Bayesian Modeling of Wood-Age Offsets in Cremated Bone

Abstract

Experimental 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 new 14C 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.

Dividing time—An absolute chronological study of material culture from Early Iron Age urnfields in Denmark

“…In both cases, we reject the earlier date (GrM-14704 and RICH-24144, respectively) because they are considerably earlier than other dates on these artefact types. Results from Aarupgaard U1834 were measured on separate bone fragments, which might have different wood-age offsets due to differential uptake of carbon from the burning atmosphere [ 22 ], although the presence of multiple individuals in the grave cannot be excluded, as observed in Late Bronze Age cremation burials in Belgium [ 113 ]. The laboratories have participated in more intercomparison studies, demonstrating results to be reproducible and comparable [ 105 , 114 ].…”

Multi-proxy analyses reveal regional cremation practices and social status at the Late Bronze Age site of Herstal, Belgium

“…Research on the choice of wood used as fuel in Bronze Age pyres in northern Europe indicated a selection of mixed timbers based on their availability around the site (Moskal-del Hoyo, 2012;O'Donnell, 2016). Therefore, the old-wood effect, if present, would have heterogeneously affected the cremated individuals and the difference in 14 C content of the cremated bone would be more statistically significantly dispersed (Snoeck et al, 2014a;Rose et al, 2020). Rather, other factors influencing the number of individuals within a cremation deposit, such as reusing of the grave or the pyre, or curation of the bones may have been at play.…”

Patterns of glacio‐isostatic adjustment in mainland Scotland: new data from western central Scotland, proximal to the zone of maximum rebound

“…Much work has been done recording shoreline characteristics within the region around the Clyde estuary, but this work has taken the form of very early Quaternary studies, site descriptions in field meeting reports and British Geological Survey reports along with brief analyses of radiocarbon dates (Smith 1836; Clough et al . 1925; Rose 1969, 1975, 1979, 1980a, b, c, 1982, 2003a, b; Bishop & Dickson 1970; Peacock 1971, 2003; Peacock et al . 1978; Browne & Graham 1981; Browne et al .…”

“…In the account below, previouswork is outlined before the present work is described and set in the context of models of glacio-isostatic uplift. Much work has been done recording shoreline characteristics within the region around the Clyde estuary, but this work has taken the form of very early Quaternary studies, site descriptions in field meeting reports and British Geological Survey reports along with brief analyses of radiocarbon dates (Smith 1836;Clough et al 1925;Rose 1969Rose , 1975Rose , 1979Rose , 1980aRose , b, c, 1982Rose , 2003aBishop & Dickson 1970;Peacock 1971Peacock , 2003Peacock et al 1978;Browne & Graham 1981;Browne et al 1983;Browne & McMillan 1984Paterson et al 1990). Hitherto, there had been no substantive study of shoreline development within the region.…”