The Physicochemical Property Of Yellow-brown Earth-Vermicular Red Earth And The Paleoenvironment Significance In Langxi County,Anhui Province

The quaternary clay deposition profile has preserved the information about material source and sedimentary environment.It is of great significance to repeat the palaeoclimate and palaeoenvironment of the quaternary periodabout Southern China.We have collectd a soil profiles of double-layer structure included Yellow-brown Earth overlying Red clay in Langxi County,Anhui Province-Based on the analysis of optically stimulated luminescence,combining with the particle-size,geochemical characteristics,environment magnetism and color index of a selective YBC-RC soil profile in Langxi County,Anhui Province.Comparing the double-layer structure profile with Xiashu loess in the middle and lower reaches of the China's Yangtze River,aiming to explore it's material source.We also compare double-layer structure with Yellow-brown Earth overlaying the reticulate red clay,in order to reveal the implications of paleo-climate and palaeoenvironmental change about the transition of the double-layer structure.The results showed that:1)The results of particle-size shows,the Yellow-brown Earth and the reticulate red clay of the section comprised no gravel(>2mm);low content of sand(>63 ?m),and silt fraction(2?10?m)is the most important component in the researched profile,aeolian particle(10?50?m)is the second major component.In conclusion,all the above preform the aeolian characteristics of the researched profile.The Langxi profile is vertically uniform in particle-size,the source and stability of the Yellow-brown Earth and the reticulate red clay.With the change of depth of the researched profile,the peak of the grain-size frequency curves of the reticular red clay is higher than that of the fine particles,while the peak of the coarse silt decreases.It reveals that the weathering intensity of the reticular red clay is higher than that of the the Yellow-brown Earth.2)The results of geochemical characteristics shows,geochemistry is mainly composed of SiO2?Al2O3?TFe2O3(TFe2O3=Fe2O3+FeO).The Langxi profile is ver-tically in geochemistry,and also shows continuous transition between YBE and RCwithout any depositional interruption.The weathering index has clear difference between the Yellow-brown Earth and reticular red clay.The underlying reticular red clay range is finer in particle-size and more intensively weathered.There is significant positive correlation between the weathering index values and clay fraction contents,indicating the weathering index are controlled by the weathering degree of the reticulate red clay.3)The results of environment magnetism shows,the Yellow—brown Earth has higher magnetic than the underlying reticular red clay.The increase of HIRM in the underlying reticular red clay indicates that more and more fine-grained magnetite and magnetite are gradually converted into goethite and hematite.This is because the Reticular red clay developed in a period of high temperature and precipitation,and the weathing and soil forming effect was enhanced significantly in southern China.4)The results of color index shows,there is high-blooded benign correspondence between L*and a*.There is significant positive correlation between a*(redness)and clay fraction contents,indicating the a*(redness)is controlled by the weathering degree of the reticulate red clay.The researched profile have obvious varieties about each physical and chemical indicators from Upper part's Yellow-brown Earth to lower part's reticulate red clay.It may reflect a significant event of the transformation of paleoclimate change in the Yangtze River in the middle and lower reaches.It has significant correspondence with the quaternary glacier and the marine isotope stage.5)The results of optically stimulated luminescence shows,the Yellow—brown Earth was developmentd in the last glacier,The boundary between the Yellow—brown Earth and the Reticular red clay is was developmentd in the transition of the last glacier and the last interglacial.So it can be considered to be a response for the middle Pleistocene major global climate change in the middle and lower reaches of the China's Yangtze River.