Isotopic evidence for glacial meltwater recharge to the Cambrian-Ordovician aquifer, north-central United States

The chemistry of water in the Cambrian-Ordovician aquifer in six midwestern states has been studied as part of the Northern Midwest Regional Aquifer-System Analysis of the U.S. Geological Survey. Dissolved-solids concentrations generally increase perpendicular to the direction of regional groundwater flow, from less than 400 mg/liter in southeast Minnesota, southwest Wisconsin, and northeast Iowa to more than 10,000 mg/liter in northwest Missouri. Isotopic ratios of hydrogen and oxygen are significantly depleted from north to south, with an areal distribution approximately parallel to the distribution of dissolved solids. For example, δ¹⁸O in southern Iowa and northern Missouri is about 6 parts per thousand lighter than δ¹⁸O of modern recharge water in Minnesota and Wisconsin. Covariance between δ¹⁸O and δD of the groundwater, similar to that of modern precipitation, suggests that the differences in isotopic ratios between groundwater and modern recharge water reflect meteoric signatures of water during past recharge events rather than geochemical processes such as isotopic exchange with aquifer materials. The pronounced parallelism between the distribution of isotopes and dissolved solids over large areas probably reflects largescale recharge of Pleistocene glacial meltwater into the aquifer system, which probably had a paleoflow system with a gradient from northeast to southwest rather than from northwest to southeast.     

Isotopic and geochemical characteristics of groundwater in the Senegal River delta aquifer: implication of recharge and flow regime

Groundwater and surface water samples were collected to improve understanding of the Senegal River Lower Valley and Delta system, which is prone to salinization. Inorganic ion concentrations and environmental isotopes (¹⁸O, ²H and ³H) in groundwater, river, lake and precipitation were investigated to gain insight into the functioning of the system with regard to recharge sources and process, groundwater renewability, hydraulic interconnection and geochemical evolution. The geochemical characteristics of the system display mainly cation (Ca²⁺ and/or Na⁺) bicarbonated waters, which evolve to chloride water type; this occurs during groundwater flow in the less mineralized part of the aquifer. In contrast, saline intrusion and secondary brines together with halite dissolution are likely to contaminate the groundwater to Na–Cl type. Halite, gypsum and calcite dissolution determine the major ion (Na⁺, Cl⁻, Ca²⁺, Mg²⁺, SO₄ ²⁻ and HCO₃ ⁻) chemistry, but other processes such as evaporation, salt deposition, ion exchange and reverse exchange reactions also control the groundwater chemistry. Both surface water and groundwater in the system show an evaporation effect, but high evaporated signatures in the groundwater may be due to direct evaporation from the ground, infiltration of evaporated water or enriched rainwater in this region. The stable isotopes also reveal two types of groundwater in this system, which geomorphologically are distributed in the sand dunes (depleted isotopes) and in the flood plain (enriched isotopes). Consideration of the ³H content reinforces this grouping and suggests two mechanisms of recharge: contribution of enriched surface water in recharging the flood plain groundwater and, in the sand dunes area where water table is at depth between 8 and 13 m, slow recharge process characterized the submodern to mixed water.     

Distinct groundwater recharge sources and geochemical evolution of two adjacent sub-basins in the lower Shule River Basin,northwest China

Based on analysis of groundwater hydrogeochemical and isotopic data, this study aims to identify the recharge sources and understand geochemical evolution of groundwater along the downstream section of the Shule River, northwest China, including two sub-basins. Groundwater samples from the Tashi sub-basin show markedly depleted stable isotopes compared to those in the Guazhou sub-basin. This difference suggests that groundwater in the Tashi sub-basin mainly originates from meltwater in the Qilian Mountains, while the groundwater in the Guazhou sub-basin may be recharged by seepage of the Shule River water. During the groundwater flow process in the Tashi sub-basin, minerals within the aquifer material (e.g., halite, calcite, dolomite, gypsum) dissolve in groundwater. Mineral dissolution leads to strongly linear relationships between Na⁺ and Cl^? and between Mg²⁺+ Ca²⁺ and SO₄ ^2??+?HCO₃ ^?, with stoichiometry ratios of approximately 1:1 in both cases. The ion-exchange reaction plays a dominant role in hydrogeochemical evolution of groundwater in the Guazhou sub-basin and causes a good linear relationship between (Mg²⁺+ Ca²⁺)–(SO₄ ^2??+?HCO₃ ^?) and (Na⁺+ K⁺)–Cl^? with a slope of ?0.89 and also results in positive chloroalkaline indices CAI 1 and CAI 2. The scientific results have implications for groundwater management in the downstream section of Shule River. As an important irrigation district in Hexi Corridor, groundwater in the Guazhou sub-basin should be used sustainably and rationally because its recharge source is not as abundant as expected. It is recommended that the surface water should be used efficiently and routinely, while groundwater exploitation should be limited as much as possible.     

