Lau event

The Lau event was the last of three relatively minor mass extinctions (the Ireviken, Mulde, and Lau events) during the Silurian period. It had a major effect on the conodont fauna, but barely scathed the graptolites, though they suffered an extinction very shortly thereafter termed the Kozlowskii event that some authors have suggested was coeval with the Lau event and only appears asynchronous due to taphonomic reasons. It coincided with a global low point in sea level caused by glacioeustasy and is closely followed by an excursion in geochemical isotopes in the ensuing late Ludfordian faunal stage and a change in depositional regime. The Lau event started at the beginning of the late Ludfordian, a subdivision of the Ludlow stage, about . Its strata are best exposed in Gotland, Sweden, taking its name from the parish of Lau. Its base is set at the first extinction datum, in the Eke beds, and despite a scarcity of data, it is apparent that most major groups suffered an increase in extinction rate during the event; major changes are observed worldwide at correlated rocks, with a "crisis" observed in populations of conodonts and graptolites. More precisely, conodonts suffered in the Lau event, and graptolites in the subsequent isotopic excursion. Local extinctions may have played a role in many places, especially the increasingly enclosed Welsh basin; the event's relatively high severity rating of 6.2 does not change the fact that many life-forms became re-established shortly after the event, presumably surviving in refuge or in environments that have not been preserved in the geological record. Although life persisted after the event, community structures were permanently altered and many lifeforms failed to regain the niches they had occupied before the event. A peak in , accompanied by fluctuations in other isotope concentrations, is often associated with mass extinctions. Some workers have attempted to explain this event in terms of climate or sea level change – perhaps arising due to a build-up of glaciers; however, such factors alone do not appear to be sufficient to explain the events.