Almada Basin Research Articles

Upper maastrichtian palynology and paleoenvironment of the Urucutuca Formation, Almada basin (BA), Brazil

Hydrocarbon exploration involving the Urucutuca Formation is taking place in several basins located mainly in the central segment of the eastern Brazilian margin, including the Almada Basin. Relatively rich accumulations of organic material and promising prospects, especially for gas, have been discovered. The Brazilian National Petroleum Agency (ANP) considers the Urucutuca Formation as a speculative play exploratory (Urucutuca-Urucutuca) in deep and ultra-deep areas of the Almada Basin, including others.The focus was on improving the understanding of the sediments of the Urucutuca Formation and establishing a palynostratigraphic outline for the upper cretaceous strata, which still need to be updated. Therefore, integrated palynological, palynofaciological, and organic-geochemical (total organic carbon -TOC) investigation methods were carried out. For this purpose, 250 m of well 1-SST-01, drilled in the onshore part of the Almada Basin in Bahia State, were analyzed using 26 core samples along the Urucutuca Formation.By typifying palynofaciological variations based on organic matter content in conjunction with palynological and geochemical data, it was possible to distinguish three palynofacies with different characteristics of the marine influence environment. Palynofacies 1, the amorphous organic matter (AOM) group, predominates with proportions up to 54.1 and a TOC of 0.75%. The high phytoclasts percentage (70%) and a TOC content of 1% characterize the Palynofacies 2. Palynofacies 3, on the other hand, has the highest content of marine palynomorphs (40%).The analysis of total organic carbon yielded values ranging from 0.04% to 1.85%, which were heterogeneously distributed throughout the borehole.The palynological succession showed a dominance of representatives of continental origin. However, marine elements (dinoflagellates and microforaminiferal inner tests) are present throughout the section.Two expressive occurrences of dinoflagellate cysts are evident throughout the section. In the basal and middle portions, quantity and diversity suggest transgressive events or at least sea-level fluctuations. Biostratigraphically, the unit could be placed in the Tricornites elongatus (P-470) Biozone of the Crassitricolporites brasiliensis (P-450) Superzone and assigned to the Eomaastrichtian. These biostratigraphic units are consistent with the proposed zonation for other basins of the Brazilian Atlantic margin.Palynofacies and palynological data allowed the observation of variations in a predominantly platform paleoenvironment, sometimes distal and sometimes more proximal, with possible transgressions.

Imaging exhumed continental and proto-oceanic crusts in the Camamu triple junction, Brazil

During the SALSA experiment, in 2014, twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Almada-Camamu, Jacuípe, and Sergipe-Alagoas basins, NE Brazil. Profile SL09 images the Almada-Camamu basin and the São Francisco craton, with 18 four-channel ocean-bottom seismometers and 22 land stations. The datasets were forward modelled and combined with pre-stack depth migration to increase the horizontal resolution of the velocity models.Our results show that sediment thickness varies between 3.8 km in the oceanward part of the profile, 4.3 km in the Almada basin and 6.5 km in the Camamu basin. Crustal thickness at the north-western edge of the profile is of around 40 km, with velocity gradients indicating a continental origin.The Camamu basin, which corresponds to the triple junction between the aborted N–S oriented Tucano rift, the SW-NE oriented Jacuipe-Sergipe-Alagoas branch, and the N–S Jequitinhonha-Almada branch, presents two crustal layers: a very thin upper layer, about 1.5 km thick, which increases seawards to 3 km in the Almada basin, and an higher velocity (HV) layer (6.8–7.2 km/s) about 4 km thick. This lower layer gradually disappears in the Almada basin. At the south-eastern edge of the profile, the resolution is lower but the thickness of the crust seems to increase up to 5 km. Deep wide-angle reflections indicate upper mantle stratification.Crustal organisation and P-wave propagation velocities in the Almada and Camamu basins indicate a transitional crust domain of exhumed continental crust affinity. In the Camamu triple junction and beneath this thin exhumed continental crust, the HV layer may probably reflect intruded materials. No exhumed upper mantle is observed along the entire profile. The easternmost part of the profile may correspond to a proto-oceanic crust. Typical oceanic crust is never imaged along the 260 km-long offshore profile.

