The Floian is the second stage of the Ordovician. 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 477.7 ± 1.4 to 470.0 ± 1.4 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, southern Sweden. The name "Floan" was proposed in 2004, but the International Commission on Stratigraphy adapted Floian as the official name of the stage.
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 477.7 ± 1.4million years ago.
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- Gradstein, F. M., ed. (2012). The Geologic Time Scale 2012. Elsevier Science Ltd. p. 504. ISBN 978-0444594259.
- "GSSP Table - Paleozoic Era". Geologic TimeScale Foundation. Retrieved 24 November 2012.
- Bergström, Stig M.; Anita Löfgren; Jörg Maletz (2004). "The GSSP of the Second (Upper) Stage of the Lower Ordovician Series: Diabasbrottet at Hunneberg, Province of Västergötland, Southwestern Sweden". Episodes 27 (4): 265–272. Retrieved 20 September 2012.
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