GeolCarp_Vol67_No6_595

GEOLOGICA CARPATHICA

, DECEMBER 2016, 67, 6, 595 – 605

doi: 10.1515/geoca-2016-0037

www.geologicacarpathica.com

An integrated paleomagnetic and magnetic anisotropy

study of the Oligocene flysch from the Dukla nappe,

Outer Western Carpathians, Poland

DÁNIEL KISS

1,2,3

, EMŐ MÁRTON

and ANTEK K. TOKARSKI

Eötvös Loránd University, Department of Geophysics and Space Science, Budapest, Hungary; dan.kiss.91@gmail.com

Geological and Geophysical Institute of Hungary, Paleomagnetic Laboratory, Budapest, Hungary; paleo@mfgi.hu

University of Lausanne, Institute of Earth Sciences, Lausanne, Switzerland (from September 2015)

Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Kraków, Poland; ndtokars@cyf-kr.edu.pl

(Manuscript received December 23, 2015; accepted in revised form September 22, 2016)

Abstract: The Dukla Nappe belongs to the Outer Western Carpathians, which suffered considerable shortening due to the

convergence and collision of the European and African plates. In this paper we present new paleomagnetic and magnetic

anisotropy results from the Polish part of the Dukla Nappe, based on 102 individually oriented cores from nine geo-

graphically distributed localities. Susceptibility measurements and mineralogy investigations showed that paramagnetic

minerals are important contributors to susceptibility anisotropy (AMS). The AMS fabrics are related to deposition/

compression (foliation) and weak tectonic deformation (lineation). The AARM fabric, that of the ferrimagnetic minerals,

seems to be a less sensitive indicator of tectonic deformation than the AMS fabric. The inclination-only test points to the

pre-folding age of the remanent magnetizations. Seven localities exhibit CCW rotation, a single one shows CW rotation.

The CCW rotated paleomagnetic directions form two groups, one showing large, the other moderate CCW rotation.

Previously published paleomagentic directions from the Slovak part of the same nappe exhibit smeared distribution

between them. The declination of the overall-mean paleomagnetic direction for the Dukla nappe is similar to those

observed in the neighbouring Magura and Silesian nappes, but it is of poorer quality.

The AMS lineations at several

localities are deviating more to the west from the present north than that of the local tectonic strikes. A possible expla-

nation for this is that the AMS lineations were imprinted first, probably still in the Oligocene, while the sediments were

soft (ductile deformation) and the folding and tilting took place during the CCW rotation.

Keywords: Outer Western Carpathians, Dukla nappe, Oligocene, flysch, paleomagnetism, anisotropy of susceptibility,

anisotropy of remanence.

Introduction

The Carpathians belong to the European Alpine system, which

was formed during the convergence and collision of the Euro-

pean and African plates. They have an arcuate shape that

extends over 1300 km from the Danube valley in Eastern

Austria to the Danube valley on the border between Romania

and Serbia (Fig. 1). Diachronous collision of the two plates

started in the Late Jurassic and has continued to the Present.

Fragments of continental blocks between the two plates were

displaced and rotated in the process of collision and initiated

folding/trusting and nappe transport in the present Outer

Carpathians during the Tertiary (Oszczypko 2006 and refe-

rences therein). The result is a considerable shortening com-

pared to the original width of sedimentary basins (e.g.,

Nemčok et al. 2000).

The process of the shortening in the Outer Western Carpa-

thians has been investigated with paleomagnetic and magnetic

anisotropy methods. Koráb et al. (1981) published paleo-

magnetic results from the Slovak part of the Dukla Nappe

(Fig. 2) suggesting moderate CCW rotation. They confined

their study to localities where the local strike correlated with

the general tectonic trend of the nappe. Their results repre sent

red pelitic sediments (Submenilite Beds) of early to middle

Eocene age, as the grey sediments sampled by them did not

yield a stable paleomagnetic signal. Márton et al. (2009)

studied the paleomagnetism and the magnetic aniso tropy of

the Paleogene (subordinately Lower Miocene) grey clay, silt

and mudstones from the Magura and the Silesian Nappes.

