Abstract
The aliphatic hydrocarbon fraction of an immature Monterey bitumen contains a high relative abundance of C 27-C 29 Δ 4 , Δ 5 , Δ 8(14) 5α - and Δ 14 5α -sterenes, each having a very similar carbon number distribution. This is the first report of abundant Δ 8(14) 5α - and Δ 14 5α - sterenes in an immature sediment. The Δ 4 and Δ 5 sterenes appear to originate directly from Δ 5 sterols. For the Δ 8(14) 5α - and Δ 14 5α sterenes we propose an origin from Δ 7 5α -sterols which may be derived from a microbial transformation of Δ 5 sterols. The presence of 5α- and 5β-steranes in an unusual ratio of ca. 55:45 suggests the formation of a high abundance of 5β-stanols via the known microbial reduction pathway of δ 5 sterols.
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