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101-652: Beginning in Cambrian time, about 550 Ma, the Iapetus Ocean began to close. The weight of accumulating sediments, in addition to compressional forces in the crust, forced the eastern edge of the North American continent to fold gradually downward. In this manner, shallow-water carbonate deposition that had persisted on the continental shelf margin through late Cambrian into early Ordovician time, gave way to fine-grained clastic deposition and deeper water conditions during

202-598: A microcontinent starting in Laurentia and accreting then to Gondwana. A third model claims Cuyania is para-autochthonous and arrived at its current place by strike-slip faults starting not from Laurentia but from Gondwana. As the Taconic orogeny subsided in early Silurian time, uplifts and folds in the Hudson Valley region were beveled by erosion. Upon this surface sediments began to accumulate, derived from remaining uplifts in

303-460: A GSSP, but it is expected to be defined in strata marking the first appearance of trilobites in Gondwana . There was a rapid diversification of metazoans during this epoch, but their restricted geographic distribution, particularly of the trilobites and archaeocyaths , have made global correlations difficult, hence ongoing efforts to establish a GSSP. The Miaolingian is the third series/epoch of

404-505: A back-arc, Sea of Japan-style tectonic model for the Taconic orogeny in the southern Appalachians include mixing of Ordovician and Grenville (ca. 1 billion year old) detrital zircons in metamorphosed sedimentary sequences, and interlayering of metamorphosed Ordovician volcanic rocks with sedimentary rocks derived from the Laurentian margin. It has been suggested that the coeval Famatinian orogeny in western Gondwana ( South America )

505-924: A convergent plate margin during the Ordovician, and the Transcontinental Arch became submerged, only to reappear in the Devonian. The Devonian also saw the deposition of the Chattanooga Shale and the Antler Orogeny in the Western Cordillera. During the Carboniferous and Permian , Laurussia fused with Gondwana to form Pangaea . The resulting Alleghanian orogeny created the Central Pangean Mountains . The mountains were located close to

606-621: A part of Gondwana before the assembly of Pangaea, was left with Laurentia during the opening of the central Atlantic. This former Gondwana fragment includes the Carolina Slate belt and parts of Alabama. The Gulf of Mexico opened during the Late Triassic and Jurassic. This was accompanied by deposition of evaporite beds that later gave rise to salt domes that are important petroleum reservoirs today. Europe rifted away from North America between 140 and 120 Ma, and Laurentia once again became

707-569: A profound change in life on Earth ; prior to the Period, the majority of living organisms were small, unicellular and poorly preserved. Complex, multicellular organisms gradually became more common during the Ediacaran, but it was not until the Cambrian that the rapid diversification of lifeforms, known as the Cambrian explosion , produced the first representatives of most modern animal phyla . The Period

808-457: A sliver of continental terrane rifted from Laurentia with the narrow Taconic seaway opening between them. The remains of this terrane are now found in southern Scotland, Ireland, and Newfoundland. Intra-oceanic subduction either to the southeast of this terrane in the Iapetus, or to its northwest in the Taconic seaway, resulted in the formation of an island arc . This accreted to the terrane in

909-542: A subduction zone was closing the narrow seaway between the North West Kunlun region of Tarim and the South West Kunlun terrane. North China lay at equatorial to tropical latitudes during the early Cambrian, although its exact position is unknown. Much of the craton was covered by shallow seas, with land in the northwest and southeast. Northern North China was a passive margin until the onset of subduction and

1010-602: A thermal event or seaway tectonism. Greenland is composed mostly of crust of Archean to Proterozoic age, with lower Paleocene shelf formations on its northern margin and Devonian to Paleogene formations on its western and eastern margins. The eastern and northern margins were heavily deformed during the Caledonian orogeny . The Isua Greenstone Belt of western Greenland preserves oceanic crust containing sheeted dike complexes . These provide evidence to geologists that mid-ocean ridges existed 3.8 Ga. The Abitibi gold belt in

1111-451: Is also unique in its unusually high proportion of lagerstätte deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. By the end of the Cambrian, myriapods , arachnids , and hexapods started adapting to the land, along with the first plants . The term Cambrian is derived from the Latin version of Cymru ,

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1212-441: Is characterised by complex, sediment-penetrating Phanerozoic-type trace fossils , and its upper part by small shelly fossils. The second series/epoch of the Cambrian is currently unnamed and known as Cambrian Series 2 . It lasted from c. 521 Ma to c. 509 Ma. Its two stages are also unnamed and known as Cambrian Stage 3 , c. 521 Ma to c. 514 Ma, and Cambrian Stage 4 , c. 514 Ma to c. 509 Ma. The base of Series 2 does not yet have

