OAE1a-Associated Interplay among Carbon Burial, Productivity, and Redox Conditions, NE Arabian Plate Margin

The Early Aptian oceanic anoxic event (OAE1a, ~120 Ma) was a brief interval (1 to 1.3 myr duration) of widespread oxygen deficiency of the ocean bottom waters that resulted in extensive organic carbon sequestration in marine sediments, coupled with major biotic, environmental, climatic, oceanic, and sea-level perturbations. This study tracks the OAE1a-associated perturbations along the NE Arabian Plate margin by using the stable carbon isotopes (δ13Corg, δ13Ccarb, and Δ13C), total organic carbon (TOC), detrital proxies (Al, Si, Ti, K), redox-sensitive (RSTE: U, V, and Mo) and productive-sensitive trace elements (PSTE: P, Cu, and Ni) from a continuous succession of the Kazhdumi Intrashelf Basin.

The interval retained a high-resolution record of carbon-isotope fluctuations, which enables correlation across the Arabian Plate and Tethys. Before and at the onset of the OAE1a (segments C2-basal C4), the basin’s bottom water was oxic, and carbonate deposition predominated with low TOC, low RSTE, and low PSTE; orbitolinids and ostreid bivalves were abundant, and bioturbation common. The conditions shifted to anoxic-suboxic through the basalmost C5 + C6 segments with high productivity by radiolarians and planktic foraminifera; several intervals with co-occurrence of high RSTE, PSTE (Cu, Ni), and TOC characterize this interval. The bottom-water conditions returned to oxic-suboxic (segments C5+C6) with deposition of predominantly dark-gray radiolarian and planktic foraminiferal wackestone with variable TOC (0.2 to 2.5%). This study resolves some of the uncertainties related to the potential culprits for the OAE1a-associated changes in bottom-water oxygenation, organic-rich layer formation, and biotic shifts along the Arabian margin of the Neo-Tethys.