The largest deflation basin in Asia reveals that the Miocene basin-filling sediments in the eastern Gobi Desert are an important dust source

Deflation is one of the most important exogenic forces in arid and semiarid regions. It not only shapes various wind erosion landforms but also releases a large amount of dust into the atmosphere. The Sunite Steppe in the eastern Gobi Desert is located in arid areas, where Neogene strata are widely distributed. However, the deflation process and its impact on landforms in this area are still unclear. We conducted comprehensive research on stratigraphy, sedimentology and geomorphology and found that there is a giant deflation basin (Sunite Deflation Basin) located to the west of the Otindag Sandy Land and to the east of the Tunggur Platform (Tamuqintala High Platform). With an area of over 8000 km2 and a volume of ∼393 km3, that deflation basin ranks second only to the Qattara Depression in North Africa and is much larger than Big Hollow in the United States; it is the second largest deflation basin in the world and the largest in Asia. Unlike the Qattara Depression (comma-like) and Big Hollow (rod-like), the Sunite Deflation Basin is shell-like in planform. The western edge of the basin is well defined with steep basin walls, indicating that the basin was developed on the ground represented by the Tunggur Platform. The basin bottom gradually becomes shallower from west to east, which is consistent with the prevailing westerly. Subordinate deflation basins, deflation mounds and blowouts are widely distributed in the Sunite Deflation Basin. The basement of the basin is mainly composed of Miocene alluvium and red clay, i.e., basin-filling sediments. The amount of dust (<20 μm) released from the basin that can be transported over long distances is preliminarily estimated to be as high as 216 km3. If all dust is deposited in the downwind loess area (∼37,200 km2) near Chifeng in Northeast China, the deposition thickness can reach ∼5.8 m. Nd isotope and U–Pb detrital zircon data suggest that the Miocene basin-filling sediments comprise aeolian deposits derived from the Gobi Desert and fluvial deposits derived from the Yinshan-Yanshan Orogenic Belt. The Sunite Deflation Basin must have begun forming after the deposition of basin-filling sediments (∼7.5 Ma) and most likely began to develop at ∼3.6 Ma as a result of the strengthened East Asian winter monsoon due to global cooling.