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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/233985500 Lithological–Stratigraphic Characteristics of the Aptian–Cenomanian Sediments of the Abkhazian Zone of the Western Caucasus Article in Moscow University Geology Bulletin · July 2012 DOI: 10.3103/S0145875212040023 CITATIONS READS 2 48 9 authors, including: Ruslan Gabdullin Ludmila Fedorovna Kopaevich Lomonosov Moscow State University Lomonosov Moscow State University 178 PUBLICATIONS 61 CITATIONS 81 PUBLICATIONS 373 CITATIONS SEE PROFILE SEE PROFILE Eugene N Samarin E. V. Yakovishina Lomonosov Moscow State University Lomonosov Moscow State University 25 PUBLICATIONS 14 CITATIONS 24 PUBLICATIONS 10 CITATIONS SEE PROFILE SEE PROFILE All in-text references underlined in blue are linked to publications on ResearchGate, Available from: Ruslan Gabdullin letting you access and read them immediately. Retrieved on: 19 September 2016 ISSN 01458752, Moscow University Geology Bulletin, 2012, Vol. 67, No. 4, pp. 218–232. © Allerton Press, Inc., 2012. Original Russian Text © R.R. Gabdullin, L.F. Kopaevich, E.A. Scherbinina, O.V. Zerkal’, E.N. Samarin, E.V. Yakovishina, A.M. Akuba, N.T. Zagrachev, G.K. Kozlova, 2012, published in Vestnik Moskovskogo Universiteta. Geologiya, 2012, No. 4, pp. 12–25. Lithological–Stratigraphic Characteristics of the Aptian– Cenomanian Sediments of the Abkhazian Zone of the Western Caucasus R. R. Gabdullina, L. F. Kopaevicha, E. A. Scherbininab, O. V. Zerkal’a, E. N. Samarina, E. V. Yakovishinaa, A. M. Akubac, N. T. Zagrachevc, and G. K. Kozlovaa a Faculty of Geology, Moscow State University, Moscow, 119991 Russia b Geological Institute, Russian Academy of Sciences. Pyzhevsky per. 7, Moscow, 109017 Russia c Department of Geology, Geodesy, and Cartography, Republic of Abkhazia, Sukhum, Abkhazia email: [email protected] Received February 21, 2012 Abstract—For the first time, a complex lithological–stratigraphic and facial study of the Aptian–Cenoma nian sediments of the Abkhazian zone of the Northwestern Caucasus was carried in sections of the Mzymta and Khipsta river valleys. As a result, the areas of distribution of potential oilsource rocks in these sediments, which correspond to the events of the OAE1 and OAE2 global paleoecological crises, oil reservoir rocks and rockscaps were defined. Keywords: Western Caucasus, Aptian, Albian, Cenomanian, OAE1, OAE2 DOI: 10.3103/S0145875212040023 INTRODUCTION bodies, which contain rocky argillo–carbonaceous rocks (marls, rarely limestones). The argillaceous 1 This work presents the results from the study of the parts of the section are hidden by landslide bodies and lithological composition of the Aptian–Albian and are not exposed at the surface. The new data were Cenomanian sediments in the Abkhazian zone (in the obtained due to drilling and construction works in the Western Caucasus, in the Mzymta River valley) and in Mzymta River valley. Based on these works it became the area between the valleys of the Psou and Ingur riv possible to study the lithology of this interval of the ers, which were carried out by the author’s team in the section in detail. 2008–2011 period, as well as presenting data that con firm the age of these sediments. The sections we studied were tested for the occur rence of nanoplankton to distinguish landslide argilla The study included: ceous rocks from primary clays. In addition, it was a) a description of natural and artificial outcrops found that the proportion of argillaceous rocks in the and the borehole cores from several tens of boreholes section is much higher than previously thought. and their comparative analysis, b) selection of samples This allows us to consider the Aptian and Albian for petrographic and geochemical studies, as well as bituminous strata not only as potential oilsource dating the Nanoplankton complex, and c) an analysis rocks, but also as a regional cap. In order to confirm of the literature materials and their comparison with this, a number of outcrops were described in the new data. Mzymta River valley, in the area of the Kepsha settle It was established that the data about the lithologi ment, and outcrops on the right bank of the Khipsta cal composition of the Aptian–Albian and Cenoma River, in the area of the village of Otkhara (Uatkhara). nian sediments, which were based mainly on the The scheme of the studied sections is shown in the description of natural outcrops, differ from those that insert map (Fig. 1). were obtained during the study of the sections of bore holes that were drilled in sediments of the same age. In particular, we found that the proportion of argillaceous Research Methods rocks in the Aptian–Albian and Cenomanian sedi During the field works we carried out, the natural out ments is much higher than was previously thought. crops and the borehole cores were studied. In the samples The mapping of the territory made it possible to obtain that were taken from sections, the nanoplankton com the data on the material compositions of sediments by plex was