Telychian
{{short description|Third stage of the Silurian and last stage of the Llandovery}}
{{Infobox geologic timespan
| name = Telychian
| color = Telychian
| time_start = 438.5
| time_start_uncertainty = 1.1
| time_end = 433.4
| time_end_uncertainty = 0.8
| image_map = Silurian plate tectonics.png
| caption_map = Paleogeography of the Telychian, 435 Ma
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| timeline = Silurian
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| name_formality = Formal
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| celestial_body = earth
| usage = Global (ICS)
| timescales_used = ICS Time Scale
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| chrono_unit = Age
| strat_unit = Stage
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| timespan_formality = Formal
| lower_boundary_def = FAD of the graptolite Spirograptus guerichi
| lower_gssp_location = El Pintado section,
| lower_gssp_coords = {{Coord|37.9853|N|5.9285|W|display=inline}}{{cite web |title=Global Boundary Stratotype Section and Point |url=https://stratigraphy.org/gssps/ |publisher=International Commission of Stratigraphy |access-date=3 August 2024}}
| lower_gssp_accept_date = 2024{{cite journal |last1=Gutierrez-Marco |first1=Juan Carlos |title=Silurian Treasures in Spanish UNESCO Global Geoparks |journal=Silurian Times |volume=29 |pages=16–21 |date=2021 |doi=10.13140/RG.2.2.13314.15044 |url=https://silurian.stratigraphy.org/files/SilurianTimes29.pdf}}{{cite web |title=Silurian Telychian and Aeronian stage GSSPs have been relocated |url=https://stratigraphy.org/news/151 |website=stratigraphy.org |publisher=International Commission on Stratigraphy |access-date=1 March 2024}}
| upper_boundary_def = Imprecise. Currently placed between acritarch biozone 5 and LAD of Pterospathodus amorphognathoides. See Llandovery for more info.
| upper_gssp_candidates = None
| upper_def_candidates = A conodont boundary (Ireviken datum 2) which is close to the murchisoni graptolite biozone.
| upper_gssp_location = Hughley Brook, Apedale, UK
| upper_gssp_coords = {{Coord|52.5811|N|2.6389|W|display=inline}}
| upper_gssp_accept_date = 1980{{cite journal |last1=Holland |first1=C. |title=The State of Silurian Stratigraphy |journal=Episodes |date=1982 |volume=1982 |pages=21-23 |url=https://stratigraphy.org/gssps/files/sheinwoodian-ludfordian.pdf |access-date=11 December 2020}}
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In the geologic timescale, the Telychian is the third and final age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon. The Telychian Age was between 438.5 ± 1.2 million years ago (Ma) and 433.4 ± 0.8 Ma. The Telychian Age succeeds the Aeronian Age and precedes the Sheinwoodian Age.{{cite book |isbn=9780521786737|title=A Geologic Time Scale 2004|last1=Gradstein|first1=Felix M.|last2=Ogg|first2=James G.|last3=Smith|first3=Alan G.|year=2004}} 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
{{main|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, {{Ma|Wenlock|{{period start error|Wenlock}} 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.