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In passive continental margins, the brittle reactivation of shear zones and their role in the deformation and deposition of sedimentary basins are still a matter of debate. In this research, we investigated the role of the brittle reactivation of Precambrian shear zones in the nucleation of rift and postrift faults in the onshore portion of the Sergipe-Alagoas and Pernambuco basins in northeastern Brazil. We combine and interpret a dataset of aeromagnetic and topographic data, associated with reflection seismic and borehole data, to analyze the evolution of a portion of the Atlantic continental margin of Brazil. Our results indicate that in the crystalline basement, the magnetic lineaments are correlated with ductile structures as shear zones, and the continuity of these lineaments in the Sergipe-Alagoas and Pernambuco basins is interpreted as the shear zones below the sedimentary cover of these basins. We document the following phases of the brittle reactivation of basement shear zones: (1) the opening of the South Atlantic Ocean in the Early Cretaceous under an extensional stress regime and (2) tectonic inversion induced by the Mid-Atlantic Ridge push and the Andean Cordillera rise in the Neogene-Quaternary under a predominantly strike-slip stress regime. During the rift phase, the brittle reactivation of the shear zones controlled the locations and architectures of the rifts. These structures acted as zones of weakness and were reactivated as normal faults. The brittle reactivation of shear zones was still active during the postrift phase and was responsible for the development of compressional structures. The reverse faulting and related folding pattern indicate tectonic inversion in the Late Cretaceous-Cenozoic. The structures formed during the postrift phase under a strike-slip regime are consistent with the present-day stress field, indicating that tectonic inversion is an active phase of the Brazilian margin.

The Borborema Province BP (NE Brazil) consists of a complex rock mosaic composed mainly by Proterozoic metasedimentary belts that amalgamate Archean-to-Paleoproterozoic gneiss-migmatite complexes. It is a key region to understand the West Gondwana amalgamation, during the Pan-African/Brasiliano orogeny because it is an important portion of the orogen located between the Sao Francisco-Congo and West African cratons. We present the deep-rooted crustal framework of the BP interpreting the lateral contrasts of density and magnetization using the first available regional coverage of gravity and aeromagnetic data. The external boundaries of the BP having deep-rooted crustal significance are the Transbrasiliano shear zone, to the west, and the limit with the Sao Francisco craton, to the south. The latter limit is marked by a gravity anomaly which is the typical gravity signature of collisional sutures. Inside the BP crustal block, the Pernambuco, Patos, and Jaguaribe shear zones are identified as the major structures, based on termination and/or truncation criteria of geophysical anomalies. The three shear zones correspond to geophysical lineaments which conform with the Transbrasiliano shear zone, forming a single splay that opens to the northeast/east direction. The external boundaries and major shear zones divide the BP crustal block into four internal major domains of contrasting geophysical characteristics, namely the Southern, Transversal Zone, Rio Grande do Norte, and Ceara geophysical domains in analogy with the division based on surface geology. However, compared with the delimitations based on surface geology, there are three differences: the Medio Coreau belt is not positioned over the BP crustal block, a portion of the Parnaiba basin baseament should be included in the BP crustal block, and the basement beneath the folded-and-thrusted metasedimentary rocks of the Casa Nova Group (which form the nappes of the Riacho do Pontal belt) is part of the Sao Francisco craton crustal block. A subdivision of each major domain is also presented. Of special relevance is a pattern of alternate-polarity, quasi-parallel aligned geophysical anomalies present in the Transversal Zone domain, suggesting a clear alternation of high-density/high-susceptibility with low-density/low-susceptibility deep-rooted crustal subdomains. This geophysical pattern is compatible with a tectonic model of terrane collage.

