Trialing the application of controlled exposure experiments for optical exposure dating on quartzite quarry surfaces in Washington State.

Optically stimulated luminescence (OSL) depth profiling utilizes an OSL-at-depth signal to extrapolate an exposure age from rock surfaces. Exposure ages are commonly obtained by fitting the forms of luminescence depth profiles, which depend on parameter estimates of light attenuation and defined rates of luminescence bleaching. Current procedures for obtaining these parameters for a rock surface require matching luminescence depth profiles from compositionally and morphologically matched rock surfaces with known exposure ages, which limits the accuracy and applicability of the technique. A modified procedure is presented to improve the accuracy and applicability of luminescence surface exposure dating, that aims to reliably determine light attenuation and luminescence bleaching parameters directly from the rock surface of interest using luminescence saturated samples subjected to controlled light exposures. Both this proposed 'controlled exposure experiment' technique and the proximal rock matching technique were tested on decade surface exposed quartzite quarry samples from eastern Washington, USA. Parameters derived from the controlled exposure technique, using natural sunlight equivalent to the sampling site, produced the most accurate ages. Data scatter in the luminescence depth profiles substantially limit age accuracies of all techniques. However, the trials of the controlled exposure experiment techniques show procedural insight and potential in offering comparable depth profiling applications to current extrapolative techniques at sites where either no proximal rock surfaces exist, or proximal samples are deemed problematic. A combination of incorporating equivalent solar paths and average solar radiations of the site may provide the most accurate parameter extrapolations for controlled exposure experiments, and the technique should be investigated with more refined datasets. • OSL depth profiles produced from two sample sources on the same quarry site are compared. • Controlled exposures using natural site-equivalent sunlight show promise for extrapolating parameters for exposure dating. • Insight into how simulated and natural sunlight exposures uniquely influence luminescence depth profiles. [ABSTRACT FROM AUTHOR]