The Hannut 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 northern 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 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...

, alternating with moer 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 layers. On top of this the lithology

Lithology

The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...

 changes to limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

, siltstone

Siltstone

Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...

 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,...

 and the top of the formation is formed by a layer of glauconite

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...

 bearing sand. The Hannut Formation was formed during the early to middle Thanetian

Thanetian

The Thanetian is, in the ICS' Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or series. It spans the time between and . The Thanetian is preceded by the Selandian age and followed by the Ypresian age...

 age (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...

, about 57 million years ago).

The formation is named after the town of Hannut

Hannut

Hannut is a municipality of Belgium. It lies in the country's Walloon Region and Province of Liege. On January 1, 2006 Hannut had a total population of 14,291...

 in the province of Liège

Liège (province)

Liège is the easternmost province of Belgium and belongs to the Walloon Region. It is an area of French and German ethnicity. It borders on the Netherlands, Germany, Luxembourg, and in Belgium the provinces of Luxembourg, Namur, Walloon Brabant , and those of Flemish Brabant and Limburg . Its...

.

Lithologies

The Hannut Formation can be about 100 meters thick in the Campine Basin and about 55 meters thick in the Mons Basin. In between these two basins the thickness varies between 40 and 20 meters. The formation is subdivided into five members:

• The Chercq Member, tuffite
  Tuffite
  Tuffite is a tuff containing both pyroclastic and detrital materials, but predominantly pyroclasts ....
  
  , clay and glauconite
  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...
  
   bearing sand layers. This member is most distinctively recognizable in the province of Hainaut;
• The Lincent Member, a locally lithified, predominantly clayey layer. It occurs in and around the Hesbaye
  Hesbaye
  Hesbaye or Haspengouw , is a region spanning the south of the Belgian province of Limburg, the east of the Belgian provinces of Flemish Brabant and Walloon Brabant, and the northwestern part of the province of Liège.The Limburgish portion contains the cities of Tongeren, Sint-Truiden, Bilzen and...
  
   region;
• The Halen Member, clayey silt and silty sand;
• The Waterschei Member, calcareous clay and silty clay. It occurs in the northeast of Belgium;
• The Grandglise Member, the upper glauconiferous sand. It is almost always present.

Stratigraphic relations

In Belgian lithostratigraphy

Lithostratigraphy

Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology...

 the Hannut Formation is one of the two formations 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...

. The other formation is the younger 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....

 (continental and lagoon

Lagoon

A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...

al sands and clays from the late Thanetian age), which is normally found on top of the Hannut Formation. In the northern and eastern parts of Flanders

Flanders

Flanders is the community of the Flemings but also one of the institutions in Belgium, and a geographical region located in parts of present-day Belgium, France and the Netherlands. "Flanders" can also refer to the northern part of Belgium that contains Brussels, Bruges, Ghent and Antwerp...

 the Hannut Formation lies stratigraphically on top of the Heers Formation

Heers Formation

The Heers Formation is a geologic formation in the subsurface of Belgium. The formation consists of sand and marl and was deposited in the shallow sea that covered Belgium during the middle to late Selandian age of the Paleocene epoch....

 (middle Paleocene sands and marls).

The Hannut Formation correlates

Correlation

In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....

 with parts of the Landen Formation

Landen Formation

The Landen Formation is a lithostratigraphic unit in the subsurface of the Netherlands. This formation shares its name with the Belgian Landen Group, but the Belgian unit is thinner and has different definitions...

 in the Netherlands

Netherlands

The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

.
(eds.); 2001: Paleogene and Neogene lithostratigraphic units (Belgium), Geologica Belgica 4(1-2), p. 135-152.