排序方式： 共有37条查询结果，搜索用时 15 毫秒
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利用2015年8月至2016年7月在印度河上游流域Bagrot山谷降水稳定同位素（δ18O和δD）观测结果以及当地气象资料，利用同位素示踪及统计分析方法，并结合HYSPLIT模型，对研究区降水稳定同位素变化特征、大气水线以及水汽来源进行了分析。结果表明，观测期间Bagrot山谷降水稳定同位素的季节变化明显，δ18O与δD秋冬季偏低，春夏季偏高，且与气温变化一致，存在显著的温度效应，而降水量效应不明显。而且发现，研究区局地大气水线截距和斜率均低于全球的，反映了降水过程中云下二次蒸发作用较为强烈，特别是，不同的降水形态导致该研究区局地大气水线的斜率和截距不同。当液态降水（降雨）发生时，由于在较为干旱的气候环境下，雨滴在降落的过程中受到二次蒸发相对较强，使得局地大气水线的斜率和截距偏低；而当固态降水（降雪）发生时，由于温度较低，受再循环水汽和二次蒸发的影响较小，导致局地大气水线的斜率和截距均偏高。Bagrot山谷及其周边地区，从南到北局地大气水线的斜率相差不大，而其截距总体上随着纬度升高而降低，可能与云下二次蒸发导致稳定同位素发生的不平衡分馏逐渐强烈有关。通过Bagrot山谷站点降水稳定同位素观测结果并结合HYSPLIT模型的后向追踪，研究还发现，研究区全年主要受西风环流以及局地环流的影响。但与研究区以北的临近站点（慕士塔格、和田等）相比有所不同，由于Bagrot山谷位置更靠南，其仍然偶尔受到来自南方的海洋性水汽影响。这一研究结果可能对该地区树轮稳定同位素记录的解译具有一定的指示意义。 相似文献
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Zakaria ENDUT NG Tham Fatt Jasmi Hafiz ABDUL AZIZ Sebastien MEFFRE Charles MAKOUNDI 《《地质学报》英文版》2015,89(6):1914-1925
The Penjom Gold Mine is located 30 km from the Bentong-Raub Suture at the western boundary of the Central Belt in Peninsular Malaysia. Gold mineralization hosted within the vein system is associated with pyrite, arsenopyrite, and minor base metals including galena. Trace element and lead isotope analysis was undertaken on nine samples that represent two stages of galena formed during two tectonic events. Both the Pb isotopes and the trace elements show that the first stage galena within the mineralized areas at the footwall has different geochemical characteristics compared with galena in non mineralized areas in the hanging wall, suggesting that galena crystallized from two different ore fluids and probably at two different times. Higher Te, Se and Bi in the galena from the mineralized area may indicate hydrothermal fluids that migrate through the structural conduit and leached out the metal along the pathway that consist of dominant carbonaceous unit. The Pb isotopic ratio composition are transitional between the bulk crustal growth and an upper crustal growth curve, indicating that derivation was from arc rocks associated with continental crust or a crustal source that includes arc volcanic and old continental sedimentary rocks. 相似文献
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Nisar Ahmed Perveiz Khalid Hafiz Muhammad Bilal Shafi Patrick Connolly 《Acta Geophysica》2017,65(5):991-1007
The use of seismic direct hydrocarbon indicators is very common in exploration and reservoir development to minimise exploration risk and to optimise the location of production wells. DHIs can be enhanced using AVO methods to calculate seismic attributes that approximate relative elastic properties. In this study, we analyse the sensitivity to pore fluid changes of a range of elastic properties by combining rock physics studies and statistical techniques and determine which provide the best basis for DHIs. Gassmann fluid substitution is applied to the well log data and various elastic properties are evaluated by measuring the degree of separation that they achieve between gas sands and wet sands. The method has been applied successfully to well log data from proven reservoirs in three different siliciclastic environments of Cambrian, Jurassic, and Cretaceous ages. We have quantified the sensitivity of various elastic properties such as acoustic and extended elastic (EEI) impedances, elastic moduli (K sat and K sat–μ), lambda–mu–rho method (λρ and μρ), P-to-S-wave velocity ratio (V P/V S), and Poisson’s ratio (σ) at fully gas/water saturation scenarios. The results are strongly dependent on the local geological settings and our