Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/6341

O Doutorado Acadêmico pertence ao Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).

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Análise integrada dos depósitos de caulim na região do Rio Capim: fácies, estratigrafia, petrografia e isótopos estáveis
(Universidade Federal do Pará, 2006-09-29) SANTOS JÚNIOR, Antonio Emídio de Araújo; ROSSETTI, Dilce de Fátima; http://lattes.cnpq.br/0307721738107549
The kaolin deposits that occur in the Rio Capim area, east of Cametá Sub-Basin, are inserted in the Ipixuna Formation. This unit distinguishs for presenting one of the largest worldwide kaolin concentrations of excellent quality to the cellulose industry. Beyond the economic character, a great volume of academic works focusing these kaolin deposits had led to pedological and geochemical approaches, but without taking into account their sedimentologic aspects, which are important to understand their genesis. Detailed sedimentologic and stratigraphic studies of the Rio Capim kaolin have been increasingly carried out in the last years, which led to the paleoenvironmental interpretations for the Ipixuna Formation, as well as to discuss better the mode of formation of the soft and semi-flint kaolin units that are typical of this unit. These works served to motivate the integration of sedimentologic and stratigraphic data with optical studies combined with hydrogen and oxygen isotope geochemistry in order to discuss the geologic processes involved in the origin and evolution of the soft and semi-flint kaolin units. The sedimentological analysis consisted in a more detailed facies description and stratigraphic analysis of newly open quarries that were not available during previous investigations. The additional exposures led to a better characterization of the lower kaolin unit, known as the “soft kaolin”, which is well stratified, favoring facies analysis. Hence, the soft kaolin unit consists of kaolinitized sandstones and kaolinitized pelites that were formed in tidally influenced fluvial channels (Facies Association A), tidal channel (Facies Association B), tidal flat/mangrove (Facies Association C), and tidal sand bar/tidal sandy flat (Facies Association D). These depositional environments are attributed to a tide-dominated estuarine system. Petrographic studies and scanning electronic microscopy (SEM) of the kaolin deposits in the study area had their composition was strongly modified after sedimentation. The soft kaolin consists of kaolinitized quartz sandstone and either laminated or massive pelites, which are composed by fragments of meta-volcanic lithic and volcanic felsic rocks, as well as metamorphic and granitics rocks. These lithologies were strongly modified during kaolinitization, as revealed by the intense replacement of the framework grains by kaolinite of three types, named herein as Ka, Kb and Kc kaolinites. Ka kaolinite occurs dominantly associated with kaolinitized sandstones, being characterized by pseudohexagonal crystals 10-30 μm in diameter, which are organized as booklets or vermicular forms that reach up to 400 μm in length. Kb kaolinite dominantes in the pelites, and consists of pseudohexagonal crystals 1-3 μm in diameter, occurring as isolated, face-to-face and parallel to pseudo-parallel crystals. Kc kaolinite forms pseudohexagonal to hexagonal crystals of 200 nm in diameter. It occurs dispersed through the soft unit, increasing significantly in abundance in association with paleosols at the top of the unit. The semi-flint kaolin deposits are constituted mainly of reworked grains derived from the underlying soft kaolin unit that are mixed with grains derived from metamorphic and granitic sources. These deposits are dominantly composed of Kc kaolinite that was formed during weathering. The deuterium (δD) and oxygen (δO) isotope analysis of the kaolin deposits from the study area helped to discuss better the evolution of the different types of kaolinites described above. Hence, the soft kaolin deposits display δO values varying between 6.04 ‰ and 19.18 ‰ in the Ka+Kb kaolinites, and between 15.38 ‰ and 24.86 ‰ in the Kc kaolinite. The δD values from this unit vary from – 63.06 ‰ to 79.46 ‰, and from –68.85‰ to -244.35‰ in the Ka+Kb and Kc kaolinites, respectively. The semi-flint kaolin deposits are characterized by δO and δD values ranging from 15.08‰ to 21.77‰, and from -71.31‰ to -87.37‰, respectively. Based on these data and on the isotopic composition of both meteoric and ground waters, it was possible to conclude that the kaolinites had not been formed in balance with modern weathering. These values represent the isotopic composition during the time of formation of the kaolinites, as well as mineralogical contamination of framework grains that are now replaced by kaolinites.