Vulnerability analysis to contamination of the water aquifer and soil infiltration rate of Almada basin of the river and the adjacent coastal area

Esta pesquisa teve como objetivo a identificacao de areas vulneraveis a contaminacao do aquifero freatico da Bacia do Rio Almada e area costeira adjacente, Bahia - Brasil. Para tanto, foi realizada a caracterizacao da area de estudo, com base em dados primarios e pre-existentes; bem como da taxa de infiltracao e da caracteristica fisica do solo. O mapa de vulnerabilidade a contaminacao do aquifero freatico foi obtido a partir da integracao das caracteristicas climatica, declividade, profundidade do nivel freatico, solo e uso e ocupacao do solo, por meio de algebra de mapas em ambiente de Sistema de Informacao Geografica (SIG) na escala de 1:100.000, classificado em cinco graus de vulnerabilidade, assim identificados: muito baixo, baixo, medio, alto e muito alto. Os resultados apontaram que as areas com maior vulnerabilidade a contaminacao do aquifero freatico situam-se, principalmente, na regiao costeira, nos locais relacionados aos solos arenosos, baixa declividade e nivel freatico raso. Os 15 pontos de amostragem de solo permitiram caracteriza-lo como de textura arenosa com elevados teores de areia (fina + grossa) - acima de 90% da composicao granulometrica e valores de taxa de infiltracao entre 0,00005 e 0,00075 cm/s. As informacoes levantadas e analisadas constituem produtos que poderao subsidiar tomadas de decisoes, priorizando acoes que venham a minimizar os danos ambientais como forma de resguardar a qualidade ambiental, orientar o manejo do solo e a recuperacao ambiental. ABSTRACT Analysis of vulnerability to phreatic aquifer contamination and infiltration rate of the soil of Almada River Watershed and adjacent coast – BA . This research aimed to identify areas vulnerable to phreatic aquifer contamination Almada River Watershed and adjacent coastal area, Bahia - Brazil. Therefore, it was performed to characterize the study area, based on the primary and preexisting; well as the permeation rate and physical characteristics of the soil. The map of vulnerability to phreatic aquifer contamination was obtained from the integration of climate characteristics, slope, water table depth, and soil use and occupation of land by means of map algebra environment in Geographic Information System (GIS) on the scale of 1:100,000, classified into five degrees of vulnerability, thus identified: very low, low, medium, high and very high. The results showed that areas with greater vulnerability to phreatic aquifer contamination are located mainly in the coastal region, in areas related to sandy soils, low slopes and shallow groundwater. The 15 points allowed soil sampling characterize it as sandy with large amounts of sand (fine + coarse) - over 90% of the particle size distribution and infiltration rate values between 0.00005 and 0.00075 cm/s. The information gathered and analyzed are products that can support decision making, prioritizing actions that will minimize environmental damage as a way of protecting environmental quality, direct soil management and environmental remediation. Keywords: land use and occupation ; geographic information system; environmental planning.

Crustal architecture of the Almada Basin, NE Brazil: an example of a non-volcanic rift segment of the South Atlantic passive margin

