During the two-year Marie Skłodowska-Curie Fellowship (2023–2025), the fellow carried out an extensive programme of fieldwork, laboratory analyses, and methodological developments in ESR dating. Fieldwork missions in Senegal and Ghana provided new quartz samples for supplementary dating. More than 30 samples from 24 Stone Age sites were analysed across diverse depositional environments.
Laboratory work was conducted mainly at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH, Spain), leveraging its state-of-the-art ESR facilities, including two X-band ESR spectrometers (EMX and ELEXSYS) at low temperature using a nitrogen cooling system. Complementary OSL analyses were performed in collaboration with the OSL laboratory at CENIEH. Additional ESR experiments were performed at the Leibniz Institute for Applied Geophysics (LIAG, Hannover, Germany) to implement and test the Single Aliquot Regenerative (SAR) protocol, using an X-band ESR spectrometer (ELEXSYS) at low temperature with a nitrogen cooling system and employing a heating system and X-ray irradiators. Together, these activities enabled the fellow to test, optimise, and validate ESR protocols across a wide range of depositional and taphonomic contexts in western Africa, providing robust methodological developments and reliable chronological results for Middle Stone Age sites. Key technical and scientific results were achieved and are summarised below:
1. Improving the accuracy of ESR dating methods through optimisation of experimental protocols
The project focused on improving ESR dating on quartz grains. Working with quartz from western Africa proved challenging because the chronological signals were often very weak. The fellow developed a new detection protocol, the “Twin Windows” method, which enhances signal clarity and allows for more reliable age measurements. This method was first tested on samples from Côte d’Ivoire. Additionally, many samples displayed noisy or distorted signals that made age estimates uncertain. A new correction procedure was therefore developed to remove background noise and adjust the data, leading to more accurate equivalent dose determinations (one of the key parameters used to calculate ESR ages).
2. Modern analogue correction model
A model was developed to adjust ESR ages by comparing them with modern samples. In some western African sites, quartz grains were not fully reset before their deposition, leaving a residual dose that can represent up to 30% of the natural signal. By subtracting this residual dose, ESR ages show better agreement with OSL dating results. This correction helps explain why some ESR ages appeared too old—particularly in sites with fluvial or colluvial deposits.
3. Describing the behaviour of quartz during irradiation
The Single Saturating Exponential (SSE) function, when applied to the initial data points, provides the best description of signal evolution with increasing dose, producing ESR ages closely matching OSL ages. This represents a methodological advance in modelling dose–response curves and ensures greater consistency between ESR and OSL chronologies.
4. Testing and comparing ESR dating procedures
Two main ESR approaches were tested: the traditional Multiple Aliquot Additive Dose (MAAD) method and the Single Aliquot Regenerative (SAR) method. While the traditional MAAD method gave consistent results with OSL dating in many cases, it is less precise for very old samples (between 400,000 and 100,000 years), whereas the SAR method, tested in a few samples from Senegal, produced more precise results. The choice of ESR dating procedure must be adapted to the site type and its geological conditions.
5. Evaluation of ESR performance across different depositional contexts
The performance of ESR dating was evaluated under a range of environmental conditions. Under ideal conditions—such as well-bleached coastal deposits along the western coast of Senegal—MAAD yields results consistent with OSL. However, in less favourable contexts, such as fluvial deposits in Côte d’Ivoire or Guinea, uncertainties in equivalent dose and age estimates can reach up to 36%. These findings highlight the importance of considering depositional history and bleaching conditions when interpreting ESR ages.
6. Dating applications across diverse environments
The methodological developments were applied to a large regional dataset covering approximately 20 Stone Age sites across Senegal, Côte d’Ivoire, Guinea, and Mali, as well as new collections from four additional MSA sites in Senegal and Ghana. These sites represent a wide range of depositional environments, including coastal, fluvial, tropical forest, and inland Sahelian contexts. Among the 20 targeted sites (plus four new MSA sites), 16 yielded exploitable ESR results—representing a 75% success rate. This demonstrates the strong potential of the refined ESR protocols for obtaining reliable chronologies across diverse geomorphological and taphonomic settings in West Africa.
