THE ILLAWARRA REVERSAL IN THE PERMIAN OF THE HRONIC NAPPE 229
GEOLOGICA CARPATHICA, 54, 4, BRATISLAVA, AUGUST 2003
229236
EVIDENCE OF THE ILLAWARRA REVERSAL IN THE PERMIAN
SEQUENCE OF THE HRONIC NAPPE (WESTERN CARPATHIANS,
SLOVAKIA)
ANNA VOZÁROVÁ
1
and IGOR TÚNYI
2
1
Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University, Mlynská dolina,
842 15 Bratislava, Slovak Republic; vozarova@fns.uniba.sk
2
Geophysical Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 28 Bratislava, Slovak Republic; geoftuny@savba.sk
(Manuscript received December 14, 2001; accepted in revised form June 23, 2003)
Abstract: The magnetostratigraphic investigation on the profile of the Upper CarboniferousPermian belonging to the
Hronic Nappe in the Nízke Tatry Mts (Western Carpathians, Central Slovakia) revealed occurrence of the first order time
marker, the so-called Illawarra Reversal (265 Ma), within the 2nd megacycle of the Maluiná Formation sequence.
Key words: Carpathians, Hronic Unit, Late Paleozoic, magnetostratigraphy, Illawarra Reversal.
Introduction
Magnetic polarity stratigraphy is now thoroughly integrated
into biostratigraphy and chemostratigraphy. It is ordering of
sedimentary or volcanic rock strata complexes into intervals
characterized by the direction of characteristic remanent mag-
netic polarization of the rocks, being either normal polarity (in
the direction to the north pole of that time) or reversed polarity
(to the south pole of that time). The dipole nature of the main
geomagnetic field means that polarity reversals are globally
synchronous with the process of reversion taking 10
3
10
4
years. Magnetic polarity stratigraphy can therefore provide
global stratigraphic time lines.
A sequence from the time span 300250 Ma has been analy-
sed using a combination of lithostratigraphic, biostratigraphic,
isotope-geochronometric and magnetostratigraphic temporal
information. This sequence is continuously preserved from the
underlying Upper Carboniferous rocks to the overlying Lower
Triassic rocks.
The objective of this paper is especially to put forward a
more precise ordering of the Carboniferous-Permian strata of
the Hronic Nappe by the method of magnetostratigraphy. The
complete profile of the Upper Carboniferous-Permian se-
quence of the Hronic Unit in the Nízke Tatry Mts was analy-
sed by standard magnetostratigraphic methods. We chose the
localities in the Ipoltica and Dikula Valleys (Fig. 1) which
consist of non-metamorphosed as well as relatively good out-
cropped volcano-sedimentary sequences. In this sedimentary
rock complex we assume the preservation of primary rema-
nent magnetic polarization.
Geological setting and brief
lithostratigraphic characteristics
The Late Paleozoic volcano-sedimentary complexes in the
basal part of nappes of the Hronic Unit are denoted as the Ipol-
tica Group, which consists of the Niná Boca and Maluiná
Formations (Vozárová & Vozár 1981, 1988). The tectonic
basement of the Ipoltica Group, located in the Ipoltica and
Dikula Valleys to the S of the Èierny Váh river on the north-
ern slopes of the Nízke Tatry Mts, consists of the Veporic
Unit, mostly of the Mesozoic of the Ve¾ký Bok Group. The in-
ternal structure of the Ipoltica Group sedimentary sequences is
affected by Alpine thrusting and faulting processes. Variable
tectonic reduction is evident mainly in the sedimentary rock
sequences of the Niná Boca Formation.
The Ipoltica Group is a volcano-sedimentary sequence con-
sisting of many small-scale autocyclic sedimentary cycles re-
peatedly occurring one above another. Varied siliciclastic sed-
iments, andesite-basalt volcanics associated with minor
volcaniclastics, absolutely dominate in the entire complex.
Occurrences of evaporites and caliche horizon are rare. The
whole sequence of the Ipoltica Group shows typical coarsen-
ing upward and change in the colour of sediments from grey to
red-grey and red. The cumulative thickness is estimated at
25002800 m.
