Geonomos

A MINERALOGIA DOS SOLOS TROPICAIS: ESTADO DA ARTE E RELAÇÃO COM O USO E MANEJO

Thiago T. C. Pereira — 2021-02-26

The mineralogy of the tropical soils: state-of-the-art linked with land use and management. Part of the whole sorption and plant nutrition process are associated with the mineral matrix of soils. The goal of this study is to present a review of state-of-the-art about mineralogical characterization in the Brazilian tropical soils, in order to show details about soil genesis, as well as to analyze the mineralogy versus land use and management. In general, the understanding of mineralogy is necessary in tropical systems due to enormous quantitative, qualitative and geographic coverage of minerals constituting soils, especially in kaolinitic, oxydic (Fe) Latosols, and even gibbsites, besides those contained in Argisols and Cambisols, mainly. Thus, magnetite and maghemite could also have a greater a ention within soil classiﬁcation system due to a large occurrence in Brazilian soils and relationship between magnetic susceptibility and some management practices. In this way, classiﬁcation systems are prepared based on the knowledge and ordering from soil studies, including mineralogy, that directly aﬀect the management of agricultural areas, as well as those for environmental recovery and conservation.

Keywords: Latosols (Oxisols); Iron oxides; Gibbsite; Kaolinite.

A Serra das Cambotas: terminação Meridional do Supergrupo Espinhaço no Quadrilátero Ferrífero, MG

Ana P. C. Daher — 2021-02-26

The stratigraphic positioning of rocks grouped as Cambotas Formation (Quadrilátero Ferrífero, southeast of São Francisco Craton) has been the subject of discussion since its characterization in the 1960s. Our study provides structural and stratigraphic data of the Cambotas Formation, obtained in its type-section along with the Tamanduá and Cambotas mountain ranges, with the aim of deﬁning the stratigraphic-temporal relationships that characterize the Cambotas Formation and its surroundings. Also presents isotopic data (U-Pb in LA-ICP-MS) intended to shed light on the age of the unit, The large shear zone systems already described in the literature were observed, as well as the textural and sedimentological characteristics. The Cambotas Formation corresponds to a unit that groups together orthoquartzites and arcosian quartzites, whose basic stratigraphic relationship is controlled by tectonic contacts, through the Fundão-Cambotas Shear Zone System, and by the Córrego do Garimpo Fault. For provenance via U-Pb isotopic analysis in LA-ICPMS of detrital zircon grains, a sample collected from the Cambotas Formation in its type-section, in the homonymous mountain range, corresponding to ﬁne-grained orthoquartzite, in which 210-zircon grains collected and analyzed. The results indicate maximum sedimentation age during the Statherian, around 1755 ± 71 Ma, the peaks of ages between 1923 and 3010 Ma indicates a signiﬁcant contribution of Paleoproterozoic to Neoarquean sources. In the light of current stratigraphic knowledge, the peak of concordant analyzes with Statherian age (~ 1.7 Ga) discards the correlation between the Cambotas Formation and the Minas or Rio das Velhas supergroups. With this, we propose that the Cambotas Formation conﬁgure the southern termination of the Espinhaço Supergroup, corresponding to a restricted basin, with a multiplicity of source areas. This variety relates to the structural and stratigraphic complexity to which the northeastern region of the current Quadrilátero Ferrífero was subjected during its genesis. The sample provides an age similar to other works in the same area, validating the stratigraphic proposals presented.

Keywords: Cambotas Formation, Quadrilátero Ferrífero¸ U-Pb Geochronology.

Caracterização geológica-estrutural da conexão Araçuaí - São Francisco na área-tipo da Formação Rio Pardo Grande (Supergrupo Espinhaço, Minas Gerais)

Ana L. B. Araújo — 2021-02-26

In Serra do Espinhaço Meridional, the region between the districts of Rodeador (Monjolos) and Conselheiro Mata (Diamantina), in Minas Gerais, is located in the contact between the southeastern portion of the São Francisco Craton and the western portion of the Araçuaí Orogen. The Córrego Pereira and Rio Pardo Grande formations (Conselheiro Mata Group), Duas Barras Formation (Macaúbas Group), and Sete Lagoas, Serra de Santa Helena and Lagoa do Jacaré formations (Bambuí Group) outcrop in the area, besides metabasic Neoproterozoic dikes from the Pedro Lessa Suite that cut through the Espinhaço Supergroup units. The geological and structural characterization of the area was carried out, with emphasis on the Rio Pardo Grande Formation, top unit of the Espinhaço Supergroup, li le studied until then. The Rio Pardo Grande Formation was deposited in a marine platform and is constituted, at the base, by metarritmites, metapelites and ﬁne metarenites (Fácies Fl), with lenses of thick metarenite and metaconglomerate (facies Gsm), and metadolomites with stromatolytic structures at the top (Facies De). The registration of Facies Gsm metaconglomerates indicates the occurrence of a marine regression at the end of the deposition of the Conselheiro Mata Group, modifying the depositional model of the unit. The region's structuration is marked by expressive ductile and ruptile deformations developed during the Brasiliano Event, separated in two diﬀerent deformation phases. The main features are two large NNW-SSE axis anticlinals in the eastern portion of the area, a thrust fault of N-S direction and east dip forming a regional ramp-ﬂat context, regional wide open folds with west vergency and also considerable subvertical fractures oriented by WNW-ESE and NNW-SSE. The cinematic indicators in the region point out to mass transport form east to west.

