Caractérisation des horizons manganésifères de l’Ordovicien supérieur de Sardaigne : relation avec la glaciation fini-ordovicienne

Ghienne JF;Bartier D;Leone F;LOI, ALFREDO

2000-01-01

---

Abstract

Mn-rich crusts interbedded within glacially-related Hirnantian deposits of Sardinia result from starved sedimentation in isolated sub-basins. These latter result from low glacio-eustatic sea-levels on the North-Gondwanian platform. During very low sea-levels, large supplies of fresh water are responsible for oxidizing conditions allowing Mn-oxides concretions to form. During relatively higher sea-levels, sea water inflows result in water stratification, reducing conditions and Mn-carbonate concretions. A hydrothermal origin associated with a rifting event is suggested for the manganese. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.