Timing and provenance of loess in the Sichuan Basin, southwestern China

Loess-like sediments (locally called the Chengdu Clay) are widely distributed in the Sichuan Basin, at the eastern margin of the Tibetan Plateau (TP), southwest China. Geomorphology, sedimentology/pedology, grain size distributions and quartz oxygen isotopic ratios collectively demonstrate the aeolian origin of the Chengdu Clay and its main source area on the TP. Evidence also supports its transport by the Westerlies and the Tibetan winter monsoon. The magnetostratigraphy of the Huagai loess section of the Chengdu Clay (on the highest river terrace of the Anchang He River) indicates that the sediments began accumulating at about 825 ka BP. This suggests the establishment of a circulation system similar to the present-day system related to the rapid uplift of the TP at that time.