Navegando por Assunto "Bacia do Amazonas"

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Análise do regime hidrológico e da disponibilidade hídrica da Bacia do Rio Amazonas
(Universidade Federal do Pará, 2017-05-25) AGUIAR, Rogério de Souza; ROCHA, Edson José Paulino da; http://lattes.cnpq.br/2313369423727020
The Amazon lives year after year the dynamics of Floods and lowing in its rivers. However, significant variability of river discharges in the face of historical series of climate data has become more persistent over the years. This study aims to analyze the influence of the temporal variability in the basin scale on the Amazon river regime, based on the flows observed in the hydrological station of the Agência Nacional de Águas - ANA, located in Óbidos, State of Pará, in a historical series of January / 1970 to December / 2013. Besides the time, the study analyzed the intensity of oceanic mechanisms on the Brazilian Amazon basin in each year of the series. As expected, time influenced the annual interannual flow rate of 98.723 m3/s for the 44 years of the analyzed series. However, the average flow rate of the Amazon River was around 134.000 m3/s, with a peak flow rate of 105.000 m3/s (as occurred in November) in the hydrological regime of effluent up to an order of 239.000 m3/s (as in June) in the flood regime. It was also identified that El Niño and La Niña phenomena modulated extreme climatic events causing negative and positive SST anomalies differentiated over the Amazon basin, between 1970 and 2013, with a significant relation in the effluent and flood flows. The interannual analysis showed that the years of low registered flows, had the characteristic of persistence of occurrence in relation to the registered high flows. At the end of the analyzed period, from 1989, there was a seasonal increase in relation to the average amplitude of the flow of 87.727 m3/s due to the strong minimum levels recorded. When analyzing the normalized flow, it was observed the persistence of low flow in the current year of the El Niño phenomenon and also of the following year. After verifying this below-average persistence of flow in the series studied, the research sought to investigate the storage and availability factors of the Amazon River. In determining the water availability of the Amazon River, the Percentis method (specifically the quantum order Q95%) was used. The analyzes of the available flows obtained by the 95% quantile show that the years of the El Niño phenomenon did not reflect the decrease in the flow of the Amazon River in all years of the series, since there were years of occurrence that did not present critical indices of water availability. It was concluded that the flow behavior in the Amazon basin was influenced by positive and negative SST anomalies modulated by the intensity of El Niño and La Niña, and there was not sufficient water availability for the maintenance of the ecosystems of the Amazon basin. Thus the study showed that naturally the annual flows of the Amazon River do not reach, in their totality, the minimum value determined for the historical series by the law. In addition to that the hydrological variabilities in the Amazon are not caused only by the phenomena of El Niño or La Niña.
Acesso aberto (Open Access)
Análise faciológica da Formação Alter do Chão (Cretáceo, Bacia do Amazonas), próximo à cidade de Óbidos, Pará, Brasil
(2012-03) MENDES, Anderson Conceição; TRUCKENBRODT, Werner Hermann Walter; NOGUEIRA, Afonso César Rodrigues
Cretaceous deposits of the Alter do Chão Formation, exposed on the banks of the Amazon river, near the town of Óbidos - PA, record a succession of sandstones, conglomerates and mudstones. Seven lithofacies have been recognized which comprise massive conglomerate (Cm), trough cross-bedded sandstone (St), planar cross-bedded sandstone (Sp), climbing cross-laminated sandstone (Sl), massive mudstone (Mm), bioturbated mudstone (Mb) and deformed mudstone (Md). These facies are organized in fining-upward cycles, 1 to 6m thick, and have been grouped into two associations: channel fill and overbank deposits belonging to a fluvial meandering system. The channel-fill deposits include lenticular gravel bars composed of facies Cm and St, sandy bedforms with facies St, Sp and Sl, and lateral accretion bar, consisted of facies St, Sp and Mm, but with distinct migration with regard to that of the sandy bed forms. While paleocurrent measurements from facies St and Sp of sandy bedforms indicate a preferred orientation of paleoflow to SW and a subordinate flow to S, the lateral accretion bar migrates to E/ESE. The following overbank elements have been recognized based on their geometric relationships: muddy floodplain deposits including abandoned channel plug, crevasse splay channel filled with facies St and Sp and natural levee deposits composed of facies St, Sl and Mm. While the muddy channel plug overlies sandstones, the crevasse channel fill is in contact with mudstones of the floodplain and also cuts through fine-grained sandstones and mudstones interpreted as natural levee deposits. Adjacent muddy lenses in the same stratigraphic level on sandstone but with smaller width than that of the abandoned channel are attributed to swales, filled during floods, capping lateral accretion bar.
Acesso aberto (Open Access)
Depósitos costeiros e microbialitos da Formação Itaituba, o Pensilvaniano da borda sul da Bacia do Amazonas, região de Placas, Pará.
