Katian
Second stage of the Upper Ordovician
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The Katian is the second stage of the Upper Ordovician. It is preceded by the Sandbian and succeeded by the Hirnantian Stage. The Katian began 452.8 million years ago and lasted for about 7.6 million years until the beginning of the Hirnantian 445.2 million years ago.[7] During the Katian the climate cooled which started the Late Ordovician glaciation.
| Katian | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Paleogeography of the Katian, 450 Ma | |||||||||||
| Chronology | |||||||||||
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| Etymology | |||||||||||
| Name formality | Formal | ||||||||||
| Usage information | |||||||||||
| Celestial body | Earth | ||||||||||
| Regional usage | Global (ICS) | ||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||
| Definition | |||||||||||
| Chronological unit | Age | ||||||||||
| Stratigraphic unit | Stage | ||||||||||
| Time span formality | Formal | ||||||||||
| Lower boundary definition | FAD of the graptolite Diplacanthograptus caudatus | ||||||||||
| Lower boundary GSSP | Black Knob Ridge section, Oklahoma, United States 34.4305°N 96.0746°W | ||||||||||
| Lower GSSP ratified | 2006[5] | ||||||||||
| Upper boundary definition | FAD of the graptoliteNormalograptus extraordinarius | ||||||||||
| Upper boundary GSSP | Wangjiawan section, Wangjiawan, Yichang, China 30.9841°N 111.4197°E | ||||||||||
| Upper GSSP ratified | 2006[6] | ||||||||||
Naming
The name Katian is derived from Katy Lake (Atoka County, Oklahoma, United States).[8]
GSSP
The GSSP of the Katian Stage is the Black Knob Ridge Section in southeastern Oklahoma (United States). It is an outcrop of the Womble Shale and the Bigfork Chert, the latter containing the lower boundary of the Katian. The lower boundary is defined as the first appearance datum of the graptolite species Diplacanthograptus caudatus. This horizon is 4.0 m above the base of the Bigfork Chert.[9][10]