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91.
Mohammed R. Moufti Károly Németh Nabil El-Masry Atef Qaddah 《Central European Journal of Geosciences》2013,5(2):254-271
Al Wahbah Crater is one of the largest and deepest Quaternary maar craters in the Arabian Peninsula. It is NW-SE-elongated, ~2.3 km wide, ~250 m deep and surrounded by an irregular near-perpendicular crater wall cut deeply into the Proterozoic diorite basement. Very few scientific studies have been conducted on this unique site, especially in respect to understanding the associated volcanic eruption processes. Al Wahbah and adjacent large explosion craters are currently a research subject in an international project, Volcanic Risk in Saudi Arabia (VORiSA). The focus of VORiSA is to characterise the volcanic hazards and eruption mechanisms of the vast volcanic fields in Western Saudi Arabia, while also defining the unique volcanic features of this region for use in future geoconservation, geoeducation and geotourism projects. Al Wahbah is inferred to be a maar crater that formed due to an explosive interaction of magma and water. The crater is surrounded by a tephra ring that consists predominantly of base surge deposits accumulated over a pre-maar scoria cone and underlying multiple lava flow units. The tephra ring acted as an obstacle against younger lava flows that were diverted along the margin of the tephra ring creating unique lava flow surface textures that recorded inflation and deflation processes along the margin of the post-maar lava flow. Al Wahbah is a unique geological feature that is not only a dramatic landform but also a site that can promote our understanding of complex phreatomagmatic monogenetic volcanism. The complex geological features perfectly preserved at Al Wahbah makes this site as an excellent geotope and a potential centre of geoeducation programs that could lead to the establishment of a geopark in the broader area at the Kishb Volcanic Field. 相似文献
92.
Application of a revised hydrostratigraphical classification and nomenclature to the Mesozoic and Cenozoic succession of Saudi Arabia 总被引:1,自引:0,他引:1
Abdulaziz M. Al-Bassam Mohammed E. Al-Dabbagh Mohammed Tahir Hussein 《Journal of African Earth Sciences》2000,30(4):917
At the dawn of the 21st century many parts of the world are suffering a shortage of water resources. Arid and semi-arid areas in particular are facing challenges and increasing pressure is being put on their groundwater management plans. Such a situation created an urgent need to put forward a design for classification and nomenclature that can help to differentiate highly productive zones from small locally exploited productive zones. A previously proposed hydrostratigraphical classification and nomenclature scheme is revised, modified, and applied to the Mesozoic-Cenozoic sedimentary succession of Saudi Arabia. The scheme utilised in the present paper is modified to include, in addition, productivity, water quality criteria, usability, and recharge as criteria reflecting the hydrogeological importance of the productive zones.The Triassic Sudair Mega-aquitard forms the lower hydrostratigraphic boundary for the Ad-Dahna'a Aquasystem. The Ad-Dahna'a Aquasystem comprises two aquagroups: the Riyadh and Rub'Al-Khali Aquagroups. Each aquagroup is in turn subdivided into superaquifers, aquifers and possibly subaquifers, separated by aquitards of different ranks. The physical and hydrogeological characteristics of each unit are also discussed. 相似文献
93.
94.
Shamim A. Dar K. F. Khan Saif A. Khan Akhtar R. Mir H. Wani V. Balaram 《Arabian Journal of Geosciences》2014,7(6):2237-2248
The paper presents the uranium (U) concentration and distribution pattern in the Paleoproterozoic phosphorites of Lalitpur district of Uttar Pradesh. The study of thin sections, SEM and XRD reveal that apatite is the essential phosphate mineral while quartz and feldspars are the dominant gangue in the phosphorites of the investigated area. The collophane is observed to be mostly oolitic in form and microspherulitic in texture. The major element geochemistry indicated that the phosphorite samples are rich in P2O5, CaO, SiO2 and Fe2O3 whereas depletion of MgO, MnO, K2O and Al2O3 was observed. The CaO/P2O5 ratio ranges from 1.13 to 1.46 which is slightly lower than that of cations and anions substituted francolite (1.621) and close to that of carbonate-fluorapatite (1.318). The trace element geochemistry indicates that the phosphorites of Lalitpur have the significant range of U concentration (1.67 to 129.67 μg/g) which is more than that of Th (0.69 to 0.09 μg/g) among the analysed trace elements in the phosphorite samples of the area. The positive correlation of U with P2O5, CaO and U/P2O5 indicates a close association of U with phosphate minerals like collophane (apatite), whereas negative correlation of U with SiO2 and Fe2O3 may be due to mutual replacement. The antipathetic relationship of U with Ni may be an indication of high oxidizing conditions, whereas sympathetic relationship of U with K2O points towards higher alkaline conditions of the basin of deposition during phosphatization. The variable concentration of U and its relationship with significant major and trace elements in most of the phosphorite samples lead one to believe that the deposition of these phosphorites might have taken place in highly alkaline medium during fairly oxidizing to weakly reducing environmental conditions of geosynclinal basin. 相似文献
95.
