GeolCarp_Vol64_No5_399

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, OCTOBER 2013, 64, 5, 399—408 doi: 10.2478/geoca-2013-0027

Introduction

Turiec Basin (TB) is one of the most typical intramontane
Neogene depressions of the Western Carpathians. It is situated
in the northern part of Slovakia, elongated in the NNE—SSW
direction. It is about 40 km long and 10 km wide (Kováč et al.
2011; Fig. 1).

This basin, belonging to the region of the Western Car-

pathians, is well covered by geophysical data. Seismic, gravity,
geoelectric, and thermal measurements have been collected
there at various scales. Deep seismic profile K-III (Hrdlička et
al. 1983) has shown that the TB is a zone with higher effective
velocities, where v

velocities 5.8—6.0 km/s occur at depth of

9 km. At the K-III profile the depth of the Moho discontinuity
was  set  to  35 km  with  a NNE  dip.  Regional  seismic  profiles
4HR/86,  4AHR/86  and 519/87  (Tomek  et  al.  1987)  brought
information  about  the  geological  structure,  structure  of  the
Tertiary sedimentary fill, as well as its relation to the crystal-

3D gravity interpretation of the pre-Tertiary basement in the

intramontane depressions of the Western Carpathians:

a case study from the Turiec Basin

MIROSLAV BIELIK

1,3

, MARTIN KRAJŇÁK

, IRINA MAKARENKO

, OLGA LEGOSTAEVA

VITALY I. STAROSTENKO

, MARIÁN BOŠANSKÝ

, MICHAL GRINČ

and JOZEF HÓK

Department of Applied and Environmental Geophysics, Faculty of Natural Sciences, Comenius University, Mlynská dolina, pav. G,

842 48 Bratislava, Slovak Republic; bielik@fns.uniba.sk

Institute of Geophysics, National Academy of Sciences of Ukraine, Palladin av. 32, 03680 Kiev, Ukraine

Geophysical Institute of the Slovak Academy of Sciences, Dúbravská cesta 9, 845 28 Bratislava, Slovak Republic; geofmiro@savba.sk

Department of Geology and Paleontology, Faculty of Natural Sciences, Comenius University, Mlynská dolina, pav. G, 842 48 Bratislava,

Slovak Republic

(Manuscript received February 6, 2013; accepted in revised form June 5, 2013)

Abstract: New results related to the thickness and density of the sedimentary fill of the Turiec Basin allowed us to
construct the first original stripped gravity map for this typical intramontane Neogene depression of the Western
Carpathians. The stripped gravity map of the Turiec Basin represents the Bouguer gravity anomalies corrected for the
gravity effect of the density contrast of its Quaternary-Tertiary sedimentary basin fill. It means that the map reflects the
gravity effects of the density inhomogeneities which are located beneath the sedimentary basin fill. This map is there-
fore suitable for the interpretation of the structure and composition of the pre-Tertiary basement. Based on the new data
analysis, two different density models of the sedimentary fill were constructed. The 3D density modelling was used to
calculate the gravity effect of the density models. The stripped gravity maps were produced by subtracting the density
model gravity effects from Bouguer anomalies. The regional trend was also removed from the stripped gravity maps.
The residual stripped gravity maps were consequently used for geological interpretation of the pre-Tertiary basement of
the Turiec Basin. The pre-Tertiary basement of the Turiec Basin can be divided into northern and southern parts due to
its gravity characteristics. Furthermore the northern part can be split into two domains: western and eastern. The crys-
talline basement of the western domain is probably formed by the Hercynian crystalline basement of the Tatric Unit. In
the eastern domain the basement could consist mostly of the Mesozoic complexes of the Fatric Unit. The southern part
of the pre-Tertiary basement of the Turiec Basin is built predominantly by Mesozoic complexes of the Hronic Unit. It is
suggested that the Hronic Unit also forms the bedrock of the volcano-sedimentary complex of the Kremnické vrchy
Mts. The resultant stripped gravity maps and the map of total horizontal gravity gradients have also proven to be very
useful for the interpretation of faults or fault systems in the study area. Various faults, particularly of NNE-SSW and
NW-SE directions were discovered. The analysis of the faults indicates clearly that the contact of the Turiec Basin with
the Malá Fatra Mts and the Ve ká Fatra Mts is tectonic.

