Iron Sulfides and Sulfur Isotopes in Sediments from the Nankai Trough, Japan

We present first results of the iron and sulfur geochemistry from sediments from the shallow mega splay fault system at the Nankai Trough, collected during the IODP 316 Expedition. The objective of this research is to better understand the impact of dynamic systems on biogeochemical processes as well as microbiological signals in deep subsurface sediments, and to study linkages between the sulfur and iron cycle and the impact on highly dynamic sedimentary systems on these cycles. We measured the concentrations of acid volatile sulfur (AVS) and chromium reducible sulfur (CRS) from sediments at stations C0004 and C0008. The sediments at these stations are characterized by shallow sulfate/methane transition zones where released hydrogen sulfide reacts with reactive iron minerals to form iron sulfides. The alteration of iron oxides and their primary signals is reflected in the AVS and CRS data. We furthermore determined the sulfur isotope composition of AVS, CRS and pore water sulfate. Our data show a high variability, that may be caused by different sulfur sources and biochemical sulfur cycling, which relate to the tectonic and sedimentary complexity of the Nankai Trough.