Contribution of cathodoluminescence to the knowledge of manganese speciation into pelagic limestones.: Determination of the control of sea-level variations on third-order sequences during the Upper Jurassic.

Mn contents analysis of pelagic carbonates from the Upper Jurassic of the Vocontian trough (Chateauneuf-d'Oze section, Hautes-Alpes) allowed the definition of six third-order eustatic sequences that agree with the chronostratigraphic chart [17]. Cathodoluminescence intensity enables a semi-quantitative approach of Mn trapped in the calcite lattice; thus, CL-results show that most of Mn is found in the pelagic limestones as Mn2+. The Mn content variations observed in the low stands (low Mn contents) and in the high-stand systems tract samples (hi,oh Mn contents) reflect the sea water Mn content variations, which appear to be linked to the hydrothermal activity, especially by the ocean ridge. In the Vocontian realm, third-order sequences of the Upper Jurassic seem to be controlled by tectono-eustatism. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.