Geological Survey Of Brazil Research Articles

Hydrochemistry and Contamination in Sedimentary and Fractured-Rock Aquifers of The Upper Rio Negro Basin – Amazonas/Brazil

The Amazon region has the largest hydrographic network on the planet. However, cities and communities along rivers obtain water from tube wells without studying the chemical quality and, consequently, the potability of their water. In specific geological contexts, there is a significant probability of natural contamination by arsenic in groundwater in the region, already attested in previous works in the Solimões, Madeira and Amazonas rivers basins, but not yet found in the Negro river basin. As the Negro is the second largest river in the Amazon Basin, it has become necessary to study the chemical quality of its groundwater, relating it to the geology of the region. In this work, water samples were collected from 21 wells and 4 water springs used for human consumption, following the protocols proposed by the US – EPA. In the field, the physicochemical parameters of the in-situ water were measured, and alkalinity tests were carried out on the samples. The cations were analyzed at INPA and the anions at the Geological Survey of Brazil (SGB). From the 25 samples, 16 had analises results within acceptable ionic balance values, and 12 of the 16 had at least one of the following elements in concentration above World Health Organization and Brazilian Guideline Values: Al, As, Fe, Mn and Pb. The presence of values below the GV, but above what is considered natural, of NO3- in 66% of the contaminated points, associated with the shallow depth of most of the wells, installed in areas of recent sedimentary deposits and that do not show any or few signs of care demonstrate that the contamination in these localities is of anthropic origin. Two samples (16% of the contaminated samples) are from deep wells installed in fractured aquifers, which in this case indicate contamination of geogenic origin. Arsenic was found in association with iron and aluminum in a well installed in alluvial sediments, which indicates that more studies are needed for this specific geologic formation to know the quality of this water. For other locations and cities, short, medium and long-term measures are needed to prevent anthropogenic contamination of aquifers.

Las unidades morfoestructurales de la cuenca hidrográfica del río Formoso, Bonito - Mato Grosso do Sul - Brasil: analizando un sistema cárstico

The morphostructural units of the Formoso River hydrographic basin (Bonito – Brazil) are unique in Brazil and configure the karst landscapes of Serra da Bodoquena. The present research aims to identify and spatialize the karst units inside a semi-detail scale and analyze their correlation with the regional landscape. Thus, the database is based on: 1) technical information offered by The Geological Survey of Brazil; 2) data offered by the Radam/Brasil Project; 3) altimetric charts of the study area; 4) field trip data to develop and verify the regional karst landscape. The authors observed a major presence of carbonated rocks in the study area (64.93%) and a minor but significant presence of terrigenous rock extension (35.07%). The main geological formations of the study area are the Cuiabá Group (terrigenous rocks) and Corumba Group (carbonated rocks). The regional landscape conditions of the Formoso River Hydrographic basin directly influence superficial water characteristics creating translucent water. The karst area presents classical characteristics with caves, mogotes, dolines, and river sinks. In addition, the area presents significant pedological variation and complexity that influence the local canopy cover with human activity all over the study area, affecting the landscape and threatening the karst scenario.

Environmental Geochemical Analysis in the Yanomami Indigenous Land, Mucajaí River Basin, State of Roraima, Brazil.

The Yanomami Indigenous Land in the Amazon has a long history of illegal artisanal gold mining, leading to concerns about mercury (Hg) contamination. This study has conducted a geochemical analysis to assess Hg contamination from these mining activities. Geological materials, including river water and stream sediments, were collected from 14 predetermined points based on the Geological Survey of Brazil's methodology. The results revealed that water samples did not show Hg contamination above the limits set by the National Council of the Environment (Conama) Resolution 357. However, two stream sediment samples, particularly PJS009 and PJS010 collected from the Mucajaí River, exceeded the Conama Resolution 454's limit of 0.17 mg/kg. A Hg content of 0.344 mg/kg was found in the sediment sample PJS009, the one collected further upstream in the Mucajaí River, and 1.386 mg/kg was found in sample PJS010, also in the Mucajaí River in the region shortly before the Fumaça Waterfall, indicating that the sediments of the Mucajaí River may be contaminated with Hg from the Fumaça Waterfall upstream.

