1. INTRODUCTION

As industrial raw material, as hydrogeologic reservoir or as barren measures to be pierced when drilling mineshafts, the Cretaceous has frequently been studied since the mid 19th century.  Descriptions of exposures or sections of wells and boreholes were compiled by J. Cornet  (1923), enlarged by Leriche (1929), synthesised by Marlière (1954, 1957), formalised by Marlière and Robaszynski (1975), by W.M. Felder (1975) and by H.J. Albers et al. (1978). 

The main subdivisions for the Cretaceous which have been in use in Belgium for a very long time, were transcribed into the legend of the Geological map at 1/40,000 by the Belgian Geological Council (1929). The cartography at 1/25,000 of the new geological map has made the need for anactualisationof this legend obvious. It is with that purpose that the names of the lithological units – formations, members, and beds – have been revised at the request of the National Belgian Geological Committee. The result of this revision is presented in the following texts and figure.

 

The texts indicate the major data on the units including a short description, their stratotype and age.

 

 

The figure indicates the position of the lithological units in relation to the chronostratigraphic divisions in stages. The different columns are:

 

System, stages and substages: the chronostratigraphic units used follow the proposals or recommendations of the IUGS (Remane ed., 2000) or were discussed during the Second Symposium on Cretaceous Stage Boundaries in Brussels, September 1995 (Rawson et al., 1996). Between the Jurassic and Cretaceous systems the sedimentary “enregistrement” is very slight or evenabsentor irregular. In continental facies the Jurassic-Cretaceous boundary cannot be placed accurately.

 

Radiometric age: the numbers corresponding to the column “Ages s/c” marked herein come from Hardenbol et al. (1998) and from Remane ed. (2000).

 

Regional columns: the Cretaceous facies differ substantially from region to region. Four columns indicate the succession of the lithological units specific for each region. From West to East the following regions have been taken into account:

The Cretaceous of these two regions is very similar in the Cenomanian- Turonian interval.

 

Northern France: the terminology used in geological literature for the eastern part of the Pas-de-Calais has not beenformalisedand the lithological units correspond to the terms which are used sinceGosseletand have been defined in the “Lexique Stratigraphique International” (Sornay coord., 1957) and in the “Synthèse géologique du Bassin de Paris” (Mégnien coord., 1980).

 

Mons Basin: many of the nowformalisednames were originally used by F.L. Cornet and Briart, by Rutot and Van den Broeck in the 19^th century, or by Marlière (1936), or by Robaszynski (1975a-c). These papers contain the original descriptions of the lithological units, redefined andformalisedherein.

 

Note:  in some of the early map sheets of the “Carte géologique de la Wallonie” at 1/25,000 new formation and member names have been presented (e.g. Doremus, 1997, for map sheet Hertain-Tournai) whenformalisednames already existed for the same formations and members (Robaszynski, 1975a-c). These new names are considered herein as junior synonyms.

 

Brabant-Namur (Méhaigne – Petite Gette area), Thudinie, Haute-Ardenne: between Mons and Liège Cretaceous strata are rarely exposed. They have often only been visible by ground works, or temporary trenches or boreholes. They were generally deposited in shallow environments in arenaceous, coarse grained, often glauconitic, facies, sometimes decalcified by the proximity of the topographic surface (this does not apply to Upper Maastrichtian white chalks in Orp-Jauche deposited when the sea levels were very high). The “glauconie de Lonzée” near Gembloux (northern part of Namur) is present as a thin, arenaceous –glauconitic facies.

Similarly in Thudinie, between the Sambre and Meuse rivers, above a glauconitic facies occur partially decalcified coarse-grained chalks.

In the Haute-Ardenne from marly facies and residual flints macro- andmicrofaunashave been collected. For the Hockai outcrop, Bless & P.J. Felder (1989) studied the benthic Foraminifera (Bolivinoides) which suggest a Campanian-Maastrichtian age; based on macrofauna (bivalves, brachiopods, and echinoids) from several outcrops in the Hautes-Fagnes, Dhondt & Jagt (1997) suggested an early Late Maastrichtian age – thus showing that the maximum transgression took place at the same time on the Hautes-Fagnes and in the Orp-Jauche region.

 

Liège-Limburg area: The lithological units and their interpretation into formations and members were mainly formalised by W.H. Felder (1975), Albers et al. (1978) and Albers & W.H. Felder (1979).