Robert Mokrik, Lehte Savitskaja, Leonid Savitski50

Mokrik R., Savitskaja L., Savitski L. Aqueous geochemistry of the Cam-brian–Vendian aquifer system in the Tallinn intake, northern Estonia.Geologija. Vilnius. 2005. No. 51. P. 50–56. ISSN 1392-110X.

Identification of seawater intrusion is based on intake observationresults in the groundwater chemistry and isotopes. Indications of the sa-line front of marine origin can be obtained from the cation exchangeprocess which is reflected in the groundwater chemical composition byCa–Cl and Na–HCO3 types of groundwater. The Na–Ca exchange evi-dences are accompanied by sulfate reduction reaction, dissolution anddeposition of carbonates, which are also confirmed by the distributionand evolution of content of stable and radioisotopes in the groundwaterof the Cambrian–Vendian aquifer system on the Tallinn intake, northernEstonia.

Key words: groundwater chemistry, seawater intrusion, cation exchange,chloride and bromide ratio, stable isotopes, Baltic Basin

Received 29 March 2005, accepted 16 May 2005

Robert Mokrik. Department of Hydrogeology and Engineering Geologyof Vilnius University, M. K. Èiurlionio 21, LT-2009, Vilnius, Lithuania. E-mail: robert. mokrik@gf.vu.ltLehte Savitskaja and Leonid Savitski. Geological Survey of Estonia, Ka-daka tee 82, 12618, Tallinn, Estonia. E-mail: savitskaja@egk.ee

Robert Mokrik,

Lehte Savitskaja,

Leonid Savitski

Aqueous geochemistry of the Cambrian–Vendianaquifer system in the Tallinn intake, northernEstonia

GEOLOGIJA. 2005. Nr. 51. P. 50–56© Lietuvos mokslø akademija, 2005© Lietuvos mokslø akademijos leidykla, 2005

Hidrogeologija • Hydrogeology • Ãèäðîãåîëîãèÿ

INTRODUCTION

As a result of intensive exploitation, a vast depres-sion cone exceeding 100 km has formed at the Tal-linn intake situated in the coastal area of northernEstonia. The lowest altitude of the potentiometriclevel (more than 30 metres b.s.l) is concentrated atthe intake center. In 1977, by observation wells ofthe Tallinn intake, a fast increase in total dissolvedsolids (TDS) was detected. Chemical and isotopicdata indicated that many factors control the rise ingroundwater salinity. The resources of coastal ground-water of the Cambrian–Vendian aquifer system arelimited and consist mainly of natural reserves for-med during the last glaciation. The long-time over-

exploitation of the Tallinn intake resulted in saliniza-tion not only in the Cambrian–Vendian sandstonesbut also in the basement water, which kept brackishgroundwater because of seawater intrusion. The sa-linity in the Tallinn intake had been discussed ear-lier by many authors, but the seawater intrusion wasnever assessed from the point of view of cation ex-change processes formed by Ca–Cl and Na–HCO3types of groundwater. Based on hydrochemical andisotopic data, it is concluded that the recent seawa-ter intrusion into the aquifer system previously pala-eorecharged by glacial water is generally accompa-nied by ion exchange which caused the present freshand saline groundwater distribution in the Tallinnintake (northern Estonia).

Aqueous geochemistry of the Cambrian–Vendian aquifer system in the Tallinn intake, northern Estonia 51

Increased salinity since 1977 has been observedin many wells drilled into the Cambrian–Vendianaquifer system at Kopli Peninsula site of the Tallinnintake. In earlier studies, several attempts have beenmade to determine the origin of salinization. Oneopinion is that salinization is attributed to many sour-ces, such as brackish groundwater upcoming fromthe basement and seawater intrusion (Mokrik et al.,1987). According others, the detectable intrusion ofmodern seawater into the aquifer system should beruled out (Savitski and Belkina, 1985; Yezhova etal., 1996; Karro et al., 2004). Thus, the origin offresh groundwater in the Cambrian–Vendian aquifersystem as well as the brackish basement water is notclear.

