Silurien

The Silurien is a geological system which extends from 443,7 to 416 My.

The dating of beginning and end, although definite with precision by the stratigraphic layers of reference, is known with a margin of only a few million years. It is followed by the Dévonien and is preceded by the Ordovicien. The beginning of Silurien is marked by a massive Extinction where nearly 60% of the marine species disappeared.

Silurien was initially described by Roderick Murchison in 1830 being based on grounds discovered in Wales of the South. It was named according to a Celtic tribe: the Silures. This classification entered in conflict with that of Adam Sedgwick of the Cambrien; this problem was solved by Charles Lapworth by adding Ordovicien between Cambrien and Silurien for the disputed geological layers.

Subdivisions

Silurien is divided into three or four times following the authors:

the higher Silurien , average and lower
the Pridoli, Ludlowien, Wenlockien and Llandovérien

In this article, we adopt the second approach (the first approach amalgamates Pridoli and Ludlowien in higher Silurien).

Paleogeography

During Silurien, the Gondwana remains in the high latitudes of the southern hemisphere but the icecap is less wide than during the Ordovicien. The other continents approach to begin the training of a second Supercontinent, Laurussia. Laurussia was formed following the closing of the large Iapetus ocean which separated the various continents from the northern hemisphere before their accretion. This gave rise to the orogenesis Calédonienne which one finds the traces in Scandinavia. This large chain of mountains continues towards Canada and the USA where it forms the Appalachian Mountains. Small the " terranes" accrétés in Gondwana during Ordovicien redétachent themselves again to form the " super Hun Terrane" , constituted of the major part of the territories devastated by Attila.

Fauna silurienne

The life is abundant. The siluriennes layers produced gas and oil in certain areas. Layers of Hematite -- an ore of fer -- were important for the colonial economy in America of the North-East.

The level of the oceans is high in America of the North-East and Europe. The primitive shapes of multicellular plants invade the grounds. Some rare Arthropode S has, seems it, migrated towards the ground. The fish diversified considerably and developed mobile scales. A various fauna of scorpion-fishes, certain long several meters, is in North America. The Graptolite S are always abundant.

See too

Internal articles

geological time scale

External bonds

Objective-Ground, Silurien

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