Editing Atlantic Ocean (section)

== Geology and plate tectonics ==
The Atlantic Ocean is underlain mostly by dense [[mafic]] oceanic crust made up of [[basalt]] and [[gabbro]] and overlain by fine clay, silt and siliceous ooze on the abyssal plain. The continental margins and continental shelf mark lower density, but greater thickness [[felsic]] continental rock that is often much older than that of the seafloor. The oldest oceanic crust in the Atlantic is up to 145 million years and is situated off the west coast of Africa and the east coast of North America, or on either side of the South Atlantic.<ref>{{Cite web|url=https://www.researchgate.net/publication/259634936|via=ResearchGate|title=The geological history of the North Atlantic Ocean|last1=Fitton|first1=Godfrey|last2=Larsen|first2=Lotte Melchior|pages=10, 15|year=1999}}</ref>

In many places, the continental shelf and continental slope are covered in thick sedimentary layers. For instance, on the North American side of the ocean, large carbonate deposits formed in warm shallow waters such as Florida and the Bahamas, while coarse river outwash sands and silt are common in shallow shelf areas like the [[Georges Bank]]. Coarse sand, boulders, and rocks were transported into some areas, such as off the coast of Nova Scotia or the [[Gulf of Maine]] during the [[Pleistocene]] ice ages.<ref>{{Cite report|url=https://pubs.usgs.gov/pp/0529a/report.pdf|archive-url=https://ghostarchive.org/archive/20221009/https://pubs.usgs.gov/pp/0529a/report.pdf|archive-date=9 October 2022|url-status=live|title="Atlantic Continental Shelf and Slope of the United States – Geologic Background"|first1=K. O.|last1=Emery|publisher=United States Geological Survey|year=1962|page=16}}</ref>

=== Central Atlantic ===
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 | image1 = Blakey 200Ma - COL.jpg
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 | footer = Opening of the central Atlantic 200–170 Ma
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The break-up of [[Pangaea]] began in the central Atlantic, between North America and Northwest Africa, where rift basins opened during the Late Triassic and Early Jurassic. This period also saw the first stages of the uplift of the Atlas Mountains. The exact timing is controversial with estimates ranging from 200 to 170&nbsp;Ma.<ref>{{Harvnb|Seton|Müller|Zahirovic|Gaina|2012|loc=Central Atlantic, pp. 218, 220}}</ref>

The opening of the Atlantic Ocean coincided with the initial break-up of the supercontinent [[Pangaea]], both of which were initiated by the eruption of the [[Central Atlantic Magmatic Province]] (CAMP), one of the most extensive and voluminous [[large igneous province]]s in Earth's history associated with the [[Triassic–Jurassic extinction event]], one of Earth's major [[extinction event]]s.<ref>{{Harvnb|Blackburn|Olsen|Bowring|McLean|2013|p=941}}</ref>
Theoliitic [[Dike (geology)|dikes]], [[Aquatic sill|sills]], and lava flows from the CAMP eruption at 200&nbsp;Ma have been found in West Africa, eastern North America, and northern South America. The extent of the volcanism has been estimated to {{cvt|4.5e6|km2}} of which {{cvt|2.5e6|km2}} covered what is now northern and central Brazil.<ref>{{Harvnb|Marzoli|Renne|Piccirillo|Ernesto|1999|p=616}}</ref>

The formation of the [[Central American Isthmus]] closed the [[Central American Seaway]] at the end of the Pliocene 2.8&nbsp;Ma ago. The formation of the isthmus resulted in the migration and extinction of many land-living animals, known as the [[Great American Interchange]], but the closure of the seaway resulted in a "Great American Schism" as it affected ocean currents, salinity, and temperatures in both the Atlantic and Pacific. Marine organisms on both sides of the isthmus became isolated and either diverged or went extinct.<ref>{{Harvnb|Lessios|2008|loc=Abstract, Introduction, p. 64}}</ref>

=== North Atlantic ===
{{See also|Opening of the North Atlantic Ocean|NATO}}

Geologically, the North Atlantic is the area delimited to the south by two conjugate margins, Newfoundland and Iberia, and to the north by the Arctic [[Eurasian Basin]]. The opening of the North Atlantic closely followed the margins of its predecessor, the [[Iapetus Ocean]], and spread from the central Atlantic in six stages: [[Iberian Peninsula|Iberia]]–[[Newfoundland (island)|Newfoundland]], [[Porcupine Bank|Porcupine]]–North America, Eurasia–Greenland, Eurasia–North America. Active and inactive spreading systems in this area are marked by the interaction with the [[Iceland hotspot]].<ref>{{Harvnb|Seton|Müller|Zahirovic|Gaina|2012|loc=Northern Atlantic, p. 220}}</ref>

