Arenig

In geology, the Arenig (or Arenigian) is a time interval during the Ordovician period and also the suite of rocks which were deposited during this interval.

History

The term was first used by

Merioneth, North Wales. The rock-succession in the Arenig district has been recognized by W. G. Fearnsides

(“On the Geology of Arenig Fawr and Moel Llanfnant", Q.J.G.S. vol. lxi., 1905, pp. 608–640, with maps). The above succession is divisible into:

A lower series of gritty and calcareous sediments, the "Arenig Series" as it is now understood;

A middle series, mainly volcanic, with shale, the "Llandeilo Series"; and
The shale and limestones of the
Bala or Caradoc
Stage.

It was to the middle series (2) that Sedgwick first applied the term "Arenig". In the typical region and in North Wales generally the Arenig series appears to be unconformable upon the Cambrian rocks; this is not the case in South Wales.^[1]

The Arenig series is represented in North Wales by the

Llanvirn" Series of H. Hicks was equivalent to the bifidus^{[clarification needed]} shale and the Lower Llandeilo Series.^[1]

Events

The Arenig rocks were deposited during a sudden worldwide rise in sea level resulting in widespread marine transgression. The early Ordovician surge in marine diversity also began around this time.^[3]

Brachiopod fauna

Incertae sedis brachiopods of the Floian^[4]

Eurorthisina
Tegulella

Acrotretida of the Floian^[4]

Lingulida of the Floian^[4]

Orthida of the Floian^[4]

Paternida of the Floian

Dictyonites

Pentamerida of the Floian

Strophomenida

Strophomenida of the Floian

Trimerellida of the Floian

Dinobolus

Cephalopoda

Actinocerida

Upper

The following is a list of Actinocerid genera whose fossils are geochronologically found first in upper Arenig strata. These genera may survive into later portions of the Arenig stage, or even into later geological stages. This list should not be thought of in terms of the lifespan of the genera included.

Orthocerida

Orthocerids of the Floian^[5]

Eobactrites

Barrandeocerida of the Floian^[5]

Plectoceras

Ellesmerocerida of the Floian^[5]

Endocerida

Lower

The following is a list of Endocerid genera whose fossils are geochronologically found first in lower Arenig strata. These genera may survive into later portions of the Arenig stage, or even into later geological stages. This list should not be thought of in terms of the lifespan of the genera included.

Upper

The following is a list of Endocerid genera whose fossils are geochronologically found first in upper Arenig strata. These genera may survive into later portions of the Arenig stage, or even into later geological stages. This list should not be thought of in terms of the lifespan of the genera included.

Intejocerida of the Floian

Oncocerids of the Floian

Phthanoncoceras
Valhalloceras

Nautiloids of the Floian

Tarphycerida

Lower

Upper

Trilobite fauna

Trilobites of the Floian^[6]

Agnostida of the Floian'^[6]

Galbagnostus
Geragnostella

Asaphida of the Floian^[6]

Corynexichida of the Floian^[6]

Lichida of the Floian^[6]

Odontopleurida of the Floian^[6]

Phacopida of the Floian

Proetida of the Floian

Ptychopariida of the Floian^[6]

External links

palaeos

References

^ ^a ^b One or more of the preceding sentences incorporates text from a publication now in the public domain: Howe, John Allen (1911). "Arenig Group". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 2 (11th ed.). Cambridge University Press. p. 452.
^ ICS; see Ordovician
^ "Palaeos Paleozoic : Ordovician : The Arenig Age". Archived from the original on 2007-11-13. Retrieved 2007-12-11.
^ ^a ^b ^c ^d Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on brachiopoda)". Bulletins of American Paleontology. 364: 560. Archived from the original on 14 October 2004. Retrieved 27 April 2008.
^ ^a ^b ^c Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on cephalopoda)". Bulletins of American Paleontology. 364: 560. Archived from the original on 7 May 2008. Retrieved 17 April 2008.
^ ^a ^b ^c ^d ^e ^f ^g Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on trilobita)". Bulletins of American Paleontology. 364: 560. Retrieved 19 April 2008.

[EB1911-1] One or more of the preceding sentences incorporates text from a publication now in the public domain: Howe, John Allen (1911). "Arenig Group". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 2 (11th ed.). Cambridge University Press. p. 452.

[2] ICS; see Ordovician

[3] "Palaeos Paleozoic : Ordovician : The Arenig Age". Archived from the original on 2007-11-13. Retrieved 2007-12-11.

[Sepkoski_Brach-4] Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on brachiopoda)". Bulletins of American Paleontology. 364: 560. Archived from the original on 14 October 2004. Retrieved 27 April 2008.

[Sepkoski_Ceph-5] Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on cephalopoda)". Bulletins of American Paleontology. 364: 560. Archived from the original on 7 May 2008. Retrieved 17 April 2008.

[Sepkoski_Trilob-6] ^ ^a ^b ^c ^d ^e ^f ^g Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on trilobita)". Bulletins of American Paleontology. 364: 560. Retrieved 19 April 2008.

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