José Eloi Guimarães Campos

ORIGEM E EVOLUÇÃO TECTÔNICA DA BACIA SANFRANCISCANA

This paper presents data about the origin and tectonic evolution of the Phanerozoic cover of the Sao Francisco Craton, defmed as the Sanfranciscana Basin. The tectonic compartmentation allowed the subdivision in the Abaete (south portion) and the Urucuia sub-basins (middle-north portion). The stratigraphy and sedimentology of the Phanerozoic successions are as follows: Santa Fe Group (Permo-Carboniferous) - subdivided into the Floresta and Tabuleiro formations. Areado Group (Early Cretaceous) comprising the Abaete, Quirico and Tres Barras forraations. Mata da Corda Group (Late Cretaceous) composed by the Patos and Capacete formations. Urucuia Group (Late Cretaceous) composed by the Posse and Serra das Araras formations. Chapadao Formation (Cenozoic) represents the sandy, unconsolidated, recent covers of talus, residual or alluvium origin. Paleozoic epyrogenesis characterized the onset of tectonism in the Sanfranciscana Basin. During the Mesozoic the basin has undergone tectonic reactivations finishing with neotectonic activity in Cenozoic times. The origin of the basin, as well as its tectonic evolution had been controlled by the Sao Francisco Craton marginal fold-and-thrust belts (Brasilia and Aracuai belts), by the South Atlantic opening (rift phase) and by transform oceanic fractures (drift phase).

Geologia do Grupo Paranoá na porção externa da Faixa Brasília

The Paranoa Group represents a psamo-pelitic-carbonated succession deposited in shelf conditions. The stratigraphy of this important lithostratigraphic sequence of the Brasilia Fold Belt was originally proposed by letter-code designation that includes 11 units with the following stratigraphic stacking: SM, R1, Q1, R2, Q2, S, A, R3, Q3, R4 and PC. The present paper formalizes these units and proposes the following denomination to the formations, named from base to top: Ribeirao Sao Miguel, Corrego Cordovil, Serra da Boa Vista, Serra Almecegas, Serra do Parana, Ribeirao Picarrao, Ribeirao do Torto, Serra da Meia Noite, Ribeirao Contagem, Corrego do Sansao and Corrego do Barreiro. The deposition of the Paranoa Group is considered to have been processed in the Mesoproterozoic (1,542 to 1,042 Ma). This age interpretation is supported by the stratigraphic position (as it occurs over the post-rift phase sediments of the Arai Group and under slates and carbonates of the Bambui Group), by the presence of conical stromatolite (conophyton) and by isotopic data. The sedimentation was controlled by transgressive-regressive cycles, including grading and traction processes, debris flows, tides, waves, storms and basin bottom paleogeography. The sediments were affected by low-grade metamorphism and the deformation resulted in the formation of monoclines, different styles of folds (chevrons, in box and cylindrical ones) and folding interference resulting in domes and structural basins. The regional deformation of the Paranoa Group is mainly controlled by the Parana and Rio Maranhao thrust systems and by the Ribeirao Sao Miguel shear belt.

Application of shallow seismic profiling to study riverbed architectural facies: a case study of the Tocantins river (Pará - Brazil)

To date, the vast majority of river sedimentology study has relied on two main categories of observation: direct observation of shallow trenches, cut faces and cores or geophysical survey on dry and shallow regions of braid bars. In this study, a sub-bottom profiler was used to investigate the stratigraphy of the lower course of the Tocantins River in the Amazon region, between the city of Tucurui and the village of Nazare dos Patos. The interest in this specific region lies on the possible variation of the fluvial regime due to the installation of the dam of the Tucurui hydroelectric plant and the perspective that such river would become navigable as soon as the canal lock will be completed. Collected data show a detailed variety and complexity of architectural elements, as well as internal structure of sandy macroforms. Furthermore, the results allowed the identification of three main environments linked to channel sedimentation processes: by-pass, transition and deposition environments, whose distribution is linked to channel dynamics and bedrock topography. The application of the study is manifold, once it provides not only an insight into sedimentary structure of alluvial forms and sedimentation history, but also elements demanded to plan eventual engineering works for river navigability.

