Nowe dane o strefie Kurdwanów – Zawichost i tektonice obszaru od Buska po Nidę i Wisłę

Abstract

Przedstawiono budowę geologiczną utworów kredowych i trzeciorzędowych obszaru między Buskiem, Nidą i Wisłą., Przebieg głównych dyslokacji, tj. strefy Nidy oraz strefy Kurdwanów – Zawichost stanowiących jego ramy tektoniczne, został zlokalizowany na podstawie zdjęcia satelitarnego. Analiza zdjęć lotniczych pozwoliła wyróżnić dwa systemy uskoków i spękań: laramijski o kierunku NW – SE (140–150°) i alpejski (sarmacki) o kierunku ENE – WSW z przewagą uskoków o azymucie zbliżonym do 70°.Uskoki laramijskie mają charakter zrzutowy, natomiast alpejskie – przesuwczy. Podnoszenie się kredowego zrębu Nidy oraz nasunięcie z SSW ku NNE bloku Mędrzechowa, wchodzącego w skład strefy dyslokacyjnej Kurdwanów – Zawichost, spowodowało powstanie szeregu potomnych zrębów i rowów tektonicznych warunkujących budowę geologiczną i morfologię całego badanego obszaru. NEW DATA ON THE KURDWANÓW – ZAWICHOST ZONE AND THE TECTONICS THE BETWEEN BUSKO AND NIDA AND VISTULA RIVERSThe studied area is built of Cretaceous (Campanian – Maestrichtian) marls and opokas often cropping out but mainly covered by Badenian and Sarmatian deposits.The latter are represented by clays and gypsum typical of the northern marginal zone of marine Miocene of the Carpathian Foredeep.On the basis of analysis of air photos there was prepared tectonic map of the area stretching between Busko – Krzyżanowice and Nida river. In this area, characteristic eroded outcrops of gypsum are covered by a thin clay cover (or thick in the case of tectonic troughs) or clearly mark in the morphology when the cover is missing. Complex, geological structure of this area, additionally complicated by subsequent karst processes is explained and its geological model (system of blocks) is proposed. Directions and distribution of very closely spaced dislocations cutting Cretaceous and Tertiary rocks are carefully determined. In order to explain the origin of so complex geological structure it appeared necessary to extend the studies on the Nida area on the west and south of the Vistula river (in this way comprising Czarkowy area sensu lato which was studied by T. Osmólski in 1972). The main tectonic features of the extended area include so-called Nida horst made of Cretaceous rocks on the west and complex Kurdwanów – Zawichost tectonic zone on the south. The two zones are the only dislocations with pre-Tertiary foundations in this area. They were, finally shaped in the latest Badenian and at the beginning of the Sarmatian when linear Kurdwanów – Zawichost dislocation was cut by NE – SW oriented faults and blocks delineated by these faults were pushed to NNE by over thrusting. Carpathians. At present, the front of en echelon translocated blocks delineated by SW – NE oriented faults marks northern boundary of the Carpathian Foredeep and the faults are used by the Vistula river (Fig. 5).The block situated between Dunajec and Vistula rivers, named Mędrzechów by the authors, was pushed against NW – SE oriented small block structures originating in the brackets of the Nida and Vistula rivers. This resulted in change of direction of these structures into sublatitudinal (T. Osmólski, 1972) and origin of a network of Sarmatian faults. The network of faults and translocations from the area between Nida river, Krzyżanowice and Busko is genetically different as, they originated from uplifting of the Nida horst. The blocks of Cretaceous Nida horst are accompanied by parallel' series of gypsum-covered blocks. On NE, the latter adjoin a shallow Winiary – Kamieniec trough infilled with Sarmatian clays.All these blocks were translocqted along Sarmatian dislocations delineating them and pushed to NE on the Winiary – Kamieniec trough.Synchroneity of tectonic movements in both zones (the peak of tectonic phenomena coinciding with the turn of the Badenian and Sarmatian) and similarity in scale, nature and direction of these phenomena indicate that they are genetically related. The uplifting of the Nida horst was most intense in times of formation of the depression, that is downawarping of blocks in the Kurdwanów –Zawichost zone along SW – NE oriented faults which represent northern boundary of both these blocks and the Foredeep.Younger faults from the area between Busko and Nida river (dated at the turn of the Badenian and Sarmatian) are of the strike-slip type, with predominating direction of 70° (system I), whereas older, Laramie faults are vertical, NW–SE oriented (140–150°, system II) and with downthrusts up to 100 m. It follows that the younger tectonics does not repeat directions nor type of the older. South of the Kurdwanów – Zawichost zone, faults are SSW – NNE oriented (azimuths: about 30°) and cut the Kurdwanów – Zawichost line, and are of the strike-slip, type whereas those SW – NE oriented and delineating the Carpathian Foredeep on the north are of the downthrust type.Besides classic methods of field mapping, methods of interpretation of air photos and, for tracing course of tectonic lines of the Nida horst arid Kurdwanów – Zawichost zone, interpretation of satellite photos carried out by J. Bażyński were used in the studies.