In the geologic timescale, the Asselian is the earliest geochronology age or lowermost chronostratigraphic stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Asselian lasted between and megaannum. It was preceded by the Gzhelian (the latest or uppermost subdivision in the Carboniferous) and followed by the Sakmarian.
Stratigraphy
The Asselian Stage was introduced into scientific literature in 1954, when the Russian stratigrapher V.E. Ruzhenchev split it off from the
Artinskian. At the time, 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 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]
The base of the Asselian Stage is equivalent to the base of the Cisuralian Series and the Permian System. It is defined as the point in the stratigraphic record where of the conodont Streptognathodus isolatus first appear. The global reference profile for the base (the GSSP) is located in the valley of the Aidaralash, near Aqtöbe in the Ural Mountains of Kazakhstan.[; 1998: Proposal of Aidaralash as Global Stratotype Section and Point (GSSP) for base of the Permian System, Episodes 21(1): pp 11–18.] Other reference species which approximate the base of the Asselian include Streptognathodus invaginatus and Str. nodulinearis (conodonts) and Sphaeroschwagerina vulgaris and Sph. fusiformis (Fusulinida).
The top of the Asselian stage (the base of the Sakmarian stage) is at the first appearance of conodont species Mesogondolella monstra.
Asselian biostratigraphy is mostly defined by the evolution of Streptognathodus. There is some debate over the exact sequence of species; one option, according to Henderson (2018),
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zone of Streptognathodus postfusus / Streptognathodus barskovi
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zone of Streptognathodus fusus
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zone of Streptognathodus constrictus
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zone of Streptognathodus sigmoidalis
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zone of Streptognathodus cristellaris
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zone of Streptognathodus glenisteri
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zone of Streptognathodus isolatus
Regional equivalents
In North America, the regional equivalent of the Asselian is the
Nealian stage. The Nealian (lower
Wolfcampian) is named after the Neal Ranch Formation in the Glass Mountains of west Texas.
In South China, the Asselian is equivalent to at least the lower part of the regional Zisongian stage of the Chuanshanian Series.
Both the Nealian and Zisongian are defined by fusilinid assemblages, so their precise correlation to the conodont-based global timescale is uncertain.
The Asselian occupies a portion of major terrestrial sediment units in Europe, namely the Autunian series of France and the lower Rotliegend of Germany.
Notable formations
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Altenglan Formation (Germany)
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Archer City Formation (Texas, USA)
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Council Grove Group (in part) (Kansas / Nebraska, USA)
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Dunkard Group
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Goldlauter Formation (Germany)
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Manebach Formation (Germany)
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Meisenheim Formation (Germany)
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Muse Formation (France)
External links
