Grain-size distribution analysis of Quaternary sediments from the southern part of the Lodz region in Poland: a computational-methods approach
Eighteen samples of Quaternary unconsolidated sediments from the Piotrków Plateau and the Radomsko Hills in central Poland have been analysed for their average grain size, sorting, skewness and kurtosis. The analysis was carried out by seven computational methods of interpolation and nine extrapolation methods. It appears that linear interpolation, the traditional method (DOS), and the Josek and Gradistat Programs give comparable results, but that quadratic interpolation and the method of moments should not be applied since they yield unreliable results. The method of moments gives unduly high or unduly low parameter values because of the application of different, i.e. incomparable measures in the applied formulae. It should be stressed that only extrapolation provides, if performed under the right conditions, the possibility to determine some parameters, in particular skewness values.
The petrographical features of the medium- and coarse-grained gravels (4-10 mm and 20-60 mm, respectively) of weathered and fresh (unweathered) deposits indicate, in combination with so-called indicator and statistical erratics, that two glacial lobes joined in the borderland of the Polish Lowlands and Uplands. Lower Palaeozoic limestones become less frequent in the fner gravel fraction, whereas crystalline rocks and fints become more frequent. The petrographical analysis of the coarser gravel fraction indicates that the ice sheet advanced from the NE to NNW (the Widawka lobe) and from the NE to ENE (the Rawka, Pilica and Luciąża lobes). The source areas of the gravel deposited by the Warthian ice sheet were magmatic and sedimentary areas of both the Baltic and the SE Sweden basins.
The heavy-mineral assemblages of Pleniglacial fluvial sediments were analysed for two river valleys, viz. the Luciąża River (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 taken 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 underwent 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 processes were largely controlled by the climatic changes during the Pleistocene.