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The northwestern foreland of Tunisia (El Kef region and its surroundings) is a key area to study the tectonics of main E-W basement strike-slip faults and related structures. To achieve this goal, we used multidisciplinary approaches including field work , paleo-stress analyses and geophysical data. These approaches allowed us to propose a new structural model based on the evolution in space and time of Riedel shear type faults and to highlight their role in the structuring of the study region. During the Mesozoic , E-W normal oblique-slip basement faults (D1: Ghardimaou fault, D2: El Kef-Ouergha fault, D3: Jebel Harraba-Guern Halfaya fault and D4: Tajerouine fault) controlled the architecture and the subsidence of the El Kef Basin within a transtensive setting by block tilting , NE-SW negative flower structures, Triassic salt ascent and deposits thicknesses and facies variations. During the Eocene and Late Miocene , the NW-SE shortening (tectonic inversion) is expressed by the oblique reactivation of the pre-existing E-W faults as dextral strike-slip faults. This reactivation is accompanied by map-scale Riedel shear type faults, where D1, D2, D3 and D4 formed the principal displacement zones (PDZs). The successive movements of these faults cut the study area in several right-lateral shear bands in which subsidiary Riedel fractures (R, R', X, P, T and Y) and NE-SW folds are developed. Fault slip data and fractures analyses, across the study area, show several fracture systems which interact under a NW-SE SH max. During Quaternary, the NNW-SSE shortening reactivated the preexisting E-W fault networks (PDZs). It also, formed N S left-lateral strike-slip faults, NW-SE grabens , NE-SW reverse faults, and ENE en echelon folds arranged within Riedel shear bands.

International audience; The Bou Jaber ore deposit is one of the numerous diapir-related Pb–Zn–F–Ba deposits of the Dome Zone in Northern Tunisia. Its location is controlled by the regional NE-SW Tajerouine Fault.Ore minerals are hosted in the Late Aptian limestones (Serdj Formation) as open space filling and stratabound replacement bodies. According to Bouhlel et al. (2016), the poly-phase mineralization resulted from the successive activity of three mineral systems, a Pb–Zn, then a barite, and eventually a fluorite deposition system. The latter, from the Late Miocene, is demonstrated in the present study.The fluorite system is characterized by the involvement of oil in the hydrothermal fluids. This oil was produced in the local environment of the deposit from the thermal maturation of the Albian Fahdene black shale source-rock at temperature range of~140 °C–~100 °C. Two brines were involved in the fluorite hydrothermal system. The first one (L1) is a Ca-rich brine (≥20 wt % bulk salinity), with Na/Ca ≤ 0.18, which is thought to have long resided in the basement, before its transfer into the Jurassic reservoir (Upper Nara Formation) and its eventual mobilization at the time of ore deposition. The second brine (L2), less saline (≤14 wt % bulk salinity) is more sodic, with Na/Ca up to 0.53, and represents unmodified brine originated from the nearby Triassic salt. The L1 brine was F-bearing, whereas the L2 brine was associated with oil. Fluorite deposition occurred at the estimated shallow depth of 1.7 km from cooling of the L1 brine due to the first isobaric cooling from ~160 °C to 135 °C under sub-lithostatic conditions (36 MPa). This stage is followed by mixing with the newly incoming L2 brines (transporting oil) along a sub-isochoric decompression path (down to the hydrostatic pressure at 17 MPa) and continuously cooling from 135 °C to 125 °C. The cooling and mixing caused fluorite deposition after which a transient heat advection episode (up to 145 °C) caused late calcite deposition prior to the end of hydrothermal circulation.

