SURFACE SEDIMENTS AT THE SUBAQUEOUS YELLOW RIVER DELTA: CLASSIFICATION AND DISTRIBUTION

Based on the grain-size analysis of surface sediments recently sampled at the subaqueous Yellow River Delta, the classification and spatial distribution of the surface sediment are presented. The results indicate that the surface sediments at the subaqueous Yellow River Delta are primarily composed of sandy silt and silt, mostly characterized by positive to strongly positive skewness, relatively poor in sorting, and wide to very wide kurtosis. The surface sediments around the presently active delta lobe are mostly sandy silt, relatively coarse in grain size, whereas the surface sediments are relatively fine-grained in offshore area away from the present river mouth. Compared with the investigation in 1980s, the recent surface sediments at the subaqueous Yellow River Delta seem to be coarser in grain size. The significant changes might be attributed to the enhanced erosion along the delta coast due to insufficient sediment supply from the Yellow River. Meanwhile, the sediment delivered from the river to the sea has been much coarser since the Water-Sediment Regulation in 2002, which resulted in considerable accumulation of coarser sediments around the present river mouth. The distribution of sedimentation rate at the subaqueous Yellow River Delta indicates that the river-delivered sediments are mostly accumulated at the present river mouth and along the delta coast, together with northward and northeastward transport corresponding to the accumulation of fine-grained sediment in the central Bohai Sea and sediment export to the Bohai Strait through the Laizhou Bay, respectively. In addition, the high accumulation rate of coarse-grained sediments around the present river mouth implies the trapping effects from the tide-induced shear front. Our results indicate that both sediment supply and sedimentary dynamic environment play predominant roles in the distribution of surface sediments at the subaqueous Yellow River Delta.