Groundwater geochemical evolution in the northern portion of the Guarani Aquifer System (Brazil) and its relationship to diagenetic features

The groundwater flow pattern in the northern portion of GAS (Guarani Aquifer System) is characterized by the existence of four regional recharge areas located in São Paulo, Mato Grosso do Sul and Goiás states. From these areas of recharge the regional flow is radial and directed toward the center of the Paraná Sedimentary Basin. Local discharge occurs in portions of outcrop regions. The groundwater has low mineralization and can be classified as Ca or Ca–Mg–HCO₃ type, Na–HCO₃ type and Na–HCO₃/Cl/SO₄ type, this sequence represents the hydrochemical evolution. The mechanisms responsible for this evolution are dissolution of feldspars and removal of the carbonate cement from the sandstone mineral framework, followed by ion exchange, responsible for the increase in the Na concentration and decrease of Ca, and, finally, enrichment in Cl and SO₄ derived from underlying aquifer units. The hydrochemical evolution is consistent with diagenetic features that are observed in the sandstones, with the presence of siliceous cement in the outcrop areas, and carbonate cement toward the center of Paraná Basin.     

Assessment of groundwater recharge and water fluxes of the Guarani Aquifer System, Brazil

The groundwater recharge and water fluxes of the Guarani Aquifer System in the state of Sao Paulo in Brazil were assessed through a numeric model. The study area (6,748 km²) comprises Jacaré-Guaçú and Jacaré-Pepira River watersheds, tributaries of the Tietê River in the central region of the state. GIS based tools were used in the storage, processing and analysis of data. Main hydrologic phenomena were selected, leading to a groundwater conceptual model, taking into account the significant outcrops occurring in the study area. Six recharge zones were related to the geologic formation and structures of the semi-confined and phreatic aquifer. The model was calibrated against the baseflows and static water levels of the wells. The results emphasize the strong interaction of groundwater flows between watersheds and the groundwater inflow into the rivers. It has been concluded that lateral groundwater exchanges between basins, the deep discharges to the regional system, and well exploitation were not significant aquifer outflows when compared to the aquifer recharge. The results have shown that the inflows from the river into the aquifer are significant and have the utmost importance since the aquifer is potentially more vulnerable in these places.     

Relation between sedimentary framework and hydrogeology in the Guarani Aquifer System in São Paulo state,Brazil

This paper presents the results of a new investigation of the Guarani Aquifer System (SAG) in São Paulo state. New data were acquired about sedimentary framework, flow pattern, and hydrogeochemistry. The flow direction in the north of the state is towards the southwest and not towards the west as expected previously. This is linked to the absence of SAG outcrop in the northeast of São Paulo state. Both the underlying Pirambóia Formation and the overlying Botucatu Formation possess high porosity (18.9% and 19.5%, respectively), which was not modified significantly by diagenetic changes. Investigation of sediments confirmed a zone of chalcedony cement close to the SAG outcrop and a zone of calcite cement in the deep confined zone. The main events in the SAG post-sedimentary history were: (1) adhesion of ferrugineous coatings on grains, (2) infiltration of clays in eodiagenetic stage, (3) regeneration of coatings with formation of smectites, (4) authigenic overgrowth of quartz and K-feldspar in advanced eodiagenetic stage, (5) bitumen cementation of Pirambóia Formation in mesodiagenetic stage, (6) cementation by calcite in mesodiagenetic and telodiagenetic stages in Pirambóia Formation, (7) formation of secondary porosity by dissolution of unstable minerals after appearance of hydraulic gradient and penetration of the meteoric water caused by the uplift of the Serra do Mar coastal range in the Late Cretaceous, (8) authigenesis of kaolinite and amorphous silica in unconfined zone of the SAG and cation exchange coupled with the dissolution of calcite at the transition between unconfined and confined zone, and (9) authigenesis of analcime in the confined SAG zone. The last two processes are still under operation. The deep zone of the SAG comprises an alkaline pH, Na–HCO₃ groundwater type with old water and enriched δ¹³C values (<?3.9), which evolved from a neutral pH, Ca–HCO₃ groundwater type with young water and depleted δ¹³C values (>?18.8) close to the SAG outcrop. This is consistent with a conceptual geochemical model of the SAG, suggesting dissolution of calcite driven by cation exchange, which occurs at a relatively narrow front recently moving downgradient at much slower rate compared to groundwater flow. More depleted values of δ¹⁸O in the deep confined zone close to the Paraná River compared to values of relative recent recharged water indicate recharge occur during a period of cold climate. The SAG is a “storage-dominated” type of aquifer which has to be managed properly to avoid its overexploitation.     

