From Wikipedia, the free encyclopedia
- This article is about a geological period. For other meanings see Arenig (disambiguation).
In geology, the Arenig group is the name applied to the lowest stage of the Ordovician System.
[edit] History
The term was first used by Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighborhood of Arenig Fawr, in 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.
[edit] North American Deposits
The Arenig series is represented in North Wales by the Garth grit and Ty Obry beds, by the Shelve series of the Corndon district, the Skiddaw slates of the Lake District, the Ballantrae group of Ayrshire, and by the Ribband series of slates and shale in Wicklow and Wexford. It may be mentioned here that the "Llanvirn" Series of H. Hicks was equivalent to the bifidus shale and the Lower Llandeilo Series.
[edit] In Geochronology
In the geologic timescale, the Arenig is the age of the Lower Ordovician epoch of the Ordovician period of the Paleozoic era of the Phanerozoic eon that is comprehended between 478.6 ± 1.7 Ma and 471.8 ± 1.6 Ma (million years ago), approximately. The Arenig age succeeds the Tremadocian age and precedes the Stage III age.
[edit] Events
The Arenig age began with a worldwide sudden rise in sea level rise in sea level (marine transgression). The early ordivician surge in marine diversity also began around the beginning of the Arenig age.[1].
[edit] Brachiopod Fauna
Incertae Cedis Brachiopods of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Acrotretida
Acrotretids of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Lingulida
Placeholders of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Orthida
[edit] Paternida
Placeholders of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Pentamerida
Placeholders of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Strophomenida
Placeholders of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Trimerellida
Placeholders of the Floian |
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A of a variety of fossil brachiopods.
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[edit] Cephalopod Fauna
[edit] Actinocerida
- Metactinoceras
- Ordosoceras
- Polydesmia
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.
[edit] Anarcestida
Anarcestids of the Floian |
Taxa |
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An illustration of a variety of fossil nautiloids.
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[edit] Barrandeocerida
Barrandeocerids of the Floian |
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An illustration of a variety of fossil nautiloids.
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[edit] Ellesmerocerida
Ellesmocerids of the Floian |
Taxa |
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Description |
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An illustration of a variety of fossil nautiloids.
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- Campendoceras
- Dartonoceras
- Kaipingoceras
- Kugeloceras
- Lobosiphon
- Manitouoceras
- Mcqueenoceras
- Mysticoceras
- Notocycloceras
- Oderoceras
- Parapiloceras
- Phragmosiphon
- Platysiphon
- Pliendoceras
- Retroclitendoceras
- Stenosiphon
- Subpenhsioceras
- Utoceras
- Yorkoceras
- Vaginoceras
- Chisiloceras
- Cyrtovaginoceras
- Tallinnoceras
- Juaboceras
- Penhsioceras
- Ventrolobendoceras
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.
- Allopiloceras
- Choreanoceroides
- Escharendoceras
- Lebetoceras
- Loxochoanella
- Sewardoceras
- Telleroceras
- Clitendoceras
- Coreanoceras
- Cotteroceras
- Piloceras
- Endoceras
- Proterovaginoceras
- Cyrtendoceras
- Anthoceras
- Chaohuceras
- Proterocameroceras
- Thylacoceras
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.
- Allocotoceras
- Cassinoceras
- Chihlioceras
- Cyclocyrtendoceras
- Cyptendoceras
- Kirkoceras
- Lobendoceras
- Najaceras
- Protocyclendoceras
- Yehlioceras
- Nanno
- Dideroceras
- Lobocyclendoceras
- Meniscoceras
- Paracyclendoceras
- Cacheoceras
- Perkinsoceras
- Williamsoceras
- Manchuroceras
- Schmidtoceras
[edit] Intejocerida
Intejocerids of the Floian |
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An illustration of a variety of fossil nautiloids.
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[edit] Oncocerida
Oncocerids of the Floian |
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An illustration of a variety of fossil nautiloids.
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Nautiloids of the Bajocian |
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An illustration of a variety of fossil nautiloids.
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[edit] Tarphycerida
- Deltoceras
- Pseudancistroceras
- Seelyoceras
- Alaskoceras
- Moreauoceras
- Pilotoceras
- Shumardoceras
- Pycnoceras
- Campbelloceras
- Aphetoceras
- Aethoceras
- Bentoceras
- Centrotarphyceras
- Clytoceras
- Cycloplectoceras
- Eichwaldoceras
- Eurystomites
- Hardmanoceras
- Holmiceras
- Pionoceras
- Trocholitoceras
- Wichitoceras
- Tarphyceras
- Litoceras
- Curtoceras
- Arkoceras
- Estonioceras
- Tragoceras
[edit] Trilobite Fauna
Oncocerids of the Floian |
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Description |
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Drawing of a trilobite fossil.
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[edit] Agnostida
Oncocerids of the Floian |
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Drawing of a trilobite fossil.
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[edit] Asaphida
[edit] Corynexichida
Oncocerids of the Floian |
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Drawing of a trilobite fossil.
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[edit] Lichida
Oncocerids of the Floian |
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Description |
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Drawing of a trilobite fossil.
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[edit] Odontopleurida
Oncocerids of the Floian |
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Description |
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Drawing of a trilobite fossil.
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[edit] Phacopids
Oncocerids of the Floian |
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Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
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[edit] Proetida
Oncocerids of the Floian |
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Drawing of a trilobite fossil.
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[edit] Ptychopariida
Oncocerids of the Floian |
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Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
Drawing of a trilobite fossil.
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[edit] External links
[edit] References
- ^ http://www.palaeos.com/Paleozoic/Ordovician/Arenig.htm
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on brachiopoda)". Bulletins of American Paleontology 364: p.560.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on cephalopoda)". Bulletins of American Paleontology 364: p.560.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew ex ey ez fa fb fc fd fe ff fg fh fi fj fk fl fm fn fo fp fq fr Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (entry on trilobita)". Bulletins of American Paleontology 364: p.560.
This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.