GeolCarp_Vol67_No2_177

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doi: 10.1515/geoca-2016-0012

Structural evolution of the Turňa Unit constrained by fold

and cleavage analyses and its consequences for the regional

tectonic models of the Western Carpathians

ALEXANDER LAČNÝ, DUŠAN PLAŠIENKA and RASTISLAV VOJTKO

Department of Geology and Palaeontology, Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6,

842 15 Bratislava 4, Slovakia;

lacny@fns.uniba.sk, plasienka@fns.uniba.sk, vojtko@fns.uniba.sk

(Manuscript received September 16, 2015; accepted in revised form March 10, 2016)

Abstract: The Turňa Unit (Turnaicum, Tornaicum) is one of the three nappe systems involved in the geological struc-
ture of the inner zones of the Western Carpathians. The unit is formed by a system of partial nappes and duplexes, which
overlie the Meliata Unit s.l. and are overridden by the Silica Nappe. The Slovenská skala partial nappe in the investi-
gated area includes clastic sediments of the mid-Carboniferous, Permian and Early Triassic age, followed by mostly
deep-water Middle—Upper Triassic succession predominantly composed of carbonates. Structural analysis of cleavage
planes and folds was carried out predominantly in the Lower Triassic Werfen Formation. The measured deformational
structures are polygenetic and were principally formed in three successive deformation stages. The first deformation
stage is represented by bedding-parallel, very low-grade metamorphic foliation that was related to nappe stacking and
formation of the Mesozoic accretionary wedge during the latest Jurassic and earliest Cretaceous. The second deforma-
tion stage is represented by systems of open to closed, partly asymmetric folds with SW—NE oriented, steeply NW- or
SE-dipping axial-plane cleavage. Regionally, the folded bedding planes are usually moderately SE-ward dipping, the
NW-ward and subvertical dips are less common. The mesoscopic fold structures predominantly occur in the SW—NE
trending anticlinal and synclinal hinge zones of large-scale folds. These structures evolved in a compressional tectonic
regime with the NW—SE to N—S orientation of the maximum compressional axis. The third observed deformation stage
was activated during ENE—WSW oriented shortening. This stage is chiefly represented by open, kink-type folds. Some
inferences for regional structures and tectonic evolution of the area are discussed as well.

Key words: Western Carpathians, Turňa Unit, Slovenská skala partial nappe, structural analysis, folds, cleavages,
tectonic model.

Introduction

The  Western  Carpathians  represent  the  Alpine  collisional
belt that is conventionally subdivided into the External, Cen-
tral,  and  Internal  Western  Carpathians  (EWC,  CWC  and
IWC,  respectively  –  see  e.g.,  Plašienka  et  al.  1997;
Froitzheim  et  al.  2008).  In  principle,  the  EWC  (so-called
Flysch  Belt)  represent  the  outer  accretionary  wedge  of  the
Carpathian orogen formed in response to the Eocene to Mid-
dle Miocene subduction of an oceanic basin connected to the
Northern  Penninic  zone  (Valais-Rhenodanubian-Magura
Ocean,  or  “Carpathian  embayment”  –  e.g.,  Schmid  et  al.
2008). The EWC are separated from the CWC by a narrow
zone  with  an  intricate  structure  known  as  the  Pieniny  Klip-
pen Belt that includes several units derived from the Middle
and Southern Penninic zones stacked and later laterally dis-
persed  during  the  latest  Cretaceous  to  Miocene.  The  CWC,
as  a  counterpart  of  the  Austroalpine  nappe  system  of  the
Eastern  Alps,  is  composed  of  three  crustal-scale  thick-
skinned thrust sheets (the Tatric, Veporic and Gemeric from
bottom  to  top)  and  three  large-scale  cover  nappe  systems
(Fatric,  Hronic  and  Silicic)  which  were  all  individualized
and stacked during the late Early and early Late Cretaceous
Palaeoalpine (ca 120—90 Ma) orogenic processes (Plašienka
et  al.  1997).  The  southern  CWC  zones  (Vepor-Gemer  area)

are closely linked to the outer IWC units, namely to the Me-
liatic-Turnaic-Silicic nappe pile. These nappe units are inter-
preted  as  being  closely  related  to  the  Middle  Triassic
opening  and  Late  Jurassic  closure  of  the  north-western
branch  of  the  Neotethys  (Meliata  Ocean  pro  parte),  along
with the other units exhibiting evolutionary trends similar to
the Southern Alpine and Dinaridic domains (Transdanubian
and Bükk units, respectively), which occur to the north-west
of  the  Mid-Hungarian  Shear  Zone  (e.g.,  Kovács  1992;
Kovács et al. 2011).

Nevertheless, there are still many uncertainties concerning

the  original  palaeogeographic  position  of  some  rootless
allochthonous  thrust  sheets  like  the  Turňa  or  Silica  nappes,
owing to their ambiguous or even opposing structural versus
palaeogeographical links. For instance, assuming the general
northward  progradation  of  the  Western  Carpathian  orogen,
the structural superposition of Silica over Turňa over Meliata
units and some north-vergent thrust-sense criteria would in-
dicate the original palinspastic position of the Turňa and Silica
nappes south of the Meliata Ocean (Grill et al. 1984; Hók et
al.  1995;  Rakús  1996;  Mello  et  al.  1997;  Lexa  et  al.  2003;
Csontos & Vörös 2004; Dallmeyer et al. 2008). On the con-
trary,  facies  relationships  of  especially  the  Middle—Late
Triassic complexes apparently point to the “northern” shelf-
slope  settings  of  these  units  (e.g.,  Mandl  2000;  Gaál  2008;

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Schmid et al. 2008; Gawlick et al. 2012). Even a combined
view  was  presented  by  Grill  et  al.  (1984),  Kozur  (1991),
Kozur  &  Mock  (1997),  Less  (2000),  Kovács  (1992,  1997)
and Kovács et al. (1989), whereby the Turňa (Torna in Hun-
garian terminology) and similar units in the Rudabánya Hills
of  north-eastern  Hungary  were  placed  on  the  southern,
whereas  the  Silica  (Aggtelek)  Nappe  was  on  the  northern
Meliata margin. These contradictory views evidently call for
new data that would clarify at least the most uncertain points
of the Meliata-related puzzle.

Our contribution concerns the structural pattern and tec-

tonic  evolution  of  one  problematic  fragment  of  this  ambi-
guously  interpreted  tectonic  system  –  the  Slovenská  skala
partial nappe, which is interpreted at present as an element of
the Turnaic thrust sheet occurring in the western part of the
Slovak  Karst  Mts.  and  surrounding  areas  (Fig.  1).  Thus  the
aim of this paper is to describe the principal mesoscopic de-
formation structures recorded in the Turnaic Slovenská skala
partial  nappe,  especially  fold  and  cleavage  systems,  and  to
interpret  their  relationships  to  macrostructures  as  clues  for
deciphering the nappe stacking processes and structural his-
tory of the area.

