Pirometamorfismo nos arenitos da Formação Açu, Bacia Potiguar, NE do Brasil

Pyrometamorphism results from conditions of high temperatures and very low pressures provoked by the intrusion of hypabyssal basic bodies into sedimentary or metassedimentary hosting rocks. The onshore portion of the Potiguar Basin in NE Brazil offers examples of this type of metamorphism nearby the contacts of Paleogene to Neogene plugs, sills and dikes of diabases and basalts crosscutting sandstones, siltstones and shales of the Açu Formation (Albian-Cenomanian). The thermal effects over these rocks are reflected on textures and minerals assemblages that characterize the sanidinite facies of metamorphism, often with partial melting of the feldspathic and mica-rich matrix. The liquid formed is potassic and peraluminous, with variably colored rhyolitic glass (colorless, yellow, brown) comprising microcrystals of tridymite, sanidine and clinoenstatite, besides residual detrital clasts of quartz and rarely zircon, staurolite and garnet. Lenses of shale intercalated within the sandstones display crystallites of Fe-cordierite (sekaninaite), mullite, sanidine, armalcolite (Fe-Ti oxide) and brown spinel. The rocks formed due to the thermal effect of the intrusions are called buchites for which two types are herein described: a light one derived from feldspathic sandstone and siltstone protoliths; and a dark one derived from black shale protoliths. Textures indicating partial melting and minerals such as sanidine, mullite, tridymite and armalcolite strongly demonstrate that during the intrusion of the basic bodies the temperature reached 1,000-1,150°C, and was followed by quenching. Cooling of the interstitial melts has as consequences the closure of pores and decrease of the permeability of the protolith, which varies from about 17-11% in the unaffected rocks to zero in the thermally modified types. Although observed only at contacts and over small distances, the number of basic intrusions hosted within the Potiguar Basin in both onshore and offshore portions leaves opened the possibility of important implications of the thermal effects over the hydrocarbon exploration in this area as well in other Cretaceous and Paleozoic basins in Brazil

Caracterização geológica tridimensional e monitoramento de dunas no litoral oriental do Rio Grande do Norte

This work presents geophysical and geological results obtained in a dunefield located in the east coast of Rio Grande do Norte State, with the aim to recognize the aeolian body depositional geometries to a future geologic modeling of the aeolian petroliferous reservoirs. The research, which was done in blowouts region situated at Nisia Floresta Municipally, included the characterization of external geometries with GPS and internal geometry analysis by GPR. Data was integrated in GoCAD software, where it was possible the three-dimensional characterization and interpretation of the studied deposits. The interpretation of GPR profiling allowed identifying: First-order bounding surfaces that separated the aeolian deposits of the Barreiras Formation rocks; Second-order bounding surfaces, which limit dune generations and Third-order bounding surfaces, a reactivation surface. This classification was based and adapted by the Brookfield (1977) and Kocurek (1996) propose. Four radarfacies was recognized: Radarfacies 1, progradational reflectors correlated to foresets of the dunes, Radarfacies 2, plain parallels reflectors related to sand sheets, Radarfacies 3, plain parallels reflectors associated to reworking of the blowout dune crest and Radarfacies 4, mounded reflectors associated to vegetated mound of sand or objects buried in subsurface. The GPR and GPS methods was also employed to the monitoring of dunefields susceptible to human activities in Buzios Beach, where the constructions along the blowout region and the tourism are changing the natural evolution of the deposits. This fact possibly to cause negative impacts to the coastal zone. Data obtained in Dunas Park, a unit environmental conservation, was compared with information of the Buzios Beach. There is a major tendency of erosion in Buzios, specifically in blowout corridor and blowout dune

Caracterização geomorfológica e paleogeográfica da plataforma continental adjacente a foz do Rio Apodi-Mossoró, RN/Brasil

