ABSTRACT

A lacustrine sediment has been subjected to laboratory heating at 68–325°C for 24h. Various lipid classes were extracted from the unheated and heated sediment samples and analyzed by gas chromatography and GC-MS. The compounds recognized include; saturated and unsaturated fatty acids, β-, ω- and (ω-1)-hydroxy acids, α, ω-dicarboxylic acids, fatty alcohols and n-alkanes. The carbon and nitrogen contents and the KMnO₄ oxidative degradation products (α, ω-diacids) of geopolymers (kerogen and humic compounds) in the extracted residues were determined. The absorbance at 400nm of humic compounds extracted from the residue was also measured. Most of the extractable (unbound + bound) lipid class compound concentrations increase with temperature from 150 to 250°C. This can be interpreted in terms of: (1) a release of compounds incorporated and/or associated with geopolymers in a tightly bound form, and/or (2) their production by α-, β-, ω- and (ω-1) oxidation of certain precursors or by other mechanisms. Some organic compounds decompose after reaching maximum concentrations at different temperatures: β-hydroxy acids (154°C), ω-hydroxy acids (179°C), (ω-1)-hydroxy acids (179°C), n-alcohols (229°C), phytanic acid (254°C), α, ω-dicarboxylic acids (279°C). However, alkanoic acids do not decrease even at 325°C. Normal alkanes increase throughout the heating. Their concentrations at 325°C are 16 times higher than in the unheated sediment. The amounts of KMnO₄ degradation products (diacids) of geopolymers drastically decrease at temperatures higher than 200°C, which implies that structural changes of kerogen and humic compounds occur upon heating. Absorbance of humic compounds also shows a drastic change at the same temperatures.