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Hydraulic conclusions from chemical considerations: groundwater in sedimentary environments in the central part of the Pannonian Basin, Hungary
Abstract
Hydro-chemical and isotopic data from different aquifers in the Great Hungarian Plain (the central part of the Pannonian Basin) were evaluated down to a depth of 2,740 m. The chemical and isotopic composition of water is influenced by its origin and by chemical and mixing processes. The analytical data and chemical considerations, together with geology, pressure conditions and evolution history of the area, explain the evolution of the subsurface water. Most of the samples are of meteoric origin, but there were some samples with a non-meteoric contribution, as indicated by the water stable isotopes, and these were identified as seawater trapped during the sedimentation in Lake Pannon. The sea contribution is traceable by the shifts in δ18O and δ2H and the chemical composition of the water, and is explained with an upward-driving force. Chemical considerations and spatial variability of the dissolved components suggest that distinct water bodies, each with a specific origin and chemical evolution, can be separately identified. Although in the Quaternary layers there are water bodies that can be considered to display complete flow systems (from recharge to discharge), in most water bodies present infiltration was not identified. The lack of recent recharge to several water bodies in various places and depths suggests a separation of the recharge and the discharge that occurred not in space, but in time. A possible explanation of the cessation of recharge is a significant change in the hydraulic circumstances, probably the surface elevation.
... As a scale component, calcium carbonate (CaCO 3 , aragonite, and/or calcite) precipitation is widespread in low-to moderate-enthalpy geothermal facilities tapping deep limestone and dolomite aquifers [6,7]. Although the aquifers of the Szeged Geothermal Systems (SE Hungary, Great Hungarian Plain) are traditionally considered being siliciclastic ones (mainly very fineto fine-grained sandstones) with dominantly Na-HCO 3 -type thermal water [3,9], relatively high carbonate scale deposition rates have been observed especially in the pipes between the production wells and their buffer tanks [7]. In Szeged, construction of a new districtheating geothermal system is in progress (Figure 1; wells H-1 and H-2), so a better characterization of the geothermal reservoir is essential to understand the water-rock interactions in this region. ...
... Recently, some papers reported the man-made (technical/operational) effects of the district-heating geothermal systems in Szeged [2][3][4]7]. Additionally, hydrogeological and hydrochemical conditions in the Great Hungarian Plain were extensively studied applying state-of-the-art geochemical methods [9][10][11][12][13][14][15][16][17][18]. Mineralogical and micropetrographic features of the Miocene-Pliocene geothermal reservoir sandstones in the study area and the related information about scaling potential, however, have not received much attention in the literature. ...
... The subsurface of the Great Hungarian Plain has been subdivided into six regional hydrostratigraphic units which are the followings: pre-Neogene aquiclude, pre-Pannonian aquifer, Endrőd aquitard, Szolnok aquifer, Algyő aquitard with aquifer lenses, and Great Plain (Nagyalföld) aquifer [9,11]. The Szolnok aquifer, corresponding to the Szolnok Formation (Figure 4), is a cyclic alternation of consolidated sandstones, siltstones, and clayey marl beds, whereas the Great Plain aquifer is dominated by unconsolidated sands and coarse clastics, belonging to the Újfalu and Zagyva Formations. ...
