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Laurentia or the North American Craton is a large continental
craton A craton (, , or ; from el, κράτος ''kratos'' "strength") is an old and stable part of the continental lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial p ...
that forms the Geology of North America, ancient geological core of North America. Many times in its past, Laurentia has been a separate
continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of th ...

continent
, as it is now in the form of North America, although originally it also included the cratonic areas of
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an autonomous territory An autonomous administrative division (also referred to as an autonomous area, entity, unit, region, subdivision, or territory) is a subnational administra ...

Greenland
and also the northwestern part of
Scotland Scotland ( sco, Scotland, gd, Alba Alba (Scottish Gaelic Scottish Gaelic ( gd, Gàidhlig or Scots Gaelic, sometimes referred to simply as Gaelic) is a Goidelic language (in the Celtic languages, Celtic branch of the Indo-European ...

Scotland
, known as the
Hebridean Terrane The Hebridean Terrane is one of the terranes that form part of the Caledonian orogeny, Caledonian orogenic belt in northwest Scotland. Its boundary with the neighbouring Northern Highland Terrane is formed by the Moine Thrust Belt. The basement is ...

Hebridean Terrane
. During other times in its past, Laurentia has been part of larger continents and
supercontinent In geology Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers sim ...
s and itself consists of many smaller
terrane In geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they change over time ...
s assembled on a network of Early
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 541million years ago. It is the most recent part of the Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest par ...
orogenic Orogeny is the primary mechanism by which mountains are formed on continents. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. This leads to both structural deformation Deformation ...
belts. Small
microcontinent Continental crustal fragments, partially synonymous A synonym is a word, morpheme A morpheme is the smallest meaningful lexical item in a language. A morpheme is not a word. The difference between a morpheme and a word is that a morpheme bou ...
s and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologi ...

Precambrian
craton seen today. The craton is named after the
Laurentian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a large area of exposed Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history ...
, through the
Laurentian Mountains The Laurentian Mountains (French: ''Laurentides'') are a mountain range A mountain range is a series of mountains ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity ...
, which received their name from the
Saint Lawrence River The St. Lawrence River is a large river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its c ...
, named after
Lawrence of Rome Saint Lawrence or Laurence ( la, Laurentius, lit. "laurelled"; 31 December AD 225 – 10 August 258) was one of the seven deacons of the city of Rome , established_title = Founded , established_date = 753 BC , founder ...
.


Interior platform

In eastern and central Canada, much of the stable craton is exposed at the surface as the
Canadian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a large area of exposed Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of History of the Ea ...

Canadian Shield
; when subsurface extensions are considered, the wider term
Laurentian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a large area of exposed Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history ...
is more common, not least because large parts of the structure extend outside Canada. In the United States, the craton bedrock is covered with sedimentary rocks on the broad interior platform in the
Midwest The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four Census Bureau Region, census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of ...
and
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland ''Flatland: A Romance of Many Dimensions'' is a satire, satirical novella by the English schoolmaster Edwin Abbott Abbott, first publi ...
regions and is exposed only in northern Minnesota, Wisconsin, the New York
Adirondacks The Adirondack Mountains () form a massif In geology, a massif ( or ) is a section of a planet's Crust (geology), crust that is demarcated by geologic fault, faults or Lithospheric flexure, flexures. In the Plate tectonics, movement of the c ...
, and the
Upper Peninsula of Michigan The Upper Peninsula of Michigan – also known as Upper Michigan or colloquially the U.P. – is the northern and more elevated of the Peninsulas of Michigan, two major landmasses that make up the U.S. state of Michigan; it is separated from t ...

Upper Peninsula of Michigan
. The sequence of rocks varies from about 1,000 m to in excess of 6,100 m (3,500–20,000 ft) in thickness. The cratonic rocks are
metamorphic Metamorphic rocks arise from the transformation of existing rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the mineral ...

metamorphic
or
igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock i ...
with the overlying
sedimentary layer Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sedimentary layer
s composed mostly of
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
s,
sandstone Sandstone is a clastic sedimentary rock of a clast (sand grain), derived from a basalt Basalt (, ) is a fine-grained extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ('' mafic ' ...

sandstone
s, and
shale Shale is a fine-grained, clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defi ...

shale
s. These sedimentary rocks were largely deposited from 650 to 290 million years ago. The oldest bedrock, the Archean provinces
Slave Slavery and enslavement are both the state and the condition of being a slave, who is someone forbidden to quit their service for an enslaver, and who is treated by the enslaver as their property Property is a system of rights that gives ...

Slave
, Rae, Hearne,
Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. The List of U.S. states and territories by area, 10th largest state by area, it is also the List of U.S. states and territories b ...
,
Superior Superior may refer to: *Superior (hierarchy) In a hierarchy A hierarchy (from the Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) in which the items are represented as being "ab ...
, and Nain, are located in the northern two thirds of Laurentia. During the Early Proterozoic they were reactivated and covered by sediments, most of which has now been eroded away.


