Evidence for euphotic zone anoxia during the deposition of Aptian source rocks based on aryl isoprenoids in petroleum,Sergipe–Alagoas Basin,northeastern Brazil |
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| Institution: | 1. WA Organic and Isotope Geochemistry Center, The Institute for Geoscience Research, Department of Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;2. Center for Exploration Targeting and Biogeochemistry Center, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;3. Institute of Geoscience, Kiel University, Ludewig-Meyn Str. 10, 24118 Kiel, Germany;4. Geochemistry & Isotope Biogeochemistry Group, Marine Geology Department, Leibniz-Institute for Baltic Sea Research, Seestrasse 15, D-18119 Warnemünde, Germany;5. Department of Earth, Atmospheric and Planetary Sciences, MIT, E25-633, 45 Carleton Street, Cambridge, MA 02139 USA;6. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia;7. School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia |
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| Abstract: | Four crude oil samples from the Sergipe–Alagoas Basin, northeastern Brazil, were analyzed using full scan gas chromatography–quadrupole mass spectrometry (GC–qMS) for biomarkers, in order to correlate them using aromatic carotenoids thereby enhancing knowledge about the depositional environment of their source rocks. The geochemical parameters derived from saturated fractions of the oils show evidence of little or no biodegradation and similar thermal maturation (Ts/(Ts + Tm) for terpanes, C29 αββ/(αββ + ααα), C27, and C29 20S/(20S + 20R) for steranes). Low pristane/phytane ratios and the abundance of gammacerane and β-carotane are indicative of an anoxic and saline depositional environment for the source rocks. Moreover, we identified a large range of diagenetic and catagenetic products of the aromatic carotenoid isorenieratene, including C40, C33, and C32 diaryl isoprenoids and aryl isoprenoid derivatives with short side chains and/or additional rings. These results indicate anoxia in the photic zone during the deposition of the source rocks. |
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