Diagenetic and catagenetic transformations of sequestered biomarkers

Abstract

In recent years, it has been established that functionalised precursor lipids can be sequestered in high-molecular-weight organic matter fractions of immature sedimentary rocks by reaction with reduced inorganic sulphur species. On the other hand, biomarkers that originate from these precursors are known to occur in a free form in more mature sedimentary rocks and crude oils. The work described in this thesis is directed towards understanding the diagenetic and catagenetic pathways of biomarkers sequestered in high-molecular-weight fractions of immature organic-rich sedimentary rocks, using a combined thermal and chemical degradation approach. In the first part of this thesis (Chapters 2-6), the results of artificial maturation experiments (hydrous pyrolysis) with two immature sulphur-rich sedimentary rocks are described. Analysis of low-molecularweight hydrocarbons and organic sulphur compounds and chemical degradation of highmolecular- weight organic matter reveals that large changes in biomarker speciation occur already during diagenesis. A distinction can be made between thermally stable forms of biomarkers (e.g. hydrocarbons, alkylthiophenes and ketones) and thermally labile forms (e.g. sulphur- and oxygen-bound compounds). In the second part of this thesis (Chapters 7-9), a range of novel diagenetic and catagenetic products of the carotenoids isorenieratene and ~-carotene is identified, and the reactions that lead to their formation are outlined. The occurrence of carotenoid derivatives in sedimentary rocks up to 450 Ma indicates that the geological preservation potential of carotenoids, which is generally regarded low due to the extended double bond system, is higher than previously thought.