HR: 1330h
AN: PP32B-0283    [PDF]
TI: Behaviour of Structural Carbonate Stable Carbon and Oxygen Isotope Compositions in Bioapatite During Burning of Bone
AU: * Munro, L E
EM: lmunro3@uwo.ca
AF: The University of Western Ontario, Dept. of Earth Sciences, London, ON N6A 5B7 Canada
AU: Longstaffe, F J
EM: flongsta@uwo.ca
AF: The University of Western Ontario, Dept. of Earth Sciences, London, ON N6A 5B7 Canada
AU: White, C D
EM: white2@uwo.ca
AF: The University of Western Ontario, Dept. of Anthropology, London, ON N6A 5C2 Canada
AB: Bioapatite, the principal inorganic phase comprising bone, commonly contains a small fraction of carbonate, which has been substituted into the phosphate structure during bone formation. The isotopic compositions of both the phosphate oxygen and the structural carbonate oxygen are now commonly used in palaeoclimatological and bioarchaeological investigations. The potential for post-mortem alteration of these isotopic compositions, therefore, is of interest, with the behaviour of structural carbonate being of most concern. In bioarchaeological studies, alteration of bone isotopic compositions has the potential to occur not only during low-temperature processes associated with burial but also during food preparation involving heating (burning, boiling). Here, we examine the stable isotopic behaviour of structural carbonate oxygen and carbon, and coexisting phosphate oxygen during the burning of bone. Freshly deceased (6$<$8 months) white-tailed deer leg bones ({\it Odocoileus virginianus}) were collected from Pinery Provincial Park, Ontario, Canada. Each long bone was sectioned and incrementally heated from 25 to 900$\deg$C, in 25$\deg$ intervals. The samples were then ground to a standardized grain-size (45$<$63$\mu$m), and changes in bioapatite crystallinity (CI) were determined using powder X-ray diffraction (pXRD), and Fourier transform infra-red spectroscopy (FTIR). Combined differential thermal and thermogravimetric analyses (DTA/TG) were used to evaluate weight loss and associated reactions during heating. Stable carbon isotope compositions of the bioapatite remain relatively constant ($\pm$1$\permil$) during heating to 650$\deg$C. A 4$\permil$ increase in stable carbon isotopic composition then occurs between 650-750$\deg$C, accompanied by an increase in CI, followed by a 10$\permil$ decline at temperatures above 800$\deg$C, as carbonate carbon is lost. Carbonate and phosphate oxygen isotopic compositions are correlated over the entire heating range, with carbonate being enriched relative to phosphate by about 8-10$\permil$ below 500$\deg$C, 5-6$\permil$ between 500-700$\deg$C, and 8-10$\permil$ above 700$\deg$C. CI and oxygen isotopic compositions of carbonate and phosphate are not well correlated. Only modest CI changes are recorded from 25-675$\deg$C, compared with much larger changes in oxygen isotopic composition, especially above 300$\deg$C. On average, original isotopic compositions are largely preserved for both phosphate ($\pm$1$\permil$) and carbonate ($\pm$2$\permil$) oxygen at $<$300$\deg$C. At higher temperatures, however, both phosphate and carbonate oxygen in the bioapatite are systematically depleted of oxygen-18 relative to original values.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting