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5.2.2. La Roche à 7 Heures Formation – RSH (old:Rv2)

Author: Beugnies, 1960.

Description: Formation subdivided into two members. The unnamed lower member – (old: Rv2a) has at the base thick quartzite beds; the thickness of the basal quartzite beds diminishes laterally to the east. The unit contains more quartzite than slate and becomes gradually more slaty than quartzitic upward; characterised by grey quartzite in 1 to 4 m thick beds; slumps and convolute laminations are often present; locally conglomeratic bands occur, mostly in the lowermost part of the unit; the less frequent slate is black, fine-grained with a mat appearance and is exploitable as roofing slate (Beugnies, 1960; Belanger, 1998 ms). The La Folie Member – (LFO, old: Rv2b), is a black slate vein, composed of an alternation of grey quartzite beds a few decimetres or more thick and of slate layers up to several meters thick.

Stratotype: outcrops in the crags “La Roche à 7 Heures”, north-east of Monthermé, Meuse valley. The La Folie Mbr has its stratotype in the abandoned roofing slate quarry, south of Fumay, left bank of the Meuse.

Area: Rocroi Massif.

Thickness: 170 to 400 m, with 10 to 30 m for the La Folie Mbr (Beugnies, 1960).

Age: Most of the formation contains acritarchs of the Zone 2, dated as the upper part of the Middle Cambrian (Vanguestaine, 1992).

(M. VANGUESTAINE, I. BELANGER)