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A interpretação visual de pares estereoscópicos obtidos a partir da imagem Google Earth Pro, em diferentes escalas, propiciou o reconhecimento de diversas morfoestruturas anelares na Bacia do Paraná, no Rio Grande do Sul cuja geometria é essencial para a locação de sítios favoráveis à captação de água subterrânea. O estudo efetuado resultou no reconhecimento de cinco megadomos e sete morfoestrutuas anelares com diâmetros entre 10 e 20km. Estas morfoestruturas foram analisadas em função de padrões de drenagem e mapeamento de “dipslopes”, visando a identificação de sítios positivos ou negativos para a acumulação de água subterrânea. A metodologia foi testada através de dados de poços localizados em três morfoestruturas (duas localizadas na região de Quaraí, uma na região de Muitos Capões) para validação da metodologia proposta. Os resultados encontrados indicaram que em domos e antiformes, o centro da estrutura e suas proximidades são negativos para a captação de água subterrânea, enquanto que em bacias e sinclinais o centro e proximidades da estrutura são sítios positivos. Também as bordas das morfoestruturas com padrão de drenagem anelar, tanto domos como bacias, delimitadas por padrão de drenagem anelar, consistem em sítios positivos.

The object of this study is magnesian clay minerals present in carbonate rocks of the post-rift phase of the pre-salt in the Santos Basin. These rocks developed in an Aptian-age alkaline lacustrine environment. This study summarizes the formation of clay minerals associated with different lithotypes in a range of 19 m and a depth of more than 5100 m. They were characterized from petrographic analysis by optical microscopy, X-ray diffraction (total sample and clay fraction), and modeling by Newmod®, and examined and analyzed by scanning electron microscopy. An approach based on identifying lithotypes and characterization of microsites allowed us to understand the occurrence of different clay minerals. Kerolite was the most abundant mineral in the sampled range. It occurs in lamellar aggregates under greater preservation of the original rock lamination and in association with spherulites and shrubs. The Stv/Ker mixed layers occurs in the same association, and formed finer unlaminated aggregates associated with the more intense dolomitization and silicification processes. Saponite occurs associated with detrital minerals forming clayey levels intercalated with microcrystalline carbonates. Fluids with a high Mg/Si and pH &lt, 9 favor the precipitation of kerolite. The increase in pH during diagenesis may be responsible for the formation of Stv/Ker mixed layers.

Dust particle studies in ice cores from the tropical Andes provide important information about climate dynamics. We investigated dust concentrations from a 22.7 m ice-core recovered from the Quelccaya Ice Cap (QIC) in 2018, representing 12 years of snow accumulation. The dust seasonality signal was still preserved with some homogenization of the record due to surface melting and percolation. Using a microparticle counter, we measured the dust concentration from 2–60 µm and divided the annual dust concentration into three distinct groups: fine particle percentage (FPP, 2–10 µm), coarse particle percentage (CPP, 10–20 μm) and giant particle percentage (GPP, 20–60 μm). Increased dust was associated with the warm stage of the Pacific Decadal Oscillation index (PDO) from 2014–2017 with significant increases in FPP and a relative decrease in GPP. There was a positive correlation between PDO and FPP (r = 0.68, p-value&thinsp

Clays are used in cosmetology with different applications, which are conditioned to the chemical and mineralogical composition and physical-chemical characteristics of these materials. Therefore, the aim of this work was to evaluate the potential application of Melo Bentonite (BEM), clay from Uruguay through different tests. Initially, it was performed the characterization of BEM by X-ray Diffraction (XRD), X-ray fluorescence spectroscopy (XRF), thermal analysis (TGA/DTG), particle size distribution and surface area. The microbial content of natural Melo Bentonite clay was also verified. Two calamine suspensions were formulated with bentonite clay, one containing BEM and the other containing bentonite clay (BE), both at concentration of 5% w/w in glycerin. Bentonite clay was used in accordance to standard. The suspensions were characterized through tests of sedimentation rate, viscosity and pH determination. The physical-chemical characterization of BEM indicated compatible characteristics with those of clay; it was observed only smectite and quartz reflections as crystalline phases and in terms of chemical composition the major presence of silicon, aluminum and magnesium was verified. The microbiological evaluation showed that microbial content of Melo Bentonite presents acceptable limits, according to the Brazilian legislation for cosmetic products. BE was tested by a suspending agent. The sedimentation amount obtained for the suspention that was prepared with BEM was (0.73 mL/min) and with BE (0.63 mL/min). BEM is a better agent suspensor than BE. The viscosity presented by the sample containing BEM was lower than that containing BE; both of them showed non-Newtonian behavior and pseudoplastic flow. The pH of the sample containing BEM was close to neutral (7.72 ± 0.005), while the pH of the sample containing BE was 8.17 ± 0.026. The results showed a possible application of BEM in cosmetic products.

