The Heers 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 consists of 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 marl

Marl

Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...

 and was deposited in the shallow sea that covered Belgium during the middle to late Selandian

Selandian

The Selandian is in the geologic timescale an age or stage in the Paleocene. It spans the time between and . It is preceded by the Danian and followed by the Thanetian. Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "Middle Paleocene".-Stratigraphic...

 age of the 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...

 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 formation is subdivided into two members: at the base green, 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...

 sand (Orp Member), on top calcareous 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 marl in which plant fossil

Fossil

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

s have been found (Gelinden Member). This sequence formed during a marine transgression. The Orp Member represents a near coastal marine environment, the Gelinden Member formed in shallow marine circumstances but further from the land.

The Heers Formation occurs in the subsurface of 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...

. In Limburg

Limburg (Belgium)

Limburg is the easternmost province of modern Flanders, which is one of the three main political and cultural sub-divisions of modern Belgium. It is located west of the river Meuse . It borders on the Dutch provinces of North Brabant and Limburg and the Belgian provinces of Liège, Flemish Brabant...

 it reaches its maximal thickness at about 60 meters. The Heers Formation is stratigraphically on top of Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 and early Paleocene deposits, such as the Opglabbeek Formation

Opglabbeek Formation

The Opglabbeek Formation is a geologic formation in the subsurface of the eastern part of Belgian Limburg. The formation consists of lagoonal and fluvial clay and sand and was deposited during the early Selandian...

 or the Houthem Formation

Houthem Formation

The Houthem Formation, named after the Dutch town of Houthem, is a geological formation that crops out in the south of Belgian and Dutch Limburg. It has also been found in borings in the northeastern part of the Campine Basin...

. The Heers Formation is almost everywhere overlain by the 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...

 (clay, sand and 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....

 from the late Paleocene).

The Orp and Gelinden members are also recognized 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...

 (north of Belgium). Dutch stratigraphers see them as part 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...

.

1988

Formatie van Heers, in: : Voorstel lithostratigrafische indeling van het Paleogeen, Belgische Geologische Dienst, Brussels

City of Brussels

The City of Brussels is the largest municipality of the Brussels-Capital Region, and the official capital of Belgium by law....

, p. 52-58. (eds.); 2001: Paleogene and Neogene lithostratigraphic units (Belgium), Geologica Belgica 4(1-2), p. 135-152