(Universidade Federal do Pará, 2019-12-29) OLIVEIRA, Fernando Andrade de; ROMERO, Guilherme Rafaelli; SILVA JUNIOR, José Bandeira Cavalcante da; http://lattes.cnpq.br/8615194741719443
The Itaituba Formation in the Amazon Basin represents a Bhaskiriana-Moscowian carbonate succession, composed of fossiliferous limestone, fine dolomite, fine to coarsegrained sandstone, gray shales and evaporites. Outcrop-based facies and stratigraphic analysis combined with microfacies study allowed the paleoenvironmental reconstitution of the Itaituba Formation, on the southern border of the Amazon Basin, Southwestern of Pará State. The 14mthick carbonate succession with occurrence of microbialites, consists of 9 facies and microfacies, such as: a) laminated shale (F1); b) laminated sandstone (Al); c) laminated siltstone (Sl); d) massive sandstone (Mm); e) mudstone with desiccation cracks (Mg); f) wackestone bioclastic (Wb); g) packstone bioclastic (Pb), h) oncolitic floatstone (Fo) and i) boundstone. These facies are grouped into two facies association (AF): AF1, lagoon / tidal flat deposits, consisting of facies Fl, Al, Sl, Mm, Mg, Wb, related to the flat and laterally continuous buildings with predominance of facies F1, interlayed by centimeter layers of facies Wb and Pb, organized in a fining upward cycle and; and AF2, shoal / barrier island, constituted by Pb facies and Fo and Bd facies, with Pb displayed in continuous flat and lateral bodies and Fo and Bd in lensshaped bioherms. Fo facies are the oncolytic microbilites and associated with microstromatolites, described as M1 and M2a morphotypes, and Bd facies, include columnar stromatolitic forms, described as M2b and M2c morphotypes. The depositional model of the Itaituba Formation in the Placas-PA region consists of a coastal system with lagoon, shoals / barrier island and tidal flat. Microbialites developed in the coastal region in the Amazon Basin during the Bashkirian-Moscovian transition, representing a transition to more restrictive environmental conditions in relation to fauna and flora, and more conducive to the proliferation of cyanobacteria, with probably increased alkalinity in water. These cyanobacteria evidences are record, for the first time, in Carboniferous rocks of the Amazon Basin improved the knowledge related to the carbonate fabric dispersion during the implantation of the Itaituba epicontinental sea in the Western Gondwana.
Acesso aberto (Open Access)
Efeitos hidrotermais em rochas carbonáticas-siliciclásticas da Formação Itaituba, Pensilvaniano da Bacia do Amazonas, região de Uruará (PA)
(Universidade Federal do Pará, 2020-10-26) SOUZA, Isabele Barros; SOARES, Joelson Lima; http://lattes.cnpq.br/1345968080357131
Carbonate and siliciclastic rocks from the Neocarboniferous period are widely recorded in the western and central-western portions in the Uruará region, State of Pará, on the southern edge of the Amazon Basin. These deposits are represented by the Itaituba Formation, from which a 35 m drill was described and five carbonate microfacies (calcimudstone, dolomudstone, bioclastic wackestone, bioclastic packstone and bioclastic grainstone rich in terrigenous) and eigth siliciclastic facies (massive claystone, black shale, siltstone with truncated crosslamination, siltstone with low-angle cross-lamination, siltstone with parallel laminate, sandstone with truncated cross-laminate, sandstone with parallel laminate and massive sandstone) were describe. From petrographic analysis, cathodoluminescence, X-ray diffraction, scanning electron microscopy and dispersive energy spectroscopy, it was possible to identify the main hydrothermal and diagenetic processes that affected these rocks. In the carbonate rocks, micritization, dissolution, calcitization, mechanical and chemical compaction and cementation were observed. In sandstones, quartz overgrowth, carbonate cementation and chemical compaction occur. During the Triassic-Jurassic period, great volcanism event occurred in the central portion of the West Gondwana supercontinent, known as the Central Atlantic Magmatic Province (CAMP), with the placement of dikes and basalt sills represented in the Amazon Basin by the Penatecaua Magmatism. The percolation of hydrothermal fluids in the late phase of this magmatism, promoted several changes in the mineralogy and textures of these rocks, among them hydraulic fracturing, formation of vugular porosity, precipitation of mineral assemblages typical of hydrothermalism such as - saddle dolomite, calcite, apatite, pyrite, chalcopyrite, galena, sphalerite, iron and titanium oxides, chlorites, talc, garnet, fluorcarbonate enriched in REE, saponite and corrensite - in the venules, and silicification of the matrix and carbonate grains. Organic geochemistry analysis in the samples of carbonate and shale, exhibit extremely low total organic carbon values, with low maturity, generating type IV kerogen, probably originated from oxidized organic matter. Thus, the present work intends to expand the study of rocks that occur in subsurface in the Uruará region, enabling the understanding of depositional and diagenetic processes active in their formation and its alteration due to the hydrothermal effect.
Acesso aberto (Open Access)
Effect of seasonal flooding cycle on litterfall production in alluvial rainforest on the middle Xingu River (Amazon basin, Brazil)
(Universidade Federal do Pará, 2015-08) CAMARGO-ZORRO, Mauricio; GIARRIZZO, Tommaso; JESUS, Allan Jamesson Silva de
The assumption for this study was that litterfall in floodplain environments of the middle Xingu river follows a pattern of seasonal variation. According to this view, litterfall production (total and fractions) was estimated in four alluvial rainforest sites on the middle Xingu River over an annual cycle, and examined the effect of seasonal flooding cycle. The sites included two marginal flooded forests of insular lakes (Ilha Grande and Pimentel) and two flooded forests on the banks of the Xingu itself (Boa Esperança and Arroz Cru). Total litterfall correlated with rainfall and river levels, but whereas the leaf and fruit fractions followed this general pattern, the flower fraction presented an inverse pattern, peaking in the dry season. The litterfall patterns recorded in the present study were consistent with those recorded at other Amazonian sites, and in some other tropical ecosystems.
Acesso aberto (Open Access)
Estratigrafia, análise de fácies e proveniência das unidades litoestratigráficas aflorantes na região de Presidente Figueiredo AM, borda norte da Bacia do Amazonas.