We investigate the role of reactivation of Precambrian basement fabric in the tectono-sedimentary and geomorphological evolution of the Paraiba Basin, continental margin of northeastern Brazil, during the Cretaceous, Neogene, and Quaternary. This basin represents part of the last bridge between South America and Africa before the last breakup stage of the South Atlantic rifting in the early Cretaceous. The Paraiba Basin infill is composed of siliciclastic and carbonate Cretaceous units, as well as aeolian, fluvial and marine Quaternary units. We used shuttle radar imagery, aeromagnetic, wellbore and field data. The reduced-to-the-pole magnetic map (RTP) indicates the continuity of the steeply dipping Precambrian basement shear zones beneath the Paraiba Basin. The combined analysis of surface and subsurface data shows that NE–SW and E–W-striking shear zones were subjected to brittle reactivation in the Aptian–Middle Albian during the basin opening and again in the Neogene–Quaternary, forming a system of horsts and grabens along the basin; some of these structures such as the E–W-oriented Pernambuco shear zone present modern-day seismicity. N–S- and mainly NW–SE-striking transfer faults cut across Aptian–Middle Albian to Neogene–Quaternary strata. These four main fault directions control main river channels and alluvial valleys up to 2 km wide. Topographic breaks up to 50 m were created by late reactivation of rift faults, which mark the boundary between horsts and grabens along the basin. In addition, structural data evidence syn-tectonic faulting with vertical offsets up to 80 m in the Cretaceous and up to 70 m in the Neogene–Quaternary. We conclude that shear zones across the study area are long-lived structures that have behaved as weakness zones. Their neotectonic brittle reactivation has controlled sediment deposition and landform development, which continued through the Neogene–Quaternary.

Global, full-fit plate reconstruction models predict a significant presence of oceanic floor in Northeast Brazil and West Africa during Albian time, while rifting was under earlier stages in the Pernambuco and Paraiba basins. We call it the Albian breakaway gap. Sedimentary, biostratigraphic and geochronological data from the Pernambuco and Paraiba basins challenge the timing of sea floor spreading in this region. In the onshore Pernambuco Basin, there are abundant outcrops of syn-rift continental siliciclastic rocks of Aptian–Albian age interbedded with intrusive and extrusive magmatic rocks (dated ca. 102 ± 2 Ma). Salt has been recognized on seismic data within the Pernambuco Basin, but there is no record or seismic indication of salt within the Paraiba Basin. Three interpreted seismic transects provide important clues about the type of intraplate margin developed in this region. Syn and post-rift magmatism within the onshore and offshore segments of the Pernambuco Basin indicate significant melt production during (and after) the main stretching phase. On the other hand, the abruptly-necked Paraiba Basin displays seismic evidence of seaward dipping reflectors, side by side with rift sediments, suggesting the development of an Albian volcanic intraplate margin. In addition, gravity and magnetic data, on the Brazilian side, suggest a wide transition from continental to pure oceanic crust in the Pernambuco and Paraiba basins, as well as at their African counterparts: Douala, Rio Del Rey, and Lower Benue, where either oceanic crust or proto-oceanic wide crust has been recognized. Instead of pure oceanic crust, as predicted by globally balanced plate motion reconstructions, the continent-ocean transitional domain was composed in part by stretched continental crust and partially by a wide embryonic or proto-oceanic crust. In fact, a continuous and regional mid ocean ridge was only defined at the end of Albian/early Cenomanian when the South America plate was completely separated from the African plate.

The increasing importance of carbonate rocks as aquifers, oil reservoirs, and for urban problems is demanding detailed characterization of karst systems, a demand that can be partially satisfied with GPR imaging. However, the goal of imaging and interpreting karstified carbonate rocks is notoriously difficult due to the complex nature of the geometry of the dissolution and the GPR intrinsic limitations. One way forward is the direct comparison of GPR images with similar outcropping rocks. A joint study involving a 200 MHz GPR survey, unmanned aerial vehicle imagery (UAV), and outcrop characterization is presented aiming to improve the interpretation of sedimentary structures, fractures and karst structures in GPR images. The study area is a 500 m wide and 1000 m long carbonate outcrop of the Jandaira Formation in Potiguar basin, Brazil, where sedimentary, fracture, and karst features can be directly investigated in both vertical and horizontal plan views. The key elements to interpret GPR images of karstified carbonate rocks are: (1) primary sedimentary structures appear in radargrams as unaltered imaged strata but care must be taken to interpret complex primary sedimentary features, such as those associated with bioturbation; (2) subvertical fractures might appear as consistent discontinuities in the imaged strata, forming complex structures such as negative flowers along strike–slip faults; (3) dissolution may create voids along subhorizontal layers, which appear in radargrams as relatively long amplitude shadow zones; and (4) dissolution may also create voids along subvertical fractures, appearing in radargrams as amplitude shadow zones with relatively large vertical dimensions, which are bounded by fractures.

