Changes

==Biodegradation and sterane distributions==

==Biodegradation and sterane distributions==

[[file:oiloil-and-oilsource-rock-correlations_fig8-40.png|300px|thumb|{{figure number|1}}ααα-20R steranes (regular steranes with the 20R configuration) are lost selectively during the early stages of severe biodegradation, followed by loss of all ααα steranes. From Curiale<ref name=ch08r12>Curiale, J., A., 1994, [http://archives.datapages.com/data/specpubs/methodo2/data/a077/a077/0001/0250/0251.htm 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: [http://store.aapg.org/detail.aspx?id=1022 AAPG Memoir 60], p. 251–260.</ref> reprinted with permission from AAPG.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-40.png|300px|thumb|{{figure number|1}}ααα-20R steranes (regular steranes with the 20R configuration) are lost selectively during the early stages of severe biodegradation, followed by loss of all ααα steranes. From Curiale<ref name=ch08r12>Curiale, J. A., 1994, [http://archives.datapages.com/data/specpubs/methodo2/data/a077/a077/0001/0250/0251.htm Correlation of oils and source rocks—a conceptual and historical perspective], in L. B. Magoon, and W. G. Dow, eds., The [[Petroleum system]]—From Source to Trap: [http://store.aapg.org/detail.aspx?id=1022 AAPG Memoir 60], p. 251–260.</ref> reprinted with permission from AAPG.]]

[http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx Biodegradation], where severe, can also cause major changes in sterane and triterpane distributions. The ααα-20R steranes (regular steranes with the 20R configuration) are lost selectively during the early stages of severe biodegradation, followed by loss of all ααα steranes. [[:file:oiloil-and-oilsource-rock-correlations_fig8-40.png|Figure 1]] illustrates this trend. It shows the m/z 217.2 mass chromatograms of three oils from central Myanmar in successive stages of biodegradation, ranging from not degraded (top) to extremely degraded (bottom). The severely degraded oil has lost almost all of its regular steranes, with greater loss of 20R than 20S. Gas chromatograms of these three oils are shown in Figure 8-20.

[http://www.oiltracers.com/services/exploration-geochemistry/oil-biodegradation.aspx Biodegradation], where severe, can also cause major changes in sterane and triterpane distributions. The ααα-20R steranes (regular steranes with the 20R configuration) are lost selectively during the early stages of severe biodegradation, followed by loss of all ααα steranes. [[:file:oiloil-and-oilsource-rock-correlations_fig8-40.png|Figure 1]] illustrates this trend. It shows the m/z 217.2 mass chromatograms of three oils from central Myanmar in successive stages of biodegradation, ranging from not degraded (top) to extremely degraded (bottom). The severely degraded oil has lost almost all of its regular steranes, with greater loss of 20R than 20S. Gas chromatograms of these three oils are shown in Figure 8-20.