Constraining the age of the Middle Stone Age locality of Bargny (Senegal) through a combined OSL-ESR dating approach

Abstract

The Middle Stone Age (MSA) is the major chrono-cultural phase associated with the emergence and evolution of Homo sapiens in Africa. Despite its importance, the MSA has not been evenly well investigated across Africa, and West Africa in particular remains poorly understood. Although new research is beginning to fill in this crucial gap of knowledge, MSA chronologies in West Africa only rely on Optically Stimulated Luminescence (OSL) dating. In this context, the increasing use of a multi-method dating approach appears essential to strengthen this emerging geochronological framework. Here, we apply such approach to constrain the age of Bargny locality, located in close proximity to the modern Senegalese coast (South of Dakar), and which documents one of the oldest MSA occupations in West Africa. Specifically, we combine OSL and Electron Spin Resonance (ESR) methods to date the MSA sites of Bargny 3 (BG3) and Bargny 1 (BG1). A mean OSL age of 127±8 ka may be proposed for the MSA of BG3, which is in good agreement with a mean Ti-H ESR age of 125±14 ka from the same unit. Interestingly, similar ages are obtained by OSL (144±7 ka) and Ti-H ESR (138±14 ka) for the MSA horizon from BG1. While these results illustrate the great potential of the combined OSL-ESR dating approach to establish robust chronologies, they also contribute to improve the geographical and chronological resolution of the MSA record in West Africa. More specifically, they also corroborate the presence of MSA occupations along the Senegambian coast around the MIS 6-MIS 5 transition. In combination with the associated estuarine environments and mangrove forest, the evidence from Bargny adds to the known diversity, and likely complex behaviour, of early human populations living by Africa’s coastlines.