geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

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

History

The term was first used by Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood of

Arenig Fawr is a mountain in Snowdonia, North Wales, close to Llyn Celyn reservoir, alongside the A4212 road, A4212 between Trawsfynydd and Bala, Gwynedd, Bala. Location Arenig Fawr is the highest member of the Arenigs, Arenig range, with , a smaller nei ...

, in Merioneth,

North Wales North Wales ( ) is a Regions of Wales, region of Wales, encompassing its northernmost areas. It borders mid Wales to the south, England to the east, and the Irish Sea to the north and west. The area is highly mountainous and rural, with Snowdon ...

. 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 Llandeilo () is a town and Community (Wales), community in Carmarthenshire, Wales, situated where the River Towy is crossed by the A483 road, A483 on a 19th-century stone bridge. At the 2021 United Kingdom census, 2021 census the community had ...

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 The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

rocks; this is not the case in South Wales. 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 Ayrshire (, ) is a Counties of Scotland, historic county and registration county, in south-west Scotland, located on the shores of the Firth of Clyde. The lieutenancy areas of Scotland, lieutenancy area of Ayrshire and Arran covers the entirety ...

, and by the Ribband Series of slates and shale in

Wicklow Wicklow ( ; , meaning 'church of the toothless one'; ) is the county town of County Wicklow in Republic of Ireland, Ireland. It is located on the east of Ireland, south of Dublin. According to the 2022 census of Ireland, 2022 census, it had ...

and

Wexford Wexford ( ; archaic Yola dialect, Yola: ''Weiseforthe'') is the county town of County Wexford, Republic of Ireland, Ireland. Wexford lies on the south side of Wexford Harbour, the estuary of the River Slaney near the southeastern corner of the ...

. It may be mentioned here that the " Llanvirn" Series of H. Hicks was equivalent to the bifidus shale and the Lower Llandeilo Series.

Geochronology

In the

geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron ...

, the Arenig or Arenigian refers to an age of the Early Ordovician epoch, between 477.7 and 470 million years ago, contemporary with the Floian of the ICS, based on a section in Sweden ( Diabasbrottet quarry) and with the same boundaries. The Arenig and Floian rocks are the upper part of the Lower Ordovician and follow the Tremadocian ( Gasconadian in North America) which is the lower part. Either is followed by the Middle Ordovician ICS Dapingian or by the Llanvirnian of older chronologies. The Arenig and equivalent Floian are represented in North America by the upper three stages of the

Canadian Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...

which is followed by the Middle Ordovician Whiterockian which is the lower part of the now shortened Chazyan.

Events

The Arenig rocks were deposited during a sudden worldwide rise in sea level resulting in widespread

marine transgression A marine transgression is a geologic event where sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling with water ...

. The early Ordovician surge in marine diversity also began around this time.

Brachiopod fauna

;''

Incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s of the Floian *'' Eurorthisina'' *'' Tegulella'' ; Acrotretida of the Floian *'' Acanthambonia'' *'' Cyrbasiotreta'' *'' Eoconulus'' *'' Issedonia'' *'' Karnotreta'' *'' Lurgiticoma'' *'' Multispinula'' *'' Mylloconotreta'' *'' Numericoma'' *'' Orthisocrania'' *'' Polylasma'' *'' Pomeraniotreta'' *'' Pseudocrania'' *'' Scaphelasma'' *'' Schizotreta'' *'' Torynelasma'' ; Lingulida of the Floian *'' Acanthorthis'' *'' Aulonotreta'' *'' Dictyobolus'' *'' Ectenoglossa'' *'' Elliptoglossa'' *'' Monobolina'' *'' Paldiskites'' *'' Paterula'' *'' Pseudolingula'' *'' Quasithambonia'' *'' Rafanoglossa'' *'' Volborthia'' ; Orthida of the Floian *'' Acanthorthis'' *'' Acanthotoechia'' *'' Anchigonites'' *'' Angusticardinia'' *'' Anomalorthis'' *'' Antigonambonites'' *'' Apomatella'' *'' Astraborthis'' *'' Crossiskenidium'' *'' Dalmanella'' *'' Desmorthis'' *'' Diparelasma'' *'' Eodiorthelasma'' *'' Eosotrematorthis'' *'' Estlandia'' *'' Euorthisina'' *'' Famatinorthis'' *'' Fasciculina'' *'' Ferrax'' *'' Ffynnonia'' *'' Fistulogonites'' *'' Glossorthis'' *'' Glypterina'' *'' Hesperonomiella'' *'' Incorthis'' *'' Jaanussonites'' *'' Ladogiella'' *'' Lomatorthis'' *'' Monorthis'' *'' Munhella'' *'' Nereidella'' *''Neumania'' *'' Nocturneilla'' *'' Notoscaphidia'' *'' Oligorthis'' *'' Orthambonites'' *'' Orthidiella'' *'' Orthidium'' *'' Orthis'' *'' Oslogonites'' *'' Panderina'' *'' Paralenorthis'' *'' Paurorthina'' *'' Paurorthis'' *'' Phragmorthis'' *'' Platystrophia'' *'' Platytoechia'' *'' Polytoechia'' *'' Pomatotrema'' *'' Prantlina'' *'' Productorthis'' *'' Progonambonites'' *'' Protohesperonomia'' *'' Protoskenidiodes'' *'' Pseudomimella'' *'' Raunites'' *'' Rhynchorthis'' *'' Shoshonorthis'' *'' Sinorthis'' *'' Taphrorthis'' *''Tarfaya'' *'' Treioria'' *'' Trematorthis'' *'' Valcourea'' *'' Virgoria'' ; Paternida of the Floian *'' Dictyonites'' ; Pentamerida of the Floian *'' Acanthorthis'' *'' Acanthoglypha'' *'' Boreadocamara'' *'' Camerella'' *'' Doloresella'' *'' Hesperotrophia'' *'' Idiostrophia'' *'' Imbricatia'' *'' Karakulina'' *'' Liricamera'' *'' Lycophoria'' *'' Porambonites'' *'' Rectotrophia'' *''Rosella'' *'' Rugostrophia'' *'' Stenocamara'' *''Syntrophia'' *'' Syntrophinella'' *'' Xenelasma''