Seafloor spreading led to the extension of the crust and the formation of troughs and sedimentary basins. The Rockall Trough opened between 105 and 84 million years ago although the rift failed along with one leading into the [[Bay of Biscay]].{{sfn|Fitton|Larsen|1999|p=15}}

Spreading began opening the [[Labrador Sea]] around 61 million years ago, continuing until 36 million years ago. Geologists distinguish two magmatic phases. One from 62 to 58 million years ago predates the separation of Greenland from northern Europe while the second from 56 to 52 million years ago happened as the separation occurred.

[[Iceland Plateau|Iceland]] began to form 62 million years ago due to a particularly concentrated mantle plume. Large quantities of [[basalt]] erupted at this time period are found on Baffin Island, Greenland, the Faroe Islands, and Scotland, with ash falls in Western Europe acting as a stratigraphic marker.{{sfn|Fitton|Larsen|1999|p=10}} The opening of the North Atlantic caused a significant uplift of continental crust along the coast. For instance, despite 7&nbsp;km thick basalt, Gunnbjorn Field in East Greenland is the highest point on the island, elevated enough that it exposes older Mesozoic sedimentary rocks at its base, similar to old lava fields above sedimentary rocks in the uplifted Hebrides of western Scotland.{{Sfn|Fitton|Larsen|1999|pp=23–24}}

The North Atlantic Ocean contains about 810 [[seamount]]s, most of them situated along the Mid-Atlantic Ridge.<ref>Gubbay S. 2003. Seamounts of the northeast Atlantic. OASIS (Oceanic Seamounts: an Integrated Study). Hamburg & WWF, Frankfurt am Main, Germany</ref> The [[OSPAR Convention|OSPAR]] database (Convention for the Protection of the Marine Environment of the North-East Atlantic) mentions 104 seamounts: 74 within national [[exclusive economic zone]]s. Of these seamounts, 46 are located close to the [[Iberian Peninsula]].

=== South Atlantic ===
{{Multiple image
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 | image1 = Gondwana115Ma hg.png
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West Gondwana (South America and Africa) broke up in the Early Cretaceous to form the South Atlantic. The apparent fit between the coastlines of the two continents was noted on the first maps that included the South Atlantic and it was also the subject of the first computer-assisted plate tectonic reconstructions in 1965.<ref name="Eagles-intro">{{Harvnb|Eagles|2007|loc=Introduction, p. 353}}</ref><ref>{{Harvnb|Bullard|Everett|Smith|1965}}</ref> This magnificent fit, however, has since then proven problematic and later reconstructions have introduced various deformation zones along the shorelines to accommodate the northward-propagating break-up.<ref name="Eagles-intro" /> Intra-continental rifts and deformations have also been introduced to subdivide both continental plates into sub-plates.<ref name="Seton-2012-p217">{{Harvnb|Seton|Müller|Zahirovic|Gaina|2012|loc=South Atlantic, pp. 217–218}}</ref>

Geologically, the South Atlantic can be divided into four segments: equatorial segment, from 10°N to the Romanche fracture zone (RFZ); central segment, from RFZ to Florianopolis fracture zone (FFZ, north of Walvis Ridge and Rio Grande Rise); southern segment, from FFZ to the Agulhas–Falkland fracture zone (AFFZ); and Falkland segment, south of AFFZ.<ref name="Torsvik2009-p1316">{{Harvnb|Torsvik|Rousse|Labails|Smethurst|2009|loc=General setting and magmatism, pp. 1316–1318}}</ref>

In the southern segment the Early Cretaceous (133–130&nbsp;Ma) intensive [[magmatism]] of the [[Paraná and Etendeka traps|Paraná–Etendeka Large Igneous Province]] produced by the [[Tristan hotspot]] resulted in an estimated volume of {{cvt|1.5e6|to|2.0e6|km3}}. It covered an area of {{cvt|1.2e6|to|1.6e6|km2}} in Brazil, Paraguay, and Uruguay and {{cvt|0.8e5|km2}} in Africa. [[Dyke swarm]]s in Brazil, Angola, eastern Paraguay, and Namibia, however, suggest the LIP originally covered a much larger area and also indicate failed rifts in all these areas. Associated offshore basaltic flows reach as far south as the Falkland Islands and South Africa. Traces of magmatism in both offshore and onshore basins in the central and southern segments have been dated to 147–49&nbsp;Ma with two peaks between 143 and 121&nbsp;Ma and 90–60&nbsp;Ma.<ref name="Torsvik2009-p1316" />

