The Floian is the second stage of the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

Period. It succeeds the

Tremadocian The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from to million years ago. The base of the Tremadocian is defined as the First appearance datum ...

with which it forms the Lower Ordovician series. It precedes the Dapingian Stage of the

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Ma (milli ...

. The Floian extended from to million years ago. The lower boundary is defined as the

first appearance In comic books and other stories with a long history, first appearance refers to the first issue to feature a fictional character. These issues are often highly valued by collectors due to their rarity and iconic status. Reader interest in fir ...

of the

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

species '' Tetragraptus approximatus''.

History and naming

The base of this stage was ratified by the

International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes unofficially referred to as the International Stratigraphic Commission, is a daughter or major subcommittee grade scientific organization that concerns itself with stratigraphy, strati ...

(ICS) in 2002. The Floian Stage is named after Flo, a village in

Västergötland Västergötland (), also known as West Gothland or the Latinized version Westrogothia in older literature, is one of the 25 traditional non-administrative provinces of Sweden (''landskap'' in Swedish), situated in the southwest of Sweden. Vä ...

, southern

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

. The name "Floan" was proposed in 2004, but the ICS adapted Floian as the official name of the stage.

GSSP

The

GSSP A Global Boundary Stratotype Section and Point (GSSP), sometimes referred to as a golden spike, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. ...

of the Floian is the lower Tøyen Shale in Diabasbrottet Quarry () which is an outcrop of a shale-dominated stratigraphic succession. The lower boundary of the Floian is defined as the first appearance of '' Tetragraptus approximatus'' which is about 2.1 above the Cambrian strata. Radiometric dating has set the

-Floian boundary at million years ago. The upper boundary which is also the base of the Dapingian stage is defined as the first appearance of the

conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

species '' Baltoniodus triangularis'' at the GSSP in the Huanghuachang Section,

Hubei Hubei is a province of China, province in Central China. It has the List of Chinese provincial-level divisions by GDP, seventh-largest economy among Chinese provinces, the second-largest within Central China, and the third-largest among inland ...

Province,

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

Regional stages

Partial analogues of Floian stage in Baltoscandia are Hunneberg stage (lower) and Billingen stage (upper). On the Siberian Platform, Ugorian stage corresponds to Floian.

Major events

The global Billingen Transgressive Event occurred in the Early Floian age. Black graptolitic argillites of Gorny Altai as well as conglomerates and

gritstone Gritstone or grit is a hard, coarse-grained, siliceous sandstone. This term is especially applied to such sandstones that are quarried for building material. British gritstone was used for millstones to mill flour, to grind wood into pulp for ...

s of Salair,

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

, possibly correlates with this event.

Paleontology

Discovered in the Floian strata of

Newfoundland Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...

, coral-like

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s of '' Reptamsassia divergens'' and ''Reptamsassia minuta'' are the oldest example of

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

intergrowth of modular species. This allows to judge the level of development of

reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...

ecosystems of the Early Ordovician.

Conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

s '' Serratognathus'', '' Prioniodus'' and '' Oepikodus'' were distributed in

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

Indochina Mainland Southeast Asia (historically known as Indochina and the Indochinese Peninsula) is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to th ...

and

Australasia Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...

during the Floian age. Two species of '' Paroistodus'' are known from the Floian deposits of Baltoscandia and South China. Several thousand chemically isolated

specimens including genera '' Baltograptus'' and '' Pseudophyllograptus'' were collected from the upper Floian sediments of Skattungbyn,

Dalarna Dalarna (; ), also referred to by the English exonyms Dalecarlia and the Dales, is a (historical province) in central Sweden. Dalarna adjoins Härjedalen, Hälsingland, Gästrikland, Västmanland and Värmland. It is also bordered by Nor ...

, central

. Presented mostly by juveniles and isolated siculae, these graptolites inhabited primarily in shallow water environment.

Trilobites Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, ...

of the genera '' Tsaidamaspis'', '' Zhiyia'' and '' Liexiaspis'' were found in the Floian part of the Duoquanshan Formation, northwest China. '' Falloaster anquiroisitus'', an

asterozoa The Asterozoa are a subphylum in the phylum Echinodermata, within the Eleutherozoa. Characteristics include a star-shaped body and radially divergent axes of symmetry. The subphylum includes the classes Asteroidea (the starfish or sea stars), ...

n of problematic classification, is known from the Floian Garden City Formation of

Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...

, USA.

References

External links

* * * {{Geological history, p, p, state=collapsed . Ordovician geochronology