Pierre BULTYNCK & Léon DEJONGHE

Preface

1Lithostratigraphic units were, together with biostratigraphic and chronostratigraphic units, the three formal stratigraphic categories recognized in the first edition of the International Stratigraphic Guide (ISG), International Subcommission on Stratigraphic Classification of IUGS, 1976. In the second edition of this guide (1994), two new categories of formal stratigraphic units have been added (Unconformity - bounded units and Magnetostratigraphic polarity units) and the chapter on lithostratigraphic units was revised.

2We should keep in mind that what the ISG recommends is not a code like the international codes for botanical or zoological nomenclature. However, the recommendations of the ISG are followed by a great majority of countries and therefore an official, largely accepted lithostratigraphic scale, should be a basic task of each IUGS member country. The last official general stratigraphic scale of the geological map of Belgium at 1:40,000 (1929, translated in Dutch in 1932) is based on stratigraphic concepts from the beginning of the 20^th century when stratigraphers didn't make a formal distinction between lithostratigraphic, biostratigraphic and chronostratigraphic units. In the period 1988-1990, the Flemish and Walloon regions started new geological mapping programs respectively at the 1:50,000 and 1:25,000 scales. The present lithostratigraphic guide of Belgium is based on one hand on these new geological maps of the Walloon and the Flemish regions and, on the other hand on recent stratigraphic investigations by experts of the two regions. The approach followed in the present lithostratigraphic guide is best clarified by quoting some of the recommendations mentioned in the second edition of the ISG.

• Lithostratigraphic units are the basic units of geologic mapping and are an essential element of the stratigraphy of the area.

• Lithostratigraphic classification is usually the first approach in stratigraphic work...

• Definition and recognition of lithostratigraphic units must be based on the lithological composition of actual rock material.

• Only major lithologic features readily recognizable in the field should serve as the basis for lithostratigraphic units.

• Fossils may be important in the recognition of a lithostratigraphic unit either as minor but distinctive physical constituents or because of their rock forming properties...

3The lithostratigraphic guide of Belgium is subdivided into ten chapters dealing respectively with Cambriam-Ordovician-Silurian formations, Devonian formations, Lower Carboniferous formations, Upper Carboniferous formations, Permian formations, Triassic and Jurassic formations, Cretaceous formations, Paleogene and Neogene formations, Quaternary formations. The different chapters have been prepared by the respective national stratigraphic subcommissions set up by the Belgian National Committee for Geological Sciences.

Subcommission	Chairperson	Secretary
Quaternary	F. Gullentops	F. Bogemans
Neogene and Paleogene	P. Laga	S. Louwye
Cretaceous	F. Robaszynski	A. Dhondt
Jurassic and Triassic	R. Monteyne	F. Boulvain
Upper Carboniferous	A. Delmer	M. Dusar
Lower Carboniferous	E. Poty	B. Delcambre
Devonian	P. Bultynck	L. Dejonghe
Silurian, Ordovician and Cambrian	A. Herbosch	J. Verniers

4Each chapter includes an introduction and the descriptions of the formations according to a standard model including the following items: name of the formation and acronym, authors, description, stratotype, area in which the formation is recognized, thickness, age and eventually remarks. The first name and date of the item "authors" refers to the author(s) who introduced the name; the last reference concerns the author(s) who defined the lithostratigraphic unit in the meaning accepted in the present lithostratigraphic guide.

5Finally, although the present lithostratigraphic guide is the result of discussions within the respective national stratigraphic subcommissions, we have to notice that all lithostratigraphic units described herein are not accepted by some stratigraphers involved with some specific part of the stratigraphic column. The chairperson and secretary of each subcommission had the responsability for the content of the final draft of the contribution of their subcommission. Within the Quaternary commission, the members did not reach a unanimous agreement and divergent views on the stratigraphy and/or lithological description as well as alternative classification systems were published in a special volume of Geologica Belgica, 1999, vol. 2 (1-2): "Quaternary Geology of Belgium: New Perspectives". Moreover, as this guide is published by Geologica Belgica, comments and critics can be submitted to the Executive Editor for eventual publication in the reviews column of the journal or elsewhere.

6The guest editors acknowledge W. De Vos (Geological Survey of Belgium) for reviewing the English of the different contributions.

7References

8Aardkundige Raad, 1932. Algemeen stratigrafisch register van de uitvoerige aardkundige kaart van België. Imprimerie des Travaux publiques, Bruxelles, 46 p.

9Conseil Géologique, 1929. Légende générale de la carte géologique détaillée de la Belgique. Annales des Mines de Belgique, 30, 39-80.

10International 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, 200 p.

11International 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., 214 p.

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A propos de : Pierre BULTYNCK

A propos de : Léon DEJONGHE