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Neoproterozoic successions of the São Francisco Craton, Brazil: the Bambuí, Una, Vazante and Vaza Barris/Miaba groups and their glaciogenic deposits

By
Aroldo Misi
Aroldo Misi
Metallogenesis Group, Department of Geology and Research Center on Geophysics and Geology (CPGG), Federal University of Bahia, Instituto de Geociências, Campus da Federação 40170-290, Salvador, Bahia, Brazil
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Alan J. Kaufman
Alan J. Kaufman
Departments of Geology and ESSIC, University of Maryland, College Park, Maryland, USA
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Karem Azmy
Karem Azmy
Department of Geology, Memorial University of Newfoundland, St. John's, Canada
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Marcel Auguste Dardenne
Marcel Auguste Dardenne
Institute of Geosciences, University of Brasilia, Brasilia (DF), Brazil
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Alcides Nóbrega Sial
Alcides Nóbrega Sial
NEG-LABISE, Department of Geology, Federal University of Pernambuco, Recife (PE), 50670-000, Brazil
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Tolentino Flávio De Oliveira
Tolentino Flávio De Oliveira
Votorantim Metais, P.O. Box 03, 38780-000, Vazante, MG, Brazil
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Published:
January 01, 2011

Abstract

The Neoproterozoic successions of the São Francisco Craton are primarily represented by the Bambuí and Una groups, deposited in cratonic epicontinental basins, and by the Vazante and Vaza Barris/Miaba groups, which accumulated on passive margins on the edges of the craton. The epicontinental basins comprise three megasequences: glaciogenic, carbonate platform (marine) and dominantly continental siliciclastics. Possible correlative sequences are observed in the passive margin deposits. At least two major transgressive–regressive sea-level cycles occurred during the evolution of the carbonate megasequence, which lies above glaciomarine diamictites of probable early Cryogenian (i.e. Sturtian) age. C, O, Sr and S isotope trends from analyses of well-preserved samples, together with lithostratigraphic observations, provide reasonable correlations for most of the Neoproterozoic successions of the São Francisco Craton. The 87Sr/86Sr record of these successions, ranging from 0.70769 to 0.70780, supports the proposed correlation with the Bambuí, Una and Vaza/Barris successions, and with the basal units of the Vazante Group. In addition, C-isotope positive excursions ranging from +8.7 to +14‰ and negative excursions from –5.7 to –7‰ VPDB in the Bambuí, Una and Vaza-Barris successions provide key markers for correlations. The precise ages of the sedimentation in these successions remains a matter of debate, but organic shales of two units of the Vazante Group have been dated by Re–Os techniques in two different laboratories, both yielding Mesoproterozoic ages. The Neoproterozoic and Mesoproterozoic successions preserve significant glaciogenic deposits.

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Contents

Geological Society, London, Memoirs

The Geological Record of Neoproterozoic Glaciations

Emmanuelle Arnaud
Emmanuelle Arnaud
University of Guelph, Canada
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Galen P. Halverson
Galen P. Halverson
McGill University, Canada
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Graham Shields-Zhou
Graham Shields-Zhou
University College London, UK
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Geological Society of London
Volume
36
ISBN electronic:
9781862394117
Publication date:
January 01, 2011

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