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Late Quaternary variations in paleoerosion rates in the northern Qilian Shan revealed by 10Be in fluvial terraces
Geomorphology ( IF 3.9 ) Pub Date : 2021-04-21 , DOI: 10.1016/j.geomorph.2021.107751
Qingying Tian , Eric Kirby , Wenjun Zheng , Huiping Zhang , Hao Liang , Zhigang Li , Weitao Wang , Tao Li , Yipeng Zhang , Binbin Xu , Peizhen Zhang

Understanding the pace of erosion through space and time may provide insight into how tectonic and climatic processes conspire to drive landscape evolution. However, determining whether erosion rates in a given locality have varied with past climate change remains challenging, and the mechanisms invoked to explain variations in past erosion rates are not well understood. In this study, we evaluate past rates of erosion during the late Quaternary along the northern Qilian Shan, the range bounding the northeastern margin of the Tibetan Plateau. We measured the concentrations of cosmogenic 10Be from fluvial deposits atop 5 terraces along the Hongshuiba River and average 10Be concentrations at the time of terrace formation. We also determined terrace ages by combining 5 10Be depth profiles and 15 OSL samples of overlying loess. Our results confirm previous dating of this terrace sequence using cosmogenic exposure ages of boulders and depth profiles in terrace gravels and indicate that terrace treads span glacial-interglacial cycles over the past ~200 ka. We exploit this exceptionally dense sampling of 10Be to evaluate differences in cosmogenic 10Be concentrations at the time of terrace formation along the Hongshuiba River. Analysis of 48 individual determinations of “inherited” 10Be concentrations reveal that fluvial sediment in terraces abandoned during the last glacial and penultimate glacial periods are 3–4 times greater than concentrations in sediment atop terraces formed during interglacial times. Paleoerosion rates within the Hongshuiba watershed appear to have been ~200 m/Myr during glacial episodes but increased to ~500–700 m/Myr during interglacial times, similar to recent erosion rates inferred from 10Be in modern sediment. These results point to likely changes in the mean residence time of sediment with the watershed that fluctuate in association with 100-ka glacial-interglacial cycles. We suggest that reductions in erosion rates associated with glacial conditions may have been driven by changes in catchment hydrology during cold and dry periods.



中文翻译:

10 Be在河床阶地揭示的祁连山北部古侵蚀速率的第四纪晚期变化

了解随着时间和空间的侵蚀速度,可以深入了解构造和气候过程如何共同推动景观演变。然而,确定给定地区的侵蚀率是否随过去的气候变化而变化仍然具有挑战性,并且人们对于解释过去的侵蚀率变化的机制还缺乏很好的理解。在这项研究中,我们评估了北祁连山第四纪末期过去的侵蚀速率,该范围以青藏高原东北缘为界。我们测量了沿红水坝河沿5个阶地上的河流沉积物中的成因10 Be的浓度,并在阶地形成时平均了10 Be的浓度。我们还通过组合5 10确定露台年龄是深度剖面和上覆黄土的15个OSL样本。我们的研究结果证实了该阶地序列的先前年代,使用的是大块岩的宇宙成因暴露年龄和阶地砾石的深度剖面,并表明阶地踏步跨越了过去〜200 ka的冰川间冰期循环。我们利用这种异常密集的10 Be采样来评估沿红水坝河阶地形成时宇宙成因10 Be浓度的差异。分析“继承”的10个48个单独的确定被浓度显示,在最后的冰川期和倒数第二个冰川期被废弃的阶地中的河流沉积物比在间冰期形成的阶地上的沉积物浓度高出3–4倍。红水坝流域内的古侵蚀速率在冰川事件期间似乎为〜200 m / Myr,但在冰间期则上升至〜500–700 m / Myr,这与现代沉积物中10 Be推断出的近期侵蚀率相似。这些结果表明,随着流域与100ka冰川-冰川间周期的变化,流域内沉积物的平均停留时间可能会发生变化。我们建议,与冰川条件相关的侵蚀速率降低可能是由于在寒冷和干旱时期流域水文学的变化所致。

更新日期:2021-05-05
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