Search

The thesis is composed of two parts. A full index to the contents of each part is given at the beginning of the thesis, together with an index for all the figures and tables. PART I is concerned with the thermal and catalytic alteration of organic matter. The Introduction reviews the origin of hydro-carbons in sediments and discusses the possible precursors for these compounds. The probable biogenic or abiogenic routes leading to the formation of hydrocarbons in Nature are also discussed. Section 1 is concerned with the thermal and catalytic alteration of an n-alkane (n-octacosane). The products of alteration are examined by thin layer chromatography (t.l.c.) and capillary column gas-liquid chromatography (g.l.c.). The results are discussed and appear to indicate that thermal and catalytic alteration of alkanes and other straight chain lipid materials could be a contributory process to the generation of petroleum. Section 2 is concerned with the thermal alteration of an Eocene sediment (Green River shale, ca. 60 x 10e6 years old) con- ducted at different temperatures and for varying periods of time. The hydrocarbon content of the shale is examined IA each experiment and compared to the corresponding fraction isolated from a sample of untreated sediment. The results are discussed and show that a slow thermal alteration of the organic matter contained in a sediment may be one of the causes of the changes in distribution patterns for the hydrocarbons found for sediments of different ages. PART II is concerned with the isolation and characterisation of cycloalkanes from an Eocene sediment (the Green River shale, ca. 60 x 106 years old). The Introduction briefly discusses the pathways of biosynthesis of triterpenes. It goes on to examine the relationships between the triterpenoid and steroid distributions found in Nature and compares these with the cycloalkane compounds isolated from sediments. A preliminary chemotaxonomic survey for steroids and triterpenoids in plants is attempted. Section 1 discusses the use of high resolution g.l.c. for the analysis of cycloalkanes. Authentic compounds are used as standards and their retention behaviour compared with the cycloalkane components from the branched and cyclic alkane fraction isolated from the Green River shale. Section 2 discusses the use of mass spectrometry for the identification of cycloalkanes. Studies of the mass spectra of authentic steranes and triterpanes provide some general rules which are used to predict partial fragmentation patterns of other triterpane structures. Low voltage mass spectrometry of steranes and triterpanes is studied as a further extension of the g.c.-m.s. technique. Section 3 applies the techniques described in Sections 1 and 2. Combined capillary column gas chromatography - mass spectrometry is used for the analysis of the cycloalkanes found in the branched and cyclic alkane fraction from the Green River shale. Cholestane, ergostane, stigmastane, hopane and gammacerane are identified by the combined technique and tentative structures assigned to other components in the mixture. The General Experimental section for Part II discusses, among other things, the advantages of using high resolution capillary column g.l.c. The appropriate modification of a g.l.c. instrument and the method of preparation and coating of capillary g.l.c. columns are fully discussed. Finally the difficulties encountered and largely overcome in the use of capillary columns in a g.c.-m.s. instrument are discussed.