Luminescence Dating of Sand from the Kelso Dunes, California. Unpublished MSc Dissertation

Abstract: A relatively new luminescence dating technique, infra-red stimulated luminescence (IRSL), has been used to date dune sand from the Kelso Dunes, eastern Mojave Desert, California. This is the first time the technique has been applied to desert aeolian sands. The IRSL technique measures the time since sediment grains were last exposed to light, by sampling a highly light-sensitive signal which reduces rapidly to a negligible level when so exposed. The technique can be used to date very young samples. Of the ten samples dated, the surface sample gave an age of 40 + 17 years, while subsurface samples gave high-precision middle and late Holocene dates. These results, obtained from the upper 8 m of the sand mass, indicate significant aeolian activity during the later part of the Holocene. Clustering of IRSL ages from the data so far available suggests that the aeolian activity may have been episodic. The principal aim of this study is to evaluate the relatively new luminescence dating technique of infra-red stimulated luminescence (IRSL) when applied to dune sand from a desert environment. The technique, in common with other lumi-nescence techniques, measures the time since samples were last exposed to light. It is, there-fore, likely to be suitable for determining the timing of periods of aeolian activity and dune formation. As with almost all desert dune areas, no direct, independent age control is available for the Kelso Dunes in the Mojave Desert; how-ever, the dunefield was considered a good test area because there were areas with different dune orientation, indicating different periods of aeolian activity. Geological background The Kelso Dunes are located at latitude 34~ longitude 115 ~ in the eastern Mojave Desert, San Bernardino County, California, and comprise, in terms of sand volume and height, the largest dunefield in the Mojave Desert (Figs 1 & 2). The Mojave River, draining north from the San Bernardino Mountains, is the only through-flowing river of any consequence in the Mojave; today floodwaters f om heavy precipi-tation in the river's source area only fill the river's terminal basin, Silver Lake playa, in exceptionally wet years. On emerging fro