DEGEO - Artigos publicados em periódicos

URI Permanente para esta coleção

http://www.repositorio.ufop.br/handle/123456789/9

Navegar

Agora exibindo 1 - 20 de 942

Early Cretaceous bivalves of the Romualdo Formation, Araripe Basin, northeastern Brazil.
(2024) Guerrini, Vitor Bonatto; Matos, Suzana Aparecida; Fürsich, Franz Theodor; Rodrigues, Mariza Gomes; Varejão, Filipe Giovanini; Warren, Lucas Veríssimo; Assine, Mario Luis; Simões, Marcello Guimarães
The fossil-rich Romualdo Formation (late Aptian/early Albian), Araripe Basin, northeastern Brazil, contains world-renowned Fossillagerstatten characterized by exceptionally preserved fossils. Macro- € invertebrates in this formation are primarily represented by mollusks, echinoids, and decapod crustaceans. Mollusk shells are abundant in certain stratigraphic intervals, forming coquinas or shell pavements. Despite recent advances in our understanding of the taxonomy of certain groups, compre-hensive taxonomic studies are lacking for almost the entire bivalve fauna. Therefore, a detailed taxonomic analysis is presented here. The described bivalves include four new genera (Araripenomia, Ciceromya, Inversatella, Australoeocallista), and six new species (Araripenomia infirma, Inversatella cearensis, Ciceromya edentulosa, Australoeocallista juazeiroi, Legumen kaririense, and Corbulomima delicata), in addition to Musculus maroimensis, Crassatella maroimensis, “Myrtea” sp. and “Tellina” sp. This bivalve fauna mainly consists of cosmopolitan and endemic brackish/marine genera, with Tethyan affinities. The fauna is not homogeneously distributed in the sedimentary succession of the Romualdo Formation, but is constrained to the third order highstand systems tract. Bivalves recorded from muddy facies are strongly dominated by infaunal and semi-infaunal suspension feeders. Assemblages of the sand-dominated facies, with dense shell accumulations of semi-infaunal to epifaunal byssate and infaunal suspension feeders, were formed under shallow, higher energy conditions. Despite the degree of generic endemicity, the mytilids, anomiids, crassateliids, astartids, tellinids, and corbulids are related to the bivalve fauna of the Early Cretaceous Riachuelo Formation of the Sergipe-Alagoas Basin, as previously demonstrated for the bakevelliids and echinoids. Indeed, the Romualdo bivalve fauna is, in part, a modified and impoverished brackish/marine fauna of the Riachuelo Formation.
Mineral-scale insights into the petrogenesis of the 3.30 Ga rhyolite in the Contendas-Mirante region, northern São Francisco Craton, Brazil : implications from results of plagioclase and biotite analyses.
(2023) Farias, Eliana Marinho Branches; Lana, Cristiano de Carvalho; Zincone, Stéfano Albino; Queiroga, Gláucia Nascimento; Graça, Leonardo Martins
The 3.30 Ga high-silica volcanic system of the Gavião Block, São Francisco Craton, represents the remnants of within-plate magmatism related to an intracontinental rift. However, the petrogenetic processes that may have taken place in the relatively shallow primitive continental crust has not been fully constrained due to a scarce record. Petrographic and chemical analyses in biotite, as well as in-situ Sr isotope ratios in plagioclase, were used to trace petrogenetic processes and physicochemical conditions of the magmatic system. The subvolcanic rock has a well-preserved primary volcanic feature represented by magma flow textures, euhedral to subhedral plagioclases, rapakivi microstructures, and glomerocrysts. Plagioclase populations formed at two distinct stages recorded by trace elements and Sr isotope. Plagioclase phenocrysts and rapakivi phenocrysts have a slight enrichment of light rare earth elements (LREE), Sr/Ba ratio, and slight variation of Sr isotopes composition. Meanwhile, other phenocrysts and rapakivi crystals have low LREE, Sr/Ba, and a limited variation of Sr isotope ratio. Mineral chemistry evidence points to country rock assimilation during plagioclase formation and a crustal source for primary biotites under oxidized conditions.
3D geoelectric modeling to characterize ferruginous caves in Brazil, using numerical and physical simulation.
