Navegando por Assunto "Bacias sedimentares"

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Acesso aberto (Open Access)
Adaptação do método de Bott para contraste de densidade variando com a profundidade
(Universidade Federal do Pará, 2013-08-23) GOMES, Karina Palheta; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491; SANTOS, Darcicléa Ferreira; http://lattes.cnpq.br/5813659873067927
We present a new method to estimate the basement relief of a sedimentary basin through the analytic extension of the expression of the slab Bouguer for the case of a density contrast between the basement and the sediments decreasing monotonically with depth according to a hyperbolic law. The method requires that the noise in data have a standard deviation smaller than 0.01 mGal. The basement relief estimates are obtained at positions located directly below each observation. The methodology was applied on synthetic data from a simulated sedimentary basin presenting smooth basement relief. The method produced estimated basement topographies close to simulated basement topographies. The method was also applied to three sets of real Bouguer anomalies: Recôncavo Basin (Brazil), Büyük Menderes Graben (Turkey) and San Jacinto Graben (United States). The solutions produced by the proposed method attained maximum basement depth estimates in accordance with the available geological information: 6 km to Reconcavo Basin, 1.6 km to Büyük Menderes Valley, and 2.2 km to San Jacinto Graben.
Acesso aberto (Open Access)
Aplicação do gravímetro de poço em problemas de avaliação de formação no Brasil
(Universidade Federal do Pará, 1992-02-27) GONÇALVES, Carlos Augusto; EVANS, Hilton Bernard
The first borehole gravity survey in Brazil was carried out during October and November of 1990 in Sergipe-Alagoas basin through a joint program between the Federal University of Pará, PETROBRAS and United States Geological Survey. The principal purpose of the survey was to test the applicability of this tool in Brazilian sedimentary basins. Another purpose was to compare the borehole gravimeter (BHGM) data with existing open-hole density log (CDL). The survey was conducted in three wells in Carmópolis field and the data were transformed to miligals, corrected for tide, drift and terrain effects and preliminary density values calculated. The region in which the surveys were carried out consists of an evaporite sequence overlying basement rock ocurring relatively near the surface. The large contrast between these units and the rest of sedimentary section results in vertical gravity anomalies. It is necessary to correct the BHGM density data for these anomalies. The resulting BHGM density data were then compared to that obtained from the CDL. Furthermore, lithology parameters defined from well log data were used to calculate porosities from both the BHGM and CDL density data, showing possible new oil intervals that can be tested.
Acesso aberto (Open Access)
Atenuação de múltiplas pelo método WHLP-CRS
(Universidade Federal do Pará, 2003-01-28) ALVES, Fábio José da Costa; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617
In the sedimentary basins of the Amazon region, the generation and accumulation of hydrocarbons is related to the presence of diabase sills. These rocks present a great impedance contrast to the host rocks what turns to cause the generation of internal and external multiples with similar amplitudes the primary events. These multiples can predominate over the information originated at the deeper interfaces, making more difficult the processing, interpretation and imaging of the seismic section. In the present research work, we conducted de multiple attenuation in synthetic commonsource (CS) seismic sections by combining the Wiener-Hopf-Levinson for prediction (WHLP) and the common-reflection-surface-stack (CRS) methods. We denominated this new combination under the name and label of WHLP-CRS method. The deconvolution operator is calculated from the real amplitudes of the seismic section trace-by-trace, and this strategy represents efficiency in the process of multiples attenuation. Multiples identification is carried out in the zero-offset (ZO) section simulated by the CRS-stack applying the periodicity criteria between the primary and its repeated multiples. The wavefront attributes, obtained by the CRS-stack, are employed to move the shifting windows in the timespace domain, and these windows are used to calculate the WHLP-CRS operator for the multiple attenuation carried out in the CS sections. The development of the present research had several intentions as: (first) avoid the inconveniencies of the processed ZO section; (second) design and apply operators in the CS configuration; (third) extend the WHL method to curved interface; (fourth) use the good results obtained in the new CRS-stack technology whose application extends to migration, tomography, inversion and AVO.