The integrated evaluation of soil geochemistry, aerogammaspectrometry (eTh), geological and structural mapping associated with the description of boreholes and outcrops in the Cacapava do Sul region, southernmost Brazil, led to the discovery of two carbonatite bodies. They are located near the eastern and southeastern border of Cacapava do Sul Granite and intrude the Passo Feio Complex. The carbonatite system is composed of early pink-colored alvikite followed by late white beforsite dikes. The carbonatites are tabular bodies concordant with the deformed host rocks. Petrographic and scanning electron microscopy show that the alvikites are dominantly composed of calcite with subordinate apatite, magnetite, ilmenite, biotite, baddeleyite, zircon, rutile, pyrochlore-like and rare earth element minerals. Beforsite is composed of dolomite and has the same minor and accessory minerals as the alvikite. U-Pb zircon geochronology via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was performed on a beforsite sample, yielding a 603.2 ± 4.5 Ma crystallization age. The carbonatite was emplaced an Ediacaran post-collisional environment with transpressive tectonism and volcanic activity marked by shoshonitic affinity.

Carbonatites were recently discovered in Southern Brazil, which increased the interest to evaluate the economic potential of these uncommon rocks, especially the Três Estradas Carbonatite. Carbonates are the dominant minerals of fresh rock followed by apatite, but the weathering process makes apatite abundant. We focused on apatite from the carbonatite using conventional petrography and electronic microscopy associated with microprobe, micro-Raman and Fourier-transform infrared spectroscopy. Results demonstrate the existence of four types. The primary type is associated with the rock crystallization and the subsequent three others are associated with weathering processes. The alteration mechanism was favorable for initial carbonate leaching and subsequent increase of phosphate with late precipitation of three new apatite generations. The deduced model involves long exposure during polycyclic climate changes, intercalating periods of warm dry with humid climate. The apatite types differ chemically and morphologically and have distinctive characteristics that are suitable to be used to differentiate them. These properties should be considered in future planes of industrial processes to transform apatite into single superphosphate, a basic input for fertilizer production.

This paper proposes the generation and closure of a proto-ocean and formation of an island arc in the Neoproterozoic Passo Feio Metamorphic Complex (PFMC), Cacapava do Sul region, southern Brazil. The PFMC, Sao Gabriel Terrane, consists of a Neoproterozoic supracrustal metavolcano-sedimentary sequence intruded by the Cacapava Granite. The study uses petrography, whole-rock geochemistry and mineral chemistry to identify the geochemical affinity and tectonic environment of the amphibolites contained in PFMC, the basalts and pillow lavas of Arroio Mudador Formation and dikes intruded in nearby volcanogenic rocks of Hilario Formation. The applied methods allow the metamorphic facies classification of ­prehnite-pumpellyite for the basalts and pillow lavas, greenschist for the dikes and lower amphibolite for the amphibolites. The discriminant diagrams indicate from tholeiitic to alkaline affinities for the Hilario Formation dikes. The basalts, pillow lavas and amphibolites have basaltic to basaltic-andesite composition and predominant tholeiitic affinity, interpreted as derived of the same protolith. The geotectonic diagrams mostly indicate volcanic arc basalts. The proposed evolution model starts with a proto-ocean opening through the Bossoroca Arc rifting around 760Ma, where an island arc is formed (PFMC rocks), precipitation of carbonates and marls, subsequent closure, two metamorphism events and the Cacapava Granite intrusion around 562 Ma.

