Heating and diagenesis-induced heterogeneities
in the chemical composition and structure
of archaeological bones from the Neolithic site
of Chalain 19 (Jura, France)
Bone materials, including numerous fragments of burned bones, are often found at archaeological sites. A comparative study of burned and unburned bone materials originating from the lacustrian site 19 of Chalain Lake, Jura, France, was conducted in order to assess their potential to yield information on past lifeways. The bones were analysed using various complementary physico-chemical methods (SEM-EDX, microPIXE/PIGE, FTIR, XRD, TEM-EDX) taking into account their chemical and structural heterogeneity. Through this “high resolution” approach, it was possible to observe the modifications of the bone mineral phase induced by heating and the processes of soil diagenesis, at the scale of the sample.
Our research has made it possible to distinguish the markers that characterise the diagenesis and heating of the specimens. The markers of heating could be used as quantitative indicators of the heating temperature reached by the bone prior to being buried. In addition, the results show different modification mechanisms depending on the possible heating of the bone prior to burying. Specifically, the concentration profiles determined on cross-sections by PIXE/PIGE make it possible to reveal an increase in exogenous chemical species at the centre of the heated sample, in contrast with the unburned bones which show higher concentrations of exogenous elements at the edge than at the centre. Thanks to the nanoscale structural analysis by transmission electron microscopy (TEM), it was possible to correlate the specific modifications of the elemental composition with the size of the apatite crystals present in the specimens.
This method can now be applied to other archaeological problems such as the investigation of various funerary customs or the taming of fire, in the knowledge that it can be applied to a small number of samples that must consequently be carefully selected from a larger corpus in order to be representative.
To cite this article
Reiche I., 2010 – Heating and Diagenesis-Induced Heterogeneities in the Chemical Composition and Structure of Archaeological Bones from the Neolithic Site of Chalain 19 (Jura, France), in Théry-Parisot I., Chabal L., Costamagno S., The taphonomy of Burned Organic Residues and Combustion Features in Archaeological Contexts, Proceedings of the round table, May 27-29 2008, CEPAM, P@lethnology, 2, 129-144.
Characterization of burnt bones
in archaeological context:
a Comparative Study of Modern and Fossil Material
by Infrared Spectroscopy
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 (<500°C) 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 the ν1ν3PO4 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 250°C in the Magdalenian levels of the site of Bize-Tournal, while crystallinity by itself allowed only the clear identification of bones burnt above 500°C. 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.
To cite this article
Lebon M., 2010 – Characterization of Burnt Bones in Archaeological Context: a Comparative Study of Modern and Fossil Material by Infrared Spectroscopy, in Théry-Parisot I., Chabal L., Costamagno S., The taphonomy of Burned Organic Residues and Combustion Features in Archaeological Contexts, Proceedings of the round table, May 27-29 2008, CEPAM, P@lethnology, 2, 145-158.