Niná Boca Formation. It is generally a coarsening upward
siliciclastic sedimentary sequence consisting of numerous re-
peated small-scale autocyclic fining-upward cycles. The facies
distribution of the Niná Boca Formation indicates channel
and overbank deposits, alternating with interdistributary-chan-
nel and lacustrine sediments deposited in permanent humid
climate. The deposits are predominantly grey to black co-
loured. This fluvial and/or fluvial-deltaic and lacustrine sedi-
mentary association was interrupted by synsedimentary sub-
aerial volcanism. It is manifested by abundant redeposited
volcanogenic detrital material mixed with non-volcanic detri-
tus and the sporadic occurrences of thin layered dacitic tuffs as
well as exceptionally dacitic lava flows. The gabbro-diorite
dykes are integral part of the Niná Boca Formation. They are
comagmatic with the Permian andesitic-basaltic volcanites of
the Maluiná Formation.
The Niná Boca Formation is characterized by macroscopi-
cally conspicuous stratification. The thickness of these beds is
almost constant, but laterally variable. Tabular bodies of sand-
230 VOZÁROVÁ and TÚNYI
stones are dominant. They are massive and/or graded bedded
and cross-bedded, rarely with parting lineation. The horizon-
tal planar lamination is typical of finer-grained sediments,
very fine-grained sandstones, siltstones and mudstones. It is
characterized by alternating laminae of sedimentary material
of variable grain-size and colour. Finer-grained laminae are
darker and contain flakes of clastic micas and carbonized
plant detritus. The colour of sediments changes according to
grain-size, mineral composition of detrital material, amount of
primary matrix and carbonized plant detritus.
Macroflora from the uppermost part of the Niná Boca For-
mation proved the Stephanian BC age (Sitár & Vozár 1973).
The palynological analysis of Planderová (1973) distin-
guished the Stephanian AB and the Stephanian CD microf-
lora assemblages.
Maluiná Formation. The Maluiná Formation sequence is
developed gradually from the underlying Niná Boca Forma-
tion. It comprises a thick succession of red-beds (more than
2000 m in places), which consists of alternating conglomer-
ates, sandstones and shales. Lenses of dolomites, gypsum and
calcrete/caliche horizons occur locally. Small-scale fining-up-
ward sedimentary cycles in the order of several meters, as
well as three regional megacycles arranged one above the oth-
er, are the most typical sedimentary feature. The polyphase
synsedimentary andesitic-basaltic volcanism of tholeiitic
magmatic trend is the further significant phenomenon. Fossil
remnants of the channel bar and point bar deposits associated
with flood plain and natural levee sequences are dominant
within the lower part of the three megacycles. The sediments
of the Maluiná Formation were generally deposited in a flu-
vial and fluvial/lacustrine depositional system during perma-
nent semiarid/arid climate.
The microflora proved the Early and Late Permian age of
the Maluiná Formation. The following assemblages were de-
scribed by Planderová (in Planderová 1973; Planderová &
Vozárová 1982): 1. The Autunian assemblage, corresponding
approximately to the 1st megacycle sediments; 2. The Saxo-
nian assemblage, specifying age of the 2nd megacycle sedi-
ments; 3. The Thuringian assemblage, determining age of the
3rd megacycle sediments.
Fig. 1. Schematic geological map (modified according to Vozár in Biely et al. 1992) with indication of measured profile and sample loca-
tions in the northern slope of the Nízke Tatry Mts. Explanation: 1. Middle Triassic carbonate rock complexes. 2. Lower Triassic clastic
sediments. 37. Maluiná Formation: 3 3rd megacycle sediments; 4 andesite-basalts of the 2nd eruption phase; 5 2nd megacycle
sediments; 6 1st megacycle sediments; 7 andesite-basalts of the 1st eruption phase. 89. Niná Boca Formation: 8 sediments;
9 Permian dioritic sills and dykes. 10. Mesozoic metasediments of the Ve¾ký Bok Group. 11. Overthrust line. 12. Strike and dip bed.
13. Location of investigated localities.
THE ILLAWARRA REVERSAL IN THE PERMIAN OF THE HRONIC NAPPE 231
Distinct fining upward is a dominant lithological feature of
all the three megacycles. The lower part of the megacycles
consists of coarse-grained sediments: conglomerates and very
coarse-grained sandstones. The beds are mostly thicker than
1 m. Erosive contacts between beds are frequent. Sediments in
the lower part of the megacycles are of light-grey colour with
greyish-pink, rusty-grey and light green-grey shades. In con-
trast to the base, the middle parts of the megacycles show dis-
tinct fining upward small-scale cyclicity, relatively decreasing
thickness of beds, as well as dominance of finer-grained sedi-
ments over sandstones and significant ascent of red or violet-
red colour of sediments. The top parts of the megacycles con-
sists of the finest sediments, thin-bedded very fine-grained
sandstones and siltstones alternating with thicker dominant
mudstones. Prevalent are red, red-violet and greyish-red sedi-
ments. These fine-grained sediments contain layers of cal-
crete/caliche horizons, variable lenses of dolomite limestones,
dolomite and scarce gypsum. They represent playa and conti-
nental sabcha deposits.
