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Authors: Dumont (1849a), Laga & De Geyter (1988).

Description: this marine unit consists mainly of whitish grey, calcareous marl with imprints of leaves, covering green, glauconitic sand.

Stratotype: stratotypes have only been designated for the members.

Area: the eastern part of northern Belgium. Outcrops are locally found in the Hesbaye area, a.o., at Heers and Orp-Jauche.

Thickness: maximum about 60 m in the east. It decreases to the west and to the north.

Members: the formation is subdivided into the Orp Mbr and the Gelinden Mbr.

Age: Middle and Late Selandian.

Remarks: the formation is also discussed by De Geyter (1981), De Saporta & Marion (1873, 1877), Dumont (1851), Gosselet (1874), Gulinck (1965a), Herman (1972), Le-riche (1903), Moorkens (1972b, 1982), Schumacker-Lambry (1978), Steurbaut (1998), Thielens (1871) and Vincent (1873).