Sedimentary Characteristics And Sediments Origin In The Middle-Western Area Of The South Yellow Sea In China Since The Holocene

The South Yellow Sea is a typical continental shelf sea. It is very important for supplying the content of our country continental shelf research and empoldering resource to study scientifically sedimentary characteristics of territorial benthal environment. This dissertation analyses synthetically sedimentary characteristics of the Middle-Western Area of the South Yellow Sea and discusses the origin of sediments using 316 grain-sized datum, 181 common and trace and REE elements datum respective, 181 clay mineral datum and 156 detrital mineral datum from surface sediments and using 4 datum from core sediments. The data comes from"1:100 ten thousand geologic survey of the Nantong extent". The study includes mainly the undermentioned contents.(1) The dominating grain size type of surface sediments is silt (according to Folk classification, 1970) high reaching 47% content. Besides, the major and key grain size range of surface sediments are composed of 1.14Ф～10.13Ф,3.92Ф～7.44Фsuccessively and, the surface sediments can be divided into four types including sandy silt, silty sand, sandy mud and silt. There are four clusters based on R-mode cluster analysis of the grain size data: First cluster is composed of 5.5Ф～10.5Фand second of -0.84Ф～-3.2Ф,situating coarser part and finer part on the frequent distribution curves. Third cluster consists of 3.5Ф～4.5Фand fourth of 1.5Ф～2.5Ф,corresponding the silty sand (or muddy sand) and sand. The Q-mode cluster analysis of the grain size data can be divided into four types or six types or eight according to different rescaled distance cluster combine. The typical samples analysis show that the main factors controlling the grain size characters in the study area are the Yellow Sea coastal current, tidal current of sand ridge and the North Jiangsu current, with the distribution of particle factions, grain size parameters and sediments movement style being associated closely with the direction and intensity of the Yellow Sea current.The sedimentary grain size becomes big gradually from the northern YNH90 to the southern YNH142, and the major sediments are silt (Z) with high content clay in the core YNH90 and YNH109 sediments. Besides, the major sediments are sandy silt (sZ) and silty sand (zS) respective in the core YNH111 and YNH142 sediments. The average Mz(Ф) are composed of 4.58Ф～7.22Фand the sedimentaryσI and SkI become big gradually.(2) The composition of detrital minerals with grades of exceed 0.25mm and 0.25～0.063mm in the surface sediments are tested. The reseach result shows that the heavy minerals are mainly amphibole, epidote, mica, garnet, magnetite, autogenypyrite etc. The light minerals are mainly fedspar, quartz and calcite. Illite and smectite are mainly clay minerals with the highest and secondly content in the surface sediment, and the clay minerals combination style are illite-smectite-kaolinite-chlorite.(3) The common elements such as SiO₂, Al₂O₃, CaO, Fe₂O₃, K₂O etc. are higher concent in the sueface sediment; besides, the trace elements such as Sr, Rb, V, Zn, Cr, B, Cu etc. are higher concent in the sueface sediment. Chondrite-normalized REE distribution patterns of samples in the sueface sediment are characterized by the negative gradient, negative Eu abnormally and Ce normally.The R-mode cluster analysis of the common and trace elements indicates that the numerous elements such as Al₂O₃, Rb, K₂O, Li, Corg, Cr, U, V, Ni, MgO, Co, Fe₂O₃, Zn, Cu, Th, TiO₂, Pb etc. are apt to be transited suspendly by clay and organic matter. Correlation analysis show that clay is correlated positively with Al₂O₃, K₂O, Fe₂O₃, MgO, Corg, Co, Cr, V, Ni, Rb, Li, U, Zn and negatively with Sr, SiO2, CaO, CaCO₃, MnO; besides, the most elements are correlated positively with silt and SiO₂ are correlated positively with sand; thirdly, the elements such as Fe2O3, V, Ni, Co,MgO etc. have reciprocally high positive correlation and the elements such as Cu, Pb, Zn are correlated negatively with CaO, CaCO3, Sr, MnO.(4) The triangular map with end members of illite, smectite and chlorite+kaolinite suggests that the material sources of the study area are still associated with the Huanghe River and Changjiang River matter. The differential functions DF and the material sources index PI show that the material sources of sediments based on core YNH109 are still associated with the Changjiang River matter, and have alienative correlation with Keoran River matter.