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Grain shape is used less frequently in identifying the origin of sediments than grain size distributions and/or surface microtextures because of technological limitations. In addition, systematic studies on grain shape change of sand‐sized sediments from a source‐to‐sink perspective are lacking, and yet the evolutionary mechanism of grain shape along the sediment transport pathway remains poorly understood. Here, we investigated grain shape changes in sand‐sized sediments ranging from mountains to dune fields using an efficient and quantitative dynamic image analysis technique. By means of the detailed hydro‐geomorphic analysis and field sampling in a quasi‐closed sedimentary system, we collected 41 samples from the Hulunbeier Sandy Land (HSL) in northern China and its potential source region. Also, 21 typical fluvial deposit samples from different river systems in China were collected for comparison. We identify that the sphericity, symmetry, aspect ratio, and mineralogical maturity of the fluvial deposits from mountains are significantly lower than the eolian sand in dune fields. Despite the apparent inheritance of sediments from the mountains to the dune fields, the abrupt changes in the sedimentological and geochemical properties along their pathway suggest that multiple cycles of eolian abrasion within the HSL modify the sediments significantly after they are transported away from the fluvial environments. The well‐defined separation between eolian sand and fluvial deposits by grain shape parameters such as sphericity and symmetry underscores that grain shape can be a powerful tool for tracing sediment transport history in paleoenvironmental or extraterrestrial studies. Plain Language Summary: The shape, size, and surface morphology of sand grains are important for understanding the traveling story of the grain. This study focuses on the shape and geochemical composition changes of the sand grains from the Great Khingan Mountains to the Hulunbeier Sandy Land (HSL) in northern China. We measured the grain shape of each sample by capturing the images of millions of individual grains using high‐frame‐rate cameras and image analysis techniques. We found that the windblown sand is more spherical than the river sand in the mountains. This obvious difference can be used to clarify the traveling history of grains with unknown origins. The abrupt shift of both grain shape and geochemical compositions between river sand and windblown sand along the sediment traveling pathway indicates that the windblown sand in the HSL experienced a long period of wind modifications. Elongated particles and soft minerals, such as feldspars, were rounded and/or reduced in size, while more spherical and harder particles, such as quartz, were enriched in dune fields. Key Points: Repeated eolian abrasion in dune fields significantly increases dune sand's grain sphericity, symmetry, and geochemical maturityQuantitative grain shape data can be a powerful tool for tracing sediment transport history and identifying sediments of unknown originsGrain shape is difficult to differentiate the depositional environments in areas where eolian‐fluvial interactions dominate [ABSTRACT FROM AUTHOR]

The evolution of barchan‐to‐parabolic dunes can be driven by vegetation establishment, which may be linked to climate change and/or human activity. However, little is known of the impact of changes in wind strength on vegetation development and the resulting impacts on the evolution of dune morphology and sedimentological characteristics. To address this issue, we studied the morphology and grain‐size characteristics of barchan, barchan‐to‐parabolic and parabolic dunes in the Mu Us Desert in north China, which was combined with an analysis of changes in normalized difference vegetation index (NDVI) and climatic variables during 1982–2018. The results reveal a trend of increasing growing‐season NDVI which was related to a significant decrease in drift potential (DP). Therefore, we suggest that the initiation of dune transformation was caused by the reduced wind strength which favored the establishment and development of vegetation. To reveal the response of sedimentological reorganization during the processes of dune transformation, grain‐size characteristics along the longitudinal profile of the three different types of dunes were examined. The decreasing wind strength led to the transport of fine sands on the upper part of the windward face of the dunes, resulting in a progressive coarsening of the grain‐size distribution (GSD) and a reduction in dune height at the crest area. No distinct trend in sorting and mean grain‐size was observed on the windward slope of the barchan‐to‐parabolic dune, indicating that the sand in transit had little influence on the GSD. Conversely, progressive sorting and coarsening of the sand occurred towards the crest of the parabolic dune. This indicates that vegetation development limited the transport of sand from upwind of the dune, and affected a shift in the dune source material to the underlying source deposits, or to reworked pre‐existing aeolian deposits, and resulted in the trapping of sand in the crest area. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents the environmental history and its responses to palaeoclimatic changes since the start of the Holocene in the eastern portion of the desert belt (sand seas and sandy lands) in northern China by comparing the aeolian sandpalaeosol sequences and their palaeoclimatic proxies. The optically stimulated luminescence (OSL) ages of the aeolian sandpalaeosol sedimentary sequences and a series of palaeoenvironmental proxies show that: (1) The large-scale dune landscape currently in the Kubuqi Sand Sea was formed during the Holocene in general; and the palaeosol was generally developed during the period of 4–2 ka, indicating conditions favorable for vegetation growth, soil development, and organic carbon accumulation due to increased precipitation or effective moisture and weakened aeolian activities; the large-scale expansion of dunes in the recent 2 ka is closely linked to human activities. The variable discharge of the Yellow River with diversions for irrigation may have resulted in a more consistent supply of aeolian particles for dune field expansion. (2) The dune landscape of the Hunshandake Sandy Land was likely formed around 12 ka, and before this, the western part of the Hunshandake Sandy Land would have been covered by a single large lake; it was obviously wetter than today in the sandy land during the period of 9.6–3 ka and the palaeosols were developed at the same time. But the aeolian activities have not been completely dormant in this long-lasting wetter epoch; because the Holocene wetter period was likely time-transgressive across the region. (3) The palaeosol of the Hulunbuir Sandy Land began to develop as early as 14.5 ka, probably continuing until the last 2 ka. The palaeosol development of various dune fields in the eastern portion of the desert belt (sand seas and sandy lands) in northern China is spatially heterogeneous, and even the palaeosol development time in different locations within each sandy land is inconsistent. During the middle Holocene (especially the 7.5–3.5 ka), all the sandy lands were stabilized in general and the intensity of aeolian activities was significantly weakened. The number of palaeoenvironmental records in the eastern portion of the desert belt (sand seas and sandy lands) in northern China has increased rapidly in the past decade, but the amount of published data still does not match the vast extent of the dune fields. It does require much more in-depth palaeoenvironmental studies for a full understanding of the relationship between aeolian activities and climate change in northern China. [ABSTRACT FROM AUTHOR]

