Characterization of a key sequence of the French Palaeolithic: geovisualization and intra-site spatial analysis of La Roche-à-Pierrot, Saint-Césaire

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Located in Saint-Césaire, east of Saintes, in Charente-Maritime (France), the archaeological recordof La Roche-à-Pierrot is at the heart of the debates concerning the Middle/Upper Palaeolithictransition. To this day, La Roche-à-Pierrot constitutes the only site to have provided a relativelycomplete Neandertal skeleton associated with a transitional industry, the Châtelperronian, whichwas until then attributed to Modern Humans. Discovered in 1976, the site was the subject of severalexcavation campaigns conducted by F. Lévêque from 1977 to 1987 and in 1993 (with an additionalseason led by A. M. Backer in 1997). Since 2013, new excavation campaigns have been conducted,first by F. Bachellerie (UMR 5199-PACEA) for two years, then by I. Crevecoeur (UMR 5199-PACEA)since 2015. The main objectives of the new geoarchaeological investigations are to 1) re-evaluatethe archaeostratigraphic sequence, 2) characterize the geomorphological processes responsible forthe site formation, and 3) evaluate their impact on the archaeological assemblages and their spatialintegrity (taphonomy).Spatial representations and analyses of the Lévêque’s excavation data are an invaluable aidfor evaluating the coherence of the first archaeo-stratigraphy established in the 1970s. A 3Dreconstruction of Lévêque’s spit record stemming from the reassessment of the faunal collection(Rougier et al., In Crevecoeur et al., 2016) was developed for exploratory purposes to evaluate thefeasibility of modeling the data recorded during the first excavations. This visualization, associatedwith calculations of coherence index and similarity index, allows on one hand to understand theinconsistencies of the first described archeo-sequence, and on the other hand, to reveal the spatialorganization of the archaeo-stratigraphical units. To go further, the coherence and similarity indiceswere analyzed according to methods usually used in geography such as the global and local Moranautocorrelation indices. As a result, an interactive visualization application allows researchers toexplore the stratigraphic units spatially as well as on the value of their indices. According to a specificprotocol, all of the piece-plotted objects from Lévêque’s excavations have X, Y and Z coordinates(Lévêque, 2002). Thanks to this precise recording system, supplemented by archaeozoological data(Morin, 2004), a database containing almost 6000 lithic and faunal pieces, with their 3D location,has been produced. Several 2D representations along with spatial analyses (using Getis and Ordindex, hot spots) of all the recorded objects from the Middle-Upper Palaeolithic levels, including theanalysis of the orientation and inclination of the objects (Todisco, 2015), have been computed.These spatial analyses contribute to a better understanding of the general organization of theartifacts / ecofacts of La Roche-à-Pierrot. They will be invaluable in anticipating fieldwork in thecoming years and will be a useful tool for interpreting our observations.