Sequence stratigraphy and cyclicity in the Middle Eocene of the Fayoum ranges,Western Desert,Egypt: Implications for regional sea level changes     

Mohamed S. Abu El Ghar 《Marine and Petroleum Geology》2012,29(1):276-292

The Middle Eocene deposits in the Fayoum Ranges are composed of complex alternative clastic (claystone and sandstone) and carbonate (limestone and dolostone) facies and dominated carbonate (limestone) facies. Facies are arranged mainly in regression and shallowing upward (emergence) cycles and sequences. Field stratigraphic and microfacies analysis of the study area permits recognition of four major sequences, reflecting 3rd-order cycles. Depositional sequences and cycles are bounded by subaerial erosive surfaces or caliche deposits, ferruginous crust, and by their correlative conformities. Sequence-1 consists of two shallowing-upward cycles (dominate carbonate facies), each of which starts with nummulitic wackestone, capped with nummulitic packstone including Globigerinatheka subconglobata subconglobata biozone. These cycles were deposited under tropical to subtropical conditions as evidenced by the carbonate nature of the rocks and the abundance of nummulites, which need warm conditions for their flourishing. Sequence-2 consists of four emergence cycles based with claystone and capped with wackestone including Morozovella lehneri biozone. The duration (Ma) of sequence-2 (Morozovella lehneri zone) is 3.05 Ma (44.25 Ma for the upper of TA3 3.3 to 41.2 Ma for the lower of TA3 3.5). Sequence-3 includes three rock units (includes Trucorotaloides rohri biozone). The lower unit involves lowstand systems tract, the middle unit contains transgressive systems tract and the upper rock unit includes highstand systems tract. The lowstand systems tract consists of emergence cycles of mixed clastic- carbonate facies, clays at the base and capped with wackestone and packstone facies. The transgressive systems tract consists of dominant carbonate facies, wackestone at the base and capped with packstone facies. Sequence 4 involves transgressive systems tract. The duration of both sequence-3 and sequence 4 has been estimated as 1.8 Ma.  相似文献   

Trends in rainfall and runoff in the Blue Nile Basin: 1964–2003     

Zelalem K. Tesemma  Yasir A. Mohamed  Tammo S. Steenhuis 《水文研究》2010,24(25):3747-3758

Most of the water from the Nile originates in Ethiopia but there is no agreement on how land degradation or climate change affects the future flow in downstream countries. The objective of this paper is to improve the understanding of future conditions by analysing historical trends. During the period 1964–2003, the average monthly basin‐wide precipitation and monthly discharge data were collected and analysed statistically for two stations in the upper 30% of the Blue Nile Basin and monthly and 10‐day discharge data of one station at the Sudan–Ethiopia border. A rainfall–runoff model examined the causes for observed trends. The results show that, while there was no significant trend in the seasonal and annual basin‐wide average rainfall, significant increases in discharge during the long rainy season (June to September) were observed at all three stations. In the upper Blue Nile, the short rainy season flow (March to May) increased, while the dry season flow (October to February) stayed the same. At the Sudan border, the dry season flow decreased significantly with no change in the short rainy season flow. The difference in response was likely due to the construction of weir in the 1990s at the Lake Tana outlet that affected the upper Blue Nile discharge significantly but affected less than 10% of the discharge at the Sudan border. The rainfall–runoff model reproduced the observed trends, assuming that an additional 10% of the hillsides were eroded in the 40‐year time span and generated overland flow instead of interflow and base flow. Models concerning future trends in the Nile cannot assume that the landscape runoff processes will remain static. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Mineralogical Characteristics of the Separated Magnetic Rutile of the Egyptian Black Sands     

Mohamed I. Moustafa 《Resource Geology》2010,60(3):300-312

The Egyptian black sands contain several economic minerals, such as ilmenite, magnetite, garnet, zircon, rutile and monazite. During the concentration and separation of a high-grade rutile concentrate a bulk magnetic fraction is obtained. This fraction is composed mainly of opaques, titanhematite, ilmenite–titanhematite exsolved intergrown grains, magnetic leucoxene in addition to chromite, and magnetic rutile. The magnetic rutile occupies 6 wt.% of the bulk magnetic fraction or approx. 4 wt.% of the original rutile content in the raw sands. Most of magnetic rutile crystals are contaminated with opaque inclusions, staining-coating and/or composite locked grains. This magnetic rutile has a magnetic range from strongly paramagnetic to very weak paramagnetic. Electron microprobe analysis for twenty-three magnetic rutile grains identified mineral components of rutile, titanhematite, pseudorutile, leached pseudorutile and ilmenite in decreasing order of abundance. Some other inclusions are also detected in the different magnetic rutile grains. They are most probably garnet, silica, amphibole, ilmenite, feldspar, mica and zircon. The presence of these inclusions reflect the derivation of magnetic rutile of various crystalline igneous and metamorphic rocks. The magnetic susceptibility of magnetic rutile depends on the associated mineral components and their relative volumes in comparison to the rutile mineral component. Magnetic susceptibility of magnetic rutile is also related to both type and size of the associated mineral inclusions. The average chemical composition of the magnetic rutile is 66.34 wt.% TiO₂, 21.71 wt.% Fe₂O₃, 6.39 wt.% SiO₂, 1.80 wt.% Al₂O₃, 1.19 wt.% CaO and 0.10 wt.% Cr₂O₃. Thus, the contamination of magnetic rutile in the non-magnetic rutile concentrate would decrease the market value of the rutile concentrate. Alternatively these magnetic rutile grains are recommended to be blended with magnetic leucoxene or some types of ilmenite concentrate to improve the overall marketable specifications especially for both of Ti, Fe and Cr contents.  相似文献   

The palaeogeographic position of Central Iberia in Gondwana during the Ordovician: evidence from zircon chronology and Nd isotopes     

Fernando Bea  Pilar Montero  Cristina Talavera  Mohamed Abu Anbar  Jane H. Scarrow  José F. Molina  Juan A. Moreno 《地学学报》2010,22(5):341-346

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Seismic stratigraphy of the NW Moroccan Atlantic continental shelf and Quaternary deformation at the offshore termination of the southern Rif front     

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   

Porosity and mineralogy evolution during the decay process involved in the Chellah monument stones     

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   

Contamination of superficial sediments by heavy metals and iron in the Bizerte lagoon,northern Tunisia     

Amor Ben Garali  Mohamed Ouakad  Moncef Gueddari 《Arabian Journal of Geosciences》2010,3(3):295-306

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   

Effect of sulphates and curing period on stress–strain curves and failure modes of soil–lime–natural pozzolana mixtures     

Hamid Gadouri  Khelifa Harichane  Mohamed Ghrici 《Marine Georesources & Geotechnology》2013,31(9):1130-1148

Abstract

An 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   

Book reviews     

Barry Floyd  William J. Torry  Mohamed A. Mohamed Salih  P. P. Karan  Wolf Tietze  Nikolaos Zahariadis  Torsten Malmberg 《GeoJournal》1987,14(1):137-140

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Population growth and food supply margin in Pakistan     

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