南海北部陆坡一统峡谷群地貌特征及控制因素分析

    GEOMORPHOLOGICAL CHARACTERISTICS AND CONTROLLING FACTORS OF THE YITONG CANYON GROUP ON THE NORTHERN SLOPE OF THE SOUTH CHINA SEA

    • 摘要: 基于最新的高分辨率多波束全覆盖测深数据、单道地震和多道地震剖面数据,对南海北部陆坡一统峡谷群9条峡谷的地形地貌及沉积特征进行了分析:峡谷群自陆坡向深海盆方向呈聚敛型,横断面主要呈“V”型,谷壁对称发育,坡度较陡; 研究区海底地层受多条断裂控制,呈典型阶梯状发育,海底断陷、重力滑塌面和小型滑坡体等海底不稳定地质灾害高度发育,说明峡谷群海底环境处于极不稳定状态。在研究区海底峡谷群地貌演化过程中,西沙海槽区域沉降等新生代构造运动控制着峡谷群地貌格局的形成; 来自北部陆架的充足沉积碎屑物质的输入往往伴随着高密度浊流、海底滑坡、坍塌等海底灾害的发生,控制着峡谷群的进一步发育; 相对海平面变化直接改变了研究区的沉积环境,为陆源碎屑物质的搬运提供了更加直接的通道,这也是诱发陆坡海底失稳、塑造峡谷群地貌特征的重要因素之一。

       

      Abstract: Based on the latest high-resolution multi-beam bathymetric data, as well as the single-channel and multi-channel seismic profiles, this paper analyzed the topographic and depositional features of the group of nine canyons on the northern slope of the South China Sea. The canyon group converges from the continental slope to the deep-sea basin, in "V" shaped cross-sections, with rather symmetrical valley walls and steep slopes. The submarine strata in the study area are disturbed by faults, and developed in a stepped manner. Unstable geological hazards, such as submarine faults, gravity sliding surfaces and small landslides are highly developed, which suggests that the submarine environment of the canyon group is very unstable. Cenozoic tectonic movements, such as the regional subsidence of Xisha Trough, doubtlessly contributed to the formation of the geomorphic pattern of the canyon groups. Agreat amount of sediment debris from the northern shelf was mainly contributed by high-density turbidity currents derived from submarine landslides, collapses and other submarine disasters, which accelerated the further development of the canyon group. Relative sea level changes directly change the sedimentary environment of the study area and provide a more direct channel for the transport of enormous terrigenous clastic materials. This is also one of the important factors that induced the instability of the seabed on the slope and shaped the geomorphological characteristics of the canyon group.

       

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