To better understand the responses of authigenic minerals in sediments of the gas hydrate geo-system, some authigenic carbonates in sediments from IODP Expedition 311 were analyzed for the purpose 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 irregular aggregations. The delta (super 13) C PDB of collected authigenic carbonates recorded typical extremely negative values as low as -41.50 ppm, indicating the involvement of methane in the anaerobic oxidation of methane (AOM) under methane seepage in a gas hydrate geo-system. The delta (super 18) O PDB of the authigenic carbonates generally decreased with depth, possibly implying a decreasing environmental temperature during carbonate precipitation from the lower (older) to the upper (younger) part of the sediment column. This study thus has significant meaning for exploring for potential marine gas hydrates in China and in deciphering ancient methane hydrate-associated sedimentary records.