Chañares Formation
The Chañares Formation is a geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Provence, Argentina. The claystones and tuffs of the formation date to the Carnian stage of the Late Triassic and were deposited in a fluvial to lacustrine environment.
Chañares Formation Stratigraphic range: Carnian ~237–235 Ma | |
---|---|
Type | Geologic formation |
Unit of | Agua de la Peña Group |
Underlies | Ischichuca Formation |
Overlies | Tarjados Formation |
Thickness | 750 m (2,460 ft) (includes Ischichuca Fm.) |
Lithology | |
Primary | Claystone |
Other | Tuff |
Location | |
Coordinates | 29.8°S 67.8°W |
Approximate paleocoordinates | 49.9°S 37.8°W |
Region | La Rioja Province |
Country | |
Extent | Ischigualasto-Villa Unión Basin |
Type section | |
Named for | Chañares River |
Chañares Formation (Argentina) |
The formation represents the onset of the first syn-rift phase in the Triassic rift basin and is the lowermost stratigraphic unit of the Agua de la Peña Group, unconformably overlying the Tarjados Formation of the Paganzo Group. The Chañares Formation is overlain by the Ischichuca Formation and both formations have a combined maximum thickness of 750 metres (2,460 ft).
The Chañares Formation has provided a rich faunal assemblage, including many of the earliest crocodylomorph fossils, as Tropidosuchus, Chanaresuchus, and Gualosuchus, as well as other archosaurs; Lewisuchus admixtus, Lagerpeton, Marasuchus lilloensis, Gracilisuchus, Luperosuchus and Pseudolagosuchus major. Cynodonts are represented by Probainognathus and Massetognathus and other therapsids include Dinodontosaurus.
Description
The Chañares Formation is the lowermost unit of the Agua de la Peña Group, representing the onset of the first syn-rift phase of the basin. The combined thickness of the overlying Ischichuca Formation and the Chañares Formation is 750 metres (2,460 ft).[1] It was originally thought to be formed during the Ladinian age of the Middle Triassic epoch, in the Triassic Period of the Mesozoic Era; Marsicano et al. (2016) dated it to early Carnian (235–234 Ma), Late Triassic.[2] 2020 U-Pb dating of the lower Los Rastros Formation overlying the Ischichuca Formation yielded an age of 234.47 ± 0.44 Ma, making the Chañares Formation lowermost Carnian.[3]
The formation overlies the Tarjados Formation and is overlain by the Ischichuca Formation. The formation is exposed in the Ischigualasto Provincial Park, a World Heritage site in Argentina.[4] The formation of claystones and tuffs was deposited in a fluvial to lacustrine environment.[5][6]
Fossil content
Some localities are well known for their abundance of tetrapod fossils. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter being the most abundant tetrapod taxon in the formation represented by Massetognathus pascuali and M. teruggii.[7]
Other notable tetrapods present from the formation are the archosaurs. Ornithodirans include Lewisuchus,[8][9] Lagerpeton,[10] and Marasuchus.[11]
Other archosaurs include Gracilisuchus[12] and Luperosuchus.[13] Three proterochampsids are known from the formation, Tropidosuchus, Chanaresuchus, and Gualosuchus. They are very similar in appearance, but differ in size and cranial proportions.[14] Tropidosuchus had an estimate body mass of about 3 kilograms (6.6 lb), Gualosuchus of approximately 10 kilograms (22 lb), and Chanaresuchus weighed about 20 kilograms (44 lb).[5]
In 2018, plant remains and palynomorphs preserved in the coprolites produced by large dicynodonts, and a study on their implications for inferring the diet of dicynodonts from the formation were described.[15] Also tetrapod burrows, likely produced by small eucynodonts, were described.[16]
Other fossils
References
- Aceituno Cieri et al., 2015, p.60
- Marsicano et al., 2016
- Mancuso et al., 2020
- Kent et al, 2014, p.7959
- Arcucci et al., 2019, p.3
- Chañares Tetrapod Assemblage at Fossilworks.org
- Romer, 1967, III
- Romer, 1972, XIV
- Bittencourt, 2014, p.2
- Romer, 1972, X
- Sereno & Arcucci, 1994
- Romer, 1972, XIII
- Romer, 1971, VIII
- Romer, 1971, XI
- Pérez et al., 2018
- Fiorelli et al., 2018
- Agua Escondida at Fossilworks.org
Bibliography
- Arcucci, A., and C.A. Marsicano. 1999. A distinctive new archosaur from the Middle Triassic (Los Chañares Formation) of Argentina. Journal of Vertebrate Paleontology 19. 228–232. Accessed 2019-03-28.
- Arcucci, A.B. 1987. Un nuevo Lagosuchidae (Thecodontia-Pseudosuchia) de la fauna de Los Chañares (Edad Reptil Chañarense, Triasico Medio), La Rioja, Argentina. Ameghiniana 24. 89–94. Accessed 2019-03-28.
- Bittencourt, Jonathas S.; Andrea B. Arcucci; Claudia A. Marsicano, and Max C. Langer. 2014. Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs. Journal of Systematic Palaeontology _. 1–31. Accessed 2019-03-28.
- Fiorelli, Lucas E.; Sebastián Rocher; Agustín G. Martinelli; Martín D. Ezcurra; E. Martín Hechenleitner, and Miguel Ezpeleta. 2018. Tetrapod burrows from the Middle–Upper Triassic Chañares Formation (La Rioja, Argentina) and its palaeoecological implications. Palaeogeography, Palaeoclimatology, Palaeoecology 496. 85–102. Accessed 2019-03-28.
