Abstract
A recent study into prescreening techniques to identify bones suitable for radiocarbon dating from sites known for poor or variable preservation (Brock et al. 2007, 2010a) found that the percent nitrogen (%N) content of whole bone powder was the most reliable indicator of collagen preservation. Measurement of %N is rapid, requires little preparation or material, and is relatively cheap. The technique reduces the risk of needlessly sampling valuable archaeological objects, as well as saving time and money on their unsuccessful pretreatment prior to dating. This method of prescreening is now regularly used at the Oxford Radiocarbon Accelerator Unit (ORAU). In the original study, linear regression analysis of data from 100 bones from 12 Holocene sites across southern England showed that when 0.76% N was chosen as a threshold, 84% of bones were successfully identified as containing sufficient (i.e. >1%) or insufficient (i.e. <1%) collagen for dating. However, it has been observed that for older, Pleistocene bones the failure rate may be higher, possibly due to the presence of more degraded, short-chain proteins that pass through the ultrafilters used in pretreatment, resulting in lower yields. Here, we present linear regression analysis of data from nearly 600 human and animal bones, antlers, and teeth, from a wide range of contexts and ages, to determine whether the 0.76% threshold identified in the previous study is still applicable. The potential of carbon:nitrogen atomic weight ratios (C:N) of whole bone to predict collagen preservation is also discussed.
Highlights
We published the results of a study seeking to find one or more criteria that could be used to prescreen bones from sites known to have poor or variable collagen preservation and to identify those samples suitable for radiocarbon dating (Brock et al 2007, 2010a). 1 4 C dating is a costly and time-consuming process, and prescreening to identify which samples contain sufficient collagen for dating (i.e. > 1 % weight yield at Oxford Radiocarbon Accelerator Unit (ORAU): van Klinken 1999) can save time and money, but can prevent the unnecessary destruction of samples that are shown to be unsuitable for dating
The %N content of whole bone powder cannot distinguish between nitrogen present as collagen and non-collagenous proteins (NCP), or that which is present from soil, e.g. proteins, nitrates, or humic acids
Samples that yield < 1 % wt collagen are not routinely dated at ORAU, nor are those yielding
Summary
We published the results of a study seeking to find one or more criteria that could be used to prescreen bones from sites known to have poor or variable collagen preservation and to identify those samples suitable for radiocarbon dating (Brock et al 2007, 2010a). 1 4 C dating is a costly and time-consuming process, and prescreening to identify which samples contain sufficient collagen for dating (i.e. > 1 % weight yield at ORAU: van Klinken 1999) can save time and money, but can prevent the unnecessary destruction of samples that are shown to be unsuitable for dating. 1 4 C dating is a costly and time-consuming process, and prescreening to identify which samples contain sufficient collagen for dating The study analyzed nearly 300 Holocene human and animal bones from gravel sites in southern England and found that the most successful method of predicting which samples would be suitable for dating was measurement of the percent nitrogen (%N) content of whole (raw) bone. Fresh modern bone contains -3.5-4.5% nitrogen (Stafford et al 1988), of which - 9 0 % is present as collagen and the remaining 10% as non-collagenous proteins (NCP) (Sillen and Parkington 1996). It should be noted that measurement of %N content cannot specify the amount of non-nitrogenous soil-derived organic matter present in a specimen (Hedges and van Klinken 1992). Predicting the collagen content of some bones that are highly contaminated and/or degraded will always be problematic
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