Editing Cambrian (section)

== Paleogeography ==
Reconstructing the position of the continents during the Cambrian is based on [[Paleomagnetism|palaeomagnetic]], [[Biogeography|palaeobiogeographic]], [[Tectonics|tectonic]], geological and [[Paleoclimatology|palaeoclimatic]] data. However, these have different levels of uncertainty and can produce contradictory locations for the major continents.<ref name="Keppie-2024">{{Cite journal |last1=Keppie |first1=Duncan Fraser |last2=Keppie |first2=John Duncan |last3=Landing |first3=Ed |date=2024-04-23 |title=A tectonic solution for the Early Cambrian palaeogeographical enigma |journal=Geological Society, London, Special Publications |language=en |volume=542 |issue=1 |pages=167–177 |doi=10.1144/SP542-2022-355 |issn=0305-8719|doi-access=free }}</ref> 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.<ref name="Keppie-2024"/>
[[File:Gondwana and Laurentia.png|thumb|Approximate positions of Gondwana, Laurentia and Baltica in the middle Cambrian (c. 500 Ma). AT: Armorican terrane, CA: Carolinia, CU: Cuyania, EA: East Avalonia, FA: Famatina arc, GA: Ganderia, IB: Iberia, MX: Mixteca–Oaxaca block, WA: West Avalonia. Plate boundaries: red - subduction; white - ridges; yellow - transform.<ref>{{Cite journal |last=Domeier |first=Mathew |date=2016-08-01 |title=A plate tectonic scenario for the Iapetus and Rheic oceans |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X15002014 |journal=Gondwana Research |volume=36 |pages=275–295 |doi=10.1016/j.gr.2015.08.003 |bibcode=2016GondR..36..275D |issn=1342-937X}}</ref><ref name="Torsvik-2017" /> |alt=Paleogeographic map showing Gondwana close to the south pole, Laurentia at the equator and Baltica in between.]]

Most models show [[Gondwana]] stretching from the south polar region to north of the equator.<ref name="Torsvik-2017">{{Cite book |last1=Torsvik |first1=Trond H. |url=https://www.worldcat.org/title/968155663 |title=Earth history and palaeogeography |last2=Cocks |first2=L. R. M. |date=2017 |publisher=Cambridge University Press |isbn=978-1-107-10532-4 |location=Cambridge, United Kingdom |oclc=968155663}}</ref> 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.<ref name="Keppie-2024"/>

[[Laurentia]] lay across the equator, separated from Gondwana by the [[Iapetus Ocean]].<ref name="Torsvik-2017" /> Proponents of Pannotia have Laurentia and [[Baltica]] close to the Amazonia region of Gondwana with a narrow Iapetus Ocean that only began to open once Gondwana was fully assembled c. 520 Ma.<ref>{{Cite journal |last1=Dalziel |first1=Ian W. D. |last2=Dewey |first2=John F. |date=2019 |title=The classic Wilson cycle revisited |url=https://www.lyellcollection.org/doi/10.1144/SP470.1 |journal=Geological Society, London, Special Publications |language=en |volume=470 |issue=1 |pages=19–38 |doi=10.1144/SP470.1 |bibcode=2019GSLSP.470...19D |issn=0305-8719}}</ref> Those not in favour of the existence of Pannotia show the Iapetus opening during the Late Neoproterozoic, with up to c. 6,500&nbsp;km (c. 4038 miles) between Laurentia and West Gondwana at the beginning of the Cambrian.<ref name="Torsvik-2017" />

Of the smaller continents, Baltica lay between Laurentia and Gondwana, the Ran Ocean (an arm of the Iapetus) opening between it and Gondwana. [[Siberia (continent)|Siberia]] lay close to the western margin of Gondwana and to the north of Baltica.<ref name="Wong Hearing-2021">{{Cite journal |last1=Wong Hearing |first1=Thomas W. |last2=Pohl |first2=Alexandre |last3=Williams |first3=Mark |last4=Donnadieu |first4=Yannick |last5=Harvey |first5=Thomas H. P. |last6=Scotese |first6=Christopher R. |last7=Sepulchre |first7=Pierre |last8=Franc |first8=Alain |last9=Vandenbroucke |first9=Thijs R. A. |date=2021-06-23 |title=Quantitative comparison of geological data and model simulations constrains early Cambrian geography and climate|journal=Nature Communications |language=en |volume=12 |issue=1 |pages=3868 |doi=10.1038/s41467-021-24141-5 |pmid=34162853 |pmc=8222365 |bibcode=2021NatCo..12.3868W |issn=2041-1723|hdl=1854/LU-8719399 |hdl-access=free }}</ref><ref name="Torsvik-2017" /> Annamia and [[South China craton|South China]] formed a single continent situated off north central Gondwana. The location of [[North China craton|North China]] is unclear. It may have lain along the northeast Indian sector of Gondwana or already have been a separate continent.<ref name="Torsvik-2017" />

