Direct ESR dating of a pliocene hominin from Swartkrans

Two fragments of a hominin tooth (Australopithecus robustus) and two bovid teeth from the Hanging Remnant of the Swartkrans Formation were analysed wi th ESR. Research was complicated by the fact that the samples came from a c urated collection and their precise provenance is unknown. The environmenta l dose rate was reconstructed by a series of in situ gamma spectrometric me asurements and elemental analyses of a range of sediment samples. U-series isotopic analyses indicated that each of the teeth had a significantly diff erent uranium uptake history, rendering the assumptive early U-uptake and l inear U-uptake models ineffective. ESR and U-series data were combined to c alculate open system ages, resulting in a best estimate of 1630 +/- 160 ka for the Hanging Remnant. An open-system model which provides the maximum ag e for given U-series and ESR measurements yielded an estimate of about 2100 ka. Two bovid teeth from Member 2, previously estimated to be between 1 .0 and 2 .0 Ma, yielded age estimates of between about 100 and 200 ka. No known ge ochemical processes are likely to explain this severe age underestimation. Vile conclude that these samples are of Middle to Upper Pleistocene age and their presence in Member 2 was either due to reworking or inadequate strat igraphical discrimination of these deposits. (C) 2001 Academic Press.