Ages of the Magmatism and the Opening of the South Atlantic Ocean

The analysis of published and unpublished 368 K/Ar radiometric ages of basic, intermediate and alkaline volcanic rocks, related to the post-Paleozoic magmatism linked to the opening of the South Atlantic Ocean, yields some important evidence concerning the break up of the Gondwana supercontinent. At the Brazilian Equatorial margin, the Gondwana break up started in the Permo-Triassic, when the opening of the Equatorial South Atlantic Ocean began and spread out south-eastward up to the present day Amazon River mouth. During the middle Jurassic/lower Cretaceous (pre-Aptian), the continuity of this separation, towards the Potiguar Basin, was coeval with the northward opening of the south-east Brazilian margin, up to the Espírito Santo State latitude. The relationship between large volcanic events in the basins and the resistance to the rifting process development offered by the cratonic area was shown by the trend of the magmatic age. Along the equatorial margin, the fragmentation resistance caused by the São Luis / West African craton is manifested by a large basic magmatism described in the Tacutu, Acre, Solimões, Amazonas and Parnaíba basins. A similar mechanism along the south-east margin, is proposed for the magmatism described in the Paraná Basin which is associated with the fracturing resistance offered by the São Francisco/Congo cratonic area. The integration of geochronological, micropalentological, sedimentological and geochemical data from the basins of the east Brazilian continental margin supports a model to explain the final disruption between South America and Africa during Cenonian/Turonian time. This model implies that 90 Ma basic magmatic rocks, related to the oceanic crust formation, probably occur offshore from the present-day eastern Brazilian coast line

Datação de Processos Diagenéticos em Arenitos-Reservatório de Hidrocarbonetos: Uma Revisão Conceitual

Geochronology has became a powerfull tool for diagenetic studies in siliciclastic rocks as it supply parameters for the definition of their depositional or diagenetic ages. This development occurred particularly in the last decades, with analytical techniques improvements and application of oil exploration. Sandstones are important hydrocarbon reservoir-rocks in many basins of the world. Sandstones devoid of fossils with defined ages lack precise chronostratigraphic definition. Such lack of definition limits the precision of the generation-migration-accumulation models developed for the exploration and exploitation of these reservoirs. However, many sandstones contain diagenetic minerals which represent the possibility of dating the deposition of these sandstones, or episodic diagenetic fluid migration through radiometric 40K-40Ar, 40Ar-39Ar and 87Rb-87Sr methods. In the present work, we show that these methods have been successfully applied to samples of reservoirsandstones all over the world. The improvement of the radiometric methods applied to sedimentary rocks yielded significant results concerning depositional or diagenetic ages.Geochronology has became a powerfull tool for diagenetic studies in siliciclastic rocks as it supply parameters for the definition of their depositional or diagenetic ages. This development occurred particularly in the last decades, with analytical techniques improvements and application of oil exploration. Sandstones are important hydrocarbon reservoir-rocks in many basins of the world. Sandstones devoid of fossils with defined ages lack precise chronostratigraphic definition. Such lack of definition limits the precision of the generation-migration-accumulation models developed for the exploration and exploitation of these reservoirs. However, many sandstones contain diagenetic minerals which represent the possibility of dating the deposition of these sandstones, or episodic diagenetic fluid migration through radiometric 40K-40Ar, 40Ar-39Ar and 87Rb-87Sr methods. In the present work, we show that these methods have been successfully applied to samples of reservoirsandstones all over the world. The improvement of the radiometric methods applied to sedimentary rocks yielded significant results concerning depositional or diagenetic ages

INTERCONECTIVIDADE DE AQUÍFEROS E OS EFEITOS DA DRENAGEM ÁCIDA DE MINA NA QUALIDADE DAS ÁGUAS DA BACIA CARBONÍFERA DE SANTA CATARINA (SC)

