Brain antium

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system series step ≈ age ( mya )
higher higher higher younger
Ordovician Upper Ordovician Brain antium 443.4
⬍
445.2
Katium 445.2
⬍
453
Sandbium 453
⬍
458.4
Middle Ordovician Darriwilium 458.4
⬍
467.3
Dapingium 467.3
⬍
470
Lower Ordovician Floium 470
⬍
477.7
Tremadocium 477.7
⬍
485.4
deeper deeper deeper older

The hirnantian is in the Earth's history the top chronostratigraphic stage of Oberordovizium series and thus of the Ordovician at all. Geochronologically it corresponds roughly to a period of approximately 445.2 to approximately 443.4 million years. The brain antium replaces the katium and is in turn terminated by the rhuddanium , the lowest level of the Silurian .

Naming and history

The Hirnantium is named after the village of Cwm Hirnant near Bala in northern Wales . The name was proposed by John Bevis Beeston Bancroft in 1933.

Definition and GSSP

The lower limit is defined by the first appearance of the graptolite species Normalograptus extraordinarius . It also coincides with the base of a larger positive carbon-13 isotope deviation and the onset of pronounced sea level lowering triggered by the onset of major glaciation. The upper limit (and thus the limit to the Silurian) is defined by the first appearance of the graptolite species Akidograptus ascensus ; only a little later the graptolite species Parakidograptus acuminatus appears for the first time. The northern Wangjiawan profile in Wangjiawan , 42 km north of the city ​​of Yichang ( Hubei Province , China ), was determined as the Global Stratotype Section and Point ( GSSP ) .

literature

  • John Bevis Beeston Bancroft: Correlation tables of the stages Costonian-Onnian in England and Wales. 4 p., Privately published, Blakeney, Gloucestershire 1933.
  • Xu Chen, Jiayu Rong, Junxuan Fan, Renbin Zhan, Charles E. Mitchell, David AT Harper, Michael J. Melchin, Ping'an Peng, Stan C. Finney and Xiaofeng Wang: The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (the uppermost of the Ordovician System). Episodes, 29 (3): 183-196, Beijing 2006 ISSN  0705-3797 PDF .
  • Stig M. Bergström, Stanley C. Finney, Chen Xu, Daniel Goldman and Stephen A. Leslie: Three new Ordovician global stage names. Lethaia, 39: 287-288, Oslo 2006 ISSN  0024-1164 .
  • JT Temple: Upper Ordovician brachiopods from Poland and Britain. Acta Palaeontologica Polonica, 10: 379-450, Warsaw 1965 ISSN  0567-7920 .

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