Sciences De La Terre Et De L'Univers

... D'après Brunet-Moret et al " la surface d'évaporation créée par une telle cuvette suffisait largement pour absorber les débits provenant des ... l'accumula-tion des dépôts du Continental terminal sur le Timétrine et la région de Gao est interprétée par • Jacques QUENSIÈRE (3 ...

... Structural and volcanic geomorphology of the Tibesti Mountains The Tibesti Mountains have a surface area of approxi-mately 100.000 sqkm and are composed of ... Their main eruption centres are the Toon and Yega calderas, measuring 9x11 and 17x11 km respectively. ...

Lithostratigraphic, palaeoenvironmental and palaeogeographic evolution of the Ben-Zireg flysch (Lower
Visean, Algeria).
The anticlinal structure of Ben-Zireg is located in the marginal zone of Sahara, near the Algerian-
Moroccan border. It represents a key region situated between the Mesetian domain in the North and
the Anti-Atlas-Ougarta field in the South. In this area, the sedimentological and geodynamic aspects
of the Carboniferous series have been little studied in the previous studies. The present work is mainly
field-based and focuses on stratigraphic and facies analysis in order to characterize the depositional environments
and palaeogeography of the “flysch de Ben-Zireg” formation assigned to the lower Visean.
Based on lithologic and sedimentologic characteristics, we can subdivide the “flysch de Ben-Zireg”
formation into four informal units. From the base to the top they are: 1) the “pre-flyschoïde” unit is
well developed at the Oued “des trois palmiers” section. It is composed of whitish pelites commonly
contains small bivalves and fishes, followed by an alternation of green pelites with sandstones and bioclastic
limestones containing transported mollusc shells. The sandstone beds show massive bedding,
parallel lamination and small-hummocky cross-stratification; 2) the “wildflysch” unit shows differences
in characters and thickness from one locality to another. It is dominated by slumped green pelites
including metric to plurimetric olistoliths, debris-flows, and turbidite sandstone and conglomerate
intercalations. The age of the exotic elements ranges from Ordovician to Lower Carboniferous (Tournaisian);
3) the “flyschoïde” unit can be traced from east to west of the northern side of the anticlinal
structure of Ben-Zireg. It consists mainly of regular alternation between green pelites and light brown
turbidite sandstone beds, showing high sand/pelite ratio. Individual sandstone beds are tabular, laterally
continuous and often a sharp planar or smooth irregular erosive base. Synsedimentary deformations
(slumps), thin pebbly levels, flute-, groove and load-casts occur locally. The main characteristic of the
sandstone beds is the occurrence of the Bouma (1962) divisions, with normal graded bedding, parallel
lamination, convolute bedding, water-escape structures and current ripples. Trace fossils are rare.
Hectometric olistoliths of eifelian reef and cambrian-ordovician sandstones are also intercalated in the
middle part of the “flyschoïde” unit; and 4) the “post-flyschoïde” unit represent the uppermost part of
the studied succession. It is composed of an alternation of green pelites with sandstone, conglomerate,
bioclastic limestone and calcareous sandstone beds.
Facies analysis is the main tool for interpreting the environmental setting of the lower Visean deposits
outcropping in the Ben-Zireg area. Based on field observations such as lithology, texture, grain
size, sedimentary structures, fossil content and boundary features of beds, nine facies types have been
recognized, described and interpreted in terms of depositional environment. The vertical and lateral
distribution of the facies types F1-9 revealed four distinct facies associations, AFA to AFA, that reflect
different environmental settings: The AFA is restricted to the lowermost (“pre-flyschoïde”) and uppermost
(“post-flyschoïde”) parts of the lower Visean succession.” It is interpreted as a marine offshore to
shoreface, storm-wave influenced deposits; The AFB represents the lower portion of the “wildflysch” unit.
It consists of a thick slumped pelites including several debris flows levels and olistoliths from previous
formations, conglomeratic channels and turbidite sandstone beds. This disorganized facies association
is the result of tectonic instability and mass-transport processes (slumps and debris flows) at the non
channelized base of slope apron with sheet turbidite; The AFC represents the middle part of the “wildflysch”
unit. It includes channelized conglomerate beds and turbidite sandstones in alternation with
green pelites containing olistoliths of different sizes. These sedimentary facies form thinning-upward
and fining-upward cycles of some meter-thick, interpreted as mid-fan channel-fill and channel-fringe
deposits. The AFD coincides with the deposition of the “flyschoïde” unit. It is characterized by monotonous
alternations of sharp-based turbidite sandstones and interbedded pelites. These alternations
are organized in metric thinning-upward sequences of a great lateral continuity and high sand/pelite
ratio. They can be referred to lobe-fan fringe environments. The marker chaotic level (eifelian and
cambrian-ordovician olistoliths) is interpreted as the product of destabilization of the inner foredeep
slope sediments, probably in relation to the tectonic thrust, or the decreasing sea-level.

