Tremadocian

The Tremadocian is named after the village Tremadoc in Wales. The name was proposed by Adam Sedgwick in 1846 (as "Tremadoc group").

The GSSP for the beginning of the Tremadocian is the Green Point section ({{Coord|49.6829|N|57.9653|W|display=inline}}) 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.{{cite web|url=https://timescalefoundation.org/gssp/detail.php?periodid=141&top_parentid=77|title=GSSP for Tremadocian Stage|website=timescalefoundation.org|language=en|archive-url=https://web.archive.org/web/20240404223916/https://timescalefoundation.org/gssp/detail.php?periodid=141&top_parentid=77|archive-date=2024-04-04|url-status=live}} The boundary lies within the Broom Point Member, of the Green Point Formation which is part of the Cow Head Group. The first planktonic graptolites appear 4.8 m above the first appearance of Iapetognathus fluctivagus at Greenpoint section.

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.{{cite web|url=https://timescalefoundation.org/gssp/detail.php?periodid=140&top_parentid=77|title=GSSP for Floian Stage|website=timescalefoundation.org|language=en|archive-url=https://web.archive.org/web/20240404223914/https://timescalefoundation.org/gssp/detail.php?periodid=140&top_parentid=77|archive-date=2024-04-04|url-status=live}}

In 2015, the Lawson Cove section in Millard County, Utah, was proposed as an Auxiliary boundary Stratotype Section and Point (ASSP) for the Tremadocian stage and Ordovician system. In addition to the first appearance datum of I. fluctivagus, fossils of olenid trilobite Jujuyaspis and planktonic graptolite Anisograptus matanensis are present in a nearby section.{{cite journal|author=James Frederick Miller, Kevin Ray Evans, Rahymond Lindsay Ethington, Rebecca L. Freeman, James Loch, John E. Repetski, Robert L. Ripperdan, John F. Taylor|year=2015|title=Proposed Auxiliary Boundary Stratigraphic Section and Point (ASSP) for the base of the Ordovician System at Lawson Cove, Utah, USA|journal=Stratigraphy|volume=12|issue=3|pages=219–236|doi=10.29041/strat.12.4.02|language=en}} In 2017,{{cite web|author=Ian G. Percival|year=2017|url=https://ordovician.stratigraphy.org/files/Ordovician_News_2017.pdf#page=4|title=Ordovician News Number 35|publisher=Subcommission on Ordovician Stratigraphy|page=4|language=en|archive-url=https://web.archive.org/web/20231024203351/https://ordovician.stratigraphy.org/files/Ordovician_News_2017.pdf#page=4|archive-date=2023-10-24|url-status=live}} the Xiaoyangqiao section near the Dayangcha Village, North China, was proposed as the second ASSP for the base of Tremadocian/Lower Ordovician. The first planktonic graptolites can be found right below the Cordylodus lindstromi Conodont Zone in this section.{{cite journal|author=Xiaofeng Wang, Svend Stouge, Jörg Maletz, Gabriella Bagnoli, Yuping. Qi, Elena G. Raevskaya, Chuanshang Wang, Chunbo Yan|year=2021|title=The Xiaoyangqiao section, Dayangcha, North China: the new global Auxiliary Boundary Stratotype Section and Point (ASSP) for the base of the Ordovician System|journal=Episodes|volume=44|issue=4|pages=359–383|doi=10.18814/epiiugs/2020/020091|doi-access=free |language=en}} Both ASSPs were approved through supermajority vote by the Subcommission on Ordovician

Stratigraphy in 2016 and 2019, respectively. However, in 2021, the International Union of Geological Sciences (IUGS) proposed to deny the use of specific points and replace them by Standard Auxiliary Boundary Stratotypes (SABS) for more "flexible" correlations with GSSPs.{{cite journal|author=Martin J. Head, Marie-Pierre Aubry, Werner E. Piller, Mike Walker|year=2023|url=https://pure.aber.ac.uk/ws/portalfiles/portal/64951362/IUGS046_01_35.pdf|title=The Standard Auxiliary Boundary Stratotype: a proposed replacement for the Auxiliary Stratotype Point in supporting a Global boundary Stratotype Section and Point (GSSP)|journal=Episodes|volume=46|issue=1|page=35—45|doi=10.18814/epiiugs/2022/022012|doi-access=free |access-date=2024-05-06|language=en|archive-url=https://web.archive.org/web/20240202012850/https://pure.aber.ac.uk/ws/portalfiles/portal/64951362/IUGS046_01_35.pdf|archive-date=2024-02-02|url-status=live}}

