EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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9 resultados
Resultados da Pesquisa
Item Peritidal microbialites in the upper Araras Group : Morphotypes, potential preservation and the relation with the Ediacaran-Cambrian unconformity in the Araras-Alto Paraguai Basin, southern Amazon Craton.(2022) Romero, Guilherme Raffaeli; Santos, Renan Fernandes dos; Nogueira, Afonso César Rodrigues; Rudnitzki, Isaac Daniel; Fairchild, Thomas RichThe Proterozoic biosphere was dominated by shallow-marine and intertidal bacterial biota, as evident from a robust record of microbialites in carbonate rocks. The lower Ediacaran successions in the southeastern Amazon Craton, Brazil represented by carbonates rocks of the Araras Group, record excellent occurrences of microbialites implying significant evidence for shallow marine colonization post-Snowball Earth Events (∼635 Ma). Microbialites occur at the lower and upper units of this group -Mirassol D'Oeste and Nobres, respectively with the lower associated to the Marinoan glaciation event. The upper unit, Nobres Formation, is here described with outcrop-based facies analysis discontinuously exposed in the Araras-Alto Paraguai basin. This allowed the paleoenvironmental reconstructions of the carbonate peritidal settings, organized in tidal flats and sabkha meter-scale cycles. Fifteen levels of microbialites have been described, with 4 morphotype associations. These microbialites colonized upper tidal flat zones forming stromatolite deposits of bulbous domes, stratiform, pseudo-columnar, and “cerebroid” forms. The recurrent cyclicity indicates a residence time of hydrodynamic and climatic variations for a long time producing minimum morphological changes without any decline evidence. In addition, no metazoan competition was observed in these strata. The siliciclastic inflow observed in the top of Nobres Formation is interpreted as seasonal variations that imprint turbidity in the shallow waters causing a diversification of the morphology of microbialites. The microbialite record in the Nobres Formation do not show any evolutionary trend or apparent decline, that has been attributed to the evolution of substrate-modifying metazoans, but suggest a continuous record truncated by the Ediacaran-Cambrian unconformity found at the upper portion of the Araras Group.Item Permian mixed carbonate–siliciclastic lagoon coastal system in West-Central Gondwana.(2021) Silva, Rafael Oliveira; Leite, Mariangela Garcia Praça; Rudnitzki, Isaac Daniel; Lima, Wagner SouzaAlthough in recent years mixed carbonate–siliciclastic platforms have been increasingly recognized in the Perm- ian of Western Gondwana, there is no detailed description of these mixed systems in West-Central Gondwana. This study focuses on the Permian of the Sergipe–Alagoas Basin (NE Brazil), with the aim of filling this knowledge gap. Based on sedimentological data and microfacies analysis, six facies associations (FA) were identified: FA1 is an eolian–fluvial system, composed of stratified sandstones, FA2 and FA3 represent a mixed tidal flat–lagoon sys- tem composed of microbialites, pelitic/micritic sediments and intraclastic packstones, FA4 represents shoreface wave deposits composed of laminated sandstones and silicified grainstones, and FA5 and FA6 are interpreted as a barrier–tidal inlet system, composed of oolitic/intraclastic grainstones, subtidal microbialites, and mixed rudstones. Facies associations reflect the paleoenvironmental conditions of a coastal environment, with dunes and small rivers adjacent to a mixed carbonate–siliciclastic ramp. This is defined as a lagoon system associated with tidal flats protected from the high-energy region by carbonate shoals and microbial constructions. These de- posits represent the eastern portion of a shallow epicontinental sea that covered lowlands inWest-Central Gond- wana within the arid–semiarid belt, whose climate characteristics are reflected in eolian deposits, desiccation structures, mixed carbonate–siliciclastic facies, and fossil records. The main diagenetic feature observed in petro- graphic analyses was an early diagenetic silicification. Although the absence of spiculites and shelf configuration did not allow a correlation with the Permian glass ramp model, similarities were observed with Eocene glass ramps of Australia, and a relationship with the Permian Chert Event is suggested.Item Aspectos diagenéticos dos carbonatos da Formação Itaituba, norte da Bacia do Amazonas.