Acesso aberto (Open Access)
Evidências geofísicas e geológicas da CAMP nas bacias sedimentares do Pré-Cambriano e Fanerozoico do sul do Cráton Amazônico.
(Universidade Federal do Pará, 2019-03-16) REZENDE, Gabriel Leal; MARTINS, Cristiano Mendel; http://lattes.cnpq.br/8303640454649778; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The sedimentary basins in the Southwestern Tocantins and Southern Tapajós provinces were affected by the emplacement of large Triassic-Jurassic basaltic rocks volumes termed as Central atlantic Magmatic Province (CAMP), result of the Pangea break up and opening of the Central Atlantic Ocean. Two basins, object of this study, were implanted over Tonian metamorphic rock of the Northern Paraguay Belt and Paleo to Mesoproterozoic rocks of the Amazonian Craton: 1) the Paleozoic Parecis Basin; and 2) the Late Cryogenian-Ordovician Intracratonic Basin or Araras-Paraguay Basin, afterwards inverted during the Ordovician. The mapped basalt exposed locally in these basins reach 5 % in volume, being the most ocurrences at the Chupinguaia and Tangará da Serra regions, states of Mato Grosso and Rondônia, respectively. These exposed basalts are not compatible with the great volume and magnitude related to the CAMP, which have motivated the research in subsurface of other occurrences. The reinterpretation of previous geophysical and geological methods combinated with a crustal modelling allowed a new interpretation to the gravity field related to the intracrustal density contrast or residual gravimetric field for this part of Amazonia Craton. The anomaly in this field allowed to identify higher density bodies within the Paleozoic Parecis and Araras-Paraguai basins, interpreted as continental tholeiitic flood basalts associated to the CAMP, reaching a volume 3 million of km3. The study of the residual gravimetric anomaly based on crustal modelling applied here can be effective to guide future works in the mapping in subsurface of highly density rocks associated to the basalts, allowing to obtain the probable distribuition in area and contributing for a better understanding about the magmatic events of the CAMP in sedimentary basins.
Acesso aberto (Open Access)
Interpretação de perfis dos carbonatos fraturados da Bacia do Pará-Maranhão
(Universidade Federal do Pará, 1991-09-27) LARANJEIRA, Alberto Antônio dos Santos; EVANS, Hilton Bernard
The purpose of this study is to present an evaluation of the Tertiary carbonate sequence in the Pará-Maranhão basin, based on the interpretation of well logs. Two wells, X and Y, were selected to be studied. The data processing was carried out using the LOGCALC software facilities installed on the Petrobrás IBM-3090 computer, and also the DLPS routines of the VAX-8600 at the Universidade Federal do Pará. Three distinct carbonate rock types were identified. The discrimination of these lithotypes allows a close control of the matrix parameters, and better volumetric estimates (porosities and saturations). The evaluation of porosities and saturations is difficult in this area because of the characteristics of the carbonate rocks: the lithology is complex, the water salinity is low, about 10,000 ppm equivalent NaCl, the matrix density is high, and the carbonates are fractured. The fractures strongly influence the logging tool responses, including the fracture identification log, the porosity logs, the resistivity logs, and the spectral gamma logs of 1-PAS-11 well. These fractures also cause the porosity exponent, m, to be low, less than 1.5, a value generally related to fractured rocks. Models developed by Rasmus (1983) and by Porter et al.(1969) were tested for the saturation estimates. The Archie relationship, with characteristic values for a and m, was also applied in this study. In the fractured zones, the variable porosity exponent gives better results than other models, for calculating water saturations. Thus, we can locate and evaluate the fracture zones by using the Archie relationship with the variable porosity exponent, mR, from the Rasmus model, referred to in this study as Rasmus saturation.
