Magnetic Properties Of Surface Sediments From The East China Sea Inner Continental Shelf And Its Implications For The Provenance

Transportation of terrigenous sediments to the sea by wind and river is a complete Source-to-Sink(S2S)circulation of the earth surface system.This process is essential to understand the earth surface system,sediment transportation and deposition on the continental margin.Rivers and marginal seas are the most important archive of S2S study.The East China Sea(ECS),located between the largest continent(Asia)and the largest ocean(Pacific),receives riverine inputs from one of the largest rivers in the world,the Yangtze River.However,the transportation and deposition of terrigenous materials in the ECS have not been studied in details.Sediments of different grain sizes can record physical and chemical processes during the transportation and document the information of the provenance.Therefore,multi-parameter magnetic measurements were carried out on the surface sediments of the ECS,which were collected from cruise of the National Natural Science Foundation of China in 2011 and 2013,in order to trace the sources and find transportation of sediments on the ECS inner continental shelf.The samples from the ECS were separated to four grades(<2 ?m,2-10 ?m,10-63 ?m,>63 ?m)using the centrifugal method,which is based on the Stokes Law theory.The recovery rate of this grain size separation process is about 94%,with the highest value over 97%,which indicates that the separation using the centrifugation is feasible and effective.The material loss is related to the content of fine particles(<10 p,m).Laser diffraction particle size analyzer was performed to evaluate the reliability of the grain size separation.However,the laser analyzer has a poor discrimination of particles that smaller than 10 ?m..Therefore,when using the laser particle size analyzer,it is recommended to use<10 ?m,10-63 ?m,and>63 ?m to represent clay,silt,and sand components,respectively.The magnetic results of the bulk sediments showed that the magnetic minerals of the sediments from the Yangtze River estuary and the ECS are both dominated by pesdo single-domain(PSD)magnetite,with a small contribution from hematite.The concentration of magnetic minerals from the western part of the muddy area are high and gradually decrease to the east.The magnetic grains of the sediments from the land side are fine,and become coaster toward the outer shelf.The magnetic characteristics of the sized samples showed that the magnetic minerals mainly exist in the fine-grained sediments(<10 ?m).Moreover,in the<2 ?m and 2-10 ?m grades,the magnetic mineral concentration gradually decrease from the shore to the ocean,and from north to south,which indicates the direction of the ECS coastal current.Comprehensive analyses of the magnetic characteristics of surface sediments from the ECS and the surrounding rivers indicate that sediments from the ECS mainly come from the Yangtze River,with small contribution from the other small rivers from southeastern China.