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Organic compounds: environmental indicators (view source)
Revision as of 17:09, 29 January 2014
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{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Critical elements of the petroleum system
| chapter = Oil–oil and oil–source rock correlations
| frompg = 8-1
| topg = 8-71
| author = Douglas W. Waples, Joseph A. Curiale
| link = http://archives.datapages.com/data/specpubs/beaumont/ch08/ch08.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
==Environments indicated by steranes==
The relative amounts of C<sub>27</sub>, C<sub>28</sub> and C<sub>29</sub> steranes in oils are controlled by the types of photosynthetic organisms that contributed to the organic matter. A dominance of C<sub>27</sub> steranes is almost always associated with marine organisms. Most nonmarine organic matter has a dominance of the C<sub>29</sub> sterane precursors, but C<sub>29</sub> steranes can dominate in marine systems as well. The abundance of C<sub>28</sub> steranes in marine systems may depend primarily on geologic age<ref name=ch08r16>Grantham, P., J., Wakefield, L., L., 1988, Variations in the sterane carbon number distributions of marine [[source rock]] derived crude oils through geological time: Organic Geochemistry, vol. 12, p. 61–73., 10., 1016/0146-6380(88)90115-5</ref> but this idea is controversial. In nonmarine systems, there is no proposed relationship between C<sub>28</sub> sterane abundance and age. C<sub>30</sub> steranes (''n''-propylcholestanes) are usually less abundant than the other regular steranes and occur only in samples deposited where marine organisms lived.<ref name=ch08r32>Moldowan, J., M., Seifert, W., K., Gallegos, E., J., 1985, Relationship between petroleum composition and depositional environment of petroleum [[source rocks]]: AAPG Bulletin, vol. 569, p. 1255–1268.</ref>
==Example of steranes==
The figure below shows m/z 217 mass fragmentograms from two oils showing quite different distributions of regular steranes. The top example is dominated by C<sub>29</sub> steranes with only moderate amounts of C<sub>27</sub> and C<sub>28</sub>. The bottom sample, in contrast, shows similar amounts of all three homologs plus moderate amounts of the C<sub>30</sub> steranes (four unlabeled peaks to the far right).
[[file:oiloil-and-oilsource-rock-correlations_fig8-23.png|thumb|{{figure number|8-23}}See text for explanation.]]
The figure below shows a ternary diagram, a convenient and common way of displaying basic data on sterane distributions. This example shows the relative proportions of the C<sub>27</sub>, C<sub>28</sub>, and C<sub>29</sub> regular steranes for several extracts from two distinct facies within the nonmarine Elko Formation (Eocene/Oligocene) of Nevada. The lignitic siltstones are dominated by terrestrial plant material, whereas the oil shales are made up of lacustrine algae.
[[file:oiloil-and-oilsource-rock-correlations_fig8-24.png|thumb|{{figure number|8-24}}From Palmer;<ref name=ch08r38>Palmer, S., E., 1984, Hydrocarbon source potential of organic facies of the lacustrine Elko Formation (Eocene/Oligocene), northeast Nevada, in Woodward, J., Meissner, F., F., Clayton, J., L., eds., Hydrocarbon source rocks of the greater Rocky Mountain region: Denver, Rocky Mountain Association of Geologists, p. 491–511.</ref> reprinted with permission from Rocky Mountain Assoc. of Geologists.]]
==4-methylsteranes==
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.
==Example of distribution of 4-methylsteranes==
The figure below 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).”
[[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.]]
==Environments indicated by 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.
Figure 8-23 shows two distinct distributions of diasteranes. The top oil has very few diasteranes, indicating a possible lack of clay in the source rock. The bottom oil, in contrast, has similar amounts of diasteranes and regular steranes and probably comes from a clastic source.