The Ibaré Lineament is a shear zone that sections the Western portion of Sul-riograndense Shield, affecting the orthogneissic rocks of Santa Maria Chico Granulitic Complex, acting as a conduct for hydrothermal fluids. The studied hydrothermal mineralogy reflects a propylitic alteration paragenesis that is composed of Fe-clinochlore, epidote, albite, calcite and quartz, typical low-pressure paragenesis (< 2,000 bar). This mineral association reflects an equilibrium in a neutral to slightly alkaline pH. Using the new approach for chlorite geothermometry, an average formation temperature of 274°C was obtained, compatible with the stability of polytype IIb chlorite and with the irregular textures of twinning in calcites. The fluid inclusions in quartz establish a low-salinity system (2.45 wt.% NaCl eq.) and an average temperature of 175°C. The obtained temperatures are interpreted as a continuum cooling model with meteoric fluids entrance. The system pressure is evaluated from isochores, reaching an average value of 1,560 bar. This is the first temperature and pressure estimate to the Ibaré Shear Zone, which enabled the establishment of a shallow hydrothermal system (epithermal) with fluid interaction from magmatic and meteoric sources, confirmed by the behavior of carbon and oxygen stable isotopes, which indicated an the origin from mixed sources.

International audience; Andean tropical glaciers have shown a clear shrinkage throughout the last few decades. However, it is unclear how this general retreat is associated with variations in rainfall patterns in the Amazon basin. To investigate this question, we compared the annual net accumulation variations in the Bolivian Cordillera Real (Andes), which is derived from an ice core from the Nevado Illimani (16° 37′ S, 67° 46′ W), covering the period 1960–1999 using the Amazonian Rainfall Index, Northern Atlantic Index (TNA), Multivariate ENSO Index (MEI), and Pacific Decadal Oscillation (PDO). The accumulation rate at the Nevado Illimani ice core decreased by almost 25% after 1980, from 1.02 w.eq. a−1 (water equivalent per year) in the 1961–1981 period to 0.76 w.eq. a−1 in the 1981–1999 period. The Northern Amazonian Rainfall (NAR) index best reflects changes in accumulation rates in the Bolivian ice core. Our proposal is based on two observations: (1) This area shows reduced rainfall associated with a more frequent and intense El Niño (during the positive phase of the MEI). The opposite (more rain) is true during La Niña phases. (2) Comparisons of the ice core record and NAR, PDO, and MEI indexes showed similar trends for the early 1980s, represented by a decrease in the accumulation rates and its standard deviations, probably indicating the same causality. The general changes observed by early 1980s coincided with the beginning of a PDO warm phase. This was followed by an increase in the Amazonian and tropical Andean precipitation from 1999, coinciding with a new PDO phase. However, this increase did not result in an expansion of the Zongo Glacier area.

This work correlates surface and ground water composition to the substrata, and traces how water chemistry evolves at Brazil’s largest coal mine, the Candiota Mine. The water is dominated by SO4, Fe, Ca, and Mg. A pH range of 2.7–3 in the pit lakes is attributed through chemical models to concomitant pyrite oxidation and carbonate dissolution along with slow hydrolysis of aluminosilicate minerals and buffering provided by several iron oxy-hydroxide species. The Fe deficit of the surface water relative to the expected values is mainly due to precipitation of Fe sulfate salts, hydroxysulfates, and oxyhydroxides in the waste piles and their runoff. A progressive decrease in oxygen partial pressure with increased lake depth leads to destabilization of the iron oxyhydroxides/hydroxysulfates formed near the surface, which explains their absence from the lake sediment. Although interacting with similar rock types, the groundwater has a significantly different composition than the surface water, with less salinity and a pH of 5–6.5, due to limited oxygen and its evolution in a nearly closed system that stabilizes at higher pH values, which is controlled by carbonate/bicarbonate buffering.

In a subduction zone, water-rich pelagic sediments overlying the subducting oceanic plate are accumulated, forming an accretionary wedge. A portion of these sediments, primarily smectites, can subduct and lose the water present in their pores, but the mechanism of the clay structural transformation and its composition are not well-defined. Smectite clay minerals can remain stable, carrying water at pressures corresponding to the upper mantle and thus contributing to the occurrence of melting and metasomatic processes in the mantle. In this work, we performed several high-pressure and high-temperature experiments to verify the structural behavior of a potassium-saturated smectite under various pressure and temperature conditions: (1) atmospheric pressure at two different temperatures (100 °C to 700 °C); (2) room temperature (25 °C) and pressure up to 11.5 GPa — diamond anvil cell (DAC) experiments; (3) under pressures of 2.5 GPa and 4.0 GPa and temperatures from 200 °C to 700 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy (FTIR) analysis on all samples studied suggest that, under elevated pressures (2.5 GPa, which corresponds to a depth of approximately 75 km, and 4.0 GPa, equivalent to a depth of approximately 120 km), smectite remains stable until 200 °C. With increasing temperature, the initial structure partially loses its interlayer H 2 O and transforms into a mixed layer of illite/smectite, which is maintained until 400 °C under 2.5 GPa and until 300 °C under 4.0 GPa. Beyond these conditions, with increasing temperature, the smectite loses all of its interlayer H 2 O and transforms into muscovite. Additionally, at room temperature, smectite is stable under nearly 12 GPa. These results contribute significantly to the understanding of how pelagic sediment dehydration and transformation occur in the subduction process, as well as the behavior of smectite under the influence of increasing pressure and temperature.