Acesso aberto (Open Access)
O cenozoico superior do centro-oeste da Bacia do Amazonas: paleobotânica do embasamento cretáceo e evolução do Rio Amazonas
(Universidade Federal do Pará, 2018-11-08) BEZERRA, Isaac Salém Alves Azevedo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
At the end of the Neogene and during the Quaternary, the development of the Amazon River caused significant paleoenvironmental and geomorphological changes that generated current ladscape at Amazonia. Previous models elaborated on a continental scale were based on data obtained from a drill core carried out on the Atlantic continental shelf, distant 200 km of the Amazon River mouth, suggesting the establishment of this drainage with Andean provenance from the Middle to Upper Miocene. In contrast, studies based on outcrops in the western and central portions of the Amazon have indicated younger ages for this ecosystem, from Pliocene to Quaternary. The sedimentological-stratigraphic study of the fluvial terraces of the Amazon River, exposed in the center-west portion of the Amazon Basin, assisted by luminescence geochronology, allowed to sequence the sedimentation events and discuss the paleoenvironmental and paleogeographic since Late Neogene. The studied Neogene- Quaternary deposits overlies Cretaceous rocks whose sedimentological and paleobotanical study revealed the preservation of impressions and counter-impressions of leaves and other macro-plant remains in pelites interpreted as flood plain and abandoned channel deposits of meandering rivers. The first record of angiosperms in this unit with possible affinities to the families Moraceae, Fagaceae, Malvaceae, Sapindaceae and Anarcadiaceae with appearance from Late Cretaceous, and the family Euphorbiaceae with record starting in the Mid- Cretaceous confirm the Cretaceous age for these rocks. The terraces of the Amazon River informally subdivided into lower and upper units are composed of sand, gravel and clay, organized in finning upward cycles representative of channel filling and overbank deposits. The lower unit was interpreted as a record of the proto-Amazonas, with migration to the east and deposition around 2 Ma. During this stage, the alluvial plain was restricted, preferentially following weakness zones coincident with fractures in the Paleozoic and Cretaceous basement. The climatic oscillations during the Quaternary and the increase of the volume of orographic rains in the headwaters region of the fluvial systems, in the eastern flank of the Andean ridge modified the hydrological regime, amplifying the escarpment erosion. The gradual expansion of the alluvial plain formed a large area of 120 km around 1 Ma to 140 ka, recorded by the upper unit deposits. At this stage, the eastern portion of the Amazon Basin topographically higher restricted the Pleistocene sedimentation in minimum accommodation space. The lower unit deposits are correlate in part to the Miocene-Pliocene deposits of the Amazon Basin, while the upper units are correlate with the Pleistocene deposits of the Solimões and Amazon basins. The dynamics of the construction of the Amazon River valley during the end of the Neogene and Quaternary was influenced by neotectonics (106 yr) and climatic oscillations (104-105 yr). The landscape of the central-eastern portion of the Amazon dominated no Pleistoceno by terra firme in elevated areas was governed by the dynamics of expansion and contraction of the alluvial plain. At the end of the Quaternary, the várzea formed by floodplains within the alluvial plain, which used to occupy a wide area, became increasingly restricted by the continuous processes of fluvial incision during the glacial maximum (18 to 22 ka). The continuous lateral migration of the meandering channel to the north led to the confinement of the channel by the fluvial scarps developed in the Cretaceous basement, which culminated in the current landscape in the Center-East of the Amazon. Testing the reliability and accuracy of some Pleistocene and older OSL ages for Amazon River deposits revealed that are much more minimum ages than buried ages for pre- Quaternary deposits.
Acesso aberto (Open Access)
Desenvolvimento da vegetação e morfologia da foz do Amazonas-PA e rio Doce-ES durante o Quaternário tardio
(Universidade Federal do Pará, 2013-11-05) FRANÇA, Marlon Carlos; PESSENDA, Luiz Carlos Ruiz; http://lattes.cnpq.br/0425441943533975; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
This work compares the vegetation and morphological changes occurred along the littoral of the Marajó Island, Amazonian littoral, and the coastal plain of the Rio Doce, southeastern Brazil, during the Holocene and late Pleistocene/Holocene, respectively, focused specifically on the response of mangroves to sea-level fluctuations and climate change, which have been identified in several studies along the Brazilian coast. This integrated approach combined radiocarbon dating, description of sedimentary features, pollen data, and organic geochemical indicators (δ13C, δ1₵N and C/N). On coastal plain of the Doce River between ~47,500 and ~29,400 cal yr BP, a deltaic system was developed in response mainly to sea-level fall. The post-glacial sea-level rise caused a marine incursion with invasion of embayed coast and broad valleys, and it favored the evolution of a lagoonal/estuary system with wide tidal mud flats occupied by mangroves between at least ~7400 and ~5100 cal yr BP. Considering the Marajó Island during the early and middle Holocene (~7500 and ~3200 cal yr BP) mangrove area increased over tidal mud flats with accumulation of estuarine/marine organic matter. It was a consequence of the marine incursion caused by post-glacial sea-level rise, further driven by tectonic subsidence. Dry conditions in the Amazon region during this time led to a rise is tidal water salinity and contributed to mangrove expansion. Therefore the effect of relative sea-level (RSL) rise was determinant to the mangrove establishment in the southeastern and northern region. During the late Holocene (~3050 – 1880 cal yr BP) the mangroves in both regions were retracted to a small area, with some areas replaced by freshwater vegetation. This was caused by the increase in river discharge associated to a wet period recorded in the Amazon region, and considering the coastal plain of the Doce River (southeastern Brazil), the mangroves shrank in response to an increase in fluvial sediment input associated to a sea-level fall.
