Characteristics Of Grain Size And Element Geochemistry Of Garze A Section On West Sichuan Plateau

The West Sichuan Plateau is adjacent to the Qinghai-Tibet Plateau, the loess-paleosol sequence which is widely distributed in the western Sichuan plateau, has mainly formed since the Late Early Pleistocene. The loess paleosol sequence is one of the best continuous records of the paleoclimate on the margins of the Qinghai-Tibet Plateau. It records the evolutionary process of this period Paleoclimate circulation system and its relation to the phased evolution of the Qinghai-Tibet Plateau and is crucial for understanding the regional environmental response to the uplift of the plateau.This paper take the Garz e A section in the Garz e area on West Sichuan Plateau as research object. First of all, on the basis of the framework of age sequence of the Garz e A section(the bottom age is about 1.16MaB.P.), do a preliminary analysis of the time sequence of grain size proxy, discuss the Chronological Link Between the Abrupt Change of the Loess Grain size Sequence and uplift of the plateau from Late Early Pleistocene. Next, select the loess-paleosol sequence of S0-L6 stratigraphic of the Garze A section as the material, do an analysis of its distribution of element geochemistry, and do a preliminary study on geochemical distribution in loess layer and paleosol layer, chemical characteristics and their paleoclimatic significance.Garz e A section, in the time scale of tectonic, the grain size time sequence which is reacting the environmental evolution process of this area can be divided into three stages.The first period from 1.16 to 0.90 Ma is a relative wet stage,the second period from 0.90 to 0.60 Ma is an accelerated drying stage,and the third period from 0.60 Ma to now, The climate is cold and dry. In the climatic evolution process of the 1.1 MaBP bottom boundary problem, atmospheric circulation enhance event of about 0.9～0.8MaBP, the drought events of about 0.6 Ma,the Mid-Pleistocene Climatic Transition (MPT) has a good consistency with the phased uplift of south-eastern Tibetan Plateau in time scale. The research results of geochemical elements which seclected from the loess-paleosol sequence of S0-L6 stratigraphic of Garze A section show that:(1)The percentage content of major elements and its oxides of SiO2, Al2O3, MgO, K2O, MnO, and TiO2 and the percentage content of trace elements V, Cr, Co, Ni, Cu, Zn, Rb, Ba are alternating with the loess layer and paleosol layer, from low to high cycle showing cycle variation characteristics, while CaO and Sr are opposite;(2)In the process of chemical weathering, the major elements of Garz e A section show a strong carbonate leaching, and the elements of Si, Al, Fe, K, Ti have a considerable similarity between each other,while Ca with a difference;(3)Major elements of Fe, K, Mn, Al, Ti and trace elements of V, Ni, Cu, Rb, Ba have an significantly positive correlation with the content of 2～8μm clay fractions, are mainly hosted in the clay particles; Major elements of Fe, K, Mn,Al, Ti and trace elements of V, Ni, Cu, Rb, Ba have negative correlation with the content of 30～64μm coarse silt between each other,the reason may be come from dilution effect of coarse silt to the adsorption of clay.