GEOLOGICA CARPATHICA, FEBRUARY 2006, 57, 1, 41—46
Late Neogene counterclockwise rotation in the SW part of the
, BOGOMIR JELEN
, BRUNO TOMLJENOVIĆ
, DAVOR PAVELIĆ
, PÉTER MÁRTON
, RADOVAN AVANIĆ
and JAKOB PAMIĆ
Eötvös Loránd Geophysical Institute of Hungary, Palaeomagnetic Laboratory, Columbus 17—23, H-1145 Budapest,
Hungary; Phone: +36 1 3193203, Fax: + 36 1 2480379, firstname.lastname@example.org
Geological Survey of Slovenia, Dimičeva 14, SLO-1109 Ljubljana, Slovenia; email@example.com, firstname.lastname@example.org
University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, HR-10000 Zagreb, Croatia;
Eötvös Loránd University, Geophysics Department, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary; email@example.com
Institute of Geology, Sachsova 2, HR-10000 Zagreb, Croatia; firstname.lastname@example.org
Croatian Academy of Sciences and Arts
(Manuscript received March 21, 2005; accepted in revised form June 16, 2005)
Abstract: Earlier paleomagnetic studies suggested that counterclockwise rotating Adriatic microplate could have
triggered the youngest rotations in the Hrvatsko Zagorje area (in the Slavonian Mts) and in the Mura-Zala Depression.
Since the named areas are located quite far from the Eastern Adriatic coast, we decided to study the Krško and
Karlovac Basins, which are situated in-between. From the collected 12 paleomagnetic localities (Badenian through
Pontian sediments) ten yielded good paleomagnetic directions as a result of laboratory processing and statistical
evaluation. They definitely point to the counterclockwise rotation of the area in post Early Pontian times. The angle
of the rotation is about 20° ( D =337°, I =50°, k =48,
= 10°). Thus, we have found a missing tectonic link from the
Hrvatsko Zagorje, Slavonian Mts and the Mura—Zala Basins to the Adriatic microplate and collected further paleomag-
netic evidence for end of Miocene or even younger important tectonic movements in the South Pannonian Basin.
Key words: Neogene, South Pannonian Basin, paleomagnetism, rotation.
At the southwestern rim of the Pannonian Basin in eastern
Slovenia and northwestern Croatia, different pre-Neogene
tectonic units are juxtaposed due to the complex tectonic
evolution of this area (Fig. 1; Haas et al. 2000 and referenc-
es therein). These units are mostly composed of Paleozoic
and Mesozoic rocks of Dinaric, South Alpine and East Al-
pine affinity and comprise the basement overlain by Neo-
gene sediments of the Mura Depression, Hrvatsko Zagorje,
Sava Folds basins, including the Krško and Karlovac Ba-
sins. Paleomagnetic directions so far obtained for the Neo-
gene sediments of the Mura Depression and the Hrvatsko
Zagorje Basin show westerly declinations of remarkable
consistency, which imply a definitely post Early Pontian,
perhaps even a Lower Pliocene counterclockwise (CCW)
rotation of these basins together with basins of similar age
in the Slavonian Mts (Márton et al. 2002a,b). According to
the interpretation of Márton et al. (2002b, 2003) this rota-
tion is connected to the NNE motion and CCW rotation of
the Adriatic microplate (Anderson & Jackson 1987; Calais
et al. 2002; Devoti et al. 2002). This interpretation, howev-
er, is hampered by the fact that the Mura Depression, the Hr-
vatsko Zagorje Basin and the Slavonian Mts are located far
away from the Eastern Adriatic coast, which belongs to the
recently also moving and CCW rotating Adriatic micro-
plate. By paleomagnetic measurements of Neogene sedi-
ments outcropping along the southwesternmost margin of
the Pannonian Basin in Slovenia and Croatia, that is on the
northern rims of the Krško and Karlovac Basins, respective-
ly, we intended to “reduce the distance” and to fill up the
data gap. Accordingly, we had to answer the question of
whether the Badenian—Pontian sediments in this area pro-
vide a tectonic link towards Adria, or call for an interrup-
tion and alternative interpretation.
