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91.
Shreerup Goswami Kamaljyoti Das Mrutyunjaya Sahoo Soumyaranjan Bal Sanghamitra Pradhan Kamal Jeet Singh Anju Saxena 《Arabian Journal of Geosciences》2018,11(17):524
The present megafloral assemblage recorded from the Barakar sediments of Dholpahar section along Singda rivulet near Gopal Prasad Village in Talcher Basin comprises of equisetaceous stems, Gangamopteris buriadica, Palaeovittaria kurzii and 19 species of the genus Glossopteris. Record of Gangamopteris, Palaeovittaria and many narrow mesh forms of Glosspteris viz., G. angustifolia, G. churiensis, G. communis, G. recurva, G. spatulata, G. stenoneura, G. tenuifolia, G. vulgaris and G. zeilleri from two older fossiliferous horizons demonstrates that these fossils were preserved during Lower Barakar sedimentation. The report of middle and broad mesh forms of Glossopteris viz., G. barakarensis, G. browniana, G. indica, G. intermittens, G. karharbariensis, G. nakkarea, G. oldhamii, G. taeniensis and G. retifera in the youngest fossiliferous horizons reveals that these fossils were preserved during the deposition of Upper Barakar sediments. The continuation of some of the Karharbari plant fossils in the early phase of Barakar Formation and their disappearance in the flora of Late Barakar suggests a shift in the climatic setup. Palaeoclimate and palaeovegetation of this area are also summarised in this study. Moreover, the fossil assemblages of different fossiliferous beds of Dholpahar section demonstrate the evolution of midrib and meshes in different reticulate leaves. 相似文献
92.
Natural Hazards - The probabilistic seismic hazard analysis (PSHA) has been performed for Bangladesh using background seismicity, crustal fault, and subduction zone source models. The latest ground... 相似文献
93.
Kamal Abdel-Rahman El-Sayed 《地震研究》2008,31(2):160-170
根据埃及Gasco天然气公司工程场地的现场调查资料、地震活动性和地震灾害评估结果,对该场地进行了评估.通过浅源地震波折射勘探,对8个地震剖面上的土壤和岩石的弹性动态常数进行了分析.场地地面模型包括两层,分析表明它们具有从中值到高值的弹性动态常数,说明场地有良好的土壤条件和基岩岩性.同时,我们搜集和分析了研究区周围150 km半径范围内的历史和仪器记录地震,从构造环境、地震活动性、地质构造和主要地震的断层面解等方面进行了研究,认为场地受4个震源区的影响:苏伊士中部海湾、开罗-苏伊士地区、开罗西南和Beni-Suef地区.我们采用地震活动性统计方法并结合专家判定,确定了这些震源区内最大地震的矩震级(MW).另外,依据场地峰值加速度(PGA)和反应谱,用随机方法对场地进行了地震灾害评估.4个震源区中,Beni-Suef地区距离工程场地最近,其PGA最大值为9.34cm/s2,但这个值很小,表明地震不会对工程场地产生破坏性影响.最后,我们还模拟了阻尼为1%、3%和5%时的伪加速度场地反应谱. 相似文献
94.
Taheri Kamal Missimer Thomas M. Taheri Milad Moayedi Hossein Mohseni Pour Fathollah 《Natural Resources Research》2020,29(2):1163-1191
Natural Resources Research - Many arid regions in the world suffer from over-exploitation of local groundwater resources leading to the degradation of freshwater aquifer systems, drying of spring... 相似文献
95.
