Próba poznania struktury depresji północnosudeckiej

Jerzy Milewicz



The North-Sudetic Depression is one of the main tectonic units of the western Sudety Mts. Its origin was related to the Variscan tectonic epoch, during which upper Carboniferous basin was formed in its southern part. Acid and mafic igneous intrusions took place in the Lower Permian. Saalian tectonic phase was marked by erosion of some parts of the Lower Rotliegendes section. Neokimerian movements resulted in formation of two deformation systems, WNW-ESE and NE-SW, as well as in different degree erosion of a sedimentary cover, which is evidenced by the fact that Cretaceous rocks are overlying the strata differing in age from the Keuper to the early Paleozoic. The present structure of the North-Sudetic Depression was formed in the Tertiary. The lowermost structural surface is represented by the surface of the base of sedimentary series. This surface descends down to 2,000 m below sea level to form flat "bottom" (see Fig. 8). A step above the flat surface, at the depth of 2,500 m below sea level, is inferred in the western part of the depression. The lowermost structural horizon comprises deposits of the earliest westphalian, Stephanian and early Permian age (Ist cycle). It is developed in the southern part of the depression, extending northward up to the Jerzmanice fault and attaining ca. 400 m in thickness. The horizon of the Lower Rotliegendes (IInd cycle) is discordantly overlying the strata of the Ist cycle and it also overpasses maximal extent of the latter horizon. The IInd cycle also comprises igneous rocks and varies from 130 to 350 m in thickness. The strata of the Upper Rotliegendes horizon are overlying the eroded surface of the IInd cycle sedimentary and igneous rocks and the metamorphic substrata. Its thickness rises from 200 to 520 m northwards, which suggests that its sedimentary basin entered the Fore-Sudetic block. Close to the end of the tectonic movements, deposits of the Rotliegendes were thrown down to the depth of 1,300 m below sea level in the eastern part and to 1,800 m below sea level in the western part of the depression (Fig. 9). Zechstein horizon is represented over the entire area of the depression. Littoral and open marine facies may be distinguished. Zechstein strata are the thickest in NW part of the depression (260 m thick), wedging out towards the south and south-east. Buntsandstein horizon is entirely developed in sand facies and is characterized by rather uniform thickness (over 500 m) ,over the whole area of the depression, which indicates that neither smaller units nor tectonic blocks have marked themselves during its deposition. At present, Röt-Muschelkalk horizon is recorded in the northern part of the depression, in the south up to the Jerzmanice fault. In turn, Upper Cretaceous horizon is found on the entire area, and may be divided into off-shore (sandy) and open-marine (marIy) zones. In that horizon, a synsedimentary trough formed in the southern part of the depression, where Cretaceous rocks are over 1,100 m thick; outside that trough, Cretaceous rocks are much thinner, attaining ca. 600 - 700 m in thickness.

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