Their results pointed to a general 50° CCW rotation of the

Magura nappe and of the central and eastern segment of the

Silesian nappe, and somewhat larger for the western part of the

Silesian Nappe), which must have taken place after the Oligo-

cene (Márton et al. 2016). The AMS (anisotropy of magnetic

susceptibility) measurements revealed that the magnetic folia-

tion was due to compaction and the magnetic lineation to weak

compressional deformation. The Czech part of the Outer

Western Carpathians was studied extensively with magnetic

anisotropy, which revealed that the magnetic fabrics are due to

weak tectonic deformation or compaction and sedimentary

transport (for a summary see Hrouda et al. 2009).

This study presents new paleomagnetic and magnetic

anisotropy results of the Oligocene flysch from the Polish part

of the Dukla Nappe. The paleomagnetic directions were

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GEOLOGICA CARPATHICA

, 2016, 67, 6, 595 – 605

obtained with standard methods, and so were the low field

magnetic susceptibility anisotropy (AMS) and the anisotropy

of anhysteric remanent magnetization (AARM) measure-

ments. Supplementary mineralogy investigations also were

carried out to determine the carrier of the remanence and the

contributors of the ferri and paramagnetic minerals to the

AMS fabric. Finally the data were interpreted in the terms of

the rotational and strain history of the nappe.

Geological background and sampling

Geological background

The Western Carpathians have been subdivided into two

parts, the Inner Carpathians and the Outer Carpathians, which

are separated by the Pieniny Klippen Belt. The Outer Carpa-

thians contain the sediments of several basins that were located

between Africa and Stable-Europe during the Cretaceous

and Paleogene. The present-day tectonic features were

formed mostly in the early-middle Miocene as a result

of the thrusting and folding during the convergence and

collision of the ALCAPA and the European plates (Oszczypko

2006).

The Western Outer Carpathians are a north-verging thrust-

and-fold belt composed largely of Lower Cretaceous to Lower

Miocene flysch, but Upper Jurassic and Lower Cretaceous

volcanics and carbonates are also present (e.g., Kováč &

Plašienka 2002). The studied, Polish part of the belt comprises

five rootless nappes that are completely detached from their

basement and form an accretionary wedge with northern ver-

gency. The nappes are the following, from south to north:

Magura, Dukla, Silesian, Subsilesian and Skole (Fig. 2). They

are of different lithostratigraphic composition and structure.

The wedge is flatly thrust over the Miocene sediments of the

Carpathian Foredeep. It is 70 – 80 km wide on the surface and

in the south it reaches the depth of 15 – 20 km (Tomek 1993;

Tomek & Hall 1993). In the traditional view, the wedge started

to form in the Oligocene (Pescatore & Ślączka 1984; Roca et

al. 1995; Oszczypko 2006). More recently synsedimentary

deformation studies (Swierczewska & Tokarski 1998) sug-

gested that deformation in the Magura Nappe started in the

Eocene and a similar conclusion was reached from balanced

cross sections (Nemčok et al. 2006).

The present study deals with the Polish part of the Dukla

Nappe, which continues in Slovakia and in Ukraine and a large

part of it is situated below the Magura Nappe (Ślączka et al.

2005). The Magura and Silesian nappes (Fig. 2) are composed

Fig. 1. The tectonic subdivision of the Carpatho–Pannonian region. The yellow area of the Outer Carpathians characterized by Tertiary nappe

transport and the arrows refer to the rotation of the microplates (after Márton et al. 2009). The study area is indicated with a rectangle (for more

precise location see Figs. 2 and 3).

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PALEOMAGNETIC AND MAGNETIC ANISOTROPY STUDY OF OLIGOCENE FLYSCH FROM DUKLA NAPPE

GEOLOGICA CARPATHICA

, 2016, 67, 6, 595 – 605

of large scale folds and thrust sheets whereas the Dukla and

Skole nappes are characterized by imbricated thrusts (e.g.,

Mastella 1988). The former nappe shows widespread presence

of olistostromes (Cieszkowski et al. 2009). The sequence of

the Dukla Nappe starts with Cretaceous sediments and is

terminated by the Oligocene Krosno beds. The latter are made

of calcareous sandstones and calcareous claystones (Ślączka

et al. 2005).

