ABSTRACT

Ubiquitous pockmarks in continental margins are important to understand the tectonic and sedimentary history and flow activity of their host margins. The study of an extensive field of pockmarks in the South China Sea (SCS) is important both scientifically and economically, for the exploration of oil, gas, and gas hydrate resources and the prevention and control of marine geological disasters. We report our new findings on the characteristics, distribution, and genesis of pockmarks in the SCS based on interpretation of high-resolution multibeam bathymetric data and multichannel seismic profiles collected in the past decade. Three pockmark fields (total area 572,824 km²), are recognized in the northern, western, and southern continental margins of the SCS. The pockmarks are highly variable in shape: circular, elliptical, crescent-shaped, elongated or forming a chain in plan view and U-, V- or W-shaped in cross-section. Pockmarks are normally 10–200 m in diameter, with maximum diameters/axial lengths of 7.3 km for circular, 5.5 km for elliptical, 8.6 km for crescent-shaped, 9.5 km for elongated, and 30 km for chain-type pockmarks. Pockmarks are normally less than 35 m deep, with a maximum depth of 341 m at the southwestern SCS margin. These pockmarks might have originated from methane seepages or from pore fluids from deeper sources, which migrated vertically along gas chimneys, mud diapirs, mud volcanoes, faults or buried channels. In addition to possible structural controls, the pockmark morphologies are affected by bottom currents.

摘要

大陆边缘无处不在的麻点对于了解其寄主边缘的构造和沉积历史以及流动活动非常重要。南海大面积麻坑研究对于油气资源、天然气水合物资源勘探和海洋地质灾害防治具有重要的科学和经济意义。我们根据对过去十年收集的高分辨率多波束测深数据和多道地震剖面的解释，报告了关于 SCS 中麻点的特征、分布和成因的新发现。三个麻点（总面积 572,824 平方公里²)，在南海北部、西部和南部大陆边缘得到承认。麻点的形状变化很大：圆形、椭圆形、新月形、细长形或在平面图中形成链状，横截面呈U形、V形或W形。麻点直径一般为10～200m，圆形麻点的最大直径/轴向长度为7.3km，椭圆形麻点为5.5km，月牙形麻点为8.6km，细长麻点为9.5km，链式麻点为30km。麻点深度通常小于 35 m，南海西南部边缘的最大深度为 341 m。这些麻点可能源自甲烷渗漏或来自更深源的孔隙流体，这些流体沿气烟囱、泥底辟、泥火山、断层或埋藏通道垂直迁移。除了可能的结构控制之外，