5.1.2 Les 4 Fils Aymon Formation - QFA (old: Dv2)
Author: Beugnies, 1960.
Description: Subdivided into two members. the unnamed lower member (old: Dv2a): at the base several meters of quartzite beds occur, covered by an alternation of quartzite, one meter thick, and slate a few centimetres thick. The less coarse-grained quartzite is light-coloured (white, pink or greenish), the slate is green or red; the slate contains some ilmenite, but no or very little magnetite. The sediments of this unit are generally coarser than the Longue-Haie Fm. Beds are lens-shaped. The quartzite beds of one meter thickness or more are often conglomeratic. The La Renaissance Member – (LRE, old: Dv2b): in the north is a vein of light-coloured, purple/violet, red roofing slate; only one quartzite bed occurs within the member; in the south the colour is green.
Stratotype: crags of “Les 4 Fils Aymon” north of the village Château-Regnault, Meuse valley; stratotype of the La Renaissance Mbr in the abandoned roofing slate quarry, south-east of Fumay, right bank of the Meuse.
Area: The unnamed lower mbr has a composition changing according to the area. It is quartzitic and slaty in the south, the region of Deville and Monthermé, quartzitic in the north-east, the region of Fumay, Haybes, Oignies, Rimogne and Eteignières, and coarse arkosic in the north-west, the region of Bruly, Gué d’Hossus and Petite-Chapelle (Beugnies, 1960).
Thickness: 95 to 270 m for the formation, with 15 to 25 m for the La Renaissance Mbr (Beugnies, 1960).
Age: The ichnofossil Oldhamia radiata is present in the slaty lower part of the formation in the north of the massif (Dewalque in Malaise, 1874b; Beugnies, 1960); this genus appears above the Cambrian-Precambrian boundary (Crimes, 1992). According to new observations by A. Seilacher (pers. comm., 1998) the genus Oldhamia is restricted in range to only the Tommotian or Nemakitian-Daldynian (early Early Cambrian). Acritarchs in the upper part of the lower mbr, above the Oldhamia occurrences, belong to the Zone 0, correlated with the Early Cambrian to early part of the Mid Cambrian (Vanguestaine, 1992). Thus an Early Cambrian to early Mid Cambrian age is proposed for the lower mbr.
(M. VANGUESTAINE)