Identification of the four rearranged hopane series in geological bodies and their geochemical significances

Abstract

Saturated fractions in a total of 23 oil samples and hydrocarbon source rocks from the Songliao, Tarim, and Ordos Basins have been analyzed by GC–MS and GC–MS–MS. According to the relative retention, mass spectral characteristics, and comparison with existing literature, a complete carbon number distribution ranging from C27 to C35 (without C28) in the 17α(H)-diahopane series and early-eluting rearranged hopane series is identified. Compounds in the 18α(H)-neohopane series (Ts and C29Ts) and 21-methyl-28-nor-hopane series (29Nsp and 30Nsp) are also noted. These four series of rearranged hopanes seem to occur in both brackish-saline lacustrine and coal measure environments. However, the coal measure and swamp environments being under an oxic condition, compared with brackish-saline lacustrines, are presumably more helpful to the formation of 30E. Diversity in the content and distribution patterns indicate that rearranged hopanes could serve as good indicators of organic facies, depositional environment and maturity in petroleum geology.