Sedimentary Characteristics And Provenance Of The Mud Sediments In The Zhoushan Area Of The East China Sea

The sedimentary characteristics, composition and provenance of mud sediments in the Zhoushan area of the East China Sea were analyzed in this paper. The composition and distribution of the grain size, minerals and elements for surface sediments were investigated. Based on the result, the hydrodynamic force, sediments distribution and the sources of the sediments were analyzed. Based on the distribution of grain size, minerals and elements for Core ZSC-7 sediments, the sedimentary records, environment indications and sources were investigated.Grain size analysis of the surface samples from the study area was carried out using the laser grain size analyzer. According to Folk's classification(1970), sediments in the area could be divided into silt, sandy silt, sand and locally sandy gravel in this area, with silt as the major. The sandy sediments from islands in the west of this area mainly derived from near source. The mud sediments in the east of this area derived from Yangtze River is transported with suspension by the East China Sea coastal current. Clastic minerals of the study area are quartz-feldspar-hornblende-epidote- flaky mineral-metallic mineral group, which indicated that the sediments derived from rivers and near source. The geochemical characteristics of the surface sediments show that elements aboundance is obviously controlled by grain size. The concentrations of many elements in fine-grained sediments is great higher than those in coarse-grained, with a wide range of variations. According to the distribution of elements, the sediments of the study area are mainly composed of terrigenous composition, such as SiO2, TiO2, and biogenic compositions, such as CaO,CaCO3. The biogenic sediments dilute the terrigenous sediments. The elements, such as Fe2O3,FeO and MgO, rich in the east of the study area, where is influenced by the East China Sea Coastal Current and Taiwan Warm Current. Some elements, such as Al,K,Co,Cr,Ni,Zn,Zr,mainly hosted in the fine-grained sediments, rich in the east of the study area. The normalized Rare Earth Elements (REE) patterns (Chondrite-normalized REE distribution patterns and NASC-normalized REE distribution patterns) of the mud surface sediments of the study area are similar to the sediments derived from the Yangtze River, which shows that the surface sediments mainly derived from the Yangtze River. The normalized Rare Earth Elements (REE) patterns of the coarse-grained sediments shows that the sediments are influenced by the sediments derived from near source instead of the sediments derived from Yangtze River and Yellow River.The sedimentary environment of core ZSC-14 and ZSC-99 was discussed, which are located in the north and south of the study area respectively. The grain size compositions sensitive to the sedimentary environment were taken by the analysis of grain size grade vs. standard deviation. All above analyses show that the mud sediments derived from the Yangtze River is transported with suspension by the East China Sea coastal current. The analysis of major elements and trace elements in core ZSC-7 indicated that the concentrations of the most elements including Al,K,Mg,Cr,Co,Ni etc. minished when grain size largen. The chondrite-normalized REE patterns exhibit that LREE are great richer than HREE in the sediments of core ZSC-7, and there is remarkable minus-abnormity of Eu, representing typical terrigenous components. In total, the REE characteristics and normalized REE patterns of the sediments in core ZSC-7 are very close to the sediments derived from the Yangtze River, obviously inclining to terrigenous aggradation.The core ZSC-7 registered the sediment evolvement process in the certain history period. The clay minerals, major elements, trace elements and Rare Earth Elements (REE) of the mud in the study area are analyzed. The results show that they are similar to those of the Yangtze River. Based on above studies, and combing with the correlation analysis of different elements, DF function and the clustering analysis of trace elements, the author concluded that the sediments of core ZSC-7 in the mud area mainly derived from the Yangtze River.