干旱区生态环境知识资源中心

Arid and semi arid northern China holds some of the world’s most significant sand sea and loess deposits. In particular, arguably the most important late Cenozoic wind-blown dust archives on land are exposed on the Chinese Loess Plateau. The origin of this loess-forming dust and its relationship to adjacent sand seas is unclear and has been the subject of considerable debate. Polarization of opinion over the sources of loess also reflects uncertainty over its relationship to large river systems and to the sources of proximal desert sands. It is critical to resolve this in order to elucidate the origins of sand seas, to determine the activity of past dust emitting regions and to fully exploit loess climate archives. Here we combine zircon U-Pb, fission-track and double dating with heavy mineral analysis to test the role of proximal deserts and rivers in contributing dust to the Loess Plateau. We focus on the Mu Us desert to test hypotheses over its sediment sources and because previous studies have often presented contrasting interpretations over its importance as a loess source. Spatial complexity of zircon ages and heavy mineral assemblages in Mu Us sand rules out significant aeolian mixing and shows that grains originating in northern Tibet dominate in the western Mu Us, with local sources dominating in the east of the desert. The western Mu Us far-travelled grains are shown to be delivered by the Yellow River and associated systems. Crucially, the western Mu Us grains and Yellow River grains show U-Pb age distributions and heavy mineral assemblages virtually identical to those of the Quaternary loess. Thus, our results demonstrate that the Yellow River and associated systems transports large quantities of sediment from northern Tibet to the Mu Us desert and further suggest that the river contributes a significant volume of material to the Loess Plateau. This provides the first evidence of a genetic link between the Yellow River and formation of the Chinese Loess Plateau and suggests a greater role for fluvial activity in past dust and desert sand sea formation. (C) 2013 Elsevier Ltd. All rights reserved.