GEOLOGICA CARPATHICA, 51, 6, BRATISLAVA, DECEMBER 2000
DUCTILE DEFORMATION AND REVISED LITHOSTRATIGRAPHY
OF THE MARTONYI SUBUNIT (TORNA UNIT, RUDABÁNYA MTS.),
and BALÁZS KOROKNAI
Department of Applied and Environmental Geology, Eötvös University, Múzeum krt. 4/a, 1088 Budapest, Hungary
Geological Research Group of the Hungarian Academy of Science, Eötvös University, Múzeum krt. 4/a, 1088 Budapest, Hungary
(Manuscript received April 16, 2000; accepted in revised form October 17, 2000)
Abstract: New structural observations and mapping resulted in the reinterpretation of the Martonyi Subunit, part of the
metamorphic Torna Unit, NE Hungary. This low-grade metamorphosed Triassic sequence contains lower Anisian
Gutenstein Dolomite, a thin transitional pelagic sequence (Bódvarákó Formation?), Carnian Tornaszentandrás Slate, late
Carnian-Norian Pötschen Limestone. This stratigraphy is closer to the Bódvarákó windows than to any other Torna
subunits. The original sedimentation area could be located on thinned continental crust, relatively close to the oceanic
crust of the Meliata branch of the Neotethys. The whole sequence suffered three phases of ductile deformation during
Alpine (Cretaceous?) tectogenesis. First, layer-parallel foliation developed (D
), most probably connected to first order
nappe stacking. The second deformation phase (D
) is marked by upright, chevron-type folding (D
). Detachment faults
could form at the top of the Gutenstein Dolomite in order to accommodate space problems at fold hinges. The chevron
folds were flattened later, during a progressive D
phase associated with the development of axial plane cleavage and
steep reverse faults. The structural style varies depending on locations within folds and on lithology suggesting strain
partitioning during the D
phase. Small kink folds with oblique axes can be related to reactivation of steep faults with
oblique slip during the D
phase, at the transition of brittle-ductile deformation field. The whole unit was thrust upon
non-metamorphic unit(s) (D
due to strike-slip displacement along the Darnó Zone sensu lato during the
late Cretaceous and/or Tertiary.
Key words: Mesozoic, Inner Western Carpathians, NE Hungary, Torna Unit, ductile deformation, folds, foliation,
A metamorphic Triassic succession in the Rudabánya Mts. be-
tween Tornaszentandrás and Martonyi villages (Fig. 1) be-
longs to the Torna Unit sensu Less (1981, 2000) and Grill et al.
(1984). Following this original definition, the metamorphic
Torna sequence generally contains Anisian platform (ramp)
carbonates (Gutenstein Dolomite, Steinalm Limestone), Upper
Anisian-Ladinian basinal limestone (Szentjánoshegy Fm.),
Carnian slate (Tornaszentandrás Fm.), upper Carnian-Norian
cherty Pötschen Limestone (Fig. 2). These rocks suffered an-
chi to epizonal metamorphism indicated by metamorphic pet-
rological data (Árkai & Kovács 1986).
The metamorphic sequence between Tornaszentandrás and
Martonyi villages shows some peculiarities. Steinalm Lime-
stone is definitely missing, and only the slate-cherty lime-
stone couplet was considered to belong to the Torna Unit
(Less et al. 1988; Grill 1989; Less 1998). Anisian Gutenstein
Dolomite is closely associated in map view with metamor-
phic rocks. Mapping and boreholes demonstrated that the
metamorphic cherty limestone-slate couplet is situated above
the Gutenstein Dolomite. However, the above mentioned au-
thors did not observe metamorphic foliation, internal ductile
deformation of the dolomite, therefore they considered this
rock to be non-metamorphic. They assigned the dolomite to
the adjacent, non-metamorphic Bódva Unit which geographi-
cally surrounds the metamorphic Martonyi sequence (Figs. 2,
3). This opinion also suggests that the slate and cherty lime-
stone would form a higher nappe unit. Because this upper
Martonyi nappe is clearly metamorphic, this juxtaposition
would only be possible after the metamorphism. Less et al.
(1988) and Less (1998, 2000) suggested Miocene emplace-
ment of this neoallochthonous metamorphic nappe. This
thrusting would be connected to the left-lateral displacement
of the Darnó Zone which bounds the whole area on both
sides (Fig. 1).
In our paper we present a new structural map of the Marto-
nyi Subunit derived from new mesoscale structural observa-
tions. They show that the Gutenstein Dolomite is the normal
stratigraphic base of the slate-limestone couplet and under-
went the same epizonal metamorphism and three phases of
The Martonyi sequence is situated in the northeastern part of
the Rudabánya Mts., in northeastern Hungary and forms a sub-
unit of the metamorphic Torna Unit (Fig. 1). It consists of
metamorphic Triassic rocks surrounded by non-metamorphic,
Present address: Geological Institute of Hungary, Stefánia 14, 1143 Budapest, Hungary; email@example.com, firstname.lastname@example.org
356 FODOR and KOROKNAI
Permian-Jurassic rocks of the Bódva Unit and by Late Mi-
ocene (Pannonian sensu lato) sediments (Fig. 3).
Less et al. (1988), Less (1998) attributed two main lithologi-
cal members to the metamorphic Triassic suite of the Martonyi
Subunit (Fig. 2). The Tornaszentandrás Formation contains
brownish grey or black slate with well-developed foliation.
