Aplicação do Índice Relaçáo Declividade-Extensão - RDE Na Bacia do Rio do Peixe (SP) para Detecção de Deformações Neotectô nicas

This paper presents the identification of tectonic deformation through the application of the stream-gradient index (slope x length) method in the Rio do Peixe hydrographic basin, located in western State of Sã o Paulo. The main principle used is that river valleys are the best tools for this type of analysis because of their fast adjustment to even the most gentle crustal deformations. This type of analysis for structural studies is extremely useful in the western region of the State of São Paulo, where deep chemical weathering results in a thick regolith and scarce outcrops. The stream length index is the ratio of the altimetric amplitude of each drainage and the natural logarithm of its length. The value obtained is plotted on maps at the median point of each drainage, allowing the drawings of lines with the same values (isodefs). Three anomalies (A, B and C) were identified along the Rio do Peixe valley representing uplift sectors indicated by the formation and distribution of Upper Quaternary deposits in terraces and modern fluvial plains and alluvial fans. In correlation with known tectonic data for this region it is possible to attribute the A and B anomalies to the Ribeirão Preto and Presidente Prudente crustal sutures, respectively. The smaller C anomaly needs further field investigation, but it could be associated with the Três Lagoas crustal suture. It must be emphasised that these sutures are inherited from the Precambrian Basement which had a strong influence on the Phanerozoic evolution in the whole sedimentary and volcanic stratigraphic pile of the Paraná Basin and on the dominant structural lineaments directions developed therein .The A, Band C anomalies are suggestive of renewed uplift as a result of neotectonic action in modern times.

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.

Proveniência e idade do metamorfismo das rochas da faixa Brasilia, na região de tapira (SW de Minas Gerais)

The Brasilia Fold Thrust Belt at Tapira area (SW of Minas Gerais State, Brazil) has four different litho-tectonic domains imbricated by thrust faults with vergency to the São Francisco Craton. Sm/Nd isotopic studies were undertaken and the results show different model and metamorphic ages for the thrust sheets. Rocks from the lower thrust sheet yield a metamorphic age of 543 Ma while the upper thrust sheet has a metamorphic age of 581 Ma. The TDM model ages are similar for both thrust sheets, between 1.7 and 2.2 Ga. Because of their lithologic characteristics, the thrust sheets are interpreted as having been deposited in a distal continental platform environment, their main source being Paleoproterozoic rocks of the São Francisco Craton. The upper thrust sheet rocks presents a metamorphism age of 612 Ma and a bimodal distribution of TDM model ages between 1.3 and 1.9 - 2.0 Ga, respectively. The lithologic and isotopic characteristics of this thrust sheet the rocks are interpreted as a result of deposition on a continental slope or oceanic floor environment, with mixed contributions from Paleo - and Mesoproterozoic rocks of the São Francisco Craton. In spite of the small number of analyzed samples and the uncertainties inherent to the Sm/Nd method the metamorphisms are not considered to be synchronous in the different thrust sheets. This is to be expected in a thrust belt system, in which the more metamorphosed thrust sheets are juxtaposed to less metamorphosed ones.

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.

Geoquímica de gnaisses do arco magmático de goiás na região sul do estado de goiás

Granitic to trondhjemitic gneisses from the Pontalina region in the southern part of Goiás State, Central Brazil, have calcic to calc-alkaline, metaluminous to peraluminous compositions. They have low concentrations of alkaline elements, and are enriched in Ba, Sr, K, Rb in relation to Nb, Y, Zr and REE, and have negative anomalies of Nb and Ti, features which are similar to those of magmas generated in magmatic arc environments. Those rocks were previously interpreted as part of the basement of the Brasília Belt, attributed to the Archean to Paleoproterozoic, but new Sm - Nd isotopic data indicate a neoproterozoic age (TDM = 0,9 a 1,2 Ga), and the preliminary geochemical data reveal compositions similar to the gneisses of the other regions belonging to the Goiás Magmatic Arc.

