Stratigraphic and structural evolution of the Blue Nile Basin,Northwestern Ethiopian Plateau

The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains ∼1400 m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early–Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigraphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases: (1) pre‐sedimentation phase, include pre‐rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time; (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic–Early Jurassic fluvial sedimentation (Lower Sandstone, ∼300 m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, ∼30 m thick); (c) Early–Middle Jurassic deepening of the basin (Lower Limestone, ∼450 m thick); (d) desiccation of the basin and deposition of Early–Middle Jurassic gypsum; (e) Middle–Late Jurassic marine transgression (Upper Limestone, ∼400 m thick); (f) Late Jurassic–Early Cretaceous basin‐uplift and marine regression (alluvial/fluvial Upper Sandstone, ∼280 m thick); (3) the post‐sedimentation phase, including Early–Late Oligocene eruption of 500–2000 m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of ∼300 m thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic–Cretaceous NE–SW‐directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW‐trending rift, within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW–SE‐directed extension related to the Main Ethiopian Rift that formed NE‐trending faults, affecting Lower volcanic rocks and the upper part of the Mesozoic section. The region was subsequently affected by Quaternary E–W and NNE–SSW‐directed extensions related to oblique opening of the Main Ethiopian Rift and development of E‐trending transverse faults, as well as NE–SW‐directed extension in southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E–W‐directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N‐, ESE‐ and NW‐trending extensional structures within the Blue Nile Basin. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrochemical characteristics of groundwater in the Zhangye Basin, Northwestern China

The Zhangye Basin, located in arid northwest China, is an important agricultural and industrial center. In recent years rapid development has created an increased demand for water, which is increasingly being fulfilled by groundwater abstraction. Detailed knowledge of the geochemical evolution of groundwater and water quality can enhance understanding of the hydrochemical system, promoting sustainable development and effective management of groundwater resources. To this end, a hydrochemical investigation was conducted in the Zhangye Basin. Types of shallow groundwater in the Zhangye Basin were found to be HCO₃ ⁻, HCO₃ ⁻–SO₄ ²⁻, SO₄ ²⁻–HCO₃ ⁻, SO₄ ²⁻–Cl⁻, Cl⁻–SO₄ ²⁻ and Cl⁻ . The deep aquifer groundwater type was found to be HCO₃⁻–SO₄²⁻ throughout the entire area. Ionic ratio and saturation index calculations suggest that silicate rock weathering and evaporation deposition are the main processes that determine the ionic composition in the study area. The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification and the Wilcox diagram. In the study area, the compositions of the stable isotopes δ¹⁸O and δD in groundwater samples were found to range from −4.00 to −9.28‰ and from −34.0 to −65.0‰, respectively. These values indicate that precipitation is the main recharge source for the groundwater system; some local values indicate high levels of evaporation. Tritium analysis was used to estimate the ages of the different groundwaters; the tritium values of the groundwater samples varied from 3.13 to 36.62 TU. The age of the groundwater at depths of less than 30 m is about 5–10 years. The age of the groundwater at depths of 30–50 m is about 10–23 years. The age of the groundwater at depths of 50–100 m is about 12–29 years. For groundwater samples at depths of greater than 100 m, the renewal time is about 40 years.     

Hydrochemical characteristics and salinity of groundwater in the Ejina Basin, Northwestern China

A hydrochemical investigation was conducted in the Ejina Basin to identify the hydrochemical characteristics and the salinity of groundwater. The results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area. The ionic ration plot and saturation index (SI) calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area. Most of the stable isotope δ¹⁸O and δD compositions in the groundwater is a meteoric water feature, indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation. Based on radioactive isotope tritium (³H) analysis, the groundwater ages were approximately estimated in different aquifers. The groundwater age ranges from less than 5 years, between 5 years and 50 years, and more than 50 years. Within 1 km of the river water influence zone, the groundwater recharges from recent Heihe river water and the groundwater age is about less than 5 years in shallow aquifer. From 1 km to 10 km of the river water influence zone, the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer. The groundwater age is more than 50 years in deep confined aquifer.     

