GeolCarp_Vol57_No3_177

GEOLOGICA CARPATHICA, JUNE 2006, 57, 3, 177—184

www.geologicacarpathica.sk

Synsedimentary slumping in fold-and-thrust system of the

Magura Zone: evidence from olistoliths in the Beloveža

Formation (Zbludza area, Poland)

JANUSZ OLSZAK

AGH University of Science and Technology, Faculty of Geology, Geophysics and Environment Protection, Mickiewicza Str. 30,

30-059 Kraków, Poland; joszak@geol.agh.edu.pl

(Manuscript received May 12, 2005; accepted in revised form October 6, 2005)

Abstract: An accumulation of blocks of thick-bedded sandstones and marls, interpreted as olistoliths, was found in
the Beloveža Formation in the SE part of the Beskid Wyspowy range (Polish part of the Outer Western Carpathians).
The host sediments are bluish shales and thin-bedded fine-grained sandstones. Some bodies of marls and sandstones,
up to several millions of cubic meters in volume and standing out in relief, are also interpreted as olistoliths. The
olistoliths were deposited during synsedimentary shortening of the Magura Basin, by submarine slumps moving down
the slope of an accretionary prism, across depositional zones. The olistoliths described here resemble in their charac-
teristics and geological position those known from the Kamienica Nawojowska valley. This similarity may suggest that
olistoliths may have wider extent in this part of the Magura Nappe.

Key words: Outer Western Carpathians, Magura Nappe, Bystrica Subunit, olistoliths.

Introduction

Olistoliths have been found in the deposits of the Magu-
ra Nappe quite recently. They were earlier found in other
units of the Polish part of the Outer Western Carpathians:
Silesian Nappe (Szymakowska 1976) and Skole Nappe
(Dżułyński et al. 1979; Kotlarczyk 1988). In the Magura
Nappe, olistoliths have been found in the Kamienica Na-
wojowska valley (Bromowicz 1996, 1998), Jaworki
(Cieszkowski et al. 2003) and in the vicinity of Żywiec
and Sucha Beskidzka (Chodyń et al. 2003). Large sub-
marine slumps described earlier in the Magura Nappe, in-
clude those at Szczawa (Cieszkowski et al. 1987) and at
Poręba Wielka (Książkiewicz 1958), the latter described
as “wildflysch” by Burtan & Łydka (1978) and as chaot-
ic deposits—tectonic-melange (Oszczypko-Clowes & Osz-
czypko 2004).

The present author found large blocks of thick-bed-

ded sandstones and marls in the deposits of the Bystrica
Subunit, near Zbludza and Wola Kosnowa (Fig. 1). Some
of these rocks are in marked contrast with the host sedi-
ments of bluish shales and thin-bedded fine-grained sand-
stones.

Geological setting

The area between Zbludza and Wola Kosnowa (the SE

part of the Beskid Wyspowy) belongs to the Bystrica
(Nowy Sącz) Subunit of the Magura Nappe (Paul 1980).
The oldest strata exposed at the surface in this part of the
Bystrica Subunit belong to the Łabowa Shale Formation
(Lower and Middle Eocene; Fig. 1), which is overlain by

the Beloveža Formation (Early—Middle Eocene), up to
350 m thick in the Zbludza section (Oszczypko 1991;
Fig. 2). In the southern part of the area the Beloveža For-
mation is overlain by a series, 100—150 m thick, de-
scribed by Oszczypko (1991) as the Bystrica Formation
(Fig. 1) and composed of thick-bedded blue-grey, firmly
cemented marls (Łącko Marls), fine-grained sandstones
and shales. Higher in the section lies a series of rocks
lithologically similar to the Beloveža Formation but
with the Łącko marls – the Żeleźnikowa Formation. It is
overlain by the Maszkowice Member of the Magura For-
mation (Oszczypko et al. 1992), developed as thick-bed-
ded sandstones and submarine slumps with intercalations
of very thick-bedded Łącko marls. In the northern part of
the area, the Beloveža Formation is overthrusted on
thick-bedded sandstones of the Modyń Mountain
(Fig. 1). These sandstones belong probably to the Masz-
kowice Member as is indicated by the presence of the
Łącko marls, whose outcrops were found in the southern
margin of the Modyń range.

