System (period) | Series | Stage (age) | Lower boundary, Ma | |
---|---|---|---|---|
Silurian | Llandovery | Rhuddanian | 443,8±1,5 | |
Ordovician | Upper | Hirnantian | 445.2±1.4 | |
Katian | 453.0±0.7 | |||
Sandbian | 458.4±0.9 | |||
Middle | Darriwilian | 467.3±1.1 | ||
Dapingian | 470.0±1.4 | |||
Lower | Floian | 477.7±1.4 | ||
Tremadocian | 485.4±1.9 | |||
Cambrian | Furongian | Stage 10 | older | |
Subdivisions and "golden spikes" according to IUGS as of September 2023[1] |
The Ordovician (pron.: /ɔrdəˈvɪʃən/) is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 485.4 ± 1.9 to 443.4 ± 1.5 million years ago. It follows the age 10 of the Cambrian period and is followed by the Rhuddanian age of the Silurian period. It is characterized by the significant climate changing from greenhouse to icehouse and the Great Ordovician Biodiversification Event.
History[]
The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods respectively. Lapworth, recognizing that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, realized that they should be placed in a period of their own. While recognition of the distinct Ordovician Period was slow in the United Kingdom, other areas of the world accepted it quickly. It received international sanction in 1960, when it was adopted as an official period of the Paleozoic era by the International Geological Congress.
Definition[]
The Global Stratotype Section and Point (GSSP) of the Ordovician system as well as the Lower Ordovician series and the Tremadocian stage was ratified in 2000. The lower boundary was fixed in the Green Point Section on the island of Newfoundland near Canada, and the first appearance of the conodont species Iapetognathus fluctivagus is related to it.[2]
Ordovician subdivisions[]
The Ordovician system is divided into three series and each includes two or three stages. The series and stages from upper to lower are:
- Upper Ordovician series (corresponds to the Late Ordovician epoch)
- Hirnantian
- Katian
- Sandbian
- Middle Ordovician series/epoch
- Darriwilian
- Dapingian
- Lower Ordovician series (corresponds to the Early Ordovician epoch)
- Floian
- Tremadocian
In geochronology, all stages correspond to the same ages.
In some regions, other stages are used. In the United Kingdom, where the Ordovician system was firstly identified, it includes the regional stages, and they were used worldwide until 2008, when the British stages were replaced by those whose boundaries were much more easily correlated on other continents. Only Tremadocian, the lowermost British stage of the Ordovician, is used in international chronostratigraphic chart.
Life in the Ordovician[]
Life continued to flourish during the Ordovician as it did in the Cambrian, although the end of the period was marked by a significant mass extinction. Invertebrates, namely mollusks and arthropods, dominated the oceans. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. Life had yet to diversify on land.
References[]
- ↑ "Latest version of international chronostratigraphic chart". International Commission on Stratigraphy. https://stratigraphy.org/chart#latest-version.
- ↑ "GSSP Table - Paleozoic Era". https://timescalefoundation.org/gssp/index.php?parentid=77.