Katian

The Katium is in Earth's history, the second stage of the chronostratigraphic Oberordovizium series of the Ordovician. The level corresponds approximately to the geochronological period of about 453 to about 445.2 million years ago. The Katium following the Sandbium and is in turn replaced by Hirnantium.

Naming and history

The name of the stage stems 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 Stig Bergström.

Definition and GSSP

The lower limit is the first appearance of the graptolite - type Diplacanthograptus caudate. The border coincides with the lower limit of the " Guttenberg carbon isotope excursion -13 " together, a world observed deviation in the C13 isotope ratio. The upper limit is defined by the first appearance of the graptolite - type Normalograptus extraordinarius. It also coincides with the base of a larger positive carbon -13 isotope and the beginning of a distinct deviation sea lowering, which is triggered by the beginning of a larger icing. The official reference profile ( GSSP = " Global Stratotype Section and Point" ) for the Katium is the Black Knob Ridge profile, about 5 km north-east of Atoka (Oklahoma, USA).