par Préat, Alain 
;Mamet, Bernard ;Bernard, Alain ;Gillan, David
Référence Sedimentary geology, 126, 1-4, page (223-242)
Publication Publié, 1999-07
;Mamet, Bernard ;Bernard, Alain ;Gillan, David Référence Sedimentary geology, 126, 1-4, page (223-242)
Publication Publié, 1999-07
Article révisé par les pairs
| Résumé : | Two Devonian red carbonate rock sections are studied in the Montagne Noire, at Coumiac (Frasnian/Famennian) and at the Pic de Vissou (Eifelian/Givetian). The sediments are grey-red mudstones and wackestones rich in pelagic fossils. They are characteristic of an outer ramp. The Coumiac sequence is condensed with numerous hardgrounds and hiatuses. The Pic de Vissou succession is more complete and shallower origin. In both cases, the origin of the red coloration of the micritic matrix is probably linked to bacterial activity which produced submicronic hematite. Both iron and manganese concentrations are low (average 0.2%). Bacteria from ferruginous microstromatolites, blisters, microtufts, 'hedgehogs' filling sponge perforations and thin continuous mineralized films (probably biofilms). Hardgrounds are underlined by ferruginous microstromatolites. The origin of the matrix color is probably related to the destruction of these bacterial constructions, the submicronic hematite ultimately coating the crystal faces of the calcite mosaic. During early lithification, microfissures appeared and were invaded by microbial colonies. Scanning electron microscopy (SEM) shows that these colonies are composed of spheroidal beads. This suggests continuity of the bacterial activity during early diagenesis. Later on, these early fissures were cut by burrows. Subsequently a secondary fissure network transected all the previously mentioned sedimentary structures. This late fissure network is characterized by diagenetically remobilized hematite and/or calcite. The latest alterations are stylolites and ultimate tectonic fractures. |
