南海北部陆坡分类及成因分析

Classification and Genesis of Continental Slopes on the Northern South China Sea

陆坡形态隐含了丰富的地质信息,其差异性是大陆边缘沉积、侵蚀过程长期交互作用的结果。利用横跨南海北部的二维地震测线,采取曲线拟合的研究手段,在南海北部识别出了下凹型、平直型、"S"型等三种类型的陆坡。下凹型陆坡发育在莺歌海-琼东南西部、珠江口中部两个陆坡区,但其成因不同,前者主要受控于快速的沉积物供给,而后者受到陆架边缘三角洲进积和海底峡谷侵蚀的联合作用;平直型陆坡仅见于琼东南东部地区,其主控因素为弱的沉积物供给和较快的构造沉降;"S"型陆坡发育在珠江口地区的两翼,其形成明显受到海流和内波等外作用的改造。不同类型的陆坡具有特定的地层叠置样式、陆架坡折迁移轨迹类型和沉积体系分布特征。对陆坡类型的研究有助于建立沉积过程和产物的预测模式,从而指导古代陆坡的深水油气勘探。

The longitudinal morphology of continental slopes contains significant geological information, and the variations in morphology have been related with the long-term interaction of sedimentary and erosional processes. Basing on a series of 2D seismic profiles crossing the margin of the northern South China Sea, we have utilized a curve fitting procedure to investigate the morphology of continental slopes and recognized three types of continental slopes, concave-up, planar, and sigmoidal. Concave-up slopes develop within the Yinggehai-western Qiongdongnan area and are thought to be dominated by rapid sediment supply. The central Pear River Mouth area also has concave-up slopes, but they are mostly attributed to the progradation of shelf-edge deltas as well as the erosion of a giant submarine canyon. The sigmoidal slopes are mainly distributed on the two flanks of the Pearl River Mouth area, which resulted from the shaping process of ocean currents and internal waves. A certain type of continental slope tends to have its own stratal stacking pattern, shelf-edge trajectory trend and characteristic depositional systems. Investigation oi modern slope morphology can help build up the conduit-sink models, thus providing useful guidance for deep-water hydrocarbon exploration on ancient buried slopes.