GeolCarp_Vol67_No1_83

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, FEBRUARY 2016, 67, 1, 83—104 doi: 10.1515/geoca-201

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Cenozoic structural evolution of the southwestern Bükk Mts.

and the southern part of the Darnó Deformation Belt

(NE Hungary)

ATTILA PETRIK

, BARBARA BEKE

, LÁSZLÓ FODOR

and RÉKA LUKÁCS

Eötvös University, Department of Physical and Applied Geology, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary;

petrik.atus@gmail.com

MTA-ELTE Geological, Geophysical and Space Science Research Group, Hungarian Academy of Sciences at Eötvös University,

Pázmány Péter sétány 1/C, 1117 Budapest, Hungary

MTA-ELTE Volcanology Research Group, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary

(Manuscript received May 28, 2015; accepted in revised form October 1, 2015)

Abstract:  Extensive  structural  field  observations  and  seismic  interpretation  allowed  us  to  delineate  7  deformation
phases in the study area for the Cenozoic period. Phase D1 indicates NW—SE compression and perpendicular extension
in the Late Oligocene—early Eggenburgian and it was responsible for the development of a wedge-shaped Paleogene
sequence  in  front  of  north-westward  propagating  blind  reverse  faults.  D2  is  represented  by  E—W  compression  and
perpendicular extension in the middle Eggenburgian—early Ottnangian. The D1 and D2 phases resulted in the erosion of
Paleogene suites on elevated highs. Phase D2 was followed by a counterclockwise rotation, described in earlier publica-
tions. When considering the age of sediments deformed by the syn-sedimentary D3 deformation and preliminary geo-
chronological ages of deformed volcanites the time of the first CCW rotation can be shifted slightly younger (~17—16.5 Ma)
than previously thought (18.5—17.5 Ma). Another consequence of our new timing is that the extrusional tectonics of the
ALCAPA unit, the D2 local phase, could also terminate somewhat later by 1 Myr. D4 shows NE—SW extension in the
late Karpatian—Early Badenian creating NW—SE trending normal faults which connected the major NNE—SSW trending
sinistral faults. The D5 and D6 phases are late syn-rift deformations indicating E—W extension and NW—SE extension,
respectively. D5 indicates syn-sedimentary deformation in the Middle Badenian—early Sarmatian and caused the syn-
sedimentary thickening of mid-Miocene suites along NNE—SSW trending transtensional faults. D5 postdates the second
CCW rotation which can be bracketed between ~16—15 Ma. This timing is somewhat older than previously considered
and  is  based  on  new  geochronological  dates  of  pyroclastite  rocks  which  were  not  deformed  by  this  phase.  D6  was
responsible for further deepening of half-grabens during the Sarmatian. D7 is post-tilt NNW—SSE extension and in-
duced the deposition of the 700 m thick Pannonian wedge between 11.6—8.92 Ma in the southern part of the study area.

Key words: Bükk Mts., Cenozoic, fault pattern, stress field, seismic profile, deformation band.

Introduction

The Darnó Zone is an important NNE-SSW trending struc-
tural element located in north-eastern Hungary and reaching
the southernmost part of the Slovak Repu

blic (Fig. 1a). T

Darnó  Fault  which  is  an  element  of  the  Darnó  Zone  is  re-
stricted  only  to  the  area  of  Darnó  Hill  and  can  be  followed
up to Bükkszék village. The Darnó Fault is a moderately SE
dipping  thrust  putting  the  Mesozoic  rocks  onto  Oligocene
sediments  (Fig. 1b)  (Schréter  1951;  Telegdi-Róth  1951;
Fodor et al. 2005). The western footwall block of the fault is
characterized by a gentle monoclinal basin filled with thick

Late Oligocene—Early Miocene sequences (Fig. 1b) (Jaskó
1946). The Darnó Line first defined by Pantó (1956) con-
nects the Darnó Fault with Uppony Fault further to the north-
east and goes up to the Rudabánya Hills.

The Darnó Deformation Belt (DDB) includes all the

NNE—SSW oriented Cenozoic structural elements which ex-
tend from the Darnó Fault sensu stricto up to the north-
western margin of the Bükk Mts. (Fig. 2) (Fodor et al. 2005).
The Darnó Line and its tectonic influence on Late Oli-

gocene—Early Miocene sedimentation has been recognized
for a long time (Bál

di 1986; Sztanó & Tari 1993; Sztanó &

Józsa 1996) but the tectonic evolution of the southern part of
the DDB has been less investigated and understood.

Our research area also includes the southwestern part and

foreland  of  the  Bükk  Mts.  Special  emphasis  is  given  to  the
Felsőtárkány  graben  (FG)  which  has  a  particular  structural
position  while  cutting  across  the  Mesozoic  rocks  (Fig. 2).
Our  knowledge  about  the  Cenozoic  development  of  the  FG
is  poor  and  a  systematic  structural  analysis  was  not  carried
out although Csontos (1999) and Fodor et al. (2005) briefly
described a few major Miocene structures.

The aim of our study is to outline and reveal the Cenozoic

structural  evolution  of  the  southwestern  part  of  the  Bükk
Mts.  in  much  more  detail  than  in  the  previous  studies  (e.g.
Tari 1988; Csontos 1999; Fodor et al. 1999, 2005). We also
connect  the  deformation  phases  of  the  Southern  Bükk  fore-
land of Petrik et al. (2014) to those of the Darnó Fault sensu
stricto. The other objective of our paper is to specify the ki-
nematics and the time of fault activity and reveal new fault
indications for the study area in the Cenozoic period.

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Methods

A combination of methods was used to understand the tec-

tonic  evolution  of  the  area.  Our  investigation  is  primarily
based  on  extensive  field  work  covering  not  only  the  study
area  but  also  the  southwestern  part  of  the  southern  Bükk
foreland as well. In this study we present only the most im-
portant sites (17 si

tes, see Table 1) in ter

ms of Cenozoic evo-

lution. We mainly focused on measuring brittle structural
elements (faults, joints, deformation bands) in rocks with
different Cenozoic ages.

We calculated stress tensors from slickenside lineations on

fault  planes  using  Tector  1994  software  with  the  algorithm
described  by  Angelier  (1984,  1990).  This  software  deter-
mines the reduced stress tensor including the position of the
three  principal  stress  axes  and  their  relative  magnitude
(

Φ=σ

—

). The

Φ value ranges from 0 to 1 depen-

ding on the stress state that acted on the fault planes. The

principal stress axes (

) are orthogonal to each other

and the resolved shear stress perpendicular to them is zero.
σ

indicate the maximum, the intermediate and the

minimum  compression  direction,  respectively.  When  suffi-
cient  data  was  available  we  used  automatic  phase  separa-
tion  often  combined  with  manual  separation  (Angelier  &
Manoussis  1980).  During  stress  tensor  calculation  we  took
into account the average misfit angle (

α) between measured

striae and the calculated shear stress (

τ) (ANG criterion) and

the misfit between the direction and size of a maximum cal-
culated shear vector and the unit vector along the striae
(RUP criterion) (Angelier 1984, 1990). We accepted a fault
was part of a stress field when these parameters were below
22.5° and 45 %, respectively. Based on Anderson’s assump-
tion (Anderson 1951) we estimated the main stress axes for
faults without striae and joints.

Backtilting of measured structures was also applied to re-

veal whether the deformation might have taken place before,

Fig. 1. A – Schematic structural position of the study area within the Carpathians. The inset shows the study area and the Bükk Mts. with
its most prominent structures (Fodor 2010). B – Schematic geological NNW—SSE oriented cross section indicating the different aged sub-
basins and their rock piles for the NHSSPB (Petrik et al. 2014). The Slovak part of the NHSSPB drawn after Fusán et al. (1987). Major
fault systems are displayed. Note the syn-sediment thickening of Paleogene rocks in front of propagating reverse faults and their pinching
out north-westward. Note the normal reactivation of the Darnó Zone. Post-rift rock suites only appear in the Vatta-Maklár Trough. See lo-
cation of section on Fig. 2.

Fig. 2. Simplified geological map of the study area with the position of investigated sites, important boreholes, seismic profile and geologi-
cal cross sections. Note the dominance of NE—SW trending faults which were modified with respect to original base maps of Less et al.
2005.

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during or after a specific tilting event in order to determine
the relative chronology among stress fields. We took into ac-
count  the  average  dips  of  Eocene,  Oligocene  and  Miocene
volcanoclastic  levels.  We  made  two  scenarios  for  tilting  of
beds  because  dip  data  show  spatial  variations  even  if  mea-
sured from the same stratigraphic horizons; one of them sup-
poses  a  more  significant  tilting  (altogether  35°  for  the
Eocene)  and    a  more  moderate  scenario  (altogether  25°  for
the Eocene).

Syn-sedimentary deformations allowed us to delineate the

structural  phases  more  precisely.  Deformation  bands  were
also important, while they could form closely after sedimen-
tation or only much later. The prevailing deformation mecha-
nism  in  these  bands  refers  to  the  host  rock  porosity  and  its
state  of  consolidation  which  is  irreversibly  changing  over
time.  Consequently,  the  differences  in  deformation  mecha-
nism within generations of bands give us relative chronology
between  them  based  on  subsidence  history.    Thin  sections
were made from each deformation band to examine their de-
formation mechanism. We analysed and compared them un-
der  a  light  microscope.  The  differences  in  deformation
mechanism  within  generations  of  bands  gave  us  a  relative
chronology  between  them  based  on  subsidence  history.  Fi-
nally,  each  deformation  band  was  integrated  into  the  struc-
tural phases of the study area.