This fine-grained, siliciclastic sediment contains a few lime-
stone intercalations which prove a lower to middle Carnian
age (Kovács et al. 1989). To the south, this slate becomes more
sandy-silty and/or marly, but the transition toward the Red-
nekvölgy Beds (member of the Tornaszentandrás Fm.) seems
to be continuous.
The upper Carnian-lower Norian Pötschen Formation is
built up by cherty limestone and marlstone. The transition
from the underlying slate is gradual, represented by a frequent
alternation of slate, limestone beds and/or marlstone. The age
Fig. 1. Situation of the Martonyi Subunit in northeastern Hungary (a) and cross section (b) through the northern Rudabánya Mts., showing the
main tectonic units (after Less et al. 1998; Mello 1997).
DUCTILE DEFORMATION AND LITHOSTRATIGRAPHY OF MARTONYI SUBUNIT 357
of this formation is defined by conodonts. Several locations
yielded upper Carnian-lower Norian fauna (Kovács 1986;
Kovács et al. 1989).
Anisian Gutenstein Dolomite is a dark grey, massive or
thick-bedded dolomite rarely containing algal mats. We will
try to demonstrate that in contrast to Less et al. (1988) and
Grill (1989) the Gutenstein Dolomite forms the normal
stratigraphic part of the metamorphic sequence.
The transition between the Gutenstein Dolomite and the
overlying Tornaszentandrás Slate is generally badly exposed,
but locally (often in scree) we have found specific rocks.
These are dark grey (calcareous) dolomite with black chert
nodules, brown dolomitic limestone, dark grey cherty lime-
stone. In the Martonyi M-10 borehole, and on the surface in its
surroundings, platy marlstone, dolomitic marlstone with extra-
clasts (olistoliths?) can be also observed. The thickness of this
transitional formation is 20 m in the M-10 borehole and is un-
derlain by the Gutenstein Dolomite. Several samples yielded
middle Anisian (Pelsonian) conodonts (Kovács, pers. com-
mun.). This age and the similar lithology permit a correlation
with the middle Anisian-Ladinian black cherty limestone of
the Bódvarákó Formation cropping out in the Bódvarákó tec-
tonic window (Figs. 13; Kovács et al. 1989). In the following
description we will use the term transitional beds or Bód-
varákó Formation indicating the uncertain identity of these
Boundaries of the Martonyi Subunit
The study area is connected to the Darnó Zone, a broad, ma-
jor Cretaceous? to Miocene shear zone which separates the
Rudabánya Mts. from the Aggtelek Mts. to the west and from
the Szendrõ Paleozoic to the southeast (Fig. 1). Sinistral
strike-slip character of the zone was demonstrated by Zelenka
et al. (1983) using regional data and by Szentpétery (1997) by
the distribution of Oligocene-Lower Miocene formations. In
Fig. 2. Stratigraphic columns of the investigated area (NE Rudabánya Mts.), after Less (2000), Less et al. (1998) and Kovács et al. (1989)
and our own observation for the Martonyi Subunit.
358 FODOR and KOROKNAI
our paper we adopted the definition that the zone includes the
whole Rudabánya Mts. (for a review of the zone see Zelenka
et al. 1983; Less 2000).
The Martonyi Subunit is situated within the Darnó Zone
sensu lato. Its boundaries are always interpreted as tectonic
(Less et al. 1988). At its northeastern part, a NNE trending
fault is supposed to represent the boundary of the metamorphic
rocks toward Pannonian sediments (Less et al. 1988) (Fig. 3).
The fault certainly existed before the Pannonian, but its activi-
ty during or after the Pannonian is not clear; the contact may
be stratigraphical (Pelikán P., pers. commun.). The (pre-Pan-
nonian) fault may be a branch of the Darnó shear zone. At the
southeastern side of the Martonyi Subunit, the eastern bound-
ary fault juxtaposes non-metamorphic Mesozoic rocks against
the metamorphic Torna sequence; several branches of the
Darnó Zone cut through this eastern stripe of the non-meta-
morphic sequence (Balogh & Pantó 1952; Grill 1989).
At its southern tip the metamorphic Martonyi Subunit is in-
terpreted to thrust over the non-metamorphic Bódva Unit
(Less et al. 1988). The western boundary of the Martonyi Sub-
unit is represented by a N-S trending fault. Its subvertical dip
is supported by straight map view. Along the northwestern
boundary of the Martonyi Subunit, a Middle to Upper Triassic
metamorphic sequence is bounded by a steep fault, followed
by a narrow stripe of Lower Triassic rocks supposedly also in-
cluding the Permian evaporitic melange of the Bódva Unit
(Fig. 3). This fault may also be a branch of the Darnó Zone
and represent the thrust contact of the neoallochthonous Mar-
tonyi nappe sensu Grill (1989) and Less et al. (1988).
Other metamorphic sequences in the surroundings
Further west from the stripe of the Bódva Unit, the an-
chimetamorphic Bódvarákó sequence occurs in two tectonic
windows (Figs. 2, 3) (the Bódvarákó window sensu stricto
and the Kõrös-völgy window). The windows contain Guten-
stein Dolomite and black, cherty limestone (Bódvarákó For-
mation). Its age is middle Anisian-upper Ladinian (Kovács et
al. 1989). This deep water limestone is overlain by the Nyúlt-
kertlápa Beds, greenish grey slate, siltstone, occasionally
with limestone olistoliths. Although no stratigraphic age is
known, these beds are considered to be Upper Triassic (?)-
Jurassic (?) (Kovács et al. 1989). Pelikán (pers. commun.)
considers this rock to be the equivalent of the Lower Triassic
of the Bódva Unit, thus the metamorphic suite would end
with the Bódvarákó Formation. The rocks suffered anchizon-
al metamorphism (Árkai 1982). On the other hand, Kovács
(pers. commun.) considers this olistostromal formation to be
the equivalent of the Telekesoldal olistostromes of Late Ju-
The Bódvarákó windows and the surrounding (overlying)
Lower Triassic is bound by a narrow stripe of red marl and
claystone containing non-metamorphic Triassic olistoliths of
LadinianNorian age (Figs. 2, 3; Kovács 1986). On the basis
of pelagic olistoliths, this uppermost Triassic-Jurassic (?) sedi-
ment is assigned to the Bódva Unit.