Geochemical mapping by stream sediments of the NW portion of Quadrilátero Ferrífero, Brazil: Application of the exploratory data analysis (EDA) and a proposal for generation of new gold targets in Pitangui gold district

Quadrilátero Ferrífero (QF) is a worldwide known metallogenetic province and has in its NW portion the Pitangui greenstone belt, one of the new frontiers for gold exploration in that region, presenting important gold deposits, such as Turmalina and São Sebastião. Among several actions of the geological and mineral resources projects carried out by Geological Survey of Brazil (SGB/CPRM) in the QF region, a high-density geochemical survey (1 sample/4 km2) by stream sediments was accomplished in its NW portion to better understand the behavior and distribution of chemical elements along the main geological units, especially those related to gold mineralization (Au, As, Sb, Bi, etc.). The exploratory data analysis (EDA), regarding uni-, bi-, and multivariate analyses, point to an important chemical control of the stream sediments by the geological units and help to describe some lithological features and to understand the behavior and distribution of hydrothermal processes and gold mineralization. This procedure defined the main geochemical associations, including the association As, Sb, Cu and Bi linked to Ni, Cr and Co, interpreted as gold mineralization hosted in the metavolcanosedimentary lithotypes. The staged factor analysis (SFA) considering compositional data (CoDa), logistic function, and fractal model approaches provided the generation of the geochemical mineralization probability index (GMPI), which produce a GMPI map for gold mineralization. The calculations did not take into account the gold concentrations but only the pathfinder elements and the model validation by the prediction-area plot, confirm the high performance of this approach. The gold mineralization map, in addiction to satisfactorily predicting the location of most known gold occurrences, was able to indicate new potential targets for prospecting new gold deposits.

ID‐TIMS Sm‐Nd and Sr Isotope Ratios of Reference Material Basalt Ribeirão Preto (BRP‐1)

This work presents Sm‐Nd and Sr isotopic ratios of the BRP‐1 (“Basalt Ribeirão Preto”) reference material (RM) based on repeated TIMS measurements over twelve years carried out by the LAGIR laboratory, Brazil. The BRP‐1 RM was produced by the Brazilian Geological Survey from a ca. 130 Ma within‐plate basalt, collected from a quarry near Ribeirão Preto city in the Paraná basin. Isotope ratios were measured using a TRITON mass spectrometer. Instrumental bias and fractionation corrections were performed based on repeated measurements of the certified RMs JNdi‐1 and NIST SRM 987. The measured Nd and Sr isotopic ratios of BRP‐1 are: 143Nd/144Nd = 0.512408 ± 0.000010 (2s), and 87Sr/86Sr = 0.706011 ± 0.000017 (2s). The mass fractions of Sm and Nd are 11.0 ± 0.2 and 51.9 ± 0.6 μg g‐1, respectively, showing no significant differences compared with the accepted values from the literature. No significant difference between measurements was observed, whether digesting samples in single or batch mode, using metal‐jacketed PTFE bombs or PFA vials, or with or without the addition of a spike. The accuracy of these results was evaluated through the measurement of well‐characterised USGS RMs, such as AGV‐1, BCR‐1, BHVO‐1, G‐2 and GSP‐1.

Influence of climatic phenomena and deforestation on hydroenvironmental fragility, Gurupi River watershed, Northern Brazil

