Study on authigenic pyrite in sediments of gas hydrate geo-system in the Shenhu area,South China Sea

Shenhu area of South China Sea is one of the most important research areas for natural gas hydrate in China.Geochemical and mineralogical characteristics were investigated in ten sediment samples,which included the sediments of gas-hydrate-bearing layer,collected from W19 Bsite in Shenhu area.Analyses of major elements and X-ray diffraction indicated that several layers contained pyrite with unusual high content.The SEM images revealed that the pyrite crystals became more euhedral and the morphology varied from aggregate framboids to single framboid and finally tiny grain types as sediment depth increased,and some intermediate products in the textural evolution were also identified.Both 53.0 mbsf(meters below seafloor)and 140.4 mbsf layers were observed with significant abundances of pyrite.At the 140.4 mbsf layer,pyrite filling the chamber of the foraminifer shell was common and coupled with a large amount of columnar pyrite,which might be related to the anaerobic oxidation of organic matter and methane,espe