1313-793: Is now the Atlantic coast of North America. This caused an episode of mountain-building called the Taconic orogeny . As the mountains raised by the Taconic orogeny were subsequently eroded, they produced the immense Queenston Delta , recorded in the rocks of the Queenston Formation . There was also violent volcanic activity, including the eruption that produced the Millburg/Big Bentonite ash bed. About 1,140 cubic kilometers (270 cu mi) of ash erupted in this event. However, this does not seem to have triggered any mass extinction. Throughout

1414-610: Is the "southward" continuation of the Taconic orogeny. This has been explained by adding that Laurentia could have collided with western Gondwana in early Paleozoic times during the closure of the Iapetus Ocean. According to this view the Cuyania terrane would be an allochthonous block of Laurentian origin that was left in Gondwana. But such views are challenged since Cuyania is alternatively suggested to have drifted across Iapetus Ocean as

1515-627: The Altai-Sayan terranes. Some models show a convergent plate margin extending from Greater Avalonia, through the Timanide margin of Baltica, forming the Kipchak island arc offshore of southeastern Siberia and curving round to become part of the Altai-Sayan convergent margin. Along the then western margin, Late Neoproterozoic to early Cambrian rifting was followed by the development of a passive margin. To

1616-572: The Arequipa-Antofalla block united with the South American sector of Gondwana in the early Cambrian. The Kuunga Orogeny between northern ( Congo Craton , Madagascar and India ) and southern Gondwana ( Kalahari Craton and East Antarctica ), which began c. 570 Ma, continued with parts of northern Gondwana over-riding southern Gondwana and was accompanied by metamorphism and the intrusion of granites . Subduction zones , active since

1717-566: The Basin and Range Province has been stretched up to 100% of its original width. The area experienced numerous large volcanic eruptions . Baja California rifted away from North America during the Miocene . This block of crust consists of Proterozoic to early Paleozoic shelf and Mesozoic arc volcano formations. The Holocene being an interglacial , a warm spell between episodes of extensive glaciation. Several climate events occurred in Laurentia during

1818-547: The Jiangshanian c. 494 Ma to c. 489.5 Ma, which have defined GSSPs; and the unnamed Cambrian Stage 10 , c. 489.5 Ma to 485.4 ± 1.9 Ma. The GSSP for the Cambrian–Ordovician boundary is at Green Point , western Newfoundland , Canada, and is dated at 485.4 Ma. It is defined by the appearance of the conodont Iapetognathus fluctivagus . Where these conodonts are not found the appearance of planktonic graptolites or

1919-557: The Mazatzal orogeny at 1.65 to 1.60 Gya, accreting the 1.71 to 1.65 Gya Mazatzal province; the Picuris orogeny at 1.49 to 1.45 Gya, which may have welded the 1.50 to 1.30 Gya Granite-Rhyolite province to Laurentia; and the Grenville orogeny at 1.30 to 0.95 Gya, which accreted the 1.30 to 1.00 Gya Llano-Grenville province to Laurentia. The Picuris orogeny , in particular, was characterized by

2020-671: The Permian Basin . Sedimentary beds deposited in the southwest in the early Triassic were fluvial in character, but gave way to eolian beds in the late Triassic. Pangaea reached its height about 250 Ma, at the start of the Triassic . The breakup of Pangaea began in the Triassic, with rifting along what is now the east coast of the U.S. that produced red beds , arkosic sandstone , and lake shale deposits. The central Atlantic ocean basin began opening at about 180 Ma. Florida, which had been

2121-511: The Phanerozoic eon. During the late Cambrian through the 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 brought a cooling period, although

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2222-647: The Western Interior Seaway ran from the Gulf of Mexico to the Arctic Ocean , dividing North America into eastern and western land masses. From time to time, land masses or mountain chains rose up on the distant edges of the craton and then eroded down, shedding their sand across the landscape. Chalk beds of the Niobrara Formation were deposited at this time, and accretion of crustal fragments continued along

2323-510: The coastal plain of New Jersey . In general, basement rocks to the west of Cameron's Line are regarded as autochthonous , meaning that they have not been significantly displaced by tectonic processes . The rocks to the west of Cameron's Line include metamorphosed sedimentary material originally comprising ancient continental slope, rise, and shelf deposits. The rocks to the east of Cameron's Line are allochthonous , which means they have been shoved westward over autochthonous basement rocks on

2424-614: The continental flood basalts of the Kalkarindji large igneous province (LIP) began to erupt. These covered an area of > 2.1 × 10 km across northern, central and Western Australia regions of Gondwana making it one of the largest, as well as the earliest, LIPs of the Phanerozoic. The timing of the eruptions suggests they played a role in the early to middle Cambrian mass extinction . The terranes of Ganderia , East and West Avalonia , Carolinia and Meguma lay in polar regions during