The study area, Pannonian Basin (Central Europe), is characterized by high heat flow and presence of low-enthalpy geothermal waters. In the Szeged Geothermal Systems (Hungary), having Miocene to Pliocene sandstone aquifers with dominantly Na–HCO 3 -type thermal water, unwanted carbonate scaling was observed. An integrated approach consisting of host rock and scale mineralogical and petrographic analyses as well as water chemistry led to a better understanding of the characteristic natural (geogenic) environmental conditions of the geothermal aquifers and to highlight their technical importance. Analyses of the reservoir sandstones showed that they are mineralogically immature mixed carbonate-siliciclastic rocks with significant macroporosity. Detrital carbonate grains such as dolomite and limestone fragments appear as important framework components (up to ~20–25%). During water–rock interactions, they could serve as a potential source of the calcium and bicarbonate ions, contributing to the elevated scaling potential. Therefore, this sandstone aquifer cannot be considered as a conventional siliciclastic reservoir. In mudrocks, a significant amount of organic matter also occurs, triggering CO 2 producing reactions. Correspondingly, framboidal pyrite and ferroan calcite are the main cement minerals in all of the studied sandstone samples which can suggest that calcite saturation state of the thermal fluid is close to equilibrium in oxygen-depleted pore water. Analysis of the dominant carbonate crystals in the scale can suggest that growth of the feather dendrites of low-Mg calcite was probably driven by rapid CO 2 degassing of CO 2 -rich thermal water under far-from-equilibrium conditions. Based on hydrogeochemical data and related indices for scaling and corrosion ability, the produced bicarbonate-rich (up to 3180 mg/l) thermal water has a significant potential for carbonate scaling which supports the aforementioned statement. Taking into consideration our present knowledge of geological setting of the studied geothermal systems, temporal changes in chemical composition and temperature of the thermal water during the heating period can indicate upwelling fluids from a deep aquifer. Regarding the pre-Neogene basement, hydrologic contact with a Triassic carbonate aquifer might be reflected in the observed chemical features such as decreased total dissolved solids and increased bicarbonate content with high scale-forming ability. The proposed upflow of basin-derived water could be channeled by Neogene to Quaternary fault zones, including compaction effects creating fault systems above the elevated basement high. The results may help to understand the cause of the high carbonate scale precipitation rates in geothermal systems tapping sandstone aquifers.
... The chemical composition of groundwater is influenced by water origin, aquifer rock types and groundwater flow pattern ( Vars?nyi et al. 2015). The following hydroche- mical sequence of dominant anions, HCO 3 ? SO 4 ? Cl, along the groundwater flow path on a global scale has been described by many authors (Chebotarev 1955, Stuyfzand 1999, T?th 1999). The shift of the dominant anion from HCO 3 to Cl along the flow path is also associated with increasing mineralization due to a ...
The strategic project of economic development in the Dornogobi Province in Mongolia is dependent on water supply. Thus a comprehensive hydrogeological characterization was focused on the Upper Cretaceous multi-aquifer system north of Sainshand City. A conceptual model was developed to discover the groundwater flow pattern essential to correct the setting of the numerical model of groundwater flow created using MODFLOW to assess the natural recharge of the aquifer. The conceptualization was based on geological and hydrogeological characterization. However, especially the evaluation of hydrochemistry proved to be the key factor revealing the principal feature of the groundwater flow pattern, which is the presence of preferential flow zones. These zones allow for intensive transfer of relatively fresh Na(Mg,Ca)‒HCO3 dominated groundwater into discharge areas where it leaks into the Quaternary aquifer. The numerical model suggested an enormous natural recharge of 22 100 m³/d, originating in 64% of the preferential flow zones.
... This pattern can be interpreted by the mixing of waters initially present in the correspondingmostly lacustrinereservoirs with waters flowing from/through marine strata containing halite. It is worth mentioning that the chlorinity of the waters studied from Neogene aquifers of the Flysch Zone of E-Hungary varies with depth in a similar way (see Figure 6a of Varsányi et al., 2015). By interpreting this pattern, the authors of that paper are taking into consideration upward-migrating saline waters. ...
In spite of its considerable size and the presence of mature oil source rocks, the Neogene Danube Basin is characterized by the absence of commercial oil accumulations. However important CO2 fields have been discovered in the basin that are recently possibly explained by displacement of oil by later migration of CO2 into the reservoirs. Previous studies performed independently in the southern, Hungarian part of the basin (known as the Little Hungarian Plain) have attempted to model petroleum generation/migration history, to identify sources of the CO2, to understand tectonic evolution of the basin and its deep water flow regime. We are attempting to combine the results of these studies in order to interpret the fluid migration history and reveal the influencing processes. This work supports the hypothesis that CO2 could have played a key role in preventing formation of oil accumulations. During the latest Miocene early mature oil and saline water, the latter formed by dissolution of up to now unidentified halites, moved together toward the Mihályi High, a regional uplifted structure in the central part of the basin. Modest amounts of oil could have been trapped there while saline water mixed with the low salinity water of the reservoirs, with the CO2 arriving later and displacing the oil. © 2018 Society of Exploration Geophysicists and American Association of Petroleum Geologists.
