A Routine ESR Technique for Dating Calcite Speleothems

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Abstract
The electron spin resonance (ESR) methods employed for measuring the dose accumulated by calcite since its deposition (the equivalent dose) have varied enormously from laboratory to laboratory. Following a detailed study of the stability and dose response of the ESR signals present in calcite, we previously reported that the signal at g=2.0005 (±0.0003) is the only one suitable for dating the last million years. The measurement of this signal requires great care as there is often significant interference from a very sharp signal at g=2.0001 (±0.0002) produced by grinding, and a short-lived radiation sensitive signal at g=2.0020 (±0.0003) which has previously not been recognised. Annealing techniques have been developed to remove interference from the latter and check for instabilities in the g=2.0005 signal which appear to be due to re-crystalisation of the calcite. A routine experimental procedure is described which in our experience produces reliable equivalent doses, and the advantages of the ESR technique are discussed.

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