Distinctive hydrocarbon biomarkers from fossiliferous sediment of the Late Proterozoic Walcott Member, Chuar Group, Grand Canyon, Arizona

Roger E. Summons*, Simon C. Brassell, Geoffrey Eglinton, Evan Evans, Robert J. Horodyski, Neil Robinson, David M. Ward

*Corresponding author for this work

    Research output: Contribution to journalArticle

    131 Citations (Scopus)

    Abstract

    Abundant extractable hydrocarbons, in association with well preserved kerogen, have been recognised in a dolostone from the Chuar Group (approx. 850 Ma). The biomarkers present include C15-C30, acyclic isoprenoids, C26-C28 steranes, C27-C35 hopanes and extended tricyclic terpanes. Among the striking characteristics of the distributions are the dominance of steranes and methyl steranes lacking side-chain alkylation and the presence of putative C29-C35 neohopanes and gammacerane. The high abundance of steranes is consistent with the presumed eukaryotic affinities of several types of microfossils, including Chuaria, present in associated mudstones. This stratum is the oldest in which gammacerane has been found, and suggests contributions from protozoa to the depositional environment which appears to have been hypersaline. There is a strong correlation between the carbon isotopic composition of the kerogen and that of the various polarity fractions of the bitumens. Chemical degradation and pyrolysis of the kerogens yielded n-alkanes with similar characteristics to the bitumens, but there are differences in the patterns of distribution of the acyclic isoprenoid, sterane and triterpane biomarkers.

    Original languageEnglish
    Pages (from-to)2625-2637
    Number of pages13
    JournalGeochimica et Cosmochimica Acta
    Volume52
    Issue number11
    DOIs
    Publication statusPublished - 1988

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