Preferential lipid-Mineral associations in some "oil shales"

Lipids were extracted from "oil shales" following stepwise dissolution of minerals. The lipid fraction associated with the silicate minerals (mostly clays) is of more aromatic and polar composition than the lipid fraction associated with carbonate minerals, while the readily extractable lipid fraction is predominantly aliphatic. n-Alkane distribution patterns and the C-isotope composition of the respective lipid fractions, which are indicative of their biologic precursors, show that these differences are probably caused by selective adsorption in some cases. In others they are due to different provenance and sedimentation processes of minerals and organic matter. They are obliterated in "oil shales" affected by a natural pyrolitic thermal event.