Fałd Brzanka-Liwocz (Polskie Karpaty Środkowe)

Henryk Świdziński


The Brzanka-Liwocz fold (Polish Central Carpathians)

The Brzanka—Liwocz fold is one of the principal individualized fold within the Silesian nappe in the central part of the Polish Outer Carpathians. It is extending for 38 km between the locality Siemiechów (near Zakliczyn on the Dunajec River) and the Wisłoka River. The eastern prolongation of this fold known as the Podzamcze fold extends east of the Wisłoka River and differs somewhat in structure from the Brzanka— Liwocz fold proper. Two series are distinguished in the structure of the Brzanka—Liwocz fold: the folded flysch and the Quaternary cover. The oldest members of the flysch series are exposed in the core of the fold. They consist of shales, predominantly black, described by V. Uh1ig (1883) under the name of „black Liwocz shales” containing poorly preserved ammonites. The studies of the present author indicate that at least two members can be distinguished within the Liwocz shales in the sense of Uhlig. The older member, i.e. the „Lower Liwocz shales” corresponds to the Upper Cieszyn shales (Valanginian — Hauterivian) in the standard division of the Silesian series of the Carpathian Flysch, while the upper member (Upper Liwocz shales) is equivalent to the Verovice beds (Barremian — Aptian) and the Lgota beds (Albian — Lower Cenomanian) in the standard division.

This member consists of marly shales, c. 200—300 m thick, strongly folded, exposed in the core of the fold. Rare sandstone beds are 1—5 cm thick, thicker beds being exceptional. The sandstones are fine-grained, dark-grey with calcareous cement. Convolute bedding is present in the thicker beds. Joints are healed with calcite. Thin intercalations of siderite are present occasionally. The „Lower Liwocz shales” correspond lithologically to the Upper Cieszyn shales, differing only in one feature: the sandstones contain sometimes a siliceous cement locally abundant, and forming bands of black flint within the sandstone beds. The presence of red clayey shales within the black Liwocz shales require further study. Some of these red shales 'belong undoubtedly to the Godula beds. However, the geological position of other occurrences of red shales remains unsolved. In an apparently normal stratigraphic succession occurs a narrow band of red shales separating the Upper Cieszyn shales from the Verovice beds. Hitherto no red shales were known in the Lower Cretaceous of the Polish Carpathians.

This member consists of black shales, non-calcareous, with very rare and thin beds of dark quartzitic sandstones. The shales contain occasionally small sphaerosiderites. The lithologic development and the position in the succession permits to correlate this member with the Verovice beds.

These beds form the uppermost part of the upper member of the „Liwocz shales” . They are present both in the northern and in the southern limb of the Brzanka-Liwocz fold. The profile of the Lgota beds begins with non-calcareous black shales and siliceous sandstones, thin- and medium-bedded, often with black flint bands in the middle part of the beds. Siderite intercalations are present occasionally. The upper part of the profile of the Lgota beds consists of quartz sandstones, light-coloured, thick-bedded, accompanied by siliceous sandstones, and thick-bedded greywackes. Locally the light-coloured thick-bedded sandstones contain intercalations of glauconitic sandstones, dark-green, containing fragmented bryozoa, crinoids, and mollusc shells.

The Godula beds show differences in their lithological development in the two limbs of the Brzanka-Liwocz fold. In the southern limb wiiere the succession is normal the base of the Godula beds, poorly exposed, consist probably of red shales, followed by tough glauconitic sandstones, dark-grey, thick-, medium- and thin-bedded, alternating with green and black shales. A few intercalations of red shales are present among greenish micaceous sandstones just below the peak of Liwocz. Sandstones of the same type are forming the peak of Liwocz. Variegated shales and glauconitic sandstones are filling a narrow syncline, contacting tectonically with the uderlying black shales of the Lower Cretaceous. In the southern limb of the Brzanka-Liwocz fold they are passing into the overlying Istebna beds. In the eastern extremity of the fold the Godula beds are nearly completely tectonically reduced. In the northern limb of the fold the sandstones are poorly developed and the Godula beds consist chiefly of variegated shales.

Similarly as in the classical profile of the Istebna beds in the Silesian Beskid range, this member consists in the Brzanka-Liwocz fold of the LowTer Istebna beds (Senonian) composed of thick-bedded sandstones followed by the Upper Istebna beds (Palaeocene) composed of two black shale series separated by a sandstone complex. The sandstones of the Istebna beds are thick-bedded, light-coloured, feldspathic, poorly cemented. The sandstones of the Upper Istebna beds have a calcareous cement irregularly distributed in the beds, resulting in the formation of large balls during weathering. The shales of the Istebna beds are black and dark-grey, often sandy, and contain locally lenses of siderite and intercalations of thin-bedded tough laminated sandstones.

