Belt Supergroup

The Belt Supergroup is an assemblage of primarily fine-grained sedimentary rocks and mafic intrusive rocks of late Precambrian (Mesoproterozoic) age. It is more than 15 kilometres (10 mi) thick, covers an area of some 200,000 km2 (77,220 sq. mi), and is considered to be one of the world's best-exposed and most accessible sequences of Mesoproterozoic rocks.[1] It was named after the Big Belt Mountains in west-central Montana. It is present in western Montana and northern Idaho, with minor occurrences in northwestern Washington and western Wyoming.[2] It extends into Canada where the equivalent rocks, which are called the Purcell Supergroup, are exposed in southeastern British Columbia and southwestern Alberta.[3] The rocks of the Belt Supergroup contain economically significant deposits of lead, zinc, silver, copper, gold, and other metals in a number of areas,[4] and some of the Belt rocks contain fossil stromatolites.[5]

Spectacular outcrops of Belt rocks can be seen in Glacier National Park in northwestern Montana[6] and in Waterton Lakes National Park in southwestern Alberta.[7]

Belt Supergroup
Stratigraphic range: Mesoproterozoic
Kintla Peak
Belt Supergroup strata exposed on Kintla Peak in Glacier National Park.
TypeGeological supergroup
Sub-unitsMany
UnderliesFlathead Formation
OverliesArchean and Paleoproterozoic rocks
Thicknessmore than 15 kilometres (10 mi)
Lithology
PrimaryMudstone, argillite
OtherSandstone, quartzite, conglomerate, intrusive rocks
Location
RegionMontana, Idaho, Washington, Wyoming
CountryUnited States
Type section
Named forBig Belt Mountains, Montana
Idaho Batholith
Geologic map of the Belt Supergroup in Idaho

Lithology and sedimentology

The Belt Supergroup is dominated by fine-grained sedimentary rocks, primarily mudstones, siltstones, fine-grained quartzose sandstones and limestones. Most have undergone weak metamorphism to greenschist facies, and as a result the mudrocks are commonly classified as argillites and the sandstones as quartzites.[8] The Belt Supergroup also includes lesser amounts of coarser grained sandstones[9] and conglomerates.[10] Mafic intrusive rocks are present locally in the lower portion.[11]

Much of the sedimentation probably occurred between about 1450 and 1400 Ma (million years) ago.[11] Sedimentary structures are well preserved in most of the Belt rocks despite their great age. The sedimentation is unusual in that 1) there is an abundance of fine-grained sediment and very little coarser sediment, 2) there is a lack of sequence boundaries that are common in Phanerozoic sediments, and 3) cyclic and rhythmic deposition occurred over long periods of time.[2][8] The Belt Supergroup is also noted for "Molar Tooth" structures in carbonates (a bacterial degassing structure) and various types of stromatolites.[5]

Paleogeography and environment of deposition

Paleogeographic reconstructions indicate that the Belt Supergroup accumulated in a fault-bounded rift basin that existed where the North American craton and another landmass were joined in a supercontinent called Columbia/Nuna.[9] The basin appears to have been a closed "lacustrine" environment, or at least not completely open marine.[2][8] Depositional environments are thought to have ranged from ancient floodplains and exposed mudflats to deep water.[8]

Evidence of the basin-bounding faults exists on all sides of the Belt basin except the west, which rifted away during subsequent continemtal breakup. The identity of the joined landmass remains controversial. The Siberian craton, Australia and eastern Antarctica have all been suggested based rock ages and paleomagnetic information.[11][12]

Stratigraphy and distribution

The Belt Supergroup was deposited unconformably on Archean and Paleoproterozoic rocks. It reaches thicknesses of more than 15 kilometres (10 mi) and is present in western Montana and northern Idaho, with minor occurrences in northwestern Washington and western Wyoming. Because of this widespread extent, the rock types and formation names of the Belt Supergroup vary depending upon location. In western Montana and northern Idaho the Belt is divided into the following four groups[2] (youngest to oldest):

  • Missoula Group - Fluvial sands and muds derived from the south.
  • Piegan Group (Middle Belt Carbonate) - Carbonate muds alternating with laminae of clastic muds.
  • Ravalli Group - Subaerially deposited sands and muds, mostly fluvial, derived from the southwest.
  • Lower Belt - Heterogeneous coarse- to fine-grained clastic and carbonate rocks, mostly deep-water deposition with sediments derived from the southwest, and mafic sills.

