Plio-Pleistocene History of River Incision and Catchment Erosion From Cosmogenic 26 AL and 10 BE in Cave Sediments

河流穿过基岩的速度和模式决定了景观如何响应其构造和气候环境而演变。了解长期的河流切割过程对于理解地貌演化、构造隆升模式、气候变化的地貌记录以及土地利用和大坝建设对环境的影响具有重要意义。然而，由于长期的河流切割速率以前很难测量，河流切割速率仍然缺乏约束，河流切割的理论模型在很大程度上仍然未经检验。最近，宇宙核素技术为估算长期河流切割速率和流域侵蚀速率提供了新的工具。现在有可能在与河流剖面演变相关的时间尺度上推断河流切口和集水区侵蚀率的详细历史。该项目利用肯塔基州格林河（Green river）沿岸洞穴中保存的河流沉积物中的合成铝26Al和铍10Be，来推断过去500万年来河流切割和流域侵蚀的历史。由于洞穴提供了一个免受侵蚀的环境，洞穴沉积物可能会在数百万年里不受干扰。绿河沿着许多洞穴流动，包括猛犸洞穴系统，这是迄今为止世界上最大的洞穴系统，有超过500公里的调查通道。这些洞穴是河流沉积物的巨大储存库，记录了过去5-10万年河流的切割历史。对猛犸洞穴系统沉积物进行密集采样，可以详细重建过去500万年的河流切口和集水区侵蚀，这段时间包括了几次主要的气候变化。沿着绿河的长度进行额外的采样将允许研究河流在同一时间跨度内的纵向剖面演变。这些数据将提供河流切口和集水区侵蚀的记录，其范围和细节前所未有。本研究旨在通过同时测量流域侵蚀（河流泥沙的来源）和河流下游速率来探索泥沙供应对河流切割的影响。它还应该有助于澄清气候变化对河流下游和景观演变的影响。该研究将为检验和约束河流穿过基岩的最基本假设提供急需的数据。

9706011 Granger The rate and pattern of river incision through bedrock determines how landscapes evolve in response to their tectonic and climatic environment. Understanding long-term river incision processes is important for understanding landform evolution, patterns of tectonic uplift, the geomorphic record of climate change, and the environmental impacts of land use and dam construction. However, because long-term river incision rates have previously been very difficult to measure, river downcutting rates remain poorly constrained, and theoretical models of river incision remain largely untested. Recently, cosmogenic nuclide techniques have provided new tools for estimating both long-term river incision rates and catchment erosion rates. It is now possible to infer detailed histories of river incision and catchment erosion rate over timescales relevant to river profile evolution. This project uses comogenic 26Al and 10Be in river sediments preserved in caves alongside the Green River, Kentucky, to infer the history of river incision and catchment erosion over the past 5 million years. Because caves provide an environment protected from erosion, cave sediments may be left undisturbed for millions of years. The Green River flows alongside numerous caves, including the Mammoth Cave system, by far the world's largest cave system with over 500 km of surveyed passage. These caves are a vast repository of river sediment, recording the river's incision history over the past 5-10 million years. Intense sampling of the Mammoth Cave system sediments will allow a detailed reconstruction of river incision and catchment erosion over the past 5 million years, a timespan which includes several major climate changes. Additional sampling along the length of the Green River will allow a study of the river's longitudinal profile evolution over the same timespan. These data will provide a record of river incision and catchment erosion unprecedented in its scope and detail. This research is des igned to explore the influence of sediment supply on river incision, by simultaneously measuring both catchment erosion (the source of river sediment) and river downcutting rates. It should also help clarify the influence of climate change on river downcutting and landscape evolution. This study should provide much-needed data to test and constrain the most fundamental hypotheses of river incision through bedrock.