Journal of the Geological Survey of Brazil 2024-01-08T11:32:12+00:00 Evandro Klein Open Journal Systems <p><strong>SCOPE AND MISSION</strong></p> <p><strong>Journal of the Geological Survey of Brazil (JGSB)</strong> is a peer-reviewed, open-access, multidisciplinary periodical, published three times a year (April, August, and December) by the Geological Survey of Brazil, which is attached to the Ministry of Mines and Energy of Brazil.</p> <p>Our Mission is the dissemination of original, high-quality scientific research, and in-depth reviews of relevant subjects that cover all disciplines of the Earth Sciences in Brazil, and elsewhere, intending to be of interest to a broad audience of geological scientists.</p> Gamma-ray spectrometry, magnetic and gravity signatures of Archean nuclei of the Borborema Province, Northeastern Brazil 2023-12-07T18:22:18+00:00 Roberto Gusmão de Oliveira Nitzschia Regina Rodrigues Domingos Walter Eugênio de Medeiros Vladimir Cruz de Medeiros Frank Gurgel Santos Marcus Flavio Nogueira Chiarini Marília de Araújo Costa Rodrigues <p>Gamma-ray spectrometry, as well as magnetic and gravity data, are used to investigate the geophysical signatures of the Archean nuclei of the Borborema Province. Natural radioactivity, magnetic anomalies, and residual Bouguer gravity anomalies of the Archean nuclei exhibit distinct signatures in relation to adjacent Proterozoic domains. Gamma-ray spectrometry data reveal eTh enrichment in relation to K and eU contents in Archean units. Assuming that K and U were the dominant isotopes, this relative enrichment of eTh can be explained by the fact that Th radioisotopes have a longer half-life than the other two radionuclides and that 4.56 Ga has elapsed since Earth's formation. The intensity of the total magnetic gradient in Archean units is greater than in Proterozoic units in most nuclei. The Archean units underwent deformation and metamorphism in the Brasiliano/Pan-African Orogeny; therefore, the magnetic characteristics now observed in Archean mafic-ultramafic rocks, iron formations and gneiss-migmatite complexes are the joint result of their primary properties and the superposed effects of the orogeny. All Archean nuclei of the Borborema Province show positive residual Bouguer gravity anomalies. This could be due to the conservation of the main petrophysical properties of the Archean lithosphere, and their preservation during the intense granitization that occurred in the Brasiliano/Pan-African Orogeny. As magnetic and gravity methods provide information from depth, it is possible to infer the continuity of some Archean nuclei beyond the limits established by surface geological data. Based on these results, it will be possible to use geophysical signatures to investigate the possible existence of unknown Archean units in the province.</p> 2024-02-20T00:00:00+00:00 Copyright (c) 2024 Journal (JGSB) and the authors A field guide to the sand-rich turbidite systems of the Taciba Formation, Itararé Group, Paraná basin, Brazil 2023-11-28T11:26:20+00:00 Claus Fallgatter Paulo Sérgio Gomes Paim Victoria Valdez Buso Carolina Danielski Aquino Deise Marli Siveira <p>This field guide provides a detailed outcrop logistics, access and description of the sand-rich turbidite deposits of the Taciba Formation (Rio do Segredo Member), the uppermost unit of the Pennsylvanian Itararé Group (Paraná Basin), which crops out in the Santa Catarina State, southern Brazil. This area has become a classic destination for professional’ field courses and students interested in outcrop analogous to offshore turbidite reservoirs. Although some of the outcrops have been widely described, some localities remain unexplored. These turbidite systems are here subdivided on the basis of their degree of confinement, relative to the Precambrian basin floor topography. The bedrock morphology was shaped during the Late Paleozoic Ice Age. Advance and retreat phases of glaciers are represented by superficial scouring into the crystalline basement. This glacially-carved topography in turn controlled the subsequent sedimentation by forming a basal nonconformity in the Taciba Formation. Thus, the turbidity currents and their deposits, exposed in three main areas along the eastern margin of the Paraná basin, were classified as confined and/or unconfined. This field guide is also valuable for nourishing the ongoing debate on the turbidity currents interpretations based on sedimentological descriptions of the main localities and their major features. Field guides are quite popular in North America and Europe, among other places, but not so popular in Brazilian literature. The present contribution aims to bring details on some little known turbidite-outcropping localities of the Taciba Formation. It also intends, through its format, to attract interest the of national and international geologists on Brazilian key outcrops and offer a synthesis and a starting point for teaching purposes and future studies.</p> 2024-02-09T00:00:00+00:00 Copyright (c) 2024 Journal (JGSB) and the authors Investigation of Archean gamma-ray fingerprint: Methodology and tectonic application in central Brazil 2023-10-03T18:45:37+00:00 Marcus Flavio Nogueira Chiarini Loiane Gomes de Moraes Elton Luiz Dantas Reinhardt Adolfo Fuck Elias Prado Raphael Teixeira Corrêa Jaime Scandolara Antônio Frasca Joseneusa Rodrigues Andre Menezes Saboia <p>Gamma-ray spectrometric responses of Archean rocks were studied in order to define a characteristic signature for these rocks. As the half-life of the most frequent Thorium isotope (<sup>232</sup>Th – half life of 14.05 Ga) is more than 3 times longer relative to the Uranium isotope (<sup>238</sup>U – half life of 4.50 Ga), a low response of radiation intensity in the spectral range of decay series of Uranium relative to that of Thorium is expected for Archean rocks. Based on this theoretical aspect, associated with gamma-ray spectrometric responses parametrically studied in several Archean areas of Brazil, gamma-ray and magnetometric structural interpretation, follow-up field studies, micropetrography, lithogeochemistry, and geochronology (U-Pb in zircon), it was possible to define and identify previously unidentified Archean rocks (2.82 Ga) tectonically imbricated amid Neoproterozoic magmatic arc terrains. This discovery has geotectonic implications regarding the magnitude of the Transbrasiliano Lineamento and its potential to fragment large Archean blocks and arrange them aligned within the Tocantins Province, Central Brazil.</p> 2024-01-08T00:00:00+00:00 Copyright (c) 2024 Journal (JGSB) and the authors Inference of minerals at Redondão kimberlite crater, Parnaíba Basin, Brazil, based on interpretation of airborne gamma-ray spectrometry and ASTER data 2023-11-15T01:00:24+00:00 Adolfo Silva <p>This work reports how minerals at Redondão kimberlite pipe may be inferred through integrated interpretation of airborne gamma-ray spectrometry data and multispectral images derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Using several processing techniques (e.g. K, eTh, and eU concentration maps, K/eTh, K/eU, and eU/eTh ratio maps, K image inverse map, profile analysis for radiometric data and; spectral indexes and mineral distribution and abundance maps for ASTER data), it was observed that K concentrations within Redondão kimberlite intrusion are high enough to be distinct from the surroundings and at least three spectral signatures of endmembers extracted from ASTER images suggest that chlorite, diopside, and phlogopite minerals may be present within Redondão kimberlite crater and the near surroundings. Although the sources of K concentrations are unclear, it probably is composed of different minerals and phlogopite may be one of them. The spectral signatures of chlorite, diopside, phlogopite may be derived from clastic materials and products derived from ultramafic mineral weathered, but new studies are recommended to improve distribution and abundance maps of these minerals. These new studies may include hyperspectral sensor images and rock-spectra data. The results reported here be useful for further research whose goal is to map kimberlites using remotely sensed images not only in the study area, but also in other locations with similar geologic context.</p> 2024-01-08T00:00:00+00:00 Copyright (c) 2024 Journal (JGSB) and the authors