External Rif Research Articles

Crustal structure beneath the Rif Cordillera, North Morocco, from the RIFSIS wide‐angle reflection seismic experiment

AbstractThe different geodynamic models proposed since the late 1990s to account for the complex evolution of the Gibraltar Arc System lack definite constraints on the crustal structure of the Rif orogen. Here we present the first well‐resolved P‐wave velocity crustal models of the Rif Cordillera and its southern continuation toward the Atlas made using controlled‐source seismic data. Two 300+ km‐long wide‐angle reflection profiles crossed the Rif along NS and EW trends. The profiles recorded simultaneously five land explosions of 1Tn each using ∼850 high frequency seismometers. The crustal structure revealed from 2‐D forward modeling delineates a complex, laterally varying crustal structure below the Rif domains. The most surprising feature, seen on both profiles, is a ∼50 km deep crustal root localized beneath the External Rif. To the east, the crust thins rapidly by 20 km across the Nekkor fault, indicating that the fault is a crustal scale feature. On the NS profile the crust thins more gradually to 40 km thickness beneath Middle Atlas and 42 km beneath the Betics. These new seismic results are in overall agreement with regional trends of Bouguer gravity and are consistent with recent receiver function estimates of crustal thickness. The complex crustal structure of the Rif orogen in the Gibraltar Arc is a consequence of the Miocene collision between the Iberian and African plates. Both the abrupt change in crustal thickness at the Nekkor fault and the unexpectedly deep Rif crustal root can be attributed to interaction of the subducting Alboran slab with the North African passive margin at late Oligocene‐early Miocene times.

Organic-walled dinoflagellate cysts from the Upper Cretaceous–lower Paleocene succession in the western External Rif, Morocco: New species and new biostratigraphic results

Palynological investigation of the Upper Cretaceous–lower Paleocene succession from the Tahar section near Arba Ayacha in northwestern Morocco (westernmost External Rif Chain) reveals the presence of rich, diverse and well-preserved dinoflagellate cyst assemblages. For the first time in the study region, biostratigraphic interpretations based on the dinoflagellate cyst assemblages from the studied interval allow the recognition of the upper Maastrichtian and Danian. Relevant upper Maastrichtian–Danian global dinoflagellate cyst events include: the First Appearance Datum of the upper Maastrichtian species Disphaerogena carposphaeropsis, Glaphyrocysta perforata, and Manumiella seelandica; the Last Appearance Datum of the Cretaceous taxa Dinogymnium spp., Isabelidinium cooksoniae, and Pterodinium cretaceum; and the First Appearance Datum of the earliest Danian markers Carpatella cornuta, Damassadinium californicum, Membranilarnacia? tenella, and Senoniasphaera inornata. We formally describe the biostratigraphical range and potential of two new dinoflagellate cyst species, namely Nematosphaeropsis silsila Guédé and Slimani nov. sp., and Pterodinium ayachensis Guédé and Slimani nov. sp. Both species are found in the westernmost External Rif Chain and are restricted to the upper Maastrichtian.

Associations de kystes de dinoflagellés des séries du Jurassique supérieur (Oxfordien–Tithonien) du Rif externe (Prérif interne et Mésorif, Maroc) et comparaisons régionales

A biostratigraphic study of dinoflagellate cysts of the Upper Jurassic series from the eastern External Rif Chain, has been achieved for the first time on four outcrop sections : the DM section (Douar Marticha), the TB section (the Tarhchenna “Sof”), the KSD section (the Kef Mallou “Sof”) and the Y section (Douar Lamriene) among which three sections (TB, KSD and Y) are well-dated by ammonites and calpionellids fauna. The DM and TB sections are complementary in terms of stratigraphy and correspond respectively to the upper part of the “Ferrysch” Formation, a thick shaly–silty and sandy sequence assigned to the Callovian-Oxfordian stages and to the El Gouzat limestones Formation (Kimmeridgian - Lower Tithonian age) and to the Tarhchenna marly limestones Formation (Upper Tithonian age) from the EL Gouzat area (Mesorif). The KSD and Y sections are also complementary and correspond to the Kimmeridgian-Lower Tithonian Msila limestones Formation and to the overlying marly limestones Massif Formation of Upper Tithonian age, outcropping in the Msila region (Internal Prerif). These four sections have shown many dinocysts rich levels, which had allowed characterizing the Middle? and Upper Oxfordian substages in the DM section. In the other sections, the dinoflagellate cyst assemblages are nearly similar to those of the Kimmeridgian–Tithonian of many sections from the Boreal, Sub-boreal and North tethyan realms, particularily from England, Russia and South-East France basin. The results of the present work confirm once again, the important value of dinoflagellate cysts, for age dating of ammonites-lacking Mesozoic sedimentary sequences and for biostratigraphic correlations.

