Carbon Exchanges between Bone Apatite and Fuels during Cremation: Impact on Radiocarbon Dates

Abstract

An important advance in the radiocarbon dating of archaeological material occurred in the late 1990s, with direct dating of cremated human remains. A crucial part of the argument was the demonstration that comparable results could be obtained from paired dates of charcoal and calcined bone from the same contexts. Recent studies, however, have noted the influence of carbon from the fuel sources, raising a question over the interpretation of the paired charcoal/bone dates. Here, fleshed modern animal joints were burned with “old” fuel of known age, providing experimental evidence under natural conditions, demonstrating a clear effect of the fuel source on the carbon isotopic composition of calcined bone. In most situations in which branchwood was used as fuel, dates on calcined bone should not show any significant offset, as the wood will be of a similar age to the cadaver. For cases in which old wood, coal, or peat are used as fuel, we expect an offset of some decades/centuries, potentially up to millennia. We observed, however, that the amount of14C intake from the fuel is extremely variable (from 39 to 95%). A strong correlation between age offset and δ13C values suggests that the latter might be useful in identifying large inputs from14C-depleted fuels. A level of caution is recommended when14C dating calcined bone in cases where fuels with an inbuilt age may have been used in the cremation process.