In the eastern part of the 2nd megacycle a local member
was defined the Kravany Beds (Novotný & Badár 1971).
They consists of grey and greenish-grey sandstones and silt-
stones with redeposited plant debris and thin uraniun-bearing
horizons.
The Autunian-Saxonian microflora assemblages correspond
approximately to the 1st and 2nd megacycles. This assump-
tion is supported by
206
Pb/
238
U and
208
Pb/
235
U dating of 263
274 Ma from uranium-bearing layers of the 2nd megacycle
(Legierski in Rojkoviè et al. 1992).
Magnetic properties of sediments and volcanics
Generally, the Upper Carboniferous-Permian continental
sediments of the Hronic Unit have stable remanent magnetiza-
tion carried by two distinct phases of magnetic minerals, one
detrital and another authigenic.
The dominant detrital magnetic mineral in the Niná Boca
Formation sandstones is ilmenite. It is associated with scarce
grains of magnetite. The burial of organic matter can result in
reducing diagenetic conditions and the formation of iron sul-
phides. Authigenic pyrite is the most common iron sulphide in
sediments and it can originate by reduction of detritital mag-
netite or titanomagnetite. It grew during diagenesis and could
carry a high fidelity record of the geomagnetic field. Titano-
magnetite and pyrrhotite are the main magnetic minerals in
the gabbro-diorite dykes.
The Permian continental red-beds of the Maluiná For-
mation have stable magnetization carried by two distinct
phases of hematite, one detrital and one authigenic. The mag-
netization of relatively coarser-grained sandstones is dominat-
ed by detrital specular hematite. Finer-grained sediments
(siltstones and mudstones) as well as primary matrix in sand-
stones tend to be dominated by fine-grained pigmentary he-
matite. Within the Kravany Beds uranium-bearing stratiform
horizons originated authigenic pyrite as a result of the bacteri-
al activity in reducing diagenetic conditions.
Magnetic minerals of the Maluiná Formation andezitic ba-
salts are represented by phenocrysts of titanomagnetite and as
well as a hematite within the recrystallized glass matrix.
According to blocking temperatures, the followed magnetic
minerals were identified: magnetite with blocking temperature
580 °C (Fig. 4 sample 31B), hematite with blocking tem-
perature 675 °C (Fig. 2 sample 20D), hematite with Fe-ox-
ides with blocking temperatures in the interval 200500 °C
(Fig. 6 sample 39B; Fig. 8 sample 42A; Fig. 10 sam-
ple 51A), somewhere hematite and magnetite or goethit with
blocking temperature ca. 120 °C.
Paleomagnetic measurements
351 rock samples from 23 outcrops of the investigated pro-
file were studied. Each sample was subjected to thermal mag-
netic cleaning. Paleomagnetic measurements were carried out
in the Paleomagnetic Laboratory of the Geophysical Institute
of the Slovak Academy of Sciences, Bratislava. The demagne-
tization step of 50 °C from the natural stage up to 650 °C was
Fig. 2. Graphs of thermal demagnetization of the Maluiná sand-
stones from Loc. 5 for sample 20D. Top stereoprojections of the
directions of remanent magnetization (small circle directions be-
fore bedding correction (in situ), great circle directions after bed-
ding correction; N north) after each demagnetization step; the
biggest point means beginning of demagnetization. Full points
downward, empty points upward direction of remanent magneti-
zation. Bottom thermal behaviour of magnetization (curve J; J =
J
o
/J
t
, where J
o
is magnetization at laboratory temperature (ca.
20 °C) and J
t
magnetization after thermal step t °C), and magnetic
bulk susceptibility (curve K; K = K
o
/K
t
,
where K
o
is magnetic sus-
ceptibility at laboratory temperature (ca. 20 °C) and K
t
after thermal
step t °C). Zijderveld diagrams of XY and XZ elements of remanent
magnetization (McElhinny & McFadden 2000).
