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 (del taO-18p) in the depositional environment. Individual fossil specimens exhibit systematic variations in the deltaO-18p values of their variou s tooth and bone components. Differences in deltaO-18p values between these skeletal components can be as high as 3.6 parts per thousand, de spite 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 samp les, also infer differential preservation of primary apatite crystalli nities among the various fossil phases. Fossil samples of dentine, cem entum, and bone have X-ray spectra with sharper and more intense peaks compared to their modern counterparts, but little change in crystalli nity is observed for fossil enamel samples. A model based on the premi se that the enamel phase preserves primary isotope signatures and that the accompanying skeletal phases are partially re-equilibrated with t he fluids associated with the microbial decomposition of the elephant' s carcass is consistent with the features of the O-18p dataset. This i sotopic evidence, in conjunction with the physical and chemical attrib utes of enamel, has led us to postulate that enamel could be preservin g primary isotope signatures while other skeletal components are affec ted to varying degrees by alteration processes in the burial environme nt.