External Rif Research Articles

Cenozoic tectono-sedimentary evolution of the external rif chain (Morocco) derived from mineralogical and geochemical analysis of mudrocks

A model of the Cenozoic tectono-sedimentary evolution of the External Rif Chain (Morocco) is provided by means of the study of the mineralogical and geochemical composition of mudrocks. To date there was a lack of homogeneous data and of a complete and extensive study of the whole External Rif Zone (ERZ). Therefore, this work shows the study of the whole ERZ where the most representative stratigraphic sections have been selected. This work provides important information about the geodynamic evolution and the variations in source-area provenance related to the growing of the Rif orogenic belt. Although there is still much work to be done, this study aims to improve the knowledge of the Cenozoic tectono-sedimentary evolution of the entire western ERZ with a homogeneous method, with a focus on the paleogeographic and paleotectonic evolution, the paleoweathering and the source areas deduced from mineralogical and geochemical data of the Cenozoic mudrocks. The bulk mineralogy is mainly characterized by the presence of calcite, quartz and dolomite plus ankerite. Feldspars have few percentages. The clay minerals are principally represented by mixed-layer illite/smectite (I/S). Illite and kaolinite are in little amount. Femic minerals, mixed-layer chlorite/smectite (C/S) and chlorite are the most abundant. The I/S features suggest a different thermal condition for the three domains. The chemical composition indicates that the mudrocks can be described as mixtures of carbonates with aluminosilicate components. The Al/Ti, Th/Cr, Th/Sc, La/Th and La/Sc ratios, the Cr/V vs. Y/Ni plot, the V-Ni-Th∗10 and La-Th-Sc ternary diagrams indicate a predominantly felsic source with a minor mafic input more evident in the Paleocene-Eocene samples of the External Intrarif and Mesorif. The External Rif Zones changed in the Cenozoic from a passive margin to a complex foreland system with the incoming of the Alpine tectonic phases. In general, the felsic contribution should be linked to the foreland area consisting in the Middle Atlas and Mesetas massifs made of a crystalline domain. This margin probably presented an intermediate narrow oceanic branch in the External Intrarif-Mesorif boundary that surprisingly should start to close during Paleogene times providing the mafic contribution. This Paleogene tectonic activity in these domains is corroborated by the thermal maturity indicating late diagenesis. The chemical weathering indices, such as the CIA (Chemical index of Alteration) and its modifications, show medium-high values and thus suggest generally moderate paleoweathering conditions in agreement with the predominant amount of I/S.

Miocene evolution of the External Rif Zone (Morocco): Comparison with similar and lateral southern Mediterranean Tethyan margins

The Miocene evolution of the External Rif Zone (NW Africa Plate) was determined through multidisciplinary analysis of fourteen successions. The updated stratigraphic framework shows how Miocene sediments rest on the Cretaceous–Paleogene terrains through unconformity surfaces, whereas it rests with sedimentary continuity in two sectors. After recognition of lithofacies and three unconformities located near the Oligocene–Aquitanian, Aquitanian–Burdigalian and Serravallian–Tortonian boundaries, the Miocene sedimentary record was divided into three stratigraphic intervals representing deep to shallow marine deposits as Aquitanian–Burdigalian, Langhian and Upper Serravallian–Missinian. The two oldest unconformites are restricted to the central sector, while the upper one is generalized and probably related to the nappe tectonics registered in all sectors of the External Rif. Data from analysis of tectofacies, petrology, mineralogy, meaning and implications of unconformities, and subsidence indicate that: (i) mass flow deposits (turbidites, slumps, olistostromes) are common in all successions but more frequent during the Lower Miocene; (ii) petrology of the detrital components of the arenites indicates recycled orogen-derived sediments, with quartz coming from erosion of metamorphic rocks of the Atlas orogen and/or the African craton; (iii) mineralogy of mudstones suggests a complex erosional evolution of local emerged areas derived from a mixture of contributions coming from the erosion of Upper Jurassic to Paleogene suites, and especially from kaolinite-rich Albian–Cenomanian to Paleogene successions with absence of a clear unroofing. The conjunction of all these clues reinforces the idea of a synsedimentary tectonics affecting the margin/basin system during the Miocene. A thickness analysis of the studied sedimentary successions allows proposing the evolution of the orogenic front and main depozones (foredeep, bulges, wedge-top and intramontane sub-basins) integrated in a complex foreland system migrating from north to south with the Atlas-Mesetas area acting as foreland during Miocene. The orogenic front moved from the Internal Intrarif to Mesorif and later to Internal Prerif. The main wedge-top basin also migrated from the Internal Intrarif to External Intrarif. The foredeep migrated from the Mesorif to the Internal Prerif, while the main forebulge was located in the External Prerif and a secondary bulge developed in the External Intrarif. Intramontane basins developed behind the orogenic front in relative extensional conditions moving from the Internal Intrarif to External Intrarif. The reconstructed Miocene evolution was inserted into a 2D paleogeographic-geodynamic evolutionary model using GPlates software, and then compared to those reported in other external margins of the western Tethys (Betic Chain, Tunisian Tell, Sicilian Maghrebids and Apennines), revealing important similarities and local differences.