modeling demonstrates that for Cambrian and Cretaceous reservoirs, K sat–μ, EEI, V P/V S, and σ are more sensitive to pore fluids (gas/water). For the Jurassic reservoir, the sensitivity of all elastic and seismic properties to pore fluid reduces due to high overburden pressure and the resultant low porosity. Fluid indicators are evaluated using two metrics: a fluid indicator coefficient based on a Gaussian model and an overlap coefficient which makes no assumptions about a distribution model. This study will provide a potential way to identify gas sand zones in future exploration. 相似文献
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M. M. Uddin A. K. M. Harun-Ar-Rashid S. M. Hossain M. A. Hafiz K. Nahar S. H. Mubin 《International Journal of Environmental Science and Technology》2006,3(4):447-453
This paper gives impact of Arsenic contaminated water on human health as well as overview of the extent and severity of groundwater arsenic contamination in Bangladesh. Scalp hair is the most important part of the human body to monitor the accumulation of this type of poison. Therefore, an experiment has been carried out by Neutron Activation Analysis (NAA) at Atomic Energy Research Establishment (AERE), Savar, Dhaka, Bangladesh on human hair of corresponding tube well water users of these areas to determine the total accumulation of arsenic to their body. Hair samples collected from the region where the groundwater was found highly contaminated with arsenic. The obtained results of arsenic concentration in the lower age (Hb) categories of users (below 12 years of age users) is in the range of 0.33 to 3.29 /gmg/g (ppm) and that in the Hu categories (upper 12 years of age users) is 0.47 to 6.64 μg/g (ppm). Where as maximum permissible range is 1 ppm certified from WHO. Results show that the peoples are highly affected where the groundwater is highly contaminated with arsenic and acts as the primary source of arsenic poisoning among the peoples of those areas. The results indicate that human population is affected with arsenic locally using the contaminated water for a long time. 相似文献
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Gerhard Müller Abdel Hafiz Mula Søren Gregersen 《Physics of the Earth and Planetary Interiors》1977,14(1):30-40
The amplitudes of the core reflection PcP are sensitive to the wave velocities and densities in the neighborhood of the core-mantle boundary (CMB). We study the amplitude ratio of the long-period phases PcP and P from two South American deep-focus earthquakes with favorable fault-plane solution, depth and magnitude, as recorded by WWNSS and CSN stations in North America.Comparison is made with long-period PcP/P amplitude ratios, derived from theoretical seismograms for a variety of CMB models. Models from previous studies, which were mainly derived from short-period PcP observations and which are characterized by discrete layers above the CMB, are almost all inconsistent with the long-period data. The data also discriminate against low nonzero S velocities below the CMB. Simple first-order-discontinuity models of the CMB, for instance according to the Jeffreys-Bullen earth model or according to recent models based mainly on free oscillations, explain the data reasonably well.Model improvements are attempted by varying the P-velocity gradient above the CMB. The best amplitude fit is obtained for a rather strong decrease in P velocity with depth in this zone which, however, gives no acceptable traveltime fit for PcP. The scatter in body-wave amplitudes is considerable even for long-period waves and may prevent the correct assessment of that part of the amplitude variation of a phase with distance that is due to the variation of velocities and densities with depth alone. 相似文献
