Dating Late Pleistocene pluvial lake shorelines in the Great Basin, USA using rock surface luminescence dating techniques: developing new approaches for challenging lithologies

Abstract. This study examines the feasibility of dating pluvial lake beach ridges using rock surface luminescence dating techniques. Dating pluvial lake highstands in the internally drained Great Basin of the United States helps us understand the timing of changes in precipitation and temperature patterns in western North America during the Late Pleistocene. The majority of highstand ages have relied on few radiocarbon ages of shell and/or charcoal sometimes coupled with luminescence dating of sand. Within our study area in the south-central Great Basin, luminescence ages of sand-size particles have successfully dated aeolian influxes of sand during arid intervals, but have not successfully dated the highstand beach ridges, the best preserved of which are largely gravel. Directly dating when these gravel clasts were last exposed to sunlight via luminescence is ideal but their limestone and volcanic lithologies prove challenging. Initial measurements from these lithologies show that feldspar luminescence signals are suited to single-aliquot regenerative (SAR) dose measurement protocols and show evidence for heterogeneous bleaching of rock surfaces. Polymineral extracts from dissolved limestone clast surfaces from Coal Valley that contain sufficient detrital sediment exhibit infrared signals measured at 50 °C (IR50) with low to moderate fading rates. Single-grain ages from detrital sediment from three clasts, calculated using the central dose model, are statistically consistent with the radiocarbon age estimate of the Pluvial Lake Coal highstand. Crushed slices from volcanic clasts from Cave Valley could be dated using a high-temperature (290 °C) post-infrared infrared stimulated luminescence (pIRIR) signal with a correction for fading. Many ages obtained from volcanic clast surfaces are observed to be several thousand years younger than the expected age of the ∼ 18–20 ka beach ridge. This suggests that the volcanic rocks have been exposed to light long after the pluvial lake highstand, likely because of bioturbation, and that their most recent burial occurred in response to climatically driven soil formation processes. Comparisons between age-depth profile plateau ages from inside volcanic rocks and independent age control suggest that gravel-sized volcanic rocks were small enough to have been bleached throughout their entire thickness in the pluvial lake beach environment and that pIRIR signals that record the time of beach ridge formation and subsequent soil formation during the Pleistocene-Holocene transition may be preserved within the rock sub-surface. This study develops novel dating approaches for challenging rock lithologies. Rock surface dating techniques for pluvial lake beach ridges in the Great Basin should be further developed with consideration of local bedrock type(s), clast size, sample collection and preparation methods, gravel bleaching processes in pluvial lake environments and the impact of soil development and bioturbation on study sites.