Kamal A. Ali Abdel-Kader M. Moghazi Ayman E. Maurice Sayed A. Omar Qiang Wang Simon A. Wilde Ewais M. Moussa William I. Manton Robert J. Stern 《International Journal of Earth Sciences》2012,101(7):1705-1722
The Humr Akarim and Humrat Mukbid plutons, in the central Eastern Desert of Egypt, are late Neoproterozoic post-collisional alkaline A-type granites. Humr Akarim and Humrat Mukbid plutonic rocks consist of subsolvus alkali granites and a subordinate roof facies of albite granite, which hosts greisen and Sn–Mo-mineralized quartz veins; textural and field evidence strongly suggest the presence of late magmatic F-rich fluids. The granites are Si-alkali rich, Mg–Ca–Ti poor with high Rb/Sr (20–123), and low K/Rb (27–65). They are enriched in high field strength elements (e.g., Nb, Ta, Zr, Y, U, Th) and heavy rare earth elements (La n /Yb n ?=?0.27–0.95) and exhibit significant tetrad effects in REE patterns. These geochemical attributes indicate that granite trace element distribution was controlled by crystal fractionation as well as interaction with fluorine-rich magmatic fluids. U–Pb SHRIMP zircon dating indicates an age of ~630–620?Ma but with abundant evidence that zircons were affected by late corrosive fluids (e.g., discordance, high common Pb). εNd at 620?Ma ranges from +3.4 to +6.8 (mean?=?+5.0) for Humr Akarim granitic rocks and from +4.8 to +7.5 (mean?=?+5.8) for Humrat Mukbid granitic rocks. Some slightly older zircons (~740?Ma, 703?Ma) may have been inherited from older granites in the region. Our U–Pb zircon data and Nd isotope results indicate a juvenile magma source of Neoproterozoic age like that responsible for forming most other ANS crust and refute previous conclusions that pre-Neoproterozoic continental crust was involved in the generation of the studied granites. 相似文献
96.
This paper reports on the numerical modelling of flash flood propagation in urban areas after an excessive rainfall event or dam/dyke break wave. A two-dimensional (2-D) depth-averaged shallow-water model is used, with a refined grid of quadrilaterals and triangles for representing the urban area topography. The 2-D shallow-water equations are solved using the explicit second-order scheme that is adapted from MUSCL approach. Four applications are described to demonstrate the potential benefits and limits of 2-D modelling: (i) laboratory experimental dam-break wave in the presence of an isolated building; (ii) flash flood over a physical model of the urbanized Toce river valley in Italy; (iii) flash flood in October 1988 at the city of Nîmes (France) and (iv) dam-break flood in October 1982 at the town of Sumacárcel (Spain). Computed flow depths and velocities compare well with recorded data, although for the experimental study on dam-break wave some discrepancies are observed around buildings, where the flow is strongly 3-D in character. The numerical simulations show that the flow depths and flood wave celerity are significantly affected by the presence of buildings in comparison with the original floodplain. Further, this study confirms the importance of topography and roughness coefficient for flood propagation simulation. 相似文献
97.
Tuhin Chakraborty Dewashish Upadhyay Sameer Ranjan Kamal L. Pruseth Jayanta K. Nanda 《Journal of Metamorphic Geology》2019,37(1):113-151
The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated forming the Greater Indian Landmass. In this study, we use the metamorphic and geochronological evolution of the Gangpur Schist Belt (GSB) and neighbouring crustal units to constrain crustal accretion processes associated with the amalgamation of the Northern and Southern Indian Blocks. The GSB sandwiched between the Bonai Granite pluton of the Singhbhum craton and granite gneisses of the Chhotanagpur Gneiss Complex (CGC) links the CITZ and the North Singhbhum Mobile Belt. New zircon age data constrain the emplacement of the Bonai Granite at 3,370 ± 10 Ma, while the magmatic protoliths of the Chhotanagpur gneisses were emplaced at c. 1.65 Ga. The sediments in the southern part of the Gangpur basin were derived from the Singhbhum craton, whereas those in the northern part were derived dominantly from the CGC. Sedimentation is estimated to have taken place between c. 1.65 and c. 1.45 Ga. The Upper Bonai/Darjing Group rocks of the basin underwent major metamorphic episodes at c. 1.56 and c. 1.45 Ga, while the Gangpur Group of rocks were metamorphosed at c. 1.45 and c. 0.97 Ga. Based on thermobarometric studies and zircon–monazite geochronology, we infer that the geological history of the GSB is similar to that of the North Singhbhum Mobile Belt with the Upper Bonai/Darjing and the Gangpur Groups being the westward extensions of the southern and northern domains of the North Singhbhum Mobile Belt respectively. We propose a three‐stage model of crustal accretion across the Singhbhum craton—GSB/North Singhbhum Mobile Belt—CGC contact. The magmatic protoliths of the Chhotanagpur Gneisses were emplaced at c. 1.65 Ga in an arc setting. The earliest accretion event at c. 1.56 Ga involved northward subduction and amalgamation of the Upper Bonai Group with the Singhbhum craton followed by accretion of the Gangpur Group with the Singhbhum craton–Upper Bonai Group composite at c. 1.45 Ga. Finally, continent–continent collision at c. 0.96 Ga led to the accretion of the CGC with the Singhbhum craton–Upper Bonai Group–Gangpur Group crustal units, synchronous with emplacement of pegmatitic granites. The geological events recorded in the GSB and other units of the CITZ only partially overlap with those in the Trans North China Orogen and the Capricorn Orogen of Western Australia, indicating that these suture zones are not correlatable. 相似文献
98.
Mustafa A. Eissa James M. Thomas Ronald L. Hershey Maher I. Dawoud Greg Pohll Kamal A. Dahab Mohamed A. Gomaa Ashraf R. Shabana 《Environmental Earth Sciences》2014,71(4):1855-1869
The Wadi Watir delta in the Wadi Watir watershed is a tourist area in the arid southeastern part of the Sinai Peninsula, Egypt, where development and growth of the community on the delta are constrained by the amount of groundwater that can be withdrawn sustainably. To effectively manage groundwater resources in the Wadi Watir delta, the origin of groundwater recharge, groundwater age, and changes in groundwater chemistry in the watershed needs to be understood. Mineral identification, rock chemistry, water chemistry, and the isotopes of hydrogen, oxygen, and carbon in groundwater were used to identify the sources, mixing, and ages of groundwater in the watershed and the chemical evolution of groundwater as it flows from the upland areas in the watershed to the developed areas at the Wadi Watir delta. Groundwater in the Wadi Watir watershed is primarily from recent recharge while groundwater salinity is controlled by mixing of chemically different waters and dissolution of minerals and salts in the aquifers. The El Shiekh Attia and Wadi El Ain areas in the upper Wadi Watir watershed have different recharge sources, either from recharge from other areas or from different storm events. The downgradient Main Channel area receives groundwater flow primarily from the El Shiekh Attia area. Groundwater in the Main Channel area is the primary source of groundwater supplying the aquifers of the Wadi Watir delta. 相似文献
99.
Kamal Abou Elmagd Mohamed Wahbi Ali-Bik Salwa Dahab Abayazeed 《Arabian Journal of Geosciences》2014,7(3):899-916
A large lower Eocene bentonite deposit at the top of Sinn El-Kaddab plateau, southern Egypt, is investigated. It forms isolated anticlinal hills as mesa and cuesta geomorphic units. The Sinn El-Kaddab plateau (497 m above sea level) with Gebel Abyad in northern Sudan represent the most southern margin of Tethys realm in East Africa. Clay and silt fractions constitute up to 95 % of the bentonite and calcium montmorillonite is the predominant phase (70–87 %). These sediments were deposited during the Paleocene–Eocene Thermal Maximum (PETM) event. Grain-size distribution in conjunction with their geologic setting argues in favor of a low energy deep hemipelagic, restricted basin within the outer shelf zone. They suggest sporadic deposition in a basin characterized by relief oscillation, in response to continuous tectonic uplifting. The sediments of the peripheral parts of the basin are more calcareous and were deposited in an arid climatic condition. Calcium montmorillonite was deposited in subtropical warm climate, with alternating wet and dry seasons. Compositionally, the bentonite shales are basic to intermediate and exhibit a rather limited range of K2O/Na2O and SiO2/Al2O3 ratios. They suggest mature polycyclic siliciclastics as the main provenance and within-plate alkali basalts as a main igneous precursor. They are the product of intensive physical weathering process in response to combined effects of both tectonic disturbance and prevailed climatic conditions during the PETM event. Geochemically, they are interpreted in terms of mixing of two end-members: pure clastic terrigenous component (inherited from the source area) and carbonate-rich matrix. 相似文献
100.
Every year, Australian oceans experience the genesis of many tropical cyclones (TCs). About 40 percent of these make landfall. Because of the enormous difference in impacts between landfalling and non-landfalling TCs on coastal communities, the benefits would be enormous if it were possible to capture early the potentiality of landfall of a TC that has undergone genesis. Published literature identifies many factors such as location, warm sea surface temperature above 26 °C, conditional instability and high relative humidity in the middle troposphere and low vertical wind shear for the genesis of cyclones. Some of these factors could hold information about the potentiality of landfall while a TC is forming. An investigation into these factors actually revealed that a landfall potential index can be developed that can capture the potentiality of making a landfall. An attractive feature of this index is that it uses values at the time and location of genesis, providing a long and useful lead time. Furthermore, it is made into a dimensionless number, which makes for easy comprehension and interpretation. 相似文献