The blocks are embedded in deposits of the Beloveža

Formation (Figs. 1, 2), often at their contact with the
Łabowa Shale Formation (flysch with variegated shales).
Some blocks are included in a submarine slump. The
submarine slump consists of thick-bedded sandstone
blocks (Fig. 3) chaotically dispersed in uniform bluish
shale matrix. The slump clearly stands out within the de-
posits of the Beloveža Formation. Its contact with the
host deposits has been clearly observed in the northern
part of the outcrop. The contacts of the other blocks with
the deposits of the Beloveža Formation are less clear be-
cause the blocks have been excavated by the stream ero-
sion and possible even slightly moved.

179

OLISTOLITHS IN THE BELOVEŽA FORMATION (POLAND)

Description of the blocks

An exotic blocks or other rock mass transported by sub-

marine gravity sliding or slumping and included within
the binder of an olistostrome are called olistoliths (Bates
& Jackson 1980). The term “olistolith” is variously de-
fined in literature. Abbate et al. (1970) considered as olis-
toliths only the blocks larger than 4 m in length, reserving
the term “clast” for the smaller ones. A giant-sized block
has been called “olisthotrymma” (Richter 1973). The au-
thor uses the term “olistolith” in a less restrictive sense
with respect to their size. The blocks described here are
about 1 m to several meters in length, though some blocks
up to million cubic meters are also discussed here. Follow-
ing Bromowicz (1998) the blocks are described as mono-
lithic – built exclusively of one rock type, usually
sandstone or marl, and polylithic – composed of various
rock types, commonly sandstones, marls and shales.

The greatest accumulation of blocks was found in the

channel of the Zbludza Stream and in its left tributary
(Fig. 4). Exposures are relatively good and long but nar-
row with respect to block size. Some of the blocks lie
loose on the outcrop, but some are still embedded in their
host sediment – grey-bluish soft plastic clay with sparce,
chaotically scattered sandstone blocks. The most represen-
tative examples of blocks are described below.

An ellipsoidal, monolithic block O1 (Figs. 4B, 5) lies

in the channel of the left tributary of the Zbludza
Stream [GPS: 597 932; 192 260]. It is a fragment of a
thick (1.5—2 m) bed of brown-grey, fine-grained, slightly
graded sandstone with scattered grains up to five milime-
ters. The outer surfaces of the block are smooth, locally
covered with slickensides and patches of fibrous calcite.
The sole of the bed (Fig. 5) is covered with depositional
structures (hieroglyphs) and numerous straight and arcu-
ate fractures, locally with small steps due to displace-
ments up to 10—12 cm high, usually smaller (Fig. 6).

Nearby lies another, larger (at least 7.5 m

in volume),

block O2 (Fig. 4B) partly excavated by the stream. This is
a block of a thick (ca. 2 m) bed of brown-grey fine-grained
sandstone with dispersed granule-size grains. Its top is flat
and the other surfaces are even.

A submarine slump series – is exposed in the channel

of the Zbludza Stream [GPS: 597 850; 192 244] over a
length of 25 m. It consists of sandstone blocks (Figs. 4, 7)
chaotically embedded in bluish shales (Fig. 3). Below are
described those blocks which have at least about 1 m in
length. Two blocks of them (at least 12 m

and 2.5 m

) are

medium-grained, feebly cemented grey sandstone rich in
shale clasts. The sandstone is rich in coalified plant detri-
tus and chaotically dispersed flakes of muscovite up to
1 mm in size. The outer surfaces of block display flattened
fragments and numerous joints of various density and ori-
entation. Another five blocks (3.3 m

; 1.2 m

; 1.1 m

;

0.4 m

; 0.3 m

) included in the slump series consist of

fine-grained blue-grey, compact sandstone in some blocks
with lamination (horizontal or convolute), devoid of
abundant muscovite and detritus. The sandstones include
clay clasts with pyrite (2—4 cm in diameter), which acquire

Fig. 2. Lithostratigraphy of Bystrica Subunit in section of the
Zbludza Stream (partly based on Oszczypko 1991).

Fig. 3. Zbludza Stream. Block of thick-bedded sandstone embed-
ded in bluish matrix. Hammer (30 cm long) as a scale.

