EM - Escola de Minas

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The Cenozoic deposits of the ancient landscapes of Quadrilátero Ferrífero highlands, Southeastern Brazil : sedimentation, pedogenesis and landscape evolution.
(2020) Varajão, Angélica Fortes Drummond Chicarino; Mateus, Ana Carolina Campos; Santos, Maria do Carmo; Varajão, César Augusto Chicarino; Oliveira, Fabio Soares; Yvon, Jacques
The Quadrilátero Ferrífero (QF), Southeastern Brazil, is a very important tropical highland region in the world’s geological context for its large and diverse Archean and Proterozoic rocks with great reserves of gold, iron, manganese, aluminum and industrial rocks, on a apparently stable geological structure. There, Cenozoic deposits perched on highland valleys show unclear genetic relationships with the underlying bedrock, with no apparent regional correlation. We studied five representative Cenozoic deposits (BR356, Água Limpa, Padre Domingos, Pau Branco and Casa de Pedra) on the highlands of the Serra da Moeda syncline, Western QF, to answer the question of their sedimentological origin, and investigate their pedological evolution. Field sampling was complemented by macromorphological, mineralogical and micromorphological analysis supported by X-ray diffraction (XRD), differential thermal analysis (DTA), infrared analysis (IR), scanning electron microscopy (SEM), micropobre and transmission electron microscopy (TEM). The evolution of these isolated highland de- posits comprises a deep-weathered source area, a tectonic activity, besides sedimentological and pedological processes, during and after the deposition. The deposits overlie deep saprolites of Precambrian rocks (Piracicaba and Itabira Groups), representing unconformable contact. The onset of the deposition was marked by torrential, coarse colluvial and large blocks landslides into the small basins generated by reactivating tectonic events during the Oligocene, producing local grabens. These tectonic basins were filled by cohesive debris and mudflow from the adjacent and previously laterized cover, developed under the hot and humid climate in the Eocene. The cover reveals an upside-down lateritic profile where morphology and kaolinite crystal properties (values of size of coherent scattering thickness ranging from 135 Å to 162 Å) in the bottom is related to the pedolith horizons of the former lateritic cover. Later, due to climate changes (during and after the Miocene), renewed weathering on these pre-weathered sediments occurred, characterized by alternating ferruginization and Fe-losses, with the superimposed generation of new pedogenic features such as nodules, ferruginous duricrusts and mottling (redox features). In addition to demonstrating that the Brazilian platform was not stable during the Cenozoic, these deposits reveal the role of polygenetic tropical pedological processes in their formation and transformation.
Genesis of soils from bauxite in southeastern Brazil : resilication as a soil-forming process.
(2017) Mateus, Ana Carolina Campos; Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drummond Chicarino; Soares, Caroline Cibele Vieira
Pedological studies using X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, and scanning electron microscopy (SEM-EDS) showed a Xanthic Ferralsol formed from the degradation of bauxite on a slope in the Caparaó region, in southeastern Brazil. We found a decrease in the number and size of bauxite fragments toward the top of the profiles, bauxite fragments that were more degraded at the top of the profiles, transformation of gibbsite into kaolinite, and absolute enrichment in silicon in the mass balance. These indicators suggest that resilication could be the major process responsible for formation of the soil; detailed studies are needed to verify the origin of the silica. The reintroduction of silica into the system occurs by the biogeochemical cycling of vegetation and, in some cases, water table fluctuations, highlighting the role of resilication as a soil-forming process in bauxite-derived soils.
Gênese de depressões fechadas em vertentes associadas à couraça aluminosa na porção sul da Serra do Caparaó, Minas Gerais/Espirito Santo.
(2016) Mateus, Ana Carolina Campos; Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drummond Chicarino; Soares, Caroline Cibele Vieira; Schünemann, Adriano Luis
A origem das depressões fechadas associadas à cobertura laterítica aluminosa nos topos dos morros e ao longo das vertentes na região de Espera Feliz, MG, divisa com Espírito Santo, foi pesquisada através de um levantamento geofísico da cobertura pedológica associado às análises morfológicas (macro e micro) de perfi s de solos. O levantamento geofísico por GPR, realizado em 2 seções ao longo de uma vertente, abrangeu duas depressões consecutivas e foi seguido do levantamento sistemático da cobertura pedológica por meio da abertura de 5 perfi s (N1, L1, L2, N2 e L3). Foram coletadas amostras deformadas para análises físicas, mineralógicas e químicas e amostras indeformadas para análise micromorfológica. No interior das depressões fechadas foi identifi cado o Neossolo Litólico húmico típico e entre as depressões ocorre o Latossolo Vermelho Amarelo distrófi co húmico. A análise lateral realizada pelo GPR e a interpretação conjunta dos atributos da cobertura revelam um sistema pedológico contínuo do topo a base da vertente. As diferenças morfológicas que levam a existência de distintas classes de solos traduzem, neste contexto, a evolução pedogeomorfológica da vertente e consequente gênese das depressões, o que teria ocorrido de maneira distinta ao modelo de subsidência por lixiviação geoquímica, mais amplamente conhecido. Dois momentos são reconhecidos: i) a origem de uma cobertura latossólica relacionada ao avanço vertical da degradação da bauxita e à bioturbação sob condições climáticas úmidas e ii) remoção de partes dessa cobertura em condições climáticas (possivelmente áridas) posteriores.

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