==Environments indicated by hopanes==
Hopanes, which originate from bacteria, are the most abundant triterpanes. A distribution with a regular decrease of homohopanes from C<sub>31</sub> to C<sub>35</sub> is thought to be associated with clastic environments.<ref name=ch08r59>Waples, D., W., Machihara, T., 1991, Biomarkers for geologists: Tulsa, AAPG, 91 p.</ref> and/or more oxidizing conditions<ref name=ch08r39>Peters, K., E., Moldowan, J., M., 1993, The Biomarker Guide—Interpreting [[Molecular fossils]] in Petroleum and Ancient Sediments: Englewood Cliffs, New Jersey, Prentice-Hall, 363 p.</ref>
==Example of homohopanes==
The figure below shows the m/z 191 mass fragmentogram of an oil displaying the most common type of homohopane distribution.
[[file:oiloil-and-oilsource-rock-correlations_fig8-26.png|thumb|{{figure number|8-26}}See text for explanation.]]
==Irregular homohopane distributions==
Irregular distributions of the C<sub>32</sub>–C<sub>35</sub> homohopanes are associated with carbonates.<ref name=ch08r59 /> and/or more reducing conditions<ref name=ch08r39 /> Unusually large amounts of the C<sub>31</sub> homohopanes are sometimes associated with coals and coaly material.<ref name=ch08r59 />
==Example of irregular homohopane distribution==
The figure below shows m/z 191 mass chromatograms for two sediment extracts from the Brac-1 well (Croatia) showing irregular homohopane distributions [relative enhancement of the C<sub>35</sub> species (left) and C<sub>34</sub> species (right)]. We would expect the oils sourced from these sediments to show these same characteristics.
[[file:oiloil-and-oilsource-rock-correlations_fig8-27.png|thumb|{{figure number|8-27}}From Moldowan et al.;<ref name=ch08r33>Moldowan, J., M., Lee, C., Y., Sundararaman, P., Salvatori, T., Alajbeg, A., Gjukic, B., Demaison, G., J., Slougue, N.-E., Watt, D., S., 1992, Source correlation and maturity assessment of select oils and rocks from the central Adriatic Basin (Italy and Yugoslavia), in Moldowan, J., M., Albrecht, P., Philp, R., P., eds., Biological markers in sediments and petroleum: Englewood Cliffs, New Jersey, Prentice-Hall, 411 p.</ref> reprinted with permission from Prentice-Hall.]]
===Environment indicated by gammacerane===
In addition to the hopane family, several other types of triterpanes that are occasionally encountered can be very useful in correlations. Gammacerane is often found in sediments deposited under abnormal salinites, including lacustrine facies. Identification of gammacerane can be difficult, however, both because it is usually only a minor component and because it elutes at different places with different chromatographic columns.
===Examples of gammacerane===
Figure 8-28 shows gammacerane in the m/z 191 mass chromatograms of two genetically related oils from southern Sicily. In this example, gammacerane elutes after the C<sub>31</sub> homohopanes. Note also the relative increase in the C<sub>34</sub> and C<sub>35</sub> homohopanes. The presence of gammacerane and the homohopane distribution suggest a strongly reducing, possibly carbonate or hypersaline depositional setting for the source rock of these oils.
[[file:oiloil-and-oilsource-rock-correlations_fig8-28.png|thumb|{{figure number|8-28}}From Ocampo et al.;<ref name=ch08r35>Ocampo, R., Riva, A., Trendel, J., M., Riolo, J., Callot, H., J., Albrecht, P., 1993, Petroporphyrins as biomarkers in oil-oil and oil-source rock correlations: Energy & Fuels, vol. 7, p. 191–193., 10., 1021/ef00038a005</ref> reprinted with permission from American Chemical Society.]]
Figure 8-29 also shows samples with gammacerane, but in this case gammacerane essentially coelutes with the C<sub>31</sub>-22R epimer. This example shows an oil from the Perla-1 well in southern Sicily and a source rock extract from the Noto Formation that correlates with it almost exactly.
[[file:oiloil-and-oilsource-rock-correlations_fig8-29.png|thumb|{{figure number|8-29}}From Mattavelli and Novelli;<ref name=ch08r29>Mattavelli, L., Novelli, L., 1990, Geochemistry and habitat of the oils in Italy: AAPG Bulletin, vol. 74, p. 1623–1639.</ref> reprinted with permission from AAPG.]]