Mohammed Ilyas Arunsala Pandy Mohd. Suhaimi Jaafar 《Journal of Atmospheric Chemistry》2001,40(2):111-121
The South-East Asian region experienced a haze episode in 1994 which was widely believed to be due to widespread forest fires in Sumatra and Kalimantan (Indonesia). Broadband measurements of the surface level solar ultraviolet-B, UV-A and Global radiation at Penang (Malaysia) are used to study the effect of the 1994 haze on effective UV-B irradiance. We find that during the haze episode, there is enhanced absorption of surface level UV-B radiation. The effect of haze on UV-A and Global radiation is much less. The reduction in absolute noon time UV-B irradiance (mostly cloud free) during the 1994 haze period was 23% relative to the UV-B irradiance during thecorresponding haze-free period in 1995. Even though the noon time radiation data minimizes the cloud effect in the results presented some cloud effect is still present. 相似文献
96.
Specific Relationship between the Surface Air Temperature and the Area of the Terra Nova Bay Polynya,Antarctica 总被引:1,自引:0,他引:1
Yifan DING Xiao CHENG Xichen LI Mohammed SHOKR Jiawei YUAN Qinghua YANG Fengming HUI 《大气科学进展》2020,37(5):532-544
Antarctic polynyas play an important role in regional atmosphere-ice-ocean interactions and are considered to help generate the global deep ocean conveyer belt. Polynyas therefore have a potential impact on the Earth’s climate in terms of the production of sea ice and high-salinity shelf water. In this study, we investigated the relationship between the area of the Terra Nova Bay polynya and the air temperature as well as the eastward and northward wind based on the ERA5 and ERAInterim reanalysi... 相似文献
97.
98.
Records of massive fish kills and paralytic shellfish poisoning (PSP) in Europe and North America go back to the 17th century. But, it was not until the 1940s when the relationship between PSP, red tide and toxic dinoflagellateGonyaulax was established. Recent records show that PSP and related poisons caused by toxic dinoflagellates in coastal waters and estuaries, are a world-wide problem. Diarrhetic shellfish poisoning (DSP) and neurotoxic poisoning (NSP), believed earlier as bacterial or viral infections are now shown to be caused by other toxic dinoflagellates such asDinophysis. The shellfish most often involved in the poisoning are mussels and clams. Other dinoflagellates,Gyrodinium, occasionally cause massive fish kills in vast coastal areas, resulting in fishery and economic losses.Factors promoting toxic dinoflagellate bloom development and PSP/DSP outbreaks are not fully understood. In previous studies, temperature was considered as the principal factor influencing dinoflagellate blooming. Recent studies showed that other factors such as salinity, sunlight, freshwater runoff and water stability are also important. Pollution from land drainage and sewage discharge in inshore waters were also implicated.Current knowledge indicates that although chemical and biotic factors are important forin-situ growth of dinoflagellate cells, convergence by thermal and tidal fronts is essential for cell accumulation and bloom development. Advances in physical oceanographic research, modelling and remote sensing enabled the detection of fronts and bordering eddies with high precision. There is a potential for an increased use of these technological advances in predicting and monitoring the bloom development.The present paper overviews the history and distribution of toxic dinoflagellates, and the physical factors influencing bloom development and PSP/DSP outbreaks. Future research needs to improve the predictability and control of this world-wide hazard are also discussed. 相似文献
99.
100.
The study of dynamics of the particle creation in relativistic viscous fluid in Robertson-Walker Universe is studied by using Brans-Dicke theory. The behaviour of these solutions with respect to Dirac's hypothesis are investigated along with the discussion of the physical parameters as well as the variable gravitational constant. By adopting a particular method of integration, exact solutions are obtained and physical interpretations are presented. 相似文献