The Belt Supergroup extends into Canada where the equivalent rocks are called the Purcell Supergroup, and are exposed in southeastern British Columbia and southwestern Alberta.[2][3]

Economic resources

The Belt Supergroup rocks host a variety of economically significant deposits of lead, zinc, silver, copper, gold, and other metals. These include the Coeur d'Alene lead-zinc-silver mining district in Idaho, which has produced about 7,400,000 tonnes of lead, 2,900,000 tonnes of zinc, and 35,600 tonnes of silver. The equivalent rocks of the Purcell Supergroup in British Columbia include the Sullivan ore body, which has also been a major producer of lead, zinc, and silver.[4]

References

  1. ^ MacLean, J.S.; Sears, J.W., eds. (2016). Belt Basin: Window to Mesoproterozoic Earth. Geological Society of America, Special Publication 522. pp. 1–384.
  2. ^ a b c d e Lori Tapanila and Paul Link. "Mesoproterozoic Belt Supergroup". Digital Geology of Idaho. Idaho State University, Department of Geosciences. Retrieved 16 September 2016.
  3. ^ a b Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. ISBN 0-920230-23-7.
  4. ^ a b Lydon, John W. "Geology and metallogeny of the Belt-Purcell Basin. In: Goodfellow, W.D. (ed.), Mineral deposits of Canada: a synthesis of major deposit types, district metallogeny, the evolution of geological provinces, and exploration methods. Geological Association of Canada, Mineral Deposits Division, Special Publication no. 5, p. 581-607" (PDF). Retrieved 29 April 2018.
  5. ^ a b O'Connor, M.P. 1972. Classification and environmental interpretation of the cryptalgal organosedimentary "Molar-Tooth" structure from the Late Precambrian Belt-Purcell Supergroup. Journal of Geology, vol. 80, no. 5, p. 592-610.
  6. ^ Alt, D.D. and Hyndman, D.W. 1986. Roadside geology of Montana. Mountain Press Publishing Co., Missoula, Montana, 427 p. ISBN 0-87842-202-1.
  7. ^ Gordy, P.L., Frey, F.R. and Norris, D.K. 1977. Geological guide for the CSPG 1977 Waterton-Glacier Park Field Conference. Canadian Society of Petroleum Geologists, Calgary, Alberta, 93 p.
  8. ^ a b c d Schieber, J. 1990. Significance of styles of epicontinental shale sedimentation in the Belt basin, Mid-Proterozoic of Montana, U.S.A. Sedimentary Geology, v. 69, p. 297-312.
  9. ^ a b Schieber, J., 1989. The origin of the Neihart Quartzite, a basal deposit of the mid-Proterozoic Belt Supergroup, Montana, USA. Geological Magazine, v. 126, p. 271-281.
  10. ^ McMannis, W.J., 1963. LaHood Formation—a coarse facies of the Belt Series in southwestern Montana. Geological Society of America Bulletin, v. 74, p.407-436.
  11. ^ a b c Evans, K.V., Aleinikoff, J.N., Obradovich, J.D. and Fanning, C.M. 2000. SHRIMP U-Pb geochronology of volcanic rocks, Belt Supergroup, western Montana: evidence for rapid deposition of sedimentary strata. Canadian Journal of Earth Sciences, v. 37, p.1287-1300.
  12. ^ "Authigenic monazite and detrital zircon dating from the Proterozoic Rocky Cape Group, Tasmania: Links to the Belt-Purcell Supergroup, North America". Precambrian Research. 250: 50–67. 2014. doi:10.1016/j.precamres.2014.05.025.
  • Winston, Don and Link, Paul K., 1993, Middle Proterozoic rocks of Montana, Idaho, and Washington: The Belt Supergroup: in Reed., J., Simms, P., Houston, R., Rankin, D., Link, P., Van Schmus, R., and Bickford, P., eds., Precambrian of the conterminous United States: Boulder, Colorado, Geological Society of America, The Geology of North America, v. C-3, p. 487–521.
  • "Digital Geology of Idaho - Mesoproterozoic Belt Supergroup"
Argillite