Geochemical and stable isotopic evolution of the Guarani Aquifer System in the state of São Paulo, Brazil

The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer System (Botucatu and Piramboia aquifers) in S?o Paulo State, Brazil. Trends of dissolved species concentrations and geochemical modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na–HCO₃ type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of groundwater flow and at present is located near to the cities of Sert?ozinho and águas de Santa Barbara (wells PZ-34 and PZ-148, respectively) in a shallow confined area, 50–70 km from the recharge zone. Part of the sodium probably enters the Guarani Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ ²H and δ ¹⁸O values in groundwater downgradient. Values of δ ¹³C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ ¹³C(DIC) in deep geothermal wells are very high (>–6.0‰) and probably indicate isotopic exchange with carbonates with δ ¹³C about –3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination to the Guarani Aquifer System. Electronic Publication     

德国南部地区上侏罗统麻姆组碳酸盐岩碳,氧稳定同位素研究

对德国南部地区上侏罗统麻姆组碳酸盐岩系列Ｃ、Ｏ稳定同位素进行了测定与研究。结果表明,Ｃ、Ｏ同位素与非碳酸盐岩组分质量分数及层厚之间存在一定的关系。石灰岩的δ１８Ｏ值略低于泥灰岩,泥灰岩的δ１３Ｃ值则比石灰岩的约低０．６‰,随着不溶残余物质量分数的增加,δ１３Ｃ值减少。通常情况下,厚层石灰岩的δ１３Ｃ值比泥灰岩的大,其原因与沉积环境和成岩作用有关     

Stochastic simulation of time-series models combined with geostatistics to predict water-table scenarios in a Guarani Aquifer System outcrop area, Brazil

Stochastic methods based on time-series modeling combined with geostatistics can be useful tools to describe the variability of water-table levels in time and space and to account for uncertainty. Monitoring water-level networks can give information about the dynamic of the aquifer domain in both dimensions. Time-series modeling is an elegant way to treat monitoring data without the complexity of physical mechanistic models. Time-series model predictions can be interpolated spatially, with the spatial differences in water-table dynamics determined by the spatial variation in the system properties and the temporal variation driven by the dynamics of the inputs into the system. An integration of stochastic methods is presented, based on time-series modeling and geostatistics as a framework to predict water levels for decision making in groundwater management and land-use planning. The methodology is applied in a case study in a Guarani Aquifer System (GAS) outcrop area located in the southeastern part of Brazil. Communication of results in a clear and understandable form, via simulated scenarios, is discussed as an alternative, when translating scientific knowledge into applications of stochastic hydrogeology in large aquifers with limited monitoring network coverage like the GAS.     

Stable 18O and 13C isotope records of Viviparus diluvianus (Kunth, 1865) shells from Holsteinian (MIS 11) lakes of eastern Poland as palaeoenvironmental and palaeoclimatic proxies

The oxygen and carbon stable isotope composition of Viviparus diluvianus shells was determined in the palaeolakes of the Holsteinian interglacial (MIS 11) in eastern Poland: the Ortel Królewski, Hrud, Ossówka, Roskosz and Szymanowo lakes. The occurrence of V. diluvianus covers the Taxus zone, the so‐called intra‐interglacial cooling period (Pinus‐Larix zone), the climatic optimum (Carpinus‐Abies zone) and the post‐optimal period with an undefined pollen zone. The isotope record of V. diluvianus shells allowed palaeoclimate and palaeoenvironmental reconstructions. δ¹⁸O and δ¹³C vary from −8.7‰ in the post‐optimal period to −4.8‰ in the optimal period, and from −10.6‰ at the beginning of the Taxus zone to −4.2‰ at the climatic optimum, respectively. A positive correlation of the isotope curves indicates closed‐water bodies, and only at Roskosz was some occasional overflow inferred. Higher oxygen isotopes correspond to an increase in temperature and/or enhanced evaporation, which is well marked in the Carpinus‐Abies zone, whereas samples enriched in ¹³C are correlated with periods demonstrating a lower water level and higher productivity in the lakes. Episodes of lake shallowing and dense aquatic vegetation occurred in the Pinus‐Larix zone and during the climatic optimum. The isotope ratios for the climatic optimum significantly exceed those of the other periods, thus pointing to warmer conditions. An estimation of relative changes of average summer temperatures using the δ¹⁸O/temperature gradient yielded variation of 1–2 °C within the lakes. Absolute temperature reconstructions indicate the effects of specific local conditions. Hence, V. diluvianus shells offer a reliable proxy in qualitative studies of interglacial lake records.     

