Search

A stratigraphic study and mapping allow defining the particular features of this area of the southwestern Middle Atlas (Morocco) during the Toarcian and the Aalenian. Numerous spectacular variations in thickness and facies are documented by the discovery of coralline build-ups dated to the Late Toarcian. They occur along the palaeostructures. Development of the structures occurred in several stages: (1) initial differentiation during the Early and Middle Toarcian; (2) homogenisation during the Late Toarcian, after the construction of the reefs. The Aalenian history is similar: differentiation (Early Aalenian)–homogenisation (Middle to Late Aalenian). Two palaeostructural trends are evident: SW–NE and transverse SSW–NNE to south–north. These caused separation of several subbasins, which alternatively deepened and shallowed, probably due to the tilting of several blocks to the southwest. To cite this article: F. El Hammichi et al., C. R. Geoscience 334 (2002) 1003–1010.

Resume Les formations cenzoiques de comblement des bassins d'avant-chaine et des bassins intramontagneux atlasiques sont subdivisees, sur la base de coupures majeures, en trois ensembles (ante syn- et post-tectonique). La tectogenose atlasique, qui reprend des structures distensives precoces, est synchrone du depot des formations neogenes et quaternaires. Celles-ci sont caracterisees par des discordances progressives le long des principaux accidents actifs. Les differents blocs de socle, et la couverture qui les surmonte, sont deformes par le rejeu d'accidents en chevauchements ou en decro-chevauchements. Le raccourcissement du socle determine le decollement plus ou moins generalise de la couverture. Les chevauchements se propagent vers l'avant-pays: ils sont soit emergents dans la couverture soit aveugles. Ces deformations se font dans un context! compressif caracterise d'abord par un raccourcissement N 150 ± 10° au Neogene, puis N-S au Quaternaire. L'implication de la partie superieure de la croute dans l'orogene atlasique marocain permet d'expliquer la creation des reliefs dont les simples redoublements de la couverture ne peuvent pas rendre compte. Le Haut Atlas peut etre interprete comme resultant de grands charriages cenozoiques, et compare a la zone axiale de la chaine pyreneenne, meme si les histoires antecenozoiques different sensiblement.

Resume Les regions du Rekkame, du Moyen Atlas et du Maroc Central presentent de nombreux centres volcaniques d'aˆge Paleogene, Neogene et Quaternaire. Dans la majoritedes cas, il s'agit d'epanchements de basanites et de nephelinites. Dans la province du Rekkame, on observe deux types particuliers de volcanisme qui se differencient par leur position stratigraphique et par leuraˆge radiometrique. Lesepanchements les plus anciens ont environ 40 Ma et recouvrent les plus hautes collines du bord Est de la gouttiere de la Moulouya ou forment des diatremes parfaitement conserves. Les plus jeunes ont 30 Ma et sont associes aux depoˆts sedimentaires du “Pontien”. Leselements majeurs et en traces analyses dans ces deux types d'epanchements indiquent un meˆme environnement tectonique de basaltes alcalins intra-plaques. Ils representent deuxepisodes distensifs au sein du regime compressif general duala collision entre l'Afrique et l'Eurasie.

A low insertion loss 2.2% bandwidth two-pole cavity filter was fabricated at 60 GHz by bonding metallized lids on each side of a 250-/spl mu/m silicon substrate. The lids are made by dry etching of a 500-/spl mu/m silicon substrate. The same process is used to etch via holes on the intermediate substrate. The position of these via holes fixes the external coupling and the coupling between the resonators. The measured unloaded quality factor is lied on the height of the cavity (1.05 mm) and is around 1100.

Le Jbel Saghro est un des deux grands appareils volcaniques alcalins récents de l'Anti-Atlas. Les laves émises sont des néphélinites à olivine, des téphrites et des phonolites. Les phonolites suivent un chemin de différentiation particulier, séparé des autres roches présentes. La géochimie des éléments majeurs et des traces reflète bien cette particularité. Vingt deux roches totales ont été datées par la méthode K-Ar. Le volcanisme récent a débuté il y a 10 Ma et s'est poursuivi au centre du stratovolcan jusqu'à 6,4 Ma. Ont fait successivement éruption des néphélinites à olivine, des néphélinites phonolitiques, des phonolites alcalines et des phonolites normales. Une deuxième séquence, formée uniquement de néphélinites à olivine, prend le relai, plus au nord, entre 5,5 et 2,8 Ma. Par ailleur, nous n'avons pas trouvé de roche plus jeune que 2,8 Ma. Le volcanisme du Saghro, comme celui du Siroua, s'est développé dans un contexte distensif local mais compressif au niveau régional, très certainement lié au système de failles E-W de la marge sud du Haut-Atlas.