(2024) Cardoso, Luiz Henrique; Bacellar, Luis de Almeida Prado; Oliveira, Nilciléia Cristina de Magalhães; Maciel, Álvaro Simões
In Brazil, the discovery of ferruginous pseudokarst caves in laterite profiles on iron mining areas has been significant. As a result, speleological legislation has restricted mining activity to protect caves considered to be most relevant, however, with subjective criteria. This requires the collection of precise data to better guide them. The application of techniques for the identification and characterization of caves is still limited, due to the irregular topography, vegetation and the obstruction of conduits and saloons by material that fell from the ceiling and walls, and it was also mobilized by miners. A relatively cheap and quick alternative to mapping the caves, compared to classical methods such as boreholes, is Electrical Resistivity (ER). Literature data are apparently controversial, as caves filled with air sometimes have high resistivity (tens to hundreds of thousands of ohms. meter), and sometimes low (up to a few thousand ohms. meter). Thus, the objectives were to investigate the electrical resistivity duality that can be observed in these caves, and present a non-invasive cave mapping methodology and a 3D geoelectric model (inverted), to be used as a reference in future field research. To this end, direct and inverse 3D geoelectrical numerical modeling was carried out to predict the electrical resistivity of typical elements in the ferruginous pseudokarst system of the Quadrilatero ́ Ferrífero (QF), southeast region, where hundreds of caves were cataloged. Field surveys, laboratory analysis of collected material and simulations in a reduced physical model validated the predictions. The results showed that moisture around ferruginous caves can attenuate the electrical signal or even mask the high resistivity of conduits and saloons filled with air. Therefore, it was the main factor considered in the geoelectric model.
Evidence of upwelling on the Brazilian continental shelf of Rio Grande do Norte.
(2023) Nogueira, Mary Lucia da Silva; Eichler, Patrícia Pinheiro Beck; Borges, Miguel Evelim Penha; Rodrigues, André Rosch; Vital, Helenice
This study evaluates Foraminiferal assemblages and their relation with grain size, calcium carbonate content, organic matter, and mineralogy of sediment samples collected at the sediment-water interface along a transect on the northern continental shelf of Rio Grande do Norte State, Brazil, adjacent to the city of Areia Branca. The sedimentary sequence of this shelf is represented by lithostratigraphic units of a marine regressive sequence dominated by four facies: Siliciclastic sand, Silicibioclastic Sand, carbonate mud, and Biosiliciclastic sand. The carbonate content ranged from 5.83% to 85% and the organic matter content from 1.16% to 27.05%. Mineralogical characters separated the predominant siliciclastic content (37% to 92%) from the bioclastic content (8% to 63%). We have identified 14 species out of 50 species of Foraminifera, associated to particular depths and sediment types as follows: (1)deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen (2)the shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica, (3)the central parts of the transect, also in the inner shelf, provide habitats for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata and Buccella peruviana is probably related to colder water temperatures and possibly the occurrence of an upwelling phenomenon for the deepest parts of the area rather than the sedimentological features discussed here.
Dramatic changes in the confluence morphology drived by an extreme hydrologic pulse: impacts to River Doce restoration.
(2024) Marciano, Alexandre Germano; Assireu, Arcilan Trevenzoli; Azevedo, Samara Calçado de; Silva, Benedito Cláudio da; Abreu, Adriana Tropia de; Nalini Júnior, Hermínio Arias
On January 2022, the Carmo River (a tributary of the Doce River) was affected by an extreme hydrological event, with 50-yr return interval. This event was 50% higher than that associated to one of the largest tailing dam failures ever reported that took place in the Gualaxo do Norte River. This delivered to Doce River, through the Carmo River, in a Y-shaped confluence, the contaminated tailing slurry. In order to understand the role of tributaries in the recovery of the Doce River, 2D hydrodynamic and 2D sediment transport models were applied at the confluence of the Carmo River with the Piranga River. Our results, based on hydraulic modeling, remote sensing, and in-situ measurements, indicated that significant amounts of sediments were trapped on the riverbanks and stone banks, making this confluence an important site for the retention of contaminated sediments, influencing sediment budgets and downstream water quality. Therefore, this confluence deserves special attention from water engineering in order to prevent the sediments retained in this area from being transported downstream during extreme events in the coming years. These results can contribute to decision-making, to identify reaches with greater susceptibility to erosion and sediment deposition and to plan the restoration of these rivers.
Lithological controls of phosphatization in oceanic islands, Equatorial Atlantic, Brazil.
