A Preliminary Study of the High Resolution Sub-bottom Stratigraphic Structures and Sedimentary Features in the Mud Area along Southern Distal Yangtze Subaqueous Delta: An example from the area off eastern Zhujiajian island

In this paper,based on 58 surface sediment samples collected in the mud deposited zone along the southern distal Yangtze subaqueous delta recently,the grain size of the surface sediment was analyzed and the sub-bottom stratigraphic structure was also measured. Results show that the clayey silt is the main type of the sediment in the study area. These sediments are characterized by high water content( 46%),high porosity,high compressibility and low shear strength which are potentially vulnerable to coast erosion. The upper part of the seismic profiles shows horizontal neritic strata. Underlying bedrocks are discovered in the area of reefs and the southern profiles. Sparse shallow gas is found in the eastern part of Profile I,with top imbedded depth about 12 m. The thickness of the Holocene sediment is 4 ~ 23 m and the sedimentation rate is estimated about 0.57 ~ 3.29 m / ka. Considering low sedimentation rate of the study area,recent accelerated human activity in the river basin,leading to decreased sediment discharge from Changjiang River,will cause a potential threat to the seabed stability of the Zhejiang coast.