Acesso aberto (Open Access)
Desenvolvimento metodológico e avaliação de contaminação por HPAs em sedimentos da baia de Guajará
(Universidade Federal do Pará, 2014-03-31) SODRÉ, Silvana do Socorro Veloso; CAVALCANTE, Rivelino Martins; http://lattes.cnpq.br/2253127527012522; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
Polycyclic Aromatic Hydrocarbons (PAHs) are pollutants with toxic effects, harmful to the environment and to human health. They are part of a group of persistent organic pollutants (POPs), which by its characteristics have an impact on the environment and are extensively studied for this reason. They may be present in particulate, dissolved and/or gaseous forms, in different environments such as soil, sediment, air, water, particulate matter in the atmosphere, organisms and food (Kennish, 2007). Natural sources of PAHs include volcanic activity, natural fires, oil oozing and biogenic processes. Anthropogenic PAH pollution may occur by incomplete oil combustion (automotive and industrial), intentional burning of wood and plantations, domestic and/or industrial wastewater, urban water flow, accidental spills of oil and derivatives. Hydrophobic and lipophilic, these substances can be easily adsorbed by sediments, so that this matter is an important reservoir for them. To evaluate the presence of these compounds in the environment, this work used High Performance Liquid Chromatography. The samples used in the development and optimization of the methodology were collected in the Guajará bay (Belém - PA). This work consisted in the development of a methodological procedure (with adaptations and optimizations) to quantify 16 PAHs in 10 points in the Guajará bay in two field campaigns, so that 20 samples were analysed. In the development stage of the analytical method, elution systems, system polarity and eluent flow were tested, among others. In order to validate the method, the following parameters were assessed: fidelity, linearity, detection limit and quantification limit. Diagnostic ratios were calculated to identify the primary sources of PAHs found in the bay. The primary sources of the 16 PAHs studied in the sediments of the bay were identified based on ΣPAHs BMM/ΣPAHsAMM; Phe/Ant; Flt/Pyr; Ant/Σ178; Flt/Σ202; B(a)P/Σ228 and Ind(123cd)pyrene/Σ276. In the first field campaign, the total concentration of light PAHs ranged from 132.3 ng.g-1 to 1704.14 ng.g-1, the ΣPAHs of the heavy ones, from 125.82 ng.g-1 to 1269.71 ng.g-1 and the total ΣPAHs, from 317.84 ng.g-1 to 3117.06 ng.g-1. In the second field campaign, the total concentration of light PAHs ranged from 76.12 ng.g-1 to 1572.80 ng.g-1, the ΣPAHs of the heavy ones, from 213.90 ng.g-1 to 1423.03 ng.g-1, and the total ΣPAHs, from 290.02 ng.g-1 to 2995.82 ng.g-1. Based on these results, the Guajará bay can be classified as moderately impacted. The combustion is the predominant source of PAHs in the sediments of the bay, followed by vegetal biomass combustion and by the contribution of oil and supplies. Most of the points studied in this work, during the two field campaigns, showed concentrations of individual PAHs above the SQGs.
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)
Evolução dos pântanos da região central da península de Bragança-PA de acordo com as mudanças do nível relativo do mar durante o holoceno
(Universidade Federal do Pará, 2016-12-07) CAMARGO, Paloma Maria Pinto; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
This work integrates data from geomorphology, sedimentary features, pollen, diatom, isotopes, mineralogy, chemical analysis and C-14 datings obtained of sediment cores sampled from Bragança Península, Pará littoral. The pollen data indicate that central and topographically higher area of Bragança Peninsula was an area dominated by mangroves, with wide expansion of Avicennia trees, marine diatom, an increased trend of sedimentary organic matter sourced from estuarine algae, and a mineralogical composition mainly formed by pyrite and hematite, typical of mangrove anoxic sediments between > 6300 and 4900 cal yr BP. Between 4900 and 4300 cal yr BP occurrs a without pollen zone, but along this interval takes place marine diatom, an increase of sedimentary organic matter sourced from marine algae and the absence of minerals formed by Fe and S. In the late Holocene (<4300 cal yr BP), the study site was recolonised mainly by herbs with Avicennia trees restricted to border of the herbaceous plain, presence of freshwater diatom remains and a significant increase trend in contribution of sedimentary organic matter of terrestrial origin (C4 plants). Precipitated minerals from enviroments under intense evaporation form the mineralogical composition. In recent decades, there is a mangrove migration to elevated surfaces occupied by herbs (C4 and C3 terrestrial plants), and an increase of sedimentary organic matter sourced from estuarine algae. An upward increase in the Sr concentration occurs along the last 10 cm. These data suggest a mangrove and salt marshes dynamic mainly controlled by the relative sea level changes. Probably, postglacial sea level rise contributed to the establishment and expansion of mangroves in the Bragança Peninsula with great impact on the expansion of Avicennia trees and marine diatoms, an increase of sedimentary organic matter sourced from estuarine algae. This environment favors the mineral precipitation for instance of pyrite. Between 4900 nd 4300 cal yrs BP, the continuous relative sea level rise causes the increase of marine/estuarine diatoms and the contribution of sedimentary organic matter sourced from marine algae. However, it caused the drowning of mangrove and associated vegetation, and consequently its disappearance from the study area, as well as the environmental conditions for sulfides precipitation. After 4300 cal yrs BP, the increase of sedimentary organic matter sourced from C4 terrestrial plants and freshwater diatoms suggest a relative sea level fall. The mineralogical composition suggests an arid environment, such as a sabkha. This process caused the recolonization of herbs (mainly C4 plants) in the topographically highest area of studied peninsula and Avicennia trees surrounding this herbaceous plain. Considering the last decades, the Avicennia trees migration to elevated herbaceous fields, the increase trend of organic matter sourced from estuarine algae and the increase in concentration of Sr during the last 10 cm suggest a modern relative sea level rise.
