Tektonika fliszu we wschodniej części Podhala

Abstract

Flysch tectonic in the extern part of the Podhale Basin (Carpathians, Poland) INTRODUCTION The Synclinorium of the Podhale Flysch is a northern part of the Inner Carpathians. It runs in the direction E-W and is bordered by the Tatra Mts. from the south and by the Pieniny Klippen Belt from the north (Fig. 1 A). The Podhale Flysch Basin is filled with the Eocene- Oligocene sediments, overlying transgressively the older, previously folded and faulted substratum belonging partly to the Tatra Mts, and partly — to the Pieniny Klippen Belt (Andrusov, 1965; Buday, 1967). It is generally accepted that this synclinorium had been formed during the Saavian phase and the subsequent phases did not play a significant role there (Birkenmajer, 1958). The tectonics of the eastern part of the northern limb of the Podhale synclinorium is discussed in the present paper (Fig. 1A). STRATIGRAPHY AND LITHOLOGY The Podhale Flysch The lithological variability is the main critérium of the subdivision of the Podhale Flysch sediments into the Szaflary-, the Zakopane-, and the Chochołów Beds (Watycha, 1968). The oldest Szaflary Beds which contact directly the Pieniny Klippen Belt are characterised by considerable share of sandstones and conglomerates. Submarine slides are frequent in these beds (Fig. IB) and numerous rock particles, possibly derived from the Klippen Belt, occur both in the conglomerates and in the submarine slide material. The fact that the mechanical groove casts are variously oriented coincides with the observations by Marschalko (1968), who observed a considerably mobility of the basin floor and of the source areas in the Flysch zone near the Pieniny Klippen Belt. The Zakopane and Chochołów Beds show rather monotonous lithology. Shales prevail over sandstones in the Zakopane Beds; nevertheless, the role of the latter is greater towards the top of the complex, and their transition to the overlying Chochołów Beds is almost unnoticeable. Both rock types are in equilibrium in the Chochołów Beds, but the sandstone layers are thicker there than in the Zakopane Beds. Organic hieroglyphs are frequent in the Chochołów Beds. Longitudinal directions of the mechanical hieroglyphs prevail in the Zakopane and Chochołów Beds. Deposition took place here in calm and more uniform conditions and the basin axis was inclined towards the east (Ra d oms k i , 1959). The total thickness of the Podhale Flysch in that area is about 2.5 km. The Pieniny Klippen Belt On the basis of th e author’s own studies and those of Birkenmajer (1957, 1964) three lithologie complexes of various resistance to mechanical deformations have been differentiated in the Pieniny Klippen Belt (Fig. IB). Complex I embraces various types of limestones, and radiolarites from the Aalenian up to the Albian in age, and is more resistant than the other rock complexes. Isolated klippes and klippen massifs are built of the rocks of this complex. Complex II embraces the Globotruncana marls and is less resistant than Complex III, composed of the Sromowce Beds. THE TECTONIC STRUCTURE The majority of tectonic structures are parallel to the course of the Podhale synclinorium and form several tectonic zones of the same direction (Halicki, 1963). The following tectonic zones have been distinguished: I — contactzone with the Pieniny Klippen Belt, II — zone of the Peri-Pieniny Flexure, III — zone of small dips, IV — axial zone of the synclinorium. Apart from those, large fault zones of an approximately meridional direction have been distinguished, i.e.: Jurgów-Trybsz, Branisko-Osturma, and Biały Dunajec (Fig. 2, 16). The Contact zone of the Podhale Flyschand the Klippen Belt he Klippen Belt contacts the Podhale Flysch along a narrow fault zone. The southern limbs are usually downfaulted and the fault amplitudes are at least several tens of meters (Fig. 2). The contact line in the area in question forms a broad arch, which convexity facing the south. It is cut by a dozen or so oblique faults (Fig. 2). A generalized direction of that contact is concordant with the strike of the adjoining beds of the Podhale Flysch. The strikes within the Klippen members are usually oblique to the contact (Fig. 4). The contact surface is vertical or inclined northward in the eastern and central parts of the area. In the western part it dips southward (Fig. 2, 3). Near-contact belts of tectonic disturbances Belts of tectonic disturbances connected with the contact zone run parallel to the contact. Within the Klippen Belt there are numerous scaled folds which occur in a zone about 200 m wide (Fig. 3). In the Podhale Flysch the influence of the contact is revealed by steeper dips of beds (Fig. 3, Table 1, Fig. 1), and by numerous faults parallel to the contact. The downfaulted limbs are on the south, as a rule. The influence of the contact zone can be observed up to the Peri-Pieniny flexure. The role of the Podhale Flysch in the Development of the Contact Zone The Globotruncana Marls and the Sromowce Beds acted as incompetent beds in