Thermotectonic and fault dynamic analysis of Precambrian basement and tectonic constraints with the Parana basin

The Precambrian crystalline basement of southeast Brazil is affected by many Phanerozoic reactivations of shear zones that developed during the end of the Neoproterozoic in the Brasiliano orogeny. These reactivations with specific tectonic events, a multidisciplinary study was done, involving geology, paleostress, and structural analysis of faults, associated with apatite fission track methods along the northeastern border of the Parana basin in southeast Brazil.The results show that the study area consists of three main tectonic domains, which record different episodes of uplift and reactivation of faults. These faults were brittle in character and resulted in multiple generations of fault products as pseudotachylytes and ultracataclasites, foliated cataclasites and fault gouges.Based on geological evidence and fission track data, an uplift of basement rocks and related tectonic subsidence with consequent deposition in the Parana basin were modeled.The reactivations of the basement record successive uplift events during the Phanerozoic dated via corrected fission track ages, at 387 +/- 50 Ma (Ordovician); 193 +/- 19 Ma (Triassic); 142 +/- 18 Ma (Jurassic), 126 +/- 11 Ma (Early Cretaceous); 89 +/- 10 Ma (Late Cretaceous) and 69 +/- 10 Ma (Late Cretaceous). These results indicate differential uplift of tectonic domains of basement units, probably related to Parana basin subsidence. Six major sedimentary units (supersequences) that have been deposited with their bounding unconformities, seem to have a close relationship with the orogenic events during the evolution of southwestern Gondwana. (c) 2005 Elsevier Ltd. All rights reserved.

Influencia do soerguimento do alto Paranaiba na sedimentacao pos- basaltica na area do Triangulo Mineiro (MG), borda NNE da Bacia do Parana

Faciologic analysis method was applied to after-basaltic sedimentary deposits in Triangulo Mineiro (MG) area. Faciologic association 1 (Adamantina formation) and unities 1 to 5 (Uberaba formation) are related to the fluvial and lake deposits: faciologic association 3 (Ponte Alta Member) and 2 (Sierra da Galga Member) represent the sedimentary deposits associated to the alluvial fans conditions. With faciologic association and unities it could be to recognize the paleogeografic and tectonic conditions in sedimentation time of that depositional tract. -English summary

Palaeomagnetism of the Mesozoic Serra Geral Formation, southern Brazil

Palaeomagnetic results from 20 volcanic sequences and 11 intrusive bodies (sills and dykes) of the Serra Geral Formation (Paraná Basin) are reported in this paper. The sequences are widespread all over the basin, while sills and dykes (Ponta Grossa arch) come from the northeastern portion. Three mean palaeomagnetic poles were computed for the Serra Geral Formation, which account for a time interval of ∼ 15 Ma. Pole SG1 is located at 85°S,108°E (α95 = 1.1°, N = 18) and represents the main phase of the magmatic activity in the basin, with a mean age of ∼ 135 Ma. Pole SG2 is located at 82°S,38°E (α95 = 7.8°, N = 2) and represents a younger magmatic phase, with an associated age of ∼ 130 Ma. Pole SG3 (72°S,37°E; α95 = 6.8°, N = 10) is the youngest pole. It is computed from the intrusive rocks and its age is assumed to be not younger than 118 Ma, the lower limit of the 'Cretaceous normal magnetic interval'. These three poles describe a shifting path, which suggest that the South American platform moved ∼ 5° southwards and rotated ∼ 10° clockwise during the Lower Cretaceous, preceding the South Atlantic opening. © 1990.

Razao Sr:Ba:Rb e tipologia de zircao em granitoides dos Estado de Sao Paulo, Parana e Minas Gerais

Chemical (Sr:Ba:Rb) and zircon typology data from the Nazare Paulista, Mairipora/Cantareira, Cunhaporanga, Tres Corregos, Morungaba, Socorro, Itu, Graciosa and Serra Carambei granitoid complexes from the states of Minas Gerais, Sao Paulo and Parana (SE/S Brazil) are presented and discussed. By the zircon typology method these complexes are refered, respectively, to the 2nd crustal, 3rd crustal/low temperature C-A, low temperature C-A, medium temperature C-A, medium/light temperature C-A, K-SA/Alkaline and alkaline series which are considered as generated under increasing temperature associated with a progressive major participation of mantle material. All these series display different positions and behaviour in the Sr:Ba:Rb diagram which reinforces the use of the zircon typology method in the study of granitoids. -from English summary

Soil humus characteristics in virgin and cleared areas of the paraná river basin in Brazil

