Edi Guimarães

University of Brasília | UnB · Institute of Geosciences

The recovery of microfossils from Proterozoic rocks is commonly challenging because of metamorphism. In this study, an application of different methods usually applied on Phanerozoic rocks to test efficiency on recovering microfossil from Proterozoic units is presented. Chemical, physical, and biological factors can influence the recovery of microf...

Ultramafic (UM) rocks are defined as igneous rocks that contain more than 90% of mafic minerals. Soils derived from ultramafic rock are generally nutrient-deficient and have concomitant high concentrations of potentially phytotoxic trace elements (Ni, Cr, Co, Mn). Consequently, to assess the dynamics of nutrients and metals in the ultramafic complex o...

Este estudio presenta una actualización del registro isotópico de la Formación de Tamengo, parte superior del Grupo Corumbá, que se encuentra en la parte meridional del Cinturón Paraguayo. Este trabajo incluye cortes estratigráficos detallados enlazados con la geoquímica de alta resolución δ13C y δ18O de dos yacimientos mineros cercanos a Corumbá (...

Se presenta en este trabajo el análisis paleontológico de 26 especies fósiles muestradas en cinco cortes de las Formaciones de Tamengo y Guaicurus en las regines de Corumbá y Ladário: canteras de Corcal y Laginha, Porto Sobramil, Porto Figueiras y Ecoparque Cacimba. Además, se añaden varias interpretaciones paleoecológicas y ambientales, basadas en...

A caracterização mineral e geoquímica de pelitos das formações Serra de Santa Helena (FSSH) e Serra da Saudade (FSS) podem contribuir para a interpretação da evolução da bacia de deposição do Grupo Bambuí, que tem sido considerada como do tipo foreland relacionada à Orogênese Brasiliana. Assim, este trabalho visa comparar a composição dos pelitos a...

The Tamengo Formation is mainly composed of dark, organic rich limestones, marls with occasional Cloudina lucianoi (Beurlen & Sommer, 1957) and intercalated layers of siltstone with occurrences of Corumbella werneri Hahn et al., 1982 and scarce occurrence of Cloudina carinata Cortijo et al., 2010. The Cloudina genus has nine species described over...

This work aimed to contribute in the sedimentometric study of the Riacho Fundo stream, affluent of Lake Paranoá, Brasília, Federal District, and historically the main sediments exporter for the entire basin. For this purpose, the flow was measured by the acoustic method with the Sontek River Surveyour M9 equipment and an automatic sampler ISCO 6712...

Source rocks from the Alagamar Formation were analysed and fifteen non-marine ostracod species and one foraminifer species were identified. Thecamoebians, gastropods, fish teeth and incertae sedis material also occurred. Among these fossils, an agglutinated foraminifer, Gaudryinella sp. aff. G. sherlocki, and occurrences of foraminiferal organic li...

Ultramafic (UM) rocks are known to be nickel (Ni) rich and to weather quickly, which makes them a good candidate to look at the Ni isotope systematics during weathering processes at the Earth’s surface. The present study aims at identifying the Ni solid speciation and discussing the weathering processes that produce Ni isotope fractionation in two...

The genus Cloudina Germs, 1972 includes seven species restricted to Ediacaran strata: 1. Cloudina lucianoi (Beurlen and Sommer, 1957) (Tamengo Formation, Brazil); 2. Cloudina hartmanae Germs, 1972 (Nama Group, Namibia); 3. Cloudina riemkeae Germs, 1972 (Nama Group, Namibia; 4. Cloudina waldei Hahn and Pflug, 1985 (Tamengo Formation, Brazil); 5. Clo...

A simple synthesis method of chitosan-functionalized Fe3O4single bondAu (Chit-Fe3O4@Au) nanoparticles (NPs) was developed. This method involves preparation of oleic acid-coated Fe3O4 (OA-Fe3O4) NPs as a precursor in step one, followed by functionalization with chitosan to obtain Chit-Fe3O4@Au NPs. Structural and magnetic properties of both synthesi...

