Navegando por Assunto "Sedimentação e depósitos"

Agora exibindo 1 - 13 de 13

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Ambiente deposicional, composição mineralógica e estudo isotópico Pb-Pb das zonas sulfetadas do Alvo São Martim, Cinturão Araguaia, sul do Pará
(Universidade Federal do Pará, 2004-07-07) LIMA, Aderson David Pires de; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
Acesso aberto (Open Access)
Análise da dinâmica das áreas de manguezal no litoral Norte do Brasil a partir de dados multisensores e hidrossedimentológicos
(Universidade Federal do Pará, 2016-12-16) NASCIMENTO JUNIOR, Wilson da Rocha; SOUZA FILHO, Pedro Walfir Martins e; http://lattes.cnpq.br/3282736820907252
The objective of this research is to analyze the dynamics of the mangrove areas in the north coast of Brazil from images of remote orbital sensors and hydrosedimentological data (flow and suspened sediment concentration). We tried to understand the existence of causality between the expansion or retraction of the mangroves with the suspened solid discharge calculated from the data of flow and suspened sediment concentration. The mangroves were mapped, using the object oriented classification technique, in the years 1975, 1996 and 2008 based on data from microwave sensors (RADAM / GEMS, JERS-1, ALOS / PALSAR). The data of fluviometric stations and sediments of the National Water Agency were used to calculate the solid discharge in suspension in the rivers Araguari, Gurupi, Pindaré, Grajaú and Mearim seeking to relate the addition and erosion in the areas of mangrove with the sedimentary load of the rivers that drain On the coast. The flow variations reflect the precipitation in the sub-basins of the analyzed rivers and presented a strong and moderate correlation with the temperature anomalies on the surface of the Pacific Ocean evidencing a relation of the El Niño and La Niña phenomena with the precipitation regimes in the Amazon. The variations of suspended sediment concentration were not related to the fluviometric variation suggesting that the annual mean oscillations are reflections of other phenomena (coverage and land use). The results show that the drainage areas of the sub-basins most impacted by the anthropic action contribute with a higher sediment load to rivers that have a higher concentration of native forest. Native vegetation contributes to containment of soil erosion and exposed soil and pasture areas are more vulnerable to soil erosion. The Gurupi, Pindaré, Grajaú and Mearim Rivers presented solid suspended load higher than or equal to the Araguari River. Analyzing the mangroves in the estuaries we noticed the addition of mangroves along the estuaries of the Gurupi and Mearim rivers (Baia de São Marcos) and the reduction of mangrove areas in the Araguari estuary. The Amazon coastal zone is subject to natural processes of great magnitude, but atrophic activities influence the natural dynamics of the region by implementing unsustainable economic practices.
Acesso aberto (Open Access)
Aspecto tectôno-sedimentares do fanerozóico do nordeste do estado do Pará e noroeste do Maranhão, Brasil
(Universidade Federal do Pará, 1992-09-16) IGREJA, Hailton Luiz Siqueira da; FARIA JUNIOR, Luis Ercílio do Carmo; http://lattes.cnpq.br/2860327600518536
A synthesis of the tectono-sedimentary evolution of the Phanerozoic at Northeastern Pará and Northwestern Maranhão is discussed with enphasis to the Bragança-Viseu and São Luis basins. This research is based on field observations, gravity (Bouguer Anomalies), magnetic, seismic, and borehole data interpretations. Five sedimentary sequences are defined: 1) Piriá-Camiranga (Cambrian-Ordovician to Silurian), 2) Lower Itapecuru (Lower Cretaceous), 3) Upper Itapecuru (Upper Cretaceous), 4) Pirabas-Barreiras (Oligocene-Mioceneto Pliocene) and 5) Pará (Quaternarg). The regional basement is an igneous-metamorphic assemblage which outcrops in two windows. The sedimentary and structural features of the Piriá-Camiranga sequence are consistent with a tectono-sedimentary model of coastal environment with fluvio-glacial influence related to a tilted blocks system induced by strike-slip motion. This sequence represents an evolutive stage coincident to the Eo-Hercynian paroxysm (Paleozoic) which ended with the closure of the Atlantic I (first geotectonic cycle of the Gondwana). The Lower and Upper Itapecuru, as well as the Pirabas-Barreiras and Pará sequences, are related to the Equatorial Atlantic opening during the Mesozoic and Cenozoic times. They are analysed by severa), authors which reached the interpretations refered to as Models of: Fracture Zones; Anti-clockwise rotation of Africa; Intumescence and fracturing; Clockwise rotation of the South America Nate; and Wrench Tectonics. These models were experimented for the studied area. The time and environments of the sedimentary processes are related to the rift and pos-rift phases of the equatorial coastal basins, but these models were not adequate to explain the structural features. A new model is proposed to explain the origin and development of the basins taking into account a regional NE-SW extension axis and formation of the Bragança-Viseu and São Luís basins with similar polarities. The tectono-sedimentary map for the Phanerozoic of the Northeastern Pará / Northwestern Maranhão enhances the compatibility of the depositional and tectonics systems with two periods of oceanic opening of the Northern Gondwana border.
