Grain size characteristics of the reticulate dunes of the Hobq Desert

Abstract

This study investigates grain-size variations in surface sediments across typical reticulate dunes at the western fringe of the Hobq Desert, China. The relationship between grain size and changes in dune morphology is characterized by analyzing sediment samples from various parts of dunes. The results indicate that, on the primary ridge, mean grain size becomes finer from the toe of the stoss slope to the top of the dune crest, with further variations down the lee slope before coarsening again within inter-dune areas. Grain-size patterns differ for the secondary ridge, where grains are finer at the stoss slope and dune crest under north wind conditions, while the toe of the lee slope has coarser sediment. The coarse grain size on the primary ridge can be attributed to the underlying sediment, which is dominated by disorderly coarse particles with multiple peaks at sizes less than or equal to 2.5 Φ. Coarser grains on the lee slope of the secondary ridge result primarily from airflow deflection at the lee slope. The stoss slope of the secondary ridge erodes as oblique airflow interacts with the dune, deflecting the airflow along its lee slope to promote longitudinal sand transport in this area. This phenomenon also causes fluctuations in mean grain size along the north-south axis of the primary ridge. The observed grain-size distribution response to changes in dune morphology appears largely influenced by the presence of a “short secondary ridge” under north wind conditions. These ridges create a narrow gap, accelerating the west wind and contributing to the coarse grain sizes on the lee slopes. This research may enhance understanding of reticulate dune development mechanisms in dual wind environments, shedding light on the dynamic sedimentary processes of these complex structures.