Abstract The Almada Basin, located in the southern Bahia State segment of NE Brazil, shares a similar sedimentation history and stress regime with the other eastern Brazilian basins. But when considering the composition of the transitional crust, a remarkably different behaviour is observed between the Almada Basin and the other eastern Brazilian basins. The architectural elements of the basin such as the reflection Moho discontinuity, the oceanic and continental basements, and the sedimentary section, as well as the tectonic style, are discussed in this study using gravity, seismic, regional geology and well-drilling results. The Almada Basin is part of a continental rift system that developed during the Early Cretaceous, heralding the Gondwana break-up and subsequently evolving into a passive divergent margin. Deep seismic profiles show the progressive thinning of the continental crust but there is no clear evidence of mantle exhumation. The Almada Basin is the conjugate margin of the South Gabon Basin in West Africa. Although both basins display similar stratigraphic record and geological evolution, the rifting mechanism resulted in a considerable asymmetric break-up. The Almada Basin is floored by the Itabunas–Salvador–Curaçá Belt of the São Francisco Craton and is characterized by Palaeoproterozoic granulites in a high-angle east-dipping thrust fault regime. However, the South Gabon Basin lies on the Neoproterozoic West Congolian Belt that is made up of low- to medium-grade metamorphic rocks in a low-angle thrust tectonic regime. The Precambrian basement fabric of both the Almada and South Gabon basins is marked by lithospheric-scale discontinuities that controlled the implantation of the rift zone and the extension style during the Mesozoic. The strong basement structural inheritance can be recognized in both the geological and geophysical records. The key architectural elements of a volcanic margin, such as large igneous provinces, seaward-dipping reflectors and the basinal syn-rift magmatism, are not recognized in the Almada Basin. Although the South Atlantic margin is mostly volcanic in the southernmost segment, the presence of these two non-volcanic segments – the southern Bahia State and the southern Gabon – are important as a record of the differences in the geotectonic process that governed the formation of the South Atlantic divergent margins.

Significado paleoambiental da família anemiaceae no cretáceo do Brasil: inferências a partir de dados palinológicos

O presente trabalho discute o significado paleoambiental da Família Anemiaceae, a partir das associações palinológicas cretáceas que contêm esporos do gênero Cicatricosisporites, presentes em diversas bacias sedimentares brasileiras - Sanfranciscana, Parnaíba, Paraná, Almada e Pernambuco-Paraíba. Nas formações Areado e Codó, respectivamente das bacias Sanfranciscana e Parnaíba, a presença de palinomorfos terrestres, aliada à abundância de Classopollis em grãos isolados e em tétrade, indica deposição próxima à área-fonte em ambiente continental de clima árido e quente. A presença de Cicatricosisporites, porém sem representatividade estatística, sugere condições avessas a esse clima. Todavia, em algumas amostras da Formação Codó, observou-se a ausência de Classopollis e a presença abundante de triletes lisos e ornamentados - inclusive Cicatricosisporites - e de Perotriletes, o que sugere fases mais úmidas. No Grupo Bauru (Bacia do Paraná) apenas um exemplar de Cicatricosisporites foi registrado, em meio à abundância de grãos efedroides típicos de ambiente árido, e de triletes cingulados e zonados, indicadores de clima úmido, o que sugere uma sazonalidade no regime pluviométrico. Nas formações Urucutuca (Bacia de Almada) e Gramame (Bacia de Pernambuco-Paraíba), a presença de palinoforaminíferos e dinoflagelados indica deposição em ambiente marinho, embora grãos de origem continental também sejam encontrados. No caso da Formação Urucutuca, Cicatricosisporites foi o táxon mais abundante entre os palinomorfos continentais. Conclui-se que Cicatricosisporites pode ser indicador de ambiente moderadamente úmido, uma vez que ocorre frequentemente associado a esporos triletes lisos e ornamentados e Perotriletes. Porém, quando está associado a grãos indicadores de clima árido e seco, sua presença geralmente é estatisticamente insignificante.

Total variation regularization for depth-to-basement estimate: Part 1 — Mathematical details and applications

We have developed an inversion approach that estimates the basement relief of a fault-bounded sedimentary basin. The sedimentary pack is approximated by a grid of 3D or 2D vertical prisms juxtaposed in the horizontal directions of a right-handed coordinate system. The prisms’ thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data. To obtain depth-to-basement estimates, we introduce the total variation (TV) regularization as a stabilizing function. This approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution. We have deduced a compact matrix form of the gradient vector and the Hessian matrix of the approximation to the TV function that allows a regularized Gauss-Newton minimization approach. Because the Hessian matrix of the approximation to the TV function is ill conditioned, we have modified this Hessian matrix to improve its condition and to accelerate the convergence of the Gauss-Newton algorithm. Tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small-slip step faults. Tests on field data from the Almada Basin, Brazil, and from the San Jacinto Graben, California, U.S.A., confirm the potential of the method in detecting and locating in-depth normal faults in the basement relief of a sedimentary basin.