Paleomagnetic sampling

Based on previous experience with the Outer Western Car-

pathian Paleogene, the Oligocene Krosno beds were selected

for the investigations in the Dukla nappe. The mudstone mem-

bers of the Krosno beds, as documented by the results from the

Silesian Nappe (Márton et al. 2009), have favourable lithologi-

cal properties for paleomagnetic as well as magnetic anisotropy

studies. This formation was sampled at nine geo graphically

distributed localities (102 individually orien ted samples) dis-

tributed over the Polish segment of the nappe. At eight loca-

lities claystones/mudstones were drilled and at one locality

(locality 1) siltstones (1a) and sandstones (1b) were also

sampled (Fig. 3). The samples were drilled with a portable

drill and oriented in situ with a magnetic compass. For each

sampled bed, the azimuth and angle of the dip was recorded.

Methods

Paleomagnetic measurements

The samples drilled and oriented in the field were cut into

standard-size specimens. The natural remanent magnetization

(NRM) of each specimen was measured in the natural state

using JR-4 and JR-5A spinner magnetometers. One specimen

per sample was stepwise demagnetized with the alternating

field (AF) or with the thermal method till the NRM signal was

lost. It was usually the AF method, which yielded better

results. This was due to the carrier of the remanent magneti-

zation, which was magnetite, while the decomposition on

heating of the invariably present pyrite resulted in spurious

magnetization seriously distorting the NRM signal from

400° C on. The demagnetization curves were analysed for

linear segments and the components decaying towards the

origin were evaluated to define the locality mean paleomag-

netic directions.

Anisotropy of magnetic susceptibility (AMS)

AMS provides information about the magnetic fabric.

Studying the magnetic fabric has the potential to unravel, for

example, the strain history of the rock and/or sedimentary

Fig. 2. The location and structure of the Outer Western Carpathians (dark) (the Subsilesian Nappe — located at the northern boundary of the

Silesian nappe — is not indicated).

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GEOLOGICA CARPATHICA

, 2016, 67, 6, 595 – 605

transport directions. Depending on the value of the mean sus-

ceptibility, AMS can be sensitive to different groups of mine-

rals. If the susceptibility is below or in the range of 10

-4

[SI]

both the ferrimagnetic and the paramagnetic minerals (e.g.,

pyrite, limonite and Fe bearing clay minerals) can be impor-

tant contributors to the AMS fabric.

The intensity and orientation of the magnetic fabric is

expressed by a second-rank symmetrical susceptibility tensor.

Geometrically it is represented by an ellipsoid with the

max

≥ k

int

≥ k

min

principal susceptibilities. In this terminology

max

is referring to the magnetic lineation direction and k

min

refers to the pole of the magnetic foliation (terms lineation and

foliation used in the following refer to the magnetic fabric).

From the principal directions several parameters can be

calculated. In this study we used the following parameters (see

Tarling & Hrouda 1993): degree of anisotropy (P = k

max

/ k

min

degree of foliation (F = k

int

/ k

min

), degree of lineation (L = k

max

/ k

int

)

and mean susceptibility (k

= ( k

max

+ k

int

+ k

min

) /3).

The AMS fabric of every individually oriented sample was

determined from low field susceptibility measurements in

15 positions with a KLY-2 Kappabridge (Jelínek 1973, 1980).

The susceptibility tensor was computed from the results by

a program written by Bordás (1990) based on Jelínek (1977).

The locality mean tensors were evaluated using the Anisoft 4.2

program (Jelínek 1978; Hrouda et al. 1990; Chadima & Jelínek

2008).

Anisotropy of anhysteric remanent magnetization (AARM)

The AARM provides information about the ferromagnetic

fabric without the effect of para- and diamagnetic minerals.

During the measurement the specimens are firstly demagne-

tized then magnetized in a given orientation and finally the

remanent magnetization is measured. These steps are repeated

in several positions and the results are evaluated in a mathe-

matically analogous way to the susceptibility tensor. The ten-

sor is also represented by an ellipsoid and the same parameters

(P, F, L, k

) are calculated.

During this study, the AARM was measured on specimens,

which had not been thermally treated before. The specimens

were demagnetized (LDA-3A demagnetizer, at 100 mT AF)

and magnetized (AMU-1A anhysteric magnetizer, at 80 mT

AF and 50 µT DF) in 12 positions, and the remanent magneti-

zation was measured on JR-4 spinner magnetometer after each

magnetization step. The data were computed with the AREF

program (Jelínek 1993) and the locality means were evaluated

with Anisoft 4.2 (Jelínek 1978; Hrouda et al. 1990; Chadima

& Jelínek 2008).

