Guichón Formation

Guichón Formation
Stratigraphic range: Aptian-Santonian ~125–85 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Paysandú Group
Underlies	Mercedes Formation
Overlies	Arapey Formation
Thickness	Up to >100 m (330 ft) (in wells)
Lithology
Primary	Sandstone
Other	Conglomerate
Location
Coordinates	32.0°S 57.7°W / -32.0; -57.7
Approximate paleocoordinates	38.4°S 30.0°W / -38.4; -30.0
Region	Paysandú Department
Country	Uruguay
Extent	Norte Basin
Type section
Named for	Guichón
Guichón Formation (Uruguay)

The Guichón Formation is a Late Cretaceous geologic formation of the Paysandú Group in Uruguay. Dinosaur remains are among the fossils that have been recovered from the formation.[1]

Description

The Guichón Formation comprises mainly pink-greyish to reddish sandstones, which contain moderate to well-sorted, subrounded, fine to medium-sized grains in a pelitic matrix. These sandstones (which compositionally are feldspathic wackes) are either massive or may instead exhibit parallel lamination, cross-lamination and graded bedding. These lithologies were deposited in southwest-trending alluvial–fluvial systems comprising low-sinuosity channels traversing through sandy plains. Subordinate to the already mentioned sandstones are conglomeratic and pelitic lithologies, interpreted as channel-fill and overbank deposits, respectively. It is inferred that the Guichón Formation was deposited in warm, semi-arid climatic conditions.[2] The formation has been correlated to the Puerto Yeruá Formation of northwestern Argentina.[3]

The formation reaches a thickness of more than 100 metres (330 ft) in wells perforating the formation.[4] It is overlain by the Mercedes Formation and overlies the Arapey Formation.[5]

Fossil content

The following fossils have been reported from the formation:[2][6]

• Udelartitan celeste[7]
• Uruguaysuchus aznarezi[8]
• Iguanodontia indet.[9]
• Theropoda indet.[9]

Fossil eggs

• Sphaerovum sp.[10]

See also

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with indeterminate dinosaur fossils
• List of fossiliferous stratigraphic units in Uruguay

References

1. Weishampel et al., 2004, pp.517-607
2. Guichón at Fossilworks.org
3. Soto et al., 2009, p.13
4. Tofalo et al., 2011, p.616
5. Tofalo et al., 2011, p.617
6. Soto et al., 2009, p.19
7. Soto, M.; Carballido, J. L.; Langer, M. C.; Silva Junior, J. C. G.; Montenegro, F.; Perea, D. (2024). "Phylogenetic relationships of a new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Uruguay". Cretaceous Research. 160. 105894. doi:10.1016/j.cretres.2024.105894.
8. Mones, 1972
9. Soto et al., 2011
10. Soto et al., 2012

Bibliography

• Soto, M.; Perea, D.; Cambiaso, A. (2012), "First sauropod (Dinosauria: Saurischia) remains from the Guichón Formation, Late Cretaceous of Uruguay", Journal of South American Earth Sciences, 33: 68–79, doi:10.1016/j.jsames.2011.08.003
• Soto, M.; Perea, D. (2011), "A new specimen of Uruguaysuchus aznarezi (Crocodyliformes: Notosuchia) from the middle Cretaceous of Uruguay and its phylogenetic relationships", Zoological Journal of the Linnean Society, 163: S173 – S198, doi:10.1111/j.1096-3642.2011.00717.x, hdl:11336/69086
• Tófalo, Ofelia; Pazos, Pablo J.; Sánchez Bettucci, Leda (2011), "Estudio composicional de sedimentitas silicoclásticas y paleosuelos de la Formación Mercedes (Cretácico Superior), Uruguay", Revista de la Asociación Geológica Argentina, 68: 615–626, retrieved 2020-08-23
• Soto, M.; Perea, D.; Veroslavsky, G.; Rinderknecht, A.; Ubilla, M.; Lecuona, G. (2009), "Nuevos hallazgos de restos de dinosaurios y consideraciones sobre la edad de la Formación Guichón - New findings of dinosaur remains and considerations on the age of the Guichón Formation" (PDF), Revista Sociedad Uruguaya de Geología, 15: 11–23, retrieved 2018-09-07
• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004), The Dinosauria, 2nd edition, Berkeley: University of California Press, pp. 1–880, ISBN 0-520-24209-2, retrieved 2019-02-21
• Mones, A (1972), "Lista de los vertebrados fósiles del Uruguay, I. Chondrichthyes, Osteichthyes, Reptilia, Aves - List of the fossil vertebrates of Uruguay, I. Chondrichthyes, Osteichthyes, Reptilia, Aves", Comunicaciones Paleontologicas del Museo de Historia Natural de Montevideo, 1: 23–35
• von Huene, F (1934), "Neue Saurier-Zähne aus der Kreide von Uruguay - New saurian teeth from the Cretaceous of Uruguay", Centralblatt für Mineralogie, Geologie und Paläontologie, Abteilung B, 1934: 183–189