Fossil polygonal structures in boulder clay
DOI:
https://doi.org/10.26485/BP/1960/7/9Keywords:
poligony gliniaste, szczeliny zmarzlinowe, procesy peryglacjalne, glina zwałowaAbstract
This study presents the results of research on polygonal structures – in till clays in the Gąbin, Brzezie and Kaptury areas of Poland – that formed under periglacial conditions. Field investigations, including exposures and vertical cross-sections, as well as analysis of the materials filling the fissures, allowed for the characteriaation and morphology of frost cracks. Three main types of forms were identified: narrow fissures forming polygon edges, forms with pronounced lateral development, and horizontal fissures connecting vertical elements of the network. These structures result from a long-term contractional process related to seasonal freezing and clay swelling. Granulometric analysis of the fissure-filling material indicates a local origin of the sands and strong influence of frost processes. The polygonal structures belong to periglacial formations from an early stage of the Baltic glaciation and represent fossil analogues of contemporary tundra polygons. It is proposed to designate these forms as “clay polygons”, characteristic of flat till-covered upland surfaces in Poland.
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