Geology and paleomagnetic sampling
The study area is located within the Sava Folds or the
Sava transpressive wedge (e.g. Placer 1998), which be-
longs to the regional NE-SW striking Zagorje—Mid-Trans-
danubian Zone (Pamić & Tomljenović 1998). The zone
is bounded by the Periadriatic-Balaton and Zagreb-Zem-
plén Lineaments to the north and south, respectively
(Fig. 1; Csontos & Nagymarosy 1998; Fodor et al. 1998;
Poljak et al. 2000; Haas et al. 2000 and references therein).
Structurally, it is characterized by predominantly E- to
ENE-striking kilometer scale folds and faults of Neogene—
Quaternary age (Placer 1998; Prelogović et al. 1998; Tom-
ljenović & Csontos 2001).
The Krško Basin is an asymmetrical syncline built up in
its core by Ottnangian to Pontian sediments more than
2000 m thick (Poljak & Gosar 2001). Following a NE trend,
MÁRTON et al.
the syncline extends without a break into the Konjščina
syncline (Hrvatsko Zagorje Basin, Šimunić et al. 1983,
Tomljenović & Csontos 2001). The syncline transits into
the Krško hills—Orlica anticline in the north, while it is
bounded by the Žumberak/Gorjanci—Marija Gorica anti-
cline or basement pop-up structure to the south. For the pur-
pose of this study we collected samples from freshly
excavated outcrops located along the northwestern limb of
the Krško syncline (Fig. 2, localities 1—4) and from syn-
clines north of it (Fig. 2, localities 8—10).
The Karlovac Basin is a NNW-trending graben located
south of Žumberak/Gorjanci Mts, bounded by ENE-dipping
listric and WSW-dipping antithetic normal faults (Tomljen-
ović & Csontos 2001). During the Neogene, these faults ac-
commodated several phases of predominantly ENE—WSW
directed extension (most probably starting in the Ottnangian)
followed by periods of shortening and inversion. The latest,
Pontian to recent (ca. 6—0 Ma) shortening is particularly well
observable along the northwestern basin margin, that is along
the southeastern slopes of Žumberak/Gorjanci Mts where
sediments of Badenian—Pontian age are exposed and were
sampled for this study (Fig. 2, localities, 5—7).
Stratigraphy, depositional style and the history of Mi-
ocene deposits outcropping on the northwestern margins of
the Krško and Karlovac Basins are similar (Fig. 3). The old-
Fig. 1. Pre-Neogene basement at the junction of the Alps, Dinarides and the Pannonian Basin with major tectonic lines and Neogene
Fig. 2. Structural map of the study area with the successful paleo-
magnetic sampling localities numbered.
LATE NEOGENE COUNERCLOCKWISE ROTATION OF THE PANNONIAN BASIN
est outcroping Neogene sediments are of Ottnangian—Kar-
patian age. Badenian is the time of marine transgression
both in the Krško and Karlovac Basins. The sea became
shallow at the end of Badenian. In the Sarmatian the salini-
ty decreased and a basin of restricted salinity formed, re-
flecting reduced connection with the sea. Typical sediments
are calcarenites and marls. The end of the Sarmatian is
marked by a general shallowing trend, due to the onset of
basin inversion (and of eustatic sea-level drop). A new sedi-
mentary cycle started with the deposition of marls in the
brackish Pannonian-Pontian lake. Upward in the succes-
sion, coarser clastic sediments appear, connected with
sandy delta progradation. Miocene deposits are conform-
ably or unconformably overlain by Pliocene and Pleis-
tocene siliciclastic deposits, accumulated in small fresh
water lakes, swamps and rivers (Verbič et al. 2000).
