HOLOCENE DUNE ACTIVITY IN SOUTHERN UTAH

Eolian deposits are common in the arid to semi-arid plateau regions of southern Utah. These partially stabilized dune fields are in areas historically affected by multi-annual droughts that have had lasting ecological and economic impact in the region. However, tree-ring reconstructions suggest that the region experienced more severe multi-decadal droughts in the past that have not been witnessed in modern times. Assuming past dune field activity relates to periods of decreased effective moisture, reconstructions of dune field activity has the potential to extend the records of aridity into early Holocene and can contribute to our understanding of natural climate variability and in the development of adaptive strategies for future climate change here.

Sand dunes are complex geomorphic landforms responsive to threshold climate conditions of aridity, wind power, vegetative cover and sediment supply. Using optically stimulated luminescence (OSL) dating and radiocarbon (14C) ages from charcoal we investigate eolian activity in two dune fields in southern Utah. Geomorphic maps were constructed for each dune field based on vegetation density and dune morphology. The stratigraphy, geomorphology, sedimentology (grain-size), and age control obtained from OSL and 14C dating are used to differentiate sediment packages and develop a chronostratigraphic record of dune activity. We interpret coeval dune activity in these dune fields as representing persistent (≥ decadal scale) regional droughts leading to changes in threshold conditions for dune mobility.

Here we present the chronostratigraphy of dune activity for the Kanab dune field, located 13 km northwest of Kanab, UT. OSL ages are also presented for San Rafael dune field, located about 25 km southwest of Green River, Utah. To best interpret the wind-drift potential for these sites we present analyses of modern wind regimes from climate stations across the region, reflective of late Holocene conditions, and discuss implications for paleowind conditions. As none of the dune fields are downwind of river systems, we present geochemical analyses to determine the sediment source for each dune field and test for changing sediment sources over time.