Extending the age range of optical dating using single 'supergrains' of quartz

Luminescence dating methods have been used to obtain reliable age estimates for quartz sediments deposited within the last 500 ka, but it has proven d ifficult to extend the age range much beyond this limit. Here we report the results of a study of individual quartz grains from Australian sedimentary deposits that range in age from similar to 250 to similar to 950 ka. A sma ll number of the grains examined are strongly luminescent and saturate at u nusually high doses. These 'supergrains' may permit, reliable age determina tion to 1 Ma, and possibly beyond. Some other grains are in, or close to, d ose-saturation, so that only minimum age estimates may be obtained. Most of the grains examined are very weakly luminescent and have palaeodoses much less than expected, while the palaeodoses of some grains cannot be estimate d because of anomalous dose-response characteristics. We offer some possibl e explanations for the behaviour of aberrant grains. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.