Collaborative Research: A Molecular Isotope Perspective on the Processes of Organic Matter Preservation in Fossils

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9504618 Engel Interpretations of the stable isotope record of residual organic matter in fossils requires a fundamental appreciation of the formation and transformation of the elemental pools of carbon and nitrogen during biosynthesis, diagenesis and preservation. A series of experiments are proposed to elucidate the effects of biosynthesis and diagenesis on the molecular and stable isotope composition of organic matter in biogenic minerals and sediments. Growth studies involving two species of planktonic foraminifera (Orbulina universa and Globigerina bulloides) will be conducted in collaboration with Dr. Howard Spero to compare the stable carbon and nitrogen isotope compositions of amino acid constituents of the shell protein to those of the diet. In addition to potentially identifying essential amino acids, the magnitude of isotope fractionations associated with trophic interactions will be assessed. A realistic assessment of biogenic signals from fossils requires an appraisal of the limits of isotope fractionation that can occur during diagenesis and the development of unambiguous criteria for evaluating the possible exchange of components with the preserving matrix. Simulation experiments are planned to evaluate the effects of diagenesis on the stable isotope composition of organic matter in fossils and sediments. Specifically, attempts will be made to assess the magnitudes of stable carbon and nitrogen isotope fractionations resulting from hydrolysis and humification. With respect to preservation, a major concern continues to be the ability to distinguish indigenous organic compounds from exogenous overprints. The further development of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) for stable nitrogen isotope analysis of amino acid enantiomers in fossils will provide an independent method for verifying the stable carbon isotope analysis of amino acid enantiomers, the development of GC/C/IRMS for stable nitrogen isotope analysis is dependent upon e stablishing isotopically reproducible combustion techniques capable of oxidation and reduction of halogenated derivatives of amino acids. An important test of this method involves molecular stable carbon and nitrogen isotope analysis of D- and L- enantiomers of individual amino acids in Cretaceous age samples, which will include dinosaur eggs and associated embryonic skeletal components. These rare samples are being provided from sites in North America and China by Dr. Dale Russell and Dr. Jack Horner. If the isotopic signals verify indigeneity, it may be possible to use molecular stable isotopes to establish the identities and trophic levels of the adults that produced the eggs. This study will also provide, to the best of our knowledge, the first direct comparison of the distribution and stable isotope composition of amino acid constituents of shell and bone from the same fossil organisms. An additional sample set of Cretaceous age dinosaurs from the western Sahara is also being provided by Dale Russell for a detailed investigation of organic matter preservation and paleoecology.