Navegando por Assunto "Gondwana"

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Acesso aberto (Open Access)
A fragmentação do Gondwana na região meio-norte do Brasil durante o mesozóico
(Universidade Federal do Pará, 2007-08-09) SOARES JÚNIOR, Adilson Viana; COSTA, João Batista Sena; http://lattes.cnpq.br/0141806217745286; 0141806217745286
South America, Africa, India, Antarctic and Australia continents formed a great and complex supercontinent called Gondwana at the end of the Precambrian. From the Mesozoic this mega-continent underwent extension and regional uplift with volcanism associated, resulting in triple junctions which evolved to rift systems. These events are related to the Wealdenian Reactivation or South-Atlantic event witch took place in the interior and the boundary of the South America plate, been followed by intense basic magmatism and extensional systems formation, with listric and planar faults. Some basin architecture are controlled by ancient shear zones reactivations. From Triassic the extension gave rise to uplifts associates to the magmatism in the weakness areas of the basement, including the Paleozoic basins in the northern Brazil. This event responds to the Pangaea break-up, the formation of the Central Atlantic Ocean and the individualization of the Laurasia and Gondwana supercontinents. The arm of the Central Atlantic in the South America evolved to rift system in the Foz do Amazonas basin and volcanism in the Parnaíba Basin during the Triassic and Jurassic. This rifting event died out towards the south and propagated to the Caribbean region, resulting in North America plate formation. From the early Cretaceous (end of Barremian and beginning of the Aptian), new phase of rifting is registred in the region, without linkage to the Central Atlantic. This had been increased the Foz do Amazonas basin and Marajó basin formation and a new phase of uplifting followed by volcanism and rifting concentrated at the Ferrer-Urbano Santos Arc, Parnaíba Basin, and the formation of the Gurupi Graben System (Bragança-Viseu, São Luís and Ilha Nova basins) and Grajaú Basin. This event includes two distinct phases: early rifting resulting in the formation of the Bragança-Viseu and Ilha Nova basins; and thermal subsidence with the formation of the São Luís and Grajaú basins, separate by short time span. These basins underwent rapid evolution, with sedimentary environment records since fluvial and lacustrine until transgressions. In the Lower Cretaceous continued the evolution of the Foz do Amazonas Basin witch the fragmentation propagating towards the SE, resulting in the formation of the Pará-Maranhão Basin and Barreirinhas Basin at the beginning of the Albian. This event is resposible for the Equatorial Atlantic Ocean individualization, with associated transgression in the Pará-Maranhão and Barreirinhas basins, as well in the São Luís, Ilha Nova and Grajaú Basins, controled by NE-SW fractures and faults in the São Marcos Bay and by partial collapse of the Ferrer-Urbano Santos Arc. During the Late Cretaceous it had reducted the extension at the Marajó Basin, stopped the fragmentation in the Gurupi Graben System and the South America and African continents were completely pulled apart, with formation of oceanic crust and passive margins in the Foz do Amazonas, Pará-Maranhão and Barreirinhas Basins. From the Upper Cretaceous, the east margin of the South America and the west margin of Africa had assumed its current configuration, withchanges related to drifting and to the Neotectonic.
Acesso aberto (Open Access)
Proveniência das rochas metassedimentares do Cinturão Araguaia com base em datações Pb-Pb em zircão e idades-modelo Sm-Nd
(2011-06) PINHEIRO, Bruno Luís Silva; MOURA, Candido Augusto Veloso; GORAYEB, Paulo Sérgio de Sousa
This paper presents single zircon Pb-evaporation ages, obtained in detrital zircon grains, and Sm-Nd (TDM) for metassedimentary rocks of the Araguaia belt, to investigate the possible source areas of these rocks, and to contribute to understanding the geologic evolution of this belt in the context of the West Gondwana amalgamation. Quartzite of the Morro do Campo Formation, located in the north segment of the belt (Xambioá region) gave Archean 207Pb/206Pb zircon ages (2.65-3.0 Ga), while in the south segment (Paraíso do Tocantins region), the 207Pb/206Pb zircon ages were mainly Meso-Neoproterozoic (1.25-0.85 Ga), and, secondarily, Paleoproterozoic (1.85-1.70 Ga). These results suggest the existence of different sources areas for this quartzite. The Sm-Nd (TDM) model ages of metapelites (slate, phyllite and micaschist) present bimodal distribution with the main population occurring between 2.1 and 1.4 Ga (mode in 1.6-1.7 Ga), and a less abundant population between 2.7 and 2.4 Ga. These data have been interpreted as mixing of Paleoproterozoic (or even Archean) sources with younger, probably Meso-Neoproterozoic, sources. The main candidates to be the sources of the metassedimentary rocks of the Araguaia belt would be those crustal segments located in the southeastern (São Francisco Craton, Goiás Massif, Goiás Magmatic Arc). The sedimentary succession deposited in the Araguaia oceanic basin and the associated magmatic rocks were transported, later, towards the east margin of the Amazonian Craton, during the main tectonic that led to the structural development of the Araguaia belt as a result of the West Gondwana amalgamation.
