南海东北陆坡海底微地貌特征及其天然气渗漏模式

海底天然气渗漏是海洋环境中广泛分布的自然现象，在世界各大洋中都有发现。海底渗漏可以极大地改变海底地貌特征，形成多种与之相关的微地貌类型。海底渗漏和天然气水合物的赋存具有密切的关系，海底渗漏区常伴有埋藏浅、饱和度高的天然气水合物。对南海东北部陆坡海域浅地层剖面、多波束测深和地震反射剖面等资料进行综合研究，识别出海底麻坑、海底丘状体、大型海底圆丘、泥火山等与海底天然气渗漏有关的微地貌类型，且麻坑、海底丘状体／大型海底圆丘、泥火山微地貌分别代表了浅覆盖层快速天然气渗漏、浅覆盖层中等速度天然气渗漏和厚覆盖层快速天然气渗漏3种天然气渗漏模式。以海底丘状体微地貌及声空白反射特征的浅层天然气聚集带，成为块状水合物最理想的发育场所，这可能成为南海北部陆坡勘察块状水合物的重要识别标志。

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 chan- ges 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 inter-pretation. 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.