Date of Award

5-2010

Degree Type

Thesis

Degree Name

Departmental Honors

Department

Geology

Abstract

Barrier Canyon Style rock art (BCS) is a unique rock art style indigenous to the middle Colorado Plateau that is of an unknown age and formed by a combination of wall preparation, rock pecking, and application of multiple pigments. It is characterized by broad-shouldered, mummy-like figures that commonly lack limbs and facial details but are accompanied by animated and realistic representations of animals. The age of BCS art remains unknown in spite of attempts to radiocarbon date accessory brush fibers in the mineral-based pigment. Yet a range of age hypotheses exist, from as young as 1600 AD to as old as the initial peopling of the continent, all based on stylistic comparisons to other rock art and figurines. This study attempts to constrain the age of BCS art by optically stimulated luminescence dating (OSL) alluvial terraces that have demonstrable cross-cutting stratigraphic relations to the type BCS rock art panel, the Great Gallery.

Horseshoe Canyon, in Canyonlands National Park of southwestern Utah, contains a series of preserved alluvial terraces that record the burial and exposure of the alcove that now hosts the BCS Great Gallery, bracketing the window of time when it was physically possible to create the art. This type panel must be younger than the erosional time period between deposition of the T2 and T1 alluvial terraces when the alcove wall became exposed. Alluvial samples from the highest exposed and preserved T2 terrace in the drainage were collected in metal tubes and analyzed using the single-aliquot regenerative (SAR) protocol of Murray and Wintle (2000). Dose-rates were calculated from bulk sediment samples using the methods of Aitken (1998) and adjusted for local shielding of cosmic radiation by bedrock overhangs.

Results from several of the alluvium samples exhibit partial bleaching issues common in ephemeral stream deposits, requiring a minimum age model analysis. Age estimates produced in this study suggest that it was not physically possible for the Great Gallery to have been created prior to 6 ka BP, rejecting several earlier hypotheses for its temporal association.

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Faculty Mentor

Joel Pederson