Quebrada del Barro Formation

The Quebrada del Barro Formation is a geological formation of the Marayes-El Carrizal Basin in San Juan Province, Argentina. This formation is the most fossiliferous portion of the Triassic Marayes Group, and is also the youngest unit of the group, overlying the El Carrizal Formation. An unconformity at the top of the Quebrada del Barro Formation separates it from the Cretaceous-age Los Riscos Formation of the El Gigante Group.[1][2][3][4] Part of the formation may be made into a provincial park following the discovery of the fossils of Ingentia, a giant sauropodomorph dinosaur which helped elucidate the early evolution of sauropods.[5]

Quebrada del Barro Formation Stratigraphic range: Norian
Type	Geological formation
Unit of	Marayes Group
Underlies	Los Riscos Formation
Overlies	Carrizal Formation
Lithology
Primary	Sandstone
Other	Siltstone
Location
Coordinates	31.9°S 67.2°W / -31.9; -67.2
Approximate paleocoordinates	40.8°S 30.0°W / -40.8; -30.0
Region	San Juan Province
Country	Argentina
Extent	Marayes-El Carrizal Basin
Quebrada del Barro Formation (Argentina)

Sedimentology

Late Triassic (220 Ma)

The Quebrada del Barro Formation formed within a rift basin during a period of renewed fracturing. It encompasses 600 to 1,400 metres (2,000 to 4,600 ft) of red sandstones, fine conglomerates, and diamictites.[3] Early hypotheses on the depositional environment proposed that the sediments formed in an alluvial fan or braided river system, while a newer proposal outlines how four different facies within the formation can be used to reconstruct a meandering semiarid floodplain deposited by mudflows and discharging in heterolithic terminal splays.[6]

Fossil content

The fauna of Quebrada del Barro is similar to that of the neighboring Los Colorados Formation which is considered to be from the Norian stage of the Late Triassic.[7] Both formations preserve fossils from groups such as sauropodomorph dinosaurs, cynodonts, and testudinatans. However, Quebrada del Barro is more abundant in sphenodontians (Sphenotitan), tritheledontid cynodonts, and coelophysoid dinosaurs (Lucianovenator), while sauropodomorphs are somewhat less common and aetosaurs are completely absent, in contrast to the Los Colorados Formation.[3] Sphenodontians and cynodonts are also abundant in microfossil assemblages.[6] In addition, the Quebrada del Barro Formation preserves some of the only pterosaur and Dromomeron specimens known from Triassic strata in Argentina. Although the sphenodontian and cynodont-dominated fauna of Quebrada del Barro is akin to that of the Faxinal del Sotorno assemblage of the Brazilian Caturrita Formation, the fauna of the Faxinal del Sotorno assemblage is otherwise indicative of an older part of the Triassic than the Quebrada del Barro Formation.[3]

Dinosaurs

Theropods of the Quebrada del Barro Formation
Genus	Species	Material	Notes	Images
Lucianovenator[8]	L. bonoi	Several specimens including vertebrae, hip fragments, and a partial tibia	A coelophysid theropod

Sauropodomorphs of the Quebrada del Barro Formation
Taxon	Species	Material	Notes	Images
Ingentia[9]	I. prima	"cervical and dorsal vertebrae, scapula"	A lessemsaurid sauropod
Leyesaurus[2]	L. marayensis		A massospondylid sauropodomorph. Known from uppermost layers which may belong to a different unit of Hettangian (Early Jurassic) age.[3]
Sauropodomorpha	sp.	Complete foot and tail vertebrae	Undiagnostic sauropodomorph remains originally referred to Riojasaurus[2][10]

Other avemetatarsalians

Non-dinosaur avemetatarsalias of the Quebrada del Barro Formation
Taxon	Species	Material	Notes	Images
Dromomeron[11]	D. gigas	A partial femur	a lagerpetid dinosauromorph
Pterosauria	sp.	Portion of a snout and ulna	an indeterminate pterosaur[3]

Pseudosuchians

Pseudosuchias of the Quebrada del Barro Formation
Taxon	Species	Material	Notes	Images
"Rauisuchidae"	sp.	Skull fragments, osteoderms	an indeterminate "rauisuchid" smaller than Fasolasuchus[3]
Crocodylomorpha	sp.	A specimen including a partial osteoderm and vertebrae fragments	Indeterminate, possibly a "sphenosuchid"[3]
Crocodylomorpha	sp.	Two incomplete specimens including osteoderms, vertebrae, and other bones	a protosuchid, possibly synonymous with Hemiprotosuchus[3]

Rhynchocephalians

Rhynchocephalians of the Quebrada del Barro Formation
Genus	Species	Material	Notes	Images
Sphenotitan[12]	S. leyesi	numerous specimens (~50% of all recovered fossils)[3]	an opisthodont sphenodontian

