93232, indonesia. 2geological engineering department, halu oleo university, kendari 93232, indonesia. 3geographic department, halu oleo university, kendari 93232, indonesia. 4physics department, halu oleo university, kendari 93232, indonesia. 5mining engineering department, halu oleo university, , kendari 93232, indonesia. * corresponding author : jahidin_geofisika@uho.ac.id tel.:+62-81-388-3535-48; fax: received: dec 13, 2019. ; accepted:may 20, 2020. doi 10.25299/jgeet.2020.5.2.4247 abstract the konawe region is part of the sulawesi southeast arm ophiolite belt where ultramafic rocks are exposed in the form of dunite and peridotite. the formation of nickel deposits is closely related to the weathering process of ultramafic rocks as a source rock. ultramafic rocks exposed to the surface will experience weathering which is influenced by many factors, including in the form of climate change, topography, and existing geological structures. the weathering process in the source rock can influence variations in chemical elements and magnetic properties in laterite soil profiles. for example, the chemical weathering might affect magnetic mineralogy and the physical weathering could affect granulometry as well as the quantity of magnetic minerals in the soil. condition of weathering of ultramafic rocks (initial, moderate and advanced) can affect nickel content in laterite sediments. the weathering profile study of serpentine mineral is an indication of the lateralization process that occurs in ultramafic rocks and is carried out through petrographic analysis of thin cuts and polish cuts. determination of weathering level like this is based on the level of weathering of the mineral serpentine. in this study, the determination of the weathering level of ultramafic rocks (initial, moderate, and continued) uses magnetic susceptibility parameter. a total of 232 ultramafic rock core samples obtained from 34 hand samples were taken from different places and weathered levels were analyzed. the results of the research have shown that the magnetic susceptibility of ultramafic rocks i n the study area varies, from 580 x 10-6 si to 4.724 x 10-6 si. based on the value of magnetic susceptibility, magnetic minerals contained in ultramafic rock samples are hematite and geotite minerals. this means that the weathering level of ultramafic rock samples is the continued weathering level. the level of continued weathering that occurs in ultramafic rocks in the study area produces nickel laterite deposits with a nickel content of 1.65 2.40% in the saprolite zone, 0.42% in the saprock zone, and 0.20 0.51% in the basic rock zone (bedrock). keywords: ultramafic rock, weathering level, magnetic susceptibility, konawe regency. 1. introduction 1.1 background of research the konawe area is part of the sulawesi southeast arm ophiolite belt. in this section, ultramafic rocks are formed in the form of dunite and peridotite (surono, 2010). the formation of nickel deposits is closely related to the weathering process of ultramafic rocks as a source rock. ultramafic rocks exposed to the surface will experience weathering which is influenced by many factors, including in the form of climate change, topography, and existing geological structures. the weathering process in the source rock can influence variations in chemical elements (maher and thompsons, 1999) and magnetic properties in laterite soil profiles (evans and heller, 2003; yulianto et al., 2003). for example, the chemical weathering might affect magnetic mineralogy and the physical weathering couldaffect granulometry as well as the quantity of magnetic minerals in the soil. the process of soil formation is divided into several zones with varying thickness and mineral element content (petrovsky and ellwood, 1999), for example in laterite soil deposits (sundari, 2012). laterite soils or commonly called laterite or red soil isa type of infertile soil that is fertile and rich in nutrient-rich soil, but it is lost because it is dissolved by high rainfall. this type of soil has a low cation exchange capacity (which causes the metabolic process of plants to be disrupted (sudarningsih, 2008). according to sembiring (2008) the land of ex-laterite nickel mining actually shows the condition of the soil that has damaged structure and compaction so that it has a negative effect on the water system and aeration which can directly affect the function and development of roots. this causes the plants to grow normally, dwarf, wither, and die. the deterioration of the soil structure also affects the soil that is unable to store and absorb water during the rainy season resulting in soil erosion. conversely, in the dry season the soil becomes hard http://journal.uir.ac.id/index.php/jgeet 60 jahidin et al./ jgeet vol 5 no 2/2020 and dense, so the soil becomes difficult to cultivate. therefore, efforts are needed to increase soil fertility. exploration of laterite nickel deposits is thought to be related to weathering of ultramafic rocks in the formation of laterite nickel deposits and the presence of erosion material spread over the surface. in humid tropical climatic conditions, ultramafic rocks decay very quickly and produce ore residues containing nickel, chromium, or iron (sudarningsih, 2008). the weathering profile study of serpentine mineral is an indication of the lateralization process that occurs in ultramafic rocks and is carried out through petrographic analysis and polish cuts (boldt, 1967). determination of weathering levels like this is based on the level of weathering of the mineral serpentine. in this study, the determination of the weathering level of ultramafic rocks (early, moderate, and continued) uses magnetic susceptibility parameter. this is new and is expected to be an inexpensive and environmentally friendly alternative method for assessing weathering of ultramafic rocks and their relationship to nickel content. an illustration of the relationship of weathering levels of ultramafic rocks with nickel content can be used to support the exploration of the presence of laterite nickel. 1.2 basic theory according to regional geology, sulawesi is located at the confluence of 3 large plates, which causes very complex tectonic conditions, where a collection of rocks from the archipelago, ophiolite, and chunks of microcontinent are carried along with subduction, collision and other tectonic processes (surono,2010). for the southeast sulawesi region which is in the east sulawesi ophiolite lane group, the rocks consist of mafic and ultramafic rocks accompanied by pelagic and melange sedimentary rocks in several places. ultramafic rocks are dominant in the southeastern arm, but the mafic rocks are dominant further north, especially along the north coast of the southeast arm of sulawesi (fig. 1). the weathering rock is a process of physical disintegration and chemical decomposition of rock material that is on the surface or near the surface of the earth (parker, 1997 in waheed, 2002). ultramafic rocks that undergo chemical weathering will change the composition of the mineral, as illustrated in table 1. fig. 1. map of the geology of the southeast arm of sulawesi (surono, 2010). table 1. mineral content at weathering level (mitchell & soga, 2005) weathering level mineral content early weathering level gypsum (also halite, sodium nitrat) calcite (also dolomite apatite) olivine-hornblende (also pyroxenes) biotite (also glauconite, nontronite) albite (also anorthite, microcline, orthoclase) moderate weathering level quartz muscovite (also illite) layer silicate (including vermiculite, expanded hydrous mica) montmorillonite continued weathering level kaolinite gibbsite hematite (also goethite, limonite) anatase (also rutile, zircon) jahidin et al./ jgeet vol 5 no 2/2020 61 2. research method samples in the form of ultramafic rocks and soil analyzed in this study were taken at pondidaha district and puriala district konawe regency. the samples were taken at the nickel mining site, rock mining, and post nickel mining. for rock samples, they are taken in the form of hand samples and made in the core for magnetic susceptibility measurement purposes and made in powder form for the measurement of mineral / elemental content. measurement of the magnetic susceptibility of ultramafic and soil rock was carried out on 232 ultramafic rock core samples obtained from 34 hand samples and 20 soil samples taken around ultramafic rocks. magnetic susceptibility values for each rock and soil sample site were measured using the ms2b susceptibilitymeter. measurement of mineral content/sample elements was performed using x-ray difraction and x-ray fluorescence. 3. results and discussion 3.1 magnetic susceptibility of samples magnetic susceptibility is a function of the concentration, grain size and type of magnetic minerals. variable magnetic susceptibility values indicate the concentration of magnetic minerals, grain size, and types of magnetic minerals that vary (jahidin et al., 2019). the greater the value of magnetic susceptibility means the more concentration of magnetic minerals. high magnetic susceptibility also shows that magnetic mineral typesare dominated by ferrimagnetic and ferromagnetic magnetic minerals, magnetic susceptibility in the medium category is dominated by paramagnetic and antiferromagnetic magnetic minerals, whereas magnetic susceptibility is very low (negative) including non-magnetic (diamagnetic) minerals. the magnetic susceptibility values for each rock and soil sample site measured using the ms2b susceptibility instrument can be seen in table 2. table 2. the magnetic susceptibility value of the samples sample type site name number of hand samples number of core samples location magnetic susceptibility value (x 10-6 si) ultramafic rock p1 2 23 rock mining (puriala district) 960 2.128 p2 2 16 rock mining (puriala district) 690 1364 p3 2 26 rock mining (puriala district) 1.610 2.860 st2 2 9 rock mining (puriala district) 1.218 4.724 st3 1 2 rock mining (puriala district) 3.700 4.364 d1 3 16 post nickel mining(pondidaha district) 679 1.439 d2 4 32 nickel mining(pondidaha district) 640 1543 d3 9 70 post nickel mining(pondidaha district) 580 1460 st1 2 6 nickel mining(pondidaha district) 666 814 st2 2 9 post nickel mining(pondidaha district) 586 901 st3 3 10 rock mining(pondidaha district) 992 1.434 st5 2 8 nickel mining(pondidaha district) 894 1.603 soil st1 1 3 nickel mining(pondidaha district) 37,9 40,3 st2 1 2 post nickel mining(pondidaha district) 334,6 -381,6 st3 1 2 rock mining(pondidaha district) 71,8 119,8 st5 3 7 nickel mining(pondidaha district) 91,4 156,6 st2 1 2 rock mining (puriala district) 959,5 991,3 st3 1 2 rock mining (puriala district) 269,2 285,9 based on the table 2, it can be seen that the magnetic susceptibility value in ultramafic rock samples and soil samples in the study area varies. ultramafic rock samples have magnetic susceptibility values ranging from580 x 10-6 si to 4,724 x 10-6 si and soilsamples have magnetic susceptibility values of 37.9 x 10-8 m3/kg to 991.3 x 10-8 m3/kg. ultrabasic rock samples such as p3, st2, and st3 sites in puriala district show a greater magnetic susceptibility than other sites. the magnitude of the magnetic susceptibility value indicates that the concentration of magnetic minerals in the sample is higher and is suspected to have a different type of magnetic mineral than the others. in soil samples taken from around the area of the presence of ultramafic rocks, the magnetic susceptibility value per unit of mass indicates that the soil samples originated from weathering of host rock (ultramafic rocks). based on the value of magnetic susceptibility and field observations, it is suspected that soil samples contain the same magnetic minerals as ultramafic rocks. from the results of the measurement of magnetic susceptibility in some ultramafic rock samples that produce two or more core samples from hand sample drilling, it is found that the magnetic susceptibility values for the cores above tend to be greater than the cores below. the above cores are samples taken from rock drilling in the uppermost structure, while the next cores are in the lower structure. the existence of the upper core has a high magnetic susceptibility compared to the bottom core due to weathering ultramafic rock always starts at the top of the structure towards the bottom structure. this allows a greater concentration of magnetic minerals in the upper core than the bottom core. the presence of magnetic susceptibility values of the lower core is higher than the upper core may be caused by the structure in the form of fractures at the bottom so that it will facilitate the entry of water and means the weathering process will be more intensive. as a result, the concentration of magnetic minerals at the bottom becomes greater and the value of magnetic susceptibility becomes higher. next, the magnetic 62 jahidin et al./ jgeet vol 5 no 2/2020 136 144 145,8 0 0 0 111,6 99 106,3 0 20 40 60 80 100 120 140 160 p1.2.1 p1.2.2 p1.4.1 p1.4.2 p1.8.1 p1.8.2 m a g n e ti c s u sc e p ti b il it y ( x 1 0 -5 s i) sample code core 1 core 2 79,5 92,4 105,5 107,1 92,7 136,4 0 0 0 0 0 0 69 94 98,4 106 82,2 118 0 20 40 60 80 100 120 140 160 p2.1.1 p2.1.2 p2.3.1 p2.3.2 p2.4.1 p2.4.2 p2.5.1 p2.5.2 p2.6.1 p2.6.2 p2.8.1 p2.8.2 m a g n e ti c s u sc e p ti b il it y ( x 1 0 -5 s i) sample code core 1 core 2 421 276 386,5 292,9 161 228,6 168 154,9 205 197,5 197 264,5 213 386,5 234 187,8 287 182,3 163,9 204 239 174,6 0 50 100 150 200 250 300 350 400 450 m a g n e ti c s u sc e p ti b il it y ( x 1 0 -5 s i) sample code core 1 core 2 susceptibility values for the cores at each site are shown in fig.2, fig. 3, fig. 4, fig. 5, fig. 6, fig.7, and fig. 8. fig. 2. magnetic susceptibility values of upper core (core 1) and bottom core (core 2) ultramafic rock samples at site p1 puriala district fig. 3 magnetic susceptibility values of the upper core (core 1) and bottom core (core 2) ultramafic rock samples at site p2 puriala district fig. 4 magnetic susceptibility values of upper core (core 1) and bottom core (core 2) ultramafic rock samplesat site p3 puriala district jahidin et al./ jgeet vol 5 no 2/2020 63 160,5 68,9 72,8 151,3 111,2 67,9 71,7 89,5 0 50 100 150 200 d1.1.4 d1.2.1 d1.2.4 d1.3.3 m a g n e ti c s u sc e p ti b il it y ( x 1 0 -5 s i) sample code core 1 core 2 114,4 89,5 95,8 85,3 107,5 95 73,1 87,5 86,3 74,8 69,2 66 117,1 154,3 100,3 92,7 90,7 74,8 94,3 76,8 70,7 71,2 72,3 72,6 66,9 64 114,5 121,8 0 20 40 60 80 100 120 140 160 180 m a g n e ti c s u sc e p ti b il it y ( x 1 0 -5 s i) sample code core 1 core 2 89,1 80,6 80,2 89,2 72 97,6 87,5 66,7 74,7 79,5 81 70,7 148,6 91 103,4 81 75,5 124,4 96,8 141,6 108,5 141 100 128 59,5 0 0 0 0 87,5 76 72,2 73,2 68,5 92,6 73,2 65,1 72 77 81,5 70 90 65 76 84 67,5 85,5 99 102 106 111 112 120,5 58 0 20 40 60 80 100 120 140 160 d 3 .1 .1 d 3 .1 .2 d 3 .1 .3 d 3 .2 .1 d 3 .2 .3 d 3 .3 .1 d 3 .3 .4 d 3 .3 .7 d 3 .4 .2 d 3 .4 .3 d 3 .4 .4 d 3 .5 .2 d 3 .5 .3 d 3 .5 .4 d 3 .5 .5 d 3 .5 .6 d 3 .5 .7 d 3 .5 .8 d 3 .6 .2 d 3 .7 .3 d 3 .7 .5 d 3 .7 .7 d 3 .7 .9 d 3 .7 .1 0 d 3 .9 .4 m a g n e ti c s u sc e p ti b il it y ( x 1 0 -5 s i) sample code core 1 fig. 5 magnetic susceptibility values of upper core (core 1) and bottom core (core 2) ultramafic rock samples at site d1 pondidaha district fig 6. magnetic susceptibility values of the upper core (core 1) and bottom core (core 2) ultramafic rock samples at site d2pondidaha district fig. 7 magnetic susceptibility values of the upper core (core 1) and bottom core (core 2) ultramafic rock sample at site d3 pondidaha district 64 jahidin et al./ jgeet vol 5 no 2/2020 fig 8. magnetic susceptibility values of core 1, core 2, core 3, core 4, core 5 ultramafic rock samples at site st3, st2, st5, and st1 pondidaha district 3.2 mineral content of samples the magnetic mineral content in the sample can be determined based on the magnetic susceptibility value. by referring to the classification of magnetic mineral types based on magnetic susceptibility prices according to hunt et al. (1995), the magnetic mineral content of ultramafic and soil rock samples can be seen in table 3. table 3. magnetic mineral content of ultramafic and soil rock samples sample type site name area magnetic susceptibility value (x 10-6 si) type of magnetic mineral ultramafic rock p1 puriala district 960 2.128 hematite (αfe2o3) geotite (feooh) p2 puriala district 690 1364 hematite (αfe2o3) geotite (feooh) p3 puriala district 1.610 2.860 hematite (αfe2o3) geotite (feooh) st2 puriala district 1.218 4.724 hematite (αfe2o3) geotite (feooh) st3 puriala district 3.700 4.364 hematite (αfe2o3) geotite (feooh) d1 pondidaha district 679 1.439 hematite (αfe2o3) d2 pondidaha district 640 1543 geotite (feooh) d3 pondidaha district 580 1460 hematite (αfe2o3) st1 pondidaha district 666 814 geotite (feooh) st2 pondidaha district 586 901 hematite (αfe2o3) st3 pondidaha district 992 1.434 geotite (feooh) st5 pondidaha district 894 1.603 hematite (αfe2o3) soil st1 pondidaha district 37,9 40,3 hematite (αfe2o3) st2 pondidaha district 334,6 -381,6 hematite (αfe2o3) ilmenite (fetio3) st3 pondidaha district 71,8 119,8 hematite (αfe2o3) ilmenite (fetio3) st5 pondidaha district 91,4 156,6 hematite (αfe2o3) ilmenite (fetio3) st2 puriala district 959,5 991,3 ilmenite (fetio3) st3 puriala district 269,2 285,9 hematite (αfe2o3) ilmenite (fetio3) jahidin et al./ jgeet vol 5 no 2/2020 65 the presence of hematite and geotite magnetic minerals in the ultramafic rock samples was also confirmed by xrd (x-ray difraction) analysis. in addition to the magnetic minerals in the form of hematite and geotite, in the ultramafic rock samples there are other minerals in the form of olivine minerals, cristabolite, wuestite, calcite, and nickel. the presence of hematite and ilmenite magnetic minerals in soil samples is also confirmed by the results of the xrf (x-ray fluorescence) analysis. based on the results of the xrf analysis, obtained elemental content in soil samples in the form of fe and ti as the forming elements of hematite and ilmenite minerals. 3.3 weathering level of ultramafic rock samples to find out the level of weathering of ultramafic rocks in the study area, an analysis was made of the presence of magnetic minerals in rock samples based on the magnetic susceptibility of the sample. with reference to the mineral content in the rock weathering level as contained in table 1, the presence of magnetic minerals in the form of hematite and geotite in the sample shows that the weathering level of ultramafic rocks in the study area is the continued weathering level. overall, a description of the weathering level of rock samples by site and sub-district in the study area can be seen in the following table 4. table 4. weathering level of ultramafic rock samples site name area type of ultramafic rock magnetic susceptibility value (x 10-6 si) type of magnetic mineral weathering level p1 puriala district olivine websterite 960 2.128 hematite (αfe2o3) geotite (feooh) continued p2 puriala district olivine websterite 690 1364 hematite (αfe2o3) geotite (feooh) continued p3 puriala district lherzolite 1.610 2.860 hematite (αfe2o3) geotite (feooh) continued st2 puriala district lherzolite 1.218 4.724 hematite (αfe2o3) geotite (feooh) continued st3 puriala district lherzolite 3.700 4.364 hematite (αfe2o3) geotite (feooh) continued d1 pondidaha district lherzolite 679 1.439 hematite (αfe2o3) continued d2 pondidaha district lherzolite 640 1543 geotite (feooh) continued d3 pondidaha district lherzolite 580 1460 hematite (αfe2o3) continued st1 pondidaha district lherzolite 666 814 geotite (feooh) continued st2 pondidaha district lherzolite 586 901 hematite (αfe2o3) continued st3 pondidaha district lherzolite 992 1.434 geotite (feooh) continued st5 pondidaha district lherzolite 894 1.603 hematite (αfe2o3) continued in the study area, determination of weathering levels of ultramafic rock samples and nickel content contained in laterite sediments was carried out on several samples representing different sites and sub-district areas. the analysis results of these samples are presented in table 5. table 5. weathering level of ultramafic rocks and nickel content weathering level name of ultramafic rock sample site name of soil samples area nickel content (%) finding in laterite sedimentary layer continued st2 st2 puriala district 2,34 saprolite continued st3 st3 puriala district 2,40 saprolite continued st1 st1.1 pondidaha district 2,37 saprolite continued st2 st2.1 pondidaha district 2,40 saprolite continued st3 st3.1 pondidaha district 0,42 saprock continued st5 st5.1 st5.2 st5.3 pondidaha district 1,65 2,08 1,96 saprolite saprolite saprolite continued d2 on the core: d2.1.5.1 d2.1.5.2 d2.1.5.3 pondidaha district 0,51 0,30 0,29 bedrock continued d3 on the core: d3.5.3.2 pondidaha district 0,20 bedrock 4. conclusion based on the finding in this study, some conclusions can be summarized, as the following : 1. the magnetic susceptibility value of ultramafic rocks in the study area varies from 580 x 10-6 si to 4,724 x 10-6 si. the magnetic susceptibility of ultramafic rock samples shows different values in the upper and lower cores where the magnetic upper core susceptibility values tend to be greater. this relates to the weathering process which always starts in the upper structure so that it allows greater concentrations of magnetic minerals. the difference in value indicates that the magnetic susceptibility parameter can explain the weathering conditions of ultramafic rocks. 2. the magnetic minerals present in the ultramafic rock samples are hematite and geotite minerals. in addition to these two magnetic minerals, there are other minerals in the form of olivine minerals, cristabolite, wuestite, calcite, and nickel. 3. based on the value of magnetic susceptibility of ultramafic rock samples which shows the magnetic susceptibility of hematite and geotite minerals, the weathering level of ultramafic rock samples in the study 66 jahidin et al./ jgeet vol 5 no 2/2020 area includes continued weathering level (magnetic susceptibility value of samples is 580 x 10-6 si to 4,724 x 10-6 si). 4. the level of weathering of ultramafic rocks can affect nickel content in lateritic nickel sediments. the level of continued weathering that occurs in ultramafic rocks in the study area produces nickel laterite deposits with a nickel content of 1.65 2.40 % in the saprolite zone, 0.42 % in the saprock zone, and 0.20 0.51 % in the basic rock zone (bedrock). acknowledgment this research was supported by university of halu oleo (uho). we thank to lppm uho for helping in funding this research through the dipa uho fund in 2019. references boldt, 1967. laterit deposites, mc. farlane publish dearing, j., 1999, environmental magnetic susceptibility: using the bartington ms2 system. chi publishing, keniloworth. evans, a.m., 1993. ore geology and industrial minerals. blackwell scientific publications, oxford,390 pp. hunt, c., moskowit, b.m., banerje, s.k., 1995, magnetik properties of rock and minerals. in t. j. ahrens (ed.), handbook of physical contants, (vol. 3, pp. 189-204), american geophysical union. isaac, r.a. dan j.d. kerber, 1971, atomic absorption and flame photometry: techniques and uses in soil, plant, and water analysis. in l.m. walsh (ed), instrumental methods for analysis of soils and plant tissue. soil sci. soc. of amer., inc. ma., wisc. usa. jahidin, ngkoimani, l.o., ilmawati, w.o.s., iradat salihin, l.m., irawati, usmardin, al firman, harisma, and okto, a., 2019, the magnetic susceptibility analyzes of motonuno lake sediment in muna regency, southeast sulawesi, indonesia, iop conf. series: earth and environmental science 311 (2019) 012037 iop publishing doi:10.1088/1755-1315/311/1/01. m.e. evans and f. heller, 2003, environmental magnetism. principles and applications of enviromagnetics. academic press, san diego (311pp). maher, b. and thompsons, r., 1999, quartenary climates, environments and magnetism, 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(eds.), quaternary climates, envand magnetism, cambridge university press, cambridge, pp. 279-322. waheed, a., 2002, nickel laterite: a short course on the chemistry, mineralogy and formation of nickel laterites, pt. inco, indonesia. sembiring s. 2008. sifat kimia dan fisik tanah pada areal bekas tambang bauksit di pulau bintan, riau. balai penelitian kehutanan aek nauli. sumatera utara. 5(2): 123-134. sudarningsih dan fahruddin, 2008. penggunaan metoda difraksi sinar x dalam menganalisa kandungan mineral pada batuan ultrabasa kalimantan selatan. staf pengajar program studi fisika fmipa, universitas lampung mangkurat. sundari, w., 2012, analisis data eksplorasi bijih nikel laterit untuk estimasi cadangan dan perancangan pit pada pt. timah eksplomin di desa baliara kecamatan kabaena barat. kabupaten bombana provinsi sulawesi tenggara. prosiding seminar nasional aplikasi sains & teknologi (snast) periode iii issn: 1979-911x, 3 november 2012: yogyakarta. surono, 2010, geologi lengan tenggara sulawesi. bandung: badan geologi, kementerian energi dan sumber daya mineral. yulianto, a., bijaksana, s., loeskmanto, w., dan kurnia, d., 2003, produksi hematit ( -fe2o3) dari pasir besi: pemanfaatan potensi alam sebagai bahan industri berbasis sifat kemagnetan, jurnal sains materi indonesia, 5 (1), 5154. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 3 2020 adji, a.s., et al./ jgeet vol 5 no 3/2020 119 research article analysis of shoreline shift using satellite imagery near makassar city rian amukti1, arif seno adji1, syamsuri ruslan2 1department center for deep-sea research, indonesian institute of sciences, ambon 97233, indonesia 2 department of fisheries and marine science, universitas muslim indonesia, south sulawesi 90231, indonesia. * corresponding author : rian.amukti87@gmail.com tel.:+62 911 322676; fax: +62 911 322700 received: june 5, 2020; accepted: july 15, 2020. doi : 10.25299/jgeet.2020.5.3.5111 abstract shoreline shift have occurred in the coastal region of makassar city in recent years due to abrasion and accretion. spatial temporal feature extraction of the makassar city region has been carried out using remote sensing techniques withradiometri, geometric corrections and composite imagein the landsat image dataset in 2009 and 2019. this study aims to analyze shoreline shift near makassar city with remote sensing technology using landsat imagery data, based on multi-temporal data with visual and digital analysis techniques between 2009 and 2019. this research contributes to local and central government as baseline data (data base) in making decisions for handling coastal areas. the results showed that the length of the makassar city coastline without including the coastline length of the islands separated from land in a row that is equal to 37.79 km in 2009. while in 2019 there was a significant change that is 49.82 km. this shows the addition of a coastline of 12.03 km in the span of 10 years. these changes are mainly caused by anthropogenic factors, namely the construction of the pier / port and the reclamation and hydrooceanographic factors, namely waves, currents and tides. keywords: makassar, abrasion, accretion, shoreline 1. introduction makassar is the capital of the province of south sulawesi, which is located in the southern part of sulawesi island, formerly called ujung pandang, located between 119º24'17'38" east longitude and 5º8'6'19" south latitude bordering the north with maros regency, east maros regency, south of gowa regency and west of the makassar strait. makassar city is the capital of south sulawesi province and is the fourth largest city in indonesia which has an area of 175.79 km2 with a length of 52.8 km consisting of coastline coastline along 36.1 km, as well as the coastline of islands and gusung along 16.7 km. makassar city has a population of 1,339,374 inhabitants, so this city has become a metropolitan city. administratively, makassar city consists of 14 districts and 143 villages. the purpose of this study is to examine in depth the pattern of shoreline shift in the coastal area of makassar city using remote sensing techniques with radiometri, geometric corrections and composite image in the landsat image dataset in 2009 and 2019 knowledge of the changes in the shape of the coastline is very important for coastal area monitoring and is aimed at effective management of coastal areas. one appropriate technique used for monitoring this coastal area is remote sensing. this technology can be used as an inventory and monitoring of natural resources that are increasingly dynamic. with different geographical conditions for each island in indonesia, monitoring can be done with the availability of real time, fast, multi-temporal, multi-spectral, multi-spatial, and sustainable data the use of landsat imagery for shoreline determination is often used, for example by using the segmentation method with the agso and bilko formula approaches, so that an optimal coastline is obtained (agus et al. 2015). the use of google earth imagery in shoreline change analysis can also be done (suwandana 2019). shoreline changes can also be analyzed using landsat data for 10 years using the digitization and overlay methods such as the bengkulu beach case (syukhriani, nofridiansyah, and sulistyo 2017). the accuracy of coastline geometry can also be analyzed using water indices on various land covers (wicaksono and wicaksono 2019). the coastline is also affected by the presence of sediments entering the river delta, by using remote sensing it can be calculated on the changes in the coastline (fan et al. 2017) according to tejakusuma (2011) in kulmawapa, et al., (2017). the coastal region is a very dynamic region. the interaction of human activities and natural activities will put pressure on the changing coastal environment. over time, the pressure on the coastal environment will continue to increase, one of which is the problem of shoreline change. the coastline is a boundary line between land and sea water. each beach has a coastline with an irregular position, it can change because of natural and human factors. factors from nature include sedimentation, coastal erosion and tides while factors from humans such as coastal excavation, reclamation, shore protection and regulation of river flow patterns .in a simple process the change in coastline is caused by wind and water that moves from a place continuously. baseline coastline changes include abrasion and accretion (sedimentation) which can occur naturally due to natural and human factors. sediment can be transported so far that it changes the position of the coastline. sediment transport along the coastline is a major cause of shoreline changes. changes in the coastline basically include abrasion and accretion (sedimentation) which can occur due to natural and human factors. sediment can be transported so far that it changes the position of the coastline (angkotasan, nurjaya, and natih 2012). changes in the coastline caused by abrasion or erosion occur due to ocean currents and sea waves that continuously hit http://journal.uir.ac.id/index.php/jgeet 120 adji, a.s., et al./ jgeet vol 5 no 3/2020 the shoreline and the existence of a relatively flat beach, while the accretion process at the beach is caused by a buildup of sediment from the land and deposited on the coast, especially through the estuary river. sediments originating from the mainland, and entering the river flow and being taken to the sea through estuaries, will also cause changes in the shape of the coastline. the mass of incoming sediment that is constantly accompanied by mud causes an increase in land area or siltation in the estuary and coastal sections. accumulation of mud that settles and is trapped by mangrove vegetation over many years will cause land emergence (fan et al. 2017). human efforts to utilize coastal areas are often not based on a good understanding of coastal behavior. as a result, many problems have arisen, one of which is abrasion and sedimentation of the coastline. based on the above background, a research is needed to find out the changes in the coastline in makassar city by utilizing technology that is easy, fast, and accurate, namely through monitoring the landsat imagery with remote sensing applications. information on shoreline changes is very important in various coastal studies, for example; coastal area management plans, disaster mitigation, abrasion-accretion studies. 2. research methods this research will be carried out in the city of makassar precisely on the coast of makassar city (fig1). this location was chosen based on the following considerations: (1) there is a change in coastline pattern in the coastal area of makassar city. (2) to examine in more detail the pattern of changes in coastline in the coastal area of makassar city. fig. 1. map of research location. the procedures performed in this study are as follows: 1. stage of obtaining image the initial stage in carrying out the image is to download landsat image data from the official usgs website (u.s geological survey). 2. import data import landsat 7 and 8 etm + imagery data to be used. landsat image data that is still in tif format is converted to raster file format and vector format for analysis in er mapper software. 3. layer stacking this process combines several different bands / channels to form the desired appearance. it is known that landsat 8 consists of 11 bands, each of which has its own uses, while landsat 7 consists of 6 bands. and to display a standard display of landsat imagery, a band / channel merging process called stacking or composite is needed. 4. radiometric and geometric corrections radiometric correction is a process to improve the visual quality of an image, in terms of correcting pixel values that do not correspond to the reflectance value or the actual spectral radiance of the object. meanwhile, geometric corrections contain geo-referenced data, both position (latitude and longitude coordinate system) and other information. 5. subset the cropping process is carried out so that the data analysis will focus on the object and area to be studied, as well as minimize the files used and speed up the processes in the er mapper when compared to processing a full scene. 6. composite image composite band process can be carried out for the classification process. the selection of the band to be used must be adjusted for the purpose of classification. the choice of band combination for observation of shoreline changes using composite color 543 for landsat 7 etm + and composite color 564 for landsat 8 oli. it is suitable for land/water distinction. 7. image sharpening image sharpening is done to further facilitate visual interpretation and understanding of an image. the advantage of digital data is that it allows us to manipulate the pixel values of adji, a.s., et al./ jgeet vol 5 no 3/2020 121 an image, even though the image has been corrected for radiometric, atmospheric, and sensor characteristics before image data is distributed to users, but the appearance of the image is still less than optimal for visual interpretation. image sharpening techniques are used in the context of image enhancement, increasing the gray scale change in pixel brightness values in terms of photographic print quality for interpretation in processing without returning to interactive digital analysis. the first step in the subjective process of digital classification. 8. digitizing the coastline after multi-temporal corrected image, the next step is the on screen digitization process. digitization is intended to change the format of raster data to vector data format. the object being digitized is the coastline. the entire digitization process uses image analysis facilities on arcgis software that can display raster and vector data at once. 9. overlay after the digitization phase is completed, the next process is to overlay the four coastlines above. after that an analysis of coastline changes in 2009 and 2019 was conducted. 10. map layout the final process of image interpretation is to make the final output in the form of maps of changes in coastline, both in the form of softcopy and hardcopy (print out). the steps in the map layout are to select the view then select the layout view. then set the map shape with the desired attributes according to the correct map making rules. after everything is finished save the data that has finished layout by selecting file> export map> jpeg> ok. fig 2. flow chart analysis of shoreline shiftnear makassar city 3. results and discussion results the results of the coastline overlay in the landsat imagery in 2009 and 2019 experienced significant coastline changes and showed abrasion and accretion. the change in the coastline was done by comparing the results of the 2009 coastline digitization and 2019. the 2009 coastline was used as the initial coastline to find out the coastline changes that have occurred over the past 10 years. the results of overlays from landsat image data in 2009 and 2019 can be seen that in all locations of research on the coast of makassar city experiencing changes in the coastline due to abrasion and accretion. in general, along the coastline of makassar city, it has been shown that in the last 10 years there has been a change in the coastline. this this consistent with the previoues research of shorline changes detection using image satelite analyse near gianyar (aryastana, eryani, and candrayana 2015), the coast experiences abrasion, if the current coastline of the year is more landward than the previous coastline and vice versa for accreted beaches. mapping shoreline changes is done with the aim to clarify the shape of shoreline changes that have occurred on the coast of makassar city over the past 10 years. mapping shoreline changes is presented in fig 3. analysis of shoreline shift overlay map of shoreline shift corrected cropping image composite projection from nutm50 to sutm50 contrast sharpening digitize landsat image 7(2009) landsat image 8tahun 2019 adji, a.s., et al./ jgeet vol 5 no 3/2020 122 a b c d fig 3. mapping coastline changes in the coast of makassar city (a) segment 1; (b) segment 2; (c) segment 3; (d) segment 4. the results of the interpretation of landsat image data in 2009, showed that the coastal area of makassar city was still lacking of community settlements, the lack of land use change as tourist attractions, ports / docks, and the construction of coastal protective structures around the coast were still lacking. the length of the coastline of makassar city in 2009 was 10.14 km in segment 1 which included biringkanaya district and tamalanrea district. segment 2 covers tallodistrict, ujung tanah district, wajo district and ujung pandang district having a coastline length of 17.48 km. 7.08 km. in segment 3 which includes tamalate district. segment 4 covers tamalate district which has a coastline length of 3.09 km. unlike the case in 2019, the increasing number of community settlements around the coast and the increasing use of land use change such as the making of docks / ports and the construction of coastal protective structures. the existence of communities that make settlements so that human factors can influence the occurrence of shoreline changes from the felling of trees which can cause erosion and littering.this can be one of the factors that influence changes in coastline in the form of abrasion and accretion along the coast of makassar city over the past 10 years. the length of the coastline of makassar city in 2019 is around 12.15 km in segment 1. segments 2 and 3 have a coastline length of 32.59 km. while segment 4 has a coastline of 5.08 km. accretion that occurred for 10 years (2009-2019) allegedly caused by coastal protective structures such as breakwater, because of the addition of land to make a breakwater. the existence of pier / port construction and reclamation. the coastal topography condition of the makassar city area is sloping, so that the materials around the residential area will be carried to the sea by the current when it rains and the existence of watersheds such as the jeneberang river, tallo river and pampang river which is a place for spreading sediment particles around the coast. table 1. the shape of shoreline changes in makassar city in each segment in 2009 2019. we use (m2) because when done in the form of spatial calculations, only one permanent caused in the area did not change from 2009-20019 (fixed) segment sub-district change abra-sion accre-tion permanent 1 2 3 4 biringkanaya tamalanrea tallo ujung tanah wajo ujung pandang tamalate tamalate 11.580,14 m2 105.233,53 m2 20.950,48 m2 45.250,39 m2 20.034,79 m2 22.615,44 m2 74.836,05 m2 18.543,62 m2 209.090,08 m2 98.183,47 m2 721.530,53 m2 59.053,95 m2 10.213,8 m2 26.492,2 m2 1.369.692,6 m2 201.070,21 m2 28.738,48 m2 total 319.044,44 m2 2.695.326,84 m2 28.738,48 m2 the results of overlays conducted on landsat 7 in 2009 and landsat 8 in 2019 produced several crossing shorelines. these results are then sorted, then grouped into changes that are abrasion or changes are accretion. after identifying the location of abrasion and beach accretion by overlapping the longest coastline with the most recent year coastline. the addition of land in 2009-2019 amounted to 2,695,326.84 m2 with an area of each namely: biringkanaya subdistrict with an area of 209,090.08 m2, tamalanrea sub-district with an area of 98,183.47 m2, tallo sub-district with an area of 721,530.53 adji, a.s., et al./ jgeet vol 5 no 3/2020 123 m2, district of ujung tanah with an area of 59,053 , 95 m2, wajo district covering 10,213.8 m2, ujung pandang district covering 26,492.2 m2, tamalate district covering 1,369,692.6 m2 for segment 3 and tamalate district covering 201,070.21 m2 in segment 4. whereas the reduction in land in 2009 -2019 amounted to 319,044.44 m2 with the respective widths namely: biringkanaya district covering 11,580.14 m2, tamalanrea district covering 105,233.53 m2, tallo district covering 20,950.48 m2, ujung tanah district covering 45,250.39 m2, wajo district covering an area of 20,034.79 m2, ujung pandang district covering an area of 22,615.44 m2, tamalate district covering an area of 74,836.05 m2 for segment 3 and tamalate district covering an area of 18,543.62 m2 in segment 4. the coastline changes that occur in the coastal area of makassar city are the same as the results of a study conducted by yulius and ramdhan (2013) about changes in the coastline in the bungus bay of padang city, which occur accretion and experience abrasion on the other side and the methods used in his research of landsat 5tm images in 2000, ikonos in 2006, alos in 2010 and spot in 2011. the factors that cause changes in the coastline in the coastal area of makassar city are caused by hydro-oceanographic factors (natural factors) and are caused by human activities. natural factors can cause changes in coastline in the form of abrasion or accretion. such as high waves, current velocity, sediment transport and tides. while anthropogenic factors (human activities) carried out in the coastal area of makassar city in the form of the construction of the port of the pier / port (biringkanaya district, tallo, ujung tanah and tamalate). the accretion was caused by the reclamation namely the process of making new land from the seabed, which will be used as a place to build buildings and serve as a tourist area,carried out by the local government in the form of the center point of indonesia (cpi) project in tamalate district segment 3. the existence of residential land use for the community, as tourist attractions in tamalate and tamalanrea districts. this is supported by the results of shuhendry's research (2004) which states that the cause of damage / changes in coastline caused by human activities (anthropogenic) including the taking or transfer of coastal protective land functions and development in coastal areas that are not in accordance with applicable rules and cause imbalances sediment transport along the coast. discussion changes in the coastline occur because, firstly due to the use of land where people build buildings on the beach, especially in the district of tamalanrea (segment 2), secondly caused by the cutting down of mangrove trees so that it causes abrasion on the shoreline, thirdly caused by natural factors namely currents and waves, although the effect is not too large but occur continuously. finally, the fourth cause is the existence of reclamation such as the construction of a wharf for fishermen in biringkanaya district, ujung tanah district and tamalate district. furthermore, the construction of the cpi (indonesian point) in tamalate sub-district is to be used as a tourist area 4. conclusion based on the results and discussion in this study, it can be concluded that: 1. coastal changes that occur in the coastal area of makassar city based on comparison of landsat 7 etm + 2009 image data with landsat 8 oli image data in 2019 there was a change in coastline in the form of abrasion and accretion. 2. changes in the coastline that occurred in the coastal area of makassar city over a period of 10 years in the form of accretion of 2,695,326.84 m2 and abrasion of 319,044.44 m2. 3. the coastline of makassar city in 2009 was 37.79 km. whereas in 2019 there was a significant change, namely 49.82 km. this shows the addition of a coastline of 12.03 km. acknowledgment we sincerely thank all parties who have helped in research and data analysis. references agus, i made, wirahadi putra, adhi susanto, and indah soesanti. 2015. “ekstraksi garis pantai pada citra satelit landsat dengan metode 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[sumber: http://ojs.uho.ac.id/index.php/jsl/article/view/3610] suwandana, endan. 2019. “depik.” depik, jurnal ilmu-ilmu perairan, pesisir dan perikanan 8(3): 193–206. syukhriani, silvy, eko nofridiansyah, and bambang sulistyo. 2017. “analisis data citra landsat untuk pemantauan perubahan garis pantai kota bengkulu.” jurnal enggano 2(1): 90–100. wicaksono, arief, and pramaditya wicaksono. 2019. “akurasi geometri garis pantai hasil transformasi indeks air pada berbagai penutup lahan di kabupaten jepara.” majalah geografi indonesia 33(1): 86–94. tejakusuma i. g. 2011. pengkajian kerentanan fisik untuk pengembangan pesisir wilayah kota makassar. jurnal sains dan teknologi indonesia. 13(2) : 82-87. yulius m., dan ramdhan. 2013. perubahan garis pantai di teluk bungus kota padang provinsi sumatra barat berdasarkan analisis citra satelit. jurnal ilmu dan teknologi kelautan tropis. 5(2) : 417-427. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://ojs.uho.ac.id/index.php/jsl/article/view/3610 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 3 2021 164 anshori, c., et al./ jgeet vol 6 no 3/2021 research article geomorphosite assessment at north karangsambung -karangbolong geopark kebumen, as tools of geotourism development chusni ansori 1,2*, i. wayan warmada3, nugroho imam setiawan3, herry yogaswara4 1 centre for geotechnology, indonesian institute of science, lipibandung, west java, indonesia, 2 doctor in geological engineering, department of geological engineering, faculty of engineering, universitas gadjah mada, yogyakarta, indonesia 3 department of geological engineering, faculty of engineering, universitas gadjah mada, yogyakarta, indonesia 4 research center for population, indonesian institute of sciences, lipi-jakarta, indonesia * corresponding author : chus001@lipi.go.id, ansorich.63@gmail.com tel.:+62-81-32663-0373 received: apr 23, 2021; accepted: sept 14, 2021. doi: 10.25299/jgeet.2021.6.3.6753 abstract geopark is a sustainable regional development concept that combines geological, biological, and cultural diversities through conservation and education activities to improve the community's welfare. kebumen regency has a national geopark karangsambung-karangbolong (gnkk) covering 543,599 km2 with 41 geosites, 8 cultures, and 8 biosites since 2018. the northern part of the area is a geological heritage that is widely used for field geological education. the study aims to identify and assess geosites and geomorphosite in the north area, describing the region's geomorphological processes and geological evolution. field research was conducted to get an overview of geological diversity, geomorphology, and geosite and determine the selected geomorphosites. those have been decided as the supporting geopark, so that their unique geological conditions must be already described. geomorphosite assessment was done quantitatively using the kubalikova method by assessing five main parameters that include; intrinsic and scientific value, the value of education, economic value, conservation value, and added value. pentulu indah (pi) is the best geomorphosite at north gnkk to look at the differences between pre-tertiary mélange landform with a tertiary volcanic sediment structure. wagirsambeng is the best geomorphosite to knows about the reversal of the geological process of the anticline and synclinal ridge. the scientific and intrinsic value of pi = 4, while wagirsambeng = 3. the educational value of pi = 4, while wagirsambeng = 2. economic value is still not satisfactory, but pi = 2, while wagirsambeng = 1.5. conservation value of p.i. = 3.5, while wagirsambeng = 2.5. added value pi = 2.75 while wagirsambeng = 1.5. based on those, geomorphosite pentulu indah is 16,26 point or a good value (87.83 %) while wagirsambeng is 10.5 point or fairly level (56.75 %) keywords: geopark, karangsambung, geomorphosite, pentulu indah, wagirsambeng, asessment. 1. introduction 1.1. background study according to (unesco, 2016), a geopark is a protected area with extraordinary geological elements – including archaeological, ecological, and cultural values where local communities are invited to protect and improve the functioning of natural heritage. key elements include geological diversity, biodiversity, and cultural diversity with the ultimate goal of protecting earth's diversity (geodiversity), environmental preservation, and broader earth science education. the global geopark network (ggn, 2021) defines geopark as areas with clear boundaries that enable sustainable local development, both on social, economic, cultural, and environmental aspects. the concept of regional development involves many stakeholders to provide significant regional impacts for conservation, education, and improving the surrounding community's welfare based on sustainable green tourism activities (green tourism). geopark has three main pillars; geodiversity, biodiversity, and cultural diversity (ansori, 2018), figure 1. geodiversity is a geological paradigm covering the diversity of geological environments, phenomena, and active processes that make up landscapes, rocks, minerals, fossils, soils, and other deposits that provide a framework for life on earth (gray, 2008). geological diversity is unique in geological appearance (rocks, minerals, and fossils), geomorphology (landscapes and physical processes), geological processes, and soil formation (murray gray, 2013). geodiversity is a neutral term that describes various abiotic phenomena on earth. geological diversity is the backbone of geo-heritage, geoconservation, and modern society itself (gray, 2018). fig 1. geopark comprises three main pillars in geological, biological, and cultural diversity for conservation, education, and local economic development (ansori, 2018). http://journal.uir.ac.id/index.php/jgeet mailto:chus001@lipi.go.id anshori, c., et al./ jgeet vol 6 no 3/2021 165 the concept of geomorphological heritage includes soil forms and processes that play a crucial role in understanding earth's history and connect with biological and cultural heritage (reynard and coratza, 2016). it is widely recognized that geomorphological processes and soil forms have a fundamental role in supporting habitats, species, and ecosystem/environmental services (gordon, j.e., barron, 2011; m. gray, 2013; gordon, j.e.; crofts, r.; diaz-martinez.e; and woo, 2017). simultaneously, geomorphological heritage includes geomorphological objects and cultural components with heritage values partly determined by the geomorphological context in which they are incorporated (panizza, m., piacente, 2009; gordon, 2012; murray gray, 2013; reynard and giusti, 2017). geodiversity elements may have different values, ranging from more concrete, economic, functional, scientific, and educational, to intangibles, such as intrinsic values, culture, and aesthetic values (m. gray, 2013). therefore, it is necessary to assess a value that is considered outstanding. a site is held to have scientific value when research conducted directly at that location or using samples collected from it has resulted in significant scientific understanding for geosciences advancement nationally and internationally. besides, sites relevant to the history of geosciences at the national and international level can also be considered to have a scientific value. geological diversity with high scientific, educational, beauty, and cultural value is made as geosite or geomorphosite (reynard, 2005) or geotope (grandgirard, 1999). a site is held to have scientific value when research conducted directly at that location or using samples collected from it has resulted in significant scientific understanding for geosciences advancement nationally and internationally (brilha, 2016). understanding geotourism begins with an understanding of the environment. geotourism was developed to reduce the negative impact of mass tourism with tourist attractions in the form of geomorphology and geological processes (newsome, d. & dowling, 2010). the natural environment is defined as an environment that includes abiotic elements, biotic and cultural elements. newsome, d. & dowling, (2010) refers to it as a component of abc (abiotic, biotic, culture). these components become a real force for geotourism development activities. a (geodiversity/abiotic), b (biodiversity), c (culturediversity) components are also the main component of the geopark, so geotourism is the main activity in geopark to drive the local economy sustainably. karangsambungkarangbolong geopark consists of 41 geosites, 8 biosites, and 10 cultures, for geotourism development in the northern part of the geopark needs to be assessed the assessment of elements of geological diversity includes a scientific value (representation, integrity, persuasion, scientific understanding), educational value (didactic potential, variation of geological elements, accessibility, safety), tourism value (scenery, geological value, accessibility, safety) (brilha, 2018). assessment of geological diversity can use scoring and weighting models. considers (ansori, 2018) that the high value of geosite candidates if the geosite has a high value on three elements of diversity at once, namely geological diversity, biological and cultural diversity. several parameters must be met to assess a site's feasibility for tourism purposes based on this geology. several researchers have researched geotourism by quantifying various agreed parameters. however, the authors still differ in terms of the parameters that need to be quantified. some of these authors are (bruschi and cendrero, 2005), (panizza, 2001), (pralong, 2005), (reynard and coratza, 2007) (serrano and gonzáleztrueba, 2005) (zouros, 2005) and (kubalíková, 2013). fig 2. research area at north area of karangsambung-karangbolong geopark, kebumen, central java, indonesia 166 anshori, c., et al./ jgeet vol 6 no 3/2021 1.2. research objective kebumen regency has had a national geopark karangsambung karangbolong (gnkk) in 2018, covering 543,599 km2 in 12 sub-districts, 117 villages consisting of 41 geosites, ten cultural sites, and eight biosites (fig.2). the northern part of the gnkk area is a geological heritage widely used for field geology education by students from indonesian and foreign universities since 1964. many locations are utilized in the field of geological education as a geosite. to be able to understand and assess landscape geosite in the north, this research was carried out. 2. methodology the research was conducted through field surveys to overview geological conditions, geological diversity, geomorphological diversity, and geosite in the research area. a selection of various geomorphological and geosite diversity in the northern region of gnkk so that the landscape is obtained describes the region's geological conditions and represents the existing geosite. to clarify the diversity of selected geology, morphological photos, rock photos, and morphological sketching are carried out. the assessment of landscape geosite was selected using quantitative methods introduced by (kubalíková, 2013). she has summarized and examined various parameters of the authors who were proposed to be quantified in evaluating the feasibility of a geosite. there are four main parameters agreed upon, namely geodiversity, geoconservation, geosite and geomorphosite. the four main parameters it is divided into five main value parameters, namely; 1. intrinsic and scientific values; 2. value of education; 3. economic value; 4. conservation value; and 5. added value. these five things are quantified (weighted) with values 0 (the method does not consider the criterion), 0.5 (partly considers the criterion), and 1 (considers the criterion). 3. result and discussion 3.1. geomorphosite geomorphological heritage/landscape geosite is also often referred to as geomorphosite, (panizza, m., piacente, 1993), geomorphological assets (quaranta, 1993), geomorphological goods (carton, a., cavallin, a. francavilla, f., mantovani, f., panizza, m., pellegrini, 1994), geomorphological sites (hooke, 1994), geomorphological geotopes (grandgirard, 1995), sites of geomorphological interest (rivas, v., rix, k., frances and cendrero, a., brunsden, 1997). geomorphological heritage includes landscapes and their genetic processes as well as their perceptions and cultural representations (paola coratza, 2018). geomorphosite is also often included as a geosite, but there is also a difference of opinion that geomorphosite does not include geosite. geological site (geosite) is a geological heritage in a geopark with certain characteristics, both individual and multiobject, and is an integral part of an evolutionary story of the formation of a region (perpres, 2019). based on field observation on 24 geosites in karangsambung geoheritage, it can be selected two geomorphosite namely pentulu indah (pi) and wagirsambeng (figure 3). pi geomorphosite as pra-tertiary mélange complex morphology, and wagirsambeng as amphitheater morphology of tertiary rock. 3.1.1. pentulu indah geomorphosite it is a natural tourism area administratively located in karangsambung village, karangsambung district, kebumen regency. located at an altitude of 275 m asl, it is about 500 m from the karangsambung geological field camp. this tourist location is managed by pokdarwis karangsambung tourism village, presenting a stunning landscape sensation on a cool expanse of pine forest on the slopes of g. paras. pokdarwis (kelompok sadar wisata) is the management of village tourism activity. if we are in this location in the morning, it feels like we are on a smooth white cloud. the more daylight will be seen, a red tinge of morning sunlight through the clouds against sindoro and sumbing mountains background (figure 4). there will be cool air with the wind's whistle and pine leaves' subtle friction during the day to evening. the site is on a layered sandstone and andesite breccia of the waturanda formation. large chunks of andesite breccia resulting from residual erosion leave uniquely attractive forms as photo spots. currently, this tourist attraction has been equipped with a variety of tourist supporting rides. the landscape's appearance provides very useful education to understand earth dynamics in the karangsambung area. there is a contrast between the topography in the north and the southern part of the valley, where the luk ulo river flows in the middle. looking to the east, it is clear that the valley of s. luk ulo separates the difference in the morphology of the rock on the left from the rock on the right in the middle. the left landscape is included in the geomorphological unit of melange s13.2 hills with steep slopes and weak erosion (ansori et al., 2020), characterized by isolated, irregular, prismatic hills. apparent dips are generally to the southeast, with steep slopes separated by a narrow valley around them. the slope of the rock layers to the southeast is in line with the slope of the mica-schist foliation at k. brengkok, with a position of n700 e / 250. you can see four hills in prismatic; based on field observations, each rock hill is different. g. gliwang (northernmost) is composed of mica schists and pelitic sediments, g. gemantung is composed of meta graywacke sandstones, g. paruk is composed of basalt and chert, and serpentinite in g. clekep (southernmost), figure 5. fig 3. geomorphosite in the northern part of geopark in the form of 1). pentulu indah (p.i.) and 2) wagirsambeng hill fig 4. the scenery from pentulu indah (p.i.) in the morning by wiwid widya k-ar dating of mica schist at brengkok river resulted in the age of 117±1.1 m.y.a (ketner et al., 1976). k-ar dating on mica schist rocks obtained 101±5.09 million years, 103.05 ± 5.15 million years (suparka, 1988), and 115 ± 6 million years anshori, c., et al./ jgeet vol 6 no 3/2021 167 (miyazaki et al., 1998). the dating of high-pressure metamorphic rocks (jadeite-glaucophane-quartz rocks) based on the k-ar dating is 124±2 million years and 119±2 million years (parkinson et al., 1998). based on rb-sr dating, the age of metamorphic rocks, i.e., amphibious epidote in luk ulo, is 119-117 million years old (hoffmann et al., 2019). ultramafic rocks (basalt and diabase) based on k-ar dating are 81±4.06 million years old and 85.03±4.25 million years old (suparka, 1988). this group of diverse rocks in morphology is known as the melange seboro complex. the hill's shape, the slope of the rocks, the north-south spread pattern, and the rocks' variation indicate that the seboro melange complex is a group of rocks with exotic blocks (asikin, 1974) and formed in the burial melange accretion zone (prsetyadi, 2007). morphology in the middle area is a strong undulating landscape – hills that include structural geomorphological unit s13.7 (ansori et al., 2020). this landscape is characterized by stepping slopes, land used as raindrop rice fields, found a large block of diabase around rice fields. lithology is composed of clay breccia with fragments of claystone, sandstone, pillow lava, conglomerates, limestone nummulites with scaly clay matrix. the layering of rocks is generally chaotic with slump structures, but some indicate the development of layers. totogan formation sediment resulting from heavy force (olistostrome) (asikin, 1974). at the same time, the valley floor of the luk ulo river is an elongated fault. luk ulo river is the largest watershed in kebumen, with a winding shape due to the river's meandering process on the pre-tertiary rock. southern morphology is a hill that stretched eastwards in the form of a series of paras mts. and prahu mts as a synclinal ridge and includes geomorphological units s9.1 (ansori et al., 2020). this morphology is characterized by regular hill and mountain forms with the flat hill, steep slopes, moderate-weak erosion. at the bottom of the hill are found boulders of andesite rocks that are fragments of breccia. the constituent rocks are volcanic breccia with layer sandstone that include the early miosen of the waturanda formation (asikin, 1974). various types of rocks with a morphological appearance that make the place a natural textbook where the concept of plate tectonics can be studied and proven to be true (ansori, c., kumoro y., hastria d., 2016). fig 5. sketch of the landscape as seen from bukit pentulu indah, the hilly landscape of mélange seboro, the undulating morphology of strongstructural hills filled with deposits of totogan fm as olistostrome, and syncline ridge morphology on the volcanic breccia of waturanda fm. fig 6. anticline mountain landscape, syncline ridges, pediment, and alluvial plains that form an amphitheater due to a topographical reversal process where the anticline peaks turn into valleys and various rocks are encountered 168 anshori, c., et al./ jgeet vol 6 no 3/2021 3.1.2. geomorphosite wagirsambeng wagirsambeng hill is one of the isolated hills located in karanggayam district. this hill is composed of deep-sea sedimentary rocks, namely chert and red limestone. this rock is located on the top of the hill leaving unique shapes resembling layer cake. this rock is very artistic and natural, with a height of about 4 meters is a very interesting shape. a chert sample (r55474) from wagirsambeng contains middle cretaceous radiolarians such as c. sphaerica (white), spongocapsula sp., novixitus sp. and alievium sp. (wakita, munasri and bambang, 1994). from all radiolarian data in this area, the luk-ulo melange complex is considered to have been deposited in early to late cretaceous time and accreted at a subduction trench during the middle to the latest cretaceous or earliest paleocene. this complex is unconformably overlain by the eocene (wakita, munasri and bambang, 1994). if the view is directed eastwards, there will be a landscape in the form of a valley extending west-east with a series of circular mountains around it in the form of horseshoes. in the southern part of the series brujul mt, waturanda mt, dliwang mt turns in bukit banda hill. the northern series is perahu mt and paras mt. this kind of landscape is often referred to as the amphitheater, a geomorphological unit of the anticline mountains s9.2 (ansori et al., 2020). this valley is a former fold formed in karangsambung but experienced a topographical reversal process; the anticline peak turned into a valley. the syncline valley turned into a synclinal ridge unit s9.1 (ansori et al., 2020). the former anticline peaks are experiencing weathering, erosion, and avalanche processes. it turns into a valley with the welaran river as an anticline axis and is included in the pediment unit. meanwhile, under a series of horseshoe-shaped mountains found strong corrugated morphology infiltrated by clay breccia of totogan fm, weak corrugated morphology composed by scaly clay of karangsambung fm, and alluvial plains where luk ulo river flows (figure 6). 3.2. geosite assessment geomorphosite assessment in the research area uses the kubalikova assessment method (kubalíková, 2013). the result assessment parameters of the pentulu indah and wagir sambeng landscape geosite can be seen in table 1. based on the assessment and weighting, it can be seen that the total value for pi is 16.26 points (87.83 %) good levels, while wagirsambeng by 10.5 points (56.75 %) with a fairly good level. each assessment variable for pi is always greater than the landscape geosite wagirsambeng. the scientific and intrinsic value of pi = 4, while wagirsambeng = 3. educational value pi = 4, while wagirsambeng = 2. economic value is still not satisfactory, but pi = 2, while wagirsambeng = 1.5. in general, conservation value has been good because of the support of regulations; although it is still not fully adhered to, the value of pi = 3.5, while wagirsambeng = 2.5. added value pi = 2.75 while wagirsambeng = 1.5. in general, the economic value needs to be improved, especially from local products and accessibility, besides the potential damage to the site and the value of beauty on the wagirsambeng site. wagirsambeng value is relatively lower because this site's location has not been managed adequately than pi sites that have had institutional managers for quite a long time. table 1. assessment of geomorphosite based on kubalicova method no variabels score extention geomorphosite pi wagirsambeng a scientific and intrinsic values 1 integrity 0 totally destroyed site 0,5 the disturbed site, but with visible abiotic features 0,5 1 a site without any destruction 1 2 rarity 0 more than 5 sites 0,5 2-5 similar sites 0,5 1 the only site within the area of interest 1 3 diversity 0 only one visible feature/processes 0,5 2-4 visible features/processes 1 more than 5 visible features/processes 1 1 4 scientific knowledge 0 unknown site 0,5 scientific papers on national level 1 high knowledge of the site, monographic studies about the site 1 1 b educational values 1 representativeness and visibility/clarity of the features/processes 0 low representativeness/clarity of the form and process 0,5 medium representativeness, especially for scientists 0,5 1 high representativeness of the form and process, also for the laic public 1 2 exemplarity, pedagogical use 0 very low exemplarity and pedagogical use of the form and process 0,5 existing exemplarity, but with limited pedagogical use, 0,5 1 high exemplarity and high potential for pedagogical use, goedidactics and geotourism 1 3 existing educational products 0 no products, 0,5 leaflets, maps, web pages 0,5 1 info panel, information at the site 1 4 actual use of a site for educational purposes (excursions, guided tours) 0 no educative use of the site, 0,5 site as a part of specialized excursions (students) 0,5 1 guided tours for public 1 c economic value 1 accessibility 0 more than 1000 m from the parking place, 0,5 less than 1000 m from the parking place, 0,5 0,5 anshori, c., et al./ jgeet vol 6 no 3/2021 169 1 more than 1000 m from the stop of public transport 2 presence of tourist infrastructure 0 more than 10 km from the site existing tourist facilities 0,5 5 – 10 km tourist facilities, 1 less than 5 km tourist facilities 1 1 3 local products 0 no local products related to a site, 0 0,5 some products 0,5 1 emblematic site for some local products d conservation value 1 actual threats and risks 0 high both natural and atrophic risks 0,5 existing risks that can disturb the site 0,5 1 low risks and almost no threats 1 2 potential threats and risks 0 high both natural and atrophic risks 0,5 existing risks that can disturb the site 0,5 0,5 1 low risks and almost no threats 3 current status of a site 0 the continuing destruction of the site 0,5 the site destroyed, but now with management measures to avoid the destruction, 0,5 1 no destruction 1 4 legislative protection 0 no legislative protection 0,5 existing proposal for legislative protection 1 existing legislative protection (natural monument, natural reservation…) 1 1 d added value 1 cultural values: the presence of historical/archaeological/religious aspects related to the site 0 no cultural features 0,5 existing cultural features but without strong relation to abiotic features, 0,5 0,5 1 existing cultural features with strong relations to abiotic features 2 ecological values 0 not important 0,5 existing influence but not so important 0,5 1 the important influence of the geomorphologic feature on the ecologic feature 1 3 aesthetic values: a number of colours; 0 0ne colour 0.25 2-3 colours 0,25 0,5 more than 3 colour 0,5 b structure of the space 0 only one pattern 0 0,25 two or three patterns clearly distinguishable 0,25 0,5 more than 3 structure c viewpoints 0 none 0,25 1-2 viewpoint 0,25 0,5 3 and more view point 0,5 total value 16,25 10,5 procentage (%) 87,8378 56,7568 4. conclusion geological diversity is the uniqueness of geological components such as minerals, rocks, fossils, geological structures, and landscapes that become the intrinsic wealth of an area representing the picture of the area's geological evolution process. geological heritage (geo-heritage) is a geological diversity with more value as a heritage because it becomes a record that has been or is happening on earth because of its high scientific value, rare, unique, and beautiful used for research and earth education. geological sites (geosite) is a geological heritage in a geopark with certain characteristics, both individual and multi-object, and is an integral part of an evolutionary story of forming a region. geomorphosite is a landscape of scientific value that describes geology's process and evolution in a region and is part of its geological history. the value of beauty and geomorphosite economy is often utilized as a place of geotourism. in the northern area of gnkk, two ideal geomorphosites describe the landform and geological processes. pi geomorphosite, the differences between geomorphology in the cretaceous melange tectonic complex, sedimentary melange rock (olisthostrome), and normal sedimentary rocks of tertiary age (miocene) can be studied. meanwhile, in the wagirsambeng geomorphosite, the geological process of the anticline and syncline hill topography reversal was observed, which resulted in the amphitheater landform. scoring is based on scientific and intrinsic value, educational value, economic value, conservation value, and added value so that pi has a good value (87.83%) while wagirsambeng has sufficient value (56.75%). the striking difference in values is mainly due to differences in geosite management. acknowledgments thank you to the head of research & development division for earth conservation and information lipi and gnkk management, which allowed us to run this research. references ansori, c., kumoro y., hastria d., w. k. 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(2005) “assessment, protection, and promotion of geomorphological and geological sites in the aegean area, anshori, c., et al./ jgeet vol 6 no 3/2021 171 greeceévaluation, protection et promotion des sites géomorphologiques et géologiques de la région égéenne, grèce,” géomorphologie : relief, processus, environnement, 11(3), pp. 227–234. doi: 10.4000/geomorphologie.398. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 sastrawan, et. al/ jgeet vol 5 no 4/2020 209 research article determining groundwater potential using vertical electrical sounding method in manggar, balikpapan city, indonesia. febrian dedi sastrawan1,*, rahmania1, meidi arisalwadi1 1physics departement, , institut teknologi kalimantan, balikpapan, indonesia. * corresponding author : febrian.dedi@lecturer.itk.ac.id tel.: +62-853-4111-2790 received:aug 17, 2020. ; accepted: dec 22, 2020. doi 10.25299/jgeet.2020.5.4.5495 abstract clean water requirement in manggar urban village of balikpapan city is rising along with population growth. the main source of clean water that can be used is ground water in the aquifer layer. the study of groundwater potential was conducted using vertical electrical sounding (ves) method to determine the presence and types of aquifer layers. the measurements along four measurement points revealed four aquifers buried in depth ranging from 48 to 53 m below the surface. the layer which is potential to be an aquifer is a sand layer with moderate-sized grain. the resistivity values for sand layer at each measurement point vary from 221 to 281ωm. the estimation of sand to be an aquifer layer was supported by the calculation of formation factors. the calculation was based on the ratio of resistivity values from pore-filling water and resistivity values from water-saturated rocks layer. the aquifer revealed in this study is categorized as unconfined aquifer because the upper layer is restricted by sandy clay. the resistivity values vary from 12.8 to 35.4 ωm which behaved as an aquitard layer. however, low resistivity values between 9.6 to 20 ωm are detected under the aquifer layer. the layer is identified as clay which behaved as an impermeable layer or aquiclude. keywords: groundwater, resistivity, aquifer, factor formation. 1. introduction manggar is one of the urban villages in balikpapan city which is now growing rapidly. manggar becomes one of the centers of heavy equipment and oil and gas industry. this situation also lead the rising of clean water needs in this area. besides that, long dry season occurs in balikpapan city, including manggar area often triggers a clean water crisis (sulistyo and abrar, 2017). clean water is an important aspect of human life (hadian et al., 2017). the requirements of clean water over time are becoming increasingly as the population gets bigger in the area. to suit water needs increasingly, the availability of clean water sources needs to be preserved. one source of clean water that can be utilized is ground water. ground water is water present beneath earth’s surfaces that fills the rock pores or soil layers (sihotang et al., 2018; suryadi et al., 2018). the one of more effective ways useful to find groundwater sources is to run geophysical survey in order to understand subsurface conditions. the geophysical method that can be used to determine the presence of groundwater sources is geoelectrical method of vertical electrical sounding (ves) (mohamaden, 2016; mohamed, 2016). ves is one type of the most important method that can be used in the field of groundwater study (abd el-gawad et al., 2017). geoelectrical method of ves reveals resistivity profiles and rock layer thickness of subsurface (sathiyamoorthy and ganesan, 2018). the rock layers have been water saturated will produce resistivity anomalies when compared to the layers have not been saturated. the resistivity anomalies obtained can be used to determine the presence of groundwater sources (mohamaden, 2016). the geoelectrical is a wonderful and effective method used for mapping of shallow and moderate subsurface conditions, therefore this method is suitable to run in groundwater surveys (alfadli and natasia, 2017). numerous authors have conducted a research about the existence of groundwater sources using geoelectrical methods (aizebeokhai et al., 2017; kayode et al., 2016; mohamaden and ehab, 2017). 2. research area setting the measurement points located at manggar urban village of balikpapan city (fig. 1). the topographical condition at the measurement points is relatively flats and dominated by red podsolic soil. red podsolic soil is very sticky when exposed to rain and very dry during the long dry season. geologically, the rock formations found in the study area are included in alluvium deposits. alluvium deposition is estimated generated in holocene age which is originated from river, swamp, beach and delta deposits consisting of gravel, sand, sandstone, and mud. one of a large river in the study area is manggar river controlling the high level of erosion and sedimentation in that area. the manggar river also affects hydrology of the area because it is directly connected to the manggar coast. this fact directly lead to the rising of groundwater pollution due to sea water. groundwater basin in balikpapan city is formed by alluvium deposits with the flow system through rock porosity or space between grains of rock layers. based on the research conducted by geological agency, there are several types of aquifers, namely unconfined aquifer and confined aquifer. the unconfined aquifer is associated with shallow depth groundwater sources ranging from 1 m to 5 m and medium depth ranging from 40 to 50 meters. while confined aquifer is associated with deep groundwater sources. http://journal.uir.ac.id/index.php/jgeet 210 sastrawan, et. al/ jgeet vol 5 no 4/2020 3. method survey of ves method was carried out at four measurement points where the length of each measuring point is 200 m. the basic principle of ves method is an electric current injected below the earth's surface through two electrodes with certain distance and potential difference appearing between the two electrodes. the measurement of ves method used schlumberger configuration electrode array (fig. 2). the electrode array consisted of two current electrodes and two potential electrodes connected to the naniura nrd 300 resistivity meter. the magnitude of the injected current and the distance between the electrodes are factors affecting of penetration depth. vertical subsurface conditions can be obtained by making variations of the current electrode spacing during field measurement activities. fig. 1. contour map of study area and the location of vertical electrical sounding (ves) method applied in groundwater survey. data obtained in this measurement are the magnitude of injected current (i) and the magnitude of the potential difference generated (v). the data collected from each measurement point are used to obtain the apparent resistivity values of the subsurface layers by using geometrical factor (k) of the schlumberger configuration. the equation of geometry factor (k) is expressed by (loke, 1999): (1) the apparent resistivity values (ρa) of subsurface are obtained by using the equation : (2) the rock resistivity values of water saturated will be proportional to the water resistivity values filled-pore (dahlan et al., 2016: arif et al., 2015). based on this relation, a formation factor (f) value is yielded in describing rock porosity. the values can be used to determine the existence of aquifer layers below the surface. the formation factor equation is the ratio between rock resistivity (ρ) and resistivity values of water filled-pores (ρa). (3) the results of hydrogeological studies are relation between rock resistivity and water resistivity of filled-pores that can be presented in table 1 (taib., 1990). the resistivity values of water filled-pores are obtained by measuring directly from residents' wellsusing a portable conductivity meter (fig. 3). fig. 2. electrode array of schlumberger configurations for resistivity measurements table 1. the classificationof formation factors in sedimentary rock ( ) formation layer ≤ 1 clay aquiclude 1-1.5 peat, clayed sand atau silf aquiclude 2 silffind sand poor to medium aquifer 3 medium sand medium to productive aquifer 4 coarse sand productive aquifer 5 gravel higlyproductive aquifer when we conducted field measurement, data obtained have to present good quality data. good quality data are obtained by performing measurement quality control (qc). qc datais performed by logarithmic curves a ½ of currents electrode spacing versus apparent resistivity values of measurement data (fig. 4) sastrawan, et. al/ jgeet vol 5 no 4/2020 211 fig. 3. conductivity meter fig. 4. curve current electrode spacing (½ ab) in meters vs apparent resistivity (ρ_a) in ωm drawn in logarithmic scale. 4. result and discussion the measurement points were located in settlements beginning to be densely-populated (fig. 6). based on the resistivity values from four subsurface 1-d resistivity model and the formation factor were obtained, thus the types of subsurface layers and the existence of aquifer layer can be identified. the average resistivity (ρa) value of water filledpores is 74 ωm. this value will be used to determine the types of subsurface layers (fig. 6). 4.1 1-d resistivity model for ves a1 the results of data processing from measurement point ves a1 were identified 1-d resistivity model consisting 4 subsurface layers indicated by variations of rock resistivity values. penetration depth can be obtained at measurement point ves a1 around 85 m from the surface. the first layer with resistivity value 36.8 ωm is identifiedas overburden. the second layer with resistivity value 26.3ωm is identified as sandy clay layer. this layer is aquitard layer found in depth range from 1.9 to 51m beneath the surface. the third layer with resistivity value 228 ωm and formation factor value 3 is identified as medium grain sizedsand behaved to be potential aquifer layer buried in depth 51to 85 m. this layer is characterized as an unconfined aquifer layer. however, low resistivity value 20 ωm appears at fourth layer in depth up to 85 m isinterpreted as clay and behave as impermeable layer or aquiclude. 4.2 1-d resistivity model for ves a2 the data processing results at ves a2 are identified 5 layers by resistivity values varied between 9.68 to 221 ωm. the first layer is overburden, then the second layer is estimated to be free aquifer layer which is located indepth range from 1.6 to 3m below the surface. this layer with resistivity value of 188ωm and the formation factor value of 2.5 obtained from the data calculation indicating this layer is a fine sand layer. the third layer is sandy clay or aquitard layer with a resistivity value of 28.7 ωm. the fourth layer is an aquifer layer with reactivity value of 221 ωm and formation factor value of 3. this layer is estimated as medium grain sized-sand that can store and transmit water buried in depth range from 52 to 82 m from the surface. this aquifer layer is characterized as unconfined aquifer layer. the low resistivity value of 9,68 ωm at the last layer is interpreted as clay and behave as an aquiclude layer. 4.31-d resistivity model for ves a3 the results of measurement point at ves a3 are identified 4 subsurface layer with penetrations depth of up to 88 m. the subsurface resistivity value from the result of data processing varies from 13 to 254 ωm. the first layer is overburden with thickness around 1m. the second layer with a resistivity value of 35.4 ωm and located in depth range from 1 to 48 m is interpreted as an aquitard layer, namely sandy clay layer. the third layer is estimated to be a unconfined aquifer layer with resistivity value of 245 ωm and formation factor valueof 3.4. this layer is estimated as medium grain sized-sand located in depth range from 48 to 88 m below the surface. while, low resistivity value appearing beneath sand layer is interpreted as clay which is buried in depth up to 88 m and behaveas impermeable layer or aquiclude. 4.4 1-d resistivity model for ves a4 1-d resistivity model of measurement point ves a4 is identified 5 subsurface resistivity layers. the first layer is overburden with thickness around 1 m. the second layer with thickness 2 m has resistivity value 145 ωm interpreted as fine sand and behaved as a free aquifer layer. the third layer with a resistivity value is 12.8 ωm interpreted as sandy clay layer buried at depth ranges between 3 to 53 m below the surface and behaved as aquitard layer. the fourth layer is estimated as a free aquifer layer atdepth ranges from 53 to 95 m. this layer has a resistivity value 281 ωm and formation factor value 3 interpreted as medium grain sized-sand. the fifth layer is clay with resistivity value 10.1 ωm and behaved as an aquiclude layer. fig. 5. subsurface 1-d resistivity model 212 sastrawan, et. al/ jgeet vol 5 no 4/2020 fig. 6. map of research area 5. conclusion geoelectrical method of vertical electrical sounding (ves) is effectively used in groundwater exploration. based on the data analysis known that high resistivity values associated with aquifer layers. this result is supported by the calculation of formation factors obtained at each measurement point. the layer with high resistivity values varies from 221 to 281 ωm and formation factor values variesfrom 2 to 3 behaved as an aquifer layer. this layer is interpreted as medium grain sized-sand with the thickness estimation around 30 m. shallow aquifer layer at point ves a2 and ves a4 is located near the surface and buried in depth from 1 to 3 m. the aquifer layers are obtained then classified as unconfined aquifer layer which is restricted by clay layer detected under the aquifer layer with low resistivity values from 9.68 to20 ωm. this study shows that the aquifer layers in manggar urban village of balikpapan city are classified as medium to productive aquifer. acknowledgements the authors would like to express many thanks to ministry of research and technology/ national agency for research and innovation for providing research funding through the lppm of institut teknologi kalimantan by pdp scheme. the authors also say many thanks to the physics students of institut teknologi kalimanta involved in measurement field activities. references abd el-gawad, a.m.s., kotb, a.d.m., hussien, g.h.g., 2017. geoelectrical contribution for delineation the groundwater potential and subsurface structures on tushka area, egypt. nriag j. astron. geophys. 6, 379–394. https://doi.org/10.1016/j.nrjag.2017.10.003 aizebeokhai, a.p., oyeyemi, 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crystalline basement environment: a case study of isuada, southwestern nigeria. j. african earth sci. 119, 289– 302. https://doi.org/10.1016/j.jafrearsci.2016.04.009 loke, d.m., 1999. electrical imaging surveys for environmental and engineering studies. cangkat minden lorong 6574525, 63. mohamaden, m.i.i., 2016. delineating groundwater aquifer and subsurface structures by using geoelectrical data: case study (dakhla oasis, egypt). nriag j. astron. geophys. 5, 247–253. https://doi.org/10.1016/j.nrjag.2016.05.001 mohamaden, m.i.i., ehab, d., 2017. application of electrical resistivity for groundwater exploration in wadi rahaba, shalateen, egypt. nriag j. astron. geophys. 6, 201– 209. https://doi.org/10.1016/j.nrjag.2017.01.001 mohamed, a.k., 2016. application of dc resistivity method for groundwater investigation, case study at west nile delta, egypt. arab. j. geosci. 9, 1–9. https://doi.org/10.1007/s12517-015-2054-6 sathiyamoorthy, m., ganesan, m., 2018. delineation of groundwater potential and recharge zone using electrical resistivity method around veeranam tank, tamil nadu, india. j. inst. eng. ser. a 99, 637–645. https://doi.org/10.1007/s40030-018-0318-3 sastrawan, et. al/ jgeet vol 5 no 4/2020 213 sihotang, j.w., osvaldus, r., munte, d.b.t., priono, n., mohamad, f., 2018. aquifer area investigation using resistivity method in cikopomayak, west java, indonesia. j. geofis. 16, 19. https://doi.org/10.36435/jgf.v16i3.375 sulistyo, t., abrar, a., 2017. characterization of thin alluvial bed aquifers in manggar river balikpapan east kalimantan indonesia. jtt (jurnal teknol. terpadu) 5, 54. https://doi.org/10.32487/jtt.v5i1.212 suryadi, a., putra, d.b.e., kausarian, h., prayitno, b., fahlepi, r., 2018. groundwater exploration using vertical electrical sounding (ves) method at toro jaya, langgam, riau. j. geosci. eng. environ. technol. 3, 226. https://doi.org/10.24273/jgeet.2018.3.4.2226 © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 4 2021 patonah, a. et al./ jgeet vol 6 no 4/2021 177 research article the transitional gabbroic rocks in bayah geological complex, western part of java, indonesia, inferred from xrf, icp-ms, and microprobe analysis aton patonah1, haryadi permana2, ildrem syafri3 1,3faculty of geological engineering, padjadjaran university, jatinangor, 45363, west java, indonesia 2research center for geotechnology lipi, jl sangkuriang bandung 40135, west java, indonesia * corresponding author : a.patonah@unpad.ac.id tel.: +62-812-2262-540 received: jun 1, 2020; accepted: dec 24, 2021. doi: 10.25299/jgeet.2021.6.4.7189 abstract gabbro, is a fossil remnant of oceanic crust in western part of java, found at bayah geological complex (bgc) and ciletuh melange complex (cmc), indonesia. it has been studied by using petrographic, x-ray fluorescence (xrf), and inductively coupled plasma-mass spectrometry (icpms) and mineralogical (microprobe) analyses. mineral and geochemical composition of these rocks provide important clues to their origins since the rocks have been deformed and gone through auto metamorphism, beside they contain the economic mineral and or rare earth elements (ree). gabbroic rocks in these two areas generally shows phaneritic to porphyritic texture, granular texture. these rocks in cmc are dominated by plagioclase (oligoclase to albite), hornblende, pyroxene, partly altered to tremolite, actinolite, chlorite, epidote, and sericite; meanwhile those of bgc dominantly consist of plagioclase, pyroxene, hornblende, some present of chlorite, actinolite, epidote and biotite as secondary minerals. in multi-element diagrams, gabbroic rocks in cmc show strong negative sr and zr, but positive nb anomaly, while those of bgc show strong negative anomaly of nb and zr. in addition, based on rare earth elements (ree) diagrams, gabbroic rocks in cmc show depleted of light rare earth elements (lree) with negative eu anomaly, while gabbro’s in bgc show enrichment of lree. these characteristics indicate that gbc’s and cmc’s gabbroic rocks came from different magma sources, one was formed by partial melting of depleted upper mantle reservoir while the other one was formed by partial melting of mantle wedge with active participation of subducted slab in an arc tectonic setting, suprasubduction zone which were formed at started upper cretaceous to paleogene, and they had retrograde metamorphism to epidote amphibolite facies. keywords: bayah geological complex (bgc), ciletuh melange complex (cmc), gabbro, ree, arc tectonic setting, retrograde metamorphism 1. introduction gabbro is one component of an ophiolite sequence, the basaltic type, can be derived by partial melting from depleted upper mantle reservoir, heterogeneous reservoir (zindler et al., 1984) or partial melting from oceanic crust which has relation with subduction process (davidson, 1986). different setting, such as arc-mechanism, has various compositions and complicated tectonic histories. according to gill (1981), basaltic rocks contain tio2 <1.3 wt.% formed in subduction zones (orogens), while basaltic rocks with tio2 > 1.3 wt.% are derived from non-orogenous environments, both oceanic and continental environments. gabbro, as part of ophiolite sequence ciletuh melange complex (cmc), western part of java, is situated within the indonesian archipelago at the southern margin of sundaland and the eurasian plate and is a part of the active sundaland margin (figure 1). this is recorded as a fragment cretaceous oceanic crust, a complex zone that has recorded the convergent history between indo-australia dan hindia plate (asikin 1974; soekamto 1975; thayib et al. 1977; martodjojo et al. 1977; suhaeli, 1977; hamilton 1979; schiller et al. 1991; parkinson et al. 1998; wakita, 2000; patonah and permana 2010; satyana, 2014). gabbro, together with other rocks (harzburgite, dunite, basalt, metamorphic rock and marine sediment) is overlain unconformity by ciletuh formation (schiller et al. 1991). some researchers have been concluded that the nature of oceanic crust (included gabbro) and the age of these rocks (rosana et al., 2015) the rock associated with suprasubduction zone and morb; satyana, (2014) explained that gabbro as part of ophiolite cmc, is a product subduction of late cretaceous. for the age dating of gabbro’s, noeradi (1994) and schiller et al. (1991), they said that as a component part of cmc, has the age of more less 55 ma or middle eocene. this implies that gabbro in cmc was formed from upper cretaceous to paleogene which associated with suprasubduction zone and morb. recently, around 20 km northwest of cmc, western part of java, another gabbro has been found in bayah geological complex (bgc) (patonah and permana 2018). the gabbro in bgc found boulders together with metapelitic rocks, it has not been found ultramafic yet. this becomes an interesting issue. therefore, this study will compare the characteristic, the chemical analysis, and petrological data of gabbro in these two complexes to find the genetic and origin of gabbro corresponding to subduction – related. moreover, this research will discuss the tectonic setting of these rocks. 1.1 geological setting geological setting of western part java is begun of mélange compex as product convergent at upper cretaceous – early paleogene melange in ciletuh melange complex, is characterized by presenting of peridotite, dunite, serpentinite, gabbro, basalt, amphibolite, greenschist, and mica schist. this mélange is overlain unconformity by ciletuh formation in ciletuh area, and bayah formation at bayah area. the study area form as part of cmc and bgc and is http://journal.uir.ac.id/index.php/jgeet mailto:a.patonah@unpad.ac.id 178 patonah, a. et al./ jgeet vol 6 no 4/2021 characterized by the occurrence of low – medium grade metamorphic rocks. in cmc, the field observation has been done in cikopo, cikepuh and citisuk rivers. in cikepuh river, pegmatitic gabbro reveals with coarse – very coarse grained and shows auto-metamorphism and altered which are characterized by the presence of actinolite and chlorite consecutive (figure 2). this rock also experiences deformation which is indicated by brecciated. serpentinized-peridotite is found in the upstream of the rivers. it has deformed which is characterized by shearing zone n280oe/30o and thrusted on the top of the sandstone with plane direction is n235oe/30o or contacts with the shale from ciletuh formation with shearing zone is n240oe/35o. geological observation upstream of the rivers along citisuk river (figure 2). pillow lava has been exposed strongly altered in this area which is characterized by the presence of chlorite and carbonate minerals besides pyroxene and plagioclase. tectonic contact between sedimentary rocks is found, and serpentinite is with plane direction of n110oe/70o. serpentinite shows moderate to coarse grain and does not indicate deformation. the coarse grain gabbro’s are found, some of the rocks show a mylonitic structure. in this location, outcrops of metamorphic rock are found with foliation plane n300oe/35o. they are covered by sedimentary rocks of the ciletuh formation. at the end of section, the pillow lava encloses unconformably above the ciletuh formation and complex ophiolite – metamorphic rock. fig 1. ciletuh melange complex is one of major components of cretaceous accretionary – collision complex of southern sundaland (modified from wakita, 2000); and bayah geological complex is located at margin of bayah dome (prihatmoko and idrus, 2020). in bgc, the field observation has been done in cisanun and cigaber rivers. in cisanun river (figure 3), gabbro generally reveals as boulders along this river, while the riverbank consists of porphyry andesite, diorite, mica schist and granodiorite (from downstream to upstream). gabbro has dark grey color, phaneritic texture, some show oriented mineral, and some others show altered mineral, dominated by plagioclase, pyroxene, hornblende, and chlorite minerals. in another river (cigaber river), gabbro’s are also revealing as boulders, but showing more fine texture than those in cisanun river. the riverbank in the river is dominated by mica schist (figure 3). fig 2. field observation in ciletuh melange complex (cmc). fig 3. field observation in bayah geological complex (bgc). 2. material and methods this paper will be focused on gabbro in those cmc and bgc. the material on this paper uses the rock samples from field observation conducted by 8 samples, 5 (five) samples from cmc and 3 (three) samples from bgc for this study (table 1). the methods that are used in this study are petrographic analysis, geochemical and microprobe analysis. the patonah, a. et al./ jgeet vol 6 no 4/2021 179 petrographic analysis has been done in laboratory of petrology and mineralogy, faculty of geological engineering, university of padjadjaran, and research center for geotechnology lipi, bandung, indonesia. table 1. mineral composition of gabbroic rocks in the research area. sample code mineral composition (%) plg px amp trem/ act ep cc chl clay op kp-2 65 0 20 7 <3 0 3 0 <3 ko-10 45 8 20 0 8 7 7 0 <5 ko-12 75 0 15 0 3 <3 0 0 <5 ko-15 50 0 25 0 7 8 <5 <3 <3 tk-16 65 7 20 0 2 3 0 0 <3 cgb 5 35 20 15 10 5 0 7 5 3 csn 4 35 25 7 8 5 0 8 7 <5 csn 13 40 25 7 8 3 0 7 5 5 noted: plg = plagioclase; px = pyroxene; amp=amphibole; trem / act = tremolite / actinolite; ep = epidote; cc = calcite; chl = chlorite; serc = sericite; op = opaque geochemical analysis using x-ray fluorescence (xrf) and inductively coupled plasma-mass spectrometry icp-ms is implemented on this study. these analyzes were done by intertek, jakarta in 2018. whole rock major element abundances were determined by xrf with fused using lithium metaborate. rare earth element and trace element were determined by inductively-coupled plasma – mass spectrometry (icp – ms) with a detection limit of 0.01 to 0.02 ppm. the analytical errors for most elements were less than 2%. furthermore, mineral chemical analysis is used in this study. the samples were carried out at ori, tokyo by using jeol super probe 733 electron probe in 1999 through cooperation project between research center for geotechnology lipi, bandung, indonesia with ocean research institute (ori – tokyo). the samples analyzed by this method are samples from cmc (kp-2, ko-10, and ko-15). data on mineral analysis calculations from microprobe are then recalculated based on 8 oxygen atoms in plagioclase; amphibole is calculated on 23 oxygen atoms with an estimate of fe2+/ fe3+ assuming  13 cations. for the calculation of the iron as follows: feo=0.85 x feo* and fe2o3 = 0.15 x feo*/0.9 the results of mineral probe analysis on amphibole are then grouped using the classification of leake et al., 1997 with the following parameters: 1. ca amphibole: cab  1.5; (na+k)a  0.5. cab  1,5; (na+k)a < 0,5 2. na ca amphibole: (na+k)a  0.5 ; (ca+nab)  1 ; 0.5 < nab < 1.5 (na+k)a < 0.5 ; (ca+nab)  1 ; 0.5 < nab < 1.5. 3. na amphibole: nab  1.5; (na+k)a  0.5 ; (mg +fe2+ + mn 2+)  2.5. nab  1.5; (na+k)a  0.5 ; (mg + fe2+ + mn 2+)  2.5 ). 3. result and discussion 3.1 petrography gabbro petrographic analysis in cmc is represented by 8 (eight) samples, while those of bgc are 3 (three) samples (table 1). based on petrographic analysis, most of the cmc’s gabbros have altered and deformed, and they show phaneritic texture (2 mm to 8 mm) and intergranular texture (kp 2). major minerals are plagioclase, hornblende with minor amount of pyroxene and opaque mineral. plagioclase has altered to chlorite, calcite, and epidote (kp 3), while most pyroxene alter to hornblende and actinolite – tremolite (figure 4a). in ko-15 sample, gabbro shows lineation, some pyroxenes in this rock have altered to actinolite – tremolite and filled the fracture in plagioclase. beside actinolite – tremolite, there is also the present of calcite, chlorite, and epidote as an alteration result of plagioclase. in ko-10, there is fine aggregate chlorite (figure 4b) which is a product of plagioclase alteration, and present of epidote and hornblende (figure 4c). in ko-12 sample, leucogabbro is dominated by feldspare (plagioclase), some hornblende (figure 4d). it has equigranular texture, medium grain, and lineation. secondary minerals which compose this rock are epidote, calcite, and opaque minerals. evidence of deformation in gabbro is shown by bending of cleavage plane in pyroxene, fractured, elongated mineral, wavy extinction in almost minerals (plagioclase, hornblende, and pyroxene). gabbroic rocks which are exposed along cisanun and cigaber rivers, bgc, show phaneritic to porphyritic texture, granular and intergrowth texture, medium to coarse grain, some minerals have lineation, fractured which is filled by chlorite and epidote minerals. the rocks are dominated by plagioclase (andesine to oligoclase) dan pyroxene and hornblende (figure 5c, 5d). secondary minerals are actinolite, chlorite, epidote, and opaque minerals (figure 5a, 5b). plagioclase has coarse grained, partly altered to chlorite and epidote. pyroxene shows pale green to brownish color, prismatic texture, poor pleochroism, partly altered to hornblende, actinolite and chlorite (figure 5a, 5c). hornblende has a green to brownish color, medium to strong pleochroism, and has cleavage one to two direction (figure 5a). actinolite has a green color, fibrous to aggregate habit, medium pleochroism, occurring as replacement product of pyroxene. chlorite has a green color, aggregate texture, poor to medium pleochroism. it occurs as an alteration result of pyroxene and plagioclase. epidote has a brownish color, granular, high relief, high birefringence, as a result of alteration from plagioclase (figure 5e, 5f). opaque mineral has a black color, fine to medium grain, and isotropic. fig 4. photomicrograph of gabbro in ciletuh mélange complex. (a) pyroxene altered to tremolite-actinolite. (b) chlorite is alteration mineral from pyroxene. (c) hornblende, epidote, and chlorite are present beside plagioclase and pyroxene; (d) some hornblende filled fracture in plagioclase. 3.2 geochemistry here is the data of geochemistry of gabbro in cmc and bgc, western part of java, indonesia (table 2). geochemical data (major elements) can be used to determine types of rock name, magmatic process, petrogenesis and tectonic setting. to determine type of rock, the data is plotted to total alkali vs silika diagram (tas). the result is that the data falls in gabbro which is particularly similar to petrographic analysis (figure 6a). 180 patonah, a. et al./ jgeet vol 6 no 4/2021 table 2. whole rock geochemical data of gabbro in western part of java, indonesia from various sources cmc 2 cmc 3 csn 4 cgb 5 csn 13 major oxides (wt%) sio2 40.85 47.39 48.12 50.65 45.05 tio2 4.74 4.55 1.04 1.16 0.78 al2o3 9.14 11.92 12.45 20.35 13.78 fe2o3 24.23 17.94 12.41 9.20 12.75 mno 0.38 0.26 0.24 0.03 0.44 cao 9.30 7.48 9.26 9.83 17.99 mgo 4.47 4.74 12.68 3.30 6.65 na2o 2.66 4.10 1.44 3.14 0.83 k2o 0.27 0.40 0.47 0.73 0.23 p2o5 1.49 0.22 0.26 0.26 0.26 cr2o3 0.02 0.01 0.07 0.01 0.06 loi 1.70 1.10 1.65 1.12 0.65 total 99.25 100.11 100.09 99.77 99.47 trace elements (ppm) v 275 393 252 305 cr 16 6 291 16 co 43 46 62 21 ni 23 24 174 16 ga 20.1 20.3 13.6 20.9 rb 2 3 9.7 18.6 sr 101 127 193 512 y 108 39.7 23.2 20.3 zr 98.4 104 34.6 11.9 nb 13.9 7.3 3.6 3.0 ba 23 24 78 141 pb <1 1 2 4 th 0.22 0.29 0.95 1.11 u 0.008 0.07 0.20 0.17 rare earth elements (ppm) la 11.9 3.8 8.1 11.8 ce 40.8 11.1 19.5 26.1 pr 6.6 2.08 2.94 3.60 nd 37 11.8 14.6 15.8 sm 12.6 4.3 4 3.8 eu 3 1.8 1.2 1.3 gd 21.3 7.3 4.4 4.0 tb 2.54 0.99 0.69 0.61 dy 17.6 7.4 4.4 3.8 ho 3.4 1.4 0.9 0.8 er 9.5 4.1 2.5 2.1 tm 1.2 0.6 0.3 0.3 yb 8.1 4 2.3 1.9 lu 1.22 0.62 0.37 0.28 (la/sm)n 0.61 0.57 1.31 2.00 (sm/yb)n 1.73 1.19 1.93 2.22 (la/yb)n 1.05 0.68 2.53 4.45 (na/nd)n 0.63 0.63 1.09 1.47 (tb/yb)n 1.43 1.13 1.36 1.46 noted: cmc 2, cmc 3 : gabbro in ciletuh melange complexe (rosana et al., 2015) csn 4, cgb 5, csn 13: gabbro in bayah area fig 5. photomicrograph under cross nicol, gabbro’s in bayah area. (a and b) present biotite, actinolite, hornblende and chlorite minerals beside clinopyroxene, and plagioclase; (c and d) pyroxene is partly altered to tremolite – actinolite; (e and f) abundance of epidote and chlorite mineral replacing plagioclase. fig 6. (a) total alkali silicate (tas) classification of gabbro in western part of java (after cox et al., 1976); (b) afm plot (irvine and baragar, 1971). from major element composition, the gabbroic rocks from western part of java are characterized by low sio2 content (40.85 – 50.65 wt.%), wide range of mgo (3.30 – 12.68 wt.%), patonah, a. et al./ jgeet vol 6 no 4/2021 181 al2o3 (9.14 – 18.15 wt.%), and fe2o3 (5.03 – 24.23 wt.%) and low cao (7.48 – 11.24 wt.%), except csn 13 and low tio2 (0.78 – 1.16 wt.%) concentration, except in cmc (table 2). lower concentration of alkali (na2o and k2o) (figure 7) possibility due to alteration process or cumulative nature of the rock (dey et al., 2018; kakar et al., 2013). it is supported by petrographic analysis that gabbroic rock in these two complexes has altered and retrograde metamorphism to epidote amphibolite, which is characterized by the presence of andesine to albite (plagioclase types), hornblende, actinolite and tremolite replacing pyroxene; epidote and chlorite replacing plagioclase. measurement of pressure and temperature of gabbro in cmc based on the qualitative analysis (mineral assemblage; oligoclase albite, hornblende, actinolite, epidote and chlorite), the rock has altered at the temperature of 300oc to 500oc and the pressure of 3 kbar to 5 kbar (blundy and holand 1990). to determine magmatic affinity, the data is plotted in afm diagram (irvine and baragar 1971). the result exhibits that gabbro fall in tholeitic to calc-alkaline affinity (figure 6b). tio2 and al2o3 contents of gabbro exhibit positive correlation with mgo (figure 7). it means that there is magmatic differentiation which is probably due to cumulate nature of gabbros. fig 7. mgo vs selective major oxide plots for gabbro in western part of java. fig 8. normalizing values after sun and mcdonough (1989). the result of trace element analysis shows variable nb (3.6 – 13.9 ppm), rb (1.5 – 16.2 ppm), sr (83.2 – 495 ppm), and y (19.5 – 108 ppm) (figure 8). the multielements patterns exhibit gabbro in bgc show enrichment of lile, except for nb and strong negative anomaly at zr (figure 8). meanhile, those of cmc exhibit positive anomaly at nb, p and sm, but negative anomaly at sr and zr. furthermore, chondrite normalized rare earth element (ree) patterns of gabbroic rocks are shown in figure 8b. samples of bgc shows enrichment of light ree [(la/sm)n = 1.31 – 2] and negative anomaly nb conforming to e-morb, while those of cmc show relatively depleted of lree [(la/sm)n = 0.57 – 0.61] with negative eu anomaly (see samples 2 in figure 8) conform to n-morb. 3.3 mineral chemistry mineral chemistry analysis is carried out on 3 (three) gabbro samples from cmc, namely ko-10, ko-15 and kp-2. minerals which are present in those rocks are amphibole and plagioclase. amphibole characterized by high content of si, mg and lower content of aliv. amphibole which composes gabbro generally varies, namely, magnesio-hornblende, actinolite, fe – hornblende, and tremolite (figure 9). plagioclase in gabbro shows low anorthite (an1-an21), namely albite to oligoclase (figure 9). these minerals are product of alteration from ca-plagioclase. potasium content generally shows low composition, lower than 0.09 atom per formula unite. based on the data, gabbroic rocks in cmc have retrograde to epidote amphibolite which are characterized by the presence of albite – oligoclase types, ca – plagioclase altered to calcite, epidote and chlorite; while pyroxene alters to hornblende and tremolite – actinolte. in addition, these rocks have deformed which are signed by wavy extinction of almost mineral, fractured and folded. indeed, it also happens to gabbro’s bgc which has autometamorphism and retrograde to epidote amphibolite with the presence of hornblende, actinolite and chlorite minerals. fig 9. type of amphibole and plagioclase (ko-10, kp-2, ko-15) in gabbro of cmc (leake et al., 1997). 3.4 discussion 3.4.1 petrogenesis the geochemical characteristic of gabbroic rocks in western part of java, indonesia shows certain number of variations in terms of their major and trace element concentration due to possibility of different magma sources. it is generally considered as part of oceanic crust formed through magma derived from depleted mantle. based on geochemical analysis, 182 patonah, a. et al./ jgeet vol 6 no 4/2021 tio2 content of gabbro in bgc is lower than 1.3% (table 2) which means that these rocks are formed at subduction (orogen) process (gill, 1981). this data is supported by high alumina (13.78 – 20.35 et%) which means that the rock associated with suprasubduction zone environments for the origin of magmas (monnier et al. 1999). furthermore, gabbroic rocks from bgc conform well with enrichment of light ree [(la/yb)n = 2.53 – 4.45], and negative anomaly at nb and zr which are related by arc related setting or subduction – related magma (fawzy and el-ela, 1997) (figure 8). it indicates that source of magmas is formed by partial melting of mantle wedge with active participation of subducted slab in an arc tectonic setting (dey et al., 2018) and possibility of relation with suprasubduction ophiolite (wallin and metcalf, 1998). depletion of hree pattern in these rocks [(tb/yb)n = 1.36 – 1.46] suggest that it is subduction-related magma derived at least in part from mantle wedge and parent magma was of relatively primitive mantle source (fawzy and el-ela, 1997). these characteristics indicate that the rocks are associated with orogenic type (wilson, 1989). gabbroic rocks in cmc are different character from those of bgc. tio2 content in cmc’gabbros show higher than 1.3 wt.% which is interpeted as non orogen association in origin. furthermore, the spidergrams of the cmc’s gabbro (figure 8) conform well with n-morb which is interpreted that the rocks are derived by partial melting of isotopically faily homogeneous, well mixed and depleted upper mantle reservoir (zindler et al., 1984). moreover, the ree patterns in these rocks show negative eu anomaly which means that the rock has fractionally crystallized plagioclase or may have been in equilibrium with a plagioclase – bearing mantle sources (wilson, 1989). based on the ree pattern of these rocks, there are two possibilities of two types of source magma in western part of java, indonesia. firstly, one is formed by partial melting of depleted upper mantle reservoir, and the other one is formed by partial melting of mantle wedge with active participation of subducted slab in an arc tectonic setting. 3.4.2 tectonic implication to understand tectonic setting for the emplacement of different magma type of western part of java, indonesia, different tectonic discrimination diagrams are used. the ce/y vs (la/yb)n diagram (saunders et al., 1988), gabbroic rocks fall in an around n morb and emorb (figure 10), suggesting their contribution possibly from depleted and enriched mantle to near crust respectively. furthermore, based on cr vs y diagram (pearce, 1982), gabbros fall in island arc tholeite (iat) and in overlapped by within plate basalt and morb (figure 11). this implies that the gabbros in western part of java are formed at morb to arc environment (suprasubduction zone) tectonic settings. fig 10. source magma characterization for gabbro in western part of java. (a) th/yb vs nb/yb plot (after pearce, 2008)); (b) ce/y vs (la/yb)n plot, modern n – morb and e morb points (sun and mcdonough, 1989). fig 11. tectonic discrimination diagram for gabbro in western part of java. (a) cr vs y plot (pearce, 1982) 4. conclusion petrological study of gabbroic rock from western part of java exhibits that there are different characteristics between cmc and gbc. gabbro in cmc is more various, more altered, and intensely deformed than those of bgc. in bgc, there are some gabbro which has been influenced by hydrothermal process which is characterized by present epidote and chlorite, also vein which is filled with epidote and chlorite minerals. these cases are supported by geochemical analysis. based on geochemical characteristic, lower tio2 (< 1.3%) in bgc included orogenic process in origin, meanwhile those of cmc is non orogenic process. furthermore, gabbro rocks show enriched lree in bgc with negative anomaly at nb and zr, meanwhile those of cmc depleted to lree with negative eu, sr and zr anomaly. the characteristic of the composition is genetically related to morb (cmc) to an arc (bgc) related tectonic setting, supra subduction zone, where the gabbroic rocks in bgc are predicted to be transitional opening continental margin products. forming gabbro in western part of java is predicted to start being formed at upper cretaceous to paleogene (middle eocene). retrograde metamorphism happens to these rocks to epidote amphibolite, which is characterized by the presence of hornblende, oligoclase to albite, actinolite tremolite, chlorite and epidote minerals. acknowledgements the authors would like to thank the director of geotechnology lipi who has given me a chance to conduct a collaboration research, and the director of research and community service and innovation of unpad who has contributed to the research so that it can be smoothly completed. references asikin, s., 1974. evolusi geologi jawa tengah dan sekitarnya ditinjau dari segi tektonik dunia yang baru. itb. blundy, j.d., holand, t.j.b., 1990. calcic amphibole equlibria and a new amphibole plagioclase geothermometer. massachusetts institute of technology, usa, pp. 208213. cox, k.g., hawkesworth, c.j., o’nions, r.k., appleton, j.d., 1976. isotopic evidence for the derivation of some roman region volcanics from anomalously enriched mantle. contrib. to mineral. petrol. 56, pp.173–180. https://doi.org/10.1007/bf00399602 davidson, j., 1986. isotopic and trace element constraint on the petrogenesis of subduction related lavas from martinique, lesser antilles. j. geophys. res 91, pp. 5943–62. dey, a., hussain, m.f., barman, m.n., 2018. geoscience frontiers geochemical characteristics of mafic and ultramafic rocks from the naga hills ophiolite , india : implications for petrogenesis. geosci. front. 9, pp. 517– 529. https://doi.org/10.1016/j.gsf.2017.05.006 patonah, a. et al./ jgeet vol 6 no 4/2021 183 el-ela, abu., fauzy. f., 1997. geochemistry of an island-arc plutonic suite : wadi dabr intrusive complex , eastern desert , egypt 24, pp.473-496. gill, j.b., 1981. orogenic andesites and plate tectonics. springler-verlag.358p hamilton, w., 1979. tectonics of the indonesian region, us geological survey professional paper 1078. washington. https://doi.org/10.1016/00036870(73)90259-7 irvine, t.., baragar, w.r.a., 1971. a guide to the chemical classification of the common volcanic rocks. can. j. earth sci. 8, pp. 523–548. kakar, i.., khalid, m., khan, m., kasi, a.., manan, r.., 2013. petrology and geochemistry of gabbros from the muslim bagh ophiolite; implications for their petrogenesis and tectonic setting. j. himal. earth sci. 46, pp. 19–30. leake, b.e., wooley, a.r., arps, c.e.s., birch, w.d., gilbert, m.c., grice, j.d., hawthorne, f.c., kato, a., laird, j., mandarino, j., 1997. nomenclature of amphiboles. rep. subcommitee amphiboles int. mineral. assoc. comm. new mineral and mineral names, pp. 295–321. martodjojo, a., suparka, s., hadiwisastra, s., 1977. status formasi ciletuh dalam evolusi jawa barat, in: proc. ikatan ahli geologi indonesia, pp. 1–13. monnier, c., girardeau, j., pubellier, m., polvfi, m., permana, h., bellon, h., 1999. petrology and geochemistry of the cyclops ophiolites .( irian jaya , east indonesia ): consequences for the cenozoic evolution of the north australian margin, pp. 1–28. noeradi, d., 1994. contribution a l’ etude geologique d’une partie occidentale de l’ile de java – indonisie. stratigraphie, analyse structurale et etude quantitative de la subsidence des bassins sedimentaires tertiares. approache de la geodynamique d’une marge continentale. parkinson, c.., miyazaki, k., wakita, k., barber, a.., carswell, d.., 1998. an overview and tectonic synthesis of the pretertiary very-high-pressure metamorphic and associated rocks of java, sulawesi and kalimantan, indonesia. isl. arc 7, pp. 184–200. patonah, a., permana, h., 2018. basement characteristic western part of java, indonesia ; case study in bayah area, banten province. int. j. adv. sci. eng. inf. technol. 8, pp. 2135–2141. https://doi.org/10.18517/ijaseit.8.5.5907 patonah, a., permana, h., 2010. petrologi amfibolit komplek melange ciletuh , jawa barat. bul. sci. contrib. 8, pp. 69–77. pearce, j.., 1982. trace element characteristics of lavas from destructive plate boundaries. in : thorpe, r.s. (ed), andesites. pearce, j.a., 2008. geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for archean oceanic crust. lithos 100, pp. 14– 48. https://doi.org/10.1016/j.lithos.2007.06.016 prihatmoko, s., idrus, a., 2020. low-sulfidation epithermal gold deposits in java, indonesia: characteristics and linkage to the volcano-tectonic setting. ore geol. rev. 121, 103490. https://doi.org/10.1016/j.oregeorev.2020.103490 rosana, m.f., yuningsih, e.t., saragih, k.d., ikhram, r., ardiansyah, n., 2015. petrologi batuan ofiolit daerah sodongparat, kawasan ciletuh, sukabumi. bull. sci. contrib. 13, pp. 221–230. satyana, a. h, 2014. new consideration on the crestaceous subduction zone of ciletuh-luk ulo-bayat-meratus: implications for southeast sundaland petroleum geology, in: proceedings, indonesian petroleum association, thirty-eight annual convention & exhibition, pp. 1–41. satyana, awang h, 2014. tectonic evolution of cretaceous convergence of southeast sundaland: a new synthesis and its implications on petroleum geology. ikat. ahli geol. indonesia, pp. 1–28. saunders, a.., norry, m.., tarney, j., 1988. origin of morb and chemically-depleted mantle reservoirs: trace element constraints. j. petrol. special li, pp. 415–445. schiller, d.m., garrard, r.a., prasetyo, l., 1991. eocene submarine fan sedimentation in southwest java, in: proceeding indonesian petroleum association, pp. 125– 181. slovenec, d., lugović, b., 2008. amphibole gabbroic rocks from the mt medvednica ophiolite mélange ( nw croatia ): geochemistry and tectonic setting, pp. 277– 293. soekamto, r., 1975. geological map of the jampang and balekambang quadrangles, java, scale 1 : 100,000. bandung. sun, s.s., mcdonough, w.f., 1989. chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. geol. soc. spec. publ. 42, pp. 313–345. https://doi.org/10.1144/gsl.sp.1989.042.01.19 thayib, e., l, s.e., siswoyo, s, p., 1977. the status of the melange complex in ciletuh area, southwest java., in: proc.of the 6th ipa convention, pp. 1–8. wakita, k., 2000. cretaceous accretionary–collision complexes in central indonesia. j. asian earth sci. 18, pp. 739–749. https://doi.org/10.1016/s1367-9120(00)00020-1 wallin, e.t., metcalf, r. v., 1998. supra-subduction zone ophiolite formed in an extensional forearc: trinity terrane, klamath mountains, california. j. geol. 106, pp. 591–608. https://doi.org/10.1086/516044 wilson, m., 1989. igneous petrogenesis. a global tectonic approach. unwin hyman, london, 566p. zindler, a., h, s., r, b., 1984. isotope and trace element geochemistry of young pacific seamounts: implications for the scale of upper mantle heterogenety. earth planet 70, pp. 175–95. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 05 no 03 2020. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content characteristics of ultramafic igneous rock ofiolite complex in asera district, north konawe regency southeast sulawesi province ............................................................. 108 resistivity models of pantar island geothermal system east nusa tenggara, indonesia .............................................................................................................................................. 113 analysis of shoreline shift using satelilite imagery near makassar city, indonesia .............................................................................................................................................. 119 the assessment of landslides disaster mitigation in java island, indonesia: a review .................................................................................................................................................... 124 the permeability of granite weathering soil in tanjungpinang, bintan island, indonesia .............................................................................................................................................. 129 identification of clay mineral content using spectral gamma ray on y1 well in karawang area, west java, indonesia ...................................................................................... 136 association between surface air temperature and land use on the campus scale....................................................................................................................................................... 143 groundwater quality assessment for drinking purpose based on physicochemical analysis in teluk nilap area, rokan hilir, riau, indonesia ....................... 151 evaluation study of walkability index in central business district (cbd) area, pekanbaru city .................................................................................................................................... 155 e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 putra b.e.p. and choanji t./ jgeet vol 1 no 1/2016 41 preliminary analysis of slope stability in kuok and surrounding areas dewandra bagus eka putra 1, *, tiggi choanji 1, * 1 universitas islam riau, jl. kaharuddin nasution, pekanbaru 28284, riau, indonesia * dewandra.bagus@eng.uir.ac.id and tiggich@eng.uir.ac.id tel.: +6281959543306 /+6282110740659 received: oct 1, 2016. revised : 15 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.5 abstract the level of slope influenced by the condition of the rocks beneath the surface. on high level of slopes, amount of surface runoff and water transport energy is also enlarged. this caused by greater gravity, in line with the surface tilt from the horizontal plane. in other words, topsoil eroded more and more. when the slope becomes twice as steep, then the amount of erosion per unit area be 2.0 2.5 times more. kuok and surrounding area is the road access between the west sumatra and riau which plays an important role economies of both provinces. the purpose of this study is to map the locations that have fairly steep slopes and potential mode of landslides. based on srtm data obtained, the roads in kuok area has a minimum elevation of + 33 m and a maximum + 217.329 m. rugged road conditions with slope ranging from 24.08 ° to 44.68 ° causing this area having frequent landslides. the result of slope stability analysis in a slope near the water power plant koto panjang, indicated that mode of active failure is toppling failure or rock fall and the potential zone of failure is in the center part of the slope. keywords: kuok, landslide, slope stability analysis, toppling failure, rock fall. 1. introduction kuok and the surrounding area have quite diverse of slope, so there are a several locations which have range from gentle slope to steep. based on the surface conditions, the level of slope affects from the condition of the rock beneath the surface. on the high level of slopes, the amount of surface runoff and water transport energy are also enlarged. this is caused by greater gravity, in line with the ground surface tilt from horizontal plane. therefore, topsoil will be eroded more and more. when the slope of the land surface becomes twice steep, then the amount of erosion become 2.0 2.5 times more per unit area [1]. so, our research will conduct on area that predicted to become dangerous based on slope stability analysis. 2. data and method data obtained from digital elevation models using srtm data with raster grid format of pixels that value of the pixels must be counted vicinity to all directions. in calculating the value of the slope of a single pixel, involving a 3x3 pixel as illustrated in figure 1 and calculations of formula quoted from [3] below. [ 𝑆𝑙𝑜𝑝𝑒 (ℎ) 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑟) ] = √[ 𝑑𝑧 𝑑𝑥 ] 2 + [ 𝑑𝑧 𝑑𝑦 ] 2 ...............................(1) [ 𝑑𝑧 𝑑𝑥 ] = [ ((𝑐+2𝑓+𝑖)−(𝑎+2+𝑔)) 8 𝑥 𝑔𝑟𝑖𝑑 𝑤𝑖𝑑𝑡ℎ ] ................................(2) [ 𝑑𝑧 𝑑𝑦 ] = [ ((𝑔+2ℎ+𝑖)−(𝑎+2𝑏+𝑐)) 8 𝑥 𝑔𝑟𝑖𝑑 𝑤𝑖𝑑𝑡ℎ ] ............................. (3) fig 1. illustration of pixels that are taken in the calculation of the slope value pixel on dem / dtm grid raster format (burrough, 1998). kinematic analysis had been conduct to determine the possibility of mode of failures in a jointed rock slope [15]. angular relationship between discontinuities and slope surface are also be applied to identify the potential and mode of failures [7]. 3. geology regional 42 putra b.e.p. and choanji t./ jgeet vol 1 no 1/2016 kuok and the surrounding area are composed by several formations and geological structures which formed the topography at recent time (figure 2). based on the geological map of pekanbaru [12] suggested that formation on the research area consist of bohorok formation (pub) consist of wacke, conglomeratic wacke and turbidite deposit; then also at the same age deposited member of tanjung pauh (pukt) of the tapanuli group that consist of muscovit chlorit cabonate schist with strong lineation. then an intrusion of granite pulaugadang triad (mpipg), consist of strong foliation of granite gneiss. on the northeast side, pematang formation was deposited containing red and mottled mudstone, breccio-conglomerates and conglomeratic sandstones. after that sihapas formations (tms) deposited on miocene which contains the conglomerate sandstone, and siltstone. the youngest formation on research area is petani formation (tup) consisting of mudstone, carbonaceous, lignite, slightly siltstone and sandstone. (fig 3). fig 2. topography map of research area structural geology conditions of the research area was formed by collision of india-australian plate to eurasian plate which resulting basement highs trending northwest southeast (metcalfe, 2012), the structural pattern formed such as folds anticline and syncline also trending from northwest southeast, accompanied with some fault lineaments in the western area of research that also has a direction parallel to the fold, along with the establishment cleavage-slates and slate cleavage [12]. fig 3. geological map of research area 4. result and discussion research area located near the water power plant koto panjang which become sorce electicity for riau province. based on slope analysis in kuok and surrounding area, there are five type related with degree of slope in research area, from nearly level to very steep slope. first, nearly level class of slope having 30% on coverage area, this class distibute on ne research area as a habitation and some part in sw are lake of koto panjang. second are moderately sloping that cover 30 % of the area, and then steep area that cover 20 % on kuok area, and class of very steep cover about 20 % in all area. some of the steep area are located near the road, used as rock mining site for local villagers, this is the potential risk that can become dangerous if landslide happens on that area. fig 4. slope map of kuok area and surroundings a slope stability analysis had been assessed to the cut slope. the slope was considered as heavily jointed slope due to a fault system that developed in the site (fig 5). putra b.e.p. and choanji t./ jgeet vol 1 no 1/2016 43 fig 5. fault breccias and slicken side feature indicating the slope was affected by a fault system. the analysis had been conducted using stereonet software to identify the mode of active failure and the potential failure zone of the slope. the slope face direction is n295e and 85o dip. overall, 193 joint sets had been plot into the stereonet and 2 sets of joint considered as major sets based on the 1% area contour analysis (fig 6). the mode of failure had been analyzed based on the relationship between slope face and major joint sets plane. the mode of failure is toppling failure or rock fall and the potential zone of failure is in the center part of slope (fig 7). fig 6. 1% area contour analysis to determine the major sets of joint. fig 7. the mode of failure is toppling failure or rock fall (indicating by green triangle) and the potential zone of failure is in the center part of the slope. 5. conclusion kuok and surrounding areas are potentially endangered for the road user because of the existence of cut slopes. some of the cut slopes are used as rock mining by local villagers and could be the trigger for landslide. the major factor of landslide occurrence is the geological structure, as the cut slopes in kuok and surrounding areas considered as heavily jointed rock slope, the possibility of slope failure is higher. acknowledgement we would like to say thanks to department geological engineering, universitas islam riau for giving us support for this research. references [1] pertanian bogor press, bogor. [2] -enhanced shaded-relief using global mapper. utah geological survey. [3] burrough, p.a., dan mcdonell, r.a. (1998). oxford university press, new york. [4] assessment of the processed srtm-based elevation data by cgiar using field data from usa and thailand and its arelation to the terrain environtment. elsevier. 409-415. [5] sipil fakultas teknik universitas borneo. tarakan. [6] ibanez, d.m., de miranda, f.p., riccomini, c.(2014). data applied to the tectonic interpretation of the a photogrametry and remote sensing. elsevier. [7] littleton, co. [8] discharge in the amazon river estimated using the 44 putra b.e.p. and choanji t./ jgeet vol 1 no 1/2016 shuttle radar topography mission digital elevation model. geophysical research letter vol 32. 1-5. [9] gondwana research. elsevier. [10] penggabungan data dem srtm 30 dengan data kontur (rbi) menggunakan metode integrasi untuk perbaikan geodesi, fakultas teknik, universitas diponegoro, semarang.. [11]park h.j. lee, j.h., kim k.m., um, j.g. (2016). -based engineering geology. elsevier.. [12] rock, n.s., aldiss d.t., aspden, j.a., clarke , m.c.g., djunuddin, a., kartawa, w., miswar, thompson, s.j., whandhoyo, r pengembangan geologi, bandung, indonesia. [13] and aspect as influencing factors on the accuracy of of physics and chemistry of earth vol 83 84. elsevier [14] s and classification using aerial photographs: a for aerial survey and earth sciences (itc). [15] press, new york [16] tambang di pt. pasifik global utama kabupaten penelitian sivitas akademika unisba (sains dan teknologi). [17] abilan lereng teknik geologi. universitas padjajaran. bandung. e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 rahmawati et al./ jgeet vol 03 no 02/2018 115 coal characteristics and cleat attributes of muara enim formation in ulak lebar and surroundings area, lahat regency, south sumatra m.a rahmawati 1, *, s.l sari 1 , a.triyoga 1 , idarwati 1 1 sriwijaya university, jl. srijaya negara, bukit besar, ilir barat i kota palembang 30139 * corresponding author: armiliatya@gmail.com telephone/fax. (0711) 370178/352870 received: 27 des, 2017. revised: 16 apr, 2018, accepted: 24 may, 2018, published: 1 june 2018 doi 10.24273/jgeet.2018.3.2.586 abstract the research conducted in ulak lebar area, lahat regency, south sumatra. the focus of this study is on the muara enim formation as it is known as the main coal-bearing formation in south sumatra basin. the research is aimed to determine the characteristics of coal based on its physical properties, also knowing the cleat development at the coal seam in the research area. the methods used such as literature study, field observation and laboratory test. field observations included the observations of coal megascopic appearance and cleat attributes analysis such as the measurements of cleat orientation, aperture, spacing and length. the analysis result of cleat at lp 2a and lp 2b shows a relatively similar such as spacing value ranged between 6 9 cm and 5.5 8.6 cm while the aperture value ranged from 0.05 0.2 cm, and 0.05 0.25 cm, whereas at lp 67 the spacing value ranged from 1.5 to 3.3 cm and the aperture valued between 0.1 0.3 cm. a rather significant difference between the cleat spacing values of lp 67 towards both previous observation stations is indicated by the geological processes occurred during the coalification process thus affected the development of cleats in coal, the geology structure control is characterized by a relatively large aperture and smaller spacing values. the laboratory test conducted is maceral analysis, shows the coal in the research area is dominantly composed of vitrinite (74,8%) and the vitrinite reflectance value is 0,40 indicating the coal classified as sub-bituminous rank. keywords: coal, cleat, muara enim formation 1. introduction coal is a combustible sedimentary rock, containing more than 50% to 70% of carbon content derived from plant material residues accumulated in sedimentary basins and sustained in chemical and physical changes, as a reaction to the effects of bacterial decay, temperature, pressure and precipitated in geological time. south sumatra basin is known as one of the largest coal producing basins in indonesia with muara enim formation as the main coal-bearing formation. muara enim formation was deposited in the regression phase making it possible for massive peatification and coalification process at the time of the formation deposition. cleats are opening-mode fractures formed naturally in a coal seam, cleats usually consisting of two types that are oriented perpendicular (butt cleat) and parallel (face cleat) to the coal beds (laubach, et al., 1997). these fractures can be formed on almost coal seams so that the control of structural stability, minability and fluid flow can be identified through the presence of cleats (mammat, 1834., milne, 1839., quoted from kendall and briggs, 1933, in laubach et al. 1997). visually cleat is an open fracture in with no parallel offsets on the cleat wall, the cleats formed in coal are closely the same as fractures in other rocks (dron, 1925., kendall and briggs, 1993., williamson, 1967., mcculloch et al., 1974, 1976., ting, 1977., campbell, 1979., kulander and dean, 1990., laubach et al., 1992, in laubach et al., 1997). the diagenesis process is the aspect which is distinguished cleats in coal with the occurrence of fractures in igneous rocks. cleats are formed in coal during the coal depositional process occurred whereas fractures in igneous rocks just occurred after the igneous rocks formed and undergo the deformation process. geographically, the research was conducted in ulak lebar and surrounding areas, lahat regency, south sumatra. this study aims to determine the characteristics of coal seen from its megascopic and microscopic properties and to know the development and characteristics of cleats in coal seams due to the influence of tectonic regimes working on muara enim formation. 