METHODS AND PURPOSE

The basic approach of the study was to collect andanalyze previously published reports and articles andto use the new interpretative data on groundwaterchemistry to define their origin and assess the hu-man impact on water geochemistry in the Tallinnintake. All these data were incorporated into waterchemistry database analysis to draw up a more com-prehensive vision of groundwater formation and toprovide an improved estimate to a qualitative analy-

sis within the aquifers and between the flow systemboundaries. The objectives of the Cambrian–Vendianaquifer system study were: (1) to delineate the ex-tent of fresh to saline water in the various hydroge-ological units and in basement rocks, (2) to analyzethe human impact on groundwater chemistry and onthe flow system in the coastal intake, and (3) toassess the current groundwater isotope distributionand to identify the trends of these changes.

Equilibrium thermodynamics of groundwater wasinterpreted using the PHREEQUE Interactive 2.8computer code program which calculates mineral sa-turation states for an aqueous solution by the che-mical analysis and physical parameters relative to car-bonate minerals and other species.

DISCUSSION

Problems and objectivesIn 1977–1978, hydrochemical observations of ground-water in Kopli Peninsula on the Tallinn intake fixedan increase in water salinity (Fig. 1). Here ground-water contained higher concentrations of TDS, chlo-ride, sulfate, sodium, calcium and other constituentsrelative to the area farther from the coast line andburied valleys. In the other sites, the backgroundchloride concentration of fresh groundwater was

about 20–150 mg/l. Themost intensive growing ofTDS was observed in theKopli site boreholes 632and 625, where it reachedup to 1.1 g/l at a growthrate 16–70 mg/l per year.In the basement borehole798, chloride content in1995–2004 has been gro-wing more rapidly (from826 to 2367 mg/l). Seawa-ter percolation occursthrough the buried valleys,which are largely developedon the coastal and seasidesubmarine parts and con-nected with the sea hydrau-lically. It is difficult to iden-tify sea water intrusion he-re, because many chemicaltypes of water spread andthe isotopic homogeneity isdisturbed. Salinization ofaquifers is a result of freshand seawater mixing and iscoupled with the ion ex-change process. The water–rock interaction processesare often masked by salini-zation in the boreholes set-

Fig. 1. Map of the study area long Tallin intake, northern Estonia.1 – observation borehole; 2 – potentiometric contour, m b.s.l.; 3 – location scheme ofthe Kopli Peninsula; 4 – contour of the buried valley. On the location scheme: 1 –observation borehole, numerator – number of the well, denominator – Cl/Br ratio; 2– Cl/Br contour; 3 – boundary of the buried valley1 pav. Talino vandenvietës (Ðiaurës Estija) tirtø plotø schema:1 – stebëjimo græþinys, 2 – pjezometrinis paviršius, 3 – Kopli pusiasalio schema, 4 –paleoárëþis. Kopli pusiasalio schemos sutartiniai þenklai: 1 – stebëjimo græþinio ëminys;skaitiklyje – græþinio numeris, vardiklyje – Cl/Br santykis; 2 – Cl/Br santykio izolinija;3 – paleoárëþis

Robert Mokrik, Lehte Savitskaja, Leonid Savitski52

ting up to the basal level of aquifers. Previous stu-dies on the ground of the stable isotopes and Br/Clratios have shown that groundwater salinity in theTallinn intake is influenced only by basement waterand has no relation with the seawater intrusion pro-cess (Savitski and Belkina 1985; Yezhova et al., 1996;Karro et al., 2004). Another opinion is that the se-awater intrusion has influenced the salinity increase(Gregorauskas et al., 1988; Mokrik, 1997). The lat-ter opinion was based on the observation of changesof the characteristic coefficient SO4

2– + Mg2+/ Cl–.This coefficient value in the Gulf of Finland waterequals to 3 · 10–1, in the fresh groundwater of theCambrian–Vendian aquifer system on Kopli Peninsu-la site from 2 · 10–1 to 2.5 · 10–1, and in the base-ment water ranges between 5 · 10–2 – 1.5 · 10–1. Ifon the investigated site there is a suction of seawa-ter salinity, the values of the characteristic coeffi-cient must increase by seawater intrusion, togetherwith growth in groundwater TDS values. And viceversa, if there is a suction of saline water from thecrystalline basement, together with the increase ingroundwater TDS its value will decrease.

