Changes

==Effects of maturation and migration==

==Effects of maturation and migration==

Sterane and triterpane concentrations decrease greatly during oil cracking. Therefore, thermal condensates (light oils) do not normally contain large amounts of steranes and triterpanes. Consequently, steranes and triterpanes are usually of little value in high-maturity oils and condensates. Furthermore, some condensates that do contain steranes and triterpanes may have picked up all or most of them during [[migration]] by extraction from the rocks through which they passed (see Waples and Machihara<ref name=ch08r59>Waples, D. W., and T. Machihara, 1991, Biomarkers for geologists: Tulsa, AAPG, 91 p.</ref> for examples and references). Finally, because triterpane and particularly sterane distributions change greatly during maturation, correlations of those biomarkers between an immature [[source rock]] and an oil can be very difficult. In such cases a strictly numerical approach, working with peak ratios and relative proportions, can be better than a visual one, since the eye can be unduly influenced by maturity-related differences instead of genetic characteristics.

[[Sterane]] and [[triterpane]] concentrations decrease greatly during oil [[cracking]]. Therefore, thermal condensates (light oils) do not normally contain large amounts of steranes and triterpanes. Consequently, steranes and triterpanes are usually of little value in high-maturity oils and condensates. Furthermore, some condensates that do contain steranes and triterpanes may have picked up all or most of them during [[migration]] by extraction from the rocks through which they passed (see Waples and Machihara<ref name=ch08r59>Waples, D. W., and T. Machihara, 1991, Biomarkers for geologists: Tulsa, AAPG, 91 p.</ref> for examples and references). Finally, because triterpane and particularly sterane distributions change greatly during maturation, correlations of those biomarkers between an immature [[source rock]] and an oil can be very difficult. In such cases a strictly numerical approach, working with peak ratios and relative proportions, can be better than a visual one, since the eye can be unduly influenced by maturity-related differences instead of genetic characteristics.

==Biodegradation and sterane distributions==

==Biodegradation and sterane distributions==