Geological setting and composition of the Turňa Unit

The Torna Unit as an independent tectonic unit composed

of  slightly  metamorphosed,  mostly  deep-marine  Middle—
Upper Triassic limestones and shales, was first distinguished
in the Rudabánya Mts. of north-eastern Hungary (e.g., Grill
et  al.  1984).  In  Slovakia,  the  term  Turnaicum  (Tornaicum)
was introduced by Vozárová & Vozár (1992) for the unit en-
countered  in  the  upper  600  metres  of  the  BRU-1  borehole
drilled in the core of the Brusník anticline (see Fig. 2). The
lower unit in this borehole is formed by olistostromes, shales
and  radiolarites  dated  as  Jurassic  (Ondrejičková  1992)  and
correlated with the Meliata Unit. The upper unit is composed
of a continuous succession of Upper Palaeozoic and Triassic
sediments  of  special  composition  differing  from  both  the
Silica Nappe that crops out south of the Brusník anticline, as
well  as  from  the  underlying  Jurassic  complexes.  Therefore
the  Turnaicum  was  distinguished  as  an  independent  nappe
unit of higher order, analogously as the Meliaticum and Si-
licicum  (see  also  Mello  et  al.  1997).  In  former  times,  rock
complexes  of  the  Turnaicum  in  Slovak  territory,  together
with  the  presently  used  terms  Meliaticum  and  Silicicum,
were considered to be either a constituent of the “South Ge-
meric  Mesozoic”  cover  of  the  Gemeric  basement  (e.g.,
Bystrický 1964), or a part of the Silica Unit after the Meliata
Unit  and  Silica  Nappe  were  differentiated  (Kozur  &  Mock
1973; Vass et al. 1986).

The Turnaicum is composed of several partial nappes

(Slovenská skala partial nappe in the investigated area, Turňa
Nappe s.s. in the eastern part of the Slovak Karst Mts.),

which  overthrust  the  Meliata  Unit  (Meliaticum)  and  are
overridden by the Silica Nappe (Silicicum). However, some
differing interpretations of the tectonic position of the Tornaic
complexes have been proposed in Hungary. For instance, the
Martonyi Unit in the Rudabánya Mts. overthrusts the Silicic
Bódva  Unit  (Less  2000;  Fodor  &  Koroknai  2000)  and  is
overridden  by  the  Meliatic  Telekesoldal  Unit  (Kövér  et  al.
2009;  Deák-Kövér  2012;  Kövér  &  Fodor  2014).  Obviously
this  area  was  affected  by  several  out-of-sequence  thrusting
events  and  interpretation  of  the  structural  positions,  as  well
as  of  the  palaeogeographic  settings  of  various  partial  units
remains controversial. This problem can only be resolved by
further detailed investigations in both southern Slovakia and
northern  Hungary,  jointly  by  researchers  from  both  coun-
tries. Our study area only concerns a piece of this puzzle and
covers the Slovenská skala partial nappe south of town Jelšava
(Figs. 1 and 2).

In order to decrease the number of local names with various

meanings to a minimum, we shall treat the terms Turňa (Tur-
naicum), Torna (Tornaicum) and its various partial nappes as
synonyms of the reduced term Turňa Unit, which will be
used throughout the following text.

Treated in this way, the Turňa Unit outcrops predominantly

in  the  southern  part  of  the  Slovenské  rudohorie,  Revúcka
vrchovina and Slovenský kras Mts. in south-eastern Slovakia
and  also  in  the  Rudabánya  Mts.  in  north-eastern  Hungary.
The  south-eastern  boundary  of  surface  occurrences  of  the
Turňa  Unit  is  formed  by  the  SE  branch  of  the  Darnó  Fault
(e.g., Fodor & Koroknai 2000), but its possible continuation
to the east and west is unknown due to burial by a thick cover
of overstepping Oligocene and Neogene sediments.

In general, the Turňa Unit embraces clastic and carbonate

deposits  of  the  Carboniferous  to  Late  Triassic  age  with
a possible, but yet undocumented extension into the Jurassic
(Fig. 1). The mid-Carboniferous (early Pennsylvanian—Bash-
kirian)  Turiec  Fm.  is  composed  of  very  low-grade,  deep-
marine  “flysch”  deposits  including  dark  pelagic  shales  and
silicites (lydites), turbiditic sandstones, acidic volcanoclastic
intercalations  and  bodies  of  carbonate  olistostromes
(Vozárová  &  Vozár  1992).  Overlying  Permian  continental
red-bed-type  clastic  strata  (Brusník  Fm.)  were  deposited
after  a  considerable  time  gap  and  consist  of  variegated
shales, siltstones, sandstones and conglomerates arranged in
several  alluvial  cycles.  Some  evaporites  like  gypsum  were
deposited  around  the  Permian/Triassic  boundary  (drilled  by
the  Držkovce  DRŽ-1  borehole  –  Mello  et  al.  1994;  cf.
Fig. 2, cross-section A).

The Lower Triassic strata are represented by the clastics-

dominated Werfen Formation, which is the most widespread
sedimentary  complex  of  the  investigated  area,  reaching  the
thickness of more than 500 metres. According to Mello et al.
(1997, 2008), the Werfen Fm. is represented by the Bódva-
szilas  Member  (originally  defined  as  a  formation  by  Hips
1996)  composed  of  variegated  sandstones  and  shales  over-

Fig. 1. Geological sketch map of the study area (framed region, see Fig. 2) and its surroundings and lithostratigraphic columns of several
sections of the Turňa Unit (simplified and supplemented according to Mello et al. 2008). Oval dashed lines mark the reinterpreted areas –
Brádno and Rákoš by Lačný et al. (2015), and Striežovce in this work.

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lain by calcareous shales, marlstones, sandy limestones and
dolostones  of  the  Szin  Member.  Sediments  of  the  Werfen
Fm.  are  interpreted  as  continental  to  shallow-marine,  red-
bed-type  deposits  of  the  supratidal  flats  and  storm-domina-
ted  inner  ramp-lagoon  (Hips  1996).  The  thick  early  Lower
Triassic sandstone-shale succession of the studied area often
exhibits  features  of  turbiditic  and/or  tempestitic  sedimenta-
tion  (graded  and  convolute  bedding,  load  casts)  and  slum-
ping  textures  indicating  a  rather  more  deep-water
environment  probably  on  the  outer  ramp.  The  Szin  marl-
stones  indicate  decreasing  terrigenous  siliciclastic  supply
and  deposition  on  the  outer  distal  ramp  below  the  storm
wave base (Hips 1996).

The Middle—Upper Triassic succession is dominated by

deep  marine  carbonates  and  shales  and  their  stratigraphy  is
almost  exclusively  based  on  conodonts  (summarized  in
Mello et al. 1997). Yet the lower Anisian part is still shallow
marine,  composed  of  dark  limestones  and  dolomites  of  the
Gutenstein  Fm.  and  light  massive  marbles  of  the  Steinalm
(Honce) Fm., but starting from the Pelsonian rifting event all
younger strata are of the deep-water pelagic facies (Fig. 1).
These include locally red and pink nodular and cherty lime-
stones  (Nádaska  and  Žarnov  limestones  of  the  Schreyeralm
facies) and siliceous shales and marls in the lower part, but
predominantly  dark  grey  nodular  marly  limestones  with
cherts  of  the  Middle  Triassic  Reifling  and  Upper  Triassic
Pötschen  fms.,  intercalated  by  most  probably  Carnian,
Reingraben-type  dark  shales  (Dvorníky  and  Tornaszentan-
drás  fms.).  However,  this  sedimentary  succession  is  not
uniformly  developed  at  all  localities,  since  considerable
lateral thickness, lithological and probably also stratigraphic
variations  occur  in  various  parts  of  the  Turňa  Unit.  For
instance, the grey Pötschen limestone is replaced by the red-
dish  Hallstatt-type  limestone  upsection  in  the  Sása  syncline
(Fig. 1).

