THE OXBOW SEDIMENTARY SUBENVIRONMENT: ITS VALUE IN PALAEOGEOGRAPHICAL STUDIES AS ILLUSTRATED BY SELECTED FLUVIAL SYSTEMS IN THE UPPER ODRA CATCHMENT, SOUTHERN POLAND

Abstract

Research was conducted in valleys of sinuous rivers that drain medium-high mountain, foreland basin and upland areas, where loose Quaternary deposits predominate. The cyclic pattern determined for deposits of the oxbow sedimentary subenvironment in the Upper Odra Basin can be expressed as a few alternative sequences. The best-developed cycle occurring on a relatively high level of probability, is represented by the unilateral transition from channel to overbank deposits and upwards-bilateral oscillations between overbank and biochemical, as well as biochemical and slope deposits. In the first stage, oxbow filling processes are usually determined by autocyclic factors (resulting from spatial relations between abandoned channels and the active channel). As a consequence, overbank and/or biochemical sediments usually overlie channel deposits. Later, allocyclic processes could easily dominate autocyclic processes. In these cases, overbank, slope and late-Holocene alluvial fan deposits were delivered to oxbow basins as a result of the influence of outside factors such as climate or human impact. In the Upper Odra catchment, facies succession in the sequences of deposits infilling abandoned channels was mainly determined by climatic factors (in the Late Vistulian, early and mid-Holocene) and anthropogenic factors (in the late Holocene, especially in the last dozen centuries or more). The course of sedimentary processes conditioned by climate and human activity was modified by orographic factors associated with spatial relations among abandoned channels and both the active channel as well as valley slopes. However, the geological structure had a smaller influence on the course of sedimentary processes in the oxbows. The diversity of bedrock lithology in the individual drainage areas determined the thickness and lithological features of the given series of deposits but not the facies succession.