The preglacial Nysa Kłodzka fluvial system in the Sudetic Foreland, southwestern Poland

Abstract

The preglacial series deposited by the Nysa Kłodzka river has a much wider extent in the Sudetic Foreland than hitherto supposed. It can be found in a 5-10 km wide belt near margin of the Sudetes Mts and an over 60 km wide belt in the Sudetic Foreland and the adjacent part of the Silesian Lowland. This series is porphyry-bearing and it is made up of four lithostratigraphic units that differ in their heavy mineral contents. The porphyry-free sediments deposited by other river systems of the Sudetic Foreland occur at the margins of the porphyry-bearing series or partially overlie it. Units I-III were deposited mainly by sinuous, suspended-load, low energy rivers and only locally by gravel-load, high energy rivers. The preglacial sediments of units I-III consist of strongly re-worked, quartz-rich material and some kaoline matrix, that most probably come from Tertiary weathering mantles of the Sudetes Mts. These fluvial sequences were deposited by rivers with widely migrating valleys and they probably reflect weak tectonic activity in the region. Unit IV was deposited by bed-load, high energy rivers which were formed during general landscape reorganisation caused by strong tectonic activity. The new valleys were incised, and as a result, local, kaolin-free material became dominant in the sequence. The vertical amplitude of tectonic movements in the Sudetic Foreland at that time was about 40-80 m, with simultaneous uplift of the Sudetes Mts of about 60-70 m. Units I-III are most probably of Late Pliocene age, whereas unit IV could have been deposited from the Early Pleistocene to the Cromerian Stage.