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91.
Martin Menzies Dan Bosence Hamed A. El-Nakha Salah Al-Khirbash Mohamed A. Al-Kadasi Abdulkarim Al Subbary 《地学学报》1990,2(4):340-350
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. 相似文献
92.
Alaa I. Ibrahim Hisham Anwer Mohamed H. Soliman Nicholas Mackie-Jones Kalvir S. Dhuga William C. Parke Jean H. Swank Tilan Ukwatta M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):535-539
A 6.4 keV emission line was discovered in an unusual burst from the soft gamma repeater SGR 1900+14 with the Rossi X-ray Timing
Explorer (RXTE). The line was detected in part of a complex multipeak precursor that preceded the unusual burst of 1998 August
29, i.e. two days after the giant flare of August 27 from the source. The origin of the line was not firmly identified and
two possible interpretations were equally plausible including (a) Kα fluorescence from a small iron rich material that was ejected to the magnetosphere during the August 27 flare, and (b) proton
or α-particle cyclotron resonance. If the iron scenario was correct, we expect to find evidence for the line during the intervening
interval between the flare and the August 29 burst, i.e. on August 28. Here we present the results of the August 28 burst
observation, taken with RXTE. We detect a total of seven bursts whose individual and joint spectra do not show evidence for
spectral lines. We also investigated a sample of nine bursts before and after the August 29 burst (from 1998 June to December)
that do not reveal evidence for a spectral line near 6.4 keV or elsewhere. These results disfavor the iron scenario and make
the proton/α-particle cyclotron resonance interpretation more plausible. The appearance of the emission line in part of a complex burst
and its absence from the studied sample indicate that the line is likely due to a transient phenomenon that may depend on
the burst morphology, energetics and the properties of the emission region.
相似文献
93.
Mohamed Ali Kalefa El-Ghali Sadoon Morad Howri Mansurbeg Miguel Angel Caja George Ajdanlijsky Neil Ogle Ihsan Al-Aasm Manhal Sirat 《Marine and Petroleum Geology》2009
Sequence stratigraphy of fluvial deposits is a controversial topic because changes in relative sea level will eventually have indirect impact on the spatial and temporal distribution of depositional facies. Changes in the relative sea level may influence the accommodation space in fluvial plains, and hence have impact on types of fluvial system, frequency of avulsion, and style of vertical and lateral accretion. This study aims to investigate whether depositional facies and changes in the fluvial system of the Lower Triassic Petrohan Terrigenous Group sandstones (NW Bulgaria) in response to changes in the relative sea level have an impact on the spatial and temporal distribution of diagenetic alterations. 相似文献
94.
Gamal M. El-Shabrawy Elena V. Anufriieva Mousa O. Germoush Mohamed E. Goher Nickolai V. Shadrin 《中国海洋湖沼学报》2015,33(6):1368-1377
Zooplankton and 14 abiotic variables were studied during August 2011 at 10 stations in Lake Qarun,Egypt.Stations with the lowest salinity and highest nutrient concentrations and turbidity were close to the discharge of waters from the El-Bats and El-Wadi drainage systems.A total of 15 holozooplankton species were identified.The salinity in Lake Qarun increased and fluctuated since 1901:12 g/L in 1901;8.5 g/L in 1905;12.0 g/L in 1922;30.0 g/L in 1985;38.7 g/L in 1994;35.3 g/L in 2006,and 33.4 g/L in 2011.The mean concentration of nutrients(nitrate,nitrite and orthophosphate) gradually increased from 35,0.16 and 0.38 ? g/L,respectively,in 1953–1955 to 113,16.4,and 30.26 ? g/L in 2011.From 1999–2003 some decrease of species diversity occurred.Average total zooplankton density was 30 000 ind./m 3 in 1974–1977;356 125 ind./m 3 in 1989;534 000 ind./m 3 in 1994–1995;from 965 000 to 1 452 000 ind./m 3 in 2006,and 595 000 ind./m 3 in 2011.A range of long-term summer salinity variability during the last decades was very similar to a range of salinity spatial variability in summer 2011.There is no significant correlation between zooplankton abundance and salinity in spatial and long-term changes.We conclude that salinity fluctuations since at least 1955 did not directly drive the changes of composition and abundance of zooplankton in the lake.A marine community had formed in the lake,and it continues to change.One of the main drivers of this change is a regular introduction and a pressure of alien species on the existent community.Eutrophication also plays an important role.The introduction of Mnemiopsis leidyi,first reported in 2014,may lead to a start of a new stage of the biotic changes in Lake Qarun,when eutrophication and the population dynamics of this ctenophore will be main drivers of the ecosystem change. 相似文献
95.