Acesso aberto (Open Access)
Depósitos lacustres rasos da Formação Pedra de Fogo, Permiano da bacia do Parnaíba, Brasil
(Universidade Federal do Pará, 2015-04-15) ARAÚJO, Raphael Neto; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permian Pedra de Fogo Formation, exposed in the east and west borders of Parnaíba Basin, northern Brazil, represent one of the most important terminal Paleozoic sedimentary record of the Western Gondwana. The main lithotypes of this unit are sandstones, shales, carbonate rocks, evaporites. The unit is famous for its large amounts of chert and presence of well-preserved Permian flora. In the last decades of the 20 th century, previous works interpreted the paleoenvironment of the Pedra de Fogo Formation as transitional fluvial-deltaic deposits, storm influenced-shallow neritic (marine) to coastal sabkha plain, lacustrine and fluvial deposits with contribution of marine-aeolian sediments and shallow to restrict sea or epicontinental type. Facies analysis focused principally on outcrops of the base and upper part of this unit, involving approximately 100 m thick of the siliciclastic succession. Eleven sedimentary facies were recognized and grouped into three facies associations (FA), representative of a shallow lacustrine depositional system associated with mudflat and ephemeral rivers. FA1 is interpreted as mudflat deposits, consisting of laminated claystone/siltstone, sandstones/pelites with mud cracks and sandstones with cross-lamination, massive and megaripple beddings. Silicified nodules and molds like popcorn indicate evaporites deposits. Other common features are silica concretions, silicified teppes and silcretes. FA2 represents deposits of nearshore and consists of fine-grained sandstones with even parallel lamination, climbing ripple cross-lamination, massive and megaripple beddings, as well as, laminated mudstone/siltstone. FA3 refers to wadi/inundite deposits, generally organized in fining upward meter-scale cycles, consisting of conglomerates and medium-grained pebbly sandstones with massive bedding and cross-stratification, and claystone/siltstone with even parallel to wavy lamination. Tabular beds are frequent in FA3 while scour-and-fill geometry is rare. The alternation of pelites and fine to medium-grained sandstones with even parallel to wavy lamination are the main framework of the Pedra de Fogo Formation. Bioturbations, shrinkage cracks and different types of siliceous concretions, as well as, teeth of fish, ostracods, bryozoans and scolecodontes are common in the studied succession. Silicified plant remains, preliminarily classified to the genus Psaronius, are found in situ, concentrated near the upper contact with Motuca Formation, considered here as excellent biostratigraphic markers for the upper Pedra de Fogo Formation. Mudflats deposits occur in the basal Pedra de Fogo succession suggesting arid and hot climates for the early Permian. The midlle Permian was predominated semiarid allowing the proliferation of fauna and flora in humid regions adjacent and into the lake margin. The ephemeral fluvial inflow or wadis carried plant remains and terrigenous to the lake generating inundites. Retreat and expansion phases characterized the Pedra de Fogo lake, induced by extreme climatic changes influencing not only the sedimentation pattern as also the fossilization of the best well-preserved Permian fauna and flora. In the late Permian, the climate again became hot and arid due to the complete aggregation of Pangea supercontinent, favoring the deposition of Motuca red beds and establishment of Sambaíba erg, near in the Permian-Triassic boundary.
