Resumo em Inglês:

Abstract This paper presents a geological study of the subvolcanic bodies present in the Pico dos Três Estados (São Paulo (SP), Rio de Janeiro (RJ), and Minas Gerais (MG)) and its surroundings at the Passa Quatro Alkaline Complex. In this study, we used field-collected data, petrography, and geochemical analysis data. From a more detailed fieldwork, we verified that the region that appeared to present only two lithologies in previous works presented a faciological complex with at least six distinct facies, with emphasis on the phonolitic body that forms the Pico dos Três Estados (2,665 m high). Still regarding fieldwork, we found that there are signs of magma mingling processes in the area. Modeling indicates that 10% of fractional crystallization was able to derive the phonolitic rocks from a trachytic liquid based on the following elements: Y, Nb, Yb, Ce, Sm, Eu, La, Nd, Hf, and Pr. The modal batch partial melting shows the possible mantle sources for the magmatism in this area. This data pointed out the involvement of an enriched mantle source in the La/Yb ratio by at least 16 times more than an Oceanic Island Basalt (OIB)-type mantle.

Resumo em Inglês:

Abstract The integrated hydrothermal evolution of the large Santa Otília Paleodune from the Botucatu paleoerg and the cover Catalán Flow from the Serra Geral Group is here evaluated in Uruguaiana, southern Paraná Basin. Methods included satellite images, field surveying, petrography, and U-Pb geochronology of detrital and volcanic zircon. The tops of the compound linear-barchan paleodunes are exposed in the topographic highs. Rhombi and bowls at the top of the silicified sandstone units are significant, as is the poor preservation of eolian layering. The fishbone-shaped dune tops are surrounded by the lavas. The oxidized top of the flow (upper Tier 2) overlies the reduced base (Tier 1), which consists of exposed, massive rocks in creek beds that are light gray-colored and contain small (10 cm) agate geodes and numerous silicified sandstone dikes. The youngest dated zircon grains from the sandstone are 225–300 Ma old (one 175 Ma age), and the main older age peaks are 450–600 Ma (predominant), 900–975 Ma, 1800–1900 Ma, and 2500 Ma; few Archean 2.5 Ga ages. The strongly altered volcanic zircon preserved in the reddened Catalán Flow yields a concordia-intercept age of 137.3 ±7.6 Ma. Complex processes are thus constrained in the evolution of the Botucatu Formation and the first Serra Geral lava flow.

Resumo em Inglês:

Abstract The Jacareacanga Group comprises mafic to ultramafic schists, metacherts, quartzites, pelitic paragneisses, and amphibolites related to siliciclastic-chemical sedimentation and mafic-ultramafic volcanism. These rocks of the Jacareacanga Group correspond to turbidite-related sediments and oceanic crust basalts of a back-arc or trench basin of the early magmatic Cuiú-Cuiú Arc of the Tapajós Domain in the Amazon Craton. Field data and petrographic analysis support the new zircon U-Pb ages obtained through LA-ICP-MS for the rocks of the Jacareacanga Group. A ± 10% concordance criterion applied, along with an exclusion of ages < 2000 Ma to mitigate interference from later events, such as granitic intrusions. Two pelitic paragneisses yielded 207Pb/206Pb ages between 2008 and 2042 Ma and mica schist ages of ca. 2056 Ma, considered to be the maximum sedimentation age of the protoliths of metasedimentary rocks. Zircon populations from the Rhyacian to the Mesoarchean indicate provenance from adjacent cratonic areas. This study shows that the Jacareacanga Basin was formed during the early Orosirian. The oldest detrital zircon ages support provenance from a magmatic arc basin of a continental margin comprising Rhyacian to Mesoarchean crust.

Resumo em Inglês:

Abstract The Northern Andes in Colombia are involved in a continuous mountain-building process along an active subduction zone, resulting in significant Cenozoic compression, leading to substantial Neogene shortening and topographic development. It is believed that, during the Miocene, some major geological structures reached their present-day elevation; this is the case of the Garzón Massif, an orographic barrier between the Middle Magdalena Valley and the Putumayo Basins. Some studies have been performed in order to understand the exhumation history of the Massif; however, whether the cooling process was slow or fast, and whether this occurs continuously or episodically, as well as the possible influence of faults on exhumation, is a matter of discussion. Using new apatite fission track thermochronology in combination with published data, we aimed to reconstruct the cooling history of the Massif. Our results show that cooling was asynchronous, with fault-bounded blocks cooling independently starting around 70 Ma. Cooling of the southernmost block (B6) occurs during Maastrichtian (~4.9°C/Myr), in blocks B2, B3, and B5 in Eocene (~5.3–5.6°C/Myr), and in blocks B1 and B5 from Late Oligocene to Miocene (~9°C/Myr and ~23°C/Myr, respectively). Faster cooling rates from the Miocene onward may be related to the accretion of the Panama-Choco block against the continent.