232 VOZÁROVÁ and TÚNYI
used. The remanent magnetic polarization as well as volume
magnetic susceptibility were measured after each demagneti-
zation step. Thermal cleaning was performed according to the
Magnetic Vacuum Control System, magnetic polarization was
measured on the spinner magnetometer JR-5 and volume
magnetic susceptibility on Kappabridge KLY-3 (all instru-
ments come from the AGICO Comp. of Brno). The demagne-
tization graphs, so-called Zijderveld-diagrams of the XY and
XZ components and stereographic projection of the remanent
magnetization were analysed. The mean paleodirection of
each locality (outcrops) was calculated using the Fisher statis-
tics (Fisher 1953).
Characteristic paleodirection of the measured sample was
chosen according to demagnetization graphs (even numbers
of Figs. 211). Two ways were used for analysis of paleomag-
netic data. At the first we considered the vectors of remanent
magnetic polarization as primary data. At the second one we
took vector differences between the steps of demagnetization,
which means the change of direction of magnetic polarization
during heating from temperature T
(i)
to temperature T
(i+1)
. The
dividing of thermal steps on three intervals (20200 °C, 200
400 °C and 400650 °C) was performed and used in both
analyses. The characteristic direction was chosen according to
Fisher statistical parameters from the six results (2 ways, 6
thermal intervals). Many samples as well as 8 localities with
remagnetization and a large dispersion of remanence direc-
tions were rejected.
The odd numbers of Figs. 211 present the stereoprojec-
tions of paleodirections for 5 localities together with the mean
direction and the circle into which the mean direction lies with
95% probability. Table 1 presents data of measured paleo-
magnetic characteristics. We can see that the localities are rep-
resented by varying numbers of samples (from 3 samples of
Loc. 9 Fig. 5, Table 1 to 14 samples of Loc. 12
Fig. 9, Table 1). The different scatter of paleodirections re-
flects the limited number of samples. The half angle of cone
of confidence varies from 8.9° to 25.0° (Table 1). Table 1
points to fact that some of the investigated rocks were weakly
Fig. 3. Stereoprojections of the paleodirections of 9 samples of the
Maluiná sandstones from Loc. 5. N north. Maltese cross
mean direction (full downward (see Fig. 9), empty upward);
circle around mean direction cone of confidence into which
mean direction (in position after bedding correction see Table 1)
lies with 95% probability (Fisher 1953; Table 1).
Fig. 4. Graphs of thermal demagnetization of the Maluiná volcani-
clastic sediments from Loc. 9 for sample 31B (see Fig. 2).
Fig. 5. Stereoprojections of paleodirections of 3 samples of the
Maluiná volcaniclastic sediments from Loc. 9 (see Fig. 3).
magnetized. Magnetic bulk susceptibility varies from 3.7 to
942.0
×
10
6
u. SI and remanent magnetic polarization from
0.061 nT to 6.867 nT (Table 1). The
α
95
circles of confidence
are comparable or equal before and after bedding correction.
Locality 6 is the only one, in which the fold test was positive.
The value of angle
α
95
in position before bedding correction
(22.7 Table 1) is greater than after bedding correction
(19.1 Table 1). Magnetic declination varies from 179°
(Loc. 17; Table 1) to 237° (Loc. 21; Table 1) and magnetic in-
clination from 44° (Loc. 21; Table 1) to 14° (Loc. 9; Ta-
THE ILLAWARRA REVERSAL IN THE PERMIAN OF THE HRONIC NAPPE 233
Fig. 6. Graphs of thermal demagnetization of the Maluiná sand-
stones from Loc. 11 for sample 39B (see Fig. 2).
Table 1: Paleomagnetic characteristics of the Maluiná Formation (sediments and volcanics). Loc. number of locality; N number of mea-
sured samples, n number of used samples; D°, I° declination and inclination of characteristic remanent magnetization; k statistical preci-
sion parameter;
α
°
95
half angle of circle of confidence into which the mean paleodirection is located with 95% probability; BBC before bed-
ding correction; ABC after bedding correction; J [nT] mean intenzity of remanent magnetization in natural state (at 20 °C);
κ
[
×
10
6
u. SI]
mean value of bulk magnetic susceptibility in natural state (at 20 °C); Pol. polarity (N normal, R reversed, I intermediate).
BBC
ABC
Loc.
N/n
Dº
Iº
k
=º
95
Dº
Iº
k
=º
95
J [nT]
k
´10
-6
u. SI Pol.