2. regional geology regional geology conditions are basic aspects worked regionally on south sumatra basin, it includes in its tectonic settings and stratigraphic sequence developed from the beginning of the basin establishment to the present time. by learning the regional geology conditions intend to projects local geology conditions of the research area conveniently with the regional geology conditions of south sumatra basin. mailto:armiliatya@gmail.com 116 rahmawati et al./ jgeet vol 02 no 03/2017 fig. 1. regional stratigraphy of south sumatra basin (decoster and addiwidjaja, 1973). 2.1 regional tectonic settings south sumatra basin is a back-arc basin formed by the subduction of indo-australian plate, oriented northward to northeast towards the eurasian plate.the plates subduction zone covered the western part of sumatra and the southern part of java. the subduction affected the rock, morphological, tectonic and structural conditions in south sumatra (pulunggono, et al. 1992). the tectonic plates collisions on sumatra produced forearc, magmatic and back-arc lines. according to pulunggono, et al. (1992) tectonic events held an important role in the development of sumatra island and the south sumatra basin and were divided into four phases as follows.  in this first tectonic phase the working stress is compression and took place in the early jurassic late cretaceous, it produced a wnw-ese oriented dextral strike-slip fault, such as the lematang fault, kepayang, saka, south coast of lampung, musi lineament and the n-s trend.  the extensional stress worked in the subsequent tectonic phases occurred in the late cretaceousearly tertiary, resulted in the occurrence of normal and growth faults oriented in n-s and wnw-ese trends. the sedimentation process began at the early tertiary filled in the base along with the activate volcanic activity, lahat formation deposited in this phase.  the following tectonic activity developed at miocene and resulted in the uplifts of the basin edges, at the same time with the deposition of clastic materials including the deposition of talang akar formation, baturaja formation, gumai formation, air benakat formation and muara enim formation.  the last tectonic event took place in plio pleistocene, with the compressional stress as the working one. in this phase, kasai formation deposited simultaneously with the occurrence of volcanism activity on the back-arc basin so that the volcanic material also deposited on the formation. furthermore, there were north-west trending of uplifts and folds across the basin put an end to the tertiary deposition in south sumatra basin. 2.2 regional stratigraphy according to decoster and addiwidjaja (1973), south sumatra basin is a back-arc basin which the first formation to be deposited occurred early eocene oligocene. sequentially from the oldest to the youngest sediment deposition in south sumatra basin are as follows (fig. 1).  the basement rocks of south sumatra basin is consisted of metamorphic and carbonate rocks at the paleozoic mesozoic aged and mesozoic aged igneous rocks.  lemat formation is the first formation to be deposited in south sumatra basin, it was deposited on late eocene early oligocene. its deposition is indicated in the deep marine environment as seen from the deposition of alluvial fan material and piedmont deposits (highland material). in addition, the sediment material deposited was poorly sorted with coarse grain-sized. the lithology composed of sand to conglomerate, coal, and also the presence of volcanic material  during the late oligocene early miocene the talang akar formation precipitated unconformably above the lemat formation. this formation is deposited in the fluvial, deltaic and marginal-shallow marine environments in the global transgression phase at the time of the compressional tectonic phase. the formation is composed of shale and fine to medium grained sands.  baturaja formation (basalt telisa member) deposited conformably over talang akar formation in early miocene, at the same time with the deposition of this formation, the coral growth proceeded very well. the lithology of this formation includes limestone which is very dominant, carbonated-clay and sandstone.  furthermore, in the early miocene middle miocene occurred the deposition of telisa formation (gumai formation). the formation deposited over the baturaja formation and was composed of shale with a thin layer of limestone and sandstone. there were also the presence of glauconitic foraminifera limestone as an attribute indicating the formation was deposited in neritic environment.  air benakat formation was deposited in deep shallow marine environment, as it is indicated the end of transgression phase. the formation rahmawati et al./ jgeet vol 02 no 03/2017 117 was deposited during middle miocene late miocene and is composed of a dark gray to bluish to a dark gray to brownish colored clay, medium to fine grained glauconite sandstone glauconite with light green brownish gray colored containing quartz and feldspar, and the intercalation of sandstone, claystone, siltstone and shale with a thin inserts of quartz sands.  over the air benakat formation, the muara enim formation was deposited conformably during late miocene pliocene. the deposited material in the formation derived from the shallowmarine, delta plain and non-marine environment, its precipitation occurred along with the decreases of sea level phase (regression phase). muara enim formation consists of sandstones, claystone, and coal.  at the late pliocene pleistocene kasai formation was deposited above muara enim formation. kasai formation is the youngest formation occurred on the basin, composed of tuffaceous sandstone, claystone, conglomerate and tuff with lignite, formed during the deformation of barisan mountains. 3. research methods the method used in the research is done through three stages, such as literature study, field observation and laboratory test. the earliest stage is a literature study, conducted before going directly into the field. the next stage is field observation, it is the data-gathering activity in field and the last stage is laboratory test which is done after going back from the field. the first step to recognize the regional geology and the local geology conditions in the research area. it is intended to give a representation of what to do and what data should be collected in the fields. the literature study conducted by reading the literature such as journal, paper, proceedings and regional geological map of destination area which has been published by previous researchers. secondly, field observation activities includes the data-gathering required for analysis and interpretation purposes. in this study, field observations included observations of the physical megascopic properties of coal outcrops as well as the analysis of cleat attributes such as orientation, aperture, spacing and length measurements at several observation stations. then, laboratory tests are conducted with coal maceral analysis, aiming to know the maceral and minerals composition in a coal sample, it is closely related to the plant species and the depositional environment conditions at the time of coalification process. the result was grouped into vitrinite groups, liptinite groups, and inertinite groups as well as the percentage of mineral matter. 4. results and discussion geographically, the research location is included in the administrative area of lahat regency, south sumatra precisely in ulak lebar and surrounding area, west merapi districts. the research area is a part of muara enim formation deposited in late miocene early pliocene. the fractures-forming in the coal seams can be affected by the sedimentation process or local geological structures control developed in the area. observations on coal outcrops in the study area were conducted in three observation stations, namely lp 2a, lp 2b and lp 67 (fig. 2). fig. 2. cleat observations map of ulak lebar area, lahat regency. 118 rahmawati et al./ jgeet vol 02 no 03/2017 4.1 coal characteristics the coal outcrops found is in a former public mining field which is no longer producing. as for the outcrops observed originated from the same coal seam that the coal megascopic physical appearance in these three observation stations are relatively the same. coal in this area has a brownish-black color with brown strike, dull luster, brittle, conchoidal fractures and has a relatively light weight. the coal seam has a relatively gentle sloping with the thickness ranging from 2 3 meters. furthermore, the overburden layers consists of gray to brownish claystone and white to yellowish white sandstone (fig. 3). maceral is the primary material of coal constituents that is associated with each other in varying proportions. the association of this maceral in megascopic-form called lithotypes. lithotypes can be observed in the form of thin bands with a thickness of from a few millimeters to several centimeters. the coal lithotype in the study area is durain as seen from the coal physical appearance and description. meanwhile, the result of the maceral analysis performed on a coal sample (table 1) shows that the coal in the research area is dominantly composed of vitrinite maceral with a percentage of 74.8% and the maximum vitrinite reflectance value amount 0.40%. according to the ward (1984) classification, such a percentage rv max value indicates the coal in the research area is included in sub-bituminous rank (table 2). fig. 3. stratigraphic profile of coal outcrop at lp 2, shows coal thickness at seam 2a ± 1.5 meter and seam 2b 0,7 meter. the picture is taken facing east. table 1. result of muara enim formation coal maceral analysis in the research area. no no sample lithology mean reflectance vitrinite (% rv random) range deviation standard n maceral composition mineral matter (%) v i l pyrite d t s f sc i r su 1 m lp 02 bb 0.40 0.35 0.45 0.03 100 59.4 15.4 8.0 10.6 1.0 1.0 4.6 xplanation : bb = coal v = vitrinite f = fusinite shc = shaly coal i = inertinite sc = sclerotinite csh = coaly shale l = liptinite i = inertodetrinite cs = carbonaceous shale d = desmocollinite r = resinite sh = shale t = telecollinite s = suberinite n = number of measurements s = semifusinite pyrite = mineral matter table 2. coal rank classification based on vitrinite maximum reflectant value (after ward, 1984). rank maximum reflectance (%rv max) sub-bituminous < 0.47 high volatile bituminous c 0.47 0.51 high volatile bituminous b 0.51 0.71 high volatile bituminous a 0.71 1.10 medium volatile bituminous 1.10 1,50 low volatile bituminous 1.50 2.05 semi-antrachite 2.05 3 (approx) anthracite >3.00 rahmawati et al./ jgeet vol 02 no 03/2017 119 4.2 cleat attributes analysis the cleat attributes analysis was conducted on three observation stations, namely lp 2a, lp 2b and lp 67. from these three locations, the analysis results were obtained (table 3) as follows.  in lp 2a observation station, the face cleat orientation was n 301 o e, and butt cleat orientation was n 040 o e with maximum stress level at n 310 o e and minimum stress level at n 220° e (fig. 4). the cleat aperture is relatively valued 0.05 0.2 cm and the spacing value ranged from 6 9 cm.  in lp 2b observation station, the face cleat orientation was n 284 o e, and butt cleat orientation was n 030 o e with maximum stress level at n 290 o e and minimum stress level at n 200° e (fig. 5). the cleat aperture is relatively valued 0.05 0.25 cm and the spacing value ranged from 5.5 8.6 cm.  in lp 67 observation station, the face cleat orientation was n 290 o e, and butt cleat orientation was n 010 o e with maximum stress level at n 295 o e and minimum stress level at n 205° e (fig. 6). the cleat aperture is relatively valued 0.1 0.3 cm and the spacing value ranged from 1.5 3.3 cm. fig. 4. face cleat orientation of lp 2a fig. 5. face cleat orientation of lp 2b fig. 6. face cleat orientation of lp 67 120 rahmawati et al./ jgeet vol 02 no 03/2017 in general, the cleat orientation formed nw se trending, with the value of the aperture, formed relatively the same ranges between 0.05 0.3 cm with open-mode fractures and partially filled with clay and pyrite minerals. there is a considerable contrast to the cleats spacing value on lp 67 towards the lp 2a and lp 2b ones, the cleats spacing value of lp 67 tend to be more dense and intense. the determination of cleats genesis is done by dividing the genesis based on the rotation angle of the cleat to the bedding plane wherein if the resulting angle between 70 90 o is classified as endogenic cleat and if the resulting corner <70 o is classified as an exogenic cleat (apriyani, n ,, et al, 2013). the cleat orientation in the research area is relatively northwest-southeast oriented and in contrast to the orientation of regional structures at the research area, which is in northeast-southwest oriented. based on the cleat rotation data plot, the resulting angle is at intervals from 67 to 84° (fig. 7) so that the majority of cleats in the study area are genetically included in the endogenic cleats in which their formation is influenced by the internal stress in the coalification process resulting from the coal matrix shrinkage. the cleats obtained are almost perpendicular to the bedding plane of coal. the relationship between coal maturity levels is inversely proportional to the presence of cleats in a coal seam. more cleats shows that the maturity level of the coal is not high yet, the higher the maturity level of the coal the less presence of cleat obtains in the coal seams. in the research area, cleats developed quite well, in lp 2a and 2b there are even pyrite minerals that fill the fracture. the presence of these minerals also affects the coal quality because it causes an increase in mineral matter content, thereby reducing the calorific value of coal. table 3. comparisons of cleat attributes in each observation stations. face cleat no cleat components observation stations lp 2a lp 2b lp 67 1. a. strike/dip n 298 o e/11 o n 296 o e/11 o n 288 o e/15 o b. orientation n 301 o e/ n 121 o e n 284 o e/ n 104 o e n 290 o e/ n 110 o e c. max. stress level n 310 o e/ n 130 o e n 290 o e/ n 110 o e n 295 o e/ n 115 o e d. min. stress level n 040 o e/ n 220 o e n 020 o e/ n 200 o e n 025 o e/ n 205 o e 2. aperture (cm) 0.05 0.2 0.05 0.25 0.1 0.3 3. spacing (cm) 6 9 5.5 8.6 1.5 3.3 4. mineral fill pyrite clay minerals butt cleat 5. a. strike/dip n 049 o e/13 o n 041 o e/13 o n 029 o e/14 o b. orientation n 040 o e/ n 220 o e n 030 o e/ n 210 o e n 010 o e/ n 190 o e 6. aperture (cm) 0.05 0.09 0.05 0.1 0.1 0.2 7. spacing (cm) 4 7 4 8 1 2 8. mineral fill fig. 7. normal cleats orientation and cleat rotation. rahmawati et al./ jgeet vol 02 no 03/2017 121 5. conclusions based on this research, it can be concluded as follows : 1. the coal outcrops found in the research area were part of muara enim formation deposited during late miocene pliocene. 2. physically, the coal obtained in ulak lebar and surrounding area has blackish brown to black color, dull luster, brittle, conchoidal fractures, and relatively light-weight with coal seam thickness ranging between 2 to 3 meters. based on its megascopic appearance the coal lithotype in the research area is in durain category based on the maceral analysis conducted on a coal sample, the coal in the research area is dominantly composed of vitrinite maceral (74,8% in composition) and the maximum vitrinite reflectance value amount 0.40, indicating the coal in the research area included in sub-bituminous rank. 3. the cleats orientation in the research relatively nw se oriented, with the value of the aperture formed relatively the same ranges between 0.05 0.3 cm with open-mode fractures and partially filled with clay and pyrite minerals. 4. most of the cleats in the study area are genetically included in the endogenic cleats in which is the formation is influenced by the internal stress in the coalification process resulting from the coal matrix shrinkage. acknowledgments acknowledgments are addressed to the whole lecturers of geology department sriwijaya university, especially for mrs. idarwati, s.t., m.t who has guided and assisted in interpreting the geological conditions in the research area, as well as our colleagues in the class who have provided us critics, suggestions and discussions in completing this study. references adiwidjaja, p. and decoster, g.l. 1973. pre-tertiary paleotopography and related sedimentation in south sumatra . bulletin of proceedings indonesian petroleoum associations, 2 amijaya, h., littke, r., 2005. properties of thermally metamorphosed coal from tanjung enim area, south sumatra basin, indonesia with special reference to the coalification path of macerals. international journal of coal geology 66 (2006) 271 295. anggayana, k., 2002. genesa batubara. departemen teknik pertambangan., fiktm, institut teknologi bandung. apriyani, n., suharmono, momen, m., djaelani, s., sodli, a., satria, a., murtani, a.,s., 2013. integrated cleat analysis and coal quality on cbm exploration in sangatta ii field, kutai basin, east kalimantan. proceedings indonesian petroleum association, 37. de. coster g. l.,1974, the geologi of central sumaatera nad south sumatera basins, proceeding indonesian petroleun assoc, 4th annual convention krestanu, a., iqbal, m., fernando, r. e., herawati., puadi, m., 2016, karakteristik cleat batubara terhadap intensitas struktur pada desa merapi timur, kabupaten lahat di formasi muara enim, cekungan sumatera selatan. proceeding, seminar nasional kebumian ke-9. p. 211215 lamberson, m.n., bustin, r.m., kalkreuth, w. (1991). lithotype (maceral) composition and variation as correlated with paleowetland environments, gates formations, northeastern british columbia. canada; international journal of coal geology 18. p. 87 124 laubach, s. e., marret, r. a., olson, j. e., scott, a. r., 1998. characteristics and origins of coal cleat: a review. international journal of coal geology 35 (1998) 175207. nasution, f. p., nalendra, s. 2017. characterization of coal quality based on ash content from m2 coal-seam group, muara enim formation, south sumatra basin. journal of geoscience engineering, environment, and technology, vol 2 no. 3. p. 203-209 nichols, g. (2009). sedimentology and stratigraphy second edition, wiley-blackwell: london prayitno, b., ningrum, n. s. 2017. development of funginite on muaraenim and lower members of telisa formations at central sumatra basin indonesia. journal of geoscience engineering, environment, and technology, vol 2 no. 2. p. 149-154 pulunggono, a., s, agus haryo., kosuma, christine. g., 1992. pre-tertiary and tertiary fault system as a framework of the south sumatra basin: a study of sar-maps. proceedings indonesian petroleum associations twenty first annual convention, ipa 9211. 37. putra, d. b. e., choanji, t. 2016. preliminary analysis of slope stability in kuok and surrounding areas. journal of geoscience engineering, environment, and technology, vol 1 no 1. p. 41-44. sari, s. l., rahmawati, m. a., triyoga, a., idarwati. 2017. impact of sulphur content on coal quality at delta plain depositional environment: case study in geramat district, lahat regency, south sumatra. journal of geoscience engineering, environment, and technology, vol 2 no. 3. p. 183-190. stopes, m.c. (1935).on the petrology of banded bituminous coals: fuel , vol. 14, 4-13 sudarmono,. t, suherman., eza, benny., 1997. paleogene basin development in sundaland an itd role to time petroleum system in western indonesia. petroleum system of se asia and australia conference, may 1997. ipa 97-or-38. ward, c.r. (1986). review of mineral matter in coal, australian coal geology,geol.soc. of australia, vol. 6 pp. 87-107. 1. introduction 2. regional geology 2.1 regional tectonic settings 2.2 regional stratigraphy 3. research methods 4. results and discussion 5. conclusions acknowledgments references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 4 2021 234 sari, e.g. et al./ jgeet vol 6 no 4/2021 research article carbon dioxide (co2) emissions due to motor vehicle movements in pekanbaru city, indonesia erza guspita sari 1, , muhammad sofwan2* 1 departement urban and planning, faculty of engineering, universitas islam riau, pekanbaru, indonesia. * corresponding author : muhammad.sofwan@eng.uir.ac.id tel.: +62-812-2007-0060 received: sept 15, 2021; accepted: dec 8, 2021 doi: 10.25299/jgeet.2021.6.4.7692 abstract land use has a very close relationship with transportation. transportation is formed as a result of the interaction between land use and its support system. good land use supported by good infrastructure will result in good movement as well. accessibility is one of the supporting factors for good interaction between transportation and land use—the better the land use conditions in an area, the greater the movement in that area. however, the interaction between land use and transportation can cause one of the problems: the increase in carbon dioxide emissions due to the more significant movement of motorized vehicles. motor vehicles are the most significant contributor to carbon dioxide (co2) emissions in the world. the further the route traveled by motorized vehicles, the more carbon dioxide (co2) emissions will increase. this study aims to analyze the average total emission of carbon dioxide (co2) resulting from transportation activities in pekanbaru city into two parts, namely: (1) based on travel time (2) based on the type of vehicle. vehicle kilometers of travel (vkt) and emission factors are the primary data in calculating carbon dioxide (co2) emissions. the research area consists of 12 zones involving 1,342 households in pekanbaru city. based on travel time, 52% of community motorized vehicle movement activities are carried out in the morning. private cars contribute 65% of carbon dioxide (co2) emissions in pekanbaru city based on the type of vehicle. this study found that a high number of motorized vehicles cannot be used as a benchmark that the resulting emissions will also be high. however, the emission of carbon dioxide (co2) depends on the fuel consumption of each vehicle. the higher the fuel consumption, the higher the amount of carbon dioxide (co2) emissions released by motorized vehicles. keywords: land use, carbon dioxide emission (co2), vehicle kilometer traveler (vkt), motor vehicles, travel behavior, emission factors 1. introduction one of the most active activities in landscape events globally is land use and land cover change (foley et al., 2005; song et al., 2009; wu et al., 2021). only 3% of the earth's surface is an urban area. however, urban areas experience many changes in land use and land cover (liu et al., 2014; wu et al., 2021). the system of activities in land use in an urban area can be interpreted as the place of origin and destination of activities. the correlation between land use and transportation can shape the movement system in urban areas. these correlations form dynamic relationships involving changes in the spatial and temporal dimensions. the transportation system can change if land use and travel demand patterns change (shaw and xin, 2003; eboli, forciniti and mazzulla, 2012). the pace of economic growth, technological progress, and regional development in urban areas triggers environmental problems and stagnant traffic (zhu et al., 2018). the high level of urbanization is the cause of land cover changes that will affect and cause problems in the environment, one of which can increase global warming (chapman et al., 2018; wu et al., 2021). global warming arises due to the interaction between land use and transportation. the problem of global warming has become the main focus because it can create severe damage in the world. experts argue that carbon dioxide (co2) emissions are one of the leading causes of global warming (baek and pride, 2014; sohag et al., 2015; rehman et al., 2021). production carbon dioxide (co2) emissions will directly affect the increase in greenhouse gases. the concentration of greenhouse gases consisting of carbon dioxide (co2) is 75%, and 25% comes from other gases. a study said that carbon dioxide (co2) emissions increased by 30% in the world after the industrial revolution in 1700 (ehsani, ahmadi and fadai, 2016). as much as 24% of the world's carbon dioxide emissions are produced by the transportation sector, sourced from the direct burning of fuels (siskos and moysoglou, 2019). globally, the urban transportation sector generates the most significant carbon dioxide (co2) emissions (li, 2011; labib et al., 2018). in 2004, the world's transportation sector produced 6.3 giga tons of carbon dioxide (co2) emissions, and 74% came from motorized vehicles. the mode of transportation that people choose depends on their level of income. motorized vehicles are one of the modes that are in great demand by the public. however, carbon monoxide (co) and carbon dioxide (co2) emissions caused by motorized vehicles will exacerbate air pollution. the speed of the vehicle determines the number of compounds released in the air. the more volume of vehicles on the road, the vehicle's speed will decrease, so that vehicle exhaust emissions will also decrease (kusumawati, tang and nurhidayah, 2013). in general, the fuel used by motorized vehicles is petroleum fuel (nurdjanah, 2015). motorized vehicles are very influential in supporting community activities in urban areas. long distances feel close if used in a motorized vehicle (sengkey, jansen and wallah, 2011). urban areas experience a relatively high movement of vehicles. the fuel consumption is also getting bigger, which causes the production of carbon dioxide (co2) emissions to increase (dodman, 2009; labib et al., 2018). production of carbon dioxide (co2) emissions generally comes from motorized vehicle activities such as motorcycles, cars, pickups, trucks, buses, and other motorized vehicles. in indonesia, 85% of urban air pollution is caused by transportation emissions increasing, motorized vehicle ownership. the lack of quality http://journal.uir.ac.id/index.php/jgeet sari, e.g. et al./ jgeet vol 6 no 4/2021 235 fuel and poor maintenance of motorized vehicle engines will produce poor exhaust emissions (gusnita, 2012). pekanbaru city is one of the capitals of riau province with the highest population growth. this growth will affect the consumptive behavior of the community towards motor vehicle ownership. what recorded that in 2018 the number of motorized vehicle ownership in pekanbaru city was 720,737 units, while in 2019, the number of motorized vehicle ownership in pekanbaru city experienced an increase of 770,836 units (badan pendapatan daerah provinsi riau, 2019). based on these data, the higher ownership of motorized vehicles and the greater fuel use will directly impact the addition of motor vehicle gas emissions in pekanbaru city. this study aims to analyze the average total emission of carbon dioxide (co2) resulting from transportation activities in pekanbaru city to predict how these transportation activities cause much environmental burden. this study only focused on carbon dioxide (co2) emissions generated from motorized vehicles, including motorcycles and private cars in pekanbaru city. 2. method 2.1 correlation between movement patterns and land use the relationship between transportation and land use activities must be balanced to achieve the main objectives of the transportation system and land use (khisty and lall, 2005). land use is closely related to transportation. every activity carried out on specific land use will cause the generation of movement and the pull of movement in meeting needs. carrying out the movement requires a transportation network, thus creating a macro and micro transportation system. the micro transportation system consists of (1) activity system, (2) network system, (3) movement system, (4) institutional system (tamin, 2000). the activity system is related to land use in a specific area to generate and attract transportation activities. the network system is a medium of transportation in carrying out the movement. the relationship between land use and transportation media gives rise to a movement pattern called the movement system. if the activity system changes, the network system and movement system will also change. land use that is changed its designation will cause the generation and attraction of different movements. the higher the intensity of land use, the higher the level of its ability to attract movement. in fig. 1, the distribution of movements carried out by the community such as work, school, shopping, recreation, socializing, and other activities can determine the location by route selection. distribution of movement causes an interaction between the movement system and the transportation system so that the distance traveled to the destination location of the movement is obtained. the existence of transportation infrastructure forms an interaction with one land use to another called accessibility. accessibility affects the movement that occurs in the land use so that it will cause changes to the land use system (wegener and fürst, 1999; wegener, 2004; eboli, forciniti and mazzulla, 2012). to create accessibility and stable activities, good transportation and land-use relations are needed. transportation produces distance, travel time, and cost. if the accessibility during the transportation is good, the activities on land use are also suitable. distance, travel time, and cost are obtained from route selection, mode selection, location selection, and vehicle ownership. meanwhile, land use must attract the movements carried out and provide comfort in the form of transportation infrastructure so that the movements carried out can run well. fig. 1 the land use transport feedback cycle 2.2 research area the study area in this research consists of the origin zone and destination zone of the movement to be carried out. this zoning is based on the division of administrative areas in pekanbaru city. this study uses household sample data. the collection of data and travel information for family members (respondents) involved 1,342 households, or 0.5% of the total household population spread across 12 sub-districts in pekanbaru city. in conducting this research, the primary data collection used a home interview survey, which is a survey to collect travel data for each family member on weekdays (monday-friday). the research location consists of the origin zone and the destination zone. a zone is the boundary of the study area, which consists of several sub-regions. each zone consists of a zone centre, which is assumed to be the initial location of movement from the zone and the end of traffic movement to the zone (intari, 2015). fig. 2 describes the division of zones in pekanbaru city, which comprises 12 zones covering all subdistricts in pekanbaru city. the division of zones is needed to see how significant the movement is that is the reference in calculating carbon dioxide (co2) emissions in pekanbaru city. each sub-district can be a movement origin zone and a movement destination zone. the selection of this zone can also determine how far the distance travelled in one trip from the origin zone to the destination zone. the choice of moda is based on which zone people want to pass through in carrying out their daily movements. 236 sari, e.g. et al./ jgeet vol 6 no 4/2021 fig. 2 research zone 2.2 correlation between movement patterns and vehicle activity the calculation of carbon dioxide (co2) emissions in pekanbaru city cannot be separated from the existence of a four-step model, namely movement generation, movement distribution, mode selection, and route selection in a study. movement generation is a pattern that is assumed to be in the form of the number of movements originating from one origin zone to the destination zone. the destination zone in question is a zone that is outside the zone of origin (tamin, 2000). the more people who are awakened in carrying out the movement will cause the distribution of various movements. the distribution of movement shows where and from where the movements made by the people in pekanbaru city. the generation and distribution of community movements in pekanbaru city will affect the choice of modes and the community's routes in carrying out their movements. the choice of moda is based on the purpose of the movement, the cost of the trip, and the time travel. usually, people in pekanbaru city are faced with two choices of transportation moda, namely public transportation and private transportation. the selection of routes for public transportation modes is usually predetermined, and the public cannot determine which route they want to take. in contrast to the private mode of transportation, the public can determine which of the shortest and fastest routes they want to pass to avoid congestion so that it is more efficient in terms of time travel. the choice of mode and route can also be influenced by people's income and the ease of getting a mode of transportation. so that from the trip generation, the trip distribution of movement, the moda choice, and the selection of routes, the pattern of community movement in pekanbaru city is obtained. the pattern of community movement produces vehicle activity data which is the primary data in calculating carbon dioxide emissions. the vehicle activities are divided into two, based on the time of movement, and the type of vehicle used when moving. vehicle kilometers of travel (vkt) are strongly influenced by data from the movement patterns carried out. the data needed to calculate vkt is the road's length and the total number of vehicles that move in a day. from the generation and the selection of moda of achieved results to the total number of vehicles of the movement carried out every day. similarly, with the distribution, and the route selection, the results obtained from the length of the path traversed the community to get to the destination zone. the pattern of movement of community-generating activities of the vehicle so in the get data on vehicle kilometres of travel (vkt). the calculation of the emissions of carbon dioxide (co2) in the city of pekanbaru requires the data type of the fuel on the mode used, vehicle kilometers of travel (vkt), and emission factors. 2.3 the concept of calculation of motor vehicle carbon dioxide (co2) emissions the household data collected is related to the travel pattern of each family member on weekdays. from this data, information will be obtained in the origin zone, destination zone, time of movement, routes, moda used, and the distance travelled by the people in pekanbaru city. the amount of carbon dioxide (co2) emissions are strongly influenced by moda selection, route selection, and fuel type. the farther the distance travelled in carrying out the movement, the more carbon dioxide (co2) emissions generated from the mode used. the choice of fuel type also dramatically affects the amount of carbon dioxide (co2) emissions. the better the choice of fuel, the less polluting carbon dioxide emissions are released when moving. the distance the vehicle travels from the origin zone to the destination zone can determine how much fuel consumption is needed in one trip made by each family member. to calculate the amount of carbon dioxide emissions required an average fuel consumption. the specific fuel consumption multiplied by the average mileage by vehicle type gives the total fuel consumption. tabel 1 it is assumed that each mode of transportation in one litre per 100 kilometres has the same specific fuel consumption (jinca, 2009). sari, e.g. et al./ jgeet vol 6 no 4/2021 237 table 1. specific fuel oil consumption for each type of vehicle in pekanbaru city transportation type fuel type specific energy consumption (liters/100 kilometers) specific energy consumption (liters/kilometers) motorcycle 2,66 0,0266 passenger car gasoline 11,79 0,1179 diesel fuel 11,36 0,1136 big bus gasoline 23,15 0,2315 diesel fuel 16,89 0,1689 medium bus 13,04 0,1304 mini bus gasoline 11,35 0,1135 diesel fuel 11,83 0,1183 bemo, bajaj 10,99 0,1099 taxi gasoline 10,88 0,1088 diesel fuel 6,25 0,0625 big truck 15,82 0,1582 medium truck 15,15 0,1515 mini truck gasoline 8,11 0,0811 diesel fuel 10,64 0,1064 the moda of transportation in pekanbaru city, motorbikes and private cars, primarily uses fuel oil types fuel. this fuel oil type is more in demand than other fuel types because the selling price of fuel oil is low, even though the content in fuel oil is not very good for public health and air quality. to calculate the amount of carbon dioxide emissions also need an emission factor. the emission factor is the emission produced every time we carry out an activity expressed by the coefficient (kementerian energi dan sumber daya mineral, 2017). tabel 2 presents the emission factor values per type of fuel. premium fuel has the most significant emission factor compared to diesel fuel (badan perencanaan pembangunan nasional, 2014). table 2. transportation fuel emission factor type of fuel emission factor (kilogram co2/liter fuel) diesel oil 2,2 fuel oil 2,6 after getting the results from the travel pattern, vehicle kilometer of travel (vkt), and selecting the appropriate emission factor, total carbon dioxide emissions can be calculated. calculation of total carbon dioxide (co2) emissions in pekanbaru city is based on the vehicle type and time. based on certain types of vehicles, total carbon dioxide (co2) emissions can be calculated by multiplying the number of vehicles originating from daily vehicle activities or daily vehicle mileage (vkt) by the vehicle emission factor. to calculate the emission of carbon dioxide (co2) can be done with equations (1) and (2) (kamruzzaman, hine and yigitcanlar, 2015; pan, yao and yang, 2016; labib et al., 2018). eik = ∑ ∑ ×𝑛𝑘=1 𝐸𝐹𝑖𝑗𝑘 𝑛 𝑗=1 × 𝑉𝑖𝑗𝑘 (1) where; eik = emissions of pollutant n = vehicle average j = fuel consumed (e.g., cng, gasoline) k = emitting vehicular type i = emission type (in the case co2) efijk = emission factor (g/km) vktijk = daily vehicle activity or daily mileage daily vehicle activity or daily vehicle mileage (vkt) is obtained from the equation (2); vkt = 𝐿𝑘 × 𝐴𝑉𝑘 (2) where; vkt = vehicle kilometers traveled (km/day). lk = road length of the selected links within the study area (kilometers) avk = average number of moving vehicles/day fig. 3 explains that the vehicle travel pattern and four-step model result in vehicle kilometer traveler (vkt) and carbon dioxide (co2) emissions. calculation of vehicle kilometer traveler (vkt) is divided into two, based on travel time and vehicle type. vehicle kilometer traveler (vkt) based on travel time is divided into three times is morning, afternoon, and evening. meanwhile, based on the type of vehicle, it only includes two motorized vehicles, is two-wheeled motorized vehicles in the form of motorcycles and four-wheeled motorized vehicles in the form of private cars. from the results of multiplying the vehicle kilometer traveler (vkt) and carbon dioxide emissions (co2), the results for daily carbon dioxide (co2) emissions can then be converted into annual carbon dioxide emissions in pekanbaru city. fig.3 design concept of carbon dioxide (co2) emissions ve h ic le trave lle r patte rn ve h ic le kilo m e te r trave lle r (vkt) vkt bas e d tim e trave ll e r vkt be s e d ve hi cl e typ e s daily co2 em issio n co2 em iss io n ba se d tim e travl le r co2 em iss io n be se d ve hic le ty pe s co2 em issio n fu e l typ e s em iss iv ity to tal n um be r o f ve hic le s fo r e a ch fu e l typ e an d em iss iv ity fo ur ste p mod e l trip ge n e rati o n trip dis tribu tio n mo da ch o ic e trip ass ig m e nt ye arly co2 em is s io n land co ve r se ttl e m e n t ag ric ult ure fo re s t ope n w at e r etc zon in g dis tric t adm i nis trati o n 238 sari, e.g. et al./ jgeet vol 6 no 4/2021 3. results & discussion 3.1 land cover in pekanbaru city plantation areas dominate as much as 75.2% of land cover in pekanbaru city and 12.6% residential areas. the city center of pekanbaru is dominated by built-up areas in the form of settlements and places of activity, namely in zone 1, zone 8, zone 4, and zone 5. meanwhile, the other zones are mixed lands whose land use consists of settlements and gardens or shrubs. as seen from fig. 4, directions of land cover development in pekanbaru city are in the southern and western parts or, more precisely, the southwest part of pekanbaru city. the eastern, southern, and northern parts are dominated by undeveloped areas, and there are some built-up areas, but they do not dominate. in this study, 12 zones are used, which are all sub-districts in pekanbaru city. these zones will be the origin zone and destination zone in the movement to be carried out. land use of an area can attract and generate movement. the majority of people in the city of pekanbaru carry out movements on land use where there are activity centers and settlements, and this is what attracts and evokes movements made by the community. fig. 4 land cover in pekanbaru city 3.2 traveller profile pekanbaru city consists of 12 districts with 83 villages and has siak, kampar, and pelalawan districts. pekanbaru city is the most important economic centre on the island of sumatra. it is also one of the cities with the highest growth, migration, and urbanization rates in riau province. population growth in pekanbaru from year to year has increased significantly, affecting the number of movements carried out. tabel 3 presents data on the profile of travellers in pekanbaru city. the ratio of the number of family members in pekanbaru city in 2018 consisted of four people, both from the external zone and the internal zone. so it is estimated that in a household in the two zones. four people will carry out the movement. when moving, people must choose the mode of transportation to support their daily activities. people tend to choose fast and cheap modes of transportation when moving. motorized vehicles are one of the leading choices of people in pekanbaru city. ownership of motorized vehicles certainly influences the movement of zones that occur in every household. the presence of a vehicle will certainly make it easier for someone to move from the origin zone to the destination zone. the movement is related to the selection of routes that the community in their activities will pass. the people of pekanbaru city, as described in tabel 4, mostly use motorbikes in their movement. the growth of motorcycle ownership has consistently increased compared to private car ownership, and this is due to the practicality and economics of motorcycles compared to private cars. in addition, the movement of motorbikes is more flexible than private cars when traffic jams occur. table 3. profile of travelers in pekanbaru city in 2018 population (thousand) number of households (thousand) population density (people/sq.km) annual population growth rate (%) household size 1.112.490 268.844 1.767 2,70 4,13 table 4. the average number of vehicle ownership by type in pekanbaru city in 2018 number of households (thousand) transportation type number of vehicles (units) average ownership (household/units) 268.844 motorcycle 917.200 3,41 private car 252.400 0,93 sari, e.g. et al./ jgeet vol 6 no 4/2021 239 table 5. number of vehicles based on travel time in pekanbaru city in 2018 time transportation type number of vehicles (units/hour) total vehicle (vehicle/hour) morning motorcycle 273.400 342.200 private car 68.800 afternoon motorcycle 181.000 242.000 private car 61.000 night motorcycle 18.000 21.100 every household in pekanbaru city owns a motorized vehicle in the form of a car or a motorcycle. from vehicle ownership data and the number of households, it can be estimated that for every one resident, there is one motorbike. for every two residents, there is one private car. in one household, many also have more than one vehicle. with an average family size of four people, it means that on average, one car is owned by every two families, or for every two households, there is one household that owns a car. as for motorcycles, each household has two or more motorcycles. most of the people of pekanbaru city on weekdays move to work and go to school. homemakers usually do it for activities such as shopping, so the percentage generated is not too large. only a tiny part of the community can carry out activities such as socializing and traveling because these activities are usually carried out on weekends (fig.5). community activities in pekanbaru city such as working, going to school, shopping, traveling, and socializing are usually carried out in the morning until noon, causing the movement of people using motorbikes and private cars to increase. meanwhile, at night, people generally stop their activities and stay at home, thereby reducing the movement they make. 97% of community movements in pekanbaru city are carried out in the morning until noon (tabel 5). motorcycles dominate the movement of people in the city of pekanbaru from the morning until the evening. respondents prefer private vehicles, especially motorcycles with relatively high mobility and economical fuel use, and are very quickly owned by zone movement actors. in addition, private vehicles are much more comfortable and safe than current public transport conditions, especially in pekanbaru city. 3.2 travel pattern as many 67% of the people in pekanbaru city carry out movements outside their original zones, referred to as a generation. awakening creates a pattern of travel from the initial zone to the end zone of community movement. the distribution of community movements in pekanbaru city spreads throughout the sub-districts. private transportation is the primary choice in pekanbaru city when making movements. people choose motorbikes as the primary vehicle they will use when moving (fig.6). motorcycles are widely chosen as a mode of transportation because of the cheap, easy, and efficient purchase price factor. in addition, most of the people in pekanbaru city are of medium and low income. the route that the community chooses to move varies depending on the distance to the destination zone. the length of travel time taken by the community in pekanbaru city is strongly influenced by selecting travel routes. private cars cover a longer average trip length than motorbikes (tabel.6). pekanbaru city usually uses motorbike transportation modes if the distance between the origin and destination zones is not too far. however, if the distance they want to go is very far, people tend to use private cars to move. fig. 5 percentage of community activities in pekanbaru city fig. 6 percentage of transportation mode selection in pekanbaru city table 6. average travel length in pekanbaru city transportation type average trip length (kilometers) motorcycle 3,97 private car 5,59 in fig.7, the most significant community travel pattern in pekanbaru city is in zone 10 to zone 9, zone 9 to zone 11, zone 11 to zone 6. the number of movements in this zone is due to the factor of community activities that tend to be dense because there are educational facilities and economic facilities in the area, resulting in a large pull and generation. land use in zone 10, zone 9, zone 11, and zone 6 is dominated by residential areas and the center of community activities, so land use attracts more significant movement than other zones. the movement of people in the city of pekanbaru generally leads to land use which is the center of community activity. the moves made by the community influence the length of the trip, and the more actions carried out, the longer the journey taken by motorized vehicles, so the higher the emission of carbon dioxide (co2) produced by motorized vehicles. 78% 22% motorcycle private car 56% 18% 25% 1% 0% work shopping school social tour 240 sari, e.g. et al./ jgeet vol 6 no 4/2021 fig. 7 travel patterns in pekanbaru city 3.4 total carbon dioxide (co2) emissions in pekanbaru city calculation of the total emission of carbon dioxide (co2) can be done with three conditions, namely using the emission factor (fe) ippc 1996, emission factor (fe) local ippc 2011, and emission factor (fe) bappenas. in this study, the total emission of carbon dioxide (co2) is calculated using the emission factor (fe) of bappenas because the 1996 ippc emission factor and the 2011 local ippc are the standards used to calculate the emission factor of motorized vehicles in the world, so the scope is too large. while in this study focused on certain vehicles in indonesia. the calculation of carbon dioxide (co2) emissions using these three emission factors is not much different. some of these reasons underlie this research using the emission factor (fe) of the national development planning agency to determine the total carbon dioxide (co2) emissions produced in pekanbaru city. the emission factor for premium fuel is 2,600 grams/liter and 2,200 grams/liter for diesel fuel. data on the average number of vehicles per hour (vehicles/hour), total vehicle mileage (kilometers), emission factors (grams/liter), and fuel consumption (liters/kilometers) are needed to obtain the total results of carbon dioxide (co2) emissions in the pekanbaru city. the most significant contributor to carbon dioxide (co2) emissions based on travel time is 52% of 394.57 tons/hour in the morning. tabel 7 shows the total carbon dioxide (co2) emissions by travel time in pekanbaru city. it is predicted that in a day, motorized vehicles can produce 9,469.75 tons of carbon dioxide (co2) emissions due to the movement of motorized vehicles. table 7. total carbon dioxide (co2) emissions based on travel time in pekanbaru city. time transportation type type of fuel emission factor bappenas (gram/liter) energy consumption (liter/km) total energy consumption (liter) average co2 emissions (gram/hour) emisi co2 average (kg/hour) pagi motorcycle fuel oil 2.600 0,0266 29.122,39 75.718.207,66 75.718,21 private car fuel oil 2.600 0,1179 50.413,33 131.074.664,76 131.074,66 siang motorcycle fuel oil 2.600 0,0266 22.310,40 58.007.050,92 58.007,05 private car fuel oil 2.600 0,1179 45.923,94 119.402.234,64 119.402,23 malam motorcycle fuel oil 2.600 0,0266 1.826,89 4.749.908,80 4.749,91 private car fuel oil 2.600 0,1179 2.161,81 5.620.717,44 5.620,72 kg/hour 394.572,78 ton/hour 394,57 table 8. total carbon dioxide (co2) emissions by vehicle type in pekanbaru city. transportation type type of fuel emission factor bappenas (gram/liter) energy consumption (liter/km) total energy consumption (liter) average co2 emissions (gram/day) average co2 emissions (kg/day) motorcycle fuel oil 2.600 0,0266 106.083,60 275.817.355,63 275.817,36 private car fuel oil 2.600 0,1179 197.184,92 512.680.793,04 512.680,79 total 788.498,15 ton/day 788,50 sari, e.g. et al./ jgeet vol 6 no 4/2021 241 in tabel 8, the details of carbon dioxide (co2) emissions by type of vehicle in pekanbaru are presented using the emission factor (fe) of the national development planning agency. the total emission of carbon dioxide (co2) in pekanbaru city in 2018 was 788.50 tons/day, and it is estimated that it will be every year. types of vehicles that contribute the most to carbon dioxide (co2) emissions are private cars with 65% of total emissions. as many as 252,400 private cars cover a total distance of 1,672,476 kilometers. the handsome subdistrict and the tenayan raya sub-district have the most significant vehicle ownership and the largest population in pekanbaru city. fig. 8 average co2 emissions (kg/hour) by vehicle type in pekanbaru city fig.8 explains that the highest carbon dioxide (co2) emissions are produced in the morning, with vehicles that contribute the most carbon dioxide emissions are private cars. most community activities in pekanbaru city are carried out in the morning. the volume of vehicles traveling is also getting bigger, which will affect the production of carbon dioxide (co2) emissions. at night the amount of carbon dioxide emissions produced by motorized vehicles decreases because the vehicles that move are also reduced. 4. conclusion concern for carbon dioxide (co2) emissions due to motorized vehicle activities are becoming increasingly important, so it is necessary to understand and identify which areas need to be controlled to produce carbon dioxide emissions. this research begins by analyzing the four-step model, then calculating the vehicle kilometer traveler (vkt), determining the type of fuel used, calculating fuel consumption, and determining the emission factor. so that the results obtained based on the type of motor vehicle carbon dioxide emissions in pekanbaru city produced 788.50 tons/day. meanwhile, based on time, the carbon dioxide emission in pekanbaru city produced 394.57 tons/hour. the most significant carbon dioxide emission in pekanbaru city comes from motorized vehicles in private cars. although motorcycles are the most numerous vehicles based on the data obtained, compared to private cars, the immense amount of carbon dioxide emissions is produced by private cars. the carbon dioxide emissions of private cars are more significant than motorcycles because the energy consumption of private cars is much higher than that of motorcycles. the high number of motorized vehicles cannot reference that the emission of carbon dioxide (co2) produced will also be high. the high emission of carbon dioxide (co2) produced by motorized vehicles is determined by fuel consumption. the greater the fuel consumption, the greater the carbon dioxide (co2) emissions released by motorized vehicles. the area of pekanbaru city is dominated by agricultural land use and also settlements. the direction of land cover development in the city of pekanbaru is in the western and southern parts of the city of pekanbaru. as a result of land development in the western and southern regions, the movement of motorized vehicles is higher in these areas. people in pekanbaru make the most significant movement on land use, which functions as a center of community activity. so that certain zones have the highest value of the activities carried out. the higher the movement of motorized vehicles on land use, the longer the distance traveled by motorized vehicles, the 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ahmad, m., irfan, m., traore, o., ali, a., 2021. towards environmental sustainability : devolving the influence of carbon dioxide emission to population growth , climate change , forestry , livestock and crops production in pakistan 125, 1–11. https://doi.org/10.1016i/j.ecolind.2021.107460 sengkey, s.l., jansen, f., wallah, s., 2011. tingkat pencemaran udara co akibat lalu lintas dengan model prediksi polusi udara skala mikro. j. ilm. media eng. 1, 119–126. shaw, s., xin, x., 2003. integrated land use and transportation interaction : a temporal gis exploratory data analysis approach. j. transp. geogr. 11, 103–115. https://doi.org/10.1016/s0966-6923(02)00070-4 siskos, p., moysoglou, y., 2019. assessing the impacts of setting co 2 emission targets on truck manufacturers : a model implementation and application for the eu. transp. res. part a 125, 123–138. https://doi.org/10.1016/j.tra.2019.05.010 sohag, k., begum, r.a., abdullah, s.m.s., jaafar, m., 2015. dynamics of energy use , technological innovation , economic growth and trade openness in malaysia. energy 1–11. https://doi.org/10.1016/j.energy.2015.06.101 song, x., yang, g., yan, c., duan, h., liu, g., zhu, y., 2009. driving forces behind land use and cover change in the qinghai-tibetan plateau : a case study of the source region of the yellow river , qinghai province , china. env. earth sci 59, 793–801. https://doi.org/10.1007/s12665-009-0075-8 tamin, o.z., 2000. perencanaan dan pemodelan transportasi, edisi kedu. ed, perencanaan dan pemodelan transportasi. institut teknologi bandung, bandung, indonesia. wegener, m., 2004. overview of land use transport models. wegener, m., fürst, f., 1999. land-use transport interaction: state of the art. institut für raumplanung fakultät raumplanung, universität dortmund. wu, h., lin, a., xing, x., song, d., li, y., 2021. identifying core driving factors of urban land use change from global land cover products and poi data using the random forest method. contents list. available sci. int. j. appl. earth obs. geoinf. 103, 1–13. https://doi.org/doi.org/10.1016/j.jag.2021.102475 zhu, z., xiong, c., chen, x., he, x., zhang, l., 2018. integrating mesoscopic dynamic tra ffi c assignment with agentbased travel behavior models for cumulative land development impact analysis. transp. res. part c 93, 446–462. https://doi.org/10.1016/j.trc.2018.06.011 © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at which the author did the work must be retained as the main, affiliation address.start by adding an asterisk (*) and then email, phone number, font gulliver 7pt. 3. abstract summary of the all research (aim, scope, result and conclusion) with maximum 300 words, justified, 8 point, and line spacing : single. for keywords wrote in italic and then separated using symbol (,) with maximum are 6 words. 4. introduction in introduction, authors should state the objectives of the work at the end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type area. the structure of manuscripts should follow the following order; title, authors, affiliations, abstract, keywords, main text, (acknowledgement), (appendix), (nomenclature), references. the items with parentheses are not mandatory. the maximum pages printed in jgeet are supposed to be 10 for an original paper and 15 for a review paper. do not include page numbers. do not add headers or footers. prescribed font is gulliver, 9 points, with an single line spacing. however, if your text contains complicated mathematical expressions or chemical formulae, you may need to increase the line spacing. running text should be justified. 5. section headings the way chapter titles and other headings are displayed in these instructions, is meant to be followed in your manuscript. level 1: gulliver, 9, bold, 6 pt spacing before heading, 6 pt spacing after heading. successive levels: times new roman, 8, bold, 6 pt spacing before heading, no spacing below heading. do not begin a new section directly at the bottom of the page, but transfer the heading to the top of the next page. cite the main scientific publications on which your work is based. cite only items that you have read. do not inflate the manuscript with too many references. avoid excessive self‐citations. avoid excessive citations of publications from the same region. check each reference against the original source (authors name, volume, issue, year, doi number). please use reference manager applications like endnote, mendeley, zotero, etc. use other published articles in the same journal as models. if you are cite using mendeley please use elsevier harvard (with title) for cite model stlye of this journal. 6. footnotes it is requested not to us any of footnotes. all references should be in the references. explanations should be preferably included in the text. 7. symbols and units, numbers if symbols are defined in a nomenclature section, symbols and units should be listed in alphabetical order with their definition and dimensions in si units. please use the si set of units as much as possible. wherever the application domain uses a different set of units widely, please minimize the use of non-standard units or non when providing numerical values followed by measurement units, please leave a regular space or nonbreaking space between each value and the measurement unit. this also includes percentages and degrees celsius (e.g. 42 % or 35 %, 234 °c, 504 k). this rule also applies to the unit for litre, which is recommended to specifying the dot as a decimal separator and the comma as a thousands separator. 8. equations make sure that placing and numbering of equations is consistent throughout your manuscript. (1) 1 1 c( ) ( )    n i i t c t n (2) left align the equation and put the number of the equation flush-right, using a right tab on the right margin. please reference equations in the text by writing: eqn. .. (do not use equation ..) in principle, variables are to be presented in italics. 9. figures and tables figures and tables should be originals or sharp prints. please use the si set of units as much as possible. figures and tables should be centered and placed either at the top or at the bottom of the page. please do not render tables as pictures and please do not use too small font sizes in the illustrations. please use the following fonts in your illustrations: gulliver, symbol, or use fonts that look similar. if your figures and tables are created in a microsoft office application (word, powerpoint, excel) then please supply 'as is' in the native format, too. regardless of the application used other than microsoft office, when your electronic artwork is finalized, please 'save as' or convert the images to one of the following formats (note the resolution requirements for line drawings, halftones, and line/halftone combinations given below):   2 2 2 1 2 dxi dyi dzi d mk xidxi yidyi zidzi dt dt dt                                   eps (or pdf): vector drawings, embed all used fonts.  tiff (or jpeg): color or grayscale photographs (halftones), keep to a minimum of 300 dpi.  tiff (or jpeg): bitmapped (pure black & white pixels) line drawings, keep to a minimum of 1000 dpi.  tiff (or jpeg): combinations bitmapped line/half-tone (color or grayscale), keep to a minimum of 500 dpi. set table number and title flush left above table. horizontal lines should be placed above and below table headings and at the bottom of the table. vertical lines should be avoided. title should use gulliver 8, with 10 pt before and 4 pt after the paragraph, left justified at the top of the table. tables have to be included into the text. if a table is too long to fit one page, the table number and heading should be repeated on the next page before the table is continued. alternatively the table may be spread over two consecutive pages (first an even numbered, then anodd-numbered page) turned by 90, without repeating the heading. 10. figure captions fig. 1 captions should be placed below each illustration, font times new roman, 7 pts. figures and figure captions should be placed center; two narrow figures may be placed side-by-side. please reference figures in the text by writing: fig. .. (do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at which the author did the work must be retained as the main, affiliation address.start by adding an asterisk (*) and then email, phone number, font gulliver 7pt. 3. abstract summary of the all research (aim, scope, result and conclusion) with maximum 300 words, justified, 8 point, and line spacing : single. for keywords wrote in italic and then separated using symbol (,) with maximum are 6 words. 4. introduction in introduction, authors should state the objectives of the work at the end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type area. the structure of manuscripts should follow the following order; title, authors, affiliations, abstract, keywords, main text, (acknowledgement), (appendix), (nomenclature), references. the items with parentheses are not mandatory. the maximum pages printed in jgeet are supposed to be 10 for an original paper and 15 for a review paper. do not include page numbers. do not add headers or footers. prescribed font is gulliver, 9 points, with an single line spacing. however, if your text contains complicated mathematical expressions or chemical formulae, you may need to increase the line spacing. running text should be justified. 5. section headings the way chapter titles and other headings are displayed in these instructions, is meant to be followed in your manuscript. level 1: gulliver, 9, bold, 6 pt spacing before heading, 6 pt spacing after heading. successive levels: times new roman, 8, bold, 6 pt spacing before heading, no spacing below heading. do not begin a new section directly at the bottom of the page, but transfer the heading to the top of the next page. cite the main scientific publications on which your work is based. cite only items that you have read. do not inflate the manuscript with too many references. avoid excessive self‐citations. avoid excessive citations of publications from the same region. check each reference against the original source (authors name, volume, issue, year, doi number). please use reference manager applications like endnote, mendeley, zotero, etc. use other published articles in the same journal as models. if you are cite using mendeley please use elsevier harvard (with title) for cite model stlye of this journal. 6. footnotes it is requested not to us any of footnotes. all references should be in the references. explanations should be preferably included in the text. 7. symbols and units, numbers if symbols are defined in a nomenclature section, symbols and units should be listed in alphabetical order with their definition and dimensions in si units. please use the si set of units as much as possible. wherever the application domain uses a different set of units widely, please minimize the use of non-standard units or non when providing numerical values followed by measurement units, please leave a regular space or nonbreaking space between each value and the measurement unit. this also includes percentages and degrees celsius (e.g. 42 % or 35 %, 234 °c, 504 k). this rule also applies to the unit for litre, which is recommended to specifying the dot as a decimal separator and the comma as a thousands separator. 8. equations make sure that placing and numbering of equations is consistent throughout your manuscript. (1) 1 1 c( ) ( )    n i i t c t n (2) left align the equation and put the number of the equation flush-right, using a right tab on the right margin. please reference equations in the text by writing: eqn. .. (do not use equation ..) in principle, variables are to be presented in italics. 9. figures and tables figures and tables should be originals or sharp prints. please use the si set of units as much as possible. figures and tables should be centered and placed either at the top or at the bottom of the page. please do not render tables as pictures and please do not use too small font sizes in the illustrations. please use the following fonts in your illustrations: gulliver, symbol, or use fonts that look similar. if your figures and tables are created in a microsoft office application (word, powerpoint, excel) then please supply 'as is' in the native format, too. regardless of the application used other than microsoft office, when your electronic artwork is finalized, please 'save as' or convert the images to one of the following formats (note the resolution requirements for line drawings, halftones, and line/halftone combinations given below):   2 2 2 1 2 dxi dyi dzi d mk xidxi yidyi zidzi dt dt dt                                   eps (or pdf): vector drawings, embed all used fonts.  tiff (or jpeg): color or grayscale photographs (halftones), keep to a minimum of 300 dpi.  tiff (or jpeg): bitmapped (pure black & white pixels) line drawings, keep to a minimum of 1000 dpi.  tiff (or jpeg): combinations bitmapped line/half-tone (color or grayscale), keep to a minimum of 500 dpi. set table number and title flush left above table. horizontal lines should be placed above and below table headings and at the bottom of the table. vertical lines should be avoided. title should use gulliver 8, with 10 pt before and 4 pt after the paragraph, left justified at the top of the table. tables have to be included into the text. if a table is too long to fit one page, the table number and heading should be repeated on the next page before the table is continued. alternatively the table may be spread over two consecutive pages (first an even numbered, then anodd-numbered page) turned by 90, without repeating the heading. 10. figure captions fig. 1 captions should be placed below each illustration, font times new roman, 7 pts. figures and figure captions should be placed center; two narrow figures may be placed side-by-side. please reference figures in the text by writing: fig. .. (do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 1 2022 alpine, f. et al./ jgeet vol 7 no 1/2022 7 research article identification of geothermal system in “diana” area, indonesia based on magnetotelluric data modelling fajar alpine 1, y. yatini*1, iqbal takodama2 1 geophysics engineering, universitas pembangunan nasional veteran, condong catur 55283, yogyakarta indonesia. 2psdg, soekarno-hatta street, no.444, pasirluyu, regol, bandung, west java 40254. * corresponding author : jeng_tini@upnyk.ac.id tel.: +85-74-319-8262; received: jul 31, 2021; accepted: mar 30, 2022. doi: 10.25299/jgeet.2022.7.1.7448 abstract these days, the number of geothermal explorations is being increased to obtain a greater new potential of geothermal energy. one of the methods that is often used is magnetotelluric (mt). by mt, the components of a geothermal system can be delineated based on the resistivity values. this research’s main purpose is mt data modelling in 1 d and 2 d to delineate the geothermal system in the research area. there are 18 point of soundings, with a distance of about 1 – 3 km for each point. bostick transformation is used in 1 d modelling while non-linear conjugate gradient inversion is used as 2 d modelling with l – curve analysis as a method to obtain an optimal value of regularization parameter. based on the analysis of 1 and 2 d models, the caprock zone was identified with a resistivity value of < 50 ωm at a depth of 500 m with a thickness of about 250 m. the reservoir zone was identified with a resistivity value range of (50 – 100) ωm located at a depth of 1000 with a thickness of about 500 m. also, fault structures have been identified at the center of the research area. the regularization parameter used for the 2 d modelling is 5, which has obtained rms values of 2.25% and 2.21% for each line. keywords: geothermal system, inversion, magnetotelluric, resistivity 1. introduction indonesia had an increase in population from year to year, which has made indonesia the 4th country in the world with the greatest population. along with the increase of the population, the energy needs increased too. energy supply should at least be 1.25% 1.30% greater than the population growth. however, the energy availability in indonesia is not proportional with indonesia’s population which keeps increasing. in the case of 2012, there was an increase of 6.20% in population, while only 3.15% of increase in total primary energy supply (tpes) (purnomo, 2014). indonesia is at the meeting of three plates which are the australian plate, eurasian plate, and pacific plate, and perhaps also the phillipine sea plate at the north of sulawesi (katili, 1975). the meeting of those plates has a role in the making of the most complex geology setting in the world. indonesia has 129 active volcanoes, which spread along indonesia’s islands. geothermal energy has a connection with volcanic events, which is why lots of geothermal systems were created in sumatra, java, southeast nusa, sulawesi, and maluku. indonesia is a country with 29 gw of geothermal reserve. geothermal energy is planned to be utilized in a greater number to become one of the renewable energies to contribute as the national energy, reaching 4% by 2025 (purnomo, 2014). one of the geophysical methods used for geothermal explorations is mt. this method used the propagation of electromagnetic wave with a great depth of penetration, which reached tens of metres to tens of kilometres (vozoff, 1991). mt can represent the subsurface of a geothermal system based on the resistivity values. mt is effective to delineate the conductive layer compared to the resistive ones (wameyo, 2005). this method is suitable for geothermal exploration because the caprock in a geothermal system can be delineated due to its conductivity which will have a contrast in values with the layer below it, reservoir. before this research was conducted, an earlier research has been done in “diana” area by kholid and marpaung (2011). this research was conducted on 36 mt sounding points, which resulted in 2-d models. the results have identified the caprock zone with resistivity value of < 100 ωm in the center of the area, which spreads to the north. the caprock zone is located in the elevation of – 1000 asl with a thickness of 500 – 1000 m. the reservoir zone is located below the caprock zone, which is at the depth of 1000 – 1500 m, which deepens to the east and west direction. the reservoir zone is bordered by a fault structure with east – west direction. in this research, bostick transformation will be used for 1 d modelling and non-linear conjugate gradient inversion for 2 d modelling. the results will be analysed based on resistivity values to identify the geothermal system components in diana “area”, which are caprock, reservoir, and fault, based on the contrast in the resistivity values shown. then, the regularization parameter tau (τ) which gives the most optimal 2-d model will be decided. last, both models will be compared and the most optimal model will be decided. 2. geology and stratigraphy http://journal.uir.ac.id/index.php/jgeet 8 alpine, f. et al./ jgeet vol 7 no 1/2022 the geothermal system in research is associated with quaternary volcanic rocks. this area is characterized with volcanic rocks which has a composition of andesitic until trachitic. the morphology in the area is dominated with steep and corrugated hills, where cone – like shapes were found in few places. this cone – like shapes were probably the centre of former eruption of young volcanics which unfolded near the manifestation area. the corrugated hills showed the erosion that occurred from the older volcanic rocks. volcanic activities in the research have occurred from the tertiary age which was predicted to be undersea volcanoes which developed to be early quaternary terrestrial volcanoes. most of the products of tertiary volcanics composed of andesitic until trachitic have eroded and caused the disappearation of the eruption source’s traces, and also caused intensive splitting which resulted in good enough permeability for fluid to flow. the next geology process is orogenesis which caused uplifting and resulted in the creation of land. along the orogenesis process, volcanic activities still went on and created a cone – like volcanic at the southwest of manifestation, with products of andesitic lava and lava breccia. cone – like volcanic in the research area is predicted to be the heat source which has leftover heat from the magma chamber. the research area was dominated by volcanic rocks that consist of lava flow which spread widely, as well as volcanic domes. there are seven fault structures that are developing. a dilational fault jog was predicted to has occurred at the intersection of these faults, which created a media for hydrothermal fluidflow to the surface. these structures’ movement patterns are two strike – slip faults and five normal faults respectively. a depression is identified by a cliff which bordered said depression that has made a curved to half – radial shape. from the morphology and structures’ patterns, this depression is predicted to be the result of collapse of foldings that occurred before. the geothermal area in this research area is predicted to be bordered by this depression, where a manifestation in shape of hot spring has appeared. the stratigrapy of the research area consists of andesit porphyr formation (tp), undivided volcanic formation (tvt), andesitic lava formation (tlt), and basaltic andesitic lava formation (tld), as shown in figure 1. based on these formations, the research area is dominated by andesite, andesitic lava, and basaltic andesite. there are also sheer joints that have created minor faults. there is also andesitic lava dome in the center of the research area, where the alteration process resulted in creation of chlorite and clays in the area. these formations occurred in the tertiary age, which made the geothermal system in this area classified as non – volcanic geothermal system. fig 1. geology map of research area “diana” (modified from kholid dan marpaung, 2011). fig 2. stratigraphy in research area, consists of andesit porphyr formation (tp), undivided volcanic formation (tvt), andesitic lava formation (tlt), and basaltic andesitic lava formation (tld) (modified from kholid dan marpaung, 2011). alpine, f. et al./ jgeet vol 7 no 1/2022 9 3. methods mt method is a geophysical method that utilizes natural em fields. this em field is generated by various physical processes which are quite complex with a very wide frequency spectrum (10-5 -10-4) hz. at fairly low frequencies (<1hz), the solar wind containing electrically charged particles interacts with the earth's permanent magnetic field, causing variations in the em field. variations in the audio frequency range (>1hz) are mainly due to meteorological activity in the form of lightning. lightning that occurs somewhere causes em waves that are trapped between the ionosphere and the earth (vawe guide) and propagate around the earth. (vozoff, 1991). the dependence of electric-magnetic phenomena on electrical properties, especially the conductivity of the medium (earth) can be utilized for exploration purposes using the mt method. this is done by simultaneously measuring the variation of the magnetic field (e) and magnetic field (h) as a function of time. information about the conductivity of the medium contained in the mt data can be obtained by solving maxwell's equations using simple models. maxwell's equations contain faraday's, ampere, gauss's laws which are shown by equations (1) to (4) 𝛻 × �⃗� = − 𝜕�⃗� 𝜕𝑡 (faraday law) (1) 𝛻 × �⃗⃗� = 𝐽 + 𝜕�⃗⃗� 𝜕𝑡 (ampere law) (2) 𝛻. �⃗⃗� = 𝑞 (gauss i law) (3) 𝛻. �⃗� = 0 (gauss ii law) (4) wherein �⃗� : electric field (v/m), �⃗� : magnetic induction (w/m), �⃗⃗� : magnetik field (a/m), 𝐽 : current density (a/m2) dan 𝑞 : density of charge (c/m3) further relationship between the displacement current �⃗⃗� , electric field �⃗� and magnetic field �⃗⃗� can be written eq (5) to (7). �⃗⃗� = 𝜀�⃗� (5) �⃗� = 𝜇�⃗⃗� (6) 𝐽 = 𝜎�⃗� (7) where ε : electrical permittivity (f/m), μ : magnetic permeability (h/m),σ : conductivity of the medium (s/m) maxwell's equations can be rewritten as eq (9)-(11). 𝛻 × �⃗� = −𝜇  �⃗⃗�  𝑡 (8) 𝛻 × �⃗⃗� = 𝜎�⃗� + 𝜀  �⃗�  𝑡 (9) 𝛻 ∙ �⃗� = 0 (10) 𝛻 ∙ �⃗⃗� = 0 (11) research in “diana” area was done based on 18 points of mt soundings. the results of these mt soundings are mt time series data. the first process to be done is to convert the time series into frequency domain. ssmt2000 software is used for fourier transform and robust processing. robust calculation processes discrete fourier transform (dft) into crosspower. this process also applied the robust calculation to reduce noise in the data. before robust processing, the parameters used have to be set up which is the robust parameter file (prm) (rogers, 2005). the result of robust processing is pseudo – resistivity and phase curves in frequency domain for every frequency. the next step is crosspower selection using mteditor software. data read by this software is mt plot file created by ssmt2000, which shows the pseudo – resistivity and phase curves, along with its crosspower for every frequency. other than that, this software also shows the characteristics from every sounding data, such as pseudo – resistivity, phase, impedance, strike direction, coherency, and others, along the frequencies obtained. (rogers, 2005). crosspowers affected by noise are deleted automatically or manually. with that, the data quality can be improved. the auto – edit option in mteditor will delete crosspowers that are too far from the average value. that is why it is recommended to begin the selection by auto – edit, then continued by editing manually. the main obyective in this process is to smooth the pseudo – resistivity and phase curves by deleting crosspowers that are affected by noise (mwakirani, 2012). after that, the next smoothing process will use winglink software. there are three types of smoothing, being sutarno one of them, which calculates smoothing of the pseudo – resistivity curve based on the phase curve. in general, sutarno is used to ensure the consistency of pseudo – resistivity and phase values. second is d+ smoothing, which associates the smoothing calculation between resistivity and phase, so the solution of 1 d earth which suits both parameters the most can be obtained. this calculation proves to be the most optimal for 2 d and 3 d data. last is numerical smoothing, which calculates the resistivity and phase curves independently (geosystem srl, 2008). in this research, d+ smoothing was used because of its calculation that associated the resistivity and phase calculation. the obtained smooth curves will be modelled in 1 d and 2 d. bostick transformation was used for 1 d modelling. bostick’s concept is trial and error, where model will be fit based on the observed data. the results from all the 1 d models will be used to make a cross section. a cross section is where the resistivity values from all the 1 d models will be interpolated. based on the cross sections for every line, the resistivity values between soundings will be obtained. non-linear conjugate gradient inversion was used for 2 d modelling. in 2 d modelling, regularization parameter that gives the most optimal model will be determined by l – curve analysing. the regularization parameter that will be determined is tau (τ). based on 1 d and 2 d models, resistivity distribution maps in determined depths will be made. 4. results and discussion the result of 1 d modelling in figure 3 shows that there are four layers under surface. not all 1 d models have the same number of layers due to the heteroginity of resistivity and phase values. in general, for all soundings, the resistivity values increased along with greater depth. this is due to the more massive and compact the rocks are in greater depths. rocks near the surface will have lower resistivity values because of its non – compact characteristic. this low compactness can be due to weathering process. points of soundings that show the pattern of increasing resistivity along with depth are mt 10, mt 11, mt 12, mt 13, dan mt 14 for 1st line, and all the soundings except mt 15a and mt 16 for 2nd line. there are few 1 d models that do not show the pattern as explained before. in sounding point mt 8 and mt 9 in the 1st line, there is a decrease in resistivity values in the third 10 alpine, f. et al./ jgeet vol 7 no 1/2022 layer. this is due to the location of the soundings that are close to the hot spring manifestation in “diana” area. the decrease in resistivity values is due to fluid flow or temperature increase which resulted by the fluid flow around it. then in mt 9a, it is shown that the resistivity value is still very low even though the depth has increased. this is due to the location of sounding which is really close to the manifestation area. this sounding point is predicted to be right above the fault that plays a role in the geothermal system in “diana” area as a media for fluid flow. then in the 2nd line, resistivity values in mt 15a has a decrease in the third layer. location of mt 15a is parallel to mt 8 from the 1st line, which is why the decrease of resistivity values is also due to fluid flow and temperature increase. mt 16 has a resistivity value that is still very low even though it has reached a greater depth, like mt 9a. so, it is predicted that there is a fault below mt 16 which has a role as a media for fluid flow. in 1 d and 2 d modelling, the value range used will be the same. the resistivity value ranges are divided into three, which are low, medium, and high. table 1 shows the classification of these resistivity values, and the interpretation for each range. all interpretations done will be based on table 1. table 1. classification of resistivity values in “diana” area no. classification resistivity range (ωm) interpretation 1 low < 50 caprock zone 2 medium 50 – 200 reservoir zone 3 high > 200 massive rocks fig 3. 1 d model of sounding point mt 10. a) apparent resistivity curve. dots represent the observed data, line represent calculated data; b) phase curve. dots represent the observed data, line represent calculated data; 1 d model, where the vertical axis represent depth and horizontal axis represent resistivity. fig 4. 1 d cross section of 1st line in “diana” area. 1st line has 8 sounding points with a distance of about 1 – 2 km. the result showed a) caprock; b) reservoir; c) fault and d) hot spring. generally, the resistivity increased with depth. mt 9a showed low resistivity until a depth of 4 km, which is caused by the fault located under the hot spring. a b d c alpine, f. et al./ jgeet vol 7 no 1/2022 11 fig 5. 1 d cross section of 2nd line in “diana” area. 2nd line has 10 sounding points with a distance of about 1 – 3 km. the result showed a) caprock; b) reservoir and c) fault. generally, the resistivity increased with depth. the cross sections of 1 d models showed that in general, the resistivity values increased along with depth. below sounding point mt 9a, there is low resistivity value of < 10 ωm from the surface until a depth of 4 km. this is due to the location of manifestation below this sounding point. the low value pattern is predicted to be a fault which is a media for fluid flow in the geothermal system of “diana” area. this fault is shown by dotted line in figure 4. the low resistivity value is associated by fluid with high salinity in a geothermal system (llera, dll, 1990). however, fluid salinity value in geothermal system of “diana” area is unable to be determined due to limitations of supporting data. in 2d modelling, there is a process to determine the right regularization parameter by l – curve analysing using microsoft excel. the l – curve analysing is done by doing 2d inversions multiple times with a different value of 𝜏 each time. from every result of those inversions, the value of roughness/rms to 𝜏 will be plotted to find its maximum curvature. the location of the maximum curvature in the l – curve shows balance between the requirements of an optimum model, which has enough smoothness as well as low enough rms value (hansen, 1992). fig 6. l – curve: roughness/rms versus parameter 𝜏. value of 𝜏 = 5, is the 𝜏 chosen. figure 6, show that maximum curvature occurred at 𝜏 = 5. so, the 2 d modelling done in this research uses parameter 𝜏 = 5. figure 7 shows the 2 d model for 1st line. the inversion was done using te and tm data, and 𝜏 of 5, as explained before. the amount of iteration used is 30. the inversion resulted in rms error of 2.25 %. low resistivity value in sounding point mt 10 until mt 14 near the surface is interpreted as caprock zone. according to ussher (2000), a zone that is located at the top of a geothermal system has a low resistivity due to temperature factor (70 – 200°c) and abundance of conductive clay. clay is the result of hyrothermal alteration that occurred in said temperature. the low value pattern below mt 11 looks declining compared with its surrounding. this is predicted to be the result from a collapse by an intrusion below it. based on the geology data, the geothermal system in “diana” area was made in a depression zone, characterized by half radial cliff as shown in the model, which is predicted to be the results from foldings that have occurred before. below sounding point mt 11, it is predicted that there is a fault resulted by said collapse, and it can be identified by the resistivity value contrast. the caprock zone is located at the centre of the line, going to northeast direction. the zone with a medium range of resistivity is right below the caprock zone, and is predicted to be the reservoir zone. this zone only reaches a depth of about 1 km. at this zone, the temperature has increased and became higher compared to the caprock zone above it. components of geothermal system that have higher temperature is characterize by higher resistivity compared to the conductive zone above it. this higher resistivity value is due to rocks’ matrix that is less conductive compared to the fluid inside it. at this zone, mineralization is dominated by results of low conductivity alteration. high temperature alteration can increase rocks’ resistivity value because of the changing process from smectite clay to illitic or chloritic clay (ussher, etc. 2000). other than that, porosity also decreases along with greater depth, and can result in higher resistivity. based on geology data and early researches, this high resistivity value is interpreted to be andesite rocks which are still very compact. then, at a depth of below 2 km, the increase of resistivity until 1000 ωm has appeared. this increase is predicted to be caused by metamorphic rocks which are characterized to be more resistive. 2 d modelling for 2nd line uses the same parameters as the 1st line. figure 8 is the result of 2 d modelling for 2nd line. this model has a rms error of 2.21 %. in this model, it is shown that the interpreted parts have the same location as the model for 1st line, which is at the northeast of the a b c c 12 alpine, f. et al./ jgeet vol 7 no 1/2022 line. there are four faults interpreted which are below sounding point mt 17a, mt 19, mt 20, and mt 21, identified by resistivity value contrast. this fault is predicted to be the result of uplift by an intrusion below, and caused collapse near the surface. this collapse is shown by the radial shape of low resistivity near the surface, which keeps declining at the centre of the line. fig 7. 2 d model of 1st line in “diana” area. 1st line has 8 sounding points with a distance of about 1 – 2 km. the result showed a) low resistivity: caprock; b) medium resistivity: reservoir; c) fault and d) hot spring. generally, the resistivity increased with depth. mt 9a showed low resistivity until a depth of 4 km, which is caused by the fault located under the hot spring. the high resistivity at 4 km depth at the northeast is interpreted as compact andesite rocks. fig 8. 2 d model of 2nd line in “diana” area. 2nd line has 10 sounding points with a distance of about 1 – 3 km. the result showed a) low resistivity: caprock ; b) medium resistivity: reservoir and c) fault. generally, the resistivity increased with depth. the hi gh resistivity at 4 km depth at the northeast is interpreted as compact andesite rocks. radial shaped caprock zone and reservoir zone suited the geology data which stated that there is a leftover cliff that makes a radial shape (kholid dan marpaung, 2011). this radial shape is predicted to occur due to an intrusion which caused uplift to the layer above it. below the caprock zone, is a zone with higher resistivity, reaching 150 ωm. this zone has a low temperature. according to ussher (2000), high temperature located at the top of a geothermal system is caused by low fluid saturation, little hydrothermal alteration, and a decrease in resistivity caused by temperature. temperature effect in caprock zone has been explained by a research by kristmannsdóttir (1979). in this research, it has been explained that at a temperature of 50 – 100°c, alteration process in geothermal system produces smectite and zeolite as alterated minerals that dominate and caused a rock to be conductive. when depth increases, resistivity increases along with it. this is due to at a temperature of 220 – 240°c, smectite and zeolite is replaced by chlorite as dominating alterated mineral. when temperature increases, epidote mineral dominate and caused resistivity to increase even more (kristmannsdóttir, 1979). that is why, it can be seen in figure 7 and 8 that a reservoir zone has higher resistivity compared to the caprock zone above it. even though reservoir zone contains fluid which can decrease resistivity value, there is no mineralization which a b c d a b c c c c alpine, f. et al./ jgeet vol 7 no 1/2022 13 produces conductive minerals that occurs in the reservoir zone. conduction by minerals will give lower resistivity compared to rocks’ pores that contain fluid (flóvenz, 2005). high resistivity value in a depth of 1 – 5 km is caused by massive rocks which has low porosity. other than rocks’ compactness, high resistivity is also caused by temperature. at high temperature of a geothermals system, non conductive minerals dominate more and caused resistivity to increase. this caused conduction by rocks’ surface and fluid in pores dominate more compared to conduction by minerals. transition from smectite to chlorite – epidote zone occurs at about 230°c (flóvenz, 2005). alteration process depends more on temperature, but porosity and permeability also affect in this process. that is why, it can be predicted that massive rocks that have low porosity at depth of 1 – 5 km and high temperature have low permeability, and caused decrease in intensity of alteration. these massive rocks are interpreted as andesite rocks based on the geology data. in figure 9, it is shown that low resistivity zone is located at the east. this shows that caprcock zone reaches a depth of 500 until 1000 m. at the west, there is also a low resistivity zone and is predicted to be the caprock zone as well. however, the caprock zone at the west only reaches a depth of about 500 m. the reservoir zone is shown by the medium resistivity zone that appeared at the same location of the caprock zone. the reservoir zone is predicted to reach a depth of about 1500 – 2000 m. at greater depth, there are massive rocks that caused high resistivity to appear. at the south, it is seen that there is a pattern that elongated with a direction of northwest – southeast. this pattern is interpreted as a fault that plays a role in the geothermal system of “diana” field. this fault is identified by the discontinuity of medium resistivity at the depth of 500 – 2000 m, where the boundary of this medium resistivity makes a straight pattern wih northwest – southeast direction. the low resistivity zone that is interpreted as the caprock zone is located at the east (figure 10). this caprock zone is at the depth of 500 until 750 m. the medium resistivity zone which is at the same location of the caprock zone at 1000 m is the reservoir zone. this reservoir zone only reaches a depth of less than 1500 m. at a depth of > 1500 m, high resistivity spreads more along with greater depth. this is caused by massiveness of rocks which keeps increasing with greater depth. at 2000 m, it can be seen that a medium resistivity value appeared, which keep decreasing even more until 3000 m at the southwest. this is caused by the manifestation in the southwest of “diana” area. this has also been explained at the discussion for 2 d model, where the low resistivity value is due to fluid flow. the decrease in resistivity is also caused by the increase in depth. at 3000 m, there is a discontiunuity between high resistivity and low resistivity which makes a straight pattern with northeast – southeast direction. this pattern is predicted to be the fault that plays a role in the geothermal system. the difference between the maps based on 1 d and 2 d can be seen from the value distribution. for the 2 d maps, it can be seen that the distribution is more directed to the line’s direction while for the 1 d maps, there are resistivity zones that gathered in a point or few points. this is because of the 1 d models that have different pattern value for every sounding point. the 2 d modelled laterally and resulted in lateral distribution on the maps. based on the models and resistivity maps, this research stated that the 2 d model is more optimal to delineate the research target. the reason for this statement is because of the 2 d model is able to show the geology condition of the area. also, the 2 d model also shows the target better laterally and more supporting in interpretation because there are no values that gathered in one point and caused closure like the 1 d maps. fig 9. resistivity distribution maps in depth based on 1 d model. a) 500 meter ; b) 750 meter ; c) 1000 meter ; d) 1500 meter ; e) 2000 meter ; f) 2500 meter dan g) 3000 meter. fig 10. resistivity distribution maps in depth based on 2 d model. a) 500 meter ; b) 750 meter ; c) 1000 meter ; d) 1500 meter ; e) 2000 meter ; f) 2500 meter dan g) 3000 meter 5. conclusions the result of this research showed that the resistivity value obtained in “diana” area from mt data processing is divided into three ranges, low, medium, and high. the caprock zone with < 50 ωm is located at depth of (500 – 750) m. the reservoir zone with (50 – 100) ωm reaches depth of less than 1500 m. a fault is identified at the centre of the research area based on the value contrast. the high resistivity that reaches 1000 ωm at below 2 km is interpreted as andesite rocks which are still very compact. second, the regularization parameter (𝜏) used in 2 d modelling is 5, and is the most optimal 𝜏 based on the l – curve analysis. this 𝜏 obtained a rms error of 2.25 % for the 14 alpine, f. et al./ jgeet vol 7 no 1/2022 1st line and 2.21% for the 2nd line. last, the 2 d model is shown to be more optimal to delineate the geothermal system in “diana” area because it was able to represent the geology of the area and showed the lateral distribution of the resistivity value. also, it do not show closures caused by gathered values in few points. acknowledgments we would like to thank pusat sumber daya mineral batubara dan panasbumi (psdmbp) for their cooperation in providing the data for this research. also, we would like to thank ms. indriati retno palupi for her discussion throughout the process of this research. references flóvenz, ó.g., spangenberg, e., kulenkampff, j., árnason, k., karlsdóttir, r. dan huenges e., 2005. the role of electrical conduction in geothermal exploration. proceedings world geothermal congress 2005, antalya, turkey. geosystem srl. 2008. a guide to using winglink. milan: geosystem srl. grandis, hendra. 2009. pengantar pemodelan inversi geofisika. hagi, jakarta. hansen, p. c., 1992. analysis of discrete ill – posed problems by means of the l – curve, siam rev, 34, 561 – 580. jones, a., g. 1983. on the equivalence of the “niblett” and “bostick” transformations in the magnetotelluric method. j geophys, 53, 72 – 73. katili, j. a. 1975. volcanism and plate tectonics in the indonesian island arcs. tectonophysics. 26, 165 – 188. kauffman, a. a., dan keller, g., v. 1981. the magnetotelluric sounding method. elsevier scientific publishing company. kholid, m. dan marpaung, h. 2011. survei magnetotellurik daerah panas bumi lili-sepporaki, kabupaten polewali mandar, provinsi sulawesi barat. prosiding hasil kegiatan pusat sumber daya geologi. kristmannsdóttir, h., 1979. alteration of basaltic rocks by hydrothermal activity at 100 300°c. developments in sedimentology, 27, 359 – 367. llera, f., j., sato, m., nakatsuka, k. dan yokoyama, h. 1990. temperature dependence of the electrical resistivity of water saturated rocks. geophysics, 56, 576 – 585. lichoro, c. m. 2015. comparison of 1-d, 2-d and 3-d inversion approaches of interpreting electromagnetic data of silali geothermal area. australia: proceedings world geothermal congress 2015. mwakirani, raymond. 2012. magnetotelluric (mt) data processing. united nations university geothermal training programme. pedersen, j., dan hermance, j., f. 1986. least squares inversion of one – dimensional magnetotelluric data: an assessment of procedures employed by brown university. surveys in geophysics, 8 (2), 187 – 231. peri, v. p., dll. 2014. shallow geophysical evaluation of the transition zone between the guarani and yrenda – toba – tarijeno aquifer systems (argentine gran chaco). revista mexicana de ciencias geologicas, 31 (1), 76 – 92. postendorfer, g. 1975. principles of magnetotelluric and prospecting. geopublication associates, 1 (5). purnomo, 2014. ketahanan energi nasional 2014. jakarta: dewan energi nasional. rodi, w., dan mackie, r., l. 2001. nonlinear conjugate gradients algorithm for 2-d magnetotelluric inversion. geophysics, 66 (1), 174 – 187. rodriguez, o. d., enriquez, o. c., fucugauchi, j. u., dan arzate, j. a. 2001. occam and bostick 1-d inversion of magnetotelluric soundings in the chicxulub impact crater, yucatán, mexico. geofisica internacional, 40 (4), 271 – 283. rogers, stuart. 2005. data processing user guide. canada: phoenix geophysics limited. rogers, stuart. 2010. v5 system 2000 mtu / mtu-a user guide. canada: phoenix geophysics limited. simpson, f. dan bahr, k. 2005. practical magnetotellurics. cambridge: cambridge university press. sofyan, y., ehara, s. dan daud, y. 2009. decades of indonesian geothermal energy growth. j. geotherm, 31(3), 167 – 176. unsworth, martyn. 2009. introduction to electromagnetic exploration methods. geophysics 223, university of alberta. unsworth, martyn. 2016. theory of electromagnetic (em) field propagation in the earth. geophysics 424, university of alberta. ussher, g., harvey, c., johnstone, r. dan anderson e. 2000. understanding the resistivities observed in geothermal systems. proceedings world geothermal congress 2000, 1915 – 1920. vozoff, keeva. 1991. the magnetotelluric method in nabighian, m.n., electromagnetic methods in applied geophysics, tulsa, okla., society of exploration geophysics, 37, pt.b, p.641-711. vozoff, keeva. 1980. electromagnetic methods in applied geophysics. australia: d reidel publishing company, geophysical surveys 4, 9 – 29. ward, s., h. dan hohmann, g., w. 1988. electromagnetic theory for geophysical applications. m. n. nabighian, ed., electromagnetic methods, theory and practice, society of exploration geophysicist, 1, 131 – 311. woldesemayet, b. 2013. processing and 1d inversion of magnetotelluric data from dubti area in tendaho geothermal field, ethiopia. united nations university geothermal training programme, 933 – 955. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 278 al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 geoelectricity data analysis for identification the aquifer configuration in bandorasawetan, cilimus, kuningan, west java province m. kurniawan alfadli 1, * and nanda natasia 1 1 faculty of geological engineering, padjadjaran university, jalan raya bandung sumedang km. 21, jatinangor, west java * corresponding author : m.kurniawan@unpad.ac.id tel.:+62-856-6929-8592; received: oct 19, 2017. revised : nov 15, 2017, accepted: nov 30, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.779 abstract indonesian water consumption is influenced by the people growth. one of water consumption fulfilment by groundwater aquifer. bandorasawetan is one of the areas which predicted have proper potential due to located in east of mt. ceremai that predicted recharge area. based on regional geological data, bandorasawetan is an undifferentiated young volcanic product which consists of lava, breccia, lapilli, and tuffaceous sand. geophysics method for groundwater prediction is 2-d geoelectrical with wenner schlumberger configuration. the result of acquisition is obtained resistivity value from 0 >1000 ohm. m. interpretation from data distribution is consist of two resistivity range that describes lithology on the research area, such as: 0 150 ohm.m contributed as aquiqlud with tuffaceous sand lithology and > 150 ohm.m interpreted as volcanic breccia lithology. volcanic breccia has a role as aquifer in study area, the conclusion is distribution of resistivity value with range > 150 ohm.m be the reference to developing groundwater resource in study area. depth of aquifer is varying, deeper to the east. in line 1, depth of the aquifer is 48 meters and in line 2, depth of aquifer be 60 meters. keywords: mt. ceremai, bandorasawetan, geoelectric, groundwater, aquifer. 1. introduction naturally, availability of water depends on water capacity in the groundwater basin. in rainy season, surface water as one of the water supplier came from runoff and groundwater. but in dry season, the water supplier only came from groundwater system. therefore, to fulfil water availability in dry season is affected by groundwater resource. groundwater form in monthly until thousand years, depends on rain and geological condition with complexity situation limited by hydrogeological boundary, hydrogeological event such as recharge, flowing, and discharge has an aquifer integration system that influences groundwater availability, with the result that groundwater is an importance and strategical resource. in order to preserve the groundwater resource continuously in unbalance system between the supplier and necessity, groundwater system must be organizing depend on social environmental, economic functions in harmonious and synergy integration. bandorasawetan has indication of groundwater potential, therefore need some investigation to ensure the fact, so the potential uses for public welfare. resistivity method or geoelectric used electrical property of materials in subsurface for obtaining anomaly and electrical subsurface distribution. this method effectively for shallow and intermediate mapping. 2. research area as geomorphology aspect, research area is located at the volcanic hill with rather steep area, it concluded from topography map, it describes that elevation of research area is at 475 575 meters (fig. 2). for the slope of fig. 3, maximum slope in research area is 15 degrees. majority is dominated by slope with tilt from 2 to 5 degrees. the classification is divided become three types, namely: 1. decline area (0 2 degrees) 2. rather steep area (2 5 degrees) 3. steepest area (>5 degrees). this varies from morphometry is described by undulation topography in research area. mailto:m.kurniawan@unpad.ac.id al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 279 fig. 1. location of resistivity acquisition fig. 2. mophography of research area fig. 3. morphometry of research area. 280 al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 fig. 4. geology regional map of research area (red box describe location of geoelectric research) 3. geology of research area regionally, research area constitutes east mt. ceremai volcanic deposition. this area including in indonesian geology regional map in cilimus sheet (fig. 4). overlapped map between geology and geoelectric location resulted that the research area located in qyu formation i.e. undifferentiated young volcanic products with lithology namely: breccia, lava, tuffaceous sand, and lapilli. from geological information, needed identification to describe the aquifer system in research area. resulted from geology are tuffaceous sand interpreted as an aquiclude, volcanic breccia has harder layer than tuffaceous sand with high resistivity value. 4. methodology geophysical investigation that used in this study is indirect non-destructive (surface) test electrical resistivity method using schlumberger array (reynold, j.m, 1998 ; santoso,d, 2002). in the wenner-schlumberger method, the depth of the identified layer is determined by the distance of the current electrode, as to obtain the resistivity in varying depths the measurements are made at varying ab spacing by increasing the interval of the current electrode. when the measured potential difference is very small with respect to the very large current electrode distance, the potential electrode spacing may be enlarged. measurements are intended to measure the value of the electrical resistance of the rock, which in a particular type of device the value is read directly, but on other types of equipment reads the current and potential. multiplication of electrical resistance value by geometry factor yields apparent resistivity value (pa). an electrical resistivity survey was made using 2-d method that aims to see the distribution of resistivity values vertically and laterally (telford et al, 1990). 4.1 data processing and interpretation apparent resistivity (ρα) value that occurred in the field measurement gives the average resistivity value through multiple heterogenic layers that have a different resistivity value (loke, 2000; loke 2004). since the apparent resistivity was cames from multiple unique layers, the value can be written in: (1) while the geometrical factor (k) can be written as: (2) al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 281 where (k) is constant, depends on the electrode arrangement used in measurement. by combining with the equation (1) and (2), (ρα) can be written as: (3) while there is no homogeneous medium in earth, the resistivity of the layer will be different. the apparent resistivity can be assumed as an apparent medium that equivalent with layered medium that measured. in an electrical resistivity survey performed in non-homogeneous medium (variable resistivity vertically and horizontally), the apparent resistivity will give a qualitative image of resistivity distribution below the surface. apparent resistivity at layered medium can be described in fig. 6. if measured medium consists of two-layer (𝜌1 and 𝜌2) where 𝜌1> 𝜌2, any current flowing between electrode a and b will give a different image at each layer. in the measurement, those medium is assumed as one single homogeny layer that has single resistivity value (𝜌1). conductance of this apparent medium is equal to sum of each layer conductance. by using specific electrode configuration, value of k can be predicted. potential and current that injected was known, than the apparent resistivity can be calculated. by changing electrode spacing for exploration necessities, the resistance value in different depth can be known. field acquisition value after the apparent resistivity was calculated, is a function of the electrode configuration and their depth of penetration. the longer distance between electrodes, deeper penetration is achieved that measured by current flowed in the electrode (santoso, 2002). the data processing result will produce 2-d geoelectric section with a certain direction with elevation information. these results show the actual distribution of resistivity values that will be correlated with geology and obtained interpretations that describe the subsurface conditions of the study area (fettter,1988; heiken, g. & wohletz, k, 1992). 5. result and interpretation the resistivity section of the modelling results from line-1 through line-4 that have been corrected against topography (fig.s 7 to 10) can be divided into several ranges of resistivity values/resistance types represented by layers of a certain colour. each colour layer can be interpreted as a package of rocks. the overlapped colour can be divided into two rock packs contained in the measurement area (table 1). with the division of the above package can be obtained interpretation results in fig 7 fig. 10. fig. 5. 2d electrical resistivity stacking chart fig. 6. apparent resistivity in layered medium 282 al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 table 1. resistivity ratio of correlation result with geology of research area resistivity description 0 150 ohm.m low resistivity values from the surface to a depth of 170 meters. the rock packet with this resistivity value is estimated as aquiqlud in the form of tufan sand rock. >150 ohm.m this high resistivity value is a harder rock in the measurement area. expected as a breccia and has a varying depth distribution. fig. 7. interpretation result line-1 fig. 8. interpretation result line-2 fig. 9. interpretation result line-3 fig. 10. interpretation result line-4 al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 283 furthermore, the results of data processing and analysis of the distribution of resistivity value can be made in the form of a fence diagram to see the distribution of distribution of rock packets in the research location. based on the fence diagram model (fig.11). the light blue line in the fence diagram above indicates the boundary of the exploration target area and below is the inversion model of 2-d geoelectric data. from this fence, diagram can be seen the direction of the measurement line is two trajectories north-south direction, one trajectory west-east direction and one trajectory southwestnortheast with the distribution of resistivity ranging from 5 ohm.m to more than 908 ohm.m. from fig. 11 it can be seen that the westward direction of the line, distribution of resistivity is increasingly in a deep position according to the topography of the measurement area. while the dimension ins thickening seen by comparing line 1 and line 2 which shows the distribution of high resistivity value that diminishes its dimension to the line 2. the depth position is shown by correlating the three lines, especially on the 2nd track which is very clear showing the value position is increasingly low and is supported by line 2 which shows a deeper position of high resistivity value. in track 1 the position of high resistivity value having a large dimension ranging from 48 meters depth while on the 2nd track the high resistivity position correlated with the track 1 starts at a depth ranging from 60 meters. in addition to the fence diagram analysis, 3d models are also created that illustrate the subsurface conditions of the distribution of resistivity values. the resistivity value is then cut with a 150 ohm.m limit above and suspected as a water-retaining layer (fig. 12 and fig. 13). fig. 11. fence diagram of the geoelectrical survey in bandorasawetan fig. 12. top view of 3d model of resistivity interpreted as aquiver, 284 al fadli, m.k & natasia, n. / jgeet vol 02 no 04/2017 fig. 13. side view of 3d model of resistivity interpreted as aquiver. from the two models presented above, it can be seen that the distribution of the resistivity value interpreted as the axis turns toward the west of the measurement area. seen in fig. 12 which shows the distribution of values> 150 ohm.m originally trending north-south then turn towards southwest. and the lateral distribution can be seen in fig. 13 where the deflection is not only on the surface but also on the bottom surface. at the bottom of the surface, the distribution of values is found deeper in the southern part compared to the north that turns westward. 6 .conclusions the results of geoelectric survey in bandorasawetan village, cilimus district, kuningan district with total four geoelectric measurements can be concluded: 1. based on the resistance value, the existing rock has a resistance value ranging from 5 to> 908 m, with varying thickness, the grouping based on the resistivity value as follows: ρ (.m) description 5 150 low resistivity >150 high resistivity 2. based on regional geological data, the measurement areas enter the depths of the qyu (the unadulterated young volcano) which has several lithologies: breksi, lava, tufan sand, and lapilli from the eruption of mount ceremai 3. from the resistivity value that is divided based on the result of correlation with geology concluded that in the measurement area there are 2 types of rock packets. low resistivity is interpreted as a tufan sand layer that is aquiqlud because it has a smooth material so that the porosity of the rock is smaller 4. the second type of rock package that is high resistivity value that has a more coherent nature and is interpreted as an aquifer breccia in the area of measurement 5. the distribution of the two values varies across each line, both packets being found starting from the surface to the maximum depth of the geoelectric data modelling. 6. from the fence diagram it can be concluded that the thickness of the high resistivity value that is as the aquifer has dimension which progressively smaller towards east and deeper to the east. references fetter, 1988, applied geology, merrill pubs.co. columbus ohio united states of america. heiken, g. & wohletz, k. 1992. volcanology and geothermal energy. university of california press. berkeley, los angeles, oxford. loke, m.h., 2000, electrical imaging surveys for environmental and engineering studies; a practical guide to 2-d and 3-d surveys, www.geoelectrical.com. loke, m.h., 2004, coursenotes: 2-d and 3-d electrical imaging surveys, www.geoelectrical.com. reynold, j.m., 1998, an introduction to applied and environmental geophysics, john wiley and sons inc, new york, p.415. santoso, djoko., 2002., pengantar teknik geofisika., departemen teknik geofisika., fakultas ilmu dan teknologi mineral., institut teknologi bandung. telford, w.m., geldart, l.p., sheriff r.e, 1990, applied geophysics, 2nd edition, cambridge university press, p.522. 1. introduction 2. research area 3. geology of research area 4. methodology 4.1 data processing and interpretation 5. result and interpretation 6 .conclusions references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 arifianto, et al./ jgeet vol 5 no 4/2020 175 research article analysis of the surface subsidence of porong and surrounding area, east java, indonesia based on interferometric satellite aperture radar (insar) data indra arifianto1, rahmat c. wibowo2* 1 department geological engineering, universitas gadjah mada, yogyakarta, indonesia. 2 department geophysical engineering, universitas lampung, bandar lampung, indonesia. * corresponding author: rahmat.caturwibowo@eng.unila.ac.id tel.: +6281 327 507 517 received: jun 17, 2016; accepted: sept 21, 2020. doi: 10.25299/jgeet.2020.5.4.5149 abstract since 2006, the mud volcano erupted in the porong area due to wellbore failure triggered by an earthquake (2006) epicenter in the jogjakarta area. the mud volcano buried several villages with mud and continued erupted until today. based on the insar data, it can be seen that the subsidence is still happening near the dam area and another area that is not related to mud volcano eruption such as the production of two gas fields in the porong area. moreover, the porong area is flat and low, less than 4 meters above sea level. the analysis shows that the subsidence rate in this area is up to 0.5 m/yr. if this subsidence is continuing, the city can be sinking and flooding during the rainy season. the prediction result from this method is about 10 years more and 36 years since in 2006 based on the mudflow rate method. keywords: surface subsidence, insar, porong, east java 1. introduction the study area is located in the working area of one of the oil companies in indonesia, namely lapindo brantas ltd. the brantas production sharing contract (psc) has a concession area of approximately 7,250 km2, which consists of three oil and gas fields in this area: wunut (wu), carat (ca), and tanggulangin (ta) (see fig. 1). in may 2006, the company drilled an exploration well in this area (banjar panji-1 well) and targeted reservoir in miocene kujung limestone (sawolo et al., 2010). however, during the drilling, the well penetrated a thick formation of under compacted shale of pliocene upper kalibeng formation (from 900 m to 1,871 m). this formation is characterized by a low-velocity interval (figure 1). the borehole was cased down to 1,091 m (pucangan fm.). after the well had penetrated to a total depth of 2,834 m (kujung fm), this time without a protective casing and they stop the operation by putting a cement plug in the steel casing. unfortunately, the jogjakarta earthquake (2006) trigger and reactivated watukosek fault that crosses the well location, which makes the mud is flowing from overpressure formation to surface through the existing fault, where the first eruption is about 200 m southwest of the banjar panji-1 well. since it started to erupt on the 29th of may 2006, the remaining lifespan of the lusi eruption is still questionable. however, it is in stable condition recently, and yet, no signs that the mudflow will stop to flow. where initially, the mud eruption up to 180,000 m3/day with the subsidence rate is up to 5 cm/day in the central vent (abidin et al., 2008 and istadi et al., 2009). the mud covers area about 7 km2, and the subsidence area may cover up to 100 km2 (davies et al., 2011). in the mid of 2011, the mud is remaining to expulse with a discharge rate of 10,000 m3/day, although it was decreased significantly from previous years when mud is flow at 100,000 m3/day, it was expected that the mudflow would continue for next 25 to 30 years. this eruption has a devastating effect on the porong district of eastern java; the flow of mud and ground surface deformation has caused significant physical, environmental, economic, and social damage to the local and regional communities. although the clay is continuing erupting, the area is also growing as a satellite city of surabaya and sidoarjo since this area is a very strategic location for business and located in the main transportation route in the east java area. since this area is experiencing deformation on the surface due to subsurface material eruption, we can use the interferometric sattelite aperture radar (insar) methodology to study the deformation rate through time in this area. by doing time series analysis, we also can predict when the mud volcano will stop to erupt since we know that the mud eruption decreased exponentially through time and very closely related to the subsidence rate as the side effect of the mud eruption. this result of this research will also be compared to an investigation of studying the probabilities calculation of the longevity mud eruption based on the geotechnical aspect by davies et al. (2011). 2. geology the basement configuration has a ne–sw structural orientationand comprises a series of well-defined basement ridges withintervening grabens serving as depocenters, which contain tertiary sediments. clastic sediment deposition and carbonate buildup ofthe ngimbang formation took place during the eocene and early oligocene. the late oligocene and miocene sequence is separated from the underlying sequence by an unconformity that served asthe foundation of ene– wsw oriented carbonate trends. this platform development, which is known as the kujung limestone,occurred in the late oligocene while the prupuh and tuban reefaldevelopment took http://journal.uir.ac.id/index.php/jgeet 176 arifianto, et al./ jgeet vol 5 no 4/2020 place in the early to middle miocene. the latestand most pronounced period of compressional tectonism began inthe late miocene time and continued episodically into the pleistocene. the resulting transpressional regime caused the left-lateralmovement that runs east-west which resulted in an east-westorientation of the anticline structures (istadi et al., 2009). subsequent pliocene and pleistocene sedimentation consistedof an eastward-prograding mudstone dominated volcaniclastic wedge of kalibeng and pucangan formation, with a thickness of 2400–3000m. the volcaniclastic materials are derived from thejava volcanic arc south of the sidoarjo area. themudstone of thekalibeng formation is over-pressured in most parts of the basinwhere the rapid pressure transition occurs. the high sedimentationrate, rapid deposition and burial of thick shale in the depocenters that occurred during pliocene and pleistocene haveresulted inzones of under-compacted shales (willumsen and schiller, 1994;schiller et al., 1994). this highly plastic zone is over-pressured dueto the presence of excessive trapped water and maturing organic-rich materials. the many mud volcanoes found in east and centraljava correlate with this thick and rapidly deposited claybearingkalibeng formation sediments. the active tectonics coupled with over-pressured maturingorganic-rich sediments makes east java an ideal setting for mudvolcanism. the existence of the ne–sw trending watukosek faultsystem in the lusi area provides the necessary conduit for mud,fluid and gases extruding from a deep horizon to flow up to thesurface to form the lusi mud volcano (istadi et al., 2009). fig.1. the study area is 10 x 10 km located in the south of sidoarjo city (left) and the ne-sw seismic line show subsurface formation and the mud volcano source (right) (istadi et al., 2009) 3. methods 3.1 data source in this paper, we used 27 sar images from ascending data, acquired by the sentinel-1 satellite between january 2019 and april 2020. the spatial and temporal baseline ranged from 15 to 250 m and 12 days to 48 days, respectively. gamma software was applied to perform the interferometric process, and included the following steps: master image selection, topographicphase removal, and interferogram generation. in the study, we employed the sbastechnology to acquire land subsidence information. the topographic phase was removed by using the 90 m resolution shuttle radar topography mission (srtm) dem data from the united states geological survey (usgs). the spatial adaptive filter and temporal filter were applied to separate the atmospheric phase, noise phase, and nonlinear deformation phase. then, two-dimensional spatial high-pass filtering was used to remove the orbital linear ramp and other longwavelength noise from the differential interferograms. a total of 27 interferogram pairs were built with spatial and temporal baselines smaller than 250 m and 24 days, respectively (fig. 2). 3.2 sb technique in sb methods (see, e.g. berardino et al., 2002; schmidt et al., 2003), a network of inter ferogram pairs is created with small temporal and geometrical baselines to limit decorrelation noise. noise is further reduced by applying range and azimuth filters (just et al., 1994) and spatial multi-looking. however, filtering reduces spatial resolution, which can fail to detect some stable isolated pixels. we use the full-resolution sb method of hooper (2008), in which pixels are identified among the candidate pixels, based on phase analysis. for sb processing, we form interferograms with an estimated mean coherence above a threshold of 0.5. we also add additional connections to ensure that there are no isolated clusters of images (see fig.2), creating a total of 27 interferograms. fig.2. a network of interferogram pairs obtained from sentinel-1 used in small baseline subset(sbas) insar, circles represent images and lines represent the interferograms formed. insar network build set the spatial 250m and temporal baselines 24 days 4. results and discussion 4.1 results the first image processing result is the interferogram sar image. this image clearly shows the effect of surface condition on the coherence and decorrelation. from satellite image, city or village have good coherence in the insar phase image, while vegetation or plantation area show scattered temporal decorrelation. this scattered could happen due to the randomness of the phase by the signal reflection of the trees. the interferometric sar image generates the deformation phase, noise phase, and the atmospheric signal. later on, this atmospheric signal will be reduced and neglected for small scale area or deformation. furthermore, some decorrelation and speckle noise can be removed by applying some filtering parameters. since we have several temporal decorrelations in our area, we can use adaptive filtering to reduce the noise on arifianto, et al./ jgeet vol 5 no 4/2020 177 our data without changing the pixel size. to do the adaptive filter is to adapt the local slope before averaging the value. in gamma, the adaptive program filter is used for complex-valued images, such as interferograms. this operation helps to reduce decorrelation noise and improves the appearance of the insar phase and helps in the unwrapping phase. for the incoherent area, we can apply masking in the software to remove lousy phase data. in this study area, bad coherence area exists inside the lusi dam, where the study target area. therefore, we don't use the masking image to analyze displacement near the vent of the mud volcano. image result from the processing that we use for analysis is mainly an unwrapping image because we will investigate the displacement in a metric unit in los (line of sight) view. in this study, we use geocode, los, filtered unwrapping image to do time series analysis. first of all, we need to export the image data to .tiff in order can be analyzed in matlab or other software. in this case, we analyze the image of the gis software. the gis software allows us to load the other geographic data from online, make a section, and easier to add a feature such as the border of the study area, dam location, georeferenced image from publications. moreover, the gis software has a simple mathematical calculator that can be used for image stacking and time series analysis. before calculating the time series analysis, we need to do calibration of the input of tiff data (geo_disp_los_m_filt.tiff). as we know, there is several insar image that has noise from the atmospheric signal, which make the undeformed area in the study area as if experiencing deformation but in the same rate (from 0.01m-0.04 m) as we can see in the following fig.3. after checking all data, we pull up or pull down the undeformed reference point to zero levels of deformation. the next step is time series analysis. the time series analysis itself helps us to track deformations trough time in our study area. furthermore, we can make a prediction of the mud eruption in our study area based on the exponential of subsidence. the processed atmospheric signal data above is then processed by computing or by applying time-series linear equation d = gm. 𝑑 = 𝐺𝑚 ->[ 0 𝜑1(𝑃) 𝜑2(𝑃) ] = [ 1 0 0 1 −1 0 0 1 −1 ] [ ∅1(𝑃) ∅2(𝑃) ∅3(𝑃) ] (1) where d is data vector of insar unwrapped phase data (geo_disp_los_m_filt), m is the deformation of each sar image in a particular time (mt0, mt1,mt2, mt3,….mtn), and g is the interferogram baseline network model (in which every subset is connected to). we assumed that mt0 is zero deformation. in this project, we doing time series in thirteen data set with the temporal baseline is 24 days, where we only choose a data set that has a continued timeline (fig.4). thus, it will be easier to create time series because we only need to add the insar deformation data of m(t0)+d(t1) to get mt1, add m(t1)+d(t2) to get mt2, etc. see the time series in the (fig. 4). in this study area, the identified deformation value is negative corresponding to subsidence since the direction azimuth is descending from north to south, and the line of sight (range) is to the east. while calculating the subsidence rate, we just divide the subsidence (in meter) with the period (in day or year) of the two-deformation time or from the slop of the plot between subsidence and time. fig.3. interferometric sar image after applying adaptive filter 0.5 (study area in the black box) and reducing the effect of the atmosphere in geo_disp_los_m_filt.tiff (red dot is the reference point) fig.4. selected interferogram 4.2 discussion as mentioned in the introduction that this area is part of the concession area of one oil company (lapindo brantas ltd). 178 arifianto, et al./ jgeet vol 5 no 4/2020 lapindo brantas has four oil fields in this block area, namely; tanggulangin, wunut, carat, and watu dakon oil field. two of them are located near the lusi eruption center. they are tanggulangin in the east of the study area and the wunut field in the west of the study area (see fig. 1). based on the time series insar image, we can see several deformations in the area. the deformation in this area corresponds to the lusi eruption center, and both of the gas field (fig.5). as we can see the significant deformation is still happening in the northeast and the west of the levee area until now, where the deformation also happened in the past in the north east levee wall and the west region in the railroad (istadi et al. 2012). therefore, the government or operator should pay attention to this area highly deformed area to prevent dam failure. from the time series map, we choose and plot three points reference in time series graph to know the subsidence rate in those three depocenters. the first point is corresponding to the lusi, the second point, which is located in the east of the study area is corresponding to the tanggulangin gas field, and the third point is located in the west of study area corresponding to wunut gas field (fig.6). this subsidence rate also becomes necessary in this area because this area is a flat and low elevation area; therefore, a significant subsidence rate within a year can lead to sinking and flooding when entering the rainy season. fig.5. average subsidence velocity in the study area, in the middle of the study area corresponding to lusi, in the northeast area is the tanggulangin gas field and in the west area is the wunut gas field. fig.6. time series analysis with temporal baseline maximum of 24 days from the graph, we can see that there is a change in the subsidence rate or displacement velocity of each point (fig.7). the subsidence rate change in the gas field must be caused by the increase of gas production in the gas field. as reported by the online media, that lapindo brantas will increase twice their production by the end of this year. that is mentioned in the news that the production of the gas field in 2018 to 2019 is around 1.1 million m3 gas/day, and they will increase the production twice to 2.2 million m3 gas/day total from two gas fields. this gas production account for the significant subsidence of the tanggulangin area and the wunut area from 0.22 m/yr to 0.6 m/yr and from 0.15 m/yr to 0.3 m/yr, respectively. from the graph, we also can see that the production increase in the tanggulangin area starts around early october, while in wunut area begins at the end of december 2019 (fig. 7). arifianto, et al./ jgeet vol 5 no 4/2020 179 inside the lusi area, the subsidence rate is decreased nonlinearly through time, which is agree with davies et al., (2011) flow rate model. davies et al. (2011) suggest that the flowrate of the lusi will decrease to less than 100 liters/day in a minimum of 26 days (fig.8). the other estimation research is by istadi et al. (2009) predict that the source of mud will be depleted in 23-35 days. however, according to davies, this analysis is flawed because the eruption will continue after the mud source depleted, and they use a constant eruption rate rather than reducing through time. then in this study, we plot the subsidence rate from our research with the initial subsidence rate acquired from abidin et al. (2008). abidin analyzes the data taken from a gps database that has an initial subsidence rate is ranging from 14 meters/year to 6.5 meters/year (exponentially decrease) near the vent center of mud volcano from may 2006 to early 2017 (figure 8). this research is also supported by deguchi et al. (2007), which show the same result from insar data, where from october to november 2006, the maximum subsidence rate was 12.4 meters/year and from november 2006 to january 2007 was 7.3 meters/year (fig.8). however there also a publication from shirzae et al. (2015) suggest that average deformation velocity from insar data during early eruption phase (20062007) is only 80 cm/year while during while the average deformation velocity in the lusi and wunut during 2006 to early 2011 is about 5 cm/year to 8cm/year, respectively. this research from shirzae et al. (2015) and one of the results from deguchi et al. (2007) shows meager subsidence rate in the early time of the eruption. this mistake is because they use a longer temporal baseline that will result in the phase unwrapping problem due to a very high deformation rate in a small area. finally, from the plot of the subsidence rate in the logarithmic scale from a few works of literature mentioned above, we can predict when is the subsidence rate decrease, which is linear with the volume of mud erupted, or flow rate of eruption is not significant anymore. in this case, we determine the subsidence rate is less than 1 cm per year is achieved in 2036 or after 30 years since the first eruption day. the result of this project is still linear with the other method of prediction of the longevity of mud eruption. fig.7. time series of surface subsidence in three reference point (ta = tanggulangin; wu = wunut) fig.8. mud eruption longevity prediction from davies et al., 2011 (left) and from this research (right) 5. conclusion in this study, we were successfully processing and applied insar to detect and calculate deformation (time series) within the study area in porong, sidoarjo. during 2019-2020, the subsidence rate in the porong area due to the mud volcanoes is exponentially decreasing in one year from 0.9 m/yr – 0.3 m/yr. due to field production, the porong area is experiencing more than twice the increase of subsidence rate from 0.22 m/yr to 0.6 m/yr in the tanggulangin area and twice subsidence rate in the wunut area (0.15 m/yr – 0.3 m/yr). this study and the previous study from davies et al. (2011) suggest that lusi will stop to erupt the mud in 2036 (after 30 years) from the subsidence rate and mud discharge rate, respectively. acknowledgements the research was supported by the erse 3900 insar course project. the authors thank the king abdullah universityof science and technology for facilities support. references abidin h.z., kusuma m.a., andreas h., gamal m., and sumintadireja p., 2008. gps-based monitoring of surface displacements in the mud volcano area, sidoarjo, east java. observing our changing earth: 180 arifianto, et al./ jgeet vol 5 no 4/2020 proceedings of the 2007 iag general assembly, perugia, italy, july 2 13, 2007. berardino, p., g. fornaro, r. lanari, and e. sansosti., 2002. “a new algorithm for surfacedeformation monitoring based on small baseline differentialsar interferograms.” ieeetransactions on geoscience and remote sensing 40 (11): 2375–2383. davies., r.j., mathias s.a., swarbrick r.e., and tingay m.j., 2011. probabilistic longevity estimates for the lusi mud volcano, east java. journal of the geological society, london, vol. 168, 2011, pp. 517–523. doi: 10.1144/0016-76492010-129. deguchi, t., y. maruyama, and c. kobayashi., 2007. monitoring of deformation caused by the development of oil and gas field using palsar and aster data, powerpoint presentation file, 14 january, ersdac (earth remote sensing data analysis center), japan. istadi b.p., pramono g.h., sumintadireja p., and alam s., 2009. modeling study of growth and potential geohazard for lusi mud volcano: east java, indonesia. marine and petroleum geology 26 (2009) 1724-1739. istadi b.p., wibowo h.t., sunardi e., hadi s., and sawolo n., 2012. mud volcano and its evolution. earth science book chapter, intech open, doi:10.5772/24944 just, d., and r. bamler. 