西非下刚果盆地深水曲流水道的地震响应特征与演化模式分析

Seismic response characteristics and evolution models of deepwater meandering channels in Lower Congo Basin,West Africa

在西非下刚果盆地内普遍存在平面外形与陆相曲流河相似的曲流水道沉积,通过分析过深水水道的高分辨率三维地震剖面,发现重复的垂向叠加和横向迁移是形成高弯度水道的主要原因,其迁移和弯度演化模式更复杂并且与陆相河流相差甚远。深水水道的演化模式可总结为4种:①纯横向迁移;②纯垂向叠加;③垂向叠加为主,各期叠加水道向水道复合体的凹岸方向偏离;④水道复合体的基底以横向迁移为主,上部以垂向叠加为主。分析引起这些差异的原因,发现流体参数和沉积颗粒的改变会引起切割和充填作用,并进一步引起侵蚀、过路或沉积作用,从而导致深水水道系统内同时存在横向迁移和垂向叠加两种过程。

Highly bending deepwater channel depositions are common developed in the Lower Congo Fan,West Africa,and the planform characteristics are similar to those of the continental meandering river.Through analysis of high resolution 3Dseismic planar-slices and cross-sections over the deepwater meandering channels,we found the main reason for the formation of its high bending is repeated vertical superposition and lateral migration,which is more complex than the continental river.The evolution models of deepwater meandering channels can be summarized as four kinds:①lateral migration;②vertical superposition;③vertical superposition with some lateral migration to the concave side;④lateral migration in the basal part and vertical superposition in the upper part.The causes of the difference were analyzed,and it is shown that changes in flow parameters and sediment grain size can generate cuts and fills,and further cause erosion,bypassing or deposition in space and time,thus result in two processes of lateral migration and vertical superposition in deepwater meandering channels simultaneously.