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The geology of Wisconsin includes Precambrian crystalline basement rock over three billion years old. A widespread marine environment during the Paleozoic flooded the region, depositing sedimentary rocks which cover most of the center and south of the state. [1]
The oldest Precambrian rocks in Wisconsin are late Archean quartzofeldspathic gneiss, migmatite and amphibolite up to three billion years old and igneous rock such as the granite of the Puritan Quartz Monzonite. Mafic and intermediate metavolcanic rocks together with metasedimentary rocks are found in the Ramsey Formation in Iron County and iron formations in Jackson County. The metasediments and metavolcanics formed first, followed by granites more than 2.7 billion years ago.
The rock record contains an uncertain age gap with younger 1.8 billion years old Proterozoic quartzofeldspathic and migmatite gneiss, with amphibolite and biotite schist. Around 1.9 billion years ago, mafic, intermediate and felsic rocks, in some cases with subordinate metasedimentary rocks, began to form and metamorphosed, reaching greenschist and amphibolite grade on the sequence of metamorphic facies. The Ironwood and Riverton Iron formations are recognized from aerial magnetic surveys. Metamorphosed argillite, quartzite, greywacke conglomerate and marble with small areas of interbedded metavolcaic rocks make up the Tyler Formation, Palms Quartzite and Bad River Dolomite. Taken together, these early Proterozoic rocks correlate with the Marquette Range Supergroup and are intruded by banded and layered migmatite gneiss, intermediate and granite intrusive rocks, as well as massive or foliated tonalite and granodiorite (which is itself intruded by aplite and pegmatite. Near Merrill are metamorphosed ultramafic and mafic intrusive rocks with a distinctive magnetic signature.
From 1.7 to 1.6 billion years ago granite and rhyolite emplaced in south-central Wisconsin. The Baraboo and Waterloo Quartzite in the south and the Barron Quartzite in the northwest are slightly younger, along with the slate, dolomite, conglomerate and chert included in Wolf River rocks at Rib Mountain, Mosinee Hill and the McCaslin Quartzites.
The Wolf River Batholith spans from Langlade County in the north to the northern part of Portage County in the south. Anorthosite and gabbro inclusions are located near Tigerton and Rapakivi-type quartz monzonite occurs near Waupaca. Syenite and the Ninemile Swamp granite occur near Wausau.
Between 1.1 and one billion years ago, the Keweenawan Supergroup formed, which now underlies northern Wisconsin, inland and south from the shore of Lake Superior beneath Douglas County, Bayfield County and parts of Burnette and Washburn counties. Gabrro, troctolite, granophyre, anorthosite and ferrogranodiorite comprises the Mellen Intrusive Complex and similar intrusive complexes at Mineral Lake, Round Lake and Clam Lake in a line running southwest from the Montreal River. Mafic volcanic rocks overlie quartzite in the Powder Mill Group and Bessemer, which begin northeast of Hayward, Wisconsin and extend northeast, meeting the string of intrusive complexes. From as far south as Polk County northeast through Burnette, Washburn, Bayfield and much of Douglas counties are the widespread basalt flows of the Chengwatana Volcanic Group in the west and the Portage Lake Volcanics in the east.
Unmetamorphosed sedimentary rocks are found in the rock record from the Cambrian, in the early Paleozoic. The feldspathic quartz sandstone and orthoquartz sandstone of Chequamegon, Devils Island and Orienta formations make up the Bayfield Group which underlies the entire Lake Superior shoreline of the state from Chequamecon Bay to the St. Louis River in the west. Most of the state, in a loop from Waupaca County in the east, south in a narrow belt to the Iowa line and west to Eau Claire, Dunn, Barron and parts of Polk and Burnett counties, the underlying rocks are sandstone with dolomite and shale belonging to the Trempeauleau, Elk Mound and Tunnel City groups. Ordovician are particularly widespread in southern and eastern Wisconsin, from the Mississippi River in the west to Kenosha, Racine and Milwaukee in the east. Along the shore, they reach Marquette and underlie the Door Peninsula. These rocks include the dolomite, sandstone and shale of the Prairie du Chien Group, Ancell Group sandstone, limestone, conglomerate and shale, Sinnipee Group dolomite and limestone as well as the shale and dolomite of the Maquoketa Formation which is overlain by the Neda Formation oolite iron oxides. A narrow band along the Lake Michigan shore from Milwaukee to south of Sheboygan, including Port Washington displays Devonian shale and limestone.
