Fekri Kamoun

Sequence stratigraphy and micropaleontology of the Triassic series from the southern part of Tunisia

Abstract The Triassic series in the southern part of Tunisia, only known from the oil exploration wells in the Kirchaou area (sandy series from Early Scythian to Ladinian) and in its Djeffara/Dahar-North outcrops (alternating series from Ladinian to Rhaetian) is now subdivided into 10 Depositional Sequences (DS) sensu Vail et al. (1987), T 1 to T 10 corresponding approximately to most of the 3 rd order eustatic cycle from the Haq et al. curve (1987). Within the DS succession, 3 basal discontinuities (or sequence boundaries) appear to be important in Tunisia: the base of T 2 , correlated to the “H Discordanz” from the “Germanic Triassic” (intrascythian); the base of T 6 (intracarnian), well-marked by the Sidi Stout angular discordance from Dahar North; the base of T 8 (intranoirian additional DS, previously recognized in Germany) pointed by the cartographic discordance of Low Stand conglomerates. The shallow-water facies from the carbonate Transgressive Systems Tracts of 7 Tunisian DS contain macrofauna, such as Myophoria , and particularly 6 successive benthonic Foraminifera assemblages, F 1 to F 6 giving chronostratigraphic informations as complement of Palynomorphs and Conodonts. Belonging to the genus Meandrospira, Triadodiscus, Aulotortus, Lamelliconus, Endothyranella, Pilamminella, Agathammina, Gandinella etc.…, most of them, commonly used as zone-indices in Europe, are new in Tunisia.

Évolution paléogéographique de la Tunisie saharienne et atlasique au cours du Jurassique

Abstract By means of palaeontologic data, the differert Jurassic formations of Tunisia are correlated along a north-south transect, from the Saharan Platform to the Northern Atlas, across the successive steps of the South-Tethyan stable palaeomargin. A palaeogeographic synthesis of the country is herein proposed, based on 11 maps established for the most important stages of this preoceanic rifting phase which is characterized by particularly active transtensional tectonics.

Le paléomagnétisme est-il un meilleur outil que la biostratigraphie et la sédimentologie pour fixer la polarité de l'Albien du Nord-Ouest tunisien ?

Abstract The results of a recent palaeomagnetic study, which are considered as proof of the overturning of the Aptian-Albian beds under the supposed saliferous intrusive bodies from northwest Tunisia, are compared with the several incompatible cartographic, stratigraphic and sedimentological data. The geological interpretation of the palaeomagnetic measures supporting the hypothesis of the non-interbedding of the evaporites is discussed and arguments are given in order to demonstrate the lateness of certain magnetizations, borne by magnetites, which are regarded by us as post-diagenetic. The palaeomagnetic tool does not seem, in the studied areas (S of Debadib, Kt ed Dalaa, J. Slata), to support the proposed setting up processes (upturning, lateral injections under cover). The non-interbedding of the evaporites would not explain either the flat-topped initial geometry of the saliferous structures, or the wells, or the gravimetric Algerian and Tunisian data. On the contrary our interpretation of the saliferous bodies emplacement, within wide ‘salt glaciers’ is more convenient to integrate the various data previously obtained on this topic.