Magnetic interaction of the magnetite (Fe3O4) nanoparticles grown on zeolite has been studied. XRD patterns show that in the presence of 25–75 mg of zeolite the average particle size of Fe3O4 decreases to ≈ 6 nm, but with the increase of zeolite content (75 mg < x < 200 mg) the Fe3O4 particles have 10.6 nm in size saturating to 3 nm above 180 mg. A...

We have studied the stoichiometry of magnetite nanoparticles using three spectroscopic techniques: Mössbauer, photoacoustic and ferromagnetic resonance (FMR). By varying the weight ratio of the Fe precursor to the reducing agent (sodium acetate) and a post-synthesis annealing, we were able to synthesize samples with different amounts of Fe vacancie...

Stabilized gold nanoparticles (Au NPs) were prepared with 4: 2.6 Au to buthyldithiol stoichiometry using modified Brust synthesis. The size of the particles falls into the 1.3–4 nm range in which the molecular cluster − metallic particle transition takes place. Stabilized particles were characterized by transmission electron microscopy (TEM/HRTEM)....

Layered double hydroxides (LDHs) are one of the very important nano-carriers for drug delivery, due to their many advantageous features, such as the ease and low-cost of preparation, low cytotoxicity, good biocompatibility, protection for the intercalated drugs, and the capacity to facilitate the uptake of the loaded drug in the cells. In our previ...

Nucleation and growth mechanism of iron oxide nanoparticles on zeolite template and their stability dependence are reported. Hyperfine field resulting from the variation of particle size indicates the effect of zeolite on particles growth; particle size decreases at lower concentration of zeolite. At higher concentration, a fraction of nano Fe 3 O...

Este trabalho mostra que Cloudina lucianoi (Beurlen & Sommer, 1957) quando comparada com as outras seis do gênero, é a única que guarda inúmeras similaridades com Cloudina hartmannae. Se a detalhada revisão de Cloudina hartmannae em andamento revelar que esta espécie é um sinônimo júnior de Cloudina lucianoi, este novo conceito leva a admitir que C...

The Proterozoic sequences in the North of Distrito Federal (Brazil) and in Bezerra and Vila Boa regions (Goiás) comprise carbonates, pelites and sandstones from Bambuí and Paranoá Groups. In Distrito Federal, such units are tectonically overlapped by metasediments of green schist facies of Canastra Group. Among the mineral constituents of the pelit...

This study aims to update the knowledge about the importance of the late Ediacaran fossil record and geochemical data from Corumbá, State of Mato Grosso do Sul, at the Brazilian-Bolivian border. The Corumbá graben system is located near a triple junction developed above a hot spot of two young (545-480 Ma) Brasiliano provinces: the mostly Bolivian...

Secondary jarosite and water-soluble iron-sulfate minerals control the composition of acid mine waters formed by the oxidation of sulfide in tailings impoundments at the (Zn-Pb-Ag) Pan de Azucar mine located in the Pozuelos Lagoon Basin (semi-arid climate) in Northwest (NW) Argentina. In the primary zone of the tailings (9.5 wt % pyrite-marcasite)...

This paper discusses the chemistry of clays and their use as raw material to produce pottery and advanced ceramic materials, approaching historical, social and economic aspects. In order to describe the process of transforming clay into ceramic a handcraft pottery production was studied. It was identified by X-ray the main minerals presented in the...

Despite high chromium concentrations in soils developed on ultramafic rocks, Cr availability is generally low, as Cr-bearing minerals are considered stable in supergene conditions. However, KH2PO4 extractions have shown high hexavalent chromium availability in Ferralsols developed on the ultramafic massif of Niquelândia (Brazil). A study combining...

The western edge of the São Francisco Basin consists of a succession of siliciclastic and carbonate rocks deposited during the Mesoproterozoic and the Neoproterozoic. This basin during the Brasiliano Orogeny was tectonically segmented into compartments without deformation and those with different intensity of deformation. The São Domingos Fault exp...

Shales and claystones in the Permian Irati Formation consist of Al-rich or Fe-Mg clay minerals in its southern/central and northern parts, respectively. The constrasting compositions indicate particular geological and paleo-environmental conditions. The purpose of this study was to determine the conditions of formation by characterizing the black s...

