THE RETENTION OF PRIMARY OXYGEN-ISOTOPE COMPOSITIONS OF FOSSIL ELEPHANT SKELETAL PHOSPHATE

Fossil elephant remains from sediments of Plio-Pleistocene age in the vicinity of Lake Turkana, Kenya, provide insights into the ability of the phosphate-oxygen system to preserve original deltaO-18 values (deltaO-18p) in the depositional environment. Individual fossil specimens exhibit systematic variations in the deltaO-18p values of their various tooth and bone components. Differences in deltaO-18p values between these skeletal components can be as high as 3.6 parts per thousand, despite the fact that equivalent phases for individual modern elephants have deltaO-18p values which vary by less than 0.6 parts per thousand. XRD traces of the different skeletal phases of modern and fossil samples, also infer differential preservation of primary apatite crystallinities among the various fossil phases. Fossil samples of dentine, cementum, and bone have X-ray spectra with sharper and more intense peaks compared to their modern counterparts, but little change in crystallinity is observed for fossil enamel samples. A model based on the premise that the enamel phase preserves primary isotope signatures and that the accompanying skeletal phases are partially re-equilibrated with the fluids associated with the microbial decomposition of the elephant's carcass is consistent with the features of the O-18p dataset. This isotopic evidence, in conjunction with the physical and chemical attributes of enamel, has led us to postulate that enamel could be preserving primary isotope signatures while other skeletal components are affected to varying degrees by alteration processes in the burial environment.