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5.2.3. Anchamps Formation – ANC (old:Rv3)

Author: Beugnies, 1960.

Description: Formation subdivided into three members: the unnamed lower member (old: Rv3a) black slate, slightly micaceous with a few thin black quartzite beds; the Crapaude-Pierre Member (CRP, old: Rv3b): a few black, pyritic, fine-grained quartzite beds, 4 m thick at most; the unnamed upper member (old: Rv3c): alternation of black “psammitic” slates and thin to medium bedded black pyritic quartzite (a few cm to 2 m). Towards the top the beds are increasingly thicker and the slate more and more sandy and micaceous. The boundary with the covering Petite-Commune Fm is placed below the first appearance of a quartzite bed of at least 5 m thickness. Many sedimentary structures of turbidites including convolute bedding are present. The cleavage planes of the slate beds have a polished aspect. Some slate beds contain chloritoids (Beugnies, 1960; Belanger, 1998 ms).

Stratotype: not yet defined; type area in the outcrops along the Meuse valley south of Fumay.

Area: Rocroi massif; the Crapaude-Pierre Mbr seems to have a remarkable continuity.

Thickness: 200 to 600 m. The upper member takes up two thirds of the thickness of the formation (Beugnies, 1960).

Age: Most of the formation contains acritarchs of the Zone 4b, dated as Mid to Late Cambrian (Vanguestaine, 1992).

(M. VANGUESTAINE, I. BELANGER)