Distinctive hydrocarbon biomarkers from fossiliferous sediment of the late Proterozoic Walcott member, Chuar group, Grand Canyon, Arizona

Journal Article · Tue Nov 01 00:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90031-2· OSTI ID:7273158

Summons, R E ^[1]; Brassell, S C; Eglinton, G; Evans, E; Robinson, N ^[2]; Horodyski, R J ^[3]; Ward, D M ^[4]

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1. Bureau of Mineral Resources, Canberra City (Australia)
2. Organic Geochemistry Unit, School of Chemistry, Bristol (England)
3. Tulane Univ., New Orleans, LA (USA)
4. Montana State Univ., Bozeman, MT (USA)

Abundant extractable hydrocarbons, in association with well preserved kerogen, have been recognized in a dolostone from the Chuar Group (approx. 850 Ma). The biomarkers present include C{sub 15}-C{sub 30} acyclic isoprenoids, C{sub 26}-C{sub 28} steranes, C{sub 27}-C{sub 35} 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 C{sub 29}-C{sub 35} 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.

• OSTI ID: 7273158
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:11; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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CARBONATE ROCKS
FOSSILS
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
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020200* - Petroleum- Reserves
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023000 - Petroleum- Properties & Composition