排序方式： 共有21条查询结果，搜索用时 15 毫秒
11.
Amel Chakroun Dalila Zaghbib-Turki Mohamed Moncef Turki 《Arabian Journal of Geosciences》2016,9(4):327
Detailed observation of the Upper Pleistocene deposits of Rafraf (Bizerte, Northeastern Tunisia) provides new data about the significant variations in facies, thickness, and faunal assemblages. This work reports, for the first time, the occurrence of a Persististrombus latus level in the Rafraf sea coast. Facies analyses added to the recorded sedimentary features were carried in order to recognize stratigraphy, paleontology, and sea level highstands. They revealed complex succession of various Upper Pleistocene environments ranging from coastal dunes to inner platforms with scatter builds by Vermetus triquetrus and P. latus. The marine Upper Pleistocene deposits rich in the Senegalese fauna P. latus draw scale steps outcropping at diverse altitudes varying between 1 and 14 m. Serial sections along the border of the Rafraf beach show the action of many faults trending EW and NW-SE. Even though these faults got low values of vertical throw, their cumulative throw values led to these different altitudes of strata containing P. latus. These altitude variations are mainly the result of the inherited geomorphology, the environmental distribution, the sea level fluctuations and the tectonic activities. 相似文献
12.
A numerical investigation of the desaturation process at the argillaceous Tournemire site has been carried out. This desaturation
is initialized by the contact of the saturated rock with the ambient air in excavated openings. The used hydraulical model
is based on the Richards’ approximation for unsaturated one phase flow coupled with the deformation of a porous medium with
anisotropic linearly elastic behavior. In relation to the extent of the desaturated zone around an excavated opening, the
intrinsic permeability and the relative permeability have been identified to be the most important model parameters. The mechanical
deformation process itself, the seasonal influences and the tunnel lining are less important for the formation of the desaturated
zone. The comparison with measured saturation values bares some difficulties but indicates the principle capacity of the applied
finite element codes to simulate the desaturation process. The consideration of seasonal changes in humidity in the ambient
air results in a constantly recurring desaturation–resaturation cycle in the near field of the openings. This seasonally influenced
zone amount 1–2 m and is nearly independent from time and from a variation of model parameters within a reasonable range.
The possibility of material weakening in this zone is of special interest, since claystone is a potential host rock for the
disposal of radioactive waste. 相似文献
13.
Mohamed SOUA Dalila ZAGHBIB-TURKI Hela BEN JEMIA Jalel SMAOUI Amel BOUKADI 《《地质学报》英文版》2011,85(6):1310-1335
In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian–Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo-environmental relevant indicators. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions. 相似文献
14.
Bourhane-Eddine Belabed Xavier Laffray Amel Dhib Mouna Fertouna-Belakhal Souad Turki Lotfi Aleya 《Marine pollution bulletin》2013
This paper presents the results of a seasonal survey of heavy metals accumulated in sediments and in the soft parts of the body of the mussel Perna perna at four stations in the Gulf of Annaba (Algeria). Pooled soft tissues from 10 mussels representing the entire range of sizes were digested in nitric acid. Statistical analysis reveals a significant seasonal effect on all the measured metals, the highest values being recorded in winter. With the exception of Cr, the levels for all metals were significantly higher in the east, at the outlet of the Seybouse River, than at all other monitoring stations. The study also shows that north-western waters are subject to a significantly lower degree of heavy metal pollution than elsewhere in the gulf. Levels were nevertheless within the limits of public health standards. 相似文献
15.
