EXTRACTABLE AND BOUND FATTY-ACIDS IN-CORE SEDIMENTS FROM THE NORDLINGER-RIES, SOUTHERN GERMANY

Gas chromatography (g.c.) and gas chromatography-mass spectrometry (g.c.-m.s.) analyses of fatty acids directly extracted by organic solvents from five sulfur-rich lacustrine sediments in the Nordlinger Ries comprise several homologous series. Saturated normal monocarboxylic acids (C-9-C-33) were the dominant series, while isoprenoid acids (C-14-C-21, except C-18), iso- (i) and anteiso (ai)-acids (C-11-C-18), hopanoic acids (C-30-C-33) and monounsaturated acids (C-16:1 and C-18:1) were minor constituents. Moreover, 10-oxoacids (n-C-16 and n-C-18) were identified in abnormally high amounts in the three samples from well NR-10. Base hydrolysis of kerogen concentrates and extractable polar fractions liberated, in addition to the fatty acid constituents belonging to the compound classes mentioned above, steroidal acids (C-28-C-31) and alpha,omega-dicarboxylic acids (C-7-C-28). The results are discussed in terms of qualitative and quantitative variations of the fatty acids in the free and bound lipid fractions. The high concentrations of fatty acids in the bitumens are attributed to early diagenesis. The carbon number distributions of n-alkanoic acids in the free and bound fractions indicate a major contribution of autochthonous sources in samples from well NR-10, and a mixed contribution of both autochthonous and allochthonous sources in samples from well NR-30. Bacterial biomarkers, including extended hopanoic acids and i-/ai-branched acids are more significant in the bound lipid fractions. The results further support previous suggestions of a broad similarity between the structure of asphaltenes and kerogen derived from the same source rock. Finally, the data confirm the extremely mild thermal history of the Nordlinger Ries sediments.