Further to the west, the metamorphic sequence of the Esz-
tramos Hill built up by Anisian platform dolomites and lime-
stones (Gutenstein and Steinalm Formations), with tuffitic
(metarhyolite) intercalations (Turtegin 1997), crinoidal dykes
at the top, Middle Anisian to Ladinian basinal carbonates and
Carnian slate with limestone intercalations (turbidites?) (Figs.
2, 3). This classical Torna sequence forms an overturned limb
of a large anticline with SE vergency (Fig. 1b; Kovács 1986;
Less et al. 1998).
The steep NW boundary of the Esztramos Hill, the narrow
stripe of upper Triassic-Jurassic(?) marlstone may represent
strike-slip faults, namely the western branch of the Darnó
Zone (Less et al. 1998). Although the Bódvarákó windows
have locally steep strike-slip or normal fault boundaries, at
other sites they are overlain by relatively flat lying thrust faults
carrying the Bódva Unit.
Metamorphic sequences near Becskeháza and Hidvégardó-
Nagykõ (Figs. 1, 2) show stratigraphy similar to the Esztramos
Hill (Kovács 1986). At the latter locality, Norian Nagykõ
limestone represents the youngest Torna sediment (Fig. 2).
This Hidvégardó-Nagykõ sequence is structurally above the
Hidvégardó series (Grill et al. 1984), which has suffered only
slight anchimetamorphic or only deep diagenetic transforma-
tion and does not belong to the Torna Unit. Supposed equiva-
lents of all these metamorphic Torna sequences in Slovakia are
described by Mello (1979) and belong to the Turnaic nappe
sensu Mello (1997).
Structural observations and measurements were carried out
in the majority of outcrops in the Martonyi Subunit. Measure-
ments included bedding, several generations of foliation and
fold hinges. Fold axes were constructed from bedding or folia-
tion data using the Sswin software. Representative cross sec-
tions were constructed from outcrop-scale observations and
mapping along sections.
We also carried out a detailed, but not complete mapping of
the area. The main goals were to check formation boundaries
and existing dip values, to control the bedding-foliation rela-
tionship. We also investigated the upper boundary of Guten-
stein Dolomite because it has crucial importance in the evalua-
tion of stratigraphic and tectonic problems.
The observed deformation characteristics are grouped into
several deformation phases that will be described below. The
separation of these phases was essentially based on classical
overprinting criteria (e.g. folded foliation, etc.). In some places
this method could be applied very effectively (like at the Tor-
naszentandrás section), in other localities bad outcrop condi-
tions generally allow us only to identify a certain part of the
Carnian slate and the Pötschen Limestone also show a
well-developed, smooth, closely spaced foliation which is
DUCTILE DEFORMATION AND LITHOSTRATIGRAPHY OF MARTONYI SUBUNIT 359
Fig. 3. Geological map of the Martonyi Subunit and its surroundings. Compilation from Less et al. (1988) and own data.
360 FODOR and KOROKNAI
Fig. 4. Main structures, fold axes within the Martonyi Subunit (white). Dip values are partly after Less et al. (1988). Stereograms use
lower hemisphere projection, Schmidt-net. Faults, formation boundaries as on Fig. 3.
DUCTILE DEFORMATION AND LITHOSTRATIGRAPHY OF MARTONYI SUBUNIT 361
parallel to bedding (S
). The bedding-parallel nature of foli-
ation can be demonstrated by thick chert layers and sandy
limestone intercalations. In the Carnian slate this first S
liation is the dominant outcrop-scale structure and can be
termed as slaty cleavage. In the cherty limestone, S
nates in the Rednek and Mile Valley section, but can hardly
be observed/demonstrated in the central part of the Tor-
naszentandrás section (Fig. 3). The thick-bedded Gutenstein
Dolomite does not seem to show observable S
However, in the upper, cherty or calcareous dolomite beds
and in the transitional beds widely spaced, bedding-paral-
lel foliation occurs that can be regarded as weakly developed
cleavage (Pl. I: Fig. 1).
This cleavage is associated with strong flattening of the
rocks which was formed with a subhorizontal position of the
beds. No macroscopic or microscopic folding was observed to
be associated with S
foliation. In the Martonyi Subunit, S
foliation represents the only structural feature of the D
phase: Outcrop-scale F
Meter-size, close to almost isoclinal, upright folds (F
cur in outcrops of Pötschen Limestone and occasionally in
slate (Pl. I: Figs. 2, 3). The axial plane is subvertical, and is
parallel to the S
axial plane foliation. The axial plane, limbs
and fold axes are trending NE-SW (Figs. 3, 4). The fold axes
are generally subhorizontal attaining 10° plunge both to NE
and SW. The geometry of these folds is of chevron type
(Ramsay 1967, 1974). Limbs of folds are planar, while the
hinge zone is narrow, sharp or subangular (classification of
Twiss & Moore 1992). The hinge zone is thickened and the
limbs are strongly boudinaged, particularly in chert beds.