180

OLSZAK

a rusty crust when weathered. The flat outer surfaces of the
blocks display numerous fractures, often filled with thick
calcite veins, of various orientation and density, often
with small displacements. There is also a block (0.7 m

)

of blue-grey compact graded sandstone, with clasts up to
5—7 mm in size. A block of the Łącko-type marl is present

Fig. 4. Sketch of detailed location of the blocks in the Zbludza Stream and its tributary.

Fig. 5. Block O1 in the left tributary of the Zbludza Stream. Ham-
mer (30 cm long) as a scale.

Fig. 6. Small displacements (steps) on the O1 block surface. GPS
receiver (11 cm long) as a scale.

near the sandstone olistoliths (Figs. 4A, 8). It is a very well
rounded ovate, strongly fractured block with a complex
array of small steps on its surface.

Two blocks have also been found SW of the center of

Wola Kosnowa. A fragment of the first O3 (Fig. 1) [GPS:
599 999; 192 090] is exposed in the bed of a nameless

181

OLISTOLITHS IN THE BELOVEŽA FORMATION (POLAND)

Fig. 7. Zbludza Stream. Slump series contact with the host deposits.

Fig. 8. Zbludza Stream. Block of the Łącko-type marl. Hammer
(30 cm long) as a scale.

Fig. 9. View from Wola Kosnowa (from east).

stream, the other O4 (Fig. 1) [GPS: 600 055; 191 970] in a
field-road scarp. However, the exposures are so poor that
neither their size nor their shapes could be determined.
Both are at least 3—4 m thick and are polylithic (sand-
stone, marl, shale); the first is distinctly stratified.

Also interesting are the blocks labelled: A, B, C and D

on Fig. 1. They are marked in relief as domed hills (Fig. 9,

see also Bogacz & Węcławik 1969), with locally steep
slopes (NE slopes of olistolith A). The minimum vol-
umes of these blocks are estimated as: A – 2.5 10

B – 0.9 10

, C – 0.12 10

, D – 0.3 10

These seem to be polylithic blocks, composed mainly of
marls and sandstones. Their shapes are ellipsoidal and their
longer axes are oriented W—E, that is parallel to the structur-
al strike and perpendicular to the direction of thrusting.
Their internal structure was recognized in a few outcrops lo-
cated in road-cuts or by inspection of loose rock fragments
in ploughed fields, where the Łącko marls predominated.

Discussion

The blocks described above are interpreted as olistoliths

on the grounds of their litology, shape and relation to en-
compassing rocks. The rock types in the olistoliths, name-
ly the marls of the Łącko type and coarse-grained
sandstone with shale clasts, may come from the higher
members of the Bystrica Formation where these types of
rocks are common. So, the very coarse-grained sandstone
olistoliths with shale clasts may come from the Maszkow-
ice Member, as this type of sandstone is characteristic in
this member (Oszczypko et al. 1990; Oszczypko 1991).
The olistolith of marl may come from the Bystrica or
Żeleźnikowa Formation or even the Maszkowice Member.
The acceptance of such a source for the olistoliths seems
paradoxical at first glance, as they would come from the
stratigraphically higher members. However, as may be
seen in the stratigraphical scheme by Oszczypko (1991),
in Middle Eocene all the lithostratigraphic members con-
cerned are diachronous (Fig. 10), reflecting the outward
migration of the sedimentation zones. During the sedi-
mentation of the Beloveža Formation, the sediments of the
Maszkowice Member were already present at surface more
internally and possibly involved in thrusting.

Data from Poręba Górna (Oszczypko et al. 1999) and

from Żeleźnikowa (Oszczypko 1986) indicate that thick-
bedded sandstones and marls occur sporadically in the up-
per part of the Łabowa Shale Formation and in the
Beloveža Formation. Therefore, the olistoliths could be

183

OLISTOLITHS IN THE BELOVEŽA FORMATION (POLAND)

supplied from the fronts of the overriding tectonic slices
(Fig. 11) and their sliding transport could be much shorter
than in the case of their provenance from the higher lithos-
tratigraphic units.

