The Paraná Basin is a large 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 do Sul states. The remainder area is distributed in eastern Paraguay, northeastern Argentina and northern Uruguay. The shape of the depression is elliptical and covers an area of about 1,500,000 km2 (580,000 sq mi), of which 110,000 km2 are in Paraguay.[1] The basin developed during the Paleozoic and the Mesozoic with a sedimentary record comprising rocks from the Ordovician right up to the Cretaceous, thus spanning the time interval between 460 and 66 million years.[2] The maximum thickness of the infill reaches 7,000 m in its central area and is composed of sedimentary and igneous rocks.[3][4][5]
The Chaco region that makes up the northwestern half (~60%) of Paraguay is a modern foreland basin[7] that extends into Argentina and Bolivia where it borders the Andeanthrust front. Superficially the Chaco Basin is an alluvial basin composed of land-derived (in contrast to marine sediments) material, mostly fine sand and clays of Paleogene, Neogene and Quaternary age.[8] On deeper levels the Paraguayan Chaco is made up by four sub-basins, the Pirizal, Pilar, Carandaity and Curupaity basins.
Carandaity and Curupaity in the northwest[9] are chieftly composed of Paleozoicsediments.
Pirizal (also called Pirity) Basin is made up mostly of Late Cretaceous and younger sediments.[7] The Pilar Basin is located mainly on Presidente Hayes Department and borders the Paraná Basin across Paraguay River to the east, geologically the basins are separated by the Asunción Anticline that roughly follows the path of Paraguay River.
In Alto Paraguay Department 240 Ma old alkaline volcanic rocks underlies younger sediments. In the 1970s these rocks were studied for their potential to host valuable phosphate and uranium minerals.[8]
Paraná Igneous Province
In a strip along Paraná Rivertholeiitic basalts belonging to the Paraná Traps makes up most of the bedrock and overlies earlier sediments of the Paraná Basin. These tholeiites were erupted in the Early Cretaceous in association with the initial opening of the South Atlantic. The Cretaceous volcanism did also create minor outcrops of potassic alkaline volcanics in a graben structure developed between Asunción and Villarrica and in Amambay Department. Cretaceous volcanism did also leave small units of sodic alkaline rocks in Misiones Department in southern Paraguay.
^ abMilani, E. J.; Melo, J. H. G.; Souza, P. A.; Fernandes, L. A.; França, A. B. (2007) Bacia do Paraná (Portuguese). IN: Cartas Estratigráficas - Boletim De Geociencias da Petrobras, Rio de Janeiro, v. 15, n. 2, p. 265-287, mai/Nov. 2007.
^ abZalan, P. V.; Wolf, S.; Astolfi, M. A. M.; Vieira, I. S.; Conceição, J. C.; Appi, V. T.; Santos Neto, E. V.; Cerqueira, J. R.; Marques, A. (1991) The Paraná Basin, Brazil. IN: Leighton, M. W.; Kolata, D. R.; Oltz, D. F.; Eidel, J. J. (Ed.). Interior cratonic basins. Tulsa, Okla.: American Association of Petroleum Geologists. pp. 707-708. (AAPG. Memoir 51).
^Milani, E. J.; França, A. B.; Medeiros, R. Á. (2007) Roteiros Geológicos, Rochas geradoras e rochas-reservatório da Bacia do Paraná (Portuguese). IN: Boletim de Geociências da Petrobras, Rio de Janeiro, v. 15, n. 1, p. 135-162, Nov. 2006/maio/2007.
^Melo, J. H. G. (1988) The Malvinokaffric realm in the Devonian of Brazil. IN: McMilillan, N. J.; Embry, A. F.; Glass, D. J. (Ed.). Devonian of the world. Calgary: Canadian Society of Petroleum Geologists, 1988, v. 1. p. 669-704. (CSPG Memoir, 14)
^ abClebsch Kuhn, Carlos Alfredo. 1991. The Geological Evolution of the Paraguayan Chaco.