Identification and significance of 3β-alkyl steranes in the Eogene lacustrine sediments and petroleum of China

The study on steranes with substitution at C-2, C-3 or C-4 positions in ring-A has become a hot field for their specific precursors in recent years[1-15]. Summons et al. firstly identified C28-C30 3β-methyl steranes in Michigan Basin and found that the p…

Identification and significance of 3β-alkyl steranes in the Eogene lacustrine sediments and petroleum of China

Several homologous series of steranes with alkyl side chains (C₁ to C₄) at the 3β position have been identified in the Jiyang Eogene lacustrine deposition. It is postulated that its precursors represent a new class of steroids, alkylated at the C-3 position with a polyhydroxy n-alkane. These precursors may have been formed by the bacterial addition of a ribose sugar to Δ²-sterenes, diagenetic alteration products of steroids synthesized by eukaryotes. 3-alkyl steroids might substitute for hopanols in bacterial membranes. When they are present in a sample, the patterns of the isomer distributions of 3-alkyl steranes are similar to desmethyl steranes except for lower rearranged ones. It is shown that the configurational isomerization of 3-alkyl steranes is trending in line with that of desmethyl steranes with increasing of maturity. The abundance of 3-alkyl steranes may be controlled by the depositional environments; they are primary in saline or near shore lacustrine, moderate in shallow lacustrine, poor in sub-deep to deep lacustrine relative to the 4-methyl steranes.