Acesso aberto (Open Access)
Detecção de mudança e sedimentação no estuário do Rio Coreaú
(Universidade Federal do Pará, 2014-09-02) RODRIGUES, Suzan Waleska Pequeno; SOUZA FILHO, Pedro Walfir Martins e; http://lattes.cnpq.br/3282736820907252
The use of new techniques to study the evolution and filling incised valleys has provided, over the years, important results was to understand how the coastal evolution of the Brazilian coastal zone. In this context, this thesis aimed to study the evolution of the estuary Coreaú River, located in the state of Ceará, in different time scales, is "Possible" (months, years), "Engineering" (years, decades) and "Geology" (hundreds, centuries, millennio), proposed by Cowell et al (2003), with the goal to assess whether changes /alterations over the years were significant or not in the estuary. As a result, we obtained the first goal, using remote sensing techniques from image sensor TM, ETM+ and OLI of Landsat 5, 7 and 8 and sensor LISS-3 of satellite ResourceSat-1 from 1985 to 2013, a change minimal in relation to morphological changes along the estuary in the last 28 years (between Possible scales and Engineering), there was an increase in this period of 0.236 km2 (3%) of the area, not bringing significant changes to the estuary. Regarding sedimentation rate, corresponding to the second goal, from the collection of nine witnesses, up to 1m deep and using radionuclídeo 210 Pb along the estuary, we obtained a rate that ranged from 0,33 cm/year 1 cm/year (between scales Geological and Engineering) near the mouth of the estuary, and with a quick sedimentation perceived on the east bank of the river, where there are younger sediments toward the west margin. Regarding the fulfillment, third and final goal from the sampling of testimonials to 18 m depth, using the sampler Rammkernsonden (RKS), profiles and stratigraphic sections that helped understand filling the valley section of the estuary of the Coreaú river were generated and that it is a fluvialmarine estuary, filling the valleys formed in group Barriers in the last 10.000 years before present. These analyzes and results serve as a basis for comparison with other estuaries, either fluvial, fluvio-marine or marine, to better understand what the possible events that dominated sedimentation along the coast of Brazil at diferent scales.
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)
Geocronologia e geoquímica isotópica dos depósitos de Cu-Au Igarapé Bahia e Gameleira, Província Mineral de Carajás (PA), Brasil
(Universidade Federal do Pará, 2002-05-10) GALARZA TORO, Marco Antonio; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
Copper sulfide + Au ore deposits are common in the Carajás Mineral Province and systematically occur in Archean metavolcano-sedimentary sequences associated or not with granitoid intrusions. Two of these deposits, Igarapé Bahia and Gameleira, have been chosen for a geochronological and isotopic study with the purpose of not only determining their ages, origin and relationships with the host rocks, but also the formation and evolution of the crustal segments within which both deposits are located. The Igarapé Bahia Group hosts the Igarapé Bahia deposit and is composed of mafic metavolcanic (MVR), metapyroclastic (MPR) and meta sedimentary rocks (MSR), besides banded iron-formations and hydrothermally altered breccias zone (HBZ). The whole rock pile is crosscut by mafic dikes (MIR). The Cu-Au ore forms disseminations to massive bodies, mostly occurring in the HBZ which marks the contacts between the MVR and the MSR/MPR rock units. Petrographic and geochemical data about the MVR (basaltic meta-andesites), MPR (laminated and lapilli metatuffs) and MIR (quartz diorites) show them all to be derived from mafic magmas of tholeiitic affiliation, in spite of the alteration evidence. These rocks also show geochemical similarities (major and trace elements, including REE) with the coeval Grão Pará Group volcanic rocks. Chloritization (dominant), carbonation, sulfidation and magnetitization are the most important types of hydrothermal alteration. The ore is chiefly composed of chalcopyrite with variable amounts of pyrite, bornite and chalcocite. Chrorite, magnetite, siderite are abundant as gangue minerals, whereas tourmaline, molybdenite, fluorite and biotite are subordinate. Pb-Pb dating on zircon yield crystallization ages of 2745±1 Ma and 2747±1 Ma for the MVR and MPR, respectively. Similar whole-rock ages were obtained for the MVR (Pb-Pb / 2776±12 Ma and Sm-Nd / 2758±75 Ma) and the MPR (Pb-Pb / 2758±36 