The Houthem Formation, named after the Dutch

Netherlands

The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 town of Houthem, is a geological formation that crops out

Outcrop

An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...

 in the south of Belgian

Belgium

Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 and Dutch Limburg

Limburg (Netherlands)

Limburg is the southernmost of the twelve provinces of the Netherlands. It is located in the southeastern part of the country and bordered by the province of Gelderland to the north, Germany to the east, Belgium to the south and part of the west, andthe Dutch province of North Brabant partly to...

. It has also been found in borings

Boring (earth)

Boring is drilling a hole, tunnel, or well in the earth.-Earth boring:Boring is used for a wide variety of applications in geology, agriculture, hydrology, civil engineering, and oil and natural gas industries...

 in the northeastern part of the Campine Basin. The formation consists of calcareous

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 and was formed about 60 million years ago, in the Paleocene

Paleocene

The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

 epoch

Epoch (geology)

An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...

.

Lithology

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

Arenite

Arenite is a sedimentary clastic rock with sand grain size between 0.0625 mm and 2 mm and contain less than 15% matrix. The related adjective is arenaceous...

s. The arenite can contain calcareous concretion

Concretion

A concretion is a volume of sedimentary rock in which a mineral cement fills the porosity . Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin con meaning 'together' and crescere meaning 'to grow'...

s, fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s and hardgrounds with shell fragments. At other places lenses of boundstone

Boundstone

Boundstone is a village in Surrey, England....

 occur, formed by red algae

Red algae

The red algae are one of the oldest groups of eukaryotic algae, and also one of the largest, with about 5,000–6,000 species  of mostly multicellular, marine algae, including many notable seaweeds...

.

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, because it has a similar lithology with the older formations in this group. Belgian stratigraphers see it as part of the Hesbaye Group

Hesbaye Group

The Hesbaye Group is a stratigraphic group in the subsurface of northeastern Belgium. This group was deposited during the early Paleocene epoch and is subdivided into two formations: the Houthem Formation and the Opglabbeek Formation...

, which contains Paleocene formations.

The base of the Houthem Formation is in the Vroenhoven Horizon, probably the Dutch and Belgian equivalent of the K–T boundary

K–T boundary

The K–T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 Ma ago. K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period...

. Below the Houthem Formation is the Late Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 Maastricht Formation

Maastricht Formation

The Maastricht Formation , named after the city of Maastricht, the Netherlands, is a geological formation in the Netherlands and Belgium whose strata date back to the Late Cretaceous, within 500k years of the K-Pg boundary, dated to 65.5 million years ago. The formation is part of the Chalk Group...

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

Opglabbeek Formation

The Opglabbeek Formation is a geologic formation in the subsurface of the eastern part of Belgian Limburg. The formation consists of lagoonal and fluvial clay and sand and was deposited during the early Selandian...

 (clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 and sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

) and the Heers Formation

Heers Formation

The Heers Formation 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 during the middle to late Selandian age of the Paleocene epoch....

 (marl

Marl

Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...

).

1993

Lithology and biostatigraphy 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