In geology, the Arenig group is the name applied to the lowest stage of the Ordovician System.


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.

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.

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.


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. [] .

Brachiopod Fauna









External links

* [ palaeos]


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  • ARÉNIG — ou SKIDDAW L’Ordovicien X correspond en gros à la majeure partie de l’Arénig ou du Skiddaw anglais. La localité type de Skiddaw est située dans le Cumberland (district des Lacs), celle de l’Arénig est située dans les Galles du Nord. L’extension… …   Encyclopédie Universelle

  • Arenig —   [englisch ærɪnɪg; nach einem Berg in Wales] das, s, Arenigien [arəniʒj jɛ̃, französisch], Arenigium, Geologie: Stufe des Ordoviziums …   Universal-Lexikon

  • Arenig — Are|nig [ ærinig] das; [s] <aus gleichbed. engl. arenig, nach dem Bergzug Arenig in Wales> erdgeschichtlicher Zeitraum; Stufe des ↑Ordoviziums (Geol.) …   Das große Fremdwörterbuch

  • arenig — əˈrānig adjective Usage: usually capitalized Etymology: from Arenig mountains, Wales : of or relating to a subdivision of the European Ordovician see geologic time table …   Useful english dictionary

  • arenig — are·nig …   English syllables

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  • Llyn Arenig Fawr — Infobox lake lake name = Llyn Arenig Fawr image lake = caption lake = image bathymetry = caption bathymetry = location = Gwynedd, North Wales coords = coord|52|55|39|N|3|43|0|W|type:waterbody region:GB|display=inline,title type = reservoir inflow …   Wikipedia

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