Dose recovery and residual dose of quartz ESR signals using modern sediments: Implications for single aliquot ESR dating

Electron spin resonance (ESR) dating is a promising method for dating sedimentary quartz beyond a million years. Here we investigate the use of modern quartz samples with well bleached optically stimulated luminescence (OSL) signals to study the bleachability of the ESR signals, and to further check the applicability of the ESR single aliquot regenerative dose (SAR) protocol. The residual doses from five samples using both the Al- and Ti-centres were in general found to be large and, especially for the Al-centre, with a large variability. Although it is known that the Ti-centre is fully bleachable in nature, a subtraction of the residual dose using a modern analogue should be considered. Dose recovery tests were performed by using the single aliquot regenerative and added dose (SARA) method, and the dose recovery ratio (measured-to-added dose ratio) was obtained from the slope of the added vs. measured dose plot. The dose recovery ratio from the Ti-centre was satisfactory for all five samples indicating the validity of the proposed ESR SAR protocol. However, only one sample yielded a SARA plot for the Al-centre. This could be explained by the decrease in sensitivity caused by the annealing step in the SAR protocol and/or to the erroneous subtraction of the intensity of the peroxy centre, which overlaps with the Al-centre.