Assessing the impact of modern recharge on a sandstone aquifer beneath a suburb of Doncaster, UK

A major water quality issue in urban areas underlain by a productive aquifer is the impact of modern recharge. Using a variety of sample sources including multi-level boreholes, detectable concentrations of CFCs and SF₆ have been found throughout the upper 50 m of the saturated aquifer beneath a suburb of Doncaster, UK, indicating that modern (<50-year old) recharge has penetrated to at least this depth. Additional support for this deep penetration is provided by the detection of sulphite-reducing clostridia and faecal streptococci. Despite the upper aquifer being a poorly cemented sandstone, the residence time indicators suggest that some modern recharge is travelling via fracture systems in addition to that moving down by simple piston flow. However, the overall impact of 80 years of steady urbanisation on water quality in the aquifer beneath this suburb has in general been limited. This is attributed to a combination of factors including previous land use, dilution by direct recharge of rainfall through green-space areas including gardens, and locally high storage in the friable upper aquifer.     

Mineralogical and geochemical evidence for coupled bacterial uranium mineralization and hydrocarbon oxidation in the Shashagetai deposit,NW China

Unusual mineral structures have recently been found in a sandstone-hosted roll-type uranium deposit in the Middle Jurassic Zhiluo Formation in the Shashagetai deposit, the northern Ordos basin, NW China. The structures possess a chemical composition and crystal structure characteristic of mineral coffinite [(USiO₄)_1−x(OH)_4x], which occurs as nanoparticles with size ranging from 5 to 25 nm. These structures are interpreted to be fossilized microorganisms, based on mineralogical biosignatures including morphology, size, occurrence of biogenic coffinite as nano-crystals, and biological elements such as P. The intimate intergrowth of coffinite with secondary pyrite of bacterial origin, as defined by low δ³⁴S values, and calcite cements with petroleum-derived carbon supports its biogenic origin. Oil inclusions in the host sandstone are characterized by abundant n-alkanes, slightly increased Pr/nC₁₇ and Ph/nC₁₈ ratios, significant amounts of demethylated hopanes and tricyclic terpanes, and the existence of unresolved complex mixtures. These characteristics are interpreted to be a result of mixing of an earlier, heavily degraded oil with a later charged fresh oil; subsequently the oils were slightly degraded. These lines of evidence lead to the proposal that the reduction of sulfate and oxidization of petroleum are likely synchronous with reduction of hexavalent [U(VI)] to tetravalent [U(IV)] uranium by sulfate-reducing bacteria (SRB). The discovery of a natural association of microorganism-like structures, a uranium mineral, and biodegraded petroleum has implications for uranium biomineralization and fossil fuel exploration.     

Numerical simulation of a managed aquifer recharge system designed to supply drinking water to the city of Amsterdam,The Netherlands

Managed aquifer recharge (MAR) is increasingly used to secure drinking water supply worldwide. The city of Amsterdam (The Netherlands) depends largely on the MAR in coastal dunes for water supply. A new MAR scheme is proposed for the production of 10 × 10⁶ m³/year, as required in the next decade. The designed MAR system consists of 10 infiltration ponds in an artificially created sandbank, and 25 recovery wells placed beneath the ponds in a productive aquifer. Several criteria were met for the design, such as a minimum residence time of 60 days and maximum drawdown of 5 cm. Steady-state and transient flow models were calibrated. The flow model computed the infiltration capacity of the ponds and drawdowns caused by the MAR. A hypothetical tracer transport model was used to compute the travel times from the ponds to the wells and recovery efficiency of the wells. The results demonstrated that 98% of the infiltrated water was captured by the recovery wells which accounted for 65.3% of the total abstraction. Other sources include recharge from precipitation (6.7%), leakages from surface water (13.1%), and natural groundwater reserve (14.9%). Sensitivity analysis indicated that the pond conductance and hydraulic conductivity of the sand aquifer in between the ponds and wells are important for the infiltration capacity. The temperature simulation showed that the recovered water in the wells has a stable temperature of 9.8–12.5 °C which is beneficial for post-treatment processes. The numerical modelling approach is useful and helps to gain insights for implementation of the MAR.

