Przekrój geologiczny przez osady czwartorzędowe nad dolną Wkrą

Abstract

GEOLOGICAL CROSS SECTION THROUGH THE QUATERNARY DEPOSITS ON THE LOWER WKRA RIVERSummaryThe article deals with the stratigraphy of the Quaternary deposits found in the area of the Lower Wkra river which, near Pomiechówek in the northern part of the Warsaw Basin, discharges itself into the Narew river (Fig. 1). The Quaternary deposits are underlain with the Pliocene ones. The geological cross section through the Wkra river valley (Fig. 2) reveals glacial deposits that belong to the South-Polish and Middle-Polish Glaciations. May be, here occurs the boulder clay the Oldest Glaciation, too. The area under consideration stretches outside of the extent of the Baltic Glaciation. The deposits of this age are represented by extraglacial facies, the Great Interglacial – by cyclic fluvial deposits with flora remains (Popieżyn) at the bottom, and the Eemian Interglacial – by lacustrine deposits with a peat intercalation (Falbogi). The composition of pollen grains from both localities has been determined by Z. Janczyk-Kopikowa (1966). The research works prove the conception known from the literature that during the Great Interglacial time the Vistula river flowed north of Modlin along the line of the Lower Wkra river valley. Moreover, there are also found new data, which are an evidence that the ice-dammed lake clays of the northern part of the Warsaw Basin, are covered with boulder clay referred to the North-Mazovian Stage. The geological cross section illustrates also that the boulder clays of the Wkra Stage and of the younger phase of this stage, i.e. of the Nasielsk phase, are separated by fluvioglacial and ice-dammed lake deposits. Vast denudation and erosional horizons evidence that at the close of the Middle-Polish Glaciation the post-glacial morphology was considerably destructed.