Acta Musei Moraviae

Clast striation in context to glacier erosion in the mountain foothill zone of the continental glaciation (Middle Pleistocene, Rychleby Mountains, Rejvíz Highland)

Only 3 % of gravel clasts (fraction 16–64 mm) and 8 % of boulders is striated and polished in glacigenic and glaciofluvial sediments on the northern foothills of the Rychleby Mts. and Rejvíz Highland. Striae occurr only on clasts of Nordic provenance, their appearance on local and Polish clasts is very rare. No striae were found on quartz clasts. Absence or only a rare occurence of striation on local clasts support current geomorphological opinions that in marginal foothill zone of the ice-sheet, the glacial erosional landforms were not formed. If the ice-sheet in its marginal zone abraded preglacial relief as well, it would be abrading also the clasts, which were eroded in the marginal zone from the bedrock. Nordic clasts are in relation to the foothill of the Rychleby Mts. and Rejvíz Highland exotic not only by its rock provenance but also by the clast morphology. Local, Polish, and quartz clasts have forms inherited from preglacial sources. Provenance defined distribution of abraded clasts can be explained palaeoglaciologicaly: Nordic clasts were striated and polished under warm-based ice-streams in Fennoscandia and Baltic Sea basin. Local, Polish and quartz clasts were eroded, transported and deposited in the cold-based marginal zone of the ice-sheet.