Resumo em Inglês:

Abstract Bathybic ostracods (i.e., bathyal and abyssal assemblages) are important indicators of temperature and productivity changes of Cenozoic marine ecosystems. The present work presents the first study on Quaternary ostracods of the Camamu Basin, off the state of Bahia, northeastern Brazilian continental margin. The analysis of 59 samples from the piston-core CMU 14 (14°24’S, 38°49’W; 965 m water depth), revealed rich and abundant assemblages. The 14C accelerator mass spectrometry (AMS) dating indicates that the studied interval covers the last 108 kyr, corresponding to the oxygen stable isotope stages (MIS) 5 to 1. Comparison with data from previous publications allowed discernment of three groups of ostracod species in CMU 14: Pandemic Group of species registered in more than one oceanic basin; Atlantic/Mediterranean Group of species restricted to the Atlantic Ocean and Mediterranean; and Brazilian Group of species restricted to the Brazilian continental margin). Four new species are herein proposed: Cytherella pindoramensis sp. nov., Ambocythere amadoi sp. nov., Pseudobosquetina pucketti sp. nov., and Bythoceratina bonaterrae sp. nov. Ostracod occurrences reveal the influence of glacial/interglacial cycles on assemblages composition. Interglacial stages 5 and 1 in the Camamu Basin are characterized by the association Bythocypris affinis–Cytherella pindoramensis sp. nov.–Cytheropteron perlaria–Bradleya dictyon; glacial stages (i.e., 2 to 4) register decreased diversity, possibly due to lower oceanic productivity.

Resumo em Inglês:

Abstract Landslide identification is important for understanding their conditioning factors, and for constructing susceptibility, risk, and vulnerability maps. In remote sensing this can be accomplished manually or through classifiers. This study compares three image classifiers (Maximum Likelihood, Random Forest, and Support Vector Machines (SVM)) used in identifying landslides in Itaóca (São Paulo, Brazil). Two datasets were used: a RapidEye-5 (5 m) image and a Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) (12.5 m). Seven pixel-based classifications were produced, two for each classifier and a binary class that identified only landslides and non-landslides. One classification contained five spectral bands (5B), while the other contained six bands (6B) and included the slope derived from the DEM. The results were validated using Kappa index and F1 score. The SVM 6B classification achieved the best results among the validation indices used herein. It identified a landslide area of 399,325 m². The results contribute to landslide mapping in tropical environments using pixel-based classifiers. However, although the SVM classification was successful, only landslides with larger areas were captured by the algorithms, confirming the importance of conducting further analyses using images with finer spatial resolution.

Resumo em Inglês:

Abstract U/Pb ages of detrital zircon from two samples of Ordovician sediments were determined and, based on similar published data, were compared with xenocrystal inheritance of Triassic and Oligocene granitoids of the Cordillera Real in order to better understand their genetic relationship and sources. The results show that the detrital zircon in the Ordovician sandstone and the inherited zircon cores in granitoids are statistically correlated. This correlation suggests assimilation of these sedimentary units by the felsic melts. Ages ranging from 300 to 2300 Ma are recorded in these inherited zircons. A high peak of Cambrian to late Neoproterozoic ages (500-750 Ma) is observed throughout metasedimentary units of the entire belt. Candidates for the main sources of these zircons include: Brasiliano or Pampean belts and/or an “in situ” hidden belt within the Central Andes or via recycling of detrital zircons in pre-existing sedimentary rocks. It is also possible that the sources lie below modern sedimentary covers but, at the time, formed high relief structures supplying recycled material into the Ordovician basins.

Resumo em Inglês:

Abstract Presented here are the results of the first studies of silicate melt inclusions hosted in quartz crystals from the two late granitic facies of the Paleoproterozoic Madeira pluton in the Pitinga mine, State of Amazonas, Brazil. The study of these magmatic inclusions in the anorogenic granites of Pitinga furnished reliable results because the original composition of the trapped silicate liquids is well preserved. Petrographic, morphological, and chemical data show that both porphyritic hypersolvus alkali feldspar granite and albite-rich granite were formed by melt-melt immiscibility from a precursor magma. After phase separation, albite-rich granite evolution was characterized by strong enrichment in F, Na, Sn, Nb, Ta, Zr, Th, Y, Rb, and REE compared to the porphyritic granite, based on data obtained from analyses of both trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and major elements by electron microprobe. These elements make up the polymetallic magmatic ore of the Pitinga mine. The contrasting evolutionary trends, peralkaline and peraluminous, stand out in the different geochemical signatures of the analyzed melt inclusions. The preliminary results of our studies on melt inclusions trapped in rare metal granite minerals from Sn-polymetallic deposits in Brazil suggest abundant possibilities for using this methodology in future petrological and metallogenic research.

