212-4 Neogene Uplift of the North American High Plains: Insights from Landscape Evolution Modeling

Session: Reconstructing Earth Surface Processes in Orogenic Systems

Presenting Author:

Authors:

Abstract:

Rivers that drain the Southern Rocky Mountains and cross the High Plains have incised deeply into the surface of the plains, yet the cause of erosion has remained elusive. The Miocene Ogallala Formation, which caps the landscape and has been fluvially eroded near the mountain front, provides a maximum age of approximately 5 Ma for the onset of incision. Researchers have proposed that rivers are responding to long wavelength, late Cenozoic tectonic tilting. However, modeling efforts that have focused on the geomorphology of the plains have suggested that tilting a landscape tends to concentrate erosion in the distal parts of the fluvial system, rather than near the mountain front.

We revive the effort to model the landscape evolution of the High Plains by treating the Rocky Mountains and High Plains as a continuous geologic system. To study how this landscape responds to tilting, we use a 2D landscape evolution model that calculates sediment transport and bedrock erosion in gravel-bed rivers. We conduct a series of experiments with the goal of understanding how the modeled landscape responds to tilting over a 5 my timescale.

When we explicitly model the gravel flux from mountains to plains, the model produces a distinct signal of erosion concentrated at the mountain front. The model provides a physical explanation for this phenomenon: erosion rate depends on both the erodibility of bedrock, which increases dramatically between the mountains and the plains, and the sediment flux, which provides cover that inhibits erosion. Because sediment is generated directly through bedrock erosion, the sediment flux exported from the mountains is low due to their low erodibility. A low sediment flux from the mountains results in rivers that are sediment-starved when they encounter the plains and can therefore scour into that surface efficiently. Fundamentally, it is the mismatch between bedrock erodibility, which increases instantaneously across the boundary between mountains and plains, and sediment flux, which increases gradually downstream, that causes incision to be concentrated at the mountain front.

Our result demonstrates that tilting is a viable mechanism to induce erosion at the contact between the Rocky Mountains and High Plains. However, the model does not produce the full depth of incision observed today, suggesting that other factors have also shaped the landscape since the late Cenozoic.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7818

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