It is assumed that deformation bands may compartmentalize aquifers or hydrocarbon reservoirs because these low-permeability structures may behave as barriers to fluid flow. To address the question whether there is, at a reservoir scale, hydraulic connectivity across a damage zone dominated by cataclastic deformation bands, we present results of two pumping tests carried out in a fluvial-deltaic phreatic sandstone aquifer from the Ilhas Group at Tucano Basin (NE Brazil) where intense concentration of deformation bands occurs. Both test sites are associated with macroscopic damage zones that are approximately 1 km in length and 15 m thick. In situ permeability measurements show values of 2000 mD for host rock and 0.1 mD for deformation bands. GPR profiles reveal good continuity of the primary sedimentary structures with almost no deformation band vertical offsets (less than 10 cm). The well locations for the pumping tests were chosen so that the damage zone is located between pumping and monitoring wells. Pumping tests in both cases revealed hydraulic connectivity across the damage zone since the observed stationary drawdown at monitoring wells was a considerable fraction of the drawdown observed in the pumped well. In one experiment using eight monitoring wells the drawdown cone is evolving through the damage zone instead of contouring it. Local deviations in the natural groundwater flow allow to say that the damage zone dimensions are quite large both in horizontal and vertical directions compared to the distances among the wells. The interpretation of all experimental results is that deformation bands do not fully compartmentalize the aquifer. Generalization of this result to hydrocarbon reservoirs has to take into account capillary effects which are not present in the studied case.

Sealing faults may have a major impact on reservoir compartmentalization and play a key role in advanced oil recovery strategies. Because of the different approaches and scales used to characterize faults, a considerable gap remains between engineers’ and geologists’ conceptions of faulted reservoirs. The fundamental difficulty in integrating these views lies in constructing realistic reservoir-scale models incorporating relevant fault properties on several scales, so that fault connectivity and its impact on fluid flow can be simulated and quantified properly. This paper is a step towards examining quantitatively the impact of fault connectivity on fluid flow at a reservoir scale. A stochastic reservoir model incorporating sealing faults was constructed. The number of faults in the model were gradually increased and several fluid flow simulations performed in order to verify the impact of fault density and fault connectivity on the spatial pressure variation. Despite being synthetic, the model incorporates some properties of an actual carbonate reservoir, the Xareu oil field (XOF) in the Ceara Basin, NE Brazil. In the XOF, thin ( 50 m) shale bed. Sealing effects may be caused by the faults because they usually have a normal slip component, so that the thick shale layer becomes juxtaposed against the thin carbonate layers, behaving as barriers to fluid flow in the carbonate layers. It appears that there is no reservoir compartmentalization in the carbonate layers because there is overall pressure depletion in XOF – all the new wells drilled in the carbonate layers, before starting production, showed formation pressure values smaller than the formation pressure measured in the first wells drilled in the field. Nevertheless, it was not understood how such communication throughout the entire reservoir (approx. 19 km 2 ) could occur, given the presence of laterally extensive faults, with up to 5 km in strike and maximum vertical displacement greater than the reservoir thickness. In the synthetic model, fault population follows a displacement-length property derived from seismic data. Sub-seismic faults were also incorporated in the model using a downscaling law. The location, direction and length of each fault were also generated stochastically. In order to quantify the ‘degree of faulting’, two criteria were used: fault density (the fraction9s ‘total fault length per occurrence area’; f 1 ) and fault connectivity (the fraction9s ‘number of fault intercepts per occurrence area’; f 2 ). By comparing f 1 and f 2 for the real and simulated versions of the XOF carbonate reservoir it is concluded that the carbonate layers remain interconnected so that compartmentalization does not exist. From a methodological viewpoint, the most important aspect of the modelling is the change of focus regarding sealing. At least for the purposes of investigating interconnection, the adequate focus is on the ‘percolation core’ of the reservoir (its hydraulically connected and undamaged parts) and not on the faults themselves, regardless of their sealing nature.

