Evolution of the Late Neogene and Eopleistocene fluvial system in the foreland of the Sudetes Mountains, SW Poland

The oldest Cainozoic fluvial deposits in Lower Silesia date from the Oligocene. During the Middle and Late Miocene times, the fluvial system of this region was only slightly modified, especially in the foreland of the West and Middle Sudetes Mts. River lengths changed, following the migration of the North Sea shorelines. A rapid rebuilding of the fluvial system took place in the foreland of the East Sudetes Mts. either in the Late or Middle Miocene. Till that time, the main river valley of this region - the Nysa Kłodzka River, related to the Paczków and Kędzierzyn Grabens - used to flow towards the East, to a bay of the Paratethys sea. The new main river, pre-Odra, started to flow towards the North not before the Grodków Graben cut meridionally the Meta-Carpathian Swell. We are of the opinion that deposits of the Poznań Formation originated in an fluvial environment because no marine and/or limnic deposits have hitherto been discovered in the area of Lower Silesia above the uppermost of the Middle-Polish lignite seams (Henryk). The pre-Odra River drained the eastern part of Lower Silesia, and flowed towards the North, at least to the Poznań region. This main river captured such smaller rivers, as: the pre-Vistula, pre-Olza, pre-Ostravica, pre-Opava, pre-Nysa Kłodzka, and pre-Bystrzyca. Rivers draining the West Sudetes Mts. flowed first towards the North, to the region of the present-day Middle Odra River, and there turned to the West. It is conceivable that these rivers curved westwards just along the line of the present-day Wrocław - Magdeburg marginal stream valley ("Pradolina"). Since the Pliocene, the Sudetic rivers have started to transport coarser, sandy, and even gravelly material to a more distant foreland. Alluvial deposits of this phase occur exclusively on uplands. Coarse-grained sediments recognized in the bottom of deep erosional incisions were redeposited under subglacial conditions during the Mesopleistocene glaciations. The presented new interpretation of origin of the Poznań Formation basin and detailed recognition of Pliocene and Eopleistocene river system should initiate a new line of research into the Late Neogene and Eopleistocene sediments.