(2021) Sousa, Elane Sampaio de; Barbosa, Roberto Cesar de Mendonça; Rudnitzki, Isaac DanielA Formação Itaituba da Bacia do Amazonas é considerada o principal intervalo selante do sistema petrolífero Barreirinha-Monte Alegre e grande parte dos dados microfaciológicos são oriundos de exposições na borda sul da bacia. Entretanto, a identificação de intervalos porosos desta unidade na borda norte tem fomentado avaliações para desvendar como os processos diagenéticos influenciaram na preservação do sistema poroso e o real papel da Formação Itaituba no sistema petrolífero. Nesse sentido, 80 seções delgadas confeccionadas a partir de amostras coletadas na borda norte da bacia, região de Urucará (AM), foram alvo de avaliação petrográfica que indicam que os principais processos diagenéticos são representados pela micritização, cimentação, neomorfismo, dolomitização, compactação física, silicificação, piritização, dissolução, desdolomitização e compactação química, atuando principalmente no contexto diagenético raso (meteórico e marinho). Os principais processos diagenéticos responsáveis pela geração de porosidade estão associados à dissolução seletiva meteórica que podem ampliar o volume poroso em até 20% quando associados a grainstones, o que abre perspectiva sobre heterogeneidade da unidade e um comportamento duplo como selante e reservatório.Item Insights into vase-shaped microfossil diversity and Neoproterozoic biostratigraphy in light of recent Brazilian discoveries.(2019) Soares, Luana Pereira Costa de Morais; Lahr, Daniel José Galafasse; Rudnitzki, Isaac Daniel; Freitas, Bernardo Tavares; Romero, Guilherme Raffaeli; Porter, Susannah M.; Knoll, Andrew H.; Fairchild, Thomas RichVase-shaped microfossils (VSMs) occur in dolostone clasts within conglomerates, breccias, and diamictites of the Neoproterozoic Urucum Formation, Jacadigo Group, southwest Brazil. Although their taphonomic history is distinct from those of other VSM assemblages, morphometric comparison of Urucum fossils with five others described previously from North America and Europe show that two of the Urucum species—the long-necked Limeta lageniformis Morais, Fairchild, and Lahr in Morais et al., 2017 and the funnel-necked Palaeoamphora urucumense Morais et al., 2017—occur in the Kwagunt and Callison Lake assemblages, as does Pakupaku kabin Riedman, Porter, and Calver, 2017 recently described from the Togari Group, Tasmania. Obelix rootsii (Cohen, Irvine, and Strauss, 2017) new combination, previously known only from the Callison Lake Formation, is documented here from the Kwagunt Formation. In addition, Trigonocyrillium horodyskii (Bloeser, 1985) and Bonniea dacruchares Porter, Meisterfeld, and Knoll, 2003, first described from the Kwagunt assemblage, have now been found in the Urucum Formation. In light of this survey, 16 of the 18 validly described VSM species are now known to occur in the Kwagunt Formation and 13 in the Callison Lake Formation, with 12 of them shared by both formations. The fact that the Urucum VSM assemblage exhibits six of seven species in common with the Kwagunt Formation—L. lageniformis, P. urucumense, Cycliocyrillium simplex Porter, Meisterfeld, and Knoll, 2003, C. torquata Porter, Meisterfeld, and Knoll, 2003, B. dacruchares Porter, Meisterfeld, and Knoll, 2003, and T. horodyskii (Bloeser, 1985)—and all but the last of these in common with the Callison Lake Formation supports correlation of these three assemblages and indicates that the source of the fossiliferous clasts within the Urucum Formation may well have been a now-vanished late Tonian carbonate platform.Item Ecological interactions in Cloudina from the Ediacaran of Brazil : implications for the rise of animal biomineralization.