Structural configuration of the Kishenehn Basin delineated by geophysical methods, northwestern Montana and southeastern British Columbia

Journal Article · Fri Jan 01 04:00:00 EST 1988 · Mountain Geologist; (USA)

OSTI ID:5342205

Constenius, K ^[1]

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1. Amoco Production Co., Denver, CO (USA)

The Oligocene Kishenehn Formation consists of a heterogeneous assemblage of conglomerates, sandstones, siltstones, mudstones/claystones, marlstones, coals, and oil shales. Analysis of these rock types reveals that variations in lithology cause dramatic changes in density. Kishenehn rock densities range from 2.00-2.31 gm/cc for oil shales to 2.36-2.62 gm/cc for conglomerates. Gravity models of the Kishenehn basin were constructed using the aforementioned density information and the surface geology. Five gravity profiles were modeled, and are consistent with the following conclusions: (1) Kishenehn sediments attain a maximum thickness of approximately 11,000 ft near the basin center and decrease in thickness symmetrically along strike; (2) no major faults transect the basin between the Flathead and Nyack fault systems; (3) the Flathead fault is a listric normal fault, and the Nyack fault is a steeply dipping normal fault antithetic to the Flathead fault; (4) minimum displacements of the Flathead and Nyack faults vary between 16,500-21,000 ft and 5,500-12,500 ft; (5) the Hyack fault changes from east-dipping near the central part of the basin to nearly vertical or overturned toward the southern end of the basin; and (6) the character of the basin changes from an asymmetrical graben in the south to a half-graben in the north. The structural position of the Kishenehn basin was controlled by variations in the amount of displacement on the Flathead fault system, and ultimately, was dependent on the nature of the Lewis footwall ramp. Results of the gravity modeling support this structural hypothesis.

• OSTI ID: 5342205
• Journal Information: Mountain Geologist; (USA), Journal Name: Mountain Geologist; (USA) Vol. 25:1; ISSN MOGEA; ISSN 0027-254X
• Country of Publication: United States
• Language: English

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BRITISH COLUMBIA
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PHYSICAL PROPERTIES
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USA