Assessing soil mixing processes and rates using a portable OSL-IRSL reader: Preliminary determinations

Employing a portable luminescence reader in a novel approach for studying soil mantles can help to both better our understanding of and determine the relative importance of the different erosional processes operating on a given landscape. By measuring bulk IRSL signal intensity of unprepared regolith samples as a function of depth, a portable reader has been used to rapidly explore patterns and rates of soil mixing within the actively uplifting San Gabriel Mountains, southern California, USA. Both IRSL and OSL measurements were taken from three different hillslope soil profiles collected within a 100 m radius, as well as a number of bedrock samples. To gauge the rates of grain mixing, bulk IRSL signals are converted to dose values by measuring IRSL growth as a function of dose in a conventional luminescence reader using smaller subsamples from key locations. These data are combined with dose rate determinations based on both in-situ NaI gamma spectrometer measurements and chemical determinations of U, Th and K, in order to convert dose values into " effective age" estimates; these values represent mixed regolith and soil, and not age of sediment deposition. This approach has generated soil turn-over histories much more complex than our simple, signal saturation-with-depth model predicts.