Résumé La variabilité du climat, une gestion non optimale de la ressource en eau et l'intensification des activités anthropiques pourraient être les trois facteurs majeurs menaçant les écoulements et l'état de la ressource en eau dans les sous-bassins algériens. C'est le cas du bassin de la Tafna dans la partie occidentale de l'Algérie. Ce bassin est situé dans une région au climat semi-aride. Outre l'influence des précipitations, nous examinerons dans cet article la contribution possible d'autres facteurs (géologiques, topographiques et anthropiques) à la variabilité des écoulements dans le bassin de la Tafna. Pour cela, en plus de l'analyse du régime pluviométrique et des débits, nous avons choisi d'analyser le baseflow index ou BFI et les débits de base. Cinq sous-bassins de la Tafna, où des données journalières de pluie et de débit étaient disponibles sur la période 1976–2006 ont été étudiés. L'analyse, qui a distingué deux sous-régions déterminées par la topographie: les bassins d'altitude et ceux de plaine, montre que, selon leur contexte géologique, les sous-bassins ont des comportements différents en terme d'écoulement. Les zones en altitude présentant un écoulement de base et un BFI plus importants que les bassins de plaine. Ceci peut être relié à la nature lithologique des formations, les bassins d'altitude présentant une composante karstique importante. Les analyses de tendance/rupture sur les précipitations annuelles ne montrent aucune tendance significative sur la période 1976–2006. On note une baisse des débits moyens annuels uniquement sur deux stations en altitude (significatives aux seuils 1 et 10% respectivement). Une tendance à une diminution significative des débits de base est obtenue sur deux bassins d'altitude et un bassin de plaine (au seuil 1 ou 5%). La baisse du BFI est significative au seuil 1% pour seulement une station d'altitude. Ceci serait le signe d'une baisse du stock dans les bassins d'altitude. La modification des écoulements de base sur certains sous-bassins de la Tafna serait donc imputable à des causes, notamment de nature anthropique, ne relevant pas d'une diminution de la pluviométrie. Editeur Z.W. Kundzewicz; Editeur associé M. Lang Citation Bakreti, A., Braud, I., Leblois, E., et Benali, A. 2013. Analyse conjointe des régimes pluviométriques et hydrologiques dans le bassin de la Tafna (Algérie Occidentale). Hydrological Sciences Journal, 58 (1), 1–19. 相似文献
16.
17.
Abdennour Mohamed Amine Douaoui Abdelkader Barrena Jesús Pulido Manuel Bradaï Abdelhamid Bennacer Amel Piccini Chiara Alfonso-Torreño Alberto 《中国地球化学学报》2021,40(2):234-250
Acta Geochimica - The agriculture in Biskra, southeastern Algeria, is based on traditional practices and characterized by small irrigated fields. In the last decades, the increasing demand in water... 相似文献
18.
Benali Amel Peresan Antonella Varini Elisa Talbi Abdelhak 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(6):775-791
Stochastic Environmental Research and Risk Assessment - An adequate characterization of the temporal features of background seismicity, namely after removal of temporally and spatially clustered... 相似文献
19.
The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for
the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique
opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough
characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted
from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the
EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations
of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase,
followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means
of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the
calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted
unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could
not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model,
the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the
EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of
the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the
numerous seasonal variations cycles and the resulting shrinkage. 相似文献
20.
Mara R. Diaz Peter K. Swart Gregor P. Eberli Amanda M. Oehlert Quinn Devlin Amel Saeid Mark A. Altabet 《Sedimentology》2015,62(7):2090-2112
Ooid formation remains elusive despite their importance as palaeoclimatic indicators and important contributors to global carbonate budget. Based on stable isotopes, nutrient and elemental analyses on solid components and ooidal leachates, this study supports the notion of microbial involvement in the development of ooids from Great Bahama Bank. Carbon and nitrogen isotopic analyses on organic fractions identified geochemical signatures of microbial activity. The δ13C values for organic carbon in the bulk (?11·9 to ?16·9‰); intercrystalline/intracrystalline (?11·9 to 16·7‰); and intracrystalline phases (?12·4 to ?17·7‰) were similar and, except for the more enriched values of ooids from Butterfly Beach, were within the range of photosynthesisers. The δ15N values for the bulk (+0·5 to ?0·2‰); intercrystalline/intracrystalline (?0·3‰ to ?0·7‰) and intracrystalline organic matter (?0·3 to ?1·7‰) showed a narrow range consistent with nitrogen fixation. While positive δ15N and δ18O values of the leached from the ooids provided evidence of denitrification, the carbonate associated sulphate δ34SCAS of the bulk sediments (+19·2 to +19·6‰) and δ34S of the leachates (+16·6 to +18·3‰) provided weak indication of sulphate reduction, suggesting either that high concentrations of isotopically enriched S are overriding bio‐signatures of sulphate reduction or that microbes are preferentially using as an electron acceptor. In contrast, the elevated sulphate concentrations of the leachates suggest the occurrence of microbial sulphide oxidation within ooids. The high Mg/Ca of the leachates and scanning electron microscope analyses provide putative evidence of amorphous calcium carbonate and a formative role in CaCO3 precipitation. Together, these findings indicate that a redox dependent microbial consortium may influence CaCO3 precipitation in the form of ooid accretion, cementation and micritization. It is also inferred that ooid deposits are not suitable indicators of palaeoclimate because ooids are affected throughout their life by a complex chain of abiotic and biological processes which can lead to large geochemical offsets. 相似文献