The Caturrita Formation is a

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 sediment ...

found in

Rio Grande do Sul Rio Grande do Sul (, , ; "Great River of the South") is a Federative units of Brazil, state in the South Region, Brazil, southern region of Brazil. It is the Federative_units_of_Brazil#List, fifth-most-populous state and the List of Brazilian st ...

, Brazil. Its

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s were deposited in the

Paraná Basin The Paraná Basin ( pt, Bacia do Paraná, es, Cuenca del Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande d ...

. The formation is from the

Upper 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. Th ...

and forms part of the

Santa Maria Supersequence The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Per ...

in the upper section of the Rosário do Sul Group.

Etymology

The formation received this name, because Caturrita is a neighbourhood (

barrio ''Barrio'' () is a Spanish language, Spanish word that means "Quarter (urban subdivision), quarter" or "neighborhood". In the modern Spanish language, it is generally defined as each area of a city, usually delimited by functional (e.g. residenti ...

) of Santa Maria. In Portuguese ''caturrita'' also refers to the

monk parakeet The monk parakeet (''Myiopsitta monachus''), also known as the Quaker parrot, is a species of true parrot in the family Psittacidae. It is a small, bright-green parrot with a greyish breast and greenish-yellow abdomen. Its average lifespan is 20 ...

Stratigraphy

The sediments of the Caturrita Formation belong to the second unit of the Santa Maria Supersequence and overlie the Alemoa Member of the

Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and oth ...

. The clayey sediments of the Alemoa Member gradually give way to the more sandy, rarely conglomeratic, Caturrita Formation, which finishes with an unconformity. After this erosional event follow the

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

sediments of the

Mata Sandstone Mata may refer to: Places * Mata, Iran, a village in Kerman Province, Iran * Mata, Israel, a Moshav in the Judaean Mountains, south-west of Jerusalem, not far from Beit Shemesh * Mata, Rio Grande do Sul, town in Brazil * Mata Island, in the Hudso ...

, the third unit of the Santa Maria Supersequence. The Caturrita Formation was once regarded as a member of the stratigraphically higher

Botucatu Formation The Botucatu Formation is an Aptian geologic formation of the Paraná and Pelotas Basins in southern Brazil and northern Uruguay. The formation is composed of quartzitic sandstones, deposited in an eolian environment.Petrolli & Pimentel, 2014, ...

or was expanded to include the Mata Sandstone. The Caturrita Formation reaches a maximum thickness of 60 meters, but generally oscillates around values of 30 meters.

Age

Until 2018 no absolute ages had been determined, but the formation was most commonly assigned to a late

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

to early

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 defi ...

age on paleontological grounds. However,

or even

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

age of this unit was also advocated in the literature. A U-Pb (

Uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

decay) dating found that the Caturrita Formation dated around 225.42 million years ago, putting it less than 10 million years younger than the Santa Maria and

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 da ...

s, from where the earliest dinosaurs are known.

Geographical occurrence

Outcrops of the Caturrita Formation are found in the Brazilian state of

. From the town of

Taquari Taquari is a municipality in the state of Rio Grande do Sul, Brazil. See also *List of municipalities in Rio Grande do Sul This is a list of the municipalities in the state of Rio Grande do Sul (RS), located in the South Region of Brazil. Rio ...

they follow for 250 kilometers a thin band in the central part of the state in an east-westerly fashion right up to Mata.

Depositional environment

The sediments of the Caturrita Formation belong to the upper section of the Santa Maria Supersequence. In terms of

sequence stratigraphy Sequence stratigraphy is a branch of geology, specifically a branch of stratigraphy, that attempts to discern and understand historic geology through time by subdividing and linking sedimentary deposits into unconformity bounded units on a variety ...

they are equivalent to a highstand systems tract. The scarlet, ephemeral, mainly clayey fluvio-lacustrine deposits of the Alemoa Member gradually cede to more sandy, occasionally gravelly deposits of a

braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment l ...

-system that was operational all-year-round. These deposits of the Caturrita Formation settled out in an alluvial flood-plain. The changeover in sedimentary facies was accompanied by a climatic change to more humid conditions. The sediments are of continental nature (

red beds Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain ...

) and form massive

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 silicates) ...

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

bodies.

Vertebrate fauna

The Caturrita Formation contains a biozone for

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...

s, the so-called “Ictidosauria Assemblage Zone″ ''Ca-1''. Ictidosaurs are

tritheledontid Tritheledontidae, the tritheledontids or ictidosaurs, is an extinct family of small to medium-sized (about 10 to 20 cm long) cynodonts. They were highly mammal-like, specialized cynodonts, although they still retained a few reptile-like ana ...

cynodonts The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

, a sister group of the

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s. This is the reason, why this biozone recently has been renamed as “Mammaliamorpha Cenozone” to underline the importance of the cynodont fossils. The Caturrita Formation also hosts the stratigraphic marker level “Jachaleria” named after the

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...

'' Jachaleria candelariensis''.

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 and other

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s have been discovered as well. In 1998 tracks of

prosauropods Plateosauridae is a family (biology), family of plateosaurian sauropodomorphs from the Late Triassic of Europe, Greenland, Africa and Asia. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosaurida ...

have been found near

Faxinal do Soturno Faxinal do Soturno is a municipality in the state of Rio Grande do Sul, Brazil. See also *List of municipalities in Rio Grande do Sul This is a list of the municipalities in the state of Rio Grande do Sul (RS), located in the South Region of Br ...

that were most likely caused by '' Unaysaurus tolentinoi''.Rafael Costa Da Silva, Ismar De Souza Carvalho, Cibele Schwanke, 2006. Vertebrate dinoturbation from the Caturrita Formation (Late Triassic, Paraná Basin), Rio Grande do Sul State, Brazil. Gondwana Research 11 (2007) 303–310. The fossil finds are concentrated around three major areas: Santa Maria and northern surroundings (Água Negra) Faxinal do Soturno Candelária and surroundings (Linha São Luis) The following taxa have been discovered so far in the Caturrita Formation:

Synapsids

Dinosaurs

Unnamed prosauropod genus present in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

Other tetrapods

Undetermined

phytosaur Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent ...

genus.

References

Bibliography

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. {{ISBN, 0-520-24209-2.