Acesso aberto (Open Access)
Inversão de dados sísmicos de reflexão a partir da curva do tempo de trânsito
(Universidade Federal do Pará, 2007) PENHA, Lidiane Nazaré Monteiro; GOMES, Ellen de Nazaré Souza; http://lattes.cnpq.br/1134403454849660; LEITE, Lourenildo Williame Barbosa; http://lattes.cnpq.br/8588738536047617
The present Masters Thesis had for objective the study of the seismic inversion problem based on flat reflectors for common-source (SC) and common- mid-point (CMP) gathers. The forward model is described by homogeneous, isotropic, plane horizontal layers. The problem is related to the NMO stack based on the optimization of the semblance function, for CMP sections corrected for moveout time. The study was based on two principles. The first principle adopted was the combination of two groups of inversion methods: A global and a local method. The second principle adopted was stripping according to the Wichert-Herglotz-Bateman theory, that establishes that to know a lower layer it is necessary to know first the upper layer. The application of the study aims at the seismic simulation of the terrestrial Solimões and marine sedimentary basins to obtain a 1D distribution of velocity and layer thicknesses of the subsurface of target horizons. In this sense, we limited the inversion experiments to 4 to 11 reflectors, once in practice the industry limits the interpretations to be to about one same number of 3 to 4 main reflectors. Stands out that this model is applicable as initial condition to the imaging of seismic sections in geologically complex regions wit h slow lateral variation of velocities. The synthetic data was produced based on geological information that corresponds to strong a priori information for the inversion model. For the construction of models related to the projects in progress, we analyzed the following relevant subjects: (1) Geology of sedimentary basins terrestrial Solimões and marine (stratigraphy, structural, tectonics and petroliferous); (2) Physics of the vertical and horizontal seismic resolution; and (3) Temporal-spatial discretization of the multi-coverage cube. The inversion process is dependent on the discretization of the wave field in time-space, on the physical parameters of the seismic survey, and of further on the resampling in the multiple coverage cube. The direct model us ed corresponds to the case of the NMO (1D) stack operator, considering a flat observation topography. The basic criterion taken as reference for the inversion and curve fit is the norm 2 (quadratic). The inversion using the simple present model is computational attractive for being fast, and convenient for allowing several other techniques be included with a logical physical interpretation; e.g., the Fresnel projected zone (ZFP), the direct calculation of the spherical divergence, Dix inversion, linear inversion by reparametrization, a priori information, and regularization. The ZFP shows to be a useful concept to establish the aperture of the spatial inversion window in the time-distance section. The ZFP represents the influence of the data in the horizontal resolution. The estimative of the ZFP indicates a minimum aperture based on an adopted model. The spherical divergence is a smooth function, and it has physical basis to be used in the definition of a data weight matrix for tomographic inversion methods. The necessity of robustness in the inversion can be analyzed in seismic sections (CS and CMP) submitted to filtering (corners frequencies: 5; 15; 75; 85; pass-band trapezoidal), where one can identify, compare and interpret the information contained. From the sections, we conclude that the data are contaminated with isolated points, what proposes methods in the class considered as robust having as reference the norm 2 (least-square) of curve fitting. The development of the algorithms used the FORTRAN 90/95 programming language, the program MATLAB for presentation of results; and the package CWP/SU for synthetic seismic modeling, picking of events and presentation of results.
Acesso aberto (Open Access)
Inversão gravimétrica do relevo de bacias extencionais através da variação total
(Universidade Federal do Pará, 2009) LIMA, Williams Almeida; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
We present a gravity inversion method to reconstruct the discontinuous basement relief of a sedimentary basin, whose density contrast between the basement and the sediments is constant, or decreases monotonically with depth, and known. The solution is stabilized using the total variation functional (VT), which does not impose smoothness on the solution. We compare the proposed method with the global smoothness (SG), weighted smoothness (SP) and entropic regularization (RE) methods using synthetic data produced by 2D and 3D basins presenting discontinuous relief. The solutions obtained with the proposed method were better than those obtained with SG and similar to the ones produced by SP and RE. Differently from SP, however, the proposed method does not require a priori knowledge about the basin maximum depth. As compared with RE, the present method is operationally simpler and requires the specification of just one regularization parameter. The VT, SG, and SP methods were also applied to the following areas: Ponte do Poema (UFPA), Steptoe Valley (Nevada, United States), San Jacinto Graben (California, United States) and Büyük Menderes (Turkey). Almost all those areas are characterized by the presence of highangle faults. In all cases, the VT produced basement relief estimates presenting sharp, high-angle discontinuities, in accordance with the tectonic setting of the areas.
