4 49 S. K. Jan & A. A. AL-Zubaidi Bull. Iraq nat. Hist. Mus. (2004) 10 (2): 49-55 MICROFACIES ANALYSIS OF GHAR FORMATION (WESTERN DESERT OF IRAQ) Sadi Kan Jan and Aqeel A. AL-Zubaidi Iraq Natural History Museum University of Baghdad, Baghdad, Iraq ABSTRACT Ghar Formation outcrop at the Iraqi western desert was studied by microfacies analysis of (13) thin sections collected from wadi Al-Ratgha ( west of Qaim ) . According to petrographic com position and organisms content ,rocks were subdivided into (4) microfacies units :bioclastic wackestone , mudstone , miliolids wackestone , and grainstone with aggregate grains microfacies .Microfacies units reflect shallow marine environment of low circulation of very warm water at the middle part . The lower and middle part interbedded with quite open marine environment below the wave base . The upper part was deposited at shallow marine environment of low circulation . The main diagenetic processes were the transformation ( type of neomorphism) and precipitation of calcite in the fractures and fossil chambers . INTRODUCTION Ghar Formation consist of sand and gravels , rare sandy limestone ,clay and anhydrite deposited in the littoral or party deltaic environment that was first described by owen and Naser ( 1958 ) at the well Zubair No. 3 ( van bellen et al,. 1958 ) . Ghar Formation cropped out at the Iraqi western , represented by Quartz sandstone and sands interbedded with sandy limestones ( AL- jumaily, 1974 ) . AL- Hashimi and Amer ( 1985 ) concluded that the formation was deposited at fluviomarine environment , AL- Zubaidi et al.(in press) observations led to near shore high energy , off shore low energy environment and transitional environment using grain size , sorting and winnowing as an indicator to the environment . The age of the formation was Miocene ( Van Bellen et al ., 1959 ) or Late Lower Miocene ( Budy 1980 ) . The aim of this study is to show the environment of deposition by using microfacies analysis of ( 13 ) thinned section from ( 13,5 )m thickness of Ghar Formation exposed in wadi AL- Ratgha (west AL- Qaim ) Iraqi western desert , Fig. 1 MICROFACIES ANALYSIS Petrographic studied of ( 13 ) thinned section , using a polarized microscope led to the recognition of the following microfacies according to ( Wilson 1975 ) and (Fluegel 1982) Fig.2 . 1- Bioclastic Wackestone Facies : the thickness of this facies is (5,3) m which have ( 40,7% ) of the total thickness . It contains broken shell, gastropoda and less than ( 1% ) of miliolids and limestone component (interclast and pellets ) in addition to quartz grains of moderatly sorted. The matrix composed of microsparite –micrite . The main diagenesis processes were calcite–cement precipitation in fractures and fossil chambers plate(1-1), along within situ transformation of aragonite to calcite such as primary broken shell of 50 Microfacies Analysis of Ghar Formatiom aragonite tansformed to secondary broken shell of calcite (Schmidt 1956) . The transformation of aragonite to calcite happens at the shallow marine water of high ratio of Mg:Ca (Fuechtbauer and Goldschmidt 1964 ) .This facies is similar to the SMF( 9 ) zone ( 7 ) which is zone of shallow marine water with open circulation . 2- Mudstone Facies: The thickness of this facies (2.8) m which have 21.5% of the total thickness . This facies plate(1-2) contains broken shell with rare amount of gastropoda and also contains detrital qartz grains 1-5 % which refer to eolian transporation in quiet marine environment without relation to high energy water ( plumley et al . ,1962) . The main diagenesis process were the precipitation of spary calcite inside the broken shell . This facies similar to the SMF (3) zone( 3 ) which indicated to quiet open marine environment below the wave base 3- Miliolids wackestone Facies : The thickness of this is (1.2)m wich have 9.2% of total thickness . This facies recognized by Miliolids of quinqueloculina 40% plate (1-4) and presence of gastropoda . broken shell and very rare Ostracods and less than 1% quartz grains . The main diageneses processes were the precipitation of calcite cement during late diagenesis processes due to tectonic uplift (Chilinger et al., 1967) and also precipitated within fossils chambers . This facies similar to the SMF(19) Zone( 8 ) which indicated to the lakes and lagoons of restricted water. 