Anisian

The Anisian was an important time period in Earth's history. It was the earliest age of the Middle Triassic series and lasted from about 246.7 million years ago to 241.464 million years ago. During this time, the world continued to change after the mass extinction that marked the end of the Permian period.

The Anisian came after the Olenekian Age, which was part of the Lower Triassic Epoch, and it was followed by the Ladinian Age. This period saw many changes in the planet's climates and landscapes, affecting the plants and animals that lived there. Scientists study the Anisian to learn more about how life recovered and evolved after a major event in Earth's past.

Stratigraphic definitions

The Anisian stage was named by Austrian geologists Wilhelm Heinrich Waagen and Carl Diener in 1895, after the Latin name Anisus for the Enns river. Its start is marked either by the first appearance of a special conodont species called Chiosella timorensis, or by a change in Earth's magnetic field. The end of the Anisian is identified by the first appearance of an ammonite species named Eoprotrachyceras curionii.

In Central Europe, the Anisian is sometimes split into four smaller parts. It also includes six special layers defined by different ammonite species: Nevadites, Hungarites, Paraceratites, Balatonites balatonicus, Kocaelia, and Acrochordiceras.

Selected formations

Some important rock layers from the Anisian age include the Sydney sandstone in New South Wales, Australia, and the Wianamatta Group, which includes the Bringelly Shale and Ashfield Shale, also in New South Wales, Australia. Other notable formations are the lower and middle Besano Formation in Switzerland and Italy, and the upper Ermaying Formation in Shaanxi and Shanxi, China.

Additional formations from this time are the Favret Formation and Prida Formation in Nevada, US, including the Fossil Hill Member, the Grès à Voltzia in France, and the Guanling Formation in Guizhou and Yunnan, China. The Moenkopi Formation in the southwestern US, and the lower and middle Muschelkalk in central Europe are also significant. The Röt Formation and Upper Buntsandstein in Germany complete this list.