A Routine ESR Technique for Dating Calcite Speleothems

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.