Structural control on landscape evolution: Examples from the Colorado Plateau
Abstract
Bedrock fracture density is widely thought to control bedrock weathering rates, yet few case studies exist in which bedrock fracture density has been demonstrated to control erosion rates or topographic development. In the Colorado Plateau many Laramide-style monoclines and anticlines have become topographically inverted, i.e. structural highs have become topographic lows, and in some cases these structures have been bisected by large rivers along the path of maximum structural curvature (MSC). In this talk I describe efforts to test the hypothesis that such inversions occur because bedrock fracture density is correlated with structural curvature, i.e., that outer-arc stretching has led to enhanced deformation and fracture development in zones of MSC, and that such inversions were favorable places for river capture. To test the hypothesis that bedrock fracture density is proportional to structural curvature, I used digital analyses of geologic maps to reconstruct fold geometries and, from those, structural curvature. I demonstrate that fracture density in the East Kaibab and Raplee Ridge Monoclines mapped continuously using a combination of field measurements and analyses of airborne and terrestrial lidar data, correlate strongly with structural curvature. Further, I show that erosion rates computed by mapping the degree of incision into the regional structural surface also correlates strongly with structural curvature. I present the results of a numerical model that quantifies the influence of structural curvature and fracture density on weathering and erosion. This model reproduces the flatirons, hogbacks, and topographic inversions characteristic of the region. To test the hypothesis that rivers preferentially follow paths of MSC, I develop a technique, inspired from the computational polymer physics literature, that identifies all possible river paths subject to relevant constraints, such as paleotopography. This approach enables the hypothesis of structural control on the establishment of transverse drainage across structures to be quantitatively assessed relative to the null hypotheses of antecedence and superposition. The results from this new method demonstrate the importance of structural control in the transverse drainage of several well-known examples in the Colorado Plateau.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP41D..06P
- Keywords:
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- 1815 Erosion;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1861 Sedimentation;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY