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Transcontinental Arch
The Transcontinental Arch refers to the islands of North America which extended from New Mexico to Minnesota and the Great Lakes region. These islands were present during the Sauk sequence, the earliest cratonic sequence. As a result of the Sauk sequence, epeiric seas covered most of North America, leaving only the craton of the Canadian Shield and the Transcontinental Arch islands exposed. The Transcontinental Arch, as originally understood, was at its peak during the Pennsylvanian, around 323 to 299 million years ago. However, the arch may have been present as early as the late Proterozoic and experienced repeated rejuvenation throughout the Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ... (521 to 252 million years ago). References Cambrian United States {{ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Caribbean Sea, and to the south and west by the Pacific Ocean. The region includes Middle America (Americas), Middle America (comprising the Caribbean, Central America, and Mexico) and Northern America. North America covers an area of about , representing approximately 16.5% of Earth's land area and 4.8% of its total surface area. It is the third-largest continent by size after Asia and Africa, and the list of continents and continental subregions by population, fourth-largest continent by population after Asia, Africa, and Europe. , North America's population was estimated as over 592 million people in list of sovereign states and dependent territories in North America, 23 independent states, or about 7.5% of the world's popula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, Huron, Lake Erie, Erie, and Lake Ontario, Ontario (though hydrologically, Lake Michigan–Huron, Michigan and Huron are a single body of water, joined at the Straits of Mackinac). The Great Lakes Waterway enables modern travel and shipping by water among the lakes. The lakes connect to the Atlantic Ocean via the Saint Lawrence River, and to the Mississippi River basin through the Illinois Waterway. The Great Lakes are the largest group of freshwater lakes on Earth by total area and the second-largest by total volume. They contain 21% of the world's surface fresh water by volume. The total surface is , and the total volume (measured at the low water datum) is , slightly less than the volume of Lake Baikal (, 22–23% of the world's surface f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sauk Sequence
The Sauk sequence was the earliest of the six cratonic sequences that have occurred during the Phanerozoic in North America. It was followed by the Tippecanoe, Kaskaskia, Absaroka, Zuñi, and Tejas sequences. The sequence dates from the late Proterozoic through the early Ordovician periods, though the marine transgression did not begin in earnest until the middle Cambrian.Monroe, JS, and R Wicander (1997) ''The Changing Earth: Exploring Geology and Evolution,'' 2nd ed. Belmont: West Publishing Company, 1997. pp. 533–534 It is one of the most striking cratonic sequences in the geological record, spreading sheets of sandstone across basement rock deep into the interiors of many continents. The transgression took place rapidly, advancing over across the Grand Canyon region in less than five million years. At its peak, most of North America was covered by the shallow Sauk Sea, save for parts of the Canadian Shield and the islands of the Transcontinental Arch. The stratigra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cratonic Sequence
A cratonic sequence (also known as megasequence, Sloss sequence or supersequence) in geology is a very large-scale lithostratigraphy, lithostratigraphic sequence in the rock record that represents a complete cycle of marine transgression and Marine regression, regression on a craton (block of continental crust) over geologic time. They are geologic evidence of relative sea level rising and then falling (transgressing and regressing), thereby depositing varying layers of sediment onto the craton, now expressed as sedimentary rock. Places such as the Grand Canyon are a good visual example of this process, demonstrating the changes between layers deposited over time as the ancient environment changed. Cratonic sequences were first proposed by Laurence L. Sloss in 1963. Each one represents a time when Inland sea (geology), inland seas deposited sediments across the craton. The top and bottom edges of a sequence are each bounded by craton-wide unconformity, unconformities (time gaps in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epeiric Seas
An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large in area and is either completely surrounded by dry land (landlocked), or connected to an ocean by a river, strait or " arm of the sea". An inland sea will generally be brackish, with higher salinity than a freshwater lake but usually lower salinity than seawater. As with other seas, inland seas experience tides governed by the orbits of the Moon and Sun. Definition What constitutes an "inland sea" is complex and somewhat necessarily vague. The United States Hydrographic Office defined it as "a body of water nearly or completely surrounded by land, especially if very large or composed of salt water". Geologic engineers Heinrich Ries and Thomas L. Watson say an inland sea is merely a very large lake. Rydén, Migula, and Andersson and Deborah Sandler of the Environmental Law Institute add that an inland sea is "more or less" cut off from the ocean. It may be semi-e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Craton
A craton ( , , or ; from "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates; the exceptions occur where geologically recent rifting events have separated cratons and created passive margins along their edges. Cratons are characteristically composed of ancient crystalline basement rock, which may be covered by younger sedimentary rock. They have a thick crust and deep lithospheric roots extending several hundred kilometres into Earth's mantle. Terminology The term ''craton'' is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons are composed of two layers: a continental '' shield'', in which the basement rock crops out at the surface, and a '' platform'' which o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canadian Shield
The Canadian Shield ( ), also called the Laurentian Shield or the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the ancient geologic core of the North American continent. Glaciation has left the area with only a thin layer of soil, through which exposures of igneous bedrock resulting from its long volcanic history are frequently visible. As a deep, common, joined bedrock region in eastern and central Canada, the shield stretches north from the Great Lakes to the Arctic Ocean, covering over half of Canada and most of Greenland; it also extends south into the northern reaches of the continental United States. Geographical extent The Canadian Shield is a physiographic division comprising four smaller physiographic provinces: the Laurentian Upland, Kazan Region, Davis and James. The shield extends into the United States as the Adirondack Mountains ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pennsylvanian (geology)
The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, on the International Commission on Stratigraphy, ICS geologic timescale, the younger of two period (geology), subperiods of the Carboniferous Period (or the upper of two system (stratigraphy), subsystems of the Carboniferous System). It lasted from roughly . As with most other geochronology, geochronologic units, the stratum, rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal Bed (geology), beds of this age are widespread. The division between Pennsylvanian and Mississippian (geology), Mississippian comes from North American stratigraphy. In North America, where the early Carboniferous beds are primarily marine limestones, the Pennsylvanian was in the past treated as a full-fledged geologic period between the Mississippian ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Late Proterozoic
The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era and succeeded by the Paleozoic era of the Phanerozoic eon, and is further subdivided into three periods, the Tonian, Cryogenian and Ediacaran. One of the most severe glaciation events known in the geologic record occurred during the Cryogenian period of the Neoproterozoic, when global ice sheets may have reached the equator and created a "Snowball Earth" lasting about 100 million years. The earliest fossils of complex life are found in the Tonian period in the form of ''Otavia'', a primitive sponge, and the earliest fossil evidence of metazoan radiation are found in the Ediacaran period, which included the namesaked Ediacaran biota as well as the oldest definitive cnidarians and bilaterians in the fossil record. According to Rino and co-workers, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleozoic
The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six period (geology), geologic periods (from oldest to youngest), Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. Some geological timescales divide the Paleozoic informally into early and late sub-eras: the Early Paleozoic consisting of the Cambrian, Ordovician and Silurian; the Late Paleozoic consisting of the Devonian, Carboniferous and Permian. The name ''Paleozoic'' was first used by Adam Sedgwick (1785–1873) in 1838 to describe the Cambrian and Ordovician periods. It was redefined by John Phillips (geologist), John Phillips (1800–1874) in 1840 to cover the Cambrian to Permian periods. It is derived from the Ancient Greek, Greek ''palaiós'' (π� ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