(Universidade Federal do Pará, 2013-11-11) NOGUEIRA NETO, Ignácio de Loiola Alvares; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
Esta dissertação apresenta os resultados de um estudo que envolve análise de fácies e de proveniência dos depósitos siliciclásticos de idades pré-cambriana e fanerozoica que constituem uma faixa continua de afloramentos na borda norte da Bacia do Amazonas. Nesse intervalo de tempo, essa borda da bacia foi caracterizada pela deposição de rochas sedimentares siliciclásticas que foram afetadas por variações climáticas extremas, como por exemplo, a Glaciação Siluriana. A Formação Prosperança (Grupo Purus, Proterozoico) e o Grupo Trombetas (Ordoviciano-Devoniano), representado pelas formações Nhamundá e Manacapuru, são as unidades litoestratigráficas que melhor registraram esses eventos paleoclimáticos na Bacia do Amazonas. A Formação Alter do Chão (Grupo Javari, Cretáceo) cobre as unidades anteriormente citadas. As fácies da Formação Prosperança estão todas relacionadas a ambientes flúvio–deltaicos e são compostas por arenitos, conglomerados e pelitos. Essas fácies foram agrupadas em três associações interpretadas como prodelta/lacustre, frente deltaica e planície braided. Quanto ao Grupo Trombetas, as fácies da Formação Nhamundá estão relacionadas a ambientes costeiros e são compostas por arenitos, pelitos e diamictitos. Essas fácies foram agrupadas de acordo com suas características em três associações e interpretadas como shoreface superior, shoreface inferior e glacial costeiro. As fácies da Formação Manacapuru estão relacionadas a ambientes costeiros e são compostas por intercalações de arenitos, pelitos e folhelhos. Essas fácies foram agrupadas em três associações representativas dos ambientes de fácies litorânea transicional, costa afora e transição shoreface–foreshore. O registro de vida nos depósitos siliciclásticos das formações Nhamundá e Manacapuru é caracterizado pela presença de traços fósseis e raros fósseis. Os traços fósseis são encontrados mais comumente nas fácies arenosas em ambas as formações. Fósseis são encontrados em folhelhos betuminosos e caracterizados por conchas de braquiópodes que sugerem a passagem de um ambiente anóxico para um ambiente com condições de manutenção da vida. Por fim, os depósitos cretáceos da Formação Alter do Chão registram uma sucessão formada por arenitos, conglomerados e pelitos. As litofácies foram agrupadas em duas associações interpretadas como depósitos de preenchimento de canal e como depósitos externos ao canal, depositadas em um sistema fluvial do tipo meandrante com variação de sinuosidade do canal e de carga mista (mixedload). Quanto aos seus constituintes minerais, a Formação Prosperança apresenta abundância de minerais estáveis, elevada maturidade composicional, com índice ZTE médio de 86,6%. Em geral, os minerais possuem forma de prismas longos, arredondados e angulosos. A Formação Nhamundá apresenta abundância de minerais estáveis, elevada maturidade composicional, com índice ZTR de 83%. Os minerais são comumente arredondados a secundariamente angulosos. A Formação Manacapuru apresenta abundância de minerais estáveis, elevada maturidade composicional e índice ZTRE de 86,4%. Os minerais são geralmente arredondados e raramente angulosos. A Formação Alter do Chão apresenta grande abundância de minerais estáveis com índice ZTRE de 96,5%. Os minerais são geralmente angulosos e raramente arredondados. Foram também realizadas análises geocronológicas pelo método U-Pb nos grãos de zircão através de LAMC-ICP-MS na Universidade de Brasília. As idades obtidas, com o auxilio dos dados de paleocorrente e assembleia de minerais pesados, indicaram as possíveis áreas-fonte. As principais áreas-fonte dos sedimentos da Formação Prosperança provavelmente são regiões localizadas ao norte/noroeste da borda norte da Bacia do Amazonas, sendo as rochas da Província Maroni-Itacaiúnas (2,2-1,95 Ga) as prováveis fontes e a idade máxima de deposição de 1,5 Ga. Para a Formação Nhamundá, os dados sugerem uma idade máxima de deposição de cerca de 0,5 Ga e indicam idades entre 0,5 e 2,8 Ga, assim como para a Formação Manacapuru. Essas idades de deposição indicam que as principais áreas-fonte são formadas por rochas de idade neoproterozoica e mesoproterozoica. Os zircões de idade neoproterozoica podem ter sido oriundos de retrabalhamento de rochas mais antigas, mas há também a possibilidade de que a fonte dos zircões neoproterozoicos e mesoproterozoicos ser a Laurásia ou até mesmo serem oriundos dos cinturões brasiliano/pan-africanos do oeste africano. Os terrenos de idade mesoproterozoica, expostos a sudoeste do Cráton Amazônico e reunidos nas províncias geocronológicas Sunsás e Rondoniana-San Ignácio, podem ter sido a fonte dos zircões neoproterozoicos. Os dados sugerem como áreas-fonte para a Formação Alter do Chão, as regiões localizadas a norte/nordeste da borda norte da Bacia do Amazonas, sendo a Província Maroni-Itacaiúnas (2,2-1,95 Ga), considerada como a principal fonte potencial para os arenitos dessa formação. Alternativamente, existe a possibilidade desses zircões provirem do retrabalhamento de formações mais antigas como, por exemplo, a Formação Prosperança.
