GeolCarp_Vol68_No4_318

GEOLOGICA CARPATHICA

, AUGUST 2017, 68, 4, 318 – 328

doi: 10.1515/geoca-2017-0022

www.geologicacarpathica.com

The pre-Cainozoic basement delineation by

magnetotelluric methods in the western part

of the Liptovská kotlina Depression

(Western Carpathians, Slovakia)

MARIÁN FENDEK

, TOMÁŠ GRAND

, SLAVOMÍR DANIEL

, VERONIKA BLANÁROVÁ

VINCENT KULTAN

and MIROSLAV BIELIK

1, 3

Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6, 842 15 Bratislava, Slovakia; fendek@fns.uniba.sk,

blanarova@fns.uniba.sk, bielik@fns.uniba.sk

KORAL Ltd., Sládkovičová 5, 052 01 Spišská Nová Ves, Slovakia; grand@koral.sk, daniel@koral.sk, kultan@koral.sk

Earth Science Institute of the Slovak Academy of Sciences, Dúbravská cesta 9, 840 05 Bratislava, Slovakia; geofmiro@savba.sk

(Manuscript received September 2, 2016; accepted in revised form March 15, 2017)

Abstract: The geology and hydrogeology of the Liptovská Kotlina Depression were studied by means of new geo physical

methods. Controlled source audio-frequency magnetotellurics enabled us to delineate the relief of the pre-Cainozoic

basement in the western part of the Liptovská Kotlina Depression into two segments with different lithostratigraphic

units. Our complex findings disprove the interconnection between the Bešeňová and Lúčky water bearing structures

located in the study area. The results were interpreted in the form of a resistivity cross section and resistivity model.

The geological interpretation of the obtained results, taking into account the other geophysical and geological constrains

showed that the pre-Cainozoic basement has a tectonically disrupted, broken relief. The Bešeňová and Lúčky structures

appear to be isolated by the Palaeogene sediments (sandstone, claystone) and in the deeper part also by marly carbonates

and marlstones of the Jurassic age belonging to the Fatricum. It was confirmed that the structural connectivity of

geothermal aquifers in the area between the Bešeňová and Lúčky–Kaľameny should not exist. The assumption of different

circulation depth was also confirmed by geothermometry and existing radiocarbon analyses applied on groundwater in

both areas.

Keywords: geothermal aquifer, mineral water, magnetotellurics, geothermometry, radiocarbon analysis, Liptovská

Kotlina Depression, Western Carpathians.

Introduction

Geological structure is one of the essential conditions for infil-

tration, accumulation and exploitation of geothermal and

mine ral waters. Successful simultaneous long-term exploita-

tion of both types of groundwater is conditioned by isolation

of aquifers in respective structures. The structure of the geo-

thermal waters in the western part of the Liptovská Kotlina

Depression in Bešeňová elevation and structure of mineral

waters in Lúčky–Kaľameny area can be used as an example.

The Liptovská Kotlina Depression is one of the 27 prospective

geothermal areas of the Slovak Republic. This 611 km

depres-

sion is located in northern Slovakia (Fig. 1a). It is elongated in

the E–W direction and bordered by the Chočské vrchy Mts.,

Západné Tatry Mts., Veľká Fatra Mts., Nízke Tatry Mts. and

Kozie Chrbty Mts. The possibility of obtaining and utilizing

the geothermal and mineral waters in the basin was manifested

in the past by a number of natural springs of mineral water in

the area of Bešeňová, Lúčky, Liptovská Štiavnička, Liptovský

Ján and in other localities. Boreholes were drilled in all of

these localities in the last century (Remšík & Fendek 2005).

Both structures: (1) structure of geothermal waters in

Bešeňová and (2) structure of mineral waters in Lúčky are

located close to each other in the western part of the basin.

Bešeňová is located in the central western part of the basin;

the Lúčky mineral water structure is located on the

north-western margin of the basin in the Chočské vrchy Mts.

(Fig. 1b). The discharge area of the geothermal structure

in Bešeňová is located at a distance of 4.0 – 4.5 km to the

south-east from the area of the mineral water structure in

Lúčky.

The mineral waters in Bešeňová manifested themselves for

centuries in the form of natural outflows producing Quaternary

limestone deposits — travertines. These can be found in the

surroundings of the village, e.g. in an abandoned travertine

quarry, but also in travertine cascades, which were included

into Slovak natural heritage list in 1951. Geothermal water

exploration in Bešeňová started in the late 1970s by drilling

the borehole BEH-1. Because of borehole casing corrosion,

the borehole was destroyed and a new borehole ZGL-1 was

drilled in 1987 (Fendek 1998). This borehole was the basis

for buil ding of geothermal facilities in Bešeňová. It is

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GEOLOGICA CARPATHICA

, 2017, 68, 4, 318 – 328

complemented by two other boreholes FGTB-1 and FBe-1

(Fendek & Fendeková 2015).

