关键词: 浑善达克沙地, 粒度, 磁化率, 环境记录

Abstract: For the sake of the fully understanding of the environmental features of the Otindag Sandy Land of Inner Mongolia Autonomous Region, China, five typical sections of the sand area were selected and studied by the author of this paper. Three of them are in the southern border and the other two are in the hinterland and northern border respectively. For obtaining the new information about the desertification of the whole Otindag Sandy Land area in different regions and different periods, we collected two hundred and seven sedimentary samples at intervals of 5 cm or 10 cm and measured their granularity and the quality susceptibility. By comparing the measured data, it shous that the paleo-aeolian sands are the mark of the movement and expansion of the desert; paleosol is the mark of the stablization and contract of the desert and also the product of the action of pedogenesis on paleo-aeolian sand. The present environment condition was studied by searching for the record of the surface sand.
Fig.3 shows that the curves of grian-size data (the mean, ＜60μm (%) ) and susceptibility value can be subdivided into three part ranging from the bottom to the top. On the basis of the field work and quality susceptibility value and grain size characteristics analyzing, the following conclusions can be drawn： (1) the grain size of the east area is coarser than that of the west area; the grain size of the north area is coarser than that of the south area. What is more, the grain size of the hinterland is much coarser than that of the border area, which indicates that the grain size has much relation on the provenance and subaerial environment and the forming process of the Otindang sandy land was mainly influenced by East Asia monsoon. (2) As time went on, it shows that the Otindag Sandy Land had been expanding during the last glaciation, and which can be testified by paleo-aeolian sands in the section. The postglacial age was the best period of pedogenesis in the whole Otindag sandy land. At the present, though not as typical as the postglacial age, the area is in a pedogenesis period, and the grain size on the subaerial land is coarsening severely, which shows the great influence of human activity on desertification.

Key words: Otindag sandy land, grain-size composition, quality suceptibility, environmental record