La Amarga Formation

The La Amarga Formation is a geologic formation with outcrops in the Argentine provinces of Río Negro, Neuquén, and Mendoza. It is the oldest Cretaceous terrestrial formation in the Neuquén Basin.

La Amarga Formation
Stratigraphic range: Barremian-Early Aptian
~130–120 Ma
TypeGeological formation
Unit ofRayoso Group
Sub-unitsPuesto Antigual, Bañados de Caichigüe & Piedra Parada Members
UnderliesLohan Cura Formation
OverliesAgrio Formation
Thickness160 m (520 ft)
Lithology
PrimarySandstone
OtherMudstone
Location
Coordinates39.6°S 70.2°W / -39.6; -70.2
Approximate paleocoordinates39.6°S 35.2°W / -39.6; -35.2
RegionRío Negro, Mendoza & Neuquén Provinces
Country Argentina
ExtentNeuquén Basin
Type section
Named forLa Amarga Arroyo
Named byMusacchio
Year defined1970
La Amarga Formation (Argentina)

The type locality is La Amarga Arroyo and China Muerta Hill.[1] The La Amarga Formation unconformably overlies the marine Agrio Formation of the Mendoza Group. It is in turn overlain by the Lohan Cura Formation, separated by another unconformity.

Composition

There are three members within the La Amarga Formation.

  1. The oldest is the Puesto Antigual Member, which is approximately 28.9 metres (95 ft) thick and consists mainly of sandstone deposited in the channels of a braided river system. Paleosols, or soil deposits, are well-developed.
  2. The Bañados de Caichigüe Member is the next highest, approximately 20.9 metres (69 ft) thick. Alternating limestones, shales, and siltstones make up this member, indicating a lacustrine (lake) environment.
  3. Youngest and thickest is the Piedra Parada Member, approximately 109.4 metres (359 ft) thick in some sections. This member consists of alternating sandstones and siltstones from an ancient alluvial plain, with some swamp and paleosol deposits.

Fossil content

Most of the tetrapod fossils found in the La Amarga come from the Puesto Antigual Member, including:

Dinosaurs

Dinosaurs of the La Amarga Formation
GenusSpeciesProvinceMemberNotesImages
Amargasaurus[2] A. cazaui[2] Neuquén[2] Puesto Antigual "Braincase and associated postcranial skeleton."[3]
Amargastegos A. brevicollus Neuquén Puesto Antigual Considered dubious by Galton & Carpenter (2016), material referred to Stegosauria indet.[4]
Amargatitanis A. macni Neuquén Puesto Antigual "Two caudal vertebrae, an incomplete right ischium, a right femur, an incomplete right tibia, an incomplete right fibula, a right astragalus, and an incomplete right metatarsal I."
Ligabueino[2] L. andesi[2] Neuquén[2] Puesto Antigual "A cervical neural arch, a mid to posterior dorsal neural arch, a posterior dorsal centrum, the left femur, left ilium, articulated pubic shafts, and two pedal phalanges."[5]
Stegosauria indet.[6] Indeterminate Neuquén Puesto Antigual "Supraorbital, cervical and caudal vertebrae, dermal armor".[4][6]
Zapalasaurus Z. bonapartei Neuquén Piedra Parada

Other tetrapods

Other tetrapods of the La Amarga Formation
GenusSpeciesProvinceMemberNotesImages
Amargasuchus A. minor Neuquén Puesto Antigual A trematochampsid crocodylomorph, found in association with the holotype of Amargasaurus
Pterosauria indet.[7] Indeterminate Neuquén An isolated femur
Vincelestes V. neuquenianus Neuquén Puesto Antigual A cladotherian mammal
Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

See also

  • List of dinosaur-bearing rock formations

References

  1. Musacchio, 1970
  2. Weishampel et al., 2004, "Dinosaur distribution (Early Cretaceous, South America).", pp.563-570
  3. "Table 13.1," in Weishampel et al., 2004, p.264
  4. Galton & Carpenter, 2016
  5. Carrano et al., 2011
  6. Pereda Suberbiola et al., 2012
  7. Montanelli, 1987

Bibliography

  • Galton, Peter M., and Kenneth Carpenter. 2016. The plated dinosaur Stegosaurus longispinus Gilmore, 1914 (Dinosauria: Ornithischia; Upper Jurassic, western USA), type species of Alcovasaurus n. gen.. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 279. 185–208.
  • Pereda Suberbiola, Xabier; Peter M. Galton; Heinrich Mallison, and Fernando Novas. 2012. A plated dinosaur (Ornithischia, Stegosauria) from the Early Cretaceous of Argentina, South America: an evaluation. Alcheringa: An Australasian Journal of Palaeontology 37. 1–14. doi:10.1080/03115518.2012.702531
  • Carrano, M.T.; M.A. Loewen, and J.J.W. Sertic. 2011. New Materials of Masiakasaurus knopfleri Sampson, Carrano, and Forster, 2001, and Implications for the Morphology of the Noasauridae (Theropoda: Ceratosauria). Smithsonian Contributions to Paleobiology 95. 1–53.
  • Weishampel, David B.; Peter Dodson, and Halszka Osmólska (eds.). 2004. The Dinosauria, 2nd edition, 1–880. Berkeley: University of California Press. Accessed 2019-02-21. ISBN 0-520-24209-2
  • Montanelli, S. B. 1987. Presencia de Pterosauria (Reptilia) en la Formación La Amarga (Hauteriviano-Barremiano), Neuquén, Argentina. Ameghiniana 24. 109–113.
  • Musacchio, E. 1970. Ostrácodos de la superfamilias Cytheraceae y Darwinulaceae de la Formación La Amarga (Cretácico inferior), provincia del Neuquén, Argentina. Ameghiniana 7. 301–318.

Further reading

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