New ophiolite slivers in the External Rif belt, and tentative restoration of a dual Tethyan suture in the western Maghrebides

AbstractOphiolite slivers have been described recently in the core of the External zones of the Central Rif belt. The present work aims at illustrating new ophiolite slivers further east and discussing the structural position and tectonic emplacement of all these oceanic floor remnants. Their basement consists of gabbros previously dated at 166±3 Ma and their cover includes mafic breccias, micrites and radiolarites. These oceanic slivers are located within the Mesorif nappe stack at the bottom of the Senhadja nappe that roots beneath the Intrarif Ketama unit and was thrust over the more external Mesorif and Prerif units during the Cenozoic inversion of the North African paleomargin. These oceanic crust (OC) slivers belong to the same Mesorif suture zone as the Beni Malek serpentinites and Ait Amrâne metabasites from eastern Rif that also include marbles with ophiolitic clasts and derive from an ocean-continent transition (OCT) domain. After examination of the varied hypotheses that have been suggested to account for the emplacement of these units in the External Rif, we propose that obduction sampled an oceanic corridor opened between the Mesorif and Intrarif domains at the emplacement of the Rif Triassic evaporite basin. The Intrarif block should have been then separated from the African passive margin and connected with the Flysch domain south of the passive margin of the Alboran domain. The pre-collision structure of the Rif transect would involve two hyper-extended passive margins separated by a narrow oceanic transform fault corridor. Therefore the Tethys suture in the western Maghrebides would be split by the Intrarif block and would involve the Flysch zone in the north and the ophiolite bearing Mesorif suture zone in the south.

Oceanic units in the core of the External Rif (Morocco): Intramargin hiatus or South-Tethyan remnants?

The aim of this paper is to describe the mafic rocks that crop out in the central-western Mesorif Zone (External Rif Belt), and discuss their geodynamic signification. Basalt flows, olistoliths and breccias occur in Oxfordian–Berriasian deposits of Mesorif units ascribed to the distal part of the African paleomargin. The climax of volcanic activity is observed at the northern border of a Kimmeridgian carbonate platform progressively dismembered during the Tithonian–Berriasian. In spite of the alteration of the basalts, their petrological and geochemical characters point to E-MORB affinities. The studied gabbro massifs (Bou Adel, Kef el Rhar west and north) occur as restricted slivers or klippes within the Senhadja nappe or mélange of the internal Mesorif, which overlies the basalt-bearing units and other, more external Mesorif units. The compositions range from troctolitic olivine gabbro to ferrogabbro with frequent ortho- to heteradcumulate textures; they display typical tholeiitic affinity. The gabbro massifs are crosscut by trondjhemite dykes and overlain by metabasalts, fault-scarp breccias, ophicalcites, marbles and radiolarites. Composition featuring initial near liquid composition, display multi elements patterns close to those of E-MORB, with a weak Eu negative anomaly and evidence of slight crustal contamination. These gabbro massifs were regarded as Jurassic–Cretaceous intrusions, locally dated (K–Ar) at 166±3Ma. Conversely, we assume they represent discrete samples of a Jurassic–Cretaceous oceanic basement (ophiolites), emplaced tectonically in the Senhadja nappe (mélange) of the central Mesorif. The correlation of both these types of mafic rock associations (paleomargin basalts and ophiolite klippes) with the serpentinites of the eastern Mesorif (Beni Malek) and Oran mountains (Algeria) is then briefly discussed. We conclude that the previous hypothesis of an intramargin “Mesorif suture zone” must be reconsidered, being challenged by that of a major, syn-collisional “Oran-Mesorif Strike-Slip Fault”. In the latter hypothesis, the newly described Mesorif oceanic klippes would represent allochthonous remnants of the Ligurian–Maghrebian (Tethyan) oceanic domain.

A Cretaceous–Palaeogene boundary geological site, revealed by planktic foraminifera and dinoflagellate cysts, at Ouled Haddou, eastern external Rif Chain, Morocco

