HOLOCENE DUNE ACTIVITY IN HIGH PLATEAU DESERTS – SOUTHERN UTAH

Modern high elevation deserts occur across southern Utah on the central Colorado Plateau. Steep, rocky ridges of Paleozoic and Mesozoic sedimentary sequences have eroded to form a bench and step landscape, cut by steep canyons and arroyos. Sand dunes, mostly stabilized by sparse scrub-steppe vegetation, with some actively migrating sand dunes, typify the modern bench landscapes. In addition to supporting a diverse, unique ecological community of plants and animal, the region has an extensive prehistoric cultural record. Migrations of Ancestral Puebloan communities within this region is concurrent with multi-decadal droughts seen in tree-ring records from peripheral regions. Multi-decadal scale droughts, not experienced in modern times, are a concern based on predicted future climate change. Improved understanding of past aridity can inform adaptive strategies for current communities impacted by increased, longer term aridity here.

Sand dunes are complex geomorphic landforms responsive to threshold climate conditions of aridity, wind power, 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. Geomorphic maps for each dune field based on vegetation density and dune morphology are constructed as a first order evaluation of landscape processes. 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. In addition to the record of past dune mobility we present analyses of modern wind regimes from climate stations across the region, reflective of late Holocene conditions. We present geochemical and grain size analyses 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 records.