Periglacial Phenomena at Slatinice South of Most, Bohemia

Abstract

In the area of the Slatinice coal-mining field periglacial phenomena have been ascertained which have never before been discovered in any basin area. These periglacial phenomena occur mostly in the overlying beds of the present Tertiary sediments. Quarternary sediments in the above-mentioned area have achieved only a slight thickness exceptionally reaching 2 m. They are built of loess loams mixed with terrace gravel-sands and phonolitic material. Besides, they contain solifluction Miocene overlying sands, less often clays or weathered brown coal. The origin of different types of periglacial phenomena depends upon the occurrence of various Tertiary rocks in the Quarternary base. Accordingly, four main sections may be distinguished in the area of the Slatinice field. There is the section comprising substratum clays, a brown coal seam, overlying sands and clays. In the section where the substratum clays get thicker periglacial phenomena occur only in the part where the Quarternary mantle is thicker (in other parts they have been denuded). Mostly polygonal loess loams mixed with gravels and undulated or folded substratum clays have been ascertained. In the part where the brown coal seam gets wider another three zones may be distinguished two of which depend entirely on the thickness of Quarternary sediments, the third occurring in the swamps in the southwestern part of the mining field. No typical phenomena could have been discovered in the last zone since only mechanical weathering took place in the homogeneous carboniferous substance. The seam has been strongly affected by weathering down to the depth of two or more metres. In the zone with a thicker loess cover again polygonal soils, ice pots and ice wedges have been ascertained. In the zone with the minimum Quarternary cover the seam was heavily deformed by frost. Again its form reminds us of the ice wedges. A frostcleft was found here as well. In the section with overlying sand besides slight solifluctions no periglacial phenomena have been developed. Finally, in the section with overlying clays perfect ice cauldrons containing loess soils and gravels have been discovered. In sections, where polygonal soils have been ascertained, a perfect net of polygonal fields is supposed to have been created on the surface. Individual polygonal fields are marked out by the sifted out coarse-grained clastic material. From what was said above it becomes obvious that it is considerably difficult to state the time of origin of the phenomena. Guessing by the thick soil horizon developed on the surface of the Quarternary sediments we may presume that periglacial phenomena in the area of the present quarry of the Slatinice field date most probably from the las two stadials of Würm glaciation, i. e. Würm II and Würm III.