Water pollution sources assessment by multivariate statistical methods in the Tahtali Basin,Turkey

In this study, multivariate statistical methods including factor, principal component and cluster analysis were applied to surface water quality data sets obtained from the Tahtali River Basin, Turkey. Factor and principal components analysis results revealed that surface water quality was mainly controlled by agricultural uses and domestic discharges. Cluster analysis generated two clusters. Based on the locations of the sites consisted by each cluster and variable concentrations at these stations, it was concluded that agricultural discharges strongly affected north and northeast part of the region. These methods are believed to assist water managers to understand complex nature of water quality issues and determine priorities to improve water quality.     

Source and distribution of metals in urban soil of Bombay,India, using multivariate statistical techniques

Simplification of a complex system of geochemical variables obtained from the soils of an industrialized area of Bombay is attempted by means of R-mode factor analysis. Prior to factor analysis, discriminant analysis was carried out taking rock and soil chemical data to establish the anthropogenic contribution of metals in soil. Trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) are expressed in terms of three rotated factors. The factors mostly indicate anthropogenic sources of metals such as atmospheric fallout, emission from different industrial chimneys, crushing operations in quarries, and sewage sludges. Major elements (Na, Mg, Al, Si, P, K, Ca, Ti, Mn, and Fe) are also expressed in terms of three rotated factors indicating natural processes such as chemical weathering, presence of clay minerals, and contribution from sewage sludges and municipal refuse. Summary statistics (mean, standard deviation, skewness, and kurtosis) for the particle size distribution were interpreted as moderate dominance of fine particles. Mineralogical studies revealed the presence of montmorillonite, kaolinite, and illite types of clay minerals. Thus the present study provides information about the metal content entering into the soil and their level, sources, and distribution in the area.     

Evaluation of the processes affecting vertical water chemistry in an alluvial aquifer of Mankyeong Watershed, Korea, using multivariate statistical analyses

Vertical variations of redox chemistry and groundwater quality were investigated in an alluvial aquifer beneath an agricultural area, in which deep groundwaters are free of NO₃, Fe, and Mn problems that are frequently encountered during the development of alluvial groundwaters. This study was performed to identify and evaluate vertical chemical processes attenuating these chemical species in the study area. For this study, the processes affecting groundwater chemistry were identified by factor analysis (FA) and the groundwater samples collected from six multilevel samplers were hierarchically classified into three different redox zones by cluster analysis (CA) based on the similarity of geochemical features. FA results indicated three major factors affecting the overall water chemistry: agricultural activities (factor 1), redox reactions (factor 2), and remnant seawater (factor 3). The groundwater quality in the study area was revealed to be controlled by a series of different redox reactions, resulting in different redox zones as a function of depth. It was also revealed that the low Fe and Mn levels in the groundwater of the deeper part are associated with sulfate reduction, which led to precipitation of Fe as iron sulfide and adsorption of Mn on it.     

Hydrochemical characterization of groundwater in Balad district,Salah Al-Din Governorate,Iraq

The assessment of hydrochemical quality of groundwater is very important to explore its nature and usefulness. In this paper, groundwater quality evaluation is carried out in the Balad district, Salah Al-Din Governorate, Iraq. A total of 28 groundwater samples are collected from shallow tube wells and analyzed for various physicochemical parameters. Groundwater suitability for drinking is evaluated based on the World Health Organization (WHO) and Iraqi standards, and suitability of groundwater for irrigation is assessed based on various hydrochemical parameters. The results reveal that the dominant types of groundwater based on piper diagram are mixed CaMgCl and CaCl. Gibbs ratio indicates that the groundwater in the studied area is affected by the evaporation process. The cation-anion exchange reaction in the studied area demonstrates that 54% of the groundwater samples indicate a direct base (cation-anion) exchange reaction, while 46% of the groundwater samples indicating the chloro-alkaline disequilibrium. Furthermore, generally all of the groundwater samples are unsuitable for drinking and irrigation. Cluster analysis reveals two different groups of similarities between the groundwater samples, reflecting different pollution levels in the studied area.     

