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Facies and carbon isotope studies in southern Tibet suggest that the Toarcian extinction was diachronous

Hallam A.

Volumina Jurassica

2006

Vol. 4, no. 1

168-168

A record of the Toarcian (Early Jurassic) mass extinction is reported from eastern Tethyan (Tibetan) locations for the first time, using both nannopalaeontological and carbon isotope evidence. These show a similar succession of events to those seen in western Tethys and Boreal northern Europe but with a considerable delay in their timing. Thus, transgression and spread of oxygen-poor bottom waters is seen, but the onset of the dysaerobic deposition occurs late in the stage in Tibet whilst in western Tethyan and Boreal locations they develop near the base of the stage. The benthic extinctions were similarly delayed, with the result that the two principal victims of the crisis in the western Tethyan Realm, the lithiotid bivalves and the lituolid Foraminifera, persisted until high in the Toarcian in eastern Tethys. The Toarcian extinction event was therefore a protracted crisis associated with the diachronous onset of oxygen-poor deposition in marine settings.