Sedimentary evolution of a Late Pleistocene temperate red algal reef (Coralligène) on Rhodes,Greece: correlation with global sea‐level fluctuations     

JÜRGEN TITSCHACK  CAMPBELL S. NELSON  TIM BECK  ANDRÉ FREIWALD  ULRICH RADTKE 《Sedimentology》2008,55(6):1747-1776

Autochthonous red algal structures known as coralligène de plateau occur in the modern warm‐temperate Mediterranean Sea at water depths from 20 to 120 m, but fossil counterparts are not so well‐known. This study describes, from an uplifted coastal section at Plimiri on the island of Rhodes, a 450 m long by 10 m thick Late Pleistocene red algal reef (Coralligène Facies), interpreted as being a coralligène de plateau, and its associated deposits. The Coralligène Facies, constructed mainly by Lithophyllum and Titanoderma, sits unconformably upon the Plio‐Pleistocene Rhodes Formation and is overlain by a Maerl Facies (2 m), a Mixed Siliciclastic‐Carbonate Facies (0·2 m) and an Aeolian Sand Facies (2·5 m). The three calcareous facies, of Heterozoan character, are correlated with established members in the Lindos Acropolis Formation in the north of the island, while the aeolian facies is assigned to the new Plimiri Aeolianite Formation. The palaeoenvironmental and genetic‐stratigraphic interpretations of these mixed siliciclastic‐carbonate temperate water deposits involved consideration of certain characteristics associated with siliciclastic shelf and tropical carbonate shelf models, such as vertical grain‐size trends and the stratigraphic position of zooxanthellate coral growths. Integration of these results with electron spin resonance dates of bivalve shells indicates that the Coralligène Facies was deposited during Marine Isotope Stage 6 to 5e transgressive event (ca 135 to 120 ka), in water depths of 20 to 50 m, and the overlying Maerl Facies was deposited during regression from Marine Isotope Stage 5e to 5d (ca 120 to 110 ka), at water depths of 25 to 40 m. The capping Aeolian Sand Facies, involving dual terrestrial subunits, is interpreted as having formed during each of the glacial intervals Marine Isotope Stages 4 (71 to 59 ka) and 2 (24 to 12 ka), with soil formation during the subsequent interglacial periods of Marine Isotope Stages 3 and 1, respectively. Accumulation rates of about 0·7 mm year^?1 are estimated for the Coralligène Facies and minimum accumulation rates of 0·2 mm year^?1 are estimated for the Maerl Facies. The existence of older red algal reefs in the Plimiri region during at least Marine Isotope Stages 7 (245 to 186 ka) and 9 (339 to 303 ka) is inferred from the occurrence of reworked coralligène‐type lithoclasts in the basal part of the section and from the electron spin resonance ages of transported bivalve shells.  相似文献   

华北地台东部石炭系—二叠系优质煤储层形成分布控制因素   总被引：5，自引：1，他引：4  

金振奎  苏妮娜  王春生 《地质学报》2008,82(10):1323-1329

优质煤储层在此指厚度大、分布广、储集物性好的煤层。沉积相对优质煤储层的形成和分布有重要控制作用。通过浅海和泻湖淤积填平发育起来的潮坪环境和三角洲环境是最有利的优质煤储层形成环境,煤储层厚度大、分布广。沉积环境对煤储层中的灰分含量和镜质组含量有重要影响,而灰分含量和镜质组含量又直接影响煤储层的储集物性。灰分充填了煤储层中的孔隙,其含量越高,储集物性越差;镜质组有利于割理的形成,其含量越高,储集物性越好。由于在灰分含量、煤岩显微组分等方面的差异,潮坪环境沉积的煤储层的储集物性优于三角洲的煤储层,下三角洲平原沉积的煤储层优于上三角洲平原沉积的煤储层。海平面变化对优质煤储层的形成和分布也有重要控制作用。高位体系煤储层富集,单层厚度大,横向分布相当稳定,尤其是高位体系域晚期,是形成优质煤储层最有利的层位。而水进体系域煤储层稀少,单层厚度小,横向分布不稳定,不利于优质煤储层形成。  相似文献   

Use of sinkhole and specific capacity distributions to assess vertical gradients in a karst aquifer     

Kurt J. McCoy  Mark D. Kozar 《Environmental Geology》2008,54(5):921-935

The carbonate-rock aquifer in the Great Valley, West Virginia, USA, was evaluated using a database of 687 sinkholes and 350 specific capacity tests to assess structural, lithologic, and topographic influences on the groundwater flow system. The enhanced permeability of the aquifer is characterized in part by the many sinkholes, springs, and solutionally enlarged fractures throughout the valley. Yet, vertical components of subsurface flow in this highly heterogeneous aquifer are currently not well understood. To address this problem, this study examines the apparent relation between geologic features of the aquifer and two spatial indices of enhanced permeability attributed to aquifer karstification: (1) the distribution of sinkholes and (2) the occurrence of wells with relatively high specific capacity. Statistical results indicate that sinkholes (funnel and collapse) occur primarily along cleavage and bedding planes parallel to subparallel to strike where lateral or downward vertical gradients are highest. Conversely, high specific capacity values are common along prominent joints perpendicular or oblique to strike. The similarity of the latter distribution to that of springs suggests these fractures are areas of upward-convergent flow. These differences between sinkhole and high specific capacity distributions suggest vertical flow components are primarily controlled by the orientation of geologic structure and associated subsurface fracturing.  相似文献   