Methods

Structural investigations were carried out by the classic,

field-based methods of structural analysis. The fundamental
structural elements (bedding, cleavage, folds) were measured
during the fieldwork. Meso-scale folds were preferably used
for  analysis  of  the  fold  orientation,  along  with  bedding
attitudes  in  limbs  in  large-scale  folds.  The  deformation  re-
gime  operating  during  folding  was  determined  using  the
orientation  data  of  bedding  planes,  fold  axes  and  axial
planes, since these largely reflect orientation of the principal
shortening  direction,  being  generally  perpendicular  to  the
maximum  compression  axis  in  simply  folded  regions.  Fold
axes  and  axial  planes  were  constructed  from  measured  fold
limbs using the

π pole method (construction of β axes), or by

direct measuring of fold axes at outcrops (e.g., Ramsay
& Huber 1987). Fold orientation and statistics were computed
and visualized with the TectonicsFP version 1.7.7 software

(Ortner et al. 2002). Cleavages and bedding planes are
shown by rose and pole diagrams, the fold axes are plotted as
points and the computed axial planes are visualized as great
circles.

Cleavage is a type of planar structure in rocks that deve-

lops as a result of deformation and metamorphism and is su-
perimposed  on  the  primary  bedding-parallel  foliation  in
sedimentary  rocks.  It  predominantly  forms  in  fine-grained
rocks  affected  by  pressure  solution  and  is  approximately
parallel  to  the  XY  plane  of  the  finite  strain.  If  the  cleavage
displays a geometric relationship with the fold axial planes,
it is referred to as axial plane cleavage.

Field structural investigations were carried out throughout

the  area  of  the  Slovenská  skala  partial  nappe.  The  western
part of the study area, especially steep slopes of the Blžská
dolina  and  Drienocká  dolina  valleys,  provided  a  number  of
good  outcrops  for  fold  and  cleavage  analyses.  There,  the
structural measurements were mostly performed in the western
and northern parts of the investigated area in the surroundings
of  the  settlements  of  Hrušovo,  Striežovce,  Potok,  Lipovec,
Rovné,  Rákoš,  Nandráž,  Ratková,  Kameňany,  Držkovce,
Sása and Jelšava (see Fig. 2). On the contrary, the structural
investigations  were  hampered  in  the  south-eastern  part,  due
to  the  less  expressive  morphology  and  absence  of  sharply
incised  valleys.  Altogether  176  outcrops  were  analysed  and
documented  during  the  fieldworks  and  in  total  272  bedding
planes,  92  cleavage  planes,  53  measured  and  constructed
fold  axes  and  46  fold  axial  planes  have  been  recorded  and
used for the structural analysis.

The well-developed and preserved folds and cleavages

were  observed  predominantly  in  the  Lower  Triassic  silici-
clastic deposits of the Bódvaszilas and marly Szin members
of the Werfen Fm. Alternation of layers with different rheo-
logical  properties  (competent  vs.  incompetent)  resulted
in comparatively  rich  structural  record  in  the  Werfen  Fm.
On the other hand, the competent and mostly massive Middle
and Upper Triassic carbonates usually did not provide good
exposures for the mesoscopic structural analyses.

Results of mesoscopic structural analysis

On the basis of structural analysis, a heterogeneous group

of measured structures was identified. Geometry and over-
printing criteria of cleavages and folds indicate the presence
of three main deformational stages, in addition to synsedi-
mentary structures.

The first observed deformation is characterized by discrete

foliation, which is subparallel to the primary S

bedding.

The  second  structural  paragenesis  consists  of  folds  and
cleavages that developed in a compressional tectonic regime
with orientation of the principal shortening axis in the NW—
SE  to  N—S  direction.  In  contrast,  the  third  deformational
phase  was  activated  during  the  compressional  tectonic  re-
gime with the ENE—WSW orientation of the main compression.

Fig. 2. Tectonic map and cross-sections showing the principal map-scale structures of the investigated area: 1 – Brusník anticline;
synclines: 2 – Striežovce, 3 – Rybník, 4 – Sása, 5 – Potok, 6 – Tri peniažky-Slovenská skala.

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Pre-tectonic structures

The pre-tectonic, synsedimentary and soft-sediment defor-

mation structures were recorded in the Bódvaszilas Member
with regularly alternating sandstone and shale beds. In addi-
tion to commonly observed graded bedding, some other tex-
tures  characteristic  for  event  sedimentation  of  tempestites
and  turbidites  were  recorded  –  sole  markings,  particularly
load  casts  enhanced  by  superimposed  layer-parallel  com-
pression and cleavage development (Fig. 3G), and convolute
bedding in some beds (Fig. 3A). Occasionally, the ball-and-
pillow  structures  were  detected  as  well.  Besides  these,  spo-
radic  soft-sediment  slump  folds  were  observed  in  a  quarry
near Hrušovo village. These are small-scale bedding contor-
tions confined to certain slump beds, which are showing no
geometric  relations  to  tectonic  folds  developed  in  the  fully
indurated  sediments  characterized  below.  Their  hinges  are
moderately to steeply dipping and slightly curved (Fig. 3B),
while their axes plot in the NW—SE (ca 145°) direction after
back-tilting  of  bedding  into  a  horizontal  position.  Their
asymmetry  indicates  a  generally  south-westward  inclined
palaeoslope of the sedimentary basin.

First deformation stage

The first observed deformation stage D

is related to verti-

cal flattening achieved by compaction and pure shear con-
traction in shales and by a volume loss due to pressure
solution especially in marlstones and limestones. This defor-
mation is characterized by discrete S

foliation which is pene-

trative in shaly and marly sediments of the Werfen and also
of the Dvorníky fms. In the studied cases, it is macroscopi-
cally parallel to bedding, hence forming a combined S

folia-

tion. However, an obliquity of S

foliation with respect to the

sedimentary lamination given by alternation of clay-rich and
silty  layers  was  detected  in  some  thin  sections  (Fig.  4A).
Hence,  although  not  directly  observed,  it  might  be  inferred
that  the  structural  paragenesis  of  the  D

stage also includes

small-scale intrafolial folds F

. If so, the D

structures would

indicate not only deep burial, but also the layer-parallel shear
likely reflecting crustal thickening due to thrust stacking,
which is otherwise obvious from the regional context. This is
also corroborated by a very low-grade metamorphic recrys-
tallization, which accompanied development of the S

folia-

tion. The estimated burial depths reached some 10—15 km
(see below).

In the Triassic carbonates, the S

foliation is less distinc-

tive, forming anastomozing arrays of solution seams in mar-
ly limestones of the Reifling and Pötschen fms. Dolomites
and massive limestones often lack traces of this foliation,

whilst in pure, coarse-grained marbles of the Steinalm
(Honce) Fm. it is sometimes outlined by indistinct schistosi-
ty and oriented smears of ferruginous pigment.

Second deformation stage

The second deformation stage D

resulted from the general

NW—SE to N—S compression with a common development
of F

folds and their axial-plane S

cleavage. In the studied

area, the D

stage is dominantly represented by meso-scale

folds with SW—NE oriented axes (Fig. 5D). It can be stated
from  the  measured  dips  of  fold  limbs  and  axial  planes  that
the metre-scale folds are mostly symmetrical, and only locally
slightly asymmetrical. Their axial planes are mostly steeply
SE-dipping up to vertical (Figs. 3D and F, 5E), but the north-
west dips are common as well (Fig. 3C and E). The associated
axial-plane  cleavage  is  subvertical  and  generally  WSW—
ENE  trending,  parallel  to  the  regional  strike  of  the  bedding
(Fig. 5A and C). The S

foliation is represented by the zonal

crenulation cleavage formed by pressure solution in marl-
stones of the Szin Member (Figs. 4B, 3E and F), or by the
discrete spaced cleavage in shales and siltstones of the Bód-
vaszilas Member (Fig. 3G).

