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43-915: The formation overlies the Chañares Formation (and/or the Ischicuca Formation ), and is overlain by the Ischigualasto Formation . The formation belongs to the Agua de la Peña Group of the Ischigualasto-Villa Unión Basin , where it is exposed in the Ischigualasto Provincial Park , a World Heritage Site in Argentina. The up to 1,000 metres (3,300 ft) thick formation of claystones , mudstones and sandstones

86-816: A fluvial to lacustrine environment . The formation is most prominently exposed within Talampaya National Park , a UNESCO World Heritage Site within La Rioja Province. The Chañares formation is the lowermost stratigraphic unit of the Agua de la Peña Group , overlying the Tarjados Formation of the Paganzo Group , and underlying the Los Rastros Formation . Though previously considered Ladinian in age, U-Pb dating has determined that most or all of

129-806: A climatic event (known as the Carnian pluvial episode characterized by substantial rainfall) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations. Another extinction occurred at the Carnian-Norian boundary, ending the Carnian age. The Carnian was named in 1869 by Mojsisovics . It is unclear if it was named after the Carnic Alps or after the Austrian region of Carinthia ( Kärnten in German) or after

172-409: A few sandstone and conglomerate beds near the top of the upper member. These indicate that the depositional regime continued to shift towards the deltaic environment of the overlying Los Rastros Formation. The coarser beds also contain a few rare body fossils from fish and tetrapods . A white tuff near the base of the upper member has been dated to 233.7 ± 0.4 Ma, while a zircon cluster from

215-412: A high concentration of volcanic ash and debris, ranging from glassy shards at the base to weathered bentonites at the top. Nearby volcanic eruptions likely impacted the local climate and river systems, shifting the depositional regime from a stable braided fluvial system to one dominated by shallow floodplains and lahars . Marsicano et al. (2016) obtained a CA-TIMS U-Pb age of 236.1 ± 0.6 Ma from

258-442: A hip height exceeding 75 cm. These prints are found in deltaic sandbars , parallel to the lakeshore. While some sources tentatively interpret these as theropod footprints, the generalized nature of Triassic dinosaurs and their relatives prevent a precise referral. Some of the tridactyl trackways also preserve hand prints, with quadrupedal pseudosuchians or other archosaurs as likely trackmakers. Named reptile ichnotaxa from

301-604: A large portion of the formation was deposited in the early Carnian (237–234 Ma), near the start of the Late Triassic . 2020 U-Pb dating of the overlying lower Los Rastros Formation yielded an age of 234.47 ± 0.44 Ma, making the vast majority of the Chañares Formation lowermost Carnian. Nevertheless, the Ladinian-Carnian boundary may still lie within the first few meters of the formation, despite

344-402: A sandy tuff at the top of the formation was dated to 233.6 ± 1.1 Ma. Tetrapod burrows, likely produced by small eucynodonts, have been described from the lower section of the formation. A large dicynodont fossil preserves taphonomic markers which help to reconstruct the sequence of burial, decay, and fossilization responsible for articulated fossils in the formation. A diverse insect fauna

387-596: A siltstone bed immediately below the first major fossil layer within the bluish facies. Ezcurra et al. (2017) later studied a slightly older sandstone bed using LA-MC-IMP-MS U-Pb dating. They found a date of 236.2 ± 1.1 Ma from a cluster of the three youngest zircons . The most productive and historically relevant fossil beds of the Chañares Formation lie within these volcaniclastic layers. The layers are replete with massive calcareous concretions , some up to 2 meters in width. They commonly preserve articulated skeletal material, often complete skeletons from multiple taxa in

430-618: A single concretion. Well-preserved fossils found within concretions typically represent smaller taxa, which were buried rapidly after death. Volcanic catastrophes such as lahars, ash falls, or pyroclastic flows are the preferred cause of these rapid mass mortality events . More fragmentary fossils are also occasionally found outside of concretions, much like fossils of the underlying Tarjadia AZ. Fossils found outside concretions are typically from large animals, and were probably buried more slowly (albeit still fairly rapidly) by gradual processes. The classic Chañares fauna, recently codified as

