Oxygen isotope signatures of quartz from major Asian dust sources: Implications for changes in the provenance of Chinese loess

摘要

We present a systematic investigation of the oxygen isotopic composition of quartz in both fine and coarse fractions (<16 and 16-63 lm) from major dust source regions in East Asia, including the Mongolian Gobi, the northern Chinese deserts, the Taklimakan desert, and the Qaidam Basin. The results demonstrate that the quartz oxygen isotope ratios of the Taklimakan desert and the Mongolian Gobi are more heterogeneous compared with the other areas. The quartz δ~(18)O values of both the fine and coarse fractions from the various sources are overlapped to varying degrees, thus making it difficult to differentiate them. Nevertheless, the quartz δ~(18)O values of both fractions exhibit an increasing trend from the Mongolian Gobi, to the northern Chinese deserts, and then to the Taklimakan desert. This implies that the geological settings of the source areas are different, which in turn results in differing contributions of high-temperature igneous rocks. The combination of quartz δ~(18)O results with other quartz-based provenance tracers can clearly differentiate the three major source areas, i.e., the Taklimakan desert, the Mongolian Gobi, and the northern Chinese deserts. In addition, comparison of our results with previous δ~(18)O measurements of fine-grained quartz from the Luochuan loess sequence suggests the likely glacial-interglacial fluctuations in dust provenance. Finally, we suggest that the combination of quartz δ~(18)O signatures and other dust provenance tracers can potentially improve the recognition of long-term fluctuations in the provenance of Chinese loess-red clay deposits.