Młode ruchy tektoniczne przedgórza Karpat w okolicy Krakowa i ich wpływ na ewolucję dolin Wisły i Raby

Abstract

YOUNG TECTONIC MOVEMENTS IN THE CABPATHIAN FORELAND,  VICINITES OF CRACOW, AND THEIR INFLUENCE UPON THE EVOLUTION OF THE VISTULA AND RABA RIVERSSummaryGeological structure of the Carpathian foreland, between Bochnia and Brzesko Nowe, has been investigated by means of seismic and drilling works carried on in the recent years by the Petroleum Industry.  A macro-radial pericline, built up of Pre-Cambrian, Devonian and Lower Carboniferous formations, has been investigated. It occurs between the Vistula and Raba Rivers, within the area of the Niepołomice virgin forest. The pericline is discordantly overlain by Jurassic and Cretaceous formations; higher up, there rest Tortonian and locally Sarmation deposits (Fig. 1).A lack of Cenomanian deposits within the pericline of the Niepołomice virgin forest, and changes in their thickness towards the east, point to a fact that the process of uplifting of this tectonical element revived after the Upper Jurassic time. An analogous phenomenon took place after deposition of evaporites of the Lower Tortonian, as well.Between Niepołomice and Uście Solne, the Vistula River valley is about 6–9 km in breadth. The valley is cut by a very complicated system of dead channels that are evidence of numerous changes in the river bed (Fig. 2). At present, the Vistula River rolls its waters in this area along the left side of the valley, whereas in the region north of Niepołomice and below the Nida mouth, it takes usually its central part, meanders and dead channels being regularly developed on its either side. In the area here considered, a tendency exist to move the river bed from south-east to north-west.An analogous feature is characteristic of the Raba River valley, north of Bochnia. The river flows here also on the left, i.e. on the westerly side of the valley, and leaves behind some well developed dead channels, at a distance of about 2–3 km, east of the present bed. The original mouth of the Raba River was situated approximately 6 km east of the present one.A tendency to move the oldest, buried Vistula River bed towards south-east can be observed on the cross section (Fig. 3) made on the basis of the data from the drillings situated between Brzesko Nowe and Uście Solne. After reaching its extreme position (Fig. 2), and after deposition of fine-grained sands and loams, the movement of the river bed changed its direction. At that time, the dead channel system was formed. This process must have taken place at the Holocene, or Young Pleistocene time, since the dead channels are not damaged considerably.The observation of distribution and of evolution of the Vistula River and Raba River dead channels, and the comparison of these phenomena with the data obtained from drillings lead to a conclusion that at the Miocene time some movements, responsible for the uplifting of the substratum, existed within the area of the Niepołomice virgin forest. The movements caused the formation of both macro-radial cupola of anhydrites and deep, probably antecedent incision of the Vistula and Raba River valleys into the Miocene formations.After the stabilization of the Vistula River bed, at the time of which the valley was being filled in with the fluvioglacial and fluvial deposits that reached approximately a half of the present-day height, the northerly part of the pericline began to sink. However, this movement was slow and caused a “sliding” of the Vistula River bed to the north-west only, without producing any greater disturbances of water-course. At the time, a system of meanders was formed, the dead channels being now its remainder.Sinking process of the substratum has involved some changes in the course of the Raba River bed, and moved it to the west. The present-day undermining of the Vistula River bank in the area of the northernmost meanders demonstrates that the process of shifting the Vistula River bed has not as yet been finished.A coincidence of fault lines in the substratum with the system of dead channels of the Raba River, and with the development of certain meanders of the Vistula River may suggest a rejuvenation of old tectonic lines at the Quaternary time.