Toarcian turnover

The term Toarcian turnover, alternatively the Toarcian extinction, the Pliensbachian-Toarcian extinction, or the Early Jurassic extinction, refers to the wave of extinctions of that marked the end of the Pliensbachian stage and the start of the Toarcian stage of the Early Jurassic period, c. 183 million years ago.

The Toarcian turnover was most strongly manifested in aquatic lifeforms, notably in mollusk groups like ammonites; its reach was global in extent, as evidenced by research in Japanese waters, the Andean basin, and the floor of the former Tethys Sea. Evidence points to anoxic bottom waters as the probable cause of these marine extinctions, linked in turn to the massive volcanism of the Karoo-Ferrar eruptions in the relevant era.