This study focuses on the fate of chromium during ultramafic weathering under tropical conditions. Three soils were studied along a characteristic catena on the ultramafic outcrop of Niquelândia, Brazil. In these soils, the Cr-bearing minerals are inherited chromites (15.4–26.8 wt.% Cr) and magnetites (0.4–4.8 wt.% Cr) and secondary minerals such a...

Intrusive rocks are an important heat source for the maturation of organic matter contained in sediments from the Parana Basin, South America. In this study, we have investigated the geochemical effects induced by the thermal effect of a 13-m thick basic sill intruded on carbonates and black shales of the Permian Irati Formation, which constitutes...

This survey determined the physical and chemical properties of the gravel place where urban sludge from Rio Descoberto's Water Treatment Plant is disposed. Physical, chemical and biological analysis of the soil samples (n=54), sludge samples (n=2), chemical coagulant (n=20) and samples from superficial waters (n=9) and water table (n=60) were perfo...

This survey determined the physical and chemical properties of the gravel place where urban sludge from Rio Descoberto's Water Treatment Plant is disposed. Physical, chemical and biological analysis of the soil samples (n=54), sludge samples (n=2), chemical coagulant (n=20) and samples from superficial waters (n=9) and water table (n=60) were perfo...

At Niquelândia, Cr extracted from the soil (5,000–9,300 mg.kg−1) is likely the result of the Cr-bearing Fe-oxides compared to the Cr-spinels, showing that low Cr-containing minerals present in the dunite (enstatite, olivine and clay minerals) have been completely dissolved. The chromites, accumulated inside soil profiles, have undergone chemical we...

J.S. de Alvarenga et al. 37(4 -suplemento): 999-1007, dezembro de 2007 Arquivo digital disponível on-line no site www.sbgeo.org.br 999 Variações dos isótopos de C e Sr em carbonatos pré e pós-glaciação Jequitaí (esturtiano) na região de Bezerra-Formosa, Goiás Resumo Na borda ocidental do Cráton do São Francisco são encontradas rochas carbonáticas n...

The aim this paper is to develop a methodology of lateritlc manganese identification using Imaging spectroscopy, In this study was used the Airborne Visible/InfraRed Imaging Spectrometer (AVIRIS) image, The AVIRIS Is an imaging sensor that measures the solar reflected spectrum from 400 nm to 2500 nm at 10 nm Intervals, The study area Is located at...

A Bacia Potiguar, localizada na margem equatorial brasileira, originou-se durante a fragmentação do supercontinente Gondwana no Neojurássico-Eocretáceo. A Formação Alagamar (Aptiano-Eoalbiano) é reconhecida como geradora de petróleo principalmente na parte submersa da bacia. Constituída por folhelhos ricos em matéria orgânica, carbonatos e arenitos...

Pb concentration and Pb isotopic composition are known to represent powerful tools to investigate the history of Pb pollution in water and sediments. In this paper, we present and discuss the results of a detailed study of sediments deposited in the Paranoá Lake, a 44-year-old artificial reservoir in Brasília, central Brazil. Pb concentration and i...

The Brazilian Central Plateau is constituted of the two main geomorphic surfaces: the South American surface and the Velhas surface. These surfaces were developed during the Cretaceous Superior and Tertiary and are covered by deeply weathered Latosols. The South American surface is the oldest and occupies the highest position in the landscape (950...

Much informations about the geology and chemical composition of a drainage basin is recorded in the fluvial and lacustrine sediments. The Paranoá Lake basin is formed of rocks from the Paranoá Group, which is composed of shales, overlain by sand-siltic rhytmite and quartzites. The Paranoá Lake lies on violet shales, costituted by illite and kaolini...

Soil samples from the King George Island, Antarctica, have been studied by 57 Fe Mossbauer spectroscopy, X-ray diiractometry, radiometry, neutron activation analysis and chemical analytical methods. X-ray diiractometry measurements have identiied soils containing dif-ferent v olume ratios of quartz, feldspar, chlorite as well as hematite. The diier...

Greywackes are matrix-rich sandstone, in general, containing chemically unstable minerals, which under tropical weathering conditions give origin to thick weathering profiles, depleted in base cations and rich in metals hydroxides. This work deals with a thin weathering profile developed on a proterozoic greywacke, under tropical conditions in cent...