The biostratigraphy of carbonate deposits of the middle and upper eocene in northeastern off-shore Tunisia

Abstract

Several holes drilled recently off the coast of northeastern Tunisia (Gulf of Hammamet and the Pelagian Sea) have cut into a thick formation of entirely carbonate rocks of Priabonian and Upper Lutetian age. These deposits with a “Liburnian” facies have no equivalent on-shore in the outcrops of the Tunisian Eocene. They are characterised by an unusual brackish-marine faunal association and by the total absence of argillaceous layers and detrital siliceous material. This formation, well dated by its microfauna and by the age of the layers which surround it, can be divided into three distinct units, from top to bottom: 1. (1) Limestones with Miliolidae, Peneroplidae, Pseudochrysalidina, Lituonella and Discorinopsis and with dasycladacean algae; at their top, layers rich in Microcodium can be observed. 2. (2) Marine platform limestones with Nummulites and Discocyclina. 3. (3) Crystalline and vacuolar dolomites which are probably secondary. Identical facies to those of the upper unit can be found in outcrops on the islet of Lampione in the Pelagian Sea. Therefore, and for the first time, we can establish that they are of Late Eocene age. Moreover, a comparison has been made between the facies on Lampione and those facies which have been previously described in the southern Apennines, characterising the “Spirolina cenozone”. The possibility of a younger age for this cenozone (Late Lutetian and Priabonian rather than Paleocene) is envisaged.