Stratigraphie et sédimentologie des dépôts marins et continentaux d’âge éocène moyen à miocène en Tunisie centrale (région du Djebel el Kébar)

• Gilles Merzeraud ^[1] ; El Mabrouk Essid ^[2] ; Wissem Marzougui ^[2]
  1. [1] Université Montpellier
  2. [2] Office National des Mines
• Localización: Bulletin de la Société Géologique de France, ISSN 0037-9409, Vol. 187, Nº. 1, 2016, págs. 11-25
• Idioma: francés
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• Resumen

  • The Kasserine area, in central Tunisia, is for a long time considered by many authors as an emerged island (or islets), since the upper Cretaceous until the middle Miocene. In the eighties, continental deposits were described and dated Eocene. At that time, no marine deposit older than middle Miocene were thus known in central Tunisia, and the only Eocene marine strata, were located in periphery of the emerged zone, in phosphatic basins. It is in the area of Djebel el Kebar, which is situated at the eastern edge of the Kasserine region that a detailed study of the Eocene-middle Miocene deposits was carried out. In the studied series, four major unconformities are observed and correlated on the whole of the site. Between these surfaces, three successive sedimentary units are observed from base to top and are composed of limestone, glauconite and clay deposits (unit I), shell beds limestone (unit II), conglomerate, sandstone and silty-clay (unit III).

    Paleontological and biostratigraphic results: An important fossils locality was discovered in Djebel el Kebar, in glauconitic marine deposits of the first sedimentary unit. Fauna, very rich, contains many marine (shark, ray, sirenian, etc.) and continental forms (rodent, hyracoid and primate). The new dating clearly indicates that the deposits of the lower part of the series are Bartonian in age.

    Sedimentological results: Thirteen facies were identified and the exceptional conditions of outcrop in Djebel el Kebar have allowed us to map the lateral facies evolution. The sedimentary environments were reconstituted and their succession shows a very shallow water-depth carbonate platform (wave dominated and influenced by storms and tide), passing upward into a sandy fluvial and estuarine environment.

    Tectono-sedimentary and sequential evolution: A sequence stratigraphic framework was proposed, in which, on both sides of unconformities primarily of tectonic origin, three very partially preserved sequences (> 3 Ma) are compatible with the second order of Vail et al. [1991]. In these sequences, the major part of the studied series is set up in transgressive system tracts and highstand system tracts. The fossil locality then seems to be associated with several episodes with condensation, formed during the transgressive part of the second order cycle.

    Conclusions: The first, new and important result of this work, is the characterization and dating of marine deposits older than middle-Miocene in Djebel el Kebar, in central Tunisia. The studied area is thus not in the emerged part of the zone of Kasserine during the Eocene. Between Bartonian and lower-Miocene, marine facies, evolve within an environment of very shallow marine carbonated platform. A major event (flexure coupled with eustatic fall in Miocene) would cause a change of depositional profile, the arrival of coarse terrigenous material and the installation of a continental fluvial and estuarine sedimentary environment. Finally the whole of the series records large scale tectono-eustatic changes, responsible of several second order sequences, partially preserved.