Chellai El Hassane

espanolEn el Alto Atlas de Marrakech (Marruecos), la sucesion de depositos triasicos proporciona un analogo de afloramiento para los sistemas continentales con influencia marina en el seno de una cuenca de rift abortado, y permite el estudio de las facies y del control de la tectonica y el clima sobre los depositos. Este estudio se focaliza en el analisis de la formacion de areniscas de Tighadwine, que son el equivalente de las areniscas de Oukaimeden (F5) en el conjunto de los Altos Plateaux de la vertiente norte del Alto Atlas de Marrakech. Se trata de una formacion dominada por depositos fluviales con influencia de mareas. El analisis sedimentologico permite la descripcion e interpretacion detallada de las facies. La formacion de areniscas de Oukaimeden se compone de cuerpos arenosos canalizados alternando con depositos limo arcillosos lenticulares formando barras de areniscas fluviales y de facies de desbordamiento. En alternancia con las facies fluviales, se observan tambien ar...

An expanded succession of organic-rich marlstones and limestones deposited in the Tarfaya Basin provides an outstanding opportunity to closely retrace climate evolution and sea-level changes during the Cretaceous greenhouse period. We present high-resolution X-ray fluorescence (XRF) scanning and bulk carbon- and oxygen-isotope records from two newly drilled sediment cores in the Tarfaya Atlantic coastal basin, which recovered a continuous Upper Turonian to Campanian succession of ∼290 m thickness. The XRF core scanning records reveal three long-term oscillations in the abundance of terrigenous elements (increase of Al, Ti, K, Si, and Fe normalized against Ca), which correspond to progressive transgressive phases followed by rapid regressions during the Coniacian and early Santonian. Sea-level highstands during this interval corresponding to the Coniacian−Santonian oceanic anoxic event 3 (OAE 3) are characterized by overall oxygen-depleted to anoxic conditions at the seafloor (indicated by the high organic carbon content, the presence of laminations, and low log[Mn/S], high log[V/Ca], and high log[Br/Ca]). The upper Santonian interval marks the transition from anoxic to oxic bottom-water conditions, prevalent through the early Campanian. The composite bulk carbonate δ 13 C curve exhibits strong similarities to the global stacked δ 13 C reference curve, characterized by negative excursions in the early Coniacian (Navigation and East Cliff events) and late Santonian (bracketed by the Haven Brow and Buckle events) and by positive excursions in the latest Turonian (Hitchwood event), middle Coniacian (Wight Fall event), and at the Santonian-Campanian boundary. During the early Campanian, enhanced accumulation of fine-grained carbonate and clay-rich hemipelagic sediments, increasing bulk carbonate δ 18 O, and low log(Br/Ca) and log(V/Ca) values indicate climate cooling, associated with a substantial improvement in bottom-water ventilation. Two long-term δ 13 C cycles of ∼2 m.y. duration, probably related to variations in Earth’s orbital eccentricity, are associated with the long-term cooling trend initiating the Campanian−Maastrichtian climate transition toward a cool greenhouse state.