... Moreover, these geochemical processes are responsible for the spatial and temporal variations of the groundwater's chemistry (Matthess 1982;Kumar et al. 2006). Varsányi et al. (2014) say that the analytical data and chemical considerations, together with geology, pressure conditions, and evolution history of the area, explain the evolution of the subsurface water. The spatiotemporal monitoring and assessment of groundwater used for drinking and irrigation is essential for sustainable safe use of water. ...
This study focuses on chemical analysis of 180 different groundwater samples in Al-Kharj governorate, Saudi Arabia.Thedistributionofchemicalconstituents(major,minor, and trace elements) is determined and compared with drinking and irrigation water standards. The water quality index (WQI) is applied to investigate groundwaters suitability for drinking. The obtained results indicated that the concentrations of dissolvedsalts,solublecationsandanions,andnitrate,wereabove permissible limits set by drinking water standards, WHO, for most wells. The WQI concluded that 65.2 % of studied wells are considered poor water Bclass (III)^, 24.9 % are very poor water Bclass (IV)^, 6.1 % are unsuitable water for drinking Bclass (V)^, and only 3.9 % are good water for drinking or Bclass (II). Most groundwater is contaminated with nitrate with anaverageconcentrationof 14.7mgL−1. Thewater evaluation forirrigationposesthat69.4%ofstudiedwellsareclassifiedas moderately saline; however, the remaining are classified as severe saline water. The US Salinity Laboratory’s diagram reveals that majority of studied waters fall in class C4–S1, the area of very high salinity and low sodium hazards. Durov and Piperdiagramsrevealedthatthemajorityofinvestigatedwaters
are magnesium-calcium/sulfate–chloride water type. The Gibbs’s diagram revealed that the chemical weathering of rock-forming minerals and evaporation are influencing the groundwater quality. The hydrochemical modeling indicates thatallwatersamplesareundersaturatedforhaliteandsaturated for anhydrite and gypsum. The approach of this research could be applicable to similar situations worldwide.
The use of saline groundwater in irrigation due to the limited availability of fresh water is one of the main causes of land degradation in arid and semi-arid environments. The agro-ecosystem of Siwa Oasis was monitored over a period of two decades. A stable isotope study, oxygen-18 and deuterium, indicated that Siwa groundwater is of meteoric origin. Siwa has two groundwater aquifers: a shallow limestone aquifer, LA, with highly saline water (Total Dissolved Solids, TDS, up to 6848 mg/L), and a deep Nubian sandstone aquifer, NSA, containing fresh water (TDS 192–256 mg/L). The sodium adsorption ratio, SAR, of LA water is high with an average value of 13.9 while the SAR of NSA water is low with an average value of 2.1. Schoeller and Piper’s diagrams showed that LA water was of sodium, chloride-sulfate type, while the NSA water was classified as sodium carbonate and bicarbonate water type. Saturation Index (SI) calculations showed that both the LA and NSA water were undersaturated to halite minerals. Consequently, there is room to accommodate extra Na⁺ and Cl⁻ from halite. Most Siwa land is irrigated with LA water due to low drilling costs. LA groundwater and Siwa soils were found to be deteriorating dramatically and the average water and soil salinity increased by 30–36% per decade. No change in NSA water quality was recorded over the same period. Interventions for the restoration of the deteriorated Siwa ecosystem are summarized. The approach conducted in this study can be repeated in similar ecosystems.
The demand for water is rapidly increasing in Egypt, because of high population and agriculture production growth rate, which makes research of water resources necessary. The regional multi-aquifer system of the Miocene–Pleistocene age is discharged in Wadi El Natrun area. Intensive aquifer overexploitation and agricultural development in the area are related to groundwater quality deterioration. Hydrochemical and hydrogeological data was evaluated to determine the groundwater origin and quality in the south-eastern part of wadi, which appears to be more significant for water supply owing to lower groundwater salinity. The dominance of the high mineralised Cl groundwater type was found; however, also less mineralised SO4 and HCO3 types were identified there. Based on the ion relations, halite and gypsum dissolution and ion exchange are the most important hydrochemical processes forming the groundwater chemical composition. The Cl dominated groundwater matches the discharge part of the regional hydrogeological system. Contrary, the presence of HCO3 and SO4 hydrochemical types corresponds to the infiltration and transferring parts of the hydrogeological system indicating the presence of zones conducting low mineralised groundwater. The discharge area of the over-pumped aquifer in Wadi El-Natrun lies 23 m beneath the sea level with the shoreline being at the distance of 100 km, thus there is a real risk of seawater intrusion. Using the hydrochemical facies evolution diagram, four samples in the centre of the discharge area indicate advanced seawater intrusion. The zones of the highest demand for groundwater quality protection were indicated based on a spatial pattern of hydrogeochemical composition.
