Nowe dane o budowie podłoża Karpat na południe od Wadowic

Andrzej Ślączka


New data on the structure of the basement of the Carpathians south of Wadowice

The borehole Potrójna IG-1, situated about 20 km south of the northern Carpathian border (Fig. 1), reached the basement of the Carpathians, yielding new data on the extent of the Carboniferous formation and the Cambrian rocks encountered beneath the Flysch masses. Directly below the Carpathian overthrust there is a Miocene conglomerate (Dębowiec conglomerate) of several dozen metres in thickness, overlying the Carboniferous rocks (Fig. 3). The Upper Carboniferous, about 580 m thick, represented by the Lower Westfalian' and the Lower Namurian with a hiatus comprising the Namurian B and C, contains numerous coal seams, up to 5 m thick. The coal occurrences show that the Upper Silesian Coal Basin continue to the South, far under the Carpathians. As appears from seismic data, the Upper Carboniferous may extend farther both west and south-east. The Lower Carboniferous rocks, attaining a thickness of 170 m, represent the shaly Culm facies containing a limestones lenses. The boundary between the Upper and Lower Carboniferous is not distinct and has been arbitrarily assumed to run where brackish fauna gives way to marine fauna. The Culm is underlain ' by complex 500 m thick of limestones and dolomites almost completely devoid of the index fossils. The few fossils preserved indicate that the carbonate rocks represent mainly the Upper Devonian. The uppermost part of the carbonate sediments contain numerous intercalations of quartzouse clastic rocks and may also include the lowermost Carboniferous. The lowermost part of the carbonate rocks discussed i. e. the dolomites may be assigned to. the Middle Devonian. The carbonate rocks are underlain by a several — metre thick series of variegated claystones showing thin intercalations of conglomerates (Pl. I, fig. 2). The microflora preserved in claystones (Upper Emsian) is indicative of continental environment (Konior, Turnau, 1973). Both, the claystones and conglomerates form a characteristic horizon varying in thickness and extending over a vast area (Figs. 1 and 2). Underlying the rock under consideration and separated from them by a sharp boundary, there is a 150 m thick complex of white conglomeratic sandstones. The complex begins with monomictic quartz conglomerates (Fig. 2). The presence of trace fossils of the Scolithos type (PI. I, fig. 3, Pl. II, fig. 1) and the occurrence of criss-cross bedding indicates that these sandstones represent presumably tidal zone sediments. The sandstones here discussed are similar to the s. c. Scolithos sandstones known from the boreholes located between Bielsko and Mogilany (Ml) (Figs. 1 and 2). The Scolithos sandstones were previously regarded to be of the Lower Devonian age (Konior, 1969); at present, however, they are assigned to the Lower Cambrian on the ground of trilobites found above them in the borehole Goczałkowice IG 1 (Kotas, 1972). Almost horizontal position of the sediments, their inconsiderable thickness and the lithology similar to that of the Cambrian rocks reported from the Fennoscandian platform support the opinion that the Lower Cambrian rocks in the area described were accumulated on an epicontinental platform. The thickness of the Cambrian rocks increases to the north and north-east. This evidences that platform was inclined in that direction, passing into the Holy Cross Mts. géosynclinal area. Beneath the Lower Cambrian rocks there lies a 23 m thick complex of red polymictic, arkosic conglomerates (Pl. IV, fig. 2 ), differing clearly from the overlying Lower Cambrian monomictic conglomerates. The lack of fossils in the arkosic conglomerates makes the precise dating of them impossible; however stratigraphie position of these rooks indicates that they may represent the remnants of a Eocambrian molasse consequent upon the Assynthian orogeny. Sediments of similar type have been also found in the same position in the borehole Piotrowice 1 (Fig. 2). The conglomérâtes lies unconformably on eroded, vertical layers of variegated and dark-grey metaargillites and mataaleurites (Pl. I, fig. 3; Pl. II). The two latter rocks are similar to the Precambrian rocks found in the boreholes Opatkowice (Kicuła, Wieser, 1970) and Goczałkowice (Kotas, 1972). They also show similarity to the rocks recorded (Heflik, Konior, 1974) in the lowermost part of the borehole Piotrowice 1, and to some sediments of the Cracow region which are regarded to be of the Silurian age. The Eocambrian metaargillites in Potrójna IG-1 are separated from those in the region of Goczałkowice-Piotrowice by the Andrychów zone of crystalline rocks (Fig. 3). It may be inferred that in the basement of the sedimentary rocks there is an anticlinal structure with a crystalline cote and flanks made up of metaargillites that represents a fragment of the Assynthian, or even older, orogenic belt.

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