The hills A, B, C and D (Fig. 1) may be considered as partly

excavated olistoliths of rocks more resistant to weathering
and erosion than their surrounding. They would thus be olis-
toliths of the Łącko-type marls (except for olistolith D), sup-
plied from the neighbouring Bystrica Formation.

The presence of olistoliths in the Beloveža Formation

indicates synsedimentary translation of sediments within
the Magura sedimentary basin by submarine gravity
movements. Such processes are corroborated by the pres-
ence of the submarine slump series, within the Beloveža
Formation. The poor cementation of the blocks, the nu-
merous fractures with slickensides visible on their surfac-
es, dense jointing and the prevalent smoothing on their
outer surfaces, all suggest that the blocks were subject to
transport and rounding. The outer surface of the olis-
tolith in the left tributary of the Zbludza Stream (Fig. 5),
characterized by a dense array of fine steps and the ovate
marl olistolith with the complex array of small steps on
its surface (Fig. 8), may be shaped by dilation during the
transport of poorly lithified sediment (Hoedemaeker
1973). Slickensides on the outer surfaces and calcite
veins in some olistoliths may come from a sedimentary
series that was already subject to tectonic deformation
soon after deposition.

Mobilization of large-scale mass-movements, capable of

translating sediments across depositional zones, required
northward inclination of the basin bottom in the southern
part of the depositional realm of the Magura Nappe (cf.
Bromowicz 1998), that is in the direction opposite to the
ongoing southward subduction (Oszczypko 1992; Nem-
čok et al. 2000). The pile of flysch nappes apparently
formed as an accretionary prism (Fig. 11) involving a ma-
jor part of the Magura Basin fill scraped off its basement.
The growth of the accretionary prism favoured the divi-
sion of the basin into longitudinal depositional zones,
now reflected in the diachronous lithostratigraphic units,
and at the same time led to downslope mass movements
across the depositional zones. A similar explanation, with
a subduction zone and an accretionary prism has been ac-
cepted by Kemkin (1996) for the origin of the turbidite-
olistostrome formations in the southern part of the
Sikhote-Alin range in Russia.

The olistoliths from Zbludza and Wola Kosnowa are

similar in geological position and size to those described
by Bromowicz (1998) from the Kamienica Nawojowska
valley, ca. 40 km east of the studied area. Blocks of sever-
al cubic meters and of the order of a million cubic meters
in size occur at both localities. Both have the same posi-
tion within the Beloveža Formation of the Bystrica Sub-
unit. The tectonic position of both sites is subject to the
same controversy. On the geological maps by Burtan et al.
(1981) and Żytko et al. (1989) both sites lie at the north-
ern margin of the Bystrica Subunit, and on the maps by
Paul (1980) and Malata et al. (1996) they are somewhat re-
moved from this margin.

Conclusions

The olistoliths found in the Beloveža Formation may

be interpreted as the result of synsedimentary shortening
of the Magura Basin, due to the southward subduction of
its basement. The occurrence of mass movements was
favoured by the northward gradient of the basin bottom,
related to the growth of an accretionary prism, and to
seismic activity characteristic of subduction zones and
active thrust faults. The characteristics of the olistoliths
indicate that their emplacement occurred before com-
plete lithification.

The similarity in lithology, size and setting of the olis-

toliths described here and those in the Kamienica Nawo-
jowska suggests that they may be present in an extensive
zone of the Bystrica Subunit, between both localities or
even beyond them. Thus the phenomenon considered
hitherto as a local one, may have a regional extent. The
poor exposure, typical of the Outer Carpathians makes
such olistoliths difficult to recognize, especially if their
lithology is not in such striking lithological contrast
with the embedding flysch strata, as in the case of so
called “exotics” of crystalline rocks, Paleozoic or Meso-
zoic limestones. A search for olistoliths in the Eocene of
the Magura Nappe, similar to those from Zbludza, Wola
Kosnowa and Kamienica Nawojowska may reveal their
importance for the reconstruction of the synorogenic sed-
imentation in the Magura realm.

Acknowledgments:

I express my sincere thanks to Profes-

sors J. Bromowicz, G. Haczewski and N. Oszczypko for
their assistance in the field and critical remarks on the
draft of this paper. This research has been supported by
statutory project AGH University of Science and Tech-
nology.

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