Acesso aberto (Open Access)
Evolução geoquímica das crostas lateríticas e dos sedimentos sobrepostos na estrutura de Seis Lagos (Amazonas)
(Universidade Federal do Pará, 1996-03-19) CORREA, Sandra Lia de Almeida; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The study of the mineralogical and geochemical evolution of the lateritic crusts and the overlying sediment in the structure of Seis Lagos (Amazonas State) has been based on the analyses of samples from the surface lateritic crusts and from three boreholes as well. In the chemical characterization of the examined material, it has been used both classic and spectroanalytic methods, while in the mineralogical characterization, x-ray diffraction, optical microscopy, infrared spectroscopy and thermogravimetry (DTA and DTG) have been employed. Energy dispersive system analyses (EDS) have been performed and applied to the micromorphologic study of the crusts and sediments from the Esperança Basin. In siderite samples, it has been determined 13C and 18O isotopic contents as well as the 87Sr/86Sr isotopic ratios. The Rb/Sr method has been used in an attempt to date whole samples and siderites from the carbonatic breccias. The textural, mineralogical and geochemical features observed, both in the surface crusts and in the profile of the borehole number 1, point to a lateritic origen for those materials. The carbonatitic signature of the crusts is indicated by typical minerals of carbonatites and associated rocks such as ilmenorutile, Nb-rutile, Nb-brookite, pyrochlore and monazite, which are resistant to lateritic processes; by high and anomalous contents of Nb, REE, as well as, Mn, Th, Co, Zr, Sc, V, Mo and Be. The profile of the borehole number 3 is arranged in well distinct horizons, what is characteristic of lateritic profiles, shows chemical and mineralogical compositions indicative of a lateritic derivation from aluminosilicatic iron-poor rocks, as those of the wall rocks (granites and gneisses) of Seis Lagos. The sediments of the Esperança Basin show evidence of being derived from the different horizons which make up the lateritic profiles, with a significant vegetable- and animal-derived organic contribution. The materials which constitute the carbonatic breccia are thought to be originated from lateritic ferruginous crust due to the existing geochemical similarities among them, to the presence of resistate minerais of the ferruginous crust and to the presence of essentially iron-bearing minerais, typical of sedimentary-diagenetic environment, such as pyrite and siderite. The carbonaceous clay proved to be derived from lateritic clayey horizons, as those of the profile of the borehole 3, and the deposition of this layer took place in a moment of lower subsidence rate in the Esperança Basin, when the ferruginous crust, positioned at higher levels, were being eroded and the cayey horizons were exposed. The sapropelite layer indicates, considering its large thickness, that a development of a long-lasting acid and reducing environment might have taken place; its chemical and mineralogical composition received contributions from latentes, mainly from the clayey horizons; and the pyrite formation has been the sanie of that of the carbonatic breccia. The beige-colored clay bed, as it is indicated by its chemical and mineralogical composition, was also formed by clayey-horizons material. In the carbonatic breccia of the Esperança Basin, typical caxbonatite minerals have not been found, except for the resistates (ilmenorutile, Nb-rutile, Nb-brookite, pyrochlore and monazite) and siderite, where the last one is not a common constituent of those rocks. Lateritic minerals, however, such as gibbsite and those of the crandallite group have been found. The geochemical filiation reported among crusts, carbonatic breccias, clay/sapropelite and clayey lateritic horizons is noteworthy. The nonalignment of the points plotted in isochronic diagram (87Rb/86Sr vs. "Sr/"Sr), obtained either from the whole sample or the individual siderite analyses of the carbonatic breccia are not compatible with homogenous rocks, as it would be expected for carbonatites, although they are with the thick sedimentary pile. The mineralogical, geochemical and isotopic data demonstrate that the carbonatic breccia composition does not correspond to that of the carbonatites and thus the sediments of the Esperança Basin, including the carbonatic breccia, might have had the various horizons of the lateritic profiles as their source, where the ferruginous crust might have largely been the source for the sediments of the base of column (probably the basal portion of the basin) as well as the clayey horizons of the upper beds might have been. This made possible that, along all the extension of the stratigraphic column, the geochemical signature of the carbonatitic source rock, from which the laterites were generated, was transferred to the sedimentary rocks as well as it was also preserved in the laterites.