Asymmetrical folds with the SE-dipping S

cleavage were

documented for instance in shales of the Bódvaszilas Mem-
ber located 1.5 km south-east of the village of Lipovec (Li-
povec  04  site;  Fig.  3D)  along  the  forest  road  cut  in  the
Lipovský potok stream valley. Folded Lower Triassic strata
of the Turňa Unit are also well exposed in the Drienok Val-
ley to the east of the Lipovec 04 site. Axial planes constructed
from measured fold limbs are generally subvertical with the
SW—NE  strike  and  small  dip  fluctuation  towards  the  north-
west  or  south-east  (Fig. 5E).  In  the  competent  layers  (pre-
dominantly  sandstone),  open  folds  predominate,  while
folding of the incompetent strata (mainly siltstone and shale)
generated close to tight, in places up to isoclinal folds with
well-developed S

cleavage.

Mesoscopic folds with NW-dipping axial planes occur in

southern limbs of larger outcrop-scale anticlines, where they
seem to be passively rotated due to increase of amplitude of
the large-scale folds. The locality Žliabok 2 (ŽLA 02) occur-
ring in the Ve ký Blh Valley, north of the village of Hrušo-
vo,  may  serve  as  an  example.  The  outcrop  exposes  shales
and sandstones of the Bódvaszilas Member. The lower por-
tion  of  the  outcrop  contains  thick-bedded  sandstones  with
a well-developed open fold with a steeply NW-dipping axial
plane, whereas the upper part of the outcrop is composed of
shales  with  minor  folds  (Fig.  3C).  The  dips  of  cleavage
planes,  particularly  in  incompetent  shales,  vary  from  steep
north-western  dip  up  to  subvertical  position  and  thus  the

Fig. 3. A – convolute bedding in the Bódvaszilas shale-sandstone sequence, small quarry near village of Hrušovo. B – slump fold with
steeply plunging axis, the same locality. C – outcrop Žliabok 02 in the Blh valley showing dependence of F

fold dimensions on the com-

petency contrast between the thick bedded sandstones at the bottom and shales in the upper part of the outcrop. Yellow lines trace the bed-
ding, blue lines indicate the S

cleavage planes. D – outcrop at the Lipovec locality with asymmetric, NW-verging fold F

. E – Z-shaped

folds, Szin marly shales, incision cut of the Turiec River north of Sása village. F – S-shaped folds at the Drieňok outcrop, forest road cut
about 1 km NW of the Drieňok gamekeeper’s lodge. G – load casts and ball-and-pillow structures in the sandstone-rich Bódvaszilas Mem-
ber modified by subvertical cleavage S

, rock cliff above the road 500 m NW of settlement Potok. H – outcrop near Kameňany village

documenting minute F

fold structure.

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cleavage forms an indistinct fan around
the larger-scale fold hinge.

A slightly different folding style was

observed in soft marly shales of the Szin
Mb., for example, in the limbs of the Sása
synform.  The  metric,  close  to  tight  folds
are  accompanied  by  cm-scale  Z-,  S-  and
M-type  secondary  parasitic  folds  in  their
limbs  and  hinges  (Fig.  3E  and  F).  The
Szin  marlstones  are  the  least  competent
rocks  of  the  Turňa  Unit,  which  accounts
for  development  of  the  most  compressed
structures with penetrative S

crenulation

cleavage preferably in these sediments
(Fig. 4B).

Third deformation stage

In addition to the WSW—ENE oriented

cleavage, which was activated during

Fig. 4. A – photomicrograph of laminated
shales and siltstones of the Bódvaszilas Mem-
ber documenting development of the S

folia-

tion (horizontal solution seams) obliquely to
bedding. Scale bar is in the lower left corner.
B – crenulation cleavage S

in marlstones of

the Szin Member.

Fig. 5. A – rose diagram of the bedding planes; B – contour diagram of poles to bedding; C – rose diagram of two cleavage systems –
S

in black and S

in grey; D – measured and constructed fold axes of the area: black points indicate F

and grey points F

axes; E – fold

axial planes calculated from the fold limbs.

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the NW—SE to N—S compression, the NW—SE to N—S orien-
ted, non-penetrative S

planar structures were also observed

(Fig. 5C). The S

planes are widely spaced and developed

under  the  compressional  tectonic  regime  with  the  generally
WSW—ENE  orientation  of  the  maximum  shortening  axis
parallel  to  the  axial  planes  of  angular  and  kink-type  folds,
which  were  observed  predominantly  in  shales  and  marl-
stones of the Werfen Fm. (Fig. 3H). In more competent rocks
like  thick-bedded  to  massive  sandstones,  the  S

foliation is

nearly missing. Apart from the measured F

fold axes, axial

undulation of F

folds is documented by the girdle of F

axes

(Fig. 5D). They indicate a later modification of F

folds by

the WSW—ENE compression, as well.

Interpretation and discussion

Map-scale structures of the Slovenská skala partial nappe

In the studied area, the Turňa Unit overthrusts slices of the

Meliatic  Bôrka  Nappe  and  the  Gemeric  Lower  Paleozoic
basement and Upper Paleozoic cover rocks to the north, and
is  overridden  by  the  Silica  Nappe  in  the  south  (Figs.  1  and
2). However, the tectonic affiliation of some occurrences of
Meliatic  rocks,  as  shown  in  Fig.  1,  was  reinterpreted  by
Lačný  et  al.  (2015).  Based  on  lithology  and  structural  rela-
tionships they are now considered to be the frontal elements
of the Turňa Unit.

In the present paper, we also reinterpret the position of the

Meliatic  tectonic  inlier  (window)  near  the  village  of
Striežovce (cf. Gaál 1982) in the western part of the investi-
gated region (Figs. 1 and 2). Our view is based on the general
structure of this occurrence of Middle—Upper Triassic forma-
tions  that  are  surrounded  by  the  upper  Lower  Triassic  Szin
marlstones,  thus  indicating  a  synclinal  structure.  Moreover,
the  Triassic  carbonates  in  the  synclinal  core  do  not  exhibit
the typical “Meliatic” structure with olistolites embedded in
Jurassic shales, but fragments of continuous successions can
be  documented.  Consequently,  the  sequence  of  metamor-
phosed Triassic carbonates located in this syncline is now re-
garded  as  a  component  of  the  Turňa  Unit.  The  presence  of
red  marly  and  siliceous  shales  of  probably  Ladinian  age
(work in progress) near the village of Hrušovo is a particu-
larity of the Striežovce succession, indicating its more distal
passive margin position with respect to other Turňa succes-
sions.

The map-scale structures of the Turňa Unit (Slovenská

skala  partial  nappe)  have  a  slightly  arcuate  shape  changing
from  SW—NE  strike  in  the  western  up  to  W—E  strike  in  the
eastern part of the area (Fig. 2). This trend is well expressed
by axes of several subparallel anticlinal and synclinal zones,
which  were  thoroughly  described  and  named  already  by
Gaál  &  Mello  (1983).  Macroscopic  synclines  are  filled  by
upper  Lower  Triassic  Szin  marlstones  and  the  widest  ones
also  by  Middle—Upper  Triassic  carbonates  and  shales  (Tri
peniažky-Slovenská  skala,  Sása  and  Striežovce  synclines,
Fig. 2). These map-scale synclines are clearly asymmetrical
with steeply south-dipping axial planes, as seen in cross-sec-
tions  constructed  from  the  bedding  attitudes.  The  northern

limbs of synclines along the northern edge of the Turňa Unit,
at the contact with the underlying Gemer Unit (Tri peniažky-
Slovenská skala; Fig. 2), are truncated by moderately south-
dipping reverse faults linked to the basal overthrust plane in
places (e.g., the Rákoš area – cf. Lačný et al. 2015; Fig. 2),
or  imbricated  with  the  underlying  Meliatic  complexes
(northern  slopes  of  the  Tri  peniažky  Hill).  In  a  map  view
(Fig.  2),  the  macroscopic  synclines  appear  to  be  non-cylin-
drical,  with  doubly-plunging  hinges  (e.g.,  the  Sása  and
Striežovce brachysynclines). This might be a cumulative ef-
fect of a sinistral transpression especially in the western part
of  the  area  with  SW—NE  structural  trends  (see  Lexa  et  al.
2003),  and  the  superimposed  W—E  shortening  with  large-
scale, gentle folds with roughly N—S oriented axes revealed
by the mesoscopic structural analysis (see below).

