Cechsztyn w otoczeniu bloku przedsudeckiego

Abstract

Badania stratygraficzne przeprowadzone w otoczeniu bloku przedsudeckiego pozwalają na rekonstrukcję paleogeografii cechsztynu na obszarze bloku. Ogólnie ujmując, blok przedsudecki był zalany w PZ1, w dutej mierze wynurzony w PZ2 i ponownie zalany w PZ3. W północnej w bloku istniała trwała strefa elewacyjna (elewacja szprotawska), zaznaczająca się w równym stopniu podczas sedymentacji całego cechsztynu. Na południe o~ niej ciągnęła się strefa depresyjna (depresja sieroszowicka), zaznaczająca się w PZ1 oraz w PZ3. Kolejna strefa elewacyjna występowała bardziej na południe i ciągnęła się do brzegu basenu. Elewacja szprotawska i przyległa do niej depresja sieroszowicka mają założenia starsze, akcentowane podczas ruchów śród- i pocechsztyńskich. Pewien wpływ na rozwój sedymentacji wywarły również ruchy pionowe całego bloku przedsudeckiego.THE ZECHSTEIN IN THE NEIGHBOURHOOD OF THE FORE-SUDETIC BLOCKThe results of stratigraphic-paleogeographic studies on the Zechstein in the North-Sudetic Depression, along with those ,obtained for coeval rocks at eastern side of the Fore-Sudetie block (Figs. 1 - 8) make it possible to state that the area of the block was generally submerged in PZ1, largely emerged in PZ2 and once more submerged in PZ3 (Figs. 9-10).In northern part of the block, there existed a stable elevation zone, Szprotawa Elevation, the nature of which is clearly accentuated by the North-Sudetic Depression. A depressional zone, Sieroszowice Depression, was stretching south of the Szprotawa elevation. The direction (WNW-ESE) and extent of the depression coincide with the axis of maximum thickness of the Zechstein Limestone (Fig. 9). The zone was marked in PZ1 and PZ3 and an intense erosion took place before the deposition of the Bundsandstein in its western part.The stable elevation zone and adjoining depression follow old tectonic trends. The Szprotawa Elevation represents southern part ,of an area markedly elevated in times of sedimentation of the Saxonian (Fig. 9) whereas the northern part of the elevation was much less clearly marked during sedimentation of the Rotliegendes. The analysis of material concerning the Rotliegendes implicates existence of a WNW-ESE oriented zone of increased thickness of Saxonian rocks, south of the elevated area. The old tectonic trends, bearing a significant influence on the development of the Zechstein in the Fore-Sudetic block and adjoining areas, were accentuated in result of intra-Zechstein (at the turn of the Zechstein Limestone and Lower Anhydrite, PZ1 and PZ2, and PZ2 and PZ3) and post-Zechestein (but pre-Bundsandstein) moveinents. The movements were followed by fairly intense erosion due to which the Zechstein cover was evidently less than 150 m thick in the area of the Fore-Sudetic block at the end of the Zechstein.Reconstruction of the Zechstein paleogeography in the Fore-Sudetic block and its neighbourhood indicates that the development of sedimentation was influenced not only by the above mentioned tectonic elements but, on a minor scale, vertical movements of the whole Fore-Sudetic block. According to Z.Deczkowski and I. Gajewska (1979), the Middle Odra River system of Alpine dislocations has developed within fault zone already active in the Early Permian. As it was stated by J. Znosko (in press), the foundations of that system are related to the boundary of Variscan internides and externides.