===Environment and age indicated by oleananes===
Oleanane (two major isomers exist) originates from terrestrial flowering plants of Late Cretaceous or, more commonly, Tertiary age and as such is very valuable in correlation problems when deciding whether an oil comes from a source rock that is young or old.<ref name=ch08r45>Riva, A., Caccialanza, P., G., Quagliaroli, F., 1988, Recognition of 18β(H)-oleanane in several crudes and Cainozoic-Upper Cretaceous sediments. Definition of a new maturity parameter: Organic Geochemistry, vol. 13, p. 671–675., 10., 1016/0146-6380(88)90088-5</ref>
===Example of oleanane===
The figure below shows three mass chromatograms (m/z 191.18, 177.16, and 217.20, from top to bottom) for an oil from central Myanmar. The peak marked “o” is a combination of 18α(H) and 18β(H) oleanane. The tallest peak in the m/z 191 mass chromatogram is hopane, and the peaks indicated by solid dots are bicadinanes.
===Environment indicated by bicadinanes===
Bicadinanes are among the very few compounds that give substantial peaks in both the m/z 191 and 217 fragment ions. Bicadinane resins are derived from terrestrial plants that evolved in the Tertiary. The primary source plants, dipterocarps, spread slowly through Southeast Asia during the middle to late Tertiary. Bicadinanes are rare in other places and at other times, except from the Tertiary of New Zealand and Australia, where they probably originated from other species.<ref name=ch08r34>Murray, A., P., Summons, R., E., Bradshaw, J., Pawih, B., 1993, Cenozoic oil in Papua New Guinea—evidence from geochemical analysis of two newly discovered seeps, in Carman, G., J., Carman, Z., eds., Petroleum Exploration and Development in Papua New Guinea: Proceedings of the Second PNG Petroleum Convention, Australian Geological Survey, p. 489–498.</ref> Bicadinanes are often found together with oleanane.
Figure 8-30 shows bicadinanes in an oil sample from Myanmar. Note that the bicadinane peaks (indicated by solid dots) appear in all three fragment ions.
[[file:oiloil-and-oilsource-rock-correlations_fig8-30.png|thumb|{{figure number|8-30}}From Curiale;<ref name=ch08r12>Curiale, J., A., 1994, Correlation of oils and source rocks—a conceptual and historical perspective, in Magoon, L., B., Dow, W., G., eds., The [[Petroleum system]]—From Source to Trap: AAPG Memoir 60, p. 251–260.</ref> reprinted with permission from AAPG.]]
===Environment indicated by c<sub>x</sub> and c<sub>z</sub> triterpanes===
Two triterpanes, often called “C<sub>z</sub>” and “C<sub>x</sub>,” are also empirically associated with terrestrial organic matter, but their origin is unknown. They can be seen in Figure 8-26. C<sub>z</sub> 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 (e.g., <ref name=ch08r39 />). C<sub>x</sub> is probably a neohopane. They often co-occur with other terrestrial markers, such as high C<sub>29</sub> steranes, oleanane, and bicadinanes, but they can also occur alone.
===Example of c<sub>x</sub> and c<sub>z</sub> triterpanes===
Figure 8-31 shows m/z 191 mass chromatograms of three oils from the Cooper/Eromanga basin of Australia. The highest relative concentrations of C<sub>z</sub> and C<sub>x</sub> 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<sub>z</sub> and C<sub>x</sub> (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<sub>x</sub> often coelutes with T<sub>m</sub> (peak “b” in this figure).
[[file:oiloil-and-oilsource-rock-correlations_fig8-31.png|thumb|{{figure number|8-31}}From Philp and Gilbert<ref name=ch08r42 />); reprinted with permission from Elsevier.]]
===Environment indicated by 28,30-bisnorhopane===
Sometimes in great abundance, 28,30-bisnorhopane has been found in a few important source rocks and related oils (Monterey Formation, Kimmeridge Clay). It is probably of microbial origin. Because bisnorhopane is most common in sulfur-rich environments, its origin may have to do with bacteria that participate in the sulfur cycle. Denis Miiller (personal communication, 1994) notes that in the Monterey oils of southern California, bisnorhopane contents are proportional to sulfur contents.
