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Basal till and subglacial conditions at the base of the Upper Odra Lobe (southern Poland) during the Odranian Glaciation

Salamon T.

Geological Quarterly

2014

Vol. 58, No. 4

779–-794

The objective of this contribution is detail characteristics of the basal till and the conditions in the base of Upper Odra Lobe. The lobe was formed in a foremountain area. Its central part was a Niemodlin Plain and the W part of the Racibórz Basin, surrounded by areas that have a much more varied relief.Particular attention is paid to the conditions at the ice sheet base, generatingthe dynamics ofglaciermovement. The study is based on analysis of the basal till. Three sites with basal till lying on different types of substratum (more typical for the study area) are presented. The basal till of the Upper Odra Lobe is characterized by spatial variations. Different intensities of its deformation indicate that large lateral differences in conditions occurred in the lobe substratum. The lithology controlled the rate of basal water pressure, and thus the strength of both the subglacial sediments and the ice-bed coupling. Various strain rates in the till profiles indicate that the conditions at the ice-sheet base also changed with time. The ice sheet was highly mobile, even on the coarse-grained substratum. The low permeability of the Quaternary substratum, and the relatively small thickness of the Quaternary sands and gravels resulted in a high water pressure at the ice-sheet base. The movement of the Upper Odra Lobe was concentrated in the basal zone of the ice sheet. The main mechanism of basal motion was sliding and deformation of the subglacial sediments. Deformation probably occurred in restricted areas and did not have a pervasive character.

Rekonstrukcja kierunków ruchu lodu w obrębie lobu górnej Odry

Salamon T.

Przegląd Geologiczny

2012

Vol. 60, nr 10

539–-545

The Upper Odra Lobe - the southernmost part of the Scandinavian ice sheet during the Odranian (Drenthe) glaciation - was formed in the area of the Niemodlin Plain and the western part of the Racibórz Basin. It created a complex structure consisting of several sublobes: Odra, Nysa, Ruda and Klodnica sublobes. The study focused on the basal till deposited during ice sheet advance. Ice flow directions and the general pattern ofice mass distribution in the Upper Odra Lobe were defined based on the clast fabric. The resulting distribution of ice-flow palaeodirections suggest that the Upper Odra Lobe was formed by the mass of ice moving divergently from the Opole Plain located to the north of the Racibórz Basin. Ice-flow lines coincide with the pattern of major geomorphological units. The most intensive movement of the ice took place in the depression of the central part of the Silesian Lowland. From there, in the vicinity of the Niemodlin Plain, the ice sheet moved in different directions, forming smaller sublobes in several valleys. Strong relationship between the ice flow directions and morphology confirms the idea of a smaller ice sheet extent in the Racibórz Basin and Moravian Gate. Highly concentrated flow of ice in the back-lobe area, interpreted in this study, suggests that the lobe development resulted not only from the ice sheet adapting to the basement relief, but was also conditioned by a spatially varying distribution of ice, i.e. increased ice supply to the Niemodlin Plain and the western part ofthe Racibórz Basin.