The geology of Montana includes thick sequences of Paleozoic, Mesozoic and Cenozoic sedimentary rocks overlying ancient Archean and Proterozoic crystalline basement rock. Eastern Montana has considerable oil and gas resources, while the uplifted Rocky Mountains in the west, which resulted from the Laramide orogeny and other tectonic events have locations with metal ore. [1]
The oldest rocks in Montana are part of the Archean Wyoming Craton in the center and east of the state, primarily between Livingston and Red Lodge as well as small areas in the Little Belt Mountains around Neihart and the core of the Little Rocky Mountains south of Harlem. Drill cores indicate that these rocks underlie much of the Great Plains.
The Pony Group, Cherry Creek Group and the Stillwater Complex are examples of Precambrian metamorphic rock units The first two groups are made up of folded and metamorphosed marine sedimentary rocks. They were subsequently intruded by gabbro, diabase and granite. The Stillwater Complex, by contrast, is made up of ultrabasic igneous rocks exposed at the surface in Park, Stillwater, and Sweet Grass Counties. Together, these three rock formations formed between 2.54 and 1.69 billion years ago.
The Pony Group and Cherry Creek Group are overlain by the Belt Series sedimentary rocks, which deposited after a period of erosion that left a large unconformity. These shallow water rocks from the Neoproterozoic range between 35,000 and 50,000 feet thick, overlain by additional Middle Cambrian sedimentary rocks.
Belt rocks make up the mountains around St. Mary Lake at Glacier National Park. Deposition took place in a broad trough extending southeast to the Big Snowy Mountains as well as to the southwest through Three Forks, Whitehall the Highland Mountains, and Armstead.
The Lewis Overthrust is a geologic thrust fault structure of the Rocky Mountains found within the Glacier National Park and the bordering Waterton Lakes National Park in Canada. The structure was created due to the collision of tectonic plates about 59-75 million years ago that drove a several mile thick wedge of Precambrian rock 50 mi (80 km) eastwards, causing it to overlie softer Cretaceous age rock that is 1300 to 1400 million years younger.
Regional low-grade metamorphism altered sandstone, carbonates and silty shale to quartzite, argillite and dolomite. Geologists divide the rocks into four units, from oldest to youngest the pre-Ravalli rocks, the Ravalli, the Piegan, and the Missoula groups. In some locations, late Precambrian sills, dikes and lava flows are found. The Sunshine Mine in the Coeur d'Alene district of Idaho, which is in correlates with the Ravalli Group. Uranium mineralized in the rock 1.19 million years ago, giving a young age for limit for the surrounding rocks.
Thick sequences of sedimentary rock deposited during the Paleozoic, reaching thicknesses of up to 10,000 feet. Sixteen miles west of Missoula and further west, all Paleozoic rocks have eroded away. To the east, Paleozoic rocks are exposed and upturned along the Rocky Mountains.
Most Paleozoic rocks originated in a marine environment, particularly dolomite and limestone together with shale, siltstone, sandstone, and evaporites such as gypsum, anhydrite and salt.
During the Mesozoic, one mile thick sedimentary rocks accumulated across 55 percent of the state. They are exposed at the surface due to the Black Hills uplift and the Cedar Creek Anticline. Marine rocks alternate with terrestrial sandstone, indicating a string of marine transgression and regression events. In the Cretaceous, the Laramide orogeny began to assemble the Rocky Mountains, intruding granite in Ravalli County as well as the Boulder Batholith and Tobacco Root Batholith. Tuff and andesite lava flows resulting from volcanic eruptions is found interbedded in sedimentary rocks.
Continued uplift due to the Laramide orogeny drove accelerated erosion in the Cenozoic. Eastern Montana lowlands were covered in up to 4000 feet of sediment. The Fort Union Formation in the east, made up of the Tongue River, Lebo and Tullock members is a remnant of Paleocene deposition. It is overlain by Wasatch Formation mudstone and stream conglomerate which has been significantly eroded. Intermontane valleys preserve thick sequences of Oligocene and Miocene rocks that are rare in other parts of the Eastern Plains. These sediments vary considerably, from claystone, mudstone and siltstone to bentonite, diatomaceous earth, coal and tuff. The Pliocene Flaxville Formation is the youngest rock unit in Montana.
