The Aalter Formation ( nl, Formatie van Aalter, abbreviation: Aa; named after the town of Aalter in

East Flanders , native_name_lang = , settlement_type = Province of Belgium , image_flag = Flag of Oost-Vlaanderen.svg , flag_size = , image_shield = Wapen van O ...

) 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 northwest

Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to th ...

. The formation consists of

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

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 ...

, deposited in the shallow sea that covered northern and central Belgium in the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

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 ...

. The Aalter Formation crops out in the provinces of East Flanders and

West Flanders ) , settlement_type = Province of Belgium , image_flag = Flag of West Flanders.svg , flag_size = , image_shield = Wapen van West-Vlaanderen.svg , shield_size = , image_map ...

and forms a maximally 30 meters thick layer in the subsurface. To the east, the formation wedges out and becomes thinner. Due to this wedging out, the formation does not occur anymore in the province of Antwerp. The base of the formation consists of glauconiferous clayey

alternating with organic rich (

humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...

and

peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficien ...

) layers (the Aalterbrugge Member). On top of this is a sequence of clay, sand and

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) ...

layers, rich in

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 (the Beernem Member). The top of the formation consists of fossil rich, glauconiferous fine sand (the Oedelem Member). The Aalter Formation was formed during the late

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

to early

Lutetian The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Midd ...

ages Ages may refer to: *Advanced glycation end-products, known as AGEs *Ages, Kentucky, census-designated place, United States * ''Ages'' (album) by German electronic musician Edgar Froese *The geologic time scale, a system of chronological measuremen ...

, giving it an age of around 48 million years. It is part of the Zenne Group and is covered by the

Brussel Formation The Brussel Formation ( nl, Formatie van Brussel; french: Formation de Bruxelles; abbreviation: Br) is a geologic formation in the subsurface of central Belgium. The formation is named after the Belgian capital, Brussels. It consists of shallow mar ...

. If the Brussel Formation is absent, the

Lede Formation The Lede Formation ( nl, Formatie van Lede; abbreviation: Ld) is a geologic formation in the subsurface of Belgium. The formation is named after the town of Lede in East Flanders. It consists of shallow-marine limestone and sandstone, deposited in ...

can be found on top of the Aalter Formation. Both are like the Aalter Formation part of the Zenne Group. Stratigraphically below the Aalter Formation are deposits of the Gentbrugge Formation (late Ypresian marine clays and sands).

Fossil content

Chondrichthyes

References

Bibliography

* (eds.); 2001: ''Paleogene and Neogene lithostratigraphic units (Belgium)'', Geologica Belgica 4(1-2), p. 135-152 Geologic formations of Belgium Eocene Series of Europe Paleogene Belgium Lutetian Stage Ypresian Stage Aalter {{Europe-geologic-formation-stub

Fossil content

Chondrichthyes

See also

References

Bibliography