Ireviken event
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Axis scale: millions of years ago.
The Ireviken event was a minor extinction event at the Llandovery/Wenlock boundary (mid Silurian, ). The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species go extinct; 80% of the global conodont species also become extinct in this interval.
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[edit] Anatomy of the event
The event lasted around 200,000 years, spanning the base of the Wenlock period.[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]
[edit] 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]
[edit] 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]
[edit] 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:.
- ^ 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:.
- ^ 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, 451-492.
