Sequence mapping of Holocene coastal lowlands: the application of the Streif classification system in the Belgian coastal plain

A geological map of the Holocene deposits of a portion of the western Belgian coastal plain is presented. The map differs from a conventional geological map which is of little use for coastal lowlands because of the high lateral and vertical variability in lithology in the subsoil. The method of sequence maps was chosen because these maps allow the representation of the entire vertical sequence of the Holocene deposits. A sequence map is constructed on the basis of profile types consisting of the vertical succession of the various mapping units. In order to produce a user-friendly map, preference was given to lithogenetic units instead of formal lithostratigraphic units for the determination of mapping units. The organisation of the mapping units was established according to the Streif classification system. The application of the system is demonstrated with two different sequence maps each constructed on a different level of the hierarchic system: a general sequence map and a special sequence map showing further differentiation.