(2017) Kerber, Bruno Becker; Pacheco, Mírian Liza Alves Forancelli; Rudnitzki, Isaac Daniel; Galante, Douglas; Rodrigues, Fabio; Leme, Juliana de MoraesAt the Ediacaran/Cambrian boundary, ecosystems witnessed an unparalleled biological innovation: the appearance of shelled animals. Here, we report new paleoecological and paleobiological data on Cloudina, which was one of the most abundant shelled animals at the end of the Ediacaran. We report the close association of Cloudina tubes with microbial mat textures as well as organic-rich material, syndepositional calcite and goethite cement between their flanges, thus reinforcing the awareness of metazoan/microorganism interactions at the end of the Ediacaran. The preservation of in situ tubes suggests a great plasticity of substrate utilization, with evidence of different life modes and avoidance behavior. Geochemical analysis revealed walls composed of two secondary laminae and organic sheets. Some walls presented boreholes that are here described as predation marks. Taken together, these data add further information regarding the structuring of shelled animal communities in marine ecosystems.Item Ichnologic evidence of a Cambrian age in the southern Amazon Craton : implications for the onset of the Western Gondwana history.(2017) Santos, Hudson Pereira; Mángano, Maria Gabriela; Soares, Joelson Lima; Nogueira, Afonso César Rodrigues; Bandeira, José; Rudnitzki, Isaac DanielColonization of the infaunal ecospace by burrowing bilaterians is one of the most important behavioral innovations during the Ediacaran-Cambrian transition. The establishment of vertical burrows by suspension feeders in high-energy nearshore settings during Cambrian Age 2 is reflected by the appearance of the Skolithos Ichnofacies. For the first time, unquestionable vertical burrows typical of the Skolithos Ichnofacies, such as Skolithos linearis, Diplocraterion parallelum and Arenicolites isp., are recorded from nearshore siliciclastic deposits of the Raizama Formation, southeastern Amazon Craton, Brazil. Integration of ichnologic and sedimentologic datasets suggests that these trace fossils record colonization of high-energy and well-oxygenated nearshore sandy environments. Chronostratigraphically, the presence of these vertical burrows indicates an age not older than early Cambrian for the Raizama Formation, which traditionally has been regarded as Ediacaran. Therefore, the Raizama ichnofauna illustrates the advent of modern Phanerozoic ecology marked by the Agronomic Revolution. The discovery of the Skolithos Ichnofacies in these shallow-marine strata suggests possible connections between some central Western Gondwana basins.Item Deciphering pyritization-kerogenization gradient for fish soft-tissue preservation.(2017) Osés, Gabriel Ladeira; Voltani, Cibele Gasparelo; Prado, Gustavo Marcondes Evangelista Martins; Galante, Douglas; Rizzutto, Márcia de Almeida; Rudnitzki, Isaac Daniel; Silva, Evandro Pereira da; Rodrigues, Fabio; Rangel, Elidiane Cipriano; Rendón, Paula Andréa Sucerquia; Pacheco, Mírian Liza Alves ForancelliSoft-tissue preservation provides palaeobiological information that is otherwise lost during fossilization. In Brazil, the Early Cretaceous Santana Formation contains fish with integument, muscles, connective tissues, and eyes that are still preserved. Our study revealed that soft-tissues were pyritized or kerogenized in different microfacies, which yielded distinct preservation fidelities. Indeed, new data provided the first record of pyritized vertebrate muscles and eyes. We propose that the different taphonomic pathways were controlled by distinct sedimentation rates in two different microfacies. Through this process, carcasses deposited in each of these microfacies underwent different residence times in sulphate-reduction and methanogenesis zones, thus yielding pyritized or kerogenized softtissues, and a similar process has previously been suggested in studies of a late Ediacaran lagerstätte.Item Carbonaceous and siliceous Neoproterozoic vase-shaped microfossils (Urucum Formation, Brazil) and the question of early protistan biomineralization.