Ischigualasto-Villa Unión Basin

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Ischigualasto-Villa Unión Basin
Cuenca de Ischigualasto-Villa Unión
Map showing the location of Ischigualasto-Villa Unión Basin
Map showing the location of Ischigualasto-Villa Unión Basin
Location of the basin in Argentina
Coordinates29°32′S 68°05′W / 29.533°S 68.083°W / -29.533; -68.083
LocationSouthern South America
RegionArgentine Northwest
Country Argentina
State(s)La Rioja & San Juan Provinces
CitiesVilla Unión
BoundariesSierras Pampeanas (N & E), El Alto Fault (SE), Valle Fértil Fault (W)
Part ofTriassic rift basins
Area~80,000 km2 (31,000 sq mi)
River(s)Talampaya River
Basin typeRift
PlateSouth American
OrogenyBreak-up of Pangea (Early Triassic)
Andean (Cenozoic)
AgeLate Permian-Late Triassic

The Ischigualasto-Villa Unión Basin (Spanish: 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 San Juan Province. The basin borders the Sierras Pampeanas in the east, the western boundary of the basin is formed by the Valle Fértil Fault, bordering the Precordillera, and it is bound in the southeast by the El Alto Fault, separating the basin from the Marayes-El Carrizal Basin.

The basin started forming in the Late Permian, with the break-up of Pangea, when extensional tectonics, including rifting, formed several basins in Gondwana; present-day South America, Africa, Antarctica, India and Australia. The accommodation space in the Ischigualasto-Villa Unión Basin was filled by an approximately 3.5 kilometres (11,000 ft) thick succession of volcaniclastic, eolian, alluvial, fluvial and lacustrine deposits in various geologic formations. The Cenozoic evolution of the basin is mainly influenced by the Andean orogeny, producing folding and faulting in the basin.

The basin is of paleontological significance as it hosts several fossiliferous stratigraphic units providing many fossils of early dinosaurs, synapsids, turtles, mammals, the earliest crocodylomorphs, fish, amphibians and flora, as well as ichnofossils. The Ischigualasto Provincial Park and Talampaya National Park in the basin were designated UNESCO World Heritage Sites in 2000.


The Ischigualasto-Villa Unión was recognized as a sedimentary basin by Stipanicic and Bonaparte in 1979. The basin stretches across a small area in northeastern San Juan Province and southwestern La Rioja Province in northwestern Argentina. The basin is bound by the Valle Fértil Fault to the west, separating the basin from the Precordillera, and the El Alto Fault in the southeast, forming the boundary with the Marayes-El Carrizal Basin. To the northeast, the basin ranges to the Sierras Pampeanas.[1] The basin is a rift basin that started forming early in the break-up of Pangea and its southern latitude paleocontinent Gondwana in the Late Permian to Early Triassic, providing a sedimentary column of approximately 3.5 kilometres (11,000 ft) of Triassic sediments.[2]

The area of the basin is sparsely populated, with Villa Unión in the north of the basin. The Talampaya and Chañares Rivers cross the basin.


The stratigraphy of the Ischigualasto-Villa Unión Basin contains sediments of the Triassic. The earliest deposition occurred in the Early Triassic (Olenekian) with the redbeds of the Talampaya and Tarjados Formations. This sequence is separated from the overlying Agua de la Peña Group by a regional unconformity.[3]

Age Group Formation Sequence Environment Maximum
Quaternary alluvium
Neogene Hiatus
Norian Agua de la Peña Los Colorados Formation Second post-rift Fluvial-lacustrine 1,000 m (3,300 ft) [4][5]
Carnian Ischigualasto Formation Second syn-rift Floodplain 900 m (3,000 ft) [4]
Los Rastros Formation First post-rift Deltaic-lacustrine 1,000 m (3,300 ft) [4]
Ischichuca Formation First syn-rift 750 m (2,460 ft) [4]
Chañares Formation Fluvial-lacustrine [4][6]
Angular unconformity
Early-Mid Triassic Paganzo Tarjados Formation Pre-rift Arid fluvial 250 m (820 ft) [4][7]
Olenekian Talampaya Formation Aeolian-fluvial 400 m (1,300 ft) [4]
Angular unconformity
Paleozoic Basement Tuminico Formation [8]
Precambrian Valle Fértil Complex [9]

Paleontological significance[edit]

The Ischigualasto-Villa Unión Basin is renowned for hosting the Lagerstätte of the Ischigualasto Formation and several other fossiliferous formations that have provided several fossils of synapsids and early dinosaurs, fish, insects, flora, and ichnofossils. The basin represents one of three locations in Argentina where Triassic trackways were found, together with the Cuyo Basin to the south and Los Menucos Basin in Río Negro Province.[10]

Many of the earliest known crocodylomorphs come from the Ischigulasto-Villa Unión Basin. The Chañares Formation has provided fossils of three different sized crocodylomorphs; Tropidosuchus of about 3 kilograms (6.6 lb), Gualosuchus of approximately 10 kilograms (22 lb), and Chanaresuchus weighing about 20 kilograms (44 lb).[6] In Los Colorados Formation, the crocodylomorphs Hemiprotosuchus leali and Coloradisuchus abelini were found.[11][12]

See also[edit]


  1. ^ Spalletti, 1997, p.37
  2. ^ Schencman, 2015, p.220
  3. ^ Arcucci et al., 2004, p.558
  4. ^ a b c d e f g Aceituno Cieri et al., 2015, p.60
  5. ^ Kent et al, 2014, p.7959
  6. ^ a b Arcucci et al., 2019, p.3
  7. ^ Balabusic et al., 2001, p.28
  8. ^ Aceituno Cieri et al., 2015, p.59
  9. ^ Monetta et al., 2000, p.647
  10. ^ Citton et al., 2018, p.5
  11. ^ Martínez et al., 2018, p.1
  12. ^ Arcucci et al., 2004, p.561


Chañares Formation
Los Colorados Formation
Los Rastros Formation

Further reading[edit]