Radiocarbon dating of bone apatite by step heating

Abstract

Summary and Analysis The choice of pretreatment methods is critical to the success of the step heatingmethod as dating results varied widely depending upon the pretreatment used. Theuse of an acetic acid wash followed by a NaOCl/acetic acid wash gave the bestresults. Performing solution transfers under a nitrogen atmosphere may have im-proved dates as well, but more likely the success of Dent series 4 is due to the useof tooth enamel. The success of the dates from Murray Springs supports this con-tention as solution transfers were not performed under nitrogen. All of the seriesgenerally showed a trend of increasing age with increased extraction temperature.The lowest temperature fraction consistently produced the youngest dates and inthree series (e.g., Dent series 2 and 4, Murray Springs) were significantly offsetfrom the general trend of the other samples. This suggests that perhaps CO 2 re-leased at very low temperatures ( 500 C) is derived in part from a highly ex-changeable fraction of carbonate, perhaps that absorbed to crystal surfaces aspostulated by Hedges et al. (1995:289).The general patterning seen in the Dent data suggests a system composed of aseries of carbonate fractions that vary in their susceptibility to exchange, with noparticular temperature fraction being totally immune. A simple model shows howtemperature-age spectra may evolve with increased contamination (Figure 3). Themodel shows five temperature fractions, each being less susceptible to exchangethan the previous lower temperature fraction. As a bone becomes increasinglycontaminated, the slope of temperature-age spectra becomes increasingly steep.This occurs because low temperature fractions, being more susceptible to ex-change, are contaminated at a greater rate than high temperature fractions. If sucha model is accurate, it provides a convenient means of estimating the amount ofcontamination affecting a sample based on shape of the temperature-age spectrumproduced. Spectra with a steep slope tend to produce