Earth:Tremadocian
| Tremadocian | |
|---|---|
| 485.4 ± 1.9 – 477.7 ± 1.4 Ma | |
| Chronology | |
| Etymology | |
| Name formality | Formal |
| Usage information | |
| Celestial body | Earth |
| Regional usage | Global (ICS) |
| Time scale(s) used | ICS Time Scale |
| Definition | |
| Chronological unit | Age |
| Stratigraphic unit | Stage |
| Time span formality | Formal |
| Lower boundary definition | FAD of the Conodont Iapetognathus fluctivagus. |
| Lower boundary GSSP | Greenpoint section, Green Point, Newfoundland, Canada [ ⚑ ] 49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W |
| GSSP ratified | 2000[1] |
| Upper boundary definition | FAD of the Graptolite Tetragraptus approximatus |
| Upper boundary GSSP | Diabasbrottet quarry, Västergötland, Sweden [ ⚑ ] 58°21′32″N 12°30′09″E / 58.3589°N 12.5024°E |
| GSSP ratified | 2002[2] |
The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from 485.4 to 477.7 million years ago. The base of the Tremadocian is defined as the first appearance of the conodont species Iapetognathus fluctivagus at the Global Boundary Stratotype Section and Point (GSSP) section on Newfoundland.[3]
Naming
The Tremadocian is named after the village Tremadoc in Wales. The name was proposed by Adam Sedgwick in 1846 (as "Tremadoc group").
GSSP
The GSSP for the beginning of the Tremadocian is the Greenpoint section ( [ ⚑ ] 49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W) in Gros Morne National Park, in western Newfoundland. It is defined as the first appearance of the conodont species Iapetognathus fluctivagus. This horizon can be found 101.8 m above the Greenpoint section datum within bed number 23.[3] The boundary lies within the Broom Point Member, of the Green Point Formation which is part of the Cow Head Group.[1] The first planktonic graptolites appear 4.8 m above the first appearance of Iapetognathus fluctivagus at Greenpoint section.[1]
The Tremadocian ends with the beginning of the Floian which is defined as the first appearance of Tetragraptus approximatus at the GSSP in Diabasbrottet quarry, Västergötland, Sweden.[3]
Regional stages
In North America the first stage of the Ordovician is the Gasconadian Stage. In Baltoscandic region the stages corresponding to Tremadocian are Pakerort stage (older) and Varangu stage (younger).
Evolution
The Cambrian Stage 10-Tremadocian boundary is marked by the Cambrian-Ordovician extinction event. It led to the extinction of many brachipods, conodonts and severely reduced the number of trilobite species. Overall the amount of biodiversity of the Cambrian was maintained. The evolutionary radiation that would eventually triple the amount of genera during the Ordovician (the Great Ordovician Biodiversification Event) slowly picks up during the Tremadocian.[4]
Conodonts diversified during the Tremadocian, though not to the same extent as they would in the following Floian.[5] Planktonic graptolites, an important index fossil, appear during the Tremadocian.[1]
The middle of the Tremadocian witnessed an extinction event known as the Mid-Tremadocian Extinction Event[5] or the Base Stairsian Mass Extinction Event,[6] which is particularly known to have affected Baltican conodonts.[5] This extinction event may have been caused by anoxia.[7][8]
Ocean and climate
The Early Ordovician in general was a time of transgression. The climate was slowly cooling throughout the Ordovician.[9]
References
- ↑ 1.0 1.1 1.2 1.3 Cooper, Roger; Nowlan, Godfrey; Williams, S. H. (March 2001). "Global Stratotype Section and Point for base of the Ordovician System". Episodes 24 (1): 19–28. doi:10.18814/epiiugs/2001/v24i1/005. https://stratigraphy.org/gssps/files/tremadocian.pdf. Retrieved 6 December 2020.
- ↑ 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. doi:10.18814/epiiugs/2004/v27i4/005. https://www.researchgate.net/publication/279891211. Retrieved 13 December 2020.
- ↑ 3.0 3.1 3.2 "GSSP Table - Paleozoic Era". Geologic TimeScale Foundation. https://engineering.purdue.edu/Stratigraphy/gssp/index.php?parentid=77.
- ↑ Sepkoski, J. J. (1995). "The Ordovician Radiations: Diversification and Extinction Shown by Global Genus-Level Taxonomic Data". pp. 393–396. http://archives.datapages.com/data/pac_sepm/094/094001/pdfs/393.htm.
- ↑ 5.0 5.1 5.2 Stouge, Svend; Bagnoli, Gabriella; Rasmussen, Jan A. (1 July 2020). "Late Cambrian (Furongian) to mid-Ordovician euconodont events on Baltica: Invasions and immigrations". Palaeogeography, Palaeoclimatology, Palaeoecology 549: 109151. doi:10.1016/j.palaeo.2019.04.007. https://www.sciencedirect.com/science/article/abs/pii/S003101821830302X#!. Retrieved 13 November 2022.
- ↑ Lu, Xinze; Edwards, Cole T.; Kendall, Brian (15 January 2023). "No evidence for expansion of global ocean euxinia during the base Stairsian mass extinction event (Tremadocian, Early Ordovician)". Geochimica et Cosmochimica Acta 341: 116–131. doi:10.1016/j.gca.2022.11.028. https://www.sciencedirect.com/science/article/abs/pii/S0016703722006433. Retrieved 30 December 2022.
- ↑ Edwards, Cole T.; Fike, David A.; Saltzman, Matthew Ross; Lu, Wanyi; Lu, Zunli (1 January 2018). "Evidence for local and global redox conditions at an Early Ordovician (Tremadocian) mass extinction". Earth and Planetary Science Letters 481: 125–135. doi:10.1016/j.epsl.2017.10.002. https://www.researchgate.net/publication/320592024. Retrieved 30 December 2022.
- ↑ Saltzman, Matthew Ross; Edwards, Cole T.; Adrain, Jonathan M.; Westrop, Stephen R. (1 September 2015). "Persistent oceanic anoxia and elevated extinction rates separate the Cambrian and Ordovician radiations". Geology 43 (9): 807–810. doi:10.1130/G36814.1. https://pubs.geoscienceworld.org/gsa/geology/article-abstract/43/9/807/131953/Persistent-oceanic-anoxia-and-elevated-extinction?redirectedFrom=fulltext. Retrieved 30 December 2022.
- ↑ Munnecke, Axel; Calner, Mikael; Harper, David A.T.; Servais, Thomas (1 October 2010). "Ordovician and Silurian sea–water chemistry, sea level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology 296 (3–4): 389–413. doi:10.1016/j.palaeo.2010.08.001. Bibcode: 2010PPP...296..389M.
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