La Amarga Formation

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La Amarga Formation
Stratigraphic range: Barremian - early Aptian
Type Geological formation
Sub-units Puesto Antigual Member
Bañados de Caichigüe Member
Piedra Parada Member
Underlies Lohan Cura Formation
Overlies Agrio Formation
Thickness 160 m (520 ft)
Location
Region Río Negro, Mendoza & Neuquén Provinces
Country  Argentina
Type section
Named for La Amarga Arroyo & China Muerta Hill
Named by Musacchio, 1970

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.

The type locality is La Amarga Arroyo and China Muerta Hill (Musacchio, 1970). 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.

Age[edit]

Era: Mesozoic
Period: Early Cretaceous
Faunal stage: Barremian through early Aptian
Absolute Age: 130 to ~120 mya

Composition[edit]

There are three members within the La Amarga Formation.

The oldest is the Puesto Antigual Member, which is approximately 28.9 meters thick and consists mainly of sandstone deposited in the channels of a braided river system. Paleosols, or soil deposits, are well-developed.

The Bañados de Caichigüe Member is the next highest, approximately 20.9 meters thick. Alternating limestones, shales, and siltstones make up this member, indicating a lacustrine (lake) environment.

Youngest and thickest is the Piedra Parada Member, approximately 109.4 meters thick in some sections. This member consists of alternating sandstones and siltstones from an ancient alluvial plain, with some swamp and paleosol deposits.

Vertebrate paleofauna[edit]

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

Possible indeterminate stegosaurid remains located in Provincia de Neuquen, Argentina.[1]

Dinosaurs[edit]

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.
Dinosaurs of the La Amarga Formation
Genus Species Province Member Notes Images

Amargasaurus[1]

A. cazaui[1]

Neuquén[1]

Puesto Antigual

"Braincase and associated postcranial skeleton."[2]

Amargastegos

A. brevicollus

Neuquén

Puesto Antigual

Considered dubious by Galton & Carpenter (2016), material referred to Stegosauria indet.[3]

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[1]

L. andesi[1]

Neuquén[1]

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."[4]

Stegosauria indet.[5]

Indeterminate

Neuquén

Puesto Antigual

"Supraorbital, cervical and caudal vertebrae, dermal armor".[3][5]

Zapalasaurus

Z. bonapartei

Neuquén

Piedra Parada

Other tetrapods[edit]

Misc. Tetrapods of the La Amarga Formation
Genus Species Province Member Notes Images

Amargasuchus

A. minor

Neuquén

Puesto Antigual

A trematochampsid crocodylomorph, found in association with the holotype of Amargasaurus.

Pterosauria indet.[6]

Indeterminate

Neuquén

An isolated femur.

Vincelestes

V. neuquenianus

Neuquén

Puesto Antigual

A cladotherian mammal.

See also[edit]

Footnotes[edit]

  1. ^ a b c d e f g h Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Cretaceous, South America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 563-570. ISBN 0-520-24209-2.
  2. ^ "Table 13.1," in Weishampel, et al. (2004). Page 264.
  3. ^ a b Galton, Peter M. & Carpenter, Kenneth, 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(2): 185-208
  4. ^ Carrano, M.T., Loewen, M.A. and Sertic, J.J.W. (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: 53pp.
  5. ^ a b Pereda-Suberbiola, Xabier; Galton, Peter M.; Mallison, Heinrich; Novas, Fernando (2012). "A plated dinosaur (Ornithischia, Stegosauria) from the Early Cretaceous of Argentina, South America: an evaluation". Alcheringa: An Australasian Journal of Palaeontology. 37 (1): 1–14. doi:10.1080/03115518.2012.702531. 
  6. ^ Montanelli, S. B. 1987. Presencia de Pterosauria (Reptilia) en la For mation La Amarga (Hauteriviano-Barremiano), Neuquén, Argentina. Ameghiniana 24:109-113

References[edit]

  • Leanza, H.A, Apesteguia, S., Novas, F.E. & de la Fuente, M.S. 2004. Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages. Cretaceous Research. 25(1): 61-87.
  • 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.