Hydrochemical framework of groundwater in the Ankobra Basin,Ghana

Hydrochemical and stable isotope (¹⁸O and ²H) analyses of groundwater samples were used to establish the hydrochemistry of groundwater in the Ankobra Basin. The groundwater was generally mildly acidic, low in conductivity and undersaturated with respect to carbonate phases. Major ions except bicarbonate were low and dissolved silica was moderately high. Silicate minerals weathering is probably the main process through which major ions enter the groundwater. Groundwater samples clustered tightly along the Global Meteoric Water Line suggesting integrative, smooth and rapid recharge from meteoric origin. The majority of the boreholes and a few hand dug wells cluster towards the Ca–Mg–HCO₃ dominant section of the phase diagram, in conformity with the active recharge and short residence time shown by the isotope data. Aluminium, arsenic, manganese, iron and mercury were the only trace metals analysed with concentrations significantly above their respective detection limits. Approximately 20%, 5%, 40% and 25% respectively of boreholes had aluminium, arsenic, iron and manganese concentrations exceeding the respective WHO maximum acceptable limits for drinking water. The relatively large percentage of boreholes with high concentration of aluminium reflects the acidic nature of the groundwater.     

矿区地下水系统水质分类判别的多元统计分析

以某矿区地下水系统为例,对该矿区地下水水化学资料进行了多元统计分析方法耦合应用研究,主要包括利用因子分析对存在相关关系的离子变量进行空间降维处理,找出能够反映众多离子信息的基础变量(正交因子),以其作为系统聚类变量;运用系统聚类法获取能代表各地下水子系统水化学特征的典型水样;使用贝叶斯逐步线性判别分析建立地下水各子系统水化学判别模型(判别函数),并对随机检验样品进行判别归属和判别模型统计检验。结果表明:这是一种稳定性较好且切实有效的、适用于矿区地下水系统水化学分类及水源水化学判别的方法。     

Identification of influencing factors for groundwater quality variation using multivariate analysis

This paper reports the results of multivariate analysis on the major-ions data present in groundwater collected in a hydrogeochemical survey of a hard rock terrain in Andhra Pradesh, India. The use of factor analysis is proposed, as a first step, for identifying the processes influencing the hydrogeochemical variations in groundwater. As a result of the application factor analysis, three factors were obtained, which explained characterization of groundwater quality and identified the sources for the presence of ions and its variations in concentrations and their geochemical processes. The natural dissolution of existing rocks of granites and granitic gneisses is the common influencing source for its hydrogeochemical character in the study area, but at some localized zones, the human-influenced sources of agricultural, industrial and urbanization are the dominating factors. The spatial and seasonal variation of the hydrogeochemical processes associated with the factor variables in the groundwater quality of the study area were analysed and evaluated.     

Hydrochemical characteristics of groundwater in the Kingston Basin,Kingston, Jamaica

The Kingston Basin in Jamaica is an important hydrologic basin in terms of both domestic and industrial sector. The Kingston hydrologic basin covers an area of approximately 258 km² of which 111 km² underlain by an alluvium aquifer, 34 km² by a limestone aquifer and the remainder underlain by low permeability rocks with insignificant groundwater resources. Rapid development in recent years has led to an increased demand for water, which is increasingly being fulfilled by groundwater abstraction. A detailed knowledge of the water quality can enhance understanding of the hydrochemical system, promoting sustainable development and effective management of groundwater resources. To achieve this, a hydrochemical investigation was carried out in the Kingston Basin. Results showed that the water is Na–Ca–Cl–HCO₃ and Na–Ca–HCO₃ type with higher concentrations of nitrate, sodium and chloride as the leading causes of contamination in most of the wells. High concentrations of nitrate correlate with wells from areas of high population density and could be attributed to anthropogenic causes, mainly involving improper sewage treatment methodologies or leaking sewer lines. Jamaica, owing to its island nature, has the continuous problem of saline water intrusion, and this is reflected in the higher levels of chloride, sodium and conductivity in the water samples collected from the wells. The wells studied show higher concentrations of chloride ranging from around 10.2 mg/l in wells located approximately (4931.45 m) from the coast to around 234 mg/l in the well located near to the coast. The conductivity values also closely correlate with the chloride levels found in the wells.     