(2024) Duarte, Eduardo Baudson; Varajão, Angélica Fortes Drummond Chicarino; Oliveira, Fábio Soares de; Renac, Christophe; Schaefer, Carlos Ernesto Gonçalves Reynaud; Corrêa, Guilherme Resende
The São Pedro and São Paulo archipelago (SPSPA) is noteworthy for its unusual lithology when compared to other oceanic archipelagos, consisting of mylonitized and serpentinized peridotites, and rare carbonate sedimentary rocks. There, marine bird species use these substrates as a nesting ground and excrement deposition (i.e. guano), resulting in widespread phosphatization of local substrates. The unique geological nature of the SPSPA makes it particularly fascinating for geochemical and mineralogical research since diverse lithological, microstructural and microchemical attributes are present. This study aims to investigate the microscale chemical and mineral composition of the phosphatization materials in SPSPA, in relation to different geological substrates and associated mineralogy. Speleothems of secondary phosphates formed in fractures and on the walls, as a result of guano percolation. The microstructural control is the primary factor, which depends on the degree of rock fracturing. Wider and interconnected fractures allow the gravitational flow of cations and phosphate rich solutions with resulting phosphatization. Secondary factor is the substrate/guano interaction, which contributes to the precipitation of secondary phosphate minerals. The microchemical control is influenced by the degree of serpentinization, which leads to the generation of iron phosphates with structural potassium and aluminum. Phosphatization of sedimentary rocks is associated with pre-existing fractures and cavities, as well as the carbonate composition of the rock. This study enhances our understanding of varying ornithogenesis in the SPSPA, with a specific emphasis on the process of phosphatization of oceanic islands. Understanding this process can assist in understand the genesis of phosphate deposits in comparable environments, enhancing the knowledge of the biogeochemical cycle of phosphorus on Earth.
Lithological control on the formation of ferruginous duricrusts in the Espinhaço Range (Minas Gerais, Brazil).
(2023) Milagres, Alcione Rodrigues; Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drumond Chicarino; Varajão, César Augusto Chicarino; Medeiros Júnior, Edgar Batista de; Ramanaidou, Erick Raymond
The Espinhaço Range is the scene of a long history of exposure to chemical weathering and erosion processes since the Cretaceous. As a result, ferruginous duricrusts can be considered as the fingerprint of the long-term surface process and may provide us critical clues about changes in paleo-environmental features during the Cenozoic. In addition, specifically for the Diamantina plateau, located in the state of Minas Gerais (Brazil), there is great interest in studying the duricrusts of the Espinhaço Range, because they are associated with diamond mining, explored since the eighteenth century and which gave its name to the region. Even so, few studies have contributed to understanding their formation and morphological diversity. Mineralogical, geochemical, and micromorphological studies were undertaken to understand the processes involved in the formation of the two representative types of ferruginous duricrust, linked to phyllites of Espinhaço Supergroup: platy and massive types. The platy duricrust develops from the weathering of a banded ilmenite-hematite phyllite where the alteromorphization of its compositional banding and original foliation leads to the formation of an isalteritic duricrust. The massive duricrust, associated with diamond mining, is genetically linked to a quartz-phengite phyllite. Both duricrust profiles show relative enrichment in Fe and P and depletion of the other major elements compared to the saprolite, however, the iron concentration was 10 times greater in the massive than the platy duricrust. The REEs show similar distribution patterns with preferential leaching in both duricrusts. The compositional and textural variation of the phyllite in the Diamantina Plateau leads to the distinct evolution of two representative duricrusts profiles. The mineralogical, micromorphological, and geochemical analyses reinforce the lithological control in the formation of these two different types of ferruginous duricrusts in the study area, located in similar topographic and climatic conditions.
Geodiversity and abiotic ecosystem services in parks from the far north of Minas Gerais : educational and geotourism potential.
(2023) Pressi, Leonardo Frederico; Castro, Paulo de Tarso Amorim
The state parks from the far north of Minas Gerais are strategic for raising society's awareness about the importance of nature. Considering that in the State Parks of Montezuma, Caminho dos Gerais (PECGerais), and Serra Nova e Talhado (PESNT), there are important abiotic ecosystem services, geodiversity must be incorporated into environmental interpretation activities. In this work, sites intended for public use were evaluated regarding their educational and touristic potential related to geodiversity and the degradation risk. Geosites and geodiversity sites were selected in which geological processes can be approached by weaving relationships with biodiversity and cultural aspects to encourage visitors to have a holistic view of nature. These sites also encourage discussion on various Sustainable Development Goals – SDGs. Considering that they are located in a region with a semi-arid climate and that these parks are essential for the water supply in their surroundings, aspects related to water resources are of great relevance and may unequivocally be addressed in all selected sites, especially in the Talhado Canyon (PESNT), Gameleiras Dam (PECGerais) and in the Lagarto Rock (PEM). The intrinsic relationship between geodiversity and biodiversity is observed at the Peatlands of Gerais Santana (PESNT), Vereda das Piranhas Trail (PECGerais) and the Lavra Trail (PEM) sites. The relationship between geodiversity and cultural aspects of the region are evident in all selected sites. The high educational and geotourism potential, associated with the low degradation risk, indicates that all these sites are useful for public use activities.
Accretionary and collisional processes of the Brasiliano Orogeny recorded by the Tonian La Tuna ophiolite, Dom Feliciano Belt, Uruguay.