The studied subsurface water samples represent different depositional environments from the Late Miocene lacustrine and fluviatile (delta-slope, delta-plain) facies to the Pliocene and Quaternary lacustrine, fluviatile and terrestrial ones in the upper 2500 m of the sediments, in the central part of the Pannonian Basin. The study area covers about 25,000 km² and comprises two sub-basins and an area above uplifted basement. Spatial distribution of dissolved arsenic indicates the highest range of the arsenic concentrations (0–180 μg/l) in the groundwater from the Quaternary fluviatile aquifers in both sub-basins. Comparing the measured pH and redox potential to the stability diagrams in the AsOH, FeCO2H2O, and semiquinone-hydroquinone systems it was observed that in the pe-pH diagram, most samples from the Quaternary and Pliocene sediments appear in the stability field of HAsO4²⁻, FeOOH, and semiquinone (Q3−•), and are grouped along a line with a slope similar to those of the redox boundaries between HAsO4²⁻and H3AsO3⁰, and also semiquinone (Q3−•) and hydroquinone (H2Q²⁻) species. The samples from the shallowest, unconfined Quaternary aquifers are above the line, and whereas those from the deepest, Upper Miocene aquifers are below the redox boundary of the standard-state systems. The mobilising processes in the different depositional environments are explained on the basis of the position of the samples in the pe-pH stability diagrams. The spatial distribution of arsenic concentrations in groundwater is attributed to the availability of mobilisable arsenic in the sediments rather than to the other elements of the mobilising processes, such as the type of the chemical reactions, redox circumstances, or temperature.
Groundwater flow influences hydrochemical patterns because flow reduces mixing by diffusion, carries the chemical imprints of biological and anthropogenic changes in the recharge area, and leaches the aquifer system. Global patterns are mainly dictated by differences in the flux of meteoric water passing through the subsoil. Within individual hydrosomes (water bodies with a specific origin), the following prograde evolution lines (facies sequence) normally develop in the direction of groundwater flow: from strong to no fluctuations in water quality, from polluted to unpolluted, from acidic to basic, from oxic to anoxic-methanogenic, from no to significant base exchange, and from fresh to brackish. This is demonstrated for fresh coastal-dune groundwater in the Netherlands. In this hydrosome, the leaching of calcium carbonate as much as 15 m and of adsorbed marine cations (Na+, K+, and Mg2+) as much as 2500 m in the flow direction is shown to correspond with about 5000 yr of flushing since the beach barrier with dunes developed. Recharge focus areas in the dunes are evidenced by groundwater displaying a lower prograde quality evolution than the surrounding dune groundwater. Artificially recharged Rhine River water in the dunes provides distinct hydrochemical patterns, which display groundwater flow, mixing, and groundwater ages.
Uplifted crystalline basement highs have played an important role in the hydrologic history of the Pannonian Basin providing conduits for fluid migration during basin evolution. Petrographic, stable isotope, electron microprobe and fluid-inclusion studies support a five–step basin evolution; (1) formation of crystalline core-complexes, (2) percolation of meteoric water through shear zones, (3) basinwide thermal subsidence, (4) hydrologic inversion, and (5) tectonic inversion.Brittle fractures in the basement are the results of uplift during core complex formation and contain pyrite, kaolin, illite, chlorite, calcite, and quartz. Hydrocarbon stains between calcite and quartz and yellow fluorescent, primary, hydrocarbon inclusions in quartz are indicative of migrations of hydrocarbon-bearing fluids during uplift from mid-crustal depth. Further uplift was associated with meteoric water infiltration along shear-zones as recorded by light δ13C and δ18O values, low trace element concentrations, all-liquid primary fluid inclusions and encased pollens and cuticules of terrestrial plants in a second fracture-calcite crystallised after quartz. A simultaneous meteoric influence in the overlying Pannonian (12.7–3 Ma) sediments is indicated by extensive plagioclase dissolution, calcite cement geochemistry and low-salinity, all-liquid fluid inclusions. The thermal subsidence of the basin led to isolation of the hydrologic system from the surface. Diminishing meteoric influence is recorded by increasing fluid inclusion salinities of secondary inclusions in calcite and quartz in the basement fractures and of primary inclusions hosted in late calcite and quartz in the sediments. A sudden decrease of the fluid inclusion salinities from 4.5 to 1 wt.% NaCleq. at ∼130°C both in burial cements and fracture-filling minerals represents a newly established hydrological system, which redistributed the interstitial fluids, including hydrocarbons. This hydraulic inversion is indicated by abundant fluorescent, secondary fluid inclusions in fracture-filling minerals. Finally, the Pliocene to recent tectonic inversion reopened fractures in the crystalline basement, and induced a rapid crystallisation of laumontite.These results support a long-standing (late Miocene to recent) hydraulic connection between fractured crystalline basement and overlying sediments in the central part of the Pannonian Basin.