Paleozoic rocks in eastern Wisconsin today make up the Niagara Escarpment, a shelf of rock extending from Door County to Horicon Marsh. The cliffs along the escarpment are primarily formed by the early Silurian Mayville Dolostone; the rocks that make up the escarpment were deposited within the Michigan Basin. Continued subsidence of this basin during deposition meant that many of the rock layers in eastern Wisconsin have been tilted towards the east. [2]
Very few rocks from the Mesozoic are preserved in Wisconsin, other than occasional areas of non-marine Cretaceous gravel and clay rich in iron. Select rocks in the Driftless Area have yielded ammonite fossils from the middle Turonian period, when Wisconsin was covered by the Western Interior Seaway. [3]
No rocks from the Paleogene or Neogene period are known from Wisconsin; however, abundant Quaternary deposits can be found as a result of the last Ice Age. The most recent glacial cycle, the Wisconsin Glaciation, began about 31,500 years ago and receded from the state by around 7,000 years ago. During this time the Lake Michigan Lobe and the Green Bay Lobe moved across the state; also present were the Chippewa, Superior, Wisconsin Valley, and Langlade lobes. These glacial lobes carved out deep valleys and deposited sediments up to 600 feet deep. [4] [5] Much of central and southwest Wisconsin were never glaciated, leaving the earlier river-generated topography intact; this area is known as the Driftless Area. [6]
The Llano Uplift is a geologically ancient, low geologic dome that is about 90 miles (140 km) in diameter and located mostly in Llano, Mason, San Saba, Gillespie, and Blanco counties, Texas. It consists of an island-like exposure of Precambrian igneous and metamorphic rocks surrounded by outcrops of Paleozoic and Cretaceous sedimentary strata. At their widest, the exposed Precambrian rocks extend about 65 miles (105 km) westward from the valley of the Colorado River and beneath a broad, gentle topographic basin drained by the Llano River. The subdued topographic basin is underlain by Precambrian rocks and bordered by a discontinuous rim of flat-topped hills. These hills are the dissected edge of the Edwards Plateau, which consist of overlying Cretaceous sedimentary strata. Within this basin and along its margin are down-faulted blocks and erosional remnants of Paleozoic strata which form prominent hills.
The geology of Massachusetts includes numerous units of volcanic, intrusive igneous, metamorphic and sedimentary rocks formed within the last 1.2 billion years. The oldest formations are gneiss rocks in the Berkshires, which were metamorphosed from older rocks during the Proterozoic Grenville orogeny as the proto-North American continent Laurentia collided against proto-South America. Throughout the Paleozoic, overlapping the rapid diversification of multi-cellular life, a series of six island arcs collided with the Laurentian continental margin. Also termed continental terranes, these sections of continental rock typically formed offshore or onshore of the proto-African continent Gondwana and in many cases had experienced volcanic events and faulting before joining the Laurentian continent. These sequential collisions metamorphosed new rocks from sediments, created uplands and faults and resulted in widespread volcanic activity. Simultaneously, the collisions raised the Appalachian Mountains to the height of the current day Himalayas.
The geology of Somalia is built on more than 700 million year old igneous and metamorphic crystalline basement rock, which outcrops at some places in northern Somalia. These ancient units are covered in thick layers of sedimentary rock formed in the last 200 million years and influenced by the rifting apart of the Somali Plate and the Arabian Plate. The geology of Somaliland, the de facto independent country recognized as part of Somalia, is to some degree better studied than that of Somalia as a whole. Instability related to the Somali Civil War and previous political upheaval has limited geologic research in places while heightening the importance of groundwater resources for vulnerable populations.
The geology of the Democratic Republic of the Congo is extremely old, on the order of several billion years for many rocks. The country spans the Congo Craton: a stable section of ancient continental crust, deformed and influenced by several different mountain building orogeny events, sedimentation, volcanism and the geologically recent effects of the East Africa Rift System in the east. The country's complicated tectonic past have yielded large deposits of gold, diamonds, coltan and other valuable minerals.
