O rozmiarach przesunięć poziomych w północnych Karpatach Fliszowych

Henryk Świdziński


The extent of horizontal displacements in the Northern Flysch Carpathians

Transverse shortening in the Carpathian geosyncline results from overthrusts of nappes and folding of flysch rocks within these nappes. The extent of overthrusts was estimated formerly only by indirect reasoning, e.g. on the basis of facial differences between rocks of the individual tectonic units. Numerous bore-holes drilled in the Carpathians confirmed the existence of the nappe structure of the Carpathian range, and provided data permitting to estimate the magnitude of transverse shortening of the Carpathian geosyncline. The present paper dealing chiefly with Northern and North-Eastern Carpathians (Fig. 1) was presented at the XX-th Session of the International Geological Congress in Mexico (1956) and, similarly as other papers presented there, was not published hitherto.

North-Eastern Carpathians In the North-Eastern Carpathians the flysch is thrust over Miocene sediments filling the Carpathian foredeep. Two zones are distinguished within the Miocene sediments: an autochtonous zone not folded, and a folded zone extending along the front of the Carpathians and thrust over the former (M. Cizancourt, 1925). The extent of this overthrust proved by drilling amounts to 5—6 km (Cz. Kuźniar 1939, T. Chlebowski 1947, W. B. Sollogub 1955). Along the front of the Carpathians, the Miocene rocks are folded together with the flysch, forming the so-called „deep-seated folds”. Two such folds were distinguished in ithe region of Borysław (A. Heim 1919, K. Tołwiński 1934—37, I. K. Klitochenko et al. 1960 — Fig.2). Adding the extent of the overthrusts of these two folds determined in bore-holes a total of c. 8,5 km is obtained. The flysch beds of the Skole „nappe” are thrust over the deep-seated folds in the discussed region. The extent of this overthrust is estimated as at least 8,5 km. Adding this to the previously obtained value, a total overthrust of not less than 17 km is obtained. However the general character of tectonic deformations in the discussed region suggests that the true displacement of the front of the Carpathians by thrusting over the Miocene rocks is larger and amounts to 20 km at least. The Skole nappe consists of several smaller units having the character of recumbent folds thrust one upon another with ventral limbs worn out (B. Bujalski, 1925, 1938). In the region of Nadworna (Fig. 3) the proven overthrust of the first fold of the Skole „nappe” amounts to not less than 12 km while the second fold is thrust over the first one for at least 10 km. Stretching out the folds in the Miocene rocks and adding the overthrusts of the first two folds of the Skole „nappe” a total displacement of the frontal zone of the Carpathians amounting to not less than 40 km is obtained. Farther east (Fig. 4, 5, 6) the minimum value of thrusting of the front of the Carpathians over the foreland is estimated as 27 km. The geological structure of the front of the Carpathians has the same character on the entire length of the North-Eastern Carpathians. Therefore it may be assumed, that the front of the flysch Carpathians is thrust over the Miocene in this region for at least 20—25 km. Adding the thrusting and folding of the Miocene rocks, the total thrusting of the marginal flysch units to the north-east over the foreland is estimated as at least 30—40 km. Northern and Western Carpathians. The structure of the front the Carpathians changes west of Przemyśl. The deep-seated folds disappear, the Skole „nappe” terminates west of Tarnow, while structurally higher nappes — the Sub-Silesian nappe and the Silesian nappe reach the front of the Carpathian range. In the region of Bochnia the Lower Tortonian beds folded together with the flysch are overlain by a scale of the Sub-Silesian nappe (Fig. 7, upper cross-section) (K. Skoczylas-Ciszewska, 1952). Bore-holes proved that this scale is thrust for 3 km over the Miocene beds. On the western end of the Northern Carpathians it has been proved by bore-holes that the Sub-Silesian nappe is overriding the Miocene for more than 7 km (Fig. 8). The higher Silesian nappe is thrust over the Sub-Silesian nappe for at least 10 km. It is estimated therefore, that the Silesian nappe was pushed to the north for at least 20 km.