Chert layers often form decimetre-scale, third-order drag
folds on limbs of larger folds (Pl. I: Fig. 3). Thinning of fold
limbs can result in segmented fold hinge zones (rootless
folds) in chert (Pl. I: Fig. 4).
axial surface foliation
The axial plane of chevron folds is parallel to closely spaced
. These S
planes are always subvertical (dip >
80°), while the dip of bedding is about 4080° (Pl. I: Figs. 2, 3,
4). The centimetre-scale, zig-zag-like appearance of the bed-
ding planes is the consequence of the intersection of the well-
foliation and bedding (S
) (Pl. I: Fig. 2). Folia-
tion is often refracted in the more competent chert layers. In
the most deformed rocks, bedding cannot be determined, but
was completely transposed parallel to the S
axial surface foli-
ation. A prominent example of gradual transposition can be
observed at the Tornaszentandrás section, where S
seen on limbs of F
folds while only S
occurs in the most
strongly deformed core (Pl. I: Figs. 24). This transposition,
although not general, makes it difficult to separate the bedding
parallel first foliation (S
) and the axial plane foliation of F
) in many outcrops, from Tornaszentandrás up to the
folds together with the S
axial plane surfaces belong
to the second (D
) deformation phase. As described in the fol-
lowing chapter, structures of the D
phase dominate the map
view of the study area. Generally, chert was deformed in a rel-
atively more brittle way (e.g. boudinage), while limestones
show absolutely ductile rheology during deformation. The
ductile nature of the F
folds together with the S
gue for anchi to epizonal metamorphic conditions.
phase: Kink folds (F
foliation planes were frequently folded by small
folds with kink geometry. Such folds occur mainly in the Tor-
naszentandrás Slate or locally in marly Pötschen Limestone
beds. The hinge zone is sharp to subangular, limbs are planar.
Each pair of folds is composed of one shorter and two longer
limbs. Fold shape varies along axial planes and folds die out
within a few half-wavelength (Pl. I: Fig. 5). Fold axes general-
ly plunge subhorizontal or moderately to the NE or N, but lo-
cally are close to vertical (Fig. 4). The number of kink folds
varies in the different sections. They are lacking in the Mile
Valley, less frequent at Tornaszentandrás, and abundant in the
Nagy-Rednek Valley, where they often form larger, outcrop-
scale structures (Fig. 5c).
Although they seem to be geometrically rather similar, the
interpretation of these kink folds might be complex. Difficul-
ties arise mainly because of the variable plunge of axes and
dip of axial planes. The folds with subhorizontal axes may
simply represent disharmonic drag folds on limbs of larger F
folds. The shear sense deduced from the kink asymmetry is al-
ways in accordance with their position on the given fold limb.
The attribution of the kinks to the D
phase is also supported
by the parallelism of outcrop- to map-scale F
fold axes and
Folds with moderate to steep axes could belong to a slightly
younger deformation phase (D
). Oblique plunge may indicate
a strike-slip component of shortening, and thus the transpres-
sional character of the deformation. The separation of D
folds is, however difficult since fold axes do not form well-
separated classes but a continuous spectrum of dip and orien-
tation (Fig. 4).
In the Nagy-Rednek Valley, some small (dm-scale) folds
have (N)NW trending axes (Fig. 4, stereogram above bottom
left corner). These folds occur on NW trending beds of F
kink folds. We interpret that the F
kink folds refolded earli-
er, small F
folds; their original NE trending axes became
NW trending ones.
Map-scale structures (F
and cross sections
The most characteristic structure of the study area is the rel-
atively constant NE strike of beds (and parallel S
) and the
presence of NE trending stripes of different rock units. The
Pötschen Limestone is bordered by Carnian slate on both sides
forming a continuous belt from Tornaszentandrás to Málnás
Hill, while several belts of limestone and slate are present east
and southeast from the M-10 borehole (Fig. 3).
Dip values, cross sections and small-scale structures prove
that parallel distribution of formations reflect strong folding on
362 PLATE I
DUCTILE DEFORMATION AND LITHOSTRATIGRAPHY OF MARTONYI SUBUNIT 363
map-scale. Except for few locations, the dolomite always dips
under the overlying Carnian slate or Bódvarákó Formation.
Dip direction is always similar in closely located dolomite/
slate outcrops, but dip degree is frequently smaller in dolo-
mite. This different dip degree may simply reflect different po-
sition within the fold (e.g. approaching fold hinge in the dolo-
mite) or can be explained by other reasons (discussed later).
In the northeastern part of the area, two belts of dolomite
surround the slate and cherty limestone belts. This arrange-
ment is considered to be a syncline. Two sections at Tor-
naszentandrás show details of this structure (Fig. 5a). The
Ragya Creek crosses the village, and its northern side repre-
sents the type locality of the Carnian Tornaszentandrás Slate
(Less 1987). From the southeast, the section begins with Ani-
sian Gutenstein Dolomite outcropping both below the church
and on the southern side of the Ragya Creek. Bedding can oc-
casionally be determined using sedimentary lamination.
On the southwestern side of the Ragya Creek, black chert,
cherty or platy dolomite, thin-bedded limestone occur (in
scree) above the dolomite. This 1015 m thick sequence is fol-
lowed by the Tornaszentandrás Slate. The upper part of this
slate contains black limestone intercalations, overlain by the
alternation of limestone and marlstone. The slate gradually
changes to limestone, cherty limestone of the Pötschen Forma-
tion which form the central and northern part of the section. In
the Sáros Valley, the section can be continued more to the
NW. This part exposes the slate-limestone transition while
more to the northwest, scree of the slate occurs (Fig. 3).