Carboniferous activity in southern Santa Catarina State has been developed over a century and the lack of environmental management in mining projects caused significant changes in the water resources of the Araranguá Watershed. In addition to changes in water quality, collapses in underground mines caused the fracturing of overlying layers allowing the expansion of aquifer systems and surface waters interaction processes. In order to better understand these processes, samples of 9 wells from Rio Bonito Aquifer System, 4 wells from Alluvial Fan Aquifer System and 6 from surface waters of the same catchments were analyzed. Hydrochemical analysis indicates a predominance of calcium and sodium bicarbonate waters which in contact with acid mine drainage are transformed into sulfated waters. The isotopic composition of the samples shows similarity to the isotopic composition of meteoric waters, contributing to the hypothesis of the strong interaction between groundwater, waters from water table and surface waters, which occurs due to the brittle tectonics affecting gondwanic lithologies, and is intensified by the presence of underground mines. Keywords: Hydrochemistry, Stable isotopes, Groundwater, Acid mine drainage.A atividade carbonífera no sul de Santa Catarina se desenvolve há mais de um século e a falta de gerenciamento ambiental nos empreendimentos mineiros causou significativas alterações de qualidade nos recursos hídricos da Bacia Hidrográfica do Araranguá. Além da alteração na qualidade das águas, ocorreram fenômenos de colapso e abatimento de minas subterrâneas que ocasionaram fraturamento das camadas sobrejacentes, e permitiram a ampliação dos processos de circulação dos sistemas aquíferos com corpos hídricos superficiais. Com objetivo de melhorar o entendimento destes processos, foram analisadas amostras das águas de 9 poços do Sistema Aquífero Rio Bonito, 4 poços do Sistema Aquífero de Leques Aluviais e 6 amostras de águas superficiais das mesmas microbacias onde estão instalados os poços. As análises hidroquímicas indicam uma predominância de águas bicarbonatadas cálcicas e sódicas, que quando em contato com a drenagem ácida de mina são transformadas em águas sulfatadas. A composição isotópica em termos de isótopos de oxigênio e de hidrogênio das amostras evidencia semelhança com a composição isotópica das águas meteóricas. Este fato contribui com a hipótese da forte interação da água subterrânea com as águas freáticas e superficiais, que ocorre devido à tectônica rúptil que afeta as litologias gonduânicas, e é intensificada pela presença das minas de subsolo

Cimentação Carbonática em Reservatórios Siliciclásticos - O Papel da Dolomita -

Carbonates are important diagenetic cements in siliciclastic rocks thus important to determine these rocks as hydrocarbon reservoirs. The cement is the material had chemically precipitated partial or totally pore filling, affecting rock values of porosity and permeability. The acknowledgment of diagenetic patterns those are associated to the carbonatic cement precipitation and their impacts in the reservoirs quality can decrease the risks of exploration and exploitation of new reservoirs. Therefore is necessary the knowledge of origin and processes of carbonate cement’s precipitation. These cements have distribution patterns, mineralogy, textures and isotopic compositions which vary spatial and temporally, depending of perform conditions in each diagenetic environment. One of the most important diagenetic cement is dolomite and the dolomite’s group is compound by dolomite and ankerite. These minerals can be differentiated by analytical techniques such as optical petrography, staining techniques, cathodoluminescence, scanning electron microscopy and isotopes. Besides that, dolomite cement shape in a reservoir can display different forms: rhombs, poikilotopic and saddle in a variety of dimensions, pore filling, replacing detrital carbonate grains, concretions, nodules or stratified layers. Primaries calcite and aragonite replaced can promote precipitation of dolomite through increase of temperature and by presence of Mg-being fluids. The main entrance conditions to form dolomitic cement are: (i) alkaline solutions from pre-existence rocks weathering or evaporitc environments; (ii) marine waters; (iii) clay alteration; (iv) CaCO3 polymorphs dissolution; (v) dissolution of bioclasts. An interesting example of dolomitic cementation is the Carmópolis Member of the Muribeca Formation, hydrocarbon reservoir of the Camorim Field (Sergipe-Alagoas Basin, northeastern Brazil).Carbonates are important diagenetic cements in siliciclastic rocks thus important to determine these rocks as hydrocarbon reservoirs. The cement is the material had chemically precipitated partial or totally pore filling, affecting rock values of porosity and permeability. The acknowledgment of diagenetic patterns those are associated to the carbonatic cement precipitation and their impacts in the reservoirs quality can decrease the risks of exploration and exploitation of new reservoirs. Therefore is necessary the knowledge of origin and processes of carbonate cement’s precipitation. These cements have distribution patterns, mineralogy, textures and isotopic compositions which vary spatial and temporally, depending of perform conditions in each diagenetic environment. One of the most important diagenetic cement is dolomite and the dolomite’s group is compound by dolomite and ankerite. These minerals can be differentiated by analytical techniques such as optical petrography, staining techniques, cathodoluminescence, scanning electron microscopy and isotopes. Besides that, dolomite cement shape in a reservoir can display different forms: rhombs, poikilotopic and saddle in a variety of dimensions, pore filling, replacing detrital carbonate grains, concretions, nodules or stratified layers. Primaries calcite and aragonite replaced can promote precipitation of dolomite through increase of temperature and by presence of Mg-being fluids. The main entrance conditions to form dolomitic cement are: (i) alkaline solutions from pre-existence rocks weathering or evaporitc environments; (ii) marine waters; (iii) clay alteration; (iv) CaCO3 polymorphs dissolution; (v) dissolution of bioclasts. An interesting example of dolomitic cementation is the Carmópolis Member of the Muribeca Formation, hydrocarbon reservoir of the Camorim Field (Sergipe-Alagoas Basin, northeastern Brazil)