Outer part of North-Eastern Carpathians. The outer part of North-Eastern Carpathians is formed by the Skole „nappe”, consisting of several relatively narrow recumbent anticlines with worn ventral limb (so-called „scales”) thrust one uppon another. The number of these scales is variable, ranging up to twelve. The greatest proven overthrust of the largest scale amounts to 3 km. The inner Carpathian Synclinorium, extending south of the Skole „nappe” and filled with the youngest flysch rocks of Oligocene age is strongly foldest. Its maximum width amounts to 30 km (Fig. 15). Inner part of North-Eastern Carpathians. The Kostrzyca-Skupowa unit (B. Świderski 1925, 1930) called also the Shipot unit (H. Świdziński, 1936) is the rust over the Inner Carpathian Synclinorium in this region. On the Czarna Cisa river the minimum extent of this overthrust is 3,5 km. The Pietros-Burkut tectonic unit, neighbouring the Shipot unit from the south constitutes a zone of strongly recumbent folds. The extent of the recumbency ranges up to 3 km (A. Tokarski, 1948). The innermost part of the North-Eastern Carpathians consist of the crystalline massif of Maramures. The massif is thrust over its foreland, the greatest visible extent of overthrust amounting to 4 km. The true overthrust is certainly much greater, and estimates of 18 km were published (L. G. Tkachuk, 1957). There are no data permitting to evaluate the magnitude of overthrusts of the remaining tectonic units of this part of the Carpathians (Fig. 15). Only in the case of one of the folds of the Dukla-Użok zone a visible overthrust has a minimum length of 2 km. Outer part of Northern Carpathians. The style of tectonic structure changes on the passage from the North- Eastern to the Northern Carpathians. The fold structures present in the former region are replaced by large flat overthrusts dominating in the latter one. The great overthrust of the Silesian nappe develops north of Krosno from a diapiric anticline. Torn apart slices of the Sub-Silesian nappe are present at the front of the Silesian nappe. The minimum averthrust of the Sub-Silesian nappe over the Skole nappe proved by bore-holes amounts to 8 km (Fig. 10 and Fig. 11). The Silesian nappe is thrust over the Sub- Silesian nappe for at least 9 km. It follows, that the Silesian nappe was displaced in relation to the Skole „nappe” for at least 17 km. Farther west the amplitude of this displacements probably increases. In the western part of the Northern Carpathians the Sub-Silesian nappe occur as torn apart slices at the front of the Silesian nappe, and appears also in tectonic windows within this tectonic unit (Fig. 15). The tectonic window of Lanckorona (M. Książkiewicz 1936) lies at a distance of 10 km from the front of the Silesian nappe, the tectonic window of (J. Nowak 1927, A. Tokarski 1967) Żywiec at a distance of 25 km, and the zones of tectonic windows of Rajibrot — Żegocina (M. Książkiewicz , 1953) at a mean distance of 16 km. Thus, in this part of the Carpathians the Silesian nappe is thrust over the Sub-Silesian nappe for 15—25 km. This overthrust is independent from the overriding of the Miocene rocks by the entire flysch which was discussed previously. External Klippes. So-called External Klippes are present at the contact of the Sub- Silesian and the Silesian nappes in the vicinities of Andrychów near Wadowice (M. Książkiewicz, 1935). They consist of block of crystalline and sedimentary rocks entirely different from the coeval flysch roks. This indicates the existence of another tectonic unit in the area of Wadowice. This unit is preserved only in the form of tectonic blocks. It is concluded therefore that the true overthrust of the Silesian nappe on the Sub-Silesian nappe is larger than that indicated by the present position of these two units. Magura nappe The Magura nappe forms the southernmost and the largest tectonic unit od the Flysch Carpathians. In the Northern Carpathians this nappe lies very flatly over its foreland (H. Świdziński 1947). Near Gorlice and Jasło it forms two large „tectonic peninsulae” and a few klippes (Fig. 12). Each of the peninsulae is 10—12 km long, and the klippes lie north of them. The last klippe is situated 25 km north of the front of the Magura nappe. However the length of the overthrust of this tectonic unit is still greater, as rocks belonging to the Inner Carpathian Synclinorium are present in tectonic windoiws well inside the Magura nappe. The distance from the northernmost klippe to the tectonic window at Bodaki amounts to 30 km (Fig. 12 and Fig. 13). This is the minimum value of the overthrust of the Magura nappe. The distance of other tectonic windows in the Magura nappe from the front of the nappe are following: for the Mszana Dolna window — 15 km, for the Smilno window (Fig. 12) — 25 km. The window of Ujście lies at a distance of 40 km from the northernmost klippe of the Magura nappe. THE

