Early Ordovician
Early/Lower Ordovician | |
---|---|
Baltoniodus triangularis | |
Upper boundary GSSP | Huanghuachang section, Huanghuachang, Yichang, China 30°51′38″N 110°22′26″E / 30.8605°N 110.3740°E |
Upper GSSP ratified | 2007[6] |
Atmospheric and climatic data | |
Mean atmospheric O2 content | c. 11.5 vol % (55 % of modern) |
The Early Ordovician is the first
History
Definition
The Global Boundary Stratotype Section and Point (GSSP) of the Lower Ordovician, which is also a GSSP of the Tremadocian stage and the whole Ordovician system, is established in the Green Point section in the west of the Newfoundland, Canada (49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W) and corresponds to the first appearance datum (FAD) of the conodont Iapetognathus fluctivagus at the 101.8 m above the base of the outcrop. Doubts have been expressed about the identification of the index taxon, but it occurs below the Rhabdinopora and related graptolites.[13] The GSSP of the Floian, the second and last stage of the Lower Ordovician, is established in the Diabasbrottet Quarry, Sweden, (58°21′32″N 12°30′09″E / 58.3589°N 12.5024°E) and defined by FAD of the graptolite Tetragraptus approximatus.[14][13]
Two Auxiliary boundary Stratotype Sections and Points (ASSPs) were also established for the Lower Ordovician/Tremadocian: the first one in the Lawson Cove section in
Biostratigraphy
The global stages of the Lower Ordovician, as well as of other series, are also subdivided into stage slices (time slices), which are corresponding to the base of conodont or graptolite zones. In addition to the global stages, the Tetragraptus approximatus Zone is also defined in the regional subdivisions of the UK and Australia, and the Didymograptus protobifidus Zone in those of North America, Australia and Baltoscandia.[11]
Conodont (c) and graptolite (g) zones of the Lower Ordovician:[11] | ||
---|---|---|
Series | Stage (ICS) | Stage slice |
Lower Ordovician
|
Floian | Didymograptus protobifidus Zone (g) |
Oepikodus evae Zone (c) | ||
Tetragraptus approximatus Zone (g) | ||
Tremadocian | Paroistodus proteus Zone (c) | |
Paltodus deltifer Zone (c) | ||
Iapetognathus fluctivagus Zone (c) |
North America
The following conodont zones are distinguished in Early Ordovician deposits of Boothia Peninsula, Canada (from upper to lower):[17]
- Oepikodus communis and Reutterodus andinus (Ship Point Formation, Floian);
- Rossodus manitouensis and Acodus deltatus/Oneotodus costatus (upper part of Turner Cliffs Formation, Tremadocian);
- Cordylodus angulatus (lower part of Turner Cliffs, Tremadocian).
Asia
Graptolite (g) and conodont (c) zonal subdivisions of southern Siberia (from upper to lower):[10][18]
- Ps. angustifolius elongatus/E. broggeri (g), D. protobifidus (g), Ph. densus (g), upper part of Oepikodus evae (c), plus chitinozoan Conochitina raymondi Zone (Floian);
- Lower part of Ph. densus (g), Ac. balticus (g), lower part of Oepikodus evae (c) (Floian);
- T. approximatus (g), upper part of Paroistodus proteus (c) (Floian);
- Lower part of Paroistodus proteus (c) (Tremadocian);
- K. kiaeri/Ad. tenellus (g), B. ramosus/Tr. osloensis/Al. hyperboreus (g) (Tremadocian);
- Iapetognathus fluctivagus (c) (Tremadocian).
Australia
On the Australian scale, the global Lower Ordovician roughly corresponds to the Lancefieldian, Bendigonian, Chewtonian and lower Castlemainian stages.[19]
Approximate correlation of graptolite (g) and conodont (c) zones of New South Wales:[19] | ||
---|---|---|
Series | Australian stage | Zone |
Lower Ordovician
|
Castlemainian (lower part) | Isograptus victoriae lunatus (g), upper part of Oepikodus evae (c) |
Chewtonian | Isograptus primulus (g), Oepikodus evae (c) | |
Didymograptus protobifidus (g), Oepikodus evae (c) | ||
Bendigonian | Upper part of Pendeograptus fruticosus (g), lowermost Oepikodus evae (c) | |
Lower parts of Pendeograptus fruticosus (g), uppermost Prioniodus elegans (c) | ||
Pendeograptus fruticosus (g), Prioniodus elegans (c) | ||
Lancefieldian | Uppermost Tetragraptus approximatus (g), lowermost Prioniodus elegans (c) | |
Lower part of Tetragraptus approximatus (g), uppermost Paroistodus proteus (c) | ||
Araneograptus murrayi (g), Paroistodus proteus (c) | ||
Upper part of Aorograptus victoriae (g), lower part of Paroistodus proteus (c) | ||
Lower part of Aorograptus victoriae (g), upper part of Paltodus deltifer (c) | ||
Psigraptus jacksoni (g), lower part of Paltodus deltifer (c) | ||
Anisograptus (g), upper part of Cordylodus angulatus (c) | ||
Rhabdinopora fl abelliformis parabola (g), Cordylodus angulatus (c) | ||
Lower part of Cordylodus angulatus (c) |
Paleogeography
The
Climate
In 2007, Bassett et al. analyzed the oxygen isotope values of Early Ordovician strata of the Lange Ranch section in central Texas and concluded that tropical sea temperatures at that time could have reached 37°C or 42°C.[22] Similar results were recovered by Trotter et al. in 2008, after oxygen isotope analysis of conodonts from the four paleoplates located in the Early Ordovician at low latitudes.[23] Authors of the 2021 article give values in accordance with the study by Song et al. (2019): from 43.9°C 485 million years ago to 37.1°C 470 million years ago.[20][24] High temperatures that persisted throughout the Early Ordovician affected the biodiversification later, in the Middle Ordovician.[25] CO2 level in Early Ordovician atmosphere was high while oxygen levels varied from approximately 10% to 13%.[20]
