Coupled C–S–Fe Geochemistry in a Rapidly Accumulating Marine Sedimentary System: Diagenetic and Depositional Implications

In the present study, we have investigated the C-S-Fe systematics in a sediment core (MD161-13) from the Krishna-Godavari (K-G) basin, Bay of Bengal. The core covers the late Holocene period with high overall sedimentation rate of similar to 573 cm kyr(-1). Pore fluid chemical analyses indicate that the depth of the present sulfate methane transition zone (SMTZ) is at similar to 6 mbsf. The (Delta TA + Delta Ca + Delta Mg)/Delta SO42- ratios suggest that both organoclastic degradation and anaerobic oxidation of methane (AOM) drive sulfate reduction at the study site. The positive correlation between total organic carbon content (TOC) and chromium reducible sulfur (CRS) content indicates marked influence of organoclastic sulfate reduction on sulfidization. Coupled occurrence of S-34-enriched iron sulfide (pyrite) with C-12-enriched authigenic carbonate zones is the possible records of paleo-sulfate methane transition zones where AOM-driven-focused sulfate reduction was likely fueled by sustained high methane flux from underlying gas-rich zone. Aluminum normalized poorly reactive iron (Fe-PR/Al) and La/Yb ratios suggest increasing contribution from Deccan basalts relative to that of Archean-Proterozoic granitic complex in sediment flux of Krishna-Godavari basin during the last 4 kyr.