Angélica Fortes Drummond Chicarino Varajão

Relief evolution of the Quadrilátero Ferrífero (Minas Gerais, Brazil) by means of ( 10 Be) cosmogenic nuclei

This paper investigates the evolution of the relief within the so-called Iron Quadrangle (Quadrilatero Ferrifero) in Minas Gerais, Brazil, by means of quantification of erosion processes, which affected the principal rock types of the region. The method used is based on measurement of in-situ produced cosmogenic 10Be concentration in fluvial sediments. The results indicate that the regional landscape evolution is controlled by lithotypes: the most resistant areas correspond to substrates developed on itabirites and quartzites (long-term erosion rates between 0.29 to 2.35 m/My) and, whereas the most fragile ones developed on schist-phyllites (long-term erosion rates between 7.95 to 11.82 m/My) and granite-gneisses (long-term erosion rate at 12.92 m/My).

Óxidos de ferro de solos formados sobre gnaisse do Complexo Bação, Quadrilátero Ferrífero, Minas Gerais

The objective of this work was to characterize iron oxides from B-horizons of three soil profiles developing on gneiss of the Bacao Complex geodomain in the Quadrilatero Ferrifero, Minas Gerais, Brazil. Samples were collected from the uppest, middle and lowest segments along the slope. The earth fine fractions (mean diameter, f = 2 mm) were separated for all samples. The chemical composition of the major elements was determined with the X-ray fluorescence technique; the mineralogical analysis was performed with powder X-ray diffractomer and Mossbauer spectroscopy. All samples have similar mineralogical composition, with a general occurrence corresponding to the sequence quartz >> gibbsite > kaolinite > goethite. From the 4.2 K-Mossbauer results, the coexistence of goethite (major) and hematite is confirmed. The isomorphic aluminum contents, as they were deduced from the hyperfine fields, lead to the following chemical formulas for goethites: aFe0.79Al0.21OOH (upslope), aFe0.75Al0.25OOH (midslope) and aFe0.78Al0.22OOH (downslope). The iron oxides transformation dynamics in B horizons along the slope is a useful indicator of the paleo-climatic oscillations in this area: aluminous goethite is an indicator of humid paleo-environments, whereas aluminous-poorer goethite reveals drier pedogenic conditions.

Genesis of clayey bodies in Quadrilátero Ferrı́fero, Minas Gerais, Brazil

Abstract This work deals with macromorphological, mineralogical, micromorphological and geochemical studies in clayey bodies from Quadrilatero Ferrifero in order to define their genesis and formation conditions in this geologic province from Minas Gerais State. Methodologies, based on the description of outcrops and drill cores, using X-ray diffraction (XRD), differential and gravimetric thermal analyses (DTA-TG), scanning electron microscopy (SEM), optical analysis of thin sections and chemical analyses allowed for the definition of two different genetic types of clayey bodies. One type, SET 1, occurs upon saprolitic material from Paleoproterozoic rocks in unconformity contact. It is constituted, from the base to the top, by four facies: nodular, ferruginous kaolinitic, mottled kaolinitic, and massive kaolinitic. The origin of this set is related to the deposition of lateritic materials by gravitational process. The faciological differentiation of this set is related to the syn-depositional process and postdepositional mechanisms of ferruginization and deferruginization. The second type, SET 2, is composed by an ilmenitic–kaolinitic tabular facies in discordant relationships with the saprolite material from Paleoproterozoic rocks. The origin of this second set is related to “in situ” alteration of intrusive rocks of acidic composition.

Argilas bentoníticas da península de Santa Elena, Equador: pilarização, ativação ácida e seu uso como descolorante de óleo de soja

Two samples of calcic bentonite of the Santa Elena Peninsula, Ecuador, were pillared with Al13 ions in the ratio of 10, 15 and 20 meq of Al g-1 of clay, calcinated at 573, 723 and 873 oK and acid activated with 4, 6 and 8 mol L-1 H2SO4. Analyses by X-ray diffraction, X-ray fluorescence, differential and gravimetric thermal, density, surface area and porosity, were applied in order to study the modifications occurred in the crystalline structure of the montmorillonite. The 8 mol L-1 H2SO4 acid-activated 15 meq of Al g-1 of clay at 573 oK Al-pillared samples indicated the best results in the bleaching of the soybean oil measured by UV-visible spectrophotometer.

