Organofacies and paleoenvironment of the Oligocene Maikop series of Angeharan (eastern Azerbaijan) |
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| Institution: | 1. Department of Applied Geosciences and Geophysics, Montanuniversität Leoben, Peter-Tunner-Str. 5, A-8700 Leoben, Austria;2. Azerbaijan National Academy of Sciences, Geology Institute, 29 A.H. Javid Pr., Baku 370143, Azerbaijan;3. Institute of Earth Sciences, Karl-Franzens University, Heinrichstr. 26, A-8010 Graz, Austria;4. Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt;5. Institute of Atmospheric and Environmental Sciences, Department of Environmental Analytical Chemistry, J. W. Goethe-Universität, Altenhöferallee 1, D-60438 Frankfurt a.M., Germany;1. Takuvik International Research Laboratory, Québec Océan, Laval University (Canada) - CNRS, Département de biologie and Québec-Océan, Université Laval, Québec, Canada;2. Laboratoire des Sciences de l''Environnement MARin (LEMAR), UMR 6539 CNRS/Ifremer/IRD/UBO, Institut Universitaire Européen de la Mer (IUEM), Technopôle Brest-Iroise, Plouzané, France;3. ArcticNet, Québec Océan, Département de Biologie, Université Laval, Quebec, QC, Canada;4. Axe santé des populations et pratiques optimales en santé, Centre de recherche du CHU de Québec, Université Laval, Québec, Canada;1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China;2. University of Chinese Academy of Sciences, Yuquan Road, Beijing 100049, PR China;3. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;1. Department of Earth Sciences, University of California, Riverside, CA 92521, USA;2. Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA;1. GFZ German Research Centre for Geosciences, Sec. 3.2 Organic Geochemistry, Telegrafenberg D-14473, Germany;2. Laboratory of Petroleum Engineering and Exploration (LENEP), North Fluminense State University (UENF), Macaé, Rio de Janeiro 27910-970, Brazil;1. Department of Geology, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Iran;2. Petroleum Geology and Geochemistry Research Centre, (PGGRC), Shahid Chamran University of Ahvaz, Iran;3. National Iranian Oil Company, Exploration Directorate, Tehran, Iran |
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| Abstract: | The Maikop Formation, deposited in eastern Azerbaijan during Oligocene and Early Miocene times, contains prolific source rocks with primarily Type II organic matter. Paleontological analyses of dinoflagellate cysts revealed a Lower to Upper Oligocene age for the investigated succession near Angeharan. A major contribution of aquatic organisms (diatoms, green algae, dinoflagellates, chrysophyte algae) and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n-alkane distribution patterns, composition of steroids and δ13C of hydrocarbon biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria, chemoautotrophic bacteria, as well as green sulfur bacteria. Higher inputs of terrigenous organic matter occurred during deposition of the Upper Oligocene units of the Maikop Formation from Angeharan mountains. The terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the Shamakhy–Gobustan area.High primary bioproductivity resulted in a stratified water column and the accumulation of organic matter rich sediments in the Lower Oligocene units of the Maikop Formation. Organic carbon accumulation during this period occurred in a permanently (salinity-) stratified, mesohaline environment with free H2S in the water column. This is indicated by low pristane/phytane ratios of all sediments (varying from 0.37–0.69), lower methylated-(trimethyltridecyl)chromans ratio in the lower units and their higher contents of aryl isoprenoids and highly branched isoprenoid thiophenes. Subsequently, the depositional environment changed to normal marine conditions with oxygen deficient bottom water. The retreat of the chemocline towards the sediment–water interface and enhanced oxic respiration of OM during deposition of the Upper Oligocene Maikop sediments is proposed.Parallel depth trends in δ13C of total OM, n-alkanes, isoprenoids and steranes argue for changes in the regional carbon cycle, associated with the changing environmental conditions. Increased remineralisation of OM in a more oxygenated water column is suggested to result in low TOC and hydrocarbon contents, as well as 15N enriched total nitrogen of the Upper Oligocene units. |
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