Acesso aberto (Open Access)
Taxonomia de brachiopoda (Família Discinidae Gray, 1840) da Formação Manacapuru (Siluro-Devoniano), Bacia do Amazonas, sudoeste do Pará
(Universidade Federal do Pará, 2020-05-29) CORRÊA, Luiz Felipe Aquino; RAMOS, Maria Inês Feijó; http://lattes.cnpq.br/4546620118003936; 4546620118003936
Discinoids are inarticulate brachiopod exclusively marine with two organophosphate valves that arise during Ordovician and can be divided into four living genera. The remarkable marine transgressions at northwest Gondwana during Silurian-Devonian transition collaborated to make discinoids so abundant in South America during Devonian. Despite this big radiation during Devonian, rare records of this group are studied in Amazon and Parnaíba basins. In layers of Manacapuru Formation (Amazon Basin Siluro-Devonian), Ererê Formation (Amazon Basin Meso-Devonian) and Pimenteiras Formation (Parnaíba Basin Eifelian-Frasnian) there are occurrences with no taxonomic detailing. On the other hand, discinoids are easily found in Devonian deposits of Paraná Basin, especially in Ponta Grossa and São Domingos formations, as pointed by well advanced studies. This work aims the taxonomic study of brachiopods (Family Discinidae) of Manacapuru Formation, at the south border of the Amazon Basin, collected during “Paleontological Patrimony Rescue Program” of Belo Monte Hydroelectric Plant, at Vitória do Xingu city, Pará state. Four sampling points (C3P1, C9P1, C13P1 e C14P1) compose the stratigraphic profile of the study area, that consists, from bottom to top, of crystalline basement followed by a nearly 0.5 meters layer of massive fine grained sandstone, interlayered with clay lenses, but discinoids occur only in sandstone portions. Above that, a fine-grained sandstone layer display incipient lamination with disseminated discinoids. Finally, there is a nearly 2.1 meters layer of laminated siltstones where discinoids are concentrated at the bottom, associated with Rhynchonelliformeas; at the top of the layer, isolated lingulids occur. 272 brachiopods samples were analyzed: 205 Discinidae, 57 Rhynchonelliformea and 10 Lingulids. The focus of this research lies in Linguliformeas brachiopods that belongs to Family Discinidae. Taxonomic studies in 205 discinoids samples pointed to three species of Orbiculoidea d’Orbigny, 1847: O. baini Sharpe, 1856, (10 specimens), O. bodenbenderi Clarke, 1913 (5 specimens) and O. excentrica Lange, 1943 (34 specimens). In addition, O. sp. 1 (18 specimens) and O. sp. 2 (19 specimens) were preliminarily identified as Orbiculoidea, but the nomenclature was kept open; another 99 Orbiculoidea samples classification remained undefined due to poorly preserved samples. 20 specimens of Gigadiscina Mergl & Massa, 2005 also remained with open classification. Although some papers mention Orbiculoidea genera in Manacapuru Formation, this is the first record of O. baini, O. bodenbenderi, O. excentrica and Gigadiscina genera in this formation, as well as the first documented occurrences of these species and genera in North of Brazil. The discinoids association studied in this paper (Gigadiscina? sp., O. baini, O. bodenbenderi, O. excentrica, O. sp. 1 and O. sp. 2) is the oldest (Lochkovian) record in South America (e.g. Paraná Basin / Pragian-Givetian; Alto das Garças sub-Basin / Givetian; Parecis Basin / Pragian; Chacoparanense Basin / Pragian; Pre-Argentinian Range / Pragian) and this can be explained by two main reasons: Laurasia and Gondwana (the main continental blocks) were apparently close enough to allow the cosmopolite invertebrate larvae (e.g. Orbiculoidea) to cross the oceans more easily. So, Amazon Basin was closer to Laurasia during Eodevonian, what made easier for these organisms to firstly accommodate in this basin. The other reason is that the global eustatic sea level increased during Eodevonian, leading to the great marine transgressions that reached many portions of Gondwana, favoring the emergence of shallow seas at northwest Gondwana, which is a favorable environmental condition for inarticulate brachiopods colonization, represented by the discinoids in marine sediments of Manacapuru Formation described in this paper. Shallow marine coast environments are the main habitat of Orbiculoidea genera. This affirmation relies, in a certain proportion, in the current distribution of discinoids in less than 30 meters depths: 92,7% of Orbiculoidea fossil records are associated to shallow marine conditions. Therefore, the presence of O. baini, O. bodenbenderi, O. excentrica, and Gigadiscina? sp. in Manacapuru Formation layers suggest a shallow marine environment, in agreement with what is already proposed for the upper portion of this formation.