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.