Fluvial and estuarine sandstones of the Aptian Mucuri Member of the Mariricu Formation are the main reservoir rocks in the onshore portion of the Espirito Santo Basin, Brazilian eastern margin. These sandstones are contemporaneous with the major lacustrine pre-salt reservoir rocks which are currently the target of exploration offshore. The sandstones are texturally and compositionally immature, rich in feldspars, biotite, garnets and other heavy minerals, and are interpreted to have been derived from the erosion of igneous and medium-high grade metamorphic-plutonic terrains under dry climatic conditions. Early diagenetic processes have significantly impacted the reservoir qualities of the sandstones. Detrital feldspars were dissolved and replaced by kaolinite. Biotite was replaced and expanded by pyrite, calcite, kaolinite and/or smectite. The growth of authigenic rims and coatings of smectitic clays was the most important diagenetic process in most of the sandstones, except for those cemented by abundant poikilotopic calcite. Coarse-crystalline pyrite replaced primary constituents, particularly biotite and mudstone intraclasts, and all other diagenetic constituents. Mechanical compaction, although relatively limited, was the main process of porosity reduction, except in sandstones with abundant calcite cement. Primary intergranular porosity was commonly strongly reduced by calcite or smectite cementation and by compaction, but intragranular and mouldic secondary pores were generated by the dissolution of detrital feldspars and heavy minerals. Characterizing the diagenetic patterns of the Mucuri sandstones is important for increasing the recovery from producing oilfields and also for the development of analogous reservoir rocks elsewhere.

Este estudo avaliou por técnicas de sensoriamento remoto, a cobertura de gelo nos Andes Bolianos em uma área piloto(cordilheira Três Cruces, localizada entre 67º22’—67º32’W e 16º47’—16º09’S). Foram examinadas as antigas posições frontais de algumas geleiras dessa cordilheira, pela análise de imagens satelitais, dados cartográficos, e pelo cálculo de mudança na espessura do gelo (diferenças de volume e elevação). O monitoramento foi efetuado entre os anos de 1975 e 2004 (29 anos) nas geleiras: Jankho Loma, San Enrique, Laramkkota, Malla Chuma, Campanani, Jacha Pacuni e c5250. No geral, a partir de 1975, as frentes das geleiras diminuíram em todas as direções, as retrações máximas e mínimas das frentes de gelo foram de 437 m (Laramkkota) e 181 m (San Enrique). O recuo médio das sete geleiras estudadas foi de aproximadamente 12m a-1. Nas áreas cobertas por gelo na cordilheira, em média, ocorreu uma redução de 18% em 29 anos, ou seja, aproximadamente - 0,009 km2 a-1. Neste período a geleira c5250 foi a que teve a maior perda relativa (cerca de 50% de sua área). Por outro lado, a geleira Campanani, de maior superfície, foi a que perdeu proporcionalmente menor área (6% do total). A análise dos modelos digitais de elevação indicou redução geral no volume de gelo durante o período, apresentando uma perda média de aproximadamente 1,55 m equivalente água a-1. A retração das massas glaciais da cordilheira Tres Cruces é consistente com o aquecimento atmosférico regional e com a redução generalizada das geleiras nos Trópicos. Using remote sensing techniques, this study surveyed a pilot area of the Bolivian Andes ice cover, located at the Tres Cruces Cordillera (67º22’—67º32’W e 16º47’—16º09’S). Analyses of satellite imagery, cartographic data and estimates of ice thickness changes (differences in volume and elevation) have provided information on past front positions of some glaciers in this cordillera. Monitoring was carried out from 1975 to 2004 (29 years) for the following glaciers: Jankho Loma, San Enrique, Laramkkota, Malla Chuma, Campanani, Jacha Pacuni and c5250, including a total ice covered area of 13.7 km2. Generally, from 1975 onwards, glacier fronts receded. Maximum and minimum ice front retreats were 437 m (Laramkkota) and 181 m (San Enrique). The mean retreat for the 7 studied glaciers was approximately 12 m a-1. On average, these glaciers lost 18% of their total areas over 29 years (i.e., a loss of approximately of 0.009 km2a-1). During this period, the c5250 glacier (0.48km2 in 1975) had the greatest relative loss (about 50% of its total area). On the other hand, the Campanani glacier, the largest one (4.26 km2 in 1975), lost the smallest proportional area (6% of its total area). The snow line in 2004, determined at a 5,300 m altitude, was used to calculate the proportion between the accumulation and total areas in each glacier. All studied glaciers in 2004 had an accumulation area proportionally greater than 60%. Analyses of the elevation digital models (EDMs) point to a general reduction of the ice volume during the period, on average 1.55 m water equivalent a-1. The retreat of ice masses in Tres Cruces Cordillera is concomitant to regional atmospheric warming and to the general reduction of glaciers in the Tropics.

