|Subdivision of the Permian system|
according to the ICS, as of 2017.
In the geologic timescale, the Asselian is the earliest geochronologic age or lowermost chronostratigraphic stage of the Permian. It is a subdivision of the Cisuralian epoch or series. The Asselian lasted between 298.9 and 295 million years ago (Ma). It was preceded by the Gzhelian (the latest or uppermost subdivision in the Carboniferous) and followed by the Sakmarian.
The Asselian stage was introduced into scientific literature in 1954, when the Russian stratigrapher V.E. Ruzhenchev split it from the Artinskian. At that moment the Artinskian still encompassed most of the lower Permian - its current definitions are more restricted. The Asselian is named after the Assel River in the southern Ural Mountains of Kazakhstan and Bashkortostan.
The base of the Asselian stage is at the same time the base of the Cisuralian series and the Permian system. It is defined as the place in the stratigraphic record where fossils of the conodont Streptognathodus isolatus first appear. The global reference profile for the base (the GSSP or golden spike) is located in the valley of the Aidaralash River, near Aqtöbe in the Ural Mountains of Kazakhstan. The top of the Asselian stage (the base of the Sakmarian stage) is at the first appearance of conodont species Streptognathodus postfusus.
The Asselian contains five conodont biozones:
- zone of Streptognathodus barskovi
- zone of Streptognathodus postfusus
- zone of Streptognathodus fusus
- zone of Streptognathodus constrictus
- zone of Streptognathodus isolatus
|Amphibians of the Asselian|
|Boskovice Furrow, Czech Republic|
|Abo Formation, New Mexico and Seymour, Baylor County, Texas|
|Synapsids of the Asselian|
|Les Télots, Margennem, Autun, France|
|locality 3, Cutler Formation, San Miguel County, Colorado, USA|
|Kasimovian-Asselian||Ludwikowice Formation, Nowa Ruda, Poland|
||H. baylei: Les Télots, Autun, France
||Haptodus grandis may require its own genus.|
Kenilworth, Kenilworth Sandstone Formation, Warwickshire Group, Warwickshire, England; Autun, France, Cutler Formation, Arizona, Colorado, New Mexico and Utah; Fort riley, Chase Group, Kansas, Green Formation, Dunkard Group, Ohio; Wellington Formation, Oklahoma; Clyde Formation, Texas and Oklahoma; Admiral Formation; Belle-Plains Formation; Wichita Group, all three in Texas,
|Königin-Carola-Schacht locality, Dresden , Döhlen Formation, lower Rotliegend Group, Döhlen Basin, Saxony, Germany|
|Gzhelian-Artinskian||New Mexico; Utah-Arizona border region; possibly England||The English specimen known as S?. brittanicus ) is now generally classified as Sphenacodontidae incertae sedis separate from the other Sphenacodon species so may need reassigning.|
- "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
- Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press
- The Nonmarine Permian: Volume 30 of Bulletin of the New Mexico Museum of Natural History and Science, page 48. Editors Spencer G. Lucas, Kate E. Zeigler, 2005
- Davydov, V.I.; Glenister, B.F.; Spinosa, C.; Ritter, S.M.; Chernykh, V.V.; Wardlaw, B.R. and Snyder, W.S.; 1998: Proposal of Aidaralash as Global Stratotype Section and Point (GSSP) for base of the Permian System, Episodes 21(1): pp 11–18.