Acesso aberto (Open Access)
Inversão gravimétrica do relevo do embasamento usando regularização entrópica
(Universidade Federal do Pará, 2007) OLIVEIRA, Alexandre de Souza; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
We present a new gravity inversion method, which estimates the basement relief of a sedimentary basin, whose sediments may present a constant or a decreasing density contrast with depth relative to the basement. The method combines the minimization of the first-order entropy measure with the maximization of the zeroth-order entropy measure of the solution vector (depths to the basement). The interpretation model consists of a set of rectangular juxtaposed vertical prisms with known density contrasts and whose thicknesses represent the depths to the basement relief and are the parameters to be estimated. The minimization of the first-order entropy favors solutions presenting abrupt discontinuities, and the maximization of the zeroth-order entropy is employed just to prevent its excessive minimization. We applied our method to synthetic data simulating: (i) intracratonic basins with smooth or discontinuous relief, and (ii) faulted marginal basins. In the case of a smooth basement relief, it was well delineated by the entropic regularization, and by the global and weighted smoothness. In the case of a faulted basement, either in intracratonic or marginal basins, the entropic regularization and the weighted smoothness delineated the basement relief with good precision, differently from the global smoothness. The entropic regularization, however, did not require the knowledge of the basin’s maximum depth. We applied our method to four sets of real Bouguer anomalies. The first one comes from a profile across a bridge located in the campus of the Federal University of Pará, Belém. The solution delineated the known, discontinuous topography below the bridge. The second set comes from the northern portion of Steptoe Valley, Nevada. The solution delineated a discontinuous basement relief in accordance with the known geological setting of the area. The third set comes from the San Jacinto graben, situated in California, United States. The solution indicated an asymmetric graben, as already reported by other authors. The fourth data set comes from the Büyük Menderes graben, western Turkey. The solutions presented large vertical displacements on the northern border, which is confirmed by geological information.
Acesso aberto (Open Access)
Inversão gravimétrica estável do relevo da base e da variação da densidade com a profundidade em aterros sanitários
(Universidade Federal do Pará, 2003-10-21) TEIXEIRA, Wlamir Abreu; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
The present method assumes a decrease in the density contrast of a sedimentary basin according to a hyperbolic law in a waste landfill and uses two approaches: (1) the estimation of the bottom of a waste landfill assuming that the gravity anomaly, the density contrast at the surface and the decaying factor of the density contrast with depth are known; (2) the estimation of the density contrast at the surface and of the decaying factor of the density contrast with depth, assuming that the gravity anomaly and the relief of the waste landfill bottom are known. A variation of the latter approach consists in using the known depth values to the landfill bottom to produce a fitted gravity anomaly and estimate the density contrast at the surface and the decaying factor of the density contrast with depth via minimization of the Euclidean norm of the residual vector between the observed and fitted anomalies. In both cases the interpretation model is a set of vertical rectangular 2D prisms whose thicknesses are parameters to be estimated and represent the depth to the interface separating sediments and basement. The solutions of both problems are stable because of the incorporation of additional a priori information about the smoothness of the estimated relief. The presented method was applied to synthetic data produced by simulated waste landfills having maximum depth to the bottom smaller than 15 m and presenting smooth relief. The results were consistent and demonstrated the effectiveness of the method in both approaches. The method was also applied to the residual Bouguer anomaly from the Thomas Farm, Indiana, USA, leading to the conclusion that the density contrast of the landfill is either constant or present a maximum variation of about 0.09 g/cm3.
