Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating

Anomalous-fading rates were measured in K-feldspars separated from 49 sediment samples, mainly from North America. The intensity of the optically stimulated luminescence was found to decrease linearly with the logarithm of time since irradiation between 2 days and ~1 year of storage at room temperature. Anomalous-fading rates ranged from 2% to 10% per decade, a decade being a factor of 10 in time since irradiation. The sample provenances were sufficiently varied that anomalous fading appears to be ubiquitous. We have experimented with correction of optical ages for anomalous fading on the assumption that the observed fading can be extrapolated a further four decades in time. The corrected ages are in satisfactory agreement with independent ages. These results are restricted to the low-dose region of the dose response and are not expected to be applicable to samples older than ~20–50 ka.

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