| With the use of X-photograph method,ultraviolet Spectrophotometry,X-ray diffration,ICP-AES(MS) analysis method, surficial sedimentary sequences of different sub-environments in the subaqueous Yangtze River Delta are studied. And undisturbed surficial sediment sample records are then analyzed, including high resolution records of grain size,BSi content,mineral and elements composition, which show a good response of delta front sedimentation to the Changjiang material flux and ocean environment. Based on the above records, characters of sedimentation in both summer-autumn and winter-spring are analyzed respectively. This is the first study about the sediment records on the scale of a year or even seasons in this area.The results show that sediments in the subaquous Yangtze River Delta are mainly silt clay. From the coast to the seaside, the grain size is gradually coarser. Surficial sequences are charactered by block structures, horizontal laminations and bioturbation strauctures. And the distribution of the bioturbation structure is largely spatial different in the Subaqueous Yangtze River Delta. From the delta front to prodelta and transitional zone to shelf environment, the bioturbation index is varied as low-high-low.This kind of response is the key point according to which sequences that deposit in different seasons can be identified.The delta front surficial sequence gives a good response to the seasonal variations of Changjiang sediment flux and delta environment. In summer and autumn, large sediment flux, weak ocean energy and high primary production result to finer sediment and high content of BSi in the sequence. While in winter and spring, when the sediment flux decreased, the ocean energy becomes stronger and the primary production gets to low, there will be croaser sediment and low content of BSi which deposit to the sequence. Mineral composition of the Sediment in summer and autumn is very near to those come from Yangtze River, in which major minerals are quartz, feldspar and clay minerals while calcite and dolomite appear as minor minerals. In the sediment, Al2O3> TFe>CaO> K2O>MgO>Na2O>Ti2O3,they constitute 34% of all. The content of Al2O3 in the sediment is16.02%, while the contents of CaO and Na2O about 4.31% and 1.17% respectively. Total content of the six heavy metal elements which are studied is 291.85×10-6, in which Zn>Cr>Cu>Pb>As>Cd. Total Ree is about 219×10-6, in which light Ree weight as 4.34 times as heavy ones. Compared with winter and spring, sediment in summer and autumn is high in Al2O3 and heavy metals, low in CaO and Na2O.Mineral composition of the Sediment in winter and spring is also near to those come from Yangtze River, and in which major minerals are quartz, feldspar and clay minerals while calcite and dolomite appear as minor minerals too. Similar to summer and autumn ones, in the winter and spring sediment, Al2O3> TFe>CaO> K2O>MgO>Na2O>Ti2O3,and they constitute about 34% of all. However, the content of Al2O3 in the sediment is15.34%, and the contents of CaO and Na2O are 4.63% and 1.34% respectively. Total content of Zn, Cr, Cu, Pb, As and Cd tend to be 265.42×10-6, Total Ree has no difference which weight about 219×10-6, and the content of light Ree is about 3.4 times higher than heavy ones. Compared with summer and autumn, sediment in winter and spring shows low contents of Al2O3 and heavy metals, but high CaO and Na2O.There is a good positive correlativity between the thickness of sediment sequence and the sediment flux of Changjiang. During1992~2005, which period that is researched, the annual deposite thickness ranges from 1.1cm to 3.6 cm. And the maximum thickness—3.6cm is deposited in 1998 when the sediment flux of Changjiang is 401 milion tons, while the minimum—1.1cm happens in 2004 when the sediment flux is only about 147 million tons.
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