The history of use of mineral springs in Lúčky area as a real

spa began already in 1761 (Fendek et al. 1999). In modern

history, the Lúčky Spa was focusing on the treatment of gyne-

cological and oncological diseases since 1950; however in

2005 Spa returned to the treatment of the kinetic apparatus,

also offering suitable conditions for prevention and treatment

of osteoporosis. Mineral water from the boreholes HGL-3 and

BJ-101 (Valentina) is being used in all pools and separate spas.

The water is also suitable for drinking and is available not only

for the accommodated guests, but also for the general public.

The discussion on possible interferences of water utilization

from the two structures was raised because of intense utiliza-

tion of geothermal and mineral waters in the area. The use of

mineral water for curative purposes is preferred to energy use

in Slovakia, as is codified by Act No. 538/2005 Z.z. on natural

curative waters, natural curative spas, spa places and natural

mineral water.

No structural-geological investigation was done in this area

up to the present aiming to confirm or disprove the inter-

connection between the two structures, from which water is

intensively utilized.

There were three main objectives of the research: (1) to

delineate the relief of the pre-Cainozoic basement, (2) to seg-

ment it into lithostratigraphic units, and (3) to confirm or

disprove the interconnection between the Bešeňová and Lúčky

water bearing structures. Controlled source audio-frequency

magnetotellurics (CSAMT) was the main method used. This

was the first utilization of the CSAMT method in geothermal

research in Slovakia. The geothermometry and analysis of

radiocarbon dating results, applied to sources in both areas

were used as supporting methods.

Hydrogeothermal conditions of the Liptovská

Kotlina Depression

The Liptovská Kotlina Depression is an intra-montane

depression in the Inner Western Carpathians. It is filled by

Palaeogene sediments with thicknesses ranging from 100 m

(Bešeňová elevation) to 1700 m (Liptovská Mara depression).

Palaeogene flysch sediments are represented by alternation of

clays and clayey shales with sandstones. Clays mostly prevail.

At the base, basal conglomerates are developed.

The substratum consists of the Mesozoic Hronicum and

Fatricum, which form elevated and sunken morphostructures.

The Hronicum is a higher tectonic unit then the Fatricum

(Fig. 1b). The lowest tectonic unit is the Tatricum cover Unit

with the same rock composition as in the Fatricum; however,

its presence has not been proven yet by drilling works.

The vertical, tectonically derived superposition of Mesozoic

successions gave arise to aquifer-aquitard stratification.

The Fatricum is referred as a bottom, while the Hronicum

Fig. 1. a — Location of the Liptovská kotlina Depression. b — Geological conditions and location of objects of interest in the Liptovská

Kotlina Depression (Remšík et al. 1998; Maďar et al. 2005). Explanation: 1 — Hronicum (a – bedrock, b – on the surface); 2 — Fatricum

(a – bedrock, b – on the surface); 3 — cover Unit; 4 — Crystalline; 5 — overthrust line (a – proved, b – assumed); 6 — faults (assumed);

7 — isolines of the Palaeogene bottom in m a.s.l. (a – proved, b – assumed); 8 — geothermal borehole; 9 — oil borehole.

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FENDEK, GRAND, DANIEL, BLANÁROVÁ, KULTAN and BIELIK

GEOLOGICA CARPATHICA

, 2017, 68, 4, 318 – 328

along with the Central Carpathian Palaeogene Basin (CCPB)

is referred as a top system. The bottom system includes base

aquiclude represented by a Lower Triassic horizon typically

comprising quartzites, sandstones and sandy shales (Werfenian

shales) beneath the bottom aquifer of Middle Triassic carbo-

nates — limestones and dolomites complex. The aquifer of the

bottom system is overlain by an aquitard corresponding to

Upper Triassic–Middle Jurassic organogene and detritic lime-

stones overlapping to Middle Jurassic–Lower Cretaceous

pelitic limestones (clayey, marly) that alternate spatially with

radiolarites, nodular limestones, claystones and marlstones.

The top hydrogeological system involves aquifers of the

Hronicum, represented by Middle Triassic carbonates hydrau-

lically connected to CCPB represented by the Middle–Upper

Eocene Borové basal formation (Gross et al. 1980) composed

of breccias and conglo merates that pass to detritic carbonates

and rare organogene limestones; beneath the top aquifuge

recog nized as Upper Eocene–Oligocene formations of Huty

(claystones dominated) and Zuberec (flysch dominated).

