Migration of large-scale bedforms and preservation of crossbedded sets in highly accretional parts of tidal channels in the Oosterschelde, SW Netherlands

Abstract

Recent large-scale crossbedded sands have been studied in two construction pits of the 'Delta Project' in the Oosterschelde, The Netherlands. The deposits form long crested megaripples of about two metres high at a depth of 4 to 17 metres below Mean Sea Level. Crossbedded sets have been analysed for stand-still phases of megaripple migration during the subordinate tide (pause planes). An average lee side accretion rate ofthe dunes was calculated from the cyclic neap to neap tide change in thickness of the sand layers between successive pause planes. Information on the morphodynamics of the environment of deposition and the rate of accumulation of the discussed units was acquired through some particular sedimentary structures and through the study of series of hydrographic charts of the area. The latter information also strongly suggests a wide occurence of alike sedimentary units in the subsurface of shoals of the Oosterschelde mouth and outer delta. Finally the thickness and the number of the sets in relation to sandwave migration and rate of accumulation is discussed.