1994. “phase statistics of interferograms with applications to syntheticaperture radar.” applied optics 33 (20): 4361–4368. sawolo n., sutriono e., istadi b.p., darmoyo a.b., 2010. was lusi caused by drilling? – authors reply to discussion. marine and petroleum geology 27 (2010), 1658-1575. schiller, d.m., seubert, b.w., musliki, s., abdullah, m., 1994. the reservoirpotential of globigerinid sands in indonesia. in: proceedings of the 23rdannual convention, proceedings of the indonesian petroleum association,vol. 1, p. 189ff. schmidt, d. a., and r. burgmann. 2003. “time-dependent land uplift and subsidence in thesanta clara valley, california, from a large interferometric synthetic aperture radar data set.”journal of geophysical research 108 (b9): 2416–2428. shirzae m., rudolph m.l., and manga m., 2015. deep and shallow sources for the lusi mud eruption revealed by surface deformation. geophys. res. lett., 42, 5274– 5281, doi:10.1002/2015gl064576. willumsen, p. and schiller, d.m., 1994. high quality volcaniclastic sandstone reservoirsin east java, indonesia. in: 23rd annual convention, vol. i. ipa, pp. 101–111. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 5 no 4 2020 kuswandi, et al./ jgeet vol 5 no 4/2020 191 research article disaster mitigation for palu city residents in dealing with liquefaction disasters in accordance of spatial patterns of palu city, central sulawesi province, indonesia. yudi kuswandi1, jossi erwindi2, moh. sapari dwi hadian2, dicky muslim2 1study programs of regional innovation postgraduate school, padjadjaran university, indonesia. 2research center for environment, engineering and geological disaster, padjadjaran university, indonesia. * corresponding author : bob.debuilders76@gmail.com tel.:+62-821-2150-4138 received: oct 1, 2020; accepted: dec 08, 2020. doi 10.25299/jgeet.2020.5.4.5653 abstract potential natural hazards in palu city by paying attention to the real physical characteristics of palu city are categorized as having a high level of disaster hazard. the geological character of both the geological structure and geological engineering in the palu region shows the great potential for geological disaster hazards. on september 28, 2018, at 18: 02 cit, an earthquake measuring 7.4 on the richter scale, the quake's center located in 26 km of donggala district and 80 km northwest of palu city. by observing the epicenter's location and the depth of the hypocentral earthquake, it appears that this shallow earthquake occurred due to activity in the palu koro fault zone. this fault is the most active in sulawesi and is the most active in indonesia with a movement of 7 cm per year. liquidity disasters or ground liquefaction are also the effects of an earthquake. shocks a massive quake causes the soil to melt this thing occurs when the saturated soil loses strength and stiffness due to stress. the petobo area and the balaroa perumnas are close to the palu koro active fault line and the land in the area is composed of soft material from the sedimentation process. this area is shallow groundwater with high soil permeability values, namely in the petobo area and perumnas balaroa. the purpose of this study is to analyze the potential liquefaction disaster in palu city and analyze the palu city resident ability against liquefaction hazard prone. this research uses a descriptive qualitative analysis method. potential liquefaction disasters were analyzing qualitatively based on geological conditions and disaster locations. disaster mitigation capabilities were analyzed qualitatively based on the palu city spatial pattern. one of the hazards caused by an earthquake that has the potential to be a disaster in palu city is liquefaction. the ability of residents to mitigate liquefaction in palu city is influenced by local wisdom which is reflected in ancient times when people lived in the highlands or hills. the concept of building structures, land use, and spatial planning patterns in palu city which can reduce the threat of liquefaction. keywords: disaster, geology, liquefaction, spatial pattern, mitigation. 1. introduction 1.1 sub introduction palu city area is part of sulawesi island which becomes gather area of the three plates are indo-aussie, eurasia, and the philippines that condition makes it very vulnerable to tectonic earthquakes. the indo-aussie plate moves to the north around 50-70 mm/year and knocking down under the inner sumaterajava sea trough until western timor island in nusa tenggara timur bock., in (pakpahan et al., 2015). at the same time, the pacific plate crashed into the north side of irian island and the islands north of maluku at a speed of 120 mm/year, it is twice faster than in the western and southern indonesian area bock., in (pakpahan et al., 2015) which causes the formation of active faults to include the palu-koro fault, the matano fault connected to the sliding fault line, the mendoke fault, and the lewanopo fault. the city of palu has a high-level disaster risk because bypassed the active fault palu koro, palu city is one of the cities with a high level of disaster hazard compared to other regions, because it is passed by an active palu koro fault, so it is prone to earthquakes and other associated disasters such as ground movements, tsunamis, and liquefaction. (bnpb, 2013) the regional geology of palu and the surrounding area are dominated by the quarter consisting of fluviatile and alluvium deposits. this natural condition has several bad potentials include liquefaction potential. based on the geological map review sheet palu, sulawesi scale 1: 250,000 rabsukamto, et al, in (widyaningrum, 2012) the investigation area consists of 2 (two) formations rocks, namely alluvium and coastal deposits (qap) and molasa celebes serasin and serasin (qtms) as shown in figure 1. base on the result of technical geological analysis, the city of palu is divided into two technical geology units, namely the alluvium and the coastal sedimentation units (qap) and the molasa celebes sarasin and seracin unit (qtms). the area formed by alluvium deposits can be explained as the soil layer generally consists of sand in the upper part, silt in the middle, and clay in the lower part. (marjiyono et al., 2013) palu city spatial plan 2010-2030 regulated in palu city regional regulation no. 16 of 2011 is one of the operational guidelines for development in palu city. as one of the guidelines in development, especially the physical development of urban space in palu city, the neighbourhood association http://journal.uir.ac.id/index.php/jgeet mailto:bob.debuilders76@gmail.com 192 kuswandi, et al./ jgeet vol 5 no 4/2020 (rtrw) of palu city must be able to become a tool of operation for directing and control the dynamic of physical development. the issue of global climate change is also felt in palu city and characterized by an earthquake and causes various problems and disruptions to the city's system of activities, such as problems related to global climate disasters (floods, droughts, and other disasters) and disasters resulting from the earthquake, namely liquefaction (pemerintah daerah, 2010). the ancestors of the palu community have recorded liquefaction events in local terms, which indicates that they have recognized them for a long time. the liquefaction is called ‘nalodo’ which means sucked up by the mud. nalodo (liquefaction) is one of the disasters causing damage to infrastructure include the people's houses that’s why knowledge about a disaster is important especially for disaster mitigation for further cases. (balitbang pupr, 2018) this paper aims to analyze the potential for liquefaction disasters in palu city and analyzing the disaster mitigation capacity of the peoples against liquefaction prone disasters in palu city, southeast sulawesi province. fig 1. geological map of palu and surrounding area fig 2. flow chart methods 2. methods the methodology in this study uses a qualitative descriptive analysis method. this research is needed to raise and geological map palu area and its surroundings central sulawesi province n road river interval contour lines 100 m information 1. geology 2. topography source : rab. sukamto, 1973 palu strait location of the investigation area mutiara airport geological map palu area and its surroundings central sulawesi province n road river interval contour lines 100 m information 1. geology 2. topography source : rab. sukamto, 1973 palu strait location of the investigation area mutiara airport geological map palu area and its surroundings central sulawesi province n road river interval contour lines 100 m information 1. geology 2. topography source : rab. sukamto, 1973 palu strait location of the investigation area mutiara airport alluvium and coastal sediments gravel, sand, mud and coral limestone (qap) molluscs celebes sarasin and sarasin conglomerate, sandstone, mudstone, coral limestone and marl, some weakly hardened (qtms) geological map palu area and its surroundings central sulawesi province n road river interval contour lines 100 m information 1. geology 2. topography source : rab. sukamto, 1973 palu strait location of the investigation area mutiara airport preparation preliminary studies formulation of the problem and research objectives primary data : field survey field conditions soil damage observation post-earthquake and liquefaction building data collection secondary data: 1. geomorphological map of palu city 2. regional and population data of palu city 3. palu city geological map research data analysis disaster mitigationgeological structure conclusions and suggestions finish discussion proposal formulation of the problem and research objectives kuswandi, et al./ jgeet vol 5 no 4/2020 193 analyze a problem. the research is then described in an analysis to arrive at conclusions according to the original objectives. this type of qualitative descriptive research is a research method that utilizes qualitative data and describes a descriptive history. this type of qualitative descriptive research is often used to analyze social events, phenomena, or circumstances. this type of qualitative descriptive research is a combination of descriptive and qualitative research. this type of qualitative descriptive research displays the results of the data as they are without any manipulation or other treatment processes (sugiyono, 2012:6). the potential for a liquefaction disaster is analyzed qualitatively based on the geological conditions and the location of the disaster. disaster mitigation capabilities are analyzed qualitatively based on the palu city spatial plan. flow chart methods are shown in figure 2. 3. results and discussion natural disaster-prone is a spatial designation that is part of a protected area that has certain characteristics both on land and in waters that often experience landslides, tidal waves/tsunamis, floods, volcanic eruptions, and earthquakes. the function of determining natural disaster-prone areas is to determine a zone that cannot be used as a development location if the risk of disaster is high enough. 1) serious prevention and response in natural disasters 2) minimizing casualties due to natural disasters 3) performance criteria for spaces prone to natural disasters include: 4) no development, if the risk of disaster is high enough 5) serious implementation of prevention and response in natural disasters. 6) minimizing the number of casualties due to natural disasters (peraturan_gubernur, 2019). the potential danger of natural disasters in palu city by paying attention to the natural physical characteristics of palu city is categorized as having a high level of disaster hazard. the geological character of both the geological structure and engineering geology in the palu area shows great potential for geological disaster hazards. the character of the slopes and soil types, as well as rainfall, contributed to earthquakes, tsunami, liquefaction, floods, and landslides (wicaksono, 2019). in the palu city area based on the results of the analysis identified the types of disasters that often occur and recur in palu city are: 1) earthquake as an area through which the palu koro active fault passes, palu city is an area that has high earthquake potential. 2) tsunami – the effect from large force earthquake causes wave in the ocean, or due to landslides that occur in the sea. the city of palu often experiences this tsunami, in history recorded the greatest earthquake occurred in 1977 with a tsunami’s height of up to 15 meters. the people of palu city recognize this tsunami phenomenon as standing water. 3) liquefaction – disasters of liquefaction are also the effects of an earthquake. huge earthquake shocks cause the ground to melt. this occurs when saturated soil loses strength and stiffness due to stress. this area located close to the palu koro active fault line, and the land in the area is composed of soft material resulting from sedimentation. this area is shallow-groundwater with high soil permeability value beside in the petobo area, there are many ‘seepages’ or groundwater seepages. 4) flood – palu city is passed by many rivers. the big one is called palu river. 5) landslide – prone to landslides in areas with slope rates> 30%, generally on medium to high altitudes (rakhmawan et al., 2019). the concept of the palu city spatial pattern in terms of the landscape morphology of palu city is divided into 3 area categories, namely lowlands, highlands, and mountains/hills as shown in figure 3. fig 3. concept of spatial pattern based on morphology in palu city the concept of palu city spatial pattern is reviewed based on the morphological characteristics of the palu city landscape, which is divided into three regional categories, namely lowlands, highlands, and mountains/hills. 1) mountainous/hilly area type a 194 kuswandi, et al./ jgeet vol 5 no 4/2020 a. areas with slope rates> 40% with elevations> 2000 meters above sea level. b. directed to protected areas. 2) plateau type b a. areas with slope rates of 20-40% with an altitude of 500-2000 meters above sea level. b. aimed at a buffer zone between a cultivation area and a protected area. 3) lowland type c a. areas with a slope of 0-20% with a height of <500 meters above sea level. b. directed to the area of cultivation (development of the city of palu). liquefaction disaster in the city of palu (pemerintah daerah, 2019a). a qualitative approach to liquefaction potential applies to small scale or rock formations. the results of the qualitative method are a general description of the liquefaction potential. these results can be used as a basis for determining further qualitative investigation in more detail. the phenomenon of liquefaction is the impact of an earthquake in an area composed of loose sand layers with a shallow groundwater level (<9.0 m) and is influenced by the intensity and duration of the earthquake shock and the distance from the epicenter. according toyoud, in pusgen, 2018), soil layers that are prone to liquefaction are in a relatively limited geological area. liquefaction generally occurs in alluvial fan deposits, alluvial plains, beaches, former lakes, and estuaries. the loose layer of fine sand beneath the ground surface in the coastal areas and plains of palu city is very vulnerable to liquefaction. the phenomenon of soil mass flow and soil oscillation movement occurred in several regions. the liquefaction that occurs in the hammer city occurs after an earthquake shaking, which causes the collapse of the land and buildings above it, the ground changes from initially solid and becomes liquid behavior and loses its strength. liquefaction occurs in loose sandy soils and water-saturated medium which experience an increase in excess pore water pressure due to the blocking of the earthquake waves to the soil surface. sand and silty sand are types of soil that are subject to liquefaction (mina et al., 2018). the loose layer of fine sand beneath the ground surface in the coastal areas and plains of palu city is very vulnerable to liquefaction. the phenomenon of soil mass flow and soil oscillation movement occurred in several areas. the location in the palu city of the liquefaction disaster is a depressed area around a large old alluvial sphere, and also the event is followed by an alluvial fan with a relatively smaller size (flood cone) on high topography. the depressed territory is the area of sediment deposits that have the potential to become areas of floodplain and high sedimentation area. (harun mallisa et al., 2009). the mechanism of liquefaction occurs in palu city is shown in figure 4 (bappenas, 2019a). fig 4. the mechanism for liquefaction (nalodo) in palu city. the causes of the liquefaction disaster in palu city are several things, namely: 1) the condition of sandy soils which are not tightly bound (loose) making it possible to melt 2) shallow groundwater-surface <of 5 meters. 3) the tilt gradient corresponding to (≥2º) 4) the condition of a hard rock layer as a hood. a. the triggering factor of the liquefaction disaster in palu city are: 1) the vibration from an earthquake. 2) there is an unusual pore pressure. b. areas that occur liquefaction in the city of palu, namely: 1) in areas around active faults. 2) active fault cliffs form alluvial fans. 3) in the flood sediment area at the end of the alluvial fan. 4) in the large alluvial fan boundary area.(bappenas, 2019b). liquefaction is a unique phenomenon that soil material behaves more like a liquid than a solid so that it completely loses its durability sni 8460: 2017 (badan standarisasi nasional, 2018). the liquefaction disaster criteria, according to sni 8460: 2017 concerning geotechnical design requirements are generally found when soil material gets cyclic force under the condition of being compressed (undrained) such as an earthquake. during rapid undrained cyclic loading, pore pressures cannot easily escape. as a result, the effective stress decreases to zero, where there is almost no contact between each particle. because the old alluvial fan new alluvial fan new alluvial fan new alluvial fan old alluvial fan old alluvial fan crac k zon e palu rive rs ground level new alluvial fan flood sediment palu rivers sedimentation sedimentation from old alluvial geology (lithology type) groundwater level gravel/coarse sand deep (>10 m) fine sand/ a thin silt layer shallow (distressed aquifer ’confine aquifer’) fine sand/ a thin silt layer shallow shallow sand/ a thin silt layer/ gravel palu riversrice fiedslandslide areanew alluvial fan area source : jica disaster map kuswandi, et al./ jgeet vol 5 no 4/2020 195 condition of rock formation has not yet occurred compaction (liquefication) in palu city is still in process (the age of the rocks is still young), which is dominated by alluvial deposits, so that if a shock occurs (earthquake) will occur when the force causes force instability and results in decreased pore pressure, as a result, there is compaction (janat et al., 2017). liquefaction is a disaster that can damage the condition of infrastructure, so knowledge of the potential and vulnerability of liquefaction is very important, especially in spatial planning in the palu area (bappenas, 2019b). based on the results of a study there are 3 categories of potential liquefaction hazards in palu city (widyaningrum, 2012) is shown in figure 5. fig 5. the liquefaction danger zone of palu city. on september 28, 2018, a liquefaction disaster occurred, especially in petobo and balaroa sub-districts,where buildings and roads were severely affected. the liquefaction-prone zone plan (krb) is divided into four classification zones: 1. disaster-prone zone 1 covering an area of 3,391.27 hectares spread across all districts. 2. disaster-prone zone 2 covering an area of 1,732.69 hectares and unaffected sub-districts are north palu district and tawaeli district. 3. disaster-prone zone 3 covering 671.50 hectares with the same distribution as liquefaction-prone zone 2. 4. disaster-prone zone 4 covering an area of 205.75 hectares spread across the districts of west palu, ulujadi, tatanga, and south palu (bpbd, 2018). palu city disaster-prone zone mapis shown in figure 6. fig 6. palu city disaster prone zone map liquefaction hazard zone map palu and surrounding area central sulawesi province n zoning the hazard area very high potential high potential very low potential petobo liquefaction location 2018 road river interval contour lines 200 m sondir location topography information palu strait mutiara airport 196 kuswandi, et al./ jgeet vol 5 no 4/2020 the widespread risk of palu city liquefaction disaster is shown in table 1. table 1. widespread risk of palu city liquefaction disaster 3. mitigation of liquefaction disaster from liquefaction disaster mitigation analyses conducted based on directions from the palu city spatial pattern and also from the disaster prone areas (krb) it is expected to be a concrete step to be carried out in liquidation disaster mitigation in palu city, namely: 1) all land use and building use must comply with the land use zoning regulations determined by the rtrw and rdtr (bappenas, 2019c). 2) all buildings must follow the indonesian building code and related sni regulations. non-engineered buildings must follow the main requirements or design prototypes described in pupr regulation no. 5/prt/m/2016. additional requirements for building structures are explained here for each type of disaster (kementrian_pupr, 2016). 3) each building unit must be equipped with water wells to release excessive groundwater pressure. the requires a well with a diameter of> 1m and a depth of> 15m (bappenas, 2019b). 4) the building foundation must be a raft foundation (mat slab) with reinforced concrete (rc mat slab structure). mat slab must be a single unit and not separate. even though the foundation uses piles, the building base must still use rc mat slab in anticipation if the piles do not function during the liquidation one building is not allowed to use several types of foundation designs (pemerintah daerah, 2019b). 5) engineered buildings must be designed following sni1726 with additional earthquake priority factors that use the risk class one class above for each building (pemerintah daerah, 2019b). 4. conclusion and suggestion considering the risk of liquefaction due to the earthquake and reconstruction efforts in the palu city area, proper mitigation efforts are very important to reduce the impact of earthquakes in the future. base on the explanation before it can be concluded that the ideas of liquidation disaster mitigation for the community have begun to implement although there is still a lot of work to be done in supporting the safety of the community in the face of liquefaction disasters that occur in palu city. acknowledgments the first thanks go to allah swt for the abundance of grace and pleasure. next to the two mothers who always pray, and my beloved wife and beloved children and dr. mohamad sapari dwi hadian, s.t., m.t. and dr. ir. dicky muslim, m.sc., as the supervisor who has given direction and input in this study. references badan standarisasi nasional, 2018. sni 8460-2017 persyaratan perancangan geoteknik. balitbang_pupr, 2018. kajian gempa palu provinsi sulawesi tengah 28 september 2018 (m7.4), pusat litbang perumahan dan pemukiman, balitbang pupr pusat. bappenas, 2019a. proyek pengembangan rencana ketahanan risiko bencana regional di sulawesi tengah. palu. bappenas, 2019b. proyek pengembangan rencana ketahanan risiko bencana regional di sulawesi tengah. bappenas, 2019c. proyek pengembangan rencana ketahanan risiko bencana daerah di sulawesi tengah tentang perencanaan tata ruang berdasarkan pengurangan risiko bencana di sigi. palu. bnpb, 2013. kejadian bencana indonesia awal tahun 2013, majalah gema bnpb. bpbd, 2018. kawasan rawan bencana di kota palu, analisis kebencanaan. harun mallisa, turu’allo, g., mallisa, z., 2009. mikrozonasi seismic dan analisis respon site specific kota palu. smartek 7, 1–9. janat, n.r., wilopo, w., indrawan, i.g.b., 2017. kajian geologi teknik di kawasan pertambangan emas poboya, palu, sulawesi tengah, proceeding, seminar nasional kebumian ke-10 peran ilmu kebumian dalam pembangunan infrastruktur di indonesia. kementrian_pupr, 2016. peraturan menteri pekerjaan umum dan perumahan rakyat republik indonesia nomor 05/prt/m/2016. marjiyono, kusumawardhani, h., soehaimi, a., 2013. struktur geologi bawah permukaan dangkal berdasarkan interpretasi data geolistrik, studi kasus sesar palu koro. j. geol. dan sumberd. miner. 23, 39–46. mina, e., kusuma, r.i., sudirman, s., 2018. analisa potensi likuifaksi berdasarkan data spt (studi kasusproyek pembangunan gedung baru untirta sindang sari ). j. fondasi 7, 11–21. https://doi.org/10.36055/jft.v7i1.3298 pakpahan, s., ngadmanto, d., masturyono, 2015. analisis kegempaan di zona sesar palu koro, sulawesi tengah. lingkung. dan bencana geol. 6, 253–264. pemerintah daerah, 2019a. materi teknis rencana pola ruang. pemerintah daerah, 2019b. lampiran materi teknis revisi rtrw kota palu. palu, pp. 80–92. pemerintah daerah, 2010. peraturan daerah kota palu nomor : 16 tentang wilayah kota palu. districts risk land area (ha) districts. mantikulore low liquifaction risk 595,50 high liquifaction risk 585,26 no information 17.914,30 districts. palu barat no information 523,26 districts palu selatan low liquifaction risk 30,86 high liquifaction risk 1.389,07 no information 513,41 districts palu timur high liquifaction risk 3,33 no information 570,48 districts palu utara no information 2.928,24 districts tatanga low liquifaction risk 1,93 high liquifaction risk 15,02 no information 1.462,00 districts tawaeli no information 5.924,29 districts ulujadi high liquifaction risk 42,75 no information 6.411,04 kuswandi, et al./ jgeet vol 5 no 4/2020 197 peraturan_gubernur, 2019. peraturan gubernur sulawesi tengah nomor 10 tahun 2019 tentang rencana rehabilitasi dan rekontruksi pasca bencana. rakhmawan, m.u., sutaryono, s., setiowati, s., 2019. potensi pengadaan tanah berbasis kebencanaan di kota palu. j. tunas agrar. 2, 1–18. wicaksono, g., 2019. palu vertical settlement, fakultas muhamadiyah surakarta. surakarta. widyaningrum, r., 2012. penyelidikan geologi teknik potensi liquifaksi daerah palu , provinsi sulawesi tengah. kementrian energi dan sumber daya miner. 43. © 2020 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 4 2021 184 putra, u.g. et al./ jgeet vol 6 no 4/2021 research article interpretation of subsurface fault through multi-level second vertical derivative gravitational data in bittuang geothermal working area, south sulawesi, indonesia ullil gunadi putra1*, william jhanesta2,3, iskandarsyah1 1 geophysics study program, department of geosciences, universitas indonesia, depok 16424, indonesia 2 laboratory of geophysical modelling, department of geosciences, universitas indonesia, depok 16424, indonesia 3 energis indonesia, wisma anugerah, depok 16425, indonesia * corresponding author : ullil.gunadi@ui.ac.id tel.:+62-895-6027-23393 received: sept 19, 2021; accepted: dec 24, 2021. doi: 10.25299/jgeet.2021.6.4.7744 abstract the research was conducted in bittuang, tana toraja regency, south sulawesi province, as one of the geothermal prospect areas and targets for the initial stage of the government exploration drilling program for the 2020-2024 period. one aspect of geothermal is the manifestation control structure as a fluid migration path from below the surface. therefore, identification of existing struc tures in the bittuang geothermal area was carried out and confirmed the surface geological structure contained in the bittuang geothermal geological map. in determining the presence of a fault and knowing its characteristics such as the type of fault, the direction of the d ip, and the magnitude of the dip of the fault, the gravity data is processed using the multi-level second vertical derivative (ml-svd) method. to strengthen the interpretation, the results from the ml-svd were matched with the data from the horizontal gradient (hg) method and the geological data of the structure of the study area. from this process, there are 27 faults in the bittuang geothermal area, two of which are indicated as controlling faults for the manifestation of the balla group and the cepeng group. this research is expected to describe faults in the bittuang geothermal area, which can support detailed exploration activities. keywords: gravity, ml-svd, structure, geothermal 1. introduction energy needs in indonesia and the world have increased yearly, while fossil energy is decreasing and is not environmentally friendly, making it an option that new renewable energy (ebt) is needed as an alternative. one of the renewable energy sources that can be utilized which is geothermal energy. geothermal is a source of thermal energy in hot water, water vapor, rocks, and associated minerals and other gases that are genetically inseparable in a geothermal system. this research was conducted in the bittuang area, south sulawesi, with geothermal manifestations in fumaroles, hot springs, alteration of rocks, and dead solfatara fields. the bittuang field is one of the targets for the initial stage of the exploration drilling program carried out by the indonesian government for the 2020-2024 period. in geothermal exploration activities, geophysical methods have a crucial role in determining geothermal aspects, one of which is the gravity method. the gravity method is widely used and applies to detecting subsurface structures associated with geothermal systems (jhanesta and supriyanto, 2021a; nishijima and naritomi, 2017; supriyanto et al., 2017; uwiduhaye et al., 2018). although gravity is not the main geophysical method used in geophysical exploration, previous studies show that structural analysis with gravity data is quite effective. this study aims to detect the presence of subsurface structures as a controller for the emergence of geothermal manifestations with a physical approach. the ml-svd method is used to map the distribution of the structure and estimate the dip value and slope of the fault. finally, this research can know the fault characterization much better so that it is expected to reduce uncertainty in geothermal exploration and increase the probability of success in drilling activities. 2. field review administratively, the bittuang geothermal area is included in tana toraja regency, south sulawesi province. based on the geological map (fig 1), the rock in the bittuang geothermal area has ten rock units, consisting of seven volcanic rock units, one sedimentary rock unit, one intrusive rock unit, and one metamorphosed rock unit. the stratigraphic order from the youngest age to the oldest age is lava of mt karua 3, pyroclastic fall of mt karua, pyroclastic flow of mt karua, lava of mt karua 2, lava of mt karua 1, intrusion of rattebombong, lava of mt ruppu, lava of mt panusuk, sandstone, and metamorphic rocks (indonesian geological agency, 2009). meanwhile, the structures found in the bittuang area are the collapsed structure, normal faults, and several horizontal faults. http://journal.uir.ac.id/index.php/jgeet putra, u.g. et al./ jgeet vol 6 no 4/2021 185 fig 1. geological map of bittuang geothermal working area after indonesian geological agency (2009). (bla = balla groups hot springs, cpg = cepeng groups hot springs, fum = fumarole) fig 2. ternary diagram of bittuang geothermal manifestations after kusnadi and setiawan (2009). it reveals that the balla groups have chloride characteristics, while the cepeng groups are bicarbonate types. collapse structure is a part that has collapsed due to the void in the earth's bowels due to the eruptive activity of mt karua. the normal faults found in the bittuang geothermal area generally have a northeast-southwest, southeastnorthwest direction, and some have an almost south-north direction, namely the tombilangi fault and the balla fault controls the emergence of the balla and cepeng geothermal manifestation. the strike – slip fault in this area has a northeast-southwest direction that cuts rocks and preexisting structures that cause the shift of rocks around the area (indonesian geological agency, 2009). 186 putra, u.g. et al./ jgeet vol 6 no 4/2021 fig 3. residual anomaly gravity map. it reveals low anomaly distribution on the center of research area and high anomaly distribution on the south to north-eastern side. fig 4. (a) horizontal gradient anomaly map and (b) second vertical derivative anomaly map of bittuang geothermal field. according to kusnadi and setiawan (2009), the bittuang geothermal area has two groups of geothermal manifestations based on the location where these manifestations appear. these groups are the balla manifestation group and the cepeng manifestation group. the balla manifestation group has geothermal manifestations in hot springs (bla-1 and bla-2 in fig 1), fumaroles (fum in fig 1), alteration rocks, and inactive or dead solfatara zones. in comparison, the cepeng manifestation group has geothermal manifestations in the form of hot springs (cpg-1 and cpg-2 in fig 1). putra, u.g. et al./ jgeet vol 6 no 4/2021 187 fig 5. ml-svd map of bittuang geothermal field. the spectrum colours represent the various upward continuation levels. red solid lines show the slicing lines of hg and ml-svd. fig 6. hg and ml-svd graphs indicate subsurface structure related to the geothermal system. dash lines represent the hg value, while the solid lines represent the ml-svd value for each slicing lines. balla-1, balla-2, and balla-3 hot springs which are in the balla manifestation group have characteristics such as clear water, sulfur smell, slightly salty taste, and bubbling gas, with temperatures between 48.1℃ to 96.7℃ at air temperature 22.5℃ with a ph of about 8.4 and a discharge of 1 liter/second, and around the hot springs there are 188 putra, u.g. et al./ jgeet vol 6 no 4/2021 deposits of sintered silica, for more details can be seen in table 1. table 1 characteristics of balla-1, balla-2, and balla-3 hot springs after indonesian geological agency (2009). characteristics balla-1 balla-2 balla-3 temperature (℃ ) 96.7 90.5 48.1 air temperature (℃ ) 22.5 21.6 18.8 ph 8.4 7.75 5.4 debit (liter/second) 1 0.5 2 electrical conductivity (µs/cm) 9700 8400 222 sio2 (mg/liter) 179.7 153.04 114.85 na (mg/liter) 1848 15.04 50.80 k (mg/liter) 92.6 68.5 13.61 ca (mg/liter) 5.57 12.08 9.28 mg (mg/liter) 1.5 1 0.07 li (mg/liter) 10.4 7.9 0.04 cl (mg/liter) 2459.71 2144 80.13 so4 (mg/liter) 378.58 331.67 4 hco3 (mg/liter) 223 91.17 49.35 b (mg/liter) 85.18 76.86 0.76 as (mg/liter) 8 331.67 0.1 f (mg/liter) 1 0.5 0.3 al (mg/liter) 0.16 0.1 fe (mg/liter) 0.09 0.07 0.07 co3 (mg/liter) nh4 (mg/liter) ion balance (%) 2.43 0.2 -2.07 meanwhile, the cepeng-1 and cepeng-2 hot springs which are in the cepeng manifestation group have the characteristics such as clear water, sour taste, and no gas bubbles, for more details can be seen in table 2. table 2 characteristics of cepeng-1 and cepeng-2 hot springs after indonesian geological agency (2009). characteristics cepeng-1 cepeng-2 temperature (℃) 37.6 39.8 air temperature (℃) 22.1 20.1 ph 6.28 5.97 debit (liter/second) 1 2 electrical conductivity (µs/cm) 2630 1241 sio2 (mg/liter) 159.86 170.25 na (mg/liter) 210.96 65.68 k (mg/liter) 13.30 4.56 ca (mg/liter) 190.20 119.34 mg (mg/liter) 105.60 45.90 li (mg/liter) 1.20 0.48 cl (mg/liter) 376.40 105.11 so4 (mg/liter) 60.33 4 hco3 (mg/liter) 998.25 592.94 b (mg/liter) 9.21 0.93 as (mg/liter) f (mg/liter) 0.5 0.5 al (mg/liter) fe (mg/liter) 4.73 3.09 co3 (mg/liter) nh4 (mg/liter) ion balance (%) -0.24 -0.58 based on the chemical characteristics and types of hot water using a triangular diagram of cl-so4-hco3 and na-kmg, presented in fig 2 (giggenbach, 1991), balla-1 hot springs, balla-2, and balla-3 are located in the chloride zone. this zone is thought to be related to water originating from the reservoir of the geothermal system. the balla manifestation group is indicated to rule out near the upflow zone due to the presence of fumaroles, high temperature in hot springs, and silica sinter. while the cepeng manifestation group is indicated as an outflow zone because it has a low temperature, neutral water ph, bicarbonate water characteristics, and the dominant influence of surface water in the formation of hot water (kusnadi and setiawan, 2009). furthermore, based on the na-k-mg ternary diagram, balla-1 hot springs and balla-2 hot springs are in the partial equilibrium zone, where this zone indicates that the existing fluid has interacted with the surrounding rock or known as water-rock interaction, thus forming hot water with a high temperature (90-96 ℃). meanwhile, the balla-3 hot spring is in the immature water zone, which indicates that the temperature of the manifestation has a lower temperature, which is between 37-48 ℃. the condition is influenced by the fluid that interacts with the surrounding rocks in a hot state and interacts with meteoric water. 3. methodology this study uses satellite gravity data from the global gravity model plus (ggmplus), which has a resolution accuracy of up to 200 m (hirt et al., 2013). for gravity processing, ggmplus data is extracted using matlab software to obtain the gravity disturbance value. before carrying out advanced geological interpretation, this data needs to be processed further by performing basic gravity data processing, such as free air correction, bouguer correction, and terrain correction to obtain a complete bouguer anomaly (abdel, 2011). the subsurface delineation process is carried out using derivative analysis, namely horizontal gradient (hg) and ml-svd. this method is able to detect geological boundaries with a high-value response, but only on structures that are formed vertically (blakely, 1995). calculations can be done with the following equation: 𝐻𝐺 = √( ∂𝑔 ∂𝑥 ) 2 + ( ∂𝑔 ∂𝑦 ) 2 (1) where ∂𝑔 ∂𝑥 and ∂𝑔 ∂𝑦 are the first derivatives of the gravitational anomaly in the x and y directions, respectively. the high anomalous response in hg does not always indicate a structure related to the geothermal system (jhanesta and supriyanto, 2021a). therefore, other methods and supporting data are needed to strengthen the interpretation. the ml-svd method is a technique that is used to estimate dip and slope faults by applying an svd filter on the results of upward continuation (rosid and naufal, 2019). in this study, the upward continuation process is carried out from 0 m to 2000 m with a continuation interval of 200 m. the dip calculation is done by calculating the arctan value from the linear regression equation gradient between fault location and upward continuation level. at the same time, the slope direction is estimated by analyzing the shifting direction of the zero-svd value (jhanesta and supriyanto, 2021b). 4. results and discussion 4.1. gravity anomaly putra, u.g. et al./ jgeet vol 6 no 4/2021 189 the estimation of the average rock density of the study area using the f-h method, based on the curve generated using this method, the gradient from the line equation is 2.40, which is also the average density value of the study area. based on geological data, the study area is dominated by pyroclastic flows consisting of ash-lapilli-sized tuff. there are also pumice, sticky, and rhyolite-dacitic compositions. the results of the petrographic analysis conducted by the indonesian geological agency; the rock is rhyolite. pyroclastic flows are extrusive igneous rocks. according to schon (2015), the density of extrusive igneous rocks with a rhyolite composition is between 2.15 gr/cc to 2.6 gr/cc. thus, the average density of the study area of 2.40 gr/cc obtained represents the pyroclastic flow with the dominant rhyolite composition in the study area. the gravity anomaly residual map (fig 3) shows the high anomaly in red while the low anomaly is light purple with values ranging from -8.5 mgal to 5.7 mgal. if referring to the geological map of the research area (fig 1), the high anomaly values are in pleistocene rhyolite rock, which is a pyroclastic flow unit of mt karua, some lava with a dacite composition of pleistocene age which is a lava unit of mt karua-2, granite rock of pliocene age which is a rattebombong intrusion unit, and some parts of miocene sedimentary rock. according to (saibi et al., 2008), the high anomaly value can also be interpreted as an indication of a structure that is higher than its surroundings below the surface. this can be indicated by the presence of se-nw trending structures located in the se and ne of the study area. while the medium to low anomalies found in the middle to the western part of the research area are generally located in miocene andesite rocks which are the lava units of mt panusuk, some are in miocene basalt rocks which are the lava units of mt ruppu, some are in basalt, dacite, and andesite of pleistocene age which is a unit of lava from mt karua 1, 2, and 3. this low anomaly can also be indicated by the alteration process in these rocks and is reinforced by the presence of manifestations in the form of fumaroles and hot springs in areas that have low anomalies. 4.2. horizontal gradient on the hg map (fig 4a), the range of hg values ranges from 0 to 0.0085 mgal/m. the anomalous contrast patterns on the hg map are spread throughout the study area. when referring to the structural geological data, the faults located in sw, ne, se, nw, and the center of the study area shows an anomalous contrast from the hg value with the fault plane at the maximum value of the anomalous contrast. slicing is carried out on the hg map at the location where the fault is thought to be to ensure and display more accurate results. as previously discussed, there are nine slicing paths with the svd map at all upward continuation levels. table 3. fault characteristics based on derivative analysis. fault name dip fault slope direction fault type p01a 64.93º se reverse fault p01b 72.64º nw normal fault p01c 66.70º se normal fault p01d 75.38º nw normal fault p02a 78.07º nw normal fault p02b 56.77º se reverse fault p02c 75.80º nw normal fault p02d 64.00º se normal fault p03a 72.88º nw normal fault p03b 77.24º se reverse fault p03c 75.61º nw normal fault p04a 60.32º sw normal fault p04b 74.54º ne normal fault p04c 70.93º ne normal fault p04d 81.88º sw reverse fault p04e 78.26º ne normal fault p05a 79.23º ne reverse fault p05b 82.50º sw normal fault p05c 82.13º ne normal fault p06a 76.00º sw reverse fault p06b 70.76º ne reverse fault p06c 77.51º nw normal fault p07a 68.38º se reverse fault p07b 85.84º se reverse fault p07c 60.19º sw normal fault p08a 71.05º nw normal fault p09a 77.55º nw normal fault p09b 84.58º nw normal fault 4.3. multi-level second vertical derivative the second vertical derivative (svd) process is carried out on the contours of the gravity anomaly and all contours of the upward continuation of the residual anomaly from a height of 200 m to a height of 2000 m so that 11 svd maps were sliced together with the hg map. from the 0 m, 200 m, and 2000 m svd maps (fig 5), high svd values are indicated by red color, and low svd values are indicated by light purple colors, while svd = 0 is indicated by yellow color (fig 4b). in the svd analysis, the value of svd = 0 indicates the presence of a fault plane and is confirmed by the maximum hg value. besides that, it is also necessary to pay attention to the maximum and minimum svd values of the anomalous 190 putra, u.g. et al./ jgeet vol 6 no 4/2021 contrast to determine the type of fault. nine slicing lines were also performed on the anomalous contrasts estimated as subsurface faults (fig 6). the ml-svd map is shown in fig 5. the red color indicates the shallowest structure, while the blue color represents the deepest. on an upward continuous svd with a height of 200 m, the resulting svd anomaly contour is almost similar to the svd anomaly contour at 0 m, where there is still anomalous contrast indicated as a local fault. meanwhile, at an altitude of 2000 m, the resulting svd anomaly contour is more regional than the 0 m svd anomaly contour. this can be seen in the smoother contours and there are only a few anomalous contrast patterns indicated as continuous faults to a depth of 2000 m (middle and north-eastern part of the study area), unlike those found in the 0 m svd anomaly contour and the svd contour. results of upward continuation at an altitude less than 2000 m. from the svd map at each depth from the upward continuation, the movement of the fault from this shift value svd = 0 of the svd map per depth can be seen. from the movement of the value of svd = 0, the approximate direction and the dip of a fault can be determined. 4.4. fault interpretation based on derivative analysis on nine paths in the bittuang geothermal area, the correlation between the hg curve and the ml-svd curve adapted to the structural geological map of the indonesian geological agency (2009) results in an indication of the subsurface structure in the form of 27 faults (fig 6). of the 27 faults, nine faults are normal faults with a dip towards nw, two normal faults with a dip towards se, three normal faults with a dip towards sw, four normal faults with a dip towards ne. as for the rising fault, five faults with a dip to the se, three faults with a dip to the ne, and one fault with a dip to the sw. normal faults dominate faults in the bittuang geothermal area. the result is under the field survey by the indonesian geological agency (2009), which states that the faults in the bittuang geothermal area are generally normal faults with ne-sw and se-nw fault directions. from the results of this study, there is also a strike – slip fault with a ne-sw direction that cuts rocks and pre-existing structures. these results are also confirmed by the value of the gravitational anomaly, which does not have anomalous contrasts in the horizontal structure, which is probably along the eastern to the north-western part of the central part of the bittuang geothermal area. the gravity method is not suitable for detecting horizontal faults because the gravity method detects the subsurface density contrast on the same horizontal as indicated by the resulting gravitational anomaly contrast value. while the horizontal fault does not have a density contrast in the same horizontal, so the resulting gravity value does not have anomalous contrast. based on the results obtained from processing satellite gravity data in the bittuang geothermal area, overall, it conforms with the geological map of the structure of geological research (indonesian geological agency, 2009). based on the geochemical research, the geothermal manifestations of bittuang are in two different locations. the first location is in the balla manifestation group, while the second is in the cepeng manifestation group. control faults around the location cause the emergence of geothermal manifestations to the surface. for the balla manifestation group, the controlling structure of the manifestation is probably the p07a fault located on line 7. the fault is a normal fault with a dip of 68.38º to the nw direction, which continues to a depth of 1400 m from the surface of the residual anomaly. thus, if later drilling is carried out at a location near the upflow zone, drilling can be carried out in the nw part of the presence of the zone controlling structure (fault p07a). meanwhile, information on dip size and fault depth can consider how far and how deep the drilling point is from the control fault location. as for the cepeng manifestation group, the controlling structure of the manifestation is probably the p09b fault which is on line 9. the fault is a normal fault with a dip of 84.58º to the nw direction, which continues to a depth of 2000 m from the surface of the residual anomaly. thus, if drilling is carried out in a location near the outflow zone, drilling can be carried out in the nw part of the presence of the zone controlling structure (p09b fault). 5. conclusion finally, the ml-svd method can identify and characterize existing faults in the bittuang geothermal prospect area. based on the analysis of 9 lines, there are 27 faults detected from the gravity data of the ggmplus satellite. normal faults dominate faults in the bittuang geothermal area. the average dip of all faults in the study area is 74.77º with nw, ne, se, and sw dip directions. the gravity method cannot identify a transform fault that is characterized by the absence of contrasting gravitational anomalies. the p07a fault located on line 7 is indicated as the controlling fault in the balla manifestation group. the fault is a normal fault with a dip of 68.38º to the nw, which continues to a depth of 1400 m from the surface of the gravity anomaly. meanwhile, the p09b fault on line 9 is indicated as the controlling fault in the cepeng manifestation group. the fault is a normal fault with a dip of 84.58º to the northwest, which continues to a depth of 2000 m from the surface of the residual anomaly. acknowledgments the author would like to thank the indonesian geological agency and energis indonesia for providing the geological and geochemical data and the department of geosciences universitas indonesia for research funding. references abdel, z.m., 2011. geothermal exploration and numerical modeling at gulf of suez, egypt. kyushu university. blakely, r.j., 1995. potential theory in gravity and magnetic applications. cambridge university press, new york. giggenbach, w.f., 1991. chemical techniques in geothermal exploration, application of geochemistry in geothermal reservoir development. unitar/undp cent. small energy resour. rome 11, 119–133. hirt, c., claessens, s., fecher, t., kuhn, m., pail, r., rexer, m., 2013. new ultrahigh-resolution picture of earth’s gravity field. geophys. res. lett. 40, 4279–4283. https://doi.org/10.1002/grl.50838 indonesian geological agency, 2009. integrated investigations of geology, geochemical and geophysics bittuang geothermal region-tana toraja regency south sulawesi. geological agency, memr, putra, u.g. et al./ jgeet vol 6 no 4/2021 191 bandung. jhanesta, w., supriyanto, 2021a. derivative filter of gravity data to detecting the structural control geothermal manifestation, mount endut gwa, indonesia, exploration geophysics. jhanesta, w., supriyanto, 2021b. application of multi-level second vertical derivative (ml-svd) method to identify subsurface structure in mount endut geothermal prospect area, indonesia, in: the 2nd digital indonesia international geothermal convention (diigc) 2021. kusnadi, d., setiawan, d.i., 2009. penyelidikan geokimia daerah panasbumi bittuang kabupaten tana toraja, provinsi sulawesi selatan. geological agency, memr, bandung. nishijima, j., naritomi, k., 2017. interpretation of gravity data to delineate underground structure in the beppu geothermal field, central kyushu, japan. j. hydrol. reg. stud. 11, 84–95. https://doi.org/10.1016/j.ejrh.2015.11.022 rosid, m.s., naufal, m.a., 2019. characterization of geological structure based on multi level second vertical derivative (ml-svd) gravity data, journal of geophysical research. saibi, h., nishijima, j., hirano, t., fujimitsu, y., ehara, s., 2008. relation between structure and lowtemperature geothermal systems in fukuoka city, southwestern japan. earth, planets sp. 60, 821–826. https://doi.org/10.1186/bf03352833 schon, j.h., 2015. physical properties of rocks fundamentals and principles of petrophysics. elsevier. supriyanto, noor, t., suhanto, e., 2017. analysis of gravity data beneath endut geothermal prospect using horizontal gradient and euler deconvolution. aip conf. proc. 1862. https://doi.org/10.1063/1.4991298 uwiduhaye, j. d. a., mizunaga, h., saibi, h., 2018. geophysical investigation using gravity data in kinigi geothermal field, northwest rwanda. j. african earth sci. 139, 184–192. https://doi.org/10.1016/j.jafrearsci.2017.12.016 © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 yuskar y./ jgeet vol 1/2016 59 geo-tourism potential of sand bars and oxbow lake at buluh cina, kampar riau, indonesia yuniarti yuskar 1 ,* 1 geological engineering, universitas islam riau jl. kaharuddin nasution no 113 pekanbaru, 28284, indonesia * corresponding author: yuniarti_yuskar@eng.uir.ac.id tel.:+62-82169254941 received: oct 1, 2016. revised : 15 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.8 abstract buluh cina village is located at siak hulu district, kampar regency, riau province and its about 25 km from pekanbaru city. this village is designated as tourism village by the government of riau province. this research aims to optimize the potential geo-tourism by understanding the strengths and weaknesses aspect which is owned by buluh china village. so it can increase the number of tourists who visit buluh cina village. the method used is the field survey and literature review. the village is surrounded by a tropical rain forest with an area of over 100 hectares and it divided by the kampar kanan river. fluvial meandering system of this river form the main channel (river), sandbars, natural levee, floodplain and oxbow lake. geo-tourism potential that can be developed are sand bars and oxbow lake. buluh china village has had a tourist attraction, but there are still some weaknesses, such as floods in the rainy season and some support facilities are not optimal. keywords: geo-tourism, sand bar, oxbow lake, buluh cina 1. introduction buluh cina village is plain area with an elevation of 2 6 m above sea level. the village is divided by the kampar kanan which is one of the major river in riau province with a length of 413 km. kampar river on the island of sumatra in indonesia originates in the mountainous bukit barisan of west sumatra, and empties into the malacca strait on the island's eastern coast. the landscape of research area is characterized mainly by active channels, abandoned channels, natural leeve, back-swamps and floodplain (yuskar y and choanji t., 2016). this makes the village buluh china as objects geotourism with sediment quarter.these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. fig 1. location of buluh cina village (yuskar y and choanji t., 2016) buluh cina village designated as tourism village by the government of riau province. but seen from the number of tourists who come to the buluh china village is still few in number. the study aims to optimize the tourism potential, especially geotourism is owned by the village. geotourism is tourism activities related to objects and tourist destinations related to geological phenomena (brahmantyo, 2008). buluh cina village consists of 4 hamlet. there are dusun 1, dusun 2, dusun 3 and dusun 4. dusun 1 and 2 are located across the kampar kanan and to achieve it takes about 5 minutes by boat. in this area there was the tourist sites such as oxbow lakes and sand bar. 2. geomorphology and geological setting meanders developed by the erosion of bank closest to the thakweg, accompanied by deposition on the opposite side of the channel where flow is sluggish and the bedload can no longer be carried (page 135 nichols, 2009). kampar kanan river is considered as fluvial meandering system because there are erosion of the outer bank and deposition of bedload on the inner bank the channel. sediment deposit on the inner bank is referred to as a point bar. here distinction between the meandering and river sinuosity along the kampar kanan river is deposited young alluvium (qh) during holocene-aged. young alluvium (qh) are consist of gravels, sands and clays. the stratigraphy formation in the buluh cina mailto:yuniarti_yuskar@eng.uir.ac.id 60 yuskar y./ jgeet vol 1/2016 village are older alluvium (qp) aged pleistocene to holocene. this sediments are consist of gravels, sands, clays, vegetation rafts and peat swamps (m.c.g. clarke, w.kartawa, a.djunuddin, e. suganda dan m.bagdja, 1982). 2. methodology the methodology used in this research is a field survey and literature review. field surveys conducted to obtain the location data that can be used as objects of geo-tourism and pay attention to surrounding circumstances associated with the facilities available to support the geo-tourism. it also conducted a discussion with local people to obtain daily information society and tourism activities which have been implemented. 3. sand bar deposit and oxbow lake 3.1 sand bar deposit the basic dynamics of flow around meanders leads to erosion on the outside parts of bends and deposition on the point bars. (boggs, s.jr. 2006. p.252). sediment of point bar deposited medium sand with good sorting and upwards-fining couplets during flood events (yuniarti and tiggi, 2016). point bar located in kampar kanan river bends forming a broad sand and beautiful landscape that can be an ideal location as a tourist spot. some societies have to capitalize on this location as an interesting tourist attraction to visit but in general, this location still minimal visitors. fig 2. sand in kampar kanan river bends which are sand bars of the fluvial meandering system. fig 3. satellite image that showing geometrical changes the position of the river and image of point bar as result from river migration, and (b). erosion at the nothern side of the river (yuskar and choanji, 2016). 3.2 oxbow lake the abandoned meander loop becomes isolated as an oxbow lake and will remain as an area of standing water until it becomes filled up by deposition from floods and or choked by vegetation. the deposits of an oxbow lake may be recognized in ancient fluvial sediments as channel fill made up of fine grained and sometimes carbonaceous (nichols, 2009). the formation process of oxbow lake can be an interesting story for tourists. thus it is necessary given naming to attract tourists. for example calling it "danau sungai purba". furthermore the local community also have knowledge about unique formation of the lakes in the village. fig 4. depositional architecture of a meandering river; sandstone bodies formed by lateral migration of the river channel remain isolated when the channel avulses or is cut-off form an oxbow lake (nichols, 2009). fig 5. location of oxbow lakes in the buluh cina village (image from google earth 2012). there are 11 oxbow lake in the buluh cina village namely rengas, rawan, lagun, tuok tonga, new lake, tanjung baling, pinang dalam, pinang luar, rayo, tanjung baling and bunte lake. the lakes is located in the tropical rain forest covers 100 ha. oxbow lakes have visited both by tourists and researchers in various scientific fields. yuskar y./ jgeet vol 1/2016 61 fig 6. one of the oxbow lakes in buluh cina village fig 7. tropical rain forests around the oxbow lakes 4. recommendations potential geotourism and aspects of disaster in buluh cina village geo-tourism aspects that can be developed in buluh cina village, namely: a. the presence of the river with the floating ponds and a fish-producing areas with the ecosystem is still maintained. in addition, the river is often used as a location for the people's party like canoe racing. b. sandbars showing a broad of sand and pasture with oil palm trees c. oxbow lake with tropical rain forests and lakes into the fishing location for local residents and visitors. d. other aspects that can be developed is the cultural aspect. this is indicated by houses on stilts that are home to indigenous malay population. besides the potential geo-tourism is owned by buluh cina village also there is a potential disaster such as flooding and forest fires. buluh cina village is a flood plain. floodplains are dynamic feature that co-evolve with channel so at present no universal theory is available to predict floodplain width in natural rivers (as a function of drainage area, bankfull discharge, or sediment flux, etc) because floodplain morphology dynamically integrates across these and the other factors, over some unconfined time interval in the environment history of the watershed (patrick belmont, 2011). fig 8. existing stilt house at buluh cina village floods that happen periodically in this area also bring finer sediment such as silt and mud that characterize overbank deposit but not significant shown in this area. therefore, in floodplain formation, lateral accretion gives bigger contribution than vertical accretion. lateral accretion deposit characterize with fine to medium sand while overbank characterize with finer sediment (silt and clay) (yuskar, 2016). it should be considered by the community. to overcome the floods that occurred in the rainy season which is by building stilt houses. it is also useful to conserve malay culture so that it becomes an attraction for tourists. while in the dry season, forest fires often occur whether caused by natural processes or by human intervention due to land clearing. then it needs to be increased alertness and severe sanctions to persons who carry out the forest fire. 5. optimizing the utilization of geo-tourism in an effort to utilize optimally geo-tourism, the local community must be involved and play an active role in managing the geo-tourism and requiring coordination with government institutions. based on the discussions have been done with buluh cina village community, the community have attempted to preserve the nature and the ecosystem in the area. however economic standard is still is low then some people sell the land area and make their land as oil palm plantations. therefore 62 yuskar y./ jgeet vol 1/2016 optimization of geotourism in this area expected to improve the local economies. so that preservation of nature will be maintained. several things that should be met, namely establisment and improvement of public facilities. previously have been built some facilities and signposts by pt. chevron pacific indonesia and named this area as . however, the existing facilities are not well maintained and should be repaired to make it better. fig. 9. several facilities that have been built by pt. chevron pacific indonesia aspects that must be addressed to increase the number of tourists to this area are: 1. the promotion of the region by organizing events locally, nationally and internationally 2. improvement of public facilities such as signposts, public toilets, road improvements etc. 3. establishing culinary locations and sale of souvenirs typical of the area. 4. provision of homestay for travelers who want to stay in this area. 5. presence of tour guide making it easier for tourists to explore the entire geo-tourism site. 6. conclusion several conclusions can be drawn from this study are: 1. buluh cina village has the potential of geotourism can be developed that is the sand bar, oxbow lakes, tropical rain forests and ecotourism 2. optimizing the utilization of geotourism can be done to increase the number of tourists visiting this region 3. keep doing repair of public facilities to support tourism activities in this area fig. 10. several existing facilities at buluh cina village. acknowledgements we would like to say thanks to universitas islam riau for all the support, tiggi choanji and adi suryadi has helped in collecting data in the field and the students on the department of geological engineering, faculty of engineering, universitas islam riau for helping me on this research. references [1] artikel opini, pikiran rakyat, bandung. [2] clarke, m.c.g et al (1982). geological map of the pakanbaru quadrangle, sumatra. pppg. [3] boggs, s. jr. (2006). principle of sedimtology and stratigrapy 4th ed, pearson prentice hall, new jersey, united states of america. [4] nichols, g. (2009). sedimetology and stratigraphy 2nd ed, john wiley & sons ltd, west sussex, united kingdom. [5] page, k.j et al. (2003). floodplain formation and sedimen stratigraphy resulting from oblique accretion on the murrumbidgee river, australia. journal of sedimentary research vol. 73 no.1. tulsa, oklahoma, usa. [5] yuskar, y and choanji, t. (2016). sediment deposit of floodplain formation resulting from lateral accretion surfaces on trpical area: study case at kampar river, indonesia, the 7th ijjss. e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 255 sea surface temperature and wind velocity in batam waters its relation to indian ocean dipole (iod) muhammad zainuddin lubis 1, *, wenang anurogo 1 , husnul kausarian 2 , ganda surya 1 , tiggi choanji 2 1 department of informatics engineering, geomatics engineering, politeknik negeri batam, batam kepulauan riau, 29461 indonesia. 2 department of geological engineering, jl. kaharuddin nasution no 113, universitas islam riau, 28125, indonesia. * corresponding author : zainuddinlubis@polibatam.ac.id tel+6281342578087, office : 778-469856 ext : 2510; fax: +62-778-463620 received: oct 18, 2017. revised : nov 19, 2017, accepted: nov 30, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.778 abstract this study aimed to observe the characteristics of sea surface temperature (sst) and wind velocity and its relation with the indian ocean dipole (iod) in the waters of batam. the data used in this study were the sst datasets and the wind speed of 2016 in the waters of batam. the method used in this research were the visual analysis using the data ocean view (odv) to observe at the spatial and temporal distribution of the sst and the wind speed in batam waters at different seasons. the next method is a fast fourier transform (fft). the earlier monsoon season that occurred in april has the highest wind speed with the value of 3.9 ms ** 1 for components u. as for the v, the component has the highest value of -3.6 ms ** 1 . the sst batam observed high in april occurred on 19-04-2016 with a value of 304.2 ° k (31.05 ° c). west monsoon winds that occurred in january has the highest wind speed with a value of 4.5 ms ** 1 for components u. as for the v, the component has the highest value of 5.2 ms ** 1 in the waters of batam. the highest sst in batam occurred in january on 19-01-2016 with a value of 302.8 ° k (29.65 ° c). based on the results of the fft, wind speed and sst in the waters of the island has a dominant 6-month period (semiannual). keywords: sst, fast fourier transform (fft), components u, components v. 1. introduction indian ocean dipole (iod) is identified as one of the leading modes of variability in tropical climates (sahu et al., 2012). a positive iod phenomenon (piod) is characterized by cooler water temperatures than usual that occur in the tropical eastern part of the indian ocean and warming up of ordinary water temperatures in the tropical western indian ocean (manyilizu et al., 2016), and indicating the role of iod when it weakens ensomonsoon relationship (koch-larrouy et al., 2008). indian ocean dipole (iod) has just been categorized as one of the phenomena of the relationship between the ocean and the atmosphere in the tropical sector of the indo-pacific region. thus, it can be explored the possible influence of indian ocean dipole (iod) on the indian summer monsoon rainfall (ismr) (gadgil et al., 2004). it is observed that there is a remarkable sea surface temperature effect in the equatorial indian ocean, and with the hypothesis that there is a sea surface temperature effect arising from the dynamic interaction between the marine atmosphere in the indian ocean, the dynamics of the coast will affect sea surface temperature variability in a waters (ginzburg et al., 2008; kausarian et al., 2016a; kausarian et al., 2016b; kausarian et al., 2017). in fact, it is shown by the analysis of summer boreal composite anomalous observed sea surface temperature (sst) during strong iod positive and negative years that there is a significant relationship of phase between the sst in the eastern and western tropical indian ocean for many years (sahu et al., 2012). el nino and la nina is a symptom that shows the global climate change that is affecting the climatic conditions in indonesia. el nino is an event of warming sea surface water temperature on the west coast of indonesia (gaol and manurung, 2000). la nina is the opposite of el nino. the incident began when el nino was weakened, and the hot ocean water on the coast of peru came back cold again. many iod events are shown to occur independently of el nino (kogan, 2000; naylor et al., 2001). 2. material and methodology locations that are set for research are the water territories around batam, with located between: 0o 25' 29 " n 1o 15' 00" n 103o 34' 35" e 1040 26' 04"e. the data used are monthly data, and annual data for 1 year is (january december 2016) with time interval 06:00:00, 12:00:00 for 1 month (fig. 1). mailto:zainuddinlubis@polibatam.ac.id 256 lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 fig. 1. research location (waters area around batam) 3. computer assisted data collection method (cadc) data collection using computer-assisted data collection method is the method of taking data/information sourced from the internet. data is sourced from ecmwf (http://www.ecmwf.int) with a grid format of 0.125 x 0.125. the data taken are wind speed data in the direction of the x-axis (eastwest), the y-axis direction (north-south), and sea surface temperature data (sea surface temperature). from the uniform u-direction wind pressure data for 1 year is calculated using the relationship: t = y 2 (1) t = y 2 (2) where: y 2 : the coefficient of resistance p ': air volume u // v: component velocity 10 m above sea level at wind power 3 beaufort or lowest sea level can be assumed as a fine hydrodynamic, with a barrier coefficient of about 0.8 x 10 -3 , decreasing with increasing wind speed. at beaufort wind power 4 and higher constant value, y 2 = 2,6 x 10 -3 , used, corresponds to the hydrodynamic rough surface (rossby'0). all data will be processed using ocean data view (odv) software, and matlab software. 3. spatial visual method with ocean data view (odv) ecmwf data is processed using odv application, by making time series, temperature graph (k), component graphs in the direction of the u axis (ms ** 1 ), x (ms ** 1 ) based on monthly time, and time series of temperature charts for a year. import the odv result data to ms.excel to continue the creation of fast fourier transform (fft) method using matlab application. 4. fast fourier transform method the basis for studying the frequency characteristics of a signal is the fourier transform. fast fourier transform (fft) is an algorithm for calculating fourier transform. a signal at time domain, nominal, x (t) ca is converted in a signal at the frequency domain, nominal x (f). the algorithm of the fft method as shown in the following equation. (mudelsee, 2004). this in turn allows us to introduce the fourier transform of the averaged autocovariance function of the modulated process, which is equal to its expected periodogram. through examining the expected periodogram, the properties controlling the latent random process may be inferred even when the modulating function changes very rapidly. the standard class of modulated processes are asymptotically stationary modulated (yang et al., 2014). (3) (4) psd is a variation of electricity (energy) as a function of the frequency spectrum in the form of estimated density using fft, the psd method is one of the modern spectral estimation techniques proposed during this decade (mudelsee, 2004). the research flow diagram can be seen in fig. 2. fig 2. flowchart of research 5. results and discussion batam is one of the tropical cities located in riau islands province (0o 25' 29 " n 1o 15' 00" n 103o 34' 35" e 1040 26' 04" e) which has an area of 2,950 km2 of the sea, and only 1,040 km2 of land area. previous research conducted by simbolon and halim (2005) states that skipjack catches tend to be high at low sst.the sieve yield of each diameter was dried by means of a driven, and each diameter was measured by weight with an analytical scale, the remaining sieving results in the sludge were accommodated in a residual pan and by the pipette method. based on the diameter of the grains and the weight percentage of the substrate components are clay depth (diameter <0.004 mm), mud (diameter 0.004 0.063), sand (diameter 0.063 2.00 mm) and gravel (2-8 mm). lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 257 (a) (b) (c) (d) (e) fig. 3. (a) component speed u, (b) component velocity v, (c) graph of sea surface temperature in batam waters, (d) sea surface temperature distribution, (e) component velocity u and v with sea surface temperature month january 258 lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 (a) (b) (c) (d) (e) fig. 4.(a) component speed u, (b) component velocity v, (c) graph of sea surface temperature in batam waters, (d) sea surface temperature distribution, (e) component velocity u and v with sea surface temperature transitions 1 the catch is high during the southwest monsoon and the beginning of the northeast monsoon. sea levels, observations, satellite data, and observer stations of sea-level pressure and precipitation used to describe the evolution of sea surface temperature anomalies, surface wind velocity north and west, and rainfall patterns during the main periods in the east and middle for the tropical pacific (wang et al., 2017). to evaluate the cause of weather and climate change in batam city, data on global climate change (enso) is needed, which will affect the batam region the circulation of seawater in indonesian waters is influenced by the monsoon wind system. since the monsoon wind system is constantly blowing, although relative speed is not great, it creates an excellent condition for the occurrence of a current pattern (amri et al., 2013). in the western seasons, lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 259 the current pattern of surface waters of indonesia shows the current moving from the south china sea to the java sea. the java sea, the current then moves into the flores sea until it reaches the banda sea, while at the time of the southeast monsoon, the direction of the current completely reverses towards the west which eventually leads to the south china sea (utama et al., 2017; surya et al., 2017). the condition of the seasons in indonesia is divided into 3. this wind blows as the sun is in the southern hemisphere, which causes the continent of australia is experiencing summer, resulting in minimum pressure and the continent of asia is cooler, resulting in maximum pressure. the physical parameters of the sea in batam can be seen in fig. 3. west monsoon winds that occur in january at coordinates 1 ° 5 '0 "n, 104 ° 2' 0" e looks the highest wind speed with a value of 4.5 ms ** 1 for component u. component v has the highest value 5.2 ms ** 1 . the highest batam sea temperature (sst) in january occurred on 19-01-2016 with a value of 302, 8 ° k (29.65 ° c). the transitional season 1 is the turn of the west monsoon to the east monsoon (fig. 4).transition season 1 which occurs in april at coordinates 1 ° 5 '0 "n, 104 ° 2' 0" e shows the highest wind velocity seen with a value of 3.9 ms ** 1 for component u. as for component v has value highest -3.6 ms ** 1 . the highest sea surface temperature (sst) of batam in april occurred on 1904-2016 with a value of 304.2 ° k (31.05 ° c). the east monsoon or southwest monsoon is the wind that blew in july-september in indonesia. this wind blows when the sun is in the northern hemisphere. the asian continent receives more heat than the sun so that the asian continent is the area of minimum pressure (fig. 5). southeast monsoon winds that blow in the sms area become the factor that evokes an upwelling. the wind blowing will generate a water mass transport known as ekman transport. generally, upwelling phenomenon in the coastal area is formed by ekman dynamic process in the surface layer. (a) (b) (c) fig. 5. (a) component velocity u, (b) component velocity v, (c) graph of sea surface temperature in batam waters, (cont.) 260 lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 (d) (e) fig. 5 (cont.) (d) sea surface temperature distribution, (e) velocity of u and v component component with moon sea surface temperature july. (a) (b) (c) (d) (e) fig. 6. (a) component velocity u, (b) component velocity v, (c) graph of sea surface temperature in batam waters, (d) sea surface temperature distribution, (e) velocity of u and v component component with sea surface temperature october lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 261 july at coordinates 1 ° 5 '0 "n, 104 ° 2' 0" e shows the highest wind velocity seen with a value of 5.05 ms ** 1 for component u. as for component v has value highest 6.08 ms ** 1 . the highest sea surface temperature (sst) of batam in january occurred on 19-03-2016 with a value of 303.2 ° k (30.05 ° c). the transitional season 2 is the turn of the east monsoon to the west monsoon (fig. 6). the 2nd transition season occurs in october at coordinates 1 ° 5 '0 "n, 104 ° 2' 0" e shows the highest wind speed seen with a value of 6.6 ms ** 1 for component u. as for component, v has the highest score of 4.85 ms ** 1 . the highest batam sea temperature (sst) in january occurred on 19-032016 with a value of 302.87 ° k (29.72 ° c). the exposure of heat as a process of shifting from the sea to the atmosphere gives rise to cooling of the ocean surface, which is proportional to the amount of evaporation. the rate of evaporation as the transfer of heat from the ocean to the atmosphere is an average of 1m / year or about 3 mm / day (ashok, 2001). the result (fig. 7) above shows that the identical u component is more normal to change the wind direction and its speed in comparison with component v. the u component has the highest value in december worth 5.26 ms ** 1 with a positive value which means that the wind moves in the direction west. and for component v maximum value existed in january with value reaching 10 ms ** 1 with a negative value which means the wind move eastward. time series sea surface temperature (sst) can be seen in (fig. 8). fig. 7. graph of component u, and v annual period 262 lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 fig. 8. time series sea surface temperature (sst) period and indian ocean dipole index in 2016 sst in batam waters (1 ° 5 '0 "n, 104 ° 2' 0" e) during annual period (fig. 3-6). during the course of the west monsoon event, the waters of batam (january-february) have sea surface temperature with low value. significant changes occur during the transition season 1, sea surface temperature in the rock waters rises and falls randomly. the occurrence of east monsoon causes the sea surface temperature in the waters of batam to rise in temperature, and at the time of the transition season, 2 sea surface temperatures around batam experiencing the temperature drop is not so drastic. indian ocean where lower sst is usually found off the west coast of sumatra and warmer ssts exist in most of the western indian ocean. the mass of water coming out of west sumatera intensively out in transition season i, only in 2005 seen flow twice season in one year that transition season i and transition season ii. this is accompanied by nieblas et al., (2014), that the current of south java is the current passing through the western coast of sumatra-south java occurring semi-annually, with the strongest currents occurring during the transitional periods i and ii. in 2016, especially in june to november, moderate negative iod is taking place with an index of -0.65. at the same time, the sst in batam waters is decreasing. this indicates that iod negative can cause the decrease of sst in batam. fig. 9 shows the distribution of periods owned by the wind and sst velocities in batam waters by 2016. the wind speed in the waters of batam has a predominant period of 6 months (semiannual). however, the wind speed in the waters of batam also has another period, namely intra-seasonal (35-90 days) and 10 monthly. besides wind speed, sst in batam waters also has a semiannual dominant period. this indicates that seasonal factors are strongly influencing changes in sst and wind in the waters of batam. 6. conclusion the results of this study concluded that the temperature and wind velocity characteristics associated with indian ocean dipole (iod) in batam waters have low sea surface temperatures. the sea surface temperature is highest in the 1st transition and in the east monsoon season, whereas in the east monsoon season it decreases. sea surface temperature is highest in april-may, and the lowest is in february-march. the u component is highest in december with the west (+ positive, and for the highest v component in january with the south (negative) direction. sea surface temperature significantly.based on fft results, wind speed and sst in batam waters have a dominant period of 6 months (semiannual). references akhir, m.f., daryabor, f., husain, m.l., tangang, f. and qiao, f., 2015. evidence of upwelling along peninsular malaysia during southwest monsoon. open journal of marine science, 5(03), p.273. amri, k., manurung, d., gaol, j.l. and baskoro, m.s., 2013. karakteristik suhu permukaan laut dan kejadian upwelling fase indian ocean dipole mode positif di barat sumatera dan selatan jawa barat. jurnal segara, 9(1), pp.23-35. gadgil, s., vinayachandran, p.n., francis, p.a. and gadgil, s., 2004. extremes of the indian summer monsoon rainfall, enso and equatorial indian ocean oscillation. geophysical research letters, 31(12). gaol, j.l. and d. manurung, 2000. el niño southern oscillation impact on sea surface temperature derived from satellite imagery and its relationships on tuna fishing ground in the south java seawaters. aars. conference in taipeh. ginzburg, a., kostianoy, a., & sheremet, n, 2008. sea surface temperature variability. the black sea environment, pp.255-275. kausarian, h., sri sumantyo, j.t., kuze, h., aminuddin, j. and waqar, m.m., 2017. analysis of polarimetric decomposition, backscattering coefficient, and (a) (b) (c) fig. 9. fast fourier transform (fft) (a) component u (ms ** 1 ), (b) component v (ms ** 1 ) (c) sea surface temperature (sst) in 2016 lubis, muhammad. z. et al./jgeet vol 02 no 04/2017 263 sample properties for identification and layer thickness estimation of silica sand distribution using l-band synthetic aperture radar. canadian journal of remote sensing, 43(2), pp.95-108. kausarian, h., sumantyo, j.t.s., kuze, h., karya, d. and panggabean, g.f., 2016. silica sand identification using alos palsar full polarimetry on the northern coastline of rupat island, indonesia. international journal on advanced science, engineering and information technology, 6(5), pp.568-573. kausarian, h., sumantyo, j. t. s., kuze, h., karya, d., & wiyono, s, 2016. the origin and distribution of silica mineral on the recent surface sediment area, northern coastline of rupat island, indonesia. arpn journal of engineering and applied sciences, 12(4). pp.980-989. koch-larrouy, a., madec, g., iudicone, d., atmadipoera, a. and molcard, r., 2008. physical processes contributing to the water mass transformation of the indonesian throughflow. ocean dynamics, 58(3-4), pp.275-288. kogan, f.n., 2000. satellite-observed sensitivity of world land ecosystems to el nino/la nina. remote sensing of environment, 74(3), pp.445-462. lubis, m.z. and si, m., 2016. signal processing for power spectral density (psd). signal processing for marine acoustic and dolphin using matlab, edition. manyilizu, m., penven, p. and reason, c.j.c., 2016. annual cycle of the upper-ocean circulation and properties in the tropical western indian ocean. african journal of marine science, 38(1), pp.81-99. mudelsee, m., 2014. extreme value time series. in climate time series analysis (pp. 217-267). springer international publishing. naylor, r. l., falcon, w. p., rochberg, d., & wada, n, 2001. using el nino/southern oscillation climate data to predict rice production in indonesia. climatic change, 50(3), pp.255-265. nieblas, a.e., demarcq, h., drushka, k., sloyan, b. and bonhommeau, s., 2014. front variability and surface ocean features of the presumed southern bluefin tuna spawning grounds in the tropical southeast indian ocean. deep sea research part ii: topical studies in oceanography, 107, pp.64-76. sahu, n., behera, s.k., yamashiki, y., takara, k. and yamagata, t., 2012. iod and enso impacts on the extreme stream-flows of citarum river in indonesia. climate dynamics, 39(7-8), pp.1673-1680. simbolon. d. dan a. halim, 2005. suhu permukaan laut dan kaitannya dengan hasil tangkapan ikan cakalang dan madidihang di perairan sumatera barat. buletin pemanfaatan sumberdaya perairan. institut pertanian bogor. bogor. surya, g., khoirunnisa, h., lubis, m.z., anurogo, w., hanafi, a., rizky, f., timbang, d., situmorang, a.d., guspriyanto, d., ramadhan, w.r. and mandala, g.f.t., 2017. karakteristik suhu permukaan laut dan kecepatan angin di perairan batam hubungannya dengan indian ocean dipole (iod). dinamika maritim, 6(1), pp.1-6. utama, f.g., atmadipoera, a.s., purba, m., sudjono, e.h. and zuraida, r., 2017, january. analysis of upwelling event in southern makassar strait. in iop conference series: earth and environmental science (vol. 54, no. 1, p. 012085). iop publishing. wang, c., deser, c., yu, j.y., dinezio, p. and clement, a., 2017. el niño and southern oscillation (enso): a review. in coral reefs of the eastern tropical pacific (pp. 85-106). springer netherlands. wulandari, p.d., pujiyati, s., hestirianoto, t. and lubis, m.z., 2016. bioacoustic characteristic click sound and behaviour of male dolphins bottle nose (tursiops aduncus). j fisheries livest prod, 4(160), p.2. yang, x.j., baleanu, d. and machado, j.t., 2014. application of the local fractional fourier series to fractal signals. in discontinuity and complexity in nonlinear physical systems (pp. 63-89). springer international publishing. 1. introduction 2. material and methodology 3. computer assisted data collection method (cadc) 3. spatial visual method with ocean data view (odv) 4. fast fourier transform method 5. results and discussion 6. conclusion references uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 6. no 4. december 2021 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 06 no 04 2021. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content the transitional gabbroic rocks in bayah geological complex, western part of java, indonesia, inferred from xrf, icp-ms, and microprobe analysis ........................ 177 interpretation of subsurface fault through multi-level second vertical derivative gravitational data in bittuang geothermal working area, south sulawesi, indonesia ....................................................................................................................... 184 groundwater effect on slope stability in open pit mining: a case of west kutai regency, east kalimantan, indonesia ............................................................................. 192 understanding mud volcano system using hele-shaw (h-s) experiment: seismic confirmation at east java mud volcano .................................................................... 206 resistivity method for characterising subsurface layers of coastal areas in south sulawesi, indonesia ........................................................................................................... 217 diagenesis study of jatiluhur formation at cipamingkis river, bogor regency, west java, indonesia .................................................................................................................... 226 carbon dioxide (co2) emissions due to motor vehicle movements in pekanbaru city, indonesia .......................................................................................................... 234 hydrogeochemical and characteristics of groundwater in teluk nilap area, rokan hilir, riau ............................................................................................................................ 243 fluid inclusion study of epithermal quartz veins from the kyaukmyet prospect, monywa copper-gold ore field, central myanmar ........................................... 248 diagenesis study of jatiluhur formation at cipamingkis river, bogor regency, west java, indonesia .................................................................................................................... 255 cover jgeet vol 6 no 4 december 2021.pdf (p.1) editorial member.pdf (p.2) preface vol 6 no 4.pdf (p.3-4) e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 natasia n. et al./ jgeet vol 1/2016 51 stratigraphy seismic and sedimentation development of middle baong sand, aru field, north sumatera basin nanda natasia 1, *, ildrem syafri 1 , muhammad kurniawan alfadli 1 , kurnia arfiansyah 1 1 faculty of geological engineering, universitas padjadjaran, jl.raya bandung sumedang km.21 jatinangor. * corresponding author : nanda.natasia@unpad.ac.id tel:+62-22-7796-545 received: oct 1, 2016. revised : 15 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.7 abstract this paper defines the stratigraphic sequence focused on middle baong sand. the analyses aim to understand the sedimentation pattern regarding to sequence stratigraphy model including its lateral and vertical succession based on seismic and well data. the study can be used in ranking the prospect for new oil field. based on the analyses in 39 seismic sections and 2 wireline log, the area are consist of three depositional sequences, namely sequence i (consist of hst i) sequence ii (consist of tst ii and lst ii), and sequence iii (consist of tst iii). baong formation are deposited when the sea level are rising regionally at middle miocene (n7-n15) makes the sediment deposited in deep water environment. while middle baong sand are deposited in the minor falling stage placed at n13 (middle of middle miocene). in this episode, there is a change in depositional setting from bathyal to middle neritic. clastic origin of this deposits were interpreted came from south-south west direction or from bukit barisan where at that time is started to uplift. keywords: seismic stratigraphy, baong formation, aru, north sumatera. 1. introduction popular geophysical method now days in exploration is seismic reflection because it could gave valuable information to geologist about detail of subsurface condition, such as stratigraphy and the geological structure. the information extracted from seismic data further used as as tool for hydrocarbon prospecting at interesting area. through an understanding of sequence stratigraphy, seismic data can be used to give us the information about important geological factors which control patterns of stratigraphy layer. considering many prospect in north sumatra that have not been explored, it was very interesting to accomplish stratigraphic sequence analysis in order to obtain new oil and gas reserves, particularly in the area of aru (fig 1). one of the main reservoir in the area is middle miocene baong formation that deposited in deep water environment dominated by shally facies. at the time of the deposition of this formation occurs transgressive phase resulting the coarse sediments known as the middle baong formation. fig 1. location map of research area 52 natasia n. et al./ jgeet vol 1 no 1/2016 2. methodology research object included seismic reflection used in subsurface mapping and interpretation of seismic stratigraphy as well as conceptual application to obtain information about sequence stratigraphy in research area. a. wireline log analysis the wireline log data is used for : determination of depositional bed boundary used in analysis (middle baong sand) determination of electro facies boundary based on sp log deflection b. seismic interpretation this interpretation is used to determination of horizon boundary distribution in 2d and system tract horizons by analyze the seismic internal configuration. 3. regional geology main characteristic of north sumatera basin is a series of north south fault patterd that formed high and low structure (horst and graben or half graben (fig 2). the structural trend is controlled by the basement main configuration that influenced by north south tectonic activity. the early tertiary sediment at north sumatera basin was known as a product syn-rift deposition at early oligocene early miocene (fig 3). according to caughey & wahyudi, 1993 (in darman & sidi, iagi, 2000), this depositional mainly consist of silisiclastic sediment from parapat formation, bruksah and bampo. while neogene deposition consist of clastical and carbonate deposition (fig 3). fig 2. tectonic pattern of north sumatera basin (lemigas, 2005) natasia n. et al./ jgeet vol 1 no 1/2016 53 fig 3. regional stratigraphy of north sumatera basin (caughey & wahyudi, 1993 (in herman & hasan, iagi, 2000) baong formasion was deposited coincide with regional sea level rise. it shown with global sea level rising at 15,5 million years ago (n8-n9) and supported by depositional enviroment changing from paralic to bathyal which related to major subsidence. 4. seismic interpretation 39 seismic section is used in this research (fig 4). section interpretation is specially on middle baong sand depositional, marking by green horizon and the bottom is marking by red horizon (fig 5). fig 4. base map of research area fig 5. seismic section that shown horizon separation in baong formation depositional 5. electro facies depth of well i is 2025 meters. the position of middle baong sand in 1750 2020 meters. in the first well consist of four facies that can be difference by deflection pattern from log curve, namely :  facies i : found at interval between 1980 2020, identified by finning upward log curve  facies ii : found at interval between 1930 1980, identified by log blocky pattern  facies iii : found at interval between 1815 1930, identified by coarsening upward  facies iv : found at interval between 1750 1815, identified by blocky pattern. in the second well, middle baong sand located at 1850 2400 m. classificated with three facies from log, namely :  facies i : found at interval between 1935 2040, identified by log blocky pattern  facies ii : found at interval between 1880 1935, identified by coarsening upward pattern  facies iii : found at interval between 1850 1880, identified by blocky pattern. 54 natasia n. et al./ jgeet vol 1 no 1/2016 sw ne well to well correlation were made based on the electro facies analysis (fig 6) fig 6. electro facies corelations between well i and ii the lower part of middle baong sand is bounded by thick shale facies known as lower baong shale, while in the upper part was bounded by upper baong shale. the lithology interpretation were done based on well data interpretation combined by seismic internal configuration. the sismic data shown that the sediment in the area is deposited in lowstand system tract that spread from west to east area. the high structure is in the north area. there are four seismic facies on middle baong sand that can be observed in seismic section. they are identified based on its internal seismic configuration and termination of the waveflet (fig 7). a. facies i. the lowest part of middle baong sand. characterized by downlap termination and sigmoid progradation. this facies can be found in every trajectory of the seismic with almost similar thickness. based on termination and internal configuration that present in this facies, it can be identified as highstand system tract sediment. b. facies ii is the second layer of the middle baong sand. characterized by interal sub paralel cofiguration. this facies was not developed in every trajectory of the seismic, lenses can be identified in seismic cross-section, lies from south to north south. c. facies iii is the third layer of this middle baong sandstone. characterized by downlap termination. this facies developing almost on all trajectory of the seismic. lenses can be identified by the seimic cross section. this facies lies from north to north east, which lenses lies from south to south west of the resarch area. based on termination and internal configuration that identified in this facies, it can be interpreted as low stand system tract sediment. d. facies iv. the upper part of middle baong sand. characterized by internal subparalel. this facies can be found in every trajectory of the seismic. based on termination and internal configuration that identified in this facies, it can be interpreted as transgresive system tract sediment. based on seismic data analysis, research area consists of three sedimentation sequences, which are :sequence i that consist of highstand system track (hst)-1, sekuen ii, consist of transgressive sytem track (tst)-ii, and sekuen iii that consits of low stand system track (lst)-iii and trasngressive system tract (tst)-iii (fig 8). the lateral continuity of each of the sytem track were relatively similar, spreading almost all over the research area, because of the relative similar location and the time of sedimentation. the pattern of spreading affected by the geometry of sedimentary base which is the upper part of lower baong shale. in general, the highland lies in the south south west area, while the lowland area lies in north-north east area. this condition affect the thickness of natasia n. et al./ jgeet vol 1 no 1/2016 55 system track which tend to thicker to north east filling the lower part. the middle baong sandstone in the research area is a member of baong formation, in lithostratigraphic dominated by deep sea shale facies. while in the middle sandstone baong contain sandstone intercalated with shale. this caused by changing of water depth from bathyal to middle neritic caused by tectonic activity and drop of sea level present at the time of deposition (situmoreang et., al., 1994). this condition affected the acomodation space and sediment supply. regionally, sandstone of baong formation in midlle part exist on the two part of basin, but the sedimentation not reach to basement basin (deposenter) from north sumatera aru basin due to minimun sedimen acomodation. regionally, previous research prove that in the early midlle miocene (n7-n13) base part of baong sedimen resource is from malaka shelf in north part. on that time, malaka shelf and ashan arc been the mainly resource of sedimen in north sumatera basin. fig 7. downlap, sigmoid progradation and sub-parallel configuration on seismic section fig 8. system tract on seismic section initiation of uplift of bukit barisan has been start at this time. at the midlle miosen (n13-n14), uplift of bukit barisan became more intensive which cause reduction of sea level regionally. beside that, in that time occur basin deformation, north position of high elevation change to be south/south west, the sedimentation direction drastically change from malaka shelf on the north part be came from bukit barisan on south/south west part of basin. sandstone baong sedimentation in the middle part came from uplift of bukit barisan (situmorang, b, dkk, 1994). 56 natasia n. et al./ jgeet vol 1 no 1/2016 structural pattern in peak of sedimentation of part baong sandstone, in 400msec subsurface or 700 meters is fold with north west south east direction in south west position. sinklin area in north east part of the research area (fig 9). result of compressional tectonic activity in the midlle miocen caused uplift the south west edge of basin and bukit barisan. compressional tectonic phase is related with subduction activity between indian plate and eurasian plate which caused uplift of south/south west part of basin and formed magmatic trace in bukit barisan as the sedimen material resource from midlle part of baong sandstone. the orientation of fault direction changed from orientation occur on pre-tesier basement and belumai formation with north west south east orientation and north south direction. while fault in middle miocene is interpreted with north west south east direction which most of caused by rectification result from fault previously. this fault pattern controlled high elevation structure. in south/south west part and lower elevation structure in north/north east, sedimentation of baong sandstone is interpreted came from high elevation erosional in south/south west direction and continuously deposit in north/north east lower elevation. fig 9. schematic configuration of structure in research area in middle miocene (n13 n16), without scale sedimentation of the basin is started by transgresive sequence of pre-baong such as parapat formation, bampo and belumai. this sequence is deposited continuously until middle miocene when this area is covered by sea until the deposition of baong shale in base part. sedimentation material resource predicted from east direction of basin, that is from malaka shelf which dominated by fine grained sediment. in late of middle miocene, occurred uplift of bukit barisan and influence the depositional environment at that time. sea levels begin to shrink and change bathyal environment be top and middle neritic. at that time there was a change of origin deposition material that originally came from the east be from the west (fig 10) (bukit barisan). due to this depositional environment changes, the type of sediment at this time is changed, originally dominated by fine grained material into gradually change into intercalation of sandstone and shale. distribution of the deposit is thickened in the middle area of research and thinning gradually towards the northeast and southwest areas and wedge in the southwest area. development of middle baong sandstone started by sea level regression phase in n11 and initiation the uplift of bukit barisan caused shallowing of depositional environment from bathyal to middle neritic (geology of indonesia chapter 2). with the regression phase and uplift of the bukit barisan provide large sediment supply in natasia n. et al./ jgeet vol 1 no 1/2016 57 bukit barisan high elevation and deposit middle baong sand (fig 10). fig 10. sedimentation history of middle baong sand deposition of middle baong sand end with the quiesence of tectonic activity. high elevation caused by tectonic activity previously eroded and resulted in the seismic unconformity above middle baong sand. sea level becomes bathyal again, and the resulting depsits was also changed back into shale. the upper baong shale start to deposits. conclutions 1. there are four electrical facies can be found in the region, namely: facies 1 characterized by fining upward pattern logs, facies 2 which is characterized by a blocky log patterns, facies 3 is characterized by upward coarsening patterns and facies 4 characterized by a blocky pattern 2. the depositional sequence of middle baong sand consists of low stand system tract, transgressive system tract, and high stand system tract. the sequences can divided into three depositional sequences 3. basin configuration while middle baong sand deposited is southwest northeast direction. high structural is located in the south / southwestern area while lower structural has north / north-east direction. tectonic activity in the area is compressional tectonic. references [1] bemmelen, r.w., van, 1949. the geology of indonesia. gov. printing office. the hague netherland [2] bp migas, 2004. studi pengelolaan cadangan dan sumber daya hidrokarbon, buku-2, unpublised report basement configuration as a product of tectonic activity pre middle baong sand . rising of sea level (transgressive system tract) decrease of sea level (lowstand system tract) rising of sea level (transgressive system tract) sw ne decrease of mean sea level and initiation of bukit barisan uplift profide coarser sediment and change of sedimentation direction. 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[21] walker g.r., dkk., 1992, facies models respon to sea level change, geological association of canada. http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 2 2021 harahap et al./ jgeet vol 6 no 2/2021 99 research article mapping of sediment on the waters around panjang island, banten bay, indonesia syawaludin a. harahap1,*, lintang p. s. yuliadi1, noir p. purba1, awal a. aulia2 1 marine science department, faculty of fisheries and marine science, universitas padjadjaran, jatinangor, 45363, indonesia. 2 study program of marine science, faculty of fisheries and marine science, universitas padjadjaran, jatinangor, 45363, indones ia. * corresponding author: syawaludin.alisyahbana@unpad.ac.id tel.:+62-813-8018-3431 received: may 05, 2020; accepted: may 28, 2021. doi 10.25299/jgeet.2021.6.2.5057 abstract this study was conducted to map the surface sediment conditions in the waters around panjang island, banten bay. the survey method was conducted in february 2015 by taking sediment samples using a grab sampler at 15 stations. sediment analysis was conducted to determine the grain size using the granulometry method which was then processed using the kummod-sel software to obtain the composition and texture of the sediment. the results of processing sediment samples at each station obtained that the grain size of sediments in the waters around panjang island ranged from -0.7 to 2.6 in the phi (φ) scale. sediment composition consists of sand and gravel, with sand dominance of 89.1 %. sediment textural classification consists of only 4 categories i.e. very coarse sand, coarse sand, medium sand, and fine sand. in general, the pattern of sediment distribution follows the pattern of water depth, where fine sand occupies deeper areas. meanwhile, medium sand dominates surface sediment distribution in the study area. keywords: banten bay, grain size, panjang island, phi (φ) scale, sedimentation 1. introduction 1.1 background banten bay is located on the north coast of java island, about 60 km west of jakarta. administratively, this area belongs to the northern coastal region of serang regency, banten province and geographically, is located at 5.90833 to 6.06667 southing and 106.06667 to 106.25000 easting connected to the java sea in the north and the west, south to east, the bay is bordered by the coastline of the mainland of java island. topographically, banten bay waters are relatively shallow water with an average depth of 7 m with characteristics of muddy and sandy beaches and the composition of soil material consisting of mud, clay, silt, and sand (boer et al., 2006). sea currents generally have speeds reaching 35 cm/sec, indicating eastward direction during west monsoon and east monsoon current direction turning westward (mustikasari et al., 2012; satriadi, 2013; wisha et al., 2015). banten bay has a relatively small beach wave that is less than 1 m high. in this bay, there are approximately 12 islands, of which panjang island is the largest in the geographical position of 6.42167 to 6.47000 southing and 106.36917 to 106.42667 easting. along the coast of panjang island to the surrounding waters in the gulf of banten there are coastal ecosystems and biological resources i.e. mangrove ecosystems, seagrass beds, and coral reefs. the potential damage to these ecosystems is very large due to environmental degradation. for example, the occurrence of changes in mangrove areas which are increasingly reduced due to coastal abrasion and land conversion (anurogo et al., 2018; arfando, 2008), the area of seagrass ecosystems have also diminished (setiawan et al., 2012), even starting more than two decades ago (kiswara, 1994), as well as coral reef ecosystems in most parts of this region are already in a damaged condition (soedharma et al., 2017). one important factor that plays a role in the degradation of ecosystems in the coastal environment is sedimentation originating from dredging and runoff. runoff from land for example through rivers certainly brings suspended material from land especially sediments (e.g. mud and sand) (kiswara, 1994). the speed of the sedimentation process that occurred in the banten bay waters was triggered by human activities such as sand/natural rock mining, hill leveling, and sea reclamation/dredging for industrial expansion and port development (rahwawan et al., 2017). seen from its location, panjang island is strongly influenced by the condition of the waters current because the position of panjang island is directly facing the java sea to the north and at the same time is facing the river estuary flow from the west and south. river surface water carries tiny materials that then end up on the high seas and carried by ocean currents, thus forming sedimentation. sediment accumulation and siltation in semi-enclosed areas (e.g. bay waters) are strongly influenced by high sedimentation rates and also due to weak ocean currents (rahmawan et al., 2020). changes in the morphology of the coast and the bottom of the waters occur as a result of the migration of sediment that takes place through the mechanism of erosion, transportation, and deposition. the sediments that are moved are sediments located on the surface of the bottom of the waters (poerbondono and djunarsjah, 2005). sedimentation is closely related to geomorphic agents http://journal.uir.ac.id/index.php/jgeet 100 harahap et al./ jgeet vol 6 no 2/2021 that work therein. the main geomorphic agents that cause or influence the processes and dynamics of coastal waters are waves, currents, and wind. transporting sediments through rivers to the ocean is an important pathway in the global geochemical cycle and a key component of the soil denudation system (walling et al., 2003). sediments that settle in the sea is a mixture of grains of various sizes (bockelmann et al., 2018). the transportation and accumulation of sediments become a major factor in the process of silting and changes in the depth of a waters (jumarang et al., 2012). understanding sediment dynamics in complex environments is correct and important management in the process of mitigating or protecting ecosystems from the effects of human activities (ferrarin et al., 2016). the role of surface sediments at the bottom of the waters is quite important because it becomes a means of growth of aquatic benthic biota, as a nutrient provider and as a place for anchoring roots of marine vegetation such as seagrasses and mangroves (atmadja and sulistija, 1988). furthermore, (yuniarti et al., 2019) states that sedimentation that occurs at the bottom of the waters is highly correlated with uniformity and abundance index of macrozoobenthos. another important function of the sediment is as a habitat for various types of bacteria that have an important role in the food chain cycle in coastal waters. however, sediment particles that are mobilized at a time from one place to another (bracken et al., 2015), the sediment particles can be a carrier agent of pollutants. furthermore, sediments carrying pollutants settle and accumulate at the bottom of waters originating from the mainland as well as those originating from surface waters such as oil spills, heavy metals, plastic waste and other toxic and dangerous substances (arifin et al., 2012; peng et al., 2017; polidoro et al., 2017; rochyatun and rozak, 2008; wasserman et al., 2016; yu et al., 2018). thus, sediment can also be used as an indicator of pollution because of its role as a “sink” for pollutants from the mainland. fig. 1. map of study the area and position of panjang island in banten bay. 1.2 state of the art studies related to sediment in banten bay is still limited. research conducted by van den bergh et al. (2003) and boer et al. (2006) related to the deposition of sedimentary deposits generated only by the 1883 krakatau eruption tsunami. satriadi (2013) conducted a study to find out the distribution of suspended sediments associated with the construction of bojonegara harbor, banten. a relatively new study is a study conducted by rustam et al. (2018) to see the characteristics of surface sediment distribution and composition of organic matter and the rate of sedimentation. however, sediment samples taken are limited to represent coastal areas close to the mainland. 1.3 the aim of the study to complement the information already available, this research is important to do. the purpose of this study is to map the surface sediment conditions around the waters of panjang island, banten bay. studies on mapping sediment, both on a local and regional scale have been carried out and are very helpful in conducting analyzes and predictions about the distribution of sediment properties (bockelmann et al., 2018). 2. data and method a field survey for sediment sampling was conducted in february 2015. samples were taken using grab samplers at 15 stations using a purposive sampling technique, in which the determination of location points represented the central part of banten bay around panjang island waters. surface sediment samples taken are in water depths ranging from 1.5-15 m (see table 1 and fig. 2). sediment samples are then taken to the laboratory for washing, drying and sieving processes. sediment grain size analysis using granulometry method by sifting 100 gr of dry weight of sediment samples using the automatic sieve shaker tool. sediment grain size data is then processed using the kummod software package. this application software has been integrated with sediment classification/nomenclature (folk, 1980) and is designed to determine the type of sediment based on grain size analysis (susilohadi, 1986). the grain size and classification of sediment can be seen in table 2. classification is done based on the scale of harahap et al./ jgeet vol 6 no 2/2021 101 wentworth (1922) which is then converted to the phi (φ) scale (w. c. krumbein, 1934, 1938). meanwhile, to determine the nomenclature of sediment type is based on shepard's (1954) theory namely the sediment classification ternary diagram used and developed by folk (1954), (1980); blair and mcpherson (1999) (see fig. 3). to achieve the objectives of this study, data related to the sediment grain size obtained were further analyzed by making a sediment distribution map. mapping is done to make it easier to analyze data spatially with a geographic information system approach (gis) using arcgis tool. this map distribution is done by interpolation technique using the inverse distance weighted (idw) method. the idw method provides more accurate interpolation results, for example, compared to the kriging method (pramono, 2008). this is because all the results using the idw method provide values close to the minimum and maximum values of the sample data. interpolation not only estimates the target variable at unsampled locations but also quantifies the remaining uncertainty (bockelmann et al., 2018). the resulting map becomes information material to describe the condition of the sediment in the study area. table 1. location coordinates for sediment sampling and water depth station depth (meter) long. (oeast) lat. (osouth) 1 -14.40 106.14005 -5.94791 2 -5.70 106.14012 -5.96695 3 -9.10 106.12860 -5.95941 4 -6.80 106.13001 -5.96096 5 -7.80 106.14003 -5.98238 6 -4.80 106.12658 -5.98207 7 -1.60 106.14339 -5.99671 8 -7.50 106.17197 -5.99481 9 -8.00 106.17290 -5.97983 10 -8.40 106.16300 -5.95843 11 -7.70 106.18631 -5.95882 12 -4.00 106.19141 -5.96025 13 -8.00 106.19115 -5.97184 14 -8.60 106.18430 -5.96346 15 -8.70 106.17184 -5.95357 fig. 2. map location of sediment sampling stations. station coordinates are recorded using a global positioning system (gps), while depths are recorded using echo sounders. depth contour (bathymetry) is constructed (interpolated) from the depth data at each station fig. 3. sediment classification ternary diagram source: derived from folk (1954) 102 harahap et al./ jgeet vol 6 no 2/2021 table 2. sediment grain size and classification grain size of sediment aggregate name (wentworth class) unified classification phi (φ) scale millimeters inches <−8 >256 >10.1 boulder gravel −6 to −8 64–256 2.5–10.1 cobble −5 to −6 32–64 1.26–2.5 very coarse gravel −4 to −5 16–32 0.63–1.26 coarse gravel −3 to −4 8–16 0.31–0.63 medium gravel −2 to −3 4–8 0.157–0.31 fine gravel −1 to −2 2–4 0.079–0.157 very fine gravel sand 0 to −1 1–2 0.039–0.079 very coarse sand 1 to 0 0.5–1 0.020–0.039 coarse sand 2 to 1 0.25–0.5 0.010–0.020 medium sand 3 to 2 0.125–0.250 0.0049–0.010 fine sand 4 to 3 0.0625–0.125 0.0025–0.0049 very fine sand 8 to 4 0.0039–0.0625 0.00015–0.0025 silt mud 10 to 8 9.8×10-4–3.9×10-3 3.8×10−5–1.5×10-4 clay 20 to 10 9.5×10-7– 9.8×10-4 3.8×10−8–3.8×10−5 colloid source: combined from (wentworth, 1922) and (w. c. krumbein, 1938) 3. result 3.1 sediment composition the sediment composition was related to the matrix soil texture (foster et al., 1985). the analysis results related to the composition of the sediment at each station in the study site can be seen in fig. 4. the sediment composition consists only of gravel and sand with an average composition of 10.9 % for gravel compared to 89.1 % for sand. thus, the sand component is the predominant type of sediment, with percentages ranging from 49.9 99.8 %. this agrees with the results of the study by rustam et al. (2018) although with a different percentage range. the largest percentage of sand texture is at station 10 with the sand composition of 99.8 % compared to gravel with 0.2 %. only at station 3 the percentage of gravel is greater than the percentage of sand that is 50.1 % gravel and 49.9 % sand. this result is different from research conducted by van den bergh et al. (2003) which states that deposition in the bay is dominated by clayey silt. the presence of coarse-sized sediments shows that the currents and waves in the area are relatively strong, coarse fractions are generally deposited in open areas associated with the high seas, while fine sediments deposited on currents and waves are completely calm. oceanographic conditions in the southeast and southwest of panjang island with stronger currents because sedimentary coarse-sized (sand-gravel) sediments to quickly settle, while the fine fraction cannot settle and are carried away to quieter places. clay and silt grains are usually deposited in waters with deep depth contours because of the very fine grain size that is easily trapped in the contours of the deep ocean floor (karl, 2001). coarse sand and gravel follow the law of the principle of deposition or erosion (force to lift). for finer grain deposition, what is needed is a current with a low speed and relatively deep depth (setiady et al., 2015). fig. 4. compositions of sediment fraction 1,1 0,9 50,1 4,6 27,8 6,2 39,3 1,9 0,8 0,2 14,5 1,4 2,6 11,9 0,1 98,9 99,1 49,9 95,4 72,2 93,8 60,7 98,1 99,2 99,8 85,5 98,6 97,4 88,1 99,1 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 f r a c ti o n ( % ) station gravel sand harahap et al./ jgeet vol 6 no 2/2021 103 3.2 distribution of sediment in this study, the distribution of sediment is described based on the grain size and the classification of sediment. grain size is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. widely accepted and used as the practical standard for objective and detailed description of grain size needed for communicating observations and deductions about sediment and sedimentary rocks (blair and mcpherson, 1999). the results of processing sediment samples at each station obtained that the grain size of sediments in the waters around panjang island ranged from -0.7 to 2.6 in the phi scale. the smallest sediment grain size is 2.6 in phi units located at station 9, located right in the middle of the bay (southeast of panjang island waters). meanwhile, the largest sediment size is at station 3 with a phi value of -0.7 located in the southwestern waters of panjang island. we can also see that of the 15 sampling stations, there are 4 stations in the area with a grain size of 0-1 phi scale, i.e. stations 4, 5, 7, and station 14. most of the distribution stations are in areas that have sediment grain size measuring 1 to 2 phi scale which is as many as 7 stations. the seven stations are sequences 1, 2, 6, 8, 11, 12, and 13. in the meantime, there are 3 stations i.e. stations 9, 10, and station 15. meanwhile, only station 3 is in the area with sediment grain sizes of -1 to 0 phi scale (fig. 5). stations 3, 4, 5, 6, and station 7 can be said to represent the area in the western part of the bay which is an area that is adjacent to the industrial area, fishing settlement, and port area. the process of developing the bojonegoro port is possible to have brought relatively large size sediment grains to this area. sediment at station 3 has the largest grain size, this is because the area at the sampling point is the location closest to the location of port development activities. research conducted by satriadi (2013), illustrates that the direction of sediment transport does indeed lead to this region. this is in line with the results of research conducted by rustam et al. (2018) around the coast of banten bay, the texture of the sediments found reflects the existence of “reworked” sediment due to dredging during the construction of the bojonegara port (port construction began in 2005). fig. 5. map of sediment grain size distribution pattern the pattern of sediment grain size distribution is interpolated from the phi value at each station. the output value for a cell using idw is limited to the range of the values used to interpolate. because idw is a weighted distance average, the average cannot be greater than the highest or less than the lowest input (watson and philip, 1985). the interpolation results are then reclassified based on the range of sediment grain size which can be seen in table 2 so that it is obtained divided into four classes as seen in fig. 5 the pattern of sediment grain size distribution shows that from the west to the center of the bay, the grain size of the sediment is getting smaller. furthermore, from the middle part of the bay towards the east, the size of the sedimentary grain shows a trend of enlarging again. large grains will settle to areas close to where the sediment was originally originated from, while small grains can be transported further. fine sediments will be easier to move and tend to be swept faster than coarse size because they are transported in the form of suspension (nugroho and basit, 2014). sedimentation of fine sediment grains can prevent the flow of waters in these locations tends to be quiet because the size of fine sediment grains is deposited in areas with slow current waters. further distribution analysis is related to the sediment class type. the size of sediment grains is key in determining sediment classification as shown in table 2. sediment classification refers to the shape, size, and three-dimensional arrangement of the particles that make up sediment or sedimentary rock. classification for sediment and sedimentary rocks is widely used because of its objectivity and practicality. this classification is a flexible polynomial scheme in which various sediment attributes are systematically listed. the roots of this scheme are the textural classes (e.g., gravel sand), which are qualified by other attributes in an adjective string (blair and mcpherson, 1999). as the results of the sediment grain size analysis previously presented, it shows that the sediment at the study site is dominated by sand. the type of sand sediment that covers on the bottom of the water at the study site has a class type in the category of very coarse 104 harahap et al./ jgeet vol 6 no 2/2021 sand to fine sand with a grain size range of 1.00 0.025 mm. this shows that the sediment has undergone a deposition process. the deposition process is characterized by the deposition of fine to coarse-sized sediments (nugroho and basit, 2014). furthermore, if we look at fig. 6, it can be seen that the pattern of distribution of this type of sand sediment type changes following the pattern of water depth contours. from the west to the middle of the waters have a distribution pattern from coarse sand to fine sand. in the eastern part, surface sediment is dominated by coarse sand. in the middle of banten bay, it is dominated by finer sand sedimentary types, with the right pattern between sediments with medium sand types. this is due to its location being protected by panjang island with waters deeper than its surroundings, while the type of sediment in the east is dominated by medium sand. fig. 6. map of surface sediment texture distribution in the waters around panjang island, banten bay 4. discussion the difference and distribution of sediment grain size are influenced by several factors, such as distance from the coastline, distance from the source (river), source of sediment material, topography, and sediment transport mechanism (abuodha, 2003). referring to gemilang et al. (2017), the more towards land or near river mouths and mangrove areas, the grain size of the sediment tends to be more subtle, while the grain size facing the open sea and further from the river mouth the grain size is coarser. this explains the reason why the size of sediment grains taken away relatively far from river mouths in waters around panjang island is greater than those taken around transitional waters from land to sea or in river mouths, as a study conducted by rustam et al. (2018). the grain size of sediments tends to be more coarse taken at sample points far from land, indicating that sediment deposits in the area have relatively strong currents and waves because coarse fractions are generally deposited in open areas associated with open seas (nugroho and basit, 2014). the sediment type obtained in this study only consists of gravel and sand, it is possible, because the sampling points of the station are located in the middle of the bay which is relatively far from the mainland, especially the distance from the river mouth. the pattern of direction and speed of the current is also a determining factor for the distribution of sediments in areas rather far from the mainland. coastal areas close to the mainland to the shallow waters around them, fluvial processes, tides and waves, and their interactions are the main controlling factors in the process of sediment deposition. these factors have a significant impact on the patterns of sediment distribution and sedimentary facies produced, as well as the architecture and morphology of sedimentary units (ainsworth et al., 2011, 2008; boyd et al., 1992; galloway, 1975; hoitink et al., 2017). current movements that occur in banten bay are generally generated by tidal forces as well as wind for surface currents (wisha et al., 2015). at high tide or low tide, the speed of the current can increase so that the sediment that has been deposited can move to another place due to erosion and sedimentation (triatmodjo, 1999). although the position of banten bay is surrounded by many small islands which are a barrier to the entry of large energy into the inner bay waters and also makes it limited in water hydrodynamics, but the influence of strong currents results in a coarse fraction settling faster in the region. in general, the distribution of sediment type is distributed in groups from north to south with medium sand type dominating surface bottom sediments in the study area. 5. conclusions based on the results of this study, it is known that the type of sediment distributed in the waters around panjang island, banten bay consists only of sand and gravel. sand composition ranges from 49.9 99.8 % and gravel ranges from 0.2 % to 50.1%. this means that most of the surficial sediment in the study area is sandy with an average composition of 89.1 %. sediment grain size ranges from -0.7 to 2.6 in the phi scale. based on the sediment grain size, there are 4 texture categories i.e. very coarse sand, coarse sand, medium sand, and fine sand (measuring 1.00 0.025 mm). medium sand is a texture that dominates surface sediments in the waters around panjang island, banten bay. changes in sediment texture show a transverse distribution pattern (from west to east). in the western part, the sediment texture is more varied, however, it is more dominated by the coarse sand sediment texture, while in the eastern part it is dominated by medium sand type harahap et al./ jgeet vol 6 no 2/2021 105 sediment texture. meanwhile, the distribution of sediment types is distributed in groups in one type from north to south. in general, the pattern of sediment distribution follows the pattern of water depths, where the finer texture i.e. fine sand occupies deeper areas. acknowledgments thank to the leaders and staff at the faculty of fisheries and marine sciences, universitas padjadjaran who have provided support so that this study activity can be carried out well. furthermore, thanks to komitmen team that has helped in conducting field surveys and also to the referees for their constructive comments and suggestions. references abuodha, j.o.z., 2003. grain size distribution and composition of modern dune and beach sediments, malindi bay coast, kenya. j. african earth sci. 36, 41– 54. https://doi.org/10.1016/s08995362(03)00016-2 ainsworth, r.b., flint, s.s., howell, j.a., 2008. predicting coastal depositional style: influence of basin morphology and accommodation to sediment supply ratio within a sequence stratigraphic framework, in: hampson, g.j., steel, r.j., burgess, p.m., dalrymple, r.w. 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geoscience, engineering, environment, and technology vol 6 no 4 2021 mairizki, f., et al./ jgeet vol 6 no 4/2021 243 research article hydrogeochemical and characteristics of groundwater in teluk nilap area, rokan hilir, riau fitri mairizki1,*, arief yandra putra2, widya adiza putri1, ferdyansyah1 1 department of geological engineering, faculty of engineering, univeristas islam riau, pekanbaru, indonesia 2 department of chemistry education, faculty of teacher training and education, universitas islam riau, pekanbaru, indonesia * corresponding author : fitrimairizki@eng.uir.ac.id tel.:+62-852-7897-3771 received: nov 21, 2021; accepted: dec 24, 2021. doi: 10.25299/jgeet.2021.6.4.8136 abstract groundwater plays important role as the main water resource for human needs. the vulnerability of groundwater to contaminants both naturally and by human activities can be not avoided as a trigger for groundwater quality degradation. hydrogeochemical become important highlights in groundwater studies because groundwater conditions in quality and quantity influenced by the geological formation of rock minerals in aquifer. naturally, the condition of the research area which consists of peat swamps can also affect the characteristics of groundwater. the aims of this research are to determine groundwater types and groundwater facies in study area with an analytical approach using stiff diagram and piper diagram. the method used was purposive sampling by collecting data from dug wells at the research site. 5 samples from dug wells were used as representatives in the groundwater facies analysis. the groundwater facies analysis was carried out by measuring the concentration of major ions such as na, k, ca, mg, cl, so4, and hco3. the highest groundwater level was in the northern part of study area (7,84 m) while the lowest groundwater level was in the southwest part of study area (2,05 m). the results showed three types of groundwater based on stiff diagram as sodium chloride (nacl), sodium sulfate (naso4) and magnesium sulfate (mgso4). the lithology conditions that composed the aquifer affected the facies or origin of groundwater. the alluvium layer in the research area which rich in sodium (na+) minerals with chloride (cl-) or sulfate (so42-) anions forms chloride sulfate facies (cl+so4) which were located in the middle to the south of the study area and sodium (potassium) chloride (sulfate) facies (na(k)cl(so4)) which were distributed in the northern part of study area. keywords: hydrogeochemical, groundwater type, groundwater facies, stiff diagram, piper diagram 1. introduction groundwater plays important role because it has become the main water resource for human needs such as drinking water, domestic purposes, industrial, irrigation and the others (taufiq et al., 2017). groundwater is an economic and strategic commodity in several areas. it is estimated that 70% of population’s clean water needs and 90% of industrial water needs come from groundwater. groundwater has several advantages including groundwater quality relatively better than surface water and unaffected by the season, groundwater reserves easier to obtain, and it does not need network to distributed. on the other hand, the vulnerability of groundwater to contaminants both naturally and by human activities can be not avoided as a trigger for groundwater quality degradation (mairizki, f., and cahyaningsih, c., 2016). the presence of pollutants from garbage disposal area (satrio, 2017), industrial activities (naslilmuna et al., 2018) and agriculture or domestic waste (sasongko et al., 2014) are some factors that causing a decrease in both on the quality and quantity of groundwater. utilization activities, management, monitoring and evaluation of groundwater resources must refer to the standards that have been set. for this reason, many research has been carried out on monitoring groundwater quality which used as a source of drinking water in various countries (annapoorna, h., and janardhana, m., r., 2015); (lalitha et al., 2016); (khan, a., and khan, m., a., 2018); (ibrahim, m., n., 2019); (siringoringo et al., 2019); (mairizki, f., et al., 2020). hydrogeochemical become important highlights in groundwater studies. this due to groundwater conditions in quality and quantity influenced by the geological formation of rock minerals that will form chemical elements or compounds. the interaction between groundwater and rock minerals in aquifer will dynamically affect the process of groundwater hydrogeochemical. there have been a lot of studies on hydrology, geochemistry and characteristics of groundwater (hadian et al., 2017); (dianardi et al., 2018); (afriyani et al., 2020); (putra, d., b., e., et al., 2021). therefore, the aims of this research are to determine groundwater types and groundwater facies in study area with an analytical approach using stiff diagram and piper diagram. 