473-581: A two-substage subdivision is common: others prefer a three-substage organization of the stage as follows: In the Tethys domain , the Carnian Stage contains six ammonite biozones: The Otischalkian land vertebrate faunachron corresponds to the early late Carnian, while the Adamanian land vertebrate faunachron corresponds to the latest Carnian. The paleogeography of the Carnian was basically

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516-432: Is generally similar to the bluish facies in appearance, with wide beds of fine-grained volcaniclastic sediments with a pale grey color. Unlike the bluish facies, concretions and body fossils are absent, having been replaced by Taenidium worm burrows. These burrows likely indicate that the environment had transitioned into a lacustrine (lake) ecosystem by the time that the upper member was deposited. Some outcrops preserve

559-631: Is given below. Many Carnian vertebrates are found in Santa Maria Formation rocks of the Paleorrota geopark . The lower Carnian fauna of the San Cassiano Formation ( Dolomites , northern Italy ) has been studied since the 19th century. Fossiliferous localities are many, and are distributed mostly in the surroundings of Cortina d'Ampezzo and in the high Badia Valley, near the village of San Cassiano , after which

602-755: Is known from the Ischichuca Formation, which is sometimes considered equivalent to the Chañares Formation. Plant remains and palynomorphs preserved in the dicynodont coprolites were described in 2018 . Though it is difficult to determine the affinities of the larger plant fragments, the palynomorphs are more conclusive. They belong to a broad range of plants, most abundantly pollen from umkomasiales (a type of seed fern ), and in smaller portions from podocarpacean and voltzialean conifers . Spores from humid-loving groups such as bryophytes , lycopsids , true ferns , and algae were also present but rare. The palynomorph taxa generally resemble those of

645-654: Is rare due to the historical significance of the Chañares Formation. As a result, some authors restrict the Ischichuca Formation to a few layers of lake and delta sediments between the Chañares and Los Rastros formations, while others reject using it in the first place. The Chañares formation was originally thought to be deposited during the Ladinian stage of the Middle Triassic . However, Uranium-Lead radiometric dating by Marsicano et al. (2016) later found that

688-644: The Dicroidium flora which is common in other late Ladinian-early Carnian units. More precisely, the flora is intermediate between the temperate Ipswich flora of far southern Gondwana , and the hot, subtropical Onslow flora which developed along the southern shore of the Neotethys . This transitional character is also observed in the flora of the Ischigualasto Formation , as well as the Flagstone Bench Formation of Antarctica . Curiously,

731-651: The Carnia historical region in northeastern Italy. The name, however, was first used referring to a part of the Hallstatt Limestone cropping out in Austria . The base of the Carnian Stage is defined as the place in the stratigraphic record where the ammonite species Daxatina canadensis first appears. The global reference profile for the base is located at the Stuores-Wiesen near Badia in

774-570: The Los Rastros Formation , which was deposited between the Chañares and Ischigualasto Formations, preserves a typical Ipswich flora. This likely indicates that all three formations lie at a latitude which allows them to quickly shift between the different floras during small climatic changes. Plant macrofossils are absent from the Chañares Formation (in contrast to the Los Rastros and Ischigualasto formations). Nevertheless, fossil wood, foliage, and reproductive structures have been described from

817-570: The Massetognathus - Chanaresuchus Assemblage Zone, is characteristic of this section of the formation. The largest components of the ecosystem include dicynodonts (namely Dinodontosaurus ) and indeterminate carnivorous paracrocodylomorphs , similar to taxa from the underlying Tarjadia AZ. By far the most common fossils belong to three species of cynodonts : Massetognathus pascuali , Probainognathus jenseni , and Chiniquodon theotonicus . These three species comprise nearly 3/4ths of

860-573: The Paganzo Group , and is conformably overlain by greenish lake and delta sediments of the Los Rastros Formation . The Chañares Formation has also had an interesting history with the lower part of the Ischichuca Formation . This sequence of sediments on the western edge of the basin has occasionally been considered to take priority over the Chañares Formation and the lower part of the Los Rastros Formation. However, this

903-479: The Santa Maria Formation (e.g. Staurikosaurus and Buriolestes ) originated during the Carnian, around 230 Ma . In this stage the archosaurs became the dominant faunas in the world, evolving into groups such as the phytosaurs , rhynchosaurs , aetosaurs , and rauisuchians . The first dinosaurs (and the pterosaur Carniadactylus ) also appeared in this stage, and though at the time they were small and insignificant, they diversified rapidly and would dominate

