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Title: Lying through your teeth : strontium diagenesis in archaeological enamel
Author: Lewis, Jamie
ISNI:       0000 0004 5918 0181
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Strontium isotopes are one of the most effective means to characterise mobility in past societies. However the technique proceeds on the basis that Sr recovered from archaeological calcified tissues is biogenic in origin and has not been contaminated by exogenous Sr. Whilst archaeological bone has been shown to be susceptible to uptake of diagenetic Sr, enamel appears to be resistant to alteration. However tooth enamel is the same mineral as bone and is in contact with the same burial environment so why should it be completely immune to diagenesis? This thesis attempts to investigate Sr uptake in archaeological enamel. From an assessment of the literature and trace element uptake models it is clear that uptake of diagenetic Sr into teeth will cause mixing of diagenetic and biogenic Sr in enamel. Thus detection of diagenetic Sr in teeth requires accurate and precise measurements of ⁸⁷Sr/⁸⁶Sr with high spatial resolution. LA-MC-ICP-MS is ideally suited to this but its application to bioapatites is challenging due to isobaric interferences. Here a method is presented which uses a customised plasma interface to reduce the effect of isobaric interferences and enable accurate and precise determinations of ⁸⁷Sr/⁸⁶Sr by LA-MC-ICP-MS. Diagenetic uptake of Sr into archaeological enamel should also cause mixing of biogenic and diagenetic Sr in stable isotope space. Thus if Sr isotopes could be shown to undergo mass dependent fractionation with trophic level this could be used to detect diagenetic Sr. Here stable Sr fractionation is demonstrated between the feed and dental tissues of a cohort of pigs raised on controlled diets. The results show a 0.3 %0 shift in δ⁸⁸Sr with trophic level. The rate and likely mechanism for Sr uptake in bone is assessed by measuring Sr concentration profiles in a suite of archaeological bones by LA-ICP-MS. The results show that the most likely mechanism for Sr uptake is by diffusion with adsorption. Bone is expected to reach equilibrium with the burial environment between 2,200 and 4,000 years, however the biogenic Sr isotope ratio is likely to be compromised long before equilibrium is reached. Strontium concentration, ⁸⁷Sr/⁸⁶Sr and δ⁸⁸Sr profiles are measured in a series of archaeological teeth to assess diagenetic uptake of Sr. Diagenetic uptake of Sr in archaeological enamel is detected with all three of these techniques. Uptake in enamel is consistent with a model of diffusion with adsorption and enamel is likely to reach equilibrium with the burial environment in 67,000 ± 26,000 years. However the biogenic Sr isotope signal will be compromised on significantly shorter time scales. Comparisons of measured uptake profiles with uptake models allows for current enamel decontamination procedures to be assessed. For Holocene age teeth, current decontamination methods are likely sufficient to remove diagenetically altered enamel. For older teeth, whilst decontamination procedures will remove some diagenetic Sr and LA-MC-ICP-MS methods may help to resolve mixing of diagenetic and biogenic Sr for some teeth it will only be possible to return an approximation of the biogenic Sr isotope ratio.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available