Fluvial and aeolian sandstones of the Sergi Formation are the most important reservoirs of the Recôncavo Basin, Brazil. Optical and scanning electron microscopy, X-ray diffraction and infrared spectroscopy revealed the occurrence of dickite, a clay mineral indicative of deep burial conditions (T >100ºC), in the shallow Buracica (630–870 m) and Água Grande (1300–1530 m) oilfields. Vermicular dickite replaces K-feldspar and plagioclase grains, and fills intra- and inter-granular pores. Its vermicular habit is a product of pseudomorphic kaolinite transformation during burial. The presence of dickite is in accordance with the intensity of compaction, post-compactional quartz cementation and δ18O values of calcite cements (T up to 109ºC). These petrological features of deep burial, as well as apatite fission-track analyses, indicate that uplift and erosion of at least 1 km, and probably >1500 m, affected the central part of the Recôncavo Basin and possibly the entire region. This uplift has not been detected previously by conventional structural and stratigraphic models.

J. MARCELO KETZER, L. FERNANDO DE ROS and NORBERTO DANIUniversidade Federal do Rio Grande do Sul, Instituto de Geocieˆncias, Avenue. Bento Gonc¸alves, 9500,91501–970, Porto Alegre, Brazil. (E-mail: jm@ketzer.com.br, lfderos@inf.ufrgs.br, norberto.dani@ufrgs.br)Keywords Clay infiltration, diagenesis, kaolinite, microtexture, sandstone.INTRODUCTIONThe recently published paper by Du Bernard C Moraes & De Ros, 1990; Weibel, 1998;Salem et al., 2000; Fig. 1A). This is becausemechanical infiltration is most effective andextensive in semi-arid climatic conditions (Kess-ler, 1978; Walker et al., 1978; Moraes & De Ros,1990), under which smectitic clays are the mostcommon weathering products. Conversely, kaoli-nite is characteristically formed in humidclimatic conditions, under which infiltration isuncommon or volumetrically insignificant(Ketzer et al., 2003a).Despite finding the occurrence described by DuBernard & Carrio-Schaffhauser (2003) interesting,we identified problems in their methodology anddiscussion. The present discussion aims to com-ment on these points, and to suggest an alter-native interpretation of the origin, timing andeffects on compaction and reservoir quality of thedescribed clays in the Nubian sandstones.ORIGIN OF KAOLINITEDu Bernard & Carrio-Schaffhauser (2003) de-scribed two types of kaolinite occurrence in theNubian sandstones: (i) finely crystalline (1–5lm)and (ii) coarsely crystalline aggregates (>50lm).The finely crystalline kaolinite consists of brown(under uncrossed polarizers) colour, pore-fillingaggregates with meniscus shape. A close inspec-tion of the backscattered (BSE) scanning elec-tronic microscope (SEM) images provided by DuBernard and Carrio-Schaffhauser (their fig. 5Cand D), suggests that the meniscus aggregates arecomposed of several kaolinite booklets (fig. 1B).This morphology is typical of diagenetic, authi-genic kaolinite. Such evidence indicates an au-thigenic origin for the finely crystalline kaolinite,as opposed to the infiltrated origin proposed byDu Bernard and Carrio-Schaffhauser. Hence, thiskaolinite most probably resulted from the in situreplacement of mechanically infiltrated, possiblysmectitic clay minerals, owing to active circula-tion of meteoric water through the sandstones.The origin of the fluids responsible for thekaolinitization of the precursor infiltrated claysshould be constrained by O and H isotopicanalyses of the kaolinite (Morad et al, 2003).The preservation of the meniscus morphology ofthe infiltrated clay aggregates after kaolinitizationresulted from the inheritance of the texture of theprecursor clay mineral by the kaolinite. It is nosurprise that such preservation occurs, as pseudo-morphic replacement is rather common amongclay minerals (e.g. in the chloritization or illiti-zation of kaolinite, Morad et al.,1998; De Ros,1998). The variable, in places random, orientationof some kaolinite booklets is typical of authigenicaggregates and thus has no direct relationshipwith ‘differences in water volume within themeniscus’, as suggested by Du Bernard andCarrio-Schaffhauser (p. 1227). Additionally, therelevance of the theoretical discussion on theaspects of the menisci geometry (pp. 1225–1227)to the interpretations of the authors is not clear.X-ray diffraction analysis from the

