PRELIMINARY GEOCHRONOLOGY OF SAND RAMPS, CORAL PINK SAND DUNES, UTAH

Sand ramps are topographically-controlled features that accumulate aeolian, fluvial, and alluvial sediments, and have been shown to preserve long records of landscape evolution in arid and semi-arid regions (Lancaster and Tchakerian, 1996). This study investigates the geochronology of relict sand ramps in the Coral Pink Sand Dunes (CPSD), Utah, a small (18 km2) dune field on the northwest Colorado Plateau. Optically stimulated luminescence (OSL), radiocarbon dating, and soil profiles are used to understand past climate-controlled geomorphic changes preserved in these features.

The CPSD sand ramps are located in the southeastern portion of the dunefield, against the base of the Moquith Mountains. Incision of Sand Wash, an ephemeral channel, has separated the sand ramps from the modern, active dune field. Incision has also formed deep tributary channels beginning from the base of the Moquith Mountains and graded to the local base level created by Sand Wash. Sand ramps are considered to be relict structures because these channels are not being infilled by aeolian or alluvial sediments. Samples were collected from exposed vertical faces in Sand Wash and tributaries, at locations where aeolian deposits show original sedimentary structures and are capped by debris flow deposits up to 7 meters thick.

Previous work in the active region of the CPSD field shows multiple phases of past aeolian activity correspond to periods of regional aridity (Wilkins et al., 2007). While OSL ages of shallow aeolian exposures in the active core of the dune field extends to the middle Holocene (up to 4 Ka), the topographically-controlled sand ramps preserve a longer record of deposition. Preliminary OSL ages show aeolian activity on the sand ramps occurred during major Quaternary climate change events, including a late Pleistocene glacial-interglacial transition (59.15 +/- 19.04 Ka) and warming phase (14.82 +/- 3.18 Ka).

A chronostratigraphy for the sand ramps will be constructed from additional aeolian deposits and overlying debris flows, and used to develop possible models for sand ramp formation and dissection from the modern dune field. By comparing our chronostratigraphy to those of nearby fluvial terrace systems and paleo-drought/flood reconstructions, we can understand how Quaternary climate change influenced this landscape.