The Brussel 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 central 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 is named after the Belgian capital, Brussels

Brussels

Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...

. It consists of shallow marine 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 calcareous

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....

 sands, deposited in the sea that covered Belgium 45 million years ago, in 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...

.

The Brussel 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 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...

 and the north of the provinces of Namur

Namur (province)

Namur is a province of Wallonia, one of the three regions of Belgium. It borders on the Walloon provinces of Hainaut, Walloon Brabant, Liège and Luxembourg in Belgium, and on France. Its capital is the city of Namur...

 and Hainaut. It is normally about 30 meters in thickness. In 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...

 and Antwerpen the formation can be found in the subsurface.

The Brussel Formation is subdivided into five members: the Archennes Member (conglomerates

Conglomerate (geology)

A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...

), the Bois de la Houssière Member (quartzite

Quartzite

Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...

s), the Chaumont-Gistoux 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...

 quartzites), the Diegem Member (glauconiferous quartzite) and the Neerijse Member (glauconiferous calcareous sand). The formation consists either of cross-bedded

Cross-bedding

In geology, the sedimentary structures known as cross-bedding refer to horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation...

 non-calcareous sands alternating with thin beds of 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 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...

 or calcareous fine sands with traces of 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...

.

The formation was formed during the early 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...

 age (about 46 million years ago) and is part of 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...

. Stratigraphically on top of the Brussel Formation is the Lede Formation

Lede Formation

The Lede Formation is a geologic formation in the subsurface of Belgium. The formation is named after the town of Lede in East Flanders. It consists of shallow-marine limestone and sandstone, deposited in the former sea that covered Belgium during the Eocene....

 (also part of the Zenne Group), or when this formation is absent the Maldegem Formation

Maldegem Formation

The Maldegem Formation is a geologic formation in the Belgian subsurface. The formation consists of alternating marine clay and sand strata, deposited during the late Eocene....

 (Bartonian

Bartonian

The Bartonian is, in the ICS's geological timescale, a stage or age in the middle Eocene epoch or series. The Bartonian age spans the time between and . It is preceded by the Lutetian and is followed by the Priabonian age.-Stratigraphic definition:...

) or Tongeren Group

Tongeren Group

The Tongeren Group is a lithostratigraphic unit in the subsurface of Belgium. It consists of shallow marine, epicontinental and/or continental clays and sands from the late Eocene to early Oligocene epochs .The Belgian Tongeren Group correlates with the Dutch Tongeren Formation...

 (Priabonian

Priabonian

The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene epoch or series. It spans the time between and...

 to Rupelian

Rupelian

The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene epoch/series. It spans the time between and . It is preceded by the Priabonian stage and is followed by the Chattian stage....

). The Brussel Formation is normally lying stratigraphically on top of the Aalter Formation

Aalter Formation

The Aalter Formation is a geologic formation in the subsurface of northwest Belgium. The formation consists of marine clay and sand, deposited in the shallow sea thet covered northern and central Belgium in the Eocene epoch....

 (part of the Zenne Group) or deposits 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...

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