Chronology of dozens of Late Paleolithic sites in the Ulan Buh Desert, northwest China

The Ulan Buh Desert (UBD) is located in the arid region of northwest China, where a number of lithic artifacts have been surface collected in the past. However, due to the lack of clear in situ archaeological horizons, research on the age and environmental background of prehistoric human occupation in UBD is still in its infancy. Since 2020, field investigations have been conducted in the UBD and 37 new Paleolithic sites have been discovered, including two in situ buried sites (WL1-B and WL36) and 35 surface sites. The lithic collections encompass two different industries: 1) microlithic assemblages primarily composed of microblades; and 2) non-microlithic collections predominantly represented by flakes. The ages of the in situ buried sites were dated by Optically Stimulated Luminescence (OSL) and Accelerator Mass Spectrometry (AMS) ¹⁴C, while the ages of the layers below the surface sites were determined via OSL. The dating results indicate human foragers occupied the eastern part of UBD (Region IV) at ∼8.5–8.4 ka (WL1) and ∼7.3 ka (WL36). In addition, the stratigraphy of WL1-B and WL36 have consistent regional characteristics, with the upper layer dominated by sandy loess layers and the lower layer dominated by sandy layers. Based on the positional relationship between the stone artifacts and the sandy loess layer, the residual sandy loess layers near the stone artifacts from the surface sites are speculated to be likely related to their original depositional context. As such, the age derived from the surface sites may serve as a reference for the approximate age of human occupation in other regions of UBD, between around 9.8–5.7 ka, which is generally consistent with the age of the two in situ buried sites. During the Early-Middle Holocene, the UBD was dominated by a relatively humid environment, which would have provided opportunities for human expansion and occupation in an area that is currently near-uninhabitable desert.