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51.
RésuméLes formations tertiaires du système de piedmonts atlasiques du Sud marocain montrent de nombreuses silicifications qui affectent les différents faciès de la série : les grès calcaires, les conglomérats, les calcaires lacustres, aussi bien que les faciès plus argileux. Les accidents siliceux sont de tailles et de faciès variés, allant d’échardes millimétriques à des masses pluri-décimétriques. Dans les faciès argileux (torba), ce sont des plaquettes et des tubules de silice translucide. Dans les calcaires, ce sont surtout des faciès silexoïdes, à morphologies variées et à contours irréguliers. Dans les grès calcaires, ce sont des silicifications scoriacées, quelquefois disposées suivant un réseau de conduits anastomosés,La pétrographie révèle que les dépôts de silice dans les vides forment une part importante des silicifications. Les silicifications translucides des faciès argileux sont entièrement formées de concrétions de calcédoine. Dans les grès calcaires, les silicifications résultent de la cimentation des grains de quartz détritiques par des dépôts de silice fibreuse et d’opale, après dissolution du ciment calcaire primaire. Dans les calcaires, certaines silicifications correspondent à la cimentation de micro-brèches karstiques par des quartz géodiques; même les plages qui apparaissent très homogènes, formées de quartz microcristallin, révèlent une porosité primaire importante. Il y a alternance de phases de dépôt de silice et de dissolution de la matrice calcaire. A côté de ces dépôts dans les vides existent aussi des épigénies, c’est à dire le remplacement de la matrice calcaire avec préservation des structures, sans formation de vides. Néanmoins, ces épigénies sont limitées à la bordure de vides à dépôts de silice.Les silicifications sont dues à des processus diagénétiques tardifs. L’essentiel de la silice est constitué par des dépôts dans des vides ce qui permet de faire des hypothèses sur la nature des solutions nourricières. La régularité des dépôts tout autour des vides indique un milieu saturé, au sein d’une nappe. En raison de la solubilité relativement faible de la silice dans les eaux superficielles, des débits importants sont nécessaires pour renouveler constamment la silice précipitée des solutions. Ceci conduit à envisager des climats relativement humides à l’époque de la silicification, ainsi que l’existence de reliefs et de paysages incisés pour générer les écoulements de nappe suffisants. 相似文献
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RésuméUne étude a été effectuée dans la zone Nord-Ouest du bassin versant de la Medjerda avec pour objectif de fournir de nouvelles connaissances sur la qualité des eaux ainsi que sur le type de relation qui peut exister entre les variables physico-chimiques, bactériologiques et les indices de diversité/densité de la méiofaune. Les résultats montrent une dégradation de la qualité du cours principal de la Medjerda et de trois de ses affluents Nord (augmentation de la salinité, teneur en nitrate, matière organique, coliformes…). Les indices de diversité et d’équitabilité suivent cette évolution régressive des variables physico-chimiques et apportent de nouvelles connaissances sur le type et la qualité du sédiment.
Editeur Z.W. Kundzewicz ; Editeur associé B. Touaïbia 相似文献
53.
Abstract The Complex Terminal (CT) and Plio-Quaternary (P-Q) aquifers in the Chott Gharsa plain in southwestern Tunisia have been investigated with the aid of chemical and isotopic tools. It has been demonstrated that groundwater from the CT is mainly of palaeo-origin, especially in the western and central parts of the plain where the most negative values of δ18O and δ2H were observed (between??8.1 and??7.6‰ for δ18O, and??60 to??57‰ for δ2H), combined with low concentrations of radiocarbon (6.8–7.5 pmc) and absence of tritium. Modern recharge of the aquifer occurs only in the eastern part of the system where younger waters were observed, as indicated by their stable isotope composition, relatively high radiocarbon content and presence of tritium. Groundwater from the P-Q multi-layer aquifer represents mixtures of ascending deep CT waters and modern water recharging the P-Q aquifer system. Isotope mass balance was used to quantify mixing proportions. The calculations showed that the contribution of deep CT groundwater to the P-Q aquifer system reaches about 75% in the western and central parts of the plain where the CT aquifer remains strongly artesian. This contribution decreases to about 15% towards the eastern part of the plain, as a consequence of significant reduction of artesian pressure in this area of the CT aquifer. Chemical data suggest that mineralization of the studied groundwater systems is controlled mainly by dissolution of evaporative minerals (halite, anhydrite and gypsum) and cation exchange reactions with the matrix, possibly enhanced by recent anthropogenic disturbance of the system caused by lowering of the water table due to heavy exploitation and return flow of saline irrigation water into the P-Q aquifer. Editor D. Koutsoyiannis; Associate editor E. Custodio Citation Yangui, H., Abidi, I., Zouari, K., and Rozanski, K., 2012. Deciphering groundwater flow between the Complex Terminal and Plio-Quaternary aquifers in Chott Gharsa plain (southwestern Tunisia) using isotopic and chemical tools. Hydrological Sciences Journal, 57 (5), 967–984. 相似文献
54.
