BLACK MESA REVISITED: NEW OSL AGES PROVIDE EVIDENCE OF MIS3 AND MIS2 EOLIAN ACTIVITY ON BLACK MESA, NORTHEASTERN ARIZONA

Our research focuses on the most extensive eolian deposits on the Colorado Plateau located on Black Mesa in northeastern Arizona. Here we report new optically stimulated luminescence (OSL) ages obtained on sediments sampled in soil-stratigraphic context from eolian landforms. OSL dates from three falling dunes downwind from the Hopi Mesas indicate that eolian sediments were deposited in tributaries to the Tusayan Washes as early as 32.4 +/- 2.59 ka, with the largest volumes of sand deposited before 20 ka. In marked contrast, the oldest eolian deposits on mesa top positions date to the Pleistocene-Holocene climatic transition (~12-8ka). Our work compliments and parallels other studies in arid regions of the southwestern U.S. (e.g., Wells et al., 1990; Reheis et al., 2005; Holliday et al., 2006) that demonstrate large volumes of wind-blown sand were transported and deposited under late Pleistocene conditions. Environmental circumstances conducive to generating and/or transporting large volumes of sand, by both the fluvial and eolian systems, on the southern Colorado Plateau were evidently maximized during marine isotope stages 3 and 2, not during the middle to late Holocene as argued by Stokes and Breed (1993). Large volumes of sand with high infiltration capacity have likely dampened runoff and erosion providing a more stable landscape conducive to human occupation on Black Mesa.