Jequitinhonha Basin Research Articles

Pressure Prediction for a Block of the Jequitinhonha Basin, Brazil

Pressure Prediction for a Block of the Jequitinhonha Basin, Brazil

Non-Hyperbolic Velocity Analysis of Seismic Data from Jequitinhonha Basin, Northeastern Brazil.

Normal moveout (NMO) velocity is used in seismic data processing to correct the data from the moveout effect. This velocity depends on the medium above the reflector and it is estimated from the adjustment of a hyperbolic function that approximates the reflection time. This approximation is reasonable for media formed by isotropic layers. For deeper exploration targets, which effectively behave as anisotropic media, the NMO velocity estimate from the hyperbolic approximation becomes imprecise. One possibility is the use of non-hyperbolic approximations for the reflection time and deeming the medium to be anisotropic. However, these approximations make the NMO velocity estimation a more complex problem, since the anisotropic parameters are unknown. In this study the NMO velocities for a vertical transverse isotropy medium are estimated using two non-hyperbolic reflection time approaches. For comparing the two methodologies that estimate NMO velocity, a 2-D dataset from Jequitinhonha Basin is used and it presents anisotropic behavior. The results show that this approach produces more consistent results than the conventional approach, which ignores the anisotropy of the medium.

A new species of Hyphessobrycon (Characiformes, Characidae) from the upper Rio Jequitinhonha basin, Minas Gerais, Brazil, with comments on morphological similarities with Stethaprioninae species from headwater environments.

A new species of Hyphessobrycon is described from a marshland area in the headwaters of Rio Jequitinhonha basin, Minas Gerais, Brazil. The new species differs from congeners by presenting a single well-delimited conspicuous humeral blotch, rounded to vertically oval, restricted to the area dorsal to the lateral-line row of scales, without a narrower downward extension, greatest body depth anterior to dorsal-fin origin, bony processes in anal and pectoral-fin rays of males and four teeth in the inner row of the premaxillary bone. The new species presents a set of morphological features shared by some species currently assigned to Hasemania, Myxiops and to the Astyanax scabripinnis complex. Some of these features are discussed.

CONTROLE ESTRUTURAL DA DEPOSIÇÃO MESOZOICA NAS BACIAS DA MARGEM CONTINENTAL BRASILEIRA

The sedimentary fill of the Brazilian marginal basins is made up, when complete, of three suites reflecting the evolutionary stages of the continental margin: (1) the lower clastic non-marine suite was deposited in two stages, the basal section in a pre-rift stage, and the upper section in a rift-valley stage: (2) the middle suite, including the evaporitic section and the overlying shelf carbonates, was deposited in a stage of tectonic quiescence; (3) the upper marine suite, including some paralic and continental sediments, was deposited in a stage of vertical differential movements along flexure lines. The Upper Jurassic non-marine sediments of the basal section in Brazil (Sergipe-Alagoas, Reconcavo, and Almada Basins), correlate well with those of West Africa (Gabon and Congo Basins) showing a symmetric areal distribution. The absence of this Upper Jurassic section, south of the Jequitinhonha Basin in Brazil and the Cuanza Basin in West Africa is probably due to non-deposition in uplifted areas coinciding with sites of Early Cretaceous volcanic activity. The juxtaposition of the uplifted-volcanic areas in Brazil and Africa in a pre-drift arrangement suggests the existence of a hot-spot, active in Late Jurassic-Early Cretaceous times. An earlier rifting in the uplifted areas is suggested by the presence of Wealdian evaporites in the Santos and of Aptian marine sediments in the Pelotas Basin. Both sediment types are older than their lithological - environmental counterparts along the continental margin from the Campos to the Sergipe Basin. Along the northern margin, from the Amazon delta to the Potiguar Basin, the pre-rift and rift-valley stages are not well known. There is evidence of Early Cretaceous rifting in aborted rift-valleys [v.g. the Sao Luiz Basin) and also of Late Cretaceous compressional forces. The relationship between, and the duration of the tensional and compressional forces are still unclear.