In the northern and central parts of the investigated area,

the synclines alternate with somewhat wider open anticlines
composed  of  the  Bódvaszilas  shales  and  sandstones.  How-
ever,  the  southern  anticlinal  zone  at  the  contact  with  the
overriding  Silica  Unit  is  more  complicated.  The  dominant
structure  is  the  large  Brusník  anticline  cored  by  the  Upper
Palaeozoic rocks of the Turiec and Brusník fms (Fig. 2). The
axis  of  this  anticline  plunges  rapidly  to  the  NE;  hence  this
structure  can  be  classified  as  a  brachyanticline  or  pericline.
Close  to  the  east,  the  Brusník  pericline  is  juxtaposed  by
another  antiform,  which  is  the  Držkovce  tectonic  window
exposing the Meliatic complexes, which likely underlay the
whole Turňa Unit in this area, as was revealed by the BRU-1
borehole.  This  borehole,  drilled  in  the  core  of  the  Brusník
anticline, encountered Jurassic olistostromatic complexes of
the  Meliata  Unit  directly  below  Carboniferous  rocks  of  the
Turiec Fm. (Vozárová & Vozár 1992).

Another borehole DRŽ-1 drilled directly in the Držkovce

tectonic window penetrated several alternating slices of Me-
liatic  and  Turnaic  rocks  (Mello  et  al.  1994).  The  latter  are
mostly  composed  of  Lower  Triassic  shales  and  presumably
Upper  Permian  coarse-grained  clastics  (Brusník  Fm.),  as
well as shales and evaporites with blocks of serpentinites and
various  carbonates.  The  evaporitic  mélange  with  blocks  of
ultramafic magmatites resemble the Perkupa Fm. of northern
Hungary (e.g., Réti 1985), or the Haselgebirge salt breccias
of the Northern Calcareous Alps (Kirchner 1980; Schorn et
al.  2013).  If  present  in  a  sedimentary  succession,  the  ex-
tremely  incompetent  evaporites  serve  as  décollement  hori-
zons and are often found at the soles of far-travelling cover
nappes,  where  they  often  incorporate  various  footwall-de-
rived exotic fragments.

Based on its internal structure, the Držkovce tectonic win-

dow may be interpreted as a large-scale, imbricated duplex
structure (Fig. 2, cross-section A), which was formed in front
of the buttressing Brusník antiform. Accordingly, it most
probably originated after the main overthrusting phase of the
Turňa Unit and can be classified as an out-of-sequence thrust
structure of the D

stage.

The two anticlinal macrostructures – the Brusník peri-

cline and the Držkovce imbricated antiform – are laterally
substituted in a coulisse-like way, the Brusník pericline
being a more southern one (Fig. 2, sections A and B). This
suggests that the Brusník body is somewhat structurally

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independent internal part of the Turňa Unit formed by addi-
tional  post-thrusting  shortening,  large-scale  folding  and
thrusting with development of a steep imbricated structure in
its  front  (Fig.  6).  Moreover,  the  basal  detachment  reached
deeper  structural  levels  within  the  Palaeozoic  rocks  here,
whilst further north it is stepping up into the main evaporitic
décollement  horizon  and  then  into  Triassic  sediments.  As
a result, the overall geometry of fold-and-thrust structures of
the  Turňa  Unit  points  to  its  northward  thrusting  direction
in the investigated area.

In general, the bedding planes dip towards the SE and NW

throughout the study area with the average inclination be-
tween 60 and 70° (Fig. 5A, B). Locally, the bedding is sub-
vertical. Rocks are also affected by superimposed, in places
penetrative cleavage related to mesoscopic folding. Cleavage
is steeply NW- or SE-dipping dependent on position within
large-scale fold structures, as will be described below.

The studied region is also affected by a set of transversal,

generally  NW—SE  striking,  map-scale  faults.  A  majority  of
them  are  related  to  the  post-thrusting,  most  likely  Miocene
tectonic activity. However, short local faults that cut carbo-
nate complexes in synclinal cores can be interpreted as tear
faults  that  were  active  simultaneously  with  growth  of  the
synclines.

Origin and evolution of the Meliata-Turňa accretionary
wedge

The largest part of the studied area is composed of incom-

petent shales of the Werfen Fm., which are characterized by
the penetrative, bedding-parallel S

foliation produced by

vertical flattening of originally gently dipping strata. Relying
on  the  supposed  palaeogeographical  position  of  the  Turňa
Unit on the flanks of the Meliata Ocean, its origin was most
probably caused by a tectonic burial related to formation of
the accretionary wedge during subduction processes and clo-
sure of the Meliata Ocean in the Late Jurassic to earliest Cre-
taceous  times  (e.g.,  Faryad  1995,  1999;  Mello  et  al.  1998;
Mock et al. 1998; Árkai et al. 2003; Dallmeyer et al. 2008).
As  a  result,  all  rocks  of  the  Turňa  Unit  were  buried  within
the  nappe  pile  of  the  accretionary  wedge  and  were  affected
by a very low-grade metamorphism.

However, the conditions of metamorphism seem to vary

from  place  to  place  and  no  direct  petrologic  determinations
of  the  pressure-temperature  conditions  of  the  Turňa  Unit
rocks are available yet from the investigated area. Referring
to  data  obtained  from  Meliatic  rocks  of  the  Držkovce  and
Meliata tectonic windows (see Fig. 2), and from the possibly
Turňa Unit metasediments near Hačava village further to the

Fig. 6. Scheme of development of large-scale fold and thrust structures of the Turňa Nappe in the examined area. A – deformation stage
D

during the thrust stacking period and growth of the accretionary wedge. B – situation after the D

stage characterized by out-of-

sequence thrusting. Not to scale.

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east,  the  maximum  P-T  conditions  may  be  estimated  to
300—350 °C at 300—400 MPa (Árkai et al. 2003). According
to  K-Ar  dating  of  white  K-mica  concentrates,  the  thermal
peak of this metamorphic event probably occurred during the
earliest  Cretaceous,  some  145—140  Ma  ago  (Árkai  et  al.
2003).  Analogous  rocks  of  the  Turňa  (Torna)  Unit  in  the
Rudabánya Mts. of northern Hungary provided similar meta-
morphic temperatures of approximately 300—350 °C at pres-
sures of 300—450 MPa (Árkai & Kovács 1986; Kövér et al.
2009).  This  prograde  metamorphic  event  was  coeval  with
partial  retrogression  of  the  Meliata  HP/LT  rocks  in  the
greenschist-facies conditions (e.g., Faryad 1995, 1999; Dall-
meyer  et  al.  2008)  and  likely  reflects  the  maximum  thicke-
ning of the wedge due to thrust stacking, including exhumed
blueschist Meliata slices at the wedge sole (Fig. 6A).

Subsequent D

compression and out-of-sequence thrusting

within the accretionary prism might have been induced by its
frontal collision with the Gemeric margin of the Central
Western Carpathian block (Fig. 6B). It resulted in develop-
ment of the SW—NE striking, in places fanning S

foliation.