International audience; The Djebel El Hamra Pb-Zn-Ba-Sr (Hg) deposits in northern Tunisia are hosted in a post-nappe anticline with a core of a Triassicevaporite diapir affected by the NE–SW-trending Ghardimaou-Cap Serrat lineament. Three stages of mineralization occurred inthe Triassic dolostone: stages I and II caused alternating deposition of sulfate (Ba, Sr) and sulfide (sphalerite, galena) minerals;stage III formed late-stage calcite-marcasite-cinnabar. Zebra textures record the syntectonic transition from compression toextension in the Late Tortonian-Messinian interval. Two fluid end-members were involved in sulfate deposition: one lowsalinity(L1, ~3 wt% eq. NaCl) fluid, probably from a meteoric origin, and a Na-Ca-Cl brine (L2, ~22 wt% eq. NaCl) solutionwhich originated from the Triassic diapiric source. A third end-member fluid (L3) with long residence time in the basement wasalso involved in the Pb-Zn deposition. The δ34S values froma cluster of sulfates around +16‰, show a Triassic evaporate source.The sulfur in sphalerite resulted from bacterial sulfate reduction (BSR); however, crystallization in a closed system resulted in arange of δ34S between +1.6 and +26.5‰. The δ34S values in galena (−28.4 to +8.2‰) are consistent with a BSR and thermochemicalsulfate reduction (TSR) origin of the sulfur. Secondary ion mass spectrometry (SIMS) lead isotope data in galena(207Pb/204Pb: 15.595 to 16.193, 206Pb/204Pb: 18.673 to 18.939, 208Pb/204Pb: 38.330 to 40.572) point to local contributions(sedimentary and Cenozoic magmatic rocks) to the main source from the Precambrian basement. Ore deposition occurred at adepth of about 2 km at temperatures between 80 and 250 °C. A shallow magmatic heat source was the cause of these thermalfluctuations.

In Tunisia, land degradation is mainly caused by heavy rainwater. The complexity of this natural phenomenon in the catchment area of the Ayda river located in the highlands of Siliana, Tunisia, is linked to a rather reduced vegetal cover because of the hardness of the climate and the anthropic actions. It covers an area of 7.30 Km2 drained mainly by Ayda river. It is characterized by moderately rugged terrain with a minimum altitude of 844 m and maximum of 1182 m. For slopes, they can be very strong by 70% but also in some locations does not exceed 6%. Several methods and models are commonly used for water erosion study. The revised universal soil loss equation (RUSLE) was chosen in our study. It is an empirical and spatialized model, based on the characteristics of the watershed, such as the slope, the vegetation, and the state of erosion of its soils and their protection. Integration of this model data with geographic information system (GIS) allowed us to establish an erosion risk map to quantify soil loss, target areas of high erosion, and direct erosion control measures. Each of these factors has been expressed as a thematic map. The resulting soil loss map shows a variation in the erosion rate value, between 9 t/ha/year downstream of Ayda river and a maximum value 330 t/ha/year towards land without vegetation and areas with high slope values mainly in the southwestern part of the basin at Djebel Barbrou and Kef Guedouara respectively, which are the most vulnerable to water erosion.

Calcified aquatic larval cases were recognized and identified in the Pleistocene tufa masses of Jebel El Mida, Gafsa, southern Tunisia. These larval constructions belong to three main insect families: caddisflies (Trichoptera, Hydropsychidae), midges (Diptera, Chironomidae) and aquatic moths (Lepidoptera, Pyralidae) that inhabited tubes in the tufa and spun nets. Each insect community has its distinctive characteristics of larval constructions that allow their recognition. The larval constructions recognized comprise fixed and portable (for caddisflies) dwelling cases and silken retreats and feeding capture nets. These last-mentioned are almost completely eroded and only remnants are preserved. The spatial distribution of these larval cases within the tufa is not random but, rather imposed by some specific paleohydraulic conditions. It's the reason why aquatic insect larval constructions are considered as prominent tool for the reconstruction of tufa and travertine depositional environments. Chironomid fixed dwelling cases (diameters range from 0.6 mm for clustered tubes to 3 mm) indicate the deposition of tufa under lotic (flowing) or lentic (standing) water conditions. The later hydraulic condition is shared with hydropsychids with fixed retreats (0.2–4 mm in diameter). Portable case-building caddisflies (case length ranging from 5 to 20 mm, and diameter from 3 to 5 mm at the cephalic end) prefer lentic conditions and are almost completely missing in high-energy flowing water locations that are preferred by pyralids (tubes are between 5 and 10 mm long and 3 mm in diameter). These insect families benefit from inhabiting the tufa by the availability of construction materials of their cases and the necessary space for their development.

