Neerijse Member

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

Parent unit Brussels Formation
Child units
Lithological description White to pale yellow, when glauconiferous greenish yellow, medium sand. The grain size central value is comprised between a lower value range of 150 to 175 μm and an upper value range of 250 to 300 μm. The carbonate content (if not decalcified) is between 2 and 15%; most of this is fine mud. Micro- and macrofossils are often present. Commonly, the sand is moderately sorted and a fraction of fine sand is present. In that case, always a small admixture (much less than 2%) of very fine, light green glauconite pellets is found. This unit has low to medium dark glauconite content facies. In certain areas, a gradually increasing admixture of coarser, dark green to blackish coloured glauconite pellets has been observed (ann. 1). The dominant primary sedimentary structure is parallel master bedding, inclined at a small angle and dipping to ESE. The master beds show a gradually decreasing slope near the bottom of the Formation. Thin and thicker, up to 1 m thick, cross beds occur and are incorporated in the master fill style. Sometimes they constitute stacks of cross beds. The cross beds have a (very) dominant foreset dip to NNE, with rare occurrences of dips to SSW, and numerous mud drapes testifying to tidal currents. In numerous outcrops, the sand is strongly homogenized due to bioturbation. Between the opposites of relatively non-bioturbated cross beds and completely homogenized beds, all possible grades of increasing bioturbation occur. Locally, faintly wavy to structureless bedding is present in sharply bounded packages. In most cases, numerous siliceous concretions are present, varying from capriciously shaped “grès fistuleux” (including “pierres de grottes”) to slab-shaped “grès lustrés”. They tend to be very hard and make drilling and excavating difficult. In structureless facies, siliceous stones are rare and often spherical, to absent. No carbonate stone beds occur. In places where this Member has been decalcified, the Member remains identifiable by its grain size. Decalcification brings about a change in colour: it has turned yellow, brownish yellow or greenish brown due to the fact that non soluble grains such as glauconite are concentrated and grains are limonite coated. Often, local limonite cementation has occurred during or following decalcification. Decalcification is found only in the outcrop area and in this case tends to occur primarily near the flanks of the valleys (geomorphology) and near the surface (vadose zone). Decalcification fronts are generally sharp and may form capricious surfaces. In the decalcified facies of the Unit, the chalcedony cemented concretions have turned more or less brittle.
Area of occurrence
Type locality De Kock sandpit in Ganzemansstraat, Neerijse (X 167320, Y 167360, lower and middle part of sandpit face, approximately from about 45 to 60 m TAW). Note: the upper part, from about 60 to 70 m TAW, in the Neerijse sandpit is the decalcified facies of the Machelen Member. In the immediate vicinity of this reference section, both the calcareous facies of the Machelen Member and the Bierbeek Member have been found in outcrop.
Alternative names
Authors Houthuys, R., Vandenberghe, N. & Matthijs, J.
Date 12/01/2023
Cite as Houthuys, R., Vandenberghe, N. & Matthijs, J., 2023. The Neerijse Member, 12/01/2023. National Commission for Stratigraphy Belgium.


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