In the Bódvaszilas shale-sandstone strata, the related F

folds

are  open  to  closed,  partly  slightly  asymmetrical  showing
both the north-western and south-eastern inclinations of axial
planes.  The  model  of  fan-wise  arrangement  of  fold  axial
planes  developed  during  a  single  deformation  phase  is  out-
lined in Fig. 7A. The model is based on numerous examples
from  structural  geology  textbooks  (e.g.,  Ramsay  &  Huber

1987) of polyharmonic folds resulting from a variable litho-
logy, thickness and competence contrast of strata in a de-
formed multilayer. These fold patterns predominantly occur
in the SW—NE trending anticlinal hinge zones and cores of
large-scale folds.

In the less competent media, like the Szin marlstones, the

minor tight to isoclinal folds were tightened by flexural flow
and pressure solution along the S

cleavage planes. The con-

sequential fold geometry shows typical Z-, M- and S-type
“parasitic” folds (conceptual model in Fig. 7B). These folds
mostly occur in limbs of large-scale folds.

The deformation record of this second tectonic phase was

also  observed  in  the  Meliata  Nappe  close  to  the  village  of
Držkovce, while mesoscopic structures of this stage were not
detected with certainty in adjacent parts of the Silica Nappe.
The reason could be either a higher structural position of the
Silica  Nappe  and  its  decoupling  from  the  underlying  de-
formed units within the wedge, or that it was still not a part
of the Neotethyan accretionary wedge during the Late Juras-
sic  and  Early  Cretaceous.  However,  the  Silica  Nappe  as
a whole  is  also  affected  by  large-scale,  W—E  trending  fold-
thrust structures in the Slovenský kras Mts. (Mello et al. 1997)
and also in the adjacent Aggtelek-Rudabánya Mts. in north-
ernmost Hungary (Less et al. 1988; Hips 2001; Kövér et al.
2009;  Deák-Kövér  2012).  However,  relics  of  Upper  Creta-
ceous,  Gosau-type  sediments  (conglomerates,  fresh-water
limestones, palaeokarst fillings) incorporated into these struc-
tures point to their post-Cretaceous age (Mello et al. 1997).

Shortening in the ENE—WSW direction

This tectonic stage is characterized by the orientation of

the principal compression axis in the WSW—ENE direction.
The F

fold group is represented by less distinct, open to

closed and mostly angular folds and kink bands, in places ac-
companied by the approximately N—S oriented, widely
spaced subvertical planes subparallel to the F

axial planes

(Fig. 5C). Due to a more brittle character of D

structures

compared to D

and D

, indicating some exhumation be-

tween the D

and D

stages, the D

structures are considered

to be younger than the D

structural association. Modifica-

tion of D

structures by the D

phase is also indicated by

a girdle of F

fold axes (Fig. 5D), interpreted as their plunge

undulation due to superimposed F

macroscopic folding.

However, the measured F

fold axes are poorly presented

in tectonograms (Fig. 5D) for several reasons. The first rea-
son  is  the  less  significant  manifestation  of  this  event  in  the
field. The second important reason can be the morphology of
the  area,  where  most  of  the  incised  valleys  with  well-out-
cropping  rocks  trend  in  a  NW—SE  direction.  Consequently,
only  a  few  outcrops  that  would  trend  perpendicularly  to  D

structures are present.

Nevertheless, structures of this deformation stage were

also  observed  in  the  Meliata  and  Silica  units.  For  example,
a set  of  kink  folds  was  studied  in  Lower  Triassic  strata  of
the Silica Unit near Krásnohorská Dlhá Lúka village south of
the town of Rožňava. Their 5 measured axes plunge modera-
tely  (30—60°)  towards  the  SE  (105—170°).  The  folds  of  this
direction  were  also  described  from  the  Hungarian  territory

Fig. 7. Two models of outcrop-scale fold types in the investigated
area. A – fold pattern in the shale-sandstone multilayer of the
Bódvaszilas Mb. Initial indistinct S

cleavage related to minute

folds  in  shales  was  rotated  around  hinges  of  the  younger  larger-
scale  fold  limbs  of  a  thick  sandstone  bed  to  form  a  cleavage  fan.
B – Z- and S-type fold tracks in soft marly shales of the Szin Mb.
modified  by  fold  tightening  and  pressure  solution  along  the  S

cleavage. Both types produce folds with either NW- or SE-dipping
axial planes.

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(e.g., Fodor & Koroknai 2000; Hips 2001). It is worth noting
that  the  same  orientation  of  the  palaeostress  field  with  the
W—E to WSW—ENE maximum horizontal compression axis
was  also  recorded  in  the  Mesozoic  to  Lower  Eocene  sedi-
ments  throughout  the  Western  Carpathians,  but  the  Upper
Eocene to Oligocene strata do not contain any record of this
event (e.g., Vojtko et al. 2010; Sůkalová et al. 2012).

Geodynamic inferences

In general, the overall structural evolution of the Turňa

Nappe with the three distinct deformation stages D

, D

and

as described here is virtually identical with that of the

Torna (Martonyi) Unit in the Rudabánya Mts. (Fodor & Ko-
roknai 2000; Kövér et al. 2009; Deák-Kövér 2012) and in the
main aspects also with that of the Meliatic units (Mock et al.
1998;  Mello  et  al.  1998;  Faryad  1999;  Dallmeyer  et  al.
2008).  The  overall  situation  implies  that  both  the  Meliatic
and  Turnaic  units  were  constituents  of  an  accretionary  belt
that  developed  during  the  terminal  stages  of  closure  of  the
Neotethyan  Meliata  Ocean  in  the  Late  Jurassic.  This  initial
phase of the accretionary wedge is recorded by structures of
the  D

deformation stage, mainly the penetrative, bedding-

parallel S

low-grade metamorphic foliation. Subsequently,

the Early Cretaceous collision of the accretionary wedge
with the southern Gemeric margin led to its overthrusting
and the development of the D

fold-and-thrust structures that

dominate the present broad-scale structure of the Turňa Unit
(Fig. 2).

Notwithstanding the present close structural and metamor-

phic relationships of the Turňa Unit with the underlying Me-
liatic  rocks,  their  earliest  structural  and  metamorphic
histories  appear  to  be  diverse.  The  rock  complexes  that  are
currently  affiliated  with  the  Meliaticum  represent  a  very
heterogeneous  group  of  units  with  differing  sedimentary,
metamorphic and structural histories. Commonly interpreted
as  a  subduction-related  mélange  (e.g.,  Dallmeyer  et  al.
2008),  the  Meliaticum  could  be  differentiated  into  at  least
three particular units (Fig. 8):

1) The Bôrka Nappe (blueschist unit – Leško & Varga

1980; Mello et al. 1998) in the lowermost structural position,
directly  overlying  the  Gemeric  basement-cover  complexes,
was  affected  by  HP-LT  metamorphism  at  ca  160—150  Ma
(Maluski et al. 1991; Faryad 1995, 1999; Faryad & Henjes-
Kunst 1997; Faryad et al. 2005; Dallmeyer et al. 2008) and
then exhumed from the subduction channel and incorporated
into  the  accretionary  wedge.  It  is  important  to  note  that  the
Bôrka  Unit  was  derived  from  a  distal  continental  passive
margin,  including  the  Permian  clastic  sediments,  and  does
not include true oceanic elements (Mello et al. 1998).

2) The chaotic oceanic mélange complexes, also known as

the Jaklovce Unit, contains variously sized blocks of basalts,
serpentinites,  blueschists,  acid  volcanites,  radiolarites  of
Middle—Upper Triassic and Jurassic age, variegated Triassic
shallow-  and  deep-water  carbonates  (e.g.,  the  lower  unit  in
the  Brusník  borehole),  and  even  blocks  derived  from  the
Variscan,  possibly  Gemeric  basement  (gneisses  and  amphi-
bolites – Faryad & Frank 2011). All these are embedded in
a  Jurassic  radiolarite-shale-sandstone  matrix,  whereby  the

chaotic complexes show a partially sedimentary and partially
tectonic origin.

