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Line 122: − Fig. 2. Modified Van Krevelen diagram for organic facies A through D. (After Jones, 1987.)+ − − Fig. 3. Van Krevelen-type diagram for organic facies A through D, using Rock-Eval parameters on whole-rock samples. Discrimination of organic facies CD and D is analytically less definitive than others, and thus these boundaries are represented by gray shading.
→Kerogen types
Before enumerating the criteria for discriminating kerogen types, it is important to consider the "mineral matrix effect." Some mineral (polar clay) constituents retard the release of hydrocarbons from powdered whole rock samples during Rock-Eval pyrolysis, under-evaluating the quantity, quality, and thermal maturation data. Although this factor, the mineral matrix effect, is well known to organic geochemists, it is frequently overlooked when interpreting Rock-Eval-dependent values used to determine kerogen type and organic facies. The mineral matrix effect occurs when polar clays react with polar organic molecules during the nonhydrous Rock-Eval procedure.<ref name=Esptl1980>Espitalie, J., M. Madec, and B. Tissot, 1980, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0064/0001/0050/0059.htm Role of mineral matrix in kerogen pyrolysis: Influence on petroleum generation and migration]: American Association of Petroleum Geologists Bulletin, v. 64, p. 59-66.</ref><ref name=Hrsfld1980>Horsfield, B., and A. G. Douglas, 1980, The influence of minerals on the pyrolysis of kerogens: Geochimica et Cosmochimica Acta, v. 44, p. 1110-1131.M</ref><ref>Orr, W. L., 1983, Comments on pyrolitic hydrocarbon yields in source-rock evaluation, in M. Bjoroy et al., eds., Advances in Organic Geochemistry 1981, p. 775-787.</ref><ref name=Dmbcki1983>Dembicki, H., B. Horsfield, and T. Y. Ho, 1983, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0067/0007/1050/1094.htm Source rock evaluation by pyrolysis-gas chromatography]: American Association of Petroleum Geologists Bulletin, v. 67, p. 1094-1103.</ref><ref name=Ktz1983>Katz, B. J., 1983, Limitations of Rock Eval pyrolysis for typing organic matter: Organic Geochemistry, v. 4, p. 195-199.</ref><ref>Peters, K. E., 1986, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0003/0300/0318.htm Guidelines for evaluating petroleum source rocks using programmed pyrolysis]: American Association Petroleum Geologists Bulletin, v. 70, p. 318-329.</ref><ref>Crossey, L. J., E. S. Hagan, R. C. Surdam, and P. W. Lapointe, 1986, Correlation of organic parameters derived from elemental analysis and programmed pyrolysis of kerogen: Society of Economic Paleontologists and Mineralogists, p. 36-45</ref><ref>Langford, F. F., and M. M. Blanc-Valleron, 1990, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0074/0006/0000/0799.htm Interpreting Rock-Eval data using graphs of pyrolizable hydrocarbons vs. total organic carbon]: American Association Petroleum Geologists Bulletin, v. 74, p. 799-80</ref>
Before enumerating the criteria for discriminating kerogen types, it is important to consider the "mineral matrix effect." Some mineral (polar clay) constituents retard the release of hydrocarbons from powdered whole rock samples during Rock-Eval pyrolysis, under-evaluating the quantity, quality, and thermal maturation data. Although this factor, the mineral matrix effect, is well known to organic geochemists, it is frequently overlooked when interpreting Rock-Eval-dependent values used to determine kerogen type and organic facies. The mineral matrix effect occurs when polar clays react with polar organic molecules during the nonhydrous Rock-Eval procedure.<ref name=Esptl1980>Espitalie, J., M. Madec, and B. Tissot, 1980, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0064/0001/0050/0059.htm Role of mineral matrix in kerogen pyrolysis: Influence on petroleum generation and migration]: American Association of Petroleum Geologists Bulletin, v. 64, p. 59-66.</ref><ref name=Hrsfld1980>Horsfield, B., and A. G. Douglas, 1980, The influence of minerals on the pyrolysis of kerogens: Geochimica et Cosmochimica Acta, v. 44, p. 1110-1131.M</ref><ref>Orr, W. L., 1983, Comments on pyrolitic hydrocarbon yields in source-rock evaluation, in M. Bjoroy et al., eds., Advances in Organic Geochemistry 1981, p. 775-787.</ref><ref name=Dmbcki1983>Dembicki, H., B. Horsfield, and T. Y. Ho, 1983, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0067/0007/1050/1094.htm Source rock evaluation by pyrolysis-gas chromatography]: American Association of Petroleum Geologists Bulletin, v. 67, p. 1094-1103.</ref><ref name=Ktz1983>Katz, B. J., 1983, Limitations of Rock Eval pyrolysis for typing organic matter: Organic Geochemistry, v. 4, p. 195-199.</ref><ref>Peters, K. E., 1986, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0003/0300/0318.htm Guidelines for evaluating petroleum source rocks using programmed pyrolysis]: American Association Petroleum Geologists Bulletin, v. 70, p. 318-329.</ref><ref>Crossey, L. J., E. S. Hagan, R. C. Surdam, and P. W. Lapointe, 1986, Correlation of organic parameters derived from elemental analysis and programmed pyrolysis of kerogen: Society of Economic Paleontologists and Mineralogists, p. 36-45</ref><ref>Langford, F. F., and M. M. Blanc-Valleron, 1990, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0074/0006/0000/0799.htm Interpreting Rock-Eval data using graphs of pyrolizable hydrocarbons vs. total organic carbon]: American Association Petroleum Geologists Bulletin, v. 74, p. 799-80</ref>
[[File:KerogenTypeFig2.png|thumb|350px|{{figure number|2}}Modified Van Krevelen diagram for organic facies A through D. (After Jones, 1987.)]]
Pioneers of pyrolysis found that some minerals inhibit hydrocarbon expulsion during whole-rock pyrolysis and not during kerogen pyrolysis.<ref name=Esptl1980 /><ref name=Hrsfld1980 /><ref name=Dmbcki1983 /> The effect of different matrix constituents<ref name=Esptl1980 /><ref name=Hrsfld1980 /><ref name=Dmbcki1983 /><ref name=Ktz1983 /> varies from strongest to weakest: illite > Ca-bentonite > kaolinite > Na-bentonite > calcium carbonate > gypsum.<ref name=Esptl1980 /> Variations in the mineral matrix effect related to organic richness occur in whole-rock samples with TOC values less than 10%.<ref name=Esptl1980 /><ref name=Hrsfld1980 /><ref name=Dmbcki1983 />
Pioneers of pyrolysis found that some minerals inhibit hydrocarbon expulsion during whole-rock pyrolysis and not during kerogen pyrolysis.<ref name=Esptl1980 /><ref name=Hrsfld1980 /><ref name=Dmbcki1983 /> The effect of different matrix constituents<ref name=Esptl1980 /><ref name=Hrsfld1980 /><ref name=Dmbcki1983 /><ref name=Ktz1983 /> varies from strongest to weakest: illite > Ca-bentonite > kaolinite > Na-bentonite > calcium carbonate > gypsum.<ref name=Esptl1980 /> Variations in the mineral matrix effect related to organic richness occur in whole-rock samples with TOC values less than 10%.<ref name=Esptl1980 /><ref name=Hrsfld1980 /><ref name=Dmbcki1983 />