Study On The Sedimentary Environment Evolution Of Kushuiyang Eastern Sandy Ridge Since The Late Pleistocene, Jiangsu Offshore, Southern Yellow Sea

South Yellow Sea radial sand ridge system contains a lot of information about sea level changes, land and sea interactions, climate change and environmental evolution.They are the best carrier for studying marine environmental change after the polar ice cores, deep-sea sediments and loess deposits. Radial sand ridges is a giant sea accumulation by the Yellow River and Yangtze River in the Western Pacific Rim, and is a typical product of interaction between land and sea. Kushuiyang eastern sandy ridge is the large type of accumulated sand ridges in the northeast of the South Yellow Sea radial sand ridges, The genesis and sedimentary environment changes of the tidal channel since the late Pleistocene is of great significance to understanding dynamic changes of the whole radial tidal sand ridge system.The borehole is locatde on the Kushuiyang eastern sandy ridge areas (33°27.178' N and 122°5.617'E). The depth of this hole footage is 30.8m, but the actual core length is 24.8m, core rate is 80.5%. The core was firstly logged and sampled in lab,and then a series of analysis including:grain size, susceptibility, foraminifera, mineral were carried out. Further, combined with sedimentary facies, the formation and long term evolution of sand ridges was analyzed.The results have shown the core is mainly composed of clay silt,silty clay, fine sand silt and silt. Minerals mainly contain light minerals (quartz, feldspar), heavy minerals contain the highest content of hornblende, epidote second. Size distribution is based on the silt, with the average of 52.7%, followed by sand, an average of 40.9%, clay with the average of 6.4%. The average particle size changed between 1.85～6.50 average of 4.70. Four sedimentary face have been distinguished:(1) Coastal plain facies (30.80～22.75m):It consists of clay and silty clay, foraminifera content significantly reduce with a single species,it is a coastal or shallow water Sedimentary environment. It contains large amounts of heavy minerals of authigenic pyrite.(2) coastal tidal (22.75～20.44m):silty clay sediment with a color of olive black, This face comprises a section of the accumulation of shell fragments and clay layers, called mixed sediments. this layer may be judged as the lack of formation. there is a clear sign which represents sedimentary environment of Corbicula leana Prime and the clam box (undetermined species) fragments, the environment is considered as the coast tidal flat facies.(3) shallow marine estuaries (20.44～9.42m):silty clay and clay silt sediments, there is the obvious erosion interface among layers.Form bottom to up,it is form the fluctuating shallow subtidal deposition to the stability deep water shallow marine deposits, there were two cycles for a typical shallow marine sedimentary facies. It consists of abundant foraminifera, with the typical shallow marine foraminifera combination of A.beccarii-Elphidium sp., this layer formed in between 4290～2005a BP.(4) Tidal sand ridge facies (9.42～0m):fine sand silt and clayey silt, olive gray,it is composed of oblique bedding of sand and the massive sand with biological burrows. The erosion interface appears at the 450cm, and it divided into two section.The water power from the bottom to up is gradually weakened. Cumulative degree of probability is characterized by a double jump, reflecting the fluctuation trend of the reciprocating motion. The distribution of their c-m and modern tidal sand ridge area is consistent. Susceptibility is maximum in this layer. Foraminifera content directly reduced.