Evidence of quaternary transtensional tectonics in the Nekor basin (NE Morocco)

The geodynamic processes in the western Mediterranean are driven by both deep (mantle) processes such as slab‐rollback or delamination, oblique plate convergence and inherited structures. The present‐day deformation of the Alboran Sea and in particular the Nekor basin area is linked to these coeval effects. The seismically active Nekor basin is an extensional basin formed in a convergent setting at the eastern part of the Rif Chain whose boundaries extend both onshore and offshore Morocco. We propose a new structural model of the Nekor basin based on high‐resolution offshore data compiled from recent seismic reflection profiles, swath bathymetry acquisitions and industrial seismic reflection profiles. The new data set shows that the northern limit of the basin is oriented N49° with right‐stepping faults from the Bousekkour–Aghbal fault to the sinistral Bokkoya fault zone. This pattern indicates the presence of an inherited left‐lateral basement fault parallel to the major inherited Nekor fault. This fault has been interpreted as a Quaternary active left‐lateral transfer fault localized on weak structural discontinuities inherited from the orogenic period. Onshore and offshore active faults enclose a rhombohedral tectonic Nekor Basin. Normal faults oriented N155° offset the most recent Quaternary deposits in the Nekor basin, and indicate the transtensional behaviour of this basin. The geometry of these faults suggests a likely rollover structure and the presence at depth of a crustal detachment. Inactive Plio‐Quaternary normal faults to the east of the Ras Tarf promontory and geometries of depocentres seem to indicate the migration of deformation from east to west. The local orientations of horizontal stress directions deduced from normal fault orientations are compatible with the extrusion of the Rifian units and coherent with the westward rollback of the Tethyan slab and the localization of the present‐day slab detachment or delamination.     

Report on the Diatoms and Dinoflagellates Distribution along the Algerian Coasts: Inter-Region Comparison

The phytoplankton group’s composition is an excellent indicator of the state of coastal waters. The aim of this study is to explore spatial variability of phytoplankton in shallow coastal areas from different regions (East, Center and West) of the Algerian coast. The quantitative and qualitative study of the phytoplankton population was conducted on samples taken during the 2012-2013 period by the research vessel GRINE BELKACEM. The qualitative results show a significant diversity of diatoms and dinoflagellates, which rank first and second in the total flora (Fr > 50%). This finding is also confirmed quantitatively by the abundance values in both 2013 and 2012 samples which largely exceeds the average value in most other areas of the western region (56%) and slightly exceeding 52% in all central areas which represent an equi-distribution between diatoms and dinoflagellates. The Dinoflagellates contribute significantly to the quantitative richness in the eastern region (>60%). The minimum value of Dia/Dino index, recorded in the eastern region confirms the dominance of the dinoflagellates especially in Skikda (0.31) (Skikda).However, our results reveal the presence, in smaller proportion, of other groups such as the cocolithophoridae and euglenophyceae.     

Evaluation of hydraulic conductivity through particle shape and packing density characteristics of sand–silt mixtures

Abstract

This study aims to evaluate the relationship between saturated hydraulic conductivity with particle shape and packing density characteristics of silty sand soils. The article presents a series of hydraulics tests performed on three kinds of sand with different particles shapes (Chlef rounded sand, Fontainebleau sub-rounded sand and Hostun sub-angular sand) mixed with low plastic rounded Chlef silt in the range of 0–30% fines content. The sand–silt mixture samples were tested in the constant-head permeability device at a loose relative density (D_r = 18%) and a constant room temperature (T?=?20?°C). The obtained results indicate that the measured saturated hydraulic conductivity (K_s) correlates very well with the fines content (F_c), packing density in terms of [maximum void ratio “e_max,” minimum void ratio “e_min,” predicted maximum void ratio “e_max”_pr and predicted minimum void ratio “e_min”_pr] and particle shape characteristics ratios in terms of roundness ratio (R_r = R_hs/R_mixture) and sphericity ratio (S_r = S_hs/S_mixture) of the silty sand materials under consideration. Moreover, the analysis of the available data show a noticeable success in exploring the prediction of the saturated hydraulic conductivity (K_s) based on the particle shape and packing density characteristics (R_r, S_r, e_max, and e_min) of the studied sand–silt mixture samples.     

Filtration of kaolinite particles in a saturated porous medium: hydrodynamic effects

A study was undertaken on physical clogging of a porous medium by injecting suspended particles (SP), ranging in diameter from 1.7 to 40 μm, into a sand-filled column. Long-term tracer tests were carried out at various flow velocities. Retention of the SP is significantly influenced by the flow velocity. At low flow velocities, retention is confined to a limited length of porous medium, from the entrance of the column, leading to a substantial modification of the hydraulic characteristics of the porous medium. However, at high flow velocities, a much greater length of the porous medium is affected. Particle-size analyses indicate that the particle-size distribution (PSD) of recovered particles changes with time, while the PSD of retained particles changes with depth and time. At the beginning of the filtration process, larger particles were mainly retained at the column entrance. As the injection volume increases, the larger particles penetrate more deeply into the porous medium, and the size of particles observed in the effluent gradually increases. This study highlights the influence of flow velocity, duration of filtration, and the particles’ polydispersity, on the hydraulic characteristics of the porous medium.