Abstract: Gas hydrate or combustible ice, as new-type hydrocarbon resource in the special areas, is an ice-like white crystal solid formed by water and natural gas (methane) compound under a certain condition of temperature and pressure, which is buried in shallow depositional strata of deep sea continental slope and rise, characterized by cleanness, high density of energy, broad distribution, large scale, shallow burying and good physicochemical conditions for accumulation. In the continental slope and rise areas of South China Sea with structural features of passive margin distribute a great number of petroliferous sedimentary basins. Since Late Miocene, these basins have undergone persistent regional subsidence with calm tectonic movement, high sedimentary speed, abundant marine organic sediments. All these provide the favorable geologic and deposit-forming conditions such as source, temperature, pressure and structure for shaping the gas hydrate. Since 1999, nine-year gas hydrate survey has been made in such four sea areas as Dongsha, Shenhu, Xisha and Qiongdongnan in the northern South China Sea by Guangzhou Marine Geologic Survey, and eighteen numbers of aerial surveys and researches have been completed. And many seismic markers or pseudo-submarine reflectors (PSR), geological markers and geochemical markers have been found in succession. Finally, the sample of gas hydrate is successfully obtained by drilling in May 2007. China becomes the fourth country that has obtained real gas hydrate samples after America, Japan and India.

Key words: gas hydrate, seismic marker, PSR, northern South China Sea