Brachiopod decline preceded the Early Toarcian mass extinction in the Northern Caucasus (northern Neo-Tethys Ocean) : a palaeogeographical context

Abstract

Brachiopods were affected strongly by the Early Toarcian mass extinction within the Northern Caucasus, which at that time was a large region on the northern margin of the Neo-Tethys Ocean. However, their decline preceded the mass extinction event, and it took place in the mid-Pliensbachian with only one species survived in the Domerian. To understand the causes of this phenomenon 7 precise palaeogeographical reconstructions have been produced for the Northern Caucasus. It is proposed that a mid-Pliensbachian deepening of the Caucasian Sea and an associated oxygen depletion stressed brachiopod assemblages. Data from some European regions and South America suggest a high diversity in the late Pliensbachian. In contrast, brachiopod diversity decreased in the Bakony Mountains of Hungary in the latest Pliensbachian and on the Pacific margin of North America in the late Pliensbachian. The decline which preceded the Early Toarcian mass extinction was a regional phenomenon unrelated to the mass extinction itself.