The Opglabbeek Formation 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 eastern part of Belgian Limburg. The heterogeneous formation consists of

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 ...

that was deposited lagoonally and fluvially during the early Selandian (Middle

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 ...

, about 60 million years old). The formation is named after the town of

Opglabbeek Opglabbeek (; li, Glabbek) is a village, former municipality located in the Belgian province of Limburg. In 2018, Opglabbeek had a total population of 10,332. The total area is 24.98 km². The municipality consisted of the following commun ...

in Limburg. The Opglabbeek Formation is subdivided into two members: the Opoeteren Member (red clay with layers of

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 ...

) and the Eisden Member (fine sand with

crag Crag may refer to: * Crag (climbing), a cliff or group of cliffs, in any location, which is or may be suitable for climbing * Crag (dice game), a dice game played with three dice * Crag, Arizona, US * Crag, West Virginia, US * Crag and tail, a g ...

s). The Opglabbeek Formation's thickness ranges between and , reaching its greatest thickness as it abuts the Roer Valley

Graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

. It lies stratigraphically on top of the

Houthem Formation The Houthem Formation, named after the Dutch town of Houthem, is a geological formation 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 formation co ...

(early Paleocene calcareous

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) ...

). It is the lateral equivalent of the Hainin Formation. On top of it lies 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 ...

(Middle Paleocene sands and

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 ...

s). The Opglabbeek Formation is part of the Hesbaye Group and can be

correlated In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics ...

with parts of the

Landen Formation The Landen Formation (abbreviation: LA) is a lithostratigraphic unit (a set of rock strata) in the subsurface of the Netherlands. This formation shares its name with the Belgian Landen Group, but the Belgian unit is thinner and has different defin ...

of adjacent areas in the southern

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 ...

References

Geologic formations of Belgium Paleocene Series of Europe Paleogene Belgium {{Europe-geologic-formation-stub