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Arenig

Adapted from Wikipedia · Adventurer experience

A scenic view of Arenig Fawr, a beautiful mountain in Wales.

In geology, the Arenig (or Arenigian) was a time during the Ordovician period. This was an important time when many new kinds of life began to appear in the oceans.

Arenig Fawr, the mountain which lends its name to the geological series

The Arenig is also the name for the rocks formed during this time. By studying these rocks, scientists can learn about what the world was like millions of years ago. They find clues about the ancient seas, the creatures that lived there, and how the Earth’s surface has changed over time.

Because the Arenig was from such an early time, it helps us understand how life on our planet developed. It is an important part of learning about Earth’s long history.

History

The name "Arenig" was first used in 1847 by a scientist named Adam Sedgwick. He used it for rocks found near Arenig Fawr in North Wales. These rocks are from a time called the Ordovician period.

Scientists studied these rocks and split them into three groups. The first group has gritty and chalky sediments. The second group has volcanic rocks mixed with shale. The third group has shale and limestone rocks. You can find these rock layers in places like North Wales, the Lake District, and parts of Ireland.

Geochronology

In the geologic timescale, the Arenig or Arenigian was a time during the Early Ordovician epoch. It happened about 477.7 and 470 million years ago. This time is the same as what is called the Floian in the ICS. Both are part of the upper part of the Lower Ordovician.

The Arenig came after the Tremadocian stage and before the Middle Ordovician. In North America, these stages are linked to the top three parts of the Canadian stage. They come before the Whiterockian stage of the Middle Ordovician.

Events

The Arenig rocks formed when sea levels rose quickly around the world. This caused oceans to cover many lands. At the same time, more sea creatures began to appear, showing the growth of life in the oceans.

Main article: marine transgression

Brachiopod fauna

Brachiopods are old sea creatures from a time called the early Ordovician period, known as the Floian stage. Many kinds of brachiopods have been found from this time.

Here are some brachiopod groups and species from the Floian stage:

Cephalopoda

Actinocerida

  • Metactinoceras
  • Ordosoceras
  • Polydesmia

The following list shows Actinocerid genera whose fossils are found first in upper Arenig rock layers. These genera might appear in later parts of the Arenig stage or even later times.

Orthocerida

Orthocerids of the Floian

Barrandeocerida of the Floian

Ellesmerocerida of the Floian

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 list shows Endocerid genera whose fossils are found first in lower Arenig rock layers. These genera might appear in later parts of the Arenig stage or even later times.

Upper

The following list shows Endocerid genera whose fossils are found first in upper Arenig rock layers. These genera might appear in later parts of the Arenig stage or even later times.

Intejocerida of the Floian

Oncocerids of the Floian

Nautiloids of the Floian

Tarphycerida

  • Deltoceras
  • Pseudancistroceras
  • Seelyoceras

Lower

Upper

Trilobite fauna

Trilobites lived during the Floian stage of the Ordovician period. Many kinds of trilobites have been found from this time.

Asaphus

Types of trilobites from the Floian stage include:

Colpocoryphe grandis

Other groups of trilobites from this time are:

Related articles

Geology
Ordovician
Marine transgression
Somalinautilus
Adam Sedgwick
Arenig Fawr

This article is a child-friendly adaptation of the Wikipedia article on Arenig, available under CC BY-SA 4.0.

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