Acesso aberto (Open Access)
Fácies, petrografia e geoquímica da Formação Codó neo-aptiano, bacia de São Luís - Grajaú
(Universidade Federal do Pará, 2005) PAZ, Jackson Douglas Silva da; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136; ROSSETTI, Dilce de Fátima; http://lattes.cnpq.br/0307721738107549
The Codó Formation is an important geological unit in Brazil, representing the only record of Neoaptian rocks exposed along the Brazilian equatorial margin. This unit consists of bituminous black shales, limestones and evaporites, which are particularly well represented in the south and east margins of the São Luís-Grajaú Basin, around the towns of Codó and Grajaú, State of Maranhão. These areas were investigated in order to: 1. improve the depositional system, discussing the hypothesis that the Codó Formation was produced in a lacustrine setting; and 2. reconstruct the paleohydrological conditions with basis on the integration of facies, stratigraphy, petrography and isotope (C, O,Sr and S) data. Hence, the field data presented herein confirmed a lacustrine system for the Codó area, where prevailed stable, well-stratified, saline lakes characterized by periods of closure, anoxia and salt precipitation in the central saline lakes. On the other hand, ephemeral conditions with development of a sabkha/saline pan complex prevailed in the Grajaú area, where salts precipitated mostly in the marginal portions of the system (i.e., marginal saline pans and mudflats). Studies focusing facies and stratigraphy also revealed that in both areas the Codó Formation is arranged into several shallowing-upward cycles formed by progradation of marginal into central lake deposits. Three types of cycles were distinguished, referred to here as lower, intermediate and higher rank cycles. The lower rank cycles correspond to millimetric interbeddings of: a) bituminous black shale and evaporite; b) bituminous black shale and calcimudstone; c) bituminous black shale and peloidal wackestone-packstone; d) grey/green shale and calcimudstone; e) grey/green shale and peloidal wackestone-packstone; f) grey/green shale and ostracodal wackestone/grainstone; h) ostracodal wackestone/grainstone and/or calcimudstone with cryptomicrobial mats and ooidal/pisoidal packstone. These are attributed to seasonal deposition with basis on their regular nature forming very thin cycles resembling varves. The intermediate rank cycles average 1.7 m thick and are formed by complete and incomplete cycles. Complete cycles show an upward transition from central to intermediate and then marginal facies associations, and include two types: C1 cycles with central lake deposits consisting of evaporites and black shales; and C2 cycles with central lake deposits formed by gray/green shale. Incomplete cycles are those formed by successions lacking at least one of the facies associations, consisting of either central and intermediate lake deposits (cycles I1) or intermediate and marginal lake deposits (cycles I2). The higher rank cycles average 5.2 m thick and consist of four depositional units, which display shallowing-upward successions formed by both complete and incomplete, intermediate rank cycles that vary their distribution upward in the section, and are bounded by sharp surfaces. Unit 1, the lowermost one, averages 2.7 m in thickness, being entirely composed by thin I1 cycles. Unit 2 averages 5.2 m thick, and displays all of the aforementioned intermediate cycles, especially complete ones. Unit 3, averaging 2.6 m thick, consists of 80% of cycles I2. Finally, unit 4, which averages 2.2 m in thickness, displays only incomplete cycles, though its uppermost part was not preserved due to erosion during the development of the Aptian sequence boundary. The detailed sedimentological characterization and the stratal stacking patterns of the intermediate and higher rank cycles support a genesis linked to syn-sedimentary tectonic activity, particularly suggested by high facies variability, limited lateral extension, as well as frequent and random thickness changes of the intermediate-rank cycles. Additionally, the matching between the four higher rank cycles with four stratigraphic zones having different styles of soft-sediment deformation structures previously described in the literature as resulting from seismic activities, is a further argument to corroborate this interpretation. Therefore, the several episodes of lake shallowing recorded in the intermediate and higher rank cycles of the Codó Formation are attributed to fluctuations in the lake water level, triggered by seismic pulses alternating with sediment deposition. The petrographic analysis of the evaporites from the Codó Formation allowed to better defining both the lake-sabkha-saline pan depositional system and the post-depostional histories. Seven evaporite morphologies were recognized: 1. chevron (selenite) gypsum; 2. nodular/lensoidal gypsum/anhydrite; 3. acicular gypsum; 4. mosaic gypsum; 5. brecciated gypsum/gypsarenite; 6. pseudo-nodular anhydrite/gypsum; and 7. rosettes of gypsum. Despite of this large variety of evaporite phases, the chevron gypsum, the nodular/lensoidal gypsum/anhydrite and the brecciated gypsum/gypsarenite record the preservation of primary features. The association of these morphologies with deposits displaying cyclic horizontal bedding, attributed to lake level fluctuations eventually culminated with subaerial exposure, reinforces this interpretation. Even acicular gypsum and mosaic gypsum, which replaced the chevron and brecciated gypsum/gypsarenite, respectively, formed under the influence of the depositional surface. Burial phases of gypsum are only recorded in the pseudo-nodular anhydrite/gypsum, attributed to salt mobilization induced by halokinesis. In addition, rosettes of gypsum, which crosscut the other evaporite morphologies, diagenetic in origin, have probably formed as the latest evaporite phase of the study area, under the influence groundwater and/or surface weathering. In the present