The Jurassic climate change in the northwest Gondwana (External Rif, Morocco): Evidence from geochemistry and implication for paleoclimate evolution

The present work deals with Jurassic deposits belonging to the External Rif chain. It is well known that the Jurassic time was a crucial period in the earth's history as witness of significant climate changes. This work aims to provide a preliminary reconstruction of the regional Jurassic paleoclimate of the northwest Gondwana hinterland and its global paleogeographic context. We used diverse geochemical proxies to unravel paleoclimate of the Jurassic sediments accumulated in the Atlantic and Tethysian hyperextended passive margins bordering the northwest Gondwana. We reconstituted their paleo-humidity, paleo-precipitation, paleo-weathering, paleo-productivity, paleo-floral landscape distribution in the Gondwanaland, the paleo-redox, paleo-oxygenation and paleosalinity of the bordering oceanic sinks. The obtained results indicate that the early Jurassic climate was cool with low rainfall and productivity, while the middle Jurassic was characterized by a semi-moist warm climate with high chemical weathering and subsequent seaward terrigenous supply. The Uppermost Jurassic climate was warm, semi-moist to moist with a return to an arid cold climate marked by high rainfall amount which yielded more terrigenous material to the bordering Tethysian and Atlantic hyperextended passive margins around the northwest Gondwana hinterland. The result of this research reveals, among others, the control of the first-order geodynamic processes on the Jurassic mid-latitude climate change, such as plate tectonics reorganization, oceanic seafloor spreading, and subsequent volcanic activity. The latter may triggered a climate shift from early Jurassic dry “cool” to middle-late Jurassic wet warm “greenhouse” climate conditions around the northwest Gondwanaland. Besides, the Jurassic climate change may have been also controlled by successive mega-monsoons that occurred through the Inter-Tropical Convergence Zone (ICZ) over margins and oceanic realms bordering the northwest Gondwanaland.

Study of vulnerable zones to soil instability by radar remote sensing, case of the Temsamane region in north Morocco

The Temsamane massif is part of the external Rif of Morocco and is distinguished by more intense deformations, linked to its topographical, lithological and structural characteristics. Many natural hazard phenomena, and therefore damage and loss of resources and people, are present. The detailed work on these activities remains much localized using traditional techniques. The analysis using differential interferometry techniques of Synthetic Aperture Radar (SAR) images (DINSAR) made it possible to determine the instability and vulnerability to subsidence risks from two images from the Sentinel satellite of two different years (2018 and 2022). The results obtained show the presence of some areas of subsidence in the urban sector, the continuation of shrinkage and slight uplift in the relief areas, and generally instability in rural areas.

Landslide Susceptibility Assessment in Western External Rif Chain using Machine Learning Methods

Landslides are a major natural hazard in the mountainous Rif region of Northern Morocco. This study aims to create and compare landslide susceptibility maps in the Western External Rif Chain context using three advanced machine learning models: Random Forest (RF), Extreme Gradient Boosting (XGBoost), and K-Nearest Neighbors (KNN). The landslide database, created by satellite imagery and field research, contains an inventory of 3528 cases of slope movements. A database of 12 conditioning factors was prepared, including elevation, slope, aspect, curvature, lithology, rainfall, topographic wetness index (TWI), stream power index (SPI), distance to streams, distance to faults, distance to roads, and land cover. The database was randomly divided into training and validation sets at a ratio of 70/30. The predictive capabilities of the models were evaluated using overall accuracy (Acc), area under the receiver operating characteristic curve (AUC), kappa index, and F score measures. The results indicated that RF was the most suitable model for this study area, demonstrating the highest predictive capability (AUC= 0.86) compared to the other models. This aligns with previous landslide studies, which found that ensemble methods like RF and XGBoost offer superior accuracy. The most important causal factors of landslides in the study area were identified as slope, rainfall, and elevation, while the influence rate of TWI and SPI was the minimum. By analyzing a larger inventory of landslides on a more extensive scale, this study aims to improve the accuracy and reliability of landslide predictions in a west Mediterranean morphoclimatic context that encompasses a wide variety of lithologies. The resulting maps can serve as a crucial resource for land use planning and disaster management planning. Doi: 10.28991/CEJ-2023-09-12-018 Full Text: PDF