In North America the first stage of the Ordovician is the Gasconadian Stage.{{cite web|url=https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1208&context=kgs_mc|title=Kentucky Stratigraphy With Stage Correlations|publisher=University of Kentucky|archive-url=https://web.archive.org/web/20240416105805/https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1208&context=kgs_mc|archive-date=2024-04-16|url-status=live}} In the Baltic region, the stages corresponding to Tremadocian are the Pakerort stage (lower) and the Varangu stage (upper).{{cite journal|author=Paškevičius, Juozas|year=2007|url=https://epublications.vu.lt/object/elaba:6171925/6171925.pdf|title=Correlation of the Ordovician regional stages of the Baltic palaeobasin with new global stages|journal=Geologija|volume=|issue=57|pages=30–36|issn=1392-110X|language=en|archive-url=https://web.archive.org/web/20240416112357/https://epublications.vu.lt/object/elaba:6171925/6171925.pdf|archive-date=2024-04-16|url-status=live}}{{cite web|url=https://paleobiodb.org/classic/displayTimescale?scale=180|title=Ordovician of the Baltic|website=Paleobiology Database|access-date=2024-04-20|archive-url=https://web.archive.org/web/20240416113415/https://paleobiodb.org/classic/displayTimescale?scale=180|archive-date=2024-04-16|url-status=live}}

The Cambrian-Tremadocian boundary is marked by the Cambrian-Ordovician extinction event. Overall the amount of biodiversity of the Cambrian was maintained.{{cite web|last=Sepkoski|first=J. J.|title=The Ordovician Radiations: Diversification and Extinction Shown by Global Genus-Level Taxonomic Data|year=1995|pages=393–396 |url=http://archives.datapages.com/data/pac_sepm/094/094001/pdfs/393.htm|access-date=2024-04-20|language=en|archive-url=https://archives.datapages.com/data/pac_sepm/094/094001/pdfs/393.htm|archive-date=2022-10-04|url-status=live}} At the beginning of the Tremadocian, about 485.4 million years ago, biodiversity, which had been at a low level, began its long increase phase, known as the Great Ordovician Biodiversification Event.{{cite journal|author=Yiying Deng, Junxuan Fan, Shengchao Yang, Yukun Shi, Zhengbo Lu, Huiqing Xu, Zongyuan Sun, Fangqi Zhao, Zhangshuai Hou|year=2023|url=https://www.researchgate.net/publication/369096101|title=No Furongian Biodiversity Gap: Evidence from South China|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=618|issue=1|page=111492|doi=10.1016/j.palaeo.2023.111492|language=en}}

At the Furongian‒Tremadocian boundary, a mantle plume event occurred on the territory of the northwestern Gondwana, which is now the Iberian Peninsula. Ollo de Sapo magmatic event continued in this region further into Ordovician.{{cite journal|author=Josep Maria Casas, J. Brendan Murphy, Teresa Sanchez-Garcia, Jacques de Poulpiquet, José-Javier Alvaro, A. Díez-Montes, Joan Guimerà|year=2023|url=https://www.researchgate.net/publication/374674894|title=Does the Ollo de Sapo magmatic event support Furongian-Tremadocian mantle plume activity fringing NW Gondwana?|journal=International Geology Review|volume=66 |issue=10 |pages=1956–1970 |doi=10.1080/00206814.2023.2263787|language=en}}

