• Pliocene fossils;
  • diagenesis;
  • carbon isotopes;
  • oxygen isotopes


Mammalian tooth enamel carbonates from a Pliocene site at Allia Bay in northern Kenya show variable carbon and oxygen isotopic alteration. Sample screening by cathodoluminescence, prior to isotopic analysis, identified areas of extensive chemical alteration and others that were minimally altered. The luminescent patterns were used to guide sampling for the isotope study. Carbon stable isotope ratios of the apatite carbonate from luminescent enamel exteriors differ from the ratios in the enamel interiors and the magnitude of difference varies widely. The interior of the enamel usually retains the carbon isotope ratios expected based on faunal identification, but in a minority of cases, all of the enamel appears to be altered isotopically. Among fauna with an apparent mixed feeding signal, it is particularly difficult to determine whether the δ13C value is due to an actual mixed feeding strategy during life or to alteration toward sediment values. Palaeoecological reconstructions based on the δ13C values of enamel carbonate in browsing fauna would be affected, in many cases, since differences of 1‰ are significant for such reconstructions. Even so, careful selection of unaltered enamel sections should avoid this problem. Palaeodiet reconstruction would be less affected except in those cases where the alteration approaches 5‰. In such cases, a mixed feeding strategy would be the erroneous interpretation of the data. Oxygen isotope ratios in the enamel carbonates show no pattern and the retention of biogenic values is unlikely. For this reason, palaeotemperature reconstructions, based on the δ18O values of the enamel carbonate, would not be possible at this site. Copyright © 2003 John Wiley & Sons, Ltd.