General order kinetics model for OSL rock surface exposure dating

Abstract

Dating of rock surface using optically stimulated luminescence (OSL) is an emerging tool to estimate exposure age and post exposure erosion rates. The present study points out the lacuna in the mathematical model that is used for this method. So far, all existing research, use first order kinetics (FOK) model. The FOK model predicts an exponential decay of OSL signal of polymineral rock with sunlight exposure, which is contrary to the observation. The non-exponential decay of OSL signal, more precisely infrared stimulated luminescence (IRSL) of feldspar, can be better explained by general order kinetics (GOK). Thus, we propose a new GOK model for OSL surface exposure dating. Present theoretical study shows, for FOK model the OSL (IRSL) depth profile propagates faster with time of light exposure than actual. Consequently, the FOK model predicts lower exposure age. The propagation of OSL profile with time depends on order of kinetics of the GOK model. We demonstrate how the order of kinetics can be constrained through laboratory bleaching experiment. The impact of the GOK model on exposure age and upper age limit, for different order of kinetics are presented. We apply this new GOK model on experimental data, available in the literature (Luo et al. in Geophysical Research Letter 49: e2022GL099526, 2022), of OSL depth profile on exposed fault scarp and reevaluate the exposure ages for different order of kinetics to validate the GOK model. We conclude that the GOK model better explains the IRSL of feldspar than the FOK model and should be preferred for OSL rock surface dating.