Cross dating by uranium-thorium, uranium protactinium and radiocarbon of secondary carbonate cave deposits: the search for validation criteria of samples and ages. Application to rock art – ApART

Initially, the approach will be tested in the unadorned cave of Soyons in Ardèche, which will serve as an experimental site. It will then be applied to prehistoric decorated sites: Cueva de Nerja, los Hornos de la Pena, Navarro in Spain, the Grotte aux Points in Ardèche and the ornate shelters in the forest of Fontainebleau. The approach will include: i) characterization of samples (mineralogy, geochemistry, etc.) to detect possible alterations in the initial structure of minerals and select those that are favorable for dating; ii) dating by the coupling of several methods (230Th / 234U, 14C, and test of the 231Pa / 235U chronometer) in order to compare their respective results (verification of an evolution in a closed system) and to assess, ultimately, the relevance of the ages obtained by placing them in their archaeological context iii) methodological work to miniaturize the samples for each of the methods used aimed at increasing the preservation of archaeological sites. In the case of relatively thick samples, miniaturization will make it possible to multiply the dating on the same veil and thus to verify the stratigraphic coherence. The three project partners have complementary skills which are recognized internationally. These are the GEOPS (UMR 8148) for the mineralogical and chemical characterization of carbonate samples by several techniques, the LSCE (UMR 8212) for the chronological study of the samples, based on the uranium / thorium and carbon-14 dating methods and the 'IPREM (UMR5254) for laser ablation approach and chemical characterization. ApART also integrates prehistorians whose role will be crucial in the choice of samples and the interpretation of the results. They are from the Univ de Cordoba, Salamanca in Spain, Univ. de Paris 1) and curators (Musée de Soyons, SRA Rhône-Alpes)

The article published in 2020 in the Journal of Archeological Science (Vol 117 - 105120), entitled «U-series dating at Nerja cave reveal open system. Questioning the Neanderthal origin of Spanish rock art ”which presented the first results of the ANR ApART had a strong impact on the archaeological community, which became aware of the biases linked to the mobility of uranium within certain carbonate samples, and on the chronology

Applications of the experimental characterization and dating methods developed in ApART to several caves or prehistoric decorated sites (Los Hornos de la Pena, Cueva de Nerja, Navarrovarro in Spain, Grotte aux Points in France

Pons-Branchu, E., Sanchidrián, J. L., Fontugne, M., Medina-Alcaide, M. Á., Quiles, A., Thil, F., & Sanchidrián, H. V. (2020). U-series dating at Nerja cave reveal open system. Questioning the Neanderthal origin of Spanish rock art. Journal of Archaeological Science, 117, 105120.

Cross dating by uranium-thorium, uranium protactinium and radiocarbon of secondary carbonate cave deposits: the search for validation criteria of samples and ages. Application to rock art (ApART)

Abstract
The ApART project responds to the challenges described in the 2018 ANR action plan "Innovative, integrative and adaptive societies" and its axis 5: "Cultures, creation, heritage". The objective of the ApART project is twofold: to develop methodologies of study adapted to the conservation of heritage objects, while extending our knowledge of parietal art.
Obtaining relevant results when dating samples of cave carbonates is a real scientific issue that will have a significant impact in the field of prehistory. While decorated Paleolithic caves are very abundant, especially in France, the majority of them contain wall decorations engraved or traced with metal oxides which cannot be dated directly by the carbon 14 method; their chronology therefore remains very uncertain. The fact that many drawings are covered with carbonate deposits that can be dated by radionuclear methods makes it possible to meet this challenge by opening up a new field of investigation for research on Paleolithic art. Until now, researchers involved in the dating of these parietal deposits have used only the uranium-thorium method, without information on the geochemical evolution of the system, hence the impossibility of assessing the reliability of the results obtained. The ApART project, in contrast, will focus on combining several dating methods (231Pa/235U and 230Th/234U and 14C) on the same sample in order to compare their respective results. Our previous studies have also shown that it is essential to characterize the mineralogical structure and diagenesis of samples with physico-chemical methods to verify that they can be reliably dated.
The investigations carried out in ApART are thus manifold: they relate to the definition of validation criteria for the different dating methods thanks to preliminary characterization studies of the samples. The second part concerns the miniaturization of samples, an essential objective for studies concerning samples of decorated walls.
The multidisciplinary approach of ApART is based on the close collaboration of several laboratories with complementary skills, internationally recognized expertise and state-of-the-art instrumentation. ApART also integrates parietalist prehistorians and curators whose role will be crucial in the choice of samples and the interpretation of the results.
In order to preserve the decorated caves, our protocols will first be developed and tested on samples taken from caves without parietal art, before being put into practice on samples of decorated caves (the cave at the Points, Bois d’Argeville rockshelter in France; Nerja, Navarro, and Askondo caves in Spain). This field work will be conducted in close consultation with the prehistorians in charge of their study, who have already filed sampling applications with the authorities. The objective of the ANR ApART, based above all on the consultation of the different partners, both in archaeological sites and in laboratories, will, in the long term, enable a reliable methodology to be developed that will be able to respond to both the requirements of maximum conservation of cave walls and parietal art while obtaining fully relevant and validated dates. In the more distant future, the contributions of ApART will open up new perspectives for the study of parietal art.