The Upper Istebna beds are followed by variegated shales with. an intercalation of the Ciężkowice sandstone and green shales of the hieroglyphic beds. The Ciężkowice sandstone displays a typical development, being very thick-bedded, light-coloured, pebbly and non-calcareous. The described succession is characteristic for the southern limb of the fold. In the northern limb the Lower Eocene consists entirely of variegated shales 200—300 m thick, with rare lenticular intercalations of manganosiderites.

The Upper Eocene begins with Globigerina marls, a few metres thick, greenish-grey, light-coloured on weathered surfaces Both soft and hard varieties are present. The marls are overlain by the Menilite beds, c. 80 m thick, beginnning with basal hornstones a few m thick, followed by brown- -black fissile shales. The latter contain in their upper part numerous intercalations of medium- and thick-bedded sandstones, grey coloured, micaceous, poorly cemented. They are similar to the sandstones of the overlying Krosno beds, and the presence of glauconite is a feature common with the Magdalena sandstones. Very good exposures of the Menilite beds are situated on the right bank of the Wisłoka river, south of Kołaczyce (Fig. 4).

The thick-bedded sandstones of the lower complex reach a thickness of c. 400 m. The sandstones are grey, micaceous, usually soft, but occasional intercalations of hard sandstones form ribs and hills marked in the morphology. Graded bedding is common. The valley of the Wisłoka river offers good exposures of the Krosno beds.

Slope loams are forming a continuous cover especially on the northern and eastern slope of Mt Liwocz. The loams are silty, yellow-coloured, homogenous and often loess-like. Their thickness reaches a few metres in the lower part of the slopes decreasing towards the summit. „Mixed” gravels consisting of pebbles of Carpathian and Scandinavian rocks and larger erratic boulders are present at the base of the loams. The pebbles and boulders of Scandinavian rocks are derived from the destroyed moraine of the Mindel glaciation. The loams are partly a produce of frost weathering of the flysch rocks and were formed in a periglacial climate which returned at least three times over the described area. A part of the loams may represent a true sub-aerial loess, related with the Wurm glaciation. Two levels of flats are distinctly marked in the morphology. The higher level, 40—50 m above the river bed is more extensive than the lower 20—25 m one. The both flats are remnants of high alluvial terraces the first formed during the Mindel glaciation and the second during the Riss glaciation. The both terraces are composed of gravels consisting almost exclusively of pebbles of flysch rocks. The admixture of Scandinavian rocks is very small. Both terraces are covered by loess. The principal terrace forming the bottom of the Wisłoka river valley is elevated 5—10 m above the river bed. This terrace is composed of alluvial material deposited during the Wiirm glaciation, overlain by silty gravels of Holocene age. The flood terrace extending along the river beds is 1,5—2 m high. Numerous landslides are present on the area of occurrence of Eocene variegated shales and of the shales of the Istebna beds. Landslides and creep of weathered material are common on the northern slopes of the Liwocz Mt.

The Liwocz fold has a very complicated tectonic structure. The lack of good exposures, especially in the northern part of the area hampers the elucidation of all details of its structure. The southern limb of the Liwocz anticline consisting of the Istebna beds and the Godula beds dipping to the south-west has a fairly regular structure. The Lower Cretaceous rocks forming the core of the anticline are intensely folded, steeply dipping, locally fractured and rolled out. Squeezing out of beds is also marked in the northern limb of the anticline, resulting in abnormal contacts e.g. of the Lgota beds with the shales of the Upper Istebna beds. The younger part of the northern limb composed of Eocene variegated shales, Menilite shales and Krosno beds has a fairly regular structure. Complications of structure of the southern limb are also marked at the eastern extremity of the Liwocz anticline, where step-faults cause a gradual reduction of very thick complexes of the Godula beds and Istebna beds. Numerous transverse and longitudinal faults are crossing the Liwocz anticline. The most distinct „principal fault” (Fig. 2, A—B) crosses the entire fold and shifts the eastern block northward. The differences in the structure of the Liwocz fold and of the Podzamcze fold suggest the presence of another fault zone separating these two tectonic units. This fault zone determined the location of the gap valley of the Wisłoka river.

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