Navegando por Assunto "Rochas sedimentares"

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Ambiente flúvio-deltáico influenciado por maré e tempestade da Formação Rio Maria, leste da Província Carajás (SE) do Cráton Amazônico
(2012-12) NASCIMENTO, Marivaldo dos Santos; OLIVEIRA, Camila Vilar de; ALTHOFF, Fernando Jacques
The Rio Maria Formation is a siliciclastic sedimentary sequence deposited in an eiperic sea formed along of eastern edge of the Carajás Province – the oldest Archean province of the Amazonian Craton – being intruded by rapakivi-type granite (1.88 Ga). Four facies associations have been recognized: prodelta-distal bar, delta-front/shoreface, delta-plain/distributaries and fluvial channels. Large-scale hummocky-swaley cross-stratifications (> 1 m) attest storm waves-influenced in upper shoreface deposits (tempestites). Bipolar cross-beddings with drape and reactivation surfaces reflect tidal-influence. Quartzarenite, sublitharenite and subarkose modal frameworks indicate stable continental block (craton interior) source. Heavy-minerals assemblages (e.g. zircon, tourmaline, staurolite, epidote, etc.) provide evidence of contribution from felsic plutonic igneous and metamorphic rocks. Well-rounded zircon grains can be associated to reworked sediments or metamorphic sources. These litotypes can be related to Rio Maria Block, which includes granitoid and metassedimentary rocks of the Rio Maria granite-greenstone terrain (3.0 – 2,86 Ga).
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Aspectos fundamentais das medidas e interpretação de registros paleomagnéticos em rochas sedimentares da Formação Longá-Bacia do Parnaíba
(Universidade Federal do Pará, 1984-09-21) ALENCAR, Benaia Vieira de; PACCA, Igor Ivory Gil; http://lattes.cnpq.br/8172887185665918
Palaeomagnetic data for the upper Palaezoic and, in particular, the Devonian of South America are still very limited and therefore polar wandering curves cannot be established. We investigated the paleomagnetism of 43 stratigraphic horizons of the Upper Devonian Longá Formation. The results should make a contribution towards a better definition of that curve. Sampling was done according to the block method in profiles on highway PI-13 between Teresina, Barras and Batalha, and on highways PI-24 and BR-230 between Floriano, Nazaré do Piauí and Oeiras, all in the state of Piauí. Investigations were carried out at the "Laboratório de Paleomagnetismo" of the University of São Paulo and completed at the laboratory of the NCGG of the Federal University of Pará. In this study, we employed the technique of progressive demagnetization by alternate fields up to 700ºe and/or temperatures up to 670-700ºC. Interpretation of the data was done using vector diagrams of Zijderveld, curves type J-T/C of variation of magnetic intensity with variations of temperature or magnetic field and also by graphs of variation of the direction of the vectors of magnetization. Calculations of mean direction and poles were done following the statistical method of Fisher. Four directions of remanent magnetization were identified: 1. A secondary magnetization of chemical origin (CRM) and reverse polarity due to formation of hematite probably by deuteric alteration after magnetite. This magnetization (identified as B) shows palaeomagnetic Carboniferous - Permian age with pole coordinates: 80°S, 3°E; A95 = 13.6°. 2. A hard isotherm component (IRM) with spectre totally superimposed on the initial magnetization which was not affected by the treatment of the samples. This magnetization (identified as D) shows an almost constant direction around declination point 234.23º and inclination 41.94º. 3. A group of directions of soft magnetization of viscous origin (VRM), identified as C, with mean direction: declination= 15º and inclination = -20°. These were removed at temperatures between 300 and 600°C. 4. The principal magnetization, of normal polarity, identified as A, is probably of detrital origin (DRM). Its palaeomagnetic pole coordinates: 48°S, 331ºE; A95= 9.9° is consistent with the Upper Devonian age of the Formation. This magnetization is believed to be the original one. The palaeomagnetic poles relative to magnetizations A and B as well as other poles for South America were rotated to Africa following, the pre-drif configuration of Smith and Hallam (1970) and there is agreement when compared to the African and Australian poles of the same age. The measured polarities are consistent with the magnetostratigraphic scales of Irving and Pullaiah (1976) and Khramov and Rodionov (1981).