Environmental isotopes (18O, 2H, and 87Sr/86Sr) as a tool in groundwater investigations in the Keta Basin, Ghana

Analyses of environmental isotopes (¹⁸O, ²H, and ⁸⁷Sr/⁸⁶Sr) are applied to groundwater studies with emphasis on saline groundwater in aquifers in the Keta Basin, Ghana. The ⁸⁷Sr/⁸⁶Sr ratios of groundwater and surface water of the Keta Basin primarily reflect the geology and the mineralogical composition of the formations in the catchments and recharge areas. The isotopic compositions of ¹⁸O and ²H of deep groundwater have small variations and plot close to the global meteoric water line. Shallow groundwater and surface water have considerably larger variations in isotopic compositions, which reflect evaporation and preservation of seasonal fluctuations. A significant excess of chloride in shallow groundwater in comparison to the calculated evaporation loss is the result of a combination of evaporation and marine sources. Groundwaters from deep wells and dug wells in near-coastal aquifers are characterized by relatively high chloride contents, and the significance of marine influence is evidenced by well-defined mixing lines for strontium isotopes, and hydrogen and oxygen stable isotopes, with isotopic compositions of seawater as one end member. The results derived from environmental isotopes in this study demonstrate that a multi-isotope approach is a useful tool to identify the origin and sources of saline groundwater. Electronic Publication     

Hydrogeological and hydrochemical investigation of groundwater using environmental isotopes (18O, 2H, 3H, 14C) and chemical tracers: a case study of the intermediate aquifer,Sfax, southeastern Tunisia

Major element concentrations and stable (δ¹⁸O and δ²H) and radiogenic (³H and ¹⁴C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water–rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ¹⁸O and δ²H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO₄ and Ca-Na-Cl-SO₄. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ¹⁸O and δ²H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.

     

Applications of Light Stable Isotopes(C,O, H) in the Study of Sandstone Diagenesis: A Review

This article reviews the applications of light stable isotope, including carbon, oxygen and hydrogen, in thestudies on origin and formation temperature of authigenic carbonate, quartz and clay minerals. Theoretical knowledge andanalytical methods for major light stable isotopes are introduced in detail. Negative and positive δ¹³C values indicatesignificant differences on the origin of carbonate cements. The δ¹⁸O value is an effective palaeotemperature scale forauthigenic minerals formation. Various fractionation equations between δ¹⁸O and temperature are proposed for carbonatecements, quartz cements and clay minerals, whose merit and demerit, applicable conditions are clarified clearly. Clumpedisotope analysis can reconstruct the temperature of carbonate precipitation with no requirement on the δ¹⁸O of initial waters,which makes temperature calculation of carbonate cements formation more convenient and accurate. Hydrogen and oxygenisotopes mainly reflect the origin of diagenetic fluid for clay mineral formation, providing reliable evidence for diageneticenvironment analysis. This work aims at helping researchers for better understanding the applications of light stable isotopein sandstone diagenesis.     

Annual periodicity of the 18O16O and 13C12C ratios in the coral Montastrea annularis

The isotopic ratios ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ show an annual periodicity in the coral Montastrea annularis from Bermuda, Jamaica and Barbados. The abundances of ¹⁸O and ¹³C are positively correlated in the Jamaica and Barbados samples, but inversely related in the Bermuda sample. Annual high density growth bands are formed during the season of warmest water temperature at all 3 sites and are enriched in ¹⁶O. M. Annularis has a constant displacement from oxygen isotopic equilibrium and accurately records seasonal temperature variations via the temperature-dependent aragonite-water fractionation factor. Light intensity, through the activity of the coral's endosymbiotic algae, regulates the depth-dependent and seasonal variations in the skeletal carbon isotopic composition.     

