Desert pavement morphology and dynamics, Big Bend National Park, Texas

Desert pavements consist of a one- to two-layer thick surface armory of stones overlying finer, virtually stone-free material which often adopts the appearance of a meticulously tiled mosaic. They cover half of the arid land surface in North America and are usually concentrated on low-sloping alluvial fans and desert piedmont surfaces. McFadden et al. (1987) suggested the accretionary mantle model of desert pavement formation, following research on pavements atop the Cima volcanic complex in the Mojave Desert. However, the wide-spread applicability of this model to diverse lithologies and geomorphic environments remains to be seen. No research has been conducted on desert pavement at Big Bend National Park (BBNP), Texas, despite the occurrence of well-developed pavements in the park and surrounding regions of the Chihuahuan Desert. This research highlights three diverse desert pavement sites at BBNP through a detailed geomorphic assessment including location of desert pavement distribution, classification into surface mosaic units, examination of sediment and soil characteristics, and determination of lithology of the pavement clasts. At each BBNP study area, values for desert pavement clast size, sorting, and percent ground cover were compared to the parameters set forth in Wood et al. (2002) to classify the desert pavements into surface mosaics based on degree of development. Sediment analysis and soil profile photographs were used to characterize the surface sediments and subsurface soil horizons. To determine geologic origin, dominant lithologies of the pavement clasts were compared to outcrop and bedrock samples and to published geologic maps of BBNP. Desert pavements in this study differ significantly in surface texture, soil characteristics, geologic origin, and degree of development compared to the typical pavements of the Mojave Desert used in much of the fundamental research. Results indicate that the desert pavements at BBNP may not have been derived from bedrock and evolved in-situ, as suggested by the accretionary mantle model. Primarily, a combination of fluvial processes and weathering appears more influential to desert pavements in the semi-arid environment of BBNP. This study presents a new perspective on desert pavement geomorphology in Big Bend National Park and serves as a baseline for continued research.