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.
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).
Central and northern Netherlands. Southward, commonly indistinct transition into interfingering fluvial sand and clay (Waalre Formation).
North Sea: not differentiated; UK: not present; GER: not differentiated; BEL: not present.
late Pliocene - early Pleistocene.
Origin of name
Named after the village of Balk in the northern Netherlands.
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.
TNO-GDN ([YEAR]). Balk Member. In: Stratigraphic Nomenclature of the Netherlands, TNO – Geological Survey of the Netherlands. Accessed on [DATE] from https://www.dinoloket.nl/en/stratigraphic-nomenclature/balk-member.