HOLOCENE CHRONOSTRATIGRAPHY AND PALEOCLIMATE IMPLICATIONS OF DUNE FIELDS ACROSS SOUTHERN UTAH

Sand dunes are threshold systems capable of recording past changes in effective moisture and aridity, and are sensitive to sustained, decadal-scale drought. Records of past drought can provide a reference to past climate variability and expected extremes in an area. Such records provide data for climate modeling refinement, as well as regional and community strategic planning efforts.

We use optically stimulated luminescence (OSL) dating and radiocarbon ages from charcoal to investigate eolian activity in two dune fields in southern Utah, located 250 km apart in the central Colorado Plateau. Dune forms in this semi-arid region have been mapped and auger samples obtained from mapped units, typically to depths of 3.5 m with two OSL samples from each core. In addition to OSL ages, chronostratigraphic reconstructions are based on grain size analysis, geochemistry, organic and magnetic properties, and identification of paleosols (representing periods of dune stability). Sand supply for both dune fields is largely derived from local weathering of the Jurassic Navajo Sandstone Formation.

The Kanab dune field, located 13 km northwest of Kanab, Utah, covers approximately 12.5 km² and is oriented WSW. Active and stabilized parabolic and other dune forms and sand sheets have been identified. Initial OSL results from the windward (presumed older) end of the dune field have identified at least four periods of dune activation between 8 and 2 ka. The San Rafael Desert dune field, located approximately 25 km southwest of Green River, Utah is composed of multiple dune fields encompassing a much larger area (>2500 km² ). Linear dunes oriented NNE dominate the region, but isolated dune fields of barchanoid and parabolic dunes are also present. Preliminary OSL ages identify at least five periods of dune formation between 13 and 0.5 ka.

We interpret coeval dune activity the dune fields to represent persistent (at least decadal scale) regional droughts. Alternatively, chronologically distinct patterns of dune activity are interpreted to reflect local disturbances or changes in vegetative cover and sand supply. Further analyses will refine chronologies of both sites for regional comparison between dune fields and with existing proxy records of Holocene climate in the Colorado Plateau.