How to measure the ESR intensity of the Al centre in optically bleached coarse quartz grains for dating purpose?

Abstract

The ESR intensity of the Al signal has been traditionally extracted from the measurement of the amplitude between the top of the first peak and the bottom of the last peak. However, a recent study showed the limitations of this method. As a follow-up, we investigated and compared various Al signal intensity extraction methods to evaluate their impact on the De estimation of several coarse-grained quartz samples (100-200 μm) from Early Pleistocene to modern-age deposits. In particular, we tested the potential of using the area of the Al signal near g=2.0603, as it is theoretically free of any major interfering signals. However, our results show that the extraction methods related to this area do not offer any substantial advantages over the traditional method. Instead, measurement of the ESR intensity is more time consuming, and resulting dose response curves are more scattered. Actually, most Al intensity extraction methods tested in this study return equivalent dose (De) estimates (as well as bleaching coefficient values) within error, suggesting that the interfering signals do not seem to strongly bias the ESR dose evaluation in those coarse-grained quartz samples. This outcome provides additional support in favor of the use of the traditional method. However, the significant inter-sample variability observed in our study nevertheless shows the necessity to extend this investigation to a larger number of samples of various grain sizes, origins and chronologies in order to identify more meaningful patterns on a larger scale.