Luminescence chronologies for sediments recording paleoseismic events and slip rate for the central Garlock fault, California, USA

Luminescence dating has a significant role to play in providing chronological control for lacustrine and alluvial sediments that record both tectonic and climatic events. However, poor characteristics in some environments mean that the well-established method of OSL (optically stimulated luminescence) dating of quartz is not well-suited for the material available. In order to overcome this significant limitation, a range of methods based on the IRSL (infra-red stimulated luminescence) and ITL (isothermal thermoluminescence) of K-feldspar are currently under development. The site of El Paso Peaks, California has an established C-14 chronology spanning the last 7,000 years for a series of playa sediments comprising silts and fine sands, with occasional incursions of coarser sands and gravels from the alluvial fan that forms one side of the small ephemeral lake basin. Another barrier is formed by a shutter ridge of the left-lateral central Garlock fault, and this succession of sediments records at least six seismic events. Following collection of a suite of 24 luminescence samples distributed throughout the upper part of this succession, this site provides a rare opportunity to test different luminescence dating protocols in a rigorous fashion. At the site of Christmas Canyon West, a few miles further east, numerous small offsets of depositional and erosional alluvial fan features provide the opportunity to determine slip rates for a variety of timescales spanning the past couple of thousand years, besides forming a record of the timing of several discrete depositional episodes representing local high precipitation events. We review the challenges involved in developing a reliable luminescence chronology for sediment deposition in these contexts, and in relating this chronology to significant environmental events.