First evidence of the early cretaceous oceanic anoxic events (MBE and OAE1a) in the southern Tethyan margin (NE-Tunisia): biostratigraphy and shale resource system

Abstract The Jebel Oust region (north-eastern Tunisia) recorded two levels of marine black shale in the Lower Cretaceous marly series. Geodynamic evolution, biostratigraphic and Rock–Eval analysies allow classifying those shales as unconventional oil resource systems that were deposited during oceanic anoxic events: Middel Barremian Event "MBE" Early Aptian "OAE1a". Paleogeographic evolution highlights transgressive–regressive cycles: first one is Valanginian-Early Barremian, second Late Barremian–Early Aptian. Each deposit occurs at end transgression coincides with highest sea level. During Barreman–Aptian interval, sedimentation was controlled by extensional faults a system tilted fault blocks which reactivated several times. Kerogen type I, II origin III marls. Tmax values indicate "oil window" stage. Average transformation ratio around 67% 82%, respectively, source rock related to relatively high thermal maturity degree due deep burial later. Estimated initial hydrocarbon generation potential moderate high. Oil saturation index records an crossover" indicating expelled migrated hydrocarbons from organic-rich organic-poor facies. petroleum mature rocks enclose all elements characterizing "shale hybrid combination juxtaposed organic-lean facies associated open fractures".