The role of geodiversity on the groundwater resource potential in the upper Blue Nile River Basin, Ethiopia

Groundwater has been the main source of water supply for large cities and towns over the last few decades in the upper Blue Nile River Basin, Ethiopia. However, provision is often unsuccessful because of poor well productivity, difficult drilling conditions, poor well positioning, or sometimes due to poor water quality. The growing pressure of urban population and industrial development is focusing unprecedented attention on the groundwater potential of the basin. The purpose of this work is to spatially characterize the groundwater potential of the upper Blue Nile River Basin with respect to variable recharge and geodiversity. The study shows that from the annual recharge obtained using the base flow separation method, the renewable groundwater potential in the basin was estimated to be in the range of 1.2 and 2 billion m³/year. The aquifers in the area are divided into three categories: low to moderate productivity (≈3.5 l/s) which includes crystalline basement rocks, acidic lava flows and domes, and very fine alluvial sediments; moderate to high productivity (≈5.5 l/s) that includes Mesozoic sedimentary rocks (sandstone, limestone, gypsum, dolomite); and high to very high productivity (≈20 l/s) which includes basic lava flows of the Trap series, Quaternary lava flows and alluvial sediments.     

Hydrochemical characteristics and geochemistry evolution of groundwater in the plain area of the Lake Baiyangdian watershed,North China Plain

Water cycle and water quality in the Lake Baiyangdian watershed of the North China Plain have undergone great changes due to over-pumping of groundwater and wastewater discharge.In this paper,hydrogeochemical data was collected to analyze the hydrochemical characteristics and geochemistry evolution of groundwater.The study area was divided into two typical parts.One was in the upstream plain area,where over-pumping had resulted in significant decline of groundwater level;the other one was located in the downstream area near the Fu River and Lake Baiyangdian(Lake BYD region).In addition to the natural weathering of minerals,excessive fertilizer was also a main factor of higher ion concentration in groundwater.According to studies,due to good permeability,these regions were easy to be polluted even with deep groundwater depth.However,upstream shallow groundwater and surface water,including lake water,domestic along with industrial wastewater were all sources of present shallow groundwater in the Lake BYD region.Results indicated that anthropogenic activities rather than minerals much matter to the groundwater in these regions.Particularly,wastewater largely decided the groundwater quality,which suggested that the management and restoration of surface water quality was crucial to groundwater protection.     

Identification of the origin of salinization in groundwater using multivariate statistical analysis and geochemical modeling: a case study of Kaohsiung,Southwest Taiwan

The study of brine aquifers in southern Taiwan is highly complicated by hybrid geochemical reactions, which obscure important geochemical information. Using multivariate analysis on major and minor ion compositions normalized by Cl⁻ content, chemical constituents were combined into two principal components representing brine mixing and mineral precipitation. Comparing to multivariate analysis on the original data, this procedure reveals more geochemical information. It demonstrates that the brine groundwater of the region is primarily composed of highly evaporated seawater. The evaporation ratio is >70%; a point at which calcite, dolomite and gypsum precipitate. Oxygen and hydrogen isotopic compositions confirm this inference; and further, geochemical modeling quantitatively determined the evaporation ratio to be about 85%. Natural boron contamination is a consequence of brine groundwater. Two evolutionary trends in the plotting of the Cl/B ratio versus Cl⁻ can be identified: (1) Cl/B ratio decreases with boron being released from clay minerals when brine aquifers are flushed with freshwater; and (2) Cl/B ratio increases when seawater of a high Cl/B ratio infiltrates coastal aquifers.     