The low 14C concentration (below 3–4 pmC) couldsuggest that the age of groundwater corrected by 13Cis about 26–34 ka BP, indicating that a recharge be-cause of the cold climate conditions took place be-fore the Late Weichselian, during the Denekamp In-terstadial time, when the Estonian territory was notcovered by the Late Weichselian ice sheet. A modelof palaeorecharge formed during the Denekamp inthe western part of the Estonian Homocline, whereaquitard clays of the Lontova Regional Stage arereplaced in facies by the terrigenous complex of theVoosi Formation deposits, was also proposed (Mok-rik, 1997). Based on the stable isotope data and noblegas analyses, a tunnel valley subglacial drainage hy-pothesis was built up (Vaikmäe et al., 2001). A mo-re extended model embraces subpermafrost commu-nication within aquifers with the isotopically deple-ted surface waters through the talik zones beforethe Last Glacial period, taking into account also la-ter total effects of subglacial recharge after glacierdegradation, Baltic Ice Lake (BIL) influence, the Bal-tic Sea water intrusion and modern meteoric rechar-ge in the terrestrial part of the Baltic artesian basin.This model was firstly analyzed by Mokrik andMaþeika (2002). As follows from the above, the ge-nerally accepted model of groundwater formation inthe Cambrian–Vendian aquifer system is complica-ted and requires further elaboration.

Seawater intrusion identificationOur new re-interpretation of the chemical-isotopicdata confirmed that seawater intrusion took placehere, because two types of groundwater, Na–HCO3and Ca–Cl, are predominant. If seawater intrudes tothe fresh groundwater aquifer, Na+ ions will be ex-

changed against Ca2+ ions adsorbed on the clays and,vice versa, the reverse process takes place with re-freshening, when fresh water flushes in saline seawa-ter (Appelo, Geirnaert, 1983; Appelo, Postma, 1993).As a result of the sea and fresh water mixing pro-cess via Na–Ca cation exchange reaction, seawaterbecomes saline of Ca-Cl type and fresh water ofNa–HCO3 type. When Ca–HCO3 type groundwatermixes with Na–Cl type water, the calcite dissolutionis driven by subsaturation due to loss of Ca2+ fromsolution and formation of NaHCO3 and CaCl2 typegroundwater (Appelo, Postma 1993):

2NaCl + Ca(HCO3)2 = 2NaHCO3 + CaCl2. (1)

In the Na–HCO3 type groundwater, characteristic isan increase of HCO3

–, when water pH becomes highbecause of the evident carbonate dilution process.The Ca–Cl type water is the result of carbonate pre-cipitation driven by enrichment of solution after ca-tion exchange. Dissolution of carbonates moves themixture on the Piper diamond towards the Na+ +K+

– HCO3– and Ca2+ + Mg2+ – HCO3

– corners. At thebeginning of Na–Ca cation exchange intensities re-sulted increase in the Ca2+ content and that effectsa lowering of pH and solution due to subsaturatedwith respect to dolomite and calcite, which movethe changes in groundwater chemistry into SO4

2– +Cl– and Ca2+ + Mg2+ corner. In this case, deposi-tion of carbonates prevails:

MgCl2 + Ca(HCO3)2 = CaCl2 + CaMg(CO3)2 +2H2O +2CO2. (2)

When sodium type groundwater conservatively mi-xed with Mg–Cl or Ca–Cl types seawater, a Na–Cltype residual solution with a tendency to enrichmentby carbonates will be obtained:

2NaHCO3 + MgCl2 = 2NaCl + MgCO3 + H2O+ CO2, (3)

2NaHCO3 + CaCl2 = 2NaCl + CaCO3 + H2O+ CO2. (4)

The wedges of seawater intrusion in conditions ofaquifer reduction coincided to first into sulfate re-duction process by the reaction:

SO42– + 2CH2O = H2S + 2HCO3

–. (5)

This reaction moved groundwater chemical composi-tion from a conservative mixing line between freshand saline seawater with parallel shift towards theSO4

2– + Cl– side on the Piper diamond plot.The content of ions in groundwater at the Tallinn

intake sites is very variable; the dominant anions areHCO3

– and Cl– and the dominant cations are Na+

Aqueous geochemistry of the Cambrian–Vendian aquifer system in the Tallinn intake, northern Estonia 53

and Ca2+. Groundwater affected by seawater intru-sion by the salinity is generally Ca–Cl type, at thesame time the SO4

