) is a geologic formation in the 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...

 subsurface

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....

. This 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 northern Hainaut, southern West- and East-Flanders and in Walloon Brabant

Walloon Brabant

Walloon Brabant is a province of Wallonia in Belgium. It borders on the province of Flemish Brabant and the provinces of Liège, Namur and Hainaut . Its capital is Wavre...

. 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...

 from the 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....

 age (early 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...

, about 52 million years old).

The Kortrijk Formation consists predominantly of clay, sometimes 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...

y or silt

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

y. The formation generally becomes sandier to the east, in Brabant and the Campine

Campine

The Campine is a natural region situated chiefly in north-eastern Belgium and parts of the south-western Netherlands which once consisted mainly of extensive moors, tracts of sandy heath, and wetlands...

 area. In some places fossil

Fossil

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

s or bioturbation

Bioturbation

In oceanography, limnology, pedology, geology , and archaeology, bioturbation is the displacement and mixing of sediment particles and solutes by fauna or flora . The mediators of bioturbation are typically annelid worms , bivalves In oceanography, limnology, pedology, geology (especially...

 occur. In the westernmost part of Belgium it can be 125 meters thick, but it gradually wedges out to the east.

The Kortrijk Formation is subdivided into at least four members: the Mont Héribu Member, Orchies or Saint-Maur Member, the Moen or Roubaix Member and the Aalbeke Member. The Kortrijk Formation forms the lowest part of the Ieper Group

Ieper Group

The Ieper Group is a group of rock strata in the subsurface of northwest Belgium. The group is subdivided into three marine formations, all formed during the Ypresian, a single age of the geologic timescale...

 and is stratigraphically overlain by the younger Tielt Formation

Tielt Formation

The Tielt Formation is a geologic formation in the subsurface of Belgium. The formation crops out in the north of Hainaut, in the southern and central parts of West- and East-Flanders and in Walloon and Flemish Brabant...

 (late Ypresian marine sand), part of th same group. The Kortrijk Formation lies on top of late 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...

 formations like the Tienen Formation

Tienen Formation

The Tienen Formation is a geologic formation in the subsurface of northern Belgium. The formation crops out in the province of Hainaut and the Hesbaye region in the province of Limburg. It has a late Thanetian to early Ypresian age....

 or Hannut Formation

Hannut Formation

The Hannut Formation is a geologic formation in the subsurface of northern Belgium. The formation consists of marine clay and silt, alternating with moer sandy layers. On top of this the lithology changes to limestone, siltstone and sandstone and the top of the formation is formed by a layer of...

, both part of the Landen Group

Landen Group

The Landen Group is a lithostratigraphic unit in the Belgian subsurface. The group consists of two formations of Thanetian to Ypresian age...

.