Magmatismo associado com o estágio pré-evaporítico da Bacia de Campos foi estudado a partir de testemunhos de quatro furos de sondagens. Os dados levantados são importantes no contexto da evolução tectônica e estratigráfica da bacia. O objetivo deste trabalho foi a caracterização dessas rochas a partir da petrografia, litoquímica, química mineral e composição isotópica Sr-Nd. A aplicação das metodologias de estudo convencionais foi dificultada devido ao grau de alteração das rochas, marcado por modificações mineralógicas (substituição de minerais por argilominerais, palagonitização do vidro vulcânico, sericitização dos plagioclásios e presença de vesículas), ao elevado valor de perda ao fogo (LOI) e à identificação de sedimentos arenosos englobados pela rocha vulcânica. Para minimizar os efeitos da alteração, empregaram-se metodologias que permitiram avaliar o grau de alteração das amostras e a mobilidade dos elementos químicos na rocha total. Os resultados obtidos estabelecem que as rochas vulcânicas são basaltos originados a partir de magmas com composição subalcalina, toleítica a transicional, baixo TiO2 e alto magnésio. Os elementos terras raras (ETR) e o padrão de distribuição dos elementos traço estão em conformidade com o padrão dos basaltos toleíticos baixo TiO2 da Formação Serra Geral e são diferentes dos enriched-mid ocean ridge basalt (E-MORB) e dos ocean island basalts (OIB) do oceano Atlântico, embora alguns elementos tenham comportamento similar. O piroxênio dominante é a augita e, quimicamente, confirma que os basaltos pertencem à série subalcalina, bem como ao intervalo de transição entre as séries cálcio-alcalina e toleítica. Isotopicamente, as amostras estudadas incidem fora do campo estabelecido como “mantle array”; e seguem o comportamento dos basaltos da Bacia de Campos com alto potássio. Os parâmetros levantados estabelecem a correlação das rochas vulcânicas do Andar Alagoas da Bacia de Campos com os basaltos intracontinentais da Bacia do Paraná.

A morfologia de canais é resultado do ambiente em que se encontram, assim como de todas variáveis físicas atuantes. Se a desembocadura está situada em zonas costeiras, a tendência à instabilidade é amplificada pelo próprio meio. Neste artigo são apresentados os resultados do estudo morfodinâmico do canal de comunicação entre a Lagoa do Peixe e o Oceano Atlântico, localizado no Parque Nacional da Lagoa do Peixe, litoral médio do Rio Grande do Sul, Brasil. Também é medida a variabilidade da linha de praia adjacente ao parque. Com o objetivo de determinar a classifica- ção do canal e sua dinâmica natural, foram utilizados uma série de 47 anos de imagens Landsat (1973 – 2009), dados de precipitação da Agencia Nacional de Águas e equações. A interpretação da série temporal e os cálculos das médias de precipitação permitiram descrever o canal da Lagoa do Peixe como um canal de maré, com mecanismo de assoreamento morfodinâmico influenciado pelo regime de precipitação pluviométrica. Os resultados das equações indicaram como fatores determinantes à sua oclusão o prisma de maré e transporte e deposição sedimentar em frente a desembocadura, associados à deriva litorânea de padrão bidirecional da área de estudo. Sua desembocadura possui caráter intermitente e é instável quanto ao seu posicionamento e geometria. A mobilidade da linha de praia adjacente ao Parque Nacional da Lagoa do Peixe foi verificada pelo método de pontos extremos, pixel a pixel, entre duas imagens Landsat de mesmo mês, uma de 1987 e outra de 2009, sendo constatada erosão ao sul da desembocadura do canal da Lagoa do Peixe e acreção ao norte da mesma., The inlets morphology is a result of the environment in which they are, as well as all active physical variables. If the mouth is situated in coastal areas, the trend towards instability is amplified by the environment itself. This paper presents the results of a morphodynamic study of the communication inlet between the Lagoa do Peixe and the Atlantic Ocean, located in Lagoa do Peixe National Park, middle coast of Rio Grande do Sul, Brazil. It is also measured the variability of adjacent shoreline to the park. In order to determine the classification of the inlet and its natural dynamics, was used series of 47 years of Landsat images (1973-2009), rainfall data of the National Water Agency and equations. The interpretation of the time series and the calculation of averages precipitation allowed to describe the Lagoa do Peixe inlet as a tidal inlet, with silting morphodynamic mechanism, influenced by the rainfall regime. The results of the equations indicated as key factors to its occlusion tidal prism, sediment transport and deposition in front of the mouth, associated with the longshore bidirectional pattern of the study area. The inlet has intermittent character and is unstable on its position and geometry. The mobility of the adjacent shoreline to the Lagoa do Peixe National Park was verified by the method of extreme points, pixel by pixel, between two Landsat images of the same month, one of 1987 and other of 2009, erosion being found south of the mouth of the Lagoa do Peixe inlet and accretion to the north of it.