The brazilian marginal basins have a huge potential to generate and accumulate petroleum. Incised valleys which are eroded in response to a fall of relative sea level are related to potential reservoir as well, modern drowned-valley estuaries serve as harbors to petroleum and salt industries, fisheries, waste-disposal sites and recreational areas for a significant fraction of the world s population. The combined influence of these factors has produced a dramatic increase in research on modern and ancient incised-valley systems. This research is one expression of this interest. The integrated use of satellites images and high resolution seismic (bathymetry, sides scan sonar) was used on the Apodi River mouth-RN to characterizes the continental shelf This area is located at the Potiguar Basin in the NE Brazilian Equatorial Atlantic margin. Through bathymetric and side scan sonar data processing, a digital Terrain Model was developed, and a detailed geomorphologic analysis was performed. In this way was possible to recognize the geomorphologic framework and differents sismofacies, which may influence this area. A channel extending from the ApodiMossoró river mouth to the shelf edge dominates the investigated area. This structure can be correlated with the former river valley developed during the late Pleistocene sea level fall. This channel has two main directions (NW-SE and NE-SW) probably controlled by the Potiguar Basin structures. The western margin of the channel is relatively steep and pronounced whereas the eastern margin consists only of a gentle slope. Longitudinal bedforms and massive ridges also occur. The first are formed doe to the shelf sediment rework and the reef-like structures probably are relics of submerged beachrock-lines indicating past shoreline positions during the deglacial sea-level rise. The sub-bottom seismic data allow the identification of different sismic patterns and a marcant discontinuity, interpreted as the Upper

Análise da vulnerabilidade ambiental no estuário do Rio Curimataú/Cunhaú, Baía Formosa e Canguaretama - RN

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

analise da dispersao de ondas de superficie na provincia borborema, Nordeste do Brasil

The Borborema Province, Northeastern Brazil, had its internal structure investigated by different geophysical methods like gravity, magnetics and seismics. Additionally, many geological studies were also carried out to define the structural domains of this province. Despite the plethora of studies, there are still many important open aspects about its evolution. Here, we study the velocity structure of S-wave in the crust using dispersion of surface waves. The dispersion of surface waves allows an estimate of the average thickness of the crust across the region between the stations. The inversion of the velocity structure was carried out using the inter-station dispersion of surface waves of Rayleigh and Love types. The teleseismic events are mainly from the edges of the South and North American plates. The period of data collection occurred between 2007 and 2010 and we selected 7 events with magnitude above 5.0 MW and up to 40 km depth. The difference between the events back-azimuths and the interstation path was not greater than 10. We also know the depth of the Moho, results from Receiver Functions (Novo Barbosa, 2008), and use those as constrains in inversion. Even using different parameterizations of models for the inversion, our results were very similar the mean profiles velocity structure of S-wave. In pairs of stations located in the Cear´a Central Domain Borborema the province, there are ranges of depths for which the velocities of S are very close. Most of the results in the profile near the Moho complicate their interpretation at that depth, coinciding with the geology of the region, where there are many shear zones. In particular, the profile that have the route Potiguar Bacia in inter-station, had low velocities in the crust. We combine these results to the results of gravimetry and magnetometry (Oliveira, 2008) and receptor function (Novo Barbosa, 2008). We finally, the first results on the behavior of the velocity structure of S-wave with depth in the Province Borborema

Estruturação da seqüência vulcano-sedimentar Rio Mata Cavalo (Morro do Pilar, MG, Brasil) baseada na análise qualitativa de dados geofísicos

Geofísica terrestre (magnetometria e radiometria) foi utilizada como ferramenta de apoio ao mapeamento geológico em uma área de pesquisa mineral da Companhia Mineradora de Minas Gerais (COMIG), denominada Alvo Bueiro, localizada a sudeste da cidade de Morro do Pilar, na Serra do Espinhaço, Estado de Minas Gerais. A integração de informações de geologia de superfície com os dados geofísicos correspondentes permitiu definir quatro zonas: A, B, C e D. A Zona A, caracterizada por altos valores de susceptibilidade magnética e baixos valores de radiometria, é composta por itabiritos do Grupo Serra da Serpentina. A Zona B, pertencente ao mesmo grupo, é constituída por filitos cinza e metassiltitos e mostra baixa susceptibilidade magnética; interrupções nas linhas de contorno foram interpretadas como decorrentes de falhas de empurrão. A Zona C, relacionada à Seqüência Vulcano-Sedimentar Rio Mata Cavalo, é caracterizada por uma expressiva anomalia do campo magnético total em xistos máficos e ultramáficos com lentes de formações ferríferas e filitos carbonosos negros; esta zona hospeda as mais importantes anomalias geoquímicas de ouro conhecidas na área em estudo. A Zona D, correspondente a ortognaisses cisalhados do Complexo Dona Rita, mostra os mais elevados valores de radiometria do Alvo Bueiro e baixas respostas magnéticas.

