NOVEL APPLICATIONS OF LUMINESCENCE DATING CONSTRAIN THE AGE OF BARRIER CANYON STYLE ROCK ART IN CANYONLANDS NATIONAL PARK, UTAH

Barrier Canyon style (BCS) rock art is a famously impressive and controversial style of pictograph unique to the middle Colorado Plateau. The age of BCS art remains unknown, despite a broad range of hypotheses and previous attempts at direct radiocarbon dating. It has been proposed that BCS rock art is as old as the latest Pleistocene peopling of the continent, to as young as very latest Fremont (~600-700 years old), with most scholars preferring a pre-Fremont origin in either early or late Archaic time. This study rules out several of these hypotheses, constraining the age of BCS art through the OSL dating of an alluvial terrace deposit and a rockfall event that have incontrovertible cross-cutting relations to the type BCS rock art panel, the Great Gallery in Canyonlands National Park.

Our prior mapping and chronostratigraphic work in the Horseshoe drainage documented correlatable alluvial terraces. Relations at the Great Gallery indicate that the BCS art must be younger than the episode of incision between T2 and inset T1, as it exposed the previously buried alcove surface that the rock art lies upon. Single-aliquot and single-grain ages of terrace deposits (most are minimum-age model estimates due to partial bleaching) indicate the incision happened between 9 and 3 ka. This provides a maximum age constraint, with the rock art very likely being less than 6000 years old.

For a minimum-age constraint, we have dated a rockfall event (a first for OSL methods, to our knowledge) that removed part of the figures at the Great Gallery panel. We analyzed both the down-facing rock surface of a pigmented talus block and the near-surface grains of sediment the boulder landed upon. Single-grain results indicate the rockfall is about 900 years old. An AMS radiocarbon date from an opportune leaf trapped beneath the talus boulder confirms this age for the rockfall.

BCS rock art at its type locality therefore can be constrained to between ~6000 and 900 years old. Archaeologically, this indicates a late Archaic or early Fremont origin, ruling out older and younger hypotheses.