The hydrogeological function of Quaternary cover varies with

regard to grain size. The maximal thickness of the Hronicum

sequence is up to 1000 m; The Fatricum sequence reaches the

maximal thickness of 1500 m (Remšík et al. 2005).

The spatial distribution of the Hronicum and Fatricum in

the basement of the Palaeogene sediments is very variable

(Fig. 1b). Both units are presented equally in the western part

of the basin and they can occur next to each other. The Hroni-

cum dominates in the middle and southern part of the basin,

whereas the Fatricum sequence prevails in the northern part.

Sequences of the Hronicum and Fatricum form the mountain

ranges which surround the basin and represent infiltration

areas for the hydrogeothermal structures (Remšík & Fendek

2005).

Hydrogeological conditions in the area are controlled by the

geological-tectonic structure. Geothermal waters in the

Liptovská Kotlina Depression are discharged through natural

springs and boreholes. Beneath the Palaeogene filling there

may be one to three hydrogeothermal structures positioned

one above another in which geothermal waters are mostly

associated with Triassic dolomites and limestones (“carbo-

nates” throughout the following text) of the Hronicum and

Fatricum and, possibly, also of the cover (autochthonous) Unit

(Fig. 1b). These hydrogeological structures are largely open

(having recharge areas on the adjacent slopes of surrounding

mountains, as well as transit-accumulation and discharge

areas) or semi-open (discharge area is missing). The Triassic

carbonate aquifers with geothermal water are from 300 to

1200 m thick (Remšík et al. 2005).

The mineral waters in Lúčky are bound to Triassic carbo-

nates of the Fatricum as proved by the results of BJ-101 and

HGL-3 boreholes in Lúčky (Teplianka brook valley) and

HGL-2 borehole in Kaľameny, located in the neighbouring

Kaľamenianka brook valley. Results of geothermal boreholes

ZGL-1, FGTB-1 and FBe-1 in Bešeňová showed that geo-

thermal waters accumulate in Triassic carbonates of the the

Hronicum and Fatricum. It is supposed that formation of

geothermal water takes place in Fatricum carbonates. Both

structures (Lúčky and Bešeňová) are classified as open struc-

tures with infiltration, transit-accumulation and natural

discharge areas (Fričovský et al. 2016).

Geothermal waters occurring in the Hronicum Triassic

carbonates at depths of 500 to 2800 m have the temperature of

20 to 90 ºC while those in similar rocks of the Fatricum at

depths of 900 to 4000 m could be 25 to 125 ºC hot (Fričovský

et al. 2014). The temperature of geothermal waters occurring

in Triassic carbonates of the cover Unit at depths of 2500 to

5000 m might amount to 70 –150 ºC. It is necessary to accent

that expected temperatures are given by geological conditions

and the geometry of the geothermal structure and calculated

by stationary thermal modelling. Temperatures measured in

the borehole ZGL-1 Bešeňová in static conditions are given in

Table 1.

The Liptovská Kotlina Depression is tectonically divided

into a system of elevations and depressions. The Bešeňová

elevation hydrogeothermal structure is associated with a N–S

protuberant morphological elevation of the pre-Cainozoic

basement in the western part of the Liptovská Kotlina

Depression. The elevation is tectonically limited to the sur-

rounding depressed structures. The Ivachnová depression on

the west is divided by the Bešeňová–Partizánska Ľupča fault

and Liptovská Mara depression on the east is divided by the

Liptovské Kľačany–Vlachy–Ľubela fault system (Gross et al.

1980). The Chočské vrchy Mts. to the north are divided by the

Prosiecky fault (Bezák et al. 2004) and to the south, fault

swarms lineate a system to the Nízke Tatry Mts. The Bešeňová

elevation is considered the most active zone regarding geo-

thermal activity, with a mean heat flow density recalculated

for 66.04 mW.m

-2

(Fričovský 2011) in comparison to a mean

heat flow for the whole Liptovská Kotlina Depression geo-

thermal field calculated for 55 mW.m

-2

. The local maximum

measured rises to 76.9 mW.m

-2

in the ZGL-1 Bešeňová bore-

hole within a centre, while the local minimum decreases down

to 55 mW.m

-2

towards the southern margin (Král & Remšík

1996).

Laterally, the Bešeňová elevation is recognized as an

open hydrogeological structure (Remšík & Fendek 2005).

Infiltration zones are identified at the distal northern slopes

of the Nízke Tatry Mts. close to Demänova valley or at its

Table 1: Temperatures measured in the borehole ZGL-1 Bešeňová at

static conditions.

