Orp Member

Formal (NAM & RGD 1980). Amended (Van Adrichem Boogaert & Kouwe 1997).
Lithological description

Very fine-grained (105-150 µm), light- to dark-green/grey, glauconitic, partly calcareous sand, with some intercalated clay beds. Locally contains shells. Locally, the unit comprises two coarsening-upward successions.

Depositional setting

Shallow to open marine. Marine transgressive sand, deposited in a water depth of less than 50 m.

Definition of lower boundary

Sharp and unconformable when overlying Mesozoic deposits. Mild unconformable but sharp when overlying the Houthem Formation or the Swalmen Member.

Definition of upper boundary

Sharp contact with the overlying Gelinden Member (in the southeastern Netherlands). Rather sharp contact with the overlying Liessel Member in the rest of the Netherlands.

Thickness indication
Up to 120 m.
Geographical distribution
Regional correlation
UK: no equivalent; GER: Hückelhoven Beds; BEL: the Heers Formation comprises two members: the Sand of Orp overlain by the Marls of Gelinden. The Dutch Orp Member is the equivalent of the Belgian Sand of Orp (Marechal & Laga 1988).
late Paleocene (Selandian).
Depth (thickness) AH:
1412 - 1423 m AH (11 m)
Origin of name
Named after the village of Orp in the Belgian province of Walloon Brabant. 
Previous name(s)
Heers Member (NAM & RGD 1980). Renamed in accordance with Maréchal & Laga (1988) as Orp Member.
Reviewed by (date)
Geert-Jan Vis (2019).
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.
Cite as
TNO-GDN ([YEAR]). Orp Member. In: Stratigraphic Nomenclature of the Netherlands, TNO – Geological Survey of the Netherlands. Accessed on [DATE] from https://www.dinoloket.nl/en/stratigraphic-nomenclature/orp-member.