The carbon isotopic compositions of individual compounds from ancient and modern depositional environments

athways of carbon flow in depositional environments have been identified using compound-specific isotope analyses in conjunction with biomarker identities and distributions. This work examines factors influencing the isotopic compositions of individual compounds and, consequently, that of preserved sedimentary organic matter. Specifically, isotope effects associated with reactions resulting in the production and degradation of organic matter in the water column and reactions affecting preservation during diagenesis are considered in three projects.;The first documents the preservation of the isotopic compositions of hydrocarbons altered by diagenetic reactions. Isotopic compositions of structurally-related polycyclic aromatic hydrocarbons (PAH) from the Messel Shale (Eocene) show little variation with increased unsaturation. Lack of isotopic fractionation related to aromatization indicates either that isotope effects associated with these reactions are small or that the reactions are essentially quantitative within a given sediment volume.;The influence of environmental conditions on the isotopic composition of sedimentary organic carbon is documented by a comparison of the...