Ammonites and stratigraphic succession of the middle Toarcian – lowermost Aalenian from the Jebel Amergou (Moulay Bouchta area, Internal Prerif Zone, External Rif belt, northern Morocco)

In the Rif Belt, the Toarcian–Aalenian outcrops are rare. The most important of these outcrops are those of the northern side of Jebel Amergou (70 km northwest of Fez). These outcrops, consisting of lumpy marlstones and marly limestones, are rich in ammonites. A section (JAM) located in a small ravine near Douar Amergou have been studied. Its stratigraphic series (20 m-thick), called the Amergou Formation, is divided into two members. The lower member yielded in the levels 3 and 4 a rich ammonite fauna from the middle Toarcian (Bifrons and Gradata zones) and some ammonites from the upper Toarcian (Bonarellii and Speciosum? zones); the upper member, divide into two levels, yielded in the level 2 rare ammonites from the lower Aalenian (Opalinum Zone). 44 species of ammonites have been identified, described and illustrated for the first time from the Toarcian–lower Aalenian succession of the Rif Belt. Most of these species are common to several basins of both, the northern and the southern margins of the Tethys and the NW European province.

Provenance and source-to-sink of lower-middle Jurassic sediments from hinterland mounts to NW-Gondwana hyper-extended passive margin (Prerif sub-domain, External Rif, Morocco): First evidence from sedimentary petrology and detrital Zircon geochronology

The present work deals with the provenance of lower-middle Jurassic successions belonging to the External Prerif Foreland basin, which remains till now misunderstood and requires a deep investigation dealing with sedimentary petrology and Zircon geochronology. Detrital modal signatures, mudrocks geochemistry combined with Zircon geochronology of lower middle Jurassic pre-orogenic successions of the External Prerif basin have been used to detect provenance relationships with potential Precambrian and Variscan orogenic belts of the Anti-Atlas, Western Meseta, and the exotic “Sehoul Block”. The analyzed sandstone suites, mudrocks, and marls have been collected from Jebel Outita, Jebel Zerhoune, and Dhar N'sour sections which were accumulated in different depositional paleoenvironments evolving down-slope from proximal delta to bathyal and deep-sea basin. These early-middle Jurassic deposits belonged to the NW-Gondwana hyper-extended margin during the earliest rifting-drifting stages of the western Tethyan Ocean edge. The analyzed terrigenous sandstone suites are siliciclastic hybrids characterized by lithic arkoses, feldspathic litharenites, and litharenites framework composition. Detrital sandstone modes reflect provenance from a continental block and recycled orogens with 90% of confidence. These results were corroborated by various provenance ratios (Th/Sc, Th/Co, Th/Cr, Cr/Th, and La/Sc) which indicate felsic source rocks close to the Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values, with probably minor mafic supply. Indeed, the provenance inferred from detrital Zircon geochronology points to different high-grade metamorphic, plutonic basements and overlying sedimentary source rocks aged from Paleoproterozoic to middle-Late Devonian, related to basement source rocks of the exotic “Sehoul Block”, the Western Meseta, and the Central and Occidental Anti Atlas belts.

Dinoflagellate-based age control and biostratigraphic correlations of the Eocene and Oligocene (Lutetian–Chattian) sediments in the El Habt tectonic Unit, western External Rif Chain, Morocco (NW Africa)

Dinoflagellate-based age control and biostratigraphic correlations of the Eocene and Oligocene (Lutetian–Chattian) sediments in the El Habt tectonic Unit, western External Rif Chain, Morocco (NW Africa)

Paleogene evolution of the External Rif Zone (Morocco) and comparison with other western Tethyan margins

