Characterization of a key sequence of the French Palaeolithic: geovisualization and intra-site spatial analysis of La Roche-à-Pierrot, Saint-Césaire
Résumé
Located in Saint-Césaire, east of Saintes, in Charente-Maritime (France), the archaeological record
of La Roche-à-Pierrot is at the heart of the debates concerning the Middle/Upper Palaeolithic
transition. To this day, La Roche-à-Pierrot constitutes the only site to have provided a relatively
complete Neandertal skeleton associated with a transitional industry, the Châtelperronian, which
was until then attributed to Modern Humans. Discovered in 1976, the site was the subject of several
excavation campaigns conducted by F. Lévêque from 1977 to 1987 and in 1993 (with an additional
season 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-evaluate
the archaeostratigraphic sequence, 2) characterize the geomorphological processes responsible for
the site formation, and 3) evaluate their impact on the archaeological assemblages and their spatial
integrity (taphonomy).
Spatial representations and analyses of the Lévêque’s excavation data are an invaluable aid
for evaluating the coherence of the first archaeo-stratigraphy established in the 1970s. A 3D
reconstruction 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 the
feasibility of modeling the data recorded during the first excavations. This visualization, associated
with calculations of coherence index and similarity index, allows on one hand to understand the
inconsistencies of the first described archeo-sequence, and on the other hand, to reveal the spatial
organization of the archaeo-stratigraphical units. To go further, the coherence and similarity indices
were analyzed according to methods usually used in geography such as the global and local Moran
autocorrelation indices. As a result, an interactive visualization application allows researchers to
explore the stratigraphic units spatially as well as on the value of their indices. According to a specific
protocol, 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 Ord
index, hot spots) of all the recorded objects from the Middle-Upper Palaeolithic levels, including the
analysis 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 the
artifacts / ecofacts of La Roche-à-Pierrot. They will be invaluable in anticipating fieldwork in the
coming years and will be a useful tool for interpreting our observations.