Chemostratigraphic Characterization of Euxinic Environments as an Indicator of Good Organic Matter Preservation: The Case of the Ouatt-2X Well, Abidjan Margin, Ivorian Sedimentary Basin
Twenty-seven (27) samples from an offshore petroleum well in the Ivorian sedimentary basin were investigated to characterize euxinic environments using chemostratigraphic proxies and to evaluate their role in organic matter preservation within Cenomanian-Turonian sedimentary deposits. Two complementary methodological approaches were employed: (i) Rock-Eval pyrolysis, used to determine Total Organic Carbon (TOC) content and assess the source rocks’ petroleum potential through the S2 parameter, and (ii) X-ray fluorescence (XRF)-based chemical analysis, used to quantify trace elements and evaluate their influence on the evolution of depositional paleoenvironmental conditions. The results reveal significant enrichment in trace elements such as uranium, vanadium, copper, nickel, and molybdenum, indicating anoxic to euxinic conditions throughout the studied interval. The intensity of these reducing conditions is greatest at the base of the section and generally decreases upward, punctuated by a distinct re-oxygenation episode, here identified as a separate megasequence. Among the trace elements identified, vanadium and molybdenum emerge as the most robust redox indicators, whereas nickel and, to a lesser extent, copper, carry a dual signal reflecting both redox conditions and biological productivity. The intervals displaying the highest trace-element enrichments also correspond, according to Rock-Eval data, to good-to-excellent source rocks, with TOC contents ranging from 1.49 to 4.24 wt.% and S2 values from 2.48 to 27.49 mg HC/g rock. These results indicate that source-rock quality results from the conjunction of at least two factors: sustained primary bioproductivity and redox conditions limiting the activity of bottom-water organic-matter grazers, although basin restriction, sedimentation rate, detrital dilution, and post-depositional metal redistribution cannot be excluded as contributing controls.
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