ARCHITECTURE AND LONG-TERM EVOLUTION OF A TIDAL SANDBANK - THE MIDDELKERKE BANK (SOUTHERN NORTH-SEA)

The internal structure of the Middelkerke Bank (one of the Flemish Ban ks located in the southern North Sea off the coast of Oostende, Belgiu m) has been studied in the framework of the Marine Science and Technol ogy (MAST) program co-funded by the European Community. A dense grid o f high and very high resolution seismic profiles has been used, as wel l as several vibrocorings. Seven major seismic units can be identified in the Quaternary sediments, bounded by major discontinuities correla ted across the whole study area. The lower units clearly appear as bei ng deposited during periods of relative low sea level (channel infilli ngs, shoreface, estuarine and/or ebb-tidal delta deposits). The presen t shape of the bank results partly from recent erosional processes, re working the underlying deposits. Thus, the lower part of the bank as a morphological feature does not consist of ''offshore tidal sands''. T he master bedding of the upper part of the bank consists of inclined r eflectors, dipping at an angle of about 5 degrees in the same directio n as the bank's ''steep'' face. These reflectors, very similar to thos e described by Houbolt (1968), are interpreted as being the result of alternating periods of deposition and erosion related to the episodic combination of tidal currents and storms.