Abstract

Examination of some residual organic substances in Upper Jurassic rocks has shown several relationships between rock types and organic constituents. The organic C and N content as well as the residual amino acids and carbohydrates of these samples were discussed in an earlier paper. The nearshore marine and non-marine Jurassic rocks have relatively more of the organic N represented by amino acids or amines, while the basinal and neritic samples have more of the organic N in the heterocyclic form or in humic complexes. Both the presumed saturated and aromatic hydrocarbon residues, extracted from littoral and neritic non-reservoir Jurassic rocks and separated chromatographically, are roughly equal in amount and are similar to modern occurrences. In basinal Jurassic rocks the aromatics tend to exceed the saturates, although exceptions occur. Several possible polycyclic aromatic hydrocarbons were detected in the basinal and some neritic, but less definitely in littoral samples. Residual asphaltenes in the Jurassic rocks are much less in amount than in Recent equivalents, probably because of post-depositional changes. Trace amounts of probably aromatic and heteroaromatic substances are widespread in the Jurassic samples studied. Among the substances possibly represented are: anthracene, naphthalene, pyridines, quinolinic acid, pyrazine, aniline, pyrimidine, purine, and several possible polycyclic aromatic hydrocarbons. Of these, anthracene and the pyridines occur most commonly, and also have been recognized in samples of other ages. The basinal marine Jurassic samples tend to have a predominance of 1-ring residual aromatics, where as the neritic and littoral samples seem to have relatively more 2- and 3-ring aromatics and porphyrins. No relation was found between the larger fossil remains and organic residues in the samples studied; the nannofossils may contribute to the organic residues but no quantitative relationship was found. Conclusions by others that air and surface water temperatures were higher in central North America during the Jurassic than at present are supported by the present study. Such contributing factors as organic productivity, preservation of organic residues, redox potentials, mineralogy, and color of sediment are discussed in relation to the residual organic matter.

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