2. study area teluk nilap village is located in kubu babussalam subdistrict, rokan hilir, riau province. topographically, this village is low land with altitude about 6-10 m from sea level and groundwater source depth ≤ 5 m. the people use groundwater for domestic purposes. however, the people in the study area feel a change in environmental condition including the decrease of groundwater quality. based on previous research, there were known that most of groundwater in the study area was yellow-brown in color (putra, a., y., and http://journal.uir.ac.id/index.php/jgeet 244 mairizki, f., et al./ jgeet vol 6 no 4/2021 mairizki, f., 2019), had an acidic ph (putra, a., y., and mairizki, f., 2020), and contained fe metal in high level (putra, a., y., and mairizki, f., 2020). according to regional physiography, the study area is a part of central sumatra basin which consist of two formation including older superficial deposits (qp) and young superficial deposits (qh) (fig.1). the older superficial deposits consist of clays, vegetation rafts, silts and clayey gravels. on the other hand, young superficial deposits composed by clays, silts and clean gravels, vegetation rafts and peat swamps. astronomically, the research area is located between 2o0’27.82’’-2o1’48.56” north latitude and 100o37’24.65”100o38’43.84” east longitude with an area ± 6,78 km2 and 15 dug wells as samples (fig.2). fig. 1. regional geological map of study area fig. 2. dug well location map of study area 3. methodology the method used was purposive sampling by collecting data from dug wells at the research site. groundwater level data such as topographic data, elevation and depth of dug wells were measured directly in the field. the groundwater types and facies analysis were carried out by measuring the concentration of major ions such as sodium (na), potassium (k), calcium (ca), magnesium (mg), chloride (cl), sulfate (so4), and bicarbonate (hco3) at the water quality laboratory, faculty of civil engineering, bandung institute of technology based on standard methods for the examination of water and wastewater (apha). 5 samples from dug wells were used as representatives in the groundwater facies analysis. groundwater sampling using plastic bottle, the bottle must be full fill of groundwater, there should be no air bubbles in it, and the water temperature was kept in a stable condition to prevent the change of chemical component in water. the measurement results were analyzed by using stiff diagram and piper diagram. stiff diagram was used to analyze dominant ions and groundwater types while piper diagram was used to identification groundwater facies. 4. result and discussion 4.1 groundwater flow direction map groundwater flow direction map had been generated from measuring the groundwater elevation in each dug well. there mairizki, f., et al./ jgeet vol 6 no 4/2021 245 were 15 dug wells measured in determining groundwater flow direction in research area. groundwater elevation was in range 2,05-7,84 m (table 1). table 1. information of groundwater dug well in study area well id depth (m) groundwater elevation (m) s1 3,34 7,84 s2 2,00 5,00 s3 3,50 4,75 s4 1,70 6,45 s5 2,20 6,80 s6 3,50 5,66 s7 1,50 3,00 s8 3,70 3,49 s9 1,10 5,50 s10 2,96 2,05 s11 2,60 5,10 s12 1,40 4,40 s13 2,60 4,10 s14 3,15 4,07 s15 1,68 3,88 based on groundwater flow direction map (fig.3), the northern part of research area has the highest groundwater elevation value, groundwater in this area flows in all directions to the locations with lower groundwater contours. the same thing happened in the southeastern part, where groundwater flows in all directions to locations with low groundwater contours. in contrast to the southwest, which has low groundwater level, this area gets groundwater recharge from all directions. fig.3. groundwater flow direction map 4.2 types and facies of groundwater the geochemistry of groundwater is affected by the geochemical reaction and water mixing or contamination from the surroundings. groundwater changes, especially depending on the relationship with the rock type and water composition. hydrogeochemical facies is one of the methods used to interpret flow patterns and origin of groundwater chemistry (gemilang et al., 2019). hydrogeochemical analysis shows several major ions that have significant role in the groundwater characteristics. the dominant ions found were sodium and sulfate (table 2) while the determination of groundwater facies uses the major ions concentration which has been converted into milliequivalents per liter (meq/l) (table 3). table 2. concentration of each major ion in groundwater sample (mg/l) table 3. concentration of each major ion in groundwater sample (meq/l) the presence of abundant sodium was influenced by the rocks that composed its aquifer which are sedimentary rocks. water trapped in sedimentary rock which is rich in clay minerals and stored for a long time will have sodium in high concentration. the presence of sulfate was found in sedimentary rocks in the form of sulfide minerals. when these minerals were weathered and contact with water, sulfur will be oxidized to sulfate ion which then dissolve in water. the presence of potassium in groundwater was not dominant, especially since this element is difficult to separate from its silicate bonds. some groundwater samples did not contain carbonate. this can be due to the high level of weathering in study area, the soil in humid climate area will have carbonate content that can be decrease because the leaching process. 4.2.1. stiff diagram of groundwater stiff diagram shows the water type based on dominant cation and anion in groundwater samples. several water types had found, such as sodium chloride (nacl), sodium sulfate (naso4), and magnesium sulfate (mgso4). sodium became governing cation to determined groundwater types, and sulfate became dominant anions that are ruling in determination groundwater types in research area (fig. 4, fig. 5, fig. 6). fig.4. stiff diagram of sodium chloride type (s1) fig.5. stiff diagram of sodium sulfate type (s2, s12) well id parameters (mg/l) na k ca mg cl so4 hco3 s1 113 7,61 11,7 15,3 125 61,1 158 s2 35,2 7,30 7,5 18,3 81,7 150 0 s7 35,3 5,88 15 30,1 62,3 279 0 s11 37,1 6,27 5,84 36,1 52,5 160 0 s12 45,3 7,68 11,7 11,6 58,4 82,5 45 max 113 7,68 15 36,1 125 279 158 min 35,2 5,88 5,84 11,6 52,5 61,1 0 aver 53,18 6,95 10,35 22,28 75,98 146,52 40,6 well id parameters (meq/l) na k ca mg cl so4 hco3 s1 4,91 0,19 0,58 1,26 3,52 1,27 2,59 s2 1,53 0,19 0,37 1,50 2,30 3,13 0 s7 1,53 0,15 0,75 2,48 1,75 5,81 0 s11 1,61 0,16 0,29 2,97 1,48 3,33 0 s12 1,97 0,19 0,58 0,95 1,64 1,72 0,74 max 4,91 0,19 0,75 2,97 3,52 5,81 2,59 min 1,53 0,15 0,29 0,95 1,48 1,27 0 ave 2,31 0,18 0,51 1,83 2,14 3,05 0,67 246 mairizki, f., et al./ jgeet vol 6 no 4/2021 fig.6. stiff diagram of magnesium sulfate type (s7, s11) 4.2.2 piper diagram of groundwater piper diagram used to identify the facies and evolution of groundwater in the study area. there are several groundwater facies determined from the cation triangle (left side), such as calcium type (a), sodium or calcium type (b), magnesium type (c) and no dominant type (d). sodium or calcium type and magnesium type were the dominant type of groundwater from cation plot. on the other hand, there are several groundwater facies determined from the anion triangle (right side), there are bicarbonate type (e), chloride type (f), sulfate type (g) and no dominant type (h). sulfate type was the most dominant type of groundwater from anion plot. therefore, the diamond of piper diagram showed several groundwater facies namely chloride sulfate water (l) and sodium (potassium) chloride (sulfate) water (p) (fig.7). fig 7. piper diagram of groundwater sample based on fig.7, it can be seen that there were two types of groundwater facies in research area. the first facies as alkaline earth water higher alkaline content predominantly chloride with 3 sample points (l). this facies characterizes the groundwater content enriched by chloride brine and generally sediment rocks rich in na+. the second facies as alkaline water predominantly sulfate-chloride with 2 sample points (p). this facies characterizes the origin of groundwater mixed with chloride brine, as well as interaction of rocks that rich in clay minerals from na+ dominant alluvium layer. the research area that composed by alluvium layer rich in sodium (na+) minerals with chloride (cl-) or sulfate (so42-) anions will form groundwater facies alkaline earth water higher alkaline content predominantly chloride or alkaline water predominantly sulfate-chloride (putranto et al., 2020). 4.2.3. groundwater facies distribution map according to the analysis of major ion content, stiff diagram and piper diagram, the groundwater facies were divided into two types, namely na(k)cl(so4) facies (p1) and cl+so4 facies (p2). na(k)cl(so4) facies were found in s1 and s12 which located in the northern part of study area while cl+so4 facies were found in s2, s7 and s11 which are located in the middle to the south of the study area (fig.8). fig 8. groundwater facies distribution map 5. conclussion groundwater conditions in quality and quantity influenced by the geological formation of rock minerals in aquifer. the condition of research area which consists of peat swamps also affect the characteristics of groundwater. in conclusion, the highest groundwater level was in the northern part of study area at s1 (7,84 m) while the lowest groundwater level was in the southwest part of study area at s10 (2,05 m). the results showed three types of groundwater based on stiff diagram as sodium chloride (nacl), sodium sulfate (naso4) and magnesium sulfate (mgso4). the lithology conditions that composed the aquifer affected the facies or origin of groundwater. the alluvium layer in the research area which rich in sodium (na+) minerals with chloride (cl-) or sulfate (so42-) anions forms cl+so4 facies which were located in the middle to the south of the study area 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kagabu, m., iskandar, i., hutsoit, a., m., shimada, j. 2017. impact of excessive groundwater pumping on rejuvenation processes in the bandung basin (indonesia) as determined by hydrogeochemistry and modeling. hydrogeology journal, 26(4), 1263-1279. http://dx.doi.org/10.1007/s10040-017-1698-8. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). https://doi.org/10.12911/22998993/%2099740 https://doi.org/10.20961.ge.v4i1.%2019176 http://doi.org/10.22216/jk.v5i1.5277 https://doi.org/10.4491/eer.2020.006 https://doi.org/10.29122/jtl.vl8il.48 http://dx.doi.org/10.1007/s10040-017-1698-8 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 kusnadi, s/ jgeet vol 02 no 04/2017 272 slope stability analysis based on type, physical and mechanical properties rock in teluk pandan district, east kutai regency, east kalimantan province sujiman kusnadi 1, * 1 faculty of engineering, university kutai kartanegara tenggarong, east kalimantan. * corresponding author : kasnadisujiman@gmail.com received: nov 7, 2017. revised : nov 15, 2017, accepted: nov 30, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.87 abstract the research title is slope stability analysis based on type, physical and mechanical properties rock in teluk pandan district, east kutai regency, east kalimantan province. aimed to determine the lithology in the research area and to find out how the amount of slope that will be a landslide at that location. how the research with the analysis of coring drilling results are then analyzed in the laboratory of rock mechanics to get the characteristic of physical and mechanical properties of the rocks. methods of data analysis using hoek and bray methode with rockslide software. the results showed that in the area study has a sedimentary rock lithology fine to medium detritus, such as claystone, siltstone and sandstone, as well as inserts are coal and shale. based on the results of laboratory analysis of rock mechanics obtained density between 2,648 to 2,770. while the test results obtained value triaxial cohesion between (6.66 9:05) kg / cm 2 , friction angle in between (37.19 44.08) o , cohesion residual (2.72 3.10) kg / cm 2 , residual friction angle (27.22 32.44) o . while the direct shear test the cohesion of the summit between (6.66 9:05) kg / cm 2 , friction angle in the cohesion peak (36.15 43.00) o , cohesion residual (2:22 to 3:10) kg / cm 2 , friction angle in the cohesion residual (37.22 33.85) o . the simulation results stability of the slope stability hoek and bray using rockslide software, the result is that if the slope with a single slope stability, the stability of the slope is 60 o , and if the slope with the stability of the slope overall stability of the slope is 48 o . keywords: slope stability, rock type, rock physical properties, mechanical properties of rocks 1. introduction in principle, landslides occur when the driving force on the slope is greater than the barrier force. retaining force is generally influenced by rock strength and soil density. while the driving force is influenced by the magnitude of the slope angle, water, weights and soil type of rock soil. the threat of landslide usually occurs in wet months, due to increased rainfall intensity. the long dry season causes the evaporation of water in the soil surface in large quantities, resulting in the emergence of pores or cavities in the soil, which resulted in cracks and ground fractures. when it rains, water will infiltrate the cracked soil so that the soil will quickly expand again. at the beginning of the rainy season and the high intensity of rain usually occurs water content in the soil becomes saturated in a short time (hoek and bray, 1974 in koesnaryo.et. al., 2003). heavy rains that descend at the beginning of the season can cause landslides, because through soil fractures or water rocks will enter and accumulate at the bottom of the slope, causing lateral movement. with the vegetation on the surface will prevent the occurrence of landslides, because the water will be absorbed by plants and plant roots will also work to bind the soil. the steep slopes or cliffs form will enlarge the driving force (nandi, 2007). the study associated with avalanches in 2012 mention that stable slope design studies are needed in the exploitation of coal mines, especially in open pit systems. mining requires slope design in various ways. in rock formations containing a layer of loose material such as quartz sand in the balikpapan formation as well as kampung baru formation in sangasanga, east kalimantan, the determination of the weighting of the slope masses needs to be corrected to find the safest slope angle. the smr (slope mass rating) correction results involving the smr value and rmr (rock mass rating) are: 1) smr = 68.22 ln (rmr) 225.5 (for logarithmic equations); 2) smr = 1,262 rmr 22.30 (for linear equations); 3) 0.082 rmr 1.580 (for power equations); and 4) smr = 9,191e0,029 rmr (for exponential equations). meanwhile, according to azizi., ma, and handayani., r. in 2011, on characterization of input parameters for single slope stability analysis (case study at pt tambang batubara bukit asam tbk, tanjung enim, south sumatera) the results showed mailto:kasnadisujiman@gmail.com kusnadi, s / jgeet vol 02 no 04/2017 273 the distribution of cohesion function and friction angle in is uniform, the distribution of density function is beta, and the distribution of security factor function is uniform. up to 40-meter slope height and slope angle of 60o, the slope is still stable (probability slope of zero slopes). the landslide disaster in various parts of the world is so devastating, such as the incident in madukara sub-district, banjarnegara district, central java on march 27, 2016. the regional disaster management agency reported that the damaged houses 17 units were lightly damaged 2 units, and were directly threatened by landslide 7 units, with a total of 267 refugees from 73 families (tempo.co. banjarnegara dated march 29, 2016). implementation of the model applied by hoek and bray is expected to overcome the problem of avalanche, especially in east kalimantan. 2. methodology the mass of rocks scattered in nature is a collection of unequal materials (heterogeneous). each rock/material has characteristics that differ from each other. characteristics of rock mass in a particular area, it is necessary to measure or observe directly to the material or rocks in the area. the field investigation that has been conducted, intends to take samples of rock material located in the research area. the samples taken are cores from full coring geotechnical drilling. each layer of lithology is sampled as a representation of lithology in the field. method of drilling activity is by coring method. boring unit has used the type of jacro 175 with the ability to penetrate layers of rock up to a depth of ± 100-150 m below the surface. coring is a coal drilling activity to sample coal seams using a core barrel with double tube. the coring results obtained an example of rock layers, which will be used for coal quality analysis and physical analysis and geomechanics analysis. table 1. bore hole location no . bore hole locatio n eastin g (m) northin g (m) elevati on (m) 1 geotecnic teluk pandan 25,252 527,998 122 laboratory testing. laboratory testing is done to know the material characteristics that are in the research location. the parameters to be used in the modelling are the physical properties and mechanical properties of the material (soil/rock). rock samples for geotechnical studies were tested in rock mechanics laboratories. types of tests that have been carried out are physical properties, namely: original sample weight, sample volume, original content weight, moisture content, dry content weight, specific gravity, pore number, porosity, degree of saturation and dry content weight, saturated content weight, triaxial test, un-confined compressive strength (ucs), and shear test. the results of laboratory testing from the field are physical properties test, uniaxial traction strength test and triaxative compressive strength test, then analyzed using hoek and bray method (1974), with rockslide system 3. results and discussion the material in nature is generally is a stable state (stabile), meaning that the stress distribution of the material is in equilibrium. however, if there is any activity causing the disruption of the slope material stress, the forces present in the soil or rock will seek to achieve a new equilibrium by reducing the load, especially in the form of landslide. factors affecting slope equilibrium. stability of a slope is influenced by several things, among others: 1. geometry of slope geometry slopes consisting of slope and altitude greatly affect the stability of a slope. the bigger the slope and the height of the slope, the steadiness diminishes. in addition, hoarding and slaughtering activities will cause the addition and subtraction of the load so that the material stability will change. 2. physical and mechanical properties of rocks physical properties of rocks that affect the steepness of stability include: the weight of the contents (density), porosity, and water content. while the mechanical properties of rocks that affect the steepness of the slope include: compressive strength (ucs), tensile strength, and shear strength (cohesion and internal shear angle). 3. geological structure and characteristics geological structures that influence the steepness of the slope include: fault, joint, fold, bedding plane, and crack. the geological structure is a weak field and as well as a place to seep the water and can cause the occurrence of tension crack causing rocks to become easily landslides. 4. hydrological and hydrogeological conditions on the slope the existence of water, especially ground water, affects the stability of a slope, because the soil water has a pressure known as pore water pressure which can cause an uplift force which is very influential on the occurrence of landslide due to decrease shear strength. 5. external styles external forces that can affect the stability of a slope include: vibrations caused by earthquakes, explosions, loading and others. 6. weathering weathering greatly affects the stability of the slope. temperatures that quickly change in a short time will accelerate the process of weathering rocks. for tropical weathering occurs faster. therefore, rock outcrops on the tropical slopes will be more rapidly weathered and this leads to an avalanche of slopes. 274 kusnadi, s / jgeet vol 02 no 04/2017 3.1 condition of lithology of research area based on the topographic map of the study site, there are variations in elevation ranging from 30 100 m. weakly to moderate corrugated morphological conditions are found 100% in the work area (5 20º slope angle). the lithology of the research area was sedimentary rock which is dominated by sandstone, siltstone and claystone with main composition is quartz. in addition, there are rocks, sometimes present conglomerates. the geological structures encountered are shear faults and the presence of synclinal structures. the flow patterns in the study area are controlled by rock resistance levels that tend to be the same between the formations. the growing flow pattern is subdendritic. subterranean lithologic conditions in the drilling location from the ground up are as follows: rocky, grey, medium hard, open packing, medium sorting, coating structures, medium permeability, sometimes very delicate sandstones. the thickness of this rock unit is 9.6 meters. above it is deposited in harmony of claystone, grey colour, coating structure, medium hardness, silica, good sorting, closed packing, poor permeability, clay grain size, thickness of this rock unit is 8.70 meters. next is deposited again sandstone unit, light gray, medium hardness, fine grain, layer structure, there are carbonstone clay inserts, clay and coal, good sorting, closed pack, medium permeability, thickness of this rock unit is 21.65 meter. above the sandstone unit there is a unit of claystone, the thickness of this rock unit is 26.25 meters, with sandstone inserts, coal and carbonaceous clay. above it again there are rocks, with thick 10.63 meters, with coal inserts and carbonaceous clay. then on top of it there are a claystone 5.42 meters thick with coal inserts, and carbonaceous clay. constantly precipitated consecutively rocks, then sandstones, clay again and sandstones, last claystone then sandstone. fig. 1. columnar section of borehole in teluk pandan district. east kutai. east kalimantan kusnadi, s / jgeet vol 02 no 04/2017 275 3.2 slope-forming materials the most dominant type of drilling is 31,04%, followed by 22,02% in sequence of stone, 15,6% sandstone, 15.12% carbonaceous clay, 7.28% sandstone, 6.80% coal and 1.98% soil. rock types can be seen in table 2 and fig. 2. table 2. lithology type of drilling no. lithology percent 1 soil 1.98% 2 claystone 31.04% 3 carbonaceous clay 15.12% 4 siltstone 22.02% 5 sandstone 7.28% 6 coal 6.80% 7 sandy clay 15.76% fig 2. type of rock in drilling research area 3.3 strength of rock in the drilling based on rqd (rock quality designation) the bottom layer has an ugly strength and then above the coal coating strength is good to very good, then the rocks above. the types of lithology and drilling can be seen in table 3. condition of rock strength at drill hole based on result of laboratory analysis of rock mechanics obtained by weight of type between 2,648 until 2,770. in the triaxial test there was total cohesion between (6.66 9.05) kg / cm2, total angle between (37.19 44.08) o , residual cohesion (2.72 3.10) kg / cm2, residual slide angle (27.22 32.44) o . while on the direct shear test the peak cohesion between (6.66 9.05) kg / cm2, the inner shear angle at peak cohesion (36.15 43.00) o , residual cohesion (2.22 3.10) kg / cm2. deep sliding angle on residual cohesion (37.22 33.85) o . this indicates that the rocks at the study sites are included in moderate strength. the existing lithology in the study area is generally moderate to moderate sedimentary rocks, such as claystone, limestone and sandstone, and there are coal inserts, flakes. the condition of drilling result lithology in telukpandan subdistrict of east kutai regency. east kalimantan province can be seen in fig. 3. table 3. lithology and rqd of research area nomor lithology rqd (%) 1 claystone 87 2 sandstone 27 87 3 claystone 50 89 4 sandstone 67-97 5 claystone 53-93 6 sandstone 100 7 claystone 33-100 8 carbonaceous clay 99 9 sandstone 100 10 clayey sand 90-100 11 carbonaceous clay 31 12 siltstone 11-87 13 claystone 85 14 siltstone 78 15 coal 100 16 siltstone 81-100 17 sandy clay 38-96 18 sandstone 10-97 19 coal 57-100 20 claystone 90 21 sandy clay 32 22 claystone 32 23 siltstone 56-66 24 claystone 0 25 siltstone 0 fig. 3. drilling lithology conditions in telukpandan subdistrict, east kutai regency. east kalimantan province. 0,00% 5,00% 10,00% 15,00% 20,00% 25,00% 30,00% 35,00% percent 276 kusnadi, s / jgeet vol 02 no 04/2017 table 4. characteristics of rock strength at drilling no. lab 1 2 3 4 5 rock code sample r13 r24 r33 r53 r64 soil and rock classification zst sst zst sst sst heavy-volume characteristics water content w % 5.38 6.84 4.88 9.75 5.19 specific gravity gs 2.770 2.676 2.692 2.648 2.703 original content weight ɣ g/cm 3 2.494 2.210 2.455 2.244 1.979 weight of dry contents ɣd g/cm 3 2.366 2.069 2.340 2.044 1.881 weight of saturated content ɣsat g/cm 3 2.512 2.296 2.471 2.272 2.185 porosity n % 14.56 22.70 13.05 22.78 30.40 pore number e 0.17 0.29 0.15 0.30 0.44 the degree of saturation sr % 87.51 62.38 87.49 87.48 32.11 plasticity characteristics the liquid limit ll % 28.31 np np np 23.38 plastic limit pl % 15.61 np np np 14.86 shrinkage limit pi % 12.69 np np np 8.52 shrinkage index sl % 0 np np np 0 activity a % 1.81 np np np 1.06 grain graduated characteristics clay (bs < 0.002 mm) (astm < 0.005) % 7 0 hard of sedimentary rock 0 8 % 27 0 0 20 silt % 63 4 4 32 fine sand % 10 86 hard of sedimentary rock 91 21 medium sand % 0 0 5 27 coarse sand % 0 0 0 0 gravel % 0 0 0 0 characteristics of strength triaxial test total cohesion c kg/cm 2 8.22 7.28 9.05 6.66 7.79 total shear angle φ o 37.19 44.08 39.28 43.61 43.57 residual cohesion cr kg/cm 2 2.79 2.54 3.10 2.32 2.72 residual shear angle φ o 27.22 32.44 29.28 31.72 32.23 direct shear test peak cohesion cp kg/cm 2 8.22 7.28 9.05 6.66 7.79 total of shear angle φ o 36.15 43.00 38.22 42.52 42.48 residual cohesion cr kg/cm 2 2.74 2.43 3.02 2.22 2.60 angle of internal friction φ o 27.22 33.85 29.53 33.41 33.37 note: np : non-plastics, cst : claystone, zst : siltstone, sst : sandstone 3.4 analysis and recommendations of slope stability of research areas 3.4.1. highwall slope research area a) single slope (individual slope) stability analysis for single slopes is done with the following approach: a. single slopes that will be studied in the form of slopes that will occur avalanches. b. single slope modelling was performed on each lithology with 10 m high simulation with a slope angle of 60º. c. the value of fk (security factor) as the basis 1.30. d. modeling is applied with the average properties approach of each lithology in the borehole. f. the simulation results can be seen in fig. 3. 3.4.2. overall slope (overall slope) the approach to performing an overall slope analysis that is represented by the properties of the drill hole slope stability simulation results in order to simplify the various parameters is as follows. a. the entire slope to be studied is a slope that will occur avalanches. kusnadi, s / jgeet vol 02 no 04/2017 277 b. the overall slope modelling is done on each cross section of geotechnical drilling by taking each rock unit in the study area. c. the overall slope in accordance with the recommendation is at the location of the drilling with angle 48 o for all rock type material. d. the value of fk (security factor) as the basis 1.30. e. model data input with average lithologic properties approach on drill hole. f. analysis on high condition of single slopes 10 meters by 3 meters. g. the simulation results can be seen in fig. 4. fig. 4. results from simulation without blasting in the research area conclusion the study, which is located in teluk pandan subdistrict, east kutai regency, east kalimantan province, has the following conclusions: 1. from the drilling results made known that the rocks that make up the research area are moderate-grained sandstone rocks with very fine-grained (clay). while based on rqd (rock quality designation) rock layers are rocks that have medium to good strength, but sometimes low power. 2. the result of slope stability analysis in the study area, with single slope and done on existing rock layers, then obtained a height of 10 m slope and slope angle of 60 º with security factor 1.30. but for the overall slope height slope of 100 m with slope angle of 48o and 3 meters, for all layers of rock with security factor 2,588. references aprilla f., dkk., 2014. analisis tipe longsoran dan kestabilan lereng berdasarkan orientasi struktur geologi di dinding utara tambang batu hijau,sumbawa barat. 1 jurusan teknik geologi, universitas gadjah mada, indonesia. seminar nasional kebumian ke-7 dan simposium pendidikan geologi nasional. jurusan teknik geologi, fakultas teknik, universitas gadjah mada, yogyakarta, 30-31 oktober 2014. p. 1-15. chambers, j. l. c, & daley, t., 1995. a tectonic model for the onshore kutai basin, east kalimantan, based on an integrated geological and geophysical interpretation. indonesian petroleum association, proceedings 24th annual convention, jakarta, (i):111 130. clay k., dooley t., ferguson a., poblet j., june 2000. tectonic evolution of sanga-sanga block mahakam delta kalimantan indonesia, aapg bulletin, 16(6):765-786 fetter.,c.w., 1994. applied hydrogeology. third edition. university of wisconsin. oshkosh. prentice hall. englewood cliffs. new jersey 07632. gordon h. wood, et all., 1988. coal resource classification system of the united state geological survey, circular p. 891. hall, r., 2001. cenozoic reconstructions of se asia and the sw pacific : changing pattern of land and sea, proceeding ipa 27 annual convention, p.153-184 koesnaryo., hariyanto. r, widodo. p., 2003. mekanika batuan untuk rekayasa pertambangan, jurusan teknik pertambangan, fakultas teknologi mineral, yogyakarta. p.161. nandi., 2007. longsor. jurusan pendidikan geografi. fakultas pendidikan ilmu pengetahuan sosial. upi. bandung. p.1-45. notosiswoyo. s., prodjosumarto. p., 1964., pengantar analisis kemantapan lereng, diktat kuliah, jurusan teknik pertambangan, fakultas teknologi mineral, itb bandung. p.1-76. rai. m. a., 1993. analisis kemantapan lereng pit design. disajikan dalam kursus perencanaan tambang, direktorat pertambangan umum, pusat pengembangan tenaga pertambangan. p.198. supriatna, sukardi, rustandi, peta geologi lembar samarinda skala 1 : 250.000, pppg bandung, 1994. 1. introduction 2. methodology 3. results and discussion 3.1 condition of lithology of research area 3.2 slope-forming materials 3.3 strength of rock 3.4 analysis and recommendations of slope stability of research areas 3.4.1. highwall slope research area 3.4.2. overall slope (overall slope) conclusion references e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol xx no xx 20xx rahmaniah, et al./ jgeet vol 6 no 4/2021 217 research article resistivity method for characterising subsurface layers of coastal areas in south sulawesi, indonesia rahmaniah1, ayusari wahyuni1*, muhammad fawzy ismullah massinai2, a mun’im1, muhammad altin massinai2 1physics department, faculty of science and technology, uin alauddin makassar, makassar, 92111, indonesia. . 2geophysics department, faculty of mathematics and natural science, hasanuddin university, makassar, indonesia. * corresponding author : ayusari_wahyuni@uin-alauddin.ac.id tel.:+62-853-9611-8764; received: jan 15, 2021; accepted: dec 28, 2021. doi: 10.25299/jgeet.2021.6.4.6242 abstract the data presented in this paper are related to the characterization of a subsurface layer of coastal area in south sulawesi. this research will fill the gap in the resistivity method study which is this method not yet use in the coastlines area, especially area influenced by seawater and coastal condition impact like south sulawesi. the method used in this study is the method of resistivity wenner configuration by taking the data 1-2 lines each region with lengths 45 m, 75 m, 105 m, and 120 m respectively. data processing using non-linear least square optimization with that of the 2d inversion software res2dinv. the results show that the area is underlain by two layers of lithologic sections. in some sections interpreted by sandy layer, clay, sandstone, alluvium, sandy in seawater and metal minerals. from the analysis of the layers, all regions show the resistivity minimum is 0.00849 ωm and 8.04 ωm maximum resistivity. the result of this research can give n insight to study the large coastal area subsurface. keywords: geo-electrical, wenner configuration, coastal area, resistivity, subsurface layers. 1. introduction rock lithology in an area has different types depending on the geological and climate conditions of the area. this paper focuses on examining subsurface lithology around the coast in 4regenciesand one city in south sulawesi. because south sulawesi is one of the provinces with almost all areas having coastlines, researchers want to find out lithological information around the coastal area, especially wanting to investigate further the potential of quartz sand around the coast of south sulawesi. geoelectrical methods are very commonly used in conducting subsoil or subsurface investigations for various cases. many studies have been done on this subject as follows: geotechnical and engineering site investigations (nur islami, 2019); groundwater explorations (island and balaji, 2013)(hafeez, sabet and zayed, 2018)(rabeh et al., 2018)(bayewu et al., 2018)(aboh, 2015); mapping subsurface structures (wo and bania, 2019); mapping of soil and groundwater contamination (xu et al., 2019)(ganiyu et al., 2020); environmental studies (wilson, ingham and mcconchie, 2006)(kumar, priju and prasad, 2015)(fadili et al., 2017); mapping of growth fault (khalili and mirzakurdeh, 2019); soil characterization for engineering purposes (arjwech et al., 2020)(an et al., 2020)(abudeif et al., 2019); ore deposit explorations (arjwech et al., 2020)(youssef, el-gawad and farag, 2018)(hariri et al., 2019); archaeological investigations (yilmaz et al., 2019); bedrock detections (woźniak and bania, 2019). the geoelectrical method is a method used to determine the nature of electric current in the earth by detecting it on the earth’s surface. this detection involves measuring the potential, current and electromagnetic fields that occur either by injection current or naturally. one of the geoelectrical methods used in the measurement of electric current and to study the subsurface geological conditions is the resistivity method. the wenner resistivity-meter is a measurement device using wenner configuration to determine the apparent resistivity of concrete facings. measurements are assumed to be carried out on a semi-infinite homogeneous material (bonnet and balayssac, 2018). this research will fill the gap in the resistivity method study which is this method not yet use in the coastlines area, especially area influenced by seawater and coastal condition impact like south sulawesi. this research’s main targets aredetermining the subsurface structures and lithology of the investigated site in the coastal area, which is 4 regencies and one city in south sulawesi, indonesia; pinrang regency, barru regency, maros regency, parepare city, and bone regency. the result of this research can give new information to use resistivity method in the coastal area and additional insight to find mineral potency in south sulawesi or another area which have large coastal area. 2. methods and materials a geoelectrical survey was done using the resistivity method with wenner configuration. data is collected by using a single channel resistivity. the wenner resistivity-meter is a measurement device using wenner configuration to determine the apparent resistivity of concrete facings. measurements are assumed to be carried out on a semi-infinite homogeneous material (bonnet and balayssac, 2018). the wenner method consists of four equispaced electrodes and the tips are placed in contact 218 rahmaniah, et al./ jgeet vol 6 no 4/2021 with the concrete surface. a current is sent through the two outer electrodes (figure 1). by measuring the voltages through the inner electrodes, the apparent resistivity is calculated through ohm’s law and the solution is given by the following equation: ρ = kv i fig 1. current and potential electrodes in the wenner configuration (aboh, 2015). from the figure 1, it can be seen that the distance c1pi = p2c2 = a and the distance c1p2 = p1c2 = 2a, using equation (1). where ρ is the apparent resistivity, a is the electrode spacing, v is potential measured between the inner probes and i the current applied through the outer electrodes (presuel-moreno, liu and wu, 2013) and k is wenner configuration factor (equation 2).the length of c1c2 and p1p2is5 meters. the location is on the edge of a river that has slightly watery soil conditions. data collection conditions with sunny weather or dry season. data collection was carried out on sunday,24 march2020. k = 2πa this research was conducted in march 2020 using the resistivity method with a wenner configuration. measurements were made 1 – 2 lines each location with lengths consist of 45 m, 75 m, 105 m, and 120 m. the location area shown located at the beachside is shown in figure 2 and the coordinate location of each point is shown in table 1. we chose five locations that assumed representative of coastal area in south sulawesi. the data analysis process was carried out to obtain a 2d crosssection and subsurface resistivity values. then the process of data interpretation is done by adjusting the geological conditions at the study site and connecting by the list of the telford table resistivity (table 2). images for the resistivity survey are presented as the cross-section of the resistivity profile. the data were interpreted by comparing with the geology of the area (figure 5) and matching with values of electrical resistivity of earth materials. rock boundaries indicated on the resistivity profiles are certainly based on the available lithological borehole information. the images obtained, which are based on the 2d inversion of the field data. the color bar indicates the range of electrical resistivity values in the unit of ohmmeters (ωm). the color scale is logarithmic and consistent with contour intervals (arjwech et al., 2020). thisstudy focusesonthe measurement of the field by resistivity meter. the number of data measurements isfive of the data field. (a) (b) fig 2. maps location study area: (a). pinrang regency; (b). pare-pare city (2) (1) rahmaniah, et al./ jgeet vol 6 no 4/2021 219 (a) (b) (c) fig 3. maps location study area: (a). maros regency; (b). bone regency; (c). barru regency. table 1. gps and elevation point gps location latitude longitude 1 3o 42' 17" 119o 37' 46" pinrang 2 4o 3' 11.9" 119o 36' 7.3" parepare 3 4o 3' 13.7" 119o 37' 10.3" parepare 4 5o 1' 55.7" 119o 28' 01.3" maros 5 5o 1' 51.6" 119o 28' 01.9" maros 6 4o 56' 45.6" 120o 18' 15.3" bone 7 4o 56' 43.4" 120o 18' 18.4" bone 8 4o 6' 26.6" 119o 36' 31.5" barru 220 rahmaniah, et al./ jgeet vol 6 no 4/2021 table 2. resistivity of minerals (w.m.telford, 1990) materials resistivity (ohm-meter) pyrite 0.01 – 100 quartz 500 800.000 calcite 1 x 1012 1 x 1013 rock salt 30 1 x 1013 granite 200 100.000 andesite 1.7 x 102 45 x 104 basalt 200 100.000 limestone 500 10.000 sandstone 200 8.000 shales 20 2.000 sand 1 1.000 clay 1 – 100 ground water 0.5 – 300 sea water 0.2 magnetite 0.011.000 dry gravel 600 10.000 alluvium 10 – 800 gravel 100 – 600 3. result and discussion resistivity measurements at the five points show inversion two-dimension results processed by res2dinv software. the interpretation of the electrical resistivity tomography section is based on table 2 and the geological condition around the data acquisition point. pinrang regency is the first point in this research. in this location, measure with 1 line which length of a line is 105 m with 5 m electrode spacing. the processing used in 3 iterations and got 5.3% on error. it is accepted on resistivity inversion processing. the resistivity section (figure 5) has depth with a range of 1.25 to 17.3 m and a resistivity range between 2.65 and 35.4 ωm. it can be interpreted as two layers. the first layer is characterized by relatively high electrical resistivity ranges, from 8.04 to 35.4 ωm. this layer was interpreted as sand until 17.3 m depth. on other hand, the second layer is characterized as a boulder by resistivity result between 2.65 and 5.55 ωm is a shalysand layer. the depth of this layer is around 6.76 to 17.3m. a mineral or rock has a different resistivity value, the size of the resistivity of rock and mineral depends on the factors that influence it and the electrical properties of the rock or mineral itself. the resistivity values for minerals or rocks that are conductors are in the range of 1-107 ωm for example sand, silt, clay, sandstone, and granite. the resistivity value is large when the rock or mineral can conduct small electric currents and the resistivity is small when the rock or mineral ability is large. based on the geological map in figure 4, namely the geological map of majene and palopo sheets, it is known that the rock composition of pinrang regency consists of alluvial deposits and andesitic sandstones. alluvial deposits consist of sand, clay, silt, and gravel. it is known that sand is a material whose main mineral constituent is quartz, clay is a mineral containing fused quartz, and it is also known that the oldest alluvial will produce granite. granite is an igneous rock that contains quartz. the interpretation of the resistivity section is confirmed by this explanation that pinrang consists of sand and shalysand. fig 4. geology map pinrang regency area rahmaniah, et al./ jgeet vol 6 no 4/2021 221 fig.5. an inverse model resistivity section, pinrang regency area pare-pare city is the second point measurement. this location consists of 2 lines with 120 m and 75 m length with 5 m electrode spacing. the research location is located on the geological map of pangkajene and watampone western parts, sulawesi with the qac formation, are the alluvium deposition, lake, and coast(van_bemmelen, 1970). the processing used by 5 iterations and got error are 16.7% on the first line and 23.6% on the second line. it is quite above standard but accepted on resistivity inversion processing. the resistivity section (figure 5) consists of two lines. the first line has depth with a range of 1.25 to 19.8 m while the second line is 1.25 to 12.4 m. the resistivity range on the first line is lower than the second line, between 0.0849 to 14.5 ωm. interpretation results by referring to the geological map (figure 7) and table 2 can be assumed that on the first line (figure 5, above) there is a type of layer with a resistivity value of 0.00849 – 0.177 ωm, which is at the electrode position at a distance of 45–75 m, and the electrode position is 90–105m at a depth of about 2 – 20m. meanwhile, at the resistivity value of 0.369 – 14.5 ωm, it can be assumed that the alluvium, lake, and beach sediment layers are quartz sand filled with seawater so that the resistivity value is relatively small at a depth of 0–198 m. in the second track (figure 6, below) after geoelectric measurements have been made with a track length of 75 m, it can be assumed that the first layer is a layer of quartz sand with a resistivity value of 8.35 – 26.5 ωm at a depth of 0–4m. while in the next layer, it is assumed that the sand contains seawater so that the resistivity value is relatively small, is 0.468 – 4.69 ωm at a depth of 3 – 12.4 m. it can show in fig 5.the blue color meaning is the low resistivity value, the green and yellow colors indicate moderate resistivity values and red to purple indicates high resistivity values. fig 6. an inverse model resistivity section, pare-pare city area. above: first line; below: second line. this research was conducted in the kuri caddi beach area, nisombalia village, marusu, maros regency, south sulawesi province. the data obtained using the resistivity method with the wenner configuration consists of 2 tracks with a track length of 120 m each with an electrode spacing of 5 m. the processing used 5 iterations and got errors are 20.5% on the first line and 16.9% on the second line. it is accepted although quite above standard on resistivity inversion processing. the resistivity section (figure 7) consists of two lines. all lines have depth with a range of 1.25 to 19.8 m. the resistivity range on the second line is lower than the first line, between 0.156 to 9.13 ωm geological conditions based on figure 9 (left), that the research location is in the qac formation, namely the alluvium and beach sediment formation in the form of gravel, shaly-sand, mud, and coral limestone. after data processing and interpretation by referring to geological maps and resistivity tables, it can be assumed that the resistivity results show similar geological conditions. the first line is consists of two layers (figure 7, above). the first layer is a layer of coastal sediment in the form of sand with seawater with a resistivity value of 0.302 – 0.956 ωm, at a depth of 0 – 10 m. while the resistivity value of 1.70 – 17.0 ωmcan be assumed as a layer of beach sediment in the form of sand at a depth of 3–19.8 m. in the second line (figure 8, below) it can be assumed that the first layer is a layer of beach sediment in the form of sand with seawater inserts with a resistivity value of 0.156 – 0.892 ωm which is located at a depth of 0 – 15 m. layers with resistivity values of 1.60 – 9.13 ωmcan be assumed to be a layer of beach sediment in the form of sand at a depth of 0 – 19.8 m. 222 rahmaniah, et al./ jgeet vol 6 no 4/2021 fig 7. geology map pare-pare city area fig 8. an inverse model resistivity section, maros regency. above: first line; below: second line. this research was conducted in the tete beach area, bone pute village, kec. tonra kab. bone, south sulawesi province. the data obtained using the resistivity method with the wenner configuration consists of 2 lines each with a length of 120 m with an electrode spacing of 5 m. the processing used in 5 iterations and got an error of around 26% on each line. it is accepted so it can continue to the interpretation step. the resistivity section (figure 9) consists of two lines. all lines have depth with a range 1.25 to 19.8 m. the resistivity range on every line is very low, around 0.156 to 2 ωm. geological conditions at the study site are in figure 10 (right) with the type of formation qac. qac formation: alluvium and coastal deposits. in the results of measurements and data processing, a subsurface image in the form of a 2d cross-section is obtained. in the process of determining the type of subsurface structure, it can be done by observing the geological map of the research location and table 2. in the first line (figure 8, above) there are several types of layers. the resistivity value of 0.126 – 2.01 ωm can be assumed to be a layer of alluvium and beach deposits in the form of quartz sand with seawater inserted at a depth of 0 – 198 m. while the resistivity value of 0.0417 – 0.0725 ωm can be assumed to be a mineral-containing layer because the dominant layer has a low resistivity value, which is at the electrode position of 15 – 25 m, 45 – 55 m, and 60 – 80 m. in the second line, it can be interpreted that the resistivity value of 0.129 – 2.87 ωm is suspected to be a layer of alluvium deposits and the beach is in the form of quartz sand with seawater inserted at a depth of 0 – 19.8 m. meanwhile, at a resistivity value of 0.0374 – 0.0695 ωm, it can be assumed that layers containing minerals are found at the electrode positions of 10 – 15 m, 45 – 60 m, and 75 – 85 m, the layer is suspected to be a mineral layer because the resistivity value is dominantly lower than the value of another resistivity. rahmaniah, et al./ jgeet vol 6 no 4/2021 223 fig 9. an inverse model resistivity section, bone regency. fig 10. geology map.left: maros regency area;right: bone regency area. fig 11. an inverse model resistivity section, barru regency area the last point in this research is barru regency. this research was conducted in kupa village, malluse tasi, barru regency, south sulawesi province. the location of data collection in barru regency is almost close to the location of data collection in the city of pare-pare, which is the point of measurement carried out on the coast. figures 10 show 1 line measurement using the wenner configuration.the processing used by 5 iterations and got 12.9% on error. it is accepted on resistivity inversion processing. the resistivity section (figure 11) have depth with range 0.75 to 7.46 m and resistivity range between 0.0946 and 4 ωm. the results of this line show two types of subsurface layers, the first layer in the form of quartz sand deposited with sea water which has a resistivity value of about 0.165 – 4.55 ωm at a depth of 0 – 6 m. the second layer is obtained the resistivity value of 0.0948 ωs. which is a layer that contains metal minerals at 2-∞ m depth. from this result also shows the similarity of data from research conducted in barru regency (ariansyah et al., 2020).at this location, only 7.46 m depth can be detected, due to the limited length of the line at the research site. the geological conditions at the study site are in figure 12 with the type of qac formation. qac formation: alluvium and beach deposits with lithology types of gravel, sand, clay, mud, and coral limestone. the resulting 2d cross-section confirms the geological conditions. overall interpretation results indicate the presence of several materials such as a sandy layer, shale/clay, sandstone, alluvium, sandy in seawater, and metal minerals. from the analysis of the layers, all regions show the minimum resistivity is 0.00849 ωm and the maximum is 8.04 ωm. it shows in table 3. 224 rahmaniah, et al./ jgeet vol 6 no 4/2021 fig 11. geology map barru regency area table 3. resistivity interpretation and their inferred lithologies. ves no. no of layers resistivity (ohm-m) depth (m) inferred lithology area / region 1 1 8.04-35.4 1.25-17.3 sandy layer pinrang 2 2.65-5.55 6.76-17.3 shaly-sand layer 2 1 0.00849 0.177 2-20 metal minerals pare-pare 2 0.369 14.5 0 -19.8 sandstone in seawater 3 1 8.35 26.5 0-4 sandy layer pare-pare 2 0.468 4.69 3 12.4 sandy in seawater 4 1 0.302 0.956 0 10 sandy in seawater maros 2 1.70 17.0 3-19.8 sandy layer 5 1 0.156 0.892 0 15 sandy in seawater maros 2 1.60 9.13 0 19.8 sandy layer 6 1 0.126 2.01 0 -19.8 alluvium layer bone 2 0.0417 0.0725 2-15 metal minerals 7 1 0.129 2.87 0 19.8 alluvium layer bone 2 0.0374 0.0695 1.25 10 metal minerals 8 1 0.165 4.55 0 6 sandstone barru 2 0.0948 2-∞ metal minerals conclusions in this research, the results show that the area is underlain by two layers of lithology sections. in some sections interpreted by sandy layer, shale/clay, sandstone, alluvium, sandy in seawater and metal minerals. from the analysis of the layers, all regions show the minimum resistivity is 0.00849 ωm and the maximum is 8.04 ωm. this result can give additional sightseeing and information on coastal development in the further. acknowledgments we want to give our biggest appreciation to lppm alauddin islamic university makassar. references aboh, h. o. 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(2018) ‘nriag journal of astronomy and geophysics iron ore prospecting based on very low frequency-electromagnetic and geoelectrical resistivity at wadi abu subeira , northeastern aswan , south egypt’, nriag journal of astronomy and geophysics. elsevier b.v., 7(2), pp. 253–263. doi: 10.1016/j.nrjag.2018.08.002. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 2 2021 buntoro et al./ jgeet vol 6 no 2/2020 81 research article feasibility study on the application of dynamic elastic rock properties from well log for shale hydrocarbon development of brownshale formation in the bengkalis trough, central sumatra basin, indonesia. aris buntoro1, c. prasetyadi2, ricky adi wibowo3, a.m. suranto1* 1* petroleum engineering department, universitas pembangunan nasional veteran yogyakarta, indonesia 2 geological engineering department, universitas pembangunan nasional veteran yogyakarta, indonesia 3 pt. pertamina (persero), indonesia *corresponding author : su_ranto@upnyk.ac.id tel : +62 8179432855 received: nov 30, 2020; accepted: may 20, 2021. doi: 10.25299/jgeet.2021.6.2.5944 abstract in modeling the hydraulic fracking program for unconventional reservoir shales, information about elasticity rock properties is needed, namely young's modulus and poisson's ratio as the basis for determining the formation depth interval with high brittleness. the elastic rock properties (young's modulus and poisson's ratio) are a geomechanical parameters used to identify rock brittleness using core data (static data) and well log data (dynamic data). a common problem is that the core data is not available as the most reliable data, so well log data is used. the principle of measuring elastic rock properties in the rock mechanics lab is very different from measurements with well logs, where measurements in the lab are in high stresses / strains, low strain rates, and usually drained, while measurements in well logging use the principle of measured downhole by high frequency sonic. vibrations in conditions of very low stresses / strains, high strain rate, and always undrained. for this reason, it is necessary to convert dynamic to static elastic rock properties (poisson's ratio and young's modulus) using empirical equations. the conversion of elastic rock properties (well logs) from dynamic to static using the empirical calculation method shows a significant shift in the value of young's modulus and poisson's ratio, namely a shift from the ductile zone dominance to the dominant brittle zone. the conversion results were validated with the rock mechanical test results from the analog outcrop cores (static) showing that the results were sufficiently correlated based on the distribution range. keywords: elastic rock properties, well log, shale hydrocarbon, brownshale formation 1. introduction the development of shale hydrocarbon requires depth interval information with high britteness values based on knowledge of geology and rock mechanics as a basis for hydraulic fracking planning that can connect natural fractures to drain hydrocarbons optimally (grieser and bray, 2007; jin et al., 2014). this research was conducted on brownshale formation, pematang group, bengkalis subbasin as the main source rock in the central sumatra basin based on well log data of well bs-03 (carnell, 1997; j. katz, 1995). the well log data from the well bs-03 is the only well that penetrates the brownshale formation which is used to determine the brittleness distribution of the brownshale formation with the crossplot correlation of poisson's ratio and young's modulus. if complete sonic log data are available, the elastic rock properties can be calculated, namely poisson’s ratio and young's modulus, where the crossplot of these parameters can be used to identify ductile and brittle region (grieser and bray, 2007). grieser & bray (2007) stated that ductile rocks have low young's modulus and high poisson's ratio, whereas brittle rocks have high young's modulus and low poisson's ratio. the brittleness of shale hydrobarbon can also be calculated from the sonic log data based on the transit time (∆t), which is processed first to produce p wave velocity (vp) and s wave velocity (vs) data, then used to calculate the poisson’s ratio and young's modulus which describe the ease of the rock to crack. the crossplot of the poisson's ratio and young's modulus shows that high young's modulus and low poisson's ratio in rocks tend to be brittle (alsaif et al., 2017). calculation of the elastic rock properties (poisson's ratio and young's modulus) from the well log measured by sonic high vibration frequencies, the value is not the same as the measurement in the lab (core). thus, a conversion must be done from dynamic to static using empirical equations (basuki, 2017; jin et al., 2014; luo et al., 2015). the poisson's ratio value for isotropic rocks varies between 0 0.5, but in general, poisson's ratio values range from 0.05 0.45. for example, shale has a poisson's ratio value ranging from 0.05 0.32 (rai et al, 2011). the value of the modulus of rock elasticity varies from one rock sample from one geological area to another, due to differences in rock formation and the minerals that form it (alfreds r. jumikis, 1979). 2. study area and brownshale formation in the central sumatra basin 2.1. study area of bengkalis sub-basin the study area is located in bengkalis sub-basin, riau province, indonesia, where the study site is the work area of two oil company operators, which contributed to the research data and allowed to publish this paper. 2.2. brownshale formation of pematang group the brownshale formation was deposited in a lacustrine depositional environment, which consists of fine layered shale, brown to black in color, which indicates a sedimentary http://journal.uir.ac.id/index.php/jgeet 82 buntoro et al./ jgeet vol 6 no 2/2021 environment with calm water conditions, consisting of delta deposits and turbidite fans (heidrick, 2018). the brownshale formation is rich in organic matter, and is the main source rock that supply hydrocarbons to oil and gas fields in the central sumatra area. the well bs-03 is located on the margin of the north bengkalis sub-basin depocentre and penetrates the brownshale formation within the eocene-oligocene pematang group, and is deposited in a lacustrine environment (longley, 1990). the brownshale formation, pematang group is only found in sub-surface, where the thickness can reach more than 1,800 meters (grieser and bray, 2007), oil-prone brownshale formation can reach a thickness of more than 580 meters. equivalent lacustrine rock stratigraphy, also characterized as an oil source rock, is found in the karbindo coal mine, kiliranjao sub-basin to the southwest of the bengkalis sub-basin, as a location for outcrop analog coring (heidrick, 2018; sunardi, 2015). fig 1. study area of bengkalis sub-basin (modified from (us energy information administration (eia), 2015) 3. methodology overview the research workflow is schematically shown in figure 2. since in-situ core data from the brownshale formation pematang group, bengkalis sub-basin were not available, the dynamic to static conversion of elastic rock properties from well log data of well bs-03 calculations validated with outcrop analog core data. figure 2 describes the process of calculating the static (core) and dynamic (well log) elastic rock properties (poisson's ratio and young's modulus). dynamic calculations from well log calculations must be converted to static, and validated with static data from the outcrop analog cores. 4. literature review determination of rock mechanical properties by laboratory tests can be done in the presence of core samples from the wells to be analyzed, but not all wells are cored, therefore an empirical approach is required in the equation with data obtained from well logs. sonic log is a logging tool that is used to determine the mechanical rock properties, whose working principle is to use sound speed waves that are sent or transmitted into the formation by the transmitter, where the sound reflected back will be received by the receiver. the time it takes for sound waves to reach the receiver is known as the transit time interval (δt). the speed of propagation of waves produces a variety of different types of waves, in which the primary wave (compression) and secondary wave (transverse) applications are the main types of waves. surface waves are currently more focused, namely the ultrasonic wave velocity is determined based on the travel time and the length of the path. the p wave has a higher velocity than the s wave, so that when it hits rocks, different wave types also occur different attenuation. experimentally, the s wave is more difficult to obtain than the p wave, but in its application the s wave is more widely used to calculate young's modulus (e) and poisson's ratio (ʋ). fig 2. research workflow core (out cr op analog)  poi sson s r at i o (n )  young s modul us (e) v – e cr osspl ot (st at i c) correl at ed wel l log dat a dynamic t o st at ic conver si on of el ast ic rock propert i es fr om w el l log rel at ed t o shale hydr ocar bon devel opm ent in t he bengkal i s tr ough , cent r al sumat r a basi n, indonesi a val id for i dent ifyi ng t he br it t leness of r ocks in br ow nshale developm ent  gamma ray log  sonic log validation  poi sson s r at i o (v)  young s modul us (e) v – e cr osspl ot (dynamic) conver si on dynami c t o st at i c v – e cr osspl ot (st at i c) buntoro et al./ jgeet vol 6 no 2/2021 83 the empirical equation from the p wave velocity and s wave velocity data can be used to calculate the dynamic young’s modulus of rocks, but due to the limitations of the sonic log data which only has p wave velocity, the s wave value is calculated using the castagna equation (1985) as follows: vs = 0.862 vp 1.172 (1) with dynamic young's modulus equation proposed by fjær et al. (2008), can be calculated young’s modulus as follows: e = ρ𝑉𝑠 2 (3𝑉𝑝 2 − 4 𝑉𝑠 2) (𝑉𝑝 2 − 𝑉𝑠 2) (2) where; vp = primary wave velocity (km/sec) vs = secondary wave velocity (km/sec) ρ = rock density (g/cc) e = young’s modulus (mpa) dynamic poisson's ratio of rock can be determined using empirical equations obtained from p-wave velocity and s-wave velocity data with the equation according to zoback (2007): υ = 1−2 [ 𝑣𝑠 𝑣 𝑝 ] 2 2 [1− [ 𝑣𝑠 𝑣𝑝 ] 2 ] or υ = 𝑉𝑝 2−2 𝑉𝑠 2 2 (𝑉𝑝 2 − 𝑉𝑠 2) (3) where; vp = primary wave velocity (km/sec) vs = secondary wave velocity (km/sec) υ = poisson’s ratio (dimensionless) the principle of measuring elastic rock properties in the rock mechanics lab is very different from measurements with well log, where the measurement in the lab is in high stresses / strains, low strain rates, and usually drained conditions, while measurements in well logging use the principle of measuring downhole by high frequency sonic vibrations is in very low stresses / strains, high strain rate, and always undrained condition (basuki, 2017). for this reason, a dynamic conversion to static elastic rock properties (poisson's ratio and young's modulus) is required using the empirical equation, as follows:  dynamic poisson’s ratio (𝝂d) to static poisson’s ratio (𝝂s): wang (2000) proposed the empirical equation of undrained dynamic poisson’s ratio is often comparable to the drained static poisson’s ratio (𝝂d≈𝝂s), in the following relation; 𝑣𝑠 = 3𝑣𝑑−𝛽𝐵(1+𝑣𝑑 ) 3−2𝛽𝐵(1+𝑣𝑑 ) (4) where; 𝝂 = biot’s effective stress constant b = skempton’s coefficient dynamic young’s modulus (ed) to static young’s modulus (es): eissa & kazi (1998) proposed the empirical equation of young's dynamic modulus (ed) to the static young modulus (es) for sandstones and shales; es=10^(0.02+0.77log (ρb.ed)) (5) dynamic young’s modulus (ed) often overestimates rock stiffness in general: es < ed. 5. result and discussion 5.1. static elastic rock properties crossplot of the brownshale based on outcrop analog core data the brownshale zone with a thickness of about 56 meters at karbindo coal mine (kiliranjao) is composed of 4 facies units, namely: unit e, unit f, unit g, and unit h. unit e consists of an intercalation of red and gray shale, clay-silt grains, carbonates and locally containing grains of sand. unit f consists of an intercalation of red, gray to brown shale, the size of clay grains silt, carbonate and contains many gastropods. unit g consists of an intercalation of red and gray shale, the size of the clay grains silt, carbonate and locally containing grains of sand. unit h consists of an intercalation of gray and brown shale, grain size of clay silt, carbonate and locally containing grains of sand (figure 3). figure 4 shows the crossplot of elastic rock properties (poisson's ratio vs young's modulus) from the results of rock mechanics tests based on shale outcrop analog cores at the karbindo coal mine (kiliranjau) which represents each facies unit of shale hydrocarbon, which consists of six core samples, namely: cores b-2a, b-6, b-8, b-15, b-17, b-21, and b-22. fig 3. outcrop of brownshale formation and profiles at the karbindo coal mine, kiliranjao area 84 buntoro et al./ jgeet vol 6 no 2/2021 fig 4. static elastic rock properties (poisson's ratio vs young’s modulus) crossplot of the brownshale based on outcrop analog cores data 5.2. dynamic elastic rock properties crossplot of the brownshale based on well log data geomechanical analysis of well log data from well bs-03 as the only well that penetrated the brownshale formation in the bengkalis sub-basin area with a depth interval of 10,420 11,642 feet (thickness: 1,222 feet) can be used as a basis for the development of shale hydrocarbon. crossplot of dynamic elastic rock properties (dynamic poisson's ratio vs dynamic young's modulus) from the results of the geomechanical analysis of bs-03 well log data on the brownshale formation from all depth intervals is shown in figure 4, where the distribution of elastic rock properties is more dominant in the ductile region, with dynamic poisson's ratio values at several depth intervals can reach 0.4, because of the intercalation laminated shale / sand section. the poisson's ratio (ʋ) for shale only varies between 0.05 and 0.32, and sandstones have a poisson's ratio value in the range 0.05 to 0.4 (rai, et al, 2014). figure 5 shows the influence of the intercalation laminated shale / sand section which causes the dynamic poisson's ratio value to reach 0.4, so it can be concluded that not all brownshale formation intervals are brittle, but at some depth intervals are ductile. 5.3. dynamic to static conversion of elastic rock properties crossplot of the brownshale based on well log data the principle of measuring elastic rock properties in a rock mechanics lab is very different from measuring with a well log. therefore, it is necessary to convert dynamic to static elastic rock properties (poisson's ratio and young's modulus) using the empirical equation proposed by wang (2000) for poisson's ratio, and the empirical equation proposed by eissa & kazi (1998) for young's modulus. the crossplot resulting from the conversion of dynamic elastic rock properties to static brownshale formation from well log data is shown in figure 5. fig 5. dynamic elastic rock properties (poisson's ratio vs young’s modulus) crossplot in the brownshale formation interval from the well log data of well bs-03 from figure 6, it is very clear that there is a change in the crossplot value from dynamic to static of elastic rock properties, where the poisson’s ratio value shifts to the left significantly, and young's modulus value goes downward, where in dynamic conditions the distribution is more dominant in ductile region and after converting in static conditions the distribution becomes more dominant in brittle region. 5.4. validation of static elastic rock properties of well log data using outcrop analog cores data from the results of the dynamic to static conversion of elastic rock properties (poisson's ratio and young's modulus) using empirical equations, it is very clear that there is a change in the crossplot value from dynamic to static elastic rock properties, where the poisson's ratio values shifts to the left is quite significant, and the young's modulus values shifting downward, which in dynamic conditions the distribution is more dominant towards the ductile region and after converting in static conditions, the distribution becomes more dominant towards the brittle region. regarding of shale hydrocarbon development in the brownshale formation, pematang group, bengkalis sub-basin, validation must be carried out with core data, so that it is more accurate to identify brittleness rock, because core data is not available, outcrop analog cores data is used. fig 6. the crossplot conversion of dynamic to static of elastic rock properties, where in dynamic conditions the distribution is more dominant in ductile region and after converting in static conditions the distribution becomes more dominant in brittle region. b-22 b-21 b-2a b-6 b-8 b-15 b-17 0 20 40 60 80 100 0 0,1 0,2 0,3 0,4 0,5 s ta ti c y o u n g 's m o d u lu s (m p a ) static poisson's ratio outcrop core data (surface) brittle region ductile region static outcrop analog (modified from perez & marfurt, 2013) 0 20 40 60 80 100 0 0,1 0,2 0,3 0,4 0,5 d y n a m ic y o u n g 's m o d u lu s (m p a ) dynamic poisson's ratio well log data (subsurface) brittle region ductile region dynamic (modified from perez & marfurt, 2013) shale sand composite log static shale sand (modified from perez & marfurt, 2013) 0 20 40 60 80 100 0 0,1 0,2 0,3 0,4 0,5 s ta ti c y o u n g 's m o d u lu s (m p a ) static poisson's ratio well log data (subsurface) outcrop core data (surface) brittle region ductile region 0 20 40 60 80 100 0 0,1 0,2 0,3 0,4 0,5 d y n a m ic y o u n g 's m o d u lu s (m p a ) dynamic poisson's ratio well log data (subsurface) brittle region ductile region dynamic (modified from perez & marfurt, 2013) shale sand buntoro et al./ jgeet vol 6 no 2/2021 85 figure 7 shows the validation of the crossplot static elastic rock properties of the well log data using outcrop analog cores data. from figure 6, it is confirmed that the validation of the static elastic rock properties of the well log data with the rock mechanics test results from the outcrop analog cores has a strong correlation, so that the outcrop analog data is valid and representative to be used in the initial study of shale hydrocarbon development in the brownshale formation, pematang group, bengkalis sub-basin. fig 7. the validation of the crossplot static elastic rock properties (poisson's ratio vs young’s modulus) of the well log data using an outcrop analog cores. 6. conclusions crossplot dynamic elastic rock properties of the brownshale formation in the well bs-03 has an intercalation of the laminated shale / sand section from the top to the bottom interval, where the distribution of dynamic elastic rock properties is more dominant in the ductile region, so it can be concluded that not all brownshale formations are brittle, but some depth intervals are ductile. the value of dynamic elastic rock properties (dynamic poisson's ratio and dynamic young's modulus) calculated from the well log data is higher than the static value of the core measurements in the rock mechanics lab, so a conversion must be done from dynamic to static using core data to validate. from the results of the dynamic to static conversion of elastic rock properties (poisson's ratio and young's modulus), there is a change in the crossplot value from dynamic to static elastic rock properties, where the poisson's ratio value shifts to the left significantly, and the young's modulus value shifts downward, where in dynamic conditions the distribution is more dominant in ductile region and after converting in static conditions the distribution becomes more dominant in brittle region. validation of the static elastic rock properties crossplot of the well log data using the outcrop analog cores data, it is confirmed that the validation results have a strong correlation, so that the outcrop analog data is valid and representative to be used in the initial study of shale hydrocarbon development in the brownshale formation, pematang group, bengkalis subbasin. acknowledgments this work was carried out with support from kementerian riset dan teknologi / badan riset dan inovasi nasional indonesia that has given funding for this research and malacca strait emp group and cpp block bob pt. bumi siak pusakopertamina hulu for contributing data and permission for publication. references alfreds r. jumikis, 1979. rock mechanics. trans tech publications. alsaif, n.a., hage, a.r., hamam, h.h., 2017. mineralogy and geomechanical analysis for hydraulic fracturing: an integrated approach to assess rock fracability in sandstone reservoirs, in: day 1 mon, november 13, 2017. spe. https://doi.org/10.2118/188606-ms basuki, d., 2017. introduction to geopressure prediction, workshop of geomechanics application in borehole stability. carnell, 1997. the syn-rift petroleum system of central sumatra, in: ipa pre-conference field trip. grieser, w.v., bray, j.m., 2007. identification of production potential in unconventional reservoirs, in: all days. spe. https://doi.org/10.2118/106623-ms heidrick, t.l., 2018. a structural and tectonic model of the coastal plains block, central sumatra basin, indonesia, in: proc. indon petrol. assoc., 22nd ann. conv. indonesian petroleum association (ipa), jakarta. https://doi.org/10.29118/ipa.572.285.317 j. katz, b., 1995. stratigraphic and lateral variations of source rock attributes of the pematang formation, central sumatra. bull. geol. soc. malaysia 37, 13–31. https://doi.org/10.7186/bgsm37199502 jin, x., shah, s.n., roegiers, j.-c., zhang, b., 2014. fracability evaluation in shale reservoirs an integrated petrophysics and geomechanics approach, in: all days. spe, pp. 153–166. https://doi.org/10.2118/168589-ms longley, i.m., 1990. pematang lacustrine petroleum source rocks from the malacca strait psc, central sumatra, indonesia, in: proc. indon petrol. assoc., 19th ann. conv. indonesian petroleum association (ipa), jakarta. https://doi.org/10.29118/ipa.1601.279.297 luo, x., were, p., liu, j., hou, z., 2015. estimation of biot’s effective stress coefficient from well logs. environ. earth sci. 73, 7019–7028. https://doi.org/10.1007/s12665015-4219-8 sunardi, e., 2015. the lithofacies association of brown shales in kiliran jao subbasin, west sumatra indonesia. indones. j. geosci. 2, 77–90. https://doi.org/10.17014/ijog.2.2.77-90 us energy information administration (eia), 2015. technically recoverable shale oil and gas resources in indonesia. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). b-22 b-21 b-2a b-6 b-8 b-15 b-17 0 20 40 60 80 100 0 0,1 0,2 0,3 0,4 0,5 s ta ti c y o u n g 's m o d u lu s (m p a ) static poisson's ratio well log data (subsurface) outcrop core data (surface) brittle region ductile region static shale sand composite log outcrop analog (modified from perez & marfurt, 2013) http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 7. no 1. march 2022 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor adi suryadi b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 07 no 01 2022. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content clean water supply in tasikmalaya municipality, opportunities and challenges ...................................................................................................................................... 1 identification of geothermal system in “diana” area, indonesia based on magnetotelluric data modelling ................................................................................................ 7 serpentinization study on ultramafic rock at morombo area, lasolo islands district, north konawe regency, southeast sulawesi, indonesia ........................................ 15 effects of corn stalks ash as a substitution material of cement due to the concrete strength of rigid pavement ...................................................................................... 21 characteristics of kedondong trass and bobos trass as cement raw material, cirebon, west java, indonesia ................................................................................................... 27 rapid land cover change in the south sumatera peat area associated with 2015 peat fires .............................................................................................................................. 34 page 1 cover jgeet vol 6 no 1 march 2021.cdr uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 6. no 1. march 2021 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. (indonesia) manager editor catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 06 no 01 2021. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content proxapertites from walat formation, sukabumi, west java, indonesia. ............................ 1 microscopy observation of samosir formation paleosoil, tuktuk sidaong, north sumatera, indonesia ......................................................................................................... 9 the soft layer thickness estimation using microtremor measurement to identify landside potential in watukumpul, central java, indonesia ................................. 16 hydrothermal alteration and ore metal mineralisation at temon, pacitan, east jawa, indonesia. .................................................................................................................... 24 hydrocarbon prospectivity in the undrilled area of aima field in the niger delta basin, nigeria. ..................................................................................................................... 34 evaluation of groundwater quality status around gunung tugel landfill in kedungrandu village, patikraja district, banyumas regency, central java, indonesia. ....................................................................................................................................... 42 analysis of gravity anomaly decomposition and depth to basement, case study: cenozoic bogor basin, indonesia. ................................................................................. 51 analysis of gravity anomaly decomposition and depth to basement, case study: cenozoic bogor basin, indonesia. ................................................................................. 58 geology, rock geochemistry and ore fluid characteristics of the brambang copper-gold porphyry prospect, lombok island, indonesia. .................................................. 67 page 1 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 3 2021 utomo, j. et al./ jgeet vol 6 no 3/2021 141 research article the influence of external cfrp string reinforcement on the behavior of flexural rc elements junaedi utomo1*, nauval rabbani2, sri tudjono3, han aylie3, sukamta3 1department of civil engineering, atma jaya yogyakarta university, yogyakarta, indonesia. 2master program in civil engineering, diponegoro university, semarang, indonesia. 3department of civil engineering, diponegoro university, semarang-indonesia. * corresponding author : junaedi.utomo@uajy.ac.id tel.: +62811268405 received: oct 12, 2020; accepted: aug 16, 2021. doi: 10.25299/jgeet.2021.6.3.5685 abstract external reinforcement is an excellent method for improving the load carrying capacity and ductility behaviour of reinforced concrete members in flexure. enhancement becomes a necessity when current standards mandate a higher performance compared to older codes. external reinforcement is an environmentally friendly and sustainable solution, since demolition and re-building could be postponed, and the building can be used while work in conducted on the members. carbon fiber reinforced polymers (cfrp), having a low weight-to-volume ratio and an excellent resistance to corrosion, can be used as external reinforcement to effectively increase the flexural and shear strength of a member. to evaluate the effectiveness of cfrp strings, two types of reinforced concrete t-beams were tested. the specimens consist of a strengthened member in both shear and flexure using cfrp wraps and cfrp strings, and a conventional reinforced concrete beam. the specimens were subjected to a one-pointloading system to simulate high shear stresses in combination with a maximum bending moment at mid-point. the installation of cfrp strings was conducted using the near surface mounted (nsm) method, while the sheets were externally bonded reinforcement (ebr). the strings and sheets were impregnated and pultruded on side. the test results showed that the strings and wraps substantially increased the ultimate load carrying capacity and ductility of the member. the ultimate load enhancement was found to be 32% from 117kn to 154kn, and the vertical deformation improved 25% from 16 mm to 20 mm. the failure mode was characterized by initial debonding of the strings in the interface between the strings and the epoxy, followed by string-rupture. the two strings ruptured concurrently, due to stress re-distribution within the member. keywords: external strengthening, carbon fiber reinforced polymer (cfrp), flexure, load-carrying capacity. 1. introduction the requirements for seismic design changes, as it is influenced by the shifting of earthquake zone mapping. existing reinforced concrete flexural members therefore requires reevaluation and, most probably, improvements in terms of their load-carrying capacity. to achieve this goal, an element might necessitate additional reinforcement or external strengthening. among the methods of steel jacketing and section enlargement, external strengthening using carbon fiber reinforced polymer (cfrp) provides a simple and less invasive technique to enhance the load-carrying capacity of a member. structural strengthening using cfrp as external reinforcement is proven to be effective for seismic rehabilitation of structures over the past decades (mugahed amran et al., 2018). carbon fiber frp is chosen for this experiment considering the advantages as compared to other fibers such as aramid and glass. these advantages are: very high strength, lightweight, corrosion resistance, and the ease in application. cfrp is widely used for strengthening of concrete structures (el gamal et al., 2019). in terms of cfrp application, two methods are available; the first being the externally bonded reinforcement (ebr) and secondly, the near surface mounted (nsm) method. the ebr method can be applied for shear and flexural strengthening, the types of cfrp that are commonly assessed are sheets and laminates. the characteristics of this method are that the cfrp is attached entirely to the outer concrete surface using an epoxy resin or bonding agent. the concrete surface usually requires grinding prior to application of the cfrp. the compatibility between the concrete member and the cfrp is dependent on the performance of the interface between the epoxy and the concrete, and the epoxy and cfrp. the concrete, therefore, has to meet a minimum compressive strength to ensure that rupture in the concrete adjacent to the bond-area will not occur. research has been conducted to investigate the flexural response of cfrp strengthened members based on the ebr method. it was found that the use of wrap-type cfrp increased the flexural capacity up to 45%, while debonding between the cfrp and epoxy resin was the failure mode (tudjono et al., 2015). this mode of failure was reported by other researchers, concluding that especially for ebr, debonding becomes the most likely failure mode (breña et al., 2003; kotynia et al., 2008; shin and lee, 2003). the nsm method, on the other hand, per definition provides a better bond performance since the cfrp is fully or partially embedded in the concrete near the surface of the member. the application of nsm requires the implantation of the cfrp within the concrete member; a groove needs to be constructed near the concrete surface, deep enough to house the cfrp member. from the point of view of application, rods, bars or plates could be used. the nsm method is mainly utilized for flexural strengthening. one of the major advantages of this system is that debonding can be prevented. experiments on the nsm bond performance have previously been carried out to illustrate the capacity and failure behavior based on the direct pull-out and shear pull-out tests (budipriyanto et al., 2018; han http://journal.uir.ac.id/index.php/jgeet 142 utomo, j. et al./ jgeet vol 6 no 3/2021 et al., 2018; lee et al., 2013; soliman et al., 2011). the results showed that the parameters affecting the bond behavior are: the concrete strength, groove depth, the type of epoxy material, the embedment length, and characteristics of the cfrp material. additionally, experiments of beams under static loading (bilotta et al., 2011; dias et al., 2018; tudjono et al., 2018) provided a picture of the failure behavior of nsm members. all results revealed that in general the nsm provides a better bond performance compared to the ebr. in this study, cfrp carbon strings were utilized as flexural strengthening, based on the dry lay-up nsm system, in combination with shear strengthening using the sheets wet layup ebr method. the experiment focused on the effectiveness of the composite element in terms of load-carrying capacity enhancement and the failure behavior at ultimate. the specimens were t-sections in bending based on the experiments conducted by (tudjono et al., 2015) and (sapulete, 2018). the results were compared to an identical specimen having the same dimensions and material properties, without the cfrp external reinforcements. comparing the two systems, the significant disparity is in the fibers-resin interaction. for the wet lay-up ebr method, a layer of epoxy resin is attached to the concrete surface, and on top of this layer, the cfrp sheets are placed. an additional layer of the same resin is brushed into the sheets. the strings using the nsm method were based on the dry lay-up method; the strings were pre-impregnated (pre-preg) before placed into the concrete. a different type of epoxy resin is used for this purpose, and the main objective is to enhance the absorbance of resin into the fibers. pre-preg is customarily performed at the manufacturing plant but could also be conducted on-site. the disadvantage of the latter is that the impregnation process is not as perfect as in the plant, and the geometry of cross-section will more likely be non-uniform. 2. research objective the objective of this study is to analyze the effectiveness and influence of external reinforcement using a combination of shear and flexural cfrp reinforcement. the sheets are utilized as external shear reinforcement, and strings were used for improving the load carrying capacity and ductility of the member. the string will provide additional tensile force in the tensile area of the beam, and the sheets enhance the shear capacity while simultaneously producing a confined condition to the concrete in compression zone. the behavior of the reinforced member is studied through the crack load and ultimate load levels, while the vertical deformation was measured at first concrete cracking and at ultimate. the comparison of these data to the control element without external reinforcement is used for analyzes. further, the failure mode and crack propagation are visually observed to explain the data outcome and failure phenomenon. further, the failure mode deviation to the reinforced concrete member without external reinforcement is studied, and the behavior of strings are investigated to provide possible improvements both for the producer and the applicator at the field. 3. specimen specifications and external strengthening the experimental study included three t-beams sections with a length of 2500 mm. the specimens were simply supported with a clear span of 2300 mm. the elements were tested monotonically, with a one-point loading system applied at mid-span. an increment load of 20 kn/minute was applied on the member till failure (fig. 1). one conventional reinforced beam was produced and numerated as bc. this element functioned as a controlling element and as a comparison instrument to the two cfrp reinforced members denoted as bs1 and bs2. the section dimensions and conventional steel reinforcements are shown in fig. 2a. the concrete had a 28 -day cylindrical compression strength (f’c) of 38.4 mpa, and the 19 mm tensile steel reinforcement had a yield strength ( fy) of 433 mpa. the 16 mm compression reinforcement had a yield strength (fy) of 416 mpa. ø6 mild steel bars with a distance of 250 mm apart were used as stirrups. the elastic modulus of elasticity was 200 gpa. fig 1. specimen specification and loading system the specimens bs were externally reinforced in shear and flexure. the shear reinforcement was applied on the web of the member using the so -called u configuration based on the ebr method. cfrp sheets with widths of 100 mm were placed with a distance of 30 mm ( fig. 2 and fig. 3). the section as seen in fig. 2a is the controlling element, designed based on the older codes, without external cfrp reinforcement while fig. 2b is the cross section of the specimen with the two cfrp string reinforcements situated at the tensile area of the t-section. the cfrp sheets were unidirectional woven carbon fiber fabrics with a thickness of 0.129 mm. the composite material had a tensile strength of 4.3 gpa and a tensile modulus elasticity of 225 gpa in combination with an ultimate 1.91% elongation. the sheet consists of one layer applied by the wet lay-up process. the epoxy resin functioning as bonding agent was thixotropic epoxy-based impregnating resin. a) specimen bc b) specimen bs fig 2. cross-section details and specifics shear force diagram moment force diagram p 2500 2300 1 0 0 2 0 0 600 2d16 ϕ6-250 2d19 1 0 0 2 0 0 112,5 375 112,5 shear frp flexure frp 150 150 utomo, j. et al./ jgeet vol 6 no 3/2021 143 fig 3. details of external shear cfrp reinforcement for the flexural reinforcements, cfrp strings were used (fig. 4a). the strings were impregnated with an epoxy resin agent and pultruded (fig. 4b). cfrp strings are unidirectional carbon fibers with a tensile strength of 4 gpa and a tension modulus of elasticity of 240 gpa in combination with an ultimate strain of 1.6%. the approximate diameter of pultruded strings was measured to be 10 mm with a tensile strength of 2 gpa and a tension modulus of elasticity of 230 gpa. the mechanical properties of the sheets and string were similar except for the ultimate tensile strength. contradictory to the shear reinforcements, the strings were attached to the extreme tensile concrete fibers using the nsm method. a different type of resin from the resin used for impregnation purposes was used to attach the strings into the groove. the strings were situated on the tensile part of the section, i.e. the flange. two longitudinal strings with a distance of 375 mm were used (fig. 2b). a) cfrp string details b) pultrusion process fig 4. cfrp string details and pultrusion the sequence of the nsm strings was as follows: a groove with a width and depth of 1.5 times the string diameter was prepared; the groove was cleaned throughout by sandblasting and kept dry; the strings were impregnated and pultruded to straighten the individual fibers in the longitudinal direction; a layer of the bonding resin was placed in the groove, followed by the strings; the strings were pushed towards the bottom of the groove, and the gap was further filled with the bonding resin (fig. 5); the surface was leveled and the resin was allowed to cure. a) groove preparation b) initial epoxy resin application c) placement of cfrp into groove d) final resin application and leveling fig 5. nsm string placement 4. experimental research the experimental setup is shown in fig. 6. to induce a negative moment to simulate the position of the beam near the beam-column joint, the specimens were turned over with the flange on the bottom of the member. this has a practical reason since it is far simpler to induce a force downwards within the loading frame. this method has been used in previous research by (sapulete, 2018; tudjono et al., 2018, 2015). a load cell type clc-500kna with a capacity of 500 kn was used to record the monotonic load increment produced by the hydraulic jack with an increment rate of 20kn per minute. the increment was reduced to 10kn approaching the ultimate design load. two displacement transducers with type cdp-100mt and a sensitivity of 100 x 10-6 strain/mm and maximum capacity of 100 mm were used to record the displacement during the loading sequences. the two transducers were situated on both sides of the web as can be seen in fig. 7 and demonstrated in fig. 6. all data were digitalized using a data logger. to monitor the horizontal movements of the specimens, a displacement transducer with type cdp-25m and a sensitivity of 500 x 10-6 strain/mm and maximum capacity of 100 mm was placed at mid-point, horizontally at the center of gravity of the section’s member. the concrete strength was obtained from six cylinders with a dimension of 100 by 200 mm that were prepared simultaneously during the production of the t-beam specimens. the cylinders were kept moist by submerging them, and then were dried. the t-beam specimens were cured by using a wet blanket during the 28-day period. additional data such as temperature, humidity and the specimens’ physical irregularities were recorded and used as secondary data when applicable. 2300 100100 nsm frp string frp sheet 30 100 144 utomo, j. et al./ jgeet vol 6 no 3/2021 fig 6. loading test fig 7. experimental setup 5. results and discussion 5.1. load carrying capacity based on the experimental data, a summary of results is reported in table 1. the data consist of the load magnitude when the first crack in the concrete in tension (pcrack) appeared and the ultimate load (pmax) and the corresponding vertical displacements (δcrack and δmax). since the deviation of test results between bs21 and bs2 were small, the average values were presented. all data were recorded at mid-span area of the beam. table1. experiment data code name pcrack (kn) pmax (kn) ∆crack (mm) ∆max (mm) bc 29.01 116.87 1.37 20 bs 36.02 154.36 1.87 16 in fig. 8 the internal force equilibrium comparison is presented. the bc specimen’s capacity is a contribution of the concrete and steel in compression and the steel in tension. the reinforced section has an additional force component that originated from the cfrp strings situated at the extreme tensile fibers. the amount of this external reinforcement should take into account the shifting of the neutral axis, so that the failure mode will remain as under reinforced. fig 8. internal vector component comparison 5.2. crack pattern and failure modes the final crack pattern of bc and bs is shown in fig. 9. specimen bc unmistakably failed in flexure. vertical cracks started at mid-span in the tension zone and propagated vertically towards the neutral axis of the section. this confirms that the flexure stresses dominated the failure behavior in this region. secondary vertical cracks appeared adjacent to this first crack, and as the first crack widened, the secondary cracks grew both in length and width towards the intersection between the web and the flange. from here on, these cracks started to 2300 100100 hydraulic jack load cell horizontal lvdt hydraulic jack load cell lvdt vertical lvdt 1150 1 0 0 2 0 0 112.5 375 112.5 strain stress εst εsc εcc εst εsc εcc εfrp tst tfrp tst csc cccneutral axis bc bc bs csc ccc 112.5 375 112.5 1 0 0 2 0 0 150 neutral axis bs strain stress utomo, j. et al./ jgeet vol 6 no 3/2021 145 deviate from their vertical path, and diverge with an angle of approximately 45-degrees inwards, as can be seen clearly in fig. 9a. the specimens bs showed an initial flexure crack at midspan; the secondary cracks were more evenly distributed as compared to bc (fig. 9b). as was the case of bc, the cracks deviated into shear cracks, but contradictory to bc, these cracks started to diverge into shear cracks even in the flange area. when cracks became wider, the tensile steel yielded, resulting in the crushing of concrete in the compression zone. the element lost its internal force equilibrium and the large strain disparities in the interface between the epoxy and concrete resulted in debonding at around the mid-point area. the vertical deformation of the member increased rapidly, since the remaining cfrp bond at the far end of the beams was the only internal force component counteracting the external load. finally, the cfrp strings ruptured and the tests were terminated (fig. 10). a) bc b) bs fig 9. crack pattern at failure fig 10. failure mode: (1) epoxy debonding and (2) cfrp rupture 5.3. analysis the strengthened members have a substantially better performance in terms of load-carrying capacity. the members bs had a 33% capacity improvement when compared to the control element bc. the context of this increase originated from the additional tensile component provided by the cfrp strings and the enhancement in concrete compression strength due to the confinement endowed by the shear reinforcement. the increase in concrete compression strength due to shear reinforcement was studied by aylie et al., (2015), huang et al., (2018), and bouamra and ait tahar, (2017). the combination of the additional tension component provided by the cfrp strings, and concrete confinement in the compression area, resulted in an increase in the internal moment, and thus an improvement in load-carrying capacity (fig. 8). as for the load level at which the first crack appeared, it can be seen that the cracking load for bs is 24% higher as compared to bc. the cracking moment depends on the tensile strains in the extreme concrete fibers, which in turn is a function of the beam’s curvature. the curvature is influenced positively by the stiffness of the member. the stiffness of specimens bs was improved by the presence of the strings, which have a noticeably higher elastic modulus when compared to the concrete. the confined concrete in the compression zone also added to the stiffness of the section. after the concrete cracked, the bond between the strings and concrete remained intact and controlled the deformation of the member through the shear strength that prevented the propagation of cracks in the tension zone to a certain degree. a state of internal prestressing was induced in these extreme tension layers, explaining the lesser vertical displacement at ultimate. the observation of the strings revealed that the bond at the far ends of the beams was maintained up till failure. the crack pattern of bc is strongly influenced by the flexure mode. the first crack at mid-span is vertical and distinctively caused by high flexure stresses and strains. the secondary cracks, on the other hand, are initiated by flexure stresses in the extreme tensile fibers of the flange, but reaching the junction between the flange and the web, the section width becomes significantly smaller. this, in combination with a reduced bending moment that can be seen in fig. 1, resulted in the domination of shear stresses and explains the circa 45-degree crack deviation. the collapse of the member is categorized as under-reinforced flexure. the specimens bs failed due to a combination of flexureshear stresses; this was concluded from the deviation in crack angle that occurred in the flanges. the secondary cracks were distributed more evenly, with a closer distance apart. the presence of the cfrp strings prevented the formation of large cracks, the yielding process of the conventional steel was prolonged and enabled the cracks to distribute more evenly. the combination of flexure-shear cracks in the flanges resulted due to the fact that only the web, and not the flange, was externally reinforced with the cfrp sheets. the bond within the cfrp string interface remained integral up till the crushing of the concrete in compression, and debonding started at the center part of the beam. the remaining bond at the far ends produced high stresses in the strings that finally ruptured. 6. conclusion 146 utomo, j. et al./ jgeet vol 6 no 3/2021 the study looked into the behavior of externally reinforced flexural members using cfrp elements. the sheets were wet lay-up and were used as shear reinforcement based on the ebr method. the strings were dry lay-up and equipped as flexural reinforcement in the tensile area based on the nsm approach. the test results concluded that a combination of external shear and flexure reinforcement can significantly improve both the load-carrying capacity and the deformation behavior. the enhancement in flexural strength is mainly a contribution of the internal force equilibrium improvement that originated from the cfrp in the tension zone, and the increase in concrete compression strength is a result of confinement from the shear reinforcement. it is interesting to study to which degree the contribution of both these factors are, since the amalgamation of these two methods also shifted the failure mode from underreinforced flexure to under-reinforced flexure-shear. the two external reinforcements also influenced the member’s stiffness positively. the vertical deformation of the member was reduced substantially, even under increasing load levels. the load levels at which the first crack occurs was controlled by the presence of the tensile cfrp reinforcement. the extended first cracking has an affirmative effect on conventional steel corrosion control. the test results suggested that the bs member could still be categorized as underreinforced, but since the failure mode was a product of many additional factors, this cannot be seen as a general failure mode. the crack distribution was also more evenly distributed, with less crack-widths, which has a positive impact on controlling environmental influences such as humidity and possible chemical components to both concrete and conventional reinforcement. in a nutshell, the proposed system is sufficient in rejuvenating an under-capacitated member with minimal effort. the system is best used for low-rise and medium-rise buildings. acknowledgment the authors would like to acknowledge pt. sika indonesia, the structural and material laboratory of the diponegoro university and the research cooperation between nihon university in japan, atma jaya university in yogyakarta and diponegoro university in semarang. references aylie, h., antonius, okiyarta, a.w., 2015. experimental study of steel-fiber reinforced concrete beams with confinement. procedia eng. 125, 1030–1035. https://doi.org/10.1016/j.proeng.2015.11.158 bilotta, a., ceroni, f., di ludovico, m., nigro, e., pecce, m., manfredi, g., 2011. bond efficiency of ebr and nsm frp systems for strengthening concrete members. j. compos. constr. 15, 757–772. https://doi.org/10.1061/(asce)cc.1943-5614.0000204 bouamra, y., ait tahar, k., 2017. mechanical performance of a confined reinforced concrete beam. procedia struct. integr. 5, 155–162. https://doi.org/10.1016/j.prostr.2017.07.086 breña, s.f., bramblett, r.m., wood, s.l., kreger, m.e., 2003. increasing flexural capacity of reinforced concrete beams using carbon fiber-reinforced polymer composites. aci struct. j. 100, 34–46. budipriyanto, a., han, a.l., hu, h.t., 2018. bond-shear behavior of frp rods as a function of attachment configuration. j. adv. civ. environ. eng. 1, 9–17. https://doi.org/10.30659/jacee.1.1.9-17 dias, s.j.e., barros, j.a.o., janwaen, w., 2018. behavior of rc beams flexurally strengthened with nsm cfrp laminates. compos. struct. 201, 363–376. https://doi.org/10.1016/j.compstruct.2018.05.126 el gamal, s.e., al nuaimi, a., al-saidy, a., al-shanfari, k., 2019. flexural behavior of rc beams strengthned with cfrp sheets using different strengthening techniques. j. eng. res. 16, 35–43. https://doi.org/10.24200/tjer.vol16iss1pp35-43 han, a., gan, b.s., budipriyanto, a., 2018. 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c.a., 2018. studi eksperimental pengaruh perkuatan lentur fiber reinforced polymer rod pada balok dan efektivitasnya (thesis). diponegoro university. shin, y.s., lee, c., 2003. flexural behavior of reinforced concrete beams strengthened with carbon fiberreinforced polymer laminates at different levels of sustaining load. aci struct. j. 100, 231–239. soliman, s.m., el-salakawy, e., benmokrane, b., 2011. bond performance of near-surface-mounted frp bars. j. compos. constr. 15, 103–111. https://doi.org/10.1061/(asce)cc.1943-5614.0000150 tudjono, s., lie, h.a., gan, b.s., 2018. an integrated system for enhancing flexural members’ capacity via combinations of the fiber reinforced plastic use, retrofitting, and surface treatment techniques. int. j. technol. 9, 5–15. https://doi.org/10.14716/ijtech.v9i1.298 tudjono, s., lie, h.a., hidayat, b.a., 2015. an experimental study to the influence of fiber reinforced polymer (frp) confinement on beams subjected to bending and shear. procedia eng. 125, 1070–1075. https://doi.org/10.1016/j.proeng.2015.11.164 © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 3 2022 natul, a. et al/ jgeet vol 7 no 3/2022 95 research article a comparison of geologic structure detection of sumatera island using goce satellite gravity data and sgg-ugm-2 data al shida natul 1, leni sophia heliani2* 1 magister program geomatics engineering, engineering faculty, gadjah mada university, yogyakarta, 55281, indonesia 2geodetic engineering department, engineering faculty, gadjah mada university, yogyakarta, 55281, indonesia * corresponding author : lheliani@ugm.ac.id tel :+62-27-452-0226; fax: +62-27-452-0226 received: jan 27, 2022; accepted: aug 20, 2022. doi: 10.25299/jgeet.2022.7.3.8863 abstract goce gravity satellite data can be used for regional fault detection because the observation area is wide and not limited by area. in this study, goce satellite data is used to detect geological structures on the island of sumatra, the results of which are used as the basis for disaster mitigation. goce data and sgg-ugm-2 were processed using the goce user toolbox (gut) software to produce a gravity disturbance map and a complete bouguer anomaly map. the goce obtained results were validated using the sgg-ugm-2 high-resolution gravity model data. the calculation results obtained that the gravity disturbance value from the goce data was around -140 to 200 mgal, while the value of the gravity disturbance from the sgg-ugm-2 data was around -180-300 mgal. the goce gravity disturbance map and the sgg-ugm-2 can detect the subduction trench, mentawai fault, and west andaman fault on sumatra island with negative values, while the sumatran fault zone (sfz) along sumatra island with positive values in line with the presence of mountain ranges. the results of the sgg-ugm-2 data processing for the gravity disturbance are more detailed than goce because the sgg-ugm-2 data degree is higher than that of goce. goce complete bouguer anomaly value is around 40-560 mgal, while the value of complete bouguer anomaly sgg-ugm-2 is around 60-560 mgal. the complete bouguer anomaly maps from goce and sgg-ugm-2 can detect patterns from the subduction trench, mentawai fault, and west andaman fault but cannot clearly detect sfz. the complete bouguer anomaly can also detect differences between oceanic and continental crust. the goce and the sgg-ugm-2 complete bouguer anomaly map show almost similar patterns and the ability to detect geological structures for sub and regional sumatra island. in addition, goce data detect geological structures more clearly than grace data. keywords: goce, sgg-ugm-2, gravity disturbance, complete bouguer anomaly, sumatran fault zone 1. introduction the island of sumatra is in the subduction zone between the indian–australian plate and the eurasian plate at a speed of 50 to 70mm/year (prawirodirdjo et al., 2000; natawidjaja & triyoso, 2007). the subduction zone stretches from the sunda strait to the andaman sea. in addition, on the island of sumatra, there is a mainland fault that stretches for 1900 km called the sumatran fault zone (sfz). the fault line on the island of sumatra is characterized by the appearance of hills, shifts in river channels along the fault, and lakes that occur due to the shifting of the earth. this fault line crosses the island of sumatra along the bukit barisan (putri et al., 2016). the sfz has a history of major earthquakes, with more than 19 earthquakes since 1892 of magnitude 6.5 or greater (hurukawa et al., 2014). every five years, on average, there is a massive earthquake along the sfz (natawidjaja, 2018). land earthquakes originating from active faults cause severe losses and damage compared to earthquakes originating in the ocean with the same magnitude (sugiyanto et al., 2011). one aspect of earthquake disaster mitigation efforts is the identification of fault locations through geological structure analysis (muksin et al., 2019). analysis of geological structures can be carried out using gravity satellite data, which has a wide observation area and is not limited by area. the gravity method for geological studies is based on measuring variations in earth's gravity caused by differences in the density of subsurface rocks (telford et al., 1990). gravity satellite data is able to provide information related to the redistribution of plates, atmosphere, mantle, hydrosphere, and the earth's centrosphere below the satellite orbit (saraswati & anjasmara, 2010). the principle of gravity satellite is the measurement of satellite orbital perturbation caused by the presence of a gravitational field measured using gravity sensors such as accelerometers, gravity gradiometers, and accurate distance measurements (zhang et al., 2011). there are two gravity satellites: gravity recovery and climate experiment (grace) and the gravity field and steady-state ocean circulation explorer (goce). grace is a gravity satellite developed by the national aeronautics and space administration (nasa) and the german aerospace center for scientific information on static and time-variable gravity fields of the earth (chen et al., 2018). grace's spatial resolution is about a few hundred kilometers because grace's altitude is about 400 s.d. 500 km which is insensitive to small-scale gravity signals (li et al., 2014). http://journal.uir.ac.id/index.php/jgeet mailto:lheliani@ugm.ac.id 96 natul, a. et al/ jgeet vol 7 no 3/2022 goce satellite is a gravity satellite launched by the european space agency (esa) and capable of measuring gravity gradients using a 3-axis gradiometer and has an accuracy of up to 1 mgal and a spatial resolution of less than 100 km (european space agency, 2014). apart from satellite data, there are also high-resolution global geopotential model data such as sgg-ugm-2. earth gravity model sgg-ugm-2 is a high-resolution earth gravity model combined from goce, gravity recovery and climate experiment (grace) data, and egm2008. this model shows promising performance in gps validation (liang et al., 2020). this study aims to demonstrate the effectiveness of goce satellite data for regional fault identification and compare the results with sgg-ugm-2. this research paper focuses on using the gravity disturbance and the complete bouguer anomaly from goce and sgg-ugm-2 data in detecting faults. it is hoped that additional geological information can be obtained from the two satellite data and can be an effective method for detecting regional geological structures as a disaster mitigation effort, especially in areas that are difficult to reach by terrestrial methods. 2. geologi setting the map of the geological structure of sumatra in figure 1. describes the structure of sumatra, which is dominated by the subduction of the indian plate to the northeast under the island of sumatra. the sfz is a dextral horizontal fault that stretches along the island through the center of the mountain range from northwest to southeast with compression and extension zones, forming uplift and pullapart basins that form grabens along with the fault system (barber et al., 2005). the sfz stretches for 1.900 km in the western part of sumatra island, consisting of 19 segments with a length of about 35 to 200 km (sieh & natawidjaja, 2000). the forearc area includes a subduction trench part of the sunda trench, an accretion complex composed of seabed material exfoliated from the indian plate. the forearc ridges that rise above sea level to form forearc islands and forearc basins located between the ridges and volcanic arcs on the mainland. sumatra. the backarc region is a tertiary sediments basin that extends northeast from the mountain range across the malacca strait to the east coast of the malay peninsula. tertiary sediments were formed by palaeogene rifting and subsidence and were filled by neogenes up to the present sedimentation (barber et al., 2005). fig. 1. map of geological structure of sumatra (source : barber et al., 2005) 3. methods the research location for detecting regional geological structures was carried out, covering the entire island of sumatra in a geographical position of -70 to 6.50 n and 94.50 to 1080 e. the data used include go_cons_gcf_2_tim_r6e with degree 300, sgg-ugm-2 with degree 2190, and topographic gravity field models data. the data is obtained from http://icgem.gfzpotsdam.de/. the spatial resolution of goce and sgg-ugm2 be determined using, πr nmax ......………………………………………………..(1) where r is the earth’s radius (6,371 km) and nmax degree. the spatial resolution of go_cons_gcf_2_tim_r6e data is 67 km. while the spatial resolution of sgg-ugm-2 is 9.1 km. https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/goce http://icgem.gfz-potsdam.de/ http://icgem.gfz-potsdam.de/ https://earth.esa.int/web/guest/missions/esa-operational-eo-missions/goce natul, a. et al/ jgeet vol 7 no 3/2022 97 in addition, the default dem (gut ace2 bathy 5m) data from the gut (goce user toolbox) software is used. supporting data are faults shapefile data (sfz, subduction trench, mentawai fault, west andaman fault), geological structure maps, and sumatra administration. figure 2 explains goce and sgg-ugm-2 data processing to get the value of gravity disturbance and complete bouguer anomaly using gut software with a grid of 0.050. processing gravity disturbance using gut ace 2 batch 5 m data while processing complete bouguer anomaly requires topographic gravity field models data for terrain correction. gravity disturbance is a kind of free air anomaly that is reduced to the normal earth ellipsoid surface as the reference surface, usually used for estimating the geoid height. the equation for gravity disturbance 𝛿𝑔 is as follows (bauer marschallinger et al., 2015): 𝛿𝑔 = 𝑔𝑃 − 𝛾𝑃………………………………………….(2) with 𝑔𝑃 the difference between the observation gravity g and the normal gravity 𝛾 at the same point p on the geoid. the complete bouguer anomaly map is an anomaly distribution that describes the general subsurface geological conditions, a combination of regional anomalies and residual anomalies. the complete bouguer anomaly equation ∆𝑔𝐶𝐵 is as (bauer marschallinger et al., 2015): ∆𝑔𝐶𝐵 = ∆𝑔𝐹𝐴 − 𝑔𝑆𝐵 − 𝑔𝑇 ……………………………(3) with ∆𝑔𝐹𝐴 free air anomaly, 𝑔𝑆𝐵 simple bouguer anomaly, and 𝑔𝑇 terrain correction. the bouguer anomaly was compiled with a reduced density of 2670 kg/m3 for the density of crust and 1020 kg/m3 for the density of water (rio & dinardo, 2011). visualization of gravity disturbance map and the complete bouguer anomaly map using surfer software. furthermore, the gravity disturbance map and the complete bouguer anomaly map are overlaid with supporting data in qgis software for interpretation and analysis purposes. gut ace2 bathy 5m data goce data gravity disturbance sgg-ugm-2 data fault, plate boundaries, and administrative boundaries topografi gravity field model data gravity disturbance complete bouguer anomaly complete bouguer anomaly gravity disturbance goce map gravity disturbance sgg-ugm-2 map geological structures detection geological structures detection complete bouguer anomaly goce map complete bouguer anomaly sgg-ugm-2 map geological structure detection comparison result of comparison of geological structure detection fig 2. research diagram 98 natul, a. et al/ jgeet vol 7 no 3/2022 fig 3. gravity disturbance goce map fig 4. gravity disturbance sgg-ugm-2 map natul, a. et al/ jgeet vol 7 no 3/2022 99 4. result and discussion 4.1 gravity disturbance the results of processing the gravity disturbance from the goce data are shown in figure 3 with values around 140 to 200 mgal and from the sgg-ugm-2 data shown in figure 4 around -180 to 300 mgal. the value of the color bar range of figure 3 and figure 4 is made the same, around 200 to 320 mgal with an interval of 20. this aims to see the differences and similarities in the results of the gravity disturbance goce and sgg-ugm-2. the goce and sgg-ugm-2 gravity disturbance maps show the same pattern for the subduction trench, mentawai fault, and west andaman fault, which is dominated by negative gravity disturbance values around 200 to -10 mgal. this interpretation is also validated by the shapefile data of the subduction trench, mentawai fault, and west andaman fault, which are overlaid on the two maps. the goce and sgg-ugm-2 gravity disturbance maps show the sfz zone pattern on land, which is dominated by high positive gravity disturbance values. on the goce gravity disturbance map, the high value is around 40 to 200 mgal. meanwhile, on the gravity disturbance map sggugm-2, the high value is around 40 to 300 mgal. the high gravity disturbance value in the sfz zone may be influenced by the mass of the bukit barisan, including an active volcano on the mainland of sumatra island. these results were also validated with secondary data from sfz shapefiles and active volcanoes. the sfz pattern from the sgg-ugm-2 gravity disturbance map (figure 4) is more detailed for sfz detection than the goce gravity disturbance map (figure 3). 4.2 complete bouguer anomaly the complete bouguer anomaly displays the anomaly that the terrain has corrected in the study area (asniar et al., 2020). figure 5 shows a complete bouguer anomaly map from goce, whose values are around 40 to 560 mgal. figure 6 shows a complete bouguer anomaly map of sgg-ugm-2 with values ranging from 60 to 560 mgal. figures 5 and 6 also have the same color bar range, so you can see the similarities and differences between the two results. the value of the complete bouguer anomaly on the mainland of sumatra island is dominated by low values of around 40 to 240 mgal. it is different from the gravity disturbance value, which is dominated by high values on the mainland of sumatra island. the difference is because the complete bouguer anomaly takes into account rock mass and topography, while the gravity disturbance is not taken into account. terrain correction in the gut software is done globally, there is no distance limit so that the results of the complete bouguer anomaly are smoother. the complete bouguer anomaly maps from goce and sgg-ugm-2 show the sfz clearly in certain areas such as aceh, north sumatra, west sumatra, and jambi. meanwhile, the complete bouguer anomaly map from sgg-ugm-2 shows the sfz from aceh to lampung. in the suspected pattern of sfz, the value of complete bouguer anomaly is very low, around 40 to 160 mgal. in the mentawai zone the fault and west andaman fault can also be detected. other information obtained from the complete bouguer anomaly maps of goce and sgg-ugm-2 clearly shows the subduction trench and a clear distinction between oceanic crust and continental crust. the effect of high and low anomaly is due to differences in subsurface density. the high anomaly in the southwest figure 5 and figure 6 show that the density of the oceanic crust (indo-australian plate) is higher than that of the continental crust (eurasia plate). the complete bouguer anomaly map of sgg-ugm-2 and goce did not have a significant difference. it is necessary to measure gravity in the field to validate this research. fig 5. complete bouguer anomaly goce map 100 natul, a. et al/ jgeet vol 7 no 3/2022 fig 6. complete bouguer anomaly sgg-ugm-2 map 4.3 comparison the gravity disturbance map (from goce and sggugm-2) detects the sfz, mentawai fault, west andaman fault, and subduction trench better than the complete bouguer anomaly map (from goce and sgg-ugm-2). the sgg-ugm-2 gravity disturbance map is clearer and more detailed in detecting geological structures of sfz compare to goce gravity disturbance. meanwhile, goce and sggugm-2 complete bouguer anomaly maps are better at detecting subduction trench and differences between ocean crust and the continental crust. the goce and sggugm complete bouguer anomaly maps are similar but sggugm complete bouguer anomaly maps more clearly detect geological structures. the results of fault detection, subduction trench, and differences between the ocean crust and the continental crust can be used for disaster mitigation and other geodynamic studies. the goce interpretation results are similar to the study conducted by julzarika et al., (2020) using grace data in the sunda strait. the results of the gravity disturbance and bouguer anomaly from grace can detect faults and plate boundaries. geological structure detection research using goce is wider in area than the research study using grace. in addition, goce has better spatial resolution and spatial coverage than grace, in solid earth studies, goce regional focus shows different anomalies in certain areas (van der meijde et al., 2015). therefore, goce more clearly detects geological structures such as faults and plate boundaries than grace. 7. conclusion based on the research that has been done, the gravity disturbances and the complete bouguer anomaly from goce and sgg-ugm-2 data can detect regional geological structures of the island of sumatra. the results of the goce and sgg ugm gravity disturbances shows clearly the subduction trench, mentawai fault, west andaman fault, and sfz. the results of the complete bouguer anomaly can better detect the subduction trench and the difference between the oceanic crust and continental crust. the results of this research can be used for disaster mitigation and other geodynamic studies. the novelty of this study is related to the comparison of goce and sgg-ugm-2 data that can be used for the detection of regional geological structures whose results can be used for disaster mitigation and other geodynamic studies. acknowledgements the authors would like to thank the website http://icgem.gfz-potsdam.de/home for providing goce, sgg-ugm-2, and topographic gravity field models satellite data. processing gravity disturbance and complete bouguer anomaly using gut software which is available for free https://earth.esa.int/eogateway/tools/goce-user-toolbox. references asniar, safani, j., & asfar, s. 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(2011). gravity anomaly from satellite gravity gradiometry data by goce in japan ms9.0 strong earthquake region. procedia environmental sciences, 10(part a), 529–534. https://doi.org/10.1016/j.proenv.2011.09.086 © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 7. no 2. june 2022 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. rosana, ph.d (indonesia) prof. dr. abdul rahim samsudin (malaysia) prof. dr. h. detri karya, s.e, m.a (indonesia) prof. dr. ir. h. sugeng wiyono, mmt. editor in chief dr. eng. husnul kausarian b.sc.(hons), m.sc. 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. 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doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 01 no 01 2017 prayitno b./ jgeet vol 1 no 1/2016 63 limnic condition in rheotrhopic peat type as the origin of petai coal, central sumatra basin, indonesia budi prayitno 1, * 1 geological engineering, universitas islam riau * corresponding author: budiprayitno@eng.uir.ac.id received: oct 1, 2016. revised : 15 nov 2016, accepted: nov 20, 2016, published: 1 dec 2016 doi : 10.24273/jgeet.2016.11.9 abstract petrographic coal is the study of organic and inorganic components of bearing coal formation. this study aims to determine the composition, depositional facies, type and stage of the genesis of coal in the area of research. this research method using a diagram approach diessel, 1986, calder et al., 1991 to determine the depositional facies and peat ecosystems formation of coal carrier. microscopic observations using carl zeiss microscope and point counter model f was conducted to determine the micro-organic components of coal. based on microscopic investigation of the overall sample average abundance maceral vitrinite reached 66.3%, 30.32% mineral matter, maceral liptinite 3:26%, and to absent maceral inertinit no indicates oxidation process that occurs during the decomposition of organic matter. syngenetic depositional pyrite component type spread sporadically on the surface of the coal seam in the form frambiodal and particulates. facies deposition of coal based on the calculation of tissue prevetion index versus gelification index show faises limnic while the calculation of ground water index versus vegetation index show atmosphere rheotropic mires (correlation +) supported the absence maceral inertinit and funginite, hypothesized water level in stable condition was high watertable during the decomposition process takes place in an atmosphere ph 6-8 and eh balanced. average rate comparison gelifikasi the preserved tissues of plant cells (tellocolinite) is smaller than the 23.6% plant cell tissue is not preserved (desmocollinite) amounted to 52.6% indicated from plants of the type herbaceous plant. keywords: coal, depositional, ground water index, vitrinite. 1. introduction 1.1 background the astronomical part of indonesia is at 0 ° 0'00'' 10 ° 0'00'' 0'00'' lu and 0 ° 10 ° 0'00''ls separated by the equator and 90 ° occupy 0' 00''bb 140 ° 0'00''bt. indonesian region based on geographical conditions has a tropical climate and is at the eastern hemisphere. in indonesia every year only changing two seasons, the rainy season and dry season. in general, the intensity of peat accumulation is affected by the tropical climate (dehmer, 1993;. grady et al, 1993; esterle and ferm, 1994; hawke et al., 1999). climate, geology, vegetation and hydrological regime significantly determine the accumulation of peat and its associated facies including the composition of maceral. the latter can be used for reconstruction of the peat accumulation. hydrological regime and vegetation type influencing the peat accumulation have commonly been indicated with groundwater index (gwi) and vegetation index (vi), respectively (calder et al., 1991). gwi can be used to show the development of paleo-mires as well as their type varying from rheotrophic to ombrotrophic mires (e.g. widodo, 2008; amijaya and littke, 2005). the degree of preservation of peat deposit has commonly been reconstructed by tissue preservation index (tpi), whereas, the relative dryness (telmatic) and wetness (limnic) of the peat-forming conditions by gelification index (gi) (e.g. diesel, 1986; lamberson et al., 1991). in the object of this study part of the lower members of telisa formation (early to middle miocene) is investigated with respect to its maceral composition. the depositional environments relating to the degree of preservation, vegetation type, hydrological regime and wetness of the paleo-mire has been reconstructed. 1.2. geological setting location research based on geological framework of sumatra in back arc central sumatra basin. whereas the development tektonostratigrafi central sumatra basin can be described as the following stages: pre-rift stage (eocene); sediments of the pre-rift stage are relatively poorly represented in sumatra, but are more common elsewhere in sundaland. in central sumatra basin it can be seen from the presence of limestones and conglomerates 64 prayitno b./ jgeet vol 1 no 1/2016 nummulitic early tertiary and mélanges deposition (van bemmelen 1949; budhitrisna & andi mango 1990; samuel et al. 1997). horst and graben stage (latest eocene-oligocene) in the late eocene, or earliest oligocene, continental margin sedimentation was brought to an end by the development of horst and graben structures throughout sundaland. a similar sequence of events occurred not only in sumatra, but also in many other areas, including the java sea, the gulf of thailand and the south china sea. sediment formation in central sumatra represented by pematang and kelasa formation. transgressive stage (late oligocene-mid-miocene) following the change in tectonic regime in the late oligocene the whole region underwent regional subsidence in a sag phase, the effects of which extended well to the east of sumatra into malaysia. at the same time the arc system of sumatra started developing and the area of the barisan mountains became an important source of sediments for the forearc and backarc basins. the rate of subsidence was greater in the backarc area than in other areas. initially sedimentation outpaced the rate of subsidence, with sediments transported over greater distances, so that the basins were filled with fluvial units which extended well beyond the margins of the original rift basins to rest unconformably on the basement horsts. in central sumatra basin sediment from sihapas group consists of several formations; lakat formations, defined by de coster (1974) and the menggala formation, defined by mertosono & nayoan (1974). maximum transgression stage(mid-miocene) the maximum transgression of sumatra in the midmiocene is not distinguished here as a distinct tectono-stratigraphic stage, but this term is often used to indicate formations of maximum marine shale deposition and minimum clastic influx. in the maximum transgressive phase, subsidence outpaced sedimentation and the sea gained access to almost the whole area. in the central part of the basin the baong consists almost entirely of shale with one significant sandstone incursion, from the malacca platform to the east. this sandstone is of n12-14 (mid-miocene) age and has been called the 'middle baong sand' in this area. cameron et al. (1980) mentions the "lower baong sand" is equivalent to the top of the formation ombilin, telisa and gumai in north and central sumatra basin. the middle baong sandstones and the upper baong shale by mulhadiono et al. (1978, 1982), is part of the regression phase. regressive stage (mid-miocene-present) in the mid-miocene, regional sag in sumatra slowed down. while the forearc and backarc basins continued to subside, the barisan mountains emerged and became an important source of sediments. in the backarc basins from the late mid-miocene onwards turbiditic sandstones become an increasing component in the deep water formations. the peak activity and erosion of mountains row appointment lasts for late pliocene accompanied by intense volcanic activity along with the deposition of minas formation. 2. methods the coal samples were then crushed to a maximum size of 1 mm and placed in resin blocks. the sample blocks were polished with a specified polisher. microscopic investigation was carried out with a carl zeiss microscope and point counter model f was conducted to determine the microorganic components of coal. during maceral analysis, 500 points with a minimum distance of 0.2 mm between each point were counted from the polished sections. the maceral composition is expressed as percent (% volume). maceral classification used in this study refers to iccp (2001). mean random huminite reflectance measurements were performed on the surface of huminite particles under oil immersion. fifty points of huminite reflectance were made on each sample. fig1. carl zeiss microscope and point counter model f with 500 x magnification depositional environments of the petai coal were reconstructed based on the maceral composition. some indices namely tissue preservation index (tpi) and gelification index (gi) according to diessel (1986) and lamberson et al. (1991) were determined. the indices were applied to investigate the degree of humification and the wetness of the paleo-mires. vegetation index (vi) and groundwater index (gwi) based on calder et al. (1991) were also calculated. the indices were used for the reconstruction of the type of paleomires developed in the deltaic basin. the indices were calculated by the following formulae. prayitno b./ jgeet vol 1 no 1/2016 65 fig 2. formulae for measurement of tpi, gi, gwi, and vi 3. result investigation under the microscope of the overall sample average abundance maceral vitrinite reached 66.3%, 30.32% mineral matter, maceral liptinite 3.26%, and inertinit maceral absence indicates no oxidation process that occurs during decomposition of organic material. maceral desmocollinite composition as the main coal in the study area followed by maceral densinite and tellocolinite respectively 45-68%, 34-36% and 19 21%. based on the comparison of the above composition can be interpreted structure of plant origin low density easily decomposed. decomposition of organic materials can be perfect if the peat layer is always in wet conditions or underwater. while maceral resinite and cuntinite abundant on the surface of the coal samples which indicate many species of plants contain cellulose, maceral species is very easily digested by aerobic bacteria and tissue composed of epidermis. pyrite component based on the distribution pattern included in the depositional syngenetic is spread sporadically on the surface of the coal seam in the form of particulate and frambiodal he presence of pyrite in the form frambiodal indicate the level of water surface of the peat layer was far above / high water table with no presence maceral funginite supported. maceral funginite only be present if the peat layers that are in unfavorable humidity conditions and water level slightly above the peat layer. while maceral corpogelinite is relatively rare, there were only 0.6% occupy the sample composition 4p / 1/16. while the composition of the present tellocolinite as a comparison between maceral preserved maceral vitrinite is not preserved indicates the degree of gelifikasi quite instrumental in the process of decomposition of peat. while the composition of the present tellocolinite as a comparison between maceral preserved maceral vitrinite is not preserved indicates the degree of gelifikasi quite instrumental in the process of decomposition of peat. coal facies interpretation is based on the calculation tissue reindexs prevention versus gelification reindexs indicate conditions transgresive limnic phase. supporting data on which to base is not the presence of funginite above the sample surface coal polishes, maceral funginite only be present if the peat layer is at water level slightly above the peat layer. the presence of pyrite in the form frambiodal syngenetic also provide evidence of water level far above the surface of the peat layer. sedimentation pattern formation of coal carrier complement the data supporting the form of intercalation of clays with sandstone rock is very smooth smooth insertion of coal. while the calculation result reindexs versus groundwater vegetation indexs indicate the type rheotrhopic mires. peat swamps with rheotrhopic atmosphere allows the water supply can be derived from surface water and groundwater that is likely peat layer is always in wet conditions. fig 3. resinite associated with desmocolinite in coal, reflectant white light, 500x. sample 6105/16. fig 4. corpogelinite and pyrite associated with desmocolinite in coal, reflectant white light, 500x. sample 6103/16. resinite desmocolinite corpogelinite tellocolinite tellocolinite pyrite 66 prayitno b./ jgeet vol 1 no 1/2016 fig 5. pyrite framboidal associated with desmocolinite in coal, reflectant white light, 500x. sample 6105/16. figure 6. pyrite and cutinite associated with densinite in coal, reflectant white flouresance , 500x. sample 6102/16 figure 7. diagram tpi vs gi fig 8. diagram tpi vs gi for detemine depositional environtment fig 9. diagram vi vs gwi telocolinite pyrite desmocolinite cuntinite prayitno b./ jgeet vol 1 no 1/2016 67 fig. 10. generalized tectono-stratigraphy of {he tertiary in the backarc basins of sumatra. the diagram is highly simplified as most units interfinger and most boundaries fig. 11. the development of the stratigraphic terminology for the tertiary of the central sumatra basin. 