Estratigrafia do Grupo Araí: registro de rifteamento paleoproterozoico no Brasil Central

The Arai Group is characterized by a succession of low-grade metassedimentary and metavolcanic rocks that overlaps the Aurumina Suit and the Ticunzal Formation. The related basin fill-succession of the Arai Group was probably deposited in an intracontinental rift, which evolution initiated before 1,77 My in the Paleoproterozoic. Originally this unit was subdivided in the Arraias Formation (continental sequence) and Trairas Formation (marine sequence). However, the analysis, compilation and integration of the geologic data, mainly related to the sedimentary geology and the tectono-stratigraphy, had shown the necessity to formalize four unit subdivisions, including the Agua Morna, Arraias, Caldas and Trairas formations. The Agua Morna Formation represents a braided river fluvial deposicional system, evolved in an intracontinental SAG basin type, during a pre-rift phase, and representing the Agua Morna Tectonosequence submitted to thermal subsidence processes. The Arraias Formation represents a thick package of continental sediments, subdivided in four members: Cubiculo (aluvial fans), Prata (braided river), Mutum (aeolian), Ventura (lacustrine) and Buracao (volcanic and pyroclastic), representing the Arraias Tectonosequence, which constitute the infilling of the main rift phase, under mechanic subsidence. The Caldas Formation represents the transitional depositional sequence of the Arai Group, subdivided in two informal members related to beach system: Lower Member (backshore and foreshore) and Upper Member (shoreface). The Trairas Formation represents the marine sequence, subdivided in the Boqueirao Member (mixed platform dominated by tides), Rio Preto Member (siliciclastic platform dominated by tides) and Rosario Member (mixed platform dominated by tides), integrating the Trairas Tectonosequence and developed during flexural subsidence (post rift phase). Here the rewied stratigraphy has shown well functional for mapping and regional correlations in different areas of occurrence of the Arai Group in Central Brazil.

A Formação Jequitaí na região de Vila Boa, GO: exemplo de sedimentação por geleiras terminais no Neoproterozóico

RESUMO: A Formacao Jequitai, localizada na base do Grupo Bambui, constitui um importante registro das condicoes climaticas e deposicionais do Meso/Neoproterozoico na borda Oeste do Craton Sao Francisco. Sua ocorrencia e registrada em contato discordante sobre as diferentes unidades que compoem o Grupo Paranoa e e lateralmente descontinua. Na regiao do municipio de Vila Boa, a Formacao Jequitai ocorre como uma sequencia basal de camadas metricas de arenitos e grauvacas sobrepostas por uma camada decametrica de diamictito macico, seguido de uma camada metrica de arenito calcifero. Toda a sequencia e recoberta por dolomitos de capa tipicos de condicoes pos-glaciais da Formacao Sete Lagoas. O registro sedimentar sugere se tratar de depositos glaciogenicos preservados em paleovales que sofreram rapida inundacao apos a sua deposicao, indicando a ocorrencia de geleiras terminais ainda em condicoes continentais erodindo o Grupo Paranoa anteriormente a geracao do Grupo Bambui. As feicoes petrograficas das rochas psefiticas sugerem a existencia de diamictitos ressedimentados e a ocorrencia de possiveis tilitos apenas de forma localizada. PALAVRAS-CHAVE: Formacao Jequitai; diamictito; glaciacao Neoproterozoica; esturtiano; geleiras terminais.A Formacao Jequitai, localizada na base do Grupo Bambui, constitui um importante registro das condicoes climaticas e deposicionais do Meso/Neoproterozoico na borda Oeste do Craton Sao Francisco. Sua ocorrencia e registrada em contato discordante sobre as diferentes unidades que compoem o Grupo Paranoa e e lateralmente descontinua. Na regiao do municipio de Vila Boa, a Formacao Jequitai ocorre como uma sequencia basal de camadas metricas de arenitos e grauvacas sobrepostas por uma camada decametrica de diamictito macico, seguido de uma camada metrica de arenito calcifero. Toda a sequencia e recoberta por dolomitos de capa tipicos de condicoes pos-glaciais da Formacao Sete Lagoas. O registro sedimentar sugere se tratar de depositos glaciogenicos preservados em paleovales que sofreram rapida inundacao apos a sua deposicao, indicando a ocorrencia de geleiras terminais ainda em condicoes continentais erodindo o Grupo Paranoa anteriormente a geracao do Grupo Bambui. As feicoes petrograficas das rochas psefiticas sugerem a existencia de diamictitos ressedimentados e a ocorrencia de possiveis tilitos apenas de forma localizada.