2– content is depleted, because asulfate reduction is normally decreased if chloride con-centration grows. Only periodically in many boreholes(613, 615, 645, 694 etc) a rise in SO4

2– up to154 mg/l was fixed. Magnesium content on average isalso low (10–16 mg/l), except in seawater intrusion pla-ces where it rises up to 40–60 mg/l. The main seawa-ter intrusion chemical parameters in boreholes couldbe calcium, sodium, magnesium chloride and sulfate.After Karro et al. (2004), calcium and potassium le-vels are high in groundwater, magnesium lies close tothe seawater dilution line (SDL), and sodium is de-pleted with respect to chloride in the production wells.They conclude that this reflects derivation from theweathering of the crystalline basement and is not re-lated with seawater intrusion. The increase in calcium,according to those authors, is attributed to anorthitehydrolysis during its change into kaolinite, when intosolution more Ca2+ is released. Similarly, they claim

that sodium results from plagioclase alteration, and itis possible that it is later adsorbed on clay minerals(Karro et al., 2004). However, the dominant clay mi-neral in the Cambian–Vendian section is illite, follo-wed by quartz and K-feldspar (Mokrik et al., 2000).Our chemical thermodynamics calculations, however,revealed that the groundwater on the seawater intru-sion site in Kopli Peninsula belongs to the gibbsite,kaolinite, muscovite or seawater stability plots (Mok-rik, 2003). The silica content in groundwater is low(mean, 4–11 mg/l) and indicates a weak dissolution ofsilicate minerals. Thus, plagioclase weathering cannotrelease many cations into solution. Evidence of seawater Na+ exchange is taken up by the clays as theexchanger; Ca2+ is released into solution and thuschanges the palaeorecharged fresh groundwater to aCa–Cl type water. As an exchanger here act the cla-yey layers of the Lontova and Kotlin aquitards, alsoQuaternary clays in the buried valleys and the clayeyweathering core of the crystalline basement. The Na–Ca cation exchange process is well displayed in the

Fig. 2. Chebotarev diagram of the major chemical com-pounds in the Cambrian–Vendian aquifer system.1 – borehole number; 2 – seawater intrusion direction; 3– dilution direction; 4 – change direction of chemical com-position; A – groundwater of glacial deposits in buriedpaleovalley2 pav. Kambro–vendo vandeningo komplekso poþeminiovandens cheminiø komponentø pasiskirstymas Èebotariovodiagramoje:1 – græþinio numeris, 2 – jûros intruzijos átakos trendas, 3– ledyno tirpsmo vandens átakos trendas, 4 – cheminëssudëties pokyèio kryptis; A – paleoárëþiø glacialiniø nuogu-lø vanduo

Fig. 3. Piper diagram1 – seawater; 2 – snow water; 3 – borehole samples; 4 –direction of changes in groundwater chemistry3 pav. Piperio diagrama:1 – jûrinis vanduo, 2 – sniego tirpsmo vanduo, 3 – ëminys,4 – poþeminio vandens cheminës sudëties pokyèio trendas

Robert Mokrik, Lehte Savitskaja, Leonid Savitski54

diagrams (Figs. 2 and 3). In the Chebotariov diag-ram, the localities of boreholes 798, 646, 600, 613,632, 154 are moved far away from the SDL whereconservative fresh–saline sea water mixing takes pla-ce. The largest movement toward Ca–Cl type wasfound in the borehole 798, which recovered the base-ment rocks. Figure 4 shows that in 1995 in the bore-hole 798 groundwater an active sulfate reduction de-pleted the SO4

2– content and a sharp increase in Cl–

ion concentration lowered the characteristic coefficientSO4

2– + Mg2+/Cl–, but then followed a rise in its va-lues, which rapidly changed the groundwater chemist-ry and moved the sample position in the diagram tothe vicinity of Ca–Na–Cl type waters. In Fig. 4, thegroundwater composition is represented by the cha-racteristic coefficient SO4