Daniela Comelli Massimo D'orazio Luigi Folco Mahmud El‐Halwagy Tommaso Frizzi Roberto Alberti Valentina Capogrosso Abdelrazek Elnaggar Hala Hassan Austin Nevin Franco Porcelli Mohamed G. Rashed Gianluca Valentini 《Meteoritics & planetary science》2016,51(7):1301-1309
Scholars have long discussed the introduction and spread of iron metallurgy in different civilizations. The sporadic use of iron has been reported in the Eastern Mediterranean area from the late Neolithic period to the Bronze Age. Despite the rare existence of smelted iron, it is generally assumed that early iron objects were produced from meteoritic iron. Nevertheless, the methods of working the metal, its use, and diffusion are contentious issues compromised by lack of detailed analysis. Since its discovery in 1925, the meteoritic origin of the iron dagger blade from the sarcophagus of the ancient Egyptian King Tutankhamun (14th C. BCE) has been the subject of debate and previous analyses yielded controversial results. We show that the composition of the blade (Fe plus 10.8 wt% Ni and 0.58 wt% Co), accurately determined through portable x‐ray fluorescence spectrometry, strongly supports its meteoritic origin. In agreement with recent results of metallographic analysis of ancient iron artifacts from Gerzeh, our study confirms that ancient Egyptians attributed great value to meteoritic iron for the production of precious objects. Moreover, the high manufacturing quality of Tutankhamun's dagger blade, in comparison with other simple‐shaped meteoritic iron artifacts, suggests a significant mastery of ironworking in Tutankhamun's time. 相似文献
96.
This is an overview of the mode of formation of the Nile Gorge in northern Egypt. It is based on the interpretation of the Shuttle Radar Topography Mission (SRTM) data along with detailed analysis of landsat image, geological map and seismic data. The results show that the current course of the Nile was caused by a differential uplift of two plateaus: Ma'aza, to the east, and Western Desert plateau, to the west of the river. This uplift is caused by dynamic forces resulting from subsurface convection processes. It also contributed to the formation of several drainage systems, basins and structural features. Abundant faults and fractures that are parallel to the Nile Valley on both flanks that are associated with uplift are proven to be contemporaneous with formation of the river. We conclude that understanding of the uplift is crucial to visualizing the Nile course and its geodynamic formation. The information derived from the SRTM data reveals invaluable knowledge in support of the presented remotely sensed geological features. The paper clearly explains the stages of formation of the Nile segments in space and time and structural controls on the path of the Nile River in Egypt. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
97.
The discoveries of binary asteroids have opened an important new field of research concerning the calculation of potential generated by irregular bodies.Some of them have an elongated shape.A simple model to describe the motion of a test particle in that kind of potential requires consideration of a finite homogeneous straight segment.We construct this model by adding an inhomogeneous distribution of mass. To be consistent with the geometrical shape of the asteroid,we explore a parabolic profile of the dens... 相似文献
98.
