Megaripple cross-bedding as a tool for the reconstruction of the Palaeo-hydraulics in a Holocene subtidal environment, S.W. Netherlands

Abstract

Large-scale cross-bedded sets from a Holocene subtidal sequence exposed in a construction pit at the mouth of the Oosterschelde were used for comparative studies with present-day tidal processes. The periodic variation which can be observed within a large-scale cross-bedded set of a subtidal megaripple is used to reconstruct the tidal hydraulic parameters such as the shear velocity, the tidal current velocity and the tidal range. In addition to this, the aperiodical variation of the set is used to evaluate the storm-induced components of these parameters. The main steps of the procedure are: (1) the identification of the tidal features of the set such as the lateral bundle sequence; (2) an appropriate selection of the sediment transport rate function; and (3) the development of a function relating the tidal range with the shear velocity based on an estimate of the water depth. Additionally a simple expression is derived, which relates the ratio of the astronomical tides and the atmospheric disturbance to the mean standard deviation of the bundle thicknesses. The calculated tidal current velocities, tidal ranges and its standard deviations from a subrecent example show a good agreement with the actual hydraulic parameters.