Other reptiles

Other reptiles of the Quebrada del Barro Formation
Taxon	Species	Material	Notes	Images
Archosauriformes	sp.	Maxilla, caudal vertebra, metatarsal, indeterminate limb bone (tibia?)	Various indeterminate fragments likely belonging to pseudosuchians or dinosauromorphs[4]
Waluchelys	W. cavitesta	2 partial skeletons and carapaces	an australochelyid stem-turtle[13][3]

Synapsids

Synapsids of the Quebrada del Barro Formation
Taxon	Species	Material	Notes	Images
Tritheledontidae	sp.	36 specimens, including a partial skeleton	an undescribed tritheledontid cynodont. May be two taxa based on two morphotypes: "long-snout" and "short-snout".[3]

References

1. Gardini et al., 2009, p.554
2. Cecilia Apaldetti, Ricardo N. Martinez, Oscar A. Alcober and Diego Pol (2011). Claessens, Leon (ed.). "A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina". PLOS ONE. 6 (11): e26964. doi:10.1371/journal.pone.0026964. PMC 3212523. PMID 22096511.CS1 maint: multiple names: authors list (link)
3. Martínez, Ricardo N.; Apaldetti, Cecilia; Correa, Gustavo; Colombi, Carina E.; Fernández, Eliana; Malnis, Paula Santi; Praderio, Angel; Abelín, Diego; Benegas, Laura G.; Aguilar-Cameo, Andrea; Alcober, Oscar A. (August 2015). "A New Late Triassic Vertebrate Assemblage from Northwestern Argentina". Ameghiniana. 52 (4): 379–390. doi:10.5710/AMGH.27.04.2015.2889. ISSN 0002-7014.
4. Gianechini, Federico A.; Codorniú, Laura; Arcucci, Andrea B.; Castillo Elías, Gabriela; Rivarola, David (March 2016). "Archosauriform remains from the Late Triassic of San Luis province, Argentina, Quebrada del Barro Formation, Marayes–El Carrizal Basin". Journal of South American Earth Sciences. 66: 110–124. doi:10.1016/j.jsames.2015.12.012. ISSN 0895-9811.
5. "Uac wants a provincial park in the cradle of Ingenia Prima". Naaju. Retrieved 2018-07-15.
6. Colombi, Carina E.; Martínez, Ricardo N.; Correa, Gustavo; Fernández, Eliana; Malnis, Paula Santi; Praderio, Angel; Apaldetti, Cecilia; Abelín, Diego; Alcober, Oscar; Aguilar-Cameo, Andrea (October 2015). "First Argentine Microfossil Bonebed from the Upper Triassic Marayes—El Carrizal Basin, San Juan Province". PALAIOS. 30 (10): 743–757. doi:10.2110/palo.2014.055. ISSN 0883-1351.
7. Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Triassic, South America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 527–528. ISBN 0-520-24209-2.
8. Ricardo N. Martínez; Cecilia Apaldetti (2017). "A late Norian-Rhaetian coelophysid neotheropod (Dinosauria, Saurischia) from the Quebrada del Barro Formation, northwestern Argentina". Ameghiniana. in press. doi:10.5710/AMGH.09.04.2017.3065.
9. Apaldetti; Martínez, Ricardo N.; Cerda, Ignatio A.; Pol, Diego; Alcober, Oscar (2018). "An early trend towards gigantism in Triassic sauropodomorph dinosaurs". Nature Ecology & Evolution. 2 (8): 1227–1232. doi:10.1038/s41559-018-0599-y. hdl:11336/89332. PMID 29988169.
10. "Riojasaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 41. ISBN 0-7853-0443-6.
11. Ricardo N. Martínez; Cecilia Apaldetti; Gustavo A. Correa; Diego Abelín (2016). "A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, northwestern Argentina". Ameghiniana. 53 (1): 1–13. doi:10.5710/AMGH.21.06.2015.2894.
12. Martinez, R. N.; Apaldetti, C.; Colombi, C. E.; Praderio, A.; Fernandez, E.; Malnis, P. S.; Correa, G. A.; Abelin, D.; Alcober, O. (2013). "A new sphenodontian (Lepidosauria: Rhynchocephalia) from the Late Triassic of Argentina and the early origin of the herbivore opisthodontians". Proceedings of the Royal Society B: Biological Sciences. 280 (1772): 20132057. doi:10.1098/rspb.2013.2057. PMC 3813332. PMID 24132307.
13. Sterli, Juliana; Martínez, Ricardo N.; Cerda, Ignacio A.; Apaldetti, Cecilia. "Appearances can be deceptive: bizarre shell microanatomy and histology in a new Triassic turtle (Testudinata) from Argentina at the dawn of turtles". Papers in Palaeontology. doi:10.1002/spp2.1334. ISSN 2056-2802.

Bibliography

• Gardini, Carlos; David Rivarola; Maximiliano Agüera, and Gerónimo Candela. 2009. Estructura de la región Sierra de Guayaguas-Marayes, Provincias de San Juan y San Luis. Revista de la Asociación Geológica Argentina 65. 551–565. Accessed 2018-09-08.