Characteristics Of Sediments Around The Badain Jaran Desert

The Badain Jaran Desert is the second largest desert of China; the area is about 5.2 million square kilometers. Its climate is extremely arid, its dryness is between 7 and 12. Under the control of the Mongolia high pressure belt, the Badain Jaran Desert mainly presents the typical continental climate. Desert deposit characteristic is important information to represent the evolution and the development of the desert, which can not only demonstrate the material source of the desert, but also can be used to discuss its sedimentary environment.Taking the Badain Jaran Desert surrounding sediment as the research object, through field investigation and laboratory analysis, using the theory of blown sand physics, this paper specifically is measured and analyzed the sediment grain size and element geochemical characteristics in the studying area, which can come to the following preliminary conclusions;(1)The surrounding grain size composition of sediments of Badain Jaran Desert are mainly composed of fine sand and the sand. Among them, fine sand content changes in the range of 4.31-54.52%, the average content is 37.09%; the sand content changes in the range of 8.33-51.88%, the average content is 22.70%; clay content changes in the range of 0～24.71%; silt content changes in the range of 0.01-12.84%, the average content is 2.21%; very fine sand content changes in the range of 0.88～35.99%, the average content is 18.41%; coarse sand content changes in the range of 0～38.67, the average content is 9.82%; very coarse sand content changes in the range of 0-29.62%, the average content is 4.54%.(2) The edge sediment separation of the Badain Jaran Desert is poorer, followed by medium separation, but overall is poor separation; skewness is mainly negative bias, the proportion of extremely negative bias and symmetric comes to the next; kurtosis is mainly medium kurtosis, the proportion of sharp narrow kurtosis and very sharp narrow kurtosis is lower. Average sediment particle size is roughly positively correlated with kurtosis, with the decrease of the average sediment particle size, the kurtosis is also becoming narrower.(3) Through Sahu (1964) discriminant formula, we can get the Badain Jaran Desert marginal sedimentary environment is complex, in addition to the beach sedimentary environment, there are other sedimentary environments. It can be thought that the Badian Jaran Desert’s surface sediment source is varied, the sediments are mostly ancient flood alluvial accumulation and also grow out of mountains’stream transport and accumulation.(4) The major chemical elements of surface sediments are similar in the Badain Jaran Desert and the major elements are SiO2、Al2O3、CaO, the average percentage are 76.81%,8.75% and 3.11% respectively, the sum of the three achieves 85.40% of the total weight; among the average content of trace elements, the Nb content is the lowest, only 8.57μg·g-1; while Ba has the highest average content, reaching 570.62μg·g-1. The value of variation coefficient of elements V、Gr、Co、Ni、Cu、Rb、Sr、Y、Zr、Nb、 Ba、Pb is small, they all less than 0.5(the largest variation coefficient is Pb, only 0.4), which indicates the spatial difference of the whole desert is not prominent.(5)Compared the geochemical elements’standardized value of the sediments in the Badain Jaran Desert edge to UCC, in addition to the content of CaO and SiO2 are similar to UCC,the rest of main elements’average content have different degrees.The composition of trace elements, Cr and Ni show concentration, the content of Ba, V, Zr are similar to UCC,the rest of trace elements are rendered as obvious leaching condition, of which the most leaching is Nb. That indicates the Badain Jaran Desert’s surface sediment were fully circulated and mixed after a long transportation, deposition and weathering, which made part of the elements’composition are close to the upper continental crust chemical content, others are leaching and enrich.(6) The chemical index value of the Badain Jaran Desert’s surface sediment is between 33.7 and 49.3,the average is 41.9, lower than the upper continental crust’s average value 48.0, which indicates this desert received less chemical weathering and no obvious clay mineral contents.From regional point of view, the south and the north desert have almost the same average of CIA, it shows they have the similar chemical weathering degree. It can suggest the Badain Jaran Desert is mainly under physical weathering in the dry and windy condition, while has less chemical weathering.