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961.
962.
Nissrine Maad Pascal Le Roy Mohamed Sahabi Marc-André Gutscher M. Hssain Nathalie Babonneau Marina Rabineau Brigitte Van Vliet Lanoë 《Comptes Rendus Geoscience》2010,342(9):731-740
A recent high resolution seismic survey was carried out along the North-West Moroccan Atlantic continental shelf to perform sequence stratigraphy and to better understand the link between the onshore observations across the western termination of the Rif front and the multibeam bathymetric data previously collected across the Gulf of Cadiz. Seismic interpretation clearly shows evidence of deformation affecting the Pleistocene sedimentary cover. This is mainly located between the Lalla Zahra ridge and the Neogene nappes that outcrop at the seabed to the North of Larache, where the identified structures bound the upper part of a gravitationally spreading lobe and are interpreted to be developed by activation of the major tectonic structures located at the southern front of the Rif Cordillera. The offshore extension of the Lalla Zahra Ridge is characterised by an east-west trending major folded and faulted corridor. This structure marks the active front of Prerifan area and corresponds to a major Quaternary kinematic boundary in the western prolongation of the ENE-WSW trending Jebha fault. 相似文献
963.
Abderrahim Samaouali Larbi Laânab Mohamed Boukalouch Yves Geraud 《Environmental Earth Sciences》2010,59(6):1171-1181
The objective of this work is to study the decay process involved in the historical Roman Chellah located in the Rabat city
(Morocco). This monument is made up of porous calcarenite stone. Several samples, taken from altered and unaltered blocks,
were analyzed by the water saturation, the mercury intrusion porosimetry techniques and using the scanning electron microscopy
coupled to energy dispersive X-ray spectrometer (SEM–EDX). To perform a reliable chemical analysis, some samples were also
analyzed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The mercury porosimetry results show a bimodal
porous network for this porous material, the deterioration process of these stones involved an increase in porous volume of
about 2%. The lowest porosity observed in the unaltered block is connected to the presence of sparitic cement which causes
a partial inter-granular porosity clogging. The highest porosity of the deteriorated block without crust is due to the increase
in inter-granular space. SEM photographs of the unaltered sample show the presence of the porous primary grains, of ovoid
forms and millimeter-length sizes, and of the secondary grains, of rhombohedric forms and micro size. Porosity is essentially
located between the primary grains and can be completely clogged by secondary precipitations. Various forms of deterioration
are observed on the altered samples such as the dissolution of the secondary grains edges, wells of dissolution and also the
presence of argillaceous residues on the surface. This last was also detected by the ICP-AES and EDX analysis which show an
increase of the silicon and aluminum contents toward the surface. 相似文献
964.
According to the norms adopted by the National Network of observation of the marine life quality (RNO 1997) and US National Oceanic and Atmospheric Administration (US NOAA 1999), the superficial sediments of the Bizerte lagoon (northern Tunisia) show a contamination by nickel, which is the probable
consequence of the closeness to the industrial zone, and by lead, the result of detrital material rich in lead of the geological
lands of Jbel Kchabta and Jbel Messeftine. In the lagoon southern and eastern sectors, the contamination of superficial sediments
is essentially by copper, zinc, nickel and iron. This pollution is related, on one hand, to the rejections of the steelworks
El Fouledh and the military arsenal, and on the other hand, to Menzel Bourguiba waste disposal. The rest of the lagoon is
exempted from any metallic contamination of the surface sediments. The enriched zones in manganese and zinc correspond to
the higher contents in kaolinite and in smectite. Positive correlations were recorded between the percentage in fine fraction
on the one hand, and the sedimentary contents in TOC, total nitrogen and heavy metals on the other hand. The majority of the
analysed elements are “argilophilous” except zinc and manganese, which are clayey organophile. These results show that this
lagoon receives concentrations in anthropogenic metals that risk provoking more or less important disruptions, which are harmful
and irreversible on the fauna and flora of this lagoon and on the whole ecobiological equilibrium. 相似文献
965.
Hamid Gadouri Khelifa Harichane Mohamed Ghrici 《Marine Georesources & Geotechnology》2013,31(9):1130-1148
AbstractAn experimental investigation was undertaken in order to assess the effect of sodium (Na2SO4) and calcium (CaSO4·2H2O) sulphates and curing period on stress–strain curves and failure modes of grey (GS) and red (RS) clayey soils stabilised by lime (L), natural pozzolana (NP) and their combinations (L–NP). Several soil–L–NP mixtures were studied to be used as subgrade soils for road pavements. Stress–strain curves were obtained from unconfined compressive strength (UCS) test made on several soil–L–NP specimens after curing for 7 and 120 days. Tests results showed that the use of L or L–NP without sulphates produced a significant increase in peaks stress of both clayey soils and then modified their stress–strain curves from nonlinear to linear behaviour almost up to 70% of peak stress after a longer curing period. However, the presence of 2% Na2SO4 or any CaSO4·2H2O content provided beneficial effects on peaks stress and stress–strain curves of both stabilised clayey soils and then improved their linearity almost up to 95% of peak stress after curing for 120 days. In contrast, the presence of 6% Na2SO4 caused undesirable effects. In addition, both sulphates greatly affected the failure modes of soil–L–NP specimens, particularly at a later stage. 相似文献
966.