Ma). A Pb-Pb age of 2764±22 Ma for the chalcopyrite and gold suggests the mineralization to be contemporaneous with the host Igarapé Bahia Group. Similar Pb-Pb ages are recorded on chalcopyrite from the HBZ (2772±46 Ma), MVR (2756±24 Ma), MPR (2754±36 Ma) and MIR (2777±22 Ma), and in gold from the MVR (2778 Ma). All these geochronological data support a syngenetic to late syngenetic origin of the Igarapé Bahia Cu-sulfide + Au ores. Pb-Pb ages of 2385±122 and 2417±120 Ma obtained by leaching of the BHZ chalcopyrite may indicate a period of remobilization probably related to tectonic reactivations of the Carajás-Cinzento Strike-Slip System. δS18 values of +0.1 to +4.2%0 in ZBH sulfides (mostly chalcopyrite) corroborate both the involvement of magmatic hydrothermal fluids and exhalative deposition, whereas δC13PDB values of -7.28 to -15.78‰ in ZBH siderite suggest the mantle as a likely source for the homogeneous CO2- rich fluids responsible for the carbonate precipitation (carbonatic source) although, if it does not have evidences of the existence of this type of rock in the Carajás region. In turn, δO18PDB values of -15.51 to -20.96%0 in the same siderite indicate some contribution of meteoric waters to the fluids that altered the breccias. The Gameleira ore deposit is hosted by the Archean Igarapé Pojuca Group which consists of mafic metavolcanic rocks (MVR), amphibolites, schists, banded iron-formations and hydrothermalites. Neoarchaean mafic intrusive rocks (MIR), Paleoproterozoic quartz-feldspathic apophyses and granitoids crosscut all the Igarapé Pojuca rocks. Petrographical and geochemical data allow the MVR and MIR to be classed, respectively, as basaltic meta-andesites and quartz diorites of tholeiitic affiliation. The schistose rocks can be classified as plagioclase-quartz-biotite schist. Biotitization, chloritization, sulfidation, tourmalinization and silicification are the most remarkable types of hydrothermal alteration. The ore occurs chiefly in veins and veinlets and is characterized by selvages of chalcopyrite, pyrite, pirrhotite, bornite, molybdenite, rare cubanite, besides quartz, tourmaline, fluorite, chlorite and biotite. The MVR seem to be contemporaneous with those of the Grão Pará, Igarapé Bahia and Igarapé Salobo groups, adopting the age of the Grão Pará Group as the age of formation of these rocks. Dating of the MIR (Pb-Pb on zircon) yields a value of 2705±2 Ma interpreted as the crystallization age of these rocks and similar to those found for the mafic sills (2.70 to 2.65 Ga) that occur in the neighboring Águas Claras deposit. Pb-Pb ages of 2615±10 and 2683±7 Ma on zircon from a saprolith of the Igarapé Pojuca Group domain probably represent rocks coeval with those sills. Pb-Pb ages of 2646±30 Ma (MVR / whole-rock), 2422±12 Ma (vero sulfides) and 2218±14 Ma (leaching of chalcopyrite) are indicative of a superimposed event on the Igarapé Pojuca metamorphic rocks, either the emplacement of granitoid intrusions (1.87-1.53 Ga) or the reactivation of the Caraj ás-Cinzento Strike-Slip System. This event probably caused remobilization of pre-existing ore as well as (partial or total) resetting of the Pb isotopic system. Both the Igarapé Bahia and the Igarapé Pojuca groups, and other greenstone-like metavolcano-sedimentary sequences of Carajás, overlie a basement made up of rocks that are contemporaneous with the Xingu and Pium complexes as well as with the Arco Verde tonalite, which are the likely sources of the inherited zircon found in the MVR and MIR of the Igarapé Bahia Group and dated at 3.03-2.86 Ga. Therefore, the ranges of 3.03-2.86 and 2.76-2.74 Ga represent, respectively, well-defined periods of crust formation and expressive volcanism in the northern portion of the Carajás Mineral Province. Sm-Nd model ages (TDM) of 3.17-2.99 Ga, obtained for the rocks of both the Igarapé Bahia and Gameleira deposits are consistent with those determined for the basement rocks and granitoids that occur in the Carajás Mineral Province. ΕNd(t) values for these rocks (-0.36 to -2.12) indicate nor only participation of older crust material in the parental magmas but also that magmas were generated in a continental rift environment. This supports the current hypotheses about the tectonic environment of formation of the Itacaiunas Supergroup to which belong both the Igarapé Bahia and the Igarapé Pojuca groups. In conclusion, both studied deposits seem to have a similar primary genesis, but distinct further history in the Neoarchaean and Paleoproterozoic times, which certainly affected their mineralizations.
