1Preliminary reports on the concepts and uses of lithostratigraphic, biostratigraphic and chronostratigraphic units were delivered at the International Geological Congress of Montreal, Canada, 1970. They were subsequently formalised as International Stratigraphic Guides (Hedberg, 1976; Salvador, 1994). The recommendations of the International Commission on Stratigraphy (ICS, see: http://www.stratigraphy.org/) of the International Union of Geological Sciences (IUGS, see: http://www.iugs.org/) have generally been well accepted by the Belgian community of geologists as represented by national stratigraphic subcommissions set up under the Belgian National Committee of Geological Sciences. However, the application of these recommendations has taken some time and the need has been felt for documents to synthesise the current situation regarding stratigraphic units named from Belgium and adjacent areas.

2In 2001, thanks to the collaboration of 44 geologists, a guide to a revised lithostratigraphic scale of Belgium was published in Geologica Belgica (Bultynck & Dejonghe, 2001).

3A similar volume dealing with the chronostratigraphic units was thought to be necessary to summarise the current scientific knowledge regarding series, stages and substages named from Belgium and adjacent areas. This is particularly relevant at the present time because the status of a number of stages and other units, some of worldwide application, has been changed as a result of recent decisions of the International Commission on Stratigraphy. As publications on chronostratigraphic units are scattered in various journals, excursion guides and books, such a "state of the art" document would have the additional advantage of facilitating the efficient dissemination of information on the current and recommended usage of these units.

4This matter was discussed at two meetings of the Belgian National Committee of Geological Sciences held on 13 March and 6 November 2003. A further meeting, on 4 March 2004, was held with the presidents and secretaries of the Belgian stratigraphic subcommissions to examine a proposal regarding the content of a publication devoted to stages named from Belgium and adjacent areas. Decisions were made as to the subdivisions of the book, the framework of each contribution, and possible authors. A first evaluation of the progress of the work was made on 8 June 2004 during a meeting of 10 participants. At that time, instructions to authors were finalised and corresponding authors for each unit were chosen.

5The present volume is the result of this effort. It is divided into 4 parts:

6- Part I is concerned with all the chronostratigraphic units, named from Belgium and adjacent areas, which are currently accepted as internationally valid stages by the International Stratigraphic Commission. For each of these units (shown in red in column 5 of Figure1), a summary is given of material derived from important publications that led to their definition and acceptance as international units. Each summary contains the following items: (1) name: the name of the stage in English, Dutch, German and French; (2) age: the interval of geological time represented by the unit (expressed as absolute age); (3) author: the author(s) who initially defined the unit, the detailed reference of the corresponding publication, and a selection of the text defining the unit for the first time; (4) historical type area: the area or locality from which the unit was named, including its position on a topographic map at the scale 1:10,000 and a reference to the corresponding geological map; (5) description: a brief description of the unit; (6) historical background: evolution of the use of the term and the reason(s) it was chosen as an international unit; (7) lithology: includes a description of the lithological characters of the stage in Belgium and any lateral variations in lithology and thickness, the corresponding formations and members, and the boundaries in the reference section(s); (8) sedimentology and palaeogeography: including a short description of palaeoenvironment(s); (9) palaeontology: with emphasis on the biostratigraphic data relevant to the unit and the most useful markers; (10) chronostratigraphy: criteria used to date and correlate the stage; (11) geochronology: radiometric data, if available; (12) structural setting: brief mention of the structural context; (13) reference sections in Belgium and GSSP: important reference section(s) in Belgium, together with an indication where the Global Standard Section and Point (GSSP) of the base of the unit is defined (14) main contributions: references of main publications concerning the unit (names of authors and year); (15) remarks: (16) references.

7- Part II concerns the substages, listed in red in column 6 of Figure 1, whose international status is still under discussion.

8- Part III refers to Belgian chronostratigraphic units (column 7 of Figure 1) that have been used internationally until recently but which are now relegated to use at regional level only (as series, stages or substages). The characters and history of each unit are presented and the corresponding internationally accepted unit is cited. The term Waulsortian, which has not been applied to a stage, in Belgium or elsewhere, for more than a century but which has instead acquired international status as a facies term, will be presented in this section.

9- Part IV includes units (shown in the last column of Figure 1) whose use should be avoided in future. Each unit is defined briefly and the reasons why the term should be abandoned are stated. Some of these terms can easily be replaced by the name of the corresponding formation (e.g. Ledian should be replaced by Lede Formation; Bruxellian by Brussels Formation; Revinian by Revin Group). Other terms have proved to be strongly diachronous and hence inappropriate for chronostratigraphic purposes. A few (e.g. Paniselian, Scaldisian) cannot even be used as lithostratigraphic units because they incorporate strata that are no longer related to the current lithostratigraphic framework. Old terms, not used for more than 65 years, will not be discussed. The descriptions are grouped into two papers: one with the Paleozoic units, the other with Mesozoic and Cenozoic units.

