The Lower Miocene volcaniclastic sedimentation in the Sicilian sector of the Maghrebian Flysch Basin: geodynamic implications

Abstract Volcaniclastic debris-rich formations, characterising the Troina–Tusa Unit in the Sicilian Maghrebian Chain, are examined. The Troina–Tusa Unit terrains sedimented in the Maghrebian Flysch Basin, which, from Jurassic to Early Miocene, constituted the southernmost branch of the Western Tethys, located between Africa and the Mesomediterranean Terrane margins. New field, biostratigraphic and petrographic data enable a reconstruction of the palaeogeographic and structural evolution of the Flysch Basin immediately before its deformation. All the studied formations transpired to be Burdigalian in age. The sandstone compositions, showing different source areas (magmatic arc, recycled orogen and continental block), indicate a provenance for the clastic material from a crystalline basement with an active volcanic arc, replaced by a remnant volcanic arc, which was rapidly completely eroded. The source area that has been considered is Sardinia, where Upper Oligocene–Aquitanian calc-alkaline volcanites are widespread, but the sedimentological characteristics and the Burdigalian age do not fit with this provenance. The Burdigalian calc-alkaline arc should be located on the internal side of the Troina–Tusa Basin, above the already stacked Peloritanian units. A migration of the volcanic activity, connected with the subduction plain roll-back, can be envisaged from the Sardinia Block to the Peloritanian Chain, this latter still docked to the Sardinia–Corsica massif

Cartografía de alta resolución de la cubierta del suelo y clasificación de los cultivos en la cuenca del Loukkos (norte de Marruecos): Un enfoque que utiliza las series temporales de SAR Sentinel-1

[EN] Remote  sensing  has  become  more  and  more  a  reliable  tool  for  mapping  land  cover  and  monitoring  cropland. Much of the work done in this field uses optical remote sensing data. In Morocco, active remote sensing data remain under-exploited despite their importance in monitoring spatial and temporal dynamics of land cover and crops even during cloudy weather. This study aims to explore the potential of C-band Sentinel-1 data in the production of a high-resolution land cover mapping and crop classification within the irrigated Loukkos watershed agricultural landscape in northern Morocco. The work was achieved by using 33 dual-polarized images in vertical-vertical  (VV)  and  vertical-horizontal  (VH)  polarizations.  The  images  were  acquired  in  ascending  orbits  between  April 16 and October 25, 2020, with the purpose to track the backscattering behavior of the main crops and other land  cover  classes  in  the  study  area.  The  results  showed  that  the  backscatter  increased  with  the  phenological  development  of  the  monitored  crops  (rice,  watermelon,  peanuts,  and  winter  crops),  strongly  for  the  VH  and  VV  bands, and slightly for the VH/VV ratio. The other classes (water, built-up, forest, fruit trees, permanent vegetation, greenhouses, and bare lands) did not show significant variation during this period. Based on the backscattering analysis and the field data, a supervised classification was carried out, using the Random Forest Classifier (RF) algorithm.  Results  showed  that  radiometric  characteristics  and  6  days  time  resolution  covered  by  Sentinel-1  constellation gave a high classification accuracy by dual-polarization with Radar Ratio (VH/VV) or Radar Vegetation Index and textural features (between 74.07% and 75.19%). Accordingly, this study proves that the Sentinel-1 data provide useful information and a high potential for multi-temporal analyses of crop monitoring, and reliable land cover mapping which could be a practical source of information for various purposes in order to undertake food security issues.[ES] La teledetección se ha convertido en una herramienta cada vez más fiable para cartografiar la cubierta vegetal y controlar las tierras de cultivo. Gran parte de los trabajos realizados en este campo utilizan datos ópticos de teledetección. Además, en Marruecos, los datos de teledetección activa siguen estando infrautilizados, a pesar de su importancia para el seguimiento de la dinámica espacial y temporal de la cubierta vegetal y de los cultivos, incluso con tiempo nublado. Este estudio tiene como objetivo explorar el potencial de los datos de la banda C de Sentinel-1 en la producción de una cartografía de alta resolución de la cubierta del suelo y la clasificación de los cultivos dentro del paisaje agrícola de la cuenca del Loukkos de regadío en el norte de Marruecos. Este trabajo se ha realizado utilizando 33 imágenes de doble polarización vertical-vertical (VV) y vertical-horizontal (VH). Las imágenes fueron adquiridas en órbitas ascendentes entre el 16 de abril y el 25 de octubre de 2020, con el propósito de rastrear el comportamiento de retrodispersión de los principales cultivos y otras clases de cobertura del suelo en el área de estudio. Los gráficos obtenidos muestran que la retrodispersión aumenta con el desarrollo fenológico de los tres cultivos monitorizados (arroz, sandía, cacahuetes, cultivos de invierno), fuertemente para las bandas VH y VV, y ligeramente para el ratio VH/VV. Las otras clases (agua, edificado, bosque, árboles frutales, vegetación permanente, invernaderos y tierras desnudas) no muestran una variación significativa durante este periodo. A partir del análisis de retrodispersión y de los datos de campo, se llevó a cabo una clasificación supervisada, utilizando el  algoritmo  Random Forest Classifier (RF). Los resultados muestran que las características radiométricas y la resolución temporal para los 6 días cubiertos por la constelación Sentinel-1 dan una alta precisión de clasificación por polarización dual con Ratio de Radar (VH/VV) o Índice de Vegetación de Radar y características de la textura (entre  74,07%  y  75,17%).  En  consecuencia,  este  estudio  demuestra  que  los  datos  de  Sentinel-1  proporcionan  información útil y un alto potencial para los análisis multitemporales de seguimiento de los cultivos, así como una cartografía fiable de la cubierta terrestre que debería ser una fuente de información práctica para para varios propósitos a fin de acometer cuestiones de seguridad alimentaria.Nizar, EM.; Wahbi, M.; Ait Kazzi, M.; Yazidi Alaoui, O.; Boulaassal, H.; Maatouk, M.; Zaghloul, MN.... (2022). High Resolution Land Cover Mapping and Crop Classification in the Loukkos Watershed (Northern Morocco): An Approach Using SAR Sentinel-1 Time Series. Revista de Teledetección. (60):47-69. https://doi.org/10.4995/raet.2022.17426OJS47696

