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3.2.3. Dave Formation - DAV

Authors: Michot, 1932; emend. Michot, 1954.

Description: In the type area: bluish black shale, often fine micaceous or sandy, locally calcareous; around Fosses and Tihange black shale and mudstone with thin dark micaceous siltstone or sandstone intercalations. In the area around Neuville-sous-Huy keratophyre lavas, feldspathic tuffs and tuffites are present (Michot, 1954); in the area around Neuville-sous-Huy: in the middle part, a >48 m coarse shale, slightly quartzitic, brownish grey or dark greenish grey, compact bedded, rarely laminated, containing the lowest volcanoclastic bed of the area; the upper part (>94 m) consists of an alternation of greenish grey, olive green and red fine shale, compact bedded, with some minor clayey fine sandstone and at least 8 layers of keratophyre or volcano-sedimentary arkose (Maes et al., 1978).

Stratotype: southern flank of the Fond de Dave valley, near the village of Dave, 450-550 m east of the railway Namur-Dinant (Michot, 1932, 1934).

Area: Condroz inlier.

Thickness: Estimated at 280 m (Michot, 1957).

Age: The following graptolite biozones have been recognised: Cephalograptus acuminatus, Mesograptus modestus, Monograptus convolutus (black shale level of the Gazelle river), Monograptus sedgwicki, M. turriculatus, Monograptus crispus, Monograptus crenulatus, ranging from the bottom to the top of the Llandovery (Michot, 1954). Graptolites from Neuville-sous-Huy were described of the M. turriculatus, M. crispus, M. griestoniensis and M. crenulata biozones (Telychian, upper Llandovery) (Maes et al., 1978). A characteristic acritarch assemblage is present in the upper Telychian, dominated by many Domasia spp. (Martin, 1969a); Red beds occur from the top or above the M. turriculatus biozone till the lower Wenlock, but mostly in the griestoniensis and lower M. crenulata biozones. The 12 volcanic or volcano-sedimentary beds are situated from the M. turriculatus till the lower Wenlock (Maes et al., 1978). Samples from the Neuville-sous-Huy area contain chitinozoans from the dolioliformis and longicollis global biozones confirming the Telychian age for this part of the formation (Verniers, unpublished data).

Remarks: Synonym: Schistes de Dave, Assise de Dave.

(J. VERNIERS)