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946-529: The Val Badia in the region of South Tyrol , Italy . The top of the Carnian (the base of the Norian) is at the bases of the ammonite biozones of Klamathites macrolobatus or Stikinoceras kerri and the conodont biozones of Metapolygnathus communisti or Metapolygnathus primitius . There is no established, standard usage for the Carnian subdivisions, thus, while in some regional stratigraphies

989-507: The Chañares Formation dates to the early Carnian stage of the Late Triassic . The Chañares Formation has provided a diverse and well-preserved faunal assemblage which has been studied intensively since the 1960s. The most common reptiles were proterochampsids ( Chanaresuchus , Tropidosuchus , and Gualosuchus ) , which lived alongside true archosaurs such as Lewisuchus , Lagerpeton , Marasuchus , Gracilisuchus , and Luperosuchus . Cynodonts were abundant, represented by

1032-601: The Ischichuca Formation. 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 the Norian . Its boundaries are not characterized by major extinctions or biotic turnovers, but

1075-707: The Los Rastros Formation include Rhynchosauroides sp. ( sphenodonts or other small reptiles) and Rigalites ischigualastianus (large quadrupedal pseudosuchians). Another form of trackway consists of numerous non-overlapping sets of broad rounded depressions on a heavily trampled wackestone surface. They may have been left by a herd of dicynodonts walking down to the lakeshore. Palaeophycus tubularis invertebrate burrows are also abundant. The Los Rastros Formation has produced many insect fossils, with most new species belonging to blattopterans ( cockroaches and kin), coleopterans ( beetles and kin), or hemipterans (true bugs). Among Triassic formations of South America,

1118-536: The Los Rastros Formation is a poorly-preserved temnospondyl amphibian. Tetrapod footprints are a conspicuous type of ichnofossils (trace fossils) found in the Los Rastros Formation, particularly at the Quebrada de Ischichuca locality near Cerro Bola. Most of the trackways are symmetrical prints created by animals with a narrow bipedal stance, three toes contacting the ground, and a raised fourth toe. They were presumably early dinosaurs or dinosauromorphs , with

1161-586: The Los Rastros Formation's insect diversity is only rivaled by the Potrerillos Formation in the Cuyo Basin. Other invertebrate fossils from the Los Rastros Formation include Lioestheria ("conchostracans" or clam shrimp ) and Paleomutella (freshwater mussels). Indeterminate corixids (water boatmen) are also known from the Gualo locality. A wide variety of plant fossils are known from

1204-568: The Los Rastros Formation, including both microfossils and macrofossils . Most species from the formation have been listed by Lutz et al. (2011) and Pedernera et al. (2020). Cha%C3%B1ares 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 which were deposited in

1247-408: The ancestry of dinosaurs and pterosaurs. Several communal latrines are known from the bluish facies, preserving dicynodont coprolites filled with plant remains. The olive-grey fluvial section and the bluish-grey volcaniclastic section collectively form the lower member of the Chañares Formation. They are overlain by an upper member, which is practically devoid of body fossils. The upper member

1290-529: The base of the upper Carnian (Tuvalian). The bivalve genus Halobia , a bottom-dweller of deep sea environments, differentiated from Daonella at the beginning of this age. Scleractinian coral reefs, i.e., reefs with corals of the modern type, became relatively common for the first time in the Carnian. The earliest unequivocal dinosaurs , such as those from the Ischigualato Formation (e.g. Herrerasaurus and Eoraptor ) and those from

1333-487: The best sources of Carnian-age tetrapods in South America, along with the slightly younger Ischigualasto Formation which lies above the Los Rastros Formation. The Chañares Formation is the lowermost unit of the Agua de la Peña Group , representing the onset of the first syn-rift phase of the Ischigualasto-Villa Unión Basin . It unconformably overlies red fluvial (river) sediments of the Tarjados Formation of

