In Belgian lithostratigraphy the Hannut Formation is one of the two formations of the Landen Group. The other formation is the younger Tienen Formation (continental and lagoonal sands and clays from the late Thanetian age), which is normally found on top of the Hannut Formation. In the northern and eastern parts of Flanders the Hannut Formation lies stratigraphically on top of the Heers Formation (middle Paleocene sands and marls).