68 prayitno b./ jgeet vol 1 no 1/2016 table 1. maceral compositions table 2. result analisis of vitrinite reflectance komposisi maseral batubara (%) maseral group sub maseral maseral 1p/1/16 2p/1/16 3p/1/16 4p/1/16 vitrinite (huminite) telovitrinite telocollinite 11.0 11.0 27.0 detrovitrinite (humodetrinite ) densinite 16.0 21.0 18.0 1.0 desmocollinite 20.4 26.0 23.4 60.4 gelovitrinite (humocolinite) corpogelinite 0.6 liptinite (exinite) sporinite cutinite 1.6 1.0 2.6 resinite 1.6 1.6 2.6 2.0 inertinite funginite minerals matter oksida pyrite 32.4 28.4 34.0 6.4 clay 28.0 11.0 11.0 reflectansi vitrinite result no no sampel standar deviation (%) max reflectane (%) min reflectane (%) mean reflectane (%) rank coal 1 2p/1/16 0.02 0.54 0.47 0.50 sub-bituminous a 2 3p/1/16 0.02 0.56 0.50 0.52 sub-bituminous a 3 4p/1/16 0.02 0.62 0.55 0.58 sub-bituminous a value of tpi andgi maseral analysis result no no sampel tpi gi coal fasies gwi vi paleo-enviro calder et al., 1991, 1 2p/1/16 0.11 1 limnic 3.581 0.423 rheotrophic 2 3p/1/16 0.5 1 limnic 4.090 0.47 rheotrophic 3 4p/1/16 0.127 1.006 limnic 0.6 0.45 rheotrophic prayitno b./ jgeet vol 1 no 1/2016 69 conclusions coal composition by microscopic investigation, the type of organic matter derived from the wet marsh plants (high gi, low tpi) or limnic conditions. whereas the spread in the form of pyrite mineral frambiodal lines indicate the condition of surface water is high on the surface layer of peat (high gwi, low vi) or rheotropic mire. the above interpretation is also supported by the absence of fungal growth. references [1] barber, m. j. crow, j. s. milsom. (2005). sumatra geology, resources and tectonic evolution (geological society memoirs, no. 31) geological society of london .p86 97. [2] calder, j.h., gibling, m.r. and mukhopadhyay, p.k. (1991) peat formation in a westphalian b piedmont setting, cumberland basin, nova scotia: implications for the maceral-based interpretation of rheotrophic and raised paleo-mires. bulletin de la société géologique de france 162, 283-298. [3] diessel, c.f.k. (1986) on the correlation between coal facies and depositional environment. proc. 20th symp. dept. geol., university of newcastle, nsw, pp. 19-22. [4] iccp training course on dispersed organic matter (2011).organic petrology, macerals, microlithotypes, lithotypes, minerals, rank. departamento de geociências, ambiente e ordenamento do território, faculdade de ciências da universidade do porto porto, portugal [5] iccp (2001) the new inertinite classification (iccp system 1994). fuel, v.80, pp.459-471. [6] suárez-ruiz isabel organic petrology: an overview. instituto nacional del carbón (incar-csic) oviedo spain. pp.201 224. [7] isabel suárez-ruiz deolinda flores, joão graciano mendonça filho, paul c. hackley d(2012). review and update of the applications of organic petrology: part 1, geological applications. international journal of coal geology 99 (54 11). [8] komang anggayana, basuki rahmad, h. h. arie naftali and agus haris widayat. limnic condition in ombrotrophic peat type as the origin of muarawahau coal, kutei basin, [9] indonesia. journal geological society of india vol.83, may 2014, pp.555-562. [10] styan, w.,b., & bustin, r.m., (1983), petrography of some fraser delta peat deposits: coal maceral and microlithoty peprecursors intemperateclimatepeats. international journal of coal geology, 2, 321-370. composition group of maseral and mineral matter no no sampel vitrinite (% v) liptinite (% v) inertinite (% v) mineral (% v) 1 2p/1/16 58.00 2.6 39.40 2 3p/1/16 52.24 2.6 45.16 3 4p/1/16 89.00 4.6 6.40 table 1. maceral compositions http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 2 2022 hussain, a. et al./ jgeet vol 7 no 2/2022 39 research article analysis of grain morphology, mineral composition, and ore grade on gold placer deposits in bantimurung, pangkep regency, south sulawesi, indonesia angga al amin husain1, ulva ria irfan1*, irzal nur2 1 geological engineering department, faculty of engineering, hasanuddin university, makassar, indonesia. 2 mining engineering department, faculty of engineering, hasanuddin university, makassar, indonesia. * corresponding author : ulvairfan@yahoo.com tel.:+62-811466670; fax: +62-411840216 received: mar 21, 2022; accepted: jun 30, 2022. doi: 10.25299/jgeet.2022.7.2.9164 abstract the information through social media shows that there is quite an intense placer mining activity by local residents in the bantimurung area, tondong tallasa district, pangkep regency. this study as a preliminary research aims to determine the grain morphology characteristics of mineral composition and metal grade in gold placer deposits in the study area. the data collected were eight samples. the collected samples were prepared into thin section, polished and observed using a microscope to identify the mineral composition and grain morphology. the grades of au metal and its associated metals consisting of ag, zn, pb, and cu in the placer samples were analyzed by the aas method. petrography shows abundant of quartz, plagioclase, biotite and pyroxene minerals it might be indication of mineralization of epithermal. ore petrography shows pyrite present along the river, silver is also found quite a lot along the river. meanwhile, covellite, magnetite, sphalerite, and garnet were found only slightly at the sampling station this mineral composition indicates that the source of the placer deposits was epithermal. the grain morphology of the thin-section observation shows that quartz dominant has a high sphericity with character of roundness tends to be very angular to sub-rounded from upstream to downstream of the river. plagioclase tends to have sub rounded roundness and high sphericity. biotite tends to have a high sphericity with roundness from upstream to downstream is very angular, then angular, then sub-rounded. pyroxenes tend to have high sphericity with very angular and angular roundness. au content is directly proportional to cu and inversely proportional to zn, pb, and ag. statistically au affects the content of cu by 50.97%. it can be concluded that au is genetically associated with cu, however au grains that were still attached to the mineral and had not been separated from other minerals so that it could not be seen visually. this can also indicate that the source of this placer deposit is not far from the study site. au grade corelated with stream sediment types it is 97,86 ppm for channel bar and 94,16 ppm for point bar, based on this we conclude the downstream has higher grade of au compare to the upstream. keywords: grain morphology, placer deposits, stream sediment, baturappe-cindako volcanic, bantimurung, 1. introduction information through social media shows that there is quite an intense placer mining activity by local residents in the bantimurung area, tondong tallasa district, pangkep regency. based on the results of field observation, information was obtained that this mining activity has been going on for decades, with productivity reaching 10 gram per day, with a large number of mining scattered along the river (fig. 1). fig. 1. activities of residents panning for gold in the study area south sulawesi province in regional geology is located in the magmatic-plutono-volcanic tertiary arc of west sulawesi (darman and sidi, 2000; hall and wilson, 2000). in this region, mineralization and hydrothermal gold deposits are only dominantly found in the north sulawesi region, which is an active magmatic arc area (carlile et al., 1990; carlile and mitchell, 1994; kavalieris et al., 1992). there are very few indications and the presence of hydrothermal gold deposits in south sulawesi province which is a shoshonitic k-alkaline arc. the gold mineralization prospects that have been reported in the south sulawesi region are only in the sasak district, tana toraja (cu-au porphyry); awak mas, luwu (mesothermal au); and palopo (anomaly au-pb-zn-cu and quartzcarbonate veins containing gold)(idrus et al., 2017; idrus and nur, 2011; nur et al., 2015; van leeuwen, 2018; van leeuwen and pieters, 2011). globally, placer-type gold deposits are also found in the alder gulch area, virginia, montana. the gold placer is the result of the quartz veins being eroded (roy et al., 2018). the same thing was also found in the arizona gold placer deposits associated with schist, granite, and gneiss, where the veins tend to be deeper than the mesothermal and hypothermal types (youngson t and and craw, 1999). the gold placer in eastern siberia is indicated to originate from gold-quartzlow-sulfide types as the primary source due to the mineralogy-geochemical characteristics of the placer http://journal.uir.ac.id/index.php/jgeet 40 hussain, a. et al./ jgeet vol 7 no 2/2022 originating from the lena-viluy region bordered by rivers (interfluves)(kazhenkina and nikiforova, 2016). until now there has been no publication of research results related to the type and source of gold mineralization in this area. this study as a preliminary study aims to determine the grain morphology characteristics of mineral composition and metal grade in gold placer deposits in the study area. based on the regional geological conditions, this area is very promising for the formation of hydrothermal gold mineralization. the tondong tallasa area and its surroundings are composed of melange lithology and metamorphic rocks bordering the propylitized volcanic rocks. propylite is one of the alteration types/zones bordering hydrothermal gold mineralization (hedenquist et al., 2000; simmons et al., 2005; sukamto, 1982). 2. regional geology regionally, bantimurung area, tondong tallasa district, pangkep regency is included in the geological map sheet pangkajene and watampone western part, sulawesi (sukamto, 1982). stratigraphically, the rock formations in and around the study site from oldest to youngest are: metamorphic rocks, melange complexes, propylitized volcanic rocks, mallawa formation, tonasa formation, and diorite intrusive rocks (fig. 2). fig. 2. regional geological map of the research area and its surroundings. stratigraphically, the rock formations located at the research site from oldest to youngest are: metamorphic rocks, melange complexes, propylitized volcanic rocks, mallawa formation, tonasa formation, and diorite intrusive rocks (sukamto, 1982) metamorphic rock (s): mostly consisting of schist and few genes; contains the minerals glaucophan, garnet, epidote, mica, and chlorite; generally sloping to the northeast, partially brecciated, and reversed to the southwest; this unit is not less than 2000 m thick and has a fault contact with the surrounding rock units; k/ar dating of schists on east bantimala yields an age of 111 million years. melange complex (m): tectonic mixed rock consisting of growakes, breccias, congomerates, sandstones; grazed, gray shale, red shale, red radiolarian chert, slate, schist, ultramafic, basalt, diorite and clay; this rock collection is leafy, mostly tilted to the northeast and shears up to the southwest; this unit is not less than 1750 m thick, and has a fault contact with the surrounding rock units; this complex is mesozoic in age. propylitized volcanic rocks (tpv): breccia, lava and tuff; generally andesitic, partially tractic and basalt; the top is inlaid with red shale and limestone; breccia components vary, from a few cm to more than 50 cm, tuff-bonded which amounts to less than 50%; lava and breccias are dark gray to greenish-grey in color, strongly brecciated and propylized, containing large amounts of carbonates and silicates; k/ar dating on basalt east of bantimala yields an age of 58.5 million years (lower paleocene); this unit is about 400 m thick; unconformably overlain by the eocene rocks of the tonasa formation and the malawa formation; intruded by granodiorite and basalt rocks. mallawa formation (tem): sandstone, conglomerate, siltstone, claystone, and marl, with inserts of coal and claystone seams or lenses; the sandstones are mostly quartz sandstone, some are arkosa, grewake, and tuffaceous, generally light gray and light brown in color; generally brittle, less dense; the conglomerate is partially compact; claystone. limestones and marls generally contain unexamined molluscs, and are light gray to dark gray in color; coal in the form of lenses several centimeters thick and in layers up to 1.5 m; based on its fossil content, it is estimated that it is of eocene age with a parallax to shallow environment; the thickness of this formation is not less than 400 m; overlain with the limestones of the tonasa formation and unconformably overlaid by the propylitized volcanic rocks. tonasa formation (temt): solid coral limestone partially shattered; white and light gray; bioclastic limestone and calcarenite; white light brown and light gray, some well layered, interspersed with tuffaceous globigerina marl; the lower part contains bituminous limestone, hussain, a. et al./ jgeet vol 7 no 2/2022 41 localized with limestone breccia and sandy limestone inserts; near malawa, in the camba area, limestone containing glauconite was found, and in several places in the ralla area limestone was found containing a large amount of schist and ultramafic rock; the layered limestone contains many large foraminifera, the marl contains many small foraminifera and some sandy marl layers contain many large shells (pelecypoda) and snails (gastropods); solid limestones are generally strongly fractured; in the tanetteriaja area there are three alternating marl lanes with a new layer of limestone; its fossil content indicates an age range from early eocene to middle miocene, and shallow to deep neritic environments and lagoons; the thickness of this formation is estimated to be not less than 3000 m; superimposed on the rocks of the malawa formation and intruded by sills, rifts, and igneous stocks of basalt, trachytic, and diorite composition. diorite (d): intrusive of diorite and granodiorite, mainly stock and some cracked, mostly porphyry texture, light gray to gray in color; diorite exposed to the north of bantimala and to the east of biru through the sandstone of the balangbaru formation and ultramafic rocks; the breakthrough that occurred around camba consisted partly of porphyry granodiorite, with many phenocrysts in the form of biotite and amphibole, and broke through the limestones of the tonasa formation and the rocks of the camba formation; the dating of k/ar granodiorite from east of camba on biotite results in an age of 9.03 million years (upper miocene). fig. 3. picturization of sampling station at study area. boulders of altered diorite present around sampling station with vein texture indicate mineralization on study area. geological structures that develop in this area are reverse and shear faults. reverse fault is a lithological contact between the older melange complex and the younger mallawa formation. two shear faults are found in this area, the shear fault in the east has an almost west-east direction and is a lithological contact between the rocks of the mallawa formation and the propylitized volcanic rocks. meanwhile, the shear fault in the west is almost north-south and is a right-hand (dextral) shear fault that shifts the rock blocks of the tonasa formation and mallawa formation to the south (fig. 2). stream sediment will be found in-side of the river’s curve (stations 1, 2, 3, 5, 6, 7, and 8) and between rocks (station 4). 3. method 3.1 stream sediment sampling sampling was carried out using a mini shovel as deep as 30-45 cm in the sediment stream for 350 gram each station (irfan et al., 2021; tonggiroh and nur, 2019). then the samples were sieved to be separated based on grain size into <10 mesh, 16 mesh, 40 mesh, 70 mesh, and >120 mesh. the sequence of sample numbering is done from downstream to upstream. total of 8 stations were sampled along the river towards the upstream with an estimated distance of about 5 km from the placer gold mining location (fig. 3). fig. 4. types of stream sediment on study area 5 of 8 stations of placer was identified in this study as primary sedimentary bodies occupying the majority of space in this river (channel bar) (fig. 4) and the rest (station no 6, 7, and 8) was accumulates on the inside bend of streams (point bar) (hu et al., 2017; kleinhans and van den berg, 2011; olson, 2017). table 1. stations characteristic on study area station characteristic river flow bar 1 down stream channel bar 2 down stream channel bar 3 down stream channel bar 4 down stream channel bar 5 up stream channel bar 6 up stream point bar 7 up stream point bar 8 up stream point bar 3.2 grain petrography microscopic analysis was carried out by observing the thin section for altered minerals and polishing section for ore minerals using a nikon eclipse lv 100n pol polarizing microscope (husain et al., 2021). microscopic analysis was also carried out to identify the morphology of the mineral grains. morphology of grains in this paper refers to grain size, degree of roundness and sphericity of the grains. microscopic analysis was conducted in the preparation room of the geological engineering department, faculty of engineering, hasanuddin university. 3.3 geochemistry the grades of au metal and its associated base metals consisting of ag, zn, pb, and cu in the placer samples size >120 mesh was analyzed by atomic absorption spectrometry (aas) method. aas analysis was carried out using the buck scientific type 205 atomic absorption spectrophotometer at the analytical chemistry laboratory, department of chemistry, faculty of mathematics and natural sciences, universitas hasanuddin. grade of au will be compared with other base metal and >120 mesh grain size for correlation analysist. 4. result 4.1 grain size analysis 42 hussain, a. et al./ jgeet vol 7 no 2/2022 grain size <10 mesh shows random pattern from downstream to upstream, this was caused by the variative size of material on this class of size. class 16 mesh shows a perfect consistent increasing from downstream to upstream of mass. while class 40 mesh shows random pattern from downstream to upstream, this was caused by the size was between coarse and fine grains. finally, the class 70 and >120 mesh shows perfect consistent decreasing from downstream to upstream of mass ( ). overall distribution of grain size on study area was towards to sediment transportation theory (yi et al., 2012). based on the graph (error! reference source not found.), it can be concluded statistically that the fine grain size, which is <120 mesh from upstream to downstream, has an effect on ag content for 74.24% (inversely proportional), cu content for 55.28% (directly proportional). the concentration of other metals was not significantly affected by grain size, namely pb 49.74% (inversely proportional), au 29.05% (directly proportional), zn 0.63% (inversely proportional). table 2. result of the placer samples grain size measurement no. st size (mesh) <10 16 40 70 >120 1 m a ss ( g ra m ) 83 20 117 106 24 2 81 24 89 133 24 3 76 72 81 103 18 4 62 84 104 91 10 5 74 86 129 55 6 6 61 103 110 69 7 7 63 111 83 86 6 8 104 135 53 53 4 fig. 5. statistical relationship of grain >120mesh in percentage with ore grade 4.2 mineralogy and grain morphology 4.2.1 petrography the results of microscopic observations showed that 4 minerals were observed (fig. 6), that is quartz (qz) with transparent absorption color with white interference color, no pleochroism (-), low intensity, sub-anhedral shape, low relief, no cleavage, conchoidal fragments, mineral size <0.03 mm, has no twins, darkening angle 1-4°. fig. 6. photomicrograph of thin-section samples showing mineral features: quartz, plagioclase, biotite, and pyroxenes plagioclase abbreviated white gray with gray-black interference color, no pleochroism (-), moderate intensity, sub-anhedral mineral form, moderate relief, one-way perfect mineral cleavage, flat fracture, mineral size 0.050.18 mm, has twins carlsbad-albite, dark angle 30-36°, oblique dark type. pyroxene’s absorption color gray with blue-purple-black interference color, high intensity, subanhedral shape, high relief, one-way perfect cleavage, flat fragments, mineral size <0.05 mm, no twinning, darkening angle 32-35°, italic dark type. biotite absorption color is blackish brown with reddish brown interference color, dichroic pleochroism, moderate intensity, sub-anhedral shape, moderate relief, one-way perfect cleavage, flat fracture, mineral size 0.04-0.06 mm, darkening angle 87°. the results showed that quartz and plagioclase minerals were appear at each station, biotite absence on station 1 and pyroxenes absence on station 2 (table 3). the abundant of quartz indicate the present of vein, with plagioclase and pyroxene it might be indication of mineralization of epithermal (burkett et al., 2015; idrus and handayani, 2017; purwanto et al., 2018; wahyudi, 2011). biotite present indicate the low sulfidation mineralization (enríquez et al., 2018; syafrizal et al., 2017; villaplaza et al., 2017; irfan et al., 2017)). table 3. mineral distribution as a result of microscopic observations on thin-section samples to the distribution of stations no mineral station 1 2 3 4 5 6 7 8 1 quartz ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ 2 plagioclase ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ 3 biotite ✓ ✓ ✓ ✓ ✓ ✓ ✓ 4 pyroxenes ✓ ✓ ✓ ✓ ✓ ✓ ✓ hussain, a. et al./ jgeet vol 7 no 2/2022 43 the grain morphology of the thin section observation (fig. 7) shows that quartz has a high sphericity at stations 1, 2, 3, 5, 6, and 8. while at stations 4 and 7 it has a low sphericity. the character of roundness tends to be very angular to sub-rounded from upstream to downstream of the river. plagioclase tends to have sub rounded roundness and high sphericity at all stations. biotite tends to have a high sphericity with roundness from upstream to downstream is very angular, then angular, then subrounded. pyroxenes tend to have high sphericity with very angular and angular roundness. fig. 7. morphology characteristics (roundness and sphericity) of alteration mineral grain. 4.2.2 ore petrography the results of microscopic observations (fig. 8) showed 10 ore mineral were observed (table 4) namely cassiterite (cst) with blackish gray color, anhedral shape, anisotropic, no pleochroism, mineral size 0.1-0.5 mm found at stations 1, 4, 5, and 7. silver (ag) is bright white, subhedral-anhedral form, isotropic, no pleochroism, mineral size <0.3 mm found at stations 1, 3, 4, 6, 7, and 8. table 4 mineral distribution as a result of microscopic observations on thin-section samples to the distribution of stations no mineral station 1 2 3 4 5 6 7 8 1 cassiterite ✓ ✓ ✓ ✓ 2 silver ✓ ✓ ✓ ✓ ✓ ✓ 3 chalcopyrite ✓ ✓ ✓ ✓ ✓ 4 pyrite ✓ ✓ ✓ ✓ ✓ ✓ ✓ 5 covellite ✓ ✓ 6 magnetite ✓ 7 sphalerite ✓ ✓ 8 garnet ✓ 9 tennantite ✓ ✓ ✓ 10 gold ✓ chalcopyrite (cp) is bright yellow in color, anhedral form, anisotropic, no pleochroism, mineral size of 0.05 mm is found at stations 1, 2, 4, 5, and 8. pyrite (py) is yellowish white, subhedral-anhedral form, there is striation, anisotropic, does not have pleochroism, mineral size 0.1 0.3 mm is found at all stations except station 6. fig. 8. photomicrograph of a polished incision sample showing: cassiterite, silver, chalcopyrite, pyrite, dan covellite (a); magnetite (b); sphalerite dan garnet (c); chalcopyrite dan tennantite (d); dan gold (e) covellite (cv) blue color, anhedral shape, does not have pleochroism, mineral size 0.005 mm is found at station only found at stations 1 and 8. magnetite (mag) blackish gray color, euhedral-subhedral form, isotropic, no pleochroism, mineral size <0.25 mm found only at station 2. sphalerite (sph) gray color, shape subhedral-anhedral, isotropic, no pleochroism, mineral size 125 m found at stations 3 and 7. 44 hussain, a. et al./ jgeet vol 7 no 2/2022 garnet (gr) brown color, anhedral shape, anisotropic, no pleochroism, mineral size 0.3 mm found at station 3. tennantite (tn) grayish white color, sub shape hedralanhedral, anisotropic, no pleochroism, size <0.025 mm found at stations 5, 6, and 7. gold (au) golden yellow, euhedral form, isotropic, lacks pleochroism, mineral crystal size 0.1-0.3 cm was found at station 8. mineragraphic observations showed pyrite was present at almost every station. next is silver also found quite a lot along the station. meanwhile, covellite, magnetite, sphalerite, and garnet were found only slightly at the sampling station. grain morphology observations of polished section (fig. 9) showed cassiterite has a low sphericity. the roundness character is sub-roundness at station 1 then decreases to very angular at stations 4 and 5, and becomes angular at station 7. sliver has a high sphrecity where the roundness character tends to be sub-rounded at stations 1, 3, 7, and 8, and becomes angular at stations 6 and 8. chalcopyrite has a high sphericity at stations 4, 5, and 8 while at stations 1 and 2 it has a low sphericity. the roundness character from upstream to downstream is very angular then angular and becomes sub-rounded. pyrite has a high sphericity. the roundness character of pyrite is sub-angular at station 1, then becomes very angular at stations 4, 5 and 7, and becomes angular at stations 7 and 8. covellite has a high sphericity where roundness from upstream to downstream is angular and then becomes sub-rounded. magnetite has a low sphericity with very angular roundness. sphalerite has a low sphericity with very angular roundness. garnet has a low sphericity with very angular roundness. tennantite has a high sphericity with sub-angular roundness. gold has a low sphericity with very angular roundness. high sulfidation epithermal deposits are characterized by the assemblage of enargite luzonite covellite and pyrite sulfide ore minerals, low sulfidation epithermal by pyrite pyrrhotite arsenopyrite and fe-rich sphalerite, and intermediate sulfidation epithermal by tennantite tetrahedrite low-fechalcopyrite and sphalerite (einaudi et al., 2003; sillitoe and hedenquist, 2003; simmons et al., 2005). ore petrographic (mineragraphic) observations show that pyrite is present at almost every station. next is silver is also found quite a lot along the station. meanwhile, covellite, magnetite, sphalerite, and garnet were found only slightly at the sampling station. this mineral composition indicates that the source of the placer deposits at the study site is epithermal low sulfidation or epithermal high sulfidation (aluç et al., 2020; burkett et al., 2015; enríquez et al., 2018; idrus and handayani, 2017; pratomo et al., 2021; purwanto et al., 2018; syafrizal et al., 2017; villaplaza et al., 2017; wahyudi, 2011). fig. 9. morphology characteristics (roundness and sphericity) of ore mineral grain 4.3 grade of au and its associated metals the results showed that the distribution of the value of au varied along the river. au content is directly proportional to cu and inversely proportional to zn, pb, and ag. statistically au affects the content of cu by 50.97%. however statistically station 1 shows only 2,5 ppm of cu hussain, a. et al./ jgeet vol 7 no 2/2022 45 compares to other station it could reach to 72,3 ppm in average. table 5. the results of aas analysis of the grade of ag, au, cu, pb, and zn metals from the placer samples in the research area st grade (ppm) au cu pb zn ag 1 81,8 2,5 58,2 126,4 23,7 2 101,4 76,1 37,3 171,7 35,3 3 96,5 71,3 64,5 135,0 30,7 4 100,5 57,8 24,7 185,5 21,0 5 109,1 65,6 54,3 131,5 20,7 6 98,2 67,6 43,0 97,1 20,3 7 95,0 80,1 31,9 167,1 21,0 8 89,3 87,7 26,5 155,0 23,1 based on the results of statistical analysis of geochemical data as described above, it can be concluded that au is genetically associated with cu, and vice versa not associated with minerals carrying the elements zn, pb, and ag because it has a negative correlation with au, this may be because the source placer is an au-cu deposit. table 6. relation of gold to associated metal at the study area. no element relation with au r2(%) r 1 cu direction 25.98 50.97% 2 zn inverse 1.52 12.33% 3 pb inverse 0.3 5.47% 4 ag inverse 1.52 12.33% fig. 10. statistical relationship of grain au with other base metal (zn, pb, cu, and ag) on study area au grade corellated with stream sediment types it is 97,86 ppm for channel bar and 94,16 ppm for point bar, based on this we conclude the downstream has higher grade of au compare to the upstream. microscopic observations show au was appear at station 8 only, but on aas au was found along the station, this could be caused by au grains that were still attached into the mineral carrier and had not been separated from other minerals so that it could not be seen visually. this can also indicate that the source of this placer deposit is not far from the study site. 5. discussion the percentage of grain size >120, 70, and 40 mesh tends to increase from upstream to downstream of the river, and vice versa for grain-sized16 and <10 mesh. the grain morphology of the thin-section observation shows that quartz dominant has high sphericity with the character of roundness that tends to be very angular to sub-rounded from upstream to downstream of the river. plagioclase tends to have sub-rounded roundness and high sphericity. muscovite has low sphericity at stations upstream, then becomes high downstream. the roundness of muscovite from upstream to downstream is very angular, angular, and then sub-rounded. hornblende tends to have low sphericity with roundness from upstream to downstream is very angular, then angular, then sub-rounded. biotite tends to have high sphericity with roundness from upstream to downstream is very angular, then angular, then subrounded. pyroxenes tend to have high sphericity with very angular and angular roundness. grain morphology shows the presence of angular and very angular roundness, a variety of sphericity from high to low even the presence of altered diorite boulder with quartz vein it is clear the source of the anomaly of base metal in the study area is quite near. it has a strong indication the source might be from the diorite intrusion in the east of the study area. au grade is 97,86 ppm for channel bar and 94,16 ppm for point bar, and the distribution of au grades increases in the river from upstream to downstream, and the range of au grades is 81.79 109.14 ppm with an average of 96.47 ppm. based on this we conclude the downstream has a higher grade of au compared to the upstream. the average grade of cu at the study site was 63.5775 ppm with a range of 2.5 87.66 ppm, the grade of cu constantly increased from stations 4 to 8. the average grade of ag was 24,475 ppm with a range of 20.3 35,3 ppm, ag grade tends to increase from upstream to downstream at station 2. the average grade of pb is 42.5325 ppm with a range of 24.68 64.46 ppm, pb grade increase from station 8 to station 5 then pb grade becomes varied from station 4 to station 1. the average grade of zn was 146.15 with a range of 97.06 185.52 ppm zn grade distribution did not show a significant pattern. the results showed that the distribution of the value of the element au content varied along the river. au content is directly proportional to cu content and inversely proportional to zn, pb, and ag. statistically, au affects the content of cu by 50.97%. the grain morphology of the thin-section observation shows that quartz dominant has high sphericity with a character of roundness that tends to be very angular to subrounded from upstream to downstream of the river. plagioclase tends to have sub-rounded roundness and high sphericity. muscovite has low sphericity at stations upstream, then becomes high downstream. the roundness of muscovite from upstream to downstream is very angular, angular, and then sub-rounded. hornblende tends to have 46 hussain, a. et al./ jgeet vol 7 no 2/2022 low sphericity with roundness from upstream to downstream is very angular, then angular, then subrounded. biotite tends to have high sphericity with roundness from upstream to downstream is very angular, then angular, then sub-rounded. pyroxenes tend to have high sphericity with very angular and angular roundness. in microscopic observations, au metal was found at station 8 only, but on aas au was found along with the station, this could be caused by au grains that were still attached to the mineral and had not been separated from other minerals so that it could not be seen visually. this can also indicate that the source of this placer deposit is not far from the study site. au-grain during transporting from upstream after being released from associated minerals will stick to other au-grain all the way downstream, this might cause the small percentage of au on fine grain. petrography shows abundant quartz indicates the presence of veins; it might be an indication of mineralization of epithermal (irfan et al., 2017); (nur et al., 2019). ore petrography shows pyrite present along the river, silver is also found quite a lot along the river. meanwhile, covellite, magnetite, sphalerite, and garnet were found only slightly at the sampling station. this mineral composition indicates that the source of the placer deposits at the study site is epithermal low sulfidation or epithermal high sulfidation (aluç et al., 2020; burkett et al., 2015; enríquez et al., 2018; idrus and handayani, 2017; pratomo et al., 2021; purwanto et al., 2018; syafrizal et al., 2017; villaplaza et al., 2017; wahyudi, 2011). although augrain visually on microscope present only on 1 station it could be cause the location is quite near of mineralization so the au-grain is still in very fine grain size which it’s hard to identify through microscope beside that the au-grain might be still trapped in carrier mineral is the other reason au-grain doesn’t appear on ore petrography but appear on chemistry analysist. geochemistry shows that the distribution of au varied along the river. au content is directly proportional to cu and inversely proportional to zn, pb, and ag. statistically au affects the content of cu by 50.97%. however statistically station 1 shows only 2,5 ppm of cu compares to other station it could reach to 72,3 ppm in average. it can be concluded that au is genetically associated with cu, and vice versa not associated with minerals carrying the elements zn, pb, and ag because it has a negative correlation with au, this may cause the source placer is an au-cu deposit or epithermal high sulfidation. 6. conclusion  metallic minerals identified from the study site are cassiterite, covellite, magnetite, sphalerite, garnet, tennantite, and gold as well as abundant silver, chalcopyrite, and pyrite, while the transparent minerals identified are quartz, plagioclase, muscovite, hornblende, clay minerals, biotite, and pyroxenes.  morphologically mineral transparant was very angular until sub-rounded, as well metallic minerals except gold and sphalerite was very angular caused of source relative closer which is diorite intrusion on the east of study area.  au 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http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 1 2022 34 putra, r. et al./ jgeet vol 7 no 1/2022 research article rapid land cover change in the south sumatera peat area associated with 2015 peat fires raden putra1,2*, tastaptyani k nufutomo1, yuni lisafitri1, novi k sari1, alfian zurfi1, deni o lestari2,3, muhammad u nuha2,4 1department of environmental engineering, faculty of regional and infrastructure technology, institut teknologi sumatera, lamp ung 35365, indonesia 2research and innovation center for disaster mitigation and early detection of wildfires, institut teknologi sumatera, lampung 35365, indonesia 3department of atmospheric and planetary science, faculty of science, institut teknologi sumatera, lampung 35365, indonesia 4department of geomatics engineering, faculty of regional and infrastructure technology, institut teknologi sumatera, lampung 35365, indonesia * corresponding author : raden.putra@tl.itera.ac.id tel: +62 721 8030188 received: feb 10, 2021; accepted: mar 30, 2022. doi: 10.25299/jgeet.2022.7.1.6395 abstract the peat fire events in indonesia, particularly the south sumatra area, changed the appearance of surface vegetation. the fires usually occur during the dry season from july to october. this study aims to evaluate land cover changes due to 2015’s peat fire in the south sumatra peatlands. remote sensing techniques using a normalized difference vegetation index (ndvi) method were used to identi fy the change of vegetation density in the study area. the results showed that 69% of the total south sumatra peatland was burned due to the 2015 peat fire event. the level of vegetation density was considerably decreased by fire events. the degradation in the burne d area was dominated by land cover class of ferns/shrub. the peat fires during the observation period have a negative impact on the peat ecosystem, so improvements are needed in peatland management practices. improvements need to be made in fire prevention and management practices, as well as restoration of burnt land. keywords: abstract peat fire, ndvi, burned area, degradation 1. introduction peatland is a unique ecosystem that provides multiple benefits of significant carbon sequestration, water catchments, and rich biodiversity (agus et al., 2013; page et al., 1999). human activities such as deforestation, land conversion, and man-made fires are the primary pressures to peat degradation. in the current management practices, peatland is under a serious threat of land degradation in southeast asia, particularly in indonesia. (hooijer et al., 2006; jaenicke et al., 2010; miettinen et al., 2012b). the south sumatera peatlands have been degraded in the past two decades due to deforestation, illegal logging, and man-made fires (miettinen et al., 2016; thorburn and kull, 2015). the peat fire event commonly occurs during the dry season from june to november (miriam e marlier et al., 2015; miriam e. marlier et al., 2015a, 2015b). during the fire events, an incomplete combustion release carbon to the atmosphere and critically contribute to global warming. moreover, peat material and surface vegetation burning generate haze disaster, which is deteriorated wildlife, human health, economy, and climate. the previous studies have reported that up to 300 people died in indonesia, malaysia, and singapore caused by the severe haze pollution during september-october in 2015 (harrison et al., 2009; koplitz et al., 2016; miriam e. marlier et al., 2015b). on the other hand, the fires also reduce the biodiversity and the appearance of surface vegetation along the burnt area (page and hooijer, 2016; sloan et al., 2017). the objective of this study is to evaluate the land cover change due to the 2015 peat fires on the south sumatera peatlands. remote sensing techniques using the normalized difference vegetation index (ndvi) method were used in determining vegetation density in the study area. the ndvi identification was afterward analyzed spatially by overlaying with land use maps in order to evaluate the change of each land-use class. 2. data and method 2.1 study area south sumatra region has about 9% (1.48 million ha) of the indonesian peatlands (wahyunto et al., 2004). based on the data provided by the indonesian national board for disaster management (bnpb) in 2016, south sumatra is the region that experienced the worst peat fires in indonesia during the 2015 dry season. the south sumatra peat area is located near the eastern coast of sumatera bounded by 101° 35’ 0” e 105° 55’ 0” e and 01° 10’ 0” s 04° 50’ 0” s (see figure 1). 2.2 hotspot data hotspot data were used to identify the south sumatera peat fires during august november 2015. the hotspot data were obtained from the moderate resolution imaging spectroradiometer (modis) sensor on the terra and aqua satellites with a resolution of 1 km. those data were available online at the fire information for resource management system (firms) website (https://firms.modaps.eosdis.nasa.gov). hotspot data were analyzed by spatial buffer methods following the modis spatial resolution. the results show the burned area, which http://journal.uir.ac.id/index.php/jgeet putra, r. et al./ jgeet vol 7 no 1/2022 35 use to observe the change of vegetation density in the study area. fig. 1. location of the study area, also shown are the distributions of peat area 2.3 satellite images the vegetation density analysis in study area identified by landsat 7 and 8 satellite images. these images had a spatial resolution of 30 meters with a coverage area of 185 x 185 km. the vegetation density determination observed preand post2015 peat fires event through landsat data recorded in 2013 and 2016. the research area covered 4 sheets of the landsat imagery, namely 123-062, 124-061, 125-061, 125-062, and 124-062 (path-row). the data were provided by the united states geological survey (usgs), earth explorer, and were available online at http://earthexplorer.usgs.go. the images had been registered and geo-corrected from the source. the atmospheric correction has been undertaken by the preprocessing landsat tools in the qgis software version 2.18.2. the calibration landsat tool acquired the radiometric correction. 2.4 ndvi and spatial analysis normalized difference vegetation index (ndvi) is a method of analyzing satellite imagery and commonly used to identify the surface vegetation density and land cover changes. the ndvi values were calculated by comparing the red and nir bands of the landsat sensor system (equation 1). ndvi = ((nir – red)) / ((nir + red)) (1) the ndvi values range from –1 to +1. the higher the ndvi value, the more dense the vegetation, and the lower the ndvi value, the sparser the vegetation. (bharathkumar and mohammed-aslam, 2015; meneses-tovar, 2011). this study divided the ndvi value into six vegetation density classes, each with its own vegetation density weight (see table 1). table 1. classification of ndvi value ndvi value ndvi class ndvi weight < 0.0 non-vegetation 1 0.0 – 0.2 very low vegetation 2 0.2 – 0.4 low vegetation 3 0.4 – 0.6 moderate vegetation 4 0.6 – 0.8 high vegetation 5 0.8 – 1.0 very high vegetation 6 the difference in the weights of the 2016 and 2013 ndvis is used to evaluate changes in vegetation density (equation 2). the positive change values indicate that surface vegetation is growing, while negative values suggest that it is degrading. the classification of changes in vegetation density resulted in 11 classes, as shown in table 2. furthermore, changes in vegetation density were analyzed towards land cover data in 2013 (data collected from putra et al., 2019) using the spatial overlay method to determine the characteristics of changes in each land cover class. changed value = ndviweight 2016 – ndviweight 2013 (2) table 2. classification of the changing area changed values classes -5 very high degradation -4 high degradation -3 moderate degradation -2 low degradation -1 very low degradation 0 unchanged 1 very low veg. increase 2 low veg. increase 3 moderate veg. increase 4 high veg. increase 5 very high veg. increase 3. results and discussion during the 2015 dry season (june-november), there were 21,173 hotspots detect over the peatlands of south sumatra (see figure 2). according to the buffer analysis, the extent of the burnt area at the observation area in 2015 was estimated to be 7,132 km2, or approximately 69 percent of the entire area of peatland in south sumatra. on the other hand, the spatial analysis presents fires spread evenly in the research area. next, the identification of vegetation density before and after the 2015 fire period was carried out in the buffer area which is considered as a burnt area. in 2013, the vegetation density index shows the state of the research area which is dominated by very high and high vegetation density classes. as shown in figure 3, the eastern half of south sumatra's peatlands have very high vegetation density characteristics, while the rest ranges between moderate and low vegetation density. while the ndvi analysis in 2016 shows a different condition, most of the observations area was dominated by high and moderate vegetation density classes. significant changes took place in the eastern part of the observation area, where most of the 36 putra, r. et al./ jgeet vol 7 no 1/2022 area was classified as medium and low vegetation density classes. noted, due to the availability of data and information, the southeastern part of the observation area was identified as a non-vegetation class in 2013 and 2016. the comparison of the area of vegetation density in 2013 and 2016 in each class is presented in figure 4. the decrease in area occurred in the very high and high density classes, while the increase in area occurred in the moderate and low density classes. these findings indicate that the fires event in 2015 caused the surface vegetation in the study area to be degraded. fig. 2. the hotspots distribution and burned areas on south sumatra peatlands in 2015. fig 3. vegetation density levels before and after 2015 fire event (left: 2013, right: 2016) fig. 4. comparison of vegetation density areas between 2013 and 2016 the land cover change in the research area is the result of the 2013 and 2016 ndvi map overlays (figure 3). during the observation period, there were two types of land cover changes, namely a decrease (degradation) and an increase 0% 10% 20% 30% 40% 50% non vegetation very low vegetation low vegetation moderate vegetation high vegetation very high vegetation 2013 2016 putra, r. et al./ jgeet vol 7 no 1/2022 37 in the density of surface vegetation (vegetation increase). based on table 3, land cover change is dominated by degradation, where 53% of the study area experienced a decrease in vegetation density classes with varying degrees. while the rest did not experience a change in vegetation density (about 34%) and another 11% experienced an increase in vegetation density. the changes that occur are closely related to the 2015 peat fire period, where the burned area (figure 2) experienced a decrease in vegetation density class or was degraded. on the other hand, the increase in vegetation density in a small part of the study area was forced by vegetation growth during the observation period. table 3. percentage of land cover change in mk-phr area changed class hectare % very high degradation 11,301.90 1.70 high degradation 9,817.19 1.48 moderate degradation 48,282.49 7.26 low degradation 106,843.32 16.05 very low degradation 181,928.17 27.34 unchanged 230,297.37 34.61 very low veg. increase 69,164.22 10.39 low veg. increase 7,583.04 1.14 moderate veg. increase 264.53 0.04 high veg. increase 9.73 0.00 total 665491.98 100.00 fig. 5. the levels of changes in vegetation density due to the 2015 fire event more than half (64%) of burned and degraded peatlands had been identified as a fern/ shrub land cover class. the land cover type of industrial plantation and secondary psf (peat swamp forest) was estimated to 24% degradation of the total burned and degraded peatlands (see table 4). surprisingly, the industrial plantation was burned and degraded since this type of land cover was considerably managed land. in addition, fire and degradation in secondary psf class indicated that fire was used for land preparation, as mentioned in several previous studies (miettinen et al., 2012a). those negative impacts, as above-mentioned was an alarming rate to many crises. some policy reformation is needed to alleviate the management failures of peat fires. future improvements and actions should be conducted, such as forest policy reform, improved land use planning, improved governance, addressing market failures, and other changes (pagiola, 2000). to prevent and make sustainable forest management, many stakeholders, who play important roles, should make the system works and better to avoid future possible peat fire events. table 4. distribution of land degradation based on the land-use class due to 2015 fire event land cover class degradation (ha) total very high high moderate low very low ha % ferns/ shrub 8,255.28 5,583.67 25,958.26 67,483.20 123,211.62 230,492.03 64.55 small holder area 495.23 775.21 670.98 2,135.47 7,393.53 11,470.41 3.21 secondary psf 50.32 250.87 4,670.26 12,793.79 20,892.85 38,658.09 10.83 industrial plantation 519.63 2,477.06 14,901.68 14,906.26 15,037.94 4,7842.57 13.40 cleared area 1,888.75 442.21 1,984.27 8,360.62 11,884.05 24,559.90 6.88 built-up area 28.60 106.93 31.99 48.06 330.51 546.09 0.15 primary psf 0.84 0.56 26.98 908.74 2,584.03 3,521.16 0.99 38 putra, r. et al./ jgeet vol 7 no 1/2022 4. conclusions the severe peat fires event in 2015 had burned more than half area (69%) of south sumatra peatlands. the change of vegetation density indicated not only degraded vegetation but also vegetation regeneration based on observed preand post-fire event. the majority of vegetation density change in the 2015 was caused by land degradation, in which the classes of vegetation density turned into a lower class. the total of land degradation area remained of 53% of the total burned area with varying levels of degradation. all land cover classes in the burned area were degraded due to fires with varying percentages. the results point out that peatland fires had a negative impact and became a serious issue on peat ecosystems in the research area. south sumatra's peatlands are still potentially at high risk of peat degradation since the land cover is dominated by ferns/ shrub. the prevention and proper forest management are needed to avoid future degradation of peat ecosystems. 5. acknowledgments this study is fully funded by the “guru besar under 45 (gbu45)” 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plantations in sumatra, indonesia: complex realities for resource governance, rural development and climate change mitigation. asia pac. viewp. 56, 153–168. https://doi.org/10.1111/apv.12045 wahyunto, ritung, s., suparto, h. subagjo, 2004. map of peatland distribution area and carbon content in kalimantan. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn :2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 02 2018 94 rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 macerals analysis seam m2 muaraenim formation, : implication toward coal facies and coal rank in kendi hill, south sumatra y.m rajagukguk 1, *, s. nalendra 1 1 sriwijaya university, jl. srijaya negara, bukit besar, ilir barat i kota palembang 30139 * corresponding author: yonathanmangatur@yahoo.com received: 29 apr 2018. revised: 25 may 2018, accepted: 29 may 2018, published: 1 june 2018 doi: 10.24273/jgeet.2018.3.2.670 abstract the muaraenim formation is a coal bearing formation in south sumatra basin of the late miocene pliocene. muaraenim formation based on coal seam content is divided into four seam, are: m1, m2, m3 and m4. coal seam in this area include in seam m2 member, with the general characteristics of the presence of silicified coal on the roof and floor of coal seams as a marker. the administration of the research area is located in east kendi hill, south sumatra. the kendi hill is composed of adesite igneous rocks that intruded muaraenim formation in unconformity at the time of pleistocene. this study aims to determine the environment of coal depositional based on maceral analysis and determine the factors influence the physical characteristics of coal seams in kendi hill. data that has been obtained from the field, then conducted a selection process.the number of samples analyzed were nine sample based on near and far to the kendi hill spread from the southern, central, and northern of the location. the result of the analysis will display the maceral diagram. megascopically, coal seam in the kendi hill are black, dull with bright, uneven subchoncoidal, blackish brown in streak, have a pyrite and resin. the thickness of the coal seams ranges from 0,45 to 14 meters. based on the maceral analysis, the coal seam in the muaraenim formation is composed dominated by vitrinite, then liptinite, inertinite and mineral matter pyrite (1,6-6,6%). vitrinite reflectance of coal in the research area ranges from (0,37-0,48%) that included to the sub-bituminous high volatile bituminous c. from the results of tissue preservation index and gelification index value indicated that the coal facies in the research area was a limnic to wet forest swamp. whereas the deposition of the muaraenim formation in deltaic environment (transitional lower delta plain). keywords: coal, maceral, muaraenim formation, south sumatra basin 1. introduction indonesia is a country that has a lot of natural resources, one of which is a natural wealth in the field of energy is coal. in the current state of coal in indonesia has a variety of physical characteristics of formation. according to horne (1978) the sedimentary environment affects the distribution, thickness, and severity of coal. based on characteristics of coal deposition environment, it divided into four (4); barrier and back-barrier, lower delta plain, transitional lower delta plain, and upper delta plain. furthermore, according to diessel (1986) and diessel (1992) the presence of the smallest element in coal is very important to be a specific environment and discussed maceral content, coal rank, coal facies on chemical and biology based on tissue preservation index (tpi) and gelification index (gi). the role of the maceral is based on the properties they possess, including the nature of the attribute and scalar nature. furthermore used the ward (1986) classification to know coal rank of the research area based on the vitrinite reflectance value (rv) obtained from the laboratory test. the environment of coal depositional based on horne (1978) and coal facies determination theory diessel (1986) still used by pratama and amijaya (2015) as reference for determining the depositional environment and coal facies based on organic petrographic analysis. this research aims to determine the environment of coal depositional based on maceral analysis, determine the coal facies and coal rank in kendi hill and determine the factors influence physical characteristics of coal seams in the research area. the administration of the research area is located in east kendi hill, pulau panggung village, muaraenim regency, south sumatra (fig. 1). access to the research area can be reached from the city of palembang through the land route cross sumatra + 200 km to tanjung enim district, and continued through the village path of the pulau panggung by using a four-wheeled. spatial area of research is located in sub basin of south palembang, whereas stratigraphy is in muaraenim formation (tmpm), kasai formation (qtk), and andesite intrusion (qpva). 2. geological setting the location of the research area is in the muaraenim formation and units of young volcano (andesite intrusion). mailto:yonathanmangatur@yahoo.com rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 95 fig. 1. location map of research area. the muaraenim formation conformably overlaying with airbenakat formation that composed of sandstone, sandy claystone, tuffaceous sandstone and mudstone with coal intercalation (heryanto, 2006). muaraenim formation is a coal bearing formation in south sumatra basin of the late miocene pliocene. according to shell (1978), in ideal condition muaraenim formation is divided into several members, namely m1, m2, m3, and m4 (fig. 2). member of m2 consists of clay, carbonaceous clay, siltstone, claystone, and coal. m2 member have three main layers; seam c (petai seam), seam b (suban seam), and seam a2 (mangus seam). petai seam is the lower limit on seam m2 which has the characteristics of the availability of silicified coal on the floor. suban seam between the petai seam and mangus seam, which has a thick enough silicified coal on the floor. mangus seam is the upper limit on seam m2 which has the characteristics of the availability of silicified coal on the top seam. the unit of the young volcano (kendi hill) is one of the intrusions of igneous rocks located in the research area of pleistocene. the intrusion is formed on the surface because of the flow of magma derived from shallow dome that causes uplift, fault, and fold (fig. 3) (amijaya and littke, 2006). fig. 2. coal stratigraphy columns of muaraenim formation. seam m2 (modified from shell, 1978). 96 rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 fig. 3. geological map and geological section of the muaraenim area (modified from bamco, 1983; gafoer et all., 1986 on amijaya and little 2006). 3. methods the research used descriptive-observative methods, used consisted of literature study, field observation in the from of measured section to know geometry, lithology, sediment structure and physical description coal seam. the method used in sampling is channel sampling, taking representative of coal seam from floor to roof then mixed into one plastic sample. the analyzed coal samples were nine (9) samples with coal deployment analyzed each located in the northern part of research area amounting three samples, in the center of research area were three samples, and in the southern of research area were three samples representing each coal seam. the sample of coal taken is distinguished by near and far from kendi hill. samples located near kendi hill are north coal samples and those far from kendi hill are southern coal samples. the method of maceral analysis on coal, tool used is point counter to identify and calculate the number of macerals, then ray reflection microscope function to know the type of maceral and mineral present in coal with the number of observations on each sample as much as 500x. as for measuring the reflectance value of the vitrinite maceral group to determine the rank of the coal, the measurements were carried out under an immersion oil medium. based on the results of the analysis, the depositional environment, coal facies, and coal rank of the research area can be determined by the consisting of maceral content and vitrinite reflectance. 4. result and discussion 4.1 depositional environment seam m2, muaraenim formation in kendi hill based on environment analysis of coal deposition, muaraenim formation is included into the transitional lower delta plain (fig. 4). according to this model, the transitional lower delta plain depositional environment is composed of repetition lithology (from bottom to top) from roof seam c (petai) to floor seam a2 (mangus) is coal, claystone, sandstone layer, siltstone, sandstone, claystone, and coal seam. lithology on research area consisting of claystone, siltstone, and sandstone with parallel laminae carbonaceous, indicated sedimentary coal bearing on seam m2 found vertically in the transition environment of upper delta plain to lower delta plain with some layers showing tidal deposits associated with fine-grained material deposits. sub-deposition environment found is crevasse spays, swamp, and interdistributary channel. fig. 4. coal depositional environment on seam m2 based on horne (1978). crevasse spays are deposits of flooded outflows associated with swamp environment that erode levee and chop, allowing the water to overflow into the floodplain on the left and right sides of the river to formed crevasse splays deposit. characteristics of sediment found in the area of fine grains with parallel laminae carbonaceous structure composed by fine sandstone and siltstone with thick enough. swamp is a environment containing coal-forming plants with lithology mudstone and claystone filling in the fracture of coal during deposition process. interdistributary channel is an environment is formed with weak energy and calm conditions, that in this zone will be deposited lithology material siltstone and claystone dominant. this area subenvironment acts as interburden between coal seam (fig. 5). the encounter of impurities in the coal seam is resin and pyrite, indicated the coal in this area composed by organic materials derived from large trees. thus the environment of coal deposition is the terrestrial. while the presence of mineral matter pyrite in coal indicated the influence of other marine environment. (fig. 6). rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 97 based on maceral analysis conducted on nine samples of coal and then recalculated into tissue preservation index (tpi), d (detrovitrinite: desmocollinite), t (telovitrinite: telocollinite), ti (teloinertinite; fusinite + semifusinite + sclerotinite) and gelification index, v (vitrinite: telocolinite + desmocollinite), ti (telocollinite: fusinite + semifusinite + sclerotinite). the recalculation results are ploted into the facies diagram tissue preservation index (tpi) versus gelification index (gi). the coal seam m2 in the research area ot the southern, central, and northern parts is deposited in the transition environment, ie the limnic (lower delta plain) to the wet forest swamp (upper delta plain). according the maceral analysis, the coal seam m2 in the muaraenim formation is composed dominated by vitrinite (69-82,6%), liptinite (0,65,6%), inertinite (9,8-20,8%) and mineral matter pyrite (1,6-6,6%) (table 1). value of tissue preservation index (tpi) on seam m2 shows value vary with value ranges between (0,35-1,43%). the varying prices of tissue preservation index (tpi) in indicated changes in plant composition and peat type in the research area likely due to changes in deposition environment. tissue preservation index (tpi) value >1indicates the high percentage of the presence of wood plants shown by the presence of abundant telocollinite maceral, while the tissue preservation index (tpi) value <1 indicates maceral derived from herbaceous plants. based on gelification index (gi) on seam m2 shows relatively high value ranges from (3,31-8,42%) indicating that the oxidation process does not take place predominantly, which is shown by the low inertinite content (table 2). diessel diagram results show that coal seam m2 in muaraenim formation is formed in the range lower delta plain to upper delta plain. the lower delta plain environment is spread in limnic stages dominated by shrubs. while the upper delta plain environment is formed at the wet forest swamp stage, it has a relatively high tissue preservation index (tpi) value and is dominated by telocollinite. for lower delta plain environment showed low tissue preservation index value and gelification value with predominantly desmocolinite maceral still affected by seawater (fig. 7). this is evident from the presence of pyrite minerals (1,6-6,6%) in the seam m2 muaraenim formation indicating that the deposition of coal in the research area is influenced by rising sea levels (fig. 8). table 1. result and description of coal seam m2, muaraenim formation, in kendi hill based on maceral analysis note : bb = coal v = vitrinite f=fusinite shc = shaly coal i = inertinite sc = sclerotinite csh = coaly shale l = liptinite d = desmocolinite cs = carbonaceous shale t = telecolinite s = semifusinite sh = shale al = alginite sb = suberinite n = number of measurments pyrite = pyrite r = resinite no . no. cont o litholog y mean reflectan t vitrinite (% rv random) rang e (%) standard deviatio n n component maceral (%) materia l mineral (%) v i l pyrite d t s f sc r sb al 1 yr-cs bb 0,45 0,40 0,48 0,02 200 39,0 35,4 7,0 13,4 0,6 1,6 3,0 2 yr-bs bb 0,42 0,37 0,47 0,03 200 50,4 23,4 9,0 9,6 1,0 1,0 5,6 3 yr-as bb 0,43 0,360,50 0,03 200 46,0 31,6 10,4 7,4 0,6 0,6 3,4 4 yr-cm bb 0,47 0,430,53 0,03 200 43,0 37,4 8,6 8,8 0,6 1,6 5 yr-bm bb 0,37 0,340,39 0,01 200 45,0 24,0 6,4 14,4 1,0 2,6 6,6 6 yr-am bb 0,41 0,370,44 0,02 200 66,0 16,6 3,4 6,4 2,6 2,0 1,0 2,0 7 yr-cu bb 0,48 0,430,54 0,03 200 61,4 13,4 9,6 9,0 1,0 1,0 4,6 8 yr-bu bb 0,46 0,420,50 0,02 200 59,0 18,6 3,4 11,0 1,4 1,0 0,6 5,0 9 yr-au bb 0,44 0,400,47 0,02 200 69,0 9,0 3,6 0,6 11,0 1,0 1,4 2,0 2,4 tpi = telovitrinite + teloinertinite detrovitrinite + gelovitrinite + inertoditrinite + geloinertinite gi = vitrinite + geloinertinite teloinertinite + detroinertinite 98 rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 fig. 5. seam m2 stratigraphy column (no scale) with coal deposited on transitional lower delta plain based on horne, 1978. seam c seam b seam a2 west east rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 99 meanwhile, the value of vitrinite reflectance of coal in the research area ranges from (0,37-0,48%) that included to the sub-bituminous high volatile bituminous c (table 3). high percentage of vitrinite reflectance value in seam m2 is inseparable from the influence of intrusion igneous rocks in kendi hill, which caused the coal seams in the northern part higher than the coal seams in the central and southern part ranged from (0,44-0,48%), while the average value of vitrinite reflectance at the center is (0,37-0,47%) and in the southern is (0,42-0,45%) (table 2). 4.2 coal characteristics, seam m2 muaraenim formation in kendi hil the coal outcrop in the research area is found around kendi hill, in muaraenim formation, south sumatra as coal-bearing formation in the research area. coal geometry at the research area is influenced by the intrusion of kendi hill, so that the coal seam has a strike that follows kendi hill shape and dip a relatively erect. coal distribution at the research area is relative north west to south east and north to south (fig. 9). fig. 6. the presence of pyrite and resin in coal seam m2 coal characteristics in kendi hill megascopically are black, dull with bright, uneven subchoncoidal, blackish brown in streak, have a pyrite and resin. the thickness of the coal seams ranges from 0,45 to 14 meters, which consists of seam c = 5-8meters, seam b = 11-14meters, and seam a2 = 6-7meters. the main characteristics of the main seam is seen from the presence of impurity coating on each seam in the form of silicified coal. characteristics of seam c is the existence of silicified coal on the floor, on seam b the existence of silicified coal on the floor, and seam a2 the existence of silicified coal on the roof (table 4). physically the seam c is more compact than seam b and seam a2. that because seam c is in a zone closer to the intrusion of andesite in kendi hill so that the seam c coal layer has better quality and rank than seam b and seam a2. fig. 7. tpi and gi diagrams in research area. fig. 8. pyrite associated with telocollinite and semifusinite associated with desmocollinite, reflectance white light 500x. pyrite resin 100 rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 table 2. coal rank classification according to vitrinite reflectance maximum no zone sample code tissue preservation index (tpi) gelification index (gi) mean refletance vitrinite (rv %) 1 north yr-au 0,35 5,13 0,44 2 yr-bu 0,56 5,38 0,46 3 yr-cu 0,52 4,02 0,48 4 center yr-am 0,4 8,42 0,41 5 yr-bm 0,99 3,31 0,37 6 yr-cm 1,27 4,62 0,47 7 south yr-as 1,07 4,36 0,43 8 yr-bs 0,82 3,97 0,42 9 yr-cs 1,43 3,65 0,45 table 3. coal rank classification according to vitrinite reflectance maximum. rank maximum reflectance (%rv max) subbitominous <0.47 high volatile bituminous c <0.47 <0.51 high volatile bituminous b 0.51 0.71 high volatile bituminous a 0.71 1.10 medium volatile bituminous 1.10 1.50 low vilatile bituminous 1.50 2.05 semi antrachite 2.05 3.0 (approx) antrachite > 3.0 table 4. description of coal characteristics seam m2. parameter layer seam a2 seam b seam c strike/dip n335 0 e/67 0 n334 0 e/70 0 n325 0 e/75 0 thickness 6 7 m 11 14 m 5 8 m colour black black black luster vitrain vitrain vitrain cleavage uneven subchoncoidal uneven subchoncoidal uneven subchoncoidal streak black his brown blackish brown black roof silicified coal floor silicified coal silicified coal rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 101 fig. 9. map of distribution pattern of coal layer of research area 5. conclusions based on this research, it can be concluded as follows: 1. the sedimentary environment and coal bearing formation in seam m2 muaraenim formation in kendi hill, south sumatra based on measured stratigraphic cross section are transitional lower delta plain with subenvironment crevasse spays, swamp,and distributary channel. 2. based on the result of maceral analysis and diagrams tissue preservation index and gelification index diessel conducted on nine samples of coal, it is suggested that the deposition environment of coal in the research area is transtion of limnic (lower delta plain) to wet forest swamp (upper delta plain), with maceral composition consists of vitrinite (6982,6%), liptinite (0,6-5,6%), inertinite (9,820,8%) and mineral matter pyrite (1,6-6,6%). organic materials that develop in research area dominated by plants of shrubs and wood plants with type maceral telocollinite and desmocolinite. 3. the value of vitrinite reflectance coal in research area ranged from (0,37-0,48%) that included to the sub-bituminous high volatile bituminous c. the closer to intrusion andesite kendi hill the vitrinite reflectance is higher (northern, 0,44-0,48%) than that of coal away from the intrusion zone (center, 0,37-0,47% and southern, 0,42-0,45). 4. coal characteristics kendi hill, seam m2 muaraenim formation are black, dull with bright, uneven subchoncoidal, blackish brown in streak, have a pyrite and resin with the thickness of the coal seams ranges from 0,45 to 14 meters. acknowledgment acknowledgment tribute to pt. prima mulia sarana sejahtera who has permitted researcher, then thanks to the authors addressed to the field supervisor mr. lulu sishandi and mr. fathulah hayyan assy ari who have provided input and information. references amijaya, h., littke, r., 2006. properties of thermally metamorphosed coal from tanjung enim area, south sumatra basin, indonesia with special reference to the coalification path. international journal of coal geology, 66, 271 295. diessel, c.f.k., 1986. on the correlation between coal fasies and depositional environment. proceedings 20th symposium of department geology, university of new castle, new south wales, 19-22. 102 rajagukguk, y.m & nalendra, s. / jgeet vol 03 no 02/2018 diessel, c.f.k., 1992, coal bearing depositional system, spinger verlag berlin. 423-430. heryanto, r. 2006. perbandingan karakteristik lingkungan pengendapan, batuan sumber, dan diagenesis formasi lakat di lereng timur laut dengan formasi talangakar di tenggara pegunungan tigapuluh, jambi. jurnal geologi indonesia. 1. horne, j.c., ferm, j.c., caruccio, f.t., baganz, b.p. 1978, depositional models in coal exploration and mining planning in appalachian region, aapg bulletin 62, 2379 2411, america. pratama, p.a.d., amijaya, h., 2015, lingkungan pengendapan batubara formasi warukin berdasarkan analisis petrografi organik di daerah paraingin, cekungan barito, kalimantan selatan, proceeding, seminar nasional kebumian ke-8 academia-industry linkage 15-16 oktober 2015; grha sabha pramana. prayitno, b., 2016a. limnic condition in rheotrhopic peat type as the origin of petai coal , central sumatra basin , indonesia. j. geoscience, engineering, environment, and technology 1, 63 69. prayitno, b., & ningrum, n. s. 2017. development of funginite on muaraenim and lower members of telisa formations at central sumatra basin indonesia. journal of geoscience, engineering, environment, and technology 2, 149-154. doi: 10.24273/jgeet.2017.2.2.342 shell mijbouw et al. 1978. geological map the south sumatra coal province scale 1: 250.000. ward, c.r. 1986. review of mineral matter in coal, australian coal geology, geol.soc. of australia, 6, 87107. 1. introduction 2. geological setting 3. methods 4. result and discussion 4.1 depositional environment seam m2, muaraenim formation in kendi hill 4.2 coal characteristics, seam m2 muaraenim formation in kendi hil 5. conclusions acknowledgment references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 1 2022 hasria et al./ jgeet vol 7 no 1/2022 15 research article serpentinization study on ultramafic rock at morombo area, lasolo islands district, north konawe regency, southeast sulawesi, indonesia hasria1*, febiyanti1, masri1, ali okto1, muliddin1, erzam s. hasan2, la hamimu2, sawaludin3, la ode muhammad iradat salihin3, wahab4 1department of geological engineering, halu oleo university, kendari, indonesia 2department of geophysical engineering, halu oleo university, kendari, indonesia 3department of geography, halu oleo university, kendari, indonesia 4department of mining engineering, halu oleo university, kendari, indonesia * corresponding author : hasriageologi@gmail.com tel.:+62-85241857853 received: apr 5, 2021; accepted: mar 30, 2022. doi: 10.25299/jgeet.2022.7.1.6643 abstract the research is in morombo area, north konawe regency, southeast sulawesi. the purpose of this study was to determine the characteristics of serpentinized ultramafic rock and serpentine paragenesis. research was conducted using field observations and laboratory analysis consisting of petrographic and geochemical analysis in the form of x-ray fluorosence (xrf). petrographic analysis was carried out to identify the mineral content and textures in the rock and to determine the percentage of serpentine minera l presence. both of these rocks are petrographically dominated by primary minerals olivine and clinopyroxine and secondary minerals namel y lizardite, chrysotile, antiorite and opaque minerals. the xrf analysis was to determine the elements of ni, fe, co, mgo, sio2, cao, al2o3 and p in ultramafic rocks. the results of petrographic analysis show that serpentinized ultramafic rocks in the study area co nsist of serpentinized dunite and serpentinized peridotite. the formation of clay minerals in rocks does not o ccur because of the low serpentinization process in the rock. the results of xrf analysis showed that all samples in the bedrock showed ni content above 0.2%. this is caused by the enrichment of ni which is interpreted as a result of the serpentinization process along with the formation of lizardite in the rock. the serpentinization sub-processes in the study area comprised by hydration, serpentine recrystallization, and deserpentinization. serpentine paragenesis is formed from the mid-oceanic ridge ocean floor, the orogenic phase to weathering. substitution of mg by ni in ultramafic rocks will produce ni-serpentin. it is estimated that in the research area lizardite and chrysotile lizardite and chrysotile are the causes of ni enrichment in bedrocks. the serpentinization characteristics of ultramafic rocks in the study area show a low to moderate level of serpentinization. keywords: serpentine, serpentinization, ultramafic, morombo. 1. introduction serpentinization is an exothermic, hydration reaction in which water reacts with mafic minerals such as olivine and pyroxine to produce lizardite, antigorite, and/or chrysotile (palandri and reed, 2004, in kurniadi et al., 2017). or in other words, the conversion process of olivine and pyroxine minerals in ultramafic rocks (peridotite and dunite) is replaced by serpentine minerals. according to (moody, 1976) ultramafic rocks that experience hydration will make part or all of the rock body undergo a serpentinization process. knowledge of serpentinization will be very important in determining the composition of the host rock, determining the temperature and pressure conditions during hydration and being able to determine the fluid composition and fluid source (moody, 1976). as is known no less important, knowledge of serpentinization will also be useful for exploration activities, especially exploration of laterite nickel deposits, because the majority of laterite nickel ore production comes from chemical weathering of serpentinized ultramafic rocks (freyssinet and butt, 2005; hasria et al., 2019a,b; 2020; 2021). an understanding of sepentinization will also be needed in assessing the tectonic processes associated with the displacement mechanism of ultramafic rocks during the rock deformation process (oud, 2010). in this study, the characteristics of the serpentinized rocks include the level of serpentinization in the rock and its chemical content based on x-ray fluorescence (xrf) data. so that information support the determination of serpentine mineral paragenesis is obtained. the area selected as a research location for conducting research on ultramafic rock serpentinization is morombo area, lasolo kepulauan district, north konawe regencyt, south east sulawesi (figure 1). in this area, there is an ophiolite strip that runs along the east coast of the southeast sulawesi arm, from tolo bay to tinobu and tanjung laonti (rusmana et al, 1993) to characterize the hialu lane. in this area, an ultramafic rock complex spreads out wide and becomes the iup area of pt. bumhi karya http://journal.uir.ac.id/index.php/jgeet 16 hasria et al./ jgeet vol 7 no 1/2022 utama, which has been operating since 2017. some of these factors underlie the authors to conduct research related to serpentinization studies in ultramafic rocks in the morombo area, lasolo kepulauan district, north konawe regency, south east sulawesi (figure 1). fig 1. geology map lasusua kendari, ( modified from rusmana et al., 1993 ). 1. research methods the method used in this study is divided into four stage namely: (1) desk study, (2) fieldwork (3) laboratory analysis and (4) data interprestasion. 2.1 desk study at this stage secondary data collection and literature review of the results of previous studies were carried out relating to the geological conditions of the study area. 2.2 fieldword this research is located in the morombo area, iup pt. bhumi karya utama, lasolo islands district, north konawe regency, southeast sulawesi (figure 1). field work includes observation and mapping of surface geology and representative sampling, geomorphological, lithological and structural geological observations. the secondary data collected in the form of bedrock test data obtained in the laboratory of pt. bhumi karya utama and other data that support the research.. 2.3 laboratory analysis this analysis includes petrology, petrography, and geochemistry. petrology analysis begins with megascopic description of the sample. petrographic analysis aims to identify mineral content and specific textures in rocks and to determine the percentage of serpentine minerals. the geochemical analysis aims to determinate the major elements in bedrock is ni, ni, fe, co, mgo, sio2, cao, al2o3 and p. petrographic analysis was carried out at the geological engineering laboratory of the teknik faculty of hasanudin university and geochemical analysis in the form of xrf (x-ray fluoresence) analysis was carried out at pt. bhumi karya utama. 2.4 data interpretation the interpretation of the data in this study includes all relevant data from the results of field and laboratory work which are evaluated and compiled to produce research objectives. 3. result and discusision 3.1. characteristics of serpentinized ultramafic rock 3.1.1 serpentinization on ultramafik rock by petrography analysis the number of station in this study was 44 stations, but there were 9 representative samples analyzed by petrography. petrographic analysis result showed that the characterisics of ultramafic rocks in the study area divided into 2 rock types, namely serpentinized dunite and serpentinized peridotite (streckeisen, 1974). a. dunite serpentinized dunite serpentinized covers 36% of the total area of the study area and is found mostly in hilly landscape. based on petrographic analysis, serpentinized dunit rock found at st 12 h1, st. 5 h1, st 3 h3, st 5 h5, bkn 17 and bkn 20. petrographic analysis result on st 5 h1 showed the mineral composition in rock sample consisted of 83% olivine, 10% chrysotile, 5% lizardite and 2% opaque minerals (figure 2,b). microscopis appearance showed olivine minerals have been broken down and to be replaced by serpentine minerals which form a mesh texture. chrysotile is present as a secondary mineral in the form of veins that fill the hasria et al./ jgeet vol 7 no 1/2022 17 fractures. at figure 2d, the percentage of antigorite is 11% with a non pseudomorphic texture because it does not show its original mineral form. almost all the samples that were observed microscopically showed incomplete mineral olivine crystals. this mineral crystal has been broken apart showing a fractured texture. and the fractions of the olivine crystals have been filled with lizardite by showing the mesh structur (figure 2f). based on microscopic analysis, presence of serpentine minerals in dunite serpentinized rocks is different, at st 5 h1 for serpentinized rocks by 15%. st 12 h1 for serpentinized rocks by 40%, st 3 h3 for serpentinized rocks by 65%, st 5 h5 for serpentinized rocks by 40%, bkn 17 for serpentinized rocks by 27%, and bkn for 20 for serpentinized rocks by 42%. of the six samples, the average rock undergoes a low serpentinization rate, which was bellow 45%. except for st 3 h3, the rock serpentinization rate occurred with a high intensity, namely 65% (jacques, 2002). fig 2. sample and microscopis appearance st 5 h1 (a,b). sample and microscopis appearance showed antigorite minerals with a non pseudomorphic structure at bkn 17 (c,d). sample and microscopis appearance of sample point st 3 h3 showed lizardit mineral-rich with a mesh structure (e,f). chrysotile mineral (cry), lizardite mineral (lz), antigorite mineral (atg), olivine mineral (ol), clinopiroksin mineral (cpx), and opak mineral (opq). b. peridotites serpentinized peridotite serpentinized covers 39% of the total area of the study area and is found mostly in hilly and plain landscapes (figure 3). based on petrographic analysis, serpentinized peridotite rocks found at st 4 h1, bkn 8 and bkn 11. petrographic analysis result on st 4 h1 showed the mineral composition in rock sample consisted of 65% olivine, 18% clinopiroksin, 5% chrysotile, 10% lizardite and 2% opaque minerals (figure 3f). petrography analysis result of the serpentinized peridotite rocks are almost the same as the serpentinized dunit rocks, which distinguish only the abundance of the mineral olivine which is less. lizardite comes with a mesh texture to fill the fractures. chrysotile veins are also seen to cut other minerals. based on microscopic analysis, presence of serpentine minerals in dunite serpentinized rocks is different, at st 4 h1 for serpentinized rocks by 15%. bkn 8 for serpentinized rocks by 20%, (figure 3d) and bkn for 11 for serpentinized rocks by 10% (3b). of the three samples, the average rock undergoes a low serpentinization rate, which was bellow 45% (jacques, 2002). fig 3. sample and microscopic appearance of sample point bkn 8 (a,b). sample and microscopic appearance of sample point bkn 11 (c,d). sample and microscopic appearance of sample point st 4 h1. chrysotile mineral (cry), lizardite mineral (lz), olivine mineral (ol), clinopyroxine minerals (cpx), and opaque minerals (opq). 3.1.2 serpentinization on ultramafik rock by xrf data. the geochemical analysis of bedrock was carried out using x-ray fluorescence (xrf), to get the major element namely ni, fe, co, mgo, sio2, cao, al2o3, and p. the determination of main element of ultramafic rocks in the study area was carried out on 6 samples representing rock units contained in the study areas, namely the peridotite serpentinized and dunite serpentinized that had been previously performed petrographic analysis to determine the mineral content contained in the rock. the sedimented rocks tend to be rich in oxides. serpentinization will tend to substitute magnesium in brucite into iron compounds. this can be seen from the bkn 17 for serpentinized by 27% and the bkn 20 for serpentinized by 42% (table 1) both of these samples have more serpentine mineral presentations than the other. the same thing is also shown in the geochemical sample in the southern part which is represented by bso 25 for serpentinized by 15%. the enrichment of the mgo element is shown by serpentinized rocks and will gradually decline due to the substitution of magnesium by iron compounds as in bkn 17. in this case there is a negative trend between mgo and feo. the typical weathering results of ultramafic rocks, especially in serpentinized dunite and dunite, the low al content will limit the formation of clays such as in bkn 17 and bkn 20 which are dunite rocks. in other rocks which are peridotite such as bkn 11, the aluminum content is also quite low, which is interpreted because of the abundant presentation of olivine minerals compared to bkn 8. 18 hasria et al./ jgeet vol 7 no 1/2022 table 1. assay bedrock in research area no hole id from to mat xrf analisis ni (%) fe (%) mgo (%) sio2(%) al2o3 (%) 1 bkn-17 29 30 brk 0.38 7.74 24.61 36.86 1.16 2 bkn-20 13 14 brk 0.29 7.02 32.02 32.95 0.79 3 bkn-08 7 8 brk 0.26 6.66 27.56 37.46 2.19 4 bkn-11 9 10 brk 0.23 6.42 27.53 32.16 1.09 5 bs025 32 33 brk 0.89 7.616 6 bs044 19 20 brk 0.69 5.256 3.2 serpentinization stage in morombo area based on its morphology, serpentine minerals are divided into 3 namely chrysotile, lizardite, and antigorite (wicks and o,hanley, 1988). the serpentinization process in olivine is followed by an opaque mineral, namely magnetite. the nonpseudomorph texture is shown in the antigorite which develops as a sheet. the vein texture in the rock is dominated by chrysotile and lizardite with a mesh texture. o’hanley (1991) divides 3 subproces of serpentinization, namely hydration, serpentine recrystallization, and deserpentinization (table 2). in the research area, the hydration sub-process is the role of h2o or exostermic reactions that cause the presence of a mesh texture by lizardite and chrysotile minerals. the formation of serpentinite by hydration of peridotite results in a decrease in rock density (o’hanley, 1992). recrystallization sub-process that converts the mineral lizardite into chrysotile. and the deserpentinization subprocess is to produce h2o and antigorite which comes with an interprenetrating texture and is endothermic. according to (mevel, 2003) it seem that serpentinization does not occur at a constant volume and apart from hydration and oxidation, the main elements of the rock are less affected. the average density of fresh peridotite is about 3.3 g/cm3 and serpentinite has a density of about 2.5 g/cm3. therefore, serpentinization is responsible for the decrease in density. from this it means that there is an inverse correlation between density and degree of serpentinization. in the extensional environment of the mid-ocean ridge (mor), this increase in volume is likely accommodated by tectonic activity, as evidenced by the vein system. table 2. subprocess of the serpentinization process ( o’hanley, 1991) sub process characteristics of reactions (resulting minerals & textures) reacsions entalphy change (kj/mol h2o) hydrasion h2o-consumming heat-evolving (lizardit ± chrysotile or antigorite mesh-rim texture) 2f + 3w = c3 + b -71,69 -21,5 serpentine recrystallization h2o-conservative, heatconsumming (lizardit hourglass&lizardit ± chrysotile ± antigorite interlocking texture) l = c c + 0,11sio2 = a+0,07w c=a+0,16b 3507,0 17,32 deserpentinization h2o-evolving, heatconsuming (antigorite± brucite interprenasting texture) 20b+a-34f+51w a=18f+4t+27w 70,98 78,0 a = antigorite ; b=brucite ; c=chrysotile ; f=forsterite ; l=lizardit ; t=talc ; w=steam in the expansion phase of the ocean floor, the first generation serpentine minerals will be formed (figure 4). serpentinization begins at high temperatures, in the range of 300–500° c. formed in this phase which slowly penetrates the body of the primary mineral olivine to produce antigorite with an interpreted structure as a sheet followed by the formation of magnetite. an overview of mineral assemblages in serpentinite from the mid-ocean ridges also shows the dominance of lizardite and chrysotile minerals with magnetite (mevel, 2003). this means that after the formation of antigorite, there is a decrease in temperature to form small amounts of lizardite and chrysotile. the presence of lizardite affects the microstructure of the rock. the reaction between peridotite and seawater at 300° c produces lizardite in this main phase. the presence of fractures by intersecting each other will result in loss of alignment of the pseudomorphic texture of the primary mineral. the orogenic phase is the formation of the second generation of serpentine minerals which are formed as a result of the uplifting process. at a temperature of ± 250º c and the presence of pressure and the addition of water, the mineral crystals of olivine or pyroxine are slowly changing and producing lizardite with a fractured structure in more than one direction. the presence of a mesh texture in rocks also indicates that there is a hydration process (o’hanley, 1992). the hydration process in rocks occurs because of the subduction zone formed by tectonic activity between continental plates and oceanic plates. the serpentinization layer that is formed comes from the hydration process, which occurs when the movement is above the surface (guillot et al., 2015). furthermore, the appointment process occurs, in this phase, chrysotile minerals are present with hasria et al./ jgeet vol 7 no 1/2022 19 the appearance of mineral morphology that are fibrous and present with a vein texture formed at a temperature of ± 200ºc. veins that form in rocks also prove that there is a process of adding volume to rocks. the presence of chrysotile minerals as a replacement for the mineral olivine is evidenced by the clear trace of olivine crystals around the chrysotile mineral body. meanwhile, the presence of chrysotile as a replacement mineral clinopyroxine is still low. the bkn 8 sample showed the presence of 72% clinopyroxine. according to (guillot et al., 2015) clinopyroxine-rich rocks are formed near the surface during orogenic processes. the presence of chrysotile minerals is dominated by olivine. chrysotile mineral with a vein texture is interpreted as a type of chrysotile mineral that is formed at low temperature and pressure, which is close to the surface. this type of crysothyl mineral formation process is thought to have lasted until now. the development of the vein texture in rock outcrops filled with stringy chrysotile minerals is influenced by the weathering process. this type of chrysotile is also interpreted as a replacement for lizardite due to the recrystallization process. fig 4. ultramafik rocks serpentinization scheme in research area 3.3 implication serpentinization on ni in bedrock according to (sufriadin, 2009) ultramafic rock that undergoes serpentinization and does not undergo serpentinization will have different characteristics in its laterite nickel deposits. the differences that occur can be seen from the mineral composition, chemical compounds, the thickness of the limonite and saprolite zones, the character of the boulder in the saprolite zone and even the color of the laterites produced. the serpentine which replaces olivine is usually devoid of aluminum and chromium but contains some nickel, which is equivalent in composition to olivine. in contrast, serpentine from bastite contains aluminum and chromium. the amount of iron in serpentine varies with associated magnetite abundance, thereby reflecting oxidizing conditions. when recrystallization occurs, secondary serpentine often takes the form of chrysotile, replacing primary lizardite. the serpentine in veins also tends to have less substitution, which is consistent with the fact that al, cr, ni are relatively immobile during the change, therefore remaining in their original microstructural site, and with chrysotile predominance. in general, the ni content in fresh ultramafic rock is 0.2% and the highest is 0.3%. the entire sample shows a ni content above 0.2% and the highest is at bso 25 and bso 44 where ni content reaches 0.89% and 0.69%. in all these samples it is interpreted that ni enrichment occurs due to the serpentinization process. according to mavel (2003) substitution of al and fe3⁺ for si can occur at the tetrahedral site, and fe2⁺, fe3⁺, cr, al, ni, and mn for mg at the octahedral site. lizardite tends to receive more substitutions than chrysotile, and is usually more alenriched, although the compositions do overlap. in highly serpentinized rocks, ni-rich lizardite is the main ore mineral. based on this, it is estimated that lizardite and chrysotile in rocks are the carriers of ni or ni-serpentin (figure 5). lizardite which contains ni is nepouite containing 6-33% ni (butt and cluzel, 2013) and chrysotile which contains ni is pecroaite. as for ni and mg ion exchange reactions in serpentine minerals can occur with the reaction equation below. fig 5. plotting the relationship between si, mg, fe+ni with ni hydrous silicate (modified from brand et al., 1998) however, if you look again at the low serpentinization level in the rock, it is only 15%. the high level of ni at bso 25 and bso 44 can be interpreted because the high concentration of ni content also comes from the primary mineral content, namely olivine because serpentinization only occurs locally in bedrock (sufriadin, 2013). 4. conclusion 1. rock characteristics in the study area when viewed from the level of serpentinization that takes place is divided into 2, namely low serpentinization level and medium serpentinization level. a high degree of serpentinization occurs in dunite rocks but the spread of serpentinization is not evenly distributed in all types of dunite rocks. the high degree of serpentinization covers only a small area and is dominated by low serpentinization. geochemically, mgo element enrichment is shown by serpentinized rocks. however, the magnesium content in rocks will be substituted by iron compounds so that there will be a reduction in its content and iron (fe) compounds in the rock will be higher followed by the presence of magnetite. and rocks that are not serpentinized tend to be rich in oxides. al formation occurs due to the low level of serpentinization and will inhibit the formation of clay minerals. 2. in the research area, serpentine mineral paragenesis is formed through several tectonic phases characterized by the presence of serpentine minerals with a distinctive structure. first, the expansion phase of the ocean floor produces antigorite with a structure 20 hasria et al./ jgeet vol 7 no 1/2022 interpreting as a sheet followed by the formation of magnetite. after the formation of antigorite, there is a decrease in temperature to form lizardite. second, the orogenic phase, which produces lizardite with a fractured and mesh structure which indicates the hydration process. furthermore, when the removal is formed chrysotile minerals which are present as veins. the weathering process of exposed rock will convert lizardite minerals into chrysotile. 3. all samples in bedrock showed ni content above 0.2% and the highest at bso 25 and bso 44, which contained ni content reaching 0.89% and 0.69%. in all these samples, ni enrichment is interpreted due to the serpentinization process along with the formation of lizardite in the rock. acknowledgements the authors are very thankful pt. bhumi karya utama for facility for the research access and permission, so to assistance during field work. authors also would like to thank to the head of the geological engineering laboratory, hasanuddin university, who gave me permission to use the laboratories. references brand, n. w., butt, c. r. m., & elias, m. 1998. nickel laterites: classification and features. agso journal of australian geology & geophysics, 17(4), 81–88. david, s., & o’hanley. 1991. fault-related phenomena associated and serpentine with hydration recrystallization during serpentinization souvernp. canadian mineralogist, 29, 21–35. freyssinet, ph., butt, c.r.m, m. r. . 2005. ore-forming processes related to lateritic weathering. economic geology 100th anniversary volume, 681–722. guillot, s., schwartz, s., reynard, b., agard, p., & prigent, c. 2015. tectonic significance of serpentinites. tectonophysics, 646,hal 1–19. https://doi.org/10.1016/j.tecto.2015.01.020 hasria., anshari, e., muliddin., restele, l. o., & zulkifli, l. o. m., 2019a.the effect of geological structure on the distribution of nickel (ni) and iron (fe) contents in laterite nickel deposits in the saprolite zone of pt. manunggal sarana surya pratama, district lasolo islands, north konawe regency, southeast sulawesi. technology research journal mining, 6(1), 38–45. hasria., anshari, e., & rezky, t. b., 2019b. effect of bedrock and geomorphology on laterization and distribution of ni and fe content in the laterite nickel deposit at pt. tambang bumi sulawesi, village pongkalaero, bombana regency, southeast sulawesi. journal of application geography and technology, 3(1), 47–58. hasria., asfar, s., ngkoimani, l.o., okto, a., jaya, r.i.m.c., sepdiansar, r. 2021. the influence of geomorphology on the distribution of nickel and iron elements in laterite nickel deposits in buton regency, central-southeast sulawesi. geosapta journal 7(2), 103-114. hasria., hasan, s.h., deniyatno., salihin, l.m.i., asdiwan, 2020. characteristics of ultramafic igneous rock ophiolite complex in asera district, north konawe regency southeast sulawesi province. journal of geoscience, engineering, environment and technology 5(3), 114-118. jacques, b. 2002. field determination of serpentinisation at soroako. lectures notes pt. inco, sorowako. kurniadi, a., rosana, m. f., yuningsih, e. t., pambudi, l. 2017. karakteristik batuan asal pembentukan endapan nikel laterit di daerah madang dan serakaman tengah. geoscience journal, 1(2), 149– 163. mevel, c. 2003. serpentinization of abyssal peridotites at mid ocean ridges. comptes rendus geoscience, 335, 825–852. https://doi.org/10.1016/j.crte.2003.08.006 moody, j. b. 1976. serpentinization: a review. lithos, 9(2), 125–138. https://doi.org/10.1016/00244937(76)90030-x o’hanley, d. s. 1992. solution to the volume problem in serpentinization. geology, 20(8), 705–708. https://doi.org/10.1130/00917613(1992)020<0705:sttvpi>2.3.co;2 oud, k. 2010. serpentinization and fracture formation in peridotites on otrøy, western gneiss region, norway: late stage pt-conditions and implications for tectonic decompression. thesis. sufriadin. 2013. mineralogy geochemistry and leaching behavior of the soroako nickeliferous laterite deposits, sulawesi,indonesia. disertasion. sufriadin, idrus, a., pramumijoyo s,. warmada, i. w., nur, i., s. 2009. serpentinisasi pada batuan ultramafik dan implikasinya terhadap eksplorasi endapan nikel laterit. proceedings of international conference earth science and technology. yogyakarta. hal. 161168 © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). https://doi.org/10.1016/j.tecto.2015.01.020 https://doi.org/10.1016/0024-4937(76)90030-x https://doi.org/10.1016/0024-4937(76)90030-x https://doi.org/10.1130/0091-7613(1992)020%3c0705:sttvpi%3e2.3.co;2 https://doi.org/10.1130/0091-7613(1992)020%3c0705:sttvpi%3e2.3.co;2 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 2 2022 pamungkas, g et al./ jgeet vol 7 no 2/2022 49 research article residual strength parameter method for slope stability on a toll road with expansive clay goji pamungkas1* , thomas triadi putranto2, suharyanto3, muhrozi4, yanuar niko priambodo5 1,3,4 department of civil engineering diponegoro university, jalan prof sudharto sh semarang, central java , indonesia. 2 department of geological engineering diponegoro university, jalan prof sudharto sh semarang, central java, indonesia. 5 pt waskita karya batang semarang toll road project, semarang, central java, indonesia. * corresponding author : gojipamungkas@students.undip.ac.id tel.:+62-81-224-644-083; fax: received: apr 4, 2022; accepted: jun 30, 2022. doi: 10.25299/jgeet.2022.7.2.9251 abstract the decreasing stability phenomenon needs to be considered during the design of cut slopes on problematic soil. excavation slope of toll road construction tends to fail when it lies above clay-shale strata. certain common correlations and ordinary analytical methods are not recommended for safety calculation. this study is intended to find out the characteristic of clay-shale and proper slope inclination design on semarang batang toll road. the behaviour of a clay-shale area on the cut slope of batang-semarang toll road segment sta 438+000–sta 439+000 was identified. the degradable and expansive properties caused slope failure of the initial design with an inclination of 1 h: 1 v. laboratory tests found that the soil had a clay faction > 40% and can be categorized as high plasticity (ll > 50%). an empirical approach determined that the residual shear strength decreased to phi < 6 degrees. to describe the swelling after the excavation stage, the flow deformation was determined by a finite element simulation. during the swelling phase, the pore water pressure was maintained at a certain value, and a gentler slope fulfilled the minimum safety factor with an inclination of 1 v: 3 h. furthermore, the shear strength of the clay-shale was reduced to that for a fully softened material, and all the slope factors for safety moved to a critical state. according to the simulation, the minimum suggested slope inclination is 5 h: 1 v. this approach is important for the maintenance of pore water pressure and the prevention of an additional reduction in the shear strength so as to avoid slope failure on clay-shale regions in the yielding stage. keywords: residual, expansive, clay, slope, stability, toll-road 1. introduction technical and non-technical challenges may be encountered during the construction of new roads. one of the challenges is the cut slope stability. according to knappett & craig (2012), the cut slope safety factor decreases due to a decrease in the pore water pressure. conversely, if the slope is a fill or embankment slope, the safety factor increases for long-term conditions when compared to the safety factor at the end of construction (eos). the decreasing safety factor phenomenon needs to be considered during the design of cut slopes. on semarang batang toll road segment sta 438+000 – sta 439+000, the slope comprises 15-20 meters of cut slope with an initial inclination design of 1.00h:1.00h. however, slope failure occurred during construction due to its geotechnical condition. the slope consisted of weathered claystone, clay-shale and very expansive clay. the sta 438+400 segment after the slope failure is displayed in figure 1 and figure 2. figure 1 shows soft clay debris after the slope failure. when compared to the original condition, the hard clay stone transformed into clay with a low shear strength. the slope failure did not only occur in the high cut profile. slope failure also occurred in the sta 439+000 segment with a cut slope as high as 2.50 – 3.00 meters. however, because the height was not as high as that in sta 438+400, the debris material did not close the main road. another case of construction on clay-shale is found on cipularang toll road km 97+500. on this case, more than 10 meter height of embankment lies on clay-shale strata. based on field investigation, the failure mechanism is triggered by strength degradation of clay-shale due to stripping works (irsyam, susila, & himawan, 2006) . the behavior of cut/excavated slopes on problematic soil must be distinguished from that on ordinary soil. certain common correlations and ordinary analytical methods are not recommended for the calculation of the geotechnical design on problematic soil whether technically and economical aspect (onochie & rezaei, 2016). most of problematic soil which might lead to failure are expansive clays, dispersive soils, and collapsible soils (rezaei, ajalloeian, & ghafoori, 2012). the soil behaves differently than ordinary soil when it is exposed to and interacts with the surrounding environment. certain problematic soils show good behavior in their original condition. when the soil interacts with water, it shows behavior that is opposite to that of the original condition. according to boggs (2009), shale is a terminology for classifying sedimentary rocks that have lamination. clayshale is an indurated rock with a laminated size less than 10mm. according to the neuendorf et al. (2011), shale is http://journal.uir.ac.id/index.php/jgeet 50 pamungkas, g et al./ jgeet vol 7 no 2/2022 defined as fine-grained sedimentary rock that becomes settled and lithified due to the consolidation process. the typical character of shale is to have the appearance of a sheet that is consistent with its bedding. the material quality of shale may decrease over time if it is taken from its original source. when it has undergone a stress release, the mechanical behavior also changes. shale may change from a rock-like material to soil-like material and completely degrade to silt or clay. however, highdurability shale still maintains the mechanical behavior of stone (richardson , 1985). on semarang – solo toll road, similar case of clay-shale slope failure is found on km 438, an excavation slope with more than 35 meters of slope height. when the clay-shale is exposed, the slope shows good behavior and stable condition. the failure is started when the wetting and drying cycle is occurred. this process causes the clay-shale weathering, so that the shear strength is also decreased. according to laboratory test, the residual strength of clayshale on this location decreased to 8.3 kpa for saturated cohesion and 4.6 degree for saturated internal friction of angle (alatas, kamaruddin, nazir, & irsyam, 2015). according ro pardoyo, et al. (2020), semarang bawen clayshale strength is decreased to 59% for ucs value and 36 % for modulus elasticity parameter (e50) after 90 minutes drying process. (a) (b) fig. 1. slope failure along the: (a) sta 438+000; and (b) 439+000 segments at end of the construction stage (a) (b) fig 2. slope failure along the sta 438+000 segment during: (a) early road operations; and (b) a recent failure in 2021 clay-shale instability may be caused by the texture and structure of the sediment and the mineral structure. the texture is related to the clay fraction in the clay-shale. if the amount of clay fraction increases, the clay-shale tends to be a problematic material. the sediment structure of clay-shale, such as the joints, degree of fissility (sheet appearance), and bedding, may affect its stability when it is on a sloped area. the mineral structure can be recognized by microscopic examination only. stark & duncan (1991) studied the mechanical behavior and failure mechanisms of the clay-shale at the san luis dam in the united states. clay-shale is classified as fissured stiff clay. the high shear strength of clay-shale on the original source indicated that it is an over-consolidated material. when the condition is dry, clay-shale has a high shear strength for the peak strength parameter. otherwise, when clay-shale encounters dry and wet conditions repeatedly, it reaches a fully softened condition. when failure begins, the clay-shale has undergone degradation of its residual condition. when the construction of cut slopes removes the vertical stress that overburdens clay-shale, the balance of the horizontal stress changes. according to (bell, 1978), as for a spring, when the stress in a loaded spring is released, the potential energy is also released. the clay-shale rebounds as result of this stress release. clay-shale durability is affected by the stress release and depends on the bonding strength of each shale. the bonding strength depends on the mineral composition. unstable clay-shale behavior is mostly caused by the mineral content. according to wilson & wilson (2014), expansive behavior on clay-shale that belongs to the smectite shale group is caused by the interaction between na and the water content. according to putera, et al. (2017), the unloading of the stress will increase surrounding water content which is caused by dispersing interparticle bond. if the bonding strength is low, then clay-shale heaving occurs as result of increasing the rebound value. the heaving process may be compounded by interactions with water through the gaps between the mineral sheets of montmorillonite. this phenomenon is known as the swelling of clay-shale. the swelling causes a drastic decrease in the shear strength. in extreme conditions, a decrease in the shear strength occurs continuously until it reaches the residual strength. 2. research method 2.1 engineering parameter approach pamungkas, g et al./ jgeet vol 7 no 2/2022 51 upon referring to recent geotechnical research, it is clear that common correlations and assumptions during the design process are not applicable for clay-shale. the research of clayshale mechanical behavior has shown important information. at first, skempton (1964) suggested the use of the residual strength parameter for long-term stability analysis on a slope comprised of clay. the residual strength was obtained by a back calculation method. gartung (1986) and irsyam et.al. (2007) divided the clay into four weathered zones. zone 1 comprises fresh and unweathered rocks. zone 4 is a clay zone that has met the final stage of weathering. gartung (1986) stated that the average value of the residual friction angle (ϕ_r) is about 8.6 degrees. however, when using these values, the engineering design will be very conservative and inefficient. the recommended residual strength for engineering design by gartung (1986) is c' = 20 kpa at ϕ'= 20 (see on fig.3). stark and hussain (2013) proposed a correlation to determine the residual shear strength based on the clay fraction and liquid limit. the correlation was obtained from a number of engineering tests by using reversal ring shear. the correlation equation is shown in figure 4. fig 4. empirical correlation for drained residual secant friction angle based on the liquid limit (ll), clay size fraction (cf), and effective normal stress by stark and hussain (2013) 2.2 slope stability analysis method slope stability analysis with long-term parameters is conducted by using field investigation and laboratory test data. the field investigation data consists of existing conditions, borehole and n-spt. the stratigraphy is generated based on n-spt and cpt data for finite element method (fem) analysis. to conduct simulations with fem analysis, it is necessary to know the ideal drainage behavior of the soil material at a certain loading condition. during fem analysis, there are two drainage behaviors: 1) undrained; and 2) drained. the undrained condition is used if the loading on the soil increases the pore water pressure and does not have time to dissipate. the drained condition is used if loading increases the pore water pressure, but dissipation occurs instantly. the first stage of a fem calculation is generating the initial static stress. after the initial static stress calculation, the factor of safety (fos) calculation can be conducted by finding the soil plastic point. at the critical state, the soil becomes plastic and forms a plastic point with an extreme incremental strain. the plastic points form a band of failure planes so that the safety factor can be obtained. a slope almost 20 meters height with a critical cut on the semarang batang toll road is located on the sta 438+400 segment. two cpt tests and geotechnical drilling with an nspt test were conducted. all cpt tests were concluded at a depth of 8 – 10 meters. the drilling was conducted until a depth of 20 meters was reached. the slope stratigraphy, as shown in figure 5, had four layers: 1) a weathered layer, 2) a stiff clay layer, 3) a hard clay layer, and 4) a soft rock layer. the material properties of the layers are listed on table 1. in table 1, a shear strength difference between the nspt and cpt can be seen. a comparison of the field test shows that the cpt data is greater than the n-spt data, possibly because of the different times of the tests. the cpt test was conducted several months earlier than the n-spt test. thus, the simulation used the n-spt data, as it was close to the actual conditions. however, the different results between the cpt and n-spt tests indicated that the weathering process of the clay-shale along the sta 438+400 segment occurred rapidly. fig 3. clay-shale shear strength proposed by gartung (1980) 52 pamungkas, g et al./ jgeet vol 7 no 2/2022 stark & hussain (2013) proposed an empirical method to obtain the residual parameters based on the amount of the clay fraction and liquid limit. to validate the clay fraction and liquid limit results, a swell test and durability test must be conducted. yulistiawati & zaman (2018) conducted a laboratory test for several samples from the sta 438+400 segment. the laboratory test results can be seen in table 2 and table 3. pt cnd geoteknika (2018) conducted a further investigation on the sta 438+000 segment due to a request by pt waskita karya. two samples were taken from bh 01 for laboratory analysis. the laboratory test results can be seen in table 4. the low shear strength indicates that softening of the clay occurred. as shown in table 4, the liquid limit value was smaller than that from yulistiawati and zaman (2018). therefore, the liquid limit value and clay fraction from table 4 were used as input parameters for the stark and hussein (2013) residual strength correlation. the residual parameters can be seen in figure 6 and table 5. table 1. shear strength parameters based on field tests layer nspt cpt (kg/cm2) unit weight saturated (kn/m3) unit weight dry (kn/m3) weathered layer 10 45 17 18 stiff clay (softening) 15 70 17 18 very stiff clay 22 100 17.5 19 soft rock 50 250 19 20 table 2. atterberg limit test result for the sta 438+400 segment (yulistiawati and zaman, 2018) sample colour atterberg limit not oven dried oven dried classification pl pi (%) (%) (%) (%) bstr-2 black 100 92 anorganik 33.83 58.17 bstr-3 greyish black 88 82.5 anorganik 34.31 48.19 bstr-4a grey 61.5 66 anorganik 37.41 28.59 bstr-4b black 83.6 83.6 anorganik 36.21 47.39 bstr-4c black 88 83.6 anorganik 31.78 51.82 bstr-5 reddish clay 89 78.6 anorganik 39.34 39.26 bstr-6 black 89 86 anorganik 16.54 69.46 bstr-7 greyish brown 81 90 anorganik 37.17 52.83 bstr-8 greyish brown 77.3 88 anorganik 39.47 48.53 bstr-9 grey 46 45 anorganik 29.92 15.08 bstr-10 light grey and white 48.5 58 anorganik 23.98 34.02 table 3. grain size distribution and clay-shale durability for the sta 438+400 segment (yulistiawati and zaman, 2018) sample slake durability (%) free swelling (%) hydrometer sieve analysis 1st cycle 2nd cycle sand (%) silt (%) clay (%) passing # 40 (%) passing #200 (%) soil class. bstr-2 3.34 0 355 0 48 52 100 100 clay bstr-3 0.00 0 155 22.22 38.78 39 98.21 77.78 clay bstr-4a 0.00 0 100 32.56 32.44 35 94.77 67.44 clay bstr-4b 1.96 0 130 10.39 41.61 48 100 89.61 clay bstr-4c 7.98 2.89 115 20 39 41 99.78 80 clay bstr-5 3.81 0 110 21.61 38.4 40 100 78.4 clay bstr-6 0.00 0 270 3.66 36.34 60 100 96.34 clay bstr-7 0.85 0 220 0 42 58 100 100 clay bstr-8 0.00 0 240 9.21 43.79 47 100 90.79 clay bstr-9 52.16 41.03 87.5 15.38 41.62 43 100 84.62 clay bstr-10 12.00 10.97 90 30.57 34.43 35 95.73 69.43 clay table 4. index properties provided by a contractor for the sta 438+400 segment (cnd geoteknika, 2018) sample atterberg limit sieve analysis triaxial uu ll pl pi clay silt sand gravel 𝑐𝑢 𝑢 (%) (%) (%) (%) (%) (%) (%) kpa deg. 3.50 – 4.00 118 35 83 52 46 2 0 85.7 6.2 9.50 – 10.00 93 36 57 52 47 1 0 21.2 11.8 pamungkas, g et al./ jgeet vol 7 no 2/2022 53 fig 5. slope stratigraphy interpretation on the sta 438+400 segment based on cnd geoteknika (2018) 2.3 slope stability simulation many researchers in geotechnical engineering have been conducted slope stability simulation of clay-shale. pratama (2021) calculate the clay-shale slope stability by using limit equilibirum method (lem) and probabilistic approach. the residual strength parameter is assumed on certain correlated value of 𝑐𝑟 and 𝜙′𝑟. the simulation result show that slope safety is affected by ground water table. the limitaion of lem can not simulate the contribution of swelling in failure mechanism by using only simple mohrcoulomb model. the simulation of the slope stability was conducted by using fem analysis (sigma/w). the most crucial aspect for the design of a cut slope is the determination of the safe slope inclination for the long-term stability based on sni 8460:2017. residual parameters were used for the clayshale shear strength parameter. the stability calculation was simulated for 5 stages of excavation. each excavation stage was simulated using 10-time steps for a duration 10 days. the model geometry was simplified and idealized as two main layers composed of a clay-shale layer and claystone layer. for the initial stress calculation, the groundwater level was set at a depth of 2 meters. the sigma/w calculation using the coupled-stress/pore water pressure change method requires specific values for the volumetric water content (vwc) and hydraulic conductivity function. the vwc is the critical parameter of unsaturated soil mechanics due to its role to describe the yield stress–suction and shear strength–suction relationships (sheng, 2011). according to chao, et al. (2014) the vwc has relationship with water content change during wet/dry cycle. the vwc is obtained by using the clay sample function. the hydraulic conductivity was set based on the van genuchten equation with a saturated conductivity of 10-9 m/s for the claystone and 10-8 m/s for the clay-shale. the clay-shale softening was simulated by using the elastic-plastic mohr-coulomb model as it can describe elastic and plastic deformations clearly (li, vanapalli, & li, 2016). for the initial stage calculation, the peak shear strength was used to describe the short-term stability of a proposed slope inclination design. the simulation was continued using the parameters in table 5. during the excavation stage, the clay-shale (weathered layer) used the shear strength parameter suggested by gartung (1980). after the 5th excavation, the swelling process was simulated for 10 years. the pore water pressure was assumed and maintained at -20 kpa along the surface boundary. the slope stability calculation was conducted by using finite element stress slope/w at the end of the swelling simulation. the final stage of the simulation conducted the stability calculation with the residual parameter by using the strength reduction method. the simulation stages are listed on table 6. the slope stability simulation was conducted for 5 proposed slope inclinations. the slopes were 1v:1h, 1v:2h, 1v:3h, 1v:4h, and 1v:5h in the simulation. all the proposed slope inclination safety factors were checked for all conditions (e.g., the eos, swelling, and residual condition). therefore, the simulation can suggest the most suitable inclination design for a slope cut from weathered clay-shale. table 5. shear strengths for the fem stability simulation strata friction angle 𝜙′ (degree) cohesion 𝑐′ (kpa) elastic modulus (kpa) poisson ratio 𝜐 unit weight saturated (kn/m3) unit weight dry (kn/m3) weathered layer (peak strength) 20 60 9000 0.2 17 18 weathered layer (residual) 6.00 6.50 4000 0.2 17 18 weathered layer (fully softened) 6.00 17.00 4000 0.2 17 18 weathered layer (design strength) 20 20 8000 0.2 17 18 claystone 25.00 100 15000 0.3 17.5 19 54 pamungkas, g et al./ jgeet vol 7 no 2/2022 fig 6. residual strength correlation by ll dan cf based on stark and hussein (2013) 3. result and discussion the short-term calculation results satisfied the safety factors for the slope stability. the peak strength parameter during excavation analysis provided a safety factor value at the eos stage that was too optimistic. for example, the safety factor at the 1v:1h inclination was 1.62. from the 1v:1h simulation result, it can be predicted that the safety factor would be more satisfied for a gentler slope. the slope stability simulation results are listed in table 7 and figure 7. according to renania & martin (2020), stability simulation using peak strength can produce over optimistic safety factor for strain-softening soil. table 6. simulation stages for slope stability analysis sta 438 stage analysis type duration remarks proposed existing design undrained behaviour short term simulation initial stress in situ 0 day initial condition 1st excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 2nd excavation stage coupled stress/ pwp change 10 days 2 meter excavation 3rd excavation stage coupled stress/ pwp change 10 days 2-meter excavation depth 4th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 5th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 6th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 7th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 8th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 9th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth 10th excavation stage coupled stress/ pwp change 10 days 2 meter excavation depth swelling phase coupled stress/ pwp change 3650 days slope stability fos finite element stress all time steps residual strength stress redistribution last step slope stability residual fos finite element stress last step in table 7, it can be seen that the optimum design for the slope inclination is 1.00v:1.00h. the safety factor for this 1.00v:1.00h design satisfies the minimum fos > 1.50 criterion. the use of a gentler slope inclination is inefficient in terms of construction budget and time. however, the peak strength parameter is not recommended for use in the long-term stability of clay-shale slopes. the weathering and swelling phenomena must be considered when determining the optimum design for clay-shale slope inclinations. according to qi & vanapalli (2016), ignoring the softening parameter may lead to unstable slope design especially for expansive soil. in table 7, it can be seen that the optimum design for the slope inclination is 1.00v:1.00h. the safety factor for this 1.00v:1.00h design satisfies the minimum fos > 1.50 criterion. the use of a gentler slope inclination is inefficient in terms of construction budget and time. however, the peak strength parameter is not recommended for use in the long-term stability of clay-shale slopes. the weathering and swelling phenomena must be considered when determining the optimum design for clay-shale slope inclinations. table 7. slope stability simulation results by using the peak strength parameter slope inclination safety factor 1.00v : 1.00h 1.50 1.00v : 2.00h 1.83 1.00v : 3.00h 2.17 1.00v : 4.00h 2.64 1.00v : 5.00h 3.07 the simulation continued to calculate the clay-shale slope stability considering the weather and swelling conditions. for this stage, the peak strength parameter turned into the design strength, as suggested by gartung (1970). the stability simulation resulted in a lower safety factor than the peak strength. the 1.00v:1.00h slope 0 50 100 150 200 0 100 200 300 400 500 600 700 s h e a r s tr e ss ( k p a ) normal effective stress (kpa) fully soften residual stress pamungkas, g et al./ jgeet vol 7 no 2/2022 55 inclination had the minimum fos of 1.11 at the eos or after the initial swelling time. however, at the end of the swelling simulation, the fos decreased to 1.02. for the 1v:5h inclination, the fos decreased from 2.27 to 2.01. this phenomenon also occurred for the other slope inclination design. the decrease in the fos as a function of time is shown on figure 8. as shown in figure 8, the slope safety factor decreased gradually along with the swelling time. it seems that the minimum design for the slope inclination is 1v:3h, as the safety factor meets the minimum criterion (fos > 1.50) at the end of the swelling time. however, the swelling simulations still used the design strength, not the fully softened and residual strength. by using the residual and fully softened parameters, the safety factor was calculated based on the pore water pressure and deviatoric strain. the slope stability simulation results with the residual strength are listed in table 8. the critical slip surface was obtained based on the deviatoric strain. as shown in table 8, the stability factor increased as the slope inclination decreased if the fully softened parameter was used. however, the stability factor changed when the shear strength parameter was reduced to the residual strength. for a slope inclination from 1.00v:1.00h to 1:00v:5.00h, the stability had a similar tendency in the critical safety factor range. the simulation stability for a slope inclination from 1.00v:1.00h to 1:00v:5.00h did not reach the minimum fos. all the proposed slope inclinations failed for that fos if the residual parameter was used. (a) (b) (c) (d) (e) fig 7. result simulation by using the peak strength parameter: (a) slope failure plane 1.00v:1.00h inclination; (b) slope failure plane 1.00v:2.00h inclination; (c) slope failure plane 1.00v:3.00h inclination; (d) slope failure plane 1.00v:4.00h inclination; (e) slope failure plane 1.00v:5.00h inclination; 56 pamungkas, g et al./ jgeet vol 7 no 2/2022 fig 8. fos change during the swelling phase table 8. slope stability simulation results by using the peak strength parameter slope inclination fully softened critical safety factor residual critical safety factor range 1.00v : 1.00h 0.69 0.46 – 0.56 1.00v : 2.00h 0.77 0.48 – 0.58 1.00v : 3.00h 0.83 0.46 – 0.56 1.00v : 4.00h 1.03 0.46 – 0.56 1.00v : 5.00h 1.16 0.47 – 0.57 fig 9. yield zone propagation on slope sta 438: (a) 1.00v:1.00h at eos, (b) 1.00v:1.00h swelling, (c) 1.00v:2.00h eos, (d) 1.00v:2.00h swell, (e) 1.00v:3.00h eos, (f) 1.00v:3.00h swelling, (g) 1.00v:4.00h eos, (h) 1.00v:4.00h swelling, (i) 1.00v:5.00h eos, and (j) 1.00v:5.00h swelling. pamungkas, g et al./ jgeet vol 7 no 2/2022 57 the plastic yield point can be used to identify the propagation of a slope failure zone. at the eos, the yield (failure) zone was located near on the excavation base. this means that no failure or yielding occurred at the construction stage. hereinafter, the yield zone changed when the swelling phase occurred. the yield zone propagated deeper and spread wider into the slope (figure 9). the yield or failure zone propagation decreased the stability factor during the construction stage and swelling phase. similar to the swelling stage, the yield zone also propagated when the fully softened and residual parameters analysis was done. the zone spread deeper and wider than the stage before. at the fully softened simulation stage, the yield zone spread to over half of the entire slope. hereinafter, the yield zone spread throughout the entire clay-shale region at the residual simulation. the soil deterioration also contributes to long-term reduction of stability factor (postilla, et al., 2021). all the proposed slope inclinations did not reach the minimum safety factor (fos < 1.00) for this condition. the simulation may not be used to predict the time to failure of a slope. however, the simulation is intended to investigate the swelling and shear strength reduction influence on the progress of slope failure. the failure occurred simultaneously and was caused by the pore water pressure equilibration that occurs after the construction ends. based on the recent condition, the failure still occurred even when the slope was gentler. this may have been caused by a decrease in the clay-shale residual strength. the reduction zone occurred deeper so that the failure continued until the equilibrium state (fos > 1.00) was reached. from the stability simulation results, it may be concluded that it is important to control the pore water pressure change after excavation is done. the swelling phase occurs as result of pore water pressure equilibration and stress release due to excavation. if the pore water pressure along the slope cannot be maintained at a certain level, the safety factor will continue to decline. however, it is also important to prevent further softening of clay-shale. during the simulation, if the entire clay-shale strength changed to the residual parameter, the slope inclination must be very gentle to be stable. 4. conclusion slope stability analysis for a degradable material requires a special approach to investigate the long-term stability. clay-shale stability may have a satisfactory fos at the end of construction. due to the expansive behavior, the fos decreases as result of pore water pressure equilibration and stress release due to excavation. the simulation may not be used to predict the time to failure, but it can be used to investigate failure behavior and the possibility of slope progressive failure. by understanding the clay-shale slope condition and behavior, the proper design and reinforcement can be determined. for this case, the minimum suggested slope inclination is 1.00v:5.00h. acknowledgment we would like to thank for the support from pt waskita karya batang semarang project, department of civil engineering diponegoro university, all the reviewers (before the submission) and who have given valuable inputs as well as the corrections to improve the quality of the paper. references alatas, i., kamaruddin, s., nazir, r., & irsyam, m. 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(2012). geotechnical properties of problematic soils emphasis on collapsible cases. international journal of geosciences,, 03(01), 105-110. richardson , d. (1985). relative durability of shale -a suggested rating system. proceedings of the 36th annual highway geology symposium . clarksville: indiana department of highways. sheng, d. (2011). review of fundamental principles in modelling unsaturated soil behaviour. computers and geotechnics, 38(6), 757-776. skempton, a. (1964). long-term stability of clay slopes . géotechnique, 14(2), 77 102. stark, t., & duncan, j. (1991). mechanisms of strength loss in stiff clays. journal of geotechnical engineering, 117(01), 139-154. stark, t., & hussain, m. (2013). drained shear strength correlations for slope stability analyses. journal of geotechnical engineering, 139(6), 853-862. wilson, j., & wilson, l. (2014). clay mineralogy and shale instability: an alternative conceptual analysis. clay minerals, 49, 127–145. yulistiawati, w., & zaman, m. (2018). a study upon the behaviour of clay shale soil of the kerek formation on the excavation work of batang-semarang toll road (sec. stat. 437+700 to stat. 439+120). semarang: diponegoro university. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 02 no 04 2017 yuskar, y. et al./ jgeet vol 02 no 04/2017 249 structural geology analysis in a disaster-prone of slope failure, merangin village, kuok district, kampar regency, riau province yuniarti yuskar 1 , dewandra bagus eka putra 1 , adi suryadi 1 , tiggi choanji 1 , catur cahyaningsih 1 1 department of geological engineering, universitas islam riau, jl. kaharuddin nasution no 113 pekanbaru, 28284, indonesia. * corresponding author : yuniarti_yuskar@eng.uir.ac.id tel.: .:+62-821-6935-4941 received: sept 02, 2017. revised : 1 nov 2017, accepted: nov 15, 2017, published: 1 dec 2017 doi : 10.24273/jgeet.2017.2.4.691 abstract the geological disaster of landslide has occurred in merangin village, kuok subdistrict, kampar regency, riau province which located exactly in the national road of riau west sumatra at km 91. based on the occurrence of landslide, this research was conducted to study geological structure and engineering geology to determine the main factors causing landslides. based on measurement of the structural geology found on research area, there were fractures, faults and fold rocks which having trend of stress n 2380 e, plunge 60, trending ne-sw direction. several faults that found was normal faults directing n 2000 e with dip 200 trending from northeast-southwest and reverse fault impinging n 550 e with dip 550, pitch 200 trending to the northeast. fold structures showing azimuth n 2010 e trending southeast-northwest. from geological engineering analysis, the results of scan line at 6 sites that have rqd value ranges 9.4% 78.7 % with discontinuity spacing 4 20 cm. so, it can be concluded that the formed structure was influenced by the extensive northeast-southwest tectonic phase, then continued through north-south tectonic phase, and ended by a tectonic period with directing from northeast-southwest. rock mass rating classification showing value 62 76, which also resulted that rocks in the study area have weathered on the outside but still in good condition (good rock). however, this condition of structure has caused the formation rocks producing weak zone that became one cause of the occurrence of landslides. keywords: landslide, geological structure, rqd, rock mass rating. 1. introduction the landslide was one of the geological disaster (mckean et al, 2004; booth et al, 2009; & tarolli et al, 2012),. it has several intrinsic parameters which are considered are; slope geometry, slope material (rock or soil type), structural discontinuities, landuse and landcover and groundwater (raghuvanshi et al , 2014), and for studying it need avalaibility of database files (wirtz et al, 2012). this landslide often occur in pekanbaru west sumatra roads, especially at km 91 (fig 1.). the impact of the avalanche which directly hit the road makes difficult for vehicles to mobilize and congestion up to several kilometres. this case certainly very harmful to its users. the purpose of this research was to determine the effect of landslide disaster based on geology analysis that occurred in the area. 2. geology regional research area was part of central sumatra basin, consist of basement (bohorok formation), greywacke, conglomeratic, and metasediment rock. the pre-tersier framework of sumatra consists of a mosaic of continental and oceanic microplate accreted in the late triassic when mergui, malacca and east malaya microplate were joined together to form sunda land. further accretion involving the west coast woyla terrain followed in the late mesozoic (pullonggono, 1984). cenozoic structural development involved three geometrically and kinematically distinct episode of faulting and folding. three include: 1) eo-oligosen rifting (f1) along old basement breaks of n nne strike and reactivation of wnw-trending regional basement arches; 2) early miocene (f2) crustal sagging, regional dextral wrenching, local counterclockwise kinking (150-250) of older n-s faults and development of n 0 200 e striking transtensional fracture zone; and 3) middle miocene to recent (f3) wsw directed thrusting and reverse faulting along older wrench faults of nnw-strike, ssw-verging monoclinal flexuring across older nw wnw trending basement breaks, and transtensional rifting alon element of n-nne strike (heidrick and aulia, 1993). fracture frequency important to distinguish high/low-frequency fracture zone and mailto:yuniarti_yuskar@eng.uir.ac.id 250 yuskar, y et al./ jgeet vol 02 no 04/2017 find damage zone (putra and choanji, 2016). the majority of fault-related fracture is shear fracture arc basin, barisan vulcanic arc, and sumatra fault conjugate to the fault (saputra and sapiie, 2005). 3. methodology this research conducted by doing measurement on geological data, such as fractures, faults and folds. folds and faults are directly measured at sites to gain the stress data by using stereography methods. meanwhile, the fracture data, was collected by performing scan line method. also there are several measurements to identified fracture, which are: type of shear fractures or tension fractures, strike and dip, mineral filled, distance, trace length. so based on the data, furthermore, stereography and rose diagram analyzes were performed to determine the direction of stress, type of faults, and folds, angle and plunge direction. rock mass rating system also used to classify rock mass based on uniaxial comprehensive strength parameter, rock quality designation (rqd), space of discontinuity, discontinuity condition, and groundwater condition by using geological hammer that used to determine rock strength in the field and being converted into ucs value using index classification of rock material by hoek and brown 1980. indirect rqd method was used in this method because of the absence of core log. rqd value calculated using palmstrom (1982) formula: rqd = 115 3,3 jv where : jv = total fractures per m3. fig 1. research location map. table 1. stress analysis result of fault fault plane strike /dip pitch direction σ 1 σ 2 σ 3 stress direction st1 n140 0 e/45 0 n343 0 e 2 0 , n1 0 e 37 0 , n270 0 e 52 0 , n95 0 e north-south st2 n205 0 e/65 0 n212 0 e 27 0 , n179 0 e 60 0 , n335 0 e 10 0 , n83 0 e north-south st3 n20 0 e/35 0 n48 0 e 37 0 , n34 0 e 21 0 , n142 0 e 43 0 , n254 0 e northeast-southwest st7 n200 0 e/70 0 n241 0 e 68 0 , n164 0 e 18 0 , n12 0 e 10 0 , n278 0 e nnw-sse yuskar, y. et al./ jgeet vol 02 no 04/2017 251 4. result 4.1 fold analysis fold structures that had been found in the study area were classified into type of recumbent fold and symmetrical fold of interbedded sandstoneclaystone (fig. 2). the stress consists of δ1 n 222 0 e with 30 0 plunges, δ2 n322 0 e with plunge 17 0 and δ3 n76 0 e with plunge 55 0 (fig. 2). the lithology of this folds was consist of sandstone what has grey colour, non-calcareous, fracture filled by quartz veins and metasediment of claystone. low metamorphism process had been shown in the outcrop by the presence of foliation, so this outcrop was called meta-sedimentary rock. so based on the analysis, this folded structure interpreted caused by a compression on northeastsouthwest direction. 4.2 fault analysis there are 4 (four) fault structures that had been found in the study area (table 1). firstly, normal fault system had found in station 7. fault structure happens on lithology pebble claystone, it was indicated by weak zone and slickenside. slickenside shows the fault plane in n290 0 e/70 0 with 70 0 pitch and southwest movement direction. analysis of stereographic projection showing the stress direction of normal fault is in northwest-southeast (fig. 3). the stress value of the fault gives δ1 in n52 0 e direction with 68 0 plunges, δ2 in n207 0 e direction with 20 0 plunges and δ3 in n299 0 e with 10 0 plunges. station 2 also showing the same analysis result as station 7. the other fault system was a reverse fault in station 1, having length size 55 m and 22 m high, which consist of greywacke, low metamorphic sandstone, phyllite, conglomerate, quartzite and mylonite. from the measurement, it has indicated that this fault has azimuth value of 140 0 e/ 45 0 , pitch 30 0 and trend n 330 0 se directing northwest. therefore, the stress resulting δ1 1 0 trending and classified as right reverse fault in st 1, its called gulamo right reverse fault. (fig. 4). fig 2. fold structure st 6 at research location (left) and stereographic analysis of fold structure (right) fig 3. fault structure in st 7 at research location classified as normal fault (left) and stereonet analysis of normal fault structure (right) 252 yuskar, y et al./ jgeet vol 02 no 04/2017 fig 4. reverse fault in st 1 on research location. fig 5. stereographic analysis of reverse fault at research location. 