Triassic

Triassic
source
Name	Triassic
Color	Triassic
Top boundary def	First appearance of the ammonite Hildoceras
Top boundary gssp	Kuhjoch, Karwendel, Austria
Top gssp acceptance	2010
Bottom boundary def	First appearance of the conodont Hindeodus parvus
Bottom boundary gssp	Meishan, Zhejiang, China
Bottom gssp acceptance	2001
Caption map	Paleogeography of the Triassic, c. 250 Ma
Time scale	ICS
Celestial body	earth
Usage	Global (ICS)
Timespan formal	251.902–201.4 Ma
Chrono unit	Period
Strat unit	System
Timespan oxygen	~16.5 vol %, (atmospheric)
Timespan co2	~1750 ppm, (atmospheric)
Timespan sea level	Relatively stable, then rising from the Carnian onwards

Triassic. The Triassic is a geologic period and system that spans from the end of the Permian to the beginning of the Jurassic, approximately 251.9 to 201.4 million years ago. It is the first period of the Mesozoic Era and is subdivided into three epochs: the Early Triassic, Middle Triassic, and Late Triassic. This interval witnessed the gradual recovery of Earth's biosphere following the catastrophic Permian–Triassic extinction event and laid the foundation for the age of dinosaurs.

Etymology and history

The term "Triassic" was coined in 1834 by the German geologist Friedrich von Alberti, based on the distinctive three-part (triassic) division of rock strata found widely across Germany and northwestern Europe. This tripartite division corresponds to the Bunter Sandstone, Muschelkalk, and Keuper formations. The period's formal definition and its placement within the Phanerozoic geologic time scale were solidified through later work by figures like Roderick Murchison and the identification of key index fossils, such as ammonites and conodonts. The ratification of the Global Boundary Stratotype Section and Point (GSSP) for its base at Meishan, Zhejiang in China in 2001 formally defined its start.

Geology

The Triassic System is represented globally by a variety of sedimentary rocks, including widespread continental red beds like the Newark Supergroup in North America and the Sherwood Sandstone Group in the United Kingdom. Significant marine deposits are found in the Tethys Ocean realm, such as the Hallstatt Limestone of the Alps. Major tectonic events included the ongoing assembly of the supercontinent Pangaea and the early rifting phases that would later open the Atlantic Ocean, such as the initiation of the Central Atlantic Magmatic Province. The period's end is marked in many regions by a hiatus or unconformity, often overlain by Jurassic strata like the Blue Lias.

Paleogeography and climate

During the Triassic, almost all of Earth's landmass was consolidated into the single supercontinent Pangaea, with a vast global ocean known as Panthalassa and a large eastward embayment called the Tethys Sea. The interior of Pangaea was extremely arid, evidenced by extensive desert deposits and evaporite basins like those preserved in the Cheshire Basin. The climate was generally hot and dry, with no evidence of polar ice caps, though a significant pluvial episode known as the Carnian Pluvial Event occurred, linked to volcanic activity from the Wrangellia Terrane. Atmospheric carbon dioxide levels were high, contributing to a greenhouse climate.

Life

Following the Permian–Triassic extinction event, terrestrial and marine ecosystems were dominated by disaster taxa like the hardy Lystrosaurus. The marine realm saw the rise of modern-type scleractinian coral reefs, new ammonite families, and marine reptiles such as ichthyosaurs and plesiosaurs. On land, key plant groups included cycads, conifers, and ginkgoes. The period is most famous for the emergence and diversification of the first true dinosaurs, like Herrerasaurus and Coelophysis, as well as other archosaurs including the ancestors of crocodiles and pterosaurs. The first true mammals, small shrew-like creatures such as Morganucodon, also appeared in the Late Triassic.

Extinction events

The Triassic was punctuated by several extinction events. The most significant was the Triassic–Jurassic extinction event at its conclusion, which severely affected marine life, including the final demise of the conodonts and major reductions in ammonite and brachiopod diversity. On land, it led to the extinction of many large archosaur groups, clearing ecological space for dinosaurs to dominate the Jurassic. Earlier crises include the end-Carnian extinction, possibly linked to the Carnian Pluvial Event and volcanism from the Wrangellia Terrane. These events are recorded in sections like the Pucara Group in Peru and the Luning Formation in Nevada.

Category:Triassic Category:Geological periods Category:Mesozoic