967.
Mohamed Ismail Siddiqi Dr. 《GeoJournal》1985,10(1):83-89
Conclusion Population growth in Pakistan is alarming. The long and continuing shortage of foodgrains at intervals and increasing competition for land use have resulted in deterioration in yield per hectare, and low reproduction of livestock, although hard struggle is going on for self sufficiency. The margin in food supply has arrived even in those areas where the production has been abundant, and vulnerable to crop failure and other emergency causes. Provision against these dangers call for the maintenance of adequate national reserves, which can be brought into action at an early stage of the emergency.The area under agriculture can be increased through improved programmes of soil conservation and development of barani (rain fed areas) with cost-benefit consideration. Several million hectares of barani areas have fertile soils and are suitable for agricultural development. It has been estimated that 45 billion m3 of river water flows into the Arabian Sea. A part of the water sources is properly harnessed and could possibly change the economic conditions of the barani region. A number of regions are covered by hard texture of the soil, mechanization will have to be introduced in these areas to increase production much beyond the level of margin. Soil conservation measures have already been initiated and in some cases demonstrated to farmers, but the reclaimed virgin lands up to 1973 were very little, just 46.5 ha of virgin lands and 72 ha of cultivated area from the Soan and Potwar uplands. It is expected that 300,000 ha of cultivated area, 10,000 ha of gullied land will be reclaimed through soil conservation methods in the current Fifth Year Plan.Pakistan has great water potential. The remedy lies in wise judicious and scientific water management. Inadequate natural and artificial drainage systems are causing water-logging and salinity. An accelerated programme for recovering lost land is already in operation. Many land reforms were introduced from time to time, but the production result is not of great significance. Restrictions were imposed on consolidated holdings. The economic level of such holding above subsistence have not yet been taken into consideration. It is, therefore, necessary, to make a thorough analysis of agricultural problems, particularly with the foodgrain crops, with reference to population growth, the efforts should continue till the food supply occupies the supreme position by increasing production and reducing the rate of population growth by adopting socio-economic methods. 相似文献
968.
The Pan-African basement exposed in the Meatiq area west of Quseir, Egypt, consists of an infracrustal basement overthrusted by a supracrustal cover. The infracrustal rocks were developed as a result of an old orogeny referred to as the Meatiqian orogeny where granite—gneiss, migmatitic gneisses and migmatized amphibolites were formed. The granite—gneiss represents a deformed granite pluton emplaced at 626±2 Ma, whereas the migmatitic gneisses and amphibolites are of mixed igneous and sedimentary parentage. In view of the data so far available, the nature of the Meatiqian orogeny could not be deciphered. In spite of the young isotopic ages, it is suggested that at least the metasedimentary gneisses represent older rocks in the stratigraphic sequence of the infracrustal basement.The supracrustal cover represents a part of an extensive ophiolitic mélange obducted onto the infracrustal basement during the next orogeny (Abu Ziran orogeny) which culminated at 613±2 Ma. An active continental margin-type regime can adequately explain the evolution of such a supracrustal cover. During obduction, the ophiolitic mélange and the upper 2 km thick part of the infracrustal basement were intensely deformed and metamorphosed under PT conditions of the greenschist—epidote amphibolite facies. The deformed infracrustal basement was converted into mylonitic—blastomylonitic rocks and schists composing five thrust sheets, and subsequently intruded by synkinematic granitoid sheets. Later, both the infracrustal basement and the overlying supracrustal cover were isostatically uplifted, subjected to complex shallow folding giving rise to the major Meatiq domal structure, and were intruded by a postkinematic adamellite pluton at 579±6 Ma. 相似文献
969.
Mohamed Adel Sharaf 《Earth, Moon, and Planets》1988,42(2):115-131
In this paper of the series, the literal analytical expressions for the Fourier expansion of the Earth's spherical harmonic potential will be explored in terms of the sectorial variables
j
(i)
introduced in Paper IV (Sharaf, 1982) to regularize the highly-oscillating perturbation force of some orbital systems.Now at the Department of Astronomy, King Abdulaziz University Jeddah, Saudi Arabia. 相似文献
970.
Mohamed Zerka Jean-Yves Cottin Michel Grégoire Jean-Pierre Lorand MHamed Megartsi Mohamed Midoun 《Comptes Rendus Geoscience》2002,334(6):387-394
Numerous ultramafic xenoliths occur within the A??n–Temouchent volcanic complex (Northwestern Oranie, Algeria). Most of them are type I mantle tectonites (lherzolites and harzburgites) and composite xenoliths (harzburgite/clinopyroxenite) are rare. Only a few samples of spinel lherzolites display relatively fertile compositions when the major part of type I xenoliths have refractory major element compositions but enriched LREE contents showing that they have been affected by mantle metasomatism. The composite xenoliths are witnesses of reactions of alkaline magmas with the upper mantle. An asthenospheric rising, in relation with the large strike slip fault affecting the North African plate margin at Trias time is proposed as a possible geodynamical setting. To cite this article: M. Zerka et al., C. R. Geoscience 334 (2002) 387–394. 相似文献