Distribution of surface sediment types and sedimentary environment divisions in the northern South China Sea

A total of 224 surface sediment samples collected from the northern South China Sea were studied in terms of grain size and carbonate content, to understand the sediment transport patterns and the corresponding depositional environments in the region. Results revealed that sediments in the study area could be divided into the following types:gravelly sand, coarse sand, medium sand, fine sand, silty sand, sandy silt, sand-silt-clay, clayey silt, silty clay, and clay.The abyssal-bathyal sediments could be divided into eight types, namely, siliceous clay, calcareous clay, calcareous and siliceous clay, foraminifer ooze, calcareous clayey silt, calcareous sand-silt-clay, and siliceous clayey silt. Among them,the silty clay, clayey silt, sand, sandy silt, and clay are the major types, accounting for more than 80% of the area total.Factor analysis of grain size parameters and carbonate content was used to discriminate different depositional environments. Results showed that the above parameters may be divided into three types and the study area could then be divided into four subareas. The factor 1 acts on subareasⅠ and Ⅱ. Clayey sediments are distributed in subarea Ⅰ,which is mainly located in the deep waters in the southeast. The medium and fine sand zones are distributed in subareaⅡ, which normally occurs on the outer continental shelf off the west of Guangdong Province and the offshore areaalong the coast of South China. The factor 2 acts on subarea Ⅲ, where silt of coarse and medium sizes is mainly distributed on the slope in the southeast off Hainan island and off the Pearl River Estuary, and on the outer shelf southwest off Taiwan. The factor 3 acts on subarea Ⅳ, where coarse sand is mainly distributed on the inner continental shelf southwest of Taiwan.