Planktic foraminifera and organic-walled dinoflagellate cyst investigations in the Ouled Haddou outcrop (eastern external Rif Belt) in northern Morocco, revealed a continuous sedimentation and a complete record of the Cretaceous–Palaeogene (K–Pg) transition. Both planktic foraminifera and dinoflagellate cyst assemblages observed in the studied Maastrichtian–Danian boundary interval are diverse and well-preserved and contain numerous chronostratigraphically significant bio-events that have allowed a high resolution biostratigraphic analysis, based on the first and last occurrences of index species and also on the massive disappearance and abundance changes of different taxa. Planktic foraminifera allow correlation of the studied interval with the uppermost Maastrichtian Abathomphalus mayaroensis Zone and the lower Danian Guembelitria cretacea, Parvularugoglobigerina eugubina, Parasubbotina pseudobulloides and Subbotina triloculinoides zones. A mass extinction of planktic foraminifera is observed at the end of the Abathomphalus mayaroensis Zone. This mass extinction is followed by three renewal steps of planktic foraminifera in the basal Danian. The Cretaceous–Palaeogene boundary is placed just above the mass extinction of Globotruncanids and Heterohelicids and below the first appearences of earliest Danian markers genera Globoconusa, and Parvularugoglobigerina.According to dinoflagellate cysts, the recognition of the latest Maastrichtian and earliest Danian is based on global bio-events, including the first occurrence of the latest Maastrichtian species Disphaerogena carposphaeropsis, Glaphyrocysta perforata, and Manumiella seelandica, the latest Maastrichtian acme of Manumiella seelandica, and the first occurrence of the earliest Danian markers Carpatella cornuta, Damassadinium californicum and Senoniasphaera inornata. The dinoflagellate Damassadinium californicum Zone characterizing the Danian in the Northern Hemisphere is recognized in this section. The Cretaceous–Palaeogene boundary is placed, at the same position determined by Planktic foraminifera, immediately above the acme of Manumiella seelandica and the last appearance of few Cretaceous taxa such as Dinogymnium spp. and Alisogymnium euclaense, and directly below the first occurrences of Carpatella cornuta, Damassadinium californicum and Senoniasphaera inornata. However, in contrast to calcareous planktic foraminifera, dinoflagellate cysts did not undergo a mass extinction at the K–Pg boundary, but shows important changes in the relative abundances of different species or groups of morphologically related species.Both planktic foraminifera and dinoflagellate cyst assemblages suggest deposition in subtropical to warm temperate province, but in an austere sea environments under a regressive regime during the uppermost Maastrichtian and open sea environments under a transgressive regime during the lower Danian. Dinoflagellate cysts indicate relatively stable warm conditions during the upper Maastrichtian, followed successively by cooler conditions in the uppermost Maastrichtian and at the K–Pg boundary, a gradual warming alternated by 3 rapid successive cooling pulses in the lower most Danian, and then a gradual returning to relatively warm conditions.The Ouled Haddou section needs to be preserved as a geoheritage site, because it is the sole Moroccan section with a good quality and an easy access, and hosts a complete registration of the Cretaceous–Palaeogene boundary transition.

Evidence of extensional metamorphism associated to Cretaceous rifting of the North-Maghrebian passive margin: The Tanger-Ketama Unit (External Rif, northern Morocco)

The distribution pattern of diagenetic conditions to very low-grade metamorphism in the eastern Rif has been determined based on a study of clay-mineral assemblages and illite crystallinity of Mesozoic metapelites. Low-grade conditions were reached in marbles and also in the Beni-Malek serpentinites, as suggested by the mineral assemblages present in the marbles and antigorite growth in serpentinites. Previous thermochronological data are based on i) 40Ar/39Ar in amphiboles from greenschists, ii) K/Ar in white micas from metasandstones, and iii) fission tracks in apatites and zircons from metasandstones. These data indicate a Late Cretaceous age (80 Ma) for the very low- to low-grade metamorphism. We propose an evolutionary model for the Tanger-Ketama Unit consisting of a Lower Cretaceous sequence deposited in half-graben basins over an exhumed serpentinized mantle in a setting similar to the West Galician non-volcanic margin. The sediments underwent diagenesis to very low-grade metamorphism under relatively high heat flow in this extensional setting. Miocene contractional deformation of the Tanger-Ketama Unit resulted in a penetrative crenulation cleavage associated to asymmetric inclined folds. This crenulation developed, mostly by solution-transfer processes, without significant mineral growth. Miocene metamorphism reset the apatite fission-tracks, but metamorphic conditions were not high enough to reset either the K/Ar ages or the zircon fission tracks.

Calpionelles et microfaunes pélagiques du Jurassique supérieur – Crétacé inférieur dans les Formations Shal et Kolur (Montagnes du Talesh, chaîne de l’Elbourz, Nord-Ouest Iran). Répartition stratigraphique, espèces nouvelles, révision systématique et comparaisons régionales