Acesso aberto (Open Access)
Inversão gravimétrica estável do relevo do embasamento e da variação da densidade com a profundidade em bacias sedimentares
(Universidade Federal do Pará, 2003-10-21) COSTA, Denis Carlos Lima; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
The present method assumes a decrease in the density contrast of a sedimentary basin according to a hyperbolic law and has two objectives: (1) to estimate the basement relief of the sedimentary basin assuming that the gravity anomaly, the density contrast at the surface and the decaying factor of the density contrast with depth are known; (2) to estimate the basement relief, the density contrast at the surface and the decaying factor of the density contrast with depth, assuming that the gravity anomaly and the depth to the basement at a few points are known. In both cases the interpretation model is a set of vertical rectangular 2D prisms whose thicknesses are parameters to be estimated and represent the depth to the interface separating sediments and basement. The solutions of both problems are stable because of the incorporation of additional a priori information about the smoothness of the estimated relief and about the depth to the basement at a few locations, presumably provided by boreholes. The method was tested with synthetic gravity anomalies produced by simulated sedimentary basins presenting smooth relief. The results showed well-resolved estimated relieves. Besides, estimated density contrasts at the surface and the decaying factors of the density contrast with depth close to the true ones were obtained, indicating the potentiality of the proposed method in gravity interpretations of sedimentary basins. The method was applied to the Bouguer anomaly from Recôncavo Basin, producing an estimated relief with a maximum depth of 6 km, a figure similar to the one obtained from seismic interpretations. The estimates of the surface density contrast and of the decaying factor of the density contrast with depth were -0.30 g/cm3 and 30 km, respectively, producing an estimate of 4% for the maximum sediment compaction.
Acesso aberto (Open Access)
Inversão gravimétrica rápida do relevo do embasamento aplicando o funcional da variação total
(Universidade Federal do Pará, 2013-08-23) SANTOS, Raphael Di Carlo Silva dos; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491; SANTOS, Darcicléa Ferreira; http://lattes.cnpq.br/5813659873067927
We present a new 2D linear inversion gravity method to estimate the discontinuous basement relief of a sedimentary basin. The method uses an interpretation model consisting of a set of 2D juxtaposed horizontal ribbons whose thicknesses are the parameters to be estimated. The density contrast between the basement and the sediments is assumed constant and known. The estimates of the thicknesses were stabilized with the Total Variation functional (TV) which permits solutions presenting local discontinuities in the basement relief. The estimates of the basement relief are produced by solving a single linear system of equations in the L1 norm. Because linear inversion methods underestimate the depth of the basement relief for sedimentary basins thicker than 500 m, we amplify the depth estimates through by modifying the matrix associated with the interpretation model. This procedure in general leads to overestimated depths which are corrected through the expression of the anomaly of a Bouguer slab. Tests on synthetic and real data produced similar results as compared with the nonlinear method, but required less computational time. The ratio R between the computational times required by the nonlinear and the proposed methods to produce similar solutions increases with the number of observations and parameters. For example, for 60 observations and 60 parameters R is equal to 4 whereas for 2500 observations and 2500 R increases to 16.8. The proposed method and the nonlinear inversion method were also applied to real gravity data from Steptoe Valley, Nevada, U.S.A. and from Ponte do POEMA at the Campus of Guamá, in Belém, producing solutions which are similar to the ones produced by the nonlinear method but required a smaller computer time.
Acesso aberto (Open Access)
Investigação por eletroresistividade de ambientes cársticos no município de São João de Pirabas - PA
(Universidade Federal do Pará, 1996-04-25) LOPES, Eduardo Salgado; RIJO, Luiz; http://lattes.cnpq.br/3148365912720676
This Thesis discusses the investigation of karst regions using vertical eletrical soundings and dipole-dipole resistivity surveys. The studied area is localized in the northeast of state of Pará, in the district of São João de Pirabas. In this place, during the drilling of water well, the exploration crew from Fundação Nacional de Saúde, faced some problems due to the presence of cavities in the limestone of the Pirabas Formation. In order to analyse this problem, we carried out vertical eletrical soudings using the Schulumberger array. The maximum lenght of AB/2 used was 600 meters. The apparent resistivity sounding curves were initially interpreted with a 1D model computer program. The eletrical soundings located near the well in which karst cavities detected, were interpreted with a 2D model computer program. The algorithm used in the 2D program was the finite element method. The results of the interpretation of eletrical soundings of many models show that the anomalies of resistivities due the presence of karst cavities are very small. Therefore, the method of Schulumberger eletrical soundings does not have enough resolution to identify precisaly the presence of karst cavities at the subsurface. On the other hand, the numerical results for the dipole-dipole surveys show that the technique is by far more efficient than Schulumberger soundings for detection of karst cavities. However, the dipole-dipole method is much more dificult and expensive to be carried out in the field than the Schlumberger sounding method. Also, its interpretation is much more elaborated than the Schlumberger soundings.