     

云南澜沧老厂深部斑岩钼(铜)矿成矿物质来源的同位素地球化学证据

通过对云南澜沧老厂深部斑岩钼(铜)矿的S、Pb、H、O同位素地球化学特征的综合分析研究,探讨了隐伏斑岩型矿床的成矿物质来源.研究表明:斑岩钼(铜)矿体主要硫化物的δ34S在3.99‰～+1.8‰之间,平均值为- 1.32‰,分布范围较窄,指示硫具有壳-幔混合源特征;隐伏的成矿花岗斑岩和矿石中主要硫化物的铅同位素组成的变化范围和平均值均具明显的相似性,206pb/204pb比值变化于17.863～ 18.701之间(平均值为18.411),207pb/204 Pb值变化于15.448～15.733之间(平均值为15.628),208 Pb/204 pb值变化于37.753～39.104之间(平均值为38.615),指示矿区斑岩型矿体中的原始铅具有壳-幔混合源的特点,深部地幔也是重要源区之一;斑岩型钼(铜)矿体脉石矿物石英的δ18QH2O在-9.51‰～+9.41‰之间,δD在- 93‰～- 46.2‰之间,指示斑岩矿体成矿流体介质水既有岩浆水又有大气降水,其中,在远离主岩体的外接触带大气降水(雨水)参与成矿的程度相对较高.     

Alleviating drought and water scarcity in the Mediterranean region through managed aquifer recharge

Drought and water scarcity can significantly impair the sustainable development of groundwater resources, a scenario commonly found in aquifers in the Mediterranean region. Water management measures to address these drivers of groundwater depletion are highly relevant, especially considering the increasing severity of droughts under climate change. This study evaluates the potential of managed aquifer recharge (MAR) to offset the adverse effects of drought and water scarcity on groundwater storage. Los Arenales aquifer (central Spain), which was unsustainably exploited for irrigation in the second half of the twentieth century, is employed as a case study. Two neighbouring zones within this aquifer are contrasted, namely, Los Arenales (LA) and Medina del Campo (MC). The primary difference between them in terms of water resources management is the wide-scale implementation of MAR systems in LA since the early 2000s. Several groundwater statistical methods are used. Groundwater-level trend analysis and average piezometric levels show in LA a faster recovery of aquifer storage and less susceptibility to drought compared to MC. On the other hand, standardised precipitation indexes and standardised groundwater level indexes of detrended groundwater-level time series, which do not include the effects of MAR, show that LA can be more negatively affected by drought and groundwater abstraction. The sharper recovery of piezometric levels in LA when considering MAR, and bigger drought impacts observed when the effects of this measure are removed, demonstrate that MAR can effectively alleviate the impacts of water scarcity and drought, providing an adaptation solution to climate change worldwide.

     

Degradation of groundwater quality in coastal aquifer of Sabratah area,NW Libya

Overextraction of groundwater is widely occurring along the coast where good quality groundwater is at risk, due to urbanization, tourist development and intensive agriculture. The Sabratah area at the northern central part of Jifarah Plain, Northwest Libya, is a typical area where the contamination of the aquifer in the form of saltwater intrusion, gypsum/anhydrite dissolution and high nitrate concentrations is very developed. Fifty groundwater samples were collected from the study area and analysed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters electrical conductivity, sodium, potassium, magnesium, chloride and sulphate which can be attributed to seawater intrusion. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 30 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high nitrate concentration towards the south of the region. Seawater intrusion and deep salt water upconing result in general high SO₄ ^2? concentrations in groundwater near the shoreline, where localized SO₄ ^2? anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO₄ ^2? concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer.     

A comparison of the geochemical response to different managed aquifer recharge operations for injection of urban stormwater in a carbonate aquifer

Managed aquifer recharge (MAR) is increasingly being considered as a means of reusing urban stormwater and wastewater to supplement the available water resources. Subsurface storage is advantageous as it does not impact on the area available for urban development, while the aquifer also provides natural treatment. However, subsurface storage can also have deleterious effects on the recovered water quality through water–rock interactions which can also impact on the integrity of the aquifer matrix. A recent investigation into the potential for stormwater recycling via Aquifer Storage Transfer and Recovery (ASTR) in a carbonate aquifer is used to determine the important hydrogeochemical processes that impact on the recovered water quality. An extensive period of aquifer flushing allows observation of water quality changes under two operating scenarios: (1) separate wells for injection and recovery, representing ASTR; and (2) a single well for injection and recovery, representing Aquifer Storage and Recovery (ASR).     