Two sections corresponding respectively to the Shal (Callovian – Lower Berriasian) and Kolur Formations (Berriasian – Valanginian in the sampled interval) have been studied in the Talesh Mountains (North-West Iran), an area whose sedimentary successions formed on the northern margin of the Eastern Tethys during the Mesozoic. This study allowed the identification of the different calpionellid zones and sub-zones defined in basin successions of the Western Tethys. In the upper part of Shal Formation the Chitinoidella boneti (base of the Upper Tithonian) and B1 sub-zones (base of the Calpionella alpina zone, lowermost Berriasian) have been recognized. The rich and diverse calpionellid faunas allowed us to recognize in the Kolur Formation B3 (top of the C. alpina zone), C1, C2 (Calpionella elliptica zone), D1, D2, D3 (Calpionellopsis zone) subzones and E (Calpionellites zone) and F (Tintinnopsella zone). The E zone has been subdivided in two sub-zones: E1 and E2, which is characterized by the disappearance of the genus Calpionellopsis. Thirty calpionellid species have been described. Fifteen of them are new: Calpionellites medius nov. sp., Calpionellites minor nov. sp., Remaniella longocadischiana nov. sp., Remaniella minicadischiana nov. sp., Tintinnopsella curva nov. sp., Tintinnopsella duranddelgai nov. sp., Tintinnopsella elmii nov. sp., Tintinnopsella largovalata nov. sp., Tintinnopsella lehegarati nov. sp., Tintinnopsella longovalata nov. sp., Tintinnopsella maxilonga nov. sp., Tintinnopsella minicarpathica nov. sp., Tintinnopsella pseudoblonga nov. sp., Tintinnopsella pseudocarpathica nov. sp. and Tintinnopsella pseudosimplex nov. sp. Amongst the other pelagic microfossil groups, Globochaete and calcispheres (“microproblematics”), often abundant in Western Tethyan Upper Jurassic – Lower Cretaceous pelagic successions, are absent in the Shal Formation and extremely rare in the Kolur Formation despite its lithofacies usually suited for preservation of such microfossils. It is worth noting that in Kolur section the peak of Cadosina fusca in the D1 sub-zone and the occurrence of Stomiosphaera wanneri in the C zone have been observed similarly to successions of Moroccan external Rif. As in most basins of the Western Tethys, Saccocoma remains are frequent in the upper part of the Shal Formation and disappear after the appearance of Chitinoidella in the uppermost Tithonian. Radiolarians with spherical tests are represented by two morphologies:one of common size, called morphology A, occurs at different levels of both Shal and Kolur Formations, while the larger one, called morphology B, occurs in the Upper Tithonian of the Shal Formation and becomes frequent in the Berriasian – Lower Valanginian beds of the Kolur Formation. The first morphology is relatively frequent in coeval successions of Western Tethyan basins, while the second is rarely reported in the literature. Holothurian sclerites are often abundant in the Lower Berriasian – Lower Valanginian interval, whereas they are rare (or scarcely reported in the literature) in coeval successions of the southern margin of the Western Tethys. Chitinoidella, calpionellids, Saccocoma, protoglobigerinid forams, radiolarian of the morphology A are fossil groups that commonly occur in Tethyan basins. On the contrary, Globochaete and calcispheres were seemingly adapted to local ecological conditions, which were probably different from those of the study area. However, preservation bias for these particular microfossils cannot be excluded in the Kolur section, which is locally affected by faulting.

New species of organic-walled dinoflagellate cysts from the Maastrichtian–Danian boundary interval at Ouled Haddou, northern Morocco

Slimani, H., Louwye, S. & Toufiq, A., September 2012. New species of organic-walled dinoflagellate cysts from the Maastrichtian–Danian boundary interval at Ouled Haddou, northern Morocco. Alcheringa 36, 341–358. ISSN 0311-5518. Seven new dinoflagellate cyst species and subspecies, previously figured under open nomenclature, from Maastrichtian and Danian deposits of Ouled Haddou (eastern external Rif Chain) in northern Morocco are formally described, and their stratigraphic ranges are clarified. Conosphaeridium lifum sp. nov. and Kenleyia chabaka sp. nov. have fibrous and reticulate wall surfaces, respectively. Oligosphaeridium saghirum sp. nov. is a small cyst with funnel-shaped distal process extremities. Spiniferella cornuta subsp. kacira subsp. nov. and Fibrocysta brevispinosa sp. nov. are distinguishable by their very short processes. Riculacysta chaouka sp. nov. is characterized by its perforate spinose ectophragm. Andalusiella bacita sp. nov. is a small and spindle-shaped cyst with only a single antapical horn.

Activités volcaniques sous-marines à la limite Jurassique-Crétacé dans le Rif externe (Maroc). Âge et relation avec la sédimentation et la paléogéographie du sillon rifain externe

Following the recent stratigraphic works carried out on the Jurassic-Cretaceous boundary in the external Rif chain (Mesorif area and Bou Haddoud nappe), numerous submarine volcanism traces have been discovered in Upper Oxfordian to Upper Berriasian deposits. These traces display various aspects: volcaniclastic complexes incorporated within Upper Berriasian marls; volcanic lavas and basalt clasts included in the breccias with clay matrix of Upper Oxfordian to Lower Berriasian age, or in brecciated Lower Tothonian calcareous beds of the Early Tithonian. These submarine volcanic activities took place in a carbonate platform environment during the Kimmeridgian to Early Tithonian interval or in a pelagic basin from Late Tithonian onwards. They caused an intense brecciation of Upper Jurassic carbonate formations and a general dismantling of marly calcareous alternations of Upper Tithonian-Lower Berriasian. Therefore, the Upper Tithonian-Lower Berriasian deposits are marked by frequent stratigraphic gaps in many outcrops of Mesorif, Prerif areas and in the Bou Haddoud nappe.

