南海北部陆坡神狐海域SH-CL38站位的粒度特征及沉积记录

南海北部陆坡神狐海域发育众多海底峡谷，其物质来源、地貌形态、水动力条件、沉积过程复杂，海底滑坡和浊流频发。虽然通过地球物理（多波束和反射地震等）能够识别出数米至百米的滑坡体，但对于浅层海底重力流、浊流和异重流等沉积体系的高分辨率识别还受到很多限制。本研究以南海北部陆坡海底峡谷群12号峡谷脊部下游的SH-CL38站位岩芯沉积物为研究对象，通过粒度测试和浮游有孔虫氧同位素组成分析，将该站位岩芯划分为3个层段：第Ⅰ层段（0～285 cm）、第Ⅱ层段（285～615 cm）以及第Ⅲ层段（615～800 cm）。其中第Ⅱ层段的粒度参数、有孔虫的氧同位素组成明显不同于其他层段，这表明该层段形成时的水动力条件、沉积环境发生了突变。而且第II层段的285～505 cm和505～615 cm具有明显不同的概率累积曲线特征，粒度数据也分布在C-M图上不同的区域。基于此，我们认为该站位的异常沉积层是受深水沉积作用和末次冰期海平面变化的影响，285～505 cm层段发育浊流沉积，而505～615 cm层段可能是浊流或重力流引发的沉积物失稳。

Sediment grain size characteristics of the Core SH-CL38 in the Shenhu area on the northern continental slope of the South China Sea

A number of submarine canyons has been found in the Shenhu area on the northern continental slope of the South China Sea. Sediment sources, topographic features, hydrodynamic conditions, and depositional processes in these canyons are very complex, owing to the occurrence of submarine landslides and related turbidity currents. Landslides are found, by means of geophysical surveys, such as multi-beam bathymetric survey and high-resolution multi-channel seismic profiles, varying in scale from several to hundred meters. However, the high-resolution identification of the depositional systems, such as gravity flow, turbidity current, and hyperpycnal current on the shallow seafloor remains difficult. In this study, we analyzed the columnar sediments taken from the sampling station of SH-CL38 which is located in the lower reaches of the canyon on the northern slope of the South China Sea. According to the grain size distribution patterns of sediments and the oxygen isotope composition of foraminifera, the core sediments of SH-CL38 can be subdivided into the three units: Unit Ⅰ (0～285 cm), Unit Ⅱ (285～615 cm) and the Unit Ⅲ (615～800 cm). The physical and geochemical features of the Unit II, including grain size and the oxygen isotope composition of foraminifera are obviously different from those of the other two units. This suggests that the hydrodynamic conditions and depositional environment have been sharply changed while the Unit II was deposited. The grain size distribution patterns and the probability cumulative curves at 285～505 cm and 505～615 cm in depth are completely different and located in different areas of the C-M diagram. Based on the data mentioned above, it is concluded that the sediments of SH-CL38 is deposited in a deep-water environment under the influence of sea level change. The sediments of 285～505 cm is related to the turbidity current, while the 505～615 cm is formed in an instable environment under the influence of turbidity current or gravity flow.