Grain size and geochemical study of the surface deposits of the sand dunes in the Mu Us desert, northern China

Material components and geochemical behaviour of desert deposits are closely related with the level and degree of the desertification. In this research, we systematically carried out a grain size and geochemical study of the surface sediments from fixed, semi-fixed, semi-mobile and mobile sand dunes and discussed their link with the desertification in the Mu Us Desert, northern China. Grain size results indicated that the main components of the different sandy sediments were predominantly 200-300-mu m coarse grain size. Along with the stronger desertification, the fine material content (clay and silt) and mean grain size (phi) became lessened, while the coarse particle is remarkably increased due to the repeated wind sorting during that process. These sandy deposits were mainly transported by saltation and creep; the increased creep and decreased saltation and suspended components were probably a response to the lessened fixation degree of the dunes. Geochemical analysis demonstrated that the surface sandy deposits were mainly composed of SiO2, Al2O3 and Na2O, which was very similar to the geochemical constituents of the other deserts in northern China. These sandy surface sediments, with their relatively high Ca and Na content, incur little or no geochemical weathering, which is probably attributable to the arid conditions and the lack of effective weathering. Additionally, an A-CNK-FM diagram indicated that decreased Fe and Mg contents were possibly related to the stronger abrasion and sorting during the desertification process. Copyright (c) 2016 John Wiley & Sons, Ltd.