Elmi Serge, El Hammichi Fatima, Benshili Khadija, Faure-Muret A. Découverte de récifs toarciens dans le moyen Atlas marocain. In: Documents des Laboratoires de Géologie, Lyon, n°156, 2002. STRATI 2002. 3ème congrès français de stratigraphie. Lyon, 8-10 juillet 2002. pp. 102-103.

Archaeocyathan Fauna from the western Anti-Atlas (northern and southern slopes) and the western High Atlas. Lower Cambrian, Morocco. Examination of archaeocyath collections from the Western Anti-Atlas (northern and southern slopes) and from the High Atlas (Ounein) shows the probable presence of seven genera found for the first time in Morocco and seven new species. These data are included within a general revision of the previously described moroccan faunas. Archaeocyathan assemblages are recognized for each lower Cambrian Formation., L'examen des récoltes d'archéocyathes de l'Anti-Atlas occidental (bords nord et sud) et du Haut Atlas (Ounein) a révélé la présence probable de sept genres qui n'avaient pas encore été trouvés au Maroc et a permis la description de sept nouvelles espèces. Ces données sont incluses dans une révision générale des faunes marocaines. Les ensembles fauniques caractéristiques des Formations du Cambrien inférieur peuvent ainsi être définis., Debrenne Françoise, Debrenne M., Faure-Muret Anne. Faune d'Archéocyathes de l'Anti-Atlas occidental (bordures Nord et Sud) et du Haut Atlas occidental. Cambrien inférieur, Maroc. In: Géologie Méditerranéenne. Tome 17, numéro 3-4, 1990. Le paleozoïque du Maroc. I – Cambrien – Dévonien (Paléontologie – Biostratigraphie) pp. 177-211.

This report lists acritarchs found in the various countries studied for I.G.C.P. Project No. 2. The results are provisional as collecting was not always made in accordance with the adopted rules. The research on the acritarchs from different levels in the Precambrian of the countries studied for I.G.C.P. Project No. 2 has given very encouraging results, which have generally confirmed the stratigraphic attribution of successive series based on other criteria. However, the microphytoplankton proved to be very poor in acritarchs, and those of great longevity predominated. This could possibly be due to low temperatures in the seas which surrounded the then northern Atlantic Ocean, as well as to the shallow-water environments and low salinity of this basin.

In the Armorican Massif we discovered a stratigraphic and orogenic succession identical to the successions encountered in other countries which we studied for I.G.C.P. Project No. 2. As in Morocco, the regional rejuvenation was most intense during the first Proterozoic orogeny (Lihouides = Sveco-Fenno- Karelides = Hudsonides = Bouazzerides): only the Icartian relicts permit recognition of the importance of the Archaean Basement. Rejuvenation was also very strong during the Pan-Atlantic Thermotectonic Episode. It profoundly modified the ages the two Cadomian belts, which delayed recognition of their true ages and history. Cogne´created the term Pentevrian in 1959 for the ancient basement of the Brioverian. Leutwein (1968) dated it at ca. 1000 Ma, which is in fact the date of its rejuvenation. Its formations have been divided ( Roach et al., 1972 ) between the Archaean (2500–2700 Ma) and the Lihouian (= Karelian 1900–2000 Ma). Thus, it would be the equivalent of the American Grenvillian which also rejuvenated the Archaean-Hudsonian basement. 1000 Ma is not the age of the first Cadomian orogeny which is well-dated by the Coutances diorite (1300 Ma); it is therefore the age of the second Cadomian belt which was entirely rejuvenated by the Pan-Atlantic Episode. It is known that this last great Precambrian Armorican belt was levelled out by the pre-cover surface dating, also ca. 1000 Ma (Normandy). A redefinition of the Pentevrian would be desirable to avoid misunderstanding.

In the northern part of the Auron region, Alpes-Maritimes, France, the terrain is composed of a continuous series of relatively undisturbed upper Triassic to Neocomian (Cretaceous) beds, which, in the southern part of the region, were subjected to overthrusting.

The Lanvaux anticline in southern Brittany, France, is composed essentially of a core of granite intruded in Brioverian (Precambrian) schists, and lower Paleozoic formations. The Brioverian schists were metamorphosed prior to intrusion of the granite. Emplacement of the granite was in the nature of a diapir-like injection of a more or less consolidated mass during crustal movements at the end of the Precambrian which in their final stages crushed the granite in places.

Discusses the stratigraphic position of Microcodium- bearing formations in the border zone of the Argentera-Mercantour massif in the French Alps, and argues in favor of an organic (algal) origin for Microcodium, which appeared in the upper Senonian (Cretaceous) and persisted, in places, until the middle or upper Lutetian (Eocene).

The High Atlas is an intracontinental folded belt which evolved from narrow subsiding basins in the Early Mesozoic times; folds and thrusts with a double vergence formed since the Upper Cretaceous till the Pleistocene.

Aperçu historique Les formations christallophyliennes et cristallines Les terrains sédimentaires primaires Les terrains sédimentaires secondaires et tertiaires, pas de résumé