Resumo em Inglês:

Abstract Paleohelcura tridactyla is a trackway characterized by up to three round tracks per series, typically arranged linearly or triangularly, often with a medial impression. This pattern is consistently found in several eolian deposits and has been described in the Botucatu Formation in Brazil, an eolian sandstone unit in the Paraná Basin deposited during the earliest Early Cretaceous under arid conditions. Here, we describe a new small morphotype of Paleohelcura tridactyla in the Botucatu Formation. This morphotype is smaller than previously described specimens of Paleohelcura tridactyla, and although it shares a similar size with Paleohelcura araraquarensis, it differs both in track morphology and series arrangement. We propose three hypotheses for the new morphotype: (1) The trackway may have been produced by the juvenile stage of the arthropod responsible for the larger Paleohelcura tridactyla tracks. (2) The size difference may indicate sexual dimorphism within the same species. (3) Alternatively, it could represent a different arthropod species, which is smaller in size but leaves similar track patterns. This discovery reinforces the ichnotaxonomical distinction between P. tridactyla and P. araraquarensis and raises the possibility that another arthropod species may have been present in the Botucatu Paleodesert fauna.

Resumo em Inglês:

Abstract Lateritic formations are widespread in eastern Amazon, occurring as bauxite-bearing mature profiles on plateaus or as immature ones in lowlands. Climate and landscape evolution over the Neogene were analyzed via mineralogical (XRD), textural (optical microscopy), and geochemical (ICP-OES, ICP-MS) methods carried out in a selected lateritic profile outcropping in Abel Figueiredo. The profile features columnar and nodular iron crust, overlaid by a spherulitic horizon formed of hard fragments in clayey matrices, covered by yellow topsoil. Major minerals include hematite, goethite, kaolinite, and quartz, with minor anatase and heavy minerals. Hematite and goethite dominate lower horizons, while kaolinite, quartz, Al-goethite, and anatase appear in the matrix and topsoil. Trace elements were immobilized by iron oxyhydroxides and anatase or maintained in zircon and other resistate minerals. Mineralogy and geochemical distribution indicates a transition from iron crusts to fragmented iron crust, followed by physical reworking, leading to the formation of nodules and spherulites, with clay accumulation in between. In a final stage, a topsoil developed over the profile. This set of events requires an alternation between humid tropical climate with more arid conditions, with implications to rainforest and savanna development, resulting in mineral formation and chemical or physical decomposition.

Resumo em Inglês:

Abstract The Proterozoic pre-collisional basins of the Araçuaí orogen consist of a succession of superimposed basins that overlie the eastern margin of the São Francisco Craton. This report proposes new stratigraphic and tectonic models for the evolution of the pre-collisional basins of the Araçuaí orogen. They are younger than the Rhyacian orogeny and predate the Ediacaran orogeny. The Orosirian Costa Sena sineclisis was a submerged, N-S asymmetric basin. The onset of the Statherian Espinhaço rift system followed, consisting of four asymmetric rifts, bounded by N-S, west dipping normal faults. The faults are connected at depth to a detachment, exposed at the eastern border of the southern Espinhaço range. The taphrogenic process was caused by an asthenospheric heat flow, from underneath the São Francisco proto-Craton, moving eastward, below the Gouveia complex. After a geological hiatus greater than 400 Ma, the basin activity resumed when the temperature below the Gouveia complex was high enough to create a thermal heat flow, directed toward the east, below the Guanhães complex. Asthenospheric heat flow acting below a younger detachment zone governed the development of the remaining Stenian Tonian Cryogenian pre-collisional basins, continental breakup and oceanic crust generation.

Resumo em Inglês:

Abstract The Novo Mundo granitic Complex lies in the southernmost margin of the Amazonian Craton, Brazil. New petrological, geochemical, U–Pb and Sm–Nd isotopic data allow us to propose a new petrogenetic model for granite genesis in the southernmost portion of the Craton. Earlier studies attribute the complex to the Tapajós–Parima Tectonic Province. Four granitic facies have been identified: quartz monzonite, monzogranite, biotite granodiorite, and syenogranite, all of which are crosscut by diabase dikes. The monzogranite has primary muscovite. The biotite from the granites shares chemical signatures with that of volcanic arc settings. Petrographic data, mineral chemical, lithogeochemical, and isotopic data allow conclude that the Novo Mundo rocks into I-type, meta– to peraluminous, and calc–alkaline to alkali-calcic granites which are compatible with volcanic arc settings and varying degrees of crustal contribution. U–Pb LA–ICP–MS ages of magmatic zircons (quartz monzonite 2032 ± 6 Ma; monzogranite 2029 ± 4 Ma; biotite granodiorite 1989 ± 6.2 Ma; syenogranite 1987 ± 7.4 Ma) and TDM Nd model ages (2.52-2.15 Ga; ɛNd(t) = -2.0 to +1.81) indicate that the granites originated from either mantle-derived or juvenile Orosirian crustal melts, with additional continental crust input. The weak positive ɛNd(t) anomalies suggest an upwelling asthenospheric mantle that provided the thermal input to remelt the lower crust, as well as the isotopic data emphasize varying levels of crustal reworking during arc evolution. These ages are coeval with the evolution of the Paleoproterozoic Cuiú-Cuiú Magmatic Arc emplaced during the main stage of arc subduction in the region (2.05-1.99 Ga). The proposed evolutionary model suggests that quartz monzonite and monzogranite are associated with the early stages of arc evolution. The granodiorite records the contribution of juvenile sources, correlated with episodes of mafic magma influx, while the syenogranite represents the final stages of the arc formation, indicating a predominance of continental crustal contribution. The new data, combined with recent studies, allow us to suggest the existence of a Paleoproterozoic continuous magmatic arc into the south part of the Amazonian craton instead of the previously defined tectonic provinces previously defined in the literature.

Resumo em Inglês:

Abstract Studies integrating ichnology and sedimentology in paleoenvironmental interpretations are rare in Brazilian rift successions. This study applies an integrated ichno-sedimentological analysis to a well core from the Resende and Tremembé Formations (Cenozoic Taubaté Basin) to reconstruct paleoenvironmental conditions. Three paleoenvironments were identified: alluvial fan, braided river, and lacustrine. The alluvial settings is characterized by coarse-grained deposits displaying bioturbation intensity and sporadic trace fossils, dominated by Palaeophycus and Skolithos, reflecting opportunistic colonization. Braided river deposits consist of stacked sandstones with trough cross-bedding and a trace-fossil assemblage with Palaeophycus, Skolithos, Macanopsis, and Taenidium. The lacustrine environment is characterized by dark shale interbedded with fine-grained sandstones, including ostracod-rich white beds. Sparse beds containing Planolites indicate a complex lacustrine system with potential variations in salinity and oxygenation. Comparison with previous studies suggests that ichnofossils and paleosols reflect water table fluctuations and humid conditions in the Resende Formation. For the Tremembé Formation, ichnofossil data, palynomorphs (Botryococcus and Pediastrum), and taphonomic signatures in fishes suggest a dynamic environment with fluctuating water levels, periodic salinity increases, and decreased oxygen levels.

Resumo em Inglês:

Abstract The Sana (Sana suite) and Itaoca (Nova Friburgo suite) granites, emplaced in the Oriental Terrane of the Ribeira Belt during the Cambrian–Ordovician, provide key insights into post-collisional magmatism in a Gondwana segment marked by crustal recycling. We present new Sm–Nd and Rb–Sr isotope data for 26 samples from both plutons, combined with petrographic information, to evaluate magma sources and the applicability of I- and S-type classification. The Sana Granite is strongly peraluminous and dominantly S-type, derived mainly from metasedimentary sources of the São Fidélis Group with minor arc-derived input, supported by isotopic evidence and rare titanite (< 1%). In contrast, the Itaoca Granite is metaluminous, titanite-rich, and consistent with I-type, reflecting melting of mafic to high-K orthogneisses of the Rio Negro Magmatic Arc. Mixing models suggest ternary contributions from arc and sedimentary reservoirs but remain exploratory due to limited Sr data for sources. Both plutons share overlapping Nd and Sr isotope fields, with initial 87Sr/86Sr ratios of 0.7008–0.7078 and consistently negative εNd(t) (–11 to –13), highlighting isotopic convergence in the Oriental Terrane. These results show that, despite contrasting S- and I-type traits, both granites reflect hybridization and a shared tectonic framework, emphasizing the limitations of strict isotopic classification and the need for integrated petrographic approaches.