In recent decades, climatic and anthropogenic pressures have caused serious environmental problems. The joint analysis of geo-environmental variables, through geoprocessing techniques, can support the estimation of the contribution of each environmental component to hydro-environmental fragility (HF). The aim of this work was to analyze the contribution of climatic phenomena and deforestation in the HF of the Gurupi River Watershed (GRW). Precipitation data were extracted from the Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS); land use and cover were obtained from the MapBiomas Project; drainage network was acquired from the National Water and Sanitation Agency (ANA); slope data were gathered from the National Institute for Space Research (INPE); soil data were obtained from the Brazilian Agricultural Research Corporation (EMBRAPA); geomorphological units were extracted from the Brazilian Institute of Geography and Statistics (IBGE); and rock data were based on the Geological Survey of Brazil (CPRM). For the mapping of HF, the Analytic Hierarchy Process (AHP) was adopted to weigh the importance of each variable in four extreme precipitation year scenarios (1989, 2012, 2015, and 2019). It was observed that spatial precipitation is considerably different in extreme years. Results showed that deforestation has increased over the years; and that static geo-environmental variables (drainage, slope, soils, geomorphological units, and rocks) have larger feature domains that favor the increase of HF in the GRW. The HF of the GRW showed significant differences in the analyzed scenarios. Policies and environmental conservation programs are needed in the GRW.

PATRIMÔNIO GEOLÓGICO DO PAMPA BRASILEIRO ONDE AÇÕES DE GEOCONSERVAR, GEOPRESERVAR E GEOPROTEGER SÃO OS DESAFIOS DO SÉCULO XXI

The biome of the “Pampa” in Brazil is a restricted area located in the state of Rio Grande do Sul, that extends for 153.254 Km2 and constitutes 1.79% of the national territory. Unfortunately, it has been severely impacted by agribusiness activities. The present study will show a strategic importance for the environmental preservation of the “Pampa” geoheritage. The goals are to reset the borders of the “Pampa”, to identify geosites of scientific value, and to evaluate the risks of environmental degradation with the aim to propose geoconservation actions. The material for this study came from Brazilian Institute of Geography and Statistics, Geological Survey of Brazil and edited using the geographic information systems program ArcGIS - ESRI®. The evaluation methodology used consists of the systematic registration of geological sites using different scales and values, and by mathematical criteria showing the relevant value and the degrees of environment degradation risks. The results present three maps showing the borders (limits) of the “Pampa” biome, geodiversity, and geosites and in as well as frames and charts, which contain the scientific value and the degree of environmental degradation risk of the six geosites. This information will be useful in proposing a course of action for geoconservation such as: the creation of conservation units, geoparks and the updating of environment legislation. The proposed actions are fundamental for spatial planning, based on the best practices of sustainable development, as geoconservation, geopreservation and geoprotection still remain the major challenges of the 21st century.

Are there geogenic relationships for Lithium between geology, geochemical anomalies and low levels of violence in the region of Guanambi, State of Bahia, NE Brazil? / Existem relações geográficas para o Lítio entre geologia, anomalias geoquímicas e baixos níveis de violência na região de Guanambi, Estado da Bahia, NE do Brasil?

Lithium has been applied for therapeutic purposes in the treatment of mental health disorders, such as bipolar affective disease, in the prevention of behaviour changes, and may be related, to some extent, to the reduction of suicide and violence. In Brazil, the main occurrences of lithium are found in the east/northeast region. In the Guanambi domains, in south-central Bahia, until recently, there were no references to lithium occurrences. The geology of the region is characterized by the monzo-syenitic batholith of Guanambi and its associated late intrusions (2.05Ga), where important manifestations of a pneumatolithic character are described. There are also evaporitic levels, interspersed with carbonate members of the São Francisco Supergroup (Bambuí Group - 650Ma). The Geological Survey of Brazil (CPRM) carried out an extensive geochemical survey, sampling and analysing water, sediments and soils. The geostatistical treatment and interpretation of these data revealed the existence of lithium anomalies in the Guanambi domains, in sites that spatially overlap the rocks of the Guanambi batholith and the carbonate rocks of the Bambuí Group. According to Atlas da Violência (2019), in Guanambi the homicide rate was 30.8 deaths per 100,000 inhabitants, that is, it is lower than the average homicide rate in Brazil (31.6 deaths per 100,000 inhabitants), or the average rate in Bahia (48.8 deaths per 100,000 inhabitants). The relationships between lithium and health can be addressed by medical geochemistry. This article is relevant to the community of geoscientists and health planners, whose objective is to investigate the hypothesis put forward of the effective relationship between geogenic lithium levels and the homicide rate in these sites in the State of Bahia.