=== Laurentia ===
During 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.<ref name="Torsvik-2017" />

After the Late Neoproterozoic (or mid-Cambrian) [[rift]]ing of Laurentia from Gondwana and the subsequent opening of the Iapetus Ocean, Laurentia was largely surrounded by [[passive margin]]s with much of the continent covered by shallow seas.<ref name="Torsvik-2017" />

As Laurentia separated from Gondwana, a sliver of continental [[terrane]] rifted from Laurentia with the narrow [[Taconic orogeny|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 [[Accretion (geology)|accreted]] to the terrane in 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.<ref name="Domeier-2016">{{Cite journal |last=Domeier |first=Mathew |date=2016 |title=A plate tectonic scenario for the Iapetus and Rheic oceans |url=https://linkinghub.elsevier.com/retrieve/pii/S1342937X15002014 |journal=Gondwana Research |language=en |volume=36 |pages=275–295 |doi=10.1016/j.gr.2015.08.003|bibcode=2016GondR..36..275D }}</ref>

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 County, Arkansas|Ouachita]] embayment with a new ocean established that continued to widen through the Cambrian and Early Ordovician.<ref name="Domeier-2016" />

=== Gondwana ===
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.<ref name="Torsvik-2017" />

The [[craton]]s that formed Gondwana came together during the Neoproterozoic to early Cambrian. A narrow ocean separated [[Amazonian craton|Amazonia]] from Gondwana until c. 530 Ma<ref>{{Cite journal |last=Evans |first=David A. D. |date=2021 |title=Pannotia under prosecution |url=https://www.lyellcollection.org/doi/10.1144/SP503-2020-182 |journal=Geological Society, London, Special Publications |language=en |volume=503 |issue=1 |pages=63–81 |doi=10.1144/SP503-2020-182 |bibcode=2021GSLSP.503...63E |issn=0305-8719}}</ref> and the [[Arequipa-Antofalla]] block united with the [[South America]]n sector of Gondwana in the early Cambrian.<ref name="Torsvik-2017" /> The [[Kuunga orogeny|Kuunga Orogeny]] between northern ([[Congo craton|Congo Craton]], [[Madagascar]] and [[Geology of India|India]]) and southern Gondwana ([[Kalahari craton|Kalahari Craton]] and [[East Antarctic Shield|East Antarctica]]), which began c. 570 Ma, continued with parts of northern Gondwana over-riding southern Gondwana and was accompanied by [[metamorphism]] and the [[Igneous intrusion|intrusion]] of [[granite]]s.<ref>{{Cite journal |last1=Grantham |first1=Geoffrey H. |last2=Satish-Kumar |first2=M. |last3=Horie |first3=Kenji |last4=Ueckermann |first4=Henriette |date=2023 |title=The Kuunga Accretionary Complex of Sverdrupfjella and Gjelsvikfjella, western Dronning Maud Land, Antarctica |url=https://www.jstage.jst.go.jp/article/jmps/118/ANTARCTICA/118_230125/_html/-char/ja |journal=Journal of Mineralogical and Petrological Sciences |volume=118 |issue=ANTARCTICA |pages=230125 |doi=10.2465/jmps.230125|doi-access=free }}</ref>

[[Subduction|Subduction zones]], active since the Neoproterozoic, extended around much of Gondwana's margins, from northwest Africa southwards round South America, [[South Africa]], [[East Antarctic Shield|East Antarctica]], and the eastern edge of West Australia. Shorter subduction zones existed north of [[Arabian-Nubian Shield|Arabia]] and India.<ref name="Torsvik-2017" />

The [[Famatinian orogeny|Famatinian]] [[continental arc]] stretched from central Peru in the north to central Argentina in the south. Subduction beneath this proto-[[Andean orogeny|Andean]] margin began by the late Cambrian.<ref name="Domeier-2016" />

