The Tielt Formation is a geologic formation in the 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....

 of 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 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 north of Hainaut, in the southern and central parts of West- and East-Flanders and in Walloon

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...

 and Flemish Brabant

Flemish Brabant

Flemish Brabant is a province of Flanders, one of the three regions of Belgium. It borders on the Belgian provinces of Antwerp, Limburg, Liège, Walloon Brabant, Hainaut and East Flanders. Flemish Brabant also completely surrounds the Brussels-Capital Region. Its capital is Leuven...

. It 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...

 very fine 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...

 and 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...

, deposited in the shallow sea that covered Belgium during the middle and 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....

 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 50 million years ago).

The Tielt Formation is 50 meters thick at most. It is subdivided into three members: the Kortemark Member, the Egemkapel Member and the Egem Member (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...

 fine sand). The formation lies stratigraphically on top of the Kortrijk Formation

Kortrijk Formation

The Kortrijk Formation is a geologic formation in the Belgian subsurface. This formation crops out in northern Hainaut, southern West- and East-Flanders and in Walloon Brabant. The formation consists of marine clay from the Ypresian age .The Kortrijk Formation consists predominantly of clay,...

 (early Ypresian sandy clay and silt). In the northwestern part of Belgium, 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 clay and silt) covers the Tielt Formation. If the Gentbrugge Formation is absent, the younger 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...

 (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...

calcareous sand) is directly found on top of the Tielt Formation.
(eds.); 2001: Paleogene and Neogene lithostratigraphic units (Belgium), Geologica Belgica 4(1-2), p. 135-152.