===Example of 28,30-bisnorhopane===
The figure below shows the m/z 191 mass fragmentogram of an oil with a high relative concentration of 28,30-bisnorhopane, eluting to the left of norhopane (C<sub>29</sub> hopane).
[[file:oiloil-and-oilsource-rock-correlations_fig8-32.png|thumb|{{figure number|8-32}}See text for explanation.]]
===Environments indicated by tricyclic terpanes===
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.
===Example of tricyclic terpanes===
The figure below shows the m/z 191 fragmentogram for an unusual oil in which the tricyclic terpanes (left side of the chromatogram) strongly dominate the pentacyclics.
[[file:oiloil-and-oilsource-rock-correlations_fig8-33.png|thumb|{{figure number|8-33}}See text for explanation.]]
===Environments indicated by diterpanes===
Other diterpane and sesquiterpane distributions are also used for correlations. Most diterpanes originate from terrestrial resins, but microbial sources are also known.<ref name=ch08r39 /> Sesquiterpanes derive primarily from terrestrial plant resins. Most resin-derived compounds are of Tertiary or possibly Late Cretaceous age.
===Example of diterpanes===
The figure below shows m/z 123 mass chromatograms of two oils from northeast China. The differing sesquiterpane distributions show that the oils are not derived from the same source rock facies.
[[file:oiloil-and-oilsource-rock-correlations_fig8-34.png|thumb|{{figure number|8-34}}From Huang et al.;<ref name=ch08r19>Huang, Y., Ansong, G., Jiamo, F., Guoying, S., Biqiang, Z., Yixian, C., Maofen, L., 1992, The investigation of characteristics of biomarker assemblages and their precursors in Damintun ultra-high wax oils and related source rocks: Organic Geochemistry, vol. 19, p. 29–39., 10., 1016/0146-6380(92)90025-S</ref> reprinted with permission from Elsevier.]]
===Environments indicated by 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.
===Carotanes often not analyzed===
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.
===Example of carotanes===
The figure below 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.
[[file:oiloil-and-oilsource-rock-correlations_fig8-35.png|thumb|{{figure number|8-35}}Modified. Copyright: Peters and Moldowan (1993); courtesy Prentice-Hall.]]
===Summary of application of GC/MS to correlation studies===
The following table summarizes the application of GC/MS to correlation studies.
{| class = "wikitable"
|-
! This class of compound …
! May indicate an origin of …
|-
| C<sub>27</sub> steranes
| Marine organisms (minor amounts occur in nonmarine organisms)
|-
| C<sub>29</sub> steranes
| Marine or nonmarine organic matter
|-
| C<sub>30</sub> steranes
| Marine or lacustrine organisms
|-
| Diasteranes
| Clastic environment
|-
| Hopanes
| Bacteria
|-
| Gammacerane
| Abnormal salinites
|-
| Oleanane
| Late Cretaceous or Tertiary terrestrial flowering plants
|-
| Bicadinanes
| Tertiary terrestrial plants
|-
| C<sub>z</sub> and C<sub>x</sub> triterpanes
| Terrestrial organic matter or environment
|-
| 28,30-bisnorhopane
| Microbes
|-
| Tricyclic terpanes
| Bacteria or ''Tasmanites''
|-
| Diterpanes
| Terrestrial resins or microbes
|-
| Sesquiterpanes
| Terrestrial plant resins
|-
| Carotanes
| Anoxic marine or lacustrine environment
|}
==See also==
* [[Molecular parameter data]]
* [[Data obtained by gas chromatography]]
* [[How is GC/MS done?]]