Recursos hídricos superficiais da região sul de Santa Catarina - background geoquímico da região afetada pela mineração de carvão

ABSTRACT In the environmental reclaiming process, it is essential to distinguish between chemical elements concentrations that occur naturally in water resources (geochemical background), from those originated from anthropogenic activities. Despite the environmental efforts that have been carried out for more than two decades in the southern Brazilian region impacted by coal mining, its geochemical background is still not completely known. Filling this environmental knowledge gap was the objective of this work, which systematically analyzed the results of monitoring efforts carried out by the Geological Survey of Brazil (SGB/CPRM) across three years. Quality parameter distributions of rivers and streams unaffected by anthropogenic impact were analyzed. The database was used to perform principal component analysis (PCA) and cluster analysis, and to define the background values, which was done through the boxplot and ± 2 MAD (Median Absolute Deviation) methods. The results of multivariate statistical analyses clustered the monitoring sites into two groups, one related to the sedimentary rocks of the Paraná Basin and another to the crystalline basement rocks. The sedimentary group had a greater correlation with the parameters Eh, SO42-, Ca, Mg, EC, Mn, Acidity, Zn and Na; while, and the crystalline rocks group were better correlated with pH, Cu, Al, K, and Fe. The results of the geochemical background were similar for both methods, with values of pH, Fe, Al, and Mn being slightly different from those defined in Brazilian legislation (CONAMA 357/05 and MS 888/21).

Avaliação da capacidade de modelos hidrológicos-hidrodinâmicos de larga escala para mapear o risco de inundação no sul do Brasil

ABSTRACT Mapping flood risk areas is important for disaster management at the local, regional, and national scales. The aim of this study was to evaluate the ability of large-scale models to obtain flood hazard maps. The models were compared to the estimates developed by the Brazilian Geological Survey (CPRM) for different return periods (RP). The floods were evaluated for the municipalities of Uruguaiana, Montenegro and São Sebastião do Caí in the Rio Grande do Sul state. It was shown that the flood mapping generated by MGB covers larger areas (greater than 1000 km2; Siqueira et al. 2018), with a lower cost of obtaining for large scales. The - Hit Rate of the regional and continental MGB model versions with the CPRM maps ranged from about 40% to 90% in different cities, and the Hit Rate between the regional model and the CPRM map increased with the increased return period floods. The continental model compatibility was similar for all analyzed RPs. Our results suggest the agreement in terms of Hit Rate of current large-scale hydrological-hydrodynamic models to assess flood hazard.

Recharge assessment in the context of expanding agricultural activity: Urucuia Aquifer System, western State of Bahia, Brazil

Groundwater recharge rate estimation is crucial to sustainable development of aquifers in intensely pumped regions, such as the Urucuia Aquifer System (UAS). A sedimentary aquifer in Western Bahia, Brazil, that underlies one of the major agricultural areas of the country where there has been major growth of irrigated areas. This study seeks to evaluate the recharge component of the water budget in the UAS area, based on three complementary techniques. The double-ring infiltrometer test was used to evaluate surface infiltration capacity, an important control on recharge. Water level data from wells (2011–2019 period, 19 wells) in the Brazilian Geological Survey's Integrated Groundwater Monitoring Network (RIMAS-CPRM) was used to estimate the aquifer recharge using the water table fluctuation (WTF) method. Additionally, this study used the Soil Water Assessment Tool (SWAT) model in two selected sub-basins to estimate deep recharge from the surface hydrological data. The results of the infiltrometer tests show a notable difference in the infiltration rates between the natural vegetation zones and cropped areas. The WTF and SWAT simulations results suggest similar ranges of recharge rate (an average of 24% of precipitation, in both methods). Results of the study indicate equivalence of these methods to estimate the recharge in sedimentary unconfined aquifers as UAS.