1
27/16
133
-57
31.8
6.6
133
-57
31.8
6.6
1.170
676.6
I
2
19/12
352
63
10.7
13.9
351
43
10.7
13.9
0.256
593.6
N
3
23/ -
-
-
-
-
-
-
-
-
-
-
4
30/10
206
-34
15.8
12.5
200
-19
15.8
12.5
0.633
82.6
R
5
18/9
241
-21
31.5
9.3
230
-26
31.5
9.3
0.906
56.9
R
6
15/5
212
-53
12.3
22.7
184
-30
17.0
19.1
0.304
39.2
R
7
20/5
94
-41
14.3
20.9
126
-33
14.3
20.9
0.183
61.7
I
8
10/6
61
82
16.5
17.0
4
37
16.5
17.0
0.068
213.1
N
9
4/3
260
-30
53.8
17.0
247
-14
53.8
17.0
1.119
267.0
R
10
19/ -
-
-
-
-
-
-
-
-
-
-
11
16/9
251
-38
13.1
14.8
220
-24
13.1
14.8
0.245
31.3
R
12
18/14
36
61
12.7
11.6
11
38
12.7
11.6
0.244
38.5
N
13
12/ -
-
-
-
-
-
-
-
-
-
-
14
13/6
70
32
18.8
15.9
57
33
18.8
15.9
0.239
63.4
N
15
15/9
99
40
25.8
10.3
60
35
25.8
10.3
0.254
118.5
N
16
4/ -
-
-
-
-
-
-
-
-
-
-
17
5/5
183
-48
10.3
25.0
179
-24
10.3
25.0
0.061
3.7
R
18
9/3
318
60
48.2
18.0
318
60
48.2
18.0
6.795
272.5
I
19
21/ -
-
-
-
-
-
-
-
-
-
-
20
13/ -
-
-
-
-
-
-
-
-
-
-
21
8/6
274
-30
59.4
8.8
237
-44
57.3
8.9
6.867
942.0
R
22
16/ -
-
-
-
-
-
-
-
-
-
-
23
15/ -
-
-
-
-
-
-
-
-
-
-
Fig. 7. Stereoprojections of the paleodirections of 9 samples of the
Maluiná sandstones from Loc. 11 (see Fig. 3).
ble 1) in the case of reversed magnetic polarization. Normal
magnetized samples have declinations between 351° (Loc. 2;
Table 1) and 60° (Loc. 15; Table 1) as well as inclinations be-
tween 33° (Loc. 14; Table 1) and 43° (Loc. 2; Table 1). If fol-
lowing criterions for antiparallel directions are used: reversed
when declination is 210°±40° and inclination is 30°±20°
and normal when declination is 30°±40° and inclination is
30°±20°, the localities 1, 7, and 18 show intermediate direc-
tions (Table 1). They cannot be used for magnetostratigraphic
interpretations.
Discussion and conclusion
The results are summarized in a schematic magnetostrati-
graphic profile for the Late Paleozoic of the Hronic Unit
(Fig. 12).
The set of the measured Upper Carboniferous samples is
small. The samples from Loc. 1 correspond to a system of
gabbro-dioritic dykes, which is coinstantaneous with the
234 VOZÁROVÁ and TÚNYI
Maluiná Formation andesite-basalt lava flows. The obtained
data polarity are intermediate (Table 1). The Upper Carbonif-
erous sediments of the Niná Boca Formation from Loc. 2 are
normally magnetized.
Indications of reversed magnetization were practically
found within the whole sedimentary sequence of the first
megacycle and the lowest part of the second megacycle of the
Maluiná Formation, localities 4, 5, 6, 9 and 11. Locality 7 is
intermediately magnetized (Table 1). There are significant in-
dications for normally magnetized samples from Loc. 8,
which corresponds to andesite/basalts of the first erruption
phase. A significant change in the polarity occurs between the
outcrops 11 (reversed) and 12 (normal) in the lower part of the
2nd megacycle (Fig. 12). Locality 13 is inhomogeneously
magnetized (
α
95
= 43°), it shows an intermediate direction,
and 9 of the 12 samples are not used for the calculation of the
mean direction. Therefore, locality 13 cannot be used for
magnetostratigraphic interpretations (Table 1). The middle
and the upper part of the second megacycle has indications
only for normal polarity (Fig. 12). The direct overlier of
Fig. 8. Graphs of thermal demagnetization of the Maluiná sand-
stones from Loc. 12 for sample 42A (see Fig. 2).
Fig. 9. Stereoprojections of the paleodirections of 14 samples of
the Maluiná sandstones from Loc. 12 (see Fig. 3).
Fig. 10. Graphs of thermal demagnetization of the Maluiná mud-
stones and sandstones from Loc. 15 for sample 51A (see Fig. 2).