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Caracterização faciológica e diagenética da Formação Barro Duro-Bacia de Barreirinhas
(Universidade Federal do Pará, 1990-06-06) ROSSETTI, Dilce de Fátima; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
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Diagênese da formação guia, Ediacarano da Bacia Araras -Alto Paraguai, sul do Cráton amazônico
(Universidade Federal do Pará, 2022-10-31) SANTOS, Caio Silva dos; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Guia Formation is a limestone unit of the Araras Group, exposed in central region of South America. They correspond to Ediacaran (622-614Ma) carbonate platform deposits, developed in an epicontinental sea. This deposits unconformably overlies diamictite of Puga Formation related to 635Ma Marinoan glaciation, also distributed over the metamorphic basement. The Guia Formation, aim of study, is composed of limestones interbedded with thin layers of black shales. The data were obtained from an analysis of a 350m stratigraphic profile in one of the best exposition of Guia Formation in a COPACEL mine open pit in Nobres town, State of Mato Grosso. The unit consist in six lithofacies, grouped in one facies association that records a deep carbonate platform: bituminous lime-mudstone, massive lime-mudstone and lime-mudstone rich in terrigenous grains, carbonate shale, carbonate breccias and deformed breccias. These rocks were intensive affected by diagenetic process such as aggrading neomorphism, organic matter maturation, physical compaction, spar calcite cement, dolomitization, chemical compaction and hydrocarbon migration. Aggrading neomorphism affect the matrix, turn it to microspar and pseudospar with hipidiotopic mosaic. The micrite rich in organic matter is partially dissolved by fluids capable of dissolving the matrix, generating the vug pores. That pores are cemented by spar calcite. This cement has coarse granulation, subhedral crystals, when it fills fractures it presents crystals with rhombohedral cleavage, with two directions. In cathodoluminescence, the cement has orange to red bright when it fills vug fracture, and it has zoned pink bright luminescence filling pore vug. The stylolites form serrated surfaces of low amplitude, insoluble material, composed by clays, quartz, and organic matter compound its. Dolomitization affects the rocks in three moments: the first one is the replacement of spar calcite filling fractures with subeuhedral dolomites in hipidiotopic mosaic and opaques minerals inclusions, the second on is the filling by the matrix replacement with anehedral dolomites; the third one is the formation of saddle dolomite associated with hydrocarbon. Spot analysis with SEM/EDS, shows a large amount of Ca, ang low range of Mg, Si, S, Ca, Mn, Fe, Ni, Zn, Sr, Cd, Ba and Pb. Reasserting that carbonate are scant changed by diagenetic/dolomitizing fluids. These rocks are part of the Araras Petroleum System, the Total Organic Content Analysis (TOC) indicated values between 0.04 and 0.50%, classified as a low to medium potential. The association among the petrographic and geochemistry data suggest that the bitumen migration occurred at 610 Ma, during thermal uplift of the Araras Intracratonic Basin, before the deposition of the Alto Paraguai Group, which led to exposure of the Araras Group and oxidation of the hydrocarbon, allowing the identification of type IV kerogen. Rock Eval pyrolysis, Hydrogen Index and Oxygen Index data of these rocks, do not have the potential to generate oil or gas, and are constituted by oxidized organic matter, with immature thermal evolution.
