Ireviken event

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Key events in the Silurian
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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[edit]

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[edit]

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[edit]

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[edit]

Anoxic event

References[edit]

  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. ^ a b c d 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. ^ a b c d 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.