The Chaco Basin ( es, Cuenca Chaco, es, Cuenca Chaco Paranaense or es, Cuenca Chaco-Paraná) is a major

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subside ...

in Central South America around the borders of

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 ...

, Bolivia and

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

. The basin forms part of the larger

Paraná Basin The Paraná Basin ( pt, Bacia do Paraná, es, Cuenca del Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande d ...

. Superficially, the Chaco Basin is an

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. All ...

basin composed of land-derived (in contrast to marine sediments) material, mostly fine sand and clays of Paleogene, Neogene and Quaternary age. On deeper levels the Paraguayan Chaco is made up by four sub-basins, the Pirizal, Pilar, Carandaity and Curupaity basins.

Stratigraphy

The basin is part of the megaregional

, of which it occupies its western portion. The basin is subdivided into the Western Chaco (''Chaco Occidental'') and Eastern Chaco (''Chaco Oriental''). The

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

stratigraphy of the Chaco Basin comprises the Middle to Late Carboniferous Sachayoj Formation, the

Late Carboniferous Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

Charata Formation and the Early Permian Chacabuco Formation.Cuenca Chaco Paranense
/ref> The Neogene cover contains the

Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

Paraná Formation,Brea et al., 2013, p.28 the Late Pleistocene (

Lujanian The Lujanian age is a South American land mammal age within the Pleistocene and Holocene epochs of the Neogene, from 0.8–0.011 Ma or 800–11 tya. It follows the Ensenadan. The age is usually divided into the middle Pleistocene Bonaerian stag ...

in the SALMA classification)

Chaco Formation Chaco may refer to: Places in South America * Chaco Basin, spanning Argentina, Bolivia, and Paraguay * Chaco Department, a historical department in Paraguay and proposed in Bolivia * Chaco Province, a province in the northeastern part of Argenti ...

,Quebrada Agua Blanca
at Fossilworks.orgMapa Geológico del Paraguay, 1986, p.42 also described as

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

,Filí, 2001, p.28 and the substratum-forming Fortín Tres Pozos Formation in the

Formosa Province Formosa Province () is a province in northeastern Argentina, part of the Gran Chaco Region. Formosa's northeast end touches Asunción, Paraguay, and the province borders the provinces of Chaco and Salta to its south and west, respectively. Th ...

of northern Argentina.Zurita et al., 2009, p.279Soibelzon et al., 2010, p.315

References

Bibliography

* * * * * {{Sedimentary basins of Argentina Sedimentary basins of Argentina Sedimentary basins of Bolivia Sedimentary basins of Paraguay Foreland basins * Geology of Santa Cruz Department (Bolivia) Geology of Tarija Department