* [[Examples of correlations using GC/MS]]
* [[Limitations of GC/MS]]
* [[Data obtained by high-performance liquid chromatography]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch08/ch08.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Critical elements of the petroleum system]]
[[Category:Oil–oil and oil–source rock correlations]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Critical elements of the petroleum system
| chapter = Oil–oil and oil–source rock correlations
| frompg = 8-1
| topg = 8-71
| author = Douglas W. Waples, Joseph A. Curiale
| link = http://archives.datapages.com/data/specpubs/beaumont/ch08/ch08.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
==Environments indicated by steranes==
The relative amounts of C<sub>27</sub>, C<sub>28</sub> and C<sub>29</sub> steranes in oils are controlled by the types of photosynthetic organisms that contributed to the organic matter. A dominance of C<sub>27</sub> steranes is almost always associated with marine organisms. Most nonmarine organic matter has a dominance of the C<sub>29</sub> sterane precursors, but C<sub>29</sub> steranes can dominate in marine systems as well. The abundance of C<sub>28</sub> steranes in marine systems may depend primarily on geologic age<ref name=ch08r16>Grantham, P., J., Wakefield, L., L., 1988, Variations in the sterane carbon number distributions of marine [[source rock]] derived crude oils through geological time: Organic Geochemistry, vol. 12, p. 61–73., 10., 1016/0146-6380(88)90115-5</ref> but this idea is controversial. In nonmarine systems, there is no proposed relationship between C<sub>28</sub> sterane abundance and age. C<sub>30</sub> steranes (''n''-propylcholestanes) are usually less abundant than the other regular steranes and occur only in samples deposited where marine organisms lived.<ref name=ch08r32>Moldowan, J., M., Seifert, W., K., Gallegos, E., J., 1985, Relationship between petroleum composition and depositional environment of petroleum [[source rocks]]: AAPG Bulletin, vol. 569, p. 1255–1268.</ref>
==Example of steranes==
The figure below shows m/z 217 mass fragmentograms from two oils showing quite different distributions of regular steranes. The top example is dominated by C<sub>29</sub> steranes with only moderate amounts of C<sub>27</sub> and C<sub>28</sub>. The bottom sample, in contrast, shows similar amounts of all three homologs plus moderate amounts of the C<sub>30</sub> steranes (four unlabeled peaks to the far right).
[[file:oiloil-and-oilsource-rock-correlations_fig8-23.png|thumb|{{figure number|8-23}}See text for explanation.]]
The figure below shows a ternary diagram, a convenient and common way of displaying basic data on sterane distributions. This example shows the relative proportions of the C<sub>27</sub>, C<sub>28</sub>, and C<sub>29</sub> regular steranes for several extracts from two distinct facies within the nonmarine Elko Formation (Eocene/Oligocene) of Nevada. The lignitic siltstones are dominated by terrestrial plant material, whereas the oil shales are made up of lacustrine algae.
[[file:oiloil-and-oilsource-rock-correlations_fig8-24.png|thumb|{{figure number|8-24}}From Palmer;<ref name=ch08r38>Palmer, S., E., 1984, Hydrocarbon source potential of organic facies of the lacustrine Elko Formation (Eocene/Oligocene), northeast Nevada, in Woodward, J., Meissner, F., F., Clayton, J., L., eds., Hydrocarbon source rocks of the greater Rocky Mountain region: Denver, Rocky Mountain Association of Geologists, p. 491–511.</ref> reprinted with permission from Rocky Mountain Assoc. of Geologists.]]
==4-methylsteranes==
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.
==Example of distribution of 4-methylsteranes==
The figure below 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).”
[[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.]]
==Environments indicated by 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.
Figure 8-23 shows two distinct distributions of diasteranes. The top oil has very few diasteranes, indicating a possible lack of clay in the source rock. The bottom oil, in contrast, has similar amounts of diasteranes and regular steranes and probably comes from a clastic source.
