Geochemical composition and provenance of aeolian sands in the Ordos Deserts, northern China

摘要

Identifying the provenance of aeolian sediments in deserts is of great importance for understanding the Earth surface processes. In this context, we conducted detailed fieldwork in the Ordos Deserts (Maowusu and Kubuqi) in the middle portion of the desert belt in northern China, and measured the major, trace and rare earth elements (REE) of aeolian sands and their potential source rocks and sediments. Our results show that aeolian sands in the eastern (northeastern) and western (southwestern) Maowusu (Mu Us) Sandy Land exhibit different degrees of mineralogical maturity and Eu/Eu* values. Thus, we interpret that these aeolian sands have different provenances, though in the same sandy land. Our data suggest that the local lacustrine sediments and sandstones are the main sources of aeolian sands in the eastern province of the Maowusu Sandy Land, while aeolian sands in the western Maowusu Sandy Land and the Kubuqi Desert have the same external sources. The comparison of geochemical compositions of sediments in the Ordos Deserts with their potential sources in adjacent regions indicates that there is no genetic linkage between the Helan Mountains, the Yinshan Mountains and the Ordos Deserts although they are not far apart. The Qilian Orogenic Belt in the northeastern margin of the Tibetan Plateau is, however, the most likely original provenance for the western Maowusu (Mu Us) Sandy Land and the Kubuqi (Hobq) Desert, but with fluvial sediments in the Ningxia-Inner Mongolian section of the Yellow River as the immediate source. In one side, our results demonstrate that dune fields that are close to each other can have significantly different source sediments. On the other hand, our work suggests that some dune fields and landforms that are far apart from one another, e.g., the Badain Jaran Desert in western Inner Mongolia, the Ordos Deserts and the fluvial sediments in Ningxia-Inner Mongolian section of the Yellow River, can share the same ultimate sources.