ESR Dating of Pleistocene Deposits

Abstract

<p> Near Medicine Hat, Alberta, Pleistocene deposits are exposed on numerous bluffs along the South Saskatchewan River. The Quaternary beds are very fossiliferous, yielding a large number of mammal bones and teeth. The enamel (calcium hydroxyapatite) portion of teeth within the sediments, is used to date the deposits with the electron spin resonance (ESR) dating method. The ESR age is strongly dependent on the dose rate which in turn depends on the uranium accumulation in the tooth fragments. Two U uptake models are used based on an early and a continuous, linear accumulation of uranium.</p> <p> At young, well dated sites the ESR ages are in relatively good agreement with independent estimates. For slightly older samples (approx. 100 ka), the linear U uptake model comes closer to the estimated age at one site, but at another site, the early U uptake model agrees more favourably with the estimated age. Based on the ESR ages, several older sites can be assigned to interglacial stages 7, 9 and 13, however, these ages are much younger than those determined by faunal and stratigraphic correlation (>0.5 Ma). Samples with extremely high U contents in dentine and enamel gave unreliable ESR results. These samples may have experienced a late stage of U accumulation.</p>