An integrated study based on ground penetrating radar (GPR) profiles, vibracore descriptions, water-well logs, and radiocarbon dating in a coastal deposit located in the northern region of Rio Grande do Norte State, northeastern Brazil, allowed us to identify Holocene transgressive and regressive barriers. The construction process for the studied coastal barrier is different from that proposed for the Holocene coastal plains along the eastern Brazilian coast, where the hydraulic barrier set up by large rivers for sediments transported by longshore currents has caused a strongly positive longshore sediment imbalance. In the study area, interpretation of the GPR images, within the constraints of vibracores data, allowed us to interpret five radar facies and four radar boundary sequences for these coastal deposits, which were built up during the Holocene coastal evolution of the region. As a result, the geometry of the coastal barrier was reconstructed. Based on barrier geometry, sediment ages, stratigraphic records, and sedimentation patterns, we propose a barrier evolutionary model for the Holocene for the study region. During the Holocene highstand, a transgressive barrier was deposited and a lagoon extended landward. During the sea-level fall soon after the Holocene highstand, the deposition of a regressive barrier (forced regression) started. This deposition was induced by the coastal geometry and high amounts of eolian sediments supplied by east-northeast winds. Also during this period of sea-level fall, the beach face became wider, and thus more subjected to wind action, facilitating the deposition of the first eolian deposits. These sediments were transported to the nearly formed embayment, providing a surplus for the construction of the regressive barrier. During the regressive phase, tidal channels closed and the lagoon became isolated from the open sea. The geometry of both the regressive and transgressive barriers as well as the stratigraphic relation between the sedimentary deposits suggest that the Holocene highstand in this region was not more than 1.4 m above present-day mean sea level.

Current hydrogeological research in NE Brazil aims to better understand factors controlling storage and percolation of ground water in crystalline terrains, due to the fact that a large proportion (about 60%) of this region is formed by igneous and metamorphic rocks. As part of this effort, we present an integrated geophysical–geological study of a fractured bedrock aquifer located in the Caicara farm, near Equador city, Rio Grande do Norte State, NE Brazil. Pumped wells in this site present very different yields, in spite of short distance of only 20 m. The main lithologies of the site are quartzite and micaschist. Combined interpretation of geophysical images (Resistivity and Ground Penetrating Radar—GPR) and field structural geologic data revealed that the fractured bedrock aquifer is composed of three sets of discontinuities: SW-dipping subhorizontal joints, parallel to the ductile fabric of the country rocks which are probably release joints; NE-dipping subhorizontal fractures, oblique to ductile trend; and subvertical fractures which are orthogonally distributed along N–S and E–W directions. Important subvertical fracture zones occur at a regular spacing of about tens of meters. Fractures in the E–W direction are relatively open, as compared to fractures in the N–S direction. Probably, E–W fractures were opened by the current neotectonic stress regime in NE Brazil, which is controlled by E–W compression and N–S extension. It was possible to rank the hydrogeologic potentiality of water well siting as a function of fracture density and proximity to recharge zones, in this way explaining why wells could present very different yield results on the site. The most favorable places for well siting are intersections of subvertical fracture zones located near drainage because highly fractured zones could be, in this way, connected with recharge zones mainly in alluvial deposits. On the other hand, the least favorable places for well siting lie outside subvertical fractures and far from recharge zones. Intermediate hydrogeological potentialities occur in two cases: at a point near the recharge zone but where there is a low density of fractures, or at point far from the recharge zone but where there is a high density of fractures.

