Geomorphic and geochronologic study in and near Grand Canyon: Testing landscape responses to climate change and exploring the paleo-longitudinal profile of the Colorado River

地貌对气候变化的响应和高耸地形的切割是地貌学中基本但尚未完全理解的问题。大峡谷景观包含了对这两个更大过程的异常完好和暴露的记录。我们更大的研究小组正在进行的工作表明，东部大峡谷对米兰科维奇尺度气候变化的强烈地貌响应叠加在约150米/米的较长期切割速率上，沿大峡谷长度变化的切割速率可能与第四纪断裂有关。我们对东部大峡谷第四纪地层进行了详细的填图和初步测年，形成了一个新的旱地气候响应概念模型，其中包括中晚更新世气候变化期间山坡、支流和科罗拉多河干流之间的复杂联系和反相关系。一幅区域切割的画面正在浮现，它相对活跃，空间可变，暴露了丰富的景观对气候变化的响应记录。我们建议将光激发发光、原位宇宙核素和U系列测年与详细的野外地貌研究相结合，对大峡谷头部、内部和末端三个关键位置的壮观山坡和冲积地层进行研究。我们在东部大峡谷的实地考察和地质年代学导致了两个研究重点和相关的假设，我们建议解决。首先是当地集水区对气候的反应。我们的东部大峡谷景观对气候响应的工作概念模型(包括在最近提交给GSA公告的手稿中)比以前的模型更具体和详细。它突出了旱地的独特反应，并与预测的全球变暖变化有关。我们建议通过研究预测的沿支流上下移动的时间推进沉积和切割来检验和完善这一模型，我们假设这是导致科罗拉多河支流和主干沉积和切割意外反相的原因。我们的工作假设是，这种反相现象一方面是由于当地沉积物供应的产生和沉积信号沿集水区向下传递的滞后时间造成的，另一方面是由于当地大量的沉积物供应而导致基准面沿集水区下降的信号的延迟所致。这一假设可以通过详细的沉积学、地层学，特别是地质年代学研究来检验。第二个研究重点是科罗拉多河沿其区域剖面的基岩切割。我们建议在科罗拉多河沿岸两个新的研究地点增加长期切割率测定，以补充我们在大峡谷东部和西部现有的数据。对科罗拉多州这条450公里断面上的冲积地层、沉积物成分和切割速率的比较是记录这条河流的长期演变和测试假想的短带或切割波穿过河流系统的基础，以响应活跃的飓风-托罗维普断裂带或更古老的排水捕获的新构造强迫。在三个研究地点壮观地保存和暴露了完整的山坡-支流-主干第四纪地层学，结合使用三种互补的地质年代学方法，将阐明当地景观和大陆规模的河流之间的复杂联系及其对气候和构造扰动的反应。此外，本研究还将对三种测年方法进行有益的比较，有助于完成对这一著名地区景观演化的初步认识。我们来自不同机构的研究人员和学生的参与，对初学者的培训，以及通过国家公园管理局向公众传达结果的框架，确保了拟议的研究将产生广泛的影响。

The response of landscapes to climate change and the incision of elevated terrain are fundamental yet incompletely understood issues in geomorphology. The Grand Canyon landscape contains an unusually well-preserved and exposed record of both of these greater processes. Ongoing work by our larger research group indicates that strong landscape responses to Milankovich-scale climate changes have been superimposed on longer-term incision rates of ~150 m/my in eastern Grand Canyon, and that variable incision rates along the length of Grand Canyon can be related to Quaternary faulting. Our detailed mapping and initial dating of the Quaternary stratigraphy in eastern Grand Canyon has resulted in a new conceptual model for dryland responses to climate that includes complex linkages and out-of-phase relations between hillslopes, tributary streams, and the mainstem Colorado River during middle-late Pleistocene climate changes. A picture is emerging of regional incision that is relatively active and spatially variable, and that exposes a rich record of landscape responses to climate change. We propose research that combines optically-stimulated luminescence, in situ cosmogenic nuclide, and U-series dating with detailed field-geomorphic research on the spectacular hillslope and alluvial stratigraphy at three key locations at the head, within, and at the terminous of Grand Canyon. Our fieldwork and geochronology in eastern Grand Canyon has led to two research emphases and related hypotheses we propose to address. First is local catchment responses to climate. Our working conceptual model of landscape responses to climate in eastern Grand Canyon (included in a manuscript recently submitted to GSA Bulletin) is more specific and detailed than previous models. It highlights the unique responses of drylands and is pertinent to the changes predicted with global warming. We propose to test and refine this model by investigating the predicted time-transgressive aggradation and incision moving down and up tributary streams, which we hypothesize is responsible for the unexpected antiphasing of tributary and mainstem Colorado River aggradation and incision. Our working hypothesis.that such antiphasing is caused on one hand by a lag time associated with the production of local sediment supply and the passing of that sedimentary signal down the catchment, and on the other hand by a delay in the progression of the signal of base-level fall up the catchment due to locally great sediment supply.is testable via detailed sedimentologic, stratigraphic, and especially geochronologic study. The second research emphasis is the bedrock incision of the Colorado River along its regional profile. We propose to add long-term incision rate determinations at two new study sites at key points along the length of the Colorado River to complement our existing data in eastern and western Grand Canyon. Comparison of the alluvial stratigraphy, deposit composition, and incision rates along this 450-km transect of the Colorado are basic to recording the river.s long-profile evolution and testing for hypothesized knickzones or waves of incision passing through the fluvial system in response to neotectonic forcing at the active Hurricane-Toroweap fault zone or much older drainage capture. The spectacular preservation and exposure of the complete hillslope-tributary-mainstem Quaternary stratigraphy at the three study sites, in combination with the use of three complimentary geochronologic methods, will elucidate the complex linkages between the local landscape and a continental-scale river and their responses to climatic and tectonic perturbations. In addition, this research will provide an enlightening comparison of the three dating methods, and will help complete the emerging understanding of landscape evolution of this famous area. Our involvement of researchers and students from diverse institutions, training of beginning scientists, and framework for communicating results to the public via the National Park Service insure that the proposed research will have broad impact.