Application of MODFLOW and geographic information system to groundwater flow simulation in North China Plain, China   总被引：2，自引：0，他引：2  

Shiqin Wang  Jingli Shao  Xianfang Song  Yongbo Zhang  Zhibin Huo  Xiaoyuan Zhou 《Environmental Geology》2008,55(7):1449-1462

MODFLOW is a groundwater modeling program. It can be compiled and remedied according to the practical applications. Because of its structure and fixed data format, MODFLOW can be integrated with Geographic Information Systems (GIS) technology for water resource management. The North China Plain (NCP), which is the politic, economic and cultural center of China, is facing with water resources shortage and water pollution. Groundwater is the main water resource for industrial, agricultural and domestic usage. It is necessary to evaluate the groundwater resources of the NCP as an entire aquifer system. With the development of computer and internet information technology it is also necessary to integrate the groundwater model with the GIS technology. Because the geological and hydrogeological data in the NCP was mainly in MAPGIS format, the powerful function of GIS of disposing of and analyzing spatial data and computer languages such as Visual C and Visual Basic were used to define the relationship between the original data and model data. After analyzing the geological and hydrogeological conditions of the NCP, the groundwater flow numerical simulation modeling was constructed with MODFLOW. On the basis of GIS, a dynamic evaluation system for groundwater resources under the internet circumstance was completed. During the process of constructing the groundwater model, a water budget was analyzed, which showed a negative budget in the NCP. The simulation period was from 1 January 2002 to 31 December 2003. During this period, the total recharge of the groundwater system was 49,374 × 10⁶ m³ and the total discharge was 56,530 × 10⁶ m³ the budget deficit was −7,156 × 10⁶ m³. In this integrated system, the original data including graphs and attribution data could be stored in the database. When the process of evaluating and predicting groundwater flow was started, these data were transformed into files that the core program of MODFLOW could read. The calculated water level and drawdown could be displayed and reviewed online.  相似文献   

Impacts of at-site wastewater disposal systems on the groundwater aquifer in arid regions: case of Sfax City, Southern Tunisia     

Ibticem Chamtouri  Habib Abida  Hafedh Khanfir  Salem Bouri 《Environmental Geology》2008,55(5):1123-1133

Groundwater in Sfax City (Tunisia) has been known since the beginning of the century for its deterioration in quality, as a result of wastewater recharge into the aquifer. An average value of 12 × 10⁶ m³ of untreated wastewater reaches the groundwater aquifer each year. This would result not only in a chemical and biological contamination of the groundwater, but also in an increase of the aquifer piezometric level. Quantitative impacts were evaluated by examining the groundwater piezometric level at 57 surface wells and piezometers. The survey showed that, during the last two decades, the groundwater level was ever increasing in the urban area with values reaching 7 m in part; and decreasing in Sidi Abid (agricultural area) with values exceeding −3 m. Groundwater samples for chemical and microbial analysis were collected from 41 wells spread throughout the study area. Results showed significantly elevated levels of sodium, chlorides, nitrates and coliform bacteria all over the urban area. High levels (NO₃: 56–254 mg/l; Na >1,500 mg/l; Coliforms >30/100 ml) can be related to more densely populated areas with a higher density of pit latrine and recharge wells. Alternatively results showed a very variable chemical composition of groundwater, e.g. electrical conductivity ranges from 4,040 to19,620 μs/cm and the dry residual varies between 1.4 and 14 g/l with concentrations increasing downstream. Furthermore a softening of groundwater in Set Ezzit (highly populated sector) was observed.  相似文献   

Hydrogeochemical investigations and groundwater provinces of the Friuli Venezia Giulia Plain aquifers,northeastern Italy   总被引：2，自引：0，他引：2  

Franco Cucchi  Giuliana Franceschini  Luca Zini 《Environmental Geology》2008,55(5):985-999

Water resources are a key factor, particularly for the planning of the sustainable regional development of agriculture, as well as for socio-economic development in general. A hydrochemical investigation was conducted in the Friuli Venezia Giulia aquifer systems to identify groundwater evolution, recharge and extent of pollution. Temperature, pH, electric conductivity, total dissolved solids, alkalinity, total hardness, SAR, Ca²⁺, Na⁺, K⁺, Mg²⁺, Cl⁻, SO₄ ²⁻, NO₃ ⁻, HCO₃ ⁻ _, water quality and type, saturation indexes and the environmental stable isotope δ¹⁸O were determined in 149 sampling stations. The pattern of geochemical and oxygen stable isotope variations suggests that the sub-surface groundwater (from phreatic and shallow confined aquifers) is being recharged by modern precipitations and local river infiltrations. Four hydrogeological provinces have been recognised and mapped in the Friuli Venezia Giulia Plain having similar geochemical signatures. These provinces have different degrees of vulnerability to contamination. The deep confined groundwater samples are significantly less impacted by surface activities; and it appears that these important water resources have very low recharge rates and would, therefore, be severely impacted by overabstraction.  相似文献   

