Plejstoceńskle osady jeziorne w stanowisku Hrud I k. Białej Podlaskiej

Abstract

Badania palinologiczne serii osadów jeziornych ze stanowiska Hrud I pozwalają odnieść jej akumulację do interglacjału mazowieckiego o sukcesji typu Białej Podlaskiej. Okrzemki zachowane w tej serii reprezentują taksony najbardziej typowe dla interglacjału mazowieckiego (Cyclotella vorticosa, C. comta var.lichvinensis), choć spotykane również w osadach interglacjału lubawskiego (Pilicy). Ślimaki serii jeziornej (Lithoglyphus jahni, Viviparus diluvianus) określają jej wiek jako nie młodszy od interglacjału mazowieckiego. Małżoraczki (Scottia browniana, S. tumida) spotykane są w osadach  tego interglacjału, jak też w osadach niemieckiego odpowiednika interglacjału lubawskiego. Wymieniona seria jeziorna zachowana jest między dwoma poziomami glin zwałowych. Górna część tej serii wraz z przykrywającą ją gliną zwałową najmłodszego na tym obszarze poziomu glacigenicznego jest zaburzona glacitektonicznie. Wiek TL tej gliny został określony na 161-174 ka, co, przy uznaniu wiarygodności tych dat, może upoważniać do wiązania jej ze zlodowaceniem Warty.PLEISTOCENE LAKE SEDIMENTS OF THE SITE HRUD I NEAR BIAŁA PODLASKAIn the Hrud area, about 10 km to the north from Biała Podlaska, several meter thick lake sediments mantled with youngest glacial deposits of the Warta Glaciation (Stadial) - J. Nowak (1977) - or the Odra Glaciation (L Lindner, 1988a) were studied (Figs 1-4). These lake sediments in the site Hrud I are composed of silts, sands, gyttja and marl and have been deposited in a vast lake. Sediments of the latter have been already preliminary analyzed from geologic, palynologic and diatomologic points of view in the Ossówka area (Lindner et al., 1990). Preliminary palynologic analyses of ancient lake sediments in the Hrud area indicate (Fig. 5) that in the site Hrud I the plant communities around the lake started with boreal forests to compact yew-pine forests with spruce and alder, being the first phase of a climatic optimum of the Mazovian Interglacial with the Biała Podlaska type of floristic succession (K.M. Krupiński, 1988a). In turn the diatomologic studies prove that the diatom flora of the site Hrud I is most similar to the one from the site Ossówka and it is represented by taxons typical for lakes of the Mazovian Interglacial (Cyclotella vorticosa, C. comta var. lichvinensis), although they are also noted in sediments of the Lubawa Interglacial (S. Marciniak, 1983, 1986; I. Tuszyńska-Gruza, 1984). These diatoms describe primarily severe climatic conditions in the lake area and then, with gradually improving climate, more favourable trophic conditions and lowering of the water table. Increased participation of alkaliphilous, littoral and periphytonic diatoms in middle part of analyzed sediments indicates a longer trend of shallowing of the lake, presumably during the climatic optimum of the interglacial. Studies of the fossil fauna from the site Hrud I indicate (Tab. 1-4) that preserved snails Lithoglyphus jahni and Viviparus diluvians define the analyzed lake reservoir as any younger than the Mazovian Interglacial. The ostracods Scottia browniana and S. tumida, previously considered for key ones of the Mazovian and older interglacials, are noted in sediments of this site and have been recently found in Germany in sites that could correspond with the Lubawa Interglacial. These analyses as well as identified species of molluscs prove that development of the lake in this time was accompanied by the climate similar to the present one but slightly cooler. TL age of the till (from 161 ±24 to 174±25 ka) that covers lake sediments of the site Hrud I suggests, if correctness of this age is accepted, to connect this till with the Warta Glaciation (Stadial) - J. Nowak (1977) - and to refer interglacial sediments of the Biała Podlaska type to a chronostratigraphic setting of any of the warmings within the Middle Polish Glaciations.