Resumo em Inglês:

Abstract The objective of this short paper was to provide some advice on how to write a geoscience paper of international standard and to warn against some common pitfalls. It is focused on how to structure a paper and stresses the importance of building its contents around a well-defined problem. Furthermore, the importance of moving away from outdated and counterproductive ways of describing and interpreting deformation is emphasized. In particular, describing structures and tectonic evolution in a poorly founded scheme of multiple deformation phases and making stress interpretations from structurally complex and heterogeneous rocks where rotations and stress perturbations are difficult or impossible to account for are strongly discouraged. Instead, I encourage the use of modern structural geology and tectonics ideas that, among other things, allow for composite and overprinting structures to form progressively and diachronously with a wide variation in style and orientation during a single deformation history. Also, more emphasis should be put on strain and kinematics, toning down the use of stress. After all, stress is only observed through strain and kinematics; going from one to the other is not straightforward in general, and particularly difficult in ductilely deformed rocks.

Resumo em Inglês:

Abstract This study presents new sedimentology data and attempts to understand coastal processes, sedimentary dynamics and stratigraphic patterns of the Rio Bonito Formation (early Permian) in Paraná Basin, southern Brazil. The study was performed based on the description of five cores, located in a small-scale area - São Gabriel City - in Rio Grande do Sul State, southern Brazil. Eighteen facies were described and grouped into nine facies associations. Later, these facies associations were then grouped into three depositional systems: fluvial, tide-dominated estuary and wave-dominated shallow-marine depositional systems. A paleoenvironmental evolution is proposed using three block diagrams showing the paleoenvironmental stage (S1, S2, and S3). S1 contains the oldest part of the sedimentary record with predominance of fluvial system deposits, S2 comprises dominantly estuarine system deposits, and S3 is mostly composed of shallow-marine deposits. ­Stratigraphic framework showed a general retrogradacional tendency, with thickness variations along the systems tracts that allowed for the construction of a curve of accommodation changes to the Rio Bonito Formation in the region of São Gabriel during the early Permian. This study contributes to a better understanding of the fluvial discharges, tidal and oscillatory (wave) currents and their interactions and dominances along stratigraphic records of coastal deposits.

Resumo em Inglês:

Abstract The Manacapuru Formation, Amazonas Basin, outcrops on the margins of a highway in the region of Presidente Figueiredo, state of Amazonas. A systematic palynological and a lithofaciological analysis was carried out aiming to contribute to the paleoenvironmental understanding of the Manacapuru Formation and its respective age. The present work uses the analysis of the chitinozoan for biostratigraphic purposes as a tool. A total of 27 samples were collected in which an assemblage of lower Lochkovian can be recognized, whose characteristic species are Angochitina filosa, Cingulochitina ervensis, Lagenochitina navicula, and Pterochitina megavelata. It was possible to identify an intense reworking in the exposure, evidenced by the presence of paleofaunas ranging from Ludfordian to Pridolian, which may be associated to the constant storm events that reached the shelf. The lithofaciological analysis allowed the recognition of 6 predominantly muddy sedimentary lithofacies with sandy intercalations that suggest deposition in an offshore region inserted in a shallow marine shelf and influenced by storms.

Resumo em Inglês:

ABSTRACT: The occurrence of earthquakes associated with the opening of groundwater wells is a very rare phenomenon. We present the results from a magnetotelluric profile of about 4 km-long that crosses a seismic zone near the town of Bebedouro, in the Northeastern part of the intra-cratonic Paraná basin, in Brazil. The seismic activity is thought to be caused by a raise in pore-pressure within a fractured basalt aquifer due to the natural injection of water from the shallow aquifer into the basalt. Regularized 2D inversions of the magnetotelluric data show that the basalt layer presents both electric resistivity (60-300 ohm-m) and thickness (400-600 m) within the expected ranges for the study area. However, an unforeseen abrupt change (~200 m) in the basalt thickness has been observed. This variation occurs close to the Western limit of the seismic zone and it nearly coincides with a geoelectric basement deepening of about 600 m. We interpret these lateral contrasts as a fault system that probably controlled the deposition of the Permian to Jurassic volcano-sedimentary sequence under the study area. Our study suggests that a preexisting structure affecting the basement and the basaltic layer is determinant in favoring seismicity associated with the opening of water wells.

Resumo em Inglês:

Abstract The Fazenda Bonfim emerald deposit lies within the Seridó Belt. It is a classic example of deposit formed through metasomatic interactions between Be-rich granite intrusions and Cr(± V)-rich mafic-ultramafic rocks. The setting of the emerald mineralization was built under strong strike-slip dynamics, which produced serpentinization and talcification of mafic-ultramafic host-rocks, and was followed by syn-kinematic emplacement of Be-rich albite granite, favoring hydrothermal/metasomatic processes. The structural control and lithological-contrast were fundamental to the fluid flow and the best ore-shoot geometry, developed in the S-foliation intra-plane at the contact zone (phlogopite hornfels) between mafic-ultramafic rocks and the albite granite. Subsequently, an albitization process, linked to the final-stage of magmatic crystallization, led to an overall mineralogical and chemical change of the albite granite. 207U-235Pb data revealed inheritance ages from Archean to Neoproterozoic and a crystallization age of 561 ± 4 Ma for albite granite. However, 40Ar/39Ar data revealed plateau age of 553 ± 4 Ma for phlogopite hornfels, interpreted as the closure time for the metasomatic event responsible for the nucleation and growth of emerald crystals. The short interval of time between U-Pb and Ar-Ar data indicates an intense, but not protracted, metasomatic history, probably due to low volume of intrusive magma.