Character Of Grain Size And Elements Of Simply Eolian Sand-dust System During The Last Glacial Period In Ganbei Region And Its Typomorphic Midels

As one of the important geological archives,loess deposits have provide a great deal of information about global climate change in Quaternary recent decades.Controversy still exists about provenance identification of loess materials based on the element geochemistry.Element geochemistry-based source tracing of loess in complex sedimentary system in arid and semiarid areas,such as in central Asia,for extensive sources of complicated geological background and probably retransportion and resedimentation activities of detritus involved,was unclear and unidentifiable at some degree.This is because highly mixing of materials during transportation.To aviod this kind of defects of geochemistry-based source tracing of loess,along the simple sedimentary system of eolian deposits from sand to clayey silts,i.e the D-D section(roughly paralleling the present winter wind direction),nine profiles was selected to sample the aeolian deposits dating to the last glacial period.Grain size and element measurement on 65 loess samples were carried out to analysize the characteristics of the simple loess sedimentary system of D-D and to construct the grain size and element-based typomorphic model of this simple eolian deposits cell.Moreover,aeolian deposits from HG-C profile(belong to the D-D cell)in Dingshan town,Jiujiang and CS profile on the northern slope of Yuelu hills in Changsha,Hunan province also sampled to verify the validity of typomorphic model of eolian deposits cell for source tracing of loess.The results are as follows:(1)The Furong-Zhouxi cell of eolian deposits shows a systematic tendency of grain size and element geochemistry from D-D-01 profile(upwind direction of winter monsoon)to D-D-09profile(downwind direction of winter monsoon),indicating the intrinsic character of a cell.(2)Grain size and element-based models of the Furong-Zhouxi cell of eolian deposits can be reconstructed on granularity components,grain size parameters and typical stable elements ratios.These models,representing the basic characters of the Furong-Zhouxi cell of eolian deposits from the upward direction to the downward direction,also were named as the typomorphic models of the Furong-zhouxi cell.(3)Provenance identification of loess materials can be carried out based on these typomorphic models,which,avoiding the uncertainty and multiple solutions of source tracing by comparing the relation between the model(an unit)and specific profiles(also probablysystematical)provides a new idea and method for source tracing.