MICROTOPOGRAPHIC FEATURES OF THE NORTHEASTERN SLOPE OF THE SOUTH CHINA SEA AND GAS SEEPAGES

Submarine gas seepage is a widely distributed natural phenomenon in marine environment,and has been discovered almost in all the oceans. Submarine gas seepage may bring about great changes in seafloor topography,forming many kinds of seeping microtopographys. Submarine gas seepage is closely related with the occurrence of gas hydrate. Shallowly buried gas hydrate always occurs in submarine gas seepage areas. Sub-bottom profiles,multi-beam geomorphologic data and seismic data from the northeastern slope of the South China Sea were collected by the authors for integrated interpretation. Micro topographic features, such as pockmarks, submarine domes, large-scale submarine hummocks, mud volcanoes and authigenic carbonate mounds were identified. Our studies suggest that the pockmark may indicate a thin-bed and high-speed gas seepage, the submarine dome or large-scale submarine hummock indicate a thin-bed and middle-speed gas seepage, and the mud volcano indicate a thick-bed and high-speed gas seepage. Submarine domes and acoustic blank indicate the areas where gas accumulated in shallow strata and suitable for the formation of block-hydrate. They may be used as an important indicator of block-hydrate occurrence on the Slope in northeastern South China Sea.