Sedimentary Origin Of The Clinoform In The Post-middle Holocene Off The Northern Jiangsu Coast Area

There is a larger clinform under the Old Yellow River subaqueous delta topset in the northwestern part of the southern Yellow Sea,little research has been done on this sedimentary body in the past.In this paper,the bordhole SYS-1601 in this area was used to measure the composition of sedimentary grain size,major and trace elements,rare earth elements(REE),Sr-Nd isotopes and clay minerals of<2 ?m sediments.Unexposed sediments were taken at appropriate location in the core for Optically Stimulated Luminescence(OSL)test,and the formation time and source of the sediments were comprehensively discussed.We also measured the geochemical characters and clay minerals composition of the<2 ?m composition of the surface sediments collected from potential source(the Huaihe River,the Yellow River and the Yangtze River)in the same laboratory to avoid the system errors caused by different instrument test and reduce the effect of different grain size.It will achieve better results when identifying the sediments source of the clinform in Jiangsu offshore.The experimental results of the surface sediments of the three Rivers showed that the contents of Ti,Li,Zn,Cu,Sc,Zr,Y and Nb elements in the sediments of three rivers are quite different.The average 87Sr/86Sr radio of the Huaihe River sediments is 0.72908,which is between those of the Yangtze and Yellow River sediments(average 0.73238 and 0.72589,respectively).The average 143Nd/144Nd isotope compositions of the three rivers are similar.The differences of REE parameters for the sediments of the three rivers are relatively small.And the upper continental crust-and chondrite-normalized patterns are also similar,but there is a large difference in the element abundances.The contents of smectite and kaolinite in the Huaihe River sediments were between those of the Yangtze and Yellow River sediments,the Illite contents in the Huaihe River sediments were higher than those in the Yangtze and Yellow River sediments,and the chlorite contents in the Huaihe River sediments were lower than those in the other two rivers.According to the lithological characteristics of the borehole SYS-1601,the results of OSL and AMS 14C dating of the sample,combined with previous research results,the upper 15.2 m of the core is the thickness range of the clinform that we wanted to study.Based on the results of OSL and AMS 14C dating,it is estimated the research object was formed in the middle Holocene.The clinform can be divided into three units,DU1 to DU3,based on the vertical distribution characteristics of the sedimentary grain size composition and the vertical distribution characteristics of geochemistry,combined with the core structure.The provenance of DU3(6174 cal.yr BP-3152 cal.yr BP)is more complicated.Apart from that the Huaihe River transports the material to the research area directly,the resuspended sediments,the Yellow River and the Yangtze River material,from the erosion in the northern Jiangsu were also transported to the research area.With the gradual increase of human acticities in the Huaihe River basin and the development of the farming economy,a large amount of land in the river basin was reclaimed and soil erosion intensified,resulting in the increase of the sediment content in the Huaihe River,which in turn led to the provenance of DU2(3152 cal.yr BP-1128 AD)is mainly from the Huaihe River.The Yellow River directly entered to the northern Jiangsu area in 1128 AD,that make the Yellow River material directly entered to the northern Jiangsu area and the provenance of DU1 was mainly from the Yellow River.