Stratigraphy of the Hameima and lower Fahdene Formations in the Tadjerouine area (Northern Tunisia)

In the Tadjerouine area of north-western central Tunisia, the Albian transgression is characterized by deposition of alternating marls, limestones and sandstones (Hameima Fm) that overly massive platform carbonate rocks (Serdj Fm). The continuing transgression results in deposition of a thick series of marls and shales with subordinate carbonate beds (Fahdene Fm). A detailed study of the Hameima Fm, previously ascribed to the Late Aptian, shows that this formation can be subdivided into three members, all of earliest Albian age (Leymeriella tardefurcata Zone). The top of the Hameima Fm is slightly diachronous in the study area. A similar study of the Lower Shales of the Fahdene Fm demonstrates that they belong to the L. tardefurcata Zone and to the lower part of the Douvilleiceras mammillatum superzone. The overlying Allam limestones, formerly considered Middle Albian in age, are mainly of late Early Albian age (upper part of the D. mammillatum Superzone and Lyelliceras pseudolyelli Zone), although an extension into the lower Middle Albian cannot be ruled out. The Allam limestones are abruptly overlain by a diachronous series of Late Albian shales (Middle Shales of the Fahdene Fm), thus evidencing a stratigraphic hiatus of most of the Middle Albian and part of the early Late Albian. Our new data will lead to revision of the range of some Aptian/Albian orbitolinids and Albian planktic foraminifera.