Depth (m)

Temperature (°C)

Depth (m)

Temperature (°C)

7.0

1100

48.0

100

15.0

1200

52.0

200

19.0

1300

55.0

300

22.0

1400

59.0

400

25.0

1500

62.5

500

28.5

1600

66.0

600

32.0

1700

68.0

700

35.0

1800

71.0

800

38.0

1900

73.0

900

42.0

2000

76.0

1000

45.0

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GEOLOGICA CARPATHICA

, 2017, 68, 4, 318 – 328

southern margin considered as the preference recharge area

(Fričovský et al. 2016). However, there is the migration of

fluids from the Liptovská Mara depression structure (located

to the east) expected, as shown by analysing the regional

piezometric level distribution (Fendek & Remšík 2005).

The infiltration area of the Lúčky mineral water structure

was placed by Kullman & Zakovič (1975) in the area with

occurrence of the Fatricum carbonates in the upper part of the

Suchá dolina valley and in the area of occurrence of the

Hronicum dolomites to the north-east of the Liptovské

Matiašovce village. The transit-accumulation area was placed

in the carbonate complex of limestone and dolomites of the

Fatricum in the Chočské vrchy Mts. between the Suchá dolina

valley and the Ráztočné valley. The groundwater flows mostly

along the Prosiecky fault which separates the Chočské vrchy

Mts. from the Liptovská Kotlina Depression.

The main Ca-Mg-HCO

-SO

chemical type of geothermal/

mineral water prevails in the basin, values of total dissolved

solids (T.D.S.) amount to about 0.4–5.0 g.l

-1

. Data on selected

geothermal boreholes in the basin are in Table 2.

Gases are represented mainly by CO

. Sulphates in geother-

mal waters (Remšík & Fendek 2005) came largely from Lower

Triassic formations with evaporates (δ

S = 23.3 to 27.1 ‰);

the isotopic composition of oxygen in the geothermal waters

shows that they are of meteoric origin.

Methods

Geophysical methods

The CSAMT measurement is a geophysical technique

classified as an electromagnetic frequency domain method

belonging to the group of magnetotelluric methods (Zonge &

Hughes 1991; Routh & Oldenburg 1999; Simpson & Bahr

2005). A manmade controlled primary electromagnetic field is

transmitted into the ground using wide range of frequencies.

The primary field generates eddy currents in the rocks as

the electromagnetic waves propagate through the Earth.

The secon dary electromagnetic field produced by the eddy

currents is registered by the receiver and the signal is used to

calculate the electric resistivity of the rocks below the surface.

The depth penetration of the method is determined by the

frequency of the electromagnetic signal, each of the used

frequencies provides information on rock resistivity from

a different depth. A wide range of frequencies enables us to

receive a semi-continuous resistivity structured profile from

the surface up to the maximum depth of penetration (Simpson

& Bahr 2005).

The method can be utilized for various geological (Zhiguo

& Qingyun 2007; Grandis & Menvielle 2015) and hydrogeo-

logical applications including geothermal exploration. Depth

penetration, high production and relatively low costs compa-

ring with seismic, predetermine CSAMT as a fast and effec-

tive method utilized in geothermal exploration and recently

it became one of the principal geophysical techniques.

Application of the magnetotelluric methods at the sites of the

Bešeňová and Lúčky hydrogeothermal structures faced two

challenges. One of them was the required depth penetration of

2 km determined by the assumed depth of the pre-Cainozoic

basement. The required depth of penetration is on the edge of

the applicability of the CSAMT method and may require use

of the lowest possible frequencies in the AMT (audio magne-

totelluric) range which are utilized in far-field zone modifica-

tion. Therefore, the logical solution would be to use the classic

magnetotelluric (MT) method utilizing Earth’s natural elec-

tromagnetic fields at frequencies far below 1 Hz. This approach

would assure the overreaching of the required depth of pene-

tration of 2 km. However, the existence of external cultural

noise was a factor playing a role against usage of the classic

MT technique. Considering the facts above, a straight magne-

totelluric (MT) testing survey was conducted at a couple of

Table 2: Data on selected geothermal boreholes in the Liptovská Kotlina Depression.

