Analysis Of Grain Size And Magnetic Susceptibility Of Sandy Sediment In Jincheng Road Section Of Changxing Island

At the end of late Pleistocene,the global climate has many cold and warm changes.Each cold and warm cycle has an impact on the sedimentary environment at that time.That makes the change of sediment characteristics at the end of late Pleistocene.In this paper,the sandy sediment profile of Jincheng Road,Changxing Island,Dalian city is taken as the research object.Through the qualitative description and quantitative analysis of the grain size characteristics,magnetic susceptibility characteristics and photoluminescence age data of the sandy sediment profile,the sedimentary characteristics,sedimentary environment and material sources of the sandy sediment profile are discussed.Use the Ris? TL/OSL-DA-20C/D reader made in Denmark to analyse the the data of the optically stimulated luminescence of No.2 sandy sediment sample in Binhai garden.The results show that the age of sample formation is about 48 Ka at the depth of 170 cm,58 Ka at the depth of 220 cm and 78 Ka at the depth of 320 cm.It is suggested that the profile developed at the end of late Pleistocene and experienced about 78 Ka.Use the LS13 320 laser diffraction particle size analyzer produced by Beckman Kurt Co.,Ltd.to measure the particle size of the No.2 sandy sediment sample in Binhai garden.The results show that the main components of No.2 sandy sediment in Binhai garden are medium sand and fine sand,with the average content accounting for 31.58% and 34.82% of the profile respectively,and the average content of clay and silt only accounting for 3.23% and 8.89%;the average median particle size of the profile is 2.11?,the average standard deviation is 1.31,the average deviation is 0.3,and the average kurtosis is 1.49.It shows that the profile is sandy sediment in the late Pleistocene,with coarse grain composition.Use the MS-2 magnetic susceptibility meter produced by British bartington company to test the magnetic susceptibility of No.2 sandy sediment sample in Binhai garden.The results show that the average value of low frequency susceptibility is15.06 10-8SI,the average value of high frequency susceptibility is 13.39 10-8SI,and the average value of frequency susceptibility is 10.89%.According to the 4-degree polynomial regression equation provided by Lu Houyuan,the average annualtemperature and precipitation can be calculated.The average annual temperature is0.6? and the average annual precipitation is 134.94 mm.The magnetic susceptibility value and annual average temperature are relatively low and the annual average precipitation is less,indicating that the sedimentary environment during the development and formation of the profile is relatively cold and dry.Based on the comprehensive analysis of the age,grain size and magnetic susceptibility of the sandy sediments in Binhai Huayuan No2,the grain size and magnetic susceptibility characteristics of the profile are consistent with the changes of sedimentary environment.It can be inferred that in the sub glacial period of Dali glacial period,the cooling of the climate led to the decrease of marine water volume and the regression of the sea,and the desertification of the continental shelf occurred in the Huanghai Bohai shelf region,which provides the material source for the accumulation of sandy sediments in Changxing Island region.