Resumo em Inglês:

Abstract Poorly lithified siliciclastic rocks correspond to important post-salt reservoirs in the Southeastern Brazilian Margin offshore basins. These reservoirs present challenges regarding the prediction of the hydraulic behavior of faults due to low cohesion leading to diffuse brittle deformation. To improve the understanding of the deformation influence on the reservoir quality of these rocks, this paper presents a 3D modeling method based on an outcrop analog composed of Paleogene poorly lithified fluvial siliciclastic deposits in the Volta Redonda Basin (Continental Rift of Southeastern Brazil). A database was collected containing a 3D digital terrain model of the outcrop, a 1:50-scale geological section, permeability and porosity measurements, and lithological and sonic log from a well drilled upon the outcrop to the basement. Two models were built: one using traditional methods for industry where properties were uniformly distributed throughout the grid and a second model where sectors were delimited and populated with data from deformed rocks, highlighting the impact of tectonic structures (faults and deformation bands) on fluid flow, reducing the permeability by one order of magnitude, and increasing the flow time between wells by more than 10%. This study contributes to improving reservoir modeling accuracy, enhancing the understanding of fluid flow behavior in complex, deformed, poorly lithified rocks.

Resumo em Inglês:

Abstract Situated between the Campos and Santos basins, the Cabo Frio High emerges as a focal point of heightened magmatic activity during the Santonian–Campanian and the Eocene period following the breakup of these basins. The geodynamic framework associated with these events took place during their passive margin stage, wherein magmatic occurrences could potentially be attributed to the reactivation of significant geological structures or thermal enhancement facilitated by proximal hotspots, within a context of lithospheric thinning (i.e., Trindade Plume). This investigation unveils novel Sr–Nd–Pb–Hf isotope data derived from alkaline magmatic rocks extracted from three boreholes strategically positioned within the Cabo Frio High area. The evolutionary trajectory of these rocks reflects the intricate processes of assimilation and fractional crystallization. The results of the analysis and binary mixing modeling point out to an involvement of both depleted (characterized by Depleted Mantle [DM]/Mid-Ocean Ridge Basalt [MORB] or HIMU compositions) and enriched (manifesting as the Enriched Mantle I [EMI] and the Enriched Mantle II [EMII]) sources in the genesis of these magmas. Moreover, the discerned incorporation of a fertile Ocean Island Basalt (OIB-like) reservoir hints at a plausible association with the Trindade Plume, amplifying the complexity of the magmatic genesis within the studied region.

Resumo em Inglês:

Abstract The structure of two superposed layers within a redox-altered basaltic flow is restricted to the Paraná Volcanic Province among large igneous provinces. World-class amethyst-geode and agate-geode deposits occur in reduced Tier 1 of the Cordillera Flow (> 100 km long). Satellite and drone-sourced imagery, several field surveys, and 11 new geochemical analyses were used in this study. The lower Tier 1 (10 m thick) consists of massive rocks without cooling joints, whereas the barren Tier 2 is massive with colonnade. The flow is identified from the stratigraphy and chemical composition (e.g., 1.3 wt.% TiO2). The presence of poikilitic microphenocrysts of magnetite (mostly plagioclase inclusions) is a distinctive feature. Tier 2 rocks are chemically similar to the original lava; Tier 1 displays a decrease in SiO2 and K2O contents and an increase in Fe2O3T. Reducing and acidic hot water formed amethyst and agate deposits in Tier 1. Curved shapes (erosional remnants with agate) were formed by silicification of the lower portion of the flow. The interaction of the Guarani Paleoaquifer with the lava flow formed the two layers: the geodes and the curved portions. Other provinces may have similar features where hot aquifer water was available below the basalt.

Resumo em Inglês:

Abstract The Upper Jurassic to Lower Cretaceous Botucatu Formation of the Paraná Basin consists primarily of trough cross-bedded eolian sandstone deposited in an intracontinental desert. In southeastern Brazil, an unusual occurrence of conglomerate and coarse-grained sandstone unconformably overlies the Neoproterozoic basement and is overlapped by volcanic rocks of the Serra Geral Formation. This represents one of the few documented occurrences of fluvial facies described for the Botucatu Formation in the northern part of the basin. To determine its depositional system and source area, we conducted facies and paleocurrent analysis, detrital grain modal counting, macroscopic provenance, and conventional heavy mineral analysis. The integrated analysis suggests that the studied succession was deposited by an ephemeral fluvial system at the margins of the extensive dune fields of the Botucatu paleodesert. Paleocurrent data and detrital composition indicate sediment dispersal toward the SE, with a possible source area associated with a recycled orogen to the NW (Brasília Belt). Although ephemeral rivers acted as important sediment suppliers for this continental-scale desert, recycling of eolian sediments by fluvial systems is not ruled out. Finally, using a multi-proxy approach, we present a paleogeographic scenario for the northern margin of the Botucatu paleodesert during the last period of Gondwana, prior to its initial rifting.

