Characterization of Burnt Bones in Archaeological Context: a Comparative Study of Modern and Fossil Material by Infrared Spectroscopy

Abstract

The identification of burnt bones in an archaeological context can entail characterization techniques such as infrared spectroscopy. However, it is often difficult to clearly distinguish bones burnt at low temperatures (<500oC) because the alterations that occur during heating are similar to those that occur during burial. Moreover, these analyses are generally carried out on samples reduced to powder and they do not permit us to take into account the heterogeneity of the bone material.In order to address these various problems, we became interested in theν1ν3PO4 domain, whose study, on modern bones burnt under experimental conditions, allowed us to establish parameters that make it possible to evaluate the crystallinity of the samples (1030/1020 ratio) and to gather information on the crystal structure of the mineral phase (wavenumbers of the peaks centred near 961, 1022, 1061, and 1092 cm-1.) In particular, the wavenumbers of these various peaks have made it possible to identify bones burnt at temperatures as low as 250oC in the Magdalenian levels of the site of Bize-Tournal, while crystallinity by itself allowed only the clear identification of bones burnt above 500oC. This method can therefore contribute to an improved identification of bones burnt at low temperatures in an archaeological context. Moreover, this analytical protocol will make it possible to study the spatial variations in the composition of bone material by infrared micro-spectroscopy and thus to define and distinguish the alterations occurring during heating and during diagenesis.