research, isotope studies aiming paleoenvironmental purposes were motivated by both confirmation of strong depositional influence for at least great part of the evaporites from the Codó Formation (i.e., primary and eodiagenetic gypsum), and the low diagenetic modification recorded for the limestones. Results of these approaches show that expansion/contraction cycles in both studied areas were accompanied by significant changes in isotope values. The wide dispersion of Sr and S isotope data within individual depositional cycles reinforces the lack of significant diagenetic modification as suggested by the petrographic analysis, and confirms the utility of these isotopes as environmental tools. Additionally, a non-marine brine source is suggested by 87Sr/86Sr ratios ranging from 0.707824 to 0.709280, which are higher than those from late Aptian seawater (i.e., between 0.70720 and 0.70735). The δ34S varies from 16.12 to 17.89 %o(V-CDT) in the Codó area, which is also in disagreement with late Aptian marine values (ranging from 13 to 16 %o(V-CDT)). Both geochemical tracers were influenced by facies characteristics, and thus a model is provided where expansion of saline pan/lake systems led to decreasing 87Sr/86Sr values due to the inhibition of the 87Sr from clay minerals originated during the internal draining of mudflats. During expansion peaks, the 87Sr/86Sr values were lower due to submergence of mud flats and introduction of external 87Sr-depleted waters related to weathering of Permian to Neocomian marine limestones and evaporites, as well as Triassic to Neocomian basaltic rocks. Furthermore, the sulphur isotope values decrease in the southern margin of the basin from 14.79 to 15.60 %o(V-CDT) probably due to increased evaporation in shallower water settings. While the studies of Sr and S isotopes emphasized the evaporites of the Codó Formation, the analysis of C and O isotopes were carried out on the carbonates. The data revealed a wide distribution of dominantly low δ13C and δ18O values, ranging from –5.69‰ to –13.02‰ and from –2.71‰ to –10.80‰, respectively. It was also observed that these ratios vary according to seismically-induced shallowing-upward cycles, in general becoming lighter in their bases, where central lake deposits dominate, and progressively heavier upward, where marginal lake deposits are more widespread. In addition to confirm a depositional signature for the analysed samples, this behavior led to introduce a seismic-induced isotope model. Hence, lighter isotope ratios appear to be related with flooding events promoted by subsidence, which resulted in the development of a perennial lake system, while heavier isotope values are related to ephemeral lake phases favored through uplift and/or increased stability. Furthermore, the results show that a closed lake system dominated, as indicated by the overall good positive covariance (i.e., +0.42 to +0.43) between the carbon and oxygen isotopes, though open phases are also recorded by negative covariance values of –0.36.
Acesso aberto (Open Access)
Geoquímica dos sedimentos de manguezais do nordeste do estado do Pará: um exemplo do estuário do rio Marapanim
(Universidade Federal do Pará, 2006-01-20) SILVA, José Francisco Berrêdo Reis da; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The northeast coast of Pará state was geologically built on fluvial valleys partially submersed during the Holocene, where the mangroves of Marapanim estuary were developed. Adjacent to the mangroves, iron sediments and Latosol of Barreiras Formation (Tertiary) are the main source of silt, clays and sands. Despite the ecological, social and economic mangrove significance, there is a lack of geologic information focusing the processes and the magnitude of mineralogical and geochemical transformations occurring in these ecosystems on the Brazilian north coast, which is the main goal of this research. To reach the purposed objectives topographic studies were run, as soon as a short description about the mangroves. Sediments were sampled in the end of both rainy and dry seasons and submitted to in situ interstitial salinity, Eh and pH measurements. To these samples were also run chemical analysis to determine SiO2, Al2O3, Fe2O3, TiO2, P2O5, Na2O, K2O, CaO, MgO, L.I. (lost on ignition) and granulometric analysis. Trace elements were determined by using ICPM-MS; minerals were determined by using X-ray diffraction and SEM techniques. Surface and interstitial water were sampled during neap and spring tides, in periods with both higher (March, June and July) and lower (September, November and December) pluvial precipitation. These samples were submitted to chemical analysis to determine H4SiO4, SO4 2-, ΣH2S, NH4 +, Cl-, PO4 3-, Na+, Mg2+, Ca2+, K+, total alkalinity and dissolved iron. Salinity, Eh and pH were also measured. The mangroves are typically from intertidal zones and are represented by a mixture of Rhyzophora mangle and Avicennia germinans developed under semidiurnal macro tides, totally submersed during the ebb-tides and weekly exposed during the spring-tides, under a rainy tropical weather, hot and humid with remarkable climatic seasonality. The mangrove sediments are predominantly silt-clayed, rich in organic matter (C: 1 to 4% grade). Those sediments were originally deposited over sand bars, which smooth morphology and sedimentological aspects promote vegetal colonization, drainage network evolution and sediments development, increasing its consistency. The tropical chemical weathering acts over the source areas producing quartz, low crystal kaolinite grains, iron oxides and other dissolved chemical substances like silica, aluminum and heavy metals which are incorporated to the mangrove sediments, with diatoms and Na+, K+, Ca2+ e Mg2+ ions from marine contributions. At the mangrove, the original material is reworked throughout intensive biological activity and geochemical processes developed in the presence of different organic matter grades and the reactive surface of biogenic silica (diatoms), originating minerals in total or partial equilibrium within the new conditions. The autigenic minerals are pyrite, smectite, K-feldspars, halite, gypsum, jarosite beyond quartz and remobilized iron oxy-hydroxides. Mangrove sediments present high grades of dissolved sulfide ions (6 to 40 mmol/L) while in depth, sulfate ions are consumed. Dissolved sulfide is formed from organic matter mineralization under bacteriological sulfate-reduction, which final product is the pyrite. In depth, total dissolved iron grades are reduced close to zero due to the reaction with part of the dissolved sulfide to form solid sulfide (pyrite). This reaction occurs in an extremely reductor chemical environment (-200
