Interglacystadiał zlodowacenia krakowskiego z Jasionki koło Rzeszowa

Abstract

The interstadial of the Cracovian glaciation from Jasionka near Rzeszów

The palynologically studied borehole sectio from Jasionka occurs north of Rzeszów within the Subcarpathian “pra-dolina” (Urstromtal) (fig. 1). The formation of the Subcarpathian “pra-dolina” most probably goes back to a period before the Cracovian (Mindel) glaciation. Undoubtedly, as early as in the Pleistocene times a large river flowed in the “pra-dolina” at the foot of the Carpathians. The bottom of that river was on a higher level than the floor of the valley at the time of the Cracovian glaciation. The geological section I-I (fig.2) cuts the "pra-dolina" at a point where the presence has been observed of but the lowest of its terraces formed during the oldest stadial of the Cracovian glaciations, while the rock floors of the higher terraces with the Pre-Pleistocene times occur at an altitude of 210-215 and 220-230 m a.s.l. The·petrographic composition and character of gravels of which all the terraces consist, is very much the same. It is characterised by the side-by-side occurrence of Carpathian rocks and an admixture of Tatric rocks (Werfenian quartzites and granites). Scandinavian crystalline rocks are absent here. These are "impoverished":gravels (fig. 4). During the G II-1/max. interglacistadial (interstadial) of the Cracovian glaciation which preceded the ice invasion of the Subcarpathian·region, the “Pra-dolina” was already a morphologically mature from. It was a relatively broad and deeply incised valley (about 40 m), with a well developed system of terraces. The river in the valley no longer eroded downward but it meandered along that broad valley. Lateral erosion and accumulation occurred in alternation in the various sectors of the flood terrace there. lt is to this period that we may refer the fossil oxbow-lake from the vicinity ,of Jasionka, filled in by organogenic sediments (series II). The palynological profile described by M. Dąbrowski (1967) indicates a distinct increasing warmth of interstadial order of magnitude. The ice-sheet of the Cracovian glaciation (G II max.) invaded the area here considered and covered the fluvial and oxbow--lake deposits of the Subcarpathian “pra-dolina" with a layer of glacial accumulation deposits (series IV). In the vicinity of Jasionka this series is considerably degraded because of the subsequent processes of erosion and denudation. The petrographic composition of the gravel fraction from the glacial series very obviously differs from the deposits of fluvial accumulation, chiefly in the presence of pebbles of crystaline rocks from Scandinavia and in that of Cretaceous rocks from the Highland of Little Poland (Małopolska), (fig. 4). This undoubtedly indicates ;the glacial character of the deposits. The presence of organogenic deposits underlying the glacial series reliably indicates the occurrence of interglacistadial conditions before the maximum ice-sheet advance. This would be a confirmation of S. Z. Różycki's opinions (1961, 1967) with respect to the occurrence of older stadials of the Cracovian glaciation prior to its maximum extent. These stadials never reached the area of the Sandomierz Lowland.