(2023) Pinto, Viter Magalhães; Debruyne, David Jozef Cornelius; Leitzke, Felipe Padilha; Hartmann, Leo Afraneo; Queiroga, Gláucia Nascimento; Lana, Cristiano de Carvalho
Accretionary to collisional orogenies such as the Brasiliano Orogeny of eastern South America present the opportunity to distinguish between oceanic-continental (accretionary) and continental (collisional) processes. However, the multitude of geotectonic processes involved and the reduced degree of preservation of the accretionary stage restrain the interpretation of evidence. This study focuses on a metasomatite associated with the La Tuna Ophiolite in the southern Dom Feliciano Belt of the Uruguayan Shield, as these can provide crucial insights into the accretionary stage of the Brasiliano Orogeny. The metasomatite occurs as a meter-sized massive tourmalinite body surrounded by a meter-wide chloritite lens, both enclosed by the La Tuna serpentinite. Our SEM-EDS and EPMA data revealed that the serpentines from the La Tuna ophiolite are antigorite and lizardite, while chlorite was identified as clinochlore. Abundant inclusions of sheridanite chlorite in dravite tourmaline suggests that tourmaline overgrew chlorite. Dravite crystals revealed the presence of three diffuse zones with minor compositional variations, mainly enrichments in Ca and Fe towards the rims. The U-Pb LA-ICP-MS dating of metasomatic zircon yielded ages of 743.2 ± 3.4 Ma (n = 22) for the chloritite and 743.1 ± 2.4 Ma (n = 31) for the tourmalinite. High δ11B values (+12.1‰ to + 18.1‰) of tourmaline (LA-ICP-MS) suggest that the metasomatic event was caused by seawater-derived fluids in a fluid-dominated environment. The single metasomatic U-Pb age combined with the high δ11B values suggest that the metasomatites underwent more intense metasomatic events than those associated with the Bossoroca (− 8.5‰ to +1.8‰) and the Ibar ́e ophiolites (+3.2‰ to +5.2‰) further north in the São Gabriel Terrane of the Dom Feliciano Belt. Nonetheless, a few spots in tourmaline located within fracture zones and in contact with chlorite displayed negative (c. − 5‰) and low positive δ11B values (c. 2‰). These are interpreted as overprinting by crustal fluids, either during the tectonic emplacement of the La Tuna Ophiolite or during exhumation. The calculated TDM Hf model ages for zircon in tourmalinite and chloritite range from 0.74 to 1.09 Ga and their εHf(T) values range from +4.9 to +11.2, indicating derivation from depleted mantle sources. The data corroborate earlier results indicating that the associated La Tuna amphibolites have composition similar to N-MORB. Furthermore, the trace element composition of zircon in the metasomatites is consistent with an oceanic environment (U/Yb < 0.1). Geotectonically, the La Tuna metasomatites formed at 743 ± 2 Ma in an oceanic setting, most likely in a juvenile Adamastor Ocean basin. During the collisional stage of the Brasiliano Orogeny, the La Tuna Ophiolite was tectonically emplaced within the <666 Ma La Micaela Schist of the Paso del Dragon ́ Complex. As such, this study on the La Tuna Ophiolite contributes direct evidence on the oceanic evolution leading up to the accretionary stage of the Brasiliano Orogeny and provides new constraints on the transition towards the collisional stage.
Millennial-scale variability of water supply, vegetation and fire activity on a tropical wetland in central Brazil.
(2023) Cassino, Raquel Franco; Sabino, Shirley Maria Lima; Caixeta, Mariana Letícia; Oliveira, Diego Alves de; Gomes, Makênia Oliveira Soares; Sant’Anna, Eneida Maria Eskinazi; Augustin, Cristina Helena Ribeiro Rocha
The Pandeiros wetland is a tropical wetland located in the ecotone between the Cerrado and the Caatinga, in central Brazil. It has a key ecological importance for vegetation biodiversity, hydrological cycles, fauna reproduction and feeding, and for local human populations. Here, we investigate millennial-scale variability of water supply, vegetation structure and fire activity in the Pandeiros wetland during the Late Holocene and discuss forcing mechanisms that affected flooding, vegetation cover and fire regime within this fragile ecosystem. Our study is based on the previously studied pollen record of the Pandeiros palm swamp and on new charcoal analyses of two sediment cores that cover the last 4500 cal years, and their comparison to modern pollen and to available paleoclimatic data. Our results show that both local rainfall at the Pandeiros River basin and southern rainfall at the upper Sao ̃ Francisco River were important in maintaining water supply for the Pandeiros wetland during the last millennia. Our data also suggest that during Late Holocene the arboreal cover declined in the Cerrado of the Pandeiros Basin, an opposite trend to that observed in the wetter Cerrado-Atlantic Forest ecotone. We propose that increasing summer insolation in Southern Hemisphere was an important factor in maintaining low arboreal cover and open savanna vegetation on the drier areas around the Pandeiros wetland. Regarding fire activity, we suggest that until around 2600 cal yr BP, climate conditions were the most important driver of fire activity, in which drier conditions favored the intensification of fire, whereas subsequently, anthropic activities appear to have become an important fire inducer. Our findings highlight the multiple environmental aspects that have influenced the Pandeiros wetland history during the last four thousand years, including monsoon variability, insolation variation and human occupation.
