Application of neutron activation analysis to the study of element concentration and exchange in fossil bones

It has long been known that a variety of elements are introduced into voids in the structure of bone during fossilization. Visual examination of the cross-section of many bones in the early stages of fossilization reveal a staining which is most intense near the outer surface. This suggests that concentration gradients must exist for elements entering the bone. To investigate this possibility quantitatively, we have determined elemental concentrations in such bones as a function of depth below the outer surface. Using a SLOWPOKE reactor, we have analysed a number of samples of bone taken from secondary deposits of river sediments in the Old Crow region of the Yukon Territory, Canada. Our preliminary work indicates the decrease in concentration with depth into the cortex for previously recognized post-mortal elements such as U, F, Ba, Mn and Fe. Our measurements show that V, Sc, and Co also vary in this way and can be included in this group. As the hollow central shafts of bones are approached, concentrations increase again. Bones found in the Old Crow region display a variety of surface staining ranging from almost white through red to brown and black. There is a strong correlation between Fe and less positive relations between F and Ba, and staining. Highest Mn concentrations occur at the surfaces of light-coloured bones in which the staining is restricted to the outer 1 mm. Because of the wide range of concentrations which exist amont post-mortal elements in these bones, correlations among these elements can be studied. Manganese and barium, for example, are correlated within each bone, but the correlation patterns differ from bone to bone. These relationships must reflect the nature of the chemical processes associated with the deposition of the elements within the bones. A comparison of these patterns show that some of the bones have been exposed to more than one set of environmental conditions. This data thus provides a way of studying these processes in bones in which the introduction of elements from the environment has not completely and uniformly filled all the available voids.