It follows from the preceding discussion, that the existence of the following overthrusts is firmly established in the Northern Carpathians:
1. The front of the Flysch Carpathians thrust over the Miocene for not less than 12—13 km
2. The Sub-Silesian nappe thrust over its foreland for not less than 7—8 km
3. The Silesian nappe thrust over the Sub-Silesian nappe for not less than 10—25 km
4. The magura nappe thrust over its foreland for not less than 20—40 km.
In the above calculations the transverse shortening of the geosyncline due to folding of the individual tectonic units was not considered. This transverse shortening of the Skole nappe in the North-Eastern Carpathians calculated for three cross-sections averaged 60 per cent. The present width of the Skole nappe amounting to 25 km, the original width of this unit is estimated as 62,5 km, the transverse shortening amounting to 37,5 km. A similar value of transverse shortening due to folding was obtained for the Inner Carpathian Synclinorium (61—66 per cent). At the present width of this unit amounts on the average to 20 km, the transverse shortening is estimated as 30 km. Assuming by analogy a similar percentage of shortening (60 per cent) for the tectonic units lying farther south, and taking into account their average width amounting to 20 km, the transverse shortening for the part of the Flysch Carpathians is astimated also as 30 km. Adding the preceding estimates we obtain:
1. Displacement of the front of the North-Eastern Carpathians towards the north-east, average 35 km
2. Transverse shortening of the Skole nappe 37 km
3. Horizontal displacement of the „scales” inside the Skole „nappe” on the average 8 „scales”, minimum displacement 1 km each 8 km
4. Transverse shortening of the inner Carpathian Synclinorium 30 km
5. Transverse shortening of the southern flysch zone 30 km Total 140 km
This is the minimum distance for which the inner border of the flysch zone in the North-Eastern Carpathians should be pushed back to find its original position. In the Northern Carpathians the calculation of the transverse shortening of the geosynclinal due to folding of the individual tectonic units is much more difficult. This shortening was conservatively estimated as amounting to 40 per cent. Taking into account the width of the flysch zone ranging from 60 to 100 km, the estimated values of the shortening will range between 40 and 65 km. Adding the length of overthrust calculated above (60 km) a total shortening 100—125 km is obtained. The Pieniny Klippen Belt, bordering the Flysch Carpathians from the south, should be pushed back south, for that distance to find its original position. The transverse shortening in the Northern Carpathians calculated above is smaller than in the North-Eastern Carpathians; this is caused by the following factors: a) a low estimated value of the overthrust of the front of the Carpathians over the foreland, b) not accounting for the overthrust of the Silesian nappe over the Skole nappe, c) not accounting for the transverse shortening related with the External Klippes of Andrychów. It follows from the evidence of large horizontal displacements in the Flysch Carpathians that the crystalline massifs of the Inner Carpathians can be no longer regarded as autochtonous. To find their original position these massifs should be pushed back even farther south than the southern border of the flysch zone, as the transverse shortening of the Pieniny Klippen Belt must be taken into account. However, the extremely complicated structure of the Pieniny Klippen Belt makes impossible even a crude estimate of the original width of that zone.

CONCLUSIONS The foregoing discussion may be summarized in the following conclusions: 1. The existence of large horizontal displacements was established in the Northern and in the North-Eastern Carpathians. Some of the individual tectonic units were displaced for 30—40 km. 2. The style of tectonic structure of the Flysch Carpathians markedly changes in the west-east direction. Flat overthrusts are predominating in the Western and Northern Carpathians. More regular folds are present in the North-Eastern Carpathians, but large horizontal displacements occur also in this part of the range. 3. The stretching back of the flysch cover results in the necessity of assuming large horizontal displacements of the crystalline massifs of the Inner Carpathians. Both the massifs of the Slovakian Block with the Tatra Mts and other mountain ranges, and the Maramures massif in the East can not be considered as autochtonous or even as parautochtonous and are not connected under the flysch cover with the rigid foreland of the Carpathians. 4. It follows from the establishment of large horizontal displacements that the problem of nappes in the Carpathians becomes rather a problem of terminology, and not an open question in the discussion of the structure of the Carpathians. It should be emphasized, that the tectonic style of the Carpathians differs markedly in some cases from that of the Alps. The most alpine character is displayed by the overthrust of the Magura unit, and the complex of the Silesian and Sub-Silesian units in the western part of the Northern Carpathians. These units may be properly termed nappes. 5. The presence of thin covers of flysch rocks of low rigidity, displaced over large distances is especially characteristic for the tectonics of the Northern Flysch Carpathians. The present author considers very difficult to explain the origin of such structural forms only by lateral (tangential) compression. The tectonic style of the Magura nappe led M. Lugeon in 1937 to reconsider the discarded theory of gravitational gliding „théorie d’écoulement tectonique” (M. Lugeon 1941, p. 82). 6. The presence of these thin nappe covers, the „en coulisse” structure of the Northern Carpathians, the relation of the Carpathians to the foreland, and the markedly heterogenic structure of this foreland, are contradicting in the opinion of the present writer, the theory of underthrusting („Unterschub”) proposed by H. Stille (1953).

Full Text: