Oxygen Isotope Compositions of Fossil Biogenic Phosphates: Climate Reconstruction in East Africa

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With National Science Foundation support Dr. Margaret Schoeninger and her colleagues will initiate a long term project to reconstruct East African Plio-pleistocene climatic variation based on the analysis of phosphate oxygen incorporated into tooth enamel. This first stage of the research will be directed to the study of enamel to determine the extent of post depositional alteration or diagenesis. The group will develop tests which determine whether or not diagenesis has occurred so that samples can be selected accordingly. To accomplish this goal they will collect both enamel and associated geological samples and determine the degree to which host rocks are lithified. This will be compared to the degree of enamel chemical alteration. Infrared spectra will be obtained since preliminary information indicates that recrystallized apatites are identifiably different from unaltered phosphates. Fluorine content, which increases with diagenetic alteration, will also be measured and several other indicators of change examined as well. With such data it should be possible to determine if unaltered samples exist and determine criteria to select them. If the project is successful it will provide a methodological tool of value to many geochemists, biochemists and related scientists. It will also set the stage for the next step of this research. Depending on diet and thermoregulation the oxygen isotope ratios in different species of animal reflect different climatic variables and through analysis of samples from carefully controlled stratigraphic contexts it is possible to monitor changes in temperature humidity and rainfall over time. The researchers hope to establish a climatic record for the Northern Turkana area of Kenya over the period from ca. 5 million years ago to recent times. Against these data it will then be possible to examine the evolution of mammalian species including hominids. This region is particularly important because of the rich fossil materials it contains. Many scientists have speculated on the relationship between species change and climate and this research will provide important data to address the issue.