Permian

see also: Etymology of Permian

The Permian one is a geological system which extends from 299 to 251 million years. The Permian one was named according to the town of Perm in Russia. The Permian one is preceded by the Carbonifère and followed by the Trias.

As for all the old geological periods, the stratigraphic layers of reference are well-known but their exact dating is prone to variations of a few million years, according to the authors. The end of this period is marked by a massive extinction which is gone back to way a little more precise.

The Permian one was subdivided a long time in Permien inferior and Permien superior (it was called Duas by comparison with Sorted). The commission of UNESCO for stratigraphy, divides it today into three Series: Permian inferior or Cissuralien, Permian average or Guadalupien and higher Permien or Lopingien.

! Modern nomenclature |}

The stages Kungurian, Artinskien and Sakmarien until were not formally defined today by the international commission of Stratigraphy of UNESCO and can still vary. For the precise definitions of the stages to refer to.

The alpine stages are still sometimes used in the alpine geological system, i.e. the overall East-West assembly lines between the the Pyrenees and the Indonesia (the Alps, Yugoslav Dinarides, Monts Taurus Turkish, the Caucasus, Iranian Zagros, the Himalayas, etc).

The limits between nomenclatures old, international and alpine are fluctuating and entirely do not correpondent themselves.

The mean level of the sea remained rather low during the Permian one and the coastal maritime life remained limited by the gathering of all the major continental masses into only one Supercontinent, the Pangée: only one continent - even a very large continent - is less length of coast than six to eight smaller continents.

The Permian one ends in most massive of the extinctions of species recorded by the paleontologists: the Extinction of Permian the. 90 to 95% of the sea life is extinct like nearly 70% of the terrestrial species. The causes of this extinction are still in debate. Most often quoted are an asphyxiation of the oceans (or Anoxie), a Volcan major ism in Siberia, significant drops of the sea level (or regression) or a combination of several causes. The indices of a meteoritic impact going back to this time recently (2006) were discovered in the Antarctic, in the Ground of Wilkes, were caused by a Météorite 48 km in diameter. The majority of the paleontological and geochemical indicators state however that if impact there were, this one did nothing but draw on the ambulance or the hearse, taking place in a passably deteriorated environment.

The dominant forms of life are varied: plants, of large Amphibien S and large Reptile S including the ancestors of the Dinosaure S. the sea life is rich in Mollusque S, Échinoderme S and Brachiopode S. the last Trilobite S disappeared before the end from the Permian one. The fossilized shells of two invertebrates are often used to identify the geological layers of the Permian one: the fusulinidés , Foraminifères Benthique S which disparraissent quasi completely in extreme cases between the Permian means and superior, and the Ammonite S whose modern equivalent is the nautilus. One also often uses the jaws of Conodonte S, one almost Vertébré marine missing at the end of the Trias.

All the ground masses, except for a portion of the Southeast Asia agglomerated in only supercontinent called Pangée which extended from the equator to the poles with an ocean corresponding: Panthalassa (the universal sea ). Only one large continent created climatic conditions implying of great temperature variations to the liking of the seasons (continental Climat) as well as a mode of rain of the type Mousson. The deserts seem to be very wide on Pangée. The dry conditions supported the Gymnospermes, of the plants whose seeds are encapsulated in a protection, other plants as the Fougère S which disperse spores. The modern first Arbre S (Coniferous S) appeared during the Permian one.

Outcrops

Plusieures zones are particularly rich in outcrops of deposits dating from the Permian one: For the marine sediments:

mountains of the the Ural, close to Perm
the China,
the state of the Texas to the the United States where the Permian basin presents one of the known thickest deposits. Particularly in the Guadalupe Mountains (which gave their name to the Guadalupien).
assembly lines between the Italian Dolomites and the the Himalayas: Dolomites, Dinarides, Hellenides, Taurus, Zagros, Oman, the Himalayas senso lato .

For the continental sediments:

mountains of the the Ural, close to Perm
areas of Arlit and Agadez, where two new fossils of Amphibien S ( Nigerpeton ricqlesi and Saharagesta moradiensis ) were found in 2003, letting think that there was in this zone of forms of life different from those of Southern Africa and Russia. A new scientific campaign works in Niger since November 2006, under the direction of American Christian Sidor (of the university of Washington).
basins of Karoo (South Africa) and of Bowen (Australia)

See too

geological time scale

External bonds

University off California with a more modern stratigraphy of Permian the
University of Berkeley with a more traditional stratigraphy

Refer

1 Ogg, Jim (international secretary of the company of stratigraphy); Overview off Total Boundary Stratotype Sections and Points (GSSP' S) http://www.stratigraphy.org/gssp.htm status October 2007.

2 Total and Platenary Changes, Volume 55, Issues 1-3, pp. 1-236 (January 2007) Environmental and Biotic Changes during the Paleozoic-Mesozoic Transition, Elsevier Publication, Amsterdam.

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