We present a new, stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast. The subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated. Any vertical line must intersect the basement relief only once, and the mass deficiency must be concentrated near the earth’s surface, subject to the observed gravity anomaly being fitted within the experimental errors. In addition, upper and lower bounds on the density contrast of each prism are introduced a priori (one of the bounds being zero), and the method assigns to each elementary prism a density contrast which is close to either bound. The basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts, the latter occupying the upper part of the discretized region. The method is stabilized by introducing constraints favoring solutions having the attributes (shared by most sedimentary basins) of being an isolated compact source with lateral borders dipping either vertically or toward the basin center and having horizontal dimensions much greater than its largest vertical dimension. Arbitrary laws of spatial variations of the density contrast, if known a priori, may be incorporated into the problem by assigning suitable values to the nonnull bound of each prism. The proposed method differs from previous stable methods by using no smoothness constraint on the interface to be estimated. As a result, it may be applied not only to intracratonic sag basins where the basement relief is essentially smooth but also to rift basins whose basements present discontinuities caused by faults. The method’s utility in mapping such basements was demonstrated in tests using synthetic data produced by simulated rift basins. The method mapped with good precision a sequence of step faults which are close to each other and present small vertical slips, a feature particularly difficult to detect from gravity data only. The method was also able to map isolated discontinuities with large vertical throw. The method was applied to the gravity data from Reco⁁ncavo basin, Brazil. The results showed close agreement with known geological structures of the basin. It also demonstrated the method’s ability to map a sequence of alternating terraces and structural lows that could not be detected just by inspecting the gravity anomaly. To demostrate the method’s flexibility in incorporating any a priori knowledge about the density contrast variation, it was applied to the Bouguer anomaly over the San Jacinto Graben, California. Two different exponential laws for the decrease of density contrast with depth were used, leading to estimated maximum depths between 2.2 and 2.4 km.

In order to enhance our knowledge about the tectonic processes responsible for the geological evolution of the Borborema Province and adjacent regions, the National Institute of Space Research (INPE) and the National Observatory (ON) are conducting Electromagnetic Induction studies in northeastern Brazil, which are being supported by the National Institute of Science & Technology for Tectonic Studies (INCTET) project during the past three years. Such studies contemplate the deep geophysical probing of this region with Magnetotelluric surveys (MT) and Transient Electromagnetic soundings (TEM) along several geoelectric transects and an array of Geomagnetic Depth Soundings (GDS), which complement other geophysical methods. The focus of this study is directed to the identification of geoelectric variations in electric conductivity at distinct lithospheric depths and associations of geoelectric strikes and anisotropy with structural grain and stress patterns, particularly in the long ubiquitous structural features that cross the province and that constitute major geoelectric heterogeneities, at the near surface crust and also in the lower crust and upper mantle. The preliminary results indicate a lithosphere with a very variable electrical resistivity. The upper-mid crust shows up as a very resistive layer, overlying a less resistive lower crust and upper mantle. In some areas the mantle is very resistive, characteristic of a cratonic origin. Exceptions to a resistive crust are found under the Serido belt, Jatoba rift basin and the Araripe intracratonic basin, marked by an underlying conductive crust. Laterally, the deeper portion of the crust and upper mantle is highly segmented in blocks with alternating juxtaposed higher and lower resistivities. This pattern is suggestive of highly deformed regions by transform dominated tectonic regimes, with the presence of contrasting mechanically strong cratonic-like keels against weaker zones likely subjected to delamination processes that might have produced magmatic related lithospheric re-fertilization by metasomatism. Introduction The National Institute of Science & Technology for Tectonic Studies congregates many geoscientists from several Brazilian research institutions with the purpose of studying the deep crust and upper mantle structures. It is multidisciplinary in its approach, merging different techniques and methodologies, which allow the study of the Earth’s interior based on different properties of its constituting rocks. The focus of this research is the study of the crust and upper mantle of the Borborema Province and adjoining Sao Francisco Craton and Parnaiba Basin. The Borborema Province is a complex association of crustal blocks with differing ages, origin and geologic evolution, and which were amalgamated during the last orogenic event that took place in what is now the Brazilian territory, namely the late Neoproterozoic-early Phanerozoic Brasiliano orogeny, composing the Gondwana supercontinent. Therefore, Electromagnetic Induction studies are being developed with the goal of making a major contribution to a better comprehension of the actual articulation of the amalgamated crustal blocks and the role of large transcurrent lineaments in bringing these blocks together, through an integrated multidisciplinary geophysical study.

The best locations for water wells in crystalline terrains of semiarid lands are narrow, densely fractured and altered belts, normally associated with fault zones and folding axes. A simple electrical procedure, based on vertical soundings and multiple resistivity profiling, has been successfully applied for the structural mapping of these two-dimensional aquifers in northeast Brazil. The apparent resistivity sections constructed from partial electrical sounding measurements taken at a closely spaced interval along a traverse were interpreted using a finite-difference algorithm. This scheme allowed detailed description of the lateral and vertical extent of fractured aquifers and some of their hydrogeophysical characteristics. The results of a selected case study from Bahia state compare satisfactorily with available geophysical logs and production data of existing wells.

