Stable Carbon and Oxygen Isotopes Characteristics of the Authigenic Carbonates in Recovered Sediments during IODP 311 Expedition

To understand better the responses of authigenic minerals in sediments of the gas hydrate geo-system,some authigenic carbonates in sediments from IODP 311 Expedition were analyzed for the purposes of studying their mineral components,textures,and stable carbon and oxygen isotopes.XRD and SEM results show that Fe-dolomites and calcites are the dominant minerals in the authigenic carbonates,which occurred mainly in pore-rich spheroids and un-regular aggregations.The δ13 CPDB of collected authigenic carbonates recorded the typical extreme negative values is low to-41.50‰,indicating the involvement of methane in the anaerobic oxidation of methane(AOM)under the methane seepage in gas hydrate geo-system.The δ18OPDB of the authigenic carbonates generally decreased with depth,possibly implying a decreasing environment temperature during carbonate precipitation from lower(old) to upper(new) part of sediment column.This study thus has a significant meaning in exploring the potential marine gas hydrate in China and in deciphering the ancient methane hydrate-associated sedimentary records in the Earth history.