In the dolomite, we did not observe any microscale struc-
tures which can be related to ductile deformation, only brittle
fractures occurred. Thin sections already showed that internal
deformation of dolomite beds did not modify the shape of oo-
ids (Less Gy., pers. commun.).
At the northwestern end of the section (near to the pub and
in the Sáros Valley) the transition between the slate and
cherty limestone dips to the SE at 4560° (Figs. 4, 5a). The
southeastern part exposes dolomite, the overlying slate and the
transition to cherty limestone dipping 4560° to the NW or
WNW. In that way the slate and its upper transition clearly
forms a syncline (F
), that was already described by Vitális
(1909). Because the dolomite dips concordantly under the
slate, they seem to be folded together. The youngest member,
the cherty limestone occurs in the core of this syncline. The
bedding versus S
relationship indicate two northwest-ward
and two southeast-ward younging parts of the Ragya section at
Tornaszentandrás. This pattern suggests two decametric, close
synclines and one anticline, while F
folds of a smaller order
also occur (Fig. 5a).
We could follow this F
syncline up to the Siket Valley to
the SW (Figs. 3, 4). Here the SE limb is truncated by a steep
fault which puts steeply southeast-dipping dolomite against
Carnian slate. The thickness of the dolomite belt decreases
southwestward, indicating its tectonic truncation. This contact
is interpreted as a reverse fault. The dip values of the follow-
ing slate suggest the presence of two synclines and one anti-
cline in the Siket Valley. The dolomite core of the anticlines
can be followed to the western slope of the Pizondor, where a
N-S trending fault truncates the folded structure. This fault can
be traced southward, across the Mile and Nagy-Rednek sec-
tions (Figs. 3, 5).
Mile Valley section
The Mile section is running NW-SE along the upper part of
the Mile Valley (Fig. 5b). The importance of this section that it
shows the best outcropped cross-section through the dolomite.
Due to easily observable bedding, a large open anticline can be
demonstrated. Its NW limb is tectonically reduced and is in
contact with Carnian slates. The fold axis is parallel to folds
near Tornaszentandrás and represents the same F
phase (Fig. 4). The only difference is that the interlimb angle
is larger (~100°), the hinge zone is subrounded, thus the fold
style is far from a chevron fold.
On the southeastern side the dolomite is followed by the
slate. The transition is represented by 5 m thick cherty lime-
stone which was interpreted by Less et al. (1988) as Pötschen
Limestone. The close geometric situation to dolomite makes it
probable that this rock is the previously described transitional
beds. Further to the southeast, the Carnian slate is overlain by
Norian cherty limestone which forms a syncline (Fig. 5b).
The anticline in dolomite is cut by a fault which is sub-par-
allel to the valley. However, the fold axis can be projected to-
ward another occurrence of dolomite, near the boreholes Mar-
tonyi M-9, -10.
This section runs parallel to the Mile section, further to the
SW in the Nagy-Rednek Valley. At the northwestern end of
the section, the Carnian slate is in tectonic contact with east-
dipping Gutenstein Dolomite (Fig. 5c). The dip of the dolo-
mite is gentle but becomes steeper at the southeastern end of
the 300 m long exposure. The slight change in dip degree and
orientation is related to folding. Like in the Mile section, this
fold can be attributed to F
folds, although the shape is open
and the hinge is subrounded. The Martonyi M-9 borehole pen-
etrated 150 m of dolomite from the bottom of the valley and
reached the deepest stratigraphic level within the Martonyi
Subunit. The borehole Martonyi M-10 has reached the Guten-
stein Dolomite which is covered by the 20 m thick transition-
Plate I: Structural elements in the Martonyi Subunit. See Fig. 3 for
locations and Fig. 5 for position on sections. Fig. 1. Bedding-paral-
cleavage in cherty dolomite, north of Pizondor. Fig. 2. Close,
fold at Tornaszentandrás, church hill. Fig. 3. S
plane foliation, isoclinal F
folds (Tornaszentandrás, church hill).
Fig. 4. Transposition of bedding (S
) into S
foliation, and related
rootless folds in cherts (arrow), south of Tornaszentandrás. Fig. 5.
Kink folds in marlstone, south of Tornaszentandrás, in the Sáros
valley. Fig. 6. aPanoramic view of the main tectonic units in the
NE Rudabánya Mts. Note higher topographic (and tectonic?) posi-
tion of Martonyi Subunit over the Bódva and Bódvarákó Units.
View from west, from the road Perkupa-Bódvaszilas; bInterpreta-
tive drawing for Fig. 6a.
364 FODOR and KOROKNAI
Fig. 5. Cross sections in the Martonyi Subunit, locations on Fig. 3. Note different scale at section (a). No vertical exaggeration.
DUCTILE DEFORMATION AND LITHOSTRATIGRAPHY OF MARTONYI SUBUNIT 365
al beds. This is covered by folded Carnian slate, then grey
cherty limestone follows. 80 m southward the slate dips below
the younger cherty limestone. Slate-marlstone-sandstone con-
stitute the remaining 250 m.