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Estudo da geometria e cinemática das rochas sedimentares arqueanas da mina do Igarapé do Azul – Carajás-PA
(Universidade Federal do Pará, 2006-09-18) SILVA, Daniela Cristina Costa da; PINHEIRO, Roberto Vizeu Lima; http://lattes.cnpq.br/3251836412904734
The Igarapé Azul Mn Mine is geologically situated along the Carajás Fault trace, in the central portion of the Carajás Strike-slip System. The Mn ore deposit is related to politic sedimentary rocks of the Azul Member on the basal portion of the Águas Claras Formation (Archaean). This unit overlain unconformably the Grão Pará Group (Nogueira et al., 1995). At present day three explotation pits are opened in the mine: (1) Main Mine (Mine 1); (2) Mine 2 and (3) Mine 3. In these locations excellent outcrops of siltstones intercalated with finegrained mudstones, sandstones and Mn-layers are exposed. These rocks are organized in folds and normal/reverse faults sets under heterogeneous deformation, partitioned in different scales. The geologic sections exposed in the mines show the dominance of siltstones intercalated with mudstones in contact with pelitic manganesiferous rocks and ore (Mn bioxide). Primary structures such as hummocky stratification, cross stratification and parallel laminations are common in these rocks. Bedding with thickness of centimeters to a few meters (30-50 cm) represents the main primary structure, used as the main deformation marker observed in rocks. The Igarapé Azul Mn Mine is divided into two blocks separated by normal fault with displacements of tens of meters, where the north block is up in relation to the south one. The south block is poorly deformed, with irregularities in bedding which dips at shallow angles towards south, subsequently positioning the ore layer in deeper levels at S direction. In the north block bedding shows heterogeneous behavior. Deformation is more expressive in this region, with the ore deformed by folds and reverse faults. Faults show vertical along-dipping kinematics with dextral conjugated displacements of oblique character. This region can be defined as a major strain corridor. The kilometer-scale corridor observed at the north block follows the NW-SE trend, in concordance with the main domains separated by the faults described above, characterized as curvilinear asymmetric folds with NW and SE shallow plunge axes (10º-25º). These folds are sectioned by sinuous NW-SE and/or E-W normal faults with shallow dips (10º-30º) associated with dextral strike-slip faults, which generate drag folds. Straight or sinuous NW-SE reverse faults and sub-vertical fault zones are observed. The individual folds in this area are flexural reverse structures with en echelon geometry and similar orientation to the curvilinear folds: shallow SE plunging axes. The features described above drawn a gentle kilometer-scale antiform, which results from bedding accommodation in response to the faulting deformation. The parallelism of the features observed in the Igarapé Azul Mn Mine and the main lineaments which drawn the Carajás Fault suggest a close relation between important deformational episodes occurred during the tectonic history of the Carajás Fault. Faults with normal kinematics associated to directional dextral component of displacement are the major exposures in the area and are related to the dextral transtensional episode responsible for installation of the Carajás Fault prior to 2.6 Ga (Pinheiro, 1997). Folds, thrust faults and subvertical fault zones would be related to deformation under sinistral transpressional regime; a second event responsible for the reactivation and tectonic inversion of most of the primary structures near the Carajás Fault zone (Pinheiro, 1997; Pinheiro e Holdsworth, 2000; Lima, 2002).
Acesso aberto (Open Access)
O padrão de distribuição dos elementos traços na Formação Pedra de Fogo, permiano da Bacia do Maranhão e seu emprego como indicador de ambientes de sedimentação
(Universidade Federal do Pará, 1982-05-07) OLIVEIRA, Consuelo Macias de; SCHWAB, Roland Gottlieb
The present investigation consisted of a geochemical study of the medium and upper layars of the Pedra do Fogo Formation aiming at correlating its elemental distribution pattern with the sedimentary environment where that formation was deposited. Pelitic material with carbonate content below 30% was sampled in the three different outcrops of the Pedra do Fogo Formation for mineralogical and chemical analyses. Illite and dolomite, with subordinate amounts of smectite, calcite, quartz and K-feldspar were determined by X-ray diffraction techniques as the constituents of the mineral assemblages. Trace element (B, Ba, Co, Cr, Cu, Ga, Li, Mn, Ni, P, V, Pb, Sr, Rb and Zn), CO2 and K concentrations were determined by emission spectrography, atomic absorption spectrometry and colorimetry. B, Ga, K, Rb and V were found to be preferentially fixed in illite. Co, Cr, Cu, Na and Pb show only a partial preference for this mineral, but it is likely that the presence of iron oxides also controls their distribution. Mn is dominantly fixed in the carbonate phases, while Li, O, Sr and Zn have no special tendency for fixation in either minerals. However, Li and Zn distribution might be partly controlled by the smectite content of the samples. Likewise P and Sr distributions seem to be heavily conditioned by the salinity variations that occurred during the deposition of those sedimentary layers. Most analyse'd elements have concentrations below the respecti.ve world average found for shales. Botb the presence of carbonate and specially the low salinity of the environment probably account for that difference. The interpretation of the chemical data based on B-V, Ga-B, B-K2O and B-Ga-Rb diagrams and on B content indicates a wite range of variation for the medium salinity during the deposition of the Pedra do Fogo rocles. Accordingly, the observed sequence is composed of intercalations of marine and fresh water sediments, the latter being dominant. The marine intercalations are more frequent in the bottom of the sampled stratigraphic section and become progressivily rarer towards the top layers which were deposited in a typically fresh water environment. The different parpmeters used in the chemical interpretation of the depositional environment of the Pedra do Fogo Formation are internally consistent and agree very well with the geological and paleontological information that has been gathered by other authors.
