Znaczenie profilu z Ponurzycy dla badań genezy i wieku preglacjału Mazowsza

Abstract

THE PONURZYCA SEQUENCE AND IMPLICATIONS FOR THE ORIGIN AND AGE OF THE MAZOVIA PREGLACIALSummaryGeological field studies carried out in the Otwock area provided materials discussed in the present paper. The geological structure has been recognized from geological mapping and drilling records. Five boreholes encountered a sedimentary series that, in its thickness, position and composition, shows some affinities to the preglacial sediments of the south Mazovia alluvial fan.Detailed geological and palynological studies created a basis for a new interpretation of the deposition and age of the sediments of the Otwock area. This is of substantial significance for the recognition and interpretation of all the preglacial sediments in Mazovia and areas adjacent in the south. The best results have been obtained from the Ponurzyca sequence that most likely is situated in a narrow zone of Quaternary basement disturbances. However, no disturbance evidence has been found in the preglacial sediments.The preglacial sediments of the Otwock area lie at the top of a highly monotonous Pliocene series accumulated under large-scale depositional rythm. In contrast, the preglacial sediments (74–104 m a.s.1.) have a small and very variable depositional rythm (depositional cycles I, II, III, IV and depositional sequences 1-11). Stratigraphically the discussed preglacial sediments are overlain by sediments of the Kromer, Mazovia (Great), and Eemian Interglacials and of the South Polish (Cracow), Middle Polish Glaciations and extraglacial sediments of the Baltic Glaciation. Holocene sediments also occur above the preglacial material.Two depositional areas of the preglacial series – the valley and the upland area (Fig. 1) as well as two facies types of the sediments have been distinguished near Otwock. Sediments laid down by streams that formed fans prevailed. The fiuvial sediments are separated by lacustrine material that terminates the majority of the depositional cycles and sequences. Lacustrine sediments are fairly abundant and sometimes make up more than 50% of the whole sequence. Hence the lacustrine-fluvial (the Ponurzyca sequence) and the fluvial-lacustrine (other sequences) facies types have been distinguished. The sediments show some features of the deluvial transport indicating that this was an additional accumulation factor.Within the preglacial series of Ponurzyca abundant plant remnants indicate these sediments to be of Quaternary age and to correspond, in the sections examined, to two warm periods of interglacial character separated by a cool period with a climate close to subarctic (L. Stuchlik, 1975).The substantial clues pointing to the Quaternary age of the sediments are the very frequent lithological changes that distinguish them from the Pliocene sequence. This variation corresponds to the rapid climatic rythms that are known to occur in the period of Quaternary glaciations. It should be mentioned, however, that the climatic changes evidenced by palynological results do not fully coincide with the depositional sequences the origin of which must be due to other factors as well.The new stratigraphic units distinguished on the basis of the Ponurzyca sequence are proposed to be named (going upwards) the Ponurzyca Interglacial the Otwock Glaciation and the Celestynów Interglacial. The Uppermost part of the Ponurzyca preglacial series probably belongs to the Podlasie Glaciation. Geological evidence indicates the possibility of a detailed division of the Otwock Glaciation into units of the stade and phase rank.At present the Ponurzyca sequence (Fig. 2) is of reference value for the stratigraphy of the older part of the Quaternay in the Polish Lowlands.