Late Triassic

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Late/Upper Triassic
~237 – 201.4 ± 0.2 Ma
Chronology

The Late Triassic is the third and final

Ma and 201.4 Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. The corresponding series of rock beds is known as the Upper Triassic. The Late Triassic is divided into the Carnian, Norian and Rhaetian ages
.

Many of the first dinosaurs evolved during the Late Triassic, including Plateosaurus, Coelophysis, Herrerasaurus, and Eoraptor. The Triassic–Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth.[8]

Etymology

The Triassic was named in 1834 by Friedrich von Alberti, after a succession of three distinct rock layers (Greek triás meaning 'triad') that are widespread in southern Germany: the lower Buntsandstein (colourful sandstone), the middle Muschelkalk (shell-bearing limestone) and the upper Keuper (coloured clay).[9] The Late Triassic Series corresponds approximately to the middle and upper Keuper.[10]

Dating and subdivisions

On the geologic time scale, the Late Triassic is usually divided into the Carnian, Norian, and Rhaetian ages, and the corresponding rocks are referred to as the Carnian, Norian, and Rhaetian stages.[11]

Triassic

Edmund von Mojsisovics in the 1860s. The base of the Late Triassic (which is also the base of the Carnian) is set at the first appearance of an ammonite, Daxatina canadensis. In the 1990s, conodonts became increasingly important in the Triassic timescale, and the base of the Rhaetian is now set at the first appearance of a conodont, Misikella posthernsteini. As of 2010, the base of the Norian has not yet been established, but will likely be based on conodonts.[12]

The late Triassic is also divided into

Late Triassic life

Following the

extinct Pycnodontiformes became more abundant in the Late Triassic.[14]

Carnian Age

The Carnian is the first age of the Late Triassic, covering the time interval from 237 to 227 million years ago.[11] The earliest true dinosaurs likely appeared during the Carnian and rapidly diversified.[15][16] They emerged in a world dominated by

rauisuchians, which the dinosaurs gradually began to displace.[17]

The emergence of the first dinosaurs came at about the same time as the Carnian pluvial episode, at 234 to 232 Ma. This was a humid interval in the generally arid Triassic. It was marked by high extinction rates in marine organisms, but may have opened niches for the radiation of the dinosaurs.[18][19]

Norian Age

The Norian is the second age of the Late Triassic, covering the time interval from about 227 to 208.5 million years ago.

ceratitid ammonites.[21]

The Manicouagan impact event occurred 214 million years ago. However, no extinction event is associated with this impact.[22][23]

Rhaetian Age

The Rhaetian Age was the final age of the Late Triassic, following the Norian Age,

bivalves, and many types of reptiles
did not survive through this age.

Climate and environment during the Triassic Period

During the beginning of the Triassic Period, the earth consisted of a giant landmass known as Pangea, which covered about a quarter of earth's surface. Towards the end of the period, continental drift occurred which separated Pangea. At this time, polar ice was not present because of the large differences between the equator and the poles.[citation needed] A single, large landmass similar to Pangea would be expected to have extreme seasons; however, evidence offers contradictions. Evidence suggests that there is arid climate as well as proof of strong precipitation. The planet's atmosphere and temperature components were mainly warm and dry, with other seasonal changes in certain ranges.[citation needed]

The Middle Triassic was known to have consistent intervals of high levels of humidity. The circulation and movement of these humidity patterns, geographically, are not known however. The major

Carnian Pluvial Event
stands as one focus point of many studies. Different hypotheses of the events occurrence include eruptions, monsoonal effects, and changes caused by plate tectonics. Continental deposits also support certain ideas relative to the Triassic Period. Sediments that include red beds, which are sandstones and shales of color, may suggest seasonal precipitation. Rocks also included dinosaur tracks, mudcracks, and fossils of crustaceans and fish, which provide climate evidence, since animals and plants can only live during periods of which they can survive through.

Evidence of environmental disruption and climate change

The Late Triassic is described as semiarid. Semiarid is characterized by light rainfall, having up to 10–20 inches of precipitation a year. The epoch had a fluctuating, warm climate in which it was occasionally marked by instances of powerful heat. Different basins in certain areas of Europe provided evidence of the emergence of the "Middle Carnian Pluvial Event." For example, the Western Tethys and German Basin was defined by the theory of a middle Carnian wet climate phase. This event stands as the most distinctive climate change within the Triassic Period. Propositions for its cause include:

  • Different behaviors of atmospheric or oceanic circulation forced by plate tectonics that may have participated in modifying the carbon cycle and other scientific factors.
  • heavy rains due to shifting of the earth
  • sparked by eruptions, typically originating from an accumulation of igneous rocks, which could have included liquid rock or volcanic rock formations

Theories and concepts are supported universally, due to extensive areal proof of Carnian siliciclastic sediments. The physical positions as well as comparisons of that location to surrounding sediments and layers stood as basis for recording data. Multiple resourced and recurring patterns in results of evaluations allowed for the satisfactory clarification of facts and common conceptions on the Late Triassic. Conclusions summarized that the correlation of these sediments led to the modified version of the new map of Central Eastern Pangea, as well as that the sediment's relation to the "Carnian Pluvial Event" is greater than expected.