Imaging exhumed lower continental crust in the distal Jequitinhonha basin, Brazil

Twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Camamu-Almada, Jacuípe, and Sergipe-Alagoas basins, NE Brazil, during the SALSA experiment in 2014. Profiles SL11 and SL12 image the Jequitinhonha basin, perpendicularly to the coast, with 15 and 11 four-channel ocean-bottom seismometers, respectively. Profile SL10 runs parallel to the coast, crossing profiles SL11 and SL12, imaging the proximal Jequitinhonha and Almada basins with 17 ocean-bottom seismometers. Forward modelling, combined with pre-stack depth migration to increase the horizontal resolution of the velocity models, indicates that sediment thickness varies between 3.3 km and 6.2 km in the distal basin. Crustal thickness at the western edge of the profiles is of around 20 km, with velocity gradients indicating a continental origin. It decreases to less than 5 km in the distal basin, with high seismic velocities and gradients, not compatible with normal oceanic crust nor exhumed upper mantle. Typical oceanic crust is never imaged along these about 200 km-long profiles and we propose that the transitional crust in the Jequitinhonha basin is a made of exhumed lower continental crust.

Jequitinhonha Basin: Structural aspects, relationship with igneous activity, and hydrocarbon exudations

The Jequitinhonha Basin (JB) is one of the sedimentary basins in the Brazilian Eastern Margin. Although several regional studies have been conducted to define its tectonic framework and petroleum system, neither one is very well-understood. For instance, the extent and influence of the volcanic rocks in the petroleum system of the JB are still matters of debate among geoscientists. We found a new integrated interpretation for the structural framework of JB in which we discover the major faults, the mapped volcanics, and a new basement map. Finally, we evaluate the correlation of known exudation occurrences with our findings. Several exudation occurrences are observed in the evaporite province (to the north), although only one exudation occurrence is seen in the Royal Charlotte domain (to the south) thus corroborating the negative impact of the Abrolhos magmatic event for the petroleum systems in the JB. At least seven exudation occurrences are observed in the oceanic crustal domain. This fact strengthens the possibility of the existence of an Urucutuca-Urucutuca postrift petroleum system.

Description of a new species of Pareiorhaphis (Loricariidae: Neoplecostominae) from the rio Jequitinhonha basin, Minas Gerais, eastern Brazil

ABSTRACT A new species of the loricariid genus Pareiorhaphis is described based on specimens from several tributaries of the upper and middle rio Jequitinhonha basin, Minas Gerais State, eastern Brazil. The new species increases the number of known species of Pareiorhaphis to 25 and, at the same time, represents the second member of the subfamily Neoplecostominae reported from the rio Jequitinhonha basin. The new species is diagnosed from all remaining congeners by a putative autapomorphic feature related to the color pattern: a well-defined, dark brown stripe on the median series of lateral plates that extends along the flank from the posterior margin of compound pterotic to the caudal-fin base. The shallow caudal peduncle and the comparatively larger number of dentary teeth also distinguish the new species from most congeners. The new species is also compared to Pareiorhaphis stephanus, a syntopic congener with similar traits.

A new annual fish of the genus Simpsonichthys (Cyprinodontiformes: Cynolebiidae) from the upper Rio Jequitinhonha basin, Brazil.

A new species of Simpsonichthys is described from the upper rio Jequitinhonha basin, Minas Gerais, eastern Brazil. It is diagnosed from all congeners by presenting an A-patterned frontal squamation. Additionally, males of the new species differs from all congeners by the color pattern of body, the color of iris, the absence of contact organs in the pectoral fin, presence of scales on anal-fin base, pectoral-fin length, caudal fin length, and eye diameter. Females of the new species can be diagnosed from remaining congeners by the pectoral-fin length. The conservation status of the new species is evaluated. Comments on the relationships of the new species within the genus Simpsonichthys are presented.

