Sistemática dos bivalves devonianos da Formação Ponta Grossa, Bacia do Paraná, Rio Verde de Mato Grosso, MS: implicações paleogeográficas e paleoambientais
Dias, H.Q.G. (2025). Sistemática dos bivalves devonianos da Formação Ponta Grossa, Bacia do Paraná, Rio Verde de Mato Grosso, MS: implicações paleogeográficas e paleoambientais. MA Thesis. Universidade Estadual Paulista (UNESP): Rio Claro. 56 pp.
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Document type: Dissertation
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Pragian/Emsian. Malvinoxhosan. Paleoenvironmental Interpretation. |
| Abstract |
This study presents a detailed description of a newly discovered, fully marine bivalve-dominated assemblage from Early Devonian strata of the Ponta Grossa Formation, located in the Rio Verde de Mato Grosso region, Alto Garças Sub-basin, central Brazil. This discovery fills a significant gap in our understanding of the taxonomy and geographic distribution of benthic invertebrates in the Devonian Paraná Basin. It is one of the few systematic studies on Devonian bivalves from this basin, a group often overlooked despite its geological importance for paleoenvironmental interpretations and biocorrelations. The molluscan fauna consists of species belonging to common and widespread genera, such as (Nuculites africanus, Nuculites sharpei, Nuculites sp., Palaeoneilo magnifica, Nuculana viator, “Acharax” bainii, and Pholadella epops), along with a new bivalve species (Devonomya gondwanica gen. et sp. nov.), and indeterminate species (Anomalodesmata indet.). The excellent preservation of some specimens reveals key morphological features that are documented here for the first time. The bivalves are predominantly found within concretions, with many specimens retaining closed, articulated shells — some likely preserved in situ — without signs of mechanical abrasion and fragmentation, suggesting an autochthonous to parautochthonous assemblage. The marine bivalve collection from Rio Verde de Mato Grosso is dominated by shallow infaunal, deposit-feeders, which constitute ca. 53% (n= 31 de 58) of the specimens in the studied biota, followed by shallow infaunal, suspension-feeders. These are typical of low-energy, offshore-prodeltaic environments, likely inhabiting soft, fine-grained siliciclastic sediments rich in organic matter, under oxygen-deficient conditions. The identified species are mainly distributed along the Gondwana Interior and South African, Falkland Islands/Malvinas and Western Antarctica bioregions. However, some species (N. sharpie, P. magnifica) are also shared with coeval strata in Bolivia and Argentina. The species (N. africanus, N. sharpei, P. magnifica, N. viator, “A.” bainii, and P. epops) are the same found in the Pragian-Emsian bivalve assemblages of the Jaguariaíva Member, Ponta Grossa Formation, in the Apucarana Sub-basin, Paraná State, southern Brazil. This suggests a full connection between the Apucarana and Alto Garças Sub-basins, facilitated by the widespread marine transgression during the deposition of the studied bivalve-bearing strata (=Jaguariaíva Member) of the Ponta Grossa Formation. Finally, these bivalves are elements of the climax benthic fauna of the Malvinoxhosan bioregion during the Pragian-Emsian in the Paraná Basin. |
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