Characteristics of Grain Size Distributions of Surface Sediments in the Eastern South China Sea

Grain size analysis, parameter calculation and multivariate statistics have been carried out based on 179 surface sediments collected from the Eastern South China Sea, and using related data, characteristics of frequent distributi on, sediment movement style and sedimentary environments have been researched. T he major class of surface sediments of the Eastern South China Sea are composed of 4.0～10.0(coarse silt-coarse clay), the key class consist of 6.0～8.0(fi ne silt), mean( M z ) of ashy sediments is 4.46～6.40 and the average is 5.69. There are three clusters based on R-mode cluster analysis of the grain size data: First cluster is composed of 1.5～3.0 and 9.5～14.0, situating co arser part and finer part on the frequent distribution curves. Second cluster co nsists of 3.5～5.0 and third of 5.5～9.0. The grain size classes are well cl ustered and their feature is clear. The result of R-mode factor analysis shown that the eigenvalue of prior 4 factors is 94.50%, factor 1 and 2 is main factors . Factor 1 is composed of minus loads of coarse silty class and plus loads of cl ayey materials. Factor 2 consists of minus loads of very grained sand class and plus loads of fine silty materials. Factor 3 and 4 are composed of suspended sed iments(0.06～0.12 μm)and medium sand(250～354 μm) materials, respectively . The factor effect districts are related to the sediment provenance, current, s ea floor feature and sedimentation. Contents of silt and clay shows general tren ds of increasing from north to south, and similar to the trends of mean and kurt osis. Coefficients of sorting and skewness indicate the boundary of sediment typ es between northern and southern South China Sea locate about 17°N because thei r values change heavily up and down near 17°N. According to analysis of grain s ize, composition and biogenic fossil assemblage of the core sediments, the follo wing layers of 187.5～190 cm, 287.5～280 cm and 377.5～380 cm in 69 sediment column collected from the northern continent slope, 157～187 cm and 187～194 c m in 149 column from the abyssal plain, 280～350 cm in 323 column from the sout hern continent slope are characterized by the turbidity deposits.