Telychian
| Telychian | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chronology | |||||||||||||
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| 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 | Just above LAD of the Brachiopod Eocoelia intermedia, below FAD of lowest succeeding species Eocoelia curtisi | ||||||||||||
| Lower boundary GSSP | Cefn-cerig Road Section, Llandovery, Wales, UK 51°58′12″N 3°47′24″W / 51.9700°N 3.7900°W | ||||||||||||
| Lower GSSP ratified | 1984[4] | ||||||||||||
| Upper boundary definition | Imprecise. Currently placed between acritarch biozone 5 and LAD of Pterospathodus amorphognathoides. See Llandovery for more info. | ||||||||||||
| Upper boundary definition candidates | A conodont boundary (Ireviken datum 2) which is close to the murchisoni graptolite biozone. | ||||||||||||
| Upper boundary GSSP candidate section(s) | None | ||||||||||||
| Upper boundary GSSP | Hughley Brook, Apedale, UK 52°34′52″N 2°38′20″W / 52.5811°N 2.6389°W | ||||||||||||
| Upper GSSP ratified | 1980[5] | ||||||||||||
In the geologic timescale, the Telychian is the age of the Llandovery epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 438.5 ± 1.2 Ma and 433.4 ± 0.8 Ma (million years ago), approximately. The Telychian age succeeds the Aeronian age and precedes the Sheinwoodian age.[6] The name of the interval is derived from the Pen-lan-Telych Farm near Llandovery, Powys, Wales.
It ended with the Ireviken event.
Ireviken event
The Ireviken event was the first of three relatively minor extinction events (the Ireviken, Mulde, and Lau events) during the Silurian period. It occurred at the Llandovery/Wenlock boundary (mid Silurian, 433.4 ± 0.8 million years ago). The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species became extinct; 80% of the global conodont species also become extinct in this interval.
Anatomy of the event
The event lasted around 200,000 years, spanning the base of the Wenlock epoch.[2][7]
It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle.[7] The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka.[7] The final two data are much further spaced, so harder to link with Milankovic changes.[7]
Effects
The mechanism responsible for the event originated in the deep oceans, and made its way into the shallower shelf seas. Correspondingly, shallow-water reefs were barely affected, while pelagic and hemipelagic organisms such as the graptolites, conodonts and trilobites were hit hardest.[2]
Geochemistry
Subsequent to the first extinctions, excursions in the δ13C and δ18O records are observed; δ13C rises from +1.4‰ to +4.5‰, while δ18O increases from −5.6‰ to −5.0‰.[2]
Paleontology
Agnathans
| Agnathans of the Telychian | ||||
|---|---|---|---|---|
| Taxa | Presence | Location | Description | Images |
| Jamoytius | Rhuddanian-Telychian | It had an elongated body and a dorsal fin and an anal fin near the back third of its body. |  | |
Cephalopods
| Cephalopods of the Telychian | ||||
|---|---|---|---|---|
| Taxa | Presence | Location | Description | Images |
| Cameroceras | Dapingian-Homerian | The shallow seas of Laurentia, Baltica and Siberia.[8] | Head was soft muscular tissue at the opening of hard cone-like shell. |  |
References
- ^ Jeppsson, L.; Calner, M. (2007). "The Silurian Mulde Event and a scenario for secundo—secundo events". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 93 (02): 135–154. doi:10.1017/S0263593300000377.
- ^ a b c d Munnecke, A.; Samtleben, C.; Bickert, T. (2003). "The Ireviken Event in the lower Silurian of Gotland, Sweden-relation to similar Palaeozoic and Proterozoic events". Palaeogeography, Palaeoclimatology, Palaeoecology. 195 (1): 99–124. doi:10.1016/S0031-0182(03)00304-3.
- ^ "Chart/Time Scale". www.stratigraphy.org. International Commission on Stratigraphy.
- ^ Holland, C. (June 1985). "Series and Stages of the Silurian System". 8 (2): 101–103. doi:10.18814/epiiugs/1985/v8i2/005. Retrieved 15 December 2020.
{{cite journal}}: Cite journal requires|journal=(help) - ^ "GSSP for the Rhuddanian Stage". International Commission on Stratigraphy.
- ^ Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004). A Geologic Time Scale 2004. ISBN 9780521786737.
- ^ a b c d Jeppsson, L (1997). "The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events". In Brett, C.E.; Baird, G.C. (eds.). Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. New York: Columbia University Press. pp. 451–492.
- ^ Frey, R.C. 1995. "Middle and Upper Ordovician nautiloid cephalopods of the Cincinnati Arch region of Kentucky, Indiana, and Ohio" (PDF). U.S. Geological Survey, p.73
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