Contrasting sulfidization in the turbidite and hemipelagic sediments of Bengal Fan

Abstract

We report for the first time, contrasting sulfidization profiles in a sedimentary sequence comprising of clay-silt turbidites and hemipelagic dominated deposits in a channel-levee complex of the middle Bengal Fan. The results show the focusing of acid volatile sulfur (AVS), elemental sulfur contents and marked increase in total reducible sulfur concentrations within the clay-silt turbidite rich zone relative to the overlying hemipelgaic rich zone. The large spread in delta34SAVS (-36.6 to +64.4‰) and delta34SCRS (-43.7 to +39‰) coupled with 34S enrichment spikes in turbidites dominated zone are tell-tale signatures of rapid consumption of pore-water SO42- reduction in a closed system conditions created by turbidite depositions. In contrast, delta34SCRS values ranging from -50 to +2.8‰ recorded in the hemipelagic rich zone suggest dominantly early-diagenetic pyritization close to the sediment-water interface. The present study signifies the importance of turbidite fan sedimentation in the biogeochemical cycle of sulfur, carbon, and iron and enhances the scope of global Fe-S-C burial estimation in the marine realm.