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ABSTRACT

Sedimentary structures are examined in recent alluvium that was deposited in an environment transitional between fluvial and estuarine. The depositional sequence in vertical section reveals three units, that vary according to type and association of sedimentary structures, and lithology.

  • 1
    The lower unit is characterized by large-scale trough cross-stratification. Sedimentary structures suggest a fluvial environment in which water and sediment movement were uni-directional but subject to periodic fluctuations.
  • 2
    The middle unit displays an alternation of small-and large-scale cross-stratification, which is directionally bi-modal due to tidal action. Both water and sediment movement were bi-directional and highly variable in intensity. A vertical gradation in dimension of structures shows successive weakening of tidal currents as deposition proceeded.
  • 3
    The upper unit is characterized by flaser and lenticular bedding and small-scale trough cross-stratification, ascribed to an estuarine regime of low intensity.

The observed transition from a fluvial to an estuarine environment is tentatively related to increased tidal action, caused by the destruction of large parts of reclaimed land bordering the Oude Maas, following severe floods in this area during the 14th and 15th centuries, A.D.