La plateforme carbonatée constantinoise pendant l’intervalle aptien-albien

Abstract

Constantinois platform, considered as parautochthonous structure overlapped by Tellian units, is composed of carbonate and cilico-clastic sedimentation during the Aptian-Albian interval. The main objective of this study is to determine environmental conditions of aptian-albian facies and to evaluate tectonic control on sedimentary discontinuities setting up of Djebels Felten, Karkara, Zouaoui and Kheneg. Three lithostratigraphic formations have been identified: Kheneg algal limestones (lower Aptian), Zouaoui bioconstructions (upper Aptian) and Felten marl-limestones (Albian). The facies and depositional environments of the Aptian-Early Albian rocks are identified based on their lithology, sedimentary structures, fossil content and microfacies. These allowed to identify a deposition model as isolated platform. This is characterized by lagoon-reef sedimentation during Aptian, which evolves towards a flooded platform with hemipelagic sedimentation during lower Albian. These changes, dated at least upper aptian, are marked by the development of emersion and condensation discontinuities. The magnetic susceptibility changes recorded in the studied sections made it possible to recognize several factors, which influenced magnetic signal such as platform morphology; sedimentary discontinuities; the detrital input and sedimentary condensations facies. Diagenetic study, based essentially on the identification of early cements developed in these discontinuities, allowed a better pinpointing the paleoenvironmental mechanisms developed during Aptian-Albian transition. Three major depositional sequences can be distinguished and indicate a deepening trend that generally coincides with the sea level rise, recorded in the Cretaceous seas. The correlations carried out on all the sections studied made it possible to propose an uplift of the platform and a tilting from North to South during at least the end of the Upper Aptian. The sedimentological study, of Constantine region massifs, shows an undoubted result as to the sedimentary origin of the upper aptian discontinuities, interpreted by some authors as thrust contact.