Grain size distribution pattern of surface sediments and its implications for transportation trend: A case from the waters off Zhongsha Islands, the South China Sea

232 surface sediment samples taken from offshore Zhongsha Islands were analyzed so as to better understand the sources, depositional environment and transporting patterns of the sediments. 6 types of sediments are recognized. i.e. sand, silty sand, sandy silt, silt, sandy mud and mud, dominated by sandy mud and mud. The coarser sediments, which usually have higher sorting, are mainly distributed in the water areas surrounding the Islands. Cluster analysis and principal component analysis are used for the study of component contents, grain size parameters and water depth. In consideration of the influences of sediment sources and seabed topography, the study area is divided into five depositional subareas: platform, platform terrace, slope around platform, trough and ridge, and deep-sea basin subareas. In combination with the depositional environment classification, grain size trend analysis is conducted. The results suggest that the sediments are mainly provided by the Zhongsha platform and the Xisha uplift, dispersed in surrounding waters, and finally deposited in the Zhongsha Trough. The sediment transportation is jointly influenced by sediment sources, seabed topography and water hydrodynamic conditions, under the control of monsoon, tide, wave and ocean current.