Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea Anja Reitz a,⇑ , Thomas Pape b , Matthias Haeckel a , Mark Schmidt a , Ulrich Berner c , Florian Scholz a , Volker Liebetrau a , Giovanni Aloisi a,d , Stephan M. Weise e , Klaus Wallmann a a Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany b MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany c BGR – Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany d CNRS-UMR 5125, Laboratoire de Pale ´oenvironnements e Pale ´ obiosphe `re, Universite ´ Claude-Bernard Lyon I, 69622 Villeurbanne, France e UFZ Helmholtz Centre for Environmental Research, Theodor-Lieser-Str. 4, 06120 Halle, Germany Received 7 July 2010; accepted in revised form 14 March 2011; available online 22 March 2011 Abstract Four seep sites located within an 20 km 2 area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salin- ity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110 °C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C 15+ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated. Ó 2011 Elsevier Ltd. All rights reserved. 1. INTRODUCTION Pore fluids, gases, and sediments expelled at cold seeps provide valuable insight into sedimentary diagenetic pro- cesses because their chemistry is affected by the interaction with surrounding sediments and rocks. Processes that affect pore water chemistry are (i) decomposition of organic mat- ter (Jørgensen, 1982; Martin et al., 1993; James and Palmer, 2000; Buffett and Archer, 2004; Hensen and Wallmann, 2005), (ii) sedimentary mineral precipitation and dissolu- tion processes (Chan and Kastner, 2000; Brown et al., 2001; Da ¨hlmann and de Lange, 2003), (iii) interaction with 0016-7037/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2011.03.018 ⇑ Corresponding author. Tel.: +49 431 6002234; fax: +49 431 6002928. E-mail address: areitz@ifm-geomar.de (A. Reitz). www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 75 (2011) 3250–3268