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Detailed gravity data integrated with geological data and mining well data are analysed to constrain the shape of the Triassic evaporitic body at Jebel El Mourra (northern Tunisian Atlas) and the mechanism of its emplacement at the surface. The gravity data analysis included the construction of a gravity anomaly maps, and synthetic and forward 2.5D gravity models. The complete Bouguer and residual gravity anomaly maps indicate a positive amplitude gravity anomaly over the Triassic evaporitic outcrops and prominent NE–SW‐trending features associated with the boundary of the Triassic rocks and surrounded layers. A NW–SE‐trending gravity model that crosses the Triassic evaporitic outcrop at Jebel El Mourra shows that the positive gravity anomaly can be explained by a deep‐rooted salt diapir. Conventional models of salt dome formation suggest that they produce negative gravity anomalies; however, this study shows that this model is not universal. The studied area is an example of a diapir expressed by positive gravity anomaly and this result is supported by synthetic gravity models at different stages of salt piercing. 相似文献
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The present work aimed to determine the mineralogical composition of Ypresian series and to clarify the influence of the dissolution of siliceous frustules on the genesis of fibrous clay minerals. The specimens sampled from CPG trench are mainly constituted of silica-rich rocks at Mides area located at the western part of Gafsa-Metlaoui basin. The samples were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to determine texture of constituents. The data obtained indicate that the bulk rock samples are mainly made up of opal CT and clay minerals. The latter consists of palygorskite-sepiolite minerals associated with smectite and few amount of illite. The trend of mineralogical composition indicates that fibrous clay minerals are more concentrated at the upper part. SEM observations indicated that palygorskite mineral appears as thread-like facies, which surround foliated texture of smectite in the lower part of the Mides section, although with the low Mg activity confirmed by the absence of dolomite. But, at the upper part of the Mides section, SEM observations revealed the occurrence of siliceous frustules, which have numerous dissolved areas and replacement of carbonate tests by silica. The dissolution saturated the depositional environment with silica which is required for the formation of palygorskite and sepiolite minerals, in addition to high Mg activity confirmed by the presence of dolomite in the bulk rock, which is required basically for the formation of sepiolite. Although the genesis mode of palygorskite and sepiolite is similar with very little difference, the genesis of sepiolite needs a high alkalinity than the formation of palygorskite. 相似文献
3.
The Upper Proterozoic volcanism of northwestern Africa is characterized by the predominance of calc-alkaline rocks. Volcanics with tholeiitic affinities and alkali basalts are rare. The geochemistry and the relative proportions of calc-alkaline rocktypes in the Silet zone (Algeria) and the Ouarzazate formation (Morocco) are similar to those of recent island arc suites where basalts are most abundant while in the Tassendjanet and Gara Akofo zones (Algeria) they resemble contintal margin volcanic suites with a predominance of andesites. The volcanic rocks have undergone low-grade metamorphism which strongly affected alkali and alkali-earth elements and also to a smaller degree, the less mobile elements such as REE, Zr, Hf, Nb, and P. The geochemistry of the calc-alkaline rocks point to a complex origin involving low-pressure fractional crystallization, crustal contamination and derivation from a source already enriched in LILE. 相似文献
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Salima Chakroun Wafa Mechti Mongi Herchi Mohamed Essghaier Gaied 《Arabian Journal of Geosciences》2018,11(3):60
Three mixtures (M1, M2, and M3) of the Eocene clay deposits were collected from Ain M’Dheker (Enfidha, Tunisia). These mixtures have been treated by hydrochloric acid in order to improve their physico-chemical characteristics. Optimum conditions for activation were conducted by varying several parameters such as the acid concentration, time, and temperature activation. The activation condition effect on surface area is studied. A representative raw (M3) and activated (AM3) mixtures were used in industrial application: Sunflower oil and Black 194 dyes (textile waste). M3 and AM3 were used to leach sunflower oil by varying the clay amount introduced. Results of the bleaching power of used samples were compared to that found by commercial bentonite imported from Germany (Tonsil), having a surface area of 725 m2/g. Indeed, an amount of 1% of AM3 gives a 60% decolorization similar to that found by commercial clay. Also, the ability of raw and activated clay to remove the dye (Acid Black 194) from effluent has been studied firstly at different pH and in second time by varying the adsorbent amount. Then, an amount of 0.025 g is sufficient to give a higher adsorption capacity for M3 than AM3. Consequently, Ain M’Dheker clay deposits can be use in other environmental application even without any treatment. 相似文献
6.