Borborema Province (BP) has a very complex history, but up to now, few geophysical data have been used to constrain its evolution history. This paper presents the first integrated gravity/magnetic/geological data interpretation of the tectonic framework of the province. BP is a Proterozoic fold belt extended between the Sao Luis - West Africa and Sao Francisco - Congo/Kasai cratons. Currently, as a result of an increase in geochronologic data, there is growing evidence that its evolution has occurred by a mechanism of terrane collage. This evolution model suggests that large crustal blocks were put together during Meso and Late-Proterozoic events, resulting in crust growing by the arrival of pieces of crust or by the addition of new crusts. Interpretation of regional magnetic and gravity maps revealed the boundaries between crust blocks or compartiments inside BP. As result of the integrated interpretation, it is proposed that BP is formed by the union of at least 11 crust blocks. Boundaries between these blocks form long lineaments in NE-SE direction, in some cases showing vergences to E-W direction. The major block to the south of BP is the Sao Francisco Craton. The boundary between BP and the craton is still a controversial question, but the geophysical data suggest that N-S lineaments, which occur inside the craton, prolong below Riacho do Pontal and Sergipano hrust fold belts, which are part of BP. In this way, the plate associated to the craton lies beyond its geologically mapped north limit.

This paper presents the use of GPR (Ground Penetrating Radar) as an investigation tool of the spatial distribution of faults and fractures in a reservoir analogue exposed at surface. In this multidisciplinary study of a faulted reservoir analogue, the observed fault geometry and any associated fracture system has been sampled by different methodologies, at different scales, to verify the hypothesis of scale invariance. The aim of this survey is to establish the spatial continuity and distribution of these faults and fracture at different scales, from outcrop down to a few tens of meters. The survey of this analogue reservoir was carried out in The Tucano Basin, where good oil reservoir analogues are exposed. Our strategy is: (1) to test the image of macroscopic scale faults using GPR; (2) compare surface structural data (in several scales) with the GPR data. The final objective is to test predictive methods for the characterization of the spatial distribution of faults and fractures on reservoirs.

Gravity inversion results aiming to estimate the crystalline basement relief of the onshore Potiguar Basin are presented. It is assumed that the density contrast between the sediments and the crystalline basement is constant and known. The sediments are approximated with vertical rectangular prisms whose thicknesses, representing the depths to crystalline basement, are the parameters to be estimated from the gravity inversion. In all cases, the inversion process was stabilized with smoothness constraint on the spatial variation of the basement relief. Besides the gravity data, we used information about the basement relief obtained from boreholes and from seismic interpretation. These data were combined in order to compose three different scenarios simulating different phases during the exploratory development of the basin. In the first scenario we used the gravity data only. In the second scenario we worked with two combinations, first we combined the gravity data with information from boreholes, and second, with the basement relief reference model that resulted from the seismic interpretation. Finally, in the third scenario, we used the gravity data, the information from the boreholes and the reference model obtained from the seismic interpretation. In all scenarios, we obtained reliable estimates for the basement relief. Concerning the discrepancies among the results, the estimates obtained with additional constraints (from boreholes and/or seismic interpretation) increased the overall resolution of the basement relief and the reliability of the absolute depth values. However, it is important to stress that the first scenario already yielded a reliable estimate to the basin relief. If one takes into account the huge difference both in financial cost and environmental impact associated with gravity and seismic surveys, respectively, as well as with borehole drilling, this result highlights the great importance of properly using the gravity data in the initial exploratory phase of the basin.Keywords: gravity inversion, basement relief, Potiguar Basin, constrained inversion. RESUMO. Este trabalho apresenta aplicações de inversão gravimétrica para a estimativa do relevo do embasamento cristalino da Bacia Potiguar emersa. Admite-se que o contraste de densidade entre os sedimentos e o embasamento da bacia é constante e conhecido. O pacote sedimentar é aproximado por um conjunto de prismas lateralmente justapostos cujas espessuras, ou profundidades até o embasamento, são os parâmetros a serem estimados na inversão. Em todos os casos, o processo de inversão foi estabilizado com o uso do vínculo de suavidade na variação espacial do relevo do embasamento. Além das medidas gravimétricas, foram utilizados dados de poços e/ou oriundos da interpretação sísmica, em diferentes combinações, de modo a simular diferentes etapas, ou cenários, de exploração da bacia ao longo do tempo. No primeiro cenário foram utilizados somente dados gravimétricos. No segundo cenário, simulamos duas situações, em ambas adicionando outras informações aos dados gravimétricos: na primeira delas, adicionamos somente vínculos de poços e, na segunda, apenas um modelo sísmico de referencia para o embasamento. Por fim, no último cenário foram agregados aos dados gravimétricos os dados de poços e o modelo sísmico. As estimativas obtidas para o relevo do embasamento revelaram nitidamente o arcabouço da bacia em todos os cenários. Em relação às variações das profundidades entre os cenários, as inclusões dos vínculos dos poços e do modelo sísmico aprimoraram a resolução global dos resultados, como esperado. Contudo, é relevante destacar que a inversão no primeiro cenário já forneceu um relevo bastante aproximado do arcabouço conhecido da bacia. Se levarmos em conta as grandes diferenças de custo financeiro e de impacto ambiental, respectivamente associados com os levantamentos gravimétrico e sísmico, bem como com a perfuração de poços, esse resultado evidencia a grande importância de uma adequada utilização dos dados gravimétricos nas fases exploratórias iniciais de uma bacia.Palavras-chave: inversão gravimétrica, relevo do embasamento, Bacia Potiguar, inversão vinculada.

