Ireviken event
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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[edit]
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[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.[7][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]
References[edit]
- ^ 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.
- ^ a b c d e 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.
- ^ "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
- ^ 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. (eds.). Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. New York: Columbia University Press. pp. 451–492.
- ^ 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.
- ^ 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. doi:10.1016/j.palaeo.2010.01.009. Retrieved 26 December 2022.
- ^ 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.