Heers Formation
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The Heers Formation (; ; abbreviation: Hs) 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
Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...
. The formation consists of
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
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 ...
and was deposited in the shallow sea that covered Belgium during the middle to late
Selandian The Selandian is a stage in the Paleocene. It spans the time between . It is preceded by the Danian and followed by the Thanetian. Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "middle Paleocene". Stratig ...
age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...
of 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 ...
. The formation is subdivided into two
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 ...
: at the base green, glauconiferous sand (Orp Member), on top calcareous
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 marl in which plant
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 have been found (Gelinden Member). This sequence formed during a
marine transgression A marine transgression is a geologic event where sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling with water ...
. The Orp Member represents a near coastal marine environment, the Gelinden Member formed in shallow marine circumstances but further from the land. The Heers Formation occurs in the subsurface of the northern and eastern parts of
Flanders Flanders ( or ; ) is the Dutch language, Dutch-speaking northern portion of Belgium and one of the communities, regions and language areas of Belgium. However, there are several overlapping definitions, including ones related to culture, la ...
. In
Limburg Limburg or Limbourg may refer to: Regions * Limburg (Belgium), a province since 1839 in the Flanders region of Belgium * Limburg (Netherlands), a province since 1839 in the south of the Netherlands * Diocese of Limburg, Roman Catholic Diocese in ...
it reaches its maximal thickness at about 60 meters. The Heers Formation is stratigraphically on top of
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 ...
and early Paleocene deposits, such as the Opglabbeek Formation or the Houthem Formation. The Heers Formation is almost everywhere overlain by the
Hannut Formation The Hannut Formation (; ; abbreviation: Hn) is a geologic formation in the subsurface of northern Belgium. The formation consists of marine clay and silt, alternating with more sandy layers. On top of this the lithology changes to limestone, sil ...
(clay, sand and
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
from the late Paleocene). The Orp and Gelinden members are also recognized in the
Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...
(north of Belgium). Dutch stratigraphers see them as part 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 def ...
.


References


Bibliography

* Laga, P. & De Geyter, G.; 1988: ''Formatie van Heers'', in: Maréchal, R. & Laga, P.: ''Voorstel lithostratigrafische indeling van het Paleogeen'', Belgische Geologische Dienst,
Brussels Brussels, officially the Brussels-Capital Region, (All text and all but one graphic show the English name as Brussels-Capital Region.) is a Communities, regions and language areas of Belgium#Regions, region of Belgium comprising #Municipalit ...
, p. 52-58. () * Laga, P.; Louwye, S. & Geets, S. (eds.); 2001: ''Paleogene and Neogene lithostratigraphic units (Belgium)'', Geologica Belgica 4(1-2), p. 135-152. Geologic formations of Belgium Paleocene Series of Europe Paleogene Belgium {{Europe-geologic-formation-stub