--> ABSTRACT: Regional Source Rock Potential of Kishenehn Formation, Northwest Montana, by Joseph A. Curiale and Steven W. Sperry; #91038 (2010)

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Regional Source Rock Potential of Kishenehn Formation, Northwest Montana

Joseph A. Curiale, Steven W. Sperry

The Kishenehn Formation of northwest Montana and southeast British Columbia consists of 3 to 5 km of Oligocene nonmarine shales and lignites. These fluvial and lacustrine sediments were deposited atop Precambrian Belt rocks in a northwest-southeast elongated half-graben. Geochemical source rock analyses have been performed for the first time on samples from the western portion of the Kishenehn basin, exposed at twelve locations near the North and Middle Forks of the Flathead River, in Montana and Canada. Six locations contain paper-thin calcareous shales with excellent petroleum source potential; the richest shales crop out at the southern edge of the basin. Specific molecular markers are present in these samples, including several suites of diagenetic steroidal hydrocarb ns. Land-plant molecular input suggests nearshore deposition for the southernmost samples.

Average total organic carbon contents and hydrogen indices in the Kishenehn Formation exceed 6% and 500 mg/g, respectively; total carbonate content averages 26%. Approximately half of the samples contain predominantly Type I organic matter; most of these are from exposures of the Coal Creek member of the Kishenehn, along the Middle Fork of the Flathead River. All of the exposed Kishenehn in the western portion of the basin is thermally immature or marginally mature, having vitrinite reflectance values of 0.28 to 0.51% Ro. Detailed source rock and molecular analysis of these marginally mature samples can be used to infer chemical characteristics of hydrocarbons generated at depth in the basin.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.