Dolomitization and isotope stratigraphy of the Vazante Formation, São Francisco Basin, Brazil

Oceanic redox conditions in the Late Mesoproterozoic recorded in the upper Vazante Group carbonates of São Francisco Basin, Brazil: Evidence from stable isotopes and REEs

“…Thus, it is of some interest that remarkable negative ␦ 13 C shifts have been documented in cap carbonates of the upper Vazante Group diamictites of east-central Brazil (Azmy et al, 2001(Azmy et al, , 2006, which has recently been determined to have formed in the late Mesoproterozoic (Azmy et al, 2008). The current investigation presents evidence from Th, U and other REE variations in the carbonates to evaluate the redox conditions associated with the glacial event that formed them.…”

“…Previous chemostratigraphic studies of the C-isotope and 87 Sr/ 86 Sr (least radiogenic signature 0.706841) profiles of the Group, particularly those from the Lapa carbonates, suggested a possible correlation with similar isotopic profiles of Sturtian (800-650 Ma) sequences on the Congo Craton (Azmy et al, 2001(Azmy et al, , 2006Misi et al, 2007). However, the recent radiometric measurements of Azmy et al (2008) suggest an age of between 1.0 and 1.1 Ga for the Vazante Group.…”

“…The stratigraphy of the marginal marine sediments of the Vazante Group (Fig. 2) has been studied in detail and refined by several authors (e.g., Dardenne, 1978;Dardenne and Walde, 1979;Madalosso, 1979;Karfunkel and Hoppe, 1988;Fairchild et al, 1996;Azmy et al, 2001Azmy et al, , 2006Dardenne, 2001;Misi, 2001;Misi et al, 2007). Sediments in the eastern part of the basin are generally preserved but they become highly deformed and metamorphosed (amphibolite to granulite facies) to the west near the Brazilia Fold Belt (Dardenne, 1978;Fuck et al, 1994).…”

Modelamento metalogenético dos depósitos de zinco de Vazante, Fagundes e Ambrósia, associados ao Grupo Vazante, Minas Gerais

“…Sua evolução têm sido considerada contemporânea à do Grupo Paranoá, mesoproterozóico, que aflora no segmenro norte da Faixa Brasília (campos Neto, I 984; Fuck, 1994), à do Grupo Bambuí, neoproterozóico, que representa a Principal cobertura do Cráton do são Francisco (Misi,200 I ; 200 l), ou, ainda, intermediária em relação à evolução destes dois grupos (Pimentel et ol., 1999;Dardenne, 2001 o Grupo Aroí (Barbosa et al, 1969) foi gerado em um sistema de rift paleoproterozóico e const¡tui parte do embasamento sobre o qual foram depositadas as seqüências mesoneoproterozóicas da Faixa Brasília (Dardenne, 2000;P¡mentel et ol., 2001 O Grupo Serro do Mesø (Marini et al,l97T) const¡tui uma espesse seqüência metamorfisada em fácies anfibolito compostâ por quartzito conglomerático que grada Pãra quartz¡to fìno, laminado, com muscovita, intercalado em mica xistos com granada, estaurolitã e cianita com lentes de cálcio-xistos e mármores no topo. Segundo Dardenne (2000)' idades da t4 sedimentação entre 1,574 e 1,470 Ga obtidas neste unidade, podem ser indicativas da associação deste grupo com sucessões pós-rift do Grupo Araí.…”

C- and Sr-isotope stratigraphy of the São Caetano complex, Northeastern Brazil: a contribution to the study of the Meso-Neoproterozoic seawater geochemistry

“…Few works (e.g Knoll et al 1995, Hall and Veizer 1996, Frank et al 1997, Kah et al 1999, 2001, Bartley et al 2001, Azmy et al 2001, Maheshwari et al 2002, Bartley and Kah 2003 have supplied reliable chemostratigraphic information for the construction of well constrained C-and Sr-isotope secular variation curves. Therefore, establishing factors that affected the seawater geochemistry during this time span has remained difficult.…”