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MPC-03 Precambrian isotope chemostratigraphy
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C-, Sr-isotope and Hg stratigraphies of Neoproteroic cap carbonates of the Sergipano belt, northeastern Brazil
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Alcides Nobrega Sial, Federal University of Pernambuco (Brazil)
Valderez Pinto Ferreira, Federal University of Pernambuco (Brazil)
Claudio Gaucher, Facultad de Ciencias (Uruguay)
Marinho Alves Silva Filho, Companhia de Pesquisa de Recursos Minerais (Brazil)
Marcio Martins Pimentel, University of Brasilia (Brazil)
Luiz Drude Lacerda, Universidade Federal Fluminense (Brazil)
Emmanoel Vieira Silva Filho, Universidade Federal Fluminense (Brazil)
Wilker dos Santos Cezario, Federal University of Pernambuco (Brazil)
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Two cap carbonates have been identified in the Vaza Baris Domain of the Sergipano belt, northeastern Brazil. The older one is represented by the Jacoca Formation carbonate which rests on the Ribeiropolis Formation diamictites and the younger one, by the Olho D'Agua Formation carboantes overlying Palestina Formation diamictites.
The time interval for deposition of these cap carbonates is constrained by the age of the Ribeiropolis Formation (730Ma) and the age of the Frei Paulo Formation on top of the Olho D'Agua carbonates (615 Ma). Values of d13C for the Jacoca Formation are around -5‰ in fourl sections examined.
For the Olho D'Agua carbonates, however, negative values (around -5‰) in the basal portion are replaced up section by values close to 0‰, and above by values from + 8 to + 10‰. An attempt to demonstrate that the CO2 for cap carbonate deposition was mantle-derived (with d13C values around -5‰) using Hg contents as a proxy, revealed that Hg in Jacoca carbonates are much higher (locally up to 280 ng.g-1) than usually seen in carbonates (< 3 ng.g-1) but within the range for carbonates deposited concomitantly to volcanic activities (e.g. Tertiary Punta Rocallosa Formation carbonates, Chile), up to 80 ng.g-1. >87>Sr/86Sr for Jacoca (0.70717 to 0.70732) and for Olho D'Agua carbonates (0. 70787 to 0.7082) point to deposition within the Sturtian interval.
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