Blackwell B A, Schwarcz H P, Schick K, Toth N
Dept of Geology, McMaster University, Hamilton, Ontario, Canada.
Appl Radiat Isot. 1993 Jan-Feb;44(1-2):253-60. doi: 10.1016/0969-8043(93)90228-3.
A single radiation-sensitive ESR signal at g = 2.0018 occurs in fossil tooth enamel, but not in modern teeth. In dating fossil teeth, the equivalent radiation dose (AD) needed to produce the observed ESR signal is the integral with respect to time of the natural, environmental dose rate (ED) experienced by the tooth during burial. Since the age depends on the U uptake history assumed, three dates are normally calculated assuming early U uptake (EU), continuous (linear) U uptake (LU), or recent U uptake (RU). Generally the LU ages agree best with known ages determined by other methods, but the EU and RU ages are respectively the minimum and maximum ages. Longola Spring Mound, in Central Zambia, contains a Late Stone Age collection occurs on the mound surface. Embedded in layer near the base is a much older layer containing Middle Stone Age artifacts and bone material. Four ungulate teeth collected from the lower layer were ESR dated. EU, LU, and RU ages for each tooth agree very closely, but ages range from 14 to 96 ka. Although the layer may be a two component deposit with teeth averaging 18 +/- 2 ka and 91 +/- 3 ka, high sedimentary Th concentrations and ESR isochrons suggest that gamma ext dose estimates are in error. LU dates estimated from isochron plots average 204 +/- 86 ka, while LU ages calculated with the average isochron-derived gamma ext = 10.79 +/- 1.89 mrad/a average 220 +/- 62 ka. More excavation and dating are necessary to determine if the isochron data is reasonable.(ABSTRACT TRUNCATED AT 250 WORDS)