Sources of groundwater recharge at the confluence of the Niles, Sudan

 Due to the rapid expansion of the Sudanese capital city far away from its three Niles, it has become a necessity to estimate the sustainability of the groundwater resources in this arid area. The purpose of this study – based on the stable-isotopic composition of groundwater – is to identify the sources of recharge and their relative contribution. The results show that groundwater infiltrated from the Niles under the present prevailing arid climate, with greater contribution from the White Nile compared to the Blue Nile, occupies an extension of 12 km from the Niles within the two main aquifers. Paleogroundwater of meteoric origin, infiltrated in the cooler pluvial earlier Holocene, occupies the outer zones beyond the Niles' effect. A rational utilization policy is recommended to preserve the finite groundwater resources. Received: 27 August 1998 · Accepted: 2 March 1999     

Assessment of groundwater quality using multivariate statistical techniques in Hashtgerd Plain, Iran

Multivariate statistical techniques, such as cluster analysis (CA), factor analysis (FA), principal component analysis (PCA), and discriminant analysis (DA), were applied for the evaluation of variations and the interpretation of a large complex groundwater quality data set of the Hashtgerd Plain. In view of this, 13 parameters were measured in groundwater of 26 different wells for two periods. Hierarchical CA grouped the 26 sampling sites into two clusters based on the similarity of groundwater quality characteristics. FA based on PCA, was applied to the data sets of the two different groups obtained from CA, and resulted in three and five effective factors explaining 79.56 and 81.57% of the total variance in groundwater quality data sets of the two clusters, respectively. The main factors obtained from FA indicate that the parameters influencing groundwater quality are mainly related to natural (dissolution of soil and rock), point source (domestic wastewater) and non-point source pollution (agriculture and orchard practices) in the sampling sites of Hashtgerd Plain. DA provided an important data reduction as it uses only three parameters, i.e., electrical conductivity (EC), magnesium (Mg²⁺) and pH, affording more than 98% correct assignations, to discriminate between the two clusters of groundwater wells in the plain. Overall, the results of this study present the effectiveness of the combined use of multivariate statistical techniques for interpretation and reduction of a large data set and for identification of sources for effective groundwater quality management.     

Hydrochemical evolution and water quality along the groundwater flow path in the Sandıklı plain, Afyon, Turkey

 An unconfined aquifer system suggests an open system in the study area. Hydrochemical evolution is related to the flow path of groundwater. The groundwaters are divided into two hydrochemical facies in the study area, 1) Ca–Mg–HCO₃ and 2) Ca–Mg–SO₄HCO₃. Facies 1 has shallow (young) waters which dominate in recharge areas during rapid flow conditions, whereas facies 2 may show shallow and mixed waters which dominate intermediate or discharge areas during low flow conditions. Ionic concentrations, TDS, EC and water quality are related to groundwater residence time and groundwater types. The groundwaters in the plain are chemically potable and suitable for both domestic and agricultural purposes. Received: 20 May 1996 · Accepted: 30 July 1996     

柴达木盆地大柴旦地区地下水水化学特征及演化规律

地下水在干旱/半干旱地区的生态环境保护中起着主导作用.柴达木盆地北缘的大柴旦湖地处西北干旱区,其生态环境较为脆弱,了解该地区的地下水水化学演化特征,对这一生态敏感地区的地下水可持续利用至关重要.本研究通过采集该地区28个具有代表性的水样,运用数理统计、Piper图、Gibbs图、离子比值、饱和指数和反向水文地球化学模拟...     

苏丹迈努特盆地油气成藏机理和成藏模式

苏丹迈努特盆地是中国石油天然气集团公司在海外最大的勘探项目．快速高效发现大油田是跨国勘探的主要目的。本文在过去三年的石油地质综合研究和勘探的基础上,系统总结盆地的独特石油地质特征和油气聚集规律。迈努特盆地三期裂谷的叠置．早白垩世是最主要的一期,形成了主力烃源岩;晚白垩世弱裂谷期,沉积了一套以砂岩为主的地层;古近纪又发育一期裂谷．是主力成藏组合发育时期。特定的构造—地层特征和演化史,决定了盆地独特的油气成藏机理和成藏模式——跨时代油气聚集模式。这一模式的建立为最终发明储量达5亿吨的大油田提供了理论基础。