Navegando por Autor "MEDEIROS, Renato Sol Paiva de"

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Depósitos carbonáticos-siliciclásticos da porção superior da Formação Piauí, carbonífero da bacia do Parnaíba, região de José de Freitas-PI
(Universidade Federal do Pará, 2015-07-22) MEDEIROS, Renato Sol Paiva de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The northwestern margin of the Gondwana, in the Neocarboniferous period, was influenced by a large transgressive-regressive event, depositing thin carbonate sequences from Andean basins to center-southern portions of the paleocontinent, such as the stratigraphic boundaries of the Parnaíba Basin. The Higher Member of the Piauí Formation in the Parnaíba Basin, studied in the region of José de Freitas, displays richly fossiliferous carbonate deposits overlapped by prograding clinoforms, defining the transition from a transgressive system tract to an highstand system tract. The facies and stratigraphic analysis of this succession allowed the individualization of 17 sedimentary facies and microfacies grouped in four facies associations (FA): the FA1 – Campo de Dunas – is below to the further FA and is composed by thin and average sandstone, with well selected and rounded grains, displaying plane parallel stratification with high level of bioturbation, cross-tubular stratification and translatant subcritically climbing ripple cross-lamination. The FA2 - Shallow sea deposits – is composed by a carbonate plain with tubular and continuous layers of solid carbonate and fossiliferous peloids interspersed with thin lenses of bituminous shale. The FA3 – Frente Deltaica and FA4 – Prodelta consist of pelitic layers and thin and average sandstones, arcosians and quartz sandstones, marked by surfaces of subaerial exposure with shrinkage cracks, cemented by carbonate, arranged in continuous tabular layers or in the form of sigmoidal lobes, as well as liquefaction structures of the types load cast and flame, and fluidization of the type disruption of layers, which distort the strata. The facies data corroborate the idea that the sea in the Pennsylvanian retrograded up to the border of the Parnaíba Basin, and later with the Appalachian orogeny (300 Ma) the top of the Parnaíba River arched and stepped back the marine incursion, followed by a progradational event on marine deposits.
Acesso aberto (Open Access)
O Pensilvaniano da Bacia do Parnaíba, norte do Brasil: implicações paleoambientais, paleogeográficas e evolutivas para o Gondwana Ocidental
(Universidade Federal do Pará, 2019-02-21) MEDEIROS, Renato Sol Paiva de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The end of the Paleozoic Age was marked by landmasses tectonic movements that were forming the supercontinent Gondwana, which stretched mainly in the southern hemisphere, surrounded by the Panthalassa oceans to the west and Tetis to the east. During the Carboniferous period, there were several cycles of climatic variations in the earth's history, evidenced in glaciogenic icehouse and greenhouse carbonate deposits, both in the paleocontinent Gondwana and in Laurasia. These global cycles of eustatic variation were recorded in the epicontinental seas, as they represent the thawing phase and eustatic level increase in a greenhouse period, which together with a favorable paleogeography form extensive marine transgressions over the continental blocks, with cyclic stacking patterns, called cyclothems (eg., terrestrial; terrestrialmarine mixed; marine and restricted marine / evaporitic pattern). Records of these events in northern Brazil are found in the intracratonic basins, particularly in the Balsas Group of Parnaíba Basin, where the exhibits allow us to assess the Pennsylvanian sedimentary history. The sedimentary succession studied belongs to the Piauí Formation Upper Member, described among the cities of José de Freitas, União, Miguel Alves and Lagoa Alegre, and exhibits richly fossiliferous carbonate deposits overlapped by thick pelitic packages and progradant clinoforms. Seventeen sedimentary facies were grouped into four facies associations (FA), representative of a shallow carbonate platform, adjacent to a coastal dune field, later replaced by lacustrine-delta deposits. The FA 1- coastal dune field/interdune comprises well selected, intensely bioturbed, fine to medium sandstones with plane-parallel stratification, tabular crossbedding and climbing translatent lamination. The shallow-sea deposits FA 2 consists of a succession of fossiliferous carbonate rocks, laterally continuous for hundreds of meters, interspersed with bituminous shale. These carbonates were dolomitized and have negative δ13Ccarb values covariate with positive values of δ18Ocarb, suggesting that the supersaturated fluid volume was sufficient to change not only δ18O but also δ13C. The FA 3- suspension lobes/mouth bar and FA 4- lacustre prodelta consist respectively of sigmoidal cross-stratification and planeparallel stratification sandstones and intercalated fine sandstones and pelites. The thick politic layers of prodelta in contact with FA 2 feature quartz grains with morphology texture of windorigin sediments, with textures such as bulbous and smooth edges, upturned plates, irregular depressions, and percussion marks. Subarea exposure surfaces in carbonate marked by shrinkage cracks and dissolution features indicate the end of carbonate sedimentation (eg., Marine Sequence - Highstand System Tract) with the Pennsylvanian Sea Retreat and Confinement in an extensive lacustrine system. (eg., Continental Sequence – High Accommodation System Tract) in the central portion of Gondwana. The FA 4 mineral clay assembly confirms the aridest climatic pattern to the top of the studied succession, presenting mainly smectites and illite. This marine retraction was concomitant with the Appalachian orogeny (300 Ma) that caused the uplift in western Gondwana and definitively disconnected the Itaituba-Piaui epeiric sea from the Panthalassa ocean to the west. Restricted seas or lakes were progressively beset by prograding hipopycnal flows with the establishment of the most extreme arid conditions triggered during Pennsylvanian.