Mineralogy and photo-statistics

During the study magnetic mineralogy experiments, IRM

(Isothermal Remanent Magnetization) acquisition and thermal

demagnetization of three-component IRM accompanied by

the susceptibility monitoring were carried out. These methods

are suitable to investigate sediments, they are based on the

different coercivites and unblocking temperatures of the mag-

netic minerals (Lowrie 1990).

Thin-sections made from some samples were the subjects

for a basic petrography. Rock forming minerals were

identified and micas and opaque accessories were observed.

Polished sections were prepared from a claystone/

mudstone and a siltstone sample and ore minerals and their

orientation observed. Two samples with similar grain sizes

were used for XRD (X-Ray Diffraction) measurements to

identify which minerals are present in larger concentrations

than 5 %.

Oriented thin-sections cut along the bedding plane were

used for photo statistics to unravel the statistical alignment of

elongated particles. This method has been used previously to

determine sedimentary transport direction in ignimbrites

(Capaccioni & Sarocchi 1996; Capaccioni et al. 1997; Biró et

al. 2015). The x and z directions were marked on the thin

sections, so the comparison between the anisotropy principal

directions and any grain fabric orientation direction was

possible. For the photo-statistical grain shape analysis the

scanned thin-sections (scanned with 2000 dpi resolution) were

processed in ENVI EX 4.8 and ESRI ArcGIS 10.0 Desktop

environment. ENVI EX 4.8 was used for automatized detec-

tion of grains based on spatial and spectral features. On the

scanned images individual minerals (especially mica) are not

distinguishable so microphotos were also made. As the

contrast was too small for the automatized method, distin-

guishable micas were digitized manually. The azimuth of the

a-axis and the elongation (a-axis / b-axis) of each grain-derived

polygon were calculated using the Zonal Geometry as Table

Tool function of ESRI ArcGIS 10.0. Further processing of

the attributes related to individual grains was done using

GEOrient 9.5 software.

Fig. 3. The Polish part of the Dukla Nappe, with the localities and the

locality mean AMS lineation directions (at locality 1 directions are

enlarged for better visibility and at locality 2 locality mean direction

cannot be given).

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Results

Paleomagnetism

The paleomagnetic directions with statistical parameters

were determined for eight localities (Table 1). The locality

mean paleomagnetic directions are highly scattered before

tilt corrections (Fig. 4a). After correction for local tilts, the

inclinations become less scattered than before, the inclina-

tion-only test is positive at 100 % for the seven CCW rotated

localities (k

/ k

= 3.95 with the limit = 2.69 and I° = + 49.7°) and

for all of the localities (k

/ k

= 3.48 with the limit = 2.48 and

I° = + 47.4°), suggesting that the remanences were acquired

before folding. The above inclinations are shallower than the

expected inclinations in a European framework (+ 59.7° and

+ 63.4° calculated from the European APWs by Besse and

Courtillot 2002 and Torsvik et al. 2012, respectively). Five

locality mean directions cluster (localities 1a, 4, 7, 8 and 9),

exhibiting large CCW rotations. Two of the remaining loca-

lities (3 and 5) suggest significantly smaller CCW rotation,

one locality (6) exhibits CW rotated declination (Fig. 4b).

Anisotropy of Magnetic Susceptibility (AMS)

AMS measurements revealed that the locality mean suscep-

tibilities are in a range of 1–3*10

-4

[SI] and the degrees of

anisotropy are between 0.9 % and 8.7 % (Table 2). For most

localities, the AMS fabrics are foliated and the minimum

directions are sub-vertical after tilt correction. Exceptions are

localities 1, 6 and some samples from locality 2. The AMS

fabrics of both the siltstone (1a) and the sandstone (1b) are

lineated and the poles of foliations are somewhat deflected

from the vertical. Samples from locality 6, and three samples

from locality 2 (drilled from the same bed) exhibit horizontal

poles of foliations (Fig. 5), and the magnetic fabric is inverse

(PL 1456, 0 °C; max: 336/72, int: 74/3, min: 165/18). Inverse

fabric can be due to the presence of either single domain mag-

netite or siderite (Tarling & Hrouda 1993; Chadima et al.

