Original definition by NAM & RGD (1980). Amended (Van Adrichem Boogaert & Kouwe 1997).
Best described as a stacking of coarsening-upwards sequences at the scale of tens of metres. The proportion of clays is highest in the lower upper part of the member. The uppermost part stands out on logs as a relatively homogeneous and clean sand. The member is well-developed in the Roer Valley Graben. On the Peel and Venlo blocks the proportion of argillaceous sediments is very low. The sands are fine-grained, grey-green and glauconitic. Locally the sands may have a dark grey-green to black colour and comprise glauconites, marine molluscs and otoliths.
Middle neritic to littoral marine environment. The topmost sands seem intensively reworked.
Definition of lower boundary
Conformably or mildly unconformably overlies the Steensel Member or the Boom Member of the Rupel Formation. In the southern distribution area of this member, the boundary is placed at the base of a distinct clay layer.
Definition of upper boundary
Overlain by the clays that constitute the middle part of the Veldhoven Formation. In the axial zone of the Roer Valley Graben the boundaries are conformable.
UK: Skade Formation; GER: Grafenberg Formation; BEL: Voort Formation covers probably only part of the Dutch Voort Member, as far as age is concerned (Marechal & Laga 1988).
late Oligocene (Chattian).
Origin of name
Named after the village of Voort, near Zolder in the Belgian province of Limburg.
Voort Sand Member. The lithological affix has been deleted by Van Adrichem Boogaert & Kouwe (1997), because the member does not consist of sands only.
Maréchal, R., Laga, P. (eds.) 1988. Voorstel lithostratigrafische indeling van het Paleogeen - Nationale Commissies voor Stratigrafie. Commissie: Tertiair, Belgische Geologische Dienst, Brussel, 208 p.
NAM & RGD 1980. Stratigraphic nomenclature of The Netherlands. Verhandelingen van het Koninklijk Nederlands Geologisch Mijnbouwkundig Genootschap 32, 77 p.
Van Adrichem Boogaert, H.A. & Kouwe, W.F.P. 1997. Stratigraphic nomenclature of The Netherlands, revision and update by RGD and NOGEPA, Section I, Tertiary. Mededelingen Rijks Geologische Dienst, 50, 1-39.
TNO-GDN ([YEAR]). Voort Member. In: Stratigraphic Nomenclature of the Netherlands, TNO – Geological Survey of the Netherlands. Accessed on [DATE] from http://www.dinoloket.nl/en/stratigraphic-nomenclature/voort-member.