Internal structure of some tidal mega-ripples on a shoal in the Westerschelde estuary, the Netherlands: report of a preliminary investigation

Abstract

Ebb mega-ripples on a sandy shoal in the Westerschelde estuary (SW-Netherlands) were studied in crossseCtion. The internal structure is dominated by large scale ebb-directed cross-stratification of a particular type showing flood induced erosional and/or depositional modifications. The characteristics betraying the tidal origin of the crossstratified structure are: 1. Erosional unconformities (diastems) between the successive cross-stratal bundles that build one large scale set. 2. Regular alternations between such bundles and conformably inclined solitary trains of small scale sets containing upslope directed cross-strata. 3. The isolated occurrence of a ± 1 dm-thick coset of small scale cross-strata conformably intercalated between two of the above mentioned bundles. 4. (Sub)horizontal cosets, of small scale cross-stratification erosively separating vertically successive large scale ebbsets. The above mentioned features confirm the subordinate and rather erosional, activity of the flood currents as compared with that of the ebb.