2006). In the present case, after heating the samples to 460 °C,

the fabric becomes normal (PL 1456, 460 °C max: 162/18,

int: 71/5, min: 327/71), which points to the decomposition

of siderite, similarly to the case in the Skole nappe (Márton et

al. 2010).

All localities, no matter whether the fabrics are dominantly

foliated or lineated, are characterized by well-defined AMS

lineations. Some of them are aligned with the general NW–SE

tectonic trend of the Dukla nappe, others are quite different

(Fig. 3).

Anisotropy of Anhysteric Remanent Magnetization (AARM)

The sandstone at locality 1 (1b) exhibits highly scattered

AARM directions, and only two samples were measurable

from locality 2. For the rest, the AARM fabrics are dominantly

foliated (Table 2). As in the case of AMS, the foliation poles

are typically within 10° of the vertical, except at localities 1a

and 9. AARM lineations are well grouped on the locality level

for localities 4, 5, 6, and 7, but exhibit moderate or large scatter

at the other localities.

Mineralogy and photo-statistics

The IRM acquisition curve and the three-component IRM

demagnetization show that a low-coercivity mineral domi-

nates (Fig. 6). It is most probably magnetite, since the IRM

signal still exists at the temperature of dramatic increase of

Locality

Lat.N, Lon.E

Lithology

n/no

D°

I°

dip

Lipowica 1

PL 1514-527

49°31’43”

21°40’51”

claystone

silt

12/14

– 39

110

– 65

70/30

Lipowica 2

PL 1555-561

49°31’49”

21°40’45”

sandstone

0/7

Unstable NRM

280/40

280/60

Lipowica stream

PL 1562-567

49°31’30”

21°41’04”

claystone/

mudstone

0/6

Disintegrated during measurement

45/45

60/30

Jaśliska

PL 1258-269

49°26’09”

21°48’07”

11/12

341

+44

348

+42

50/8

Posada Jaśliska

PL 1445-455

49°26’34”

21°28’17”

10/11

334

+68

273

+47

240/40

Wisłok Wielki

PL 1246-257

49°24’27”

21°58’49”

12/12

178

– 8

174

– 31

200/25

Wisłok Wielki 2

PL 1456-467

49°23’19”

21°59’28”

11/12

+62

+32

55/30

Smolnik 1

PL 1409-420

49°15’21”

22°06’56”

8/12

318

+66

115

274

+38

115

245/40

Smolnik 2

PL 1421-432

49°14’38”

22°07’58”

10/12

317

+65

264

+54

220/30

Michów

PL 1395-408

49°13’18”

22°11’38”

13/14

331

+65

240

+61

200/40

Table 1: Summary of locality mean paleomagnetic directions based on the results of principal component analysis (Kirschvink 1980).

Localities are numbered according to Fig. 3. Key: Lat.N, Lon.E — Geographical coordinates (WGS84) measured by GPS, n/no: number of

used/collected samples (the samples are independently oriented cores); D, I (Dc, Ic) — declination, inclination before (after) tilt correction;

k and α

— statistical parameters (Fisher 1953).

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the susceptibility at 400 °C (probably due to decomposition of

pyrite) which prevents obtaining stable IRM components up to

the Curie point of magnetite. The simultaneous existence of

magnetite and pyrite in the Krosno beds was also observed in

the Silesian Nappe (Márton et al. 2009).

In thin sections quartz and carbonates as the main ingre-

dients but also opaque minerals, limonite and mica (mostly

in the siltstone) were found. Ore-microscopy proved that

the opaque minerals are indeed magnetite and pyrite (Fig. 7).

The XRD measurements showed that in addition to quartz,

calcite, dolomite, albite more than 5 percent of clay minerals,

probably with Fe content, are present in the studied samples.

The 2000 dpi resolution was not enough to detect the

required number of grains in the claystone/mudstone thin-

sections and they also lacked the required number of micas for

statistical evaluation. In the siltstone both methods (scanned

image and micro photo) revealed a lineated fabric, but the

directions obtained are perpendicular to each other (Fig. 8).