This work presents geochemical characterization of isolated kerogen out of clay fraction using petrography studies, infrared absorption and solid state 13C nuclear magnetic resonance (NMR) spectroscopy, with N‐alkane distributions of saturated hydrocarbon. Mineralogical study of clay mineral associations was carried out using X‐ray diffraction (XRD), on Ypresian phosphatic series from Gafsa‐Metlaoui basin, Tunisia. The XRD data indicate that smectite, palygorskite and sepiolite are the prevalent clay minerals in the selected samples. In this clay mineral association, the N‐alkane (m/z = 57) distribution indicates that the marine organic matter is plankton and bacterial in origin. The kerogens observed on transmitted light microscopy, however, appear to be totally amorphous organic matter, without any appearance of biological form. The orange gel‐like amorphous organic matter with distinct edges and homogenous texture is consistent with a high degree of aliphaticity. This material has relatively intense CH2 and CH3 infrared bands in 13C NMR peaks. This aliphatic character is related to bacterial origin. Brown amorphous organic matter with diffuse edges has a lower aliphatic character than the previous kerogen, deduced from relatively low CH2 and CH3 infrared and 13C NMR band intensities. 相似文献
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The former agro-pastoral system which prevailed in the Tunisian Sahara had developed a pastoral resource management which preserved the rather fragile ecological equilibrium. Nowadays in the Tunisian Sahara nearly all former nomads are settled around the villages and irrigated areas which were created with the official aim of utilizing the Sahara. The sedentarization of the nomads has provoked two phenomena: a concentration and an increased density of population around the newly founded oases on the one hand and a depopulation of the more remote steppes on the other hand. Actually this demographic disequilibrium threatens the ecological equilibrium which existed in the past. It has caused a multiplication of the stocking of the actual pastures and increases the risk of degradation of the peripheral and easily accessible grazing-grounds. It exercises an excessive pressure on the environment through the intensive human activities and the satisfaction of new needs. This pressure manifests itself in the enlargement of the circles of degradation around the oases and the intensification of aeolian dynamics. A regeneration of the former organically developed eco-system is impossible without conscious reference into the local traditions and without consideration of the complexity of interelationship of the various factors. 相似文献
8.
Ridha Abdessalem Gharbi Lassaâd Chihi Mongi Hammami Abdelkader Soumaya Ali Kadri 《Comptes Rendus Geoscience》2005,337(14):1293-1300
The geodynamic evolution of the diapir of Zag Et Tir is the result of the coexistence of the diapiric and tectonic activity from the Upper Cretaceous until the Quaternary. The interference of the tectonic and diapiric phenomena is at the origin of the basin individualization with differential sedimentation during the Miocene. This explains the current distribution of the Neogene deposits on both sides of Zag Et Tir Triassic structure. The submeridian faults that subdivide our sector played a significant role during the Atlasic compression, inducing an unequal distribution of the folds on both sides of these accidents, as well in kind as in number, showing the anteriority of the faults compared to the folds. To cite this article: R.A. Gharbi et al., C. R. Geoscience 337 (2005). 相似文献
9.
Evidence for Triassic salt domes in the Tunisian Atlas from gravity and geological data 总被引：3，自引：1，他引：3
Chokri Jallouli Mongi Chikhaoui Ahmed Braham Mohamed Moncef Turki Kevin Mickus Ramdhane Benassi 《Tectonophysics》2005,396(3-4):209-225
Detailed gravity data were analyzed to constrain two controversial geological models of evaporitic structures within the Triassic diapiric zone (Triassic massifs of Jebel Debadib and Ben Gasseur) of the northern Tunisian Atlas. Based on surface observations, two geological models have been used to explain the origin of the Triassic evaporitic bodies: (1) salt dome/diapiric structure or (2) a “salt glacier”. The gravity analysis included the construction of a complete Bouguer gravity anomaly map, horizontal gravity gradient (HGG) map and two and a half-dimensional (2.5D) forward models. The complete Bouguer gravity anomaly map shows a prominent negative anomaly over the Triassic evaporite outcrops. The HGG map showed the location of the lateral density changes along northeast structural trends caused by Triassic/Cretaceous lithological differences. The modeling of the complete Bouguer gravity anomaly data favored the diapiric structure as the origin of the evaporitic bodies. The final gravity model constructed over Jebel Debadib indicates that the Triassic evaporitic bodies are thick and deeply rooted involving a dome/diapiric structure and that the Triassic material has pulled upward the younger sediment cover by halokinesis. Taking in account kinematic models and the regional tectonic events affecting the northern margin of Africa, the above diapirs formed during the reactive to active to passive stages of continental margin evolution with development of sinks. Otherwise, this study shows that modeling of detailed gravity data adds useful constraints on the evolution of salt structures that may have an important impact on petroleum exploration models. 相似文献
10.
The Late Proterozoic calc-alkaline andesitic rocks of the Tassendjanet volcanic complex, north-western Hoggar, Algeria resemble the continental margin rocks and also are closely comparable to the Archaean andesites. Most Tassendjanet rocks were affected to various extents by low grade hydrous metamorphism which led to an increase of Na, P, Fe, Ti, and V and a decrease of Mg, Ca, Sr, Cr, and Ni. Although K, Rb, Ba, and Li are enriched in the majority of altered rocks, these elements are strongly depleted in the albitized Na-rich volcanics. REE are enriched in albitized andesites but their fractionation patterns remain unchanged. The trace element data are consistent with the derivation of the Tassendjanet andesites by partial melting of an upper mantle source enriched in LILE and presumably overlying the subduction zone. 相似文献