LATEST PLEISTOCENE PALEOHYDROLOGY OF THE WILLCOX BASIN, SOUTHEASTERN ARIZONA AND IMPLICATIONS FOR SOUTHWEST PALEOCLIMATE

Radiocarbon and stratigraphic evidence from paleoleke shoreline and paleowetland deposits indicate that, following the Last Glacial Maximum (~24 – 19 Ka cal BP), conditions along the floor of Willcox Basin in southeastern Arizona (32^oN) were dominated by persistent wetlands that were periodically submerged during transgressions of paleolake Cochise. Lake level reached 1,272-1,275 m at ~19.0 Ka cal BP, 16.9 - 16.3, 15.2 - 15.0, and 14.4 - 13.8 Ka cal BP, as well as during a highstand which remains undated. Possibly synchronous with this event, an abrupt rebound in the water table caused deposition of organic-rich, fine grained wetland deposits near 1,274 m beginning at ~12.9 Ka cal BP. After 10.8 Ka cal BP, the lake had permanently regressed below 1,271 m, where extensive wetlands gave way to spatially limited and ephemeral spring activity. The proximity in timing of highstands in the Estancia Valley in central New Mexico (34^oN) and several other closed basins throughout the Great Basin and Mojave suggests a common climatic cause with well-documented changes elsewhere in the northern Hemisphere. Paleohydrologic changes across western North America and the mid-latitudes during the last deglaciation resulted from hemispheric cooling and equatorward shifts in the Westerlies precipitation belt, induced by disruption of the Meridional Overturning Circulation by meltwater pulses and Heinrich events.