Sediment Characteristics And Transport Processes Of Fine-Grained Material Over The Northern Yellow Sea

In order to reconstruct the depositional history of ancient epicontinental seas, it is important to understand sediment characteristics and transport processes of fine-grained sediment on modem continental shelf environments. A large number of seabed and suspended sediment samples, shallow seismic profiles and ADCP data were obtained during two cruises to the northern Yellow Sea. Based upon grain size, clay mineral and geochemistry analyses, and ADCP data processing, the fine-grained sediment characteristics and transport processes are discussed, and the performance of a Cilas 940L laser particle sizer is evaluated and compared with pipette and sieving methods. In addition, the feasibility and in-situ calibration of suspended sediment concentration measurements with ADCP are analyzed. The reproducibility of measurement on Cilas 940L appears to be satisfactory. Sample processing procedure is responsible for the magnitude of the error in the measurement. Cilas 940L give a lower fraction of clay particles (<84)) by 40 % on average than pipette data. The results obtained with the Cilas 940L show somewhat larger mean grain size and lower sorting coefficient than pipette/sieving results. Such differences may be attributed to the different principles of the methods (i.e. differences in the definition of grain size) and particle properties, especially non-sphericity shapes. Over the study area, fine-grained material is distributed mainly over the central northern Yellow Sea and near the coastline of Shandong Peninsula and Dalian Bay, whereas coarse- grained material is found to the east of Miaodao lsands and in the northwestern part of the area. Correlations between the grain size parameters are present. In general, except that the sand near Miaodao Isands is coarse grained and well sorted, the sediment with a large mean grain size is associated with a poorer sorting coefficient and higher positive skewness value, than a small size. Grain size trend analysis shows that sediments along the northern coast of Shangdong Peninsula are transported towards the east and northeast. Accumulation is taking place in the central area, as indicated by the convergence of the grain size trends. It is suggested that grain Ill size trend analysis is applicable to large-scale continental shelf areas. Sufficiently small sampling interval is necessary to delineate transport patterns in detail and a uniform (grid-iron) sampling grid is relatively good for assessing the direction of transport vectors. It should be noted that the sediment transport vector contains information on transport direction, rather than the magnitude of transport rate. ADCP has the potential to measure the suspended sediment concentration under the condition that the grain size distribution does no vary considerablly little during the survey period. An in-situ calibration formula has been developed and used to calculate the concentration profile. The results indicate that calibration with different depths can improve the measurement accuracy and meet the demand of sediment dynamics research. The deposit over the central part of the northern Yellow Sea is characterised by homogeneous mud, without large vertical variations in grain size. The thickness of the mud deposft decreases from the south to the north. The accretion rate is 1-2 mm/yr, which is equivalent to a vertical flux of 6-10 x lO6tlyr over the area of 6250 km2. The clay minerals and...