Strophomenida

; Strophomenida of the Floian *'' Acanthorthis'' *'' Ahtiella'' *'' Aporthophyla'' *'' Borua'' *'' Calyptolepta'' *'' Christiania'' *''Ingria'' *'' Leptestia'' *'' Petroria'' *'' Plectambonites'' *'' Reinversella'' *'' Schedophyla'' *'' Taffia'' *'' Tourmakeadia'' ; Trimerellida of the Floian *'' Dinobolus''

Cephalopoda

;

Actinocerida The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which depo ...

*'' Metactinoceras'' *'' Ordosoceras'' *'' Polydesmia''

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. *'' Leurorthoceras'' *'' Nybyoceras'' *'' Actinoceras'' *''

Wutinoceras ''Wutinoceras'' is a genus of now extinct Nautiloidea, nautiloid cephalopods of the Wutinoceratidae family. It exhibits orthoconic Actinocerida, actinocerids with ventral siphuncles composed of broadly expanded segments.Memoir 2, Studies of the ...

'' *'' Ormoceras'' *''

Adamsoceras ''Adamsoceras'' is a genus of actinocerids of the family Wutinoceratidae, with spheroidal siphuncle segments like '' Ormoceras'', but having a reticular canal system like ''Wutinoceras''. Adamsoceras has a slender, gently expanding, orthoconic ...

'' *''Georgina''

Orthocerida

; Orthocerids of the Floian *'' Eobactrites'' ; Barrandeocerida of the Floian *'' Plectoceras'' ;

Ellesmerocerida The Ellesmerocerida is an extinct order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shell ...