The Paleogene evolution of the NW margin of the African Plate (Western External Rif Zone) was studied by means of multidisciplinary analyses of twenty-one stratigraphic logs, including tectofacies recognition, petro-mineralogical results, and thicknesses analysis. Four stratigraphic intervals were recognized separated by three unconformities coarsely aligned with the Cretaceous–Paleogene, Eocene–Oligocene and Oligocene–Miocene boundaries, respectively. Tectofacies appear from the late Ypresian being more frequents from the Oligocene as the tectonic activity increases. The petrology of detrital suites indicates recycled orogen-derived sediments, with quartz supplied from metamorphic rocks of the Atlas orogen and/or the African craton. On the basis of Mesozoic clay mineral assemblages reported in the literature, the clay mineralogy of mudstones suggests upper Jurassic to upper Cretaceous terrains from the Internal Intrarif as the main source area of the Paleocene–Eocene successions, with sediment provenance reversion during the Oligocene and additional contribution of Paleocene to lower Eocene suites. The different displacement capability of the identified aluminic-magnesic clay mineralogy enabled to deduce the relative proximity of the source area. These findings point out a complex sedimentary evolution characterized by a mixture of different lithotypes dating back to upper Jurassic. X-ray parameters helped to identify evidences of synsedimentary tectonics overprinting the inherited mineralogy during some periods with weak burial diagenesis at most. During the Paleogene a foreland basin is formed mainly in the Mesorif and Prerif sub-domains. This foredeep was represented by two ‘sub-geosynclines’ separated by a relative bulge located in the External Mesorif. The Internal Intrarif could represent the relative orogenic front, advancing on the External Intrarif. The Eocene forebulge was located in the Ridges Domain, while the Gharb Basin was the backbulge of the system. During the Oligocene the depocentral area migrated southward and a homogeneization of thicknesses took also place in the whole margin. In this new configuration, the foredeep would be located in the External Mesorif (previously a relative bulge) while the Ridges Domain and the Gharb Basin continued to act as the system forebulge and backbulge, respectively. A comparison with the Paleogene evolution of other western Tethys external margins (Betic Chain, Tunisian Tell, Sicilian Maghrebids, and Apennines) has revealed more similarities than differences. The effects of the Eo-Alpine tectonics are recognized everywhere even if they decrease both from N to S, and from W to E in the different considered margins. The evolution of the compared margins shows a common pre-foredeed (Paleocene-Eocene) and beginning of foredeep (Oligocene) stages in the foreland basins.

The Cenozoic evolution of the Intrarif (Rif, Morocco)

AbstractThis paper provides an understanding of the sedimentary-tectonic evolution of the Cenozoic strata of the El Habt and Ouezzane Tectonic Units (Intrarif, External Rif) in Morocco. New data provide information about the depositional architecture and enable a correlation of the evolution of the External Rif in Morocco with that of the Betic Cordillera in Spain and the Tunisian Tell, which provides new insights for hydrocarbon exploration in the region regarding possible source, reservoir, and seal rocks. The reconstructed Cenozoic succession was bio-chronologically defined, and the major unconformities and stratigraphic gaps were identified. The presence of these unconformities allowed three main stratigraphic sequences to be defined by age: Danian p.p., early Ypresian–early Bartonian p.p., and the early Rupelian–early Serravallian p.p. Three secondary stratigraphic sequences in the former upper main sequence were also defined by age: early Rupelian–late Chattian p.p., Burdigalianp.p., and the Langhian–Serravallian p.p. The depositional setting evolved from deep basin during the Late Cretaceous–Paleocene to external platform-slope during the Eocene–Miocene. The Cenozoic sandstones contain metamorphic and sedimentary rock fragments derived from a recycled orogen source area. The clay mineralogy in the Cenozoic strata consists of associations of Ill+(I–S) ± Sme, Ill+(I–S) ± Sme+Kln and Ill+(I–S) ± Sme+Kln+Chl. These associations indicate an initial unroofing in the Paleogene period, then in the Cretaceous period, and finally in the Late Jurassic period during the Eocene–Oligocene. This detritus was followed by variable amounts of a sedimentary mix of Paleogene to Late Jurassic terrains due to several phases of erosion and deposition partly related to syn-sedimentary tectonics during the Miocene. Equivalent features (similar types of sediments, tectofacies, gaps, and unroofing) were also recognized along the Betic Cordillera in Spain and Maghrebian Chain (Morocco and Tunisia) and interpreted as related to a pre-nappe tectonic activity of soft basement folding, which occurred during the Paleogene after the generalized tectonic inversion (from extension to compression) occurred in the Late Cretaceous. The Upper Cretaceous is considered to be the hydrocarbon source rock, while the fractured Eocene and the porous Oligo-Miocene suites are proposed as possible hydrocarbon reservoirs. The Cenozoic stratigraphic architecture and the nappe structure of the region could provide the necessary trap structures.

Geochemistry and Petrogenesis of Lower Jurassic Mafic Rock Suites in the External Rif Belt, and Chemical Geodynamics of the Central Atlantic Magmatic Province (CAMP) in Northwest Morocco