Along the northern margin of Gondwana, between northern Africa and the [[Armorican terrane|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.<ref name="Murphy-2021">{{Cite journal |last1=Murphy |first1=J. Brendan |last2=Nance |first2=R. Damian |last3=Cawood |first3=Peter A. |last4=Collins |first4=William J. |last5=Dan |first5=Wei |last6=Doucet |first6=Luc S. |last7=Heron |first7=Philip J. |last8=Li |first8=Zheng-Xiang |last9=Mitchell |first9=Ross N. |last10=Pisarevsky |first10=Sergei |last11=Pufahl |first11=Peir K. |last12=Quesada |first12=Cecilio |last13=Spencer |first13=Christopher J. |last14=Strachan |first14=Rob A. |last15=Wu |first15=Lei |date=2021 |title=Pannotia: in defence of its existence and geodynamic significance |url=https://www.lyellcollection.org/doi/10.1144/SP503-2020-96 |journal=Geological Society, London, Special Publications |language=en |volume=503 |issue=1 |pages=13–39 |doi=10.1144/SP503-2020-96 |bibcode=2021GSLSP.503...13M |issn=0305-8719|hdl=20.500.11937/90589 |hdl-access=free }}</ref> This subduction extended west along the Gondwanan margin and by c. 530 Ma may have evolved into a major [[transform fault]] system.<ref name="Murphy-2021" />

At c. 511 Ma the [[Flood basalt|continental flood basalts]] of the [[Kalkarindji]] [[large igneous province]] (LIP) began to erupt. These covered an area of > 2.1 × 10<sup>6</sup> km<sup>2</sup> 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 [[Extinction event|mass extinction]].<ref name="Murphy-2021" />

==== Ganderia, East and West Avalonia, Carolinia and Meguma Terranes ====
The terranes of [[Ganderia]], East and West [[Avalonia]], [[Carolina terrane|Carolinia]] and [[Meguma terrane|Meguma]] lay in polar regions during the early Cambrian, and high-to-mid southern [[latitude]]s by the mid to late Cambrian.<ref name="Domeier-2016" /><ref name="Keppie-2024"/> 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.<ref name="Domeier-2016" /> However, some models show these terranes as part of a single independent [[Continental fragment|microcontinent]], Greater Avalonia, lying to the west of Baltica and aligned with its eastern ([[Timanide Orogen|Timanide]]) margin, with the Iapetus to the north and the Ran Ocean to the south.<ref name="Keppie-2024"/>
[[File:Gondwana, China and Siberia.png|thumb|Approximate positions of Siberia, Gondwana, North and South China, Baltica and smaller terranes in the middle Cambrian (c. 500 Ma). AN: Annamia, CM: Central Mongolian terrane, JA: Japan arc, KHT: Kazakhstania terranes, MOO: Mongol-Okhotsk Ocean, NC: North China, QT: Qinling terrane, SC: South China, TA: Tarim microcontinent, VT: Variscan terranes. Plate boundaries: red - subduction; white - ridges; yellow - transform.<ref name="Torsvik-2017" /><ref>{{Cite journal |last=Domeier |first=Mathew |date=2018-05-01 |title=Early Paleozoic tectonics of Asia: Towards a full-plate model |url=https://www.sciencedirect.com/science/article/pii/S1674987117302074 |journal=Geoscience Frontiers |series=Greenstone belts and their mineral endowment |volume=9 |issue=3 |pages=789–862 |doi=10.1016/j.gsf.2017.11.012 |bibcode=2018GeoFr...9..789D |issn=1674-9871|hdl=10852/71215 |hdl-access=free }}</ref> |alt=Paleogeographic map showing Gondwana close to the south pole, Siberia, North and South China near the equator and Baltica to the south of Siberia.]]

=== Baltica ===
During the Cambrian, Baltica rotated more than 60° anti-clockwise and began to drift northwards.<ref name="Domeier-2016" /> This rotation was accommodated by major strike-slip movements in the Ran Ocean between it and Gondwana.<ref name="Torsvik-2017" />

Baltica lay at mid-to-high southerly latitudes, separated from Laurentia by the Iapetus and from Gondwana by the Ran Ocean. It was composed of two continents, [[Baltic Shield|Fennoscandia]] and [[Sarmatian craton|Sarmatia]], separated by shallow seas.<ref name="Torsvik-2017" /><ref name="Domeier-2016" /> The [[sediment]]s deposited in these [[Unconformity|unconformably]] overlay Precambrian [[Basement (geology)|basement]] rocks. The lack of coarse-grained sediments indicates low lying [[topography]] across the centre of the craton.<ref name="Torsvik-2017" />

