Abstract
ABSTRACTExperimental studies have shown that significant carbon exchange occurs between bone-apatite and the pyre atmosphere during cremation, which can cause a calendar date offset between the radiocarbon (14C) event and the date of cremation. There are limited empirical data available to assess the magnitude of such wood-age offsets, but the aim of this paper is to test if they can be modeled statistically. We present new14C dates on modern bone cremated in realistic open-air experiments and on archaeological samples of cremated bone and associated organic material. Experimental results demonstrate a wide range of carbon exchange with a mean of 58.6 ± 14.8%. Archaeological results indicate that the wood-age offsets have an approximately exponential distribution. We test whether the default Charcoal Outlier_Model in OxCal v4.3, developed to reduce the impact of wood-age offsets in dates of charcoal, is appropriate for cremated bone, but find that it slightly underestimates apparent offsets. To counter the intrinsic age of both pyre fuel and unburned bio-apatite, we instead propose a bespoke Cremation Outlier_Model, which combines an exponential distribution of calendar age offsets with a minimum offset, and provides better estimates of the actual dates of cremations.
Highlights
Experimental studies (Zazzo et al 2009, 2012; Hüls et al 2010; Van Strydonck et al 2010) have shown that only a fraction of original bone apatite carbon remains in the bone after cremation, but that there is a significant carbon uptake from the pyre atmosphere, which is derived mainly from the burning fuel
To counter the intrinsic age of both pyre fuel and unburned bio-apatite, we instead propose a bespoke Cremation Outlier_Model, which combines an exponential distribution of calendar age offsets with a minimum offset, and provides better estimates of the actual dates of cremations
We have demonstrated significant variation in carbon exchange in experimentally cremated bone (CB), with % carbon exchange among samples from single pyres ranging from 29.3 ± 0.5% to 83.5 ± 0.4%
Summary
Experimental studies (Zazzo et al 2009, 2012; Hüls et al 2010; Van Strydonck et al 2010) have shown that only a fraction of original bone apatite carbon remains in the bone after cremation, but that there is a significant carbon uptake from the pyre atmosphere, which is derived mainly from the burning fuel This was not realized almost two decades ago when a pioneering study on radiocarbon (14C) dating cremated bone (CB) demonstrated that dates on the bio-apatite of fully calcined bone were comparable to those on associated charcoal (Lanting et al 2001). Carbon exchange between the bone and the combustion atmosphere will cause a calendar date offset between the calibrated 14C measurement and the main event of interest (the date of cremation), which we will in the present paper refer to as a wood-age offset
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