Complex patterns of steroidal biomarkers in Tertiary lacustrine sediments of the Biyang Basin, China

Gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS) and gas chromatography–mass spectrometry–mass spectrometry (GC–MS–MS) with co-injected synthetic standards were used to analyse the biomarker patterns of some Tertiary lacustrine clayey dolomites from the Biyang Basin, China. The lithology, low Pr/Ph ratio and high gammacerane content of these sediments indicated that high salinity prevailed during their deposition. The distributions of steroidal hydrocarbons were particularly unusual and several pseudohomologous series, including regular steranes (C27–C29), 4-methyl steranes (C28–C30 including dinosteranes), 3β-ethyl steranes (C29–C31), lanostanes (C30–C32), and a variety of other 3β-alkylated steranes were identified. 3β-n-Propylcholestane, 3β-n-propylstigmastane and 4,4-dimethylcholestane were identified using authentic standards and this is the first time these compounds have been unambiguously characterised in sediments.