Some 2D reflection seismic profiles located south of the

study  area  were  also  investigated  to  better  understand  the
subsurface  structures.  Geological  profiles  were  constructed
by using borehole data and our structural observations. The
faults  on  seismic  profiles  have  been  correlated  with  their
counterparts  on  geological  profiles.  Using  combinations  of
these  methods  we  produced  schematic  sequential  structural
cartoons depicting the main Cenozoic fault systems.

Geological background

The study area includes the southern part of the Darnó

Deformation Belt and the southwestern part of the Bükk
Mts. (NE Hungary) (Fig. 2). Mesozoic deposits represen-
ting different nappes are composed of Triassic carbonates,
Middle Triassic volcanoclastic rocks and Jurassic siliciclas-
tic sequences with Middle Jurassic basalt suites and radiola-
rite

(Fig. 3). Th

ese rocks were folded into NE—SW trending

anticlines and synclines during or after Late Jurassic—Early
Cretaceous nappe stacking (Csontos 1999). The Paleogene
history of the study area is strongly tied to the evolution of
the  North  Hungarian-South  Slovakian  Paleogene  Basin
(NHSSPB) which is interpreted as a flexural basin situating
in  a  retroarc  position  with  respect  to  the  Western  Car-
pathian  orogenic  arc  (Tari  et  al.  1993).  The  beginning  of
the  basin  formation  is  marked  by  an  uppermost  Eocene
transgressive sequence including terrestrial to shallow-ma-
rine  clastics  and  limestone  (Báldi  &  Báldi-Beke  1985;
Nagymarosy  1990).  The  average  dip  of  the  Eocene  rocks
varies between 25° and 35° but locally can reach 45°. Due
to tectonic subsidence they were covered by shallow bathyal
marls, laminated claystone and thick siltstone of Early Oli-
gocene  age  (Fig. 3)  (Báldi  1986;  Less  2005).  The  average
dip of Oligocene deposits ranges from 15° to 25°. The last
phase  in  basin  evolution  is  represented  by  Late  Oligocene
to  earliest  Miocene  (Eggenburgian)  fine-  to  medium-
grained  clastics  west  of  the  Darnó  Fault.  However,  the
Miocene part seems to be missing in the study area due to
the “Intra-Egerian” denudation which was the result of tec-
tonic uplift and/or the TB1.3 eustatic cycle (Báldi & Sztanó
2000). The first major tilting (I. Tilting) can be attributed to
this denudation in the earliest Miocene time (Fig. 3). Sedi-
mentation was influenced by eustatic sea level changes and
in a minor way by local fault activity (Sztanó & Tari 1993;
Báldi  &  Sztanó  2000).  The  largest  such  fault  in  the  study
area,  the  Darnó  fault  acted  as      a  SE-dipping  reverse  fault
creating  a  deep  flexural  sub-basin  (

Fig. 1b

, Sztanó & Tari

1993; Tari et al. 1993; Fodor et al. 2005). In the study area,
th

e Lower

Miocene rock suites are mainly confined to the

Darnó Zone where a small fault-controlled fan-delta (Darnó
Conglomerate)  was  deposited  at  the  eastern  margin  of  NH-
SSPB  (Fig. 3)  (Sztanó  &  Józsa  1996).  The  age  of  this  con-
glomerate  is  well  constrained  by  radiometric  and  bio-
stratigraphic  data  indicating  ~21.4—20.9  Ma  (Less  et  al.
2015). In the southern Bükk foreland correlative sediments
were not proved unequivocally, or alternatively, if present,
they  are  represented  by  continental  variegated  clay,  con-
glomerate (Less 2005).

Sites

X coord.

(lat.)

Y coord.

(long.)

Number

of data

1. Kis-Eged
(Triassic)

47.91892 20.40772

2. Kis-Eged
(Eocene)

47.91514 20.40777

3. Kis-Eged
(Oligocene)

47.91618 20.41052

4. Noszvaj
(Oligocene)

47.93634 20.46443

5. Eger, Wind
(Oligocene)

47.89863 20.40075

6. Andornaktálya
(Oligocene)

47.86966 20.40888

7. Kis-Hill
(Eggenburgian)

47.95060 20.15334

8. Pétervására
(Eggenburgian)

48.02101 20.09856

9. Eger, Tihamér
(Ottnangian)

47.87909 20.40395

10. Bátor
(Ottnangian–Karpatian)

47.96782 20.26044

11. Sirok
(Early Badenian)

47.92972 20.19362

12. Felnémet
(Middle Badenian)

47.93365 20.38435

13. Egerbakta
(Middle Badenian)

47.94082 20.29232

14. Demjén
(Middle Badenian)

47.83465 20.34455

15. Ftárkány
(Sarmatian)

47.97711 20.41543

16. Bambara
(Sarmatian)

47.97640 20.43542

17. Novaj
(Pannonian)

47.86708 20.47287

Table 1: The investigated sites with their geographical coordinates
and the number of measured data.

CENOZOIC STRUCTURAL EVOLUTION OF THE SW BÜKK MTS AND NE HUNGARY

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The evolution of the NHSSPB was terminated by a regional

unconformity and denudation associated with a second tilting
event (II. Tilting) in the middle part of the Early Miocene,
ca. 20—19 Ma ago. Paleogene sediments outcrop exclusively
on the eastern margin of the FG due to the earliest Miocene
and Mid-Late Miocene erosional events (Fig. 2).

During the Early Miocene the NHSSPB was dextrally dis-

placed from its original continuation, from the North Slove-
nian  Paleogene  Basin  by  the  combined  Periadriatic-Balaton
Fault  system  (PAF)  (Kázmér  &  Kovács  1985;  Báldi  1986;
Csontos  et  al.  1992;  Fodor  et  al.  1998).  Post-19 Ma  evolu-
tion  was  part  of  the  formation  and  evolution  of  the  exten-
sional  Pannonian  Basin  system  (Royden  &  Horváth  1988).
The rock suites in the Pannonian Basin are divided into pre-
rift,  syn-rift  and  post-rift  sediments  and  volcanites.  Exten-
sive rhyolitic and dacitic pyroclastic rocks were produced by
many  explosive  eruptions  of  late  Early  to  Mid—Miocene
times in the Pannonian Basin (e.g. Szabó et al. 1992). These

volcanic rocks are exposed exceptionally well in the southern
Bükk  foreland  and  can  give  radiometric  age  constraints  on
the  Miocene  stratigraphy  and  geodynamic  evolution  of  the
area (Márton & Pécskay 1998; Póka et al. 1998; Szakács et
al.  1998;  Harangi  et  al.  2005;  Lukács  et  al.  2005,  2007,
2009;  Pentelényi  2005).  New  U-Pb  ages  on  zircons  of
the  pyroclastic  units  in  the  Bükk  foreland    indicate  that  the
oldest  pyroclastic  unit  (“lower  unit”)  is  somewhat  younger
(~18.5—17.9 Ma; Lukács et al. 2014a,b), than previously sug-
gested  (21—18.5 Ma;  Márton  &  Pécskay 1998),  the  “middle
volcanoclastic level” is restricted to ca. 16 Ma (Lukács et al.
2014a,b)  in  contrast  to  the  former  suggestion  of  between
17.5—16,0 Ma (Márton & Pécskay 1998), while the “upper”
volcanoclastic level involves several units, spanning broadly
from 15 to 14 Ma (Lukács et al. 2015).

In our study area the “lower” and “middle” pyroclastic

rocks can be found sporadically, preserved in karstic depres-
sions (Hartai 1983; Pelikán 2005). In the Southern Bükk

Fig. 3. Lithostratigraphic chart of the study area. Standard stages and their absolute ages are based on Lourens et al. (2004). Central Paratethys
stages and their absolute ages are based on Hohenegger et al. (2009); Popov et al. (1993); Steininger et al. (1996). The U/Pb radiometric ages of
volcanoclastic levels are taken from Lukács et al. (2014a,b). The Sr-age of Darnó Fm. is taken from Less et al. (2015). Note that the Mesozoic
is not time proportional. Major tilting events and associated geological events are also demonstrated. DZ – Darnó Zone, DF – Darnó Fault.