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Hafiz U. Rehman Tahseenullah Khan Hao‐Yang Lee Sun‐Lin Chung Mamoru Murata M. Qasim Jan 《Island Arc》2019,28(6)
We report Permian (ca. 272 Ma ±5.4 Ma) felsic dykes that intrude into the Neoproterozoic (ca. 750 Ma) magmatic suite of the Nagar Parkar Igneous Complex (NPIC), the western extension of the Malani Igneous Suite (MIS). The NPIC consists of Neoproterozoic basement amphibolites and granites (riebeckite–aegirine gray granites and the biotite–hornblende pink granites), all of which are intruded by several generations of mafic and felsic dykes. Granitic magmatism occurred in the Late Neoproterozoic (ca. 750 Ma) due to the subduction‐, followed by the rift‐related tectonic regime during the breakup of the Rodinia supercontinent. U–Th–Pb zircon and monazite CHIME age data of 700–800 Ma from the earlier generation porphyritic felsic dykes suggest the dyke intrusion was coeval or soon after the emplacement of the host granites. Our findings of Permian age orthophyric felsic dykes provide new insights for the prevalence of active tectonics in the MIS during late Paleozoic. Textural features and geochemistry also make the orthophyric dykes distinct from the early‐formed porphyritic dykes and the host granites. Our newly obtained age data combined with geochemistry, suggest the existence of magmatism along the western margin of India (peri‐Gondwana margin) during Permian. Like elsewhere in the region, the Permian magmatism in the NPIC could be associated with the rifting of the Cimmerian micro‐continents from the Gondwana. 相似文献
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Rhys Harris Robert McCall Oliver Randall Muhammad Hafiz Bin Tawang Rhys Williams Jonathan G. Fairman David M. Schultz 《Geology Today》2017,33(6):210-215
The transition from the Triassic to Jurassic is associated with dramatic changes in Earth's climate. Pangaea was breaking up as North America rifted away from Africa, the Central Atlantic Magmatic Province erupted, and the concentration of atmospheric carbon dioxide increased dramatically. This article summarises the changes in Earth's climate associated with this transition, including a discussion of the various impacts of the increased carbon dioxide on the Earth system, the question of whether the wet episode in the Carnian was a global or regional event, the formation of bauxite deposits, and how dinosaur distributions changed over time. Palaeoclimate model simulations reveal the spatial changes in climate between the Triassic and Jurassic, illustrating the subtropics becoming slightly cooler and wetter despite the warming trend for the Earth's average temperature. 相似文献
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作为一种较为特别的微生物碳酸盐岩类型,核形石以双重属性而著称：① 以不平滑的皮层和较大的大小而常常被解释为微生物成因,从而区别于而成因存在着较大争议的鲕粒,所以,核形石也可以作为一种包覆颗粒类型;② 作为微生物碳酸盐岩的一种类型而被归为相互不连接的球状叠层石,因为核形石形成在围绕着核心的序列式纹层化作用过程之中,并且表现为球形或椭球型的生物沉积构造。在山西繁峙茶坊子剖面寒武系苗岭统张夏组块状鲕粒滩相灰岩的顶部,密集发育着厘米级别大小的高能泥晶核形石,核形石灰岩的厚度接近1 m,从而组成一个块状鲕粒滩相灰岩之上特征性的核形石灰岩帽。该层厚度较小的（小于1 m）核形石灰岩中的核形石,具有以下特征：① 厘米级别的大小（1至3 cm）;②球形或椭球形的形态学特征;③核形石皮层主导性的泥晶和少量的微亮晶构成;④核形石皮层中较高密度保存的丝状蓝细菌鞘化石;⑤核形石间特别的凝块基质,以及明显的丝状蓝细菌鞘化石构成的凝块。尽管穿越成岩作用过滤器去解释古代核形石复杂的形成机理将存在着巨大的挑战,也尽管形成这些核形石复杂的生物膜钙化作用机理还没有得到完全而且准确的了解,但是,山西省繁峙县茶坊子剖面张夏组顶部的核形石,壮观的宏观特征,核形石皮层中直接的微生物化石证据,尤其是在核形石内较为丰富的丝状蓝细菌鞘化石,使其成为一个了解光合作用生物膜建造核形石的典型实例,而且成为了解发育在高能鲕粒滩相灰岩之上最为特别的“藻坪”沉积的一个较为典型实例。 相似文献