The Parnaíba Basin (Portuguese: Bacia do Parnaíba) is a large cratonic sedimentary basin located in the North and Northeast portion of Brazil. About 50% of its area is in the state of Maranhão, and the other 50% is in the states of Pará, Piauí, Tocantins, and Ceará. It is one of the largest Paleozoic basins in the South American Platform. The basin has a roughly ellipsoidal shape, occupies over 600,000 km2, and is composed of ~3.4 km of mainly Paleozoic sedimentary rock that overlies localized rifts.Daly, Michael C.; Andrade, Vander; Barousse, Chuck A.; Costa, Rafaela; McDowell, Kenneth; Piggott, Neil; Poole, Alan J. (2014). "Brasiliano crustal structure and the tectonic setting of the Parnaíba basin of NE Brazil: Results of a deep seismic reflection profile". Tectonics. 33 (11): 2102–2120. ISSN 1944-9194
The basin as named after the Parnaíba River, which is approximately long, and runs relatively parallel to the major axis of the basin.
Regional Setting
It is located between the Amazonian Craton to the west and the São Francisco Craton to the south east. The São Luís Craton sits north of the basin and the Borborema Province is to the east. The basin currently covers a Precambrian basement composed of Archean to early Proterozoic cratonic blocks, Late Proterozoic Brasiliano/Pan-African fold belts and basement inliers.de Castro, D.L., Oliveira, D.C. & Hollanda, M.H.B.M. Geostatistical Interplay Between Geophysical and Geochemical Data: Mapping Litho-Structural Assemblages of Mesozoic Igneous Activities in the Parnaíba Basin (NE Brazil). Surv Geophys 39, 683–713 (2018).
The existence of a Parnaíba block was hypothesized from geophysical evidence, petrography, geochronology of the basement rocks,CordaniI, U.G., Brito Neves, B.B., Fuck, R.A., Porto, R., Thomaz Filho, A. & Cunha, F.M.B. 1984. Estudo preliminar de integração do Pré-Cambriano com os eventos tectônicos das bacias sedimentares brasileiras. Paper presented at Ciência Técnica Petróleo, Seção Exploração de Petróleo. Petrobras, Rio de Janeiro, Brazil, internal report. and from collisional tectonic models.Brito Neves, B.B., Fuck, R.A., Cordani, U.G. & Thomas, A. 1984. Influence of basement structures on the evolution of the major sedimentary basins of Brazil: a case of tectonic heritage. Journal of Geodynamics, 1, 495–510.Nunes, K.C. 1993. Interpretação integrada da Bacia do Parnaíba com ênfase nos dados aeromagnéticos. Proceedings of the 3rd International Congress of the Brazilian Geophysical Society, 1, 152–157, Rio de Janeiro, Brazil.Klein, E.L., Luzardo, R., Moura, C.A.V. & Armstrong, R. 2008. Geochemistry and zircon geochronology of Paleoproterozoic granitoids: further evidence on the magmatic and crustal evolution of the São Luís cratonic fragment, Brazil. Precambrian Research, 165, 221–242
It was regarded as one of the continental fragments inherited by the South American platform after the dispersal of the Rodinia supercontinent to form the Gondwana supercontinent. The São Francisco Craton and São Luis Craton existed before the opening of the Atlantic Ocean in Mesozoic times, were part of larger cratonic landmasses, and probably surrounded a central Parnaíba block presently concealed under the basin's sediments.Coelho, D. L., Julià, J., Rodríguez-Tribaldos, V., & White, N. (2018). Deep crustal architecture of the Parnaíba basin of NE Brazil from receiver function analysis: implications for basin subsidence. Geological Society, London, Special Publications, 472(1), 83-100. To the west, the Araguaia suture zone represents the final Neoproterozoic collision between the Amazonian craton and the Parnaíba block and, to the east, the Transbrasiliano Lineament marks the border with the Borborema Province.Reinhardt A. Fuck, Benjamim Bley Brito Neves, Carlos Schobbenhaus, Rodinia descendants in South America, Precambrian Research, Volume 160, Issues 1–2,
2008, Pages 108-126, ISSN 0301-9268, .Brito Neves, B.B. & Fuck, R.A. 2013. Neoproterozoic evolution of the basement of the South American Platform. Journal of South American Earth Sciences, 47, 72–89
