Open main menu

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)
Coordinates39°36′S 70°12′W / 39.6°S 70.2°W / -39.6; -70.2Coordinates: 39°36′S 70°12′W / 39.6°S 70.2°W / -39.6; -70.2
Approximate paleocoordinates39°36′S 35°12′W / 39.6°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 is located in Argentina
La Amarga Formation
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.


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 contentEdit

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


Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
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


A. cazaui[2]


Puesto Antigual

"Braincase and associated postcranial skeleton."[3]


A. brevicollus


Puesto Antigual

Considered dubious by Galton & Carpenter (2016), material referred to Stegosauria indet.[4]


A. macni


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."


L. andesi[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]



Puesto Antigual

"Supraorbital, cervical and caudal vertebrae, dermal armor".[4][6]


Z. bonapartei


Piedra Parada

Other tetrapodsEdit

Other tetrapods of the La Amarga Formation
Genus Species Province Member Notes Images


A. minor


Puesto Antigual

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

Pterosauria indet.[7]



An isolated femur.


V. neuquenianus


Puesto Antigual

A cladotherian mammal.

See alsoEdit


  1. ^ Musacchio, 1970
  2. ^ a b c d e f g 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.
  3. ^ "Table 13.1," in Weishampel, et al. (2004). Page 264.
  4. ^ 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
  5. ^ 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.
  6. ^ 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.
  7. ^ Montanelli, S. B. 1987. Presencia de Pterosauria (Reptilia) en la For mation La Amarga (Hauteriviano-Barremiano), Neuquén, Argentina. Ameghiniana 24:109-113

Further readingEdit