BLACK MESA REVISITED: NEW OSL DATES PROVIDE EVIDENCE OF LATE FULL-GLACIAL AND EARLY HOLOCENE EOLIAN ACTIVITY ON BLACK MESA, NORTHEASTERN AZ

Eolian deposits and landforms dominate much of the Colorado Plateau, however, the ultimate sources of sand and the relationships of these deposits to climate change are still not well understood despite decades of study. In particular, 1) age control in eolian systems has been problematic until recent advances in optically stimulated luminescence (OSL) dating techniques and 2) the dynamic operation of eolian systems (e.g. plant-soil-eolian landform interactions) is more complex and interactive than previously assumed. For example, once large volumes of sand are emplaced as an erg, what set of environmental factors enable stabilization or destabilization of the deposit?

Our recent research focuses on the extensive eolian deposits on Black Mesa in northeastern Arizona. We will report new OSL ages obtained on sediment that was sampled from eolian landforms with a high degree of preservation potential. Preliminary OSL dates on a stratigraphic section described in a falling dune downwind from the Hopi Mesas indicate that the eolian sediment was deposited between17.2 ± 0.81 ka and 9.68 ± 0.25 ka. Lack of soil development within the eolian deposits of the falling dune suggests that deposition was more or less continuous from late full glacial conditions to the earliest Holocene in this location. Our data do not replicate results and interpretations of Stokes and Breed (1993) who postulated that large volumes of sand were initially deposited on the nearby Moenkopi Plateau at ~100 ka and that subsequent eolian activity was restricted to relatively minor reworking and redeposition of these older materials predominantly during the Holocene. Instead, 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 show wind-blown sand was transported and deposited not only during hot and dry interglacial periods, but also during the cooler and effectively moister late Pleistocene. Environmental circumstances conducive to generating and/or moving large volumes of sand on the southern Colorado Plateau may have been maximized during full glacial conditions and/or the glacial transition.