Acesso aberto (Open Access)
O Grupo Águas Claras da Serra dos Carajás, Paleoproterozoico do Cráton Amazônico : fácies, litoestratigrafia e sequências deposicionais
(Universidade Federal do Pará, 2018-09-24) ARAÚJO FILHO, Roberto Costa; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Águas Claras succession constitutes a siliciclastic unit with 800 m thick approximately which occurs in the Carajás Basin, Northern Brazil. The evaluation of FD06 drill core of Serra dos Carajás revealed a complex stacking for this sucession, compound by four units denominated here of A, B, C and D formations. The facies analysis allowed the identification of nine lithofacies grouped in three facies associations (FA), representative of braided fluvial, marine and deltaic depositional systems. FA1 - braided river plain - consists of conglomerates with massive bedding and incipient cross stratification, as well as fine to coarse-grained sandstone with massive bedding, cross lamination, tabular and trough cross stratifications organized in metric fining upward cycles. FA2 - foreshore/shoreface - comprises deposits constituted by fine to medium-grained sandstone with low angle cross lamination, planeparallel lamination and massive bedding. FA3 - delta front - includes fine to medium-grained sandstone with sigmoidal cross bedding, cross lamination and massive bedding organized in cycles with coarsening upward tendency. The Formation A constitutes a braided fluvial AF1 deposits interbedded with coarse tuff levels that indicate subaerial volcanic events adjacent to fluvial system during lowstand systems tract. The Formation B is composed exclusively by braided fluvial AF1 deposits developed in lowstand systems tract. The Formation C comprises coastal deposits and marine environments of the AF2 foreshore/shoreface accumulated during transgressive systems tract. This unit also includes host strata of primary manganese mineralization. The Formation D is composed predominantly by braided AF1 fluvial deposits and subordinately by deltaic AF3 packages, developed in lowstand systems tract. The sandstones of these formations were classified as quartz-arenites partially altered by hydrothermalism, indicated mainly by recurrent chloritization throughout the sucession. The stratigraphic stacking of the unit suggests a sedimentation with progradational-retrogradationalprogradational tendency. This sedimentation is likely related to events of thermal (initial) and flexural subsidence, responsible for to generate the accommodation space and to develop the depositional systems. The formations of the Águas Claras Group are inserted in three third order depositional sequences, composed by different systems tracts that reflect Águas Claras sea level fluctuations during of Paleoproterozoic of the Carajás Basin.
Acesso aberto (Open Access)
Hidrodinâmica e transporte de sedimentos em uma área de manguezal na planície costeira de Bragança, Amazônia Oriental – Brasil
(Universidade Federal do Pará, 2012-10-04) MIRANDA, Artur Gustavo Oliveira de; ROLLNIC, Marcelo; http://lattes.cnpq.br/6585442266149471; SOUZA FILHO, Pedro Walfir Martins e; http://lattes.cnpq.br/3282736820907252
The physical processes that occur in intertidal areas are essential for the existence of mangrove ecosystem, due process interaction between oceans and estuaries, with mangroves. The tidal channels represent the most important and peculiar features of coastal environments, due your circulatory system basics which controls both the tidal flow as the channel morphology. This paper presents a set of data to analyze and understand the hydrodynamic process and sediment dynamics in the coastal plain of Bragança, specifically the region known as Furo do Meio tidal channel. At this region were carried out topographic and hydrodynamic collection of data, physicochemical properties of water measurements, surficial sediment collection, and quantification of sedimentation rate according the seasonality pattern (March, July, September and December). As this study demonstrated, the tidal channel presented a well defined bidirectional flow, though the area vegetated by mangrove presented a turbulent flow, so the variation of current speed in both morphological units vary according to seasonality. The average concentration of suspended solids (CSS), between the months from March to September, remained at around 400 ppm in the channel. To the tidal flat dominated by mangrove forest, an average of approximately 21,000 ppm was obtained, while in the month of December, these values were lower than those recorded in previous months, where the maximum CSS in the channel was around 270 ppm and in the mangrove was 1000 ppm. There was not a direct relationship between the CSS and the mangrove channel, where high CSS in the mangrove is associated with the remobilization of the sediment itself at tide input in this area; there was not a significant sedimentary input of mangrove to the channel. Changes in topographical elevation corroborates the values obtained in measurements of trappers and the variation of sedimentary textural classes between fine silt and fine sand are associated with the seasonal hydrodynamic variation.
