Editing Ordovician (section)

==Paleogeography and tectonics==
[[File:Earth Paleogeography 480 Ma (Early Ordovician, Tremadocian).png|thumb|Paleogeographic map of the Earth in the early Ordovician, 480 million years ago{{citation needed|reason=the image on Wikimedia Commons is unsourced|date=February 2025}}]]
[[File:Earth Paleogeography 470 Ma (Early-Middle Ordovician, Dapingian).png|thumb|Paleogeographic map of the Earth in the middle Ordovician, 470 million years ago{{citation needed|reason=the image on Wikimedia Commons is unsourced|date=February 2025}}]]
[[File:Earth Paleogeography 450 Ma (Late Ordovician, Katian).png|thumb|Paleogeographic map of the Earth in the late Ordovician, 450 million years ago{{citation needed|reason=the image on Wikimedia Commons is unsourced|date=February 2025}}]]
During the Ordovician, the southern continents were assembled into [[Gondwana]], which reached from north of the [[equator]] to the [[South Pole]]. The Panthalassic Ocean, centered in the northern hemisphere, covered over half the globe.<ref>{{cite book |last1=Torsvik |first1=Trond H. |last2=Cocks |first2=L. Robin M. |title=Earth history and palaeogeography |date=2017 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |isbn=9781107105324 |page=102}}</ref> At the start of the period, the continents of [[Laurentia]] (in present-day [[North America]]), [[Siberia (continent)|Siberia]], and [[Baltica]] (present-day northern Europe) were separated from Gondwana by over {{convert|5000|km||}} of ocean. These smaller continents were also sufficiently widely separated from each other to develop distinct communities of benthic organisms.{{sfn|Torsvik|Cocks|2017|p=102}} The small continent of [[Avalonia]] had just rifted from Gondwana and began to move north towards Baltica and Laurentia, opening the [[Rheic Ocean]] between Gondwana and Avalonia.<ref>{{cite journal |last1=Pollock |first1=Jeffrey C. |last2=Hibbard |first2=James P. |last3=Sylvester |first3=Paul J. |title=Early Ordovician rifting of Avalonia and birth of the Rheic Ocean: U–Pb detrital zircon constraints from Newfoundland |journal=[[Journal of the Geological Society]] |date=May 2009 |volume=166 |issue=3 |pages=501–515 |doi=10.1144/0016-76492008-088|bibcode=2009JGSoc.166..501P |s2cid=129091590 }}</ref><ref>{{cite journal |last1=Nance |first1=R. Damian |last2=Gutiérrez-Alonso |first2=Gabriel |last3=Keppie |first3=J. Duncan |last4=Linnemann |first4=Ulf |last5=Murphy |first5=J. Brendan |last6=Quesada |first6=Cecilio |last7=Strachan |first7=Rob A. |last8=Woodcock |first8=Nigel H. |title=A brief history of the Rheic Ocean |journal=Geoscience Frontiers |date=March 2012 |volume=3 |issue=2 |pages=125–135 |doi=10.1016/j.gsf.2011.11.008|doi-access=free }}</ref>{{sfn|Torsvik|Cocks|2017|p=103}} Avalonia collided with Baltica towards the end of Ordovician.<ref>{{cite journal |last1=Trela |first1=Wieslaw |date=15 July 2005 |title=Condensation and phosphatization of the Middle and Upper Ordovician limestones on the Malopolska Block (Poland): Response to paleoceanographic conditions |url=https://www.sciencedirect.com/science/article/abs/pii/S0037073805001910 |journal=Sedimentary Geology |volume=117 |issue=3–4 |pages=219–236 |doi=10.1016/j.sedgeo.2005.05.005 |access-date=21 May 2023 |archive-date=22 May 2023 |archive-url=https://web.archive.org/web/20230522055504/https://www.sciencedirect.com/science/article/abs/pii/S0037073805001910 |url-status=live }}</ref>{{sfn|Torsvik|Cocks|2017|p=112}}

