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3.2.5. Jonquoi Formation - JON

Author: Michot, 1954.

Description: Unfossiliferous homogeneous unit of green shale (Michot, 1954); mudstone and green shale with rare thin clayey micaceous siltstone or fine sandstone beds (Martin, 1969a); olive green shale with intercalated grey-blue, green or grey-brown finely laminated shale, sometimes sandy, and a rare calcareous decimetric nodule level (Maes et al., 1978).

Stratotype: not clearly defined; area around the hamlet of Jonquoi, near the city of Fosses (Martin, 1969).

Area: Condroz inlier.

Thickness: ± 300 m (Michot, 1957).

Age: At Haute-Calange the Cyrtograptus rigidus graptolite biozone was found (Michot, 1954); in the park of Neuville-sous-Huy two levels from the C. rigidus or C. lundgreni graptolite biozones and 700 m east of Neuville-sous-Huy the C. linnarsoni (= C. rigidus) biozone were recognised (late Sheinwoodian or early Homerian, mid or late Wenlock) (Rickards in Maes et al., 1978).

(J. VERNIERS)