2525-610: The shelf edge. The position of the equator during the Late Ordovician epoch ( c.  458  – c.   444 Ma) on Laurentia has been determined via extensive 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 and loose shells or nonamalgamated brachiopod shell beds. These beds imply

2626-564: The trilobite Jujuyaspis borealis can be used. The boundary also corresponds with the peak of the largest positive variation in the δ C curve during the boundary time interval and with a global marine transgression. Major meteorite impact structures include: the early Cambrian (c. 535 Ma) Neugrund crater in the Gulf of Finland , Estonia, a complex meteorite crater about 20 km in diameter, with two inner ridges of about 7 km and 6 km diameter, and an outer ridge of 8 km that formed as

2727-621: The "missing" arc terrane typical of Taconic-aged rocks in New England and Canada. Instead, the Iapetus margin of this part of Laurentia appears to have faced a back-arc basin during the Ordovician, suggesting that Iapetus oceanic crust was subducted beneath Laurentia—unlike the New England and Canadian segments of the margin, where Laurentia was on the subducting plate. In contrast to the Ordovician geologic history of New England, rocks in Alabama, Georgia, Tennessee, and North Carolina—including those of

2828-682: The 19 km diameter Glikson crater (c. 508 Ma) in Western Australia; the 5 km diameter Mizarai crater (500±10 Ma) in Lithuania; and the 3.2 km diameter Newporte structure (c. 500 Ma or slightly younger) in North Dakota , U.S.A. Reconstructing the position of the continents during the Cambrian is based on palaeomagnetic , palaeobiogeographic , tectonic , geological and palaeoclimatic data. However, these have different levels of uncertainty and can produce contradictory locations for

2929-536: The Amazonia region of Gondwana with a narrow Iapetus Ocean that only began to open once Gondwana was fully assembled c. 520 Ma. Those not in favour of the existence of Pannotia show the Iapetus opening during the Late Neoproterozoic, with up to c. 6,500 km (c. 4038 miles) between Laurentia and West Gondwana at the beginning of the Cambrian. Of the smaller continents, Baltica lay between Laurentia and Gondwana,

3030-677: The Archean Slave , Rae , Hearne , Wyoming , Superior , and Nain Provinces, is located in the northern two thirds of Laurentia. During the Early Proterozoic they were covered by sediments, most of which has now been eroded away. Greenland is part of Laurentia. The island is separated from North America by the Nares Strait , but this is a Pleistocene erosional feature. The strait is floored with continental crust and shows no indications of

3131-509: The Cambrian and Early Ordovician. Gondwana was a massive continent, three times the size of any of the other Cambrian continents. Its continental land area extended from the south pole to north of the equator. Around it were extensive shallow seas and numerous smaller land areas. The cratons that formed Gondwana came together during the Neoproterozoic to early Cambrian. A narrow ocean separated Amazonia from Gondwana until c. 530 Ma and

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3232-477: The Cambrian, Laurentia lay across or close to the equator.  It drifted south and rotated c. 20° anticlockwise during the middle Cambrian, before drifting north again in the late Cambrian. After the Late Neoproterozoic (or mid-Cambrian) rifting of Laurentia from Gondwana and the subsequent opening of the Iapetus Ocean, Laurentia was largely surrounded by passive margins with much of the continent covered by shallow seas. As Laurentia separated from Gondwana,

3333-710: The Cambrian, lasting from c. 509 Ma to c. 497 Ma, and roughly identical to the middle Cambrian in older literature [1] . It is divided into three stages: the Wuliuan c. 509 Ma to 504.5 Ma; the Drumian c. 504.5 Ma to c. 500.5 Ma; and the Guzhangian c. 500.5 Ma to c. 497 Ma. The name replaces Cambrian Series 3 and was ratified by the IUGS in 2018. It is named after the Miaoling Mountains in southeastern Guizhou Province , South China, where

3434-560: The Dahlonega gold belt (Georgia and North Carolina), Talladega belt (Alabama and Georgia), and eastern Blue Ridge (Georgia, Tennessee, and North Carolina)—are not typical of a volcanic arc in its strictest sense. Instead, these rocks have geochemical and other characteristics typical of back-arc basins, which form behind the volcanic arc on the overriding plate. The presence of these early-middle Ordovician (480 - 460 million year old) back-arc basin rocks in direct or faulted contact with rocks of

3535-533: The Ediacaran Timanian Orogeny was coming to an end. In this region the early to middle Cambrian was a time of non-deposition and followed by late Cambrian rifting and sedimentation. Its southeastern margin was also a convergent boundary , with the accretion of island arcs and microcontinents to the craton, although the details are unclear. Siberia began the Cambrian close to western Gondwana and north of Baltica. It drifted northwestwards to close to

