Ireviken event

Key events in the Silurian

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Lau event

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Mulde event^[1]

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Ireviken
event^[2]

Key events of the Silurian Period.
Axis scale: millions of years ago.

The Ireviken event was a minor extinction event at the Llandovery/Wenlock boundary (mid Silurian, 433.4 ± 2.3 million years ago). The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species went extinct; 80% of the global conodont species also become extinct in this interval.

Anatomy of the event

The event lasted around 200,000 years, spanning the base of the Wenlock epoch.^[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.^[3] The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.^[3] The final two data are much further spaced, so harder to link with Milankovic changes.^[3]

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.^[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]

References

↑ 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.
↑ 2.0 2.1 2.2 2.3 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.
↑ 3.0 3.1 3.2 3.3 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. Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. New York: Columbia University Press. pp. 451–492.