PORTABILITY OF CARTOGRAPHIC SYMBOLS LIBRARY FOR OPEN STANDARDS

Abstract. The Geological Survey of Brazil has a library of palaeontology symbols to use in geological mapping works, currently in bitmap format and adapted for ESRI platform. This type of representation has presented anti-aliasing problems when reduced, in addition to not being suitable for map presentation on the web, according to OGC (Open Geospatial Consortium) specifications. This work presents a reproducible method in any symbol library type. The method consists of converting the symbol library to open-source format, resulting an OpenType font file, which can be installed on any operating system and view each symbol font in any software that has this functionality, such as a GIS (Geographic Information Systems) software. The need to develop font construction technique is due to improving typographic quality of cartographic representations and making library compatible with main GIS softwares. Those 61 pictorial palaeontology symbols were converted, one by one, to SVG (Scalable Vector Graphics) format. We imported each symbol as a glyph in FontForge font editor. Major computer platforms use OpenType format due to its wide availability and typographic flexibility, including provisions to deal with diverse characteristics of internationally symbolic alphabet systems. There is even the possibility of symbols standardizing in the UTF-8 alphabet system, an issue for the scientific community to study. The advantage of using the SVG format is its size, a compact text file, and has an excellent compression factor. In addition, version-control repositories, like GitHub, can store SVG files, which would facilitate content management. The adopted method proved to be applicable to any cartographic symbols library with good results. Rendering tests on different platforms (web or desktop) showed no noticeable differences. One of the most important aspects of the method presented in this work was to make cartographic symbols library public and open-source for use by the geoscientific community, regardless whether an open-source or proprietary platform is used, and so, the Geological Survey of Brazil will be able to distribute geological symbology patterns, according to Open Data definition.

Machine Learning Provides Effective Leak Detection in Carbon Sequestration Projects

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201552, “Leak Detection in Carbon Sequestration Projects Using Machine Learning Methods: Cranfield Site, Mississippi, USA,” by Saurabh Sinha, SPE, University of Oklahoma and Los Alamos National Laboratory; Rafael Pires De Lima, Geological Survey of Brazil; and Youzuo Lin, Los Alamos National Laboratory, et al., prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, 5–7 October. The paper has not been peer reviewed. Saline aquifers and depleted hydrocarbon reservoirs with good seals located in tectonically stable zones make an excellent storage formation option for geological carbon sequestration.Ensuring that carbon dioxide (CO2) does not leak from these reservoirs is the key to any successful carbon capture and storage (CCS) project. In the complete paper, the authors demonstrate automated leakage detection in CCS projects using pressure data obtained from the Cranfield reservoir in Mississippi in the US. Results indicate that even simple deep-learning architectures such as multilayer feed-forward neural networks (MFNNs) can identify a leak using pressure data. Introduction Several methods that use different types of data currently are available to detect leaks. Although some of the methods are a direct indicator of CO2 presence, they cannot provide an early warning for the leaks, thus delaying remedial measures. An ideal process for the identification of leakages requires constant and repetitive comparisons of different data. Machine-learning (ML) techniques are ideally suited for this task. In this work, the authors demonstrate the use of ML techniques such as linear model, random forest, and MFNN on time-series signals obtained from a pressure-pulse test. The methodology uses the time-series data instead of 2D images or 3D voxels, thus providing a computational advantage. The authors write that an ML algorithm can distinguish between a pressure signal corresponding to a leak vs. the pressure signal corresponding to a baseline nonleak case. The trained models can then be used as an early-warning system to flag anomalous data to then be analyzed by a human interpreter. Background A pressure-pulse test uses at least two wells: an injection well and a monitoring well. The reservoir is then shocked by a series of predetermined cycles of injection and shut-ins (i.e., a pulse). The response then is recorded at the monitoring well with a pressure gauge that measures the target formation pressure. The test may be repeated with different pulses to understand the reservoir properties better. A harmonic pulse is preferred over a square wave because it allows for spectral decomposition of the pulse to analyze the reservoir response at different frequencies. Three wells are used in the study: F1, F2, and F3. Well F1 is the injector well, where alternative cycles of injection of CO2 and shut-in are carried out. Well F2 is the monitor well, which remains shut in for the duration of the test and where the pressure is monitored with the use of a pressure gauge. An artificial leak is simulated in the test by opening a surface valve at Well F3.

