Sediments And Environmental Evolution Of The Hunshandake Sandy Land Since The Late Glacial Epoch

This work carries out a temporal-spatial analysis and comparison in facial pattern, grain-size, and susceptibility of the sediments of the Hunshandake Sandy Land (HSL) on the basis of studies of more than fifty geological sections, a number of samples collected from surface sands as well as results derived from previous studies. The preliminary results of this work provide new environmental information of the working area, which makes it possible to have a brief discussion about the evolution of the HSL since the Late Glacial Epoch. This work can be summarized as the followings.Firstly, evidence from depositional pattern suggests that the HSL has experienced an expansion-contraction circle since the Late Glacial Epoch. The expansion and movement of the HSL or desert in early stage were clearly marked by the presence of paleo-aeoline sands. The occurrence of paleosoal characterized the stabilization and contraction of the HSL and also indicated the activity of pedogenesis on the paleo-aeilian sands. The study of the surface samples demonstrates that the present day is experiencing another warm-dry environment but the pedogenetic activity is not as great as the Optimum. The data collected in this study indicates that the paleosol layer is thicker in the southeast region than in the northwest and thicker in the north region than in the south. Additionally, the data shows that the summer monsoon influenced the sandy land but to a different degree in different places.Secondly, the paleo-climate index drawn from the analysis of the grain-size and susceptibility of the strata suggests the presence of three different periods in the evolution of the HSL, which reflects that the paleo-climate change was in congruence with the desertification and the facial change of the deposits. The deposits are coarser in grain in the west area than in the east and coarser in the south area than in the north. Furthermore, the grain size of the deposits is much coarser in the hinterland than in the marginal areas. These differences suggest that the grain-size and the formation of paleosol were closely related to the provenance and its surface environment. Meanwhile, the formation of the HSL was primarily influenced by East Asian monsoon and controlled by ice climate.Thirdly, the sandy desertification of the HSL consists of three types: the local type, the windblown type and coarse-grained type.Finally, the surface sands of the HSL are coarser at the present day than the past and the desertification of the land is currently rather rigorous.