"Argillite" may also refer to Argillite, Kentucky.

Argillite ( ) is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts of silt-sized particles. The argillites grade into shale when the fissile layering typical of shale is developed. Another name for poorly lithified argillites is mudstone. These rocks, although variable in composition, are typically high in aluminium and silica with variable alkali and alkaline earth cations. The term pelitic or pelite is often applied to these sediments and rocks. Metamorphism of argillites produces slate, phyllite, and pelitic schist.

Big Belt Mountains

The Big Belt Mountains are a section of the Rocky Mountains in the U.S. state of Montana. Situated mainly in the Helena National Forest, the mountains are used for logging and recreation for the surrounding residents. Nearby is Helena, Montana, Canyon Ferry Lake, the Missouri River, Townsend, Montana, and White Sulphur Springs, Montana. The highest point in the Big Belt Range is Mount Edith at 9,504 feet (2,897 m) while the center of the range is 7,385 feet (2,251 m)The Big Belts lie primarily between the Missouri River drainage to the west and the Smith River drainage to the east. Today, they are traversed by U.S. Highway 12 between Townsend, Montana in the Missouri drainage, and White Sulphur Springs, Montana in the upper Smith River drainage.The gulches on the western slopes of the Big Belts were noted historically for rich gold placer strikes. The richest was the 1864 and 1865 placer gold strikes in Confederate Gulch, including Montana Bar, which was one of the most concentrated gold placer strikes ever made.The range takes its name from the fact it is situated in a long belt-like arc. It stretches 75 miles, making it a mid-length subrange of the Rocky Mountains. To the east are the Little Belts and to the south, somewhat continuing this arc, are the Bridger Mountains.

The Belt Supergroup series of rocks, which are primarily Precambrian mudstones, were named after this mountain range and the adjacent Little Belt Mountains. A particularly well-known example of exposed Belt Group mudstones in alternating purplish-red or pale bluish-green layers in the Big Belt Mountains is in Wolf Creek Canyon along Interstate 15 between Helena and Great Falls. While these rocks were named after these ranges of western-central Montana, and are found in them, they are more exposed and better known in northwestern Montana, northern Idaho, and southeastern British Columbia, namely around Flathead Lake, Glacier National Park.

Gates of the Mountains Wilderness

The Gates of the Mountains Wilderness is located in the U.S. state of Montana. Created by an act of Congress in 1964, the wilderness is managed by Helena National Forest. A day use campground near the Gates of the Mountains, Meriwether Picnic site, is named in honor of Meriwether Lewis.

Gates of the Mountains Wilderness (then known as the Gates of the Mountains Wild Area) was the site of the 1949 Mann Gulch fire, which claimed the lives of 13 firefighters and which was the subject of Norman Maclean's book Young Men and Fire.

U.S. Wilderness Areas do not allow motorized or mechanized vehicles, including bicycles. Although camping and fishing are allowed with proper permit, no roads or buildings are constructed and there is also no logging or mining, in compliance with the 1964 Wilderness Act. Wilderness areas within National Forests and Bureau of Land Management areas also allow hunting in season.

