Resumo em Inglês:

Abstract The Quadrilátero Ferrífero (QF) is a globally known region for its world-class metallic deposits. Although its Precambrian units have been vastly studied since the 1960s due to economic importance, the Cenozoic geological record represents an upcoming subject of interest. The occurrence of Cenozoic sedimentary deposits has been noticed since the end of the 19th century, but most of them are not yet fully characterized. This paper brings a complete description, mapping, 3D modeling, and simulations of the sedimentary deposit named Bandeira Basin, Serra do Tamanduá, QF. Based on field data, such as mapping and drill core database analysis, three drill cores were selected for further investigation and detailed description. The Bandeira Basin can be characterized and subdivided into three units: Unit A: found only in the southeast area and shows exclusively sediments from the Nova Lima Group; Unit B: intermediate unit that occurs in central and southeast areas, with Rio das Velhas Supergroup as a possible source of the sedimentary material; and Unit C: occurs at the top, and it is essentially colluvial deposits from Minas Supergroup units. The contacts between units are abrupt or erosive, recording successive deposition stages. The basin is thicker on its central and southwest ends and thinner on the east and north, where part of the basement outcrops. Cenozoic tectonic events were probably active in this area, controlling the sedimentary processes, with the NW-SE and NE-SW lineaments reactivated, triggering sediment deposition and migration to the deepest spot of the basin. These sediments were 3D modeled in Leapfrog Geo, the visualization of any given region of interest, in the modeled scale. This methodology allowed an assertive characterization of sedimentary filling and could be applied to other basins. This comprehension is important because these sediments are used indirectly or directly in civil projects.

Resumo em Inglês:

Abstract The Bauru Supersequence comprises two chronocorrelates groups, namely, Caiuá and Bauru. While substantial efforts have been dedicated to detailed mapping in the eastern portion of the Bauru Basin, the western part, specifically the Caiuá Group, remains unresolved and undivided. The aim of this research was to characterize the occurrence area of the Rio Paraná Formation in the state of Mato Grosso do Sul, which is located in the Midwest region of Brazil, as well as its lithostratigraphic characteristics, and the implications for a better understanding of the paleoclimate and paleogeography of that region during the Cretaceous. The Rio Paraná Formation is constituted by six lithofacies: sandstone with cross-stratification (Sct), sandstone with trough cross-stratification (Sct-t), sandstone with cross-stratification pebbles (Sctp), massive sandstone (Sm), massive sandstone with fragments of basalt (Smb), and sandy mudstone (Fme). It was possible to group three facies associations: large-size eolian dunes, interdunes, and sand sheet deposits. The direction of paleocurrent is southwest, which is similar to those previously recognized in the eastern part of the basin and chronocorrelates basins in Brazil. Based on the results obtained in this research, it was possible to provide evidence for the future paleogeographic reconstruction of the Late Cretaceous in South America.

Resumo em Inglês:

Abstract On the southern edge of the Amazonian Craton, the Mirassol d’Oeste and Guia formations constitute the cap carbonate of the Araras Group. Petrography, X-ray diffraction, and quantification of terrigenous material allowed the identification of detrital grains (e.g., mica, quartz, and feldspar) in different proportions and diagenetic features. The sequential leaching of carbonates along a section of the upper portion of the Guia Formation yielded 87Sr/86Sr ratios increasing from 0.7070 to 0.7077, which is considered the primary Sr isotopic signature of seawater. The increasing continental influx of dissolved Sr from freshwater accounts for the increase in 87Sr/86Sr along the section. Such abrupt change toward more radiogenic values is also observed in carbonate layers soon after the Marinoan glaciation, elsewhere in the world. The same samples provided Nd-TDM model ages (1.84–2.54 Ga) comparable with those of the continental crust of the Paleoproterozoic provinces of the Amazonian Craton, which forms the basement of the Araras Group. The ԐNd(635Ma) values between -4.7 and -11.1, probably indicate the presence of Nd from the suspended material transported by continental waters to the ocean where the carbonates precipitated. The random variations of Nd-TDM ages and ԐNd values suggest important and rapid variations in the continental contribution to the post-Marinoan oceans.

Resumo em Inglês:

Abstract This research aims to obtain tomographic images to interpret the seismic stratigraphic profile around the San Rafael (SR) knickpoint using seismic tomography. The SR waterfall on the Coca River sinkhole in February 2020 caused regressive soil erosion, suggesting that the knickpoint is highly unstable. Seismic tomography for the P-wave velocity model, utilizing data from 14 stations in the permanent Ecuadorian seismic network, produced vertical cross-sections at azimuths of 0°, 45°, 90°, and 80°. These sections reveal geological formations and their transition to volcanic deposits, while a horizontal cross-section illustrates the extent of the volcanic deposits. The tomographic images facilitated the identification and correlation of seismic stratigraphy with the area's geological features. The most unstable materials for erosion lie from 0 km to 1.5 km with velocities of up to 3.5 km/s. The erosive process impacts the population and infrastructure settled on the banks of the Coca River with a high susceptibility to erosion in zone 1, with velocities of 3 km/s and a 10 km extension. The Coca Codo Sinclair Dam (CCSD) is located in zone 2, with velocities of 3.8 km/s extending up to 40 km with medium susceptibility to erosion.

Resumo em Inglês:

Abstract The Atuba Complex occurs in the eastern region of Paraná State, located in the Southern Ribeira Belt. It is comprised of the Curitiba Terrane, northward of the Luís Alves Terrane, and southward of the Apiaí Terrane. This research was carried out by means of detailed petrography, microtectonics, and brittle and ductile structural analysis. The Atuba Complex is composed of migmatites, felsic granulites, granitoids, quartzites, phyllonites, schists, amphibolites, and cataclasites. The lithotypes are cut by diabase or gabbro dikes, lamprophyre dikes, pseudotachylites, and quartz, epidote, carbonate, or chlorite veins. The migmatites are characterized by two migmatization phases, the first composed of tonalitic leucosomes and the second formed by granitic leucosomes. The stromatic and mylonitized migmatites suggest dislocation creep mechanisms and dynamic recrystallization processes, mainly in quartz and feldspars. During the initial phase, melting reactions took place through dehydration, while in the subsequent phase, melting was facilitated by the presence of water-fluxed. The Atuba Complex comprises two foliations, Sn-1 (Dn-1 phase) and Sn (Dn phase). The Sn-1 surface (compositional banding) presents a ductile and anastomosed aspect with an N45W/55NE attitude, whereas the Sn mylonitic foliation is defined by the presence of mineral flattening or stretching and by the orientation of amphibole and biotite shapes, with a maximum plane of N45E/85NW. The observed faults and fractures strike in the NE-SW and NW-SE main directions. The paleostress study provided the recognition of a NE-SW sigma 1 associated with a NW-SE-striking sigma 3 for the left-lateral strike-slip faults and an E-W compressive SHMAX and an N-S distensive SHMIN for the right-lateral strike-slip faults.