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Paleoambiente da Formação Prosperança, embasamento neoproterozóico da Bacia do Amazonas
(2011-03) BARBOSA, Roberto César de Mendonça; NOGUEIRA, Afonso César Rodrigues
The Neoproterozoic Prosperança Formation represents a sedimentary cover of southern Guyana Shield and is poorly exposed when contrasted with Paleozoic record of Amazonas and Solimões basins. Conglomerates, arkosic sandstones and mudstones are the characteristics deposits filling basement grabens. This unit is overlain unconformably by neoproterozoic carbonate rocks of Acarí Formation (observed only in cores). These formations represent the sedimentary basement of oil producing Paleozoic basins of the Amazon region. The precise characterization and paleoenvironmental reconstruction of Prosperança Formation are important for their distinction from Paleozoic units. Stratigraphic analysis was carried out at lower Negro River, State of Amazonas. Four facies associations were interpreted as products of a fluvial-deltaic system: prodelta/lacustrine, delta front, foreshore/shoreface and distal braided plain. Mudstones distributed along several kilometers suggest a sedimentary basin probably of lacustrine/restricted sea origins. Complex structured deltaic lobes were fed by braided distributaries that migrated mainly to SE. Sandstones generated under oscillatory/combined flux are conformable with shoreline deposits. Planar to trough cross-bedded sandstones are related to migration of subaqueous dunes, associated to fluvial-braided processes. Lenses of conglomerate, planar to trough cross-bedded sandstones, possibly of paleozoic age, which overlies unconformably the Prosperança Formation migrated to NW as product of proximal braided plain system and is in contrast to the S-directed cross-stratification of the Prosperança sandstones.
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Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS
(Universidade Federal do Pará, 2015-09) REDES, Letícia Alexandre; SOUSA, Maria Zélia Aguiar de; RUIZ, Amarildo Salina; LAFON, Jean Michel
The Taquaral Granite is located on southern Amazon Craton in the region of Corumbá, westernmost part of the Brazilian state of Mato Grosso do Sul (MS), near Brazil-Bolivia frontier. This intrusion of batholitic dimensions is partially covered by sedimentary rocks of the Urucum, Tamengo Bocaina and Pantanal formations and Alluvial Deposits. The rock types are classified as quartz-monzodiorites, granodiorites, quartz-monzonites, monzo and syenogranites. There are two groups of enclaves genetically and compositionally different: one corresponds to mafic xenoliths and the second is identified as felsic microgranular enclave. Two deformation phases are observed: one ductile (F1) and the other brittle (F2). Geochemical data indicate intermediate to acidic composition for these rocks and a medium to high-K, metaluminous to peraluminous calk-alkaline magmatism, suggesting also their emplacement into magmatic arc settings. SHRIMP zircon U-Pb geochronological data of these granites reveals a crystallization age of 1861 ± 5.3 Ma. Whole rock Sm-Nd analyses provided εNd(1,86 Ga) values of -1.48 and -1.28 and TDM model ages of 2.32 and 2.25 Ga, likely indicating a Ryacian crustal source. Here we conclude that Taquaral Granite represents a magmatic episode generated at the end of the Orosirian, as a part of the Amoguija Magmatic Arc.
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Petrologia dos carbonatos da formação Itaituba na região de Aveiro - PA
(Universidade Federal do Pará, 1983-12-22) FIGUEIRAS, Alexandre José Martins; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
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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.