Lithological evidence, benthic foraminiferal census counts, and X-ray fluorescence (XRF) scanner-derived elemental data were integrated with planktonic foraminiferal biostratigraphy and bulk carbonate stable isotopes to retrace the Turonian to early Campanian paleoenvironmental evolution and sea-level history of the Tarfaya Atlantic coastal basin (SW Morocco). The lower Turonian is characterized by laminated organic-rich deposits, which contain impoverished benthic foraminiferal assemblages, reflecting impingement of the oxygen minimum zone on the shelf during a sea-level highstand. This highstand level is correlated to the global transgressive pulse above the sequence boundary Tu1. The appearance of low-oxygen tolerant benthic foraminiferal assemblages dominated by Gavelinella sp. in the middle to upper Turonian indicates an improvement in bottom water oxygenation, probably linked to offshore retraction of the oxygen minimum zone during a regressive phase. This interval is marked by major regressive events expressed by a series of erosional truncations associated with the prominent sequence boundaries Tu3 and/or Tu4. Dysoxic–anoxic conditions recorded in the upper Santonian of the Tarfaya Basin coincide with the eustatic sea-level rise prior to Sa3 sequence boundary. The lower Campanian transgression, only recorded in the southern part of the Tarfaya Basin, coincided with substantial deepening, enhanced accumulation of fine-grained clay-rich hemipelagic sediments and improved oxygenation at the seafloor (highest diversity and abundance of benthic foraminiferal assemblages). Stable isotope data from bulk carbonates are tentatively correlated to the English Chalk carbon isotope reference curve, in particular the Hitch Wood Event in the upper Turonian, the Navigation Event in the lower Coniacian, the Horseshoe Bay Event in the Santonian and the Santonian/Campanian Boundary Event.

The survey of sedimentological and lithostratigraphic Liassic facies of the Todrha–Dades area (southwestern part of the central High Atlas) permits to establish new data on the Tagoudite formation. Its environment deposit and its micropalaeontological content are evidenced in relation with the geodynamic evolution of the High Atlas Basin during the Early Toarcian. To cite this article: M. Ettaki, E.H. Chellaï,

This work reports for the first time evidence for an Ediacaran glaciation in Morocco on the West African Craton that we have named the Bou-Azzer glaciation. It is represented by glacially eroded surfaces and sedimentary features observed in Precambrian outcrops in two inliers of the Anti-Atlas Belt. The commonly accepted stratigraphic framework constrains the glacially eroded surfaces to post-date a regionally defined D2 deformational age known to be between 605 and 595Ma. A minimum age for the glaciation is less certain but likely ...

Seismic data analysis of the Qasbat-Tadla Basin allows the deciphering of the main tectonic and sedimentary events that characterised the Hercynian orogen and its role in the basin's structural development. The global tectono-sedimentary framework involves structural evolution of an orogenic foreland basin and was the source of rising geotherms in an epizonal metamorphic environment. The complementary effects of these parameters

Résumé. Située à la jonction entre la plaine de la Haute-Moulouya et le Haut-Atlas central, la région de Midelt a connu au cours du Jurassique une évolution géodynamique conditionnée par la dislocation de la plate-forme carbonatée liasique. Cet événement, ...

Late Precambrian stratas in the Anti-Atlas Mountains (Morocco) show a succession of poorly-known conglomerates into the Tiddiline Formation (Fm), the uppermost part of the so-called" PIII Formation", and base of Adoudounian Formation. This study proposes to differentiate the conglomerates according to their sedimentation processes and the nature of their pebbles. Preliminary results show that the top of Tiddiline Fm and the base of the Adoudounian Fm are fluvial-origin deposits with channelised, very-coarse conglomerate ...

An expanded succession of organic-rich marlstones and limestones deposited in the Tarfaya Basin provides an outstanding opportunity to closely retrace climate evolution and sea-level changes during the Cretaceous greenhouse period. We present high-resolution X-ray fluorescence (XRF) scanning and bulk carbon-and oxygen-isotope records from two newly drilled sediment cores in the Tarfaya Atlantic coastal basin, which recovered a continuous Upper Turonian to Campanian succession of ~290 m thickness. The XRF core scanning records reveal three long-term oscillations in the abundance of terrigenous elements (increase of Al, Ti, K, Si, and Fe normalized against Ca), which correspond to progressive transgressive phases followed by rapid regressions during the Coniacian and early Santonian. Sea-level highstands during this interval corresponding to the Coniacian–Santonian oceanic an-oxic event 3 (OAE 3) are characterized by overall oxygen-depleted to anoxic conditions at the seafloor (indicated by the high organic carbon content, the presence of laminations, and low log[Mn/S], high log[V/Ca], and high log[Br/Ca]). The upper Santonian interval marks the transition from anoxic to oxic bottom-water conditions, prevalent through the early Campanian. The composite bulk carbonate δ 13 C curve exhibits strong similarities to the global stacked δ 13 C reference curve, characterized by negative excursions in the early Coniacian (Navigation and East Cliff events) and late Santonian (bracketed by the Haven Brow and Buckle events) and by positive excursions in the latest Turonian (Hitchwood event), middle Coniacian (Wight Fall event), and at the Santonian-Cam panian boundary. During the early Campanian, enhanced accumulation of fine-grained car-bonate and clay-rich hemipelagic sediments, increasing bulk carbonate δ 18 O, and low log(Br/Ca) and log(V/Ca) values indicate climate cooling, associated with a substantial improvement in bottom-water ventilation.

