ESR dating of megafauna enamel teeth from Lagoa Uri de Cima Archaeological Site (Pernambuco, Northeastern Brazil)

Abstract

Excavations in the Lagoa Uri de Cima Archaeological Site (Salgueiro, Pernambuco, Brazil) revealed considerable Pleistocene mammalian fossils and lithics in multiple sedimentary layers of the ancient lake, currently dry. The site was found in 2010 during the construction of an open-air system of canals to connect water sheds of the semi-arid regions with the São Francisco River. The coexistence of a variety of extinct mammals and archaeological remains suggested the possibility of further light on the question of overlapping occupation of Northeastern Brazil by megafauna and humans in the Late Pleistocene. Electron spin resonance (ESR) dating of tooth enamel of mammal fossils can provide valuable information on the chronology of this site. This work presents the ESR dating of four teeth of two mammal species: Toxodon platensis (2) and Haplomastodon waringi (2). Dose-response curves were constructed using T1-B1 and T1-B2 amplitudes of the ESR signal of the hydroxyapatite CO2−radical, measured with a Bruker EMX-10+ X-band spectrometer. To verify the experimental protocol and the reliability of the exponential fittings for additive-doses and ESR signal intensities, the dose-response curve of one Toxodon platensis sample was independently obtained with a Jeol FA-200 X-band spectrometer. Equivalent dose to age conversions were carried out with the ROSY ESR dating program, with the external dose rate given by the environment and cosmic radiation and the internal dose rate given by probable uranium uptake models. The results show ages varying from 12,000 to 19,000 years for the four samples. The stratigraphical consistency is sub-optimal, but can be explained by the overall geomorphology of the site. These results place the creation of the lowest sedimentary levels of Lagoa Uri de Cima within the Late Pleistocene.