Proposição de critérios para avaliação e delimitação de bacias hidrogeológicas

The designation of the “hydrogeologic basin” terminology still needs to be complemented regarding the definition and application aspects. One of the approaches without theoretical and conceptual basement is related to the criteria for definition the boundaries of the hydrogeologic basins and the relationships with the overland watersheds. The available technical literature is very restricted and incomplete. Because of this, the objective of the present paper is to contribute with the knowledge on the hydrogeologic basins, as well as to characterize a terminology to be used for futures hydrogeologic studies. Potenciometric surfaces mapping, hydrology, hidrochemistry, tracing tests and geophysics are among the main applied techniques to the delimitation of the hydrogeologic basins. The integrated wate resource management, the study of borders aquifers, the definition of well protection perimeter and the remediation study on polluted aquifers are some of the cases where the knowledge of the hydrogeologic boundaries is very important.

Hydraulic characterization from porous aquifers of the Brazilian Federal District

Hydraulic conductivity (K) in unsaturated soil is a key input parameter for modeling subsurface water and solute movements. K-values are also important to better define the potential of aquifers and to optimize water resources management activities. Since K-values are usually not readily available, different techniques are applied to estimate them. This study aimed to estimate unsaturated K-values from porous aquifers found in the Federal District of Brazil. Infiltration tests were conducted in different soil types using the open-end-hole approach and the permeability test using shallow boreholes with specific depths, as reported by Heitfeld in 1979. Soil structure was taken into consideration in such estimations. In order to consider important soil properties such as soil texture and bulk density, K-values were also estimated by means of pedotransfer functions (PTFs). Soil texture was determined in the laboratory and used as input parameter for PTFs. Results from open-end-hole method and permeability test compared to those obtained from pedotransfer functions. K-values from four different shallow porous aquifers systems encountered in the Federal District varied from 10-8 ms-1 to 10-6ms-1. Highest K-values were found in Oxisols while the lowest rates were found in Inceptisols. Decreasing conductivity trend was found with increasing depth due to the increase of loamy soils. Variations in the rate of hydraulic conductivity indicated heterogeneity of porous aquifers due to differences in textural and structural characteristics of the soils.

The Jequitaí Formation at the Boa Vista Ridge, town of Vila Boa, GO: example of sedimentation by neoproterozoic terminal glaciers

RESUMO: A Formacao Jequitai, localizada na base do Grupo Bambui, constitui um importante registro das condicoes climaticas e deposicionais do Meso/Neoproterozoico na borda Oeste do Craton Sao Francisco. Sua ocorrencia e registrada em contato discordante sobre as diferentes unidades que compoem o Grupo Paranoa e e lateralmente descontinua. Na regiao do municipio de Vila Boa, a Formacao Jequitai ocorre como uma sequencia basal de camadas metricas de arenitos e grauvacas sobrepostas por uma camada decametrica de diamictito macico, seguido de uma camada metrica de arenito calcifero. Toda a sequencia e recoberta por dolomitos de capa tipicos de condicoes pos-glaciais da Formacao Sete Lagoas. O registro sedimentar sugere se tratar de depositos glaciogenicos preservados em paleovales que sofreram rapida inundacao apos a sua deposicao, indicando a ocorrencia de geleiras terminais ainda em condicoes continentais erodindo o Grupo Paranoa anteriormente a geracao do Grupo Bambui. As feicoes petrograficas das rochas psefiticas sugerem a existencia de diamictitos ressedimentados e a ocorrencia de possiveis tilitos apenas de forma localizada. PALAVRAS-CHAVE: Formacao Jequitai; diamictito; glaciacao Neoproterozoica; esturtiano; geleiras terminais.A Formacao Jequitai, localizada na base do Grupo Bambui, constitui um importante registro das condicoes climaticas e deposicionais do Meso/Neoproterozoico na borda Oeste do Craton Sao Francisco. Sua ocorrencia e registrada em contato discordante sobre as diferentes unidades que compoem o Grupo Paranoa e e lateralmente descontinua. Na regiao do municipio de Vila Boa, a Formacao Jequitai ocorre como uma sequencia basal de camadas metricas de arenitos e grauvacas sobrepostas por uma camada decametrica de diamictito macico, seguido de uma camada metrica de arenito calcifero. Toda a sequencia e recoberta por dolomitos de capa tipicos de condicoes pos-glaciais da Formacao Sete Lagoas. O registro sedimentar sugere se tratar de depositos glaciogenicos preservados em paleovales que sofreram rapida inundacao apos a sua deposicao, indicando a ocorrencia de geleiras terminais ainda em condicoes continentais erodindo o Grupo Paranoa anteriormente a geracao do Grupo Bambui. As feicoes petrograficas das rochas psefiticas sugerem a existencia de diamictitos ressedimentados e a ocorrencia de possiveis tilitos apenas de forma localizada.

