AMQ abs Valente et al TEPRO 243-246.pub Available online http://amq.aiqua.it ISSN (online): 2279-7335 Alpine and Mediterranean Quaternary, Vol. 31 (Quaternary: Past, Present, Future - AIQUA Conference, Florence, 13-14/06/2018), 243 - 246 KARST SINKHOLES FORMATION AND SPATIAL DISTRIBUTION: CLUES FROM THE SOUTHERN APENNINES (ITALY) Ettore Valente 1, Alessandra Ascione 1, Nicoletta Santangelo 1, Antonio Santo 2 1 Dip. di Scienze della Terra, dell’Ambiente e delle Risorse (DiSTAR), Università degli Studi di Napoli Federico II, Napoli, Italy 2 Dip. di Ingegneria Civile, Edile ed Ambientale (DICEA), Università degli Studi di Napoli Federico II, Napoli, Italy Corresponding author: E. Valente ABSTRACT: Sinkholes that affect both carbonate rocks and alluvial plain deposits are widely distributed in the southern Apennines. Karst sinkholes, in particular, are generally clustered within High Sinkhole Concentration Area (HSCA). A geological and geomorphologi- cal study of some, selected HSCA, has been carried out, aimed at constraining hypotheses on both factors that control sinkhole spatial distribution and causative mechanisms of karst collapses. Based on independent evidence on the active tectonic framework and deep fluid rising in the HSCA, karst sinkhole phenomena appear related the hypogenic karst controlled by the rise of acidic fluids along active faults. KEYWORDS: Sinkholes, karst sinkholes, active faults, southern Apennines 1. INTRODUCTION The term sinkhole broadly indicates any medium- sized, sub-circular depression without considering its origin (Beck, 1984). The same term is adopted for both karst related and anthropogenic collapses (Santo et al., 2011; Scotto di Santolo et al., 2018). Regarding karst sinkholes, a genetic classification has been recently proposed by Gutierrez et al. (2008). Karst sinkholes occur in the entire southern Apennines, however they are densely distributed in specific areas labelled High Sinkhole Concentration Area - HSCA, sensu Santo et al. (2011). Recent studies highlight the occurrence of some peculiar geological and geomorphological features in the HSCA, such as the occurrence of active faults that are inferred as acting as pathways for the rise of deep fluids (Santo et al., 2011, 2017). Karst collapse sink- holes are also often associated with gas vents and min- eral springs. We have carried out a study aimed at the charac- terisation of the main geological and geomorphological features of some of the HSCA. Selected areas are (from the NW to the SE) the Pratella area, the Telese - Solo- paca area and the Contursi area (Fig. 1). The investi- gated areas are characterised by the occurrence of mineral and/or thermal springs. Furthermore, in all of the investigated areas deep fluid inputs are either testified by gas vents, or inferred from mineralogy and geochem- istry of precipitated minerals (Ascione et al., 2018; Santo et al., unpublished data). We have combined geological and geomorphological investigations aimed at reconstructing local geological setting and at detect- ing evidence for active faulting in the study areas. The aim of our study is to constrain hypotheses on causative mechanisms of karst sinkhole formation and factors that control karst sinkhole spatial distribution. 2. MATERIAL AND METHODS The study areas are located in the axial portion of the Southern Apennines and include the Telese - Solo- paca and the Contursi area already identified by Santo et al. (2011). In addition, the Pratella area has been investi- gated on the basis of the recent paper of Ascione et al. (2018). Detailed geological and geomorphological inves- tigations have been carried out. The geological analysis was based on the combination of field surveys with strati- graphical data of both published and unpublished bore- holes. The latter ones, in particular, provided useful con- straints on the spatial distribution and features of both outcropping and buried Quaternary deposits. The geo- morphological investigation has been based on the analysis of detailed topographic maps (1:5000 scale technical map of the Regione Campania) and has been addressed to the recognition and mapping of fault con- trolled features such as fault scarps, triangular facets, river bends, wind gaps, water gaps, beheaded valleys, besides sinkholes. The latter have been classified as either karst collapse sinkholes or alluvial plain sinkholes. Mineral, sulphurous and hot springs have been also mapped. Mineralogical and geochemical data within study areas have been derived from the literature. All of such information has been plotted on a simpli- fied geological map of the southern Apennines, in which information on active and capable faults (derived from detailed, local scale, and the Ithaca database, http:// sgi.isprambiente.it/geoportal/catalog/content/project/ ithaca.page) and epicentres of moderate to strong earth- https://doi.org/10.26382/AIQUA.2018.AIQUAconference quakes has been included. Locations of epicentres has been extracted from the Parametric Catalogue of Italian Earthquakes (Rovida et al., 2016), with the exception of the 280 B.C., 346, 847, 1349, 1456 and 1805 earth- quakes, whose locations are from Galli & Naso (2009). 