Several global events are observed in sediments of the Tremadocian age: the Acerocare Regressive Event, Black Mountain Transgressive Event (both in the Early Tremadocian), Peltocare Regressive Event, Kelly Creek Regressive Event, and Ceratopyge Regressive Event (the last two in the Late Tremadocian).{{cite journal|author1=N. V. Sennikov|author2=O. T. Obut|author3=E. V. Lykova|author4=A. V. Timokhin|author5=R. A. Khabibulina|author6=T. A. Shcherbanenko|year=2021|url=https://www.gt-crust.ru/jour/article/view/1209/550|title=Event Stratigraphy and Correlation Problems of the Ordovician strata of Gorny Altai and Salair|journal=Geodynamics & Tectonophysics|volume=12|issue=2|page=246—260|doi=10.5800/GT-2021-12-2-0523|language=ru|doi-access=free}} Lithological features of the Black Mountain event are observed in Australia and Gorny Altai, Russia. The Ceratopyge Regressive Event records in Baltica at the end of the Apatokephalus serratus zone. Above the disappearance of Ceratopyge fauna, sediments are presented in a more depleted form due to the decreased sea level in the Late Tremadocian.{{cite web|author=Frisk, Åsa|year=2004|url=https://uu.diva-portal.org/smash/record.jsf?pid=diva2%3A95377&dswid=7475|title=Trilobite biostratigraphy of the Tremadoc Bjørkåsholmen Formation on Öland, Sweden (WOGOGOB-2004 Conference materials)|publisher=Uppsala University|language=en|archive-url=https://web.archive.org/web/20240506143104/https://uu.diva-portal.org/smash/record.jsf?pid=diva2%3A95377&dswid=7346|archive-date=2024-05-06|url-status=live}}

The middle of the Tremadocian witnessed an extinction event known as the Mid-Tremadocian Extinction Event or the Base Stairsian Mass Extinction Event,{{cite journal |last1=Lu |first1=Xinze |last2=Edwards |first2=Cole T. |last3=Kendall |first3=Brian |date=15 January 2023 |title=No evidence for expansion of global ocean euxinia during the base Stairsian mass extinction event (Tremadocian, Early Ordovician) |url=https://www.sciencedirect.com/science/article/abs/pii/S0016703722006433 |journal=Geochimica et Cosmochimica Acta |volume=341 |pages=116–131 |doi=10.1016/j.gca.2022.11.028 |s2cid=254361718 |access-date=2024-04-15|url-access=subscription }} which is particularly known to have affected Baltican conodonts.{{cite journal |last1=Stouge |first1=Svend |last2=Bagnoli |first2=Gabriella |last3=Rasmussen |first3=Jan A. |date=1 July 2020 |title=Late Cambrian (Furongian) to mid-Ordovician euconodont events on Baltica: Invasions and immigrations |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821830302X#! |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=549 |page=109151 |doi=10.1016/j.palaeo.2019.04.007 |s2cid=146630424 |access-date=2024-04-15|url-access=subscription }} This extinction event may have been caused by anoxia.{{cite journal |last1=Edwards |first1=Cole T. |last2=Fike |first2=David A. |last3=Saltzman |first3=Matthew Ross |last4=Lu |first4=Wanyi |last5=Lu |first5=Zunli |date=1 January 2018 |title=Evidence for local and global redox conditions at an Early Ordovician (Tremadocian) mass extinction |url=https://www.researchgate.net/publication/320592024 |journal=Earth and Planetary Science Letters |volume=481 |pages=125–135 |doi=10.1016/j.epsl.2017.10.002 |access-date=2024-04-15|doi-access=free }}{{cite journal |last1=Saltzman |first1=Matthew Ross |last2=Edwards |first2=Cole T. |last3=Adrain |first3=Jonathan M. |last4=Westrop |first4=Stephen R. |date=1 September 2015 |title=Persistent oceanic anoxia and elevated extinction rates separate the Cambrian and Ordovician radiations |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/43/9/807/131953/Persistent-oceanic-anoxia-and-elevated-extinction?redirectedFrom=fulltext |journal=Geology |volume=43 |issue=9 |pages=807–810 |doi=10.1130/G36814.1 |access-date=2024-04-15|url-access=subscription }}

