A Study On The Characteristics Of Aeolian Sediments In The Gurbantunggut Desert

Xinjiang Uygur Autonomous Region is the province with the largest desert area and serious desertification in China.The Gurbantunggut Desert,located in the northern Junggar Basin,is the largest immoblized and semi-immoblized desert in China.Its unique desert landforms and environmental characteristics,It attracts the attention of geomorphologists and desert scholars.As the material basis for the development of aeolian landforms,sediments are extremely important for determining the source of the desert material and the sedimentary environment,and are the basic link in the study of regional aeolian landforms.Based on field observations and sampling,this paper studies the micromorphology;,grain size,geochemical elements,and mineral characteristics of surface sediments in different areas and different types of dunes in the Gurbantunggut Desert by using relevant theories of desert sedimentology.Based on this,the material source and formation mechanism of the Gurbantunggut Desert are discussed,and the following main conclusions are drawn:(1)The roundness of the particles in the Gurbantunggut Desert is relatively poor,mainly angular and subangular,and there are few round quartz particles.The surface microstructure of sand particles mostly appeared butterfly pits,irregular impact pits,hemp pits and cracks,and surface morphologies such as shell-shaped fractures,V-shaped pits and crescent impact pits appeared less,indicating that during the formation of the desert,mechanical weathering was the most significant,and water flow and chemical weathering were weak.(2)The surface sediments of the Gurbantunggut Desert are dominated by fine sand and medium sand,and the content of silt and coarse sand is small.For different areas of the desert,the distribution of the content of extremely fine sand,fine sand and silt sand from the southeast to the northwest gradually decreased,while the distribution of medium sand,coarse sand and extremely coarse sand gradually increased;for different types of dunes,In other words,the grain size is mainly composed of fine sand and medium sand.There are significant differences in the natural distribution frequency curves of different types of dunes:dendritic dunes are unimodal,while honeycomb dunes,linear ridges,and barchan dunes(chains)are bimodal,with a peak particle size range The difference is small,and the frequency curve of barchan dunes(chains)is higher than other types of peaks.The average particle size of the surface sediments in the Gurbantunggut Desert is 2.14?,showing a spatial pattern that gradually tapers from northwest to southeast;the average sorting coefficient is 1.00?,medium sorting,and overall sorting performance From the north to the south,the law gradually improved;the skewness averaged 0.11,showing a nearly symmetrical and positively skewed distribution as a whole;the kurtosis average value was 1.08,and the overall appearance was moderately peaked.The average particle size of different types of dune sediments is also different.Honeycomb dunes and barchan dunes(chains)are mainly fine sands,while linear ridges and dendritic dunes are mainly medium sands.In terms of sorting coefficients:honeycomb dunes and barchan dunes(chains)sorting,etc.,linear ridges and dendritic dunes are poorly sorted;in terms of skewness,honeycomb dunes,linear ridges and dendritic dunes are positively distributed,and barchan dunes The(chains)is nearly symmetrically distributed;in terms of kurtosis:barchan dunes(chains),dendritic dunes,and linear ridges all have medium peak distributions,and honeycomb dunes have narrow peak distributions.(3)The composition of the constant elements in the surface sediments of the Gurbantunggut Desert is basically the same in different regions and different types of duns.They are mainly SiO2,and the average content is above 60%.SiO2 is the most stable and easy to be enriched in the process of sand particle transportation and deposition.While the average content of other constant element oxides is lower than the average content of UCC,the migration leaching rate is:P>Mg>Fe>Ti>Ca>Na>Al>K>Mn>Si.The composition of trace elements in the surface sediments of the Gurbantunggut Desert is also roughly similar in different regions and different types of dunes,with Ba,Sr,Zr,and Rb contents higher.Moreover,the migration and leaching of trace elements in different areas and different types of desert dunes are basically the same.The migration and leaching rate of each trace element is:Th>Nb>Cu>Zn>Ni>Sr>La>V>Ga>Rb>Zr>Ba>Y.The sand material of the Gurbantunggut Desert is deposited in a cold and dry environment,and the desert is in the primary stage of being largely unweathered or very weakly weathered.(4)The composition of light minerals in the Gurbantunggut Desert is mainly quartz,feldspar and calcite.The light mineral content is high,with an average content of 95.2%,while the heavy mineral content is less,only 2.2%.Although the total content of heavy minerals is very low,it is rich in species and most stable heavy minerals.The heavy mineral characteristic index indicates that the western and southern Gurbantungut deserts are more weathered than other regions,and the maturity of heavy minerals is higher in the northern,central,and southern regions of the desert,indicating that the source areas of the sediments in these regions are far away,and the carrying distance is long.The diversity of the mineral composition of the Gurbantunggut Desert is caused by the multi-source nature of its sand material.The various clastic materials in the mountains around the Junggar Basin are the main source of the desert.Broken debris is also an important source.