Brazilian Journal of Geology, Volume: 51, Issue: 2, Published: 2021
  • Insights into the strain history of Neoproterozoic limestones in the Paraguay Belt using stylolites Article

    Seoane, Kauê; Domingos, Fábio Henrique Garcia

    Abstract in English:

    Abstract Tectonic stylolites are indicators of compressive deformation episodes in rocks and are commonly studied in terms of their geometrical attributes’ length (L), and maximum (D max ) and average (D avg ) amplitudes. These parameters were analyzed for vertical stylolites from a sinistral strike-slip fault zone in limestones from the Guia Formation, Paraguay Belt, and compared mathematically to scarce vertical stylolites away from the fault zone. The study aimed to understand the role of strain-induced stylolites on the thinning of faulted limestone layers. Stylolites range from 2.66 up to 28.15 mm in length and from 0.143 up to 1.378 mm in amplitude. The total contractional strain (ϵ) was calculated for 49 stylolites with maximum amplitude peaks of 0.762 mm, using the Kostrov formula. The strain produced layer thinning and growth of the stylolite population. Regions of high stylolite concentration accommodated 16.92% contractional strain, whereas strain values of 3.29% are present in portions with low stylolite density. Layer thinning is directly proportional to contractional strain (ϵ) values spatially induced by faulting. The stylolite morphology plays an essential role in the permeability structure at the reservoir scale, where it can act as a barrier or a channel for fluid flux.
  • Accretionary models for the Neoproterozoic evolution of the Borborema Province: advances and open questions Article

    Santos, Lauro Cézar Montefalco de Lira; Caxito, Fabricio

    Abstract in English:

    Abstract The current knowledge on the accretionary evolution of the Borborema Province is evaluated considering recently published data and interpretations. Early to late Neoproterozoic eclogite, ophiolite, and magmatic arc remnants have been documented and point to oceanic crust consumption. Isotopic contrasts as well as geophysical anomalies across the major domain boundaries are suggestive of collisional sutures and a speculative model of terrane accretion is presented here. On the other hand, the lack of concise evidence for some of the proposed deep-seated structures as well as putative lithospheric continuity in both sides of it suggest reworking of previously continuous lithosphere through intracontinental deformation in localized sectors of the province interior. It is patent that one model does not preclude the other and available evidence so far has triggered the emergence of conciliatory proposals for the Neoporterozoic history the Borborema Province.
  • Influence of preexisting structures on the variation of neotectonic paleostress orientation in an area of the Southeastern Brazilian Margin ARTICLE

    Brêda, Thaís Coelho; Mello, Claudio Limeira; Moraes, Anderson

    Abstract in English:

    Abstract The Southeastern Brazilian Margin presents a NE-SW-striking structural framework, which is characteristic of the Neoproterozoic Ribeira Belt. Other important structural trends along the area are associated with E-W and NW-SE-striking structures, being most related to the Mesozoic-Cenozoic tectonic evolution. A succession of Cenozoic tectonic events has been described by many authors in the Southeastern Brazilian. Among those Cenozoic tectonic events, a Neogene to Quaternary E-W dextral strike-slip regime (EW-DT) shows a wide distribution, presenting some variations in the stress field orientation. This research investigates the influence of the preexisting structural framework on the variation of the paleostress field orientation associated with the EW-DT tectonic event in a selected area in the onshore continental margin of the Southeastern Brazil. The study was carried out in three main stages: lineament analysis, paleostress field analysis, and numerical mechanical modeling. The paleostress field related to the EW-DT tectonic event in the studied area presents: NNW-SSE-striking maximum horizontal stress, and counterclockwise rotation influenced by the structural framework. Regarding this, the regional variation of the paleostress field is influenced by a preferential reactivation of NE-SW-striking structures while sets of approximately E-W-striking structures are the main local control of counterclockwise rotation of the stress field.
  • Support method for interpretation of regional groundwater monitoring in urban areas ARTICLE

    Pileggi, Fabio; Hirata, Ricardo; Aranda, Nataly; Conicelli, Bruno

    Abstract in English:

    Abstract Urban centers radically alter hydrological cycles, causing unintended consequences for the environment, such as the creation of extensive contamination plumes in unconfined aquifers. The Environmental Agency of the State of São Paulo has observed this issue since 1994. Therefore, this study aimed to create a method using nitrate as an indicator of contamination that permits an assertive interpretation of changes in the groundwater quality in monitoring wells of regional networks. The method was applied in ten cities with monitoring wells in the Bauru Aquifer System. The results correlated the presence of nitrate with the time and dynamics of land use in the capture zones of the wells over 54 years (1962-2016). In areas with sewer networks installed before 2001 and urban occupation greater than 60% of urban occupation in the capture zones, there was an increase in nitrate concentration of at least 35%. Likewise, extending this new method to other wells will make it possible to identify the causes of nitrate and other contaminants in the groundwater-monitoring network in the State of São Paulo.
  • How Ground Penetrating Radar helps to understand the Nhecolândia lakes landscape in the Brazilian Pantanal wetland Article

    Taioli, Fabio; Santos, Mauricio Guerreiro Martinho dos; Assine, Mario Luis; Mendes, Deborah

