5.37 Neffe Formation - NEF
Authors: de Dorlodot, 1895; Conil & Naum, 1977; Hance, 1982; Paproth et al., 1983; Delcambre & Pingot, 1993.
Description: The Neffe Fm as defined here does not include the first sequence of Conil & Naum (1977), which displays the typical characters of the underlying Salet Fm. In the stratotype area (eastern part of the DSA), the formation comprises thick-bedded, pale crinoidal limestones (bioclastic packstones to grainstones). In contrast, the uppermost part is finer-grained and locally contains oncoids and stromatolites. In the ASA, CSA, NSA and in the western part of the DSA, the dominant facies (Moha facies - MOH; Laloux et al., 1996a, 1996b) comprises thick-bedded to massive, pale, oolitic limestones (grainstones) with abundant clasts. Locally, the uppermost part of the formation can be similar as in the eastern part of the DSA. In the Vesder area (eastern part of the CSA), the formation is locally dark-grey to black in colour (Dison Facies - DIS; Laloux et al., 1996a, 1996b). Locally, the Neffe Fm is more or less dolomitized, mainly in the lower part. Macrofossils are abundant (brachiopods, gastropods and rugose corals).
Stratotype: The railway cutting on the left flank of the Meuse valley, 400 m south of the bridge at Dinant, was designated as the stratotype of the Neffe Fm (Paproth et al., 1983). The access of this section is dangerous. Furthermore, the section is of limited interest because it is incomplete. The railway cutting in the Dinant station exposes a complete section (Conil & Naum, 1977) and is designated here as the new stratotype, as suggested by Delcambre & Pingot (1993).
Area: The Neffe Fm is widespread in the Namur – Dinant basin, extending from the Boulonnais to Aachen area, except in the HSA.
Thickness: This ranges from 20 m at the eastern extremity of the NSA up to 170 m in some part of the DSA. It is about 65 m in the stratotype.
Age: Late Moliniacian (Cf4dForaminifer Subzone, Conil & Naum, 1977; RC5 Coral Zone). The oldest Siphonodendron (S. ondulosum) appears at the base of the formation; Dorlodotia briarti is common in the Moha facies. The Neffe Fm corresponds to the HST of the third-order sequence 6 of Hance et al. (2001).