Typologia litostratygraficzna osadów plejstoceńskich w północnej Pobrzeża Szczecińskiego

Abstract

Autorzy podjęli kolejną próbę wykorzystania metody taksonomii dendrytowej dla systematyzacji rezultatów standardowych badań litologiczno-petrograficznych. Pozwala ona bowiem w sposób szybki i prosty uzasadnić charakter powiązań litostratygraficznych osadów plejstoceńskich. Stwierdzono, że taksonomiczne uporządkowanie rezultatów badań uziarnienia pomocne jest przy ustalaniu genezy osadów, natomiast analogiczna taksonomia składu petrograficznego żwirów różnicuje materiał pod względem wiekowym. Uporządkowanie taksonomiczne składu minerałów ciężkich uwypukla odrębności facjalne niezależnie od wieku i ich genezy. Zastosowana metoda pozwoliła w obrębie badanego obszaru na wydzielenie dwóch różnowiekowych poziomów. Poziom starszy. związany z osadami zlodowacenia południowopolskiego i interglacjału mazowieckiego, oraz poziom młodszy reprezentowany przez utwory zlodowacenia środkowo i północnopolskiego.

LITHOSTRATIGRAPHIC TYPOLOGY OF PLEISTOCENE DEPOSITS IN NORTHERN PART OF THE SZCZECIN COASTAL AREA

Pleistocene deposits from six boreholes in northern part of the Szczecin coastal region (Fig.·1) were covered by standard lithological·petrographic studies. Figure 2 presents simplified geological columns of these boreholes. Laboratory studies covered granulation, petrographic composition of the 10-5 mm fraction, composition of the 0.25-:0.1 mm fraction of heavy minerals and, partly, mineral composition and roundness of quartz grains of the 1.0-0.5 mm fraction. Fig. 3 presents averaged results of laboratory studies for individual complexes of Pleistocene deposits.

The .results of standard lithological-petrographic analyses of Pleistocene deposits were subjected to taxonomic processing with the use of dendrite method (J. Perkal, 1967). That method was successfully used by the present authors in their studies on lithology (W. Iłaszewski, R. Racinowski, 1979; R. Racinowski, 1974; R. Racinowski, A. Socilan, 1918). The averaged classes (fractions) of a given type of laboratory tests for individual complexes of deposits are arranged in rows from the lowest values to the highest. Median values and their characteristic confidence intervals were calculated with confidence level equal 0.05 (L.P. Aszmarin et al., 1971) for the rows. This resulted in subdivision of the rows in three parts: middle, close to the median, and two most distant from the former, negative and positive. After analysing the degree of overlap of features common for all the sedimentary complexes, there were calculated distances between the complexes and taxonomic dendrites were constructed with reference to the smallest distances between them (Figs. 4 - 7).

The taxonomic ordering of the results of analyses of granulation (Fig. 4) was found to be helpful in reconstructions of origin of a deposit. Analogous taxonomy of petrographic composition of gravels (Fig. 5) differentiates the material with reference to its age. Taxonomic ordering of composition of heavy minerals (Fig. 6) accentuates differences in facies of deposits, regardless of their age and origin. Summative taxonomic dendrite (Fig. 7) differentiates deposits primarily with reference to their origin and later age.

Taxonomic comparisons showed the existence of strong connections between tills and limnoglacial deposits in the studied area. The latter appeared related to fluvioglacial and glacial deposits. This suggests significant influence of water reservoirs and flowing water on formation of deposits during the whole Pleistocene.

The used method of dendrite taxonomy made possible methodologically valid systematization of sedimentary complexes into glacial and interglacial. The identified sedimentary complexes are related to the South-Polish Glaciation. Masovian Interglacial and Mid- and North-Polish Glaciations. At the present stage of studies. any further zonation of Pleistocene deposits would be hazardous.