A Geomorphic Framework for Interpreting Continental Interior Mountain Belt Exhumation: The Laramide Example

解释大陆内部山带折返的地貌框架：以Laramide为例罗伯特安德森和伊丽莎白Safran-0003604在大约8000万到5000万年前，Laramide造山带抬升了一系列高的、逆冲断层边界的山脉，形成了大陆内部一些最引人注目的山脉景观。 这些山脉和其间的沉积盆地横跨怀俄明州、科罗拉多、蒙大拿州、犹他州和南达科他州的大部分地区。 解释了整个美国西部的构造和气候历史。S.取决于假设Laramide景观演变，但这种演变仍然不清楚。 争论的中心是两个地貌事件的意义、时间和原因，证据记录在一套独特的Laramide地貌中。 广泛的，高海拔的表面低的局部救济覆盖狭窄的基岩脊记录一段时间的下降，在大多数的Laramide范围的局部救济。 随后的区域侵蚀在山脉中形成峡谷，在盆地填充物中形成宽而深的洼地，并被许多河流阶地所打断。 以前的研究人员试图将这些地貌的发展与区域构造或气候强迫相关联。 然而，Laramide地貌显然不能以简单的方式反映外部强迫，因为有限的年代测定表明它们的年龄不同。 这一发现阻碍了建设一个区域连贯的地质历史，并到目前为止，没有过程为基础的模型已经提出来解释它。这项研究将解决地貌机制，侵蚀活动可能已经在不同的时间触发整个内部山区景观。 PI假设，即使是一个简单的强迫事件将产生复杂的侵蚀模式，给定一组联锁的范围和流域连接的综合排水网络。 他们将定量地解决这一假设，集中在挖掘插曲，形成了Laramide景观在新生代晚期。 他们的方法将包括：（1）通过使用宇宙成因放射性核素确定盆地内地貌和河流沉积物的年代，改善对Laramide盆地挖掘时间的限制;（2）通过描述花岗岩山脉的地貌特征，改善对挖掘前山脉形态的限制，他们认为花岗岩山脉是其他Laramide山脉古代状况的现代模拟;（3）建立区域和山脉尺度景观演化的数值模型，为数据解释提供机制框架。

ABSTRACTA Geomorphic Framework for Interpreting Continental Interior Mountain Belt Exhumation: The Laramide ExampleRobert Anderson and Elizabeth Safran EAR-0003604Between about 80 and 50 Myr ago, the Laramide orogeny uplifted a series of high, thrust fault-bounded mountain ranges that form some of the most dramatic mountain landscapes of the continental interior. These ranges and the intervening sedimentary basins stretch across much of Wyoming, Colorado, Montana, Utah, and South Dakota. Interpretations of the tectonic and climatic history of the entire western U. S. hinge on assumptions about Laramide landscape evolution, and yet this evolution remains ill-understood. The debate centers on the significance, timing, and cause of two geomorphic episodes, evidence for which is recorded in a suite of distinctive Laramide landforms. Widespread, high-elevation surfaces of low local relief capped by narrow bedrock spines record a period of declining local relief in most of the Laramide ranges. A subsequent period of regional erosion produced canyons in the ranges and broad, deep depressions in the basin fills, punctuated by numerous river terraces. Previous researchers have tried to correlate the development of these landforms with regional episodes of tectonic or climatic forcing. However, the Laramide landforms apparently do not reflect external forcing in a simple way, because limited dating suggests that they vary in age. This finding has hindered the construction of a regionally coherent geologic history, and to date no process-based model has been put forth to explain it.This study will address geomorphic mechanisms by which erosional activity might have been triggered at different times throughout this interior mountain landscape. PIs hypothesize that even a simple forcing event would produce complex erosional patterns, given a set of interlocking ranges and basins linked by an integrated drainage network. They will quantitatively address this hypothesis, focusing on the exhumational episode that shaped the Laramide landscape during the late Cenozoic. Their approach will involve: 1) improving constraints on the timing of Laramide basin exhumation by using cosmogenic radionuclides to date landforms and deposits of fluvial origin within the basins; 2) improving constraints on pre-exhumation range morphology by characterizing the geomorphology of the Granite Mountains, which they view as a modern analogue to the ancient condition of other Laramide ranges; and 3) developing numerical models of both regional and mountain range-scale landscape evolution to provide a mechanistic framework for data interpretation.