Sedimentary Characteristics And Environmental Significance Of Zhifu Profile In Yantai City,Shandong Province

The loess depositional sequence along the warm temperate coast of China is patchy distributed along the Bohai-North Yellow Sea coast,mainly in the northwest windward profile of Liaodong Peninsula,Miaodao Islands and Shandong Peninsula.This set of desert-loess deposits contains abundant paleoenvironmental information,which is of great importance to the demonstration of the problem of "East Asian monsoon evolution-sea level change-desertification of the Bohai shelf-aeolian deposits".Evidence is needed.On the basis of field investigation,Zhifu profile,located in the north of Shandong Peninsula,is selected to work.Its sedimentary sequence consists of sandy loess,loess and paleosol overlapping deposits.Based on the photoluminescence dating,the climatic characteristics of the last interglacial-last glacial period and their relationship with the East Asian monsoon are inverted by using the climatic indicators such as sediment grain size and chroma.The conclusions are as follows:(1)Zhifu profile can be divided into two stages: MIS5 and MIS4.Among them,MIS5 can be divided into five sub-stages: MIS5e(118.5-124.9ka BP),MIS5d(105.2-118.5ka BP),MIS5c(94.7-105.2ka BP),MIS5b(83.4-94.7ka BP)and MIS5a(70.18-83.4ka BP).MIS4 is(62.85-70.18 ka BP)indicating that the Zhiqiu profile is the product of the last interglacial period to the middle and early stage of the last glacial period.(2)The Zhifu profile is dominated by silt(74.95%),clay(10.05%)and ultra-fine sand(9.57%)followed by fine sand-coarse sand(3.98%)with an average particle size of 5.77? and a sorting coefficient of 2.05,which has regional characteristics.The power-exponential function relationship method and the granularity end element method were used to re-analyze the granularity results,and the fractal dimension values and environmental sensitive granule groups were calculated and extracted respectively.The results show that the sediments in Zhifu profile have good fractal structure,and the average fractal dimension of the whole profile is 2.324.Four groups of sensitive grains indicating environmental changes are obtained,namely CEM1(3-8?m),CEM2(56?m),CEM3(80?m)and CEM4(112.468?m).(3)The grain size parameters,fractal dimension values,environmental sensitive grains and chroma of sediments in Zhifu profile show obvious changes in the vertical direction,revealing that MIS5 e,MIS5c and MIS5 a are warm periods,MIS5 d,MIS5b and MIS4 are cold periods,and they have experienced three climatic cycles on the orbital scale.These cold and warm stages are highly synchronized with the summer monsoon ups and downs indicated by the magnetic susceptibility of Chaona loess,the winter monsoon changes indicated by the Xifeng loess>32?m grains and the transgression/regression events recorded by benthic foraminifera in the Bohai Bay.