Balk Member

Formal (Bosch 2003).
Lithological description

Grey clay, sandy, mostly non-calcareous, devoid of shells. Intercalated layers of fine to medium sand, non-calcareous and devoid of shells. Light grey very fine to fine sand, devoid of shells, fining westward.

Depositional setting

Coastal plain (possibly delta top, including alluvial plain). Regionally, marine influence.

Definition of lower boundary

Sharp contact with glauconitic, commonly shelly, shallow-marine fine sand (Breda Formation). Gradual transition into or sharp contact with finer and more calcareous shallow-marine sand (Oosterhout and Maassluis Formations), or into non-calcareous, micaceous and brown fluvial sand and clay (Waalre Formation).

Definition of upper boundary

Gradual transition into fluvial sand (Peize Formation, undifferentiated).

Thickness indication
Up to about 20 m.
Geographical distribution
Central and northern Netherlands. Southward, commonly indistinct transition into interfingering fluvial sand and clay (Waalre Formation).
Regional correlation
North Sea: not differentiated; UK: not present; GER: not differentiated; BEL: not present.
late Pliocene - early Pleistocene.
Type section
Not yet determined.
Depth (thickness) AH:
Not yet determined.
Origin of name
Named after the village of Balk in the northern Netherlands.
Previous name(s)
Reviewed by (date)
Wim Dubelaar (2018), Sytze van Heteren (2019).
Bosch, J.H.A. 2003. Beschrijving lithostratigrafische eenheid. Nederlands Instituut voor Toegepaste Geowetenschappen TNO. Utrecht.
Cite as
TNO-GDN ([YEAR]). Balk Member. In: Stratigraphic Nomenclature of the Netherlands, TNO – Geological Survey of the Netherlands. Accessed on [DATE] from