Tectonic setting

The metamorphic and igneous rocks of the "
basement complex A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the boiler, water heating, water heate ...
" of Laurentia were formed 1.5 to 1.0 billion years ago in a tectonically active setting. The younger sedimentary rocks that were deposited on top of this basement complex were formed in a setting of quiet marine and river waters. During much of Mississippian time, the craton was the site of an extensive marine carbonate platform on which mainly limestones and some
dolomiteDolomite may refer to: *Dolomite (mineral) Dolomite () is an anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and ...
s and evaporites were deposited. This platform extended from either the present
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, are a system of mountains in eastern North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (nor ...

Appalachian Mountains
or
Mississippi Valley The Mississippi River is the second-longest river and chief river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes ...
to the present
Great Basin The Great Basin ( es, Gran Cuenca) is the largest area of contiguous endorheic watersheds – those with no outlets – in North America North America is a continent A continent is any of several large landmasses. Gene ...
. The craton was covered by shallow, warm, tropical epicontinental or epicratonic sea (meaning literally "on the craton") that had maximum depths of only about 60 m (200 ft) at the shelf edge. During
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
times, such a sea, the
Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea Inland may refer to: Places Sweden * Inland Fräkne Hundred, a hundred of Bohus ...
, ran from the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin 400px, Diagrammatic cross-section of an ocean basin, showing the various geographic features In hydrology Hydrology (from Greek: wikt:ὕδωρ, ὕδωρ, "hýdōr" meaning ...

Gulf of Mexico
to the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major s. It spans an area of approximately and is also known as the coldest of all the oceans. The (IHO) recognizes it as an ocean, although some call it the Arctic Medit ...

Arctic Ocean
, dividing North America into eastern and western land masses. Sometimes, land masses or
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at least ...

mountain
chains rose up on the distant edges of the craton and then eroded down, shedding their sand across the landscape.
Subduction Subduction is a geological process in which the oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. O ...

Subduction
of the continent towards the Northwest, that lasted approximately 1.4 to 1.2 billion years, likely caused enrichment of the
lithospheric A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
mantle beneath the orogenic belts of the
Grenville ProvinceThe Grenville Province is a tectonically complex region, in Eastern Canada, that contains many different aged accreted terranes from various origins. It exists southeast of the Grenville Front and extends from Labrador , nickname ...

Grenville Province
. This enrichment is thought to have contributed to the formation of the major supercontinent
Rodinia Rodinia (from the Russian Russian refers to anything related to Russia, including: *Russians (русские, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *Rossiyane (росси ...

Rodinia
.


Volcanism

The southwestern portion of Laurentia consists of Precambrian basement rocks deformed by continental collisions (violet area of the image above). This area has been subjected to considerable
rifting In geology Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they change over ...
as the
Basin and Range Province The Basin and Range Province is a vast physiographic region Physiographic regions of the world are a means of defining Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Eart ...
and has been stretched up to 100% of its original width. The area contains numerous large volcanic eruptions.


Equatorial location

The position of the equator during the
Late Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-E ...
( million years ago) on Laurentia has been determined via expansive shell bed records. Flooding of the continent that occurred during the Ordovician provided the shallow warm waters for the success of sea life and therefore a spike in the carbonate shells of shellfish. Today the beds are composed of fossilized shells or massive-bedded ''Thalassinoides'' facies (MBTF) and loose shells or nonamalgamated
brachiopod Brachiopods (), phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a ...
shell beds (NABS). These beds imply the presence of an equatorial climate belt that was hurricane free which lay inside 10° of the equator at 22.1°S ± 13.5°. This ecological conclusion matches the previous paleomagnetic findings which confirms this equatorial location.


Paleoenvironmental change

Several climate events occurred in Laurentia during the
Phanerozoic The Phanerozoic Eon is the current in the , and the one during which abundant and has existed. It covers million years to the present, and it began with the Period when animals first developed hard shells preserved in the fossil record. The ...
eon. During the late
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
through the
Ordovician The Ordovician ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other eart ...

Ordovician
, sea level fluctuated with ice cap melt. Nine macro scale fluctuations of "Global hyper warming", or high intensity greenhouse gas conditions, occurred. Due to sea level fluctuation, these intervals led to mudstone deposits on Laurentia that act as a record of events. The late
Ordovician The Ordovician ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other eart ...

Ordovician
brought a cooling period, although the extent of this cooling is still debated. More than 100 million years later, in the
Permian The Permian ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
, an overall warming trend occurred. As indicated by fossilized invertebrates, the western margin of Laurentia was affected by a lasting southward bound cool current. This current contrasted with waters warming in the Texas region. This opposition suggests that, during
Permian The Permian ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
global warm period, northern and northwestern
Pangea Pangaea or Pangea () was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology ...

