|477.7 ± 1.4 – 470.0 ± 1.4 Ma|
|Regional usage||Global (ICS)|
|Time scale(s) used||ICS Time Scale|
|Time span formality||Formal|
|Lower boundary definition||FAD of the Graptolite Tetragraptus approximatus|
|Lower boundary GSSP||Diabasbrottet quarry, Västergötland, Sweden|
|Upper boundary definition||FAD of the Conodont Baltoniodus triangularis|
|Upper boundary GSSP||Huanghuachang section, Huanghuachang, Yichang, China|
The Floian is the second stage of the Ordovician geologic 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 477.7 to 470 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 million years ago.
|Agnathans of the Floian|
|Tremadocian-Floian||Stairway Sandstone, Alice Springs, Australia|
|Cephalopods of the Tremadocian|
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- Lindskog, A.; Costa, M. M.; Rasmussen, C.M.Ø.; Connelly, J. N.; Eriksson, M. E. (2017-01-24). "Refined Ordovician timescale reveals no link between asteroid breakup and biodiversification". Nature Communications. 8: 14066. doi:10.1038/ncomms14066. ISSN 2041-1723. PMC 5286199. PMID 28117834.
It has been suggested that the Middle Ordovician meteorite bombardment played a crucial role in the Great Ordovician Biodiversification Event, but this study shows that the two phenomena were unrelated
- "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
- Bergström, M.; Löfgren, Anita; Maletz, Jörg (December 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 13 December 2020.
- Chen, Xu; Bergström, Stig; Zhang, Yuan-Dong; Fan, Jun-Xuan (2009). "The base of the Middle Ordovician in China with special reference to the succession at Hengtang near Jiangshan, Zhejiang Province, southern China" (PDF). Lethaia. 42: 218–231. doi:10.1111/j.1502-3931.2008.00148.x. Retrieved 13 December 2020.
- "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" (PDF). Episodes. 27 (4): 265–272. Retrieved 20 September 2012.