Permian bivalves of the Taciba Formation, Itarare group, Parana basin, and their biostratigraphic significance

A small and poorly diversified bivalve fauna from Taciba Formation, Itarare Group, Parana Basin (State of Santa Catarina, Mafra Municipality), is described in this paper for the first time, based on new findings. The fauna is recorded in a 30 cm thick interval of fine sandstone locally at the top of Taciba Formation, in the Butia quarry. The studied fossil-bearing sand-stone bed is a marine intercalation recording a brief eustatic rise in sea-level, probably following glacier retreat and climate amelioration at the end of a broad glacial scenario. The fauna is mainly dominated by productid brachiopods, which are not described here, and rare mollusk shells (bivalves and gastropods). Two bivalve species were identified: Myonia argentinensis (Harrington, 1955), and Aviculopecten multiscalptus (Thomas, 1928). The presence of Myonia argentinensis is note-worthy since this species is also present in the Baitaca assemblage found in marine siltstones (Baitaca assemblage) of the Rio do Sul Formation, cropping out at the Teixeira Soares region, Parana State. This species is also recorded in the bivalve fauna from the Bonete Formation, Pillahinco Group, Sauce Grande Basin, Buenos Aires Province, in Argentina. Hence, the marine bivalves of the Taciba Formation are associated with the transgressive event that characterizes the Eurydesma fauna, indicating a Late Asselian-Sakmarian age for the bivalve fauna. Presence of the Myonia argentinensis megadesmid species reinforces the Gondwanic nature of the studied fauna.

Viés Analítico em Estudos Tafonômicos com Macroinvertebrados: Implicações (Paleo)Ambientais e (Paleo)Ecológicas

A review of recent literature shows that most taphonomic studies of Holocene and fossil macrovertebrates are not methodologically standardized. Hence, results from distinct studies are not comparable, even among researches sharing virtually identical goals, targeting the same biological group of similar age and depositional environment. The effects of the shell size in the taphonomic analysis are still poorly understood. In order to study this issue, the taphonomic signatures (articulation, valve type, fragmentation, abrasion, corrosion, edge modification, color alteration, bioerosion and encrustation) of brachiopod shells (Bouchardia rosea (Mawe)), from Ubatuba Bay in the northern coast of São Paulo State, were investigated according to the sieve sizes. In the study area, 14 collecting stations were sampled via Van Veen grab sampler, along a bathymetric gradient, ranging from 0 to 35 m of depth. Bulk samples were sieved through 8 mm, 6 mm, and 2 mm mesh sizes, yielding a total of 5.204 shells. The results indicate that, when taphonomic signatures were independently analyzed per size classes (8 mm, 6 mm, and 2 mm), the taphonomic signatures are recorded in a complex and random way. Additionally, cluster analysis showed that the similarity among the clusters vary according to the considered sieve size. Thus, the sieve size plays an important role in the distribution of taphonomic signatures in shells of distinct sizes. These results suggest that the concentration of the taphonomic analysis on one class (e.g., the largest sieve size, 8 mm) is not always the best method. Rather, the total data (all sieves included) seems more accurate in recording the whole spectrum of taphonomic processes recorded in shells of a given assemblage.

Tafonomia de tempestitos conchíferos amalgamados da formação Teresina em Rio Preto (Estado do Paraná, permiano médio, bacia do Paraná) e suas implicações paleoambientais

The deposits of the Permian Teresina Formation are mainly characterized by fi ne-grained siliciclastic rocks and centimetric intercalations of tempestites (bioclastic sandstones and coquinas). Despite the relevance of the bivalve-rich carbonate beds of the Teresina Formation to paleoenvironmental studies, their taphonomy is still poorly studied. The fossil concentration studied in this work was found in a quarry in the city of Irati, Rio Preto district, Parana State. The fossil concentration is located in the middle/upper portion of the unit, far from the top. The studied bed is a bioclastic, intraclastic, peloidal, grainstone/ packstone, with abundant bivalve shell fragments, pelitic and micritic intraclasts, peloids, rare ooids and oncoids, as well as permineralized of Lycophyta microphylles and fish scales. The grains of this carbonate concentration show: high degree of time-averaging, variable degree of packing (dense to disperse), no sorting and chaotic orientation. Notably, the concentration includes a mixture of elements which are indicative of: a) restrictive, low energy, carbonate environment (peloids, ooids and oncoids); b) subaerial environment surrounding the main body of water (Lycophyta microphylles) and c) quiet-water environment punctuated by storm events, where the suspension-feeding bivalves thrived. At least four depositional events caused by storm fl ows were recorded. The amalgamated nature of the bed is a result of storm events in an intracratonic basin with very low seafl oor slope and low rates of sedimentation and subsidence.