Key words: Western Carpathians, Turiec Basin, applied geophysics, gravity, 3D density modelling, stripped gravity map.

line basement in the TB. The basin is well covered by gravity
measurements  in  a scale  of  1 : 50,000  (Zbořil  et  al.  1975;
Szalaiová & Stránska 1978). The main acquisition of the geo-
electrical survey (Zbořil et al. 1985) yielded a definition of a
relief  of  the  pre-Tertiary  basement  with  thick  accumulations
of Tertiary sediments. The geothermal characteristics are also
well known in the TB. The basin represents an area of higher
temperatures compared to the surrounding region. The results
from borehole GHŠ-1, in the southern part of the basin, show
a  temperature  of  35 °C  at  500 m  depth,  49 °C  in  1000 m
depth, and 64 °C in 1500 m depth (Fendek et al. 1990).

Geophysical measurements carried out for the TB were

summarized by Šefara et al. (1987). The last geophysical
measurements were performed and interpreted by Panáček et
al. (1991). The results consist of the physical properties of
the rocks, additional geoelectrical profiling and vertical elec-
trical sounding, and geological-geophysical interpretation of
the geological structure in the TB.

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The development of the TB and the evolution of its land-

scape  were  reconstructed  by  means  of  geological  research
(structural  geology,  sedimentology,  paleoecology,  and  geo-
chronological  data),  as  well  as  by  geophysics  and  geomor-
phology (e.g. Hók et al. 1998; Kováč et al. 2011).

On the basis of the geophysical constraints, a two dimen-

sional interpretation of the gravity field in the TB by the den-
sity modelling method was presented by Bielik et al. (2007,
2009) and Grinč et al. (2010). Krajňák et al. (2012) extended
this study by the calculation of the first preliminary stripped
gravity  map  in  the  TB.  This  preliminary  stripped  gravity
map  did  not  take  into  consideration  the  real  topography  of
the basin. The upper boundary of the density model was ap-
proximated  only  by  sea  level  (0 m).  This  approximation  is
inadequate  for  a  high  quality  interpretation  of  the  gravity
field by the stripping gravity method.

From this point of view the main goal of the paper presented

here is to apply 3D gravity modelling for the calculation and
presentation of new, more precise, stripped gravity maps in
the TB. The improvement of the new stripped gravity maps

Fig. 1. Geographical position of the TB (modified after Kováč et al.
2011 and Krajňák et al. 2012).

presented  here  dwells  in  the  construction  of  more  precise
density models including the topography of the basin. On the
basis  of  the  resultant  stripped  gravity  maps  calculated  for
two different density models, and corrected for the regional
gravity  anomalies,  we  also  present  a  geophysical  and  geo-
logical interpretation of the structure and composition of the
pre-Tertiary basement of the TB.

Geology

The Turiec Basin is the northernmost intramontane depres-

sion  of  the  Central  Western  Carpathians  filled  with  Paleo-
gene,  Neogene  and  Quaternary  deposits  (Figs. 1,  2).  Its
northern  margin  (Kováč  et  al.  2011)  is  formed  by  the
Krivánska  Malá  Fatra  Mts,  which  are  predominantly  com-
posed  of  the  Hercynian  crystalline  basement  of  the  Tatric
Unit. The western flank of the basin is part of the Lúčanská
Malá  Fatra  Mts,  while  the  eastern  flank  borders  the  Ve ká
Fatra Mts. Both are composed of Mesozoic complexes of the

Fig. 2. Schematic geological map of the TB and its surroundings
(modified after Bielik et al. 2007; Kováč et al. 2011).