SISTEMAS PETROLÍFEROS ATÍPICOS NAS BACIAS PALEOZOICAS BRASILEIRAS – UMA REVISÃO

Sistemas petrolíferos atípicos são reconhecidos pelas transformações do conteúdo orgânico ou mineral de rocha encaixante, causada essencialmente pelo efeito térmico da dispersão do calor da soleira ígnea. Pode ser identificado pela auréola de contato, tendo como principal finalidade indicar se a rocha encaixante foi inserida na janela de geração de óleo e gás. O objetivo deste trabalho foi realizar uma revisão bibliográfica sobre os sistemas petrolíferos atípicos das principais bacias paleozoicas brasileiras e contribuir no conhecimento destes sistemas petrolíferos. No Brasil, exemplos de geração atípica ocorrem nas bacias paleozoicas do Solimões, Parnaíba e Paraná com acumulações de óleo e gás. Os intervalos de tempo com maior potencial para existência de rocha geradora nestas bacias são Siluriano, Devoniano e Permiano, que podem estar associados a soleiras com idades em torno de 200 Ma e 130 Ma. Conclui-se que nas bacias paleozoicas brasileiras, os sistemas petrolíferos atípicos são: (1) Bacia do Paraná - Vila Maria-Alto Garças/Iapó (.), Vila Maria-Furnas (.), Ponta Grossa-Itararé (!), Irati-Piramboia (!) e Irati-Rio Bonito (!); (2) Bacia do Parnaíba - Tianguá-Ipu (!), Tianguá-Jaicós (?), Pimenteiras-Cabeças (!), Pimenteiras-Poti (.), Pimenteiras-Pimenteiras (.) e Longá-Poti (.); e (3) Bacia do Solimões - Jandiatuba-Juruá (!), Jandiatuba-Uerê (.) e Uerê-Uerê (.)

Evolução Tectono-Estratigráfica e Paleoclimática da Formação Maricá (Escudo Sul-Rio-Grandense, Brasil): um Exercício de Geologia Histórica e Análise Integrada de uma Bacia Sedimentar Neoproterozóica

