Ireviken event

The Ireviken event was a minor extinction event at the Llandovery/Wenlock boundary (mid Silurian, Ma|Wenlock|period start error|Wenlock million years ago).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.

Anatomy of the event

The event lasted around 200,000 years, spanning the base of the Wenlock period.cite book
author = Jeppsson, L
year = 1997
chapter = The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events
editor = Brett, C.E., Baird, G.C.
title = Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications
publisher = Columbia University Press
location = New York
pages = 451-492]

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, conodonts and trilobites were hit hardest.

Geochemistry

Subsequent to the first extinctions, excursions in the d13c and delta|18|O records are observed; d13c rises from +1.4‰ to +4.5‰, while d18o increases from −5.6‰ to −5.0‰.

References