Unravelling Cremated Bone – Structural, Elemental and Isotopic Studies

Cremated bone occurs in many archaeological sites as small grey and white fragments. The high temperatures reached during heating induce structural, elemental and isotopic changes to bone apatite (the inorganic fraction of bone). These changes are investigated here by infrared spectroscopy and mass spectrometry (δ13Cap, δ18Oc, δ18Op and 87Sr/86Sr) in both modern heated bone and archaeological cremated specimens. The results of various heating experiments (in laboratory and natural conditions) highlight the significant carbon and oxygen exchanges with the fuel used as well as with bone organic matter (mainly collagen). While not informing on dietary practice and hydrology as is the case with unburned bone/tooth, the carbon and oxygen isotope ratios of calcined samples together with infrared spectroscopy results provide information on the conditions in which the bone was burned (e.g. presence of fuel, size of the pyre, temperatures reached, dry or fresh bone, etc.). In contrast, the effect of burning on the strontium present in bone is minimal. Furthermore, as observed through artificial contamination experiments, post-burial alterations also appear to be extremely limited, which is to be expected due to the higher crystallinity of calcined bone apatite compared to unburned bone and even enamel. These experiments demonstrate that calcined bone provides a reliable substrate for mobility studies using its strontium isotope composition. The results of this work greatly extend the application of strontium isotopes to places and periods in which cremation was the dominant mortuary practice, or where unburned bone and enamel do not survive. Furthermore, carbon and oxygen isotope analyses and infrared spectroscopy provide insights into the reconstruction of ancient cremation practices.