OPTICAL DATING EQUIVALENT DOSE DISTRIBUTIONS ACROSS GRAIN SIZE FRACTIONS: A DETAILED ANALYSIS OF AN ANTARCTIC FAN SAMPLE

Modern data collection procedures for optical dating (OSL SAR procedures) allow statistically significant equivalent dose data sets to be collected from sediment samples. Analysis of these dose distributions has lead to significant improvements in accuracy and reporting precision for optical ages. As part of ongoing work to date high-elevation fan deposits in Antarctica we have had an opportunity to collect OSL dose distribution data from six (6) grain-size fractions isolated from a single field sample. The full data set is comprised of nearly 7000 OSL measurements made on over 570 single aliquots and covers grain sizes from 45 to 425 microns. The nature of sediment transport and deposition in fan deposits would be anticipated to produce a wide range of solar resetting histories (partial bleaching) of sediment grains and, thereby, highly heterogeneous dose distributions, so our initial intent in conducting this study was to explore the data set for the grain size fraction that produced the optimum dose distribution properties of OSL dating. Our results show an unexpected consistency in distribution shape, asymmetry, and measures of central tendency across grain sizes. Although subtle, and perhaps lacking statistical significance, some grain size optimums can be seen in parameters such as data dispersion and measures of precision. The results of this study are significant in that they provide data about solar exposure histories across grain size ranges in a fan deposit setting. The results also reinforce the utility of OSL data, above and beyond age determination, in process geomorphological research.