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Fatric or Hronic Nappes and the  Hercynian crystalline com-
plex of the Tatric Unit. The Tatric crystalline basement of the
Žiar Mts and the volcano-sedimentary complex of the Krem-
nické vrchy Mts restrict the basin to the south (Fig. 2). The TB
is  a  westward  dipping  halfgraben  (Kilényi  &  Šefara  1989;
Kováč et al. 2011). The pre-Neogene basement of this basin
consists of the Central Western Carpathian paleo-Alpine tec-
tonic  units,  which  mainly  comprise  Mesozoic  complexes,
and  also  Paleogene  post-nappe  sedimentary  cover  in  its
northern part (Fusán et al. 1987; Kováč et al. 2011).

The Paleogene and Early Miocene deposits crop out on the

eastern and north-eastern margin, as well as in the footwall
of  the  Miocene  basin  fill.  They  represent  a  basal  formation
containing  coarse-grained  deposits  to  clays,  claystones,
sandstones  and  deposits  of  turbidity  flows  lying  directly  on
the  Mesozoic  basement.  The  Late  Badenian  initial  rifting,
caused by transtensional to extensional tectonic regime, led
to subsidence in the southern part of the TB, where the vol-
cano-sedimentary andesite complex of the Turček Formation
was deposited. Late Miocene clockwise rotation of the prin-
cipal compressional axis to a NNE-SSW led to the Pannon-

ian subsidence of the TB and the synrift sedimentation of the
principal fill of the TB – the Martin Formation deposited in
isolated basin surrounded by uplifted mountains. Pelitic grey
clay is a dominant lithological type, along with clay with the
presence  of  coal  pigment,  thin  lignite  coal  seams,  sand  and
sandstone.  The  uniform  dip  of  the  sedimentary  sequence
points  to  the  long-term  activity  of  faults  near  the  western
margin  of  the  depression  (Hók  et  al.  1998).  These  played  a
dominant role during the basin’s evolution. In the time from
the  latest  Pannonian  to  Pontian,  the  coarse-grained  alluvial
fans of the Abramová and Blážovce Members were deposited
on  the  margin  of  the  uplifted  central  part  of  the  Lúčanská
Malá  Fatra  Mts.  They  were  deposited  on  the  pre-Neogene
basement and the Middle Miocene pelitic sediments. Toward
the  basin,  the  marginal  coarse-grained  subaereal  sediments
are  interfingering  with  fine-grained  lacustrine  deposits.  In
some places they partly intercalate with clays of the Martin
Formation.  During  the  Pontian  and  Early  Pliocene,  the
change  of  tectonic  regime  led  to  the  end  of  subsidence  and
the end of deposition followed by the uplift of the whole TB
catchment (Kováč et al. 2011). A rapid uplift of the crystal-

Fig. 3. Complete Bouguer gravity anomaly map calculated by
Kučera & Michalík (in Bielik et al. 2007). MGL – Martin gravity
low, SPGL – Slovenské Pravno gravity low, NDGL – Nový
Dvor gravity low.

Fig. 4. Map of the pre-Tertiary basement depth calculated by
Kučera & Michalík (in Bielik et al. 2009). MS – Martin sub-ba-
sin, SPS – Slovenské Právno sub-basin, NDS – Nový Dvor sub-
basin.

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line basement of the Krivánska Malá Fatra Mts is documented
by the Upper Pliocene Bystrička Member and the Pleis-
tocene alluvial fans of the Podstráne Member, containing
Tatric material derived only from the mountains.

3D density modelling and stripped gravity map

The 3D gravity (density) modelling method was applied to

generate the stripped gravity map from the Bouguer  gravity
map in the TB. The Bouguer gravity map was compiled from
Bouguer  gravity  anomalies  rather  than  gravity  disturbances
(c.f. Vajda et al. 2006, 2007),  since  the  geophysical  indirect
effect  (e.g.  Vajda  et  al.  2006;  Vajda  &  Pánisová  2007)  is
negligible on the regional scale of the TB from the viewpoint
of our study and interpretation (c.f. Vajda & Pánisová 2007).
Stripping  is  often  applied  in  geophysical  studies,  on  global
or regional scale, to unmask the signal of unknown sources,
when the signal of known sources/structures can be computed
(e.g.  Vajda  et  al.  2008;  Tenzer  et  al.  2009,  2012a,b).  Strip-
ping is particularly useful in geophysical and geological in-
vestigations  of  the  basement  and  the  deep-seated  structure
beneath  sedimentary  basins  (e.g.  Bielik  1988;  Bielik  et  al.

