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Abstract: Diagenetic alteration may limit the potential use of the biogenic composition of fossil bone as a reliable source of information for dietary, environmental and climatic reconstructions. One of the key parameters used to determine the state of preservation of fossil remains is their crystallinity. This can be evaluated by means of infrared spectroscopy, measuring the “splitting factor” (IRSF). However, the crystallinity may fail to describe the extent of chemical and mineralogical changes occurring during fossilization, and cannot be used alone as a reliable indicator of biogenic signal preservation. In this study, modern bones were experimentally heated in order to monitor the changes of FTIR spectral features related to an evolution of mineral properties. Further spectroscopic proxies of the mineral composition and structure were defined and calibrated. This method was then applied on unburnt, charred and calcined bones coming from three archaeological sites (Bize-Tournal, Organc 3 and Song Terus). The results obtained on modern and fossil bones demonstrate that low temperature heating and diagenetic processes may induce similar effects on bone mineral, while these processes are clearly distinct from those occurring during high temperature heating (>550 °C). The comparison between charred and calcined fossil bones shows that heating over 550 °C reduces the reactivity of the mineral phase and prevents compositional and structural characteristics from experiencing diagenetic modification. Applied to unburnt fossil bones, the proxies developed in this study, easily obtained from FTIR spectra, provide a more reliable evaluation of the degree of preservation than IRSF alone and contribute to a better understanding of the diagenetic processes. [Copyright &y& Elsevier]

Derivative Fourier transform infrared (FTIR) spectroscopy and curve fitting have been used to investigate the effect of a thermal treatment on the ν 1 ν 3 PO4 domain of modern bones. This method was efficient for identifying mineral matter modifications during heating. In particular, the 961, 1022, 1061, and 1092 cm−1 components show an important wavenumber shift between 120 and 700 °C, attributed to the decrease of the distortions induced by the removal of CO3 2− and HPO4 2− ions from the mineral lattice. The so-called 1030/1020 ratio was used to evaluate crystalline growth above 600 °C. The same analytical protocol was applied on Magdalenian fossil bones from the Bize–Tournal Cave (France). Although the band positions seem to have been affected by diagenetic processes, a wavenumber index—established by summing of the 961, 1022, and 1061 cm−1 peak positions—discriminated heated bones better than the 1030/1020 ratio, and the splitting factor frequently used to identify burnt bones in an archaeological context. This study suggest that the combination of derivative and curve-fitting analysis may afford a sensitive evaluation of the maximum temperature reached, and thus contribute to the fossil-derived knowledge of human activities related to the use of fire. [ABSTRACT FROM AUTHOR]