The La Amarga Formation is a geologic formation with outcrops in the Argentine provinces of Río Negro, Neuquen Province, Neuquén, and Mendoza Province, 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 unconformity, unconformably overlies the marine (ocean), marine Agrio Formation of the Mendoza Group. It is in turn overlain by the Lohan Cura Formation, separated by another unconformity.


There are three Geologic unit, members within the La Amarga Formation. # The oldest is the Puesto Antigual Member, which is approximately 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 thick. Alternating limestones, shales, and siltstones make up this member, indicating a Lake, lacustrine (lake) environment. # Youngest and thickest is the Piedra Parada Member, approximately 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: *a crocodilian (''Amargasuchus'') *a dicraeosaurid sauropod (''Amargasaurus'')Weishampel et al., 2004, "Dinosaur distribution (Early Cretaceous, South America).", pp.563-570 *a diplodocoid sauropod (''Zapalasaurus'') *a titanosaurian sauropod *an abelisauroid theropod (''Ligabueino'') *a stegosaur (''Amargastegos'') *a mammal (''Vincelestes'')


Other tetrapods

See also

* List of dinosaur-bearing rock formations



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Further reading

* * {{DEFAULTSORT:Amarga Formation, La La Amarga Formation, Geologic formations of Argentina Lower Cretaceous Series of South America Cretaceous Argentina Sandstone formations Mudstone formations Alluvial deposits Fluvial deposits Lacustrine deposits Paleontology in Argentina