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foreland,  the  pyroclastic  rocks  can  be  found  in  NE—SW
trending stripes (Fig. 2) (Pentelényi 2005; Less et al. 2005).
Some boreholes north-east and north-west of the Bükk Mts.
revealed that the lower rhyolitic tuff is covered by an Ottnan-
gian—Karpatian fluviatile-paludal sequence including several
coal seams (Salgótarján Fm., Pelikán 2005). The coal seams
tend to be paralic in the upper part and are often intercalated
by sandstone and sandy silt indicating a normal salinity envi-
ronment (Ádám 2006; Püspöki et al. 2009). The relationship
between  the  volcanic  rocks  and  sedimentary  formations
(Pelikán 2005), and the new preliminary U-Pb ages (Lukács
et  al.  2014a,b;  Lukács  et  al.  2015)  indicate  that  the  coal-
bearing  sequence  is  younger,  and  could  involve  only  the
upper Ottnangian (ca. 18 Ma) and Karpatian. This formation
appears  on  the  surface  west  of  the  FG  where  several  bore-
holes (Szk-6, Szk-8) encountered it unconformably overly-
ing  Mesozoic  rocks  (Fig. 2).  The  deposition  of  the
Salgótarján  Fm.  partly  overlaps  with  the  Karpatian  basal
conglomerate and sandstone which was deposited on a coastal
plain (Egyházasgerge Fm.) (Fig. 3) (Pelikán 2005). This se-
diment  crops  out  at  the  north-western  margin  of  the  FG
where  it  overlies  unconformably  the  Mesozoic  rocks  and
consists  of  a  transgressive  sequence  containing  Mesozoic
limestone  and  dolomite  pebbles  (Fig. 2)  (Pelikán  2005).  At
the south-eastern margin of the FG some patches of Karpa-
tian  sediments  were  also  mapped  (Fig. 2).  Closer  to  the
Darnó Fault this formation is overlain by Karpatian shallow
bathyal  siltstone  (Fig. 3)  interbedded  by  sandstone  layers
(Garáb  Fm.)  (Pelikán  2005).  This  formation  is  restricted  to
the  westernmost  part  of  the  study  area  where  its  thickness
varies  between  100—150 m.  The  Early  Badenian  sediments
and  middle  volcanoclastic  rocks  are  found  sporadically  in
the DDB area in the vicinity of Szilvásvárad (Pelikán 2005).
The  upper  volcanoclastic  level  appears  on  the  surface  in
the  FG  and  further  to  the  west  with  variable  thickness
(~50—150 m)  (Fig. 2).  It  tends  to  be  pinched  out  in  a  west-
ward  direction  close  to  the  Darnó  Line.  Some  boreholes
(Verps-3, 4), southwest of the study area revealed more than
500 m  thick  pyroclastic  rocks  of  Badenian  and  Sarmatian
age  in  the  hanging-wall  block  of  a  major  NE—SW  trending
transtensional  fault.  The  wedge-shaped  syn-sedimentary
thickening of these rocks in the tilted blocks was associated
with the third major tilting event (Fig. 3). These rocks can be
the  temporal  equivalent  of  the  middle  and  upper  volcanic
level. In the FG the upper volcanoclastic rocks are overlain
by  shallow  marine/nearshore  sandstone,  tuffitic  sandstone
(Kozárd Fm.) with Sarmatian vertebrates (Fig. 3) (Kessler &
Hír 2012). The thickness of the Sarmatian rocks is variable
in  the  Felsőtárkány  graben,  but  in  the  Southern  Bükk  fore-
land, in the hanging-wall blocks of normal faults it can reach
500 m (Pelikán 2005).

For a long time, the Late Miocene sedimentation was con-

sidered post-rift, but new structural data demonstrate ongoing

faulting  at  least  up  to  8 Ma  in  the  study  area  (Petrik  et  al.
2014) and in the whole Pannonian basin (Fodor et al. 2013).
The thick Late Miocene (Pannonian in local terms) sedimen-
tary unit consists of lacustrine marlstone, followed by basin
floor  sandy  turbidites,  clayey  slope  deposits,  sandy  deltaic
and  variegated  fluvial  suites  (Magyar  et  al.  1999,  Sztanó  et
al.  2013).  The  second  major  tilting  occurred  during  the  be-
ginning of this sedimentation, in the early Late Miocene and
was  accompanied  by  syn-tectonic  thickening  of  the  early
Pannonian  sediment  pile,  particularly  the  formations  below
the slope unit (Petrik et al. 2014). This thickening can be as-
sociated  with  the  fourth  major  tilting  event  of  the  area
(Fig. 3). In the FG and in the southern Darnó DB Pannonian
sediments  are  missing  on  the  surface  and  were  only  pre-
served  in  the  syn-sedimentary  NE—SW  trending  Vatta-
Maklár Trough south of the study area (Tari 1988; Petrik et
al. 2014). This distribution is due to the post-Pannonian ero-
sion induced by neotectonic (Quaternary) uplift of the Bükk
Mts.  and  their  margins  (Dunkl  et  al.  1994).  This  uplift  was
accompanied by very modest post-sedimentary tilting which
can  be  estimated  from  the  dip  degree  of  the  uppermost
imaged Late Miocene horizons to be 1—2°.

The most relevant structures of the DDB are the NNE—

SSW trending normal faults (Fig. 2). These faults are respon-
sible for sudden thickness changes within the Miocene
sequences. The NNE—SSW trending faults are connected to
the NE—SW trending major faults of the Vatta-Maklár
Trough (Fig. 2). We will discuss the geometry and kinema-
tics and age of these faults in the successive chapters.

Results

Main structural phases

The Cenozoic structural evolution history of the study area

can be divided into 3 main separate periods on the basis of
the fault kinematics, the time of fault activity and their in-
fluence on sedimentation.

Pre-rift deformations

D1 phase (Eocene? — early Eggenburgian)
This deformation is characterized by NW—SE compression

and perpendicular extension but small deviation in

direc-

tion can be observed

(Fig. 4,

sites 1, 2, 3, 5, 6, 7). The D1

phase was observed in Upper Eocene to Oligocene rocks and
Eggenburgian conglomerate of the Darnó Fm.

The NE—SW trending conjugate reverse faults and oblique

dextral strike slip faults are the main structures of this defor-
mation phase (Fig. 4). Small scale (~5 cms) reverse offsets
and folds with NE—SW trending axes can be associated with
this phase. In site 5 (Fig. 4), NW—SE trending dilational

Fig. 4. The summary table of stress fields and main deformation phases. RUP (in %), ANG (in degree) criteria and phi value are indicated
for stress tensor calculation. After the value of criteria, the number of unfitted data is also displayed. The structural data of site 8 were mea-
sured by L. Fodor and F. Bergerat (Paris).

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band filled with syntectonic sediment matrix clearly indi-
cates NE—SW

extension during Late Oligocene sedimenta-

tion (Petrik et al. 2014

NW—SE trending deformation bands

in Eggenburgian con-

glomerate are related to this phase and indicate NE—SW ex-
tensional  deformation.  These  bands  show  a  disaggregation
type deformation mechanism and indicate early deformation
which can be attributed to a stress field which occurred soon
after sedimentation. Another argument of the earliest timing
of  these  bands  is  two  sets  of  relative  chronological  criteria.
The  NW-SE  striking  bands  are  slightly  reversely  displaced
by  a  set  of  NE—SW  trending  deformation  bands  (Fig. 5a).
These  bands  can  belong  to  the  earliest  deformation  phase
due to their strikes which perfectly fit into the D1 phase. The
disaggregation  type  deformation  mechanism  also  supports
early deformation at a shallow depth (<1 km) (Fossen 2007).
On  the  other  hand  the  following  deformation  structures
(third in relative order) suggest more consolidated host rock
where calcite-infilled lenses as a marker of displacement are
already  present  along  the  bands.  This  observation  shows
a transitional character from deformation bands toward dis-
crete  faults  and  belongs  to  the  following  D2  phase
(Fig. 5b,c).

The structures belonging to this phase might predate the

second major tilting event (ca. 20—19 Ma) proven by the
backtilting test (Petrik et al. 2014).

On NW—SE trending seismic profiles some NW-vergent

blind reverse faults can be presumed resulting in folding and
wedge-shaped  thickening  of  Paleogene  sediments  (Fig. 6).
North-westward  the  Paleogene  sediments  are  thinning  and
pinching  out  on  the  flank  of  an  elevated  high.  Some  small-
scale SE-vergent backthrusts were often associated with pro-
pagating  reverse  faults  (below  Verp-3  borehole,  Fig. 6).
Above  some  blind  reverse  faults  the  Mesozoic  rocks  are
directly overlain by Early to Mid-Miocene pyroclastic rocks
(Verp-2, Esz-1 boreholes). Paleogene sediments are missing
on  these  elevated  highs  due  to  either  or  both  the  earliest
Miocene  erosion  or  original  non-deposition.  In  the  FG  area
the  Paleogene  rocks  only  crop  out  in  the  south-eastern  part

of the Nagy-Eged Hill (Fig. 2). If we project the subsurface
architecture  of  sediments  and  faults  of  seismic  profiles  into
the  area  of  the  FG,  similar  wedge-shaped  Paleogene  sedi-
ments  can  be  presumed  below  the  Mid-Miocene  tuffs  and
sandstone (Fig. 7). In this case the precursor basin of the FG
would be bounded by NW-vergent blind reverse faults on its
eastern side. From the w

estern margin of the FG Paleogene

sediments are missing as proven by boreholes which reached
Mid-Miocene sediments directly above Mesozoic rocks
(K-31, K-34 boreholes) (Figs. 2, 7).

Thickening of Paleogene sediments in front of the propa-

gating reverse faults along with syn-sedimentary dilational
bands in late Oligocene sandstone suggest that the age of the
D1 phase can be put into Late Oligocene time, although an
Early Oligocene onset cannot be ruled out. However, defor-
mation bands in site 7 (Figs. 2, 4) allow us to extend the upper
time limit of the D1 phase into the early Eggenburgian.

D2 phase (middle Eggenburgian—early Ottnangian)
This deformation is represented by E—W compression and

perpendicular  extension  (Fig. 4,  sites  1,  3,  4,  7,  8).  This
phase  has  dominantly  strike-slip  character  with  NW—SE
trending  sinistral  and  NE—SW  trending  dextral  strike-slip
faults. This deformation affected siliciclastic rocks with ages
ranging  from

Late

Oligocene to Eggenburgian. The lower

volcanoclastic unit was not involved in this deformation.
Fractured pebbles

in Upper

Oligocene conglomerate indicate

syndiagenetic deformation because fractures could not be
traced in the matrix (Fig. 4, site 5). Some conjugate NE—SW
dextral and NW—SE trending sinistral cataclastic deforma-
tion bands in Eggenburgian conglomerate were also attributed
to this phase (Fig. 4, site 7). This D2 phase postdates or/and
partially overlaps with the second major tilting.

