Bivalves da Formação Rio do Rasto, Permiano, Bacia do Paraná, Brasil: implicações evolutivas e paleoecológicas
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Data
2018-10-10
Autores
Guerrini, Vitor Bonatto [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As faunas de bivalves endêmicos do Permiano do Grupo Passa Dois, mundialmente conhecidas, evoluíram a partir de ancestrais marinhos em um enorme mar epicontinental, isolado, acompanhando a progressiva continentalização/aridização da Bacia do Paraná, Brasil, no Paleozoico Superior. No entanto, até o momento, os bivalves que se desenvolveram nos ambientes marginais de águas doces da Bacia do Paraná foram pouco estudados. Neste contexto, na presente dissertação é apresentada uma detalhada análise sistemática dos bivalves dos membros Serrinha e Morro Pelado, da Formação Rio do Rasto, Grupo Passa Dois. As implicações evolutivas, paleoecológicas e paleogeográficas dos dados são discutidas. No total, foram examinados 204 espécimes, preservados, principalmente, como moldes compostos em argilitos avermelhados. Três assembleias de bivalves foram identificadas: a- Terraia decarinata e b-Terraia cf. T. decarinata, no intervalo de transição entre os membros Serrinha e Morro Pelado, e c- Palaeomutela australis, que é registrada na parte basal do Membro Morro Pelado. A primeira assembleia (= 137 exemplares) é composta por Terraia decarinata sp. nov. (67,88%), seguida de Relogiincola delicata gen et sp. nov. (9,50%), Palaeomutela australis sp. nov. (4,38%) e Palaeomutela platinensis (Reed) (0,73%), além de conchas indeterminadas (17,52%). A segunda assembleia (= 32 exemplares) é dominada por Terraia cf. T. decarinata sp. nov. (56,25%), seguida de Terraia decarinata sp. nov. (9,37%), Palaeomutela platinensis (Reed) (6,25%), além de conchas mal preservadas, indeterminadas (28,13%). A terceira assembleia (= 35 espécimes) inclui Palaeomutela australis sp. nov. (51,43%), Relogiincola delicata gen et sp. nov. (11,43%) e Palaeomutela platinensis (Reed) (2,86%), além de espécimes indeterminados (34,28%). Estas assembleias são quase que monoespecíficas e incluem bivalves de uma mesma guilda ecológica (i.e., escavadores rasos, suspensívoros), sugerindo condições de alto estresse ambiental. Todas as assembleias contêm Palaeomutela Amalitzky, gênero cosmopolita, típico de ambientes de águas doces, do Paleozoico Superior. Notavelmente, ambos os gêneros Relogiincola gen. nov. (Pachydomidae Fischer) e Terraia Cox (Crassatellacea Ferussác) que ocorrem em associação com Palaeomutela Amalitzky têm afinidades com bivalves registrados nas unidades subjacentes à Formação Rio do Rasto, do Grupo Passa Dois. Isso mostra que alguns gêneros endêmicos que evoluíram in situ na Bacia do Paraná adaptaram à vida em condições límnicas. Nas três assembleias de bivalves, espécies características da porção basal e média do Membro Serrinha [Leinzia similis (Holdhaus), Oliveiraia pristina (Reed), Cowperesia emerita Mendes, Terraia curvata (Reed) e T. altissima (Holdhaus)] não foram registradas, indicando importante mudança faunística nas malacofaunas. As assembleias bivalves estão seguramente posicionadas em estratos sedimentares situadas acima das últimas ocorrências de Terraia altissima (Holdhaus) e Cowperesia emerita Mendes, na Formação Rio do Rasto. Na Formação Gai-As, Bacia de Huab, Namíbia, estas espécies ocorrem no limite Wordiano-Capitaniano, Guadalupiano. Portanto, as assembleias contendo Palaeomutela Amalitzky devem ser mais jovens que as que registram Terraia altissima (Holdhaus), e Cowperesia emerita Mendes, sendo, provavelmente, capitanianas. Conchas de Palaeomutela Amalitzky são também encontradas na porção inferior do Grupo Beaufort, das bacias sedimentares africanas (África do Sul, Tanzânia, Zimbábue e Zâmbia). Estes registros podem corresponder à máxima expansão paleobiogeográfica de Palaeomutela Amalitzky no Gondwana ocidental, durante o Permiano Superior.
