Uranium and Thorium content in bone phases studies – a step to U-series dating of fossil bones

Direct dating of fossil bones using the U-series method is considered impossible because of the processes of accumulation and diffusion of uranium during the time when bone is buried in sediment. Commonly applied mathematical models allow the evaluation of the environmental influences and capability of bone, as a whole, to exchange uranium isotopes. In our research, a different solution of Uranium uptake problem has been elaborated. By considering a bone as a complex system of organic and inorganic phases, an attempt to estimate the capacity of the Uranium and Thorium uptake of the phases was made. This method showed that collagen, in comparison with other bone phases, has extremely low values of uranium content and, additionally, that these values do not exceed the range of uranium concentrations in recent bones (i.e., less than 0.2 ppm). According to this data, we presume that pure fossil collagen is not subject to uranium accumulation. Furthermore, some U-series dates of fossil collagen extracted from Ursus spelaeus bones colected in Magurska Cave (Tatra Mts, Poland) were calculated, and comparison of these dates with radiocarbon ones seems to show acceptable accordance.