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Cenozoic tectono-sedimentary evolution of the external rif chain (Morocco)derived from 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.
Ternary diagram of SiO2-5*Al2O3-2*CaO of the studied mudrocks. UCC (Upper Continental Crust; McLennan et al., 2006) and PAAS (Post- Archaean Australian Shales; Taylor and McLennan, 1985).
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.
cite as: Perri, F., Cavalcante, F., Martín-Martín, M., Sánchez-Navas, A., Alcalá, F.J., 2024. Cenozoic tectono-sedimentary evolution of the external rif chain (Morocco) derived from mineralogical and geochemical analysis of mudrocks. Mar. Pet. Geol. 170, 107124. doi: 10.1016/j.marpetgeo.2024.107124
Cenozoic detrital suites from the Internal Betic-Rif Cordilleras (S Spain and N Morocco): implications for paleogeography and paleotectonics
A synthesis of Cenozoic detrital suites from the Internal Betic-Rif Cordilleras is discussed in relations with major paleotectonic phases during growth of orogenic belts. The discussion has been focused on the Malaguide and Ghomaride complexes that have a Cenozoic sedimentary detritic cover. The heterogeneous petrographic composition of coarse detrital rocks, and the mineralogy and geochemistry of mudrocks indicate a multiple source area consisting in metamorphic, and recycled siliciclastic and carbonate source rocks, with a minor supply of mafic rocks during the early Miocene. The siliciclastic coarse detrital suites plot mainly in a wide area at the Qm-Lt side in a Qm-F-Lt diagram reflecting their transition between a craton, quartzose recycled, quartzose transitional orogenic, and finally lithic transitional orogenic provenance type. The Paleocene-Eocene successions seem to be affected by higher weathering effects than the Oligo-Miocene ones. Significant recycling and reworking processes should take place during the Paleocene-Eocene and the Oligo-Miocene before the final deposition. The source areas were characterized by non-steady-state weathering conditions reflecting a progressive cooling contemporaneous to the typical evolution of source areas where active tectonism allows erosion within weathering profiles developed on source rocks. A sharp increase of siliciclastic content together with the changes in sorting-recycling-weathering suggests abrupt changes in the source area starting from Oligocene. This fact allows subdividing the succession into the lower (Paleocene-Eocene) and the upper (Oligocene-Early Miocene) cycles. Lower cycle was contemporaneous to the Eo-Alpine tectonic phase, which was reflected in the Malaguide and Ghomaride domains by basement folding and deep tectonics with fault-propagation folds, accomplished by minor rising or reliefs and deepening of subsidence areas. Contrarily, the upper cycle took place during the Neo-Alpine phase, when in the Malaguide and Ghomaride domains, thrustings should become superficial contemporaneous to subduction and stacking of tectonic units.
This led to a strong increasing of rising areas reflected in the sedimentation by the occurrence of coarse terrigenous deposits in wedge-top basins. The early Miocene also shows the influence of volcanism in the Mediterranean region, and/or the erosion of magmatic-metamorphic rocks derived from deep tectonic levels affected in the Eo-Alpine phase or belonging to the Hercynian bedrock. This evolution fits well with recent paleogeographic-geodynamic models for the western-central Mediterranean.
Cite as: Martín-Martín, M., Perri, F., Critelli, S., 2023. Cenozoic detrital suites from the Internal Betic-Rif Cordilleras (S Spain and N Morocco): implications for paleogeography and paleotectonics. Earth-Science Rev. 243, 104498. https://doi.org/10.1016/j.earscirev.2023.104498
The Eocene carbonate platforms of the Ghomaride Domain (Internal Rif Zone, N Morocco): a segment of the westernmost Tethys
The Eocene platform deposits in the Moroccan Ghomarides have been studied. These marine carbonate platforms were located in the westernmost Tethys approximately 30°N and 0°–10°W during the Cuisian to Bartonian. The study includes observations from fossiliferous assemblages (such as larger benthic foraminifera and colonial corals), their palaeoenvironment aswell as rock texture and fabric. Eight microfacieswere identified that represent different ramp environments in a ‘distally-steepened carbonate ramp’ type of platform. The studied deposits are organised into a transgressive succession composed of three sedimentary cycles: lower Cuisian, middle Cuisian and middle Lutetian to Bartonian. In the lower cycle, photic inner to mid ramp environments in mesotrophic conditions were prevalent. In the second cycle, photic inner ramp (sea-grass) to mid ramp environments inmesotrophic to oligotrophic conditions were observed. The upper cycle, which is more extensive and variable, represents mesophotic mid ramp to aphotic slope environments and changes gradually from oligotrophic to eutrophic conditions. During the Eocene, larger benthic foraminifera were dominant overtaking the zooxanthellate corals in the Tethys regions. Nevertheless, our study and the performed comparison with other Tethyan sectors have revealed that in some areas both coexisted in similar proportions. In some western Tethys regions close to the Atlantic Ocean, coinciding with areas influenced by upwelling currents, larger benthic foraminifera and coral build-ups were replaced by oyster reefs. The Ghomaride Domain represents an intermediate case between fossil assemblages of the northern Tethyan margin and eastern sector of the southern margin of the Tethys, with a dominance of larger benthic foraminifera but with a certain presence of corals as well. A good correlation exists between Eocene warm intervals and carbonate platform deposits in these domains. Contrarily, during cooling ones shallowing and gaps in the sedimentation are registered.
