Górnokredowe osady w Sudetach wpływ tektoniki na ich sedymentację

Stanisław Radwański

Abstract


UPPER CRETACEOUS DEPOSITS IN SUDETES AND INFLUENCE OF TECTONICS UPON THEIR SEDIMENTATION

Summary

In Sudetes, the Cretaceous deposits were formed depending upon negative and positive tectonic movements that were a reflection of an orogen active in the Carpathian geosyncline. The deposits are developed in sandstone-carbonate facies, and belong to one sedimentary cycle which begins with a marine transgression and ends with a marine regression. The Cenomanian transgression is responsible for the formation of two basins in the area of Sudetes: North-Sudetic Basin and Middle-Sudetic basin. At the Cenomanian time and in the lower horizon of the Lower Turonian time, the sedimentation in these basins was restricted. Fauna, mainly with Exogyra and Pecten forms, was poor. Degradation of the elevations that surrounded the basins, transgressive widening of the basins and increased possibility of mutual connection led to the change in sedimentary regime (allochtonous into an incomplete autochthonous), visible in the upper horizon of the Lower Turonian. Thus, a hindrance that impeded the exchange of fauna with the open see was removed. Consequently, in the upper horizon of the Lower Turonian, the Cretaceous sea was not only characterized by its largest extent in the Sudetes, but the existing fauna also obtained its cosmopolitan character. Despite a tendency of Sudetes to subside and a tendency of the sea to enlarge, only the Strzegom massif supplied the arenaceous material to the Jerzmanice trough.
The Middle Turonian belongs to the regressive phase of a sedimentary cycle. The regression is proved by the sublittoral joint sandstones coming from the elevated crystalline massifs of Sudetes. The arenaceous material was first accumulated in the near-shore zones of the basins, and then brought by currents towards the deeper parts of these basins. So, the sea was restricted to a smaller area.
In the Middle and Upper Turonian, the uplifting movements, restricted mainly to the area of the crystalline massifs, took place with interruptions, and were of various intensity. At the Upper Turonian time, the source Izera-Karkonosze area was considerably widened. At the Turonian-Coniacian boundary a periodical withdrawal of the sea began from the south-eastern area of the North-Sudetic basin. Most probably, it was connected with the uplifting of part of the Kaczawskie Mountains. If we accept that the Lower Coniacian deposits point to a rapid increase in the intensity of the uplifting movements that have reached far beyond the area of the crystalline massifs, then the possibility of interruption in the connection between the two Sudetic basins must have existed already in this substage. The sea withdrew from the area of 'the Middle Sudetes probably at the close of the Lower Coniacian. The. Upper Coniacian marls and the Santonian siltstones are known to occur only in the North-Sudetic basin, in the region of a deep bore hole, near Przewóz. These deposits are hidden under a, thick cover of Tertiary formations. Probably at the close of the Santonian time the sea withdrew from the area of the North Sudetes.


Full Text:

PDF