Resumo em Inglês:

Abstract The main reservoirs in the Linguado Field are grainstone and packstone carbonates composed of oolites, oncolites, pelloids, and rare bioclasts, of the Quissamã Formation (Albian-age) and coquinas of the Coqueiros Formation (Aptian-age). Within Quissamã Formation, facies have high porosity variations and their 3D characterization is of utter importance to allow for a better location of the wells. The objective of this study was a volumetric characterization of Quissamã Formation by means of an adapted classical workflow composed of well-seismic tie, seismic preconditioning, seismic interpretation, seismic inversion, petrophysical properties estimation, and porosity geostatistical modeling. Seismic inversion results allowed the interpretation of a horizon to separate the carbonate platform in an upper zone, with low acoustic impedance, from a lower zone, with high acoustic impedance. Finally, behavioral knowledge of acoustic impedance and the porosity distribution within the Albian carbonate platform helped to better characterize the distribution of carbonaceous facies allowing the confirmation that commercial wells were drilled in low acoustic impedance and high porosity regions. It was also possible to confirm that a well, declared as noncommercial, was drilled in a poor reservoir region with high acoustic impedance and low porosity and identified other locations that were not yet drilled but could represent potential targets.

Resumo em Inglês:

Abstract Basaltic aquifers are an important source of water supply in many regions worldwide. Because of their cooling process, flood basalts normally have complex internal structures and unpredictable permeable zone distribution. Geophysical profiling is a reliable tool used to identify the vertical variations of physical properties within the flood basalts, mainly to distinguish between low and high permeability intervals. In this study, a detailed analysis of drill cuttings, and geophysical logging of two depth wells helped to identify the typical response of main facies of flood basalts in the Serra Geral aquifer system. The evidence obtained from this work confirms that flood basalts may be classified as multilayer aquifer systems in which a highly permeable top covers a center with low permeability as a result of recurrent floods. In several cases, permeable layers are represented by a weathering horizon developed between two flood events. This study uses an empirical model to estimate the porosity based on acoustic velocity logging. A useful model based on a well-established Kozeny-Carman model was developed to predict the permeability of basaltic rocks using porosity data. The results obtained allow to identify the permeable intervals of basaltic aquifers and to estimate their hydraulic properties.

Resumo em Inglês:

Abstract The nature of the extensive silicic units of the Paraná Igneous Province is still heavily debated. The silicic rocks that outcrop in the Palmas plateau (Southwestern Parana State) show aphyric texture and TiO2 < 0.86%, being classified as Palmas-type rhyolites. Physical volcanology criteria are used here to constrain their origin. Textural and structural variations are observed in these rocks, resulting in the description of nine lithofacies: pitchstone; banded vitreous rhyolite; aphanitic rhyolite; rhyolite with planar disjunctions; massive rhyolite; compositionally banded rhyolite; amygdaloid rhyolite, rhyolite with quartz levels, and altered rhyolite. Folded compositional banding associated with volcanic conduits, well-defined lobes and basal autobreccias attest to an effusive origin for most lithofacies. They occur as domes or extensive tabular bodies, fed by volcanic conduits. For both domes and tabular units, the faciological sequence involves (from bottom to top): altered rhyolite; aphanitic rhyolite or rhyolite with tightly-spaced planar disjunctions; monotonous rhyolite with decimetric-spaced planar disjunctions; and top portions with fast cooling features. Only banded vitreous rhyolite differs due to the presence of shards and gas-escape pipes, aspects that imply in a pyroclastic nature. Therefore, a secondary pyroclastic flow created by lava collapse is suggested as its origin, although further studies are required.

Resumo em Inglês:

Abstract Magnetic fabric and rock magnetism studies were performed on the three facies of the Anta granite (SE of Rio de Janeiro State, southern Brazil). This intrusion is roughly elliptical (∼ 14 km2), NE-SW oriented and composed of granodiorite, monzodiorite, quartz-diorite, syenogranite, and monzogranite. It shows solid-state deformation and tectonic foliation at its borders and is apparently isotropic in the central part where the internal fabrics are impossible or very difficult to measure through classical techniques. Magnetic fabrics were determined by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). The AMS and AARM fabrics are coaxial for all facies. The parallelism between AMS and AARM tensors excludes the presence of a single domain (SD) effect in the AMS fabric. Several rock-magnetism experiments performed on one specimen from each facies show that, for all units, magnetic susceptibility and fabrics are carried by magnetite grains. Most of the magnetic foliations are steeply dipping in all facies, and are roughly parallel or sub-parallel to the foliation measured in the field and in the country rocks. In contrast, the magnetic lineations present mostly low plunges for almost the whole pluton, except for one site where it is steep (> 60°). Thin section analysis show that rocks from the borders of the Anta pluton are solid-state deformed, indicating that the borders of the pluton were affected by the regional strain during its emplacement. On the other hand, the lack of solid-state deformation at outcrop scale and in thin sections precludes deformation in the central part of the pluton to be determined, where igneous textures are preserved. This evidence allows us to interpret the magnetic fabrics observed in this part of the pluton as primary in origin (magmatic) and acquired when the rocks were solidified as a result of magma flow, in which steeply plunging magnetic lineation suggests that a feeder zone could underlain this area. Our data suggest that the regional deformation partially affected the emplacement of the Anta granite.

