Les mud-mounds du dévonien moyen du bassin de l'Ahnet et ses régions limitrophes ( sud-ouest algérien) Sédimentologie - diagenèse
Résumé
The mud-mounds with stromatactis of Givetian, occupy the western margin of the basin of Ahnet (Algeria). These monticules seem equivalent to potential tanks analyzed in sub-surface. These monticules are presented under two types of morphology which follow alignments of preferential directions, NS and NW-SE. The mud-mounds, several tens of meters thickness, are mainly made up by a heart of boundstone with stromatactis and laterally by sides made up of packstones with encrinites. The construction of the mud-mounds, of which the duration is estimated at two million years, falls under the varcus zone (lower Givetian). The principal factors of construction are initially the framework morphostructural basin and its tectonic evolution. The position of the mud-mounds on the east sides and soft anticlines is a direct consequence of the structuring imposed by the precambrian faults N-S and the intragivetian faults (N60° and N110°). The origin and the development of the mud-mounds of Ahnet are governed by the fluctuations of the sea level and they develop in external ramp which his orientation is N-S. These mud-mounds shows a good porosity (30 %) which during the hiding, is gradually filled. Secondary porosities are associated processes of fracturing, dolomitization and dissolution. Key words : Mud-mounds, stromatactis, sedimentology, tank, carbonates, Algeria, Ahnet, Givetian.