On seismic profiles Eggenburgian rocks are identified

based on their distinct seismic character from the overlying
volcanoclastic units (Fig. 6). They are found in front of blind
reverse faults and are displaced in both reverse and normal
ways indicating strike-slip deformation. In the hanging-wall
block of major reverse faults the top of the Oligocene is

Fig. 5. Outcrop-scale structures at site 7 (Figs. 1, 4), just near the Darnó Fault. In photo A deformation bands (black dotted lines) are repre-
sented by sets of anastomosing structures which are darker than the host sandstone. One set of bands are thicker (1—1.5 cm) and crosscut by
thinner (0.3—0.5 cm) apparently reverse bands, which gives their relative chronology. In photo B, viewed from above, the deformation band
is an almost 1 cm thick visibly finer grained zone with negative relief (white dashed line), in which the main clasts are reoriented parallel to
the band (black lines) and generally contain small calcite lenses (photo C) indicating transitional stage to faults. Sedimentary bedding is
marked by black dashed lines.

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eroded and covered by Mid Miocene volcanoclastic suites
(Fig. 6). This erosion or original non-deposition might be
tied to both the first and second major tilting events during
the earliest Miocene.

At the southern elevated highs of the Vatta-Maklár Trough

the Late Oligocene

was also eroded and covered by Early-

Mid-Miocene volcanoclastic rocks as biostratigraphic data
prove (Majzon 1961). North of these elevated highs several
hundred metres of poorly dated terrestrial suites with con-
glomerate levels were drilled below the lower volcanoclastic
level in the Vatta-Maklár Trough.

The conjugate deformation bands in Eggenburgian con-

glomerate indicates post-tilt deformation as opposed to those
belonging  to  the  D1  phase.  The  structures  belonging  to  D2
show  post-  or  partially  syn-tilt  deformation  with  respect  to
a  second  major  tilting  which  took  place  ca.  20—19 Ma.  D3
deformation  was  not  observed  in  the  lower  volcanoclastic
units therefore the upper age limit is ~18.5—17.9 Ma indicated
by new zircon U-Pb age results (Lukács et al. 2014a,b).

Syn-rift deformations

All syn-rift phases indicate pre-tilt deformation with re-

spect to the early Late Miocene tilting event proven by posi-
tive back-tilt tests

(Fig. 4).

Early syn-rift phase (D3, late Ottnangian—early Karpatian)
This deformation is characterized by NNE—SSW extension

(Fig. 4., sites 6, 8, 9, 10). D3 is very similar to D2 in terms of
extensional direction but this stress field is exclusively repre-
sented by extensional structures. This deformation was

observed in rocks with ages ranging from

Late

Oligocene to

early Karpatian. The lower volcanoclastic unit was already
involved in this deformation.

Conjugate WNW—ESE trending normal faults clearly indi-

cate NNE—SSW extension. Some conjugate weakly cata-
clastic deformation bands forming in the still poorly
consolidat

ed Upper Olig

ocene sandstone also show a similar

extensional direction. In Ottnangian-Karpatian sandstone
(Salgótarján Fm.) we observed syn-sedimentary deformation
along a WNW—ESE trending normal fault

(Fig. 8a)

. Along

the  fault  some  layers  accommodate  the  deformation  by  fol-
ding  while  others  indicate  2—3 cm  normal  offset;  this  beha-
viour is due to the competence contrast. In the hanging wall
block,  the  equivalent  layers  show  small-scale  thickening.
Downward along the fault a thick silty layer forms an exten-
sional monocline without displacement (Fig. 8a). This struc-
ture  may  indicate  a  long-segmented  normal  fault.  A  few
covered normal faults in the Ottnangian lower volcanoclastic
suite also indicate syn-sedimentary NNE—SSW extension at
that time (Fig. 8b). Along these WNW—ESE oriented normal
faults 10—15 cm offsets were observed.

The age of this stress field is Ottnangian-early Karpatian

constrained by syn-sedimentary deformation structures, and
also by the possible timing of the subsequent rotational de-
formation (see Fig. 3).

Paleomagnetic measurements from lower volcanoclastic

suites indicate 45—50° CCW rotation (Márton 1990; Márton
& Pécskay 1998). The first CCW rotation was bracketed be-
tween 18.5—17.5 Ma (Márton & Márton 1996; Márton &
Pécskay 1998). Fodor (2010) was the first to establish NNE—
SSW extension as a first sign of the Pannonian rifting. This

Fig. 8. A – The syn-sedimentary WNW—ESE trending normal faults in site 10. Across the fault some layers accommodate the deformation
by folding while others indicate 2-3 cm normal offset. Downward along the fault an extensional monocline developed in a thick silty layer.
B – Covered faults in lower volcanoclastic units in site 9. Along the normal faults 10—15 cm displacement can be seen.

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phase  should  predate  the  first  CCW  rotation  because  of  the
good  correlation  between  paleomagnetic  data  and  apparent
stress  axes  rotations  (Fodor  2010).  He  placed  this  rotation
in  the  Ottnangian.  Our  observation  on  syn-sedimentary  or
covered faults may suggest that the first CCW rotation seems
to be slightly younger than previously thought and can pro-
bably  be  placed  within  the  Karpatian  (Fig. 3).  The  exact
timing  depends  on  the  age  of  volcanoclastics  and  the  age  of
site 10.

D4 phase (late Karpatian-Early Badenian)
The D4 phase is demonstrated by NE—SW extension

(Fig. 4,  sites  6,  7,  8,  9,  11).  Sediments  correlative  to  this
deformation phase are preserved in the western margin of the
DDB  and  the  Felsőtárkány  graben  (FG).  NW—SE  trending
conjugate  normal  deformation  band  faults  with  calcite-
infilled lenses (Fig. 5b,c) belong to this phase. Some oblique
dextral  faults  of  pre-existing  WNW—ESE  oriented  normal
faults  indicate  post-D3  deformation  (site 8,  Fig. 4).  The  D4
phase  already  affected  the  Early  Badenian  rocks  in  Sirok
(site 11,  Fig. 4)  where  NNE—SSW  trending  sinistral  and
NW—SE  trending  dextral  strike-slip  faults  were  identified
by Bergerat et al. (1984) and again by Fodor et al. (2005).
This  is  the  reason  why  we  postulate  that  the  dominant  ex-
tension  may  have  been  accompanied  by  strike-slip  defor-
mation.

Márton & Fodor (1995) and Fodor et al. (1999) suggested

that the D4 extension can be bracketed between the first and
second phase of rotation in NE Hungary. Accepting this
idea, this D4 phase can be placed in the latest Karpatian to
Early Badenian.

Late syn-rift deformations

D5 pha

se (Middle Badenian—early Sarmatian)

This phase is one of the most represented structural phases

in the study area and it is characterized by E—W extension
(Fig. 4, sites 10, 12, 13, 14, 15, 16). The D5 phase includes
N—S to NNE—SSW trending conjugate normal faults and de-
formation bands (Figs. 9, 10). N

—S trending conjugate defor-

mation  bands  in  Sarmatian  sandstone  (in  site  16)  crosscut
each  other  and  indicate  E—W  extension  (Fig. 10).  NW—SE
dextral  and  NE—SW  sinistral  conjugate  strike-slip  faults
along  with  cataclastic  type  deformation  bands  with  similar
orientations are also common in the study area (Fig. 4, site 14)
and  also  in  the  Southern  Bükk  foreland  (Fig. 4).  NW—SE
oriented  normal  faults  of  the  D4  phase  were  reactivated  as
oblique dextral faults during the D5 phase.

We investigated several sites in the FG area where the up-

per volcanoclastic units and

early

Sarmatian sandstones out-

crop (Fig. 4, sites 12, 15, 16). The D5 phase was present in
all  of  these  sites  and  always  indicated  the  oldest  deforma-
tional event. A covered normal fault indicating syn-sedimen-
tary  E—W  extension  in  Sarmatian  tuffitic  sandstone  is  also
part  of  this  D5  phase  (

Fig. 9

). Along this antilistric normal

fault a syntectonic sediment wedge was formed. Close to the
antilistric fault the gently tilted layers become folded due to
fault drag or they form an extensional monocline above the
upward propagating normal fault (Fig. 9). The upper part of

this  wedge  is  a  well-seen  discordance  surface  above  which
the  layers  are  mainly  sub-horizontal  and  cover  the  upward
continuation  of  the  fault.  An  impressive  N—S  trending  nor-
mal  fault  was  observed  in  the  upper  volcanoclastic  unit  re-
sulting  in  50 cm  displacement  of  a  pyroclastic  channel.
Along  this  fault  multiple  oblique  dextral-normal  striations

Fig. 9. Covered normal fault in Sarmatian tuffitic sandstone (in
site 15) indicating E—W extension of the D5 phase. Along the nor-
mal concave upward/antilistric fault a syn-sedimentary wedge was
formed. Close to the fault the sub-horizontal layers are folded due
to drag effect or indicate an earlier extensional monocline above an
upward propagating normal fault.

Fig. 10. Two sets of deformation band crosscut each other at site
16. The first (1) generation of bands with almost decimetre offset
are crosscut by numerous younger bands (2) with smaller, cm scale
offsets, all related to the D5 phase.

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were detected indicating rejuvenation of the D5 phase fault
during the D6

phase (Fig. 11).

