SHIFTING SANDS: DUNE ACTIVITY RECORDS OF NATURAL MOISTURE VARIABILITY IN THE CENTRAL COLORADO PLATEAU

Eolian deposits are common in modern, high elevation deserts across southern Utah in the central Colorado Plateau. Dune fields, mostly stabilized by sparse scrub-steppe vegetation, with some actively migrating sand dunes, typify the modern landscapes. Historically this region is affected by multi-annual droughts with adverse ecological and economic impacts. However, tree-ring records from peripheral areas record multi-decadal droughts during the late Holocene coinciding with prehistoric migrations and settlement abandonments in Ancestral Puebloan communities. Similar long-duration droughts have not been witnessed in modern times. Reconstructions of dune field activity can provide records of aridity extending into early Holocene due to the linkage between dune activity and decreased effective moisture. Understanding natural moisture variability in the region can aid in our development of adaptive strategies for future climate change.

Sand dunes are complex geomorphic landforms responsive to threshold climate conditions of aridity, wind velocity, vegetative cover and sediment supply. We investigate eolian activity in two dune fields in southern Utah using optically stimulated luminescence (OSL) dating and radiocarbon (14C) ages from charcoal, filling a regional gap in available paleoclimate records. Geomorphic maps constructed for each dune field using dune morphology and vegetation density form the basis for our systematic sampling plan. Stratigraphy, geomorphology, sedimentology (grain size) and age control obtained from OSL and 14C dating are used to differentiate sediment packages and develop dune chronostratigraphy. We interpret contemporaneous dune-field activity to represent persistent, regional droughts leading to changes in threshold conditions for dune mobility.

Here we present a chronostratigraphy of dune activity for the Kanab dune field in southwestern Utah and review preliminary chronostratigraphy for San Rafael dune field in southeastern Utah. Geochemical and grain-size analyses are used to determine the sediment source for two dune fields and discuss geomorphic processes contributing to dune field development. Finally, we discuss the implications for the Holocene climate changes recorded in our dune activity record.