Nouri Hatira

Preuves paléomagnétiques de la non-interstratification des évaporites du Trias dans l'Albien du Maghreb oriental

In northwestern Tunisia, a paleomagnetic study was carried out on Albian levels, objects of controversy. They are considered to be either overturned strata on the limb of diapirs, or in their upright position as the floor of a salt glacier. After correction for the apparent dip, the polarity of the primary magnetization is always reversed, and the magnetization directions are relatively scattered. The Earths magnetic field was always of normal polarity during the Albian, so that these levels are overturned. The scattering of the magnetization direction points out moreover that the tilting occurred around axes of various orientations. All these observations show that the evaporitic bodies were emplaced in diapirs, and that the notion of a salt glacier interbedded within the Albian sediments has to be given up.

Le Trias a caractere extrusif de la zone des domes; example de la structure de Debadib-Ben Gasseur (Tunisie septentrionale)

The Debadib-Ben Gasseur anticlinal structure, situated between El Kef and the Algero-Tunisian border, belongs to one of the main diapiric, alignments of the oriental Maghreb. It constitutes an elliptic form oriented NE-SW. The heart is occupied by Triassic residual evaporites containing basaltic volcanites which seem to indicate an extensional setting during the Triassic period. The contact between the saliferous bodies and surrounding Cretaceous-Tertiary age rocks is locally underlined by conglomerates including reworked Triassic blocks and glauconite, suggesting a sedimentary contact. Biostratigraphic and sub-surface data could indicate, in terms of model reconstitution, an extrusive system with numerous phases starting in the Aptian and acting until the Tertiary period. However, tectonic events are clearly expressed during the Miocene.

Paleomagnetism as a structural polarity criterion: application to Tunisian diapirs

Abstract In the Upper Aptian–Albian units, close to Triassic displaced bodies of northwestern Tunisia, the primary magnetization acquired during the Cretaceous period of normal magnetic polarity yields an unquestionable structural polarity criterion. The use of this criterion confirms the diapiric origin of these Triassic bodies and aids understanding of the evolution of the diapirs. It also appears to be a useful tool for the analysis of the geometry of overturning. An Eocene halokinesis on the platform south of the Tunisian Channel is also indicated by analysis of magnetic overprint in the Jebel Slata.