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5.19 Ourthe Formation - OUR

Authors: Fourmarier, 1922; Groessens, 1975; Paproth et al., 1983.

Description: Grey-blue, thick-bedded to massive, crinoidal limestones (packstones to rudstones). Macrofossils (rugose and tabulate corals, brachiopods) are common but are not diversified. The limestones produce a fetid smell when freshly broken.

Stratotype: Bunker section, 450 m north of the Scay bridge, on the left bank of the R. Ourthe, at Comblain-au-Pont (CSA).

Area: CSA and DSA. The formation is well developed in the CSA where it is extracted as an ornamental stone (“Petit Granit”). It passes laterally into the Bayard Fm in the DSA.

Thickness: About 25 m.

Age: Ivorian (Polygnathus communis carina Conodont Zone, RC3bCoral Subzone, Conil et al., 1991). Foraminifera of the Cf2 Zone die out within the formation. The Ourthe Fm corresponds to the main part of the HST of the third-order sequence 3 (Hance et al., 2001).