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{{short description|First of three relatively minor extinction events during the Silurian period}}
{{Silurian graphical timeline}}
The '''Ireviken event''' was the first of three relatively minor [[extinction event]]s (the '''Ireviken''', [[Mulde event|Mulde]], and [[Lau event|Lau]] events) during the [[Silurian]] period. It occurred at the [[Llandovery epoch|Llandovery]]/[[Wenlock epoch|Wenlock]] boundary (mid Silurian, {{Ma|Wenlock|{{period start error|Wenlock}}&nbsp;million years ago}}). The event is best recorded at [[Ireviken]], [[Gotland]], where over 50% of [[trilobite]] species became extinct; 80% of the global [[conodont]] species also became extinct in this interval.

==Anatomy of the event==
The event lasted around 200,000 years, spanning the base of the Wenlock epoch.<ref name=Munnecke2003/><ref name=Jeppsson1997>{{cite book|author =Jeppsson, L|year=1997|chapter=The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events|editor1=Brett, C.E. |editor2=Baird, G.C. |title=Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications|publisher=Columbia University Press|location=New York|pages=451–492}}</ref> It is associated with a period of global cooling.<ref name="TrotterEtAl2016PPP">{{cite journal |last1=Trotter |first1=Julie A. |last2=Williams |first2=Ian S. |last3=Barnes |first3=Christopher R. |last4=Männik |first4=Peep |last5=Simpson |first5=Andrew |title=New conodont δ18O records of Silurian climate change: Implications for environmental and biological events |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=February 2016 |volume=443 |pages=34–48 |doi=10.1016/j.palaeo.2015.11.011|bibcode=2016PPP...443...34T }}</ref><ref>{{cite journal |last1=Lehnert |first1=Oliver |last2=Männik |first2=Peep |last3=Joachimski |first3=Michael M. |last4=Calner |first4=Mikael |last5=Frýda |first5=Jiři |date=15 October 2010 |title=Palaeoclimate perturbations before the Sheinwoodian glaciation: A trigger for extinctions during the 'Ireviken Event' |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=296 |issue=3–4 |pages=320–331 |doi=10.1016/j.palaeo.2010.01.009 |doi-access=free |bibcode=2010PPP...296..320L }}</ref><ref name=Munnecke2003/>

It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the [[Milankovic cycles|Milankovic]] obliquity cycle.<ref name=Jeppsson1997/> The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.<ref name=Jeppsson1997/> The final two data are much further spaced, so harder to link with [[Milankovic cycle|Milankovic changes]].<ref name=Jeppsson1997/>

==Casualties==
The mechanism responsible for the event originated in the deep oceans, and made its way into the shallower shelf seas. Correspondingly, shallow-water reefs were barely affected, while pelagic and hemipelagic organisms such as the [[graptolite]]s, [[conodont]]s and [[trilobite]]s were hit hardest.<ref>{{cite journal |last1=Smolarek |first1=Justyna |last2=Trela |first2=Wiesław |last3=Bond |first3=David P. G. |last4=Marynowski |first4=Leszek |date=4 February 2016 |title=Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: sedimentary and geochemical controls on the Ireviken Event in a deep marine setting |url=https://www.cambridge.org/core/journals/geological-magazine/article/abs/lower-wenlock-black-shales-in-the-northern-holy-cross-mountains-poland-sedimentary-and-geochemical-controls-on-the-ireviken-event-in-a-deep-marine-setting/F12E14EB73896AE55BA97FDFFE1FED58 |journal=[[Geological Magazine]] |volume=154 |issue=2 |pages=247–264 |doi=10.1017/S0016756815001065 |access-date=27 March 2023}}</ref><ref name=Munnecke2003/>

==Geochemistry==
Subsequent to the first extinctions, excursions in the [[Δ13C|δ<sup>13</sup>C]] and [[Δ18O|δ<sup>18</sup>O]] records are observed; δ<sup>13</sup>C rises from +1.4‰ to +4.5‰, while δ<sup>18</sup>O increases from −5.6‰ to −5.0‰.<ref name=Munnecke2003/>

==See also==
*[[Anoxic event]]

==References==
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[[Category:Extinction events]]
[[Category:Silurian]]
[[Category:Isotope excursions]]