Sedimentology and stratigraphy of a tidal sand bank in the southern North Sea

A set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over, a tidal sand bank (the Middelke rke Bank) provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body. Five sedime ntary facies are distinguished. They range from clay to pebble and display various types of bedding and lithologies corresponding to different deposit ional environments. A succession of four Late Quaternary units are defined on the basis of the stratigraphic framework given by the seismic grid. The first unit represents the infill of a palaeovalley system by tidally influe nced sedimentary facies. It is followed by extensive and thick lagoonal or sub-tidal deposits. The third unit reveals the development of a landward pr ograding storm-dominated sand bar. This unit is dominated by clean fine san d. The last unit corresponds to the present-day tidal sand-bank. It shows t he typical offshore tidal sand bank facies (cross-bedded sand) prograding i n an offshore direction. Like other banks located in a more offshore positi on, the Middelkerke Bank is a composite bank incorporating facies which do not occur in 'classic' tidal sand banks. (C) 1999 Elsevier Science B.V. All rights reserved.