Irati Formation

Irati Formation is the name of a geological formation of the Paraná Basin in Brazil. It has previously been dated as Late Permian using palynomorphs, but is now dated as Early Permian using zircon ages obtained from bentonite layers. The base of the formation has been dated at 278.4 ± 2.2 Ma.[1][2] Exposures of the Irati Formation are to be found in the South (Geopark of Paleorrota), southeastern Brazil and in the states of Goiás, Mato Grosso, São Paulo, Paraná, Santa Catarina, Rio Grande do Sul and Mato Grosso do Sul.[1] The formation is part of the Passa Dios Group, underlying the Serra Alta Formation and overlying the Palermo Formation. The formation has been deposited in a restricted marine environment.[3] The Irati Formation, with a maximum thickness of 80 metres (260 ft), was defined and named by White in 1908.[4]

Irati Formation
Stratigraphic range: Early Permian
~278.4–270 Ma
The Irati Formation belongs to the Gondwana I megasequence
TypeGeological formation
Unit ofPassa Dois Group
UnderliesSerra Alta Formation (Paraná Basin)
Teresina Formation (Pelotas Basin)
OverliesPalermo Formation
Area1,000,000 km2 (390,000 sq mi)
Thicknessup to 80 m (260 ft)
Lithology
PrimaryBlack shale
OtherSandstone
Location
Coordinates25.5°S 50.7°W / -25.5; -50.7
RegionParaná & Pelotas Basins
Goiás, Mato Grosso do Sul, Mato Grosso, São Paulo, Paraná, Santa Catarina, Rio Grande do Sul
Country Brazil
Type section
Named byWhite
Year defined1908
Approximate paleocoordinates45.8°S 29.7°W / -45.8; -29.7

The Paraná Basin in South America

Fossil content

The formation is particularly famous for the occurrences of the mesosaurs Mesosaurus tenuidiens,[5] and Stereosternum tumidum. Other fossils found in the formation are Myelontordoxylon camposii,[6] and crustaceans of the genera Paulocaris, Pygaspis, Liocaris, and Clarkecaris.[7] It is considered time equivalent to the Whitehill Formation of the Ecca Group of the Karoo Supergroup of southern Africa and the Mangrullo Formation of Uruguay.[8]

  • Reconstruction of Mesosaurus
  • Reconstruction of Stereosternum

See also

References
  1. Da Costa, 2015, p.28
  2. Ventura Santos et al., 2006
  3. Diduch, 2011, p.21
  4. Da Costa, 2015, p.12
  5. Irati at Fossilworks.org
  6. Diduch, 2011, p.24
  7. Diduch, 2011, p.23
  8. Piñeiro et al., 2012, p.299

Bibliography
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