Other geographic features of the Ordovician world included the [[Tornquist Sea]], which separated Avalonia from Baltica;{{sfn|Torsvik|Cocks|2017|p=102}} the Aegir Ocean, which separated Baltica from Siberia;<ref>{{cite journal |last1=Torsvik |first1=Trond H. |last2=Rehnström |first2=Emma F. |title=Cambrian palaeomagnetic data from Baltica: implications for true polar wander and Cambrian palaeogeography |journal=[[Journal of the Geological Society]] |date=March 2001 |volume=158 |issue=2 |pages=321–329 |doi=10.1144/jgs.158.2.321|bibcode=2001JGSoc.158..321T |s2cid=54656066 }}</ref> and an oceanic area between Siberia, Baltica, and Gondwana which expanded to become the Paleoasian Ocean in Carboniferous time. The [[Mongol-Okhotsk Ocean]] formed a deep embayment between Siberia and the Central Mongolian [[terrane]]s. Most of the terranes of central Asia were part of an equatorial archipelago whose geometry is poorly constrained by the available evidence.{{sfn|Torsvik|Cocks|2017|pp=102, 106}}

The period was one of extensive, widespread tectonism and volcanism. However, [[orogenesis]] (mountain-building) was not primarily due to continent-continent collisions. Instead, mountains arose along active continental margins during accretion of arc terranes or ribbon microcontinents. Accretion of new crust was limited to the Iapetus margin of Laurentia; elsewhere, the pattern was of rifting in back-arc basins followed by remerger. This reflected episodic switching from extension to compression. The initiation of new subduction reflected a global reorganization of tectonic plates centered on the amalgamation of Gondwana.<ref>{{cite journal |last1=van Staal |first1=C.R. |last2= Hatcher | first2= R.D. Jr. |year=2010 |title=Global setting of Ordovician orogenesis |journal=Geol Soc Am Spec Pap |volume=466 |pages=1–11 |doi=10.1130/2010.2466(01)|isbn=9780813724669 }}</ref>{{sfn|Torsvik|Cocks|2017|p=102}}
 
The [[Taconic orogeny]], a major mountain-building episode, was well under way in Cambrian times.{{sfn|Torsvik|Cocks|2017|pp=93-94}} This continued into the Ordovician, when at least two [[Volcanic arc|volcanic island arcs]] collided with Laurentia to form the [[Appalachian Mountains]]. Laurentia was otherwise tectonically stable. An island arc accreted to South China during the period, while subduction along north China (Sulinheer) resulted in the emplacement of ophiolites.{{sfn|Torsvik|Cocks|2017|pp=106-109}}

The [[ash fall]] of the Millburg/Big Bentonite bed, at about 454 Ma, was the largest in the last 590 million years. This had a [[dense rock equivalent]] volume of as much as {{convert|1140|km3||}}. Remarkably, this appears to have had little impact on life.<ref>{{cite journal |last1=Huff |first1=Warren D. |last2=Bergström |first2=Stig M. |last3=Kolata |first3=Dennis R. |title=Gigantic Ordovician volcanic ash fall in North America and Europe: Biological, tectonomagmatic, and event-stratigraphic significance |journal=[[Geology (journal)|Geology]] |date=1992-10-01 |volume=20 |issue=10 |pages=875–878 |doi=10.1130/0091-7613(1992)020<0875:GOVAFI>2.3.CO;2|bibcode=1992Geo....20..875H }}</ref>

