海底麻坑的构型、特征、演化及成因——以西非木尼河盆地陆坡为例

Architecture,Character,Evolution and Genesis of Seabed Pockmarks:A Case Study to the Continental Slope in Rio Muni Basin,West Africa

基于高分辨率三维地震数据，研究了西非木尼河盆地海底麻坑的构型、演化模式及成因机制。海底麻坑分为孤立麻坑和条带状麻坑（简称麻坑带），麻坑带由较多的单个麻坑呈条带状排列聚集而成，单个麻坑的面积在0.2～0．6km2，麻坑深度约20～60m。过孤立麻坑或横切麻坑带的地震剖面上，麻坑及其之下地层具有U形反射特征，显示麻坑之下有气烟囱发育。并具有振幅增强、同相轴下拉的特征：顺麻坑带走向的地震剖面具有脊一槽相间的地形特征。研究区的麻坑带受古深水水道控制．麻坑带与古水道的平面分布相吻合。由古水道控制形成麻坑带的演化模式可以划分为四个阶段：古水道超压形成、古水道超压释放、麻坑物质冲洗、麻坑形成。海底麻坑的成因机制具有多样性，但基本上都是由海底地层中的流体发生渗漏或喷发所形成的。

Based on high-resolution 3D seismic data, the seabed pockmarks can be divided into isolated pockmarks and pockmark belts by their distribution in Rio Muni Basin, West Africa. Pockmark belts are distributed along meandering bands on seafloor. A single seabed pockmark can be in a range from 0.2 to 0.6 km2 in area and from 20 to 60m in depth. The seismic profiles across the isolated pockmarks or seabed pockmark belts illustrate U-shaped reflection characters of them an d the underlaying beds with increasing amplitudes and pulling-down seismic events, which implies the existence of gas chimneys under these seabed pockmarks, The seafloor along the strikes of the seabed pockmark belts is characterized by a ridge-by-swale topography. The distribution of the seabed pockmark belts are controlled by the palaeochannels so that the distribution of pockmark belts is coherent with that of alaeochannels in plane. The evolution of the seabed pockmark belts that are controlled by palaeochannels can be divided into four stages： overpressure build-up stage, overpressure release stage, pockmark sediments expulsion stage and pockmark formation stage. The genesis of pockmarks is relative to some geological conditions but all of pockmarks have been associated with fluids seepage or expulsion in sea floor strata.