Tectonic analysis of belt terrane of northwest Montana-northern Idaho and its implications for oil and gas potential west of disturbed belt
From a recently completed comprehensive regional geologic map and cross sections across the Cordillera of the northwestern United States, the following conclusions have been made. (1) Paleozoic as well as probable late Precambrian Belt miogeoclinal sedimentation developed west of northern Idaho off the edge of the continental crust. (2) Mesozoic orogeny started west of the continent margin, shifted east, and did not involve the Disturbed belt until earliest Tertiary time. Thus, a significant time span separated mobility and uplift in the core region of the orogene from thrusting of the foreland. (3) Immediately following thrusting, the entire northwest was swept by a 40-50 m.y. extensional orogeny involving, from place to place, widespread calcalkaline magmatism, listric faulting on a grand scale, subhorizontal detachment faults, and basement mylonitization. This tectonism influenced the Belt region by fragmentation and eastward tilting of strata and thrusts, and creation of structural relief on the pre-Belt basement surface by normal faulting. Regional cross sections show no serious obstacles to the presence of an autochthonous or detached slab of Paleozoic rocks beneath the overthrust Belt section, although subhorizontal mylonitic rocks are not outside the realm of geologic possibility. Nevertheless, oil and gas favorability beneath Belt rocks is affected by such factors as ratio of source rock to reservoir rock, thermal and/or pressure conditions after overthrusting, and the postmigrational effects of Eocene extensional tectonism (i.e., dip reversals, magmatism, and fragmentation).
- Research Organization:
- Applied Geologic Studies, Inc., Englewood, CO
- OSTI ID:
- 5462227
- Report Number(s):
- CONF-8408161-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 68:7; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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020200* -- Petroleum-- Reserves
Geology
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03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
CENOZOIC ERA
FEDERAL REGION VIII
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
IDAHO
MINERAL RESOURCES
MONTANA
NATURAL GAS DEPOSITS
NORTH AMERICA
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCES
SOURCE ROCKS
TECTONICS
TERTIARY PERIOD
USA