Prospecção geofísica em ocorrência de cobre localizada na bacia sedimentar do Camaquã (RS)

Estudos de pesquisa mineral são fundamentais para o reconhecimento e a incorporação de novas reservas. Esse trabalho apresenta os resultados de aplicação do método geofísico da eletrorresistividade numa ocorrência mineralizada em carbonatos de cobre, por meio da técnica de caminhamento elétrico em arranjo azimutal. A área de estudos está inserida na bacia sedimentar do Camaquã, formada por um conjunto de unidades estratigráficas sedimentares e vulcanogênicas, onde são descritas diversas ocorrências cupríferas. A presença de azurita e malaquita em fraturas e zonas de maior porosidade em arenito encaixante define a geologia local. Os modelos de inversão revelam anomalias circulares de resistividade moderada para até 25m abaixo da ocorrência aflorante e anomalias de baixa resistividade em profundidades abaixo de 25m, além de áreas adjacentes com alta resistividade. Indicadores de mineralização descritos para ocorrências de cobre estudadas, no âmbito da bacia sedimentar do Camaquã, ocorrem na área de estudos e permitem caracterização em termos de resistividade elétrica. Áreas com silicificação apresentam alta resistividade, enquanto que valores intermediários são atribuídos a zonas com carbonatação e, finalmente, áreas de baixa resistividade, provavelmente, indicam concentrações de sulfetos disseminados.

Drill holes in shells of Permian benthic invertebrates

Newly discovered benthic fossils and specimens illustrated in the paleontological literature indicate that drilling predators (or parasites) were present in the Permian. New field data from southern Brazil document the first drill holes ever reported for Permian bivalve mollusks. In addition, a literature review revealed drill holes in shells of articulate brachiopods from Russia, Greece, and West Texas. Holes range in size from 0.1 to 5.8 mm and are typically round, cylindrical, singular penetrations perpendicular to the valve surface. Incomplete, healed, and multiple holes are absent. Drilling frequency, a proxy for predation intensity, is very low: less than 1 percent (this estimate may be seriously affected by taphonomic and monographic biases). Literature data suggest that frequency of drilled specimens varied significantly among higher brachiopod taxa. The geography and stratigraphy of drilled specimens indicate that drilling organisms were worldwide in their occurrence and continuously present in marine ecosystems throughout the Permian. This report is consistent with other recent studies indicating that although drillers were continuously present throughout the Phanerozoic, drilling intensity was lower in the Late Paleozoic and early Mesozoic.

A stratigraphic chart of the Late Carboniferous/Permian succession of the eastern border of the Parana Basin, Brazil, South America

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Calcretes of the Bauru Group ( Cretaceous), Brazil; petrology and geological significance.

Reinterprets petrologic studies and their geologic significance in the light of recent literature on the calcretes in the world, and the recent revision of Bauru Group stratigraphy.-from English summary

Concepcoes estratigraficas em analise de Bacias: A) a estratigrafia tradicional

This article is the first part of an overall theme dealing with different stratigraphic approaches to basin analysis. The traditional stratigraphy, based on formal units, is discussed here with an attempt to analyse their principles, methods and purposes. Using the Permian carboniferous sequence of Parana Basin as a paradigm, some critical inferences concerning the limitations of such an approach in environmental reconstruction are attained. -English summary

Concepcoes estratigraficas em analise de bacias: C) a estratigrafia genetica

The present work fits the concepts of depositional systems and depositional sequence as paralithostratigraphic and parachronostratigraphic units, respectively, and discusses the advantages of using this approach in environmental reconstructions. The depositional system concept came to a focus as a link between sedimentology and stratigraphy since it represents both a facies association and a mapping unit. Additionally, the depositional sequence represents the sedimentary episode of relative sea level change, in interaction with basin paleophysiography. In such a way a time-space diagnosis is reached in environmental interpretation as illustrated by the Permian-Carboniferous sequence of the Parana Basin. -English summary

Afloramento - modelo da Formacao Piramboia

This short paper describes an outcrop that is a very good example of the aeolian sedimentation in the Piramboia Formation (Triassic) in the Parana Basin. -English summary

Marcos estratigraficos regionais na Formacao Palermo: caracterizacao dos picos radioativos

During a basinal scale study on Palermo Formation (Upper Permian, Parana Basin) high elevated Gamma Ray picks were identified mainly in the lower third of that stratigraphic unit. Those Gamma Ray signatures have been used as good regional stratigraphic markers. From them it was possible one chronostratigraphic analysis of Palermo Formation as pointed out by previous papers (Perinotto). Potassium40 is the responsible for the high Gamma Ray picks in the Palermo Formation. -from English summary

