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3.1.7 Oxhe Formation - OXH

Authors: Malaise, 1900; emend., Maillieux, 1926a; Michot, 1954; Dean, 1991.

Description: Black micaceous shale with isolated black quartzite beds (Dewalque, 1894); blackish, micaceous and fossiliferous quartzite and black shale (Malaise, 1900); blackish green coarse shale with greenish quartzite intercalations (Martin, 1969a); most commonly micaceous mudstone and siltstone (sometimes cleaved), occasional thin (up to 10 cm) impersistent beds of fine-grained sandstone within the mudstone; all rocks are blue grey when fresh, and brown or brown-green on weathering (Dean, 1991); dark grey micaceous mudstone, compact bedded, with intercalated centimetric to decimetric quartzitic sandstone and siltstone beds, often very micaceous, laminated to obliquely stratified; the dark grey colour changes by weathering to (dark) brown or greenish-brown (De Geest, 1998 ms).

Stratotype: not defined exactly, but contains the outcrops in the middle and western part of the Oxhe geological inlier, along the river Ri d’Oxhe/Ohe, at the localities of Fond d’Ohe and Petit Fond d’Ohe.

Area: only in the Oxhe inlier (Condroz inlier).

Thickness: estimated in the western part of the inlier: 200 m (Dean, 1991); possibly up to 900 m (De Geest, 1998 ms).

Age: Longvillian, upper substage of Burrellian, Caradoc, based on trilobites (Dean, 1991); acritarchs indicate an Arenig-Llanvirn (ex-Llandeilo) interval (Martin in Dean, 1991); the chitinozoan assemblages from the upper half of the formation compare well with those from the Burrellian stage in the Caradoc type area in U.K. (De Geest, 1998 ms).

Remarks: Synonyms: Included as part of the Vitrival-Bruyère Fm by Michot (1954); Assise of, shale of, sandstone of, quartzite and shale of, horizon of Oxhe or Fond d'Oxhe; Horizon of Oxhe with Trinucleus concentricus, considered equivalent of the Climacograptus wilsoni zone (Maillieux, 1926a) and later considered equivalent of the base of the Pleurograptus linearis zone (Maillieux, 1930a); “Schistes d'Oxhe” with Cryptolithus gibbifrons (Maillieux, 1930a); “Zone à Cryptolithus gibbifrons” (Michot, 1954); Oxhe Fm (Dean, 1991).