Simultaneous 3D depth-to-basement and density-contrast estimates using gravity data and depth control at few points

We have developed a gravity-inversion method for simultaneously estimating the 3D basement relief of a sedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack, assuming prior knowledge about the basement depth at a few points. The sedimentary pack is approximated by a grid of 3D vertical prisms juxtaposed in both horizontal directions of a right-handed coordinate system. The prisms’ thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data. To estimate the parameters defining the parabolic decay of the density contrast with depth and to produce stable depth-to-basement estimates, we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes. We applied our method to synthetic data from a simulated complex 3D basement relief with two sedimentary sections having distinct parabolic laws describing the density-contrast variation with depth. The results provide good estimates of the true parameters of the parabolic law of density-contrast decay with depth and of the basement relief. Inverting the gravity data from the onshore and part of the shallow offshore Almada Basin on Brazil’s northeastern coast shows good correlation with known structural features.

Magnetic Basement Depth Inversion in the Space Domain

We present a total-field anomaly inversion method to determine both the basement relief and the magnetization direction (inclination and declination) of a 2D sedimentary basin presuming negligible sediment magnetization. Our method assumes that the magnetic intensity contrast is constant and known. We use a nonspectral approach based on approximating the vertical cross section of the sedimentary basin by a polygon, whose uppermost vertices are forced to coincide with the basin outcrop, which are presumably known. For fixed values of the x coordinates our method estimates the z coordinates of the unknown polygon vertices. To obtain the magnetization direction we assume that besides the total-field anomaly, information about the basement’s outcrops at the basin borders and the basement depths at a few points is available. To obtain stable depth-to-basement estimates we impose overall smoothness and positivity constraints on the parameter estimates. Tests on synthetic data showed that the simultaneous estimation of the irregular basement relief and the magnetization direction yields good estimates for the relief despite the mild instability in the magnetization direction. The inversion of aeromagnetic data from the onshore Almada Basin, Brazil, revealed a shallow, eastward-dipping basement basin.

Characterization of turbidites from the Urucutuca Formation of the Almada Basin, Bahia, Brazil, using seismic and petrophysical well log data

Fifty seismic lines and petrophysical logs from 15 wells were used to characterize the reservoirs of the Urucutuca Formation palaeo-canyon in the Almada Basin. The resulting 3D geological model allowed the Urucutuca Formation and its turbidite canyons to be evaluated as potential petroleum reservoirs. The log analyses indicate great variations in effective porosity (reaching a maximum value of 25%) and the clay content of the sandstones (ranging from less than 5% to greater than 40%). Other relevant factors in this context are the sandstone and calcarenite thicknesses which reach 243 m and 93 m, respectively. Information obtained from the seismic lines indicates that there was a strong tectonic influence on the geometry of the Almada Canyon, resulting in the formation of two canyons that join in the offshore portion of the basin. The connection between the canyons has been observed to extend from the continent to 27 km offshore. The results indicate that the Urucutuca Formation is an important horizon for future oil exploration, having favourable genetic and petrophysical characteristics.

Gravity data as a tool for detecting faults: In-depth enhancement of subtle Almada’s basement faults, Brazil

We demonstrate the potential of gravity data to detect and to locate in-depth subtle normal faults in the basement relief of a sedimentary basin. This demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere. We inverted the gravity data from the onshore Almada Basin in northeastern Brazil, and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging. The inversion method delineated well both the discontinuities with small or large slips and a sequence of step faults. Using synthetic data, we performed a systematic search of normal fault slips versus fault displacement depths to map the fault-detectable region in this space. This mapping helps to assess the ability of gravity inversion to detect normal faults. Mapping shows that normal faults with small [Formula: see text], medium (about [Formula: see text]), and large (about [Formula: see text]) vertical slips can be detected if the maximum midpoint depths of the fault planes are smaller than 1.8, 3.8, and [Formula: see text], respectively.

