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Discovery of oil seeps in the Flathead region led to wildcat drilling by 1902. Exploration on the U.S. side stopped by 1910 because of the formation of Glacier Park, and the fact that the oil seeps were in Precambrian sedimentary rocks. Exploration continued through the 1930s on the Canadian side with drilling in the vicinity of major oil seeps. Exploration in Canada from the 1950s to present has included seismic work and six wildcat tests in the Flathead region. A land play has been going on in northwestern Montana for the past several years and recently released seismic data have demonstrated major structures that apparently involve Paleozoic rocks. Plans for drilling have been announced.
The Glacier-Waterton and Flathead region are on the Lewis thrust plate. At the Sage Creek, British Columbia, oil seeps, drilling in 1952 penetrated the Lewis fault after drilling 4,400 ft (1,341 m) of Precambrian sedimentary rocks, and then drilled a strongly faulted sequence of upper Paleozoic carbonates and sandstones with several oil shows. The Precambrian rocks on the Lewis plate in the U.S. thin into Canada, eventually to zero where Paleozoic and Mesozoic rocks are carried by the Lewis fault. An area of hundreds of square miles of Paleozoic and Mesozoic outcrop, including the Fernie basin, is present immediately across the international boundary from areas of Montana which have been mapped as containing great thicknesses of Precambrian sediments. In the northern Whitefish Range o Montana, nearly 40 mi (64 km) from the leading edge of the Lewis thrust, is 30 mi2 (78 km2) of Paleozoic and Mesozoic outcrop containing several petroliferous units. This sequence is the only part of the extensive Paleozoic and Mesozoic outcrop of southeastern British Columbia which extends into the U.S., but it is important in understanding the involvement of Paleozoic and Mesozoic rocks in complexly faulted northwestern Montana. The Whitefish Range Paleozoic and Mesozoic sequence is cut by several minor thrust faults as well as having been overthrust by the Hefty plate, present now as klippe on the highest peaks of Paleozoic rocks. The Couldry and Tuchuck faults cut these rocks a few miles to the west.
Between the Whitefish Range and the Livingstone Range of Glacier Park lies the Kishenehn basin, a graben to half-graben formed by the listric normal Flathead fault on the Lewis plate. This basin is filled with Oligocene Kishenehn formation, a fluvial
to lacustrine sequence, which may be as thick as 16,000 ft (5 km) on the east side, thinning to a few thousand feet or to zero on the west where fault bounded. The Kishenehn formation contains lignite and oil shale beds which may be buried deep enough in parts of the basin to generate hydrocarbons; recent drilling discovered oil and gas shows at less than 200 ft (61 m).
The presence of oil and gas shows in many formation as well as the presence of major structures containing porous host beds indicates that this area has an excellent potential for the discovery of hydrocarbons.
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