Quartz grain surface microtextural evidence for provenance of the Quaternary aggradation red earth deposit,southern China |
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| Abstract: | The Quaternary aggradation red earth(QARE) deposit in the middle reaches of the Yangtze River(MRYR) in southern China provides important evidence for understanding the paleoenvironment. However, its provenance remains controversial. In this study, the surface microtextures of grains from the QARE were observed, and compared with those of grains from the loess deposit on the Loess Plateau in northern China. The results show that the surface microtextures and morphologies of the quartz grains in the QARE are distinctly different from those in the northern loess, indicating that the deposits in the two regions have different provenances. The Gobi and deserts in inland northwestern China are not considered as the primary provenance for the QARE in southern China. It is suggested that the large areas of dry and bare river and lake beds and floodplains in the MRYR, which became exposed during glacial periods, provided the dominant source for materials in the QARE. We suggest that against the background of the middle-Pleistocene climate transition(MPT), regional aridification and a strengthened east Asian winter monsoon(driven by global cooling and the rapid uplift of the Tibetan Plateau) were primary drivers for the initiation of the QARE deposit in the MRYR region in southern China. The development of large areas of aeolian red earth deposit is direct evidence of environmental deterioration in the MRYR, indicating a cold and dry environment with frequent aeolian activity, in an area that now experiences a warm and humid subtropical monsoon climate. The results are also evidence of a regional response in the mid-subtropics of southern China to the MPT global cooling event around 1.2 Ma. |
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