Acesso aberto (Open Access)
Mapeamento do relevo do embasamento de bacias sedimentares através da inversão gravimétrica vinculada
(Universidade Federal do Pará, 1998-03-02) BARBOSA, Valéria Cristina Ferreira; MEDEIROS, Walter Eugênio de; http://lattes.cnpq.br/2170299963939072; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
We present three new stable gravity inversion methods to estimate the relief of an interface separating two media. Solution stability is attained by introducing a priori information about the interface, through the minimization of one (or more) stabilizing functional. These methods are, therefore, characterized by the physical and geological information incorporated to the problem. The first method, named global smoothness, estimates the depths to the interface at discrete points by assuming that the density contrast between the media is known. To stabilize the inverse problem, we introduce two different constraints: (a) proximity between the true and estimated interface depths at a few isolated points, and (b) proximity between the estimated depths at adjacent points. The combination of these two constraints impose a uniform degree of smoothness all over the estimated interface, minimizing, simultaneously, the misfit between the known and estimated depths at a few boreholes, for example. The second method, named weighted smoothness, estimates the interface depths at discrete points, assuming that the density contrast is known a priori. In this method, it is incorporated the information that the interface is smooth almost everywhere, but at a few fault discontinuities. To incorporate this attribute to the estimated relief, we developed an iterative process where three kinds of constraints are imposed on parameters: (a) weighted smoothness between values of adjacent parameters, (b) lower and upper bounds on the estimated depths, and (c) proximity between the values of the parameters and a known numerical value. Starting with an initial solution produced by the global smoothness method, this method enhances initially estimated geometric features of the interface; that is, flat areas will tend to become flatter and steep areas will tend to become steeper. This is accomplished by weighting the constraints which require proximity between adjacent parameters. The weights are updated at each iteration so as to enhance the discontinuities detected in a subtle way by the global smoothness method. Constraints (b) and (c) are used both to compensate for the decrease in solution stability due to the introduction of small weights, and to reinforce flatness at the basin bottom. Constraint (b) imposes that any depth be nonnegative and smaller than an a priori known maximum depth value whereas constraint (c) imposes that all depths be closest to a value deliberately violating the maximum depth. The trade-off between these conflicting constraints is attained with a final relief presenting fiat bottom and steep borders. The third method, named minimum moment of inertia, estimates the density contrasts of a subsurface region discretized into elementary prismatic cells. It incorporates the geological information that the interface to be mapped encompasses an anomalous source which besides presenting horizontal extents much larger than its largest vertical extent, exhibits bordes dipping either vertically or toward the center of mass, and that most of the anomalous mass (or mass deficiency) is concentrated, in a compact way, about a reference level. Conceptually, these information are introduced through the minimization of the moment of inertia of the anomalous sources with respect to a reference level coinciding with the mean topographic surface. This minimization is performed in a subspace of parameters consisting of compact sources and presenting bordes which dip either vertically or toward the ce4ter of mass. Effectivelly, these informations are introduced by means of an iterative process starting with a tentative solution dose to the null solution, and adds, at each iteration, a contribution which has minimum moment of inertia with respect to the reference level, in such a way that the estimate of the next iteration does not violate the bounds on the density contrast and minimizes, at the same time, the misfit between the observed and the fitted data. Additionally, the iterative process "freezes" a density estimate if it becomes very dose to either bound. The final solution at the end of the iterative process is an estimated solution exhibiting a compact mass distribution concentrated about the reference level, whose