Environmental geology problems in the Tyrrhenian coastal area of Santa Marinella, province of Rome, central Italy   总被引：1，自引：0，他引：1  

U. Chiocchini  G. Gisotti  A. Macioce  F. Manna  A. Bolasco  C. Lucarini  G. M. Patrizi 《Environmental Geology》1997,32(1):1-8

 The Tyrrhenian resort of S. Marinella (central Italy) is subjected to significant anthropogenic pressures during the summer vacation period, a common situation all along the Italian coast. Located 65 km NW of Rome on the southern slopes of the Tolfa Mountains, S. Marinella is built on a gently sloping, E–W trending belt which is cut by 14 N–S oriented ephemeral streams that discharge into the Tyrrhenian Sea. The low to medium permeability turbiditic sandstones which outcrop along this belt belong to the Late Cretaceous Pietraforte unit. Three environmental problems are addressed in this study. The first problem is related to the high water supply demand during the summer months which has forced local residents to dig a large number of wells. Extensive pumping from these wells has caused salt-water intrusion into the Pietraforte, thus compromising the domestic use of the groundwater. The second problem consists of the illegal dumping of urban solid waste, material that represents a hazard during significant rain events as well as a possible cause of groundwater contamination. The final issue addressed concerns the flooding potential of the 14 ephemeral streams that cross the inhabited area of S. Marinella, a risk which is highlighted by the disastrous flood which occurred on 2 October 1981 and during the period of the Roman Emperor Settimio Severo (205 A.D.). Some suggestions are proposed to mitigate and contain the effects of these problems. Received: 7 November 1995 / Accepted: 5 December 1996  相似文献   

海南岛东南海岸带景观生态规划   总被引：3，自引：0，他引：3  

汪永华  李若英 《地域研究与开发》2006,25(5):103-107

对海南岛东南海岸带进行了景观生态规划。根据海南岛东南海岸带的自然资源条件与经济运行特点，将研究区划分为4个生态区：近岸热带海洋旅游区；海水养殖区；海岸平原粮牧生态区；生态林业区。各区的生态与社会经济特征不同，在利用与管理各生态区的过程中应该采取不同的对策措施，即加强宣传教育与宏观管理，以重点项目建设为契机，加快生态经济建设，优化生态经济结构。建立生物多样性管护区。  相似文献   

Variability of sulfur along the coastal salt marshes, Quanzhou Bay, China     

《中国地球化学学报》2006,25(B08):11-11

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High-resolution sedimentary record of lead in the coastal mud of the East China Sea in the past one hundred and fifty years     

Yunchao HAO Zhigang GUO Dejiang FAN 《中国地球化学学报》2006,25(B08):13-13

In the East China Sea （ECS）, there are some mud areas, including the south coastal mud area, the north coastal mud area, and the mud area to the southwest of Cheju Island. X-ray fluorescence （XRF） techniques and Thermal Ionization Mass Spectrometry （TIMS） were used to study the high-resolution sedimentary record of Pb concentrations and Pb stable isotopic compositions in the past one hundred and fifty years in the coastal mud of the ECS. Pb concentrations of a ^210Pb dating S5 core in the study area have increased rapidly since 1980, and reached the maximal value with 65.08 μg/g in 2000, corresponding to the fast economic development of China since the implementation of the ＂Reform and Open Policy＂ in 1978; ^206Pb/^207Pb ratios generally had stabilized at 1.195 from 1860 to 1966, and decreased gradually from 1966 to 2000, indicating that the anthropogenic source Pb contribution to the ECS has increased gradually since 1966, especially since 1980. Pb concentrations decreased distinctly from 2000 to 2003 and ^206Pb/^207Pb ratios increased from 2001 to 2003, corresponding closely to the ban of lead gasoline from 2000 in China. From 1950 to 2003, there occurred four distinct decrease events of ^206Pb/^207Pb, possibly responding to the Changjiang River （Yangtze River） catastrophic floods in 1998, 1991, 1981 and 1954; from 1860 to 1966, there were two decrease periods of ^206Pb/^207Pb, which may respond to the catastrophic floods of Changjiang River in 1931 and 1935, and 1870. As a result of the erosion and drowning by the catastrophic floods, the anthropogenic lead accumulated in soil and water environments over a long period of time was brought into the Changjiang River, then part of them was finally transported into the ECS, which leads to changes in Pb stable isotopic composition.  相似文献   

