End-member modeling of the grain size record of loess in the Mu Us Desert and implications for dust sources

Abstract

The arid and semiarid northern region of China is the most important loess region in the world. In this region, loess records from the Chinese Loess Plateau (CLP) have been studied extensively, but they are often underrepresented in sedimentological-palaeoenvironmental studies dealing with sites in the Mu Us Desert. Thus, the dust sources and sedimentary characteristics of loess in the Mu Us Desert are poorly understood. To address this, 9 loess sections and 44 modern surface samples with different sediment types in the Mu Us Desert are analyzed to determine their grain size distributions. The grain size dataset is subdivided into three end-members (EMs) using EM modeling, and the EM modeling results of loess and surface sediments are compared. Through the above work, we obtain the following information. (1) The modes of EM1, EM2 and EM3 are 16 μm, 70 μm and 234 μm, respectively, thus representing different transport processes from different dust sources. Among them, EM1 represents long-term suspension from distant sources, EM2 represents short-term suspension and saltation driven by dust storms from local sources, and EM3 represents saltation with shorter transport distance than EM2. (2) From northwest to southeast, the content of loess in EM1, EM2 and EM3 shows a gradual decreasing trend, a gradual increasing trend, and a gradual increasing or irregular trend, respectively. This spatial distribution indicates that although the winter monsoon is the main driving force for loess materials, it is not the main controlling factor of the loess grain size. The loess grain size of the Mu Us Desert is greatly affected by the dust sources. (3) The dust sources of loess in the Mu Us Desert are complex. In addition to the common dust sources with the CLP loess, there are also the contributions of local loose sediments, such as alluvial-lacustrine sediments, floodplain sediments and dune sands from the Mu Us Desert.