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Desertification is a key environmental concern in arid and semi-arid regions. The sedimentological and geochemical characteristics of sediments are closely related to desertification processes, but the relationship between them is still unclear. This study aimed to identify the sedimentological and geochemical characteristics of different sediments in the Taklamakan Desert and to monitor changes in sediment composition as the intensity of desertification varied in the last decades. We examined the grain size, major, trace and rare earth elements of surface sediments collected from loess, sandy loess, fluvial sands, vegetated dunes and mobile dunes along the Keriya River in the Taklamakan Desert. Major element analysis found that loess had the highest degree of chemical weathering, while weathering of surface sediments on dunes (both mobile and vegetated ones) was relatively weak. Trace and rare earth element analysis found sediments were mainly derived from the West Kunlun and West Tianshan Mountains. This study also analyzed vegetation and wind data from 2000 to 2018 and found that the intensity of desertification processes weakened. The near-surface mean wind speed also decreased from 2000 to 2018, resulting in an increase in both the grain size of aeolian sediments on the surface of mobile dunes and the degree of chemical weathering. Additionally, this study confirmed that clay-sized components can be carried by high-altitude westerlies or formed by pedogenesis. With the strengthening of westerlies and the increase of chemical weathering, it is likely that more clay components will be added to the loess located on the northern slope of the Kunlun Mountains. This study demonstrates that the landscape evolution of the Keriya River in the Taklamakan Desert is primarily driven by fluvial processes, vegetation and wind dynamics, and that these processes may be affected by the intensity of desertification. [ABSTRACT FROM AUTHOR]

The Kubuqi Desert is the only active sand sea in the semiarid regions of northern China and occurs along the southern margin of the Yellow River. Little is known about the age and origin of this large (17,000 km 2 ) sand sea with a present annual precipitation of 200‐480 mm. Sand drift potentials indicated net capable winds for aeolian transport are from the northwest, though winds are stronger to north beyond the dune field than within the sand sea. Geomorphic and stratigraphic observations indicate that Holocene aeolian sand often drapes over bedrock and river terraces as a palimpsest landscape. Field investigations identified four stratigraphic sections with multiple aeolian sand units and palaeosols, with age control by optically stimulated luminescence (OSL) dating of quartz grains. Palaeosols are weakly developed, mostly accumulative A horizon with organic carbon content < 1% and reflect sand sheet deposition possibly in a steppe environment. Although sediments near river channels or former lakes might give old ages, the initial formation and age of the Kubuqi sand sea should be judged from the occurrence of the sandy palimpsest of the landscape that is OSL dated to the Holocene in general. The latest period of aeolian reactivation may be related to human activity associated with grazing and farming from lost cities in the Kubuqi Desert during the Han (206 B.C. – A.D. 220) and the Tang (A.D. 608 – 907) Dynasties. Also, variable discharge of the Yellow River with local diversions for irrigation and throughout the catchment resulted in possibly an increased supply of aeolian particles for dune field expansion in the past 2 ka. [ABSTRACT FROM AUTHOR]

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]