A COMPARISON OF NUMERICAL DATING TECHNIQUES AT A LATE QUATERNARY SPIT-SHORELINE COMPLEX, NORTHERN END OF SILVER LAKE, MOJAVE DESERT, CALIFORNIA

Quantifying rates of Quaternary landscape evolution and paleoenvironmental change, and establishing Quaternary stratigraphic frameworks in drylands has been difficult mainly because radiocarbon dating cannot be readily applied in environments with sparse organic material. The development of optically stimulated luminescence (OSL), cosmogenic radionuclide (CRN) surface exposure, and new technical advances in amino acid racemization (AAR) and U-series dating, however, now allows successions of sediments and landforms to be dated to define the timing and durations of various phases of development of a sedimentary record. Yet few studies provide intercomparisons between these techniques to test the validity and applicability of newly evolving methods, as well as established radiocarbon dating. To compare several dating techniques, we focused on a late Quaternary spit-beach complex in the Mojave Desert, CA where radiocarbon, OSL, CRN, AAR and U-series dating methods could be applied. Our results show that the spit-beach complex began to develop ~25 ka and has contined to evolve throughout the Holocene. TCN dates of ~25 ka, define the initial erosion of shoreline benches, while the radiocarbon dates of 15-9 ka, supported by AAR, for the spit show progressive lake level changes in Lake Mojave during the Lateglacial and Early Holocene. In contrast, OSL dates suggest that the spit formed during the mid-late Holocene. High concentrations of detrital thorium within tuff inhibited the use of U-series dating at this site. This study illustrates that each of the geochronological methods contributes to an estimate of the timing and duration of a physical/geochemical event in the history of the spit-beach. Detailed studies at key sites, such as this, will help refine methods and will provide insights into new ways of utilizing numerical dating techniques to provide details on chemical and physical processes within arid and semi-arid environments.