4.3 fractures structure analysis there are 9 (nine) sites of fractures structure (location 1, 3, 8. 9. 10. 12. 13. 14 and 15) shows a similar stress direction in northeast-southwest (fig 6.). the stress in station 1 consists of δ1 in n238 0 e direction with 6 0 plunges, δ2 in n344 0 e direction with 43 0 plunges and δ3 in n142 0 e with 6 0 plunges. the stress in station 5 consists of δ1 in n3 0 e direction with 3 0 plunges, δ2 in n184 0 e direction with 4 0 plunges and δ3 in n193 0 e with 3 0 plunges. the stress in station 12 consist of δ1 in n30 0 e direction with 19 0 plunges, δ2 in n263 0 e direction with 59 0 plunges and δ3 in n127 0 e with 22 0 plunge. the geological structure such as fold, fault and fracture are formed due to extensional stress at rifting phases and then strike/ slip system continue. and the last, compressional stress are worked in this area and still active until recent. yuskar, y. et al./ jgeet vol 02 no 04/2017 253 (a) (b) (c) fig. 6. fracture structure analysis in at location (a) st 1, (b) st 8, and (c) st 12. 4.4 geological engineering analysis based on 6 scan lines data in the research area, the ucs (uniaxial compressive strength) value of slope in the study are 25100 mpa, from the hillside 2-6, the percentage of rqd value was in the range 32 42. table 2 shows the overall calculation of rmr parameters. from the table, rmr value in each section of scanline ranging from 61 to 80 and the slope can be classified as a class ii rock (good rock). table 2. calculation of rmr value of each scan line hillside rmr value 2 37 3 58.5 4 14 5 37 6 40.75 5. discussion the analysis result of fracture, fault, and fold structures showed that the structure was formed by tectonic in phases f1, f2, and f3 254 yuskar, y et al./ jgeet vol 02 no 04/2017 (heidrick and aulia, 1993). in the research area, showed northeast-southwest direction formed by the compression force in phase f3 in the central sumatra basin. the fault structure found in metasedimentary rocks at permo-carbon is a normal fault formed by extensional forces at eocene-oligocene f1 phase which subsequently reactivated by phase f3. continued by strike-slip fault structure that formed at phase f2 which reactivates the fault. the compressional stress also created the formation of folds. the research area was showing stress value that still active until today where located near weak zone, indicated by the discovery of the destruction zone and mylonite zone. the active movement of the tectonics is become one indicator for landslides in rocks with intensive weathering, whereas in rock that relatively hard and compact is still showing good rock category. so the conclusion was still in probability due to rocks that have been weathered and affected by the active movement of tectonics can be one cause of landslides in the research area. 6. conclusion the research area was an active structural zone consisting of fracture, fault and folds trending northeast-southwest. the structures formed are the result of tectonic phases that work in the research area. it is interpreted that tectonic was trending northeastsouthwest and north-south. based on the rmr analysis, research area showed that the rocks that have weathered on the outside but still in good condition (good rock). references booth am, roering jj, perron jt. automated landslide mapping using spectral analysis and highresolution topographic data: puget sound lowlands, washington, and portland hills, oregon. geomorphology 2009;109:132 147. clarke drr., p3g .1982. peta geologi lembar pakanbaru, sumatera. pusat penelitian dan pengembangan geologi, bandung. eubank, r.t., & makki, a. c., 1981, structural geology of the central sumatra back-arc basin, proceeding ipa, 10 th annual convention, p 285 317. heidrick, t.l., dan aulia, k., 1993, a structural and tectonic model of the coastal plain block, central sumatra basin, indonesia, proceeding ipa, 22 th annual convention, jakarta. mckean j, roering j .2004. objective landslide detection and surface morphology mapping using high-resolution airborne laser altimetry. geomorphology;57:331 351. papagiannaki, k., lagouvardos, k., & kotroni, v .2013. a database of high-impact weather events in greece: a descriptive impact analysis for the period 2001e 2011. natural hazards and earth system science, 13, 727e736. http://dx.doi.org/ 10.5194/nhess-13-727-2013. raghuvanshi, t.k., ibrahim, j., ayalew, d .2014. slope stability susceptibility evaluation parameter (ssep) rating scheme an approach for landslide hazard zonation. j. afr. earth sci. 99, 595 612. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geosci. eng. environ. technol. 1, 41 44. pulonggono, a and cameron, n. r.., 1984, sumatran microplate, their characteristic and their role in evolution of central sumatra basins: proceedings indonesian petroleum association, 13 th annual convention, p. 121 143. saputra, h.n and sapiie, b., 2005, analogue study of basement fractured reservoirs in kotopanjang area, central sumatra: proceedings indonesian petroleum association, 33 th annual convention. tarolli p, sofia g, dalla fontana g .2012. geomorphic features extraction from highresolution topography: landslide crowns and bank erosion. nat hazards 2012;61:65 83. wirtz, a., kron, w., löw, p., & steuer, m .2012. the need for data: natural disasters and the challenges of database management. natural hazards, 1e23. http:// dx.doi.org/10.1007/s11069-012-0312-4. abstract 1. introduction 2. geology regional 3. methodology 4. result 4.1 fold analysis 4.2 fault analysis 4.3 fractures structure analysis 4.4 geological engineering analysis 5. discussion 6. conclusion references http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 2 2022 novrianti et al./ jgeet vol 7 no 2/2022 59 research article laboratory study on the utilization of jackruit skin waste into carboxymethyl cellulose and their effect on the rheological properties of drilling mud novrianti1*, adi novrianyah1, idham khalid1, zata dini amani1 1petroleum engineering study program , faculty of engineering , riau islamic university jln kaharuddin nst no. 113 marpoyan , pekanbaru , riau, indonesia * corresponding author : novrianti@eng.uir.ac.id tel.:+6281-2220-0048-9 received: jun 10, 2021; accepted: jun 30, 2022. doi: 10.25299/jgeet.2022.7.2.7066 abstract the value rheology of drilling mud must be in accordance with the conditions of wellbore that do not lead to the occurrence of the problems at the time of drilling. one of the efforts to improve the rheology of drilling mud is by adding carboxymethyl cellulose (cmc) which is useful for increasing viscosity and binding water. this study aims to identify the effect on the use of cmc originating from jackfruit skin to the rheological properties of drilling mud. jackfruit skin is an underutilized organic waste and the structure of jackfruit skin contains 50-55% cellulose. manufacturing phase of synthesizing cmc skin jackfruit includes the process of delignification, alkalization, carboximetilation, and sieve sample to be powdered cmc and subsequently carried out the test of plastic viscosity, yield point , gel strength by using a fann vg meter and mud cake using a marsh funnel and volume filtration using a filter press . the added mass of cmc jackfruit skin were varied from 1 g, 2 g, 3 g, 4 g to 5 g. the results suggest that the addition of jackfruit skin cmc has an effect on the rheology of drilling mud. increasingly many additions additive cmc skin jackfruit who use the increasingly highvalue rheology mud drilling were obtained. furthermore, the addition of cmc jackfruit skin starting from 1gr – 5 gr meets the api 13, a standard for the value of yield point/viscosity plastic, plastic viscosity and maximum volume of filtrate. while the value of gel strength which meets the api 13 a is with the addition of cmc jackfruit skin as much as 5 grams. keywords: carboxymethyl cellulose (cmc), jackfruit skin, drilling mud 1. introduction drilling mud rheology is considered as one of the critical aspects to determine the success of drilling operations (li et al., 2015). the success of a drilling operation depends on the use of the drilling fluid used, where a good composition of a drilling mud makes it possible to reduce drilling operating costs (benyounes et al., n.d., 2015). to improve the efficiency of drilling operations, drilling fluid must have the properties of rheological (viscosity, the value of yield point , shear stress and the gel strength), prevention of fluid loss, stability under certain temperature and pressure under operational conditions, as well as having the ability to minimize contamination with other types of fluids such as salt water, calcium sulfate, cement, and potassium (fink, 2012) . the rheological properties of drilling fluids must be monitored frequently during drilling operations to avoid problems related to changes in physical properties, such as yield point and viscosity values which are often associated with problems with inefficient / removal of cuttings and loss of mud fluid into the formation which is a serious problem to be evaluated in improving the efficiency of wellbore cleaning (elkatatny et al., 2016). the addition of carboxymethyl cellulose (cmc) to the drilling mud resulted in a significant increase in viscosity changes, as well as a substantial increase in yield point value (ghannam, n.d., 2014). research on the use of bagasse as cmc and its application to the thickening time test showed that the addition of cmc additives to cement suspension was shown to increase the thickening time by 66%. the research (ghannam, n.d., 2014) proved the addition of 050% cmc, the suspension bentonite can increase the shear stress and apparent viscosity. based on the information at the top of the research is going to utilize the materials of organic as additive cmc for mud drilling which according to (ghannam, n.d., 2014), drilling mud with the addition of cmc were extracted from the bark of jackfruit is recommended to optimize the rheological properties of the suspension fluid. the content of cellulose which is contained in the skin jackfruit (kn) has potential to be used as an ingredient raw manufacture of cmc. according to the central statistic of plant fruits and vegetables indonesia 2017 annual crop production in q1 jackfruit in riau region is as much as 4,596 tons and 4,313 tons in q2 . besides being used as a mixture of animal feed (agustono et al., 2017) jackfruit skin waste has not been utilized optimally by the community so that it has the potential to be used as a drilling mud cmc additive. laboratory scale research was conducted to determine the effect of adding jackfruit peel cmc additives to the rheological value of drilling mud so that later it can be applied in the oil and gas industry. http://journal.uir.ac.id/index.php/jgeet 60 novrianti et al./ jgeet vol 7 no 2/2022 2. methods preparation of tools and materials are early step that made prior to the implementation of laboratorium test. there are 2 stages in this research where the first is the manufacture of cmc based basic skin of jackfruit and the lab nature test of rheology with the addition of additives cmcbased basic skin of jackfruit. the jackfruit skin used for own content of cellulose which contains cellulose is characterized by elements of c (carbon). table 1. results of jackfruit composition element percentage (%) c 53.1% o 41.89% making the cmc additives from jackfruit skin consists of delignification process which serves to separate the lignine to cellulose that can be done by addition of acid or base so that it can dissolve the lignine compounds (nur et al., 2016) . the delignification process in this study is to soak the sample powder that has been sifted with a sieve size of 100 mesh into naoh in a ratio of 1: 6 for 12 hours at room temperature and then wash it using distilled water until it reaches a neutral ph. fig. 1. the process of immersing jackfruit skin samples in naoh fig. 2. process of drying sample using a vacuum bleaching serves to whiten the sample so it can change the color of the sample to be brighter. h2o2 is used in this process is the oxidation reagent which is used to oxidize the lignin structure so it can break the chain of lignine molecules (nur et al., 2016). the bleaching process in this study was by mixing the sample with a 2% h 2 o 2 solution with a ratio of 1: 6. then heating it at a temperature of 60o c while stirring for 2 hours and then washing the sample with distilled water until it reached a neutral ph. fig. 3. samples that have been vacuum-dried fig. 4 sample immersion process with h2o2 fig. 5 drying of bleached samples alkalization is a process of developing the structure of cellulose so it can easily substitute cmc reagents into the cellulose structure (nur et al., 2016). the alkalization process in this study was carried out by placing the sample in the reactor and then adding it with distilled water and 2 propanol then heating and stirring for about 10 minutes at 250 c. then driping 20 ml of 15% naoh solution and stirring the sample for 1 hour at 80o c. fig. 6. carboxymethylation process carboxymethylation is a process of substitution of anhydroxyl groups in each ahydroglucose unit using carboxymethylation reagents (nur et al., 2016). carboymethylation process in this research is to mix the sample and reagents monocloroasetate with different concreations of warming and stirring for 1 hour at 80oc which aims to change the content of cellulose is still solids into fine fibers. the monocloacetic reagent used here is a mixture of acetic acid and hcl compounds with the same concreations (in this process, 15% is used) as much as 100 ml. fig. 7. heating the sample at 80o c novrianti et al./ jgeet vol 7 no 2/2022 61 after the cmc of the jackfruit skin is obtained, the next step is to tet the rheology of the drilling mud. there are 6 samples tested in this study: table 2. drilling mud sample sample name mud composition s0 standard sludge (ls) s1 ls + 1 gram cmc kn s2 ls + 2 grams cmc kn s3 ls + 3 grams cmc kn s4 ls + 4 grams cmc kn s5 ls + 5 grams cmc kn to test the viscosity, plastic viscosity, yield point, and gel strength using fann vg meter where the mud is stirred with 600 rpm for 10 seconds. then let mud sat for 10 seconds the move the rotor to 3 rpm and read the maximum deviation on the ponter scale. then, stirred back the mud with 600 rpm for 10 seconds then stirred back for 10 minutes and let the mud for 10 minutes and read the maximum deviation after it moved to 600 rpm. the plastic viscosity is calculated using the equation below, 300600 cc p  (1) while the yield point value used the following equation below, (2) the value of gel strength is calculated by comparing the deviation of time between 10 seconds and 10 minutes. fig. 8. calculating sample flow time for viscosity fig. 9. sample experiment using fann vg meter 3. result and discussion based on the research, the results are followed, a. viscosity table 3. result of standard mud viscosity and standard sludge + cmc jackfruit skin fig. 10. viscosity time vs. cmc weight based on the graph above, it can concluded that cmc that made from jackfruit skin was able to increase the viscosity of drilling mud up to 3 times with the addition of 5 grams of jackfruit skin compared to the initial flow before the standart mud was added to cmc which caused by the alkalinization in plant fiber. the jackfruit peel which causes cracks in the plant structure thereby increasing the absorption of cellulose along with the increase of viscosity which is in accordance of research (pratama et al., 2017). b. yield point table 4. result of yield point standard mud and standard mud + cmc jackfruit skin fig. 10. yield point vs. cmc weight the yield point resulted from the test above show that the addition of cmc that made from jackfruit skin to standart mud can increase the value up to 2 times with the addition of 5 grams of cmc compared to the initial yield point where this is pb cy  300 0 10 20 30 0 1 2 3 4 5 y ie ld p o in t (l b /1 0 0 f t2 ) cmc weight (gram) yield point mud composition viscosity (second) increased viscosity time by addition of cmc (%) standard sludge (ls) 18,1 0 ls + 1 gram cmc kn 20,88 15,35 ls + 2 gram cmc kn 24,1 33,14 ls + 3 gram cmc kn 43,57 140 ls + 4 gram cmc kn 66 264,64 ls + 5 gram cmc kn 80 341,98 mud composition yield point (lb/100 ft2) increased yield point by addition of cmc (%) standard sludge (ls) 7 0 ls + 1 gram cmc kn 9 28.7 ls + 2 gram cmc kn 13 85 ls + 3 gram cmc kn 14 100 ls + 4 gram cmc kn 18 157 ls + 5 gram cmc kn 23 228.57 62 novrianti et al./ jgeet vol 7 no 2/2022 influenced by increasing number of conditions of total solids contained in the mud system (wijayanto & bayuseno, 2016) (rubiandini, 2009). c. gel strength table 5. result of gel strength standard mud and standard mud + cmc jackfruit skin fig. 11. gel strength vs. cmc weight based on the calculations test above, the value of gel strength moves up with the addition of cmc weight of jackfruit skin with an average increase in gel strength per addition of 1 gram of cmc is about 5% . similar to the yield point , the increase in gel strength is also caused by an increase in viscosity which is directly proportional to the increase in gel strength (wardani, 2017). d. plastic viscosity table 6. result of plastic viscosity standard mud and standard mud + cmc jackfruit skin fig. 12. plastic viscosity vs. cmc weight it can be seen from the results of plastic viscosity tests above, the increase in plastic viscosity tends to be stable with the addition of 1 gram of cmc jackfruit skin with an average percentage increase of 99.98%. this caused by mechanical friction due to the amount of contact area that occurs between solid particles and the existing liquid phase (putra, 2015). e. filtration loss table 7. result of filtration loss volume standard mud and standard mud + cmc jackfruit skin fig 13. filtration volume vs. cmc weight based on the results above, it can be concluded that the use of jackfruit skin managed to minimize the volume of filtrate that separated from the drilling mud up to 37.5% with the addition of 5 grams of cmc. this caused by the addition of cmc which binds water and forms a gel in liquid phase (endang bekti1, yuli prasetyowati2, 2011) and increases the viscosity of the drilling mud. f. mud cake table 8. result of mud cake volume standard mud and standard mud + cmc jackfruit skin fig. 14. mud cake vs. cmc weight mud composition gel strength (lb/100 ft2) increased gel strength by addition of cmc (%) standard sludge (ls) 0.4 0 ls + 1 gram cmc kn 0.44 4 ls + 2 gram cmc kn 0.5 10 ls + 3 gram cmc kn 0.56 16 ls + 4 gram cmc kn 0.636 19.6 ls + 5 gram cmc kn 0.69 29 mud composition plastic viscocity (cp) increased plastic viscosity by addition of cmc (%) standard sludge (ls) 7 0 ls + 1 gram cmc kn 10 42.8 ls + 2 gram cmc kn 12 71.4 ls + 3 gram cmc kn 14 100 ls + 4 gram cmc kn 16 128.57 ls + 5 gram cmc kn 18 157.14 mud composition filtration loss (ml) decreased filtration loss by addition of cmc (%) standard sludge (ls) 16 0 ls + 1 gram cmc kn 15 6.25 ls + 2 gram cmc kn 14 12.5 ls + 3 gram cmc kn 12.55 21.9 ls + 4 gram cmc kn 11 31.25 ls + 5 gram cmc kn 10 37.5 mud composition mud cake (mm) decreased mud cake volume by addition of cmc (%) standard sludge (ls) 0.9 0 ls + 1 gram cmc kn 1,225 32,5 ls + 2 gram cmc kn 1,3 40 ls + 3 gram cmc kn 1,35 45 ls + 4 gram cmc kn 1,425 52,5 ls + 5 gram cmc kn 1,5 60 novrianti et al./ jgeet vol 7 no 2/2022 63 based on the results below, it can be concluded that the use of jackfruit skin in standard mud can increase the thickness of mud cake with an average thickness increase of about 20%. based on (apriyanti, 2013) (hadziqoh et al., 2019), the maximum ideal thickness of mud cake is 3/8 inch or 9.525 mm. when compared with the addition of cmc in standard mud, the test results are still far below the maximum value in previous studies. this caused by the nature of cmc which can change the liquid phase into a gel so that it binds water and solids in the liquid phase (endang bekti, yuli prasetyowati, 2011) (endang bekti, yuli prasetyowati, 2011) the comparison between each values with the addition of cmc using jackfruit skin to the specification 13 a as follows; table 9. the comparison of yield point/ plastic viscosity with standard api 13 a mud composition yield point / viscosity plastic (lb/100 ft2) api 13 a spesification yield point/plastic viscosity standard sludge (ls) 1 max. 3 lb/100 ft2 ls + 1 gram cmc kn 0,9 max. 3 lb/100 ft2 ls + 2 gram cmc kn 1,083 max. 3 lb/100 ft2 ls + 3 gram cmc kn 1 max. 3 lb/100 ft2 ls + 4 gram cmc kn 1,125 max. 3 lb/100 ft2 ls + 5 gram cmc kn 1,278 max. 3 lb/100 ft2 table 10. the comparison of gel strength with standard api 13 a mud composition gel strength (lb/100 ft2) api 13a spesifitcation gel strength standard sludge (ls) 0,4 2/4 – 4/5 lb/100ft 2 (0,67 – 0,8 lb/100ft 2 ) ls + 1 gram cmc kn 0,44 2/4 – 4/5 lb/100ft 2 (0,67 – 0,8 lb/100ft 2 ) ls + 2 gram cmc kn 0,5 2/4 – 4/5 lb/100ft 2 (0,67 – 0,8 lb/100ft 2 ) ls + 3 gram cmc kn 0,56 2/4 – 4/5 lb/100ft 2 (0,67 – 0,8 lb/100ft 2 ) ls + 4 gram cmc kn 0,636 2/4 – 4/5 lb/100ft 2 (0,67 – 0,8 lb/100ft 2 ) ls + 5 gram cmc kn 0,69 2/4 – 4/5 lb/100ft 2 (0,67 – 0,8 lb/100ft 2 ) table 11. the comparison of plastic viscosity with standard api 13 a mud composition plastic viscosity (cp) api 13 a spesification plastic viscosity standard sludge (ls) 7 minimum 10 cp ls + 1 gram cmc kn 10 minimum 10 cp ls + 2 gram cmc kn 12 minimum 10 cp ls + 3 gram cmc kn 14 minimum 10 cp ls + 4 gram cmc kn 16 minimum 10 cp ls + 5 gram cmc kn 18 minimum 10 cp table 11. the comparison of fluid loss with standard api 13 a mud composition filtrartion loss (ml) api 13 a spesification filtration loss standard sludge (ls) 16 maximum 15 ml ls + 1 gram cmc kn 15 maximum 15 ml ls + 2 gram cmc kn 14 maximum 15 ml ls + 3 gram cmc kn 12.55 maximum 15 ml ls + 4 gram cmc kn 11 maximum 15 ml ls + 5 gram cmc kn 10 maximum 15 ml 4. conclusion based on research that has been done, the addition of jackfruit skin affects the rheological of drilling mud where the addition of cmc up to 5 grams can increase the viscosity value up to 3 times and the yield point value up to 2 times and reduce the amount of filtrate volume up 37.5% and per 1 gram the addition of cmc can increase the percentage of gel strength value by 5% and the value of plastic viscosity to 99.98% and increase the thickness of the mud cake with an average thickness of up to 20%. in addition, the value of yield point, plastic viscosity, and the maximum volume of the filtrate obtained from the addition of 1 gram to 5 grams of jackfruit skin in accordance with the standards of api specifications 13a. while the standard value of gel strength which is at the standard value of the 13a specifications in the advance of 5 grams of jackfruit skin of cmc table 11. acknowledgements the authors would like to acknowledge this research as supported by the riau islamic university and declare no conflict of interest. references agustono, b., lamid, m., ma, a., & elziyad, m. t. 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(2017). "evaluation of the effect of the temperature on physical properties of kclpolymer sludge for well "x" field "y" at hole 17 1/2 " jurnal petro  vi(4), 130–137. wijayanto, s. o., & bayuseno, a. . (2016). wijayanto. analisis kegagalan material pipa ferrule nickel alloy n06025 pada waste heat boiler akibat suhu tinggi berdasarkan pengujian : mikrografi dan kekerasan, 2(1), 33–39. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 3 2022 110 sahara, r., et al./ jgeet vol 7 no 3/2022 research article assessment of geosite and geomorphosite at south solok aspiring geopark area rina sahara1, budhi setiawan1* 1 geological engineering study program, university of sriwijaya, palembang 30139, indonesia. * corresponding author: budhi.setiawan@unsri.ac.id tel.:+6282285635787 received : may 31, 2022; accepted: sep 6, 2022. doi: 10.25299/jgeet.2022.7.3.9520 abstract south solok is one of the five districts designated as the aspiring of the ranah minang geopark. various reliefs and geological structures cause the diversity of landscapes to be an attraction for tourists and ecosystems with biodiversity. the study intends to ide ntify geosite and geomorphosite in the south solok area with field observations to describe the state of geology, geomorphology of geosite sites, and geomorphosite. site assessment is carried out quantitatively with five assessment parameters; scientific, educational, functional, tourist, and posting activities on tourist sites on social media. field observation found 17 sites classified into four groups, specifically waterfalls, manifestations of hot springs, geomorphological landscapes, and caves. based on the results of the highest value representation obtained by the batukapal cave sites with a value of 44.86% and the lowest at timbulun waterfall at 0.1%. of the 17 sites, four sites are considered the main sites in the research area: suliti waterfall, sapan maluluang hot spring manifestation, batukapal cave, and camintoran. keywords: social media, local community, geodiversity, sustainability 1. introduction the introduction describes an overview of geoparks, geosite, and geomorphosite. in addition, describe the geological state of the research area. 1.1 background geopark is a protected area consisting of elements of geological, archaeological, ecological, and cultural values of local communities utilized and preserved. in addition, geological diversity, biodiversity, and cultural diversity are essential elements of an earth park (unesco, 2016). geopark promotes geological features through information media activities, conservation and education, and geological resources through geotourism and sustainable development (newsome and dowling, 2018). a geosite or geological site is a part of geological heritage rather than a geopark with specific characteristics individually and a combination of several objects and cultural diversity, biodiversity, and cultural part of the story of the trueness of a region (presiden republik indonesia, 2019). geosite is part of a geographical system with a significant structure, function, and origin, including natural and anthropic heritage (artistic, historical) (mihai ielenicz, 2009). geomorphosite is landforms associated with value, while geomorphological landscapes are part of the earth's surface and can be seen, felt, and exploited by humans. (reynard, 2005). according to (kubalíková, 2014), the geomorphosite acts as a landform that has the potential to be a tourism site and has an assessment point of view from humans. geomorphological or geomorphosite refers to rocks and reliefogenic, which indicates a process used as a historical site, archaeology with a specific frequency, and utilized as tourism. characteristics in geomorphosite are obtained from elements also found in geosite objectively (mihai ielenicz, 2009). geosite and geomorphosite over time, have degraded from the existence of anthropogenic activities that have the potential to threaten physical properties, resources available in geosite and geomorphosite (prosser et al., 2018). south solok is one of the five districts of the geopark ranah minang with a geological heritage of volcanic landscapes, karsts, rocks, and geological structures equipped with biodiversity ecosystems and cultural diversity. the area does characterize by various reliefs as well as complex geological structures. it becomes the main factor forming the landscape of the research area and provides an attraction for tourists. they are launching the aspiring geopark solok selatan part of the ranah minang geopark towards preparing a master plan which is one of the four requirements for proposing a geopark: dossier, geological heritage, masterplan, and governing bodies. the proposed dossier raised the theme “shallow geothermal phenomena and volcanic peaks in southeast asia.” geopark ranah minang with dossier “living in harmony with the great sumatran fault.” where it is in the barisan mountains and the sumatra fault zone, seven segments pass through the minang domain area from pasaman angkola segment, barumun segment, sumpur segment, sianok segment, sumani segment, suliti segment at the research site that overlaps with the siulak segment in the south solok region, which is actually in the jambi region (sieh and natawidjaja, 2000). west sumatra has a beautiful area with a landscape of hills, mountains, lakes, valleys, and karst. additionally, the diversity of biology, culture, history and relics of the japanese colonial period are monumented. this is additional to west sumatra in developing the ranah minang geopark to the national geopark through its three pillars: http://journal.uir.ac.id/index.php/jgeet mailto:budhi.setiawan@unsri.ac.id sahara, r., et al./ jgeet vol 7 no 3/2022 111 conservation, education, and community economic development. south solok tourism has not been studied much scientifically. as a result of the geosite, these geomorphosites still have problems attracting diverse visitors and long-term solutions to protection and conservation. in addition, the sites’ location in an area with inadequate infrastructure, asset maintenance, and processing systems are essential points in the sustainability of geosite and geomorphosite. the research aims to involve geosite and geomorphosite assessments by scientific, educational, functional, tourist, and social media. it then evaluates the scientific and educational value of obtaining the main sites of geosite and geomorphosite and proceeds with revealing their geological, cultural, and biological diversity. finally, it proposes a planning and development strategy oriented towards tourism promotion and education. this information will help attract students or scientists to take more investigations regarding the acceleration of the south solok geopark. in addition, it is increasing the creative economy of local people and knowledge of local people and knowledge of the importance of maintaining, introducing, and preserving tourist sites. 1.2 research objective south solok is located in the eastern part of west sumatra province. south solok is bordered by jambi province to the south, west of south pesisir regency, north of solok regency, and east of dhamasraya regency. geologically the research area is between the barisan mountain and passed by the suliti segment, which length 95 km from mount talang to mount kerinci. the suliti segment is part of the sumatra fault segment. the fault pattern that affects this area is a sliding fault directed northwestsoutheast and a normal fault northwest-southeast. the three significant tectonic events influence the geological structure: the middle mesozoic orogenesa, late cretaceous – eocene, and pliocene orogenesa plistosen (darman, 2013). fig 1. research area stratigraphy of deposited rocks in the pre-tertiary to quarternary period consisting of metamorph base rocks (pre-mesozoic), metamorph rocks (mesozoic), metamorph scattered rocks (mesozoic cenozoic), and volcanic rock series (tertiary quarternary) (rosidi et al., 1976) based on rpijm, south solok regency has a tropical climate with temperatures of 20 °c to 33 °c, rainfall of 1,600-4,000 mm / year with humidity ranging from 80%. excellent flow and spring water. large rivers generally have sufficient depth, permanent and relatively heavy currents, and hilly landscapes. 2. methodology the writing of this research is presented in the reflection of the study (ansori et al., 2021; briggs et al., 2021; brilha, 2016; hoang et al., 2021; reynard et al., 2016, 2007) summarized in four stages (figure 2). the beginning of research was preceded by the study of literature on geology and geomorphology of research areas. continued field observations are divided into two parts: documentation and descriptive data. the documentation contains information on the location name, coordinates, azimuth, elevation, and image of each site. while geological and geomorphological conditions are based on field observations, map analysis and literature studies are activities of descriptive data. the description does not focus on geomorphological or geological features, but the location’s availability of infrastructure, culture, and biology is also outlined. the next stage of a quantitative assessment of geosite and geomorphosite refers to (gajek et al., 2019; hausmann et al., 2018) covering five parameters: scientific, educational, functional, tourist, and posting activities on geosite or geomorphosites on social media (table 1). the five assessment parameters above are scientific and educational as the central values. fig 2. workflow of research in contrast, functional, tourist, and social media are secondary site use and management values. this study uses an instagram platform to look at representations of the number of posts and likes on the images of each geosite and geomorphosite posted. tourists widely use instagram to take pictures of tourist sites through mobile apps. in addition, the application programming interface (api) makes it easy to access images on platform searches. (hausmann et al., 2018). quantitative assessment to determine geosite and geomorphosites that have the potential to be the leading site in the acceleration of the south solok geopark and evaluate whether it is affected by human activities. the data collected is then sorted to determine which areas have the highest amount of value overall by representing databases based on (1) intrinsic value in scientific, cultural, and aesthetics; (2) the capacity of use on education and function;(3) protective measures against integrity as well as site threats. the last is a synthesis containing scientific information, maps, photographs, and diagrams. synthesis is divided into four parts, first presenting the assessment results of each geosite and geomorphosite. second, advertise the location of each site in the form of a map. third, analyzing and selecting the potential of geosite and geomorphosite to obtain potential main sites in the research area also explains the state of geology, geomorphology, culture, and biology. the last section provides management advice that can contain the proposal for the protection and management of the site. 3. result and discussion 112 sahara, r., et al./ jgeet vol 7 no 3/2022 3. 1 geosite and geomorphosite a field survey illustrated in figure 3 shows the distribution of cultural diversity maps, geosites, and geomorphosite in the research area. in this case, 17 geosites and geomorphosites were identified and classified into four types: the manifestation of hot springs, waterfalls, geomorphological landscapes, and caves. the assessment of each geosite and geomorphosite is summarized in table 2. geosite and geomorphosites commonly found are waterfalls of seven sites, geomorphosite with six landscape sites and batukapal cave as a rare site (figure 4). waterfalls are formed of geological structures in the form of faults with a waterfall height of 10 40 meters and an elevation of 450 meters to 1310 meters. the geomorphological is the appearance of rolling hills, valleys, lowlands, rivers, and mountains that stretch from 250 meters to 1248 meters. table 1. criteria for the quantitative assessment variables extention low value: 0 medium value: 1 high value: 2 scientific representativeness the outcrop lacks typical characteristics the outcrop features an incomplete the outcrop features all typical characteristics rarity >3 similar sites 1 of 3 sites the only site in the region scientific knowledge no publications 3-5 publications more than 5 publications diversity one feature 2-3 features >3 features extensiveness <10 m 10 to 20 m >20 m education observation conditions vegetation, weathered material obstructs vegetation, weathered material partially obstructs no obstacles to observation education product lack of products 1-2 products more than 2 products didactic potential for students and specialists only for pupils of secondary schools for all levels of education possibility sampling no possibility only with permission unlimited education diversity geological values only geological, biotic abiotic, biotic, cultural functional capacity <10 persons 11 to 20 persons >20 persons safety threats to safety occur moderate no threats at all limitation to access problems with access access medium good access conditions accessibility >20 min 10 to 20 min <10 min other education sites lack of other sites within a 5 km radius 2-3 sites within a 5 km radius >4 sites within a 5 km radius tourist scenic value lack of scenic value moderate scenic value interesting vantage point location to tourists trails site located >1 km from a trail sited located 100 m – 1 km from a trail sited located on a trail or path degree of degradation the high degree of human impact a moderate degree of human impact no visible signs of degradation distance from tourist centers >15 km away 5-15 km away <5 km away accommodation and restaurants >30 km away 10-20 km away <10 km away social media number of posts likes pictures table 2 criteria for the quantitative assessment sites description scientific education functional tourist social media image post likes a. hot spring balun hot spring 3 6 7 8 2 58 ambayan hot spring 5 5 6 7 2 108 sapan maluluang hot spring 9 7 9 7 105 1,484 b. waterfall suliti waterfall 6 6 4 5 130 1,628 timbulun waterfall 2 2 3 6 1 32 kupitan waterfall 5 6 4 6 45 404 tansi 4 waterfall 5 7 6 6 133 2,362 tansi 3 waterfall 5 6 4 6 104 4,672 twin waterfall 5 7 7 6 198 1,587 jenjang waterfall 5 7 9 8 7 104 c. geomorphology ampalu river landscape 7 7 9 9 1 125 sangir river landscape 7 7 9 8 17 698 laras hill 6 6 9 8 147 774 bangun rejo hill 6 6 8 8 73 1,342 liki garden 6 6 9 8 195 3,804 camintoran 6 6 5 6 342 4,827 d. cave stone cave 10 6 5 7 689 20,365 sahara, r., et al./ jgeet vol 7 no 3/2022 113 fig 3. distribution of cultural, geosite, and geomorphosite diversity maps in the research area using geological base maps (rosidi, h.m.d and pendowo, 1996) fig 4. geosite and geomorphosite research area 3.2 main geomorphosite potential quantitative assessment criteria for the geosite and geomorphosite of 17 sites are described in a pie chart (figure 5). the quantitative evaluation of scientific value results represented all aspects of each geosite and geomorphosite—integrated educational interests range from abiotic, biotic, geological, and cultural. the 114 sahara, r., et al./ jgeet vol 7 no 3/2022 quantitative evaluation shows scientific and educational scores for the batukapal cave. other sites depict geodiversity with low to moderate scientific and educational value. secondary value analysis that some inventory sites have a high aesthetic value from the beauty of nature, the scenery that offers a beautiful panorama. it is functionally limited by low access. meanwhile, the use of social media is at a low to moderate level. the quantitative assessment showed the highest value at the batukapal cave site with a percentage of 44.86% and the lowest percentage at timbulun waterfall with 0.1%. representation of geological heritage as well as scientific and educational parameters as the central assessment is proposed by three geosite and one geomorphosite as the main sites in the acceleration of the south solok geopark, namely suliti waterfall, sapan maluluang hot spring manifestation, batukapal cave and camintoran. fig 5. representation of geosite and geomorphosite quantitative assessment result 3.2.1 suliti waterfall suliti waterfall is located in north pakan rabaa, koto parik gadang diateh district, south solok regency. the beautiful scenery completed by the height of the waterfall reaching 40 meters is at an elevation of 1310mdpl. the outcrop characteristics describe the features of the waterfall, which indicate the geological structure of the suliti segment of the sumatra fault. this waterfall generally comprises andesite lava lithology by volcano rocks (qou) (figure 6). the arrangement of terraced andesite lava rocks close to the waterfall becomes an exciting photo spot, complemented by the splashing of transparent water flow, animal sounds, and soothing air. the journey to the location can be reached using a vehicle and then followed by walking with an estimated time of ± 2 hours from the parking lot through the geomorphological landscape of hills used by the local community for farming activities. types of plants in the form of mangosteen fruit commodities that grow up to 7 to 25 meters, rubber trees, and cinnamon. endemic plants of dewwood (podocarpus spp) with beautiful and delicate fibre quality. in addition, a small black paok topu bird measuring 16 cm with a characteristic black head, red belly, pale blue patches on the wings, and a short blue eyebrow line behind the eyes. carrion flowers are found in the pakan rabaa area (amorphophallus titanum becc) (indonesia, 2019). the slope is sloping too steep, and the vegetation is quite dense. weathering and erosion activity is high due to the large flow of the river, as well as the appearance of rocks that are the size of boulders and hard compactness. this location has the potential for special interest tourism as the study of the geological structure, petrography, and geomorphology. especially the sumatra fault study, the suliti segment, which is part of the seven segments in sumatra. the ends of the segments are at the upper lake and lower lakes, with a width of 4 km, up to mount kerinci, which overlaps with the siulak segment (sieh and natawidjaja, 2000). fig 6. (a) suliti waterfall (b) showing a geological structure like fault, the composed lava andesite lithology 3.2.2 sapan maluluang hot spring manifestation the manifestation of the sapan maluluang hot spring is related to active tectonics and quaternary volcanism in the research area through fissures and hot water faults appearing on the surface due to pressure from within the earth (figure 7). the shape of this hot spring contains water that also produces a foam of water dominated by mud and clay. in addition, there is silica sintered in the interlude of hot springs. sinter silica has sufficient silk content, and when the temperature is lower than hot springs causes it to settle and become slightly denser (figure 7). this hot spring is near the mount kerinci area, and there are five source points at the location at an altitude of 866 meters above sea level, surrounded by hills to mountains depicting conical landscapes. three locations can be reached, while two locations are viewed from a distance. temperature values range from 43°c -to 91°c and ph 6.87.4, with silica sinter electrical resistivity value of 30.41 34.19ωm (permanda and putra, 2017). the local district government has utilized this place as a hot spring tourist attraction from 2014 until now. access to the location is in good condition to be traveled using a motorcycle or car. fig 7. (a) hot springs 1 (b) hot springs 2 (c) hot springs 3 (d) 5 hot springs from a distance (e) silica sintered interlude on hot spring manifestations 1 (f) hot spring pools. 3.2.3 batukapal cave batukapal cave is at an elevation of 300mdpl and is a typical landscape of limestone that resembles a ship's cabin. this limestone is part of the perm-carbon-aged row sahara, r., et al./ jgeet vol 7 no 3/2022 115 formation (pb) with a shallow marine deposition environment. at the last perm of west sumatra, sibumasu experienced a collision event, switching in the barisan formation (rosidi et al., 1976). raised limestone undergoes dissolution triggered by exposure to meteoric water (rain). this process developed groundwater flow to the karst system and formed a cave morphology with the structure of cave mouths, underground rivers, stalactites, stalagmites, and columns (figure 8). the cave ceiling has a height of 80 meters and an area of ±27 hectares. at the top is a hole where rays radiate into the cave’s walls when the sun rises. the multilevel arrangement of rocks and forming spacious rooms equipped with an alloy of yellow, green, and red colors in each hallway depict the shape of the beautifully painted walls. multilevel rock arrangements and forming spacious rooms. fig 8. (a) the appearance of the mouth of the cave (b) stalactites, stalagmites, subterranean rivers (c) column (d) banyan trees. batukapal cave is one part of the ranah minang geopark, which was stipulated by menteri energi dan sumber daya mineral (esdm) in 2021. furthermore, the same year, goa batu kapal won second place in the anugrah pesona indonesia (api) award in the hidden paradise category. as a result, the tourism conscious group (pokdarwis) developed this site, nagari sungai kunyit, sangir balai janggo district, south solok regency. the naming of batukapal cave is taken from its unique formation by the local community. according to legend, it was a shipwreck that capsized and cursed and turned into stone. therefore, each room has a naming from the community starting from bundo kanduang, aline, and batik because it resembles batik carvings and the shape of praying for people. the beauty of the light reflected from the sunlight emit colorful patterns and can be enjoyed over the bridge from wood as a facility for visitors. it is a nest for leaf-nosed bats (rhinolophus), seriti birds (collocalia esculenta), and mossnested swallows (collocalia vanikorensis). in addition, there is a banyan tree (ficus banjamina) with a height of up to 50 meters. the access needed to the tourist site passes through public and local roads, which are 185 km h from the capital of west sumatra province-padang. 2 km before the location will enter oil palm land with red dirt roads. 3.2.4 camintoran the camintoran site is at an elevation of 1240 meters above sea level, which an area of 16 hectares. administratively located in nagari lubuak gadang sangir subdistrict. this location is used as a campground above the clouds with temperatures reaching 12 °c. in addition, aerospace and agro-tourism tourism objects are developing to improve the community's economy. the view of mount kerinci or indrapura peak, with a height of ±3,805 meters, is visible nearby, and a large-scale expanse of morphological landscapes (figure 9). landscapes draw geological processes that occur in the research area and play an essential role in the environment, culture, ecosystems, and species. camintoran peak is one of the paragliding spots for athletes to train. beautiful as well as enchanting scenery from a height. it is said that camintoran land is an ancient city lost in the swarna bumi era, which was once located at an altitude of 1,230 meters above sea level at the waist of mount kerinci. the distance from the provincial capital to the location of 172 km, 2 km before the area, will pass through a gravel road that is difficult to reach by ordinary vehicles. however, it is not a barrier for visitors to arrive. fig 9. (a) the appearance of the top of mount kerinci (b) morphological landscape. 3.3 strategic planning and development sustainable development in geosite, geomorphosite to improve community society, enhance the economy and educational facilities for conservation, environment, ecosystems, species, and better site protection. some geosite and geomorphosite are degraded due to the natural impact of weathering and erosion. this has the potential to be a risk to the safety of visitors. when the weather rains, the road conditions are slippery and prone to landslide disasters. therefore, the need to integrate the idea of inheritance in the field of education, launching an inventory of geological heritage in the form of platforms that facilitate the integration of heritage into territorial management. improving tourist infrastructure and creating well-defined tracks are equipped with interpretation panels to introduce geosite and geomorphosite and reduce human activities' threats. structured management by prioritizing visitors' safety and comfort and building a tourism awareness group (pokdarwis) that is active in each subdistrict for the smooth running and maintenance of tourist sites. conclusion south solok is one of the areas included in the ranah minang geopark section. the climate is tropical and has 80% humidity. the succession of geological events part of the sumatran fault suliti segment makes it a natural charm organized in a geological area or geopark. four main sites are considering scientific and educational parameters from four geosite and geomorphosite classifications: suliti 116 sahara, r., et al./ jgeet vol 7 no 3/2022 waterfall, sapan maluluang hot spring manifestation, batukapal cave, and camintoran. the 40-meter-high suliti waterfall is composed of andesite lava lithology. the outcrop reflects the typical waterfall formed from the presence of geological structures. the sapan maluluang hot spring with five source points and silica sintered manifestation is formed due to the research area's tectonic activity and quaternary volcanism. batukapal cave is a rock landscape resembling a ship cabin that is dissolved so that there is a unique endocardial structure, namely the mouth of the cave, underground river, stalactites, stalagmites, and columns. finally, camintoran has a geomorphological landscape on a large scale at an elevation of 1240 meters above sea level. it was one of the options for camping while enjoying the morning chill while enjoying the sunrise until the opening of the peak of mount kerinci. south solok has launched the preparation of the aspiring geopark solok selatan masterplan with a dossier with the theme "shallow geothermal phenomena and volcanic peaks in southeast asia.” geomorphological phenomena and panoramic diversity improve the quality of geological heritage, which is also complemented by biodiversity and cultural diversity ecosystems. most visitors are only interested in the beauty of the landscape. therefore, it is necessary to integrate the idea of inheritance in education and launch an inventory of geological heritage in the form of platforms that facilitate the integration of heritage into territorial management. improving tourist infrastructure and creating well-defined tracks are equipped with interpretation panels to introduce geosite and geomorphosite and reduce threats associated with human activities. the sustainable management and development of geosite, geomorphosite aimed at improving people's welfare, economy, and conservation educational facilities also play an essential role in the environment, culture, ecosystems, and species. providing provisions to guides helps with safe travel and will improve the quality of tours of each site. in addition, to promoting cultural information, ecosystems add value to each location and tourist’s visits. acknowledgments gratitude for the grace of allah swt so that the author can complete the research. thank you to muhammad fadhli's colleagues 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http://creativecommons.org/licenses/by-sa/4.0/ uir press p-issn 2503-216x e-issn 2541-5794 journal of j eet geoscience engineering environment and technology journal of j eet geoscience engineering environment and technology issne-issn journal of geoscience, engineering, environment and technology volume 6. no 3. september 2021 issn (print) : 2503-216x issn (online): 2541-5794 uir press jgeet p-issn 2503-2161 e-issn 2541-5794 (journal of geoscience, engineering, environment, and technology) publish periodically four times annually scope of journal paper covering the following aspects of geology, earth and planetary science, engineering, environtment, and technology address of secretariat and paper submitting jl. kaharuddin nasution no 113 marpoyan damai pekanbaru, riau 28284 phone.(0761) 72126 , fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id; web: http://journal.uir.ac.id/index.php/jgeet executive editorial advisor prof. josaphat tetuko sri sumantyo, ph.d (japan) prof. mega f. 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(indonesia) manager editor catur cahyaningsih b.sc (hons) m.sc.(indonesia) tiggi choanji s.t, m.t (indonesia) editorial member dr. eng. takahiro miyazaki (japan) dr. evizal abdul kadir s.t., m.eng (indonesia) dr. luong nguyen (vietnam) dr. mursyidah, m.sc. (indonesia) dr. anas puri s.t, m.t (indonesia) dr. eng. muslim, m.t (indonesia) dr. emi sukiyah, st., mt (indonesia) dr. sapari dwi hadian, mt (indonesia) dr. vijaya isnaniawardhani, s.t, m.t (indonesia) good fried panggabean, s.t, m.t (indonesia) katia nagamine urata, m.eng (brazil) mirza muhammad waqar, m.sc (pakistan) kageaki inoue, m.eng (japan) yuta izumi, m.eng (japan) joko widodo, s.si, m.si (indonesia) yuniarti yuskar s.t, m.t (indonesia) dewandra bagus ep., b.sc (hons) m.sc. (indonesia) budi prayitno s.t, m.t (indonesia) adi suryadi b.sc. (hons) m.sc. (indonesia) babag purbantoro, s.t, m.t (indonesia) pakhrur razi, s.si, m.si (indonesia) eunice wanjiku nduati m.agr (kenya) muhammad zainuddin lubis s.ik m.si (indonesia) http://journal.uir.ac.id/index.php/jgeet preface welcome to the journal of geoscience, engineering, environment and technology (jgeet). jgeet is a peer reviewed, open access and online journal in english for the enhancement of research in various areas of science and engineering. the aim of the jgeet is to give a highly readable and valuable addition to the literature which will serve as an indispensable reference tool for years to come now, we’re publishing new volume 06 no 03 2021. we are pleased the scientist and researcher to publish in this journal. this journal discussed the topic related to the areas of geoscience, engineering, environment, and technology. as the editor-in-chief of the jgeet, i take this opportunity to express my sincere gratitude to authors who have chosen jgeet to disseminate their research. further, i would like to thank executive editorial advisor, journal manager, editorial member and other supporting staff for the success of this journal. we are more than happy to receive contributions for our next issue from academicians, researchers, scholars and practitioners to ensure the consistency and the success of the journal. thank you very much. editor-in-chief list of content groundwater conservation strategy based on water balance at muarabungo groundwater basin, indonesia ................................................................................................... 127 a tracer streamline practice for re-evaluation waterflood pattern to introduce a cyclic water injection scheme ............................................................................. 131 the influence of external cfrp string reinforcement on the behavior of flexural rc elements .................................................................................................................... 141 total organic carbon (toc) value prediction in source rock potential at north east java basin, indonesia ............................................................................................... 147 comparison of granitoid characteristics west kalimantan and karangsambung based on mineralogical and geochemical aspects ............................... 152 geomorphosite assessment at north karangsambung -karangbolong geopark kebumen, as tools of geotourism ........................................................................... 164 biometric similarity test of the population of t. (zaria) bantamensis tjicumpaensis with t. (zaria) javana as a form of phylogeny and evolutionary proximity ......................................................................................................................................... 172 http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 3 2021 172 pandita, h., et al./ jgeet vol 6 no 3/2021 research article biometric similarity test of the population of t. (zaria) bantamensis tjicumpaensis with t. (zaria) javana as a form of phylogeny and evolutionary proximity hita pandita1*, ani apriani1 1 department of geological engineering, institut teknologi nasional, yogyakarta, indonesia. * corresponding author : hita@sttnas.ac.id tel+6285800081053/fax:+62 274 487249 received: apr 25, 2021; accepted: sept 22, 2021. doi: 10.25299/jgeet.2021.6.3.6780 abstract biometric aspects in the turritellidae family need to be studied as an important identification parameter. zaria, which is one of the sub genera in the turritellidae family, deserves to be tested in order to determine the feasibility of the biometric aspect as an identification parameter. this paper aims to provide an overview of the benefits of the biometric aspect as an identification parameter. the method used to re-identify the biometric and morphological aspects of the t. (zaria) bantamensis tjicumpaensis population with t. (zaria) javana. the results of the identification were carried out by a t-test on the biometric aspect to see the similarity of the biometric aspects of the two populations. based on the results of the ttest on the parameters of the wsut: wang and wsut: l ratio, it shows that the two zaria species are the same. meanwhile, from the morphological aspect, there is a slight difference in the early growth peripherals. keywords: biometrical, zaria, turritellidae, t-test, morphological 1. introduction biometry is one method of identification of fossils, in the form of measurements of certain parts of the body. the biometric aspect as an identification parameter in fossils has not been widely used as a key parameter in determining species (imbrie, 1956; pandita et al., 2013). this is because a sufficient amount of sample data is needed to be able to see the pattern of the biometrics. therefore, research on the role of biometry as an important parameter in fossil identification needs to be carried out continuously. zaria, which is a group of fossils from the turritellidae family, is a sub-genera of turritella which is interesting to study from its biometric aspect. this is due to the fact that numbers of species of zaria found on java island are morphologically similar, but are separated into different species (pandita, 2014). this condition is also shown between t. (zaria) javana from the location of the cijarian-sukabumi river and t. (zaria) bantamensis from the cimadur-bayah area. the two populations are almost similar morphologically. seeing this problem, it is necessary to study the biometric aspects of the two populations between t. (zaria) javana and t. (zaria) bantamensis tjikumpaensis. 2. objectives the purpose of this paper is to provide a morphological and biometric description of the population of zaria bantamensis tjikumapensis and zaria javana. the aim is to find out how the biometric aspects provide clarity of the speciiation of the two populations and the opportunities for their phylogeny of closeness. this study is also aimed at reintroducing the biometric parameters used by pandita et al., (2013). 3. materials the research sample is a collection stored in the bandung geology museum and the itny paleontology laboratory with a total of 52 samples. the samples came from two locations in west java province and banten province. the sample t. (zaria) bantamensis tjicumpaiensis came from the bayah (byh) location with coordinates 06o 54' 09,2"s and 106o 14' 48,5"e. while the t. (zaria) javana sample came from the cijarian river with location coordinates 06o 59' 31.3 "s and 106o 38' 01.6" e (figure 1). fig 1. the sampling locations were from the bayah (byh) area in banten province and the cijarian river (cjr) in the sukabumi area of west java province 4. methods the method in this research is to re-identify the morphological and biometric aspects of the two sample populations stored in the itny paleontology laboratory. the http://journal.uir.ac.id/index.php/jgeet pandita, h., et al./ jgeet vol 6 no 3/2021 173 sample coded cjr03 is a population of zaria javana, and byh01 is a population of zaria bantamensis tjikumpaensis. after the identification was carried out, statistical analysis was carried out using linear regression and t-test on biometric parameters. identification of morphological aspects is using parameters from (kotaka, 1959); (marwick, 1957); merriam, 1941). these parameters include: 1) the number of main spiral ribs, 2) peripheral patterns, 3) room shape, 4) sutures, 5) keel characters and 6) apertura (figure 2). the biometric aspect uses the parameters proposed by pandita et al., (2013). these parameters include: 1) l (shell length), 2) wsut (last chamber suture diameter), 3 wang (last chamber diameter) (figure 2). fig 2. identification parameters of zaria the statistical test conducted is the similarity test using two methods. the first method uses linear regression. the second method uses the independent t-test, while the formula used (hasan, 2004) is as follows: where: t = value of acceptance if -t(1-1/2)< t < t(1-1/2) x1 & x2 = mean values n1 & n2 = number of population s = is the average standard deviation the formula for the average standard deviation of the two populations: where: s1 & s2 = standard deviation value of each tested population. 5. systematic description the taxonomic systematics used in the preparation of the classification refers to leloux and wesselingh, (2009). class : gastropoda cuvier, 1797 sub class : prosobranchia milne-edwards, 1848 order : mesogastropoda thiele, 1925 super family : cerithiacea fleming, 1822 family : turritellidae loven, 1847 genera : turritella lamarck, 1799 sub genera: zaria grey 1847 species: turritella (zaria) bantamensis tjicumpaiensis martin, 1905 figure: 3 turritella tjicumpaiensis — (martin, 1905): 232, pl. 35, figs 549-550 turritella tjicumpaiensis martin — van der vlerk, 1931: 254 turritella (turritella) bantamensis tjicumpaiensis martin — (shuto, 1974): 144 turritella (turritella) bantamensis tjicumpaiensis martin — (shuto, 1978): 103 turritella (turritella) bantamensis tjicumpaiensis martin — (skwarko, s.k.; sufiati, 1994): f9 material: paratype. shell preservation is not complete, protoconch is loose. the number of preserve whorl about 8 to 9 whorls. specimens are stored in the itny paleontology laboratory sample code byh01 is 11 specimens, and at the geology museum bandung the sample code is b-29 as 6 specimens and 14c as 6 specimens. fig 3. turritella (zaria) bantamensis tjicumpaiensis: a) complete shell b) early teleconch, c) adult teleconch, scale bar = 1 cm. 5.1 morphologic descriptive the shell that appears is predominantly small, although some are larger than 60 mm. at the beginning of its growth, the main spiral ribs that appear are 4, with a multicostate structure. the shape of the suture is initially channelized and then changes to subcarinate at the 8th or 9th whorl.the three main rib spiral numbers 1, 2 and 3 are counted from the anterior with strong expression starting from the 8th or 9th whorl at the bottom of the room. the shape of the aperture is rounded (figure 3). based on the character of the growth line, this species is closer to the zaria sub-genera. 174 pandita, h., et al./ jgeet vol 6 no 3/2021 table 1. biometrical aspect of t. (zaria) bantamensis tjicumpaiensi no.spec l(mm) wang wsut (o) n whorl wang:l wsut:l wsut:wang byh01-1 121.30 26.80 19.90 10.00 15.00 0.2209 0.1641 0.7425 byh01-2 57.50 16.30 11.60 13.00 14.00 0.2835 0.2017 0.7117 byh01-3 36.60 11.35 8.10 13.00 11.00 0.3101 0.2213 0.7137 byh01b-1 48.40 13.10 9.65 10.00 8.00 0.2707 0.1994 0.7366 byh01b-2 45.20 12.80 9.50 10.00 8.00 0.2832 0.2102 0.7422 byh01b-3 45.10 11.40 8.60 8.00 9.00 0.2528 0.1907 0.7544 byh01b-4 36.65 10.90 8.20 9.50 7.50 0.2974 0.2237 0.7523 byh01b-5 33.80 10.70 8.20 9.50 7.00 0.3166 0.2426 0.7664 byh01b-6 37.45 10.65 8.30 10.00 8.00 0.2844 0.2216 0.7793 byh01b-7 40.35 10.60 7.70 9.00 9.00 0.2627 0.1908 0.7264 byh01b-8 43.10 13.00 9.80 8.50 9.00 0.3016 0.2274 0.7538 b29-1 50.60 14.90 10.00 8.50 13.00 0.2945 0.1976 0.6711 b29-2 49.90 13.30 9.40 10.00 12.00 0.2665 0.1884 0.7068 b29-3 53.00 15.60 11.70 9.50 11.00 0.2943 0.2208 0.7500 b29-4 93.00 22.00 15.50 8.00 17.00 0.2366 0.1667 0.7045 b29-5 90.90 21.30 16.00 11.00 14.00 0.2343 0.1760 0.7512 b29-6 29.20 8.80 5.30 9.00 10.00 0.3014 0.1815 0.6023 14c4-1 63.25 17.70 13.20 10.00 12.00 0.2798 0.2087 0.7458 14c4-2 60.45 16.00 11.65 9.50 13.00 0.2647 0.1927 0.7281 14c4-3 62.70 17.10 11.65 10.00 12.00 0.2727 0.1858 0.6813 14c4-4 71.90 17.85 12.60 10.00 14.00 0.2483 0.1752 0.7059 14c4-5 55.80 14.50 10.50 9.50 13.00 0.2599 0.1882 0.7241 14c4-6 58.00 14.80 10.60 9.00 14.50 0.2552 0.1828 0.7162 mean 55.83 14.85 10.77 9.76 0.2736 0.1982 0.7246 s 21.65 4.29 3.18 1.25 0.0253 0.0208 0.0375 species: turritella (zaria) javana martin, 1883 figure 4 turritella javana martin, 1883: 233, pl. 11, fig. 27. turritella javana martin –(martin, 1884): 171. turritella javana martin – (martin, 1905): 227. zaria javana (martin) – (shuto, 1974): 140. zaria javana (martin) – (skwarko, s.k.; sufiati, 1994): f15. material : lectotype. shell preservation is not complete, protoconch is loose. the number of preserve whorl about 9 to 11 whorls. total specimen is 29, stored in laboratory of paleontology itny．code number cjr03. fig 4. turritella (zaria) javana: a) complete shell b) early teleconch, c) adult teleconch, scale bar = 1 cm. 5.2 morphologic descriptive shell including small to medium sized. in the early rounds made up four primary spirals appears at the beginning teloconch. whorl shape tends tricostate formed by spiral into 1, 2 and 3 are sorted from the anterior, with a spiral rib to 2 expressed slightly stronger than the other two. a fine spiral located under the posterior sutures as a spiral 4. sutures at the beginning teleconch shaped channelled.start whorl to 7 there is a change of sutures and pheriperal form. forms bicarinate appear in the center of the whorl that is formed by a spiral rib of the anterior second and third. relative changes to subcarinate sutures. lateral growth line strongly curved with a single sinus, and basal sinuses also appeared at the bottom. aperture somewhat elliptical until rounded. pandita, h., et al./ jgeet vol 6 no 3/2021 175 table 2. biometrical aspect of t. (zaria) javana no.spec l(mm) wang wsut (o) n whorl wang:l wsut:l wsut:wang cjr3a-1 51.90 14.75 10.45 15.00 12.00 0.28420 0.20135 0.70847 cjr3a-2 61.20 14.65 10.35 13.00 13.00 0.23938 0.16912 0.70648 cjr3a-3 53.80 14.90 10.25 13.50 11.50 0.27695 0.19052 0.68792 cjr3a-4 57.60 15.00 10.85 13.00 12.50 0.26042 0.18837 0.72333 cjr3a-5 56.30 16.35 11.15 13.00 12.00 0.29041 0.19805 0.68196 cjr3a-6 52.50 13.70 9.70 14.50 11.50 0.26095 0.18476 0.70803 cjr3a-7 45.30 13.30 8.95 13.50 11.50 0.29360 0.19757 0.67293 cjr3a-8 54.20 14.65 10.00 14.00 12.50 0.27030 0.18450 0.68259 cjr3a-9 53.40 13.40 9.40 13.50 12.00 0.25094 0.17603 0.70149 cjr3a-10 43.40 12.85 9.10 14.50 11.50 0.29608 0.20968 0.70817 cjr3a-11 46.40 12.95 9.30 14.50 12.00 0.27909 0.20043 0.71815 cjr3a-12 40.25 11.15 8.45 13.00 10.00 0.27702 0.20994 0.75785 cjr3b-1 53.60 15.00 10.70 12.50 11.00 0.27985 0.19963 0.71333 cjr3b-2 59.90 15.50 11.30 13.50 11.50 0.25876 0.18865 0.72903 cjr3b-3 42.10 13.60 9.60 13.50 11.00 0.32304 0.22803 0.70588 cjr3b-4 53.45 13.55 9.50 14.00 11.00 0.25351 0.17774 0.70111 cjr3b-5 54.40 15.10 11.10 13.00 10.80 0.27757 0.20404 0.73510 cjr3b-6 48.00 14.40 9.85 13.00 11.00 0.30000 0.20521 0.68403 cjr3b-7 54.85 15.25 10.85 13.00 10.80 0.27803 0.19781 0.71148 cjr3b-8 50.80 13.50 10.00 13.50 11.00 0.26575 0.19685 0.74074 cjr3b-9 55.75 15.45 11.70 13.00 10.80 0.27713 0.20987 0.75728 cjr3b-10 53.70 15.70 11.80 14.50 11.00 0.29236 0.21974 0.75159 cjr3b-11 65.00 15.60 11.00 12.50 12.50 0.24000 0.16923 0.70513 cjr3b-12 43.00 12.10 8.70 13.00 11.00 0.28140 0.20233 0.71901 cjr3b-13 49.30 15.30 11.10 13.50 10.00 0.31034 0.22515 0.72549 cjr3b-14 50.00 15.60 11.30 13.50 11.00 0.31200 0.22600 0.72436 cjr3b-15 52.70 15.50 10.80 13.00 12.00 0.29412 0.20493 0.69677 cjr3b-16 49.40 15.20 10.70 13.00 11.00 0.30769 0.21660 0.70395 cjr3b-17 46.70 13.65 9.60 14.00 10.00 0.29229 0.20557 0.70330 mean 51.69 14.40 10.26 13.48 0.28011 0.19958 0.71258 s 6.24 1.36 0.82 0.72 0.02102 0.01578 0.02182 6. result phenotypically, the two populations have almost the same morphological physical characteristics, there are only differences in the peripheral pattern in early teleconch, where t. (zaria). javana has a tricostate pattern (figure 4b), while t. (zaria). bantamensis has multicostate (figure 3b). seeing this, it is necessary to test the similarity on biometry whether the two populations are indeed different or the same. biometric data has been presented in tables 1 and 2. fig 5. linear regression pattern of the parameters wsut: l ratio between z. javana (cjr03) with z. bantamensis tjicumpaiensis (byh01). the first study conducted a linear regression pattern analysis to see if there was no relationship between the two species. the wsut: l and wsut: wang ratios show that the two species have parallel and coincided linear lines (figures 5 and 6). based on this, the two populations have the same growth pattern. the second study was analyzed using a two-way difference test known as the t-test. data processing using excel program. the acceptance level used ( = 0.05) is a number commonly used in the t-test. so that the acceptance limit for the total number of the two populations of 52 samples is -2.008 <t0 <2.008 is obtained from the t distribution table (hasan, 2004). based on the results of the t-test test, it shows that the two parameters produce a value of t0 = 0.27736 for the wsut: l ratio and t0 = 1.406124 for the wsut:wang ratio (table 3). the two values fall into the acceptance range, so that the two populations can be considered to have the same pattern. fig 6. linear regression pattern of the parameters the wsut: wang ratio between z. javana (cjr03) with z. bantemensis tjikumpaensis (byh01). 176 pandita, h., et al./ jgeet vol 6 no 3/2021 table 3. t-test results on two parameters of the ratio of wsut: l and wsut: wang from two populations of species z. javana (cjr03) with z. bantemensis tjikumpaensis (byh01). samples number spesies sample s size (n) t0 wsut:l wsut:wang t-test (wsut:l) t-test (wsut:wang) =0.05 s t s t boj03 z. bantamensis 28 2.004 0.1700 0.7303 0.0151 -7.3660 0.0250 2.6722 cjr03 z. javana 29 0.1996 0.7126 7. discusion seeing the test results of both the linear regression pattern and the t-test test for both populations can be said to have the same character. the separation of the two as different species needs to be reviewed, considering that from a biometric point of view they both have similarities. almost all morphological parameters of the two populations are also the same, with a slight difference in the peripheral pattern at the early teleconch. however, the initial growth pattern by kotaka, (1959), marwick, (1957) is one of the factors that differentiate species, so it is difficult to propose that both species are the same. however, by looking at the proximity of the biometric aspects and spiral rib patterns in adult teleconch, the two have a close phylogeny relationship. in terms of geology, these two populations or species come from two different locations. t. (zaria) javana comes from the nyalindung formation which is thought to have formed in the upper miocene (pandita et al., 2013). meanwhile, z. bantamensis comes from the cimanceuri formation (byh01) where the formation is estimated to be in the early pliocene age (pandita, 2014). combining with the age of appearance of the two species, of which t. (zaria) javana is older, namely the upper miocene, it is certain that t. (zaria) bantamensis tjicumpaiensis evolved from t. (z) javana. conclusion both populations of the sub-genus zaria show the same biometric characteristics. meanwhile, in the morphological aspect, there is a small difference in early teleconch. however, because the early teleconch by kotaka (1959) was the determining parameter of the species, the two populations could not be categorized as the same species. this condition implies the need for a ranking test on the identification parameters of turritella (zaria) as well. acknowledgment gratitude is conveyed to itny for providing research funding in the 2020 budget year, through a fundamental research program. references hasan, 2004. analisis data penelitian dengan statistik. bumi aksara, yogyakarta. imbrie, j., 1956. biometrical methods in the study of invertebrate fossils, in: bulletin of the american museum of natural history. american museum of natural history, new york, pp. 214–251. kotaka, t., 1959. the cenozoic turritellidae of japan. sci. rep. 31, 1–135. leloux, j; wesselingh, f.p., 2009. types of cenozoic mollusca from java in the martin collection of naturalis. nmnh, 765. martin, k., 1905. modulus delphinula, in: martin, k. (ed.), die fossilien von java auf grund einer sammlung von dr. r. d. m. verbeek und von anderen. i. band. gasteropoda. mit einem anhange über: die foraminiferen führenden gesteine. sammlungen des geologischen reichs-museums in leiden, leiden, pp. 221–285. martin, k., 1884. systematischer theil: mollusca. i. glossophora. a. gasteropoda. in: martin, k. 1883-1887. palaeontologische ergebnisse von tiefbohrungen auf java, nebst allgemeineren studien ueber das tertiaer von java, timor und einiger 155 leloux & wesselingh. the mart. sammlungen des geol. reichs-museums leiden. ser. 1, beiträge zur geol. ost-asiens und aust. 3, 43– 184. marwick, j., 1957. generic revision of the turritellidae, in: procedings of the malacological society. malacological society, london, pp. 144–166. merriam, c.w., 1941. fossil turritellas from the pasific coast region of north america. sci. publ. 26, 1–214. pandita, h., 2014. paleontologi moluska neogen famili turritellidae di pulau jawa sebagai dasar penyusunan biozonasi turritellidae. institut teknologi bandung. pandita, h., zaim, y., rizal, y., 2013. relationship of biometrical aspect of turritellidae with geochronological aspect in west java. int. j. geosci. 4, 777–784. https://doi.org/10.4236/ijg.2013.44071 shuto, t., 1978. notes on indonesian tertiary and quaternary gastropods mainly described by the late professor k. martin ii. potamididae and cerithiidae (contributions to the geology and palaeontology of southeast asia, cxcix). geol. palaeontol. southeast asia 19, 113–160. shuto, t., 1974. notes on indonesian tertiary and quaternary gastropods mainly described by the late professor k. martin i. turritellidae and mathildidae (contributions to the geology and palaeontology of southeast asia, cxliv). geol. palaeontol. southeast asia 14, 135–160. skwarko, s.k.; sufiati, e., 1994. gastropoda, in: molluscan in indonesia cenozoic biostratigraphy (a computerized compilation),. geol. res. dev. centre, bandung, p. 796. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 1 2022 1 permana, s. et al./ jgeet vol 7 no 1/2022 research article clean water supply in tasikmalaya municipality, opportunities and challenges sulwan permana1, adi susetyaningsih2, dicky muhamad fadli3 1,2,3institut teknologi garut , jl. major syamsu no.1, jayaraga, tarogong kidul, garut regency, west java 44151, indonesia. * corresponding author : sulwanpermana@itg.ac.id tel.:+62-82-2400-72165; fax: +62-262-232-773 received: jul 6, 2021; accepted: mar 30, 2022. doi: 10.25299/jgeet.2022.7.1.7293 abstract currently, there are three sub-districts in tasikmalaya city that are still vulnerable to clean water, namely kawalu, tamansari, and cibeureum sub-districts. pdam tirta sukapura, owned by the tasikmalaya regency government, has not been able to meet clean water needs, so the tasikmalaya municipality government plans to build a new pdam as an alternative. pdam is a regional company with the main task of providing services and providing drinking/clean water to the community. the ciwulan river in cibeuti village is a source of water that will be used as a collection point. rain data was taken from 2 stations, namely gunung satria and cikunten ii stat ions, for ten years. the evapotranspiration value was calculated using the penman-monteith method. the calculation of the discharge in the intake area, namely ciwulan-cibeuti with a watershed area of 405 km2, used the nreca method using parameters taken from the calibrated ciwulansukaraja station. the calibration parameters are psub = 0.86; gwf = 0.22, reduction coefficient = 0.80; and nse = 0.764. the determination of the dependable flow is calculated using the weibull method. the magnitude of the q90 dependable flow is 4.3 m3/s. the projected population for the next 15 years is estimated at 307,857 people, so the amount of water needed is around 0.535 m3/s. opportunities for business entities to participate in building pdam are wide open, with the certainty of return plus profits or independent management by business entities within a certain period of time. the challenge for the government and business entities is to provide reasonable prices to customers and new networks. keywords: ciwulan-cibeuti, dependable flow, nreca calibration. 1. introduction the establishment of tasikmalaya city is inseparable from the history of the establishment of tasikmalaya regency as its parent regency. in 1976 its status was increased to an administrative municipality. the milestone of the birth of the city of tasikmalaya occurred on october 17, 2001, through law number 10 of 2001 concerning the establishment of the tasikmalaya municipality. the tasikmalaya municipality has ten sub-districts and 69 urban villages with a population of 716,160 people (pemerintah kota tasikmalaya, 2019). sources of drinking water supply generally come from surface water such as rivers, reservoirs, and lakes. as a result of anthropogenic activities, there is an uncontrolled decrease in water quality and a decrease in quantity due to drought (shaheed & mohtar, 2015). water is one of the natural resources which is very vital not only for life but also for the development of the nation (sukereman et al., 2015). clean water is currently a vital need for the community. currently, three sub-districts in tasikmalaya municipality are still vulnerable to clean water, namely kawalu, tamansari, and cibeureum sub-districts. until now, the need for clean water is supplied by the pdam tirta sukapura. pdam tirta sukapura is one of the regionalowned enterprises owned by the tasikmalaya regency government whose task is to provide drinking/clean water for the people of tasikmalaya regency and tasikmalaya municipality. pdam tirta sukapura is owned by the tasikmalaya regency government. until now, pdam tirta sukapura has not fully served the needs of the people of the tasikmalaya municipality, so the tasikmalaya municipality government plans to build its pdam, primarily to help do the people in the three sub-districts. the development of this pdam is an opportunity and a challenge for the tasikmalaya municipality government and business entities/investors to participate in the development. the river used as the source of extraction is the ciwulan river, which is located in cibeuti urban village, kawalu subdistrict. this river is the boundary between tasikmalaya municipality and tasikmalaya regency. the ciwulan river has an automatic water level measuring station, namely the ciwulan-sukaraja station and its tributary, the cikunir river, namely the asta station. figure 1 shows the location of the study area and the location of the gunung satria and cikunten 2 rain stations. 2. methodology 2.1. rainfall the hydrological cycle is an important process because it maintains the availability of surface water for living things. evapotranspiration is part of the hydrological cycle playing an important role in the domestic water supply (farah et al., 2017). the impact of climate change results hydrological processes, including increased rainfall, especially when extreme events occur (othman et al., 2016). the ciwulan river is managed by the ciwulan-cilaki river basin technical service unit. the government has widely used the ciwulan river for public welfare, such as http://journal.uir.ac.id/index.php/jgeet 2 permana, s. et al./ jgeet vol 7 no 1/2022 providing raw water for the community and irrigation. inappropriate agricultural practices can lead to overexploitation of water leading to water scarcity (nair et al., 2020). fig 1. location of the ciwulan-cibeuti study area the upstream of the ciwulan river are located on mount karacak with an altitude of 1838 m above mean sea level and mount cikuray in garut regency with a height of 2821 m and empties into the indian ocean. currently, the condition of the central watershed has changed land use. the need for wildland causes the physical and environmental carrying capacity of the watershed to decrease (herman et al., 2020). the place for taking ciwulan river water is an outlet and is used as a downstream catchmen area (watershed). the area of the watershed, climatological conditions and soil characteristics are important parameters in determining river discharge. the area of the watershed with outlets in cibeuti urban village is 405 km2. figure 2 shows the outlet of the ciwulan-cibeuti watershed. fig 2. outlet of the ciwulan-cibeuti watershed the rainfall stations calculated in this study consist of two rainfall stations measured by manual measuring instruments, namely the gunung satria rainfall station in cigalontang district at an elevation of 548 m, and the cikunten 2 rainfall station in singaparna district at the height of 548 m. 417 m. the rainfall data taken into account in this study is ten years, from 2011 to 2020. the dominant land uses in the ciwulan-cibeuti watershed are rice fields, dryland forests, and plantation forests. figure 2 shows outlet of the ciwulan-cibeuti watershed. the calculation of the area's average rainfall is done by using the thiessen method. 2.2 evapotranspiration important climatic variables are temperature and rainfall, as well as the impact of drought on agriculture as a source of livelihood in the region (schilling et al., 2020). four climatological parameters such as temperature, duration of sunshine, relative humidity, and wind speed are needed to calculate the evapotranspiration value calculation of evapotranspiration using the penmanmonteith method. the data source for the four parameters was taken from the tasikmalaya municipality in figures book. 𝐸𝑇𝑜 = 0.408∆𝑅𝑛+𝛾 900 (𝑇+273) 𝑈2(𝑒𝑠−𝑒𝑎) ∆+𝛾(1+0.34𝑈2) (1) eto = reference plant evapotranspiration, (mm/day) rn = net solar radiation above ground level, (mj/m2/day) t = average air temperature, (o c) u2 = wind speed at a height of 2 m above ground level, (m/s) es = saturated water vapor pressure, (kpa) ea = actual water vapor pressure, (kpa) ∆ = slope of the curve of water vapor pressure with respect to temperature, (kpa/o c) γ = psychrommetric constant, (kpa/0 c) 2.3 hydrological modeling land use conditions in the upper ciwulan river and rainfall are important parameters in determining river discharge (permana et al., 2019). the ciwulan river, which will be used as a water collection point, does not have a water level measuring instrument, so to get the discharge value, hydrological modeling must be done. the hydrological model used in this study is the national rural electric cooperative association (nreca) model. figure 3 shows the discharge simulation scheme of the nreca model. the calibration of the model parameters, namely the surface soil characteristics at a depth of 0 – 2 m (psub) and the surface soil characteristics at a depth of 2 – 10 m (gwf), was carried out on the discharge data at the ciwulansukaraja station for three years, from 2015 to 2017 with a watershed area of 524 km2. ciwulan-sukaraja station is approximately 6.6 km from the water collection point. to permana, s. et al./ jgeet vol 7 no 1/2022 3 assess the predictions of the hydrological model, the nashsutcliffe (nse) efficiency test was used is shown in equation (2). the prediction of the hydrological model will be of good value if the nse value is close to 1. figure 4 shows the location of ciwulan-sukaraja awlr station. 𝑁𝑆𝐸 = 1 − ∑ (𝑄0 𝑡−𝑄𝑚 𝑡 ) 2𝑇 𝑡=1 ∑ (𝑄0 𝑡−𝑄0̅̅̅̅ ) 2𝑇 𝑡=1 (2) nse = nash-sutcliffe 𝑄0 𝑡 = observed discharge at time t 𝑄𝑚 𝑡 = modeled discharge at time t 𝑄0̅̅̅̅ = the mean of observed discharges fig. 3. schematic of the nreca mode fig 4. ciwulan-sukaraja awlr station. 2.4 population availability of raw water is the main requirement for agriculture and household needs (permana, 2018). another parameter related to the pdam development plan is the population in the three sub-districts. the population in the three sub-districts is 242,450 people, with an average population growth rate of 1.605% (tasikmalaya municipality in figures 2021). in meeting future water needs, it is necessary to project the population in three sub districts critical to project population numbers in three sub districts. the projected population is calculated using the geometric method. population projections are carried out for the next 15 years. this projection is taken by taking into account the government's readiness to build pdam. the geometric method is shown in equation (3). 𝑃𝑛 = 𝑃0(1 + 𝑟) 𝑛 (3) where pn is the population in the nth year, p0 is the population in the initial year, and r is the total population growth (%). many residents in kawalu and tamansari sub-districts have opened home industry businesses, so the need for water for the industry is urgent. industrial water requirements for production activities, including raw materials, workers, and other forms of support for the industry (chandrasasi et al., 2020). 4 permana, s. et al./ jgeet vol 7 no 1/2022 3. result and discussion 3.1 average rainfall and evapotranspiration calculating the average rain area using the thiessen method with the area of influence cikunten 2 station is 18.13%, and gunung satria is 81.87%. the results of the calculation of the average regional rain are shown in table 1. evapotranspiration is a combination of evaporation from the soil surface and transpiration from plants. the results of the calculation of monthly evapotranspiration based on equation (1) using the penman-monteith method are shown in table 2. 3.2 calibration and dependable flow the location where the water is taken does not have a water level measuring device, so it cannot directly calculate the amount of flow. the calculation of the amount of flow at the site is done by modeling. therefore calibration is ried out on the ciwulan-sukaraja station to obtain calibration parameters. the calibration parameters are used to calculate the flow rate at the collection location. the resulting calibration parameters include: initial groundwater reservoir (gw = 20 mm), deep surface soil characteristics (gwf = 0.22), and surface soil characteristics (psub = 0.86). figure 5 shows the results of the time series calibration from 2015 to 2017. the nse value is 0.764. the flow duration curve calibration shows the probability that the discharge will be equal to or exceeded from the observed and modeled discharges. dependable flow is the amount of available discharge to meet water demand by considering the risk of failure (sebayang & fahmia, 2021). figure 6. shows the calibration of the flow duration curve. the initial moisture storage value was tested, where the difference in values for january and december did not exceed 200 mm. the calibration of the initial moisture storage is shown in figure 7. fig 5. times series calibration fig 7. initial moisture storage calibration fig 6. flow duration curve calibration fig 8. flow duration curve table 1. average rainfall (mm) month year 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 jan 94,7 222,4 269,4 211,6 170,6 252,2 131,6 206,6 279,7 171,3 feb 125,4 192,3 294,5 186,6 194,9 282,2 129,6 319,9 330,1 269,0 mar 207,3 258,1 299,4 175,5 162,2 290,8 119,0 218,7 325,8 260,3 apr 224,5 213,1 285,0 200,1 105,6 169,8 163,0 306,2 303,5 299,5 may 165,7 164,3 211,3 167,7 68,0 172,0 145,7 242,1 182,4 226,4 jun 77,4 87,3 27,9 100,5 20,2 78,5 26,0 147,6 54,5 212,1 jul 63,5 217,6 27,2 33,6 3,2 139,2 81,8 6,5 40,6 105,3 aug 4,6 10,5 182,9 26,4 2,8 244,3 46,1 8,4 1,1 27,8 sep 5,3 9,4 153,1 124,1 21,1 300,4 116,2 73,5 2,5 107,6 oct 143,9 231,4 294,2 212,0 36,8 221,5 289,0 105,3 1,8 199,9 nov 260,5 190,0 156,8 198,5 174,2 290,5 258,1 271,3 55,5 158,0 dec 246,5 249,8 167,9 220,6 189,0 183,3 154,9 304,7 144,2 180,5 0 5 10 15 20 25 0 3 6 9 12 15 18 21 24 27 30 33 36 d is c h a rg e (m 3 /s ) time (month) time series calibration 2015 2017 nreca data 0 5 10 15 20 25 0,0 0,2 0,4 0,6 0,8 1,0 d is c h a rg e ( m 3 /s ) probability duration curve calibration (2015-2017) nreca data 0 200 400 600 800 1000 0 3 6 9 12 15 18 21 24 27 30 33 36 m o is tu re s to ra g e ( m m ) time (month) moisture storage 0 5 10 15 20 25 30 0,0 10,0 20,0 30,0 40,0 50,0 60,0 70,0 80,0 90,0100,0 d is c h a rg e ( m 3 /s ) exceedance probability (%) flow duration curve permana, s. et al./ jgeet vol 7 no 1/2022 5 table 2. evapotranspiration (mm) month year 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 jan 118,0 119,2 118,7 120,1 127,9 131,8 88,3 128,8 135,4 132,3 feb 118,4 122,7 119,3 110,3 104,6 128,7 103,3 118,9 121,7 126,7 mar 138,6 138,6 136,5 139,8 122,5 135,5 132,8 137,7 139,1 137,2 apr 121,4 123,1 119,8 132,3 107,3 131,8 116,7 127,0 131,3 130,3 may 117,4 118,9 115,3 118,5 109,5 111,9 117,7 122,4 124,0 119,7 jun 92,0 90,7 92,8 109,8 108,7 105,3 100,5 105,7 115,3 112,3 jul 101,7 101,6 104,1 138,9 98,6 128,5 119,1 105,9 110,5 113,5 aug 130,0 130,4 129,3 135,0 103,8 122,1 136,9 114,0 113,1 116,3 sep 132,8 134,3 134,2 134,6 93,7 121,1 128,8 128,2 133,9 130,9 oct 145,0 149,7 149,5 155,5 103,4 130,9 119,0 133,8 145,2 127,3 nov 134,4 128,8 131,1 118,2 113,3 113,7 109,1 115,1 121,9 119,0 dec 124,3 121,3 120,1 116,0 104,6 108,8 141,9 126,6 133,5 128,1 table 3. modeling discharge (m3/s) month year 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 jan 0,78 10,86 13,47 12,81 10,37 6,33 13,07 12,19 17,29 4,60 feb 2,24 11,31 17,93 14,26 13,81 8,82 12,75 19,95 24,30 8,05 mar 5,66 12,93 17,90 11,54 11,08 10,57 8,84 15,65 23,75 9,39 apr 9,24 13,32 20,08 12,93 8,85 8,97 10,46 20,57 25,50 13,29 may 8,39 11,42 17,69 11,77 6,36 9,01 9,30 19,07 20,09 12,87 jun 5,84 8,88 12,47 8,93 5,12 6,31 6,62 16,11 14,82 13,80 jul 4,33 12,35 9,41 6,53 3,87 6,11 5,00 11,19 11,18 9,43 aug 3,38 7,69 10,62 5,10 3,02 9,89 3,90 8,73 8,72 7,13 sep 2,72 6,20 9,42 4,95 2,43 14,44 3,82 7,04 7,03 6,11 oct 3,19 8,69 13,84 7,41 1,83 13,08 12,03 5,52 5,31 8,44 nov 8,62 9,06 10,95 9,49 5,04 17,63 15,02 12,03 4,28 8,13 dec 10,68 11,76 10,65 11,43 7,12 14,68 10,60 15,32 4,44 8,53 based on the values of the calibration parameters, the resulting discharge from the modeling at the water intake is in the cibeuti urban village with an average monthly discharge of 10.22 m3/s. the discharge modeling results are shown in table 3. the dependable flow calculation using the flow duration curve method uses the weibull probability formula, such as equation (4), where m is the data rank, n is the number of data, x is the discharge data series, and x is the dependable. the flow duration is shown in figure 8. 𝑃(𝑋 ≥ 𝑥) = 𝑚 𝑛+1 100% (4) based on the flow duration curve in figure 8, it is obtained that q90% is 4.3 m3/s (4300 l/s). water needs for households and urban areas with a population of 500,000 – 1,000,000 people are 120-150 l/person/day (directorate general of human settlements, 1996). 3.3 population projection because the population continues to increase, so that many agricultural areas are converted into settlements (permana et al., 2019), the need for clean water infrastructure will become a community's dream. the population projections taken into account are only in three sub-districts because those three sub-districts still require clean water services. the population projection calculation uses geometric methods such as equation (3). pn =p0 (1+r)n = 242450 (1+0.01605)15 =307.857 people. by taking the water requirement of 150 l/person/day, for the next 15 years, approximately 46.178.550 l/day or 535 l/s of water will be needed. 3.4 opportunities and challenges the opportunity to build a new pdam is big enough for the tasikmalaya municipality government to serve some communities in three sub-districts that are still vulnerable to clean water, thereby eliminating dependence on pdam tirta sukapura. in addition, it will not use apbd funds in building new pdam. the opportunity for business entities is quite large. it has the opportunity to participate in building pdam because of the certainty of returns plus profits or being fully managed by the business entity within a certain period of time. the cooperation scheme is also accelerating the fulfillment of clean water for the community in three sub-districts. meanwhile, the challenge for the tasikmalaya city government is to provide clean water services to the community at a reasonable price. as a major provider of funds, the business entity aims to help and expand the clean water network at a reasonable price and provide a 24-hour service guarantee to customers. however, customers will pay a little more. 4. conclusion 6 permana, s. et al./ jgeet vol 7 no 1/2022 three sub-districts in tasikmalaya municipality are still vulnerable to clean water, so the government plans to build its pdam, not depending on pdam tirta sukapura. the location where the water level is taken does not have a water level measuring instrument, so to determine the amount of discharge, hydrological modeling using the nreca method is used. the calibration of the model parameters was carried out at the ciwulan-sukaraja station, and the results were used to calculate the discharge in the ciwulan-cibeuti watershed. the dependable flow based on the flow duration curve is 4300 l/s. based on population projections for the next 15 years, 535 l/s is required so that a maximum of only about 12.5% of the available discharge is used for clean water needs. the pdam development plan is both an opportunity and a challenge for the government and business entities. the development does not burden the apbd and can expand the clean water network at a reasonable selling price. acknowledgments authors wishing to acknowledge institut teknologi garut that supports and funds this research publication. references chandrasasi, d., montarcih limantara, l., & wulan juni, r. (2020). analysis using the f. j. mock method for calculation of water balance in the upper konto subwatershed. iop conference series: earth and environmental science, 437(1). https://doi.org/10.1088/17551315/437/1/012019 farah, n., ahmad, a., askari, m., & harun, s. (2017). sensitivity analysis of a fao penman for potential. 7, 21–30. herman, r., wim andiesse, v., & siti rahmi, o. (2020). changes in land use affect dependable discharge in the miu river basin. matec web of conferences, 331, 04004. https://doi.org/10.1051/matecconf/202033104004 nair, a. v., balu nellippallil, a., das, a. k., hall, j., allen, j. k., & mistree, f. (2020). identifying sustainable solutions for sanitation, energy, and water needs in off-grid indian villages. international design engineering technical conferences and computers and information in engineering conference, 84010. othman, m. a., zakaria, n. a., ab. ghani, a., chang, c. k., & chan, n. w. (2016). analysis of trends of extreme rainfall events using mann kendall test: a case study in pahang and kelantan river basins. jurnal teknologi, 78(9–4),63–69. https://doi.org/10.11113/jt.v78.9696 pemerintah kota tasikmalaya. (2019). sejarah kota tasikmalaya. kominfo kota tasikmalaya. https://portal.tasikmalayakota.go.id/index.php/q/s ekilas_sejarah permana, s., susetyaningsih, a., zhafirah, a., & mulyana, s. (2019). effect of changes in climatological parameters on water flow. journal of physics: conference series,1402(2). https://doi.org/10.1088/17426596/1402/2/022008 permana, s, johari, g. j., yogaswara, d., & walujodjati, e. (2019). the water availability effectiveness in weirs. journal of physics: conference series, 1402, 22009. https://doi.org/10.1088/17426596/1402/2/022009 permana, sulwan. (2018). technical feasibility analysis of reservoir on agricultural area. matec web of conferences, 197, 10–13. https://doi.org/10.1051/matecconf/201819710006 schilling, j., hertig, e., tramblay, y., & scheffran, j. (2020). climate change vulnerability, water resources and social implications in north africa. regional environmental change, 20(1). https://doi.org/10.1007/s10113-020-01597-7 sebayang, i. s. d., & fahmia, m. (2021). dependable flow modeling in upper basin citarum using multilayer perceptron backpropagation. international journal of artificial intelligence research, 4(2), 75. https://doi.org/10.29099/ijair.v4i2.174 shaheed, r., & mohtar, w. h. m. w. (2015). potential of using rainwater for potable purpose in malaysia with varying antecedent dry intervals. jurnal teknologi, 72(1), 57–61. https://doi.org/10.11113/jt.v72.3156 sukereman, a. s., suratman, r., & sin, c. w. (2015). the need for land use assessment in enhancing the implementation of integrated water resource management (iwrm). jurnal teknologi, 73(5), 143– 149. https://doi.org/10.11113/jt.v73.4332 © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at which the author did the work must be retained as the main, affiliation address.start by adding an asterisk (*) and then email, phone number, font gulliver 7pt. 3. abstract summary of the all research (aim, scope, result and conclusion) with maximum 300 words, justified, 8 point, and line spacing : single. for keywords wrote in italic and then separated using symbol (,) with maximum are 6 words. 4. introduction in introduction, authors should state the objectives of the work at the end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type area. the structure of manuscripts should follow the following order; title, authors, affiliations, abstract, keywords, main text, (acknowledgement), (appendix), (nomenclature), references. the items with parentheses are not mandatory. the maximum pages printed in jgeet are supposed to be 10 for an original paper and 15 for a review paper. do not include page numbers. do not add headers or footers. prescribed font is gulliver, 9 points, with an single line spacing. however, if your text contains complicated mathematical expressions or chemical formulae, you may need to increase the line spacing. running text should be justified. 5. section headings the way chapter titles and other headings are displayed in these instructions, is meant to be followed in your manuscript. level 1: gulliver, 9, bold, 6 pt spacing before heading, 6 pt spacing after heading. successive levels: times new roman, 8, bold, 6 pt spacing before heading, no spacing below heading. do not begin a new section directly at the bottom of the page, but transfer the heading to the top of the next page. cite the main scientific publications on which your work is based. cite only items that you have read. do not inflate the manuscript with too many references. avoid excessive self‐citations. avoid excessive citations of publications from the same region. check each reference against the original source (authors name, volume, issue, year, doi number). please use reference manager applications like endnote, mendeley, zotero, etc. use other published articles in the same journal as models. if you are cite using mendeley please use elsevier harvard (with title) for cite model stlye of this journal. 6. footnotes it is requested not to us any of footnotes. all references should be in the references. explanations should be preferably included in the text. 7. symbols and units, numbers if symbols are defined in a nomenclature section, symbols and units should be listed in alphabetical order with their definition and dimensions in si units. please use the si set of units as much as possible. wherever the application domain uses a different set of units widely, please minimize the use of non-standard units or non when providing numerical values followed by measurement units, please leave a regular space or nonbreaking space between each value and the measurement unit. this also includes percentages and degrees celsius (e.g. 42 % or 35 %, 234 °c, 504 k). this rule also applies to the unit for litre, which is recommended to specifying the dot as a decimal separator and the comma as a thousands separator. 8. equations make sure that placing and numbering of equations is consistent throughout your manuscript. (1) 1 1 c( ) ( )    n i i t c t n (2) left align the equation and put the number of the equation flush-right, using a right tab on the right margin. please reference equations in the text by writing: eqn. .. (do not use equation ..) in principle, variables are to be presented in italics. 9. figures and tables figures and tables should be originals or sharp prints. please use the si set of units as much as possible. figures and tables should be centered and placed either at the top or at the bottom of the page. please do not render tables as pictures and please do not use too small font sizes in the illustrations. please use the following fonts in your illustrations: gulliver, symbol, or use fonts that look similar. if your figures and tables are created in a microsoft office application (word, powerpoint, excel) then please supply 'as is' in the native format, too. regardless of the application used other than microsoft office, when your electronic artwork is finalized, please 'save as' or convert the images to one of the following formats (note the resolution requirements for line drawings, halftones, and line/halftone combinations given below):   2 2 2 1 2 dxi dyi dzi d mk xidxi yidyi zidzi dt dt dt                                   eps (or pdf): vector drawings, embed all used fonts.  tiff (or jpeg): color or grayscale photographs (halftones), keep to a minimum of 300 dpi.  tiff (or jpeg): bitmapped (pure black & white pixels) line drawings, keep to a minimum of 1000 dpi.  tiff (or jpeg): combinations bitmapped line/half-tone (color or grayscale), keep to a minimum of 500 dpi. set table number and title flush left above table. horizontal lines should be placed above and below table headings and at the bottom of the table. vertical lines should be avoided. title should use gulliver 8, with 10 pt before and 4 pt after the paragraph, left justified at the top of the table. tables have to be included into the text. if a table is too long to fit one page, the table number and heading should be repeated on the next page before the table is continued. alternatively the table may be spread over two consecutive pages (first an even numbered, then anodd-numbered page) turned by 90, without repeating the heading. 10. figure captions fig. 1 captions should be placed below each illustration, font times new roman, 7 pts. figures and figure captions should be placed center; two narrow figures may be placed side-by-side. please reference figures in the text by writing: fig. .. (do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at which the author did the work must be retained as the main, affiliation address.start by adding an asterisk (*) and then email, phone number, font gulliver 7pt. 3. abstract summary of the all research (aim, scope, result and conclusion) with maximum 300 words, justified, 8 point, and line spacing : single. for keywords wrote in italic and then separated using symbol (,) with maximum are 6 words. 4. introduction in introduction, authors should state the objectives of the work at the end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type area. the structure of manuscripts should follow the following order; title, authors, affiliations, abstract, keywords, main text, (acknowledgement), (appendix), (nomenclature), references. the items with parentheses are not mandatory. the maximum pages printed in jgeet are supposed to be 10 for an original paper and 15 for a review paper. do not include page numbers. do not add headers or footers. prescribed font is gulliver, 9 points, with an single line spacing. however, if your text contains complicated mathematical expressions or chemical formulae, you may need to increase the line spacing. running text should be justified. 5. section headings the way chapter titles and other headings are displayed in these instructions, is meant to be followed in your manuscript. level 1: gulliver, 9, bold, 6 pt spacing before heading, 6 pt spacing after heading. successive levels: times new roman, 8, bold, 6 pt spacing before heading, no spacing below heading. do not begin a new section directly at the bottom of the page, but transfer the heading to the top of the next page. cite the main scientific publications on which your work is based. cite only items that you have read. do not inflate the manuscript with too many references. avoid excessive self‐citations. avoid excessive citations of publications from the same region. check each reference against the original source (authors name, volume, issue, year, doi number). please use reference manager applications like endnote, mendeley, zotero, etc. use other published articles in the same journal as models. if you are cite using mendeley please use elsevier harvard (with title) for cite model stlye of this journal. 6. footnotes it is requested not to us any of footnotes. all references should be in the references. explanations should be preferably included in the text. 7. symbols and units, numbers if symbols are defined in a nomenclature section, symbols and units should be listed in alphabetical order with their definition and dimensions in si units. please use the si set of units as much as possible. wherever the application domain uses a different set of units widely, please minimize the use of non-standard units or non when providing numerical values followed by measurement units, please leave a regular space or nonbreaking space between each value and the measurement unit. this also includes percentages and degrees celsius (e.g. 42 % or 35 %, 234 °c, 504 k). this rule also applies to the unit for litre, which is recommended to specifying the dot as a decimal separator and the comma as a thousands separator. 8. equations make sure that placing and numbering of equations is consistent throughout your manuscript. (1) 1 1 c( ) ( )    n i i t c t n (2) left align the equation and put the number of the equation flush-right, using a right tab on the right margin. please reference equations in the text by writing: eqn. .. (do not use equation ..) in principle, variables are to be presented in italics. 9. figures and tables figures and tables should be originals or sharp prints. please use the si set of units as much as possible. figures and tables should be centered and placed either at the top or at the bottom of the page. please do not render tables as pictures and please do not use too small font sizes in the illustrations. please use the following fonts in your illustrations: gulliver, symbol, or use fonts that look similar. if your figures and tables are created in a microsoft office application (word, powerpoint, excel) then please supply 'as is' in the native format, too. regardless of the application used other than microsoft office, when your electronic artwork is finalized, please 'save as' or convert the images to one of the following formats (note the resolution requirements for line drawings, halftones, and line/halftone combinations given below):   2 2 2 1 2 dxi dyi dzi d mk xidxi yidyi zidzi dt dt dt                                   eps (or pdf): vector drawings, embed all used fonts.  tiff (or jpeg): color or grayscale photographs (halftones), keep to a minimum of 300 dpi.  tiff (or jpeg): bitmapped (pure black & white pixels) line drawings, keep to a minimum of 1000 dpi.  tiff (or jpeg): combinations bitmapped line/half-tone (color or grayscale), keep to a minimum of 500 dpi. set table number and title flush left above table. horizontal lines should be placed above and below table headings and at the bottom of the table. vertical lines should be avoided. title should use gulliver 8, with 10 pt before and 4 pt after the paragraph, left justified at the top of the table. tables have to be included into the text. if a table is too long to fit one page, the table number and heading should be repeated on the next page before the table is continued. alternatively the table may be spread over two consecutive pages (first an even numbered, then anodd-numbered page) turned by 90, without repeating the heading. 10. figure captions fig. 1 captions should be placed below each illustration, font times new roman, 7 pts. figures and figure captions should be placed center; two narrow figures may be placed side-by-side. please reference figures in the text by writing: fig. .. (do not use figure ..). 11. concerning references in order to give our readers a sense of continuity, we encourage you to identify jgeet articles of similar research in your papers. please, do a literature check of the papers published in jgeet in recent years at jurnal.uir.ac.id/jgeet/index. for citation and model citation we are using elsevier harvard (with title), you can find it using mendeley or other reference manager program or using citation machine on the internet, such as http://www.citationmachine.net/elsevier-harvard/cite-a-report/manual. references must be listed at the end of the paper. do not begin them on a new page unless this is absolutely necessary. authors should ensure that every reference in the text appears in the list of references and vice versa. indicate references by (putra and choanji, 2016), (natasia et al., 2016) or (selley et al., 2005). recommendations for references are: book rothery, d.a., 2008. geology. mcgraw-hill companies, blacklick, oh. or selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 magazine geo 2010 hailed as the best geoscience event in mideast., 2012. . oil & gas news. journal schopf, t.j.m., 1978. the structure of geology . david b. kitts. the journal of geology 86, 278 279. doi:10.1086/649684 thesis coons, r.l., 1966. precambrian basement geology and paleozoic structure of the mid-continent gravity high. (thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should 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doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 4 2021 aulia, i. et al./ jgeet vol 6 no 4/2021 255 research article diagenesis study of jatiluhur formation at cipamingkis river, bogor regency, west java, indonesia intan aulia1,*, rezky aditiyo1 1 geology study program, faculty of mathematics and natural science (fmipa), universitas indonesia, depok 16424, indonesia. * corresponding author : rezkyaditiyo@sci.ui.ac.id tel.:+821-1973-3387 received: sept 16, 2021; accepted: dec 31, 2021. doi 10.25299/jgeet.2021.6.4.7726 abstract diagenesis studies in the jatiluhur formation are still relatively new, especially in the cipamingkis river. this research can provide information in the form of components and characteristics of sandstone in the jatiluhur formation which can be used as a basis for further research or useful information in the oil and gas industry. knowledge of diagenetic could be one of the factors that affect in raservoir quality, espesially in sandstone. in this study, data collection was carried out through surface mapping, which is 55 rock samples were obtained from stratigraphic measuring section with a path length of ±2 km in the cipamingkis river. the data is in the form of information on sedimentarry structure, textures and composition. there were 23 sandstone and 2 limestone samples which were then subjected to petrographic analysis, x-ray diffraction (xrd) and scanning electron microscopy (sem). the results of study are several features of diagenesis were found including compaction that works in the form of point contact, long contact, concavo-convex contact and suture contact and dominated by mechanical compaction, while in limestone there is a brittle fracture feature in bioclasts. the ceme nt found in the form of calcite cement, quartz and clay minerals that the form of kaolinite, smectite and illite, while the limestone is in the form of blocky and fibrous to bleded which is filled with calcite minerals. dissolution occurs in the minerals of quartz, feldspar, and mica. the mineral replacement that is commonly found occurs in quartz and feldspar minerals. in limestone, there is an intergranular micritization. the dominant type of porosity found was interparticle with an average of 10.4% found between 3 – 23%. the history of diagenesis that occurs in rocks in the jatiluhur formation begins with the initial deposition of eogenesis, followed by burial mesogenesis and ends with telogenesis which reveals rocks on the surface. keywords: diagenesis features, diagenesis history, jatiluhur formation, petrography, xrd, sem 1. introduction the cipamingkis river is part of the jatiluhur formation which is exposed to the surface. administratively, the cipamingkis river is located in jonggol district, bogor regency, west java (fig. 1). the jatiluhur formation in naming the subsurface lithostratigraphic unit in the west java basin is called the cibulakan formation, this formation has an important role in the hydrocarbon field (abdurokhim, 2017). in other words, the cipamingkis river can be analogized as a representative of the reservoir in the upper cibulakan formation. diagenesis is defined as a change in the physical and chemical characteristics of sediments after being deposited or buried (milliken, 2003). diagenesis consists essentially of a broad aspect of physiochemical and biological processes after deposition, when primary and interstitial mineralogy react to achieve textural and geochemical equilibrium with their environment (curtis, 1977). in the petroleum industry, diagenesis can provide information on the distribution of porosity in sandstones to control hydrocarbon migration pathways (worden & burley, 2003). studies on diagenesis in the jatiluhur formation are still relatively new, especially in the cipamingkis river. research that has been carried out in the jatiluhur formation, especially the cipamingkis river, includes a study of the genetics of mixed siliciclastic and carbonate rock deposits by abdurrokhim and ito (2013), the stratigraphic sequence of the jatiluhur formation by abdurrokhim (2013) and a study of rocks originating from tectonic arrangements in sandstones in the jatiluhur formation by rahman et al (2019). based on the previous research mentioned above, the author will research on diagenesis in the jatiluhur formation which has never been published before. research on diagenesis can provide information in the form of components and characteristics of rocks in the jatiluhur formation which can be used as a basis for further research or useful information in the oil and gas industry. the purpose of this study was to find out how the diagenesis features developed in a stratigraphic meansuring section of sandstones and limestone that exposed in part of the cipamingkis river through data collection using surface mapping methods and explain the history of diagenesis in the jatiluhur formation. 2. general geology the jatiluhur formation is included in the bogor basin which is currently in a volcanic back arc setting (hall & morley, 2004) as a response to subduction between the eurasian and indo-australian plates which are on the southern edge of the eurasian plate. this basin developed as a result of its flexibility to volcanic arc loading (waltham et al, 2008). since the pliocene, the bogor basin has become http://journal.uir.ac.id/index.php/jgeet 256 aulia, i. et al./ jgeet vol 6 no 4/2021 part of the volcanic order in the sunda-java arc-trench system, and as a whole has been influenced by the comparative tectonic regime and has led to the development of thrust faults and fold axes with an east-west trend (abdurrokhim & ito, 2013). the jatiluhur formation is composed of siliciclastic rocks and intercalated by limestone in a slope-shelf system or continental shelf environment with middle miocene to early late miocene ages (abdurrokhim & ito, 2013). according to martodjojo et al (2003) this formation is covered by limestones of the klapanunggal formation in the north. then the southern part is covered by deep sea deposits which are the cantayan formation (sudjamiko, 1972). limestone by the klapanunggal formation and deep sea deposits by the cantayan formation are covered by claystone which is the subang formation (fig. 2). fig 1. location of research area; (left) map of the cipamingkis river (google earth, 2021); (right) west java province administration map (jabarprov.go.id). fig 2. cenozoic stratigraphy in the bogor basin and north west java (left) modified from sujanto and sumantri (1977), martodjojo (2003), suyono et al (2005), abdurrokhim (2017). 3. methods the data collection was carried out by measuring the stratigraphic section (measurement section) measured from the south of the cipamingkis river to the north (fig. 2). the total length of this measurement is ± 2.5 km. then corrections are made to get the actual thickness of the section, which is ± 100 m. rock sampling was carried out on each representative facies in measuring the stratigraphic section. then obtained 56 rock samples consisting of siliciclastic sedimentary rocks such as claystone, siltstone, sandstone and limestone. while the sandstone obtained as 25 samples in this measurement. a total of 23 sandstone and 2 limestone samples were made into thin section and given bluedye solution on the sandstone samples meanwhile red alizarine solution on the limestone samples, using a polarizing microscope with observation methods in the form of plane polarized light (ppl) and cross polarized light (xpl). this analysis was conducted to determine the rock facies microscopically, mineral content, porosity, and other diagenesis features. xrd analysis was carried out on 4 sandstone samples using the rigaku smartlab device with theta angles between 5° to 65°. this analysis was to determine the dominance of primary minerals and clay minerals contained in these rocks. sem analysis was carried out on 2 sandstone samples using a phenom prox device that operates at an accelerating voltage of 15 kv. this analysis to determine the detail of mineral morphography and porosity in sandstone (fig 3). 4. result 4.1 compaction compaction occurs as a response to the compaction of sandstone due to the load on it during the burial process, causing increased contact between grains (worden & morad, 2003). through thin section analysis, sandstone samples were observed based on the contact between grains consisting of point contact, long contact, concavoconvex contact, and suture contact (fig. 4 a). by looking at the dissolution that occurs in quartz and feldspar minerals, as well as the intensity of compaction in mica minerals, we aulia, i. et al./ jgeet vol 6 no 4/2021 257 can show the type of compaction process that works on these rocks (schmidt & macdonald, 1979). based on petrographic analysis, it was found that point contact and long contact type were found in all sandstone samples in the jatiluhur formation. these two types of contact indicate the occurrence of mechanical compaction that occurs between quartz mineral fragments. in the concavo-convex contact type, almost all sandstone samples were found, but for suture contact it was only found in eight sandstone samples. the existence of the suture contact type is one indication of the chemical compaction process, so that the sandstone samples that have this type can be classified into rocks that have undergone a chemical compaction process. in the limestone samples in this section, the compaction that occurs due to burial is characterized by brittle fracture grains and tighter intergrain relationships (fig. 4 b). fig 3. stratigraphic logs of the jatiluhur formation in measuring stratigraphic section with a layer thickness of ±100 m at the cipamingkis river. 258 aulia, i. et al./ jgeet vol 6 no 4/2021 fig 4. (a) the petrography of cpm-2.5 ii consists of point contact (red arrow), long contact (yellow arrow), concavo-convex contact (green arrow) and suture contact (blue arrow); (b) the compaction of the cpm 3.4 sample (bf: brittle fracture), shows that some of the algae bioclasts have brittle fracture, thus showing discontinuities. 4.2 cementation after seen through a thin section, quartz cement was found in almost all of the sandstone samples. the quartz cement was found in the vicinity of the quartz fragments that looked like the result of the dissolution of the mineral (fig 5. a). quartz overgrowth that occurs in quartz minerals generally has a thickness equal to the thickness of the layer formed on quartz grains (waugh, 1971). quartz cement generally occurs during burial in the diagenesis process with temperatures above 70°c (bjørlykke & egeberg, 1993). calcite cement generally has the property of filling pores or spaces between particles locally (worden & morad, 2003). it’s presence was found in almost all of the samples. calcite cement was seen filling the intergranular space in most of the samples (fig 5 b). in addition, calcite cement was also found around dissolved quartz and feldspar minerals (fig 5 c). the cementation that occurs in limestone samples has a pore-filling character in the form of intergranular and moldic filled with calcite carbonate mineral. the calcite cement showed a blocky and fibrous to bladed morphology (fig 5 d-e). based on sem analysis, it was found that cement is made of clay minerals including kaolinite, smectite, and illite-smectite. kaolinite cements are generally present as pore fillers and sometimes appear as replacement minerals (chima et al, 2018). at low ph conditions, water with low ionic content and the occurrence of weathering processes also early diagenesis can trigger changes in feldspar minerals to clay minerals like kaolinite (worden & morad, 2003). kaolinite has a hexagonal euhedral crystal morphology that is thin and arranged like a stack of books and its presence is not spread, but only centered at several points (fig 6 a). the presence of kaolinite can be a marker of the early phase of diagenesis (eodiagenesis). albite cement is also found as euhedral character that fills the rock pores. in this sample (fig 6. b) it can be seen that albite crystals have a low enough relief so that it can be estimated that these crystals fill the pores in the rock. albite is basically formed when detrital k-feldspar or calcitic plagioclase is replaced by albite (ramseyer et al, 1992). the interlayer cement in the form of a mixture of illite and smectite was found to fill the rock pores (fig 6. c). smectite looks like a small fraction in the form of thin fibers or flakes that coat detrital grains, while illite has an elongated and needle-like morphology (chima et al, 2018). early weathering and water flow in the eogenetic zone can lead to the growth of smectite cement (worden & morad, 2003). then smectite can undergo a progressive change to become illite at a temperature of 70 – 90 °c (boles & franks, 1979). illite cement can also be formed due to changes in kaolinite with high potassium, silica and aluminum compositions (chima et al, 2018). fig 5. (a) cementation through petrographic observations on the cpm-1.2 sandstone sample, the type of quartz cement was found which was marked with a red arrow, calcite cement that filled the interparticles and was located around the quartz grains was marked with a yellow arrow; (b) cementation of calcite interparticle filling between quartz grains; (c) calcite cementation is found around the feldspar grains; (d) in the sample cpm-1.19 a limestone in the form of blocky cementation (bl) and neomorphism; (e) fibrous to bladed (ftb) cementation. fig 6. (a) sem analysis on cpm-1.2 shows kaolinite (k) mineral that colonizes and fills rock pores; (b) albite minerals (a) that are euhedral in shape and fill rock pores; (c) illite-smectite (i-s) mineral which is characterized by a needle-like morphology of illite and smectite which is textured around the quartz grains. a b c d e a c a b b aulia, i. et al./ jgeet vol 6 no 4/2021 259 4.3 dissolution the dissolution that occurs in quartz and calcite minerals is generally found as partial dissolution, where only part of the fragments undergo dissolution (fig 7a). however, an indication of complete dissolution was found in one of the samples (fig 7 b). this is because the shape of the isolated porosity in the matrix looks like the morphology of the quartz mineral. other minerals that undergo a partial dissolution process are mica and feldspar minerals (fig 7 c-d). dissolution of mica minerals was found in rock samples cpm-1.4 which was characterized by the presence of porosity around the mineral. likewise with the dissolution of feldspar minerals, where porosity was found in these minerals. the appearance of dissolved feldspar in the sandstone indicates the burial depth of this rock is 1.5 to 4.5 km, with temperatures between 50° to 150°c (wilkinson et al, 2001). dissolution in limestone samples occurred in a small part in the cpm-1.19 sample. dissolution can affect calcite cement, grains, mud matrix, to dolomite crystals (boggs, 2013). in this sample, dissolution resulted in secondary porosity of the interparticle type and opened a space between the calcite cement and the bioclast (fig 8 a). the secondary porosity found in the sandstone of the jatiluhur formation is the result of the dissolution process of mineral fragments contained in the rock. the commonly found secondary porosity is the result of dissolution of the minerals quartz, calcite, mica, and feldspar (fig 8 d-e-f-g). in addition, porosity with fracture type was found in several samples, this type is characterized by long and continuous porosity morphology, caused by stress experienced by the rock (fig 8 h-i). all rock samples in the jatiluhur formation sandstone have primary porosity (except limestone in cpm3.4) with an average porosity of 10.4% which is found between 3 – 23%. the primary porosity commonly found is of the interparticle type, with porosity characteristics located between fragments or inter-porous spaces (fig. 8 bc). fig 7. dissolving features based on petrographic analysis; (a) partial dissolution of quartz (red circle) and calcite cement (yellow circle) in sample cpm-2.7 ii c; (b) complete dissolution.(red circle) on sample cpm-3.7; (c) dissolution of mica minerals (red arrows) in sample cpm-1.4; (d) dissolution of feldspar minerals (red arrows) in the sample cpm-3.5. 4.4 mineral replacement mineral replacement in this process is defined when a dissolved mineral and another mineral are deposited in a dissolved place simultaneously (boggs, 2013). after petrographic observations, it was found that several mineral changes occurred in the sandstone of the jatiluhur formation, there are the replacement of quartz minerals by calcite minerals, replacement of feldspar minerals by calcite minerals and changes in the clay matrix by carbonate minerals (fig 9 a-b-c). in limestone samples, the micritization process is common in both limestone samples. the greatest abundance of micritization was found in the limestone samples from cpm-3.4 (fig 10). micritization is generally found in the inter-grain matrix and a small portion is found enveloping the grains or at the edges of the preserved fossil grains with a dark brown color. intensive micritization will usually occur in some warm water environments so that the carbonate grains are reduced almost completely to micrite (boggs, 2013). fig 8. mineral replacement; (a) quartz change by calcite cement (red circle) on cpm-3.2; (b) replacement of feldspar by calcite cement (red arrow) on cpm-1.4 a; (c) substitution of matrices by calcite cement (red arrow) in cpm-1.2 samples; (d) mikritization in cpm-1.19 a samples a mikritization occurs around the bioclast grain; (e) mikritization occurs in the matrix between grains in the cpm-3.4 sample a b c d d e 260 aulia, i. et al./ jgeet vol 6 no 4/2021 4.5 diagenesis history eodiagenesis eogenesis is defined as the early diagenesis stage where the processes operating at this stage are largely controlled by the depositional environment (berner, 1980). generally, the maximum depth of eogenesis is 1 – 2 km with temperatures between 30° – 70° c (morad et al, 2000). the dominant process working at this stage is compaction due to early burial. at this stage the rocks in the jatiluhur formation were deposited in a shallow marine environment and slowly buried. birnessite mineral from xrd analysis is one of the environmental markers of deposition of sandstone in the jatiluhur formation. birnessite mineral is formed due to the deposition of nodule concentrations formed in the sea (burns, r.g. & burns, v.m, 1977). in addition, the gluconite mineral found in the petrographic analysis in the cpm-3.4 sample indicates a depositional environment that occurred in the marine environment. the compaction process that works dominantly at this stage is the rearrangement of grains which is marked by point contact on contact between grains (fig 4 a). most of the sandstones through petrographic analysis show a point contact which then develops into a long contact at a deeper environtment. several clay minerals that are early markers of early stage diagenesis were found in the sem analysis, such as kaolinite and smectite minerals. kaolinite can be present at this stage as a replacement ofthe mineral feldspar which is unstable at increasing pressure and temperature. the formation of autigenic gluconite minerals occurs in open-shelf environments deeper than 50 m, under sub-oxic conditions between the sediment bed surface and water (lópez-quirós et al, 2019). this condition occurs due to low sedimentation rates and subsurface current activity that leads to sediment deposition (lópez-quirós et al, 2019). in marine environments with redox conditions (low oxygen) generally occurs the formation of pyrite with a distinctive morphology (boggs, 2013). pyrite minerals can form as cement or replace other materials (boggs, 2013). fig 10. illustration of the initial deposition process at the eogenesis stage by producing point contacts and long contact due to loading of sediments on top (qz: quartz, fs: fossils, fp: feldspar, mc: mica, al: algae). mesodiagenesis diagenesis stage after eogenesis is mesogenesis (morad et al, 2000). this stage is defined as a diagenesis process that occurs during burial that is not influenced by the depositional environment and it is the initial stage of metamorphism (worden and burley, 2003). most of these regimes occur at depths of 100 – 1000 m with temperatures of 200° – 250° c (worden & burley, 2003). due to the load of the overlying rock during the burial process, the compaction process in this regime occurs more intensely, which is characterized by the appearance of concavoconvex contacts to suture contacts that can be seen through petrographic analysis (fig 4. a). in the cpm-3.4 sample, found bioclasts that have brittle fracturing due to this compaction process (fig 7. a-b-c-d). in the cpm-2.2 sample which was carried out by xrd analysis, it was found that the mineral faujasite was generally formed at a temperature of 100° 200°c, indicating that the burial process at this stage was around that temperature. as the temperature increases, some minerals that are unstable under certain conditions will eventually dissolve to turn into other minerals. one of the dissolving processes that occur is in feldspar minerals which are unstable at certain pressure and temperature conditions and then turn into albite clay minerals. smectite mineral which have continue to increasing pressure and temperature also slowly turns into illite based on sem analysis on sample cpm-1.2. other dissolution also occurs in quartz and calcite minerals are generally found as partial dissolution (fig 7). however, an indication of complete dissolution was found in the cpm-3.7 sample, but could not be further identified for the type of mineral. another dissolved mineral is mica, which results a secondary porosity (fig 7). cementation also occurs at the mesogenesis stage. the dominant cements formed are calcite and quartz cement (fig 5. a). through petrographic analysis, most of the calcite cement was found to fill the interparticles between grains. some of quartz cement is present by covering the quartz grains. this cement is present significantly at a temperature of 70° – 80° c (giles et al, 2000). other cementation was also seen based on sem analysis, where the presence of illitesmectite cement. smectite in higher temperature increase will be unstable, and will turn into an illite when the temperature is more than 90°c (worden & morad, 2003). fig 11. illustration of the deposition process is increasingly causing the brittle fracturing feature, convex convex and suture contact (red arrow), as well as the coating (red box), and cementation on some items (qz: quartz, fs: fossils, mc: mica, por: porosity, bf: brittle fracture, sq: quartz cement, sc: cement calcite). telodiagenesis telogenesis is the final stage of diagenesis that occurs in rocks that have tectonic processes so that they are exposed to the surface, generally influenced by meteoric water (worden & morad, 2003). in addition, at this stage further al qz fp qz qz fs mc qz bf qz qz sq por fs sc fp aulia, i. et al./ jgeet vol 6 no 4/2021 261 dissolution occurs in mineral fragments and alteration occurs, especially in feldspar minerals (boggs, 2013). all rock samples included in the measurement stratigraphic section in the jatiluhur formation are surface outcrops located on the floor and walls of the river. some samples are indicated to have been affected by meteoric water, thereby changing some of the rock composition and the growing dissolution process (fig 7). in the xrd analysis of the cpm1.17 sample, clinochlore was found. clinochlore (fig. 12) is a member of the chlorite mineral, which is mostly formed as a result of altered biotite minerals (rahman et al., 2011). this indicates that the exposed rock in this sample has undergone an alteration process due to the influence of meteoric water (fig. 13). fig 12. x-ray diffraction displays the percentage of major mineral types in cpm-1.17 samples; mineral faction in x-ray shooting (left); the percentage of mineral compositions on rocks (right). fig 13. illustration at the phase of telogenesis when dissolving is increasingly developing (red arrow) and produces more secondary porosity and cementation around more detrential items (qz: quartz, fs: fossils, mc: mica, fp: feldspar, por: porosity, sq: quartz cement, sc: cement calcite, sp: secondary porosity). 5. conclution 1. the diagenesis features that develop in rocks in the jatiluhur formation are as follows: a. compaction feature that works in the form of point contact, long contact, concavo-convex contact and suture contact. and dominated by mechanical compaction. the compaction on limestone samples is brittle fracture that occurs in bioclasts. b. cementation found in sandstone is in the form of calcite cement, quartz and clay mineral cement such as kaolinite, smectite and illite. in the limestone, cementation is in the form of blocky and fibrous to bladed which is filled with calcite mineral. c. dissolution feature was found to occur in the minerals quartz, feldspar, and mica. d. mineral replacement that are commonly found are replacement in the quartz and feldspar, meanwhile in limestone, there is an intergranular micritization. e. the dominant type of porosity found was the interparticle type with an average porosity of 10.4% which was found to be 3 – 23%. 2. the history of diagenesis that occurs in rocks in the jatiluhur formation begins with the initial deposition of eogenesis, burial mesogenesis and ends with telogenesis which is exposed on the surface. acknowledgements writer would like to thank mr. rezky aditiyo, m.t. as supervisor in this research, sedimentology and stratigraphy at west java prosiding research group, universitas indonesia and geology major of universitas indonesia for providing field equipment and laboratory support. this research financially supported by universitas indonesia through the hibah publikasi terindeks internasional (puti) saintikes no. nkb3643/un2.rst/hkp.05.00/2020. references abdurrokhim. 