Home – Home – Jornals – Russian Geology and Geophysics 2004 number 7

Ancient oils from East Siberia and southern Oman were analyzed for aliphatic biomarker hydrocarbons (n-alkanes, 12- and 13-methylalkanes, and aliphatic isoprenoids) and cycloaliphatic hydrocarbons of sterane and terpane series using gas-liquid chromatography and chromatography/mass spectrometry. For the terpane series, the abundances of hopanes, homohopanes, moretanes, and tri- and tetracyclic terpanes were studied. Based on the analytical data, the oil generation conditions and the composition of their initial organic matter have been established. All studied Proterozoic oils show a predominance of low-molecular n-alkanes, a pristane/phytane ratio of <1, high concentrations of 12- and 13-methylalkanes and tricyclic cheilanthanes, and a predominance of ethylcholestanes among the steranes. In the hopane series, C₃₅ homohopane dominates over its C₃₄ homologue. These oils are catagenetically mature. They formed, most likely, from planktonic and bacteriogenic shallow-sea organic matter buried in anoxic environment.