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Comptes Rendus Géoscience
Volume 339, n° 13
pages 831-839 (octobre-novembre 2007)
Doi : 10.1016/j.crte.2007.07.014
Received : 27 Mars 2007 ;  accepted : 17 July 2007
Hyperactive neotectonic near the South Rifian front : Lifted Late Quaternary lagunal deposits (Atlantic Morocco)
Néotectonique hyperactive près du front sud-rifain. Niveaux lacunaires récents soulevés (Maroc atlantique)
 

Aïcha Benmohammadi a, Roger Griboulard b, , Bendahhou Zourarah c, Christian Carruesco b, Khalid Mehdi c, Aziz Mridekh d, Abderahmane El Moussaoui a, Asmae Mhamdi Alaoui c, Pierre Carbonel b, Laurent Londeix b
a Département de géologie, faculté des sciences, université Ibn-Tofaïl, B.P. 133, Kénitra, Morocco 
b UMR CNRS EPOC-5805, université Bordeaux-1, avenue des Facultés, 33405 Talence cedex, France 
c Laboratoire Géosciences marines', département de géologie, université Chouaib Doukkali, B.P. 20, 24 000 El Jadida, Morocco 
d Laboratoire de géologie appliquée, équipe Technologie des ressources en eau', B.P. 133, Kénitra, Morocco 

Corresponding author.
Abstract

The recent discovery of emerged and lifted lagunal deposits near the Moulay Bouselham lagoon (North Moroccan Atlantic coast), up to 32m above sea level, requires a new model to explain the evolution of this ecosystem. All the studies on these deposits seem to indicate that we are dealing with very recent lagoonal levels. The main problem is to explain the altitude of these deposits. Likely explanations are a historical tsunami, tempest, and/or a very strong neotectonics in this area. We choose the later hypothesis because it matches the occurrence of an argilokinetic tectonic in front of the North Atlantic Moroccan margin. In this tectonic context, results of 14C analysis data, i.e. 2400±250 BP for one outcrop and 2170±215 BP for a value in a core taken in the lagoon, we obtain a rate of uplift of about 14mm/yr. Therefore, this region corresponds to an important tectonic junction between the stable Meseta to the south, the Rifian domain to the north and the accretionary prism, in relation with the subduction of the Atlantic crust under the African and European plates to the west. Moreover, in front of the studied site, many mud volcanoes have been observed in the Gulf of Cadiz, near the Moroccan margin.

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Résumé

La découverte récente de dépôts lagunaires émergés à proximité de la lagune de Moulay Bousselham (littoral nord-atlantique marocain) et situés à des altitudes atteignant +32m au-dessus du niveau marin actuel nécessite de proposer un nouveau modèle de mise en place de ces dépôts. Toutes les études indiquent qu'il s'agit de dépôts relativement récents (2400±250 ans BP au 14C). Les explications les plus plausibles font intervenir (1) des dépôts tsunamogènes, (2) une forte tempête, ou (3) une tectonique récente très importante. Toutes les hypothèses sont discutées, et nous retenons celle d'une néotectonique très active, en relation avec l'existence en mer, à quelque distance, d'une argilocinèse capable de mettre en place des volcans de boue très importants. Cette tectonique argilocinétique est contrôlée par la position de cette région, à la jonction entre la Meseta stable au sud, le domaine Rifain au nord et le prisme d'accrétion généré par la subduction du plancher atlantique sous les plaques Africaine et Européenne.

The full text of this article is available in PDF format.

Keywords : Lifted lagoonal deposits, Neotectonic, Atlantic subduction, Moulay Bouselham Lagoon, Morocco

Mots clés : Dépôts lagunaires soulevés, Néotectonique, Subduction atlantique, Lagon de Moulay Bouselham, Maroc


1  Merja : local terminology for an area with more or less water, temporary or permanent, which received this water from different origins [16].


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