Igneous intrusive rocks are associated with metals such as copper, gold, silver, lead, zinc and tungsten. In the Idaho Batholith, Boulder Batholith and Tobacco Root Batholith, intrusive granite bodies are particularly common and often contain metal ore. Precambrian rocks in the southwest contain corundum, talc, iron ore, graphite, sillimanite and kyanite in the Cherry Creek Group, while chromite is common in the Stillwater Complex that spans Stillwater and Sweet Grass counties. The western third of Montana has sedimentary rocks from the Paleozoic and Mesozoic which are potential sources of phosphate rock, limestone, silica, crushed stone and clay. In places bentonite has been mined from altered volcanic ash beds in Cenozoic intermontane sedimentary basins.
Central Montana has metal ore deposits that have been mined in the Little Rocky Mountains, the North Moccasin Mountains, the Judith Mountains and the Little Belt Mountains. The region also has significant production of oil and natural gas from the Cat Creek anticline, the Kevin-Sunburst dome and the Sweet Grass arch. Mesozoic sandstones are a primary reservoir rock. Some Cretaceous sandstone, for example The Third Cat Creek sandstone at the base of the Kootenai Formation, the Virgelle sandstone member of the Eagle Sandstone, and the Fox Hill Sandstone, are valuable ground water aquifers all dating to the Cretaceous. The Kootenai Formation also contains clay usable for brick and tile. Much of central Montana is underlain by Jurassic and Cretaceous coal beds.
Although there are no metal ore deposits in the eastern third of the state, the region holds more than 90 percent of Montana's coal reserves. The coal is part of the Paleocene Fort Union Formation, particularly the Tongue River Member. The eastern region produces petroleum, principally in the western Williston Basin and the Cedar Creek Anticline. Most hydrocarbons come from Paleozoic rocks, although some are sourced from Cretaceous rock. Bentonite is mined from Cretaceous beds in Carter County. [2]
The geology of the Grand Teton area consists of some of the oldest rocks and one of the youngest mountain ranges in North America. The Teton Range, partly located in Grand Teton National Park, started to grow some 9 million years ago. An older feature, Jackson Hole, is a basin that sits aside the range.
Texas contains a wide variety of geologic settings. The state's stratigraphy has been largely influenced by marine transgressive-regressive cycles during the Phanerozoic, with a lesser but still significant contribution from late Cenozoic tectonic activity, as well as the remnants of a Paleozoic mountain range.
The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through central New Mexico and which is part of the great mountain system known as the North American Cordillera.
The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North Dakota, South Dakota, southern Saskatchewan, and south-western Manitoba that is known for its rich deposits of petroleum and potash. The basin is a geologic structural basin but not a topographic depression; it is transected by the Missouri River. The oval-shaped depression extends approximately 475 miles (764 km) north-south and 300 miles (480 km) east-west.
The main points that are discussed in the geology of Iran include the study of the geological and structural units or zones; stratigraphy; magmatism and igneous rocks; ophiolite series and ultramafic rocks; and orogenic events in Iran.
The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.
The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.
The geology of South Dakota began to form more than 2.5 billion years ago in the Archean eon of the Precambrian. Igneous crystalline basement rock continued to emplace through the Proterozoic, interspersed with sediments and volcanic materials. Large limestone and shale deposits formed during the Paleozoic, during prevalent shallow marine conditions, followed by red beds during terrestrial conditions in the Triassic. The Western Interior Seaway flooded the region, creating vast shale, chalk and coal beds in the Cretaceous as the Laramide orogeny began to form the Rocky Mountains. The Black Hills were uplifted in the early Cenozoic, followed by long-running periods of erosion, sediment deposition and volcanic ash fall, forming the Badlands and storing marine and mammal fossils. Much of the state's landscape was reworked during several phases of glaciation in the Pleistocene. South Dakota has extensive mineral resources in the Black Hills and some oil and gas extraction in the Williston Basin. The Homestake Mine, active until 2002, was a major gold mine that reached up to 8000 feet underground and is now used for dark matter and neutrino research.
