ORIGIN AND LATE QUATERNARY EVOLUTION OF THE MOHAWK SAND DUNES IN SOUTHWESTERN ARIZONA

The Mohawk sand dunes, covering an area of ~145 km² in southwestern Arizona, preserve eolian stratigraphic archives with significant potential to improve our understanding of late Quaternary landscape changes in the northern Sonoran Desert. We hypothesize that the origin and evolution of the Mohawk dune system is connected to three potential sand sources; the lower reach of the Gila River, alluvium derived from local granitic mountain ranges, and/or the northeastern extension of the Gran Desierto erg. Using trace element geochemistry, mineralogy, historic wind data, and luminescence dating, the objectives of this study were to discover the origin of the eolian sand in the Mohawk dune field and identify connections between periods of dune activity, local alluvial histories, and paleoclimatic proxy records. The results of this research reveal the Mohawk sand dunes have a complex origin tied to local granite-derived alluvial sources and late Pleistocene aggradation cycles along the lower Gila River. Close temporal associations between alluvial deposition and periods of dune construction over the late Quaternary signify the Mohawk dunes are largely a supply-limited system. However, sand supplies currently stored in stabilized outlier dunes upwind of the main dune field suggest sediment availability is also a factor. Post-LGM climate change had a pronounced effect on the evolution of the Mohawk dunes by promoting fluxes in regional groundwater levels and limiting sand supply to the northern dune system following late Pleistocene incision of the Gila River. During the Holocene, eolian sands were sourced almost exclusively from local granitic alluvium and the timing of major dune activity was closely associated with periods of alluvial fan and trunk drainage sedimentation numerically dated to 10-8, 3-2, and 0.8-0.5 ka. This study highlights the often complex connections between alluvial sediment supply, climate change, and dune construction in southwestern dune fields.