REFINING THE PROCEDURES FOR PORTABLE LUMINESCENCE READER MEASUREMENTS BY CALIBRATION WITH KNOWN AGE SAMPLES: PROTOCOLS AND NEXT STEPS

Portable luminescence readers are exciting new tools that have the potential to rapidly determine the age structure of late Quaternary stratigraphic columns, but their use has been limited in the past decade and the full potential of the technology has not been realized. Our aim is to broaden the utility and application of the portable machine, such that it is used as more than just a “screening tool” and allows for approximate dates to be generated in the field. This is important because high-resolution age profiling can reveal details about the temporal dynamics of climate cause and ecosystem effect, often while researchers are still in the field. Here, we compare new portable luminescence reader measurements of total photon counts with a suite of robust, highly resolved ages from middle to late Pleistocene-age paleowetland deposits in the Las Vegas Valley of southern Nevada. Our results show that total photon counts correlate with age, with a quadratic equation providing the best fit to the data. Significant scatter is present in the data, which is likely the result of dose rate variations, multiple sediment sources, and transport mechanisms that include both eolian and fluvial processes. The observed scatter can be reduced significantly using a simple pre-treatment procedure involving a 250μm sieve and neodymium hand magnet to normalize particle sizes and remove magnetic grains. Following this treatment, age estimates based on the reader measurements have an average error of 30±18% when compared against known ages. These findings confirm that portable reader measurements scale with age in paleowetland deposits, allowing its use in establishing rapid, albeit approximate, chronologies for these deposits throughout the American Southwest. With this protocol in place, the next steps for a wider and more varied field based experiment will be presented.