Optical dating of Yardang sediments and its implications for past flood events on the border of the Badain Jaran Desert, Northern China

The unique landscape of numerous lakes distributed in between megadunes in the Badain Jaran Desert (BJD) has attracted much research attention. The lakes are considered to be recharged by groundwater because of the absence of surface runoff and the very limited precipitation in the region. However, the source of the groundwater and recharge mechanism for the lakes is controversial. Ancient flood sediments, indicated by the residual Yardang landforms, are distributed on the southwestern fringe of the BJD, close to the Beida and Heli Mountains which form the southwestern border of the desert. At the present day, flooding between the mountains and the BJD occurs during heavy rainfall events. Ancient river courses identified on an alluvial fan by remote sensing images interpretation revealed that the floodwater originated in the Beida and Heli Mountains. In this study we conducted optically stimulated luminescence (OSL) dating of sequences of ancient flood sediments in the BJD. The results showed that in the southern border of the BJD, flood events occurred during marine isotope stage (MIS) 7, MIS 5, and in the middle Holocene. Since the gradient of groundwater flow beneath the alluvial fan is from the Beida Mountains to the BJD, and the ground-water table responds to the local rainfall, we conclude that at least part of the groundwater of the BJD is derived from ancient and modern mountain flood events and is supplied as belowground runoff beneath the alluvial fan. The rainfall triggers flooding in the southwestern mountains, which recharges the BJD groundwater and subsequently the BJD lakes.