Viséan

 ( Mississippian Geochronology ) 

The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from to Megaannum. It follows the Tournaisian age/stage and is followed by the Serpukhovian age/stage.

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Name and definitions The Viséan Stage was introduced by Belgium geologist André Dumont in 1832. Dumont named this stage after the city of Visé in Belgium's Liège Province. Before being used as an international stage, the Viséan Stage was part of the (West) European regional geologic time scale, in which it followed the Tournaisian Stage and is followed by the Namurian Stage. In the North American regional scale, the Viséan Stage correlates with the upper Osagean, the Meramecian and lower Chesterian stages. In the Chinese regional time scale, it correlates with the lower and middle Tatangian series.; 2006: Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian–Carboniferous–Permian Correlation Chart 2003 (DCP 2003), Palaeogeography, Palaeoclimatology, Palaeoecology 240 (1-2): pp 318–372.

The base of the Viséan Stage is at the first appearance of the fusulinid species Eoparastaffella (morphotype 1/morphotype 2). The type locality for the stage base used to be in a road section below the castle of Dinant in Belgium, but this type locality proved to be insufficient for the purpose of stratigraphic correlation. A GSSP has been proposed in the Luzhai Formation near Penchong in the Chinese province of Guangxi.; 2003: A proposed Global Stratotype Section and Point for the base of the Visean Stage (Carboniferous): the Pengchong section, Guangxi, South China, Episodes 26 (2), pp 105–115 The top (the base of the Serpukhovian and Namurian) is laid at the first appearance of the conodont Lochriea,; 2005: Late Visean/early Serpukhovian conodont succession from the Triollo section, Palencia (Cantabrian Mountains, Spain), Scr. Geol. 129, pp 13–89 or at the base of the biozone of goniatite Cravenoceras.

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Biota The Carboniferous-Earliest Permian Biodiversification Event began in the Viséan, coinciding with the start of the main phase of the Late Palaeozoic Ice Age.

The late Viséan saw the widespread reappearance of after their devastation during the Hangenberg event.

One of the that lived during the Visean age was Westlothiana, a reptile-like amphibian. Though originally thought to be the earliest discovered amniote, more recent research has cast doubt on this interpretation.

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Biostratigraphy The Visean contains four conodont biozones:

• Lochriea nodosa Zone
• Lochriea mononodosa Zone
• Gnathodus bilineatus Zone
• Gnathodus texanus Zone

In British stratigraphy, the Visean is subdivided into five substages. From youngest to oldest, these are:; 2006: The Carboniferous system, use of the new official names for the subsystems, series and stages, Geologica Acta 4(3), pp 403–407.

• Brigantian
• Asbian
• Holkerian
• Arundian
• Chadian (the lower part of this substage falls in the Tournaisian)

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Further reading

• ; 1832: Mémoire sur la constitution géologique de la province de Liège, Mémoires couronnés par l'Académie Royale des Sciences et Belles-Lettres de Bruxelles 8 (3), VII.

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External links

• Upper and lower time scales for the Carboniferous at the website of the Norwegian network of offshore records of geology and stratigraphy
• Visean, Geowhen Database
• The Viséan age, www.palaeos.com

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