Active surface deformation and sub-lithospheric processes in the western Mediterranean constrained by numerical models

Research Article| September 01, 2010 Active surface deformation and sub-lithospheric processes in the western Mediterranean constrained by numerical models Eugénie Pérouse; Eugénie Pérouse 1Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifique)-Université Montpellier 2, 34095 Montpellier, France Search for other works by this author on: GSW Google Scholar Philippe Vernant; Philippe Vernant 1Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifique)-Université Montpellier 2, 34095 Montpellier, France Search for other works by this author on: GSW Google Scholar Jean Chéry; Jean Chéry 1Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifique)-Université Montpellier 2, 34095 Montpellier, France Search for other works by this author on: GSW Google Scholar Robert Reilinger; Robert Reilinger 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Simon McClusky Simon McClusky 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Eugénie Pérouse 1Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifique)-Université Montpellier 2, 34095 Montpellier, France Philippe Vernant 1Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifique)-Université Montpellier 2, 34095 Montpellier, France Jean Chéry 1Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifique)-Université Montpellier 2, 34095 Montpellier, France Robert Reilinger 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Simon McClusky 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Publisher: Geological Society of America Received: 14 Dec 2009 Revision Received: 20 Apr 2010 Accepted: 27 Apr 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (9): 823–826. https://doi.org/10.1130/G30963.1 Article history Received: 14 Dec 2009 Revision Received: 20 Apr 2010 Accepted: 27 Apr 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Eugénie Pérouse, Philippe Vernant, Jean Chéry, Robert Reilinger, Simon McClusky; Active surface deformation and sub-lithospheric processes in the western Mediterranean constrained by numerical models. Geology 2010;; 38 (9): 823–826. doi: https://doi.org/10.1130/G30963.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We present the results of dynamic modeling of the western Mediterranean that accounts for observed global positioning system (GPS) surface deformation of the Alboran Sea and surrounding Rif and Betic Mountains as the result of the combined effects of relative motion of the Eurasian and Nubian plates, low strength in the Alboran Sea region and sub-lithospheric processes occurring beneath the External Rif domain. Assuming that the lithosphere behaves elastically over the short time period of the GPS observations, an elastic plate model is considered in our study, including an area of weak lithosphere (factor of 10) centered on the Alboran Sea and in which lateral boundary conditions consist of the Nubia-Eurasia oblique convergence. Sub-crustal processes are modeled by application of a horizontal traction on a small area (patch) at the base of the elastic plate. Our modeling studies demonstrate the need for sub-crustal or sub-lithospheric, southwestward-directed forcing to account for observed southwestward motion of the Rif and Betic domains. Based on the location, orientation, and small area of the traction patch, we hypothesize that forcing is associated with delamination and rollback of the subducted African continental lithospheric mantle beneath the External Rif zone, due to the pull of the oceanic part of the Western Mediterranean slab, a dynamic process that may be similar to that where the over-riding plate is driven toward the subduction zone during slab rollback. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Stratigraphy, age and petrography of the Beni Issef successions (External Rif; Morocco): Insights for the evolution of the Maghrebian Chain