The cactus tree, species Opuntia ficus-indica, is a primary material of many products in various domains such as cosmetics, medicine and nutrition. In the present work, we assess its potential as a flocculant. We tried a technique which adopts three sequential treatments that used coagulation, flocculation and sedimentation processes under certain operating conditions. For this purpose, we used the aluminum sulfate (AS) as coagulant and fresh cladodes juice (FCJ) as bioflocculant. All tests were carried out on high turbid urban wastewater collected from the Metlaoui's Wastewater Treatment Plant (MWTP) (in Gafsa in southwest Tunisia). Experiments with this couple AS/FCJ show very interesting results: a high-removal of turbidity (TUR), suspended solids (SS) and chemical oxygen demand (COD). The percentages of abatement of these parameters are respectively 93.65%, 82.75% and 64.30%. The experimental results of the present study prove that the turbidity, SS and COD removal efficiency of new technique is superior to that of conventional process (with only AS). By this technique, we save 50% in AS dose. Moreover, flocs formed by the treatment using AS/FCJ are coarse and readily settleable.

Heavy metals in industrial wastes do worldwide significantly influence surface waters, soils, and human health. The relationships between geochemical stream sediment composition and industrial pollution by phosphate mud flood were examined to assess the severity level of the heavy metal contamination due to the mining activities in the Gafsa-Metlaoui basin (Tunisia). A statistical approach based on linear correlations and principal components analysis of 8 metal contents was used in stream sediment, which was applied to 21 samples of surveyed Metlaoui stream. Within the final model, four Eigen factors did explain almost 90% of the total variance matrix (F1: 42.25%, F2: 19.60%, F3: 15.50 and F4: 10.15%). Three main metal associations were found in the Metlaoui stream sediment. The first was concerned with Titanium (Ti) and Zirconium (Zr) as conservative elements. The second related to the important role of Manganese (Mn) with Iron (Fe) hydroxides in fixing metals. Finally, the third one consisting of Zinc (Zn), Nickel (Ni), Copper (Cu) and Molybdenum (Mo) is all known to be linked to local mining activities sources. The overall degree of contamination was in the following order (high to low): Ti > Zr > Zn > Mo > Mn > Ni > Fe > Cu, but the extent of the contamination did decrease downstream from the mining activity. Phosphate mining activity, especially washing phosphate, leads to an unwanted heavy metals contamination in the nearby surrounding environment.

The Sidi Salem reservoir was built in Beja, a semi-arid region in Northwestern Tunisia, for such purposes as the protection of the lower valley against floods, irrigation, water supply, and power generation. It is the biggest reservoir in Tunisia. It is a 73-m high, 814 Mm3 water storage capacity compacted-earth dam. The seismic events in the studied area were monitored by a seismic network operated by the National Institute of Meteorology. The main aim of this study was to establish the correlation between water level in the reservoir and the induced seismicity. The first earthquake susceptible to be an induced event was found out in 1987 with magnitude of 5 after complete filling of the dam. Shortly afterwards, there was an increase in the number of seismic events, and many earthquakes were noted. It was suggested that this induced seismicity took place after the reservoir loading effect and also the postponed effect of the diffusion of pore pressure. The comparison between the seismic data and reservoir water level indicated that there was a correlation between the changes in the water level and the seismic activity.