We present new field evidence, geochemical and isotopic data, and age constraints on Lower Jurassic mafic rock suites within a >200-km-long curvilinear belt in the Rif orogenic belt in northern Morocco and show that these rock assemblages formed as part of the Central Atlantic Magmatic Province (CAMP). The CAMP represents a large igneous province that straddles the edges of the modern peri-Atlantic continents. It developed ~200 Ma, following the initiation of the breakup of Pangea. Main magmatic rocks in the Rif External Zone include basaltic lavas, massive dolerite, and isotropic and cumulate gabbros, all intruded by dolerite and trondhjemite dikes and sills. Available U-Pb zircon ages from dolerite, gabbro, and trondhjemite dike rocks are , , and , respectively. Based on their geochemical affinities and isotopic compositions, the analyzed rocks define basalt-dolerite and gabbro-cumulate gabbro-trondhjemite groups. The basalt-dolerite group samples are subalkaline in nature and have low TiO2 contents, whereas the gabbro-cumulate gabbro-trondhjemite group samples are alkaline and display high TiO2 values. Most samples are tholeiitic in character and show large-ion lithophile and light rare earth element enrichment and high field strength element depletion compared with normal mid-ocean ridge basalt (MORB). Samples of both groups display low 143Nd/144Nd201 Ma (0.51182–0.51262) and high 87Sr/86Sri ratios with ɛNd values ranging from −1.51 to +4.85. The basalt-dolerite group rocks have enriched MORB compositions, compatible with the low-Ti CAMP suites, whereas the gabbro-cumulate gabbro-trondhjemite group rocks have oceanic island basalt compositions reminiscent of high-Ti CAMP suites in other continents. Magmas of the gabbro-cumulate gabbro-trondhjemite group underwent differentiation through tholeiitic fractionation. Magmas of the rocks of both groups included melt components, originated from partial melting of a previously subduction-modified subcontinental lithospheric mantle. Our results indicate that the Early Jurassic CAMP magmatism in northern Morocco marked a major episode of continental magmatism before the opening of the Maghrebian Tethys between Africa and Iberia in the latest Jurassic.

Paleoenvironmental and paleoclimatic changes during the Late Cretaceous and Cretaceous–Paleogene (K/Pg) boundary transition in Tattofte, External Rif, northwestern Morocco: implications from dinoflagellate cysts and palynofacies

This paper presents a quantitative study of dinoflagellate cysts (dinocysts) and palynofacies of the Campanian–Danian marly succession at the village of Tattofte (western External Rif, northwestern Morocco). The paleoenvironmental and paleoclimatic interpretations, inferred from this palynologic analysis, are compared to coeval sequences of other areas in the Northern Hemisphere. Changes in the relative abundances of dinocyst taxa, which are paleoenvironmental indicators, throughout the section suggest a deposition in a marine inner to outer neritic setting. The upper Campanian dinocyst assemblage is characterized by the presence of outer neritic-oceanic and low productivity indicator taxa (e.g., Spiniferites spp., Odontochitina spp.) and cold-water taxa (e.g., Manumiella spp., Chantangiella spp., Laciniadinium spp.), whereas, the lower Maastrichtian assemblage is characterized by inner neritic, high productivity and warm-water indicator taxa (e.g., Palaeocystodinium spp., Andalusiella spp.). The upper Maastrichtian dinocyst assemblage displays a return to an outer neritic environment under a transgressive regime, but with a cooling pulse and a moderate productivity. However, the Cretaceous–Paleogene (K/Pg) boundary interval records remarkable changes in the relative abundances of dinocyst taxa, indicating an inner neritic (coastal) setting, which is the most proximal in the study section; such changes reflect instable paleoenvironmental conditions which may be related to global cooling periods, likely caused by the Deccan volcanism in India and/or the Chicxulub asteroid impact in Mexico at the K/Pg boundary. In the Danian, the dinocyst relative abundances indicate a gradual return to stable environmental conditions.A quantitative analysis of the kerogen plots (palynomorphs, phytoclasts and amorphous organic matter (AOM)) reveals five types of palynofacies, generally indicating oxic to suboxic marine environments. The upper Campanian and upper Maastrichtian (lowermost part) strata are characterized by a playnofacies (V), indicating a distal shelf, while the lower Maastrichtian and lower Danian (uppermost part) strata record a playnofacies (III), reflecting an intermediate inner-outer neritic environment. However, the K/Pg boundary transition is characterized by playnofacies types (I) and (II), indicating a proximal (coastal) environment.

Three new organic-walled dinoflagellate cysts from the Upper Cretaceous deposits in the western External Rif, northwestern Morocco: Taxonomy and stratigraphic distribution

