The Source And Composition Of Fine-Grained Sediment Deposited On The East China Sea Shelf

It is an important task to analyse the change of sediment properties during transportation from rivers to marine settings. Total of 146 sediment samples were collected from the East China Sea Shelf (ECSS) and five rivers, including Huanghe River, Changjiang River, Qiantang River, Ou River and Min River. The sediment grain-size and the contents of rare earth elements (REE) were measured with laser particle size analyzer and ICP-MS respectively. Results show that absolute REE content (ΣREE) and the ratio of LREE (light REE)/HREE (heavy REE) are different in the sediments between rivers. There are higher REE contents in <2μm and 2-31μm fractions in Changjiang Estuary surface sediments, and the bulk sediment REE contents are dominated by the value of the advantage size fractions. In the study area, absolute REE contents of sediments are higher near the estuaries, and it trend downward in seaward direction on the inner shelf of East China Sea. The LREE/HREE ratio has a tendency of increase southward from 28°N, whilst hydrodynamic conditions dominant the spacial distributions of the surficial sediment's REE parameters. In some cases, the current flows tend to remove the coarser light grains from initial populations, whilst deposit the finer heavy mineral grains. In most situations, the currents will change the ratio of sediment constituents, for example between silts and clays. As a result, the various values of absolute REE content or LREE/HREE ratio in different bulk sediments arose from the change of size-fractions, rather than represent their different sources. Under the long-term stable hydrodynamic environment i.e. the East China Sea Shelf, new sediment transport model based on the size and density gradation concept may help to understand the spatial distribution patterns of REE parameters.About 260 surface fine-grained (<31μm and 2μm, mainly) sediment samples were collected from ECSS, and measured with ICP-MS, ICP-OES and X-Ray Diffraction. Similar to the bulk sediments, those fingerprints, i.e. clay minerals, major elements and trace elements in the surface fine-grained sediments of the ECSS, are variable in spacial distributions. By now, we haven't found the absolute stable numerical fingerprints and the reasons of changing. Therefore, we choose the indicators (e.g. clay minerals and trace elements) which can discriminate different river sediments, and use the statistical Clustering and Discriminant Analyses to judge the source of ECSS sediments qualitatively.According to clustering analysis results based on four main clay minerals and trace elements, we conclude that the <31μm fractions sediments of the Changjiang-Like mainly distribute in the central and western regions of ECSS, and they come from modern Changjiang River; the fine-grained sediments in southeastern part of ECSS might originate from the Yellow River, or from the relict sediments formed in dry and cold climates such as Pleistocene Ice Age and then mixed with fine modern riverine sediments under marine hydrodynamic processes.