Resumo em Inglês:

Abstract The Ribeira Belt in southern Brazil records the Neoproterozoic tectonic evolution associated with the amalgamation of Western Gondwana, and its shear zones provide critical constraints on transcurrent–transpressive deformation regimes. Within this framework, the Atuba Complex in the Curitiba Terrane hosts the São Jorge quarry, where metatexites preserve evidence of progressive deformation. This study investigates feldspar intracrystalline plasticity and quartz–feldspar microstructures to better understand deformation mechanisms and their significance for strain partitioning during the evolution of the Curitiba Shear Zone. Petrography, structural analysis, finite strain quantification (Fry, Polar, Rf/ϕ), and electron backscatter diffraction (EBSD) were combined to characterize deformation fabrics. This research analyzes feldspar crystals to investigate intracrystalline plasticity, while finite strain quantification was primarily based on quartz grains, which serve as reliable markers for bulk strain estimates. Three deformation stages were identified: (i) ductile shear producing mylonitic metatexites with steep NE–SW foliation and sinistral kinematics, (ii) overprinting brittle–ductile deformation, and (iii) late brittle fracturing. Quartz microstructures, including lobate boundaries and grain boundary migration, indicate deformation temperatures exceeding 500°C, while feldspar exhibits undulatory extinction, subgrain formation, and moderate dynamic recrystallization. EBSD data reveal a crystallographic preferred orientation of albite consistent with {100}<010> slip, also suggesting deformation at ~500°C. Finite strain ratios are low (R ≈ 1.5-2.1), reflecting the last local increment of deformation rather than the total bulk strain, and indicating limited strain accumulation despite localized intense shearing. Brittle–ductile overprints are marked by fractures, fault zones, grain-size reduction, and comminution. Taken together, we interpret the deformation at the São Jorge quarry to be progressive, transitioning from ductile to brittle regimes within a transcurrent–transpressive setting. This interpretation provides new constraints on the structural evolution of the Atuba Complex and Curitiba Terrane and contributes to broader models of strain accommodation in the southern Ribeira Belt during the Brasiliano Orogeny.

Resumo em Inglês:

Abstract Since its definition over 120 years ago, several key sedimentological and stratigraphic questions have emerged regarding the Estrada Nova succession (Serra Alta and Teresina/Corumbataí formations) of the Paraná Basin. These units developed during the disconnection of basin waters from Panthalassa and the progressive continentalization of southwestern Gondwana during the Permian, marking a distinctive stage in basin evolution. To clarify this interval, we integrated stratigraphic, sedimentological, paleontological, and geochronological data with detailed facies analysis across 28 measured sections in Mato Grosso, Goiás, São Paulo, and Paraná states. This regional survey refined stratigraphic correlation among late Permian units and revealed basin-scale filling patterns not previously recognized. Fischer diagram analysis allowed construction of accommodation curves showing striking similarities across successions in the northwestern, central, and southern basin. The recognition of a consistent stratigraphic architecture suggests depositional responses to climatic fluctuations, subsidence, and base-level changes were more homogeneous and synchronous than assumed. From a lithostratigraphic perspective, our revised framework simplifies debated stratigraphy by reaffirming the Serra Alta Formation throughout the basin, confirming correlation between Corumbataí and Teresina, and proposing that the upper Corumbataí and lower Rio do Rasto Formation may have been deposited contemporaneously, separated by local topographic highs.

Resumo em Inglês:

Abstract Rosário-16 (R-16) is a hypabyssal transitional kimberlite, divided into two volcanic pipes, R-16-A and R-16-B, within the Kimberlite Province of Rosário do Sul (KPRS), southeast of the Paraná Basin (PB), southeast Brazil. The saprolite outcrops, within a NE/SW structure, occur next to the Rosário-6 alnöite, comprising microcrysts of olivine, Mg-chromite, Mg-ilmenite, diopside, phlogopite, fluorapatite, and perovskite. R-16 also contains microxenocrysts, potentially derived from peridotitic macrocrysts, characterized by electron microprobe analyses. Calculation of pressure, representative temperature (based on averaged mineral compositions), and oxygen-fugacity conditions using geothermobarometers for olivine and spinel, and an oxygen barometer for perovskite, indicates pressures of ≥ 4 GPa, a representative temperature of ~1135 °C, and ƒO2 (oxygen fugacity) values between ΔNNO = –3.92 and –1.35. Chemical analyses indicate that CO2 metasomatism in R-16 was less than Rosário-6 alnöite. We found that CO2 reactions occurred in the mantle at higher pressures in R-16, resulting in the generation of kimberlitic magma through silicate interaction with carbonatitic liquids. The similarity between the ƒO2 versus temperature profiles of R-16 and high/low-Ti PB tholeiites suggest a heterogeneously metasomatized mantle source for the KPRS with the emplacement of R-16 favored by the Gondwana breakup.