La Amarga Formation

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The La Amarga Formation is a lithostratigraphic formation , which in Argentina open is. These are continental sedimentary rocks that can be dated to the Lower Cretaceous ( Barremian to Lower Aptian ). The La Amarga Formation belongs to the Neuquén Basin and is the oldest continental formation of this sedimentary basin . It is particularly famous for its wealth of fossils, including the remains of dinosaurs .

location

This formation was first described by Roll (1939) and named by Musacchio (1970). The type locality is the Wadi La Amarga and the nearby northern slope of the China Muerta Hill, about 70 km south of the city of Zapala in the Argentine province of Neuquén . The La Amarga Formation is part of the Neuquén Basin and is underlain by the marine Agrio Formation and overlaid by the continental Lohan Cura Formation . It is discordantly separated from both formations (by sedimentation gaps).

construction

This formation reaches a thickness of about 159 meters. It is divided into three sub-formations ( eng. Member ): At the base is the Puesto-Antigual-Member with a thickness of about 29 meters. This subformation consists of fluviatil deposited sandstones of a Zopfstromsystem . The middle subformation is the Bañados-de-Caichigüe-Member with a thickness of approx. 21 meters, which consists of white to yellowish limestones , which alternate with black slate and greenish siltstones . The limestones were deposited lakustrin (in a lake). The Piedra Parada member , the uppermost subformation, takes up more than two thirds of the sequence with a thickness of approx. 109 meters and consists of light brown to reddish, fine to medium-grain sandstones, which alternate with reddish and brown to greenish siltstones . The sediments of this subformation were deposited by a river system; there are also indications of swamping and soil formation ( paleo soils ).

Fossils

The La Amarga Formation is of particular scientific importance due to its wealth of fossil vertebrates. These fossils come mainly from the lower subformation, the Puesto-Antigual-Member, and include the remains of sauropod , thyrophore and theropod dinosaurs , crocodile relatives and mammals. Sauropods were represented by the dicraeosaurids Amargasaurus , the original Diplodocoidea Zapalasaurus and the titanosaur Amargatitanis . Other remains could be attributed to the original representatives of the Titanosauriformes and Rebbachisauriden . Thyrophore dinosaurs are represented by the fragmentary remains of a stegosaur - the only known stegosaur from South America so far. Theropod dinosaurs are represented by the abelisaur Ligabueino ; teeth were also found that can be ascribed to a large tetanuric . Crocodile relatives appeared with the Mesoeucrocodylia Amargasuchus . Mammals are represented by the Cladotheria Vincelestes neuquenianus - it is the only mammal described so far from the Lower Cretaceous South America.

Individual evidence

  1. ^ A b Fernando E. Novas: The age of dinosaurs in South America . Indiana University Press, Bloomington 2009, ISBN 978-0-253-35289-7 , pp. 151-152, 172 .
  2. ^ A. Roll: La cuenca de los estratos con dinosaurios al sur del río Neuquén. Informe inédito. Yacimientos Petrolíferos Fiscales, 1939
  3. ↑ E. Musacchio: Ostrácodos de la super familias y Cytheraceae Darwinulaceae de la Formación La Amarga (Cretacico inferior), provincia del Neuquen, Argentina . In: Ameghiniana . tape 7 , 1970, pp. 301-318 .
  4. ↑ Leonardo Salgado, Ismar de Souza Carvalho, Alberto C. Garrido: Zapalasaurus bonapartei, un nuevo dinosaurio saurópodo de La Formación La Amarga (Cretácico Inferior), noroeste de Patagonia, Provincia de Neuquén, Argentina . In: Geobios . tape 39 , no. 5 , August 2006, p. 695-707 , doi : 10.1016 / j.geobios.2005.06.001 .
  5. ↑ a b Héctor A. Leanza, Sebastián Apesteguı́a, Fernando E. Novas, Marcelo S. de la Fuente: Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages . In: Cretaceous Research . tape 25 , no. 1 , January 2004, p. 61-87 , doi : 10.1016 / j.cretres.2003.10.005 .
  6. ^ Sebastián Apesteguía: The sauropod diversity of the La Amarga Formation (Barremian), Neuquén (Argentina) . In: Gondwana Research . tape 12 , no. 4 , October 2007, p. 533-546 , doi : 10.1016 / j.gr.2007.04.007 .