Both the slate and limestone form close to tight folds with
subvertical axial plane (Fig. 5c). Two anticlines and two syn-
clines can be detected in the slate while one syncline is sup-
posed in the limestone. Here, SE-vergent overturned beds also
occur along a 20 m long part. However, this local feature is not
convincing to attribute vergency for the folding (in contrast to
Less et al. 1998). The limestone mainly shows layer-parallel
), subvertical S
is only rarely seen. On the other
and not only S
foliation occurs in the slate. The
slate is frequently deformed by cm to meter-scale, asymmetric,
disharmonic kink folds. The axes of kinks are dipping N to NE
with moderate plunge (Fig. 4).
The first S
foliation was most probably formed due to
deep tectonic burial (e.g. thrusting) representing the first D
event in the study area (Fig. 6a). The K-white mica b
suggest transitional medium/high pressure conditions (Árkai
& Kovács 1986). Corresponding loading was produced by
higher nappes of undiscussed origin. This first order nappe
stacking probably occurred during the subduction of the Meli-
ata oceanic branch of the Neotethys. During subduction, the
Martonyi Subunit was incorporated into the nappe pile from
the thinned continental crust, while the Bódvarákó sequence
might represent the close vicinity of the oceanic crust.
In accordance with Grill (1989), we did not observe any
shear criteria giving a well-defined direction of tectonic trans-
port of first order nappe stacking within the Martonyi Subunit.
The only indication comes from an outcrop from the nearby
Esztramos Hill showing S-vergent small intrafoliational folds
(Csontos & Hips 1997; Less et al. 1998). In spite of this weak
indication, we have no conclusion up to now on the direction
of primary nappe stacking and subduction from outcrops in the
Rudabánya Mts. Clear indication of vergency cannot be de-
duced from D
either, because the F
folds are upright without
any prominent asymmetry. NW dipping, steep foliation (S
described by Less et al. (1998) represent, in fact, exceptions
and cannot be used for vergency determination. The southeast-
ern vergency at Tornaszentandrás, reported by Hók et al.
(1995) also lacks convincing field evidence.
Because of the lack of characteristic synkinematic minerals,
we cannot unambiguously decide whether D
ated with higher P and/or T values of metamorphism.
Spatial and temporal model for D
Cross sections and dip data show that map-scale folds have
smaller tightness and larger bluntness in dolomite than in the
slate-cherty limestone couplet. One consequence of different
fold shape through the stratigraphic section is the detachment
of Pötschen Limestone and probably the slate from the dolo-
mite base. This detachment surface can be located close to the
upper boundary of the dolomite, in the marly Bódvarákó For-
mation. Marly layers of these beds could form duplexes at or
ductily flow into hinge zones of F
folds (stage D
, Fig. 6b).
Such thickening can be suspected at the anticline hinge near
the Martonyi M-10 borehole, (the only well-preserved hinge
zone in Bódvarákó Fm.) where the thickness of these beds
seems to be larger than usual.
De Sitter (1958) showed that chevron type folds lock up
when folds attain a 60° interlimb angle. This value can be
somewhat different, if frictional properties between layers
change (Ramsay 1974). In upright folds, this limit may repre-
sent 50°60° of fold limb dip. Additional shortening (if it oc-
curs) should be accommodated by other type of structures.
Gray & Willman (1991) observed, that further steepening of
fold limbs is due to penetrative horizontal flattening and verti-
cal lengthening of folds which can be observed in any scale
and reflected by diverse strain markers. Development of folia-
tion along the axial plane of such flattened chevron folds start-
ed only at this flattening stage and not earlier.
This observation can be applied in the interpretation of
structures near Martonyi. In the dolomite, dip values rarely ex-
ceed 4550° which is close to the natural limit of fold limb
dip. Up to this stage, folding is accommodated by flexural
folding, which is possible even in the rigid dolomite. Further
shortening by fold-flattening resulted in steepening of fold
limbs only in the slate and particularly in the Pötschen Lime-
stone which are suitable to suffer such a pervasive ductile de-
formation at this low-grade metamorphic stage. The Pötschen
Limestone in cores of synclines suffered the highest deforma-
tion, and shows the steepest fold limbs and the appearance of
axial plane foliation (as was demonstrated at the Tor-
naszentandrás section, Fig. 5a). Horizontal flattening locally
resulted in complete parallelism of S
The lack of S
foliation, the relatively moderate dip of fold
limbs in the dolomite suggest that fold flattening (D
did not occur in this rigid lithology. The additional shortening
can be accommodated by brittle faulting of the dolo-
mite. Relatively steep reverse or reverse-strike-slip faults
could break through fold limbs in dolomite (Fig. 6c). These
faults can bend to a subvertical, layer-parallel position in the
Pötschen Limestone. Such steep faults were observed at some
locations (particularly in the NW part of Mile and Rednek sec-
tions and at the Nagy-Oldal) and are supposed at other locali-
ties. Their steep dip is supported by straight map view (inter-
section of faults and topography). Different deformational
mechanism across the folds may account for certain strain par-
titioning (horizontally and vertically) during the D
The presence of kinks with moderate to vertical axes (D
phase) may suggest oblique shortening with respect to the F
fold axes (Fig. 6c). This oblique shortening could also be asso-
ciated with oblique-slip reactivation of steep faults cutting
through the F
folds. This transpressional deformation could
occur at shallower crustal depth, at the transition of the brittle-
It is difficult to determine the age of the ductile deformation
phases. From regional geodynamic models (e.g. Grill et al.
366 FODOR and KOROKNAI
1984) one can speculate late Early Cretaceous age for D
phase, while older D
(nappe stacking) may be of Late Juras-
sic? to Early Cretaceous age.