3) The sedimentary unit of Jurassic deep-water deposits

with  olistostromes  and  olistoliths  of  various  Triassic  carbo-
nates and Ladinian radiolarites, but with poorly represented
real oceanic material. This is loosely designated as the Meliata
Unit s.s. (e.g., Mock et al. 1998) and can belong to various
units of higher order – possibly upper parts of the Meliatic
Jurassic complexes occurring below the Turňa-Silica nappes
(for  instance  the  Držkovce  window  and  Brusník  borehole),
or more commonly it seems to form synclines, originally Ju-
rassic  sedimentary  basins,  in  the  Turňa  and/or  Silica  units
(like the Meliata type locality – Aubrecht et al. 2012). The
relationship  of  ophiolite-free  and  ophiolite-bearing  olis-
tostromes/mélanges is not clear, possibly the former underlie
the latter, as it was documented in the Darnó Mts. of northern
Hungary  (Kovács  1988;  Dimitrijević  et  al.  2003;  Kovács  et
al. 2010).

The first phases of development of the Meliata accretio-

nary complex composed of detached Jurassic sediments and
various mélange/olistostrome complexes are indirectly dated
by  commencement  of  synorogenic  clastic  sedimentation
during  the  late  Early?—Middle  Jurassic.  The  rock  composi-
tion  of  the  wedge  was  completed  during  the  latest  Jurassic
by  incorporation  of  the  exhumed  blueschist  complexes  and
termination  of  synorogenic  sedimentation  before  the  Kim-
meridgian.  Sediments  younger  than  Oxfordian  are  virtually
absent in the whole Meliata-Turňa-Silica nappe stack, except
for  shallow-water  Kimmeridgian—Tithonian  limestones
found as pebbles in Senonian and Oligocene conglomerates
(Mišík & Sýkora 1980). These indicate that the accretionary
wedge was partially sealed by a shallow carbonate platform
which was completely eroded later (Plassen platform of un-
certain  position  in  Fig.  8).  Subsequently,  ca  150—140  Ma
ago,  various  Meliata-Turňa  rock  complexes  were  buried  to
depths  of  some  10—15  km  in  lower  parts  of  the  wedge  and
underwent  a  prograde  metamorphic  recrystallization  (Árkai
et al. 2003), while the older blueschists of the Bôrka Nappe
were partly retrogressed (e.g., Faryad 1999; Dallmeyer et al.
2008).  The  early  phase  of  blueschists  exhumation  occurred
ca 147 Ma, as indicated by the electron microprobe dating of
retrogression-related  monazite  (Méres  et  al.  2013).  These
processes are only feebly registered by the structural record
of the first deformation stage D

, however.

Later on, both the Turňa and Meliata units collided with

and were thrust over the underlying Gemericum as a united
structural complex (Fig. 6). The thrusting event ca 140—130
Ma  (Vozárová  et  al.  2008)  was  followed  by  the  subsequent
stage  of  exhumation,  collapse  and  cooling  of  the  wedge
some 130—120 Ma ago, as documented by (U-Th)/He zircon
thermochronology  from  the  Meliatic  rocks  (Putiš  et  al.
2014). Simultaneously, detritus of the HP minerals appeared
for the first time in sediments of this age — in the Barremian—
Aptian,  Urgon-type  platform  limestones  occurring  as  peb-
bles in the Albian—Cenomanian conglomerates of the Klape
Unit (Méres et al. 2015; cf. Fig. 8). After this thrusting event,
the Meliata-Turňa stack became a component of the southern
Central  Western  Carpathian  orogenic  wedge,  including  the
underlying  Gemer  and  Vepor  basement-cover  thrust  sheets,

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Fig. 8. Synoptic presentation of depositional environments, magmatic events and tectonometamorphic processes of tectonic units that are
discussed in the text. Magmatic rocks: A – alkaline; CTH – continental tholeiites; BAB – back-arc basalts. Black asymmetrical arrows
indicate main thrusting events. Dispersal pathways of clastic material derived from ophiolite and blueschist complexes, as well as from
vanished temporary carbonate platforms, are shown by thick grey-shaded arrows. Note that tectonic units are arranged according to their
present structural position from the lower (left) to the upper (right). This does not necessarily imply their original palinspastic relations,
however. Note also that the original position of the presently completely eroded carbonate platforms (Plassen, Urgon) is not constrained by
any direct data. Time scale according to www.stratigraphy.org.

which  propagated  northwards  during  the  Albian—Turonian
(110—90  Ma).  By  this  time,  erosional  products  of  Meliatic
rocks became commonly present in “exotic” conglomerates
of the Pieniny Klippen Belt and adjacent zones (Fig. 8; see
e.g.,  Plašienka  &  Soták  2015  for  the  latest  summary).
The ensuing thickening of the orogenic wedge rear and its
subsequent  extensional  collapse  and  cooling  are  well  con-
strained  by  the  Late  Cretaceous  thermochronological  data
in  the  time  span  ca  90—55  Ma  (e.g.,  Janák  et  al.  2001;
Koroknai  et  al.  2001;  Plašienka  et  al.  2007;  Hurai  et  al.
2008;  Králiková  2013;  Méres  et  al.  2013,  2015;  Vojtko
et al.  2016;  for  the  reviews  see  also  Putiš  et  al.  2009  and

Jeřábek  et  al.  2012).  In  the  southern  Central  Western  Car-
pathian  zones  (Vepor-Gemer  Belt),  material  of  the  Meliatic
ophiolites  occurs  massively  in  the  uppermost  Cretaceous—
lowermost  Palaeocene,  Gosau-type  conglomerates  (e.g.,
Hovorka et al. 1990) – cf. Fig. 8.

Nevertheless, the yet unresolved question remains: How is

the  Silica  Nappe  related  to  the  structures  of  the  underlying
Meliatic-Turnaic  units?  The  conventional  concept  considers
the Silica Nappe in the Slovak-Aggtelek Karst Mts. and its ana-
logues  further  north  (Stratená,  Vernár,  Muráň  and  Drienok
nappes  –  “Silicicum”  s.l.)  as  the  non-metamorphosed  cover
nappe system, which in the highest structural position within

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the  Palaeoalpine  thrust  stack  of  the  Central  Western
Carpathians.  The  Silicic  nappes  are  overlying  various  units
(Gemeric,  Veporic,  Hronic  –  Fig.  8)  with  a  distinct
metamorphic  and  structural  discordance  (e.g.,  Kozur
& Mock 1973, 1987, 1997; Mello et al. 1997; Plašienka et al.
1997). On the contrary, some other data indicate that the Si-
licicum is composed of several partial units that are of hetero-
geneous  origin  from  the  lithostratigraphic-facies  and
structural-metamorphic  points  of  view  (e.g.,  Havrila
& Ožvoldová 1996; Vojtko 2000; Gawlick et al. 2002; Hav-
rila  2011).  Consequently,  the  present  concept  of  the  Silici-
cum  as  a  unified  superunit  might  be  misleading  and  its
various  subunits  could  be  of  different  palaeogeographic
provenances,  structural-metamorphic  histories  and  times  of
final  emplacement.  It  is  not  to  be  excluded  that  the  Silica
Nappe  is  not  a  coherent  body,  but  its  slightly  metamor-
phosed subunits were possibly components of the early accre-
tionary  wedge,  whilst  the  flat-lying  carbonate  slabs  may
have  glided  to  their  present  position  later,  during  the  late
Cretaceous—earliest Palaeogene gravitational collapse of rear
parts of the orogenic wedge.

