Changes

[[file:oiloil-and-oilsource-rock-correlations_fig8-31.png|left|200px|thumb|{{figure number|9}}m/z 191 mass chromatograms of three oils from the Cooper/Eromanga basin of Australia. From Philp and Gilbert;<ref name=ch08r42 /> reprinted with permission from Elsevier.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-31.png|left|200px|thumb|{{figure number|9}}m/z 191 mass chromatograms of three oils from the Cooper/Eromanga basin of Australia. From Philp and Gilbert;<ref name=ch08r42 /> reprinted with permission from Elsevier.]]

Two triterpanes, often called “C_z” and “C_x,” are also empirically associated with terrestrial organic matter, but their origin is unknown. They can be seen in [[:file:oiloil-and-oilsource-rock-correlations_fig8-26.png|Figure 4]]. C_z has also been called compound X<ref name=ch08r42>Philp, R., P., Gilbert, T., D., 1986, Biomarker distributions in oils predominantly derived from terrigenous source material, in Leythaeuser, D., Rullkötter, J., eds., Advances in Organic Geochemistry 1985: New York, Elsevier, p. 73–84.</ref> and has been shown to be a diahopane.<ref name=ch08r39 /> C_x is probably a neohopane. They often co-occur with other terrestrial markers, such as high C₂₉ steranes, oleanane, and bicadinanes, but they can also occur alone.

Two triterpanes, often called “C_z” and “C_x,” are also empirically associated with terrestrial organic matter, but their origin is unknown. They can be seen in [[:file:oiloil-and-oilsource-rock-correlations_fig8-26.png|Figure 4]]. C_z has also been called compound X<ref name=ch08r42>Philp, R. P., and T. D. Gilbert, 1986, Biomarker distributions in oils predominantly derived from terrigenous source material, in D. Leythaeuser, and J. Rullkötter, eds., Advances in Organic Geochemistry 1985: New York, Elsevier, p. 73–84.</ref> and has been shown to be a diahopane.<ref name=ch08r39 /> C_x is probably a neohopane. They often co-occur with other terrestrial markers, such as high C₂₉ steranes, oleanane, and bicadinanes, but they can also occur alone.

[[:file:oiloil-and-oilsource-rock-correlations_fig8-31.png|Figure 9]] shows m/z 191 mass chromatograms of three oils from the Cooper/Eromanga basin of Australia. The highest relative concentrations of C_z and C_x occur in the oil that appears to have the lowest absolute concentration of other triterpanes (Karmona), as judged by the greatest amount of noise in the baseline. C_z and C_x (unlabelled but visible to the left of peak “b” in the Karmona sample) are probably more resistant to thermal destruction, and thus increase in relative concentration as other triterpanes are destroyed at high levels of maturity.<ref name=ch08r59 /> C_x often coelutes with T_m (peak “b” in this figure).

[[:file:oiloil-and-oilsource-rock-correlations_fig8-31.png|Figure 9]] shows m/z 191 mass chromatograms of three oils from the Cooper/Eromanga basin of Australia. The highest relative concentrations of C_z and C_x occur in the oil that appears to have the lowest absolute concentration of other triterpanes (Karmona), as judged by the greatest amount of noise in the baseline. C_z and C_x (unlabelled but visible to the left of peak “b” in the Karmona sample) are probably more resistant to thermal destruction, and thus increase in relative concentration as other triterpanes are destroyed at high levels of maturity.<ref name=ch08r59 /> C_x often coelutes with T_m (peak “b” in this figure).