Along Baltica's northeastern margin subduction and arc magmatism associated with the Ediacaran [[Timanide Orogen|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.<ref name="Domeier-2018">{{Cite journal |last=Domeier |first=Mathew |date=2018 |title=Early Paleozoic tectonics of Asia: Towards a full-plate model |url=https://doi.org/10.1016/j.gsf.2017.11.012 |journal=Geoscience Frontiers |volume=9 |issue=3 |pages=789–862 |doi=10.1016/j.gsf.2017.11.012 |bibcode=2018GeoFr...9..789D |issn=1674-9871|hdl=10852/71215 |hdl-access=free }}</ref>

Its southeastern margin was also a [[convergent boundary]], with the accretion of island arcs and microcontinents to the craton, although the details are unclear.<ref name="Torsvik-2017" />

=== Siberia ===
Siberia began the Cambrian close to western Gondwana and north of Baltica. It drifted northwestwards to close to the equator as the Ægir Ocean opened between it and Baltica.<ref name="Torsvik-2017" /><ref name="Wong Hearing-2021" /> Much of the continent was covered by shallow seas with extensive [[Archaeocyatha|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.<ref name="Torsvik-2017" />

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 region|back-arc]] volcanism. These now form the [[Altai-Sayan region|Altai-Sayan]] terranes.<ref name="Torsvik-2017" /><ref name="Domeier-2018" /> 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.<ref name="Keppie-2024"/>

Along the then western margin, Late Neoproterozoic to early Cambrian rifting was followed by the development of a passive margin.<ref name="Domeier-2018" />

To 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.<ref name="Torsvik-2017" />

=== Central Asia ===
During the Cambrian, the terranes that would form [[Kazakhstania]] later in the Paleozoic were a series of island arc and [[Accretionary wedge|accretionary complexes]] that lay along an intra-oceanic convergent plate margin to the south of North China.<ref name="Domeier-2018" />

To the south of these the Tarim microcontinent lay between Gondwana and Siberia.<ref name="Torsvik-2017" /> Its northern margin was passive for much of the Paleozoic, with thick sequences of [[Carbonate platform|platform carbonates]] and [[Fluvial sediment processes|fluvial]] to marine sediments resting unconformably on Precambrian basement. Along its southeast margin was the [[Altyn-Tagh|Altyn]] Cambro–Ordovician accretionary complex, whilst to the southwest a subduction zone was closing the narrow seaway between the North West [[Kunlun Mountains|Kunlun]] region of Tarim and the South West Kunlun terrane.<ref name="Domeier-2018" />

=== North China ===
[[File:Life on the platform margin of the Miaolingian sea, North China.png|thumb|250px|Life reconstruction of the Linyi Lagerstätte in Northern China]]
North China lay at equatorial to tropical latitudes during the early Cambrian, although its exact position is unknown.<ref name="Wong Hearing-2021" /> Some models show that it lies below the equatorial latitudes.<ref>{{Citation |title=Cambrian |date=2016 |work=Earth History and Palaeogeography |pages=85–100 |editor-last=Cocks |editor-first=L. Robin M. |url=https://www.cambridge.org/core/books/abs/earth-history-and-palaeogeography/cambrian/022132ED90B5FE8E36C692DA601D92D5 |access-date=2025-02-06 |place=Cambridge |publisher=Cambridge University Press |isbn=978-1-316-22552-3 |editor2-last=Torsvik |editor2-first=Trond H.}}</ref> Much of the craton was covered by shallow seas, with land in the northwest and southeast.<ref name="Torsvik-2017" />

Northern North China was a passive margin until the onset of subduction and 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|Qinling Orogenic Belt]]), together with Qilian-Qaidam, Altyn belts, and South West Kunlun terranes.<ref name="Domeier-2018" />

=== South China and Annamia ===
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 the western Australian sector. This northward drift is evidenced by the progressive increase in [[limestone]]s and increasing [[fauna]]l diversity.<ref name="Torsvik-2017" />

The northern margin South China, including the South Qinling block, was a passive margin.<ref name="Torsvik-2017" />

Along the southeastern margin, lower Cambrian volcanics indicate the accretion of an island arc along the Song Ma suture zone. Also, early in the Cambrian, the eastern margin of South China changed from passive to active, with the development of oceanic volcanic island arcs that now form part of the [[Geology of Japan|Japanese terrane]].<ref name="Torsvik-2017" />