  • High interest concerning the Triassic Period has fueled the need to uncover more information about the period's climate. The Late Triassic Epoch is classified as a phase entirely flooded with phases of monsoonal events. A monsoon affects large regions and brings heavy rains along with powerful winds. Field studies confirm the impact and occurrence of strong monsoonal circulation during this time frame. However, hesitations concerning climatic variability remains. Upgrading knowledge on the climate of a period is a difficult task to assess. Understanding of and assumptions of temporal and spatial patterns of the Triassic Period's climate variability still need revision. Diverse proxies hindered the flow of palaeontological evidence. Studies in certain zones are missing and could be benefited by collaborating the already existing but uncompared records of Triassic palaeoclimate.
  • A specific physical piece of evidence was found. A fire scar on the trunk of a tree, found in southeast Utah, dates back to the Late Triassic. The feature was evaluated and paved the path to the conclusion of one fire's history. It was categorized through comparison of other modern tree scars. The scar stood as evidence of Late Triassic wildfire, an old climatic event.

Triassic–Jurassic extinction event

The extinction event that began during the Late Triassic resulted in the disappearance of about 76% of all terrestrial and marine life species, as well as almost 20% of taxonomic families. Although the Late Triassic Epoch did not prove to be as destructive as the preceding Permian Period, which took place approximately 50 million years earlier and destroyed about 70% of land species, 57% of insect families as well as 95% of marine life, it resulted in great decreases in population sizes of many living organism populations.

The environment of the Late Triassic had negative effects on the

gastropods, marine reptiles and brachiopods
were greatly affected and many species became extinct during this time.

Causes of the extinction

Most of the evidence suggests the increase of volcanic activity was the main cause of the extinction. As a result of the rifting of the super continent

Central Atlantic Magmatic Province, for about 500,000 years. These intense eruptions were classified as flood basalt eruptions, which are a type of large scale volcanic activity that releases a huge volume of lava in addition to sulfur dioxide and carbon dioxide. The sudden increase in carbon dioxide levels is believed to have enhanced the greenhouse effect, which acidified the oceans and raised average air temperature. As a result of the change in biological conditions in the oceans, 22% of marine families became extinct. In addition, 53% of marine genera and about 76–86% of all species became extinct, which vacated ecological niches; thus, enabling dinosaurs to become the dominant presence in the Jurassic Period. While the majority of the scientists agree that volcanic activity was the main cause of the extinction, other theories suggest the extinction was triggered by the impact of an asteroid, climate change, or rising sea levels
.

Biological impact

The impacts that the Late Triassic had on surrounding environments and organisms were wildfire destruction of habitats and prevention of photosynthesis. Climatic cooling also occurred due to the soot in the atmosphere. Studies also show that 103 families of marine invertebrates became extinct at the end of the Triassic, but another 175 families lived on into the Jurassic. Marine and extant species were hit fairly hard by extinctions during this epoch. Almost 20% of 300 extant families became extinct; bivalves, cephalopods, and brachiopods suffered greatly. 92% of bivalves were wiped out episodically throughout the Triassic.

The end of the Triassic also brought about the decline of corals and reef builders during what is called a "reef gap". The changes in sea levels brought this decline upon corals, particularly the calcisponges and scleractinian corals. However, some corals would make a resurgence during the Jurassic Period. 17 brachiopod species were also wiped out by the end of the Triassic. Furthermore, conulariids became extinct.

References

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  3. ^ Retallack, G. J.; . Retrieved 29 September 2007.
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  8. S2CID 15895416.{{cite journal}}: CS1 maint: numeric names: authors list (link
    )
  9. ^ Friedrich von Alberti, Beitrag zu einer Monographie des bunten Sandsteins, Muschelkalks und Keupers, und die Verbindung dieser Gebilde zu einer Formation [Contribution to a monograph on the colored sandstone, shell limestone and mudstone, and the joining of these structures into one formation] (Stuttgart and Tübingen, (Germany): J. G. Cotta, 1834). Alberti coined the term "Trias" on page 324 :
    "… bunter Sandstein, Muschelkalk und Keuper das Resultat einer Periode, ihre Versteinerungen, um mich der Worte E. de Beaumont’s zu bedeinen, die Thermometer einer geologischen Epoche seyen, … also die bis jezt beobachtete Trennung dieser Gebilde in 3 Formationen nicht angemessen, und es mehr dem Begriffe Formation entsprechend sey, sie zu einer Formation, welche ich vorläufig Trias nennen will, zu verbinden."
    ( … colored sandstone, shell limestone, and mudstone are the result of a period; their fossils are, to avail myself of the words of E. de Beaumont, the thermometer of a geologic epoch; … thus the separation of these structures into 3 formations, which has been maintained until now, isn't appropriate, and it is more consistent with the concept of "formation" to join them into one formation, which for now I will name "trias".)
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  11. ^ a b c d Ogg, Ogg & Gradstein 2016.
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  17. ^ . Retrieved 22 October 2019.
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  20. ^ Olsen, P.E.; Schneider, V.; Sues, H.-D.; Peyer, K.M.; Carter, J.G. (2001). "Biotic provinciality of the Late Triassic equatorial humid zone". Geological Society of America, Abstracts with Programs. 33 (2): A-27.
  21. . Retrieved 23 November 2021.
  22. .
  23. ^ Ramezani, J., S. A. Bowring, M. S. Pringle, F. D. Winslow, III, and E. T. Rasbury (2005). "The Manicouagan impact melt rock: a proposed standard for intercalibration of U-Pb and 40Ar/39Ar isotopic systems". 15th V.M. Goldsmidt Conference Abstract Volume, p. A321.

Sources

Further reading