Is there a hidden near surface salt diapir in the Guelma Basin,north-east of Algeria?

The diapiric province of north-eastern Algeria and Tunisia extends NE–SW over several hundreds of kilometres. Available, geophysical and geological investigations were focused on the study of known diapiric outcrop. In contrast to the existing work, our study is focused on to identify a new hidden near surface salt diapir in the Guelma Basin, north-east of Algeria.Integrated geophysical study comprising aeromagnetic, gravimetric and DC resistivity data calibrated with existing well information provides new insights into the geometry of the geologic structure of Guelma Basin. Spatial correlation between magnetic low, strong gravity minimum and resistivity high reveal a hidden near surface salt diapir. The Guelma salt diapir is topped by a local topographic high which follows exactly the underlying salt body. Joint gravity-magnetic modelling indicates that salt is deeply rooted and has a dome-like shape. The Guelma salt diapir was triggered by normal faulting and is directly controlled by regional extension.     

Gravity and magnetotelluric investigations to elicit the origin of Hammam Faraun hot spring,Sinai Peninsula,Egypt

There is a clear correlation between the principal areas of current geothermal development and the seismically active boundaries of the moving segments of lithosphere defined by the plate tectonic models of the Earth. The tectonic position of Egypt in the northeastern corner of African continent suggests that the most important areas for geothermal exploration are in the region where a cluster of hot springs with varied temperatures was located around the Gulf of Suez. Gravity and magnetotelluric surveys were made in the area of Hammam Faraun hot spring, which represents the most promising area for geothermal development in Egypt. These surveys were carried out for the purpose of eliciting the origin of Hammam Faraun hot spring. The results of the analyses and interpretations of these data show that the heat source of the hot spring is due to uplift of hot basement rock. This uplift may cause deep circulation and heating of the undergroundwater.     

Induction of tributyltin-binding protein type 2 in Japanese flounder, Paralichthys olivaceus, by exposure to tributyltin-d27

In this study, individual Japanese flounder were intraperitoneally injected with 2 μg tributyltin-d27 (TBT-d27) fish⁻¹. Blood samples were collected on day 7 after injection. TBT-binding protein types 1 and 2 (TBT-bp1, -bp2) in the blood serum were quantified by western blotting analysis. As a result, the concentration of TBT-bp2 in TBT-d27 treated group increased to 220% of that in the solvent control, whereas the TBT-bp1 concentration decreased to 65% of that in the solvent control. Additionally, a positive relationship between the concentrations of TBT-bp2 and TBT was observed in blood sera of wild and cultured flounder. We suggest that TBT-bp2 is produced in response to TBT exposure and may play an important role in fish physiology.     

Modalités de recharge d’un aquifère en zone semi-aride : cas de la nappe du Trarza (Sud-Ouest Mauritanie)

Résumé

L’aquifère du Trarza s’étend sur environ 40 000 km² dans le Sud-Ouest mauritanien, entre le fleuve Sénégal au Sud, l’Océan Atlantique à l’Ouest et la chaîne métamorphique des Mauritanides au Nord et à l’Est. La nappe libre est contenue dans les sédiments du Continental Terminal et du Quaternaire. Les campagnes de terrain menées entre 2010 et 2012 ont significativement complété les quelques mesures anciennes. Le croisement d’approches hydrodynamiques et géochimiques a montré que, dans cette zone semi-aride, la dynamique de la nappe est influencée par les multiples changements, actuels et anciens, de l’environnement (depuis les transgressions quaternaires jusqu’aux différents barrages régulant le cours du fleuve Sénégal). La nappe est principalement alimentée par l’infiltration latérale des eaux de surface du fleuve Sénégal et, dans une moindre proportion, par les précipitations. La minéralisation des eaux souterraines résulte d’interactions eau-roches et minéraux silicatés et alumino-silicatés et est localement influencée par des traces des transgressions quaternaires. L’évaporation marque fortement les eaux de surface avant et durant leur infiltration. Des calculs encore très préliminaires suggèrent une recharge annuelle inférieure ou égale à 5% des précipitations, soit de 5 à 10 mm.

Editeur Z.W. Kundzewicz

Citation Mohamed, A.-S., Marlin, C., Leduc, C., et Jiddou, M., 2014. Modalités de recharge d’un aquifère en zone semi-aride: cas de la nappe du Trarza (Sud-Ouest Mauritanie). Hydrological Sciences Journal, 59 (5), 1046–1062.     

Numerical estimation of carbonate rock properties using multiscale images

Characterizing the pore space of rock samples using three‐dimensional (3D) X‐ray computed tomography images is a crucial step in digital rock physics. Indeed, the quality of the pore network extracted has a high impact on the prediction of rock properties such as porosity, permeability and elastic moduli. In carbonate rocks, it is usually very difficult to find a single image resolution which fully captures the sample pore network because of the heterogeneities existing at different scales. Hence, to overcome this limitation a multiscale analysis of the pore space may be needed. In this paper, we present a method to estimate porosity and elastic properties of clean carbonate (without clay content) samples from 3D X‐ray microtomography images at multiple resolutions. We perform a three‐phase segmentation to separate grains, pores and unresolved porous phase using 19 μm resolution images of each core plug. Then, we use images with higher resolution (between 0.3 and 2 μm) of microplugs extracted from the core plug samples. These subsets of images are assumed to be representative of the unresolved phase. We estimate the porosity and elastic properties of each sample by extrapolating the microplug properties to the whole unresolved phase. In addition, we compute the absolute permeability using the lattice Boltzmann method on the microplug images due to the low resolution of the core plug images. In order to validate the results of the numerical simulations, we compare our results with available laboratory measurements at the core plug scale. Porosity average simulations for the eight samples agree within 13%. Permeability numerical predictions provide realistic values in the range of experimental data but with a higher relative error. Finally, elastic moduli show the highest disagreements, with simulation error values exceeding 150% for three samples.     