Hungary lies in the central part of the Pannonian Basin, surrounded by the ranges of the Alps, Carpathians, and Dinarides. The geology of the country can be summarized as a process whereby complicated plate collision-type orogeny was followed by the formation of a young basin in which a relatively complete sequence of basin infill has been preserved. The handbook “Geology of Hungary” presents an outline of the main features of the geology and geohistory of the region in a single volume, illustrated by a great number of color figures and photos for the benefit of foreign geoscientists interested in this area. The volume follows the evolutionary history of the major structural units prior to their juxtaposition in the Tertiary and discusses the subsequent evolution of the Pannonian Basin. Due to the geohistorical approach to this study it was necessary to extend the scope of the discussion beyond the present-day political boundaries of Hungary, to cover most of the Pannonian region.
Theoretically, three types of flow systems may occur in a small basin: local, intermediate, and regional. The local systems are separated by subvertical boundaries, and the systems of different order are separated by subhorizontal boundaries. The higher the topographic relief, the greater is the importance of the local systems. The flow lines of large unconfined flow systems do not cross major topographic features. Stagnant bodies of groundwater occur at points where flow systems meet or branch. Recharge and discharge areas alternate; thus only part of the basin will contribute to the baseflow of its main stream. Motion of groundwater is sluggish or nil under extended flat areas, with little chance of the water being freshened. Water level fluctuations decrease with depth, and only a small percentage of the total volume of the groundwater in the basin participates in the hydrologic cycle.
To establish the increase in temperature and the time span of the transition between the Late Glacial Maximum (LGM) and the Holocene, the noble gas content, 18O, 2H, 13C δ values, 3H and 14C activity and chemistry were studied in a groundwater flow system in Quaternary sediments in Hungary. The study area is a sub-basin of the Pannonian Basin, where the C isotope ratios are not influenced by carbonate reactions along the flow path, because the only water–rock interaction is ion exchange. The δ18O and δ2H values indicate a cold infiltration period, followed by warming, and, finally, warm temperature conditions. The noble gas data show that the average infiltration temperature was 3.3°C in the cold, 12.9°C in the warm, and intermediate in the transitional stage. Using the noble gas temperatures, geochemical batch modelling was performed to simulate the chemical processes. Based on the geochemical model, δ13C and 14C0 (initial radiocarbon activity) in the recharging water were calculated. Transport modelling was used to simulate the distribution of chemical components, δ18O, δ2H and 14C0, along the flow path. It was found that the main processes determining the chemical composition of the groundwater were dissolution/precipitation of calcite and dolomite during infiltration near the surface, and ion exchange along the flow path. In the recharge area the δ13C and 14C0 were controlled by dissolution and precipitation of carbonate minerals, C speciation, and fractionation processes. All these processes were influenced by the recharge temperature. NGTs calculated from the dissolved noble gas concentrations showed an average of 3.3°C for cold, and 12.9°C for warm infiltration, i.e. for the LGM and for the Holocene. The temperature difference was thus 9.1±0.8°C, which is one of the largest degree of warming detected by noble gases so far. The alkalinity indicates that carbonate reactions were unimportant along the flow path. Owing to the temperature dependence of the equilibrium constants, temperature conditions during infiltration have to be taken into consideration in radiocarbon age calculation. Dispersive transport along the flow path modified the chemical and isotopic composition of infiltrated water. The contribution of the old pore water, which was free of the 14C isotope, resulted in uncertainties in radiocarbon age determination. It was concluded that determination of the radiocarbon age or mean residence time requires detailed knowledge of the hydraulic conditions of groundwater.