Hydrogeologic controls on groundwater recharge and salinization: a geochemical analysis of the northern Hueco Bolson aquifer, Texas, USA

Identification of hydrogeologic controls on groundwater flowpaths, recharge, and salinization is often critical to the management of limited arid groundwater resources. One approach to identifying these mechanisms is a combined analysis of hydrogeologic and hydrochemical data to develop a comprehensive conceptual model of a groundwater basin. To demonstrate this technique, water samples were collected from 33 discrete vertical zone test holes in the Hueco Bolson aquifer, located within the Trans-Pecos Texas region and the primary water resource for El Paso, Texas, USA and Juárez, Mexico. These samples were analyzed for a suite of geochemical tracers and the data evaluated in light of basin hydrogeology. On the basis of δ²H and δ¹⁸O data, two regional recharge sources were recognized, one originating from western mountain-fronts and one from through-flow of the adjacent Tularosa aquifer. Chloride concentrations were strongly correlated with lithologic formations and both Cl/Br and ³⁶Cl ratios suggested the primary chloride source is halite dissolution within a specific lithologic unit. In contrast, sulfur isotopes indicated that most sulfate originates from Tularosa basin Permian gypsum sources. These results yielded a more comprehensive conceptual model of the basin, which suggested that chloride salinization of wells is the result of upconing of waters from the Fort Hancock formation.     

Isotopic evidence of lead sources in Loire River sediment

Sediments along the Loire River (central France) were investigated by means of Pb isotopes determined on the labile sediment fraction, or acid-extractable matter (AEM). The combination of trace elements and Pb isotopes allows deciphering the origin of the elements (i.e. natural or anthropogenic) and their history, in the sediment from two small watersheds (one draining basalt, the other one granite–gneiss), both in present-day suspended matter in Loire River water, and in sediment from the Loire estuary. Crustal weathering, as confirmed by the Pb-isotope ratios for most sample points, is the main source of Pb in the upstream part of the Loire River, as well as that transported in the middle part of the basin and in the estuary. Among anthropogenic sources, the use of Pb-isotopic compositions shows an influence of agriculturally-derived Pb inputs and a major input of Pb derived from gasoline, particularly in the estuary due to harbor activities.     

岩背和塌山含锡花岗斑岩的同位素地球化学物征和物质来源

笔者选择了岩背和塌山两个含锡花岗斑岩进行了系统的同位素地球化学研究。岩背花岗斑岩的全岩 Rb-Sr 等时线年龄（114Ma）和塌山花岗斑岩颗粒锆岩 U-Pb 年龄（138Ma）表明，这两个含锡花岗斑岩都是燕山晚期岩浆活动的产物。这些岩石具有较低的εNd值，较高的（37Sr/86Sr）i值、207Pb/204Pb值和δ18O值以及较古老的Nd模式年龄。同时，它们明显为富集SiO2、K2O、Rb、F和Sn，并具有强的负 Eu 异常和弱的Ce负异常。这些特征都相似于华南陆壳改造系列花岗岩，它们的母岩浆可能来源于     

黔西北铅锌矿床硫同位素地球化学研究

位于扬子地块西南缘的川滇黔铅接壤区,是我国独具特色的铅锌银多金属矿集区,黔西北铅锌矿床是其重要的组成部分。黔西北铅锌成矿区内业已发现铅锌矿床(点)100余处,其赋矿围岩为泥盆至二叠系白云岩或白云质灰岩,而其分布严格受到三条区域性构造带的控制,其中大部分矿(化)体产于北西向褶皱+断裂构造体系中。在系统收集前人发表的有关矿床硫同位素数据基础上,对成矿流体中硫的来源及形成机制进行了详细的探讨。11个矿床的150件硫化物硫同位素组成介于+3.5‰⁺20.3‰,多数集中在+6‰+20.3‰,多数集中在+6‰⁺20‰分布,峰值处于+10‰+20‰分布,峰值处于+10‰⁺14‰,具有明显的塔式正态分布特征。可见硫化物明显富集重硫同位素,与在0‰附近的陨石硫不同。前人研究发现泥盆至二叠系沉积地层中,普遍发育膏盐层,其中硫酸盐硫同位素组成介于+12‰+14‰,具有明显的塔式正态分布特征。可见硫化物明显富集重硫同位素,与在0‰附近的陨石硫不同。前人研究发现泥盆至二叠系沉积地层中,普遍发育膏盐层,其中硫酸盐硫同位素组成介于+12‰⁺28‰,与泥盆至二叠纪海水硫酸盐硫同位素组成相似(+18‰+28‰,与泥盆至二叠纪海水硫酸盐硫同位素组成相似(+18‰⁺30‰)。硫酸盐热化学还原(TSR)可以使体系中的硫同位素组成降低15‰,因此,黔西北铅锌矿床成矿流体中的还原硫主要是TSR的产物,即蒸发岩是主要的硫源。     

