FLUVIAL NETWORK EXPANSION INTO CLIFFBAND LANDSCAPES: PRELIMINARY WORK ON THE ORIGINS AND RETREAT OF MIGRATING TRANSVERSE ESCARPMENTS ON THE COLORADO PLATEAU, USA

Cliff bands and strike valleys are common features in landscapes of dipping sedimentary rock. Channel networks within strike valleys exhibit a variety of morphologies, ranging from internally-drained basins to strike-parallel streams joining larger, strike-perpendicular rivers. The geologic and environmental conditions that cause these differences are complex and likely depend on factors such as rock strength, valley width, dip angle, layer spacing, climate, regional uplift, and fluvial incision rate. In this presentation, we discuss a new mechanism that connects the evolution of a strike valley channel network to baselevel changes within the greater, regional river basin.

In the Tununk and Blue Gate Shale strike valleys of central Utah, dozens of small (~10 m), strike-perpendicular escarpments (which we call Migrating Transverse Escarpments, or MTEs) are retreating away from tributaries of the Colorado River. These features appear to be created by base level perturbations within the tributary river catchments and subsequently transmit those signals into the strike valleys. As they retreat, MTEs expand the river network by capturing and integrating flat-lying reaches that either are internally drained or flow over the edge of an underlying escarpment. This process may be of particular importance when MTEs form near a drainage divide between large rivers, priming them to facilitate regional-scale river basin reorganization.

We begin to study the origins and retreat dynamics of MTEs throughout central Utah by establishing a long-term monitoring site at a single MTE (TNNK-1a). The age of the MTE is constrained by dating fluvial terraces that pre and post-date its formation using cosmogenic ¹⁰Be, radiocarbon, and OSL techniques. Ephemeral channel and hillslope erosion rates are measured using analogue erosion pins, regolith creep markers, and SFM photogrammetry; these are coupled with rainfall, regolith moisture, and regolith / atmospheric temperature measurements from remote sensors to characterize the impact of individual weather events on surface erosion. Field data will be used to calibrate numerical models that elucidate the extent to which MTEs may have shaped the Colorado River basin by assessing their behavior under various climate regimes and base level changes.