AbstractThis paper presents the hazard mapping of groundwater in the Tlemcen urban area (TUA). First, we identified the potential pollution sources (of industrial, agricultural and urban origins) existing in the studied area that can affect the karstic groundwater. It is the most important reserve and the main source of drinking water supply of this area. Then, we mapped all these hazards on a topographic map at scale 1:25,000. Finally, a classified hazard map was established. This investigation clearly shows that the groundwater of TUA is far from being safe from the risk of pollution. Adequate and urgent actions must be taken in order to eliminate or to reduce the risks of contamination of this water resource which is highly vulnerable because of the lack of protection perimeters.

The adsorption of lead onto date palm fibers (palm fibers) and leaf base of palm (petiole) has been examined in aqueous solution by considering the influence of various parameters such as contact time, solution pH, adsorbent dosage, particle sizes, ionic strength, and temperature. The adsorption of Pb(II) increased with an increase of contact time. The optimal range of pH for Pb(II) adsorption is 3.0–4.5. The linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both models fitted well. The monolayer adsorption capacity of Pb(II) on palm fibers and petiole was found as 18.622 and 20.040 mg/g, respectively, at pH 4.5 and 25°C. Dubinin-Radushkevich (D-R) isotherm model was also applied to equilibrium data. The mean free energy of adsorption (2.397 and 4.082 kJ/mol) onto palm fibers and petiole, respectively, may be carried out via physisorption mechanism. Pseudo-first-order rate equation and pseudo-second-order rate equation were applied to study the adsorption kinetics. In comparison to first-order kinetic model, pseudo-second-order model described well the adsorption kinetics of Pb(II) onto palm fibers and petiole from aqueous solution. From the results of the thermodynamic analysis, Gibbs free energy ΔG, enthalpy change ΔH, and entropy ΔS were determined. The positive value of ΔH suggests that interaction of Pb(II) adsorbed by palm fibers is endothermic. In contrast, the negative value of ΔH indicates that interaction of Pb(II) ions by petiole is exothermic. The negative value of ΔG indicates that the adsorption of Pb(II) ions on both palm fibers and petiole is a spontaneous process.

Background, Aim and Scope Humic acids (HAs) are the most important humified component of dissolved organic carbon (DOC) present in sewage water used for irrigation. It is well known that HAs affect the toxicity and availability of heavy metals (HMs) in soil-plant systems, and may increase the human exposure to HMs in contaminated soil through plant uptake. This study was conducted to assess the effects of HAs on HM availability, plant growth and HM uptake. Materials and Methods: With wheat (Triticum aestivum) as a test plant, a greenhouse pot experiment was conducted to investigate the effects of HAs in irrigation water on the phytoavailability of cadmium (Cd) and lead (Pb) in soil. Cd and Pb were added to the soil at concentrations of 1.5 and 150 mg/kg, respectively. Wheat seedlings grown in Cd and Pb-contaminated soil were watered with 4 levels of HA solution (0, 140, 280 and 560 mg/kg of HAs, respectively). Results: In control and Pb treatments, both plant biomass and plant HM concentrations increased with increasing concentrations of HAs in the solution. Plant biomass was markedly decreased when metal concentrations in plants increased, particularly in Cd and Cd/Pb treatments. In the soil, extractable metals, and water soluble organic carbon (WSOC) and its fractions significantly increased with increasing HA concentrations. Discussion: The results suggested that the application of HAs in barren soils may improve plant nutrition by mobilizing soil nutrients and providing plants with carbon sources. On the other hand, HAs present in sewage water may increase both the availability and transfer of HMs in the soil-plant continuum and subsequently increase human exposure to HMs in polluted soil. Conclusions. Conclusions: HA solution as irrigation water significantly increased HM availability to plants cultivated in the HM-amended soil and may increase the environmental risk of sewage irrigation. Recommendations and Perspectives: These results suggested that, when assessing the effect of sewage irrigation on soil quality, HAs contained in sewage water should be taken into consideration.