Reducing variability in OSL rock surface dating profiles

Abstract

In recent years, rock surface dating has seen the emergence of a technique based on optically stimulated luminescence (OSL). This application translates the depth of OSL signal bleaching within a rock surface into an exposure age or erosion rate at 1-10 4 a timescales. Considerable effort has been undertaken to improve our understanding of OSL rock surface dating, yet a large amount of uncertainty associated with the method remains. Specifically, OSL profiles measured into rock surfaces can be highly scattered. Potential causes of this scatter could be lithological heterogeneity that modify bleaching rate throughout the rock, variability in surface erosion or experimental artefacts. Here, we report experiments that were conducted to explore whether experimental artefacts could contribute to the scatter in OSL profiles measured from rock surfaces exposed in Zermatt, Switzerland. This was done by varying the following parameters: (i) heating rate, (ii) isothermal holding time, (iii) luminescence signal detection filters, (iv) the sequential order of optical stimulations, and (v) core diameter. Our results indicate that sample temperature, for both preheating and stimulation, may exert a strong influence on the OSL profiles obtained. Thermal lag, i.e. the temporal offset between sample temperature and the instrument temperature, can be significant for rock slices if a heating rate of 5 °C s −1 is used and if rock slices are placed directly on the instrument carousel. To reduce this effect, our results suggest future studies place samples in metal cups, reduce the heating rate and increase preheating and holding times prior to optical stimulation, to allow samples to heat at the desired rate and reach the required temperatures. • Variability in heating increases noise in luminescence depth profiles. • Thermal lag causes heating to vary between rock slices. • Suggestions for the optimization of rock surface dating protocols are given.