ESR DATING OF CORALS AND PRE-ANNEALING EFFECTS ON ESR SIGNALS

Corals commonly exhibit electron spin resonance (ESR) signals of A (g = 2.0057), B (g = 2.0031), and C (g = 2.0007). Preannealing using a modern coral sample at 120-180-degrees-C has significantly changed gamma-ray sensitivities of the ESR signals. The sensitivities of all the three signals at first increased and then decreased with the pre-annealing. These results suggest that the amount of sources of the signals changes with geologic time. This effect can cause underestimation of ESR ages for Holocene and latest Pleistocene corals, and can cause overestimation for Early and Middle Pleistocene corals using signal C. Possible models associated with a monomer and a trimer of cation impurities for signals C and A, respectively, are discussed based on third order trap decay kinetics.