Diagnostic sedimentary structures of the fluvial-tidal transition zone – Evidence from deposits of the Rhine and Meuse

Abstract

AbstractIn mesotidal settings the transition of a coastal plain estuary to the river is marked by the change of a multiple ebb and flood channel configuration to a single channel system. At high river discharge fluvial processes operate, whereas in periods of low discharge the flow is complicated by a tidal component and a landward intrusion of the salt wedge. These hydraulic and morphological characteristics make the transitional zone different from the ‘pure’ fluvial and estuarine environment. Inspection of published and unpublished data from a number of outcrops of Recent and Tertiary deposits of the Rhine reveals that also in a sedimentary sense a transitional zone can be recognized. In order to separate this zone from the upstream fluvial and downstream estuarine environment a sedimentological definition of the fluvial-tidal zone is proposed being the part of river that lies between the landward limit of observable effects of tidal-induced flow deceleration on fluvial cross-bedding at low river discharge and the most seaward occurrence of a textural or structural fluvial signature related to the high river stage.