Acesso aberto (Open Access)
Estudos hidrogeoquímicos e geofísicos na região da Braquidobra de Monte Alegre-PA
(Universidade Federal do Pará, 2005-04-11) LOPES, Elem Cristina dos Santos; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Monte Alegre brachyanticline is located in the central-western Pará and is one of the most striking structures of the Paleozoic Amazon sedimentary basin. The dome outcropping surface is elliptical with axes of 30 and 20 km trending NESW and NW-SE, respectively. At the present erosion level, rocks of the Ererê, Barreirinha, Curiri, Oriximiná, Faro, Monte Alegre, Itaituba and Alter do Chão formations, as well as the Penatecaua diabase are exposed. Thermal springs with temperatures from 29 to 37ºC issue out of the Ererê Formation. The present study focuses on the physico-chemical characterization of surface and groundwater that occur within the dome and on the interaction with their mineral environment. In addition, the thermal waters are also characterized isotopically and their subsurface temperatures estimated with basis on the silica and Na-Ca-K geothermometers. Gravimetric and resistivity methods were applied aiming at detecting potential sources that could account for the heating of the thermal waters. The Piper diagrams show a wide chemical variation for both the surface and groundwater which spread over the bicarbonate, calc-sulfate and sodic-chloride fields. The thermal waters are chemically more homogeneous and fall on the bicarbonate and sodic-chloride fields. This variability reflects the composition of the rocks through which the waters migrate, whose components result mainly from hydrolysis and redox reactions involving pyrite and sulfate minerals. Most water samples are in equilibrium with kaolinite as deduced from activity diagrams constructed at 25ºC, 1 atm and at quartz saturation. The thermal water samples cluster near the boundary kaolinite-sericite, whereas a few samples of surface waters that drain the Itaituba Formation plot near the line separating the kaolinite and leonhardite stability fields. The samples of the Menino Deus thermal spring collected in October/2002 reached equilibrium with sericite but failed to equilibrate with paragonite despite their Na/K ratios being higher than unity. Furthermore, most water samples are saturated with quartz. During the dry season, sample FT-27 and those from the Menino Deus thermal spring presented higher silica contents causing them to equilibrate with pyrophyllite. Isotopic data show that the Monte Alegre thermal waters have a meteoric origin with δ18O and δD values coincident with the global meteoric water line, although slightly enriched in deuterium. The excess of deuterium varies seasonally, being recorded values of 11,8-14,8 ‰ in the dry season and 4-9,5 ‰ in the wet season. Sub-surface temperatures for the thermal waters estimated with the silica geothermometer yield mean values of 71°C (wet season) and 83°C (dry season). Average water circulation depths ranging from 1560 m (wet season) to 1900 m (dry season) were calculated assuming a geothermal gradient of 30°/km and using the estimated sub-surface temperatures. After infiltrating into the ground, these meteoric waters are heated and rise back to the surface through a channel way network, particularly NE-SW and N-S-trending faults which truncate the brachyanticline flanks. Gravimetric surveys allowed to infer the presence of a lacolith-like body at a depth of about 1.3 km. This body is thicker close to the central portion of the brachyanticline. Contact relationships between sedimentary units and the laccolith could also be defined. Likewise, fractures and faults could be mapped at depth whose traces are visible on SRTM radar images. Resistivity profiles did not identify any thermal anomaly in the area, but they confirm the lithological diversity of the geological units as well as faults that may have served as conduits to the fluids.
Acesso aberto (Open Access)
Fáceis litorâneas glaciais da formação Nhamundá (Siluriano inferior), na região de Presidente Figueiredo, AM, Bacia do Amazonas
(Universidade Federal do Pará, 1998-11-29) SOARES, Emílio Alberto Amaral; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
Acesso aberto (Open Access)
Fáceis sedimentares e evolução diagenética dos arenitos da Formação Faro (Eo-Carbonífero) da Bacia do Amazonas
(Universidade Federal do Pará, 1993-01-11) AMADOU, Ba Ibrahim; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
Acesso aberto (Open Access)
Fácies e proveniência de depósitos siliciclásticos cretáceos e neógenos da bacia do Amazonas: implicações para a história evolutiva do proto-amazonas.
(Universidade Federal do Pará, 2015-06-23) MENDES, Anderson Conceição; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Siliciclastic deposits exposed near the channel of the modern Amazon River and overlaid by Neogene units have been attributed to the Cretaceous, formally named as Alter do Chão Formation. Integrated studies based on sedimentology, stratigraphy, trace fossils, petrography of sandstones and heavy minerals, as well as, U-Pb dating of zircon grains allowed reconstitute the depositional paleoenvironment and infer the probable source areas of these Cretaceous deposits in the Amazon Basin. Despite its wide geographical distribution throughout the Amazonas Basin, stratigraphic and sedimentological studies of Alter do Chão Formation were located in areas where there was not allowed a better paleoenvironmental and paleogeographic reconstruction. These deposits record the evolution of a large-scale fluvial system or “Big River”, with meandering pattern in the central-eastern Amazonas Basin, while in the western portion of the basin, predominate an anastomosed configuration with large overbank zones colonized by animals and plants. The recorded of this biologic activity are traces fossil of Taenidium, Planolites, Diplocraterion, Beaconites, Thalassinoides, adhesive meniscate burrows and excavations of insects and vertebrates, as well as, root marks. The fluvial succession consists of kaolinitized and locally silicified conglomerates, sandstones and pelites, grouped in eight architectural elements, Gravel Bar, Sand edforms, Lateral Accretion Bar, Levee, Channels, Crevasse Splay Lobes, Abandoned Channel Fills and Overbank Fines. The expressive terrigenous supply probably came of uplifted areas related to Gurupá Arch, eastern limit of the basin, and zircon grains ages range from 1.8 to 2.9 Ga, indicate the Maroni-Itacaiúnas and Central Amazon provinces as main cratonic sources of sediments. The massive sediment input reflected in the hundreds of meters thick of cretaceous deposits, extense for thousands of kilometres, suggests expressives drainages from the craton, feeding an approximate E-W-oriented "Big River”. Probably, the Late Cretaceous paleogegraphy will be similar to current configuration of the modern Amazon River, but with opposite migration, directioned to the Pacific Ocean. The unconformity between Alter do Chão Formation and Neogene deposits attests long period of subarial exposure in the Amazon Basin during the Paleogene, coincident with the development of lateritic-bauxitic profiles. Paleocurrent measures confirms the flow reversion to the east, in direction of Atlantic, during the Neogene. Additionally, the spectrum of zircon grains ages, ranging from 0.5 to 2.7 Ga, comparable to obtained for Quaternary deposits, indicates cratonic and mainly Andean sources, recording the beginning of the Amazon River. The results obtained here allowed, by first time, to propose a transcontinental drainage model for the Late Cretaceous, as weel as, to record the initial sedimentation of proto-Amazon river during the Neogene.
