Re-Os age constraints and new observations of Proterozoic glacial deposits in the Vazante Group, Brazil

• Published in: Precambrian Research
• Main Authors: Geboy, NJ, Kaufman, AJ, Walker, RJ, Misi, A, de Oliviera, TF, Miller, KE, Azmy, K, Kendall, B, Poulton, SW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2013
• Subjects: Arctic; Canada
• Online Access: https://eprints.whiterose.ac.uk/80332/; https://eprints.whiterose.ac.uk/80332/1/Re-Os%20age%20constraints%20and%20new%20observations%20of%20Proterozoic%20glacial%20deposits%20in%20the%20Vazante%20Group,%20Brasil.pdf; https://doi.org/10.1016/j.precamres.2013.10.010

A new Re-Os radiometric age date for an organic-rich shale horizon from the Vazante Group in Brazil, coupled with geological observations, provide evidence for late Mesoproterozoic glacial episodes, conflicting with the general view of greenhouse conditions marked by a eustatic high stand at this time. Field observations of a reverse fault juxtaposing older Mesoproterozoic sedimentary rocks above younger Neoproterozoic strata provide a new stratigraphic framework and reconcile the apparent inversion of U-Pb detrital zircon ages through the succession. Combined, the geochronological, geochemical and stratigraphic evidence suggest that the Vazante Group sediments accumulated along a passive margin of the São Francisco craton and are correlative with the neighboring Paranoá Group. Biomarker, sulfur isotope and iron speciation analyses support the interpretation of a strongly stratified water column during post-glacial transgression and deposition of one of the bituminous shale horizons. The relationship of the glaciogenic Vazante Group to other late Mesoproterozoic successions, such as the non-glacial Atar Group in West Africa and Bylot Supergroup in arctic Canada, however, remains enigmatic.