http://localhost:8080/tede/handle/tede/3 2026-04-20T14:13:10Z http://localhost:8080/tede/handle/tede/200 “ANÁLISE CICLOESTRATIGRÁFICA DOS DEPÓSITOS SEDIMENTARES DA BACIA POTIGUAR DURANTE O INTERVALO CENOMANIANO-TURONIANO” Evelyn Paiva do Nascimento, Evelyn Paiva do Nascimento Daniel Ribeiro Franco, Daniel Ribeiro Franco Exploratory sedimentary basins require continuous chronostratigraphic refinement. However, in continental settings, this remains challenging due to the complex and dynamic erosional processes of fluvial and fluvio-estuarine systems, which often obscure the depositional record. Consequently, investigating the influence of orbital cycles - an approach that can aid in refining chronostratigraphic frameworks - in these records is also a challenge. As a result, studies on this topic are relatively uncommon in the literature, despite the growing recent interest from the scientific community. In this context, the fluvio-estuarine deposits of the Açu Formation, in the Potiguar Basin - an important exploratory basin located on the Brazilian equatorial margin - represent an special sedimentary archive in which T-R cycles can be traced laterally for tens of kilometers. This makes them an interesting subject for cyclostratigraphic analysis in non-marine environments. This study investigates the influence of orbital forcing on the Açu Formation, correlate cycles influenced by orbital variations in the wells, and establish the preserved time interval through the construction of an Astronomical Time Scale (ATS). Cyclostratigraphic analyses were performed using time series techniques on gamma-ray logging data from three wells, focusing on two third-order sequences deposited from the Cenomanian-Turonian boundary (approximately 101 to 93 million years ago). Statistical methods including correlation coefficient (COCO) and the null hypothesis (H0), were applied to determine the ideal sedimentation rate (SAR) and test the record of astronomical cycles. The Integrated Error Prediction Filter Analysis (INPEFA) was used to identify trends in the sedimentary record, improving the correlation of matching cycles. The cyclostratigraphic results demonstrate the imprint of orbital forcing on the sedimentary deposits, consistent with the astronomical solutions for the Cenomanian-Turonian interval. The inferred sedimentation rates range from approximately 3 to 8 cm/kyr, consistent with similar depositional environments. The identification of spectral bands corresponding to the long eccentricity cycle (405 ka) allowed for the construction of a floating ATS for the Cenomanian-Turonian interval in the basin and the estimation of the recorded time. Since the good preservation of orbital signals in fluvio-estuarine environments is uncommon - limiting the number of cycle-stratigraphic studies - this research provides important insights into the behavior of orbital signals and basin filling in this type of paleoenvironment. Furthermore, as this interval includes hydrocarbon-bearing deposits, the findings contribute to the advancement of cyclostratigraphic studies in exploratory basins, with potential applications for chronostratigraphic correlation. Observatorio Nacional Dissertação 2025-06-13T00:00:00Z http://localhost:8080/tede/handle/tede/197 MULTISCALE INVERSION OF ONSHORE-OFFSHORE ELECTROMAGNETIC DATA FROM SOUTHEAST BRAZIL AND SANTOS BASIN SANTOS BENEVIDES, ARTUR FONTES, SERGIO LUIZ In this work, magnetotelluric (MT) and Controlled Source Electromagnetic (CSEM) methods have been used to assess the deep and shallow geoelectrical nature of the Earth underneath Southeastern Brazilian onshore margin and the adjoining offshore Santos basin (SB). It was investigated the Southern Brasilia and Ribeira Orogenic Belts (BROB) and SB underlying lithosphere by three-dimensional MT imaging using 174 amphibious MT dataset. 3D conductivity models reveal the presence of a highly heterogeneous crust in BROB, whereas it is uniformly resistive below the SB continental shelf region. A resistive segmented layer (of about 60-80 km), and another moderately resistive lower layer (of 80-100 km) are key features of the lithosphere. Excepting the above, a steeply dipping sub-lithospheric conductor is associated with a confined asthenosphere upwelling and might be related with the surface deformation hills of BROB below the coast-parallel São Paulo-Rio de Janeiro dyke swarms. Deep lithospheric roots of ~200 km were found beneath part of BROB, which is thinning out to be ~75 km below the SB continental shelf and probably becomes thinner towards the deeper ocean coincident with the lithosphere-asthenosphere boundary (LAB) found in seismic tomography, speculating that the opening of the South-Atlantic Ocean probably uplifted the lithosphere underneath it. It is also investigated the relationship between deep crustal structure and the deformation in the overlying sedimentary wedge in SB and evolution of the salt-related ‘Albian Gap’. It was found beneath this wedge, the resistive continental crust is ~35 km thick across the Cretaceous hinge line and thereafter thins seaward to ~21 km over a lateral distance of ~80 km defining a domain of highly extended and faulted crust. The models show a mantle-associated basement high and evidence of significant dislocation of the overlying sedimentary wedge which spatially coincides with the Albian Gap and a previously proposed Moho high. This implies a coupled deformation of the basement and the sedimentary wedge. It is proposed that magmatism or lower crustal flow may have played a significant role in the inferred displacement at the Albian Gap. Finally, it is presented a CSEM processing workflow from a data set recently public available in SB intesecting the main MT profile. A methodology involving joint inversion of MT and CSEM data incorporating a practical weighting scheme and constraints is also