Acta Musei Moraviae

The middle pleistocene sediments in northwestern part of Vidnava lowland (Paczków graben margin) – ground penetrating radar survey

The Vidnava Lowland in the northern Sudetic Foreland is characterized by extensive alluvial and fluvial sediments deposited during the Weichselian. Pre-Weichselian deposits are very rare and occur as isolated relics only. The Písečník Hill (288 m a.s.l.) with adjacent plateau represents one of the largest relics in the western part of the lowland. It consists of Elsterian glacitectonites, infills of subglacial cavities, and meltout tills, underlain by Neogene deposits. A ground penetrating radar (GPR) survey of the deposits was undertaken in order to identify buried sedimentary units. The GPR profiles revealed five facies and two subfacies: GPR1a (channel infill – large-scale bedsets of dunes, lateral-downstream accretion); GPR1b (mid-channel bar – bedload sheets, low relief dunes, vertical-downstream accretion); RF2 (channel infill: dunes and transverse bars, downstream-vertical accretion or upstream accretion on mid-channel bar-head); RF3 (scours infill or bar margin deposits, lateral-downstream accretion); RF4 (climbing dunes along channel outer bank); RF5 (coarse gravelly to bouldery sheet flow deposits). The sedimentary architecture of RF1–RF4 facies is interpreted as a part of braided river channel-belt with mid-channel bars and side bars separated by sinuous channels. The internal structure of the deposits and abundant erratics indicate the deposition in ice-marginal river or ice-marginal valley. The RF5 facies is interpreted as a Saalian alluvial fan in superposition above the glaciofluvial deposits.