Pseudo-permafrost fissure forms in the lacustrine chalk near Laska near Brusy

Abstract

In the vicinity of Laska near Brusy (Pomerania), lacustrine sediments occur that rest on high terraces of the Duże Głuche and Małe Głuche lakes. In the upper part of the lacustrine chalk, interesting fissure-like forms have been identified that contrast sharply with the stratified lake chalk. At the top of the chalk, they form wedge-shaped structures reaching depths of 1–2 metres, which then transition into fracture cracks. In plan view, these forms create a widely spread irregular network of polygons with diameters of about 1 metre. It has also been found that the wedges are filled with chalk debris. According to the author, the described forms originate from the rapid drying of the sediment. The infilling of the wedges with chalk material must have occurred within a short period, most likely as a result of increased rainfall intensity. The author assumes that these forms were created immediately after the sudden drainage of lake waters caused by a capture event during the Littorina Sea phase. This note signals the presence of wedges, which could – in the absence without favourable observation conditions and without palynological data – be mistakenly identified as permafrost (frost) wedges.