Abstract

Holocene anastomosing fluvial systems have been described from a wide variety of environments, which usually have in common the presence of a rapidly rising base level. Although it has been suggested that this fluvial style can be expected in coastal areas and adjacent inland areas influenced by rapid sea-level rise, few anastomosing fluvial systems from such areas have been reported. The occurrence of alternating meandering and anastomosing fluvial systems in the Holocene Rhine-Meuse Delta (central Netherlands) is discussed here. It is shown that the two fluvial styles not only have distinctive plan morphology but also can be identified on the basis of facies-architectural criteria (width/thickness ratio of channel-belt sand bodies and geometry of overbank deposits). The distribution of channel patterns in the study area is described by means of a simple time-space model. It is argued that the principal condition for the development of anastomosing fluvial systems in this area is the combination of rapid (> 1.5 mm/yr) vertical aggradation (caused by rapid sea-level rise) and a cohesive subsoil, consisting of thick (at least 3-4 m) clay and organic beds. In the case of the Rhine-Meuse Delta, a low gradient, which has been mentioned as an important factor by many authors, need not always lead to channel anastomosis. Modern anastomosing fluvial systems may be more widespread than hitherto supposed, and may be especially abundant in deltaic settings.

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