The worldwide known, endemic bivalve faunas of the Permian Passa Dois Group evolved from marine ancestors in a huge, isolated epeiric sea, accompanying the progressive aridization/continentalization of the Paraná Basin, Brazil. However, until now the bivalves that developed during times of marked freshening events were poorly studied. In this context, an exhaustive systematic survey of the bivalves from the uppermost part of the Serrinha and the Morro Pelado Members, Rio do Rasto Formation, Passa Dois Group, is presented. The evolutionary, paleoecologic, and paleogeographic implications of the data are also discussed. In total, 204 specimens were examined, which were mainly preserved as composite molds in mudstones. Three bivalve assemblages were recorded, namely: a- Terraia decarinata and b- Terraia cf. T. decarinata assemblages, both in the transitional interval between the Serrinha and Morro Pelado Members, and c- Palaeomutela australis assemblage that is recorded in a massive reddish sandy mudstones in the basal part of the Morro Pelado Member. The first assemblage (= 137 specimens) is composed by Terraia decarinata sp. nov. (67.88%), followed by Relogiincola delicata gen et sp. nov. (9.50%), Palaeomutela australis sp. nov. (4.38%), and Palaeomutela platinensis (Reed) (0.73%), plus 17.52% of undetermined shells. The second assemblage (= 32 specimens) is dominated by Terraia cf. T. decarinata sp. nov. (56.25%), followed by Terraia decarinata sp. nov. (9.37%), Palaeomutela platinensis (Reed) (6.25%), and 28.13% of poorly preserved, undetermined shells. The third assemblage (= 35 specimens) includes Palaeomutela australis sp. nov. (51.43%), Relogiincola delicata gen et sp. nov. (11.43%), and Palaeomutela platinensis (Reed) (2.86%), plus 34.28% of undetermined specimens. These assemblages are almost monospecific, and represented by bivalves of the same ecological guild (i.e., shallow burrowers, suspension feeders), suggesting high environmental stress. All studied assemblages yielded Palaeomutela Amalitzky, a typical Late Paleozoic, cosmopolitan, freshwater bivalve. Notably, both Relogiincola gen. nov. (Pachydomidae Fischer) and Terraia Cox (Crassatellacea Ferussác) that also occur in association with Palaeomutela Amalitzky have affinities with bivalves recorded in the underlying units of the Passa Dois Group. This shows that some endemic genera that evolved in situ in the Paraná Basin have adapted to live under limnic conditions. In the three bivalve assemblages, typical species found in the basal and mid portion of the Serrinha Member [Leinzia similis (Holdhaus), Oliveiraia pristina (Reed), Cowperesia emerita Mendes, Terraia curvata (Reed) and T. altissima (Holdhaus)] were not recorded, indicating a major faunal turnover in the molluscan assemblages. The bivalve assemblages are securely recorded in sedimentary strata above the last occurrences of Terraia altissima (Holdhaus), and Cowperesia emerita Mendes in the Rio do Rasto Formation. In the Gai-As Formation, Huab Basin, Namibia, these species occur in the Wordian-Capitanian limit, Guadalupian. Therefore, the assemblages containing Palaeomutela Amalitzky should be younger than those recording Terraia altissima (Holdhaus), and Cowperesia emerita Mendes in the Rio do Rasto Formation, and are probably Capitanian in age. Shells of Palaeomutela Amalitzky are also found in the lower Beaufort Group of African sedimentary basins (South Africa, Tanzania, Zimbabwe, and Zambia). These records may correspond to the maximum paleobiogeographic expansion of Palaeomutela Amalitzky within the western Gondwana, during the Late Permian.