Sedimentation and pedogenic features in a clay deposit in Quadrilátero Ferrífero, Minas Gerais, Brazil.

The clay deposit of Caxambu Hill occurs in a NW/SE oriented graben originated by syntectonic sedimentation during Cenozoic. Four facies were identified (fragmentary, nodular, massive and friable) and their differentiation is related to gravity mass-flow processes. The fragmentary facies is composed of extraclast fragments of the local Paleoproterozoic basement and sand size quartz-grains dispersed in a kaolinite-muscovite-goethitehematite matrix. The nodular facies is constituted by lithorelictal and pedorelictal nodules dispersed in a similar matrix as in the fragmentary facies. The massive facies is characterized by quartz grains dispersed in a kaolinite, hematite and goethite matrix with minor amounts of muscovite. The friable facies differs from the massive facies by its channel morphology, higher quartz and kaolinite content and the presence of millimetric clay-balls. The fragmentary facies is considered as deposited during the early stage of opening of the basin. After that, under sub-arid conditions, the slumping of lateritic materials from the surrounding regolith led to the formation of the nodular and massive facies. The friable facies was originated by the action of unidirectional flow that reworking the clayey sediments. The increasing of kaolinite content towards the top is related to the chemical weathering action after the deposition of the sediments.

A comparison of properties of clay minerals in isalteritic and in degraded facies

Abstract The mineralogical, geochemical and micromorphological features of an isalteritic clay facies, which originated from weathering of an anorthosite, were compared to those of clay facies derived from the degradation of a bauxite developed from the same rock. The isalteritic clay was formed by the hydrolytic alteration of plagioclase, whereas the degraded clays were formed by decomposition of gibbsite and neoformation of kaolinite. This resilification process resulted from the reintroduction of silica via the oscillation of the phreatic level and/or the decomposition of organic matter on the surface. The degradation process was gradual and yielded two different facies: (a) degraded clays with almost total decomposition of gibbsite, and (b) degraded clays with gibbsite nodules. Morphologically, the isalteritic clays differ from the degraded clays because they contain larger hexagonal and pseudo-hexagonal crystals. The degraded clays have more irregular crystal shapes, ranging from laths to anhedral shapes.

DENUDAÇÃO QUÍMICA E REBAIXAMENTO DO RELEVO EM BORDAS INTERPLANÁLTICAS COM SUBSTRATO GRANÍTICO: DOIS EXEMPLOS NO SE DE MINAS GERAIS

Os interfluvios entre as grandes bacias hidrograficas do Brasil oriental correspondem, muitas vezes, a degraus morfologicos que dividem planaltos escalonados. Esses degraus sao feicoes escarpadas resultantes da diferenca de intensidade dos processos erosivos nas cabeceiras dessas grandes bacias. Esse artigo apresenta um estudo da denudacao quimica em dois degraus dessas bordas interplanalticas localizadas no sudeste de Minas Gerais: (i) o degrau de Cristiano Otoni (250m) divisor das bacias dos rios Sao Francisco (terras altas ou planalto superior) e Doce (terras baixas ou planalto inferior) e, (ii) o degrau de Sao Geraldo (450m) que divide as bacias dos rios Doce (terras altas ou planalto superior) e Paraiba do Sul (terras baixas ou planalto inferior). Para entender a dinâmica da denudacao quimica nessas bordas escarpadas, foram monitorados o total de solidos dissolvidos (TDS), o Eh, o pH, a vazao de 21 bacias hidrograficas distribuidas ao longo de ambas vertentes dos degraus (terras altas e frente da escarpa) no final dos periodos chuvoso (abril) e de estiagem (agosto) em um mesmo ano hidrologico (2009). As bacias amostradas situam-se sobre o mesmo substrato litologico (granitoides). Utilizando os dados de TDS e vazao foram calculadas as taxas de denudacao quimica (ton.ano-1.km-²) e as taxas medias de rebaixamento do relevo (m.Ma-1) para as bacias amostradas. Os resultados revelaram que as aguas fluviais dos degraus estudados apresentam assinaturas geoquimicas distintas: (i) nas terras altas, os valores de pH sao sempre acidos (≈ 6,35) e nas escarpas, levemente basicos (≈ 7,10); (ii) os valores de TDS (carga dissolvida) nas terras altas (≈ 10,00 mg.L-1) sao menores que os encontrados nos frente das escarpas (≈ 35,00 mg.L-1 para Sao Geraldo e, ≈ 18,00 mg.L-1 para Cristiano Otoni). As taxas de rebaixamento do relevo ocasionadas pela denudacao quimica sao semelhantes em ambas as terras altas (≈ 2,40 m.Ma-1). Em contrapartida, a frente da escarpa da Serra de Sao Geraldo apresenta taxa de denudacao quimica mais elevada (7,06 m.Ma-1) do que o Degrau de Cristiano Otoni. (4,25 m.Ma-1). Essa diferenca foi interpretada como diretamente relacionada a altura das escarpas, 450 e 250 m, respectivamente.