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(2003). sandstone diagenesis: the evolution of sand to stone. sandstone diagenesis, 1–44. https://doi.org/10.1002/9781444304459.ch © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ author guideline journal of geoscience, engineering, environment, and technology 1. paper title who will cite your article. identify the main issue of the paper. begin with the subject of the paper. the title should be accurate, unambiguous, specific, and complete. do not contain infrequently-used abbreviations. the title of the paper should be in 16 pt bold font gulliver-regular and be centered. the title should have 0 pts space above and 12 pts below. 2. authors name and affiliations write author(s) names without a title and professional positions such as prof, dr, production manager, etc. do not abbreviate your last/family name. always give your first and last names. write clear affiliation of all authors. affiliation includes a name of department/unit, (faculty), a name of university, address, country. please indicate corresponding author (include email address) by adding an asterisk (*) in superscript behind the name. author names should be in 12 pt gulliver-regular with 6 pts above and 12 pts below. author addresses are superscripted by numerals and centered over both columns of manuscripts. author affiliations university name / institution / research study / company should be in 7 pt gulliver-regular. the body of the text should commence two lines (24 points) below the last address. present/permanent address. if an author has moved since the work described in the article was done, or was visiting at the time, a 'present address' (or 'permanent address') may be indicated as a footnote to that author's name. the address at which the author did the work must be retained as the main, affiliation address.start by adding an asterisk (*) and then email, phone number, font gulliver 7pt. 3. abstract summary of the all research (aim, scope, result and conclusion) with maximum 300 words, justified, 8 point, and line spacing : single. for keywords wrote in italic and then separated using symbol (,) with maximum are 6 words. 4. introduction in introduction, authors should state the objectives of the work at the end of introduction section. before the objective, authors should provide an adequate background, and very short literature survey in order to record the existing solutions/method, to show which is the best of previous researches, to show the main limitation of the previous researches, to show what do you hope to achieve (to solve the limitation), and to show the scientific merit or novelties of the paper. avoid a detailed literature survey or a summary of the results. to prepare your paper, use directly this template and simply replace this text by your text. these instructions are to be followed strictly, and it is strongly advised to use the styles indicated in this document between square brackets. it is strongly advised not to use formatting or styles in your paper different from the ones mentioned here. the book size will be in a4 (210 x 297 mm). left margin 30mm, right margin 2mm, top margin 20mm and bottom margin: 20mm. please make sure that you do not exceed the indicated type area. the structure of manuscripts should follow the following order; 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(thesis). dissertation beukeboom, t.j., 1976. the hydrology of the frisian islands (dissertation). report khairani, s., n.d. tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya (rep.), tinjauan batupasir silika sebagai energi sumber daya alam terbarukan di daerah batam dan sekitarnya website petrology/mineral physics [www document], n.d. [www document]. jsg news rss. url http://www.jsg.utexas.edu/research/disciplines/petrology-mineral-physics/ (accessed 12.19.16). when preparing your reference list, the following should be avoided: • references not cited in the text. • excessively referencing your work. • insufficiently referencing the work of others. some examples of how your references should be listed are given at the end of this template in the t format and font size. when you are referencing conference proceedings, page numbers should be provided. if proceedings are not available, the lecture identification e.g. lecture number should be provided instead. when you are referencing websites, an author or authoring institution should be provided. the date of the last access should be provided as well. the hyperlinks (blue colour and underlining) should be removed from email addresses and web references. you do not need to repeat http:// as modern browsers do not require it. however the date of the last access should be always provided. 12. acknowledgements collate acknowledgements in a separate section at the end of the article before the references and do not, therefore, include them on title page, as a footnote to the title or otherwise. list here those individuals who provided help during the research (e.g., providing language help, or proof reading the rticle, etc.). acknowledgement can be write in this paper or not. using 9 pt font gulliver-regular , 6 pt after headings. 13. references natasia, n., syafri, i., alfadli, m.k., arfiansyah, k., 2016. stratigraphy seismic and sedimentation development of middle baong sand , aru field , north sumatera basin. j. geoscience, engineering, environment, and technology 1, 51 58. putra, d.b.e., choanji, t., 2016. preliminary analysis of slope stability in kuok and surrounding areas. j. geoscience, engineering, environment, and technology 1, 41 44. selley, r., robin, l., cocks, m., plimer, i., 2005. encyclopedia of geology. geology 3345. doi:10.1016/b0-12369396-9/00102-7 trouw, r., passchier, c., wiersma, d., 2009. atlas of mylonitesand related microstructures. springer, berlin heidelberg. doi:10.1007/978-3-642-03608-8 uir press issne-issn jl. kaharuddin nasution no 113 pekanbaru, riau 28284 phone.(0761) 674674, fax. 0761-674834 e-mail: jgeet@journal.uir.ac.id website: http://journal.uir.ac.id/index.php/jgeet 1: front cover page 2 page 3 4: back cover 5: book_print page 1 page 2 page 3 page 4 5. section headings http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 4 2021 248 oo, t.n. et al./ jgeet vol 6 no4/2021 research article fluid inclusion study of epithermal quartz veins from the kyaukmyet prospect, monywa copper-gold ore field, central myanmar toe naing oo*1,2, agung harijoko1, lucas donny setijadji1 1department of geological engineering, faculty of engineering, gadjah mada university, yogyakarta, indonesia 2department of geology, west yangon university, yangon, myanmar * corresponding author : toenaingoo.geol84@gmail.com tel.: +62-812-289-256-46 received: sept 16, 2021; accepted: dec 31, 2021. doi 10.25299/jgeet.2021.6.4.7726 abstract the kyaukmyet prospect is located near the main ore bodies of the kyisintaung and sabetaung high-sulfidation cu-au deposits, monywa copper-gold ore field, central myanmar. lithologic units in the research area are of mainly rhyolite lava, lapilli tuff and silicified sandstone, mudstone and siltstone units of magyigon formation which hosted to be polymetallic mineralization. our field study recorded that epithermal quartz veins are hosted largely in rhyolite lava and lapilli tuff units. those quartz veins show crustiform, banded (colloform), lattice bladed texture and comb quartz. the main objectives of the present research in which fluid inclusion studies were considered to conduct the nature, characteristics and hydrothermal fluids evolution from the epithermal quartz veins. in this research, there are three main types of fluid inclusions are classified according to their phase relationship (1) two-phase liquid-rich inclusions, (2) the coexisting liquid-rich and vapor-rich inclusions, and (3) only vapor-rich inclusions. microthermometric measurements of fluid inclusions yielded homogenization temperatures (th) of 148–282 °c and final ice-melting temperature (tm) of -0.2°c to -1.4°c . the value of (tm) are equal to the salinities reaching up 0.35 to 2.07 wt % nacl equiv. respectively. estimation formation temperature of the quartz veins provide 190°c and 210°c and paleo-depth of formation are estimated to be between 130m and 210m. petrography of fluid inclusion and microthermometric data suggest that fluid boiling as well as mixing processes were likely to be happened during the hydrothermal fluid evolution at the kyaukmyet prospect. according to the characteristics of many parameters including petrography of fluid inclusion, microthermometric data, paleo-depth, evidence of quartz vein textures and types of hydrothermal alteration from the kyaukmyet prospect allows to interpret these data to be the low-sulfidation epithermal system. keywords: kyaukmyet, epithermal quartz veins, fluid inclusions, formation temperature, paleo-depth, monywa copper-gold ore field 1. introduction the kyaukmyet prospect is a well-known for a low sulfidation (ls) epithermal deposit which situated in the western part of chindwin river (monywa city), monywa copper-gold ore field, which is belonged to the wunthopopa magmatic arc (also known as wuntho popa arc), central myanmar (figure 1,2). in general, monywa coppergold ore field is a very foremost epithermal copper-gold deposit as recognized by its the second largest deposit in the south east mainland asia and ore containing more than 7 × 107 tons of cu and 3 to 10g/t au (htet, 2008; a. h. g. mitchell et al., 2011; zaw, swe, myint, & knight, 2017). the prospect area was discovered by ivanhole copper company limited in 1995 during the extensive exploration in the search for cu-au deposit, au-ag deposit and base metals mineralization in the monywa copper-gold ore field. an exploration program discovering of copper-gold and polymetallic mineralization had been searched by based on the detailed on geological and geophysical investigation. geologically, the prospect area is mainly composed of rhyolite lava, lapilli tuff and silicified sandstone, mudstone and siltstone units (figure 3). on the basis of field investigation, the characteristics and different types of epithermal quartz veins observed such as banded (colloform) quartz vein, crustiform quartz vein, comb quartz and lattice bladed texture in the kyaukmyet prospect is shown in (figure 4). those quartz veins are trending nearly ene-wsw direction because of controlling regional structure. htet, (2008) and naing oo, harijoko, & setijadji, (2021)reported that a typical characteristics of quartz vein textures as well as minor adularia at kyaukmyet prospect remark on a ls epithermal deposit. previous research has also demonstrated that, in the kyaukmyet prospect area of ore mineralization had occurred in veins, filling structurally in weak fractures (htet, 2008). the mineralized veins commonly show complex nature of brecciation, banding, vuggy, comb and lattice bladed texture. moreover, mineralization veins are found in silicified zone where gold is intimately associated with base metals sulfide mineral assemblages along with gangue mineral assemblages consisting mainly of quartz, adularia, sericite and calcite (htet, 2008; naing oo et al., 2021). the rhyolite lava as well as lapilli tuff rock units in the kyaukmyet prospect are mainly recognized by distinct alteration mineral assemblages and zoning which are associated with areas of epithermal gold mineralization. most common hydrothermal alterations in the research area are silicic alteration (quartz, adularia, calcite, pyrite), argillic alteration (illite, illite/smectite, quartz, sericite, chlorite) and propylitic alteration (chlorite, epidote, quartz pyrite) (htet, 2008; naing oo et al., 2021). this paper aims to emphasize study on fluid inclusion of epithermal quartz http://journal.uir.ac.id/index.php/jgeet mailto:toenaingoo.geol84@gmail.com oo, t.n. et al./ jgeet vol 6 no4/2021 249 veins from the kyaukmyet prospect especially to determine the formation temperature, trapping pressure, paleo-depth, density and to identify the characteristics of hydrothermal fluid condition. 2. geologic setting myanmar is situated in mainland of southeast asia and prosperous in mineral resources and a very complex tectonic region which lie in the eastern boundary of indiaasia collision zone and characterized by a well-known right lateral movement of sagaing fault. a. h.g. mitchell et al., (2007), searle et al., (2007) and lee, chung, & yang, (2016) reported that they are tectonically connected to the eastern tip of alpine himalayan to the north as well as the andaman sea to the south (figure 1). based on the tectonic events, myanmar can be classified into two distinct tectonic provinces including the eastern province as well as the western province (liu et al., 2016). the eastern part is made up of the mogok mandalay mergui belt and the shan plateau whereas the western part is composed of the wuntho-popa magmatic arc and the indo-myanmar ranges (figure 1). in general, a n-s trending of the wuntho-popa magmatic arc has played a prominent geological factor and a very important mineral resources in myanmar. in deep, the wuntho popa magmatic arc has belonged to different type of mineral deposits, such as hs type epithermal copper-gold deposit, ls epithermal deposit and mesothermal gold deposit (htet, 2008; a. h. g. mitchell et al., 2011; naing oo et al., 2021; zaw, 1990; zaw et al., 2017). geologically, it is characterized by the occurrence of both mesozoic volcanic and intrusive rocks which are widely distributed by cretaceous-pliocene sedimentary formations. accordingly, the wuntho popa magmatic arc is composed dominantly of upper cretaceous to tertiary granodioritic intrusive rocks, and with minor part of volcanic rocks of upper cretaceous to quaternary ages (a. mitchell, chung, oo, lin, & hung, 2012; a. h. g. mitchell et al., 2011; zaw et al., 2017). the monywa copper-gold ore field is located within the wuntho popa magmatic arc, central part of myanmar (a. h. g. mitchell et al., 2011; zaw, 1990; zaw et al., 2017) (figure 1). in the monywa copper-gold ore field, mesozoic volcanic rocks are mainly intruded by upper cretaceous age of granodiorites (a. h. g. mitchell et al., 2011). based on the previous research (htet, 2008; a. h. g. mitchell et al., 2011), the monywa copper-gold ore field of high-sulfidation (hs) copper-gold deposit and low-sulfidation (ls) gold-silver deposit in the monywa copper-gold ore field are spatially and temporally related to basement rocks as well as granitic intrusions. meanwhile, the basement rocks are widely spread out by volcanic rocks such as andesite, quartz andesite porphyry, dacite, and rhyolite (figure 2). most copper-gold (high-sulfidation type) and gold-silver (lowsulfidation type) deposits between the chindwin river and powintaung are mainly formed by the late oligocene to middle miocene magyigon formation as well as porphyry intrusions (figure 2). fig 1. simplified geological map of myanmar illustrating outline of wuntho popa magmatic arc, principal tectonic units and major quaternary calc-alkaline volcanoes (modified after lee et al., 2016; searle et al., 2007). 250 oo, t.n. et al./ jgeet vol 6 no4/2021 fig 2. regional geological map of the monywa copper-gold ore field and the black rectangle is the kyaukmyet prospect (modified after a. h. g. mitchell et al., 2011). fig 3. geological map with distribution of quartz vein at kyaukmyet prospect (modified from htet, 2008). 3. sample preparation and analytical methods fluid inclusion studies have played a crucial method to reveal the conditions of hydrothermal ore-forming fluids in mineralization system and their origin. in the field study, the different types of epithermal quartz vein samples were collected systematically from the surface outcrops at kyaukmyet prospect, monywa copper-gold ore field in order to perform for fluid inclusion studies. representative sample selections were carefully determined and considered to be intimately associated with ore mineralization and clear quartz samples which are accessible to recognize as well as elucidate for fluid inclusions studies under transmitted light microscope. in support of microthermometric analysis, the doubly polished thin sections were made from representative quartz vein samples in order to conduct for studying of fluid inclusion. the thickness of quartz wafers are approximately between 100-200µm, depending upon the transparent quality of quartz samples. firstly, these quartz wafers were performed by transmitted light microscope in order to examine petrography of fluid inclusion where shapes, sizes and nature of appearances and phases in the fluid inclusions were recorded on the basis of the standard citations of (bodnar, reynolds, & kuehn, 1985; roedder, 1984). subsequently, about 57 primary fluid inclusions from the crustiform, and banded (colloform) quartz vein samples were measured to get microthermometry data. applying the equations of bodnar, (1993), the values of salinity were considered from the final ice-melting temperature (tm). fluid inclusions microthermometry was performed applying a linkam th600 combine heating and cooling stages with a range of temperature of -196-600°c and reproducibility of ±0.1°c, in kyushu university, japan, mounted on a nikon polarizing microscope with axiovison software where reproducibility of temperature is ±0.1°c. 4. result 4.1 vein textures vein textures in the kyaukmyet prospect area can be classified into three principal categories i.e. primary, recrystallization and replacement textures according to the paragenetic as well as textural evidence which support for the elucidation of their source as well as environment of formation (morrison, dong, & jaireth, 1995). oo, t.n. et al./ jgeet vol 6 no4/2021 251 in this study, the most common occurrence of primary textures include comb, banded (colloform) and crustiform quartz textures (figure 4a-e). replacement texture consists of lattice bladed quartz texture (figure 4f). crustiform texture is noted as a primary texture and characterized by distinguishing feature of epithermal veins (buchanan, 1981). this texture is commonly observed as symmetric relative to the footwall and hanging wall of the vein. the crustiform texture in quartz is composed of dominantly sequential development of banded quartz with a variety of textures including comb, lattice blade, microcrystalline and colloform (figure 4a,b). in general, it is caused as a product of fluid conditions whereas two fluids of cooling depressurization and isothermal mixing, interaction fluidhost rocks, and the fluid boiling is the significant processes during the evolution of hydrothermal system (buchanan, 1981). otherwise, fluid boiling has produced in the hydrothermal fluid system as a result of dropping confining pressure. fournier, berger, & bethke, (1985), roedder, (1984), and bodnar et al., (1985) revealed that banded (colloform) texture is represented as a primary texture and generally characterized by a distinguishing feature an aggregates of chalcedonic in fine rhythmic bands in support of silica minerals (figure 4c,d). it is also recognized by the occurrence of asymmetrical with their spherical, botryoidal, reniform, or mammillary surfaces indicating towards the center of the veins (figure 4c,d). comb texture is a primary texture and attributes to groups of parallel or subparallel euhedral quartz crystals elongated perpendicular to vein walls (figure 4e). it is typically formed from fluid slightly supersaturated with quartz, indicating slowly changing or very mildly fluctuating of the physical conditions as well as chemical nature of the temperature, pressure and ph solution throughout crystals growth (fournier et al., 1985). simmons & christenson, (1994) stated that lattice bladed texture is mainly designated by a product of aggregate of platy calcite with considerable interstices each other’s (figure 4f) which results from boiling solution. fig. 4. photographs showing representative epithermal quartz veins texture of (a) crustiform quartz vein in mineralization, (b) crustiform quartz vein with bladed texture , (c,d) banded (colloform) quartz veins in mineralization (e) comb quartz and (f) lattice bladed texture from the kyaukmyet prospect. (note: figure (a) and (c) used for fluid inclusions studies) 4.2. petrography of fluid inclusion on the basis of their time of entrapment relative to the formation in the quartz crystals, fluid inclusions were identified as not only primary but also secondary in origin based on the standard citations of roedder, (1984) and bodnar et al., (1985). in support of this research, a total of 6 quartz vein samples from two different quartz veins crustiform and banded (colloform) were conducted for fluid inclusion studies. initially, quartz wafers of crustiform and banded (colloform) quartz vein samples were analyzed under transmitted light microscope in order to identify petrography of fluid inclusion. this analyzing comprises studying on sizes, shapes, mode of appearances and fluid inclusions types respectively. most of primary fluid inclusions occur as a variety of shapes including subrounded, negative crystal shapes and irregular shapes that are typically ranging from 5µm to a maximum 20µm and most inclusions were approximately 20µm across. a total of 57 representative primary fluid inclusions were identified and measured from the crustiform and banded (colloform) quartz vein samples. secondary fluid inclusions were also present from the samples along with primary inclusions. they were also less common and their sizes were generally less than 5 µm. microthermometric data from the secondary fluid inclusions were not deplorable. according to their phase relations as well as their behavior during freezing and heating experiments, there are three main types of fluid inclusions are distinguished at kyaukmyet prospect: (1) two-phase liquid-rich inclusions, (2) the coexisting of two-phase liquid-rich and vapor-rich inclusions and (3) only vapor-rich inclusions (figure 5). in general, the liquid to vapor ratios at room temperature occur as liquid rich (10-30% vapor phase) and vapor rich (60-90% vapor phase) by volume (optical estimation). on the other hand, the coexistence of two-phase liquid-rich and vapor-rich fluid inclusions are point out that epithermal quartz vein samples are considered to be fluid boiling or or immiscible fluid system (bodnar et al., 1985) (figure 5b). fig. 5. photomicrographs of (a) two-phase liquid-rich inclusions, (b) coexisting liquid-rich and vapor-rich inclusions, and (c) only vapor-rich inclusions in crustiform and banded (colloform) quartz vein samples at kyaukmyet prospect. 5. discussion the fluid inclusion study has played a crucial role to know the estimating the temperature of homogenization 252 oo, t.n. et al./ jgeet vol 6 no4/2021 and final ice-melting temperature. in support of this research, typical primary two-phase liquid-rich and vapor rich fluid inclusions from the crustiform and banded (colloform) quartz vein samples were systematically prepared and selected to carry out for microthemometric measurements. fluid inclusions microthermometric analysis was undertaken on all 57 primary fluid inclusions from 6 samples of quartz veins and 2 quartz vein samples of crustiform and banded (colloform) quartz veins. those two different quartz veins were measured to conduct for homogenization temperature (th) and final ice-melting temperature (tm). according to the fluid inclusions data, the homogenization temperature of primary fluid inclusions is 165-279°c (mean of 222°c) for crustiform quartz vein and 148-282°c (mean of 215°c) for banded (colloform) quartz vein respectively. frequency distributions of homogenization temperature (th) of two different quartz veins (figure 6a and 6b) display that the mode of homogenization temperature of primary fluid inclusions give between 180-200°c for crustiform quartz vein and 200-220°c for banded (colloform) quartz vein respectively. the results of final ice melting temperatures in those vein samples from the kyaukmyet area are varied from -0.2°c to -1.2°c (mean of -0.7°c). the apparent fluid inclusion salinities were interpreted based on the final icemelting temperature and by using bodnar’s equation (1993) where salinities value is ranged from 0.35 to 2.07 wt.% nacl equiv. (mean of 1.2 wt.% nacl equiv.). in fact, salinity and homogenization temperature has played a crucial role to estimate the formation temperature, pressure of trapping, paleo-depth, fluid evolution processes (boiling, mixing and dilution) and mineral deposit types. wilkinson, (2001) stated that a plot diagram of homogenization temperature (th) and salinity of fluid inclusions was considered to classify the type of deposits. the results of this study, low homogenization temperature (th) and low salinity values suggest that a plot of these fluid inclusions microthermometric data from the kyaukmyet prospect is considered to be consistent with epithermal deposit field (figure 7). meanwhile, from th versus salinity diagram, fluid inclusion densities of the kyaukmyet area are typically ranged from 0.7 to 0.9 gcm-3 (figure 7). besides, the correlation between fluid inclusions salinity (wt% nacl equiv.) and homogenization temperature (th) are likely to be revealed as a fluid evolution processes, including boiling, cooling, and mixing (wilkinson, 2001). in a correlation diagram of th versus salinity for fluid inclusions in quartz veins from the kyaukmyet prospect is also displayed in (figure 8). from the diagram despite the small data set, it can be observed that the occurrence of a broad range variation of fluid inclusion salinities and homogenization temperature whereas the trend of increasing salinities with decreasing temperature. fluid inclusion microthermometric data shows trends of increasing salinity with decrease temperature (negative direction) indicating that an evidence of boiling condition. salinity variation pointed out boiling or effervescence in the system, however important salinity increases might have been took place by continuous boiling in the restrained fractures (wilkinson, 2001). on the other hand, fluid mixing also could be formed by combination or mixing with more or less saline solutions as a result of some fluid inclusions in specific temperatures showed their fluid mixing trends in figure 8. alternatively, the formation temperatures of quartz veins refer to first peak of histograms illustrating the primary fluid inclusion of homogenization temperatures under the boiling condition (bodnar et al., 1985). in this place, formation temperature of the research area can be envisaged that 190°c for crustiform quartz vein and 210°c for banded (colloform) quartz vein respectively (figure 6a and 6b). as a consequence, an estimation of formation temperature of quartz veins from the microthermometry was then interpreted for the paleo-depth of formation, and pressure of trapping applying a boiling point curve (figure 9) (haas, 1971). based on the present results of formation temperature, applying the boiling point curve supported by (haas, 1971) likewise considering of 2 wt% nacl equiv. and an estimate for paleo-depth of formation is 130m to 210m under the water table in the hydrothermal system which is equivalent to the hydrostatic fluid pressure between 12 and 19 bars respectively (figure 9). fig 6. th histograms of the primary fluid inclusions showing (a) banded (colloform) quartz vein and (b) crustiform quartz vein from the kyaukmyet area (n= number of fluid inclusion). fig 7. th vs salinity diagram showing various types of mineral deposits (wilkinson, 2001) and a plot of kyaukmyet fluid inclusions points lie in the epithermal deposit field. oo, t.n. et al./ jgeet vol 6 no4/2021 253 fig 8. salinity and th plot diagram of the kyaukmyet prospect epithermal quartz veins illustrating the trend of fluid evolution processes (wilkinson, 2001). fig 9. an estimated for paleo-depth of formation of epithermal quartz veins from the kyaukmyet prospect applying the boiling point curve with formation temperature and salinity (after haas, 1971). 6. conclusion on the basis of current understanding from the all available data including petrography of fluid inclusion as well as microthermometric measurements, epithermal quartz veins of the kyaukmyet prospect are belonged to typical characters of low salinity as well as low homogenization temperature (th) values. in support of fluid inclusion petrography, the coexisting of liquid-rich and vapor-rich fluid inclusions as well as only vapor-rich inclusions strongly suggested that they were occurred as a fluid boiling event in the hydrothermal system of the research area. in addition, the occurrence of lattice bladed texture, crustiform and banded (colloform) primary quartz veins texture that supported again for fluid boiling feature observed. the occurrence of wide range variation in fluid inclusion salinities and homogenization temperature indicated that evidence of fluid boiling condition as well as fluid mixing with more or less saline solutions. accordingly, the primary fluid inclusions in the crustiform and (banded) colloform quartz veins possess salinities ranging from 0.35 wt% to 2.07 wt% nacl equiv. and homogenization temperatures from 148 to 282°c. plotting these data on the salinity versus homogenization temperature diagram indicated that the kyuakmyet epithermal quartz veins formed at low salinity as well as low temperature by fluid boiling and fluid mixing during the evolution of hydrothermal fluid system. in general, low-salinity fluids can be generated by the mixing of meteoric water with magmatic fluids (wilkinson, 2001). this suggests that the low-salinity (0.35-2.07 wt% nacl equiv.) of the kyaukmyet epithermal quartz veins are likely to be produced by the mixing of a dominant meteoric water with minor amounts of magmatic fluid. in a subsequent study, a compilation of salinity and homogenization temperature, the kyaukmyet fluid inclusions of microthermoetric data is occupied in the epithermal deposit field. furthermore, based on th and salinity data, fluid inclusion densities for the kyaukmyet area are between 0.7-0.9 g/cm3. in contrast, the microthermometric data of primary fluid inclusions in the crustiform and banded (colloform) quartz veins from the kyaukmyet prospect indicated that an estimation of formation temperature provides 190 to 210°c and their formation of paleo-depth are estimated at 130m to 210m. pressure of trapping at those depths are between 12 and 19 bars, respectively. all of these current conducting available data from fluid inclusions petrography and microthermometric data, formation temperature, an estimation of paleo-depth and evidence of quartz vein textures, and alteration mineral assemblages, the kyaukmyet prospect is considered to be consistent with a low-sulfidation (ls) epithermal system. acknowledgments funding for this paper was supported by the aun/seed-net (jica program). the authors are immensely grateful to prof. dr. akira imai, assoc. prof. dr. kotaro yonezu and laboratory members from the kyushu university, japan for their huge support and insightful suggestions on the data analysis as well as interpretation. the authors also would like to thank the 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(2017). copper deposits of myanmar. geological society memoir (vol. 48, pp. 573–588). geological society of london. © 2021 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 6 no 4 2021 206 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 research article understanding mud volcano system using hele-shaw (h-s) experiment: seismic confirmation at east java mud volcano muhammad burhannudinnur1*, dardji noeradi2 1 department of geological engineering, universitas trisakti, jakarta, indonesia. 2 department of geological engineering, institut teknologi bandung, bandung, indonesia. * corresponding author: burhan@trisakti.ac.id tel.:+62811836263 received: oct 18, 2021; accepted: dec 27, 2021. doi: 10.25299/jgeet.2021.6.4.7889 abstract numerous researchers have carried out studies on the mud volcano system in east java. however, there have been no experiments on the mud volcano system's mechanism, including overpressure confirmed by direct subsurface data. therefore, this study aims to directly evaluate the mud volcano system's mechanism using the hele-shaw (h-s) experiment with the subsurface data confirmation. the h-s experiment utilized four primary materials: quartz sand diameter below 250 µm and 320 µm to analogize the porous layer. gypsum flour clay is the ductile layer, while mud from the kuwu and kesongo mud volcanoes is the original material from nature. wax repres ents impermeable material. the sealing layer is made of wax, and oxygen represents the natural fluids of the rock formation. the overpressured zone is created by pumping oxygen into a layer of quartz sand covered by a wax as an impermeable layer. pressure is measured digitally, and the process is continuously recorded to produce traceable data. each material was experimented on individually to determine the critical phase characteristics, valve fault structure geometry, and validation with seismic interpretation. the results indicate that the critical phase of the mud volcano system is characterized by the dome structure at the surface, with high intensify of gas and oil seepage. piercement structure geometry is shown by plumbing of fluidization zone, which becomes shallower than before. furthermore, each material's piercement structure geometry shows a consistent pattern, with differences in the density of the fault and pressure structures. thus, the h-s experiment's validation with seismic interpretation shows a similar geometry in pressure structures and valve faults as the mud volcano system's migration paths. keywords: mud volcano system, hele-shaw, overpressured, valve fault, critical phase 1. introduction the process of a mud volcano system from the formation of source material rock, migration to the eruption, and its associated structures needs to be adequately understood. analogous experiments with heleshaw allow us to see the process of the occurrence of a mud volcano system and describe the geometry of the evolving structure to be modeled. the geometry model of this structure will be compared with the geometry from below the surface using seismic data. this analog experiment assumes natural conditions are represented under these modeling conditions. in addition, the initial parameters of the experiment exclude the effect of initial temperature and pressure. subsequently, the elements and processes in the generative, migration, and extrusion subsystems were formulated. east java is an area where research on mud volcano systems has often been carried out, including a study by satyana on mud diapir and mud volcano around east java to the madura oil and gas fields, especially in the "f" field (satyana and asnidar, 2008). meanwhile, burhannudinnur discussed the characteristics of a unique mud volcano in east java, including within the research area, and discussed the kradenan mud volcano complex in great detail in terms of exploration prospects and risks (burhannudinnur, 2012; burhannudinnur et al., 2012). mud gas play is a new exploration play for unconventional gas that can be found associated with the mud volcano system (burhannudinnur, 2019). the mud volcano system in the kradean and kesongo areas has a potential geohazard risk. the area and depth of the potential geohazard risk area can be predicted by integrated analysis of the strain ratio and sedimentation rate distribution (burhannudinnur, 2020) an analog experiment continually develops to explain geological symptoms of structure-tectonics, sedimentation, and ground motion. previous studies conducted a mud volcano analog experiment through the simple sandbox and fluid experiments. generally, this experiment uses the principle of buoyancy, as in the diapir model. according to price et al., 1990, analogous experiments of low-density materials' motion in high-density materials are an early concept developed for diapir modeling. in the sandbox experiment, the mud volcano material was modeled with silicon, for instance, salt diapir (letouzey et al., 1990; talbot, 1995). thus, this modeling provides an overview of the pressure structure using diapir but cannot explain the fluid and pressure present in the mud volcano or the eruption mechanism. an analog experiment was conducted with hele-shaw (h-s) to simulate the mud volcano system as well as extrusion mechanism, provide an analog enabling easier understanding of the extrusion process in nature, and as a validation test for seismic interpretation. thus, the h-s modeling's results are the pressure structure and valve faults' geometry models and several simulations of the mud volcano extrusion mechanism. about:blank burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 207 the hele-shaw (h-s) method is a thin glass box modeling, enabling the processes inside the glass box to be observed visually. h-s boxes are often used in material modeling to test physical material properties while sprayed, flowed, or under a specific temperature as well as pressure (nermoen et al., 2010; rigord et al., 2005). researchers introduced this method for modeling glass grains' response to pressurized gas flow (johnsen et al., 2008). the experiments by rigord et al. (2005) developed a tool to study the response of a thin glass grain layer immersed in a slow-flowing liquid under controlled pressure, and the tool is designed to allow liquid flow from bottom to top. subsequently, the liquid flow rate is measured and controlled to determine the turbulence effect. the thin layer of glass grains becomes unstable and unbalanced with increased liquid flow. this increase does not lift the entire thin layer of glass grain but forms a channel or column of the granular fluidization zone, connecting the bottom and top. the glass grains emerge to the surface to form eruptions similar to jets of water, deposited on the surface, with a hole diameter about 32 times the grain size. nermoen et al. (2010) also designed an experimental tool to study the fluidization process. the h-s device in this study was vertically oriented, filled with 250 µm glass beads, and injected with pressurized gas, with variations in the glass grain layer thickness and inlet diameter. consequently, the fluidization zone forms a divergent cone in the form of a pressure structure. the surface's morphological characteristics on the pressure structure have similarities to morphology in nature, including mud volcanoes, hydrothermal, kimberlite pipes, or geysers symptoms. modeling with the hele-shaw (h-s) method implies making a tool intended to model the mud volcano system and obtain an overview of the valve fault formation mechanism, geological structural geometry of the mud's motion through the layer above, observe the geometry and material motion from the overpressure zone to the mud volcano extrusion. furthermore, hele-shaw is a vertical modeling method assumed to represent the geological section of the research area. the initial condition of h-s modeling is static, and the pore pressure is under hydrostatic conditions. 2. methodology 2.1. hele-shaw design and manufacture in this study, the h-s equipment and methods were designed and modified based on reference tools provided by rigord et al. (2005), johnsen et al. (2008), and nermoen et al. (2010). the main equipment consists of an h-s wall, support table, inlet, hose line, and a gas cylinder. meanwhile, the supporting equipment includes a pressure measuring instruments, computers, bsr software, on-screen video recorders, cameras, digital scales, levelers, funnels, pipes, and calipers. the h-s wall is a tool made of two parallel glasses 100 cm long and 75 cm tall, separated by a distance of 0.8-1 cm at the bottom and closed at the two sides (airtight), and open at the top. furthermore, the material, particularly the compressed gas, is modeled outward rather than out of the three sides. an inlet was installed 8 cm from the bottom to prevent gas from flowing along the sand or equipment bottoms. fig. 1 shows the hele-shaw modeling scheme and set of tools and an example of the experiment implementation. 2.2. selection of material types the material selection and use in modeling referred to the reports of several related research, including sandbox modeling at the geodynamic engineering geology laboratory, faculty of earth sciences and technology, bandung institute of technology, referring mazzini et al., (2009). in previous studies, material selection considered several factors: low cohesiveness and bearing capacity, brittle and ductile materials, easy-to-form structures, high porosity, safety, and ease of obtaining materials. table 1 shows some materials variations used in h-s modeling and sandbox modeling, while fig. 1 shows a simplified diagram of h-s modeling tools installation. table 1. material variations in h-s modeling and sandbox researcher material type material layer density (gr/cc) material density (gr/cc grain size (µm) k (md) porosity (%) hele-shaw (nermoen et al., 2010) glass granules 1,547 2,460 280±50 120 37,11 oxygen sandbox (sapiie and hadiana, 2007) quartz sand 1,500 250 hele-shaw (rigord et al., 2005) glass granules 1,530 2,190 80-400 and 280±50 26 30,14 water sandbox modification (mazzini et al., 2009) silica granules 50-100 chinese clay low glass granules 118-380 air this research quartz sand 1,500 250-320 mud from the kuwu and kesongo mud volcanoes 1,453 2,560 (dry) 1-50 oxygen wax gypsum <100 208 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 fig. 1: simplify diagram of the main h-s modeling tools installation (a) hele-shaw kit with quartz sand filling; (b) pressure cable with digital pressure record; (c) high-pressure oxygen gas cylinder. the materials used in this experiment were assumed to represent natural material conditions, and the details are outlined below. (1) quartz sand below 250 µm and 320 µm diameter to model layers with high porosity, low cohesiveness, low bearing capacity, assisted by the geodynamic laboratory, geological engineering department, faculty of earth sciences and technology (fitb), bandung institute of technology. (2) gypsum flour was assumed to represent a more ductile layer and was purchased from a chemical store. (3) mud from the kuwu and kesongo mud volcanoes containing different water and material represent the actual material condition in nature. mud from kuwu (sample no b-80) has a composition dominated by smectite, 95% clay grains, and inherent moisture by 11.5%. meanwhile, mud from kesongo (sample no b-81) is more granular, has almost equal kaolinite and illite content, and has a 6% inherent moisture. (4) waxes were obtained from chemical shops and used to create impermeable coatings or insulation. (5) oxygen represents natural fluids as material released during formations to create an overpressured zone for safety reasons and is not adsorbed by granules. 2.3. equipment performance testing this test is necessary to determine the leakage and the h-s equipment's ability to accept pressure, the sensitivity of pressure changes towards the experimental material layers' height variations, and the distance between the glass at the middle and edges. the test measured the pressure at different material layer heights for the same material type from the inlet top end. the material used was loose quartz sand measuring 250 µm with layer height (h) measured from the inlet end ranging between 10 and 40 cm. data recording began with assembling the modeling equipment for this test, as shown in fig. 1. the supporting equipment to be made is outlined below. (1) digital extech 750 (data logger) pressure meter with 200 pa resolution for digital pressure measurement. (2) laptops and software required to record data. (3) camera, with the ability to record 30 frames per second for video recording to record geometry and process the fluidized zone (4) high pressure oxygen gas cylinder (200 kg / cm2). (5) flexible pipe with a size of 4 mm, hole diameter 2.5-3 mm, and able to withstand pressures up to 50 psi along with the connector. (6) bsr software to record and save the data (7) preparation of other supporting tools, including digital scales and rulers. (8) preparation of modeling materials (quartz sand, mud, and wax). in each experiment, the material used was weighed to ease the thickness control, then poured slowly through the funnel from the top to the desired height (h), and measured from the inlet's end. the sand is leveled rather than compacted according to height and made layer by layer as required. subsequently, high oxygen gas pressure was injected into h-s through the inlet. the oxygen flow rate (q) was controlled at a constant flow rate. the valve was opened slowly to avoid turbulence in the material, located near the flow meter, 8 cm away from the gas cylinder. meanwhile, the pressure (p) was recorded at a t-junction, 8 cm away from the inlet, using an extech pressure meter. in this modeling, the gas input was controlled manually, while the pressure variations measurement was carried out automatically by an extech pressure meter. in addition, digital images were recorded at a rate of 30 frames per second with the high-resolution olympus vg-140 camera; 14 megapixels; 5x wide; and optical zoom by 4.7-23.5 mm, and o2 entered slowly, increasing until deformation occurred in the layer above. the pressure in the model increased to form a high pressure or fluidization channel up to 8.5 kpa, before erupting, then reducing to 7.0 kpa. critical phase condition refers to the time of highest pressure before erupting. fig. 2 shows an example of the recording results and the pressure profile. the equipment's test results did not leak, the gas continued to flow, and the distance between the hele-shaw glass wells did not change. meanwhile, the subsequent test measures pressure at various sand heights to test the equipment and material sensitivity. the tool has a sensitivity and readiness to perform further experiments, even with the increase in layer height thickness or pressure. the distance between the glass walls was measured with a caliper to determine the distance stability during the test. the h-s equipment is then suitable for use in cases where there are very small or no changes in distance. fig. 3 shows the test results, and the graph of pressure on material layer height shows a linearly proportional relationship with regression reaching 0.917. this high regression indicates that the hele-shaw model equipment is functioning correctly and sensitive to pressure, with changes in the layer height. the sediment height (h) further increases critical pressure, while the distance between the glass in the middle extended less than 0.02 mm at a 32cm layer height. thus, the change in length is minimal, indicating the glass is strong enough to withstand the material and consequent pressure; therefore, there is no significant volume change in the hele-shaw tool. a b c burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 209 fig. 2: an example of the pressure profile experiment (p) results on the material height measured from the inlet tip to the material layer's surface (h = 17 cm). this figure shows the development of quartz sand behavior during the initial oxygen injection until eruption, from 1s to 26s. the model's pressure increases to form a high pressure or fluidization channel until 8.5 kpa, before the eruption, followed by a reduction to 7.0 kpa. fig. 3: graph of equipment testing. the pressure increases as the layer height (h) get thicker, indicating the equipment did not leak during the experiment and is suitable for modeling. 3. result and discussion 3.1. experiment with material variations this experiment aims to determine the material response to the injection of compressed gas from the bottom. the method replaces the experimental material and records pressure data and a video from the beginning, where oxygen is first injected until an eruption occurs. experiments were conducted on four materials, including 80 µm, 250 µm, and 320 µm size quartz sand, gypsum, and mud from the kesongo and kuwu mud volcanoes. the four materials showed the same response after pressure reached a critical condition by forming pressure and dome structure on the surface (fig. 4). however, the use of mud in this modeling responds differently from the other three materials. the pressure structure and fluidization zone geometric developments are not observable while using mud. the mud material is not used to model the pressure structure geometry in the subsequent stage. 3.2. critical phase characteristics the h-s section's critical pressure pattern and geometric expression are observable in this experiment. based on experiments and observations from the model, the critical pressure phase's characteristics in the h-s model are obtained, as outlined below. (1) the release of small gas and sand eruptions at numerous points, with the gas eruption's position on the surface changing and a fluidization channel visible below the surface. (2) the dome structure found on the experimental layer's surface is associated with a lot of gas seepage. the fluidization zone's position becomes shallower in-depth, increasing to a more superficial level. in the h-s cross-section, fluidization channels are seen by pressurized gas passage fig. 5 illustrates the model characteristics in the critical pressure phase, and these characteristics apply to field and subsurface data in an integrated manner. 210 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 fig. 4: experiment with four types of materials. the result forms the same structure at a critical pressure, a dome structure on the surface. fig. 5: characteristics of a critical phase on the surface. (a) a small gas burst at several points, often with a pressure structure at the bottom. (b) gas seepage next to the sloping dome, resulting from the breakthrough. (c) another example of gas seepage. (d) dome structures on the surface are associated with gas seepage. 3.3. the geometry of pressure structures the development of pressure/piercement structures has been tested in three materials, 250 µm and 320 µm quartz sand and gypsum. fig. 6. a to l show the development from initial conditions to eruption in the three materials. the pressure structure's detailed geometry for the three materials shows a consistent pattern development, with differences in the fault and pressure structures' densities and widths. therefore, structure intensity is tighter in finer gypsum and quartz sand (250 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 211 µm). in gypsum material, a fan-like structure tends to develop and occur in more than one fluidizing channel. repeated experiments were carried out by recording from the start of oxygen injection to material extraction to determine the pressure structure's consistency. furthermore, a description consistent with the presence of a positive pressure structure similar to a "positive flower structure" was obtained. fig. 6: fault geometry variations of piercement structure in eruption and post-eruption models for various experimental materials. (a, b, and c) fault geometry in 320 µm quartz sand. (d, e, and f) fault geometry in 250 µm quartz sand. (g, h, and i) fault geometry in gypsum. (j, k, and l) show details of fault geometry patterns in each material. surface subsidence occurs after the eruption but remains an overpressured zone in the deep zone. 3.4. validation of seismic interpretation with heleshaw model the validation model was performed using a modeling scale of 1 cm representing 100 meters. the thickest sediment in kradenan is 3,000 m (burhannudinnur, 2012); however, the sidoarjo counterpart is not obtainable from seismic data but was estimated to be over 4,000 m from the region to 15,000 feet (kusumastuti et al., 1999; burhannudinnur et al., 2012). in addition, the material layer height measured from the top of the inlet is 30 cm. heleshaw modeling is basically vertical and close to 2d, however, in this experiment, a lateral scaling referring to sandbox modeling, where 1 cm = 1 km was used, and the length of 100 cm represents a route passing through kradenan or sidoarjo areas (40-70 km). validation of valve fault geometry in sidoarjo is represented by xx-07 (fig. 7) and xx-126 (fig. 8) seismic lines. fig. 7 shows the main fault in green. the main faults develop into small ones while cutting the strong reflection, forming a pattern similar to a small fan's radius. the seismic reflection forms a positive curve as a pressure structure. according to fig. 7, the seismic section's fault and pressure structure show similar geometries and patterns compared to the geometry of the modeling results. meanwhile, fig. 8 shows the seismic interpretation's validation, using an analog model with hele-shaw in the sidoarjo area, for random reflection patterns and pressure structures similar to shear fault geometry with positive flower structure geometry. the formation of seismic pressure structure in the kradenan area was selected by two routes, xx-08, under banjarlor and cangkringan (fig. 9), and xx-09 (fig. 10), under crewek. fig. 9 shows a vertical channel with random characters, representing a mud material supply channel and a pressure structure, closely similar to the h-s model. also, the xx-09 seismic line through the crewek mud volcano is highly similar and a fitting representation of the seismic and model from hele-shaw. 212 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 fig. 7: (a) valve fault in seismic data xx-07, sidoarjo. (b) valve faults in h-s models. the upward pressure pattern obtained by pushing/piercing the material through the main fault causes a series of valve faults. minor faults are closely similar between seismic and h-s models. the pressure migration causes a new valve structure above other points (green circles) occurring in models and seismic. fig. 8 (a): fault's development on the is possibly modeled with h-s. (b) interpreted seismic w-e banjarpanji-1 well ((tingay, 2014)). (c) valve fault geometry/piercement structure around bjp-1. (d) interpreted seismic data s-n bjp-1well (sawolo et al., 2009). burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 213 fig. 9: (a) mud volcano system at madura offshore (istadi et al., 2012). (b) mud volcano system in h-s model. (c) seismic line xx-08 onshore seismic around mv. kuwu, east java. they have a similar structural pattern, vertical plumbing from random reflection with dome or pressure structures at the top, bounded by main faults. fig. 10: the interpreted seismic passing xx-12 (a) through the crewek mud volcano shows seismic's random zones matching the h-s model geometry (b, c red box). 214 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 3.5. h-s modeling of overpressure materials lateral movement h-s lateral movement modeling aims to understand the occurrence of lateral migration of overpressured materials. the initial condition of the model is to make two inlets; the first inlet is at the bottom of the model, while the second is on the side of the sealing layer above the overpressured layer. this second inlet represents a minor fault as a migration path. the position of the minor fault (second inlet) has an impermeable layer above the porous layer 12 cm from the projection of the first inlet. based on the results, after being injected with oxygen, the quartz sand layer under the sealing layer slowly forms an overpressured zone between the quartz sand and wax layers. furthermore, the push or flow changes upward and moves sideways until a small fault is found. these faults in the sealing layer become channels for the overpressure material to rise and push upward, forming valve faults and pressure structures, then moving and extruding to the surface (fig. 11). lateral movement is also caused by compacting differences in the same material layer. fig. 12. b shows the difference of gypsum compaction at the middle and edges, causing the gas not to penetrate sideways, then upwards, rather than vertically. lateral movement of material with overpressure in nature also occurs under the surface. for instance, the seismic route xx-10 passes through kesongo mud volcano, and in the ngimbang formation, overpressure and connection by faults form the kesongo mud volcano on the surface. this fault also acts as an overpressure migration route into the zone above. meanwhile, the tawun formation forms a large overpressure zone, reaching 7 km below the younger formation sealing layer. in the tawun formation, the overpressure zone is characterized by a random and blurry reflection pattern, forming an irregular geometry similar to a chamber or pocket. another distinctive feature is the presence of vbright around the channel and minor faults and polygonal faults in the tawun formation outside the reflection pattern random geometry (fig. 13). according to fig. 14, the hele-shaw modeling confirms overpressure conditions are spread under the sealing layer before finding faults or fractures or moving forward in search of a weaker zone. the presence of an overpressured zone in the ngimbang formation from random seismic reflection data supports the existence of fossil data from rock fragments with oligocene ages, and this age is in accordance with the ngimbang-kujung formation. also, the main faults serving as the material supply channel are seen in the seismic data of mud volcanoes and are supported by petrographic data of rock fragments with scour, micro folding, and stylolite structures, showing strongly deformed rock samples. fig. 11: (a) initial model of h-s sand layer sealing layer insert (green wax), minor fault as the second inlet, with h22 cm. (b-e) highpressure gas penetrates the layer below. (f, g) the gas presses move sideways and concentrate under the seal. (h) the gas penetrates minor faults, second inlet. (i) fluidization in the second inlet. burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 215 fig. 12: (a) detailed figure of the movement of the overpressure material. (b) overpressured material moves along weak zones, even in a homogeneous material (gypsum), probably controlled by differences in gypsum compaction at the middle and edges. fig. 13: (a) seismic cross-section, random reflection channel pattern, v-bright, and random/chaotic reflection. (b) velocity interval section, white is the lowest velocity while red-purple are high velocity (burhannudinnur et al., 2021) 216 burhannudinnur, m. et al./ jgeet vol 6 no 4/2021 fig. 14: the high-pressure zone h-s model pushes the sealing layer (thick mud) upward forms an anticline structure at the bottom seal layer. the model shows the high-pressure layer unable to break through the seal, h = 30 cm, at p = 17 kpa (2.5 psi). 4. conclusion the critical phase and the pressure structure pattern characteristics are shown in the dome structure pattern as the fluidization zone becomes shallower than the source. each material's pressure structure geometry shows a consistent pattern, with differences in only the fault and pressure structure densities. in addition, the h-s experiment's validation with seismic interpretation shows the same geometry in the form of pressure structures and valve faults as a migration path from the mud volcano system. the valve's geometry and fault pattern are only observable in quartz or gypsum sand, but not the mud. thus, h-s modeling is suitable for validating the fan-like fault structure's geometric pattern in a mud volcano system at seismic. acknowledgments acknowledgments are addressed to the department of geological engineering, ftke trisakti university, and the authors' colleagues who cannot be mentioned one by one who has provided input and discussions, pt. pertamina ep for the research permission, all parties who helped in this research. references burhannudinnur, m., 2020. the potentials prediction of kradenan and kesongo mud volcano systems in east java. int. j. adv. sci. technol. 29, 533–5 41. burhannudinnur, m., 2019. mud gas play. j. phys. conf. ser. 1402, 66022. https://doi.org/10.1088/17426596/1402/6/066022 burhannudinnur, m., 2012. komplek mud volcano kradenan, in: proceeding pit iagi yogyakarta 2012 the 41st iagi annual convention and exhibition. pp. 207–2011. burhannudinnur, m., karyono., sudradjat, a., 2021. gunung lumpur dan fenomena lumpur sidoarjo, pertama. ed. cv. galeripadi, jakarta/bandung. burhannudinnur, m., noeradi, d., sapiie, b., abdassah, d., 2012. karakater mud volcano di jawa timur, in: proceeding pit iagi yogyakarta 2012 the 41st iagi annual convention and exhibition. pp. 201–206. istadi, b.p., wibowo, h.t., sunardi, e., hadi, s., sawolo, n., 2012. mud volcano and its evolution, in: imran ahmad dar (ed.), earth sciences. intech, pp. 375– 434. https://doi.org/10.5772/24944 johnsen, ø., toussaint, r., måløy, k.j., flekkøy, e.g.f., shmittbuhl, f., 2008. coupled air/granular flow in a linear hele-shaw cell. phys. rev. e. stat. nonlin. soft matter phys. 77 1 pt 1, 011301. https://doi.org/ 10.1103/physreve.77.011301 kusumastuti, a., darmoyo, a.b., suwarlan, w., sosromihardjo, s.p.c., 1999. the wunut field: pleistocene volcaniclastic gas sands in east java, in: proceedings of the 27th annual convention of the indonesian petroleumassociation and exhibition. indonesian petroleum association, jakarta, pp. 195– 215. letouzey, j., werner, p., marty, a., 1990. fault reactivation and structural inversion. backarc and intraplate compressive deformations. example of the eastern sunda shelf (indonesia). tectonophysic 183, 341– 362.https://doi.org/10.1016/0040-1951(90) 90425-8 mazzini, a., nermoen, a., krotkiewski, m., podladchikov, y., planke, s., svensen, h., 2009. strike-slip faulting as a trigger mechanism for overpressure release through piercement structures. implications for the lusi mud volcano, indonesia. mar. pet. geol. 26, 1751–1765. https://doi.org/10.1016/j.marpetgeo.2009.03.001 nermoen, a., galland, o., jettestuen, e., fristad, k., podladchikov, y., svensen, h., malthe-sorenssen, a., 2010. experimental and analytic modeling of piercement structures. j. geophys. res. solid earth 115, 1–15. https://doi.org/10.1029/2010jb007583 rigord, p., guarino, a., vidal, v., géminard, j., 2005. localized instability of a granular layer submitted to an ascending liquid flow. granul. matter 7, 191–197. https://doi.org/10.1007/s10035-005-0214-1 sapiie, b., hadiana, m., 2007. mechanism of some rift basins in western indonesia, in: proceedings of 31st annual convention of the indonesian petroleumassociation and exhibition. indonesian petroleum association, jakarta. satyana, a.h., asnidar, 2008. mud diapirs and mud volcanoes in depressions of java to madura: origins, natures, and implications to petroleum system, in: proceedings of 32nd annual convention of the indonesian petroleumassociation and exhibition. indonesian petroleum association, jakarta. sawolo, n., sutriono, e., istadi, b.p., darmoyo, a.b., 2009. the lusi mud volcano triggering controversy: was it caused by drilling? mar. pet. geol. 26, 1766–1784. talbot, c.j., 1995. molding of salt diapirs by stiff overburden, in: jackson, mps; roberts, dg; snelson, s. (ed.), salt tectonics: a global perspective: aapg memoir 65. the american association of petroleum geologists, pp. 61–75. tingay, m., 2014. initial pore pressures under the lusi mud volcano, indonesia. interpretation 3, se33–se49. https://doi.org/10.1190/int-2014-0092.1 © 2021 journal of geoscience, engineering, environment, and technology. all rights reserved. this is an open-access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). about:blank about:blank about:blank e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 1 2022 marin, j. et al./ jgeet vol 7 no 1/2022 27 research article characteristics of kedondong trass and bobos trass as cement raw material, cirebon, west java, indonesia jenian marin1,*, tri winarno1, shofiana nadia fairuz1 1 department of geological engineering, diponegoro university, jl. prof. soedarto, sh, tembalang, semarang, jawa tengah, indone sia * corresponding author : jenianmarin@gmail.com tel.:+62-82-116-548-503 received: nov 26, 2021; accepted: mar 30, 2022. doi: 10.25299/jgeet.2022.7.1.8180 abstract the use of cement materials in construction continues to increase every year, consumes lots of raw material and emits co 2 from clinker production. to eliminate this negative effect, alternative materials are needed. trass is natural pozzolan which is formed from silica-alumina rich volcanic rocks. as supplementary cementitious material, trass is sufficiently durable and reduce clinker proportion in cement mixture, thus more environmentally friendly. this research aims to determine characteristics and composition of kedondong trass and bobos trass, cirebon, west java as raw material for pozzolan cement. the study was conducted using petrography and xrd analysis to determine mineralogy of rocks. xrf analysis was carried out to determine chemical composition as well as other tests to determine trass quality. kedondong trass is originated from andesite intrusion and andesitic breccia, while bobos trass is formed from hyperstheneandesite intrusion. based on mineralogy analysis, trasses have similar mineral composition consist of plagioclase, quartz, pyroxene, hornblende, and sanidine. xrd analysis shows abundance of cristobalite and tridymite from each samples. this mineralogy is confirmed by geochemistry result, which is the samples contain more than 70% sio2 + al2o3 and less than 4% so3. other chemical characteristics that have been tested are moisture content, ignition loss, and clay content in which all of those parameters meet the industrial standard for cement material. keywords: trass, supplementary cementitious material (scm), pozzolanic cement, cirebon 1. introduction cement production in indonesia has dubbed to be one of the largest in the world. by the last decade, domestic sales is consistently rising every year to fulfill demand from development of national infrastructures.the highest growth is in 2011, which was 17.7% with volume of 48 million tons. later, local and multinational cement producers are expanding their production capacity (asosiasi semen indonesia, 2018). regular portland cement production has massive carbon footprint which significantly contribute to climate change. more than 4 billion tonnes of cement manufactured each year emits for around 8% of the world’s co2 emissions (lehne and preston, 2018). this high emissions is linked to the clinker production, a mixture of raw materials fused together by heat, for the main ingredient of cement. clinker is a product of chemical conversion called calcination in which limestone (caco3) is converted to lime (cao). during its process, co2 is released in the kiln at 600 – 900 c (gibbs et al., 2001) as follows: caco3 + heat  cao + co2……………. (1) natural pozzolans can be used as clinker substitution in cement blends because its cementitious properties, known as pozzolanic activity. pozzolan is defined as siliceous and aluminous materials that has little to no cementitious properties on its own, but when finely grounded and combined with calcium hydroxide in water, it has ability of hydraulic binding (çullu et al., 2016). benefit of pozzolans including low heat of hydration, high strength, low permeability, and low alkaline-silica reaction. mineral deposits with pozzolanic rocks of volcanic origin, particularly pyroclastic materials from explosive eruption possess pozzolanic properties without extensive processing. trass is one of variety of volcanic ash which possesses pozzolanic properties. as a volcanic active regions, indonesia is rich in volcanic rocks which some of these are already used as natural pozzolan in national’s cement industry. one of national cement manufacturer operate in the study area (fig.1) at palimanan, cirebon regency, west java, produced ordinary portland cement and pozzolanic cement. by local people, natural pozzolans in the study area is more commonly referred to as trass. kedondong and bobos are two quarries location used by the manufacturer, hence the name, kedondong trass and bobos trass. aims of this study is to provide information on trass characteristics and its prospect in this country as supplementary cementitious materials (scm). 2. geological setting study area is part of bogor zone physiography, a neogene sedimentary sequences intruded by many volcanic rocks, now is a strongly folded anticlinorium (satyana et al., 2002; van bemmelen, 1949). rock formations in the study area is mainly dominated by 28 marin, j. et al./ jgeet vol 7 no 1/2022 plio-pleistocene volcanic rocks on top of miocenepliocene marine sediments (fig.1). kromong limestone consists of miocene reef limestone complex in the northern part of study area, which is the main material for cement. kaliwangu formation is pliocene marine sediments rich in molluscs, consist of shale intercalated with sand and gravel. on top of those, plio-pleistocene volcanic rocks are andesitic-tuffaceous kromong breccia, undifferentiated volcanic rocks, and andesite intrusions (aswan et al., 2013; djuri, 1995; jambak et al., 2015). fig 1. location and regional geology map of study area 3. methodology 3.1 research methods from geological map, the two locations have different rock type in which kedondong trass is originated from kromong breccia while bobos trass is originated from andesite intrusion. samples were obtained directly in the field from existing quarries of two locations, 9 samples from kedondong and 10 samples from bobos. laboratory analysis were carried out to determine characteristics of trass as follows: a. thin section samples were prepared to identify mineralogical and petrographical characteristics under polarizing microscope. both fresh rock and altered rock samples were used to compare this aspect. b. x-ray diffraction (xrd) analysis of powdered bulk samples was conducted to determine whether silica minerals were present in trass. this is to accomodate one of requirement in which trass must contain crystalline silica such as tridymite and cristobalite. geochemistry of samples were determined using x-ray fluorescence (xrf) analysis, most importantly to identify some of the major elements comprising sio2, al2o3, fe2o3, cao, mgo, na2o, k2o, and so3. c. moisture content was determined by weighing 100 gr of samples before and after drying 1-2 hours in the oven. for loss on ignition parameter: 1 gr of finely ground samples was heated in the crucible at 500°c for 30 minutes. followed by igniting the samples in the furnace of 1000°c for 1 hour. after being cooled in the dessicator, samples are weighed again. d. clay content was determined by adsorption test: mixing 5 gr of finely ground samples 25 ml aquades using magnetic stirrer for 5 minutes, and then adding 2 ml methylene blue. clay particle will react and adsorbed by methylene blue. stain test on filter paper was conducted until a light blue halo showed in the paper by adding more methylene blue, that means all clay was adsorbed (chiappone et al., 2004). the more methylene blue is added to show the blue halo, the higher is clay content in the samples. 3.2 specifications of trass the intrinsic capacity of pozzolans is depend of chemical composition, which is varies greatly in volcanic deposits (yu et al., 2017). after chemical criteria meets the requirement, most raw materials need to be processed to meets the physical criteria such as fineness, moisture, and strength (sleep and masley, 2018). american standard for testing materials (astm) c618-94a 1993 (astm, 1993) specifies standard chemical composition of raw and calcined natural pozzolans for use in concrete as shown by table 1. according to national standard of sni-04-1989-f (badan standardisasi nasional, 1989), trass can be used sources: dem srtm of cirebon (usgs, 2020) regional geology map (djuri, 1995) datum utm wgs 1984 zone 48 s marin, j. et al./ jgeet vol 7 no 1/2022 29 in light construction with several requirements based on building classes (table 2.). trass commonly used for portland pozzolan cement (ppc) mixture, concrete, plastering, or brick mixture. table 1. astm c618-94a 1993 for natural pozzolans. chemical compound wt % range sio2 40.76 – 56.20 al2o3 17.35 – 27.95 fe2o3 7.35 – 13.15 h2o 3.35 – 10.70 cao 0.82 – 10.27 mgo 1.95 – 8.05 sio2 + al2o3 minimum 70.0% so3 maximum 4.0% na2o maximum 1.5% moisture content maximum 3.0% loss in ignition maximum 10.0% table 2. trass requirement from sni-04-1989-f requirement class 1 class ii class iii 1. free moisture at 110°c in wt% < 6 6-8 8-10 2. fineness (% maximum of particle larger than 0,21 mm) < 10 10-30 30-50 3. maximum binding time in days 1 2 3 4. compressive strength after 14 days (kgf/cm2) 100 100-75 75-50 based on astm and sni standard, pt. indocement tunggal prakarsa tbk at palimanan unit establishes a modified standard parameter of trass for its manufacture as shown by table 3. to meet the standard several samples of trass must go through chemical and physical analysis such as xrf analysis, moisture, loss on ignition, and clay content. xrd analysis is also conducted to make sure any crystalline silica presents in trass samples. table 3. trass quality requirement in pt. indocement tunggal prakarsa tbk palimanan unit parameter requirement 1. total sio2 + al2o3 minimum 70.0 wt. % 2. so3 maximum 4.0% 3. moisture 1% – 5.6% 4. loss on ignition maximum 10% 5. clay content maximum 5% 6. silica must be present (tridymite, cristobalite) 5. results 5.1 lithology of the quarries lithology observed in the field from the two quarry are slightly different as expected by regional geology map. kedondong quarry which from regional geology map is part of kromong breccia, is covered by two type of andesitic rocks (fig.2). the first one is andesitic breccia which characterized by moderately weathered, brownish color, cobble-pebble sized andesite fragment inside tuffaceous matrix. this breccia is intruded by dark-grey andesite which formed a morphologically distinctive intrusion hill than its surroundings. andesite has sheeting joint structure, intensively weathered with some fresh andesite still present, composed by plagioclase and hornblende phenocryst in fine grained groundmass. fig 2. lithology found in kedondong quarry fig 3. weathered hypersthene-andesite in bobos quarry n n n 30 marin, j. et al./ jgeet vol 7 no 1/2022 bobos quarry located in volcanic hills morphology and identified as andesite intrusion from regional geology map. from the quarry observation, we also found fine grained hypersthene-andesite which consistent to the reference. exposed rocks also exhibit moderately to highly weathered condition, resulted in softer and yellowish rocks (fig.3). dominant phenocryst is plagioclase with pyroxene accessory in aphanitic groundmass. in both location, the degree of weathering greatly changes original texture, structure, and overall appearance of rocks even though the fresh rocks are still present to be observed. beside of original rock composition, this process is important to bring in pozzolanic properties of trass deposits. 5.2 mineralogy and petrography of rocks mineralogy is inspected by thin section observation of samples from both locations. while both kedondong and bobos have similar composition of andesitic rocks, there is slightly difference in mineralogical and petrographical aspect as shown by table 4. both rocks are composed of plagioclase as dominant phenocryst (40-50%), pyroxene, hornblende, quartz, and opaque mineral. the fragments have similar composition with andesite from intrusion. bobos andesite contains more pyroxene (hypersthene) and less glassy groundmass (fig.6). other than fresh hand specimens, altered samples were also being inspected through thin section, showing leached texture, altered rim in some phenocryst, and finer groundmass in all rocks. kedondong andesite has less phenocryst and more glassy groundmass than bobos andesite (fig,4). meanwhile, thin section of andesitic breccia from kedondong shows abundant volcanic glass matrix, along with minor fine grained crystal and opaque mineral surround the andesitic fragments (fig.5). table 4. mineralogy of rocks from kedondong and bobos samples mineral content characteristics kedondong andesite plagioclase (labradorite), hornblende, pyroxene, quartz, opaque minerals porphyritic texture, glassy groundmass andesitic breccia volcanic glass, plagioclase, quartz, opaque mineral, hornblende tuff as dominant matrix supporting andesite fragments bobos hyperstheneandesite plagioclase (labradorite), orthopyroxene, hornbende, quartz, opaque mineral porphyritic texture, little to no glassy groundmass fig 5. thin section of matrix part from kedondong’s andesitic breccia: (a) plane polarized and (b) cross polarized fig 6. thin section of bobos andesite: (a) plane polarized and (b) cross polarized (pl : plagioclase, qz : quartz (i10), hb : hornblende (b10), op : orthopyroxene (h5)) 0 0,5 mm 0 0,5 mm marin, j. et al./ jgeet vol 7 no 1/2022 31 5.3 trass mineralogy the result from petrographical analysis is supported by xrd analysis of powdered bulk sample, as summarized by table 5. all of the samples show r-wp less than 10% which are considered good and fit (toby, 2021). although there are two different rocks in kedondong, they are regarded as one because in this section, we are focusing on trass characteristics which is the main commodity of the quarry. according to the xrd analysis, trass samples from both quarry contain quartz, plagioclase, kaolinite, sanidine, tridymite, cristobalite, and hematite. tridymite and cristobalite are crystalline silica which are important to contribute pozzolanic activity. kedondong trass contains 0.67% 9.42% tridymite and 6.0% 20.26% cristobalite. at kedondong quarry, samples from breccia have higher quartz content but lower in other silica. andesite samples are relatively more weathered than breccias, so it is related to the lower abundance of quartz as resistant mineral. bobos trass contains 0.8% – 2.52% tridymite and 0.2% 5.36% cristobalite. the abundance of crystalline silica is differ significantly, where kedondong trass are higher in tridymite and cristobalite than bobos samples. this might be correspond with higher percentage of groundmass in kedondong rocks as shown by petrographical analysis. kaolinite as alteration product also present, in which kedondong trass also contains at higher percentage than bobos trass. table 5. test results of xrd analysis from kedondong and bobos trasses (in percent) table 6. test results of geochemistry analysis using xrf method from kedondong and bobos trasses code moisture content (%) loi (%) clay content (%) major oxides (wt%) sio2 al2o3 fe2o3 cao mgo na2o k2o so3 sio2 + al2o3 kedondong kd 1 10.80 3.26 4.4 69.69 15.84 3.39 3.37 0.00 2.97 1.41 0.024 85.5 kd 2 13.62 3.20 3.0 68.44 15.9 3.61 3.6 0.17 3.01 1.44 0.022 84.3 kd 3 4.15 2.88 2.5 71.67 15.91 3.15 2.98 0.00 3.08 1.57 0.023 87.6 kd 4 1.58 2.27 2.6 70.88 15.06 3.39 3.69 0.00 3.17 1.46 0.020 85.9 kd 5 2.83 1.88 1.6 71.21 15.04 3.25 3.77 0.06 3.37 1.48 0.021 86.3 kd 6 4.77 2.50 2.0 71.15 15.43 3.30 3.45 0.00 3.25 1.45 0.018 86.6 kd 7 3.09 1.74 1.2 71.81 15.43 3.00 3.51 0.00 3.32 1.50 0.020 87.2 kd 8 2.80 2.19 1.6 71.24 15.34 3.32 3.47 0.02 3.20 1.48 0.032 86.5 kd 9 4.08 2.68 1.4 69.67 15.82 3.32 3.69 0.00 3.11 1.54 0.026 85.5 bobos sls b1 5.05 4.37 1.6 70.52 15.12 3.03 3.60 0.39 2.99 1.55 0.037 85.6 sls b2 6.55 5.05 2.0 70.86 15.77 2.89 3.62 0.00 3.35 1.65 0.037 86.6 sls b3 12.8 2.68 4.6 68.21 16.10 3.17 3.05 0.28 2.66 1.59 0.035 84.8 sls b4 4.77 2.61 2.5 70.44 15.19 3.24 3.52 0.07 3.38 1.62 0.034 85.6 b2 1.14 1.63 1.4 69.47 14.86 2.91 4.56 0.37 3.58 1.59 0.036 84.0 b3 0.93 2.6 1.2 68.75 14.76 2.61 3.69 0.00 3.57 1.57 0.028 83.0 b4 1.60 1.03 1.4 71.87 15.23 2.97 3.28 0.38 3.69 1.59 0.011 87.0 b5 4.62 2.77 2.6 70.95 15.42 3.28 2.99 0.28 3.07 1.59 0.007 86.3 b6 1.68 1.57 1.8 70.67 15.02 2.94 3.67 0.34 3.55 1.60 0.025 85.6 code r-wp* quartz sanidine plagioclase kaolinite tridymite cristobalite hematite kedondong kd 1 6.86 26.48 20.17 40.55 5.37 0.84 5.73 0.86 kd 2 6.34 26.75 20.75 40.65 4.91 0.93 5.60 0.41 kd 3 6.68 25.88 20.17 41.70 5.65 0.67 5.53 0.40 kd 4 7.67 0.06 12.30 52.38 7.94 8.42 18.70 0.20 kd 5 7.92 0.55 14.35 56.73 2.64 5.47 20.05 0.21 kd 6 7.40 0.33 17.39 53.29 3.43 7.59 17.61 0.36 kd 7 8.05 0.21 17.84 49.24 5.35 8.55 18.17 0.65 kd 8 9.06 0.42 17.36 46.80 8.79 9.4 16.92 0.32 kd 9 7.58 0.19 15.62 46.60 10.57 6.81 19.80 0.41 bobos sls b1 6.69 28.95 21.01 42.6 2.83 1.48 3.13 0.13 sls b2 6.39 30.80 20.90 42.64 1.84 0.80 3.02 0.65 sls b3 5.48 30.87 21.21 31.18 14.31 1.26 1.17 0.13 sls b4 6.94 27.97 20.38 47.24 0.31 1.30 2.80 0.28 b2 8.07 23.16 20.94 47.51 0.56 2.52 5.31 0.08 b3 7.93 31.55 20.71 45.60 0.46 1.38 0.30 0.20 b4 7.21 23.89 21.66 46.82 0.16 2.30 5.17 0.11 b5 6.28 33.46 20.47 42.25 2.74 0.94 0.14 0.09 b6 6.83 24.26 20.92 47.67 0.20 1.59 5.36 0.11 32 marin, j. et al./ jgeet vol 7 no 1/2022 5.4 chemical properties of trass in the quarries, trasses have a variation of physical appearance that rather different than fresh rocks. kedondong trass still contains fine-medium grained minerals between highly weathered groundmass. bobos trass has finer mineral grains but relatively more compact than kedondong trass. chemical properties have been analysed from 18 samples as summarized by table 6. result of water content analysis showed that most of samples contain less than 5.6% moisture within the standard criteria, with the exception 4 samples have 6.55%-13.62% moisture. this high moisture results might be correlated with weather, sampling, and preparation technique as the sampling was conducted in january when rainfall is quite high. loss on ignition (loi) of samples ranges between 1.57% 5.05% which is also meet the standard. clay content in trass samples is determined by adsorption test using methylene blue. the result showed range of 0.4% 4.6% clay content among the samples. the standard trass has less than 5% clay content. geochemistry have been analysed from 18 powdered bulk samples using xrf method. all samples have no striking difference chemistry as follows: sio2 as highest compound at 68.21% 71.81% and al2o3 at 14.76% 16.10%, that make the sum of silica and alumina constituent at about 83.0% 87.58%. so3 as one of quality parameter is present at very small amount of 0.007% 0.037%. the chemical analysis shown the sum of sio2 + al2o3 > 70% and so3 content < 4%. this result is within the standard of chemistry criteria from astm and the manufacturer. 6. quality of trass as scm kedondong trass and bobos trass have been used as supplementary cementitious material by pt. indocement tunggal prakarsa tbk palimanan unit. bobos quarry located farther than kedondong quarry from the production facility. lithology of kedondong quarry are andesitic breccia and andesite intrusion, composed of minerals such as plagioclase, quartz, pyroxene, and hornblende with abundant volcanic ash/glass. bobos’ hypersthene-andesite intrusion contains less volcanic glass due to the abundance of crystals. volcanic glass is a highly reactive, unstable, and vulnerable to alteration. this alteration activates pozzolanic properties in material (montanheiro et al., 2004). tridymite and cristobalite are crystalline silica detected by xrd analysis in all trass samples. the presence of silica is also required as a condition that material has pozzolanic activity (waani and elisabeth, 2017). nearly all results from chemical test of trass samples are within the company standard and astm standard as well. as natural pozzolans, kedondong and bobos trass contain 83% 87% silica and alumina originated from intermediate volcanic rocks. in addition to durability aspect, silica and alumina compounds are responsible for reacting with hydroxides to produce calcium silica hydrate (c-sh).this byproduct of water and cement reaction is a strong binding agent which desired in the mixture (sleep and masley, 2018). generally, the higher sio2 in natural pozzolans, the better pozzolanic activity (çavdar and yetgin, 2007). sulfur trioxide in trass samples is far below the maximum threshold standard of 4%. moisture content, loi, and clay content also conform to the standards of trass. based of all chemical requirement, kedondong and bobos trass can be used as one of the cementitious material to reduce clinker. conclusions kedondong trass and bobos trass are originated from andesitic breccia and andesite intrusion, product of intermediate volcanic activity. rock composition shows abundant volcanic glass and silica as pozzolanic agent. trass samples have been tested chemically including silica+alumina content, sulphur trioxide content, moisture content, loi, and clay content. the results are meet the company and astm standard for supplementary cementitious material. while all of chemical requirements are within standard, it is recommended to test the physical requirement which correspond to pozzolanic properties such as fineness and compressive strength. acknowledgements the authors want to thank to universitas diponegoro, especially to faculty of engineering that has been supported the research fund and the opportunity given to publish the manuscript. the author also thank the support of pt. indocement tunggal prakarsa tbk. references asosiasi semen indonesia, 2018. cement industry in indonesia. asi a glance. url https://asi.or.id/asi-at-a-glance/ (accessed 9.2.21). astm, 1993. standard specification for fly ash and raw calcined natural pozzolan for use as a mineral admixture in portland cement concrete, in: annual book of astm standards: construction vol.04.02 concrete and aggregates. astm, philadelphia. aswan, a., rijani, s., riza, y., 2013. shell bed identification of kaliwangu formation and its sedimentary cycle significance, sumedang, west java. indones. j. geosci. 8. https://doi.org/10.17014/ijog.v8i1.151 badan standardisasi nasional, 1989. sni s-04-1989-f: spesifikasi bahan bangunan bagian a, bahan bangunan bukan logam. jakarta. çavdar, a., yetgin, ş., 2007. availability of tuffs from northeast of turkey as natural pozzolan on cement, some chemical and mechanical relationships. constr. build. mater. 21. https://doi.org/10.1016/j.conbuildmat.2006.0 5.034 chiappone, a., marello, s., scavia, c., setti, m., 2004. clay mineral characterization through the methylene blue test: comparison with other experimental techniques and applications of the method. can. geotech. j. 41. https://doi.org/10.1139/t04060 çullu, m., bolat, h., vural, a., tuncer, e., 2016. investigation of pozzolanic activity of volcanic rocks from the northeast of the black sea. sci. eng. compos. mater. 23. https://doi.org/10.1515/secm-2014-0092 djuri, m., 1995. peta geologi regional lembar arjawinangun jawa barat. bandung. marin, j. et al./ jgeet vol 7 no 1/2022 33 jambak, m.a., syafri, i., isnaniawardhani, v., benyamin, rodriguez, h., 2015. facies and diagenetic level of the upper cibulakan and parigi formation, in randegan and palimanan area. indones. j. geosci. 2. https://doi.org/10.17014/ijog.2.3.157-166 lehne, j., preston, f., 2018. making concrete change: innovation in low-carbon cement and concrete. url https://www.chathamhouse.org/2018/06/mak ing-concrete-change-innovation-low-carboncement-and-concrete (accessed 11.10.21). montanheiro, t.j., yamamoto, j.k., kihara, y., 2004. serra geral formation são paulo state, brazil: a potential source for natural pozzolans. mater. lett. 58. https://doi.org/10.1016/j.matlet.2003.06.015 satyana, a.h., armandita, c., raharjo, b., syafri, i., 2002. new observations on the evolution of the bogor basin , west java : opportunities for turbidite hydrocarbon play. bul. geol. inst. teknol. bandung – ed. khusus 42 tahun pengabdi. prof. dr. soejono martodjojo, m.sc. dep. tek. geol. fiktm, itb, bandung, 2002. sleep, m.d., masley, m.d., 2018. the use of mt. mazama volcanic ash as natural pozzolans for sustainable oil and unpaved road improvement. portland. https://doi.org/10.15760/trec.202 toby, b.h., 2021. r factors in reietveld analysis: how good is good enough? powder diffr. 21. https://doi.org/10.1154/1.2179804 van bemmelen, r.w., 1949. the geology of indonesia. vol.ia: general geology of indonesia and adjacent archipelagoes. government printing house, the hague, netherlands. waani, j.e., elisabeth, l., 2017. substitusi material pozolan terhadap semen pada kinerja campuran semen. . j. tek. sipil 24. https://doi.org/10.5614/jts.2017.24.3.7 yu, l., li, l., zhou, s., 2017. evaluation of pozzolanic activity of volcanic tuffs from tibet, china. adv. cem. res. 29. https://doi.org/10.1680/jadcr.15.00075 © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 03 no 01 2018 harinder, d & shankar s./ jgeet vol 03 no 01/2018 1 experimental study to reinforce the weak subgrade soil for low-volume roads by coir geotextile mats d harinder 1 *, s. shankar 2 1 national institute of technology, warangal, india. * corresponding author: hariatnitw@gmail.com tel.:+918106857040 received: nov 08, 2017. revised : feb 15, 2018, accepted: feb 26, 2018, published: 1 march 2018 doi: 10.24273/jgeet.2018.3.01.882 abstract the construction and maintenance of pavement over the weak subgrade soil become the challenging task to the pavement engineering. one of the major reasons of subgrade failure of pavement is weak subgrade. the weak subgrade soil noticed a black cotton (bc) soil. the bc soil subgrade poses several serious problems to the pavement such as rutting, fatigue, reflecting crack and undulation of the pavement. to minimize this problem of pavement, there are many conventional stabilization techniques were adopted and reported. but these techniques are not applied effectively into the pavement to stabilize the weak subgrade. to address this problem, to give the additional strength to the pavement geosynthetics are taken as alternate material for stabilization of pavement. in the present study, an attempt is made in the laboratory with four types of coir mats by using the fabricated mould. the study is conducted in the form of two-layer pavement system. the pavement model layer is prepared as subgrade and sub-base with bc soil and sandy gravel soil respectively. the prepared fabricated mould is tested by using the wheel tracking test (wtt) under moving traffic loading condition. this study concluded that the suitable placement position and the types of coir mats can be affect the suitable coir mats can effectively reduce the deformation, so that it can be used over the weak subgrade to improve the performance of the lvrs. keywords: coir mats, reinforcement, separation, subgrade, sub-base, wtt. 1. introduction the performance of the roads largely depends on the properties and types of soil for the construction pavement. the larger numbers of factors are affecting the service life and maintenance of the pavement. this includes the environmental factors, traffic loading, ageing and occupied in large area of the country. the bc soil subgrade poses several problems to the roads in the form of rutting, fatigue, reflecting, and uneven or undulation in pavement structure. in this case, particularly the replacement of subgrade soil or to stable the weak subgrade is necessary to provide the stable pavement. but due to local constraint, the adoptions of both the techniques are unsuitable. in a particular case, alternate, past construction and stable locally available materials become necessary in pavement engineering. in view of the above consideration, an alternate material such as geosynthetics are used in pavement application to provide the additional strength and improve the performance of the weak subgrade. the use of geosynthetics in pavement application have been starting form many of the studies were conducted on the pavement using the polymeric materials. few of the studies were also adopted with natural geotextile in pavement application. the uses of geotextile in pavement application are gain governing promises entire the world, due to their function and easy installation process over the weak subgrade. the function of geotextile are reinforcement, separation, drainage and filtration help in settling the pavement, provide additional strength and improved the service life of the pavement. in view of the above associate problem and benefits with geotextile, an attempt is made in the laboratory to evaluate the performance of the coir mats and its benefits to the pavement by conducting wtt under moving load condition. the present study is conducted with the four types coir geotextile are coir composite (cc), geogrid + non-woven coir mat (gg+nwcm), woven coir mats (wcm) and non-woven coir mats to the reinforcement of weak subgrade for lvrs. the test was conducted using the fabricated mould size are 300mm x 300mm x 200mm and 300mm x 300mm x 300mm. the samples are prepared in the fabricated mould with bc soil as subgrade and sandy gravel as sub-base soil (two-layer pavement section) with varying thickness of pavement layer as per the modified cbr test protocol. the sample was tested using the wtt apparatus under moving load condition. 2 harinder, d & shankar s./ jgeet vol 03 no 01/2018 2. geosynthetics the problem of pavement generally associated with the strength of the subgrade and sub-base soil. the construction of pavement over the soft soil, clay soil, and silt soil poses several problems to the pavement, in the form of rutting and fatigue, reflection cracks and uneven surface of the pavement (rao, 2000; brian, 2001; rama, 2010). this problem occurs due to its high swelling, shrinkage, settlement characteristic and also volume change behaviour of bc soil (yang, 2007) during various seasons under the dry and wet condition. to prevent these problems, many of the conventional techniques were adopted and restrict the problem of pavement. but these conventional methods are not eco-friendly neither economical for the construction of pavement and also difficulties during the construction of pavement in the field such as mixing of soil, compaction etc. to overcome with this problem, geosynthetics are taken as alternate materials is used in pavement construction from the past four decades. during the past few decades, geosynthetics have gained universal attention across all over the world, the possible types of soil subgrade either to overcome the subgrade deficiency or enhance permanent life and performance (al-qadi et al 2008; jersey et al, 2012,; khodaii et al, 2008 and zornberg et al, 2009). the geotextile acts a tension member and reduce the deformation and the vertical stress over the subgrade (giroud and noiray, 1981) and improve the performance of the roads. the maximum tension effect is available to decrease the bearing capacity of the pavement when the uses of woven and non-woven coir mats are placed over the interface (babu, 2007). the presence of the geosynthetics layer in the pavement system increase the later system and stiffness of the base/sub-base material while reducing the vertical stress and deformation of the subgrade (perkins, 1999) are reported. one of such applications can be in the unpaved road over soft subgrade where the rate of plastic deformation due to repeated traffic loads is faster during the initial stage and gets stabilized later (fannin and sigurdsson, 1996). various investigators stress the high cost of geosynthetics and stringent environmental protection requirements make it important to explore alternative natural products to make the constructions cost-efficient and ecofriendly (sarsby, 2007; chauhan, 2008). the study investigated that the polymeric geocell improves the performance of the unpaved roads over the poor subgrade, quarry dust shown the better performance than the other materials (pokhaerl 2011). to studied the performance of the geogrid reinforcement, indicates that the use of geosynthetics in pavement over the poor subgrade soil tends to reduce the sub base thickness with increasing traffic volume (charles, 2014). to addressing the problem of pavement, to prevent this problem this study examines the coir geotextile mats can effectively serve as reinforcement, separation, drainage materials over the weak subgrade soil for lvrs. the study is conducted under moving loading condition in the laboratory, to correlate laboratory study with the field study using the accelerated pavement test track (apt). 3. materials the subgrade soil consists of clay having a liquid limit (ll) of 58% and plastic limit (pl) of 27%. the clay is classified as ch as per indian standards and had a specific gravity of 2.62. optimum moisture content (omc) and maximum dry density (mdd) was obtained as 17% and 17 kn/m3 respectively in standard proctor test. the soaked california bearing ratio (cbr) value obtained is 1 for ch soil. table 1. the basic properties of the coir geotextile the properties of the coir values length (mm) 15-30 density (g/cc) 1.14-1.41 breaking elongation (%) 27 diameter (mm) 0.1-1.5 specific gravity 1.12 modulus of elasticity (gpa) 8.14 water soluble (%) 5.20 similarly, the sub-base materials are sandy gravel were used. the properties of these materials are optimum moisture content (omc=8.0), maximum dry density (mdd= 18.7kn/m3), shear parameter (c=0and φ=31o). the soaked and unsoaked california bearing ration (cbr) is 6 and 13 are presented respectively. the four types of coir mats were used in the study. the properties of the coir geotextile mats are given in table1. the types of coir geotextile used in the study shown in the below fig. 1. the notations of the coir geotextile as follow: cc=coir composite, wcm= woven coir mat. the mechanism of coir geotextile mats over the weak subgrade as shown in fig. 2. the conventional pavement load distribution characteristics and separation of two-layer material are shown. the fig 2b shown the reinforcement and separation of layer material, without possibility of intermix with the composite mats. harinder, d & shankar s./ jgeet vol 03 no 01/2018 3 fig. 1. types of coir geotextile mats used in the study similarly lower the reinforcement and improper mixing of two-layer material is given in fig 2c. the cc and gg+nwcm significantly reduce the settlement and also effectively work to possess the separation function than the wcm. the wcm gives the less reinforcement than the cc and gg+nwcm and also in sufficient to give the separation function due to its opening mesh size. 4. experimental setup the wheel tracking test apparatus (wtt) are used for this investigation with varying contact pressure of moving load to simulate the field condition. it was developed by british national rail road research institute (generally used for measuring the plastic deformation of bituminous asphalt concrete). the wtt apparatus height of the loading lever has been raised using the fabricated angle sections. the fabricated angles are controlling the enable to the loading onto pavement model section. the maximum load applied on to the pavement has 55 kg, through the moving wheel of diameter 200mm, width of 50mm made of solid rubber. to run the wheel over the model section three phase motor with 75kw, 400v power motor is used. the experimental setup is shown in fig. 3. fig.3. experimental setup with the data accusation system fig. 2. mechanisms of coir geotextiles 4 harinder, d & shankar s./ jgeet vol 03 no 01/2018 5. result and conclusion in the laboratory, the model pavement layers were prepared as two-layer pavement system. the pavement layer was prepared as subgrade and subbase with and without placement of coir mats between the subgrade and sub-base layer (reinforcement and un-reinforcement of coir geotextile mats). the subgrade as a bc soil and the sub-base as a sandy gravel soil are prepared and compacted in the fabricated mould of size thickness as 200 mm. as shown in above table 2 the maximum and the minimum number of wheel passes are variable, the number of wheel passes depends on the position of the coir mats and also the types of the coir geotextile. the maximum number of wheel passes (800) at 40 mm rut depth was found at the h/4 position with reinforcement of cc. the varying thickness of subgrade and subbase with and without reinforcement of coir mats along with rut depth and wheel passes also are given in table 2 with sandy gravel sub-base soil. in the laboratory study, the placement of coir mats at h/2 position the number of wheel passes with sandy gravel sub-base soil and without provision of the coir mats. from the study it was observed that the higher repetition is occurs with (gg+nwcm) at h/4 position compared with other types of coir geotextile mats. it was also noticed that the performance of the coir mats are uniform due to placing of higher thickness of sub-base soil. the repetition were found at h/2 position is occurs due to the sub-base soil, the failure are notice in sub-base soil due to lower shear strength and cbr values. fig. 3 shows the rut depth and a number of wheel passes at the h/2 position of sandy gravel soil. table 2 pavement component layers with variable thickness of subgrade (bc) and sub-base (sandy gravel) with and without coir geotextile. s.no pavement model section with 300 mm x300 mm x 200 mm position of coir mats absorb rut depth (mm) number of wheel pass 1 bc-sg bc-sg-cc bc-sg-gg-nwcm bc-sg-wcm bc-sg-nwcm h/2 40.0 40.0 40.0 40.0 40.0 280 350 190 290 150 2 3 4 5 6 bc-sg bc-sg-cc bc-sg-gg+nwcm bc-sg-wcm bc-sg-nwcm h/3 40.0 40.0 40.0 40.0 40.0 300 390 430 350 300 7 8 9 10 11 bc-sg bc-sg-cc bc-sg-gg+nwcm bc-sg-wcm bc-sg-nwcm h/4 40.0 40.0 40.0 40.0 40.0 290 800 650 580 270 12 13 14 15 fig. 3. rut depth along with number of wheel passes at h/2 position coir mats. 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 r u t d e p th i n m m ( 4 0 m m ) number of wheel passes bc soil + sandy gravel bc soil + wcm + sandy gravel bc soil + nwcm + sandy gravel bc soil + cc + sandy gravel bc soil + cc+nwcm + sandy gravel harinder, d & shankar s./ jgeet vol 03 no 01/2018 5 the provision of coir mats at h/3 position in between subgrade and sub-base shown the differentiate in number of wheel passes depth for same rut depth. the woven coir mats increase the rut depth due to the higher thickness of coir mat than the woven coir mat. the provided coir mats at h/3 position taken the maximum load than the h/2 position with coir composite materials. the coir composite material possesses the reinforcement and separation functions to the subgrade and reduces the deformation of the pavement structure. the coir geotextile mats are ensured the multi-function in pavement application such as reinforcement, separation, and drainage (ali khodii imadi, 2009). the number of wheel passes and rut depth at h/3 position is showed in fig. 4. fig. 4. rut depth and number of wheel passes at h/3 position of sg soil the two-layer pavement model section was prepared with the incorporation of coir geotextile at the h/4 position in order to reduce the sub-base soil materials. during the laboratory study it seen that the higher repetition are found at h/4 position than the h/2 and h/3 position, the placement of coir mats at h/4 position performed as a reinforcement material than the h/2 and h/3 position, and transferred the load towards the edge of the pavement. the placement of coir mats at h/4 position with reducing the sub-base thickness is showed the better performance due to its tension membranes act immediately due to placing near to the tire load from the top of the sub-base. the rut depth and number of wheel passes at h/4 position is shown in fig. 5. fig. 5. rut depth and number of wheel passes at h/4 position of sg soil the laboratory study is performed to evaluate the effectiveness of coir mats with fabricated mould of size 300mmx300x300mm. the study were conducted as a two-layer pavement system with and without provision of coir mats at h/2, h/3 and h/4 position in between subgrade and subbase layer tested by using the wtt apparatus. the deformation of fabricated mould are noted with respective their number of wheel passes. the placement of coir mats, rut depth along with the number of wheel passes are given in table 3. from the table 3 it was notice that the high number of repetition was found at h/2 position by using the cc and gg+nwcm coir geotextile with higher thickness of sub-base soil with same rut depth. the lower number of wheel passses were noticed with reinforcement of nwcm at h/3 position. the reinfoced with cc and gg+nwcm coir geotextile mats at h/3 position greatly reduced the deformation and sub-base thickness and increse the repetetion 1040 and 1160 respectively. table 3 pavement component layers with variable thickness of subgrade (bc) and sub-base (sandy gravel) with and without coir geotextile. s.no pavement model section with 300mmx300mmx300mm position of coir mats absorb rut depth (mm) number of wheel pass 1 bc-sg bc-sg-cc bc-sg-gg+nwcm bc-sg-wcm bc-sg-nwcm h/2 40.0 40.0 40.0 40.0 40.0 670 1400 1500 948 700 2 3 4 5 6 bc-sg b-sg-cc bc-sg-gg+nwcm bc-sg-wcm bc-sg-nwcm h/3 40.0 40.0 40.0 40.0 40.0 170 420 480 356 190 7 8 9 10 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 r u t d ep th i n m m ( 4 0 m m ) number of wheel passes bc soil + sandy gravel bc soil + wcm+ sandy gravel bc soil + nwcm + sandy gravel bc soil + cc + sandy gravel bc soil + cc+nwcm + sandy gravel 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 number of wheel passes r u t d ep th i n m m ( 4 0 m m ) bc soil + sandy gravel bc soil + wcm+ sandy gravel bc soil + nwcm+ sandy gravel bc soil + cc + sandy gravel bc soil + cc+nwcm + sandy gravel 6 harinder, d & shankar s./ jgeet vol 03 no 01/2018 s.no pavement model section with 300mmx300mmx300mm position of coir mats absorb rut depth (mm) number of wheel pass 11 bc-sg bc-sg-cc bc-sg-gg+nwcm bc-sg-wcm bc-sg-nwcm h/3 40.0 40.0 40.0 40.0 40.0 345 1040 1160 490 408 12 13 14 15 fig. 6. rut depth and number of wheel passes at h/2 position of sg soil. the un-reinforced pavement model layer system showed the lower repletion at h/3 position than the reinforced model layer, which is shown with block color trend line in fig. 6. the reinforcement of model layer with sandy gravel sub-base soil with at h/2 position showed the higher repetition than the h/3 and h/4 position. in this case, the sub-base soil thickness is increased than the other case such as h/3 and h/4 position. due to this increased thickness of sub-base soil increase the repetition improved the performance of the pavement. the rut depth and the number of wheel passes with sandy gravel soil at h/2 position is shown in fig. 6. fig. 7 rut depth and number of wheel passes at h/3 position of sg soil. the provision of coir mats with lower strength of sub-base soil will causes failure pavement and reduce the performance of the coir geotextile and also the pavement. in this case, the placement of coir mat at h/3 position with the sandy gravel soil showed the lower repetition 170 with the unreinforcement model layer. the reinforcement with coir mats at h/3 position is also showed the less number of wheel passes 480 with gg+nwcm coir mats. it was found that the provision of coir geotextile mats at h/3 position with sandy gravel sub-base soil inappropriate to improve the performance of the pavement. the rut depth and number of wheel passes at h/3 position is shown in fig. 7. fig. 8. rut depth and number of wheel passes at h/4 position of sg soil. the reinforcement of pavement model-layer system with four type of coir mats at h/4 position having the better reinforcement than the h/3 position with the sandy gravel sub-base soil. in this case the placed coir mats at h/4 position act as a tension member and the maximum load will take place by the coir mats. the thicknesses of coir mats also play key role to improve the load bearing capacity of the pavement. the higher the thickness of coir mats (cc, gg+nwcm, and nwcm) reduces the deformation. the thickness of coir mats gives the additional strength to the pavement, reduces the vertical deformation, help in slow setting of pavement with proper separation. the provision of coir mat at h/4 position, the rut depth and the number of wheel passes are shown in fig. 8. the laboratory study was performed to determine the performance of the geotextile with varying thickness of fabricated mould and evaluated the effectiveness of coir mats. the application and its utilization in lvrs. the maximum numbers of wheel passes occur at the h/3 position with reinforcement of gg+nwcm. in this case, the woven coir geotextile mats act as a 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 0 10 20 30 40 r u t d e p th i n m m number of wheel passes bc soil + sandy gravel bc soil + wcm + sandy gravel bc soil + nwcm + sandy gravel bc soil + cc + sandy gravel bc soil + cc+nwcm + sandy gravel 0 100 200 300 400 500 0 10 20 30 40 r u t d e p th i n m m number of wheel passes bc soil + sandy gravel bc soil + wcm + sandy gravel bc soil + nwcm + sandy gravel bc soil + cc + sandy gravel bc soil + cc+nwcm + sandy gravel 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 0 10 20 30 40 r u t d e p th i n m m number of wheel passes bc soil + sandy gravel bc soil + wcm + sandy gravel bc soil + nwcm + sandy gravel bc soil + cc + sandy gravel bc soil + cc+nwcm + sandy gravel harinder, d & shankar s./ jgeet vol 03 no 01/2018 7 reinforcement material and the non-woven mats purely act as separation material. when the nonwoven coir mats attached with the geogrid it gives the additional reinforcement to the pavement structure. in addition to this, the coir geotextile acts as a separation and drainage material over the subgrade. 6. conclusions the results of the study have demonstrated the potential of coir geotextile in lvrs over the weak subgrade. this paper reviewed the concept of utilization of coir geotextile and it composite mats for lvrs. maximum repetitions are found with coir composite at h/2, h/3 and h/4 position in case of 200mm thickness of the mould. in case of 300mm thickness of mould higher repetition are obtained with cc and gg+nwcm at h/2 position as 1400 and 1500 respectively. the cc and gg+nwcm coir mat shown the better reinforcement at h/4 position in both cases. the cc mats more significant to gives the reinforcement and separation of function to pavement and improved the performance. the sub-base soil parameter such as c and ϕ (0 and 31 0 ) play a key role to place the geotextile irrespective of the thickness of sub-base soil. the increase thickness of sandy gravel sub-base soil increase the repetition later its fails due to the improper shear strength. the nwcm mats are more significant in term of reinforcement and separation than the wcm. the higher thickness of coir mats (nwcm) more effecting to reduce the deformation over the weak subgrade. 7. references rao, subba, k.s. 2000. swell-shrink behaviour of expansive soils geotechnical challenges. indian geotechnical journal, 30 (1). brian, albrecht, a., and benson, craig, h. 2001. effect of desiccation on compacte natural clays. journal of geotechnical and geo environmental 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e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 3 2022 manyoe, i.n. et al./ jgeet vol 7 no 3/2022 117 research article application of lineament density extraction based on digital elevation model for geological structures control analysis in suwawa geothermal area intan noviantari manyoe1,*, ronal hutagalung1 1 geological engineering major, faculty of mathematics and natural science, universitas negeri gorontalo, bone bolango regency, gorontalo, indonesia. * corresponding author : intan.manyoe@ung.ac.id tel.:+62-812-8002-3410 received: nov 12, 2021; accepted: sep 23, 2022. doi: 10.25299/jgeet.2022.7.3.8085 abstract the tectonic condition of gorontalo, which is located in the north of sulawesi island has implications for the spread of geothermal potential. the area in gorontalo with the largest geothermal potential is the suwawa area, bone bolango regency. therefore, t his study aims to develop a model of lineament extraction from a digital elevation model and analyze the geological structure control based on the lineament distribution. this research is useful for the development of knowledge in the geothermal field, especially the study of permeability and structural control in geothermal areas. this research is beneficial for the community because it can detect the permeability zone in more detail which is the basis for the utilization of geothermal potential. the factors studied in this study are the geological lineament density and the geological structures. to achieve the research objectives, extraction methods and model analysis include analysis of permeable and control of geological structures. the lineament extraction model from the digital elevation model in the suwawa geothermal area shows that there is a moderate to high agreement for lineament extraction from national dem data and low to moderate agreement for lineament extraction from srtm data. the lineament distribution showing moderate to high density occupies the southern, eastern, and western parts of the suwawa geothermal area. the presence of a lineament controls the circulation of geothermal fluids in the suwawa geothermal area. keywords: model, geothermal, geology, lineament, structure. 1. introduction geothermal energy is energy that comes from the interior of the earth which is formed due to the heat content in the earth interior. this overview describes the mechanisms of heat transfer in the mantle and crust (barbier, 2002). the sources of geothermal energy in the world are categorized into geothermal reservoirs with high enthalpy and geothermal reservoirs with low enthalpy (kaczmarczyk et al., 2020; martín-gamboa et al., 2015). the use of geothermal in the world is used directly or indirectly and has been proven to be able to encourage economic progress (glassley, 2010; rybach, 2015). geothermal resources are closely related to regional tectonic conditions (tzanis et al., 2020). gorontalo, which is located in eastern indonesia, is flanked by the indoaustralian, eurasian and pacific macro plates (advokaat et al., 2017) and the philippine microplate (hall et al., 1995) which has implications for geothermal spread (manyoe and hutagalung, 2020). plate collisions cause magmatism. the activity of magma and residual magma can cause heating of the accumulated subsurface water and become a geothermal reservoir (manyoe and hutagalung, 2020; siahaan et al., 2005). gorontalo's geothermal potential is located in the areas of suwawa, pentadio, bongongoayu, dulangeya and pohuwato. gorontalo's geothermal potential has not been fully utilized as well as the world's geothermal potential. geothermal utilization in gorontalo is focused on direct use of the tourism sector. one of the areas that has the largest geothermal potential is the suwawa geothermal area, bone bolango regency. the sumawa geothermal working area consists of lombongo, pangi, libungo, hungayono. tulabolo timur. research that has bee carried out in the suwawa geothermal area which provide a lineament extraction model for the suwawa geothermal area has only been carried out in the libungo area (manyoe and hutagalung, 2021, 2020). it is important to research the lineament density extraction model to determine the development of the extraction model and control of geological structures in the research area. the lineament density extraction model will be based on a digital elevation model. the control structure will be made based on the distribution of the lineament in the study area. this research will cover the information gap in the geothermal field in the research area that has not been carried out by previous researchers. this research is useful for the development of geothermal science, especially the development of extraction and control models of geological structures in geothermal areas. the purpose of this study is to develop a lineament extraction model from a digital elevation model in the suwawa geothermal area. to analyze the control of geological structures based on the lineament distribution in the suwawa geothermal area. extraction is a process to http://journal.uir.ac.id/index.php/jgeet 118 manyoe, i.n. et al./ jgeet vol 7 no 3/2022 detect lineament based on digital data. in this study, lineament extraction is based on a digital elevation model. the development of the lineament extraction model in this study was based on national demnas and srtm. 2. methods 2.1. research location astronomically, the suwawa area and its surroundings are located at coordinates 0°27'0” 0°34'5” north latitude and 123°8'0” 123°18'5” east longitude. based on its geographical position, the research area is located in central suwawa district, south suwawa district, and east suwawa district. lombongo geothermal is located in central suwawa district and libungo geothermal is located in south suwawa district. pangi geothermal, east tulabolo geothermal and hungayono geothermal are located in east suwawa district. the research area is in the bone bolango regency, gorontalo province. fig. 1. regional geology of research location (apandi and bachri, 1997). the research area is part of the volcanic-plutonic strip of north sulawesi, which is mostly composed of volcanic rock and breakthrough rock (hinschberger et al., 2005; sompotan, 2012). the order of rocks from the oldest to the youngest rocks based on the regional geological map of the kotamobagu sheet by (apandi and bachri, 1997) is the bilungala volcanic rock formation (tmbv), bone diorite (tmb), pinogu volcanic rock (tqpv) and qpl formation (lake deposits). bilungala volcanics (tmbv) and bone diorite (tmb) formed in the middle miocene to early pliocene. pinogu volcanics (tqpv) formed in middle pliocene to early plistocene. lake deposits (qpl) formed in middle plistocene to holocene (apandi and bachri, 1997; perelló, 1994). 2.2 data collection lineament data collection is done by downloading digital elevation model data or dem from the geospatial information agency (big) and the united state geological survey (usgs). table 1. the value of each parameter used in the line algorithm (abduh et al., 2021). no extraction parameters score 1 radi (radius filter) 10 2 gthr (gradient threshold) 75 3 lthr (length threshold) 25 4 fthr (line fitting error threshold) 3 5 athr (angular difference threshold) 1 6 dthr (linking distance threshold) 40 the straightness detection and extraction process uses the segment tracing algorithm (sta). an effective method for automatic lineage detection and extraction is the segment tracing algorithm (sta) (koike et al., 1995) because it can detect more lineaments at low contrast and parallel to solar illumination on optical sensor satellite images than other similar methods. 2.2. data processing and interpretation the straightness detection and extraction process is carried out on a digital elevation model derived from ifsar data (5m resolution), terrasar-x (5m resolution) and alos palsar (11.25 m resolution) and stereo-plotting masspoint data. the detection and extraction process is continued using a geographic information system (gis) application to compare the extraction results with regional geological structures. the analysis was carried out by looking at the distribution pattern of the lineament and the regional geological structure. the comparison of lineament patterns and regional geological structures is continued with data processing using the rockworks application to obtain the direction of the lineament stress. furthermore, a geological structure control analysis was carried out based on the lineament distribution. 3. result and discussion the research area based on physiographic studies is divided into northern volcanic mountains, northern intrusive mountains, northern karst mountains, southern volcanic mountains, southern intrusive mountains, southern karst hills, fluvial plains, and coastal plains. the fluvial plain occupies the central part of the study area. the coastal plain occupies the southern part of the study area. the northern volcanic mountains are composed of breccia lithology, tuff, lapilli tuff, dacite, and rhyolite. the northern karst mountains are composed of limestone. the northern and southern intrusive mountains are composed manyoe, i.n. et al./ jgeet vol 7 no 3/2022 119 of diorite, granodiorite, and granite. the southern karst hills are composed of reef limestones. fluvial plains are composed of claystone, sandstone, and gravel. the coastal plain is composed of sand, clay, silt, gravel and gravel. there are 5 (five) areas with geothermal potential in the suwawa area. manifestation data collection is carried out at 9 (eight) points. two points in the lombongo area, 1 (one) point in the pangi area, 2 (two) points in the libungo area, 2 (two) points in the hungayono area and, 2 (two) points in the east tulabolo area. the types of geothermal manifestations of libungo 1 and libungo 2 are hot springs. the hot springs are located at an altitude of 44 meters above sea level and 30 meters above sea level. the temperature of libungo hot springs is in the range of 81-82.6 °c. the air temperature ranges from 30-32 °c. the flow direction of libungo 1 and libungo 2 hot springs is northeast-southwest with a discharge of 1.20 m3/s for libungo 1 and 4.50 m3/s for libungo 2. the chemical characteristics of libungo hot springs can be seen from the ph value. libungo 1 and libungo 2 hot springs have a ph of 7.8. libungo 1 and libungo 2 hot springs have iron oxide deposits. other physical characteristics are odorless, tasteless, and colorless. the types of geothermal manifestations of lombongo 1 and lombongo 2 are hot springs. the hot springs are located at an altitude of 112 meters above sea level and 107 meters above sea level. the temperature of the libungo hot springs is in the range of 42-48 °c. the flow direction of lombongo 1 and lombongo 2 hot springs is northeastsouthwest with a discharge of 0.213 m3/s for lombongo 1 and 0.31 m3/s for lombongo 2. the chemical characteristics of lombongo hot springs can be seen from the ph value. lombongo 1 hot spring has a ph of 5 and lombongo 2 has a ph of 6. the lombongo 1 and lombongo 2 hot springs have iron oxide deposits. other physical characteristics are odorless, tasteless, and colorless. the type of geothermal manifestation of pangi is hot springs. the hot springs are at an altitude of 112 meters above sea level. the temperature of pangi hot springs is in the range of 56 °c. the flow direction of pangi hot spring is northeast-southwest with a discharge of 0.213 m3/s. the chemical characteristics of pangi hot springs can be seen from the ph value. pangi hot spring has a ph of 5. pangi hot spring has iron oxide deposits. other physical characteristics are odorless, tasteless, and colorless. the types of geothermal manifestations of hungayono 1 and hungayono 2 are hot springs. the hot springs are at an altitude of 165 meters above sea level. the temperature of the hungayono hot springs is in the range of 30-33 °c. the flow direction of hungayono 1 and hungayono hot springs is northeast-southwest with a discharge of 0.0004632 m3/s for hungayono 1 and 0.0004632 m3/s for hungayono 2. chemical characteristics of hungayono hot springs can be seen from the ph value. hungayono 1 hot spring has a ph of 6.1 and hungayono 2 has a ph of 6.3. hungayono 1 and hungayono 2 hot springs have deposits of iron oxide and travertine. another physical characteristic for the two hot springs of hungayono is that it smells of iron, tastes salty, and is colorless. the types of geothermal manifestations of east tulabolo 1 and east tulabolo 2 are hot springs. the hot springs are located at an altitude of 185 meters above sea level and 129 meters above sea level. the temperature of the east tulabolo hot spring is in the range of 47-50 °c. the air temperature ranges from 30 °c. the direction of flow of the east tulabolo 1 hot spring is east-west and east tulabolo 2 is southwest-southeast with a discharge of 0.0030 m3/s for east tulabolo 1 and 0.00015 m3/s for east tulabolo 2. chemical characteristics of the tulabolo hot spring east can be seen from the ph value. the tulabolo timur 1 and tulabolo timur 2 hot springs have a ph of 6.3. tulabolo timur 1 and tulabolo timur 2 hot springs have sulfur deposits. other physical characteristics are sulfur odor, salty taste, and colorless. the lineament extraction model was developed from a digital elevation model in the suwawa geothermal area. the development of the lineament extraction model was obtained from national dem and srtm. comparisons will be made on the results of data processing and analysis using national dem and srtm, then structural control analysis on the emergence of hot springs based on national dem and srtm. fig 2. the extraction of lineament of data national dem and srtm. national dem and srtm data extracted in the geomatica application resulted in straightness in the suwawa geothermal area. national dem data was obtained from geospatial information agency while srtm data was obtained from usgs. lineament extraction parameters are radi 10, gthr 75, lthr 25, fthr 3, athr 1, and dthr 40. the extraction results show that lineament extraction from national dem produces more lineaments than lineament 120 manyoe, i.n. et al./ jgeet vol 7 no 3/2022 extraction from srtm. subsequently, the alignment between the extraction lineament and the regional geological structure of the suwawa geothermal area was made (figure 9). fig 3. region rapprochement extraction of alignment with the geological structure. agreements are made in four areas, namely region 1, region 2, region 3, and region 4. region 1 is an agreement between lineament extraction with geological structures trending northwest-southeast and east-west. region 2 is an area of correspondence between lineament extraction with geological structures trending northwest-southeast and east-west. region 3 is an area of conformity between lineage extraction and geological structures trending northwestsoutheast and east-west. the southwest part of region 3 has regional geological structures trending northwestsoutheast and northeast-southwest. region 4 is an area of conformity between lineage extraction and geological structures trending northwest-southeast and east-west. fig 3. verification area 1 between regional geological structure with lineament of extraction result from national dem and srtm. the result of lineament extraction in region 1 shows the number of lineaments from national dem data is 176 and the number of lineament extractions from srtm data is 18. there is a regional structure with a northwest-southeast trend which is cut by an east-west trending regional structure. the regional geological structure trending northwest southeast in region 1 is a geological structure located in the northern part of the suwawa geothermal area. the regional structure with a northwest-southeast trend is a right-hand fault and the regional structure with an east-west trend is a normal fault. there is a correspondence between lineament extraction from national dem data and srtm data with regional geological structures. the regional geological structure trending northwest-southeast from the national dem data is in high agreement with the lineament extraction with a northwest-southeast trend. the regional geological structure with an east-west trend from the national dem data corresponds highly to the east-west trending lineage extraction. the regional geological structures trending northwest-southeast and east-west from the srtm data are in low agreement with the lineaments extraction trending northwest-southeast. the result of lineament extraction in region 2 shows the number of lineaments from national dem data is 194 and the number of lineament extractions from srtm data is 20. there is a regional structure trending northwest-southeast and a regional structure trending east-west. the regional geological structure trending northwest-southeast in region 2 is a geological structure located in the middle of the manyoe, i.n. et al./ jgeet vol 7 no 3/2022 121 suwawa geothermal area. the regional structure with a northwest-southeast trend is a right-hand fault. the regional structure with an east-west trend is a normal fault. there is a correspondence between lineament extraction from national dem data and srtm data with regional geological structures. the regional geological structure trending northwest-southeast from the national dem data is in high agreement with the lineament extraction with a northwest-southeast trend. the regional geological structure with an east-west trend from the national dem data is moderately consistent with the eastwest trending lineage extraction. the regional geological structure trending northwest-southeast from the srtm data is low in agreement with the lineament extraction with a northwest-southeast trend. there is no lineament in the east-west trending structure from the srtm data so it does not have a match. the result of lineament extraction in region 3 shows the number of lineaments from national dem data is 188 and the number of lineament extractions from srtm data is 21. there is a regional structure trending northwest-southeast and regional structure trending east-west. in the southwest part of region 3 there is a regional geological structure trending northwest-southeast and northeast-southwest. fig 4. verification area 2 between regional geological structure with lineament of extraction result from national dem and srtm. fig 5. verification area 3 between regional geological structure with lineament of extraction result from national dem and srtm. the regional geological structure trending northwestsoutheast in region 3 is a geological structure located in the southeastern part of the suwawa geothermal area. the regional structure with a northwest-southeast trend is a right-hand fault. regional structures trending east-west and northeast-southwest are normal faults. there is a correspondence between lineament extraction from national dem data and srtm data with regional geological structures. the regional geological structure trending northwest-southeast from the national dem data is in high agreement with the lineament extraction with a northwest-southeast trend. the regional geological structure with an east-west trend from the national dem data is moderately consistent with the eastwest trending lineage extraction. the southwest part of region 3 has a regional structure trending northwestsoutheast which corresponds to moderate and northeastsouthwest which corresponds low to the lineament. the regional geological structure trending northwestsoutheast from the srtm data is low in agreement with the lineament extraction with a northwest-southeast trend. the regional geological structure with an east-west trend from national dem data corresponds low to the east-west trending lineage extraction. the southwest part of region 3 has a regional structure trending northwest-southeast 122 manyoe, i.n. et al./ jgeet vol 7 no 3/2022 which corresponds to low and northeast-southwest which corresponds low to the lineament. the results of lineament extraction in region 4 show that the number of lineaments from national dem data is 56 and the number of lineament extractions from srtm data is 3. there is a regional structure with a northwestsoutheast trend and an east-west trending regional structure. the regional geological structure trending northwest-southeast in region 4 is a geological structure located in the western part of the suwawa geothermal area. the regional structure with a northwest-southeast trend is a right-hand fault. the regional structure with an east-west trend is a normal fault. fig 6. verification area 4 between regional geological structure with lineament of extraction result from national dem and srtm. there is a correspondence between lineament extraction from national dem data and srtm data with regional geological structures. the regional geological structure trending northwest-southeast from the national dem data is in high agreement with the lineament extraction with a northwest-southeast trend. the regional geological structure with an east-west trend from the national dem data is moderately consistent with the eastwest trending lineage extraction. the regional geological structures trending northwest-southeast and east-west from the srtm data are low in agreement with the lineaments extraction trending northwest-southeast. the result of lineament extraction from national dem and srtm data shows that lineament extraction from national dem data produces a larger number of lineaments than lineament extraction from srtm data. the results of lineament verification from national dem and srtm data with regional geological structures show that lineament from national dem data has a moderate to high agreement with regional geological structures. meanwhile, the lineament of the srtm data has a low to moderate agreement with the regional geological structure. 5.3 geological structure national dem and srtm data extracted and processed using geomatics and geographic information systems (gis) applications produced a lineament density map (figure 15). lineament density maps can be used to determine the permeability of the suwawa geothermal area. areas with good permeability have high straightness density values. based on the lineament density map, it is interpreted that the suwawa geothermal area is divided into high, medium and low density areas. the high density area occupies the southern, eastern and northern parts of the suwawa geothermal area. the medium density area occupies the southern, eastern and northern parts of the suwawa geothermal area. the low density area occupies the northwest part of the study area extending to the center of the suwawa geothermal area and the southwest part of the suwawa geothermal area. fig 7. density of suwawa geothermal area straightness. manyoe, i.n. et al./ jgeet vol 7 no 3/2022 123 the southern, eastern and northern parts of the study area are included in the medium to high density area because they are associated with the geological structure of the study area with a northwest-southeast trend and an east-west trending structure. the appearance of hot springs in the suwawa geothermal area is in a medium to high density area which is also influenced by geological structures that are in line with the lineament. the high lineament density in the suwawa geothermal area has implications for a good level of permeability. the northwest part extends to the center of the suwawa geothermal area, which is included in the low density area. likewise, in the southwest part of the suwawa geothermal area which is included in the low density area. these two parts are not associated with geological structures. the part of the suwawa geothermal area that falls into low density is the fluvial plain and coastal plain. the absence of lineament in this section results in a low level of lineament density which has implications for poor permeability. based on the lineament density map, the study area is dominated by high density areas. the high-density areas are scattered in the southern, eastern, and northern parts of the suwawa geothermal area so that in general the research area has a good level of permeability. geothermal areas with good permeability levels are interpreted as areas with good water infiltration rates. thus, the presence of a lineament controls the circulation of geothermal fluids in the suwawa geothermal area. 4. conclusion the lineament extraction model from the digital elevation model in the suwawa geothermal area shows that there is a moderate to high agreement for lineament extraction from national dem data and low to moderate agreement for lineament extraction from srtm data. lineament distribution showing moderate to high density occupies the southern, eastern, and western parts of the suwawa geothermal area. the presence of a lineament controls the circulation of geothermal fluids in the suwawa geothermal area. acknowledgments the authors would like to thank to the research and community service center of universitas negeri gorontalo for funding this research. references abduh, a.g., usman, f.c.a., tampoy, w.m., manyoe, i.n., 2021. remote sensing analysis of lineaments using multidirectional shaded relief from digital elevation model (dem) in olele area, gorontalo. j. phys. conf. ser. 1783. https://doi.org/10.1088/17426596/1783/1/012095 advokaat, e.l., hall, r., white, l.t., watkinson, i.m., rudyawan, a., boudagher-fadel, m.k., 2017. miocene to recent extension in nw sulawesi, indonesia. j. asian earth sci. 147, 378–401. https://doi.org/10.1016/j.jseaes.2017.07.023 apandi, t., bachri, s., 1997. peta geologi lembar kotamobagu, sulawesi. pusat penelitian dan pengembangan geologi, bandung. 