黔西北典型铅锌矿床碳-氧同位素地球化学研究

黔西北铅锌成矿区内广泛发育中-小型铅锌矿床,这些矿床的分布严格受到区域性构造的控制,特别是北西向构造。本文以产于不同构造中典型矿床为代表,在分析和收集热液方解石、蚀变围岩和远矿围岩C-O同位素组成基础上,探讨成矿流体中CO2可能的来源。结果显示,热液方解石C-O同位素组成介于海相碳酸盐岩和地幔C-O同位素组成之间,更靠近海相碳酸盐岩,同时热液方解石C和O同位素组成间略呈负相关关系,表明成矿流体中的CO2来源比较复杂,可能地幔、沉积物有机质和海相碳酸盐岩都有贡献。不同矿床间热液方解石C-O同位素组成略有差别,可能与热液流体与不同矿床围岩间C-O同位素交换程度不同或各端元参与程度不同有关。本文分析显示系统的C-O同位素地球化学研究有望揭示成矿流体演化过程或约束不同端元贡献比例。     

Generation and accumulation of Quaternary shallow gas in eastern Qaidam Basin, NW China

1INTRODUCTION SHALLOW(MOSTLYBIOGENIC)GASACCOUNTSFOROVER20%OFTHEWORLD’SDISCOVEREDGASRESERVES(RICEAND CLAYPOOL,1981;CLAYPOOLANDKAPLAN,1974),AND REPRESENTSONEOFTHEUNCONVENTIONALENERGYSOURCES THATINCREASINGLYATTRACTTHEATTENTIONOFPETROLEUMGEOL OGISTS.NUMEROUS…     

塔里木盆地寒武-奥陶系烃源岩的分子地球化学特征

对塔里木盆地下古生界样品的地球化学分析表明,上奥陶统良里塔格组、中上奥陶统却尔却克群烃源岩与其他烃源岩具有明显的差异,具有低的C28甾烷、24-降胆甾烷、甲藻甾烷、甲藻三芳甾烷与伽马蜡烷含量以及高的C24四环萜烷、重排甾烷含量等特点。柯坪地区中上奥陶统萨尔干组、印干组页岩伽马蜡烷、C28甾烷相对含量与寒武系、中下奥陶统黑土凹组烃源岩具有相似性。萨尔干组、印干组烃源岩中生物标志物的绝对含量很低。柯坪地区寒武系玉尔吐斯组、中上奥陶统萨尔干组、上奥陶统印干组、满东地区中下奥陶统黑土凹组等较强沉积环境的泥质烃源岩伽马蜡烷、C28甾烷、特殊甾烷的相对含量与海相原油主体有较大差异。上奥陶统印干组烃源岩较高含量的三芳甲藻甾烷、24-降重排胆甾烷和24-降胆甾烷化合物的检出表明,断代生物标志物的提法值得商榷。     

Quaternary geology in Zanskar,NW Indian Himalaya: evidence for restricted glaciation and preglacial topography

Research into the Quaternary geology of the NW Himalaya has concentrated on the elucidation of the glacial sequence. However, whilst the main ranges of the Himalaya have been subjected to numerous glaciations and are now an obvious alpine glaciated terrain, much of the landscape in Zanskar and Ladakh is more equivocal and does not appear to have been glaciated during this time. These landscape facets may therefore have a much older origin and relate to preglacial events.In Zanskar, the main ice source in all glaciations was the strongly glaciated and still glacierized north slope of the main Himalaya. This ice then flowed generally northwards in the valleys of the Zanskar river and its tributaries leaving between them a landscape supporting only a few and scattered minor local glaciers. Evidence of early glaciation has been found on isolated valley-side remnants >200 m above the present rivers. Reconstruction of these preglacial valley cross profiles show them to be generally broad and shallow, with gentle slopes. This is in distinct contrast to the present major valley systems which can usually be divided into two parts—a lower unglaciated fluvially eroded section, such as the Lungnak (Tsarap Lingti Chu) Gorge and an upper broad glacial section, such as the Stod (Doda) valley.Down-valley extent of glaciation is defined by the upper ends of unglaciated fluvial gorges. Laterally, the glaciers were confined progressively to their valleys. Inevitably there is only evidence of successively smaller subsequent glaciations, but the tectonic uplift of the southern ranges may have been a factor in this forming an increasing barrier to the snow-bearing monsoon winds.