Characteristics of quartz grains in the middle and lower reaches of the Hutubi River, NW China, and its paleo-environmental significance

Abstract

Quartz sand characteristics in the downstream floodplain of the Hutubi River, located near the oasis–desert transition zone at the southern edge of the Gurbantunggut Desert, were examined to understand the sedimentary dynamics and processes. By analyzing three fluvial–lacustrine–eolian profiles and collecting surface sediment samples from different reaches of the Hutubi River, the characteristics of quartz sand were examined using optically stimulated luminescence (OSL) dating and scanning electron microscopy (SEM). The qualitative and quantitative results reveal spatial variations in surface sedimentary quartz sand, reflecting a transition from glacial–hydraulic interaction to alluvial dominance, followed by a balance between eolian and alluvial processes, and ultimately eolian dominance. The quartz sand within the profiles exhibits sub-rounded and rounded shapes, with significant alluvial-pluvial characteristics, indicating a predominance of fluvial processes within the lower sections of the profiles, while the upper sections exhibit a higher occurrence of eolian microstructures. Overall, the study area experienced a shift from a relatively high-energy and stable depositional environment during the mid-Holocene to a relatively low-energy and unstable condition in the Late Holocene. This was evidenced by stable fluvial–lacustrine deposition between 8 and 6ka and subsequent transitions between high and low-energy hydraulic processes, accompanied by wind erosion and frequent changes in sedimentary environments since 4.2ka.