Variance in pIRIR signal bleaching for single grains of feldspar

Abstract

Evaluating remnant doses is crucial for luminescence dating of late Holocene sedimentary deposits, especially when slow-bleaching feldspar pIRIR signals are employed. Previous research demonstrated that the bleaching capacity varies between individual grains, but only a few attempts have been made to quantify this. In this research, we evaluate variance in bleachability at a single-grain level for a low-temperature pIRIR signal from K-rich feldspar extract. The research is conducted through experimental exposure to natural sunlight of two natural samples. The degree of zeroing is monitored over exposure times up to 100 min and related to the recuperation values obtained on the same grains from the standard pIRIR sequence. We find a positive correlation between recuperation doses of grains and their residual doses, which suggests that recuperation provides a proxy for grain bleachability. In addition, we combine our dataset of bleachability with information on the difference between IRSL₅₀ and pIRIR₁₇₅ equivalent doses determined on the same grain (D_e ratio), which allows us to identify grains for which light exposure was too limited to reset both signals. The results demonstrate that prior inheritance, light exposure, and grain bleachability all may impact the residual dose of grains, resulting in overdispersion in equivalent dose distributions. Combining the assessment of bleachability with the information on the D_e ratio can support the identification of best-bleached grains in a natural sample. Finally, the different bleachability of individual grains demonstrates that it may not be advisable to subtract the mean residual dose from paleodoses obtained with a minimum age model and for Holocene-aged deposits.