The isotopic composition and diagenesis of human bone from Teotihuacan and Oaxaca, Mexico

We analyzed archaeological human bone from Teotihuacan and Oaxaca, dating from about 300 BC to 750 AD to distinguish ethnic groups within Teotihuacan using oxygen isotopes. Sixty-eight analyses of bone phosphate δ18O were made of 64 individuals. In addition to oxygen isotopic analysis, the bones were examined using FTIR spectra, with some additional DNAA and ICP-MS analyses. Little change occurs in the bone apatite until the amount of collagen (as combustible organics) has been reduced considerably, when the bone becomes softer and FTIR crystallinity increases. The δ18O of the phosphate (δp) appears to be unaltered even after extensive diagenesis and, probably, solution. On FTIR plots the relative area of the carbonate peak to the main phosphate peak decreases with diagenetic level. The bones absorb some metals rapidly after burial, for example uranium, which then leach out as diagenesis of the bone apatite progresses. Other metallic elements increase irregularly in concentration as alteration proceeds.