Mineralogical evaluation of a new global ilmenite resource from the coast of southern Brazil.
(2024) Wust, Cássia Fatima; Rizzi, Monique Aparecida Marchese; Takehara, Lucy; Queiroga, Glaucia Nascimento; Girelli, Tiago Jonatan; Chemale Júnior, Farid
The presence of superficial deposits of heavy minerals along the Rio Grande do Sul Coastal Plain has generated much interest because of their potential as a new world-class resource. A detailed mineral characterization study of sixteen samples of ilmenite concentrates from the Sao ̃ Jos ́e do Norte deposit was conducted using electronic microprobe and magnetic susceptibility analyses. The results showed that the ilmenite concentrates have a TiO2 content (54.24 wt %) consistent with a mineral assemblage dominated by primary ilmenite and hydrated ilmenite. Histograms and graphs of the variation in minor element concentrations showed enrichment in TiO2, MnO, and Cr2O3 in the altered products and loss of iron and manganese oxides during increased weathering. The alteration ratios measured by the Ti/(Ti + Fe) variation in ilmenite range from 0.50 to 0.65. The altered grains contain primary ilmenite/hydrated ilmenite and pseudorutile phase associations. Different degrees of alteration in the grains were magnetically differentiated, with a greater concentration of the alteration products in the less magnetic fractions. Those altered grains with low magnetic susceptibility may play a critical role during mining because they behave differently from fresh and unaltered grains. This study confirms that the alteration process alters the physical–chemical characteristics of the minerals. Therefore, the degree of alteration influences the metallurgical processing of this ore. The comparison with other deposits shows that the degree of ilmenite alteration of Quaternary world-class deposits is less intense than that of Pliocene to Eocene Australian deposits.
Mineralogical fingerprint of iron ore tailings in Paraopeba river bedload sediments after the B1 dam failure in Brumadinho, MG (Brazil).
(2022) Laureano, Fernando Verassani; Ribeiro, Rogerio Kwitko; Guimarães, Lorena; Leão, Lucas Pereira
The study presents SEM-based automated mineralogy to distinguish between natural sediments and iron ore tailings deposits from the Paraopeba River, after the failure of B1 Dam in Brumadinho, Minas Gerais, Brazil. Samples were obtained from borehole cores drilled over channel bars and banks eight months after the failure. After preliminary facies description, sediments from 54 chosen intervals were subjected to density measurement, X-ray diffraction (XRD), SEM-based automated mineralogy (QEMSCAN) analysis and determination of geochemical major components. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) revealed six main mineral associations governed by different contents and ratios of quartz, kaolinite and hematite. Natural sediments are predominantly composed of mineral associations containing kaolinite, quartz and quartz + hematite with density values ranging from 2.5 to 3.3 g/cm3. Tailings deposits have density values higher than 3.5 g/cm3 and are mainly composed of hematite with occasional occurrences of kaolinite + hematite. Because of geological complexity and historical terrain occupation and usage, geochemical anomalies are common in the Paraopeba River sediments. Our data suggests that mineralogical oriented studies should precede detailed geochemical investigations, to enhance the understanding of the source of such anomalies and the environmental jeopardy associated to the occurrence. In this sense, SEM-based mineralogy has an enormous potential in environment studies.
Monazite age and composition from a granite-pegmatite system : a link between pegmatites of the São João del Rei Pegmatitic Province and the newly defined high-K Restinga Metagranite, Minas Gerais, Brazil.