Three new species of organic-walled dinoflagellate cysts (dinocysts) have been spotted during our palynological investigations in the Upper Cretaceous deposits from the western External Rif Chain, northwestern Morocco. They have been previously mentioned and figured under different names, but have not been formally described. In this paper, the formal descriptions of these new species are presented, based on several specimens observed within rich, diverse and well-preserved upper Campanian dinocyst assemblages from the Sekada, Tattofte and Bou Lila sections. Canningia wilsonii sp. nov. is a holocavate cyst, characterized by having densely packed pillars, supporting a finely reticulate ectophragm on the mid-dorsal surface to coarsely reticulate elsewhere, mainly in the periphery. Impagidinium sekadensis sp. nov. is distinguished by the combination of a smooth central body wall, rigid and well-developed sutural septa, narrow longitudinal apical plates (1′, 4′) which are rarely separated (partially) by a discontinuous sutural septum, a strongly leavorotatore cingulum and a narrow sulcus with a differentiated posterior sulcal (ps) plate. Nematosphaeropsis lilaensis sp. nov. differs from the published species of Nematosphaeropsis by having a smooth central body wall and numerous sutural (gonal and intergonal) processes that are flexible, hollow and joined proximally by low and discontinuous sutural ridges and distally by pairs of thin penitabular trabeculae. The taxonomic synonyms and stratigraphic ranges of the new species, as well as their comparison with published dinoflagellate taxa, which morphologically resemble them, are given and discussed.

Distribution of Dinoflagellate cyst assemblages and palynofacies in the Upper Cretaceous deposits from the neritic Bou Lila section, External Rif (northwestern Morocco): Implications for the age, biostratigraphic correlations and paleoenviromental reconstructions

As a part of our palynological investigations of the Upper Cretaceous deposits from the Rif Chain, the present study of the dinoflagellate cyst assemblage distribution and palynofacies was carried out in the Bou Lila section, located northeast of the city of Ksar El-Kébir (External Rif, northwestern Morocco). The study focused on the age refinement and interpretation of paleoenvironmental conditions within the basin during the sediment deposition. The analyzed samples are rich in palynomorphs, formed essentially of diverse and well-preserved dinoflagellate cysts, which are associated with phytoclasts and rare microforaminiferal test linings, spores, pollen grains and algae.The Bou Lila section is assigned to the late Campanian, based on dinoflagellate cyst taxa, whose first appearance datums (FADs) or last appearance datums (LADs) are markers of the late Campanian. These taxa include Areoligera coronata, Areoligera senonensis, Cerodiniuum diebelii, Chatangiella? robusta, Cribroperidinium wilsonii subsp. wilsonii, Impagidinium rigidaseptatum, Odontochtina operculata, Odontochitina costata, Palynodinium grallator, Raetiaedinium belgicum, Rigaudella appenninica, Trichodinium castanea subsp. castanea, Trigonopyxidia ginella, Trithyrodinium evittii, Trithyrodinum suspectum, Xenascus ceratioides and Xenascus wetzelii. The high diversity of the dinoflagellate cyst taxa made it possible to correlate the Bou Lila section with biostratigraphically well-calibrated upper Campanian sequences from several Tethyan and also Boreal sites, including the type Campanian area and the GSSP for the base of the Maastrichtian in southwestern France and the type Maastrichtian area in Limburg.The fluctuations in the relative abundances of the selected dinoflagellate cyst groups and other quantitative palynological parameters allow a recognition of three paleoecological zones. They indicate a gradual passage from an inner neritic setting, with high productivity conditions in the most basal part of the section, to a stable outer neritic setting in the upper part of the section.The palynofacies analyses are in general agreement with the dinoflagellate cyst results, indicating a passage from a proximal depositional environment in the lowermost part of the section to a distal depositional environment in the uppermost part of the section. The dinoflagellate cyst assemblage indicates a subtropical to temperate setting, with the presence of the northern high-latitude cold-water species Palynodinium grallator, suggesting a short cooling episode or also conditions of water stratification during the late Campanian.

Tectono-Sedimentary Cenozoic Evolution of the El Habt and Ouezzane Tectonic Units (External Rif, Morocco)

An interdisciplinary study based on lithostratigraphic, biostratigraphic, petrographic and mineralogical analyses has been performed in order to establish the Cenozoic tectono-sedimentary evolution of the El Habt and Ouezzane Tectonic Units (External Intrarif Subzone, External Rif, Morocco). The reconstructed record allowed identification of the depositional architecture and related sedimentary processes of the considered units. The Cenozoic successions were biochronologically defined allowing, at the same time, identification of unconformities and associated stratigraphic gaps. The presence of five unconformities allowed for the definition of the main stratigraphic units arranged in a regressive trend: (1) lower Paleocene interval (Danian p.p.) assigned to a deep basin; (2) Eocene interval (lower Ypresian-lower Bartonian p.p.) from a deep basin to an external carbonate-siliceous platform; (3) lower Rupelian-upper Chattian p.p. interval deposited on unstable slope with turbidite channels passing upward to an external siliciclastic platform; (4) Burdigalian p.p. interval from a slope; (5) Langhian-Serravallian p.p. interval from slope to external platform realms. The petrography of the arenites and calcarenites allowed for the identification of the supplies derived from erosion of a recycled orogen (transitional and quartzose subtypes). The clay-mineralogy analysis indicates an unroofing (first erosion of Cretaceous terrains followed by upper Jurassic rocks) always accomplished by erosion of Cenozoic terrains. Several tectofacies checked in some stratigraphic intervals seem to indicate the beginning of deformation of the basement generating gentle folds and first activation of blind thrusts, mainly during the Paleogene. A preorogenic tectonic framework is considered as responseto the generalized tectonic inversion (from extension to compression) as frequently registered in the central-western peri-Mediterranean areas. The large volumes of reworked terrigeneous supply during the latest Oligocene-Miocene p.p. indicates the beginningsof the synorogenic sedimentation (foredeep stage of the basins) controlled by active tectonics.

