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Prof
Christopher
Bronk Ramsey
Research Laboratory for Archaeology and the History of Art
Oxford Radiocarbon Accelerator Unit
University of Oxford
Dyson Perrins Building
South Parks Road
OX1 3QY
UK
Tel: 01865 273931
Radiocarbon Dating Bone Samples Recovered from Gravel Sites is an Aggregates Levy Sustainability Fund project as disbursed by English Heritage. The project was undertaken by the Oxford Radiocarbon Accelerator Unit.
Radiocarbon pre-treatment chemistry is costly and time-consuming and so it is often not feasible to attempt to date bones, especially in large numbers, from gravel sites or others known for poor bone preservation. However, sites which predominantly yield bone which contain insufficient surviving collagen to date (ie <1% of the pristine amount) do include a small fraction of bones in which collagen is better retained.
A range of pre-screening criteria which could be used on-site, in museums, or the laboratory were tested to determine which, if any, could be used to identify those suitable for radiocarbon dating prior to collagen extraction. For this project 298 human and animal bones were analysed from 12 sites across southern England (Etton and Haddenham Causewayed Enclosures; Mount Farm, Berinsfield; Cleveland Farm; RMC Land, Harlington; Bestwall Quarry; Brandon Staunch Meadow; Holloway Lane; Eynesbury; Huntsman's Quarry; Imperial College Sports Ground; Kingsmead Quarry).
All bones were subject to hardness, colour (hue, saturation, brightness), microporosity and bulk powder density analysis. Following this, a sub-sample of 200 bones were chosen for elemental analysis (percent carbon and nitrogen and C:N atomic ratio of whole bone) and Fourier Transform Infrared Spectroscopy (splitting factor and carbonate : phosphate ratio). Of these bones, 100 were chosen for full radiocarbon pre-treatment. The percentage yields of collagen, insoluble residue and <30kD residue were calculated and the stable isotopic values and C;N atomic ratio of the purafied collagen measured. 20 samples underwent amino acid analysis and 18 samples were studied using small-angle X-ray scattering (SAXS). Photographs of 297 of the original 298 bones are also included in this dataset.
The measurement of whole bone percent nitrogen was consistently the most reliable predictor of suitability for radiocarbon dating. No other pre-screening criterion, or combination of criteria, showed a correlation with collagen preservation, either within the entire study or datasets from individual archaeological sites.