3. RESULTS 3.1 Pratella area The Pratella area (box A in Fig. 1) is located to the southwest of the Matese ridge. The Pratella area is characterised by carbonate hills, whose elevations range between 300 and 500 m a.s.l., which are dis- sected by the Lete river valley. In the Pratella area, the Lete mineral spring is located. The carbonate hills of the Pratella area are interposed between Quaternary lacus- trine deposits that crop out in the Ciorlano area, to the north, and Ailano area, to the south. Quaternary lacus- trine deposits in the areas of Ailano and Ciorlano form terraces that are dissected and eroded at variable de- grees, whose elevation ranges between 230 and 280 m a.s.l. Geological, geomorphological and stratigraphical data allowed the recognition of several extensional fault strands with evidence of activity in the late Quaternary, with prevailing E-W and N-S orientations that affect both the carbonates and the alluvial deposits (Ascione et al., 2018). Karst sinkholes in the Pratella area are clustered along the carbonate hills. They are mainly distributed along an E-W direction, and are aligned with some ac- tive fault strand. The lacustrine basins of Ciorlano and Ailano are characterised by several gas vents and diffuse gas emission. The spatial distribution of the gas vents and gas emissions shows alignments that are consistent with orientation of active faults (Ascione et al., 2018). Geochemical data point to strong CO2 emission, which is among the highest gas emissions in non-volcanic 244 Fig. 1 - Spatial distribution of sinkholes in the southern Apennines plotted on a simplified geological map (modified from Santo et al., 2011 and Ascione et al., 2013). White boxes indicate HSCA investigated in this study. A: Pratella area; B: Telese - Solopaca area; C: Contursi area. Valente E. et al. 245 areas in the world (Ascione et al., 2018). Isotopic analy- ses of C in the CO2 suggest a crustal origin of the emit- ted gas, probably due to thermo-metamorphism of bur- ied Apulian carbonates triggered by buried magmatic bodies (Ascione et al., 2018). 3.2. Telese - Solopaca area The Telese - Solopaca area (box B in Fig. 1) is located to the north of the Mt. Camposauro massif. The latter consists of carbonate rocks and is bounded to the north by a wide piedmont area made up of slope and alluvial fan deposits interbedded with tephra layers. The Calore river valley limits the Camposauro northern slope and its piedmont to the north (Amato et al., 2018). The Solopaca village falls in this area, whereas the Telese village is located at the base of Mt. Pugliano, an isolated carbonate hill located to the northeast of Solopaca. Amato et al. (2018) point to the occurrence of several normal faults with evidence of activity in the late Quater- nary. Active fault strands affect the entire Camposauro piedmont and the Telese area, and are mainly E-W and NE-SW trending. Sinkholes occur in the surrounding of both the Solo- paca and Telese villages. Sinkholes in the Solopaca area affect the alluvial fan conglomerates. They are NE- SW aligned and placed close to some of the NE-SW trending active faults, while sinkholes in the Telese area affect the top surface of Mt. Pugliano, and are also aligned with fault strands. Here, thermal spring of Telese and large travertine bodies also occur, with �13C isotopic values of the carbonates indicating a crustal contribution (Santo et al., 2011; Ascione et al., 2014). Mineralogical and geochemical analyses of gypsum rich cursts/patina precipitated close to Telese hot springs and inside the sinkholes have been carried out by Santo et al. (2018). Isotopic analyses of �34S and �18O indicate a deep origin of sulphate leading the authors to hy- pothesize the presence of a deep-seated sulphur source. 3.3. Contursi area The Contursi area (box C in Fig. 1) is dominated by the ~1600 m high Mt. Marzano carbonate massif which is bounded, to the south, by San Gregorio Magno and Buccino intramontane basins, filled by late Quaternary fluvio-lacustrine deposits. Several evidences of recent faulting have been identified in these area, resulting in few km long fault strands affecting both the Mt. Marzano and the adjoining intramontane basins (Ascione et al., 2013). Sinkholes have been identified along the carbon- ate southern slope of Mt. Marzano and related alluvial fans. In addition, sinkholes affect the top surface of Mt. Pruno close to Contursi village. Here, a thermal hot spring is also present. Their distribution is consistent with some of the active fault strands recognized by As- cione et al. (2013) and Santo et al. (2011). Santo et al. (unpublished data) carried out a detailed mineralogical investigation of limestones and related precipitates close to sinkhole and mineral spring. The author found isotopic composition of S and O compatible with a deep source. 