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5.33. Dendre Group – DEN

 

Authors: Groessens et al., 1982; Paproth et al., 1983; Conil & Delcourt, 1989; Hennebert, 1999.

Description: The Montils, Grand-Chemin, Pont-de-Lens, Cambron and Montignies formations are included in the Dendre Group. They comprise dark limestones and dolomites, often crinoidal, rich in brachiopods and fasciculate corals (Conil & Delcourt, 1989; Hennebert, 1999). Black chert is locally very abundant. Paproth et al. (1983) included the Lens Fm into the group, but this formation is usually pale and easily distinguishable from the others justifying to be not grouped with them.

Stratotype: The Dendre Valley between Lens and Ath.

Area: Western HSA, at least from Péruwelz to Seneffe.

Thickness: About 460 m in the type area (Doremus & Hennebert, 1995a); about 550 m in the Laplaigne – Péruwelz area (Hennebert, 1999).

Age: Moliniacian (Groessens et al., 1982).

5.33.1. Montils Formation – MOT

Authors: Groessens et al., 1982; Paproth et al., 1983; Conil & Delcourt, 1989; Doremus & Hennebert, 1995a, 1995b.

Description: Brown, coarse-grained, oolitic dolomite with inconspicuous undulating or lenticular bedding. Black or grey chert is present. Several levels of hard grounds have been recognized. Towards the west, an oolitic limestone level occurs at the base of the formation. The formation overlies the Malon-Fontaine Fm.

Stratotype: Old quarry situated SE of the old tannery of the Montils, at Brugelette.

Area: Western HSA, at least from Péruwelz to Seneffe.

Thickness: About 80 m in the type area.

Age: Moliniacian (Groessens et al., 1982).

5.33.2. Grand-Chemin Formation - GRC

Authors: Groessens et al., 1982; Paproth et al., 1983; Conil & Delcourt, 1989; Doremus & Hennebert, 1995a, 1995b.

Description: Brown, crinoidal dolomite with brachiopods and corals (mainly syringoporids), with some variations from bottom to top. The dolomites are dark and fine-grained with chert in the lower part, but become well-bedded, medium grained, and almost devoid of chert in the upper part. Concentrations of calcite geodes typically occur at some levels. The formation overlies the Montils Fm.

Stratotype: Several small exposures along the "Grand Chemin" at Brugelette.

Area: Western HSA, at least from Péruwelz to Seneffe.

Thickness: About 150 m in the type area.

Age: Moliniacian (Groessens et al., 1982).

5.33.3. Pont-de-Lens Formation – PDL

Authors: Groessens et al., 1982; Paproth et al., 1983; Conil & Delcourt, 1989; Doremus & Hennebert, 1995a, 1995b.

Description: Dark, argillaceous limestones, with dolomitic intercalations and black chert. Very fossiliferous (brachiopods). The limestones produce a fetid smell when freshly broken. The formation overlies the Grand-Chemin Fm.

Stratotype: Old quarry on the right bank of the R. Dendre, at Pont de Lens (Brugelette).

Area: Western HSA, at least from Péruwelz to Seneffe.

Thickness: 35 m in the type area.

Age: Moliniacian (Groessens et al., 1982).

5.33.4. Cambron Formation – CAB

Authors: Groessens et al., 1982; Paproth et al., 1983; Conil & Delcourt, 1989; Doremus & Hennebert, 1995a, 1995b.

Description: Dark, medium- to coarse-grained, crinoidal dolomite with corals and brachiopods. Chert nodules are abundant and pale silicification occurs locally, with corals and brachiopods. The formation is similar to the Grand-Chemin Fm, but is more cherty. It overlies the Pont-de-Lens Fm.

Stratotype: Old quarry at Bollignies (Cambron-Casteau).

Area: Western HSA, at least from Péruwelz to Seneffe.

Thickness: About 130 m in the type area.

Age: Moliniacian (Groessens et al., 1982).

5.33.5. Montignies Formation - MOG

Authors: Groessens et al., 1982; Paproth et al., 1983; Conil & Delcourt, 1989; Doremus & Hennebert, 1995a, 1995b.

Description: Dark, argillaceous, cherty and very fossiliferous limestones. The limestone produces a fetid smell when freshly broken.

Stratotype: Exposures in the "Val de la Marquette" at Montignies-lez-Lens.

Area: Western HSA, at least from Péruwelz to Seneffe.

Thickness: 65 m in the type area.

Age: Moliniacian (Groessens et al., 1982).