In the Beni Issef Massif, nearly 30 km west of Chefchaouen (Morocco), the thickest post-nappe succession within the Rifian sector of the Maghrebian Chain seals the tectonic contact between the Intrarifian External Tanger and Loukkos Units, related to the Rifian External Domain. This succession is very important for the reconstruction of the deformation timing of the Rifian Maghrebids. The age of its base, in fact, is an important constraint for defining an upper boundary to the stacking of both the Intrarifian and Maghrebian Flysch Basin Units, because clasts fed by the Melloussa and Numidian Flysch Nappes are abundant in the conglomerate layers. Field and biostratigraphic analyses pointed out the presence of a Lower Beni Issef Fm, unconformable on the Intrarifian External Tanger and Loukkos Units, and an Upper Beni Issef Fm, unconformable on both the Intrarifian Units and the Lower Beni Issef Fm. The Lower Beni Issef Fm, 150 m thick, consists of lenticular conglomerates with huge blocks in a marly-clayey matrix, followed by marls and minor sandstones. It deposited in a siliciclastic platform, shows a fining upward trend and is affected by metre- to hectometre-sized, locally reversed, folds. Samples collected 45–50 m above the base of the formation resulted not older than Late Tortonian in age, but an older age for the base of the formation cannot be excluded. The Upper Beni Issef Fm, up to 550 m thick, starts with coarse conglomerates followed by medium- to coarse-grained well-bedded sandstones and by grey-blue marls and mudrocks. It indicates deposition in a channelized marine delta, with evolution towards pro-delta pelites, and shows sub-horizontal or gently dipping beds towards the east. Biostratigraphic data indicate a probable Messinian age for this formation. The composition of the arenites of both Lower Beni Issef and Upper Beni Issef Fms is quartzolithic and all samples show a notable content of monocrystalline well-rounded quartz and sedimentary lithic fragments. Detrital modes, all falling in the Quartzose Recycled and Transitional Recycled fields, suggest a provenance from recycling of sedimentary successions, easily recognizable in the Flysch Basin and External Units, mainly the Numidian Nappe sandstones. A Tortonian age of the Lower Beni Issef Fm would agree with the Late Serravallian age of the uppermost beds of the External Tanger Unit and indicate that the most probable age for the stacking of the Intrarifian Units falls in the Late Serravallian-Middle Tortonian time span. The Lower Beni Issef Fm was involved in a compressive tectonic phase testified by north-south striking folds. Later, probably during Messinian, the Upper Beni Issef Fm deposited in a younger intramontane basin, resting on both the Intrarifian Units and the Lower Beni Issef Fm. Successively, the Upper Beni Issef Fm was passively transported piggyback on top of the fold and thrust belt during later tectonic evolution of the Rifian Maghrebids. This tectonic evolution results quite similar to that recognized in the Tellian and Sicilian Maghrebids and also in the southern Apennines.

Tectonic evolution of the Betic–Rif arc: New constraints from 40Ar/ 39Ar dating on white micas in the Temsamane units (External Rif, northern Morocco)

The Betic–Rif orogen, at the western end of the Mediterranean, is a key region to improve our knowledge on the Africa–Eurasia convergence. The Temsamane units, in spite of their external position in the Rif (northern Morocco), underwent medium-pressure low-temperature (MP–LT) conditions (ca. 7–9 kbar; 330–430 °C). We propose a new tectonic and metamorphic evolution scenario for the Rif (southern) branch of the orogen on the basis of first 40Ar/ 39Ar dating on petrologically and structurally characterized white micas. Three groups of 40Ar/ 39Ar ages are observed: (1) Chattian or older Si-rich (highest-pressure) mica relics, (2) 15–12.5 Ma corresponding to the micas defining the foliation and (3) Messinian or younger late micas and alteration. We propose that the MP–LT metamorphic event in the External Rif is Oligocene in age, highlighting a subduction event during this period which could be almost contemporaneous with the burial of HP–LT units from the internal Rif (Alboran Domain). The exhumation of these units characterized by an intense E–W stretching and by top-to-the-west shear senses, is Middle to Late Miocene in age. We propose a correlation of tectonic and metamorphic events at the Betic–Rif arc scale. We argue that the exhumation of the external units of the Rif (1) is younger than that of the Alboran Domain (internal) unit of the Rif, and mirrors a different tectonic setting, but (2) strongly resembles to that documented in the lower Alboran Domain units of the Betics. We show that a regional E–W extension is recorded on both sides of the Betic–Rif arc during the Middle Miocene. This extension probably reflects back-arc deformation of an eastward dipping subduction that retreated westward during the Middle to Late Miocene in the Western Mediterranean.

New paleomagnetic data from Oligocene–upper Miocene sediments in the Rif chain (northern Morocco): Insights on the Neogene tectonic evolution of the Gibraltar arc

In this paper, we present new paleomagnetic data from Tertiary sedimentary sequences of the Rif chain. Paleomagnetic results show that the Rif chain underwent different patterns of vertical axis rotations depending on the tectonic location of the sampled sites. Whereas no paleomagnetic rotations have been measured either in the upper Miocene postnappe basins located along the Mediterranean coast or in the upper Miocene Fes‐Taza foreland basins, upper Miocene thrust top sequences from the external Rif show a significant amount (20° ± 13° in average) of counterclockwise rotations. The spatial distribution of paleomagnetic rotations shows that tectonic rotations, as observed in other arcs of the Mediterranean region, are confined to the orogenic wedge and do not extend to the foreland domain. Paleomagnetic results from this study contribute to better constrain the age of paleomagnetic rotations in the Rif chain, showing that counterclockwise rotations, previously measured only in Mesozoic units, extended into upper Miocene deposits. These results, together with recent published data from the Betics, suggest that the bending of the Gibraltar Arc was not completely achieved by the late Tortonian‐Messinian, enhancing the role of vertical axis rotations in the late Miocene to Recent tectonic evolution of the Gibraltar Arc.

