The formation consists of sand and marl and was deposited in the shallow sea that covered Belgium during the middle to late Selandian age of the Paleocene epoch.
The Orp Member represents a near coastal marine environment, the Gelinden Member formed in shallow marine circumstances but further from the land.
The Heers Formation occurs in the subsurface of the northern and eastern parts of Flanders.
The Orp and Gelinden members are also recognized in the Netherlands (north of Belgium).
This article about a specific stratigraphic formation in Europe is a stub.