Navegando por Assunto "Permiano"

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Estudo sedimentológico da formação Pedra de Fogo-Permiano: Bacia do Maranhão
(Universidade Federal do Pará, 1979-10-17) FARIA JUNIOR, Luis Ercílio do Carmo; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
The Pedra de Fogo Formation of the Early-Middle-Permian in the Maranhão Basin is characterized by a ciclic sedimentation with fine sandstone intercalated with siltstones, shales and carbonatic banks which have abundant sílex beds and concretions. On surface this unit is divided into three members named Basal' Silex, Middle and Upper, Trisidela. Silicified oolites, pellets, coquinas with ' fish remains, stromatolitic beds and wood remains are found in the Pedra de Fogo. Formation sediments. The lithologies indicate a shallow, restricted, marine environment ' with two transgressions phases separated by a regression phase. The lateral facies changes reflect the sedimentary dynamism and suggest that the marine environment progressed from a transitional, deltaic to shallow neritic one. The main source areas of the clastic sediments and some of the sílica are, located in the northestern to the southern parts of the Basin and derived ' from the Borborema and São Francisco Provinces rockes. The Tocantins and. Tapajós Provinces to the west and southest have supplied material also. The climate during the Pedra de Fogo sedimentation has varied from moderate to arid as a consequence of the northward South American continent slow migration. The Maranhão had tectonic stability during the Permian. The marine in cursions took place from west, through the Amazonas Basin. Besed on the cyclothemes thickness, it seems that the Pedra de Fogo sedimentation occured from the water level oscilations in the Basin, which had also motivated the transgressions and regressions phases and whose origin should be related to the climatic changes during the Permian time.
Acesso aberto (Open Access)
Evolução de um sistema lacustre árido Permiano, parte superior da Formação Pedra de Fogo, borda oeste da Bacia do Parnaíba
(2014-12) ANDRADE, Luiz Saturnino de; NOGUEIRA, Afonso César Rodrigues; SILVA JÚNIOR, José Bandeira Cavalcante da
Stratigraphic and facies analysis in the Filadélfia region, TO, BR, at the western of the Parnaíba Basin, allowed redefine the paleoenvironment of the upper portion of the Pedra de Fogo Formation of Permian age. The studied deposits are a series of approximately 100 m thick, predominantly siliciclastic, with subordinate carbonates and evaporites, where were defined 21 sedimentary facies that could be grouped into six facies associations (AF): AF1) Lacustrine with ephemeral river deposits; AF2) Storm wave-influenced lake deposits; AF3) Continental sabkha deposits; AF4) Central lake deposits; AF5) Eolian dunes field deposits; and AF6) Lake/oasis deposits with inunditos. These associations indicate that during Permian, an extensive lacustrine arid system developed adjacent to eolian dunes fields and continental sabkha, as well as with contributions from ephemeral rivers. Fluvial incursions into lakes propitiated the formation of suspension lobes and sheet flows (AF1). Sabkha plains (AF3) were formed in the marginal portions of the lake that eventually were influenced by storms waves (AF2), while central zone were site of intense pelitic deposition (AF4). The low supply of eolian sand in this system resulted in the formation of restricted dune fields (AF5), with development of interdune lakes (oasis), where proliferating giant ferns, sporadically flooded by ephemeral rivers (AF6). The facies associations data, corroborated by the paleogeography of the region during the Late Permian, indicate that settling of the top part of the Pedra de Fogo Formation was laid during a hot and arid climate.
Acesso aberto (Open Access)
Paleoambiente e paleoclima da Formação Pedra de Fogo da Bacia do Parnaíba e sua correlação com os eventos globais de silicificação.
(Universidade Federal do Pará, 2019-09-02) ANDRADE, Luiz Saturnino de; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Pedra de Fogo Formation of the Parnaíba Basin, Northern Brasil is a sedimentary unit that has one of the most important sedimentary records of the early Permian (Cisuralian), characterized mainly by intense silicification. Although previous works have contributed to the understanding of its paleoenvironment, important gaps regarding the sedimentary and paleoclimatic conditions that favored the great concentration and preservation of silica, due to the global changes occurred at the beginning and along of the Permian, still remain inconclusive. Problems as to which sources of silica contributed most to the expressive chert content were never satisfactorily explained. There is no reference to the organic and/or inorganic origins, nor is little known about the conditions and processes that led to the preservation of silica deposits and concretions, as well as the genesis of the known occurrence of carbonates. In order to fill these gaps and/or contribute to a better understanding of the depositional processes in the Pedra de Fogo Formation. This study made facies and stratigraphic analysis, and petrography, complemented by cathodoluminescence image, XRD and SEM-EDS analysis of the permian deposits exposed in the east and southeast portions of the Parnaíba Basin. The main sedimentary facies were grouped into facies associations representative of braided fluvial-aeolian systems from the top Piauí Formation (Carboniferous). This deposits are overlain by lacustrine-sabkha system, wave-dominated nearshore-lacustrine and ephemeral streamsdeposits of the Permian Pedra de Fogo Formation. In general, this unit was deposited in an arid, endorheic lacustrine system, often affected by storm regimes and fed by unconfined flows. Although the arid climate was predominant, this system keeps seasonally, relatively high levels of moisture sufficient to maintain and proliferate its thriving taphoflora, formed mainly by Ferns and Gymnosperms tree. This flora colonized the lakeshore, both in relatively wet and dry periods, as a way to compensate for the low humidity in macroenvironmental. Cyclic variations between the records of organosedimentary structures (microbial mats and stratiform stromatolites) and gymnosperm stem in life position were interpreted as the recurrent migration of the lacustrine shoreline, in response to the expansion and contraction phases of these lakes, triggered by climatic seasonality in the southwestern portion of Pangea. Probably, the flora of the Pedra de Fogo Formation was an important catalyst for the expressive silicification that characterizes this predominantly syndepositional / eodiagenetic unit. This silicification is formed largely by microquartz, under conditions of supersaturation in silica, high enough to preserve the delicate cyanobacteria filaments, as well as pinnules ferns and gymnosperm stems in life position. The occlusion of fractures and dissolution voids (secondary pores), by mosaic megaquartz mosaic, chalcedony spherulites and two generations of chalcedonic overlays, in addition to large crystals (mm) in coarse mosaic calcspar are indicative of polycyclic silicification and circulation of carbonate fluids to mesogenetic zones. The presence of gridwork microtexture indicates that the genesis of silicification is similar to the Magadi chert-type (Rift Valley of Kenya), but from distinct sources, given the absence of volcanic sources associated with Pedra de Fogo deposits.