Seismic sequence stratigraphy of the Jurassic of the central Atlas, Tunisia

The compilation of outcrop and available subsurface data provided by wells drilled in the Tunisian Atlasic zone has permitted the establishment of a general palaeogeographical reconstruction showing the Jurassic basin and platform distribution. New seismic interpretation also helped in characterizing several seismic sequences within the buried Jurassic series and in setting up several seismic stratigraphic sections, isochron and isopach maps. In the Sidi Aïch and Majoura zones, the Jurassic series were subdivided into five second-order sequences (JSI–JSV) bounded by major unconformities that can be followed from one area to another.The sequences of the uppermost part of the early Jurassic (Toarcian) and those of the middle to late Jurassic interval show important variations in thickness and facies, indicating the development prior to the Toarcian of an irregular and relatively deep shelf, comprising subsiding zones and high platform domains. The gaps and discontinuities, well documented at surface within the North South axis (NOSA) as well as in the Tunisian range further to the north, have been identified also in the subsurface, especially within the highest blocks of the buried Jurassic system of the Atlas. In the subsurface they are expressed by the geometric relationships of the reflectors, which end near the edges and completely disappear on the crests of the blocks.