Diagenetic and catagenetic transformations of sequestered biomarkers

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