The Modern Sedimentary Characteristics And Provenance Analysis Of The Liaodong Bay

The Liaodong Bay located in northern of the Bohai Sea is one of the most important marine economy development areas of China. It is of great significance for understanding the sediment dynamics as well as evaluating the contribution of surrounding rivers as provenances in the Liaodong Bay,. In order to discuss the depositional environment and source regions, we systematically collected140surface and4core samples and determined their grain size, mineralogical and geochemical features in this contribution.The analytical result of the grain sizes shows that the surface sediments are characterized by sandy silt (sZ), sandy mud (sM) and muddy sand (mS). The grain size characteristic of the underlying core sediments typically represents the shallow water deposition during the Holocene transgression, by contrast, the upper sediments were deposited after the sea level reaching to the highstand. According to the sediment types, sources and hydrodynamic conditions, the study area can be divided into five different deposition parts:the mud deposit in the northern Liaodong Bay, the sandy deposit in the western Liaodong Bay, the mud deposit in the southwestern Liaodong Bay, the sandy deposit in the Liaodong shoal and the residual deposit in the central Liaodong Bay.In line with the mineralogical analysis, the light minerals mainly consist of quartz, plagioclase and K-feldspar, with the maturity index>1and the source area index>10. The heavy minerals, on the contrary, are dominated by hornblende and epidote, with the ATi index>50%, the GZi index>90%and the ZTR index<5, respectively. Based on the distinct mineral assemblages, the study area herein is divided into five mineral zones. Furthermore, the mineral characteristics of our investigation also indicate that the input material by coastal rivers especially the Liaohe River is the major source to these deposits in the study area. However, the contributions of current-delivered materials and the erosion detritus from the coastal islands should not be neglected. Overall, the sediment distribution is controlled by the tide and coastal currents.As indicated by the geochemical results, the most important major elements in the deposits of our study area are Si and Al and most of the enrichment features of elements follow the"grian-size control" law. Compared to the background values from the surrounding regions, the elements of this study area have a pro-continentality feature. As normalized to chondrite, the sediments show an obvious offset towards to continent crust.As compared to the upper crust standard curve, the sediment in study area is rich in MREE and lacks significant Ce, Eu anomalies.Altogether three sandy sendiment areas have been identified in the Liaodong Bay:1) the Liugu River sandy deposits in the west,2) the mid-east sandy deposits,3) the sandy deposits in the Liaodong shoal. Our study shows that the Liugu River sandy deposit is a newly discovered sand deposition zone and the material source mainly comes from the Liugu River. The mid-east sandy deposit is formed as a consequence of the old residual sand sediments derived from the erosion matrrial of the costal islands.whereas the old sand of the Liaodong shoal comes from the sand ridge substances, which is delivered by tide to northward.