The Evolution of a Perched, Low-Relief, Soil-Mantled Landscape in the Pinaleño Mountains, SE Arizona

Abstract:

To shed light on the processes driving weathering, soil production and erosion in steep landscapes that maintain steep, rocky catchments where soil cover is pervasive, we examine relationships among catchment-mean erosion rate, mean soil thickness, and soil production efficiency on the low-relief, soil-mantled landscape with uniform lithology and climate at the crest of the Pinaleño Mtns in SE Arizona. Both above and below knickpoints on channels draining the upper low-relief landscape, but within the narrow band of elevation where climate is uniform, I utilize high-resolution soil thickness measurements coupled with terrestrial cosmogenic nuclide soil production rate measurements to quantify the efficiency of soil production in this landscape. I present shallow seismic survey data to describe variability in soil thicknesses at a high-resolution scale useful to describe hillslope process. These data are calibrated by soil pit measurements of soil down through saprolite and fractured bedrock.

Channel profiles around the edges of the low-relief landscape suggest a transient response to some tectonic disturbance, either due to rock uplift and basin subsidence during Basin and Range tectonic forcing, or more recent incision and base-level drop in adjacent drainage systems. A suite of catchment-averaged erosion rates recently measured along the flanks of this range support the hypothesis that this upper transient surface has been preserved after a late Miocene-Pliocene Basin and Range disturbance that has since been followed by slow topographic decay.