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Petrographic analyses and indicator erratics of gravels of the Odra lobe

Górska-Zabielska M., Zabielski R.

Studia Quaternaria

2010

Vol. 27

17-25

Fennoscandinavian erratics found in the glacial deposits till and in the glaciofluvial sediments within the main limit of the Odra glacier lobe (NW Poland and NE Germany), have been examined in two fractions: of 4-10 mm and 2060 mm. The most numerous in the fraction of 4-10 mm are: crystalline rocks (Cr; 35-40%) originating in the Protero zoic Baltic Shield as well as Lower Palaeozoic limestones (LPL; 35-40%) - from the sedimentary sheet covering the Proterozoic Baltic Shield in the area of central Baltic Sea. Percentage of sandstones (S) amounts to 10-15%. The re maining rock types (several percent each) are: Palaeozoic shales (PS), the outcrops of which are localized in Scania (Skane) and on Bornholm, Cretaceous limestones (CL) and flintstones (F) originating from the western part of the southern Baltic Sea as well as quartz (Q), milk quartz (MQ) and isolated grains of Devonian dolomites (DD). From the analysis of indicator erratics, which was carried out in the 20-60 mm fraction, it appears that mainly the outcrops localized in Smaland (e.g. red and grey Viixjo granites, Paskallavik porphyries or Tessini and Kalmarsund sandstones) as well as in Scania (Hoor and Hardeberga sandstones) and Region Blekinge-Bornholm (e.g. Karlshamn and Halen granites as well as Nexo and Bavnodde sandstones) had been subjected to the glacial plucking. Theoretical boulder centres (TBC, German: TGZ das Theoretische Geschiebezentrum, Uittig 1958), which were calculated for 23 samples, are localized mostly in a small area in Smiiland, between 15°E-16°E and 56.5°N-58.5°N. Apart from indicator erratics the statistical ones are numerous, that are first of all grey and red Lower Palaeozoic limestones with their outcrops localized at the bottom of the central Baltic Sea. Taking into account the TBC values of indicator erratics as well as high percentage of statistical erratics it can be pronounced that the section of central and western Baltic Sea as well as the one of south-eastern Sweden had been subjected to the heaviest glacial plucking by that part of the Pleistocene ice-sheet which reached the studied area during the Pomeranian Phase.

Conditions of sedimentation in the Weichselian glaciomarginal zone of northeast ern Germany

Górska-Zabielska M.

Geological Quarterly

2008

Vol. 52, No 2

157-157

The conditions of glacigenic sedimentation during the Pomeranian Phase of the Weichselian Glaciation in northeastern Germany are reconstructed on the ba sis of the typical lithofacies successions and the depositional architecture of the distal and proximal parts of a sandur, as well as of those in the hinterland area of the glaciomarginal zone. The proximal parts of the sandur are characterized by the occurrence of boulders, pebbles and gravels, and horizontally stratified sands cut by large channel troughs in the upper parts. The occurrence of the channel structures indicates frequent torrential ablation floods. Horizontally and cross-stratified rhythms of sandy and gravelly lithofacies, indicating pulsatory ablation flows, are also frequent. The distal part of the sandur is dominated by horizontally stratified sands and sands with low- angle tabular cross-stratification. In the hinter land of the Pomeranian Glaciation, a thick layer of till is present, which locally is glaciotectonically deformed. Moraines left during glacial retreat, with gravity-redeposited till, are also present.