Anomalous radiocarbon dates from the early medieval cremation graves from Broechem (Flanders, Belgium) : reservoir or old wood effects?

As part of the study of the early medieval cemetery at Broechem (Belgium), human bones from 32 cremation graves have been dated through radiocarbon (14C) analysis. It was noted that many of the dates were not in accordance with the chronological ranges provided by the characteristics of the cultural artifacts deposited in the graves. In fact, the human bones were “older” than the artifacts. Subsequently, a number of animal bones (in all cases from domestic pigs) was radiocarbon dated, yielding dates that were more consistent with the information from the cultural artifacts than the human bones. The dates obtained on human and pig bones from the same grave often differed around 100 radiocarbon years. This paper tries to find an explanation for the pattern observed, concentrating on two hypotheses: aquatic reservoir versus old wood effects. The evaluation takes into account additional radiocarbon dates derived from charcoal fragments of the funeral pyre, from both short-lived and long-lived taxa. A conclusive explanation for the anomalous radiocarbon dates could not be reached but clear suggestions can be put forward for future experimental work that will without doubt shed more light upon the interpretational problems raised