Desconhecido
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.
Acesso aberto (Open Access)
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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Resposta dos manguezais do Amapá, Rio Grande do Norte, Sul da Bahia e Espírito Santo às mudanças climáticas e flutuações do nível do mar durante o holoceno
(Universidade Federal do Pará, 2016-09-15) ALVES, Igor Charles Castor; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
The present work integrates geomorphological, sedimentological, and palynological data with radiocarbon dating, as well as δ13C, δ15N, and C/N from sedimentary organic matter from Amapá, Rio Grande do Norte, Sul da Bahia e Espírito Santo. Along the northern littoral, the area occupied by mangroves and marine influenced were larger than today, between >8750 and ~2250 cal yr BP., forming a continuous mangrove belt. However, mangroves were replaced by freshwater vegetation in areas influenced by the Amazon River discharge during the late Holocene. The elevated tidal flats occupied by herbs indicate a transition from marine influence with mangroves to a phase dominated by herbs and terrestrial organic matter at about 400 cal yrs BP. During the last decades have occurred a mangrove migration trend to more elevated surfaces. The mangroves from the Ceará-Mirim River, Rio Grande do Norte, have occurred within the modern tidal range since ~7000 cal yrs BP, and was not found indications of marine influence above the modern tidal range. However, studies developed 34 km upriver on Jucuruçu River, Prado-Bahia, indicate mangroves and estuarine organic matter between ~7400 and ~5300 cal yrs BP. During the late Holocene, the mangroves migrated to the mouth of this river. Similar dynamic was identified along the Linhares littoral, Espírito Santo, where the upper limits of tidal flats were dominated by mangroves during the middle Holocene, followed by beach ridges progradation over mangrove muddy layers during the late Holocene. During the last centuries the mangroves have established over herbaceous plains with an increase trend of estuarine organic matter. Regarding the mangrove dynamic from Northern Brazil, the sea level rise and the lower Amazon fluvial discharge during the early and middle Holocene caused the development of a continuous mangrove line. It was fragmentated during the late Holocene due to the increase of river freshwater discharge that caused a significant decrease of tidal water salinity in areas near the mouth of Amazon River. The mangrove migration to lower zones since ~400 cal yrs BP was followed by an inverse displacement during the last decades. It was caused by a relative sea level fall in a century time scale and a relative sea level rise in a decadal time scale. In the Rio Grande do Norte littoral, the mangrove establishment was basically controlled by the post-glacial sea level rise up ~7000 cal yrs BP, when it reached its modern level. However, in Prado, southern Bahia littoral, and Linhares, Espírito Santo, mangroves migrated to higher surface according to sea level rise until 2.7 m above the modern Relative Sea Level-RSL, together with a decrease of fluvial discharge at about 5300 cal yrs BP. Later, the RSL decreased to its modern level and occurred an increase of fluvial discharge during the late Holocene. During the last centuries, the mangroves from Linhares may have reacted to a relative sea level rise. Based on these data, is possible to anticipate the mangrove dynamic until the end of century XXI. Considering RSL rises, probably, the mangrove areas along the Brazilian littoral will shrink by its drowning. Regarding the north, northeast and southeastern littoral, even with a RSL rise tolerable by mangroves, the consequences of the RSL rise to mangroves will depend on topographic surface available to its migration and climatic conditions. The geomorphologic and climatic setting more damaging to mangrove is one with a limited coastal plain suitable for mangrove migration under a RSL rise associated to an increase of fluvial discharge. In this situation, besides the mangroves are being drowned by a sharp topographic transition between the coastal plateau and the coastal plain, there would be no possibility of mangrove displacement within the estuarine valleys and deltaic plains, because the increase of fluvial discharge would hamper the development of tidal plains with appropriate pore water salinities to establishment and survival of mangroves.
