Diagnostic sedimentary structures of the fluvial-tidaltransition zone – Evidence from deposits of the Rhine andMeuse

Abstract

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