Abstract
Abstract. In this study, we examined the residual doses of the quartz electron spin resonance (ESR) signals from eight young fluvial sediments with known luminescence ages from the Lower Rhine terraces. The single aliquot regenerative (SAR) protocol was applied to obtain the residual doses for both the aluminium (Al) and titanium (Ti) impurity centres. We show that all of the fluvial samples carry a significant amount of residual dose with a mean value of 1270 ± 120 Gy for the Al centre (including the unbleachable signal component), 591 ± 53 Gy for the lithium-compensated Ti centre (Ti-Li), 170 ± 21 Gy for the hydrogen-compensated Ti centre (Ti-H) and 453 ± 42 Gy for the signal that originated from both the Ti-Li and Ti-H centres (termed Ti-mix). To test the accuracy of the ESR SAR protocol, a dose recovery test was conducted and this confirmed the validity of the Ti-Li and Ti-mix signal results. The Al centre shows a dose recovery ratio of 1.75 ± 0.18, whereas the Ti-H signal shows a ratio of 0.55 ± 0.17, suggesting that the rate of signal production per unit dose changed for these signals after the thermal annealing. Nevertheless, all fluvial sediments investigated in this study carry a significant residual dose. Our result suggests that more direct comparisons between luminescence and ESR equivalent doses should be carried out, and, if necessary, the subtraction of residual dose obtained from the difference is essential to obtain reliable ESR ages.
Highlights
When sedimentary quartz was first investigated for electron spin resonance (ESR) dating 35 years ago by Yokoyama et al (1985), a bleaching test was performed and an optically unbleachable residual signal for the Al centre was detected
We show that all of the fluvial samples carry a significant amount of residual dose with a mean value of 1270 ± 120 Gy for the Al centre, 591 ± 53 Gy for the lithium-compensated Ti centre (Ti-Li), 170 ± 21 Gy for the hydrogen-compensated Ti centre (Ti-H) and 453 ± 42 Gy for the signal that originated from both the Ti-Li and Ti-H centres
The results clearly show that the ESR De for all samples are significantly larger than the optically stimulated luminescence (OSL) De of Lauer et al (2011), and residual subtraction is highly recommended if a representative modern analogue sample is available
Summary
When sedimentary quartz was first investigated for electron spin resonance (ESR) dating 35 years ago by Yokoyama et al (1985), a bleaching test was performed and an optically unbleachable residual signal for the Al centre was detected. Tsukamoto et al (2017) used modern aeolian quartz samples, whose OSL signal is well bleached, to investigate the bleachability of the ESR signals We define the residual dose as the ESR De values minus the OSL De of the same sample, and this includes both bleachable and unbleachable components of the Al centre These young sediments are investigated using the ESR SAR protocol and its performance is monitored by conducting dose recovery tests
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