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Rochas encaixantes, alteração hidrotermal e caracterização dos fluídos relacionados à formação do corpo sequeirinho do depósito Cu-Au do Sossego, Região de Carajás
(Universidade Federal do Pará, 2006-09-06) ROSA, Ana Glória Noronha; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Sossego Cu-Au deposit is located at about 25 km NW of Canaã dos Carajás city (PA), southern of the Carajás transcurrent system, at the contact zone between the Archean granitic-gneisses of the basement and the Grão Pará Group rocks. This deposit is made up of five ore bodies, being Sequeirinho and Sossego the most important. The present work focused primarily on the Sequeirinho ore body, but observations have been occasionally extended of the Sossego ore body. Its main purpose was to study the hydrothermal fluids responsible for the alteration and mineralization of the Sossego deposit. Several rock types have been recognized in the deposit area: granitoids, both granular (GRA) and porphyritic (MVA), mafic volcanic (Grão Pará Group) and intrusive (GBA) rocks, biotite-rich rocks (BIX), magnetitites (MAG), ore (BSE) and dikes. These rocks are variably deformed and altered, some being essentially products of the hydrothermal alteration, namely the magnetitites and ores. The petrographic study allowed to infer that the granitic (albite + quartz +actinolite + chlorite + epidote) and mafic intrusive (scapolite + Cl-K-Fe- hastingsite ±actinolite + albite + chlorite + epidote + magnetite) had as protoliths mainly quartzdiorites and gabbros/ diorites, respectively. The BIX are mylonitized granitoids that interact with high saline fluids and are characterized by a fine banding in which light bands, composed basically of quartz and/or marialitic scapolite), alternate with black bands composed dominantly of Clbiotite, Cl-K-Fe- hastingsite and tourmaline. The MAG have magnetite contents higher than 50% and variable amounts of apatite, epidote, albite, titanite and chalcopyrite, whereas the BSE consist of chalcopyrite±siegenite + magnetite + apatite + scapolite. Felsic (quartzdiorite and riolitic/riodacitic in composition) and diabase/gabbro dikes cut the above mentioned rocks Albitization, sericitization, silicification, chloritization, epidotization, actinolitization and scapolitization, are the most important types of hydrothermal alteration, although biotitization and Fe-metasomatism also occur. The carbonation represents the final stage of the alteration. Microthermometric studies of fluid inclusions (FI) trapped in quartz, scapolite, apatite and calcite crystals from different rocks of the Sequeirinho ore body reveal aqueous fluids that may be represented, in a simplifying way, by the H2O–NaCl–CaCl2, H2O–NaCl–CaCl2–FeCl2 e H2O–NaCl–FeCl2 chemical systems. The FI show variable salinity (0.2 to 57% wt. % eq. NaCl) and homogenization temperatures that range from 100 to 480ºC. Saturated FI, corresponding to the H2O–NaCl–CaCl2, have their salinity estimated in terms of the main solutes at 15-26% NaCl and 15-23% CaCl2. FI trapped In calcite crystals show salinity between 2 and 15 wt. % eq. NaCl and the 100 to < 275ºC range as the most frequent homogenization temperature interval. The evolution of the Sossego hydrothermal system involved two primary fluids (a) H2O–NaCl–CaCl2 and (b) H2O–NaCl– FeCl2. As these fluids gradually mixed, they generated a third fluid (c) H2O–NaCl–CaCl2–FeCl2 which is interpreted to be responsible for the mineralization and associated alteration. All fluids show evidences of dilution most likely by superficial water. Fluid a is related to albitization, amphibolitization and scapolitization, whereas fluid b was the one that should have carried large amounts Fe to be later deposited as magnetitites. Fluid c is interpreted to be responsible for actinolitization, epidotization and chloritization as well as by the main stage of the mineralization. High saline fluids (>30 wt. % equiv. NaCl) are assigned to interaction with preexisting evaporite and/or exahalite layers that have been dissolved out by metamorphic processes. Magmatic aqueous fluids have also contributed to the Sossego hydrothermal system as well as meteoric waters whose influx caused strong dilution and cooling of the fluids. Comparatively to other Carajás Cu-Au deposits, the aqueous fluids related to the Sossego hydrothermal system show more similarities with those of the Archean Igarapé Salobo and Igarapé Bahia deposits, despite having a distinct typology. Most likely, these similarities arise from the fact that all three deposits are associated with metavolcanosedimentary sequences of the Itacaiunas Supergroup which resulted in part from exhalative activity and might have locally included evaporite beds. As halite was dissolved out, the resulting high saline fluids infiltrated into and were stored in the rock pores from which they might have subsequently migrated in response to thermal and/or tectonic disturbances.