The evolution of microbial biosynthetic pathways is reflected in the changing composition of crude oil through geological time. Why use crude oils and not source rock extracts? Oils are widely available, accessible, abundant, and carry the same kind of evolutionary information that is buried in sedimentary rocks. Also, oils reflect the natural average in the variation in source rock organofacies. Studies suggest that several key biomarker ratios in crude oils are useful in determining source rock type and geologic age. For example, the ratio of C28 to C29 of steranes in marine oils changes as a function of geological age (see plot below). Dinosteranes, hydrocarbon biomarkers derived from dinoflagellate sterols show time-dependent changes in abundance in petroleum. Oleanane, a hydrocarbon biomarker for angiosperms, shows a remarkable increase in abundance, even in marine oils, commensurate with the Cenozoic rise to prominence of flowering plants (e.g Moldowan et al., 1994, 1996 references below).
C28 to C29 sterane ratio for oils from marine shales/marls.
Data points represent averages for multiple oils from the same source.
The goal of this proposed project is to measure a large number of new geochemical parameters contained in GeoMark’s crude oil database. Numerical methods will be used to determine the best combination of key oil biomarker parameters to predict source rock type and geologic age. Multivariate statistical models will be constructed and confidence limits will be determined. Errors introduced by uncertainties in source rock age in the oil training set and biomarker ratio variations from multiple oils from the same source will be quantified. Key oil samples will be reanalyzed using GC-MS-MS techniques in order to determine which additional biomarker parameters (e.g., C26 and C30 steranes as well as plant-derived diterpanes) will enhance the predictive capabilities of the models.
A recent chapter by Knoll et al. highlights some of the key research in this field over the past few years.
- Moldowan, J. M., B. J. Huizinga, et al. (1994). The molecular fossil record of oleanane and its relationship to angiosperms. Science 265: 768-771.
- Moldowan, J. M., J. Dahl, et al. (1996). Chemostratigraphic reconstruction of biofacies: Molecular evidence linking cyst-forming dinoflagellates with pre-Triassic ancestors. Geology 24: 159-162.