Nordstrandite from Lages represents the first occurrence of this mineral in an oxisoil that does not involve the influence of a calcareous substrate. This is also the first reported occurrence in Brazil. Nordstrandite occurs near the city of Lages only in the weathered bedrock facies, mostly where the circulation of meteoric water is restricted. There is also a close association between nordstrandite and the weathering of modified pseudoleucite structures. The interaction of meteoric water and feldspathic alkaline country rock with uncommon texture and mineralogy (rich in nepheline, sodalite, nosean, analcime and natrolite) promotes the development of solutions enriched in alkaline ions with basic pH, necessary to form nordstrandite. A detailed study by X-ray diffraction (XRD) and infrared (IR) spectroscopy in natural or chemically leached samples was performed to identify the Al(OH) 3 polymorphs of gibbsite and nordstrandite.

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Esta nota explicativa se refere ao mapa geológico de parte da Folha Arroio América (SH.22-Y-A-IV-1 / MI 2995/1) e tem por base os resultados obtidos durante o Projeto Arroio América, executado em 2003 por professores e alunos do Curso de Geologia da Universidade Federal do Rio Grande do Sul. Diversas unidades litoestratigráficas foram reconhecidas, algumas das quais são inéditas e formalmente designadas. A principal estrutura regional reconhecida é denominada Zona de Cisalhamento Arroio América (ZCAA), composta por diversas zonas miloníticas subverticais de direção NE e cinemática transcorrente esquerda dada por lineação de estiramento de baixo caimento. Significativas reativações de antigos lineamentos em condições rúpteis são encontradas, bem como estruturas rúpteis de direção NW que afetam o embasamento e as rochas sedimentares de idade neoproterozoica a permiana. As sequências de embasamento mais antigas são ortognaisses do Complexo Cambaí, e as rochas supracrustais do Complexo Metamórfico Arroio Marmeleiro (CMAM). Os Dioritos Arroio Branquilho formam uma unidade inédita de biotita-hornblenda dioritos e quartzo-dioritos foliados, que compreendem duas subunidades cogenéticas – a fácies equigranular média e a fácies fina. As relações estruturais observadas indicam que seu posicionamento é anterior à ZCAA. O Tonalito Arroio dos Carros (TAC) e os Granitoides Rincão dos Encerrados (GRE) são também unidades inéditas, correlacionadas à Suíte Lagoa da Meia Lua. O TAC compreende hornblenda tonalitos foliados, de granulação média a grossa, e sua foliação magmática grada para uma foliação milonítica devido a seu caráter sintectônico à ZCAA. Os GRE são biotita tonalitos a granodioritos equigranulares finos a médios, tardi-tectônicos em relação à mesma zona de cisalhamento. O Granito Passo da Chácara, igualmente inédito, é a unidade granítica mais jovem, compreendendo biotita leucossienogranitos fracamente foliados a maciços. A Formação Maricá é composta por arenitos arcóseo-líticos com intercalação subordinada de conglomerados e folhelhos. Evidências localizadas de condições anquimetamórficas são constatadas, bem como clivagem ardosiana em composições pelíticas. É subdividida em duas fácies, uma resultante de sistema fluvial anastomosado e outra formada em condições marinhas rasas. O Monzonito Tapera, bem como as formações Hilário, Cerro da Pedra e Acampamento Velho, são subunidades do Grupo Bom Jardim. No Monzonito Tapera são reconhecidas quatro fácies com base em características texturais e composicionais: monzonítica plutônica, leucodiorítica plutônica, diorítica plutônica e hipoabissal monzonítica. Nas rochas encaixantes do CMAM, são descritos efeitos de metamorfismo de contato em condições de fácies hornblenda cornubianito. A Formação Hilário compreende derrames andesíticos e diques de andesitos e lamprófiros. A Formação Cerro da Pedra