Résumé: La série sédimentaire de Sidi Chennane est caractérisée par une sédimentation rythmique en séquences élémentaires et de dépôt qui ressemble dans ses grands traits à celle du reste du gisement des Oulad Abdoun. En revanche elle se distingue par la présence la plus prononcée de perturbations locales désignées par l’exploitant sous le vocale « dérangement ». Ces dérangements posent un problème inquiétant au cours de l’exploitation et demeurent un obstacle réel dans les chantiers de défruitage du phosphate. Cette étude se propose pour emparer de près cette problématique dans son aspect géologique, afin de les caractériser et de saisir leur origine. Ces « dérangements » se présentent avec une morphologie subcirculaire à subconique de dolines et une structure chaotique de matériaux anarchiques d’un dénivelé vertical de plis d’une dizaine de mètres. Ce sont des paléokarsts de type fontis. Ils sont constitués par mélange de matériel bréchique très altéré de couleur jaunâtre rouille ...

ABSTRACT The objective of the present work is to study the formation of the passive continental margins of the Central Segment of the South Atlantic, most particularly the Congo and Angola margins. We propose a combined approach, which integrates structural constraints based on geological cross-sections (based on seismic data) and global constraints based on plate kinematic reconstructions. The structural study is based on : i) MCS and refraction data collected during the ZaiAngo programme (a joint project conducted by Ifremer and Total) ; ii) proprietary, industrial seismic data (courtesy of Total) from the Angola margin and iii) on all available seismic lines from the Africa and Brazil conjugated margins, between Walvis Ridge and the Equatorial Fracture Zones. Based on theses data, three structural domains (continental, transitional and oceanic) have been defined, the major characteristics of which are : Crustal thinning occurs abruptly, mostly below the continental slope, over a lateral distance of less than 50 km. The top of the crust deepens as the Moho shallows. Only a few extensional structures are observed ; tilted blocks are very few (one or two, depending on the profile), found only on the upper part of the slope and sealed by a discordance prior to salt deposition. The transitional domain is characterized by the existence of a pre-salt basin lying over a thin crustal layer. No tilted blocks are observed in this domain and reflectors within the pre-salt sediment series are parallel to the base of the Aptian salt, over distances greater than 100 km, precluding the possibility of any significant deformation that would imply large horizontal motions. Two types of crust are observed in the transitional domain. "Type I" crust is found below the undeformed pre-salt sediment series located below the eastern part of the basin ; it is characterized by an upper layer of thickness greater than 5 km and a abnormal velocity layer (7.2 - 7.6 km/s), up to 6 km thick. "Type II" crust is less than 5 km thick and found below the salt compressive front that affects the western part of the basin. The salt cover is continuous (no erosion surface is observed), from the continental shelf to the western termination of the basin. Salt was not deposited in a confined environment (like in the Mediterranean), but in a shallow water, lagunal environment. This imposes the zero-level and constrains the paleo-bathymetry at the time of salt deposition, which dates the latest stage of margin formation. Understanding the formation of a margin cannot be approached without studying the homolog margin. Therefore, it is of major importance to reconstruct the closure of the ocean bordered by these homolog margins and take into account the constraints imposed by the kinematic reconstructions on the lateral motions of the lithospheric plates. In order to assess the relative position of the plates at the ocean closure (prior to crustal thinning), a global study was thus performed, integrating all geophysical and geological constraints, in the ocean and on land. The role of african intra-plate deformation and its limits and their consequences have been thoroughly studied. To juxtapose the margins of the central segment of the Southern Atlantic, it is all the margins bordering the Equatorial Atlantic that need to be adjuste precisely. The kinematic study of this last region shows that the reconstruction obtained are reliable, unambiguous with a quantifiable precision The best fitting poles (obtained using the PLACA software), show that it is impossible to close the margins beyond the superposition of the salt fronts, from the Angola and Brazil margins. The geological cross-sections based on seismic data from the homolog margins indicate that a 330 km wide basin with thin (< 12 km) crust was present at the time of the fit. This basin cannot result from horizontal movement related to pure stretching or simple shear, or any model implying conservative volume. This conclusion is consistent with the existence of presalt reflectors parallel to the salt layer wich extends to the platform: the formation of the pre-salt basin must be related to vertical motions. The scenario that we propose for the evolution of the Congo-Angola margin consist in four stages: the first phase corresponds to extensional deformation limited to the few tilted blocks observed on the upper part of the slope. During the second phase, the main crustal thinning occurs, vertical motions prevailes, resulting in the formation of the continental slope and in the subsidence of the basin. The third phase corresponds to the first stress striction: deformation is concentrated in a limited section of the basin, which corresponds to the salt compression front. A proto-oceanic crust is formed, probably composed of thinned continental crust intruded by mantle material. The second stress striction corresponds to the finale phase, resulting in oceanisation senso…

