Zmeny fluvialniho stylu behem svrchniho pleistocenu a holocenu na prikladu nivy reky Ploucnice v severnich Cechach

Sedimentary record of the Ploučnice River system, which is situated in the northern part of the Bohemian Massif, provides remarkable data for the study of climatic changes since the Upper Pleistocene. Narrow and flat floodplain which is restricted by the steep wall from Cretaceous quartz sandstones of Jizera Formation was formed. This type of floodplain represents a special case in between the deeply incised valley downstream in the Děčín area and narrow deeply incised valley of a mountain river withpoorly developed floodplain deposits like in upper part of Ploučnice stream on the Ještěd Ridge.
The Ploučnice floodplain is flat, wet and silty and many paleomeanders occur there. Near the floodplain margin we found a system of sandy and gravelly elevations and paleochannels interpreted as relicts of fluvial processes during Upper Pleistocene/Lower Holocene transition. This assessment is supported by local relief, sedimentary record from hand-made boreholes and pollen analysis of a paleochannel infill. We recognized four developmental phases of the river: 1. Upper Pleistocene - braided floodplain represented by gravels and medium grained quartz sand. 2. Late Glacial/early Holocene transition - anabranching river environment represented by a succession of silty, fine to medium-grained sand with gravel. 3. Middle Holocene period - abandoned anabranching channels associated with desiccation of channel infill and incision into the previous main terrace infilling 4. late Holocene (from Middle Ages to present) - fluvial style of meandering river environment with agradation phase represented by sediments consisting of very fine- to medium-grained sand which passes downwards to sandy silt with organic matter. According to unpublished palynological data the base of the paleochannel infill indicate Lower Holocene period followed by Middle Holocene sedimentation hiatus until the Medieval Age and the upper part of sedimentary infilling belongs to Middle Ages until the present times.

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