Bone and enamel carbonate diagenesis: A radiocarbon prospective

Abstract

The debate regarding the susceptibility of bone and enamel carbonate to preserve in vivo carbon isotope ratios is as old as paleodietary research. After more than three decades of controversy, a consensus seems to have been reached, and archeological bone apatite is generally considered suitable while enamel has become the gold standard for pre-Quaternary studies. But the absence of a quantitative diagenetic test to assess the preservation of bone and enamel carbonate δ13C values is problematic. Here, radiocarbon (14C) dating is used as a tracer, to quantify carbon isotope exchange in bone, dentine and enamel carbonate during early diagenesis. Samples covering most of the range of radiocarbon dating and coming from different burial environments and climates were dated. When possible, enamel, dentine and bone from the same individuals were selected. All tissues record an uptake of modern carbon leading to a change in the radiocarbon age of the sample which becomes significant after about 8000BP. In some of the sites, enamel is older than bone or dentine carbonate from the same individual, while in others, the contrary is observed. An intermediate case where identical 14C ages were measured between bone carbonate and enamel was also observed, suggesting either a lack of alteration, or similar degree of C-isotope exchange for the two tissues. Overall, no systematic 14C difference was found between bone, dentine and enamel from the same individual suggesting that differences in crystallinity or porosity do not play a major role during the early stage of bone and enamel diagenesis and that δ13C values measured in bone apatite are as reliable as in enamel at least for the past 40,000yr.