Les formations du crétacé inférieur des massifs néritiques méridionaux

Abstract

The southern Neritic massive of Ain M'Lila constitiue one of the main outcrops of Lower Crétaceous néritic platform Constantinoise. They are part of a region located charniére convergene to the external areas of the Alpine chain Algeria and eastern Atlas area is the flat shape and Constantine notament its southern borde. The lithostratigraphic study of Lower Crétceous séries of Monts the Ain M‘Lila enabled to highlight a carbonate series of Jurrasique going to Aptian terminal. The séries ends with a hardened surface regional scale, reflecting the emergence of the flat shape to this époquee with deficiency in the Albian in most of the southern mountains. Often missing the Albian was reconu massif at Nif Ennser, represented by one hundred meter microconglomératiques of alternating limestone and marl clear. On the tectonic map, southern massive plicatves are characterized by more or less largescale structures. These plicatives structures affected by numberous faults which the most important are the dextral offsets, direction NW- SE. The sedimentological analysis permits proposed deposition model for the study area from a microfaciologique and paleoenvironmental analysis. This analysis allowed reconstituting an internal platform environment shape crossed by a recif, in which several microfacies, sorted by increasing order bathymetry were indidualisés. The internal facies of flat calm as sometimes agitated. - The supratidal - intertidal facies characterized by mudstone essentillement to wackstone to calcisphéres. - The facies of the partially protected lagoon (subtidal) benthic foraminifera in, and milioles orbitoline and algae. The reef facies subrécifaux to include: - The reef facies of reef flat: these are deposits of intraclasts, pellets, oncolites and many benthic foraminifera). - Haut-fond facies: include the packstone- grainstone Brayozoaires and rudist, echinidides, oolites and corals. - The évolutionon diagénitiques of carbonate sediments of our study area undergoes transformation diagénitiques trio’s stage: - Early diagenesis: marked by micritisation formed elements, perforations, biological crusts, and bioturbations. - Mésogenése: marked also by chemical compaction (stylolites) and mechanical (fracturing) and cementation and dolomitization. - Télogenése: marked by dolomitization, the dédolomitisation and intense fraturation (diaclase