Ireviken event

Silurian graphical timeline
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−444 — – −442 — – −440 — – −438 — – −436 — – −434 — – −432 — – −430 — – −428 — – −426 — – −424 — – −422 — – −420 — – −418 —	Paleozoic Ordovician Silurian Devonian Llandovery Wenlock Ludlow Přídolí Rhuddanian Aeronian Telychian Sheinwoodian Homerian Gorstian Ludfordian	← Lau event ← Mulde event[1] ← Ireviken event[2]
Subdivision of the Silurian according to the ICS, as of 2023.[3] Vertical axis scale: Millions of years ago

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, 433.4 ± 0.8  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.^[2][4] It is associated with a period of global cooling.^[5][6][2]

It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle.^[4] The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.^[4] The final two data are much further spaced, so harder to link with Milankovic changes.^[4]

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.^[7][2]

Geochemistry

Subsequent to the first extinctions, excursions in the δ¹³C and δ¹⁸O records are observed; δ¹³C rises from +1.4‰ to +4.5‰, while δ¹⁸O increases from −5.6‰ to −5.0‰.^[2]

See also

• Anoxic event

References

1. Jeppsson, L.; Calner, M. (2007). "The Silurian Mulde Event and a scenario for secundo—secundo events". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 93 (02): 135–154. doi:10.1017/S0263593300000377.
2. Munnecke, A.; Samtleben, C.; Bickert, T. (2003). "The Ireviken Event in the lower Silurian of Gotland, Sweden-relation to similar Palaeozoic and Proterozoic events". Palaeogeography, Palaeoclimatology, Palaeoecology. 195 (1): 99–124. doi:10.1016/S0031-0182(03)00304-3.
3. "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. September 2023. Retrieved December 16, 2024.
4. Jeppsson, L (1997). "The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events". In Brett, C.E.; Baird, G.C. (eds.). Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. New York: Columbia University Press. pp. 451–492.
5. Trotter, Julie A.; Williams, Ian S.; Barnes, Christopher R.; Männik, Peep; Simpson, Andrew (February 2016). "New conodont δ18O records of Silurian climate change: Implications for environmental and biological events". Palaeogeography, Palaeoclimatology, Palaeoecology. 443: 34–48. Bibcode:2016PPP...443...34T. doi:10.1016/j.palaeo.2015.11.011.
6. Lehnert, Oliver; Männik, Peep; Joachimski, Michael M.; Calner, Mikael; Frýda, Jiři (15 October 2010). "Palaeoclimate perturbations before the Sheinwoodian glaciation: A trigger for extinctions during the 'Ireviken Event'". Palaeogeography, Palaeoclimatology, Palaeoecology. 296 (3–4): 320–331. Bibcode:2010PPP...296..320L. doi:10.1016/j.palaeo.2010.01.009.
7. Smolarek, Justyna; Trela, Wiesław; Bond, David P. G.; Marynowski, Leszek (4 February 2016). "Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: sedimentary and geochemical controls on the Ireviken Event in a deep marine setting". Geological Magazine. 154 (2): 247–264. doi:10.1017/S0016756815001065. Retrieved 27 March 2023.