The geology of Arizona began to form in the Precambrian. Igneous and metamorphic crystalline basement rock may have been much older, but was overwritten during the Yavapai and Mazatzal orogenies in the Proterozoic. The Grenville orogeny to the east caused Arizona to fill with sediments, shedding into a shallow sea. Limestone formed in the sea was metamorphosed by mafic intrusions. The Great Unconformity is a famous gap in the stratigraphic record, as Arizona experienced 900 million years of terrestrial conditions, except in isolated basins. The region oscillated between terrestrial and shallow ocean conditions during the Paleozoic as multi-cellular life became common and three major orogenies to the east shed sediments before North America became part of the supercontinent Pangaea. The breakup of Pangaea was accompanied by the subduction of the Farallon Plate, which drove volcanism during the Nevadan orogeny and the Sevier orogeny in the Mesozoic, which covered much of Arizona in volcanic debris and sediments. The Mid-Tertiary ignimbrite flare-up created smaller mountain ranges with extensive ash and lava in the Cenozoic, followed by the sinking of the Farallon slab in the mantle throughout the past 14 million years, which has created the Basin and Range Province. Arizona has extensive mineralization in veins, due to hydrothermal fluids and is notable for copper-gold porphyry, lead, zinc, rare minerals formed from copper enrichment and evaporites among other resources.
The geology of Bosnia & Herzegovina is the study of rocks, minerals, water, landforms and geologic history in the country. The oldest rocks exposed at or near the surface date to the Paleozoic and the Precambrian geologic history of the region remains poorly understood. Complex assemblages of flysch, ophiolite, mélange and igneous plutons together with thick sedimentary units are a defining characteristic of the Dinaric Alps, also known as the Dinaride Mountains, which dominate much of the country's landscape.
The geology of Sweden is the regional study of rocks, minerals, tectonics, natural resources and groundwater in the country. The oldest rocks in Sweden date to more than 2.5 billion years ago in the Precambrian. Complex orogeny mountain building events and other tectonic occurrences built up extensive metamorphic crystalline basement rock that often contains valuable metal deposits throughout much of the country. Metamorphism continued into the Paleozoic after the Snowball Earth glaciation as the continent Baltica collided with an island arc and then the continent Laurentia. Sedimentary rocks are most common in southern Sweden with thick sequences from the last 250 million years underlying Malmö and older marine sedimentary rocks forming the surface of Gotland.
The geology of Alberta encompasses parts of the Canadian Rockies and thick sedimentary sequences, bearing coal, oil and natural gas, atop complex Precambrian crystalline basement rock.
The geology of Wyoming includes some of the oldest Archean rocks in North America, overlain by thick marine and terrestrial sediments formed during the Paleozoic, Mesozoic and Cenozoic, including oil, gas and coal deposits. Throughout its geologic history, Wyoming has been uplifted several times during the formation of the Rocky Mountains, which produced complicated faulting that traps hydrocarbons.
The geology of Utah, in the western United States, includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism, and the formation of the basin and range terrain in the Cenozoic.
The geology of Alaska includes Precambrian igneous and metamorphic rocks formed in offshore terranes and added to the western margin of North America from the Paleozoic through modern times. The region was submerged for much of the Paleozoic and Mesozoic and formed extensive oil and gas reserves due to tectonic activity in the Arctic Ocean. Alaska was largely ice free during the Pleistocene, allowing humans to migrate into the Americas.
The bedrock under the U.S. State of Colorado was assembled from island arcs accreted onto the edge of the ancient Wyoming Craton. The Sonoma orogeny uplifted the ancestral Rocky Mountains in parallel with the diversification of multicellular life. Shallow seas covered the regions, followed by the uplift current Rocky Mountains and intense volcanic activity. Colorado has thick sedimentary sequences with oil, gas and coal deposits, as well as base metals and other minerals.
The geology of North Dakota includes thick sequences oil and coal bearing sedimentary rocks formed in shallow seas in the Paleozoic and Mesozoic, as well as terrestrial deposits from the Cenozoic on top of ancient Precambrian crystalline basement rocks. The state has extensive oil and gas, sand and gravel, coal, groundwater and other natural resources.
The geology of Lithuania consists of ancient Proterozoic basement rock overlain by thick sequences of Paleozoic, Mesozoic and Cenozoic marine sedimentary rocks, with some oil reserves, abundant limestone, dolomite, phosphorite and glauconite. Lithuania is a country in the Baltic region of northern-eastern Europe.
The geology of Peru includes ancient Proterozoic rocks, Paleozoic and Mesozoic volcanic and sedimentary rocks, and numerous basins and the Andes Mountains formed in the Cenozoic.
The geology of Yukon includes sections of ancient Precambrian Proterozoic rock from the western edge of the proto-North American continent Laurentia, with several different island arc terranes added through the Paleozoic, Mesozoic and Cenozoic, driving volcanism, pluton formation and sedimentation.