SEDIMENT FLUX AND CENOZOIC INCISION OF THE NORTH AMERICAN HIGH PLAINS

The dramatic relief exposed along the Front Range of Colorado is largely a result of post-Miocene excavation of the sedimentary rocks underlying the North American High Plains. Despite numerous studies seeking to understand whether this incision was driven primarily by changes in climate or tectonics, the cause of this late Cenozoic incision remains controversial. We evaluate this problem from the perspective of sediment flux, using simple 1-D and 2-D geomorphic models to explore the patterns of incision caused by changes in sediment load in rivers draining the eastern Rockies. We compare these patterns of incision to those driven by tectonically-induced changes in baselevel, and to the topography of the modern Rockies and High Plains. Based on our results, we suggest that the Cenozoic incision of the western High Plains could have occurred without a tectonic forcing, and could instead have resulted purely from changes in sediment flux. Such changes could have been brought about by a changing climate, or by changes in the lithology encountered by rivers flowing perpendicular to the range front. While this incision would have given rise to a modest isostatic response from the lithosphere, our modeling suggests that changes in hydrology and sediment flux could have been the initial trigger for late Cenozoic incision of the eastern Rockies and adjacent High Plains.