Gravitation and Cryoturbation Processes in the North Bohemian Tertiary

Abstract

Typical processes of periglacial climate have been repeatedly ascertained in the area of the North Bohemian Tertiary. Most remarkable are the gravitation processes. The present paper treats of the spreading of Dinas quartzites upon the quartzite substratum in the vicinity of Skšín and Bečov, which is due to solifluction. Gravitation processes that affected the doubling of the Dinas quartzite bed in the vicinity of Sedlec south of Most are especially noteworthy. The upward sequence of layers is as follows: decalciferous fossil wheathered Upper Turonian marls, 0,5-2 m thick quartzite bed, 2-4 m thick tuffites and as many as 10 m thick basalt cover composed prevailingly of basalts weathered into many-coloured argillaceous rocks. Upwards, layers repeat in the same sequence almost throughout the whole height of the hill. In layers shifted from their original position no Quarternary material has been traced. The elder Quarternary terrace (marked I1 by R. Engelmann) covers the shifted strata without any marked disruption. Since the summit part of the hill comprising the quartzites is partly isolated from its neighbourhood; we presume that the shifting of quartzites from the area occupied at the present by the valley had taken place before this valley was due to Quarternary erosion. In the open coal-mine Hrabák in the vicinity of Most remarkable folding was discovered - next to common cryopedological phenomena - consisting of an overturned fold formed by a Miocene brown-coal seam, the overlying sands and clays. These Miocene rocks are covered and partly surrounded with Pleistocene loess and deluvial loams of a phonolit skeleton. North of the "fold" overlying Miocene clays were discovered surrounded with the above-mentioned Quarternary loams. The fold phenomena in question resembles deformations of brown-coal seams occuring in brown-coal basins of Central Germany. A detailed description is given of the occurence of folded Miocene rocks. Not very extensive but intensive folding was ascertained in many exposures in the area of the basin (Tušimice near Chomutov, the mine Hrabák in the vicinity of Most, Dolany near Kadaň, Nechvalice near Teplice). It is rather interesting that almost all exposures under investigation display folded Tertiary rocks turned through territorial fires into porcelanite. The fires took place after the folding had been completed. Also the stone pavement is described that was discovered in an abandoned brick-kiln at the foot of the phonolite hill called Špičák near Most.