In the Vatta-Maklár Trough the upper volcanoclastic units

and  Sarmatian  sandstone  are  thickened  in  the  hanging-wall
block  of  the  NE—SW  trending  faults  and  are  pinching  out
north-westward, at the margins of the half graben (Petrik et
al. 2014). These faults might have acted as oblique sinistral
ones  during  the  D5  phase.  These  faults  crosscut  the  older
Paleogene  reverse  faults  making  the  subsurface  structure
more  complicated  (Figs. 6, 7).  The  observed  syn-tectonic
thickening represents the third major tilting event (Fig. 3).

Paleomagnetic data indicates no rotation for the upper vol-

canoclastic units (Márton & Pécskay 1998). The age of this
deformation is well constrained as Middle Badenian-early
Sarmatian.

D6 phase (late Sarmatian)
This phase is characterized by extension ranging from

WNW—ESE  to  NW—SE  direction  (Fig. 4,  sites  1,  5,  10,  12,
14, 15). NNE—SSW trending normal faults of phase D5 were
often  reactivated  as  oblique  normal  faults  during  the  D6
phase  due  to  the  continuous  CW  change  of  extensional  di-
rection (sites 12, 15 in Fig. 4 and Fig. 11). This deformation
was observed in Sarmatian sandstone and in the rocks of the
upper volcanoclastic level in the DDB and FG areas. Several
metres  of  normal  displacement  in  Sarmatian  sandstone  was
detected  in  the  western  margin  of  the  FG  area.  In  the  north-
western  part  of  the  DDB  (Fig. 4,  site  10)  this  deformation  is
well represented by conjugate NE—SW trending normal faults.

The FG is filled with Sarmatian and upper volcanoclastic

units but further to the west they also outcrop in the hanging-
wall blocks of NNE—SSW trending normal faults (Fig. 7).
On NW—SE trending seismic profiles the thickening of Sar-
matian units are also presumed based on borehole data
(Verps-2, Verps-3, Esz-1) (Figs. 2, 6).

In the Southern Bükk foreland some NW—SE trending re-

verse  faults  and  small  scale  associated  folds  also  belong  to
this  phase  (Fig.  4,  site  5).  In  site  14,  N—S  and  ENE—WSW
trending  dextral  and  sinistral  strike-slip  faults  were  ob-
served, respectively. These strike-slip or compressional fea-
tures  differ  in  style  from  normal  faulting,  but,  due  to  the

similarity in the horizontal stress axes, could be classified
into the D6 phase.

The age of this deformation is late Sarmatian and predates

the early Late Miocene major tilting event.

Post-rift deformation

D7 phase (early Late Miocene)
Pannonian sediments only outcrop in the southernmost

part  of  the  DDB  but  the  outcrop  conditions  do  not  allow
a  detailed  study  (Fig. 2).  In  the  southern  Bükk  foreland
ENE—WSW  oriented  normal  fault  and  deformation  bands
can  be  found  in  early  Late  Miocene  sandstone  and  indicate
NNW—SSE  extension  (Fig. 4,  site  17).  All  the  small-scale
structures of the D7 phase show syn-tilt deformation with re-
spect  to  the  early  Late  Miocene  tilting  event  proven  by  tilt
test  (Fig. 4,  sites  1,  3,  6,  13,  17).  On  seismic  profiles  the
Middle  Miocene  rocks  are  often  truncated  and  onlapped  by
Late  Miocene  sediments  indicating  early  Late  Miocene  til-
ting  (Fig. 6)  (Petrik  et  al.  2014).  In  the  entire  South  Bükk
foreland and Vatta-Maklár Trough the Pannonian sediments
are  syn-sedimentary,  thickening  southward  along  ENE—
WSW  trending  normal  faults  (Petrik  et  al.  2014).  Although
the outcrop-scale faults show somewhat younger timing, we
assume that the large-scale faulting seen on seismic lines are
marked by NNE—SSW extension of the D7 phase.

Discussion

Interpretation of the main structural phases and their
implications for the evolution of the study area

Seven main structural phases were delineated in the study

area  from  the  Late  Oligocene  up  to  early  Late  Miocene
(Figs. 4, 12).  The  combined  usage  of  field  observations,
borehole data and seismic interpretation allowed us to deter-
mine  new  structural  phases  and  to  outline  the  Cenozoic
structural evolution of the DDB in much more detail than in
the previous studies (e.g., Tari 1988; Csontos 1999; Fodor et
al.  1999,  2005).  In  addition,  we  connected  the  deformation
phases of the Southern Bükk Foreland of Petrik et al. (2014)
to those of the DDB sensu stricto (Fodor et al. 2005). The de-
lineated stress fields were classified as pre-, syn-, and post-
rift  phases  with  respect  to  the  evolution  of  the  Pannonian
Basin  although  this  classification  may  need  revision  in  the
near future.

Pre-rift deformations

Two structural phases can be tied to pre-rift deformations

(Figs. 4, 12).

The D1 phase is mainly characterized by NW—SE com-

pression and perpendicular extension during the Eocene?—

early

Eggenburgian (Fig. 4). All the structures belonging to

this phase indicate pre-tilt deformation with respect to the
second major tilting (ca. 20—19 Ma).

The time of this deformation is well constrained by a syn-

sedimentary dilational band of Late Oligocene age (

Fig. 12)

Fig. 11. N—S trending oblique normal fault of the D6 phase which
displaced a channel filled with pyroclastic rocks (in site 12). The
fault could be originated in phase D5 as dip-slip normal fault.

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(Petrik et al. 2014). The duration of the D1 phase can be ex-
tended into the early Eggenburgian because deformation
bands in Eggenburgian site 7 (~21.4—20.9 Ma) also belong
to this phase.

The syn-sedimentary thickening of Paleogene sediments

in  front  of  NW-vergent  blind  reverse  faults  postulated  on
seismic  profiles  was  also  attributed  to  our  D1  phase.  In  the
Vatta-Maklár  Trough,  several  hundred  metres  of  poorly
dated  terrestrial  sediments  below  the  lower  volcanoclastic
level  were  possibly  deposited  during  the  D1  phase  (Fig. 6,
Petrik et al. 2014). The certainly Oligocene rocks are strongly
reduced  and  the  poorly  dated  lower  Miocene  sediments  are
completely  missing  on  earlier  elevated  highs  underlain  by
NW-vergent  blind  reverse  faults  (Fig. 6)  (Földvári  2013;
Petrik  et  al.  2014).  Erosion  of  Oligocene  and  sediments  on
elevated highs can be tied to the first denudation phase and
associated tilting events (Figs. 3, 12).

The NNE—SSW oriented Darnó Line acted as a NW-ver-

gent reverse fault which resulted in the formation of a syn-
cline west of the Darnó Line (Fig. 1b) (Sztanó & Tari 1993;
Fodor et al. 2005). In this syncline the Paleogene and Eggen-

burgian  sediments  are  folded  and  thickened  toward  the  re-
verse fault (Fig. 1b) (Fodor et al. 2005). In addition to NW-
propagating  reverse  faults,  some  SE-vergent  reverse  faults
were  also  detected  on  seismic  profiles  in  the  Vatta-Maklár
Trough  and  were  interpreted  as  small-scale  backthrusts
(Fig. 6, below borehole Verps-3, (Petrik et al. 2014).

We projected the seismic interpretation into the area of the

Felsőtárkány graben (FG) in order to trace and correlate the
major NE—SW trending faults further to the NE. We presume
that one branch of the Paleogene basin could be found below
the Felsőtárkány graben (FG). Our interpretation suggests
that the precursor structure of the FG was bordered by a NE—
SW trending fault on its eastern side which could have acted
as a NW-vergent bli

nd reverse fault during the Late Oli-

gocene—earliest Miocene (Fig. 13a,b).

Below the Middle

Miocene  sediments  in  the  FG  we  presume  wedge-shaped
Paleogene rocks which pinched out northwestwardly on the
next  Mesozoic  high  (Fig. 7).  No  Paleogene  sediments  were
encountered by boreholes on this high and this lack extends
to the west, up to the Darnó Line. On the western side of the
FG  (on  the  Pirittyó  Hill)  a  blind  SE-vergent  backthrust  can

Fig. 12. Summary table about the possible time of deformation phases, CCW block rotations. Deformation bands and syn-sedimentary
structures are also placed in time along with their stress fields. References for standard stages/Central Paratethys stages and their absolute
ages see Fig. 3. Structural phases of the Darnó Zone (Fodor et al. 2005), the whole northern Pannonian unit (Fodor 2010), the Eastern Slo-
vakian Basin (Kováč et al. 1995) and the Alpine-Carpathian Junction Zone (Marko et al. 1995) were also displayed to make comparisons
with our new stress field data.

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The seismic profiles indicate that
the Esz-1 borehole drilled through
the Lower Miocene rocks directly
above the Mesozoic rocks (Fig. 6).

NW propagating Late Oligocene

reverse  faults  were  also  identified
ca.  75 km  to  the  SW  of  the  study
area (Palotai & Csontos 2010). Tari
et al. (1993) presumed that the Pa-
leogene  Basin  was  developed  as  a
retroarc  flexural  basin  by  south-
ward propagating backthrust along
the  northern  margin  of  the  NH-
SSPB  (North  Hungarian-South
Slovakian Paleogene Basin).

In summary we assume that the

studied part of the NHSSPB was
characterized

NW-vergent

folds and underlying blind reverse
faults which resulted in the forma-
tion  of  synformal  sub-basins  with
syn-tectonic  fill  (Fig. 13a,b).  One
of  the  major  faults  could  be  the
Darnó  Fault.  Small-scale  SE-ver-
gent

backthrusts

could

also

evolve.  On  the  other  hand,  the
coeval  existence  of  extensional
and  compressional  structures  of
the D1 phase can be interpreted as
noticeable  elongation  along  the
axis  of  the  compressional  folds
(Fig. 13b).  We  agree  with  Tari  et
al. (1993) that, in general, the NH-
SSPB  represents  a  flexural  basin,
but  its  postulated  boundary  is  out
of  our  study  area,  while  our
dataset  characterize  its  internal
structure.