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distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 2 2022 hasria et al./ jgeet vol xx no xx/20xx 81 research article morphotectonic control of land movements at wundulako region, kolaka regency, southeast sulawesi province, indonesia martono1, hasria1*, suryawan asfar1, muhammad arba azzaman1, la ode ngkoimani1, ali okto1, la hamimu2, irawati2, sawaludin3, la ode muhammad iradat salihin3, wahab4 1department of geological engineering, halu oleo university, indonesia 2department of geophysical engineering, halu oleo university, indonesia 3department of geography, halu oleo university, indonesia 4department of mining engineering, halu oleo university, indonesia * corresponding author : hasriageologi@gmail.com tel.: +62-852-4185-7853 received: apr 1, 2022; accepted: jun 30, 2022. doi: 10.25299/jgeet.2022.7.2.9235 abstract this research is located at wundulako district, kolaka regency, southeast sulawesi province. the purpose of this study are to determine the level of tectonic activity and the effect of tectonic activity on the land movement of the study area. based on the dem (digital elevation model) analysis, geomorphology of the study area is dominated by mountains unit that indicate the influence of tectonic activity. geomorphological aspects were analyzed to determine the tectonic classes in the study area such as watershed and non-watershed analysis. the results showed that, tectonic class of the study area is classified as very high and moderate tectonic class. the effect of tectonic class level on land movement in the study area shows a least correlation. this interprets that the cause of land movement at study area is not only influenced by tectonic factors but is also influenced by other factors such as rainfall, lithological conditions, geomorphology, earthquakes, and human activities. this shows that morphotectonic control has little effect on the land movements at wundulako district, kolaka regency, southeast sulawesi province, but is also influenced by other factors such as rainfall, lithological conditions, geomorphology, earthquakes, and human activities. keywords: morphotectonic, land movement, tectonic classes. 1. introduction 1.1 morphotectonic morphotectonic is the study of the landscape produced by tectonic activities or interactions between tectonic processes and geomorphology ((poedjopradjitno, 2012). morphotectonics is influenced by morphological conditions and tectonic processes that occurred in the past, because morphology has a spatial dimension and tectonic has a time dimension. tectonic land formation will express topographic formations that can be used as indicators of tectonic movement. topographic forms that have undergone displacement can be seen and observed through aerial photographs and imagery that provide morphotectonic features in the form of river flow patterns, hilly displacement, river deflection, alignment, fault escarpment, and river terrace appearance. while the form of topography that experiences movement at an older age will be difficult to observe by aerial photography because it has been covered by sedimentation and erosion (anfasha; et al., 2016). morphotectonic consists of several elements such as fault escarpment, wedge steps structure, fault pool, fault line valley and river flow shift. morphotectonic elements that are identified together with other physical data and seismic data can be used as a zoning classification parameter of natural disaster vulnerability in the area concerned (poedjopradjitno, 2012). to find out the tectonic activity in certain regions, morphotectonic studies are needed. morphotectonic studies themselves learn about everything related to the relationship between geological structures and landforms (wahyudi et al., 2015). 1.2 morphometry in morphotectonic studies a morphometric analysis is needed which is used to identify the character of the shape of an area and its relation to the level of tectonic activity. morphometric analysis combined with a comparison of the straightness of the flow pattern and the direction of the land movement crown can strengthen the interpretation of the tectonic state that develops in an area. tectonic processes can cause a stocky or fracture in a rock body. if the fracture is formed on a large scale then filled with water it will form into a drainage pattern, while the direction of the land movement crown can reflect a weak zone of the fault in the area (wahyudi et al., 2015). determining the level of tectonic activity in an area can be done by morphometric analysis. morphometry is defined as a quantitative measurement of landscape / morphological form. quantitative measurements follow the rules of geomorphology as objects of comparison of http://journal.uir.ac.id/index.php/jgeet 82 first author et al./ jgeet vol xx no xx/20xx landforms and calculation of parameters directly geomorphic indications which are very useful for identifying the characteristics of an area and the level of tectonic activity (hidayat, 2010). wahyudi et al. (2015) stated that to identify the level of tectonic activity based on morphometric analysis on a watershed can be done by calculating the ratio of the width of the valley floor to the height of the valley (vfw), river gradient index (sl), asymmetry of the basin (af), sinusity of the ridge surface (smf), density river (dd). comparison of valley width and height (ratio of valley floor width to valley height / vf) is the value of the ratio between width and height of valleys in an area. asymmetry factor is one of the quantitative analysis of basin drainage to detect tectonic tilting at both large and large basin drainage scales. mountain front bend (mountain front sinuosity / smf) is a series of mountains found on the front / face. mountain face bends are an index that reflects the balance between erosion forces / forces that have a cutting tendency along the face mountain ridges and tectonic forces that directly produce mountainous faces and coincide with active fault zones that reflect active tectonics (supriyadi et al., 2018). watershed morphometry calculations can be done based on the following parameters: 1. asymmetry of drainage basins (af) af = 100 (ar / at) (1) where, af : asymmetry factor ar : right hand basin area at : total area of the basin area 2. river gradient index (sl) sl = (∆𝐻 / ∆𝐿) x 𝐿 (2) where, ∆h : difference in elevation from the point to be calculated ∆l : length of river to be calculated l : total length of the river from the count point to the headwaters of the river 3. sinusity of the ridge surface (smf) smf = lmf / ls (3) where, smf : sinusity of the ridge surface lmf : the length of the surface of the mountain face ls : long straight face of the mountain 4. the ratio of valley floor to valley height (vf) vf = 2vw / [(eld esc) + (erd esc)] (4) where, vf : index vw : width of the riverbed valley erd/eld : the height of the right / left of the valley is measured from the bottom of the river esc : elevation of the valley floor 5. river density (dd) dd = l / a (5) where, dd : river density l : total length of river drainage a : the total area of the watershed river flow density illustrates the storage capacity of surface water in basins such as lakes, swamps and river bodies flowing in a watershed (rafighian et al., 2016). classification of river density (dd), tectonic activity and geomorphological index can be seen in tables 1, table 2 and table 3, resepectively. table 1. value of river density according to (utama et al., 2016). no. dd (km/km2) density class information 1 < 0,25 low the flow of the river passes through rocks with hard resistance, so the transport of sediment transported by river streams is smaller when compared to river channels that pass through rocks with softer resistance, if the other conditions that affect it are the same. 2 0,25 – 10 medium river flow passes through rocks with softer resistance, so the transport of sediment transported by the flow will be greater. 3 10 – 25 high the river channel passes through rocks with soft resistance, so the estimated transport of sediment will be greater. 4 > 25 very high the river flows through watertight rocks. this situation will indicate that the rain that becomes the flow will be greater when compared to an area with low dd through large permeability rocks. table 2. classification of the relative tectonic activity levels of the morphometric parameters referred (mulyasari et al., 2017). no morphometric parameters tectonic grade level class 1 (high) class 2 (medium) class 3 (low) 1 sl sl ≥ 500 (300 ≤ sl < 500) sl <300 2 af (af ≥ 65 or af < 35) (35 ≤ af <43 or 57≤af<65) (43 ≤ af < 57) 3 smf smf <1,1 (1,1 ≤ smf < 1,5) smf ≥ 1,5 4 vf < 0,5 0,5 < vf < 1,0 > 1,0 table 3. classification of geomorphological index grade levels (sumaryono et al., 2014) class indeks class 1 (very high) class 2 (high) class 3 (medium) class 4 (low) 1,0 ≤ – < 1,5 1,5 ≤ – < 2,0 2,0 ≤ < 2,5 2,5 ≤ 1.3 land movement earthquakes originating from the movement of active faults in addition to destroying and destroying buildings, can also cause the formation of land cracks. if the ground cracks occur on a steep slope, then the land is prone to slide (wahyudi et al., 2015). land movement movement is a process of mass transfer of rocks or soil due to gravity first author et al./ jgeet vol xx no xx/20xx 83 (gravity). this may cause many casualties or loss of property. the movement may occurs due to the natural and nonnatural controlling and triggering factors. natural disasters such as land movement or land movements often occur where such disasters are very detrimental, because they can damage various infrastructure facilities (marani et al., 2018). putra et al. (2015) defined the movement of soil / rock as movement down or out of a slope by the mass of the land or rocks making up the slope, as well as the mixing of both as a material for shredding, due to the disruption of the stability of the soil or rocks making up the slope. if the pressure force to lower the material down is greater than the pressure force to resist the movement there will be land movement, and vice versa. the cause of the ground movement can be influenced by 2 (two) factors, namely controlling factors and triggering factors. controlling factors are factors that make the condition of a slope or cliff vulnerable and ready to move, including: 1. geomorphological conditions, 2. stratigraphic conditions (rock / soil type), 3. geological structure conditions, 4. hydrological conditions and 5. land use conditions. factors are processes that change a slope from a vulnerable or ready to move condition to a critical condition and finally move, including: 1. rainfall, 2. earthquake vibrations, and 3. human activities that can result in changes in burden. 2. geological setting based on the map of the geomorphological unit of the southeast sulawesi arm, the kolaka area has a gemorphological unit, namely mountain units (mekongga mountains) and plain units. the mekongga mountains have the highest peaks with an altitude of 2790 masl. this mountain morphological unit has a rugged topography and has a northwest-southeast direction, this direction indicates that this mountain range is in the same direction as the regional fault structure pattern, namely the nw-se trending kolaka faul (fig. 1) (surono, 2013). fig 1. geomorphological map of the kolaka area (modified from surono, 2013). dem was extracted from https://tanahair.indonesia.go.id/demnas/#/demnas the plain geomorphological unit of the kolaka area occupies the west of the mekongga mountains, the formation of this plain is influenced by the shear fault structure, namely the kolaka fault. after experiencing the collision, the southeastern arm of sulawesi has left shear faults such as the lawanopo fault system, the matarombeo fault, the konaweha fault system and the kolaka fault and lineages (surono, 2013and simandjuntak et al., 1993) (fig. 2) fig 2. map of the geological structure of the island of sulawesi (modified surono, 2013 and simandjuntak et al., 1993). the fault and lineage show a pair of main directions, namely the southeast northwest direction (332o) and the northeast southwest (42o). southeast northwest direction is the general direction of the left shear fault in the southeastern arm of sulawesi (surono, 2013). 3. research methods after the required data is collected, the next step is the data processing stage by means of primary data taken from geomorphological observations to observe the geomorphological conditions of the study area, megascopic outcrop data and lithological data to see the types of lithology in the study area. then the data is further processed using analysis, namely: 3.1 structural analyses the structural data that is here are the solid direction data, the direction data land movement crown and river segment alignment direction and ridge straightness data. the muscular direction data obtained from the field were analyzed in the dips program to see the dominance of the direction and then compared with the direction of the river segment and the straightness of the ridge, while the land movement crown direction data were obtained through https://tanahair.indonesia.go.id/demnas/#/demnas 84 first author et al./ jgeet vol xx no xx/20xx direct measurements carried out in the field. river segment straightness data obtained from river flow patterns processed from the rbi map at a scale of 1: 25,000, river segment straightness and ridge straightness then input into the dips program to see the azimuth dominance of the straightness. the straightness of the river segment measured is the straightness of the river segment of the watershed in the study area. furthermore, the data on the land movement crown direction and river segment alignment were tested through different tests to see the relationship between the land movement crown direction and the river segment straightness. difference test is used to determine between two populations. in this study, the survey used a different test function to test the comparative hypothesis of two independent samples with an alpha of 0.05. different tests were carried out using spss software (wahyudi et al., 2015). 3.2 morphometric analyses analysis of morphometric data involve the valley floor valley height ratio (vfw), river gradient index (sl), mountain face sinusity (smf), drainage basin asymmetry (af), and river density (dd) calculated in das (watershed) contained in the research area. this analysis was carried out to determine the tectonic class in the study area. furthermore, the results of the calculation of morphometric analysis are determined based on the tectonic class classification, so that based on this classification, the tectonic class can be deterined in the study area. 4. results and discussion 4.1 analysis of structure the structure found in the study area can describe the tectonic process that occurs in the study area. structure in the study area in the form of solid data found at the station and the waterfall found at the station. solid data direction of the study area that has been analyzed shows the dominant direction of northwest southeast (fig. 3), the dominant direction of land movement of the study area which is spread over several research location points shows the northnorthwest south-southeast direction (fig. 4), the dominant direction of the river segment straightness is analyzed based on the river segment straightness of the study area which is known to be directed to the northeast southwest (fig. 5) and the dominant direction of the ridge line alignment that is to the northeast southwest direction (fig. 6). fig 3. rosette diagram stump direction fig 4. rosette diagram towards the land movement crown fig 5. rosette diagram of ridge straightness fig 6. rosette diagram of lineament alignment 4.2 morphometric analyses a. watershed morphometric analysis  basin asymmetry factor basin asymmetry factor is a quantitative analysis of basin drainage which aims to determine the tectonic tilt (tectonic tilting) both on the scale of small and wide drainage basins. based on the results of the analysis of the dem data processed in argis 10.3 the study area is divided into 2 main basins. from these 2 basins then an first author et al./ jgeet vol xx no xx/20xx 85 asymmetric factor analysis for each basin with area ar in basin 1 is 2102.13 km2 and at area is 5614.5 km2. the calculated value of the at / ar area is 37.44 km2. while in basin 2, ar area is 12649.06 km2 and at area is 45249.4 km2, from the calculation of at / ar area is 27.95 km2 (table 4). table 4. the value of the basin asymmetry (af) factor no name ar (km2) at (km2) af (km2) class 1 basin 1 2102.13 5614.51 37.44 medium 2 basin 2 12649.06 45249.40 27.95 active  river gradient index (sl) table 5. the result of river gradient index (sl) name length (m) different elevation (m) value of sl (gm) class length river total length river basin 1 4666.78 15456.55 100 331.2 medium basin 2 10511.34 30651.21 175 510.3 active to determine the river gradient index can be done by calculating the difference in river height you want to know the level of slope, distance and total length of the river from upstream to downstream. the results of the river gradient index analysis can be seen in table 5.  river density (dd) river density is an index that shows the number of tributaries in a watershed that can provide an overview of water storage capacity in a basin or region. determination of river flow density is an important factor in identifying runaway water velocity, the higher the density of a river an area, the greater the runaway water velocity (table 6) table 6. the value of river density (dd) name total area das (km2) total length river (km) value of dd class das 1 56.15 42.04 0.75 medium das 2 37.12 110.91 0.33 medium  valley bottom width versus valley height (vf) the value of vf is presented is table 7. table 7. the value of valley botton width versus valley height (vf) no. name esc (m) erd (m) erd esc eld eld – esc 2vw (m) vf value (m) class 1 basin 1 55 200 145 187.5 132.5 200 0.72 medium 2 basin 2 40 137.5 97.5 125 85 90 0.49 active b. non-watershed morphometric analysis  mountain front sinusity (smf) the value of smf reflects the balance between erosion forces that have a tendency to cut along ridges of mountain faces and tectonic forces that directly produce mountainous faces and coincide with active fault zones that reflect active tectonics (table 8) table 8. value of mountain face sinusity (smf) no. line lmf line ls smf value class 1 2.22 1.79 1.24 medium 2 2.86 2.32 1.24 medium 3 2.94 2.91 1.01 active 4 3.98 3.35 1.19 medium 5 2.47 1.98 1.24 medium 6 1.96 1.86 1.05 active 7 2.07 1.69 1.22 medium 8 1.45 1.26 1.15 medium 9 1.65 1.37 1.20 medium 10 1.45 1.30 1.12 medium average value 1.17 medium table 9. geomorphological index and tectonic class no name af sl vf smf index tectonic class 1 basin 1 2 2 2 2 2 medium 2 basin 2 1 1 1 2 1.25 very high based on the classification of geomorphological index and tectonic class it can be concluded that the tectonic activity class in the study area has two tectonic activity classes, namely class 1 (very high) and class 3 (moderate). this indicates that in basin 1 tectonic and deformation forces are at work while in basin 2 there is a very high tectonic and deformation force (table 9). 4.2 morphometric analyses 4.2.1 effect of tectonic class on the ground movement land movement is a process of mass transfer of rocks or soil due to gravity (gravity), this can cause many casualties or loss of property, movements that occur due to natural and non-natural controlling and triggering factors. sumaryono et al. (2014) inferred that the direction of the crown of a land movement that correlates with the direction of the river segment shows that local tectonic conditions affect the ground movement that occurs in the area. fig 7. typical land movement crown in study area based on the results of the field survey found 11 land movement points in the study area, then measuring the 86 first author et al./ jgeet vol xx no xx/20xx direction of the land movement crown from each land movement (fig. 7 and fig. 8), then the direction of the river segment and the direction of the land movement crown are tested with spps analysis to determine the correlation between the two data. spps test results between the direction of the river segment and the direction of the land movement crown showed a value> 0.05 (uncorrelated) and the percent correlation value showed 0.282 with a positive value considered to show weak correlation (table 10). from the results of the analysis that between the direction of the river segment and the direction of the land movement crown has a weak correlation level, so it can be concluded that the land movement that occurs in the study area is not only influenced by tectonic factors but also influenced by other factors such as rainfall, lithological conditions and human activities. fig 8. small land movement crown in study area table 10. the correlation value between the direction of river straightness and the land movement crown river segment land movement crown river segment persent corelation 1 ,282 sig. (2-tailed) ,086 n 38 38 land movement crown persent corelation ,282 1 sig. (2-tailed) ,086 n 38 38 5. conclusions based on the results of research that has been done, the authors conclude several points, including: 1. the results of morphometric analysis of watershed and non-watershed areas show that the research area has a level of "moderate and very high" tectonics. 2. the structure that developed in the study area is not the main factor causing the land movements occurred in the wundulako area, kolaka regency, southeast sulawesi province. acknowledgements thanks to the regent of kolaka who has given permission to do research in wundulako district, kolaka regency, southeast sulawesi province. references anfasha;, a., pranantya;, p.a., sukiyah;, e., 2016. karakteristik morfometri dan morfotektonik das cibeet segmen selaawi girijaya dan das cikundul segmen cibadak majalaya, kabupaten cianjur, provinsi jawa barat. bull. sci. contrib. 14, 185–194. hidayat, e., 2010. analisis morfotektonik sesar lembang, jawa barat. widyariset 13, 83–92. marani, m.i.r., najib, n., ali, r.k., 2018. penentuan zona gerakan tanah dan analisis kemantapan lereng di kecamatan klego, kabupaten boyolali, jawa tengah. j. geosains dan teknol. 1, 89. https://doi.org/10.14710/jgt.1.3.2018.89-98 mulyasari, r., brahmantyo, b., supartoyo, s., 2017. kuantitatif aktivitas tektonik relatif di pegunungan baturagung jawa tengah. bull. geol. 1, 40–53. https://doi.org/10.5614/bull.geol.2017.1.1.3 poedjopradjitno, s., 2012. morfotektonik dan potensi bencana alam di lembah kerinci sumatera barat berdasarkan analisis potret udara. jsdg 22, 101–113. putra, y.a., ismail, n., faisal, 2015. analisis penentuan faktor penyebab gerakan tanah di kabupaten aceh tengah, provinsi aceh. j. ilmu kebencanaan (jika), pascasarj. univ. syiah kuala 2, 96–103. rafighian, a., haryanto, i., sukiyah, e., 2016. analisis morfotektonik daerah garut selatan dan sekitarnya berdasarkan metode geomorfologi kuantitatif. semin. nas. ke iii fak. tek. geol. univ. padjadjaran 1– 7. simandjuntak, t.., surono, sukido, 1993. peta geologi lembar kolaka , sulawesi, skala 1:250.000. pusat penelitian dan pengembangan geologi, bandung. sumaryono, wahyudi, d.r., muslim, d., sulaksana, n., 2014. gempabumi pemicu longsoran pada endapan piroklastik jatuhan studi kasus: padang pariaman, sumatra barat, indonesia 220–231. supriyadi, n.s., ismawan, p.p.r., ..., 2018. karakteristik morfotektonik sub das cikapundung dan kaitanya terhadap respon litologi gunungapi kuarter. … j. surono, 2013. geologi lengan tenggara sulawesi. badan geologi, kementerian energi dan sumber daya mineral jl. diponegoro no. 57 bandung 40122 telp. 022-7215297, fax. 022-7218154. utama, a., wijaya, a., sukmono, a., 2016. kajian kerapatan sungai dan indeks penutupan lahan sungai menggunakan penginderaan jauh (studi kasus : das juana). j. geod. undip 4, 42. wahyudi, donny r., sumaryono, emi sukiyah, dicky muslim, a.r.d., 2015. morphotectonic control towards land movement in malalak region, west sumatra. j. lingkung. dan bencana geol. 6, 229–240. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 3 2022 124 khayati,n.n. et al./ jgeet vol 7 no 3/2022 research article the effect of weathered layer thickness and slope on potential areas of landslides in gerbosari village, samigaluh district, kulonprogo regency, indonesia novia nurul khayati1, sudarmaji2*, eddy hartantyo2 1program s2 fisika, fmipa, ugm, sekip utara yogyakarta,55281, indonesia 2 lab geofisika, dep fisika, fmipa, ugm, sekip utara yogyakarta, 55281, indonesia * corresponding author : ajisaroji@ugm.ac.id tel.:+62-81392840341; fax: +62-274-545183 received: mar 21, 2022; accepted: sep 23, 2022. doi: 10.25299/jgeet.2022.7.3.9161 abstract gerbosari village has a history of landslides with intensity and risk of 56 occurrences over 5 years. gerbosari village, samigaluh district, kulonprogo regency is located at geographic coordinates 7◦ 38 '45.33 "7◦ 41' 35.24" ls and 100◦ 9 '20.80 "110◦ 11' 16.52" bt with topographic conditions at an altitude around 500 1000 mdpl. this study aims to determine the subsurface structure of landslideprone areas in the form of weathered layer thickness and the effect of slope in landslide-prone areas so that it can be used in making micro zonation maps of landslide-prone areas. this study uses 43 microtremor data with a distance between points of 650 m. the microtremor signal was analysed using the horizontal to vertical spectrum ratio ( hvsr) method. from the measurement results, it is obtai ned that the value of the dominant frequency ranges from 1 22 hz, the value of the amplification factor is obtained in the range of 1 10.5, the value of the peak ground acceleration ranges from 60 300 cm/s2, the thickness of the weathered layer is obtained in the range of 12 22 meters. based on the results of the slope analysis, the study area is on a slope classified as a bit steep very steep. keywords: landslides, weathered layer thickness, microzonation, hvsr , gerbosari village 1. introduction landslides or soil movements are one of the type movements of soil or rock masses, down or out of the slopes due to disturbed soil stability or rock making up the slopes (b). the consequences of landslides are not only casualties but also damage road access so that it can paralyze economic accommodation in the area due to closed main road access in the area. landslides that occur are caused by several factors, among others, high rainfall, slope, and thickness of the weathered layer. one area that has a history of high landslide incidents is in gerbosari village, samigaluh district, kulonprogo regency where the area has a history of large landslide events of 56 incidents during the last 5 years. so it is necessary to analyse the characteristics of the soil in terms of the thickness of the weathered layer and analysis of the slope that can lead to landslides using the microtremor measurement approach. microtremor is a weak vibration on the surface of the earth which occurs continuously due to vibration sources such as earthquakes, human activities, and traffic (nakamura, 2000). this phenomenon creates a seismic wavefield, where the field is known as the microtremor (dal moro, 2015). microtremors array observation has been used for estimating deep structure (goto et.al, 2007). microtremors measurement could be used for landslide susceptibility assessment too (abdelrahman et.al, 2021). signal data from microtremor measurements consist of 3 signals in the form of a vertical component (up and down), a horizontal component (north-south), and a horizontal component (east-west). then the signal is processed using the hvsr (horizontal to vertical spectral ratio) method to produce the peak frequency and hvsr amplitude which represent the amplification and frequency of the specific local (nakamura, 2000). 2. geology samigaluh subdistrict, kulonprogo regency, which is one of the regencies in the special region of yogyakarta (diy) is located on a tectonic and volcanic route. the northern part of the diy province is bordered by the active volcanic merapi, in the southern part of the diy province it is bordered by the java trench which is a subduction route of the indo-australian-eurasia plate (marjuki and yogafanny, 2008). rahardjo et al. (1995) described the kulon progo stratigraphy as composed of quaternary volcanic rocks, alluvial deposits accompanied by the presence of a breakthrough rock complex. the rock formations from old to young consist of the nanggulan formation, kebo butak formation, jonggrangan formation, sentolo formation (husein, et al. 2007). while the research location in gerbosari village, samigaluh district, kulonprogo regency consists of the kebo butak formation (tmok) and jonggrangan formation (tmj). gerbosari village, samigaluh subdistrict, kulonprogo regency is in the kebo butak formation (tmok) and the jonggrangan formation (tmj) as shown in figure 1. the kebo butak formation (tmok) is a formation that is not aligned above the gamping-wungkal formation and is sediment. the results of volcanic activity are composed of volcanic rocks, either in the form of pyroclastic, plastic, or coherent lava (bronto et al.). http://journal.uir.ac.id/index.php/jgeet khayati,n.n. et al./ jgeet vol 7 no 3/2022 125 the constituent rocks of the kebo butak formation consist of andesite breccias, tuffs, tuff lapilli, agglomerates, and clays. several measurement points are located in the jonggrangan formation (tmj), which overlaps or hovers over it. the rock composition of the jonggrangan formation is in the form of conglomerates, marl, tuff, limestone sandstone with lignite inserts, inset limestone, and limestone, while the upper layer consists of bioherm grey limestone interspersed with marl and layered limestone. the thickness of this formation is 2,540 meters and is estimated to be miocene-pliocene (trianda et al, 2018). fig 1. geological map of the research area (rahardjo, et al. 1995) 3. method 3.1 data acquisition microtremor measurements were carried out around gerbosari village, samigaluh district, kulonprogo regency using 31 measurement points with a distance between points of 650 meters using a sampling frequency of 100 hz with a measurement duration of approximately 45 for each measurement point. microthermal measurements are based on the terms of the sesame european research project using the hvsr (horizontal to vertical spectral ratio) method analysis. the measurement used hardware instruments in the form of a set of lennarzt 3d/20s seismometer, garmin gps hand help, sesame log sheet, and software in the form of dataq instrument, geopsy, rockwork, and arcgis. 3.2 hvsr method (horizontal to vertical spectral ratio) the horizontal to vertical spectral ratio was first introduced by nogoshi and iragashi (1970) which states that there is a relationship between the horizontal and vertical component comparisons of microtremor measurements which was later developed by nakamura (1989). the horizontal-to-vertical (h/v) method has the potential to significantly contribute to site effects evaluation, in particular in urban areas (bonnefoy-claudet, 2008). the hvsr equation is stated based on the pattern below: 𝐻𝑉𝑆𝑅 = √(𝑆𝑁𝑆) 2 + (𝑆𝐸𝑊) 2 𝑆𝑉𝑆 (1) 𝑆𝑁𝑆 is the horizontal spectrum component in the surface layer in the north-south direction, 𝑆𝐸𝑊 is the horizontal spectrum component in the west-east surface layer and 𝑆𝑉𝑆 is the vertical spectrum component on the surface. 3.1 the dominant frequency (𝒇𝟎) and amplification factor (𝑨𝟎) the dominant frequency is the frequency value that often appears in an area so that it is recognized as the frequency value of the rock layers in that area. it can indicate the characteristics of the rock types that comprise it. the dominant frequency value is related to the depth of the reflected plane subsurface, where the reflected plane is the boundary between loose sediments and hard rock (bedrock). so that if the value of the dominant frequency is small, it comes from the reflection of the wave which shows the deeper of the reflection plane. the amplification factor is the magnification of the wave acceleration that occurs on the surface due to the type of soil in an area. the magnitude of the amplification value can be estimated from the contrast of the wave propagation parameters, namely the density and velocity of the bedrock and surface sediments (nakamura, 2000). the greater the difference in these parameters, the greater the amplification value of the wave propagation (gosar, 2007). if the dominant frequency value (𝑓0) is high, it means that the subsurface is composed of hard rock. and if the dominant frequency value (𝑓0) is low, it means that the subsurface is composed of soft rock (sedimentary rock). dominant frequency (𝑓0) is influenced by subsurface velocity (𝑉𝑆) and sediment layer thickness (h) (mucciarelli m, gallipoli mr. 2004). 3.2 inversion of dispersion curve hvsr curve inversion processing was conducted by using dinver software that a neighbourhood algorithm (wathelet, 2005). the assumption is that the used microtremor waves are dominated by rayleigh waves (molnar et.al, 2022). processing begins with the hvsr curve formation tmok (kebo butak formation) tmj (jonggranan formation) koluvium andesite 126 khayati,n.n. et al./ jgeet vol 7 no 3/2022 which is used as input in the ellipticity curve by providing a limitation of the initial model parameter values including p wave velocity (𝑽𝒑), s wave velocity (𝑽𝒔), density (ρ), and poisson ratio so that the error or mismatch value is obtained (misfit) is lowest (0 ≤ misfits <1). some examples of the ground profile appearance of the processing results are shown in figure 2, which shows the value of shear wave velocity (𝑽𝒔) and layer depth for each measurement point. fig 2. ground profile of inversion result 𝑽𝒔 value. 4.1 result and discussion 4.1. microzonation dominant frequency value (𝒇𝟎) and amplification factor value (𝑨𝟎) the distribution of the dominant frequency values in the study area has a range of values ranging from 1 – 22 hz. the measurement results show that almost all research areas have a dominant frequency value that tends to be low which is indicated by the blue colour except at 3 points namely n30, v27, and n8b which have high dominant frequency values which are represented by reddish-orange. the research area that has a low dominant frequency value shows that the area is an area with a very thick surface sediment thickness with a value range of 1 8 hz. on the contrary, an area that has a high-frequency value indicates that the area has a surface sediment layer that tends to be thin and hard rock shallow with a value range of 15 – 22 hz. the micro zonation of the dominant frequency values is shown in figure 3. fig 3. distribution of the dominant frequency values in the study area. the distribution pattern of the distribution shows that the north and south sides of the study area with a history of landslides that are seen directly based on field observations during the acquisition are in an area that has a lowfrequency value which indicates that the area has a thick enough surface sediment layer and it is indicated that the rock the base is at a fairly deep depth. amplification is influenced by shear wave velocity (𝑽𝒔) which is related to the rock density due to reduced rock density which will cause an increase in the amplification factor value. the level of rock density can reduce the khayati,n.n. et al./ jgeet vol 7 no 3/2022 127 amplification of shocks because the amplitude of the waves propagating in solid rock is relatively small, while in rocks with soft characteristics it will slow down the propagating waves and increase the amplitude of the waves which can cause the potential level of landslide due to shocks originating from large earth shakes. the distribution of the amplification factor value can by seen in figure 4. fig 4. distribution of the amplification factor value distribution in the study area. table 1. variation of 𝑽𝒔 value and layer depth name point value of layer 1 𝑽𝒔 value of layer 2 𝑽𝒔 value of layer 2 𝑽𝒔 layer depth 1 layer depth 2 layer depth 3 n1 357.05 897.11 1446.24 8.4097 51.002 104.29 n2 353.52 862.10 1431.61 11.222 60.405 104.12 n3 357.08 812.65 1208.58 7.536 58.04 103.647 n4 353.54 1185.01 1322.95 12.52 77.43 104.28 n5 357.05 1094.90 1418.02 7.613 53.07 102.83 n6 357.03 820.26 1432.11 8.928 80.6 102.26 n7 353.37 788.25 1000.48 5.994 56.901 103.29 n8 353.42 952.30 1197.30 4.6287 93.587 104.17 n12 352.55 888.26 1258.75 8.26 76.696 104.31 n13 353.52 812.08 989.63 7.1 55.783 104.14 n14 357.02 888.35 1221.81 10.7847 54.684 104.31 n15 356.96 905.83 1073.09 6.89 91.74 104.06 n16 357.00 796.13 1460.71 7.463 72.975 103.57 n19 357.10 844.98 1445.46 6.949 63.484 102.35 n20 353.52 764.91 1233.88 1.8716 97.381 104.304 n21 353.47 915.12 1446.56 9.666 58.048 106.668 n22 353.5 780.41 1446.35 6.4281 52.546 72.216 n23 353.5 820.3 1489.85 8.493 64.761 104.25 n26 353.38 871.36 1475.52 22.745 72.24 104.29 n27 353.51 888.04 1322.59 9.29 62.234 104.31 n28 353.53 780.58 1490.10 5.113 62.252 104.25 n29 353.49 820.28 845.16 4.769 77.462 108.14 n30 357.03 1127.84 1431.89 7.383 55.383 103.28 n31 353.504 828.59 1460.86 12.645 55.226 102.2 n24 360.68 888.39 1514.66 8.164 55.231 123.21 n25 360.62 780.48 1514.92 5.994 91.744 113.76 n18 353.55 828.55 1545.69 6.756 56.34 137.49 n17 353.52 836.92 1560.77 7.166 57.44 128.71 n11 360.66 780.08 1607.92 7.7176 52.04 137.49 n10 357.01 897.11 1560.64 9.7627 54.14 117.25 n9 353.52 812.76 1530.1 17.558 67.35 110.45 the value of the amplification factor in gerbosari village has a range of values from 1 – 10.5 and is classified into 3 classes, namely low with a value range of 1.19 – 3.12 indicated by blue. the areas with moderate amplification values have an amplification factor value range of 3.12 – 6.24 indicated by green and areas with high amplification factor values have a range of values ranging from 6.24 10.55 which is indicated by dark purple. when we see the distribution of the amplification factor value distribution in the study area, it shows a pattern in the form, on the north side and west side the amplification factor value tends to be medium-high which indicates that 128 khayati,n.n. et al./ jgeet vol 7 no 3/2022 the area has a large contrast of bedrock and surface sediments. meanwhile, the western and southern sides of the research area show a low amplification factor value. 4.2 ground profile 𝑽𝒔 ground profile 𝑽𝒔 value is a method that can be used to determine the characteristics of the constituent material so that it can be used to determine subsurface lithology. to obtain parameter values is adjusted to the geological conditions in the study area, namely, the value of 𝑽𝒔has a range between 350 – 1500 m/s, the value of 𝑽𝒑 has a value range of 250 – 2500 m/s, and the value of σ has a range of values between 0.2 – 0.5 and a density of 1200 – 2800 kg/m3. it can be assumed that there are 3 layers in the area. and the ground profile identifies 3 layers with varying depths as being shown in table 1. the first layer has a thickness variation of 1 – 22 meters, the second layer varies in thickness from 51 to 97 meters and the third layer varies in thickness from 72 to 123 meters. 4.3 microzonation of weathered layer thickness value based on the inversion results, the coating value for each point as shown in table 1 can be used to microzone the weathered layer thickness value in the area by using the thickness value in the first layer as being shown in figure 5. based on the results of microzonation in figure 3, it can be seen that most of the research areas have a high enough thickness value of the sediment layer on the northeast side, the middle side of the research area, and the southern part of the study area with a value range between 12-22 meters which is shown by green and red colour. thick weathered layers are around points n31, n26, n23, n16, n12, n11, n10b, and n9 with thicknesses of 12.6, 22.7, 8.4, 7.4, 8.2, 7.7, 9.7, and 17.5 meters. meanwhile, the areas with thin weathered layer thickness characteristics have values ranging from 4.6 7.3 meters which are indicated by the blue colour. 4.4 analysis of slopes the slope of an area that has the potential for landslides is a major factor, especially in areas with a slope of more than 15°. the slope in an area is the main controlling factor that causes landslides. a steep slope or cliff will increase the driving force. and when the driving force of a rock on a slope is greater than the bearing force, a landslide will occur. the determination of value of the slope is determined by using height data from demnas, the classification of slopes is divided into 7 classes regarding the slope classification by (sitanala,1989) as shown is in figure 6. based on figure 6, the slope of gerbosari village is dominated by a rather steep and very steep classification on the north and south sides with a history of landslides that are quite frequent. this shows that this side of the area has a high enough potential due to the effect of the slope. besides the slope, the north side has a weathered layer thickness with a high classification with a value of 16-22 meters. the soil characteristics in the area are at a frequency value of 1 5 hz which indicates that the area has soft soil types. meanwhile, on the middle side, it shows the slope with a slightly sloping rather steep classification and it is can be known that the area has the potential for landslides which is quite low when compared to the north and south sides. fig 5. microzonation of weathered layer thickness values in gerbosari village. khayati,n.n. et al./ jgeet vol 7 no 3/2022 129 fig 6. map of the slope of the village of gerbosari slopes. fig 7. the layer of weathered thickness around the n30 and n26 points. 130 khayati,n.n. et al./ jgeet vol 7 no 3/2022 4.5 landslide potential analysis based on the history of landslides that often occur in gerbosari village, landslides often occur on the north side of the research area and are around points n30 and n26. the results of the analysis show that the area is on a rather steep slope as shown in figure 6. based on the results of the inversion and a cross-section of the incision was performed to determine the thickness of the weathered layer in the area as shown in figure 7. figure 7 shows, the area is on a slope of 30 ° with a weathered layer thickness of 17m as the driving factor. the existence of a driving factor disrupts slope stability, especially on steep slopes, which can cause landslides to occur. landslides in this area are also caused by the influence of high rainfall intensity. where the slope instability is due to periodic rain which causes the water in the soil to flow laterally so that the degree of saturation of the soil increases and reduces the pore water pressure resulting in decreased shear strength. this decrease in soil shear strength and increase in shear stress causes landslides to occur. 5. conclusions the result of microtremor measurement shows that the dominant frequency is in the range of 1 22 hz. in the research area, the dominant frequency value tends to be in a low class which indicates that the area has soft soil characteristics. the amplification value in the study area shows the pattern on the north and west sides of the study area have a high enough value which indicates that the area has a small rock density which causes a high magnification of waves. the value of the amplification factor in gerbosari village has a range of values from 1 10.5. the study area is in a condition with a slope classification that is rather steep very steep with a slope of 30-> 65 °. the north and south sides, of the study area, have a very steep slope classification where in this area, there is a history of previous landslides. then, based on the inversion results for each point, the value of each layer is obtained where the layer which is assumed to be weathered is used for the analysis of the thickness of the weathered layer as a driving factor for landslides in steep areas. so, the area that has the most landslide history is on a rather steep slope very steep with a thick weathered layer 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engineering, environment, and technology 5(3), 124128. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). https://doi.org/10.5614/bull.geol.2017.1.1.3 http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 2 2022 rahmad, b. et al./ jgeet vol 7 no 2/2022 87 research article the role of inertinite characteristics and coal porosity of seam a-1 of the muara enim formation in west merapi, lahat, south sumatera, indonesia basuki rahmad 1,*, budi prayitno2 , susilawati, s.s.r3, sugeng1 , ediyanto1 , nanda ajeng nurwantari1 1department of geological engineering, universitas pembangunan nasional “veteran” yogyakarta, indonesia 2department of geological engineering, universitas islam riau (uir) riau, indonesia 3geological agency, center of resources mineral, coal and geothermal, kementerian energi sumber daya mineral, republik indones ia * corresponding author : basukirahmad@upnyk.ac.id tel.:+62-815-7927-863 received: feb 16, 2022; accepted: jun 30, 2022. doi: 10.25299/jgeet.2022.7.2.8986 abstract coal contains a complex network of nano-, meso-, and a macro-pore can store fluids and allow fluids to flow through it. nanoporosity in coal is primarily a result of molecules that have aromatic molecular structures and have been preserved in coal. most adsorbate compounds, including gases, are stored here. the study area is located in south sumatera, west merapi area, lahat regency. geologically, the area in south sumatra basin belongs to the middle-late miocene muara enim formation. using the ply-by-ply method, coal samples were taken directly from seam-a in the coal mine walls outcrop, based on macroscopically determinable lithotype information. during laboratory analyses, coal is microscopically analyzed to determine the amount of porosity, permeability, and vitrinite reflectance. the purpose of this study is to investigate the change in composition and characteristics of inertinite macerals when the porosity value is varied.. vitrinite content is between 91.00-92.80 %; liptinite 0.90-3.40%; inertinite 3.70-4.80%; mineral matter 0.7%-1.8%. withh a vitrinite reflectance average of 0.34-0.36%, the variation in composition is an indication of changes in plant communities or coal facies. it is generally classified as sub-bituminous coal (astm). porosity value of seam a upper is 1.9% and seam a lower 1.51%, permeability value seam a upper is 70.1 md and seam a lower 27.1%. composition of mineral matter in seam a upper is 0.8% and seam a lower 1.7%. the increasing number of inertinite pore is followed by lower porosity value. the inertinite maceral is predominantly aromatic with a high level of cross-linking, and exhibits a high level of aromatization and condensation. they have the highest carbon and the lowest oxygen hydrogen content. a coal maceral's porosity is composed of void spaces, such as open cell lumens preserved in semifusinite and sclerotinite. the porosity of cleats is the percentage of volume in relation to volume of coal, and the porosity of permeability. in coal, semifusinite has extensive interconnected pores that can form significant conduits for fluid flow. keywords: inertinite, porosity, mineral matter, permeability, fluid flow, vitrinite reflectance 1. introduction 1.1 sub introduction considering coalbed methane plays typically span large areas of sedimentary basins, as well as the fact that the gas is mainly stored in an adsorbed state rather than free, coal is classified as a continuous-type, unconventional gas reservoir. even though it is commonly believed that coal reservoirs are continuous, the properties of coal reservoirs are extremely heterogeneous. in fact, geologic factors can influence storage capacity, hydrocarbon content and production (isabel, 2012). the geological factors influencing commercial hydrocarbon production in sedimentary basins vary considerably. the researched area is part of the muara enim formation. according to (ginger and fielding, 2011), this formation is a filler in the middle-late miocene south sumatra basin which is composed of. carbonaceous, lenticular, laminated claystone, tuff sandstone, and coal interbedded. there are two coal seams, petai, and merapi, in the muara enim sandstone unit, and two coal seams in the muara enim claystone unit, mangus, which will be the research target in the seam-a and suban part of seam-b. coal is classified as sub-bituminous (koesoemadinata, 2002). the coal contains a complex network of nanopores (<nm), mesopores (2-50 nm), and macropores (>50 nm) that enclose fluid, through which it can be transported and stored. as stated earlier, the large majority of adsorption compounds, including gases, is stored in coal's nanoporosity, which is apparently caused by the aromatic moleculer structure of its biopolymers. (isabel, 2012). macerals of inertinite have a high aromatization and condensation rate and are formed from mainly aromatic structures with a high degree of crosslinking. there is also porosity in coal macerals such as open cell lumens preserved in fusinite that can contribute to porosity. the macropores associated with primary coal fabric are largely not interconnected, therefore, it does not appear that they play an important role in coal bed methane production. nevertheless, semifusinite can contain considerable porosity and act as an important conduit for coal fluid flow. (isabel, 2012);(diessel et al., 1992) (hodot, b.b., 1996) hodot, (1966) classified coal pores into macropores (pores http://journal.uir.ac.id/index.php/jgeet 88 rahmad, b. et al./ jgeet vol 7 no 2/2022 larger than 1,000 nm), mesopores (pores of 100 to 1,000 nm), transition pores (10 to 100 nm), and micropores (10 nm or smaller). there are various porous structures in a matrix with irregular surfaces and irregular structures. porosity of coal beds is also affected by chemical structure, composition, and characteristics (mastalerz et al., 2008; (rahmad, kusumayudha et al., 2018). in addition, the rank of coal also affects porosity (rahmad, raharjo and rahmanda, 2020). based on their size, there are four types of pores in the matrix: macro, meso, transition, and micropores. it appears that macropores are found in lowgrade coals, while the others are found in high-grade coals, according to rahmad, kusumayudha et al., 2018. the porosity of the coal will be affected by changes in the pore structure of the inertinite maceral. the more inertinite maceral in the coal, the greater the porosity of the coal, and vice versa (raharjo, 2018). inertinite maceral shows regular and irregular pore structures (size, shape, and distribution). as the pore structure in inertinite is irregular, it affects the porosity value in coal. through petrographic observations of inertinite maceral coal, it can be seen whether the pore structure of the coal is regular or irregular. this can be used to determine whether the porosity of the coal is large or small. the vitrinite reflectance (rv) is one of parameter to determine of coal rank or maturity especially in thick muara enim fomration’s coal (stach, 1982) one parameter to determine the composition of coal microscopy is from the aspect of coal type, which relates to coal-forming plant species and in its development will be influenced by biochemical processes during the peat process and the potential of coal methane gas resources in keban area, lahat south sumatera (figure 1). an objective of this study is to determine the composition and characteristics of inertinite macerals as porosity changes. fig 1. location of the research, west merapi, lahat, south sumatera fig 2. regional stratigraphy (de coster, 1974 ; ginger and fielding, 2005). rahmad, b. et al./ jgeet vol 7 no 2/2022 89 2. geological setting the south sumatera basin is one of back arc basin in sumatera island that was forming by tectonic activity of indo australian plate and eurasian plate since cenozoic to recent. cretaceous-eocene orogeny was resulting graben and half graben where filled up with terrestrial, volcaniclastic and deltaic sediment. on the early neogene was going to the transgresive system sediment such as carbonate and marine clastics. the end of neogene regressive system was very dominant producing fluvial to deltaic sediment. in this period was the beginning of high tectonic activity which produce a structural inversion and folding (darman, h., sidi, h.f., 2000) (bemmelen, 1969) within this basin area, 330510 km2, there is a tertiary sandstone outcrop called barisan hill in the southwest, as well as a shelf (sunda shield) to the east, a mountain range to the west, and the lampung highlands in the southeast (a. j. barber, m. j. crow, 1974). as mentioned previously, syn orogenic/inversion megasequence tectonics dominate the area under study, which according to (ginger and fielding, 2011) has resulted in several structural traps for hydrocarbons in the south sumatra basin. it is an east-west oriented anticline that dominates the muara tiga besar area. a similar slope of the layer is observed in the studied area to that of the northern limb of the anticline (homocline). studies were conducted in a part of the muara enim formation, an infill formation that lies within the south sumatra basin. the formation dates back to the middle-late miocene, say (ginger and fielding, 2011). a period of increased volcanic activity occurred during the late miocene in the bukit barisan mountains. fluvial-deltaic environments deposit the vast majority of sediment material. generally, the south sumatra basin stratigraphy can be viewed as consisting of one megacycle, which includes transgression followed by regression. during the transgressive phase, the talang akar, baturaja, and gumai formations were deposited. while the air benakat, muara enim, and kasai formations were deposited during the regressive (air benakat, muara enim, and kasai formations), the lemat and older lemat formations were deposited before the main transgressive. (ginger and fielding, 2011); (figure 2). the studied area consists of muara enim sandstone unit and muara enim claystone unit with their respective lithologies: carbon laminated, glauconitic sandstone, and coal interbedded. material in the claystone unit consists of lenticular claystone, tuf sandstone, and carbon laminated claystone. as shown in figure 3, the muara enim sandstone unit consists of coal seam c (petai) and seam d (merapi), the muara enim claystone unit contains coal seam a-1 (mangus, which is the target of the research) and b (suban). the rank of coal in the studied area are subbituminous-high volatile bituminous (koesoemadinata, 2002);(diessel et al., 1992) ; (diessel et al., 1992). fig 3. the stratigraphy and coal formations of muara enim (shell mijnbouw, 1978) 3. sample and methods a study of coal mining was conducted in the lahat region and its surrounding areas. field methods include observation of coal seams, sampling for gasification development planning, and collecting infrastructure data. in muara enim formation, seam mangus seam a-1 (10 meters) is the target coal seam. (figure 4). the coal samples were taken from the coal mine walls at seam-a by the ply-by-ply method and based on the appearance of the lithotype macroscopically. each sample is then reduced in size, and a composite is divided into two for archive purposes and laboratory analysis. laboratories perform the following analyses: a. coal porosity analysis, coal that has been cut into a beam shape is used to measure the porosity. the diameter of 90 rahmad, b. et al./ jgeet vol 7 no 2/2022 the beam is 2.5 cm and its height is 2 cm. in the following step, for one hour we put the dry sample into a vacuum desiccator and saturated it with kerosene. b. an examination of coal microscopically to reveal maceral, vitrinite reflectances and mineral matter. during the polishing procedure, coal samples carried out from the mining wall outcrop. in order to prepare them, a variety of materials and tools need to be used, including: (1) coal samples (2) pounder tool (3) resin/ transoptic powder (4) sieve sizes 16, 20 and 65 mesh (5) thermometers, and presses and print polished briquettes (6) grinding-polish machine (7) alumina oxide in sizes of 0.3, 0.05, and 0.01 microns; and 800 and 1000 mesh silicon carbide (8) objective glass and night candles. fig 4. coal sampling of seam a-1 to obtain enough samples for analysis, the coal samples are quartered and concentrated from drill cores. afterward, manual crushing of the coal samples was followed by sieving with mesh number 16 and 20. that grain size fractions of coal were used for petrographic analysis. coal fractions with an average size of -16 mesh + 20 mesh are mixed 1:1 with resin/ transoptic powder. a 200oc heat is then applied to the mixture in the mold. the mold is then pressed to 2000 psi after reaching 200oc and the heater is turned off. once the briquette reaches room temperature, it can be removed. as a next step, briquette polishing begins with a cutting tool (grinder-polisher) followed by smoothing with silicon carbide sizes of mesh 800 and 1,000. after that, polish with 0.3 microns, 0.05 microns, and finally 0.1 microns alumina oxide on silk or silk fabric. using the night candle holder, the polishing incisions are placed on the preparatory glass, followed by leveling. polishing incisions are analyzed under a reflectance microscope both qualitatively as well as quantitatively to determine the mineral content and minerals in coal. an investigation using reflected light and examining 500 points under 200-fold magnification. researchers conducted the analysis at the r&d center for mineral and coal technology in bandung, indonesia, under spectrophotometer polarization with fluorescence with microscope, type: mpm100, brand: zeiss, is used in the coal mining classification (2856-1986., 1986) 4. results and discussion five coal samples from west merapi were analyzed to determine the composition of the seam a-1 coal: a-1(1), a1 (2), a-1 (2), a-1 (3), a-1 (4), a-1 (5) (tables 1 and 2) is vitrinite between 91.0% 92.8% ; liptinite 0.9% -3.4% ; inertinite 3.7%-4.8%. and mineral matter 0.7%-1.8% with vitrinite reflectance value 0.34%-0.36% (rv random) which interpreted as lignite. there are several microscopic features of the maceral group of vitrinite, including telovitrinite that is light to dark gray, light layers consisting of telocollinite, which no longer acts as a matrix for showing wood fiber structure, and detrovitrinite by an average of 55.1% trapped within inertinite, liptinite, and mineral matter. in the subgroup maceral detrovitrinite, desmocollinite, dominates the larger percentage of macerals. approximately 7,8% of densinite is found in a fine sized mix of vitrinite fractions, more tightly and homogeneously distributed than attrinite. in general, gelovitrinite tends to be homogeneous, round-oval in shape, and generally isolated inside desmocollinite. only gelovitrinite maceral corpogelinite is found in the gelovitrinite subgroup (figure 5). fig 5. coal microscopic of seam a-1 rahmad, b. et al./ jgeet vol 7 no 2/2022 91 table 1. macerals and mineral matter composition and reflectance vitrinite value of seam a-1. no . a re a a g e f o rm a ti o n sample no. lithotyp e maceral analysis maceral group (% vol.) mineral matter (% vol.) rv random vitrinite (humminite) liptinite (exinite) inertinite telovitrinite (humotelinite) detrovitrinite (humodetrinite) gelovitrinite (humocolinit e) telo-inertinite detro inertinite gelo inertinit e t e x ti n it e t e x to -u lm in it e e -u lm in it e t e lo co ll in it e a tt ri n it e d e n si n it e d e sm o co ll in it e c o rp o g e li n it e p o ri g e li n it e e u g e li n it e s p ro ri n it e c u ti n it e r e si n it e l ip to d e ri n it e a lg in it e s u b e ri n it e f lo u ri n it e e x su d a ti n it e b it u m in it e f u si n it e s e m if u si n it e s cl e ro ti n it e in e rt o d e tr in it e m ic ri n it e m a cr in it e o x id e p y ri te c la y 1 l a h a t m id d le l a te m io ce n e m u a ra e n im a-1 (1) top coal, black, dull, spotly vitreous, blackish scratched , blocky 91.0 3.4 4.8 0.8 0.3 4 1. 7 2. 1 80. 9 2. 4 3.1 0. 8 0. 3 2. 6 0. 5 1. 7 1. 0 1. 1 1. 0 0. 8 2 a-1 (2) coal, dark browish blackblack, dull, rarely vitreous streaks, blackish scratche d, blocky 92.0 2.1 4.1 1.8 0.3 5 1. 9 2. 3 80. 4 2. 6 3.6 1. 2 1. 4 0. 7 1. 3 1. 4 0. 8 0. 6 1. 8 3 a-1 (3) coal, black, dull, rarely vitreous streaks, blackish scratched, blocky 91.9 2.6 3.9 1.6 0.3 5 1. 8 2. 7 81. 0 2. 3 3.2 0. 9 0. 2 0. 8 0. 4 1. 2 1. 8 1. 2 0. 6 0. 3 0. 2 1. 4 4 a-1 (4) coal, dark brownish blackblack, dull, blackish scratched, blocky 92.7 2.8 3.8 0.7 0.3 6 2. 3 2. 8 65. 0 4. 6 14. 2 3. 8 2. 3 0. 5 1. 4 1. 8 0. 3 0. 3 0. 7 1 a-1 (5) botto m coal, dark brownish blackblack, dull, blackish scratched, blocky 93.7 0.9 3.7 1.7 0.3 6 1. 9 1. 4 70. 9 8. 8 9.2 1. 5 0. 6 0. 3 2. 0 0. 7 0. 8 0. 2 1. 7 fig 5. coal microscopic of seam a-1 92 rahmad, b. et al./ jgeet vol 7 no 2/2022 table 2. macerals composition, porosity and permeability of seam a-1 no sampel rv random maceral group (% vol) mineral porosity permeability sample photo vitrinite liptinite internite matter (% vol.) % md darcy 1 a(1) top 0.34 91.0 3.4 4.8 0.8 1.9 70.1 0.07 2 a-1 (4) 0.35 92.0 2.1 4.1 1.8 1.85 41.4 0.04 3 a-1 (3) 0.35 91.9 2.6 3.9 1.6 1.75 17.7 0.18 4 a-1 (2) 0.36 92.7 2.8 4.1 0.7 1.55 48.6 0.49 5 a-1 (1) bottom 0.36 93.7 0.9 4.8 1.7 1.51 27.1 0.27 the inertinite maceral group of seam a composed by telo-inertinite and detro-inertinite. there is only maceral inertodetrinite in macro-detro-inertinite. compared with semifusinite, there is a major difference between maceral teleo-inertinite and maceral fusinite, in that the former has a higher relief and thinner cell walls. furthermore, the structure appears clearer than semifusinite. over 5% of all samples are composed of sclerotinite maceral (figure 5). the maceral sclerotintes have oval or circular forms with high reflective properties, and they are believed to come from a fungus that contains black melanin known as mycelia. mineral matter analysis shows that the coal seam from the seam-a contains pyrite that present mostly as fine crystals within the dense macerals (table 1; figure 5). porosity and permeability values of seam-a coal in east merapi of 5 coal samples (table 2) are: a-1(1), a-1 (2), a-1 (2), a-1 (3), a-1 (4), a-1 (5) show the porosity between 1.52%-1.9 % and the permeability 17.7-70.1 md. the comparison between the inertinite content and the porosity value shows that the incrasing inertinite parallelly to porosity while the permeability value tends to increase (table 2). in coal, fluids can be stored and can flow through a complex network of nanoporous (*nm), mesoporous (2-4 nm), and macroporous (>50 nm) spaces. it appears that aromatic molecular structures of biopolymers are the major source of nanoporosity in coal, and as mentioned earlier, this is where the vast majority of adsorbed compounds are stored, including the gases. the flow within the polymeric network is controlled primarily by diffusion rather than by darcy flow, and the direction of flow within the nanostructure is determined by fluid concentration gradients rather than by pressure gradients.(bustin, r. m. and clarkson, c. r., 1999); (pone, halleck and mathews, 2009) speculated that mesopores might provide space for multilayer adsorption in coal, but in reality we know less about their structure and origin. as pore sizes increase, darcian flow becomes more significant, and coal can contain macroporosities exceeding 5% at standard pressure (isabel, 2012); (mazumder et al., 2006). in coal macerals, void spaces are found in the form of open cell lumens preserved in pyrofussite. coalbed methane production appears to be limited to a few macropores associated with the primary coal fabric. however, semifusinite may have considerable porosity and may form important conduits for fluid flow. the interconnected macropore space in coal is largely defined by natural fractures, particularly cleat systems, and is therefore of primary importance to reservoir properties. the coal cleat system consists of face cleats and butt cleats, which are orthogonal fracture systems with close spacing (cm to mm scale), analogous to joints in other rock types. (figures 6 and 7). the pores structure of coal, such as pore size, pore shape, pore distribution and interconnection between pores, can determine the porosity and permeability of coal, which is influenced by the type of coal and rank of the coal (zhang et al., 2014) the matrix structure related to the abundance of pore volume, like micropores, mesoporous and macropores, is a function of coal organic matter and vitrinite reflectance (laubach, 1998); (bustin, r. m. and clarkson, c. r., 1999); (pone, halleck and mathews, 2009) ; (harpalani, s., schraufnagel, r.a., 1990); (harpalani, s., chen, g., 1995) understanding the composition of maceral is important in understanding the properties of coal pores, porosity, and coal permeability when coal rank is stable or changes rahmad, b. et al./ jgeet vol 7 no 2/2022 93 regularly (zhang et al., 2014) the composition of inertinite maceral contains more mesoporous (clarkon & bustin, 1996), in samples a-1 (1) and a-1 (2) as in figure 5 that show the presence of pores in inertinite maceral which are different, especially in shape, pore size and pore distribution, in sample a-1 (1) the number of pores in inertinite is less than that in sample a-1 (2). fig 6. cleat system of seam a-1 fig. 7. the gases bubble on permeability by cleat system of seam a-1 according (bustin, r. m. and clarkson, c. r., 1999); the increase in vitrinite reflectance will cause the number of mesoporous and micropores develop as a result of the smaller porosity. the increase in vitrinite reflectance will affect the porosity of the coal, the coal sample a-1 (1) top rv random = 0.34% has a porosity of 1.9% and sample a-1 (2) rv random = 0.35%, the porosity decrease to 1.85% (table 2). this is due to the coal processes and combined with the continuous physical compaction will decrease the coal porosity. permeability data from both samples show that sample a-1 (1) has permeability 70.1 md, while sample a-1 (2) has permeability 27.1 md. this permeability change is due to the fact that the two samples have different mineral matter, in sample a-1 (1) has mineral matter = 0.8% while sample a-1 (2) is 1.7%. mineral matter will fill the pores in coal, the more mineral matter, the flow of fluid and gas will be obstructed. conclusion the increasing inertinite content is followed by the higher porosity value porosity consists of void spaces in coal macrocrystalline materials, which can be preserved in the intracellular space in inertinite (semifusinite and sclerotinite) semifusinite has considerable pores that can conduct fluids, which can be important for coal fluid flow the increase of vitrinite reflectance causes the porosity decrease, because the pores in inertinite is developed into mesoporous and micropores the increase in mineral matter causes permeability decrease due to mineral matter filling the pores, which will inhibit the flow rate of fluids or gases. acknowledgements to universitas pembangunan nasional "veteran" yogyakarta the authors would like to thank the ministry of education and culture of the republic of indonesia as well as the institution of research and service community (lppm) for funding and pt. bara alam energi for providing opportunities and facilitating research. references 2856-1986., a. s.-a. 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(2014) ‘journal of natural gas science and engineering determining fractal dimensions of coal pores by fhh model : problems and effects’, journal of natural gas science and engineering, 21, pp. 929– 939. doi: 10.1016/j.jngse.2014.10.018. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/bysa/4.0/). http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 7 no 3 2022 132 abdurrokhim et al./ jgeet vol 7 no 3/2022 temporal variation in sandstone composition of miocene jatiluhur formation in the bogor trough, west java, indonesia abdurrokhim 1*, billy g. adhiperdana1, hendarmawan1 1faculty of geological engineering, padjadjaran university, jatinangor, 45363, west java, indonesia * corresponding author : abdurrokhim@unpad.ac.id tel.:+62-822-6103-1000 received: apr 12, 2022 accepted: sep 23, 2022 doi: 10.25299/jgeet.2022.7.3.9311 abstract bogor trough in the west java are typified by turbidity deposits with the source are mostly characterized by volcanoclastic materials from the southern area. the trough actually receipt the sediment from both volcanoclastic materials from the south and continental source from the north. but, the discussions of sediments in term of composition and temporal variation are rare to be reported, especially the sediments from the north. this manuscript intends to discuss the temporal variation in detrital compositional and depositional facies of the neogene sediments that delivered from the north (i.e., sundaland) into the bogor trough, which is represented by miocene jatiluhur formation. a total of 36 selected samples have been taken for identifying the minerals using a polarization microscope. modal analysis of the gazzi-dickinson method was applied for this provenance study of sandstones samples, which are consisting largely of quartz and feldspar, then sedimentary rock and volcanic rock fragments, glaucony, mud chips and skeletal fragments. sundaland, a continental block highland area in the north, is interpreted to have been the provenance of sediments of the jatiluhur formation, which is also considered to be the source area for the paleogene sediments. granitic igneous rocks are interpreted as the source of dominance of monocrystalline quartz grains, or the product of long-distance transport of polycrystalline quartz from metamorphic rocks but, however late miocene samples (upper part of formation) represent that the size and amount of glauconite grains are increasing, and texturally mud supported. volcanic rocks materials are also observed. the upper part of jatiluhur formation records the starvation of sediment discharge into the basin, which has been also promoted for development of carbonate reef klapanunggal formation in the self-margin setting, and suggesting that the basin have directly received or indirectly some contemporaneous volcanic provenances sediment from the southern area. keywords: provenance sediment, sandstone, facies, jatiluhur formation, bogor trough 1. introduction the bogor trough in the center part of west java was an elongated east–west trending, represented mainly by thick volcanoclastic deep-water deposits with maximum thickness in the center part around 7000 m (martodjojo, 2003), in association with shallow-marine siliciclastic and carbonate successions along the northern basin margin (abdurrokhim & ito, 2013). the trough was considered to have developed as a foreland basin, seated on the southwestern margin of sundaland in response of interaction between eurasian plate and indian-australian plate to the north (ben-avraham & emery, 1973; clements, hall, smyth, & cottam, 2009; decelles & giles, 1996; hamilton, 1979) (fig. 1). neogene sediments into the bogor trough were delivered from south, typified by volcanoclastic sediments, and from the north which is characterized by continental source sediments. however, discussion of provenance sediments, especially from the north during neogene time in association with late miocene carbonate development in the bogor trough is not yet well reported. in the jonggol area (fig. 1 & 2), an area in between bogor trough and nw java basin, a continued stratification of miocene jatiluhur formation (ca.1000 m in maximum thickness) is well exposed (sudjatmiko, 1972). the formation was developed as a slope–shelf system and is represented mainly by southto southwestward-directed paleocurrents (abdurrokhim & ito, 2013). variation of framework composition of northdelivered siliciclastic sediments in local association with carbonate deposits in the north is very crucial, as represents miocene deposits in the bogor trough, for guiding a better understanding of sediment delivery systems in the southern margin of sundaland. in this manuscript, we discuss provenance of jatiluhur formation, compositional and temporal variation of neogene sediments in the northern edge of the bogor trough, in association with development of limestone klapanunggal formation and volcanic activity. 2. stratigraphic setting bogor trough was seated on the southern margin of sundaland (fig. 1), showing an east-west physiographic elongation in the middle part of west java and part of modern magmatic arc location. the jatiluhur formation is the oldest exposure sedimentary rock unit that discovered in this area that represents the sediment source were delivered mainly from the north (abdurrokhim & ito, 2013). the formation are distributed from purwakarta to the east until bogor to the west, and were covered locally by quaternary sediments and volcanoclastic deposits (effendi, kusnama, & hermanto, 1998; sudjatmiko, 1972) (fig. 2). the formation is consisting of quartz sandstones and marl, siltstones, mailto:abdurrokhim@unpad.ac.id abdurrokhim et al./ jgeet vol 7 no 3/2022 133 claystones, limestone beds, tuffaceous breccias and basalts, and was deposited during the middle miocene (septama et al., 2021). fig 1. (a) indonesian region tectonic setting, represents indian-australian plate subducts below the eurasian plate, research area is located on the southern edge of mesozoic sundaland core (hall, 2002). (b) the outline of bogor trough and surrounding in the west java. modified mainly after martodjojo (2003). but in the research area, where the samples taken from from the cipamingkis and cileungsi river sections, the jatiluhur formation was deposited in the middle–late miocene (n12–n16) (nurani, 2010; zahara, 2012) (fig. 3). jatiluhur formation is unconformably overlaid by a volcanoclastic deposits of the cantayan formation to the south (n17–n18), and conformably overlaid by carbonate reef klapanunggal formation to the north (n14–n16). those formations are conformably overlain by marine mudstone dominated facies of subang formation (n17) ((septama et al., 2021) (fig. 2 & 4). an emergence of volcanic materials in the early neogene was interpreted as the establishment of the bogor trough, which later was extensively prograding to the north (martodjojo, 2003), and cantayan formation is the youngest deep-water volcanoclastic deposit in the research area (fig. 4). 3. samples and method in the research area, jatiluhur formation consists of siltstones and sandy siltstones, very thin to thick-bedded sandstone, thick-bedded carbonate in the upper part, channel-fill deposits, slump and slump-scar-fill deposits in the lower part (abdurrokhim & ito, 2013). fig 2. geological sketch map of bogor-purwakarta area, where research area located in the north-western part (sudjatmiko, 1972). jatiluhur formation is overlaid conformable by carbonate klapanunggal formation to the north, and to the south by volcanoclastic cantayan formation. both klapanunggal and cantayan formations developed mainly during late miocene. 134 abdurrokhim et al./ jgeet vol 7 no 3/2022 fig 3. selected measured sections from cileungsi and cipamingkis rivers indicating major biostratigraphic age datums and stratigraphic positions of sandstone samples for petrographic analyses. fig 4. thick-bedded sandstone overlaid slump deposits of the jatiluhur formation observed in the cileungsi river. figure circled for scale. there are 36 selected sandstone samples from sandstone outcrops (fig. 5 & 6), and prepared for thin section analysis using a polarizing microscope. among these samples, there are 25 samples were taken from lower part of jatiluhur formation (i.e., middle miocene deposits) and the other 11 samples were taken from the upper part of jatiluhur formation (i.e., late miocene deposits). sandstone samples were collected from various lithofacies associations, which are taken along the cileungsi and cipamingkis rivers (fig. 3). modal analysis is conducted, by using point-counting of 450 or more framework grains per thin section. for minimalizing compositional effect of grain size, the gazzi dickinson method was adopted (garzanti, 2019), although framework grains larger than 0.0625 mm in size were mainly examined by the present study. each grain was assigned to one of two components, framework and interstitial components, and framework composition was recalculated on the three categories of non-carbonate extrabasinal grains (table 1). 4. petrographic analysis 4.1. texture and composition sediments of jatiluhur formation consists of siliciclastic and carbonate. feldspar and quartz are the most prominent framework grains found in sandstone beds in the lower interval. in addition to quartz and feldspar grains, skeletal carbonate fragments and glaucony are also commonly found in the upper interval (fig. 8c & d). sandstones commonly show arenite textural framework (fig. 7a). however, small numbers of matrixrich, wacke to subwacke sandstones were also found (fig. 7b.). the size and shape of sand framework grains are diverse, and are composed angular to rounded of fineto mediumgrained, poorly sorted to moderately sorted sand grains. samples contents are mostly quartz, alkali feldspar, plagioclase, and rock fragments (extra basinal), glaucony, mudstone chip and skeletal fragments represent intrabasinal components (fig. 8b). the dominance quartz abdurrokhim et al./ jgeet vol 7 no 3/2022 135 grains are monocrystalline quartz, typified by subrounded to sub-angular shapes with locally represent strained features, overgrowth, and undulatory extinction. some polycrystalline quartz grains are locally also observed. quartz volume is ranging 3 to 72% of the total samples, with a mean of 34.6%. in the upper interval, relative grain abundance of quartz abruptly decreases, while abundance of plagioclase grains is increasing (fig. 8a). the second most common mineral frameworks are feldspar grains, and then become the most dominance mineral framework grains in the upper part (i.e. the late miocene samples). both alkali feldspars and plagioclase are observed in whole samples. the numerous of alkali feldspars are more dominance compare to plagioclase feldspars, except in few sample from the upper part intervals. although a staining method is not used in this study, feldspar grains can be distinguished from quartz, and the presence of clouded appearance and twin structures are the indicator for separating alkali feldspar and plagioclase in thin sections. plagioclase is characterized by distinctive albite twinning, (fig. 8b & d), and are common to be partly replaced by clay minerals and carbonate. total feldspar grains are ranging 31 to 91%, with a mean of 56.2%. the minor components of mineral frameworks are rock fragments, characterized by sub-rounded to rounded grains of mostly metamorphic rock fragments. in the upper part intervals, some samples represent volcanic rock materials, characterized by very coarse-grained, angular to sub-angular, and represents porphyritic texture (plagioclase phenocrysts in microlite groundmass) (fig. 8c). the groundmass comprises mostly volcanic glass and has been replaced partly by carbonate. this volcanic glass also has been altered locally become clay minerals and carbonates. the rock fragments volume is ranging of 25%, with a mean of 9.2%. glauconite minerals are observed at almost all interval, but in the upper part of jatiluhur formation samples (late miocene), size and volume of glauconite grains is increasing (fig. 8b). 4.2. classification based on percentage matrix and relative abundance of total quartz and feldspar grains and rock fragments, petrographic facies of miocene jatiluhur formation can be classified into 2 groups: (f1) feldspathic arenite, and (f2) feldspathic greywacke (fig. 7a & b). feldspathic arenites (f1) (boggs, 2009; garzanti, 2019) composed of quartz grains (monocrystalline + polycrystalline) < 90%, feldspar <40% of feldspar and the rock fragments <10%. sandstones are commonly medium-grained size, moderately sorted, consisting of fineto coarse-grained, grain-supported, carbonate cement in the matrix. coarse-grain fragments are usually skeletal fragments or foraminiferal tests. feldspathic greywacke (f2) is matrix supported, compositionally similar to f1, with the matrix abundant ranging more than 15%. this facies is commonly taken from muddy sandstones. fig 5. lenticular geometry of fine-grained sandstone bed of the jatiluhur formation observed in the cipamingkis river. figure circled for scale. figu 6. n-s stratigraphic column of the cenozoic stratigraphic units in west java (djuhaeni & martodjojo, 1989; martodjojo, 2003; septama et al., 2021) 136 abdurrokhim et al./ jgeet vol 7 no 3/2022 table 1. modal composition of the middle – late miocene jatiluhur formation sample quartz (%) feldspar (%) rock fragment (%) mono quartz (%) feldspar (%) lithic (%) 1 71.59 25.17 3.23 69.28 25.17 5.54 2 32.46 64.06 3.48 30.72 64.06 5.22 3 22.02 69.72 8.26 21.41 69.72 8.87 4 38.93 54.13 6.93 38.40 54.13 7.47 5 22.95 67.71 9.35 21.25 67.71 11.05 6 27.48 64.75 7.77 25.76 64.75 9.50 7 50.47 40.65 8.88 48.36 40.65 10.98 8 35.96 50.00 14.04 32.46 50.00 17.54 9 35.69 54.88 9.43 32.66 54.88 12.46 10 37.00 60.79 2.20 35.68 60.79 3.52 11 22.28 74.75 2.97 22.28 74.75 2.97 12 42.91 54.76 2.33 41.36 54.76 3.88 13 34.12 64.12 1.76 32.94 64.12 2.94 14 24.51 70.75 4.74 24.51 70.75 4.74 15 39.05 56.43 4.52 38.57 56.43 5.00 16 36.49 50.18 13.33 36.14 50.18 13.68 17 31.98 52.79 15.23 31.98 52.79 15.23 18 55.78 36.39 7.82 55.10 36.39 8.50 19 47.27 45.45 7.27 46.36 45.45 8.18 20 52.15 31.58 16.27 48.33 31.58 20.10 21 47.67 36.63 15.70 44.77 36.63 18.60 22 46.89 40.67 12.44 44.02 40.67 15.31 23 55.42 39.76 4.82 55.42 39.76 4.82 24 40.78 42.20 17.02 37.23 42.20 20.57 26 38.41 51.22 10.37 36.59 51.22 12.20 27 31.48 61.11 7.41 29.63 61.11 9.26 28 50.00 39.22 10.78 47.06 39.22 13.73 29 2.78 81.48 15.74 2.78 81.48 15.74 30 11.19 74.13 14.69 11.19 74.13 14.69 31 15.45 70.73 13.82 15.45 70.73 13.82 32 22.58 66.94 10.48 22.58 66.94 10.48 33 16.67 68.94 14.39 13.64 68.94 17.42 34 4.35 91.30 4.35 4.35 91.30 4.35 35 32.00 65.33 2.67 32.00 65.33 2.67 36 28.81 69.49 1.69 28.81 69.49 1.69 fig 7. mix of siliciclastic and carbonate composition of jatiluhur formation. (a) grain-supported extra basinal frame work (lower part interval of formation), largely consists of quartz and feldspar grains with minor rock fragments. (b) muddy-matrix-supported texture in upper part interval of formation. (c) grainstone (dunham, 1962) carbonate bed in the upper part of formation. (d) mix siliciclastic and carbonate fragments. note: q = quartz, p = plagioclase, k = k-feldspar, r = rock fragment q q q p k r r p k q r k abdurrokhim et al./ jgeet vol 7 no 3/2022 137 4.3. provenance the framework composition of jatiluhur formation sandstones represents that the provenance can be classified into the basement-uplifted continent blocks in association with a minor dissected arc (garzanti, 2019) (fig. 10). the paleocurrent data also indicates that sediments delivered from the north (abdurrokhim & ito, 2013). siliciclastic sediments were delivered from the sundaland in the north and/or some other northern mountains in the farther northern area, which were delivered through the shelf margin of the nw java basin trough the bogor trough that have also occurred since the paleogene time (cf. clements & hall, 2011). monocrystalline quartz domination refers a granitic igneous rocks source (garzanti, 2019; garzanti et al., 2013), or disaggregation of original polycrystalline quartz from long-distant transport from metamorphic and/or sedimentary sources. in addition, some undulatory quartz extinction and aggregation of polycrystalline quartz grain indicate that those quartz grains were product of a metamorphic rocks (i.e. first-cycle sands of low-rank metamorphic quartz (eg. garzanti & vezzoli, 2003; najafzadeh, jafarzadeh, & moussavi-harami, 2010). the feldspar grains can also interpreted to have been product from crystalline rock sources. although some plagioclase grains may have been derived originally from volcanic arc provenances to the south, since k-feldspar grains are important constituent of felsic igneous rocks, intermediate gneisses, pegmatites, and/or felsic (eg. garzanti, 2019; garzanti & vezzoli, 2003). fig 8. representative thin section photograph of upper interval jatiluhur formation sandstones (i.e. late miocene deposits). (a) coarse-grained siliciclastic and intraclasts fragments. (b) coarse-grained plagioclase and glaucony minerals. (c) coarse-grained fragment of volcanic rock. (d) plagioclase zoning. note: q = quartz, p = plagioclase, g = glauconite, r = rock fragment. fig 9. sandstone classification of the jatiluhur formation on the q (quartz)-f (k-feldspar + plagioclase)-l (rock fragment). p q r p p r g 138 abdurrokhim et al./ jgeet vol 7 no 3/2022 fig 10. framework composition of the jatiluhur formation sandstones. provenance fields are from (dickinson, 1983; weltje, 2006). qt = quartz); f = k-feldspar + plagioclase ; l = rock fragment; qm = monocrystalline quartz; lt = rock fragment + polycrystalline quartz. 5. tectonic activity although the sediments of jatiluhur formation are generally having similar composition of extrabasinal grain, there are some notes of late miocene samples (upper part of formation): (1) late miocene samples content of volcanic materials and intrabasinal materials (skeletal fragments), and (2) volumetric proportion of feldspar, especially plagioclase, is much higher than quartz and rock fragments for some samples, and also the glaucony minerals content. the late miocene succession was considered as a response to a diminishing supply of siliciclastic sediment from the hinterland, which was indicated by the presence of glauconite that is commonly formed in the starvation state of a marine-shelf environment. this condition may also fulfill the requirement for the carbonate reef of klapanunggal formation to develop. developing of shelf and shelf margin systems allow glauconite formation within the marine sediments of late miocene. this condition has been interpreted as a period of low siliciclastic discharge from the northern hinterland (clift & plum, 2008). in comparison with the middle miocene jatiluhur deposit, the late miocene jatiluhur deposit has volcanic rock fragment within its composition. these volcanic rock fragment are porphyritic in texture, contains phenocrysts of plagioclase within carbonate and microlite groundmass (fig. 8c). plagioclase and volcanic glasses may locally be exchanged by clay minerals and carbonate. relative increasing of volcanic material abundance within upper interval of the jatiluhur formation (i.e. late miocene deposits) also documents the activity of the southern volcanoes as provenance for the pyroclastic and volcanoclastic material. moreover, the presence of plagioclase grains is exceedingly abundant compared to k-feldspar and quartz grains of late miocene deposit. the plagioclase grains are coarse to very coarse, subhedral shaped with albite and carlsbad twins along with a locally developed also zoning (fig. 8d), is the common feature of feldspars formed in igneous rocks (eg. garzanti et al., 2013; najafzadeh et al., 2010). even so, an increasing of plagioclase grains abundance in the upper part of jatiluhur formation was considered as a response to an active shedding of materials from the southern mountain provenance, rather than being a plutonic igneous rocks or metamorphic in origin (garzanti & vezzoli, 2003). due to the general paleocurrents directions of the jatiluhur formation were to the south and southwest, volcanoclastic sediments may not have directly been supplied to the bogor trough and seem to have been reworked once they were deposited in the shallowmarine shelf and coastal environments in eastern and/or northern margins of the basin, except for some grains supplied as pyroclastic deposits. magmatic activities during the neogene period are represented by three phases as follows: (1) tholeiitic magmatism of the oligocene-miocene island arc, (2) tholeiitic pillow basalt during late miocene, and (3) calcalkaline magmatism of pliocene and quaternary (soeriaatmadja & noeradi, 2005). magmatic belt in java island was shifted to north since late miocene may also contribute of volcanic source materials to the bogor trough. limestone beds at the upper jatiluhur formation are interpreted to represent facies changing of the late miocene carbonate reef klapanunggal formation (abdurrokhim & ito, 2013), and this reef was drowned in association with tectonic subsidence, parallel evidence of tectonic subsidence, magmatism and increasing volcanic materials during late miocene as interpreted due to tectonic loading in the south. 6. conclusion the frame work sediments of jatiluhur formation are feldspathic arenite and feldspathic greywacke. texture is representing mainly consist of grain-supported, with several limited samples showing a mud-matrixsupported, consist of quartz (monocrystalline and polycrystalline), k-feldspar, plagioclase, rock fragment (extrabasinal arenaceous component), and glaucony, foraminiferal test and mud chips (intrabasinal component) the sediment composition was shown to have a continental origin which most likely came from the northward sundaland, just as how it has been considered for the paleogene deposit. this interpretation was also supported by the paleocurrent data. composition of the sediment was also dominated by the dominance of monocrystalline quartz grain as an indicator of a granitic igneous rocks provenance, or as the product of abdurrokhim et al./ jgeet vol 7 no 3/2022 139 polycrystalline quartz disaggregation from a metamorphic source due to a long-distance transport process. the late miocene samples indicates the increase in glauconite relative abundance, which may document the starvation period and diminishing supply. these conditions may also support the carbonate reefs development. an increasing of relative volcanic fragments abundance of the late miocene samples also indicates the magmatism activity of the southern contemporaneous southern volcanoes which that act as a sediment discharge source for the jatiluhur formation either as a direct supply such as deposit of fall-related volcanic eruptions in the south, or indirectly such as recycling from a northwestern shallow-marine shelf and coastal area. acknowledgements this research was a part of the phd project research about mix siliciclastic and carbonate deposits in the bogor trough at the department of earth sciences, chiba university, japan. the authors would like to thank dikti for the financial support of this project. fakultas teknik geologi universitas padjadjaran supported our field work and laboratory analyses. this manuscript already received the benefits from anonymous reviewer. references abdurrokhim, & ito, m. 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(2012). biostratigrafi foraminifera pada formasi jatiluhur bagian atas, sungai cileungsi dan sungai cijanggel kecamatan cileungsi, kabupaten bogor jawa barat. undergraduate thesis, universitas padjadjaran, bandung, 62 pp. © 2022 journal of geoscience, engineering, environment and technology. all rights reserved. this is an open access article distributed under the terms of the cc by-sa license (http://creativecommons.org/licenses/by-sa/4.0/) http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ http://journal.uir.ac.id/index.php/jgeet e-issn : 2541-5794 p-issn : 2503-216x journal of geoscience, engineering, environment, and technology vol 08 no 02 2023 138 olagunju, k.t., et al./ jgeet vol 8 no 2/2023 research article hydrocarbon spectra slope (hyss): a spectra index for quantifying and characterizing hydrocarbon oil on different substrates using spectra data kamorudeen tunde olagunju 1,*, callen scott allen2, samuel bamidele olobaniyi1 , kayode festus oyedele1 1 department of geosciences, university of lagos, lagos, nigeria 2 department of geography, university of mary washington, fredericksburg, va, usa. * corresponding author : kolagunju@unilag.edu.ng. tel.:+234-803-716-8057 received: june 17, 2022; accepted: june 25, 2023 doi: 10.25299/jgeet.2023.8.2.9741 abstract many sensors in optical domain allow for detection of hydrocarbons in oil spills study. however, high resolution laboratory and airborne imaging spectrometers have shown potential for quantification and characterization of hydrocarbon. available methods in literature for quantifying and characterizing hydrocarbons on these data relies mainly on shapes and positions of hydrocarbon key absorption features, mainly at 1.73 µm and 2.30 µm. shapes formed by these absorption features are often influenced by spectral features of background substrates, thereby limiting the quality of results. furthermore, multispectral sensors cannot resolve the shapes of key absorption features, a strong limitation for methods used in previous works. in this study, we present hydrocarbon spectra slope (hyss), a new spectra index that offers predictive quantification and characterization of common hydrocarbon oils. slope values for the studied hydrocarbon oils enable clear discrimination for relative quantitative analysis of oil abundance classes and qualitative discrimination for common hydrocarbons on common background substrates. data from ground-based spectrometers and airborne visible/infrared imaging spectrometer (aviris) are resampled to aviris, advanced space-borne thermal emission and reflection radiometer (aster) and landsat 7 enhanced thematic mapper’s (etm+) full width at half maximum (fwhm), in order to compute spectra slope values for hydrocarbon abundance /hydrocarbon-substrate characterization. despite limitations of nonconformity of central wavelengths and/or band widths of multispectral sensors to key hydrocarbon band, statistical significance for both quantitative and qualitative analysis at 95% confidence level (p-value ˂0.01) suggests strong potential of the use of hyss, multispectral and hyperspectral sensors as emergency response tools for hydrocarbon mapping. keywords: hydrocarbon, oil spill, hyperspectral, multispectral 1. introduction hyperspectral sensors for airborne survey and laboratory experiments possess high to very high spectral and spatial resolution. with these sensors, recent studies have revealed the potential of optical remote sensing for oil spill monitoring programs (fingas and brown 2017, holmes, graettinger, and macdonald 2017). hydrocarbons exhibit unique spectral signatures particularly in the short wave infrared region (swir); at 1.73 µm and 2.30 µm wavelength position (clark et al. 2010, kühn, oppermann, and hörig 2004a). these absorption features correspond to overtones and combination bands common in hydrocarbon compounds. absorption features at these wavelength positions and in the visible near infrared region (vnir) at 1.20 µm, are useful for detecting and characterizing hydrocarbon oil (wettle et al. 2009, liu et al. 2016, lu et al. 2013, andreou and karathanassi 2011, kühn, oppermann, and hörig 2004b, reséndez-hernández, prudencio-csapek, and lozanogarcía 2018, asadzadeh and de souza filho 2016, lammoglia and souza filho 2012b). however, absorption features in the swir provide distinct potential for quantification and characterization of hydrocarbon oil against different background materials ( lammoglia and souza filho 2012b, asadzadeh and de souza filho 2016, kühn, oppermann, and hörig 2004b, hörig et al. 2001, allen and krekeler 2010). previous studies on hydrocarbon characterization often used intricate statistical analysis (such as partial least squares regression, neural networks and other similar algorithm), which relies on shapes of the swir hydrocarbon spectra features for quantitative and qualitative mapping (lammoglia and souza filho 2012b, lammoglia and filho 2011, 2015, clark et al. 2010, scafutto and souza filho 2016). similar works on oil slick characterization on varying soil substrate also relies on shapes of swir absorption features for hydrocarbon characterization, using mathematical ratios and algorithms (asadzadeh and de souza filho 2016, kühn, oppermann, and hörig 2004a, hörig et al. 2001). some spectra indexes have also been used that considered the reflectance contrast at vnir and waveform parameters at swir for both detection and quantification (françoise et al. 2021, kühn, oppermann, and hörig 2004b, loos et al. 2012, lennon et al. 2005, li et al. 2012) these works addressed mainly detection and quantification on water and little or no focus on qualitative evaluation of hydrocarbon oil and with consideration to different background substrates. most of these works also require high resolution data to achieve hydrocarbon characterization and therefore limit the use of moderate resolution multispectral data for spill and seep study. in this paper, we introduce hydrocarbon spectral slope (hyss), which is a spectra ratio that captures two most obdurate key hydrocarbon spectral features at swir (1.73µm and 2.30µm) to quantify and discriminate hydrocarbon oil types on different substrates. this study demonstrates the potential of this spectral index for characterization of hydrocarbons on both very high and moderate spectral resolution data. since hyss uses limited spectral input, detailed shapes of key hydrocarbon diagnostic features are no longer important for http://journal.uir.ac.id/index.php/jgeet https://www.researchgate.net/institution/university-of-mary-washington/department/department-of-geography mailto:kolagunju@unilag.edu.ng olagunju, k.t., et al./ jgeet vol 8 no 2/2023 139 analysis, hence its applicability for use on multispectral data. this method requires only two spectral channels in the swir region for oil slick characterization and does not need laboratory calibration of oil slick field samples. this spectra index therefore reveals potential of both hyperspectral and multispectral satellite sensors as a future tool for fast broad search and monitoring of oil spill and seep. multispectral data are free (from european space agency: esa and national aeronautics space administration: nasa) but there are limited use of these data for oil slick quantitative and qualitative evaluation of hydrocarbon spill or seep in literature and in practice. however, multispectral sensors provide data of higher spatial and temporal coverage, useful for monitoring of large to moderate size spills and seeps. despite the stated drawback of this sensor category, advanced spaceborne thermal emission and reflection radiometer (aster) data demonstrate good potential for estimating the american petroleum index (api) gravity and relative exposure time of hydrocarbon oil on ocean seepage (lammoglia and filho 2015, lammoglia and souza filho 2012a). also, asadzadeh and de souza filho (2016) have shown the potential of worldview 3 (wv-3) for direct oil slick detection. furthermore, sun et al. (2016), detected an oil slick with 50% pixel fractional coverage by convolving airborne visible/infrared imaging spectrometer (aviris) data with land satellite (landsat) and medium resolution imaging spectrometer (meris) resolution obtained from the 2010 deep water horizon spill (dwh) in the gulf of mexico. at present, spectral resolution of operational multispectral sensors are insufficient to resolve the spectral shape of hydrocarbon oil absorption features. however, the proposed hyss index harnesses the inherent subtle differences in hydrocarbon absorption maxima by creating a slope between key and persistent spectral features in the swir. previous authors use hydrocarbon feature absorption depth for its quantification and characterization (clark et al. 2010, kühn, oppermann, and hörig 2004b, correa pabón and souza filho 2016). this study demonstrates the effectiveness of the proposed spectral index (hyss) for quantitative and qualitative evaluation of hydrocarbon oils for both high and moderate resolution data, such as those obtainable from hyperspectral and multispectral satellite sensors, while using high spectra resolution data (asd and aviris) as a precursor. hyss uses the two prominent hydrocarbon absorption features in the swir at 1.73µm and 2.30µm. absorption features at these wavelength positions occur in all common hydrocarbon oils and are persistent on most background substrates and against oil weathering (allen and krekeler 2010, correa pabón and souza filho 2016). in this article, quantitative evaluation of hydrocarbon is defined as a relative estimation of different classes of oil abundance in oil slick emulsion while qualitative evaluation is meant to discriminate hydrocarbon oil types. the objective is to increase the numbers of sensors for rapid response in oil spill and seep events, for both preliminary pollution monitoring and exploration surveys. hyss relies on measuring absorption depth which changes with oil types and thickness. oil often forms an emulsion with water, in ocean spill events, leading to oil weathering (daling and strøm 1999, mishra and kumar 2015). therefore, the spectral response of an oil slick is largely the response from oil emulsion (svejkovsky et al. 2016). the abundance of surface oil can be measured by two major parameters 1) oil slick thickness 2) and its emulsion state in term of oil-water ratio (clark et al. 2010). these parameters respond similarly on the spectral curve of an oil slick. in this study, we modelled relative oil abundance by its spectral response to oil-water ratio and thickness. oil-water ratio with higher oil content often has higher reflectance while those with lesser oil have low reflectance, same with oil thickness (clark et al. 2010, lammoglia and filho 2011). the physics behind this phenomenon is a light scattering and consequence light-loss in oil emulsion of varying thickness and composition (clark and roush 1984). as explained by clark et al. (2010), the variation on scattering of light in oil emulsion is resulted from difference in oil-water ratio, which in turn, result in wide range of spectral shapes of oil slick. the light-loss dependent in the nir therefore revealed different oil-water ratio and different thickness as varying absorption depth and shapes. figure 1 shows the discrimination of oil emulsions at different oil-water ratios as depicted by clark et al. (2010). the slope formed between absorption depths at 1.73µm and 2.30µm characterizes different oil abundance classes. these prominent absorption features are present in all hydrocarbons with an alkane component and are persistent at different weathering states, in mixtures, and against different background substrates (kühn, oppermann, and hörig 2004b, allen and krekeler 2010, correa pabón and souza filho 2016, lammoglia and filho 2011). 2. materials and method 2.1 data two different datasets are used to demonstrate the qualitative and quantitative discriminating power of hyss. first, united states geological survey (usgs) library spectra of the aviris data of oil-water ratio of dwh spill obtained by clark et al. (2010) was used for the quantitative discrimination. these spectra represent different classes of oil – water ratios at different thicknesses, further discussed in section 2.1.1 qualitative discrimination between different crudes and refined oils was demonstrated using laboratory spectra obtained by allen and krekeler (2010). these data contain spectra of common crude and refined oils on different common substrates, as further discussed in section 2.1.2 2.1.1 library spectra of oil-water ratio at sea, varying states of emulsion formed by crude oil exhibits physical expression and have been characterized by spectroscopy in previous works (aske, kallevik, and sjöblom 2002, asce 1996, daling and strøm 1999, mishra and kumar 2015). likewise, the changes in its emulsion state have been shown to significantly impact the reflectance and the waveform of hydrocarbon diagnostic features of the oil slick (lammoglia and filho 2011). here, we use aviris spectra of oil-water ratio from clark et al. (2010) , to quantify the oil abundance on water. these ratios are prepared through dehydration and rehydration, followed by mixing of proportionate amount of dwh oil slick samples with site water samples and are available as part of the usgs spectra library version 7. details on the emulsion sample preparation and the spectra measurement procedures can be found in this literature. the available oil-water ratio spectra in the usgs library version 7 dataset are: 01:99, 23:77, 40:60, 60:40, 75:25, and 92:08. except for 01:99 and 75:25, the other classes have a consistent thickness range between 0.05mm to 4mm. class 1:99 has 28mm thickness and foam, while class 75:25 has 8mm thickness. class 23:77, 40:60 and 60:40 also have 8mm thickness, which were included in the preliminary stage of the analysis. class 23:77 and 60:40 have 0.025mm thickness value while other oil – water ratio categories does not and therefore, data for this thickness value are also excluded in the analysis. since oil spectra are also sensitive to thickness value, data from the four classes of oil-water ratio (oil abundance) are further divided into four available consistent thickness classes 23:77, 40:60, 60:40 and 92:08. 2.1.2 laboratory spectra of crudes and refined oils laboratory data collected by allen and krekeler (2010) were used to demonstrate the discriminating power of the proposed 140 olagunju, k.t., et al./ jgeet vol 8 no 2/2023 hyss for different hydrocarbon-substrate combinations. these data were acquired with asd field spec™ pro-fr2 and comprise four different crude oils and three different refined oils. the oil samples are of types, refined oil and crude oil. diesel, gasoline and motor oil are the refined oil while heavy, light, intermediate sweet and intermediate sour are the crude oil used with 19.6, 42.2, 32.2, 30.3 api respectively, intermediate sweet intermediate sour crude oil have 0.4% and 1.8% respectively. spectra measurement of these oils were taken against ten common substrates. the substrates used are asphalt, bentonite, a calcareous sand, calcite-dolomite crushed aggregate, concrete, gypsum, a soil with high (2.9%) organic content, ottawa sand, a quartzitic beach sand, and senescent grass with underlying soil. the senescent grass contain underlying leaf litters and soil. however, for the purpose of this study, all spectral measurements on petri dishes are excluded from this study because they are highly transmissive and are not a naturally occurring background material. further details on the laboratory set-up and scope of data collection can be found in allen and krekeler (2010). 2.2 hydrocarbon spectra slope index hydrocarbon spectra slope (hyss) is the ratio of the difference in reflectance at diagnostic absorption band at swir (1.73µm and 2.30µm) of hydrocarbon oil to the difference in the corresponding wavelength interval. this ratio is represented by a negative slope within these diagnostic features as indicated on figure 1. the slope value is an inflection of the maximum depth of these absorption features which also reflect the light loss differentiation by hydrocarbon oil and the chemistry of the oilwater ratio and oil type. therefore, a proxy for hydrocarbon quantification and discrimination parameters. as figure 1 shows, both oil and water are highly absorptive at 2.30μm (ρ < 0.08 & <0.02, respectively). fig. 1. spectral profile of oil abundance classes and its relevance to hydrocarbon spectra slope (hyss). hydrocarbon slopes are formed between 1.73µm and 2.30µm absorption depth. (modified after clark et al, 2010) fig. 2. flow chart of methodology in this research, we use obdurate hydrocarbon absorption maxima at 1.73µm and 2.30µm (or the nearest available channel to both for multispectral sensors) for quantification of oil abundance and qualitative characterization of hydrocarbon types on different background substrates. the hyss evaluation is divided into two parts, quantitative and qualitative computation of corresponding datasets described in section 2.1.1 the flow chart in figure 2 show an overview of the methodology adopted in this study. in order to demonstrate the discriminating power of hyss at different resolutions, the full width half maximum (fwhm) of three different sensors (aviris, aster, and landsat 7 enhanced thematic mapper plus etm+) were used to resample the original asd spectra for qualitative analysis. we resampled aviris data to aster and landsat 7 bandpasses for oil – water ratio spectra for quantitative analysis. these sensors are commonly used in geo-information science and because their data are freely available. fortunately, they also have spectral channels that contain or are close to the two hydrocarbon absorption maxima for hyss. band 5 and 7 on landsat 7 contain the hydrocarbon absorption maximum at 1.73µm and 2.30µm, respectively. for aster, band 8 contains the 2.30μm feature. aster band 4 (1.60-1.70μm) ends before the 1.73μm feature. in fact, all of the oil-water mixtures reach their maximum swir reflectance in this band. fortunately, as figure 1 demonstrates, there is still a significant gradient, based on oil-water mixture ratios in this range. furthermore, these two sensors arguably adequate to represent lower bound of other moderate resolution satellite sensors that meet these criteria with higher spectral resolution (such as worldview 3 wv3). whereas multispectral sensors are limited in their ability to measure hydrocarbon-induced absorption features, hyperspectral sensors operating in the swir can resolve both the shape and the absorption maxima. the airborne aviris sensor is a useful analog in this respect for both past and future hyperspectral satellite sensors with swir coverage (e.g., hyperion, us; olagunju, k.t., et al./ jgeet vol 8 no 2/2023 141 environmental monitoring and analysis program–enmap, germany; hyperspectral precursor and application mission prisma, italy; multi-sensor micro-satellite imager –msmi, south africa; hyperspectral infrared imager–hyspiri, usa; hyperspectral imager suite-hisui alos 3, japan; hypxim ca sensor, france, and geostationary high resolution imager – gisat, india). 3.0 results and discussion 3.1 results the slope values for oil abundance were calculated for the library spectra (in aviris resolution), discussed in section 2.1.1, and the resampled spectra of aster and landsat 7fwhm. the variation of these slope values to different oil abundances classes, on these sensors’ fwhm are shown as spectra in figure 3.1. bar charts in figure 4 shows the variation of the oil-water spectra for four different oil abundance classes at four thickness values. similarly, hyss values for oil type discrimination were computed from the laboratory spectra of four crudes and three refined oils (section 2.1.2). the lab spectra, along with the resampled spectra for aviris, aster, and landsat 7 for diesel and heavy crude on different substrates are shown in figure 3.2. these spectra plots represent measurement of reflectance from different hydrocarbon oil substrate combination. fig. 3.1 spectral profile of oil abundance classes (oil – water ratio) in different colour, showing all thickness values in the same colors and at different spectral resolutions for aviris original spectra and convolved spectra for aster and landsat 7 fig. 3.2. spectral profile of hydrocarbon oil-substrates combination a) diesel b) heavy crude, showing the same hydrocarbon oil – substrate combination in the same colors and at different spectral resolutions for original asd spectra and convolved spectra for aviris, aster, and landsat 7 spectra. the discrimination of oil abundance classes and that of hydrocarbon oil types on different substrates are revealed by both the bar chart and correlation plots. the bar charts show the relative difference in slope value for each oil abundance class and thickness for aviris, aster, and landsat 7 (figure 4) and each oil type on different substrates for asd, aviris, aster, and landsat 7 (figure 6). for each plot (a,b,c,d) in figure 4, the relative difference of slope value on the bar chart shows apparent separability of oil abundance classes across high (aviris) and moderate (aster, landsat 7) resolution spectral data. in figure 5, scatter plots of the hyss value for oil abundance at the four different oil-water thickness values show a linear correlation between the aviris (original data) and aster/landsat 7 fwhm. the correlation coefficients (r2 = 0.94, p value = 0.001) on this plot suggest a clear discrimination of oil abundance classes (shown by the bubble size), regardless of the spectral resolution, despite the effect of varying oil thickness. note that the 92:08 ratio group clusters at the upper right of this plot where the slope approaches zero, due to the high absorption by this mixture in both swir wavelengths. similarly, figure 6 shows the bar chart representing relative slope values for different hydrocarbon oil/substrate combinations. figure 7 shows the correlation plots comparing the asd measurements to the convolved values for aviris, aster, and landsat 7. these relationships are discussed further in section 3.1.2. 3.1.1 estimation of oil abundance oil abundance discrimination was analysed across data for all thickness values except that of 4mm thickness. results for 4mm thickness does not follow general trend of spectral slope values of other oil thickness value. this is probably due to the opacity of this thickness and therefore, minimal scattering of light from the oil fraction. this thickness value is therefore excluded from further analysis. the greyscale bar charts in figure 4 highlight the relative difference in slope value for different oil abundance classes at different thickness (0.05mm, 0.1mm, 0.5mm and 1.85mm) as well as the influence of fhwm resolution and wavelength position of the three sensors involved in this study. the slope values of aviris, aster, and landsat 7 are represented as bars with different greyscale values. although there is an overlap between the reflectance values of the 23:77 and 40:60 ratios, the slopes of all four ratios permit discrimination using hyss. figure 3.1 shows spectra of the same oil abundance classes (oil-water ratios) in unique colours (23:77, 60:40, 40:60, and 92:08) while figure 5 shows the correlation of slope values amongst the three sensors. each circle size represents a different ratio where the largest oil-water ratios are represented as the largest circle. decreasing oil-water ratios are represented in circles of decreasing sizes. the bar chart shows a general trend of higher slope value with increasing oil abundance across all thickness values when progressing from 40:60 to 60:40 to 92:08. for three thicknesses (0.05, 0.50, 1.85mm), the 23:77 ratio have higher slope value than the 40:60 value. however, bandpasses for each sensor significantly affect the model results. variation in slope value across oil abundance classes are due primarily due to the differences in the oil content of each abundance classes and are not significantly affected by which sensor is chosen, even for multispectral sensors that do not have a bandpass that intersects precisely with the absorption maxima (e.g., aster), as long as there is a bandpass that is spectrally ‘nearby’, such as aster band 4 (1.60-1.70μm). this bodes well for the use of hyss with multispectral sensors with swir bandpasses that are close, but that do not necessarily contain the hydrocarbon absorption features of interest here. generally, hyss discrimination of oil abundance classes are statistically significant at 95% confidence level on all sensors investigated here (p-value <0.001). in summary, fhwm spectral resolution and position affect the slope values but not the discriminative power of the hyss on the hyperspectral and multispectral sensors involved in this research. https://www.wmo-sat.info/oscar/satelliteprogrammes/view/213 142 olagunju, k.t., et al./ jgeet vol 8 no 2/2023 as mentioned above, one notable deviation is the response of 23:77 oil – water slope value in all graphs, as compared to other oil abundance classes except at 0.1mm thickness. this deviation could be as a result of increase sub-pixel mixing of oil and water at low oil content of this class. note that, the 23:77 oil – water ratio is the oil abundance class with the lowest oil content in the data used for this analysis. this deviation is therefore interpreted as the influence of water spectra over the oil spectra in areal mixing. conversely, 92:08 oil – water ratio group are clustered at the upper right of the plot can be explain as higher opacity of the largest oil-water ratio, reducing the spectral variation from 1.73 to 2.30μm, resulting in higher hyss values. 3.1.2 discrimination of oil types figures 6 and 7 plots the bar charts and scatter plots of slope values computed from the original asd measurement and those computed from resampled aviris, aster, and landsat 7 spectra. in figure 6, each subplot represent each of the hydrocarbonsubstrates combination (e.g., crude and refined oil on ten different substrates). fig. 4. bar charts, showing the response of hyss value for aviris, aster, and landsat 7 at different thickness value; a) 0.05mm, b) 0.1mm, c) 0.5mm, and d) 1.85mm fig. 5 correlation of hyss values for oil abundances, as measured by different sensor each bar each represent slope value from the original asd, as well as slope value from convolved spectra for aviris, aster, and landsat 7. regardless of the substrate types, each hydrocarbon oil sample is discernible based on their slope values, even for partially (e.g., light crude) or highly (i.e., the three refined products) transparent in the swir at thicknesses similar to the oil-water ratios, permitting substrate spectral features to influence results. figure 7 shows the correlation plot of combined slope values for all hydrocarbon-substrates for all sensors shown in figure 6. due to spectral mixing of some substrates, slope value of hydrocarbon oil are notable affected. particularly, calcareous sand, ottawa sand, calcitic gravel, concrete, gypsum, quartzitic beach sand, and vegetation significantly influence hyss values for the resampled spectra at multispectral resolution (blue = aster, green = landsat 7), showing as deviation from linearity on the correlation plot (indicated with black rings on plot in figure 7). this deviations is due to coarse spectra sampling of the multispectral sensors with respect to hydrocarbon diagnostic absorption bands used in hyss and non-conformity to these absorption maxima. this is scenario is accentuated on landsat 7 spectra, with deviations resulting to zero and positive slope values, as shown in figure 6a, 6c, 6d and 6g). note that slope values for aviris (red symbols in figure 7) is rather very linear, depicting a strong potential for characterizing hydrocarbon on hyperspectral data using slope value. this is not unexpected for sensor with fine resolution which also conform precisely to wavelength positions of hydrocarbon diagnostic features that defined the slope value. most of the deviation is below a linear fit to the data, implying stronger than expected hyss values, which indicates greater differences in reflectance at 1.73 and 2.30μm than expected. the gypsum and calcareous sand substrates showed strong deviation, mainly due to a great difference (-0.25) in reflectance between 1.73 and 2.30μm, however all other substrates have reflectance values less 0.10. both quartzitic susbstrate exhibit very high transmission, particularly the ottawa sand, showing stronger than normal hydrocarbon absorption features, and consequently, higher than expected hyss values (raveia et al. 2008, satterwhite and allen 2005). this difference persists on hydrocarbon-substrate combination due to some measure of transmission for all hydrocarbon samples except for heavy crude and intermediate sour crude at 1.73μm and nearly no transmission by any hydrocarbon oil at 2.30μm. these olagunju, k.t., et al./ jgeet vol 8 no 2/2023 143 hydrocarbon (asterisks and downward triangles, respectively) are notably outliers by producing lower than expected slope values, fundamentally due to this lack of transmission and consequential near opacity at 1.73μm. hydrocarbon with relatively higher transmissions at 1.73μm, such as diesel (circles), motor oil (boxes), light crude oil (diamonds), intermediate sweet crude oil (sideways triangles) produced higher than expected slope values. in order to evaluate the trend of variation of slope values across hydrocarbon-substrates combination, we used manova to determine separability of hydrocarbon oil samples from one another. fig 6. bar charts of slope values for different fwhm resolution for different hydrocarbon oil on ten substrates: a) diesel, b) gasoline and c) heavy crude d)intermediate sweet crude e) intermediate sour crude f) light crude g) motor oil diesel gasoline heavy crude intermediate sweet intermediate sour light crude motor oil 144 olagunju, k.t., et al./ jgeet vol 8 no 2/2023 fig. 7. correlation of hyss values for all hydrocarbon on different substrates at different resolution, showing the linearity of asd measurements and slope value from convolved aviris. note the deviation from linearity of slope value from convolved aster, and landsat 7 due to the spectral response of substrates (calcareous sand -cs, ottawa sand-os, quartzitic sand –qs, calcitic gravel -cg and gypsum -gp) table 1 shows correlation value and corresponding p value for each hydrocarbon-substrates combination for each of the sensors compared to the asd lab spectra. as mentioned above, hyss value for aviris hew very strongly to the lab spectra, which is expected for a hyperspectral sensor that can measure absorption maxima with precision of ≤10 nm and with a bandpasses in the spectral range of these absorption features. on the contrary, multispectral sensors have lower correlation coefficient and pvalues. this is particularly true for results from landsat 7, none of which reaches a r value of 0.80. relatively, aster has a number of high (>0.80) r values and low p values (<0.01), due to conformity of its bandpass to 2.30μm wavelength position. table 1. correlation coefficient and p values of hyss value of different hydrocarbon-substrate combination at different resolution these poor values are a reflection of the relatively broad spectral range of landsat 7’s swir bands and the dynamic nature of both the hydrocarbon oils, as well as some of the substrates over these large bandpasses (≥0.20μm). this explained why slope value changes from negative to positive values on some hydrocarbon-substrates combination (see figure 6). as a result, both the r and p value for the affected plots are considerably lower than they are for aster (indicated with downward arrow in table 1). 3.1.3 statistical analysis of the results a multifactor analysis of variance (manova) was used to test the significant difference of hydrocarbon slope value as a bases for quantitative discrimination of the oil abundance classes and the discrimination of hydrocarbon oil types. the results showed a significant value for both analysis at 99% confidence level (see tables 2 and 3). discrimination of oil abundance classes and those of hydrocarbon oil types by slope value are highly significant with p value ˂ 0.01 at resolution for asd, aviris, aster and landsat 7. all abundance classes are significantly distinguishable at 99% confidence level, based on their slope value at all thickness value (p value= 0.000) and oil-water ratio (p value= 0.00) and at all resolution (p value = 0.463). this implies that hyss successfully distinguishes all different oil abundance classes as well as its varying thickness values. that is, hydrocarbon spectral slope values are not significantly different at the resolution of the three sensors. in other words, these three sensors were able to distinguish oil abundance classes and thickness ranges. similarly, all slope values from the original asd data and resample spectra were statistically significant at 95% confidence level (p value ˂ 0.01) for the qualitative analysis. all hydrocarbon–substrate combinations investigated in this research have high significance at 95% confidence level at all resolution (see table 3). hyss value for hydrocarbon oils investigated are significantly distinguishable at all spectral resolutions, despite the broad spectral bandpasses of aster and landsat 7, as shown on the correlation plots (figure 7) and that of quantitative analysis of oil abundance (figure 5). table 2: anova of slope value for oils abundance (oil _ water ratio) and thickness against spectral resolution oil types coefficient of correlation (r) and p value resolution asd – aviris asd – aster asd – landsat 7 diesel 0.99 / ˂0.001 0.73 / 0.016 0.49 / 0.148 ↓ gasoline 0.99 / ˂0.001 0.80 / 0.005 0.57 / 0.080 heavy crude 0.99 / ˂0.001 0.99 /˂0.001 0.61 / 0.061 intermediate sour crude 0.99 / ˂0.001 0.93 /˂0.001 0.40 / 0.248↓ intermediate sweet crude 0.99 / ˂0.001 0.89 /˂0.001 0.40 / 0.245↓ light crude 0.99 / ˂0.001 0.84 / 0.002 0.60 / 0.069 motor oil 0.99 / ˂0.001 0.71 / 0.020 0.47 / 0.172↓ table 3: multifactor anova of hyss value for hydrocarbons oils against spectral resolution and substrates hydrocarbon on substrates sum of squares df mean square fratio pvalue diesel on substrate 0.372 9 0.041 4.949 0.000 resolution 0.068 3 0.023 1.478 0.237 gasoline on substrates 0.382 9 0.042 9.065 0.000 resolution 0.028 3 0.009 0.687 0.566 heavy crude on substrates 0.070 9 0.008 8.662 0.000 resolution 0.015 3 0.005 2.162 0.109 intermediate sour crude on substrates 0.131 9 0.015 8.605 0.000 resolution 0.013 3 0.004 0.890 0.456 intermediate sweet crude on substrates 0.234 9 0.026 8.892 0.000 resolution 0.021 3 0.007 0.846 0.478 light crude on substrates 0.272 9 0.030 6.103 0.000 resolution 0.074 3 0.025 2.550 0.071 motor oil on substrates 0.300 9 0.033 4.361 0.001 resolution 0.066 3 0.022 1.717 0.181 3.2 discussion of results quantitative and qualitative analysis of hydrocarbons mixed with water and on ten different substrates demonstrates the capability of hyss method for potential hydrocarbon oil – water ratio/ thickness sum of squares df mean square f-ratio p-value oil – water ratio 0.408 3 0.136 19.794 0.000 thickness 0.288 4 0.072 7.859 0.000 sensor resolution 0.021 2 0.011 0.780 0.463 olagunju, k.t., et al./ jgeet vol 8 no 2/2023 145 characterization. hyss values suggest a significant relative discrimination of oil slick abundance classes (both in terms of oil-water ratio and thickness) and discrimination of different hydrocarbon oils on varieties of substrates at 99% confidence level across the datasets used in multifactor analysis of variance. furthermore, the observed difference in slope value of the oil abundance classes and that of the hydrocarbonsubstrates discrimination are statistically significant, with p values lower than 0.01 significance level (tables 2 and 3). for oil abundance class discrimination, statistical significance is higher than 99% confidence level at all resolution (p value = 0.000, 0.000, and 0.463). for qualitative analysis, comparing slope value from the original asd data to corresponding slope values from resampled spectra reveal the bandpass location, and effect of highly reflecting substrates, particularly calcareous sand, gypsum, and quartzitic sands produce slope values that deviate from expected linear spectral response in correlation plot (figure 7). however, hyss values for oil abundance classes and hydrocarbon-substrates analyzed in this research are statistically significant for discrimination at all sensors’ fhwm resolution. these results indicate that multispectral and hyperspectral sensors are potentially useful tools for mapping hydrocarbons, even on a wide-ranging substrates. the discriminative ability of hyss can be explained on a molecular scale by the model’s sensitivity to subtle changes in hydrocarbon absorption depths at c-h overtone and combination bands in the swir (cloutis 1989). the changes in absorption depths reflect overlapping hydroxyl (oh-) and c-h transmission and absorption, mixed in the multiple ratios outlined above. for the qualitative discrimination of hydrocarbon oil types, hyss ability to differentiate oils and refined products is a function primarily of differing transmission values for each hydrocarbon oil, as well as the underlying substrate’s reflectance. other factors, such as absorption maxima at values different than 1.73μm (e.g., gasoline) and differing asymmetric absorption feature shapes (e.g., triplets (gasoline) vs doublets (all other samples) are also likely contributors, although the relative impacts merit additional study. the observed deviation of the hyss value in the 23:77 oil – water ratio sample and from the resampled spectra are also explainable with high water content of this oil abundance class. the 23:77 oil abundance class has the highest water content. water is highly absorptive in the swir so volume scattering from the oil which reaches the water is strongly absorbed, resulting in lower contrast between reflectance values at 1.73 and 2.30μm than in the other samples. also, due to sub optimal band pass and relatively broad spectral ranges, aster and landsat 7 do not have spectral bands that coincide precisely with the key hydrocarbon bands used by the slope model (i.e., 1.73µm and 2.30µm). therefore, the input response from the inappropriate spectra channels during resampling is also another cause of slope value variation observed from resampled spectra. as observed in previous studies, result from hyss showed that quantitative and qualitative analysis of hydrocarbon oil on varying substrates can be ambiguous, due to the high transmissivity of some hydrocarbons in the shorter swir region, combined with the interference from key spectral bands of substrates (scafutto and souza filho 2016, allen and krekeler 2010). the complex interference of spectra of hydrocarbon oil-substrate investigated (as indicated in figure 6 and 7) influenced the resulting hyss value but all hydrocarbon oil types were significantly discriminated across all substrates used in this research (see table 3). even on highly reflecting substrates, hyss demonstrates a significant discriminative tendency for all studied hydrocarbon oil –substrates combination, even at resampled scales of multispectral sensors with sub-optimal bandpasses. that is, each hydrocarbonsubstrate combination as well as oil abundance/thickness classes have significantly different slope value sufficient for discrimination. it is worthy to note limitations of this study for further works on the proposed hyss spectral index. laboratory spectra and aviris spectral were used as a precursor to model response of multispectral image which depend also on other image parameters such spatial/radiometric resolution and dynamic range. although, it is adequately justified to infer that these image parameters for hyperspectral data of aviris specification or higher will perform optimally with hyss spectra index as predicted by this model. however, the effect of other image parameters on multispectral image for this spectra ratio should be investigated. on aviris spectra, effect of high water content (23:77) and higher oil content (92:08) lower the response of hyss spectra index for quantification but still with significant discrimination. the former is most likely due to the effect of water in spectral mixing while the later could be effect of opacity of crude oil to light and non-differentiation of value thickness value in analysis because of limited data volume (clark and roush 1984). in oil type discrimination on substrates, effect of moisture content of background substrates on hyss were not investigated and therefore merit further study. potential impact of hyss spectra index and contribution to knowledge of hydrocarbon mapping is the possibility of achieving fast computational assessment in spill and seep events. this is owing to the reliance of this simple spectral index on depth of absorption maximum of two most obdurate channels at swir (1.73µm and 2.30µm), which are direct response to chemical changes in hydrocarbon chemistry (clark et al, 2009). similar spectral parameters proposed for thickness discrimination used contrast of reflectance at nir region (490nm to 885nm) on oil spectra on hyperspectral and multispectral data (lennon et al, 2005, loos et al, 2012). li et al, 2012 also used a similar spectral index which uses radiance contrast of spec tir hyperspectral data at nir (580nm to 748nm). obviously, these spectral index in previous studies enhance the contrast in reflectance/radiance at nir, to discriminate oil thickness. in contrast, parameter for spectral index used in hyss is maximum absorption depth at swir, from key and obdurate diagnostic features of hydrocarbon oils, which may not only relate to differences in thickness/oil-water ratio but also oil types as indicated in this study. absorption depth of these diagnostic feature are indicative of oil chemistry, chemical changes and physics of light loss differentiation for thickness measure (clark et al 2009; clark et al, 2010, clark and roush 1984). similar to hyss, hörig et al. (2001), kühn, oppermann, and hörig (2004b) and francoise et al, 2021 used spectra indexes by considering absorption depth at 1.7µm and 2.3µm for hydrocarbon characterization. hörig et al. (2001) and kühn, oppermann, and hörig (2004b) focused on detection of hydrocarbon on polluted soil using spectral index derived from waveform parameter at these wavelength on hyperspectral data. françoise et al. (2021) proposed a spectral index for hydrocarbon characterization on water, using absorption maximum at 1.7µm, 2.3µm and 2.6µm. unlike hyss, this method does not depend only on oil spectral for oil characterization but also uses other oil slick parameters from extensive database from separate experiments. also, spectral ratio from the study does not demonstrates discrimination of hydrocarbon oil any other different substrate other than water. hyss presents a simple spectral index that uses only two obdurate absorption maximum for hydrocarbon for potential characterization across range of common background substrates, with potential for rapid broad range search for spill/seep. 146 olagunju, k.t., et al./ jgeet vol 8 no 2/2023 4. conclusion this study have demonstrated the potential of hyss for hydrocarbon quantification and characterisation with both hyperspectral and multispectral sensors. discrimination of oil abundance and oil types achieved on all studied hydrocarbon oil-substrate combinations are statistically significant at 99% confidence interval. as expected, hyss performs especially well on hyperspectral data such as asd lab instrument or aviris measurement that capture key hydrocarbon spectral features. while multispectral sensors such as aster and landsat 7 do not possess sufficiently fine resolution to resolve these key hydrocarbon spectral bands, quantitative and qualitative characterization is still statistically significant with varieties of substrates. highly reflective and transmissive substrates exhibit a spectra response that produce results that deviate from the linear responses seen in the asd and aviris data, which may limit hyss on such substrates. however, this method offers a relative quantification and characterization of hydrocarbon oil that can be deployed for broad area search particularly for mapping land and water based oil spills and seeps with hyperspectral and multispectral data. in subsequent efforts, we anticipate assessing the utility hyss for hydrocarbon quantification and characterization using imagery data. this is particularly necessary to assess the effect on hyss spectra index due to other image parameters not considered in this study, such as spatial resolution, radiometric range, bidirectional reflectance and detection limits of common hyperspectral and multispectral sensors. acknowledgement the authors thank tetfund for the scholarship for this research. spectra data of oil – water ratio were obtained from the spectra library version 7 from usgs online archive. the crude oil samples used by allen and krekeler (2010) were provided by exxonmobil. references allen, and krekeler. 2010. 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