ESTRATIGRAFIA E SEDIMENTOLOGIA DA FORMAÇÃO CARRANCAS, GRUPO BAMBUÍ, NAS REGIÕES DE BELO HORIZONTE E PITANGUI, MG
Bibliographic record
Abstract
A Formação Carrancas, aflorante próximo à região de Belo Horizonte (MG), forma a base do Grupo Bambuí (Neoproterozoico) naporção sul do Cráton do São Francisco. Neste trabalho, duas principais áreas de afloramento desta unidade foram estudadas. A primeira,denominada Área Pitangui, localiza-se a leste de Pitangui (MG) e a segunda, denominada Área BR-040, encontra-se a sul de Sete Lagoas(MG). Na Área Pitangui, a Formação Carrancas é composta por conglomerados, arenitos, pelitos e dolomitos subdivididos em quatroassociações distintas e sobrepostas às rochas metamórficas neoarqueanas do Supergrupo Rio das Velhas. Na Área BR-040 afloram gnaissesmigmatíticos do embasamento arqueano (Complexo Belo Horizonte), sobrepostos pela Formação Carrancas, onde predominam pelitos eritmitos. Em ambas as áreas de estudo, folhelhos negros podem apresentar teores de carbono orgânico total (COT) em valores variandoentre 0,4 e 1,5%. Os dolomitos róseos da Área Pitangui, em contato gradacional com ritmitos e pelitos da Formação Carrancas, apresentamaltos valores de δ13C, entre +7,1 e +9,6‰VPDB. Esses valores são incompatíveis com os valores regionais usualmente encontrados para abase da Formação Sete Lagoas, sugerindo que esses dolomitos constituem um litotipo distinto pertencente à Formação Carrancas, nãodescrito anteriormente. Nas duas áreas estudadas a Formação Carrancas é interpretada como produto de fluxos gravitacionais depositadosem calhas no embasamento da borda sul do Cráton do São Francisco, controladas por falhamentos em borda de bacia. O isolamento dessascalhas em relação ao mar aberto favoreceu a acumulação de matéria orgânica, como sugerido pelas intercalações de folhelhos negros epelos altos valores de δ13C nos dolomitos no topo da sequência.Palavras chave: Grupo Bambuí; Formação Carrancas; Sedimentação gravitacional; Bacia restrita ABSTRACT STRATIGRAPHY AND SEDIMENTOLOGY OF THE CARRANCAS FORMATION, BAMBUÍ GROUP, NEAR BELO HORIZONTE ANDPITANGUI - MG - The Carrancas Formation crops out in the vicinity of Belo Horizonte (MG) and represents the base of Bambuí Group at thesouthern margin of São Francisco Craton. In this paper, two important areas have been studied. The first one, named Pitangui Area islocated east of Pitangui (MG). The second area, named BR-040 Area is situated south of Sete Lagoas (MG). In the Pitangui Area theneoproterozoic sedimentary rocks from Carrancas Formation are represented by conglomerates, sandstones, rhythmites, pelites anddolomites subdivided into 4 different associations, and overlying neoarchean metamorphic rocks from Rio das Velhas Supergroup. In theBR-040 Area the Carrancas Formation consists mainly of rhythmites and pelites overlying archean migmatitic gneisses of Belo HorizonteComplex. In both areas, black shales can reach values of Total Organic Carbon (TOC) in a range of 0,4 to 1,5%. The base of pink dolomitefrom Pitangui Area is in gradational contact with the rhythmites and pelites and has high values of δ13C (+7,1 to +9,6%). These values areincompatible with the regional values of the base of the Sete Lagoas Formation, reinforcing that these dolomites are a distinct unit insidethe Carrancas Formation, not previously described. In both areas the Carrancas Formation is interpreted as a product of gravitational flowsdeposited on basement channels controlled by faults at the southern margin of the São Francisco Craton. The isolation of these channelsrelative to the open sea favored the accumulation of organic matter, suggested by intercalations of black shales and by high values of δ13Cin dolomites at the top of the sequence.Keywords: Stratigraphy; Carrancas Formation; Bambuí Group; Neoproterozoic
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.008 | 0.003 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".