Discussion

The majority of, the Oligocene paleomag-

netic directions from the Polish part of the

Dukla nappe indicate CCW rotation. In this

sense, the situation is similar to the Slovak

part of the nappe (Koráb et al. 1981) and to

the Silesian and Magura nappes (Márton et

al. 2009). However, in the Polish part of

the Dukla nappe the locality mean paleo -

mag

netic directions define three groups,

the majority of the localities exhibit large,

two localities moderate CCW rotations

(Fig. 4b) and one locality (6) suggests CW

rotation.

It was mentioned in a previous section that

some of the locality mean paleomagentic

inclinations, after tilt correction, are shal-

lower, than those expected in a European

Locality

N mean K

(10

-6

SI)

Max.

conf.

angle

Int.

conf.

angle

Min.

conf.

angle P (%) L (%) F (%)

D°

I°

D°

I°

D°

I°

1a Lipowica, clay and silt

PL 1514-527

AMS 12

155

192

8/7

18 20/18

307

20/8

0.9

0.6

0.3

AARM 10

26/7

336

27/9

167

13/6

8.2

2.5

5.6

1b Lipowica, sandstone

PL 1555-561

AMS

217

8/5

125

15/4

336

15/7

1.4

0.9

0.6

AARM 6

significant scatter

2 Lipowica stream

PL 1562-567

AMS

two AMS clusters of 3-3 samples. statistics cannot calculated for less than 5 samples

AARM 2

3 Jasliska

PL 1258-269

AMS 12

222

290

10/7

200

10/4

7/3

6.7

0.8

5.8

AARM 8

353

35/3

35/8

220

8/2

7.3

0.9

6.3

4 Posade Jasliska PL

1421-432

AMS 11

186

109

11/3

11/5

210

6/3

7.8

0.6

7.1

AARM 5

8/3

354

9/5

184

5/3

11.7

1.9

9.6

5 Wislok Wielki 1

PL 1246-257

AMS 13

210

255

14/11

345

0 13/10

12/9

0.8

0.3

0.6

AARM 6

161

8/3

251

13/5

11/2

10.2

1.4

8.6

6 Wislok Wielki 2

PL 1456-467

AMS

287

3/1

240

18/1

150

18/1

4.8

4.2

0.5

AARM 5

156

14/2

247

14/2

352

2/2

11.3

2.3

8.8

7 Smolnik 1

PL 1409-420

AMS 12

235

121

9/3

229

5/2

8.7

0.6

8.1

AARM 5

9/1

13/4

226

10/2

10.3

2.3

7.8

8 Smolnik 2

PL 1421-432

AMS

195

291

4/2

5/1

175

3/2

7.8

1.4

6.3

AARM 6

102

22/5

22/8

238

8/6

9.4

2.1

7.1

9 Maniow

PL 1395-408

AMS 14

166

275

7/3

184

10/3

10/7

3.1

1.0

2.1

AARM 7

225

30/6

317

30/7

10/4

8.3

1.0

7.3

Table 2: Summary of tilt corrected locality mean anisotropy directions (both AMS and AARM). Localities are numbered according to Fig. 3

and lithology is claystone/mudstone except if it is stated otherwise. Key: n/no — number of used/collected samples (the samples are inde-

pendently oriented cores); K — mean susceptibility; D, I, conf angles — declination, inclination and the related confidence ellipse of the

maximum (lineation), intermediate and minimum (pole of foliation) directions; P, L, F — degree of anisotropy, lineation, foliation.

Fig. 4. Locality mean paleomagnetic directions with α

before (left side) and after (right

side) tilt correction shown in lower hemisphere equal angle projections and the inclina-

tion-only test.

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The Slovak part of the Dukla nappe also suggests a general

CCW rotation (Koráb et al. 1981). Disregarding locality 6,

which is an outlier, the overall-mean paleomagnetic direction

for the Polish segment of the nappe is D° = 312.3°, I° = + 57.3°,

k = 9.2, α = 20.9°, N = 7 (synfolding at 45 % unfolding). This

result, combined with the tilt corrected locality mean direc-

tions for the Slovak segment (Koráb et al. 1981, neither direc-

tions before tilt corrections nor the tectonic tilt is documented),

yields D° = 328.0°, I° = + 50.7°, k = 9.7, α =14.7°, N=12.

The general CCW rotation is poorly constrained in both cases.

