The Houthem Formation, named after 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 ...

town of Houthem, is a

geological 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 expo ...

that crops out in the south of Belgian and

Dutch Limburg Limburg (; ), also known as Dutch Limburg, is the southernmost of the twelve provinces of the Netherlands. It is bordered by Gelderland to the north and by North Brabant to the west. Its long eastern boundary forms the border with the German sta ...

. It has also been found in borings in the northeastern part of the

Campine Basin The Campine () or Kempen () is a natural region situated chiefly in north-eastern Belgium and parts of the south-eastern Netherlands which once consisted mainly of extensive moors, tracts of sandy heath, and wetlands. It encompasses a large n ...

. The formation consists of

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

and was formed about 60 million years ago, in the

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), ...

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 ...

Lithology

The Houthem Formation consists of maximally 30 metres of light grey to light yellow calcareous

arenite Arenite (from the Latin ''arena'', "sand") is a sedimentary clastic rock with sand grain size between 0.0625 mm (0.00245 in) and 2 mm (0.08 in) and containing less than 15% matrix. The related adjective is ''arenaceous''. The e ...

s. The arenite can contain calcareous

concretion A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes a ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s and

hardground Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limeston ...

s with shell fragments. At other places lenses of boundstone occur, formed by

red algae Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...

. The hardgrounds make it possible to subdivide the formation into three

members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

: the Geleen Member, the Bunde Member and the Geulhem Member.

Stratigraphy

Dutch stratigraphers see the Houthem Formation as the youngest formation of the

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 ac ...

, because it has a similar lithology with the older formations in this group. Belgian stratigraphers see it as part of the Hesbaye Group, which contains Paleocene formations. The base of the Houthem Formation is in the Vroenhoven Horizon, probably the Dutch and Belgian equivalent of the

Cretaceous–Paleogene boundary The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end o ...

(K–T boundary). Below the Houthem Formation is the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Maastricht Formation The Maastricht Formation (Dutch language, Dutch: ''Formatie van Maastricht''; abbreviation: MMa), named after the city of Maastricht in the Netherlands, is a geological Formation (geology), formation in the Netherlands and Belgium whose strata dat ...

. In the Campine Basin the Houthem Formation is overlain by the Paleocene Opglabbeek Formation (

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 ...

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 ...

) and the Heers Formation (

marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...

References

Bibliography

*; 1993: ''Lithology and biostratigraphy of Upper Cretaceous-Paleocene carbonates in the Molenbeersel borehole (NE Belgium)'', Geologie en Mijnbouw 71, pp. 239-257. *; 2001: ''Paleogene and Neogene lithostratigraphic units (Belgium)'', Geologica Belgica 4, pp. 135-152. *; 1975: ''Lithostratigrafie van het Boven-Krijt en het Dano-Montien in Zuid-Limburg en het aangrenzende gebied'', in: ''Toelichting bij de geologische overzichtskaarten van Nederland'', Rijks Geologische Dienst, Haarlem, pp. 63-72. *; 1962: ''On the type locality of the Maastrichtian (Dumont, 1849), the upper boundary of that stage and on the transgression of a Maastrichtian s.l. in Southern Limburg'', Mededelingen Geologische Stichting, nieuwe serie 15, pp. 77-84. Geologic formations of the Netherlands Geologic formations of Belgium Paleocene Series of Europe Paleogene Belgium Paleogene Netherlands Valkenburg aan de Geul {{Europe-geologic-formation-stub