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4.3.3. Bihain Formation - Sm3 or BIH

Author: Geukens, 1999.

Description: Black silty slate (called “quartzophyllade” in the older literature) and greenish sandstone. The Salm-Château Mbr – (SCH, old: Sm3b): cleaved “quartzophyllade”, with thick bands of slates, often rich in pyrite, with many bioturbations. The Ruisseau d' Oneu Mbr – (ONE, old: Sm3a): greenish sandy slates with thin beds (5 cm) of sandstone with current bedding (convolute bedding and slumping).

Stratotype: Not yet defined; type area in the Bihain syncline; type area of the Salm-Château Mbr in the “cluse” of the Salm valley between Vielsalm and Salm-Château; type area of the Ruisseau d' Oneu Mbr in the tributaries of the ruisseau de Groumont, south-east of Lierneux.

Area: In the southern part of the Stavelot Massif; in the metamorphic zone the slate contains small crystals of a particular chloritoid (ottrelite).

Thickness: Salm-Château Mbr: >150 m; Ruisseau d' Oneu Mbr: 30 m; total thickness: >180 m.

Age: Mid and/or Late Ordovician based on acritarchs and chitinozoans (Vanguestaine, 1974, 1986) in the Salm-Château Mbr.