PROBLEMS ASSOCIATED WITH REWORKED TEETH IN ELECTRON-SPIN-RESONANCE (ESR) DATING

A single radiation-sensitive ESR signal at g = 2.0018 occurs in well c rystallized fossil tooth enamel, but not in modern teeth. In dating fo ssil teeth, the equivalent radiation dose (A(Sigma)) needed to produce the observed ESR signal is the integral, with respect to time, of the natural, environmental dose rate experienced by the tooth after its d eposition. Regardless of the uranium (U) uptake history assumed, a rel iable age estimate requires a good estimate for the external dose rate during the tooth's history. If teeth in a stratigraphic unit have bee n reworked from older units or are post-depositional intrusions, exter nal dose rates measured in situ do not accurately reflect those experi enced by the tooth. For teeth from a single unit, significant variatio ns in the calculated ages, A(Sigma)s, enamel or dentine U concentratio ns all indicate mixed sample collections. Where enough subsamples can be collected from single teeth, isochron analyses negate the need for a separate external dose measurement, while calculating the sample age and the external dose rate experienced by the tooth. Failing that, mo delling the sedimentary dose rates using time-averaged total external dose calculations becomes necessary. These principles are illustrated using teeth from the australopithecine sites Sterkfontein and Swartkra ns, South Africa.