Tafonomia de biválvios em calcários oolíticos da formação Teresina (Bacia do Paraná, Permiano Médio, Prudentópolis, PR)

Herein, it is presented the first detailed taphonomic study on bivalve mollusk shells preserved in the oolitic limestones of the Teresina Formation (probably Kungurian-Roadian, Lower-Middle Permian) in the eastern margin of the Parana basin. The selected beds are located in two quarries (informally named PRU 1 and PRU 2) in Prudentopolis municipality (Center-South Parana State), and positioned approximately in the middle of the formation and probably in the Pinzonella illusa Zone. The PRU 1 limestone ([approximately]30 cm thick), which is partially silicified and intercalated with predominantly pelitic rocks, is classified as a bivalve oolitic grainstone. The basal contact is erosive and the top shows symmetrical ripple marks, which are draped by shale with mud cracks. There are two fining-upwards successions characterized by dense to dispersed packing of the shells, which are usually disarticulated, randomly oriented (many nested/stacked) and mixed with some Formapelitic intraclasts. Microhummocky cross-stratification occurs a little below the top of the bed. The PRU2 bed is classified as ooidbivalve rudstone[approximately] (~5 cm thick), where all shells are disarticulated and fragmented, showing dense packing. The bivalves probably inhabited a muddy substrate and were mixed (as parautochtonous and allochthonous bioclasts) with ooids during high-energy storm events, including posterior shell displacement as a result of bioturbation. Thus, the calcareous beds represent amalgamated proximal tempestites with a complex taphonomic history, strong temporal/spatial mixing of bioclasts and limited paleoecological resolution. They are a typical example of shell beds generated in a huge epeiric sea, which was not necessarily connected to the ocean and where very low depositional-slope gradient, very slow subsidence and minimum sediment accommodation space caused frequent sediment reworking by storm related processes.

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.

Othonella araguaiana (Bivalvia, Megadesmidae) from the Corumbatai Formation (Midlle [Middle] Permian), Eastern Margin of the Parana Basin: systematic, evolutionary and biostratigraphic significances.

In this study, the occurrence of Othonella araguaiana Mendes, a rare bivalve species is reported for the first time in the Pinzonella illusa biozone, Middle Permian Corumbatai Formation, in the State of São Paulo. This species was originally described in coeval rocks of the Estrada Nova Formation (= Corumbatai) from the Alto Araguaia and Alto Garcas regions, State of Mato Grosso. The specimens of O. araguaiana were found in the base of a bioclastic sandstone bed, a proximal tempestite, in the middle of the Corumbatai Formation, in the city of Rio Claro, São Paulo State. The silicified shells and internal molds are well preserved, showing impressions of muscle scars and other internal anatomic characters (e.g., hinge), never illustrated by previous authors. In his original description, Mendes (1963) called attention to the similarity between O. araguaiana and Terraia aequilateralis, a common veneroid of the Corumbatai Formation. Conversely, Runnegar and Newell (1971) suggested that O. araguaiana belongs to Megadesmidae, being a junior synonym of Plesiocyprinella carinata (the commonest megadesmid of the Passa Dois Group). Our study indicates that O. araguaiana is indeed a megadesmid, but is distinct from the P. carinata. The new occurrence of O. araguaiana demonstrates that a) the paleobiogeographic distribution of this species is wider than previously thought (that it was restricted to the northern part of Parana Basin, Mato Grosso State); b) the molluscan fauna of the Corumbatai Formation (P. illusa biozone) in the State of São Paulo is more diverse and dominated by megadesmids; and c) the composition of the molluscan fauna of the Corumbatai Formation in Alto GarYas, State of Mato Grosso, is essentially the same as that of the P. illusa biozone of the eastern margin of the Parana Basin.

