Dealing outliers offsets radiocarbon dating

Our paper (1) proposes a new chronology for Ksâr 'Akil based on 16 accelerator mass spectrometry (AMS) determinations on shells.To minimize the possibility of dating diagenetically compromised samples, we conducted amino acid racemization analyses on the intracrystalline proteins, oxygen isotope analysis, and geochemical characterization of all dated shells.However, although the locations of the samples sent to the three laboratories involved are known, the locations of the 12 subsamples within these samples are not.We consider all 387,072 plausible spatial allocations and analyse the resulting distributions of statistics.Currently, there are no dates for the start of the IUP; thus, placing boundaries cannot be substantiated by any chronological data.Nonetheless, incorporating these boundaries in our model provides an age estimate for Ethelruda of 49.9–44.1 ka cal B.

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However, there are Bayesian statistical methods which can be used to perform this rejection in a more objective way (Christen 1994b), but these are not often used.Plots of robust regression residuals from the forward search indicate that some sets of allocations are implausible.We establish the existence of a trend in the results and suggest how better experimental design would have enabled stronger conclusions to have been drawn from this multi-centre experiment.This unstable isotope of Carbon then enters the food chain, and in doing so, forms part of all organic matter (Bayliss et al. Broadly speaking, anything that was once alive can therefore theoretically have measured the levels of radiocarbon it now contains.It is also possible to obtain radiocarbon determinations from inorganic materials if the process of producing the finished state includes the incorporation of carbon; examples of where this might be possible is the application of lime mortar as carbon dioxide is absorbed by the surface when the mortar hardens (Bowman 19).

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