Budowa geologiczna paleozoiku dębnickiego

Abstract

Tectonics of thew Palaeozoic rocks of the Dębnik region The term „Palaeozoic of Dębnik” is applied here to the Devonian (Givetian- Famennian) and Carboniferous (Tournaisian-Namurian A) carbonate rocks cropping out in the vicinity of Krzeszowice (Fig. 1). The Palaeozoic of Dębnik forms a part of the elevated Carpathian foreland and is situated to the North of the Carpathian foredeep between the villages Szklary and Czatkowice. The recent views upon the geological structure of the Palaeozoic of Dębnik can be summarized as follows: (see Siedlecki 1964, Zajączkowski 1964, 1975). 1. The opinion that this area has a fold structure is dominant. 2. As the principal structural direction there were assumed the directions NWW—SEE and NNE—SWW or meridional (Fig. 2). Some authors consider the direction SW—NE to be of significant importance (Jarosz 1926, Zajączkowski 1964, 1975). 3. The existence of faults in the Palaeozoic of Dębnik has been noticed, but their significance was underestimated. 4. Zajączkowski (1975) noticed the strike-slip faults in the Czernka valley and expressed a suggestion that the intruding magma played an important role in the formation of the Dębnik anticline. The investigations carried out by the author enabled to distinguish three areas within the limits of the Palaeozoic of Dębnik: 1. Western area — to the W of the Eliaszówka stream and Krzeszówka stream valleys. Czema flexure of the NWW—SEE direction is here the dominant tectonic form. 2. Central area — comprises the proper Dębnik anticline of the NNE— SSW direction. This area lies between the Eliaszówka and Racławka valleys. 3. Eastern and Northen area — situated to the E of the Racławka valley and to the N of the village Paczółtowice. Flat folds running in the NWW—SEE direction are the main tectonic forms, of that area. The analysis of geological structure of these areas leads to the following conclusions: — Fold structures having the NW—SE direction are absent in the Palaeozoic of Dębnik. The strikes of strata in this direction as well as minor fold structures are secondary in relation to the NWW—SEE and NNE—SSW directions. Only the last two structural directions can be testified by the data obtained from the field investigations in the Dębnik, Klucze and Brudzowice areas and in the mines situated in the north-eastern periphery of the Upper Silesia Coal Basin. So there is a marked discrepancy between the general NW—SE direction of the eastern border zone of the Upper Silesia Coal Basin, and structural directions inside the zone. — The fold tectonic features running NWW—SEE are neither alpinotypic nor mediotypic in the Stillle’s sense, but they represent a system of en échelon brachyfolds developed under the impact of a pa,ire of forces. (Willis 1934, Pavoni 1961, Tchalenko, Ambraseys 1970; Jaroszewski 1972; Harding 1973). — The main role in the structural evolution of the Palaeozoic of Dębnik played the fault tectonics — The fold deformations are either directly or indirectly connected with faults or magmatic intrusions. — The three distinguished areas (Western, Central and Eastern) correspond to separate tectonic blocks limited by en échelon faults. — While making an attempt to order in time the structures occurring in the distinguished areas, it seems that the fold forms in the Eastern and Northern areas are the oldest. They were directly followed by the faults and the intrusive tectonics. The latter was controlled by contemporeneous faulting. — Transition from fold structures showing the NWW—SEE direction in the Eastern area to the Dębnik anticline runming approximatively N—S was interpreted in various ways (Jarosz 1926, Rutkowski 1928, Konior 1934). Presently, taking into account the presence of en échelon folds running evenly with a parallel of latitude and the system of en échelon faults it seems that the meridional Dębnik anticline developed as the extension of the Żary anticline which runs approximatively east — west. One of the blocks enclosed between meridional faults was used by the intruding porphyric magma which up- lifted the Upper Palaeozoic carbonate rocks in the southern part of Żary anticline near the Racławka fault forming the Dębnik brachyanticline. The Palaeozoic of Dębnik is in close tectonic relation to the Upper Silesia Basin and Moravo-Silesian Zone. The Moravo-Silesian Zone belongs to the variscan orogenic belt and comprises well marked internides and externides showing eastern vergency of folds. The Upper Silesia Basin and its north-eastern periphery form the foreland of that orogenic zone (Fig. 8). The Upper Silesia Basin occupies the position of a foredeep and its NE periphery constitutes an uplifted part of the foreland (Fig. 9). Faults are the basic structural features of that meta-orogenie zone. There are also present fold deformations, but they are either directly or indirectly controlled by the fault tectonics. In the investigated area the NE boundary of the Moravo-Silesian foredeep is developed as a zone of en échelon faults. On the basis of the analysis of geological structure of the Palaeozoic of Dębnik, which forms an integral part of north-eastern periphery of variscan foredeep it can be stated that there are no reasons to consider the Cracow branch of Variscides as an alpin o ty pic orogen sensu Stille. The discovery of a zone of en échelon faults and brachyfolds in the NE periphery of the a Moravo-Silesian foredeep, carries some tectogenetic consequences. The Palaeozoic of Dębnik belongs to the cover of the epicaledonian platform (Znosko 1970). Its tectonic structure stays in close relation with the structure of the platform basement. This basement was consolidated most probably in Caledonian orogeny. In the area of Upper Silesia Basin the platform basement is formed by a cristalline massif consolidated in Precaledonian time. On its NE periphery developed a Caledonian lineament called the Cracow-Myszków zone (Siedlecki 1962). The lineament as about 50 km wide and shows features of fold-intrusive tectonics. From the NE it is limited by the Małopolska Massif (Pożaryski 1974). During the Cambrian-Silurian period the discussed zone underwent intensive subsidence relative to the bordering Upper Silesia and Małopolska Massifs. The Caledonian orogenic cycle brought a tectonic inversion of the zone. The Cracow-Myszków zone is separated from bordering massifs by tectonic sutures. All these structures run in NW—SE direction. This zone having a different mechanical properties than the surrounding massifs and not completely united with them was able to transmit the vertical and horizontal movements of the Earth crust. The uplift of the North-Eastern periphery of the Upper Silesia Basin and its fold-fault structure is mainly a result of these vertical movements. The gentle, en échelon folds in the Upper Palaeozoic showing the NWW—SEE direction (fig. 10 a, b) seem to be a result of an early stage of dextral strike-slip movement in the platform basement along the tectonic sutures. The result of the next stage of this movement is the system of en échelon dextral faults having a meridional orientation. It seems that these faults resulted from a law-angular system of shears acting above a tectonic suture in the platform basement.