Stable isotope (2H, 18O and 87Sr/86Sr) and hydrochemistry monitoring for groundwater hydrodynamics analysis in a karst aquifer (Gran Sasso,Central Italy)

This paper deals with chemical and isotope analyses of 21 springs, which were monitored 3 times in the course of 2001; the monitoring program was focused on the groundwater of the Gran Sasso carbonate karst aquifer (Central Italy), typical of the mountainous Mediterranean area.Based on the hydrogeological setting of the study area, 6 groups of springs with different groundwater circulation patterns were distinguished. The hydrogeochemistry of their main components provided additional information about groundwater flowpaths, confirming the proposed classification. The spatial distribution of their ion concentrations validated the assumptions underlying the hydrogeological conceptual model, showing diverging groundwater flowpaths from the core to the boundaries of the aquifer. Geochemical modelling and saturation index computation elucidated water–carbonate rock interaction, contribution by alluvial aquifers at the karst aquifer boundaries, as well as impacts of human activities.The analysis of ¹⁸O/¹⁶O and ²H/H values and their spatial distribution in the aquifer substantiated the hydrogeology-based classification of 6 groups of springs, making it possible to trace back groundwater recharge areas based on mean isotope elevations; the latter were calculated by using two rain monitoring stations. ⁸⁷Sr/⁸⁶Sr analyses showed seasonal changes in many springs: in winter–spring, the changes are due to inflow of new recharge water, infiltrating into younger rocks and thus increasing ⁸⁷Sr/⁸⁶Sr values; in summer–autumn, when there is no recharge and spring discharge declines, changes are due to base flow groundwater circulating in more ancient rocks, with a subsequent drop in ⁸⁷Sr/⁸⁶Sr values.The results of this study stress the contribution that spatio-temporal isotope monitoring can give to the definition of groundwater flowpaths and hydrodynamics in fissured and karst aquifers, taking into account their hydrogeological and hydrogeochemical setting.     

Meixnerit,Mg6Al2(OH)18·4H2O,ein neues Magnesium-Aluminium-Hydroxid-Mineral

Zusammenfassung Meixnerit, Mg₆Al₂(OH)₁₈·4H₂O, kommt als sekundäres Mineral in Klüften eines Serpentins in der Nähe von Ybbs-Persenbeug (Niederösterreich) vor. Die Kristalle sind blättchenförmig, farblos durchsichtig, optisch ein-achsig-negativ mitn ₀=1,517. Die Spaltbarkeit parallel (00.1) ist perfekt. Meixnerit ist trigonal-rhomboedrisch, RaumgruppeR m,a=3,0463 (15) Å,c=22,93 (2) Å,Z=3/8. Strukturell ist er eng mit dem Hydrotalkit verwandt. Das neue Mineral wurde zu Ehren von Herrn Prof. Dr.H. Meixner, Salzburg, benannt.

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Meixnerite, Mg₆Al₂(OH)₁₈·4H₂O, a new magnesium-aluminum-hydroxide mineral

Summary Meixnerite, Mg₆Al₂(OH)₁₈·4H₂O, occurs as a secondary mineral in cracks of a serpentine rock near Ybbs-Persenbeug (Lower Austria). The crystals are tabular, colorless transparent, optically uni-axial negative withn ₀=1.517, cleavage parallel (00.1) perfect. Meixnerite is trigonal rhombohedral, space groupR m,a=3.0463 (15) Å,c=22.93 (2) Å,Z=3/8. It is structurally related to hydrotalcite. The new mineral is named in honour of Prof. Dr.H. Meixner, Salzburg.

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Mit 1 Abbildung     

Calculation of Stable Isotope (O,C, Ca) Fractionation Factors for Apatite

The isotope fractionation β-factors have been determined for hydroxyapatite, fluorapatite, and carbon–apatite upon ¹⁸O/¹⁶O, ¹³C/¹²C, and ⁴⁴Ca/⁴⁰Ca substitutions depending on the temperature. Calculations were performed based on density functional theory (DFT). The results are expressed in terms of cubic polynomials against x = 10⁶/T(K)² and can be utilized as geothermometers if combined with β-factors of the coexisting phases. The new values of β-factors completely supersede the conventional semi-empirical (estimated by the method of increments) calibrations of isotopic equilibria involving apatite.

     

大兴安岭南段敖仑花斑岩钼(铜)矿床成矿流体来源与成矿作用:稳定同位素C、H、O、S和放射性Pb同位素约束

基于稳定同位素C、H、O、S和放射性Pb同位素的测试和分析,对大兴安岭南段敖仑花斑岩钼(铜)矿床成矿流体的来源进行了示踪,探讨了流体演化与成矿作用过程。新的稳定同位素数据显示:敖仑花矿床成矿热液具有混合来源性质;脉石矿物石英中流体的C、H、O同位素和矿石硫化物的S同位素组成指示成矿络合剂主要来自地幔,同时在热液期经历了地壳流体参与的过程;辉钼矿中放射性成因的Pb同位素组成表明,成矿物质(Mo)主要来自造山带物质,部分来自深部幔源。根据H、O同位素组成变化和已有流体包裹体资料,认为敖仑花矿床早、中阶段两次矿化的成矿机制不同:早阶段金属矿化主要与岩浆水和大气降水的流体混合有关,而中阶段大规模成矿作用主要是由流体沸腾所致。综合区域地质演化认为:敖仑花矿床是大兴安岭南段在晚侏罗世—早白垩世时期演化为弧后伸展背景、陆内造山带物质重新活化、壳幔岩浆-热液相互作用的产物,同时暗示壳幔作用强烈的地区利于内生金属矿床成矿。     

