Grain Size Characteristics Of Loess And Its Environmental Significance Since The Last Interglacial Period In Linfen Basin

Quaternary loess-paleosols are not only widely distributed,but also records the process of worldwide and partial environmental evolution in detail.Linfen Basin is located in the southeast edge of the Loess Plateau,the temperate monsoon climate zone in China.At the same time,monsoon climate is one of the most lively circumstances change element in this district.For the sake of getting partial high-resolution climate information,researches mostly used the basic particle size content index and particle size parameters in the past,and lacked other mathematical methods to capture the climate information of higher-resolution particle size components.There were certain differences in the environment indicated by particle components in different regions,and it was difficult to understand the sedimentary environment in detail without scientific analysis.The endmember analysis model was an effective tool to identify the source of multicomponent sediments and identify the transportation mode,which was proverbially used to reestablish the paleoenvironment.As a result,the object of study of this thesis is the loess-paleosol sequence of Dingcun profile in Linfen basin.On the premise of connecting with the results of the age,combining traditional grain size means with parametric end element decomposition means,the typical loess profile and the climate proxy index of deep-sea oxygen isotope through contrastive analysis.The above methods were used to reveal the features of grain size distribution and its environmental significance in the Linfen Basin on the southeastern margin of the Loess Plateau.The main findings are :According to the Shepard triangle classification,the loess in Dingcun section of Linfen Basin is mainly composed of silt,the clay silt content is less,the distribution of silt and clay silt is relatively concentrated.The calculation results of particle size parameters show that the particle size composition is complex in the whole stage,the handling power and mode are diversified,and the particle size distribution curve is wide and flat with a weak positive deviation.Three Endmembers are obtained by parametric Endmember model inversion of grain size of loess in Linfen basin : EM1 has the largest content when the grain size is 2.51 ?m,the curve trend is roomy and smoothness,with wider scope and lower crest value.It is formed by the weathering and soil formation of the East Asian summer monsoon.EM2 has the largest content when the particle size is 12.61 ?m,and the curve distribution is narrow and steep.It represents the distant sediments transported by the westerly wind at high altitude.EM3 in the particle size of 35.56 ?m accounted for the largest proportion,the curve distribution range is the narrowest,more concentrated in the coarse grain end,the curve is narrow and sharp,the peak is higher and steep,and the change range is large,which represent the near source sediment transported by the strong winter monsoon and the material brought by the short time dust storm in winter.The peak value of standard deviation of fine particles may be formed by long-distance transportation of high-altitude airflow affected by the westerly belt.The peak value of standard deviation of coarse particles may be a short-range suspended transport driven by the winter wind,or a short-range leap of particles caused by the short-term dust storm in winter by particle size-standard deviation analysis.According to the change characteristics of climate proxy index,and combined with the results of luminescence dating,we can divide climate changes in Linfen basin into five periods: In the late MIS6,the climate was relatively wintery and arid;during MIS5,the climate wad mildness and moist;during MIS4,the weather was comparatively wintery and arid;in the MIS3,the temperature was relatively warm;compared with MIS3 phase,in the early MIS2,the climate was getting colder.Grain-size end-member components and magnetic susceptibility of loess in Linfen Basin compared with typical loess profiles,we can found that in the same time the deposition thickness in the central area is greater than that in the eastern area,the deposition thickness of loess is greater than that of paleosol.Contrast with deep-sea oxygen isotope,the results show that Linfen basin is in accord with deep-sea oxygen isotope,indicating that the climate evolution of Linfen basin is controlled by global ice volume,but the internal fluctuation of each stage shows certain regional characteristics.