Pangea
(western Laurentia) remained relatively cool.


Geological history

* Around 4.03 to 3.58  Ga, the oldest intact rock formation on the planet, the
Acasta Gneiss The Acasta Gneiss is a tonalite Tonalite is an igneous, plutonic ( intrusive) rock, of felsic In geology, felsic is an adjective describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 20 ...

Acasta Gneiss
, was formed in what is now
Northwest Territories The Northwest Territories (commonly abbreviated as NT or NWT; french: Territoires du Nord-Ouest) is a federal territory A territory is an administrative division Administrative division, administrative unitArticle 3(1). , country subd ...

Northwest Territories
(older individual mineral grains are known, but not whole rocks). * Around 2.565 Ga,
Arctica Arctica or Arctida was an ancient continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is ...

Arctica
formed as an independent continent. * Around 2.72 to 2.45 Ga, Arctica was part of the supercontinent
Kenorland Kenorland was one of the earliest known supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the r ...

Kenorland
. * Around 2.1 to 1.84 Ga, when Kenorland broke apart, the Arctican craton was part of the landmass
Nena Gabriele Susanne Kerner (born 24 March 1960), better known as Nena, is a German singer and songwriter who rose to international fame in 1983 as the lead vocalist of the band Nena (band), Nena with the Neue Deutsche Welle song "99 Luftballons". I ...
along with
Baltica Baltica is a paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust 350px, The thickness of Crust (geology)#Earth's crust, Earth's crust (km) Continental crust is the layer of Igneous rock, igneous, Sedim ...
and Eastern
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...
. * Around 1.82 Ga, Laurentia was part of the supercontinent
Columbia Columbia may refer to: * Columbia (personification), the historical female national personification of the United States, and a poetic name for the Americas Places North America Natural features * Columbia Plateau, a geologic and geographic regio ...
. * Around 1.35–1.3 Ga, Laurentia was an independent continent. * Around 1.3 Ga, Laurentia was part of the landmass Protorodinia. * Around 1.07 Ga, Laurentia was part of the supercontinent
Rodinia Rodinia (from the Russian Russian refers to anything related to Russia, including: *Russians (русские, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *Rossiyane (росси ...

Rodinia
. * Around 750 Ma, Laurentia was part of the landmass
Protolaurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Mya (unit), Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the bre ...
. Laurentia nearly rifted apart. * In the
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
(635 to 541 ±0.3 Ma), Laurentia was part of the supercontinent
Pannotia Pannotia (from Greek: ''pan- Pan may refer to: Prefix *''Pan-'', a prefix from the Greek language, Greek πᾶν, ''pan'', meaning "all", "of everything", or "involving all members" of a group ** , most but not all using the prefix People * Pan ...

Pannotia
. * In the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
(541 ±0.3 to 485.4 ±1.7 Ma), Laurentia was an independent continent. * In the
Ordovician The Ordovician ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other eart ...

Ordovician
(485.4 ± 1.7 to 443.8 ±1.5 Ma), Laurentia was shrinking and Baltica was expanding. * In the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the H ...
(419.2 ± 2.8 to 358.9 ±2.5 Ma), Laurentia collided against Baltica, forming the landmass
Euramerica Laurasia () was the more northern of two large landmasses that formed part of the Pangaea Pangaea or Pangea () was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("s ...
. * In the
Permian The Permian ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
(298.9 ± 0.8 to 252.17 ±0.4 Ma), all major continents collided against each other, forming the supercontinent
Pangaea Pangaea or Pangea () was a supercontinent In geology Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí G ...

Pangaea
. * In the
Jurassic The Jurassic ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
(201.3 ± 0.6 to 145 ±4 Ma), Pangaea rifted into two landmasses:
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea Pangaea or Pangea () was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("s ...
and
Gondwana Gondwana () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (g ...

Gondwana
. Laurentia was part of the landmass Laurasia. * In the
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
(145 ± 4 to 66 Ma), Laurentia was an independent continent called North America. * In the
Neogene The Neogene ( ) (informally Upper Tertiary or Late Tertiary) is a geologic period and system that spans 20.45 million years from the end of the Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or E ...

Neogene
(23.03 ± 0.05 Ma until today or ending 2.588 Ma), Laurentia, in the form of North America, collided with
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
, forming the landmass America.


See also

*


References


External links


Paleogeography of the Southwestern US
paleogeographic history of southwestern Laurentia, goes back to 1.7 billion years ago.

– Paleogeographic history of western Laurentia, goes back to the Permian period.

from The Smithsonian National Museum of Natural History
Map of Laurentia
{{Authority control Cratons Historical continents Geology of North America Precambrian North America Natural history of North America