Grawitacyjne ześlizgi fliszu brzeżnej strefy Karpat w świetle nowej tektoniki globu ziemskiego

Stefan Połtowicz


Gravity slides of the Flysch Carpathian Marginal Zone in the light of new global tectonics

Palinspastic reconstruction of the Badenian sedimentary basin east of Kraków shows that the Carpathian margin in the Badenian had been several dozen kilometres south of its present position (fig. 1). The position of the Flysch Carpathian margin so far south at the time of the Badenian sedimentation allows for the inferences concerning the orogenic reduction of the external Flysch Carpathians. Along the geological cross-section Kraków — Nowy Targ the original width of the zones, which was taken over by the flysch deposits in the sedimentary basin, was at least 300 kilometres. The orogenic reduction of the external Flysch Carpathians exceeded 80%.

According to the plate tectonics theory the Alpine chains had been folded in the collision zone of the two continental plates, the Euroasiatic and the African (Fi|g. 2). In the Carpathians the subduction zone in the Tertiary ran along the contact line of the external and internal Carpathians, on the territory of the present-day Pieniny Klippen zone and in the narrow strip lying north of it. There exists a trace of the consumed part of the geosyncline apparent in the large regional dislocation called the „peripieninian lineament” which can be traced eastwards in Transcarpathian Ukraine and Maramureç (Roumania), The „peripieninian lineament” extends down to a considerable depth. According to the refraction method of seismic research, the Moho discontinuity is thrown down on its northern side by about 10.000 to 20.000 metres. The „peripieninian lineament” is most probably a young tectonic feature conditioned by the Middle and Late Kimmerigian faults. Along this feature at least from the Cretaceous till the end of Miocene there occurred underthrusting movements of the Euroasiatic plate and the consumption of the flysch geosyncline basement together with its foreland, and presumably of a considerable part of the Carpathian flysch (Fig. 2, 4). In the zone north of the Peripieninian lineament there is a narrow strip of the negative gravity anomalies which in the light of the new global tectonics very probably marks the regional chain of faults connected with the subduction of the Euroasiatic plate. These faults probably lie almost parallel to the Pieniny Klippen Zone (Fig. 3, 6). On the territories of western Slovakia and Poland in the „peripieninian lineament” in the Late Miocene there probably occurred subsidence movements causing the formation of the Orawa — Nowy Targ depression, filled with fresh water Neogene sediments (Fig. 5) more than 1500 metres thidk. The Tertiary suibduction zone of the Carpathian basement is still active tectonically. The contemporary uplifting movements noted in Slovakia and Maramures confirm this. The main orogenic reduction had taken place before the Badenian. The ocean crust of the flysch geosyncline basement had been consumed at that time. In the Badenian and Early Sarmatian the underthrusting movements of the basement had been temporarily weakened. The consedimentary longitudinal faults often had been formed then on the territory of the Carpathian Fordland. The longitudinal faults (NW — SE) of the Central Carpathian Foreland are specific for their greater width as compared to the transversal faults (Fig. 6). The width of the reflectionless zones is often several hundred metres and in places exceeds 1.5 kilometres. These zones may be interpreted as tension faults present in the continental plate boundary zone which is gradually subducted. The transversal dislocations (SW — NE) are often of transcurrerit or oblique-slip nature and along them there can be observed horizontal dislocations of the geologic boundaries. In the vicinity of one of these transcurrent faults a tectonic fissure was found in a borehole in the Malm limestones. Its slickensides points to horizontal displacement, (Pl. I) and it is filled with a clayey material containing Turanian microfauna. This attests to both the rejuvenation in Miocene of the older, fore-Cretaceous open fissures and their constriction as well as to the horizontal displacement after the Cretaceous.

Considerable narrowing of the flysch geosyncline and the far reaching displacement of the Carpathian nappes is usually explained by lateral stress causing the folding of the Carpathians. However, many facts indicate that in the formation of the flysch nappes, gravity tectonics played an important part. In the case of exclusive lateral stresses activity, the flysch rooks of the southernmost Magura nappe and the masses of the southern part of the lower tectonic units in the marginal Carpathians would form tectonic mega-breccias which would not be able to transfer strength farther north. Mega-breccias of this kind have never been observed anywhere. In the northern part of the Flysch Carpathians there usually are present complicated tectonic structures. There are several tectonic windows of different units of extremely intericate tectonics (Fig. 6). In the central and the southern part of the external Flysch Carpathians the tectonics is far less complicated than in the northern part. In the case of exclusive lateral stresses the most complicated structures would be formed in the southern part of the external Carpathians, in the vicinity of the active forces and not in the marginal zone of the Carpathians, on the peripheries of their activity. The fundamental cause of the tectogenesis of the marginal zone in the Carpathians was probably the equililbriufm disturbance caused by subduction and sliding northwards and north-eastwards of ,the foredeep axis. The absence of a wide zone of tensional faults in the southern part of marginal Flysch Carpathians can be explained by synchromic underthrust movements of the Carpathian basement, largely compensating for the gravity sliding of the flysch. The zone of tectonic windows of the Sub-Silesian nappe in the belt between Wadowice and Raj'brot (Fig. 7) can be the trace left over after the rupture of the Silesian nappe in front of the border of the overthrusted Magura nappe. The tensional fissures were filled with folded and diapiritioally squeezed out formations of the Sub-Silesian naippe.

