Los Colorados Formation

For other uses, see Colorado Formation.

The Los Colorados Formation is a sedimentary rock formation of the Ischigualasto-Villa Unión Basin, found in the provinces of San Juan and La Rioja in Argentina. The formation dates back to the Norian age of the Late Triassic.

Los Colorados Formation
Stratigraphic range: Norian ~227–213 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Los Colorados massif, La Rioja Province, Argentina
Type	Geological formation
Unit of	Agua de la Peña Group
Underlies	Cerro Rajado Formation
Overlies	Ischigualasto Formation
Thickness	600 m (2,000 ft)
Lithology
Primary	Sandstone, siltstone, mudstone
Other	Conglomerate, gypsum
Location
Coordinates	29.8°S 67.9°W / -29.8; -67.9
Approximate paleocoordinates	38.9°S 31.4°W / -38.9; -31.4
Region	San Juan Province La Rioja Province
Country	Argentina
Extent	Ischigualasto-Villa Unión Basin
Type section
Named for	Los Colorados Massif
Los Colorados Formation (Argentina)

The up to 600 metres (2,000 ft) thick formation comprises sandstones, siltstones, mudstones and conglomerates with gypsum layers deposited in a fluvial to lacustrine environment. The formation is the uppermost stratigraphic unit of the Agua de la Peña Group, overlying the Lagerstätte of the Ischigualasto Formation. Los Colorados Formation is partly covered by the Cretaceous Cerro Rajado Formation, separated by an unconformity.

The formation is known for its fossils of early dinosaurs, including the coelophysoid Zupaysaurus and the "prosauropods" Coloradisaurus, Lessemsaurus, and Riojasaurus.^[1] Magnetostratigraphic analysis suggests that the Los Colorados Formation was deposited between 227 and 213 million years ago.^[2]

Description

Extent of the formation in the Ischigualasto-Villa Unión Basin

Los Colorados Formation is a unit with an approximate thickness of 600 metres (2,000 ft) of the Agua de la Peña Group in the Ischigualasto-Villa Unión Basin, where it is exposed in the Ischigualasto Provincial Park, a World Heritage Site in Argentina. The formation gradually overlies the Ischigualasto Formation and is unconformably overlain by the Cretaceous Cerro Rajado Formation. The formation comprises red-colored, fine- to medium-grain–size sandstones together with siltstones and ancillary floodplain mudstones with early calcisol development. The formation was deposited in a fluvial to lacustrine environment.^[2]

Fossil content

Anapsids

Anapsids of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Palaeochersis	P. talampayensis			[3][4]

Synapsids

Synapsids of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Chaliminia	C. musteloides			A Tritheledontidae cynodont. [3]
Jachaleria	J. colorata		A skull and complete jaws.	A Kanemyeriidae dicynodont.
Tessellatia	T. bonapartei		A partial skull, including the snout, orbital region, and lower jaws.	A cynodont.[5]

Archosauromorphs

Archosauromorphs of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Fasolasuchus	F. tenax	La Rioja Province	A fragmented skull and jaws.	A giant loricatan Pseudosuchian.[1][3]
Neoaetosauroides	N. engaeus	Quebrada de los Jachaleros, El Salto (San Juan)		An aetosaur.[3]
Riojasuchus	R. tenuisceps			An ornithosuchid.[3][6]

Crocodylomorpha

Crocodylomorphs of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradisuchus	C. abelini	La Rioja Province		[7]
Hemiprotosuchus	H. leali	Quebrada de los Jachaleros, El Salto (San Juan)		[3][7]
Pseudhesperosuchus	P. jachaleri	Quebrada de los Jachaleros, El Salto (San Juan)		[3]

Dinosaurs

Indeterminate theropod remains present in the Provincia de la Rioja.^[1]

Dinosaurs of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradisaurus	C. brevis	La Rioja Province[1]	"Skull, adult"[3][8]	A massospondylid sauropodomorph.
Lessemsaurus	L. sauropoides	La Rioja Province[1]	"Partial cervical, dorsal, and sacral vertebrae, adult."[8]	A sauropodiform.
Prosauropoda	Indeterminate	La Rioja & San Juan Provinces	Includes Strenusaurus procerus.[1] "Dorsals, caudals, partial fore- and hindlimb."[9]
Powellvenator	P. podocitus	Ischigualasto-Villa Unión Basin	Known from previously undescribed partial hindlimbs	A coelophysoid.
Riojasaurus	R. incertus	La Rioja Province		A sauropodomorph.[10][3][1]
Zupaysaurus	Z. rougieri	La Rioja Province		An early theropod.[3][1]

Ichnofossils

• cf. Brachychirotherium sp.^[11]
• Chirotherium sp.^[12][13]

See also

• List of dinosaur-bearing rock formations
• Quebrada del Barro Formation, contemporaneous fossiliferous formation of the Marayel-El Carrizal Basin just southeast of the Ischigualasto-Villa Unión Basin
• Caturrita Formation, contempeoraneous fossiliferous formation of the Paraná Basin, southeastern Brazil
• Chinle Formation, contemporaneous fossiliferous formation of Arizona
• Elliot Formation, contemporaneous fossiliferous formation of the Karoo Basin, South Africa
• Fremouw Formation, contemporaneous fossiliferous formation of Antarctica