The age of sand wedges and its environmental significance at the southeast edge of Badain Jaran Desert

Abstract

Sand wedge is a product of permafrost in cold climate, and it is of great significance to restore paleoclimate and paleoenvironment. Since the early 20th century, periglacial landforms such as sand, ice, and soil wedges and glacial mud have been intensively studied in North America, Europe, and Russia. Nevertheless, the distribution of desert areas in the permafrost regions after the last glacial period is still debated in academia. Particularly, in China, it has been argued that desert areas were not the parts of ancient permafrost regions. Moreover, the studies of ancient sand wedges are mostly limited to the last glacial period. In recent years, several groups of ancient sand wedges and glacial mud have been recognized in the Badain Jaran Desert. This filled the gap in the Chinese literature regarding ancient permafrost and proved that desert region belonged to the scope of permafrost regions during the last glacial period. The newly discovered sand wedges in the southeast Badain Jaran Desert comprise sand and gravel layers. Optically stimulated luminescence dating of the filler in the sand wedges suggests that they formed during the last glacial period and the late glacial maximum, in particular. The annual average temperatures in the Badain Jaran Desert during the last glacial period were approximately −3–−6°C, and it is 12–15°C cooler than present. The filler in sand wedges was mainly poorly sorted fine sand that was not transported from afar but from nearby sand dunes. According to the sand wedge groups of the last glacial period in the desert and seasonal frozen soil, we can infer that the Badain Jaran Desert was a part of the permafrost that may have been continuous and widespread. The extent and distribution of the Badain Jaran Desert in the last glacial period was probably different than today, reflecting the dynamic nature of sand dunes. According to the law of sand dunes’ movement in the Badain Jaran Desert, combining with the characteristics of aeolian sand of the desert’s ancient permafrost wedge can indirectly infer that three large desert areas of the Alxa Plateau were connected more than ten thousand years ago when the entire Alxa Plateau was part of the permafrost; furthermore, the desert hinterland and the surrounding sand dunes would have been frozen and the movement and development of the sand dunes would have been suppressed. Surface landscape and the kinetics of the sand and landform need to be studied further. While the Badain Jaran Desert was likely a part of the cryosphere climate zone during the last glacial period, whether the Chinese northern desert belonged to the frozen earth region is still questionable.