Chemostratigraphy of the Neoproterozoic Mirassol d'Oeste cap dolostones (Mato Grosso, Brazil): An alternative model for Marinoan cap dolostone formation

E. Font (1) , A. Nédélec (1) , R.I.F. Trindade , M. Macouin (1) , A. Charrière (1)

1 LMTG - Laboratoire des Mécanismes et Transfert en Géologie

We have conducted a detailed study of the Neoproterozoic Mirassol d'Oeste cap dolostones that overlay the glacial diamictites of the Puga Formation (˜ 635 Ma, Amazon craton, Brazil) in order to understand the formation of these post-glacial dolostones. Petrographic features indicate that the dolostones are primary to early diagenetic in origin and precipitated in a moderately shallow-water platform corresponding to a carbonate ramp during transgressive conditions. Major and trace element contents, as well as C and O isotopic signatures, are consistent with an anoxic sediment influenced by sulphate-reducing bacteria. Such an environment is known to provide favourable conditions for the precipitation of dolomite as observed nowadays in modern hypersaline lagoons. Isotopic compositions of tube-like structures suggest local upward fluid seepage from the underlying cap dolostone. Our data concur with geochemical data from other Neoproterozoic cap dolostones to support a microbially-mediated model in specific environmental conditions for the formation of these unusual deposits worldwide.

Domaines: Sciences de la Terre

E. Font, A. Nédélec, R.I.F. Trindade, M. Macouin, A. Charrière. Chemostratigraphy of the Neoproterozoic Mirassol d'Oeste cap dolostones (Mato Grosso, Brazil): An alternative model for Marinoan cap dolostone formation. Earth and Planetary Science Letters, 2006, 250 (1-2), pp.89-103. ⟨10.1016/j.epsl.2006.06.047⟩. ⟨hal-00321013⟩