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5.1.1. Formation de la Longue-Haie – LLH (old:Dv1)

Author: Beugnies, 1960.

Description: Subdivided into two members. The unnamed lower member (old: Dv1a), contains at its top an alternation of green slate and 10 to 20 cm thick beds of green fine-grained quartzite, laminated or cross-bedded; at its base 5 to 6 m thick whitish quartzite beds, alternating with 1 to 2 m thick green slate layers. The lower boundary of the formation is not observed (Beugnies, 1960). The Sainte-Anne Member (SAN, old: Dv1b) alternation of quartzite beds, a few centimetres thick, and of purple, red or green slate, 0.10 to 1.50 m thick.

Stratotype: not yet defined; type area of the formation: in the Semois valley, south-east of Monthermé; stratotype of the Sainte-Anne Mbr: abandoned roofing slate quarry, west of the city of Fumay, right bank of the Meuse river.

Area: It occurs in a northern and a southern region of the Rocroi Massif, at the centre of two anticlinal structures. In the southern part of the massif in the metamorphic area, magnetite octahedrons are present in all lithologies of the Sainte-Anne Mbr, but slates contain more of them than the quartzite; the purple to red colours of the slate in the northern areas are replaced by light colours in the south. Both the presence of magnetite and the light colours are characteristic for the formation in the south.

Thickness: At least 130m with 4 to 9 m for the Sainte-Anne Mbr (Beugnies, 1960).

Age: No fossils are described from the formation: an early Early Cambrian to possibly Proterozoic age is tentatively postulated.

(I. Belanger and M. VANGUESTAINE)