Two anomalies have been detected in the Ghomaride Domain during Ypresian and Bartonian times indicating particular climatic conditions or local tectonic interferences.
Cite as: Martín-Martín, M., Tosquella, J., Guerrera, F., Maaté, A., Hlila, R., Maaté, S., Tramontana, M., Le Breton, E., 2023. The Eocene carbonate platforms of the Ghomaride Domain (Internal Rif Zone, N Morocco): a segment of the westernmost Tethys. Sediment. Geol. 452, 106423. https://doi.org/10.1016/j.sedgeo.2023.106423
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 claymineral 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 claymineralogy 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 inheritedmineralogy during some periods with weak burial diagenesis at most.
During the Paleogene a foreland basin is formed mainly in theMesorif 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.
Cite as: Martín-Martín, M., Guerrera F., Cañaveras, J. C., Alcalá F. J., Serrano, F., Maaté, A., Hlila, R., Maaté, S., Tramontana, M., Sánchez-Navas, A., and Le Breton, E. (2023). Paleogene evolution of the External Rif Zone (Morocco) and comparison with other western Tethyan margins. Sedimentary Geology, 448, 106367. doi: 10.1016/j.sedgeo.2023.106367
Provenance and paleogeographic implications for the Cenozoic sedimentary cover of the Ghomaride Complex (Internal Rif Belt), Morocco
The Cenozoic sedimentary cover from the Ghomaride Complex (Internal Rif Belt) has been studied in the Tetuan area (N Morocco) where a suite of sedimentary successions from shallow-marine to deep-marine environments crops out. For that purpose stratigraphic relations and petrological and geochemical signatures have been analyzed. Sandstone suites of the overall succession are heterogeneous and testify a multi-source area, in response of accretionary processes of the Ghomaride-Malaguide units and the exhumation of the lower units of the Internal Rif Zone (e.g. Sebtide-Alpujarride Complex). Pre-orogenic and Syn-orogenic (according to the eoalpine phase) deposits have been identified consisting in two depositional sequences: lower Paleocene and Cuisian-Bartonian, and upper Oligocene-upper Aquitanian and lower Burdigalian, respectively. Pre-orogenic deposits are mainly intra-arenite and hybrid arenites made of a minor amount of siliciclastic detritus but with abundance of intrabasinal carbonate grains. The syn-orogenic sandstone suites are quartzolithic, having abundance of low-grade metamorphic and sedimentary lithic fragments. Sedimentary lithic fragments are derived from the Mesozoic successions of the Ghomaride-Malaguide Complex while metamorphic detritus is related to an unknow Internal Rif Zone basement that was exhumed starting from the late Oligocene and mainly early Miocene. Modal analyses of sandstone suites for the extrabasinal grains mainly indicate lower rank metamorphic and sedimentary source terranes of a recycled orogen. Major and trace elements coupled to the mineralogical composition of the mudrock samples indicate a provenance from felsic source area(s) with a minor but not negligible contribution from mafic rocks mainly in the syn-orogenic suites.
Geochemical analyses (Al–Ti–Zr ternary plot) indicate minor reworking and recycling processes before the final deposition through prolonged processes of sedimentary transportation. The trends evident in both CIA and CIA’ diagrams indicate source areas characterized by moderate weathering in non-steady-state conditions with a weak change of weathering condition from the pre-orogenic to the syn-orogenic cycle. Deposition during the Paleocene and Eocene, took place in the southern continental margin of the Ghomaride-Malaguide domain as a carbonate ramp. Contrarily, sedimentation in the late Oligocene-late Aquitanian took place in wedge-top basins within the Ghomaride- Malaguide domain. These changes occurred during the Burdigalian, when back arc basins were developed in the Internal Betic-Rif Zone. The Cenozoic reconstructed record was contemporaneous of the structuring of the Circum-Mediterranean chains and the Ghomaride-Malaguide Complex played a key role in the geodynamic evolution of the Rif Cordillera, representing a key tectonic element of the western Mesomediterranean domains.
The Cenozoic evolution of the Intrarif (Rif, Morocco)
The sedimentary-tectonic evolution of the Cenozoic strata of the El Habt and Ouezzane Tectonic Units (Intrarif, External Rif) in Morocco is presented by a new work by Martín-Martin et al., (2022) in Geosphere.
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., Burdigalian p.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.
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 stablish the Cenozoic tectono-sedimentary evolution of the El Habt and Ouezzane Tectonic Units (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 bio-chronologically defined allowing, at the same time, identification of unconformities and associated stratigraphic gaps.
The presence of five unconformities allowed to define 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 to identify supplies derived from erosion of a recycled orogen (transitional and quartzose sub-types).
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 seems to indicate the beginning of deformation of the basement generating gentle folds and first activation of blind thrusts, mainly during the Paleogene. A pre-orogenic tectonic framework is considered as risponse to 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 beginnigs of the syn-orogenic sedimentation (foredeep stage of the basins) controlled by active tectonics.
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