The carbonate series of Upper Jurassic and the transitional levels to Lower Cretaceous in the western part of external Rif Mountains (internal Prerif, Mesorif, Morocco). Stratigraphy, paleogeography and tectonosedimentary evolution

The carbonate series of Upper Jurassic and the transitional levels to Lower Cretaceous in the western part of external Rif Mountains (internal Prerif, Mesorif, Morocco). Stratigraphy, paleogeography and tectonosedimentary evolution

Tectonic and metamorphic evolution of the Temsamane units, External Rif (northern Morocco): implications for the evolution of the Rif and the Betic–Rif arc

Located at an intermediate position in the External Rif nappe pile, the Temsamane units (northern Morocco) are characterized by an abnormally intense metamorphism and a penetrative ductile deformation. We present new metamorphic data showing that, in spite of their external position in the Rif, part of the Temsamane units underwent medium-pressure low-temperature (MP–LT) metamorphism (at c . 7–9 kbar and 330–430 °C), possibly during the Oligocene. Structural data show that the exhumation of these units, during Middle to Late Miocene times, was characterized by an intense approximately east–west stretching and by top-to-the-west shear senses. We tentatively propose two possible origins for the MP–LT Temsamane units: (1) an internal origin related to the subduction and the HP–LT event recorded in the Internal Rif (Alboran Domain), or (2) an external origin, implying a second subduction system within the External Rif, parallel to and almost contemporaneous with that of the Alboran Domain. This tectonometamorphic evolution of the Temsamane units is set within the context of the External Rif evolution. At a larger scale, we show that the exhumation history of the Temsamane units, which strongly resembles that documented in the core of the internal Betics, is compatible with the westward slab retreat occurring during the Middle to Late Miocene in the Betic–Rif region.

Structural evolution of the external zones derived from the Flysch trough and the South Iberian and Maghrebian paleomargins around the Gibraltar arc: a comparative study

AbstractThe Betics and Rif cordillera constitute the northern and southern segments of the Gibraltar arc. Two different fold-and-thrust belts, deriving from the South Iberian and Maghrebian paleomargins respectively, developed in front of this orogenic system. By contrast, the Flysch Trough units and the overlying Alboran crustal domain (internal zones), which are situated in the uppermost part of the orogenic wedge, are common to both branches of the arc. The Flyschs Trough units constitute an inactive accretionary prism, derived from a deep elongated trough. From three large-scale profiles and some lithostratigraphic features of the involved sedimentary sequences, the Betic and Rif external domains are compared, mainly from a structural point of view. Although they are generally considered to show major similarities, the Betic and Rif external domains are in fact strikingly different, mainly concerning the structural style, deformation timing and metamorphism: a) the thick-skinned structure in the External Rif domain vs thin-skinned in the Subbetic domain; b) the pre-Oligocene and Miocene stacking in the External Rif domain vs the exclusively Miocene one in the Subbetic domain, and c) the metamorphism present only in part of the External Rif domain (low-grade greenschists facies). By contrast, it was not possible to establish any difference in structural style and deformation timing between the Flysch units outcropping in both branches of the Gibraltar arc.

Transgressive-regressive facies cycles in late Cretaceous calciturbidites from the Mauretanian Series, Béni Ider thrust sheet, northwestern External Rif, Morocco: application of the ‘facies tract-facies sequence’ concept

Abstract Late Cretaceous mixed carbonate-siliciclastic, thin-bedded turbidites occur between the two great sandstone packages of the Mauretanian Series (the Tisirène and the Béni Ider sandstone flyschs, of early Cretaceous and late Oligocene-early Burdigalian age, respectively). The application of the facies tract-facies sequence model allows subdivision of the studied calciturbidites into five distinct facies sequences (FS.1–5), which equal five transgressive-regressive facies cycles. These cycles mainly consist of thinning upward calciturbidites, which almost all start with coarse-grained carbonate breccias, and passing upward into a shale-dominated interval. Fe-stained discontinuities, together with sedimentological and ichnological evidence, lead us to assign these two lithological components to a transgressive and a regressive trend, respectively. This result provides new insights into the sequence-stratigraphic interpretation of turbiditic successions.

Factorial correspondence analysis: a useful tool in palaeogeographical reconstructions; example from late Cretaceous calciturbidites of the northwestern External Rif (Morocco)

Abstract Factorial correspondence analysis proved to be a useful statistical tool when comparing the clastic input of distinct deposits and searching for their source area. Here we analyse and compare the reworked carbonate clastic material in the late Cretaceous calciturbidites of the Béni Ider area (Rifian External Domain) and the Internal Dorsale Calcaire (Internal Domain). The main result is that the source area for the Béni Ider calciturbidites was a neighbouring, isolated, shallow carbonate platform, the basement of which consists of a Jurassic succession of the Internal Dorsale Calcaire type. However, statistical comparison with the coeval pelagic deposits of to the latter domain leads us to exclude the Dorsale Calcaire as a possible origin of these Béni Ider calciturbidites. The source area was probably a lost carbonate platform, which should be located in the open External Domain. This result appears to be consistent with the Tariquide Ridge hypothesis and gives new insights into the palaeogeographical scheme of the flysch trough.