In this study we elucidated the relationships between geochemical composition of the stream sediment samples and industrial pollution (phosphate mud flood). We offered an approach based on multivariate statistics: the factor analysis with a series of factor score of the investigated area. This type of numerical analysis, applied to 21 samples of surveyed Metlaoui stream, should also offer an additional insight into the possible anthropogenic impacts that might be present in the stream sediment geochemistry. The model is presented in the form of a variance factor matrix in which the four factors explain almost 90% of the total system variability. As can be seen from the statistics results, the first factor (F1) predominates and accounts for almost twice as much of the total explained percentage variance as the second (F2). The other factors show a decline in magnitude (F3 and F4). Three main metal associations were individualised in the stream sediment of Metlaoui. Ti–Zr; Fe–Mn and Zn–Ni–Cu–Mo. The increase of all concentration values (Ti, Zr, Fe, Mn, Zn, Ni, Cu and Mo) reflects that the mining activity (phosphate mud flood, or airborne deposition) could be associated with Fe–Mn oxyhydroxide that play a significant role in precipitating and thus fixing heavy metals in the proximity of mine contamination source.

The objective of this study was to investigate the ability of cactus Opuntia ficus-indica, used as a natural flocculant in the treatment of phosphate clay as an industrial wastewater. It is a new process that has proven very promising in the removal of high turbidity from industrial effluents. The volume of clear water recovered (supernatant) is one of the characteristic features which allow us to judge the effectiveness of this bioflocculant. The following of the settling velocity on the one hand and the analysis of supernatant and sludge on the other hand allow us to compare the cactus-based flocculant effectiveness with that of a chemical flocculant (CF) of anionic polyacrylamide nature. The optimum pH required for maximum settling velocity was found to be 12. Obtained results indicated that after 900 seconds of settling, the highest volume of clear supernatant was obtained with the natural flocculant (740 mL/L), against 666 mL/L obtained with CF. Several analyses on recovered clear water (pH, turbidity, Cu, Zn, Fe, Cd and Cr) and on dry sludge (P2O5, CaO, MgO, organic C, SiO2 and Cd) are highlighted.

The use of conventional chemical based coagulants increases residual levels of chemical products. That is why they are considered harmful to the environment and toxic to human’s fauna and flora (Farooq et al. in Bioresour Technol 101:5043–5053, 2010). In addition, they have a relatively high procurement costs. The cost and the environmental side effects of these compounds led many researchers to investigate the possibility of using plant-based coagulants in water and wastewater treatment (Joseane et al. in Plast Polym Technol 2(3):55–62, 2013). Naturally occurring products are biodegradable and are presumed safe for human health (Muralimohan et al. in Int J Res Eng Technol 2(2):15–20, 2014).

The geological study of Miocene clays from Gram area, North West of Tunisia shows an important series of clay materials to use them in the faience ceramic. Selected samples were studied with the objective of analyzing their chemical and mineralogical composition, morphology, particle size, plasticity, thermal analysis and their ceramic aptitude to be used in the faience ceramic. Raw materials are mainly composed of illite and kaolinite are the dominant clay minerals with minor quartz and dolomite. The plasticity indexes are lower than 15.40%, suggesting that these clays are not plastic. Technical characterization was carried out on one representative mixture of Miocene clay samples. The firing characteristics (shrinkage and water absorption) were measured. The optimum firing temperature of clay mixture (M) has been established. These clays could be used in the manufacture of ceramic pieces.

In Tunisia, and in most semi-arid countries, problems related to water access by populations are very frequent, especially when irregular rainfall and arid climate combine with the insufficiency of natural water resources, as well as possible anthropic pollution. The city of Gafsa (southwestern Tunisia), is relatively highly populated due to its economic activity. In addition, Gafsa has always been threatened by water scarcity generated by the increasing rate of urbanization, and thus there is growing need for drinking water, agriculture and industry. This has led to an overexploitation of groundwater by around 132% and provoked not only the reduction of water availability but also the deterioration of water quality. Proper understanding of the hydrochemical characteristics of groundwater is important for sustainable development of water resources in this region. For this purpose, a sampling campaign was carried out in aquifers of Gafsa to measure major dissolved ions (Ca, Mg, Na, SO4 and Cl), pH ...

