Rewizja sytuacji stratygraficznej osadów tzw. interglacjału chełmińskiego w Bągarcie koło Unisławia

Abstract

Sytuacja stratygraficzna osadów jeziornych z fauną, odkrytych przez G. Massa (1902) w rejonie Chełmna i Unisławia (tzw. interglacjał chełmiński), stała się w świetle nowych badań niejasna. Nowe wiercenie wykonane w Bągarcie koło Unisławia pozwoliło stwierdzić, że badane osady leżą niżej niż to przyjmowano dotychczas, pochodzą z interglacjału eemskiego i są przykryte przez trzy poziomy glin zwałowych zlodowacenia bałtyckiego.REVISION OF THE STRATIGRAPHIC SETTING OF DEPOSITS OF SO-CALLED CHELMNO INTERGLACIAL FROM BĄGART NEAR UNISŁAWIn the course of studies on the Quaternary of the Lower Powiśle the author has found that undoubtful deposits of the Eemian Interglacial occur at larger depths than lacustrinal deposits with faunal assemblage comprising Paludina diluviana K u n t h, described from Bągart, Plutowo and Starogród between Unisław and Chełmno by G. Maas (1902). This along with new borehole data made it possible to assume that the lacustrinal deposits with Paludina diluviana may represent a warm period of the Baltic Glaciation so a control borehole was drilled at Bągart to check the validity of G. Maas's profile (Fig. 1).According to G. Maas the lacustrinal deposits were occurring between two (lower and upper) till horizons and they represent an interglacial horizon younger than deposits with marine fauna from Ostromecko and Gniewkowo, related to a preglacial marine transgression (G. Maas, 1904). The two horizons were recognized as highly important and treated as the basis in. discussions on stratigraphy of the Quaternary of that part of the country for several tens of years. Their interpretation changed in time. M. Limanowski (1922) generally followed the point of view of G. Maas, placing the, lacustrinal deposits with fresh-water fauna between tills of the Glaciations L3 and Lt and he called the period of their accumulation as “Chelmno Interglacial”. This concept became fairly popular among subsequent authors.A new borehole drilled in 1974 down to the depth of 110.3 m penetrated series of deposits of the Baltic Glaciation and Eemian Interglacial and entered the Miocene (Fig. 2). The top of deposits with fauna is here situated 14.8 m a.s.l., that is about 21.2 m lower than in the profile described by G. Maas. It follows that the lacustrine deposits which have to occur within the limits of the Baltic Glaciation according to G. Maas (Fig. 3A) actually. represent an old river-bed facies and may be correlated with the middle (Ell) of three valley series of the Eemian Interglacial differentiated here by the author (Fig. 3B). The borehole gave further support to the author's statement that the Eemian deposits are not covered by two but rather three horizons of tills of the Baltic Glaciation (BII, BIII and BIV corresponding to Toruń, Leszno and Poznań till horizons, respectively), separated by two intermoraine series.The occurrence of. gastropod Paludina diluviana K u n t h  in Eemian Interglacial deposits represents a separate problem often discussed in the literature. This problem will be the subject of further studies on the part of the present author.