In the Falkland segment rifting began with dextral movements between the Patagonia and Colorado sub-plates between the Early Jurassic (190&nbsp;Ma) and the Early Cretaceous (126.7&nbsp;Ma). Around 150&nbsp;Ma sea-floor spreading propagated northward into the southern segment. No later than 130&nbsp;Ma rifting had reached the Walvis Ridge–Rio Grande Rise.<ref name="Seton-2012-p217" />

In the central segment, rifting started to break Africa in two by opening the [[Benue Trough]] around 118&nbsp;Ma. Rifting in the central segment, however, coincided with the [[Geomagnetic reversal#Superchrons|Cretaceous Normal Superchron]] (also known as the Cretaceous quiet period), a 40&nbsp;Ma period without magnetic reversals, which makes it difficult to date sea-floor spreading in this segment.<ref name="Seton-2012-p217" />

The equatorial segment is the last phase of the break-up, but, because it is located on the Equator, magnetic anomalies cannot be used for dating. Various estimates date the propagation of seafloor spreading in this segment and consequent opening of the Equatorial Atlantic Gateway (EAG) to the period 120–96&nbsp;Ma.<ref name="GiorgioniEtAl2015">{{cite journal|last1=Giorgioni|first1=Martino|last2=Weissert|first2=Helmut|last3=Bernasconi|first3=Stefano M.|last4=Hochuli|first4=Peter A.|last5=Keller|first5=Christina E.|last6=Coccioni|first6=Rodolfo|last7=Petrizzo|first7=Maria Rose|last8=Lukeneder|first8=Alexander|last9=Garcia|first9=Therese I.|date=March 2015|title=Paleoceanographic changes during the Albian–Cenomanian in the Tethys and North Atlantic and the onset of the Cretaceous chalk|url=https://www.sciencedirect.com/science/article/abs/pii/S0921818115000211|journal=[[Global and Planetary Change]]|volume=126|pages=46–61|doi=10.1016/j.gloplacha.2015.01.005|bibcode=2015GPC...126...46G|access-date=2 December 2022|issn=0921-8181|archive-date=10 October 2023|archive-url=https://web.archive.org/web/20231010112024/https://www.sciencedirect.com/science/article/abs/pii/S0921818115000211|url-status=live}}</ref><ref name="LateAptianPalaeoceanography">{{cite journal|last1=De A. Carvalho|first1=Marcelo|last2=Bengtson|first2=Peter|last3=Lana|first3=Cecília C.|date=23 November 2015|title=Late Aptian (Cretaceous) paleoceanography of the South Atlantic Ocean inferred from dinocyst communities of the Sergipe Basin, Brazil|journal=[[Paleoceanography and Paleoclimatology]]|volume=31|issue=1|pages=2–26|doi=10.1002/2014PA002772|doi-access=free}}</ref> This final stage, nevertheless, coincided with or resulted in the end of continental extension in Africa.<ref name="Seton-2012-p217" />

About 50&nbsp;Ma the opening of the [[Drake Passage]] resulted from a change in the motions and separation rate of the South American and Antarctic plates. First, small ocean basins opened and a shallow gateway appeared during the Middle Eocene. 34–30&nbsp;Ma a deeper seaway developed, followed by an [[Eocene–Oligocene extinction event|Eocene–Oligocene climatic deterioration]] and the growth of the [[Antarctic ice sheet]].<ref>{{Harvnb|Livermore|Nankivell|Eagles|Morris|2005|loc=Abstract}}</ref>

=== Closure of the Atlantic ===
{{See also|Pangaea Proxima}}
An embryonic subduction margin is potentially developing west of Gibraltar. The [[Gibraltar Arc]] in the western Mediterranean is migrating westward into the central Atlantic where it joins the converging African and Eurasian plates. Together these three tectonic forces are slowly developing into a new subduction system in the eastern Atlantic Basin. Meanwhile, the [[Scotia Arc]] and [[Caribbean plate]] in the western Atlantic Basin are eastward-propagating subduction systems that might, together with the Gibraltar system, represent the beginning of the closure of the Atlantic Ocean and the final stage of the Atlantic [[Wilson cycle]].<ref>{{Harvnb|Duarte|Rosas|Terrinha|Schellart|2013|loc=Abstract; Conclusions, p. 842}}</ref>