density contrast distribution is dose to the upper (in absolute value) bound established a priori. All three methods were applied to synthetic and field gravity data, produced, respectively, by simulated and real sedimentary basins. The global smoothness method produced a good reconstruction of the basin structural framework even when the true basements were not globally smooth, as was the case of the Recôncavo Basin, Brazil. This method presents, however, the lowest resolution as compared with the other two methods. The weighted smoothness method improved the resolution of basements presenting disontinuities produced by gravity faults with large vertical offsets. It is, therefore, potentially useful in interpreting the structural framework of extensional basins as illustrated both with synthetic data and data from the Steptoe Valley, Nevada, USA and from Recôncavo Basin, Brazil. The minimum moment of inertia method was also applied to synthetic data and data from Recôncavo Basin and from San Jacinto Graben, California, USA. The results showed that, as compared with the other two methods, this method produces excellent estimates of a basement relief consisting of several adjacent discontinuities with small vertical offsets. This is a remarkable advantage over the weighted smoothness method which requires that the interface present few, local discontinuities with large vertical offsets.
Acesso aberto (Open Access)
Paleogeografia e paleoambiente de depósitos siliciclásticos da transição Mississipiano-Pensilvaniano da Bacia do Parnaíba.
(Universidade Federal do Pará, 2019-05-17) XAVIER, Mateus Fernandes da Silva; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The formation of the supercontinent Pangea in the passage from the Pennsylvanian period to the Mississipian led to profound changes in the sedimentation and behavior of Paleozoic sedimentary basins in the Gondwana. Orogenies resulted to expressive uplifts. One of the orogenies that affected the northern portion of Gondwana is related to the collision of Gondwana rith Laurásia that generated the Eo-Hercynian event in 320 Ma. Currently, this orogeny is related as the main responsible for the discordance present in several Paleozoic basins throughout the Gondwana. In order to test the influence of the Hercynian Orogeny in the paleogeographic and paleoenvironmental configuration, seven columnar profiles were studied on the southern, western and eastern edges of the Parnaiba Basin, where 19 facies were divided into 3 facies associations: delta front and plataform influenced by storm waves from the Poti Formation and braided fluvial from the Piaui formation. This study used facies modeling, petrography for classification of sandstones and provenance, quartz cathodoluminescence and paleocurrent analysis. The Poti Formation deposits are constituted of delta front bars with lobes dominated by sandstone facies with sigmoidal cross stratification and at the top, deltaic abandonment deposits and marine reworking. The braided fluvial deposits were divided into three architectural elements for a better understanding of their evolution. The laterally and vertically amalgamated channel-fill elements occur in the most proximal part of this system, where they have high energy and bedload transport. The non-amalgamated channel filling elements and overbanks deposits occur in the medial parts of the Piaui system, where the energy is lower when compared to proximal regions, and sediment transport is carried out by mixed load. In the medial regions there is the preservation of deposits of overbank. Paleocurrent and provenance data point to a fluvial system that migrates to NE-NW, where the main vector is north. During the Pensilvanian, the Piauí fluvial system dominated the northesat of the Gondwana migrating towards the epicontinental seas of this period, with source areas to the south od the Parnaiba Basin. It is accepted that the Carboniferous discordance would be related mainly to glacial-eustatic movements, related to the first peak of accumulation of Late Paleozoic Ice Age (LPIA) and the development of the fluvial system would be being supplied by melting waters, explaining thus the development of a perennial fluvial system in the midst of a desert system.
Acesso aberto (Open Access)
Reconstrução paleoambiental e estratigráfica de depósitos cretáceos e terciários expostos na borda sudeste da sub-bacia de Cametá, norte do Brasil
(Universidade Federal do Pará, 2002-04-01) SANTOS JÚNIOR, Antonio Emídio de Araújo; ROSSETTI, Dilce de Fátima; http://lattes.cnpq.br/0307721738107549