犹他州圣胡安河基岩蜿蜒断面对 50 ka 年尺度侵蚀率的影响

IF 2.8 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Earth Surface Dynamics Pub Date : 2024-02-07 DOI:10.5194/egusphere-2024-71
Aaron T. Steelquist, Gustav B. Seixas, Mary L. Gillam, Sourav Saha, Seulgi Moon, George E. Hilley
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引用次数: 0

摘要

摘要主要河流的切入率可能反映了排水系统重组、山坡过程、构造隆起、气候、河流切入岩石的特性以及其他自生过程的影响。在科罗拉多高原,科罗拉多河沿岸的切入率被解释为科罗拉多河水系整合所产生的突然基底变化所致。具体来说,科罗拉多河在大峡谷位置的汇合被认为形成了一个因岩性对比而增强的节理点,该节理点正在向上游后退。虽然有证据表明科罗拉多河的部分河段在 1 亿年前加速了侵蚀,但短期侵蚀速率所反映的过程的不确定性使得与长期平均侵蚀速率的比较变得模糊不清。在这项研究中,我们结合了宇宙放射性核素深度剖面暴露年龄和后红外激发发光法(p-IR IRSL),对犹他州墨西哥帽附近科罗拉多河主要支流圣胡安河附近的河流沉积物进行了年代测定。这些沉积物位于 32 米长的地层表面,年代为 28-40 ka,表明侵蚀速率为 804-1151 m Myr-1,比过去 1.2 Ma 的长期侵蚀速率 140 m Myr-1 高出近一个数量级。我们观察到由于基岩河曲断裂而被遗弃的河道沉积,这部分解释了我们的加速侵蚀速率。我们利用一个简单的几何模型,并结合我们的实地数据,证明了在某些情况下,相对于长期侵蚀速率,平面河流的演化可能会增加短期侵蚀速率。这些短期速率也可能反映了自循环和气候过程的综合作用,这限制了它们解决可能与基底或构造变化有关的长期侵蚀速率变化的能力。
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The impact of bedrock meander cutoffs on 50 ka-year-scale incision rates, San Juan River, Utah
Abstract. Incision rates of major rivers may reflect the effects of drainage reorganization, hillslope processes, tectonic uplift, climate, the properties of rocks into which rivers incise, and other autogenic processes. On the Colorado Plateau, incision rates along the Colorado River have been interpreted as resulting from abrupt base-level changes produced by the integration of the Colorado River system. Specifically, the integration of the Colorado River in the location of Grand Canyon is thought to have created a knickpoint, enhanced by lithologic contrasts, which is retreating upstream. While evidence exists for a <1 Ma acceleration of incision on parts of the Colorado River, uncertainty about the processes reflected in shorter-term incision rates muddies comparison with longer-term averages. In this work, we combine a cosmogenic radionuclide depth profile exposure age and post-Infrared Infrared Stimulated Luminescence (p-IR IRSL) to date fluvial deposits adjacent to the San Juan River, a major tributary of the Colorado River, near Mexican Hat, Utah. The deposits, resting on a 32 m strath surface, are constrained to be ∼28–40 ka, suggesting an incision rate of 804–1151 m Myr-1, nearly an order of magnitude higher than the long-term rate of ∼140 m Myr-1 over the past ∼1.2 Ma. We observe fluvial deposits that were abandoned due to a bedrock meander cutoff, which partially explains our accelerated incision rate. We use a simple geometric model, informed by our field data, to demonstrate how planform river evolution may, in some circumstances, increase short-term incision rates, relative to long-term incision rates. These short-term rates may also reflect a combination of autocyclic and climatic processes, which limits their ability to resolve longer-term changes in incision rate that may be related to changes in base-level or tectonics.
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来源期刊
Earth Surface Dynamics
Earth Surface Dynamics GEOGRAPHY, PHYSICALGEOSCIENCES, MULTIDISCI-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
5.40
自引率
5.90%
发文量
56
审稿时长
20 weeks
期刊介绍: Earth Surface Dynamics (ESurf) is an international scientific journal dedicated to the publication and discussion of high-quality research on the physical, chemical, and biological processes shaping Earth''s surface and their interactions on all scales.
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