Safekipedia

Arenig

Adapted from Wikipedia · Discoverer experience

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

In geology, the Arenig (or Arenigian) was a time interval during the Ordovician period. This period was an important time in Earth's history 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 we give to the rocks that were laid down during this time. By studying these rocks, scientists can learn about what the world was like millions of years ago. They can discover clues about the ancient seas, the creatures that lived there, and how the Earth’s surface has changed over time.

Because the Arenig comes from such an early time, it helps us understand how life on our planet developed. It is one of the building blocks for learning about Earth’s long and exciting history.

History

The name "Arenig" was first used in 1847 by a scientist named Adam Sedgwick. He used it to describe certain rocks found near a place called Arenig Fawr in North Wales. These rocks are part of a group called the Ordovician period, which was a long time ago.

Scientists have studied these rocks and divided them into three main groups. The first group is made of gritty and chalky sediments. The second group has mostly volcanic rocks mixed with shale. The third group includes shale and limestone rocks. These rock layers can be found in different places, such as North Wales, the Lake District, and parts of Ireland.

Geochronology

In the geologic timescale, the Arenig or Arenigian was an important time during the Early Ordovician epoch, roughly between 477.7 and 470 million years ago. This time matches what is called the Floian in the ICS, a system used to organize Earth's history, and both are part of the upper part of the Lower Ordovician.

The Arenig came after the Tremadocian stage and was followed by the Middle Ordovician. In North America, these stages are linked to the top three parts of the Canadian stage, which come before 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 lands. Around the same time, the number of different sea creatures began to grow, marking the start of more life in the oceans.

Main article: marine transgression

Brachiopod fauna

Brachiopods are ancient sea creatures that lived in the early part of the Ordovician period, called the Floian stage. Many different types of brachiopods have been found from this time.

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

Cephalopoda

Actinocerida

  • Metactinoceras
  • Ordosoceras
  • Polydesmia

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.

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 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.

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.

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 different types 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.

Images from Wikimedia Commons. Tap any image to view credits and license.