Phosphatic Series Research Articles

Les sondages électromagnétiques temporels comme outil de reconnaissance du gisement phosphaté de Sidi Chennane (Maroc) : apport à la résolution d'un problème d'exploitation

Exploitation of the phosphatic layers in Sidi Chennane deposit (Morocco) collides frequently with problems bound to the existence, in the phosphatic series, of sterile bodies qualified as derangements. Our study shows that these bodies, masked by the Quaternary cover can be mapped using the Time-Domain ElectroMagnetic Soundings method (TDEM). It is based on the acquisition and the interpretation of a series of tests carried out above a visible derangement in an old trench of exploitation and on 2500 TDEM soundings carried out in a virgin area of the deposit. The article concerns to the analysis of the results and of the proceeding for a possible large geophysics survey. To cite this article: A. Kchikach et al., C. R. Geoscience 338 (2006).

Durophagous Mosasauridae (Squamata) from the Upper Cretaceous phosphates of Morocco, with description of a new species of Globidens

AbstractThree durophagous mosasaur species are represented by isolated teeth in the Upper Cretaceous (Maastrichtian) phosphatic beds of Morocco. Globidens phosphaticus nov. sp. is characterised mainly by a strong heterodonty, with mid-posterior teeth being bulbous, irregularly oval in crosssection, and having an inflated posterior surface, a large eccentric located and recurved apical nubbin, vertical sulci on medial and lateral faces, no carinae and an enamel surface covered by anastomosing ridges. Teeth of Prognathodon currii are broad and tall, straight cones, slightly swollen at the base, and with two serrated carinae. These two taxa have been collected from all the phosphatic series (lower to upper Maastrichtian) in the Ganntour Basin (Morocco). Globidens phosphaticus nov. sp. is probably also represented at other Maastrichtian phosphatic sites along the southern margin of the Mediterranean Tethys. Prognathodon currii was previously known only from the Upper Cretaceous phosphates of Negev. Of the third taxon, Carinodens belgicus, only a single tooth (now lost) is known from the Oulad Abdoun Basin (Morocco); this is low, swollen, laterally compressed and bicarinate with a large apical nubbin. Previous records of this species include Europe and Brazil.

Cartographie de corps stériles sous couverture quaternaire par méthode de résistivités électriques dans le gisement phosphaté de Sidi Chennane (Maroc)

Abstract In the Ouled Abdoun sedimentary basin (Morocco), the phosphatic series is composed of regular interbedded phosphatic and marly limestone layers. Some phosphatic deposits in this basin show sterile bodies causing two kinds of problems: (1) as they are hard, compact and masked by a Quaternary cover, they disturb the exploitation in some yards and give bad reserve calculations; (2) even the use of wells and mechanical boreholes did not evidence their delimitation. Therefore, electric prospecting method has been used to evidence their geometrical shape. Petrographical and geometrical studies on these sterile bodies allowed us to choose the appropriate geophysical method to map them. The electrical resistivity survey that we used in the Sidi Chennane area shows that this technique is a good tool to contour these sterile bodies. This method is now considered as useful to the mining engineers to get round them during the exploitation. To cite this article: A. Kchikach et al., C. R. Geoscience 334 (2002) 379–386.

Trace fossil assemblages from the Albian phosphaterich sandstones of the Helvetic Shelf (western Alps)

In the Albian phosphate-rich sandstones of the Helvetic Shelf, three ichnofacies have been identified: 1, a Trypanites ichnofacies comprising Gastrochaenolites, Entobia, Rogerella, Trypanites and Caulostrepsis in condensed phosphatic series; 2, a Cruziana ichnofacies comprising Palaeophycus and Chondrites in relatively expanded series; 3, a Glossifungites ichnofacies characterized by glauconite-filled Thalassinoides and related to Upper Albian unconformities. The first and the second ichnofacies existed simultaneously in areas of different submarine topography created during a late Aptian-early Albian erosional period. All these ichnofacies developed in an open shelf environment and were linked to submarine unconformities and to phosphatization periods.

Primary, Bedded, Structureless Phosphorite of the Khubsugul Basin, Mongolia

ABSTRACT A phosphatic series of Upper Vendian (Proterozoic) to Lower Cambrian age occurs in the Khubsugul Basin, Mongolia. Unweathered, bedded, aphanitic, structureless phosphorite (microsphorite) is relatively abundant in these phosphorites. Its orthochemical precipitation in shallow water on the inner portion of the Siberian continental shelf of latest Precambrian to Early Cambrian time is established from stratigraphic and petrographic considerations. The microsphorite was the parent material for other petrographic types of phosphorite, which formed both by disintegration of the microsphorite to give intraformational conglomerate and breccia and by granulation of the microsphorite to give granular and pelletal phosphoritc. Although disintegration and granulation were due to a higher energy nvironment, little transportation of grains occurred. Dolomitization of matrix apatite was a significant part of the process of granulation. These various types of phosphorite are intimately interbedded in the lower of two phosphate units.

Phosphorites et évaporites : deux formations de milieux sédimentaires voisins étudiés dans la coupe du Paléogène de Foum Selja (Metlaoui, Tunisie)

The sedimentary phosphatic series of the Gafsa area is strongly tilted to the West of Metlaoui where they are cut by the Selja river. A detailed study of this excellent natural cross section has been carried out, and numerous samples obtained. The observed litho-logical superposition may be explained by sequences established on basis of the variations of a «chemical index», defined as the ratio between the abundance of material of chemical and biochemical origin, and the abundance of material of detrital origin. On this way the different facies may be classified by their dominant minerals in the following order : clay, calcite, dolomite, phosphate or gypsum. Clays are mainly represented by detrital montmorillonites and kaolinite, whereas attapulgite and sepiolite strongly indicate more chemical environments. The apatite is characteristically fluor -carbonate-apatite with 4 % F and 5 to 6 % CO₂. The entire El Haria -Metlaoui -Souar series corresponds to three sequences, which do not coincide with the stratigraphical divisions. The lower and upper sequences are gypsiferous, bracketing an intermediate phosphatic sequence. Gypsum and apatite can be considered as equivalent in terms of their position in the sequence ; though invariably separate minerals, their appear at the same stadium of the sequential evolution, the former chemical, the latter biochemical (with its usual suite of characteristic trace elements, particularly the group V, Ni, Cr, Zn). The behaviour of strontium is also interesting, since the study of the Sr -P2O5 diagram suggests that apatite forms by transformation of a calcium carbonate, in particular aragonite. The composition of the deposits and their succession seem to be the result of three factors working simultaneously : a vertical movement which supplies detrital material ; the opening and the closing of the connection between the basin and the open ocean, favouring either chemical restriction, or biological development ; a geochemical factor, not completely understood, which is induced by a greater or lesser abundance of magnesium.