Fig. 5. Alternative two density models of the TB sedimentary fill defined on the basis of the results published in Eliáš & Uhmann (1968),
Šefara et al. (1987), Panáček et al. (1991), Bielik et al. (2009), Grinč et al. (2010) and Krajňák et al. (2012).

2005; Alasonati Tašárová et al. 2009; Bielik et al. 2013). The
3D gravity effect of the sedimentary fill of the TB was com-
puted by the GMT-AUTO software package (Starostenko et
al. 1997, 2011; Starostenko & Legostaeva 1998, 2006).

The principle of the method is that the geological struc-

tures  are  divided  into  horizontally  and  vertically  stratified
media  with  an  arbitrary  density  distribution  in  each  layer.
The  geological  structure  is  approximated  by  inhomoge-
neous,  arbitrarily  truncated  vertical  rectangular  prisms.  An
automatization  of  the  input  of  initial  graphic  information
(maps)  by  digitization  is  also  very  useful  in  the  process  of
the modelling (Legostaeva 2000). The gravity effect of three
dimensional bodies can be determined not only by constant
densities,  but  also  by  different  densities  on  the  upper  and
lower limits having a linear or exponential vertical transition.
After the gravity effect calculation of the TB sedimentary fill
the resultant stripped gravity map is calculated by subtraction
of this effect from the complete Bouguer anomaly map.

Input data

Input data for the calculation of the stripped gravity map

in the TB comprise the map of complete Bouguer gravity

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anomalies (Michalík & Kučera in Bielik et al. 2009), the
map of the pre-Tertiary basement depth, and the density
model of the sedimentary fill.

The complete Bouguer gravity anomalies are based on

gravimetric  measurements  on  a  scale  of  1 : 25,000.  As  the
gravity  data  in  the  studied  area  have  been  acquired  and  pro-
cessed by different approaches and in different time periods it
was necessary to unify all data by re-calculations of the terrain
corrections  T1,  T2  a  T3  in  all  measured  points  (Michalík  &
Kučera  in  Bielik  et  al.  2007).  The  Bouguer  gravity  anomaly
was  calculated  using  the  WGS84  ellipsoidal  normal  gravity
formula,  height  correction  by  a  Taylor  series  expansion  of
normal  gravity  up  to  2nd  order  in  geometric  flattening  and
height  and  Spherical  Bouguer  gravity  slab  with  radius
166.7 km (Bielik et al. 2006). The Bouguer gravity anomaly,
the terrain correction and the Bullard term were calculated for
the  reduction  density  of  2.67 g/cm

(2670 kg/m

). The mean

error  of  the  gravity  differences  is  less  than  ± 0.5 mGal.  The
complete Bouguer anomalies of the TB (Fig. 3) are character-
ized by a local gravity low (amplitude of —42 mGal) with sig-
nificant  gravity  gradients  on  its  margins.  The  gravity  low
coincides  very  well  with  the  surface  of  the  TB.  The  relative
amplitude  of  this  gravity  low  is  about  —13 mGal.  The  TB

Fig. 6. Gravity effect for the first (a) and second (b) density model. MS – Martin sub-basin, SPS – Slovenské Právno sub-basin,
NDS – Nový Dvor sub-basin.

gravity low can be divided into three gravity sub-lows (Grinč
et al. 2010; Krajňák et al. 2012): the Martin gravity low (MGL),
the Slovenské Pravno gravity low (SPGL) and the Nový Dvor
gravity low (NDGL) (Fig. 3). From the regional gravity field
point of view it is possible to observe that the negative gravity
field gradually increases from the southwest to the northeast.