2– + Mg2+/Cl– relative to TDS,which shows an overall shift of the Cambrian–Vendianand Ordovician–Cambrian aquifer systems as compa-red to the SDL trend. This deviation from the SDLsuggests that these groundwaters in general were for-med by glacial water dilution into cryogenically meta-morphosed water. The Pleistocene palaeodilution lineis parallel to the SDL and is shifted in TDS towards

depletion in groundwater chemistry. In the subarea Eare placed cryopegs of the Archangelsk District (bo-reholes 1, 2, 4, 6), which are of Na–Cl salinity cryo-genic brines. In the subarea D groundwater of thenortheastern part of Estonia is depleted in Ca2+ andMg2+. This Na–Cl–HCO3 type groundwater may be aproduct of glacial dilution of cryogenic brines. Plottedon the subareas B and A groundwaters ions compo-sition is more diluted palaeogroundwater solution andreflects also recent sea water intrusion effort, whichevolve moving towards SDL in the water chemistry(boreholes 600, 615, 645, 234, 798, 646 etc). Therefo-re, Ca–Na–Cl and Na–Mg–Cl ionic compositions pre-vail. The highest placement relation to SO4

2– + Mg2+/Cl– coefficient on the palaeodilution trend occur mo-re fresh groundwater, which of Ca–MgvCl–HCO3, Na–HCO3 and Ca–HCO3 chemical compositions were in-fluenced by glacial water at the shallow depths andnear the cutting Lontova aquitard buried valleys. PlotG in Fig. 4 shows that this Ca–Mg–HCO3–Cl typegroundwater is additionally recharged by modern me-teoric water through buried valleys on the coast. Allthe other groundwaters in the Baltic Basin lie roughly

on the SDL, except the Creta-ceous and the Jurassic aquifersystems, where the Eemian In-terstadial time sea transgres-sion took place and the Holo-cene age meteoric water mi-xing in the western part of Lit-huanian and Kaliningrad Di-strict lowlands. There occur ofNa-HCO3 type fresh ground-water facies and Ca2+ lies ne-ar the SDL with respect to Cl–

ions (Mokrik, 2003). Also, twosubareas of groundwater che-mistry facies in the Baltic Ba-sin are shifted from the SDLto the right: the first of themis placed in the plot I, whereSO4

2– rich groundwater is spre-ad, and the second – in plotsC and F of Na–Ca–Cl andCa–Cl type brines occurring atthe deepest part of the Balticand Moscow basins. Thus, theanalyzed groundwater chemicalcomposition allows to conclu-de that in formation of aqui-fer systems took place not on-ly glacial water, but also per-mafrost-originated cryopegsand their diluted species.

In the Piper diagram, Ca–Cl type groundwater is placedin the area of the diamondshape where SO4

2– + Cl– as

Fig. 4. Characteristic coefficient −

+− +Cl

MgSO 224

versus TDS diagram

4 pav. Charakteringo koeficiento SO42– + Mg2+/Cl– ir bendrosios mineralizacijos

pasiskirstymo diagrama

Aqueous geochemistry of the Cambrian–Vendian aquifer system in the Tallinn intake, northern Estonia 55

well Ca2+ + Mg2+ range between 70–90% and arereplenished by seawater intrusion tongues. Chemicalanalyses of these boreholes reflect Na+ and Ca2+ ionexchange between seawater and clays. Characteristicare changes in the borehole 798 water chemistry, asin 1995, by SO4

2– reduction, bicarbonates and CO2aggressive to carbonates were actively produced. Atthat time the locality of this borehole sample wasfound in a plot where SO4

2– + Cl– and Ca2+ + Mg2+

ranged within 50–70%. Intensive seawater penetra-tion in the same borehole followed later, up since,efficacious formation of Ca–Cl salinity and carbona-tes precipitation. Carbonate deposition is followedby a fall in pH (3–6) and bicarbonate concentration(9–18 mg/l). Such manifestation occurs in many bo-reholes, e.g., in borehole 646. All in all, a huge de-viation from SDL to the direction of Ca–Cl typegroundwater is characteristic if the seawater intru-sion front is manifested more actively (boreholes 798,646, 613, 645, 632, 825, 600, 154, 616).

