The Ieper Group is a group

Group (stratigraphy)

A group in stratigraphy is a lithostratigraphic unit, a part of the geologic record or rock column that consists of defined rock strata. Groups are divided into formations and are sometimes themselves grouped into "supergroups"....

 of rock strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 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 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 group is subdivided into three 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...

 formations, all formed during 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....

, a single age of the geologic timescale (55 to 49 million years ago, the oldest age of 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...

). Both age and group are named after the West-Flemish town of Ypres

Ypres

Ypres is a Belgian municipality located in the Flemish province of West Flanders. The municipality comprises the city of Ypres and the villages of Boezinge, Brielen, Dikkebus, Elverdinge, Hollebeke, Sint-Jan, Vlamertinge, Voormezele, Zillebeke, and Zuidschote...

, for which the Dutch

Dutch language

Dutch is a West Germanic language and the native language of the majority of the population of the Netherlands, Belgium, and Suriname, the three member states of the Dutch Language Union. Most speakers live in the European Union, where it is a first language for about 23 million and a second...

 name is "Ieper".

The three formations of the Ieper Group are:

• 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,...
  
  , predominantly consisting of marine 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...
  
  . It occurs in the west and north of Belgium.
• The 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...
  
  , consisting of 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 found in the subsurface of western and central 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...
  
  , consisting of an alternation of clay, 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...
  
   and fine sand. It 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 East- and West-Flanders.

The Ieper Group lies stratigraphically on top 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...

 (upper 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...

) and below 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...

 (like the Ieper Group early Eocene in age). Unlike the Zenne Group, the Ieper Group can also occur in more southern parts of Belgium, for example in the Mons Basin.
(eds.); 2001: Paleogene and Neogene lithostratigraphic units (Belgium), Geologica Belgica 4(1-2), p. 135-152.