Offshore Drilling Operations and Fishery Monitoring Programs: A Quantitative Impact Assessment Experience in Southern Bahia, Northeast of Brazil

Introduction What should we know about small-scale fishery to infer about impact from drilling operations on shallow waters? What could we consider in drilling activities to define the sources of impact (i.e. disturbance) on fisheries catch rates? The current study is an experience on inferential statistics about these concerns. The impact of offshore drilling on small-scale fishing landings were studied in Southern Bahia, NE-Brazil. Disturbances on catch rates were assessed through a fishery monitoring program to comply with the environmental license requirements for Queiroz Galvao Exploracao e Producao – QGEP oil and gas company. A landing survey was demanded by the Brazilian Environment Institute (IBAMA) to be established in the municipalities of Ilheus, Una, Canavieiras and Belmonte, as a condition for the licensing of offshore drilling activities in the BM-J-2 block south of the state of Bahia. Thus, a Fishery Monitoring Program (“PMDP”) was designed and carried out from April 2011 to December 2013. The main objective of the monitoring program was to provide, through the analysis of fish landings data, input for an evaluation of the influence of drilling activity on the local fishing productivity index (or catch rates). An analytical approach based on the before-after controlimpact (BACI) design was conducted from the application of the analysis of covariance model fit to the landing data The study area corresponds to the area of influence related to drilling in Block BM-J-2 Jequitinhonha Basin, off the southern coast of the state of Bahia, which considered the municipalities of Ilheus, Una, Canavieiras and Belmonte (Figure 1).

Two new species of Cyphocharax (Teleostei: Characiformes: Curimatidae) from headwaters of the Jequitinhonha and São Francisco river basins,Minas Gerais, Brazil.

Two new species of Cyphocharax from southeastern Brazil are described. Both new species share with C. punctatus, and C. vanderi the presence of a midlateral series of irregular patches of dark pigmentation along the lateral line. Cyphocharax jagunco, new species, from Rio Jequitinhonha basin, is distinguished from C. lundi, C. punctatus, and C. vanderi by the number of patches of dark pigmentation along lateral line; the number of pored scales posterior to the hypural joint; the number of scales in the lateral line; and the number of scales rows above lateral line. Cyphocharax lundi, new species, from Rio São Francisco basin, is distinguished from C. jagunco, C. punctatus, and C. vanderi by the presence of dark spots above the lateral line; and the number of scales in the lateral line. Comments on the relationships of the new species within Cyphocharax are presented.

New records of Philcoxia minensis (Plantaginaceae) and Mitracarpus pusillus (Rubiaceae): conservation status assessment and notes on type specimens of two threatened species from the Espinhaço Range, Minas Gerais, Brazil

The Espinhaço Range is a vast chain of mountains comprising ca. 120,000 km2 in the central portions of Minas Gerais and Bahia states, eastern Brazil (Ribeiro et al. 2014). Although this range represents less than 1.5% of the Brazilian territory, it harbors ca. 10% of Brazil’s angiosperm flora (Ribeiro et al. 2012). Furthermore, estimates suggest that ca. 30% of the Espinhaço Range flora is endemic (Giulietti et al. 1987). This high percentage of diversity and endemism may relate to the microhabitat heterogeneity in the “campos rupestres”, a savanna-like vegetation associated with quartzite and ironstone outcrops and white sand patches, at elevations above 900 m (Conceição & Pirani 2005, Ribeiro et al. 2014). The Diamantina Plateau, a quartzite formation of the Espinhaço Range in Minas Gerais, extends from the Araçuaí Basin, in the high Jequitinhonha Basin, to the Rio das Velhas Basin (Ribeiro et al. 2014). The Serra do Cabral, another part of the Espinhaço Range, is a rectangular mountain plateau in the same state in the São Francisco Basin, located to the west of the Diamantina Plateau and separated from it by a valley ca. 40 km wide (Hatschbach et al. 2006).

Microlepidogaster discus, a new species of Hypoptopomatinae (Siluriformes: Loricariidae) from the rio Jequitinhonha basin, southeastern Brazil.

A new Hypoptopomatinae is described from the upper rio Jequitinhonha basin. The new species is distinguished from all congeners by having the ventral laminar expansions of cleithrum and coracoid bearing only 1-30 odontodes, restricted to the area near the pectoral-fin insertion; the anterior plates of mid-ventral lateral series reduced, not ventrally elongated, the first or the second markedly round; pectoral-fin unbranched ray distinctly divided distally, with 7-15 ossified segments, reaching almost half of its length; and accessory process on first epibranchial present. Microlepidogaster discus is further distinguished from its congeners by several other osteological features. The problems concerning the taxonomy of Microlepidogaster, as well as the pattern of distribution of the genus, are discussed.

