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61.
Lake Sapanca in NW Turkey is a fault originated freshwater basin fed by seasonally variable flows of 15 streams. Considerations of lake–river interaction, supported by statistical measures of 47 bottom samples, suggest that sediment transport and deposition within the lake is controlled by two types of human constructed structures in addition to natural factors: (1) the dykes constructed in the front of streams, which feed the lake by strong flows, to prevent the filling of lakebed by coarse-grained sediments; (2) the constructed regulator on the outflowing Çarksuyu stream results in a higher sedimentation rate of clay-sized material on the NE corner of the lake, which is extraordinary in the shelf environment. 相似文献
62.
Deep dissolution affects great part of soluble rocks (e.g. gypsum and anhydrite) of the Western Italian Alps. The related superficial phenomena (sinkholes, gravity-induced processes and a local worsening of geomechanical rock properties) are not limited to typical karsts landscape and cause slope instability also affecting populated sites and infrastructures. The paper aims to describe general characteristic of dissolution phenomena, to interpret their conditioning factors and evolutionary stages and to assess possible hazards due to their superficial effects.The search for evidences of deep dissolution leads to the selection of representative sites in the central part of the Western Italian Alps (Piemonte and Valle d'Aosta Region). Detailed geological and geomorphological studies have been used to classify the selected sites by type, size and variable state of activity. Very different evolutionary stages of dissolution phenomena have been interpreted by comparison of case-studies: some are early “embryonic”; others are more evolved, up to typical sinkholes, or even remodelled by other phenomena. Some cases show an extreme complexity in the interactions between corrosion phenomena and other geomorphic processes: slope deformations, from one side, and karst, fluvial and glacial phenomena, to the other. A wide range of movement rates on slope instabilities induced by deep dissolution have been estimated by topographic and geomorphic data. Geochemical data on removed rocks by dissolution indicate 0.4 mm/year values for local subsidence. Historical and technical data indicate low frequency of major dissolution-induced collapses, but highlight widespread damages to tunnels, roads and buildings, especially along slopes. 相似文献
63.
V. A. Lebedev S. N. Bubnov O. Z. Dudauri G. T. Vashakidze 《Stratigraphy and Geological Correlation》2008,16(2):204-224
Isotopic-geochronological study of the Pliocene magmatic activity in western part of the Dzhavakheti Highland (northwestern region of the Lesser Caucasus) is carried out. The results obtained imply that the Pliocene magmatic activity lasted in this part of the highland approximately 2 million years from 3.75 to 1.75–1.55 Ma. As is established, the studied volcanic rocks correspond in composition mostly to K-Na subalkaline and more abundant normal basalts. Time constraints of main phases in development of basic volcanism within the study region are figured out. We assume that individual pulses of silicic to moderately silicic volcanism presumably took place in the Dzhavakheti Highland about 3.2 and 2.5 Ma ago. 相似文献
64.
The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to
the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic
crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed
sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges
are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this
study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern
part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on
the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain,
the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary
Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into
the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks
the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran
region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and
some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such
data should be of value to the developing Indian Ocean Tsunami Warning System. 相似文献
65.
库车前陆褶皱冲断带自北向南可分为基底冲断带、箱状背斜带、梳状背斜带和挠曲褶皱带,东西方向上可分为西段、中段和东段。本文分段叙述了各变形带的变形特征,指出东段箱状背斜带不发育,秋里塔格山脉(构造带)东延未进入东段,因而总体看自西向东变形强度减弱,地形上趋于夷平。该冲断带的形成经历了两次重大的冲断活动,分别发生在中新世和早(-中)更新世;相应地,该带可分为南、北两个"盆""山"亚系统,两者在地层记录、变形期次和变形机制上尚有若干差异。库车前陆褶皱冲断带的发育,除了受南天山的冲断和向南扩展引起的近南北向挤压应力场控制外,还受到基底断裂在新生代的活化和膏盐层底辟的制约,前者以近北西向的构造变换带及其共轭发育的近北东向断层最为重要,后者既控制了秋里塔格山脉的形成(主要受垂直的挤压应力场作用),也在库车前陆褶皱冲断带东西方向的变形分段中起了重要作用。文章还讨论了变形与地貌发育的关系和在油气勘探中的指导意义。 相似文献
66.
从混凝土管材的选定、工作坑的设计及施工、顶管顶进中若干关键问题入手,介绍了手掘式顶管施工技术在成都市中心城水环境综合整治工程G标段管道排水工程中的应用。 相似文献
67.
大同盆地孔隙地下水化学场的分带规律性研究 总被引:2,自引:0,他引:2
本文通过对大同盆地2004年孔隙地下水水化学资料的分析发现,盆地内孔隙地下水的水化学特征在水平方向上具有以盆地中部为中心,呈环状分布的特点,且与盆地水动力分区具有很好的一致性。由山前冲洪积倾斜平原到中部冲湖积平原,地下水依次经历了补给区、径流区和排泄区,相应的主要水化学类型分别为HCO3型、HCO3.SO4型和HCO3.SO4.Cl型。与中深层孔隙水相比,浅层孔隙水由于水位埋深浅,蒸发浓缩强烈,易受人类活动的影响,各组分的含量较高,变化幅度较大,水化学类型也相对复杂。浅层地下水的水质呈好转趋势,深层地下水水质基本保持稳定。 相似文献
68.
西天山特克斯达坂库勒萨依序列埃达克岩的确立及钼找矿意义 总被引:9,自引:6,他引:3
库勒萨依序列斑岩体δ平均3.05,属于钙碱性系列岛弧浅成岩。 SiO2含量为57.06%~70.74%,高Al2O3、Na2O、Sr和相对富集LREE,低MgO、Y、Yb,强烈亏损HREE。Na2O/K2O>1,Sr/Y平均57.67,正Eu异常,因而具有典型O型埃达克岩特征。库勒萨依序列斑岩体与Mo异常套合好,已发现钼矿体,找矿前景良好。该埃达克岩的确立,对深化西天山区域成矿规律和指导今后找矿具有借鉴和指导意义。 相似文献
69.
长江三角洲北翼地区缺少较长尺度的第四纪海陆变迁及环境演变的深入探讨,深达423m的海安县基岩标J9孔为此提供了较好的研究对象。通过观察该孔松散层岩心,总结其沉积特征,认为岩心可明显地划分为6个特征岩性段。同时,地层古地磁测试结果显示:0~200m为布容正极性世,200~334m为松山负极性世,334m以下为高斯正极性世。综合分析岩心沉积特征并参考古地磁测试结果对地层进行了初步划分,认为:0~39m为全新世地层,39~153m为晚更新世地层,153~200m为中更新世地层,200-334m为早更新世地层,之下为新近纪地层。地层中存在晚更新世晚期特征的硬粘土标志层,指示本地不是冰后期古河谷的发育地。 相似文献
70.