Floian

The Floian is the second stage of the Ordovician Period. It succeeds the Tremadocian with which it forms the Lower Ordovician series. It precedes the Dapingian Stage of the Middle Ordovician. The Floian extended from 477.7 to 470 million years ago.[1] The lower boundary is defined as the first appearance of the graptolite species Tetragraptus approximatus.[2]

## Contents

* 1 History and naming
* 2 GSSP
* 3 Regional stages
* 4 Major events
* 5 Paleontology
* 6 References
* 7 External links

## History and naming

The base of this stage was ratified by the International Commission on Stratigraphy (ICS) in 2002. The Floian Stage is named after Flo, a village in Västergötland, southern Sweden. The name "Floan" was proposed in 2004,[3] but the ICS adapted Floian as the official name of the stage.[4]

## GSSP

The GSSP of the Floian is the lower Tøyen Shale in Diabasbrottet Quarry ( [ ⚑ ] 58°21′32″N 12°30′09″E﻿ / ﻿58.3589°N 12.5024°E﻿ / 58.3589; 12.5024) 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 about 2.1 above the Cambrian strata.[3] Radiometric dating has set the Tremadocian-Floian boundary at 477.7 million years ago.[1]

The upper boundary which is also the base of the Dapingian stage is defined as the first appearance of the conodont species Baltoniodus triangularis at the GSSP in the Huanghuachang Section, Hubei Province, China.[5]

## Regional stages

Partial analogues of Floian stage in Baltoscandia are Hunneberg stage (lower) and Billingen stage (upper).[6][7] On the Siberian Platform, Ugorian stage corresponds to Floian.[8]

## Major events

The global Billingen Transgressive Event occurred in the Early Floian age. Black graptolitic argillites of Gorny Altai as well as conglomerates and gritstones of Salair, Russia, possibly correlates with this event.[9]

## Paleontology

Discovered in the Floian strata of Newfoundland, coral-like fossils of Reptamsassia divergens and Reptamsassia minuta are the oldest example of symbiotic intergrowth of modular species. This allows to judge the level of development of reef ecosystems of the Early Ordovician.[10]

Conodonts Serratognathus, Prioniodus and Oepikodus were distributed in Kazakhstan, Korea, China, Indochina and Australasia during the Floian age. Two species of Paroistodus are known from the Floian deposits of Baltoscandia and South China.[11]

Several thousand chemically isolated graptolite specimens including genera Baltograptus and Pseudophyllograptus were collected from the upper Floian sediments of Skattungbyn, Dalarna, central Sweden. Presented mostly by juveniles and isolated siculae, these graptolites inhabited primarily in shallow water environment.[12]

Trilobites of the genera Tsaidamaspis, Zhiyia and Liexiaspis were found in the Floian part of the Duoquanshan Formation, northwest China.[13]

Falloaster anquiroisitus, an asterozoan of problematic classification, is known from the Floian Garden City Formation of Idaho, USA.[14]

## References

1. ↑ 1.0 1.1 "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
2. ↑ "GSSP for Floian Stage". Geologic TimeScale Foundation. https://timescalefoundation.org/gssp/detail.php?periodid=140&top_parentid=77.
3. ↑ 3.0 3.1 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. https://timescalefoundation.org/references/Floian.pdf. Retrieved 2024-04-20.
4. ↑ Stig M. Bergström, Stanley Finney, Chen Xu, Daniel Goldman, Stephen A. Leslie (2006). "Three new Ordovician global stage names". Lethaia 39 (4): 287–288. doi:10.1080/00241160600847439. https://www.idunn.no/doi/pdf/10.1080/00241160600847439.
5. ↑ "GSSP for Dapingian Stage". Geologic TimeScale Foundation. https://timescalefoundation.org/gssp/detail.php?periodid=138&top_parentid=77.
6. ↑ Helje Pärnaste, Viive Viira (2012). "On the lower boundary of the Floian Stage in Estonia". Estonian Journal of Earth Sciences 61 (2): 205–209. doi:10.3176/earth.2012.4.02. https://www.researchgate.net/publication/258439672.
7. ↑ "Ordovician of the Baltic". https://paleobiodb.org/classic/displayTimescale?scale=180.
8. ↑ V. E. Pavlov, Andrei Dronov, Alexander Larionov, Tatiana Yu. Tolmacheva (2022). Magnetostratigraphic Constraints on the Position of the Tremadocian–Floian Boundary at the Key Section of the Moyero River Valley (Siberian Platform) [In book: Problems of Geocosmos–2020]. Springer Nature. p. 107–114. doi:10.1007/978-3-030-91467-7. ISBN 978-3-030-91467-7. https://www.researchgate.net/publication/358137383.
9. ↑ N. V. Sennikov, O. T. Obut, E. V. Lykova, A. V. Timokhin, R. A. Khabibulina, T. A. Shcherbanenko (2021). "Event Stratigraphy and Correlation Problems of the Ordovician strata of Gorny Altai and Salair" (in ru). Geodynamics & Tectonophysics 12 (2): 246—260. doi:10.5800/GT-2021-12-2-0523. https://www.gt-crust.ru/jour/article/view/1209/550.
10. ↑ Dong-Jin Lee, Robert Elias, Brian R. Pratt (2022). "Reptamsassia n. gen. (Amsassiaceae n. fam.; calcareous algae) from the Lower Ordovician (Floian) of western Newfoundland, and the earliest symbiotic intergrowth of modular species". Journal of Paleontology 96 (3): 1—14. doi:10.1017/jpa.2021.122. https://www.researchgate.net/publication/358188752.
11. ↑ Yong Yi Zhen, Ian G. Percival, Yuan-Dong Zhang (2014). "Floian (Early Ordovician) conodont-based biostratigraphy and biogeography of the Australasian Superprovince". Palaeoworld 24 (1-1): 100–109. doi:10.1016/j.palwor.2014.10.011. https://www.researchgate.net/publication/268526802.
12. ↑ Jörg Maletz (2022). "Roland Skoglund’s late Floian graptolites from Dalarna, central Sweden". Historical Biology 35 (9): 1583-1604. doi:10.1080/08912963.2022.2104642.
13. ↑ Xin Wei, Zhiqiang Zhou (2023). "Floian, Early Ordovician trilobites from the Olongbluk Terrane, northwest China". Acta Palaeontologica Polonica 68. doi:10.4202/app.01102.2023. https://www.researchgate.net/publication/376577519.
14. ↑ Daniel B. Blake, Forest J. Gahn, Thomas E. Guensburg (2019). "An Early Ordovician (Floian) asterozoan (Echinodermata) of problematic class-level affinities". Journal of Paleontology 94 (2): 1-8. doi:10.1017/jpa.2019.82.

## External links

* "GSSP for base of the Floian Stage in the Diabasbrottet section, Mt Hunneberg, Sweden, with stratigraphic ranges of graptolites and conodonts" (in en). https://timescalefoundation.org/gssp/image.php?periodid=140&top_parentid=77&imageid=382.
* "GSSP Table - Paleozoic Era" (in en). https://timescalefoundation.org/gssp/index.php?parentid=77.
* "Floian" (in en). Subcommission on Ordovician Stratigraphy. https://ordovician.stratigraphy.org/floian.

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