The serious scholar of petrology is well aware of the discrepant level
of understanding that exists between igneous and metamorphic
petrogenesis and sediment diagenesis (also known as postdepositional
evolution). While nucleation and crystallization theory, phase
equilibria, and principles of heat and mass transport have provided
guidance for scientists to understand the formation and subsequent
evolution of igneous and metamorphic rocks, sedimentary petrologists
seem to have been left behind in detailed, descriptive characterization,
with little chemical and physical basis to unify the diagenesis of one
rock unit with any other.Of course, one cannot lay blame entirely on the
scientist: the study of sediment diagenesis is plagued by problems of
incomplete chemical reaction, the need to characterize amorphous solids
and poorly crystalline mineral phases, low temperature and pressure
conditions that result in reaction kinetics dominating over
thermodynamic equilibria, and a lot of fugitive water! Further
complications arise because most of the samples available for extensive
regional study of sediment diagenesis are those recovered during the
exploration and exploitation of hydrocarbon and mineral resources. The
processes that have controlled postdepositional chemical and physical
evolution of such samples are undeniably nonrepresentative of those
affecting the vast volumes of most sedimentary sequences.
The hydraulic gradients and velocity of underground flow, the intensity of the water exchange with the earth's surface, the relation of the water-bearing bed to water (e.g., intensive flush, hampered flush, salt accumulation), the subsurface drainage conditions, the duration of time of the contact of water with the geological formations along with the chemical composition of rock material and the water which occurs in them and the structural features of the area, are considered as the chief factors governing the salinity variation of subterranean waters.
In the central part of the Pannonian Basin we investigate formation waters from two deep sub-basins with sedimentary sequences up to 7000 m thick, and from fields above basement highs where the total thickness of the sediments is only 2000 m. In each study region the depth interval involves the Lower (lower part of the Upper Miocene) and Upper (upper part of the Upper Miocene and Pliocene) Pannonian sediments separated with a widespread aquitard, named the Algyő Formation, at the top of the Lower Pannonian. However, in the fields above basement highs, it occasionally contains sand lenses, sedimentological discontinuities, faults and fractures resulting in a more conductive character. We investigate the sources and evolution of the formation waters in two geological settings: in sub-basins and in fields above an elevated basement. We distinguish NaHCO3-type water in the sub-basins and NaCl-dominated water in the fields above the elevated basement. The isotopic composition of most NaHCO3-type samples indicates a pure paleometeoric origin, while a few samples are a mixture of paleometeoric and non-meteoric waters. The NaCl-type samples all have a non-meteoric contribution. We have developed a model for the origin and evolution of the formation water that operates for both water types and both geological conditions. The Cl− dominated water is a mixture of ascending pre-Pannonian evaporated water and freshening Lake Pannon water trapped during the Late Miocene and Pliocene sedimentation in the area above the elevated basement, where in some places the Algyő Formation is conductive. The source and evolution of the NaHCO3 non-meteoric water in the sub-basins are similar to those of the NaCl water, with the main difference being the aquitard character of the Algyő Formation in the sub-basins. The aquitard consists of siltstone and clay-marl, which has resulted in overpressure in the layers under the Algyő Formation. The ascending pre-Pannonian water, which mixes with in-situ pore water squeezed through the compacted clay by overpressure, is exposed to microfiltration. The Cl− remains behind, and the squeezed water is depleted of the heavier isotopes. These processes are shown by recent chemical and isotopic data (δ18O and δD), as well as by archival chemical and hydrological data.
