Interpretation of gravity data using 3D inversion and 2D continuous wavelet transform in Hedil deformed structures, northern Tunisia

Abstract

The Hedil region in northern Tunisia shows several geological structures associated with intense tectonic deformations that induced genesis of overthrusts and tectonic imbrications with rising of Triassic evaporites. This region constitutes a transition zone, between the Atlassic and Tellian domains, and exhibits multi-scale tectonic deformations related to the basins structure and the regional geodynamic of the Northern African margin. Gravity data processing and continuous wavelet transform, coupled with field data, lead to underline the subsurface geometric configuration and to propose an evolutionary structural framework for the studied area.The horizontal gradient magnitude (HGM) and its maxima highlight several lineaments trending NE-, E−, NW and N however the NE-SW direction is predominantly expressed. Depths of the main buried structures were estimated using the Euler deconvolution method. The highest values that exceed 3 km seem to underlines the structures associated to NE-SW, NW-SE and rarely E-W inherited features. The NE-SW oriented structures are mainly represented by overthrusts and tectonic imbrication zones that were occurred along inherited faults in the southern part of the area, as a result of the Atlassic compressional tectonics of Late Miocene and Quaternary ages. However the other lineaments correspond mainly to strike-slip and reverse. The application of 3D inversion method allows identification and characterization of geological structures in subsurface. The most deformed structures are marked by positive anomalies and are sometimes underlined by intrusion of Triassic evaporite rocks. However, the collapsed structures are underlined by negative anomalies testifying a material of low density. The extracted inversion sections highlight the deep rooted geometry of the Triassic bodies, locally associated with overturn of pierced strata.The continuous wavelet transform method was used to get an idea about the deep structures of the region, to estimate the boundary between the sedimentary filling and the Precambrian basement, and determining the depth and dipping of some identified contacts. Some uplifted structures and Triassic evaporite intrusions especially that of the Bazina are marked by risings of pre-Triassic deep causative sources. These zones of significant anomalies in the Atlassic domain are probably areas of intense deformation related to the ancient Hercynian tectonics that affected the North African margin. The identified structures should be related to the regional tectonic inversion, related to the African and European plates subduction.