The Los Rastros Formation is a

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic). ...

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 ...

fossiliferous 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 in ...

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

of the

Agua de la Peña Group Agua means water in Spanish. Agua may also refer to: Places * ''Agua de Dios'' (God's water), a municipality in Colombia * Volcán de Agua, a stratovolcano located in Guatemala Arts, entertainment, and media * ''Agua'' (film), a 2006 Argentin ...

in 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 and the northeastern part of ...

in northwestern

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 second-largest country in South America after Brazil, th ...

. Fossil

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

tracks,Weishampel et al., 2004, pp. 517-607 as well as many

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s, fossil

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

of '' Myriolepis'',Leonardi, 1994, p.20

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s and

crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

ns and

flora Flora is all the plant life present in a particular region or time, generally the naturally occurring (indigenous) native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' gut flora'' or '' skin flora''. E ...

have been reported from the formation.

Description

The formation overlies the

Chañares Formation The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstones ...

(and/or the Ischicuca Formation), and is overlain by 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 da ...

.Aceituno Cieri, 2015, p.60 The formation belongs to the

of 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 Provin ...

, 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 h ...

in Argentina.Kent et al, 2014, p.7959 The up to thick formation of

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

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

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) ...

s was deposited in a

deltaic A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rare ...

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 ...

during the first post-rift sequence in the basin. A CA-TIMS U-Pb zircon age of 234.47 ± 0.44 Ma from the lower Los Rastros Formation was published in 2020. The acquired age demonstrates that most of the overlying lacustrine strata within the basin were deposited during or after the

Carnian Pluvial Event The Carnian pluvial episode (CPE), often called the Carnian pluvial event, was an interval of major change in global climate synchronous with significant changes in Earth's biota both in the sea and on land. It occurred during the latter part of ...

(CPE) that lasted from 237 to 227 Ma approximately.Mancuso et al., 2020

Fossil content

The following fossils among others have been recovered from the formation:Los Chañares
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org ;Fish * '' Challaia elongata'' (Class Actinopterygii, Order Palaeonisciformes, Family Acrolepidae; formerly assigned to the genus ''Myriolepis'') Lopez-Arbarello et al, 2006 * '' Gualolepis carinaesquamosa'' (actinopterygian; possibly a member of the family Peipiaosteidae, making it a relative of sturgeons and paddlefish)Lopez-Arbarello et al, 2006 * '' Rastrolepis latipinnata'' (actinopterygian) Lopez-Arbarello et al, 2006 * '' Rastrolepis riojaensis'' (actinopterygian) Lopez-Arbarello et al, 2006 ;Insects

Blattoptera "Roachoids", also known as "Roachids" or "Blattoids" are members of the stem group of Dictyoptera (the group containing modern cockroaches, termites and praying mantises). They generally resemble cockroaches, but most members, unlike modern dicty ...

(cockroaches and their relatives) * '' Argentinoblatta herbsti''Martins Neto et al., 2005, p.5 * '' Argentinoblattula revelata''Martins Neto et al., 2005, p.16 * '' Condorblatta lutzae'' * '' Hermosablatta crassatella'' * '' Hermosablatta pectinata''Martins Neto et al., 2005, p.10 * '' Lariojablatta chanarensis''Martins Neto et al., 2005, p.12 * '' Mancusoblatta pulchella''Martins Neto et al., 2005, p.8 * '' Pulchellablatta nana'' * '' Samaroblatta corrientesina''Martins Neto et al., 2005, p.14 * '' Samaroblatta gualoensis''Martins Neto et al., 2005, p.13 * '' Triassoblatta argentina''

Coleoptera Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

(beetles and their relatives) * '' Argentinocupes pulcher'' * '' Argentinosyne bonapartei'' * '' Babuskaya elaterata'' * '' Ischichucasyne cladocosta''

Hemiptera Hemiptera (; ) is an order (biology), order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, Reduviidae, assassin bugs, Cimex, bed bugs, and shield bugs. ...

(true bugs and their relatives) * '' Saaloscytina carmonae'' Unknown * '' Miomina riojana'' ;Crustaceans * '' Lioestheria sp.'' ;Bivalves * '' Paleomutella sp.'' ;Flora * Calamitales *

Coniferales The order Pinales in the division Pinophyta, class Pinopsida, comprises all the extant conifers. The distinguishing characteristic is the reproductive structure known as a cone produced by all Pinales. All of the extant conifers, such as cedar, ...

Cycadales Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or ...

Equisetales Equisetales is an order of subclass Equisetidae with only one living family, Equisetaceae, containing the genus ''Equisetum'' (horsetails). Classification In the molecular phylogenetic classification of Smith et al. in 2006, Equisetales, in its ...

Osmundales Osmundaceae (royal fern family) is a family of ferns containing four to six extant genera and 18–25 known species. It is the only living family of the order Osmundales in the class Polypodiopsida (ferns) or in some classifications the only ord ...

* Rhexoxilales ;Ichnofossils * '' Rigalites ischigualastensis'' *

Prestosuchidae Prestosuchidae (in its widest usage) is a polyphyletic grouping of carnivorous archosaurs that lived during the Triassic. They were large active terrestrial apex predators, ranging from around in length. They succeeded the Erythrosuchidae as the ...

Leonardi, 1994, p.21

References

Bibliography

* * * * * * * {{ISBN, 0-520-24209-2 Geologic formations of Argentina Triassic System of South America Triassic Argentina Carnian Stage Shale formations Sandstone formations Deltaic deposits Lacustrine deposits Ichnofossiliferous formations Ischigualasto-Villa Unión Basin Fossiliferous stratigraphic units of South America Paleontology in Argentina Geology of La Rioja Province, Argentina Geology of San Juan Province, Argentina

Description

Fossil content

See also

References

Bibliography