The pre-Elsterian valley system in the Western Sudetes, southwestern Poland, and its later transformation

Abstract

This paper presents a reconstruction of the pre-Elsterian fluvial pattern in the Western Sudetes Mts using borehole and geophysical data. These valleys were blocked by the advancing Elsterian ice sheet, enabling the proglacial lakes to be formed, and most of them were later covered by the ice sheet which entered into the mountain interior. The valleys are now filled with 5-15 m of 'pre-glacial' fluvial gravels and a generally thick glacial series. The latter comprises a till and glaciofluvial and glaciolacustrine sediments, including varved clay. The former valleys occur along the axes of the present-day valleys or at their margins, or occur in watershed areas which have been recently abandoned. Post-Elsterian changes in valley pattern is due to the filling of old valleys and epigenetic incision of new valleys along the tributary valleys. The valley fragments which preserved their former position were deeply incised, with the almost complete removal of older deposits. Some fault activity has been documented for that time in the marginal zone of the Sudetes Mts. The Saalian ice sheet only entered the marginal part of the Sudetes Mts, and hydrographic changes from that time are smaller.