Studies of
Major events
The
Substantial older ("pre-GOBE") radiations are observed in the Early Ordovician sediments of South China. However, it is questionable, were they global or not.[20]
From the Furongian to the end of the Early Ordovician, 495-470 Ma, the Ollo de Sapo magmatic event occurred on the northwestern territory of Gondwana, which is now the Iberian Peninsula.[29]
Paleontology
In Early Ordovician (Floian) strata of the

Nektaspida have become less diverse after Cambrian. They most likely inhabited restricted or colder brackish seas in the Ordovician.[35] Tariccoia tazagurtensis is a member of this arthropod clade from the Lower Ordovician of Morocco.[35] In the same Fezouata Formation, Aegirocassis was discovered. This filter feeder arthropod reached over 2 m in length[36] and was the largest animal of its time.[37] Marrellomorphs, appeared in Cambrian, continued to exist in Early Ordovician.[38]

Soft-bodied and shelly organisms, including Cambrian relics as well as the new taxa of the Ordovician origin, constitute a fossil Liexi fauna, preserved in the Lower Ordovician Madaoyu Formation of Hunan, South China. Fossil specimens include bryozoans, sponges, echinoderms, polychaetes, graptolites, trilobites and conodonts.[39] Palaeoscolecidan worms, including Liexiscolex[40] and a possible Ottoia specimen, are of great interest.[39] Early Ordovician priapulids, similar to their Cambrian predecessors, are also known from northern China.[41]
In the deep-water sediments of the Early Ordovician (Floian) Al Rose Formation in the Inyo Mountains, California, the trilobite fauna have been discovered. Despite the low species diversity, this fauna is unique due to differences in the composition of families from more eastern complexes of the comparable age. Fossils identified as belonging to the Globampyx, Protopresbynileus, Carolinites, Cloacaspis, Geragnostus and Hintzeia genera. In the Early Ordovician, this territory was located near the paleocontinent of Laurentia.[42]
Mineral resources
Oil and gas exploration is underway in the Early Ordovician Tongzi and Meitan formations in Sichuan Basin[43][44] and the Early Ordovician strata of the Tarim Basin, China.[45] In the Lower Ordovician of the Tarim Basin near Tazhong, oil accumulations are found at depths of up to 9000 m.[46]
References
- PMID 10905606.
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- PMID 28117834.
It has been suggested that the Middle Ordovician meteorite bombardment played a crucial role in the Great Ordovician Biodiversification Event, but this study shows that the two phenomena were unrelated
- ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. December 2024. Retrieved January 2, 2025.
- (PDF) from the original on 2024-03-25. Retrieved 2024-06-04.
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- ^ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. Retrieved 2024-06-04.
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- ^ Stanley Finney (2005). "Global Series and Stages for the Ordovician System: A Progress Report". Geologica Acta. 3 (4): 309-316.
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- ^ Sennikov N. V.; Tolmacheva T. Yu.; Obut О. Т. (2013). "New standard of Ordovocian stages in the International Stratigraphic Chart and problems concerning its application for the territory of Russia". Всероссийское совещание-2013 [All-Russian conference 2013] (in Russian). Trofimuk Institute of Petroleum-Gas Geology and Geophysics SB RAS, VSEGEI: 97.
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- ^ N. V. Sennikov (2022). "Zonal graptolite units of Ordovician, Russia" (in Russian). IPGG SB RAS (Novosibirsk). p. 49.
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- doi:10.3389/fevo.2023.1290063.)
{{cite journal}}
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- ^ Perkins, S. (2015-03-11). "Newly discovered sea creature was once the largest animal on Earth". AAAS. Archived from the original on 2023-08-13. Retrieved 2024-06-04.
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Further reading
- Padel Maxime; Sébastien Clausen; José-Javier Alvaro; Josep Maria Casas (2018). "Review of the Ediacaran-Lower Ordovician (pre-Sardic) stratigraphic framework of the Eastern Pyrenees, southwestern Europe". .
- Padel Maxime; Sébastien Clausen; Marc Poujol; José-Javier Alvaro (2022). "Shifts in the Ediacaran to Lower Ordovician sedimentary zircon provenances of Northwest Gondwana: the Pyrenean files". .
- Carmen Rodríguez; Antonio Castro; Daniel Gómez-Frutos; Gabriel Gutiérrez-Alonso; M. Francisco Pereira; Carlos Fernández (29 January 2022). "The unique Cambro-Ordovician silicic large igneous province of NW Gondwana: Catastrophic melting of a thinned crust". hdl:10481/72840. Archivedfrom the original on 2024-04-15.
External links
- "GSSP Table - Paleozoic Era". Archived from the original on 2023-10-08.
- "GSSPs - The Cambrian System 2019: Ordovician System, Lower Ordovician Series and Tremadocian Stage". International Commission on Stratigraphy. Archived from the original on 2023-07-21.
- "The Early Ordovician". Palaeos. Archived from the original on 2022-01-20.