10It must be remembered that the use of some terms has extended beyond the bounds of stratigraphic nomenclature into the vocabulary of such disciplines as water supply, architecture, history, engineering and nature conservation. Where these traditions are well established, it is impossible to impose restrictions, particularly as these terms were above all used with a lithostratigraphic rather than a chronostratigraphic connotation. For example, the ferruginous sandstones of the Diest Formation will probably always be referred to by architects as "Diestian sandstones".

11All stratigraphic units considered in this volume are listed in an index.

12Acknowledgements

13Acting as guest editor, it is my pleasure to warmly thank the 31 authors who agreed to contribute notwithstanding the editorial constraints: Frédéric BOULVAIN (Université de Liège), Denise BRICE (Université de Lille), Pierre BULTYNCK (Royal Belgian Institute of Natural Sciences), Marie COEN-AUBERT (Royal Belgian Institute of Natural Sciences), Geert DE GEYTER (Geological Survey of Belgium), Ellen DE MAN (Geological Survey of Belgium), Dominique DELSATE (Musée national d'Histoire naturelle du Luxembourg), François-Xavier DEVUYST (Trinity College Dublin), Roland DREESEN (Flemish Institute for Technical Research, VITO), Michiel DUSAR (Geological Survey of Belgium), Eric GROESSENS (Geological Survey of Belgium), Luc HANCE (Carmeuse Coordination Center), Alain HERBOSCH (Université libre de Bruxelles), Jacques HERMAN (Geological Survey of Belgium), Patric JACOBS (Ghent University), Pieter LAGA (Geological Survey of Belgium), Alan LEES, Stephen LOUWYE (Ghent University), Bruno MISTIAEN (Université de Lille), Thierry MOORKENS, Frank MOSTAERT (Ghent University), Edouard POTY (Université de Liège), Alain PRÉAT (Université libre de Bruxelles), Francis ROBASZYNSKI (Faculté polytechnique de Mons), Philippe STEEMANS (Université de Liège), Etienne STEURBAUT (Royal Belgian Institute of Natural Sciences), Maurice STREEL (Université de Liège), Jacques THOREZ (Université de Liège), Noël VANDENBERGHE (KULeuven), Stefan VAN SIMAEYS (KULeuven) and Jacques VERNIERS (Ghent University).

14I am also indebted to the referees for their help in improving the quality of the papers: Paul BRENCKLE (Westport, Massachussets, USA), John COLLINSON (Beech, Staffordshire,UK), Ellen DE MAN (Brussels, Belgium), S. DE SCHEPPER (Cambridge, UK), Christian DUPUIS (Mons, Belgium), Kirsten Grimm (Mainz, Germany), Philip H. HECKEL (Iowa, USA), Ken HIGGS (Cork, Ireland), John W.M. JAGT (Maastricht, The Netherlands), Marie LEGRAND-BLAIN (Bordeaux, France), Stephen LOUWYE (Gent, Belgium), Alan LEES (Ireland), Bernard MAMET (Brussels, Belgium), John MARSHALL (Southampton, UK), John Miller (Edinburgh, UK), George SEVASTOPULO (Dublin, Ireland), Andy SLEEMAN (Dublin, Ireland), Carl W. Stock (Alabama, USA), Chris DUFFIN (Sutton, UK) and Noël VANDENBERGHE (Leuven, Belgium).

15The preface was highly improved with the help of Alan LEES (Ireland).

16References

17Bultynck, P. & Dejonghe, L. (editors), 2001. Guide to a revised lithostratigraphic scale of Belgium. Geologica Belgica, Special Issue, 4/1- 2: 1-168.

18Gradstein, F.M., Ogg, J.G., Smith, A.G., Bleeker, W. & Lourens, L., 2004. A new Geologic Time Scale with special reference to Precambrian and Neogene. Episodes, 27/2: 83-100.

19International Subcommission on Stratigraphic Classification (ISSC), 1976. International stratigraphic guide – A guide to stratigraphic classification, terminology and procedure (H.D. Hedberg, ed.), John Wiley and Sons, New York: 1-200.

20International Subcommission on Stratigraphic Classification of IUGS, 1994. International stratigraphic guide – A guide to stratigraphic classification, terminology and procedure. Second edition (A. Salvador, ed.). International Union of Geological Sciences & The Geological Society of America, Inc.: 1-214.

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