长江口及其邻近海域表层沉积物分布特征

CHARACTERISTICS OF SURFACE SEDIMENT DISTRIBUTION IN THE YANGTZE ESTUARY AND ITS ADJACENT WATERS

根据长江口和杭州湾北部沉积物粒度分析数据,研究表层沉积物类型、分布以及分区特征。结果表明:沉积物的分布特征受水动力条件、地貌类型以及泥沙来源等因素的综合影响,长江口表层沉积物在纵向分布上,自西向东粒径从粗到细、分选程度从好至差,在横向上自北港-北槽-南槽,沉积物粒度逐渐变细;水流动力作用强的河槽和波浪作用强的口门浅滩沉积物粒度较粗,水动力较弱的河口边滩及口外海滨区沉积物则较细。根据沉积物分布特征可将长江口及其邻近海域分为河口分汊河段沉积区、河口拦门沙沉积区、口外海滨沉积区和杭州湾北部沉积区等4个沉积区。

The characteristics of surface sediment types,distribution and deposition district in the Yangtze River Estuary and the north of Hangzhou Bay are investigated on the based of sediment particle-size data and corresponding morphology and hydrodynamics. The results suggested that the characteristics of sediment distribution are the result of combined actions among hydrodynamics,morphologic features and sediment sources. The longitudinal （from west to east） distribution of surface sediments of the Yangtze River Estuary presented from coarse to fine particle sizes, the degree of sorting from good to poor level, and transversely, in the three bifurcations of South Branch into the sea, sediment sizes gradually fined from the North Channel, North Passage to South passage. Sediment grain sizes are coarser in the main channels with strong hydrodynamics and mouth shoals with frequent wave actions, and the grain sizes are finer on the mouth tidal flats with weak hydrodynamics and on the adjacent sea area off the estuarine mouth. Moreover, according to the differences in the distribution and location of the sediments, the Yangtze River Estuary and its adjacent waters can be divided into four main sedimentary zones： （1） The bifurcational river channel sec tion of Yangtze River Estuary,where the main channel sediments are mainly fine sand and silty sand with a median size of 2.5 to 4φ and good sorting, and its side flat silty clay with a median size of 7 to 84 and poor sorting;（2） The mouth bar area alternated shoals and troughs, where the shoal sediments are slightly coarse due to wave actions; （3） The offshore area,where sediments between north and south have greater differences to about 31°20′N for the community,coarse grain sediment in the north due to shelf residual sands and North Jiangsu erosional sands, and fine grain sediment in the south because of Yangtze River source;and （4） The north of Hangzhou Bay,where sediments are mainly clayey silt.