La bordure nord de la chaîne hercynienne du Maroc, chaîne "calédonienne" des Sehoul et plateforme nord-mesetienne

Two main units constitute the Rabat-Tiflet area: The Sehoul metamorphic zone and the Bou Regreg sedimentary zone. These two areas are separated by a roughly East-West trending thrust. The Sehoul zone is characterized by a clastic sequence, several hundred meters thick, which is interpreted as a deltaic sequence. It is paleontologically dated from Cambrian time. Folds deform the rocks affected by a low-grade metamorphism. These are east-northeast trending (N 50-70 E), often isoclinal, with a vergence toward South- South-East. They are associated with a flow cleavage. The emplacement of calc-alkaline granite followed this deformation. Its contact metamorphism developed andalousite, cordierite, biotite and chlorite. The syn-kinematic development of the andalousite crystals suggests that the granite emplacement occurred during the last stages of the "sehoulian phase" . This phase is dated, on the other hand, from Late Ordovician to Early Silurian by the fact that the Upper Silurian strata rest unconformably upon the sehoulian structures. The Sehoulian phase, therefore, developed after the Early Paleozoic deformation of Kabylia. It was more or less contemporaneous with the Taconic orogeny of the Appalachians. The Bou Regreg zone is constituted by a sedimentary sequence. Generally, the sedimentary facies display strong similarities with the sequences of the Moroccan Meseta (i.e. in Central Morocco). However, several particularities are noteworthy: -The Ordovician is represented here only by the Arenig/Llanvirn and it comprises calc-alkaline volcanic rocks. -The absence of Upper Ordovician and Lower Silurian strata is attributed to the compressive events that occurred in the North (Sehoulian phase). -The first evidences of a synsedimentary extensive regime are noted since Early Devonian time. The crustal extension became obvious during Late Devonian time, when the Sidi Bettache basin opened. The Sehoul and the Bou Regreg zones were progressively brought together by a polyphase thrust. A first episode, "Late Silurian", is represented by southward directed thrusts, that are proven to predate Late Silurian in the Eastern part of the Rabat-Tiflet area. A second episode, "Hercynian", created a mylonitic zone, roughly East-West trending, where deformed and brecciated middle Devonian limestone and Late Devonian conglomerates are squeezed. Apart of this Hercynian thrust, the Hercynian deformation was relatively mild, with open folds and diagenetic to very low grade metamorphic intensity.La région de Rabat-Tiflet est constituée par deux unités principales: la zone métamorphique des Sehoul et l'axe sédimentaire du Bou Regreg, séparées par un contact tectonique de type chevauchant. La zone des Sehoul est caractérisée par une série détritique de plusieurs centaines de mètres d'épaisseur, déposée dans un environnement de type deltaïque. Elle est datée du Cambrien. Les phyllades et les quartzo-phyllades qui la constituent sont affectées par une déformation souple (phase sehoulienne du Calédonien), qui a donné des plis de direction N 50 à 70°, souvent isoclinaux, déversés ou couchés vers le SE. A ces plis est associée une schistosité cristallophyllienne. Vers la fin de cette compression, à l'Ordovicien terminal, cette zone est intrudée par un granite calco-alcalin. Celui-ci développe une porphyroblastèse à andalousite, cordiérite, biotite et chlorite. L'andalousite étant syn-schisteuse indique que le granite est syn- à post phase sehoulienne. Le Silurien supérieur transgressif, amène à dater la phase séhoulienne de l'Ordovicien terminal au Silurien inférieur. Celle-ci serait alors contemporaine de la phase taconique et postérieure à la phase kabyle. L'axe du Bou Regreg est constitué par des terrains sédimentaires d'affinité mésétienne. Il présente cependant quelques particularités: -l'Ordovicien se limite à l'Arenig/Llanvirn et comprend un volcanisme calco-alcalin inter-stratifié. -une lacune de l'Ordovicien supérieur et du Silurien inférieur, par soulèvement-compression, est contemporaine de la phase sehoulienne. -les premiers indices d'une tectonique syn-sédimentaire distensive sont perceptibles dès le début du Dévonien. Celle-ci sera développée au Dévonien supérieur lors de la formation du bassin dévono-dinantien de Sidi Bettache. Le rapprochement entre ces deux unités s'effectue en deux étapes: * la première se marque par des cisaillements que fossilisent les conglomérats transgressifs du Silurien terminal de Tiflet. Du fait de l'identité et de la continuité des faciès du Siluro-Lochkovien, on démontre que cette étape est anté-Silurien supérieur. * la seconde est hercynienne, puisque l'on retrouve dans le contact majeur, sous forme de lentilles écrasées, des calcaires du Dévonien et des conglomérats du Famenno-Tournaisien. La déformation hercynienne dans cette région est relativement peu importante. Elle s'effectue dans un niveau structural supérieur à moye

