Heavy–mineral assemblages from fluvial Pleniglacial deposits of the Piotrków Plateau and the Holy Cross Mountains – a comparative study

The heavy-mineral assemblages of Pleniglacial fluvial sediments were analysed for two river valleys, viz. the Luciąża Riv er (at Kłudzice Nowe) and the Belnianka River (at Słopiec). These sites, on the Piotrków Plateau and in the Holy Cross Mountains respectively, are located in different morphogenetic zones of Poland that were affected to different degrees by the Middle Polish ice sheets. The study was aimed at determining the kind of processes that modified the heavy-mineral assemblages in the two fluvial sediments, at reconstructing the conditions under which these processes took place, and in how far these processes caused changes in the assemblages. The heavy-mineral associations of the parent material was ta-ken as a starting point; this parent material were the sediments left by the Odranian glaciation (Warta stadial = Late Saalian). It was found that heavy-mineral assemblages in the Luciąża valley deposits are varied, particularly if compared with other fluvioglacial Quaternary deposits from the Polish lowlands, with a dominance of garnet. In the fluvial deposits of the Belnianka valley, zircon, staurolite and tourmaline dominate, with minor amounts of amphibole, pyroxene, biotite and garnet. This suggests that the deposits were subject to intensive and/or persistent chemical weathering and un-derwent several sedimentation/erosion cycles under periglacial conditions. In both valleys chemical weathering and aeolian processes were the main factors that modified the assemblages of the transparent heavy minerals; these proces-ses were largely controlled by the climatic changes during the Pleistocene