Sami Khomsi

The Late Eocene and Late Miocene fronts of the Atlas Belt in eastern Maghreb: integration in the geodynamic evolution of the Mediterranean Domain

Regional cross sections at the scale of the eastern Maghreb based on subsurface and field data allow presenting the structural styles related to the Middle-Late Eocene compressional events. The structural cross sections depict that the Late Eocene front of the Atlas Belt extends far through the Northern Africa plate margin comparatively to the Late Miocene front cropping out in the Eastern Tunisian Atlas. The sections allow proposing a new subsurface front for the Atlas belt encompassing a large part of the Pelagian-Sirt basins. The consequences of this particular configuration are discussed at the scale of the south Tethys margin and replaced in the frame of the geodynamic evolution of the Mediterranean Domain.

Neogene aquifer: geochemistry and structuring in the Sidi Saad basin, central Tunisia

The Sidi Saad basin is located in the NS axis in central Tunisia. This zone was affected by several distension and compression phases inducing the structuring and the distribution of Neogene deposits. The study area is known by the presence of important water reserves. The surface water needs for the demographic growth and for both the agricultural and industrial sector developments. So, the exploitation of deep aquifers reveals a vital issue in Tunisia whose water resources are limited. To satisfy these needs, exploration and characterization of deep aquifers is necessary. The present study, based on hydraulic and petroleum wells’ correlation, seismic line interpretation, and hydrochemistry, addresses the geometry, and the hydrogeological characterization of Miocene-Pliocene-Quaternary reservoirs is undertaken for the first time in Sidi Saad basin. The results highlight that the structural framework, based on major structures, controls the Mio-Pliocene siliciclastic deep reservoir deposits, the groundwater flow, and the sub-basin aquifer distribution. The water geochemistry study exhibits low salinities in the northern and the southeastern parts of the study area with different facies of Ca-HCO3 and Na-(Ca)-Cl-(SO4) and constitute an important source of drinkable and irrigation water.

Lithosphere Dynamics and Sedimentary Basins of the Arabian Plate and Surrounding Areas

The Arabian Shield and Red Sea region is considered one of only a few places in the world undergoing active continental rifting and formation of new oceanic lithosphere. We determined the seismic velocity structure of the crust and upper mantle beneath this region using broadband seismic waveform data. We estimated teleseismic receiver functions from high-quality waveform data. The raw data for RF analysis consist of 3-component broadband velocity seismograms for earthquakes with magnitudes Mw > 5.8 and epicentral distances between 30° and 90°. We performed several state-of-the-art seismic analyses of the KACST and SGS data. Teleseismic Pand S-wave travel time tomography provides an image of upper mantle compressional and shear velocities related to thermal variations. We present a multi-step procedure for jointly fitting surface-wave group-velocity dispersion curves (from 7 to 100 s for Rayleigh and 20 to 70 s for Love waves) and teleseismic receiver functions for lithospheric velocity structure. The method relies on an initial grid search for a simple crustal structure, followed by a formal iterative inversion, an additional grid search for shear wave velocity in the mantle and finally forward modeling of transverse isotropy to resolve surface-wave dispersion discrepancy. Inversions of receiver functions have poor sensitivity to absolute velocities. To overcome this shortcoming we have applied the method of Julia et al. (Geophys J Int 143:99–112, 2000), which combines surface-wave group velocities with receiver functions in formal inversions for crustal and uppermost mantle velocities. The resulting velocity models provide new constraints on crustal and upper mantle structure in the Arabian Peninsula. While crustal thickness and average crustal velocities are consistent with many previous studies, the results for detailed mantle structure are completely new. Finally, teleseismic shear-wave splitting was measured to estimate upper mantle anisotropy. These analyses indicate that stations near theGulf ofAqabah display fast orientations that are aligned parallel to the Dead Sea Transform Fault, most likely related to the strike-slip motion between Africa and Arabia. The remaining stations across Saudi Arabia yield statistically the same result, showing a consistent pattern of north-south oriented fast directions with delay times averaging about 1.4 s. The uniform anisotropic signature across Saudi Arabia is best explained by a combination of plate and density driven flow in the asthenosphere. By combining the northeast oriented flow associated with absolute plate motion with the northwest oriented flow associated with the channelized Afar plume along the Red Sea, we A. Al Amri (&) K. Abdelrahman M.O. Andreae M. Al-Dabbagh Geology and Geophysics Department, King Saud University, Riyadh, Saudi Arabia e-mail: alamri.geo@gmail.com M.O. Andreae Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Basin structure and water quality of the Oligocene aquifer in the Sebkhet El Behira basin (central Tunisia)

ABSTRACT The Sebkhet El Behira–Garaat El Majdoul multilayer aquifer system is composed of Mio-Plio-Quaternary and Oligocene groundwater exploited in Sidi Bouzid and Kairouan governorates. Annual withdrawal volumes from El Behira Oligocene groundwater were about 0.37 hm3 in 2005 and 0.36 hm3 in 2008. The present study of the Oligocene reservoir in the Sebkhet El Behira–Garaat El Majdoul basin is based on various data including 2D seismic sections, petroleum wells, field geological cross-sections and geochemical analysis. The gathered data allowed us to establish the tectonic framework and to define its influence on the structure of the aquifers seated in the deep Oligocene sandstone reservoirs. Three Oligocene sub-basin aquifers are defined showing different depth, thickness and petrophysical characteristics: lower salinity (<1.5 g/L) and higher porosity (30%). Two field sections in the northern and in the southern parts of Cherahil anticline exhibit the presence of four to five sandstone levels. The anticlines limit the Sebkhet El Behira–Garaat El Majdoul basin. In addition, the morphostructural configuration controls the piezometry of underground flows in the Oligocene and Mio-Plio-Quaternary unconfined aquifers. Editor D. Koutsoyiannis; Associate editor M. Besbes

Arabian plate: lithosphere dynamics, sedimentary basins, and geo-resources

This topical issue of the Arabian Journal of Geosciences focusing on the Arabian plate, its lithosphere dynamics, sedimentary basins, and geo-resources is an initiative of the Task Force 6 of the International Lithosphere Program, an international network dedicated to the study of sedimentary basins (Roure et al. 2010a, b). Summary of former activities of the ILP Task Force on sedimentary basins and perspectives