Bierbeek Member

The information on this page is a summary description.
The full formal description is available here: Bierbeek Member

Parent unit Brussels Formation
Child units
Lithological description White to pale yellow, when glauconiferous greyish green, medium-coarse to coarse sand. The grain size central value is comprised between a lower value range of 250 to 300 μm and an upper value range of 400 to 500 μm; the coarsest grains have an angular shape. In a small area in the southeast of the basin, around Eghezée, central values in the order of 1 to 2 mm are found; this very coarse facies is also included in this Member. In some boreholes, a bed of similar very coarse sand is found at or near the base of the Formation, e.g. at Bierbeek and Scherpenheuvel. Such coarse, angular grains can be found admixed in the medium to coarse sand of the thick cross beds of this Member at some locations. Carbonate content (if not decalcified) is very low, below 2%, and consists of fossil remnants. This unit can have well, moderately or poorly sorted facies. A bipolar grain size distribution is often present in the sedimentary facies X. If a fraction of fine sand is present, a small admixture (much less than 2%) of very fine, light green glauconite pellets is always found. The Bierbeek Member may either contain a considerable admixture (from 5 to up to about 30%) of coarse dark green to blackish glauconite pellets (this tends to be the case in the east of the basin) or it can be devoid of such glauconite (in the west and southeast of the basin). The cementations have different shapes and sizes and are of the type with chalcedony to microquartz cement; also their content may vary. Very well-sorted beds tend to have low numbers of siliceous concretions; beds with mud laminae like in the bottomsets of cross-beds tend to have higher contents of siliceous concretions. Locally mud layers may be marly, but they are then often silicified. Because of the low original carbonate content, decalcification doesn’t alter the aspect of this unit much. Limonite cementations are only found in decalcified occurrences of the unit.
Area of occurrence
Type locality Godts sandpit, Builoogstraat, Bierbeek (X 176760, Y170650; the exposed section from about 48 to 63 m TAW and the approximately 50 m below it, known from boreholes, that fills an internal erosion trough).
Alternative names
Authors Houthuys, R., Vandenberghe, N. & Matthijs, J.
Date 12/01/2023
Cite as Houthuys, R., Vandenberghe, N. & Matthijs, J., 2023. The Bierbeek Member, 12/01/2023. National Commission for Stratigraphy Belgium.


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