Rzeźba progu kredowego i pokrywy blokowe koło Wilkowa (Pogórze Kaczawskie)
Journal Title: Przyroda Sudetów - Year 2017, Vol 20, Issue
Abstract
Morphology of Cretaceous sandstone escarpment and block cover deposits near Wilków (Pogórze Kaczawskie, West Sudetes) An escarpment capped by quartz sandstone of Cenomanian (Upper Cretaceous) age is a prominent feature of regional relief in the northern part of the Pogórze Kaczawskie region in the West Sudetes. It is part of a regional cuesta landscape that has developed upon tilted sedimentary sequences of Permian and Mesozoic age. East of the town of Wilków the escarpment, otherwise straight in outline, takes a sinuous course and shows two distinct spurs separated by an amphitheatre. Its height is 80–100 m, with the most elevated spot on the escarpment rim at 427 m a.s.l. Cretaceous sandstone occurs only in the most elevated part of the escarpment and is underlain by a thick series of rather weak sandstone of Triassic age, whilst the footslope surface is cut across Permian sediments. Although the uppermost section of the cuesta face lacks natural rock cliffs, the slope below is littered by sandstone boulders ranging in size from 0.5 m to 8 m. At spurs the block cover is dense and thick, with boulders piled one upon another, but it becomes dispersed away from spurs and disappears within the amphitheatres. This observation, coupled with the sinuous outline of the escarpment itself, in the absence of evidence of fluvial headward erosion, suggests an increase in rock mass strength in the spur sections. Minor features to note on numerous boulders are those related to ferruginization and silification, which would account for the increasing sandstone hardness. They appear as surface crusts, thin Fe- and Si-rich layers within the rock mass and concentric bands. Both seem genetically related to tectonic deformations and movement of hydrothermal fluids with the rock, causally related to Cenozoic volcanism. There is no evidence available that boulders are produced by catastrophic release from cliff lines and subsequently transported downslope. A non-catastrophic in situ disintegration of the sandstone layer is suggested, with subsequent downward displacement (settling) as the slope surface is lowered. The role of slope processes in downslope transport of boulders in periglacial conditions remains inconclusive and requires further field experiments using geophysical techniques.
Authors and Affiliations
Filip Duszyński, Piotr Migoń, Milena Różycka, Aleksandra Michniewicz
Keywords
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