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5.21 Antoing Formation - ANT

Authors: Camerman, 1944; Hennebert et Doremus, 1997a, 1997b.

Description: The formation is lithologically similar to the underlying Tournai Formation, except that beds are slightly thicker and macrofossils become rare upwards. The trace fossil Zoophycos is common. Chert nodules are concentrated at some levels ("carbonniaux"). The Antoing Fm includes 4 members, from base to top: Lower and Upper Calonne, Gaurain-Ramecroix and Warchin Mbrs.

- Lower and Upper Calonne Mbrs – CAI and CAS (de Dorlodot, 1895; Paproth et al., 1983): Two units of dark grey, argillo-siliceous limestone, containing some chert, separated by a thick argillaceous layer. Poorly fossiliferous ("Banc à Chonetes" at the base), but Zoophycos is abundant at some levels.

- Gaurain-Ramecroix Mbr – GAU (Camerman, 1944; Paproth et al., 1983): Dark grey argillo-siliceous limestone, with chert at the base. Poorly fossiliferous but with numerous Zoophycos at some levels.

- Warchin Mbr – WAR (Camerman, 1944; Paproth et al., 1983): Dark grey to black, argillo-siliceous limestones with some very cherty levels. Poorly fossiliferous.

Stratotype: Four actively worked quarries expose the formation: the Antoing, Milieu and Lemay quarries, all situated between Antoing, Vaulx and Gaurain-Ramecroix, and the C.C.B. quarry at Gaurain-Ramecroix, which is the most complete in the upper part of the formation (as it exposes the CAS, GAU and WAR members).

Area: Western HSA, Tournai area.

Thickness: About 170 m. Lower Calonne Mbr, 22 m; Upper Calonne Mbr, 28-29 m; Gaurain-Ramecroix Mbr, 17 m; Warchin Mbr, at least 105 m in the Tournai area and about 157 m in the Leuze borehole.

Age: Ivorian, although the Warchin Mbr could be partly Moliniacian in age (Zones 10 of Mamet, in Legrand et al., 1966). The Antoing Fm is separated from the Tournai Fm by an argillaceous layer (Gras Délit) resting on a hard ground. This surface could be correlated with the surface separating the third-order sequences 3 and 4 of Hance et al. (2001) in the CSA.