New ESR dates from Lovedale, Free State, South Africa: implications for the study of tooth diagenesis

Abstract

Lovedale is the only open-air Middle Stone Age site in the Free State dated to early Marine Isotope Stage 4. Framing the chronology of this context, especially by taking into account diagenetic processes that may affect age results, is thus fundamental to understand modern human dynamics in the interior of South Africa. In a recent study, we investigated the effect of diagenesis on teeth samples collected for combined electron spin resonance and uranium-series dating at the site. By combining different characterisation methods, it was shown that the uranium (U) content of enamel varied in the specimens, and that it was positively correlated with the degree of crystallinity of carbonate hydroxyapatite, whereby larger amounts of U are associated with highly crystalline enamel. The large variability in U content was in contrast with the fact that teeth were found in the same depositional context. High levels of U in some of the samples limit the accuracy of age determinations, since several uncertainties remain regarding U uptake and leaching, which both affect dose rate modelling. In such complex cases, calculating minimum ages is the most cautious option. New samples were collected at the site during the excavation campaign in 2021. Enamel was analysed using Fourier transform infrared spectroscopy and scanning electron microscopy coupled with cathodoluminescence in order to determine its degree of atomic order and the presence of foreign ions (especially U), and the correlation between the two. We discuss here the contribution of U-uptake modelling on the age calculation, and present new ESR ages calculated assuming an early uptake of U, ranging from 84 ± 9 ka to 56 ± 5 ka. Together with previous ages obtained on the gravel layer, a weighted mean age of 64 ka can be used as a minimum age estimate for the base of the sequence. © 2023, South African Archaeological Society. All rights reserved.