é definida neste trabalho como um pacote de conglomerados formados em sistemas de leques aluviais. A fácies proximal é reconhecida na forma de para- e ortoconglomerados oligomíticos, enquanto a fácies distal é representada por ortoconglomerados polimíticos. A Formação Acampamento Velho é representada por um domo de lava e diques riolíticos associados. A Formação Rio do Sul, de idade permiana, pertencente ao Grupo Itararé, é restrita ao extremo norte da área mapeada, onde ocorrem camadas de arenito fino intercaladas com siltitos., This explanatory note refers to the geological map of part of the Arroio América Sheet (SH.22-Y-AIV-1 / MI 2995/1) and is based on the results obtained during the Arroio América Project, carried out in 2003 by professors and undergraduate students of the Geology Course, Federal University of Rio Grande do Sul. Seve ral lithostratigraphic units were recognized, some of which are newly-defined and formally named. The main large-scale structure recognized and named is the Arroio América Shear Zone (ZCAA), composed of several NE-trending, subvertical mylonitic zones of sinistral transcurrent kinematics given by shallow-plunging stretching lineation. Brittle reactivations of old trends are significant, as well as NW-trending brittle structures which affect basement and sedimentary rocks from Neoproterozoic to Permian age. The oldest basement sequences are orthogneisses of the Cambaí Complex, and supracrustal rocks of the Arroio Marmeleiro Metamorphic Complex (CMAM). The Arroio Branquilho Diorites form a newly-defined unit of foliated biotite-hornblende diorites and quartz-diorites and comprise two co-genetic subunits - the medium-grained equigranular facies, and the fine-grained facies. Structural relations indicate that their emplacement predates the ZCAA. The Arroio dos Carros Tonalites (TAC) and Rincão dos Encerrados Granitoids (GRE) are also newly-defined units, correlated to the Lagoa da Meia Lua Suite. The TAC comprises medium- to coarse-grained, foliated hornblende tonalites, and their magmatic flow foliation grades into a mylonitic one due to its syntectonic character relative to the ZCAA. The GRE are equigranular, fine to medium-grained biotite tonalites to granodiorites which are late-tectonic relative to the same shear zone. The Passo da Chácara Granite, also newly-defined, is the youngest granitic unit, and comprises weakly-foliated to massive biotite leucosyenogranites. The Maricá Formation is composed of lithic arkosean sandstones with subordinate interleaving of shale and conglomerates. Local evidences of anchimetamorphic conditions and slaty cleavage in pelitic compositions are found. Two facies units are described, the first resulting from a braided river system and the second formed in shallow marine conditions. The Tapera Monzonite, as well as Hilário, Cerro da Pedra and Acampamento Velho formations are sub-units of the Bom Jardim Group. In the Tapera Monzonite, four different facies are recognized, based on compositional and textural characteristics: monzonitic plutonic, leucodioritic plutonic, dioritic plutonic and hypoabyssal monzonitic facies. In the enclosing CMAM rocks, contact metamorphism of hornblende-hornfels conditions is described. The Hilário Formation comprises andesitic flows, as well as andesitic and lamprophyric dikes. The Cerro da Pedra Formation is presently defined to describe conglomerate packs formed in alluvial-fan systems. A proximal facies is recognized as oligomitic para- and orthoconglomerates, while a distal facies is represented by polimitic orthoconglomerates. The Acampamento Velho Formation is represented by a rhyolitic lava-dome and related dikes. The Permian Rio do Sul Formation, belonging to the Itararé Group, is restricted to the northern extreme of the mapped area, where fine-grained sandstone layers are interleaved with siltstones.