Changes

==Tricyclic terpanes==

==Tricyclic terpanes==

[[file:oiloil-and-oilsource-rock-correlations_fig8-33.png|thumb|{{figure number|11}}See text for explanation.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-33.png|left|thumb|{{figure number|11}}m/z 191 fragmentogram for an unusual oil in which the tricyclic terpanes (left side of the chromatogram) strongly dominate the pentacyclics.]]

Certain tricyclic terpanes, probably derived from bacteria, ''Tasmanites'', or both, are ubiquitous. In most facies they are less abundant than pentacyclic triterpanes such as hopanes but in some cases are dominant. However, because these tricyclics appear to be more stable, tricyclic/pentacyclic ratios also seem to be influenced by maturity, and thus may not always be reliable for correlations. The distribution of individual tricyclics and tetracyclics may also be used for correlation—especially for carbonates, where the tetracyclics are most abundant.

Certain tricyclic terpanes, probably derived from bacteria, ''Tasmanites'', or both, are ubiquitous. In most facies they are less abundant than pentacyclic triterpanes such as hopanes but in some cases are dominant. However, because these tricyclics appear to be more stable, tricyclic/pentacyclic ratios also seem to be influenced by maturity, and thus may not always be reliable for correlations. The distribution of individual tricyclics and tetracyclics may also be used for correlation—especially for carbonates, where the tetracyclics are most abundant.