Late Piocene - Pleistocene evolution of river terrace in Zhongwei Basin, northeastern margin of Tibetan Plateau, China

Abstract:

Northeastern margin of the Tibetan Plateau is a key area to understand the formation and evolution of the plateau. We describe the feature of terraces derived from deposit or down-cutting of the Yellow River in Zhongwei Basin that records the evolution of landform in this region. After clarifying the correlation among terrace remnants, we determine the age of certain terraces by TCN and ESR. The TCN dating yields age for lowest terrace buried in the basin of 2.40±0.38 Ma, and the ESR dating for upper three terraces on hillslope adjacent the margin of the basin of 2.08±0.21Ma, 1.88±0.35Ma and 1.48±0.11Ma respectively. The fact that buried terrace is older than the ones distribute on high elevation suggests that spatial variation in vertical motions of the basin. Taken with the observation and ages of these landform features, we infer to a deceleration of depression in center of the basin after terrace was buried in Late Piocene, then the basin started to uplift rapidly, causing the river gradient to steepen locally and erosion of the channel to intensify, resulting to the terrace on high elevation nearby the basin.