LUMINESCENCE DATING OF FLUVIAL SEDIMENTS FROM CHUPADEROS CANYON NEW MEXICO: COINCIDENCE BETWEEN TRADITIONAL METHODS AND ADVANCED TECHNIQUES, OR NOT?

Over the past decade luminescence dating has been a valuable tool in assessing the timing and frequency of Quaternary fault activity in and around Los Alamos National Laboratory on the Pajarito Plateau of northern New Mexico. Past efforts have utilized both thermoluminescence (TL) and Infrared-stimulated luminescence (IRSL) measurements made on poly-mineral fine-silts. These dating efforts required numerous sub-samples or aliquots to determine one age (multi-aliquot additive dose techniques ? MAAD) and are now considered ?traditional? methods. The latest, most advanced optically-stimulated luminescence (OSL) dating techniques are based on measurements made on individual quartz sand grains. These advanced techniques allow hundreds or even thousand of ages to be determined from a single field sample. The resulting data distributions can be objectively scrutinized, leading to more accurate and reliable luminescence ages.

In this project we use and compare traditional methods (IRSL MAAD) and advanced techniques, including single-grain laser luminescence (SGLL) measurements, dose distribution analysis, and error deconvolution, to date fluvial sediments from Chupaderos Canyon terraces. The terraces have been faulted and offset by seismic activity on the Guaje Mountain fault. Luminescence dating can provide a depositional chronology for the fluvial sediments that can in turn be used to constrain the timing of seismic activity.

Our results indicate that consistent ages can be obtained from both advanced objective techniques and traditional methods, however, a subjective analytical paradigm must be tolerated when considering the IRSL MAAD data. We will also discuss past inconsistencies in traditional luminescence dates from the area, such as age inversions and age over-estimates, in the context of information that can be gathered from dose distributions analysis.