Seqüência Ordovício-Siluriana e Devoniana no Flanco Norte da Bacia do Paraná

Two stratigraphic sequences characterize the basal units of the Paraná basin. The Ordovician-Silurian sequence overlie directly the Neoproterozoic basement and consists of a 55m-thick unit of coarse-grained sandstones, diamictites, fossiliferous shales and fine-grained micaceous sandstones. The Alto Garças Formation constitutes the base of the sequence and is made of coarse-grained, massive and reddish sandstones associated with conglomeratic lenses. Diamictites with pebbles of diverse composition in siltic and arenaceous matrix were deposited during the Ordovician-Silurian glaciation. Whenever the basal sandstones are absent, the diamictites directly overlie the basement. The diamictites were previously included in the Vila Maria Formation. However our study revealed that they are part of the Iapó Formation. A transgressive event following the glaciation is marked by the deposition of the Vila Maria Formation, which is characterized by fossiliferous (mollusks, brachiopods, cryptospores and microplankton) and laminated shales and siltstones, grading upward to fine-grained micaceous sandstones with hummocky cross stratification. Layers containing trace fossils (Anthrophycus) occur at the transition between the siltstones and the sandstones. The Devonian sequence is represented by 80-170 meters thick sandstones of the Furnas Formation (lower unit) and a sucession of sandstones, siltstones and shales of the Ponta Grossa Formation (upper unit). Unlike other areas of the Paraná Basin, the Ponta Grossa Formation is characterized by coarsening-upward succession beginning with fine sandstones and grading upward to coarse and very-coarse sandstone beds. Cretaceous modifying tectonics affected the Paleozoic sequences, which are cut by a series of faults, in some cases showing displacements greater than 500 meters.

The Bauru Group: A continental Cretaceous unit in Brazil - Concepts based on micropaleontological, oxygen isotope and stratigraphical data

The integration of outcrop and subsurface information, including micropaleontological data, facies and sequence stratigraphic studies, and oxygen isotope analysis, allow us to present a new stratigraphic model for the Cretaceous continental deposits of the Bauru Group, Brazil. Thirty-eight fossil taxa were recovered from these deposits, including 29 species of ostracodes and 9 species of charophytes. Seven of these ostracode species and three subspecies are new and formally described here. The associations of Chara barbosai - Ilyocypris cf. riograndensis, found in the Adamantina Formation, and Amblyochara sp. - Neuquenocypris minor mineira nov. subsp., found in the Marília Formation. Ponte Alta Member, represent two distinct groups that are respectively Turonian-Santonian and Maastrichtian (probably Late Maastrichtian) in age. Therefore, a hiatus, encompassing more than 11 Ma, separates those two formations. From bottom to top, four depositional cycles were recognized in the Bauru Group in western São Paulo: cycles 1 and 2 belong to Caiuá Formation (fluvio-lacustrine and lacustrine deposits in the Presidente Prudente region), cycle 3 to the Santo Anastácio and lower Adamantina Formation (respectively fluvial and lacustrine deposits), and cycle 4 to the upper Adamantina Formation (fluvio-lacustrine facies). An erosional unconformity separates the Caiuá and Santo Anastácio Formations (between cycles 2 and 3). The Marília Formation is a distinct unit from the underlying succession; it does not occur in western São Paulo, but is found in restricted areas of São Paulo, Minas Gerais, Mato Grosso do Sul and Goiás States. During the deposition of the Bauru Group (Aptian? to Maastrichtian) the climate was hot and arid-semiarid. Shallow lakes underwent fluctuations in expansion (wet phases) and contraction (dry phases), as well as variations in salinity. During the deposition of the Adamantina Formation (Turonian-Santonian) there were long, dry periods that caused segmentation of large lakes (due to topographic irregularities in the basaltic substrate) and sometimes exposures of the lake floors; when flooded these lake floors were colonized by extensive meadows of single species of charophytes. Small ephemeral ponds, that were hydrochemically unstable and colonized by multiple species of charophytes, were the depositional sites for the marls and mudstones of Ponte Alta Member (Maastrichtian, Late Maastrichtian?). Our micropaleontological age control, combined with the Late Cretaceous ages of volcanic ashes found in the southeastern Brazil coastal basins, and the stratigraphic position of analcimites from the Jaboticabal-SP region, suggest a Late Coniacian-Santonian age for important magmatic events occurred in the interior of Brazil (north-central São Paulo State, Triângulo Mineiro, and southwestern Goiás State).

Estratigrafia de seqüências das formações Taciba e Rio Bonito (Membro Triunfo) na região de Mafra/SC, leste da Bacia do Paraná

