The DIACHRON project focused on the thorough chronological study of Besor 27 (B27), a Middle Palaeolithic open-air site located in the Besor basin, Southern Israel. Lithic artefacts typical of the Middle Palaeolithic were excavated, together with poorly preserved bones and teeth (see figure 1), due to unfavourable environmental conditions. Teeth samples were selected for a detailed characterisation study combining the use of scanning electron microscopy, Raman and FTIR spectroscopy, followed by a complete dating study including electron spin resonance spectrometry and U-series measurements. Modern samples of similar species (caprine, cattle, and equid) were also studied in order to build a reference analogue (see figure 7-9) and highlight diagenetic changes in fossil samples, as well as fossil samples from other archaeological contexts. The characterisation study showed that diagenetic processes, such as dissolution and recrystallisation, were present in the dated samples and that the precipitation of secondary mineral phase (such as calcite) may also have happened during burial in some of the samples. For instance, none of the samples from B27 preserved the dentine, the internal tissue whose composition is similar to bone mineral (ca. 70% mineralised phase). The enamel, which is mainly composed of hydroxyapatite, the mineral component of bones and teeth, was still preserved but alterations were visible to the naked eye, and at the microscopic level (see figure 4-6). It is known that teeth are prone to diagenetic alteration as stated above, but also the uptake of trace elements in dental tissues (e.g. enamel, dentine, and cementum). In particular, the uptake of uranium (U), which is radioactive, can affect significantly the age determination. Indeed, U follows different uptake modes that can be modelled using U-series analyses (230Th/U), but the reason for such diversity is not well understood. The U-series analyses conducted on the dated samples showed that U was heterogeneously distributed in the enamel. In particular, the external and internal sides (both in contact with the sediment because no dentine was preserved), contain a greater quantity of U, confirming that diagenesis may occur at different levels within a sample and that the dose rate is affected by such diagenetic processes (see figure 3). All these observations support the necessity of using characterisation tools prior to dating, in order to take into account such complex processes for the age calculation. The ESR analyses were performed on powder aliquots, from which an average dose of ionising rays received during burial was calculated (see figure 2). The equivalent doses are included within the same range, suggesting that those samples belong to a similar radioactive environment. Finally, the age calculation was obtained combining ESR, U-series and the radioactive composition of the sediment (determined by mass spectrometry), framing the human occupation at the site to ca. 90,000-70,000 years, in agreement with luminescence dating results obtained on the sediment.