Nevertheless, they are in line with the findings from the neigh-

bouring Silesian and Magura nappes (Márton et al. 2009, Fig. 9).

Tectonic deformation in the Dukla nappe produced imbri-

cated thrusts on the large scale and also imprinted the domi-

nantly sedimentary magnetic fabrics. The deformation must

have been weak, since pencil fabric occurs only at a single

locality (Fig. 5). Well-defined AMS lineations (on locality

level) are typical. They are related to tectonic deformation as

the principal agent for the following reasons. One is that the

studied samples (except locality 1b) are fine-grained, and they

were deposited in the final stage of sedimentation from a tur-

bidite. Furthermore, the samples typically represent more than

one bed from the same locality, yet the AMS lineation direc-

tions are well grouped on the locality level. Finally, the AMS

lineations correlate with the local strikes. However, the local

strikes and the corresponding AMS lineations are variable

within the Dukla nappe. Some are near-parallel to the general

trend of the nappe, some are close to N–S or E–W. Assuming

that this phenomenon is due to local tectonic disturbances, we

can apply “rotation corrections” to the paleomagnetic decli-

nations. The method uses the angle and sense of deviation

from the general NW–SE tectonic trend of the nappe as a cor-

recting factor. The correction resulted in more incoherent

paleomagnetic directions than before. When AMS lineations

are used as proxies for the strikes the result is similar. Thus,

local tectonic disturbances in the form of local rotations are

not likely to explain the deviations from the general trend of

the nappe. A more likely mechanism may be the strain parti-

tioning within the nappe.

The studied localities typically exhibit AMS lineations,

which systematically depart in the CCW sense from the

respective local strikes (Fig. 10). This phenomenon suggests

that the ductile deformation resulting in the AMS lineations

commenced before the folds were formed, with the former

coming into being while the sediments were soft, probably

still in the late Oligocene, the latter somewhat later, during the

rotation process.

Fig. 6. IRM acquisition, normalized three- component IRM demagne-

tization and susceptibility vs. temperature curves (from top to bot-

tom). The IRM saturates fast (0.2 T) which refers to low-coercivity

magnetic minerals and the three-component IRM demagnetization

also supports that. There is an increase of susceptibility after 300 °C,

which is typical for iron-sulphides. After 400 °C (vertical, dashed

line) the susceptibility is increasing dramatically which shows that the

sample became unstable, so the demagnetization have not been

continued.

Fig. 7. Ore-microscopy images of polished thin sections. Pyrite (P)

and magnetite (M) were recognized as ore-minerals (a). The pyrite is

characterized by framboidal structure (b).

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The fabrics of the magnetic minerals

(AARM) seem to be less sensitive to defor-

mation than those of the AMS. The sandstone

of locality 1 (1b) is not oriented (solemarks

show that strong paleocurrents affected the

sandstone beds). At the other localities the

AARM foliation similarly to the AMS folia-

tion is near-parallel to the bedding plane.

AARM lineations are quite scattered in the

siltsone of locality 1 and localities 3 and 9 and

the mean AARM lineation directions are

different from those of the AMS lineations.

We infer that the ferromagnetic grains in

these cases were basically oriented by sedi-

mentary transport, since in the siltstone of

locality 1 the micas seem perpendicularly

arranged with respect to the iron minerals

(Fig. 8), showing that they are imbricated by

the current.

At the remaining localities, the AARM

lineations are clustered on the locality level.

At localities 4, 7, 8 and 6 (at the last after the

decomposition of siderite), the AMS and

AARM lineations are close to each other.

Thus, at these localities the AARM lineations

may be of the same origin as the AMS linea-

tions. At locality 5 the AARM lineation is

very well defined, yet it is almost perpen-

dicular to the AMS lineation. In this case, the

ferrimagnetic grains must have been quite

strongly oriented by water flow, and could

not be affected by weak compression.

Conclusions

The susceptibility measurements indicated

and mineralogy investigations (magnetic

mineralogy, petrography, ore-microscopy and

XRD) confirmed that paramagnetic minerals

are important contributors to the AMS fabric

of the Krosno beds of the Dukla nappe.