The geology of Niger comprises very ancient igneous and metamorphic crystalline basement rocks in the west, more than 2.2 billion years old formed in the late Archean and Proterozoic eons of the Precambrian. The Volta Basin, Air Massif and the Iullemeden Basin began to form in the Neoproterozoic and Paleozoic, along with numerous ring complexes, as the region experienced events such as glaciation and the Pan-African orogeny. Today, Niger has extensive mineral resources due to complex mineralization and laterite weathering including uranium, molybdenum, iron, coal, silver, nickel, cobalt and other resources.
The geology of Tanzania began to form in the Precambrian, in the Archean and Proterozoic eons, in some cases more than 2.5 billion years ago. Igneous and metamorphic crystalline basement rock forms the Archean Tanzania Craton, which is surrounded by the Proterozoic Ubendian belt, Mozambique Belt and Karagwe-Ankole Belt. The region experienced downwarping of the crust during the Paleozoic and Mesozoic, as the massive Karoo Supergroup deposited. Within the past 100 million years, Tanzania has experienced marine sedimentary rock deposition along the coast and rift formation inland, which has produced large rift lakes. Tanzania has extensive, but poorly explored and exploited natural resources, including coal, gold, diamonds, graphite and clays.
The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old. Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events. Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation. The East Africa Rift gives rise to thick, more geologically recent sediment sequences and the country's numerous lakes. Uganda has extensive natural resources, particularly gold.
The geological history of Zambia begins in the Proterozoic eon of the Precambrian. The igneous and metamorphic basement rocks tend to be highly metamorphosed and may have formed earlier in the Archean, but heat and pressure has destroyed evidence of earlier conditions. Major sedimentary and metamorphic groups formed in the mid-Proterozoic, followed by a series of glaciations in the Neoproterozoic and much of the Paleozoic which deposited glacial conglomerate as well as other sediments to form the Katanga Supergroup and rift-related Karoo Supergroup. Basalt eruptions blanketed the Karoo Supergroup in the Mesozoic and Zambia shifted to coal and sandstone formation. Geologically recent windblown sands from the Kalahari Desert and alluvial deposits near rivers play an important role in the modern surficial geology of Zambia. The country has extensive natural resources, particularly copper, but also cobalt, emeralds, other gemstones, uranium and coal.
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 Kentucky formed beginning more than one billion years ago, in the Proterozoic eon of the Precambrian. The oldest igneous and metamorphic crystalline basement rock is part of the Grenville Province, a small continent that collided with the early North American continent. The beginning of the Paleozoic is poorly attested and the oldest rocks in Kentucky, outcropping at the surface, are from the Ordovician. Throughout the Paleozoic, shallow seas covered the area, depositing marine sedimentary rocks such as limestone, dolomite and shale, as well as large numbers of fossils. By the Mississippian and the Pennsylvanian, massive coal swamps formed and generated the two large coal fields and the oil and gas which have played an important role in the state's economy. With interludes of terrestrial conditions, shallow marine conditions persisted throughout the Mesozoic and well into the Cenozoic. Unlike neighboring states, Kentucky was not significantly impacted by the Pleistocene glaciations. The state has extensive natural resources, including coal, oil and gas, sand, clay, fluorspar, limestone, dolomite and gravel. Kentucky is unique as the first state to be fully geologically mapped.
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 North Macedonia includes the study of rocks dating to the Precambrian and a wide array of volcanic, sedimentary and metamorphic rocks formed in the last 539 million years.
The geology of Nunavut began to form nearly three billion years ago in the Archean and the territory preserves some of the world's oldest rock units.
The geology of Missouri includes deep Precambrian basement rocks formed within the last two billion years and overlain by thick sequences of marine sedimentary rocks, interspersed with igneous rocks by periods of volcanic activity. Missouri is a leading producer of lead from minerals formed in Paleozoic dolomite.
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 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.
The geology of Kazakhstan includes extensive basement rocks from the Precambrian and widespread Paleozoic rocks, as well as sediments formed in rift basins during the Mesozoic.
The geology of North Korea has been studied by the Central Geological Survey of Mineral Resources, rare international research and by inference from South Korea's geology.
Geology of Latvia includes an ancient Archean and Proterozoic crystalline basement overlain with Neoproterozoic volcanic rocks and numerous sedimentary rock sequences from the Paleozoic, some from the Mesozoic and many from the recent Quaternary past. Latvia is a country in the Baltic region of Northern Europe.
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.
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