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| Rio Bonito Formation | |
|---|---|
| Name | Rio Bonito Formation |
| Period | Permian |
| Type | Geological formation |
| Lithology | Sandstone, siltstone, coal, shale |
| Namedfor | Rio Bonito |
| Region | Paraná Basin, Santa Catarina, Rio Grande do Sul, São Paulo |
| Country | Brazil |
Rio Bonito Formation
The Rio Bonito Formation is a Permian stratigraphic unit within the Paraná Basin, recognized for extensive coal seams, fluvial and deltaic sandstones, and fossil plant assemblages. It provided key evidence for Permian paleoenvironments in southern Gondwana, informed basin analysis across South America, and influenced resource development in Brazil and neighboring regions. Researchers from institutions such as the Brazilian Geological Survey, universities in São Paulo (state), and international teams have referenced the unit in correlations with coeval successions in Antarctica, Africa, and Australia.
The formation occurs within the intracratonic Paraná Basin and is bounded by the Dinodontosaurus Assemblage Zone-age Permian strata and overlying Triassic units. Tectonostratigraphic context ties the unit to Gondwanan assembly and late Paleozoic sedimentary dispersal linked to the Alleghanian orogeny-equivalent events in western Gondwana. Structural features such as gentle basin subsidence, regional unconformities, and fault-controlled depocenters influenced thickness variations across the states of Rio Grande do Sul, Santa Catarina (state), and São Paulo (state).
Biostratigraphic markers and radiometric ties place the unit in the Cisuralian to Guadalupian stages of the Permian. Correlations have been drawn with the Karoo Supergroup of South Africa, the Permian sequences of East Antarctica, and the Sydney Basin successions in Australia, using plant fossil assemblages and palynology. Chemostratigraphic data and detrital zircon ages from interbedded volcanic ash have assisted correlation with global Permian chronostratigraphy and with international standards such as the International Commission on Stratigraphy frameworks.
Lithologies are dominated by feldspathic sandstones, siltstones, shales, and intercalated coal seams derived from extensive peat-forming mires. Sedimentary structures include cross-bedding, ripple marks, and rooted paleosols that indicate fluvial-channel, point-bar, and floodplain facies. Petrographic studies link provenance to uplifted sources in the Mantiqueira Orogenic Belt and detrital compositions comparable to sediments in the Paraná Continental Arc reconstructions. Heavy-mineral suites and grain-size trends have been used to interpret paleocurrent directions and sediment dispersal across the basin.
The formation yields abundant plant macrofossils, including glossopterids, sphenopsids, lycophytes, and seed ferns that inform Permian floras of Gondwana. Palynological assemblages contain spores and pollen taxa instrumental for correlation with assemblage zones used by the Brazilian paleobotanical community, while coal-ball and compression fossils document peatland ecology comparable to those recorded in Gondwana Research-era studies. Trace fossils and occasional vertebrate remains have been reported in marginal facies, linking ichnofaunas to continental tetrapod groups known from Permian strata in South America and Africa.
Facies analysis supports deposition in lowland fluvial-deltaic systems with widespread mires under a temperate to cool-temperate climate influenced by high-latitude Gondwanan paleolatitudes. Climatic interpretations rely on plant physiognomy, coal petrography, and sedimentary indicators that together suggest seasonal precipitation regimes with intervals of peat accumulation and fluvial reworking. These reconstructions connect to Permian paleoclimate synthesis studies involving paleomagnetism, paleobotany, and basin modeling conducted by research groups at institutions like the University of São Paulo and international collaborators.
The formation hosts economically significant coal seams that supported regional mining in the 19th and 20th centuries and continue to be evaluated for resource potential. Coal quality ranges from lignite to sub-bituminous ranks, and associated sandstone units have served as aquifers tapped by municipal and agricultural wells. Studies on carbon content, gas generation potential, and mineability have been undertaken by the National Department of Mineral Production (DNPM) and energy companies, informing land-use planning and discussions about coal use versus conservation and carbon-management policies in Brazil.
Initial descriptions date to 19th-century geological surveys; subsequent systematic stratigraphic, paleobotanical, and sedimentological investigations expanded knowledge through the 20th century. Key contributions came from Brazilian geologists associated with the Divisão de Geologia e Recursos Minerais and academics at the Federal University of Rio Grande do Sul, with international comparative work linking the unit to Karoo-age deposits and Gondwanan floral provinces. Ongoing research integrates remote sensing, detrital zircon geochronology, palynology, and basin modeling to refine chronostratigraphy and to correlate the formation with contemporaneous Permian sequences in Antarctica, South Africa, India, and Australia.
Category:Geologic formations of Brazil Category:Permian geology Category:Paraná Basin