==Environments indicated by hopanes==
Hopanes, which originate from bacteria, are the most abundant triterpanes. A distribution with a regular decrease of homohopanes from C<sub>31</sub> to C<sub>35</sub> is thought to be associated with clastic environments.<ref name=ch08r59>Waples, D., W., Machihara, T., 1991, Biomarkers for geologists: Tulsa, AAPG, 91 p.</ref> and/or more oxidizing conditions<ref name=ch08r39>Peters, K., E., Moldowan, J., M., 1993, The Biomarker Guide—Interpreting [[Molecular fossils]] in Petroleum and Ancient Sediments: Englewood Cliffs, New Jersey, Prentice-Hall, 363 p.</ref>
==Example of homohopanes==
The figure below shows the m/z 191 mass fragmentogram of an oil displaying the most common type of homohopane distribution.
[[file:oiloil-and-oilsource-rock-correlations_fig8-26.png|thumb|{{figure number|8-26}}See text for explanation.]]
==Irregular homohopane distributions==
Irregular distributions of the C<sub>32</sub>–C<sub>35</sub> homohopanes are associated with carbonates.<ref name=ch08r59 /> and/or more reducing conditions<ref name=ch08r39 /> Unusually large amounts of the C<sub>31</sub> homohopanes are sometimes associated with coals and coaly material.<ref name=ch08r59 />
==Example of irregular homohopane distribution==
The figure below shows m/z 191 mass chromatograms for two sediment extracts from the Brac-1 well (Croatia) showing irregular homohopane distributions [relative enhancement of the C<sub>35</sub> species (left) and C<sub>34</sub> species (right)]. We would expect the oils sourced from these sediments to show these same characteristics.
[[file:oiloil-and-oilsource-rock-correlations_fig8-27.png|thumb|{{figure number|8-27}}From Moldowan et al.;<ref name=ch08r33>Moldowan, J., M., Lee, C., Y., Sundararaman, P., Salvatori, T., Alajbeg, A., Gjukic, B., Demaison, G., J., Slougue, N.-E., Watt, D., S., 1992, Source correlation and maturity assessment of select oils and rocks from the central Adriatic Basin (Italy and Yugoslavia), in Moldowan, J., M., Albrecht, P., Philp, R., P., eds., Biological markers in sediments and petroleum: Englewood Cliffs, New Jersey, Prentice-Hall, 411 p.</ref> reprinted with permission from Prentice-Hall.]]
===Environment indicated by gammacerane===
In addition to the hopane family, several other types of triterpanes that are occasionally encountered can be very useful in correlations. Gammacerane is often found in sediments deposited under abnormal salinites, including lacustrine facies. Identification of gammacerane can be difficult, however, both because it is usually only a minor component and because it elutes at different places with different chromatographic columns.
===Examples of gammacerane===
Figure 8-28 shows gammacerane in the m/z 191 mass chromatograms of two genetically related oils from southern Sicily. In this example, gammacerane elutes after the C<sub>31</sub> homohopanes. Note also the relative increase in the C<sub>34</sub> and C<sub>35</sub> homohopanes. The presence of gammacerane and the homohopane distribution suggest a strongly reducing, possibly carbonate or hypersaline depositional setting for the source rock of these oils.
[[file:oiloil-and-oilsource-rock-correlations_fig8-28.png|thumb|{{figure number|8-28}}From Ocampo et al.;<ref name=ch08r35>Ocampo, R., Riva, A., Trendel, J., M., Riolo, J., Callot, H., J., Albrecht, P., 1993, Petroporphyrins as biomarkers in oil-oil and oil-source rock correlations: Energy & Fuels, vol. 7, p. 191–193., 10., 1021/ef00038a005</ref> reprinted with permission from American Chemical Society.]]
Figure 8-29 also shows samples with gammacerane, but in this case gammacerane essentially coelutes with the C<sub>31</sub>-22R epimer. This example shows an oil from the Perla-1 well in southern Sicily and a source rock extract from the Noto Formation that correlates with it almost exactly.
[[file:oiloil-and-oilsource-rock-correlations_fig8-29.png|thumb|{{figure number|8-29}}From Mattavelli and Novelli;<ref name=ch08r29>Mattavelli, L., Novelli, L., 1990, Geochemistry and habitat of the oils in Italy: AAPG Bulletin, vol. 74, p. 1623–1639.</ref> reprinted with permission from AAPG.]]