Domínios geomorfológicos na área de ocorrência dos depósitos de espongilito da região de João Pinheiro, Minas Gerais, Brasil

Important erosive processes that took place after the Cretaceous Era were responsible for the evolution of the landscape in the Joao Pinheiro region where spongillite deposits occur. The progression of these erosive processes on the carbonate rocks led to the development of negative karstic features where the ponds present formed the spongillite deposits. Based on field studies and analysis of multispectral images, four geomorphological domains were identified: i) domain 1, represented by a plateau related to sandstones from the Areado Group that present the highest altitudes in the area; ii) domain 2, that constitutes a desiccated area related to pelites from the Areado Group; iii) domain 3, comprising a karstic planation surface associated with carbonate rocks from the Bambui Group and Pre-Bambui unit covered by Cenozoic sediments where the ponds occur; iv) domain 4, composed of gutter shaped valleys enclosing meandering of underfit streams (of the Prata and Paracatu rivers). These valleys cut through the karstic planation surface (domain 3) where Pleistocene sediments occur and characterize the more recent morphological domain.

Caracterização Mineralógica das Argilas da Península de Santa Elena, Equador

The Santa Elena Peninsula, located in the southwest of the Ecuadorian coast, consists of igneous and sedimentary rocks from the Cretaceous to the Quaternary era. The sampled clays originated from the alteration of Andean volcanic ashes found inserted in the clay rocks of the Eocene Medium to Miocene Medium (Ancon Group and, Tosagua and Progreso Formations). Mineralogical analysis (XDR, ATG and ATD), textural analysis (grain size distribution, specific surface and morphological analysis by SEM), and chemical analysis (X-ray fluorescence and CEC), have permitted the selection of four deposits that have iron-montmorillonite as their main clay mineral, in association with kaolinite and traces of mica. Clays of theses deposits have been characterized as calcic bentonites.

Pedological aspects as environmental quality indicators of a touristic trail in the Serra do Cipó National Park/MG

Soil provides important support for anthropogenic activities, and earthen trails, which have always been present in the natural landscape, are routes of access to various tourist attractions. In recent decades, trails have been widely used as a method of access and visitation to geotouristic attractions. Because trails are restricted routes, transit along these paths also transforms the route into a pathway for the spread of various negative environmental impacts, including compaction and soil erosion of the trailbed. Soil compaction is caused by changes in the soil structure that are partly induced by the use of agricultural or geotechnical machinery and traffic, and the damage is also manifested in a remarkable decrease in porosity, which has clear implications for the infiltration and percolation of water and air associated with the functional porosity of soil. Soil micromorphological characteristics contribute to the analysis of soil porous systems, and the macroporous characteristics visible at this scale include the size, shape and connectivity among voids, which can be studied using different methods of identification, measurement and interpretation. Such methods are applied to understand the pore genesis and, more importantly, the physical behavior of soil-water order management. This work presents the results of analyses of the macromorphological and micromorphological characteristics, porosity, texture and penetrometry resistance of soil profiles on the Farofa Waterfall trail in the Serra do Cipó National Park, and the aim is to provide recommendations for compaction studies along special trails. The results showed that most of the trailbed is more compressed than at the margins, which suggests the need for geoindicator studies of soil quality to monitor the visitation of the trail and improve the conservation of natural resources.