Geophysical methods applied to fault characterization and earthquake potential assessment in the Lower Tagus Valley, Portugal     

Joo Carvalho  Joo Cabral  Rui Gonalves  Luís Torres  Luís Mendes-Victor 《Tectonophysics》2006,418(3-4):277-297

The study region is located in the Lower Tagus Valley, central Portugal, and includes a large portion of the densely populated area of Lisbon. It is characterized by a moderate seismicity with a diffuse pattern, with historical earthquakes causing many casualties, serious damage and economic losses. Occurrence of earthquakes in the area indicates the presence of seismogenic structures at depth that are deficiently known due to a thick Cenozoic sedimentary cover. The hidden character of many of the faults in the Lower Tagus Valley requires the use of indirect methodologies for their study. This paper focuses on the application of high-resolution seismic reflection method for the detection of near-surface faulting on two major tectonic structures that are hidden under the recent alluvial cover of the Tagus Valley, and that have been recognized on deep oil-industry seismic reflection profiles and/or inferred from the surface geology. These are a WNW–ESE-trending fault zone located within the Lower Tagus Cenozoic basin, across the Tagus River estuary (Porto Alto fault), and a NNE–SSW-trending reverse fault zone that borders the Cenozoic Basin at the W (Vila Franca de Xira–Lisbon fault). Vertical electrical soundings were also acquired over the seismic profiles and the refraction interpretation of the reflection data was carried out. According to the interpretation of the collected data, a complex fault pattern disrupts the near surface (first 400 m) at Porto Alto, affecting the Upper Neogene and (at least for one fault) the Quaternary, with a normal offset component. The consistency with the previous oil-industry profiles interpretation supports the location and geometry of this fault zone. Concerning the second structure, two major faults were detected north of Vila Franca de Xira, supporting the extension of the Vila Franca de Xira–Lisbon fault zone northwards. One of these faults presents a reverse geometry apparently displacing Holocene alluvium. Vertical offsets of the Holocene sediments detected in the studied geophysical data of Porto Alto and Vila Franca de Xira–Lisbon faults imply minimum slip rates of 0.15–0.30 mm/year, three times larger than previously inferred for active faults in the Lower Tagus Valley and maximum estimates of average return periods of 2000–5000 years for M 6.5–7 co-seismic ruptures.  相似文献   

Up-temperature flow of surface-derived fluids in the mid-crust: the role of pre-orogenic burial of hydrated fault rocks   总被引：1，自引：0，他引：1  

C. CLARK  M.  HAND  K.  FAURE  A. SCHMIDT MUMM 《Journal of Metamorphic Geology》2006,24(5):367-387

The Walter‐Outalpa shear zone in the southern Curnamona Province of NE South Australia is an example of a shear zone that has undergone intensely focused fluid flow and alteration at mid‐crustal depths. Results from this study have demonstrated that the intense deformation and ductile shear zone reactivation, at amphibolite facies conditions of 534 ± 20 °C and 500 ± 82 MPa, that overprint the Proterozoic Willyama Supergroup occurred during the Delamerian Orogeny (c. 500 Ma) (EPMA monazite ages of 501 ± 16 and 491 ± 19 Ma). This is in contrast to the general belief that the majority of basement deformation and alteration in the southern Curnamona Province occurred during the waning stages of the Olarian Orogeny (c. 1610–1580 Ma). These shear zones contain hydrous mineral assemblages that cut wall rocks that have experienced amphibolite facies metamorphism during the Olarian Orogeny. The shear zone rock volumes have much lower δ¹⁸O values (as low as 1‰) than their unsheared counterparts (7–9‰), and calculated fluid δ¹⁸O values (5–8‰) consistent with a surface‐derived fluid source. Hydrous minerals show a decrease in δD_(H2O) from ?14 to ?22‰, for minerals outside the shear zones, to ?28 to ?40‰, for minerals within the shear zones consistent with a contribution from a meteoric source. It is unclear how near‐surface fluids initially under hydrostatic pressure penetrate into the middle crust where fluid pressures approach lithostatic, and where fluid flow is expected to be dominantly upward because of pressure gradients. We propose a mechanism whereby faulting during basin formation associated with the Adelaidean Rift Complex (c. 700 Ma) created broad hydrous zones containing mineral assemblages in equilibrium with surface waters. These panels of fault rock were subsequently buried to depths where the onset of metamorphism begins to dehydrate the fault rock volumes evolving a low δ¹⁸O fluid that is channelled through shear zones related to Delamerian Orogenic activity.  相似文献   