described by E.A. Shcherbinina (GIN RAS); studying rare outcrops and numerous large landslide 12 samples were analyzed by E.N. Samarin (Moscow 218 LITHOLOGICAL–STRATIGRAPHIC CHARACTERISTICS 219 State University) using a MARC.GV Xray fluorescent mediumgrained subrounded calcite and quartz grains spectrometer (NGO Spectron, St. Petersburg). In (5%) with single large (up to 0.75 mm) shell remains of addition, a petrographic microscope study of eight indeterminable detritus. The marl is partly gypsified samples was made by G.K. Kozlova (Moscow State (10–15%) and contains 65–70% carbonate material. University). Secondary changes occur via the development of iron oxides and pyrite. Lithological–Stratigraphic Characteristics Schematic facial profiles (Figs. 1D, 1E) of the of the Aptian–Cenomanian Sediments Aptian sediments in the Abkhazian zone were compiled on the basis of the data from ([Ob”yasnitel’naya …, In the natural exposures on the right bank of the 1971], modified). As seen in the profiles, the thickness Mzymta River, upstream from the mouth of the Kep of the Aptian sediments varies from 50 to 100 m; it sha stream (point of observation 456), the Lower increases in the southeastern direction and decreases Aptian sediments were described in a bench of argilla in the Galidzga River valley. The Aptian sediments are ceous Aleurites that were revealed at a road cut of the presented by marls with subordinate limestones. In the 1 slope (Figs. 1A, 2). upper part of the section (the Gudauta subzone) a The Aleurite is gray–brown, whitishbrown to sandstone bed, which can serve as a collector, was dis palebrown on the weathered surface, massive, with a tinguished. The macrofauna is presented predomi pelitic texture and an unbedded or very thinbedded nantly by mollusks (belemnites) and rare ammonites. structure, probably due to dispersion differentiation of In the Gumista River valley, brachiopods were found; terrigenous material. The rock is intensively bedded. in the southeastern part of the Ochamchira subzone, Due to this, aleurites can be split easily into small 2–3 cm Aucellina species occurred; other bivalves occurred plates. In addition, the aleurite is lowstrength and rarely. The areal distribution of the Aptian sedimen swells easily; small fragments can be ground to dust tary formations is shown in Fig. 4; the areas with good with little effort. In the texture of the rock, numerous reservoir properties, regional caps, and potential oil bands of reddish and brownish color occur because of source rocks are shown in Figs. 5A and 5B. superimposed ferruginization. In a natural exposure (observation point 454) at the Figure 1B shows the aleurite, which microscopi mouth of an unnamed stream on the left bank of the 3 cally is finegrained, polymictic, and greatly calcare Mzymta River in the area of the village of Kepsha (at ous (40%), with poorly manifested horizontal bedding the northern entrance of the third combined rail and 2 due to an occurrence of interlayers enriched in calcar highway tunnel of the Adler–Alpika Route in the eous material. Fractures are filled with finefiber cal unbedded Upper Aptian (Zones NC7b, NC7c)– cite. Lower Albian (NC8a, b) sediments were described The nanoplankton complex that was found in the (Fig. 2). rock contains Watznaueria barnesae, W. manivitae, On the left side of an erosional downcutting of Braarudosphaera batiliformis, Micrantolithus hos about 30 m in height, at the base of the slope, the chulzii, Nannoconus boucheri, N. grandis, N. truittii, rhythmically stratified stratum, which is composed of N. vocontiensis, Assipetra terebrodentarius, Flabellites argillaceous and aleuritic marls with interlayers of 1 2 oblongus, and Rhagodisucus gallagheri. This complex bituminous marls and argilliceous aleurites, are 1 corresponds to the Early Aptian age (Zone NC6b). exposed as a separate bench with a thickness of about For the elements of the rock bedding, the dip in 8 m. Three rhythmic lithological varieties were distin azimuth is 45° and the dip angle is 65°. guished: aleuritic marls, foliated bituminous argilla 1 In the core of boreholes that were drilled on the left ceous marls, and aleurites or aleuritic marls. This inter 1 1 bank of the Mzymta River (Fig. 2), the Lower Aptian val of the section is terrigenous–carbonate in compo 1 sediments are presented by argillaceous marls, clays, sition with a substantial proportion of argillaceous 1 and marls (the proportion of each rock type in the sec material. Rocks dip in the northeastern direction at an tion is about 30%). angle of 20–30°. The results of the geochemical analysis of 12 sam When wet, the bedding in the section becomes ples from the Lower Aptian sediments, which were much smoother, especially due to the occurrence of revealed in borehole 569, are shown in the table. argillaceous material on the bedding surface. 1 These results show that most of the marls are argilla Marls are aleuritic (often argillaceous), gray to 1 1 ceous marls [Gabdullin et al., 2011a], (Figs.

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