12 Jul 2021

12 Jul 2021

Review status: this preprint is currently under review for the journal ESurf.

Rapid Holocene bedrock canyon incision of Beida River, North Qilian Shan, China

Yiran Wang1, Michael E. Oskin1, Youli Li2, and Huiping Zhang3 Yiran Wang et al.
  • 1Department of Earth and Planetary Sciences, University of California, Davis, California, USA
  • 2College of Urban and Environmental Sciences, Peking University, Beijing, China
  • 3Institute of Geology, China Earthquake Administration, Beijing, China

Abstract. Located at the transition between monsoon and westerly dominated climate systems, major rivers draining the western North Qilian Shan incise deep, narrow canyons into latest Quaternary foreland basin sediments of the Hexi Corridor. Field surveys show that the Beida River incised 125 m at the mountain front over the Late Pleistocene and Holocene at an average rate of 6 m/kyr. We hypothesize that a steep knickzone, with 3 % slope, initiated at the mountain front and has since retreated to its present position, 10 km upstream. Terrace dating results suggest this knickzone formed around the mid-Holocene, over a duration of less than 1.5 kyr, during which incision accelerated to at least 25 m/kyr. These incision rates are much larger than the uplift rate across the North Qilian fault, which suggests a climate-related increase in discharge drove rapid incision over the Holocene and formation of the knickzone. Using the relationship between incision rates and the amount of base level drop, we show the maximum duration of knickzone formation to be 700 yr and the minimum incision rate to be 50 m/kyr. This period of increased river incision is the result of increasing excess discharge, which likely corresponds to a pluvial lake-filling event at the terminus of the Beida River and correlates with a wet period driven by strengthening of the Southeast Asian Monsoon.

Yiran Wang et al.

Status: open (until 01 Sep 2021)

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Yiran Wang et al.


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Short summary
Beida River has an over-steepened reach presently located 10 km upstream of the North Qilian mountain front. It was formed because river incision into the bedrocks inside the mountain cannot keep up with river incision into the soft sediment in the basin. The maximum duration of forming this reach is about 700 yr, with a minimum incision rate of 50 m/kyr. The formation of this reach corresponds to a humid period related to strong Southeast Asian Monsoon influence ~4 kyr ago.