Comments on the Liassic age ascribed to the Bou Adel oceanic gabbro (Central Mesorif, Morocco) by Michard et al. (2018), and stratigraphic and palaeogeographic arguments for a latest Jurassic-earliest Cretaceous age

In the median part of the Rif Belt (Mesorif Zone), Upper Jurassic-Lower Cretaceous deposits contain numerous relics of volcanic materials (basalt pebbles and interstratified lava flows), and several large gabbro massifs, especially in the Central Mesorif. The most important of these massifs, Bou Adel, was regarded as an intrusive gabbro of varying age (according to successive authors: Barremian, Late Jurassic to Senonian, and Bathonian respectively), and recently as an oceanic gabbro of latest Jurassic-earliest Cretaceous. Based on a radiometric (190±2 Ma) date from zircon grains, Michard et al. (2018) ascribed an Early Jurassic (Liassic) age to this gabbro. Consequently these authors proposed a new interpretation of the oceanic opening of the External Rif Domain related to the eastwards expansion of the Central Atlantic oceanic rift. They also hypothesized that the Upper Jurassic-Lower Cretaceous volcanic lavas and the ophiolite complexes of the Mesorif Zone are heterochronous and correspond to two, distinct and separated in time, magmatic events. This new age ascribed to the Bou Adel gabbro and the new interpretation of the oceanic opening of the External Rif disagree with the stratigraphic data and the geodynamic framework of the External Rif domain during the Mesozoic. On the base of numerous stratigraphic data and the palaeogeographic evolution, we evidence herein that the volcanic lavas and the oceanic gabbros of the Mesorif Zone all originated from the same geodynamic event related to the westwards expansion of the Tethys Ocean at the Jurassic-Cretaceous boundary, and that these oceanic gabbros are ophiolite complexes of the Senhadja and Bou Haddoud nappes, thrusted over the External Mesorif Zone during the Alpine Miocene orogeny.

Mesorif Gabbros (External Rif, North Morocco): Ophiolitic Suture Witness or a “Newly Discovered” Manifestation of the Central Atlantic Magmatic Province?

AbstractThe Rif Mountain located in Northern Morocco represents the westernmost extremity of the Peri‐Mediterranean Alpine orogenic system. This belt is classically subdivided into: 1) Internal zones (or Internal Rif which is an allochthonous metamorphic domain known worldwide thanks to the presence of large peridotite outcrops); 2) flysch zones (sediments corresponding to the original cover of the Maghrebian Tethys); and 3) External zones (or External Rif representing the North African margin remnants).The External Rif is itself subdivided into Prerif, Mesorif and Intrarif domains from the South to the North and is composed by Upper Triassic to Cenozoic sediments structured in a nappe stack. Mafic rock intrusions were reported in this External Rif since the preliminary geological studies even if they were wrongly mapped as “granites”. Later careful fieldwork and mapping studies specified nevertheless their gabbroic nature. A more recent petrological and geochemical study of a few outcrops of those gabbroic intrusions conducted the corresponding authors, encouraged by the presence of ultramafic rocks (Beni Malek serpentines) in the eastern part of the External Rif to consider those gabbros as oceanic and so, associated to “an ophiolitic suture”. Nevertheless, a recent and extended survey on the architecture and the rifting history of the Mesozoic margin of the Maghrebian Tethys focusing mainly on the Mesorif domain favor another interpretation. The detailed petrography of those mafic intrusions (mainly gabbros + dolerites and rarely extrusive rocks); their geochemical fingerprints and mainly their geochronological data (ages around 200 Ma based on U‐Pb zircon LA‐ICP dating) all together indicate clearly that those mafic intrusions are rather a “newly discovered” manifestation of the Central Atlantic Magmatic Province activity “CAMP” in the External Rif belt. The CAMP magmatism has been largely well described and characterized in all the other geological domains of Morocco (Anti‐Atlas, High Atlas, Middle Atlas and Meseta) but never described until the date in the Rif belt which highlights the importance of the results reported here.

