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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.

Luminescence decay with time often shows a power-law dependence of the form intensity , where t is time and k is usually in the range 1–1.5. It is shown here that this power law can result from the tunnelling of trapped electrons to recombination centres that are randomly distributed, and that the range of exponents matches that of the observations. The explanation accounts for the most extreme case of an observed t−1.06 dependence extending over nine decades of time.

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