Relações entre orógenos, zonas de cisalhamento, quebra continental e deformações 3-d. a história tectônica da Bacia Sedimentar de Almada, Bahia

The Almada Basin is a geometric out-pattern member in the group the onshore coastline sedimentary basins of the Bahia State and neighborhoods. This basin differs from the traditional elongated-shape trending Camamu and Reconcavo- Tucano-Jatoba basins, and shows a compact rhombohedral arrangement following N45 o , N90 o , N120 o e N-S structural lineaments. This shape directly or indirectly reflects a specific geological history influenced by the paleoproterozoic and neoproterozoic orogens, neoproterozoic shear zones and mesozoic supercontinent break-up. Several sets of fault and fractures were kinematically studied inside and around the basin, and the main stress tensors obtained using inversion methods. The structural study of the Almada Basin allowed to recognize that: (i) the initial tectonic activity was controlled by normal faults, with orthorhombic-romboedral 3-D extensional strain pattern, followed by transtensional ones characterizing the Almada Basin as a polyphasic tectonic basin, and (ii) during the transtensive phase this basin was affected by at least two almost orthogonal extensional events, indicating a possible o 1 orientation inversion during its formation and tectonic evolution. These data are crucial for prospecting groundwater and hydrocarbon in the basin onshore and offshore areas.

Teores de potássio, urânio, tório e taxa de produção de calor radiogênico no embasamento adjacente às bacias sedimentares de Camamu e Almada, Bahia, Brasil

O embasamento adjacente às bacias sedimentares de Camamu e Almada é caracterizado, principalmente, por rochas das facies granulito e anfibolito, com idades arqueanas e paleoproterozoicas, pertencentes ao orógeno Itabuna-Salvador-Curaçá. As unidades em maior proporção neste contexto são os granulitos metatonalíticos associados aos granulitos básicos e metamonzoníticos pertencentes ao cinturão Itabuna. Em menor área, tem-se o granito de Teolândia e o granodiorito de Moenda associado aos anfibolitos da banda de Ipiaú, os charnockitos e charnoenderbitos do bloco Jequié, os sienitos neoproterozóicos e os diques máficos. Os teores de K, U e Th nessas rochas variam de 0,02 a 6,33% para o K, < 0,2 a 9,10 ppm para o U e < 0,4 a 64,38 ppm para o Th. Esses teores são mais altos nos charnockitos, no granodiorito de Moenda, no granito de Teolândia e nos sienitos, têm valores intermediários nos metatonalitos e metamonzonitos e são mais baixos nos granulitos básicos. As taxas de produção de calor nessas rochas são mais altas onde os teores de K, U e Th são maiores, variando de 0,58 a 5,57 µW m-3. As áreas de abrangência dessas litologias são, contudo, pequena quando comparada com aquelas dos metatonalitos, metamonzonitos e sienitos onde as taxas variam de 0,10 a 1,44 µW m-3, 0,23 a 5,55 µW m-3 e 0,60 a 2,24 µW m-3, respectivamente. Os granulitos básicos possuem as menores taxas, entre 0,06 a 0,36 µW m-3. A distribuição das litologias nas bordas das duas bacias sugere que, no embasamento sob seus sedimentos mais recentes, deve predominar os metatonalitos, seguidos pelos metamonzonitos e com uma participação significante de sienitos no caso da bacia de Almada. Para estas litologias, as taxas volumétricas de produção de calor, com o intervalo de um desvio padrão, são 0,41 ± 0,30 µW m-3 para os metatonalitos, 0,71 ± 0,57 µW m-3 para os metamonzonitos e 1,20 ± 0,51 µW m-3 para os sienitos.