of the Floian *'' Amsleroceras'' *'' Apocrinoceras'' *'' Avoceras'' *'' Bakeroceras'' *'' Baltoceras'' *'' Catoraphinoceras'' *'' Cochlioceras'' *'' Copiceras'' *'' Clelandoceras'' *'' Cumberloceras'' *'' Cyclostomiceras'' *'' Cyrtobaltoceras'' *'' Desioceras'' *'' Diaphoroceras'' *'' Diastoloceras'' *'' Dwightoceras'' *'' Dyscritoceras'' *'' Ectocycloceras'' *'' Endorioceras'' *'' Eocyckistomiceras'' *'' Eothinoceras'' *'' Hemichoanella'' *'' Irianoceras'' *'' Kyminoceras'' *'' Lawrenceoceras'' *'' Meikeloceras'' *'' Microbaltoceras'' *'' Monogonoceras'' *'' Ogygoceras'' *'' Pictetoceras'' *'' Protocycloceras'' *'' Quebecoceras'' *'' Rangeroceras'' *'' Rhabdiferous'' *'' Rioceras'' *'' Rudolfoceras'' *'' Smithvilloceras'' *'' Somalinautilus'' *'' Somalinautilus'' *'' Somalinautilus'' *'' Vassaroceras'' *'' Veneficoceras'' *'' Ventroloboceras'' ; Endocerida *'' 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'' ;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. *'' Allopiloceras'' *'' Choreanoceroides'' *'' Escharendoceras'' *'' Lebetoceras'' *'' Loxochoanella'' *'' Sewardoceras'' *'' Telleroceras'' *'' Clitendoceras'' *'' Coreanoceras'' *'' Cotteroceras'' *'' Piloceras'' *'' Endoceras'' *'' Proterovaginoceras'' *'' Cyrtendoceras'' *'' Anthoceras'' *'' Chaohuceras'' *'' Proterocameroceras'' *'' Thylacoceras'' ;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. *'' Allocotoceras'' *'' Cassinoceras'' *'' Chihlioceras'' *'' Cyclocyrtendoceras'' *'' Cyptendoceras'' *'' Kirkoceras'' *'' Lobendoceras'' *'' Najaceras'' *'' Protocyclendoceras'' *'' Yehlioceras'' *'' Nanno '' *'' Dideroceras'' *'' Lobocyclendoceras'' *'' Meniscoceras'' *'' Paracyclendoceras'' *'' Cacheoceras'' *'' Perkinsoceras'' *'' Williamsoceras'' *'' Manchuroceras'' *'' Schmidtoceras'' ; Intejocerida of the Floian *'' Bajkaloceras'' *'' Evencoceras'' *'' Intejoceras'' *'' Rossoceras'' ; Oncocerids of the Floian *'' Phthanoncoceras'' *'' Valhalloceras'' ;

Nautiloids Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

of the Floian *'' Buttsoceras'' *'' Centroonoceras'' *'' Gangshanoceras'' *'' Geisonoceras'' *'' Glenisteroceras'' *''

Michelinoceras ''Michelinoceras'' is the oldest known genus of the Michelinocerida, more commonly known as the Orthocerida, characterized by long, slender, nearly cylindrical orthocones with a circular cross section, long camerae, very long body chambers, and a ...

'' *'' Orthoceras'' *'' Oxfordoceras'' *'' Rhynchorthoceras'' *'' Stereoplasmoceras'' *'' Tajaroceras'' *'' Wardoceras'' ;

Tarphycerida The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some, such as '' Aphetoceras'' and '' Estonioceras'', are loosely coiled and gyroconi ...

*'' Deltoceras'' *'' Pseudancistroceras'' *'' Seelyoceras'' ;Lower *'' Alaskoceras'' *'' Moreauoceras'' *'' Pilotoceras'' *'' Shumardoceras'' *'' Pycnoceras'' *'' Campbelloceras'' *'' Aphetoceras'' ;Upper *'' Aethoceras'' *'' Bentoceras'' *'' Centrotarphyceras'' *'' Clytoceras'' *'' Cycloplectoceras'' *'' Eichwaldoceras'' *'' Eurystomites'' *'' Hardmanoceras'' *'' Holmiceras'' *'' Pionoceras'' *'' Trocholitoceras'' *'' Wichitoceras'' *'' Tarphyceras'' *'' Litoceras'' *'' Curtoceras'' *'' Arkoceras'' *'' Estonioceras'' *'' Tragoceras''

Trilobite fauna

;Trilobites of the Floian *'' Canningella'' *'' Gogoella'' *'' Macrogrammus'' *'' Priceaspis'' *'' Thymurus'' ; Agnostida of the Floian' *'' Galbagnostus'' *'' Geragnostella'' ; Asaphida of the Floian Naturhistorisches Museum Vienna Dez 2006 073

