The Study To The Sedimentary Environment And Ancient Climate Of Yardang Landform Sediments In Dunhuang,Gansu

Yardang landform is a kind of typical wind erosion landforms.There are various types of yardang bodies in the research area,it is the most typical yardang landform in China even all over the world;The yardang landform in the research area contains rich geological environment information,so the study to the information has very important scientific value and science popularization value;by means of studying the grain size,magnetic susceptibility,sporopollen and combined with the sedimentology,to study the composition,sedimentary environment,paleoclimate of the research area.The research profile is a set of incomplete consolidation sediments of lacustrine facies,It forms in the age of 306?236 ka,belongs to middle-late stage of middle pleistocene.By analyzing grain size,showed that the sediments of yardang landforms in the research area is mainly composed of silt,the average content is 61.0%,the average contcnt of sand is 30.6%,the average content of clay is 8.4%,gravel content is very few.By analysing the grain size composition and parameters,grain frequency curves,cumulative probability curves of the research profile,and combined with the sedimentology feature of the profile,divided its sedimentary environments into 5 sections,it has experienced the sedimentary sequence of "lake facies(I section)-river facies(II section)-lakes(III section)-rivers(IV section)-lakes(V section)".By analysing the sporopollen data of the profile,divided the paleoclimate into 4 sporopollen zone;the egetation types has experienced the "desert steppe(? belt)-steppe(? belt)-desert steppe(? belt)-desert(? belt)".By analysing the magnetic susceptibility and sporopollen data of the profile,and combined with sedimentary feature,grain analysis of the profile,divided the paleoclimate into 4 stages,it has experienced a process of "warm dry-partial wet-dry-more dry".