The Collón Curá Formation () is a

Middle Miocene The Middle Miocene is a sub-epoch of the Miocene epoch (geology), epoch made up of two Stage (stratigraphy), stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene. The sub-epoch lasted from 15.97 ± 0. ...

fossiliferous

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

of the southern Neuquén Basin in northwestern Patagonia and the western Cañadón Asfalto Basin of central Patagonia,

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 ...

. The formation crops out from the southern

Neuquén Province Neuquén () is a Provinces of Argentina, 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. It also me ...

, the western Río Negro Province to the northern Chubut Province. The formation, with a maximum thickness of , comprises tuffs and

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 with minor siltstones, marls and

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s, deposited in a fluvial, deltaic and shallow to deep lacustrine environment in small basins separated by faults. The formation dates from the Langhian to earliest Tortonian epochs of the Middle to Late Miocene, typically Colloncuran. The Collón Curá Formation is named after Estancia Collón Curá (1 on the map in the infobox) along the Collón Curá River (2), a tributary of the Limay River in the Río Negro watershed, and lends its name to the Colloncuran, one of the South American land mammal ages. The formation has provided many fossils of

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 ...

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, among others the

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

'' Waincophis australis'', and the largest terror bird '' Kelenken guillermoi''. The

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

''Galileomys colloncurensis'' and the typothere '' Protypotherium colloncurensis'' were named after the formation.

Description

The strata of the Collón Curá Formation were first recognized by Roth in 1899, based on a thick succession of grey tuffs in the valley of the Collón Curá River. In 1929, Groeber named the unit Colloncurense, separating the sediments from the older Santa Cruz Formation, that Roth had grouped in the same unit. Yrigoyen in 1969 formally defined the stratigraphic unit as Collón Curá Formation. The type section of the formation is on both sides on the Collón Curá River. The maximum recorded thickness in the Collón Curá river valley is . In the Chapelcó Range of the Neuquén Basin, the formation is unconformably overlain by the Caleufú Formation, while

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic lava flows of the El Mirador Formation, and

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

alluvium Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

overly the Collón Curá Formation in the Cañadón Asfalto Basin.Echaurren González, Andrés. 2017
Evolución tectónica del sistema orogénico Andino en la Patagonia norte (42-44° S) (PhD thesis)
1–170.Universidad de Buenos Aires. In the Collón Curá valley, the formation covers

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 ...

sediments of the Huitrera and Cerro Petiso Formations and in places overlying crystalline

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

. In other parts of the Neuquén Basin, the formation overlies the Early Miocene Cerro Bandera Formation or the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

Angostura Colorada Formation.Geologic Map, 2007, p.112Prez, Horacio, and Gabriela Massaferro. 2013
Geología y geomorfología del tramo superior del Arroyo Comallo, Río Negro
(PDF). Contribuciones Científicas GÆA 26. 221–234. In the Cañadón Asfalto Basin, the Collón Curá Formation overlies the Ñirihuau Formation, and in the area around the Chico River in the same basin, the formation overlies the La Pava Formation. In this location, the Collón Curá Formation is unconformably overlain by the Río Negro Formation.Río Chico Colloncuran
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 The oldest age for the formation has been given as 16.1 Ma,Di Pietro, Pablo Federico. 2016
Geología de la zona del Cerro Bayo, Bajo de Gastre, Provincia de Chubut (B.S. thesis)
(PDF), 1–107.Universidad de Buenos Aires. and the top of the formation has been dated to 11 ± 1, and more precisely to 10.7 Ma. ⁴⁰Ar/³⁹Ar analysis on amphibole crystals, collected from fresh pumice clasts, revealed an age of 14.86 ± 0.13 Ma for the middle section of the Collón Curá Formation in the Gastre Sub-basin of the Cañadón Asfalto Basin.Estancia Collón Cura
at

.org Earlier estimates based on K/Ar dating on biotite minerals of the Pilcaniyeú Ignimbrite Member were given as 15 Ma (1980) and 14.1 Ma (1990). Overall, the age of the formation ranges from Langhian to earliest Tortonian.

