2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 25
Presentation Time: 1:30 PM-5:30 PM


WILKINS, David, Geosciences, Boise State Univ, 1910 University Drive, Boise, ID 83725, FORD, Richard L., Dept of Geosciences, Weber State Univ, 2507 University Circle, Ogden, UT 84408-2507, CLEMENT, William, Center for Geophysical Investigation of the Shallow Subsurface, Boise State Univ, 1910 University Drive, Boise, ID 83725 and NICOLL, Kathleen, School of Geography and the Environment, Univ of Oxford, Mansfield Road, Oxford, OX1 3TB, dwilkins@boisestate.edu

The Coral Pink Sand Dunes, an 18 km2 dune field on the Colorado Plateau along the Utah-Arizona stateline, is the site of an ongoing investigation into factors influencing dune system development. A combination of methods is used to study this dune system's response to climate change over the past 500 years.

Ground-penetrating radar imagery reveals bounding surfaces (seen as reflections) and soil layers (seen as signal attenuating layers) under active dunes, indicating the current state of dune activity is a reactivation from previous periods of stability. A radiocarbon age on the base of one of these exhumed soils in the active core of the dune field suggest a period of increased moisture beginning around 470 B.P., placing its formation at the beginning of the little Ice Age (LIA, ~1400-1850 CE). Cross-bedded aeolian sands capped by the soil were OSL dated using the single-aliquot regeneration-dose method; these ages indicate the buried sediments to have been active prior to the LIA. A disjunct stand of ponderosa pine in the extreme southern and lowest edge of the dune field provides a dendrochronological perspective; cores were collected from several trees, visually and graphically cross dated. These results reveal episodic establishment, with the oldest tree dating back to before 1560 CE, or near the beginning of the LIA. Radiocarbon ages were also obtained for several exhumed or partially buried ponderosa pine snags in the active core of the dune field that died ca. 200 B.P.

Together, the evidence suggests a period of aeolian activity preceded the Little Ice Age. Around the beginning of the LIA, increased effective moisture resulted in dune stabilization and allowed for establishment of the ponderosa below their current lower extent along the Vermillion Cliffs into the dune field. Migration of the trees may have been aided by periodic flooding, with valley-side canyon discharge from the Vermilion Cliffs dispersing seed to the lower dune field. During the LIA, dune activity was episodic with at least one sediment pulse burying and killing a stand of large ponderosa trees. The trees in the southern portion of the dune field have survived because diminishing sediment availability has limited dune movement while providing enhanced edaphic moisture conditions. Limited regeneration of new trees indicates this stand to largely be a relict of past conditions.