The D2 phase is represented by

W—E compression and perpendic-
ular extension during the middle
Eggenburgian—early

Ottnangian

(Fig. 4). The deviation in

can

reach  30—40°  with  respect  to  the
D1  phase  in  the  counterclockwise
sense.  The  D2  phase  includes
mainly  strike-slip  faults.  The
structures  belonging  to  this  phase
indicate post-tilt and partially syn-
tilt deformation with respect to the
second  major  tilting  event  which
occurred  ca.  20—19  Ma  (Figs. 3,
12).  In  the  Eggenburgian  con-
glomerate  near  the  Darnó  Hill
(Fig. 4,  site  7)  this  type  of  defor-
mation  is  represented  by  conju-

Fig. 13. A – Schematic structural pattern of the study area for the time of the D1-D2 phases (pre-
rift deformation). Note the NE—SW trending blind reverse faults of the D1 phase. B – Schematic
structural model for the time of the D1-D2 phases. See details in the text.

also be attributed to the erosion of Paleogene sediments
(Figs. 7, 13a,b). The same architecture was found on NW—
SE oriented seismic profiles 15 km to the southwest (Fig. 6).

gate cataclastic deformation bands. In the lower volcanoclas-
tic units this D2 phase is already missing thus the age of this
stress f

ield is middle Eggenburgian—early Ottnangian

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It is difficult to identify map-scale faults of this phase, but

we assume that some of the reverse faults, particularly the
steeper ones, could be reactivated as dextral faults (Fig. 13a).
On the other hand, the D2 stress field could characterize the
Mid-Hungarian Shear Zone, and the extrusion/escape tecto-
nics of the Alcapa block (Csontos & Nagymarosy 1998).

A new definition of phases D1 and D2 with respect to ear-

lier works

We suggest a new age limit for the D1 and D2 phases. Ear-

lier works either did not separate them or gave different tem-
poral boundaries. Csontos (1999) defined NE—SW and

NW—SE  compression  for  the  Eocene—Early  Oligocene  and
Late Oligocene times, respectively. The latter could be cor-
related  with  our  D1  phase.  Fodor  et  al.  (1999,  2005)  could
not  separate  clearly  the  Paleogene-Early  Miocene  deforma-
tions. On the other hand, Fodor (2008, 2010) suggested three
Paleogene—Early M

iocene phases, D6, D7, and D8 between

48—19 Ma (Fig. 12). All these phases, together, were regarded
as one of the most important deformations in Northern Hun-
gary. However, the age limits are different.

D6 indicates mainly transpressional deformation with

WNW—ESE and NW—SE shortening during the Middle
Eocene—

early

Kiscellian (Fodor 2008); the beginning of our

D1 phase could partially overlap with the end of the D6
phase (Fig. 12). D7 was characterized by NW—SE compres-
sion and perpendicular extension in

the late Kiscellian—early

Egerian (Fodor 2008); but our D1 phase was longer than in
earlier works. The D8 phase indicates E—W compression and
perpendicular extension with strike slip deformation prior to
Ottnangian (Fodor 2010); however, our D2 phase started later
than  in  earlier  works  (Fodor  et  al.  1999;  Fodor  2010).  The
strike-slip character and the stress axes of his D2 (earlier D8
phase) clearly separates it from the earlier D1 phase. On the
other  hand,  this  D2  phase  lasted  somewhat  longer  than  in
previous works, and includes the early Ottnangian (Fig. 12)
because  it  includes  partially  post-tilt  deformation  with  re-
spect to a second major tilting (ca. 20—19 Ma). If we accept
that this phase is characterized by the extrusion tectonics, it
would  have  a  smaller  time  span  than  in  previous  works
(Csontos & Nagymarosy 1998; Fodor et al. 1999).

Looking to a wider regional comparison, we also see ob-

servations of similar stress fields to our D1 and D2 phases.
As we show briefly, and with two examples on Fig. 12, these
suggested phases have different time spans than our phases.

In the Alpine-Carpathian Transition Zone (ACTZ) the

WNW—ESE  to  NW—SE  compression  was  dominant  during
the Oligocene-Eggenburgian time (D1 phase of Marko et al.
1995 in Fig. 12) which was similar to our D1, and partly to
our D2 phase. In the northern margin of the Danube Basin,
similar NW—SE compression was delineated for the Eggen-
burgian  (Marko  2012).  The  syn-sedimentary  activity  of  the
Central  Slovakian  Fault  System  (CSFS)  in  the  Central
Western  Carpathians  was  dated  to  the  Late  Eocene  when
NW—SE  compression  created  a  sinistral  transtensional  fault
zone (Kováč & Hók 1993).

In the Eastern Slovakian Basin (ESB) the NNE—SSW to

NE—SW compression was dominant during the Paleogene-

Ottnangian (D1 phase of Kováč et al. 1995 in Fig. 12) resul-
ting in the break-up of the Central Carpathian Paleogene Ba-
sin and folding of the Pieniny Klippen Belt (Kováč et al.
1995). This phase was terminated by an uplift and denuda-
tion event in the Ottnangian (Kováč et al. 1995).

Most of the delineated stress fields indicate WNW—ESE to

NW—SE  compression  or  transpression  which  are  similar  to
our D1 phase but the time span is different ranging from Late
Eocene to early Ottnangian.  Marko et al. (1995) determined
the upper limit of the D1 phase in the late Eggenburgian—early
Ottnangian as opposed to our D1 phase which terminated in
the  early  Eggenburgian.  Kováč  et  al.  (1995)  identified  the
opposite  compressio

nal direction in the ESB which lasted

until the late Ottnangian (D1 phase in Fig. 12). This diffe-
rence in compressional direction is a spatial one, and might
be explained by the curved geometry of the Carpathian oro-
gen (Jiříček 1981).

Syn-rift deformations

The D3 phase is characterized by NNE—SSW extension

during the late Ottnangian—early Karpatian (Fig. 4). The po-
sition of stress axes during phase D3 is similar to the situa-
tion  during  D2,  but  D3  clearly  involves  extensional
deformation  which  is  a  striking  difference  from  the  pre-rift
deformations.  Fodor  (2010)  separated  the  early  syn-rift
episodes  into  a  N—S  and  a  NE—SW  extensional  one.  Our
D3 phase would correspond to his regional N-S extensional
stress  field.  According  to  Fodor  (2010)  this  stress  field
started  during  the  early  Ottnangian  but  must  have  finished
before the first CCW block rotation (~18.5—17.5 Ma, Márton
& Pécskay 1998). Our observations can refine the time span
of  this  deformation.  The  D3  phase  was  syn-sedimentary
during  the  late  Ottnangian  to  earliest  Karpatian  (Figs. 8a,b,
12).  Accepting  this  refined  time  span  of  the  D3  phase,  the
time of the first CCW rotation seems to be younger (~17.0—
16.5 Ma)  than  previously  thought  (Fig. 12).  On  the  other
hand, the end of the escape tectonics would also be younger
by 1 Myr.

The D3

phase resulted in the formation of some WNW—

ESE trending map-scale normal faults in the DDB area
(Figs. 2, 14a,b). The

Darnó Line was claimed to act as

a sinistral strike-slip fault during Ottnangian—Middle Bade-
nian but some shortening and folding along restraining
bends were also presumed (Fodor et al. 2005).

In our interpretation, the NNE—WSW trending major

faults might have been inactive at this time and the WNW—
ESE  trending  normal  faults  took  up  the  deformation
(Fig. 14a,b).  In  the  hanging-wall  blocks  of  these  normal
faults  small  scale  thickening  of  Ottnangian—Karpatian  sedi-
ments could be observed in the DDB area (Figs. 7, 14a,b).

The western side of the Western Carpathians suffered

transpression with N—S maximal compression during the
Ottnangian—Early Badenian (D2 phase of Marko et al. 1995
in Fig. 12). In the northern margin of the Danube Basin
NW—SE to N—S compression was identified for the Ottnan-
gian—early Karpatian time (Marko 2012).

During the Karpatian the stress field changed from

transpression to transtension in the ESB (Kováč et al. 1995).

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The ESB was opened as a pull-apart basin by N—S compres-
sion  (D2  phase  of  Kováč  et  al.  1995  in  Fig. 12).  Our  D3
phase  covers  a  different  time  span  and  indicates  N—S
synsedimentary  extension.  This  difference  in  stress  fields
might  be  explained  by  the  paleo-geographical  positions  of
the two regions. In our study area the D3 phase indicates the
initial  syn-rift  deformation  of  the  Pannonian  Basin  (Fodor
2010),  while  in  the  Western  Carpathians  the  last  phase  of
collision  might  have  influenced  the  stress  field  suppressing
the extension.

The D4 phase is represented by NE—SW and ENE—WSW

extension  during  late  Karpatian—Early  Badenian  (Fig. 4).
This deformation was already present in the middle volcano-
clastic  units  in  the  south  Bükk  foreland  and  in  Early  Bade-
nian rocks in the DDB area. A clear relative chronology can
be seen between D3 and D4 because the E—W trending nor-
mal  faults  of  D3  tend  to  be  reactivated  as  dextral-oblique
faults  during  the  D4  phase  (Fig. 4,  sites 6,  8).  The  exten-
sional direction moved continuously in a CW direction from
the  Ottnangian  onward  as  already  stated  by  Fodor  et  al.
(1999).  The  stress  field  evolution  can  be  correlated  with
paleomagnetic  data  (Márton  &  Fodor  1995).  The  change  in
the  principal  stress  axes  between  the  D3  and  D4  phases  is
similar in magnitude to the vertical-axis rotation, and oppo-
site in sense. Thus, the change in stress field is apparent and
connected to rotation.

