Investigating the cyclicity of Neanderthal occupations at Chez-Pinaud, SW France, using high-resolution OSL dating and Bayesian analysis.

The Middle Palaeolithic site of Chez-Pinaud in Jonzac (SW France) provides an unparalleled insight into the hunting and butchering behaviour of Neanderthals from ~60 ka ¹ ago. Excavations in the late 1990’s and early 2000’s uncovered a 6-meter sedimentary sequence comprising apparently alternating thin sterile layers and artefact-rich deposits, hosting densely packed accumulations of large ungulate bone fragments and lithics of the Quina Mousterian industry ² . These periodic deposits suggest repeated occupation and abandonment of the site, where Neanderthals were not inhabiting for long periods.  Despite these observations we are still limited in a obtaining a full occupational history of the site, predominantly due to limitations in existing dating methods.

In this study a novel sampling approach was applied to improve the chronological resolution of this site, combining high-resolution Optically stimulated luminescence (OSL) dating and Bayesian modelling. A 40 x 40 x 40 cm sediment block was removed from the main Quina-bearing layer (Layer 22 ²). Under controlled orange light at the RenDaL OSL laboratory at Université de Rennes, the block was carefully excavated by scraping away sediment in horizontal layers. Coordinates of artefacts were recorded and samples for OSL dating were collected at ~1 cm intervals down the block.  Single-grain quartz OSL data were analysed using the BayLum R package ³, incorporating Bayesian statistical modelling to reduce age uncertainties and to investigate the models capacity to handle OSL ages in close temporal and spatial distribution.

Our results indicate that the top of the section represents more modern deposits (~2 ka), which are void of bone fragments. These ages suggest sediment mixing from surface disturbances such as collapsing limestone or anthropogenic activities. Beyond this modern layer, two artefact-rich occupational layers separated by a thin sterile layer are identified through plotting the 3D distribution of the artefacts. The corresponding Bayesian ages for these layers vary between 58 – 80 ka, and do not increase linearly with depth and are thus difficult to correlate directly with the individual artefact bearing layers. These varying ages raise questions over dose rates when we consider the complexity of the heterogeneous sediments in the block. Continuing modelling will be conducted with BayLum as well as further investigation into the dose rate of the samples in attempts to further investigate and increase precision of the ages.

This work underscores the value of combining precise excavation methods with Bayesian analytical approaches for OSL data to construct precise chronologies, especially in important prehistoric archaeological contexts which host well preserved and challenging chronologies.

 

References:

¹ Richter, D. et al. Thermoluminescence dates for the Middle Palaeolithic site of Chez-Pinaud Jonzac (France). Journal of Archaeological Science 40, 1176–1185 (2013).

² Airvaux, J. & Soressi, M. Le site paléolithique de chez-Pinaud à Jonzac, Charente-Maritime. Prehistoire du Sud-Ouest 8, (2004).

³ Philippe, A., Guérin, G. & Kreutzer, S. BayLum - An R package for Bayesian analysis of OSL ages: An introduction. Quaternary Geochronology 49, 16–24 (2019).