Resumo em Inglês:

Abstract The AN-34 and QT-02 iron oxide–copper–gold (IOCG) prospects are located in the northern portion of Carajás Mineral Province (CMP), where important copper IOCG deposits occur. This region lacks basic geological information on the outskirts of the large IOCG deposits, and these small prospects might provide information regarding fluid–rock interaction and alteration-mineralization styles. In these prospects, banded iron formations (BIFs), basic volcanic rocks, and granitoids are variably deformed and hydrothermally altered. The hydrothermal alteration evolved from early silicification, potassic alteration, and Fe enrichment. All these alterations are pervasive and linked to shearing structure development. They are followed by late, ductile-brittle, chloritic alteration and sodic alteration. The quartz–magnetite oxygen isotope geothermometry (δ18Oqtz–mag) and chlorite geothermometry reveal a decrease in the temperature of the hydrothermal system from 520°C ± 30°C to 273°C ± 20°C. The calculated δ18OH2O for silicification (6.6–5.8‰) and Fe enrichment (9.2–10.47‰) suggest the involvement of magmatic fluids. δ18OH2O values from 0.27 to 0.77‰ and 1.7 to 3.3‰ from late sodic alteration and hematite are compatible with meteoric fluids. Our findings shed more light on the fluid–rock interaction, hydrothermal evolution, and mineralization styles in the IOCG deposits of the northern sector of the CMP.

Resumo em Inglês:

Abstract Two tholeiitic magmatic events are recorded at the Eastern Border of the Parnaíba Basin comprising the Jurassic Mosquito Formation and the Cretaceous Sardinha Formation. They are chronocorrelated to the Central Atlantic Magmatic Province Large Igneous Province (CAMP LIP) and Equatorial Atlantic Magmatic Province (EQUAMP LIP), respectively. The latter is also chronocorrelated with the Paraná-Etendeka Province (PEMP LIP). Five groups of tholeiitic rocks are representative of magmatic episodes with different ages and tectono-magmatic context: Low-Ti Group I, High-Ti Group IIa, High-Ti Group IIb, High-Ti Group III, and High-Ti Group IV. The geochemical data of Groups I, IIa, and IIb are similar to those of tholeiitic basalts from Jurassic CAMP LIP, whereas rocks in Groups III and IV can be related to the Cretaceous EQUAMP LIP as well as High-Ti basalts of the PEMP LIP. The chemical differences between the two magmatic events indicate changes in the mantle composition underlying to the Parnaíba Basin over geological time. It is likely that the Brasiliano-Pan African orogenies, which preceded Jurassic rifting, affected the mantle sources of the Groups I and II magmas. Conversely, the composition of the mantle underlying the Parnaíba Basin was modified by the impingement of a mantle plume during the Cretaceous.

Resumo em Inglês:

Abstract The presence of deformation bands (DBs) associated with porous volcaniclastic rocks, it is ubiquitous but poorly described. In Trindade Island, the Paredão Volcano's lapilli tuffs are deposited during the Middle Pleistocene, and several deformation bands are associated with conjugate pairs geometry. To analyze the structural geometry and mineral phase of host rocks, we employed a multiscale approach that included regional fracture and geometry studies in the field, microtectonics with a support of scanning electron microscopy (SEM-EDS), and 2D petrophysical properties analysis. The analysis revealed that the deformation bands result from two mechanisms. The first is a granular flow mechanism characterized by grain rotation and matrix reorganization. This mechanism is also associated with fluid flow and matrix zeolitization. The second mechanism is a cataclastic flow marked by crystal fragmentation and the formation of a fine-grained matrix. It is observed that the pre-existence of mineral cleavages and fractures facilitates these mechanisms. The combination of these two mechanisms, driven by fluid flow, leads to the development of cataclastic bands characterized by the loss of porosity, matrix reorganization, and distinct geometric patterns. Those mechanisms are suggested to be developed in a transtensional context related to the Vitória-Trindade Fracture Zone.

