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The Numidian Aquitano-Burdigalian nappe from the Jijel region (northeast Algeria) shows an important clay-rich basal series. In this study, seven representative clay samples were collected from the Djimla and El-Milia areas of this region in order to analyse their mineralogy using X-ray diffraction and Fourier-transform infrared spectroscopy, chemical composition by X-ray fluorescence, particle size, plasticity, morphology by scanning electron microscopy and their ceramic properties. Samples were prepared by pressing the clays and firing them at 800–1100°C, and bulk density, water absorption, linear firing shrinkage, weight loss and bending strength values were determined on the fired samples. The clays are mainly composed of kaolinite and illite, with a small amount of 10–14 Å interstratified clay minerals and chlorite, associated with quartz and feldspars. The main oxides in the samples were SiO2, Al2O3and Fe2O3. The clays may be classified as moderately plastic according to their Atterberg limits. Ceramic tiles have been produced by dry pressing. At all tested firing temperatures, the clays present the required standard values for linear firing shrinkage, weight loss, bulk density, water absorption and bending strength, and they are defect-free. The main transformations were observed at 1000°C with the appearance of new crystalline phases. The measured technological properties of the investigated deposits confirm that the Numidian clays from the Djimla and El-Milia regions are suitable materials for the production of high-quality structural ceramics.

International audience; Geophysical methods have been proven to be very effective in landslide characterization. The present paper focuses on the study of land instabilities, which are affecting Tamantout Village, South of Jijel. The site is composed by marl overcoming from unstable overlying Numidian nappes, a major source of a huge spreading of debris covering slopes with inclination of 35°. This study aims are to characterize the internal structure and the hydrological conditions of the moving masses, identifying the soil movement nature and geological and geotechnical factors governing the movement. For these, Electrical Resistivity Tomography (ERT) and Shallow Seismic Refraction (SSR) methods were applied. Indeed, the results were correlated with the available geological and geotechnical data that, in turn, showed a perfect correlation with landslide structures. Occupying 450 (m) of the central part of the profile, the landslide was oriented NE-SW, represented by resistivity ranging between 1 and 10 (Ω.m) and seismic velocity between 1720 and 2235 (m/s). Numidian formation is composed of clays of 15 (m) thickness, covered by a thin layer of slope screes characterized by higher resistivity ranging from 40 to 300 (Ω.m) and a high seismic velocity oscillating between 2485 and 3120 (m/s). It represents the geotechnical bedrock with hard schistose with a depth varying from 7 to 15 which has sound appearance and well indicated lithology through boreholes and geotechnical tests. The geophysical study confirmed the existence of fracture plans associated with intraformational water flows. Reinforcement methods adapted to landslides were proposed in order to secure traffic on the one hand and surrounding land on the other hand, in addition to guaranteeing the socio-economic development in these isolated areas of Jijel province.

This study presents the first geochemical, mineralogical and petrological data on the mafic and ultramafic rocks of Texenna (Lesser Kabylia, north-eastern Algeria) with the aim of constraining their tectonic setting in the context of the Maghrebide belt. The magmatic-sedimentary complex of Texenna comprises serpentinite, metabasites (metagabbro, metadolerite and metabasalt with pillow-lava structures), and oceanic metasediments (radiolarite and calcschists). Serpentinites consist mainly of mesh textures and large bastites of lizardite, Cr-spinels altered to “ferritchromit” and chlorite, with chrysotile and chlorite veins. Their features are very similar to those of serpentinites collected from the seafloor. Pillow-lava metabasalts contain mineral assemblages of albite, epidote, chlorite, actinolite and titanite, and, despite metamorphism, have preserved many of the pillow-lava microstructures (former glassy, variolitic and spherulitic zones; former devitrification spherulites and gas vesicles; pseudomorphs after phenocrysts and microliths). Metadolerites and metagabbros have sometimes preserved their magmatic plagioclase, but are generally transformed into an assemblage of albite, calcic amphiboles, chlorite, epidote and titanite, a mineral assemblage typical of the static greenschist-facies hydrothermal metamorphism of an oceanic crust. Some deformation in the conditions of phengite-bearing greenschist-facies metamorphism is linked to the tectonic emplacement of the ophiolites in their current setting during the Maghrebide orogeny. Geochemically, the whole-rock compositions of the serpentinites indicate a harzburgite protolith, while the metabasites are tholeiitic and show the N-MORB signature for the pillow lavas and T-MORB to E-MORB affinities for the intrusive rocks (metadolerites and metagabbros). These results demonstrate for the first time that the magmatic-sedimentary complex of Texenna belongs to a true ophiolitic slice and indicate that the sedimentary cover of the Maghrebian Flysch domain was deposited over a true oceanic rather than a thinned continental crust. The Texenna ophiolites show analogies with many other ophiolites in the Western Mediterranean region, indicating that they represent remnants of the ancient oceanic lithosphere of the western Tethys (i.e., Maghrebian Tethys Ocean) that formed between Africa and Iberia during the Middle-Late Jurassic.