3636-568: The GSSP marking its base is found. This is defined by the first appearance of the oryctocephalid trilobite Oryctocephalus indicus . Secondary markers for the base of the Miaolingian include the appearance of many acritarchs forms, a global marine transgression , and the disappearance of the polymerid trilobites, Bathynotus or Ovatoryctocara. Unlike the Terreneuvian and Series 2, all the stages of

3737-599: The ICS ratify rock units based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype ) identifying the lower boundary of the unit. Currently the boundaries of the Cambrian System, three series and six stages are defined by global stratotype sections and points. The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites . The recognition of small shelly fossils before

3838-470: The Iapetus and from Gondwana by the Ran Ocean. It was composed of two continents, Fennoscandia and Sarmatia , separated by shallow seas. The sediments deposited in these unconformably overlay Precambrian basement rocks. The lack of coarse-grained sediments indicates low lying topography across the centre of the craton. Along Baltica's northeastern margin subduction and arc magmatism associated with

3939-489: The Laurentian shelf and slope-rise in the southern Appalachians suggests they were built on the margin of Laurentia, beyond the edge of the continental shelf-slope break. In the southern Appalachians, the Ordovician Laurentian margin probably resembled that seen in the modern Sea of Japan , with the continental mainland separated from a volcanic arc by a narrow, "marginal" seaway. Other lines of evidence supporting

4040-419: The Miaolingian are defined by GSSPs . The olenellids , eodiscids , and most redlichiids trilobites went extinct at the boundary between Series 2 and the Miaolingian. This is considered the oldest mass extinction of trilobites. The Furongian , c. 497 Ma to 485.4 ± 1.9 Ma, is the fourth and uppermost series/epoch of the Cambrian. The name was ratified by the IUGS in 2003 and replaces Cambrian Series 4 and

4141-423: The Neoproterozoic, extended around much of Gondwana's margins, from northwest Africa southwards round South America, South Africa , East Antarctica , and the eastern edge of West Australia. Shorter subduction zones existed north of Arabia and India. The Famatinian continental arc stretched from central Peru in the north to central Argentina in the south. Subduction beneath this proto- Andean margin began by

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4242-604: The New England region. The evidence for this is the Silurian Shawangunk Conglomerate , a massive, ridge-forming quartz sandstone and conglomerate formation, which rests unconformably on a surface of older gently- to steeply-dipping pre-Silurian age strata throughout the region. This ridge of Shawangunk Conglomerate extends southward from the Hudson Valley along the eastern front of the Catskills . It forms

4343-452: The Ran Ocean (an arm of the Iapetus) opening between it and Gondwana. Siberia lay close to the western margin of Gondwana and to the north of Baltica. Annamia and South China formed a single continent situated off north central Gondwana. The location of North China is unclear. It may have lain along the northeast Indian sector of Gondwana or already have been a separate continent. During

4444-542: The Sedgwick's "Upper Cambrian", claiming all fossilised strata for "his" Silurian series. Matters were complicated further when, in 1852, fieldwork carried out by Sedgwick and others revealed an unconformity within the Silurian, with a clear difference in fauna between the two. This allowed Sedgwick to now claim a large section of the Silurian for "his" Cambrian and gave the Cambrian an identifiable fossil record. The dispute between

4545-592: The Silurian (about 420 Ma) in the Caledonian orogeny . This produced the continent of Laurussia. During this time, several small continental fragments merged with other margins of the craton. These included the North Slope of Alaska, which merged during the Early Devonian . Several small crust fragments accreted from the late Devonian through the Mesozoic to form the Western Cordillera. The Western Cordillera became

4646-691: The Superior Province is the largest greenstone belt in the Canadian Shield. Laurentia first assembled from six or seven large fragments of Archean crust at around 2.0 to 1.8 Gya. The assembly began when the Slave craton collided with the Rae-Hearne craton, and the Rae-Hearne craton collided shortly after with the Superior Craton. These then merged with several smaller fragments of Archean crust, including

4747-642: The Taconic orogeny subsided during the late Ordovician (about 440 Ma), subduction ended, culminating in the accretion of the Iapetus Terrane onto the eastern margin of the continent. This resulted in the formation of a great mountain range throughout New England and eastern Canada, and perhaps to a lesser degree, southward along the region that is now the Piedmont of eastern North America. The expanded continental margin gradually stabilized. Erosion continued to strip away sediments from upland areas. Inland seas covering

4848-492: The Welsh name for Wales, where rocks of this age were first studied. It was named by Adam Sedgwick in 1835, who divided it into three groups; the Lower, Middle, and Upper. He defined the boundary between the Cambrian and the overlying Silurian, together with Roderick Murchison , in their joint paper " On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales ". This early agreement did not last. Due to