The reconstruction of the palaeogeography of the Badenian saliniferous basin and the arrangement of the facial zones allows for the salt and the accompanying clay deposits to be considered the main factor facilitating the flysch gravity sliding on the territory east of Wield czka. The salt is plasticized already under the pressure of 25 kG/cm2 (which is equivalent to the push of rocks 120 metres thick). It is evident that on the territory west of Dębica the conditions needed for the beginning of the salt plasticization existed already at the end of Badenian and east of Dębica in the lower part of the Lower Sarmatian. Gradual shifting of the maximum zone of sinking of the Carpathian foredeep towards north and north-east had considerable influence on the gravity Sliding of the flysch in the marginal zone of the Carpathians. The third factor operating in the process of gravity equilibrium disturbance of the flysch rocks was the uplifting of the Flysch Carpathians in Sarmatian. It was probably then that the gravity slidings on a large scale began to form. They appeared along flat surfaces of décollement and slippage of flysch into the saliferous Badenian formation and in the eastern and southern part of the Carpathian foredeep into evaporite older than Badenian (the Worotyszcze Beds). On the contemporary territory of the Carpathians between Tarnów and Przemyśl towards the end of the sedimentation of the Lower Sarmatian the difference of level between the top of the saliferous series in the Carpathian foredeep and the surface of the Carpathians was at least 2500 — 3000 metres. The average slope of the evaporites top surface was 4 — 5% (2—3°). This slope is enough to originate the gravity siidings along the plasticized salts and clay deposits. Miocene salts played a great part in the gravity slidings of the flysch in the external Carpathians only in the territory east of Wieliczka because the main saliniferous basin was not extended farther west. In the western Carpathians the role of salts was probably taken over by the clay sediments of the Sub-Silesian nappe. They formed tectonic breccia in the base of Silesian nappe. Miocene clay formations appearing under the Carpathian flysch fault participated with them in the process. The surface shape analysis of the overthrust of the Tesehen nappe, which had on a considerable area a thickness of only several hundred metres, also implies that the main factor in flysch shifting are gravity forces. So thin a rock cover could not be shifted by means of lateral compression, but it could slide into its foreland under the influence of gravity forces.

Seismic exploration and test borings in the Carpathian Foreland and the margin zone allows for reconstruction of the history of the development of the Fore-Carpathian basin in the Badenian and Sarmatian. It is illustrated by a synthetic cross-section transversaly led across the Fore- Carpathian basin in the vicinity of the eastern Polish boundaries (Fig. 6. 8). In the tectonic development of the described zone can be distinguished several stages: Stage I. Period of the evaporates sedimentation (the beginning of Middle Badenian). In the southern part of the basin the sedimentation of evaporites together with the sedimentation of salts occurred. In the northern part anhydrites and gypsum were deposited, and in the marginal zone of the basin carbonate rocks of chemical origin and clastic rocks and Lithothamnium limestones were formed. In the southern part the Miocene sea transgressed over the territory of the Carpathians. The appearance of Miocene deposits on the flysch gives evidence of this. Stage II. Period of Chodenice Beds sedimentation (Middle Badenian) and sedimentation of Graibowiec Beds (Late Badenian). Tectonic movements caused the dislocation to the north of the increased subsidence zone which resulted in quicker sedimentation in the axial part of the Fore-Carpathian basin. This part was sagging quicker than in the peripheral parts of the sedimentary basin. Saltatory increase in thickness of the deposits in the fault zones can point to the considementary character of the faults. Towards the end of Badenian, flysch rocks had been partly thrust over the Badenian deposits along the flat surfaces of décollement. Stage III. Lower Sarmatian. Further dislocation followed towards the north and northeast of the axis of the sedimentary basin and quick sagging of the bottom was compensated by sedimentation. The Lower Sarmatian deposits reached a thickness in some places exceeding 3.000 metres. The southern part of this territory had been uplifted. The vivacity of tectonic activity in the subduction zone resulted in a -gradual overthrusting of the flysch over the autochthonous Miocene deposits in the Carpathian foreland. Longitudinal faults, probably of tensive character, showed considerable activity. Stage IV Boundary of the Early and Late Sarmatian. Further uplifting of the Elysoh Carpathians caused the disturbance of the (gravity equilibrium between the margin zone of the Carpathians and the foreland. Plasticized salts under the influence of rock cover were the most easily influenced environment for the formation of gravity slidings, which encompensated the marginal zone of the Carpathians. On the territory of the Central Carpathians, Badenian salts served as the tectonic „greese”, on the territory of Eastern and Southern Carpathians — the salts of the Worotyszcze Beds. Because of wide expansion of salts in the formations of the Fore-Carpathian basin the gravity slides of the marginal flysch zone were regional phenomena. In the Western Carpathians the role of the medium facilitating the gravity flysch dislocation was taken over by clay sediments of the Sub-Silesian nappe. Stage V. Late Sarmatian — Pliocene. During the Late Sarmatian the area of the Carpathian Foreland was uplifted. This caused the regression of the sea towards the southeast. Partial erosion of the Lower Sarmatian deposits followed. Further flysh gravity slidings occurred, encompassing the area of the Carpathians about 20 km wide. The subduction zone became active, further thrusting movements followed in the Carpathian Foreland. The presentday situation is the result of the latest movements of the basement of the Carpathians and its foreland. The push of the internal Carpathian margin up to its present position occurred after the Early Sarmatian. These movements were contemporary with the analogous phenomena occurring in the foreland and in marginal zone of the Eastern and Southern Carpathians (Roumanian). This was proved on the territory of Roumania by the transgressive arrangement of the Upper Sarmatian deposits on the folded Badenian deposits and the Lower Sarmatian. Slight overthrusts were also recorded in some places within the Upper Sarmatian deposits. Only the Meotien deposits do not show dislocation (in Roumania. On the Polish territory the Miocene profile ends with the Lower Badenian deposits in the western part of the foreland and the Lower Sarmatian deposits in the Eastern part of the foreland. The time of the final push of the margin of the Carpathians cannot be directly determined. It can be done by the analysis of the development of the Fore- Carpathian basin and the marginal zone of the Flysch Carpathians.

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