The second set of input data is represented by the thickness

of  the  Tertiary  sediments  (Fig. 4).  The  first  map  of  this  type
was calculated by Kučera & Michalík (in Bielik et al. 2009).
This was solved as a 3D inverse gravimetric problem based on
Pohánka’s  formula,  which  allows  us  to  calculate  the  gravita-
tional effect of a polyhedral prism with a linear density transi-
tion with depth (Pohánka 1988). Barry’s algorithm (1991) was
used  for  the  3D  model  construction  here.  In  this  map  three
main sub-basins can be distinguished: the Martin Sub-basin
(MS), the Slovenské Právno Sub-basin (SPS) and the Nový
Dvor Sub-basin (NDS) (Fig. 4). Note that the observed grav-
ity  field  of  the  TB  (Fig. 3)  correlates  expressly  with  this
map. Spatially the largest MS correlates with the largest rela-
tive  gravity  sub-low  in  the  complete  Bouguer  gravity  map.
The SPS and NDS are the deepest depressions – more than
3000 m below sea level (b.s.l.) in the TB (Fig. 4). In the MS
several  lows  with  depths  exceeding  2000 m b.s.l.  can  be

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found.  The  SPS  and  NDS  are  separated  from  the  MS  by  the
central  basin  elevation  clearly  visible  in  the  area  of  Kláštor
pod Znievom and Moškovec, which reaches up to 500 m a.s.l.
Another  remarkable  feature  of  the  pre-Tertiary  basement
depth is located in the vicinity of Turany (north-eastern part of
the TB). In this area the relief of the pre-Tertiary basement is
formed by a plateau with an altitude around 350 m a.s.l. The
boundary  between  the  basin  and  the  surrounding  mountain
ranges appears at about 500 m a.s.l.

Density models

The study and analysis of the density measurements of the

rocks coming from drill cores of the boreholes GT-5, GT-11,
GT-12, ZGT-3 and GHŠ-1 (Panáček et al. 1991) and results
related to the density values of the sedimentary fill in the TB
(Eliáš & Uhmann 1968; Šefara et al. 1987; Bielik et al. 2009;
Grinč et al. 2010; Krajňák et al. 2012) show that rock densi-
ties vary in a wide interval vertically as well as horizontally.
Therefore, the determination of simple average densities for
the sedimentary fill in the TB is very complicated. To assess
how big is the dependence of the gravity effect of the sedi-
mentary fill on its densities, two different density models
were constructed (Fig. 5). In these models the TB was divided

into vertical rectangular prisms with a linear increase of den-
sity with depth. The average density contrasts applied in the
calculations of the gravity effects of the models were relative
to a reference density of 2.67 g/cm

, which represents the av-

erage density of pre-Tertiary basement rocks.

In the first model (Fig. 5a) the TB was divided into two

prisms, where the southern part consists of Neogene volca-
nic complexes with an average density of 2.33 g/cm

(ac-

cording  to  boreholes  GHŠ-1  –  Panáček  et  al.  1991).  This
section  differs  from  the  northern  part  not  only  by  the  pres-
ence  of  the  volcano-sedimentary  complex,  but  also  by  the
low average density of the overlying the Neogene sedimen-
tary layer (2.04 g/cm

). The density variation in the northern

part (2.40—2.50 g/cm

) is based on the overall average densi-

ties of the Neogene and Paleogene sediments from boreholes
GT-5, GT-11, GT-12, ZGT-3 (Panáček et al. 1991). In the
second density model (Fig. 5b), the average densities of the
basin’s southern part are slightly lower (2.00—2.30 g/cm

) than

in the first model (Fig. 5a). The northern part was divided into
two parts, because the eastern part is mostly formed by Pa-
leogene sediments. In its western part the defined average
densities represent the Neogene and Paleogene extreme val-
ues (2.00—2.50 g/cm

) measured in boreholes GT-5, GT-11,

GT-12, and ZGT-3. Average densities of the Paleogene sedi-

Fig. 7. Stripped gravity map for the first (a) and second (b) density model.

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ments forming the eastern basin part were defined based on
the results of Grinč et al. (2010) and Krajňák et al. (2012).

