The Tongeren Formation ( nl, Formatie van Tongeren; abbreviation: TO) is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

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 ...

of the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

. The formation consists of shallow

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

epicontinental An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...

and

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

al sediments, predominantly

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

and

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

from the late

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

and early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

epochs 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 by ...

(between 37 and 30 million years old). The Tongeren Formation is part of the Middle North Sea Group and correlates with the

Tongeren Group The Tongeren Group is a lithostratigraphic unit (a sequence of rock strata) in the subsurface of Belgium. It consists of shallow marine, epicontinental and/or continental clays and sands from the late Eocene to early Oligocene epochs (between ...

from Belgian

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks. Stratigrap ...

. The name was introduced by Belgian geologist André Hubert Dumont in 1849.

Lithologies and subdivision

The Tongeren Formation is subdivided into three members: *the Goudsberg Member, an alternation of clay with

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

nodules and thin

lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...

layers; *the Klimmen Member,

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

ceous fine sand; and *the Zelzate Member, shallow marine glauconiferous sand alternating with clay layers.

Stratigraphic position

In southern Limburg the Tongeren Formation is lies on top of formations of the Lower North Sea Group (in particular the late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

to early Eocene Dongen Formation and Landen Formation) or the Dutch

Chalk Group The Chalk Group (often just called the Chalk) is the lithostratigraphic unit (a certain number of rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England. The same or similar rock sequences occur acr ...

(represented by the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

to early Paleocene Vaals Formation,

Gulpen Formation Gulpen (; li, Gullepe ) is a village in the Dutch province of Limburg. It is approximately midway between the Dutch city of Maastricht and the German city of Aachen. Gulpen was a separate municipality until 1999, when it merged with Wittem. The ...

and Houthem Formation). In most places, the late Oligocene, marine sands and clays of the Rupel Formation are found on top of the Tongeren Formation.

References

*; 1849: ''Rapport sur la Carte géologique du Royaume'', Bulletin de l'Académie royale de Belgique 16 (2^ième partie), p. 370. () *; 1975: ''Lithostratigrafie van de Mio-Oligocene afzettingen in Zuid-Limburg'', in: (''eds.''): ''Toelichting bij geologische overzichtskaarten van Nederland'', Rijks Geologische Dienst, Haarlem, pp. 56–63. ()

External links

*; 2003
Formatie van Tongeren
TNO website ({{in lang, nl) Geologic formations of the Netherlands Oligocene Series of Europe Eocene Series of Europe Paleogene Netherlands