The contribution of the ferromagnetic

Fig. 8. The distribution of particle long-axis orientations in the plane of bedding (after

tilt correction). The data was obtained by photo-statistics from a siltstone pilot sample

(Pl 1521) from locality 1a. Both the micas (a) and the scanned particles (b) show

lineation, but they are perpendicular to each other. Most probably the micas are imbri-

cated by the paleoflow so they are apparently lineated perpendicular to the flow direction

in the bedding parallel section. The elongated scanned particles are aligned parallel to

the paleoflow, therefore both methods refers to the same sedimentary transport direction,

which lies within the confidence interval of the AARM lineation of locality 1a.

Fig. 9. Locality mean paleomagnetic directions with α

from both the Polish (this study,

without the outlier locality 6) and the Slovak (Koráb et al. 1981) parts of the nappe

(squares and diamonds, respectively), and the overall mean direction of the nappe

(full circle) with α

(left side). The overall mean paleomagnetic directions of Dukla

nappe, Magura nappe, Oravska Magura (Krs et al. 1991), Silesian nappe (Central + Eastern

part, prefolding magnetization) and Silesian nappe (Eastern part postfolding magneti-

zation) (right side).

Fig. 10. On the left the AMS directions are plotted

as a function of the local strike, and the 45° line is

indicated. All points are close to the reference line,

the AMS lineation directions correlate with the

local strikes at all localities, but the points are

located systematically below the line except three

points. Localities 1a and 1b are above the line and

locality 6 is on the line (here the AARM lineation

is indicated due to the presence of siderite).

The mean AMS lineation and strike directions with

confidence intervals of the six localities are shown

on the right. This systematic westward deflection

of the AMS lineations coincides with the general

CCW rotation.

6.1–7

5.5 – 6.1

5 – 5.5

4.4 – 5

3.8 – 4.4

3.3 – 3.8

2.7– 3.3

2.1– 2.7

1.6 – 2.1

1–1.6

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GEOLOGICA CARPATHICA

, 2016, 67, 6, 595 – 605

mineral to the AMS (identified by IRM experiment and

ore-microscopy as magnetite), must be subordinate, since it is

present in very low concentration.

At most localities, the AMS foliation is practically bedding

parallel, indicating that the deformation was weak. Early stage

pencil structure was observed only at one locality, suggesting

somewhat stronger deformation.

AMS lineation directions, which are fairly well defined, can

be related to local tectonic strikes, so they are due to tectonic

deformation. However, there are several cases where neither

the local strike, nor the AMS lineation correlates with the

general strike of the Dukla nappe. It is quite likely that strain

partitioning is responsible for the observed distribution of the

markers of extension directions.

In some cases AMS and AARM ellipsoids (the latter reflects

the orientation of the ferromagnetic grains) are not coaxial and

the AARM lineations are quite scattered. Thus, we can conclude

that the paramagnetic fabric is more sensitive to deformation

than the ferrimagnetic fabric, which preserves the characteris-

tics of a flow-oriented arrangement of the magnetic grains.

The paleomagnetic locality mean inclinations respond

positively to the inclination-only test. However, the declina-

tions define three groups. One with five members exhibits

large, the second with two members small CCW rotations,

while the third has only one locality indicating slight CW rota-

tion. “Rotation corrections” were applied to remove the effect

of possible local rotations, but they resulted in a more scat-

tered picture. Thus, local tectonic rotation postdating the

acquisition of the remanence cannot account for the results.

It is beyond doubt that the Dukla nappe suffered post-

Oligocene CCW rotation, but the magnitude is statistically

poorly defined.

The orientations of the AMS lineations at

several localities are deviating more to the west from the

present north than that of the local tectonic strikes. A possible

explanation for this is that the AMS lineations were imprinted

first, probably still in the Oligocene, while the sediments were

soft (ductile deformation) and the folding and tilting took

place during the CCW rotation.

Acknowledgements: We thank Tamás Biró, István Dódony,

Gabriella Kiss and Sándor Józsa for their guidance when car-

rying out the non-magnetic mineralogy investigations and we

also thank the Eötvös Loránd University for providing access to

the instruments and laboratories. We thank Ludivine Sadeski,

a student of EOST - University of Strasbourg, who started the

AARM measurements of the samples from the Dukla nappe

during her internship at the Paleomagnetic Laboratory. This

work was partly financed by the Hungarian Research Fund

(OTKA) project no. K105245 and from a joint project of the

Academies of Science of Poland and Hungary.

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