The Río Loro Formation is a geological formation of the

Sierras Pampeanas The Sierras Pampeanas (also called Central Sierras or Pampas Sierras) (English: Pampas Mountains) is a geographical region of Argentina. The Sierras Pampeanas are a chain of mountains that rise sharply from the surrounding pampa region of N ...

Tucumán Province Tucumán () is the most densely populated, and the second-smallest by land area, of the provinces of Argentina. Located in the northwest of the country, the province has the capital of San Miguel de Tucumán, often shortened to Tucumán. Neighb ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

whose strata date back to the

Late Paleocene The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...

of the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

, or

Riochican The Riochican () age is a period of geologic time (57.0–54.0 Ma) within the Paleocene and Eocene epochs of the Paleogene, used more specifically within the South American land mammal ages (SALMA). It follows the Peligran and precedes the Itabora ...

in the SALMA classification. The formation has been deposited in a meandering

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

environment and has a maximum noted thickness of . The formation has provided fossils of several mammals and reptiles. The crocodylian genus '' Lorosuchus'' and mammal species '' Eoastrapostylops riolorense'' were named after the formation which is correlated with the

Mealla Formation The Mealla Formation is a geological formation of the Santa Bárbara Subgroup, part of the Salta Group in the Salta Basin in northwestern Argentina whose strata date back to the Middle to Late Paleocene of the Paleogene. Description The Me ...

of the Salta Basin to the northwest of Tucumán Province.

Description

The Río Loro Formation crops out in the

Sierra Medina Sierra (Spanish for "mountain range" or " mountain chain" and "saw", from Latin '' serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a mountain range in Baja California, Mexico * Sierra de las Niev ...

, north of Tucumán city. The formation, first defined by Bossi in 1969,Babot et al., 2017, p.732 reaches a thickness of ,Georgieff, 2014, p.6 and comprises red

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

s deposited in a

meandering environment. The Río Loro Formation

unconformably An unconformity is a buried erosional or non-depositional 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 o ...

overlies the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Los Blanquitos Formation and is overlain by the Río Nío Formation. The Río Loro Formation is correlated with the

of the Salta Basin to the northeast.

Fossil content

The following fossils were reported from the formation:Río Loro Formation
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org *

Mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s **

Notoungulate Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms re ...

s *** '' Satshatemnus bonapartei'' **

Eutheria Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of Placentalia, placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians ...

*** '' Notonychops powelli''Soria, 1989 **

Xenungulata Xenungulata ("strange ungulates") is an order of extinct and primitive South American hoofed mammals that lived from the Late Paleocene to Early Eocene ( Itaboraian to Casamayoran in the SALMA classification). Fossils of the order are known f ...

*** '' Rodcania kakan''Gelfo et al., 2020 **

Placentalia Placental mammals ( infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distingui ...

*** '' Eoastrapostylops riolorense''Soria & Powell, 1981 *

Reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s **

Turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

s *** '' Podocnemis cf. argentinensis''De Broin & De la Fuente, 1993 **

Crocodylian Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchian ...

s *** '' Lorosuchus nodosus''

References

Bibliography

* * * * * * * {{citation , last1=Soria , first1=M.F. , first2=J.E. , last2=Powell , year=1981 , title=Un primitivo Astrapotheria (Mammalia) y la edad de la Formación Río Loro, provincia de Tucumán, República Argentina , journal=

Ameghiniana ''Ameghiniana'' is a peer-reviewed scientific journal covering palaeontology published by the Asociación Paleontológica Argentina. It is named after the 19th century Italian Argentine palaeontologist Florentino Ameghino. The discovery of many d ...

, volume=18 , pages=155–168 Geologic formations of Argentina Paleocene Series of South America Paleogene Argentina Thanetian Stage Riochican Sandstone formations Siltstone formations of Argentina Fluvial deposits Fossiliferous stratigraphic units of South America Paleontology in Argentina Geology of Tucumán Province

Description

Fossil content

See also

References

Bibliography