    Abstract in English:

    Abstract The Pantanal wetland is an active sedimentary basin representing a relevant depositional setting for alluvial sedimentation studies. However, sedimentation homogeneity and the lack of outcrops makes sedimentary analysis more difficult. The Lower Nhecolândia is located at the Southern edge of the Taquari river megafan, whose genetic origin has been disputed as fluvial or eolian deposition. GPR analysis was used to characterize the subsurface stratigraphy and understand the region’s geomorphic evolution. The 100 MHz GPR provided continuous good quality sections up to a depth of 8 m. Two continuous reflections are disconformities that bound three depositional sequences characterized by distinct radar facies. The lower facies presents an upper erosional truncation followed by reflections presenting ∼1.5 m deep channelized forms and concave-up low amplitude reflections. The intermediate facies (∼4 m thick) presents a base with erosional truncation followed by concave-upward forms, ∼10 m wide, 1–3 m deep, separated by 1–2 m, and offlapping geometry. The upper facies has a flat base and thickness of 2–4 m, with parallel reflections; it shows a strong correlation between the radar facies and the forms preserved in the landscape, suggesting that channelized fluvial streams did not form them. The results obtained indicate that GPR use in the Pantanal is an important method to elucidate its geologic evolution.
  • Open-system magmatic evolution and crystallization conditions of the Ediacaran shoshonitic rocks from the São João do Sabugi Pluton, Borborema Province, NE Brazil Article

    Paiva, Dayvison Bruno Cordeiro de; Vilalva, Frederico Castro Jobim; Souza, Zorano Sérgio de; Nascimento, Marcos Antônio Leite do

    Abstract in English:

    Abstract The São João do Sabugi Pluton (SJSP) (∼579 Ma) is one of the most expressive occurrences of Ediacaran, syn- to post-collisional shoshonitic rocks in the Rio Piranhas-Seridó Domain, Borborema Province, NE Brazil. The petrography, whole rock and mineral composition of this pluton were investigated to characterize its open-system magmatic differentiation processes. The pluton is composed of three rock groups: gabbro-diorite, with clinopyroxene ± orthopyroxene ± amphibole ± biotite; monzodiorite, with amphibole and biotite (± pyroxenes); and granodiorite, with biotite as the main mafic mineral. Evidences of open-system processes, including partially resorbed metasediment xenoliths, are widespread. These rocks are metaluminous, alkali-calcic and magnesian, and have shoshonitic affinity. They show relative LILE and LREE enrichment and pronounced negative Nb-Ta anomalies. Major and trace element geochemical modeling favors magma differentiation by fractional crystallization (56–62%) after crustal assimilation of ∼30% of local paragneisses and schists from the Seridó Group in a relatively stationary magma chamber at crustal depth, under pressures of 5–6 kbar, temperatures of ∼800–1,000°C and relatively oxidizing conditions. The less evolved gabbro-diorite was generated by ∼18% modal dynamic partial melting of a metasomatized mantle source.
  • Whole-rock trace element analyses via LA-ICP-MS in glasses produced by sodium borate flux fusion Article

    Leitzke, Felipe Padilha; Wegner, Aline Celuppi; Porcher, Carla Cristine; Vieira, Natália Isabel Malüe; Berndt, Jasper; Klemme, Stephan; Conceição, Rommulo Vieira

    Abstract in English:

    Abstract Trace elements provide crucial information about the origin and evolution of the Earth. One common issue regarding their analyses is the reduced analyte recovery during hot plate acid digestion for some geological samples. To overcome this, alkali fluxes (e.g., Lithium borate) have been used to produce an homogeneous synthetic glass that can be used then for both X-ray fluorescence (XRF) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In this sense, we developed a method for LA-ICP-MS whole rock trace element analyses in glasses prepared by mixing high-purity sodium tetraborate and rock powders at high-temperature. We selected six international reference materials including peridotite (JP-1), basalt (BRP-1), kimberlite (SARM-39), pyroxenite (NIM-P), diorite (DR-N) and andesite (JA-1). Glasses were produced in a fully automatic fusion machine with step heating. Run products analyses were carried out on a Thermo® Element2 SF-ICP-MS coupled to a New Wave Research® Nd:YAG (213 nm) laser ablation system and on a Thermo® Element XR ICP-MS coupled to an Analyte G2 (193 nm) LA system. Results show that glasses are homogeneous and there is good agreement (generally > 90%) between our data and literature values for most trace elements, including large ion lithophile elements (LILE), high-field strength elements (HFSE) and rare-earth elements (REE).
  • A singular Hegetotheriinae (Notoungulata, Typotheria) from the late Oligocene-Early Miocene of the Subandean Region of Bolivia Article

    Reguero, Marcelo Alfredo; Tineo, David Eric; Bona, Paula; Pérez, Leandro Martín; Vergani, Gustavo Dardo; Ruiz, Gloria González; Poiré, Daniel Gustavo

    Abstract in English:

