The environment of deposition indicated by the distribution of rare earth elements in fossil bones from Olduvai Gorge, Tanzania

Abstract

Fossil bones of Pleistocene age from Olduvai Gorge, Tanzania incorporated relatively high concentrations (up to several thousands ppm) of rare earth elements during their fossilization. The data indicate that these elements were mobile during the diagenetic processes involved in the fossilization of the bones. It is suggested that the high concentrations arose through interaction of the bone with groundwaters enriched in these, and other elements, introduced by contemporaneous carbonatitic or alkalic volcanism. The distributions of the rare earth elements within both the fossil bone and enclosing sediment are heterogeneous but spatially systematic, with concentration profiles showing a maximum in the bone at its sediment interface. Despite the relative porous nature of bone, the steepness and variability of the rare earth element profiles indicate chemical equilibrium has not been reached. Of the individual rare earth elements, Ce behaved differently from the others. Systematic variations in, and magnitudes of, the Ce anomaly within the bone cortices from different depositional environments, indicate that the redox potential of the environment during fossilization was the principal factor affecting the distribution of this element.