Multiscale analysis of dune reddening in the Sonoran Desert, Arizona, USA

The Parker Dunes, the only dune field in the Sonoran and Mojave Deserts of North America experiencing visible dune reddening, range in age from active to nearly 30,000 years before present. Different aerial and satellite remote sensing platforms reveal progressive reddening over time, as do redness ratings using Munsell color. X-ray dot maps of quartz sand grains indicate that iron X-rays are generated from coatings that cover progressively more grain area as the dunes age. Nanoscale transmission electron microscopy reveals that iron is incorporated into mixed-layered illite-montmorillonite clays, forming iron-rich “stringers” observable in back-scattered electron imagery at the micrometer scale. Light microscopy of ultrathin sections reveal these grain coatings to have an orange appearance. Our linking of iron-clay coatings at multiple-scales across multiple methodologies can only be considered preliminary because of the limited number of samples analyzed. Still, this research provides the first insight into dune color evolution in the Sonoran Desert.