The Floian is the second stage of the
Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
T ...
Period. It succeeds the
Tremadocian with which it forms the
Lower Ordovician epoch. It precedes the
Dapingian Stage of the
Middle Ordovician. The Floian extended from to million years ago. The lower boundary is defined as the
first appearance of the
graptolite species ''
Tetragraptus approximatus''.
Naming and history
The Floian Stage is named after
Flo, a village in
Västergötland
Västergötland (), also known as West Gothland or the Latinized version Westrogothia in older literature, is one of the 25 traditional non-administrative provinces of Sweden (''landskap'' in Swedish), situated in the southwest of Sweden.
Väs ...
, southern
Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic countries, Nordic c ...
. The name "Floan" was proposed in 2004, but the
International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...
adapted Floian as the official name of the stage.
GSSP
The
GSSP of the Floian is the
Diabasbrottet Quarry () which is an outcrop of a shale-dominated stratigraphic succession. The lower boundary of the Floian is defined as the first appearance of ''
Tetragraptus approximatus'' which is above the base of the
Tøyen Shale.
Radiometric dating has set the
Tremadocian-Floian boundary at million years ago.
References
{{Geological history, p, p, state=collapsed
.
Ordovician geochronology