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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 70 (1986)

Issue: 9. (September)

First Page: 1113

Last Page: 1128

Title: Bitumen Accumulation in Grosmont Platform Complex, Upper Devonian, Alberta, Canada

Author(s): C. F. Hoffmann (2), O. P. Strausz (2)


The Upper Devonian Grosmont Formation, a broad carbonate platform complex in Alberta, Canada, contains an estimated 300 billion bbl of bitumen. It has been suggested that these vast reserves are related to Lower Cretaceous Athabasca oil sands. Detailed gas chromatographic-mass spectrometric studies of a wide range of biologic marker compounds confirm this suggestion. The Grosmont Formation contains bitumen of similar maturity and source to the Athabasca deposit, but it has been subjected to a greater degree of biodegradation and water washing, possibly as a result of its reservoir rock characteristics. The difference in the degree of biodegradation is manifested by the absence of bicyclic terpanes and by the reduced concentrations of the C30 and the 22R epimers of the extended hopanes in the Grosmont bitumen. Also, the greater degree of water washing of the Grosmont bitumen is inferred from the observed distribution of the bicyclic, tricyclic, and tetracyclic terpenoid sulfides, which shows a characteristic loss of the lower molecular weight members in the carbonate bitumen. The correlation established here between the two deposits suggests that if the precursor oil has indeed undergone long-distance migration, the Paleozoic carbonates could have acted as a path for migration.

Finally, the observed distribution of steranes in the Grosmont bitumen corresponds to the suggestion that the Mannville Group shales were not the major source rocks of the oil-sand and carbonate bitumen accumulations of northern Alberta.

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