- Kent, Dennis V.; Paula Santi Malnis; Carina E. Colombi; Oscar A. Alcober, and Ricardo N. Martínez. 2014. Age constraints on the dispersal of dinosaurs in the Late Triassic from magnetochronology of the Los Colorados Formation (Argentina). Proceedings of the National Academy of Sciences 111. 7958–7963. Accessed 2018-09-08.
- Mancuso, Adriana C.; Cecilia A. Benavente; Randall B. Irmis, and Roland Mundil. 2020. Evidence for the Carnian Pluvial Episode in Gondwana: New multiproxy climate records and their bearing on early dinosaur diversification. Gondwana Research in press. . doi:10.1016/j.gr.2020.05.009
- Marsicano, Claudia A.; Randall B. Irmis; Adriana C. Mancuso; Roland Mundil, and Farid Chemale. 2016. The precise temporal calibration of dinosaur origins. Proceedings of the National Academy of Sciences of the United States of America 113. 509–513. Accessed 2019-03-28.
- Pérez Loinaze, Valeria Susana; Ezequiel Ignacio Vera; Lucas Ernesto Fiorelli, and Julia Brenda Desojo. 2018. Palaeobotany and palynology of coprolites from the Late Triassic Chañares Formation of Argentina: implications for vegetation provinces and the diet of dicynodonts. Palaeogeography, Palaeoclimatology, Palaeoecology 502. 31–51. Accessed 2018-09-08.
- Rogers, R.R.; A.B. Arcucci; F. Abdala; P.C. Sereno; C.A. Forster, and C.L. May. 2001. Paleoenvironment and taphonomy of the Chañares Formation tetrapod assemblage (Middle Triassic), northwestern Argentina: spectacular preservation in volcanogenic concretions. Palaios 16. 461–481. Accessed 2019-03-28.
- Sereno, P.C., and A.B. Arcucci. 1994. Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov. Journal of Vertebrate Paleontology 14. 53–73. Accessed 2019-03-28.
- The Chañares Triassic reptile fauna
- Romer, Alfred Sherwood. 1973. The Chañares (Argentina) Triassic reptile fauna. XX. Summary. Breviora 413. 1–20. Accessed 2019-03-28.
- Romer, Alfred Sherwood, and Arnold D. Lewis. 1973. The Chañares (Argentina) Triassic reptile fauna. XIX. Postcranial materials of the cynodonts Probelesodon and Probainognathus. Breviora 407. 1–26. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1973. The Chañares (Argentina) Triassic reptile fauna. XVIII. Probelesodon minor, a new species of carnivorous cynodont; family Probainognathidae nov. Breviora 401. 1–4. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1972. The Chañares (Argentina) Triassic reptile fauna. XVII. The Chañares gomphodonts. Breviora 396. 1–9. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1972. The Chañares (Argentina) Triassic reptile fauna. XVI. Thecodont classification. Breviora 395. 1–15. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1972. The Chañares (Argentina) Triassic reptile fauna. XIV. Lewisuchus admixtus, gen. et sp. nov., a further thecodont from the Chañares beds. Breviora 390. 1–13. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1972. The Chañares (Argentina) Triassic reptile fauna. XIII. A fragmentary skull of a large thecodont, Luperosuchus fractus. Breviora 389. 1–8. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1972. The Chañares (Argentina) Triassic reptile fauna. XII. The postcranial skeleton of the thecodont Chanaresuchus. Breviora 385. 1–21. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1971. The Chañares (Argentina) Triassic reptile fauna. XI. Two new long-snouted thecodonts, Chanaresuchus and Gualosuchus. Breviora 379. 1–22. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1971. The Chañares (Argentina) Triassic reptile fauna. X. Two new but incompletely known long-limbed pseudosuchians. Breviora 378. 1–8. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1971. The Chañares (Argentina) Triassic reptile fauna. IX. The Chanares Formation. Breviora 377. 1–8. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1971. The Chañares (Argentina) Triassic reptile fauna. VIII. A fragmentary skull of a large thecodont, Luperosuchus fractus. Breviora 373. 1–8. Accessed 2019-03-28.
- Jenkins, Farish A. 1970. The Chañares (Argentina) Triassic reptile fauna. VII. The postcranial skeleton of the traversodontid Massetognathus pascuali (Therapsida, Cynodontia). Breviora 352. 1–28. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1970. The Chañares (Argentina) Triassic reptile fauna. VI. A chiniquodontid cynodont with an incipient squamosal-dentary jaw articulation. Breviora 344. 1–18. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1969. The Chañares (Argentina) Triassic reptile fauna. V. A new chiniquodontid cynodont, Probelesodon lewisi - cynodont ancestry. Breviora 333. 1–24. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1968. The Chañares (Argentina) Triassic reptile fauna. IV. The dicynodont fauna. Breviora 295. 1–25. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1967. The Chañares (Argentina) Triassic reptile fauna. III. Two new gomphodonts, Massetognathus pascuali and M. teruggii. Breviora 264. 1–25. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1966. The Chañares (Argentina) Triassic reptile fauna. II. Sketch of the geology of the Rio Chañares-Rio Gualo region. Breviora 252. 1–20. Accessed 2019-03-28.
- Romer, Alfred Sherwood. 1966. The Chañares (Argentina) Triassic reptile fauna. I. Introduction. Breviora 247. 1–14. Accessed 2019-03-28.