Borehole

Locality

Aquifers

Perforated

interval [m]

Discharge

[l.s

-1

]

Water

temperature

[ºC]

Thermal

power

[MW

]

T.D.S. [g.l

-1

] Chemical type of water

FGL-1

Pavčina Lehota

Triassic limestones

and dolomites

1315–1570

6.0

32.0

0.42

0.40

Ca-Mg-HCO

ZGL-1

Bešeňová

Triassic dolomites

1420–1964

27.0

62.0

5.30

Ca-Mg-SO

-HCO

FGTB-1

Bešeňová

Triassic limestones

and dolomites

1622–1813

32.0

66.9

6.83

3.02

Ca-Mg-SO

-HCO

ZGL-2/A

Liptovský Trnovec

Triassic dolomites

and limestones

1624–2486

31.0

60.7

5.89

5.90

Ca-Na-Mg-HCO

-SO

ZGL-3

Liptovská Kokava

Triassic limestones

and dolomites

1475–2365

20.0

43.5

2.42

2.40

Ca-Mg-HCO

-SO

HGL-2

Kaľameny

Tectonic disruption

in Carpathian

Keuper´s shale

185–500

23.5

33.4

1.77

2.90

Ca-Mg-SO

-HCO

HGL-3 Lúčky

Triassic dolomites

322–476

25.0

35.8

2.18

3.10

Ca-Mg-SO

-HCO

BJ-101 Lúčky

Triassic dolomites

54–92

20.0

32.0

1.42

2.80

Ca-Mg-SO

-HCO

LSH-1

Liptovská Štiavnička

Triassic dolomites

89–165

10.0

21.0

0.25

3.56

Ca-Mg-HCO

-SO

Hronicum,

Fatricum,

pumping,

free outflow

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FENDEK, GRAND, DANIEL, BLANÁROVÁ, KULTAN and BIELIK

GEOLOGICA CARPATHICA

, 2017, 68, 4, 318 – 328

stations prior to employment of CSAMT. The objective was to

check if a classic MT survey could not be utilized instead of

CSAMT. One station was surveyed near the borehole HGL-2

with a known geological profile. The acquired data could not

be utilized due to high noise level. The measurements from

other stations away from the Liptovská Kotlina Depression in

Suchá dolina at the Chočské vrchy Mts. have shown lower

noise and the data was interpretable. The results have finally

confirmed the general assumption that the classic MT survey

could not be used in the parts of the Liptovská Kotlina

Depression with a well developed infrastructure at all. This

was also the case for the area of interest. The only solution was

to employ the CSAMT method in conjunction with several

chosen factors linked to equipment setting and survey tech-

niques, which would allow us to achieve the required penetra-

tion depth and to eliminate the external noise factors at the

same time. A solution was found thanks to the unique

METRONIX MT technology (http://www.geo-metronix.de/

mtxgeo/) allowing tensor measurements in a state of scalar

measurements and other factors as careful selection and testing

of the transmitter site and its distance to survey stations, para-

metric test surveys on boreholes and finally use of the maxi-

mum possible power on transmitters and use of lowest possible

AMT frequencies.

Prior to the actual survey, a set of test measurements was

conducted at the location of existing boreholes. Parametric test

measurements were undertaken near the location of boreholes

HGL-2 and ZGL-1 (Fig. 2). Test measurements at borehole

ZGL-1 were assisting in adjustment of the survey parameters

and equipment settings including the applicable range of

frequencies.

The test survey confirmed the capability of the actual set-

tings to achieve the required depth of 2 km. Inversion of the

parametric test survey also provided important information

about apparent resistivity of individual geological settings and

structures. Based on resistivity, it was not only possible to

clearly separate the low-resistive Palaeogene sediments from

the pre-Cainozoic basement, but also to assign apparent resis-

tivity to individual lithological-tectonic units within the base-

ment. This information could be later utilized in inversions

and modelling of actual survey data.

CSAMT measurements were conducted along survey line

connecting both boreholes HGL-2 and ZGL-1 (Fig. 2). It is

placed within the elevated part of the pre-Cainozoic basement

called as the Bešeňová elevation.

The total length of the survey line was 4 km and comprised

a total of 21 stations with 200 m separation. Grounded tripole

electrode system with arm length of 600 m enabling rotation

of electric current vector controlled by METRONIX TXM-22/

TXB-07 transmitter was used as source of stable, manmade

electromagnetic signal in the AMT range (0.5 Hz – 8192 Hz).

Currents reaching a maximum possible level of 30 – 40 Amp

were used to reduce the effect of external background noise.

Far-field zone modification was applied for a transmitter

distance of 10.5 km from the survey line. The METRONIX

receiver ADU-7 was employed to register the EM field at the

survey stations. Two horizontal vectors of electric component

of EM field were measured using two pairs of grounded elec-

trodes perpendicularly oriented in N–S and E–W directions.

All three vectors of magnetic component of EM field were

registered by three magnetometer probes buried in soil.

