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Line 28: + + + − + − The figure shows the distribution of 4-methylsteranes in selected rock extracts. The 414 → 231 metastable ion transition shows C<sub>30</sub> steranes methylated on the A-ring. Two major families are shown here. The dinosteranes (derived from dinoflagellates) are designated “dino,” whereas another group of 4-methylsteranes with an ethyl group at the 24 position are designated “24(Et).” − {{clear}}
Organic compounds: environmental indicators (view source)
Revision as of 16:34, 5 February 2014
, 16:34, 5 February 2014→4-methylsteranes
==4-methylsteranes==
==4-methylsteranes==
[[file:oiloil-and-oilsource-rock-correlations_fig8-25.png|thumb|{{figure number|3}}Modified from Summons et al.;<ref name=ch08r52>Summons, R., E., Thomas, J., Maxwell, J., R., Boreham, C., J., 1992, Secular and environmental constraints on the occurrence of dinosteranes in sediments: Geochimica et Cosmochimica Acta, vol. 56, p. 2437–2444., 10., 1016/0016-7037(92)90200-3</ref> reprinted with permission from Elsevier.]]
MRM analysis is useful in distinguishing ''n''-propylcholestanes from 4-methylsteranes and in assigning identities to different types of 4-methylsteranes. This sophisticated GC/MS analysis method will probably become commonplace because of its specificity in oil–oil and oil–source rock correlation efforts.
MRM analysis is useful in distinguishing ''n''-propylcholestanes from 4-methylsteranes and in assigning identities to different types of 4-methylsteranes. This sophisticated GC/MS analysis method will probably become commonplace because of its specificity in oil–oil and oil–source rock correlation efforts.
[[file:oiloil-and-oilsource-rock-correlations_fig8-25.png|thumb|{{figure number|8-25}}Modified from Summons et al.;<ref name=ch08r52>Summons, R., E., Thomas, J., Maxwell, J., R., Boreham, C., J., 1992, Secular and environmental constraints on the occurrence of dinosteranes in sediments: Geochimica et Cosmochimica Acta, vol. 56, p. 2437–2444., 10., 1016/0016-7037(92)90200-3</ref> reprinted with permission from Elsevier.]]
[[:file:oiloil-and-oilsource-rock-correlations_fig8-25.png|Figure 3]] shows the distribution of 4-methylsteranes in selected rock extracts. The 414 → 231 metastable ion transition shows C<sub>30</sub> steranes methylated on the A-ring. Two major families are shown here. The dinosteranes (derived from dinoflagellates) are designated “dino,” whereas another group of 4-methylsteranes with an ethyl group at the 24 position are designated “24(Et).”
==Diasteranes==
==Diasteranes==
Diasteranes are mainly associated with clastic environments, and they increase in relative abundance with increasing maturity. However, they are also known from nonclastic samples and can, in some cases, be abundant even in low-maturity samples.
Diasteranes are mainly associated with clastic environments, and they increase in relative abundance with increasing maturity. However, they are also known from nonclastic samples and can, in some cases, be abundant even in low-maturity samples.