Os granitóides brasilianos da faixa de dobramentos paraguai, MS e MT

The Brazilian Granitic Province from southeastern Mato Grosso do Sul and Mato Grosso region, central western Brazil, can be divided into two major groups and/or magmatic events related to the evolution of the Paraguay Fold Belt. The southern portion crops out in Mato Grosso do Sul State and is constituted by the Taboco, Rio Negro, Coxim and Sonora massifs forming NE-SW oriented, elongated small intrusions. The north portion crops out in Mato Grosso State and is constituted by the São Vicente, Araguaiana and Lajinha batholiths. Lithogeochemical aspects of the northern granites point to Type-I granites ranging from K calc-alkaline to high-K, peraluminous to metaluminous in composition, generated in an environment of continental collision and/or post- collision decompression. The southern granites are Type-I, from K calc-alkaline to high-K, peraluminous to subordinate metalummous, in a syn-collision continental arc environment with the exception of some pre-collisional facies from the Rio Negro Massif. The southern granites have less SiO 2 and K 2O, and are less differentiated and evolved than granites from the northern region. The four southern granites can be grouped into two subordinate sets with the degree of differentiation increasing from South (Taboco and Rio Negro) to North (Coxim and Sonora). The granitic rocks are characterized by a magmatism generated by melting of material from the lower crust which suggests that in this province the formation from non-cogenetic magmas with diversified compositions and distinct degrees of fractioning reaching more steady consolidated environments at the end of the collisional event in the southeastern Amazonian Craton.

Geologic e geoquímica do batólito Rapakivi Rio Branco, SW do Craton Amazônico - MT

The Rio Branco Rapakivi Batholith belongs to the Cachoeirinha Tectonic Domain, part of the Rio Negro-Juruena Geochronological Province located on the southwestern portion of the Amazonian Craton in Mato Grosso, Central Brasil. A systematic geological mapping on a 1:100.000 scale, coupled with petrographic and geochemical studies allowed to redefine this batholithic unit, to recognize faciological variations and to characterize the geochemical features of this rapakivi magmatism. The batholith is constituted by two major plutonic suites, the first forming a basic suite of fine-grained, equigranular, mesoto melanocratic gray to black lithotypes, with usually discontinuous porphyritic varieties located near the margins of the intrusion. The second one is characterized by acid to intermediate rocks constituted by porphyritic granites, in part granophyric, with rapakivi textures. They have K-feldspar phenocrysts of up to 4cm. Three distinct petrographic facies are recognized in this suite: 1. equigranular to pegmatitic monzogranites; 2. red rapakivi leuco-monzogranites; 3. dark red rapakivi monzogranites to quartz-monzonites. Rocks present SiO2 contents from 67% to 73%, show peraluminous to metaluminous compositions and define a high-K calc-alkaline to shoshonitic magmatism in an I- and A-type, post-orogenic to anorogenic intraplate environment. The magmatic processes are associated with the end of the collisional event that consolidated and stabilized the SW part of the Amazonian Craton.

Levantamento gravimétrico na região de Franca - SP e delfinópolis - MG, no reconhecimento e delimitação de feições estruturais (Zonas de Sutura)

This paper presents the results of a geophysical study carried out in northeastern São Paulo State and southwestern Minas Gerais State over an area 80 km wide and 97.5 km long in SE Brazil. The Bouguer anomaly map, and geological and structural data allowed to identify three different gravity domains - crustal blocks limited by major discontinuities -related to the structural pattern of the area. These discontinuities were interpreted as geosuture zones underlying the Paraná Basin sediments which have extensions in the Pre-cambrian Basement. The crustal discontinuities named Alterosa and Ribeirão Preto may be seen as A - type collision sutures in a triple junction arramgement. Two prominent linear anomalies are recognized in the Bouguer anomaly map, as well as the limit between the Brasilia and São Paulo crustal blocks or paleoplates. The Alterosa suture zone trends NW-SE while the Ribeirão Preto suture has a NE-SW direction. The Bouguer anomaly map provides subsidies and information on new concepts and theories leading to the refinement of tectonic models.

Metacryphaeus rotundatus, um novo elemento da fauna de trilobites calmoniidae (phacopida), da formação Ponta Grossa (Devoniano), bacia do Paraná, Brasil

Calmoniids (Delo, 1935) are the most common and abundant group of trilobites of the fossil record of the Devonian Ponta Grossa Formation in the Apucarana sub-basin. Although known since the past century, the study of calmoniids has been taxonomically and stratigraphically biased. This is because some authors centered their studies on some particular genera from a few stratigraphic horizons within the basal portion of the Ponta Grossa Formation. The analyses of 398 specimens of calmoniid trilobites of the rocks of Jaguariaiva Member of the Ponta Grossa Formation, mainly from Tibagi county in the state of Paraná, Brazil, indicate the presence of specimens that are referable to Metacryphaeus rotundatus (Kozlowski, 1923). This is the first record of M. rotundatus in Brazilian Devonian rocks. Metacryphaeus rotundatus is a conspicuous species of the Emsian rocks of the Icla Formation, Bolivia. Although the affinities of the trilobite fauna of the Devonian Paraná Basin, in the context of the Malvinokaffric realm, are with the Brazilian and South Africa provinces, this finding is in accordance with new evidence (e.g., conulariids, homalonotids trilobites), indicating the presence of cosmopolitan species with Andean affinities. Metacryphaeus rotundatus lived in a broad paleoclimatic range, from a temperate, cold temperate to a subpolar climate. Finally, in the Devonian of the Paraná Basin, M. rotundatus lived and were preserved in muddy, organic rich bottoms, deposited in offshore waters, below the storm wave base, associated to marine flooding surfaces.