The registration time of 120 seconds was chosen to register the

entire AMT frequency range (0.5 Hz – 8192 Hz) with a suffi-

cient number of stacking. Transmitter and receivers were full

synchronized using GPS time provided by GPS receivers used

for positioning at the same time.

Registered vector components of electric and magnetic field

were transformed to resistivity time/depth sounding profiles

followed by 1D and finally 2D inversion. The inversion and

modelling was controlled using existing data from parametric

test measurements at borehole sites. Inversion and modelling

results were presented in the form of a 2D resistivity section

and resistivity block model. The inversion results were assis-

ting to determine the thickness of Palaeogene clay-sandstone

sediments, depth to pre-Cainozoic basement and also litho-

logy-structural units within the pre-Cainozoic basement.

The final integrated geological geophysical interpretation

was made considering all available geological data from

surface mapping and boreholes, CSAMT survey (Fig. 2) and

archive geophysical data including DC current electric soun-

ding (VES, Fig. 2), regional airborne magnetic survey and

regional ground gravity survey. The outcome of the integrated

interpretation was a geological cross section showing both, the

principal lithology-structural units and tectonic pattern.

Geothermometry

The method was used for estimation of the depth at which

the reservoir waters are formed. Geothermometers, empirical

equilibrium functions between water and solutes implying

provenance zone temperature take advantage in slowness of

initial conditions re-equilibration at cooler temperatures.

Silica geothermometers and conventional cation geothermo-

meters were used in the study to compare reservoir conditions

at Bešeňová and Lúčky. Fričovský et al. (2015) showed that

the conventional cation geothermometers overestimated the

temperatures of geothermal waters in the Bešeňová area by

2– 4 times. The use of cation geothermometers showed the

immaturity of the system, reflected in rapid variations of

Na/K, K/Mg, and Na/Mg rations through the system. This

could be well seen on a Na–K–Mg geoindicator (Giggenbach

1988), which proved most of the cations geothermometer

invalid.

Silica geothermometry is based on the solubility of all silica

polymorphs at particular temperature and pressure conditions.

The SiO

concentration in thermal fluids is measured. Silica

geothermometers reflect the temperature-controlled solubility

of quartz and its polymorphs (chalcedony, cristobalite, and

amorphous silica), assuming equilibrium at the rock-water-

solute contact (Giggenbach 1988). Quartz is the most stable

and least soluble solid silica form in conditions of 120

(mature systems) or 180 (mature, immature systems) – 330 °C

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GEOLOGICA CARPATHICA

, 2017, 68, 4, 318 – 328

(Fournier & Rowe 1966), controlling SiO

concentration

within the range. Ambiguity appears at the 120 – 180 °C inter-

val, as chalcedony becomes metastable and more soluble.

Thereafter, below 120 °C it is possible that chalcedony con-

trols the SiO

content preferentially.

A large set of geothermometers was used for reservoir tem-

perature estimation in both areas. The best agreement between

values measured at the depth of screen placement and theore-

tical values for the Bešeňová borehole was obtained using the

Arnórsson et al. (1983) equation for chalcedony (adiabatic

boiling model):

1264

T [°C] = − 273.15, (1)

(5.31 − log C)
where C is silica oxide content.

The best agreement between measured and theoretical tem-

perature values for the Lúčky borehole was obtained using the

equation for the K–Mg geothermometer (Giggenbach 1988):

4410

T [°C] = − 273.5, (2)
14.0 + log

(

)

Mg
where K and Mg are potassium and magnesium contents,

respectively.

The K–Mg geothermometers of Giggenbach (1988) refer to

the situation where the dissolved sodium and calcium cations

are not in equilibrium state between the water and rock envi-

ronment. The critical problem of the K–Mg geothermometer is

that it reacts with the geothermal water much faster than other

geothermometers do, and it is more sensitive to carbonate

environments at low enthalpies.

Results

The results (Fig. 3) indicate an upper low-resistivity (50 Ω∙m)

layer outcropping to the surface.

Based on the results of Gluch et al. (2009) this layer is inter-

preted as Palaeogene sediments with higher content of clay

components representing together the strata of the Zuberec

and Huty formations. The thickness of Palaeogene sediments

along the survey line is variable in average about 500 m with

a general tendency towards thinning out to the south in the

direction of borehole ZGL-1.

