Navegando por Assunto "Faixa Paraguai Norte"

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A seção-tipo da Formação Serra do Quilombo, Grupo Araras, Neoproterozoico da Faixa Paraguai Norte, Mato Grosso
(2013-06) MILHOMEM NETO, João Marinho; NOGUEIRA, Afonso César Rodrigues; MACAMBIRA, Moacir José Buenano
After the last Cryogenian glaciation (ca. 635 Ma), large carbonate platforms were developed in several cratonic regions of the Earth and, despite the intense dolomitization of these deposits, paleoceanographic and paleoenvironmental pieces of information are preserved. One of the most important examples of this period in Brazil are the dolostones of Serra do Quilombo Formation, which belong to the upper portion of the Araras Group, exposed in the northern Paraguay Belt, south of the Amazonian Craton. The stratigraphic revaluation of this formation in its type-section and in a reference section in the Nobres region, based on facies and stratigraphic analyses, allowed to enlarge the paleoenvironmental interpretations and to propose a depositional model. The study succession of 140 m thick includes Serra do Quilombo Formation in sharp basal contact with the limestones of Guia Formation and the gradual contact, to the top, with the sandy dolostones of Nobres Formation, at the top. Serra do Quilombo Formation comprises a shallowing upward succession, which includes two facies associations: 1) deep to moderately shallow carbonate platform, composed of laminated dolostone rich in organic matter and a massive to laminated dolostone; and 2) storm influenced shoreface, consisting of hummocky/swaley to planar stratified sandy dolostone, sandy/oolitic dolostone with wave cross laminations and matrix-supported dolomitic breccias. Serra do Quilombo Formation represents the progradational record of a high-stand system tract, in a homoclinal carbonate ramp, installed on the southern part of the Amazonian Craton during the Ediacaran.
Acesso aberto (Open Access)
Sedimentação siliciclástica e proveniência do grupo Alto Paraguai (neoproterozóico-cambriano), borda Sul do Cráton Amazônico e faixa Paraguai Norte, estado do Mato Grosso.
(Universidade Federal do Pará, 2011-09-02) SILVA JÚNIOR, José Bandeira Cavalcante da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; 8867836268820998
The Neoproterozoic-Cambrian Alto Paraguai Group exposed in the southern Amazon Craton and the northern Paraguay Belt, western-central Brazil, represents a 2,400m thick siliciclastic succession that succeed the carbonate platform sedimentation deposited after the last Cryogenian glaciation (635 Ma). The Alto Paraguai Group consists of Raizama (fine to coarse grained sandstones, conglomerates, mudstones, pebbly mudstones and secondary chert), Sepotuba (dolomites, stromatolites, mudstones and fine to medium grained sandstones) and Diamantino (mudstones and fine to medium grained sandstones) formations. Outcropbased facies and stratigraphic analysis in combination with provenance studies using detrital zircon U-Pb dating, allowed understanding the lithostratigraphy and the depositional history of the Alto Paraguai Basin. The depositional model include the progradation of a fluvialwave-tide- and storm-dominated coastal region (upper member of the Raizama Formation) onto a shallow to moderately deep storm-influenced marine platform, locally influenced by debris flow (lower member of the Raizama Formation). Afterwards, the last transgressive event in the Paraguai Basin generated tidal flat-sabkha setting in the shallower portions of the basin to the west (lower member of the Sepotuba Formation) and a storm-dominated marine platform in the central and eastern portion of the basin (upper member of the Sepotuba Formation). The progression of the Pan-African-Brasilian orogenesis resulted in the confinement of the Sepotuba Sea as a foredeep sub-basin, against the edge of the Amazon Craton. These restricted lake/sea was filled with turbidites deposits (lower member of Diamantino Formation), lacustrine sediments (middle member of the Diamantino Formation) and progradational deltaic front deposits (upper member of the Diamantino Formation). This sedimentation was supplied by source areas of 600 to 500 Ma, located in the southeast and east of the basin, related to the Brasilia Belt and the Paraguay orogen. This stage represents the final amalgamation of Western Gondwana, marked by the closure of the Neoproterozoic Clymene Ocean between the Amazon Craton and Central Gondwana, generating the northern Paraguay Belt.
Acesso aberto (Open Access)
Tectônica pós-colisional e estratigrafia da cobertura neoproterozóica-cambriana da Faixa Paraguai Norte, região de Nobres (MT)
(Universidade Federal do Pará, 2012-07-04) SOUZA, SOUZA, Eduardo de Jesus Eduardo de Jesus; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Paraguay Belt, located in the southeast border of the Amazon Craton records important events of the geological evolution of the planet at the end of the Precambrian era. The Paraguay Belt comprises neoproterozoic metassedimentary rocks of the Cuiaba Group, overlaid unconformably by ediacaran sediments of the Paraguay Basin, which includes glacial pelites and diamictites (Puga Formation), carbonates (Araras Group) and siliciclastic rocks (Alto Paraguay Group) heterogeneously deformed. The Paraguay Belt is a neoproterozoic orogen produced by the collision of the Amazon, São Francisco and Rio de La Plata cratons. The collision took place during the Brasiliana/Pan-Africana (600-520 Ma) and Paraguay (540-490 Ma) orogenies. This research presents field based structural data from the region of Nobres that suggests a tectonic history, which explains the stratigraphy and the geometry of the studied rocks based on a model of partitioned transpression. The transpressive deformation that affected the rocks in the region is late in relation to an early colisional event classicaly describe in the belt, evidenced by: (1) the uniform pattern of deformation displayed by all studied rocks that show non-cylindrical, forced folds forming antiform-synform arrays with no vergence; (2) the distinct domains of deformation heterogeneously distributed into weakly deformed areas separated by steep dipping strike-slip faults from areas of strongly deformed rocks that show steep dipping bedding (60-85°). The bedding in strongly deformed sedimentary rocks is geometrically concordant with the foliated fabric observed in the rocks from the Cuiaba Group. This relationship suggests that the deformation that affected the sedimentary rocks of the Paraguay Basin was controlled by the early ductile fabric in the basement rocks of the Cuiaba Group. The ductile fabric was reactivated during late regional transpression and controlled the development of zones where strain was preferentially accumulated. The observed of steep dipping bedding (> 50°) and the absence of collisional structures are incompatible with the presence of thrust fault in the studied region. These observations together with the stratigraphic pattern of the sedimentary sequences of the Paraguay Basin are incompatible with the characteristics of a foreland basin. This is supported by the following evidence: (1) the absence of angular unconformities; (2) the platformal nature of the ediacaran sediments; and (3) the heterogenous geographical distributions of the lithological units in the studied regions. Thus, the sedimentary rocks of the Paraguay Basin are interpreted as a neoproterozoic-cambrian sequence deformed during a eo-paleozoic late, brittle, transpressive deformation resulting from the reactivation of early ductile fabric in the basement. It is suggested that the rocks of the Cuiaba Group, represent the Paraguay Belt, the basement for the Paraguay Basin.