Budowa geologiczna północnych stoków Beskidu Sądeckiego między Dunajcem a Popradem (Płaszczowina Magurska)

Nestor Oszczypko


Geology of northern slopes of the Beskid Sądecki Mountains between the Dunajec and the Poprad rivers (Magura nappe, Carpathians, Poland)

The Beskid Sądecki Mts. are situated in the southern part of the Polish Flysch Carpathians (Fig. 1A). The area under description constitutes their northern section, placed between the Dunajec and the Poprad rivers. The Beskid Sądecki Mts are built up of deposits of the Magura nappe the highest (southernmost) unit of the Flysch Carpathians. A few facial zones can be distinguished within this unit. They are, coming from the south, the Krynica, Sącz, Gorlice and Harklowa zones. The purpose of the present pamper was to discuss the stratigraphy and tectonics of the Sącz and Krynica zones (Fig. 1 B). The earliest deposits of the Sącz zone are the Variegated Shales (Paleocene — Lower Eocene) whose thickness amounts to ca. 40 m. Successive deposits are the Beloveza Beds (Lower Eocene), composed of fine-bedded flysch ca. 250 m thick. These beds are overlain by (dichous) Łącko Beds (Lower — Middle Eocene?) characterized by the occurrence of a few metres thick sets of the Łącko Marls (Fig. 3). Later in succession there are the Maszkowice Beds (Middle Eocene), represented by thick-bedded muscovite sandstones. The sandstones often contain shale fragments and gypsum veins (Książkiewicz, 1962). The latest deposits of the Sącz Zone are the Jazowsko Beds (Middle — Upper Eocene). They are represented by fine-bedded flysch with intercalations of variegated-shales and thick-bedded sandstones with shale fragments (Fig. 3). In the variegated shales there occurs a horizon of manganese nodules. The earliest deposits of the Krynica zone are the Ropianka (Inoceramian) Beds, characteristic of Senonian — Paleocene (Fig. 1B, 2). They are represented by fine- and middle-bedded flysch with a layer of variegated shales at the bottom. At the tap of these beds there lies a complex of thick-bedded sandstones and conglomerates. The overlying Zarzecze Beds belong to Paleocene — Lower Eocene. They are composed of fine-bedded flysch. The lower part of these beds was formerly included with the Inoceramian Beds (Oszczypko, 1973a). A successive overlying lithostratigraphic unit is known under the name of Piwniczna Beds (Ostrowicka, 1966). It is built up of thick- -bedded sandstones and conglomerates with scarce shaly-sandy intercalations. The beds under description are characterized by the presence of pebble mudstones, often disturbed by submarine slides. The age of the deposits described above was estimated approximally as Lower — Middle Eocene. The Piwniczna Beds are overlain by the Kowaniec Beds. The latter are composed of fine-bedded flysch, formerly known as the Hieroglyphic Beds (Oszczypko, 1975a). In shales there occur here and there thin layers (1—2 cm) of oxidized manganese ores. At Moszczenica, south of Nowy Sącz, these beds include intercalations of cherry-red shales containing a Middle Eocene microfauna. The latest unit of the Beskid Sądecki Mts. are the Magura Beds. Their main component are thick-bedded sandstones (1—2 m); their age was attributed approximately to Middle-Upper Eocene. The present paper correlated Paleogene lithostratigraphic units of the Sącz and Krynica facial zones (Fig. 3, 5) and discussed their facial changeability at the meridian of Nowy Sącz (Fig. 6). Comparative studies indicate that the majority of the distinguished lithostratigraphic units have diachronic boundaries. The Variegated Shales, Beloveza Beds and Lower Łącko Beds of the Sącz zone can be correlated with the Zarzecze Beds of the Krynica zone. On the other hand, the Upper Łącko Beds are equivalent to the Piwniczna Beds. The Jazowsko and Kowaniec Beds correspond to each other. In the described area of the Sącz zone there is no lithostratigraphic equivalent of the Magura Beds of the Krynica zone. The above findings indicate that basic changes in paleogeography and sedimentation conditions took place at the end of Paleocene and were effected by the Laramide orogeny. These movements resulted in activation of an alimentary region situated on the SE margin of the Magura Basin. The facial changeability discussed above is well accounted for by flysch sedimentation models, presented by Stanley et Bouma (1964) and Walker (1978). The accepted model suggests that Paleocene deposits were formed under deep-sea conditions at the slope foot and on the basin plain. The material was supplied by canyons and channels forming submarine fans. An increase in the distance from the alimentary region and a decrease in the density of slurry currents accompanied a successive sedimentation of pebble mudstones, conglomerates, sandy conglomerates, massive sandstones and typical turbidites (Middleton, Hampton, 1976). The southern part of the Krynica zone was situated nearest to the main channel. During Eocene the fan was gradually shifted to the north. In Paleocene the lenght of the Magura Basin amounted to ca. 600 km, while its width did not exceed 50—100 km. A comparison with recent submarine fans (Normark, 1978) indicates that the Magura Basin was twice as long and at least twice narrower than the Monterey Fan. On the bases of the above analogies it may be assumed that the Magura Basin was alimented by at least two fans. The distinguished facial zones constitute, at the same time, subordinate tectonic units (Nowak, 1924; Świdziński, 1963). Between the Dunajec and Poprad rivers, the longitudinal Krynica dislocation separating these -zones (Fig. 7, 8, 9, 10) is steep, often reversed (towards the south). The reversed position of beds, observed in the southern part of the Sącz zone, as well as the usually reversed position of the Krynica dislocation may corroborate the opinion that at an early stage of orogenic evolution of this part of the Magura nappe the folding stress was directed towards the south (see Nemćok, 1978). These movements were likely to take place in Late Eocene, prior to sedimentation of the Malcow Beds (Old Pyrenean phase; Żytko, 1977). Both in the Sącz and Krynica zones a pronounced reduction of southern limba of synclines was observed. It the area under description a number of transversal dislocations were found to run approximately in the S—N direction (Fig. IB, 2). It is not unlikely that those dislocations resulted from movements of the deep substratum, before the overthrust of Carpathian nappes (Nemćok, 1978).

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