employed resulting in better data fit and enhanced electromagnetic images that are validated through geological considerations. Observatorio Nacional Tese 2023-12-13T00:00:00Z http://localhost:8080/tede/handle/tede/196 CAMADA EQUIVALENTE CONVOLUCIONAL PARA PROCESSAMENTO DE DADOS POTENCIAIS TAKAHASHI TOMAZELLA, DIEGO COELHO DE OLIVEIRA JUNIOR, VANDERLEI We have developed an efficient and very fast equivalent-layer technique for gravity and magnetic data processing by modifying the forward problem calculation of an iterative method grounded on excess mass constraint that does not require the solution of linear systems and of the conjugate gradient least squares algorithm, respectively, using a discrete convolutional method. Taking advantage of the Block- Toeplitz Toeplitz-block (BTTB) structure of the sensitivity matrix, that raises when regular grids of observation points and equivalent sources (point masses or dipoles) are used to set up a fictitious equivalent layer, we have developed an algorithm which greatly reduces the number of floating-point operations (flops) and computer memory necessary to estimate a 2D physical property distribution over the equivalent layer. The structure of the BTTB matrix can be written by using only the elements of the first column of the sensitivity matrix, which in turn can be transformed into a block-circulant circulant-block (BCCB) matrix. Likewise, only the first column of the BCCB matrix is needed to reconstruct the full sensitivity matrix completely. Also, from the first column of BCCB matrix, its eigenvalues can be calculated using the 2D Fast Fourier Transform (2D FFT), which can be used to readily compute the matrix-vector product of the forward modeling in the fast equivalent-layer technique. As a result, our method is efficient to process very large datasets. Tests with synthetic data demonstrate the ability of our method to satisfactorily use the estimated equivalent sources for data processing, for example, upward-continuing the gravity and magnetic data. Our results show very small border effects and noise amplification compared to those produced by the classical approach in the Fourier domain. For the gravity case, our synthetic results show that while the running time of our method is ≈ 30.9 seconds for processing N = 1, 000, 000 observations, the iterative method grounded on excess mass constrain spent ≈ 46.8 seconds with N = 22, 500. A test with field data from Caraj ́as Province, Brazil, illustrates the low computational cost of our method to process a large data set composed of N = 250, 000 observations. Synthetic tests for magnetic data with a mid-size 100×50 grid of total field anomaly data show a decrease of ≈ 104 in floating-point operations and ≈ 25× in computation runtime of our method compared to the classical approach of solving the least-squares normal equations via Cholesky decomposition. Faster results are obtained for millions of data, showing drastic decreases in computer memory usage and runtime, allowing to perform magnetic data processing of large data sets on regular desktop computers. Our results also show that, compared to the classical Fourier approach, the magnetic data processing with our method requires similar computation time, but produces significantly smaller border effects without using any padding scheme and also is more robust to deal with data on irregularly spaced points or on undulating observation surfaces. A test with 1, 310, 000 irregularly spaced field data over the Caraj ́as Province, Brazil, confirms the efficiency of our method by taking ≈ 385.56 seconds to estimate the physical-property distribution over the equivalent layer and ≈ 2.64 seconds to compute the upward-continuation. Observatorio Nacional Tese 2021-09-27T00:00:00Z http://localhost:8080/tede/handle/tede/194 MÉTODO DE ANÁLISE DE AMBIGUIDADE DA DIREÇÃO DE MAGNETIZAÇÃO REMANENTE E DA RAZÃO DE KOENIGSBERGER EM CORPOS GEOLÓGICOS 3D MAGNETIZADOS UNIFORMEMENTE PAES GONZALEZ, SHAYANE FERREIRA BARBOSA, VALERIA CRISTINA We developed a new ambiguity analysis method for appraisal the remanent-magnetization direction and the Koenigsberger ratio (Q) of a uniformly magnetized source. Our method is grounded on a new formulation of the unit vector of the total magnetization direction which is described as the weighted sum of the unit vectors of the induced and remanent magnetization directions. The unit vectors of the induced and remanent magnetization directions are weighted, respectively, by λ, which we defined as the ratio between the induced and total magnetization intensities, and by the multiplication of λ by the Koenigsberger ratio Q. Using this formulation, we obtained analytical estimators for Q and the remanent magnetic inclination IR and declination DR. By assuming neither knowledge of the total magnetization direction nor particular interpretation model, we estimated the total magnetic inclination IT and declination DT via the equivalent-layer technique constrained by an all-positive magnetic-moment distribution. From this magnetic-moment distribution estimate, we performed a systematic search for both IT and DT to obtain a discrete data-residual map on the plane IT × DT. The ambiguity analysis consists in using the estimated and the picked IT and DT from the data-residual map considering prespecified errors, to calculate, using the analytical estimators, a family of curves of IR × Q, DR × Q, and λ × Q. These curves are quickly built up because we inverted the data only once. Tests with synthetic data illustrated a broader perspective of the relationships between the direction of remanent magnetization and the ratio Q. We also provide examples by applying this ambiguity analysis to total-field anomalies observed in various locations across Brazil, demonstrating both its effectiveness and limitations. Observatorio Nacional Tese 2023-10-25T00:00:00Z