Resumo em Inglês:

Abstract Data acquisition by automatic monitoring allows obtaining a large number of data, supporting a better understanding of the monitored region. The use of automated discharge measurement enables a better understanding of floods, the relationship between surface and groundwater flow rate values, and aquifer recharge. However, automatic instruments processing and storage may fail, leading to missing values in some intervals of the recorded time series. These missing values may be replaced by estimates from the regional flow rate or other statistical approximations. For evolved karst systems, however, those techniques may not be adequate due to their rapid discharge responses to rainfall. The aim of this paper is to develop a method able to estimate fluviometric monitoring missing values, based on time series correlation for correlated data. These estimates were obtained from automated monitoring through pressure transducers in 6 streams in a region of approximately 505 km2, predominantly covered by the carbonate and metapellitic Neoproterozoic rocks of the Bambuí Group. The proposed method is composed of four sequential steps: computing the streamflow-data autocorrelation and the cross-correlation of pluviometry with the flow rate; calculating the precipitation fraction that directly contributes to the discharge; fitting of a linear relationship between pluviometry and the monitored daily discharge, to calculate discharge values on days when automatic measurements failed; and approximation of the calculated and monitored discharge values, using a number of statistical criteria. The results show the maturity of the karst aquifer system, with fast ground-water flow and low storage, well-calibrated stage-discharge rating curves for the 2016/2017 hydrological year and that the values estimated by proposed methodology present a deviation of less than 9% over the monitored data.

Resumo em Inglês:

Abstract The area is located at the northern boundary of the Guaxupé Complex, which corresponds to the northern domain of the Socorro-Guaxupé Nappe, in the Southern Brasília Orogen, close to the Varginha Shear Zone. This study integrates petrography, mineral chemistry, optimized geothermobarometry, and trace elements thermometry data, aiming to define and characterize the metamorphic conditions and the P-T path of the granulitic rocks from the northern portion of the Guaxupé Complex. In the area, the Guaxupé Complex consists predominantly of ortho-derived rocks represented by granulitic gneisses (orthopyroxene gneisses) of felsic to mafic composition with clinopyroxene, garnet, amphibole, biotite, and rare rutile. The calculated pressure and temperature conditions record metamorphic peak around 1,078°C and 14.8 kbar, compatible with ultra-high temperature metamorphism conditions, marked by grt + cpx + opx + pl ± qtz ± rt mineral assemblages, and granulite facies re-equilibration in the sillimanite stability field at P-T conditions of 930 to 800°C and 13.5 to 11.0 kbar. The results are compatible with deeper portions of the lower crust involved in a continental collision and suggest a clockwise P-T path, typical of crustal thickening zones, followed by near-isothermal decompression during tectonic exhumation.

Resumo em Inglês:

Abstract Quartz and cassiterite crystals of granite, greisens, and quartz veins from Mocambo Granite, Carajás Province, were studied by scanning electron microscopy — cathodoluminescence and electron microprobe. Five types of quartz were identified: Qz1, magmatic and Qz2, Qz3, Qz4, and Qz5 hydrothermal. Qz1, anhedric to subhedric, luminescent and fractured at different intensities, predominating in less evolved rocks. Qz2, with low luminescence, is younger than Qz1; it occurs as irregular patches, filling fractures or forming veins that cut Qz1. Qz3, non-luminescent, resulting from continuous alteration, dissolution, and recrystallization processes; fills fractures that cut Qz1 and Qz2. Qz4 occurs in the most evolved and hydrothermalized rocks and in greisens bodies mineralized in cassiterite; is euhedral to subhedral, exhibits well-defined zoning, and has been interpreted as later than the previous one. Qz5 has poor luminescence; occurs in mineralized veins with wolframite and, secondarily, cassiterite. Qz1 shows Ti enrichment, while Qz4 associated with cassiterite is enriched with Al. Well-formed cassiterite crystals exhibit concentric zoning and low Fe, Ti, W, Nb and Mn contents. Qz5-associated cassiterite crystals form inclusions in the wolframite, suggesting that cassiterite and wolframite precipitated from hydrothermal processes at different times.