4949-422: The Western Cordillera. Northeast Mexico was added to the North American craton relatively recently in geological time. This block was formed from the Mesozoic to nearly the present day, with only small fragments of earlier basement rock . It moved as a coherent unit after the breakup of Pangaea. The Atlantic and Gulf Coasts experienced eight transgressions in the Cenozoic. The Laramide orogeny continued to raise

5050-405: The Wyoming, Medicine Hat, Sask, Marshfield, and Nain blocks. This series of collisions raised the mountains of the Trans-Hudson orogenic belt , which likely were similar to the modern Himalayas , and the Wopmay orogen of northwest Canada. During the assembly of the core of Laurentia, banded iron formation was deposited in Michigan, Minnesota, and Labrador. The resulting nucleus of Laurentia

5151-460: The accumulation of calcareous algae and the skeletal remains of coral , stromatoporoids , brachiopods , and other ancient marine fauna. The episodic eustatic rise and fall of sea level caused depositional environments to change or to shift laterally. As a result, the preserved faunal remains and the character and composition of the sedimentary layers deposited in any particular location varied through time. The textural or compositional variations of

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5252-560: The broad interior platform in the Midwest and Great Plains regions and is exposed only in northern Minnesota, Wisconsin, the New York Adirondacks , and the Upper Peninsula of Michigan . The sequence of sedimentary 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 or igneous with the overlying sedimentary layers composed mostly of limestones , sandstones , and shales . These sedimentary rocks were largely deposited 650–290 Ma. The oldest bedrock, assigned to

5353-480: The core of an independent continent with the opening of the North Atlantic in the Paleogene . Four orogenies occurred in the Mesozoic in the Western Cordillera: the Sonoma , Nevadan , Sevier , and Laramide . The Nevadan orogeny emplaced the extensive batholiths of the Sierra Nevada . The regression of the Sundance Sea in the late Jurassic was accompanied by deposition of the Morrison Formation , notable for its vertebrate fossils. During Cretaceous times,

5454-414: The cratonic areas of Greenland and the Hebridean Terrane in northwest Scotland . During other times in its past, Laurentia has been part of larger continents and supercontinents and consists of many smaller terranes assembled on a network of early Proterozoic orogenic belts . Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed

5555-416: The development of the Bainaimiao arc in the late Cambrian. To its south was a convergent margin with a southwest dipping subduction zone, beyond which lay the North Qinling terrane (now part of the Qinling Orogenic Belt ). South China and Annamia formed a single continent. Strike-slip movement between it and Gondwana accommodated its steady drift northwards from offshore the Indian sector of Gondwana to near

5656-402: The early Cambrian, and high-to-mid southern latitudes by the mid to late Cambrian. They are commonly shown as an island arc-transform fault system along the northwestern margin of Gondwana north of northwest Africa and Amazonia, which rifted from Gondwana during the Ordovician. However, some models show these terranes as part of a single independent microcontinent , Greater Avalonia, lying to

5757-461: The early Paleozoic, Laurentia was characterized by a tectonically stable interior flooded by the seas, with marginal orogenic belts . An important feature was the Transcontinental Arch, which ran southwest from the lowlands of the Canadian Shield. The shield and the arch were the only portions of the continent that were above water through much of the early Paleozoic. There were two major marine transgressions (episodes of continental flooding) during

5858-430: The early Paleozoic, the Sauk and the Tippecanoe. During this time, the Western Cordillera was a passive margin . Sedimentary rocks that were deposited on top of the basement complex were formed in a setting of quiet marine and river waters. 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

5959-566: The east (present north), Baltica and Amazonia to the south (present east), and Congo to the southwest (present southeast). The Grenville orogen extended along the entire southwest (present southeast) margin of Laurentia, where it had collided with Congo, Amazonia, and Baltica. Laurentia lay along the equator. Recent evidence suggests that South America and Africa never quite joined to Rodinia, though they were located very close to it. Newer reconstructions place Laurentia closer to its present-day orientation, with East Antarctica and Australia to

6060-478: The end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 485.4 Ma. Most of the continents lay in the southern hemisphere surrounded by the vast Panthalassa Ocean . The assembly of Gondwana during the Ediacaran and early Cambrian led to the development of new convergent plate boundaries and continental-margin arc magmatism along its margins that helped drive up global temperatures. Laurentia lay across

6161-432: The equator and produced a year-round zone of heavy precipitation that promoted the deposition of extensive coal beds, including the Appalachian coal beds in the U.S. Meanwhile, Gondwana had drifted onto the South Pole, and cycles of extensive glaciation produced a characteristic pattern of alternating marine and coal swamp beds called cyclothems . During the Pennsylvanian , the Ancestral Rocky Mountains were raised in

