Heavy minerals, Sr-Nd isotopic composition of sandy land in Hulun Buir, Inner Mongolia and their implications for Asian aeolian dust system

As an important part of Northern China Desert, Hulun Buir sandy land is of great significance to the study of dust system in Asia. The characteristics of heavy minerals and the composition of Sr-Nd isotopes are the important tools to reveal the sediment evolution process and trace the provenance. But the "grain size effect" caused by sedimentary sorting has always been the limiting factor for the composition of heavy minerals and Sr-Nd isotopes in sandy land. Totally 19 aeolian sand and fluvial sand samples were collected from Hulun Buir sandy land and screened to analyze the material composition and discuss the effect of separation on the composition of heavy minerals and Sr-Nd isotopes. Among them, 12 sub-samples (< 73 μm and 73-125 μm) were identified and analyzed for heavy minerals, and 23 sub-samples (< 63 μm, < 30 μm and < 11 μm) were determined for Sr-Nd isotopes. The results show that there are significant differences in heavy mineral content, heavy mineral index (ATi, GZi and ZTR) and heavy mineral assemblage with different particle sizes. The stable and extremely stable minerals are concentrate preferentially onto the finer particles, which enhances the overall stability of the fine-grained sediments. Different from previous studies on Sr-Nd isotopic grain size control, our results show that the ⁸⁷Sr/⁸⁶Sr ratio is slightly affected by the grain size effect, but the Nd isotopic composition is significantly affected by it, and the coarse-grained components tend to have a higher Nd isotopic ratio. The Sr-Nd isotopic composition of Hulun Buir sandy land has "time effect". It shows that the geochemical composition of the dust source area is unstable. This study is of great significance for the understanding of Asian aeolian dust system study using heavy mineral and Sr-Nd isotopic composition. The wide or multiple grain size window as well as substantial amount of samples must be considered for source tracing.