4. DISCUSSION AND CONCLUSIONS Karst sinkholes are widespread in the southern Apennines, and in several instances are found close to active faults. In some cases, such as the Pianelle sink- hole along the southern slope of Mt. Marzano, their for- mation is linked to seismic shaking related to high mag- nitude earthquakes (Santo et al., 2011; unpublished data). Independent mineralogical and geochemical evi- dence from the investigated HSCA highlights the occur- rence, in the surroundings of the karst sinkholes, of both CO2 emissions and strongly weathered carbonate rocks associated with diffuse precipitation of sulphure-rich minerals (Ascione et al., 2018; Santo et al., unpublished data). Gas vents are also found within or close to the HSCA (Ascione et al., 2018), even if their distribution is strongly controlled by the rock-type, being clustered where clayey rocks crop out. Isotopic composition of both gas emission and precipitates point to a crustal origin of rising fluids, triggered by the presence of buried magmatic bodies (Ascione et al., 2018; Santo et al., unpublished data). Overall scenario from the investi- gated HSCA suggests that enhanced dissolution that originates karst sinkholes is triggered by the presence of acidic (CO2 and/or H2S rich) fluids. Clustering of karst sinkhole phenomena appears related with localised hypogene karst controlled by the rise of acidic fluids conveyed towards the surface by active faults. REFERENCES Amato V., Aucelli P.P.C., Cesarano M., Filocamo F., Leone N., Petrosino P., Rosskopf C.M., Valente E., Casciello E., Giralt S., Jicha B. (2018) - Geomor- phic response to late Quaternary tectonics in the axial portion of the Southern Apennines (Italy): a case study from the Calore River valley. Earth Surface Processes and Landforms. Doi: 10.1002/esp.4390. Ascione A., Mazzoli S., Petrosino P., Valente E. (2013) - A decoupled kinematic model for active normal faults: insights from the 1980, MS = 6.9 Irpinia earthquake, southern Italy. Geological Society of America Bulletin, 125 (7-8), 1239-1259. Ascione A., Iannace A., Imbriale P., Santangelo N., Santo A. (2014) - Tufa and travertines of southern Italy: deep seated, fault related CO2 as the key control in precipitation. Terra Nova, 26 (1), 1-13. Ascione A., Ciotoli G., Bigi S., Buscher J., Mazzoli S., Ruggiero L., Sciarra A., Tartarello M.C., Valente E. (2018) - Assessing mantle versus crustal sources for non-volcanic degassing along fault zones in the actively extending southern Apennines mountain belt (Italy). Geological Society of America Bulletin. Doi:10.1130/B30814.1, in press. Beck B.F. (1984) - Sinkholes, their geology, engineering and environmental impact. Proceedings of the First Multidisciplinary Conference on Sinkholes, Or- lando, Fl. A.A. Balkema Publisher, Rotterdam, Netherlands, pp. 429. Galli P., Naso G.A. (2009) - Unmasking the 1349 earth- quake source (southern Italy): paleoseismological and archaeoseismological indications from the Karst sinkholes formation and spatial distribution Aquae Iuliae fault. Journal of Structural Geology. 31, 128-149. Gutiérrez F., Guerrero J., Lucha P. (2008) - A genetic classification of sinkholes illustrated from evaporite paleokarst exposure in Spain. Environmental Geol- ogy, 53, 993-1006. Rovida A., Locati M., Camassi R., Lolli B., Gasperini P. (2016) - CPTI15, the 2015 version of the Paramet- ric Catalogue of Italian Earthquakes. Istituto Nazi- onale di Geofisica e Vulcanologia. Doi: 10.6092/INGV.IT-CPTI15. Santo A., Ascione A., Del Prete S., Di Crescenzo G., Santangelo N. (2011) - Collapse sinkholes distri- bution in the carbonate massifs of central and sou- thern Apennines. Acta Carsologica, 40, 95-112. Santo A., Budetta P., Forte G., Marino, E., Pignalosa A. (2017) - Karst collapse susceptibility assessment: A case study on the Amalfi Coast (Southern Italy). Geomorphology, 285, 247-259. Santo A., Santangelo N., Balassone G., Strauss H. (unpublished data) - Hypogene karst as the key agent of high sinkhole concentration areas (Southern Apennines, Italy): mineralogical and geochemical constraints. Earth Surface Processes and Landforms, (submitted). Scotto di Santolo A., Forte G., Santo A. (2018) - Analy- sis of sinkhole triggering mechanisms in the hinter- land of Naples (southern Italy). Engineering Geol- ogy, 237, 42-52. 246 Valente E. et al. Ms. received: April 28, 2018 Final text received: May 16, 2018