===Environment and age indicated by oleananes===
Oleanane (two major isomers exist) originates from terrestrial flowering plants of Late Cretaceous or, more commonly, Tertiary age and as such is very valuable in correlation problems when deciding whether an oil comes from a source rock that is young or old.<ref name=ch08r45>Riva, A., Caccialanza, P., G., Quagliaroli, F., 1988, Recognition of 18β(H)-oleanane in several crudes and Cainozoic-Upper Cretaceous sediments. Definition of a new maturity parameter: Organic Geochemistry, vol. 13, p. 671–675., 10., 1016/0146-6380(88)90088-5</ref>
===Example of oleanane===
The figure below shows three mass chromatograms (m/z 191.18, 177.16, and 217.20, from top to bottom) for an oil from central Myanmar. The peak marked “o” is a combination of 18α(H) and 18β(H) oleanane. The tallest peak in the m/z 191 mass chromatogram is hopane, and the peaks indicated by solid dots are bicadinanes.
===Environment indicated by bicadinanes===
Bicadinanes are among the very few compounds that give substantial peaks in both the m/z 191 and 217 fragment ions. Bicadinane resins are derived from terrestrial plants that evolved in the Tertiary. The primary source plants, dipterocarps, spread slowly through Southeast Asia during the middle to late Tertiary. Bicadinanes are rare in other places and at other times, except from the Tertiary of New Zealand and Australia, where they probably originated from other species.<ref name=ch08r34>Murray, A., P., Summons, R., E., Bradshaw, J., Pawih, B., 1993, Cenozoic oil in Papua New Guinea—evidence from geochemical analysis of two newly discovered seeps, in Carman, G., J., Carman, Z., eds., Petroleum Exploration and Development in Papua New Guinea: Proceedings of the Second PNG Petroleum Convention, Australian Geological Survey, p. 489–498.</ref> Bicadinanes are often found together with oleanane.
Figure 8-30 shows bicadinanes in an oil sample from Myanmar. Note that the bicadinane peaks (indicated by solid dots) appear in all three fragment ions.
[[file:oiloil-and-oilsource-rock-correlations_fig8-30.png|thumb|{{figure number|8-30}}From Curiale;<ref name=ch08r12>Curiale, J., A., 1994, Correlation of oils and source rocks—a conceptual and historical perspective, in Magoon, L., B., Dow, W., G., eds., The [[Petroleum system]]—From Source to Trap: AAPG Memoir 60, p. 251–260.</ref> reprinted with permission from AAPG.]]
===Environment indicated by c<sub>x</sub> and c<sub>z</sub> triterpanes===
Two triterpanes, often called “C<sub>z</sub>” and “C<sub>x</sub>,” are also empirically associated with terrestrial organic matter, but their origin is unknown. They can be seen in Figure 8-26. C<sub>z</sub> 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 (e.g., <ref name=ch08r39 />). C<sub>x</sub> is probably a neohopane. They often co-occur with other terrestrial markers, such as high C<sub>29</sub> steranes, oleanane, and bicadinanes, but they can also occur alone.
===Example of c<sub>x</sub> and c<sub>z</sub> triterpanes===
Figure 8-31 shows m/z 191 mass chromatograms of three oils from the Cooper/Eromanga basin of Australia. The highest relative concentrations of C<sub>z</sub> and C<sub>x</sub> 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<sub>z</sub> and C<sub>x</sub> (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<sub>x</sub> often coelutes with T<sub>m</sub> (peak “b” in this figure).
[[file:oiloil-and-oilsource-rock-correlations_fig8-31.png|thumb|{{figure number|8-31}}From Philp and Gilbert<ref name=ch08r42 />); reprinted with permission from Elsevier.]]
===Environment indicated by 28,30-bisnorhopane===
Sometimes in great abundance, 28,30-bisnorhopane has been found in a few important source rocks and related oils (Monterey Formation, Kimmeridge Clay). It is probably of microbial origin. Because bisnorhopane is most common in sulfur-rich environments, its origin may have to do with bacteria that participate in the sulfur cycle. Denis Miiller (personal communication, 1994) notes that in the Monterey oils of southern California, bisnorhopane contents are proportional to sulfur contents.