A study of the characteristics and distribution of the soil humus fractions in representative ecosystems of central Brazil was carried out with special emphasis on the comparison between the soils under virgin vegetation-Cerrado-and those subjected to cultivation. In spite of the contrasted vegetation and cultural practices in the sites studied, the soil humus showed analogous characteristics: there was a negligible amount of plant residues, the humic and fulvic acids amounted to approximately 70% of the total organic carbon, and about 40% of these humic substances were in extremely stable association with the soil mineral fraction, the HCl-HF treatment being required for their extraction. The stability of such organo-mineral complexes increased slightly in the cultured sites. The study of the humic acid fraction showed increased oxidation and aromaticity in most of the cultivated sites: the lowest values for the IR alkyl vibrations and H/C atomic ratios and the highest ones for the optical density at 465 nm were observed in sites transformed into orchards, whereas the above changes were small in those used as pasture. The 14C NMR spectra confirmed that the proportion of polyalkyl structures decreased in the humic acids of soils subjected to cultivation, as opposed to that of carboxyl groups. In spite of the high stability inferred for the organic matter throughout the wide area examined, the samples from the original Cerrado as well as from those transformed into pastures showed, in laboratory conditions, higher mineralization rates than those from the sites subjected to cultivation. This is partly attributed to the decreased proportions of extractable humic substances in the latter. © 1992.

Caracterizacao litoquimica e aspectos petrologicos de rochas vulcanicas da Formacao Serra Geral: regiao centro-sul do Estado do Parana

This work defines the main volcanic types of Central-Southern Parana State (Serra Geral Formation), their stratigraphic relations, and which petrological process are able to explain the observed volcanic associations. -from English summary

Ecology and conservation of the jacutinga Pipile jacutinga in the Atlantic Forest of Brazil

The jacutinga Pipile jacutinga was formerly one of the most abundant game bird cracids in the Atlantic forest of Brazil. Nowadays this species is vulnerable to extinction due to hunting and habitat loss. The ecology of the jacutinga was studied at Parque Estadual Intervales, Sao Paulo, Brazil from October 1993 to December 1995 and in adjacent areas. Jacutingas were observed to feed mainly on the sugar-rich fruit of 41 species. We recorded a low index of abundance for the jacutinga (0.018) or c.1.7 birds/km2 at Intervales, one of the best protected areas within their range. Surveys carried out in the Atlantic forest of Sao Paulo found jacutinga populations in 14 localities. Probably < 1500 birds survive in the best protected areas. The species' stronghold in southeastern Brazil is in the mountains of Serra de Paranapiacaba, an area protected by several parks suffering from hunting and palm heart harvesting and threatened by a hydroelectric project.

Chronostratigraphy and radiocarbon age inversion in the Holocene regressive barrier of Paraná, southern Brazil

Twenty-two 14C datings were performed at the central sector of the Paraná coast to define Holocene regressive barrier evolution. The barrier Pleistocene substratum was ascribed an age between 40 400 and 30 000 yr BP, but it can also represent the penultimate sea level highstand during marine isotope stage 5e. The Holocene barrier samples provided ages between 8542-8279 and 2987-2751 cal yr BP, and showed at least six age inversions that were related to age differences between in situ or low-distance transported shells or trunk fragments, and high-distance transported vegetal debris, wood fragments and organic matter samples. The regressive Holocene barrier age was 4402-4135 cal yr BP near the base, and 2987-2751 cal yr BP near the top. Most of the vegetal remains were transported by ebb tidal currents from the estuaries to the inner shelf below wave base level during the mid-Holocene highstand; they were transported onshore by storm waves and littoral currents during the sea level lowering after the sea level maximum, and were deposited mainly as middle shoreface swaley cross-stratification facies. © 2008.

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.

A comparative study of aquifer systems occurring at the Paraná sedimentary basin, Brazil: U-isotopes contribution

The radioactivity due to 238U and 234U in three aquifer systems occurring within the Paraná sedimentary basin, South America, has been investigated. Uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the U-mobility coefficients between 7. 6 × 10-6 and 1. 2 × 10-3 g cm-3. These values are also compatible with the U preference ratios relative to Na, K, Ca, Mg and SiO2, which showed that U is never preferentially mobilized in the liquid phase during the flow occurring in cracks, fissures, fractures and faults of the igneous basaltic rocks. Experimental dissolution of diabase grains on a time-scale laboratory has demonstrated that the U dissolution appeared to be a two-stage process characterized by linear and second-order kinetics. The U dissolution rate was 8 × 10-16 mol m-2 s-1 that is within the range of 4 × 10-16-3 × 10-14 mol m-2 s-1 estimated for other rock types. The 234U/238U activity ratio of dissolved U in solutions was higher than unity, a typical result expected during the water-rock interactions when preferential 234U-leach from the rock surfaces takes place. Some U-isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in São Paulo State. A modeling has been also realized considering all U-isotopes data obtained in Bauru (35 samples), Serra Geral (16 samples) and Guarani (29 samples) aquifers. The results indicated that the Bauru aquifer waters may result from the admixture of waters from Guarani (1. 5 %) and Serra Geral (98. 5 %) aquifers. © 2012 Springer-Verlag.