4-Grainstone with aggregate grains facies : The thickness of this facies is (3.7)m which have 28.4 % of the total thickness . This facies recognized by aggregate grains plate (1-3) within coarse sparite crystals wich precipitated at intertidal shallow marine environment more than (10)m depth . The aggregate grains coposed insitu from lime component which found at the micrite ,this facies indicated agitated water of low water circulation ( Winland and Mattews 1974 ) .Quartz grains ,rounded to well rounded and well sorted of 40% were present at this facies which refer to near shore sediments ( fluegel 1982 ) and high energy environment wich caused the complete washing of limemud and precipitated the spary calcite . The rounded cherty gravel ( 10 ) cm at the upper part of the outcrop of studied area refer to fluvial abundance of near shore marine environment .The diagenesis process was mixing of cement ( A ) and (B ) This facies similar to the SMF ( 17 ) Zone( 8 ) which refered to very warm shallow marine of restricted circulation . Microfacies distribution of Ghar Formation arranged in Wilson model as show in fig.3 . ENVIRONMENT OF DEPOSITION Microfacies study of ghar Formation showed that the lower part composed of bioclastic wackestone facies ( 1 ) which reflect shallow marine environment (open circulation ) followed by mudstone facies( 2 ) . Which deposited in open marine environment below the wave base i.e. transgression of sea level . After that the miliolids bioclastic wackestone facies ( 3 ) which deposited in lagoons of restricted water . The upper part of the Ghar Formation composed of grainstone with aggregate grains facies ( 4 ) refered to shallow marine environment of warm water with low circulation . CONCLUSIONS 1- Four microfacies were typified from lower to upper contact : bioclastic wackestone facies ,mudstone facies , miliolids wackestone facies and grainstone with aggregate grains facies . 2- High percent of fossils were presence such as miliolids ( 40% of fossils ) while rare amount of gastropoda, broken shell and ostracods also presence in wackestone facies . 51 S. K. Jan & A. A. AL-Zubaidi 3- The main diagenesis processes were calcite-cement precipitation in the fractures and fossil chambers besides the transporation which are type of neomorphism. 4- The succession of the identifield microfacies and their zones of deposition reflects the dominance of shallow marine environment beside the quiet open sea below the wave base LITRATURE CITED Al-Hashimi. H.A.J. and Amer .R.A. 1985 . Tertiary Micrfacies of Iraq . State Organization for Minerals , Baghdad , 56 p. AL- Jumaily, R.M., 1974 .Report on the Regional Geological Mapping of the area between Iraqi –Syrian bordor –T. 1 . oil pumping , S.O.M .Library . Baghdad . AL- Zubaidi, A.A., Kahn jan .S. and AL- Amiry, J.A. 1999, Grain size and sorting as indicators of energy of depositional environment of Ghar Formation ( Late Lower Miocene ) . Buday .T. 1980 , Regional Geology of Iraq V. 1 , Stratigraphy and paleogeography .State Organization for Minerals. Baghdad, 445 p. Chilinger, G.V. , Bissell.H.J . and Fairbridge, R.W. , 1967 , Carbonate Rocks ( origin , occurrence and classification ) . Elsevier pub. Com. 471 p Fluegel.E. ,1982 Microfacies analysis of limestone , Springer- Verlag ,Berlin, 633p. Fuechtbauer and Goldschmidt,H., 1964, Ein Zechsteinanhydrit- profil mit Einlagerungen von Montmorillonit und einer abweichenden Serpentin Vareetaet- Heidelberg . Beitr. Miner. Petrogr. V.5 ,pp 187-203. Fuechtbauer,H.,and Mueller, G., 1977, Sediment-petrologie. E. Schweizer-Bartisch Verlags Buchhandlung , 784p. Owen,R.M.S. and Naser , S.N. 1958 The Stratigraphy of Kuwait –Basrah area , in Weeks, L.G ( ed.) , Habitat of oil , A A PG pub. 252-1278 Plumley,W.J . ,Risley,G.A. ,Graves., R.W. and Kaley, M.E. 1962 Energy index for limestone interpretation and classification . Mem . Amer .Ass. Petrol., Geol 85-107 Schmidt,V.1965 Facies diagenesis and related reservoir properties in Giqashed (U. Jurassic. Northwestern Germany ) ,in pray, R.C. (ed) Dolomitization and limestone diagenesis, SEPM. Spec. pub. No.13 Van Bellen,R.C. , Dunnington. H.V. Witzel. R. and Morton , D. 1959 Lexique Stratigraphique International Asie, Iraq V.3,face.10a,333p Wilson,J.L.1975 Carbonate Facies in Geologic History. 471 p Berlin .springer-Verlag Winland,H.D. and Mattews , R.K. 1974 Origin and Significance of grabstone , Bahama Island , J.Sed. PET. V. 4. pp. 927 52 Microfacies Analysis of Ghar Formatiom 53 S. K. Jan & A. A. AL-Zubaidi 54 Microfacies Analysis of Ghar Formatiom Plate-1 1. secondary broken shell 40x 2. Mudstone facies 40x 3. Aggregate grains facies 40x 4. Some species of Miliolid 100x 1 2 3 4 55 S. K. Jan & A. A. AL-Zubaidi Bull. Iraq nat. Hist. Mus. (2004) 10 (2): 49-55 ر ن الغا ق لتكوي دقي حنا ال س ل ال حلي ة (ت ء الغربي حرا ص )ال ي د حم ال بي س ا عب عق ل ن و جا خا ي د سع ي ع خ ال بي ري ف ال ا ح مت داد ة بغ جامع ة ص الخال ر قية ء لغربي الع ص را ف ىف ال ك ى ين ذ ر ل وي الغا ك س ت ر ت لدقيقة د ل ال نا ة لي ريق ط ب خرية ) ١٣( ـل رحية لقد قسم صخور التكوين ) . غرب القائم ( مت مجعها من وادى الردكة ،ش :اىل اربعة سحنات دقيقة اعتمادا على احملتوى الصخرى والعضوى وهى احلجر اجلريى الواكى الوحلى احلياتى واحلجر اجلريى الوحلى واحلجر اجلريى الواكى ان السحنات الدقيقة للتكوين تعكس . املليوليدى واحلجر اجلريى احلبيىب احلاوى على الركام ن بيئة حبرية ضحلة ذات دوران مفتوح ىف اجلزء االسفل من التكوين وبيئة حبرية ضحلة ذات دورا واما اجلزء االسفل واالوسط يتدخل مع رواسب بيئة حبرية . قليل ملياة دافئة جدا ىف اجلزء االوسط اما اجلزء االعلى من التكوين فقد ترسب ىف بيئة حبرية .مفتوحة هادئة حتت مستوى املوجة ) مورفزم نوع النيو ( االنتقالية : العمليات التحويرية الرئيسية هى . ضحلة ذات دوران قليل . باالضافة اىل ترسيب الكالسا يت ىف الكسور وغرف املتحجرات