===Example of 28,30-bisnorhopane===
The figure below shows the m/z 191 mass fragmentogram of an oil with a high relative concentration of 28,30-bisnorhopane, eluting to the left of norhopane (C<sub>29</sub> hopane).
[[file:oiloil-and-oilsource-rock-correlations_fig8-32.png|thumb|{{figure number|8-32}}See text for explanation.]]
===Environments indicated by tricyclic terpanes===
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.
===Example of tricyclic terpanes===
The figure below shows the m/z 191 fragmentogram for an unusual oil in which the tricyclic terpanes (left side of the chromatogram) strongly dominate the pentacyclics.
[[file:oiloil-and-oilsource-rock-correlations_fig8-33.png|thumb|{{figure number|8-33}}See text for explanation.]]
===Environments indicated by diterpanes===
Other diterpane and sesquiterpane distributions are also used for correlations. Most diterpanes originate from terrestrial resins, but microbial sources are also known.<ref name=ch08r39 /> Sesquiterpanes derive primarily from terrestrial plant resins. Most resin-derived compounds are of Tertiary or possibly Late Cretaceous age.
===Example of diterpanes===
The figure below shows m/z 123 mass chromatograms of two oils from northeast China. The differing sesquiterpane distributions show that the oils are not derived from the same source rock facies.
[[file:oiloil-and-oilsource-rock-correlations_fig8-34.png|thumb|{{figure number|8-34}}From Huang et al.;<ref name=ch08r19>Huang, Y., Ansong, G., Jiamo, F., Guoying, S., Biqiang, Z., Yixian, C., Maofen, L., 1992, The investigation of characteristics of biomarker assemblages and their precursors in Damintun ultra-high wax oils and related source rocks: Organic Geochemistry, vol. 19, p. 29–39., 10., 1016/0146-6380(92)90025-S</ref> reprinted with permission from Elsevier.]]
===Environments indicated by 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.
===Carotanes often not analyzed===
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.
===Example of carotanes===
The figure below 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.
[[file:oiloil-and-oilsource-rock-correlations_fig8-35.png|thumb|{{figure number|8-35}}Modified. Copyright: Peters and Moldowan (1993); courtesy Prentice-Hall.]]
===Summary of application of GC/MS to correlation studies===
The following table summarizes the application of GC/MS to correlation studies.
{| class = "wikitable"
|-
! This class of compound …
! May indicate an origin of …
|-
| C<sub>27</sub> steranes
| Marine organisms (minor amounts occur in nonmarine organisms)
|-
| C<sub>29</sub> steranes
| Marine or nonmarine organic matter
|-
| C<sub>30</sub> steranes
| Marine or lacustrine organisms
|-
| Diasteranes
| Clastic environment
|-
| Hopanes
| Bacteria
|-
| Gammacerane
| Abnormal salinites
|-
| Oleanane
| Late Cretaceous or Tertiary terrestrial flowering plants
|-
| Bicadinanes
| Tertiary terrestrial plants
|-
| C<sub>z</sub> and C<sub>x</sub> triterpanes
| Terrestrial organic matter or environment
|-
| 28,30-bisnorhopane
| Microbes
|-
| Tricyclic terpanes
| Bacteria or ''Tasmanites''
|-
| Diterpanes
| Terrestrial resins or microbes
|-
| Sesquiterpanes
| Terrestrial plant resins
|-
| Carotanes
| Anoxic marine or lacustrine environment
|}
==See also==
* [[Molecular parameter data]]
* [[Data obtained by gas chromatography]]
* [[How is GC/MS done?]]
* [[Examples of correlations using GC/MS]]
* [[Limitations of GC/MS]]
* [[Data obtained by high-performance liquid chromatography]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch08/ch08.htm Original content in Datapages]
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[[Category:Critical elements of the petroleum system]]
[[Category:Oil–oil and oil–source rock correlations]]