New structural and geodynamic coastal Jeffara model (Southern Tunisia) and engineering implications

Abstract

Thanks to its geographical position in the western Mediterranean domain, Tunisia faces, since mid-Cretaceous (Aptian/Albian time period), to the inversion of the Tethys due to the northward African plate motion toward Eurasia. The coastal Jeffara is a part of the southern zone of deformation witness of the eastward migration of Tunisia to the Mediterranean Sea. We focus herein following Perthuisot (Cartes géologiques au 1/50.000 et notices explicatives des feuilles de Houmet Essouk, Midoun, Jorf, Sidi Chamakh, 1985) and others on the neotectonic of the coastal Jeffara (southern Tunisia) and its engineering implications. Based on the results of previous studies and new evidences developed herein, we propose a new structural and geodynamic coastal Jeffara model, influenced by the continuous post lower cretaceous northward migration of northern African toward the Eurasian plates. We herein study the Digital Elevation Model (issued from SRTM), which was checked with field surveys and 2D numerous seismic profiles at depth both onshore and offshore. All data were, then, integrated within a GIS Geodatabase, which showed the coastal Jeffara, as a part of a simple N-S pull-apart model within a NW-SE right lateral transtensive major fault zone (Medenine Fault zone). Our structural, geological and geomorphological analyses prove the presence of NNW-SSE right lateral en-echelon tension gashes, offshore NW-SE aligned salt diapirs, numerous folds offsets, en-echelon folds, and so-on… that are associated with this major right lateral NW-SE transtensive major coastal Jeffara fault zone that affect the Holocene and the Villafrachian deposits. These evidences confirm the fact that the active NW-SE Jeffara faults correspond to the tectonic accident, located in the south of the Tunisian extrusion, which is active, since mid-cretaceous, as the southern branch of the eastward Sahel block Tunisian extrusion toward the free Mediterranean sea boundary. Therefore this geodynamicalmovement explains the presence, offshore, of small elongated NW-SE, N-S and NE-SW transtensive basins and grabens, which are interesting for petroleum exploration.