Acesso aberto (Open Access)
Litofácies e evolução diagenética dos arenitos da formação Monte Alegre na região do rio Tapajós, Bacia do Amazonas
(Universidade Federal do Pará, 1989-11-23) TORRES, Admilson Moreira; TRUCKENBRODT, Werner Hermann Walter
Acesso aberto (Open Access)
Litofácies e minerais pesados da Formação Alter do Chão (cretáceo), região de Óbidos-PA, parte central da bacia do Amazonas
(Universidade Federal do Pará, 2010-05-05) MENDES, Anderson Conceição; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
Cretaceous deposits exposed in riverbanks of the Amazon River, near the town of Óbidos (state of Pará), record a succession of sandstones, conglomerates and mudstones. Seven lithofacies types including massive conglomerate (Cm), trough cross-bedded sandstone (St), planar cross-bedded sandstone (Sp), cross-laminated sandstone (Sl), massive mudstone (Mm), bioturbated mudstone (Mb) and deformed mudstone (Md) have been recognized that are organized in fining-upward cycles each 1 to 6 m thick. These lithofacies have been arranged in two associations: 1-Channel fill, composed of gravel bars, sandy bedforms and lateral-accretion deposits and, 2- Overbank deposits composed of levee, crevasse splay and floodplain sediments. Cross-bed measurements in the facies St and Sp indicate a general flow system to SW. The facies analysis evidenced that the Alter do Chão formation was deposited in a fluvial meandering system, with sinuosity and mixed-load variation. Petrographic studies classified the sandstones as quartz-sandstones with kaolinitic matrix, the latter being generated by weathering. The quartz-sandstone generally consists of moderately sorted, fine to coarse, angular to subangular, and secondly, subrounded grains. The heavy mineral assemblage has high compositional maturity, with average ZTR index of 85%, represented by zircon, tourmaline, kyanite, rutile, staurolite, monazite and occasionally andalusite and spinel. Conchoidal fractures and impact marks are common to zircon and tourmaline while dissolution features occur in kyanite and staurolite. The quartz grains as well as the heavy mineral originated from igneous and metamorphic rocks. Additionally, embayments and vacuoles in quartz grains suggest volcanic origin for, at least one part of this mineral. The informations from heavy minerals, combined with paleocurrent data and U-Pb ages (Mappes, 2009), suggest as source areas for the Alter do Chão formation near Óbidos, regions located north/northeast of the study area. The Maroni-Itacaiúnas Province characterized by metavolcanic and metasedimentary rocks, as well as gneisses and granites may be considered as the main potential source for the sandstones of the Alter do Chão formation.
Acesso aberto (Open Access)
O mar epicontinental Itaituba na região central da Bacia do Amazonas: paleoambiente e correlação com os eventos paleoclimáticos e paleoceanográficos do carbonífero
(Universidade Federal do Pará, 2019-03-14) SILVA, Pedro Augusto Santos da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Carboniferous paleogeography of the West Gondwana was dominated by epicontinental seas connected with the Panthalassa Ocean to the west. 50m-thick Pennsylvanian mixed siliciclastic-carbonate transgressive succession of the Amazonas Basin, Northern Brazil, were studied in outcrops and cores using facies and stratigraphic analysis in combination with O- and C-isotopic stratigraphy. Thirty-four facies, representative of coastal to shelf depositional systems grouped in three facies associations (FA): FA1) coastal desertic deposits, consisting of fine to medium-grained sandstone, mudstone and fine-grained dolostone that corresponds to a complex association of aeolian dunes, sand sheets, interdunes, fluvial channels and lagoon deposits bioturbated by Palaeophycus, Lockeia, Thalassinoides and Rosselia trace fossils; FA2) mixed tidal flat setting, constituted by fine to medium-grained sandstone, mudstone, shale, siltstone, lime mudstone and fine dolostone interpreted as supratidal, tidal channel, tidal delta and lagoon deposits with some brachiopod and echinoderm body fossils; and FA3) carbonate shelf deposits, consisting of lime mudstone, wackestone, packstone and grainstone with allochems (ooids and peloids), terrigenous grains and abundant and diversified open shallow marine benthic organisms, including, fish remains, foraminifers, brachiopods, echinoderms, gastropods, bryozoans, trilobites, corals, ostracodes, and conodonts, interpreted as bioclastic bars and carbonate shelf deposits. The conodonts species Neognathodus symmetricus, Streptognathodus sp. and Ellisonia sp. in the FA3 indicate the Baskirian-Moscovian age. The dolomitization affected the limestone and sandstone of AF1 and AF2 replacing the micritic matrix and occur as saddle dolomite indicating mixed of meteoric and marine waters and late burial. The neomorphism of opaque micritic matrix and bivalve shells are indicated by the growing of xenotopic mosaic of calcite crystals. In contrast, the secondary calcite cement is equant, fiber, bladed and espatic. Micritization is found in the bioclast shells exhibiting micritic coatings. The autigenesis of quartz and biogenic pyrite is commonly found in FA2 and FA3. The mechanic and chemical compaction in limestone caused the porosity reduction, cementation, fractures and development of dissolution seams and stylolite. The sandstones were cemented by quartz, calcite and iron hydroxides/oxides and show concave-convex and sutured contacts between quartz grains. The predominance of eodiagenetic and subordinate mesodiagenetic features in the Monte Alegre-Itaituba succession indicated less modified framework by the diagenesis corroborating the pristine signature of δ13C values ranging from ~ -2 to ~+5.28‰. This enriched trend upsection coadunate with high organic productivity triggered by massive flourishment of euphotic-controlled benthic organisms mainly in the FA3. Five types of shallowing upward asymmetric cycles characterize the Monte Alegre-Itaituba succession. Peritidal cycles in coastal desertic (Cycle I) were formed by alternance of dolostone and sandstone with δ13C values ranging from -1.5 to +0.3‰. Cycles II consist in interbedded of sandstone-mudstone and sandstone-mudstone-floatstone rhythmites and the Cycle III constitute dolostone interbedded with sandstone. These cycles II and III were interpreted as tidal flat and lagoon deposits with δ13C values ranging from +3,98%₀ to +4, 62%₀. The Cycle IV is a rhythmite formed by wackestones/mudstones couplets while the Cycle V consists of alternance of grainstones, wackestones and lime mudstone (ABC