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1376-561: The fauna for the rest of the Mesozoic . On the other hand, the therapsids , which included the ancestors of mammals , decreased in both size and diversity, and would remain relatively small until the extinction of the dinosaurs. Conodonts were present in Triassic marine sediments. Paragondolella polygnathiformis appeared at the base of the Carnian Stage, and is considered a characteristic species. A partial list of Carnian vertebrates

1419-401: The first abundant occurrences of calcareous nanoplankton, a morphological group including the coccolithophores . There are a few invertebrates which are typical and characteristic of the Carnian. Among molluscs, the ammonoid genus Trachyceras is exclusive to the lower Carnian (i.e., Julian of the two-substages subdivision, see above). The family Tropitidae and the genus Tropites appear at

1462-455: The formation was named. This fauna is extremely diverse, including ammonoids, gastropods, bivalves, echinoderms, calcareous sponge , corals, brachiopods , and a variety of less common fossils. A collection of this fauna is exposed in the "Museo delle Regole", a museum in Cortina d'Ampezzo. The Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina yielded

1505-410: The fossils found in the formation, with almost half of the total fossils in the formation referred to Massetognathus alone. Reptile fossils are less prevalent but more diverse, with the most common belonging to the proterochampsid archosauriform Chanaresuchus . Other notable taxa include Lagerpeton , Lagosuchus , and Lewisuchus , which were among the oldest ornithodirans , elaborating on

1548-538: The lower fluvial beds of the Chañares Formation, they are taxonomically and taphonomically distinct from those of succeeding layers. The most common remains are from large dicynodonts (possibly referable to Dinodontosaurus ), the large erpetosuchid Tarjadia , and small non- massetognathine cynodonts closely related to Aleodon and Scalenodon . This ecosystem has been termed the Tarjadia Assemblage Zone, in order to distinguish it from

1591-405: The medium-sized traversodontid Massetognathus , as well as smaller carnivores such as Chiniquodon and Probainognathus . The largest animal in the ecosystem was the giant dicynodont Dinodontosaurus . An older faunal assemblage, distinguished by the large erpetosuchid Tarjadia , has been discovered in the earliest part of the formation. The formation as a whole is considered one of

1634-518: The present one. As for most of the Mesozoic, there were no ice caps. Climate was mostly arid in the tropics, but an episode of wet tropical climate is documented at least in the Paleo-Tethys. This putative climatic event is called the " Carnian Pluvial Event ", its age being between latest early Carnian (Julian) and the beginning of late Carnian (Tuvalian). In the marine realm, the Carnian saw

1677-409: The primary fossiliferous sections being well-supported as early Carnian in age. The formation is primarily sandstone , siltstone , and claystone , arranged in a specific sequence of facies . A distinct and uneven unconformity separates the base of the Chañares Formation from the underlying Tarjados Formation . In the field, this unconformity can be identified by a high-relief layer of chert at

1720-612: The same as for the rest of the Triassic. Most continents were merged into the supercontinent Pangaea , and there was a single global ocean, Panthalassa . The global ocean had a western branch at tropical latitudes called Paleo-Tethys . The sediments of Paleo-Tethys now crop out in southeastern Europe , in the Middle East , in the Himalayas , and up to the island of Timor . The extreme land-sea distribution led to "mega-monsoons", i.e., an atmospheric monsoon regime more intense than

1763-447: The slightly younger classic Chañares assemblage. No radiometric dating has been done on this section, but it may contain the Ladinian-Carnian boundary based on dates obtained within the younger facies. Above the olive-grey fluvial beds is the most fossiliferous and well-studied portion of the formation. This section is characterized by wide and massive layers of very fine bluish-grey sandstone, siltstone, and claystone. These layers have

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1806-696: The top of the Tarjados Formation. Above this unconformity lies the oldest section of the Chañares Formation, a package of olive-grey fluvial sediments. As one goes up the section, increasingly finer beds of sandstone and siltstone are interlayered with coarser lenses, corresponding to periodic sheet floods along braided rivers . Weakly-developed palaeosols can be found within this section, filled with root traces, pebbles and small brown calcareous nodules . Winding systems of burrows have also been found in this section, likely created by small cynodonts . Though fossils are relatively uncommon in

1849-492: Was deposited in a deltaic to lacustrine environment 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 (CPE). The only tetrapod body fossil reported from

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