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Sedimentation, diagenesis and syntectonic erosion of Upper Cretaceous rudist mounds in central Tunisia

NEGRA Mohamed Hédi, PURCER Bruce Harold, MRABET Ali, 1995

Special Publications of the International Association of Sedimentologists, 23, 23, 401-419, Septembre 1995

Résumé

The Upper Cretaceous carbonates of central Tunisia include lensoid mounds composed essentially of micrite locally rich in rudist and corals. Although these organisms can be closely packed and contribute

Actively to the creation of bioherms, the majority (70-80%) are scattered in micritic mounds. Their debris forms graded sequences indicating a hydrodynamic accretion. Three types of mud-mound are recognized: type 1, essentially a wackestone, contains debris of rudists, corals, echinoderms, associated peloids and scarce calcispheres. Type 2 is a composite mud-mound comprising a type l mud-mound directly overlain by a type 3 bioherm. Type 3 is a muddy. bioconstructed rudist-coral bioherm in which interrudist spaces arc filled with fine (wackestone) sediment rich in rudist-coral and echinoderm debris.

Conglomerates containing blocks reworked from the rudist carbonates are volumetrically important. They clearly indicate significant Late Cretaceous lithification and erosion. Within the mounds, early diagenesis is expressed by neogenic microspar and by interlocking or coalescing nanof