Bone collagen quality indicators for palaeodietary and radiocarbon measurements

The quality of bone collagen extracts is central to the 14C dating and isotope palaeodietary analysis of bone. The intactness and purity of the extracted gelatin ('collagen') is strongly dependent on the extent of diagenetic degradation, contamination and the type of extraction method. Possible chemical, elemental and isotopic parameters for the assessment of 'collagen' quality are discussed. The most important distinction that can be made is the one between contaminated bone (mostly from temperature zones), and bone low in collagen content (mostly from arid and tropical zones). The latter shows more variability in all quality parameters than the former. The natural level of contamination is mostly so low that stable isotopic measurements are not impaired, although 14C measurements can be. It is concluded that there is no unequivocal way to detect natural levels of contamination with the discussed parameters, although their use can identify many cases. In low 'collagen' bone, the parameters can identify the great majority of problematic samples: although deviations in these parameters do not necessarily mean isotopic alterations, the increased background found in these samples makes most samples unusable.