Luiz Fernando de Paula Barros

Síntese dos cenários paleobioclimáticos do quaternário tardio em Minas Gerais/sudeste do Brasil

In this paper, it was attempted to synthesize the natural palaeobioclimatic scenarios of the Late-Quaternary in Minas Gerais State, Southeastern Brazil, seeking for their relationship to large-scale climatic events. It was made an extensive literature review. It was looked for papers based on different methods, but with absolute datings and palaeobioclimatic implications. This kind of survey can not set precise time limits. However, some trends could be observed from the available datasets. It was proposed eight palaeobioclimatic scenarios for the last 50,000 years. The greater number of scenarios is usually found in the last 10,000 years. However, this proposal is still open due to concentration of the available data in just some regions, occurring information gaps.

Eventos Deposicionais Fluviais Quaternários e Dinâmica Recente do Vale do Rio Maracujá – Quadrilátero Ferrífero/MG

A bacia do Rio Maracuja, localizada no centro-sul do Quadrilatero Ferrifero, vem sendo amplamente estudada em razao dos abundantes vocorocamentos em rochas do embasamento cristalino. Muito pouco se sabe sobre a dinâmica fluvial dessa bacia, marcada por um grande fornecimento sedimentar aos cursos d’agua. No intuito de suprir lacunas como esta e contribuir para a compreensao da evolucao geomorfologica do Quadrilatero Ferrifero, este trabalho apresenta o quadro dos niveis e sequencias deposicionais fluviais do vale do rio Maracuja. Os registros deposicionais permitem o levantamento de reflexoes e comparacoes entre os eventos paleogeomorfologicos e a dinâmica fluvial atual. O estudo foi baseado em trabalhos de campo, com levantamento de perfis estratigraficos e caracterizacao dos niveis e sequencias deposicionais, posteriormente mapeados e representados em perfis-sintese e esquemas de secoes transversais. Os resultados mostram a existencia de tres niveis de terraco e um de planicie e sua interpretacao revela mudancas significativas no padrao de sedimentacao da bacia, antes marcada por espessos pacotes argilosos e hoje caracterizada pela arenizacao dos depositos. Morfologicamente, o Rio Maracuja vem se alterando, tendendo a apresentar um padrao entrelacado em alguns trechos, em razao do intenso fornecimento sedimentar gerado pelos vocorocamentos e por atividades antropicas, como a mineracao. O escalonamento dos niveis de terraco se mostra como resposta ao continuo soerguimento do escudo brasileiro apontado em trabalhos anteriores sobre a dinâmica fluvial no Quadrilatero Ferrifero.

Southern Serra do Espinhaço: The Impressive Plateau of Quartzite Ridges

The Southern Serra do Espinhaco (Serra do Espinhaco Meridional—SdEM) is the meridional portion of the most extensive and continuous Precambrian orogenic belt of the South American Platform. The SdEM is an imposing geomorphological and geological unit and one of the most striking geographical structures of the state of Minas Gerais, southeastern Brazil. The SdEM has an important role in the separation of drainage basins and the individualization of climate, biomes, and landscapes. The result of the long temporal combination of a diverse lithostructural context and morphogenetic agent action, the SdEM stands out for its biological wealth and the scenic beauty of its landscapes, which are marked by quartzite scarps, canyons, and crystalline water rivers with frequent waterfalls. Human occupation, which has been present since prehistoric times but has intensified since the colonial period due to exploration for precious stones, has resulted in a rich historical and cultural asset that enhances its physical environment and makes the SdEM one of the most common tourist destinations in Brazil.

Quaternary alluvial sedimentation in the Conceição river valley, southeastern Brazil

The aim of this paper is to discuss the first results of the analyses concerning indications of influences of litho structures, tectonics, and climate on the pattern and chronology of Quaternary alluvial sedimentation in the Conceicao river valley. This is a mountain tropical area located in the northeastern of Quadrilatero Ferrifero, one of Brazils most known mountainous domains and one of the worlds major iron ore producers. The used methods were based on field research and laboratory analyses of sediments, including optically stimulated luminescence dating. Eight alluvial depositional levels were identified, most of which were morphologically uncharacterized (without the configuration of terraces). Probable river diversion, sediment traps, and tilted blocks indicate the tectonic conditioning on fluvial dynamics, besides the terrace staircases. The formation of cyclic alluvial levels with gravel-bed facies cemented by iron oxides-hydroxides could be related to climatic fluctuations. Although data on luminescence dating offer critical information for the understanding of the Quaternary fluvial evolution of the area, several geological and geomorphological inconsistencies require careful analysis. Furthermore, although some ages are consistent with the specific case of the Conceicao river, these ages are significantly different to those found in other valleys of Quadrilatero Ferrifero.