International audience; Ain Allega and El Aguiba are among the largest barite-celestite deposits attributed to the Triassic period in Tunisia. They are located in the flysch zone on the eastern edge of the Triassic diapir of Jebel Hamra. The ore body consists of dolomite intensely brecciated and surrounded by marls, clay, gypsum and dolomite which forms the hanging wall of the deposit, and rimmed by Paleocene marls. The ore the surface structure, which in turn controls the mechanism of adsorption and incorporation of minor and trace elements into the growing crystal. For a solid solution, the transitional supersaturation for different growth mechanisms can be significantly different for the two end members. One of the most interesting and intriguing phenomena observed in natural crystals of the (Ba, Sr) SO4 solid solution from this study area is the development of compositional oscillatory zoning, consisting of alternating Ba-rich and Sr-rich layers. The sulfur isotope analyses show significant variability for barite and celestite (from 16.2 to 23 ‰). These values are interpreted as the result of the mixing of two sulfur end-members in the mineralizing fluids, corresponding to thermochemical sulfate reduction of Messinian seawater, together with Triassic sulfate, as sulfur sources. Fluid inclusion studies of celestite show that the BaSO4-SrSO4 solid-solution in both deposits was precipitated from hot saline solution (Th=190±20°C; 16.37 wt. % NaCl equivalent in Ain Allega and 8.2 wt. % NaCl equivalent in El Aguiba). Consequently, the precipitation could be from mixing of basinal brines with magmatic-meteoric fluid. minerals show a cap-rock type mineralization with various forms and types, in particular impregnation in dolomite, breccia cement, replacement of carbonate caprock and open space-filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are barite, celestite, calcite, dolomite and quartz .The ore minerals are hosted by the Triassic carbonate rocks, which show hydrothermal alteration, dissolution and brecciation. The study of barite-celestite solid-solution shows a bimodal distribution in which the composition is not continuous. Some intermediate compositions are missing; 20-80% SrSO4 for El Aguiba ore deposit and 50-70% SrSO4 for the Ain Allega ore deposit. X-ray diffraction peaks in the BaSO4-SrSO4 series display considerable broadening at intermediate compositions. The unit cell volume varies from 346.97 Å3 in barite (100% BaSO4) to 308.29 Å3 in celestite (100% SrSO4). This variation in cell parameters is attributed to the degree of substitution of barium by strontium since there is less variation between ionic radii of these elements. Consequently, these substitutions caused variation in morphologies, position and d-spacing of peaks (200, 011, 113, 312,122, 112, and 111). Some barite crystals have small-scale, strontium compositional banding which suggests that the crystals responded to regular fluctuations in physiochemical conditions during deposition. The degree of supersaturation in Ba2+ and Sr2+ controls the growth mechanism and consequently

The Ain Allega Pb–Zn–Sr–Ba ore deposit is located in the flysch zone on the Eastern edge of the Triassic diapir of Jebel Hamra. It is part of the extrusive Triassic evaporate formation along the Ghardimaou–Cape Serrat faults. The ore body consists of argilic–dolomite breccias surrounded by argilo–gypsum Triassic formation, which forms the hanging wall of the deposit, and rimmed by the Paleocene marls. The ore minerals show a cap-rock type mineralization with different styles particularly impregnation in dolomite, cement of breccias, replacement ore and open space filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are composed of barite, celestite, calcite, dolomite and quartz. The ore minerals are hosted by the Triassic carbonate rocks which show hydrothermal alteration, dissolution and brecciation. X-ray – crystallographic study of barite–celestite mineral series shows that pure barite and celestite are the abundant species, whereas strontianiferous barite (85–96.5% BaSO4) and barian–celestite (95% SrSO4) are minor. Primary and secondary mono-phase (liquid only) fluid inclusions are common in celestite. Microthermometric analyses in two-phases (liquid and vapour) fluid inclusions suggest that gangue and ore minerals were precipitated by a low-temperature (180 °C) saline (16.37 wt.% NaCl equivalent) solution originated possibly from a basinal brine with some input from magmatic or metamorphic fluid. Based on geology, mineralogy, texture and fluid characteristics, the Ain Allega deposit is classified as a carbonate-hosted Mississippi valley-type deposit.

