WATER, WIND, AND GRAVITY: NAVIGATING THE COMPLEXITIES OF DATING ALLUVIAL FAN DEPOSITS WITH OSL TECHNIQUES

The application and success of optically stimulated luminescence (OSL) dating to constrain the timing and rates of Quaternary geomorphological processes has grown exponentially over the past decade. These advances are due in large part to modern experimental and analytical methods, which make it possible to evaluate the OSL variability in individual field samples. Equivalent dose distributions reflect complex interactions among the intrinsic variability in solid state properties of mineral grains, measurement errors, and sediment transport dynamics that influence the degree of solar resetting experienced by sediment grains prior to burial. Reliable OSL data analysis approaches exist for sediments transported in systems where a single process dominates such as eolian, fluvial, and littoral deposits. However, sediment grains deposited in alluvial fans and colluvial packages can be influenced by numerous transport processes prior to burial, including mass movement, which is a particular challenge for OSL dating. This presentation will review past OSL analyses of sediments collected from alluvial fans and colluvial foot slopes from various sites in North America in the context of preparing to date alluvial fan deposits in the Dry Valleys region of Antarctica. The review will focus on dose distribution analysis and specific parameterizations that can be interpreted as a gauge of the degree and variability of solar resetting experienced by the sample prior to deposition. This information, in turn, may provide insight into the geomorphic processes acting on the sediments and can better inform the researcher in selecting the appropriate representative dose for age calculation. Preliminary data from two alluvial fans in the Jason Valley of Antarctica will also be presented and discussed.