Results

The gravity effects of two different density models were

calculated by the GMT-AUTO software package on the basis
of  the  3D  gravity  modelling  method.  The  analysis  of  the
gravity effect maps (Fig. 6) showed clearly that the character
of the gravity field is very similar for each model. They vary
only  in  the  amplitudes  of  the  gravity  anomalies.  These  are
smaller  for  the  first  model  (Fig. 6a),  but  higher  for  the  sec-
ond one (Fig. 6b). Note that the gravity effects in the MS and
SPS  are  —6 mGal  (—12 mGal)  for  the  first  (second)  density
model. The amplitudes of the gravity effect in the NDS are
almost the same (about —11 mGal) in both density models.

The stripped gravity maps were determined for both sedi-

mentary density models (Fig. 7a,b) by subtracting their grav-
ity effects from the complete Bouguer anomalies (Fig. 3). It
is possible to see that the character of the individual gravity
fields is very similar. Looking at more detail on the stripped
gravity maps, we can recognize immediately that their gravity

Fig. 8. The resultant stripped gravity map for the first (a) and second (b) density model corrected by regional gravity anomalies, which
were calculated for a radius of 5000 m (Bielik et al. 2007).

fields  are  affected  significantly  by  the  regional  trend.  This
trend has a decreasing tendency in the direction from SW to
NE.  This  regional  trend  reflects  the  gravity  effects  of  the
deep-seated crustal inhomogeneities (mostly the Moho grav-
ity effect (Grad et al. 2009; Csicsay 2010)). As the regional
gravity  trend  masks  the  residual  gravity  field,  which  is  the
fundamental goal of our study here, aiming at interpretation
of  the  pre-Tertiary  basement  of  the  sedimentary  basin,  it  is
necessary to remove it from the stripped gravity maps. The
same approach has also been applied in the interpretation of
gravity field in Israel (Bielik et al. 2013). For the elimination
of  the  regional  gravity  trend  we  used  the  map  of  regional
gravity  anomalies  in  the  wider  area  of  the  TB,  which  was
calculated for a radius of 5000 m (Bielik et al. 2007). The re-
sultant trend-corrected stripped gravity maps for both density
models are presented in Fig. 8a,b.

Our interpretation of the pre-Tertiary basement structure

of the TB is based on the corrected stripped gravity maps
(Fig. 8). But for this interpretation we used other known geo-
logical and geophysical constrains, which are represented by
drill data (e.g. Gašparik et al. 1974, 1991, 1995; Fendek et
al. 1990; Havrila 1997), geophysical (e.g. Zbořil et al. 1975,
1985; Hrdlička et al. 1983; Šefara et al. 1987; Panáček et al.

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1991) and geological (e.g. Gašparik et al. 1995; Rakús 1999;
Kováč et al. 2011) data, results and knowledge. A sketch of
the  pre-Tertiary  basement  structure  of  the  TB  is  shown  in
Fig. 10. The TB can be separated into northern and southern
parts. The NW-SE gravity gradient in the basin’s central part
(near  Kláštor  pod  Znievom)  is  the  boundary  between  them.
Taking  into  account  the  gravity  pattern  of  the  corrected
stripped  gravity  maps,  boreholes  data  (e.g.  ZGT-3,  GT-5,
GT-11,  GT-12,  BJ-2)  and  the  geology  of  the  surrounding
tectonic units of the TB, the northern part of the pre-Tertiary
basement  was  additionally  split  into  two  sub-parts  (do-
mains).  The  first  is  characterized  by  the  Hercynian  crystal-
line basement of the Tatric Unit. In the second the basement
consists  mostly  of  the  Mesozoic  complexes  of  the  Fatric
Nappe,  the  thickness  of  which  decreases  eastward.  In  the
first domain we also recognize another interesting part of the
pre-Tertiary  basement.  This  area  has  a  prolonged  shape  in
the NE-SW direction, being located to the west of the towns
of  Martin  and  Vrútky.  This  anomalous  gravity  field  zone
correlates very well with the Neogene alluvial Podstráne and
Bystrička  Members  (fans).  It  is  believed  that  this  type  of
anomalous  zone  also  forms  the  pre-Tertiary  basement  in  a
wider  region  of  Martin.  The  basement  here  is  probably
formed  by  Mesozoic  rocks  (not  of  great  thickness)  and  the
Tatric crystalline complex underneath.