cyclicity) passing upsection for cycles composed by wackestones and lime mudstone (AB cyclicity). The cycles IV and V are shelf deposits with δ13C values ranging from +3,65%₀ a +5,28%₀. The stacking of 53 cycles with average thickness of 1,1 m, combined with Fisher plot diagram, indicated an aggradational to retrogradational stacking pattern inserted in the lowstand to early transgressive system tract (Cycles I-III) and late transgressive system tract (Cycles IV and V). The succession was deposited in ~13 Ma and individual cycles accumulated in an approximately 0.25 my typical of fourth order cycles related to high-frequency fluctuations of relative sea level. These data were correlated to the global δ13C and sea-level curves that positioned the Monte Alegre-Itaituba succession in the Late Serpukhovian to Early Moscovian age. The influence of Late Misssipian glaciation was negligible in these deposits but the post-glacial transgression combined with slow subsidence of the Amazonas basin caused the generation of allogenic cycles I, IV and V. The cycles II and III were formed by autochthonous processes during a period of equilibrium between supply and glacioeustasy. The Monte Alegre-Itaituba succession is the record of a large Amazonia epicontinental sea that was directly connected with the Panthalassa Ocean during Pennsylvanian.
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Modelagem sísmica via métodos das diferenças finitas: caso da bacia do Amazonas
(Instituto Nacional de Pesquisas da Amazônia, 2009-03) FERNANDES, Lindemberg Lima; CRUZ, João Carlos Ribeiro; BLANCO, Claudio José Cavalcante; BARP, Ana Rosa Baganha
This paper discusses the seismic modeling in medium with strong discontinuities in its physical properties. The approach takes in consideration the existences diffractions and multiple reflections in the analyzed medium, which, at that case, is the Amazon Basin. The stability and boundary conditions of modeling were analyzed by the method of the finite differences. Sedimentary rocks deposited since the Ordovician to the present, reaching depth up to 5 Km. The bodies of diabasic between the paleozoic sediments are layers reaching thickness of hundred meters, which add to 90.000 km3, form the geology of the Amazon Basin. The occurrence of these structures is responsible for multiple reflections during the propagation of the seismic waves, which become impossible a better imaging of horizons located bellow the layers. The representation this geological situation was performed an (synthetic) acoustic velocity model. The numerical discretization scheme is based in a fourth order approximation of the acoustic wave equation in space and time The understanding of the wave propagation heterogeneous medium has improved for the application of the finite difference method. The method achieves a good resolution in the interpretation of seismic reflection events. The numerical results discusses in this paper have allowed to observed the influence of the multiple reflection in a high velocity layer. It increase a loss of energy and difficult the interpretation of the target. For this reason the integration of surface data with the well data is recommended, with the objective to get one better image of the targets below of the diabasic layer.
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Paleoambiente e diagênese da formação Itaituba, carbonífero da bacia do Amazonas, com base em testemunho de sondagem, região de Uruará, Pará
(Universidade Federal do Pará, 2014-08-04) SILVA, Pedro Augusto Santos da; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Carboniferous Itaituba Formation represents expressive retrograding carbonate sedimentation included in the sedimentary evolution of the Tapajós Group of the Amazonas basin. These carbonate consist of fossiliferous limestones, fine grained dolostones, fine to coarse grained sandstones and subordinate reddish siltstones, black shales and evaporites. Facies and microfacies analysis of drill cores from the Uruará region, State of Pará , allowed to individualize nineteen facies grouped into five facies associations : tidal plain ( FA1 ) , tidal channel ( FA2 ), lagoon ( FA3 ), bioclastic bar ( FA4 ) and outer shelf ( FA5 ). FA1 is composed of fine grained sandstone with rip-up clasts and mud cracks , marl with quartz and feldspar grains, laminated dolomudstone with fine terrigenous grains and silicified dolostone with intercalation of mudstone and disseminated quartz grains dolomitized and locally with microcrystalline quartz. FA2 consists of medium to coarse grained sandstone with trough cross-bedding and mud drapes on foresets, very fine to fine grained sandstone with wavy bedding, laminated siltstone, synsedimentary faults and convolute lamination. FA3 consists of massive red siltstone, mudstone with fossils, brachiopods and floatstone with disseminated pyrite and massive mudstone with frequent quartz grains. AF4 and AF5 exhibit abundant bioclasts represented by spines and fragments of echinoderms, shells, spines and fragments of brachiopods, ostracods, foraminifera, red algae and bilvave shells. AF4 consists of fossiliferous oolitic grainstone and grainstone with terrigenous grains, mainly monocrystalline quartz grains and the AF5 consists of fossiliferous wackestone, wackestone with terrigenous grains and massive mudstone with monocrystalline quartz grains. Subarkoses (AF1), arkoses (AF2) and lithic arkoses (AF2) predominate in the Itaituba Formation and are composed by of polycrystalline and monocrystalline quartz grains, K-feldspar, plagioclase, pyrite, detrital muscovite, mudstone, metamorphic and chert fragments and rare bioclasts. The cement is of nonferrous calcite, iron oxides/hydroxides, silica overgrowth and intergranular, moldic and sometimes elongated porosities reaching up to 11 % of the rock. The diagenetic processes in sandstone are physical compaction, quartz overgrowth, non-ferrous calcite cementation, chemical compaction, grain replacement, pyrite autigenesis, formation of iron oxides/hydroxides and alteration of plagioclase. The diagenetic processes in carbonates are: micritization, neomorphism, dolomitization, fracturing, chemical compaction, calcite cementation, secondary dissolution and mineral autigenesis. The Itaituba succession is interpreted as a lagoon/tidal flat system linked to the marine carbonate platform. Tidal flats developed on the margins of the lagoons were periodically supplied by fine (silt) terrigenous influxes that inhibited the carbonate precipitation. Bioclastic bars were cut by tidal channels (inlet) connected the lagoon with the shallow platform rich in benthic organisms.