Grypania

Grypania is an early, tube-shaped fossil from the Proterozoic eon. The organism, with a size over one centimeter and consistent form, could have been a giant bacterium, a bacterial colony, or a eukaryotic alga. The oldest probable Grypania fossils date to about 2300 million years ago (redated from the previous 1870 million) and the youngest extended into the Ediacaran period. This implies that the time range of this taxon extended for 1200 million years.

Idaho Batholith

The Idaho Batholith is a granitic and granodioritic batholith of Cretaceous-Paleogene age that covers approximately 25,000 square kilometres (9,700 sq mi) of central Idaho and adjacent Montana. The batholith has two lobes that are separated from each other geographically and geologically. The smaller Bitterroot lobe in the north is separated from the larger Atlanta lobe in the south by the Belt Supergroup metamorphic rocks that compose the Salmon River Arch. The Bitterroot lobe is 75 to 53 million years old, and the Atlanta lobe is 98 to 68 million years old. A separate and unrelated igneous center, the Kaniksu batholith, is present in the Idaho Panhandle but is generally older (~primarily 120 to 100 million years old with a limited number of younger Cretaceous components). Much of the Atlanta and Bitterroot lobes are in the Idaho Batholith ecoregion while the Kaniksu batholith is in the Northern Rockies ecoregion.

Independence mine

The Independence Mine was a larger producing mine in the Pine Creek region of the Coeur d'Alene mining district in Idaho. It produced lead, silver, and copper. The mine claim borders the Bunker Hill Sullivan mine claim, and work in on the mine was stopped in the 1940s. It was a major producer during both world wars. It also had a large hand in the development of Pinehurst, Idaho.

Its ore body was unique, and leads to question about the formation of silver valley and belt supergroup of which it was an ore body in the pritcherd formation.

Kintla Peak

Kintla Peak (10,106 ft (3,080 m)) is part of the Livingston Range in Glacier National Park in the U.S. state of Montana. It is the tallest mountain in the Livingston Range and the third tallest in Glacier National Park. It is also the most northerly peak and land area in the contiguous United States above 10,000 ft (3,000 m). The Agassiz Glacier lies below it to the southeast.Kintla Peak consists of ancient Precambrian (Mesoproterozoic) rock strata that are part of the Belt Supergroup. It is named after the Kintla Lakes, and the word "Kintla" originates from the Kootenai word for "sack". Kootenai legend states that a man had apparently drowned in one of the lakes and likened the lake to a sack where "once you got in, you couldn't get out".Kintla Peak lies the remote northwest corner of the park and a hike of almost 15 miles (24 km) from the nearest road is required just to reach the base of the mountain. The peak is notable for its large rise above local terrain; the elevation of nearby Upper Kintla Lake is only 4,370 feet (1,330 m). (Kintla Peak's northern neighbor Kinnerly Peak has an even more dramatic drop to Upper Kintla Lake.) This helps make Kintla "the most arduous climb in the northwest section of the park". The standard route is the Southeast Ridge Route, from the Agassiz Glacier basin. This route has a long approach and a large total vertical gain, and involves rock scrambling up to Class 4, in addition to some climbing on snow, depending on the season. Other routes include the East Ridge, West Face, and Upper North Face routes.

Miogeocline

A miogeocline is an area of sedimentation which occurs along the passive margin of a continent. The deposits occur as typically shallow water clastic sediments which thicken seaward to form a clastic wedge parallel to a tectonically quiescent coast. Modern examples include the continental shelf of the northern Gulf of Mexico and the Atlantic coast of North and South America.