Brazil Case Study - Tactical Response Plans and Voo's Program - A New Approach to Shoreline Protection Preparedness

ABSTRACT In the past, Brazilian Oil Spill Response Plans focused on the definition of response strategies in offshore environments, but were insufficient when it came to shoreline protection. After the occurrence of major oil spill accidents around the world and events of great repercussion in Brazil and with the intensification of oil and gas E&P activities in locations close to the coast and near environmentally sensitive areas in the country (such as Camamu-Almada and the Jequitinhonha basin), the need for additional nearshore response studies became of the utmost importance. Recently developed documents address the environmental characterization of the coast and indicate the appropriate response strategies, but a more action-oriented approach is needed. For that purpose, based on the best practices in shoreline protection worldwide, a methodology is being implemented so as to provide consistent preparedness support for the protection of nearshore resources. The methodology uses the Brazilian licensing mandatory documents in order to identify the appropriate level of protection preparedness for each of the vulnerable segments of shoreline within the domain of the E&P activity. Once the proper level of preparedness has been identified, the method indicates how to attain such result by presenting a set of tools, such as: TRP (Tactical Response Plan), VoOs (Vessel of Oportunity) Program, Advances Bases and Full Deployment Exercises. This paper provides an overview of the methodology, followed by a case study in Brazil which helps illustrate how the level of preparedness is determined and how the proposed tools help achieve such result. Therefore, it allows assessing the effectiveness of this new approach in the country. Considering Brazil's growing E&P potential, the long extent of its coastline and the abundance of sensitive resources alongshore, the methodology should be applied to other E&P projects developed in the country.

2D common‐offset traveltime based diffraction enhancement and imaging

ABSTRACTThe diffracted energy in a seismic recording contains key information about small‐scale inhomogeneities or discontinuities of the subsurface. Diffractions can therefore lead to high‐resolution imaging of subsurface structures associated with hydrocarbon traps. However, seismic diffracted signals are often much weaker than specular reflections and consequently require enhancement before they can be utilized. In this paper diffractions are enhanced relative to reflections based on two traveltime techniques, namely the modified common‐reflection‐surface approach, which uses the common‐reflection‐surface technique with some modification to tailor it for diffractions and the replacement‐media approach derived here for the purpose of a simplified parametrization of diffraction traveltimes. Both approaches are implemented in the common‐offset domain with the use of a finite‐offset central ray unlike the zero‐ or small‐offset diffraction enhancement techniques that use a zero‐offset central ray. The validity of the two moveout expressions is tested using velocity data taken from a smooth isotropic Marmousi model. A feasibility test was also carried out with respect to the new replacement‐media traveltime approximation addressing the various effects of signal‐to‐noise ratio, depth and lateral displacement of the diffractor location. Finally, diffraction enhancement and imaging was performed on 2D seismic data from the Jequitinhonha basin offshore Brazil. Diffractions were significantly enhanced and a high‐resolution image of the discontinuities of the subsurface was obtained.

Post-rift salt tectonic evolution and key control factors of the Jequitinhonha deepwater fold belt, central Brazil passive margin: Insights from scaled physical experiments

