ESR dating of aeolian sand near tennant creek, Northern territory, Australia

Abstract

Electron-spin resonance (ESR) dating of aeolian sand in the Northern Territory of Australia was carried out using the Al centres in quartz grains as part of an attempt to date prehistoric faulting associated with the 1988 Tennant Creek earthquakes. Our experiments on optical bleaching of ESR (electron spin resonance) signals show that sunlight does not completely bleach the ESR signal from the Al centre of quartz grains in this aeolian sand. The total doses were determined from the acquired ESR signal intensity, however, a correction to compensate for partial bleaching and the resultant inherited residual ESR signal, has to be carried out. By using this technique, the ESR age estimates an increase with depth, which suggests that nearly complete optical bleaching has occurred through this slice of geologic time. For age estimates younger than 50 ka, the ESR ages are in generally good agreement with independently determined TL (thermoluminescence) data; beyond 50 ka, the ESR ages are systematically older than the TL ages. The oldest ESR age estimate of 160.0 ± 5.9 ka is from a sample at 228 cm depth and ESR results from the vertical samplings yield an apparent sedimentation rate of 2.6 cm/ka.