The geochemistry of the Cambrian–Vendian aqui-fer system groundwater is not expected to be thesame in each location, because the chemical compo-sition of mixed recharge water is different. The Na–HCO3 type groundwater is displaced in the lowerpart of the Piper diamond shape, indicating that theaquifer system was subjected to the interstadial timeseawater and palaeorecharged water mixing process(boreholes 647, 163, 36, 40), and some of these arenow via buried valleys on the coastal part in re-freshening position (borehole 705). However, the che-mical composition change in the borehole 163 showsthat the influence of recent seawater has moved itslocation towards the SO4

2– + Cl– side on the Piperdiagram, i.e. toward a conservative mixing model. Na–HCO3 type background groundwater originated fromthe Pleistocene, when the re-freshening mixing of gla-ciogenic and saline interstadial groundwater of theCambrian–Vendian aquifer system occurred (Mokrik,2003). To the modern recharge direction has evolvedthe groundwater chemistry in the borehole 705 (Figs.2 and 4). Consequently, chemical changes in bore-holes 163 and 705 evidence the recent and intersta-dial time seawater, also meteoric water influence re-lative to palaeorecharged groundwaters. Thus, thechemical composition in the borehole 705 has mo-ved to the direction of the present day meteoric wa-ter composition. Different residence times of ground-water within the aquifer system hold the key to dis-tinguishing among their origin. The background 14Cconcentrations in the aquifer system are in the ran-ge 2.5–5 pmC, but in areas of the modern meteoricrecharge their values grow up to 60 pmC, like in theborehole 705. The highest influence of seawater in-trusion into palaeorecharged groundwater, evaluatedby 14C, is manifested in boreholes 646 (12.76 pmC),746 and 815 (about 16.7 pmC) and 298 (33.6 pmC).Also maintain the Br– content rise in tendency to-

ward the SDL relative to basement water on theKopli site of the Tallinn intake (Fig. 5). The relationbetween chloride and bromide in the of water sam-ples of boreholes 600 and 599 is equal to the rela-tion found in the seawater dilution line. However, insamples 614, 598 this relation is close to the base-ment water dilution trend. Other samples (boreholes615 and 613) are residual between the basement andseawater lineaments and have a tendency to movetowards the recent seawater dilution line.

Fig. 5. Br– versus Cl– diagram5 pav. Bromo ir chloro jonø pasiskirstymo diagrama

CONCLUSIONS

In the Kopli site of the Tallinn intake, northernEstonia, a clear manifestation of seawater intru-sion has been found. Salinization through seawa-ter intrusion and conversely re-freshening duringthe Late Weichselian of aquifers are accompaniedby cation exchange and palaeorecharge processesin which Ca–Cl and Na–HCO3 types of water areformed. On salinization, the deposition of carbo-nates is mostly prevented by sulfate reduction. Inthe case of a faster salinization, carbonate depo-sition took place, because sulfate reduction wasdepleted. At the re-freshened part of the aquifersystem where modern meteoric water leakage fromthe buried valleys prevails, the reverse process oc-curs when groundwater changes into Na–HCO3and Ca–HCO3 types. The re-freshening reactionsare accompanied by a decrease of calcium andmagnesium contents and lead to a renewed disso-lution of carbonates.

References

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idrogeologia. 18(2). Proceedings of the 8 th salt waterintrusion meeting. Bari, 25–29 May. 29–40.

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Mokrik R. 1997. The Palaeohydrogeology of the BalticBasin. Vendian & Cambrian. Tartu, Tartu UniversityPress. 138 p.

Mokrik R., Petkevièius R., Kirsimäe K. 2000. The Palaeo-hydrogeology of the Cambrian–Vendian Aquiferous Sys-tem in the Baltic Basin. Geologija. 31. 79–92.

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Yezhova M., Polyakov V., Tkachenko A., Savitski L., Bel-kina V. 1996. Palaeowaters of North Estonia and theirinfluence on changes of resources and the quality offresh groundwater of large coastal water supplies. Ge-ologija. 19. 37–40.

