5.3 Pont d’Arcole Formation - PDA

Authors: Dupont, 1863 (Schistes vert sombre à Spirifer octoplicatus); Groessens, 1975 (Schistes du Pont d’Arcole); Paproth et al., 1983.

Description: The formation is dominantly greenish to black shales. The carbonate content increases in the upper part with a few beds of crinoidal limestone. Bryozoans, crinoids, brachiopods including the guide Spiriferina peracuta, and some corals are usually common. In the VSA, the shales of the Pont d’Arcole Fm include numerous boulders reworked from the Hastière Fm (debris flow, La Folie Facies - LAF).

Stratotype: Outcrops along the road from Hastière-Lavaux to the Insemont hamlet, in front of the Pont d’Arcole cave (DSA) (Groessens, 1975). La Folie Facies, La Folie quarry, 2 km SE of Visé in the Berwine valley (Pirlet, 1967a; Poty, 1982).

Area: This unit can be recognized almost everywhere in the Namur-Dinant Basin.

Thickness: The thickness does not exceed 20 m in the DSA and can be as little as 3 m in the NSA.

Age: Hastarian. Siphonodella Conodont Zone; Cf1a” Foraminifer Zone, RC1gRugose Coral Zone, Palynological Zone VI (Conil et al., 1991). The formation corresponds to the upper part of the TST of the third-order sequence 2 of Hance et al. (2001).