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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Permo-triássico da Bacia do Parnaíba, Norte do Brasil: implicações paleoambientais, paleoclimáticas e paleogeográficas para o Pangea ocidental
(Universidade Federal do Pará, 2016-06-03) ABRANTES JÚNIOR, Francisco Romério; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permo-Triassic was marked by the great mass extinction of geological Earth history with losses of 90-95% of marine and terrestrial species. These were related to paleogeographic and paleoclimatic changes in part assigned to catastrophic events. In the end of Permian, arid conditions prevailed around the world as a consequence of eustatic sea level fall added to disappearance of glacial areas and large-scale closed basins multiplication. These conditions combined with the intense continentalization of Pangea supercontinent led to desertification with the development of large desert and sabka complexes. In the northern of Brazil the records of these events are found in intracratonic basins, particularly in the Parnaíba Basin. This is represented by siliciclastic-evaporitic succession from Balsas Group compound by Pedra de Fogo, Motuca and Sambaíba formations. It was recognized seven facies associations: (1) Lacustrine mudflat dominated, represented by greenish/reddish gray laminated mudstones interbedded with fine-grained sandstones and great chert content; (2) Marginal dune fields consisting of planar cross-stratified beds of fine- to medium-grained sandstones; (3) Perennial playa lake consisting dominantly of red laminated mudstones with discontinuous layers of sigmoidal sandstones; (4) Saline mudflat / Saline pan represented by reddish laminated mudstones interbedded with lenses of gypsum, limestone, and marl; (5) Sand sheet laterally consisting of continuous fine- to medium-grained sandstones with convoluted lamination, synsedimentary faults/microfaults and adhesion structures; (6) Dune fields formed by fine- to medium-grained sandstones with large-scale cross-bed sets; and (7) Volcanic plain, consisting of basalts interbedded with sandstones. During Middle Permian, the alternating between continental sabkha mudflats and shallow to deep lacustrine phases occurred in large plains in the tropical zone of western to central Pangea (AF1). This cyclicality reflected the seasonal wet and dry phases triggered by changes in the water level, low subsidence rate and narrow accommodation space. The prolonged dry stages were characterized by the advance of the marginal dune fields (AF2) as well as by establishment of large dry mudflats. In the Upper Permian, the continuous amalgamation process of supercontinent Pangea led to the uplift of central and equatorial regions resulting in the retreat of epicontinental seas. However, there were the appearance of large-scale closed basins (AF3) and extremely acid saline ephemeral lakes with saline mudflats and pans (AF4). Petrographically, the evaporate from saline pans display primary features of precipitation to eodiagenetic of gypsum and anidrite posteriorly affected by telodiagenetic processes. The extreme aridity conditions favored the decline of these great lakes and the definitive implementation of Triassic Erg. Sand sheets occurred in the marginal portion of this Erg, containing abundant ephemeral ponds and humid regions (AF5). Large dune fields advancing as consequence of the sediment availability increase, while deflation surfaces were produced by partial removal of sediment supply (AF6). The total interruption of sediment supply to the Erg in the Late Triassic provided an extreme and regional deflation surface overlapping by eojurassics volcanic rocks (AF7). The deformational analysis of the studied succession identified three different synsedimentary deformational levels at least: (I) brittle-ductile hybrid features in the contact zone between the Motuca and Sambaíba formations; (II) folds and medium-sized convolution in the middle portion of the eolic strata of Sambaíba Formation; (III) Injectites in the intertraps sandstones from Mosquito Formation. These three levels of deformed layers are separated by non- or slightly-deformed strata intervals, laterally may show a gradual increase of deformation intensity. The deformation level I occurs in the contact zone between Motuca and Sambaíba formations represented by a set of hybrid (brittleductile) features. Lateral continuity of this interval for hundreds of kilometers added to the increase in the deformation degree in the Riachão area. Furthermore, the anomalous concentration of trace elements (Cr, Co, Cu, Mn, Au, Pd, and Pt) are consistent with earthquakes of high magnitude probably product of meteoritic impact (Riachão structure). The level of strain II is marked by a set of inharmonious folds in the middle part of Sambaiba Formation. These are originated by autociclic processes related to hidroplastic deformation of sediments of sediments by dunen/draas migration and overweight. The third interval it is composed by sandstone dikes in an eojurassic volcanic rocks of Mosquito Formation. These dams were formed by hydraulic injections of sand leading to a thermal gradient increase induced by basic magmatic activities during the pre-rift phase in the Western Pangea.