relation to the Szaflary Beds. This explains why scaled folds occur at the contact zone in the Klippen Belt, while faults — in the Podhale Flysch. The same can be said about oblique structures of the Klippen Belt by the dislocation zone. Southern downfaulted parts of these structures should be situated south of the contact line under the Podhale Flysch (Fig. 5), the latter being removed by erosion to the north of the contact (M. Książkiewicz, 1973). Transversal Elevation and Oblique Faults Fold axes emerge eastward in the western part of the area, and westward — in the eastern one (Fig. 4). This phenomenon can be observed both in the Klippen Belt and in the Podhale Flysch. Thus elevational character of the area in front of the Branisko Hill is marked in the northern part of the area starting from the Peri-Pieniny flexure. It is supported by the fact that eastern limbs are downfaulted east of the Branisko Hill, and western ones — west of this massif, which can be seen in the faults cutting obliquely the contact zone (Fig. 2). Wrench Movements in the Contact Zone The most distinct horizontal displacements were noted along the faults cutting obliquely the contact east of the Branisko Hill. South-eastern limbs are displaced southwestward in all these faults (Fig. 8); it was established on the basis of an analysis of various tectonic forms (Figs 6, 7, Table 1, Fig. 2). Other directions of displacements were noted along minor faults which, according to the schemes of Moody and Hill (1956), may be regarded as associated faults. Apart from this, small displacing faults occur within the whole contact zone. They are more or less parallel to the contact. No regional arrangement of the displacement movement has been noted along these faults. The displacement phase preceded the faulting one and it was prolhably the result of the internal differentiation of the Klippen Belt. Zone of the Peri-Pieniny Flexure A belt of tectonic disturbances about 600 m broad is situated about 1j5 km south of the contact line. It runs parallel to the latter and consists of one to several flexures of the amplitudes of about 300 m (Fig. 3). Within arenaceous complexes large faults prevail over flexures. Some minor tectonic forms are also present there (Fig. 9 A, B, 10). Southern limbs are downfaulted both in faults and in flexures and the amplitudes are comparable to these in the fault zone of the contact. The above mentioned zone of flexures and faults, which is roughly parallel to the contact, runs several tens of kilometers and was even traced in Slovakia. Similar zones parallel to other massifs of the Internal Carpathians, were described by Matejka (1963), Fuśan (1963) and Mahel (1964). Their origin can be explained by the action of large faults in the substratum of the flysch (Buday, 1967). Hence the probable fault in the substratum of the Peri-Pieniny flexure would be one of the regional dislocations along which the Flysch was downfaulted in relation to the Klippen Belt (Fig. 5). The Zone of Dips Between the zone of the Peri-Pieniny flexures and the axial one dips usually do not exceed 10° (Figs 2, 11, Table 3, Figs 1, 2). East of the Branisko — Ośturnia fault the zone in question shows a shape of broad fold structure, composed of a syncline and an anticline (Figs 3, 11). The syncline borders the Peri-Pieniny flexure and the anticline — the axial zone of the Podhale synclinorium. West of the Branisko — Osturnia fault the discussed Zone is developed as a belt of beds dipping from 0° up to about 5° (Fig. 11). This belt is bordered from the south and north by reverse faults. In the southern faults the southern limbs are downfaulted, and in the northern faults — the northern ones (Table 4, Fig. 1). Hence the mentioned anticline and the belt of beds between the reverse faults may be regarded as an elevated area in relation to the adjoining parts of the synclinorium. This zone probably originated as a result of a horst, formed in its substratum along the reverse faults (Fig. 5). The occurrence of a calcareous tufa associated with the faults bordering the zone supports this opinion. Axial Zone of the Podhale Synclinorium Considerable variability of dips (Fig. 2) and numerous folds of various size (Fig. 5, 12, 14) are characteristic features of the axial zone. Anticlines in the E-W direction and can be usually traced at a length up to about 600 meters. Their turns are either rounded or roof-shaped (Figs 9 FG, H, 13, Table 4, Fig. 2). The latter occur in sandy memibers; in shaly beds the turns are rounded. The axial zone runs parallel to the northern edge of the Tatra massif. In the eastern part the direction of the axis of the Podhale synclinorium is 106/3 E, and near Jurgów — 90/9 E. The steepening of the axis was caused by the downfaulting of the eastern limb of the Jurgów—Trybsz fault zone (Fig. 16). Further to the west the axis inclination diminishes, and beyond the Biały Dunajec fault zone (Fig. 16) the axis takes a westerly tilt. The origin of tectonic structures in the axial zone is connected with compressional forces acting