2.1.19. Ciply-Malogne Phosphatic Chalk Formation - CIP
Authors: F.L. Cornet & Briart (1866), and herein.
Description: Cohesive or crumbly calcarenite, invariably intensely bioturbated, consisting of phosphate granules within a chalky matrix. The granules are brown at the surface, but grey in the sediment.
The average P2 O5is around 8 %. Bands with rounded black or brown flints with phosphate grains are sometimes intercalated between the calcarenites. Fossils are extremely common.
At the margins of the phosphatic basin, the base of this formation is marked by a conglomeratic level with chalk gravel, sponges, fragments of baculitid ammonites, all of them phosphatised whereas in the central part of the basin there is a continuous transition between this unit and the underlying Spiennes Chalk Formation.
The top of the Formation is almost always marked by a conspicuous hardground, often complex in structure, 0.4 to 1.4 m thick. This hardground was the "roof" of the underground quarries of the La Malogne Plateau where the phosphatic chalk was worked at the end of the 19th century.
Stratotype: No stratotype has been designated for the Ciply-Malogne Formation. At present the only good outcrops are in the underground quarries of the Malogne below the village of Cuesmes.
Area: MonsBasin, south of Mons at Ciply and Saint-Symphorien; north of the Mons Basin in the subsurface of Baudour.
Thickness: One to a few metres on the margin of the Ciply and Baudour basins, up to 76 m in the centre of the Ciply Basin. In the underground quarries of the Malogne the Ciply-Malogne Formation had a thickness of 10 to 12 m.
Age: Early Maastrichtian; cephalopods: Belemnella obtusa, Belemnitella pulchra, Bt. minor II, Pachydiscus cf.neubergicus, Hoploscaphites constrictus, Baculites knorrianus, Ba. baculus etc.; brachiopods: Trigonosemus palissyi; foraminifers: Neoflabellina praereticulata, Gavelinella bembix, Osangularia navarroana etc.
Remarks: - This is the "Craie grise" of F.L. Cornet & Briart (1866) and the "Craie brune" of F.L. Cornet & Briart (1874).
- References: J. Cornet (1923); Marlière (1957); Poels & Robaszynski (1988); Robaszynski & Poels (1988); Robaszynski & Christensen (1989); Kennedy (1993); Christensen (1999).
Legend : Hardground separating the calcarenites assigned to the Ciply – Malogne Phosphatic Chalk Formation, below, from the Saint Symphorien Calcarenite Formation, above. La Malogne underground quarry (photo M. Dusar).