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==Carotanes==

==Carotanes==

Carotanes—hydrocarbons derived from photosynthetic organisms and associated with anoxic marine and lacustrine facies—are also used as oil–oil and oil–source rock correlation parameters. Peters et al.<ref name=ch08r40>Peters, K., E., Moldowan, J., M., Driscole, A., R., Demaison, G., J., 1989, Origin of Beatrice oil by co-sourcing from Devonian and Middle Jurassic source rocks, Inner Moray Firth, U., K.: AAPG Bulletin, vol. 73, p. 454–471.</ref> used the occurrence of β-carotane in Devonian rocks (of the U.K. offshore) to suggest a Devonian input to the source composition of the Beatrice oil. These compounds are particularly useful in hypersaline settings. Lacustrine and marine facies containing carotanes can often be distinguished by other indicators, such as the presence of 4-methylsteranes and pristane-phytane ratios less than 1.0 for lacustrine facies.

[[file:oiloil-and-oilsource-rock-correlations_fig8-35.png|thumb|{{figure number|8-35}}Modified. Copyright: Peters and Moldowan (1993); courtesy Prentice-Hall.]]Carotanes—hydrocarbons derived from photosynthetic organisms and associated with anoxic marine and lacustrine facies—are also used as oil–oil and oil–source rock correlation parameters. Peters et al.<ref name=ch08r40>Peters, K., E., Moldowan, J., M., Driscole, A., R., Demaison, G., J., 1989, Origin of Beatrice oil by co-sourcing from Devonian and Middle Jurassic source rocks, Inner Moray Firth, U., K.: AAPG Bulletin, vol. 73, p. 454–471.</ref> used the occurrence of β-carotane in Devonian rocks (of the U.K. offshore) to suggest a Devonian input to the source composition of the Beatrice oil. These compounds are particularly useful in hypersaline settings. Lacustrine and marine facies containing carotanes can often be distinguished by other indicators, such as the presence of 4-methylsteranes and pristane-phytane ratios less than 1.0 for lacustrine facies.

Unfortunately many analyses overlook carotanes because these high-molecular-weight compounds elute very late on gas Chromatograph columns. To obtain this information, you may have to make special arrangements prior to analysis. Thus, the absence of carotanes in chromatograms may simply indicate that they were not looked for, rather than that they are truly absent.

Unfortunately many analyses overlook carotanes because these high-molecular-weight compounds elute very late on gas Chromatograph columns. To obtain this information, you may have to make special arrangements prior to analysis. Thus, the absence of carotanes in chromatograms may simply indicate that they were not looked for, rather than that they are truly absent.

The figure shows that carotanes are sometimes so abundant that they can be analyzed using gas chromatography (More definitive identification and analysis of samples in which carotanes are less abundant can be done using GC/MS.) The gas chromatograms are of the Beatrice Field oil in the Moray Firth (U.K.) and of the extract of a Devonian rock believed to be one of the source contributors.

The figure shows that carotanes are sometimes so abundant that they can be analyzed using gas chromatography (More definitive identification and analysis of samples in which carotanes are less abundant can be done using GC/MS.) The gas chromatograms are of the Beatrice Field oil in the Moray Firth (U.K.) and of the extract of a Devonian rock believed to be one of the source contributors.

==Summary of application of GC/MS to correlation studies==

==Summary of application of GC/MS to correlation studies==