Geophysical and structural survey in copper occurrence located in the northern region of the Camaquã basin (RS)

The geophysical diagnosis of mineral deposits can be extremely useful in detailing mineralized zones and is a strategy for direct sampling by probing holes for content analysis. This study involves the combined use of Electrical geophysical methods (DC resistivity and Induced Polarization), geological recognition and structural field analysis, with a study of the mineralized occurrence of copper, previously described in a systematic geochemical survey carried out by the Geological Survey of Brazil (CPRM), located in the north of the Camaquã Basin, extreme south of Brazil. The mineral occurrence is partially outcropped and consists of quartz vein shafts with malachite and relic structures of sulfides, contained in schist. Structural data obtained in the field revealed the existence of a system of fracture pairs in the directions N40-50W and N70-80E. Such information is presented in the programming of the geophysical data acquisition scheme, which consisted of 6 lines of electrical tomography with 410m each, in azimuthal disposition and Schlumberger arrangement, where all lines cross a single center and are separated according to an angle of 30°, in an attempt to cover fractures in various orientations. The 2D results reveal the existence of high chargeability zones (>40mV/V) positioned below the 40m depth. These data were interpolated in 3D visualization models and generated resistivity and chargeability maps for several depths, which integrated with previous structural data, and indicate the existence of zones with potential sulfide concentration with strong structural control, in addition to clear target recognition for direct and objective probing evaluation, with rationalization of costs.

Introduction to the special issue on "Geoconservation" of the Journalof the Geological Survey of Brazil

Introduction to the special issue on "Geoconservation" of the Journalof the Geological Survey of Brazil

The geological heritage of the state of São Paulo: potential geosites as a contribution to the Brazilian national inventory

Having a national geoheritage inventory is essential to plan effective geoconservation strategies. Since 2017, the Geological Survey of Brazil (CPRM) has been carrying out a project aimed at the Inventory of the Brazilian Geological Heritage and defined state coordinations to propose indicative lists of potential geosites based mainly on the scientific value (SV) according to the GEOSSIT platform. For the state of Sao Paulo, which was the first in Brazil to have a systematic geoheritage inventory, with 137 geosites already defined, this study intends to analyze them to propose some criteria to select the ones to compound the national list. Fifty-seven geosites were chosen according to both SV (≥ 300, following the requirements of GEOSSIT) and representativeness within each geological framework (when SV < 300). We also evaluated the selected geosites in other national initiatives, such as SIGEP (nine geosites) and the Geoparks Project (five geosites). The GEOSSIT public lists show only three of the 57 geosites already registered, a low number considering that these registrations are relevant indicators for the national inventory. The geosites were also analyzed according to the main thematic classification (eight main thematic categories, with a large number in the petrology theme - 35.10%) and general geological context (73.70% in the Mantiqueira, Parana, and Tocantins provinces and 26.30% in Emerged Phanerozoic Basins - Parana, Bauru, and Sao Paulo), according to the parameters available on GEOSSIT. The sites were also evaluated according to typology, being 33 points, 22 areas, and two sections. Regarding the statutory setting, 30% are in fully protected areas, 36% in public or private areas with non-effective statutory protection (APAs, marine land, paleontological sites, etc.), and 34% comprise public or private areas with no protection.

137Cs activity concentration in soil of Alagoas State, Brazil.

Cesium 137 is present in worldwide. To evaluate its deposition in the Brazilian state of Alagoas a total of 41 samples were collected by the Geological Survey of Brazil, then processed and analyzed by gamma-ray spectrometry with hyperpure germanium detectors. The activity concentration varied from (0.3 ± 0.1) Bq/kg to (1.1 ± 0.4) Bq/kg. The present study shows that the Borborema Plateau acts as a natural barrier to rainfall, favoring the deposition of 137Cs on the local soil.