The worldwide known, endemic bivalve faunas of the Permian Passa Dois Group evolved from marine ancestors in a huge, isolated epeiric sea, accompanying the progressive aridization/continentalization of the Paraná Basin, Brazil. However, until now the bivalves that developed during times of marked freshening events were poorly studied. In this context, an exhaustive systematic survey of the bivalves from the uppermost part of the Serrinha and the Morro Pelado Members, Rio do Rasto Formation, Passa Dois Group, is presented. The evolutionary, paleoecologic, and paleogeographic implications of the data are also discussed. In total, 204 specimens were examined, which were mainly preserved as composite molds in mudstones. Three bivalve assemblages were recorded, namely: a- Terraia decarinata and b- Terraia cf. T. decarinata assemblages, both in the transitional interval between the Serrinha and Morro Pelado Members, and c- Palaeomutela australis assemblage that is recorded in a massive reddish sandy mudstones in the basal part of the Morro Pelado Member. The first assemblage (= 137 specimens) is composed by Terraia decarinata sp. nov. (67.88%), followed by Relogiincola delicata gen et sp. nov. (9.50%), Palaeomutela australis sp. nov. (4.38%), and Palaeomutela platinensis (Reed) (0.73%), plus 17.52% of undetermined shells. The second assemblage (= 32 specimens) is dominated by Terraia cf. T. decarinata sp. nov. (56.25%), followed by Terraia decarinata sp. nov. (9.37%), Palaeomutela platinensis (Reed) (6.25%), and 28.13% of poorly preserved, undetermined shells. The third assemblage (= 35 specimens) includes Palaeomutela australis sp. nov. (51.43%), Relogiincola delicata gen et sp. nov. (11.43%), and Palaeomutela platinensis (Reed) (2.86%), plus 34.28% of undetermined specimens. These assemblages are almost monospecific, and represented by bivalves of the same ecological guild (i.e., shallow burrowers, suspension feeders), suggesting high environmental stress. All studied assemblages yielded Palaeomutela Amalitzky, a typical Late Paleozoic, cosmopolitan, freshwater bivalve. Notably, both Relogiincola gen. nov. (Pachydomidae Fischer) and Terraia Cox (Crassatellacea Ferussác) that also occur in association with Palaeomutela Amalitzky have affinities with bivalves recorded in the underlying units of the Passa Dois Group. This shows that some endemic genera that evolved in situ in the Paraná Basin have adapted to live under limnic conditions. In the three bivalve assemblages, typical species found in the basal and mid portion of the Serrinha Member [Leinzia similis (Holdhaus), Oliveiraia pristina (Reed), Cowperesia emerita Mendes, Terraia curvata (Reed) and T. altissima (Holdhaus)] were not recorded, indicating a major faunal turnover in the molluscan assemblages. The bivalve assemblages are securely recorded in sedimentary strata above the last occurrences of Terraia altissima (Holdhaus), and Cowperesia emerita Mendes in the Rio do Rasto Formation. In the Gai-As Formation, Huab Basin, Namibia, these species occur in the Wordian-Capitanian limit, Guadalupian. Therefore, the assemblages containing Palaeomutela Amalitzky should be younger than those recording Terraia altissima (Holdhaus), and Cowperesia emerita Mendes in the Rio do Rasto Formation, and are probably Capitanian in age. Shells of Palaeomutela Amalitzky are also found in the lower Beaufort Group of African sedimentary basins (South Africa, Tanzania, Zimbabwe, and Zambia). These records may correspond to the maximum paleobiogeographic expansion of Palaeomutela Amalitzky within the western Gondwana, during the Late Permian.
Descrição
Palavras-chave
Permiano, Formação Rio do Rasto, Bacia do Paraná, Palaeomutela, Gondwana, Permian, Rio do Rasto Formation, Paraná Basin