Research on basic characteristics of 2H, 18O and 14C in geothermal fluid in Guangdong Province,China

In general, previous geothermal geochemical studies in Guangdong Province mainly involves single method to cover limited aspects and areas. In that way, various methods available cannot actually provide more convincing results of geothermal fluid’s circulation system and evolution process from different dimensions, especially in terms of isotope. As a result, more comprehensive researches remain to be done on geochemistry of geothermal fluid, in particular, the space-time law of isotope’s evolution pattern as well as recharge cycle. Based on data of environmental isotopes (2H and 18O) and the isotope of radiometric dating (14C), geothermal geology, characteristics of groundwater flow field and types of goethermal reservior in Guangdong Province are taken into account in this paper, so as to analyze numerical rule and spatial distribution features of isotopes. Thus, corresponding main causes, mechanism and hydrogeological significance can be revealed to further study the potential of geothermal fluid to renew and recharge in the long run, which is conducive to enrich geothermal theories and solve existing hydrogeological problems.     

Research on basic characteristics of 2H, 18O and 14C in geothermal fluid in Guangdong Province,China

In general, previous geothermal geochemical studies in Guangdong Province mainly involves single method to cover limited aspects and areas. In that way, various methods available cannot actually provide more convincing results of geothermal fluid's circulation system and evolution process from different dimensions, especially in terms of isotope. As a result, more comprehensive researches remain to be done on geochemistry of geothermal fluid, in particular, the space-time law of isotope's evolution pattern as well as recharge cycle. Based on data of environmental isotopes(~2H and ~(18)O) and the isotope of radiometric dating(~(14)C), geothermal geology, characteristics of groundwater flow field and types of goethermal reservior in Guangdong Province are taken into account in this paper, so as to analyze numerical rule and spatial distribution features of isotopes. Thus, corresponding main causes, mechanism and hydrogeological significance can be revealed to further study the potential of geothermal fluid to renew and recharge in the long run, which is conducive to enrich geothermal theories and solve existing hydrogeological problems.     

动物牙釉结构碳酸盐碳、氧同位素测试方法的比较

不同学者用磷酸平衡法分析古哺乳动物牙齿化石碳酸羟基磷灰石中结构碳酸盐的碳、氧稳定同位素组成时，预处理方法和实验条件也不尽相同。实测结果表明，预处理条件与磷酸法制备CO2的反应温度和反应时间均可能对分析结果产生影响，需在综合运用机械和化学手段除净外表附着碳酸盐的前提下，将样品充分研磨，并彻底分解其中的有机组分和非结构碳酸盐，再制备CO2。70℃的恒温水浴可以使化学反应和同位素分馏均在短时间内结束，且较为完全、彻底，测得的同位素数据重现性好；而25℃时反应进行较缓，氧同位素测试结果有时可能不理想     

Stable isotope composition of CO2 outgassed from cores of argillites: a simple method to constrain δ18O of porewater and δ13C of dissolved carbon in mudrocks

Stable isotope characterization of porewater, and dissolved species, in mudrocks and argillaceous rocks is notoriously difficult. Techniques based on physical or chemical extraction of porewater can generate significant analytical artefacts. The authors report a novel, simple approach to determine the δ¹⁸O of porewater and δ¹³C of dissolved C in argillites. The method uses core samples placed in specifically-designed outgassing cells, sealed shortly after drilling and stored in well-controlled conditions. After 1–2 months, CO₂ naturally outgassed by argillite porewater is collected, purified and analyzed for C and O isotopes. Porewater δ¹⁸O and dissolved C δ¹³C are calculated from CO₂ isotope data using appropriate fractionation factors. This methodology was successfully applied to the Callovo-Oxfordian argillites from Bure (eastern Paris Basin, France) and the Opalinus Clay formation from Mont Terri (Switzerland). In both clay formations, results indicate that porewater is meteoric and dissolved C is of marine origin. The main advantage of the approach is that it does not induce any major physical or chemical disturbance to the clay–water system investigated. Further testing on argillaceous rocks of variable composition and organic content is needed to assess extent of applicability.