Bone Collagen Preservation at the Roonka Flat Aboriginal Burial Ground: A Natural Laboratory

Abstract

A collagen extraction procedure was performed on cortical bone samples from 86 prehistoric human interments excavated from a sand dune at the Roonka Flat archaeological site near Blanchetown, South Australia. The interments date from the Early Holocene to the period of European contact, ca. A.C. 1840. Carbon and nitrogen concentrations in extracts were used to assess collagen preservation. Over 83% (15/18) of the Early Holocene sample and 34% (23/68) of the Late Holocene sample were regarded as poorly preserved on the basis of low carbon and/or nitrogen concentrations (C < 5% and/or N < 0.5%). Approximately 67% (32/48) of the remaining sample showed good collagen preservation (C> 13% and N>4.8%) and the other 33% (16/48) was included in an intermediate preservation category. A comparison of the good, intermediate, and poor preservation categories shows a stepwise trend toward higher atomic C/N ratios and more positive δl3C values as samples become less well preserved. In general, carbon and nitrogen concentrations in extracts are lower and C/N ratios are higher in the Early Holocene versus Late Holocene sample, whereas stable carbon isotope values do not vary with duration of burial. Because extract C/N ratios, δl3C values, and yields are extremely variable, as independent criteria they are not useful in identifying degrees of bone collagen preservation. The determination of carbon and nitrogen concentrations in acid insoluble extracts provides an initial screening procedure to select bone samples for radiocarbon or stable isotope analysis.