Naturhistorisches Museum Vienna Dez 2006 073

*'' Phthanoncoceras'' *'' Ampyx'' *'' Ampyxoides'' *'' Anebolithus'' *'' Asaphus'' *'' Aspidaeglina'' *'' Australopyge'' *'' Bergamia'' *'' Bohemopyge'' *'' Borogothus'' *'' Bumastides'' *'' Ceratolithus'' *'' Cloacaspis'' *'' Cnemidopyge'' *'' Degamella'' *'' Dionide'' *'' Dionidella'' *'' Ellipsotaphrus'' *'' Falanapis'' *'' Famatinolithus'' *'' Globampyx'' *'' Gog'' *'' Hanchungolithus'' *'' Hoekaspis'' *'' Hungioides'' *'' Hunnebergia'' *'' Isocolus'' *'' Isoteloides'' *'' Lachnostoma'' *'' Lannacus'' *'' Lapidaria'' *'' Liomegalaspides'' *'' Megalaspidella'' *'' Megalaspides'' *'' Mendolaspis'' *'' Merlinia'' *'' Microparia'' *'' Mioptychopyge'' *'' Myttonia'' *'' Ningkianolithus'' *'' Niobides'' *'' Ogmasaphus'' *'' Ogyginus'' *'' Ogygiocaris'' *'' Opipeuter'' *'' Parabasilicus'' *'' Paraptychopyge'' *'' Plesiomegalaspis'' *'' Presbynileus'' *'' Pricyclopyge'' *'' Psilacella'' *'' Psilocara'' *'' Ptychopyge'' *'' Rhombampyx'' *'' Robergiella'' *'' Seleneceme'' *'' Stapeleyella'' *'' Taihungshania'' *'' Thysanopyge'' *'' Trigonocercella'' *'' Tungtzuella'' *'' Zhenganites'' *'' Zuninaspis'' ; Corynexichida of the Floian *'' Bumastus'' *'' Dysplanus'' *'' Ectillaenus'' *'' Panderia'' *'' Phillipsinella'' *'' Pseudocalymene'' *'' Theamataspis'' ; Lichida of the Floian *'' Apatolichas'' *'' Autoloxolichas'' *'' Lichakephalina'' *'' Metopolichas'' ; Odontopleurida of the Floian *'' Phthanoncoceras'' *'' Ceratocephala'' *'' Diacanthaspis'' *'' Selenopeltis'' ; Phacopida of the Floian *'' Bathycheilus'' *'' Calymenella'' *'' Ceraurinella'' *'' Colobinion'' *'' Colpocoryphe'' *'' Cybelopsis'' *'' Cybelurus'' *'' Diaphanometopus'' *'' Dindymene'' *'' Eccoptochile'' *'' Ectenonotus'' *'' Encrinurella'' *'' Encrinuroides'' *'' Evropeites'' *'' Gyrometopus'' *'' Heliomeroides'' *'' Kanoshia'' *'' Kawina'' *'' Kolymella'' *'' Lehua'' *'' Lyrapyge'' *'' Neseuretus'' *'' Nieszkowskia'' *'' Ormathops'' *'' Ovalocephalus'' *'' Placoparia'' *'' Platycoryphe'' *'' Pliomeridius'' *'' Pliomerops'' *'' Protoencrinurella'' *'' Protopliomerella'' *'' Pseudocybele'' *'' Pterygometopus'' *'' Strotactinus'' *'' Sycophantia'' *'' Synhomalonotus'' *'' Toletanaspis'' *'' Xystocrania'' ; Proetida of the Floian *'' Acidiphorus'' *'' Bathyuriscops'' *'' Benthamaspis'' *'' Biolgina'' *'' Bolbocephalus'' *'' Carolinites'' *'' Celmus'' *'' Ceratopeltis'' *'' Decoroproetus'' *'' Dimeropygiella'' *'' Eleutherocentrus'' *'' Goniophrys'' *'' Goniotelina'' *'' Grinnellaspis'' *'' Ischyrophyma'' *'' Ischyrotoma'' *'' Lutesvillia'' *'' Oenonella'' *'' Petigurus'' *'' Rananasus'' *'' Raymondaspis'' *'' Telephina'' ; Ptychopariida of the Floian *''

Anaximander Anaximander ( ; ''Anaximandros''; ) was a Pre-Socratic philosophy, pre-Socratic Ancient Greek philosophy, Greek philosopher who lived in Miletus,"Anaximander" in ''Chambers's Encyclopædia''. London: George Newnes Ltd, George Newnes, 1961, Vol. ...

'' *'' Annamitella'' *''

Balnibarbi Balnibarbi is a fictional land in Jonathan Swift's 1726 satirical novel ''Gulliver's Travels''. it was visited by Lemuel Gulliver after he was rescued by the people of the flying island of Laputa. Location The location of Balnibarbi is illus ...

'' *'' Bulnibarbi'' *'' Bvalbardites'' *'' Circulocrania'' *'' Endymionia'' *'' Etheridgaspis'' *'' Furcalithus'' *'' Gymnostomix'' *'' Lacorsalina'' *'' Leioshumardia'' *'' Lordshillia'' *'' Nambeetella'' *'' Novakella'' *'' Oopsites'' *'' Peraspis'' *'' Phorocephala'' *'' Porterfieldia'' *'' Prosopiscus'' *'' Pytine'' *'' Sagavia'' *'' Selenoharpes'' *'' Stegnopsis'' *'' Stenorhachis'' *'' Svalbardites'' *'' Tasmanocephalus'' *'' Turgicephalus'' *'' Yinpanolithus''

External links

palaeos

References

{{Reflist Early Ordovician