Determinação das espessuras do Sistema Aquífero Urucuia a partir de estudo geofísico

Resumo O Sistema Aquifero Urucuia (SAU) e um manancial subterrâneo de extensao regional, composto por subtipos de aquiferos inter-relacionados. O aquifero e constituido de quartzo-arenitos e arenitos feldspaticos eolicos bem selecionados, com presenca de niveis silicificados e, em menor proporcao, niveis conglomeraticos relacionados ao Grupo Urucuia, Neocretaceo da Bacia Sanfranciscana, que representa a cobertura fanerozoica do Craton Sao Francisco. O sistema aquifero se estende desde o sul do Piaui ate o noroeste de Minas Gerais, com maior expressao no oeste da Bahia. Apresenta um eixo divisor longitudinal que separa o fluxo subterrâneo para o oeste (bacia hidrografica do Tocantins) e para leste (bacia hidrografica do Sao Francisco). O sistema foi dividido em quatro subsistemas, assim caracterizados: aquifero livre regional; aquifero suspenso local; aquifero confinado ou semiconfinado e aquifero livre profundo. As espessuras totais do sistema aquifero, estimadas a partir da aplicacao de estudos geofisicos, apresentam valores que variam de 100 a 600 m nos 26 pontos do levantamento eletromagnetico no dominio do tempo. As espessuras saturadas variam entre 80 e 460 m. Palavras-chave: Aquifero Urucuia; metodo eletromagnetico; dominio do tempo; hidrogeologia.

Relationships of stable isotopes, water-rock interaction and salinization in fractured aquifers, Petrolina region, Pernambuco State, Brazil

The Petrolina County, Pernambuco State, Brazil, presents specificities that make it unique from a hydrogeological point of view. Water resource scarcity is both a quantitative and qualitative issue. The climate is classified as semiarid, having low precipitation, along with high temperatures and evapotranspiration rates. Aquifer zones are related to low connected fractures resulting in a restricted water flow in the aquifer. The recharge is limited and the groundwater salinity is high. Stable isotope analyses of H and O were developed in groundwater samples (with different electrical conductivity) and surface water collected in a bypass channel flowing from the São Francisco River. The results were plotted in a δD ‰ versus δ18O ‰ graph along with the curves of the global and local meteoric water line. Groundwater samples showed unexpected results showing a lighter sign pattern when compared to the meteoric waters. More negative δD and δ18O values indicate an enrichment in light isotopes, which show that this process is not influenced by surface processes, where the enrichment occurs in heavy isotopes due to evaporation. The isotopic signature observed is interpreted either as resulting from the water-rock interaction, or as resulting from recharge from paleo rains. The waters are old and show restricted flow. So the water-rock contact time is extended. In the rock weathering processes, through the hydration of feldspars, there is preferential assimilation of heavy isotopes at the expense of the lighter ones that remain in the water. Analyses of the 87Sr/86Sr ratio and isotopic groundwater dating assist in the interpretations.