中国南海北部底流对深水沉积体系的影响及其油气地质意义

Impact of bottom currents in the northern South China Sea on deep-water depositional systems and their petroleum geological implications

王星星 万杏 何云龙 孙启良

Xingxing WANG Xing WAN Yunlong HE Qiling SUN

底流是深海沉积体系形成演化的重要沉积动力之一，对深水油气与天然气水合物储层的形成、展布及物性特征具有重要控制作用。系统开展了南海北部二维和三维地震数据、钻井及测井资料综合沉积地质研究。研究结果表明：① 南海北部陆缘深水底流作用活跃且类型多样。② 中新世以来底流沉积广泛分布，受海盆构造格局演化与局部地形影响，底流沉积具有显著的时-空差异性分布，其中东北陆缘底流最为强劲。③ 底流在南海北部早中新世的大型线性侵蚀沟槽、中中新世以来的中央峡谷与迁移峡谷群以及上新世以来的树枝型峡谷体系等关键沉积地貌的形成中扮演了关键角色。④ 南海北部海底峡谷、水道等重力流沉积地貌的形成演化，对陆坡地貌具有重要改造作用，进而控制了重力流输运路径以及浊积砂体的形成与分布。⑤ 强底流地区不仅发育砂质底流沉积，还对重力流沉积进行了改造，所形成的底流改造砂是重要的深水油气与天然气水合物储层。⑥ 底流沉积研究在南海北部深水沉积区具有重要意义，应加强南海北部古海洋与构造沉降之间关系、复杂地形条件下底流沉积过程以及底流-浊流交互作用机制研究。

Bottom currents are identified as a significant driving force in the formation and evolution of deep-water depositional systems， playing an important role in governing the formation， distribution， and physical properties of deep-water hydrocarbon and natural gas hydrate （NGH） reservoirs. In this study， we conduct a comprehensive analysis of the sedimentary geology in the northern South China Sea using 2D and 3D seismic data， as well as drilling and log data. The results indicate that the northern continental margin of the South China Sea exhibits active and diverse effects of deep-water bottom currents. Bottom-current deposits formed since the Miocene are extensively distributed along this margin. Influenced by the tectonic framework evolution of marine basins and local topography， these deposits show significant spatiotemporal differences in their distribution， with the strongest bottom currents identified along the northeastern continental margin. Bottom currents have played a key role in the formation of critical sedimentary landforms in the northern South China Sea， including large-scale linear erosional troughs formed during the Early Miocene， the Central Canyon and migration canyon group that have developed since the Middle Miocene， and the dendritic canyon systems formed since the Pliocene. The formation and evolution of gravity-flow depositional landforms， such as submarine canyons and channels， in the northern South China Sea， have significantly modified the continental slope morphology， thereby controlling the gravity-flow transport pathways and the formation and distribution of turbidite sand bodies. Areas with strong bottom currents exhibit sandy bottom-current deposits. Furthermore， bottom currents in these areas modify gravity-flow deposits， with resulting bottom-current reworked sandstones serving as significant deep-water hydrocarbon and NGH reservoirs. Investigating bottom-current deposits holds great significance for understanding the deep-water sedimentary area in the northern South China Sea， and more research efforts should be directed toward the relationships between paleo-oceanic conditions and tectonic subsidence in the northern South China Sea， as well as the bottom-current depositional processes under complex topographic conditions and the mechanisms underlying interactions between bottom and turbidity currents.

10.11743/ogg20250309