IMPACTS OF CLIMATE CHANGE ON THE FORMATION AND STABILITY OF LATE QUATERNARY SAND SHEETS AND FALLING DUNES, SOUTHERN COLORADO PLATEAU, USA

Stabilized sand dunes that exhibit incipient to well-developed soil profiles are common on the southern Colorado Plateau. Eolian sediments are often thought to be active during arid conditions and stabilized as effective precipitation increases. In this study, detailed geomorphic mapping and analysis of soil-stratigraphy, in conjunction with optically stimulated luminescence dates from eolian sand dunes of the Black Mesa region of northeastern AZ, reveal a major period of eolian deposition from 17-35 ka and a period of widespread dune stabilization from 8-12 ka. Both periods are characterized by higher effective precipitation than the present throughout the region (e.g. Anderson, 2000). The mid- to late Holocene eolian record indicates some localized reactivation of previously stabilized dune forms as well as localized new dune construction resulting from local increases in sediment supply. Cooler, wetter, and more variable climatic conditions during MIS 3 and 2 resulted in increased sediment supply from stream channels and floodplains, filling tributary canyons with eolian sediments up to 60 km downwind from their source. Topographically controlled falling dunes and sand ramps on Black Mesa are preserved because of their geomorphic position and provide evidence of the paleoenvironmental state of the fluvial and eolian systems before, during, and immediately after the last glacial maximum on the southern Colorado Plateau.