The Tongeren Group is a

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

unit (a sequence of

rock strata In geology and related fields, a stratum (: strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ...

) in the

subsurface In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedro ...

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

. It consists of shallow marine, epicontinental and/or

continental Continental may refer to: Places * Continental, Arizona, a small community in Pima County, Arizona, US * Continental, Ohio, a small town in Putnam County, US Arts and entertainment * ''Continental'' (album), an album by Saint Etienne * Continen ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

s and

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

s from the late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

to early

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

s (between 37 and 30 million years old). The Belgian Tongeren Group correlates with the

Dutch Dutch or Nederlands commonly refers to: * Something of, from, or related to the Netherlands ** Dutch people as an ethnic group () ** Dutch nationality law, history and regulations of Dutch citizenship () ** Dutch language () * In specific terms, i ...

Tongeren Formation The Tongeren Formation (; abbreviation: TO) is a geologic formation in the subsurface of the Netherlands. The formation consists of shallow marine, epicontinental and continental sediments, predominantly clay and sand from the late Eocene and ear ...

. The name was introduced by

André Hubert Dumont André — sometimes transliterated as Andre — is the French and Portuguese form of the name Andrew and is now also used in the English-speaking world. It used in France, Quebec, Canada and other French-speaking countries, as well in Portugal ...

in 1849.

Subdivision

The Tongeren Group is subdivided into three formations. From top to bottom these are: *the

Borgloon Borgloon (; , ; ) is a former Municipalities of Belgium, municipality and City status in Belgium, city located in the Belgium, Belgian province of Limburg (Belgium), Limburg. On January 1, 2006, Borgloon had a total population of 10,697. The tota ...

Formation, lagunal or

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

shell rich sand and clay; *the Sint Huibrechts-Hern Formation, marine shell bearing sand and clay; *the

Zelzate Zelzate () is a municipality located in the Belgian province of East Flanders. The municipality only comprises the town of Zelzate proper. In 2021, Zelzate had a total population of 13,124. The total area is 13.71 km2. Zelzate is divided in ...

Formation, shallow marine glauconiferous sand with thin clay layers.

Stratigraphic relations

In northwest Belgium the Tongeren Group (represented in that area mostly by the Zelzate Formation) is stratigraphically lying on top of the Maldegem Formation (middle Eocene clay and sand). This formation is lacking in the east of the country, where the Tongeren Group is found directly on top of rocks with older ages, like the Landen Group. The Tongeren Group is usually overlain by deposits of the late Oligocene

Rupel Group The Rupel Group is a stratigraphic group of rock strata in the subsurface of Belgium. It is subdivided into three formations that are all marine deposits (sands and clays) of Oligocene age. Name The Rupel Group was first named by Belgian geol ...

References

* Dumont, A.; 1849: ''Rapport sur la Carte géologique du Royaume'', Bulletin de l'Académie royale de Belgique 16 (2^ième partie), p. 370.{{in lang, fr *Laga, P.; Louwye, S. & Geets, S. (eds.); 2001: ''Paleogene and Neogene lithostratigraphic units (Belgium)'', Geologica Belgica 4(1-2), p. 135-152 Geologic groups of Europe Geologic formations of Belgium Lithostratigraphy of Belgium Eocene Series of Europe Oligocene Series of Europe