A Review of Jurassic Oceanic Anoxic Events as Recorded in the Northern Margin of Africa, Tunisia

摘要

During these last years, considerable attention has been given to Jurassic oil and gas shale in the middle and high latitudes of the northern hemisphere such as the west Europe and Russian platform where the most attractive Jurassic basins are located (e.g. Cleaveland basin, UK; Boulonnais, northern France; Pechora Basin, Moscow Basin, etc). In most petroleum systems which characterize these basins, the Jurassic (mainly the early Toarcian) played the major role in hydrocarbon generation which constitutes 25% of the global reserve of hydrocarbon. Tunisian basins represented by the northern Tunisian trough, the Dorsale and the North South Axis (NOSA) belong to the southern Tethyan margin where northern and central area have recorded the early Toarcian oceanic anoxic event (T-OAE). This short lived (c. 2 Ma) period of anoxia ranges within the whole Harpoceras serpentinum Zone which corresponds to deep water environments marked by black shale accumulation. Interestingly, towards the south, the dysaerobic conditions in the Chott basin appear to have begun largely later where the oxygen depletion is assumed to have prevailed during the Callovian, whereas it was limited to the early Toarcian in the Central and Northern Tunisia only a few hundreds of kilometers away. In addition, biostratigraphic and complete geochemical review has been undertaken from published papers and unpublished internal reports to better assess these important source intervals.