Katium

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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 Katium is the second chronostratigraphic level of the Upper Ordovician series of the Ordovician in the history of the earth . Geochronologically, the stage corresponds roughly to the period from around 453 to around 445.2 million years ago. The Katium follows the Sandbium and is in turn replaced by the Hirnantium .

Naming and history

The name of the stage comes from the now dry Lake Katy ( Oklahoma , USA ), which was only about 2 km southwest of the GSSP. It was proposed in 2006 by a group of scientists led by Stig Bergström .

Definition and GSSP

The lower limit is the first appearance of the graptolite species Diplacanthograptus caudatus . The limit also coincides with the lower limit of the "Guttenberg carbon-13 isotope excursion", a deviation in the C13 isotope ratio that can be observed worldwide. The upper 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 official reference profile (GSSP = "global boundary stratotype section and point") for the katian is the Black Knob Ridge profile, about 5 km northeast of Atoka ( Oklahoma , USA ).

literature

  • Stig M. Bergström, Stanley C. Finney, Chen Xu, Daniel Goldman and Stephen A. Leslie: Three new Ordovician global stage names. In: Lethaia. 39: 287-288, Oslo 2006, ISSN  0024-1164 .
  • Felix Gradstein, Jim Ogg and Alan Smith: A Geologic timescale. Cambridge University Press 2004, ISBN 978-0-521-78673-7 .

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