Depositional History Stratigraphy of the Parnaíba basin contains depositional sequences, varying in age from Silurian to Cretaceous, marked by a progressive change in depositional environment from marine to continental. Like many other cratonic basins, the Parnaíba Basin displays a polyphase sedimentary history.Tozer, B., A. B. Watts, and M. C. Daly (2017), Crustal structure, gravity anomalies, and subsidence history of the Parnaíba cratonic basin, Northeast Brazil, J. Geophys. Res. Solid Earth, 122, 5591–5621, There are five distinct and recognizable tectonostratigraphic (TS) units that are separated by basin-wide unconformities that make up the area. These TS units include: the Riachão unit (TS-1), the Jaibaras unit (TS-2), the Parnaíba unit (TS-3), the Mearim unit (TS-4), and the Grajau unit (TS-5). The sedimentary rocks vary greatly throughout the stratigraphy of the basin and depsostional environment changes, and includes shale, siltstone, mudstone, sandstone, conglomerate, breccia, limestone, and more. Two magmatic pulses can be seen in the rock record, and are known as the Mosquito Formation and the Sardinha Formation. Most of the magmatic rocks are sub-alkaline tholeiitic basalts, and occur as dikes and sills mainly within the Silurian to Carboniferous and as magmatic flows in the Jurassic and, less commonly, in the Cretaceous.Oliveira, A. L. (2017). Geologia e Petrologia dos basaltos das formações Mosquito e Sardinha, Bacia do Parnaíba.
Grajau Unit (TS-5)
Cretaceous (deposition between ~120 and 95 million years ago) Comprises the Corda, Grajau, Codo, and Itapecuru Formations Deposition of near-shore, shallow marine, and fluviolacustrine clastic sediments has been attributed to subsidence associated with early opening of the South AtlanticRossetti, D. F., J. D. S. Paz, and A. M. Góes (2004), Facies analysis of the Codó formation (late Aptian) in the Grajaú area, southern São Luís-Grajaú Basin, An. Acad. Bras. Cienc., 76, 791–806,
Sardinha Formation
Middle Cretaceous (emergence between ~130 and 125 million years ago) Occur mainly as diabase dikes and sills and as minor basaltic flows with higher alkali content when compared to the other magmatic pulse in the basin, the Mosquito Formation Interpreted as a second phase of basaltic magmatism manifesting itself as extensive sills interlocking basin strata that is attributed to the early opening of the South Atlantic Ocean
Mearim Unit (TS-4)
Late Jurassic (deposition between ~165 and 155 million years ago) Comprises the Pastos Bons Formation Deposition of sandstone in a sabkha environment that is restricted to the center of the basin and undergoes of central "sag"Góes, A. M. O., W. A. S. Travassos, and K. C. Nunes (1993), Projeto Parnaiba: Reavaliacao e perspectivas exploratorias, paper presented at Relatorio Petrobras, DEXNOR-DINTER.Araujo, R. N., A. C. R. Nogueira, J. Bandeira, and R. S. Angelica (2016), Shallow lacustrine system of the Permian Pedra de Fogo Formation, western Gondwana, Parnaíba Basin, Brazil, J. S. Am. Earth Sci., 67, 57–70,
Mosquito Formation
Early Jurassic (emergence between ~205 and 185 million years ago) Formed mainly by lava flows that are occasionally interbedded with sandstones with lower alkali content when compared to the other magmatic pulse in the basin, the Sardinha Formation Interpreted as a phase of extrusive volcanism with the deposition of basaltic lava flowsMerle, R., A. Marzoli, H. Bertrand, L. Reisberg, C. Verati, C. Zimmermann, M. Chiaradia, G. Bellieni, and M. Ernesto (2011), 40Ar/39Ar ages and Sr-Nd-Pb-Os geochemistry of CAMP tholeiites from western Maranhão basin (NE Brazil), Lithos, 122, 137–151, . resulting from the Central Atlantic magmatic province and the opening of the central Atlantic OceanBaksi, A. K., and D. A. Archibald (1997), Mesozoic igneous activity in the Maranhao province, northern Brazil: 40Ar/39Ar evidence for separate episodes of basaltic magmatism, Earth Planet. Sci. Lett., 15, 139–153.