Abstract: Dans les recifs d'age Jurassique superieur de l'Atlas maghrebin, les cavites inter-et intrasquelettiques ont ete en grande partie colmatees par des microbialites (Stromatolites, Thrombolites), en association avec des &unknown; micro-encroutants &unknown;( ...

Dans le Haut-Atlas de Marrakech (Maroc), la succession des dépôts triasiques fournit un analogue d’affleurement pour les systèmes continentaux à influence marine au sein d’un bassin de rift avorté ; et permettent l’étude des faciès et le contrôle de la tectonique et du climat sur les dépôts. Cette étude se focalise sur l’analyse de la formation de grès de Tighadwine qui sont l’équivalent des grès de l’Oukaimeden (F5) sur l’ensemble des Hauts-Plateaux du versant nord du Haut-Atlas de Marrakech. Elle montre une formation dominée par des dépôts fluviatiles à influence de marées. L’analyse sédimentologique permet la description et l’interprétation des faciès détaillé.
La formation de grès de l’Oukaimeden est composée de corps gréseux chenalisés alternant avec des dépôts silteux argileux lenticulaires formant des barres de grès fluviatiles et de faciès de débordement. En alternance avec les faciès fluviatiles, des grès éoliens et des dépôts de cônes alluviaux, des dépôts à influence de marées sont également observés.
Cette formation comprend trois membres : Le membre inférieur déposé dans un système fluviatile éphémère. Le membre médian enregistre un changement des conditions fluviatiles en tresses vers des conditions plus humides. Le membre supérieur est caractérisé par le retour à des conditions éphémères combinées avec l’apparition de dunes éoliennes. Ce dernier montre l’enregistrement d’une aridité croissante. La partie supérieure du présent membre montre une influence de la marée, suite à une incursion marine dans le bassin. Ceci se confirme et persiste lors de la mise en place de la formation marine de faible profondeur F6. L’ensemble de la série triasique est coiffé par un événement volcanique attribué à la CAMP (Central Atlantic Magmatic Province). Quelques mesures pétrophysqiues sur les grès de l’Oukaimeden en relation avec le caractère réservoir de ces formations seront présentées ainsi que les ichnofaciès.