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Proveniência sedimentar dos depósitos cretáceos da Formação Alter do Chão, Bacia do Amazonas, região de Ponta do Curuá, Prainha-PA
(Universidade Federal do Pará, 2020-08-03) SANTOS, Raiza Renne Leitão dos; SOARES, Joelson Lima; http://lattes.cnpq.br/1345968080357131
Deposits of the Alter do Chão Formation are found along the right bank of the Amazon River and are well registered in the locality of Ponta do Curuá, municipality of Prainha, the western region of the State of Pará. The outcrops are characterized by thick layers of fine to coarse sandstones interbedded with siltstones and claystones, and subordinate subordinate conglomerates. The facies analysis carried out in these outcrops allowed the individualization of 8 sedimentary facies, grouped in three facies associations (AF), configuring a high sinuosity and mixed load fluvial meandering depositional system. AF1 comprises facies with a thicker granulometry of the studied succession and was interpreted as the filling of the fluvial channel, characterized by massive to stratified conglomerates, massive sandstones, sandstones with trough and tabular cross-bedding, sandstones with convoluted laminations and climbing crosslaminations. AF2 was interpreted as abandoned channel filling deposits and corresponds to thick layers of massive to laminated mudstones that are sporadically associated with thin layers and very thin sandstone lenses forming wavy-linsen bedding. Well-preserved leaves and trunks are present in this association. AF3 corresponds to the flood deposits, composed of massive to laminate mudstones, massive sandstones, and sandstones with trough, tabular and sigmoidal cross-stratifications. The study of heavy minerals in the sandstones of this formation showed an assembly with a predominance of ultra-stable minerals such as zircon, tourmaline, rutile and anatase, and less frequent minerals such as kyanite, staurolite, sillimanite, andalusite, and garnet. Metasedimentary sources are suggested due to the presence of aluminum-rich metamorphic minerals. Whereas, rutile and tourmaline are present in both igneous and metamorphic rocks, being more common in the latter. Well-rounded minerals suggest an origin from sedimentary deposits, in the same way that subhedral and euhedral minerals suggest first cycle sediments. The high stability of this assembly is attested by the high compositional maturity exhibited by these sandstones, with values of the ZTR index ranging from 69% to 99%. These high values indicate that chemically unstable minerals have been eliminated over geological time, probably due to the action of interstitial fluids that circulate in the porous during weathering and diagenetic processes. However, the analyzed mineral assembly is more compatible with conditions of exposure to intense chemical weathering. The effects of intrastate dissolution in the area is directly proportional to the increase in the ZTR index, being attested by the presence of corrosion textures on the surface of the minerals that were analyzed from SEM images. Thus, the mineralogical assembly would reflect the effects of the intense chemical weathering, under a humid tropical climate, imposed on the deposits of the Alter do Chão Formation that would be associated with the lateritization event responsible for the genesis of bauxite deposits during the Paleogene. Recently, the luminescence (LC) characteristics of quartz grains have been used as provenance indicators, mainly in rocks affected by weathering or rich in quartz. In this work, luminescence signals were acquired by polychromatic cathodoluminescence to establish the relationship between luminescent signals and the genesis of this mineral. The studied grains present red, blue, violet and brown colors, with different intensities: the reddish-brown tones, are generally attributed to metamorphic rocks; dark blue luminescence is a characteristic observed in quartz of plutonic origin; grains with intense LC such as blue, red and violet of high bright, are volcanic quartz. Geochronological analyzes carried out on detrital zircons using the U-Pb method allowed to determine that the main sources for the Alter do Chão Formation are Paleoproterozoic ages, subdivided into two groups: (1) 1771 to 1906 Ma; and (2) 1957 to 2037 Ma, in addition to a small Archean contribution (Neoand Meso-Archean) aged between 2529 and 2977 Ma. The data from the first group, 1771 and 1906 Ma, were correlated with the age of provenance of metasedimentary rocks from the Araguaia Belt, which occurs on the eastern edge of the Amazon Craton. Ages around 1957 and 2037 Ma are consistent with rocks from the Maroni-Itacaiúnas Province, located on the eastern edge of the basin. It is possible to mention rocks associated with late to post-collisional orogenic magmatism such as the Igarapé Careta Intrusive Suites (2065 ± 33 Ma), Parintins (2030 ± 3 Ma) and paleoproterozoic indistinguishable granitoids occurring in the Amapá Block and Carecuru Domain, in addition to rocks related to post-orogenic magmatism such as the Granodiorito Sant'Ana (1986 ± 5 Ma) of the Bacajá Domain. Archean contributions can be associated with rocks from the Central Amazon Province or even to Archean nuclei distributed in the region.
