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4.2.5. Condroz Group - CON

Authors:d’Omalius d’Halloy, 1839; Thorez et al., 1977, 1988; Thorez & Dreesen, 1986.
Description: In the Dinant Synclinorium, the Vesdre Nappe and the Theux Window, the Condroz Grp is made up of interfingering siliciclastic formations which are coarser-grained than those of the Famenne Grp and contain subordinate carbonate.  In the lower part, shales (Aye Fm), pass laterally to siltstones and sandstones (Esneux Fm).  They are overlaid by nodular limestones (Souverain-Pré Fm) or by both carbonate and siliciclastic rocks (Ciney Fm).  The Monfort Fm (and the time-equivalent Comblain-la-Tour Fm), situated in the middle of the Condroz Grp, is essentially made up of sandstones.  It is surmounted by the Evieux Fm (and the time-equivalent Beverire Fm), a complex of shale and argillaceous micaceous sandstones.
Stratotypes: Ourthe valley, between Esneux and Comblain-Fairon.
Area: Namur and Dinant Synclinoria; Vesdre Nappe, Theux Window.
Thickness: 290 to 350 m in the Dinant Synclinorium (350 m in the Ourthe valley)
Age: Middle and Upper Famennian (Fa2a, b and c). Palmatolepis rhomboidea to Bispathodus costatus or toPalmatolepis gracilis expansa conodont biozones.
Remarks: The former name of the Condroz Grp is "Condroz psammites”.  Originally, the name corresponded to a wide stratigraphic range, from part of the Middle Frasnian to the Strunian.  Later on, it was restricted to gather the Evieux and Monfort Fms.  Thorez et al. (1977), Thorez & Dreesen (1986) and others in more recent papers consider all the formations ranging from the Esneux/Aye Fms (in the lower part) up to the Evieux Fm (in the upper part) as belonging to the Condroz Grp.