Analyses of light stable isotopes in bulk organic matter and major compound classes are widely used by organic geochemists to assess the origin and thermal maturity of fine-grained sedimentary rocks. In the last five years, it has become possible to determine the carbon isotopic composition of individual organic compounds using instruments with a gas chromatograph coupled to an isotope mass spectrometer. Application of isotope ratio monitoring of individual compounds (IRM/GC-MS) to a wide range of geological problems is beginning to emerge. PIs will utilize IRM/GC-MS for a direct comparison of the isotopic composition of lipid biomarkers (organic molecular fossils) between soft tissues and organic matter within mineralized tissues of bivalve shells. Both living shells and fossil shells will be surveyed. If sufficient quantities of lipids can be extracted from shells and if lipids from the shell mimic the isotopic composition of the mantle tissues, then it should be feasible to use shell lipids for studies of molecular paleontology and paleoecology.