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6262-501: The equator as the Ægir Ocean opened between it and Baltica. Much of the continent was covered by shallow seas with extensive archaeocyathan reefs . The then northern third of the continent (present day south; Siberia has rotated 180° since the Cambrian) adjacent to its convergent margin was mountainous. From the Late Neoproterozoic to the Ordovician, a series of island arcs accreted to Siberia's then northeastern margin, accompanied by extensive arc and back-arc volcanism. These now form

6363-428: The equator, separated from Gondwana by the opening Iapetus Ocean . The Cambrian was a time of greenhouse climate conditions, with high levels of atmospheric carbon dioxide and low levels of oxygen in the atmosphere and seas. Upwellings of anoxic deep ocean waters into shallow marine environments led to extinction events, whilst periods of raised oxygenation led to increased biodiversity . The Cambrian marked

6464-477: The equator, separated from Gondwana by the western Iapetus Ocean . Sometime in the early Cambrian , around 530 Ma, Argentina rifted away from Laurentia and accreted onto Gondwana. The breakup of Pannotia produced six major continents: Laurentia, Baltica, Kazakhstania, Siberia, China, and Gondwana. Laurentia remained an independent continent until the middle Silurian . During the early to middle Ordovician , several volcanic arcs collided with Laurentia along what

6565-426: The final episode of the Taconic orogeny. Cameron's Line is the suture zone that is modern-day evidence of the collision of the island arc and the continent. Cameron's Line winds southward out of New England into western Connecticut and passes through southern New York across the Bronx , following the general trend of the East River . It extends beneath sedimentary cover on Staten Island and southward beneath

6666-443: The first trilobites, and Ediacara biota substantially earlier, has led to calls for a more precisely defined base to the Cambrian Period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland

6767-466: The globe that corresponded to the base of the Cambrian. An early date of 570 Ma quickly gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise analysis using modern radiometric dating yields a date of 538.8 ± 0.2 Ma. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in

6868-422: The impressive caprock ridge of the Shawangunk Mountains west of New Paltz . To the south and west it becomes the prominent ridge-forming unit that crops out along the crest of Kittatinny Mountain in New Jersey. Through Silurian time, the deposition of coarse alluvial sediments gave way to shallow marine fine-grained muds, and eventually to clear-water carbonate sediment accumulation with reefs formed from

6969-467: The intrusion of great volumes of granitoid magma into the juvenile crust, which helped mature the crust and stitch it together. Slab rollback at 1.70 and 1.65 Gya deposited characteristic quartzite - rhyolite beds on the southern margin of the craton. This long episode of accretion doubled the size of Laurentia but produced craton underlain by relatively weak, hydrous, and fertile (ripe for extraction of magma) mantle lithosphere. The subduction under

7070-431: The late Cambrian, triggering southeast-dipping subduction beneath the terrane itself and consequent closure of the marginal seaway. The terrane collided with Laurentia in the Early Ordovician. Towards the end of the early Cambrian, rifting along Laurentia's southeastern margin led to the separation of Cuyania (now part of Argentina) from the Ouachita embayment with a new ocean established that continued to widen through

7171-422: The late Cambrian. Along the northern margin of Gondwana, between northern Africa and the Armorican Terranes of southern Europe, the continental arc of the Cadomian Orogeny continued from the Neoproterozoic in response to the oblique subduction of the Iapetus Ocean. This subduction extended west along the Gondwanan margin and by c. 530 Ma may have evolved into a major transform fault system. At c. 511 Ma

7272-531: The lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms. The Terreneuvian is the lowermost series/ epoch of the Cambrian, lasting from 538.8 ± 0.2 Ma to c. 521 Ma. It is divided into two stages: the Fortunian stage, 538.8 ± 0.2 Ma to c. 529 Ma; and

7373-436: The major continents. This, together with the ongoing debate around the existence of the Neoproterozoic supercontinent of Pannotia , means that while most models agree the continents lay in the southern hemisphere, with the vast Panthalassa Ocean covering most of northern hemisphere, the exact distribution and timing of the movements of the Cambrian continents varies between models. Most models show Gondwana stretching from

7474-643: The midcontinent gradually expanded eastward into the New York Bight region and became the site of shallow clastic and carbonate deposition. This tectonically quiet period persisted until the late Devonian (about 360 Ma) when the next period of mountain-building began, the Acadian orogeny . In the southern Appalachians of Alabama, Georgia, and North Carolina, the Taconic orogeny was not associated with collision of an island arc with ancient North America ( Laurentia ). Geologists working in these areas have long puzzled over

7575-422: The middle Ordovician. In this period a convergent plate boundary developed along the eastern edge of a small island chain. Crustal material beneath the Iapetus Ocean sank into the mantle along a subduction zone with an eastward-dipping orientation. Dewatering of the down-going plate led to hydration of the peridotites in the overlying mantle wedge , lowering their melting point. This led to partial melting of

