Katian

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
452.8 ± 0.7 – 445.2 ± 0.9 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Paleogeography of the Katian, 450 Ma
Chronology
−485 — – −480 — – −475 — – −470 — – −465 — – −460 — – −455 — – −450 — – −445 — – P a l e o z o i c Ꞓ O r d o v i c i a n S F E a r l y M i d d l e L a t e L Stage 10 Tremadocian Floian Dapingian Darriwilian Sandbian Katian Hirnantian Rhuddanian       ← First land plant spores[1] ← Ordovician meteor event[2][3] Subdivision of the Ordovician according to the ICS, as of 2024.[4] Vertical axis scale: Millions of years ago
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 / 34.4305; -96.0746
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 / 30.9841; 111.4197
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]