Resumo em Inglês:

Abstract Mineralogical evolution of ophiolites is significant to understand paleo-oceanic crust and mantle requiring multi-proxy techniques to identify steps in the processes. We studied the Bossoroca ophiolite from the southern Brasiliano Orogen, a prime example of Tonian accretion to an oceanic island arc. Integration of field geology, aeromagnetometry, aerogamaspectrometry, electron microprobe analyses, and compositional maps of minerals led to the decoding of oceanic and continental processes. The ophiolite is highly magnetic and low-K and is positioned at the base of the superstructure. We studied amphibolite, tourmalinite, and chromite-talc-magnesite granofels from the ophiolite, Capivaras diorite from the Cambaí Complex infrastructure and one metavolcanoclastic rock from the Vacacaí Group superstructure. Honblende is zoned in all rock types. Low-Ti hornblende is compatible with medium-pressure metamorphism at 7 kbar. This M1 to M2 amphibolite facies resulted in the widespread association of olivine + talc in metaserpentinite. Dravite is similar to tourmaline from the Ibaré ophiolite. Andesine and oligoclase are dominant and albite minor. Cr-spinel in granofels recrystallized in greenschist facies; host rock originated by carbonatization of serpentinite formed in the oceanic crust along with chloritite and tourmalinite. Serpentinite rare earth elements (REE) suggest origin in depleted mantle peridotite. The ophiolite evolved in the Adamastor Ocean until incorporation into the island arc.

Resumo em Inglês:

Abstract The Middle-Upper Triassic section of the Paraná Basin is included in the Santa Maria Supersequence. This stratigraphic unit is classified as a second-order Supersequence, being subdivided into three third-order sequences in which four Assemblage Zones (AZ) based on tetrapods are recognized. In this work, chemical analyses of fossils and hosting rocks of each AZ were performed in order to verify whether the geochemical patterns of the rocks could serve to distinguish them even in the absence of fossils. For this purpose, nine samples of fossils and their sedimentary matrices were analyzed, by ICP-MS. The results show that there were changes in the chemical parameters in force at the depositional time of each sequence (and corresponding AZ). In general, the lower portion of the package was deposited under more basic and dry environmental conditions, indicated by the Ca and Ba concentrations found in the rocks and bones that contains them. By its turn, the top of the section is characterized by more acid and humid conditions, evidenced by Al, Si, and Sr increase. Such a geochemical shift from dry to humid conditions occurred just at the beginning of the Late Triassic and is probably related to the Carnian Pluvial Episode.

Resumo em Inglês:

Abstract The Morro do Chaves Formation (Barremian-Aptian of the Sergipe-Alagoas Basin) presents a sedimentary succession of approximately 150 m of thickness, composed of coquinas. Despite the sedimentological, stratigraphic, and petrophysical studies developed in coquinas, the general understanding of the relationship between sedimentary processes and meteoric diagenesis is not clear. The aim of this study is to recognize and understand the features of meteoric diagenesis in bioclastic from a well core drilled at Atol quarry. The core is composed of calcarenites and calcirudites interbedded with sandstones and shales. Taphonomic signatures show a low degree of physical alteration, without shells in life position. The main features related to meteoric diagenesis are bioclasts with bioerosive macrostructures (Caulostrepsis isp. and Oichnus isp.) and destructive micritization process. This was the main alteration process identified in the bioclasts and occurs throughout the coquinas interval and, in some beds, it was possible to distinguish three different stages of micritization. The differentiation of the stages results from different periods of variation of water depth, intensity of microorganisms attack, time of alteration, and variations in siliciclastic input. Additionally, one interval exhibits extremely micritized shells, curved fissures, and carbonate nodules, interpreted as having been deposited and subsequently altered in a palustrine environment.

Resumo em Inglês:

Abstract In the Bom Jardim de Goiás region, the Transbrasiliano Lineament shows evidence of a fault reactivation along NE-SW structures (main direction) and secondary directions related to subsequent events. To study the structural framework and reactivation inputs toward tectonic events, distinctive features of the northern Paraná Basin border were analyzed by integrating gamma spectrometry and radar data, both supported by field research. The remote sensing database obtained by the Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) sensor allowed detecting lineaments and morphometric derivatives. Besides, the developed morphogenetic process images attest to the importance of structural control on relief evolution while concentrating lineaments as a function of lithological and geomorphological domains. Airborne gamma-ray spectrometry data processing focused on Kd (Anomalous Potassium) and F-Parameter indices. In this context, the fuzzy logic and Index Overlay Method allowed multivalued integration that indicated hydrothermal products and weathering processes correlated with Kd and F-Parameter anomalies. Thus, the joint interpretation of lineaments, geomorphological domains, and Kd/F-Parameter anomalies allowed differentiating primary geological elements and products from surface dynamics, directly or indirectly related to tectonic reactivation processes.