Resumo em Inglês:

Abstract We present new high-resolution 40Ar/39Ar ages for alkaline layered gabbros and cross-cutting mafic-ultramafic and felsic dykes from the São Sebastião Island, in the northern sector of the Serra do Mar Alkaline Province, São Paulo, Brazil. Duplicate analysis of single kaersutite crystals yielded plateau ages of 88 ± 1 and 87.9 ± 0.8 Ma for a gabbro and 87 ± 1 and 86.0 ± 0.8 Ma for a picrite dyke. Two biotite aliquots from a trachyte yielded ages of 86.0 ± 0.5 and 86.2 ± 0.5 Ma, while an alkali feldspar concentrate yielded ages of 86.0 ± 0.5 Ma. The similar ages obtained for minerals with contrasting closure temperatures suggest that the results are crystallization ages and that the rocks were emplaced at shallow crustal levels. Our results, along with available high-resolution data, point to a relatively narrow time span (ca. 88-85 ± 0.6 Ma) for the entire alkaline magmatism on the island. Other alkaline occurrences both nearby and in the continent’s interior reveal similar ages, reinforcing the hypothesis that mantle decompression and upwelling of heterogeneous mantle sources led to crustal extension and fast ascension of a variety of alkaline magma types in this segment of South America.

Resumo em Inglês:

Abstract Cenozoic world-class bauxite deposits developed on sedimentary sequences of the Parnaíba and Amazon Basins. The Décio pilot mine, excavated in the Rondon do Pará bauxite deposit, exposes a 3 m thick bauxite-bearing lateritic profile on the top of a 350 m high plateau. From the base to the top, this profile is composed of clayey bauxite; porous microcrystalline bauxite; spherulitic ferro-aluminous duricrust, fragmentary on the top; as well as loose ferro-aluminous spherulites and nodules, embedded in clay. The lower horizons represent a classic lateritic succession, while the top of the profile was produced through post-lateritic reworking. During this process, Ga, Cr, Mo, As, Pb, Hg, Sb, Zn, V and Sc were captured by the iron oxi-hydroxides; and REE, Hf, Nb, Ta, Y remained carried by relict zircon. Isocon diagram and mass balance demonstrate the affinity of the bauxite with claystone from Itapecuru Formation.

Resumo em Inglês:

Abstract The southern boundary of the Patos Shear Zone (PSZ) is characterized by mylonites resulting from the deformation of Paleoproterozoic basement gneisses, Neoproterozoic metavolcanic and metasedimentary rocks, granitic and granodioritic intrusions. Among the latter, the Santa Terezinha and Catingueira plutons show stretched shapes in agreement with the the shear zone’s regional trend. Recrystallized quartz grains in these plutons accommodate deformation by dislocation creep. The host banded gneisses show similar deformation structures to the plutons. Quartz crystallographic fabrics mainly record the activity of basal and prism slip planes with local contribution of rhomb planes, whilst feldspar clasts show evidence of intracrystalline deformation in the larger porphyroclasts. These characteristics suggest that shearing occurred at lower-amphibolite facies conditions. U-Pb zircon data for the Santa Terezinha pluton yields an age of 625 ± 7 Ma, which, coupled with the pluton elongated shape and microstructure, suggests that its emplacement was pre-kinematic in relation to the Patos shear zone. Post-emplacement elongation of the granite body occurred along the strike-slip trend. Such structural and geochronological constraints highlight the close association between magma emplacement and shear zone deformation during distinct stages of the Brasiliano-Pan-African orogeny in the Borborema Province.

Resumo em Inglês:

Abstract Sequence stratigraphy is a method that unravels the evolution of sedimentation through time and space within sedimentary basins. Nowadays, the exploration and production of natural resources generated by or related to sedimentary processes depend on constructing a chronostratigraphic framework to identify sequences of distinct hierarchies. In clastic and carbonate successions, exploratory studies focus on higher-rank sequences to evaluate the potential of natural resources and to make discoveries. Conversely, lower-rank (i.e. high-frequency) sequences characterize and highlight the spatial and temporal occurrence of natural resource deposits and heterogeneities, necessary for optimizing production. For instance, high-resolution sequence stratigraphic surfaces may indicate the location of placer deposits or coal seams. In the petroleum industry, high-resolution sequence stratigraphy is applied in reservoir zonation and characterization, which are the stratigraphic essence of 3D geological and fluid flow models. Thus, this methodology can guide reservoir management, forecast and optimize production, and increase the ultimate recovery factor. Recent technological innovations such as virtual outcrop models and Ground Penetration Radar have promoted a significant advance in the visualization of surfaces and stacking patterns, making stratigraphic analysis more accurate and efficient than the traditional use of analogs.