Wiek osdów z Cetenia i Ponurzycy w świetle badań mineralogiczno-petrograficznych

Abstract

THE AGE OF DEPOSITS FROM CETEŃ AND PONURZYCA IN THE LIGHT OF INERALOGICAL AND PETROGRAPHIC ANALYSESSummaryFive rock complexes have been distinguished in the columnar section at Ponurzyca on the basis oi borehole material from Ceteń and Ponurzyca in Central Poland (material in the collection of the Geological Institute inWarsaw). The results of the analyses presented here comprised the mineral and petrographic composition, the rounding of quartz grains and grain-size composition (Fig. 1, 2).The three lower complexes (Al, A2, A3) have been compared with the series of preglacial deposits distinguished in the river-basin of the middle Vistula, while the two upper complexes (B, C) have been referred, after M. D. Baraniecka (1975) and L. Stuchlik (1975), to the Celestynów Interglacjal (Waalian) and the Podlasie Glaciation (Gònz).The rocks of complex A are characterized by a very poor rounding of quartz grains and heavy minerals, a considerable amount of white and grey feldspars, feldspar-quartz fragments, greenish cyrstalline rocks, schists and by the occurrence of the fragments of: flints lydites and silicified rocks. Garnet predominates in the heavy fraction, in the bottom and top parts of the complex (Al and A3); in the middle part (A2) there is a predominance of minerals which are resistant to weathering; zircon, tourmaline, and minerals of the TiO2 group. In all the samples examined here there are varying amounts of chlorite, up to 30 per cent. The amount of amphibole reaches 3 per cent (Fig. 2).The deposits of complex B, to which a bed of rocks from the borehole at Ceteń was compared (A. Makowska, 1976), are characterized by a poor mineral composition and a very rounded material. Apart from quartz, the deposits in question contain single feldspars, sometimes of pink colour, feldspar-quartz fragments, flints, lydites, silicified rocks and silicified gaizes. In the deposits from Ceteń there are also single fragments of grey and red crystalline rocks. Minerals which are resistant to weathering predominate in the heavy fraction. In addition there is also the andalusite-topaz group, which is known from Palaeogene deposits ofCentral Poland.The increase in the amount of amphibole is small.The deposits of complex C are characterized by a rich group of northern crystalline rocks, a distinct amount of amphibole, garnet and epidote. Amphibole grains become rounder and rounder towards the top as their number gradually decreases.The lack of limestones is the evidence of a considerable degree of weathering.