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Proveniência de depósitos albianos do grupo Itapecurú (Bacia de São Luis - Grajaú) com base em petrografia, paleocorrentes, geoquímica e idades de zircão detrítico
(Universidade Federal do Pará, 2006-06-23) NASCIMENTO, Marivaldo dos Santos; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136; GÓES, Ana Maria; http://lattes.cnpq.br/2220793632946285
The Albian deposits comprise ca. 70% of sedimentary fill of the São Luís-Grajaú Basin, with 500 m thick in their main depocenters. The origin and sedimentary evolution of these deposits is related to the breakup of Africa and South America which led to the connection of the formerly separated Central and South Atlantic oceans, in Mesozoic time. Albian exposures in the southern border of the São Luís-Grajaú Basin, Grajaú region, represent a fluvial-deltaic succession whith six depositional environments, including: delta front (mouth) bar, distal bar/prodelta, upper shoreface/foreshore, interdistributary bay/crevasse, fluvial channel and distributary channel. They consist, mainly, of fine- to medium sandstones, as well as siltstones, mudstones and intraformational conglomerate. Palaeocurrent study, petrography and geochemistry of sandstones and heavy minerals, and detrital zircon ages were utilized to investigate the provenance of this sedimentary unit. This study was performed on sandstone samples whose modal compositions plot in the quartzarenite field indicating origin from recycled orogen and continental blocks. High proportion of quartz grains, monocrystaline and polycrystalline, as well as quartzite fragments, and rounded grains of zircon and tourmaline with a wide variety of mechanical surface textures, suggest a provenance from sedimentary rocks, and that at least part of the studied sediments are multicyclic. Chemical weathering processes is little evident as indicated by absence of solution features in these mineral grains. Therefore, the modal composition can be related to the sedimentary recycling or strong reworking on depositional environment. High CIA (Al2O3/Al2O3+K2O+Na2O+CaO*x100) values suggest transportation and recycling from sources located far away from the depositional basin, which is, in turn, consistent with a provenance from the recycled orogens and continental blocks. Based on palaeocurrent patterns and RuZi the Albian succession in the south region of the São Luís-Grajaú Basin was defined four heavy mineral zones, generically named A, B, C and D, in ascending stratigraphic order. Geochemistry of tourmaline grains indicate provenance from metapelites and metapsammites, with few contributions from granite and pegmatite. Zircon Hf patterns suggest changing of the source of these zones: Zone A is characterized by an Hf unimodal distribution, while in the Zones B, C and D, is bimodal. The staurolite shows a relatively limited amount of compositional variations. Involvement of metasediments is inferred from the presence of staurolite and kyanite in the sandstones, as well as by predominance of dravite in the tourmaline populations. Discriminant function analysis using major element compositions show that these deposits were deposited in the passive continental margin (PM). PM sediments are mainly quartz-rich, sourced from craton interiors or stable continental regions, which were deposited in intra-cratonic sedimentary basins or on passive continental margin. The Albian sediments are characterized by LREE enrichment, depletion in HREE, and negative Eu-anomaly. This REE pattern, measured to infer the provenance of sediments and their relationship with average post-Archean upper continental crust, is very consistent with this interpretation. Enriched HREE concentration in the some samples may be attributed to the presence of REE bearing heavy minerals, supported by the fact that these samples have higher concentration of Th, U and Zr, reflecting natural concentration of zircon grains. Pb-Pb geochronological analyses of 238 detrital zircon grains show a direct fingerprint of Precambrian terrains (Archean to Proterozoic) in the source. Three major zircon populations were detected: Archean (3103-2545 Ma), Paleoproterozoic (2460- 1684 Ma) and Neoproterozoic (993-505 Ma); small groups of Mesoproterozoic (1570- 1006 Ma), Paleozoic (440-540 Ma) and Mesozoic (141-314 Ma) grains are also present. The Neoproterozoic component shows an increase upwards with main peaks between 550 Ma and 650 Ma. A similar pattern is shown by the Archean interval, which exhibits a strong relative increase upwards, peaking between 2725 Ma and 2926 Ma, while Paleoproterozoic component has a distinct behavior, showing an evident decrease upwards. The potential source regions were deduced on the basis of palaeocurrent patterns and correlations of detrital zircon age from the sandstones studied with U-Pb and Pb-Pb zircon data from the basement. Our data suggest that the Albian deposits, specially those of the Zone A, were preferentially sourced from the northern and northeastern regions, including São Luís Craton, Gurupi Belt and northwestern portion of Borborema Province. Paleoproterozoic and Neoproterozoic zircon ages as those found in zircons from this zone, are very common in these basement. In contrast, the sediments of zones B, C e D were supplied from the areas located to the south, southwest and, possibly east, involving the eastern portion of the Amazonian Craton/Araguaia Belt, and Borborema Province. Metassedimentary and igneous rocks with similar zircon ages (mainly Archean) have been described in these regions. The ca. 1.0 Ga detrital zircon ages show a correspondence with the Cariris Velhos Event, widely recognized in the central portion of the Borborema Province. In summary, this study demonstrates the effectiveness of an integrated approach to provenance evaluation of Cretaceous sedimentary deposits using petrography, heavy minerals and bulk sediment chemistry, zircon ages, and palaeocurrent data.

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