The term was coined in 1966 by Dietz and Holden from the miogeosyncline concept of the outdated geosynclinal theory. Dietz and Holden modified the term to miogeocline as the sedimentary deposits described were not synclinal in form.Ancient miogeoclines such as the Neoproterozoic to Cambrian Cordilleran miogeocline of the southwestern U. S., the Paleozoic Appalachian miogeocline, the Precambrian Belt Supergroup of Montana and Idaho and the Huronian sediments of Canada which were involved in the Grenville Orogeny. The Devonian to Mississippian northern Cordilleran miogeocline of northern Yukon and Northwest Territories of Canada represents an area of current research in Arctic geology. The ancient miogeoclinal sediments become attached to or accreted onto the adjacent continent following later continental collisions or orogenies. Thus the sediments of the Appalachian miogeocline became part of the Appalachian Mountains during the Appalachian orogeny.

Mission Mountains

This article is for the mountain range in Montana. For the small mountain range in British Columbia, Canada, also known as Mission Mountain, see Mission Ridge (British Columbia). For the summit in California see Mission Peak.

The Mission Mountains or Mission Range are a range of the Rocky Mountains located in northwestern Montana in the United States. They lie chiefly in Lake County and Missoula County and are south and east of Flathead Lake and west of the Swan Range. On the east side of the range is the Swan

River Valley and on the west side the Mission Valley.

The highest point in the Mission Mountains is McDonald Peak 9,820 feet (2,990 m). The range is named for its proximity to the Jesuit St. Ignatius Mission established in the mid-19th century in what is today St. Ignatius, Montana.

Neihart, Montana

Neihart is a town in Cascade County, Montana, United States. It is located in the center of Little Belt Mountains. The population was 51 at the 2010 census. It is part of the Great Falls, Montana, Metropolitan Statistical Area. It is one of only three places in the world where Neihart quartzite—reddish, coarse-grained sandstone with interbedded dark-green sandstone and shale—may be found (the town gives the mineral its name).

Purcell Supergroup

The Purcell Supergroup is composed primarily of argillites, carbonate rocks, quartzites, and mafic igneous rocks of late Precambrian (Mesoproterozoic) age. It is present in an area of about 15,000 km2 (5,800 sq. mi.) in southwestern Alberta and southeastern British Columbia, Canada, and it extends into the northwestern United States where it is called the Belt Supergroup. It was named for the Purcell Mountains of British Columbia by R.A. Daly in 1912. Fossil stromatolites and algal structures are common in some of the Purcell Supergroup rocks, and the Sullivan ore body at Kimberley, British Columbia, a world-class deposit of lead, zinc, and silver, lies within the Alderidge Formation in the lower part of the Purcell.Spectacular outcrops of Purcell and Belt Supergroup rocks can be seen in Glacier National Park in northwestern Montana and Waterton Lakes National Park in southwestern Alberta.

Quartzite

Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3). Other colors, such as yellow, green, blue and orange, are due to other minerals.

When sandstone is cemented to quartzite, the individual quartz grains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals. Most or all of the original texture and sedimentary structures of the sandstone are erased by the metamorphism. The grainy, sandpaper-like surface becomes glassy in appearance. Minor amounts of former cementing materials, iron oxide, silica, carbonate and clay, often migrate during recrystallization and metamorphosis. This causes streaks and lenses to form within the quartzite.

Orthoquartzite is a very pure quartz sandstone composed of usually well-rounded quartz grains cemented by silica. Orthoquartzite is often 99% SiO2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon, rutile and magnetite. Although few fossils are normally present, the original texture and sedimentary structures are preserved.

The term is also traditionally used for quartz-cemented quartz arenites, and both usages are found in the literature. The typical distinction between the two (since each is a gradation into the other) is a metamorphic quartzite is so highly cemented, diagenetically altered, and metamorphosized so that it will fracture and break across grain boundaries, not around them.

Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica content of the rock provides little material for soil; therefore, the quartzite ridges are often bare or covered only with a very thin layer of soil and little (if any) vegetation.

