Surface Rock Controls on the Development of Desert Varnish in the Mojave Desert, California.

While absolute dating techniques have provided age estimates of desert pavement surfaces in a variety of arid landforms, some surfaces remain unsuitable for traditional dating techniques.  Surface age and stability have a major role in determining the depth and characteristics of the V horizon as well as the development and extent of desert varnish, which occurs as a melanized surface on the dorsal sides and a rubified surface on the ventral sides of rocks composing the desert pavement.  The objectives of this study were to investigate how varnish intensity and color were related to rock properties (including height above and depth below the surface, roughness, slope, density, volume, surface area, and lithology) and how rock varnish was related to landform age. Additionally, the relationship between varnish development and V horizon depth was studied. Approximately 350 rocks ranging from 5 to 50 cm in diameter were collected from 17 previously dated sites across the Mojave Desert, California.  In the laboratory, photographs were taken to render high-resolution three-dimensional models of each rock that contained color (RGB) data. Color information was converted to the CIELAB color space and extracted from the models to quantify the development of rock varnish and its relationship to rock properties.   Initial results suggest a correlation between embedding depth and strength of varnish development that could be used to determine surface stability.  Relationships between V horizon depth and rock varnish development along with a predictive model for varnish color will be presented and discussed.