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Communication dans un congrès

Stable isotopes of oxygen and carbon compositions in the Neoproterozoic of Gabon

Abstract : Geologic evidence of tropical sea level glaciation in the Neoproterozoic remains a matter of debate in the Snowball Earth hypothesis. The Niari Tillite and the cap carbonates could record the late Neoproterozoic Marinoan glaciation in South Gabon. These cap carbonates (Sc1a Member) are located at the base of the Schisto-Calcaire Subgroup a predominantly carbonate succession that sit with sharp contact upon the Niari Tillite (Thiéblemont et al., 2009). Integrating sedimentological and stable isotope data, a consistent sequence of precipitation events is proposed, with strongly negative δ13C values pointing to a possible methane release in the cap carbonates (average δ13C value = -3.2‰) and in a further newly defined lithohermal unit (average δ13C value = -4.6‰). Subsequent shallow evaporitive platform carbonates display carbon and oxygen compositions of relatively unaltered seawater values. Strongly negative δ18O values in the lithoherms and replacement of aragonite fans by equigranular calcite suggest flushing of meteoric water derived from glacial meltwater. The lateral persitence of the Sc1a carbonate units, the uniformity of facies of the Sc1, the consistency of their δ13C and δ18O values overlying the Niari Tillite support the interpretation that these deposits are a 'cap carbonate' suite, and can therefore identified as markers of Marinoan glaciation termination and the onset of the Ediacaran Period dated at ca 635 Ma (Corkeron, 2007).
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https://hal-brgm.archives-ouvertes.fr/hal-00664207
Contributeur : Denis Thiéblemont <>
Soumis le : lundi 30 janvier 2012 - 09:49:32
Dernière modification le : vendredi 3 juillet 2020 - 09:33:52

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  • HAL Id : hal-00664207, version 1

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Alain Préat, Jean-Pierre Prian, Denis Thiéblemont, Franck Delpomdor. Stable isotopes of oxygen and carbon compositions in the Neoproterozoic of Gabon. 23th Congress on African Geology, Jan 2011, Johannesburg, South Africa. ⟨hal-00664207⟩

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