U-series dating of collagen – A step toward direct U-series dating of fossil bone?

Fossil bones are often the only material that may be dated by numerical methods. A commonly accepted method of bone dating is the radiocarbon method, but radiocarbon dating is limited to material younger than 40–60 ka. To date, direct dating of bone samples by U-series methods has not been successful because of post-depositional uranium uptake. This paper tests the use of U-series dating of bones in a new way by dating the collagen extracted from fossil bones. Low uranium content in collagen extracted from recent and fossil bones suggests that no uranium accumulates in this bone phase. Ratios of C/N, commonly used as an indicator of bone preservation, were also measured here. Modern bones and bone collagen showed 230Th activity at background levels, confirming their recent age.U-series and radiocarbon methods applied to collagen extracted from fossil bone of Ursus spelaeus collected in Magurska Cave (Tatra Mts, Poland) gave consistent results. Analyses of collagen extracted from bones collected in Biśnik Cave (Kraków-Wieluń Upland, Poland) indicate that there is a high risk of contamination by modern material, especially when working with large samples close to the dating method limit.