Sytuacja geologiczna i florystyczna plejstoceńskich osadów organogenicznych w rejonie Ossówki (południowe Podlasie)

Abstract

GEOLOGICAL AND FLORISTIC SITUATION OF PLEISTOCENE ORGANOGENIC DEPOSITS IN THE OSSÓWKA REGION (SOUTHERN POLAND) Summary In the valley-like depression situated north-east of Ossówka (Fig. 1) two horizons of Pleistocene organogenic deposits are preserved. The older one, more than 10 m thick, is composed of grey calcareous - siliceous gyttja (layer 3 on the Figs. 2 and 3~ This horizon is covered by the glacial till or ice pavement - residuum of the till. The origin of this till is associated with the last occurrence of the Scandinavian ice-sheet in this area i.e. during the Warta (20) or Odra Glaciations (1,6-14). The younger Pleistocene organogenic horizon is represented by the light-grey, grey or olive-grey calcareous and calcareous-siliceous gyttja 2 m thick, containing remains of molluscan fauna (Fig. 4 and layer 10 on Fig. 3). The upper gyttja horizon overlies the above mentioned glacial till and moraine pavement, underlying the fine sand originated during the later slope accumulation. Preliminary palynologic investigations of a few samples from the upper part of the older gyttja (section OS-1/85 on Fig. 3) show that accumulation in this part of undertill lake basin, had been taking place in the climatic conditions typical for warm interphase or cold interstage preceding the last glaciation in this area. The results of the preliminary diatom studies of the samples from the lower part of the older gyttja section (section OS-1/86) and especially the mass presence of Cyclotella vorticosa A. Berg which is the most characteristic species for lakes of the Lubawa and especially Mazovian Interglacial in Poland (15 -18, 22) may be used in attempts to correlate the undertill lake basin in Ossówka with one of these interglacial periods. Seems to support (to indicate) that the undertill basin sedimentation took place in the climatic conditions of the Mazovian Interglacial and during later warmings preceding the maximum of the Odra Glaciation, similarly as it has been proved for the Biała Podlaska (7, 11, 12, 17) and Komarno sites (9, 10, 14). The results of palynologic investigations of a dozen or so samples from the younger gyttja show that the preserved pollen can represent 2 warmings of interphase or interstage character (pollen horizons OS-2-A and OS-2-E on Fig. 4) separated by the distinct cooling (pollen horizons OS-2-B and OS-2-D on Fig. 4). The above mentioned cooling is connected with disappearance or thinning out the forest communities of the Boreal character. No diatoms have been found in this gyttja horizon, whereas some samples yielded a rich molluskan fauna. (Valvata piscinalis antiqua Sow., Bithynia tentaculata L., Pisidium casertanum Poli., P. milium Held., P. subtruncatum Maim., and Gyraulus sp.). Geologic situation of these deposits allows to relate them to 2 interstages or interphases separated by a cooling during the younger part of the Warta Glaciation or older part of the Wisła Glaciation.