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Rio de Janeiro, Brazil

Imbernon R.A.L.,University of Sao Paulo | Blot A.,CIRAD - Agricultural Research for Development | Pereira V.P.,Federal University of Rio Grande do Sul | Franco D.R.,Coordenacao de Geofisica
Revista Brasileira de Geociencias | Year: 2011

In order to provide new insights on mineralogical aspects of geochemical mapping/natural processes related to the chlorite formation (e.g. crystallochemistry and mechanisms of formation of these materials, which has been applied in different studies of environmental profiles), we investigated chlorite samples associated to the Pb-Zn-Ag sulfide ore from Canoas 1 deposit (Vale do Ribeira, state of Paraná, Brazil). By means of Mössbauer (MS) and infrared (IV) spectroscopy, we addressed some issues as those related to the chloritization processes, as well as how Zn would be incorporated into its crystalline structure. Results carried out by ME and IV spectroscopy clearly pointed out for a chlorite occurrence, which in fact incorporates Zn into its structure and also alters the structural patterns for this mineral. Moreover, ME data sets indicated the presence of Fe which is located only in octahedral sites, in trans-configuration, and the Zn emplacement by the chloritization process also occurs in the brucite layer.

Santos T.P.,Federal University of Fluminense | Franco D.R.,Coordenacao de Geofisica | Barbosa C.F.,Federal University of Fluminense | Belem A.L.,Federal University of Fluminense | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013

We performed δ18OC (Globigerinoides ruber, 250-300μm white) and SST (modern analogue technique) paleoceanographic reconstructions for the western tropical South Atlantic Ocean at the northeast Brazilian margin to assess millennial- to centennial-scale climatic shifts that may be propagated by the thermohaline circulation. The results show a progressive SST increase (~1°C) over the Holocene, with a prominent shift occurring during the mid-Holocene that may be linked to changes in insolation distribution. Furthermore, spectral and coherency analyses reveal several centennial- to millennial-scale modes of variability that are similar in both proxy records (4.1-3.8kyr, 1.5-1.0kyr, ~700yr, 570-560yr, ~390yr, ~350yr and ~330yr). Such variability could be the result of (1) solar-induced atmospheric changes at northern high latitudes (possibly propagated southward by the meridional overturning circulation and hence inducing shifts in tropical δ18Oc and sea surface temperature), and/or (2) salinity anomalies propagated from the Southern Atlantic Ocean and transmitted to the study site through the Agulhas Leakage. These climate oscillations may have had substantive effects on the Holocene climate system, especially over the tropical western South Atlantic Ocean and the South American continent. Our data show that the western tropical South Atlantic may respond to multi-centennial to millennial oscillations that are possibly triggered by external (solar) and internal (northern and southern high latitudes) climate forcing. Further investigations are necessary to illuminate the role of the western tropical South Atlantic in inter-hemispheric heat transfer. © 2013 Elsevier B.V.

Pacca I.G.,University of Sao Paulo | Frigo E.,Federal University of Pampa | Hartmann G.A.,Coordenacao de Geofisica
Frontiers in Earth Sciences | Year: 2015

The Earth's rotation can change as a result of several internal and external processes, each of which is at a different timescale. Here, we present some possible connections between the Earth's rotation variations and the geomagnetic reversal frequency rates over the past 120 Myr. In addition, we show the possible relationship between the geomagnetic field reversal frequency and the δ18O oscillations. Because the latter reflects the glacial and interglacial periods, we hypothesize that it can be used as a possible indicator to explain the length of day (LOD) variations and consequently the reversal field frequency over the past 510 Myr. Therefore, our analysis suggests that the relationships between the geomagnetic reversal frequency rates and the Earth's rotation changes during the Phanerozoic. However, more reversal data are required for periods before the Kiaman Reverse Superchon (KRS) to strengthen the perspective of using the geomagnetic reversal data as a marker for the LOD variations through geological times. © 2015 Pacca, Frigo and Hartmann.

Franco D.R.,University of Sao Paulo | Ernesto M.,University of Sao Paulo | Ponte-Neto C.F.,Coordenacao de Geofisica | Hinnov L.A.,Johns Hopkins University | And 4 more authors.
Geophysical Journal International | Year: 2012

A detailed magnetostratigraphic and rock-magnetism study of two Late Palaeozoic rhythmite exposures (Itu and Rio do Sul) from the Itararé Group (Paraná Basin, Brazil) is presented in this paper. After stepwise alterning-field procedures and thermal cleaning were performed, samples from both collections show reversed characteristic magnetization components, which is expected for Late Palaeozoic rocks. However, the Itu rocks presented an odd, flat inclination pattern that could not be corrected with mathematical methods based on the virtual geomagnetic pole (VGP) distributions. Correlation tests between the maximum anisotropy of the magnetic susceptibility axis (K1) and the magnetic declination indicated a possible mechanical influence on the remanence acquisition. The Rio do Sul sequence displayed medium to high inclinations and provided a high-quality palaeomagnetic pole (after shallowing corrections of f = 0.8) of 347.5°E 63.2°S (N = 119; A95 = 3.3; K = 31), which is in accordance with the Palaeozoic apparent wander pole path of South America. The angular dispersion (Sb) for the distribution of the VGPs calculated on the basis of both the 45° cut-off angle and Vandamme method was compared to the best-fit Model G for mid-latitudes. Both of the Sb results are in reasonable agreement with the predicted (palaeo) latitudinal S-λ relationship during the Cretaceous Normal Superchron (CNS), although the Sb value after the Vandamme cut-off has been applied is a little lower than expected. This result, in addition to those for low palaeolatitudes during the Permo-Carboniferous Reversed Superchron (PCRS) previously reported, indicates that the low secular variation regime for the geodynamo that has already been discovered in the CNS might have also been predominant during the PCRS. © 2012 The Authors Geophysical Journal International © 2012 RAS.

Rosa P.F.O.,Laboratorio Of Desenvolvimento Of Sensores Magneticos | Benyosef L.,Laboratorio Of Desenvolvimento Of Sensores Magneticos | Papa A.R.R.,Coordenacao de Geofisica | Papa A.R.R.,State University of Rio de Janeiro
Revista Brasileira de Ensino de Fisica | Year: 2016

Increasingly, the use of computers (especially using open-access programs) is tapped in science education in general and particularly in Physics. Furthermore, the scientific instrumentation remains costly and difficult to maintain. Finally, it is desirable that students are able to go beyond the simple reproduction of known results, and that with the tools at their disposal, can solve new problems or designing equipment that can represent unique advances. For these reasons, versatile simulation systems (at relatively low cost), are very well received by the scientific and academic communities, either for purely educational purposes, either for scientific research or instrumental development. Following these lines, this article describes the construction of a virtual instrument using a data acquisition system, which includes a well-known software and a particular physical method. The device allows to plot the curves of acquired data and make different analyzes on them. Although it was designed for a particular application (obtaining hysteresis curves of soft magnetic tapes), the system is flexible enough to be used after minor changes in other magnetic applications, or after changes slightly more laborious, as instruments for measuring other physical quantities. The article ultimately gives the necessary steps to address other problems involving the data acquisition and processing.

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