Significant improvement in the knowledge concerning the Neoproterozoic Maricá Formation of the Sul-riograndense Shield, southern Brazil, was obtained in the latest years. This contribution synthesizes recent data obtained though an integrated analysis of the lowermost unit of the “Camaquã Basin”. Stratigraphic and paleocurrent analyses, petrography, Sr and Nd isotope geology, U-Pb SHRIMP geochronology and Ar-Ar dating were applied to the sedimentary and volcanogenic record of the Maricá Formation in order to better constrain its depositional evolution. The Maricá Formation was deposited within a coastal to shallow marine setting, its detrital load being derived from the weathering of granite-gneissic, paleoproterozoic (1.76 to 2.37 Ga) source rocks, possibly located in the western La Plata craton. A syn-depositional, partially explosive, volcanic event was recognized and dated by U-Pb SHRIMP at 630.2 ± 3.4 Ma, positioning the inception of the “Camaquã Basin” at the end of the Cryogenian. Thus, the deposition of the Maricá Formation post-dates the global-scale Marinoan glaciation (660-635 Ma), possibly recording greenhouse paleoclimatic conditions. Field, petrographic and isotopic evidence supports this interpretation. The evolution of the Maricá Formation started during the collisional climax of the Brasiliano II orogenic system (Dom Feliciano orogen), thus the analyzed sedimentation could represent the infilling of a foreland basin. It is possible that correlative portions of the foreland system may be preserved in other sedimentary or metamorphic successions of the Mantiqueira Province, such as the Fuente del Puma (Lavalleja), Porongos, Brusque, Abapã (Itaiacoca), Cerro da Árvore and Passo da Capela units. The 507.3 ± 1.8 and 506.7 ± 1.4 Ma Ar-Ar step-heating ages obtained in K-feldspars from volcanogenic samples of the Maricá Formation are most likely associated with uplift and cooling below ca. 200ºC, possibly during the inception of the rift where the Camaquã Group (Santa Bárbara and Guaritas formations) accumulated.Significant improvement in the knowledge concerning the Neoproterozoic Maricá Formation of the Sul-riograndense Shield, southern Brazil, was obtained in the latest years. This contribution synthesizes recent data obtained though an integrated analysis of the lowermost unit of the “Camaquã Basin”. Stratigraphic and paleocurrent analyses, petrography, Sr and Nd isotope geology, U-Pb SHRIMP geochronology and Ar-Ar dating were applied to the sedimentary and volcanogenic record of the Maricá Formation in order to better constrain its depositional evolution. The Maricá Formation was deposited within a coastal to shallow marine setting, its detrital load being derived from the weathering of granite-gneissic, paleoproterozoic (1.76 to 2.37 Ga) source rocks, possibly located in the western La Plata craton. A syn-depositional, partially explosive, volcanic event was recognized and dated by U-Pb SHRIMP at 630.2 ± 3.4 Ma, positioning the inception of the “Camaquã Basin” at the end of the Cryogenian. Thus, the deposition of the Maricá Formation post-dates the global-scale Marinoan glaciation (660-635 Ma), possibly recording greenhouse paleoclimatic conditions. Field, petrographic and isotopic evidence supports this interpretation. The evolution of the Maricá Formation started during the collisional climax of the Brasiliano II orogenic system (Dom Feliciano orogen), thus the analyzed sedimentation could represent the infilling of a foreland basin. It is possible that correlative portions of the foreland system may be preserved in other sedimentary or metamorphic successions of the Mantiqueira Province, such as the Fuente del Puma (Lavalleja), Porongos, Brusque, Abapã (Itaiacoca), Cerro da Árvore and Passo da Capela units. The 507.3 ± 1.8 and 506.7 ± 1.4 Ma Ar-Ar step-heating ages obtained in K-feldspars from volcanogenic samples of the Maricá Formation are most likely associated with uplift and cooling below ca. 200ºC, possibly during the inception of the rift where the Camaquã Group (Santa Bárbara and Guaritas formations) accumulated

INUNDITOS COMO MODELO DEPOSICIONAL NO TRIÁSSICO DA BACIA DO PARANÁ: UM EXEMPLO NO GRÁBEN ARROIO MOIRÃO (RS)

O Gráben Arroio Moirão (RS) é um relicto doTriássico da Bacia do Paraná no embasamento, o Escudo Sul-Rio-Grandense. No setor noroeste do gráben foram reconhecidas características que se associam com um modelo sedimentar do tipo inundito. Foram aplicadas técnicas de mapeamento geológico de rochas sedimentares, sendo selecionados seis afloramentos para levantamento de perfis colunares com a descrição detalhada das unidades, documentação fotográfica e coleta de amostras de rochas para análises. Osperfis colunares permitiram o reconhecimento de dezoito fácies, oito sucessões de fácies, sete superfícies-chave e dois marcadores estratigráficos. A análise de fácies, das associaçõese dassucessões resultou na definição do arcabouço estratigráfico comproposição de um modelo deposicionaldo tipo inundito. O modelo atende as características da situação geológica encontrada, ou seja, um sistema composto por fluxos progradantes de baixa densidade, subaquosos, que geram litologias mal selecionadas, grãos angulosos a subangulosos.O agente transportador não é eficaz na segregação textural, é um evento episódicoenão há migração lateral de canais. A etapa de desenvolvimento de canais ocorre rapidamente por meio de feições rasas e desconfinantesqueocasionam depósitos com geometrias em lençóis ou tabulares. Sendo assim, considera-se que seja um modelo deposicional do tipo inundito

Razão Isotópica 87Sr/86Sr em Sedimentos Recentes Implicações na Datação Radiométrica das Rochas Sedimentares