(2023) Sousa, Sarah Siqueira da Cruz Guimarães; Ávila, Ciro Alexandre; Neumann, Reiner; Faulstich, Fabiano Richard Leite; Cipriano, Ricardo Augusto Scholz
Monazite geochronology (U–Pb by LA–SF–ICP-MS) and chemical composition by electron microprobe were used to characterize the genetic link between a group of pegmatites from the São João del Rei Pegmatitic Province and a newly defined high-K metagranite of the younger Rhyacian-Orosirian Ritapolis ́ magmatic arc of the Mineiro Belt. The monazite-(Ce) of four samples from the granite and ten from pegmatites yielded the REE pattern of a granite-pegmatite system, where the ∑LREE is similar, but the content of MREE, and Dy increase with the diminution of the crystallization temperature and, consequently, presenting a higher degree of differentiation. The monazite ages of 2022 ± 17 Ma and 2008 ± 8 Ma in the pegmatites correspond to a new event of crystallization of these bodies in the São João del Rei Pegmatitic Province. These pegmatites have a remarkable amount of xenotime and monazite (and absence of cassiterite) and have been characterized as REE-enriched pegmatites. These bodies are connected to the crystallization of an Orosirian high-K metagranite, which has a monazite crystallization age of 2018 ± 31 Ma. This metagranite, proposed here to be named as “Restinga Metagranite”, represents a new and the youngest pluton of the Mineiro Belt, increasing in 90 Ma the evolution time of the Ritapolis ́ magmatic arc (2.19–2.02 Ga), and the Mineiro Belt (2.47–2.02 Ga).
Modelagem dos níveis de base fluviais da bacia do rio Jacuípe, nordeste semiárido do Brasil.
(2023) Guillén, Anais del Jesús González; Nolasco, Marjorie Csekö; Castro, Paulo de Tarso Amorim
O presente artigo visou modelar espacialmente os níveis de base do rio Jacuípe e seus afluentes, localizados no estado da Bahia, Brasil. Para isso, implementaram-se produtos de sensoriamento remoto e técnicas de geoprocessamento num ambiente de Sistema de Informações Geográficas, no intuito de reconhecer automaticamente a distribuição das anomalias fluviais; determinar seus condicionantes estruturais, tectônicos, litológicos, hidrológicos e antrópicos, através de mapas temáticos de índices estruturais (Mapa de Lineamentos, Densidade de Lineamentos, Frequência de Lineamentos) e geomorfológicos (Densidade de Drenagem e Frequência de Fluxo), que foram integrados a partir da Lógica Fuzzy e da Análise Hierárquica de Processos (AHP), assim como mapas morfotectônicos (Fator de Assimetria da Bacia de Drenagem e Fator de Assimetria Topográfica Transversal) e mapas geológicos combinados com imagens orbitais do Google Earth Pro; e estabelecer as possíveis relações entre as variações dos níveis de base com a neotectônica através de dados sísmicos. Entre os principais resultados, identificaram-se 1.634 anomalias de drenagem de 2a ordem e 101 de 1a ordem, concentrando-se 90% destas últimas no alto curso. Houve um notável controle estrutural e tectônico na formação das anomalias e não se registraram indícios da ação neotectônica relacionados à reativação de falhas e à formação de knickpoints.
Multi-method characterization of rare blue quartz-bearing metavolcanic rocks of the Rio dos Remédios Group, Paramirim Aulacogen, NE Brazil.
(2023) Silva, Danielle Cruz da; Santos, Lauro Cézar Montefalco de Lira; Queiroga, Gláucia Nascimento; Santos, Glenda Lira; Tedeschi, Mahyra
The Rio dos Remédios Group comprises a supracrustal sequence that occupies the base of the Espinhaço Supergroup, São Francisco Craton, Brazil. Its basal formation, Novo Horizonte, crops out in the Paramirim region mainly as metavolcanic rocks that represent one of the fewer occurrences of blue quartz phenocrysts in South America. Their mineralogy consists of quartz and K-feldspar phenocrysts, whereas biotite, muscovite, fluorite, allanite, chlorite, sericite, zircon, and opaque phases occur immersed in a quartz-feldspar-rich groundmass. Such hetero-geneous composition is also supported by x-ray diffraction and chemical data. Electron probe microanalysis in some samples revealed the presence of two distinct groups of biotite (magmatic and neoformed), in addition to the presence of iron-rich white mica and almost pure orthoclase feldspar. Our data suggest that the studied metavolcanic rocks have maintained their magmatic characteristics, which were progressively overprinted by hydrothermal fluids and ductile-to-brittle deformation. The magmatic mineralogy is akin to strongly peraluminous and alkaline magmas, common in anorogenic settings – a fertile site for the origin of blue quartz-bearing rocks worldwide.
A new condensed freshwater-brackish water bivalve-dominated assemblage in the Aptian Crato Formation, Araripe Basin, NE Brazil and its paleoenvironmental significance.