The resistivity model shows an obvious anomaly standing

out from the general picture described above. It is semi verti-

cal 600 – 800 m wide zone of low-resistivity (50 –100 Ω∙m),

which is dipping down to a depth of over 1500 m below

surface. The zone was registered by CSAMT measurements

undertaken at 5 stations and starts about 800 m south of bore-

hole HGL-2 measured along the survey line. This anomaly

zone is interpreted as increased thickness of Palaeogene sedi-

ments (1500 – 2000 m). Such an interpretation is also sup-

ported by gravity low anomaly (Fig. 2) placed at the same

location which is indicating obvious depression in pre-

Cainozoic basement.

The Palaeogene low resistivity layer is under-bedded by

a half space of higher resistivity interpreted as pre-Cainozoic

basement of variable resistivity layers and segments (300 –

3000 Ω∙m) reflecting various Mesozoic rocks and strata.

Palaeogene sediments are under-bedded by marls and marly

limestones of the Lower Jurassic and Cretaceous. They also

contain a high proportion of clayey compound, which may

reflect interpreted low resistivity in the Pre-Cainozoic base-

ment within the low resistivity anomaly zone.

The low resistivity anomaly isolates the Triassic carbonates

of the Fatricum occurring at Kaľameny–Lúčky area from the

carbonates occurring in Bešeňová pre-Cainozoic basement

elevation hit by the borehole ZGL-1 and confirmed by

CSAMT and gravity survey (Fig. 2). Mesozoic rocks, mostly

dolomites appear underneath the Palaeogene sediments in the

western part of the Liptovská Kotlina Depression as indicated

by boreholes ZGL-1 and FGTB-1 and geophysical interpreta-

tions as well. These carbonates tectonically belong to the

Hronicum. Dolomites have higher apparent resistivity than the

marls, marly limestones, or shales and anhydrites of the

Fatricum. Considering the results of CSAMT inversion, we

may assume that compact dolomites and limestones are

charac terized by higher apparent resistivity from 400 Ω∙m up

to couple thousands Ω∙m, while the marls and marly lime-

stones of the Fatricum have lower resistivity (100 – 300 Ω∙m).

Differentiation of Middle Triassic dolomites from shale and

dolomites of the Carpathian Keuper appears to be difficult in

most cases based on resistivity. On the other hand, existing

resistivity contrast appears to be sufficient to distinguish the

dolomites from marls and marly limestones.

The high-resistivity layer (2960 Ω∙m), occurring at the

larger depths at the beginning of the resistivity section (HGL-2

borehole), could represent either compact Triassic dolomites,

of which disintegration degree decreases with the depth, or

Lower Triassic quartzites of the Lužná sequence, which were

hit by geothermal boreholes ZGL-3 in Liptovská Kokava and

FGL-1 in Pavčina Lehota (Fig. 1b). The pre-Cainozoic

basement has a obviously disturbed (eroded) and tectonically

fragmented relief, as can be seen from the measured resistivity

values of Mesozoic rocks (Fig. 3).

The geological interpretation (Fig. 4) shows that the

Hronicum is not extended continuously in the Bešeňová eleva-

tion. Hence, the Hronicum system represents the top aquifer of

the stratified Bešeňová elevation hydrogeothermal system.

The interpretation of data proves former assumptions and

expectations (e.g. Remšík & Fendek 2005) on spatial limita-

tion of the Hronicum which have further consequences for the

hydrogeological and thermal regime of the structure.

The same is also valid for shales of the Carpathian Keuper,

which are in the central part of the profile isolated by

Palaeogene sediments from the north and by marls and marly

limestone of the Lower Jurassic–Lower Cretaceous from the

south.

The continuation of the Middle Triassic dolomites from the

Bešeňová elevation towards the Kaľameny–Lúčky is dis-

rupted by Palaeogene sediments and in the deeper part also by

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, 2017, 68, 4, 318 – 328

marls and marly limestones of the Jurassic–Cretaceous age,

which, in the regional view, are considered as hydrogeological

isolators. From the regional point of view it is worth mentio-

ning that the thickness of Palaeogene sediments increases

significantly in the Ivachnová depression and the Liptovská

Mara depression which are extending to the west and the east

from the Bešeňová elevation.

Discussion

The extent of the marls and marly limestone in the pre-

Cainozoic basement is also confirmed by the stripped gravity

map of the Liptovská Kotlina Depression published by

Szalaiová et al. (2008). This map represents the corrected

Bouguer anomaly gravity map by the 3D gravitational effect

of the Palaeogene infill. Therefore it reflects the anomalies

that resources are located within the pre-Cainozoic basement.

As the studied area is characterized by the relative gravita-

tional low it can be suggested that its source could be with the

most likely the Jurassic-Cretaceous marls and marly lime-

stones, as they have not only lower resistivity but also lower

density in comparison with the Triassic dolomites (Eliáš &

Uhmann 1968).

