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Quantifying lithic surface alterations by means of confocal microscopy: the case of the châtelperronian level of La Roche à Pierrot (Saint-Césaire, France).
Aline Galland  1, *@  , Alain Queffelec  1, *@  , Solene Caux  1, *@  , Jean-Guillaume Bordes  1, *@  
1 : De la Préhistoire à l'Actuel : Culture, Environnement et Anthropologie  (PACEA)  -  Site web
Université de Bordeaux, Centre National de la Recherche Scientifique : UMR5199, Ministère de la Culture et de la Communication
Université de Bordeaux Bâtiment B8 - CS50023 Allée Geoffroy Saint Hilaire 33615 PESSAC CEDEX -  France
* : Auteur correspondant

Lithic artefacts are one of the main material witnesses allowing us to study prehistoric populations' way of life. However, post-depositional processes have an impact on the artefacts to the point of modifying their surfaces, which can be visible on a macroscopic level. These surface alterations or post-depositional surface modifications are qualitatively described by archaeologists as “glossy patina”, “edge damage”, “rounding”, etc. The aim of this presentation is to introduce a new methodology in the study of surface alterations going beyond the subjective studies undertaken until now thanks to microtopographic measurements using confocal microscopy. These surface alterations are widely visible at La Roche à Pierrot. This site is currently subjected to an archaeostratigraphic review as it setting off numerous issues regarding transition modalities between Middle and Upper Palaeolithic. Indeed, lithic industries of this transitional period, and particularly the ones attributed to the Châtelperronian are recognized for their complex surface alterations, which raises the question of their chronocultural integrity. A geological sample composed of local flint was set up in order to compare the impact of post-depositional processes in the immediate environment of the site as well as inside the excavation area. This innovative protocol allowed a quantified distinction of various states of alterations among geological and archaeological samples, especially regarding white patina and glossy patina. This research showed that the variability of surface alterations among the artefacts of a same spit, localized near the Neanderthal remains, is as important as the variability of surface alterations in the immediate environment of the site. Thus, use-wear analysis will benefit from a better understanding of surface alteration and their impact on stone tools, which usually hinders the reading of the worked materials. In addition, these results lead to become more careful concerning the association between the Neanderthal remains and the lithic artefacts at La Roche à Pierrot. Broadly speaking, this pilot study confirm the potential and the promising development of confocal microscopy in both taphonomical and use-wear studies of lithic industries.

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