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.