Les formations sédimentaires du bassin deTimgad

Abstract

Timgad basin is located at the convergence of the pre-Atlas domain which is characterized by a tectonic style marked by massive overthrusting northern (Monts Belezma and links Bou Arif -Fedjoudj) and the autochthonous domain Atlasic (Aurès massif) in south. It corresponds to a subsiding area, where are accumulated is very thick sedimentary deposits of Meso-Cenozoic age. These include two major series, a lower-calcareous marl gréso-dominant, belonging to the Mesozoic, the other upper gréso represented by Neogene marl deposits. They are separated by a major discordance related to the Miocene compressive phase .The Upper Cretaceous series has discontinuities represented by hard -sdnuorg indicating a fluctuation in sea level. Based on the types of microfacies and the paleontological content ,the depositional environment is often subject to bathymetric changes .That could be attributed to tectonic and / or a eustatism where certain maximum flooding surfaces are reported. The deepening of the marine environment starts from the Lower Cenomanian. On the tectonically, different structures are represented by the dominant direction of Atlas folds. Accidents are directions NE-SW and NW-SE dominant and have compartmentalized the Timgad Basin tilted blocks. A great tectonic accident overlapping oriented substantially EW, generated dislocations ramps facing south. On the hydrocarbon potential and based on different data (geological and geophysical), potential trapping fo hydrocarbons in the Timgad basin were estimated qualitatively. The petroleum system in the Timgad basin consists of three source rocks moderately rich organic matter; the Vraconian the Cenomanian and the Turonian. The latter seems more promising. In addition ot source rocks, the reservoirs of the basin, such as the Lower Albian, Cenomanian upper and lower Turonian represent weak petrophysical parameters, making it a bit tricky trapping or even if there would be an accumulation yield will be low . The traps identified in the basin are of mixed type, where we find the structures due to tectonics as anticlines and stratigraphic traps related to unconformity in the existence of clay and marl cover that blocks the hydrocarbon migration once trapped.