[7] During the Katian the climate cooled which started the Late Ordovician glaciation.

The name Katian is derived from Katy Lake (Atoka County, Oklahoma, United States).

[8] 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.