Triassic

The triad ( altgr. τριάς, called τριάδος = trinity, trinity ) ( adj. Triassic, rarely triadic [Note 1] ) is the lowest in the Earth's system of the Mesozoic ( Mesozoic ) in the middle Ärathem the Phanerozoic. You will geochronological recorded in the period before about 252.2 to about 201.3 million years and thus took about 51.4 million years. The Triassic is preceded Perm, you follow the law.

History and naming

The name Trias was proposed in 1834 red sandstone, Muschelkalk and Keuper of Friedrich von Alberti after the eye-catching in Central Europe tripartite division and quickly gained acceptance in the geological literature. This classic tripartite division is, however, formed only in the Germanic Basin. Accordingly, the three divisions of the Germanic Triassic are now regarded only as lithostratigraphic units. According to the international subdivision of the Triassic, although three series are also distinguished: Lower, Middle and Upper Triassic (or Lower, Middle and Upper Triassic), whose boundaries are not in conformity with the lithostratigraphically defined limits of red sandstone, Muschelkalk and Keuper.

Definition and GSSP

The lower limit of the Triassic chronostratigraphic system (and thus the Lower Triassic Series and Indusium stage) is defined by the first appearance of the conodont species Hindeodus parvus and the end of the negative carbon anomaly after the peak of the Late Permian mass extinction. The upper limit and therefore the lower limit of the law has not yet been finally determined. The limit will most likely not applied to the vicinity of the ammonite genus Erstauftretens Psiloceras. In absolute terms, which is similar to the International timescale of 2004 the period of about 251 million years ago to 199.6 million years. A slightly different dating ( lower limit already at 252.6 / - 0.2 Ma) have Mundil et al. submitted in 2004. The internationally recognized GSSP (Global Boundary Stratotype Section and Point = " profile and a global point boundary - strato type ") is the Meishan D profile in Changxing county, Zhejiang Province (China).

Subdivision of the Triassic

The Triassic system is divided into three series with a total of seven stages:

  • System: Triassic ( 252.2 to 201.3 mya ) Series: Upper Triassic ( 235 to 201.3 mya ) Level: Rhaetian ( 208.5 to 201.3 mya )
  • Level: Norian ( 228 to 208.5 mya )
  • Level: Carnian ( 235-228 mya )
  • Level: Ladinium ( 242-235 mya )
  • Level: Anisian ( 247.2 to 242 mya )
  • Level: Olenekian ( 251.2 to 247.2 mya )
  • Level: indusium ( 252.2 to 251.2 mya )

The Lower Triassic used to contain only a single stage, the Skythium, which has now been abandoned in international usage. However, it will continue to be used in the Alpine region as a regional level. Especially in the biostratigraphy other approaches the subdivision are represented. Timothy Edward Tozer was in 1965, before a four-level structure of the Lower Triassic in Griesbachium, Dienerium, Smithium and Spathium. 1978 suggested Guex before a tripartite division, by summarizing Dienerium and Smithium to a new level Nammalium.

The stratigraphic subdivision of the Triassic is mainly based on the group of ammonoids; probably only two species had the turn Permian / Triassic survived, but already in the lowermost Triassic can again find over 100 species occupy. Other important index fossils are also conodonts, bivalves (mussels ), crinoids, calcareous algae (especially Dasycladaceen ( Wirtelalgen ) ) and ostracods ( Ostracoda ).

Paleogeography

During the Permian supercontinent Pangaea had formed of the collision Sibirias, which united almost all of the continental crust of the earth in a continent apart from several terranes in eastern Palaeotethys. However, early in the Permian began the decay. In the uppermost Permian broke away from the North Rim Ostgondwanas the Cimmerian Terrane. Between this Terran Group and Gondwana was the Neotethys and the Paläotethys was subducted under this terranes. In the West, the wedge of the Neotethys extended further west. In the Upper Triassic also the opening of the North Atlantic later began to hint. Intermediate (later ) and North America (later ) Europe emerged rift systems that took up large amounts of sediments and volcanics. During the Upper Triassic saw the first marine ingressions in these rift systems.

Climate

The climate of the Triassic was warm to hot. Europe was in the subtropical desert area. Even the world's climate seems to have been rather dry: the reason was in the form of the super continent Pangaea and a resulting monsoon effect, in which the summer low-pressure areas over the land mass mainly ansaugten air from other inner parts of the country and not from the ocean, similar to the present situation in South Arabia. Inland extensive deserts were probably present. Near the geographic North Pole was located under the current reconstructions part of Eastern Siberia.

