By Paul Farrimond
The C29 hopane, 30-norhopane, is not only a member of the series of regular hopanes but also of a less common series that lack the methyl group at C-22 in the side chain, the 30-norhopanes. This second series is usually present in oils and source rocks in very low amounts, but is seen in higher abundance in carbonates and carbonate-sourced oils (Subroto et al., 1991). This explains why the C29 ab hopane peak is often unusually high in carbonate source rocks and their oils. Although this characteristic is often used in correlations, identifying the C30 member of the 30-norhopane series, which elutes immediately after the regular C30 17a(H)-hopane, will be more diagnostic. A C28 homologue, 29,30-bisnorhopane (not to be confused with 28,30-bisnorhopane) can also be found eluting after the regular C27 hopane “Tm”.
Reference:
Subroto E.A., Alexander R. & Kagi R. (1991). 30-Norhopanes: their occurrence in sediments and crude oils. Chemical Geology 93, 179-192.
