The Los Colorados Formation is a

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

rock formation A rock formation is an isolated, scenic, or spectacular surface rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock formation'' can also refer to specific sedime ...

of the

Ischigualasto-Villa Unión Basin The Ischigualasto-Villa Unión Basin ( es, Cuenca de Ischigualasto-Villa Unión) is a small sedimentary basin located in the Argentine Northwest, Argentina. It is located in the southwestern part of La Rioja Province, Argentina, La Rioja Province a ...

, found in the provinces of

San Juan San Juan, Spanish for Saint John, may refer to: Places Argentina * San Juan Province, Argentina * San Juan, Argentina, the capital of that province * San Juan, Salta, a village in Iruya, Salta Province * San Juan (Buenos Aires Underground), ...

and

La Rioja La Rioja () is an autonomous community and province in Spain, in the north of the Iberian Peninsula. Its capital is Logroño. Other cities and towns in the province include Calahorra, Arnedo, Alfaro, Haro, Santo Domingo de la Calzada, an ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...

. The formation dates back to the

Norian The Norian is a division of the Triassic Period. It has the rank of an age ( geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic ...

age of the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...

. The up to thick formation comprises

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

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.Blatt ''et al.'' 1980, ...

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...

s and conglomerates with

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywa ...

layers deposited in a

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

. The formation is the uppermost stratigraphic unit of the Agua de la Peña Group, overlying the

Lagerstätte A Lagerstätte (, from '' Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...

of the

Ischigualasto Formation The Ischigualasto Formation is a Late Triassic fossiliferous formation and Lagerstätte in the Ischigualasto-Villa Unión Basin of the southwestern La Rioja Province and northeastern San Juan Province in northwestern Argentina. The formation ...

. Los Colorados Formation is partly covered by the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Cerro Rajado Formation, separated by an

unconformity 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 ...

. The formation is known for its

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s of early

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s, including the

coelophysoid Coelophysoidea were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to th ...

Zupaysaurus ''Zupaysaurus'' (; "ZOO-pay-SAWR-us") is an extinct genus of early theropod dinosaur living during the Norian stage of the Late Triassic in what is now Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigual ...

'' and the " prosauropods" '' Coloradisaurus'', '' Lessemsaurus'', and ''

Riojasaurus ''Riojasaurus'' (meaning "Rioja lizard") was a herbivorous sauropodomorph dinosaur named after La Rioja Province in Argentina where it was found in the Los Colorados Formation in the Ischigualasto-Villa Unión Basin by José Bonaparte. It li ...

''.Weishampel et al., 2004, pp.527-528 Magnetostratigraphic analysis suggests that the Los Colorados Formation was deposited between 227 and 213 million years ago.Kent et al, 2014, p.7959

Description

Ischigualasto-Villa Unión Basin Map detail

Los Colorados Formation is a unit with an approximate thickness of of the Agua de la Peña Group in the

, where it is exposed in the

Ischigualasto Provincial Park Ischigualasto Provincial Park ( es, Parque Provincial Ischigualasto), also called ''Valle de la Luna'' ("Valley of the Moon" or "Moon Valley"), due to its moon like appearance, is a provincial protected area in the north-east of San Juan Provinc ...

, a

World Heritage Site A World Heritage Site is a landmark or area with legal protection by an international convention administered by the United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNESCO for ...

in Argentina. The formation gradually overlies the

and is unconformably overlain by the

Cerro Rajado Formation. The formation comprises red-colored, fine- to medium-grain–size

s together with

s and ancillary

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

s with early calcisol development. The formation was deposited in a

Fossil content

Anapsids

Synapsids

Eucynodontia

Archosauromorphs

Crocodylomorpha

Dinosaurs

Indeterminate theropod remains present in the Provincia de la Rioja.

Ichnofossils

* '' cf. Brachychirotherium sp.'' * '' Chirotherium sp.''Leonardi, 1994, p.25Leonardi locality 15
at

Fossilworks Fossilworks is 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 crea ...

.org

References

Bibliography

* * * * * * *

{{commons category, Los Colorados Formation * A. B. Arcucci and R. A. Coria. 2003. A new Triassic carnivorous dinosaur from Argentina. Ameghiniana 40(2):217-228 * J. F. Bonaparte. 1999. Evolución de las vértebras presacras en Sauropodomorpha volution of the presacral vertebrae in Sauropodomorpha Ameghiniana 36(2):115-187 * J. F. Bonaparte and J. A. Pumares. 1995. Notas sobre el primer craneo de ''Riojasaurus incertus'' (Dinosauria, Prosauropoda, Melanorosauridae) del Triasico Superior de La Rioja, Argentina otes on the first skull and jaws of ''Riojasaurus incertus'' (Dinosauria, Prosauropoda, Melanorosauridae), Late Triassic of La Rioja, Argentina Ameghiniana 32(4):341-349 * J. F. Bonaparte. 1981. Descripción de "''Fasolasuchus tenax''" y su significado en la sistematica y evolución de los thecodontia. Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" 3(2):55-101 * J. F. Bonaparte. 1978. ''Coloradia brevis'' n. g. et n. sp. (Saurischia–Prosauropoda), dinosaurio Plateosauridae de la Formacion Los Colorados, Triasico Superior de La Rioja, Argentina 'Coloradia brevis'' n. g. et n. sp. (Saurischia–Prosauropoda), a plateosaurid from the Upper Triassic Los Colorados Formation of La Rioja, Argentina Ameghiniana 15(3-4):327-332 * J. F. Bonaparte. 1971. Los tetrapodos del sector superior de la Formacion Los Colorados, La Rioja, Argentina (Triásico Superior) he tetrapods of the upper part of the Los Colorados Formation, La Rioja, Argentina (Upper Triassic) Opera Lilloana 22:1-183 * J. F. Bonaparte. 1969. Dos nuevas "faunas" de reptiles triasicos de Argentina wo new reptilian "faunas" of the Argentine Triassic Gondwana Stratigraphy (IUGS Symposium, Buenos Aires) 2:283-306 * J. B. Desojo and A. M. Baez. 2007. Cranial morphology of the Late Triassic South American archosaur ''Neoaetosauroides engaeus'': evidence for aetosaurian diversity. Palaeontology 50:267-276 * J. B. Desojo and A. M. Baez. 2005. El esqueleto postcraneano de ''Neoaetosauroides'' (Archosauria: Aetosauria) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 42:115-126 * M. D. Ezcurra and C. Apaldetti. 2012. A robust sauropodomorph specimen from the Upper Triassic of Argentina and insights on the diversity of the Los Colorados Formation. Proceedings of the Geologists' Association 123:155-164 * A. G. Martinelli and G. W. Rougier. 2007. On ''Chaliminia musteloides'' (Eucynodontia: Tritheledontidae) from the Late Triassic of Argentina, and a phylogeny of Ictidosauria. Journal of Vertebrate Paleontology 27:442-460 * G. W. Rougier, M. S. de la Fuente, and A. B. Arcucci. 1995. Late Triassic turtles from South America. Science 268:855-858 Geologic formations of Argentina Late Triassic South America Triassic Argentina Norian Stage Sandstone formations Mudstone formations Siltstone formations Fluvial deposits Lacustrine deposits Geology of La Rioja Province, Argentina Geology of San Juan Province, Argentina