Uraniumethorium dating method and Palaeolithic rock art Georges Sauvet a, * , Rapha € elle Bourrillon a , Margaret Conkey b , Carole Fritz a , Diego G arate-Maidagan a , Olivia Rivero Vil a a , Gilles Tosello a , Randall White c a Centre de Recherche et d'Etudes pour l'Art Prehistorique (UMR 5608 TRACES, UTM/CNRS/EHESS/Culture/Inrap), 5 Allee A. Machado, 31058 Toulouse cedex 9, France b Department of Anthropology, University of California, Berkeley, CA 94720-3710, USA c Center for the Study of Human Origins, Dept. of Anthropology, New York University, New York, NY 10001, USA article info Article history: Available online 5 May 2015 Keywords: Uranium-series dating Palaeolithic art Accuracy Causes of error abstract Dramatic progress was seen in 14 C-dating with the introduction of accelerator mass spectroscopy (AMS) which made possible the direct dating of prehistoric artworks painted or drawn with charcoal. However, in the case of engravings and red paintings, only indirect methods can be used that allow us to date deposits that have covered the works over time (TL, U/Th, oxalates, etc.). The uranium/thorium dating method gives reliable and relatively precise results in the case of massive speleothems, because the sampling is carried out at the heart of the material where the hypothesis of a closed system (that is, no exchange with the outside environment) is justified in most cases. Unfortu- nately, the situation is quite different in the case of thin layers of calcite that overlie Palaeolithic cave drawings. The conditions under which calcite forms depend largely on the hydrologic activity, which has greatly varied over the course of the Upper Palaeolithic and Holocene. In many cases, we can see that the growth of speleothems stopped during much of the Upper Palaeolithic. Consequently the ages obtained are minimum ages (terminus ante quem) which are frequently much younger than the real ages of the underlying artworks. Moreover, a much more serious but rarely considered source of error contradicts the assumption of a closed system. In thin layers of carbonate deposits and in damp media, the uranium incorporated into the calcite during its crystallization may be partially eliminated because of its solubility in water. Uranium leaching causes an artificial increase of the age that may reach considerable proportions (e.g. a negative hand in a cave in Borneo was dated to 27,000 years by U/Th whereas its 14 C age was only 8e10,000 cal BP; Plagnes et al., 2003). Due to these two contradictory sources of error, the dates given by the U/Th method may prove to be younger or older, with deviations that are much larger than the standard deviations given by labora- tories. As a result it is nearly impossible and very dangerous to base archaeological reasoning on U/Th ages of Palaeolithic artworks, so long as the dates are not confirmed by an independent method, dating the carbonates in the same samples by 14 C being the best means of detecting anomalies. The application of the U/Th method for the dating of prehistoric rock art is still experimental. Technical improvements (for less damageable sampling) and fundamental research on the causes of errors are needed. © 2015 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Numerical chronology is of paramount interest for archaeolo- gists, particularly in the case of rock art which is an essential way of understanding the hunters-gatherers societies and the cultural links among human groups during the Upper Palaeolithic. In the last twenty years, the direct dating of organic pigments by 14 C-AMS has completely renewed the study of cave art, but red paintings and engravings remain out of reach. This is why the interest is now DOIs of original article: http://dx.doi.org/10.1016/j.quaint.2015.10.016, http://dx. doi.org/10.1016/j.quaint.2015.10.015, http://dx.doi.org/10.1016/j.quaint.2016.04.020. * Corresponding author. E-mail addresses: georges.sauvet@sfr.fr (G. Sauvet), r.bourrillon@gmail.com (R. Bourrillon), meg@berkeley.edu (M. Conkey), carole.fritz@univ-tlse2.fr (C. Fritz), garatemaidagandiego@gmail.com (D. Garate-Maidagan), oliviariver@hotmail.com (O. Rivero Vila), gilles.tosello@wanadoo.fr (G. Tosello), randall.white@nyu.edu (R. White). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint http://dx.doi.org/10.1016/j.quaint.2015.03.053 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved. Quaternary International 432 (2017) 86e92