In comparison with the Northern Calcareous Alps (NCA),

the  Triassic  lithostratigraphic  succession  of  the  Turňa  Unit
roughly corresponds to the Hallstatt Zone, occurring as a re-
worked  material  in  the  Hallstatt  Mélange  of  the  Jurassic
Lammer Basin (Upper Tirolic nappe system – e.g., Missoni
& Gawlick 2011a, b; Gawlick et al. 2012). Unlike the Alpine
reworked  olistostromatic  complexes  in  secondary  position,
the Turňa and Silica units mostly show continuous sedimen-
tary  successions  in  primary  nappe  positions,  albeit  redistri-
buted  by  a  subsequent  out-of-sequence  imbrication  within
the accretionary wedge. On the contrary, with a few excep-
tions (Sýkora & Ožvoldová 1996), Middle—early Late Juras-
sic deep-water basins with mass-wasting deposits are nearly
missing in the southern Carpathian zones. This makes corre-
lation difficult, even though the Triassic facies zones can be
followed  and  mutually  related  relatively  easily.  What  ap-
pears  to  be  really  different  is  the  tectonic  structure  of  the
nappe edifice in both mountain ranges.

The southern Western Carpathian zones are regarded as

the  north-eastern  prolongation  of  the  Jurassic  Neotethyan
Orogenic Belt extending from the Dinarides, Albanides and
Hellenides  NW-ward  to  the  NCA  (Gawlick  et  al.  2012  and
references  therein).  These  southern  parts  of  the  Neotethyan
Belt  are  characterized  by  extensive  ophiolite  obduction  in
the late Middle—early Late Jurassic sealed by the Upper Ju-
rassic—earliest Cretaceous carbonate platforms (e.g., Schmid
et al. 2008). An analogous situation is inferred for the NCA,
notwithstanding  that  ophiolite  complexes  were  completely
eroded  during  the  Cretaceous  and  early  Palaeogene  (cf.
Krische et al. 2014; Gawlick et al. 2015). In all these zones
from  the  Hellenides  up  to  the  NCA,  the  obducted  ophiolite
nappes  occur  in  the  uppermost  structural  position  above  an
imbricated  thrust  stack  of  the  former  Neotethyan  passive
continental  margin  and  shelf  areas.  However,  the  structural
situation  is  very  much  different  in  the  inner  Western  Car-
pathian  zones.  As  described  above,  the  Jurassic  ophiolite-
bearing  mélange  and/or  blueschist  nappe  (Meliaticum  s.l.)
overlie  directly  and  primarily  the  Gemeric  basement/cover

complexes,  namely  the  Central  Austroalpine  unit  in  Alpine
terms.  However,  the  Meliatic  complexes  are  overridden  by
the  passive  margin  thrust  stack  in  an  “improper”  sequence,
namely first by the Triassic distal margin to upper slope suc-
cession (Turňa Unit) and then by the outer shelf successions
(Silica  Unit).  Accordingly,  the  nappe  sequence  is  precisely
the opposite of what we would expect. There are numerous
models  attempting  to  explain  this  tectonic  vs.  palaeogeo-
graphic ambiguity (e.g., Kozur 1991; Hók et al. 1995; Kozur
&  Mock  1997;  Less  2000;  Lexa  et  al.  2003;  Csontos
& Vörös  2004;  Dallmeyer  et  al.  2008;  Froitzheim  et  al.
2008; Schmid et al. 2008; Kövér et al. 2009; Kövér & Fodor
2014),  but  none  of  them  accounts  for  all  the  structural  and
facies relationships satisfactorily.

The present paper has no ambition to develop a new evolu-

tionary tectonic model of the area; neither has it directly fol-
lowed  any  of  the  previously  formulated  concepts.  In  our
opinion,  there  are  still  too  many  fundamental  uncertainties
that hamper development of a reliable hypothesis that would
agree  with  the  majority  of  existing  structural,  metamorphic
and lithofacies data. For the time being, we see relationships of
the  Meliata-Turňa  thrust  stack  with  the  overlying  complexes
that  are  presently  affiliated  with  the  Silicicum  as  the  major
open  question  of  the  structure  and  evolution  of  the  southern
Western Carpathian zones. This problem should be one of the
main targets for future research in the area concerned.

Conclusions

Structural analysis of fold and cleavage deformation struc-

tures of the western part of the Turňa Unit revealed their suc-
cessive development in three deformation stages. It is
inferred that the first deformation stage D

was related to ini-

tial stages of an accretionary wedge development formed in
response  of  the  Neotethyan  (Meliata)  Ocean  subduction
during the Late Jurassic. Thrust stacking brought about very
low-grade  metamorphism  in  lower  parts  of  the  wedge,  ac-
companied  by  vertical  flattening  and  development  of  the
penetrative, bedding-parallel foliation S

. At the same time,

the wedge incorporated Meliatic ophiolite fragments and
various mélange complexes, as well as the exhumed HP/LT
metamorphic slabs derived from the subducted distal passive
continental margin (Bôrka Nappe). These events took place
in the Late Jurassic.

Suturing of the Meliata Ocean and collision of the Meliata-

Turňa accretionary wedge with the southern passive European
margin, represented by the Gemer Unit, is recorded by the
second deformation stage D

. It is expressed particularly by

folding  on  all  scales,  whereby  the  macroscopic  asymmetric
folds with a generally northern vergence dominate the struc-
ture of the area by a system of SW—NE to W—E trending syn-
clines  filled  with  Middle—Upper  Triassic  carbonates  and
anticlines  formed  by  Lower  Triassic  clastic  sediments.  The
southernmost  Brusník  brachyanticline  also  involves  Upper
Palaeozoic  sedimentary  complexes  in  its  core.  Its  frontal
zone is complicated by the presence of an antiformal imbri-
cated duplex which exposes rocks affiliated with the Meliata
Unit (Držkovce tectonic window).

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The geometry of the mesoscopic F

folds depends on the

rheology  of  folded  media.  In  shale-sandstone  multilayers
folds are open to closed, upright to steeply inclined and form
polyharmonic sets. Marly shales are characterized by minute
tight to isoclinal folds with penetrative axial-plane cleavage
and  can  often  be  regarded  as  parasitic  folds  occurring  in
limbs  of  larger-scale  upright  folds.  Regional  considerations
point to timing of the D

stage during the Early Cretaceous

period. Deformation was followed by exhumation and ero-
sion of the former Meliata-related accretionary wedge within
the rear parts of the prograding Central Western Carpathian
collisional orogenic system. Timing of emplacement of the
overlying Silica Nappe is not clear. Whereas the D

structural

pattern points to the NW—SE to N—S shortening, the third de-
formation stage registers a “cross” folding process with
WSW—ENE oriented horizontal compression. Its expressions
are rather weak, represented by approximately N—S trending
kink bands and occasional spaced cleavage. The D

defor-

mation stage likely occurred during the latest Cretaceous to
early Palaeogene and also affected rocks of the Silica Nappe.
During  the  Oligocene  and  Early  Miocene,  the  area  was
covered by a shallow epicontinental sea. Erosional remnants
of its sediments, along with Middle Miocene volcanic com-
plexes,  still  cover  considerable  parts  of  the  southern  Car-
pathian  zones  and  largely  obliterate  the  relationships  of
Mesozoic  tectonic  units  in  this  complex  suture  zone  of  the
Carpathians.

Acknowledgements:  This  work  was  financially  supported
by the Slovak Research and Development Agency under the
contract Nos. APVV-0315-12 and APVV-0212-12. It is also
an outcome of the research project VEGA 1/0193/13. Finan-
cial support from the respective grant agencies is gratefully
acknowledged.  Constructive  review  comments  by  L.  Fodor
(Budapest)  and  J.  Hók  (Bratislava)  that  helped  to  improve
the  scientific  content  and  clarity  of  the  text  and  figures  are
gratefully acknowledged.

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