Ireviken event
{{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 events (the Ireviken, Mulde, and Lau events) during the Silurian period. It occurred at the Llandovery/Wenlock boundary (mid Silurian, {{Ma|Wenlock|{{period start error|Wenlock}} 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.{{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}} It is associated with a period of global cooling.{{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 }}{{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 }}
It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle. The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka. The final two data are much further spaced, so harder to link with Milankovic changes.
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 graptolites, conodonts and trilobites were hit hardest.{{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}}
Geochemistry
See also
References
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