Deep geometry of Triassic evaporite bodies associated with the Bazina structure, North Tunisia: new insights from gravity modeling

The Triassic outcrop in the Bazina structure is known among the largest massif in northern Tunisia. Its tectonic setting and sub-surface geometry are related to geodynamics and kinematics in North Africa and western Mediterranean domains. Gravity data processing and interpretation over the Hedil region highlight deep faulting and the geometry of Bazina structure and the neighboring ones. Enhancement of the residual anomaly, which represents the gravity response of sedimentary cover, mainly horizontal gradient map and its maxima, reveals varied oriented lineaments. The E-W conspicuous direction covers and delimits the outcropping Triassic body. However, the NE-SW major direction, highlighting eastward and southward of the Bazina structure, coincides with Cretaceous exposures. Furthermore, less extended N- and NW-trending features were highlighted. Limits and depth of deep gravity causative bodies were located using the Euler deconvolution method. 3D inversion and 2D forward gravity modeling combined with geological outcrops enabled the reconstruction of the Triassic bodies and surrounding structures. The study area reveals piercing diapiric structures and salt wrinkles. This Bazina evaporite exposure corresponds to a deep-rooted diapir marked by a southward evaporite lateral outpouring related to the Eocene Pyrenean compressive tectonic phase. The evaporite lateral flow should be controlled by reactivation of preexisting regional faults with its thermodynamic conditions and asymmetrical basin geometry.