Geochemical megaprovince of fluorine and endemic fluorosis in the middle São Francisco river, Minas Gerais-Bahia, Brazil

While conducting the National Program of Environmental Geochemistry and Medical Geology in the states of Minas Gerais and Bahia, the research team Geological Survey of Brazil – CPRM detected a large area with high levels of fluorine in the geochemical results of the soil, stream sediment and surface water. Fluorine levels were detected by an ion-selective electrode (stream sediment and soil samples) or by ion chromatography (water samples). In this low-density survey, the minimum, maximum and median fluorine grades found at the water samples were 0.005 mg/L, 7.56 mg/L and 0.05 mg/L. For the soil, the samples were 15 mg/L, 1720 mg/L and 152 mg/L, and for the stream sediment, the samples were 35 mg/L, 1076 mg/L and 262 mg/L. The region covers 25 municipalities where studies by researchers from Federal Universities of Minas Gerais and Bahia have detected a high incidence of dental fluorosis, especially where public supply is made via deep wells in the Fissure-Karst Aquifer of the Bambuí Group. Moreover, the study area is highly favorable to the mineral deposit of fluorite and secondary Pb-Zn. Because the area is much larger (99,000 km2) than the other known fluorite provinces of Brazil (Santa Catarina is 2,000 km2 and Vale do Ribeira is 5,000 km2), the designation of Geochemical Megaprovince of Fluorine in the Middle São Francisco River, Brazil, is suggested for this region.

Updated map of the mafic dike swarms of Brazil based on airborne geophysical data

Identification of mafic dike swarms and LIPs (Large Igneous Provinces) are of vital importance in geologic history because they provide information on geodynamics, mantle geochemistry, and paleomagnetism. These data provide key information for paleogeographic reconstructions with the aid of barcode matches and precise radiometric ages. Considering such issues, the Brazilian Precambrian shield can be used as a case for refining the cartography of the relevant intraplate activity (e.g., dikes, sills, flood basalts) in space and time.This work presents an updated map of Brazilian mafic dike swarms produced from airborne geophysical maps (Series 1000 – Geological Survey of Brazil). Linear and strong anomalies found on aeromagnetic maps using First Vertical Derivative of the Magnetic Field and Amplitude of the Analytic Signal were mapped on a GIS platform. The obtained data were compared to ternary radiometric maps and geological maps in order to exclude those that do not correspond to mafic dikes. The remaining structures - those believed to represent mafic dikes - were classified based on data compiled from the literature.The updated map exhibits more than 5000 elements, including dikes and magmatic suites, in which about 75% were geologically identified and divided into 60 dike swarms and 10 igneous suites and/or units. The dikes were grouped into sixteen extensional episodes from the Archean to the Cenozoic, although some are related to extension/transtension domains within regional compressive zones akin to orogenic settings. The most frequent records refer to the Proterozoic, representing intraplate episodes, some of them consistent with LIPs. The dataset also includes a large record of the Mesozoic age, which corresponds to major LIP events related to the opening of the Atlantic Ocean and the fragmentation of Gondwana.

APPLICATION OF THE PIRFICT MODEL IN THE RIMAS DATABASE

A água é considerada um recurso finito de grande importância para manutenção e subsistência dos seres vivos. O continuo crescimento das demandas torna necessário o desenvolvimento e planejamento de técnicas para supervisão e gestão dos recursos hídricos. Uma considerável parcela disponível de água doce para consumo encontra-se na forma de águas subterrâneas e que precisam ser monitoradas e usadas de forma racional, com o intuito de evitar usos não sustentáveis e explorações descontroladas. Para tanto, existem redes de monitoramento de água subterrâneas, tal qual a Rede Integrada de Monitoramento de Águas Subterrâneas (RIMAS), operada e mantida pelo Serviço Geológico do Brasil (CPRM). O presente estudo versa sobre a aplicação do software Menyanthes neste conjunto de dados como uma forma de atribuir-lhes consistência estatística e lograr preencher lacunas na referida série observada. O referido programa consiste na modelagem de causa e efeito, relacionando o histórico de chuvas com os respectivos piezogramas. Os resultados obtidos por intermédio desta aplicação fornecem perspectivas de normatizar a sistemática de preenchimento de lacunas na rede RIMAS, assim como também caminhos para prognósticos de comportamento freático frente a eventos climáticos como estiagens, similares à ocorrida entre os anos de 2013 e 2015 na região sudeste do Brasil.