Charakterystyka petrograficzna piaskowców magurskich z Beskidu Średniego

Abstract

PETROGRAPHICAL FEATURES OF THE MAGURA SANDSTONES FROM THE MIDDLE BESKID RANGE

The petrographically analysed Magura sands tones of the Middle Beskid Range (Western Carpathians) distinguish themselves by an almost complete lack of grading, rounding, as well as by a generally low and changing sphericity of grains. This particularly refers to the sandstones of M. Książkiewicz's muscovite facies (1955, 1958) of the more southern sandstone occurrence areas in the Magura unit. The Magura sandstones of glauconitic facies disclose a slightly higher degree of rounding, and a higher sphericity. In view of the high contents of matrix, both types of sandstones may be referred to the so-called C. Gilbert's wackes (1954), of which only the varieties belonging to the muscovite facies are rich in non-stable materials, like feldspars, micas and litho clastic fragments (Fig. 1, Table 1). Fully the opposite to the Magura sandstones, as regards its grading, is the slightly older Osielec sandstone. This latter contains no matrix, which is replaced only be cement being usually of secondary, calcitic nature. Thus, this is an equivalent to C. Gilbert's arenites and contains glauconite, like as the Magura sandstone of the northern regions of the Middle Beskid Range. It seems probable that this sandstone regimented at the southern shores of the Magura basin, on a miniature shelf. An extensive transport along the shore line led to a differentiation of the material building the coastal bar, into the coarse-clastic Osielec sandstone and fine-clastic hieroglyphic beds. The transportation, of the separated coarse-clastic material into the deeper parts of the basin probably took place in the form of so-called sands flows. At a later period i.e. at the time of formation of the Magura sandstones, the increased frequency and amplitude of vertical movements led to a disappearance of the shelf. The growing coastal bar was then more often destroyed by submarine slides, and turbidity currents connected with them. At the same time·the Magura sandstone of glauconitic facies was formed in the northern part of the basin and on a more stable and less inclined shore (part of the ridge separating the Magura basin from the Silesian basin). The clastic material deposited on. the miniature shelf together with the then formed glauconite, was after a short mechanical reworking above the wave base, redeposited due to the slides and turbidity currents.