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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2 resultados
Resultados da Pesquisa
Item The impact of benthic microbial communities in sediment dispersion and bedform preservation : a view from the oldest microbially induced sedimentary structures in South America.(2022) Warren, Lucas Veríssimo; Varejão, Filipe Giovanini; Quaglio, Fernanda; Inglez, Lucas; Büchi, Fernanda Miranda de Siqueira; Simões, Marcello GuimarãesThe influence of microbial communities upon sedimentary dynamics is an issue of increasing significance. Over the last decades, studies have revealed a particular class of sedimentary structures and textures produced by the interaction among distinct flows, marine substrate, and ben- thic microbial communities. We present evidence of the oldest record of microbially-induced sedimentary structures (MISS) in South Amer- ica, as recorded in low-grade metasedimentary rocks of the Early Mesoproterozoic (~1536 ± 33 Ma) Tiradentes Formation, state of Minas Gerais, SW Brazil. Types 1, 2, and 3 correspond to wrinkle, pustular, and dome structures related to flat or rippled bed surfaces, preserved in metasandstone deposited in shallow marine settings. Evidence supporting the microbial origin of these structures includes delicate morphol- ogy, degree of alignment, presence of original mat cover, and orientation of quartz grains indicating biostabilization. The presence of distinct MISS associated with well-preserved ripple marks, wrinkled surfaces, and flatbeds suggests deposition under varied energy conditions with different potentials for the preservation of surficial structures. Vertical growth of microbial communities influences sediment cohesion and stability. This reduces substrate roughness and, as a consequence, wave and current shear, thereby increasing the preservation potential of bedforms and delicate features of their bedding surfaces.Item Carbon isotopes of Mesoproterozoic–Neoproterozoic sequences from Southern São Francisco craton and Araçuaí Belt, Brazil : paleographic implications.(2004) Santos, Roberto Ventura; Alvarenga, Carlos Josá Souza de; Babinski, Marly; Ramo, Maria Luiza S.; Cukrov, Neven; Fonseca, Marco Antônio; Sial, Alcides da Nóbrega; Dardenne, Marcel Auguste; Noce, Carlos MaurícioThis paper addresses the carbon isotope variations observed on Mesoproterozoic and Neoproterozoic carbonates from the southeastern part of the Sa˜o Francisco craton and Arac¸uaı´ Belt, Brazil. Carbonates were collected across sections of the Mesoproterozoic Espinhac¸o Supergroup (Rio Pardo Grande Formation) and of the Neoproterozoic units of the Sa˜o Francisco basin, including: (i) dolomites and marls of the Macau´bas Group (Domingas Formation); (ii) dolomite pebbles and carbonatic matrix of the diamictites of the Jequitaı´ Formation; (iii) limestones of the overlying Bambuı´ Group. Limestones of the Espinhac¸o Supergroup present a flat trend of positive d13CPDB values (varying betweenC1 andC2‰), while samples of the Macau´bas Group present an upward trend of decreasing carbon isotopic values (fromC0.7 toK4.0‰). The lower d13CPDB values of this latter unit were obtained on the upper part of the section. Dolostone pebbles and carbonates in the matrix of the diamictite also present negative d13CPDB values (K3.1 and K0.6‰). Except for carbonatic pelites placed above the diamictites, that present d13CPDB of C7.7‰, limestone samples of all the sections of the Bambuı´ Group have d13CPDB values above C8‰. The data presented here reveal significant differences between carbonates from the Espinhac¸o and Macau´bas Groups, indicating that this latter unit may be correlated with the diamictites from the Jequitaı´ Formation, as already suggested by previous stratigraphic studies. The data also reveal the absence of the low positive d13CPDB carbonates (belowC3‰) frequently present at the base of the Bambuı´ Group, thus suggesting that the deposition of this unit in the Serra do Cabral and Jequitaı´ areas took place after the regional positive d13CPDB excursion observed in other parts of the basin. Hence, it is proposed that these areas were paleo-highs during the deposition of the lower portion of the Bambuı´ Group sediments.