Parnaíba Unit (TS-3)
Late Ordovician/Silurian to Early Triassic (deposition between ~445 and 220 million years ago) Interpreted as the product of basinal "sag" or cratonic basin subsidence Consists of three megasequences, separated by regional unconformities and comprising shallow marine, fluviolacustrine, and terrestrial siliciclastic sediments
Balsas megasequence
Late Carboniferous to Middle Triassic (deposition between ~310 and 220 million years ago) Comprises the Piaui, Pedra de fogo, Motuca, and Sambaiba Formations Consists of clastic sandstone and evaporites deposited in subaerial environments
Caninde megaseqeuence
Lower Devonian to Carboniferous (deposition between ~400 and 330 million years ago) Comprises the Itaim, Pimenteiras, Cabecas, Longa, and Poti Formations Consists of interbedded shallow marine and deltaic depositional environments
Serra Grande megasequence
Early Silurian to Lower Devonian (deposition between ~440 and 405 million years ago) Comprises the Ipu, Tiangua, and Jaicos Formations Consists of quartz arenites of fluvioglacial, glacial marine, and shallow marine sediments that account for a complete transgressive/regressive cycle
Jaibaras Unit (TS-2)
Cambrian (deposition between ~530 and 485 million years ago) Comprises the Jaibras Group, which is the Massapé, Pacujá, Parapuí and Aprazível FormationsPedrosa Jr, N. C., Vidotti, R. M., Fuck, R. A., Oliveira, K. M. L., & Branco, R. M. G. C. (2015). Structural framework of the Jaibaras Rift, Brazil, based on geophysical data. Journal of South American Earth Sciences, 58, 318-334. Interpreted as a rift infill resulting from a prevalent Cambro-Ordovician rifting eventde Oliveira, D. C., and W. U. Mohriak (2003), Jaibaras trough: An important element in the early tectonic evolution of the Parnaíba interior sag basin, Northern Brazil, Mar. Pet. Geol., 20, 351–383. or pull-apart infill resulting from dextral strike-slip motion on the Transbrasiliano shear zone during the Cambrian/Early Ordovician
Riachão Unit (TS-1)
Late Neoproterozoic to Cambrian (deposition between ~570 and 515 million years ago) Comprises the Riachão Package, which is Riachão I, II and III Sequences Interpreted as a Neoproterozoic rift,de Castro, D. L., Fuck, R. A., Phillips, J. D., Vidotti, R. M., Bezerra, F. H., & Dantas, E. L. (2014). Crustal structure beneath the Paleozoic Parnaíba Basin revealed by airborne gravity and magnetic data, Brazil. Tectonophysics, 614, 128-145. or a remnant foreland basin, bounded by thick skinned thrust faults of Cambro-Ordovician agePorto, A. L., M. C. Daly, and S. L. Fontes (2016), The pre-Silurian Riachao basin, a new perspective into basement configuration of the cratonic Parnaíba Basin, NE Brazil, paper presented at 48th Congresso Brasileiro de Geologia, Sociedade Brasileira de Geologia, Porto Alegre.
Tectonic Evolution
The Parnaíba basin is located above a complex basement comprising several Archaean and Proterozoic terranes that stabilized during the Brasiliano orogeny. Seismic reflection data reveal a remnant basin beneath the major pre-Silurian unconformity and the base of the sediments of the Parnaíba cratonic basin. This pre-Silurian basin, known as the Riachão basin, covers an area of at least 35,000 km2 along a north–south trend. The remnant basin is thought to have originated as a foreland basin, and is poorly constrained between 574 and 500 million years ago.
The Riachão basin The Riachão basin has sedimentation that reaches a thickness of 4 km at its maximum, and is composed of three seismostratigraphic sequences (Riachão I, II and III). These sequences are defined by onlaps and erosive unconformities.