The collected paleomagnetic samples represent marl or
clayey marl horizons of fresh artificial outcrops, such as
building sites. Distribution of sampling localities with re-
spect to their lithology, biostratigraphic ages and location
within the two basins are shown in Figs. 2 and 3. The time
represented by the studied rocks is about 9 million years,
starting with 15 Ma (Badenian) and ending with 5.6 Ma
(Pontian; Fig. 3). In spite of the young age, the sediments
are considerably tectonized, mostly due to the latest short-
ening and basin inversion of Late Pontian to Quaternary
age (Tomljenović & Csontos 2001).
Paleomagnetic measurements and results
The samples, which had been drilled and oriented in
the field (the total number of collected localities is 12,
successful localities are numbered in Fig. 2), were subjected
to paleomagnetic measurements and analysis in the Paleo-
Fig. 3. Generalized lithological column of the sampling area also
indicating environmental conditions.
Fig. 4. Examples of the demagnetization behaviour of the natural remanent magnetization (NRM) and the magnetic susceptibility. In the Zijder-
veld diagrams, full/open circles: projection of the NRM in the horizontal/vertical plane; in the others susceptibility: dots, NRM intensity: cir-
cles. Note that the intensity of NRM decays parallel to the decay of the susceptibility, indicating that the NRM is basically residing in greigite.
MÁRTON et al.
magnetic Laboratory of the Eötvös Loránd Geophysical In-
stitute of Hungary. The natural remanent magnetization
and the magnetic susceptibility were first measured in the
natural state, using JR4 and cryogenic magnetometers and
KLY-2 kappabridge, respectively. The samples were subse-
quently demagnetized: most of them thermally, some of
them by the alternating field method. The remanence was
remeasured after each heating step and also the susceptibili-
ty, in the former case. The measurements were evaluated in
the following way. Linear segments had been defined from
the demagnetization curves (Fig. 4), and the corresponding
directions subjected to statistical analysis. The exception is
one of the Badenian localities (Table 1, locality 1), where
the mean direction is based on the last demagnetization
steps, before loosing (due to the weakness of the rema-
nence) the magnetic signal.
The carrier of the natural remanence is either magnetite
(Fig. 5) (accompanied by pyrite, as indicated by the dramat-
ic increase of susceptibility on heating) or greigite (evi-
denced by a substantial decrease of the susceptibility from
300 °C, closely followed by an increase, the first indicating
phase change of the iron sulphide, the second, conversion
to magnetite, Fig. 4).
The two localities, one from the Krško Basin and one from
the Karlovac Basin failed to yield paleomagnetic direction.
The rest are statistically excellent (Pannonian—Pontian local-
ities, Table 1) or acceptable (Badenian localities, Table 1).
Discussion and conclusion
The Badenian localities (Table 1, localities 1, 2 and 8)
have westerly declinations, both before and after tilt cor-
rections. Polarities are normal.
Among the younger localities, both normal and reversed
polarities occur and their paleomagnetic directions are sig-
nificantly different from that of the present Earth field, in
the geographical co-ordinate system (before tilt correction).
Badenian localities 1, 2 and 8 (Table 1) give a positive re-
sponse to a mechanically applied tilt test (Fig. 6). The overall
mean direction in the tectonic system (after tilt corrections) is
D = 309°, I = 60°, k = 35,
= 21°, N = 3). However, one can-
not avoid noticing that two of the locality mean directions
(localities 1 and 8) practically coincide, while the third one
(locality 2) exhibits considerably larger CCW rotation than
the first two (possible because of local tectonic disturbance).
