1. INTRODUCTION + figs

Apart from some near shore marine sediments the Quaternary stratigraphy of Belgium is essentially concerned with continental deposits laid down by fluvial, eolian, slope or organo-chemical processes. These categories form the basis for the lithostratigraphic classification. Their distribution coincides to some extent with the major geographic regions: low sandy plains with adjacent coastal area in the north; undulating loess covered low plateaux in the middle; higher sloping ground on the Palaeozoic basement in the south. The basic Formation units are conceived in such a way that general users can distinguish them, while Member units necessitate specialistic knowledge. Due to the multitude of controlling factors the quaternary deposits present however great variations. This may lead to the distinction of many local Bed units of which only a few examples will be given.

For chronological assignment the base of the Quaternary is accepted at the top of the Gelasian, the base of the Middle Pleistocene at the beginning of the Brunhes magnetochron, the base of the Upper Pleistocene at the beginning of the last interglacial, the base of the Holocene at the end of the Younger Dryas. These time assignations are mostly based on climato-stratigraphic deductions, in which sediment facies, vegetation and palaeosols are of major importance.

An earlier scale was devised during the detailed geological mapping of the country from 1880 to 1910 and materialised by symbols. A time framework was indicated by al for Alluvium and q1 to q4 for divisions of the Diluvium. To these was joined a letter for a particular lithology, making up a de facto lithostratigraphical classification. The later Stratigraphical Register (1929-1932) is essentially chronostratigraphical and recognised only two Pleistocene subdivisions on faunistical arguments. Since then Quaternary research greatly developed, but even now type localities are scanty as authors are aware of the great variability of these continental sediments and hesitate to indicate a succession as typical. It must be stressed that actual analysis, in one exposure or bore- hole, deals with much finer detail than can be expressed by generalised lithostratigraphic units and aims to reconstruct past environmental change at the finest possible scale. But the lithostratigraphy presented here is adequate for geological mapping of the Quaternary mantle, especially when the mapped units represent typical superpositions of lithostratigraphic units. The distinction of local Beds may then become very significant.

Table 1 List of Quaternary lithostratigraphic units.