Silurian graphical timeline | ||||||||
This box:
| ||||||||
−444 — – −442 — – −440 — – −438 — – −436 — – −434 — – −432 — – −430 — – −428 — – −426 — – −424 — – −422 — – −420 — – −418 — |
|
| ||||||
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.
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]
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]
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]
|
| |
|---|---|
Minor events Major events Neoproterozoic Palæozoic Mesozoic Cenozoic
│
−600
│
−550
│
−500
│
−450
│
−400
│
−350
│
−300
│
−250
│
−200
│
−150
│
−100
│
−50
│
0 Millions of years before present
|
