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Mechanizm kszta towania strefy marginalnej lobu Tocznej l dolodu warciańskiego (Nizina Podlaska)

DOI: 10.2478/v10066-008-0007-8

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Abstract:

In the eastern part of the Podlasie Lowland, during the maximum extent of the Warthanian ice sheet, the Toczna lobe stretched between the Liwiec lobe to the west and the Klukówka lobe to the east (Albrycht et al. 2000; Fig. 1A). In previous geological/geomorphological studies of the Toczna lobe marginal zone, different concepts of relief development were assumed: in the zone of stationary ice-sheet front (Mojski 1972), as a result of ice-sheet advance (Nowak 1977), as a result of areal deglaciation (Falkowski et al. 1988; Nitychoruk 1994), in the zone of stationary ice-sheet front and then by areal deglaciation (Brzezina 2000; Dyjor, Brzezina 2000). According to the latest geomorphological sketch (Fig. 1B), lithofacial analysis was applied to describe the representative deposit successions of accumulation end moraine in the Juniewicze site, outwash plain in the Mostów site, and kames in the Korczówka Kolonia (Figs 2-5). This method permitted to reconstruct glaciogenic events (Fig. 6) and to draw the following conclusions: 1) Morphology and spatial distribution of the examined forms in the marginal zone of the Toczna lobe, as well as lithology of their deposits, indicate that they developed in two stages. In the first stage, the ice-front stabilized along the line of ice-sheet maximum extent: Próchenki — Kolonia Korczówka — Juniewicze. The following forms developed: a) accumulation end moraines — glaciomarginal alluvial fans dominated by sheetflows, and b) outwash plains — alluvial plains of braided rivers with different energy of channel flows. In the second stage, the marginal parts of ice masses were separated, and active ice-sheet front formed in their inner zone along the line Szyd ówka — Korczówka — Mszanna. A train of retreat end moraines was formed — glaciomarginal fans dominated by sheetflows within linearly arranged ice crevasses (derived from ice perforation by waters of supraglacial lakes). 2) The formation of marginal forms (train of end moraines and outwash plain) in the first stage of development of the Toczna lobe marginal zone confirms only a concept about dynamic equilibrium of ice masses during their maximum spread. 3) The train of retreat end moraines, formed in the second stage of development of the Toczna lobe marginal zone, evidences a considerable dynamics of ice masses during their wastage — frontal retreat, not areal one. Taking into account the previous knowledge about the marginal zone of the Warthanian ice sheet in the eastern part of the Podlasie Lowland, the proved frontal retreat of the Toczna lobe distinguished it fundamentally from the adjacent Liwiec and Klukówka lobes, which were subjected to areal retreat after the stationary phase (Mojski 1972; Terpi owski 2001; Albrycht 2004).

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