Glacier change and glacier runoff variation in the Tuotuo River basin,the source region of Yangtze River in western China   总被引：3，自引：0，他引：3  

Yong Zhang  Shiyin Liu  Junli Xu  Donghui Shangguan 《Environmental Geology》2008,56(1):59-68

Glaciers in the Tuotuo River basin, western China, have been monitored in recent decades by applying topographical maps and high-resolution satellite images. Results indicate that most of glaciers in the Tuotuo River basin have retreated in the period from 1968/1971 to 2001/2002, and their shrinkage area is 3.2% of the total area in the late 1960s. To assess the influence of glacier runoff on river runoff, a modified degree–day model including potential clear-sky direct solar radiation has been applied to the glaciated regions of the river basin over the period 1961–2004. It was found that glacier runoff has increased in the last 44 years, especially in the 1990s when a two-thirds increase in river runoff was derived from the increase in glacier runoff caused by loss of ice mass in the entire Tuotuo River basin.  相似文献   

Neural network prediction of nitrate in groundwater of Harran Plain, Turkey   总被引：2，自引：0，他引：2  

M. Irfan Yesilnacar  Erkan Sahinkaya  Muhsin Naz  Bestamin Ozkaya 《Environmental Geology》2008,56(1):19-25

Monitoring groundwater quality by cost-effective techniques is important as the aquifers are vulnerable to contamination from the uncontrolled discharge of sewage, agricultural and industrial activities. Faulty planning and mismanagement of irrigation schemes are the principle reasons of groundwater quality deterioration. This study presents an artificial neural network (ANN) model predicting concentration of nitrate, the most common pollutant in shallow aquifers, in groundwater of Harran Plain. The samples from 24 observation wells were monthly analysed for 1 year. Nitrate was found in almost all groundwater samples to be significantly above the maximum allowable concentration of 50 mg/L, probably due to the excessive use of artificial fertilizers in intensive agricultural activities. Easily measurable parameters such as temperature, electrical conductivity, groundwater level and pH were used as input parameters in the ANN-based nitrate prediction. The best back-propagation (BP) algorithm and neuron numbers were determined for optimization of the model architecture. The Levenberg–Marquardt algorithm was selected as the best of 12 BP algorithms and optimal neuron number was determined as 25. The model tracked the experimental data very closely (R = 0.93). Hence, it is possible to manage groundwater resources in a more cost-effective and easier way with the proposed model application.  相似文献   

Experimental study on the deterioration and natural remediation of the Ariake Sea tidal mud caused by the sea laver treatment acid practice and the upward seepage of pore water liquid     

Yan-Jun Du  Song-Yu Liu  Shigenori Hayashi 《Environmental Geology》2008,55(4):889-900

This study presents a laboratory study of the following two aspects: (1) the influence of sea laver treatment acid on the geoenvironmental properties of Ariake Sea tidal mud, and (2) the natural remediation effect on the sea laver treatment acid contaminated Ariake Sea tidal mud caused by the upward seepage of pore water liquid in the mud. Firstly, the mechanisms of the transport of sea laver treatment acid in the Ariake Sea tidal mud and the generation mechanisms of the upward seepage flow in the Ariake Sea tidal mud are discussed. Secondly, a series of one-dimensional laboratory infiltration tests were carried out to investigate the deterioration of the Ariake Sea tidal mud caused by the sea laver acid treatment practice. Test results reveal that the acid treatment practice caused considerable change in the geochemical properties of the mud in terms of increase in sulfide content and decrease in pH value. After the treatment by the sea laver treatment acid, the sulfide content of the mud even exceeded the safe limit value for the benthos, which represents undesirable living condition for benthos. Thirdly, series of laboratory fresh seawater infiltration tests for the deteriorated Iida site mud were conducted to illustrate this natural remediation efficiency. It is found that with the infiltration of the fresh seawater, the sulfide content of the Iida site mud was considerably reduced and pH value increased to an acceptable range for benthos living in the tidal flat mud. With the increase in the infiltration time and the hydraulic gradient, the remediation efficiency could be increased.  相似文献   

Design of shallow foundations under tensile loading for transmission line towers: An overview     

M.P. Pacheco  F.A.B. Danziger  C. Pereira Pinto   《Engineering Geology》2008,101(3-4):226-235

Tensioned foundations are common in civil engineering applications such as transmission towers, harbors, offshore structures, basement slabs under pressure, industrial equipment, etc. Procedures for the design of tensioned foundations are discussed in this paper, including specific recommendations for more common transmission tower foundations. Starting from a distinction between shallow and deep modes of failure, the paper presents the most common failure mechanisms for shallow failure in tension, including procedures for calculation of foundation tensile capacity under vertical and inclined loading. Emphasis is given to the influence of the strength of the compacted backfill compared to the strength of the natural soil, including presentation of results of full-scale loading tests.  相似文献