Sedimentary Evidence of a Mudflow Event Dated to 14−13 kyr BP in Upper Yellow River Basin, Northwestern China

Sedimentary deposits preserve geological evidence of past environmental change. During fieldwork in April 2022, we investigated and systematically sampled a well-exposed sedimentary section near Baituzhuang Village, Hualong Hui Autonomous County, Qinghai Province, in the upper Yellow River Basin of northwestern China. The section was analyzed using optically stimulated luminescence (OSL) dating, grain-size analysis, soil-color measurements, loss on ignition (LOI), and elemental geochemistry aims to determine the age and depositional characteristics of the Baituzhuang mudflow deposit and to assess its relationship with abrupt climate change during the last deglaciation. OSL ages indicate that the layer was deposited at 14−13 kyr BP, coinciding with a major climatic transition during the last deglaciation. The grain-size distribution of the Baituzhuang mudflow deposit (MFD) layer differs markedly from those of the overlying and underlying strata. The MFD layer contains a pronounced peak in sand content, a feature consistent with mudflow deposition. The soil-color data support an aqueous depositional origin for the MFD layer. In addition, LOI and elemental geochemical data show pronounced fluctuations within the MFD layer, indicating the input of exogenous material transported by the mudflow. The evidence indicates that the mudflow occurred during an abrupt transition from cold-arid to warm-humid conditions. Our results refine the reconstruction of environmental evolution in the study area since the last deglaciation. They further indicate that the mudflow event represents a rapid hydrogeomorphic response to abrupt climate change in the Upper Yellow River region, within the transitional zone between the Qinghai-Tibet Plateau and the Loess Plateau. This event provides local evidence for the sensitivity of the Upper Yellow River landscape to abrupt climatic change during the last deglaciation.