While tilt test suggests that the paleomagnetic signal of
the Badenian rocks was acquired before tilting, the same
test is negative for the younger rocks. The overall mean di-
rection calculated for the Pannonian—Pontian (and the Sar-
matian, since the soft component is obviously not primary)
localities is D = 337°, I = 50°, (statistical parameters k = 48,
= 10°, N = 6) before and D = 337°, I = 64° (k = 21,
= 13°, N = 6) after tilt corrections. Much better statistical
parameters before tilt corrections suggest that the age of the
remanence should be regarded as of post-tilting age, in spite
of the mixed polarities. The lag between deposition and ac-
quisition of the paleomagnetic signal does not hamper tec-
tonic interpretation, since the age of the deposition is so
Fig. 5. Identification of the magnetic minerals. Typical isothermal
remanent magnetization (IRM) acquisition curves (upper row),
the behaviour of the three component IRM (Lowrie 1990) on
thermal demagnetization (second row) and the change in suscepti-
bility on heating (lowermost row). The hard (squares), the medi-
um (dots) and soft (circles) components of the composite IRM
were acquired in fields of 1.0, 0.36 and 0.12 T respectively.
Fig. 6. Krško and Karlovac Basins, Neogene sediments. Regional
tilt test for Badenian (positive response to untilting) and for
younger (negative response) sediments.
young, that the time between deposition of the youngest
rock (Pontian, around 7 Ma?) and deformation (starting
around 6 Ma) is short, and the angle of the overall rotation
is not influenced by tilt correction: it is the same (about
20°) in both the geographical and tectonic systems.
As the overall-mean paleomagnetic direction for the
Badenian shows larger westerly deviation from the present
LATE NEOGENE COUNERCLOCKWISE ROTATION OF THE PANNONIAN BASIN
Table 1: Summary of the paleomagnetic directions. The mean paleomagnetic locality directions are based on the results of principal com-
ponent analysis (Kirschvink 1980), except locality 1 (for explanation, see text). Key: n/no – number of used/collected samples; D°, I°
(Dc°, Ic°) – declination, inclination before (after) tilt correction; k and
– statistical parameters (Fisher 1953). Remark: locality
4 was excluded when calculating overall-mean paleomagnetic direction, due to suspected (on revisiting the locality) slumping.
Fig. 7. Comparison between paleomagnetic overall-mean directions with confidence circles indicating the net post-Eocene rotation of the:
A – Adriatic foreland (Márton 2006); B – net post-Pannonian rotation of the Mura—Zala Depression (Márton et al. 2002a); C – net post
Early Pontian rotation of the Hrvatsko Zagorje plus Slavonian Mts (Márton et al. 2002b); D – and the net post Early Pontian rotation of the
Krško—Karlovac Basins (present study). Badenian locality mean directions are numbered (numbers refer to Table 1). Stereographic projection.
* – half of the samples without the other half after tilt correction, ** – soft component.
MÁRTON et al.
north than that of the younger age group, one is tempted
to interpret the difference as an earlier than the youngest
counterclockwise rotation, taking place after the Bade-
nian. However, the difference is due only to one locality
(number 2, Table 1 and Fig. 7) and the paleomagnetic di-
rections for the other two Badenian localities are very
close to the overall-mean paleomagnetic direction for the
younger age group (Fig. 7). Due to this situation we regard
the larger westerly declination of the Badenian group as
an indication to be followed up in the future, in contrast to
the solid evidence of the present study for a post-Early
Pontian 20° counterclockwise rotation.
Comparison between the results of the present study and
earlier published paleomagnetic directions of correspond-
ing age from the Hrvatsko Zagorje and the Mura-Zala De-
pression (Fig. 7) leads to the conclusion that the angles
and the timings of the final CCW rotations are consistent
in the whole south-western part of the basin. Since the area
of the present study is closer to the Adriatic microplate
than the previously investigated ones (Márton et al.
2002a,b) the idea of linking the rotation of the south-west-
ern Pannonian Basin to that of the Adriatic microplate be-
came better supported than it was before the present study.
Acknowledgment: The field work was financed by Slove-
nian—Hungarian Intergovernmental Scientific and Techno-
logical Project No. Slo-17/03 and a joint project of the
Academies of Sciences of Croatia and Hungary. Additional
support was provided by the Hungarian Scientific Research
Found (OTKA) Project Nos. T034364 and T029805.
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