Mohamed Najib Zaghloul

The Oued Dayr Formation: first evidence of a new Miocene late-orogenic cycle on the Ghomaride complex (Internal Domains of the Rifian Maghrebian Chain, Morocco)

This work deals with the first evidence in the Rifian Maghrebids of a Miocene clastic succession, named Oued Dayr Fm, uncorformably resting on the Ghomaride Complex. The formation starts with polymictic conglomerates, consisting of clasts coming from all the Rifian Internal Units, sharply or gradationally evolving to graded and stratified calcareous sandstones, siltstones and massive marls. The occurrence of nannofossils starting from the NN5 Biozone of Martini indicates an age no older than middle Langhian. However, considering the possible reworking of taxa and the regional framework, the possibility of a younger age cannot be excluded. The sedimentary evolution points out a subsidence rate exceeding the detritic supply, within a thrust-top basin originated during an extensional tectonic phase, affecting the exhumed internal nappe stack. The Oued Dayr Fm constitutes the first evidence of a new Miocene late-orogenic sedimentary cycle resting on the Rifian Internal Units, intermediate between the Burdigalian Oued Gharraq-Sidi Abdeslam cycle and the Pliocene deposits. In a regional framework, no middle Miocene unconformable deposits are known on the Internal Units of both the Betic Cordillera and Maghrebian Chain, while Tortonian deposits everywhere occur. A Tortonian age, therefore, can be suggested for the Oued Dayr Fm, but data demonstrating this hypothesis at present are lacking.

Textural and compositional controls on modern fluvial and beach sands of Mediterranean coastal Rif belt (Northern Rif, Morocco)

Texture and composition of beach (154 samples) and fluvial (26 samples) sands collected between the Amsa and Amter villages (Rif Thrust-Belt, Morocco) are used to characterize the hinterland petrological provinces, their drainage patterns and dispersal pathways. Multivariate analytical techniques were carried out on the textural and compositional data. The analyzed sediments are usually coarse-grained, and locally medium to fine-grained sands, varying from well sorted and graded samples (Amsa river samples) to poorly sorted and graded samples (Oued Laou, Sidi Yahia Aarab and Kanar river samples). The relationships of the coarser one percentile (C) and the median value (M) on the C-M diagram suggest that transport processes are saltation and suspension for medium to fine grained sands, and bedload-traction and rolling for coarser sand and gravels. The morphology of quartz grains, mainly characterized by angular to sub-angular shapes with V-shaped cracks and conchoidal fractures, is the result of those transport processes. Two sand petrofacies were identified and reflect the main clastic contribution of source rocks belonging to the Internal Domain Units of the Rif Belt. Sands from beaches and related fluvial systems draining Ras Akaili, Tissouka, Dhar Nesk, and Beni Mezala Mountains, have a metamorphic-sedimenticlastic petrofacies (between the Amsa and Bouhmed area) and a metamorphic-ultramafic petrofacies (between the Bouhmed and Amter area), mainly derived from the Paleozoic metasedimentary rocks of the Ghomaride and Sebtide complexes.

Petrology of lower-middle Miocene Zoumi Flysch Fm. (Mesorif sub-domain, Rif belt, Morocco): first evidence of mixed mode provenance and geodynamic setting

The Zoumi Basin was generated in a collisional tectonic setting during the Lower-Middle Miocene. The syn-orogenic flysch deposits of the basin have been well investigated by petrographic and geochemical studies to characterize the composition, source to sink routing system, and tectonic setting of the Zoumi flysch. Forty-three sandstone samples and 45 mudstone samples have been gathered from six measured stratigraphic sections. These samples have been analyzed using XRD, XRF, inductively coupled plasma-mass spectrometry (ICP-MS) for mudrocks and petrographic investigation for sandstones. The Lower-Middle Miocene Zoumi flysch is defined as sublitharenites and quartzarenites according to mineralogical content. Detrital grains are commonly subangular to subrounded, poorly sorted, and rich in quartz grains. Point counting modal analysis leads to craton interior and recycled orogen provenance with significant first-cycle sediment supply and low sedimentary recycling. Several chemical ratios (Al2O3/TiO2, La/Th, Cr/Th, Th/Sc, Zr/Sc) as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomaly suggest a dominant felsic rock sources. However, V-Ni-La*4, V-Ni-Th*10, and Th/Sc vs. Cr/Th plots do not exclude a mafic supply source nature which is evidenced by numerous ophiolitic outcrops scattered throughout the Mesorifan Subdomain (Mesorifan Ophiolitic Suture Zone).

Geochemistry of the Miocene Zoumi flysch thrust-top basin (External Rif, Morocco): new constraints on source area weathering, recycling processes, and paleoclimate conditions

This study focuses on the Lower-Middle Miocene syn-orogenic flysch deposits of the Zoumi basin to infer source area paleoclimatic conditions, the intensity of source rocks paleoweathering, and mechanical sorting and recycling effects. The mudrocks are enriched in Al2O3, Fe2O3, CaO, and TiO2 relative to PAAS and depleted in the other mobile major elements. There are high positive correlations between SiO2, Al2O3, and TiO2 and negative correlations between SiO2 and CaO. Geochemically, the mudstones are mainly classified as shales, Fe-shales, and wackes. Various discriminant diagrams were used to reveal the inferred tectonics, source paleoweathering intensity, and paleoclimatic conditions. Chemical index of alteration (CIA) and chemical index of weathering (CIW) values for Lower-Middle Miocene vary from 50 to 80% indicating low to moderate degree of source area weathering compatible with non-steady-state weathering under wet and humid paleoclimatic conditions. Locally (Zoumi mid-section) CIA values are higher (> 80) reflecting intense source area weathering, which may be attributed to high tectonic impulses and more humid conditions during deposition. The combination of ICV-CIA, Al2O3-Zr-TiO2, and Th/Sc-Zr/Sc values suggests the bulk rock is chemically immature and has experienced modest physical sorting and recycling reflecting little transportation until the final deposition.

Evoluzione tettono-sedimentaria del Complesso d’Accrezione Liguride in Appennino Meridionale

Tectono-sedimentary evolution of the Ligurian Accretionary Complex in the southern Apennines.Aim of this paper is the structural and stratigraphic analyses of the Ligurian Accretionary Complex exposed in the Campania region (Italy) in order to unraveling the deformation pattern characterizing the transition from the final oceanic subduction stages to the early stages of deformation of the foreland continental margin. Our results outline a sequence of late Early Miocene (Burdigalian) shortening events, also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin. Emplacement of the overthickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning, aiding the development of wedge-top depocenters. Early Miocene NW-SE shortening recorded by Ligurian Accretionary Complex units is completely unrelated with later (Late Miocene to Pleistocene) NE-directed thrusting in the Apennines, which was coeval with back-arc extension in the Tyrrhenian Sea. Therefore, our results emphasize the occurrence of a major discontinuity in the Neogene geodynamic evolution of the southern Apennines, whose tectonic history may be clearly subdivided, from a kinematic point of view, into pre- and syn-Tyrrhenian back-arc extension stages.