Comment on “The ultimate arc: Differential displacements, oroclinal bending, and vertical axis rotation in the External Betic‐Rif arc” by J. P. Platt et al.

[1] Platt et al. [2003a] have made a major contribution to our knowledge of the Gibraltar arc by documenting the kinematics of the Betic-Rif External zones through structural and palaeomagnetic measurements. They suggest that the ‘‘External Betic-Rif arc’’ is a thin-skinned fold-andthrust belt formed in Miocene time as a result of two causes, i.e., first, the westward component of motion of the ‘‘indenting Alboran Domain’’ (Betic-Rif Internal zones) relative to the convergent Iberian and African plates; and second, the extensional collapse of the Alboran Domain. [2] The concept of an ‘‘indenting Alboran Domain’’ goes back to the work of Andrieux et al. [1971], who referred to an ‘‘Alboran microplate.’’ We argue hereafter that the ‘‘Alboran Domain’’ did not act as an indenter, and that both its collapse and the external Betic and Rif fold belts are consequences of a slab retreat process. We also emphasize that defining the Betic and Rif external fold-and-thrust belts as a single, thin-skinned arc is misleading. [3] The crucial role of the late orogenic collapse in the building of the Betic-Rif chain goes back to the work of Platt and Vissers [1989], who assumed that it was an intracontinental collisional orogen, formed at the expense of the neighboring Iberian and African margins, without any oceanic domain nor exotic terrane in between. However, relics of lost oceans do occur (1) along the African margin, i.e., the Beni Malek serpentinites and basalts at the very edge of the margin [Michard et al., 1992] and the spilites and radiolarites at the bottom of the exotic Flyschs [Durand-Delga et al., 2000], which altogether document a former Maghrebian ocean, and (2) on top of the NevadoFilabrides units of central eastern Betics, i.e., the metaserpentinites and metabasalts of the Mulhacen complex, which document a former Betic ocean [Puga et al., 1999, 2002a, 2002b]. The occurrence of former oceanic domains makes necessary to consider subduction processes there. Some authors even assume that two subduction zones operated, first the SE dipping Alpine-Betic subduction, then the NW dipping Apenninic-Maghrebian subduction [Rehault et al., 1984; Torres-Roldan et al., 1986; Andrieux et al., 1989; Guerrera et al., 1993; Doglioni et al., 1998, 1999; Frizon de Lamotte et al., 2000; Chalouan et al., 2001; Michard et al., 2002; Chalouan and Michard, 2004]. Consistently, east dipping active subduction beneath the Gibraltar arc is currently evidenced [Morales et al., 1999; Gutscher et al., 2002]. [4] Platt et al. [2003a] accept the concept of an easterly, allochthonous ‘‘Alboran Domain.’’ In fact, the latter includes two different tectonic systems, the Nevado-Filabrides (NF) at the bottom, and the ‘‘Alboran Terrane’’ on top, which in turn consists of the metamorphic Alpujarrides-Sebtides (AS) overlain by the Malaguide-Ghomarides and Dorsale Calcaire units [Chalouan et al., 2001; Michard et al., 2002, and references therein]. The NF consists of the HT-LP Veleta schists overlain by the HP-LT Mulhacen Complex, which has the characters of a subduction tectonic complex [Puga et al., 1999, 2002a, 2002b]. Only the Alboran Terrane does represent an exotic domain of easterly origin [Bouillin et al., 1986; Michard et al., 1991, 2002]. As the Alboran Terrane formed at the onset of Neogene times an orogenic prism made of young, ductile metamorphic units, it can hardly be regarded as an ‘‘indenter,’’ which would be the initial cause of the ‘‘External Arc’’ building. We rather suggest considering that the Alboran Terrane operated as a backstop related to the subduction of the Maghrebian Tethys (see section 6). [5] Platt et al. [2003a] argue that ‘‘the present dramatic geometry of the arc is a result of extensional collapse of the Alboran Domain during the Miocene.’’ They agree that the subduction rollback hypothesis [Frizon de Lamotte et al., 1991; Lonergan and White, 1997] could be ‘‘reasonably’’ proposed, but prefer the collapse mechanism that they also consider as the cause of the opening of the Algerian basin TECTONICS, VOL. 24, TC1005, doi:10.1029/2003TC001603, 2005