The Westernmost Tethys Blog Geology mapping, basin analysis and 3D modeling

09/27/2023

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.

A synthetic column of the Eocene Ghomaride succession, highlighting the correlation with transgressive–regressive depositional trends, terrigenous-nutrient inputs, sedimentary environments, photic and trophic conditions and main biotic assemblages.

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

06/12/2023

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

Filed under: foreland basin,Morocco,PID2020-114381GB-I00,Rif,westernmost Tethys — Tags: , — messinianalicante @ 4:54 PM

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.

Paleogene stratigraphic framework of the western External Rif Zone, showing stratigraphic units, unconformities, and depositional vs. erosional gaps.

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

 

The Numidian formation in the Central-Western Mediterranean

Filed under: PID2020-114381GB-I00,westernmost Tethys — Tags: , , — messinianalicante @ 8:22 AM

The widely debated late Oligocene-middle Miocene Numidian Fm (NF) consists of supermature quartzose sediments deposited in the Maghrebian Flysch Basin (MFB) outcropping from the Betic Cordillera to the Southern Apennine passing by the Maghrebian Chain. The NF is commonly composed of three lithostratigraphic members and is characterized by two vertical successions (Type A and Type B) corresponding to different sedimentation areas in the MFB. It is noteworthy the occurrence of widespread lateral successions of the NF (Types C, D and E) indicating in some cases an interference of the Numidian sedimentation with other different depositional systems and supplies. The Type C ‘Mixed Successions’, deposited in depocentre areas, are composed of supermature Numidian supply interfingering with immature siliciclastic materials, coming from the internal portion of the MFB. The Type D consists of supermature Numidian materials supplied from the Africa Margin (external sub-domains) deposited in sub-basins on the Africa-Adria margins, outside the typical Numidian depositional area. The Type E, which stratigraphically overlies both the South Iberian Margin (SIM) and the Mesomediterranean Microplate (MM), represents the migration of the Numidian depositional system to reach the opposite margins of the MFB. The occurrence at a regional scale of all the above-mentioned lateral successions reveals a great evolutionary complexity resulting also from further constraints, which must be considered for palaeogeographic and palaeotectonic reconstructions. Another important point deals with the diachronism of the top of the NF, observed eastward from the Betic-Rifian Arc and the Algerian-Tunisian Tell (Burdigalian p.p.) to Sicily (Langhian p.p.) and up to the Southern Apennine (at least Langhian/Serravallian boundary) which can be related with eastwards delay in the MFB closure.

Tectono-stratigraphic charts concerning the Type A to Type E of the Numidian Formation depicting the lateral and vertical variability of the lithofacies, significant stratigraphic markers, surfaces and gaps of the stratigraphic record. The tectonic propagation along the chain is also represented.

The palaeogeographic reconstruction of the Numidian depositional area presented in this paper,which is also included into a global kinematic model, represents a first attempt to use the software GPlates for this subject.

Cite as: Belayouni, H., Guerrera, F., Martin-Martin, M., Le Breton, E., and Tramontana, M. (2003). The Numidian formation and its Lateral Successions (Central-Western Mediterranean): a review. International Geology Review, DOI: 10.1080/00206814.2023.2199429

06/09/2023

Eocene carbonate platform of the Malaguides of the westermost Tethys

 The Eocene Peñicas (Almería) and Harania (Málaga) stratigraphic sections from the Malaguide Complex (Betic Cordillera, South Spain) belonging to the Mesomediterranean Microplate from the westernmost Tethys (about  35◦N) have been studied. The Eocene sections cover the Cuisian to middle Lutetian deposits, which show several lithofacies representing shallow marine platform realms. Based on the fossiliferous assemblage, texture and fabrics, eight microfacies related to inner to outer ramp settings were defined. In the inner ramp of the Harania section abundant colonial corals have been recognized. The Eocene deposits are arranged into a transgressive succession composed by three minor transgressive-regressive sedimentary cycles. The Eocene fossiliferous assemblage shows a mixture of photozoan (Larger Bentic Foraminifera, green and red calcareous algae and corals) and heterotrophic (mollusks, echinoids, bryozoans, small benthic and planktic foraminifers) elements, suggesting euphotic to mesophotic conditions in oligo-mesotrophic marine warm-waters at low-middle latitudes. This assemblage indicates a transition from photozoan to heterozoan carbonates and in particular a shift towards outer marine ramp settings.

Paleogeographic and paleoenvironmental 3D-sketch model of the Central-Western Malaguides with location of facies and microfacies during the Eocene.

During the Early Eocene, the widespread distribution of Larger Benthic Foraminifera leads in the Tethyan domains to disappearance or extreme reduction of coral constructions. Nevertheless, abundant corals associated to inner ramp realms have been observed in the Harania stratigraphic section indicating that corals could continue to develop in the westernmost Tethys at the transition to the Atlantic Ocean, in contrast with respect to other Tethyan sectors. Therefore, the Ypresian-Lutetian time-span is a transitional period for the global temperature during which corals locally survived only where optimal ecologic conditions occurred, preferably in marginal contexts, as it seems to have happened in the studied area. 

Cite as: Tosquella, J., Martín-Martín, M., Guerrera, F., Serrano, F., Tramontana, M., 2022. The Eocene carbonate platform of the central-western Malaguides (Internal Betic Zone, S Spain) and its meaning for the Cenozoic paleogeography of the westermost Tethys. Palaeogeogr. Palaeoclimatol. Palaeoecol. 589, 110840. doi: 10.1016/j.palaeo.2022.110840

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