2.1.16. Obourg Chalk Formation- OBG

Authors: F.L.Cornet & Briart (1870).

Description: A fine-grained white chalk, slightly greyer than the overlying Nouvelles Formation. In the northern part of the basin it contains a few dark black flints (used by Neolithic man for tool making, sometimes even exported towards the Meuse area). In the southern part of the basin chert nodules are absent or very small. A conglomerate layer may occur at the base of the formation containing phosphatised chalk pebbles, and numerous fossils, many of them reworked.

Stratotype: No stratotype has been designated for the Obourg Formation. The Formation outcrops depending on quarrying activities at the C.C.C. and C.B.R. quarries at Harmignies (section in the C.C.C. quarry studied in Robaszynski & Christensen, 1989).

Area: MonsBasin, in outcrops and quarries along the margins; also in boreholes.

Thickness: 15 to 25 m, more in boreholes.

Age: Early Late Campanian: cephalopods: Belemnitella mucronata, Patagiosites stobaei, Glyptoxoceras retrorsum, Baculites aquilaensis; brachiopods: Carneithyris carnea, "Cretirhynchia" octoplicata; echinoids:Echinocorys cf. ovata, E. gibba, Micraster schroederi, M. stolleyi; foraminifers: Bolivinoides decoratus, Gavelinella monterelensis, Stensioeina pommerana, Globorotalites michelinianus etc.

Remarks:  References: see Spiennes Fm.