Aliphatic hydrocarbons in the bitumens of the Puertollano oil shales

The aliphatic fraction of the bitumens from 3 bands of the Puertollano oil shale field have been studied by gas chromatography and gas chromatography/mass spectrometry. Previous work published over the last years reached different conclusions about the origin of the organic matter in the Puertollano oil shales. A reappraisal of some of the biomarkers was then needed for a better understanding of the aliphatic hydrocarbons assemblage. The identified compounds, mainly n-alkanes in the medium to high boiling point region, acyclic isoprenoids and hopane-related compounds point towards a predominant algal/bacterial input. No unequivocally higher plant derived biomarkers have been detected in significant amounts, suggesting that the bulk of the organic matter derive from authocthonous organisms living in the basin. The biomarker maturity ratios indicate that the 3 Puertollano oil shales have similar maturities and are close to the onset of oil generation, assessing a slightly higher maturity than that determined by petrographic techniques.