Late Pleistocene and Holocene loess sedimentation in central and western Qilian Shan (China) revealed by OSL dating

The knowledge of loess accumulation in the central and western Qilian Shan was restricted to the time span since 13-11 ka until present. Loess deposits prior to this period have not yet been reported. In this study 23 loess samples from the northern piedmont of central and western Qilian Shan area have been dated using fine-grained quartz optically stimulated luminescence (OSL) dating technique to set up a chronological framework for the loess sedimentation in this region. Our results demonstrate that the deposition of dust was widespread since the last deglaciation (∼13 ka) until ∼3.6 ka in the northern piedmont of the central and western Qilian Shan area. Furthermore, the chronology of the loess sedimentation has been extended back at least to ∼81 ka, which is remarkably older than previously thought. The existence of suitable environmental conditions (e.g. vegetation cover) for loess accumulation can be deduced in the central and western Qilian Shan for the Holocene and late Pleistocene. However, the loess sedimentation has been revealed to be discontinuous before ∼13 ka as indicated by its episodic occurrence.