Position of the metamorphic units with respect to non-meta-
The northwestern contact of the metamorphic Martonyi
Subunit toward the Bódva Unit is represented by a well-con-
strained, moderately steep fault dipping to the southeast, be-
neath the metamorphic unit. Because the metamorphic rocks
are at higher topographical position (Pl. I: Fig. 6), they were
probably thrust (obliquely?) onto the Bódva Unit (Less 1998).
The similar topographical position of the Torna versus the
Bódva units occurs at the southern tip, but the dip of the
boundary fault is not clear.
Along the western boundary fault, near the Fehér-kõ, small,
isolated lenses of Middle Triassic carbonates occur between
metamorphic upper Triassic (Martonyi) and non-metamorphic
Lower Triassic (Bódva) rocks (Less et al. 1988) (Fig. 3; Pl. I:
Fig. 6. Schematic structural evolution of the Martonyi Subunit. See discussion in the text.
DUCTILE DEFORMATION AND LITHOSTRATIGRAPHY OF MARTONYI SUBUNIT 367
Fig. 6). These lenses can be regarded as strike-slip duplexes.
Displaced structures (folds, faults) within the Bódva Unit indi-
cate its sinistral slip (Fig. 3).
The southeastern boundary fault can be detected on the
Nagy-Rednek section which terminates in non-metamor-
phosed rocks belonging to the Rudabánya ore belt (Pantó
1956). Although Balogh & Pantó (1952) interpeted this belt as
a thrust zone, more recent data suggest strike-slip motion
(Grill 1989). The zone consists of Middle Triassic limestone
and ankeritic dolomite lenses embedded in Permian-Lower
Triassic siltstone-evaporite matrix (Figs. 1b, 3). The lens-like
map view of Anisian carbonates suggests a strike-slip origin
for the anastomosing fault branches within the Darnó Zone.
Further to the south, near Rudabánya, other evidence support
this interpretation. Among others, Pantó (1956) observed hori-
zontal slickenlines on parallel fault planes in the Rudabánya
ore body. Szentpétery (1997) indicated strongly tilted, sinis-
trally displaced Oligocene-Eggenburgian sediments.
In summary, our observations show that the Martonyi Sub-
unit is bounded by steeply or moderately dipping faults from
each side. These tectonic contacts represent sinistral strike-
slip or oblique-reverse faults (Figs. 3, 6d). We agree with
Less (2000) that the recent position of the metamorphic unit
is the result of strike-slip motion along the Darnó Zone and,
at least a slight allochthonity over the non-metamorphic
Bódva Unit. However, we cannot unambiguously decide if
the metamorphic unit represents a thin, flat lying nappe over
the Bódva (or other ?) Unit (like e.g. in the Hidvégardó-3
borehole, Kovács 1986) or just a transpressional, steep-sided
pop-up structure arising from below the Bódva Unit (Fig.
6d). The age of this brittle transpression may start in the lat-
est Cretaceous. The strongly deformed Eggenburgian and
only slightly fractured Pannonian indicate Early to Middle?
Miocene transpression. Several branches of the Darnó Zone
could be reactivated as a normal (or normal-oblique) fault after
the Pannonian, during Late MiocenePliocene (trans)tension
Stratigraphic and paleogeographic consequences
Tectonic/stratigraphic position of the Gutenstein Dolomite
Our observations show that the dolomite is generally in
contact with the Tornaszentandrás Slate. More precisely, the
thin suite of the Bódvarákó Formation can be demonstrat-
ed at a number of places. This sequence may represent the
sudden transition from platform to basinal depositional set-
ting and the whole dolomite-slate sequence could be inter-
preted as continuous.
This sedimentological-lithostratigraphical observation is
also supported by structural data. When the dip of the dolomite
can be established, it always dips below (toward) the slate.
The dip degree of both dolomite and slate are similar at the
Tornaszentandrás section (Fig. 5a). However, at several locali-
ties the slate dips more steeply than the dolomite but in the
same direction. Such a place can be found SE from the Mile
Hill, on the Nagy-Oldal and along the Nagy-Rednek and Mile
Valley sections. This sudden change in dip degree is the conse-
quence of faulting which is related to shortening during the
late stage of D
(see previous chapter). This faulting, however,
did not essentially disturb the stratigraphy.
Metamorphism of the dolomite
foliation of the cherty limestone represents
the axial plane of the map-scale synclines. This geometry sug-
gests that the map-scale syncline and outcrop-scale F
represent the same D
deformation phase. The ductile behav-
iour of the F
folds in the core and the total transposition of the
bedding demonstrate that the folding and S
formed at least in anchizonal metamorphic conditions. The ex-
act physical conditions cannot be determined but such ductile
flow of limestone indicate temperatures over 200 °C.
Map analysis and cross sections clearly suggest that the
Gutenstein Dolomite underwent F
folding. Consequently, it
suffered the same metamorphism during folding. This tectono-
metamorphic evolution contradicts the previous interpretation
of Less et al. (1988), Grill et al. (1984), Grill (1989) that con-
sider the Gutenstein Dolomite as a non-metamorphic rock be-
longing to the Bódva Unit.
This idea was partly based on the observation that original
sedimentological features of the dolomite were not significant-
ly affected by any ductile deformation processes. We agree
with this observation, but the lack of ductile deformation does
not exclude metamorphism of the rock. Considering the rheo-
logical properties of dolomite in anchi-epizonal conditions,
ductile (internal) deformation (e.g. foliation) will not appear in
contrast to limestones (Fig. 6a). Rheological differences can
also explain the lack of both S
cleavages in dolomite.
