Isotope Geochemistry of Burned Bones: Implications for Paleodietary Reconstruction and Radiocarbon Dating

Abstract

Though they are frequently found at archaeological sites, burned bones have long been neglected by geochemists. After a brief review of the mineralogy and diagenesis of vertebrate skeletal tissues, all the physico-chemical changes induced by the high temperature combustion of bones are summarized. The implications of these changes for the reconstruction of diets through stable isotope ratios analysis and for the radiocarbon dating of bone remains are then discussed. It is thus shown that the high-temperature (>600oC) re-crystallisation of the mineral fraction of bones: (1) provokes a fractionation of the isotopes that modifies the δ13C of the bone and therefore makes it unsuitable for paleo- dietary reconstructions; (2) protects the bone from chemical interactions with the surrounding environment during fossilisation, thus making calcined bone a reliable material for radiocarbon dating.The calcined bones can in turn be used to estimate the state of preservation of the unburned bones found at the same site when the collagen has not been preserved.