Aalter Formation
Encyclopedia
The Aalter Formation is a geologic formation in the subsurface
of northwest Belgium
. The formation consists of marine
clay
and sand
, deposited in the shallow sea thet covered northern and central Belgium in the Eocene
epoch
.
The Aalter Formation crops out
in the provinces of East- and West-Flanders 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 Antwerpen. The base of the formation consists of glauconiferous
clayey sand
alternating with organic rich (humus and peat
) layers (the Aalterbrugge Member). On top of this is a sequence of clay, sand and sandstone
layers, rich in fossil
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
to early Lutetian
ages, giving it an age of around 48 million years. It is part of the Zenne Group
and is covered by the Brussel Formation
. If the Brussel Formation is absent, the Lede Formation
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).
(eds.); 2001: Paleogene and Neogene lithostratigraphic units (Belgium), Geologica Belgica 4(1-2), p. 135-152.
Subsurface
Subsurface is the seventh studio album by British progressive metal band Threshold. The album was released in August 2004, and received an Album of the Month award in several European music magazines....
of northwest Belgium
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...
. The formation consists of marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
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...
, deposited in the shallow sea thet covered northern and central Belgium in the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
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...
.
The Aalter Formation 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 provinces of East- and West-Flanders 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 Antwerpen. The base of the formation consists of glauconiferous
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
clayey 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...
alternating with organic rich (humus and peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...
) layers (the Aalterbrugge Member). On top of this is a sequence of clay, sand and 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,...
layers, rich in fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
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
Ypresian
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between and , is preceded by the Thanetian age and is followed by the Eocene Lutetian age....
to early Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...
ages, giving it an age of around 48 million years. It is part of the Zenne Group
Zenne Group
The Zenne Group is a group of rock strata in the subsurface of central and northwest Belgium. The group consists of three formations, all from the Ypresian and Lutetian ages...
and is covered by the Brussel Formation
Brussel Formation
The Brussel Formation is a geologic formation in the subsurface of central Belgium. The formation is named after the Belgian capital, Brussels. It consists of shallow marine sandstone and calcareous sands, deposited in the sea that covered Belgium 45 million years ago, in the Eocene.The Brussel...
. If the Brussel Formation is absent, the Lede Formation
Lede Formation
The Lede Formation 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 the former sea that covered Belgium during the Eocene....
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
Gentbrugge Formation
The Gentbrugge Formation is a geologic formation in the west of Belgium. The formation crops out in East- and West-Flanders and also occurs in the subsurface of the province of Antwerpen...
(late Ypresian marine clays and sands).
(eds.); 2001: Paleogene and Neogene lithostratigraphic units (Belgium), Geologica Belgica 4(1-2), p. 135-152.