A multiscalar and multiproxy geoarchaeological approach to site formation processes at the Middle and Upper Palaeolithic site of La Roche-à-Pierrot, Saint-Césaire, France

The site of La Roche-à-Pierrot in Saint-Césaire (Charente-Maritime, France) produced a succession of Mousterian, Châtelperronian and Aurignacian occupations, and continues to play a central role in debates concerning the Middle-to-Upper Palaeolithic transition. The source of controversy surrounding the site relates to ambiguities concerning the overall archaeological sequence, the cultural association of the human remains found at the site and the limited number of robust absolute dates. Here, we present the results of a multiscalar, multiproxy geoarchaeological investigation of the site's sedimentary sequence. Our study integrates geomorphology, field lithostratigraphy, microstratigraphy, geochemistry and absolute dating methods (radiocarbon and optically stimulated luminescence) designed to characterize site formation processes. We propose a site formation model involving the evolution of a karstified limestone cliff from a semi-closed system to an exposed slope deposit, with sediments at the base of the cliff accumulating under periglacial conditions of MIS3, broadly between ca. 59.9 ± 3.9 ka and ca. 37.7 ka. The lowermost Mousterian occupations took place in a semi-closed, sheltered space in which sedimentary rates were low, involving mainly cryoclastic roof spall and episodic percolation of fine-grained sediment. This depositional environment generated a Mousterian archaeological palimpsest in the proximal area and translocated downslope. Subsequent Mousterian, Châtelperronian and Aurignacian remains embedded within diamictons were deposited in an open-air context, on a sloping surface at the apex of a palaeotalus, and possibly above the site, at the top of the cliff. The resulting diachronous surfaces and immature deposits were subject to solifluction and slopewash, with low sedimentary rates. Our geoarchaeological study sheds new light on previously noted spatial inconsistencies in the archaeological sequence and constitutes a rigorous framework for further archaeological research at the site, highlighting the potential of a multiscalar, multiproxy site formation research to improve stratigraphic investigation of Palaeolithic sites in similar geomorphological contexts.