Planktonic graptolites, an important index fossil, appear during the Tremadocian. Tremadocian cephalopods were not very different from their Cambrian predecessors. Specimens of Ellesmeroceras and possibly Bassleroceras, found in Santa Rosita Formation, northwestern Argentina, show that cephalopods first migrated to the waters off western Gondwana already in the early Tremadocian. In the middle Tremadocian, cephalopods became more diverse and occupied new ecological niches.{{cite journal|author=Marcela Cichowolski, N. Emilio Vaccari, Alexander Pohle, Daniel Andres Morón-Alfonso, Romain Vaucher, Beatriz G. Waisfeld|year=2023|url=https://www.researchgate.net/publication/376415649|title=Early Tremadocian cephalopods from Santa Rosita Formation in NW Argentina: the oldest record for South America|journal=Acta Palaeontologica Polonica|volume=68|issue=4|pages=583–601|doi=10.4202/app.01103.2023|language=en}} During Tremadocian there was an exchange of fauna between Avalonia and Gondwana across the Rheic Ocean, as evidenced by the findings of morphologically similar trilobites of the genus Platypeltoides in Belgium, Wales (both were parts of Avalonia) and Morocco (Gondwana).{{cite journal|author=Lukáš Laibl, Thomas Servais, Bernard Mottequin|year=2023|url=https://www.researchgate.net/publication/372942815|title=Tremadocian (Ordovician) trilobites from the Brabant Massif (Belgium): Palaeogeographical and palaeoecological implications|journal=Geobios|volume=81|issue=|pages=7–16|doi=10.1016/j.geobios.2023.04.003|language=en}}

{{Further|Ordovician#Climate_and_sea_level}}

The Early Ordovician in general was a time of transgression. The climate was slowly cooling throughout the Ordovician.{{cite journal|last=Munnecke|first=Axel|author2=Calner, Mikael |author3=Harper, David A.T.| author-link3 = David Harper (palaeontologist) |author4= Servais, Thomas |title=Ordovician and Silurian sea–water chemistry, sea level, and climate: A synopsis|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|date=1 October 2010|volume=296|issue=3–4|pages=389–413|doi=10.1016/j.palaeo.2010.08.001|bibcode=2010PPP...296..389M }}

{{Reflist}}

• {{cite web|url=https://timescalefoundation.org/gssp/image.php?periodid=141&top_parentid=77&imageid=427|title=GSSP for base of the Ordovician (base of Tremadocian Stage) at the Green Point section, Newfoundland, eastern Canada|website=timescalefoundation.org|language=en|archive-url=https://web.archive.org/web/20240404223914/https://timescalefoundation.org/gssp/image.php?periodid=141&top_parentid=77&imageid=427|archive-date=2024-04-04|url-status=live}}
• {{cite web|title=GSSP Table - Paleozoic Era|url=https://engineering.purdue.edu/Stratigraphy/gssp/index.php?parentid=77|language=en|archive-url=https://web.archive.org/web/20231008002417/https://timescalefoundation.org/gssp/index.php?parentid=77|archive-date=2023-10-08|url-status=live}}
• {{cite web|url=http://www.palaeontology.geo.uu.se/ISCS/ISCS_GSSPs.html#Ordovician_System|title=GSSPs - The Cambrian System 2019: Ordovician System, Lower Ordovician Series and Tremadocian Stage|publisher=International Commission on Stratigraphy|language=en|archive-url=https://web.archive.org/web/20230721165125/http://www.palaeontology.geo.uu.se/ISCS/ISCS_GSSPs.html#Ordovician_System|archive-date=2023-07-21|url-status=live}}
• {{cite web|url=https://ordovician.stratigraphy.org/tremadocian|title=Tremadocian|publisher=Subcommission on Ordovician Stratigraphy|language=en|archive-url=https://web.archive.org/web/20210618074338/https://ordovician.stratigraphy.org/tremadocian|archive-date=2021-06-18|url-status=live}}

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Category:Ordovician geochronology