The Happo-O’ne peridotite complex is situated in the northeastern part of the Hida Marginal Tectonic Zone, central Japan,
characterized by the high-P/T Renge metamorphism, and is considered as a serpentinite mélange of Paleozoic age. Peridotitic rocks, being massive or foliated,
have been subjected to hydration and metamorphism. Their protoliths are mostly lherzolites to harzburgites with subordinate
dunites. We found a characteristic mineral assemblage, olivine + orthopyroxene + tremolite + chlorite + chromian spinel, being
stable at low-T, from 650 to 750°C, and high-P, from 16 to 20 kbar, tremolite–chlorite peridotites of the tremolite zone. Olivines are Fo88–Fo91, and orthopyroxenes (Mg# = 0.91) show low and homogenous distributions of Al2O3 (up to 0.25 wt%), Cr2O3 (up to 0.25 wt%), CaO (up to 0.36 wt%) and TiO2 (up to 0.06 wt%) due to the low equilibration temperature. Chromian spinels, which are euhedral and enclosed mainly in the
orthopyroxenes, have high TiO2, 3.1 wt% (up to 5.7 wt%) on average, and high Cr# [=Cr/(Cr + Al) atomic ratio], 0.95 on average but low Fe3+ [=Fe3+/(Cr + Al + Fe3+) atomic ratio, <0.3]. The bulk-rock chemistry shows that the Happo-O’ne metaperidotites with this peculiar spinel are low
in TiO2 (0.01–0.02 wt%), indicating no addition of TiO2 from the outside source during the metamorphism; the high TiO2 of the peculiar spinel has been accomplished by Ti release from Ti-bearing high-T pyroxenes during the formation of low-T, low-Ti silicates (<0.1 wt% TiO2) during cooling. Some dunites are intact from hydration: their olivine is Fo92 and spinel shows high Cr#, 0.72. The Happo-O’ne metaperidotites (tremolite–chlorite peridotites), being in the corner of
the mantle wedge, are representative of a hydrous low-T, high-P mantle peridotite facies transitional from a higher T anhydrous peridotite facies (spinel peridotites) formed by in situ retrograde metamorphism influenced by fluids from the
subducting slab. They have suffered from low-T (<600°C) retrogressive metamorphism to form antigorite and diopside during exhumation of the Renge metamorphic belt. 相似文献
99.
Usama Massoud Fernando Santos Mohamed A. Khalil Ayman Taha Abbas M. Abbas 《Hydrogeology Journal》2010,18(3):699-710
The integration of geophysical data with direct hydrogeological measurements can provide a minimally invasive approach to characterize the subsurface at a variety of resolutions and over many spatial scales. The field of hydrogeophysics has attracted much attention during the last two decades. In this domain, the geophysical data inverted to geophysical models are interpreted in terms of the hydrogeology to serve as a basis for the definition of hydraulic models in the areas of interest. The hydraulic conductivity (K) value measured in a reference borehole has been combined with the electrical conductivity obtained from nearby geo-electromagnetic sounding data in the Cenomanian (Upper Cretaceous) aquifer, central Sinai, Egypt. The resulting relation was interpreted with Dar Zarrouk parameters to infer the transmissivity variations at other vertical electrical sounding locations, where K values are unknown. Coincident transient electromagnetic data have been adopted to increase accuracy while interpreting the aquifer geoelectrical properties. The results indicate that the transmissivity values in the aquifer of interest vary from 2,446 to 9,694 m2/day, and K varies from 12.9 to 57.0 m/day throughout the studied area. 相似文献
100.
Integrated geoelectrical survey for groundwater and shallow subsurface evaluation: case study at Siliyin spring, El-Fayoum, Egypt 总被引:3,自引:1,他引:2
Mohamed Metwaly Gad El-Qady Usama Massoud Abeer El-Kenawy Jun Matsushima Nasser Al-Arifi 《International Journal of Earth Sciences》2010,99(6):1427-1436
Siliyin spring is one of the many natural fresh water springs in the Western Desert of Egypt. It is located at the central
part of El-Fayoum Delta, which is a potential place for urban developments and touristic activities. Integrated geoelectrical
survey was conducted to facilitate mapping the groundwater resources and the shallow subsurface structures in the area. Twenty-eight
transient electromagnetic (TEM) soundings, three vertical electrical soundings (VES) and three electrical resistivity tomography
(ERT) profiles were carried out around the Siliyin spring location. The dense cultivation, the rugged topography and the existence
of infra structure in the area hindered acquiring more data. The TEM data were inverted jointly with the VES and ERT, and
constrained by available geological information. Based on the inversion results, a set of geoelectrical cross-sections have
been constructed. The shallow sand to sandy clay layer that forms the shallow aquifer has been completely mapped underneath
and around the spring area. Flowing of water from the Siliyin spring is interconnected with the lateral lithological changes
from clay to sand soil. Exploration of the extension of Siliyin spring zone is recommended. The interpretation emphasizes
the importance of integrating the geoelectrical survey with the available geological information to obtain useful, cheap and
fast lithological and structural subsurface information. 相似文献