ReBecca Hunt-Foster

ReBecca Hunt-Foster is an American paleontologist. She has worked with dinosaur remains from the Late Jurassic to Late Cretaceous of the Colorado Plateau, Rocky Mountains, Southcentral, and the Southwestern United States of America. She described the dinosaur Arkansaurus fridayi and identified the first juvenile Torosaurus occurrences from Big Bend National Park in North America in 2008.

Reef

A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water.

Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.

Artificial reefs (e.g. shipwrecks) sometimes have a role in enhancing the physical complexity of featureless sand bottoms, in order to attract a diverse assemblage of organisms, especially algae and fish.

Earth's largest reef system is the Great Barrier Reef in Australia, at a length of over 2,300 kilometres (1,400 miles).

Rodinia

Rodinia (from the Russian родить, rodít, meaning "to beget, to give birth", or родина, ródina, meaning "motherland, birthplace") was a Neoproterozoic supercontinent that assembled 1.1–0.9 billion years ago and broke up 750–633 million years ago.Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named 'Pangaea I'. It was renamed 'Rodinia' by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.Rodinia formed at c. 1.23 Ga by accretion and collision of fragments produced by breakup of an older supercontinent, Columbia, assembled by global-scale 2.0–1.8 Ga collisional events.Rodinia broke up in the Neoproterozoic with its continental fragments reassembled to form Pannotia 633–573 million years ago. In contrast with Pannotia, little is known yet about the exact configuration and geodynamic history of Rodinia. Paleomagnetic evidence provides some clues to the paleolatitude of individual pieces of the Earth's crust, but not to their longitude, which geologists have pieced together by comparing similar geologic features, often now widely dispersed.

The extreme cooling of the global climate around 717–635 million years ago (the so-called Snowball Earth of the Cryogenian Period) and the rapid evolution of primitive life during the subsequent Ediacaran and Cambrian periods are thought to have been triggered by the breaking up of Rodinia or to a slowing down of tectonic processes.

Tappania

Tappania is a putative eukaryotic microfossil the type acritarch found in sediments up to 1,630 million years old. Its morphology suggests it is related to fungi. Two types have been identified to date:

Tappania plana appears in Paleoproterozoic formations of India (Deonar) and northern China (Baicaoping and Beidajian), both with an age of 1,630 mya. It is a roughly spherical acritarch, 30-60 μm in diameter, with one or two small necks. Small branched and / or partitioned tubes emerge from the central body.

Tappania sp. It appears in deposits of the Neoproterozoic in northern Australia, northwestern US and central Siberia, with an age of up to 850 mya and 200-300 mya stratigraphic presence. It is larger that Flat Tappania, up to 300 μm in length, with an elongated or lobed central body from where hyphae-like tubular extensions radiate. These hyphae form a three-dimensional network around the central body.

Tobacco Root Mountains

The Tobacco Root Mountains lie in the northern Rocky Mountains, between the Jefferson and Madison Rivers in southwest Montana. The highest peak is Hollowtop at 10,604 feet (3,232 m). The range contains 43 peaks rising to elevations greater than 10,000 feet (3048 m).

Much of the central part of the range is within the Beaverhead-Deerlodge National Forest, although many, mostly small patented mining claims exist within the forest boundary. The range saw significant gold mining, especially during the 1880s to 1930s.

The high peaks have been extensively glaciated, and most of the larger stream valleys held valley glaciers during the ice age.

Windermere group

Called the Windermere Group in the United States and the Windermere Supergroup, Windermere Series, and Windermere System in Canada, the Windermere sequence of North America is an extensive assemblage of sedimentary and volcanic rocks of latest Precambrian (Neoproterozoic) age. It is present in the northern part of the North American Cordillera, stretching from Montana, Idaho, and Washington in the northwestern United States, through Alberta, British Columbia, the Northwest Territories, and the Yukon in western Canada. It was named for the Windermere map-area in the East Kootenay region of southeastern British Columbia by J.F. Walker in 1926.The Windermere rocks include Ediacaran fossils and stromatolites, and host deposits of base and precious metals.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.