Toarcian

The Toarcian ( rarely also Toarc or Toarcien ) is in Earth's history, a chronostratigraphic stage of the Early Jurassic. Geochronological this period is dated approximately from 182.7 to 174.1 million years ago. In the time interval of the Aalenian Toarcian follows, the Toarcian itself follows the Pliensbachian.

Naming and history

The Toarcian was named after the French town of Thouars. Thouars is located halfway between Angers and Poitiers. In 1842, Alcide Dessalines d' Orbigny certain close in a quarry near Thouars this stage.

Definition and GSSP

The stratigraphic determination of the Toarcian based on the group of ammonites. The beginning of the Toarcian is defined by the occurrence of the ammonite genus Eodactylites. The end is defined by the occurrence of the genus Leioceras. A GSSP ("Global Stratotype Section and Point" is about one type profile ) has not yet been finally determined.

Subdivision of the Toarcian

The Toarcian is subdivided in the Tethyan region in the following ammonite biozones:

• Pleydellia aalensis
• Dumortieria pseudoradiosa
• Phlyseogrammoceras dispansum
• Grammoceras thouarsense
• Haugia variabilis
• Hildoceras bifrons
• Harpoceras serpentinum
• Dactylioceras tenuicostatum