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Termocronologia por traços de fissão em apatita da Borba Sul da Bacia do Amazonas, na região de Itaituba (PA)
(Universidade Federal do Pará, 2010-11-09) PINA, Aline Carla Miranda de; LELARGE, Maria Lidia Vignol; http://lattes.cnpq.br/3165548495925769; MOURA, Candido Augusto Veloso; http://lattes.cnpq.br/1035254156384979
The region of Itaituba (PA) located at the South portion of the sedimentary basin of the Amazon can be defined as a border zone between this basin and the Amazonian Craton. In this region outcrop sedimentary rocks, belonging to Pitinga, Maecuru, Ererê, Barreirinha, Curiri, Monte Alegre and Itaituba Formations, representatives of sineclise phase sedimentary basin of the Amazon; sedimentary rocks the stage rift gathered in Prosperança Formation; besides igneous rocks of Iriri Group, Parauari Intrusive Suite and Maloquinha Intrusive Suite, which compose the basement of the sedimentary basin. The fission track thermochronology of apatite was used in the investigation of thermotectonic evolution of the sedimentary basin of the Amazon region of Itaituba (PA), mainly from the dating of basement rocks of the basin. The method of fission tracks in apatite is a marker thermochronologic low temperature, recording temperatures of up to 120 º C. When subjected to conditions of temperatures above the traces of apatite fission are cleared, resetting the clock geochronological for this method, and registers, thus, a new event. Thus, this tool was used to investigate the age of the tectonic processes that affected the Amazon Basin, which were also recorded in the rocks of its basement. Given the scarcity of apatite in sedimentary rocks sampled units of the Amazon basin, only a sample of the Monte Alegre Formation sandstone has been dated by fission track method. However, in the basement could be dated 20 samples, representing various rocks including rhyolites, granites and olivine-diabase of Paleoproterozoic, belonging to the three units mentioned above. The sandstone of the Monte Alegre Formation, whose age of the lithostratigraphy and Mesocarbonífero, provided apparent ages in apatite fission track AFT) from 91 Ma. Statistically this sample revealed the existence of two populations of apatite grains: a population with a mean age of 105 Ma and another population with a mean age of 64 Ma, indicating that this sample was subjected to two events thermotectonic. This fact can be confirmed through the thermal modeling also showed that the presence of two events whose ages are 106 Ma and 58 Ma. Samples of the basement were divided into three groups according to ages TFA obtained and the results of mathematical models. In group 1 TFA ages ranged from 163.0 Ma and 258.7 Ma, for group 2 ages were established between 142.1 Ma and 147.4 Ma, while samples of group 3 were between 170.1 Ma and 180.9 Ma is noteworthy that the ages of crystallization of igneous bodies sampled are between 1.8 and 1.9 Ga. The mathematical modeling of samples of groups 1 and 2 record the same epsódios, a first cooling, followed by heating and finally an episode of cooling. This last cooling event occurred about 100 Ma for all samples of these groups, except the sample IT-16 passing through the final event of cooling for 62 Ma. The thermal histories of samples IT-22 and 23 show a period of accelerated cooling compared to previous samples, their thermal histories ending at 39 Ma and 35 Ma, respectively, suggesting the existence of neotectonic events in the region. The events of approximately 100 Ma recorded in the Monte Alegre Formation sandstone and models of the samples of the basement can be related to a compressional tectonics that occurred according to the opening of the eastern equatorial Atlantic and the convergent movement of Andean subduction zone, west of South American plate. In turn the events of Tertiary age (64-58 Ma) marked these rocks may show reflections of a process where dextral transform interacted plates South American, Caribean and Nazca, reactivating old fracture zones. The various ages obtained for samples of the basement (ranging from 142.1 Ma and 258.60 Ma) are markers of major tectonic events, but may be registering the different ages at which these samples passed by the isotherm of 120 ° C, indicating thus the occurrence of a tectonic with different behavior in different areas of this region.
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Transição siluro-devoniana na borda Sul da bacia do Amazonas, entre Uruará- Rurópolis, Oeste do Estado do Pará, Norte do Brasil.
(Universidade Federal do Pará, 2019-08-04) SILVA, Eduardo Francisco da; SILVA JUNIOR, José Bandeira Cavalcante da; http://lattes.cnpq.br/8615194741719443
The Silurian-Devonian transition is characterized by drastic geographical variations in the paleocontinents geographical setting. On the Amazonas Basin South margin, whose register is observed in the contact between Pitinga and Maecuru Formations. These deposits were studied among Rurópolis and Placas regions, in the west of the State of Pará, aiming recognition and association of their sedimentary facies for paleoenvironmental reconstitution and its relation with collisional events of the supercontinent Gondwana. The deposits provenance is also desired. In this study, eight sedimentary facies were identified and grouped into two facies association: a) Shallow platform with tidal and wave influences (AF-1) corresponding to Pitinga Formation and; b) Proximal braided lowland (AF-2) corresponding to Maecuru Formation. The contact between Pitinga and Maecuru Formations is interpreten as regional erosive discordance observed in more than 300 km along all the Amazonas Basin south margin, which is tied up to accretionary stages from the supercontinent Gondwana during the Precordillera and/or glacio-eustatic effects caused by the end of Silurian glaciation. Sandstones from Pitinga Formation were classified as fine- to medium-grained, moderately well-sorted sub-arkoses and quartz-arenites. While the sandstones of Maecuru Formation are medium- to very coarse-grained, moderate- to poorly-sorted arkoses and quartz-arenites. The petrographic analysis of these deposits suggests quartz enrichment due to diagenetic processes that were also effective on the elimination of less stable minerals as indicated by the presence, in great amount, of secondare pores. The quartz-grains imaging by cathodoluminescence (CL) indicated the predominance of quartz-grains from igneous and metamorphic rocks. This technique results together with paleocurrent measurements provided substantial data for deducing that the Maecuru Formation are lithotypes from the Bacajá and Iriri-Xingu Domain. The rock bodies alignment from the source areas corroborate these interpretations. Even with reliable and convincing CL data, the lack of paleocurrent measurements made it unfeasible to accurately interpret the Pitinga Formation provenance.