Sediment mobilization study on Cretaceous, Tertiary and Quaternary lithological formations of an external Rif catchment, Morocco

ABSTRACT Soil erosion is a serious ecological problem in Mediterranean areas. The IntErO model based on the erosion potential method (EPM) and the modified universal soil loss equation (MUSLE) have been used to assess soil erosion in several basins. This study aimed to assess and evaluate the effectiveness of these methods for evaluating sediment production and deposition rates in the Arbaa Ayacha basin, Morocco, in order to estimate sediment fluxes on a catchment scale. Our findings suggest that the basin is strongly exposed to erosion owing to geological formations, slope and land use, with average losses of about 28.4 t ha−1 year−1. Erosion processes were evaluated at the erosion production (Eocene marly formations) and sedimentation zones (Quaternary terraces). The results of these models may be useful to address soil and water management in this region and to assess the impact of a river dam that will be built in the basin.

Campanian to Danian dinoflagellate cyst assemblages from the southwestern Tethyan margin (Tattofte section, western External Rif, Morocco): Biostratigraphic and paleobiogeographic interpretations

A palynological study of the Upper Cretaceous–lower Paleocene outcrop section at Tattofte (westernmost External Rif, Morocco) has produced a well-preserved palynological assemblage rich in dinoflagellate cysts (dinocysts). For the first time, these assemblages have allowed us to determine the age of this section, to highlight a new Cretaceous–Paleogene boundary, and to make paleobiogeographic interpretations. The samples analyzed yielded 209 dinocyst species and 81 biostratigraphic dinocyst events (first occurrence, or FO, and last occurrence, or LO). We recognized the upper Campanian based on the FOs of Areoligera coronata, Areoligera reticulata, Areoligera senonensis, Cerodinium diebelii and Andalusiella mauthei subsp. mauthei, as well as the LOs of Batiacasphaera solida, Odontochitina costata, Odontochitina porifera, Sentusidinium eisenackii, Trichodinium castanea and Trithyrodinium suspectum. The lower Maastrichtian is determined by the FOs of Isabelidinium bujackii, Palaeocystodinium golzowense and Trithyrodinium evittii, and by the LO of Alterbidinium acutulum, and the upper Maastrichtian is recognized primarily by the FOs of Cerodinium speciosum subsp. speciosum, Disphaerogena carposphaeropsis, Glaphyrocysta perforata and Manumiella seelandica and the LO of Dinogymnium spp. The Danian is recognized on the basis of the FOs of several taxa, including Carpatella cornuta, Danea californica and Senoniasphaera inornata. The succession of the dinocyst events in the uppermost part of the studied interval has revealed a relatively complete record across the Cretaceous–Paleogene boundary. The Cretaceous–Paleogene boundary coincides with a 8 cm-thick reddish layer, which resembles those observed previously in the Cretaceous–Paleogene boundary reference sections in the Mediterranean area, most notably the Cretaceous–Paleogene boundary stratotype at El Kef (Tunisia). The upper Campanian dinocyst assemblage indicates a subtropical to temperate setting, while the Maastrichtian and lower Danian assemblages indicate a subtropical to warm temperate setting. The incursion of a few higher latitude cold-water dinocyst species in these provinces during the latest Campanian and around the Cretaceous–Paleogene boundary may suggest a southward migration of these species, probably related to short cooling episodes and ocean circulation.

Hydrological foretelling uncertainty evaluation of water balance components and sediments yield using a multi-variable optimization approach in an external Rif’s catchment. Morocco

Sedimentary and aquatic dynamics are currently causing major environmental problems in the Mediterranean countries, water and soil resources are steadily decreasing over time. Therefore, simulation and estimation of flows and sediments have currently a direct implication in the sustainable management of water and soils. In the present study, a Mediterranean watershed (North-West of Morocco) was benefited from the functionalities of Hydrological Model SWAT, version 2012 (semi-distributed and physically based), by adopting a monthly simulation. The main objective of this study is to calibrate and validate the SWAT model in the Arbaa Ayacha watershed (18,854 ha) between 1980 and 2000 by a multi-objective optimization approach using the Sufi-2 algorithm of the SWAT-CUP program. The performance of the model was tested using three objective functions NSE, PBIAS and R2, while the sensitivity analysis of the model was performed by adjusting 19 parameters of sensitivities related to flow rates and sediment concentrations. The results obtained are satisfactory with a significant correlation between the observed and simulated values of variables flow and sediments. The results also show that evapotranspiration and surface runoff are predominante in the basin compared to the other components of the water balance, while the sediment yield was estimated at 28.09 t/ha/year. Since the model is validated in the study area, it will later be used to simulate the evolution of scenarios based on climate change and land use. It will also help to determine the best managment practices in the watershed.