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Robertas Mokrikas, Lehte Savitskaja, Leonidas Savitskis

KAMBRO–VENDO KOMPLEKSO POÞEMINIOVANDENS GEOCHEMIJA TALINO VANDENVIETËJE(ÐIAURËS ESTIJA)

S a n t r a u k aPer pastaruosius ðeðiasdeðimt metø intensyviai eksploa-tuojant poþeminá vandená Talino vandenvietëje prieð

penkiolika metø ëmë reikðtis jûrinio vandens intruzija.Dël katijonø mainø su ekranuojanèiais moliais vietomisformavosi didesnës mineralizacijos kalcio jonø turtingasvanduo. Kambro–vendo vandeningo komplekso poþemi-nio vandens cheminës sudëties analizë patvirtino, jog Ta-lino vandenvietëje, priklausanèioje Vakarø Estijos mo-noklinai, dël jûros vandens intruzijos didëjant minerali-zacijai formuojasi kalcio choridinis vandens tipas. RytøEstijos monoklinoje, kur jûrinio vandens skverbimosi ásausumà nenustatyta, vyrauja natrio hidrokarbonatinis irnatrio chloridinis poþeminis vanduo. Talino vandenvietë-je, Kopli pusiasalyje (Ðiaurës Estija), nustatytos ryðkiosjûros intruzijos apraiðkos. Formuojantis sûriam poþemi-niam vandeniui vyksta aktyvûs Na–Ca katijonø mainai irsulfatø redukcija, kuriø metø vanduo prisotinamas kar-bonatais. Padidëjus chloro jonø koncentracijai ir silpnë-jant sulfatø redukcijai ið poþeminio vandens tirpalo iðsi-skiria kalcitas ir dolomitas, suaktyvëja vandenilio jonai iriki minimumo sumaþëja hidrokarbonatø koncentracija.Intruzijos metu poþeminio kalcio chloridinio vandens su-sidarymà lemia prisotinimas karbonatais, o natrio hidro-karbonatinio, kuris susiformavo Pleistoceno pabaigoje,prieðingai – karbonatinio cemento tirpinimas.

Ðîáåðò Ìîêðèê, Ëåõòå Ñàâèöêàÿ,Ëåîíèä Ñàâèöêèé

ÃÅÎÕÈÌÈß ÏÎÄÇÅÌÍÛÕ ÂÎÄ ÊÅÌÁÐÎ-ÂÅÍÄÑÊÎÃÎ ÊÎÌÏËÅÊÑÀ ÒÀËËÈÍÍÑÊÎÃÎÂÎÄÎÇÀÁÎÐÀ (ÑÅÂÅÐÍÀß ÝÑÒÎÍÈß)

Ð å ç þ ì åÇà ïîñëåäíèå 60 ëåò ýêñïëóàòàöèè ïîäçåìíûõâîä íà Òàëëèííñêîì âîäîçàáîðå ïðîèçîøëîçàñîëåíèå, âûçâàííîå ïîäñîñîì ìîðñêèõ âîä. Âïðîöåññå èíòðóçèè ìîðñêèõ âîä ôîðìèðóþòñÿCa–Cl è Na–HCO3 òèïû ïîäçåìíûõ âîä çà ñ÷åòïðîöåññîâ ñìåøåíèÿ ïðåñíûõ è ñîëåíûõ âîä,êàòèîííîãî îáìåíà è ñóëüôàòðåäóêöèé. Ââîäîíîñíîì êîìïëåêñå îäíîâðåìåííî èìåþòìåñòî êàê âûùåëà÷èâàíèå êàðáîíàòîâ ñîáðàçîâàíèåì Na–HCO3 òèïà âîä, òàê è èõâûïàäåíèå â îñàäîê (Ca–Cl âîäû). Ïîñëåäíèåîáðàçîâàëèñü â îñíîâíîì çà ñ÷åò ïðîöåññîâêàòèîííîãî îáìåíà ñ ýêðàíèðóþùèìè ñâåðõóãëèíàìè. Ôàöèé õèìè÷åñêîãî ñîñòàâàðàñïðåäåëåíû ñëåäóþùèì îáðàçîì: íàâîñòî÷íîé ýñòîíñêîé ìîíîêëèíàëè ðàñïðîñ-òðàíåíû Na–HCO3 è Na–Cl, à íà çàïàäíîéýñòîíñêîé ìîíîêëèíàëè – Ca–Cl, Na–HCO3 èCa–HCO3 òèïû ïîäçåìíûõ âîä.