Beaverhead Formation, a Laramide Deposit in Beaverhead County, Montana

Lowell, Wayne Russell; Klepper, M.R.

doi:10.1130/0016-7606(1953)64[235:bfaldi]2.0.co;2

Cited by 13 publications

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“…38). From here to the northwest, the thrust has been interpreted to extend in several directions (Kupsch, 1950;Lowell and Klepper, 1953;Scholten and others, 1955;Scholten, 1960;Williams, 1984) . The sixth hanging wall diagram of Thrust "D" of Dubois (1982) that has crystalline basement rocks in the hanging wall.…”

Section: Four Eyes Canyon Thrust Platementioning

confidence: 96%

Contraction and extension faults in the southern Beaverhead Mountains, Idaho and Montana

Skipp¹

1985

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Geologic mapping of 340 square miles (884 square kilometers) in the southern Beaverhead Mountains demonstrates that the area is a segment of the Mesozoic to early Tertiary Cordilleran thrust belt, and a northward continuation of the Idaho-Wyoming thrust salient. Five thrust plates are bounded by major west-dipping, low-angle folded thrusts that juxtapose older strata over younger, and are characterized by east-verging concentric folds, frontal ramp anticlines, and transverse tear faults. The five thrust plates, each with a distinctive stratigraphic sequence, are, in descending structural order: Hawley Creek, Fritz Creek, Cabin, Medicine Lodge, and Tendoy. The Cabin thrust plate locally includes Precambrian (Archean(?)) basement crystalline rocks along its leading edge. These crystalline rocks probably were part of an older Precambrian block uplift cut by the eastward directed Cabin thrust. Extension faults with youngest movements ranging in age from early Eocene to Holocene offset the five thrust plates. The Divide Creek extension fault zone, along which middle Paleozoic stratigraphic section is deleted, probably is of early Eocene age. Miocene to Holocene basin-range faults offset older structures, and loci of the younger faults have shifted westward through time. Thrusts and thrust plates identified in the study area also make up a large part of the central and northern Beaverhead Mountains. The Cabin thrust plate is the most extensive of these. IX The redefined Cabin thrust is more than 125 miles (200 kilometers) long, has two major lateral ramps, has Archean(?) crystalline rocks along a 48-mile (75-kilometer) segment of its leading edge in central parts of the mountains, and Middle Proterozoic Yellowjacket Formation and overlying Lemhi Group rocks in northern parts. The Cabin plate includes Archean(?) through Lower Triassic rocks in the central Beaverheads. In the northern Beaverheads, rocks of the Yellowjacket Formation and the Lemhi Group have been thrust over Belt Supergroup rocks creating a structural culmination of Proterozoic rocks in east-central Idaho. The foreland that was overridden by the easterly transported Cabin and Medicine Lodge thrust plates was deformed by northwest to southeast directed reverse faults that probably were formed and partly eroded before the thrust plates arrived in Late Cretaceous (Maestrichtian(?)) time.

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Section: Four Eyes Canyon Thrust Platementioning

confidence: 96%

Contraction and extension faults in the southern Beaverhead Mountains, Idaho and Montana

Skipp¹

1985

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“…At the time the fault was mapped near Horse Prairie, Lowell and Klepper (1953) also mapped and named the Beaverhead Formation, which they considered to be a syntectonic conglomerate related to thrust faulting. The tectonic significance of the Beaverhead Formation has recently been discussed in detail by Ryder and Scholten (1973), Ryder and Ames (1970), and Wilson (1970).…”

Section: Summary Of Earlier Studiesmentioning

confidence: 99%

“…The Beaverhead Formation, named by Lowell and Klepper (1953), is recognized as a syntectonic deposit that resulted from regional overthrusting. Scholten (1973, p. 477^480) noted that "extensive remains of the subaerial Beaverhead conglomerate occur at the eastern margin of the overthrust belt.…”

Section: The Beaverhead Formation and The Age Of The Medicine Lodge Tmentioning

confidence: 99%

Medicine Lodge thrust system, east-central Idaho and Southwest Montana

Ruppel¹

1978

Professional Paper

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The Medicine Lodge thrust system, exposed in east-central Idaho and southwest Montana, is a major segment of the North America Cordilleran fold and thrust belt on which Precambrian and Paleozoic rocks have been telescoped and transported far east of their depositional area. The fault has overlapped rocks that initially were deposited in differing sedimentary environments on opposite sides of the northwest-trending geanticlinal Lemhi arch. The nature of the arch itself has been obscured by later thrusting, but it can be roughly reconstructed as a major landmass recurrently uplifted from Precambrian Y time at least through the Mesozoic. Although sections of the large landmass have been identified in the past as small islands, the landmass was instead a southern extension of Belt island, and it exerted a major influence on sedimentation patterns. The thrust has obscured recognition of correlative sedimentary rock units. It also appears to have controlled the distribution of volcanic rocks in satellite centers of the main field of Tertiary Challis Volcanics. The thrust system has exerted a major influence on the emplacement of granodiorite-quartz monzonite stocks and related mineral deposits in east-central Idaho. Recognition of the fault as a major influence in intrusive activity and deposition of metallic mineral deposits suggests new possibilities for mineral resource exploration in this region. And consideration of the stratigraphic, paleogeographic, and structural framework of sedimentary rocks beneath the thrust suggests the possibility of petroleum and natural gas resources in the region north of the Snake River Plain.

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“…Beaverhead sedimentation continued until the late Paleocene, when regional northwest trending thrust faults advanced from the west and the wouthwest (Ryder, 1968). been reported (cf., Klepper, 1950;Lowell and Klepper, 1953;Dorr and Wheeler, 1964) except for the one outcrop noted 3 miles south of the map area and it is near the northern margin of the proposed arch. Thus Scholten's (1967) (Fields and Petkewich, 1967 The range is flanked on all sides by intermontane basins containing Tertiary sedimentary rocks.…”

Section: Ryder 1 S Work Waspartially Published In 1967 Whereas Thatmentioning

confidence: 98%

Geology of the north end of the Ruby Range, southwestern Montana

Tysdal¹

1970

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This study consists of two parts: stratigraphy and sedimentation, and structure of rocks in the northern one-third of the Ruby Range of southwestern Montana. Detailed studies of Cambrian marine dolomite rocks in the Red Lion Formation and in the upper part of the Pilgrim Limestone resulted in their division into distinct rock units, termed lithofacies. These lithofacies contain features suggestive of subtidal, intertidal, and supratidal environments similar to those presently forming in the Persian Gulf. Stromatolitic structures occurring in the uppermost part of the Red Lion Formation are similar to those presently forming in Shark Bay, Australia.

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Beaverhead Formation, a Laramide Deposit in Beaverhead County, Montana

Cited by 13 publications

References 0 publications

Contraction and extension faults in the southern Beaverhead Mountains, Idaho and Montana

Contraction and extension faults in the southern Beaverhead Mountains, Idaho and Montana

Medicine Lodge thrust system, east-central Idaho and Southwest Montana

Geology of the north end of the Ruby Range, southwestern Montana

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