High Resolution Sedimentary Record Within a Hundred Years on the Mud Area Near the Changjiang Estuary and Discussion of Its Impacting Factors

Based on the major and trace elements and grain-size analysis,as well as the 210Pb isotope data,the sedimentary history within a hundred year of the Core ZM11 was reconstructed and the impacting factors were discussed.It was shown that the sedimentation rate is about 2.5 cm/a starting from 1950.Because the sediment was dredged during the construction of the Twin Jetty-Groyne Complex in the North Passage of the South Channel and was eroded from delta front,the sedimentation rate of the Core ZM11 within the last ten years was above 3 cm/a,while the Changjiang sediment was declining during the same period.The thickness of sediment deposited during 1998-1999 was about 20 cm,possibly induced by the 1998 major flood event that is recognized by the 0.3 cm fine-sand layer at ~ 46 cm depth.The variation of the sediment grain size in Core ZM11,presumably controlled by the complexity of subaqueous delta,is not consistent with the sediment grain size variations of the Datong gauging station.The geochemical element analysis results showed that sediment of Core ZM11 mainly come from the Changjiang River.Grain size,terrigenous material input,biological sedimentation and human activity are the major factors that resulted the element content variations of the Core ZM11.