(2024) Silva, Victor Ribeiro da; Varejão, Filipe Giovanini; Matos, Suzana Aparecida; Rodrigues, Mariza Gomes; Warren, Lucas Veríssimo; Assine, Mario Luis; Fürsich, Franz Theodor; Simões, Marcello Guimarães
The known occurrences of Early Cretaceous freshwater bivalves in the Araripe Basin are confined to the 0.85- to 2-m-thick Caldas Bed of the Crato Formation. Herein, we record a new bivalve-dominated assemblage in a siltstone bed nearly 30 m below the upper boundary with the overlying Romualdo Formation. The assemblage is composed of ecologically incompatible bivalve mollusk species, being dominated by tiny individuals of Modiolus? sp., a brackish water form. These are directly associated with the freshwater bivalves Araripenaia elliptica and Monginellopsis bellaradiata, the latter two species commonly found in the Caldas Bed. Those bivalves are mixed with carbonized, partially comminuted plant remains. Specimens of Modiolus? sp. are usually articulated and are dispersed to loosely packed or forming cm-long clusters. A few shells of the freshwater forms are also articulated. The bivalves lived in a semi-confined embayment setting with fluctuating salinity. Background brackish water conditions must have existed long enough for the Modiolus? sp. larvae to settle and develop as juvenile individuals. Rapid salinity fluctuations associated with sea level and climate variations allowed A. elliptica and M. bellaradiata to thrive in the same area. Hence, the numerically dominant shells of the brackish water forms and the freshwater bivalves have been telescoped into the same bedding plane, generating an environmentally condensed, time averaged benthic assemblage. Finally, the presence of these taxa considerably expands the vertical/temporal distribution of bivalve mollusks within the Crato Formation.
Origin and significance of macroscopic organic aggregates from the lacustrine Aptian Crato Konservat-Lagerstätte.
(2024) Varejão, Filipe Giovanini; Warren, Lucas Veríssimo; Rodrigues, Mariza Gomes; Assine, Mario Luis; Simões, Marcello Guimarães
The Crato Konservat-Lagerstätte is one of the main Mesozoic fossil sites from Gondwana, recording a wide diversity of terrestrial and non-marine aquatic fossils of great paleobiological and evolutionary significance. This conservation deposit is recorded in a 9 m-thick interval of laminite, microbialite, and grainstone deposited in a lake system with variable water level, alternating moments of hypersaline and freshwater conditions. Despite numerous studies describing new species of plants, arthropods, fish, pterosaurs, birds, and many others, there remains a significant gap in our understanding of the most common and archetypal fossils, which are the rod-shaped macrofossils found on bedding surfaces in distinct stratigraphic intervals of the Crato Konservat-Lagerstätte. The rodshaped macrofossils are up to 1.6 cm-long and 0.1 cm-wide, straight to curved compressions that preserve pyritized microfossils. Here we interpret the rod-shaped macrofossils as macroscopic organic aggregates that sank into the lakebed in a process called lake snow. During high organic productivity periods in the epilimnion, planktonic organisms thrived and produced exopolymers responsible for aggregation. Their concentrations in the limestone bedding planes reflect intensity of lake snow and environmental seasonality. Aggregates are prolate particles that are commonly oriented, suggesting their transport as bedload for short distances, which was facilitated by biostabilization by microbes and their exopolymers. Finally, pyritization was mediated by microbial communities living in the lakebed.
Mica in a sedimentary feature as evidence of humid conditions for a classic desert in Paraná Basin, southern Brazil.
(2023) Silva, Isaque Conceição Rodrigues da; Mizusaki, Ana Maria Pimentel; Queiroga, Gláucia Nascimento; Michelin, Cassiana Roberta Lizzoni; Rios, Fernando R.
In Paraná Basin, oriented mica appears into horizontal layered fine sediments feature defined as geodes with sediments. Mica is identified as biotite in a volcano-sedimentary context of Botucatu and Serra Geral formations. Throughout the accomplishment of multiple analyses such as petrography, rock chemical evaluation, Rare Earth Elements (REE) values and also the Chemical Index of Alteration (CIA) some contributions for local paleoenvironment and paleoweathering for the classic Botucatu paleodesert is proposed. Since biotite is not regular in sediments of a desert environment, the mica presence suggests that it was transported by aqueous input and deposited within the provided spaces. The arrangement of these sediments as planar cross-stratification also confirms that this process is water dependent, otherwise the preservation of the layers’ horizontality would not be preserved. The REE results of negative Ce (Cerium) anomaly in some features, geochemically implies the contribution of water column during deposition. Some geodes are intensely silicified, and in these, there is a relative preservation of Ce attributed to an intense siliceous cementation, avoiding the oxidation of Ce. Despite some differences in Ce values, these features hold similar REE patterns and CIA values indicating similar provenance for the geodes’ sediments and they were probably deposited under similar chemical conditions. The Ce difference between the slightly silicified and intensely silicified geodes shows local conditions for the values, influenced by the presence of water presence and silicification.
A method for estimating paleotemperatures from pollen assemblages applied to the quantification of the Early Holocene warming in Central Brazil.