It is also supported by the observation that a small lithological
change (larger marl content) permits the development of incip-
ient foliation at the top of the dolomite or in the transitional
On the other hand, the suggested evolution of F
gives an explanation for the lack of S
foliation. The formation
axial plane foliation is expected only at the final stage of
phase). This shortening was transferred to
faulting in the dolomite (Fig. 6c).
Consequences for lithostratigraphy of Torna units
Less (1981, 2000) defined the metamorphic Torna sequence
as containing the Anisian platform limestone (Steinalm Fm.).
The lack of the Steinalm Limestone in the Martonyi Subunit
seems to contradict its classification to the Torna Unit. How-
ever, the Bódvarákó sequence shows that platform limestone
could be replaced by pelagic sedimentation already in the mid-
dle Anisian (Kovács et al. 1989). If our structural interpreta-
tion is correct, the stratigraphy of the Martonyi Subunit is clos-
er to the Bódvarákó than to the classical Torna sequence
(e.g. Esztramos Hill). The middle Anisian platform and late
Anisian-Ladinian basinal carbonates are replaced by a very
thin suite of (dolomitic) marlstone and cherty limestone which
may be the equivalent of the deep water cherty limestone of
the Bódvarákó Formation. Both formations can indicate fast
subsidence at the margin of the carbonate platform, probably
close to the rift axis.
368 FODOR and KOROKNAI
However, the clear identity of the Martonyi and Bódvarákó
sequences cannot be declared. The middle Anisian-Ladinian
Bódvarákó Fm. is covered by the upper Triassic-Jurassic (?)
Nyúlkertlápa Beds or, by an alternative interpretation, directly
cut by a thrust plane (Pelikán P., pers. commun.).
On the other hand, the metamorphic degree of the two se-
quences is different (Árkai 1982). The Martonyi sequence suf-
fered lower epizonal metamorphism, while the Bódvarákó
window shows only anchizonal metamorphism. The deforma-
tion style of the two units seem to be different since the F
folds and S
foliation are missing from the Bódvarákó win-
dows. In any case, direct identification of the Bódvarákó with
the Martonyi sequence does not work.
The assignment of the Bódvarákó Unit to any first order tec-
tonic unit is not clear. The early subsidence, anchimetamor-
phic character led Kovács et al. (1989) and Less (2000) to as-
sign it to the Meliata Unit (sensu lato) (Fig. 2). In our paper we
suggest that this window has similar stratigraphy to the Marto-
nyi Subunit, so it may belong to the Torna Unit, too.
Our observations strengthen the conclusion of Less et al.
(1998, 2000) that the Torna Unit (and the metamorphic units in
general) incorporates diverse Triassic successions, which were
formed in different paleogeographical positions on the attenu-
ated continental crust. The Bódvarákó and the Martonyi se-
quences were probably closer to the rift axes, and their fast
subsidence may directly reflect the onset of rifting during the
earlier part of the Middle Anisian. The Esztramos, Szent-
János-hegy (Becskeháza) indicate later subsidence of the car-
bonate platform (late Middle and Late Anisian, respectively),
due to minor thinning of the continental crust, located far from
the rift axes.
Structural observations and mapping showed that the meta-
morphic sequence near Martonyi consists of Gutenstein Dolo-
mite, thin transitional beds (Bódvarákó Formation) to Car-
nian slate and cherty Pötschen Limestone. The whole
sequence suffered intense ductile deformation with two phases
of folding, associated with anchi- to epizonal metamorphism.
First, the layer-parallel S
cleavage developed due to tectonic
overburden of higher nappes. Second, upright chevron-type
folds deformed the complete sequence. Detachment along the
upper boundary of rigid dolomite probably occurred. During
the final stage of this shortening, fold limbs flattened in the
core of synclines where an axial plane foliation (S
formed. This final horizontal flattening was accommodated by
steep faulting in the dolomite. In this way, strain partitioning is
demonstrated within the sequence with different rheological
properties: shortening is accommodated by intense folding and
axial plane foliation in incompetent lithologies, and by brittle
faulting in competent lithologies. Structural style depends also
on position across the F
folds. The D
phase is marked by
kink folds with oblique axes, probably formed during
transpression, at the transition of brittle-ductile field. The
metamorphic unit was slightly or largely emplaced over non-
metamophic units (Bódva) after metamorphism, connected to
transpression along the Darnó Zone.
Because Gutenstein Dolomite suffered D
folding, it is also
a metamorphic rock, forming the normal stratigraphic base of
the sequence. The lack of Steinalm Limestone is similar to the
Bódvarákó sequence. These two units show that the Torna
Unit incorporated different Triassic sequences: all were
formed on thinned continental crust but in different paleogeo-
graphical positions across the passive margin(s) of the Neot-
ethyan Meliata oceanic branch.
Acknowledgements: The field work was supported by the re-
search project OTKA No. T 019431 of S. Kovács and T
023880 of Gy. Less. Field assistance from and discussion with
Sándor Kovács and György Less were essential for under-
standing previous ideas about the area and stimulating new
thoughts. Field discussion with D. Plaienka (Bratislava) also
contributed to new interpretations. Sándor Kovács made valu-
able corrections on preliminary versions of the manuscript.
Comments of Jozef Hók, Sándor Kovács and an anonymous
reviewer also contributed to the improvement of the text and
figures. Discussion with Pál Pelikán and László Sásdi also
helped to improve the text. This work could not be possible
without the hospitality of local villagers, particularly those of
Tornabarakony. All kinds of help and support are acknowl-
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