Response of fluvial, aeolian, and lacustrine systems to late Pleistocene to Holocene climate change, Lower Moravian Basin, Czech Republic

Abstract

Late Pleistocene to Holocene Morava River valley-fill of the eastern Czech Republic reflects the geomorphic evolution of the valley as forced by climate change. Valley-fill stratigraphy was studied through measured sections, optically stimulated luminescence (OSL) and radiocarbon dating, ground-penetrating radar surveys of relict sand dunes, archived drill-hole data, and a comparison of elevations and ages of stratigraphic units. Fluvial systems evolved from meandering with floodplains to braided during MIS 3. Braided fluvio-aeolian systems dominated through MIS 2 and the Last Glacial Maximum (LGM). Valley aggradation occurred during arid glacial times of a low water-to-sediment discharge ratio. Most valley-fill was removed at 13ka with incision by a large-bend meandering river with an estimated bankful paleodischarge 3× larger than the modern Morava River. The Holocene Morava River has varied from meandering to anabranching with low rates of floodplain aggradation. The Bzenec sand body, up to 36m thick, represents an erosional remnant bypassed during late Pleistocene incision and consists of interpreted lacustrine turbidites overlain by braided stream and aeolian dune strata. The turbidites consist of laterally continuous, thin, normally graded beds of rounded and frosted sand grains of aeolian origin. Dates and elevation data argue that the valley lake formed during the LGM through downstream damming by a braided terminal fan and sand dune complex. The turbidites are interpreted to have formed through fluvial undercutting and slumping of dune accumulations as lake level rose. This process forced an erosional unroofing of aeolian accumulations, reflected in inverted OSL dates for the turbidites.