The Katian is the second stage of the

Upper Ordovician The Late Ordovician is the third and final epoch of the Ordovician period, lasting million years and spanning from around 458.2 to 443.1 million years ago. The rocks associated with this epoch are referred to as the Upper Ordovician Series. At ...

. It is preceded by the

Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million ...

and succeeded by the Hirnantian Stage. The Katian began million years ago and lasted for about 7.6 million years until the beginning of the Hirnantian million years ago. During the Katian the climate cooled which started the Late Ordovician glaciation.

Naming

The name Katian is derived from Katy Lake ( Atoka County,

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

, United States).

GSSP

The GSSP of the Katian Stage is the Black Knob Ridge Section in southeastern

(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 First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying the geologically oldest fossil discovered, to date, of a partic ...

of the

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

species '' Diplacanthograptus caudatus''. This horizon is 4.0 m above the base of the Bigfork Chert.

References

. Ordovician geochronology {{ordovician-stub