Conchostráceos com linhas de crescimento recurvadas junto à margem dorsal (famílias Palaeolimnadiopseidae e Perilimnadiidae) da formação rio do rasto, Permiano superior, bacia do Paraná, Brasil

Some Upper Permian conchostracans from the Rio do Rasto Formation (Parana Basin, South Brazil) have very characteristic recurved growth lines at the dorsal margin. All previously described specimens were classified as Palaeolimnadiopsis subalata (Reed) Raymond. However, a re-analysis of these fossils and of additional recently- collected specimens demonstrated that not all can be included in a single species, nor only in the Family Palaeolimnadiopseidae. According to their shape and the size of the umbo, they are classified into three species. The sub-elliptic carapaces with small anterior umbo are maintained in Palaeolimnadiopsis subalata (Reed, 1929) Raymond, 1946. The sub-circular carapaces with small sub-central umbo correspond to the new species Palaeolimnadiopsis riorastensis. The small size of the umbo is a character of the Family Palaeolimnadiopseidae. The small elliptic valves with large anterior umbo are assigned to the new species Falsisca brasiliensis of the Family Perilimnadiidae, which is characterized by large umbos. Palaeolimnadiopsis has a wide chronostratigraphic distribution, but Falsisca is restricted to the Upper Permian-Lower Triassic of Europe and Asia. This interval is in agreement with the probable Late Permian age of the respective strata of the Rio do Rasto formation. Falsisca was not previously recorded in Gondwana.

Isotopic characterization of the metabasites and amphibolites of the Acungui and Setuva Groups of the Ribeira Belt

Pb, Rb, Sr, Sm and Nd isotope analyses were carried out on amphibolitic rocks from Campo Largo (PR), Rio Branco do Sul (PR) and Adrianópolis (PR) and for the metabasite from Adrianópolis and Apiai (SP), all belonging to the Açungui and Setuva Groups, southern portion of the Ribeira Belt. These occurrences were chosen because each exhibits geochemical data indicative of a mantle source, having different signatures. Geochronologic determinations are available only for the Apiai metagabbro with Neoproterozoic ages of 617 ± 4 Ma (U/Pb in zircon) and 839 ± 85 Ma (Rb/Sr, whole rock). Age determinations by Sm/Nd mineral isochron using whole rock, plagioclase and pyroxene yield values of 885 ± 53 Ma for the Apiai metagabbro and 820 ± 84 Ma for the Adrianópolis metabasite. These results agree within error with the Rb/Sr isochron of 839 ± 85 Ma may possibly be interpreted as the time of extraction of the magma from the mantle, as suggested by positive εNd(850) values (+2,76) from an Adrianópolis sample. An εNd values versus 87Sr/86Sr diagram shows that each studied occurrence plots in a different position, following approximately the mantle array trend, the most primitive being the metabasite of Adrian-acopolis, near the MORB field, and the most enriched being the amphibolite from the same region, near the enriched mantle and or crustal contamination field. The distinct difference in isotopic signatures between the amphibolite and metabasite suggests derivation from different mantle sources, as supported by available geochemical data. Nevertheless, some of the samples show isotopic evidence of the action of metamorphism, crustal contamination and weathering.

Sm-Nd system in total rock open versus closed isotopic composition in zones of high deformation

High strain shear zones of Brasiliano age, developed in Paleoproterozoic basement gneiss of the Caicó region, Borborema Province, NE Brazil, were associated with medium- to low-grade metamorphism and deformational processes that transformed porphyritic augen gneiss into muscovite quartzite, modifying their original mineralogy and chemical properties. During the last hydrothermal event mobility of major, minor and trace elements was great, whereas the pattern of Rare Earth Elements was not changed. We carried out a Sm-Nd isotopic study in these rocks in order to understand the behavior of Nd isotopes during mylonite generation. TDM model ages at around 2.6 Ga and εNd (t) values for both protolith and transformed rock suggest that the Nd isotopic system remained closed, recording the original source rock signature, despite undergoing two superposed metamorphic events. These new Sm-Nd results provide important information on the geologic evolution of basement rocks in the central Rio Grande do Norte Terrane of the Borborema Province, NE Brazil.