STUDY OF SEDIMENT GRAIN SIZES AND SOURCES FOR THE SHORT CORES COLLECTED FROM THE NORTH PASSAGE OF YANGTZE ESTUARY

This work studies the properties of sediments from 13 short cores collected in the North Passage (NP) of the Yangtze Estuary in order to study the sediment sources. The results show that the sediment grain sizes exhibit strong spatial variations vertically and laterally. In the upper part of the NP, the median diameters (D50) of the sediments are 29~40 μm and 14~18 μm on the south and north sides, respectively. However, D50 is 23~27 μm on both sides of the lower part of the NP. Along the NP, both D50 and sand content decrease seaward on the south side, but increase seaward on the north side. The bifurcated ebbing and flooding currents in the NP is responsible for the spatial variations in sediment deposition and sorting. Moreover, there are three groups of sediments of grain sizes of 7.8~26.3 μm, 37.4~126.0 μm and>193.5 μm. They are representatives of varying sediment sources. Specifically, the fine sediment is the suspended load from the river and the sea, the coarse sediment is a kind of laterally transported sediment from the adjacent shoals to the NP, and the coarsest sediment is the lag deposits after storm surges. The coarse sediment is the most sensitive portion in the NP.