Active salt deformation and rapid, transient incision along the Colorado River near Moab, Utah

Abstract

In certain settings, erosion is driven by and balanced with tectonic uplift, but the evolution of many landscapes is dominated by other factors such as geologic substrate, drainage history, and transient incision. The Colorado Plateau is an example where these controls are debated and where salt deformation is hypothesized to be locally active and driven by differential unloading, although this is unconfirmed and unquantified in most places. We use luminescence-dated Colorado River terraces upstream of Moab, Utah, to quantify rates of salt-driven subsidence and uplift at the local scale. Active deformation in the study area is also supported by patterns of concavity along tributary drainages crossing salt structures. Subsidence in Professor Valley at a time-averaged rate of _500 m/Myr (meters/million years) is superimposed upon rapid bedrock incision rates that increase from _600 to _900 m/Myr upstream through the study area. Such high rates are unexpected given the absence of sources of regional tectonic uplift here. Instead, the incision rate pattern across the greater area is consistent with a transient signal, perhaps still from ancient drainage integration through Grand Canyon far downstream, and then amplified by unloading at both the broad regional scale and at the local canyon scale. ©2015. American Geophysical Union. All Rights Reserved