Mise en évidence d’un Sénonien gypseux sous la série phosphatée du bassin des Ouled Abdoun: Un nouveau point de départ pour l’origine des zones dérangées dans les mines à ciel ouvert de Khouribga, Maroc

In the Ouled Abdoun sedimentary basin (Morocco), the phosphatic series is composed of regular interbedded phosphatic and marly limestone layers. Exploitation of the phosphate in some deposits in this basin collides frequently with problems bound to the existence, in the phosphatic series, of disturbed areas (sterile bodies) qualified as derangements by the mining engineers of the Office Cherifian Phosphate Group (OCP). Their presence in the phosphatic layers causes two kinds of problems: (1) since the whole phosphatic sequence is overlain by a Quaternary cover, we do not know their volume proportion in the phosphatic layers, and therefore the reserves estimations can be wrong (2) they are generally hard, so they complicate the phosphate extraction. Indeed, in an area containing sterile bodies, boring grid may always be tightened and boreholes filled with dynamite. The required borehole tools and use of explosives are time consuming and therefore increase drastically the cost of phosphate extraction. Their localisation would permit the mining engineers to get around them during the exploitation. Several geophysical works have carried out in the achieved in Khouribga area to localize and delimit these sterile bodies. Electric resistitivy was established as a suitable geophysical parameter to map them, but the slowness and difficulty of data collection hinders the application of these geophysical methods to the whose phosphatic deposits area (about 25000 ha). Their application in all the Ouled Abdoun basin requires the comprehension of the origin of the sterile bodies, in order to specify their formation process and to predict consequently their spacial distribution in each phosphatic deposit. Our study concerns to sedimentological and diagenetic analysis of disturbed aereas and their immediate vicinity. It made it possible to identify for the first time the existence of an evaporitic series intensely karstified at the top of the Senonian, under the phosphatic series. The senonian karsts are undoubtedly at the origin of the derangements, which are defined as the collapsing phenomena at the base of underground cavities. These bodies have a polyphase structuring and a genesis that is the consequence of on several processes (fracturing, infiltration, dissolution, collapse). Their installation began from the end of Senonian, and continues up to the Quaternary.[fr] Dans le bassin sédimentaire des Ouled Abdoun (Maroc), la série phosphatée est formée d’une intercalation régulière de niveaux phosphatés et marno-calcaires sur environ 50m de puissance. Localement, cette régularité est perturbée par la présence fréquente de structures communément appelés «dérangements». Il s’agit de masses non stratifiées, stériles, qui perturbent et alourdissent les travaux d’exploitation des couches phosphatées. Les études géophysiques expérimentales, réalisées dans les zones dérangées de la série phosphatée, ont démontré la possibilité de les cartographier sous couvertures à l’échelle décamétrique. Leur généralisation sur toute la superficie du bassin des Ouled Abdoun, nécessite une compréhension du phénomène à l’origine de ces structures. Notre étude concerne l’analyse sédimentologique et diagénétique des zones dérangées et de leur voisinage immédiat. Elle a permis d’identifier pour la première fois l’existence d’une série évaporitique intensément karstifiée au sommet du Sénonien, sous la série phosphatée. Les karsts sénoniens sont incontestablement à l’origine des dérangements ou fontis que l’on défini comme étant des phénomènes de collapses à l’aplomb de cavités souterraines. Ces fontis ont une structuration polyphasée et une genèse au dépend de plusieurs processus (fracturation, infiltration, dissolution, effondrement). Leur mise en place a débuté dès la fin du Sénonien et s’est poursuivie jusqu’au quaternaire

A long-snouted dyrosaurid (Crocodyliformes, Mesoeucrocodylia) from the Palaeocene of Morocco: phylogenetic and palaeobiogeographic implications.

International audienc

A new dyrosaurid crocodyliform from the Paleocene of Morocco and a phylogenetic analysis of Dyrosauridae

A new genus and species belonging to Dyrosauridae, Arambourgisuchus khouribgaensis, from the Thanetian (Palaeocene) of Morocco, is erected. Two more or less complete skulls and three mandibular fragments enable a reconstruction of the anatomical characteristics of this species. Dyrosaurid systematics is mainly based on mandibular characters. The comparison of this new material with several dyrosaurid species previously known provides new systematic data for this group. The width of the interfenestral bar, the shape and development of the occipital tuberosities and the shape of the supraoccipital and the basioccipital are of particular importance. A phylogenetic analysis of the dyrosaurids provides an outline of the relationships between the best known species. Chenanisuchus lateroculi is the most primitive dyrosaurid. Sokotosuchus ianwilsoni and Phosphatosaurus gavialoidesform a clade, more closely related to other dyrosaurids than to Chenanisuchus lateroculi. The relationships between Arambourgisuchus, Rhabdognathus, Congosaurus, and Hyposaurus are unclear, and the two latter taxa remain too poorly known to provide an uncontested phylogenetic result. The dyrosaurids are known from nearly all continents. The phylogenetic results suggest a North African range for basal members, and the wide distribution of Rhabdognathus and Hyposaurus confirms the possibility of transoceanic dispersal of these taxa. Unfortunately, many dyrosaurids are insufficiently known to be included in the analysis, and the present analysis considers mainly African forms. A better knowledge and the inclusion of other taxa from other geographic regions should significantly improve and modify the hypothesis