Connectivity processes and riparian vegetation of the upper Paraná River, Brazil

In fluvial systems, the relationship between a dominant variable (e.g. flood pulse) and its dependent ones (e.g. riparian vegetation) is called connectivity. This paper analyzes the connectivity elements and processes controlling riparian vegetation for a reach of the upper Paraná River (Brazil) and estimates the future changes in channel-vegetation relationship as a consequence of the managing of a large dam. The studied reach is situated 30km downstream from the Porto Primavera Dam (construction finished in 1999). Through aerial photography (1:25,000, 1996), RGB-CBERS satellite imagery and a previous field botany survey it was possible to elaborate a map with the five major morpho-vegetation units: 1) Tree-dominated natural levee, 2) Shrubby upper floodplain, 3) Shrub-herbaceous mid floodplain, 4) Grass-herbaceous lower floodplain and 5) Shrub-herbaceous flood runoff channel units. By use of a detailed topographic survey and statistical tools each morpho-vegetation type was analyzed according to its connectivity parameters (frequency, recurrence, permanence, seasonality, potamophase, limnophase and FCQ index) in the pre- and post-dam closure periods of the historical series. Data showed that most of the morpho-vegetation units were predicted to present changes in connectivity parameters values after dam closing and the new regime could affect, in different intensity, the river ecology and particularly the riparian vegetation. The methods used in this study can be useful for dam impact studies in other South American tropical rivers. © 2012 Elsevier Ltd.

Sr-Nd-Pb isotopic constraints on the nature of the mantle sources involved in the genesis of the high-Ti tholeiites from northern Paraná Continental Flood Basalts (Brazil)

There has been little research on geochemistry and isotopic compositions in tholeiites of the Northern region from the Paraná Continental Flood Basalts (PCFB), one of the largest continental provinces of the world. In order to examine the mantle sources involved in the high-Ti (Pitanga and Paranapanema) basalt genesis, we studied Sr, Nd, and Pb isotopic systematics, and major, minor and incompatible trace element abundances. The REE patterns of the investigated samples (Pitanga and Paranapanema magma type) are similar (parallel to) to those of Island Arc Basalts' REE patterns. The high-Ti basalts investigated in this study have initial (133Ma) 87Sr/86Sr ratios of 0.70538-0.70642, 143Nd/144Nd of 0.51233-0.51218, 206Pb/204Pb of 17.74-18.25, 207Pb/204Pb of 15.51-15.57, and 208Pb/204Pb of 38.18-38.45. These isotopic compositions do not display any correlation with Nb/Th, Nb/La or P2O5/K2O ratios, which also reflect that these rocks were not significantly affected by low-pressure crustal contamination. The incompatible trace element ratios and Sr-Nd-Pb isotopic compositions of the PCFB tholeiites are different to those found in Tristan da Cunha ocean island rocks, showing that this plume did not play a substantial role in the PCFB genesis. This interpretation is corroborated by previously published osmium isotopic data (initial γOs values range from+1.0 to+2.0 for high-Ti basalts), which also preclude basalt generation by melting of ancient subcontinental lithospheric mantle. The geochemical composition of the northern PCFB may be explained through the involvement of fluids and/or small volume melts related to metasomatic processes. In this context, we propose that the source of these magmas is a mixture of sublithospheric peridotite veined and/or interlayered with mafic components (e.g., pyroxenites or eclogites). The sublithospheric mantle (dominating the osmium isotopic compositions) was very probably enriched by fluids and/or magmas related to the Neoproterozoic subduction processes. This sublithospheric mantle region may have been frozen and coupled to the base of the Parana basin lithospheric plate above which the Paleozoic subsidence and subsequent Early Cretaceous magmatism occurred. © 2013 Elsevier Ltd.

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

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

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

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

Os complexos granitoides Cunhaporanga e Tres Corregos (PR) zoneamento magmatico e implicacoes geotectonicas

Geological, petrographic, chemical and zircon typology data from the Cunhaporanga and Tres Corregos granitoid complexes are presented and discussed. Both complexes of Late Precambrian age evolved by crystal fractionation. By its zircon typology the Cunhaporanga is classified as a low temperature calc-alkaline batholith and the Tres Corregos as a medium temperature calc-alkaline complex. This classification implies a major participation of mantle material during the generation of the Tres Corregos magma in relation to the Cunhaporanga ones. In this way both complexes define a magmatic zoning from NW to SE done by a increasing in the depth of magma generation. -from English summary