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Abstract: Identification of aeolian sand sources occurring in oases of desert environments is of great importance for understanding desertification processes and for developing strategies for sustainable development in arid regions. Combined with wind data and hierarchical cluster analysis, we analyzed the spatial characteristics of major and trace elements of sands sampled at the margins of the Minqin Oasis, northwestern China and its adjacent deserts (the Badain Jaran Desert and the Tengger Desert), with the purpose to identify the aeolian sand sources and their transport pathways in the region. The spatial distribution revealed by bivariate plots of Cr, Ni, Cr/V, Y/Ni, Al, V, Zr, Hf, Zr/Hf and ternary plots of major and trace elements showed that sands between the west (B – Badain Jaran Desert, BM – the dune belt between Badain Jaran and the Minqin Oasis and TNE – dune field located in the northeast margin of the Minqin Oasis) and southeast (TSW – dune field located in the southeast margin of the Minqin Oasis) sides of the oasis have different provenances, while the composition of sands in the Minqin Oasis (M) and in the dune field located in the south margin (TM) is associated with both. The variations in abundance of K, Rb, Ba and Sr were used as indicators of aeolian transport processes. Our results show that while aeolian sands from the Badain Jaran Desert can be transported over mountains and over long distances by northwest winds to the west sides of the Minqin Oasis, they cannot directly reach neither bypass the oasis to the east side. Our interpretation is that the oasis can act as an effective barrier to stop the migration of dune fields both in the Badain Jaran Desert and the Tengger Desert. However, the extensive occurrence of aeolian sands in the Minqin Oasis indicates that its role in preventing desert encroachment should not be overestimated. [Copyright &y& Elsevier]

Abstract: Sedimentary sequences occurring in desert dunes reflect changes in desert systems, and as such may contain signals useful for recognizing spatial and temporal changes of deserts and their response to regional or even global climate fluctuations. Geomorphological and palaeoenvironmental studies within the dune fields of the Asian middle-latitudes have provided some solid evidence for interpreting the history of these sand seas. Using the Hunshandake (Otindag) Sandy Land, a sandy area covered primarily by stabilized dunes and located in the semi-arid zone of eastern Inner Mongolia, China (Fig. 1), as an example, we studied the initiation and variation in the dune landscape in the eastern portion of the desert belt in northern China. On the basis of physical and biochemical indicators in the sediments and OSL chronology, we herein argue that this dune system in the middle latitudes of eastern Asia is much younger than previously assumed and that it has responded sensitively to climate change during the late Quaternary. Geological evidence from the Sandy Land suggests that most of the current dunes are of late Pleistocene or even Holocene age. Palaeosols intercalated in the aeolian sequences and their OSL chronology show that the climate of the Hunshandake was much wetter than today between 9.6 ka and 3 ka. This resulted in stabilization of the dunes in the eastern and central portions of the Sandy Land. Epochs of reworking or stabilization of the dunes are broadly consistent with the fluctuations in northern hemisphere solar radiation although with an obvious time lag. Because the increase rate of annual precipitation was not sufficient to fully stabilize the dunes in more arid part of the region, some active dunes persisted even during this long-lasting wetter epoch. We conclude that periods of Holocene dune stabilization due to palaeosol formation varied along the climate gradients across the various sandy lands of northern China, and in general it began earlier and lasted longer in the east than in the west. The general nature of the sandy lands and their counterparts in the western portion of the desert belt during the LGM and mid-Holocene climate optimum is discussed in comparison with their current states. [Copyright &y& Elsevier]