The present article is a synthesis of studies developed by fundação Norte Rio Grandense de Pesquisa e Cultura -FUNPEC and Universidade Federal do Rio Grande do Norte - UFRN for the Companhia de Águas e Esgoto do Rio Grande do Norte - CAERN, in the lower course of Doce River, RN. This paper also presents alternatives to increase the water supply from wells in the Barreiras Aquifer located to the north of Natal district, RN, considering the degraded water quality due to nitrate contamination from the right margin of Doce River. The methodology was based on the combined use of hydrogeological and geophysical techniques (gravity andelectrical resistivity). The regional structure was previously characterized by morphotectonic analysis and gravimetric and geoelectric data interpretation. According to these data, two preferential fault directions (NW and NE) directly influence local geometry of the aquifer causing abrupt variations of the saturated thickness. The potential of the Barreiras Aquifer increases gradually on the left bank of Doce River from east to west, due to larger spacing between hydrogeological equipotential surface and larger saturated thickness. These observations provided the basis to locate a new water collection area, where new wells are going to be drilled with 300 m3 /h estimated total discharge. RESUMO: O presente artigo representa uma síntese de estudos desenvolvidos pela Fundação Norte-Rio-Grandense de Pesquisa e Cultura-FUNPEC e Universidade Federal do Rio Grande do Norte-UFRN para a Companhia de Àguas e Esgotos do Rio Grande do Norte-CAERN, na área do baixo curso do Rio Doce-RN. O mesmo objetivou apontar alternativas para o incremento do abastecimento d’água proveniente de poços no Aquífero Barreiras na zona norte do município de Natal-RN, tendo em vista o agravamento da contaminação de captações da margem direita do Rio Doce por nitrato. A metodologia adotada foi fundamentada no emprego conjunto de técnicas de hidrogeologia e geofísica (gravimetria e eletrorresistividade). A estruturação regional, caracterizada previamente a partir de análise morfotectônica e interpretação de dados gravimétricos e geoelétricos, foi evidenciada nas direções preferenciais NW e NE, influenciando diretamente na geometria local do aquífero na forma de variações bruscas de sua espessura saturada decorrente dos falhamentos. A potencialidade do Aquífero Barreiras apresenta um acréscimo gradativo na margem esquerda do Rio Doce de leste para oeste, decorrente de maiores espaçamentos entre equipotenciais hidrogeológicas e espessuras saturadas maiores. Estas observações fundamentaram a locação de uma subárea a leste da captação Rio Doce da CAERN como bastante promissora para a execução de uma segunda bateria de poços, com descarga total estimada da ordem de 300 m3 /h.Palavras-chave: Aquífero Barreiras; Rio Doce-RN, Geofísica; potencialidade hidrogeológica