Lithologies

In its type locality, the Collón Curá Formation is characterized by homogeneous greyish-yellow well-consolidated massive vitrocrystalline tuffs without visible sedimentary structures, but with

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

concretions. The tuffaceous sediments contain pieces of white

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

with a vesicular character up to in size. The volcanic crystals in the tuff comprise andesine,

hornblende Hornblende is a complex silicate minerals#Inosilicates, inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common ...

and hypersthene in an argillaceous matrix. The concretions in the formation can reach up to in size and result from secondary diagenesis replacing the primary

porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

of the sediments. Around the Río Chico in the Cañadón Asfalto Basin, the formation is about thick and comprises siltstones,

s, marls and

Depositional environment

Climate sensitivity sea level and atmospheric carbon dioxide

The formation was deposited in a fluvial and lacustrine environment dominated by pyroclastic flows in small basins, separated by faults.Figari et al., 2015, p.154 The sub-Andean region of Argentina went through a phase of marine transgression during the Middle Miocene, approximately 15 to 13 Ma. The Collón Curá Formation shows growth strata in the Cañadón Asfalto Basin, indicating syn-tectonic deposition. In this basin, the formation ranges from a shallow lacustrine setting in the basal section, a deep lacustrine system with deltaic facies in the middle and upper parts. The Collón Curá Formation is correlated with the contemporaneous fluvial and lacustrine tuffaceous Chichinales Formation of the central Neuquén Basin.Geologic Map, 2007, p.49 The Collón Curá Formation, together with the underlying Ñirihuau Formation in the Cañadón Asfalto Basin, was deposited in a fragmented, possibly by pull-apart tectonic activity,

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithospher ...

setting. The climate in the early middle Miocene was hot, a period known as the Middle Miocene Climatic Optimum. This thermal maximum was followed by a period of cooling, the Middle Miocene disruption, probably related to glacial growth and the reestablishment of the ice of the East Antarctic Ice Sheet. Atmospheric concentrations of CO₂ are estimated to have dropped from about 300 to 140 ppm.

Paleontological significance

The mammal fauna of the Collón Curá Formation led researchers to establish the Colloncuran age in the SALMA classification, ranging from 15.5 to 13.8 Ma. This age, used in South America as subdivision for the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

, follows on the Friasian age, defined from the

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

an Río Frías Formation of the Aysén Basin and precedes the Laventan age, named after the Konzentrat-Lagerstätte La Venta pertaining to the Honda Group of the Upper Magdalena Valley of central

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

. The

'' Galileomys colloncurensis'', and the typothere '' Protypotherium colloncurensis'' were named after the formation.Vera et al., 2017, p.855 The fossil mammal assemblage of the Collón Curá Formation represents a fauna preceding the evolution of the Caviidae. The oldest true caviid, '' Prodolichotis pridiana'' is known from the Villavieja and La Victoria Formations of La Venta,

. Sister taxa of these caviids first appeared in the Colloncuran; '' Guiomys unica'' and '' Microcardiodon williensis'', found in the Collón Curá Formation.Pérez & Pol, 2012, p.6 In alternative classification proposed in 2012 by Pérez and Pol, ''Guiomys'' is considered an optional early caviid, pushing back the lineage to the Colloncuran.Pérez & Pol, 2012, p.12

Fossil content

Bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s

Mammals

= Meridiungulata

Astrapotheria

Litopterna

Notoungulata

= Metatherians

Sparassodonta Sparassodonta (from Ancient Greek, Greek to tear, rend; and , gen. , ' tooth) is an extinct order (biology), order of carnivore, carnivorous metatherian mammals native to South America, related to modern marsupials. They were once cons ...

Paucituberculata

=
Primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s

= Silvestro, Daniele; Marcelo F. Tejedor; Martha L. Serrano Serrano; Oriane Loiseau; Victor Rossier; Jonathan Rolland; Alexander Zizka; Alexandre Antonelli, and Nicolas Salamin. 2017
Evolutionary history of New World monkeys revealed by molecular and fossil data
BioRxiv _. 1–32.

=
Rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s

= Typotheria

= Xenarthrans

Cingulata

Pilosa The Order (biology), order Pilosa is a clade of xenarthran placental mammals, native to the Americas. It includes anteaters and sloths (which include the extinct ground sloths). The name comes from the Latin word for "hairy". Origins and taxon ...

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

References

Bibliography

;Geologic map * ;Geology * ;Paleontology * * * * {{DEFAULTSORT:Collon Cura Formation Geologic formations of Argentina Langhian Serravallian Tortonian Miocene Series of South America Neogene Argentina Tuff formations of Argentina Sandstone formations Fluvial deposits Lacustrine deposits Deltaic deposits Fossiliferous stratigraphic units of South America Paleontology in Argentina Formations Formations Geology of Chubut Province Geology of Neuquén Province Geology of Río Negro Province Geology of Patagonia Mapuche language