Abstract Tectonic rejuvenation has been widely described in ancient rifting areas of intraplate settings, despite extensive active tectonics being discontinued long ago. Various models have been invoked to justify such tectonic rejuvenation, suggesting that the long-term deformation in intraplate interiors may be more complex than once supposed. Inherited weakness zones, e.g., pre-existing faults are stress concentrators. However, not all weakness zones in plate interiors show tectonic rejuvenation and recognizing intraplate fault reactivation remains puzzling. Bedrock channels play an essential role in tectonically unstable landscapes and therefore they may unveil which pre-existing structures have been rejuvenated. Here we explore the Cinzas Catchment in order to investigate the interactions between tectonic rejuvenation, bedrock inheritance and geomorphic river signatures in an important Brazilian rifting feature, the Ponta Grossa Arch. We perform a geomorphic analysis combined with fieldwork, dating techniques and existing data to evaluate whether the geomorphic responses of the major rivers show perturbations related to the bedrock inheritance and post-rift rejuvenation. We also show that the interactions between river signatures and the bedrock fault zones are responses to post-rifting rejuvenation coupled with bedrock inheritance. This post-rifting rejuvenation is consistent with a mosaic of superimposed mechanisms which have been invoked by previous studies.

Abstract The hypothesis that geomorphometric parameters and structural-geological features are diagnostic of reactivation of the Blumenau-Soledade Lineament in central-western Santa Catarina, Brazil was tested by confronting data on asymmetry, elongation, morphological markers, drainage patterns, and river anomalies of the Pelotinhas catchment and structural data for the Serra Geral Group (Paraná Basin). The results indicate reactivation of the lineament as a dextral strike-slip fault, as the cause of an associated morphostructure characterized by an escarpment along the left bank of the river as well as being responsible for catchment asymmetry and morphometric anomalies. Although fault data indicate paleostress correlatable to regional tectonic events described in the literature, we propose that the earliest paleostress pulse possibly was active during the Paleocene-Eocene transition, with σ1 oriented NE-SW and σ3 NW-SE. In the early Paleogene, the stress system evolved as an extensional pulse. During the Paleogene and early Neogene, the paleostress field rotated with reorientation of the σ1 axis between NNW and NNE. The current tectonic regime was established between the Late Pleistocene and Holocene, with compressional stress σ1 oriented approximately WNW-ESE and σ3 NNE-SSW, as it generally occurs in the South American Plate.

ABSTRACT: The Paraná basin is one of the major morphotectures of the South American continent. Although its tectono-sedimentary evolution has been widely studied and fairly well understood, this paper aims to fill a gap in knowledge comprising the tectonic evolution after the end of its last sedimentary cycle, in the Upper Cretaceous. In this context, the Jordan River watershed, situated in the surroundings of Guarapuava municipality, south central region of Paraná State, was selected for structural and morphometric analysis where the Cretaceous volcanic rocks of Serra Geral Formation are exposed. The Jordan River watershed was studied for the influence exerted by Taxaquara Fault Zone on its morphologic evolution, since Taxaquara Fault Zone is associated to the Brazilian cycle and extends eastwards to the Ribeira belt in the state of São Paulo. The morphometric analysis consisted in the interpretation of the Jordan River watershed drainage network and relief elements, considering the distribution of existing knickpoints in the water courses. Structural analysis was based on the calculation of the stress fields responsible for the activation of local fault zones, which were determined by their spatial arrangement and the statistical and mechanical treatments of structural data. During the Oligocene and Miocene, erosional processes developed a planing surface which marks the relief in the central region of the Jordan River watershed and serves as a stratigraphic marker for the associated deformational events. Three events that contributed to the morphological framework of the Jordan River watershed were defined: an oldest one, probably active before the development of the Jordan pediplane in the Paleogene, by a NE-SW maximum horizontal stress (SHmax); and two more recent ones, being one of Plio-Pleistocene age, with a N05W SHmax, and a still active event of transtensive nature showing a N75W SHmax. The paleostress analysis points to a similarity between the Cenozoic evolution of Paraná Basin and the tafrogenic basins of southeast Brazil, revealing the amplitude of the deformation events associated to the studied period and ensuring the importance of further studies on the morphotectonic evolutions of intracratonic regions of the South American plate and their correlation to the Andean tectonic cycle.

O principal objetivo deste estudo foi detectar mudanças no microclima da cidade de Manaus (AM), Brasil e procurar indicar as possíveis causas destas flutuações e tendências observadas. Foram utilizados dados meteorológicos e da geotermia rasa. Através de dados meteorológicos determinamos um incremento nas temperaturas médias do ar de 0,27 ± 0,04ºC, durante os últimos 80 anos, baseado na normal climatológica de 1950 a 1979. Este incremento não tem sido contínuo, mas modulado pelas freqüências de meses com El Niño, La Niña e Neutros, detectados no Oceano Pacifico tropical, Região Niño 3.4. Através de dados geotérmicos determinamos um incremento de 3,17 ± 0,53ºC, que se estima esteja relacionado com o uso do solo, desde a segunda metade do século XIX. Verificamos que as perturbações transientes do subsolo de locais com cobertura vegetal são bons indicadores das variabilidades climáticas anuais recentes e que as análises dos perfis sob locais sem cobertura vegetal indicam mudanças no microclima atribuídas às atividades antrópicas, tais como, o desflorestamento e urbanização.

The main objective of this study was to detect microclimate changes in Manaus City (AM), Brazil in attempting to indicate the possible causes for the fluctuations and trends observed. Meteorological and shallow geothermal records were analyzed. The meteorological data indicated an increment of 0.27 ± 0.04ºC in the mean surface air temperature during the last 80 years with reference to the 1950-1979 climatological mean. This increment has not been continuous, but it is modulated by frequency of El Niño, La Niña e Neutral events over the tropical Pacific Ocean, Niño 3.4 region. An increment of 3.17 ± 0.53ºC was determined from geothermal data from the second-half of the 19th century, which is likely associated with the land-use changes. From shallow geothermic data under sites with vegetation cover we verified that transient perturbations are good indicators of recent annual climate variability, while analysis of temperature profiles data under sites without vegetation cover seem to indicate microclimate changes related to the anthropogenic actions like deforest and urbanization action.