GEOLOGICAL AND GEOMECHANICAL PROPERTIES OF SOME CARBONATE MARBLES AND BASALT STONE FROM MOROCCO

The natural rocks used today as well as in the history for a variety of purposes were a subject of different alteration, weathering and deterioration conditions. These conditions are strictly controlled by environment and nature of rock varieties (marble and stone). This study is a first approach to understand the relation between some geological features and behavior against salt (Na 2SO4) decay of Moroccan marbles and stones. For this purpose, widely used four dolomitic limestones, two crystalline limestones, one limestone and one basalt sample (total 8) were chosen from Morocco. Extra attention paid to choose locations being a representative of all Moroccan country. The carbonate samples (limestone and dolomite) consist of mainly dolomite and calcite with micritic and sparitic cement. The sole, non-carbonaceous sample is basalt of Khenifra containing mainly plagioclase and pyroxene. In general, both bulk-dry and powder density values of the studied rock samples are homogeneous. The limestone of Bir Jdid has the highest (10.81 %) effective porosity and dry weight loss value (4.61 %). The loss on ignition value of the Khenifra basalt has the lowest value with 1.26 %. The loss on ignition values are also relatively uniform. The obtained data indicate that outdoor uses (especially in coastal areas) of limestones of Bir Jdid and dolomitic limestones of Taza are more risky than the others

The Numidian sand event in the Western Rif Chain (Northern Morocco)

We report on new sedimentological and biostratigraphical data concerning the “Numidian sandstones” outcropping in the Western Rif Belt. The analyzed sections are located south of Tangier city, close to the 9th April dam and pertain to the Intrarif Sub-domain, which, in turn, is part of the External Rif domain. In the western peri-Mediterranean chains, the “Numidian sandstones” display constant lithological features. We analysed six well-exposed lithostratigraphic sections, which are organized in three portions: (1) the “sub-Numidian”, mainly dominated by varicolored clays, (2) the “Numidian sandstones”, which includes predominantly massive quartzarenitic sandstones, sometimes interbedded with mudstones, and, finally, (3) the “supra-Numidian”, characterized by alternation of light green marls and thin-bedded siltstones. Stratigraphic sections of the “Numidian sandstones” were measured and described to provide detailed sedimentological characterization and facies analysis. The “sub-Numidian”, thick more than 100 meters, is commonly made of varicoloured clays, which in all the studied sections shows a horizon rich in Tubotomaculum. In the study area, the “Numidian sandstones” are about 1100 m thick; their facies analysis have been performed by using Pickering et al. (1995) classification scheme. The basal part of the examined sections shows similar characteristics: proximal channels filled by very thickbedded disorganised pebbly sandstones and amalgamated structureless sandstones (Facies A1.4 and B1.1). The base of the beds is scoured and sometimes shows decimetresized mud clasts torn away from the substratum. Paleocurrents measurements, mainly indicated by flute casts, are from southeast to northwest. Upward, coarse-grained quartzarenitic sandstones mainly characterize the middle part of all the sections. They are organized in massive and thick-bedded pebbly-sandstones, micro-conglomerates (Facies A2.4 and A2.5), and disorganised thick sandstones strata, often marked by fluid escape structures (Facies B1.1), revealing flows processes controlled by high-density turbidity currents and debris flows. These deposits evolve to plurimeter- to decimetre-thick mediumgrained sandstone and mud couplets (Facies C2.3) with a mainly fining-and thinning-upward trend, which we consider to be attributable to lobe and fringe lobe deposition. Commonly, the uppermost part of the sections shows a restoration of disorganised pebbly sandstones facies (Facies A1.4). The “supra-Numidian” caps the thick “Numidian sandstones” and is made up by about 200 m of bioturbated marls rich in planktonic foraminifera and fine-grained silty/muddy deposits. These latter show sedimentary structures related to unidirectional flows, probably owed to deep contourites currents. References Pickering K.T., Hiscott R.N., Kenyon N.H., Ricci Lucchi F. & Smith R. (editors) 1995. Atlas of architectural styles in turbidite systems. London: Chapman & Hal