Characterization and Application of Dried Plants to Remove Heavy Metals,Nitrate, and Phosphate Ions from Industrial Wastewaters

Low cost adsorbents were prepared from dried plants for the removal of heavy metals, nitrate, and phosphate ions from industrial wastewaters. The efficiency of these adsorbents was investigated using batch adsorption technique at room temperature. The dried plant particles were characterized by N₂ at 77 K adsorption, scanning electron microscopy, energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy, and phytochemical screening. The adsorption experiments showed that the microparticles of the dried plants presented a good adsorption of heavy metals, phosphate, and nitrate ions from real wastewaters. This adsorption increased with increasing contact time. The equilibrium time was found to be 30 min for heavy metals and nitrate ions and 240 min for phosphate ions. After the adsorption process, the Pb(II) concentrations, as well as those of Cd(II), Cu(II), and Zn(II) were below the European drinking water norms concentrations. The percentage removal of heavy metals, nitrates, and phosphates from industrial wastewaters by dried plants was ～94% for Cd²⁺, ～92% for Cu²⁺, ～99% for Pb²⁺, ～97% for Zn²⁺, ～100% for ${\rm NO}_{{\rm 3}}^{{-} } $ and ～77% for ${\rm PO}_{{\rm 4}}^{3{-} } $ ions. It is proved that dried plants can be one alternative source for low cost absorbents to remove heavy metals, nitrate, and phosphate ions from municipal and industrial wastewaters.     

Influence of Degree of Saturation in the Electric Resistivity–Hydraulic Conductivity Relationship

The relationship between aquifer hydraulic conductivity and aquifer resistivity, either measured on the ground surface by vertical electrical sounding (VES) or from resistivity logs, or measured in core samples have been published for different types of aquifers in different locations. Generally, these relationships are empirical and semi-empirical, and confined in few locations. This relation has a positive correlation in some studies and negative in others. So far, there is no potentially physical law controlling this relation, which is not completely understood. Electric current follows the path of least resistance, as does water. Within and around pores, the model of conduction of electricity is ionic and thus the resistivity of the medium is controlled more by porosity and water conductivity than by the resistivity of the rock matrix. Thus, at the pore level, the electrical path is similar to the hydraulic path and the resistivity should reflect hydraulic conductivity. We tried in this paper to study the effect of degree of groundwater saturation in the relation between hydraulic conductivity and bulk resistivity via a simple numerical analysis of Archie’s second law and a simplified Kozeny-Carmen equation. The study reached three characteristic non-linear relations between hydraulic conductivity and resistivity depending on the degree of saturation. These relations are: (1) An inverse power relation in fully saturated aquifers and when porosity equals water saturation, (2) An inverse polynomial relation in unsaturated aquifers, when water saturation is higher than 50%, higher than porosity, and (3) A direct polynomial relation in poorly saturated aquifers, when water saturation is lower than 50%, lower than porosity. These results are supported by some field scale relationships.     

Lithospheric extension and the opening of the Red Sea: sediment-basalt relationships in Yemen*

This paper analyses new field and radiometric age data on the timing of extension, sedimentation and magmatism related to the opening of the Red Sea. The first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine Tawilah Formation of Cretaceous to early Tertiary age. The first indication of magmatism is the eruption of alkaline basalts (43.5–21.2 Ma) on to marine and non-marine sandstones of lower to middle Tertiary age. The lack of an angular unconformity at the sediment-basalt contact, over a period of 25 Myr, corroborates a diachronous relationship between the Tawilah sandstones and the Yemen Volcanics. These data also indicate that the onset of volcanism in Yemen was in the Eocene, as is the case in Ethiopia and Saudi Arabia. A passive rifting model is supported by early extension and sedimentation followed by syn- and post-tectonic magmatism.     

Changing roles controlling alternating marine and aeolian deposition and formation of Quaternary sequences in Hergla coastal escarpment (north-eastern Tunisia)

This work is meant to set a new stratigraphic framework of the Quaternary Hergla Sea Cliff deposits in eastern Tunisia including vital precisions concerning depositional environments and climatic conditions. Infrared stimulated luminescence (IRSL) data previously obtained at the Hergla region show that the Khniss unit is Tyrrhenian in age (MIS 5.5), while the Rejiche unit dates to the MIS 5.3/5.1 undifferentiated by the IRSL for the marine deposits and attributed to the MIS 4 for the dunes continental deposits. The sedimentological studies showed that the whole of the marine units of the Upper Pleistocene of Hergla were deposited in a shallow marine environment and also highlighted at least two major transgressive cycles interrupted by drops of the sea level leading to emergence. The first cycle corresponds to the Khniss unit deposit. The second cycle corresponds to the transgression of the Rejiche unit. The end of the MIS 5.5 is marked by a lagoonal sedimentation with a regressive tendency followed by an emergence period materialized by the presence of a paleosol. During the MIS 5.3/5.1, the marine deposits of the Rejiche unit correspond to infratidal carbonate sediments subjected to storms currents. They are characterized by the reworking of lithoclasts, due to the action of the storm currents. Eventually, the study of cements in the continental deposits of the Rejiche unit indicates a late evolution in a continental vadose environment, subjected to the action of meteoric waters. In terms of climatic conditions, the MIS 5.5 was hotter and wetter than the subsequent MIS 5.3/5.1.