The information on this page is a summary description.
The full formal description is available here: Flemish Hills Formation
Abbreviation
Vh
Parent unit
Child units
Lithological description
The Flemish Hills Formation consists of poorly to very poorly sorted, fine to coarse sand. The grain size coarsens upwards. Though the description of the vertical build-up was made in the Ronse area, it is believed to be valid for the North French and southern West-Vlaanderen area (Houthuys, 2014). Small to coarse (up to 15 cm) flint pebbles occur throughout the vertical profile, dispersed in the sand or in inclined or channel-like beds. Towards the top, there is an increasing admixture of coarse, often angular grains. Glauconite varies from almost none at the base to locally 20% near the top. The lower part of the sand deposit is bioturbated. The central part shows besides bioturbated beds also inclined beds and shallow channels partially filled by low-angle parallel lamination. The content of pebbles is highest in this middle part. The top part shows subhorizontal and inclined parallel lamination, and hummocky and swaley cross stratification. The successive parts show gradual transitions, and can interdigitate. The formation is devoid of carbonates and fossils. The formation is affected by limonite cementation in various, often capricious shapes and in various degrees of solidness. Thick cemented beds may be found in the top of the formation. Locally, the ironstone has been used for building stone (poudingue de Renaix, de Cassel: pudding stone, named after the dark brown cemented sand matrix containing pale flint pebbles). In the central part, rare thin, pale to salmon coloured, clay layers occur; they are rich in kaolinite (Adriaens, 2015). Houthuys (2014) presented an up-to-date interpretation of the sedimentary environment.
Age
Any age between latest Eocene and late Pliocene. Remains to be established.
Thickness
The Flemish Hills Formation is maximally 29 m thick (Cassel, France) and 25 m (Pottelberg near Flobecq). The thickness is less where the outlier hills have tops that don’t reach 25 m above the subhorizontal base surface.
Area of occurrence
The Flemish Hills Formation occurs in the top part of each of the outlier hills that constitute the row of Flemish Hills, from West to East: Cassel, Mont des Récollets, Mont des Cats, Mont de Boeschepe, Mont Noir/Zwarteberg, Rodeberg, Scherpenberg, Kemmelberg, Kluisberg/Mont de l’Enclus, Hotondberg, Muziekberg, Pottelberg, Bois de la Louvière/Livierenbos (Fig. 1 in Houthuys, 2014). It remains to be confirmed if the formation is also found west of Cassel (e.g. Noires Mottes west of Calais). It was observed in reworked remnants in borehole GSB 101W079 on Kesterheide (Gooik). There is a possible eastern outlier between Kraainem and Tervuren (awaiting new evidence, Houthuys et al., 2020).
Type locality
Disused sandpit and dump site at Lumen, municipality of Flobecq, just south of Brakelbos. The site is private-owned and the owner doesn’t allow access. Other outcrops are the sunken lane between Pottelberg and Queneau at Flobecq and the disused sandpit north of Muziekbosstraat at Ronse.
Alternative names
Diestien des Collines de Flandre (disused) / including the poudingue de Renaix, de Cassel, Formatie van de Vlaamse Heuvels, Formation des Collines Flamandes
Authors
Houthuys, R.
Date
01/09/2023
Cite as
Houthuys, R., 2023. The Flemish Hills Formation, 01/09/2023. National Commission for Stratigraphy Belgium. http://ncs.naturalsciences.be/lithostratigraphy/Flemish-Hills-Formation