Fig. 10. A sketch of the pre-Tertiary basement structure of the TB.

Fig. 9. The total horizontal gradient map.

The southern part of the pre-Tertiary basement of the TB is

formed mostly by Mesozoic complexes of the Hronic Nappe.
The continuation of the gravity high to the SE from the area
of borehole GHŠ-1, where the Kremnické vrchy Mts extend
on the surface, indicate that the Hronic Nappe forms the bed-
rock  of  this  volcano-sedimentary  complex.  The  significant
gravity  low  located  in  the  south-eastern  part  of  the  area  re-
flects the center of the Kremnické vrchy Mts. In the area of
the  surface  Neogene  alluvial  Budiš  Member  (fan)  outcrop
(Kováč et al. 2011) we discover an anomalous gravity zone,
in  which  the  basement  probably  consists  of  the  Hronic
Nappe of prevailing dolomite composition.

The resultant stripped gravity maps have also proven to be

very useful for the interpretation of faults, or fault systems,
in the study area. In the image of the gravity field the faults
are characterized by the maxima of horizontal gradients. For
this  reason,  we  evaluated  the  map  of  total  horizontal  gradi-
ents (Fig. 9) using the regularized (smoothed) derivatives in
the  Fourier  domain,  selecting  the  optimum  regularization
(low-pass  filter)  parameter  by  means  of  the  C-norm  func-
tions analysis (Pašteka et al. 2009, 2012). In the TB (Figs. 9
and 10) we found the faults and fault systems with prevailing
NNE-SSW and NW-SE directions. The analysis of the faults
shows clearly that the contact of the TB with the Malá Fatra
Mts and the Ve ká Fatra Mts is tectonic. The gravity pattern

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GEOLOGICA CARPATHICA, 2013, 64, 5, 399—408

suggests that the Blatnica fault should be the south-western-
most boundary of the area, in which the Paleogene post-
nappe sediments are a part of the Tertiary sedimentary basin
fill. In the future we would like to verify the interpreted faults
in the TB by incorporating also geoelectrical (e.g. Putiška et
al. 2012a,b) and radiometric (e.g. Mojzeš et al. 2006; Marko
et al. 2010) methods and observations.

Discussion and conclusions

Detailed analysis of densities of rocks forming not only the

Tertiary sedimentary fill of the Turiec Basin, but also the pre-
Tertiary  surrounding  tectonic  units  shows  that  in  general  the
average densities vary only a little. This applies specifically to
the  densities  of  rocks  that  are  part  of  the  Hronic  and  Fatric
Units.  The  density  differences  between  the  Tatric  crystalline
complexes and the Mesosoic complexes are also inperceptible.

Another element that is very important for the quality of

the resultant stripped gravity map is the existing lack of
knowledge on the course of the boundary between the Neo-
gene and Paleogene layers in the Turiec Basin. The local
gravity low located westward of the village of Belá indicates
that the gravity effect of the sedimentary fill here is probably
underestimated.

Nevertheless, we think that even if the results of the strip-

ping gravity method are, by definition, not unique, the re-
sults presented in the paper are important and valuable at this
stage of research in the Turiec Basin. The results show that
the applied method is very useful for investigating the struc-
ture, composition and tectonics of the basements of Tertiary
depressions in the Western Carpathians.

Acknowledgments: The authors are grateful for the support of
the Slovak Grant Agency VEGA, under grants No. 1/0095/12,
2/0067/12 and 1/0587/11. This work was also supported by
the Slovak Research and Development Agency APVV under
Grants No. APVV-0194-10, APVV-0724-11, APVV-0099-11
and SK-FR-0016-11. We would like to thank R. Pašteka for
his help in calculation of the map of total horizontal gravity
gradients. Our thanks also go to the two anonymous review-
ers for their thoughtful comments that helped to consider-
ably improve the manuscript.

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