Rozwój zapadliska przedkarpackiego między Tarnowem a Przemyślem

Stefan Połtowicz, Alicja Starczewska-Popow


The development of the Carpathian Foredeep between Tarnów and Przemyśl, Polish eastern Carpathian

The lithology of Miocene sediments (Upper Sarmation and Upper and Middle Badenian) filling the Carpathian Foredeep is described (not including evaporites). The northern limit of the Carpathian Foredeep is marked by the extend of marine Miocene rocks, while the southern one is concealed under the overthrusted Carpatian Flysch. Five lithologic complexes are distinguished in the described rocks, one in the Badenian rocks, and four in the Lower Sarmatian rocks: the I sandy complex “A”, the clayey-silty complex “B”, the II sandy complex “C” and the clayey-silty-sandy complex “D”, designated on figures according to Polish rules as M1A(5), M1(5B), M1C(5), M1C(5) respectively.

The Badenian sediments consists of siltstones and claystones with intercalations of silty sandstones, and thin beds of tuffites and dolomitic marls. The thickness of the Badenian rocks increases southward (Fig. 2 a) gradually at first near the northern margin of the sedimentary basin, while in the central part of the sedimentary basin the thickness increases stepwise in zones of synsedimentary faults. The zone of these faults marks the northern slope of the sedimentary basin, situated presently before the front of the Carpathians. The content of sand (Fig. 2b) in the Badenian rocks decreases southward. Three large fans with increased sand content are interpreted as paleo-deltas, extending south up to the present northern border of the Carpathians. The detrital material was carried in these paleo-deltas from the north, i.e. from the areas of the Holy Cross Mts, and their Mesozoic border and from the Lublin Upland. There is no evidence of supply of detrital material from the south i.e. from the Flysch Carpathians. The northern border of the Carpathians was still situated far from its present position. The present area of the occurrence of Badenian rocks represents only the original northern part of the sedimentary basin. The central and southern parts of the basin are now covered by the Carpathian overthrust. The axis of the Carpathian Foredeep migrated steadily to the north-east. The zones of active synsedimentary faults also were displaced in the same direction. Lower Sarmatian Generally the Lower Sarmatian rocks are lithologically similar to the Badenian rocks. During the sedimentation of the individual lithological complexes of the Lower Sarmatian some zones of the basin were subjected to inversional movements. This was marked especially in the eastern part of the described area, where synsedimentary grabens were transformed into horsts in the next sedimentary cycle. The rate of deposition on these horsts was smaller than in neighbouring areas. The distribution of thickness and sand content of the individual lithological complexes (Figs. 3, 4, 5 and 6) demonstrate the development of the foredeep, the migration of its axis and of zones of synsedimentary faults. The distribution of sand content in the complexes “A” and “B” (Figs. 3b and 4b) do not suggests sand transport from the south, i.e. from the Flysch Carpathians. The fans of increased sand content are developed from the north southward. These fans reach south to the present northern margin of the Carpathians, suggesting that the axis of the sedimentary basin was situated in the area now covered by the Carpathian overthrust. The distribution of sand content in the lithological complexes “C” and “D” indicate sand supply from the south. The development of cones of increased sand content from the south to the north indicate the northward shift of the axis of the Sarmatian sedimentary basin. During the deposition of the lithological complex “D” the axis of the basin was situated north of the present border of the Carpathians. The analysis of the thickness and sand content of the Miocene rocks indicate that clastic material was transported into sedimentary basin from the Holy Cross Mts, from the Ukrainian crystalline massif and from the Flysch Carpathians (Fig. 7). The sedimentary basin extended far to the south. Seismic data suggest that the southern border of this basin may be situated near the southern state boundary of Poland (Figs. 9, 10). The basement of Miocene rocks rises here to the depth of 3—4 thousands metres, while north of this zone it lies at the depth of c. 10 thousands metres. The oldest Miocene rocks (Carpathian) which are included in the structure of the marginal part of the Flysch Carpathians may be preserved in the zone of the southern part of the Miocene sedimentary basin.

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