Pedogenic And Composition Characteristics Of The Loess Soil And Its Paleo-environmental Significance In The Xiushidu Profile Of Jingyang

Loess,deep-sea sediments and polar ice cores have been hailed as the three pillars of paleoclimate studies,while multiple layers of loess and paleosol layers in the Loess Plateau have alternated with the appearance of cycles.The rich geological changes and climate-environmental information were recorded since the Quaternary period,which provided a good research material for studying the changing characteristics of the paleoclimate environment.On the basis of consulting domestic and foreign data,combined with field investigations and laboratory test methods,this thesis tested the basic physical characteristics of the soil,and uses particle size analyzer,magnetic susceptibility meter,XRF core scanner and X-ray diffractometer to investigate the grain size composition,magnetic susceptibility,constants and trace elements and mineral components of Xiushidu profile in Nanyang,Jingyang.That nvestigate the physical and chemical weathering intensity and soil development process of loess and paleosol layers,and indicate the characteristics of paleoclimate and environment changes during loess accumulation and development period.This thesis has achieved the following research results:(1)The profile loess belongs to the typical eolian loess,loess and paleosol belong to silt-grained soil.The content of fine-grained components in the paleosols is significantly higher than that in the loess layer,which reflecting the strong weathering and soiling of the paleosols.The Kd value in the paleosol layer is less than that in the loess layer,showing that the northwest monsoon activity is intense during the loess accumulation period.The C-M image,grain size image analysis and discriminant parameters of profile loess were studied to further illustrate the characteristics of the eolian characteristics.(2)The porosity of the overlying loess layer in the stratigraphic sequence is greater than that of the adjacent paleosol layer.The degree of porosity is affected by the degree of soil development.The increase of clay content makes the porosity decrease,while the water content and specific surface area of the paleosol is higher than the adjacent loess layer,and the larger specific surface area and special landforms make the paleosol layer water content higher.(3)The magnetic susceptibility values of the paleosols were higher than those of the adjacent top and bottom loess layers,and they corresponded well with alternate formations of the loess-paleosol layers.The change in the curve of frequency magnetic susceptibility indicates that the glacial period is converted to the interglacial period quickly,and the transition from the interglacial period to the glacial period is slow,reflecting the different degree of influence of the winter and summer monsoon.Changes in the magnetic susceptibility values in the same formation also indicate anomalous climatic characteristics.Using magnetic susceptibility values and the depth of CaCO3 deposition to estimate the paleoclimatic environment,while the average annual rainfall range was 233.6 to 829.3 mm,and the average annual temperature range was 2.49 to 14.37 ?.(4)The content of Al,Si,K,Fe,Ti,Mn,Rb,Zr,and Ba in the paleosol layer is higher than that of the adjacent loess layer,while the content of Ca,Cl,Rh,Sr in the loess layer is higher than that in the paleosol layer.Geochemically similar elements may have similar existence conditions.Ca and Al,Si,K,Ti,Mn,Fe,and Rb have different material sources.The high correlation between Zr and Ti indicates that they are from the same stable source of material.The ratio of Rb/Sr showed a higher value in the paleosols,but the ratio of Zr/Rb ratio was opposite to that of Rb/Sr,indicating that a strong summer monsoon intensity and strong weathering and soiling of formations.(5)The content of plagioclase,potash feldspar and hematite in the paleosol layer is relatively high,but the content of dolomite,calcite,illite,chlorite and common hornblende in the loess layer is relatively high,revealing the difference in the weathering degree of loess and paleosol layers.The study of the change characteristics of calcite/quartz,plagioclase/quartz and potash feldspar/plagioclase mineral ratios can further explain formation forming conditions and weathering effects,its reflects the developmental and soiling environment in paleosol development and loess accumulation period,and the warm and humid climate during the summer monsoon is more conducive to weather and decompose of unstable minerals.(6)The content of LOI550? in the paleosol layer is higher than that of the adjacent loess layer,while the LOI950? content of the loess layer is higher than that of the adjacent paleosol layer.That is,the ancient soil layer has a richer organic matter content,and the carbonate in the paleosol layer migrates to the underlying loess layer due to leaching and shows a higher content in the loess layer.