Joel L. Pederson, Sherman C. Young, Michael Turley, Natalie Tanski, Tammy M. Rittenour, Ron A. Harris
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引用次数: 0
摘要
基岩溪流的蜿蜒最终会导致峡谷环路被切断,而这些废弃的 "峡谷环路 "是河床和地貌保存较好的地方。我们对犹他州摩押市科罗拉多河下游杰克逊霍尔峡谷及其周围的河流阶地进行了记录和荧光测年。结果表明,在大约 200 ka 年时,rincon 被切断并废弃,同时也记录了过去 300 ky 年中这一地区快速而不稳定的侵蚀。多种条件的交汇导致了凛孔的断裂,其中包括 MIS 6 冰川气候开始时的冲积河道条件,这种条件提供了河床覆盖,并加强了对薄弱地层的横向侵蚀。此外,同时代的岩崩也部分阻塞了冲口下游的古河道,可能会形成回水,使洪水进一步冲过颈部。尽管其他研究表明,基岩河道蜿蜒和断流会产生非对称的地层阶地,并在短期内增加侵蚀速率,但这些在杰克逊霍尔林孔的记录中并不明显。这项新颖的案例研究利用了废弃基岩河道的高保存潜力,揭示了地貌演化过程中林孔形成的过程和控制因素。
The how, when, and why of an abandoned bedrock meander of the Colorado River, Utah (U.S.)
River meanders entrenched into bedrock are found worldwide, and they are famously well represented in the Colorado Plateau of the southwestern U.S. Meandering of bedrock streams can eventually lead to cutting off canyon loops, and these abandoned “rincons” are locations with high preservation of fluvial deposits and landforms. We document and luminescence date the fluvial terraces in and around the Jackson Hole rincon along the Colorado River downstream of Moab, Utah. Results indicate cutoff and abandonment of the rincon at ~200 ka and also record the rapid and unsteady incision in this region over the past 300 ky. A convergence of conditions contributed to the cutoff of the rincon, including alluvial-channel conditions at the onset of MIS 6 glacial-climate, which provided channel-bed cover and enhanced lateral erosion of weak strata. Also, a contemporaneous rock-avalanche partially obstructed the paleochannel just downstream of the breach, potentially creating a backwater that further enabled a flood to avulse across the neck. Although other studies show that bedrock-channel meandering and cutoff can generate unpaired strath terraces and short-term increases in incision rates, these are not evident in the record at the Jackson Hole rincon. This novel case study leverages the high preservation potential within abandoned bedrock meanders to illuminate the processes and controls of rincon formation during landscape evolution.
期刊介绍:
Earth Surface Processes and Landforms is an interdisciplinary international journal concerned with:
the interactions between surface processes and landforms and landscapes;
that lead to physical, chemical and biological changes; and which in turn create;
current landscapes and the geological record of past landscapes.
Its focus is core to both physical geographical and geological communities, and also the wider geosciences