Sedimentary Characteristics And Mechanism Of Mud Deposits In The Northern Yellow Sea

For a better understanding of the sedimentary characteristics and related dynamic processes of the northwestern Yellow Sea, two cruises were organized to collect sediment samples and to undertake geophysical survey and hydrodynamic measurements. Using the sediment samples and shallow seismic records obtained about cores and records, analysis of grain size distributions, 210Pb dating and geophysical interpretation as well as ADCP velocity processing have been carried out. By incorporating the processed data, the sedimentary sequence in the northwestern Yellow Sea is delineated and the sediment supply and mechanisms of the mud deposit in the study area are discussed. In addition, the reliability of 210Pb dating under certain hydrodynamic conditions is evaluated, and an approach to sequence correlation on the basis of grain size data is proposed. Shallow seismic records and grain size analysis show that the strata in the northwestern Yellow Sea can be divided into three sections. The uppermost consists of clay, located in the deep water areas, along the coast of Shandong Peninsula and the southeast coast of Liaodong Peninsula. The middle section is mainly silt, distributed in almost the same area as the section of clay. The lowermost consists of coarse-grained sand. Each of the three types of sediments, mentioned above, is exposed in the region. The architecture of the clayey and silty sections which form two-layer structure is characterized by homogeneous features, with apparent differences in grain size and seismic reflection exiting between the two sections. The vertical distribution pattern in the coarse sediments shows grain size fluctuations and differs greatly from the two sections described above. The thickness of the mud deposit reaches the greatest in the east end of Shandong Peninsula, i.e., around 30 m, whilst the accumulation rate is very small, only of the order of mm/a. Thus, it is unlikely for such a deposit to form in several thousand years after the Holocene high sea-level, implying that the supply of sediment is not derived mainly from the modern Yellow River, but perhaps from some old river. In the Bohai Strait the mud deposit becomes progressively thinner from the south to the north and from the west to the east, with a decreasing accumulation rate from the west to the east. Here, the rate is large enough to form the mud deposit since the occurrence of the Holocene high sea-level. In the central northern Yellow Sea the thickness of the mud deposit is around 8m. The 14C age of the turf in the core located at the edge of the mud deposit is around 1 0000aBP. Here, the accumulation rate is relatively small for the formation of the thick mud deposit in several thousand years. Thus, the main body of this mud deposit cannot be not formed since the Holocene high sea-level. It is coastal erosion and seabed reworking that provide the supply of sediment. The whole amount of mud deposit in the study area is of the order of 4.41 X 10. For two cores from a similar sedimentary environment, grain size parameters can be used for sequence correlation analysis. Correlation coefficients for the grain size data can be calculated between the layers of different cores. On such basis, maximum correlation can be identified; the layers with the highest correlation are likely to have the same age. Preliminary analysis has been carried out for two cores from the southern Yellow Sea, and encouraging results were obtained. Theoretically, The mathod applies to cores from the same sedimentary environment.