(2017) Soares, Luana Pereira Costa de Morais; Fairchild, Thomas Rich; Lahr, Daniel José Galafasse; Rudnitzki, Isaac Daniel; Schopf, James William; Garcia, Amanda K.; Kudryavtsev, Anatoliy B.; Romero, Guilherme RaffaeliVase-shaped microfossils (VSMs) occur in dolomitic extraclasts of indeterminate provenance within the basal diamictite of the Neoproterozoic Urucum Formation (Jacadigo Group) of west-central Brazil, having an age constrained between 889±44 Ma (K-Ar; basement rocks) and 587±7 Ma (40Ar/39Ar age of early metamorphic cryptomelane in overlying manganese ore). Early isopachous carbonate cement entombed these VSMs, preserving rare direct evidence of original wall composition that is carbonaceous (now kerogenous) in practically all specimens. Some tests are siliceous or composed of a quartz-kerogen mixture; secondary replacement explains some features of these tests, but original biomineralization seems more likely for others. This interpretation, coupled with test morphology, suggests affinity to arcellinid testate amoebae. Five VSM taxa are recognized in the deposit: Cycliocyrillium simplex Porter, Meisterfeld, and Knoll, 2003, and C. torquata Porter, Meisterfeld, and Knoll, 2003, originally described in the Chuar Group (USA), and three new monospecific genera—Palaeoamphora urucumense n. gen. n. sp., Limeta lageniformis n. gen. n. sp., and Taruma rata n. gen. n. sp. Most of the taxonomically important characteristics of these VSMs occur also in extant testate amoebae, but the combinations of some characters, such as organic-walled tests having exceptionally long necks that exhibit terminal apertures (L. lageniformis n. gen. n. sp.), are evidently novel additions to the known diversity of Neoproterozoic VSMs. Evidence of glacially influenced deposition in the conformably overlying Santa Cruz Formation may indicate that the Urucum Formation slightly preceded or was penecontemporaneous with a major Neoproterozoic glaciation, although the VSM-hosting extraclasts must be older, possibly rivaling the age of the testate amoebae of the Chichkan Formation (766±7 Ma) that are currently regarded as the oldest record of protists in the geological record.Item Geobiological and diagenetic insights from Malvinokaffric devonian biota (Chapada Group, Paraná Basin, Brazil) : paleobiological and paleoenvironmental implications.(2017) Kerber, Bruno Becker; Osés, Gabriel Ladeira; Curado, Jessica Fleury; Rizzutto, Márcia de Almeida; Rudnitzki, Isaac Daniel; Romero, Guilherme Raffaeli; Alves, Silvio Yuji Onary; Benini, Victoria Giopato; Galante, Douglas; Rodrigues, Fabio; Buck, Pedro Victor; Rangel, Elidiane Cipriano; Ghilardi, Renato Pirani; Pacheco, Mírian Liza Alves ForancelliThis study tests the presence of differential preservation in the Devonian Malvinokaffric fauna from the Chapada Group (Parana´ Basin, Brazil). Results of EDXRF, EDS, Raman Spectroscopy, and petrographic analyses show differential preservation of shells that were originally calcite as hematite and goethite fossils, while organisms with original calcium phosphate shells tend to be preserved inside phosphatic concretions. Both preservation types are commonly associated with pseudoframboids, while calcium sulfate minerals are commonly associated with hematized fossils. From this evidence, a diagenetic model for these fossils is proposed. The model includes an early diagenetic phase (characterized by anaerobic sulfate reduction and precipitation of pyrite and carbonate-fluorapatite) and a second, near-surface chemical weathering phase (characterized by the oxidation of pyrite and precipitation of iron oxyhydroxides and calcium sulfates). Acidic conditions in both phases may account for the dissolution of less stable minerals compared to calcium phosphate. It is considered that this model may assist in understanding other similarly preserved biotas, as well as enhancing understanding of the taphonomic overprint that may occur within this important and endemic Devonian biota.