Deformation characterization of a regional thrust zone in the northern Rif (Chefchaouen, Morocco)

This paper provides the structural analysis of the Chefchaouen area in the northern Rif. Here the Dorsale Calcaire superposes, by means of an excellently exposed thrust fault, onto the Predorsalian succession in turn tectonically covering the Massylian Unit. Hanging wall carbonates of the Dorsale Calcaire Unit form a WSW-verging regional fold with several parasitic structures, deformed by late reverse faults in places indicating an ENE vergence. A two hundred meters thick shear zone characterizes the upper part of the Predorsalian succession, located at footwall of the Dorsale Calcaire Unit. Here the dominantly pelitic levels are highly deformed by (i) C’ type shear bands indicating a mean WSW tectonic transport and (ii) conjugate extensional shear planes marking an extension both orthogonal and parallel to the shear direction. The Massylian Unit is characterized by a strain gradient increasing toward the tectonic contact with the overlying Predorsalian succession, where the dominantly pelitic levels are so highly deformed so as appearing as a broken formation. Such as the previous succession, conjugate extensional shear bands and normal faults indicate a horizontal extension parallel to the thrust front synchronous with the mainly WSW-directed overthrusting. The whole thrust sheet pile recorded a further shortening, characterized by a NW-SE direction, expressed by several reverse and thrust faults and related folds. Finally strike-slip and normal faults were the last deformation structures recorded in the analyzed rocks. A possible tectonic evolution for these successions is provided. In the late Burdigalian, the Dorsale Calcaire Unit tectonically covered the Predorsalian succession and together the Massylian Unit. The latter two successions were completely detached from their basement and accreted in the orogenic wedge within a general NE-SW shortening for the analyzed sector of the northern Rif. At lithosphere scale the thrust front migration was driven by roll back and slab tear mechanisms producing a synchronous arching and related counterclockwise rotation of the tectonic prism along the African margin. Radial displacement involved extension parallel to the thrust front well-recorded in the analyzed rocks. The NE-SW shortening, probably acting in the Tortonian-Pliocene interval, was related to the final compression of the Rif Chain resulting in out-of-sequence thrusts affecting the whole orogenic belt

Tsunami hazard and buildings vulnerability along the Northern Atlantic coast of Morocco –the 1755-like tsunami in Asilah test-site

Abstract Background The Atlantic Coast of Morocco is prone to tsunami inundation. Therefore, in this region, earthquake-induced tsunami hazard has been intensively investigated leading to the development of a number of coastal inundation models. However, tsunami vulnerability remains not well understood to the same extent as the hazard. In this study, we use high-resolution numerical modeling, detailed field survey and GIS-based multi-criteria analysis to assess the building tsunami vulnerability and its sensitivity to the tide variations. Asilah located in the northwestern Atlantic coast of Morocco, where the impact from the 1755 tsunami is well documented, constitutes the area of this study. Results To model the source-to-coast tsunami processes we used the COMCOT (Cornell Multi-grid Coupled Tsunami Model) numerical code on a set of bathymetric/topographic grid layers (640 m, 160 m, 40 m and 10 m resolutions) with an initial sea-surface perturbation generated using Okada’s formulae and assuming an instantaneous seabed displacement. The tsunami source models in this study correspond to four 1755-like earthquake scenarios. Results show that Asilah’s built environment is highly vulnerable to the tsunami impact that can range from 1.99 to 2.46 km2 of inundation area, depending on the source and the tidal level considered. The level of building vulnerability decreases considerably when moving away from Asilah’s coastline. Moreover, the variation in the tidal level introduces large change in the modeled tsunami impact and, therefore, affects the level of building vulnerability. Conclusion Thus, we suggest considering the effect of the tide when simulating tsunami hazard and vulnerability, particularly, in coasts where tidal variations are significant. This study provides hazard and vulnerability maps that can be useful to develop the tsunami awareness of the Moroccan coastal population

