Viséan

The Visean, Viséan or Visian is an important time in Earth's history. It is part of how scientists divide up long stretches of time. It belongs to the ICS geologic timescale.

As a stage in the stratigraphic column, the Visean was the second part of the Mississippian period. This period is the lower subsystem of the larger Carboniferous era. This was a time when much of the world had vast forests and many new kinds of life were appearing.

The Visean lasted from about 346.7 to 330.3 million years ago, marked as Ma. It came after the Tournaisian stage and was followed by the Serpukhovian stage. This period helps scientists understand the order of events on Earth long ago.

Name and definitions

The Viséan Stage was named by Belgian geologist André Dumont in 1832 after the city of Visé in Belgium’s Liège Province. Before it became an international stage, the Viséan was part of the European regional geologic time scale. It came after the Tournaisian Stage and was followed by the Namurian Stage. In North America, it matches parts of the Osagean, Meramecian, and Chesterian stages, and in China, it matches the lower and middle Tatangian series.

The start of the Viséan Stage is marked by the first appearance of a specific fusulinid species called Eoparastaffella simplex. Originally, the type location was near Dinant, Belgium, but this was not good for matching rock layers in different places. A Global Boundary Stratotype Section and Point (GSSP) has been suggested in the Luzhai Formation near Penchong in Guangxi, China. The end of the Viséan is marked by the first appearance of a conodont called Lochriea ziegleri or the start of the biozone of the goniatite Cravenoceras leion.

Biota

The Carboniferous-Earliest Permian Biodiversification Event began during the Viséan, the same time as the Late Palaeozoic Ice Age started.

In the late Viséan, animal reefs grew again after being harmed during the Hangenberg Event. One animal from this time was Westlothiana. It looked like a reptile but was really an amphibian. Scientists once thought it was one of the first animals with a special kind of egg, but now they are not sure.

Biostratigraphy

The Visean period has four special areas. These areas are named after tiny fossils called conodonts. The areas are named after Lochriea nodosa, Lochriea mononodosa, Gnathodus bilineatus, and Gnathodus texanus.

In British geology, the Visean is split into five smaller parts. From most recent to oldest, these parts are Brigantian, Asbian, Holkerian, Arundian, and Chadian. The earliest part of Chadian overlaps with the Tournaisian period.