This experiment study investigates the basin-scale salt tectonic processes and kinematic evolution of the gravity-driven deepwater fold belt in the offshore Jequitinhonha salt basin, central Brazil margin. Scaled analogue experiments, geologically constrained by 2D regional seismic interpretations, examine the salt tectonic processes and related depocentre evolution in the basin for variable margin tilt histories and depositional scenarios on appropriate time scales of post-rift basin evolution. The analogue experiments and derived 3D strain data demonstrate that early post-rift sedimentation patterns and margin tilt history were important control factors of the structural and kinematic evolution of the deepwater fold belt. The experiments produced different contractional structures varying from pinched short-wavelength synclines, via polyharmonic salt-cored folds, to thrust belts of variable widths.The salt-cored fold styles and Albian–Cenomanian minibasins characteristic of the Jequitinhonha deepwater fold belt were only reproduced in one experiment, which included isolated carbonate build-ups in the seaward salt basin at the onset of post-salt deposition. Basin evolution and salt tectonics in the Jequitinhonha Basin were dominantly controlled by gravity-gliding of the post-rift sediment succession and formation of carbonate-dominated minibasins on a thick viscous salt substratum in the seaward basin. The subsiding minibasins determined the positions of future synclines and created intervening salt ridges, which became the cores of the long-wavelength anticlines. Experiment restoration utilising time-series strain data allowed estimation of early post-rift deformation showing that strain in the Albian–Cenomanian carbonates probably is six times higher than documented in seismic data. This discrepancy would have major implications for producing realistic palaeo-depositional reconstructions or fracture analysis in the deformed carbonate reservoirs potentially targeted in the salt-cored anticlines.

Salt-structural styles and kinematic evolution of the Jequitinhonha deepwater fold belt, central Brazil passive margin

Salt structures in linked extensional–contractional systems of passive margin sedimentary basins and deepwater fold belts play an important role in the evolution of rifted continental margins. The 100 km wide Jequitinhonha Basin with its salt-detached deepwater fold belt provides insight in the post-rift salt deformation processes in deepwater fold belts of the central Brazilian continental margin.Seismic interpretation and kinematic analysis of basin-scale 2D sections provide insights into the salt tectonic processes, related depositional systems, salt basin geometry, and kinematic evolution of the deepwater fold belt. Several salt kinematic domains have been identified; the most evident is the long-term contractional domain in the distal basin, which formed impressive salt-cored anticlines, salt walls and salt massifs reaching 4 km in thickness.The post-rift basin evolution was dominated by thin-skinned deformation and was initiated by differential loading of early post-rift shallow marine carbonates. Subsequently, the system was mainly driven by gravity-gliding of the overburden on the Aptian salt detachment. The depocenters were controlled by early post-rift salt mobilization and ranged from asymmetric grabens and rollovers to minibasins with vertically-stacked or shifting depocenters and formed the basis of the deepwater fold belt architecture in the Jequitinhonha Basin.The structural styles and kinematic evolution of the deepwater fold belt were strongly controlled by the original salt thickness, the distribution of Albian–Campanian depocenters and thickness variations in the overburden sediments. Early Cretaceous short-wavelength folds have been overprinted by long-wavelength folding owing to increased strength and thickness of the overburden since Paleogene times. Large-amplitude salt-cored folds developed in the deepwater basin due to contraction of pre-existing salt walls and formed margin-parallel, NNW–SSE trending narrow structural highs separated by wide depocenters. Ongoing uplift with reduced sediment accumulation over contractional diapirs or crestal erosion of the deepwater anticlines supported long-term strain localization and positive feedback in the active deepwater contractional deformation.

Feeding and social behavior of the piabanha, Brycon devillei (Castelnau, 1855) (Characidae: Bryconinae) in the wild, with a note on following behavior

Knowledge concerning the behavior of wild freshwater fishes in Brazil is restricted to a few studies, despite such studies being able to answer fundamental questions about conservation. Species of Brycon are amongst the most threatened in the Neotropics, particularly in southeast Brazil, due to anthropogenic activities in this region. This study investigated the feeding and social behaviors of the endangered fish, Brycon devillei in the Preto River, Jequitinhonha basin, Minas Gerais State, Brazil. Behavioral data were collected by snorkeling with four spatially separated groups (habituated), and direct observations of shoals were made using an underwater video camera (a total of 448 hours of observations). This species showed diverse tactics to obtain food. However, the species proved to be predominately a specialist surface-picker, which adopted alternative tactics to find food at certain times of the year, most notably when food items on the water surface became low. Feeding frequency was shown to be negatively correlated to agonistic behavior between conspecifics. Feeding associations were also recorded between the anostomid Leporinus garmani, acting as a nuclear species, and B. devillei, as follower species. The data presented here showed the importance of conserving the riparian environment to protect B. devillei populations. Furthermore, the present study included rare observations of nuclear-follower feeding association among freshwater fishes, especially between medium-sized characiforms, being the first observations of such kind in a Cerrado stream.