The amount of carbon in organic, inorganic and gas (CH4 and CO2) components, and the concentration of dissolved organics like humic substances, short-chain aliphatic acid anions (acetate and propionate), PAHs, phenols volatile with water vapor, alkylphenols, benzene, alkylbenzenes and oil were determined in groups of formation waters from different depths and locations in two adjacent subbasins located in the central part of the Pannonian Basin (southeast Hungary). The proportions of inorganic, organic and gas carbon to total carbon content of water, and the proportion of carbon content in the identified organic compounds to TOC were calculated. These proportions are characteristic of the location of water-bearing formations. The more aromatic character of organic matter together with the high ammonium and low iodide concentrations suggest a more terrestrial sedimentation in the Szeged area than in the Körös area, where the more aliphatic character with low ammonium and high iodide concentrations indicate a more aquatic paleoenvironment. In the Körös area, formation waters are highly depleted in 13C in the whole studied depth interval, compared to the Szeged area. The high negative δ13C values of bicarbonate may be attributed to depletion of 13C in the sediment organic matter of aquatic origin, depletion of 13C in the atmospheric and soil CO2 during the infiltration period before the last glacial, and a longer residence time of water.
Aquifers of the peninsulas of Florida and northern Yucatan are Tertiary
marine carbonate formations showing many lithologic and faunal
similarities. In addition, the tropical to subtropical climates of the
two areas are similar, each having annual rainfall of about 1000 to 1500
mm. Despite similarities in these fundamental controls, contrasts in the
hydrologic and geochemical systems are numerous and striking. For
example, Florida has many rivers; Yucatan has none. Maximum thickness of
fresh ground water in Florida is about 700 meters; in the Yucatan it is
less than 70 meters. In Florida the gradient of the potentiometric
surface averages about 1 meter per kilometer; in the Yucatan it is
exceedingly low, averaging about 0.02 meter per kilometer. In Florida
the chemical character of water changes systematically downgradient,
owing to solution of minerals of the aquifer and corresponding increases
in total dissolved solids, sulfate, calcium, and Mg-Ca ratio; in the
Yucatan no downgradient change exists, and dominant processes
controlling the chemical character of the water are solution of minerals
and simple mixing of the fresh water and the body of salt water that
underlies the peninsula at shallow depth. Hydrologic and chemical
differences are caused in part by the lower altitude of the Yucatan
plain. More important, however, these differences are due to the lack of
an upper confining bed in Yucatan that is hydrologically equivalent to
the Hawthorn Formation of Florida. The Hawthorn cover prevents recharge
and confines the artesian water except where it is punctured by
sinkholes, but sands and other unconsolidated sediments fill sinkholes
and cavities and impede circulation. In the Yucatan the permeability of
the entire section is so enormous that rainfall immediately infiltrates
to the water table and then moves laterally to discharge areas along the
coasts.
The ≈ 40 000 km² Hungarian Great Plain portion of the Pannonian Basin consists of a basin fill of 100 m to more than 7000 m thick semi- to unconsolidated marine, deltaic, lacustrine and fluviatile clastic sediments of Neogene age, resting on a strongly tectonized Pre-Neogene basement of horst-and-graben topography of a relief in excess of 5000 m. The basement is built of a great variety of brittle rocks, including flysch, carbonates and metamorphics. The relatively continuous Endrőd Aquitard, with a permeability of less than 1 md (10⁻¹⁵ m²) and a depth varying between 500 and 5000 m, divides the basin's rock framework into upper and lower sequences of highly permeable rock units, whose permeabilities range from a few tens to several thousands of millidarcy. Subsurface fluid potential and flow fields were inferred from 16 192 water level and pore pressure measurements using three methods of representation: pressure–elevation profiles; hydraulic head maps; and hydraulic cross-sections.
On the basis of the degree of mineralization, approximately 40 percent of the ground water in Ross Creek Basin may be considered as fresh (TDS < 2,000 ppm), and 60 percent as brackish (2,000 < TDS < 10,000 ppm). At least 70 percent of the ground water is potable within treatable limits. Major ion analyses of over 167 water samples reveal a strikingly consistent regional pattern of hydrochemistry.
The hydrochemical pattern correlates with the flow pattern of ground water in the basin. Low total dissolved solids contents, high Ca2+:Mg2+ ratio, low SO42−, and high HCO3− occur in recharge areas, whereas opposite conditions are associated with discharge areas. In terms of hydrochemical facies, waters of the Ca-Mg-HCO3 and Na-HCO3 types are dominant in recharge areas, and those of the Ca-Mg-SO4-HCO3 and Na-SO4-HCO3 types prevail in discharge areas. The hydrochemical evolutionary trends appear to be strongly related to the flow paths.
