The Efficacy of Electron Spin Resonance for the Dating of Quartz - A Case Study of Aeolianites of the Bridgewater Formation in southeastern South Australia

Abstract

The use of electron spin resonance (ESR) spectroscopy to date Pleistocene sediments is tested using light-sensitive centres in quartz: the Al hole trapping centre and the Ti-Li and Ti-H electron trapping centres. These centres have high saturation doses with the potential to date sediments throughout the Quaternary period. Samples from aeolianites of the Bridgewater Formation from the Coorong-Gambier coastal plain in southeastern South Australia were chosen for the test. These barriers have previously been investigated in detail and sufficient age control for the validation of ESR ages are available, with the oldest structure being beyond the Brunhes-Matuyama magnetic reversal at about 780 ka. The Al, Ti-H and Ti-Li centres were studied in 28 samples from twelve aeolianite units and tested in regard to gamma irradiation, bleaching, partial bleaching and isochronal heating. Equivalent doses using the multiple aliquot additive and regenerative methods were compared for selected samples. Regeneration measurements were carried out following bleaching and thermal annealing. Sensitivity changes were monitored using dose-recovery tests and spectral analysis. The applied doses in the dose-recovery tests could be recovered from the Al and Ti-H centres. Changes in the line width and amplitude for the Ti-Li and Ti-H centre occurred, whereas the ESR signal of the Al centre did not show any changes. On exposure to natural sunlight, the Ti-Li centre bleached slower than the Al centre, with the T-H centre bleaching the fastest. Equivalent doses for samples, using the Ti-Li centre, gave systematic overestimates compared to the doses obtained from the Al and Ti-H centres, which were the same for most samples. After consideration of the methodological results, the Al centre was chosen for age calculations. The majority of the resulting ESR ages calculated for the samples are in good agreement with the age-control data. The ESR signals for the older, Middle and Early Pleistocene samples were not yet saturated. These results are very promising and show the potential of ESR spectroscopy to date sediments throughout the Quaternary period.