Ireviken event explained

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,). 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.^[1] It is associated with a period of global cooling.^{[2] [3]}

It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle.^[1] The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.^[1] The final two data are much further spaced, so harder to link with Milankovic changes.^[1]

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.^[4]

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‰.

See also

• Anoxic event

References

Notes and References

1. Book: Jeppsson, L. 1997. The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events. Brett, C.E. . Baird, G.C. . Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. Columbia University Press. New York. 451–492.
2. Trotter . Julie A. . Williams . Ian S. . Barnes . Christopher R. . Männik . Peep . Simpson . Andrew . New conodont δ18O records of Silurian climate change: Implications for environmental and biological events . Palaeogeography, Palaeoclimatology, Palaeoecology . February 2016 . 443 . 34–48 . 10.1016/j.palaeo.2015.11.011. 2016PPP...443...34T .
3. 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' . . 296 . 3–4 . 320–331 . 10.1016/j.palaeo.2010.01.009 . free . 2010PPP...296..320L .
4. 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 . . 154 . 2 . 247–264 . 10.1017/S0016756815001065 . 27 March 2023.