Geothermometry applied to mineral waters at Lúčky

(HGL-2 borehole) and geothermal waters at Bešeňová (ZGL-1

borehole) showed the following results. The chalcedony

(adiabatic boiling model) geothermometer after Arnórsson et

al. (1983) gave the value of 65.2 °C for Bešeňová what satis-

fies the circulation depth of 1580 m (see Table 1). The same

geothermometer used for Lúčky gave the result of 42.3 °C

which satisfies the circulation depth of 900 m (Table 1).

The same temperature of 42.3 °C was estimated for Lúčky

also by K–Mg geothermometer (Giggenbach, 1988). However,

the use of K–Mg geothermometers did not give acceptable

results for Bešeňová, where the temperature estimated by

K–Mg geothermometer was only 35.3 °C. The free outflow

temperature at the well head in Bešeňová is 62 °C therefore

the 35.3 °C is a highly underestimated result. It means that the

mineral water in Lúčky is formed at a much shallower depth

than the geothermal water in Bešeňová.

The former radiocarbon analysis allows us to estimate

the age of groundwater appearing in the Liptovská Kotlina

Depression. The estimated age of geothermal water of the

Bešeňová area (ZGL-1 borehole) is 27,000 years (Franko

2002) corresponding to the infiltration time during the Paudorf

interstadial (Wurm 2–3 glaciations), whereas the estimated

age of mineral waters in Lúčky and Kaľameny is 23,000 and

Fig. 4. Integrated geological-geophysical interpretation — geological section of the profile PF01.

327

BASEMENT OF THE LIPTOVSKÁ KOTLINA DEPRESSION IDENTIFIED BY MAGNETOTELLURICS

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, 2017, 68, 4, 318 – 328

18,300 years respectively, corresponding to the colder time

period in the Wurm 3 glaciation. Franko (2002) provided

a suggestion on preferential infiltration zone for Bešeňová

hydrogeothermal structure to the south and basically coun-

tered an idea of connectivity of the Bešeňová elevation and

Lúčky mineral water structure.

The isotopic composition of oxygen δ

O in geothermal

water from boreholes ZGL-1 Bešeňová, ZGL-2A Liptovský

Trnovec and in mineral water in LSH-1 borehole in Liptovská

Štiavnička is also different from the isotope composition of

oxygen in BJ-101 and HGL-3 sources in Lúčky, HGL-2 in

Kaľameny and in the main inflow to the borehole ZGL-3

Liptovská Kokava.

Another argument confirming the existence of two sepa-

rated structures is that there was no observed influence on

discharges in the Lúčky area caused by long-term hydrody-

namic testing on the borehole FGTB-1 in 2012.

Conclusions

The CSAMT method was successfully applied in the western

part of the Liptovská Kotlina Depression. Utilization of the

method enabled us to delineate the relief of the pre-Cainozoic

basement and to segment it into lithostratigraphic units.

The geological interpretation of the results showed that the

Hronicum does not extend continuously in the Bešeňová ele-

vation. The same also applies the to shales of the Carpathian

Keuper, which are isolated in the central part of the profile by

Palaeogene sediments from the north and by marls and marly

limestone of the Lower Jurassic–Lower Cretaceous from the

south. The interpretation of geophysical data available for the

western part of the Liptovská Kotlina Depression, together

with the interpretation of the CSAMT method have confirmed,

that there is no interconnection between the Lúčky mineral

water structure and the Bešeňová geothermal water structure.

The two structures are separated by a huge thickness of

Palaeogene sediments in the shallow part and also by marls

and marly limestones of the Fatricum in the deeper part, which

are considered to be hydrogeological isolators on regional

scale. In our opinion it was proven that the continual intercon-

nection of geothermal aquifers in the area between the

Bešeňová and Lúčky–Kaľameny does not exist. This study

has proven that there exist neither structural nor hydraulic

conectivity between the two structures as well. This was also

confirmed by the results of geothermometry application and

by comparison of the radiocarbon ages of groundwater in

water bearing structures. Disproving a structural and hydraulic

connectivity between the Lúčky and Bešeňová structures is

a major addition to our knowledge of the Liptov Basin geo-

thermal field and definitely supports assumptions and

suggestions given since detailed studies of these two systems

began.

Finally, the study as presented in this paper is the first

application of the CSAMT method to geothermal exploration

in the territory of the Slovak Republic.

Acknowledgements: This research has been supported by

the Slovak Grant Agency VEGA, grants No 1/0313/15 and

No. 1/0141/15, and the Slovak Research and Development

Agency, grant No. APVV-16-0146.

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