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 repre sent a new class ...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 repre sent a new class of steroids, alkylated at the C-3 po sition with a polyhydroxy n-alkane. These precursors may have been formed by the bacterial addition of a ribose sugar to ?2-sterenes, diagenetic alteration products of steroids synthesized by eukaryotes 3-alkyl steroids might substitute for hopanols in bac terial membranes. When they are present in a sam ple, the patterns of the isomer distributions of 3-alky steranes are similar to desmethyl steranes except fo lower rearranged ones. It is shown that the configu rational 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, mod erate in shallow lacustrine, poor in sub-deep to deep lacustrine relative to the 4-methyl steranes.展开更多
文摘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 repre sent a new class of steroids, alkylated at the C-3 po sition with a polyhydroxy n-alkane. These precursors may have been formed by the bacterial addition of a ribose sugar to ?2-sterenes, diagenetic alteration products of steroids synthesized by eukaryotes 3-alkyl steroids might substitute for hopanols in bac terial membranes. When they are present in a sam ple, the patterns of the isomer distributions of 3-alky steranes are similar to desmethyl steranes except fo lower rearranged ones. It is shown that the configu rational 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, mod erate in shallow lacustrine, poor in sub-deep to deep lacustrine relative to the 4-methyl steranes.