Numerous studies have explored paleoenvironmental conditions in China's dune fields around the mid-Holocene (MH), ∼6000 calendar years ago, often based on individual paleosol-aeolian sand depositional sequences and local-scale landscape dynamics. So far, continent-scale modeling studies have only indirectly assessed dune activation and stabilization processes via changes in simulated precipitation, net precipitation (precipitation minus evaporation), and effective moisture (precipitation divided by evaporation). Here we conducted a comprehensive study using gridded data on potential evapotranspiration, precipitation, and surface wind velocity from 13 climate models participating in the Paleoclimate Modeling Intercomparison Project phases 4 (PMIP4) and compared the model results with geological records. Our evaluation of spatial patterns of dune activity in northern China around the MH reveals that the intensity of annual MH dune activity exhibited significant differences between the eastern and western parts of Chinese deserts compared to those of the preindustrial period (PI). Dune activity was significantly weaker in the eastern region, while in the western part, it was considerably stronger. The key drivers of this disparity were the distinct spatial variations in near-surface wind speed and effective moisture between the two regions. Compared with the optically stimulated luminescence ages of the paleosol-aeolian sand sedimentary sequences derived from a compilation of geological records from 88 sites across northern China, the model results suggest that the weakening of dune activity and the process of dune stabilization in eastern China around the MH were mainly attributed to a significant increase in effective moisture and a concurrent decrease in near-surface wind speed due to the intensified East Asian summer monsoon. Additionally, the weakening of westerlies in western China resulted in reduced effective moisture, contributing to increased sand availability for dune development and subsequent desert expansion. • Mid-Holocene dune activity in Chinese deserts varied regionally, differing from preindustrial period. • Varied wind speed and moisture caused different mid-Holocene aeolian activities in northern China's western and eastern desert belt. • Numerical simulations aid in interpreting field-based geological findings comprehensively. [ABSTRACT FROM AUTHOR]

• Geochemical characteristics of aeolian sand from two different dune fields were studied. • Spatial differences are primarily caused by surface processes and provenances. • Aeolian sand in the Horqin Sandy Land experienced intense chemical weathering. • Coarse and fine sand fractions move via separate transportation pathways. Geochemical studies examining surface aeolian sediments are significant for understanding Earth's surface processes and determining sediment provenance in arid and semi-arid regions. However, there is limited research on the geochemical comparison of aeolian sediments formed under distinctive tectonic and climatic settings. Surficial sand samples from the Taklamakan Desert and Horqin Sandy Land in northern China were collected, and the major, trace, and rare earth elements (REEs) in the bulk samples, fine fractions (<75 µm) and coarse fractions (>75 µm) of sand were analyzed. This study aimed to explore the spatial variation in the geochemical composition of aeolian sand and its drivers. The results show that differences between the two regions are primarily caused by the intensity of chemical weathering, sedimentary recycling, and provenance. The mean chemical proxy of alteration (72.3 vs. 77.8) and the Parker's weathering values (37.8 vs. 55.8) both suggest the bulk samples from the Horqin Sandy Land experienced more intense chemical weathering, whereas physical weathering is a dominant process in the Taklamakan Desert. These differences may be attributed to the different climatic conditions in the two regions and the exposure time to weathering. A combination of the index of compositional variability and immobile trace element ratios shows that aeolian sand in the Horqin Sandy Land underwent more intense sedimentary recycling than sediments in the Taklamakan Desert. REEs ratios (such as Cr/V and Y/Ni) and the Al 2 O 3 -CaO*+Na 2 O-K 2 O (A-CN-K) diagram indicate aeolian sand in the Taklamakan Desert is probably derived from mixed source rocks of tonalite, granite, and granodiorite. Eu anomaly vs. (La/Yb) N diagrams suggest that the primary source-rocks contributing to the coarse and fine fractions in the Horqin Sandy Land are different but mainly derived from the Great Hinggan Mountains. Differences in the provenance of the fine- and coarse-grained fractions are primarily controlled by interactions between wind and fluvial systems. This study confirms that surface processes and sediment provenance in drylands of northern china have distinct spatial differences, implying that geochemical signatures in aeolian sand need to be interpreted in the specific climatic and tectonic contexts. [ABSTRACT FROM AUTHOR]