Płaszczowina skolska w regionie Czeremoszu

Jan Wdowiarz


The Skole nappe in the region of the Czeremosz

The geological description of the Carpathians in the Czeremosz region had already been published by the „Geological Atlas of Galicia“, but the first detailed mapping was commenced by B. Świderski (the Pokucie nappe), followed by Z. Pazdro, H. Teisseyre , A. Tokarski and the present writer. Litholosical and strati graphical description. Cretaceous. Inoceramian beds comprise two divisions: lower, consisting of sandstones and shales and upper formed of sandstones. Lower Inoceramian beds are represented by a few lithological types, namelly: argillaceous or marly shales, grey, pale - green or blue; flaggy sandstones, bluish - grey, calcareous; very infrequent hard marls; conglomerates and blue clays. The distribution of these types vertically and horizontally is variable and the lithological appearance of these types varies from place to place. The thickness is also variable, generally very great. Upper Inocerami an beds. On the contrary, the thickness of this sandstones series is small, 120 m at most. The main lithological type is represented by sandstones (70 — 90%), which are flaggy, calcareous, grey, brown on weathering. Subordinate shales are grey or dark grey. Seldom conglomerates are interbedded. Eocene is composed of the Jamna sandstone, Hieroglyphic beds and Menilite shales. Jamna sands tones . They are thick-bedded or flaggy sandstones alternating with green and sometimes red shales. The Jamna sandstones appear in several belts, in which they show facial differences. The bottom of this complex consists usually of thin - bedded, platy sandstones with green shales. In this case there is a gradual transition from the Inoceramian beds into the Jamna sandstone. In some places the base of the Jamna sandstone is constituted by red and green shales with intercalations of sandstones ; in such a base the contact with the Inoceramian beds is usually sharp. Very infrequently the series begins with thick - bedded sandstones at the base. Red and green shales appear, as mentioned above, just over the Inoceramian beds or a little higher up over the basal thin - bedded sandstones and under the thick-bedded sandstones; they may also be interbedded in flaggy sandstones with green shales The most frequent case is that the red shales do not appear in the lower part of the Jamna series, being probable pressed out. at places and if they do appear, traced horizontally frequently disappear and occur at short distances. The thickness of variegated beds is small, usually a few meters only. In the upper part of the Jamna series the red shales occur very infrequently and appear in a very small thickness (several cm or a few m at most) as incontinuous streaks. For the Jamna series thick - bedded sandstones are very characteristic, appearing in two and at places in three belts. They form continuous beds, but sometimes they thin out and gradually disappear; their thickness is very variable. In different belts their facial development is changeable, but on the whole these differences are small. The differences lie in the presence or absence of glauconite, in the content of calcium carbonate, competence and the weathered products. Often they form ruinous forms when weathered, which are composed of more resistant parts of the sandstone. The interbedded or covering flagstones alternating with shales are very changeable in their thickness. They form interbedded complexes among the thick-bedded sandstones; intercalations of shales, prevailing sometimes in some cross - section, may be observed. Shales are variable in colour, sometimes calcareous or silicified. Hieroglyphi c beds consist of thin-bedded, flaggy, grey or grey-green, siliceous sandstones with mostly green or sometimes grey and red shales. In many places owing to difficulties of their seperation from the Jamna series they cannot be presented in the map, but are linked with the Jamna series. Often the intercalations of thin-bedded sandstones and shales interbedded with thick-bedded Jamna sandstones are very much the same as the Hieroglyphic beds in the top of the Jamna Series. Menilite shales with Silex. They occur only in Bialoberezka and in the stream Bereznica and its affluents. In Bialoberezka in the left bank of the Czeremosz in a small exposure thin-bedded silex (hornstones) may be observed and thick siliceous marls alternating with dark, green weathering shales. They are succeeded by black shales, brown on weathering, with thin, feebly calcareous sandstones. These beds also appear in the right bank of the Czeremosz. In the western part of the region the Menilite shales contain thin bands of silex and hard siliceous sandstones in their lower part. They are covered by normal Menilite shales. Review of stratigraphy. Paul aud Tietze were the first geologists who made an attempt to solve the East Carpathians, stratigraphy. The lowest beds, consideted as Eocene were called the Ropi anka beds. Later Zube r after many years of investigations having found some fossils, (mostly shells of Inofceramus) proved the Cretaceous age of the Ropianka beds. The above lying beds were called „Platy beds“ by him, although he himself did not consider this term as very approppiate. They comprised beds lying between the „Ropianka beds and the Jamna sandstone, Later Zube r replaced they term „Ropianka beds' by „Lower Inoceramian beds“, and „Platy beds“, by „Upper Inoceramian beds“ (18). The upper boundary of the lower Inoceramian beds was laid by him where marls with fucoids disappear and bluish flaggy hierogliphic sandstones with calcite veins become prevalent“. My observation confirm this division, as I have not noticed any marls interbedded in the sandstone complex. This contains lithological types of the lower complex but on the whole the sandstones of the lower complex are different; the difference is striking especially on weathering. Zube r underlines that the sandstones become rusty or brown on weathering, and that conglomerates are infrequent in the lower division, while they are common in the upper division. He also adds that conglomerates with bryzoa and other organic fragments are frequents; also Inoceramus shells appear (18). Zube r regarded the overlying red and green shales as belonging to the upper division, but I think they should be seperated from it. B. Świderski (10), who worked north of my district, separated in his map „Inoceramian beds“ and „Platy beds“ although this last term had already been abandoned by Zube r , but in another general map (13) of Świderski Cretaceous beds were not divided. In the explanatory texst Świderski states that he had been unable to follow the subdivisions of Zuber in the whole area of the Pokucie folds. H. Teisseyre (13) in a paper regarding the region situated south from the area surveyed by the present writer, separated „Inoceramian beds“ covered by “Platy beds”, but from his description one may conclude that a part of the lower division was attached to the upper division, as the author himself surmised. In that area the seperation is not easy and requires knowledge of the area, lying on the left bank of the Czeremosz. Bujalski on his maps of Nadworna (3) and of the Prut valley (2) did not introduce any division of the Inoceramian beds. The red shales with sandstones linked by Zub e r with the Upper Ihoceramian beds should be considered as belonging to the Jamna complex. Red shales never appear in the Inoceramian beds, on the contrary they occur in overlying beds. They contain sandstones similar to some sandstones of the, Inoceramian beds, but only in passage beds do such sandstones occur; where red shales are not in contact with the Inoceramian beds but occupy a higher position, the intervening beds have the character of transition series. Red shales were separated by B u j a l s k i (2, 3) in the region of Bitków and the Prut, as a separate complex. The term of Jamna sandstone was introduced by Tietze and Paul (14), who regarded its age as Middle Cretaceous. Walter and Dunikowski having found nummulites in similar sandstones in the Western Carpathians regarded all thickbedded sandstones in the Carpatians as Eocene. However Zuber (18) who in 1884 found numerous large Inoceramus shells in this sandstone at Dora, considered this sandstone as of Upper and perhaps Middle Cretaceous age. Later workers like Bujalski, Jabłoński , Tołwiński and Weigner adscribed Cretaceous age to the Jamna sandstone, but later in their map 1:200 000 they sign this sandstone in eastern portion of the map as Eocene (1). Świderski (10) called attention to this difference of opinions; according to him, the Jamna sandstones connected with Cretaceous beds by gradual passages, should be regarded as a shallow-water deposit and probably they do not represent a continuous complex. According to Świderski in the absence of index fossils, the Jamna sandstones may be regarded as Cretaceous or Palaeocene depending on the more or less exact contact with beds, lying on their top or at the base. Tołwiński (15) on the Skole sheet regards the Jamna sandstones as Cretaceous, H. Teisseyre (13) in the Żabie district as Eocene, but without giving any proofs supporting this view. Bujalski (3) in his explanatory note to the map of the Bitkow region regards the Jamna sandstones together with red shales as belonging either to Cretaceous or to the Eocene. In the explanation of the map 1:200.000 of the Eastern Carpathians edited by Tołwiński (16) the Jamna sandstone belongs to the Eocene (although it is still marked with green colour on the map). Also Świ - dziński (12) considers the thick-bedded sandstones from Selatyn in Bukowina as belonging to the Eocene. This review indicates that there are differences in the views on the age of the Jamna sandstone. Bui there are certain proofs that the sandstone should be regarded as Eocene. In the place where Zuber found fossils apparently supporting the view of Cretaceous age of the Jamna sandstone, B u jalski (2) in a recent map marks the Inoceramian beds and not typical Jamna sandstone. It would result that the beds with Inoceramus fragments were erroneously taken by Zuber for the Jamna sandstone. The sandstones from the district of Przemyśl and Spas regarded by Zube r as the Jamna sandstone, are not belonging to this horizon, as their outlook and succession of beds indicate. Thus Zuber ’s proof of Cretaceous age of the Jamna sandstone seems now very doubtful. Nummulites which have been found in the Jamna sandstone indicate its Eocene age. The lithological development of beds associated with the Jamna sandstone resembles the Eocene beds (i. e. Hieroglyphic beds). In the investigated area nummulites have been found in the beds covering the Jamna sandstones. Besides, K. Guzik has also found nummulites in the region lying in the west, but their position is unknown to- me. On the ground of these facts, I accept Eocene age for the Jamna sandstone, although the proof cannot yet be regarded as decisive. The sandstone complex on the top of the Inoceramian beds, so far regarded as of Upper Cretaceous age, may be long to the Palaeocene. Tectonics. The described sector belongs to an unit of higher order, which has been termed the Skole nappe. Within this unit the following elements of lower order can be distinguished: 1). the syncline of Uścieryki 2). the anticline of Jasienów 3). the syncline of Kochaniec 4). the anticline of Morylewa 5). the scale of Białoberezka 6). the synkline of Pisany Kamień 7). the overthrust of Bukowiec folds situated south of the discussed area, surveyed by H. Teissseyre (13), also belong to the Skole nappe. The separation of the Skole nappe is due to J. Nowak (5). The existence of this nappe which extends far to the west, was proved by Świderski (10). In the surveyed area the Skole nappe is more narrow and less pushed forward than in neighbouring sectors. This is markedly shown in comparison with the sector of the Prut. These features are connected with the transversal elevation of Pokucie. The nappe in this area has come across an obstacle in the form of the underlying Pokucie nappe and therefore has been checked in its progressive movement toward the foreland. Owing to this the innermost folds of the nappe have been overturned southward instead of forward („plis a rebours“). and strongly faulted. The frontal part has been pushed forward and flat overturned; in connection with it the northern limb of the frontal fold has been reduced and a part of the Cretaceous pressed out. From beneath the overthrust beds the Eocene variagated shales. Menilite shales and Polanica beds appear at the surface; these beds belong to the Pokucie nappe. South of the folds, with the Cretaceons in their cores of the Skole nappe the large syncline extends, built of the Krosno beds and Menilite shales. This large „central depression“ is overthrust by the Czarnohora nappe.

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