We study the first occurrence of clinopyroxene-free garnet bearing metabasites encased in migmatitic gneisses and metapelites, in the area of Tin Begane belonging to the Laouni terrane in the Pan-African Trans-Saharan belt (Hoggar, Algeria). They present two successive parageneses after a primary assemblage characterized by the presence of high titanium amphiboles equilibrated with coarse-grained garnet, plagioclase, biotite, quartz, and rutile. The two retrograde parageneses show decompression textures with the developing of coronas- and worm-like symplectites consisting of orthopyroxene + plagioclase ± amphibole for the secondary paragenesis and plagioclase + amphibole for the late stage paragenesis. These garnet metabasites do not show high pressure paragenesese compared to those previously studied from the Laouni terrane and which are known to present at least one high pressure paragenesis involving primary pyroxenes. We investigate the exhumation of these metabasites by combining detailed petrographic and thermobarometric studies in order to constrain the P-T conditions for each metamorphic stage. The results suggest an isothermal decompression from peak granulitic conditions (850 ± 50 ° C and 0.85 ± 0.15 GPa) down to transitional granulitic conditions (830 ±50 ° C and 0.5 ±0.1 GPa) followed by a cooling episode to the amphibolite-greenschist facies transition at 480 ± 80 ° C and 0.4– 0.5 GPa. These conditions are consistent with a tectonic exhumation process most likely provoked by a lithospheric thinning accompanied by a magmatic episode and partial melting of the lower continental crust. 相似文献
55.
The purpose of the present study is to ascertain the extent of the effect that phosphate fertilizer industrial waste has on the surface and bottom sediments of the Ghannouch-Gabes coast, off the Tunisian Mediterranean Sea. To achieve this, 44 surface sediments and 3 core sediments were studied for mineralogy, trace metals (Cd, Cu, Pb, and Zn), F, CaO, and SO3. For all the analyzed elements, the spatial distribution in surface sediments showed that the area located between the commercial and the fishing port of Gabes is the most polluted zone. The ranking of metal contents was found to be Zn > Cd > Cu > Pb. The vertical distribution of trace metals indicated that the highest levels were found in the uppermost segment of the sediment cores compared to the lower depth subsurface due to a continuous input of phosphogypsum (PG) release and confirmed that the area between the two harbors suffered from several types of pollutants compared to reference core C1, collected from other non-industrialized areas. This spatial and vertical distribution is probably due to the harbor piers which acted as barriers and limited the dispersion of PG discharge. The contamination factor, the geoaccumulation index, and the pollution load index were determined. The results obtained confirm the anthropogenic impact on the levels of metal, on the fluorine, calcium, and sulfate concentrations in the area, located between the commercial harbor of Ghannouch and the fishing harbor of Gabes, whereas the concentrations of elements analyzed tends to decrease on both sides of this sector. Statistical analyses (principal component analysis) showed trace metals, fluoride, sulfate, and a large amount of calcium resulting from the same anthropogenic source. 相似文献
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Mehdi Boukri Mohammed Naboussi Farsi Ahmed Mebarki Mohamed Belazougui Omar Amellal Brahim Mezazigh Nabila Guessoum Hamid Bourenane Azzedine Benhamouche 《Bulletin of Earthquake Engineering》2014,12(6):2683-2704
Located at the North-Eastern part of Algeria (Tellian Atlas), Constantine has crucial administrative, economic, scientific and cultural importance. It has continuously experienced significant urban evolutions during the different periods of its history. The city is located in an active seismic region within Algeria and has been struck in the past by several moderate and strong earthquakes. The strongest earthquake recorded since the beginning of instrumental seismology took place on October 27, 1985 with a magnitude M \(_\mathrm{S}=\) 5.9. Constantine presents a high seismic risk, because of its dense housing and high population density (2,374 inhabitants/km \(^{2})\) . This requires a risk assessment in order to take preventive measures and reduce the losses in case of potential major earthquake. For this purpose, a scenario based approach is considered. The building damage assessment methodology adopted for the Algerian context is adapted from HAZUS approach. In the present case, the effective Algerian seismic code response spectrum (RPA 99/2003) is considered as a seismic hazard model. The prediction of the expected damages is performed for a set of almost 29,000 buildings. 相似文献
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E. Laville B. Delcaillau M. Charroud O. Dugué L. Ait Brahim G. Cattaneo P. Deluca A. Bouazza 《International Journal of Earth Sciences》2007,96(3):497-515
The South Middle Atlas front constitutes a northeast-trending shear zone, located north of the Neogene Missour basin and east
of the Taza Guercif basin. This paper analyses the Southern Middle Atlas Fault Zone (SMAFZ) deformation since the Pliocene.
The set of structures observed suggests that reverse and thrust faulting along the central part of the SMAFZ are combined
with left-lateral slip along N–S striking faults of its south-western termination and right-lateral faulting along E–NE striking
faults of the east–northeast termination. Thrusts and oblique thrust-related anticlines of the two lateral ramps partly accommodate
north-west directed motion of the African plate. The Thrusts probably resulted from rejuvenation of Jurassic normal faults;
they were active during the Upper Miocene–Pliocene and the Pleistocene. The geometries of positive inversion structures and
buttressing effects are clearly dependent on the geometry and sedimentology of the original basin-controlling fault system
and on the presence of a décollement level. Field mapping is integrated with Landsat imagery and a digital elevation model
to investigate the morphotectonic evolution of the south-eastern range front of the Middle Atlas. Geomorphological features
provide significant information on the processes that govern lateral propagation of active anticlines. Both suggest that the
deformation front may have been active since Pliocene. 相似文献
60.
JHomogenizer: a computational tool for upscaling permeability for flow in heterogeneous porous media
This paper presents an object-oriented programming approach for the design of numerical homogenization programs, called JHomogenizer. It currently includes five functional modules to compute effective permeability and simple codes for computing solutions for flow in porous media. Examples with graphical output are shown to illustrate some functionalities of the program. A series of numerical examples demonstrates the effectiveness of the methodology for two-phase flow in heterogeneous reservoirs. The software is freely available, and the open architecture of the program facilitates further development and can adapt to suit specific needs easily and quickly. 相似文献