The Houthem Formation, named after the Dutch 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 exp ...

that crops out in the south of Belgian and Dutch Limburg. It has also been found in borings in the northeastern part of the

Campine Basin The Campine (French ) or De Kempen (Dutch ) 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 encomp ...

. The formation consists of

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

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

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), E ...

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 by ...

Lithology

The Houthem Formation consists of maximally 30 metres of light grey to light yellow calcareous arenites. The arenite can contain calcareous concretions,

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 preserved ...

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

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

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

, 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 of ...

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

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Maastricht Formation The Maastricht Formation (Dutch: ''Formatie van Maastricht''; abbreviation: MMa), named after the city of Maastricht in the Netherlands, is a geological formation in the Netherlands and Belgium whose strata date back to the Late Cretaceous, within ...

. 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. 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 ...

) and the

Heers Formation The Heers Formation ( nl, Formatie van Heers; french: Formation de Heers; abbreviation: Hs) is a geologic formation in the subsurface of Belgium. The formation consists of sand and marl and was deposited in the shallow sea that covered Belgium durin ...

(

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

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