Arenig

The Arenig is a term used in geology to describe a specific time interval during the Ordovician period, a long-ago time in Earth's history. During this time, many layers of rock were formed as sediments settled at the bottom of ancient seas. These rocks, called the Arenig series, help scientists understand what the Earth was like millions of years ago.

Geologists divide the Ordovician period into smaller parts, and the Arenig is one of these parts. Studying these rocks helps experts learn about the climate, sea levels, and life that existed during this ancient time. Fossils found in Arenig rocks give clues about the plants and animals that lived in the oceans long before dinosaurs existed.

The Arenig is especially important for scientists studying the early history of life on Earth. By examining these rocks and the fossils inside them, researchers can piece together how life evolved and changed over millions of years. The Arenig helps build a picture of our planet's rich and dynamic past.

History

The term "Arenig" was first used in 1847 by Adam Sedgwick. He talked about rocks called "Arenig Ashes and Porphyries" near Arenig Fawr in North Wales. Scientists have since studied these rocks and divided them into different layers. These layers include gritty sediments, volcanic rocks mixed with shale, and shale and limestones from later times. The Arenig rocks can be found in many places, such as North Wales, the Lake District, and parts of Ireland.

Geochronology

In the geologic timescale, the Arenig or Arenigian was an age during the Early Ordovician epoch, from about 477.7 to 470 million years ago. This time period was the same as the Floian stage, as defined by a section in Sweden at the Diabasbrottet quarry. The Arenig and Floian stages were the upper part of the Lower Ordovician, coming after the Tremadocian stage and before the Middle Ordovician. In North America, these stages match the upper three parts of the Canadian series, which are followed by the Whiterockian stage of the Middle Ordovician.

Events

The Arenig rocks were formed during a time when sea levels rose quickly all around the world. This caused oceans to spread over many land areas. Around the same time, the number of different sea creatures began to grow, marking the start of more life in the oceans.

Brachiopod fauna

Brachiopods are ancient sea creatures that lived in the Floian stage of the Ordovician period. Many different types of brachiopods have been found from this time, showing the diversity of life in the ancient oceans.

Different groups of brachiopods from the Floian include:

• Incertae sedis brachiopods: Eurorthisina, Tegulella
• Acrotretida: Acanthambonia, Cyrbasiotreta, Eoconulus, and many more
• Lingulida: Acanthorthis, Aulonotreta, Dictyobolus, and others
• Orthida: Acanthorthis, Acanthotoechia, Anchigonites, and many more
• Paternida: Dictyonites
• Pentamerida: Acanthorthis, Acanthoglypha, Boreadocamara, and others
• Strophomenida: Acanthorthis, Ahtiella, Aporthophyla, and others
• Trimerellida: Dinobolus

Cephalopoda

The Arenig period includes many types of ancient sea creatures called cephalopods. Some of these are grouped under Actinocerida, such as Metactinoceras, Ordosoceras, and Polydesmia. Others belong to groups like Orthocerida, Endocerida, and Tarphycerida, each with many different genera such as Eobactrites, Amsleroceras, and Deltoceras. These creatures lived in the ancient seas during this time and left behind fossils that help scientists understand the history of life on Earth.

Lists of these genera include names like Leurorthoceras, Nybyoceras, Actinoceras, Wutinoceras, Ormoceras, Adamsoceras, Georgiana, Eobactrites, Plectoceras, 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, Vassaroceras, Veneficoceras, Ventroloboceras, 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, Allopiloceras, Choreanoceroides, Escharendoceras, Lebetoceras, Loxochoanella, Sewardoceras, Telleroceras, Clitendoceras, Coreanoceras, Cotteroceras, Piloceras, Endoceras, Proterovaginoceras, Cyrtendoceras, Anthoceras, Chaohuceras, Proterocameroceras, Thylacoceras, Allocotoceras, Cassinoceras, Chihlioceras, Cyclocyrtendoceras, Cyptendoceras, Kirkoceras, Lobendoceras, Najaceras, Protocyclendoceras, Yehlioceras, Nanno, Dideroceras, Lobocyclendoceras, Meniscoceras, Paracyclendoceras, Cacheoceras, Perkinsoceras, Williamsoceras, Manchuroceras, Schmidtoceras, Bajkaloceras, Evencoceras, Intejoceras, Rossoceras, Phthanoncoceras, Valhalloceras, Buttsoceras, Centroonoceras, Gangshanoceras, Geisonoceras, Glenisteroceras, Michelinoceras, Orthoceras, Oxfordoceras, Rhynchorthoceras, Stereoplasmoceras, Tajaroceras, Wardoceras, 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, and Tragoceras.

Trilobite fauna

Trilobites were ancient sea creatures that lived millions of years ago. During the Floian stage of the Ordovician period, many different kinds of trilobites existed. Some groups included:

Agnostida included genera like Galbagnostus and Geragnostella.

Asaphida had many members such as Asaphus, Australopyge, and Bergamia.

Corynexichida included Bumastus and Ectillaenus.

Lichida featured Apatolichas and Autoloxolichas.

Odontopleurida had Ceratocephala and Selenopeltis.

Phacopida included Calymenella and Cybelurus.

Proetida listed Acidiphorus and Bathyuriscops.

Ptychopariida encompassed Anaximander and Balnibarbi.