La Amarga Formation
Encyclopedia
The La Amarga Formation is a geologic formation
with outcrop
s 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.
Period: Early Cretaceous
Faunal stage
: Barremian
through early Aptian
Absolute Age
: 130 to ~120 mya
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. Paleosol
s, 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.
fossil
s found in the La Amarga come from the Puesto Antigual Member, including:
Possible indeterminate stegosaurid remains located in Provincia de Neuquen, Argentina.
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
with outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
s in the Argentine
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
provinces of Río Negro
Río Negro Province
Río Negro is a province of Argentina, located at the northern edge of Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean.Its capital is Viedma...
, Neuquén
Neuquén Province
Neuquén is a province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west...
, and Mendoza
Mendoza Province
The Province of Mendoza is a province of Argentina, located in the western central part of the country in the Cuyo region. It borders to the north with San Juan, the south with La Pampa and Neuquén, the east with San Luis, and to the west with the republic of Chile; the international limit is...
. It is the oldest Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
terrestrial formation in the Neuquén Basin.
The type locality is La Amarga Arroyo and China Muerta Hill (Musacchio, 1970). The La Amarga Formation unconformably
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
overlies the marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
Agrio Formation of the Mendoza Group. It is in turn overlain by the Lohan Cura Formation
Lohan Cura Formation
The Lohan Cura Formation is a geologic formation with outcrops in the Argentine provinces of Río Negro, Neuquén, and Mendoza. It is the second oldest Cretaceous terrestrial formation in the Neuquén Basin....
, separated by another unconformity.
Age
Era: MesozoicMesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Period: Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
: Barremian
Barremian
The Barremian is an age in the geologic timescale between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch...
through early Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
Absolute Age
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
: 130 to ~120 mya
Composition
There are three membersGeologic unit
A geological unit is a volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features that characterize it....
within the La Amarga Formation.
The oldest is the Puesto Antigual Member, which is approximately 28.9 meters thick and consists mainly of sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
deposited in the channels of a braided river
Braided river
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load...
system. Paleosol
Paleosol
In the geosciences, paleosol can have two meanings. The first meaning, common in geology and paleontology, refers to a former soil preserved by burial underneath either sediments or volcanic deposits , which in the case of older deposits have lithified into rock...
s, 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
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
(lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
) 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
Alluvial plain
An alluvial plain is a relatively flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms...
, with some swamp
Swamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
and paleosol deposits.
Vertebrate paleofauna
Most of the tetrapodTetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s found in the La Amarga come from the Puesto Antigual Member, including:
- a crocodiliaCrocodiliaCrocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
n (AmargasuchusAmargasuchusAmargasuchus is an extinct genus of crocodylomorph. It was a member of the Trematochampsidae, an enigmatic family of mesoeucrocodylians. Fossils have been found from the La Amarga Formation in Argentina and date back to the Barremian and Aptian stages of the Early Cretaceous...
) - a dicraeosaurid sauropod (AmargasaurusAmargasaurusAmargasaurus is a genus of dicraeosaurid sauropod dinosaur from the Early Cretaceous Period of what is now South America. It was small for a sauropod, reaching 10 meters length. It would have been a quadrupedal herbivore with a long, low skull on the end of a long neck, much like its relative...
) - a diplodocoid sauropod (ZapalasaurusZapalasaurusZapalasaurus is a genus of dinosaur described by Leonardo Salgado, Ismar de Souza Carvalho and Alberto C. Garrido, in 2006. The type species, Zapalasaurus bonapartei, was found in Neuquén Province, Argentina. It was a diplodocoid, a long-necked herbivore, and it lived during the Early Cretaceous...
) - a titanosaurian sauropod
- an abelisaurAbelisaurAbelisaurs were a group of ceratosaurian dinosaurs which lived in the Southern hemisphere during the Cretaceous period. Some well-known dinosaurs of this group include Abelisaurus, Carnotaurus, and Majungasaurus. They are known for their small arms...
oid theropod (LigabueinoLigabueinoLigabueino is a genus of noasaurid dinosaur named after Italian doctor Giancario Ligabue. It is known only from an extremely fragmentary specimen, measuring 70 cm long. In spite of initial reports that it was an adult, the unfused vertebrae indicate that the specimen was a juvenile...
) - a stegosaur
- a mammalMammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
(VincelestesVincelestesVincelestes is an extinct genus of actively mobile mammal, that lived in what would be South America during the Early Cretaceous from 130—112 mya, existing for approximately ....
)
Possible indeterminate stegosaurid remains located in Provincia de Neuquen, Argentina.
| Dinosaur Dinosaur Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of... s of the La Amarga Formation |
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|---|---|---|---|---|
| Genus | Species | Presence | Notes | Images |
Amargasaurus Amargasaurus Amargasaurus is a genus of dicraeosaurid sauropod dinosaur from the Early Cretaceous Period of what is now South America. It was small for a sauropod, reaching 10 meters length. It would have been a quadrupedal herbivore with a long, low skull on the end of a long neck, much like its relative... |
A. cazaui |
Geographically located in Provincia de Neuquen, Argentina. |
"Braincase and associated postcranial skeleton." |
 |
Ligabueino Ligabueino Ligabueino is a genus of noasaurid dinosaur named after Italian doctor Giancario Ligabue. It is known only from an extremely fragmentary specimen, measuring 70 cm long. In spite of initial reports that it was an adult, the unfused vertebrae indicate that the specimen was a juvenile... |
L. andesi |
Geographically located in Provincia de Neuquen, Argentina. |
||