Geochemical significance of β-carotane in lacustrine oils from the Shahejie Formation of the Dongying Depression, eastern China

Abstract Oils reservoired in the third (Es3) and fourth (Es4) members of the lacustrine Shahejie Formation from the Dongying Depression, Bohai Bay Basin, eastern China have been analyzed by gas chromatography–mass spectrometry. Two oil families have been classified by the data assessed using chemometric analysis, including hierarchical cluster and principal component analysis. The Family I oils from the Es4 reservoirs were mainly generated from source rocks of the Es4 Member whereas Family II oils in the Es3 and Es4 reservoirs have source input mainly from the Es3 Member inferred from a series of biomarkers, including β-carotane, phytane, gammacerane and their deried abundance ratios. Parameters derived from β-carotane, such as the ratios: β-carotane/C24 tetracyclic terpane, β-carotane/(C19 + C20) tricyclic terpanes, and β-carotane/(18α(H)-22,29,30-trisnorneohopane + 17 α (H)-22,29,30-trisnorhopane), are most useful for distinguishing the oils derived from different depositional environments. β-Carotane has a high resistance to biodegradation to at least PM level 5. The abnormally high concentration of β-carotane in a few severely biodegraded oils is attributed to the removal of most vulnerable components by biodegradation, resulting in relatively concentrated β-carotane.