The Ireviken event was the first of three relatively minor
extinction event
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
s (the Ireviken,
Mulde, and
Lau
Lau or LAU may refer to:
People
* Lau (surname)
* Liu (劉/刘), a common Chinese family name transliterated Lau in Cantonese and Hokkien
* Lau clan, one of the Saraswat Brahmin clans of Punjab
* LAU (musician): Laura Fares
Places
* Lebane ...
events) during the
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleoz ...
period. It occurred at the
Llandovery
Llandovery (; cy, Llanymddyfri ) is a market town and community in Carmarthenshire, Wales. It lies on the River Tywi and at the junction of the A40 and A483 roads, about north-east of Carmarthen, north of Swansea and west of Brecon.
Hi ...
/
Wenlock boundary (mid Silurian, ). The event is best recorded at
Ireviken,
Gotland
Gotland (, ; ''Gutland'' in Gutnish), also historically spelled Gottland or Gothland (), is Sweden's largest island. It is also a province, county, municipality, and diocese. The province includes the islands of Fårö and Gotska Sandön to ...
, where over 50% of
trilobite
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
species became extinct; 80% of the global
conodont
Conodonts ( Greek ''kōnos'', " cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, whi ...
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.
[
It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle.][ The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.][ The final two data are much further spaced, so harder to link with Milankovic changes.][
]
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, conodont
Conodonts ( Greek ''kōnos'', " cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, whi ...
s and trilobite
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
s were hit hardest.[
]
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
{{extinction events
Extinction events
Silurian events