Single-grain optically stimulated luminescence dating of quartz temper from prehistoric Intermountain Ware ceramics, northwestern Wyoming, USA

Abstract

Abstract This study applies single-grain optically stimulated luminescence (SG OSL) dating of quartz sand temper to Intermountain Ware ceramics recovered from four archaeological sites in northwestern Wyoming, USA. We show that SG OSL dating can strengthen and further refines existing archaeological site chronologies in certain settings. The SG OSL results are compared to multi-grain infrared stimulated luminescence (IRSL) dating of the polymineral (feldspar and quartz) silt fraction in the ceramic paste of the same sherds. Results from the two methods are statistically indistinguishable, although coarse-grained quartz SG OSL ages have consistently lower standard error terms due to higher relative sensitivity and avoidance of anomalous fading calculations. Moreover, the SG OSL results produced precision at two-sigma standard error greater than or equal to associated calibrated radiocarbon ages. SG OSL dating of quartz temper from Intermountain Ware ceramics provides more reliable site occupation timing than radiocarbon dating, which can be conditioned by incorporation of old wood and contamination from young soil carbon. This study highlights the importance of SG OSL dating on sherds from buried contexts when exposure to wildfires may have occurred, as ceramics recovered from the ground surface of one site after a high-intensity fire produced near-modern apparent ages, suggesting they were thermally reset during the fire. We suggest SG OSL should be applied to date similar ceramics with quartz temper to determine site age and bolster regional chronologies.