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 (Paraná 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.

Susceptibilidade erosiva do baixo curso do rio Acaraú-CE

The inadequate land use in the low course of the river Acaraú is speeding up processes of erosion in some degrees. This process is accented in the areas where caatinga was removed for implantation of pastures and agriculture. Concomitantly, the plain of flooding of the river Acaraú an accumulation of sand with the carry of these sediments, resulting in the widening of the fluvial plain and reduction of the shape water, with increase of the evapotranspiration and consequence salinization, proceeding from the local substratum. This paper aimed at the crossing of diverse space information (geomorfology, soil, declivity, geology and land use) in environment SIG, for determination of the susceptible areas to the erosion and an accumulation of sand in the low course of the Acaraú river, north of the State of the Ceará, Brazil. The results allow to evaluate the application of this tool in the planning and management of the environment, from the crossing of the type of use with the used environment and the consequent impact to the ecosystem.

Calcareous algae from Upper Albian - Cenomanian strata of the Potiguar basin (NE Brazil)

Calcareous Albian-Cenomanian strata in the Potiguar basin yield a number of microfossils, among which are calcareous algae (Dasycladales and Corallinales). This data, together with an inventory of previous discoveries, enabled the discussion of their biogeography. These benthic organisms probably came from the early Central Atlantic Ocean through its northwestern neck between Africa and South America and thus reached the early South Atlantic platforms.

Caracterização química de cromitas nos maciços de cromínia e mairipotaba, goiás, Brasil

Metaultramafic bodies tectonically emplaced within the metasedimentary sequence of the Araxá Group are associated with an ophiolitic melange in southeast Goiás. In the region of Crominia - Mairipotaba, they occur as lenticular bodies aligned E-W. Cumulate textures and geochemical data indicate that the parent rocks had harzburgitic to dunitic compositions. Relicts of primary crystals of olivine and orthopyroxene are suggestive of amphibolite facies metamorphic re-equilibration fabrics, even though the paragenesis and mineral associations of these metaultramafic rocks are typical of greenschist facies (T < 550°C and P = 5.5 kbar). The chromitites exhibit massive to breccioid structure and pull-apart texture, with chromite crystals around 0.5 mm in size. Chromite concentrations in the chromitite levels reach 70 to 85% by volume of the rock. The crystals are dispersed in the matrix, which is composed essentially of serpentine, and subordinately of chlorite and talc. The textures and geochemical data (Cr 2O 3 x TiO 2 and Mg x Cr ratios present in the chromitite) are similar to those observed in ophiolitic complexes. Hence, they correspond to allochthonous bodies (Alpine type) associated with an ophiolitic mélange.

A new permian bivalve (Megadesmidae, Plesiocyprinellinae) from the Serrinha member, Rio do Rasto Formation, Paraná Basin, Brazil

During a recent inspection in the Paleontological Collection of the Institute of Geosciences, University of São Paulo, we have identifi ed some specimens of undescribed mollusk bivalves. These called our attention for the following reasons: a) all specimens are internal molds of conjugated and closed articulated valves, some of them presenting fragments of silicifi ed shells; b) all internal molds have similar general shape and internal characters, representing specimens of the same taxon; c) the internal molds and silicifi ed valves are well preserved, including fragile structures, which are hardly preserved, such as the internal mold of the external ligament and muscle scars; d) and equally important, according to the labels of all specimens, they were collected from rocks of the Passa Dois Group (Permian), Serrinha Member of the Rio do Rasto Formation. Although who collected the shells and the precise geographic location of the specimens are still unknown, the detailed study of these fossils brings us to the conclusion that they are morphologically distinct from any heretofore published genus of the endemic fauna of bivalves from Passa Dois Group. Based in its general shape, hinge structure and muscles scars, the new form can be classifi ed under the Family Megadesmidae Vokes, 1967, the most diverse group of Permian bivalves of the Paraná Basin. The specimens are referred as Beurlenella elongatella new gen. and sp. The shell shape and taphonomy indicate that this bivalve was a shallow, rapid, active burrower, suspension feeder, probably preserved in situ, in event deposits.