AN ANALYSIS OF SPECIES DISTRIBUTION PATTERNS IN THE ATLANTIC FORESTS OF SOUTHEASTERN BRAZIL

This study analysed phytogeographic patterns of several Atlantic Forest areas in southeastern Brazil, including forest areas in the Espinhaço Range, to identify species with congruent distribution patterns and possible environmental factors that might influence these. A total of 54 floristic surveys, predominantly from semideciduous woodland sites but also including some rainforest areas, were compared using UPGMA and DCA methods as well as Jaccard analyses. The former identified four main groupings: group 1 included forests located throughout the Espinhaço Range; group 2 was formed by forest areas in the Rio Jequitinhonha basin; group 3 was formed by three distinct subgroups, one (3.1) predominantly of forest areas pertaining to the Alto Rio Grande basin, another (3.2) of upland forests of the Quadrilátero Ferrífero, and a third subgroup (3.3) of upland forests of the Serra da Mantiqueira; and group 4 encompassed forest areas in the Rio Doce, Rio Paraíba do Sul, Rio Itanhém and Rio Itapemirim basins. The prevailing relief in these basins has influenced rainfall and seasonality in these areas which, in turn, have exerted a major influence on the composition of the semideciduous forests. Geographic proximity and altitude, although important factors, play a minor role in the phytogeographic patterns analysed. Despite the floristic heterogeneity of the Espinhaço Range forests, there are physiognomic and floristic affinities among the forests within the campos rupestre vegetation. These are due to the high altitude and features of the soil.

RESERVOIR QUALITY ASSESSMENT AND PETROFACIES OF THE LOWER CRETACEOUS SILICICLASTIC, CARBONATE AND HYBRID ARENITES FROM THE JEQUITINHONHA BASIN, EASTERN BRAZIL

A study of the rift to early drift phase, fluvial, deltaic and shallow‐marine Lower Cretaceous (Upper Aptian to Lower Albian) siliciclastic sandstones, hybrid arenites and calcarenites from the Jequitinhonha Basin, eastern Brazilian margin, has shown that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework. Description of cores, wireline logs, thin sections and petrophysical (porosity and permeability) analyses were integrated in order to investigate the controls on patterns of diagenesis in these rocks, and hence of reservoir quality distribution. The results of this study will be relevant to the exploration of rift and early drift successions in Atlantic‐type passive margin settings. The study suggests that depositional facies and detrital composition impact the diagenetic evolution and the characterization and prediction of reservoir quality.Reservoir quality assessment was based on the concept of reservoir petrofacies, which is defined in terms of the main attributes affecting reservoir quality including depositional structures, textures, primary composition, diagenetic processes and products, and pore types. This paper demonstrates the practical use of the reservoir petrofacies concept in the evaluation of the controls on porosity and permeability, as well as on seismic and log signatures.

A long-term annual water balance analysis of the Araçuaí River Basin, Brazil

Semi-arid and arid areas exhibit great temporal variability in water availability. In some of these regions, a one- or two-day rainfall is followed by intervening dry periods of variable length. In recent decades, many rivers of the semi-arid portion of the Jequitinhonha Basin have been undergoing a progressive discharge reduction, mainly of their base flow, the Aracuai River is one of them. In order to understand this transformation, a long-term analysis of the annual water balance of the Aracuai River Basin was performed, the results of which are presented herein. Satellite images, hydrometeorological and river discharge data were analyzed; mean and variance tests were conducted to determine temporal homogeneity. Historical pluviometric data analysis shows no corresponding precipitation reduction and temperature undergoes only a slight increase in the same period. On the other hand, evaporation is extremely high, higher than precipitation during most of the year, leaving almost no water for infiltration (aquifer recharge) and runoff. Furthermore, the Aracuai headwaters of its tributaries are now occupied by a monoculture, Eucaliptus sp., used for paper production. Because of the decreased fluvial discharges, its lowlands, usually used for agriculture and pasture, are abandoned and partially eroded.