Composition And Distribution Characteristics Of Grain-size And Clay Minerals In Surface Sediments Of The Southern South China Sea And Their Indication To Provenance

Based on analyses of the grain size and clay minerals of the surface sediment samples recovered from Southern South China Sea(SSCS) combined with multivariate statistics analyses for these data, the main factors influencing the terrigenous clastic components and the distribution of surface sediment in research area and the mechanism of sediment transport were discussed.The grain sizes and distribution of the terrigenous clastic components of surface sediment in the study area are mainly controlled by the provenances, the ocean circulation system, the water depth and the seafloor topography, among them provenances and topography charateristics are the essential ones.Experimental results show that the major size fraction of surface sediments in the research area is dominated by medium silt-coarse clay(6.0~9.5φ),holding 90%. The sediments in the study area can be divided into 5 types: mud, silt, silty sand, sandy silt and clay; and mud is the dominant sediment type. Silt, silty sand and sandy silt distribute on continental shelf, while mud mainly distribute on continental slope The contents of sand, silt, and clay in the surface sediments is 2%, 47% and 51%, respectively. The mean grain size of sediments is 3.67~8.46φ with the average of 7.87φ. The coefficient of sorting is 1.18~2.24φ with the average of 1.34. Skewness is-1.42~2.48 and the average is-0.26. Kurtosis is 1.44~3.16 and the average is 1.64.Two groups can be defined based on the R-mode: in the first group, sediment grain sizes mainly fell within 1.0~6.5φ and 10.0~11.0φ; while in the second group, the grain sizes are within 7.0~9.5φ. Two clusters and four kinds are determined based on Q-mode cluster analysis of the grain size data, which display different transport mode. The result of R-mode factor analysis shows that the eigenvalue of prior 4 factors is 92.69%, and factor 1 is composed of plus loads of coarse silt and medium silt, and minus loads of very fine silt. Factor 2 consists of plus loads of clay and minus loads of very fine sand. Factor 3 is composed of plus loads of coarse sand, medium sand and fine sand. Factor 4 is composed of plus loads of fine silt.The clay minerals in the study area are mainly composed of illite(average 58%),followed by kaolinite(average 23%), smectite(average 12%) and chlorite(average 7%). The clay mineral assemblages are illite- kaolinite- smectite- chlorite and illite- smectitekaolinite- chlorite.Illite is mainly from Mekong River and northwestern/northern of Borneo. The smectite of southern and northern sections of study area is influenced by western of Luzon and Sumatra islands, respectively. Kaolinite is supplied by Mekong River, Malay Peninsula and Sumatra islands. chlorite is mainly from Borneo and Mekong River basins.The primary material supplyer of the research area is Mekong River; the minor ones include the Borneo, Malay Peninsula, and western of Luzon, Sumatra islands. The essential factor of the distribution of clay mineral is surface circulation system.