in the N—S direction. The Jurgów-Trybsz and Branisko-Osturnia Fault Zones A narrow zone of densely spaced normal faults of the NNW-SSE direction (Fig. 2) stretches from Trybsz to Jurgów. In the southern part of this zone the eastern limbs are downfaulted, and in the northern part — the western ones. It may thus be assumed that this zone has the character of a pivotal fault (Fig. 16). As it can be seen from observations of the Białka River terraces and from the diversification of erosion and accumulation on both sides of the river (Fig. 15), this zone exhibits recent tectonic activity. Depression within the Klippen Belt to the west of the zone in question, as well as occurrence of the calcareous tufa and springs with H2S mineralization show that this zone originated from the action of a fault situated in the substratum of the Podhale Flysch. On the basis of works by Fusan (1963), RonieWicz (1969) and Książkiewicz (1972) this zone can be prolonged to the southern side of the Tatra Massif. Another zone of densely spaced normal faults stretches from the Branisko massif to the Ostumia village. Their direction is NNW—SSE (Fig. 2). Most of those faults show downfaulted western limbs. Larger amplitudes in the northern part of this zone suggest that the Branisko-Osturnia fault zone has the character of a hinge fault. Its origin seems to be the same as that of the preceding zone. The Biały Dunajec Fault Zone Concentration of normal faults of the NNE—SSW direction and variability of the dips of strata (Fig. 16) seem to suggest that also another fault zone of the NNE—SSW direction runs along the Biały Dunajec river (fig. 16). It is prolonged in large faults cutting through the Klippen Belt, in which the eastern limbs are downfaulted (Birkenmajer, 1963, 1968). Since the western limbs are downfaulted in the southern part of this zone the whole zone of the Biały Dunajec should be also regarded as a pivotal fault. The fault pattern of the zones of Jurgów-Trybsz and Biały Dunajec (Fig. 16) shows that the area situated between them is relatively uplifted in the southern part — and relatively lowered in the northern one. This explains a considerable depression of the Klippen Belt between the Białka and Biały Dunajec rivers, and a bend to the north of the intersection line of the contact surface dipping south in that sector. TECTOGENESIS OF THE EASTERN PART OF THE PODHALE BASIN Numerous submarine slides and conglomerate layers in the Podhale flysch should be regarded as the earliest symptoms of tectonic movements in the eastern part of the Podhale Basin. According to Andrusov (1965) these phenomena should be connected with the Illyrian phase. Subsequent tectonic movements were of a two-phase character in this area. Some reverse faults in the substratum originated or were rejuvenated during the earlier, main tectonic phase. Vertical movements along these faults caused independence of the particular blocks of the substratum ;and the origin of the E-W tectonic zones. The zone of small dips is situated on an uplifted block and a lowering movement of an adjoining block and squeeze of beds between the reverse faults formed the axial zone of the synclinorium. The zone of the Peri-Pieniny flexure and the dislocation zone of the contact were also formed along such faults. The analysis of the tectonic forms reveals that the overlying flysch beds were subjected to a stress field. Its main component acted horizontally in the meridional direction, and the intermediate coincided with the parallel of latitude. It was only near the contact where this field had been reorientated. In the eastern part of the contact zone the axis of the intermediate tension was vertical with unchanged position of the axis of the maximal tension. Probably, due to the diversified structure of the Klippen Belt the tectonic transport was easier locally, towards the south. No regional rotation of the Klippen Belt was observed in relation to the Podhale Flysch. In the western part where the contact shows the character of a normal fault, the axis of maximal stress was vertical and that of the intermediate one — retained its horizontal, E-W direction. It may be assumed that the dislocation zone of the contact cuts the tectonic structures of the Klippen Belt and that these structures go down under the Podhale Flysch, up to the zone of the Peri-Pieniny flexure (Fig. 5). In a later phase a postkinematic uplift of the Podhale Flysch took place. The stress field was changed completely. The axis of the maximal stress took a vertical position, and that of the intermediate stress — a horizontal one, running in the E-W direction. Large fault zones were formed under such a stress field. Their directions were approximately meridional. They were then subjected to rejuvenation as dip slip faults of the NE-SW direction, eastward of the Branisko Hill. By analogy to other areas of the Inner Carpathians, the earlier phase should be regarded as the Saavian one, and the younger phase as the Styrian one. Some premises suggest that recent vertical movements are still in action.