7676-535: The next 900 million years, Laurentia grew by the accretion of island arcs and other juvenile crust and occasional fragments of older crust (such as the Mojave block). This accretion occurred along the southeastern margin of Laurentia, where there was a long-lived convergent plate boundary . Major accretion episodes included the Yavapai orogeny at 1.71 to 1.68 Gya, which welded the 1.8 to 1.7 Gya Yavapai province to Laurentia;

7777-643: The oldest rock on Earth, such as the Archean rock of the Acasta Gneiss , which is 4.04 billion years ( Ga ) old, and the Istaq Gneiss Complex of Greenland, which is 3.8 Ga. When subsurface extensions are considered, the wider term Laurentian Shield 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

7878-403: The order of many tens or even hundreds of kilometers. These rocks were originally deposited as sediments in a deep water basin. Cameron's Line represents the trace of a subduction zone that ceased when the Taconic island arc collided with, and became accreted onto, the eastern margin of North America. Many of the rocks east of Cameron's Line were once part of the floor of the Iapetus Ocean. When

7979-458: The peridotites within the mantle wedge producing magma that returned to the surface to form the offshore Taconic (or Bronson Hill) island arc . By the Late Ordovician, this island arc had collided with the North American continent. The sedimentary and igneous rock between the land masses were intensely folded and faulted and were subjected to varying degrees of metamorphism . This was

8080-409: The presence of an equatorial climate belt that was hurricane free which lay inside 10° of the equator. This ecological conclusion matches the previous paleomagnetic findings which confirms this equatorial location. At the end of the Cambrian, about 490 Mya, Avalonia rifted away from Gondwana. By the end of the Ordovician, Avalonia had merged with Baltica, and the two fused to Laurentia at the end of

8181-775: The present Rocky Mountains into the Paleocene. The Western Cordillera continued to suffer tectonic deformation, including the formation of the Basin and Range Province in the middle Cenozoic and the uplift of the Colorado Plateau . The Colorado Plateau was uplifted with remarkably little deformation. The flood basalts of the Columbia Plateau also erupted during the Cenozoic. The southwestern portion of Laurentia consists of Precambrian basement rocks deformed by continental collisions. This area has been subjected to considerable rifting as

8282-465: The result of an impact of an asteroid 1 km in diameter; the 5 km diameter Gardnos crater (500±10 Ma) in Buskerud , Norway, where post-impact sediments indicate the impact occurred in a shallow marine environment with rock avalanches and debris flows occurring as the crater rim was breached not long after impact; the 24 km diameter Presqu'ile crater (500 Ma or younger) Quebec , Canada;

8383-409: The scarcity of fossils, Sedgwick used rock types to identify Cambrian strata. He was also slow in publishing further work. The clear fossil record of the Silurian, however, allowed Murchison to correlate rocks of a similar age across Europe and Russia, and on these he published extensively. As increasing numbers of fossils were identified in older rocks, he extended the base of the Silurian downwards into

8484-568: The south of North China. To the south of these the Tarim microcontinent lay between Gondwana and Siberia. Its northern margin was passive for much of the Paleozoic, with thick sequences of platform carbonates and fluvial to marine sediments resting unconformably on Precambrian basement. Along its southeast margin was the Altyn Cambro–Ordovician accretionary complex, whilst to the southwest

8585-410: The south polar region to north of the equator. Early in the Cambrian, the south pole corresponded with the western South American sector and as Gondwana rotated anti-clockwise, by the middle of the Cambrian, the south pole lay in the northwest African region. Laurentia lay across the equator, separated from Gondwana by the Iapetus Ocean . Proponents of Pannotia have Laurentia and Baltica close to

8686-455: The southeast margin of the continent is thought to have contributed to the formation of Rodinia . According to the Southwest U.S. and East Antarctica or SWEAT hypothesis , Laurentia became the core of the supercontinent . It was rotated approximately 90 degrees clockwise compared with its modern orientation, with East Antarctica and Australia to the north (what is now the west), Siberia to

8787-604: The southeast margin of the continent likely caused enrichment of the lithospheric mantle beneath the orogenic belts of the Grenville Province . Around 1.1 Gya, the center of the craton nearly rifted apart along the Midcontinent Rift System . This produced the Keweenawan Supergroup , whose flood basalts are rich in copper ore. Laurentia was formed in a tectonically active world. The subduction under

8888-471: The southwestern part of Laurentia. This has been attributed either to either the collision with Gondwana or subduction under the continental margin from the southwest. Two additional marine transgressions took place during the late Paleozoic: the Kaskaskia and Absaroka. The great continental mass of Pangaea strongly affected climate patterns. The Permian was relatively arid, and evaporites were deposited in

8989-654: The stable Precambrian craton seen today. The craton is named after the Laurentian Shield , through the Laurentian Mountains , which received their name from the St. Lawrence River , named after Saint Lawrence of Rome. In eastern and central Canada, much of the stable craton is exposed at the surface as the Canadian Shield , an area of Precambrian rock covering over a million square miles. This includes some of

9090-545: The strata, as well as the changing fossil fauna preserved, are used to define the numerous sedimentary formations of Silurian through Devonian age preserved throughout the region. Cambrian The Cambrian ( / ˈ k æ m b r i . ə n , ˈ k eɪ m -/ KAM -bree-ən, KAYM - ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon . The Cambrian lasted 53.4 million years from

9191-670: The then north, Siberia was separated from the Central Mongolian terrane by the narrow and slowly opening Mongol-Okhotsk Ocean . The Central Mongolian terrane's northern margin with the Panthalassa was convergent, whilst its southern margin facing the Mongol-Okhotsk Ocean was passive. During the Cambrian, the terranes that would form Kazakhstania later in the Paleozoic were a series of island arc and accretionary complexes that lay along an intra-oceanic convergent plate margin to

9292-559: The traditional "Upper Cambrian". The GSSP for the base of the Furongian is in the Wuling Mountains , in northwestern Hunan Province , China. It coincides with the first appearance of the agnostoid trilobite Glyptagnostus reticulatus , and is near the beginning of a large positive δ C isotopic excursion. The Furongian is divided into three stages: the Paibian , c. 497 Ma to c. 494 Ma, and

9393-664: The two geologists and their supporters, over the boundary between the Cambrian and Silurian, would extend beyond the life times of both Sedgwick and Murchison. It was not resolved until 1879, when Charles Lapworth proposed the disputed strata belong to its own system, which he named the Ordovician. The term Cambrian for the oldest period of the Paleozoic was officially agreed in 1960, at the 21st International Geological Congress . It only includes Sedgwick's "Lower Cambrian series", but its base has been extended into much older rocks. Systems , series and stages can be defined globally or regionally. For global stratigraphic correlation,

9494-553: The unnamed Stage 2, c. 529 Ma to c. 521 Ma. The name Terreneuvian was ratified by the International Union of Geological Sciences (IUGS) in 2007, replacing the previous "Cambrian Series 1". The GSSP defining its base is at Fortune Head on the Burin Peninsula, eastern Newfoundland, Canada (see Ediacaran - Cambrian boundary above). The Terreneuvian is the only series in the Cambrian to contain no trilobite fossils. Its lower part

9595-415: The west of Baltica and aligned with its eastern ( Timanide ) margin, with the Iapetus to the north and the Ran Ocean to the south. During the Cambrian, Baltica rotated more than 60° anti-clockwise and began to drift northwards. This rotation was accommodated by major strike-slip movements in the Ran Ocean between it and Gondwana. Baltica lay at mid-to-high southerly latitudes, separated from Laurentia by

9696-537: The west, South China to the northwest, Baltica to the east, and Amazonia and Rio de la Plata to the south. The breakup of Rodinia began by 780 Ma, when numerous mafic dike swarms were emplaced in western Laurentia. Early stages of rifting produced the Belt Supergroup , which is over 12 kilometers (7.5 mi) thick. By 750 Ma the breakup was mostly complete, and Gondwana (composed of most of today's southern continents) had rotated away from Laurentia, which

9797-514: The western Australian sector. This northward drift is evidenced by the progressive increase in limestones and increasing faunal diversity. Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America . Many times in its past, Laurentia has been a separate continent , as it is now in the form of North America, although originally it also included

9898-544: The world, and to the disappearance of distinctive Ediacaran fossils ( Namacalathus , Cloudina ). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 to 542 Ma, are more suitable. *Most Russian paleontologists define

9999-563: Was left isolated near the equator. The breakup of Rodinia may have triggered an episode of severe ice ages (the Snowball Earth hypothesis.) There is some evidence that the fragments of Rodinia gathered into another short-lived supercontinent, Pannotia , at the very end of the Proterozoic. This continent broke up again almost at once, and Laurentia rifted away from South America at around 565 Ma to once again become an isolated continent near

10100-571: Was mostly reworked Archean crust but with some juvenile crust in the form of volcanic arc belts. Juvenile crust is crust formed from magma freshly extracted from the Earth's mantle rather than recycled from older crustal rock. The intense mountain building of the Trans-Hudson orogeny formed thick, stable roots beneath the craton, possibly by a process of "kneading" that allowed low density material to move up and high density material to move down. Over

10201-502: Was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum . Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, and it is the T. pedum ichnofossil assemblage that is now formally used to correlate the base of the Cambrian. This formal designation allowed radiometric dates to be obtained from samples across

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