Resumo em Inglês:

Abstract The Miguel Amaral Burgueño Paleontological Site is an important fossiliferous Quaternary deposit located in the middle course of the Apa River, municipality of Bela Vista, State of Mato Grosso do Sul. In this study we analyzed nineteen fossils of the Quaternary megafauna discovered in longitudinal gravel bars in fluvial deposits. The taxa are represented by Eremotherium laurillardi and Notiomastodon platensis associated with pebbles and gravel after reworking and tractive efforts by the fluvial transport. The fossils are fragmented and disarticulated with a low degree of weathering and with E-W imbrication. Taphonomic and sedimentary features indicate that the fossils were reworked from sedimentary deposits adjacent to the channel of the Apa River near the deposition site.

Resumo em Inglês:

Abstract Silicification is a diagenetic process that affects the porosity and permeability of carbonate rocks, such as those in the Itapema and Barra Velha formations, Pre-salt of Santos Basin. This contribution integrates macroscopic and microscopic descriptions of silicified intervals, identifying controls and mechanisms of dissolution, replacement, and precipitation, relating them within the diagenetic history of the formations. The pre-compaction eodiagenetic silicification comprises tabular and nodular geometries, reflecting fine-grained laminated and coarser-grained massive lithologies. The post-compaction mesodiagenetic silicification comprises irregular silica disseminated throughout carbonates. Silica bodies consist of replacive (cryptocrystalline silica, mosaic microcrystalline quartz and spherulitic chalcedony) and pore-filling textures (chalcedony and macrocrystalline quartz). The highly selective nature of the replacement suggests that carbonate dissolution initiates silica precipitation as a fluid-mediated process that transfers crystallographic information. The successive zoning with decreasing crystallinity in filling/cement textures indicates a decrease in the fluid supersaturation as the precipitation advances. These features indicate that textures and silicification mechanisms reflect precipitation physicochemical conditions. The first silica event follows the dolomitization stage that replaces primary clays and carbonates, while the second event occurs after mechanical compaction and is later followed by replacive/pore-filling barite textures. Late macrocrystalline quartz veins host primary hydrocarbon fluid inclusions, linking the second silicification event with oil migration.

Resumo em Inglês:

Abstract Although many paleogeographic reconstructions depict equatorial Brazil as being predominantly arid during the Aptian, studies using palynomorphs suggest climatic fluctuations between humid and arid phases. There is, however, a lack of studies utilizing additional proxies to demonstrate such changes. We present a case study for climatic variation in an Aptian continental to transitional system in the Araripe Basin, Brazil, applying geochemical, palynological and ostracod analyses, integrated with previously published sedimentologic and stratigraphic data from the Barbalha Formation (46 samples; drill core 1PS-06-CE). Cluster analysis of micropaleontological and weathering proxies allowed to identify seven climatic clusters (G1-G7): G1-G4 from the Batateira Beds (lower Barbalha Formation) and G5-G7 from the upper Barbalha Formation. G1-G4, linked to lacustrine facies, indicate a generally more humid interval, with proxies showing intense weathering and long-distance element transport. Paleoredox data suggests low oxygenation. In contrast, G5-G7, associated with bayhead delta environments, reflect a relative increase in aridity, with reduced weathering and evidence of subaerial exposure of organic particles. Nevertheless, humidity persisted, supported by the occurrence of pseudo amorphous organic matter and marine ichnofossils. These results show that despite an overall arid trend, significant moments of humidity were still present in equatorial Brazil during the Aptian.

Resumo em Inglês:

Abstract The analysis of sediment accumulation rates from cores collected from marine environments has enabled the reconstruction of depositional records spanning the past century using radionuclides such as 210Pb. 210Pb is a member of the 238U decay series and is commonly used to investigate recent processes owing to its half-life of 22.3 years. This radionuclide enters the marine environment through dry and wet conditions and from the decay of its parent isotopes. 210Pb is particularly effective in determining the accumulation rates within the sediment layers formed from 5 to 100 years. This study focused on the Coreaú River Estuary, located in Camocim on the Ceará coast of Brazil. Nine sediment cores collected throughout the estuary revealed steady-state sediment accumulation rates in some of the cores. In the other cores, the 210Pb profiles were slightly inconclusive. These cores exhibited substantial bioturbated mud in the upper 10–30 cm, below which the radioactivity decreased abruptly. These findings provide insights into sediment accumulation across the estuary, particularly near its mouth. Our findings indicate sediment accumulation was more rapid on the eastern bank and near the estuary mouth and was likely influenced by estuarine hydrodynamics and the influx of organic material from human activities into the secondary channels of the river. These findings highlight the importance of monitoring sediment dynamics in estuarine systems impacted by human activities and provide a foundation for future coastal management and conservation efforts. Further research incorporating additional dating methods and hydrodynamic modeling is recommended to refine sedimentation trends and their long-term implications.