LEVANTAMENTO GPR EM AFLORAMENTOS TURBIDÍTICOS DA BACIA DE ALMADA - BA

In the onshore Almada Basin, northeast Brazil, sandy and/or conglomeratic turbidites and shales outcrops of Urucutuca Formation occur. These rocks are part of an exhumed portion of the filling-section of the Almada Canyon. Such outcrops are unique examples of passive margin transgressive marine sequence turbidites in Brazil, which were sedimented during the Maastritchian/Campanian. They are analogues to some important turbidite reservoirs of Campos and Espirito Santo Basins. To aid studies of internal/external geometry and facies association which will help to improve the knowledge of the properties of such kind of rocks, a GPR (Ground Penetrating Radar) survey was performed in this region. A comparison with geological interpretations of the outcrop showed good agreement with GPR results. Furthermore, the use of 3D visualization techniques applied to GPR profiles allowed us to locate possible turbidite channels in parts of the outcrop where geological information were difficult to be assessed without drilling.

LEVANTAMENTO GPR EM AFLORAMENTOS TURBIDÍTICOS DA BACIA DE ALMADA - BA

In the onshore Almada Basin, northeast Brazil, sandy and/or conglomeratic turbidites and shales outcrops of Urucutuca Formation occur. These rocks are part of an exhumed portion of the filling-section of the Almada Canyon. Such outcrops are unique examples of passive margin transgressive marine sequence turbidites in Brazil, which were sedimented during the Maastritchian/Campanian. They are analogues to some important turbidite reservoirs of Campos and Espirito Santo Basins. To aid studies of internal/external geometry and facies association which will help to improve the knowledge of the properties of such kind of rocks, a GPR (Ground Penetrating Radar) survey was performed in this region. A comparison with geological interpretations of the outcrop showed good agreement with GPR results. Furthermore, the use of 3D visualization techniques applied to GPR profiles allowed us to locate possible turbidite channels in parts of the outcrop where geological information were difficult to be assessed without drilling.

Inversão unidimensional de perfis geofísicos de indução na caracterização dos turbiditos da Bacia de Almada - BA

In this work, we developed an one-dimensional inverse algorithm, based in the dumped least square technique, to interpret electromagnetic induction geophysical well log data. The goal was the characterization of a turbidite geological system. Thus, the forward problem consists in the exact mathematical solution of the electromagnetic response of a stratified media crossed by a borehole. The inversion scheme was used to interpret apparent resistivity data obtained in a borehole drilled in a turbidity outcrop of Almada Basin, South Bahia State/Brazil. To validate our interpretation, geologists described the lithology from samples obtained and also using gamma ray log. With the developed algorithm, it was possible to describe the resistivity and thickness of the main layers along the well, besides the bias between final model and experimental data and the fitting error. Although we know that one-dimensional inversion is very unstable, it has some advantages, as a rapidly convergence when initial model is close the correct model.

Abstract: Palynofacies in a Sequence Stratigraphy Context: An Example of an Upper Aptian Section from Almada Basin, Brazil&amp;nbsp;

Abstract: Palynofacies in a Sequence Stratigraphy Context: An Example of an Upper Aptian Section from Almada Basin, Brazil&amp;nbsp;

Abstract: Petroleum System of the Camamu Almada Basin: A Basin Modeling Approach

Abstract: Petroleum System of the Camamu Almada Basin: A Basin Modeling Approach

Roteiro geológico da Bacia do Almada Bahia

The Rio Almada Basin lies along the Bahia coast, between parallels 14° S (Taipus high) and 15° S (Olivenca high), and extend offshore until the oceanic crust. Age of sediments range from Jurassic to Recent. All the formations are exposed in a 200 km 2 area north of Ilheus, Bahia, in which three structural compartments are delineated. The field guide covers the structural aspects, visit both basements, Archean metamorphics and Proterozoic igneous rocks, but mostly describes the main outcrops of the sedimentary section. There are good outcrops of Jurassic alluvial fans reworked by aeolian process on top, lower Cretaceous rift-fill sediments, upper Cretaceous marine channelized turbidites from the drift phase, Cenozoic barrier-bar and shoreface deposits and Recent beach-rocks. A scheme is put together for a three days self-guided field trip.