Keywords: São Francisco Craton, Araçuaí Belt, Rio Pardo Grande Formation, structural characterization

A Pequena Idade do Gelo: evidências históricas e geológicas de mudança climática

Celso D. R. Carneiro — 2021-02-26

Currently, basic school teachers are challenged to address climate control factors by means of an essentially interdisciplinary approach. This goes beyond developing an ability to manipulate scientiﬁc information from diﬀerent sources; it requires an understanding of the deep implications of scientiﬁc knowledge. This research has gathered evidence about the “Litlle Ice Age”, which occurred between the 16th and 19th centuries, when there was great cooling in the Northern Hemisphere, and other worldwide eﬀects. The database retrieved by the survey is divided as historical, geological, biological, geomorphological and artistic evidence, including knowledge about dating methods of the Quaternary ancient climates. The records help building a systemic understanding of the processes determining Holocene climatic variations. Ice ages can also be related to eustatic (sea level) variations. The results reveal the availability of diﬀerent paleoclimatic models, thus enhancing the implications of such extreme events for the societies. The models allow to identify some tendencies of climatic change, not perfectly convergent.

Keywords: Paleoclimatology, Quaternary, Climate change, Environment, Geosciences.

SPELEOLOGICAL POTENTIAL OF THE SUMIDOURO STATE PARK / MG

Fernanda Mara Coelho Pizani — 2021-02-26

Thematic mapping for the speleological potential of the Sumidouro State Park / mg. The Sumidouro State Park (PESU) constitutes a Conservation Unit located in the Environmental Protection Area (APA) Karst Lagoa Santa, between the municipalities of Lagoa Santa and Pedro Leopoldo, northern portion of the Metropolitan Region of Belo Horizonte, housing a rich speleological heritage. Currently, there are 49 known cavities registered in the database of the National Center for Research and Conservation of Caves (CECAV). It is estimated that there are more caves inserted in the park not yet registered by the agency. Thus, this work aimed to develop a predictive model in order to indicate areas with a higher potential for the occurrence of caves, in the light of geotechnologies. In order to perform the speleological potential calculation, data were collected on the existing features that are intrinsically linked to the formation of caves: geology, hydrography, exokarstic features present in the study area, hypsometry and slope. After data acquisition, values were assigned to them and, through map algebra, it was possible to identify areas with a higher and very higher degree of potential for the occurrence of caves. Because of the development of this model, it is expected that it will have application in other areas of study. Future ﬁeldwork should be carried out to conﬁrm and register new cavities pointed out in the mapped areas, especially those registered as having high potential.

Keywords: karst; Apa; Lagoa Santa; speleological potential; multicriteria analysis.

ESTUDO DO POTENCIAL GEOTURÍSTICO DO PATRIMÔNIO MINEIRO DA SERRA DE OURO PRETO, SUDESTE DO QUADRILÁTERO FERRÍFERO, MG

Yanne S. Queiroz — 2021-02-26

The Ouro Preto and Mariana region, located in the southern portion of the Iron Quadrangle, Minas Gerais, hosted the nucleation of the ﬁrst urban centers in the central region of the state due to the Gold rush in the eighteenth century. The southern edge of the Mariana anticline had several gold mines that were closed after the end of the exploration of gold. Today, the region is an archaeological, historical, scientiﬁc and cultural record, closely associated with the local geology. This article aims the creation of a geoitinerary in the southern edge of the Mariana anticline, also named Ouro Preto Ridge, based on the inventory of the mining and geological heritage of the geosites of this region, done with the date gathering in ﬁeld visits. The mining galleries were highlight in this research, because they are classiﬁed as geosites according to parameters of touristic, social and environmental relevance. The visits to the geosites made the diagnostic of their situation about the heritage preservation and your relationship to touristic and environmental parameters possible. After the ending of this research, extension programs will be conducted with the local community in order to disseminate the importance of such geosites and their potential to promote a sustainable socio-economic development for the region. Therefore, through the promotion of research and extension programs involving the creation of a geoitinerary in the region, local communities can develop and rescue their identity, creating sustainable development mechanisms based on geotouristic practices.

Keywords: Geoconservation; Mining Heritage; Georoute