ABSTRACT. Several studies have tried to address the evolution of the Atlantic conjugate margins, including Brazil and West Africa. However, past research advances has been hindered by a lack of data for the marginal region in the eastern portion of northeastern Brazil, extending from the Pernambuco Shear Zone to the Touros High. This situation has imposed serious limitations on the development of a regional view of the paleotectonic and paleogeographic evolution of the margin in this area and on correlations with regional counterparts in Africa. Here, we present an investigation using regional seismic and potential field data. The results show that this region represents a basement high forming a narrow platform with a thin sedimentary cover (0.8-2.5 km) and an abrupt shelf break, which created a large bypass zone towards the slope. The analysis of a deep seismic section revealed that thinned continental crust (transitional crust) occupies a narrow zone and that the continentaloceanic boundary (COB) is located approximately 100 km to the east of the present coastline. Geophysical modeling integrated with interpretation of the seismic data suggests that this region is characterized by an abrupt thinning of continental crust, with an accompanying sudden rise of the Moho. There are also indications for the existence of a zone of extremely thinned continental crust, which was interpreted as proto-oceanic crust. Our findings suggest that the study area shows strong similarities to non-volcanic rifted margins.Keywords: Paraíba and Natal Platform Basins, continental-oceanic transition, northeastern Brazilian continental margin, Atlantic rift. RESUMO.Vários trabalhos têm tentado abordar a evolução das margens conjugadas do Atlântico, incluindo o nordeste do Brasil e o oeste daÁfrica. Entretanto, o avanço de pesquisas anteriores tem sido dificultado em razão da falta de dados na região marginal da porção oriental do nordeste do Brasil, aárea entre a Zona de Cisalhamento de Pernambuco e o Alto de Touros. Este fato tem imposto limitações ao desenvolvimento de modelos regionais sobre a evolução paleotectônica e paleogeográfica desta região, assim como na correlação com sua contraparte naÁfrica. Aquié apresentada uma investigação realizada com base em dados sísmicos e de métodos potenciais regionais. Os resultados mostraram que esta região representa um alto do embasamento que forma uma plataforma estreita com uma cobertura sedimentar pouco espessa (0,8-2,5 km) e uma quebra abrupta da plataforma, o que criou uma grande zona de bypass através do talude. A análise de uma seção sísmica profunda revelou que a crosta continental afinada (crosta transicional) representa uma estreita zona, e que o limite crosta continental-oceânica (COB) está localizado a aproximadamente 100 km a leste da atual linha de costa. A modelagem geofísica, integrada com a interpretação sísmica, indica que esta regiãoé caracterizada por um afinamento abrupto da crosta continental, com a consequente ascensão súbita da Moho. Também há evidências da existênci...
This study reports the first known occurrence of the Ediacaran fauna in northeastern Brazil (at Pacujá Municipality, northwestern state of Ceará) and presents preliminary interpretations of its significance. Regional correlation indicates that the fossils originated in the Jaibaras Basin and that they may represent a new geological system. The depositional environment can be attributed to a fluviomarine system. Nine Ediacaran species can be identified, including members of pandemic groups (e.g., Charniodiscus arboreus Glaessner, 1959; ?Charniodiscus concentricus Ford, 1958; Cyclomedusa davidi Sprigg, 1947; Ediacaria flindersi Sprigg, 1947; and Medusinites asteroides Sprigg, 1949) and endemic groups (e.g., Kimberella quadrata Glaessner & Wade, 1966; Palaeophragmodictya reticulata Gehling & Rigby, 1996; Parvancorina minchami Glaessner, 1958; and Pectinifrons abyssalis Bamforth, Narbonne, Anderson, 2008). Three ichnogenera are also present: Arenicolites Salter, 1857; Palaeophycus Hall, 1987; and Planolites Nicholson, 1873. The relative age of the deposits is between ?Ediacaran and Cambrian, and the fauna resembles the White Sea Assemblage. The bioturbation presents typical unbranched Ediacaran ichnogenera with little depth in the substrate. This previously unknown occurrence of the Ediacaran fauna reinforces the importance of the state of Ceará to Brazilian and global palaeontology.
A Bacia de Cedro, objeto desta abordagem, é uma das Bacias Interiores do Nordeste, geologicamente inserida na Zona Transversal da Província da Borborema. A recente construção da Transnordestina cortou diversas bacias do interior do Nordeste, dentre estas a Bacia de Cedro, expondo cortes nos quais afloram sedimentos anteriormente mapeados como de idade Paleozóica, se fazendo oportuna uma revisão de sua estratigrafia, uma vez que os últimos levantamentos datam de 1993. Os dados obtidos neste trabalho confirmam uma mudança significativa no empilhamento estratigráfico desta bacia, incluindo em sua estratigrafia sedimentação correspondente a fase Rifte (Cretácio inferior), e permitiram também concluir que a sedimentação composta de calcários aptianos teria uma extensão maior do que se acreditava anteriormente. As análises faciológicas e dados bioestratigráficos permitiram definir a existência da Formação Abaiara de idade aptiana nesta bacia. O novo estudo aqui apresentado muda o panorama da evolução geotectônica desta bacia e pode ter implicações importantes para outras bacias do interior do Nordeste.
The present work deals with the first record of ostracods in the Estiva Formation, Pernambuco Basin (Cupe, 1 LABIO-PE1 borehole). The Pernambuco Basin extends throughout the southern coast of the state of Pernambuco and is limited by the Pernambuco Shear Zone, in the north and by the Maragogi High, in the south. The Estiva Formation consists of continental shelf carbonates dated as Upper Cretaceous. The analysis and interpretation of the data were performed through literature review, stratigraphic data surveys, and sampling. The methodology used for the treatment of the samples consisted of the following steps: collection, weighing and fragmentation of the samples; washing and drying of the calcined materials; and screening and picking of the carbonatic microfossils. Rare ostracods were found, probably belonging to the brackish genus Fossocytheridea Swain & Brown, 1964. The recognition of the ostracod fauna and its paleoecology aims to contribute to the understanding of the Pernambuco Basin evolution.
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