There was vigorous tectonic activity along northwest margin of Gondwana during the Floian, 478 Ma, recorded in the Central Iberian Zone of Spain. The activity reached as far as Turkey by the end of Ordovician. The opposite margin of Gondwana, in Australia, faced a set of island arcs.{{sfn|Torsvik|Cocks|2017|p=102}} The accretion of these arcs to the eastern margin of Gondwana was responsible for the Benambran Orogeny of eastern Australia.<ref>{{cite journal |last1=Glen |first1=R. A. |last2=Meffre |first2=S. |last3=Scott |first3=R. J. |title=Benambran Orogeny in the Eastern Lachlan Orogen, Australia |journal=[[Australian Journal of Earth Sciences]] |date=March 2007 |volume=54 |issue=2–3 |pages=385–415 |doi=10.1080/08120090601147019|bibcode=2007AuJES..54..385G |s2cid=129843558 }}</ref>{{sfn|Torsvik|Cocks|2017|p=105}} Subduction also took place along what is now Argentina (Famatinian Orogeny) at 450 Ma.<ref>{{cite book |last1=Ramos |first1=Victor A. |chapter=The Famatinian Orogen Along the Protomargin of Western Gondwana: Evidence for a Nearly Continuous Ordovician Magmatic Arc Between Venezuela and Argentina |title=The Evolution of the Chilean-Argentinean Andes |series=Springer Earth System Sciences |date=2018 |pages=133–161 |doi=10.1007/978-3-319-67774-3_6|isbn=978-3-319-67773-6 }}</ref> This involved significant back arc rifting.{{sfn|Torsvik|Cocks|2017|p=102}} The interior of Gondwana was tectonically quiet until the [[Triassic]].{{sfn|Torsvik|Cocks|2017|p=102}}

Towards the end of the Ordovician, Gondwana began to drift across the South Pole; this contributed to the [[Hirnantian glaciation]] and the associated extinction event.{{sfn|Torsvik|Cocks|2017|pp=103–105}}

===Ordovician meteor event===
The [[Ordovician meteor event]] is a proposed shower of meteors that occurred during the Middle Ordovician Epoch, about 467.5 ± 0.28 million years ago, due to the break-up of the [[L chondrite]] parent body.<ref name=Lindskog>{{Cite journal|last1=Lindskog|first1=A. |last2=Costa|first2=M. M. |last3=Rasmussen|first3=C.M.Ø. |last4=Connelly|first4=J. N. |last5=Eriksson|first5=M. E. |date=2017-01-24|title=Refined Ordovician timescale reveals no link between asteroid breakup and biodiversification|journal=Nature Communications|language=En|volume=8|pages=14066 |doi=10.1038/ncomms14066| pmid=28117834|pmc=5286199 |bibcode=2017NatCo...814066L |issn=2041-1723 }}</ref> It is not associated with any major extinction event.<ref name=Nature1>{{cite journal |bibcode=2004Natur.430..323H |title=Fast delivery of meteorites to Earth after a major asteroid collision |last1=Heck |first1=Philipp R. |last2=Schmitz |first2=Birger |last3=Baur |first3=Heinrich |last4=Halliday |first4=Alex N. | author-link4 = Alex N. Halliday |last5=Wieler |first5=Rainer |volume=430 |year=2004 |pages=323–5 |journal=[[Nature (journal)|Nature]] |doi=10.1038/nature02736 |pmid=15254530 |issue=6997|s2cid=4393398 }}</ref><ref>{{cite journal |bibcode=1996Icar..119..182H |title=Meteoritic, Asteroidal, and Theoretical Constraints on the 500 MA Disruption of the L Chondrite Parent Body |last1=Haack |first1=Henning |last2=Farinella |first2=Paolo |last3=Scott |first3=Edward R. D. |last4=Keil |first4=Klaus |volume=119 |issue=1 |year=1996 |pages=182–91 |journal=Icarus |doi=10.1006/icar.1996.0010}}</ref><ref>{{cite journal |bibcode=2007M&PS...42..113K |title=L-chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar-39Ar dating |last1=Korochantseva |first1=Ekaterina V. |last2=Trieloff |first2=Mario |last3=Lorenz |first3=Cyrill A. |last4=Buykin |first4=Alexey I. |last5=Ivanova |first5=Marina A. |last6=Schwarz |first6=Winfried H. |last7=Hopp |first7=Jens |last8=Jessberger |first8=Elmar K. |volume=42 |issue=1 |year=2007 |pages=113–30 |journal=[[Meteoritics & Planetary Science]] |doi=10.1111/j.1945-5100.2007.tb00221.x|s2cid=54513002 |doi-access=free }}</ref> A 2024 study found that craters from this event cluster in a distinct band around the Earth, and that the breakup of the parent body may have formed a [[ring system]] for a period of about 40 million years, with frequent falling debris causing these craters.<ref name=":0" />