The East Midlands Triassic (Sherwood Sandstone) aquifer which has been the subject of detailed radiometric age studies, is used to investigate both inert and reactive constituents of groundwater as indicators of residence time. Detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data, though without radiocarbon. Several inert indicators are defined including the isotopic ratios δ¹⁸O, δ²H, ³⁶Cl, noble gas ratios, as well as the halogen elements (Cl, Br, F, I) and their element ratios. These form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions, except at outcrop where human impacts are also seen clearly. The concentrations of Cl, mainly from atmospheric sources, remain below 25 mg l⁻¹ Cl over a distance of some 30 km from outcrop. Reactive indicators, the result of time-dependent water–rock interactions, include δ¹³C, Mg/Ca, Sr/Ca, Na/Cl and show diagnostic trends along the flow lines. However the concentrations of certain trace elements — Li, Rb, Cs, Mn and Mo — which are not limited by solubility constraints show linear trends along the present day flow gradient. This water–rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the Sherwood Sandstone.
Twenty five deep-water samples collected in the southern part (Szeged area) of the Pannonian Basin were analysed for their chemical and isotopic compounds. Hydrogen and oxygen isotopes indicate that most of the waters have a palaeometeoric origin. They infiltrated during a cold period. Waters in the deepest lithostratigraphical positions are mixtures of palaeometeoric water and oil field water squeezed from the thick sequence of fine-grained sediments underlying the thermal water aquifer. Most of the waters are NaHCO3 type with 1200–4400 mg/l of TDS. Na and HCO3 increase with depth and/or temperature. Based on chemical and isotopic compositions, waters are divided into three groups and these reflect differences in the lithostratigraphy of the basin. The wide range of carbon stable isotope variation (−14.5<δ13C<0) suggests the existence of different carbon sources. In the shallowest samples soil CO2 and dissolved carbonate minerals could account for the dissolved inorganic carbon. In deeper layers additional carbon from the transformation of the sedimentary organic matter is required due to the increase of alkalinity with depth and δ13C values. The evolution of the sediment organic matter starts with kerogen formation accompanied by a CO2 production and is followed by the transformation of kerogen yielding CO2 from its oxygen-containing functional groups. Such evolution and methane formation can explain the wide range of 13C contents measured in the total dissolved inorganic carbon.
Subsidence, sedimentation and tectonic quiescence of the Pannonian basin was interrupted a few million years ago by tectonic reactivation. This recent activity has manifested itself in uplift of the western and eastern flanks, and continuing subsidence of the central part of the Pannonian basin. Low- to medium-magnitude earthquakes of the Carpathian-Pannonian region are generated mostly in the upper crust by reverse and wrench fault mechanisms. There is no evidence for earthquakes of extensional origin.2-D model calculation of the subsidence history shows that a recent increase in magnitude of horizontal compressional intraplate stress can explain fairly well the observed Quaternary uplift and subsidence pattern. We propose that this stress increase is caused by the overall Europe/Africa convergence. In Late Pliocene, consumption of subductible lithosphere at the eastern margin of the Pannonian basin was completed, and the lithosphere underlying the Pannonian basin became locked in a stable continental frame. Consequently extensional basin formation has come to an end, and compressional inversion of the Pannonian basin is in progress.
Flux equations for liquid and solute migration through clay barriers that behave as semi-permeable membranes used in waste containment and remediation applications, known as clay membrane barriers (CMBs), are discussed. The results of a simplified analysis of flow through a geosynthetic clay liner (GCL) using measured values for the chemico-osmotic efficiency coefficient (ω) of the GCL indicate a total liquid flux that counters the outward Darcy (hydraulic) flux due to chemico-osmosis associated with clay membrane behavior of the GCL. Also, the solute (contaminant) flux through the GCL is reduced relative to the solute flux that would occur in the absence of membrane behavior due to chemico-osmotic counter advection and solute restriction. Since diffusion commonly controls solute transport through GCLs and other low-permeability clay barriers, the implicit (empirical) correlation between ω and the effective salt-diffusion coefficient of the migrating contaminant is an important consideration with respect to contaminant restriction in CMBs.
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A Duna-Tisza köze rétegvíz áramlási rendszerének izotóp hidrológiai vizsgálata [Isotope hydrological study of the groundwater flow regime of Danube-Tisza region
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