Study On The Sediment Provenance Of The Piedmont Dune Area In The Southwest Margin Of Qaidam Basin

The Qaidam Desert is one of the highest and driest deserts on Earth.The Qaidam Basin has strong wind-sand activities and forms many aeolian landforms.Geomorphologists and desert researchers have paid much attention to the wind-sand landforms in the basin because they are similar to Mars,Titan and other exoplanets in external morphology.The aeolian sand geomorphology of the piedmont dune area in the southwest margin of Qaidam Basin is concentrated on the thick alluvial,diluvial fan and fluvial lacustrine strata of the Qimantage piedmont in the East Kunlun Mountains.Aeolian sediments are the key components of terrestrial sedimentary systems and are sensitive to global climate change.Therefore,the study of sediment provenance in desert areas is of great significance for understanding the formation and evolution of desert,reconstruction of arid land surface processes,and understanding the relationship between tectonic movement and material sources.In this paper,the piedmont dune area on the southwest margin of Qaidam Basin is taken as the research area.The grain size and geochemical element characteristics of different types of surface sediments in the piedmont dune area on the southwest margin of Qaidam Basin are studied in detail by using the method of grain size analysis and geochemical element analysis,and their weathering characteristics,material sources and transport paths are also discussed.The following preliminary conclusions were drawn:（1）The sediments in the piedmont dune area of the southwestern Qaidam Basin are mainly fine sand and medium sand,with the contents of 36.34% and 33.98%,respectively.The average particle size in the study area is 2.31Φ,ranging from-0.14 to4.19Φ.The separation coefficient ranged from 0.32 to 2.19Φ,with an average value of0.79Φ.The skewness distribution is nearly symmetric on the whole.The medium peak state is the dominant peak state for kurtosis.Gobi sediment has the smallest grain size but the worst sorting,while linear dune has the coarsest grain size and the best sorting.（2）The analysis of the relationship between grain size parameters shows that the sorting coefficients of barchanoid dune,transverse dune,network dune and linear dune sediment are positively correlated with the average grain size,while the barchan dune,compound transverse dune,Gobi and fluvial sediment are negatively correlated.The skewness of barchan dune,compound transverse dune,Gobi and fluvial sediment is positively correlated with the average particle size.The other sediments were negatively correlated.The kurtosis of barchanoid dune,network dune,compound transverse dune and fluvial sediment is positively correlated with the mean grain size.The other sediments were negatively correlated.There is a positive correlation between skewness and kurtosis in river sediments,and a negative correlation between skewness and kurtosis in Gobi sediments when 1<0,and a positive correlation when 1>0.（3）The natural frequency curve of the sediment in the piedmont dune area on the southwestern margin of Qaidam Basin presents unimodal and bimodal distribution patterns.Barchan dune,barchan dune chain,transverse dune,linear dune,thicket dune,composite transverse dune,Gobi and river sediment curve narrow distribution of single peak;The trellis dune curve is gentle and bimodal.（4）According to the Sahu formula,it is concluded that the sedimentary environment of the piedhill dune area in the southwest margin of Qaidam Basin is relatively complex,with aeolian,beach,shallow sea,fluvial and turbidity sedimentary environments all distributed.Gobi and fluvial sediments are fluvial environments under the combined action of different degrees of fluvial action and wind separation.The other types of dune sediments are dominated by eolian environment.（5）SiO₂,Al₂O₃ and C O are major elements in the sediments,and the average total content is more than 83%;The contents of Cl,Ba,Sr and Zr are high.Compared with the average chemical element composition（UCC）of the upper continental crust,major elements except Ca O are slightly enriched,trace elements As are highly enriched,and Co is slightly enriched.（6）The variation range of CIA in the study area was small,ranging from 40.90 to53.05,with an average CIA of 47.51.In the A-CN-K triangle map,the sediments were concentrated near the upper continental crust.In the A-CNK-FM triangle map,the sediments in the study area were concentrated and the degree of chemical weathering was weak.They were all in the primary stage of continental chemical weathering that was basically unaffected or weak.The river sediments and some of them were collected from the gobi near the river,and the degree of weathering was higher,followed by the degree of weathering of gravel ripple and interdune,and the degree of wind mineralization was the least,which was consistent with the results indicated by the chemical alteration index（CIA）.（7）The study area of sediments had the same material source.The detritus produced by weathering and denudation of rocks in the Eastern Kunlun Mountains in the southwest margin of Qaidam Basin were transported to the piedmont and deposited under the action of seasonal flowing water,forming a widespread piedmont alluvial plain,and then transformed by wind erosion to form the present surface landscape.