Warunki geologiczne występowania osadów interglacjału eemskiego w Nakle

Abstract

GEOLOGICAL CONDITIONS OF THE EEMIAN INTERGLACIAL DEPOSITS IN NAKŁOSummaryThe deposits of the youngest Interglacial in Nakło (west of Bydgoszcz) are found within an urstromtal, on a terrace about 5-7 m above the Holocene one (Fig. 1). Palynologic analysis was made by Z. Borówko-Dłużakowa (1962, 1972). In the profile D (Fig. 1) the deposits of the young-Pleistocene terrace consist mainly of gravels, showing a slight admixture at sands 2,3-3,8 m in thickness. They are underlain by the Interglacial deposits developed as lacustrine marls (0,8-1,5 m in thickness). At the bottom of the Interglacial deposits occur sands with gravel admixture (Fig. 2). In the profile B (Fig. 1), situated about two hundred fifty metres to the east-north-east, the terrace deposits occur in a series consisting mainly of sands with two thin intercalations of silts, 5,0-6,2 m in thickness (Fig. 3). The Interglacial deposits, better developed in this area, consist mainly of gyttja in two horizons separated with a not too thick bed of medium-grained sands. The upper, thinner horizon of gyttja passes to the west into a peat layer. The lower horizon is characterized by its changing thickness, mainly due to a differentiated morphology of the bottom. In borehole No 2 gyttja has been penetrated down to 15 m, without reaching its bottom. Open is the problem if the marls ascertained in profile B have been deposited in the same lake as gyttja from the profile B. Similar position above mean sea level of the top of the Interglacial deposits of both profiles might prove the existence in Nakło of one single basin or of two connected basins. Here, the top of the Interglacial deposits is situated approximately 50 m below the culmination on the adjacent part of the upland. This is a basis for the evaluation of the thickness of the deposits of the youngest glaciation in this area, and for the separation of its deposits from those of the preceding glaciation. Interesting is here the presence of humus in the lower horizon of silts (1 : 096% ), as the trace of the interstadial soil forming processes. Since in the last, main phase of the Baltic Glaciation (Leszno Stage, also called Frankfurt Stage) this area was covered with a glacier, one of the last interstadials - Bölling or Alleröd - can be taken into account. The solution of this problem will allow us to determine the age of the terrace definitively.