Fluid inclusion studies were undertaken on quartz, fluorite and calcites in the Oued Belif caldera ore district in northern Tunisia. Two main groups of inclusions were distinguished: a fluid inclusion group, of magmatic origin, with a temperature higher than 350 °C and salinity higher than 30 wt % NaCl; and a group of mixing between magmatic and meteoric fluids with temperatures and salinities ranging from 150 to 250 °C and from 15 to 25 wt % NaCl, respectively. These two groups result from hydrothermal circulations of respectively, “porphyry copper” and epithermal systems; this is confirmed by the nature of the alteration.

The Ain Allega ore deposit represents one of the most significant Pb-Zn Sr-Ba deposits of the flysch zone in northern Tunisia. The total quantity of sulphide produced is 22,700 metric tons, with 13,300 t of galena and 9,400 t of sphalerite. It is located on the eastern edge of the Triassic diapir of the Jebel Hamra. The main ore minerals include sphalerite, galena, pyrite and marcasite, and gangue minerals including dolomite, calcite, celestite, quartz and barite. The mineralization hosted by carbonate rocks, shows some evidence of dissolution and brecciation characteristic of cap-rock formation. The fluid inclusion study from the celestite suggests that the primary and secondary monophase liquid (L) inclusions are most abundant compared to the other types. The microthermometric analyses of two-phase primary inclusions display homogenization temperatures ranging from 136 to 208°C (average of 180°C) and salinities ranging from 11.34 to 24.38 equivalent weight % NaCl (average of 16.4). The calculated density, pressure and depth are 0.965 g/cm3, 18 bars and 80 m, respectively. The hydrothermal fluid resulted from mixing of basinal brines and magmatic-meteoric solutions. Geological, mineralogical and thermometric data indicate that the Ain Allega ore deposit results of a mixing of basinal fluids (Mississippi valley type deposit) and hydrothermal fluids related to a shallow intrusion.

Analyses were made of sulfur isotopes and major and minor element (Fe, Pb, Zn, Cu, Hg, Cd, Bi, S, As, Tl, Sb, …) contents of a well characterized suite of minerals from ore deposits wether associated with vulcanism, metamorphism, Cretaceous sedimentary facies or Tertiary detrital-rich and molasse deposits. Paleogeography, tectonism and ore genesis are closely related: periods characterized by intense deformation (Middle and Upper Jurassic, Middle and Upper Cretaceous and Oligocene-Miocene) enable deposition of polymetallic syngenetic/epigenetic sulfide deposits; in contrast, during tectonically less active periods, the ore genesis appear to be clearly restricted. Mineralogy, sulfur isotopes, abundant sulfosalts and minor element abundances (Ag, Hg, Cd, Bi) point to important remobilization and repetitive mineralization stages the latest of which postdated the Alpine orogeny. The origin of Upper Cretaceous mineralizations hosted in local black shales, is thought to be found in metals brought up from deep-seated, eventually endogenic hydrothermal fluids. These deposits may later act as a transition base metal source for Tertiary deposits, during and after the Alpine tectogenesis, along with the new-additions of metals from presumably endogenic sources. Even though admixtures of diagenetic connat fluids somehow hampered geochemical information, it is concluded that ore deposits from Northern Tunisia are mixed-type and closely related to paleogeographic environments and tectonical history of the region. The previous prominent role of Triassic salt diapirism as a metallogenic factor is discussed but not confirmed.