Czwartorzęd Kotliny Chodelskiej

Andrzej Ber, Krystyna Rywocka-Kenig Rywocka-Kenig




To prove the Quaternary stratigraphy in the Chodel Basin area, 14 bore holes were made by the Geological Institute. The total depth of the bore holes amounts to 302,6 m (Fig. 1).
Substratum of the Chodel Basin is built up of calcareous marls, or marly opoka of Upper Maestrichtian age. The surface of the Cretacecus formations is uneven, and reveals some relief lows of erosional-karst origin, with an amplitude reaching up to several scores of metres (Fig. 3). The Cretaceous formations are here overlain with the Quaternary deposits characterized by varying thickness, not exceeding 40 m. In the Quaternary substratum the bore hole Nr 116, made within the Bełżyce Plain adjacent to the Chodel Basin, has encountered arenaceous-marly deposits at Danian age, so far unknown in the area under consideration. A 4,5 m thick residual bed of variously grained sands with gravels and pebbles of northern rocks, referred to the South-Polish Glaciation, represents in the Chodel Basin the oldest Quaternary horizon (Figs. 3, 4 – bed 2). Sands with gravels and pebbles rest here on light-grey fine-grained sands, silty and grey-greenish at the bottom, intercalated with a 2,5· m thick parting of arenaceous silt (Figs. 2, 3, 14 – bed 3).
The sands here considered contain a thin silt layer with plant detritus, which  occurs at a depth of 22,4–23,1 m. The arenaceous-silty deposits are thought to be laid down prior to the inland ice invasion of the Maximum Stage of the Middle- Polish Glaciation. This, in turn, is represented by a layer of lower boulder clay, resting above.
To this boulder clay corresponds a grey boulder clay found in the bore hole Nr :15 within the Bełżyce Plain. The lower boulder clay is covered with inequigranular, fluvioglacial sands 0,4–6,0 m in thickness (bore holes Nr 1, 2, 4, 7, 8 and 8a; Figs. 2 and 3 – bed 5). Accumulation of these sands took place still before a new invasion cd the inland ice of the Middle-Polish Glaciation, Maximum Stage. The inland ice deposited here the upper boulder clay found at present on the Chodel Basin surface.
Granulometric-petrographical examinations of both lower and upper  boulder clays (Tables 1–3), the results of which gave such parameters as K/W – 1,09 and O/K – 1,35 for the upper boulder clay, and K/W – 1,08 and O/K – 1,34 for the lower boulder clay (fraction 0,5–1,0 cm), proved the opinion of the present authors that the deposits should be referred to one glaciation only (Middle-Polish Glaciation).
In the Chodel Basin area, the North-Polish Glaciation was expressed by the formation of arenaceous silty, frequently loamy covers of talus deposits and by frost disturbances in both Cretaceous and Middle-Polish Glaciation deposits. At the decline of the Pleistocene time, numerous dunes were formed, and arenaceous talus, deposits were blown away. Silty-arenaceous-gravelly river deposits, peaty muds, and peats belong to the youngest Holocene formations.


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