Radiometric ages of geological significance are obtained when the Rb/Sr isocronic method is applied to argillaceous sedimentary rocks. In spite of these results many questions arise when the Rb/Sr methodology is applied to sedimentary rocks, notably the behavior of the rubidium (Rb) and strontium (Sr) elements during sedimentation and during the diagenetic process. The greatest uncertainty lies in the mechanism and the timing of the strontium isotopic homogenization, with constitutes the basic assumption behind radiometric dating by the Rb/Sr method. The purpose of this work is to contribute to the clarification of the conditions for the strontium isotopic homogenization, the relation between Rb and Sr and the dimension and nature of sedimentary particles, the early process associated with the clay minerals, with sedimentation process and with intersticial fluids. Recent sediments were sampled from different environments: the deltaic region of the Paraíba do SuI River (RJ), the deltaic region of the Açu River (RN), the continental shelf associated with the Amazon River mouth (AM), the continental slope and Jacarepaguá coastal plain (RJ). The samples were analysed by X-ray diffraction, scanning electron microscope and chemical and isotopic techniques. Results obtained show that some samples reached uniform strontium isotopic composition under certain conditions. These conditions include close proximity between samples, clay fraction enriched in expansive minerals such as smectite and degraded illite associated with deposition preferentially in marine waters

GEOCONSERVAÇÃO EM GRANDES CIDADES E PROPOSIÇÃO DOS ITINERÁRIOS GEOLÓGICOS DE PORTO ALEGRE: CONTRIBUIÇÕES METODOLÓGICAS PARA VALORAÇÃO INTEGRADA DE UNIDADES GEOLÓGICAS

Os temas da geodiversidade e geoconservação emergem no século XXI como contribuições das geociências para o desenvolvimento sustentável. Devido ao gigantismo urbano, aos colapsos socioambientais e à intensa ocupação da geosfera, se faz urgente a culturalização dos temas relacionados à Terra, especialmente da sua conservação. Nesse cenário, surgem os conceitos da geodiversidade e de suas funções ecossistêmicas, bem como estratégias e metodologias para aplicação da geoconservação. Embora antigas, as estratégias de geoconservação ganharam espaço na gestão patrimonial e ambiental a partir dos anos 1990 e, desde então, diferentes propostas metodológicas vêm sendo construídas para dar suporte técnico-científico para tais ações. Este trabalho apresenta contribuições metodológicas para valoração integrada de unidades geológicas a partir da análise de seis mapas temáticos do município de Porto Alegre e da proposição de uma matriz com 12 indicadores geopaisagísticos aplicados às 22 unidades geológicas locais. Além disso, 11 geossítios são encadeados em termos de itinerários geológicos que permitem evidenciar a história geológica regional. Por fim, o presente estudo propõe os Itinerários Geológicos de Porto Alegre como tecnologia socioeducativa para auxiliar a conexão das pessoas com a paisagem onde vivem. Dessa forma, geoeducação e geoconservação podem ter papéis importantes na gestão de ambientes urbanos populosos

FEIÇÕES DE INTERAÇÃO VULCANO-SEDIMENTARES: EXEMPLOS NA BACIA DO PARANÁ (RS)

A Sequência Juro-Cretácea da Bacia do Paraná composta por arenitos eólicos da Formação Botucatu sobrepostos por derrames vulcânicos da Formação Serra |Geral, possui feições de interação vulcano-sedimentares na interface entre essas duas unidades. O intenso magmatismo de caráter básico e, secundariamente ácido, recobriu um imenso campo de dunas eólicas e permitiu a origem de diversas estruturas vulcano-sedimentares. Em afloramentos da borda atual da Bacia do Paraná, no estado do Rio Grande do Sul, observa-se uma variedade de feições de interação entre sedimentos consolidados ou inconsolidados, saturados ou não em água, com derrames de composição basáltica ou dacítica. As feições vulcano-sedimentares, encontradas na base e topo dos derrames, ocorrem de diferentes formas devido a temperatura das rochas vulcânicas e tipo de sedimento. Estas feições podem ser categorizadas de acordo com seu processo de formação em duas maneiras distintas: interação com o derrame ainda fluido, com temperatura elevada e parcialmente cristalizado, onde a presença de água ou umidade sobre os sedimentos facilita a interação; e interação a partir de processos posteriores tais como, erosão e intemperismo com o derrame já consolidado. As feições vulcano-sedimentares compreendem: estrias de fluxo, brechas, diques de arenito, fraturas com arenitos e geodos. Palavras chave: Interação, feições vulcano-sedimentares, Bacia do Paraná