    Abstract Geological studies in the northern sector of the Chaco foreland Basin, Bolivia, yielded new fossils coming from late Oligocene-late Miocene of the Petaca Formation. Few fossil mammals were known from the Subandean Region of Bolivia. We report a partially complete mandible of a hegetotheriid Hegetotheriinae (Notoungulata, Typotheria) from Abapó (Río Grande River). The specimen (YPFB-LIT-PAL-005) is very close in size and dental morphology to the late Oligocene (Deseadan South American Land Mammal Age, SALMA) — Santacrucian (early Miocene) Prohegetotherium schiaffinoi (Kraglievich 1932) from Fray Bentos (Uruguay and Argentina), Salla (Bolivia), Divisadero Largo-Potrerillos and Quebrada Fiera (Argentina). However, mandibular characteristics, as the shape with a marked change in height along its length, increasing towards the back, a prominent masseteric crest, a deep mandibular groove, and a remarkable thickening of the ventral rim of the mandible, indicate differences between this specimen and Prohegetotherium schiaffinoi and the other Hegetotheriinae. The affinity of YPFB-LIT-PAL-005 with P. schiaffinoi suggests a late Oligocene to early Miocene for the upper bearing horizon of the Petaca Formation (in Abapó), an older age than previously assigned to the top of this unit (late Miocene), and confirms the taxon distribution between ∼ 36 ° to ∼ 17 ° south latitude.
  • Water level alterations on the southern rim of the Guarani Aquifer due to the rain regime Article

    Osório, Vanessa da Conceição; Moura, Cássio Stein

    Abstract in English:

    Abstract This paper estimated the total water storage variation in the southern rim of the Guarani Aquifer System during a three-year time span, making use of data provided by the Gravity Recovery and Climate Experiment. Monthly data were used to estimate the Bouguer anomaly in Southern Brazil. A direct modeling, using the Bouguer plateau, was applied to quantitatively estimate the water volume variation of a specific thickness in the studied region. Meteorological almanac data were compared to the gravitational alterations. We found a direct proportionality between the monthly rain average and the water table level. A simple model was found to forecast water accumulation as a function of rainfall regime, which is validated by a Pearson index of 0.82 that indicates a strong correlation between pluviometric and gravimetric data. In order to raise the stored water level near the recharge area by 1 mm, approximately 3 mm of rainfall is needed.
  • Late Ediacaran lateral-escape tectonics as recorded by the Patos shear zone (Borborema Province, NE Brazil) Article

    Archanjo, Carlos José; Hollanda, Maria Helena Bezerra Maia de; Viegas, Luis Gustavo Ferreira

    Abstract in English:

    Abstract Lateral escape tectonics mediated by strike-slip fault zones are an efficient mechanism of rock deformation in the continental crust of collision zones. The Borborema shear zone system, which shows dimensions comparable to the Cenozoic extrusion of Indochina, defines a lateral escape setting of the Brasilano orogeny in Northeastern Brazil. In this paper, the timing of high-grade metamorphism and compositions of the terranes involved in the shear deformation were investigated. The Patos shear corridor deforms the Siderian to Neoarchean rocks of the Granjeiro Complex that, in turn, form the basement of Seridó-Lavras da Mangabeira metapelites. U-Pb zircon ages and Sm-Nd whole-rock isotopic compositions indicate that the 2.80 – 2.35 Ga basement sequences mainly include juvenile material, whereas zircons from synkinematic migmatites indicate that the partial melting occurred in the Late Ediacaran (ca. 565 Ma). Cooling rates provided by 40Ar/39Ar range from 12 to 17°C/Ma, indicating a differential shear zone exhumation, in agreement with a transpressive setting. The presence of allochthonous Siderian sequences dismembered along the shear zone suggests that the Seridó-Granjeiro corridor defines a major tectonic boundary connected to the collisional front defined by the convergence of São Francisco-Congo and Amazonian cratons.
  • Cyclicity and hierarchy in sequence stratigraphy: an integrated approach Invited Review

    Fragoso, Daniel Galvão Carnier; Gabaglia, Guilherme Pederneiras Raja; Magalhães, Antonio Jorge Campos; Scherer, Claiton Marlon dos Santos

    Abstract in English:

    Abstract With standardized methodology and nomenclature, the sequence stratigraphy aims to characterize multi-scale cyclical units of genetically related rocks into a hierarchical chronostratigraphic framework. From facies to basin scale, the stacking patterns and stratigraphic surfaces are recognized as sequence elements. In parallel, Earth sciences have developed a sophisticated understanding of geological processes (tectonic, climatic, and eustatic) that produce the main cyclicity observed in the sedimentary rock record. This review paper discusses how the elaboration of hierarchical stratigraphic frameworks that incorporate the knowledge of these periodic geological processes — from high- to low-frequencies — as the control of generation and preservation of sequences — from high- to low-resolutions — guarantees objective results in predicting vertical recurrence and the lateral correlation of genetic stratigraphic units. This interpretive approach of cyclic stratigraphic analysis supports the development of effective observable criteria to identify and rank sequences in multiple scales, based on cycle anatomy, recurrence, vertical trends, and mappability. This methodological improvement reduces the inaccuracies and contradictions of traditional conceptual models based on fully preserved three-dimensional depositional systems.
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