Fig. 11. Stereoprojections of the paleodirections of 9 samples of
the Maluiná mudstones and sandstones from Loc. 15 (see Fig. 3).
THE ILLAWARRA REVERSAL IN THE PERMIAN OF THE HRONIC NAPPE 235
Fig. 12. Results of magnetostratigraphic investigation of the Late Paleozoic Hronic Unit (full bold line mean inclination of the character-
ictic remanent magnetization; interrupted line mean declination of the characteristic remanent magnetization). Explanation: 1. polymict
conglomerate; 2. coarse-grained sandstone; 3. medium- to fine-grained sandstone; 4. alternation of sandstone and shale; 5. shale, mudstone
and siltstone; 6. shale; 7. andesitic basalt; 8. volcaniclastic sediment; 9. gabbro-dioritic sill and dyke; 10. overthrust plane.
Loc. 13 (Figs. 1 and 12) was correlated with the uranium-
bearing horizon, from which come 263 Ma Pb/U radiometric
dating (Rojkoviè et al. 1992). Pure microfloristic data proved
the Autunian-Saxonian assemblages: Latensina trileta, Poto-
nieisporites radiosus, P. novicus, Limitisporites rectus, Ju-
gasporites delassaucei, Vittatina ovalis (Planderová in Pland-
erová & Vozárová 1982). Therefore the Illawarra Reversal
could be between locality 11 and 12 within the lower part of
236 VOZÁROVÁ and TÚNYI
the second megacycle. Such a position agrees best with the
Pb/U age of 263 Ma (Rojkoviè et al. 1992), because the Illa-
warra Reversal has 265 Ma (Menning 1995).
A further strong change in the inclination and declination
occurs between localities 15 and 17 (locality 16 must be ex-
cluded of its big
α
95
= 55.5°), probably at the base of the 3rd
megacycle. The major part of the 3rd megacycle consists of
andesite/basalt volcanites. The localities 17 and 21 have re-
versed polarity, wheras locality 18 has an intermediate direc-
tion (Table 1).
We assume, that the sediments of the Niná Boca Forma-
tion and the whole 1st megacycle of the Maluiná Formation,
as well as the lower part of the 2nd megacycle, belong to the
Carboniferous-Permian Reversed Megazone (Menning 1995;
formerly the Kiaman Magnetic Interval Irving & Parry
1963, later abandoned by Irving & Pullaiah 1976 and replaced
by the Permo-Carboniferous Reversed Superchrone). Within
the Carboniferous-Permian Reversed Megazone (CPRM),
several normal zones (according to Menning (2001) at least
five horizons) were described. Two were identified near the
Carboniferous-Permian boundary of the Transcaucasus suc-
cession (296 Ma; Khramov & Davydov 1991). Two further
normal zones occur in the volcanics of the Tholey Subgroup
of the Saar-Nahe-Basin (291 Ma; Berthold et al. 1975). A fifth
normal zone is found in the Garber Sandstone (Oklahoma,
about 280 Ma; Peterson & Nairn 1971).
There is evidence that within the lower part of the 2nd
megacycle (Fig. 12) a systematic change in the polarity oc-
curs. This zone could be correlated with Illawarra Reversal.
This assumption is supported by the radiometric data 263 Ma
from the uranium-bearing horizon which is lithostratigraphi-
cally correlated approximately with the middle part of the sec-
ond megacycle. The age of IR is first-order time marker by
Menning (1995) at about 265 Ma. Thus, the middle and the
upper part of the 2nd megacycle as well as the 3rd megacycle
should be correlated with the Permian-Triassic Mixed Mega-
zone (Menning 1995).
The following facts were obtained by magnetostratigraphic
investigations:
1. The Autunian-Saxonian sequence is subdivided by a
strong change of polarity, which is interpreted as the Illawarra
Reversal. The magnetostratigraphic boundary represented by
this strong change of polarity falls within the 2nd megacycle
of the Maluiná Formation. Changes in the polarity are not
connected with lithological boundaries. Thus, facies below
and above the assumed Illawarra Reversal are similar.
2. The polarity determination in the whole complex of col-
lected sediments is complicated. Additional investigations
must be carried out using more outcrops and finer-grained
samples, as far as possible, to confirm our results.
Acknowledgments: This work was supported by Grant No.
1/5153/98 from the Slovak Grant Agency VEGA. The authors
are grateful to M. Menning for his helpful suggestions and
critical review of the manuscript.
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