Based on paleomagnetic measurements, the middle volca-

noclastic  units  indicate  25—30° CCW  rotation  and  suffered
only  the  second  CCW  block  rotation  which  occurred
~15—14 Ma (Márton & Fodor 1995). This means that the D4
phase  post-dates  the  first  CCW  rotation  and  predates  the
second one. Our observations would suggest a late Karpatian—
Early Badenian timing (Fig. 12). This phase can be regarded
as  the  classical  syn-rift  deformation  in  the  Pannonian  basin
which  relates  to  the  roll  back  mechanism  triggered  by  the
subducted slab below the Outer Carpathians (Royden & Hor-
váth 1988).  Our D4 corresponds to the D9b phase of Fodor
(2010) and D3 of Fodor et al. (2005). This phase was respon-
sible for the birth of many pull-apart sub-basins and half-gra-
bens  along  NNE—SSW  trending  sinistral  strike-slip  and
NW—SE  trending  normal  faults,  respectively,  (Royden  &
Horváth 1988; Fodor et al. 1999).

This time the NNE—SSW trending major faults in the DDB

area might have acted as sinistral faults (Fig. 4, site 11;
Fig. 14a,b). NW—SE trending normal faults could evolve be-
tween the major NNE-SSW trending sinistral strike-slip
faults (Fig. 14a,b).

In the ACTZ, the D2 phase of N—S compression continued

until the Early Badenian. In the ESB, NE—SW extension was
characteristic of the Early and Middle Badenian (D3+D4
phases of Kováč et al. 1995 in Fig. 12, which were similar to
our D4 phase). These phases were responsible for cessation
of strike-slip tectonics and the evolution of back-arc basins
(Kováč et al. 1995). Although the time span is shorter in our

area, the similarity of these phases can be explained by the
influence of the roll-back mechanism of the subducted slab
along the Outer Carpathians.

The D5 phase is represented by E—W to WNW—ESE

extension/transtension  during  the  Middle  Badenian—early
Sarmatian  (Fig. 4).  N—S  oriented  conjugate  normal  faults
were dominant in the sites of the FG and DDB (Fig. 4, sites
12,  13,  15,  16).  Covered  normal  faults  in  Sarmatian  sand-
stone  of  the  FG  indicate  E—W  extension  (Figs. 9,  12).  The
relative chronology between D4 and D5 is marked by reacti-
vated earlier NW—SE trending normal faults as oblique dex-
tral  ones  during  the  D5  phase.  The  syn-sedimentary
thickening and tilting of upper volcanoclastic units and Sar-
matian sediments along NNE—SSW trending faults were also
interpreted on seismic profiles and geological cross sections
(Figs. 6, 7). In our view, the FG is bordered on the east by a
major  NNE—SSW  segmented  transtensional  fault  (TF,
Tárkány  Fault)  with  sinistral-normal  components  based  on
the extensional direction of D5. The TF was responsible for
the  beginning  of  the  subsidence  of  the  FG  in  the  late  Mid
Miocene

(Fig. 15a,b).

This transtensional fault can be corre-

lated  with  NNE—SSW  trending  faults  identified  on  seismic
profiles (Fig. 6). The TF is often segmented along-strike and
connected  by  small  E—W  oriented  faults  (Figs. 2, 15a,b).
Small blocks of Paleogene to Early Miocene surrounded by
late  Mid-Miocene  rocks  on  the  eastern  side  of  the  FG  are
interpreted  as  fault  lenses  (Fig. 15a).  We  assume  that  the
other  NNE—SSW  oriented  faults  in  the  DDB  area  (such  as
Felnémet  Fault  FF,  Bátor  Fault  BF,  Pirittyó  Fault  PF)  also
acted as sinistral-normal faults (transtensional faults) during
the  D5  phase  (Figs. 2,  15a,b).  In  the  south-western  part
of  the  DDB,  the  Mid-Miocene  sediments  are  preserved  in
the  hanging-wall  blocks  of  NNE—SSW  trending  faults  (FF,
LF, PF) (Figs. 2, 15a,b).

In the Vatta-Maklár Trough the thickening of upper volca-

noclastic and Sarmatian sediments along NE—SW oriented
transtensional faults also started during the D5 phase (Petrik
et al. 2014). According to Tari (1988) this was the time for
the main subsidence of the Vatta-Maklár Trough. Fodor et
al. (2005) also delineated this WNW—ESE extension for the

Late B

adenian onward. Csontos (1999) and Tari (1988) de-

fined N—S compression and perpendicular extension with
dominant strike-slip deformation for the Mid-Miocene period.

According to paleomagnetic measurements, the upper vol-

canoclastic  units  were  not  involved  in  the  second  CCW
block rotation which took place ~15—14 Ma (Márton & Pécs-
kay  1998).  To  take  into  consideration  the  syn-sedimentary
late Mid-Miocene deformation of the D5 phase and the paleo-
magnetic data, the age of this phase is well-constrained and
followed the second CCW blockrotation and could have lasted
from  the  Late  Badenian  to  early  Sarmatian.  However,  the
new  zircon  U-Pb  age  results  of  the  upper  pyroclastic  units
(15—14.0 Ma, Lukács et al. 2015) suggest that the age of the
second  CCW  rotation  could  be  somewhat  older  (between

Fig. 14. A – Schematic structural pattern of the study area for the D3-D4 phases. Note NNE—SSW trending sinistral faults of the D4 phase
which are connected to WNW—ESE and NW—SE trending normal faults. B – Schematic structural model for the D3-D4 phases (early syn-
rift). See details in the text.

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~16—15 Ma). This means that the D5 phase could have
started sometime in the Middle Badenian, earlier than pre-

Fig. 15. A – Schematic structural pattern of the study area for the D5-D6 phases. Note the domi-
nance of NNE—SSW trending transtensional (D5 phase) and normal faults (D6 phase). The inset in
the north-eastern corner indicates the small fault lenses on the eastern side of the FG. B – Sche-
matic structural model for the D5-D6 phases (late syn-rift). See details in the text.

viously thought (Fig. 12).

In the ACTZ, the transpression

changed  to  transtension  with
WNW—ESE  extension  during  the
Middle Badenian. This resulted in
the  opening  of  pull-apart  basins
along  ENE—WSW  oriented  sinis-
tral faults (D3 phase of Marko et al.
1995  in  Fig. 12).    In  the  northern
Danube  Basin  NE—SW  compres-
sion  and  perpendicular  extension
was  identified  for  the  Badenian
which is similar to our D6 of Sar-
matian  age  (Marko  2012).    In  the
Middle  Miocene  a  change  in  ma-
ximum  compression  can  be  ob-
served  from  NW—SE  to  NE—SW
in the CSFS area which acted even
in  the  Late  Miocene  (Kováč  &
Hók  1993).  This  compression  is
similar to our D5-D6 phase but its
time  span  is  wider  than  our  D5,
D6 phases.

In the ESB, the Late Badenian is

represented  by  NE—SW  extension
which  resulted  in  transtensional
deformation  with  NW—SE  tren-
ding  normal  faults  at  its  eastern
margin  and  NNE—SSW  trending
dextral faults at its western margin
(D5 phase of Kováč et al. 1995 in
Fig. 12). This was the time for the
main  subsidence  due  to  mantle
upwelling (Kováč et al. 1995).

The D3 phase of Marko et al.

(1995) indicates similar extension
and a similar time span as our D5
phase.  The  D5  phase  of  Kováč  et
al. (1995) in the ESB indicates al-
most  perpendicular  extension  and
shorter  time  span  than  our  D5
phase (Fig. 12). This difference in
stress  direction  might  be  ex-
plained  by  the  inhomogeneity  of
the stress fields in the Late Bade-
nian—Sarmatian  due  to  the  chan-
ging  (curved)  geometry  of  the
Outer  Carpathian  nappe  front
(Fodor & Csontos 1998).

The D6 phase is characterized

by NW—SE extension during the
late Sarmatian (Fig. 4). The devia-
tio

n of minimal stress axis in a

CW direction is continuous from
Early M

iocene onward. This

phase clearly post-dates the D5
phase as is proven by oblique nor-

mal reactivation of N—S oriented normal faults of the D5
phase (Fig. 4, sites 12, 15). The youngest rocks involved in

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this deformation are upper volcanoclastic units and Sarma-
tian sandstone. All structures belonging to this phase still in-
dicate pre-tilt deformation with respect to early Late
Miocene tilting (Fig. 12).

The NE—SW trending faults became pure extensional nor-

mal faults and induced further thickening of Sarmatian sedi-
ments  in  their  hanging-wall  blocks  in  the  FG  and  in  many
small sub-basins up to the DDB (Fig. 15a,b). In our view, the
Felsőtárkány graben (FG) became a half-graben which sub-
sided continuously along the NE—SW trending TF during the
Sarmatian  although  the  kinematics  might  have  slightly
changed  from  D5  to  D6.  This  is  proven  by  south-eastward
tilting  and  thickening  of  Sarmatian  sediments  in  the  FG
(Fig. 7).  Similar  fault  kinematics  and  subsidence  were  pro-
ven  in  the  Vatta-Maklár  Trough  at  that  time  (Petrik  et  al.
2014).