(2023) Cassino, Raquel Franco
This study presents a method for the quantification of paleotemperatures from pollen records based on the predominant leaf margin trait of the genera represented in the pollen assemblages. The method presented here uses the well-known and widely used relationship between leaf margin and mean annual temperature, which is commonly applied to macrofloras to reconstruct paleotemperatures. Here, genera occurring in the arboreal vegetation of Central Brazil were analyzed respective to the presence or absence of species bearing toothed leaves. Using floristic surveys, a correlation between the proportion of genera without toothed species and the mean annual temperature was investigated. A positive linear correlation between these two variables was found for forest sites, but not for the arboreal savannas. The equation derived from the linear regression between the two variables - proportion of genera without toothed species and mean annual temperature (MAT) - was applied to pollen assemblages collected on forest sites. The equation was used to calculate estimated MATs for surface samples in order to test the validity of its application to pollen assemblages. The equation was then applied to fossil records to estimate paleoMATs for two Brazilian sites located respectively at 15.5◦ and 28◦ of latitude, during the Pleistocene-Holocene transition (between 13.6 and 10 kyr cal BP). While MAT increases of around 3 ◦C were found for the higher latitude site, no significant differences between final Pleistocene and early Holocene MATs were found for the near-equatorial site.
Mantle metasomatism and refertilization beneath the SW margin of the São Francisco Craton, Brazil.
(2023) Rodrigues, Rodrigo Antonio de Freitas; Gervasoni, Fernanda; Jalowitzki, Tiago Luis Reis; Bussweiler, Yannick; Berndt, Jasper; Botelho, Nilson Francisquini; Queiroga, Gláucia Nascimento; Castro, Marcos Paulo de; Silva, Sebastiao William da; Araujo, Brunno Abilio Ciriaco; Oliveira, Ítalo Lopes de; Klemme, Stephan
A suite of kimberlite-hosted mantle xenoliths from the Catalao ̃ region, southwestern margin of the São Francisco Craton (SFC), Brazil, consists of spinel lherzolites (type I and II) and garnet-phlogopite wehrlites. The chemical composition of these xenoliths provides evidence of enrichment and refertilization of the SFC lithosphere which were caused by distinct metasomatic agents. Garnet-phlogopite wehrlites have porphyroclastic textures and were equilibrated between 1005 and 1010 ◦C and 2.9–3.0 GPa (~99 km). They record metasomatism caused by carbonatite and proto-kimberlite melts. Type I spinel lherzolite contains spinel-pyroxene symplectites indicating garnet destabilization due to variations of the P-T conditions. The minerals in this rock were equilibrated between 975 and 990 ◦C and their chemical compositions contain evidence for carbonatite metasomatism. High-Cr and low-Al clinopyroxene of garnet-phlogopite wehrlites and type I spinel lherzolite have high Mg#, Ca/Al, La/YbN, Zr/Hf ratios, and high Sr contents, coupled with low to intermediate Ti/Eu and Ti/Nb, which also suggests that they were formed by carbonatite melt. These geochemical features, together with the presence of carbonate inclusions in the olivines, corroborate the interaction with carbonatite melt. The low-Ti-Cr phlogopite (Phl1), which is restricted to only the garnet-phlogopite wehrlites, was probably produced through the release of volatiles components from the carbonatite melt that reacted with garnet porphyroclasts. Furthermore, metasomatic reactions involving garnet-phlogopite wehrlites and a proto-kimberlite melt formed high-Ti-Cr phlogopite (Phl2), consuming the original phlogopite (Phl1). Phl2 occurs as rims around Phl1, as isolated flakes around garnets, and in the matrix of wehrlites. Therefore, we assume that the proto-kimberlite metasomatism responsible for generation of Phl2 occurred prior to the eruption of the host kimberlite magma. Conversely, type II spinel lherzolites (876–915 ◦C; ~1.5 GPa) contain evidence of metasomatic reactions with silicate melts. These samples have high cpx/opx ratios (1.10–2.93) with low-Cr and high-Al clinopyroxene, and depleted incompatible trace element compositions. Some clinopyroxene crystals, however, show some enrichment in light rare earth elements (LREE), large ion lithophile elements (LILE), and Ti. Their low Ca/Al, La/YbN, and Zr/Hf, low Sr contents, high Ti/Eu and Ti/Nb, and a strong positive correlation of Ti with the other high field strength elements (HFSE) and LREE, may indicate that these clinopyroxene crystals were formed by refertilization caused by a silicate melt that was depleted in incompatible elements. Overall, these metasomatic processes suggest a pervasive refertilization of the cratonic lithosphere where the typically depleted peridotites of cratonic regions were replaced by a pyroxene-rich lithology.

Navegar

Submissões Recentes