Effects of Lizardite Addition on Technological Properties of Forsterite-monticellite Rich Ceramics Prepared from Natural Magnesite and Dolomite

Lizardite rich peridotite has never been used to prepare ceramic specimens, especially in Morocco. For this raison, potential use of naturally abundant lazirditic material from the Rif domain, as a supply for ceramic industry, has been evaluated. The effects of lizardite addition to magnesite and dolomite mixtures on the thermomechanical properties of the calcined ceramics were also detailed. To achieve this target, natural lizardite, magnesite and dolomite samples were collected in ultrabasic Beni Bousra massif. Those raw samples were used for the synthesis of a forsterite-monticellite rich ceramics. Both raw and sintered samples were characterized by x-ray diffraction, scanning electron microscope and fourier transform infrared. The obtained results showed that both magnesite and dolomite were mainly composed of MgCO3 and CaCO3. In contrast, lizardite sample showed high amounts of SiO2, MgO and Fe2O3. An increased amount of lizardite in the initial mixtures enhanced mechanical and dimensional properties of the prepared ceramic specimens, and subsequently, the production of ceramics with the required technological properties. Thus, the preparation of Moroccan lizardite-based ceramics is technically feasible, economically justifiable and socially desirable due to the contribution to the economic growth of the raw materials sector, especially ceramic industry

Proposed magnetostratigraphy susceptibility magnetostratotype for the Eifelian-Givetian GSSP (Anti-Atlas, Morocco)

The magnetosusceptibility event and cyclostratigraphy (MSEC) record for the Eifelian-Givetian Global Boundary Stratotype Section and Point (GSSP) located in the western Sahara of southeastern Morocco is used to establish a sequence of magnetostratigraphic susceptibility units organized into magnetostratigraphic susceptibility zones (MSZ) and magnetostratigraphic susceptibility subzones (MSSZ). Magnetic susceptibility data are summarized into two complete MSZs (Atrous and Mech Irdane) and two partial MSZs (Gheris and Rissani). The Atrous (Upper Eifelian) is comprised of 3 MSSZs and the Mech Irdane (uppermost Eifelian and lowermost Givetian) of 11 MSSZs. The Eifelian-Givetian boundary falls within Mech Irdane MSSZ 2 making the magnetosubzone an important boundary marker unit. Large-scale transgressive and regressive patterns in the MSEC data establish that the Eifelian-Givetian boundary in the GSSP sequence occurs immediately after the first regressive pulse following the transgressive conditions established during the Atrous MSZ. The Lower Kačák/otomari Event occurs in Atrous MSSZ 3 and Kačák/otomari Event occurs in Mech Irdane MSSZ 1. The magnetic properties of the MSZs and MSSZs are tested by comparison with a coeval magnetostratigraphic susceptibility sequence in the Montagne Noire region of southern France

Bacteriological Quality of Seawater Bathing Areas along the Oran Coast (West northern Algeria)

Marine water of Ora