Uranium and thorium in fossil bones: activity ratios and dating

We have analysed fossil bones by U-series disequilibrium from five different sites (Ngandong and Sonde, Indonesia; Gold Ox Hill, People's Republic of China; Pestera, Romania and Ksar Akil, Lebanon). Two samples were taken from all bones: one representing surface material, and one from the inner bone (bulk) material. In general, the U concentration at the surface was found to be lower than in the bulk, resulting in higher ages. This might be explained by leaching of U from the surface area of the bone, which means that the surface material of the bones cannot be considered to be a closed system. An exception is the Gold Ox Hill series, where we found that the U concentration is roughly constant throughout the bone. Also the ages are roughly the same for surface and bulk material in this case