In the western part of the DDB (Eb-17 and Eb-18 bore-

holes  in  Fig. 2),  the  average  values  of  vitrinite  reflectance
data  deriving  from  Ottnangian  sediments  are  ~0.27—0.29 %
(Iharosné  Laczó  1982).  Similar  vitrinite  values  were  mea-
sured at ~100 m depth from early Late Miocene sediments in
the  southern  Bükk  foreland  where  they  were  interpreted  as
indications  of  at  least  600—700 m  burial  depth  during  the
Late  Miocene  (Petrik  et  al.  2014).  This  means  that  older
rocks now on the surface used to be covered by a few hun-
dred meters of sediments that have been eroded. This could
be the Sarmatian and Late Miocene suites. According to fis-
sion  track  data,  at  least  ~1 km  of  sediments  must  have  ero-
ded  from  the  Bükk  Mts.  since  the  Pliocene/Quaternary
(Dunkl et al. 1994). The sporadic occurrences of Sarmatian
and early Late Miocene sediments west of the FG can be ex-
plained  by  Pliocene/Quaternary  uplifting  of  the  Bükk  Mts.
(Dunkl et al. 1994).

In the ACTZ, the NW—SE extension associated with

strike-slip  deformation  was  dominant  during  the  Sarmatian
time which is similar to our D6 phase (D4 phase of Marko et
al. 1995 in Fig. 12). In the northern Danube Basin the ENE—
WSW compression was defined for the Sarmatian and early
Pannonian. This compressional direction is similar to that in-
dicated  by  the  few  compressional  data  from  our  D6  phase.
This shortening may represent a short-term Sarmatian inver-
sion as was suggested in other parts of the Pannonian Basin
(Horváth  1995;  Fodor  et  al.  1999).    In  the  CSFS  area  the
NW—SE  extension  resulted  in  NE—SW  trending  normal
faults  during  the  Late  Badenian—Sarmatian  time  which  is
similar to our D6 phase.

In the ESB, the N—S extension was dominant in late Sar-

matian—Pannonian (D7 phase of Kováč et al. 1995 in
Fig. 12). This N—S extension is more similar to our D7 phase
which was active in early Pannonian (Fig. 12).

Post-rift deformation

The D7 phase is represented by NNW—SSE extension

during  the  early  Late  Miocene  (Fig. 4).  The  extensional  di-
rection  tends  to  rotate  further  into  the  CW  direction.  In  the
study area Pannonian sediments are scarce on the surface but
in  the  southern  Bükk  foreland  the  E—W  oriented  conjugate
normal  faults  and  deformation  bands  belong  to  this  phase

and clearly indicate post-tilt deformation with respect to ear-
liest Late Miocene tilting (Fig. 12). Csontos (1999) supposed
N—S  compression  for  the  early  Late  Miocene  based  on  re-
verse  faults  and  folding  of  late  Pannonian  sediments  in  the
South  Bükk  foreland.    This  compression  might  indicate  a
short  period  of  intra-Pannonian  inversion.  Tari  (1988)  defi-
ned  an  ENE—WSW  trending  transtensional  deformation
along the Vatta-Maklár Trough for the late Pannonian which
can be fitted into our D7 phase.

Early Late Miocene sediments are syn-sedimentary and

thickened toward the NE—SW trending transtensional fault in
the Vatta-Maklár Trough between 11.6—8.92 Ma (Petrik et
al. 2014). We suppose that early Late Miocene rocks used to
cover the DDB area but due to the Pliocene/Quaternary up-
lift of the Bükk Mts. they were tilted 2—3° to the south and
eroded in the northern part. On NW—SE oriented seismic
profiles, the Pannonian sediments are tilted and truncated to
the north close to the Bükk Mts. (Petrik et al. 2014).

In ACTZ, the NW—SE extension was responsible for crea-

ting  host-graben  structures  along  NE—SE  trending  normal
faults (D5 phase of Marko et al. 1995 in Fig. 12). Many gra-
bens and half-grabens subsided along NE—SW trending nor-
mal  faults  in  the  Pannonian  (Kováč  et  al.  2011a).    In  the
northern  Danube  Basin,  E—W  extension  was  delineated  for
the  Pannonian  time  (Marko  2012)  which  indicates  almost
perpendicular  extension  in  comparison  with  our  D7  phase
and  also  seems  to  be  different  from  other  Western  Car-
pathian stress fields. It could be a local phase. In the Turiec
Basin in the interior of the Western Carpathians, NW—SE ex-
tension  and  perpendicular  compression  was  identified.  This
induced syn-rift deformation of the basin (Kováč et al. 2011b).

In the ESB, the N—S extension was dominant in the late

Sarmatian-Pannonian which is similar to our D7 phase (D7
phase of Kováč et al. 1995 in Fig. 12). The majority of stress
fields indicate NW—SE to NNW—SSE extension for the Pan-
nonian time which indicates that the northern part of the
Pannonian Basin was under the same stress regime.

Conclusions

The combined usage of detailed structural field observa-

tions, seismic interpretation and geological cross sections al-
lowed us to delineate 7 deformation phases in the study area
for the Cenozoic period.

The D1 and D2 phases are pre-rift deformations in the evo-

lutionary  history  of  the  Pannonian  Basin.  The  D1  phase  is
pre-tilt with respect to the earliest Miocene tilting event. D1
indicates  NW—SE  compression  and  perpendicular  extension
for the Paleogene—early Eggenburgian time based on an ear-
ly  type  of  deformation  bands  and  syn-sedimentary  thicke-
ning  of  Paleogene  suites  in  front  of  NE—SW  trending
north-westward propagating blind reverse faults. This phase
was recognized earlier but we were able to specify the upper
age limit of this phase and put it into the early Eggenburgian
based  on  deformation  in  Eggenburgian  conglomerate.  The
coeval  existence  of  extension  and  compression  can  be  ex-
plained by noticeable elongation along the axis of the com-
pressional folds.

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D2 is a middle Eggenburgian—early Ottnangian post-tilt

phase which indicates strike-slip deformation. The erosion of
Paleogene sediments above elevated highs could partly be
associated with this phase. West of the Darnó Line, the fol-
ding of Eggenburgian and reversely displaced pre-Ottnan-
gian sediments was also associated with ongoing shortening
deformation with strike slip components (Fodor 2010).

The D3 and D4 stress fields belong to early syn-rift phases

and indicate pre-tilt deformation with respect to early Late
Miocene tilting.

Phase D3 shows NNE—SSW extension and it is a well-

constrained  stress  field  based  on  syn-sedimentary  deforma-
tion  of  Ottnangian—early  Karpatian  sediments  and  covered
normal  faults  in  the  lower  volcanoclastic  unit.  This  phase
predates the first CCW rotation which has been specified and
placed  between  ~17.0—16.5 Ma  in  the  Karpatian.  Fodor
(2010) stated that this stress field must predate the escape of
the  ALCAPA  unit.  Consequently,  the  extrusion  tectonics
may terminate somewhat later by ca. 1 Myr. In our view, the
NNE—SSW trending faults of the DDB were inactive at this
time. WNW—ESE trending normal faults could have been de-
veloped inducing the small-scale thickness variations of Early
Miocene sediments.

The D4 phase can be regarded as a classical syn-rift phase

indicating NE—SW extension for the late Karpatian—Early
Badenian. This phase postdates the first CCW rotation and it
was responsible for creating NW—SE trending normal faults
which connect the major NNE—SSW trending sinistral faults.

The D5 and D6 phases are late syn-rift deformations.

Phase  D5  shows  E—W  extension  during  the  Middle  Bade-
nian—early Sarmatian constrained by syn-sedimentary defor-
mation  in  early  Sarmatian  tuffitic  sandstone.  The  syn-
sedimentary  thickening  of  upper  volcanoclastic  units  and
Sarmatian  sediments  along  NNE—SSW  trending  sinistral-
normal faults was also identified. The D5 phase was respon-
sible  for  the  beginning  of  the  development  of  the
Felsőtárkány graben (FG) along a NNE—SSW trending trans-
tensional  fault.  We  suggest  that  the  majority  of  NNE—SSW
trending faults (PF, LF, BF, TF, FF) acted as normal-sinistral
faults during the D5 phase. This phase postdates the second
CCW rotation. We were able to specify the lower time limit
of  this  deformation  which  was  previously  thought  to  have
started in the Late Badenian (Fodor et al. 2005).

D6 clearly postdates the D5 phase and indicates pure NW—

SE extension in the Sarmatian before early Late Miocene til-
ting. This phase promoted ongoing subsidence along
NNE—SSW trending faults in the DDB area and it was also
responsible for creating half grabens (e.g. Felsőtárkány gra-
ben).

The D7 phase is a post-rift deformation partly coeval with

the early Late Miocene tilting. This indicates NNE—SSW ex-
tension during 11.6—8.92 Ma. The sporadic occurrence of
Late Miocene sediments can be tied to Pliocene/Quaternary
uplift and erosion of the Bükk Mts. as fission track and vit-
rinite reflectance data indicate.

Acknowledgements: Our investigation was supported by
the Hungarian National Research Fund (OTKA No. 81530).
We are grateful to the Hungarian Horizon Ltd. and MOL

Ltd. for providing us with seismic data. We thank Elsevier
for allowing us to reuse one of our earlier published figures
(Fig. 6, Petrik et al. 2014). Réka Lukács’ work was supported
by the Hungarian National Research Fund (OTKA-
PD112584) and by the Bolyai János Research Fellowship.

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