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Anil Maheshwari, University of Rajasthan (India)
Alcides Nobrega Sial, UFPE (Brazil)
Valderez P Ferreira, UFPE (Brazil)
A.W. Romano, Institute of Geosciences (Brazil)
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A positive d13C anomaly has been reported from Paleoproterozoic carbonates of the Aravalli Supergroup, western India and Minas Supergroup, Brazil. New C- and O-isotope data generated in the present study further contribute to the knowledge of the geochemistry of the global ocean during the 2.4-2.1Ga interval. The 2.42Ga Gandarela Fm., Minas Gerais, Brazil, with red carbonate facies BIF grading into dolomites and limestones have a 13C values ranging from -1.5 to +0.5‰PDB. The overall positive C-isotope record (+2 to + 11 ‰PDB; Lomagundi phenomenon) in marine carbonates, mainly stromatolitic dolostones, in the study areas (Bari Talab, Iswal and Babarmal Formations in western India and Cercadindo and Fecho do Funil, in Minas Gerais, Brazil) is comparable to that observed in contemporaneous carbonate successions worlwide (2.3 to 2.1Ga). No evidence was found in India or Brazil for any of the three early Paleoproterozoic glacial events recognized in 2.45-2.22 Ga sedimentary successions in North America. Geological traces of these ice ages are missing along the unconformities between the Gandarela and Cercadinho Formations in Brazil and the Banded Gneissic Complex and Lower Aravalli Supergroup in India. Compositional and isotopic changes reported here allow integration of the Aravalli and Minas Supergroups into the global record of the Paleoproterozoic evolution as well as correlation with other successions of similar age.
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