Development of the fauna

The supercontinent Pangaea, which is almost contained the entire land mass and was stretched from the North Pole to the South Pole, made ​​possible the full dissemination of land animals.

In the Triassic the " Reptiles" took an enormous upswing. It created a lot of new orders. Among the already existing since the Permian therapsids occurred in the Triassic added:

  • The Wurzelzähner ( Thecodontia )
  • The dinosaurs ( Saurischia and Ornithischia )
  • Pterosaurs ( Pterosauria )
  • The crocodiles ( Crocodilia ),
  • The fin lizards ( Sauropterygia )
  • The lizards ( Sauria )
  • The Sphenodontia,
  • The turtles (Chelonia ),
  • The ichthyosaur ( Ichthyosauria ) and
  • The plaster dinosaur tooth ( Placodontia ).

This was in the Triassic - with the exception of snakes ( Serpentes or Ophidia ) - already represent all reptile groups. With Triadobatrachus already in the lower Triassic appeared the first frog. The first dinosaurs appeared in the Triassic unfolded during the subsequent systems of Jurassic and Cretaceous and were the dominant life form of terrestrial ecosystems. At the beginning there were still relatively small carnivorous forms ( theropods ) as Eoraptor and Herrerasaurus. Later, also herbivores, such as the Prosauropode Plateosaurus, which was between six and eight meters long developed. But the first mammals arose in the Triassic. However, they played a subordinate role to the extinction of the ( non- avian ) dinosaurs at the end of the Cretaceous.

At the end of the Triassic 50 to 80 % of all species died, among others, almost all land vertebrates. Here is a link with massive magma release before the breakup of Pangaea is suspected (central atlantic eruption ) or the poisoning of the shallow, warm coastal seas by large amounts of hydrogen sulfide after massive volcanic eruptions have released large amounts of carbon dioxide and sulfur dioxide.

Development of Flora

The turnaround was already in the Permian of the plant world of ferns to gymnosperms sat down in the Triassic continued. While even tree ferns were ( Cyatheales ) and horsetails still widespread in wetlands. Ginkgo, cycads ( Cycadales ) and gymnosperms were the most common plants in the terrestrial ecosystems of the Triassic. At the end of the Triassic the heyday of cycads, which lasted until the Cretaceous began. The first jaw -like had already developed in the Carboniferous ( Cordaitales, Voltziales ). But the extinction event at the end of the Permian also met this group. So the Cordaiten died eg at the end of the Permian, fully extend the Voltziales developed further in the Triassic.

A transition to the angiosperms ( angiosperms ) represent the Bennettiteen ( Bennettitales ) dar. This still belonging to the gymnosperm plant had already blossoms similar organs similar to those of angiosperms. The shape suggests pollination by insects. As a direct precursor to the angiosperms however, they are not considered. They appeared in the late Triassic to the first time and survived until the chalk into it. In the Triassic, the palm -like genus Williamsonia occurred with up to two meters tall trunks. Other genera were William Soni Ella (Middle Jurassic), Wielandiella (upper Triassic to the Jurassic into it ) and Cycadeoidea ( Lower Cretaceous ).

Among the seed ferns, the tree-shaped genus Dicroidium took the place of a Glossopteris Gondwana.

A typical representative of the spore plants for the Buntsandstein ( Lower Triassic ) is Pleuromeia, which is counted to the fossil order Pleuromeiales the Bärlapppflanzen. It resembles Sigillaria, a Bärlappgewächs of Paläophytikums.

The Triassic Period in Central Europe

The typical tripartite division of the rock units of the Triassic in the Germanic Basin can not be seen in the Alps. This area (also alpine Triassic or Triassic pelagic ) called Alpine-Mediterranean Triassic. Their predominantly marine deposits are much more powerful than that of the Germanic Triassic. Besides flachmeerischen Riffkomplexen (eg Wettersteinkalk ) there are stratified deposits of clays, limestones and marls that have arisen in deeper water.

In the Alps lie the original localities of chronostratigraphic stages of the Middle and Upper Triassic. The Skythium, single stage of the Alpine Triassic was, but not included in the international parlance.

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