Trace elements geochemistry of marine sediments and its implications for gas hydrate exploration

Gas hydrate is closely related to some major scientific issues such as energy supply and global environmental changes, and has become one of the hotspots of the world. Previous studies of the geochemical characteristics of methane seepage areas were mainly focused on shallow sediments, while the geochemical characteristics of deep sediments are ignored to certain extent. In order to explore the relationship between gas hydrate and the characteristics of trace elements in deeper sediments, 4 holes have been drilled and sampled at the Shenhu area of the South China Sea. Main, trace elements and organic carbon geochemical characteristics of the samples are analyzed and the oxidation-reduction state and their correlation with Mo and TOC discussed. The results suggest that the major elements in the sediments mainly come from terrigenous clastic material input, without obvious relationship with the process of gas hydrate enrichment. In the area rich in natural gas hydrate, Ba and Mo elements are always highly enriched showing obvious "Ba peaks" and "Mo peaks" owing to the sulfidation environment caused by the decomposition of natural gas hydrates. Therefore, the enrichment of Ba and Mo in the sediments can be used as important geochemical indicators to possible presence of gas hydrate accumulation.