Badania petrograficzne skał piaskowcowo-ilastych z Pankowa koło Świdnicy

Abstract

PETROGRAPHICAL STUDIES OF SANDSTONE-CLAY FROM PANKÓW, NEAR ŚWIDNICA (LOWER SILESIA)

Summary

During geological researches made by the Chair of Mineral Raw Materials of the Academy of Mines and Metallurgy in Cracow, an interesting exposure of sandstone-clay rocks has been encountered within the marginal area of the granite massif Strzegom-Sobótka, in the vicinity of the village Panków, near Świdnica, Lower Silesia. The rocks were examined from the point of view of their optical properties, thermal-differential analysis and chemical analysis. It results from the researches that the rocks from Panków have been formed in a somewhat different way than so far accepted. It appears that only the lowermost zone from the profile at Panków (marked on Fig. 1 by symbol 5) may be reckoned as granitic weathered material enriched in the Tertiary. However, the higher zone (4) that is represented by a typical clay rock characterized by pelitic texture and distinctly bedded structure can in no case be accepted as a formation being a result of outwash process of the underlying granite weathered material. This is proved by the results of thermal-differential analysis (Fig. 2). Character of the clay minerals in rock from the bed 4 is of illite type, and that from the bed 2 - of kaolinite-illite one. In addition, the pelitic texture and the distinctly bedded structure of the rock under consideration show that the rock has originated in a water environment and under highly quiet sedimentary conditions. In the light of the observations mentioned above, the origin of the detrital material constituting the rock from the bed 4 is not known. We can, however, assume that the material necessary to build the rock under discussion must have been brought to the basin from a remote area, as it is proved by its well sorting degree. The higher zone (3) also distinctly differs from the granite weathered material occurring at the bottom. First of all, the rocks of this zone are poor in clay minerals and characterized by psammite texture. Beside quartz and great amount of potash feldspars they contain a strikingly enormous quantity of chlorite. Character of this rock greatly resembles arkose sandstones from the vicinities of Wałbrzych, described by W. Heflik and B. Kwiecińska (1963). They differ from these latter only in having considerably lower amount of clay minerals (kaolinite), and highly greater percentage of potash feldspar and chlorite. In this connection we may assume that the rock from the zone 3 represents a material of eroded arkose sandstone occurring in the neighbouring area. Reasonableness of these presumptions is proved by the development of the rock found in the overlying zone 2. The rock is of psammitic-pelitic character. A great differentiation of detrital material it contains distinctly shows that it has originated not only due to the weathering of granites, but also from other rocks, the reconstruction of which can hardly be made. The presence of well-rounded lithoclastic fragments, pyrogenetic quartzes and strongly diagenesed clay shales may evidence that the material has originated from the weathered greywacke rocks known to occur in the neighbouring area (K. Smulikowski, H. Teisseyre, 1957). The presence of this material in the rock here considered might also prove the palaeogeographical conditions prevailing at the Tertiary time in the area studied. Thus, we can assume that at the Tertiary time Carboniferous and maybe Devonian formations were uncovered in the neighbouring areas during formation of the discussed rocks from Panków.