Ślady dolno-karbońskiej działalności wulkanicznej w rejonie Krzeszowic

Abstract

LOWER CARBONIFEROUS VOLCANISM IN THE KRZESZOWICE AREAIn 1949, within a cut to the Orlej porphyry quarry (Cracow region), a section of about 150 m. was exposed of Carboniferous beds developed as shales, mudstones and dolomitic limestones. The limestones and shales in the top portion of the section contain a rich fauna which determines their age as uppermost Visean (Czarniecki 1955). The shale series in the central part intercalated by tuffites and tuffitic conglomerates (pI. L and LI), which consist of angular shale fragments and poorly rounded porphyry fragments with diameter up to a score or so of centimetres (pI. LII, fig. 1). Microscopic analyses have shown that shale fragments occurring in tuffitic conglomerates do not differ from Orlej shales stratigraphically underlying these conglomerates. On mineral composition analyses the magmatic elements of tuffites and tuffitic conglomerates (pI. LII, fig. 2 and LIII) have been referred to rhyolites. They differ by their composition from the porphyries of the Zalas laccolith (including the Orlej porphyries), from those of Miękinia and from other acid volcanic rocks in the Cracow region. The wrirters think that the coarse clastic tuffitic material was introduced into the argillaceous Orlej series through submarine slumps associated with disturbances due to uppermost Visean volcanism. The tuffitic conglomerates and tuffites outcropping in the Orlej quarry, therefore, represent oldest volcanic activities in the Cracow region.