The Taciba and Rio Bonito (lower Triunfo Mbr) formations are divided into six depositional sequences based on cores, gamma-ray and electrical logs from shallow drillings from northern Santa Catarina State, Each sequence is formed by two systems tracts, a lower one, sandy (lowstand) and an upper one, shaly (highstand). The Taciba Formation has three sequences, S 0 to S 0 sequence S 0 has a thick turbidite sandstone at the base (Rio Segredo Member) that pinches out towards the eastern margin and even disappears in the Mafra outcrop area. Sequence S 1 varies from a thin fluvial-estuarine system to a thick turbidite sandstone of a channelized fan system; S 1 upper shaly system tract is marine in well PP-11, and it is glacially-influenced in well PP-10. Sequence S 2 is a thick sand-stone body of shallow marine origin, but restricted to one well (PP-11); its upper shaly tract is dominated by massive siltstones intercalated with thin, distal tempestites. The lower Triunfo Member (or Taciba-Triunfo transition) begins with the arrival of deltaic clastics of sequence S 3 lower tract, coarsening-up from medial- to proximal delta front sandstones. Sequence S 4 is quite similar to S 3, both showing sand-stone progradation from north to south, as opposed to the southwest-sourced transgressive diamictites. Sequence S 5 consists of fluvial deposits at well PP-12, and two transgressive cycles from wells PP-11 to PP-9, each one of them composed of fluvial-estuarine to marine systems. Well PP-10 is an exception, where the lower cycle presents deglaciation to marine deposits.

Investigação de Intrusão de Água Salgada em Aqüífero Superficial a Partir de Medidas de Resistividade Elétrica

A site investigation program was carried out to detect salt-water intrusions in a shallow sedimentary aquifer based on electrical resistivity measurements. The site is located close to Paranaguá harbor, in the Paraná State, Brasil. At this site, high chloride concentration contaminated shallow water wells used to supply water for local industries. The site investigation program included a fieldwork, dipole-dipole electrical profiling, resistivity piezocone tests, physical-chemical analysis of sampled water and interpretation of borehole logs. The resistivity piezocone tests provided two simultaneous information; the soil stratigraphy at a very detailed level and a quasi-continuous resistivity profile. Both information adequately complemented dipole-dipole electrical profiling test data. The integration of all test data allowed identifying the contaminated areas as well as guided the location of new water wells to be installed in this area.

A seqüência mafra superior \ Rio Do Sul inferior (Grupo itararé, permocarbonífero) em sondagens testemunhadas da região de mafra (SC), Margem Leste da Bacia do Paraná

The Permo-Carboniferous Harare Group crops out in the Matra area, represented by Campo do Tenente, Mafra and Rio do Sul formations; they correspond in subsurface to Lagoa Azul, Campo Mourão and Tacïba formations. A composite sampling of the Group was performed through drilling of six wells, which average 60 m in depth; three of them cored the depositional sequence here designated as Upper Mafra\Lower Rio do Sul. The Upper Mafra Formation were sampled by TC-4 and BR-5 wells, and it consists of three units: the lower two are sandy, glacial-deltaic and fluvial-deltaic in origin, corresponding to a lowstand tract. The last unit is composed of two dirtying-upward successions of sandstone, diamictite and rhythmite, interpreted as deglaciation/transgressive events, and well represented in BR-5 drilling. The Lower-Rio do Sul Formation (Lontras Shale) is formed by two marine units: the lower one is represented by shale and bioturbated siltstone which culminate the previous deglaciation, transgressive succession, while the upper one, sampled by SL-2 well, is formed by shale and thin, turbidite sandstone, attributed to a highstand tract.

Determinação da distribuição de um nível de turbidito na formação Macaé no campo de Namorado através de uso de atributos sísmicos

This study was developed on the basis of petrophysics characterization, 3D seismic interpretation, and rock-wire-log integration. The results were integrated with amplitude attribute through cross plot (rock attribute x amplitude value). 3D seismic data also allowed inteipreting the top of Lagoa Feia, Macaé, and Carapebus formations, and Outeiro Member. The analyses of the maps of structures and attributes, integrated with wire-log data, suggest that Namorado turbidite level is candidate to be mapped with stratigraphic attributes like AverageTroughAmplitude, RMS velocity and Total AbsoluteAmplitude. Lagoa Feia Formation attribute maps (Dip-Azimuth and TotalEnergy) allows to interpret a low fault density at the carbonate coquina level in the Namorado field. This level is also considered one at the best seismic reflector and an important reservoir of the Campos Basin.

Sucessão sedimentar do Grupo Bauru na região de Pirapozinho (SP)

There is yet enthusiastic debate in the literature about the environmental conditions that originated the Cretaceous deposits of the Bauru Group, despite many authors accept that arid climatic conditions widely dominant at the base, evolved to chiefly fluvial-lacustrine conditions at the intermediate portion, and to arid conditions again at the top of the unit. The Bauru Group covers an area of about 117.000 km 2 of the Paraná Basin in São Paulo State territory. Core samples of this lithostratigraphic unit collected from a drill hole at Pirapozinho (Southwest of the São Paulo State) are described and together with well log data brought new information that do not agree with the described model. It was identified in this well the Caiuá, Pirapozinho, Santo Anastácio, Araçatuba and Adamantina formations. The study of these core samples clearly showed the dominance of hydrodynamic sedimentary structures and high to medium intensity of bioturbation in whole profile. These characteristics observed in core samples and compared to patterns of geophysical logs testify the dominance of fluvial processes in the Bauru Group deposition at the studied area. These new data suggests that the paleo-environmental evolution of the unit was much more complex, showing strong lateral and vertical changes that diverges from the model more widely accepted in the literature.