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 Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood 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.
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.
Geochronology In the geologic timescale, 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,ICS; see Ordovician 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 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. The early Ordovician surge in marine diversity also began around this time.
Brachiopod fauna Incertae sedis brachiopods 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 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 Ormoceras Adamsoceras Georgina
Orthocerida Orthocerids of the Floian Eobactrites
Barrandeocerida of the Floian Plectoceras
Ellesmerocerida 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 of the Floian
Buttsoceras Centroonoceras Gangshanoceras Geisonoceras Glenisteroceras Michelinoceras Orthoceras Oxfordoceras Rhynchorthoceras Stereoplasmoceras Tajaroceras Wardoceras
Tarphycerida 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
Phthanoncoceras Ampyx Ampyxoides Anebolithus Asaphus Aspidaeglina Australopyge Bergamia Bohemopyge Borogothus Bumastides Ceratolithus Cloacaspis Cnemidopyge Degamella Dionide Dionidella Ellipsotaphrus Falanaspis 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 Annamitella Balnibarbi 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