三角洲前缘岸滩对河流来沙减少响应的敏感性探讨——以长江口门区崇明岛向海侧岸滩为例   总被引：2，自引：2，他引：2  

杨世伦  李明  张文祥 《地理与地理信息科学》2006,22(6):62-65

利用ArcGIS对1977—2004年不同时段的长江口崇明岛向海侧水下地形测量资料进行处理,并结合该区的潮滩历史遥感图片、现场高程测量以及同期大通站输沙率资料,探讨三角洲前缘岸滩冲淤演变对河流来沙减少响应的敏感性。结果表明:研究区岸滩的淤涨速率总体上在年代以上时间尺度随着长江来沙减少而下降,但由于局部滩—槽演变和海洋动力条件的影响,某些年代内和某些部位可能出现相反的趋势,使岸滩演变对河流来沙减少的响应变得复杂化。在此基础上预测今后几十年研究区的冲淤趋势。  相似文献   

3D numerical modelling of fluid flow in the Val-d’Or orogenic gold district: major crustal shear zones drain fluids from overpressured vein fields     

Georges Beaudoin  René Therrien  Catherine Savard 《Mineralium Deposita》2006,41(1):82-98

Fluid flow patterns have been determined using oxygen isotope isopleths in the Val-d’Or orogenic gold district. 3D numerical modelling of fluid flow and oxygen isotope exchange in the vein field shows that the fluid flow patterns can be reproduced if the lower boundary of the model is permeable, which represents middle or lower crustal rocks that are infiltrated by a metamorphic fluid generated at deeper levels. This boundary condition implies that the major crustal faults so conspicuous in vein fields do not act as the only major channel for upward fluid flow. The upper model boundary is impermeable except along the trace of major crustal faults where fluids are allowed to drain out of the vein field. This upper impermeable boundary condition represents a low-permeability layer in the crust that separates the overpressured fluid from the overlying hydrostatic fluid pressure regime. We propose that the role of major crustal faults in overpressured vein fields, independent of tectonic setting, is to drain hydrothermal fluids out of the vein field along a breach across an impermeable layer higher in the crust and above the vein field. This breach is crucial to allow flow out of the vein field and accumulation of metals in the fractures, and this breach has major implications for exploration for mineral resources. We propose that tectonic events that cause episodic metamorphic dehydration create a short-lived pulse of metamorphic fluid to rise along zones of transient permeability. This results in a fluid wave that propagates upward carrying metals to the mineralized area. Earthquakes along crustal shear zones cause dilation near jogs that draw fluids and deposit metals in an interconnected network of subsidiary shear zones. Fluid flow is arrested by an impermeable barrier separating the hydrostatic and lithostatic fluid pressure regimes. Fluids flow through the evolving and interconnected network of shear zones and by advection through the rock matrix. Episodic breaches in the impermeable barrier along the crustal shear zones allow fluid flow out of the vein field.  相似文献   

3D Modeling and Kinematics of the External Zone of the French Western Alps (Belledonne and Grand Chatelard Massifs, Maurienne Valley, Savoie)     

Didier Marquer  Philippe Calcagno  Jean-Claude Barfety  Thierry Baudin 《Eclogae Geologicae Helvetiae》2006,99(2):211-222

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探地雷达(GPR)在海南岛东北部海岸带调查中的应用 ^*   总被引：2，自引：0，他引：2  

殷勇  朱大奎  I.P.Martini 《第四纪研究》2006,26(3):462-469

对海南岛东北部海岸带调查采用了探地雷达(GPR)研究海岸带沙体的结构、展布和沉积序列,取得了很好的效果。文章通过和有限的露头资料对比以及对反射波形态、结构的研究,确定了海滩脊、海岸沙丘的反射特征以及潜水面的位置。雷达图像显示五龙港古海滩脊由亚水平、不连续、高振幅和透镜状反射波组成;木兰头海岸沙丘已受到人类活动的扰动,短的、陡倾斜反射可能代表未受扰动的海岸风成沙的前积层。研究表明探地雷达是一种可靠、快速和经济的地球物理方法,在砂砾质海岸可产生高质量、高分辨率和连续的反射剖面,值得加以推广。  相似文献