Origin and morphology of barchan and linear clay dunes in the Shuhongtu Basin, Alashan Plateau, China

Clay dunes are characterized by a relatively high content of silt and clay and are typically developed on the lee side margin of closed-basins in arid and semi-arid areas. Although they are widely distributed aeolian landforms on Earth, little is known about their development and distribution in Asia. Our field investigations have identified for the first time the occurrence of clay dunes in the Alashan Plateau, north China. The clay dunes occur in three isolated lowland areas of the Suhongtu (SHT) Basin and their morphologies (barchans, hooked barchans, asymmetrical barchans, and linear or seif dunes) differ substantially from those of the well-studied clay dunes in Australia, Africa and North America. These differences could be mainly attributed to the asymmetrical bimodal wind regime, prolonged drought and sediment physical properties, which indicate that dunes of any type can be formed in sand, silt or clay. Based on the known evolution of the SHT paleo-lake basin and regional climate change, we infer that the landscape of modern clay dunes in the desert of the Alashan Plateau does not predate MIS 5, and probably formed during the late Holocene. Analyses of grain-size distributions and the contents of trace and rare earth elements, combined with geomorphological characteristics, indicate that the source sediments of the clay dunes are mainly local Cretaceous-Tertiary and Quaternary red fluvial-lacustrine mudstone and sediments, while the ultimate source is the weathered and denuded products of granitoids of the East Altay Mountains. Comparison of the morphology and alignment of the clay dunes with the prevailing wind pattern tends to support Tsoar's (1984) model of the transition in dune shape from barchans to seif or linear dunes. During 2003–2013, the seif or linear dunes of the SHT Basin migrated laterally and elongated northeastward at rates of about 2–4 m/yr and 16–20 m/yr, respectively.