Geomorfologiczne kryteria identyfikacji zdegradowanych krawędzi tektonicznych w Sudetach

Piotr Migoń



Tectonic landforms of the Sudetes Mountains, being residual in its character, cannot be recognised by means of geomorphic criteria of active faulting, developed in serniaridareas of the Western United States. Fault-generated escarpments, which are a common feature of the Sudetes morphology, have been severely degraded since their origin in the Late Tertiary times. Direct evidence of faulting lacks and, therefore, indirect morphological indices have to be used while attempting to elucidate tectonic history of the area. Vertical offsets of alluvial surfaces, i.e. terraces and fans, are the only phenomena that bear unequivocal evidence of young tectonics. However, most of fluvial landforms in the Sudetes is post-Odranian in age and only Late Pleistocene faulting can be recognisedin that way. The best developed fault scarps in alluvium, up to 25 m high, occur along the Sudetic Marginal Fault and indicate considerable activity of that fault line towards the end of Quaternary. Other forms, as probable shutte ridges and deflected streams, may have several alternative origins and thus their use is limited in neotectonic reconstructions. Hydrographic changes, hanging valleys above scarps and longitudinal profiles of streams may be analysed as fault-related landforms. They can provide some information about pattern and amount of uplift and hanging valleys are the most convincing indicator of vertical movements. In resistant igneous rocks they may be preserved for more than 1 m. y., so they are relatively long-lived landforms. Geomorphological analysis of escarpments that separate Tertiary planation surfaces may also contribute to neotectonicreconstructions. Many scarps bear neither evidence of lithological control nor of retreat and if so, they are probably degraded fault-generated scarps, along which di splacementsof old morphological surfaces have taken place. It appears that any approach to recognise tectonic history of the area of residual tectonic relief, which bases on morphologiccriteria alone, needs to be supplemented by other methods.Morphometric analyses seem to be the most promising.

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