Structural analysis of Chefchaouen area in the Western Rif (Morocco)

This paper provides a structural analysis of the Chefchaouen area, in the Northern Rif. Here the Dorsale Calcaire succession tectonically superpose the Predorsalian Unit. Both successions overthrust the Massylian Unit. The carbonates of the Dorsale Calcaire are characterized by pre-orogenic structures, such as normal faults, veins and fractures, resulting from extension related to the Liassic-Dogger rifting of the Neotethys domain. The successive inclusion of these rocks in the orogenic wedge, mainly occurred in the Miocene time, has deformed the most of pre-orogenic structures in a passive fashion, without an overall reverse reactivation. The Predorsalian Unit is characterized by a two hundred meters thick shear zone located close to the contact with the Dorsale Calcaire carbonates. Here the dominantly pelitic levels are highly deformed by (i) C’ type shear bands indicating a mean WSW tectonic transport and (ii) conjugate extensional shear planes marking an extension both orthogonal and parallel to the shear direction. Such as the previous succession, conjugate extensional shear bands and normal faults indicate a horizontal extension parallel to the thrust front synchronous with the mainly WSW-directed overthrusting. Also the Massylian succession shows a progressive deformation characterized by two superposed fold sets. The whole thrust sheet pile recorded a further shortening, characterized by a NW-SE direction, expressed by several reverse and thrust faults and related folds. Finally strike-slip and normal faults were the last deformation structures recorded in the analyzed rocks

Polyphase deformation of the Dorsale Calcaire Complex and the Maghrebian Flysch Basin Units in the Jebha area (Central Rif, Morocco): New insights into the Miocene tectonic evolution of the Central Rif belt

In order to better understand the orogenic evolution of the Rif chain in the Eocene-Miocene interval, we provide new structural and kinematic data for the Jebha area, a key-sector of the Central Rif. Here the thrust sheet superposition occurs along the well-known Jebha-Chrafate lineament, widely considered as a major left-lateral transfer fault that enabled the Miocene westward migration of the internal thrust front. Our structural analysis was mainly focused on (i) the internal deformation of stacked nappes and (ii) the kinematics of the main thrust faults. Five main deformation stages were recognized for the Eocene-Miocene tectonic evolution of this area. The first orogenic pulse (D1), which occurred in the Eocene-Oligocene interval, was responsible for the tectonic stacking of the Ghomaride Nappes. Subsequently between the late Aquitanian and the late Burdigalian, imbrication (stage D2) occurred for some Internal Dorsale Calcaire thrust sheets within a dominant regional ENE-WSW shortening. At the Rif scale, different displacements of the WSW-migrating thrust front were accommodated by transfer structures including the Jebha-Chrafate fault. The following late Burdigalian-Langhian stage (D3) was defined, on the contrary, by a prevalence of the radial thrust front migration. In the Jebha area the early thrusting (stage D3a) was characterized by a main SE-vergence. In this phase the External Dorsale Calcaire and the Maghrebian Flysch Basin Units were included in the accretionary wedge. Two late D3 regional deformation phases were probably related to the buttressing effect that followed the collision of the thrust sheet pile against the crustal ramp of the External Rif domain. The first stage (D3b) consisted of an out-of-sequence thrusting recorded in the western sector of the Jebha area with the superposition of the Ghomaride Unit onto the External Dorsale Calcaire Unit, and in the eastern sector with the stacking of the Internal Dorsale Calcaire Unit directly onto the Predorsalian Unit. The second stage (D3c) included a late back-thrusting affecting the whole orogenic chain and deforming all the tectonic contacts. The fourth stage (D4) was characterized by strike-slip faulting and SW-verging folding. This latter mostly affected the successions located to the East of the Jebha village and was partially synchronous with the D3 stage. It was most probably related to the SW-migration of the internal thrust-front of the Bokkoya Dorsale Calcaire Complex and a renewed activity of the Jebha-Chrafate fault zone. The last tectonic stage (D5) included a radial extension expressed by high and low-angle normal faults